Apparatus and method for ganging multiple open circuit pumps

A ganged pumping apparatus, comprising:

• a variable displacement open circuit first pump for drawing fluid from a reservoir and displacing a pressurized output flow of the fluid through a first output line to a load;
• a first displacement varying mechanism in the first pump;
• an over-center servo actuator operatively connected to the first displacement varying mechanism so as to control the displacement of the first pump between a maximum output flow and a minimum output flow less than zero;
• a pressure compensating pilot valve connected to the load with a pilot signal line;
• a first displacement control valve fluidly connected to the output flow of the first pump and the pilot signal line connected to the load and the pressure compensated pilot valve so as to generate a first command signal to the over-center servo actuator and thereby to the first displacement varying mechanism in the first pump based upon a pilot signal from the load and the pressure compensating pilot valve;
• a variable displacement open circuit second pump for drawing fluid from the reservoir and displacing a pressurized output flow of the fluid through a second output line which is fluidly joined to the first output line in a common output line upstream of the load;
• a second displacement varying mechanism in the second pump;
• a servo actuator operatively connected to the mechanism in the second pump so as to control the displacement of the second pump between a maximum output flow and a minimum output flow;
• and
• a second displacement control valve fluidly connected to the output flow of the second pump and the pilot signal line connected to the load and the pressure compensating pilot valve to generate a second command signal which is phased offset from and substantially parallel to the first command signal.

A method of phasing a plurality of open circuit pumps, comprising:

• providing first and second variable displacement open circuit pumps each controlled by respective adjustable first and second load sensing displacement control valves to produce respective output flows;
• joining the respective output flows into a single flow upstream of a load;
• controlling the first and second load sensing displacement control valves based upon a pressure signal from a single pressure compensating pilot valve connected to the load;
• limiting the fluid displacement of the second pump to a non-negative value while allowing the displacement of the first pump to reach a negative value;
• limiting the fluid displacement of the second pump to a non-negative value while allowing the displacement of the first pump to reach a negative value;
• setting the adjustable second load sensing displacement control valve in the second pump to a different pressure setting than the adjustable first load sensing displacement control valve such that the second pump is phased with the first pump and thereby is held at the zero displacement condition while the first pump passes the zero displacement condition and assumes a negative displacement condition.

A ganged pumping apparatus, comprising:

• a variable displacement open circuit first pump for drawing fluid from a reservoir and having an output line connected to a load for displacing pressurized fluid toward the load;
• a first displacement varying mechanism in the first pump;
• an over-center servo actuator operatively connected to the first displacement varying mechanism so as to control the displacement of the first pump between a maximum output flow and a minimum output flow;
• a pressure compensating pilot valve connected to the load with a pilot signal line;
• a first displacement control valve fluidly connected to the output flow of the first pump and the pilot signal line connected to the load and to the pilot valve, to generate a pilot signal from the load and the pressure compensating pilot valve;
• to provide a first command signal to the over-center servo actuator and thereby to the first displacement control varying mechanism in the first pump;
• a variable displacement open circuit second pump for drawing fluid from the reservoir and for displacing a pressurized output flow of the fluid through a second output line which is fluidly joined to the first output line in a common output line upstream of the load;
• a second displacement varying mechanism in the second pump;
• a servo actuator operatively connected to the second displacement varying mechanism in the second pump to control the fluid displacement of the second pump between a maximum output flow and a minimum output flow;
• and
• a second displacement control valve fluidly connected to the output flow of the second pump and the pilot signal line connected to the load and the pressure compensating pilot valve to generate a second command signal which is out of phase with said first command signal.