The present disclosure relates to a rear suspension or shock absorber for a vehicle that includes a portion that includes compression of a compressible fluid and damping using a substantially incompressible fluid. In particular, the present device includes a piston that includes a compressible fluid on one side of the piston and a substantially incompressible fluid on the other side of the piston.
For many years, bicycle designers have struggled with the design of rear suspension systems. Use of air or nitrogen as the primary spring for the suspension has the benefits of reduced weight and adjustability by comparison with coil springs. The characteristics of a gas spring may be improved by providing a negative gas spring that opposes the primary, or positive, gas spring to improve initial compliance and soften re-extension (“topping out”). However, gas spring systems often suffer from friction at the dynamic seals that contain the pressure in one or more gas chambers. Designers have attempted to ameliorate this problem by spraying a small amount of lubricant, often oil, into the gas chamber on one or the other side of the piston. Such a design does not often allow for adequate lubrication, as there is no mechanical means for the lubricant to be distributed onto the surfaces in need of lubrication or to reapply the lubricant.
Accordingly, it is desirable to have a design for a rear suspension that incorporates desirable features of an air- or gas-based suspension but minimizes friction. Further, it is desirable to incorporate a lubricant that is under pressure to lubricate the dynamic pressure containment seals and dynamically sealed surfaces of the positive and negative springs. The result may be improved performance of the rear suspension to absorb and damp impact, while also allowing for on-the-fly adjustment of damping performance.