Chunhao J. Lee

Control of A Friction Launch Automatic Transmission Using a Range Clutch

Friction Launch transmissions use a wet multi-plate clutch to replace the torque converter in an automatic transmission. The main benefit of this technology is fuel economy improvement as a result of eliminating the losses in the torque converter. By using one of the range clutches inside the transmission instead of an input clutch in place of the converter, the benefits of this integrated friction launch technology, such as reduction in mass, packaging, and cost, can be enhanced. The availability of new automatic transmissions with higher number of speeds and wider overall ratio spreads makes this technology more viable than ever before. This project focuses on control issues with the friction launch clutch which include developing robust control algorithms for launch and creep, and providing damping to the driveline, when required, and ensuring acceptable vehicle drivability. This paper describes in detail the development of vehicle launch control algorithms. Vehicle test data is presented to show that the control strategy developed in this project significantly reduces the gap between the drivability of a starting clutch vehicle and a torque converter equipped vehicle.Copyright

Control of Selectable One-Way Clutch in GM Six-Speed Automatic Transmissions

Automatic transmissions use one-way clutches and regular clutches to control gear shifts. Regular one-way clutch locks in one direction and free spins (freewheeling) in the other direction and thus provides good shift quality. However, a clutch is needed if the freewheeling direction needs to be locked. The advantage of a selectable one-way clutch (SOWC) is that it can be designed to act like a regular one-way clutch, fully freewheels or locks in both directions. In the GM six-speed transmissions, there is one one-way clutch which is accompanied by a clutch CB1R to control between 1st gear and reverse direction. The study is to replace the one-way clutch and CB1R clutch with simply one selectable one-way clutch in GM 6-speed transmissions (1). This will eliminate one transmission clutch, reduce weight and cost, and improve transmission efficiency. The proposed design of transmission is applied to a GM SUV and a GM passenger vehicle. Different from a regular clutch, which can be applied with force/pressure from high slippage to lock-up between two elements, a selectable one-way clutch can only be applied to a lock-up position when the slippage between two elements is near zero speed. Also, an SOWC can only be released when there is no torque or force carried by the clutch while a regular clutch can be easily released by dropping the applied force/pressure. These requirements impose challenges of the control strategies of the SOWC, especially during the scenarios such as 2–1 engine idle downshift (engine braking) and 1–2 upshift (coasting). This paper reviews hardware design, vehicle implementation, and focuses on control of the selectable one-way clutch. Vehicle results demonstrate static and rolling garage shifts, 1–2 upshifts, 2–1 and coast downshifts. Also demonstrated is the successful application of engaging 1st gear engine braking with the SOWC. This control involves coordination between the engine speed and SOWC slip speed, and the apply/release of the device.Copyright

Torque Converter Clutch Low Slip Speed Detection and Control

A torque converter clutch (TCC) is an important element of automatic transmissions because it affects fuel economy and driveability. Although torque converters are ideal launch devices for transmissions, they are inefficient in steady-state operations. For that reason, a TCC is used to control and minimize the slip between the torque converter pump and turbine, thereby increasing the efficiency of the driveline and improving fuel economy. However, low TCC slip speeds increase the likelihood that disturbances cause the TCC to have zero slip or crash. In the absence of TCC slip, it is essential to quickly restore slip and regain driveline isolation to maintain driveability. To recover TCC slip, pressure to the TCC must be reduced significantly to overcome the effects of clutch material nonlinearities and hydraulic hysteresis. Unfortunately, large pressure reductions can also result in undesirable slip overshoot. In this investigation, the truncated sequential probability ratio test is used to achieve fast and robust detection at the low signal-to-noise ratios caused by the low TCC slip speeds. In the event of a crash, two unique TCC pressure command sequences are presented which maximize the response of the system hydraulics while also minimizing clutch slip overshoot. The effectiveness of the proposed methods are evaluated using experimental results from small and large vehicles equipped with automatic front and rear-wheel drive transmissions.Copyright