SHIFTING TOWARDS THE FUTURE
With the increased volume of traffic on our roads, more and more drivers are looking for the convenience of an automatic transmission. Keeping track with this demand, advancements in automatic transmission technology have meant that car owners can enjoy equal or even superior performance and lower fuel consumption compared to manual units.
HOW A TRADITIONAL CVT WORKS
Of all the types of self-shifters, continuously variable transmission (CVT) remains the most elegant engineering solution. It consists of two pulleys connected by a metal drive belt that transmits the engine torque. While traditional ’boxes use a fixed number of gear ratios, a CVT allows an infinite number of drive ratios between a minimum and maximum value (limited by the pulley sizes). How? Well, moving the belt up or down the conical sides of the pulleys changes the contact radius and therefore the ratio.
The main advantage of a CVT is that it allows the engine to operate in its most efficient speed-load region – and that saves fuel (even keeping engine speed constant while the vehicle is accelerating), and ensures the engine runs at peak power when maximum performance is required.
WHAT A DIRECT SHIFT CVT ADDS
CVTs have been criticised for their slow response to acceleration input from the driver, especially during pull-away. To address this concern, Toyota has developed the world’s first CVT with a mechanical first gear. Called Direct Shift CVT, it employs a traditional first gear to remove the tardiness of a CVT during take-off, before it engages the CVT at higher vehicle speeds. This has allowed Toyota engineers to reduce the size of the pulleys, while the total ratio spread of the transmission, including the mechanical first gear, is actually wider than the standard CVT. The benefits include lower engine speeds while cruising, and a more compact unit from
a packaging point of view.
Called Direct Shift CVT, it employs a traditional first gear to remove the tardiness of a CVT during take-off
An added advantage of a mechanical first gear handling the high ratio of torque multiplication is that the metal belt in the Direct Shift CVT is subjected to lower forces. The belt-contact angle on the pulleys is reduced from 11° to 9°, and while that might not seem like much, it means the hydraulic actuator can move the belt 20% faster than before – which improves response time.
For more spirited driving, you can opt to take manual control of the transmission. In this mode, the CVT mimics actual gear shifts by moving the belt in “steps” that resemble defined gear ratios. Like a traditional automatic transmission, this allows the engine revs to rise towards the redline before shifting to the next virtual gear as fast as a modern dual-clutch transmission.
This new drivetrain technology is a feature of the recently launched Corolla Hatch (as well as the Rav4 and Lexus UX). To read about the technology is one thing; best is to experience it first-hand by booking a test drive at your local Toyota dealer. You may just find that it is the automatic choice…