| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic transmission allowing automatic shift to a predetermined shift stage during signal failure to a solenoid valve, reducing shifting shock due to an excessive increase in line pressure. SOLUTION: This hydraulic control device for the automatic transmission comprises a pressure regulating valve 2 for regulating oil pressure generated by an oil pressure source 1 to the line pressure as basic oil pressure to be supplied to hydraulic servos 10, 11 for frictional engagement elements C-1, C-3 and the solenoid valve 3 for applying signal pressure corresponding to a vehicle load to the pressure regulating valve. An oil passage LT for the signal pressure to be supplied to the pressure regulating valve is provided with pressure reducing means 9 for preventing an excessive increase in the signal pressure. Thus, the excessive increase in the signal pressure to be applied to the pressure regulating valve during signal fail to the solenoid valve is prevented and the excessive increase in the line pressure is prevented, thereby avoiding the sudden engagement of the frictional engagement elements due to the supply of high line pressure and reducing shifting shock during the signal failure. |
