Between wheel and body

Every vehicle has a suspension system, i.e. a more or less complex system that connects the body or the supporting frame with the wheels and ensures efficient, comfortable and safe driving. Here is a brief compendium of knowledge about what characterizes the most popular suspension systems in passenger cars and how they work.

They used to say that the car is on wheels. And this is true in the sense that the wheels are in direct contact with the ground. But just as the human legs are only part of the lower limb, so the wheels are only the final (and at the same time the least complex) element of the complex system that holds the main body of the car. This system, commonly known as suspensemust cope with many extreme requirements - overloads arising both during acceleration and under load and no load driving conditions, must cope with body movements resulting from straight and other directions of movement, minimize the inconvenience caused by driving on rough roads or even in difficult terrain, finally ensure the comfort and safety of the driver and passengers of the vehicle.

Is there a universal one that can perfectly satisfy all these requirements and show itself well in any conditions? Of course not. Automakers have come up with several proven and commonly used solutions, but each has its own advantages and disadvantages, being a kind of functional compromise.

They bounce, lead and overwhelm

In each suspension, three main nodes can be distinguished: elastic elements; guide and connecting elements and damping elements.

The main role of spring elements is the so-called. unsprung vehicle masses (wheels, brakes, axles, some suspension elements) and maintenance of ride height. This function can be performed by leaf springs, also called flat, spiral (coil) springs, torsion bars, rubber or plastic springs, pneumatic systems.

From the beginning of the 70th century until the XNUMXs, the most commonly used spring element in vehicles, first horse-drawn and then mechanical, were springs, usually semi-elliptical in shape. We can still see them today, especially in the rear suspension of vans, pickup trucks and SUVs with dependent suspension. They are cheap, uncomplicated, capable of withstanding significant loads and, in addition, they have one important property - they can be an independent suspension system, since they can transmit forces in all three directions. Unfortunately, they provide rather poor driving comfort. They are made in the form of one flat rod or a package of flat rods made of spring steel, called feathers, interconnected by a set screw and clamps.

Vehicle rear suspension components, which are in some way derived from leaf springs, torsion bars. They are in the form of a long steel rod, a tube, or a bundle of flat rods. One end of the torsion bar is attached to the frame or car body, and the other end is pivotally connected to the control lever. The vertical movement of the wheel causes an angular displacement of the rocker arm and twisting of the rod, which, due to its elasticity, acts on the car wheel like a traditional spring.

However, at present, car manufacturers most often use a spring element. coil springsmanufactured by winding a spring steel rod around a cylindrical, conical or barrel shape. Looking under the chassis of the car, you should see one massive spring per wheel. Springs have many advantages: they take up little space, have a simple design, and at the same time have the best spring properties and are highly versatile - they are ideal for everyday use, as well as in motorsport or off-road.

An important spring element in the suspension is tilt stabilizer. Most often, it has the form of a metal rod of circular cross section, bent in a shape similar to the letter U. It is attached to the body in the middle, and the ends are connected to the rocker arms or the stand using rubber. sleeves or the so-called stabilizer links. As a result, the elastic response of the anti-roll bar reduces body roll when cornering and sway when driving over bumps. A similar role is played by reactive rods, which can be installed transversely (the so-called Panhard rods) or longitudinally.

The vast majority of suspensions require the use of additional connectors capable of transmitting transverse and oblique forces. And now he appears on the stage vakhachwhich is the most used guide element today. The control arms are articulated arms that allow the wheels to move vertically and transmit horizontal forces. Depending on the location of the axis of their rotation, control levers can be divided into: longitudinal (pulling or pushed), transverse or oblique.

Another key element of the suspension are shock absorberswhich are an inextricable pair with helical springs. They are responsible for damping body vibrations on bumps and for ensuring that the wheel remains in constant contact with the road surface. If they were not there, the car would swing like a cradle on springs and bounce off the road like a ball. The damping system indirectly affects the operation of safety systems such as ABS and ESP.

Currently, the most common telescopic shock absorbers (oil and gas-oil), especially telescopic, integrated with a helical spring, the so-called. McPherson stands. In many so-called semi-active suspensions, you can find shock absorbers with an adjustable degree of damping.

Most of the suspension elements are connected using special hinges and rubber bushings, commonly known as silent blocks.

Dependent, alone or with a beam

According to the way the individual suspension elements are connected and the principle of their operation, these systems are divided into three main categories: dependent, independent and semi-dependent suspensions with the so-called torsion beam.

The first of these types is historically the most ancient. Dependent suspension characterized by the fact that the wheels of the axle under consideration are rigidly connected to each other by mounting them on a common element, which can be a non-driving axle beam or a rigid driving axle. This arrangement means that when one of the wheels hits a bump in the road and changes position, it automatically forces the other wheel to move.

The disadvantages of this type of suspension, in addition to the not always desirable interaction of the wheels of one axle (worse than the car's handling when cornering, easy separation of the wheels from the surface), are: a large mass of the connecting element of the wheels, especially if there is a gear on the axle, and the need to find a large space for vertical movement an axle that works in tandem with the wheels - at the back it takes up space for luggage, and at the front it strains the engine up, which, in turn, raises the center of gravity of the car.

However, the dependent suspension also has advantages: the unsprung masses are small, and the suspension itself is structurally simple, durable, capable of carrying heavy loads, so they are readily used in trucks, buses and all-terrain vehicles. In a dependent suspension, you can often find leaf springs. Another solution is coil springs interacting with torsion bars.

In the case of passenger cars, independent suspensions are most often used on the front axle, and independent or on the basis of a torsion beam on the rear axle. But even if we have the same type of suspension on both axles, they are still not identical. Where does this difference come from? It's not a whim of the builders. It is only necessary to take into account an additional factor in front - the need to use a steering trapezoid, which will allow the wheels to turn.

W independent suspension each wheel of the car moves independently of the others. This requires the use of more wishbones and joysticks, but the system does not take up much space and significantly improves the comfort and traction of the car. The most common independent suspension solutions used on the front axle are the double wishbone system, the already mentioned MacPherson strut or the multi-link (multi-link) system.

The first one has the oldest metric. The steering knuckle is attached by a ball pin to two transverse transverse levers: upper and lower. Suspension arms are attached to the frame or body and have a supporting function - one of the suspension arms is supported by a spring and a shock absorber, often in the form of a suspension strut assembly. This type of suspension is very good at counteracting lateral body tilts.

However, the most popular are MacPherson speakers, named after their inventor, an American designer. Erlea S. McPhersonwho first applied his clever invention in the Chevrolet Cadet prototype in 1946. Why is this solution so popular? It is cheap, simple in design, takes up little space and is very effective. The main element of the McPherson strut is a shock absorber with a helical spring superimposed on it. The ends of the shock absorber piston rod and the spring are at the fulcrum in the wheel arch (glass).

The upper mount of the shock absorber allows the column to rotate around its axis, and hence the wheels. Its lower part is rigidly attached to the steering knuckle, and the steering knuckle - by means of a ball bearing with a transverse transverse lever. As a result, a single system simultaneously performs the spring and shock-absorbing functions and guides the wheels. The weaknesses of the MacPhersons are: the transfer of part of the vibrations from the steering system directly to the body, strong friction in the stem seat due to rotation around its axis, and the fact that the wheel is not perpendicular to the ground throughout its operation. range.

Multi-link suspension structurally, this is the highest stage of "development" of such systems. This is a rather complex combination of trailing, side, inclined and hinged arms. There is no single multi-link suspension scheme; each manufacturer has developed its own patents. "Multi-link" provides the minimum possible changes in the angles of convergence and inclination under the influence of changes in the load of the car and its movement. Simply put, even when cornering quickly, the car retains high stability and good traction. It combines high comfort with sporty driving performance, which is why we most often see them in premium cars, especially those with more weight. The owners of such cars also have a larger budget for repairs and maintenance, which is of great importance in this case, because multi-link suspension - due to the number of elements and the need to reduce unsprung weight, which often leads to it from light alloys - is very expensive. The number of advantages, however, remains so great that multi-link systems are increasingly being installed on both the front and rear axles, even in popular brands.

It is worth noting that in the category of independent suspensions on the rear axle, the variety is even greater than in the case of the front suspension. In addition to the mentioned multi-link system, systems with inclined, longitudinal and transverse transverse levers are used. All these elements - like shock absorbers and springs - each manufacturer mounts a little differently.

Semi-independent suspension

In the third type - semi-independent suspension – the movement of one wheel has minimal effect on the movement of another wheel on the same axle. This group includes, first of all, suspensions with torsion bar, consisting of two trailing arms attached on one side directly to the body, and on the other side with the help of one cross member.

Why is the beam called torsion beam? Because it is subject to deformation caused by the work of the rocker. In addition, it also acts as a stabilizer. This type of suspension remains very simple in design, fairly efficient, cheap to manufacture and repair, and also light (small unsprung masses), takes up little space (larger trunk) and has little change in camber angles due to lateral forces.

The torsion beam has been in constant use since the 70s, mainly in mini, city and compact cars. French and Far Eastern manufacturers especially like it. Due to its design, this type of suspension can only be used on a non-driving axle.

Torsion beam suspension also has a number of disadvantages: the interaction of wheel movements with each other, high torsional and shear stresses on the beam and, as a result, high loads on welds, poor body vibration isolation. and noise due to uneven surfaces.

Pneumatics, off-road, sports

There is another type of suspension - unsurpassed in comfort: air suspension. Regardless of the load, the spring parameters and therefore the ground clearance remain the same. In some cases, the standard ground clearance can be increased, which is of great importance for SUVs and SUVs. In addition, the dampers in the pneumatic system often have electronically controlled damping characteristics (gradual or stepless), which makes it possible, for example, to select a comfort mode for a quiet ride and a sport mode for a more dynamic ride.

In air suspension, traditional spring elements are replaced by special rubber bags called bellows, filled with a compressor compressed nitrogen or air. Bellows are often integrated with air springs, their pistons are connected to the rocker arms and they are connected to the wheels. Equalizing valve associated with the movement of the rocker ensures a constant suspension height. When the suspension is loaded and compressed, the system draws in extra air and releases it as the suspension system expands. Sometimes air suspension is available only on the rear axle, for example, in some station wagon models, and then it is called nivomat. Air suspensions are very sensitive to misuse and maintenance, and repair costs are usually high.

Pneumatic State Disclosure adaptive suspension, in which the actual ground clearance depends on the speed of movement - for example, when accelerating, the ground clearance decreases to lower the center of gravity. Cherry on the cake though hydropneumaticsfor which the Citroën brand is famous. The French pioneered hydropneumatic suspension in 1954 in the Traction Avant 15 Six H rear suspension and developed it on the technologically revolutionary DS and its successors: SM, CX, BX, XM, Xantia, C5 and C6.

Despite successive generations of hydropneumatics and branded solutions from other car manufacturers, the general principle of a hydropneumatic suspension spring and shock absorber is still similar to the solution we learned at DS. There are no familiar components in the suspension, such as shock absorbers, springs, springs or torsion bars. Instead, on each wheel we have a pressure system in the form of a metal ball (sphere) half filled with compressed gas and half hydraulic fluid and separated by a diaphragm. The ball is attached to an aluminum cylinder with a steel piston in the center. Suspension arms are connected to a piston rod, the work of which causes oil to flow into the cylinder, then the liquid presses on the gas, which compresses it and therefore dampens the vertical movement caused by the bumps in the wheel. Various types of sensors and electronically controlled valves play a very important role in the correct operation of hydropneumatics.

Finally, a few more words about the specifics of suspension for off-road and motorsport. Taking care of it and adapting to the tasks assigned to it is one of the most important tasks facing the owners of SUVs, as well as sports and racing cars.

W SUV Dependent suspension works best on rigid axles sprung with coil springs. The traditional suspension on leaf springs is not much inferior to it. Equally important is how you adjust the "hinges". In a conventional car, as well as in popular SUVs, a very soft long-travel suspension is generally considered a disadvantage. In the field, the opposite is true - a well-thought-out curvature of the axis, i.e. the possibility of a large wheel travel in relation to the chassis or another wheel of the same axle, significantly affects the courage of the car.

W sports cars the suspensions are stiffened and comfort is of secondary importance. Traction and grip count. Ground clearance also affects the ride quality of this vehicle. This is related to the center of gravity of the car. The lower it is, the faster and more stable we can take turns. Therefore, in sports cars you can often find coilover suspensions, in which the special design of the springs makes it easy to adjust the ground clearance of the car, and in more advanced ones, also the stiffness of the suspension. The track width is also important - the larger the wheel, the better the grip when cornering.

Suspension failures can cause premature wear of tires, suspension and steering joints, wheel bearings and body mounts, as well as increased braking distances.

That is why it is worth knowing how the suspension system works in our car, what elements it consists of and taking care of its proper performance on an ongoing basis. The state of the suspension is still underestimated in our country, although it is one of the key, constantly working components of the car, and our safety largely depends on it.