Method of controlling the partial lock-up of a torque converter in an electronic automatic transmission system

Claim 1

In a vehicle having an engine and a throttle means and a transmission system including an input member, an output member, a torque converter assembly for transmitting torque between the engine and the input member of the transmission, the torque converter assembly having a turbine operatively connected to the input member, a gear assembly for changing the ratio of torque between the input member and output member, a frictional unit for coupling the turbine of the torque converter assembly to the engine, at least one solenoid-actuated valve being movable in response to the presence or absence of electrical power for directing fluid flow from a fluid source, a slave valve, a plurality of input sensors for providing signals indicative of predetermined conditions, and a controller having memory for processing and storing the signals and predetermined values and providing output signals, a method of controlling the difference between the rotational speed of the output member of the engine and the rotational speed of the turbine of the torque converter assembly, said method comprising the steps of: checking a plurality of first predetermined conditions by the input sensors to determine whether the turbine of the torque converter assembly is precluded from being partially frictionally coupled to the engine; determining whether any of the checked plurality of first predetermined conditions prevent the turbine from being partially frictionally coupled to the engine by comparing them to stored values for the first predetermined conditions in memory which prevent partial frictional coupling of the turbine; setting a plurality of second predetermined conditions to uncouple the turbine from the engine if any first predetermined condition prevents the turbine from being partially frictionally coupled to the engine; setting predetermined initial conditions to control a duty cycle of the solenoid-actuated valve which allows and prevents fluid flow to the slave valve to allow or prevent fluid flow to a frictional unit which frictionally couples the turbine to the engine; determining whether the method is at the start of a duty cycle period of the solenoid-actuated valve for partially coupling the turbine of the torque converter assembly to the engine; checking a plurality of third predetermined conditions by the input sensors that would allow the turbine to be fully frictionally coupled to the engine to eliminate the difference between speeds if the method is at the start of a duty cycle period of the solenoid-actuated valve for controlling the slave valve; determining whether the checked plurality of third predetermined conditions allow the turbine to be fully frictionally coupled; solving a first set of predetermined equations for the duty cycle of the solenoid-actuated valve for full frictional coupling of the turbine if determined that the turbine is allowed to be fully frictionally coupled; calculating a predetermined change for the duty cycle of the solenoid-actuated valve to control slip during partial frictional coupling of the turbine of the torque converter assembly; and duty cycling the solenoid-actuated valve based on the value for the solved duty cycle.