ABSTRACT To realize better fuel economy benefits from transmissions, car makers have started the application of torque converter clutch control in second gear and beyond, resulting in greater demand on the torque converter clutch (TCC) and its control system. This paper focuses on one aspect of the control of the torque converter clutch to improve fuel economy and faster response of the transmission. A TCC is implemented to control the slip between the pump and turbine of the torque converter, thereby increasing its energy transfer efficiency and increasing vehicle fuel economy. However, due to the non-linear nature of the torque converter fluid coupling, the slip feedback control has to be very active to handle different driver inputs and road-load conditions, such as different desired slip levels, changes in engine input torques, etc. This non-linearity requires intense calibration efforts to precisely control the clutch slip in all the scenarios. In this paper, a model based control method is developed to calculate the feedforward portion of the pressure control signal. This feedforward pressure calculation is so accurate that when it is used in conjunction with the slip feedback signal, the control of the torque converter clutch becomes extremely effective in controlling the slip to desired small values and at the same time preventing clutch flares and lock ups. The proposed feedforward algorithm applies the Kotwicki model or an equivalent table lookup to predict torque across the clutch using the desired slip, current estimated engine torque, and turbine speed. This new control strategy provides more accurate control, and reacts faster during the transient conditions, such as engine torque changes and reference slip changes. The strategy has been applied anddemonstrated in various torque converters in both RWD and FWD GM transmissions. INTRODUCTION Torque converters as starting devices have been used in automobiles since the 1940's. Torque converters provide torque multiplication, smooth ratio changing on acceleration, and good driveline torsional vibration damping. It is this last characteristic that has made the torque converter an indispensable device inside a transmission. However, compared to gear sets, even the best torque converter is an inefficient device, generating sizable quantities of heat and degrading the fuel economy of the vehicle. A locking clutch (known as torque converter clutch or TCC) is generally used along with a driveline damper (or isolator) to mechanically lock up the converter to reduce losses at steady state speed conditions [ 1]. In lower gears and low vehicle speeds, the TCC cannot be applied because a locked driveline would pose driveability concerns. The idea of slipping the TCC at small slip values (10 to 25 rpm) has been successfully employed to strike a balance between fuel economy and vehicle driveability. The technology of slipping TCC is generally known as Electronically Controlled Capacity Clutch (ECCC) [ 2]. To improve fuel economy, car makers have started the application of ECCC strategy in second gear and beyond resulting in greater demand on the TCC and its control system [ 3]. In addition, the target clutch slip values are getting smaller and smaller to achieve further fuel economy benefits. To accomplish this, the ECCC control must be precise and fast-acting to prevent any crashes (clutches locking up unintentionally). In this paper, the focus is on Model Based Torque Converter Clutch Slip Control2011-01-0396 Published 04/12/2011 Kumaraswamy Hebbale, Chunhao Lee, Farzad Samie, Chi-Kuan Kao, Xu Chen, Jeremy Horgan and Scott Hearld General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-0396Downloaded from SAE International by Univ of California Berkeley, Sunday, July 29, 2018developing a model-based feedforward control to calculate the clutch pressure. Conventional ECCC control consists of a feedforward pressure that is calculated based on engine torq