Driving wheel slipping. Forces acting on a car wheel

With all the complexity of driving a car, the driver's work is ultimately reduced to the regulation of three parameters: the speed of movement, the effort and direction required for movement. And the complexity of control arises from the variety of conditions in which movement occurs, and the many options for combinations of speed, effort and direction. In each of these options, the behavior of the car has its own characteristics and obeys certain laws of mechanics, the set of which is called the theory of the car. It also takes into account the presence of the medium of motion, that is, the surface on which the wheels roll, and the air medium.
Thus, this theory covers two of the three links of the “driver-car-road” system of interest to us. But the movement of the car arises (and the laws of motion come into force) only after one or another, right or wrong action of the driver. Alas, we sometimes neglect the influence of this action on the behavior of the car. So, we do not always take into account, when examining acceleration, that its intensity depends, in addition to the characteristics of the car and the road, also on the extent to which the driver takes them into account, for example, how many seconds he spends on changing gears. There are many such examples.
The purpose of our conversations is to help the driver understand and take into account the laws of car behavior correctly. Thus, it is possible to ensure, on a scientific basis, the maximum use of the qualities of the car inherent in its technical characteristics, and traffic safety with the least expenditure of energy - mechanical (car), physical and mental (driver).
The laws of car behavior are usually grouped around the following qualities:
dynamism of movement, that is, speed properties;
patency, that is, the ability to overcome (or bypass) obstacles;
stability and controllability, that is, the ability to obediently follow the course set by the driver;
smooth running, that is, ensuring a favorable vibration characteristics of passengers and cargo in the body (not to be confused with the smooth operation of the engine and automatic transmission!);
efficiency, that is, the ability to perform useful transport work with minimal consumption of fuel and other materials.
The laws of behavior of the car belonging to different groups are largely interrelated. If, for example, a certain car does not have good indicators of smoothness and stability, then it is difficult for the driver, and in other conditions it is impossible to maintain the required speed, even if the vehicle has high dynamic performance. Even such seemingly secondary factors as acoustic data, again affect the dynamics: many drivers will prefer sluggish acceleration to intensive, if the latter is accompanied by a given model loud noise engine and transmission.
There are connecting links between the elements of the "driver - car - road" system. Between the road and the driver, this is information perceived by his vision and hearing. ”Between the driver and the car, there are controls that affect its mechanisms, and the feedback is perceived by the muscles, the driver's balance organs and, again, vision (devices) and hearing. Between the car and the road (environment) - the contact surface of the tires with the road (as well as the surface of the body and other parts of the car in contact with air).

The interrelation of the elements of the "driver - car - road" system.

Let us limit a few range of issues we are considering: we will assume that the driver receives sufficient and correct information, nothing prevents him from quickly and accurately processing it and making the right decisions. Then each law of the car's behavior is subject to consideration according to the scheme: the car moves under such and such conditions - such and such phenomena occur at the points of contact of tires with the road and the surface of the car with air - the driver acts to maintain or change this nature of movement, - the driver's actions are transmitted through the controls to the mechanisms of the car, and from them to the wheels - at the points of contact, new phenomena occur - the nature of the movement of the car remains or changes.
All this seems to be well known to motorists, but not always and not all of them interpret certain concepts in the same way. And science requires precision and rigor. Therefore, it is necessary, before studying the behavior of the car in different situations, to remind and agree about something. Thus, we will talk about what the driver has on the road.
First of all, about the weight of the car. We will be interested in only two of its so-called weight states - "total mass" and a state that we will conditionally call running. The mass is called full when the car - with a driver, passengers (according to the number of seats in the body) and cargo, and fully filled with fuel, grease and other liquids, is equipped with a spare wheel and a tool. Passenger weight is assumed to be 76 kg, baggage - 10 kg per person. In the running state, the driver is on board, but there are no passengers or cargo: that is, the car can move, but is not loaded. We will not talk about "own" (without driver and load) and even more "dry" mass (in addition, without fuel, lubrication, etc.), since in these states the car cannot move.
The distribution of its mass on the wheels, or its so-called axial load, and the load on each wheel and tire, have a great influence on the behavior of the car. In modern passenger cars in running condition, the front wheels account for 45-60% of the mass, and the rear wheels account for 55-40%. The first numbers refer to vehicles with rear-mounted engine, the second - to the front-engine. With full load, the ratio changes to approximately the opposite (at the "Zaporozhets", however, insignificantly). In trucks, the mass in the running state is distributed between the wheels almost equally, while the gross mass is in a ratio of about 1: 2, that is, the rear wheels are loaded twice as much as the front ones. Therefore, they are equipped with double slopes.
Without a source of energy, as well as without a driver, our "Moskvich" or ZIL could not move. Only on descents or after acceleration can the car cover a certain distance without the aid of the engine, consuming the accumulated energy. Most cars are powered by the engine. internal combustion(ICE). With regard to the theory of the car, the driver needs to know relatively little about it, namely, what it gives for movement. We will find out by considering the speed characteristics. In addition, you need to imagine how much the engine consumes fuel, that is, to know its economic, or fuel, characteristics.

External speed characteristic(ВСХ) of the engine shows the change in power (Ne - in hp and kW) and rotating (torque) moment (Me - in kgm) developed at different speeds of the shaft and at full opening throttle... At the bottom of the graph is an economic characteristic: the dependence of the specific fuel consumption (g - in G / l. S.-hour) on the number of revolutions per minute.

Speed ​​characteristics are graphs of changes in power and torque (torque) developed by the engine, depending on the number of revolutions of its shaft (rotation speed) with full or partial opening of the throttle valve (here we are talking about carburetor engine). Recall that the moment characterizes the effort that the engine can "provide" to the car and the driver to overcome certain resistances, and power is the ratio of effort (work) to time. The most important is the speed characteristic taken, as they say, "at full throttle". It is called external. The uppermost points of the curves are essential in it, corresponding to the highest power and torque, which are usually recorded in the technical characteristics of cars and engines. For example, for the VAZ-2101 Zhiguli engine - 62 liters. from. (47 kW) at 5600 rpm and 8.9 kgm at 3400 rpm.

The partial speed characteristic of the engine shows the change in power developed at different openings of the throttle valve of the carburetor.
As you can see, the number of revolutions with the greatest number of "kgm" is much less than the number of revolutions corresponding to the maximum "l. from". This means that if the carburetor throttle valve is fully open, then the torque at relatively low engine power and vehicle speed will be greatest, and with a decrease or increase in the number of revolutions, the torque value will decrease. What is important in this position for a motorist? It is important that the tractive effort on the wheels of the car also changes in proportion to the moment. When driving with a throttle that is not fully open (see graph), you can always increase power and torque by depressing the accelerator pedal harder.
Here, looking ahead, it is appropriate to emphasize that the power transmitted to the drive wheels cannot be greater than that received from the engine, no matter what devices are used in the transmission system. Another thing is the torque, which can be changed by introducing into the transmission a pair of gears with appropriate gear ratios.

Economic characteristics of the engine with different throttle opening.

The economic characteristic of the engine reflects the specific fuel consumption, that is, its consumption in grams per horsepower (or one kilowatt) per hour. This characteristic, like the speed characteristic, can be built for the engine to operate at full or partial load. The peculiarity of the engine is such that with a decrease in the throttle opening, more fuel has to be consumed to obtain each unit of power.
The description of the characteristics of the engine is given here somewhat simplified, but it is sufficient for a practical assessment of the dynamic and economic performance of the car.

Losses in the operation of transmission mechanisms. Here Ne and Me are the power and torque of the engine, NK and Mk are the power and torque supplied to the driving wheels.

Not all of the energy from the engine is used directly to propel the vehicle. There is also "overhead" - for the operation of transmission mechanisms. The lower this flow rate, the higher the efficiency of the transmission, denoted by the Greek letter η (eta). Efficiency is the ratio of the power transmitted to the drive wheels to the engine power measured at its flywheel and recorded in the specification for the model.
Mechanisms not only transmit energy from the engine, but also partly consume it themselves - for friction (slipping) of the clutch discs, friction of the gear teeth, as well as in bearings and cardan joints and for shaking the oil (in the case of the gearbox, drive axle). From friction and agitation of the oil, mechanical energy is converted into heat and dissipated. This "overhead consumption" is not constant - it increases when an additional pair of gears is switched on, when the universal joints operate at a steep angle, when the oil is very viscous (in cold weather), when the differential gears are actively working on a corner (when driving in a straight line, their work small).
The transmission efficiency is approximately:
- for passenger cars 0.91-0.97,
for freight - 0.85 0.89.
When cornering, these values ​​deteriorate, that is, they decrease by 1-2%. when driving on very not flat road(cardan work) - by another 1-2%. in cold weather - by another 1-2%, when driving in lower gears - by about 2% more. So, if all these driving conditions occur at the same time, the "overhead" is almost doubled, and the value of the efficiency may decrease at passenger car up to 0.83-0.88, for cargo - up to 0.77-0.84.

Diagram of the main dimensions of the wheel and tire.

A list of what is at the disposal of the driver to perform a certain transport work round off the wheels. All qualities of the car depend on the characteristics of the wheel: dynamism, economy, smoothness, stability, traffic safety. Speaking about a wheel, we mean first of all its main element - the tire.
The main load from the mass of the car is taken by the air in the tire chamber. A certain, always the same number of kilograms of load must fall on a unit of air. In other words, the ratio of the wheel load to the amount of compressed air in the tire chamber must be constant. Based on this position and taking into account the stiffness of the tire, the action of centrifugal force during the rotation of the wheel, etc., an approximate relationship was found between the dimensions of the tire, the internal pressure p in it and the permissible load on the tire G k -

where W is the coefficient of the specific carrying capacity of the tire.
For radial tires, the W coefficient is equal to - 4.25; for trucks of a larger size - 4. For tires with metric designations, the value of W is, respectively, 0.00775; 0.007; 0.0065 and 0.006. Tire sizes are entered into the equation as they are fixed in GOSTs for tires - in inches or millimeters.
It should be noted that the size of the rim diameter is included in our equation in the first degree, and the size (diameter) of the profile section is in the third, that is, in a cube. Hence the conclusion: the cross section of the profile, not the diameter of the rim, is of decisive importance for the carrying capacity of the tire. This observation can also serve as confirmation: the values ​​of the permissible tire load recorded in GOST are almost proportional to the square of the section size.
From the dimensions of the tire, we will be especially interested in the radius r to the wheel rolling, and the so-called dynamic, that is, measured when the car is moving, when this radius increases in comparison with the static radius of the wheel with the tire, from its heating and from the action of centrifugal force. For further calculations, r can be taken to be equal to half the tire diameter given in GOST.
Summarize. The driver is given: a car with a certain mass, which is distributed to the front and rear wheels; a motor with a known characteristic of power, torque and revolutions; transmission with known efficiency and gear ratios; finally, wheels with tires of a certain size, load capacity and internal pressure.
The driver's task is to use all this wealth in the most profitable way: to achieve the goal of the trip faster, safer, with the lowest costs, with the greatest convenience for passengers and the safety of cargo.

Uniform movement

It is unlikely that the driver will carry out calculations on the go, gleaned from these simple formulas. There will not be enough time for calculations, but they will only distract attention from operating the machine. No, he will act on the basis of his experience and knowledge. But still, it is better if at least a general understanding of the physical laws that govern the operation of a car is added to them.

Forces acting on the wheel:
G k - vertical load;
M k is the torque applied to the wheel;
P k - tractive effort;
R in - vertical reaction;
R g - horizontal reaction.

Let's take the seemingly simplest process - uniform movement along a straight and level road. Here, the driving wheel is affected by: torque M k, transmitted from the engine and creating a traction force P k; equal to the latter horizontal reaction R k, acting in the opposite direction, that is, along the course of the car; the force of gravity (mass) corresponding to the load G k on the wheel, and the equal vertical reaction R c.
The tractive force P k can be calculated by dividing the torque supplied to the drive wheels by their rolling radius. Recall that the torque coming from the engine to the wheels, the box and the main gear increase several times according to their gear ratios. And since losses are inevitable in the transmission, the value of this increased torque must be multiplied by the efficiency of the transmission.

Values ​​of adhesion coefficient (φ) for asphalt pavement in different conditions.

At each separately taken instant, the points closest to the road in the contact zone of the wheel with the road are motionless relative to it. If they moved relative to the road surface, the wheel would skid and the car would not move. For the points of contact of the wheel with the road to be stationary (recall - at each separately taken moment!), Good adhesion of the tire to the road surface is required, assessed by the coefficient of friction φ ("phi"). On a wet road, as the speed increases, the grip decreases sharply, since the tire does not have time to squeeze out the water that is in the contact area with the road, and the remaining moisture film makes it easier for the tire to slide.
But back to the traction force P k. It represents the impact of the driving wheels on the road, to which the road responds with an equal and opposite reaction force R r. The strength of contact (that is, adhesion) of the wheel to the road, and hence the magnitude of the reaction R r, is proportional (school physics course) to the force G k (and this is the part of the car's mass per wheel) pressing the wheel on the road. And then the maximum possible value of R r will be equal to the product of φ and the part of the mass of the car falling on the drive wheel (that is, G k). φ - coefficient of adhesion, familiarity with which took place just now.
And now we can draw a simple conclusion: if the tractive force P k is less than the reaction R r or, in extreme cases, is equal to it, then the wheel will not slip. If this force turns out to be greater than the reaction, then there will be slippage.
At first glance, it seems that the coefficient of adhesion and the coefficient of friction are equivalent concepts. For paved roads, this conclusion is quite close to reality. On soft ground (clay, sand, snow), the picture is different, and slipping occurs not from a lack of friction, but from the destruction of the soil layer by the wheel in contact with it.
Let us return, however, to solid ground. When a wheel rolls on the road, it experiences resistance to movement. By what means?
The point is that the tire is deformed. When the wheel rolls to the point of contact, the compressed elements of the tire come up all the time, and the stretched ones move away. Mutual movement of rubber particles causes friction between them. The deformation of the ground by the tire also requires energy.
Practice shows that rolling resistance should increase with decreasing tire pressure (its deformations increase), with an increase in tire circumferential speed (centrifugal forces stretch it), as well as on an uneven or rough road surface and in the presence of large protrusions and grooves of the tread.
It's on a solid road. And the tire crumbles soft or not very hard, even the asphalt softened from the heat, and part of the tractive force is also spent on this.

The rolling resistance coefficient on asphalt increases with increasing speed and decreasing tire pressure.

The rolling resistance of the wheel is estimated by the factor f. Its value grows with increasing driving speed, decreasing tire pressure and increasing unevenness of the road. So, on a cobblestone or gravel highway, to overcome rolling resistance, one and a half times more force is needed than on asphalt, and on a country road - twice, on sand - ten times more!
The force P f of the rolling resistance of the car (at a certain speed) is calculated somewhat simplistically, as the product total mass the vehicle and the rolling resistance coefficient f.
It may seem that the forces of adhesion P φ and rolling resistance P f are identical. Further, the reader will make sure that there are differences between them.
In order for the car to move, the tractive force must, on the one hand, be less than the adhesion force of the wheels to the ground or, in extreme cases, equal to it, and on the other hand, it must be greater than the resistance to motion (which, when driving at a low speed, when the air resistance is insignificant, can be consider equal strength rolling resistance) or equal to it.
Depending on the engine speed and throttle opening, the engine torque changes. It is almost always possible to find such a combination of engine torque values ​​(by corresponding accelerator pressure) and gear selection in the box so as to constantly be within the framework of the just mentioned driving conditions.
For moderately fast driving on asphalt (as follows from the table), significantly less tractive power is required than what cars are able to develop even in top gear. Therefore, you need to go with a half-closed throttle. Under these conditions, the cars are said to have a large supply of traction. This margin is necessary for acceleration, overtaking, climbing.
On dry asphalt, traction is, with rare exceptions, greater than traction in any gear in the drivetrain. If it is wet or icy, then moving in low gears (and starting off) without slipping is possible only with incomplete opening of the throttle valve, that is, with a relatively small engine torque.

Power balance graph. The intersection points of the curves correspond to the highest speeds on a flat road (right) and uphill (left point).

Every driver, every designer wants to know the possibilities this car... The most accurate information is provided, of course, by thorough tests in different conditions... With knowledge of the laws of motion of a car, satisfactorily accurate answers can be obtained by calculation. To do this, you need to have: the external characteristic of the engine, data on the gear ratios in the transmission, the mass of the car and its distribution, the frontal area and, approximately, the shape of the car, the size of the tires and the internal pressure in them. Knowing these parameters, we will be able to determine the items of power consumption and build a graph of the so-called power balance.
First, we plot the speed scale by combining the corresponding values ​​of the number of revolutions n e of the motor shaft and the speed V a, for which we use a special formula.
Secondly, by subtracting graphically (measuring down the vertical corresponding segments) from the curve external characteristics power losses (0, lN e), we get another curve showing the power N k supplied to the wheels (we took the transmission efficiency equal to 0.9).
The power consumption curves can now be plotted. Let us set aside from the horizontal axis of the graph the segments corresponding to the power consumption N f for rolling resistance. We count them according to the equation:

Draw the N f curve through the obtained points. We put aside from it the segments corresponding to the power consumption N w for air resistance. We calculate their value, in turn, according to the following equation:

where F is the frontal area of ​​the car in m 2, K is the coefficient of air resistance.
Note that luggage on the roof increases the air resistance by 2 - 2.5 times, a trailed summer cottage by 4 times.
The segments between the curves N w and N k characterize the so-called excess power, the reserve of which can be used to overcome other resistances. The intersection point of these curves (far right) corresponds to the fastest speed that the car is capable of developing on a horizontal road.
By changing the ratios or scales of the speed scales (depending on the gear ratios), you can build graphs of the power balance for driving on roads with different surfaces and in different gears.
Further, if we set aside from the curve N w the segments corresponding, for example, to the power that needs to be spent to overcome a certain rise, then we get a new curve and a new intersection point. This point corresponds to the highest speed with which the given rise can be taken without acceleration.

On the rise, the load on the wheels increases. The dotted line shows (to scale) its value for a horizontal road, black arrows - when driving uphill:
α is the ascent angle;
Н - lifting height;
S - lifting length.

Here it must be borne in mind that on uphills, the force of gravity is added to the forces opposing the movement of the car. In order for the car to move uphill, the angle of which will be denoted by the letter α ("alpha"), the tractive force must be no less than the rolling and lifting resistance forces combined.
A Zhiguli car, for example, has to overcome rolling resistance of about 25 kgf on smooth asphalt, GAZ-53A - about 85 kgf. This means that for them to overcome the rise in top gear at a speed of 88 or 56 km / h, respectively (that is, at the highest engine torque), taking into account air resistance forces of about 35 and 70 kgf, a traction force of about 70 and 235 kgf remains. We divide these values ​​by the values ​​of the total mass of the cars and we get slopes of 5 - 5.5 and 3 - 3.5%. In the third gear (here the speed is lower, and the air resistance can be neglected), the maximum climb angle will be about 12 and 7%, in the second - 20 and 15%, in the first - 33 and 33%.
Calculate once and memorize the lift values ​​your car can handle! By the way, if it is equipped with a tachometer, then remember also the number of revolutions corresponding to the greatest moment - it is recorded in the technical characteristics of the car.
The forces of adhesion of the wheels to the road on the rise and on a flat road are different. On the rise, the front wheels are unloaded and the rear wheels are additionally loaded. The traction of the rear drive wheels is increased and slippage is less likely. Front-wheel-drive vehicles have less traction when going uphill and are more likely to slip.
Before lifting, it is advantageous to give the car acceleration, to accumulate energy, which will make it possible to take the lift without a significant reduction in speed and, perhaps, also without changing to a lower gear.

Influence of the final drive ratio on speed and power reserve

It should be emphasized that both the transmission ratios and the number of gears in the box have a great influence on the dynamics of the car. From the graph, which shows the engine power curves (respectively, shifted depending on different gear ratios of the final drive) and the resistance curve, it can be seen that with a change in the gear ratio, the highest speed changes only slightly, but the power reserve increases sharply with its increase. This, of course, does not mean that the gear ratio can be increased indefinitely. Its excessive increase leads to a noticeable decrease in vehicle speed (dashed line), engine and transmission wear, and excessive fuel consumption.
There are more accurate calculation methods than those described by us (the dynamic characteristic proposed by Academician E.A. Chudakov, and others), but using them is a rather complicated matter. At the same time, there are completely simple approximate calculation methods.

With a uniform motion, there is no acceleration, therefore, the dynamic factor for thrust D is equal to the coefficient of the total resistance of the road ψ, that is, D = ψ = f to + i.

That is, using dynamic response with a known coefficient of rolling resistance of wheels f to, you can find the value of the overcome rise i when the vehicle is moving evenly with full load.

According to the task ψ = 0.082, when driving on a road of category V, we take f k = 0.03.

Then, for uniform motion, the value of the limiting angle of ascent:

α max = arctan (D max - f k), deg.

Calculations according to this formula are carried out without taking into account the action of the force of aerodynamic resistance on the car, since when overcoming the maximum possible climbs, the speed of the car is not high.

Driving without slipping is possible if the following conditions are met:

D с = a ∙ φ х ∙ cos α max / (L-Hd ∙ (φ х + f к)) ≥ D max.

D c - dynamic factor for adhesion

a- distance from the center of mass to the rear axle of the vehicle

α max - the limiting angle of the overcome rise

L- the wheelbase of the car (since the wheel formula of KamAZ is 6 * 4, then for L I take the distance from the front axle to the axle of the balancer)

Hd - height of the center of gravity

f k - rolling resistance coefficient

Hd = 1/3 * hd, where hd is the overall height

a = m 2 / m a * L, where m 2 is the weight of the car falling on the rear axle (rear bogie), m a is the total weight of the car.

According to the task, the coefficient of adhesion of wheels to the road is φ х = 0.2. For a KamAZ car:

a = 125000/19350 * 3.85 = 2.48m

Hd = 1/3 * 2.960 = 0.99

D c = 2.48 * 0.2 * cos 25 ° / (3.85-0.99 * (0.2 + 0.03)) = 0.124< D max = 0,489.

For Mercedes car:

A = 115000/200000 * 4.2 = 2.42m

Hd = 1/3 * 2.938 = 0.98m

D c = 2.42 * 0.2 * cos 22 ° / (4.2-0.98 (0.2 + 0.03)) = 0.113

Referring to the dynamic car passport, we see that since D sc

Conclusion: For a given value of φ x = 0.2, on a road with limiting angles of ascent and full load, cars move with slipping of the driving wheels.

The calculation in this course work of the limiting angles of the car's climbs to overcome allows us to conclude that the value of these angles depends, first of all, on three factors: the mass of the car, the magnitude of the traction force and the value of the rolling resistance coefficient of the wheels.

10. Determination of the maximum traction force on the hook in all gears and verification of the possibility of movement under the condition of slipping on the road ψ = 0.11 and φ x = 0.6, determination of the lowest gear at which the car will move without slipping on the specified road.

The pulling force on the hook characterizes the vehicle's ability to tow trailed links. The value of the ultimate traction force on the hook of the car is determined by the formula:

where is the ultimate pulling force on the hook, N;

- maximum tractive force in gear, N;

- the force of air resistance corresponding to the mode of movement with the maximum traction force, N;

- the force of the total road resistance, N.

To check the vehicle's ability to move according to the slipping condition, it is necessary to determine the adhesion force of the driving wheels to the road and compare the obtained value with the limit value of the traction force on the hook for each gear.

P tsc = m 2 ∙ L ∙ φ х / (a-Hd ∙ (φ х + f к)) - traction force for adhesion.

An example of calculation for a KamAZ car:

1st gear:

84.147kN; = 0.007kN; = 28.5kN.

84.147-0.007-28.5 = 55.64kN

2nd gear:

43.365kN; = 0.0254kN; = 28.5kN.

43.365-0.0254-28.5 = 14.84kN

3rd gear:

35.402kN; = 0.0382kN; = 28.5kN.

35.402-0.0382-28.5 = 6.86kN

P tsc = 125000 * 3.85 * 0.6 / (2.48-0.98 * (0.6 + 0.02)) = 151.1kN

Calculation example for a MERCEDES car:

1st gear:

97.823kN; = 0.005kN; = 29.43kN.

97.823-0.005-29.43 = 68.388kN

2nd gear:

55.59kN; = 0.0169kN; = 29.43kN.

55.59kN -0.0169 -29.43 = 26.14kN

3rd gear:

33.491kN; = 0.0464kN; = 29.43kN.

33.491-0.0464-29.43 = 4.01kN

P tsc = 115000 * 4.2 * 0.6 / (2.42-0.98 * (0.6 + 0.02)) = 159.9kN

Based on the fact that in any gear, we can say that when the car is moving, there is no slippage of the driving wheels.

Comparative table of the obtained estimated parameters of traction and speed properties, conclusions.

Conclusion: In this section, a study was made of the traction and speed properties of two cars with almost the same power.

Despite the fact that the MERCEDES engine has the same power, and the MERCEDES car itself is, in general, heavier, the high torque at medium speeds and the increased transmission ratio allow it to surpass the KamAZ car in terms of traction properties and developed hook effort. The KamAZ car has a higher maximum speed, acceleration.

In turn, the car, MERCEDES is able to overcome steeper climbs, which makes it indispensable on difficult terrain.

In order to set a stationary car in motion, traction alone is not enough. Friction is also needed between the wheels and the road. In other words, the car can only move if the driving wheels adhere to the road surface. In turn, the traction force depends on the grip weight of the vehicle Gv, i.e. the vertical load on the drive wheels. The greater the vertical load, the greater the adhesion force:

where Psc is the adhesion force of the wheels to the road, kgf; F - coefficient of adhesion; GK - adhesion weight, kgf. Driving condition without wheel slip

Pk< Рсц,

that is, if the tractive force is less than the traction force, then the drive wheel rolls without slipping. If a traction force is applied to the driving wheels, which is greater than the traction force, then the car can only move with the slipping of the driving wheels.

The coefficient of adhesion depends on the type and condition of the coating. On paved roads, the value of the coefficient of adhesion is mainly due to the sliding friction between the tire and the road and the interaction of tread particles and mismatched surface irregularities. When wetting a hard surface, the adhesion coefficient decreases very noticeably, which is explained by the formation of a film from a layer of soil particles and water. The film separates the rubbing surfaces, weakening the interaction between the tire and the coating and reducing the coefficient of grip. When the tire slides along the road in the contact zone, the formation of elementary hydrodynamic wedges is possible, causing the elements of the tire to rise above the microprotrusions of the coating. The direct contact of the tire and the road in these places is replaced by fluid friction, in which the coefficient of adhesion is minimal.

On deformable roads, the friction coefficient depends on the shear resistance of the soil and the amount of internal friction in the soil. The protrusions of the tread of the drive wheel, plunging into the ground, deform and compact it, which causes an increase in shear resistance. However, after a certain limit, soil destruction begins, and the friction coefficient decreases.

The tread pattern of the tire also affects the grip coefficient. Passenger car tires have a finely patterned tread for good grip on hard surfaces. Truck tires have a large tread pattern with wide and high lugs. During movement, the lugs cut into the ground, improving the vehicle's passability. Abrasion of the protrusions during use reduces the grip of the tire.

As the inflation pressure rises, the grip coefficient first increases and then decreases. The maximum value of the coefficient of adhesion corresponds approximately to the value of the pressure recommended for the given tire.

With the tire completely sliding on the road (slipping of the driving wheels or the skid of the braking wheels), the value of φ can be 10 - 25% less than the maximum. The lateral friction coefficient depends on the same factors, and it is usually taken equal to 0.7F. Average values ​​of adhesion coefficient vary widely from 0.1 (icy pavement) to 0.8 (dry asphalt and cement concrete pavement).

Tire adhesion is of paramount importance for road safety, as it limits the ability of the vehicle to brake intensively and drive the vehicle safely without side-slip.

The insufficient value of the coefficient of adhesion is the cause of an average of 16%, and in unfavorable periods of the year - up to 70% of the total number of road traffic accidents. The International Commission for the Prevention of Slippery Road Surfaces has established that the value of the adhesion coefficient for traffic safety conditions should not be less than 0.4.

Forces acting on the car

Car braking

Vehicle stability

Vehicle handling

Passage of the car

The car moves at a certain speed as a result of the action on it of the driving forces and forces that resist the movement (Fig. 1).

The forces that impede the movement of the vehicle include: rolling resistance forces Pf, the resistance created by the rise of the road Pa, air resistance Pw, resistance of inertial forces Pj... To overcome these forces, the car is equipped with an energy source - an engine. The torque resulting from the operation of the engine is transmitted through the power train and axle shafts to the drive wheels of the vehicle. Their rotation is impeded by the friction force that appears between the wheels and the road surface.

During rotation, the drive wheels create circumferential forces that act on the road, trying to push it back, as it were. The road, in turn, exerts equal resistance (tangential reaction) on the wheels, which causes the car to move.

The force that drives the vehicle is called traction force and is denoted by Ph. The relationship between these quantities or the limiting condition of the car's motion, at which equilibrium is ensured between the traction force and the forces of resistance to motion, can be expressed by the formula

Pk = Pf ± Pa + Pw + Pj.

This equation is called traction balance equation and allows you to establish how the pulling force is distributed over various types of resistance.

Road resistance

The rolling resistance of a tire on the road is a consequence of the energy expended on hysteresis (internal) losses in the tire and on rutting (external) losses. In addition, some of the energy is lost as a result of surface friction of tires on the road, resistance in the bearings of the hubs of the driven wheels and air resistance to rotation of the wheels. Due to the complexity of taking into account all the factors, the rolling resistance of the wheels of the car is estimated by the total costs, considering the force of the rolling resistance to be external with respect to the car. When an elastic wheel rolls on a hard road, external losses are negligible. The layers of the lower part of the tire are compressed and stretched. Friction occurs between the individual tire particles, heat is generated, which is dissipated, and the work expended on deformation of the tire does not return completely during the subsequent restoration of the tire shape. When an elastic wheel rolls, deformations in the front of the tire increase, and in the rear, they decrease.

When a hard wheel rolls on a soft deformable road (ground, snow), there are practically no losses for tire deformation and energy is spent only on deformation of the road. The wheel crashes into the ground, squeezes it to the side, pressing individual particles, forming a rut.

When a deformable wheel rolls on a soft road, energy is expended on overcoming both internal and external losses.

When an elastic wheel is rolling on a soft road, its deformation is less than when rolling on a hard road, and the deformation of the soil is less than when rolling on a hard one on the same soil.

The value of the rolling resistance force can be determined from the formula

Pf = Gf cos a,

Pf - rolling resistance force;

G is the weight of the vehicle;

a - the angle characterizing the steepness of the ascent or descent;

f is the rolling resistance coefficient, which takes into account the deformation forces of tires and pavements, as well as the friction between them in various road conditions.

The value of the rolling resistance coefficient ranges from 0.012 (asphalt concrete pavement) to 0.3 (dry sand).

Fig. 1. Forces acting on a moving vehicle

Climbing resistance. Highways consist of alternating ups and downs and rarely have long horizontal sections. The steepness of the rise is characterized by the value of the angle a (in degrees) or the value of the slope of the road t, which is the ratio of the elevation H to the position of B (see Fig. 1):

i = H / B = tg a.

The weight of a car G moving uphill can be decomposed into two force components: G sina, directed parallel to the road, and Gcosa, perpendicular to the road. The force G sin a is called the force of resistance to ascent and is denoted by Ra.

Ascent angles on paved roads are small and do not exceed 4 - 5 °. For such small angles, we can assume

i = tg a ~ sin a, then Pa - G sin a = Gi.

When moving downhill, the force of Ra has the opposite direction and acts as a driving force. Angle a and slope i are considered positive on the rise and negative on the downhill.

Modern highways do not have clearly defined sections with a constant slope; their longitudinal profile is smooth. On such roads, the slope and the force P are constantly changing during the movement of the vehicle.

Resistance to unevenness. No road surface is completely flat. Even new cement-concrete and asphalt-concrete pavements have irregularities up to 1 cm high. Under the influence of dynamic loads, the irregularities increase rapidly, reducing the speed of the vehicle, shortening its service life and increasing fuel consumption. Irregularities create additional resistance to movement.

When the wheel hits a long cavity, it hits the bottom of the wheel and is thrown up. After a strong impact, the wheel can separate from the surface and hit again (already from a lower height), making damped oscillations. Driving over short dimples and ridges is associated with additional deformation of the tire due to the force that occurs when the bump hits the bump. Thus, the movement of the car on the unevenness of the road is accompanied by continuous impacts of the wheels and vibrations of the axles and body. As a result, additional energy dissipation in the tire and suspension parts occurs, sometimes reaching significant values.

Additional resistance caused by road irregularities is taken into account by conventionally increasing the rolling resistance coefficient.

The values ​​of the rolling resistance coefficient f and the slope i together characterize the quality of the road. Therefore, they often talk about road resistance P, equal to the sum of the forces Pf and Ra:

P = Pf -f Pa = G (f cos a -f sin a) ~ G (f + i).

The expression in parentheses is called road drag coefficient and denote by the letter F. Then the resistance force of the road

P = G (f cos a -f sin a) = G f.

Windage. When the car moves, the air environment also resists it. The power consumption for overcoming air resistance consists of the following values:

Frontal drag resulting from the pressure difference between the front and rear of a moving vehicle (about 55 - 60% of the total air resistance);

Resistance created by protruding parts: footrests, fenders, license plate (12 - 18%);

Resistance arising from the passage of air through the radiator and engine compartment (10-15%);

Friction of outer surfaces against nearby air layers (8 - 10%);

Resistance caused by the pressure difference between the top and bottom of the vehicle (5 - 8%).

As the speed increases, the air resistance also increases.

Trailers cause an increase in the air resistance force due to significant turbulence of air flows between the tractor and trailer, as well as due to an increase in the outer friction surface. On average, it can be assumed that the use of each trailer increases this resistance by 25% compared to a single vehicle.

Force of inertia

In addition to the resistance forces of the road and air, the inertia forces P) influence the movement of the car. Any change in the speed of movement is accompanied by overcoming the force of inertia, and its value is the greater, the more upholstered m, aeea of ​​the car:

The running time of the vehicle is usually short compared to the total running time. So, for example, when working in cities, cars move evenly 15 - 25% of the time. From 30% to 45% of the time is spent by accelerating the movement of the car and 30-40% - by coasting and braking. When starting off and increasing the speed, the car moves with acceleration - its speed is uneven. The faster the car accelerates, the more the car accelerates. Acceleration shows how the speed of the vehicle increases in every second. In practice, the acceleration of a car reaches 1 - 2 m / s2. This means that for every second the speed will increase by 1 - 2 m / s.

The force of inertia changes as the vehicle is moving in accordance with the change in acceleration. To overcome the inertial force, part of the traction force is consumed. However, in cases where the car is coasting after preliminary acceleration or during braking, the inertia force acts in the direction of movement of the car, acting as a driving force. Taking this into account, some difficult-to-pass sections of the road can be overcome with a preliminary acceleration of the vehicle.

The magnitude of the force of resistance to acceleration depends on the acceleration of the movement. The faster the car accelerates, the greater this force becomes. Its value changes even when starting off. If the car starts off smoothly, then this force is almost absent, and with a sharp start it can even exceed the tractive force. This will lead either to a stop of the car, or to slipping of the wheels (in case of insufficient value of the coefficient of adhesion).

During the operation of the car, the driving conditions are constantly changing: the type and condition of the coating, the magnitude and direction of the slopes, the strength and direction of the wind. This changes the speed of the vehicle. Even in the most favorable conditions (driving on improved highways outside cities and towns), vehicle speed and tractive power rarely remain constant for a long time. The average speed of movement (defined as the ratio of the distance traveled to the time spent on the passage of this route, taking into account the time of stops along the way) is affected, in addition to resistance forces, by the influence of a very large number of factors. These include: the width of the carriageway, traffic intensity, road illumination, meteorological conditions (fog, rain), the presence of hazardous areas (railway crossings, congestion of pedestrians), the condition of the vehicle, etc.

In difficult road conditions, it may happen that the sum of all resistance forces exceeds the tractive force, then the movement of the car will be slowed down and it may stop if the driver does not take the necessary measures.

Car wheel adhesion to the road

In order to set a stationary car in motion, traction alone is not enough. Friction is also needed between the wheels and the road. In other words, the car can only move if the driving wheels adhere to the road surface. In turn, the adhesion force depends on the grip weight of the vehicle Gv, i.e. the vertical load on the drive wheels. The greater the vertical load, the greater the adhesion force:

Psc = ФGk,

where Psc is the adhesion force of the wheels to the road, kgf; F - coefficient of adhesion; GK - adhesion weight, kgf. Driving condition without wheel slip

Pk< Рсц,

that is, if the tractive force is less than the traction force, then the drive wheel rolls without slipping. If a traction force is applied to the driving wheels, which is greater than the traction force, then the car can only move with the slipping of the driving wheels.

The coefficient of adhesion depends on the type and condition of the coating. On paved roads, the value of the traction coefficient is mainly due to the sliding friction between the tire and the road and the interaction of the tread particles and the unevenness of the surface. When wetting a hard surface, the adhesion coefficient decreases very noticeably, which is explained by the formation of a film from a layer of soil particles and water. The film separates the rubbing surfaces, weakening the interaction between the tire and the coating and reducing the coefficient of grip. When the tire slides along the road in the contact zone, the formation of elementary hydrodynamic wedges is possible, causing the elements of the tire to rise above the microprotrusions of the coating. The direct contact of the tire and the road in these places is replaced by fluid friction, in which the coefficient of adhesion is minimal.

On deformable roads, the friction coefficient depends on the shear resistance of the soil and the amount of internal friction in the soil. The protrusions of the tread of the drive wheel, plunging into the ground, deform and compact it, which causes an increase in shear resistance. However, after a certain limit, soil destruction begins, and the friction coefficient decreases.

The tread pattern of the tire also affects the grip coefficient. Passenger car tires have a finely patterned tread for good grip on hard surfaces. Truck tires have a large tread pattern with wide and high lugs. During movement, the lugs cut into the ground, improving the vehicle's passability. Abrasion of the protrusions during use reduces the grip of the tire with the road.

As the inflation pressure rises, the grip coefficient first increases and then decreases. The maximum value of the coefficient of adhesion corresponds approximately to the value of the pressure recommended for the given tire.

With the tire completely sliding on the road (slipping of the driving wheels or the skid of the braking wheels), the value of φ can be 10 - 25% less than the maximum. The lateral friction coefficient depends on the same factors, and it is usually taken equal to 0.7F. Average values ​​of adhesion coefficient vary widely from 0.1 (icy pavement) to 0.8 (dry asphalt and cement concrete pavement).

Tire adhesion is of paramount importance for road safety, as it limits the ability of the vehicle to brake intensively and drive the vehicle safely without side-slip.

The insufficient value of the coefficient of adhesion is the cause of an average of 16%, and in unfavorable periods of the year - up to 70% of the total number of road traffic accidents. The International Commission for the Prevention of Slippery Road Surfaces has established that the value of the coefficient of adhesion for traffic safety conditions should not be less than 0.4.

VEHICLE BRAKING

Reliable and effective brakes allow the driver to drive confidently at high speed and at the same time provide the necessary driving safety.

In the process of braking, the kinetic energy of the vehicle is converted into the work of friction between the friction pads of the pads and the brake drums, as well as between the tires and the road (Fig. 2).

The magnitude of the braking torque developed by the braking mechanism depends on its design and the pressure in the drive. For the most common types of brake actuators, hydraulic and pneumatic, the pressing force on the pad is directly proportional to the pressure developed in the actuator during braking.

The brakes of modern cars can develop a torque much higher than the tire traction torque. Therefore, skid is very often observed in practice, when, with intensive braking, the wheels of the car are blocked and slide along the road without rotating. Before the wheel is locked, the sliding friction force acts between the brake linings and the drums, and the static friction force acts in the contact area of ​​the tire with the road. After blocking, on the contrary, the static friction force acts between the rubbing surfaces of the brake, and the sliding friction force acts in the contact zone of the tire with the road. When the wheel is locked, the friction in the brake and rolling is no longer expended and almost all the heat equivalent to the absorbed kinetic energy of the vehicle is released at the point of contact of the tire with the road. An increase in tire temperature will soften the rubber and reduce the grip. Therefore, the greatest braking efficiency is achieved when the wheel rolls at the blocking limit.

With simultaneous braking by the engine and the brakes, the adhesion force on the driving wheels is achieved with a lower pressure on the pedal than when braking with the brakes alone. Prolonged braking (for example, while driving on long slopes) as a result of heating the brake drums sharply reduces the coefficient of friction of the friction linings, and, consequently, the braking torque. Thus, braking with an uncoupled motor, used as an additional method of reducing the speed, can increase the life of the brakes. In addition, when braking with an uncoupled engine, the vehicle's lateral stability is increased.

Fig. 2. Forces acting on a wheel of a car during braking

Distinguish between emergency and service braking.

Service is called braking to stop the car or reduce the speed of movement in a place predetermined by the driver. The speed reduction in this case is carried out smoothly, more often by combined braking.

Emergency braking is called, which is performed in order to prevent a collision with an unexpectedly appeared or noticed obstacle (object, car, pedestrian, etc.). This braking can be characterized by the stopping distance and the vehicle's stopping distance.

Under stopping way understand the distance that the car will travel from the moment the driver detects the danger to the moment the car stops.

Braking way is called the part of the stopping distance that the car will pass from the moment the wheels start braking until the car comes to a complete stop.

The total time t0 required to stop the car from the moment the obstacle appears ("stopping time") can be represented as the sum of several components:

t0 = tр + tпр + tу + tT,

where tр is the driver's reaction time, s;

tпр - time between the beginning of pressing the brake pedal and the beginning of the action of the brakes, s;

tу is the time of increasing deceleration, s;

tT - full deceleration time, s.

Amount tnp + ty often referred to as the response time of the brake actuator.

During each of the constituent time intervals, the car travels a certain path, and their sum is a stopping path (Fig. 3):

S0 = S1 + S2 + S3, m,

where S1, S2, S3 are, respectively, the paths covered by the car during the time tр, tПр + tу, tт.

During the time tp, the driver realizes the need for braking and transfers his foot from the fuel supply pedal to the brake pedal. The time tp depends on the driver's qualifications, his age, fatigue and other subjective factors. It ranges from 0.2 to 1.5 s or more. When calculating, it is usually taken tp = 0.8 s.

The tnp time is necessary to select clearances and move all drive components (pedals, brake cylinder pistons or brake chamber diaphragms, brake pads). This time depends on the design of the brake drive and its technical condition.

Fig. 3. Braking distance and vehicle safety distance

On average, for a serviceable hydraulic drive, tпр = 0.2 s, and for a pneumatic drive - 0.6 s. For road trains with pneumatic brakes, the time tпр can reach 2 s. The segment tу characterizes the time of a gradual increase in deceleration from zero (the beginning of the action of the brakes) to the maximum value. This time is on average 0.5 s.

During the time tp + tpp, the car moves uniformly with the initial speed Vа. During the time tу, the speed decreases slightly. During the time tt, the deceleration remains approximately constant. At the moment the car stops, deceleration decreases to zero almost instantly.

The stopping distance of the car without taking into account the resistance force of the road can be determined by the formula

S = (t * V0 / 3.6) + ke (Va2 / 254Фх)

where S0 - stopping distance, m;

VA - vehicle speed at the initial moment of braking, km / h;

ke - coefficient of braking efficiency, which shows how many times the actual deceleration of the car is less than the theoretical maximum possible on a given road. For passenger cars ke ~ 1.2, for trucks and buses ke ~ 1.3 - 1.4;

Фх - coefficient of adhesion of tires to the road,

t = tр + tпр + 0.5tу.

The expression ke = V2 / (254 yx) - represents the braking distance, the value of which, as can be seen from the formula, is proportional to the square of the speed with which the car was moving before the start of braking. Therefore, if the speed of movement is doubled, for example, from 20 to 40 km / h, the braking distance will increase by 4 times.

The standards for the effectiveness of the foot brake of cars in operating conditions are given in table. 1 (initial braking speed 30 km / h).

When braking on snowy or slippery roads, the braking forces of all wheels of the vehicle reach the traction value almost simultaneously. Therefore, at Фх<0,4 следует принимать кэ= 1 для всех ав­томобилей.

Changing the direction of movement of any body can be achieved only by applying external forces to it. When a vehicle is moving, many forces act on it, while the tires perform important functions: every change in the direction or speed of the vehicle causes the appearance of acting forces in the tire.

The bus is the link between the vehicle and the roadway. It is at the point of contact of the tire with the road that the main issue of vehicle traffic safety is resolved. All forces and moments arising during acceleration and deceleration of the car, when changing the direction of its movement, are transmitted through the tire.

The tire absorbs lateral forces, keeping the vehicle on the path chosen by the driver. Therefore, the physical conditions of adhesion of the tire to the road surface determine the boundaries of the dynamic loads acting on the vehicle.

Fig. 01: Fitting the tubeless tire on the rim;
1. Rim; 2. Roll-up (Hump) on the tire bead landing surface; 3. Rim bead; 4. Tire carcass; 5. airtight inner layer; 6. Belt belt; 7. Protector; 8. Tire sidewall; 9. Tire bead; 10. Bead core; 11. Valve

Decisive evaluation criteria:
-Providing stable rectilinear motion when lateral forces act on the car
-Ensuring stable cornering Providing traction on various roadway surfaces Providing traction in various weather conditions
-Ensuring good controllability of the vehicle Ensuring comfortable driving conditions (damping vibrations, ensuring smooth running, minimum rolling noise)
-Strength, wear resistance, long service life
-Low price
-Minimum risk of tire damage when slipping

Tire slip

Tire slippage or slippage occurs from the difference between the theoretical travel speed due to the rotation of the wheel and the actual travel speed due to the adhesion forces of the wheel to the road.

By means of the given example, this statement can be clarified: let the circumference along the outer running surface of a passenger car tire be about 1.5 m.If the wheel turns around the axis of rotation 10 times while the car is moving, then the path traveled by the car should be 15 m.If slippage occurs tires, the path traveled by the car becomes shorter. Law of inertia Each physical body tends to either maintain a state of rest, or maintain a state of rectilinear motion.

An external force must be applied to the body in order to bring the physical body out of a state of rest or to deflect it from rectilinear motion. Changing the speed of movement, both during acceleration of the car and during braking, will require a corresponding application of external forces. If the driver tries to brake when cornering on an ice-covered road surface, the vehicle will tend to drive straight without any apparent tendency to change speed, and the steering response will be too sluggish.

On icy surfaces, only small braking and lateral forces can be transmitted through the wheels of the car, so driving on slippery roads is not an easy task. Moments of forces During rotational motion, moments of forces act or influence the body.

In the motion mode, the wheels rotate around their axes, overcoming the moments of inertia at rest. The moment of inertia of the wheels increases with an increase in the speed of its rotation and, at the same time, the speed of the vehicle. If the vehicle is on one side on a slippery road (for example, an icy road surface), and the other side on the road with a normal coefficient of adhesion (non-uniform coefficient of adhesion μ), then the vehicle receives a rotational motion about a vertical axis when braking. This rotational motion is called the yaw moment.

The distribution of forces, along with the weight of the body (gravity), various external forces act on the car, the magnitude and direction of which depends on the mode and direction of movement of the vehicle. In this case, we are talking about the following parameters:

 Forces in the longitudinal direction (e.g. traction, air resistance or rolling friction)

 Forces acting in a lateral direction (for example, the force applied to the steering wheels of a car, centrifugal force when cornering, or the force of a side wind or force generated when driving on a slope).

These forces are commonly referred to as the lateral slip forces of the vehicle. Forces acting in the longitudinal or transverse direction are transmitted to the tires, and through them to the carriageway in the vertical or horizontal direction, causing deformation of the tire in the longitudinal or transverse direction.

These forces are transmitted to the body of the car through:
 vehicle chassis (so-called wind forces)
 controls (steering force)
 engine and transmission units (driving force)
 braking mechanisms (braking forces)
In the opposite direction, these forces act from the road surface on the tires, and are then transmitted to the vehicle. This is due to the fact that: any force causes opposition

To ensure movement, the tractive force transmitted to the wheel by means of the torque generated by the engine must exceed all external resistance forces (longitudinal and lateral forces) that arise, for example, when the car is moving on a road with a side slope.

To assess the driving dynamics as well as the driving stability of the vehicle, the forces acting between the tire and the road surface in the so-called tire-to-road contact patch must be known. External forces acting at the contact area of ​​the tire with the road are transmitted through the wheel to the vehicle. As driving practice increases, the driver learns better and better to respond to these forces.

As the driving experience progresses, the driver becomes more and more aware of the forces acting in the tire-to-road contact patch. The magnitude and direction of external forces depends on the intensity of acceleration and deceleration of the vehicle, under the action of lateral forces from the wind, or when driving on a road with a transverse slope. The experience of driving on slippery roads stands apart, when excessive impact on the controls can derail the tires of the car into sliding.

But the most important thing is that the driver learns the correct and metered actions by the controls that prevent the occurrence of uncontrolled movement. Inappropriate driver actions at high engine power are especially dangerous, since the forces acting in the contact patch can exceed the permissible adhesion limit, which can cause the car to skid or completely lose control, and increases tire wear.

Forces in the tire-road contact patch Only strictly dosed forces in the wheel-to-road contact patch are able to provide the speed and direction of travel corresponding to the driver's desire. The total force in the contact patch of the tire with the road is made up of the following forces constituting it:

Tangential force directed around the tire circumference The tangential force Fμ is generated by the transmission of torque by the drive train or by braking the vehicle. It acts in the longitudinal direction on the road surface (longitudinal force) and enables the driver to accelerate when acting on the gas pedal or to slow down when it is acting on the brake pedal.

Vertical force (normal support reaction) The vertical force between the tire and the road surface is referred to as the radial force, or the normal support reaction FN. The vertical force between the tire and the road surface is always present, both when the vehicle is moving and when it is stationary. The vertical force on a bearing surface is determined by the fraction of the vehicle's weight on that wheel, plus the additional vertical force that results from weight redistribution during acceleration, braking or cornering.

The vertical force increases or decreases as the vehicle travels uphill or downhill, while the increase or decrease in vertical force depends on the vehicle's direction of travel. The normal support response is determined when the vehicle is stationary on a horizontal surface.

Additional forces can increase or decrease the vertical force between the wheel and the road surface (normal support reaction). So, when driving without turning, the additional force reduces the vertical component on the inner wheels to the center of rotation and increases the vertical component on the wheels of the outer side of the vehicle.

The contact area of ​​the tire with the road surface is deformed by the vertical force applied to the wheel. Since the tire sidewalls undergo a corresponding deformation, the vertical force cannot be distributed evenly over the entire area of ​​the contact patch, but a trapezoidal distribution of the tire pressure on the bearing surface occurs. The sidewalls of the tire absorb external forces and the tire deforms depending on the magnitude and direction of the external load.

Lateral force

Lateral forces act on the wheel, for example, when there is a crosswind, or when the vehicle is cornering. The steered wheels of a moving vehicle, when they deviate from the straight-line position, are also subjected to the action of a lateral force. Lateral forces are caused by measuring the direction of travel of the vehicle.