The mechanism of gas distribution of two-stroke engines. What is the phase of gas distribution? Phases timing of the two-stroke engine

The quality of the engine internal combustion engine depends on many factors, such as power, efficiency, the volume of cylinders.

Gas distribution phases are of great importance in the motor, and on how the valve overlapping occurs, the cost effectiveness of the engine, its injectivity, stability of work at idle turns.
In standard simple engines The change in the GDM phases is not provided, and such motors do not differ in high efficiency. But recently, more and more often on cars of advanced companies, such as Honda, Mercedes, Toyota, the Audi increasingly began to use power units with the ability to change offset distributional shafts As the number of revolutions in the OBS changes.

Diagram Phase Timpat Point Engine

The two-stroke engine is different from the four-stroke that the operating cycle of him passes in one crankshaft turn, at the same time on 4-stroke DVS it occurs in two turns. The gas distribution phases in the engine are determined by the duration of the opening of valves - graduation and intake, the angle of overlapping valves is indicated in the degrees of the position K / V.

In 4-stroke motors, the cycle of filling the working mixture occurs in 10-20 degrees before the piston comes to the upper dead point, and ends in 45-65º, and in some OBS and later (up to one hundred degrees), after the piston passes Bottom point. The total duration of the intake in 4-stroke motors can last 240-300 degrees, which ensures good cylinders of the working mixture.

In 2-stroke engines, the duration of the inlet of the fuel-air mixture lasts on the rotation of the crankshaft of approximately 120-150º, it also lasts less and purge, so the filling of the working mixture and the purification of exhaust gases in the two-stroke engine is always worse than in 4-stroke power units. Figure below shows the phase diagram of the T-175 motorcycle engine T-175 motorcycle engine.

Two-stroke engines are infrequently used on cars, as they have lower efficiency, worse economy and poor cleaning of exhaust gases from harmful impurities. The last factor is especially relevant - in connection with the tightening of the ecology standards, it is important that in the engine exhaust the minimum amount of CO.

But still 2-attaching internal combustion engines have their advantages, especially in diesel models:

• power units are compact and easier;
• they are cheaper;
• the two-stroke motor accelerates faster.

On many cars in the 70s and 80s of the last century, carburetor engines with a "trabrahnaya" ignition system were mainly installed, but many advanced cars for the production of cars had already begun to equip the motors of the electronic engine control system in which all major processes were ruled by a single Block (ECU). Now almost all modern cars have Esud - electronic system It is applied not only in gasoline, but also in diesel engine.

In modern electronics there are various sensors controlling the operation of the engine, sending signals to the state block power aggregate. Based on all data from the sensors, the ECU makes a solution - how much the fuel should be supplied to the cylinders on certain loads (turns), which set the ignition advance angle.

The gas distribution phase sensor has another name - the camshaft position sensor (DPRV), it determines the position of the timing of the crankshaft. It depends on its testimony, in which proportion will be supplied to the cylinders, depending on the number of revolutions and the ignition advance angle. If the DPRV does not work, it means that the timing phases are not controlled, and the ECU does not "know" in which sequence it is necessary to supply fuel to the cylinders. As a result, the fuel consumption increases, as the gasoline (diesel fuel) is simultaneously fed to all cylinders, the engine works by the rotation, on some models, the car does not start at all.

Regulator FAZ timing distribution

In the early 90s of the 20th century, the first engines were made with an automatic change in GHM phases, but here no sensor controlled the position of the crankshaft, and the phases themselves were directly shifted. The principle of operation of such a system is as follows:

• the camshaft is connected to the hydraulic coupling;
• also with this coupling has a connection and a distributor;
• at idle and small turnover of the camshaft with a camshaft are fixed in a standard position, as set by tags;
• with increasing revolutions under the influence of the coupling hydraulics, the camshaft rotates relative to the asterisk (distributor), and the timing phases are shifted - camshaft camshafts earlier open the valve.

One of the first similar developments (VANOS) was applied on M50 M50 engines, the first engines with the regulator of the gas distribution phases appeared in 1992. It should be noted that first Vanos was installed only on the inlet camshaft (M50 Motors dual-walled MRM system), and the Double Vanos system began to be used, with which the position of the exhaust and intake p / shaft was already adjusted.

What advantage gives the GHR phase regulator? At idle, the overlap of the gas distribution phases is practically not required, and in this case it even harms the engine, since the exhaust gas camshafts can get into the intake manifold, and part of the fuel will fall into exhaust systemfully burned. But when the engine operates at maximum power, the phases must be as wide as possible and the higher the turnover, the more it is necessary to overlap the valves. The coupling of changes in the GDM phase makes it possible to effectively fill the cylinders of the working mixture, and therefore increase the efficiency of the motor, increase its power. At the same time, at idle the r / trees with a coupling are in the initial state, and the combustion of the mixture is in full. It turns out that the phase regulator increases the dynamics and power of the engine, while the fuel is fairly economically consuming.

The gas distribution (SIFG) phase change system provides lower fuel consumption, reduces the CO level in exhaust gases, allows you to more efficiently use the power of the engine. Different world automakers have developed its own SIFG, not only the change in the position of the camshafts, but also the level of lifting valves in the GBC is applied. For example, Nissan applies the CVTCS system that controls the valve of the gas distribution phase adjustment (electromagnetic valve). At idle, this valve is open, and does not create pressure, so the camshafts are in the initial state. The opening valve increases the pressure in the system, and the higher the camshafts are shifted to the larger angle.

It should be noted that the SIFGs are mainly used on engines with two camshafts, where 4 valves are installed in the cylinders - 2 intake and 2 graduation.

Fixtures for installation of phases of gas distribution

In order for the engine to work without interruption, it is important to correctly set the timing phases, install in the desired position camshaft relative to the crankshaft. On all engines, the shafts are set by tags, and a lot of accuracy depends on the accuracy of the installation. If the shafts are invalid, there are different problems:

• motor unstable works at idle;
• DVS does not develop power;
• the shots in the muffler and cotton in the intake manifold occur.

If there are several teeth in the labels, it is possible that the valve can bent, and the engine will not start.

On some models of power units, special devices have been developed for the installation of gas distribution phases. In particular, for the engines of the ZMZ-406/406/409 family there is a special template with which the corners of the position of the camshafts are measured. The template you can check the existing angles, and if they are exhibited incorrectly, the shafts should be reinstalled. The device for 406 motors is a set consisting of three elements:

• two angles (for the right and left shaft, they are different);
• transportation.

When the crankshaft is set to the NMT of the 1st cylinder, the camshaft cams must perform above the upper plane of the GBC at an angle of 19-20º with an error of ± 2.4 °, and the cam tube must be slightly higher than the camshaft camshack.

There are also special devices for establishing camshafts on M56 / M54 / M52 M56 / M52 motors. In the installation of the phases of the TSBM timing, BVM includes:

Fault System Changes Solutions

Change the phases of gas distribution can different ways, and recently, the most common turn of the P / shaft is most common, although it is often used to change the valve lifting value, the use of camshafts with cams of the modified profile. Periodically, various malfunctions occur in the gas distribution mechanism, due to which the motor begins to work with interruptions, "tupit", in some cases does not start at all. The causes of malfunctions may be different:

• faulty electromagnetic valve;
• clogged mud coupling phase change;
• the chain of the gas distribution mechanism has stretched;
• faulty chain tensioner.

Often, when faults are faulty in this system:

• idle turns are reduced, in some cases, the engine stalls;
• significantly increases fuel consumption;
• the engine does not develop turnover, the machine is sometimes not accelerated even up to 100 km / h;
• the engine is badly launched, it is necessary to drive it a starter several times;
• dragonflies are heard from the CIFG coupling.

For all signs, the main reason for the problems with the engine is the failure of the SIFG valve, usually the computer diagnostics reveals the error of this device. It should be noted that the Check Engine diagnostic lamp lights up at the same time, it is not always difficult to understand that the failures occur in electronics.

Often, the MRM problems arise due to the clogging of the hydraulics - poor oil with abrasive particles clogs the channels in the coupling, and the mechanism encourages in one of the positions. If the clinical coupling is in the initial position, the engine is safely working on the XX, but does not develop turns at all. In the case when the mechanism remains in the position of the maximum overlap of the valves, the engine can be bad bad.

Unfortunately, engines russian production SIFG is not installed, but many motorists are engaged tuning DVS, trying to improve the characteristics of the power unit. The classic version of the motor upgrades is the installation of a "sports" camshaft, which is shifted by cams, changed their profile.

This p / shaft has its advantages:

• the motor becomes anger, clearly reacts to pressing the gas pedal;
• the dynamic characteristics of the car are improved, the car literally tears out.

But in such tuning there are its own minuses:

• idling turns becomes unstable, you have to set them within 1100-1200 rpm;
• increases fuel consumption;
• it is enough to adjust the valve, the internal combustion is required.

Quite often tuning exposed vAZ engines Models 21213, 21214, 2106. The problem of the VAZ drives with a chain drive is the appearance of "diesel" noise, and often it arises due to the failed tensioner. Modernization of DVS VAZ is to install an automatic tensioner instead of a regular factory.

Often, the models of engines VAZ-2101-07 and 21213-21214 are installed a single-row chain: a motor with it is quieter, moreover, the chain is less wearing - its resource is an average of 150 thousand km.

Motors work on gasoline, gas, alcohol or diesel fuel - on a 2- or 4-stroke cycle. And in any case, their character strongly depends on what is called gas distribution phases. So what are they eating them? Why do you need to regulate the phases? Let's see.

Gas exchange

From how we breathe, much depends in our lives. Yes, life itself; In the world, D.V. Approximately the same. Take a 1.5-liter VAZ 16-valve; Do you want it to pull on V at 600 min -1? For joke. The question of choosing the phases of gas distribution: We will select the profile of the camshaft camshafts so that the inlet begins to approximately 24 ° (at the corner of rotation crankshaft) After V.M.T. Fist will make so "stupid" that the valves rise only by 3 mm, and the inlet ends somewhere 6 ° after N.M.T.

The start of the release is adjustable by 12 ° B. N.T., and the exhaust valves are closed. Let just in V.M.T.; Their lift is left "by staff." Degrees and millimeters of lifting valves and there are those phases: before, later.

Check out experimentally: with properly adjustment of the ignition and the fuel injection, the modified "Four" will show the largest in 75-80 nm - somewhere on 6 hundred revolutions! Maximum power - 10-12 hp at 1500 min -1; Do not foresee. However, the motor will actually pull from the very "bottoms" - like (small) steam engine. It is a pity, no revolutions, no power he develops.

I do not like ... come from the other end: the cam profile is such that the inlet begins at 90 ° to V.T., and ends at 108 ° after N.M.T. Lifting - up to 14 mm. There is a difference? And release too: start at 102 ° B. N.T., Completion - at 96 ° after V.M.T. As Spets say, overlapping the release and intake - 186 ° at the corner of the turn of the crankshaft! So what? See: S. proper setting Ignition and injection [As well as with plates of valves of increased diameter, crushed and polished intake and exhaust channels ...] Your 1.5-liter VAZ will give out something like 185 Nm of torque - under ... 11 thousand revolutions! And at 13500 min -1, there will definite about 330 hp - without any chance. Of course, if we can withstand the timing and crank mechanism (hardly). 40 years ago Such power showed a good 3-liter engine of formula 1 ... True, below 6000 min -1 Forced VAZ will be completely dead [The "idling" turns will have to be exhibited somewhere on 3500 minutes -1 ...]; Its operating range is 9-14 thousand revolutions.

On the "Verkhakh" on the contrary: wide phases of gas distribution will allow all 100% to mobilize the resonance of gas flows on the inlet and release, as they say acoustic supervision. With the correct selection of lengths and sections (individual) intake and exhaust pipes, the coefficient of filling cylinders will reach in the zone of 11 thousand levels of level 1.25-1.35; Get the desired 185 nm.

Here is what gas distribution phases are: they are asked Gas exchange D.V. - Intake release. And gas exchange determines everything else: the flow of torque, the turret of the engine, its maximum power, elasticity ... A pair of examples can be seen how the character of the same motor changes strongly depending on the phases. Immediately there is a thought: gas distribution phases need to be adjusted - right on the go. And then, under the hood of your car, there will be no one-only engine - for all occasions, and many unequal!

As the best friend of motorists taught, "Frames decide everything." Paraphrasing the famous expression, we will take that everything solve the phases (gas distribution). Generalissimus knew how to regulate personnel issues, and the Motor Builders always sought to manage phases.

Phase age

It is easy to say, but it is difficult to do; In the 4-stroke motor, the gas distribution phase is set by the cam profile (from high-strength hardened steel). Change it along the way - the task is not simple. However, something can be done even with a constant profile, "say, to move camshaft at the corner of the rotation of the crankshaft. Back and forth; That is, the duration of the intake remains unchanged (in the 2nd example - 378 °), but it begins, and ends before. Suppose inlet valves are now open 120 ° to V.T. and close by 78 ° after N.M.T. So to speak, "earlier before." Or vice versa - on "later, later": the inlet begins at 78 ° to V.T. and ends 120 ° after N.M.T.

Such a solution (for inlet) was used for the first time at Alfa Romeo on a 2-liter 8-valve "four" twin spark [It is clear that the phase is applicable when intake and exhaust valves are driven by 2 individual camshafts; In the mid-80s, TWIN SPARK was one of the rare DOHC designs. And since then, 2 shafts in the cylinder head were widespread - just for the sake of phase mode.] - Back in 1985. It is called phase inspection and apply (on the inlet and / or on the release) is quite wide. And what does it give? A little bit, but still better than nothing. So, with a cold start of the engine with a catalytic convection neutralizer, the graduation camshaft rotated to ahead. The release begins early, and the exhaust gases of elevated temperature go to the neutralizer; It warms up faster to the working condition. Less harmful substances are emitted into the atmosphere.

Or you drive evenly at a speed of 90 km / h, only 10% of its maximum power are required from the motor. It means throttle valve strongly covered; Increased pumping losses, fuel recalculation. And if it is strongly moving inlet camshaft on "later, later", then some (for example, 1/3) fuel and air mixture is released during the compression back into the intake manifold [Do not worry, she will not go anywhere. The so-called "5-stroke" cycle.]. And the engine power is reduced (to the level of level mode necessary) without excessive inlet choke. That is, the throttle is thicker, though and closed, but not so much, the pumping losses are significantly less. Saving gasoline - and something else; Isn't it worth it?

Vtec.

The possibilities of phase is limited by what they say, "the tail pulled out - the nose was stuck." When you reduce the advance of the opening of the valves, the closure delay is increasing exactly the same.

Hour from the hour is not easier. Now, if somehow change the duration of the intake-release ... Suppose, in the 2nd example, it is reduced by it - when it is necessary, from 378 to 225 °. The engine will also work normally and "on nizakh" - without loss of power "on tops".

Dreams are carried out: 4 years after the appearance of Twin Spark with a phase process, and Honda Motor showed a 1.6-liter 16-valve B16A with revolutionary VTEC. The engine was equipped - for the first time in history - a 2-mode valve mechanism (on the inlet and release); The process went. However, sometimes you have to hear: Think, VTEC is only 2 modes. And at the engine of my "Corolla" phases are adjusted stepless - continuum of modes. Well, yes, - if you do not see two big differences ...

In our sunny country, it is customary for some reason twice a year to express people with the transfer of arrows for an hour - on the "earlier - earlier" in the spring and on the "later-later" in the fall. God is a judge, we are talking about a friend. Translate the arrows is technically simple not only for an hour every six months, but at least every day in a minute. So to speak, stepless. Folding is similar to the translation of the clock - and the effect is about the same.

And you did not try to change the duration of the daylight? Let not be infinitely, only two modes, "say, 9 hours and 12? So, Hondov engineers found the solution of the problem of this class; feel the difference. Suppose, in the "lower" mode, the duration of the intake - 186 ° (at the corner of the rotation of the crankshaft), and in the "upper" - 252 °. Radical change in gas exchange conditions: under the hood as if two unequal motors. One elastic and traveler on the "Nizakh", the other - "sharp", spinning and powerful on the "vertices"; 25 years ago about this and not dreamed. And by the way, nothing should be attached to VTEC also phase that Honda has done in the design of I-VTEC. Then, on the contrary - to give VTEC to phase inspection - will not come out; The corporate mechanism is not as simple and covered with patents.

Note: VTEC allows you to vary the inlet diagram (and release)! Not just moving it to "earlier - earlier" or "later, later", but to change the profile. High-quality promotion against banal phase mode - although only 2 modes (in later versions - as well as 3). Honda has a lot of imitators and followers: Mitsubishi Mivec, Porsche Varioocam Plus, Toyota VVTL-I. In all cases, fists of unequal profiles with blocking of the valve drive are used; Imagine it works.

Valvetronic

Well, in 2002, the Bavarian designers unveiled the famous timing of Valvetronic. And if Vtec is "Montana", then Valvetronic - "Full ...". The mass operation mechanism is already 5 years old, but the auto extinguishers have not yet comprehended its meaning and the principle of work. What are the journalists, if the BMW press service ... see and make sure: Valvetronic treasuredes are interpreted as a mechanism for changing valve lifting! And if you think about it? There is nothing easier than adjusting the rise is not more difficult than phasitis. However, Valvetronic is a sophisticated device; Probably there is something over.

We will talk about the unusual mechanism separately. In the meantime, we recognize that the Bavarian motors Valvetronic became the first motors of OTTO, the capacity of which is adjusted without inlet throttling! Like diesel engines. They cost without the most malicious details in the engine design with spark ignition; Comparable with the invention of the carburetor. Or Magneto. In 2002, the world has changed, although no one noticed ...

Electromagnets

Remove the hat before engineers BMW.And nevertheless, Valvetronic is only an episode in the development of Otto engine. Intermediate solution - waiting for radical. And it is already on the threshold: a cheekless timing with an electromagnetic drive of the valves. No camshafts with their drive, pushers, rocker, gap hydrocompensators, etc. Simply valve rod enters powerful electromagnet. [With an effort along the valve axis to 80-100 kg! Otherwise, the valves do not have time for their phases. And to ensure such efforts in the compact mechanism are not easy, which is the main difficulty of creating e-magnetic timing.], Voltage to which is supplied under the control of the CPU. That's all: on each turnover of the crankshaft, the CPU manages the moments of the beginning of the opening and closing of the valves - and their lifting height. There are no cams with their unchanged profile, there are no times and forever given phases of gas distribution.

Inlet and output diagrams are regulated freely and widely (limited only to physical processes). Separately for each of the cylinders and from the cycle to the cycle - like the moment of injection and the amount of fuel supplied. Or ignition. Essentially, the Otto engine will become for the first time in history. And will not leave any chance of diesel. As computers found themselves with the advent of micro "chips", and pocket calculators instantly outlined electromechanical counting machines. Whereas at the end of the 40s EUM were built on vacuum lamps and electromagnetic relays; Consider the spark ignition engines are still on that very stage. Well, except for Valvetronic ...

Those associated with racing automotive or motorcycle technology or just interested in the design of sports cars, well familiar with the name of the engineer Wilhelm Wilhegelmovich Beckman - author "Racing cars" and "racing motorcycles". More than once he performed on the pages "driving."

The third edition of the book "Racing Motorcycles" was published (the second was released in 1969), reworked and supplemented by information about new design solutions and analysis of the trend of the further development of two-wheeled machines. The reader will find in the essay book about the history of the origin of motorcycle sports and the effect of it on the development of the motorcycle industry, will receive information about the classification of machines and competitions, it will get acquainted with the design features of the engines, transmission, chassis and racing motorcycle systems, learns about the paths of their improvement.

Much of what is applied for the first time on sports cars is then embedded on serial road motorcycles. Therefore, familiarity with them allows you to look into the future and imagine a motorcycle of tomorrow.

The overwhelming number of motorcycle engines under construction under construction in the world works on a two-stroke cycle, so the motorists show them the greatest interest. We offer the readers of readers an excerpt from the book V. V. Bekman, dedicated to one of the most important issues of the development of two-stroke engines. We have made only minor cuts, changed the numbering of drawings and led some names in accordance with the log used in the journal.

Currently, two-stroke racing engines are superior to the power of their four-stroke rivals in classes from 50 to 250 cm3: in the class of larger working volume, four-stroke engines still retain competitiveness. Since the high forcing of the two-stroke engines of these classes is more difficult, with a more notable lack of a two-stroke process becomes more noticeable - increased flow Fuel, requiring an increase in fuel tanks and more frequent stops for refueling.

The prototype of most modern two-stroke engines of racing type is a design developed by MC (GDR). Works on the improvement of two-stroke engines made by this company were provided by racing motorcycles of the MC classes 125 and 250 cm3 High dynamic qualities, and their design to one degree or another was copied by many firms in other countries of the world.

MC racing engines (Fig. 1) have a simple design and similar to both the device and by appearance On ordinary two-stroke engines.

A - general view; B - location of gas distribution channels

For 13 years, the power of the Racing motor MC 125 cm3 rose from 8 to 30 liters. from.; Already in 1962, a liter power of 200 liters was achieved. c. / l. One of the essential elements of the engine is a disk rotating spool proposed by D. Zimmerman. It allows you to obtain asymmetric intake phases and a favorable shape of the intake path: due to this, the coefficient of filling the crankcase increases. The disk spool is made of fine (about 0.5 mm) leaf spring steel. The optimal thickness of the disk is found in an experimental way. The disk spool works as a furniture valve, pressed to the opening of the inlet channel when a combustible mixture is compressed in the crankcase. With an enlarged or reduced thickness of the spool, it is observed accelerated wear disk. Too thin disk begged towards the inlet channel, which entails an increase in the friction force between the disk and the cover of the crankcase; Increased disk thickness also leads to increased friction losses. As a result of the design of the design, the service life of the disk spool was increased from 3 to 2000 hours.

The disk spool does not contribute a special complication in the engine device. The spool is installed on the shaft by means of a sliding key or slotted compoundSo that the disk can occupy a free position and not pinch in a narrow space between the wall of the crankcase and the lid.

Compared to the classic inlet control system of the lower edge of the piston, the spool makes it possible to open an inlet window and for a long time to keep it open, which helps to increase the power both at high and on average rotation frequencies. With a conventional gas distribution device, the early opening of the inlet window is inevitably connected with the large delay of its closure: this is useful for obtaining maximum power, but is associated with the return emission of the combustible mixture in the middle modes and the corresponding deterioration characteristics of the torque and engine launchers.

On two-cylinder engines with parallel cylinders, disk spools are installed at the ends of the crankshaft, which, with protrusing on the right and on the left, the carburetors gives large dimensions in the width of the engine, increases the windshield area of \u200b\u200bthe motorcycle and worsens its external form. To eliminate this disadvantage, the design was sometimes used in the form of two paired at an angle of single-cylinder engines with a common crankcase and air cooled ("Derby", Java).

Unlike the engine of Java, the cylinders of paired engines can occupy a vertical position: it takes water cooling, since the rear cylinder is overshadowed. According to such a scheme, one of the Racing motors of the MC 125 cm3 was made.

Three-cylinder engine Suzuki. (50 cm3, liter power is about 400 l. / L) with disk spools essentially consisted of three single-cylinder engines combined in one block with independent crankshafts: two cylinders were horizontal. One vertical.

The inlet engines were constructed in four-cylinder versions. Typical examples are Yamaha engines made in the form of two paired gear transmission of two-cylinder engines with parallel cylinders; One pair of cylinders is located horizontally, the second - at an angle up. Engine 250 cm3 developed up to 75 liters. p., and the power of the version 125 cm3 reached 44 liters. from. at 17 800 rpm.

For a similar scheme, a four-cylinder Java engine (350 cm3, 48x47) with inlet spools is designed, which is two paired water-cooled twin-cylinder engines. It develops the power of 72 liters. from. at 1300 rpm. Even more power of the four-cylinder engine "Morbideli" class 350 cm3 of the same type - 85 liters. from.

Due to the fact that disk spools are installed at the ends of the crankshaft, the swelling of power in multi-cylinder structures with such an inlet system is usually made through the gear on the middle shaft between the crankcase compartments. With disk spools of the type in question, an increase in the number of engine cylinders Over four is impractical, since further pairing of two-cylinder engines would lead to very cumbersome design; Even in the four-cylinder design, the engine is obtained at the limit of permissible dimensions.

Recently, there are automatic membrane valves in the inlet channel between the carburetor and the cylinder (Fig. 2, a) on some racing engines "Yamaha". The valve is a thin elastic plate, begging under the influence of the vacancy in the crankcase and the exempt passage for a combustible mixture. In order to avoid damage to the valves, their stroke limiters are provided. With the average valve modes, the valves are quickly closed fairly to prevent the reverse release of a combustible mixture, which improves the characteristic of the engine torque. Such valves on the basis of practical observations may function normally when high-speed modes up to 10,000 rpm. With higher speed numbers, their performance is problematic.

: a - device diagram; B-Proper filling Carter; B - seats of the mixture through the valves in the cylinder; 1 - limiter; 2 - membrane; 3 - window in piston

In engines with membrane valves to improve the filling, it is advisable to support the message between the inlet channel and the piston space or the purge channel at the position of the piston near N.M.T. To do this, in the wall of the piston from the side, the corresponding windows 3 are provided (Fig. 2, b). The membrane valves provide an additional combustible mixture sucklery when a vaccine is formed during the purge in the cylinders and the crankcase (Fig. 2, B).

High power develops two-stroke engines, in which the inlet process of a combustible mixture in the Carter controls the piston, like the overwhelming majority of ordinary engines mass production. This mainly belongs to the engines of the working volume of 250 cm3 and more. Examples can serve motorcycles "Yamaha" and "Harley-Davidson" (250 cm3 - 60 l.;

350 cm3 - 70 liters. p.), as well as the Suzuki motorcycle with a two-cylinder engine of class 500 cm3 with a capacity of 75 liters. with. who took the first place in the race T.T. (Tourist Trofi) 1973. Forcing these engines is carried out in the same way as in the case of the use of disk spools, a thorough constructive study of the gas distribution organs and on the basis of the study of the mutual influence of intake and graduation paths.

Two-stroke engines regardless of the intake control system have a straightened shape of the intake path, which is directed to the pouring space, where the combustible mixture comes; In relation to the axis of the cylinder, the intake path can be perpendicular or tilted from the bottom up or top down. This shape of the intake path is favorable to use the effect of resonant superior. The flow of combustible mixture in the intake path continuously pulsates, and there are waves of pouring and increased pressure. Adjusting the intake path due to the selection of its size (length and flow sections) makes it possible to ensure the closure of the intake window at a certain interval at the moment of the input of the wavelength of the increased pressure, which increases the filling coefficient and increases the engine power.

At the values \u200b\u200bof the coefficient of filling the crankcase exceeding the unit, the two-stroke engine would have to develop twice as large compared to the four-stroke. In fact, this does not occur due to significant losses of the fresh mixture into the exhaust of mixing of the charge received into the cylinder with residual gases from the previous working cycle. The imperfection of the operating cycle of the two-stroke engine is due to the simultaneous flow of the process of filling the cylinder and its purification from combustion products, while in the four-stroke engine these processes are separated in time.

The processes of gas exchange in a two-stroke engine are of great complexity and are still poorly calculating. Therefore, the boosting of the engines is mainly carried out by experimental selection of relations and sizes of structural elements of the gas distribution organs from the inlet pipe of the carburetor to the terminal pipe exhaust pipe. Over time, extensive experience was accumulated on the forcing the two-stroke engines described in various studies.

In the first designs of the MC racing engines, the Reta-loop purge type "Shiniral" was used with two purge channels. A significant improvement in the power indicators was obtained by adding the third purge channel (see Fig. 1), located in front opposite the outlet windows. For a spa through this channel, a special window is provided on the piston. An additional purge channel eliminated the formation of a cushion of hot gases under the bottom of the piston. Due to this channel, it was possible to increase the filling of the cylinder, improve the cooling and lubrication with a fresh mixture of the needle bearing of the top head of the rod, as well as facilitate the temperature mode of the bottom of the piston. As a result, the engine power rose by 10 percent, and the pistons and breakdowns of the rod head bearing were eliminated.

The purge quality depends on the degree of compression of the combustible mixture in the crankcase; On racing engines, this parameter is maintained in the range of 1.45 - 1.65, which requires a very compact design of the crank-connecting mechanism.

Getting high liter capacities is possible due to wide distribution phases and a large width of gas distribution windows.

The width of the windows of racing engines measured by the central angle in cross section cylinder, reaches 80 - 90 degrees, which creates heavy conditions Works for piston rings. But with such a width of windows in modern engines Caps without jumpers prone to overheating. An increase in the height of purge windows shifts the maximum torque into the lower speed area, and the increase in the height of the outlet windows creates the opposite effect.

Fig. 3. Purpose systems:a - with the third purge window, b - with two additional purge channels; B - with branching purge channels.

The purge system with the third additional purge channel (see Fig. 1) is convenient for engines with a spool, in which the intake canal is located on the side, and the zone of the cylinder opposite the exhaust window is free to accommodate the purge window; The latter may have a jumper, as shown in Fig. 3, a. An additional purge window contributes to the formation of a combustible mixture flow, enveling the cavity of the cylinder (loop purge). The angles of the yield of purge channels have very significant importance for the efficiency of the gas exchange process; They depend on the form and direction of the flow of the mixture in the cylinder. The horizontal angle A, fluctuates in the range of 50 to 60 degrees, and the greater value corresponds to higher engine forcing. Vertical angle A2, equal to 45 - 50 degrees. The ratio of sections of additional and main purge windows is about 0.4.

On the engines without an spool carburetors and intake windows, as a rule, are located on the back of the cylinders. In this case, a different purge system is used - with two lateral additional purge channels (Fig. 3, b). Horizontal angle of entry A, (see Fig. 3, a) additional channels - about 90 degrees. The vertical angle of entering the purge nanalov varies for various models in fairly wide limits: on the "Yamaha" model TD2 class 250 cm3 it is 15 degrees for the main purge channels, and for additional - 0 degrees; On the model "Yamaha" TD2 class 350 cm3, respectively, 0 and 45 degrees.

Sometimes a variant of this purge system with branching purge channels is used (Fig. 3, B). Additional blowing windows are located opposite the outlet window, and, therefore, a similar device is approaching the first of the considered systems having three windows. Vertical angle of entry of additional purge channels 45 - 50 degrees. The ratio of sections of additional and main purge windows is also about 0.4.

Fig. 4. Gas movement schemes in the cylinder: a - with branching ka pool; B - with parallel.

In fig. 4 shows the gas movement schemes in the cylinder during the purge process. In the acute angle of the entry of additional purge channels, the flow of fresh mixture comes from them, removes the exhaust gases in the middle of the cylinder, not captured by the stream of the mixture from the main purge channels. Other options for purge systems are possible in the number of purge windows.

It should be noted that on many engines the duration of the opening of additional purge windows by 2-3 degrees is less than that of the main.

On some engines "Yamaha", additional purge channels were performed in the form of grooves on the inner surface of the cylinder; The inner wall of the channel is the wall of the piston under its positions near N.M.T.

The purge channel profile affects the purge process. Smooth form without sharp bends gives smaller pressure drops and improves engine performance indicators, especially in intermediate modes.

The information provided in this section show that the two-stroke engines are highlighted by the simplicity of their device.

Increasing the specific power of the engines of this type over the past decade, was not accompanied by any significant changes in the basic design; It was a consequence of a thorough experimental selection of relations and the size of previously known structural elements.

Map Design - Engine Forcing

There will be no ready-made recipes for forcing specific types of engines. All engines are different, the sizes of individual elements (for example, the exhaust system) will be changed on different chassis, characteristics will be changed. Therefore, some specific recipes in which, nevertheless, a lot of white spots will remain, can only lead to useless work.

In particular, the foundations of the theory of processes occurring in the engine, with a special focus on those issues that are the main ones during the engine forcing. Of course, in the proposed chapter, there are only those sections of the theory, the knowledge of which is necessary, so that a novice fan of karting does not spoil the engine in the desire to squeeze the maximum power from it. Also also see general recommendations About the directions should be improved by the engine to achieve positive results. General instructions are illustrated by examples of practical work on the forcing of kart engines. In addition, a number of comments are given and practical recommendations A relatively, it would seem small changes, which will improve the operation of the engine, will increase its reliability, relieve us from sometimes expensive studies on their own errors.

Phases of gas distribution

The gas distribution phases are expressed by the angles of rotation of the crankshaft, in which the corresponding cylinder windows are opened. In a two-stroke engine, we consider three phases: opening the inlet window, opening the exhaust window and opening the bypass windows (Fig. 9.3).

The opening phase of the window, for example, the graduation, call the angle of rotation of the crankshaft, measured from the moment when the top edge of the piston opens the outlet window, until the piston, moving back, closes the window. Similarly, you can define the opening phases of the rest of the windows.

Fig. 9.3. Thams timing charts:

a. -Symmetric; B - asymmetric; OD and ZD - opening and closing intake. Op and zp- opening and closing of the proof; OW and ZW - Output and closing release; a, uglons the opening of the intake and exhaust windows, respectively; B - the angle of opening bypass windows

Fig. 9.4. Comparison of sections (area under curves) for windows of different shapes

In the usual piston engine, all windows open and closed by the piston, so the phase phase diagram is symmetrical (or almost symmetric) relative to the vertical axis (Fig. 9.3, but).In the intake engines, in which the filling of the crooked chamber of the combustible mixture is carried out with the help of a rotating spool, the intake phase may not depend on the movement of the piston, so the timing phase diagram is usually asymmetrical (Fig. 9.3, b).

The gas distribution phases are comparable magnitudes for engines with different piston strokes, i.e. they serve as universal characteristics. When comparing engines having the same piston stroke, the gas distribution phases can be replaced by distances from the windows, for example, to the upper plane of the cylinder.

In addition to the phases of gas distribution an important parameter is the so-called time-section. With a gradually discovered piston window from the channel form, it depends on how the opened surface of the window increases, depending on the angle of rotation of the crankshaft (or time). The wider window, the biggest surface will open when the piston is offset down. In the same time, a larger amount of combustible mixture will be held through the window. It is advisable that when opening the window, the piston will be at once as much as possible. Many engines for this window is made expanded up. Due to this, the effect of the quick opening of the window is achieved without increasing its surface.

The growth chart of the open surface of the windows of different shapes, depending on the time, at a constant CHV engine is shown in Fig. 9.4. The total area of \u200b\u200bwindows in both cases is the same. The area under the curves of the diagram characterizes the value of the time. For the wrong form of the time-cross section.

Cylinder purge systems

Fig. 9.10. The scheme of the cylinder purge system and the cylinder mirror sweeps corresponding to them:

a - two-channel system; b - three-channel system; in - four-channel system; G - Pleasant National System

The cylinder purge system used in the capture engines is schematically represented in Fig. 9.10. Nearby shows the location of the bypass windows on the cylinder mirror scan for each of the systems: two-, three-, four- and five-channel. In those engines where the filling of the crankcase is regulated by the piston, covers and does not close the inlet window. In this case, the intake nozzle is not in the cylinder, and the ability to place an additional bypass channel appears.

The role of the graduation system

In the two-stroke engine play a huge role graduation systemconsisting of an exhaust pipe (in the cylinder and over the cylinder), an expansion chamber and silencer. At the time of opening the exhaust window in the cylinder there is some pressure that is reduced in the exhaust system. Gas expands, shock waves occur, which are reflected from the walls of the expansion chamber. Reflected shock waves cause a new pressure growth near the exhaust window, as a result of which some of the exhaust gases again falls into the cylinder (Fig. 9.11).

Fig. 9.11. Schematic representation of the sequential phases of exhaust exhaust gases:

a - opening of the graduation window; b - full opening of the window; in - closing window

It seems that it would be more profitable to get a vacuum on the graduation window when it is fully open. This will cause pumping gases from the cylinder and, thereby, filling the cylinder with a fresh mixture. However, in this case, part of this mixture together with the exhaust gases will fall into the exhaust pipe. Therefore, it is necessary to achieve increased pressure from the graduation window when it closes. In this case, a combustible mixture that fell along with the exhaust gases into the exhaust pipe will be returned to the cylinder, significantly improving its filling. It happens after closing the piston of bypass windows. As in the intake system, the wave phenomena in the exhaust system give a positive effect only near the resonant CV. By changing the dimensions, but especially the length of the exhaust system, you can also form the speed characteristics of the engine. The effect of changes in the size of the exhaust system on the engine characteristics is more significant than changing the size of the inlet system.

Basics of the combustion process

For a better understanding of the engine work, it is necessary to say a few words about the processes occurring in the engine combustion chamber. From the flow of the combustion process depends the increase in the pressure in the cylinder, which determines the engine power.

The results of the combustion of fuel perceived in the form of a crank-connecting mechanism, primarily depend on the composition of the combustible mixture. Theoretically, the ideal composition of the combustible mixture is the so-called stoichiometric composition, i.e., this in which there is so much fuel and oxygen in the mixture, which, after combustion, there are no fuel or oxygen in the exhaust gases. In other words, it will burn all the fuel in the combustion chamber, and all oxygen contained in the combustible mixture will be consumed for its combustion.

If in the combustion chamber was an excess air (lack of fuel), then this excess could not help the combustion process. However, it would be an additional mass of gas that it is necessary to "pump" through the engine and heat, using warmth for this, which would increase the temperature without this additional mass and, therefore, the pressure in the cylinder. The combustible mixture with an excess of air is called poor.

The lack of air (or excess fuel) is equally unfavorable. This would lead to incomplete combustion of fuel and, as a result, to obtain less energy. Excess fuel will be passed through the engine and evaporate. The combustible mixture with a lack of air is called rich.

In practice, to obtain the highest power, it is advisable to use a slightly enriched mixture. This is due to the fact that in the combustion chamber, local inhomogeneities of the composition of the combustible mixture arising due to the fact that it is impossible to achieve the perfect mixing of fuel with air. The optimal composition of the mixture can only be determined by the experimental way.

The volume of the combustible mixture, sucking each time in the cylinder, is determined by the working volume of this cylinder. But the mass of air located in this volume depends on the air temperature: the higher the temperature, the less air density. Thus, the composition of the combustible mixture depends on the air temperature. Because of this, you need to "configure" the engine depending on the weather. On a hot day, warm air enters the engine, therefore, to maintain the corresponding composition of the combustible mixture, it is necessary to reduce the fuel supply. On a cold day, the mass of the incoming air increases, so it is necessary to serve more fuel. It should be noted that the humidity of the air also affects the composition of the combustible mixture.

Due to all this, the temperature of even the ideal method of the mixture is significantly affected by the degree of filling the crank chamber. In a constant volume of crankcase at more high temperatures The mass of the combustible mixture will be less and, thereby, after its combustion in the cylinder will be lower pressure. Because of this, the phenomenon elements of the engine are trying to give such a form, especially the Carder (Orching) to achieve their maximum cooling.

The combustion of the mixture in the combustion chamber occurs at a certain speed, during the combustion of the crankshaft rotates to a certain angle. The pressure in the cylinder increases as the mixture burns. It is advisable to obtain the greatest pressure at the time when the work rate of the piston has already begun. To achieve this, the mixture must be lit a little earlier, with a certain advance. This is ahead, measured by an angle of rotation of the crankshaft, is called an angle for a ignition advance. Often the ignition advance is more convenient to measure the distance, which remains the piston to the top of the dead point.

Range of modifications

Before proceeding to work on the engine, it is necessary to decide which indicator we want to achieve. In five-, six-track engines of the racing category, we can strive to increase the CV, although it is known that as a result of this, the CV of the maximum moment is approaching the maximum power. We reduce the range of working revolutions, achieving in return for greater power.

In the engines of the popular category, and these are "Damba" engines with a volume of 125 cm 3 with a three-stage gearbox, one should not strive to achieve too large CV, it is necessary to achieve the largest range of working CV. In such engines (using its own nodes and aggregates), you can achieve power more than 10 kW at a speed of about 7000-8000 rpm.

It is also necessary to determine the range of refinement that we are going to perform. Need to know in advance whether this introduction to the modified engine or the refinement range will be so wide that in the end we will receive practically new engine With the preservation of several original (but modified) nodes, as required by the rule.

Assuming engine refinement, preference should be given to those operations that will significantly increase engine performance. However, it is not worth (at least at this stage of work) to provide for the implementation of such operations that require significant labor and which is known in advance that they will give minor results. Such operations include polishing of all engine cylinder channels, despite the fact that there is a universal belief in the effectiveness of this operation. Bent tests of many engines have shown that polishing of the cylinder channels increases the engine power by 0.15-0.5 kW. As you can see, the efforts spent on performing this work are completely incommensurable with the results.

Here are operations that will undoubtedly affect the increase in engine indicators: an increase in compression ratio; changing phases of gas distribution; Changing the shape and sizes of channels and windows of the cylinder; proper selection parameters of intake and exhaust systems; ignition advance optimization.

Change the degree of compression

An increase in the compression ratio, obtained by reducing the volume of the combustion chamber, leads to an increase in engine power. An increase in compression degree leads to an increase in the pressure of combustion in the cylinder by increasing the compression pressure, improve the circulation of the mixture in the combustion chamber and increase the combustion rate.

The degree of compression cannot be increased to any arbitrary value. It is limited by the quality of the fuel used, as well as the thermal and mechanical strength of the engine nodes. It suffices to say that with an increase in the effective degree of compression from 6 to 10, the forces acting on the piston increase almost twice; i.e. twice the load increases, for example, on a crank mechanism.

Taking into account the strength of the parts of the engine and the detonation properties of the available fuels, it is not recommended to use a geometric compression ratio more than 14. Increasing the degree of compression to this value requires not only the gasket removal (if it was), but also to give the corresponding cylinder head form, and sometimes the cylinder. To facilitate the calculation of the combustion chamber for different degrees, you can use the diagram shown in Fig. 9.17. Each curves refers to a specific cylinder working volume.

Fig. 9.17. The dependence diagram of the compression ratio A on the volume of the combustion chamber V 1 \u003d 125 cm 3 and V 2 -50 cm 3

In some engines with a relatively small degree of compression, its significant increase is possible only by mechanical processing. In this case, we will cry the combustion chamber and process it again. This also allows you to change the shape of the camera. Most modern engines used in karting have a combustion chamber in the form of a hat. This form should not be changed when engine improvements.

The only method of accurate determination of the volume of the combustion chamber is to fill it motor Oil Through a hole for the ignition candle (Fig. 9.18) when the piston is position in the upper dead point. With this method of measuring from the volume of oily oil, it is necessary to take away the volume of the candle hole. The volume of the candle with a short thread candle is 1 -1.1 cm '1, for a candle with long threads - 1.7-1.8 cm 3.

Pasters under the head of the cylinder in racing engines are either not used at all, or they are replaced by thin copper rings. In both cases, the surface of the cylinder and the head should be fit. The use of gaskets from a material with a low thermal conductivity coefficient is contraindicated, because it makes it difficult to the outflow of heat from the top of the cylinder sleeve carrying a significant heat load, to the head and its cooling edges. The cylinder head laying in no way should act in the combustion chamber. The protruding edge of the gasket will heat up and will become a source of gylinder ignition.

Fig. 9.18. Determination of the volume of combustion chamber

Octane number Gasoline used should correspond to the degree of compression. However, it should be borne in mind that the compression ratio is not the only factor determining the possible detonation of fuel.

Detonation depends on the flow of the combustion process, from the movement of the mixture in the combustion chamber, on the ignition method, etc. The type of fuel for a particular engine is selected by experimental. However, it does not make sense to use high-octic fuel for the engine with a low degree of compression, because the engine operation does not improve.

Purge Cylinder

The selection of the appropriate phases of gas distribution in the two-stroke engine plays a huge importance to remove the exhaust gases from the cylinder and filling it with a fresh mixture. In addition, it is necessary to direct the jets of the mixture moving from the bypass windows so that they pass through all the cylinder surches and the combustion chamber, blowing out the remnants of the exhaust gases and direct them to the graduation window.

To increase the CHV engine and, as a result, its capacity, it is necessary to significantly expand the release phase, or rather, increase the difference between the phases of the release and purge. As a result, the time during which the exhaust gases expanding, extending from the cylinder. In this case, at the time of opening overrun windows, the cylinder is already empty, the fresh charge entering it only slightly mixes with the exhaust gases.

The release phase increases due to the offset (spill) of the upper edge of the window. The release phase in racing engines reaches 190 ° compared to 130-140 ° in serial engines. This means that the upper edge can be cut into several millimeters. It is necessary, however, to take into account that as a result of the increase in the height of the exhaust window, the stroke of the piston is reduced on which the work is performed. Therefore, an increase in the height of the exhaust window pays off only if the loss in the work of the piston is compensated by improving the cylinder purge.

Due to the expediency of achieving the maximum difference between the phases of the release and purge, the opening angle of purge windows usually remains unchanged.

A significant impact on the purge quality is the size and form of overhead channels and windows. The inlet direction of the mixture into the cylinder from the bypass channel must correspond to the accepted purge system (see paragraph 9.2.4, Fig. 9.10). In the two and four-channel systems, the jet blowing systems entering the cylinder of the combustible mixture are directed over the piston to the cylinder wall, the opposite of the outlet window, and in the four-channel jet system, emanating from the windows located closer to the outlet window are usually directed to the axis of the cylinder. In systems with three or five byproof windows, one window must be located opposite the outlet window, the channel of this window should direct a fuel mixture under the minimum angle to the cylinder wall (Fig. 9.19). This is a necessary condition for the effective action of this additional jet, which is usually obtained by a decrease in its cross section, as well as the later opening of this window.

The manufacture of an additional (third or fifth) channel is a rule for engines with a rotating spool or membrane valve. In engines, in which the filling of the crank chamber controls the piston, on the site of the classic third (or fifth) bypass channel is the inlet window. In such engines there may be additional bypass channels, and the inlet window must have an appropriate form; Such a solution is shown in Fig. 9.20. In this engine there are three additional survey windows of a small size connected by a shared bypass channel, the input to which is located above the inlet window. The required intake phase is provided here by the corresponding form of the inlet window.

Fig. 9.19. The effect of the shape of the third bypass channel on the charge in the cylinder:

a - incorrect form; B- correct form

When installing on normal Engine The rotating spool in the cylinder appears the ability to make the bypass channel opposite the exhaust window. It is convenient to make a very curved short channel (Fig. 9.21, but),the flow of the mixture into which for a while closes the skirt of the piston.

The disadvantage of this solution is that the movement of the piston disrupts the normal current of the combustible mixture, but it has two important advantages: the small volume of the channel only slightly increases the volume of the crank chamber, and the combustible mixture, passing through the piston, is perfectly cooled. Almost such a channel is easy to do as follows. Two holes are made in the cylinder (bypass window and input to the channel), the ribs are cut in this place and the pad with the channel flowing in it is screwed down (Fig. 9.21.6). You can also try to cut the vertical groove in the cylinder mirror between the input to the channel and the window, the width of the groove is equal to the channel width. However, in this case, the movement of the piston down will cause some turbulization of the combustible mixture in the channel (Fig. 9.21, B).

Bypass channels should be sown to the windows in the cylinder.

Fig. 9.21. An additional bypass channel with a mixture flow through the piston:

a - principle of operation; B - part of the channel passes in an external lining; B - Channel Carved in Cylinder Mirror

The entrance to the bypass canal must have an area of \u200b\u200b50% more than the area of \u200b\u200bthe overhead window. Obviously, changing the channel cross section should be performed throughout its length. Corners of windows and channel sections must be rounded with a radius of 5 mm to increase the flow lamp.

Any errors are unacceptable when docking parts of channels located in different parts of the engine. This remark primarily concerns the place of connection of the cylinder with the engine crankcase, where the source of additional twisters of the mixture can be gasket, and the joints of the inlet and exhaust pipes with the cylinder. Vortices in the stream of mixture can also occur at the place of the joint of the cast cylinder shirt with a flooded or pinned sleeve (Fig. 9.22). Dimensions in these places must be unconditionally corrected.

In some engines, the cylinder windows are separated by the edge. This primarily concerns intake and final windows. It is not recommended to reduce the thickness of these ribs and, even more so, remove them with an increase in the area of \u200b\u200bthe window. Such ribs protect piston rings from getting into wide windows and, therefore, from breakdown. It is permissible only to give the streamlined form the edge of the inlet window, but only from the outer side of the cylinder.

Fig. 9.22. Charge violations caused by incorrect

mutual location of the cylinder liner and cast cylinder shirt

It is impossible to give an unambiguous recipe to obtain certain effects of refinement. In general, it can be said that an increase in the opening of the exhaust window increases the power of the engine, increasing the maximum power and the maximum point, but the narrowing range of working CV. A similar action has an increase in the size of the windows and sections of the channels in the cylinder.

Well illustrate these trends in the speed characteristics of the engine (Fig. 9.23) with a volume of 100 cm (the diameter of the cylinder is 51 mm, the stroke of the piston is 48.5 mm), resulting from changing the size and phases of the gas distribution (Fig. 9.24). In fig. 9.24, butthe sizes of windows in which the engine develops the largest power (curves N a.and M D.in fig. 9.23). The release phase is 160 °, purge - 122 °, intake - 200 °. The inlet window was opened at 48 ° from NMT, and was closed at 68 ° from VPT. Diameter of the diffuser of the carburetor 24 cm.

In fig. 9.24, b.showing the size of windows at which the largest working range of CV (see Figure 9.23, curves N B.and M c).The release phase is 155 °, purge - 118 ° and inlet - 188 °, opening the intake at an angle of 48 ° after NMT and closure at an angle of 56 ° after the VST. The diameter of the diffuser of the carburetor is 22 mm.

It should be noted that relatively small changes in the size and phases of gas distribution significantly changed the engine characteristics. At the engine BUTthe power is greater, but it is practically useless at a rotational speed below 6000 rpm. Option INapply to a significantly larger range of CV, and this is the main advantage of the engine without a gearbox.

Although the considered example relates to an engine that is not used in Poland, it illustrates the relationship between the form of windows and the cylinder channels and the parameters of its operation. However, it is necessary to remember what our finalization has led to the desired results, we will know only after their execution and checking the engine on the stand (or subjectively during running). Preparation of the racing engine is an infinite cycle of improvements and checks the results of this work, new improvements and checks, and other engine units (carburetor, exhaust system, etc.) have a huge impact on the engine characteristics (carburetor, exhaust system, etc.), optimal parameters which can be defined only by experiment.

It is also necessary to emphasize the great importance of the geometric symmetry of all windows and channels in the cylinder. Even a slight deviation from symmetry will have a negative effect on the movement of gases in the cylinder. A minor difference in the height of the bypass windows on both sides of the cylinder (Fig. 9.25) will cause an asymmetrical movement of the mixture and will break the action of the entire purge system. An excellent indicator that allows you to directly assess the correct direction of the flow of the mixture coming from bypass windows, are traces on the bottom of the piston. After some time, the engine work part of the bottom of the piston is covered with a layer of soot. The same part of the bottom, which is washed by a jet of freshly combustible mixture entering the cylinder, remains brilliant, as if her was washed.

Fig. 9.25. The effect of differences in the height of overlapping windows

on both sides of the cylinder on the symmetry of the charge movement

Piston and piston rings

Fig. 9.28. The dependence of the bandwidth of the input channel of the carburetor from the forum of its cross section

In modern engines, pistons made from material with a small linear extension coefficient are used, so the gap between the piston and the cylinder sleeve may be small. If we assume that the circle gap and the length of the piston skirt in the heated engine will be the same everywhere, then after cooling the piston is deformed. Therefore, the piston must receive the appropriate form during mechanical processing, which is done in practice. Unfortunately, this form is too complicated, and it can be obtained only on special machines. From this it follows that the shape of the piston cannot be changed by plumbing operations, and all sorts of chatting of the piston skirt with a file or sharpened, used everywhere after the piston is encouraged, will lead to the fact that the piston will lose the right form. In the event of an acute need for such a piston, it can be used, but you can not doubt that its interaction with the cylinder mirror will be much worse.

We must warn from using sandpaper for emergency stripping piston skirt. The grains of abrasive material are dug into mild piston material, after which the cylinder mirror is used. This will lead to the need to rocket the cylinder until the next repair size.

An approximate temperature distribution on the piston is shown in Fig. 9.29. The greatest thermal load falls on the bottom and the top, especially from the exhaust window. The temperature of the lower part of the skirt is less and dependent, first of all, from the shape of the piston. The shape of the inner surface of the piston should be such that in the cross section of the piston there were no essentials that impede heat exchange (Fig. 9.30). The heat from the piston of the cylinder is transmitted through the piston rings and the contact point of the piston skirt with the cylinder.

To reduce the weight of the piston and, thus, the reduction of forces noticeably increasing at a high speed of rotation of the engine, one can remove part of the material inside the piston, but only in its lower part. Typically, the lower edge of the piston inside ends with a collar that is a technological basis for treating the piston. This brown can be removed, leaving the thickness of the skirt in this place about 1 mm. The thickness of the piston wall should grow smoothly towards the bottom. You can slightly increase cutouts in the piston skirt under the bobbs. The shape and dimensions of these cuts should correspond to the cutouts at the bottom of the cylinder sleeve (Fig. 9.31). To change the time-section it is easiest to be easier to cut the lower edge of the piston from the inlet window, although the selection of the value of the subside is greater difficulty.

To reduce the heat load on the upper piston ring, it is recommended to make an edge groove with a width of 0.8-1 mm and a depth of 1-2 mm. Sometimes a similar groove (or even two) is made between rings. Such cuts guide the heat flux into the lower part of the piston, reducing the temperature of the piston rings.

In general, we are not able to change the view and location of the rings. We can only control the clearance in the lock (section) of a ring that should not exceed 0.5% diameter of the cylinder. It is also necessary to carefully determine the angular position of the locks so that they never fall on the windows when the piston moves (Fig. 9.32). Conducting work on the cylinder, it is also necessary to take into account the position of the locks of the piston rings.

Sometimes an easy way to reduce elasticity is applied. piston Ring By removing the champers on its inner edges. It provides the best adjacent rings to the cylinder mirror. This method is especially appropriate when changing the rings without grinding the cylinder.

Cracked mechanism

As already mentioned, in Engine 501 -Z3A.it is advisable to rearrange the cheeks of the crankshaft. After disassembling with the press above the shaft, you need to perform the following operations.

1. To deepen in the cheeks of the shaft of the nest for the lower head of the rod to the thickness of the additional discs attached to the outer surface of the cheeks (Fig. 9.35, size e).

2. Squeeze the semi-axes of the cheeks on the thickness of the additional
disks.

3. Reduce the rod thickness (Fig. 9.36) on the grinding machine. Manual processing applies only for finishing.
Thickness can be reduced even up to 3.5 mm, but provided that the connecting rod will be polished. Each scratch on the connecting rod is a voltage concentrator from which the development of cracks may have. In addition, all roundings must be made very carefully. By turning the connecting rod, it is advisable to make slots in the upper and lower heads to improve the access mixture to bearings.

4. Shorten the finger of crank up to size from(Fig. 9.36) equal to the width of the shaft after rearrangement of the cheeks, but before attaching additional disks. The finger must be shorted on both sides, it will allow you to leave the rolling tracks of the bearing rollers in the old place.

5. Weigh the upper and lower rod heads, as shown in Fig. 9.37.

6. Collect the crankshaft. Pressing the finger of the crank can be performed using the press or large vice.

Of course, after such an assembly it is difficult to achieve the alignment of the shaft semi-axle. The error can be detected by applying a steel plate to one of the cheeks (Fig. 9.38), which will lag behind another cheek. This can be corrected by hitting one of the cheeks of the Cyans (Fig. 9.39). More precisely, the shaft beating to check when it rotates in the bearings. On a chalk-covered half-sewer, Stihel denotes the places in which the beating should be reduced (Fig. 9.40). When assembling the shaft, you must remember the need to preserve the gap between the bottom head of the connecting rod and the cheeks of the shaft. This gap should be at least 0.3 mm. Too small gap in many cases is the cause of the roller bearing jamming.

7. Bring a crankshaft. This is done by the static method. Increased shaft on the prism and having hung the ship in the top head of the connecting rod, we will pick up the balanced mass so much (not to be confused with the weight of the weight of the weight) so that the shaft remains at rest at any position. The weight of the weights is part of the masses involved in the reciprocal movement, which must be balanced. Suppose that the mass of the top head of the connecting rod is 170 g, and the weight of the piston with the rings and the piston finger - 425 g. The mass that makes the reciprocating movement is 595. Assuming that equilibrium coefficient is 0.66, we obtain the mass, Which must be balanced, equal to 595x0.66 \u003d 392.7 g. Taken from this magnitude, the mass of the top head of the connecting head, we get a weight of Georgics G, suspended on the head.

The state of the static equilibrium of the crankshaft is achieved by drilling the holes in the cheeks of the shaft from the other side that pulls.

8. Make additional discs from steel and attach them to the shaft with three MB screws with secret conical heads. Before mounting the disks, it is advisable for a junction plane with a shaft to lubricate with a sealant. Screws to corner.

We add that additional discs can be fixed not to the shaft, but motionless to the inner walls of the crankcase. However, due to a loose fit of the disk to the wall, heat exchange can worsen. It should be noted that the shifting of the checker of the crankshaft does not exclude the use of thin "horseshoes".

Before starting the refinement of the cylinder, you need to make a tool for measuring the phases of gas distribution using a round tilter for this purpose with a scale of 360 ° (Fig. 9.42). Corrector install on the crankshaft of the engine, and I will attach the wire arrow to the engine.

For the unambiguous definition of the opening time and closing the windows, you can use a thin wire inserted through the window into the cylinder and the pressed piston in the upper edge of the window. The thickness of the wire on the measurement accuracy will practically not affect, but this method will facilitate the work. It is especially useful when determining the opening angle of the ink window.

Significantly facilitating the work on changing the phases of the gas distribution and sizes of channels and windows will help the removal of the implications from the cylinder mirror. Such an ottisk can be obtained as follows:

inside the cylinder put a piece of cardboard and fit it so that it is exactly lying along the cylinder mirror; His top edge must coincide with the top plane of the cylinder;

dumb end of a pencil squeeze out the contours of all windows;

on the cardboard from the cylinder, we get a cylinder mirror imprint; Along the print lines, cut the displayed windows in the cardboard.

On the obtained scan of the cylinder mirror, you can measure the distance from the edges of the windows to the upper plane of the cylinder and calculate the corresponding phases of the gas distribution (using the formulas existing in each book of engines).

Now consider how to fix the new phases of gas distribution in the engine refined. To do this, alternately install the necessary angles, measuring each time the distance from the upper edge of the piston to the upper plane of the cylinder. The measured distances are applied to the pre-made pattern.

Now we can outline a new form of windows, and then cut them on the pattern. It remains to put the pattern into the cylinder and increase the windows so that their shape coincides with designed. Using the pattern will save us from the need to multiple corners checks with an increase in windows.

Fig. 9.42. Non-reliable sensor for measuring the phases of gas distribution

The outlet valve begins to open at the end of the expansion process with ahead of N.M.T. At the angle φ O.V. \u003d 30h-75 ° (Fig. 20) and closes after V.M.T. With delay at the angle φ Z.V., when the piston moves in the filling tact in the direction to N.M.T. The beginning of the opening and closing of the inlet valve is also shifted relative to dead points: the discovery begins to V.T. Ahead of the angle φ 0. VP, and closure occurs after N.M.T. with delaying to the angle φ z.VP At the beginning of the compression tact. Most of the production and filling processes proceeds separately, but near V.M.T. Inlet and exhaust valves are open for a while at the same time. The duration of the overlap of valves equal to the amount of angles φ z.V + φ O.VP is small in piston engines (Fig. 20, a), and the combined can be significant (Fig. 20, b). The total duration of the gas exchange is φ O.V + 360 O + φ z.VP \u003d 400-520 o; At high-speed engines it is more.

Periods of gas exchange in two-stroke engines

In the two-stroke engine, gas exchange processes occur when the piston moves near N.M.T. and occupy a part of the piston in the expansion and compression tacks.

In engines with a looping scheme of gas exchange and intake, and the exhaust windows are opened by the piston, so the phases of the gas distribution and the diagram of the cross-sectional area of \u200b\u200bthe windows are symmetrical relative to N.M.T. (Fig. 24, a). In all engines with direct-flow schemes of gas exchange (Fig. 24, b), the opening phases of the outlet windows (or valves) are performed by asymmetric relative to N.M.T., thus achieving better cylinder filling. Usually intake windows and outlet windows (or valves) are closed simultaneously or with a small corner difference. Implement asymmetric phases is possible in the engine with a looping scheme of gas exchange,

if you install (on the inlet or release), additional devices are spools or valves. Due to the insufficient reliability of such devices, they are currently not used.

The total duration of the gas exchange processes in two-stroke engines corresponds to 120-150 ° the angle of rotation of the crankshaft, which is 3-3.5 times less than in four-stroke. The opening angle of exhaust windows (or valves) φ O.V. \u003d 50-90 ° B to N.M.T., and the angle of their presence of the opening φ φ \u003d 10-15 0. In high-speed engines with the release through the valves, these angles are larger, and in engines with release through windows - less.

In the two-stroke engines, the output and filling processes occur in the most part together - at the same time open intake (purge) and exhaust windows (or exhaust valves). Therefore, the air (or combustible mixture) enters the cylinder, as a rule, provided that the pressure in front of the intake windows is greater than the pressing windows (valves).

Literature:

Nalyvayko V.S., Stupachenko A.N. Syrko S.A. Methodical guidelines for laboratory work at the rate " Ship DVS", Nikolaev, NKI, 1987, 41c.

Ship engines of internal combustion. Textbook / Yu.Ya. Fomin, A.I. Gorban, V.V. Dobrovolsky, A.I. Lukin and Dru.-L.: Shipbuilding, 1989 - 344 p.: Il.

Internal combustion engines. The theory of piston and combined engines: ed. A.S. Orina, MG Kruglov -M.: Mechanical Engineering, 1983th - 372pro.

Vanhadt V.A. Ship engines of internal combustion. L. Shipbuilding, 1977.-392c.