Automotive Power Transmission Systems

2Manual Transmissions

2.1 Introduction

The gear ratios discussed in Chapter 1 that match the engine outputs for optimized vehicle performance and fuel economy are realized by different types of transmissions. Manual transmissions (MT) are the oldest type and have a history as old as the automotive industry [1]. In a manual transmission, engine power is transmitted by gear pairs on fixed axes from input to output, and gear shifts are manually made by the driver. Although the basic structure and operation principles have remained almost the same ever since the advent of automobiles, manual transmissions have undergone an evolution of changes aimed at improving ease of operation and shift smoothness. The earliest manual transmissions used sliding gears for gear shifts [2]. To make a shift, the driver would separate a gear pair by pulling one of the gears out of mesh, and then pushing and sliding another gear into mesh. It was very difficult to make shifts this way and gear grinding was unavoidable during shifts. Later versions had constant mesh gear design in which gears responsible for shifts had a dogtooth ring attached. During a shift, the driver would push a sleeve with internal spline teeth on the transmission shaft and slide it into mesh with the dogtooth ring. Tooth grinding was still unavoidable since the speed of the sleeve and the dogtooth ring were different during shifts. It was in the 1930s that synchronizers were widely applied in manual transmissions [1,2]. The ...