Caterpillar Tractor Co.

Caterpillar Inc.

Donald L Bianchetta

Sammy J Rhodes

Kenneth R Lohbauer

Lawrence F Schexnayder

John V Mount

Jesse L Field, Jr

Gene R St Germain

Allan L Freedy

Edward A Wirtz

Robert W White

Bernard J Wulff

Gregory W Heinz

A pilot control system for maintaining a constant operating hydraulic fluid pressure in a hydraulic system throughout a range of hydraulic fluid flow and temperature conditions. The pilot control system has a pilot pump and a pilot relief valve in fluid communication with the pilot pump. A first pressure reducing valve is in fluid communication with the pilot pump and the pilot relief valve so as to reduce the pressure to components downstream of the pressure reducing valve.

Pilot control system

Oil coolers are commonly used in hydraulic systems for maintaining oil below a preselected temperature under normal operating conditions. The subject oil cooler circuit includes a pilot operated valve disposed in a conduit connecting the hydraulic system to the cooler and an electromagnetic pilot valve connected to one end of the pilot operated valve. The pilot valve is spring biased to its closed position when the temperature of the oil is above a predetermined temperature and is moved to an open position when the oil temperature is at or below the predetermined temperature. The end is vented to a tank at the open position of the pilot valve so that the pilot operated valve is maintained at the closed position to prevent cold viscous oil from being transmitted to the oil cooler when the oil temperature is below the predetermined temperature.

Oil processor circuit

A hydraulic control system is designed to permit the use of a plurality of small substantially identical existing valve assemblies in place of a lesser number of larger valve assemblies. In one embodiment, a first pair of variable displacement load sensing hydraulic pumps communicate with a manifold connected to a first valve assembly and another pair of variable displacement load sensing hydraulic pump communicate with a second manifold connected to second and third valve assemblies. A crossover conduit interconnects the manifolds so that fluid from all four pumps can be used by any one of the valve assemblies or shared by two or all three of the valve assemblies. In another embodiment, a third pair of variable displacement load sensing hydraulic pumps communicate with the first manifold 12 which also has another valve assembly connected thereto. Also in this embodiment, two crossover conduits interconnect the manifolds so that the fluid from all six pumps can be used by any one of the valve assemblies or shared by two or more of the valve assemblies.

Hydraulic system using multiple substantially identical valve assemblies

A hydraulic control system has first and second actuators that can be selectively moved to a second operating position dependant upon the pressure of hydraulic fluid being simultaneously transmitted thereto through a common conduit. The force of the springs of the first and second actuators is selected so that when the pressure of the hydraulic fluid is at a preselected low pressure, only one of the actuators is moved to its second position and both of the actuators is moved to their second positions when the fluid is at a preselected high pressure. The use of a common conduit for carrying fluid to the actuators eliminates the expense and complexity of providing another flow path between rotatable parts of a vehicle.

Hydraulic control system

Load sensing hydraulic systems are useful for distributing fluid from a variable displacement pump to the individual work circuits in accordance with the demand of each work circuit. Preventing load pressure from being drained from the motors of the work circuits during some operating functions heretofore required the use of a pair of pressure compensating valves and a pair of shuttle valves at each of the directional control valves. The subject load pressure duplicating circuit includes a single load pressure duplicating valve having an end subjected to the load pressure in a signal network and reduces pump pressure entering the valve to a pressure level at the output thereof equal to the load pressure. This duplicated pressure is then utilized as the control fluid for the pressure compensating valves and a displacement controller of the pump. The system is greatly simplified by the use of only a single duplicating valve for a hydraulic system having a plurality of work circuits.

Load pressure duplicating circuit

The use of a pair of small variable displacement hydraulic pumps in a hydraulic system offers some advantages. The output of the two pumps of the known systems is normally not combined, but is selectively combined under a majority of the operating conditions. The subject load sensing hydraulic control system has first and second hydraulic circuits with each circuit having a plurality of pilot operated control valves operatively connected to a variable displacement pump. The output flow of both pumps is normally made available to both hydraulic circuits through a combiner valve so that the output capability of both pumps can be used to satisfy the demand for fluid by a single control valve or by one or more of the control valves from each circuit. A valve arrangement connects the highest load pressure of the control system to both pumps when the output flow thereof is being combined. Under certain operating conditions of some of the control valves, the combiner valve and the valve arrangement are selectively moved to a position to isolate the first and second hydraulic circuits from each other and to direct the highest load pressure of each circuit only to the displacement controller of the pump connected to that circuit.

Load sensing hydraulic control system

Control for a fluid-driven fan

Fluid circuit with zero leak load check and by-pass valve

Fluid motor control system providing speed change by combination of

An improvement is disclosed in a hydraulic system (10) having a variable displacement pump (12) and being capable of delivering pressurized fluid from the pump (12) to selectively engage at least three work circuits (18) with a first (20) of the circuits (18) being normally operable up to a first pressure and a second (22) of the circuits (18) being normally operable up to a second and lower pressure. The improvement comprises circuitry (80, 92, 94, 98, 108, 120, 122, 124, 126) for selectively operating a third (24) of the circuits (18) at one of the first or second pressures or at an upstaged pressure which exceeds the first pressure and circuitry (128) for reducing the displacement of the pump (12) in response to the third circuit (24) being operated at the upstaged pressure. Such upstaged pressure is available in a controlled manner for working against particularly heavy loads. Thus, a third and higher operating level is added to a system which already operates at at least two pressure levels.

Controlled pressure upstaging and flow reduction

PCT No. PCT/US79/00859 Sec. 371 Date Oct. 15, 1979 Sec. 102(e) Date Oct. 15, 1979 PCT Filed Oct. 15, 1979 PCT Pub. No. WO81/01034 PCT Pub. Date Apr. 16, 1981 In prior art hydraulic systems, and in particular in hydraulic systems having a cylinder means for elevating and lowering a load, there exists the possibility that the hydraulic line from a control valve to the cylinder means could rupture, allowing the load to drop before the operator could react. The present invention solves this problem by providing a blocker valve (100) in the vent line (69) of a check valve (33,34) which check valve is interposed in the main line 27 between a cylinder means (12) and a control valve (21). The blocker valve (100) is responsive to the back pressure in the main line (27) from the check valve (33,34) to the control valve (27). Thus, when the pressure in said main line (27) drops below a predetermined level due, for example, to a break in said line (27) the blocker valve (100) automatically closes the vent line (69), preventing the check valve (33,34) from releasing hydraulic fluid, and thus preventing the load (14) from dropping. In an aspect of the invention, a resolver valve (104) actuates the blocker valve (100). The resolver valve (104) communicates with the main line (27) at two positions and selects the lowest pressure between said positions.

Hydraulic load lifting system with automatic blocking valve

A hydraulic control system having a pump and circuits connecting the pump to a pair of hydraulic motors through first and second circuits is provided with a priority valve system operative to provide a priority of fluid pressure to the first motor up to a predetermined minimum pressure and thereafter to maintain the pressure in the first circuit and simultaneously supply fluid to the second motor of the second circuit. The priority valve system is also responsive to a load on a second motor to split the flow of fluid between the two motors above the predetermined minimum pressure up to a second pressure after which the second predetermined pressure is maintained in the first circuit while fluid is being supplied to the second conduit.

Hydraulic rock breaker circuit for an excavator

A three-circuit fluid system has at least one work element served by a pressurized fluid source and a plurality of work elements connected in interruptible series in each of the second and third circuits. A control system is provided for selectively diverting excess fluid from the pressurized fluid source of the first circuit to the second and third circuits in one mode of the control system and diverting excess fluid from the pressurized fluid source of the first circuit to only preselected work elements of the second and third circuits in a preselected order in another mode of the control system.

Three-circuit fluid system having controlled fluid combining

A pressure control valve is connected to selectively supply a control pressure signal to shift a relief valve from a first low pressure mode to a second higher pressure mode and for simultaneously supplying the control pressure signal to an associated variable displacement pump for reducing the relatively high output of the pump to a relatively lower output.

Hydraulic system having selective simultaneous pressure and flow control

A fluid system has at least first and second circuits each having a plurality of work elements connected in interruptible series. Control elements are provided for selectively, automatically passing fluid from one circuit to preselected positions in the other circuit in response to operation of preselected work elements.

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Coal City, IL, United States of America

Donald L Bianchetta