Hydraulic control system for automatic transmission having torque converter with lock-up mechanism

Claim 2

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.

Claim 3

A hydraulic control system as claimed in claim 1, wherein said auxiliary means comprises an auxiliary valve including a bore having a signal pressure port connected to said first signal pressure port of said bore of said lock-up control valve, an outlet port connected with said second signal pressure port of said bore of said lock-up control valve, and an inlet port connected to the second portion of the hydraulic control system, and a drain port; said auxiliary valve including a spool movable within said bore thereof between a first position wherein said outlet port thereof communicates with said drain port only and a second position wherein said outlet port communicates with said inlet port thereof only, and a spring biasing said spool thereof toward said second position thereof, said spool of said auxiliary valve having a pressure acting area communicating with said signal pressure port of said bore of said auxiliary valve so as to be exposed to the fluid pressure in the first portion of the hydraulic control system.

Claim 4

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, the hydraulic control system including means for generating a governor fluid pressure indicative of a vehicle speed of the vehicle: 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 second signal pressure port being connected to the second 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, and a second pressure acting area which communicates with said second signal pressure port; first means responsive to the governor fluid pressure for disconnecting said first signal pressure port from the first portion of the hydraulic control system and draining said first signal pressure port; and second means responsive to the fluid pressure at said first signal pressure port of said bore of said lock-up valve and the governor fluid pressure for disconnecting said second signal pressure port of said bore of said lock-up valve from the second portion of the hydraulic control system and draining said second signal pressure port; said second means including auxiliary means for draining said second signal pressure port when the fluid pressure at said first signal pressure port 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.

Claim 5

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, the hydraulic control system including means for generating a governor fluid pressure indicative of a vehicle speed of the vehicle: 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 second signal pressure port being connected to the second 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, and a second pressure acting area which communicates with said second signal pressure port; first means responsive to the governor fluid pressure for disconnecting said first signal pressure port from the first portion of the hydraulic control system and draining said first signal pressure port; and second means responsive to the fluid pressure at said first signal pressure port of said bore of said lock-up valve and the governor fluid pressure for disconnecting said second signal pressure port of said bore of said lock-up valve from the second portion of the hydraulic control system and draining said second signal pressure port; said second means including auxiliary means for draining said second signal pressure port when the fluid pressure at said first signal pressure port 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.

Claim 6

A hydraulic control system as claimed in claim 3, wherein said auxiliary means comprises an auxiliary valve including a bore having a signal pressure port, an outlet port connected with said second signal pressure port of said bore of said lock-up control valve, an inlet port, and a drain port; said auxiliary valve including a spool movable within said bore thereof between a first position wherein said outlet port thereof communicates with said drain port only and a second position wherein said outlet port communicates with said inlet port thereof only, and a spring biasing said spool thereof toward said second position thereof, said spool of said auxiliary valve having a pressure acting area communicating with said signal pressure port of said bore of said auxiliary valve; and said first means includes first speed cut valve means responsive to the governor fluid pressure for normally connecting said first signal pressure port of said bore of said lock-up control valve and said signal pressure port of said bore of said auxiliary valve to the first portion of the hydraulic control system, but draining said first signal pressure port of said bore of said lock-up control valve and said signal pressure port of said bore of said auxiliary valve when the governor pressure is lower than a first predetermined value; and said second means includes second speed cut valve means responsive to the governor pressure for normally connecting said inlet port of said auxiliary control valve to the second portion of the hydraulic control system, but draining said inlet port of said auxiliary valve when the governor pressure is lower than a second predetermined value that is lower than said first predetermined value.