Method of controlling a dual clutch transmission

A method of controlling torque transferred across each of the two clutches of a dual clutch transmission during a positive downshift, wherein the first of the two clutches drives an initial gear and the final gear and the second of the two clutches drives an intermediate gear, said method including the steps of:

• sensing engine throttle position and vehicle speed;
• determining if a two-gear positive downshift is required based on the engine throttle position and the vehicle speed;
• sensing the speed of a driven member of the first clutch in the initial gear;
• determining a desired clutch torque and slip profile for the changeover of the clutches;
• sensing the speed of a driven member of the second clutch in the intermediate gear;
• estimating the speed of the driven member of the first clutch in the final gear;
• determining a target engine speed profile based on the speed of the driven member of the first clutch, the speed of the driven member of the second clutch, the estimated speed of the driven member of the first clutch for the final gear, and the desired clutch torque and slip profile;
• determining a first time period during which the engine speed will be increased by decreasing pressure applied to the first clutch based on the speed of the first clutch and the speed of the driven member of the second clutch;
• decreasing the pressure applied to the first clutch and increasing pressure applied to the second clutch during the first time period to cause the engine speed to increase and track the target engine speed profile so that torque output of the transmission can be changed from the initial gear to the intermediate gear while maintaining the increasing vehicle speed;
• determining a second time period during which the torque transfer across each clutch will be changed over from the first clutch to the second clutch;
• simultaneously controlling the torque transfer across each clutch so that the torque output of the transmission will be changed over from the first clutch to the second clutch by linearly decreasing the torque transferred across the first clutch while linearly increasing the torque transferred across the second clutch in an inversely proportional rate to follow the desired clutch torque and slip profile and to cause the engine to track the target engine speed profile;
• disengaging a synchronizer of the initial gear and engaging a synchronizer of the final gear as the engine tracks the target engine profile speed profile and the first clutch is slipping at a greater rate than the second clutch to change over the gears driven by the first clutch;
• sensing the speed of the driven member of the first clutch after the change over to the final gear;
• determining a third time period during which the torque transfer across each clutch will be changed over from the second clutch to the first clutch;
• and
• simultaneously controlling the torque transfer across each clutch so that the torque output of the transmission will be changed back from the second clutch to the first clutch by linearly decreasing the torque transferred across the second clutch while linearly increasing the torque transferred across the first clutch in an inversely proportional rate to continue to follow the desired clutch torque and slip profile and to cause the engine to continue to track the target engine speed profile.