Patent ID: 6293765
Filing Date: 2001-09-25
Classification: E02F,F04B,F04C,F15B

Abstract:
A tandem pump circuit comprising:a high flow load valve;at least one low flow load valve;a reservoir for holding hydraulic fluid;a first pump including an input shaft and a first fixed displacement pumping mechanism connected to the input shaft for drawing fluid from the reservoir and pumping the fluid toward the high flow load valve through an output line;a first pressure relief valve connected to the output line and having a predetermined pressure relief setting;a second pump driven by the input shaft and including a second fixed displacement pumping mechanism connected to the input shaft for drawing fluid from the reservoir and pumping the fluid toward the at least one low flow load valve through an output line;a second pressure relief valve connected to the output line of the second pump and having a predetermined pressure relief setting;a first pilot pressure line fluidly connected to the output line of the first pump upstream from the first relief valve;a second pilot pressure line fluidly connected to the output line of the second pump upstream of the second relief valve;the first and second pilot pressure lines being joined together to form a third pilot pressure line;the first pilot pressure line having an orifice therein, the second pilot pressure line having an orifice therein;a normally closed pressure sequence valve fluidly connected to the third pilot line and to the output line of the second pump upstream of both the second relief valve and the second pilot line, the sequence valve including a first position in which flow from output line of the second pump to the reservoir is blocked and a second position in which flow from the second pump is drained through the sequence valve to the reservoir;the third pilot line being connected to the sequence valve so as to urge the sequence valve to an open position when pressure in the third pilot line is greater than a predetermined value, the predetermined value being less than the predetermined pressure setting of the second relief valve;whereby the sequence valve reduces the pressure in the output line of the second pump when the pressure in the output line of the first pump increases, such that a predetermined maximum input torque for both the first pump and the second pump combined is not exceeded.