Club motorists
/WANT TO KNOW EVERYTHING
Corner suspension
Ase geometry will be useful to the competent driver
Text / Evgeny Borisenkov
The simplest and, it would seem, the obvious decision is not to do any corners at all. At the same time, the wheel during the compression-out remains perpendicular to the road, in constant and reliable contact with it (Fig. 1). True, combine the central plane of rotation of the wheel and the axis of its rotation is structurally quite difficult (hereinafter referred to double suspension rear-wheel drive "zhiguli") because both ball supports Along with the brake mechanism inside the wheels are not placed. And if so, the plane and axis "diverge" to the distance A, called the shoulder of the river (when turned, the wheel is running around the AB axis). In motion, the power of resistance to rolling the native wheel creates a tangible moment on this shoulder, jumpingly changing when driving irregularities. Few who will like riding with constantly driving out of hand steering!
In addition, it will have to be pretty sweat, overcoming this very moment in turn. Therefore, a positive (in this case) of the shepherd is desirable to reduce, or even reduced to zero. To do this, you can tilt the axis of the rotation of AB (Fig. 2). It is important not to overdo it here that when the wheel does not too fell inside. In practice, this is done: a few tilting the axis of rotation (b), the desired value is made by the slope of the rotation plane of the wheel (A). Angle A and there is a collapse. Under this angle, the wheel relies on the road. The tire in the contact zone is deformed (Fig. 3).
It turns out that the car moves as if two cones seeking to rolling on the parties. To compensate for this trouble, the plane of rotation of the wheels must be reduced. The process is called convergence adjustment. As you have already guessed, both parameters are rigidly connected. That is, if the angle of collapse is zero, there should be no convergence, negative - the discrepancy is required, otherwise the tires will "burn". If the wheel camber is set differently, it will pull it towards the wheel with a large inclination.
Other two angle provide stabilization of controlled wheels - Simply put, make the car with a released steering wheel ride straight. The first, already familiar angle of the transverse inclination axis of the axis of rotation (B) is responsible for the weight stabilization. It is easy to see that with this scheme (Fig. 4) at the time of the disorder of the wheel from the "neutral" the front starts to rise. And since it weighs a lot, when the steering wheel is released under the action of gravity, the system tends to take the initial position corresponding to the movement in a straight line. True, for this you have to maintain the same, albeit a small but unwanted positive shoulder of the river.
The longitudinal angle of inclination of the axis of rotation - Caster - gives dynamic stabilization (Fig. 5). The principle is clear from the behavior of a piano wheel - in motion it seeks to be behind the legs, that is, to take the most stable position. To get the same effect in the car, the intersection point of the axis of rotation with the surface of the road (C) should be ahead of the center of the wheel contact spot with the road (D). For this, the axis of rotation and tilted along. Now, when turning the side reactions of the road attached behind ... (thanks to the Castere!) (Fig. 6) Try to return the wheel in place.
Moreover, if there is a side force on the car, not related to the turn (for example, you are traveling on Kosoyaro or with lateral wind), then the caster provides a smooth rotation of the car "under the slope" or "under the wind" with a randomly released steering wheel Turn over.
In front-wheel drive car with the Mac-Ferson suspension, the situation is completely different. This design allows you to get zero and even negative (Fig. 7b) of the river shoulder - after all, it is necessary to "shove" here inside the wheels only with the support of the only lever. The angle of collapse (and, accordingly, convergence) is easy to minimize. This is how it is: familiar vases of the "eighth" family of collapse - 0 ° ± 30 ", convergence - 0 ± 1 mm. Since the front wheels are now pulling the car, the dynamic stabilization during acceleration is not required - the wheel is no longer rolling behind the legs, but It pulls her. Small (1 ° 30 ") The angle of the longitudinal tilt of the axis of rotation is saved for braking stability. A significant contribution to the "right" behavior of the car introduces a negative shoulder of the rolling - with an increase in the rolling resistance of the wheel, it automatically adjusts the trajectory.
As you can see, it is difficult to overestimate the effect of suspension geometry on handling and stability. Naturally, designers pay her close attention. The angles for each car model are determined after a great set of tests, convective works and again tests! But only ... based on a good car. On the old, worn out machine, the elastic deformation of the suspension (first of all, rubber elements) is much larger than that of the new - the wheels are noticeably diverged from much smaller forces. But it is worth stopping, as in the statics all the angles are again in place. So adjust the breaking suspension - Martyshkin work! First you need to repair it.
It is possible to reduce all the developers efforts in other ways. For example, carefully rear back of the car. You look - Caster changed the sign and memories remained from dynamic stabilization. And if during the acceleration "athlete" can still cope with the situation, then in case of emergency braking - it is unlikely. And if Add non-standard tires And the wheels with a different departure, who will take predict what happens in the end? Previously, worn tires and "killed" bearings - Polbie. It could be worse...
Fig. 1. "Suspension without angles."
Fig. 2. In the transverse plane, the position of the wheel is characterized by angle A (collapse) and B (the inclination of the axis of the rotation).
Fig. 3. Changing the inclined wheel reminds combatting the cone.
Fig. 4. With a positive shoulder, the driver turns the wheel is accompanied by the lifting of the bodice.
Fig. 5. Caster is the angle of the longitudinal tilt axis of the axis of the turn.
Fig. 6. So "works" Caster.
Fig. 7. Positive (a) and negative (b) wrapping shoulders.
Modern cars have increasingly complex and high-quality chassis, which must comply with both comfort and sportiness and sports requirements, and, in a special extent, the safety requirements.
In order for the requirements for the chassis part to be carried out throughout the "life of the car", as well as after possible accidentsToday there are excellent opportunities for checking the geometry of the chassis and adjusting incorrect settings.
The chassis is the link between the car and the road fabric. Both the forces acting on the supporting surface of the wheel and the force of thrust and arising during the passage of turns of the lateral injection force are transmitted chassis On the road through the wheel wheels.
The running part is exposed to many forces and moments. Increasing car power, as well as increased requirements for their comfort and safety, lead to a permanent increase in the requirements for the chassis.
Explanations
Shoulder ripped
The shoulder is running - this is the distance between the center of the wheel contact spot with the road (tire print center) and the point of intersection of the axis of rotation of the controlled wheel (pivot axis) with the surface of the road.
F. 1 \u003d Brake force or strength resistance to rolling
F. 2 \u003d thrust force
r. s \u003d shoulder run
Reducing the shoulder running (painting 1b. ) Reduces the effort on the rim of the steering wheel. Small run-in shoulder reduces responses to driven wheels on the road irregularities.
When braking, a longitudinal force arises on the brake mechanismF. 1 that forms the momentF. 1 * r. S. . This moment leads to the appearance of force on the steering line and with the positive size of the shoulder runr. S. Pressing the wheel in the direction corresponding to the negative context.
W. vehicleEquipped with ABS?
For aBS work There are various longitudinal forces attached to the right and left wheel, which in the form of jolts are transmitted to steering wheel. In this case, the shoulder runs should be zero, but better if the shoulder runs will have a negative value.
The suspension of the wheels of any top can be viewed as the installed console wheel relative to the car body, so there is a longitudinal force when braking, seeking to turn this wheel, and the wheel will always strive to rotate the front part, that is, towards negative convergence. The installation of the negative shoulder of the roller will allow to get the moment of longitudinal force, which will be directed in the opposite side to the moment, seeking to turn the wheel towards negative convergence. Most cars not equipped with FBS, contours brake systems Have a diagonal compound scheme, the shoulder run is usually a negative value. Any incorrect change entered into the design of the vehicle, such as the installation of discs with an increased departure, which occurs when desired to establish wide tires, Or install the spacer between the hub and the wheel disk is unacceptable. The change in the shoulder of the runoff can have a negative effect on the stability of the straight line, especially when braking, and the loss of controllability on the rotation.
The shoulder runs is one of the most important parameters of the front suspension.
With the shoulder rolling r. s Related:
- spring offset at McPherson Rack;
- runs of wheels (the distance from the plane of the tire symmetry to the plane of the wheel disk in contact with the hub);
- effort on the steering wheel both in statics and in dynamics;
- car stability when braking;
- position bearing node In the hub, and with it the position of the wheel: the longitudinal plane of the tire symmetry should be located in the base of the bearing (s), preferably in the center (Fig. 2). Otherwise, the stated bearing resource (s) will not be achieved.
Fig. 2. The relative position of the plane of the symmetry of the tire and the base of the bearing (s): A - conical roller; b - double row ball
Departure wheels wheels are the parameter to which drivers pay attention only when, setting a wider wheel, it starts to touch the arch. And then the decision comes itself: take discs with less. "Good people" say: "Deviation ± 5 mm is permissible." And what if the factory has already used these 5 mm, what then?! And then the loss of controllability in case of emergency braking on the mixture (unequal clutch on the left and right).
A vivid example illustrating the importance of the shoulder of the runoff is given in the magazine "Automotive Industry":
Test number 1. On the car installed wheels with such that got the shoulder run r. S \u003d + 5 mm. Acceleration up to 60 km / h. Release the steering wheel (!!!) and apply emergency braking on a mixture. The result is a 720 ° turn turn - what was expected.
Test number 2. All the same but r. S \u003d -5 mm (wheels are 10 mm more than the first, by the way, it reduced a 20 mm collage). Result - 10 ° remove - unexpectedly?!
And this is the answer to those who believe that the wider of the rut, the more stable the car, and the wheels of the wheels affect only the exterior of the car.
The reason for such a different behavior of the car after, it would seem cosmetic change - Elastokinhematics steering trapezium (Fig. 3).
Fig. 3. The effect of positive (a) and negative (b) shoulder run r. S \u003d. R. 1 / COS σ (see Fig. 4) on car stability when braking:
R`x. 1\u003e R "x 1, R`x. 2 =R "x. 2 - brake forces on the appropriate wheels;
F and - inertia force attached to the mass center of the car
Fig. 4. Installation settings
If the brake force is greater, for example, on the left, then a rotating moment is acting on the vehicle mass of the car, equal to the difference in the brake force multiplied on the shoulder (half of the rut). But since the forces on the left and right are unbalanced, then the moment the moment acts on the steering
(R` * x 1 -R "* x 1) · R 1.
The steering trapezium turns (due to the deformation of the supports, levers, body). In the case of a positive shoulder, the runoff increases the rotating moment, with a negative shoulder, partially or completely compensates.
Negative shoulder running is not easy. Increase the discs (depth), the transverse angle of tilt the pivot axis and the angle of the collapse of the wheels. But with an increase in the first angle, an effort is growing on the steering wheel, and with an increase in collapse - the grip of the tires is worsened with an expensive in turn (a negative collapse is needed!). The wider the profile of tires, the more difficult it is to constructively place in the wheel brake mechanisms, hub, ball supports, steering thrust and drive.
A beautiful solution to the problem of the shoulder reduction of the runoff is the use of multi-dimensional front suspension with four ball supports (see Fig. 5).
Fig. five: Multi-dimensional suspension Front-controlled manufacturer VAG
According to the design, it is very similar to the suspension on double transverse levers of the classic triangular shape. However, instead of one ball support in the top of the triangle, two are applied - a quadrangle is formed. Such a design is inoperable without the fifth lever - steering thrust. On triangular levers, the axis of rotation of the wheel passed through the centers of the ball supports. In the new design, this axis is virtual and passes far beyond the limits of a quadrilateral (Fig. 6).
Fig. 56 Wheel rotation scheme on a multi-type front suspension (the second pair of levers is not conditionally shown)
Based on Tutorial "Operating properties of cars", A. Sh. Husainov
The correct corners of the installation of the wheels are one of the most important factors that ensure normal handling, stability and stability of the car at straight movement And when passing turns. Optimal suspension geometry parameters for each model are laid at the design stage. The set values \u200b\u200bof the setting angles of the wheels are subject to change and require periodic adjustment due to the natural wear of nodes and elements of the chassis or after repairing the suspension.
Purpose of wheel installation angles
The correctly tuned suspension geometry allows the car to more effectively perceive the forces and moments that occur in the spack of the wheel contact from the road surface during various motion modes. This ensures the predictable behavior of the car, namely: the stability of movement in a straight line, stability in turns, stabilization during disks and braking. Also, due to the absence of excessive resistance to rolling the wheels, there is a more uniform wear of the tires, which makes it possible to increase their service life.
The wheel installation angles set by the manufacturer are optimal for a particular car and correspond to its assignment and features of the suspension setup. However, if necessary, it is constructively provided by their change or adjustment. The number of parameters that can be adjusted for each car is individually.
Types of main angles of car installation
| Parameter | Axis car | Adjustable parameter | What is influenced by |
|---|---|---|---|
| Wheel collapse angle (Camber) | Front Rear | Yes (depends on the car) | Motion resistance in turn Premature wear of tires |
| Wheel convergence angle (TOE) | Front Rear | Yes | Stability with rectilinear movement Premature wear of tires |
| Rifle angle of turning axis (KPI) | Front | Not | |
| Longitudinal turn axis angle (Caster) | Front | Yes (depends on the car) | Stabilization of the car when driving |
| Shoulder running | Front | Not | Car stability when braking Stabilization of the car when driving |
Split wheel
Wheel collapse (eng. camber) Is an angle formed by the average plane of the wheel and the vertical passing through the point of intersection of the average plane of the wheel and the reference surface. Distinguish positive and negative collapse:
- positive (+) - when the top of the wheel is tilted outside (from the car body);
- negative (-) - when the upper part of the wheel is tilted inside (to the car body).
Positive and negative corners of wheel collaps Constructively CAMBER is formed by the position of the hub node and provides maximum Square Tire contact stains with expensive. In the case of duplex independent suspension The position of the hub is determined by the upper and lower transverse levers. In the formation of an angle of collapse affects the lower lever and the depreciation rack.
The deviation of the values \u200b\u200bof the corner of the rupture from the norm affect the car as follows.
- good auto stability in turns;
- the grip of the wheels during rectilinear movement is worse;
- elevated wear inner tires.
- good grip wheels with expensive;
- worsen stability in turns;
- increased wear of the outside of the tire.
Wheel alignment
Wheels (eng. toe.) - the angle between the longitudinal axis of the car and the plane of rotation of the wheel. It can also be defined as the difference between the distances between the front and the rear side of the rims of the wheels (in the figure this value is minus B). Thus, the convergence can be measured in degrees or millimeters.
Wheel alignment car There are total and individual convergence. Individual convergence is calculated separately for each wheel. This is the deviation of the plane of its rotation from the longitudinal axis of the vehicle symmetry. The total convergence is calculated as the sum of individual angles of convergence of the left and right wheels of one axis. Similarly, the total convergence in millimeters is determined. With positive way (eng. tOE-IN.) The wheels are mutually rotated inside the direction of movement, with a negative value (eng. toe-out) - outward.
Positive I. negative convergence wheel The deviation of the angle of convergence from the norm affects the car as follows.
Too big negative angle:
- increased wear of the tire on the inside;
- acute car reaction to steering.
Too big positive angle:
- worsening the trajectory of the movement;
- increased tire wear from the outside.
Crossing angle of tilt axis wheels The transverse angle of inclination axis of the turn (eng. KPI) - the angle between the axis of rotation of the wheel and the perpendicular to the support surface. Thanks to this parameter, when rotating controlled wheels, the car body is lifted, as a result, the forces arise,
Especially seeking to return the wheel into a straight position. Thus, KPI has a significant impact on the stability and stability of the car with a straight line movement. The difference in the magnitudes of the crosslinking angles of the right and left axes can lead to an auto car aside with a large inclination. This effect may manifest itself and, according to the normal values \u200b\u200bof the remaining corners of the wheels.
The angle of the longitudinal tilt axis of the wheel turn
Longitudinal tilt angle axis The longitudinal angle of tilt axis (eng. caster) -the angle between the axis of rotation of the wheel and the perpendicular to the support surface in the longitudinal plane of the car. There are positive and negative corners of the longitudinal tilt axis of the wheel turning.
Positive Caster contributes to the emergence of additional dynamic stabilization of the car when moving on medium and high speed. At the same time, turning is worsened at low speed.
Shoulder running
In addition to the above parameters, another characteristic is of great value for the front axle - the shoulder running. It is the distance between the point formed by the intersection of the axis of the wheel symmetry and the reference surface, and the intersection point of the crosslink line of the axis of rotation and the reference surface. The shoulder run is positive if the surface intersection point and the axis of the rotation of the wheel lie on the right of the axis of the wheel symmetry (zero shoulder), and the negative, if it is located on the left of it. If these points coincide - then the shoulder run-in is zero.
The value of the shoulder rolling This parameter affects the stabilization and rotation of the wheel. Optimal value for modern cars is a zero or positive run-in shoulder. The shoulder sign is determined by the collapse, transverse inclination The axis of rotation of the wheel and the departure of the wheels.
Automakers do not recommend installing wheel disks With non-standard departure, because This may entail a change in the set shoulder of the run-in to a negative value. This can seriously affect the stability and manageability of the car.
Changing wheel installation angles and adjust them
Wheel installation angles are subject to change due to the natural wear of parts, as well as after their replacement to new ones. Everything, without exception, steering thrusts and tips have threaded connectionwhich allows you to increase or decrease their length to adjust the values \u200b\u200bof the wheel convergence angles. Convergence rear wheelsAs well as the front, adjustable on all types of suspension, with the exception of the rear dependent beam or bridge.
In the original version of such a suspension designed by MacPherson, the ball hinge was located on the continuation of the axis of the amortized rack - thus, the axis of the amortized rack was the axis of rotation of the wheel. Later, for example, on the Audi 80 and Volkswagen Passat of the first generations, the ball hinge began to shift to the wheel, which made it possible to get smaller, and even the negative values \u200b\u200bof the running routing.
In this way, scrub Radius (SCRUB RADIUS) - This is the distance in a straight line between the point where the axis of turning the wheel intersects with the roadpapers, and the center of the spots of the wheel and the road (in the unloaded state of the car). When turning the wheel "runs through" around the axis of its turn on this radius.
It can be zero, positive and negative (all three cases are shown in the illustration).
For decades, most cars used relatively large positive values \u200b\u200bof the shelter. This allowed to reduce the effort on the steering wheel when parking compared to the zero shoulder of the river (because the wheel rolls when the steering wheel is rotated, and not simply turns on the spot) and free the place in the processionate space due to the removal of the "outward" wheels.
However, over time it became clear that the positive shoulder of the river could be dangerous - for example, when the wheels of one side of the side of the curb, having an excellent coefficient of the clutch, the failure of the brakes of one side, puncture of one of the tires or violation of the steering wheel, starts From hand. " The same effect is observed with a large positive shoulder of the river and when driving any irregularities on the road, but the shoulder still did small enough so that during normal driving he remained Malozamen.
Starting from the seventies-eighties, as the speeds of car movement increase, and in particular - with the distribution of McPherson suspension, easily allowing it with technical side, Cars with zero or even negative shoulder of the rolling have become massively appear. This allows you to minimize hazardous effects described above.
For example, on the "classic" models of VAZ, the shepherd was a big positive, on "Niva" VAZ-2121 due to more compact brake mechanism With a floating bracket, it was reduced almost to zero (24 mm), and on the front-wheel drive family Lada Samara, the shepher was already negative. Mercedes-Benz as a rule preferred on his rear-wheel drive models to have a zero shoulder running.
The shepherd is determined not only by the design of the suspension, but also the wheels. Therefore, when selecting non-evoded "disks" (according to the terminology adopted in technical literature, this part is called "wheel" and consists of the central part - disk and the external on which the tire is seated - rim) For a car, permissible parameters specified by the manufacturer should be observed, especially by departure, since when installing the wheels with an incorrectly selected departure, the river shoulder can change much, which significantly affects the controllability and safety of the car, as well as on the durability of its parts.
For example, when installing a wheel with zero or negative departure when the plane is provided with a positive (for example, too wide), the plane of rotation of the wheel is shifted out from the wheel not changing the axis of the wheel, and the shepher's shoulder can purchase excessive positive value - the steering wheel starts "Rush out of the hands" on each irregularity of the road, the effort on it during parking exceeds all the permissible values \u200b\u200b(due to the increase in the lever shoulder compared to the standard departure), and wear hub bearings and other pendant components increase significantly.
