BETWEEN BODY AND WHEEL
Types of modern pendants are diverse. Again, as in the 30s, all sorts of intricate designs appear and the advertisement does not tire of repeating: “… with this latest suspension the car …”, promising miracles of handling and comfort.
Alexey VOROBYEV-OBUKHOV, Mikhail GZOVSKIY
We will not be able to consider all the designs - we will focus on what unites, on the common. An indispensable accessory of any suspension is an elastic element. Once springs and springs reigned here, a little later they were joined by torsion bars and rubber blocks (say, in the suspension "Hydroelastic" on the "oostin-mini" of the first series). The rubber element became hollow, then it was decided that it was convenient to adjust the stiffness of the suspension by pressure in the cavity. Such elastic elements have been used for many years on American passenger cars and around the world - on heavy trucks and buses (even on LiAZ). Gas is able to work inside a rigid tank - it is enough to supply the latter with an elastic membrane. On the other side of the membrane there is either a rod to the suspension arm or liquid, and a hydraulic cylinder is connected to the arm. This type of suspension has been used for many years on "rovers" of different models, as well as on Citroens, starting with an unforgettable DS. True, the French included a hydraulic pump in the system: by changing the pressure, they controlled the ride height.
SHOCK ABSORBERS AND SPRINGS
Among firms that have long been experimenting with pendants is Citroen. This year, the French presented the next, third generation of hydropneumatic suspension, which, incidentally, is a panicky fear for Russian fans of used cars. Citroën claims: the novelty has been finalized and, most importantly, its hydraulic part has been simplified. Hence the extended service intervals: the first service operations are provided in five years or 200 thousand kilometers.
From a technical point of view, the suspension is interesting in the absence of shock absorbers that are familiar to us. Their role is played by spheres filled with a special fluid, and each axis of the machine is equipped with a third, additional sphere and a stiffness regulator. The principle of regulating the hydraulic suspension is to “isolate” the third sphere, when it is necessary to achieve greater rigidity, or to include it in the duty cycle, if you need to adjust the suspension more comfortably.
In order to make the system work, a hydroelectronic unit was used here: it is both the heart and the brain. It includes a computer, a hydraulic pressure accumulator and an electric motor.
Very similar to the "Citroen" design of the Australian company "Kinetic" (branch "Monroe"). It is called the “X-system”, and the “X” here is not a symbol of secrecy, but a hint of cross-connections. This suspension is intended primarily for off-road vehicles. For inquisitive readers, we present a diagram of a new suspension in two states - in a turn and with diagonal hanging. Try to carefully understand the flow of gas and liquid between the struts. Note that the Australians managed to do without the ubiquitous, it would seem, electronics with many sensors. How she will prove herself “in battle”, the all-terrain vehicle from Ford will show in 2002, and then the “X-Systems” will come to the long-awaited all-terrain vehicle of the Volkswagen.
As you understand, stabilizers are not needed in the hydropneumatic suspension - it is enough to control the flow of fluid between the spheres (or cylinders) in order to eliminate tilt in tight corners. On cars with a more traditional suspension, this is not the case - an elastic long rod links the left and right side wheels, helping in those very turns and … reducing comfort on a bad road.
It would seem that electronics has so firmly entered all the components of a modern car that it’s impossible to invent a bicycle in mechanics. Nevertheless, Kinetic said a completely new word.
One of the devices developed by her was called RFS and is attractive because it can be installed on existing cars. Here the stabilizer rods are cut in the middle, and the halves are connected to each other through the pistons of special hydraulic cylinders. The working cavities of the latter, in turn, are connected by pipelines through which the fluid flows from the front to the back and vice versa. The connection is organized so that in a turn, when the body is evenly inclined, the pistons connected, say, with the left wheels, move in one direction and fluid flow is impossible. This is equivalent to a rigid connection of the halves of the rods to each other, and the car behaves in accordance with their thickness and elasticity. Rolls of the car are sharply reduced. When driving irregularities, the wheels move “out of step”, the fluid pushed out by the front piston finds a place in the rear hydraulic cylinder, and the car appears to be deprived of the influence of stabilizers. Passengers will appreciate this as a comfortable soft suspension. Note: the system works by itself, no sensors and computers!
It’s hard to imagine a suspension without leverage. Today they are made stamped and cast, from steel and aluminum, composite ones appear. The mobility of the levers is provided by rubber bushings - silent blocks. Once, bearings were used here, then, to increase the contact area of rubbing parts, threaded bushings were mastered. The rubber won, creating an additional problem for car designers: after all, the silent block “works” only on twisting, but it is worthwhile to apply a radial force, the lever axis is shifted. Over time, we learned to take into account and use this geometry change: after all, under load (with sharp acceleration, braking), the wheel alignment angles change, which in some modes increases the stability of the trajectory. But if the calculation turned out to be wrong …
Recall the sad events associated with the Audi TT sports coupe. At high speed (for 200 km / h), when the gas was released in gentle turns, the car suddenly lost contact with the rear wheels and the road, began to rotate and flew away, at best, into a ditch. The cases frightening with their similarity multiplied, and it was no longer possible to explain them by the folly of drivers alone. Belated studies have shown that at speeds greater than 200 km / h, the load on the rear axle (and hence the grip of the wheels) has decreased dramatically, especially when braking or discharging gas. If it were a prototype, it would be easy to cope with trouble, but try to fix the lack of a production car! I had to look for a comprehensive solution, and not too big changes at once in several nodes led to success. Let's see what the suspension got. Firstly, the stabilizer bars were modernized. Not much: the front one got one millimeter thicker, the rear one lost the same amount of weight. Harder steel and front shock absorbers. Finally, a little - very little - changed the geometry of the front wishbone. Only a very attentive reader will find the differences. You see, the lower silent block has become larger and therefore softer. Now, with a certain load, the lever occupies a slightly different position, which means that the similarity collapse changes in a different way. As a result, the TT got the necessary understeer, and the trunk spoiler and electronic stabilization system completed the job.
The modern level of knowledge allows you to customize the suspension in any way you want, for any road and driving style. But what if the state of the road surface changes along the way or the driver suddenly starts up and wants to “walk” a few kilometers a la Schumacher? The only way out is to instruct the intellectual computer stuffing to quickly configure the suspension.
The new CL-coupe from Mercedes received an active suspension, in the racks of which oil is supplied under tremendous pressure, forcing one or another wheel to lower. The designers had to generously hang the car with sensors that track the course of each wheel, the angular and linear accelerations of the body and write a clever program for the control computer, but also solve other problems. For example, the speed and volume of the pumped oil turned out to be so significant that a special radiator appeared to cool it! But the result did not leave the testers indifferent: according to their reviews, the coupe seemed to fly over the road without touching the ground.
Cadillac also could not do without sensors, programs and a computer, but approached the matter differently. Its designers abandoned the construction of the pumping station, but forced the liquid itself to "change" its properties - viscosity and shear stress - on the fly. True, for this, Delfay had to add carbonyl iron microparticles to it, and electromagnets to the shock absorbers. But on the other hand, the energy consumption was only 25 watts per wheel, which is enough to either clamp it tightly or release it into free vibrations. This system will receive Sevil 2002.
If you can’t hope for a domestic analogue of the CL coupe, then something similar to the American version is already being tested on the most grateful medium - Oka! It turns out that with magnetically controlled media in parallel (and successfully!) Worked in Russia. If inventors and car factories had more money, perhaps press conferences on new technology would be organized at VAZ.
Suspension "Citroen" in the "comfortable" (above) and "normal" modes, when the third sphere does not work.
The development of the Kinetic X-system company dispenses with electronics.