Farzad Samie

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

Study of a Non-Circular Gear Infinitely Variable Transmission

Improving automobile fuel efficiency is an important research and development effort in the automotive industry. In the transmission area, it is generally understood that optimum fuel economy can be achieved via a combination of highly efficient power transfer (gears, for example) and an ability to transmit power at an infinite number of ratios (CVT, for example). In this paper, a geared infinitely variable transmission (IVT) is analyzed for efficiency through static analysis. This IVT is based on a non-circular gear concept described in [1, 2]. This IVT consists of multiple function generators with each function generator comprising two sets of non-circular gear sets whose outputs are combined with a summing planetary gear set. Each function generator provides the desired gear ratio for only a part of the driving rotation. So, multiple function generators are combined along with multiple one-way clutches to provide an infinitely variable transmission.This paper first explains the operating principle of the geared IVT. A static analysis of the IVT powerflow is derived and it is shown that this powerflow exhibits a torque recirculation phenomenon, which is not desired. This recirculation phenomenon is expected to be present in all similarly arranged IVTs where two inputs are combined using a planetary gear set to provide infinite gear ratio capability. The efficiency of the IVT is calculated based on assumed individual component efficiency and it is shown that, owing to torque recirculation, the efficiency of this transmission may not compare well with that of current automatic transmissions for a passenger car application.© 2014 ASME

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

Design, modeling, and analysis of wedge-based actuator with application to clutch-to-clutch shift:

Clutch-to-clutch shift technology is a key enabler for fast and smooth gear shift process for multi gear transmissions. However, conventional hydraulic actuation systems for clutches have drawbacks of low efficiency, oil leakage and inadequate robustness. Electromechanical devices offer potential alternative actuators. In this paper, a novel motor driven wedge-based clutch actuator, featuring self-reinforcement, is proposed. The design concept and physical structure are thoroughly described. Dynamic models for the actuation system and vehicle powertrain are validated by experiments. Upshift and downshift processes at different engine throttle openings, clutch clearances and friction coefficients are discussed. The results show that, the self-reinforcement ratio is tested as 9.6; at the same time, the shift quality is comparable to that of the conventional hydraulic actuated clutch in automatic transmissions in terms of the shift duration (about 1 s) and vehicle jerk (<10 m/s3). Taking advantage of fast response of the actuation DC motor, the wedge-based actuator is robust dealing with uncertain clutch clearance and friction coefficient. Therefore, the wedge-based clutch actuator has potential to provide acceptable performance for clutch-to-clutch shift.

Experimental and Control Study of Slipping Decay Time of a Wedge Clutch in an Automatic Transmission

A wedge clutch with a wedge ramp transfers the tangential force into an axial force. It has unique features of self-reinforcement, and can be packaged into tight spaces. This wedge clutch is developed to apply to an automatic transmission as an implementation example.The slipping decay time is found to be critical for the shifting quality. This paper focuses on the experimental study and control of slipping decay time of the wedge clutch through the influencing factors. The mechanical system of the wedge clutch applied in an automatic transmission is described and the sensors for measuring signals are installed. A transmission dynamometer is set up for experiments.The torque magnitude and direction of the motor motion are considered as actuation factors; the driveline input speed, load torque, and oil temperatures are considered as the driveline factors. The results show how influencing factors affect the slipping decay time during gear shifting.© 2012 ASME

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

Control of Multi-Plate Torque Converter Clutch With an Aggressive Schedule in an Automatic Transmission

In an automatic transmission, torque converter is the main device that transmits torque from the engine to the gear train. An open converter relies on fluid coupling to transmit torque, which causes energy loss and also causes engine to run at a higher speed. A single-plate locking or slipping clutch has been used between the pump and turbine of a torque converter so that the slip across the converter can be reduced to a level that increases the efficiency of the converter. This slip control, called Electronically Controlled Capacity Clutch (ECCC), also provides necessary damping to the driveline to ensure pleasant driveability similar to an open converter. New legislative and environmental pressures on car makers to improve fuel economy have resulted in aggressive use of ECCC in their automobiles. However, the controllability and heat capacity of the single-plate clutch limit the ability to engage the torque converter clutch (TCC) more aggressively (in earlier gears and lower vehicle speeds). At GM, an experimental multi-plate toque converter was designed, fabricated, and implemented in a RWD transmission. It was demonstrated in a 6-speed vehicle that driving pleaseability can be maintained with a more aggressive ECCC strategy. For this purpose, a control algorithm was developed to control the slip speed of the clutch and allow early ECCC starting in second gear. This paper describes in detail hardware implementation of the multi-plate clutch, development and implementation of the aggressive ECCC control strategy, and some vehicle test results.Copyright

Comparison of Efficiency Measurements and Simulation Results for Automotive Traction Drives

Mechanical Efficiency of toroidal traction drives is the key parameter for transmission engineers worldwide to accept their use in continuously variable transmissions. In this work, the traction drive efficiencies are investigated analytically as well as experimentally as a function of speed, torque, speed ratio and temperature for two different CVUs. In addition, creep at the traction contact is measured and compared with the prediction of the simulation model. In a stand-alone test rig, the drag torque associated with the power-roller thrust bearing is also measured.