2009-01-0509 Selectable One-Way Clutch in GM’s RWD 6-Speed Automatic Transmissions Farzad Samie and Chunhao Joseph Lee R&D, General Motors Corporation Brice Pawley Means Industries ABSTRACT This paper described implementation of a selectable one-way clutch in the GM’s RWD 6-speed automatic transmission [1] content to replace the current one-way clutch and low/reverse plate clutch. A selectable one-way clutch can hold torque or freewheel in one or both directions depending on the desired operating mode. In this project, it is used as the reaction element to hold torque selectively in 1 st gear and reverse. This paper describes hardware design, vehicle implementation, and control of the selectable one-way clutch. In additions, lower parasitic losses due to low/reverse clutch removal is measured and compared with production 6-speed RWD automatic transmissions. Other issues such as durability, cost, packaging, and mass are also addressed. This idea is demonstrated in a 6-speed RWD SUV. Vehicle results show very good static and rolling garage shifts as well as 1-2 upshifts, and 2-1 powered and coast downshifts. The main challenge of this work is to perform 1 st gear engine braking with the selectable one-way clutch. This is done using the electronic throttle control and precise control of the selectable one-way clutch speed. INTRODUCTION One-way clutches are used in numerous applications to selectively transmit power from one shaft to another. Both shafts may rotate but one is typically fixed to a stationary (reaction) member or housing. One-way clutches transmit torque when the rotation of one shaft relative to the other results in a type of wedging action to occur inside of the one way clutch. The wedging action is different for every type of one way clutch. When the relative rotation direction of the shafts reverses the wedging action is released and the clutch can freewheel or “over run”. One-way clutches exist in a wide variety of design types [2, 3]. All types have an inner and an outer race. In some designs these races are concentrically located with the locking members placed in between. This can be seen in the roller and sprag types shown in Figure 1 . The Mechanical Diode (MD) style shown in Figure 1 uses two plates placed facing each other. The locking member is placed axially bet ween the two plates. All styles shown use rings which are concentrically located with respect to each other about a common axis of rotation. Torque is transmitted from one race to the other through various styles and conf igurations of elements. Although the design types may differ, the functions are the same. Copyright © 2009 GM Global Technology Oper ations, Inc. Published by SAE International with permission. SAE Int. J. Engines | Volume 2 | Issue 1 307 Figure 1: Three basic types of one way clutches Disengaged multi-plate disc clutches, depending on various conditions, produce dr ag when there is relative motion between the input and the output members. One characteristic of a disengaged multi-plate clutch is that, as the relative speed between the input and output members increase, typically, so does the drag or spin loss. This spin loss contributes to decreased fuel economy. For example, the low and reverse clutch in GM’s 6-speed automatic tr ansmissions [1] is disengaged in all of the forward gears. Therefore, there is a measurable amount of overall spin loss in the transmission that can be attributed to the drag in the disengaged low/reverse (CB1R) clutch. GM has evaluated various type of selectable one-way clutch such as roller type [2], and MD type [3] in 4/5-speed automatic transmission in which the low/reverse clutch and production roller or sprag were replaced with a selectable one-way clutch. In this research project, the focus is on 6-speed automatic transmissions and the respective CB1R and traditional one-way clutches which were totally eliminated and replaced by a selectable