Shock Absorber Fluid

New shock absorber technology will convert those bumps into useful energy

If you thought that the suspension system on your car was just to…suspend your car, you would be wrong. It seems that researchers are now looking at a way to convert the energy generated by the shock that it absorbs into something more useful. For those who are unfamiliar with how shock absorbers work, they basically work by dissipating energy through a combination of coiled metal springs and hydraulic dampers.

Now there are several engineering teams that are looking to develop this new technology, which is essentially a miniature power generator for your vehicle’s wheels, and that is said to convert those bumps that you experience while driving on the road into useful energy as well as resulting in a smoother ride.

How this technology is supposed to work is that it forces fluid through a hollowed circuit that is hooked up to both a hydraulic motor and electric generator. Microprocessors will then optimize the fluid which will then translate into a smoother ride with more power. In theory they claim that it should bring fuel efficiency up an additional 6% and longer driving range for hybrid-electric vehicles.

Levant Power, the company behind this technology, is looking to start releasing this technology, the GenShock, by 2012 and it is currently being tested by military vehicles.

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Design and Functioning

Most of Öhlins suspensions are a high pressure monotube type. The fluid is put under gas pressure and the gas and the fluid are kept apart by a separating piston. The piston is usually fitted in an external reservoir, connected by a hose (Fig. 4) or fixed directly on top of the shock absorber (Fig 3). In some models everything is fitted inside the main shock absorber (Fig 2 ).

A few shock absorbers are of emulsion type, oil and gas mixed inside the shock absorber (Fig 1 ). Pressurisation of the fluid is made with nitrogen. The pressurisation prevents cavitation of the fluid and the shock absorbing action is therefore more even. The external reservoir also contributes to better cooling of the fluid, giving longer service life for the fluid as well as the components.

Öhlins shock absorbers with external rebound adjustment have an integrated temperature compensation. As the temperature increases and the fluid flows more easily the flow is controlled accordingly. The shock absorbing effect is therefore independent of the temperature. The more advanced models permit individual adjustment of compression and rebound damping.

Öhlins shock absorbers provide the possibility of adjustment, making them adaptable to most vehicles, drivers and ranges of use. All of the shock absorbers with springs have adjustable preload of the spring action.

Fluid is forced through needle valves at a low rate of flow (Fig 6) and through a number of orifices in the piston (Fig 7) at a high rate of flow. The flow through these orifices is regulated by shims (thin steel washers) that at high pressure are deflected to open for the fluid. On most models the needle valve can be adjusted from the outside.

By altering the size of the shim-stack (Fig 8) (i.e. number, thickness, diameter) the characteristics of the damping action can be changed. This should only be done by an authorized Öhlins service workshop.

Compression damping When movement of the motorcycle causes compression of the shock absorber, the fluid flows through the needle valve (combined compression and rebound valve) in the piston rod. If the velocity of the compression movement is high, i.e., in the case of rapid compression, this will not be sufficient and consequently the shims underneath the piston will open to allow for a greater rate of flow. The fluid that is displaced by the volume of the piston rod is forced into the external reservoir via a separate compression valve. The separating piston is displaced, thus increasing the gas pressure. When the spring forces the shock absorber to extend again, the fluid flows back through the needle valve. The fluid flowing into the chamber is forced by the pressure of the gas back into the shock absorber via a separate non-return valve. If the piston velocity is high, the shims on top of the piston will also open to allow the fluid to flow through.

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