Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Reexamination Certificate
1999-11-11
2001-10-02
Oberleitner, Robert J. (Department: 3613)
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
C251S129070, C251S052000
Reexamination Certificate
active
06296091
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to suspension systems and specifically to a suspension control unit incorporated in a vehicle computer controlled suspension system and to the fluid control unit and valves incorporated in the suspension control unit.
Computer controlled suspension systems use a computer to control the damping provided by each of the suspension system actuators. Typically, computer suspension systems incorporate actuators on to which are mounted electrically adjustable valves which are driven by computer to control the flow of hydraulic fluid the actuators and thus control the damping provided by the actuators.
Virtually all of these computer suspension control systems on the market use orifice controlled flow valves to regulate damping forces. There are several reasons why orifice control has become the de-facto standard. One reason is that conventional shock absorbers have always used orifice control technology, and as such orifice controlled technology is better understood and more easily adapted to computer control. Another reason is that traditional and commonly accepted feedback control theory is better implemented with orifice control techniques. Moreover, orifice control valves can be considerably smaller than the constant force (pressure regulating) valves. Furthermore, constant force valves incorporated in computer control systems, in principle, result in very harsh and totally unacceptable performance. Use of constant force valves in computer controlled suspension systems has required in many instances the use of bulky and expensive accumulators to smooth abrupt force transitions that occur with the operation of the constant force pressure regulating valves. However, orifice control valves are not capable of being constantly and very rapidly adjusted as a wheel of the vehicle coupled to a corresponding actuator moves so as to provide for optimum damping.
As such, a suspension control system is desirable that is not subject to the problems of orifice controlled valves, and which incorporates valves that are not susceptible to the adjustment limitations and instabilities of current control valves.
SUMMARY OF THE INVENTION
A suspension control unit as well as a novel fluid control unit incorporating at least a novel control valve are provided which are incorporated in a computerized suspension system which automatically and continuously monitors and control's a vehicle's ride performance to provide soft and stable ride characteristics at all times by controlling the damping provided by each of the vehicles actuators (i.e., shock absorbers). The suspension control unit comprises a fluid control unit and a vehicle actuator. The fluid control unit is coupled to an actuator of a vehicle. Specifically, each actuator of a vehicle has a fluid control unit coupled to it. In forming a suspension control unit, each fluid control unit may be maintained separate from its corresponding actuator or may be integrated with its corresponding actuator into a single package.
Each fluid control unit comprises a reservoir which receives fluid displaced by the movement of the rod (and piston) in and out of the actuator. A position sensor and preferably a Linear Variable Inductive Transformer (“LVIT”) position sensor is fitted within the reservoir to sense the volume of fluid within the reservoir. A microprocessor is coupled to the reservoir and receives signals from the position sensor for ascertaining the position of the actuator at any given time. An optional temperature sensor is also coupled to the reservoir for sensing the temperature of the fluid within the reservoir. The temperature sensor provides the microprocessor with the fluid temperature information so as to allow the microprocessor to ascertain the absolute position of the actuator by accounting for changes in the fluid volume due to temperature changes. Depending on the position of the actuator (and various other vehicle inputs), the microprocessor controls a pair of valves mounted on the reservoir for controlling the pressure of fluid entering or leaving the fluid control unit reservoir and thereby, controlling the pressure of the fluid entering or leaving the actuator and thus, controlling the damping provided by such actuator.
Each valve mounted on the reservoir comprises an annular body having a side passage and an end opening in communication with a passage on the reservoir, and a poppet slideably fitted within the body. The poppet can slide between a first seated position blocking the end opening of the valve body and a second retracted position not blocking the end opening. The poppet is moved into position blocking the end opening by a solenoid. A spring is used to slide the poppet back to a position not blocking the end opening when the solenoid is deactivated.
The poppet comprises a conical section and a cylindrical section extending from the larger diameter portion of the conical section. The conical section defines a tip portion of the poppet which is used to block the end opening of the valve body. The diameter of the largest diameter portion of the conical section is smaller than diameter of the cylindrical section. Consequently, an annular shoulder is formed extending radially around the poppet between the conical and cylindrical sections.
The conical tip section of the poppet is not exposed to the side passage when the poppet is in the seated position. As a result, the fluid pressure through the side passage is reacted against the poppet annular shoulder which is always exposed to the side passage whether the poppet is seated in the valve body or retracted from its seated position. Consequently, the fluid provides a force against the poppet annular shoulder tending to retract the poppet. A solenoid is incorporated that provides a variable force that tries to keep the valve seated in the closed position blocking the end opening of the valve body. As a result, the force set by the solenoid determines the pressure required to open the valve. Hence, the solenoid allows the valve to become an adjustable pressure regulator.
Since the area of the poppet annular shoulder exposed to the fluid pressure remains constant throughout the poppet stroke from a seated to a completely retracted position, the force generated by a given fluid pressure against the annular shoulder is constant tending to provide for a constant pressure regulation at different fluid flow rates. In other words, as the flow rate is increased, thereby increasing the fluid pressure, a larger force is reacted against the annular shoulder tending to retract the poppet further thereby canceling out the pressure created by the increased in fluid flow, thus, alleviating the instability problems associated with current valves incorporating poppets.
Moreover, applicant has discovered that a conical surface which is a section of a 70° cone, i.e., a conical surface whose surfaces are tapered at 55° relative to a plane perpendicular to the conical surfaces central axis, works optimally. This is because as the pressure on the poppet annular shoulder starts to open the valve, the fluid flow causes dynamic forces on the conical surface which would tend to close the valve (i.e., seat the poppet). However, as the poppet is retracted, the fluid pressure is reacted on a portion of the conical surface generating a retracting force as well as lateral force on the poppet. Applicant discovered that with the 55° angle, the retracting force on the conical surface tends to cancel the dynamic flow force. This results in a constant pressure drop over wide ranges of fluid flow (e.g. 0 to over 50 gallons per minute).
The movement of the poppet is stopped when a flange extending from the poppet engages an inner annular shoulder formed on the valve body. As a result, the valve body is not loaded by the tip of the poppet as with conventional poppet valves alleviating the need to use expensive hardened steel as is used in the valve body of a conventional poppet valve for enduring the pounding by the poppet tip.
A spring biased che
Christie Parker & Hale LLP
Kenmar Company Trust
Nguyen Xuan Lan
Oberleitner Robert J.
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