Control system for torque converter of automatic transmission

Claim 1

A control system for a torque converter of an automatic transmission comprising: lock-up clutch means provided in said torque converter for connecting input and output members of the torque converter directly, engaging and disengaging hydraulic means for controlling an engaging and disengaging action, respectively, of the lock-up clutch means, shift valve means provided with first and second spools in series for controlling an introduction of a driving hydraulic pressure for said engaging and disengaging hydraulic means, said first spool being subjected to a first hydraulic pressure at a first end thereof, said second spool being subjected to a second hydraulic pressure at a second end thereof opposite to said first end of the first spool, said first and second spools being subjected to a third hydraulic pressure therebetween, first control means for controlling said first hydraulic pressure, second control means for controlling said second hydraulic pressure, adjusting valve means for controlling said driving hydraulic pressure for said engaging or disengaging hydraulic means, third control means for adjusting a control pressure for controlling said adjusting valve means, said shift valve means taking, selectively, a first position wherein both the first and second spools are positioned at a first end portion of the shift valve means, a second position wherein the first and second spools are positioned at a second end portion of the shift valve means opposite to the first end portion, and a third position wherein the first spool is positioned close to the first end portion and away from the second spool and the second spool is positioned at the second end portion, said driving hydraulic pressure being introduced into said engaging hydraulic means to establish a lock-up condition of said torque converter when the shift valve means takes said first position, said driving hydraulic pressure being introduced into said disengaging hydraulic means to establish a converter condition of said torque converter when said shift valve means takes said second position, and said driving hydraulic pressure being introduced into both said engaging and disengaging hydraulic means to establish a slip condition of the torque converter when said shift valve means takes said third position.