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US 3,978,937 AGranted
Hydrostatic propulsion system
AssigneeClark Equipment Company
InventorsWillard L. Chichester, Donald A. Holtkamp
Life of this patent
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AssigneeClark Equipment Company
InventorsWillard L. Chichester, Donald A. Holtkamp
Estimating the term…
A closed recirculating hydrostatic transmission system suitable for driving a traction vehicle. The system includes a pair of hydrostatic engine driven variable displacement pumps either of different displacements or engine driven at different speed ratios and each pump being operative to drive hydrostatic motors at the various wheels and in separate closed loop drive circuits such that accurate flow division as between the circuits is effected for driving the vehicle in four-wheel drive or, at the operator's selection, for driving the motors in the one closed loop circuit at a higher speed in two-wheel drive by means of the pump of larger discharge volume. An operator's control operates both pumps together within the limits of the smaller discharge pump in four-wheel drive, and operates the larger discharge pump within the limits thereof while rendering ineffective the smaller discharge pump in two-wheel drive. Valve means enables smooth transition and shifting between two and four-wheel drive at any time. Flow divider-combiner means in each closed loop circuit adjusts fluid flow to each motor as a function of steering angle to assure positive traction at each driven wheel in either forward or reverse drive under all surface conditions, and to differentiate as required wheel speeds during vehicle steering operations. Braking may be effected by reversing pump flow at selected conditions of either decreasing, constant or increasing engine speed.
In a hydrostatic drive system for a vehicle having a prime mover, first and second traction means, and first and second hydraulic motor means for driving respective ones of said traction means, first and second variable displacement hydraulic pump means driven by the prime mover means for driving respective ones of the hydraulic motor means, said first pump means having a fluid discharge capability greater than the fluid discharge capability of said second pump means, and control means limiting the fluid discharge of said first pump means substantially to the fluid discharge of said second pump means under a first vehicle operating condition.
In a hydrostatic drive system for a vehicle having prime mover means, first and second traction means, and first and second hydraulic motor means for driving respective ones of said traction means, first and second variable displacement hydraulic pump means driven by the prime mover means for driving respective ones of the hydraulic motors, said first pump means having a fluid discharge capability greater than that of said second pump means, and control means operatively connected to said first and second pump means for operating said second pump means at substantially zero fluid discharge and permitting said first pump means to operate at said greater fluid discharge under a certain vehicle operating condition.
In a hydrostatic drive system for a vehicle having prime mover means, first and second traction means, first and second hydraulic motor means for driving respective ones of said traction means, first and second variable displacement hydraulic pump means driven by the prime mover means for driving respective ones of the hydraulic motors, said first pump means having a pumping capacity greater than that of said second pump means, a first control means connected to both said first and second pump means for maintaining substantially equal the discharge volumes thereof during operation within the pumping capacity of said second pump means, and a second control means enabling said first pump means to be operated at a capacity greater than the capacity of said second pump means.
A hydrostatic transmission system for a vehicle having first and second pairs of selectively drivable wheels comprising hydraulic fluid drive means, first and second pairs of selectively drivable hydraulic motor means for driving respective pairs of said wheels and adapted to be driven by said fluid drive means, said fluid drive means comprising first and second variable displacement hydraulic pump means for driving respective pairs of the motor means, said first pump means having a pumping capacity greater than said second pump means, control means operatively connected to said first and second pump means to effect a shift from four to two-wheel driving without interrupting the flow of traction fluid to said first motor means, said control means including transition control means operative to reconnect the circuit of the second pump means to by-pass the second motor means to facilitate smooth vehicle operation during the transition from four to two-wheel drive said control means being also operatively connected to said first and second pump means for equalizing the fluid discharge of each during four-wheel drive up to the discharge capacity of the second pump means and for operating said transition control means in shifting to two-wheel drive while releasing said first pump means to operate at its greater discharge capacity.
In a hydrostatic drive system for a vehicle having prime mover means, first and second traction means, and first and second hydraulic motor means for driving respective ones of said traction means, first and second variable displacement hydraulic pump means driven by the prime mover means for driving respective ones of the hydraulic motors, said first pump means having a maximum displacement greater than the maximum displacement of said second pump means, control means connected to both said first and second pump means for maintaining in a first control position substantially equal the displacements thereof during operation within the displacement limit of said second pump means, and said control means in a second control position enabling said first pump means to be operated at a displacement greater than the maximum displacement of said second pump means.
Dependencies are inferred from the claim text.