Pumps – Condition responsive control of drive transmission or pump...
Reexamination Certificate
1999-06-08
2001-01-30
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
C417S390000, C060S445000
Reexamination Certificate
active
06179570
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the control of the speed of a cooling fan and more particularly to a variable pump control to selectively control the speed of a hydraulic fan drive.
BACKGROUND ART
Hydraulic fan drive systems are well known in the art to drive cooling fans. In one such arrangement two different fluid motors are used in combination to provide the needed torque at higher speed. At lower speeds only one of the fluid motors is used. In other arrangements, activation of and the speed of the cooling fan is controlled in response to the temperature of the working fluid in the system. In many fan drive systems, a variable displacement pump is used to drive the fluid motor and the speed of the fluid motor is controlled by varying the displacement of the variable displacement pump. In these systems, the pump control signal is directed through a variable orifice and then subsequently through a fixed orifice to the tank or through a fixed orifice first and then through a variable orifice. The variable orifice may be controlled by a spool valve that is movable in response to a remote signal, either manual or electrical. The metering of the control signal to tank produces undesirable heat and also many times requires larger pumps since there is a constant amount of flow being passed to the tank. Additionally, using small orifices to reduce the flow loss results in an orifice that is sensitive to plugging from debris in the fluid. Likewise, when using this type of control, it may also be necessary to provide a closed logic for the fan speed. Typically, U.S. Pat. No. 5,876,185 issued Mar. 2, 1999 to Schimpf et al. teaches an arrangement that modulates the control pressure to the pump control for control of pump displacement in a given direction and bleeds off fluid flow only to change pump displacement in the opposite direction. A variable force is provided to the control spool in opposition to the spring control force in order to provide the modulated control pressure to the pump control. Additionally, the discharge pressure of the pump is applied against a differential area of the control spool in order to provide a force against the spring control force that is directly related to the discharge pressure. The control pressure to the pump control generally decreases as the discharge pressure increases but is not linear. This can cause pump control instability that requires spool dampening orifices to be added. Otherwise the control instability reduces the fan drive component life. Since the maximum pump pressure is controlled solely by the one spool and if dampening is added then the maximum pressure can overshoot again resulting in pump and motor component life reduction as well as possible life reduction in valves and components.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a pump control arrangement is provided for controlling the displacement of a variable displacement pump that receives fluid from a reservoir. The variable displacement pump has a pressure outlet port and a displacement changing actuator that is operative to change the displacement of the variable displacement pump between a minimum and a maximum position. The pump control arrangement is adapted for use in a fan drive system having a fluid motor that is fluidity connected to the variable displacement pump. The pump control arrangement includes a proportional solenoid valve arrangement connected to the pressure outlet port of the variable displacement pump and operative to control the flow of pressurized fluid to and from the displacement changing actuator. The proportional solenoid valve arrangement includes a spring biasing mechanism, a proportional valve, and a proportional solenoid, the proportional valve having first and second ends with the spring biasing mechanism disposed at the first end and a pressure chamber defined at the second end and being connected downstream of the proportional valve, the spring biasing mechanism being operative to bias the proportional valve to a position to pass flow from the variable displacement pump therethrough, and the proportional solenoid is disposed at the second end of the proportional valve and operative to provide a variable force in opposition to the spring bias acting at the first end.
REFERENCES:
patent: 4152896 (1979-05-01), Tohma et al.
patent: 4408453 (1983-10-01), Westveer
patent: 4420937 (1983-12-01), Naruse et al.
patent: 4487255 (1984-12-01), Bianchetta et al.
patent: 4738330 (1988-04-01), Suzuki et al.
patent: 5165377 (1992-11-01), Hosseini
patent: 5561978 (1996-10-01), Buschur
patent: 5800130 (1998-09-01), Blass et al.
patent: 5876184 (1999-03-01), Marcott
patent: 5876185 (1999-03-01), Schimpf et al.
patent: 5907952 (1999-06-01), Akasaka et al.
Burrows J. W.
Caterpillar Inc.
Gray Michael K.
Thorpe Timothy S.
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