Ways to prevent a car from rolling over off-road

“Ears”, “somersault”, “somersault”, “overkill” ... How many names are there for such a simple and, unfortunately, frequent off-road phenomenon as rollover. And the more serious the preparation of the car, the more chances the pilot has to earn the title of "Carlson, who was lying on the roof." Folk methods of dealing with overturning are well known. But are they effective (and if effective, how effective)? In general, you already understood that we decided to try to the best of our ability to deal with this issue. As they say, for the benefit of the prosperity of jeeping, and, of course, out of excessively developed natural curiosity...

Expeditionary Toyota was brought in as a "falling rabbit" to our unusual test. Land cruiser 105 with 1KZ engine. The choice is due to the fact that this car, for all its ceremonial-glossy appearance, at one time underwent quite serious off-road training, and, accordingly, its center of mass “jumped” far up. And the reason for this is the wheels with a diameter of 35 inches, a 3-inch lift, and even 7 centimeters of a body lift. In the end, there was an option typical car used by lovers of short and long journeys in places not covered with asphalt. Who said: "But what about Land Rover"? No, let's agree: today we are not arguing about who is more roller and expeditionary, but we are only talking about ways to prevent capsizing. In general, the introductory ones are as follows: there is a lifted TLC105 (but, I repeat, in this case, the brand and model are unprincipled), there is a platform for flipping the car, there is a sea of ​​enthusiasm and a couple of ropes. That means you can start!

Method of exotic observations

As a starting point, we overturned the car in its, so to speak, untouched state. That is, in the cabin and cargo compartment empty, and nothing lies on top of the expedition trunk either. We will have something like a “stove”, from which we will have to “dance” in an attempt to draw some logical conclusions. In fact, it must be said that all rollover tests look about the same. First, the car is placed on the platform with the wheels of one side resting on a special restrictive rail, then the limiter belts are fixed on the body. Then, obeying the pressing of the red button, a powerful hydraulic system begins to tilt the platform. At this point, we are just waiting, enjoying the spectacle. But, I must say, that at first there is nothing special to enjoy: the car just stands firmly with its wheels on the surface. But when angles of about 25–30 degrees are reached, interesting things begin to happen. First, the body rolls reluctantly (suspension travel is being worked out).

Then, if it is an SUV with dependent suspension and heavy engine, usually starts to break away from the platform front wheel. This is the so-called “first call”, indicating ... no, not about the beginning of a rollover, but only that the rebound travel of the front suspension has ended. Nevertheless, there comes a moment of extreme tension. I've seen it so many times, but I still can't get used to it... And then the car finally tore the wheels off the surface of the platform, swung sharply in the direction of the roll and hung helplessly on the belts... This is the tipping point. It's time for measurements and records. And this time we recorded the following figures: 42°13' - platform roll and 48°35' - body roll. That is, the relative body roll was 6 ° 22 '.

Yes... The figures, to put it mildly, are not record-breaking. No, for a lifted car, this seems to be normal, but it is completely unacceptable, for example, for high-speed maneuvers on a hard surface. By the way, having rolled the car over to the other side (bearing in mind the Panhard rod, which gives the asymmetry of the suspension), we got slightly different results: the empty car fell on the left side already at an angle of 41 ° 19 ', and the roll was 6 ° 45 '. We will set all further experiments with a slope to the right, passenger, side, but remember that all “left-hand drive” cars with a similar type of suspension in static turn over to the left about one degree earlier. By the way, in dynamics the difference will be even more noticeable.

Bold "Vasya"

The next stage of our experiments was the simulation of a real car loading in the conditions of an expedition or a trophy raid. Let's try the maximum first. We assumed that these are four people, approximately 100 kg in cargo hold and about 100 kg more on the top rack. "Kilograms" worked measuring bags with sand (25 kg each). Four mannequins filled with water with the original Russian names Vasily were “seated” on the chairs. Man is also almost 90 percent water, so they are almost like brothers to us. Therefore, it was not difficult for the author to imagine himself as a mannequin. So, read the fantasy on the topic “What if we were sitting inside” ... To the sound of imaginary marches back row was "filled" by two volunteers, one of whom is now writing these lines. Well, let's get started?

Oh, well, and sensations ... After all, it is known that inside the car, rolls are perceived much stronger than they should actually be. The vestibular apparatus is such a reinsurer, and don't say it... Well, I remember, I started somehow in the trial... So, stop, what is the angle now? How is it only 30 degrees?! I'm already in the car, I can barely hold on, but it's still worth it! And from above, he looks appraisingly... Andrey Kuprin (I don't know why, but I wanted to include this character in my story). Well, Andrei sat down on the left and, it seems, quite consciously was going to fall on me ... The car is still standing, and he is holding on ...

Well, finally ... 36 ° 31 ', and the wheels came off the floor. And body roll at the moment of separation is more than 10 degrees! These are the indicators… If we really sat inside, we would hardly be able to resist. But the car “fell” extremely early, while also choosing the entire suspension travel.

Okay, now we are trying without the "plastic people" sitting behind, but with the "crew" of two "Vasily" in the driver's and navigator's seats. Yes, and, of course, with a load. The rollover angle immediately jumped to the mark of 39°08' with a roll of 7°03'. That is, with a standard load of “2 people plus cargo”, we have a decrease in stability by 3 degrees. Not a lot. But we will take this value as the closest to reality as a starting point for all further torment.

Folk omens

I confess, despite the fact that I am a person of the material world, I still believe in some signs. There is a sin. Moreover, the rumor keeps talking about their exceptional, almost one hundred percent "marketability". Actually, what am I talking about? Oh yes, about folk methods of fighting the coup. The first method is this: if you do not want to roll over, reduce the pressure in the tires of the uphill slope of the bead. The car will level out and the chances of an overkill will be reduced to microscopic. Let's check? Toyota sizzles air through the inverted spools and prepares to demonstrate miracles of stability. In the left wheels, the pressure is 0.6 atm, and body roll on a flat surface is almost 4 degrees.

We press the button, and the platform slowly pushes the car to the irreparable. And here we see an interesting picture. After working out the suspension moves, the wheels begin to ... “inflate”. That is, the load on the side changes, and flat tires no longer affect anything! And indeed, we recorded a complete loss of stability at around 38 ° 35 '. The picture turned out as follows: with flat tires, the car fell earlier than with inflated ones, by more than half a degree. Let not by much, but sooner! That is, we are simply not talking about improving stability in this case. So, we cross out one “correct” way ...

The next way. The navigator hanging on the footrest (jeepers have spied this on the yachtsmen). The method is said to be quite effective. But we, according to the laws of the genre, doubt. And we will doubt while the compressor "hammers road pressure" into the tires of the experimental Land Cruiser. Well, when he finishes ... In general, I stand on the inexorably moving up bandwagon and yearn. Jokes and jokes about the heavy share of the ORD browser fly by without bouncing ... The platform rotates with a characteristic hum, the car below me goes down, and the world turns upside down. No, gentlemen, honestly, I took such an unnatural pose only for the sake of the purity of the experiment, in order to tilt the car to the maximum.

And, you know, all these torments were not in vain: working with a live counterweight gave an effect! As a result, the angle has grown to 40° 14’! We lower the platform a little, and another test participant jumps onto the power threshold. Now there are two of us, but this measure only increases the angle to 40° 54', which is less than a degree. From which we conclude: to carry two navigators for ballast is a waste. But in any case, it must be recognized that the method works. For returning one and a half degrees of stability to the car at critical corners is, to put it mildly, a lot. Let's summarize: the efficiency of "man-rolling" is quite high.

Now let's take a look at the overseas expanses, where restless spotters climb over stones, periodically keeping cars from overturning with muscular, so to speak, force. Moreover, they often succeed ... So, we need a thick rope and a dynamometer. We tie our "rope" to forwarding trunk, we attach a dynamometer to it and ... In general, I stand, holding a cable in my hands, and wait for the moment when I need to show miracles of heroic strength. And he did show it! With a force of 50 kg, I "saved" as much as 1 ° 34 'of steady state, and when I pulled up and "took a weight" of 100 kg, it turned out as much as 3 ° 40'. Well, am I not well done? Frankly, they helped me to take 100 kg (we were already pulling together), but the result is positive in any case. Conclusion: the method of pulling the car with a cable - live! At least out of the ones I've tried, it's the most effective.

Actually from folk remedies only the “barbaric” method remained. This is an artificial limitation of the suspension travel from the upper side of the slope. No sooner said than done. And now I’m already diving under the car and compressing the springs with banal tie-down straps with a “ratchet”. But since after the exercises with the rope I didn’t have much strength left, I manage to achieve a roll angle “to the side of the slope” of only 2 degrees. However, this is quite enough for the experiment ... Grunts hydraulic drives this time the stand pleased us for quite a long time, but the difference was completely invisible to the eye. But not all is lost. We take measurements... No, a miracle, of course, did not happen, but with this simple action we achieved the same result as with two "live counterweights"! Figures appeared in the notebook: 40 ° 49 'with a body roll of 4 ° 46 '. Very good result. Of course, not like in the “with a rope” option, but also quite acceptable. And what, three methods out of four - this is a very good result. I would even say positive.

All for one purpose

And now attention: instead of conclusions and smearing thoughts in pseudoscientific terms, we decided to do it easier. What will happen if we apply all the methods of combating rollover, which have given a positive result, in a united front? To the perplexed “how is it?” I answer: point one - complete unloading of the car, including dismantling the spare wheel, point two - three on the steps, point three - one person with a rope, ready to give out calibrated 50 kg of effort. And you know, despite the laughter and jokes that poured in the process of pushing the platform from the horizontal "pier", we held on, as they say, to the last. They kept, apparently, not in vain: the result is 52 degrees !!! At such angles, small crossovers turn over, and here is a frame-lifted SUV!

That is, we were able to add as much as 13 degrees to the limiting angle of a stable position of a car equipped with a full arsenal of means to ... worsen this parameter. So folk methods work, and how they work! Just don't let the wheels down.

When the car passes the turn, a centrifugal force is generated, which tends to roll the car or, as an extreme case, overturn it. The corresponding formulas for calculating these forces are given in the appendix. The magnitude of the roll depends on the magnitude of centrifugal forces and the distance between the point of application of centrifugal forces (i.e., the center of gravity of the car) and the metacenter of the car, i.e., on the magnitude of the overturning moment of the car.

A car with elastic suspension rolls relative to the metacenter, the position of which depends on the way the wheels are connected to the sprung mass of the vehicle. Figure 1 shows how to determine the position of the metacenter for the most typical wheel setups.

Rice. 1. Determination of the metacenter using various methods
wheel mounts

In the first figure, we are talking about a short oscillating axle, the oscillating center of which is marked S 1 . The coordinates of the metacenter are determined as follows: the point of contact of the tire with the ground is connected to the swing center of the wheel axle; the point of intersection of this line with the plane of symmetry of the car will give the position of its metacenter S.

The same is done in the second case, when the wheel is suspended on two wishbones of different lengths. The upper lever rotates around the point S 1 and the lower one - relative to the point S 2 . On the continuation of the axes of these levers at the point of intersection is the actual instantaneous center of oscillation of the wheel S 3 . Connecting it to the point of contact of the wheel with the road, find the metacenter S at a height h 2 above the ground at the point of intersection of this line with the plane of symmetry of the car.

The instantaneous swing center of the wheel when using the MacPherson suspension is found as follows: a perpendicular is drawn to the axis of the telescopic elastic suspension element at the upper point of its attachment and the axis of the lower arm swinging relative to the point S 1 is extended. The actual instantaneous swing center of the wheel is at their intersection, i.e., at the point S 2 ; the position of the metacenter S is determined by the method already described: it is located at a height h 3 .

When turning, the centrifugal force is applied at the center of gravity of the car, and the closer the center of gravity is to the metacenter, the smaller the overturning moment. An example of a shortened oscillating axle of a car is shown in fig. 2.

The distance from the center of gravity T to the metacenter S in this case is equal to t, the value of the overturning moment is equal to Ot, where O is the centrifugal force of the sprung mass.

This moment must be perceived and extinguished, in which the so-called return moment occurs. Its value in this case is equal to 2h"ca", where h" is the compression of the elastic suspension element; c is the stiffness of the suspension element.

Obviously, in this case, the roll of the car will be small.

If the metacenter is low, then the shoulder t will be large. The low rigidity of the elastic suspension elements also leads to an increase in the roll of the car.

To reduce the roll of the car, especially if it has a soft suspension, a stabilizer is installed on it. Most often, torsion stabilizers are used (see Fig. 3).

Stabilizer 1 also has a torsion bar. To adjust the load, one of the upper levers 2 has an adjustable length.

This is a special torsion spring mounted across the car and connected by levers to the wheels. If both wheels hit an obstacle at the same time, the stabilizer will turn but not twist. If one wheel hits an obstacle, the stabilizer, twisting, tends to raise the other wheel. When the car passes a turn, the elastic suspension element of the inner (in relation to the turn) wheel is compressed, the stabilizer tends to compress the elastic suspension element of the outer wheel (toward the turn), thereby preventing excessive roll of the car. Twisting, the stabilizer compresses the outer (turn) elastic suspension element more strongly, while the inner (turn) is unloaded.

There are many different ways to stabilize a car. When using hydraulic or air suspension you can install the simplest stabilizer - a transverse leaf spring, which is mounted in two rubber blocks, as shown in fig. 4.

Rice. 4. The front axle of a Fiat car with a transverse leaf spring mounted in two rubber blocks and serving as a stabilizer

When one wheel is raised, the spring will bend, its center will shift down, and the end of the spring on the other side will shift up.

A rear-engined car has shortened oscillating axles at the rear, and the front wheels are mounted on two wishbones. According to fig. 1 in the first figure, the height of the metacenter h 1 is large, and at the front bridge in the second figure it is small h 2 . If we consider the car as a rigid whole, then its roll will be limited mainly rear axle, which is manifested by an increased load on the outer rear wheel. Since the stabilizer redistributes the load on the wheels to some extent, and increases, and the car acquires some oversteer. If the stabilizer is set to front axle, then the value of the return moment (Nm / °) and the stability of the car against roll will increase. This will increase its load and lateral pull, as a result of which the vehicle's oversteer may change to understeer.

For a more accurate calculation of the lateral stability of the car, it is necessary to take into account the torsional elasticity of the body. Both bridges are connected by one torsion spring. It is necessary that the body has sufficient torsional rigidity and does not act as some elastic non-muffled element that affects the control of the car. The torsional rigidity of the body is expressed by the moment Nm, which causes a relative rotation of 1 ° of two planes of the body, 1 m apart from each other. The body rigidities of some cars are given in table 7.

Table 7. Rigidity of the car body

Parameters	car models
	Simka 1000	Tatra 603	Wartburg	Mercedes Benz 220SE
Front wheel track (mm)	1250	1403	1190	1470
Track rear wheels(mm)	1234	1400	1260	1485
Wheelbase (mm)	2220	2750	2450	2750
Engine displacement (cm³)	944	2472	1000	2195
Gross vehicle weight (kg)	1040	1960	1300	450	880	625	590	1080	675	970
Load force (N)	4000	6000	4000	6000
Load torque (Nm)	4000	4000	2000	3000
Max Deflection (mm)	1,08	0,52	0,64	0,67
Maximum twist (°)	-	0°9.5"	0°13.4"	0°8.28"
Bending stiffness (N/mm)	4820	11500	6000	13320
Torsional rigidity (Nm/°)	-	25300	8950	21700

Car Simka 1000 from table 7

Under the roll of a car, they usually mean its inclination relative to its axis in any direction. Moreover, such an inclination can be not only to the right, but also to the left. The roll of the car can also be present both in front and behind, and also combined depending on the load or subsidence of one of the wheels.

What can be the roll of the car? Roll types

It is important to consider that the roll of the car can be both permanent and temporary. But in each of the cases, one should be careful about this phenomenon, because the presence of even a small deviation from the norm significantly reduces the level of safe and comfortable ride and may cause an accident on the road.

Let's start with a temporary phenomenon. It can often be seen on trucks when uneven loading of the body is made. In such cases, the likelihood that the vehicle may roll over increases significantly. In this case, such situations can arise not only when driving on rough roads (especially on the side of the slope), but also when performing cornering maneuvers (especially when driving at high speed). It is corrected very simply - it is enough to correctly distribute the load over the body - this reduces the risk of an accident, and also significantly reduces the load on individual parts and components of the car.

The constant roll can also be different. If, for example, the car owner independently, deliberately raises the rear of the car a little higher than the front, thereby increasing stability vehicle during high-speed turns - it's one thing. In the same vein, a slight rise in the front part can be noted, which increases the controllability of the machine even in extreme situations(as an example, you can indicate the movement on a slippery or rough road).

Artificial roll can also be practiced if driving passenger car there is a rather obese person. In this case, to maintain balance during the ride, you can slightly raise the driver's part.

Worse if the roll was the cause long-term operation and wear, or poor quality work on the assembly and fastening of one of the wheel assemblies or suspension. In this case, the wear of parts and assemblies that are in the region of the greatest load (in fact, at the lowest point) increases significantly.

It is important to understand that driving comfort and safety in such cases remain in question (often a car with such a “disease” simply starts to “lead” in the direction of the car’s inclination, and at high speeds the probability of an accident increases significantly).

No matter how this happens, you deliberately made the roll, or it arose due to the wear of the nodes, you can be sure of one thing, the wear of rubber on the wheels located in the lower part will be significantly higher. Therefore, it is necessary to practice the deviation of the vehicle from the normal axis wisely and preferably temporarily. Otherwise, “show-offs” will eventually become very real troubles in the form of a damaged car, or significant costs for the replacement of its individual parts that have failed prematurely.

  A new way to deal with roll
The money for the car has already been spent, and you have finally moved to the stage of active motorism - you have started driving. In addition to the feeling of comfort, which nice car it will give you right away, after a while it will give you a more important feeling - a sense of security. Reliability. Confidence. And what does it consist of? You know that there is an anti-lock braking system, and the car will no longer skid when braking hard. There is traction control system- it will allow you to start off without problems on any surface. There is a convenient and simple automatic transmission, and the steering wheel turns easily, because it is equipped with hydraulic booster. Then on the list are other advancements: four steerable wheels (Honda makes it) and four-wheel drive(Audi was the first to install it on a production passenger car). Add hydropneumatic suspension like Citroen. And yet, perhaps, air conditioning and heated seats - all this is quite an achievable dream of an ordinary motorist.
Until recently, perhaps only one inconvenience remained unsurmounted: the transverse roll of the car that occurs when cornering. The feeling that arises in this case for passengers is unequivocal - a leaning car is unreliable. Indeed, the behavior of the machine in this case is unpredictable and it is difficult to control it.

What happens to a car in a turn? When moving along a curve, as you know, there is a centrifugal force. It seeks to push the car out of the turn, which is prevented only by the reaction at the point of contact of the wheels with the road (in cases where the centrifugal force exceeds the grip force of the tires with the coating, the car breaks into a skid).
The wheels of the car, rising and falling on the roughness of the road, make quite complex vertical and lateral evolutions. If we consider the displacement of a point that is in the center of the contact patch of the wheel with the road, then in the suspension one can find a certain center, relative to which these movements occur along an arc of a circle. It is called the suspension roll center. A straight line connecting the roll centers of the front and rear suspension, is called the roll axis of the car.
The centrifugal force that occurs in a turn acts laterally on the center of gravity, or, more correctly, the center of mass of the car body. It is about half a meter above the ground, but always above the roll axis. The lateral force applied to the center of mass creates a tilting moment relative to this axis, which rolls the body in a turn or swings it from side to side during a series of turns.
Centrifugal force doesn't just roll the car. It also affects passengers, throwing them from side to side and forcing them to grab the handles in search of support. It would seem easier for the driver: the fulcrum - the steering wheel - is always at hand. However, he can instinctively hang on to it and involuntarily change the trajectory of the car.
Body roll occurs not only in a turn. It also leads to inconsistent movement of the wheels on the same axle, for example, if one of them falls into a hole or on a hillock. The suspension does not have time to work, and one side of the car slightly throws up. If the road is very rough, the wheels dance on their own (a phenomenon called "shimmy" - from shimmy, there was once such a dance). The body of the car sways from side to side, and it is clear that the trajectory of its movement is not stable.
One of the main ways to reduce roll is to supply the suspension with a stabilizer. roll stability. As a rule, it is a curved bar of complex shape fixed to the body, which connects opposite suspension arms. The stabilizer bar does not prevent the wheels from lifting and lowering together, but as soon as one of them hits, for example, a bump and starts to rise separately from the other, it twists (hence the name of the bar - torsion bar) and prevents the wheel from lifting, which would lead to body swaying .
The installation of such a stabilizer, although it gives the car stability to pitching, has its drawbacks. Connecting the suspension arms to each other makes it not as independent as the name suggests. Since the rod is an elastic element, it vibrates with its own frequency, which disrupts the operation of the suspension. And in very sharp turns, such a stabilizer is even harmful - it additionally transfers the load from the inner wheel to the outer one - outer tire literally smears on the road, while the inner one is about to come off it.
Is it possible for a car to not roll at all when cornering? Theoretically, yes. For example, if you lower the center of mass of the body to the roll axis, as in Formula 1 cars that do not roll in corners. But for ordinary cars this method is not suitable for obvious reasons.

Last year, Citroen came up with a rather neat technical solution to the problem of stabilizing body roll. The method is based on the unique properties of the hydropneumatic suspension, which was first used on an experimental Citroen DS back in 1955, has since been significantly improved and is now widely used in cars of this company.
The elastic element in the hydropneumatic suspension of Citroen ("Autopilot" # 3), as you know, is a gas that fills small spheres. The load on the gas through the membrane is transferred to the hydraulic system liquids.
In early versions of the design, where there was only one sphere for each wheel, by changing the amount of fluid in the system it was possible to regulate only the clearance and position of the car body depending on the load. Then (in the Hydractive suspension) additional spheres were installed, and the control was entrusted to the computer - it became possible to change the stiffness of the suspension. The next option is the Hydractive II suspension with a modified control algorithm.
This suspension, equipped with a rather sophisticated system of sensors and a computer, monitors factors (crosswind, bumps, pits) that tend to deviate the car from moving in a straight line. Vehicle speed, throttle position, steering angle and lateral acceleration are also taken into account. With an unfavorable combination of controlled parameters, the computer disconnects the additional sphere from the general contour, increasing the stiffness of the suspension. Naturally, the stiffer the suspension, the less susceptible to roll, so a car with Hydractive or Hydractive II suspension, such as the Xantia VSX, is much more resistant to rollover than a car of any other brand.
Hydractive II works well, no doubt. But from the point of view of stabilizing roll stability, this suspension, despite its name, behaves like a passive one - it only reacts to the lateral acceleration of the car that has already occurred. Naturally, with some delay.
This did not suit Citroen specialists. In addition, it was a sin not to use the potential of the very idea of ​​hydropneumatic suspension. And there was a system of active stabilization of the transverse stability of the car, which received the ugly name SC.CAR. Since last autumn, it has been installed on serial Citroen Xantia Activa.
In fairness, it should be noted that attempts to create an active stabilization system have been made before - for the first time such a system was tested on the same experimental Citroen DS. But then there were no computers.
The Citroen Xantia Activa uses, with minor additions, the same suspension elements as previous versions. But the system works differently. The first difference is that the suspension control electronics do not wait for lateral acceleration to appear, indicating that the car has already entered the corner. Activa predicts the amount of lateral acceleration even before the turn, based on measurements of vehicle speed, angle and steering wheel speed - this increases the speed of the system.
The car, as usual, is equipped with two - front and rear - torsion bar stabilizers. But only one end of each is rigidly attached to its suspension strut. The other is connected to the opposite post by means of a small hydraulic cylinder. The hydraulic cylinders are located diagonally, one on the left front pillar, the second on the right rear.
As long as the additional central sphere is connected to a common circuit and the suspension is in a "soft" state, active system stabilization does not work - hydraulic cylinders reduce the rigidity of the torsion bar and perform only damping functions, damping its own oscillations.
If the combination of measured parameters indicates that the car has started a turn, the computer turns off the additional central sphere. At the same time, as in the usual Hydractive II, the stiffness of the suspension increases. And the active transverse stabilization system is turned on - along with the rigidity of the suspension, the rigidity of the hydraulic cylinders and, accordingly, the torsion bar, which begins to interfere with body roll, increases.
If the roll still occurs, the sensor that measures it is triggered and an additional amount of fluid is supplied to the hydraulic cylinders - this turns them into a kind of jacks that forcibly level the body. The roll sensor is triggered when the body angle exceeds 1/2 ° - a value so negligible that it is not felt by either the eye or the stomach.
The result is that the Citroen Xantia Activa does not roll even when cornering, the wheels remain perpendicular to the road, and the behavior of the car is completely predictable. Probably, the prematurely appeared expression "in a turn, as if on rails" should actually refer to this particular car.

Alexander Pikulenko

V automotive world some ideas have long been formed regarding the use of one or another type of suspension: double-lever - for sports models, dependent - for SUVs, semi-dependent - for compact cars ... But what are the reasons for these ideas, and are they true at all?

Three groups of elements can be distinguished in the suspension of a car: guides - levers, elastic - springs and stabilizers, and damping - shock absorbers. The last two, that is, stabilizers, springs and shock absorbers, are the cornerstone in most disputes about driving performance cars. And this is largely true, because the listed details determine such tangible and important parameters, as smoothness, valkost and handling character. The design of the suspension - the geometry of the levers - often remains in the shadows, although in terms of its significance and influence on the behavior of the car, it is in no way inferior to other factors.

So, what determines the design of the suspension? First of all, it sets the trajectory of the wheel during compression and rebound. Ideally, this trajectory should be such that the wheel always remains perpendicular to the road, so that the tire-to-surface contact area is maximized. However, as we will see later, this is rarely achieved: usually, in the process of compressing the suspension, the camber of the wheels changes, and in the turn they lean to the side along with the heeling body. And the greater their deviation from the vertical, the smaller the tire contact patch. Thus, the stability of the car, the level of its adhesion to the road are parameters that are entirely determined by the design of the suspension.

Collapse and convergence

The two main suspension parameters are camber and toe. Camber is the inclination of the wheel plane to the perpendicular restored to the road plane. If the upper part of the wheel is tilted outward of the car, then the camber angle is considered positive, if inward - negative. Convergence - the angle between the direction of movement and the plane of rotation of the wheel. It can be measured in both degrees and millimeters. In the latter case, convergence is understood as the difference in distances between the leading edges of the disks and the trailing ones.

In a similar way, the geometry of the levers affects handling, only here the instability of the toe of the wheels affects. The consequences are not difficult to imagine - on bumps the car begins to scour, and in the turn there is a tendency to oversteer or understeer. However, this phenomenon can also be used for good, compensating, for example, for the tendency to drift in front-wheel drive models.

As a rule, the track of the car also turns out to be unstable - even a small suspension travel can lead to its change by a couple of centimeters. All this, of course, leads to an increase in driving resistance, and ultimately to an increase in fuel consumption and accelerated tire wear. But much more dangerous is the fact that this reduces the stability of rectilinear movement, because the grip properties of the tires are “spent” not on holding the car, but on the resistance to the wheels diverging to the sides.

Against banks

Along with the center of the transverse roll, the design of the suspension also sets the center of the longitudinal roll - the point around which the body leans at the moment of braking or acceleration. And at a certain position of this point, the suspension can prevent the growth of rolls, squeezing or pressing the body in the right places. However, not all pendants have such capabilities. The most effective in this regard are the suspension on oblique levers, on double levers and multi-link. They allow you to place the roll centers exactly where you need them. The possibilities of McPherson are more modest - the range of its adjustments is narrower. And here is the pendant trailing arms does not need settings - the center of the longitudinal roll is already located in the optimal place. Dependent and semi-dependent suspensions do not allow to deal with roll - their roll center is in infinity.

The design of the suspension also affects the smoothness of the ride. Firstly, by the value of unsprung masses, which includes the mass of all levers (although not completely, since they are attached to the body at one end), and secondly, by their internal friction. The fact is that many modern suspensions, especially multi-link ones, have the ability to move only due to the deformation of rubber-metal hinges, silent blocks used to attach the levers. Replace them with rigid bearings - and the suspension will petrify, lose the ability to move, since each of the levers describes a circle around its attachment point, and these circles intersect at a maximum of two points. Using rubber-metal hinges (and with varying rigidity in different directions), it is possible to achieve more complex kinematics of the levers and still ensure the suspension travel, however, at the same time increasing friction. And the higher it is, the worse the filtering of irregularities.

But much more surprising is the effect of the suspension on the level of roll of the car. Note that this is not about springs and shock absorbers, but about the layout of the levers! It turns out that their design sets the center of the transverse roll. Simply put, the point around which the body rolls. Usually it is located below the center of gravity - the point of application of the force of inertia, and therefore the car leans outward in a turn. However, by changing the location and slope of the levers, the roll center can be increased, reducing or even completely eliminating body tilt. If this point is above the center of gravity, then the roll will appear again, but in the opposite direction - inside the turn, like a motorcycle! This is in theory, but in practice, attempts to increase the roll center are accompanied by a number of problems, such as changing the gauge too much, and therefore we are only talking about a slight decrease in rolls, but it is certainly worth it.

Thus, designing a suspension is a responsible and difficult task, and its implementation is always a search for a compromise. What solutions this search leads to, we will consider in the next issue.

Author Edition Autopanorama №3 2016