A power transmission system includes a first transmission provided in a first power transmission path, a second transmission provided in a second power transmission path, a first engagement device, a second engagement device, a third engagement device, a fail-safe valve, and an electronic control unit. The third engagement device selectively connects or interrupts one of the first and second power transmission paths. The electronic control unit is configured to, during traveling in a state where the third engagement device is released, output hydraulic pressure commands for simultaneous engagement of the first engagement device and the second engagement device. The electronic control unit is configured to, 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 and second power transmission paths which is selectively connected or interrupted by the third engagement device.

Ground wires are shared between a drive-side pulley solenoid valve and a driven-side pulley solenoid valve. Therefore, when a disconnection or short circuit occurs in the shared portion, a drive-side pulley and a driven-side pulley show substantially the same behavior. As a result, changes in the speed ratio cvt of a continuously variable transmission are suppressed and changes in vehicle behavior are also suppressed. Therefore, it is possible to suppress the degradation of drivability during the failure of the solenoid valves involved in power transmission.

A hydraulic control circuit includes: a shift valve configured to be switched between a state of supplying oil pressure to a clearance adjusting chamber of an LR brake and a state of discharging the oil pressure from the clearance adjusting chamber of the LR brake; and a linear SV configured to control the oil pressure supplied to a pressing chamber of the LR brake. The hydraulic control circuit further includes a source pressure oil passage through which oil pressure equal to the oil pressure supplied from the shift valve to the clearance adjusting chamber is supplied to a source pressure port a of the linear SV. By discharging the oil pressure in the clearance adjusting chamber at the time of opening malfunction of the linear SV, the oil pressure in the pressing chamber is also discharged through a drain port of the shift valve.

A hydraulic control device has: a modulator valve using oil pressure from a hydraulic source for adjusting a modulator pressure; driving and driven-side hydraulic actuator control valves controlling hydraulic oil from the source to driving and driven-side hydraulic actuators; a driving-side control oil pressure adjusting electromagnetic valve using the modulator pressure for outputting a control oil pressure controlling the driving-side control valve; and a driven-side control oil pressure adjusting electromagnetic valve for outputting a control oil pressure controlling the driven-side control valve, the hydraulic control device including a failsafe valve switched from a normal to a failure position based on a failure disabling electric control for the driving-side and driven-side electromagnetic valves, the modulator valve making the modulator pressure lower than a value at the normal position based on an output switching pressure generated due to switching the failsafe valve from the normal to the failure position.

A hydraulic control device that includes a second switching valve that is switchable between a third position in which the forward range pressure input from the first switching valve is output to the shift controller and the reverse range pressure is blocked when the second signal pressure is off and a fourth position in which the reverse range pressure input from the first switching valve is output to the shift controller and the forward range pressure is blocked when the second signal pressure is on.

A hydraulic control system of an automatic transmission may be applied to an automatic transmission in which a reverse speed stage is engaged by engagement of first and second friction elements. The hydraulic control system may include: a first solenoid valve being a normally open type and controlling a line pressure to generate a first hydraulic pressure; a second solenoid valve being a normally closed type and controlling the line pressure to generate a second hydraulic pressure; first and second switch valves, the first switch valve selectively supplying the first hydraulic pressure to the second switch valve; and a fail-safe valve selectively supplying the first hydraulic pressure or the second hydraulic pressure to the second friction element, wherein the second switch valve selectively supplies the first hydraulic pressure supplied from the first switch valve or a reverse speed pressure to the first friction element.

A hydraulic control system of an automatic transmission may be applied to an automatic transmission in which a reverse speed stage is engaged by engagement of first and second friction elements. The hydraulic control system may include: a first solenoid valve being a normally open type and controlling a line pressure to generate a first hydraulic pressure; a second solenoid valve being a normally closed type and controlling the line pressure to generate a second hydraulic pressure; first and second switch valves, the first switch valve selectively supplying the first hydraulic pressure to the second switch valve; and a fail-safe valve selectively supplying the first hydraulic pressure or the second hydraulic pressure to the second friction element, wherein the second switch valve selectively supplies the first hydraulic pressure supplied from the first switch valve or a reverse speed pressure to the first friction element.

A hydraulic control device for an automatic transmission where the spool is locked at the first position and the switching pressure can regulate the belt holding force of the primary pulley or the secondary pulley without switching a position of the spool when the engagement pressure is supplied to the second working oil chamber, and the spool is not locked at the first position and the switching pressure can switch the spool to the second position against the urging member when the engagement pressure is not supplied to the second working oil chamber.

A hydraulic control device has: a modulator valve using oil pressure from a hydraulic source for adjusting a modulator pressure; driving and driven-side hydraulic actuator control valves controlling hydraulic oil from the source to driving and driven-side hydraulic actuators; a driving-side control oil pressure adjusting electromagnetic valve using the modulator pressure for outputting a control oil pressure controlling the driving-side control valve; and a driven-side control oil pressure adjusting electromagnetic valve for outputting a control oil pressure controlling the driven-side control valve, the hydraulic control device including a failsafe valve switched from a normal to a failure position based on a failure disabling electric control for the driving-side and driven-side electromagnetic valves, the modulator valve making the modulator pressure lower than a value at the normal position based on an output switching pressure generated due to switching the failsafe valve from the normal to the failure position.

Provided are a hydraulic control valve, a hydraulic control system, and a transmission. The hydraulic control valve includes a valve body, a slidable valve cartridge, and a pressing mechanism. A valve hole, a first oil supply port, a second oil supply port, and an oil discharge port are formed at the valve body, and each of the first oil supply port, the second oil supply port, and the oil discharge port is in communication with the valve hole. Both the slidable valve cartridge and the pressing mechanism are accommodated within the valve hole. The slidable valve cartridge has a small end close to an end of the valve hole and a large end abutting against the pressing mechanism. The pressing mechanism is disposed at another end of the valve hole.