Hydraulic system with proportional control

Claim 2

An hydraulic system of the type having first and second hydraulic load circuits, the second circuit having a greater hydraulic flow requirement than the first circuit, characterised by a positive displacement hydraulic pump (42) connected with the load circuits, a changeable speed electric motor (44) connected with the pump (42), said pump (42) being adapted to supply the flow required by the first load circuit when the motor (44) is operated in a low speed range and to supply the flow required by the second load circuit when the motor (44) is operated in a high speed range, a proportioning valve (86) for controlling flow from the pump (42) to the second load circuit, said valve having an inlet port (144) in fluid communication with the pump outlet, a return port (154) in fluid communication with the pump inlet and a load port (152) in fluid communication with the load device, said valve including means (206) for progressively opening the load port (152) while progressively closing the return port (154), and control means for energizing the motor (44) for operation in the low speed range during opening of the load port (152) and for energizing the motor (44) for operation in the high speed range when the load port (152) is fully open and the return port (154) is fully closed, whereby the pump (42) is operated in the low speed range during transition of the return port (154) from open to close to reduce the energy loss during the transition.

Claim 3

An hydraulic system according to Claim 1, characterised in that said control means includes: a first manually actuable device for causing the motor (44) to operate in the low speed range and for controlling fluid flow to the first load circuit, a second manually actuable device coupled with the movable means (206) of the proportioning valve (86) for movement thereof, and switching means (218) for energizing said motor (44) for operation in the higher speed range when the proportioning valve (86) is fully open.

Claim 4

An hydraulic system according to Claim 2, characterised in that said second manually actuable device ccacts with said switching means (218) for causing the motor (44) to be energized for operation in the high speed range when the proportioning valve (86) is fully open.

Claim 5

An hydraulic system according to Claim 1, 2 or 3, characterised in that said control means includes regulating means (66) for maintaining the speed of the electric motor (44) within first predetermined limits during operation in the high speed range and within second predetermined limits during operation in the low speed range.

Claim 6

An hydraulic system according to Claim 4, characterised in that said electric motor (44) is a series DC motor, said energizing means is a battery (64), and said regulating means (66) includes means for applying DC pulses of variable mark/space ratio to the motor (44) and means responsive to the motor current for adjusting the mark/space ratio to regulate the motor speed within said predetermined limits.

Claim 7

A work vehicle of the type having first and second hydraulic load circuits, said second load circuit having a greater hydraulic flow requirement than the first circuit, characterised by: a positive displacement hydraulic pump (42) for supplying pressurized fluid to the load circuits, a changeable speed electric motor (44) connected with the pump (42), said pump (42) being adapted to supply the flow required by the first load circuit when the motor (44) is operated in a low speed range and to supply the flow required by the second load circuit when the motor (44) is operated in a high speed range, a first manually actuable selector means for operatively coupling the first load circuit with said pump (42) and for causing said motor (44) to be operated in the low speed range, an open centre proportioning valve (86) for controlling flow from the pump (42) to the second load circuit, said valve (86) having a valve body (208) including an inlet port (144) in fluid communication with the pump outlet, a return port (154) in communication with the pump inlet and a load port (152) in communication with a load device (56), said valve (86) including a spool (206) movable between a closed position and an open position, said closed position having the load port (152) closed to the inlet port (144) and the return port (154) open to the inlet port (144), said open position having the load port (152) open to the inlet port (144) and the return port (154) closed to the inlet port (144), a second manually actuable selector means coupled with said spool (206) for moving it between the closed and open positions for progressively decreasing the flow to the return port (154) and increasing the flow to the load port (152), and motor speed control means including switching means (218) for operating the motor (44) in the high speed range when the switching means (218) is activated, said second selector means being coupled with the switching means (218) for activating the switching means (218) when the spool (206) reaches the open position, whereby the pump (42) is operated in the low speed range during transition of the return outlet (154) from open to closed and thereby reduces the energy loss during the transition.

Claim 8

A work vehicle of the type having first and second hydraulic load circuits, said second load circuit having a greater hydraulic flow requirement than the first circuit, characterised by: a positive displacement hydraulic pump (42) for supplying pressurized fluid to the load circuits, a changeable speed electric motor (44) connected with the pump (42), said pump (42) being adapted to supply the flow required by the first load circuit when the motor (44) is operated in a low speed range and to supply the flow required by the second load circuit when the motor (44) is operated in a high speed range, a first manually actuable selector means for operatively coupling the first load circuit with said pump (42) and for causing said motor (44) to be operated in the low speed range, an open centre proportioning valve (86) for controlling flow from the pump (42) to the second load circuit, said valve (86) having a valve body (208) including an inlet port (144) in fluid communication with the pump outlet, a return port (154) in communication with the pump inlet and a load port (152) in communication with a load device (56), said valve (86) including a spool (206) movable between a closed position and an open position, said closed position having the load port (152) closed to the inlet port (144) and the return port (154) open to the inlet port (144), said open position having the load port (152) open to the inlet port (144) and the return port (154) closed to the inlet port (144), a second manually actuable selector means coupled with said spool (206) for moving it between the closed and open positions for progressively decreasing the flow to the return port (154) and increasing the flow to the load port (152), and motor speed control means including switching means (218) for operating the motor (44) in the high speed range when the switching means (218) is activated, said second selector means being coupled with the switching means (218) for activating the switching means (218) when the spool (206) reaches the open position, whereby the pump (42) is operated in the low speed range during transition of the return outlet (154) from open to closed and thereby reduces the energy loss during the transition.

Claim 9

A work vehicle according to Claim 6, characterised in that said control means comprises: regulating means (66) for maintaining the speed of the electric motor within the first predetermined limits during operation in the high speed range and within second predetermined limits during operation in the low speed range.

Claim 10

A work vehicle according to Claim 7, characterised in that said electric motor (44) is a series DC motor, said energizing means is a battery (64), and said regulating means (66) includes means for applying D C pulses of variable mark/space ratio to the motor (44) and means responsive to the motor current for adjusting the mark/space ratio to regulate the motor speed within said predetermined limits.

Claim 11

A work vehicle according to Claim 6, 7 or 8, characterised in that said vehicle is a lift truck, said first load circuit is a power steering circuit (46) and the first manually actuable selector comprises a steering wheel (14), said second load circuit is a lift circuit (48) and said second manually actuable selector comprises a lift control lever (16).