Hydraulic vehicle clutch system, drivetrain for a vehicle including same, and method

An apparatus for transferring torque from a vehicle drive train to a wheel of a vehicle, comprising:

• a clutch having a driven part and a driving part;
• a hydraulic system configured to actuate the clutch by placing the driven part into engagement with the driving part, the hydraulic system including operating structures that are configured to either act upon or be acted upon by a hydraulic fluid, the operating structures including:
• a piston configured to move the driven part into engagement with the driving part when an operating hydraulic fluid pressure is supplied to the piston,
• an on-demand variable displacement pump configured to supply the operating hydraulic fluid pressure to the first piston, the on-demand variable displacement pump being configured to be operable in a large displacement setting and a small displacement setting, and
• a purge valve connected in fluid communication with the pump and the piston;
• and the apparatus further comprising:
• a controller configured to control at least one of the on-demand variable displacement pump and the purge valve to manipulate the operating hydraulic pressure to the piston, the controller being configured to:
• 1) determine whether the operating hydraulic fluid pressure is greater or less than a maximum operating pressure of the pump when operating at the large displacement setting, 2) send a signal to operate the pump at the small displacement setting if the operating hydraulic fluid pressure is greater than the maximum operating pressure, and 3) send a signal to operate the pump at the large displacement setting if the operating pressure hydraulic fluid is less than the maximum operating pressure.