ABSTRACT In an effort to increase fuel economy and improve shift quality - the GF6 family of General Motors transmissions has been analyzed for potential enhancements. The focus of this analysis was to improve fuel economy, while increasing downshift responsiveness, and manual mode sport delays. This paper describes a variety of the hardware philosophy changes, and control methods which have contributed to the next generation of GM clutch-to-clutch 6-speed transmissions. These changes to hardware and controls have led to a composite fuel economy improvement of 4.5% with no changes to shift or torque-converter scheduling. In addition, the downshift responsiveness has been significantly improved to reduce delay times by approximately 50% while virtually eliminating the dependency on engine torque reductions - ultimately allowing for stacked downshifts to progress with minimal, if any, time between shifts. Additionally, “tap shift” delays have been significantly decreased to levels near 150 ms. INTRODUCTION The 6T30/6T40/6T45 (GF6) family of clutch to clutch transmissions was launched globally in model year 2007. The transmission was launched in Korea and has since made it's debut all over the GM portfolio, from Chevrolet Malibu and Equinox to the all new Chevy Craze. Based on global demand for fuel economical vehicles the GF6 has quickly become the highest volume unit in the GM portfolio. By improving the fuel economy achievable with a GF6 transmission, a large benefit can be realized across the world. Since debuting the GF6, GM Powertrain has continued to refine it's control system looking for better ways to improve fuel economy and performance. The team has come up with a new controls scheme that does not make any compromises. Both are achieved based on a cost effective system design approach. The system introduces several new hardware components which required new software strategies to optimize the system response times. CONTROLS ARCHITECTURE HARDWARE The complete system was analyzed to find ways to increase capacity, reduce system delays, and increase efficiency. The baseline GM control system ( Figure 1) placed a relatively small feed orifice on the high pressure side of the control valve and utilized clutch compliance devices such as waveplates and accumulators. The pressure compliance parts of the system were used to stabilize the valve from having large overshoot in pressure when the clutch control valve had to travel from a full feed position to a regulating position. The long stroke/low rate waveplates not only took up clutch volume, they also limit the pressure rise in the clutch. Gen2 GF6 Transmission Hardware and Controls Updates2011-01-1428 Published 04/12/2011 Mark A. Schang, Matthew Whitton, David Webert and Todd Berger General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-1428Downloaded from SAE International by Univ of Nottingham - Kings Meadow Campus, Tuesday, September 11, 2018Figure 1. Base and Upgrade Orificing Control Strategy Differences This provides for a highly stable clutch system that is robust to pressure device variation with the downside of not being able to quickly gain capacity. This system is optimal for base upshift and closed throttle downshift feel. Figure 2 and figure 3 show the consequences of the baseline method compared to the controls upgrade. In order to increase clutch torque capacity in gears 4, 5 and 6, the waveplate was removed and another clutch plate was added. However, when the waveplate is removed, the clutch control system is prone to instability as the system completes the fill phase of the clutch. In order to control this system, the orifice was moved downstream side of the regulator valve. This orifice placement also allowed for a less restrictive orifice configuration. This in turn allowed for a very responsive system that the regulator could have precise control over. Figure 2. Upshift Control Strategy Differences Figure 3. Downshift Contro