US 5,507,360 AGranted

Hydraulic system for dynamic braking and secondary steering system supply

AssigneeCaterpillar Inc.

InventorGerald P. Simmons

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Abstract

In certain machines, such as construction equipment, it is desirable to provide a supplemental fluid supply for hydraulic steering systems to maintain sufficient fluid flow should a failure occur in the primary fluid supply. It is also desirable to provide retarding or dynamic braking to help control speed of the machine when operating downhill with a heavy load. A ground driven pump is provided to supply fluid to a selector valve for selectively directing the output of the ground driven pump to a steering system or a dynamic braking system. The selector valve is responsive to pressure in the steering system to direct flow from the ground driven pump to the steering system when the pressure drops below a predetermined level. The operator may selectively direct flow from the ground driven pump to the dynamic braking system when dynamic braking is needed. A dynamic braking valve may be operator controlled to regulate the degree of dynamic braking required to maintain the desired machine speed under specific operating conditions. In this manner a supplemental supply is provided which may be selectively directed to the steering system or the dynamic braking system.

Claims7

Dependent claims

A hydraulic control system for a wheeled machine having an engine and a drive system for driving at least one wheel of the machine, the hydraulic system comprising:

a primary fluid work system including a primary pump driven by the engine and a motor communicating therewith, a control valve interposed the primary pump and the motor and a fluid reservoir from which the pump draws fluid,
a secondary fluid supply means including a ground driven pump connected to the machine drive system in a manner to cause the ground driven pump to be driven by rotation of the at least one wheel due to its contact with the ground while the machine is moving,
a dynamic braking system for retarding the speed of the machine during downhill operation,
a selector valve disposed in controlling relation to an output of the ground driven pump and having a first position for controllably directing the output of the ground driven pump back to an inlet thereof, a second position for directing the output of the ground driven pump to the primary fluid work system and a third position for directing the output of the ground driven pump to the dynamic braking system,
means in the dynamic braking system for controllably, variably restricting the flow of fluid from the ground driven pump to create sufficient pressure in the ground driven pump to retard movement of the machine.

2 more elements

Dependencies are inferred from the claim text.