Lock-up torque converter having clutch slip control device

Claim 1

A lock-up torque converter comprising: input and output elements rotatable relative to each other; clutch means disposed between said input and output elements and responsive to first fluid pressure for direct driving connection therebetween; valve means for controlling said first fluid pressure in response to second fluid pressure representative of relative rotation between said input and output elements and third and fourth fluid pressures representative of at least one kind of clutch slip control factors, in which said input element is a pump impeller secured to a converter cover adapted to be driven by a power source and said output element is a turbine runner cooperating with said pump impeller to form a toroidal fluid circuit and said second fluid pressure is representative of torque transmitted by said turbine runner; and a lock-up control chamber in which said first fluid pressure prevails, defined between said converter cover and said clutch means, a converter chamber defined between said clutch means and said turbine runner, first passage means for delivering said second fluid pressure to said valve means, variable opening restriction means variable in opening in response to torque transmitted by said turbine runner for draining fluid in said converter chamber into said first passage means increasingly as the torque transmitted by said turbine runner increases, said first passage means having a branch passage provided with a fixed opening restriction for draining fluid in said first passage means, second passage means for drawing thereinto said first fluid pressure from said lock-up control chamber, third passage means for delivering fluid pressure in said converter chamber to said valve means, second valve means responsive to said fourth fluid pressure for providing communication between said second passage means and said third passage means when said fourth fluid pressure is lower than a predetermined value, said first mentioned valve means having a drain port, and fourth passage means extending between said first mentioned valve means and said second valve means and communicable at the opposed ends thereof with said drain port of said first mentioned valve means and said second passage mean, respectively, said second valve means providing communication between said second passage means and said fourth passage means when said fourth fluid pressure is higher than said predetermined value, said first mentioned valve means selectively providing and obstructing communication between said fourth passage means and said drain port based upon said second, third and fourth fluid pressures.