Vehicle driving system

A vehicle driving system in which a clutch is disposed between an engine output member and an automatic transmission and the clutch is used as a start clutch that is slip-controlled when a vehicle starts, the vehicle driving system comprising:

• a regulator valve that has a pressure-regulating port and a feedback port communicating with a pressure-regulating oil passage from a source pressure and a back-pressure port communicating with a back-pressure oil passage and that adjusts a communication rate between the pressure-regulating port and the back-pressure port to regulate an oil pressure of the pressure-regulating oil passage;
• a lubricant relay valve that has an input port and an output port communicating with the pressure-regulating oil passage and that switches the input port and the output port to a communicating position or a cutoff position;
• and
• a clutch lubricant passage that communicates with the pressure-regulating oil passage via an orifice, that communicates with the output port, and that supplies lubricant to the clutch, wherein
• when the lubricant relay valve is switched to the communicating position, oil from the pressure-regulating oil passage is supplied to the clutch via the input port, the output port, and the clutch lubricant passage, a feedback pressure of the feedback port is decreased, the communication rate between the pressure-regulating port and the back-pressure port is decreased, and an amount of lubricant supplied from the back-pressure oil passage to a lubrication portion of the automatic transmission is decreased, and
• when the lubricant relay valve is switched to the cutoff position, the oil from the pressure-regulating oil passage is supplied to the clutch via the orifice and the clutch lubricant passage, the feedback pressure of the feedback port is increased, the communication rate between the pressure-regulating port and the back-pressure port is increased, and the amount of lubricant supplied from the back-pressure oil passage to the lubrication portion of the automatic transmission is increased.