Hydraulic control unit for automatic transmission

A hydraulic control unit for and automatic transmission, comprising:

• a hydraulic servo for engaging and disengaging each friction engagement elements;
• hydraulic pressure supply means for supplying hydraulic pressure to the hydraulic servo of a predetermined friction engagement element selected according to a gearshift position to be achieved;
• failure detection means for detecting a failure has occurred in the hydraulic pressure supply means;
• and
• fail-safe means for preventing a neutral condition and prevents a gearshift from a high-speed gear position to a low-speed gear position when the failure detection means detects a failure, wherein the fail-safe means is provided with a first selector valve that, according to selection, supplies or exhausts a hydraulic pressure to or from a plurality of hydraulic servos and a second selector valve that, according to selection, takes a first selector position at which a gear ratio is made larger and a second selector position at which the gear ratio is made smaller, and the fail-safe pressure causes the first selector valve to switch such that a hydraulic pressure is supplied to the hydraulic servo of each of the two clutches and the second selector valve to switch to the second selector position when the fail-safe pressure is supplied.

A hydraulic control unit for an automatic transmission, comprising:

• a hydraulic servo for engaging and disengaging each friction engagement element of a plurality of friction engagement elements;
• hydraulic pressure supply means for supplying hydraulic pressure to a hydraulic servo of a predetermined friction engagement element selected according to a gearshift position to be achieved;
• failure detection means for detecting a failure in the hydraulic pressure supply means;
• and
• fail-safe means for preventing interlock from occurring due to a plurality of friction engagement elements engaging, prevents a neutral condition from being established, and also prevents a gearshift from a high-speed gear position to a low-speed gear position when the failure detection means detects a failure, wherein the fail-safe means is provided with a first selector valve that, according to selection, supplies or exhausts a hydraulic pressure to or from a plurality of hydraulic servos and a second selector valve that, according to selection, takes a first selector position at which a gear ratio is made larger and a second selector position at which the gear ratio is made smaller, and the fail-safe pressure causes the first selector valve to switch such that a hydraulic pressure is supplied to the hydraulic servo of each of the two clutches and the second selector valve to switch to the second selector position when the fail-safe pressure is supplied.