SHOCK ABSORBER - ADAPTER
Alexander BUDKIN, Denis BOROVITSKY, Alexey VOROBYEV-OBUKHOV
We don’t know whether the Tenneco Corporation, the owner of the Monroe trademark, is familiar with the classics of Russian cinema, but it strictly follows this covenant. With the latest innovation - adaptive shock absorbers (ЗР, 1999, No. 12) it is worth getting to know each other better.
In fig. 1 and 2 show how the hydraulic characteristic of a conventional shock absorber is formed. If all its valves are “tightly” closed (see Fig. 1), leaving only the bypass channel in the piston, we obtain a very rigid linear relationship (green line in Fig. 2). Add message valves with a compensation chamber (parts 1 and 7 in Fig. 1) - the characteristic will become “softer”. In the case of instant (inertialess) opening of the valves, it will also be linear. And as a result of the fact that valve 1, which is activated during the compression process, has a larger flow area than valve 7, the characteristic will be asymmetric with respect to the origin: during the compression process it will be “softer”, and during the rebound process it will be “harder” (blue lines). When two more main compression and rebound valves located in the piston are turned on, the shape of the characteristic changes again. As each of the valves opens and the total flow area of the channels increases, it will bend, becoming less and less “rigid” (red curve). Finally, with the valves fully open, the graph will again turn into a straight line. It remains only to note that the characteristic of a real shock absorber due to the gradual opening of valves may not have straight sections at all.
Now let's see what the Monroe company was guided by calling its new shock absorbers with the Safe Tech system adaptive. They are distinguished by three features: a working fluid with an extended temperature-viscosity range, a new design of valves in the piston (with leaf springs) and a groove on the inside of the working cylinder, which forms a bypass channel (see Fig. 3). The last two features should be considered in more detail.
A valve with lamellar (disk) elastic elements works like a car spring: under the influence of the pressure of the liquid, the valve discs bend and open the corresponding channel. The size of the piston with such valves becomes smaller, the durability increases, and, most importantly, the change in stiffness of such a composite disk spring, like the spring, is nonlinear. Moreover, the law of change in stiffness in movement can be changed by selecting disks with specified diameters. To some extent, such a valve can be considered adjustable, but the main “adaptability” of the Safe Tech system is not this. As the piston moves up or down from the middle position, the cross section of the bypass channel on the cylinder wall changes, which entails a change in the hydraulic characteristics of the shock absorber - a transition from the comfort zone to the so-called control zone (Fig. 4). Thus, the characteristic changes depending on the suspension travel: with small movements, the shock absorber tries to provide comfort, with large movements it becomes stiffer.