Hydraulic control system for automatic transmission, incorporating fail safe and progressive creep control and hill hold control

For an automatic transmission for a vehicle comprising an engine, comprising a source of actuating hydraulic fluid pressure, a gear transmission mechanism which comprises a power output shaft and a plurality of hydraulic fluid pressure actuated friction engaging mechanisms and which is capable of providing any one of a plurality of speed stages according to patterns of engagement and release of said hydraulic fluid pressure actuated friction engaging mechanism, and a hydraulic speed stage switching system having a plurality of shift valves and switching over supply and non supply of actuating hydraulic fluid pressure to said friction engaging mechanisms;

• said friction engaging mechanisms including a shift brake and according to engagement of which said power output shaft of said gear transmission mechanism is prevented from turning in a direction to a hydraulic hill hold control system, comprising:
• (a) a first control means for opening a port passage when said vehicle is substantially stationary and said engine is substantially in idling operational condition;
• and
• (b) a second control means for setting up a first hydraulic fluid passage in said hydraulic speed stage switching system when said gear transmission mechanism is switched to a certain speed stage and supplying actuating hydraulic fluid pressure to said shift brake via said port passage of said first control means and said first hydraulic fluid passage set up in said hydraulic speed stage switching system so as to engage said shift brake when said first control means opens said port passage and said gear transmission mechanism is switched to said certain speed stage.