Vehicle drive unit utilizing hydraulic pump and motor

Claim 2

An hydraulic drive system to power a drive shaft of a vehicle to be driven over a wide range of speeds, comprising an engine controlled to operate at a substantially constant speed during vehicle operation, engine speed control means for varying that speed of operation of said engine dependent upon a desired sub-range of operation within said wide range, an hydraulic pump powered by the engine and providing a maximum fluid output flow depending upon said engine speed and including pump flow control means for varying the flow of fluid output from the pump, an hydraulic motor receiving fluid output from the pump and driven thereby, and means coupling the hydraulic motor to the drive shaft of the vehicle to power that drive shaft which is driven over said sub-range of operation corresponding to the speed at which said engine operates.

Claim 3

An hydraulic drive system according to claim 1, including a bypass fluid circuit coupled to said motor to permit circulation of fluid between said motor and bypass circuit without passing through said pump, check valve means in said bypass fluid circuit permitting fluid to pass therethrough in one direction only, and flow/no-flow valve means in said bypass circuit to control the flow of fluid therethrough and selectively positioned according to the direction of vehicle movement.

Claim 4

An hydraulic drive system to power a drive shaft of a vehicle comprising an engine controlled to operate at a substantially constant speed during vehicle operation, engine speed control means for varying that speed of operation of said engine, an hydraulic pump powered by the engine and including pump flow control means for varying the flow of fluid output from the pump, an hydraulic motor receiving fluid output from the pump and driven thereby, and means coupling the hydraulic motor to the drive shaft of the vehicle to power that drive shaft, in which said pump flow control means varies the volume and direction of fluid flow from said pump, and including forward/reverse and speed control means coupled to said pump flow control means for determining the direction and amount of output fluid flow from said hydraulic pump, said pump and motor including first and second fluid conduits therebetween, a bypass fluid circuit interconnecting said first and second fluid conduits, a check valve in said bypass fluid circuit passing fluid only from (a) that one of said first and second fluid conduits that returns fluid from the motor to the pump in the forward movement of the vehicle to (b) the other one of said first and second fluid conduits, flow/no-flow valve means in said bypass circuit under the control of the operator of the vehicle to control fluid flow in said bypass circuit, said flow/no-flow valve means being positioned in the no-flow position when it is desired to move the vehicle in the reverse direction.

Claim 5

An hydraulic drive system to power a drive shaft of a vehicle comprising an engine controlled to operate at a substantially constant speed during vehicle operation, engine speed control means for varying that speed of operation of said engine, an hydraulic pump powered by the engine and including pump flow control means for varying the flow of fluid output from the pump, an hydraulic motor receiving fluid output from the pump and driven thereby, and means coupling the hydraulic motor to the drive shaft of the vehicle to power that drive shaft, in which said pump flow control means varies the volume and direction of fluid flow from said pump, and including forward/reverse and speed control means coupled to said pump flow control means for determining the direction and amount of output fluid flow from said hydraulic pump, said pump and motor including first and second fluid conduits therebetween, a bypass fluid circuit interconnecting said first and second fluid conduits, a check valve in said bypass fluid circuit passing fluid only from (a) that one of said first and second fluid conduits that returns fluid from the motor to the pump in the forward movement of the vehicle to (b) the other one of said first and second fluid conduits, flow/no-flow valve means in said bypass circuit under the control of the operator of the vehicle to control fluid flow in said bypass circuit, said flow/no-flow valve means being positioned in the no-flow position when it is desired to move the vehicle in the reverse direction.