Dual pump dual pressure hydraulic circuit

A vehicle hydraulic system for a vehicle having an engine driving a transmission, the transmission having a hydrostatic unit with an actuator controlled by a high pressure circuit and having control clutches controlled by a low pressure circuit, the hydraulic system comprising:

• a high pressure positive displacement pump for supplying pressurized fluid to the high pressure circuit via a first supply line;
• and
• a low pressure positive displacement pump for supplying low pressure fluid to the low pressure circuit via a second supply line;
• a control valve controlling communication between the high pressure circuit and a reservoir;
• a pressure regulating relief valve having an inlet connected to the first supply line, an outlet connected to the second supply line and a pressure sensing port communicated with the first supply line, the relief valve opening when a demand of the higher pressure circuit is satisfied and supplying fluid from the first supply line to the second supply line at a pressure lower than the pressure produced by the higher pressure-pump;
• and
• a control unit for controlling the control valve as a function of operation of the high pressure circuit.

A vehicle hydraulic system comprising:

• a higher pressure pump for supplying pressurized fluid to a higher pressure circuit via a first supply line, the high pressure circuit forming a portion of a transmission;
• and
• a lower pressure pump for supplying pressure fluid to a lower pressure circuit via a second supply line;
• a control valve controlling communication between the high pressure circuit and a reservoir;
• a pressure regulating relief valve having an inlet connected to the first supply line, an outlet connected to the second supply line and a pressure sensing port communicated with the first supply line, the relief valve opening when a demand of the higher pressure circuit is satisfied and supplying fluid from the first supply line to the second supply line at a pressure lower than the pressure produced by the higher pressure pump;
• and
• a control unit for controlling the control valve as a function of operation of the high pressure circuit, the control unit controlling the control valve as a function of operation of the transmission.

A vehicle hydraulic system comprising:

• a higher pressure pump for supplying pressurized fluid to a higher pressure circuit via a first supply line, the high pressure circuit forming a portion of an infinitely variable transmission (IVT);
• and
• a lower pressure pump for supplying pressure fluid to a lower pressure circuit via a second supply line;
• a control valve controlling communication between the high pressure circuit and a reservoir;
• a pressure regulating relief valve having an inlet connected to the first supply line, an outlet connected to the second supply line and a pressure sensing port communicated with the first supply line, the relief valve opening when a demand of the higher pressure circuit is satisfied and supplying fluid from the first supply line to the second supply line at a pressure lower than the pressure produced by the higher pressure pump;
• and
• a control unit for controlling the control valve as a function of operation of the high pressure circuit, the control unit controlling the control valve as a function of operation of the IVT.