Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2000-07-14
2001-10-23
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C060S431000, C137S565160
Reexamination Certificate
active
06305419
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to regulating the pilot pressure that is provided as pilot pressure to a manually controlled pilot valve, which when opened in turn provides pilot pressure to operate main control valves to control flow of hydraulic fluid under pressure to various hydraulic components. Specifically the pilot valves control operation of ground drive hydraulic motors for an excavator, or another industrial vehicle, such as a skid steer loader. The manual control can be joysticks, thumb switches, pivoting operator levers or pedals.
Joysticks that control pilot valves are used for operating various hydraulic components at the present time, such as hydraulic motors that are used for ground drives and cylinders that are used for implement functions. Other controls also are used on vehicles for operating pilot valves that would in turn provide a pilot pressure to a pilot operated main valve, to control the vehicle including the speed and direction. In the case of skid steer loaders, a pump for the drive motors is controlled to limit its displacement under high load conditions by reducing the pressure available to stroke a drive motor servo piston or servo controlled pump, or a variable output main valve or control, such as a swash plate. The position of the servo piston or other controlled component in turn determines the flow rate of the pump, which in turn determines the speed of operation of the travel motor. The travel pump presently has a mechanical pressure reducing valve at its input to limit the pilot pressure supplied to the travel controllers when loads on the ground drive are high. The pilot pressure is controlled by a pump speed sensing hydraulic valve, that supplies a pilot pressure that is linearly proportional to the pump speed, which means that as the pump slows down from high loads, the pilot pressure for the travel motor pilot operated valves is reduced. In turn this limits the flow or output of the pilot valve control servo piston or pumps or the controlled valve, so less power is consumed for travel. This system has drawbacks at low speed throttle positions, because the pump speed sensor valve cannot distinguish between idle, when the pump is turned slowly by the drive engine, and high loads when the pump slows down from loading. Further, the prior art system cannot compensate well for changes in oil temperature, since oil viscosity is reduced as temperature increases and flow and pressure developed may be less at the same pump speed when the oil is hot.
In the case of pilot valve joystick controls, such as that on a mini-excavator, the pressure to pilot valves controlled by the joystick presently flows through an on/off solenoid valve, so that when the solenoid valve is on, full pilot pressure is provided to a pilot pressure operated main control valve or servo piston/pump, and when the solenoid valve is off, there is no pilot pressure and the pilot operated main controls are not moved, so travel is stopped.
It is desirable to limit the horsepower requirements of the hydraulic system so that the engine does not stall under any operating condition.
SUMMARY OF THE INVENTION
The present invention relates to reducing the pilot pressure provided to pilot valves controlled by a joystick or other travel controller on an industrial machine, through the use of a pulse width modulated (PWM) solenoid valve on the pilot pressure line. The output pulses to the PWM solenoid from a controller will determine the opening of the PWM solenoid valve. Pulse width modulated valves are known, and are used in various applications. The PWM valves will respond to open as a function of the pulse width of a train of pulses, and normally will open in proportion to the width (or duration) of the pulses. The electronic controller that provides output pulses in response to input signals can be primarily responsive to engine speed of the engine driving the hydraulic system pump. Other inputs can be used, such as oil temperature, and throttle position, and feedback signals such as measured pilot pressure and drive axle speed.
The electronic controllers are logic circuits or micro processors which will deliver an output pulse train in response to the values of input signals, as selected. For example, an increase in engine speed when used as an input would provide longer pulses (or greater pulse width), so that the pilot pressure being provided to the desired pilot valves will be close to the maximum pilot pressure. As engine speed drops, the pulse width of the output pulse train would be reduced, and the pilot pressure provided to the pilot valves would also be reduced. Likewise, for additional inputs, an increase in oil temperature would result in a greater opening of the PMW valve. The throttle position also would be sensed so that a more open throttle would provide for an increase in the pulse width, and a greater pilot pressure would be provided to the pilot valve and the controllers, such as a joystick.
Feedback signals that would indicate the actual pilot pressure could be provided so that when a desired pilot pressure is reached, the pulse width would be maintained as a maximum. Axle speed signals also could be provided as a feedback to close the control loop and maintain the pilot pressure when the axle speed was at a desired level or increase pilot pressure as the axle speed started to drop.
Piston motors can create demands for hydraulic flow and pressure that are high enough to stall the engine. Reducing the pilot pressure to travel pilot valves and controllers in response to signals that indicate engine loading increases horsepower available for operating components such as a loader or excavator boom, or a bucket. The power used for travel is reduced without stopping the travel entirely. This provides a more satisfactory operation than straight on/off pilot pressure control where all travel is stopped. It also is more sensitive to actual conditions when pilot pressure is adjusted in response to an input.
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Krieger Daniel J.
Wetzel Michael D.
Clark Equipment Company
Michalsky Gerald A.
Westman Champlin & Kelly P.A.
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