초록 ▼

A lock-up valve includes a spool movable between a clutch engagement position wherein the lock-up clutch is engaged and a clutch release position wherein the engagement of the lock-up clutch is released. A spring biases the spool toward the clutch release position. The spool has a first pressure act

A lock-up valve includes a spool movable between a clutch engagement position wherein the lock-up clutch is engaged and a clutch release position wherein the engagement of the lock-up clutch is released. A spring biases the spool toward the clutch release position. The spool has a first pressure acting area and a second pressure acting area. A fluid pressure is applied to the first pressure acting area during operation in one of the m th speed ratio and m+1 th speed ratio. An auxiliary valve is provided which allows the application of another fluid to the second pressure acting area during operation in the other speed ratio.

대표청구항 ▼

In a hydraulic control system for an automatic transmission for a vehicle having a torque converter with a lock-up clutch, the automatic transmission having a plurality of forward speed ratios including a m th speed ratio and a m+1 th speed ratio, where m is an integer, the hydraulic control system

In a hydraulic control system for an automatic transmission for a vehicle having a torque converter with a lock-up clutch, the automatic transmission having a plurality of forward speed ratios including a m th speed ratio and a m+1 th speed ratio, where m is an integer, the hydraulic control system having a first portion wherein a fluid pressure is present during operation in one of the m th speed ratio and the m+1 th speed ratio and absent during operation in the other speed ratio, and a second portion wherein a fluid pressure is present during operation in each of the m th speed ratio and the m+1 th speed ratio; a lock-up valve including a bore having a first signal pressure port and a second signal pressure port, and a spool movable within said bore between a clutch engagement position wherein the lock-up clutch is engaged and a clutch release position wherein the engagement of the lock-up clutch is released, and a spring biasing said spool toward the clutch release position, said first signal pressure port being connected to the first portion of the hydraulic control system; said spool of said lock-up valve having a first pressure acting area which communicates with said first signal pressure port so as to be exposed to the fluid pressure in the first portion of the hydraulic control system and being urged against said spring toward the clutch engagement position, said spool having a second pressure acting area which communicates with said second signal pressure port; and auxiliary means responsive to the fluid pressure at said first signal pressure port of said bore of said lock-up valve for normally connecting said second signal pressure port to the second portion of the hydraulic control system, but draining said second signal pressure port when the fluid pressure at said first signal pressure port of said bore of said lock-up valve is higher than a first predetermined value; said spring of said lock-up valve being set such that said spool of said lock-up valve assumes the clutch engagement position when the fluid pressure at said first signal pressure port of said lock-up valve is higher than a second predetermined value that is higher than said first predetermined value.