Power transmission system

A power transmission system configured to transmit power between an input rotating member to which power of a driving force source is transmitted and an output rotating member that outputs the power to a drive wheel of a vehicle, the power transmission system comprising:

• a first transmission provided in a first power transmission path between the input rotating member and the output rotating member;
• a second transmission provided in parallel with the first transmission and in a second power transmission path between the input rotating member and the output rotating member;
• a first engagement device configured to selectively connect or interrupt the first power transmission path that transmits power of the driving force source to the drive wheel via the first transmission;
• a second engagement device configured to selectively connect or interrupt the second power transmission path that transmits power of the driving force source to the drive wheel via the second transmission;
• a third engagement device configured to selectively connect or interrupt one of the first power transmission path and the second power transmission path;
• a fail-safe valve configured to interrupt one of a first oil passage that supplies hydraulic pressure to the first engagement device and a second oil passage that supplies hydraulic pressure to the second engagement device, such that simultaneous engagement of the first engagement device and the second engagement device is avoided;
• and
• an electronic control unit configured to, during traveling of the vehicle in a state where the third engagement device is released, (i) output hydraulic pressure commands for simultaneous engagement of the first engagement device and the second engagement device, (ii) determine whether both the first engagement device and the second engagement device are engaged at a time when the hydraulic pressure commands are being simultaneously output, and (iii) when it is determined that both the first engagement device and the second engagement device are engaged, prohibit traveling using the one of the first power transmission path and the second power transmission path which is selectively connected or interrupted by the third engagement device.