Automotive Power Transmission Systems

7Continuously Variable Transmissions

7.1 Introduction

As discussed in Chapter 1, continuously variable transmissions (CVT) are the ideal transmission that theoretically optimize engine matching. The idea of CVT dates back to the 15th century, the original design being credited to Leonardo da Vinci [1], who invented a mechanism with CVT functionality in 1490. CVTs have found applications in machinery that operates at relatively low power, but their applications in the automotive industry have gone through many setbacks and it is only in recent decades that the CVT vehicle market share has become significant. The British company Clyno was the first to develop a passenger car equipped with a CVT, in 1923 [1]. Not much happened for automotive CVTs since that, until, in 1961, the Dutch company DAF developed a production CVT for a small passenger vehicle with the brand name Daffodil [2]. Although this rubber CVT was not successful in the automotive industry due to its low efficiency, low torque capacity, and low reliability, it regenerated industrial interest in CVT development and inspired engineers in the design, manufacturing, and ratio control of this type of transmission. In 1987, Subaru developed a CVT vehicle named Justy which was well received by the market [3]. The Justy was a subcompact car with a 1.0 or 1.2 litre gas engine. In the same year, Ford and Fiat also launched compact cars of similar engine size equipped with CVTs. Due to limited torque capacity and reliability ...