Power plants – Pressure fluid source and motor – Having a signal – indicator or inspection means
Reexamination Certificate
2001-02-09
2003-04-01
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Having a signal, indicator or inspection means
C060S384000, C060S390000, C060S392000
Reexamination Certificate
active
06539710
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE DISCLOSURE
The present invention relates to hydrostatic vehicle power steering systems, and more particularly, to such systems for use on vehicles which typically travel at relatively higher speeds, including, but not limited to “on-highway” vehicles, such as automobiles and light trucks, as well as “high speed” tractors, i.e., those intended to travel at speeds in excess of about 30 mph. For simplicity, both types of vehicles will hereinafter be included within either of the terms “on-highway” and “high speed”.
More specifically, the present invention relates to hydrostatic vehicle power steering systems of the type including a full fluid-linked steering control unit (SCU) which controls the flow of fluid from a pressure source (such as a power steering pump) to a fluid pressure operated actuator associated with the steered wheels. Operation of the SCU occurs in response to a manual input by the vehicle operator. The system of the type to which the present invention relates further includes some form of compensation valving which can either add fluid to the actuator or subtract fluid from the actuator (i.e., to or from the conduit connected to the inlet of the actuator), in response to sensing an “error” between the steering input (steering wheel position) and the steering output (steered wheel position). A system of this type is illustrated and described in U.S. Pat. No. 6,076,349, assigned to the assignee of the present invention and incorporated herein by reference.
Implementation of a steering system of the type shown in the above-incorporated patent has involved placing a sensor somewhere on the fluid pressure actuator, to generate a steered wheel position, and placing a sensor near the steering column, to generate a signal representative of steering wheel position.
An important aspect of the SCU illustrated and described in the above-incorporated patent was to increase substantially the stiffness (spring rate) of the recentering springs, such that flow to the steering actuator may occur, in response to the initiation of steering wheel rotation, even in the absence of relative displacement of the spool valve and sleeve valve within the SCU. However, the positional relationship between the steering wheel and the fluid meter (which is determined by the stiffness of the recentering springs) is still a relatively softer connection than the positional relationship between the fluid meter of the SCU and the steered wheels, this latter positional relationship being related primarily to the compressability of the fluid and the compliance of the various system elements, including the hoses (conduits). This relatively stiff relationship between the fluid meter and the steered wheels is, however, subject to the phenomenon of leakage, which is one of the primary reasons for the system including the capability to add “compensation” fluid.
In connection with the development of the system of the above-incorporated patent, it has been determined that one or more problems occur whenever the system controller detects an error between steered wheel position and steering wheel position and begins to compensate by adding fluid between the SCU and the steering actuator. The compensation fluid added to the circuit causes a pressure rise in the steering circuit and this pressure rise impacts the fluid meter, the position of which is determined primarily by the position of the steering wheel and the relative deflection of, or displacement between the spool valve and sleeve valve of the SCU. There is a relatively softer connection (recentering springs) between the steering wheel and the fluid meter, as was described previously. One result of the pressure rise impacting the fluid meter is an undesirable increase or decrease in the resisting torque of the steering wheel, as felt by the vehicle operator.
Another problem which occurs with the system described above is the uncertainty of the relative deflection of the spool valve and sleeve valve of the SCU. This uncertainty is one of the defining limits to the controllability of the system. In other words, the difference, or error, between the steering wheel position and the steered wheel position can not be reduced below the total amount of uncertainty of the system, and the instantaneous spool-sleeve deflection may add substantially to that uncertainty.
In steering systems of the type to which the present invention relates, in which it is necessary to sense steering input motion, the performance of the steering system can be improved by increasing the resolution of the sensor which generates the command position signal. As used herein, the term “resolution” refers to the number of discrete points identifiable by the controller (vehicle microprocessor) per unit of travel.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved hydrostatic steering system adapted for an on-highway type of vehicle, or for a high-speed off-highway vehicle, which overcomes the above-described problems of the prior art system.
It is another object of the present invention to provide an improved hydrostatic steering system which accomplishes the above-stated object and which substantially improves the operator feel during a steering maneuver.
It is a further object of the present invention to provide an improved steering control unit in which a command position signal having a higher resolution can be generated easily, and without the need for substantial, expensive structure being added to the steering control unit.
The above and other objects of the invention are accomplished by the provision of an improved full fluid-linked steering system adapted to provide input movement to a pair of steered wheels of a vehicle, in response to a manual input to a steering member, the steering system comprising a source of pressurized fluid, a fluid controller, and a fluid pressure operated actuator adapted to be operably associated with a pair of steered wheels to provide the input movement thereto in response to the manual input to the steering member. The fluid controller includes a housing defining a fluid inlet port in fluid communication with the source of pressurized fluid, and a control port in fluid communication with the actuator, the fluid controller further including a fluid meter having a moveable member operable to measure fluid flow through the fluid meter. The fluid controller also includes a valve means operable to control fluid flow from the fluid inlet port to the fluid meter and to the control port in response to the manual input to the steering member. A spring biases the valve means toward a neutral position. A steered wheel position sensor is operable to transmit to a vehicle microprocessor a signal representative of instantaneous steered wheel position.
The improved steering system is characterized by an input position sensor operably associated with the fluid controller and sensing movement of the moveable member of the fluid meter, to transmit to the vehicle microprocessor a signal representative of instantaneous position of the fluid meter. The vehicle microprocessor includes a comparator for comparing the signal representative of the position of the fluid meter and the signal representative of steered wheel position and generating a command signal. The system further includes a correction valve having an inlet in communication with the source of pressurized fluid and an outlet in fluid communication with the actuator, the correction valve receiving the command signal and correcting the fluid flow to the actuator to tend to null the difference between the input position signal and the steered wheel position signal.
In accordance with another aspect of the invention, the fluid controller comprises a rotary fluid pressure device comprising a housing defining a fluid inlet port and a fluid outlet port, a fluid displacement me
Eaton Corporation
Kasper L. J.
Lopez F. Daniel
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