192 clutches and power-stop control – Elements – Thrust members – retarders – and stops
Reexamination Certificate
1999-11-08
2001-01-30
Michalsky, Gerald A. (Department: 3753)
192 clutches and power-stop control
Elements
Thrust members, retarders, and stops
C091S433000, C137S596160, C137S625640
Reexamination Certificate
active
06179107
ABSTRACT:
TECHNICAL FIELD
This invention relates to controls for selectively engageable, fluid operated friction torque transmitting assemblies and more particularly to such controls for establishing the pressure rise during engagement of the torque transmitting assembly.
BACKGROUND OF THE INVENTION
Automatic shifting transmissions use fluid operated friction torque transmitting assemblies, such as clutches and brakes, to control the speed ratio between the transmission input shaft and the transmission output shaft. The speed ratio is changed by interchanging at least one of the torque transmitting assemblies for another of the torque transmitting assemblies. It is common practice to control the pressure rise in the oncoming torque transmitting assembly with a trim valve.
The trim is generally a downstream regulator valve having a variable bias pressure imposed thereon. The bias pressure is, with the advent of electronic controls, established by a variable bleed solenoid valve. The solenoid valve has an output pressure that varies in accordance with a control voltage. An electronic device, such as a preprogrammed digital computer, establishes the desired voltage input to the solenoid valve. The output from the solenoid is a variable hydraulic bias pressure that is proportional to the voltage. The output pressure of the trim valve is proportional to the variable hydraulic pressure. The feed pressure to the trim valve is generally main control pressure which is much greater than the maximum variable hydraulic bias pressure.
The hydraulic bias pressure at the trim valve has a range of zero to approximately 70 psi. The trim valve output pressure is required to have a range of approximately zero to approximately 250 psi depending on the torque capacity required by the oncoming torque transmitting assembly. The trim valve therefore has an overall gain of approximately 3.5 which is determined by dividing the maximum output pressure by the maximum bias pressure. As can be appreciated from the above gain value, every 1.0 psi change of the bias pressure results in approximately a 3.5 psi change in the output pressure.
Since the presently available trim valves use a linear gain valve, it is extremely difficult to provide a smooth ratio interchange when it is necessary to control the oncoming torque transmitting assembly to be fully engaged at a trim valve output pressure of 50 psi or less. This means that the bias pressure is approximately 14.3 psi which is established in the lower 21 percent (%) of the output range of the solenoid valve. Accurate pressure control under these conditions requires either a very close tolerance on the valve members or extremely accurate electronic control and feedback or both resulting in higher manufacturing and inspection costs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved trim valve mechanism for controlling the pressure rise in an oncoming fluid operated friction torque transmitting mechanism (clutch or brake).
In one aspect of the present invention, a trim valve for controlling the engagement pressure of a fluid operated friction torque transmitting mechanism incorporates a spool valve member and a sleeve valve member, which are biased by spring members, and a variable control pressure source, having a range of output pressure, to provide a low gain during a first portion of the range of the pressure source and a high gain during a second portion of the range of the pressure source.
In another aspect of the present invention, one of the bias springs is a variable rate spring providing a low gain when the variable pressure is low and high gain when the variable pressure is high. In yet another aspect of the present invention, the gain is continuously variable for the entire useful range of the control pressure.
In still another aspect of the present invention, the sleeve valve has two bias springs imposing a force thereon during a portion of the stroke of the sleeve valve. In a further aspect of the present invention, a stroke limiting surface is employed to limit the stroke of the sleeve valve such that the engagement pressure is set at a maximum system value after the stroke is limited.
In one embodiment of the present invention, a trim valve has a sleeve valve slidably disposed in a valve body and a spool valve slidably disposed in the sleeve valve. The sleeve valve has an inlet port, communicating with an inlet annulus in the valve body, an outlet port, communicating with an outlet annulus in the valve body and an exhaust port, communicating with an exhaust annulus in the valve body. The valve spool has a pair of spaced lands forming spaced control surfaces that permit controlled fluid flow from the inlet port to the outlet port when a pressure increase at the outlet port is requested, and permit controlled fluid flow from the outlet port to the exhaust port when a pressure decrease is requested.
The outlet annulus of the valve body is communicated with a selectively engageable, fluid operated, multi-plate friction torque transmitting mechanism. The trim valve is controlled to establish the proper pressure at the friction torque transmitting mechanism during the engagement thereof.
The pressure request is issued by a solenoid valve in the form of a control pressure acting on one end of the spool valve. The control pressure is counteracted by a spring force at the other end of the spool valve. The sleeve valve has one end thereof subjected to the pressure at the outlet port and the other end subjected to a bias force generated by a variable rate spring. Thus as the spool valve admits increased pressure to the outlet port, the sleeve valve reacts to the pressure change at the outlet port by closing the communication at a varying rate depending on the spring rate in the bias force generated by the variable rate spring.
The sleeve valve continually moves to new linear positions in the valve body as the outlet pressure is changing. When the outlet pressure is increases to a predetermined value, the sleeve valve abuts a stop which prevents further linear travel and the outlet pressure is raised to a maximum value unrestricted by the sleeve valve.
In another embodiment of the present invention, the sleeve valve has an inner bias spring that imposed a force thereon during the entire linear movement and an outer bias spring that is engaged by the sleeve valve after a predetermined linear movement less than the entire available linear movement. When the sleeve valve is biased by the inner spring only, a first gain rate between the inlet pressure and the outlet pressure is present; and when the sleeve valve is biased by both the inner and outer springs, a second gain rate between the inlet and outlet pressures is present. As with the first embodiment, a stop surface can be incorporated to limit the linear movement of the sleeve valve thereby permitting the outlet pressure to rise to the maximum value set by the inlet pressure.
Both of the embodiments will provide a lower gain for the outlet pressure of the trim valve. This permits more accurate and consistent pressure control during operation of the torque transmitting device when low engagement pressures are required. The trim valves will, however, produce full engagement pressure at the torque transmitting device, thus retaining the overall gain available with the trim valves currently in use.
REFERENCES:
patent: 5908098 (1999-06-01), Gorman et al.
General Motors Corporation
Hargitt Laura C.
Michalsky Gerald A.
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