Hydraulic control system for automatic transmission

A hydraulic control system for an automatic transmission having a transmission gear mechanism for transmitting the engine output power by way of a plurality of power transmission paths, and friction engagement elements which are operated by a line pressure to change the power transmission path through the transmission gear mechanism, thereby effecting gear-shifting, comprising a manual shift valve for changing the driving range, a plurality of shift valves each for effecting gear-shifting assigned thereto by controlling the feed of the line pressure to the friction engagement elements corresponding to the gear-shifting according to a throttle pressure and a governor pressure, the throttle pressure and the governor pressure respectively corresponding to the engine load and the output speed of the transmission gear mechanism, and a range control valve which is disposed in a hydraulic line lines for transmitting the governor pressure to one of the shift valves to control transmission of the governor pressure to said one of the shift valves according to the driving range determined by the manual shift valve, thereby changing the shift pattern according to the driving range,

• said range control valve including a spool having on one end thereof a first pressure receiving surface for receiving a biasing force for urging the spool in one direction and a second pressure receiving surface for receiving a range control pressure which is transmitted thereto from the manual shift valve through a hydraulic line to act thereon in the direction opposite to said one direction and is disposed in one of the hydraulic lines for selectively transmitting the governor pressure to a 1-2 shift valve;
• said spool having a groove means which permits transmission of the governor pressure to the shift valve when the range control pressure acts on the second pressure receiving surface and inhibits transmission of the governor pressure to the shift valve when the range control pressure acting on the second pressure receiving surface is cut off.

A hydraulic control system for an automatic transmission having a transmission gear mechanism for transmitting the engine output power by way of a plurality of power transmission paths, and friction engagement elements which are operated by a line pressure to change the power transmission path through the transmission gear mechanism, thereby effecting gear-shifting, comprising a manual shift valve for changing the driving range, a plurality of shift valves each for effecting gear-shifting assigned thereto by controlling the feed of the line pressure to the friction engagement elements corresponding to the gear-shifting according to a throttle pressure and a governor pressure, the throttle pressure and the governor pressure respectively corresponding to the engine load and the output speed of the transmission gear mechanism, and a range control valve which is disposed in a hydraulic line for transmitting the governor pressure to one of the shift valves to control transmission of the governor pressure to said one of the shift valves according to the driving range determined by the manual shift valve, thereby changing the shift pattern according to the driving range;

• said range control valve including a spool having on one end thereof a first pressure receiving surface for receiving a biasing force for urging the spool in one direction and a second pressure receiving surface for receiving a range control pressure which is transmitted thereto from the manual shift valve through a hydraulic line to act thereon in the direction opposite to said one direction, and is disposed in one of the hydraulic lines for selectively transmitting the governor pressure to a 2-3 shift valve;
• said spool having a groove means which inhibits transmission of the governor pressure to the shift valve when the range control pressure acts on the second pressure receiving surface and permits transmission of the governor pressure to the shift valve when the range control pressure acting on the second pressure receiving surface is cut off.

A hydraulic control system for an automatic transmission having a transmission gear mechanism for transmitting the engine output power by way of a plurality of power transmission paths, and friction engagement elements which are operated by a line pressure to change the power transmission path through the transmission gear mechanism, thereby effecting gear-shifting, comprising:

• a manual shift valve which generates a predetermined hydraulic pressure in response to change of the driving range, a plurality of shift valves each having a spool provided with a governor pressure receiving surface and a throttle pressure receiving surface, the throttle pressure and the governor pressure respectively corresponding to the engine load and the output speed of the transmission gear mechanism, and a range control valve which is provided in a hydraulic line for transmitting the governor pressure to one of the shift valves to control transmission of the corresponding pressure to said one of the shift valves according to the driving range determined by the manual shift valve, said range control valve having a spool provided with a governor pressure receiving surface and a surface for receiving hydraulic pressure from the manual shift valve, said spool of the range control valve being adapted to receive a predetermined biasing force provided by a spring mount, thereby changing the shift pattern according to the driving range.