Hydraulic system for a vehicle, a vehicle transmission, and method for operating a vehicle transmission

A hydraulic system for a vehicle transmission, the transmission including two or more friction elements, the hydraulic system comprising:

• a first hydraulic circuit arranged for actuating the two or more friction elements;
• a first electric driven pump arranged for supplying hydraulic fluid to the first hydraulic circuit;
• and
• a flow restriction provided in the first hydraulic circuit between an output of the first electric driven pump and a reservoir to provide leakage of hydraulic fluid into the reservoir,
• wherein the first hydraulic circuit is arranged for generating a line pressure;
• wherein the transmission includes two or more hydraulic actuators, wherein one of the two or more hydraulic actuators is arranged for actuating a park lock system, wherein said one hydraulic actuator is hydraulically connected to the first hydraulic circuit for direct actuation of the hydraulic actuator using the line pressure,
• wherein the one hydraulic actuator is arranged for bringing or maintaining the park lock system in a park position when the line pressure is below a predetermined pressure threshold,
• wherein the first hydraulic circuit includes a valve arranged for draining the one hydraulic actuator when the line pressure is below the predetermined pressure threshold, said valve being positioned between the one hydraulic actuator and the first electric driven pump,
• the hydraulic system further comprising:
• a second hydraulic circuit arranged for lubricating and/or cooling the two or more friction elements via two cooling/lubricating lines;
• a second electric pump arranged for supplying hydraulic fluid to the second hydraulic circuit, wherein the first electric pump is arranged for delivering a higher pressure than the second electric pump;
• and
• a flow control element arranged for controlling flow and/or pressure in the second hydraulic circuit, wherein the flow control element is operated using hydraulic pressure from the first hydraulic circuit;
• wherein pressure in the first and second hydraulic circuit is controlled by the line pressure of the first hydraulic circuit;
• wherein the flow control element, for controlling flow and/or pressure in the second hydraulic circuit, comprises a pressure regulator and a directional valve, wherein the pressure regulator is configured for providing a pilot pressure for operating the directional valve;
• and
• wherein the directional uses the line pressure of the first hydraulic circuit and flow in the second hydraulic circuit is controlled by the second electric pump.