Creep torque and lock-up control for automatic transmission

A control device for an automatic transmission for a motor vehicle having an engine with a throttle, the automatic transmission including a hydrokinetic torque transmitting unit having an input element coupled with the engine and an output element, the hydrokinetic torque transmitting unit having a lock-up mechanism that is hydraulically operated and having a lock-up state where the input element is mechanically connected with the output element and a release state where the input element is fluidly connected with the output element, the automatic transmission also including a drive mechanism drivingly connected to the output element of the hydrokinetic torque transmitting unit, the drive mechanism including a hydraulically operated friction device that is engageable to establish a torque delivery path through the drive mechanism, said control device comprising:

• means for generating a servo actuating hydraulic fluid pressure for actuating the hydraulically operated friction device, said servo actuating hydraulic fluid pressure being supplied to the hydraulically operated friction device;
• means, including a lock-up control valve having a valve member movable between a lock-up position and a release position, for rendering the lock-up mechanism operable in the lock-up state when said valve member assumes said lock-up position, and rendering the lock-up mechanism operable in the release state when said valve member assumes said released position;
• means for generating a constant hydraulic fluid pressure;
• means for defining a first fluid line connecting said constant hydraulic fluid pressure generating means to said servo actuating fluid pressure generating means;
• means for defining a second fluid line connecting said constant hydraulic fluid pressure generating means to said lock-up control valve;
• means, including a drain line, for connecting said drain line selectively to said first fluid line or said second fluid line, said connecting means being operative to connect said drain line to said first fluid line when a predetermined condition of the motor vehicle is satisfied, said connecting means being operative to connect said drain line to said second fluid line when said predetermined condition fails to be satisfied;
• means for regulating the discharge of hydraulic fluid from said drain line;
• and
• means for controlling said regulating means so that an adjustment hydraulic fluid pressure variable in a first pattern builds up in said first fluid line when said predetermined condition of the motor vehicle is satisfied and an adjustment hydraulic fluid pressure variable in a second pattern builds up in said second fluid line when said predetermined condition of the motor vehicle fails to be satisfied, said adjustment hydraulic fluid pressure variable in said first pattern being supplied to said servo actuating hydraulic fluid pressure generating means to modify said servo actuating hydraulic fluid pressure, said adjustment hydraulic fluid pressure variable in said second pattern being supplied to said lock-up control valve to bias said valve member.