Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
1999-11-15
2001-04-17
Thorpe, Timothy S. (Department: 3746)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C060S413000, C060S444000, C417S212000, C417S213000
Reexamination Certificate
active
06216456
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to load sensing hydraulic systems and, more particularly, to a load sensing hydraulic system which utilizes an external network for transferring a load pressure signal to a variable displacement pump.
BACKGROUND ART
The demand for better controllability and efficiency in work machine operations have lead to an increasing use of load sensing hydraulic systems. Compared to conventional hydraulic systems, load sensing hydraulic systems containing variable displacement pumps are more efficient since both the pump flow and the pump pressure are continuously matched to the actual load. Load sensing valve system configurations can be derived from both conventional closed-center and open-center type valves and a wide variety of different system configurations are being used. Different valve configuration yield different operational characteristics. Regardless of the particular valve configuration being utilized, it is always difficult to produce a load signal which is indicative of the actual load and which can be communicated to the pump controller without utilizing special load sensing valve mechanisms. It is also difficult to duplicate a true high pressure load sensing signal for communication with the pump controller without having a high pressure source associated therewith.
It is therefore desirable to provide a load sensing signal to the pump controller of a variable displacement hydraulic pump without utilizing special porting or other special valve means to mechanically control such signal, and without utilizing structure such as pressure compensating valves within the main control valve network to accomplish this task. It is also desirable to provide a mechanism for reducing or scaling down a high pressure load signal to a desired lower pressure load signal which will be representative of the actual load being experienced by the hydraulic system.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
The present invention relates to a load sensing hydraulic control system for controlling the displacement of a variable displacement pump wherein the actual load or pressure exerted against an actuating cylinder used for controlling the movement of a work element or work attachment is sensed by a pressure transducer or other sensor means and a signal representative of the actual cylinder load is communicated to an electronic controller or other processing means. The electronic controller is operable to output a signal representative of the actual cylinder load to an electrohydraulic valve which acts as a signal duplicating valve for communicating a desired load signal to a variable displacement hydraulic pump so as to continuously adjust the displacement of the pump to control pump flow and pump pressure to match the actual cylinder load. In one aspect of the present invention, a charging valve is utilized to provide a minimum pump output flow rate and pressure to the pump and an accumulator is utilized to provide a source of pressurized fluid for generating an artificial load signal to the pump controller. In another aspect of the present invention, a pilot pump operating at a predetermined pressure is utilized to provide the desired artificial load signal to the pump controller.
The present load sensing system can be utilized with a wide variety of different types of main control valves such as a plurality of proportional valves, standard three position valves, split spool type valves, and other actuating valves coupled to appropriate actuators, motors or other devices for accomplishing a particular task where load sensing capability is desirable. The present system provides load sensing capability outside of the main control valve network, which design is less expensive, it includes fewer complex components, it saves wear and tear on the pump, and it provides a separate source for matching pump performance with the actual cylinder load.
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Blackwell Sanders Peper & Martin
Caterpillar Inc.
Solak Timothy P.
Thorpe Timothy S.
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