Hydraulic fan drive system including variable displacement pump

A vehicle engine cooling and steering gear drive system comprising:

• (a) an engine driven variable displacement pump including a pumping element operable to deliver fluid at a rate generally proportional to engine speed for any given displacement, said pump having fluid inlet and outlet ports and including fluid pressure actuated means to vary the displacement of said pump, said pump comprising the sole source of pressurized fluid for said system and having a fluid delivery rate of at least Z at engine idle and maximum pump displacement;
• (b) a hydraulic fan motor having fluid inlet and outlet ports, said fluid inlet port being in series fluid communication with said pump outlet port, said fan motor having a fan speed at engine idle corresponding to a fluid flow rate of approximately Y, and a fan peak speed corresponding to a fluid flow rate of approximately X;
• (c) flow control valve means having its inlet in fluid communication with said outlet port of said fan motor, said flow control valve means having primary and secondary fluid outlets and being operable to communicate a fluid flow rate of approximately Z from said fluid inlet to said primary outlet over substantially the entire range of operating engine speeds and to communicate substantially all fluid flow in excess of Z from said inlet to said secondary outlet, Z being substantially less than X;
• (d) a steering gear mechanism having inlet and outlet ports, said inlet port being in fluid communication with said primary outlet of said flow control valve means, said outlet port of said steering gear mechanism and said secondary outlet of said flow control valve means being in fluid communication with said fluid inlet port of said pump;
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• (e) control valve means in fluid communication with said fluid outlet port of said pump and being operable to communicate a control fluid pressure to said pressure actuated means of said pump, said control valve means including valve means responsive to demand for cooling and being operable (1) at a first relatively lower temperature to communicate a control fluid pressure to maintain the fluid delivery rate of said pump at Y and (2) at a second relatively higher temperature to communicate a control fluid pressure to maintain the fluid delivery rate of said pump at X, over substantially the entire range of operating engine speeds.

A vehicle engine cooling and steering gear drive system comprising:

• (a) an engine driven variable displacement pump including a pumping element operable to deliver fluid at a rate generally proportional to engine speed for any given displacement, said pump having fluid inlet and outlet ports and including fluid pressure actuated means to vary the displacement of said pump, said pump comprising the sole source of pressurized fluid for said system and having a fluid delivery rate of at least Z at engine idle and maximum pump displacement;
• (b) a hydraulic fan motor having fluid inlet and outlet ports, said fluid inlet port being in series fluid communication with said pump outlet port, said fan motor having a fan speed at engine idle corresponding to a fluid flow rate of approximately Y, and a fan peak speed corresponding to a fluid flow rate of approximately X;
• (c) flow control valve means having its inlet in fluid communication with said outlet port of said fan motor, said flow control valve means having primary and secondary fluid outlets and being operable to communicate a fluid flow rate of approximately Z from said fluid inlet to said primary outlet over substantially the entire range of operating engine speeds and to communicate substantially all fluid flow in excess of Z from said inlet to said secondary outlet, Z being substantially less than X;
• (d) a steering gear mechanism having inlet and outlet ports, said inlet port being in fluid communication with said primary outlet of said flow control valve means, said outlet port of said steering gear mechanism and said secondary outlet of said flow control valve means being in fluid communication with said fluid inlet port of said pump;
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• (e) control valve means defining a valve bore in fluid communication with said fluid outlet port of said pump and main flow control orifice means, a movable valve member disposed in said valve bore, and being operable to control the control fluid pressure in said pressure actuated means, said valve member being positioned in accordance with a control pressure differential representative of the pressure differential across said main flow control orifice means, said control valve means including pilot valve means responsive to the demand for cooling and being operable to maintain said control pressure differential substantially constant, whereby (1) at a first relatively lower temperature, the fluid delivery rate of said pump is maintained at Y and (2) at a second relatively higher temperature, the fluid delivery rate of said pump is maintained at X, over substantially the entire range of operating engine speeds, said pilot valve means being operable, in response to a change between said first and second temperatures, to vary instantaneously said control pressure differential to cause a change in the fluid delivery rate of said pump between Y and X, respectively, thereby re-establishing said control pressure differential.