Shock absorbers are used in conjunction with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the vehicle.
The most common type of shock absorbers for automobiles is the dashpot type which can be either a mono-tube design or a dual-tube design. In the mono-tube design, a piston is located within a pressure tube and is connected to the spring mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the pressure tube into an upper working chamber and a lower working chamber. The piston includes compression valving which limits the flow of damping fluid from the lower working chamber during a compression stroke and rebound valving which limits the flow of damping fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. Because the compression valving and the rebound valving have the ability to limit the flow of damping fluid, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass.
In a dual-tube shock absorber, a fluid reservoir is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. A base valve assembly is located between the lower working chamber and the fluid reservoir to control the flow of dampening fluid. The compression valving of the piston is moved to the base valve assembly and is replaced by a compression check valve assembly. In addition to the compression valving, the base valve assembly includes a rebound check valve assembly. The compression valving of the base valve assembly produces the damping force during a compression stroke, and the rebound valving of the piston produces the damping force during a rebound or extension stroke. Both the compression and rebound check valve assemblies permit fluid flow in one direction, but prohibit fluid flow in an opposite direction; however, they are designed such that they do not generate a damping force.
In applications where a low level of flow restriction is a priority for the check valve assemblies, the working surface for lifting the check valve disc must be maximized. In addition, this low flow restriction level also calls for a very lightweight disc. When first reviewing the design for the check valve assembly, it may seem logical to utilize a valve spring, which has a low stiffness. This design choice is overruled by the need for a fast closing check valve assembly, as well as the need to avoid “chuckle” noise when the shock absorber is mounted on the vehicle.
As the check valve disc becomes lighter and thinner, and the area of the check valve disc which is acted upon by fluid pressure becomes greater, the check valve disc becomes very sensitive to the high fluid pressure which urges the check valve assembly into its closed position.
The continued development of check valve assemblies has been directed towards reducing the level of flow restriction without compromising the sensitivity of the check valve assembly to the high pressure fluid which urges the check valve assembly into its closed position.