Automotive Power Transmission Systems

5Automatic Transmissions: Design, Analysis, and Dynamics

5.1 Introduction

Automatic transmissions (AT) that use planetary gear trains (PGT) and clutches for power transmission and ratio changes are the dominating transmission type in the automotive industry. This type of transmission dates back to the late 1930s [1,2], and they are conventionally termed automatic transmissions since they were the only production type for many decades before other types of automatic transmission, such as CVT and DCT, were applied in scale in the automotive industry. Early automatic transmissions [3] for rear wheel drive (RWD) vehicles provided three forward and one reverse gears, and were designed on an architecture that consisted of a torque converter, planetary gear train sets, and hydraulically controlled clutches, as illustrated in Figure 5.1. This design architecture or its variations stayed almost unchanged for more than three decades. Before the 1970s, passenger vehicles were almost exclusively RWD, and the vast majority of automatic transmissions had three forward speeds. Only a few high end models were equipped with four‐speed automatic transmissions, with the fourth gear as a direct drive [4]. The oil crisis in the 1970s called for the development of more fuel efficient passenger vehicles that are lighter and front wheel driven (FWD). An early type of FWD AT that provided three forward and one reverse gears is illustrated in Figure 5.2. As shown in the figure, in an FWD transmission, ...