Brakes – Internal-resistance motion retarder – Using magnetic flux
Reexamination Certificate
2002-01-08
2003-12-30
Schwartz, Christopher P. (Department: 3683)
Brakes
Internal-resistance motion retarder
Using magnetic flux
C188S266200, C188S282200, C188S282500, C188S313000, C188S322150
Reexamination Certificate
active
06668986
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to fluid dampers for vehicles and more particularly, to dampers of the type which are known as “active”.
The invention is specifically applicable to and will be described with particular reference to a mono-tube shock absorber or strut which is electrically controlled to function with two different damping characteristics. However, those skilled in the art will recognize that the invention is also applicable to twin tube shock absorbers and struts and, in theory, may be applicable to dampers having variable damping rates.
BACKGROUND OF THE INVENTION
The typical fluid dampers used in vehicle suspensions, such as hydraulic shock absorbers and struts, filter out road inputs from being transferred to the vehicle's body and associated passenger compartment by dissipating energy. Two common types of vehicle fluid dampers, each having a cylinder and piston, are mono-tube and twin tube shock absorbers. The preferred embodiment of this invention is directed to mono-tube shock absorbers and struts.
As is well known, a mono-tube shock absorber essentially comprises a cylinder or tube filled with hydraulic fluid and into which extends a piston rod having a piston fixed to its end. Generally, the upper end of the piston rod extending out of the tube is adapted for connection to the sprung mass (body) of a motor vehicle and the lower end of the tube or cylinder is connected to the unsprung mass (wheel assembly) of the vehicle. Relative movement of the sprung and unsprung masses of the vehicle produces relative axial movement of the piston which is in sealing sliding engagement with the tube walls and divides the tube into two chambers, conventionally referred to as a rebound chamber on one side of the piston and a compression chamber on the opposite side.
Relative movement of the piston within the cylinder is provided by valving that controls fluid flow from the pressurized chamber past or through the piston to the unpressurized chamber. Two of the more common passive types of valves used in fluid dampers are deflected disc type valves (digressive valves) and blow-off type valves. With a deflected disc valve, a disc stack is positioned as an obstruction in a fluid flow path. During piston movement, once sufficient pressure is developed, the disc stack is deflected to provide an increased flow area. The extent to which the disc stack resists deflection principally determines the damping characteristics of the fluid damper. In a blow-off valve, a single valve disc is generally biased by a spring to normally close-off a fluid flow passage. Sufficient fluid pressure causes the valve to lift, compressing the spring and providing an increased fluid flow area. Different rate springs and preloads allow the valve to blow-off at different pressures thereby regulating damping loads. This invention relates to disc-type valves.
The ride handling characteristics of a damper for a motor vehicle (load vs velocity performance curve) is determined by the rebound and compression characteristics of the piston valve in a passive mono-tube application. However, it is desirable to have at least a two stage damper for both rebound and compression. For example, during vehicle cornering maneuvers in which the piston undergoes low speed compression, it is desirable for the vehicle to have stiff or “firm” ride handling characteristics. Conversely, when the vehicle travels over pot holes at relatively high vehicle speeds in which the piston undergoes high speed compression, it is desirable to have “soft” ride handling characteristics. Different vehicles require different handling characteristics. Conventional mono-tube shock absorbers with passive valves can only affect a compromise.
The prior art has long recognized this problem and has developed designs in which the valve orifice, which controls the damping forces, is electrically adjustable. Conceptually, sensors determine the operating condition of the vehicle and algorithms determine a desired orifice size based on the operating conditions. Electronics generate an orifice size signal inputted to electrical apparatus which mechanically adjusts the orifice size. While conceptually sound, there are problems in the commercial implementation of this concept.
The prior art has recognized such problems and has developed a solenoid actuated, shuttle type, shut-off valve. More particularly, an economical solenoid can be designed to fit into a piston rod and develop sufficient force to move a spring biased shuttle valve from an unenergized position to an energized position. A mono-tube piston can be equipped with two passive valves, each controlling rebound and compression, with one of the two valves selectively cut in or out of operation by the solenoid shuttle valve. For example, both valves operate to provide the soft suspension for highway cruising while only one valve operates to provide the stiff compression for cornering. The solenoid is actuated automatically by sensors sensing or predicting the operating conditions of the vehicle. Additionally, the vehicular operator can be provided with a manual override control that forces the solenoid into an energized or de-energized condition. This invention is applicable to this type of active damper and uses a solenoid to selectively cut in and out a passive valve.
Two-stage, solenoid operated active dampers are described in detail in U.S. Pat. No. 5,690,195 to Kruckemeyer et al., issued Nov. 25, 1997 and U.S. Pat. No. 5,706,919 to Kruckemeyer et al., issued Jan. 13, 1998. The '195 patent illustrates an arrangement where the hydraulic fluid passes in parallel to different valves and the '919 patent illustrates an arrangement where the hydraulic fluid passes serially through the two valves. This invention is an improvement over the '919 and '195 patents, specifically, the '195 parallel flow patent. The '195 patent is incorporated by reference herein, specifically for its disclosure of the solenoid, the solenoid actuated shuttle valve and the digressive disc stack valve working in conjunction with the solenoid which are substantially the same as that disclosed herein.
The '195 patent uses a bi-directional digressive disc stack valve for the passive valve which is always on and typically provides the firm ride handling characteristics of the vehicle. As is well known, bi-directional, digressive disc stack valves cannot provide independently set flow rates for both rebound and compression. Because this valve is normally used to provide the firm handling characteristics of the vehicle, it is highly desirable for the manufacturers, especially those manufacturing “performance” vehicles, to be able to independently set or tune the rebound and compression spring rates of this valve. This is not possible in the '195 patent.
A more subtle point is that a valve for the firm mode requires relatively high, unimpeded flow rates through the piston. That is, a valve always provides the flow restriction in a passage, i.e., the orifice. However, the passage upstream or downstream of the orifice affects flow through the orifice, i.e., a backpressure at certain flow rates can affect flow through the orifices. Again, the function of the firm valve is to assure high flow rates. Because bi-directional disc stack valves require flow in one direction to unseat the outer edge of the disc and opposite flow to unseat the inner edge of the disc, a serpentine flow path to the orifice often occurs. Such a flow path could adversely affect performance of the valve at certain conditions, i.e., high flow producing turbulence.
SUMMARY OF THE INVENTION
Accordingly, it is an important aspect of the invention to provide an improved, parallel flow active damper, especially suited for mono-tube applications, in which at least one of the parallel valves can independently control the flow rate through the damper for both rebound and compression damper modes.
In accordance with one aspect of the invention, a vehicular damper is provided which includes a cylinder and a piston
Dellinger Darin Duane
Moradmand Jamshid Kargar
Neal Robert Alan
Delphi Technologies Inc.
Kramer Devon
McBain Scott A.
Schwartz Christopher P.
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