Hydraulic circuit with a return line metering valve and method of operation

A hydraulic system comprising:

• a source of hydraulic fluid under pressure;
• a tank for hydraulic fluid;
• a shared return line;
• a return line metering valve connecting the shared return line to the tank;
• a source sensor providing a signal indicating the pressure of hydraulic fluid from the source;
• a return line sensor providing a signal indicating a level pressure of hydraulic fluid in the shared return line;
• a plurality of hydraulic functions connected to the source and to the shared return line for operating mechanical members on a machine, wherein at least one of the plurality of hydraulic functions comprises:
• (a) an actuator having first and second ports,
• (b) a first control valve connecting the source to the first port of the actuator,
• (c) a second control valve connecting the first port of the actuator to the shared return line,
• (d) a third control valve connecting the source to the second port of the actuator,
• (e) a fourth control valve connecting the second port of the actuator to the shared return line,
• (f) a first sensor producing a signal indicating a level pressure of hydraulic fluid at the first port, and
• (g) a second sensor producing a signal indicating a level pressure of hydraulic fluid at the second port;
• and
• a controller having inputs connected to the source sensor, return line sensor, first sensor and the second sensor and having outputs connected to the first control valve, second control valve, third control valve, fourth control valve and return line metering valve, the controller responding to the signals from respective ones of the sensors by operating the return line metering valve to control an amount of pressure in the shared return line.

A method of operating a hydraulic system for a plurality of hydraulic functions on a machine, wherein one of the hydraulic functions includes an actuator with a first and second ports and includes a valve assembly which controls flow of hydraulic fluid under pressure from a source selectively to one of the first and second ports and the flow of fluid between the other one of the first and second ports and a shared return line for a plurality of functions, that method comprising:

• sensing pressure of the hydraulic fluid provided by the source;
• sensing pressure of the hydraulic fluid in the shared return line;
• sensing pressure of hydraulic fluid at the first port;
• sensing pressure of hydraulic fluid at the second port;
• determining a desired pressure for the shared return line in response to the steps of sensing pressure;
• and
• operating a return line metering valve connected between the shared return line and a tank for the hydraulic system to control pressure in the shared return line to the desired pressure.

A hydraulic system comprising:

• a supply line coupled to a source of hydraulic fluid under pressure;
• a tank for hydraulic fluid;
• a return line;
• a return line metering valve connecting the return line to the tank;
• a plurality of hydraulic functions each of which comprises an actuator and a first valve element coupling the actuator to the supply line and a second valve element coupling the actuator to the return line;
• a sensor mechanism which senses pressure across one of the first valve element and the second valve element in one of the plurality of hydraulic functions;
• and
• a controller having an input connected to the sensor mechanism and having outputs connected to the first valve element and second valve element of each of the plurality of hydraulic functions and to the return line metering valve, the controller responding to a signal from the sensor mechanism by operating the return line metering valve to control pressure in the shared return line.