CTI Symposia put CVTs centre stage:
Are the benefits of stepless transmissions still underrated?
The ideal: stepless acceleration!
In high-powered electric automobiles like Tesla models or the BMW i3, drivers can feel like pilots already. For powerful, seamless acceleration right up to full speed, they simply apply full thrust.
In conventional automobiles, automatic shift transmissions use high numbers of gearsteps to map that ideal as closely as possible. As an interesting alternative, stepless transmissions are now being discussed intensively again.
CTI Symposia with a global outlook
The CTI Symposium USA dedicated a special session to CVTs (Continuously Variable Transmissions). They are also on the agenda at the upcoming Symposium in Shanghai, where numerous expert talks will provide a good opportunity to take a closer look at CVTs – particularly with regard to Asian markets. As Dr. Hong Jiang, AVL China, points out, the average speed in Beijing is just 22.81 km/h, with a great deal of shifting involved. In driving scenarios like these, CVTs can use their advantages to the full.
Sceptical Europeans, delighted Japanese
CVTs have always been highly popular in the Japanese market, where one new automobile in three has a CVT. Their popularity is also growing in the USA, their second most important market. In Europe, where many drivers still prefer manual shifts and love direct feedback from the engine, CVTs have had an uphill battle so far. Globally, CVTs now hold a 9 percent market share.
Most experts expect that figure to increase significantly in the next few years. Dr. Ryozu Hiraku, General Manager Powertrain Nissan Motor, says one important reason is that CVTs are the best solution for the automobiles of the future, which will either drive automatically or be increasingly automated.
Thanks to a wealth of technical innovations, CVTs are fit for tomorrow’s markets and look set to find high acceptance levels among drivers all over the world.
Stepless transmissions in the fast lane
Gone are the days when people said CVTs were just for snowmobiles and scooters! The basic virtues are just too good to ignore: more comfort through smooth, seamless power transmission, and high efficiency because the engine can run at optimal rpm across a wide range of road speeds.
The new CVT generation features numerous improvements. The hydraulic system, steel thrust belt and drag link conveyor chain have all been significantly optimised, and a torque converter has been integrated as a launch element. Jatco reports a 5 percent efficiency hike for its CVT7 W/R, plus an optimum gear ratio spread of 8.7. Fixed gearsteps have also been added, by means two planetary wheel sets and clutches. The gearsteps engage automatically on demand, or as an overdrive or underdrive.
An interesting study from General Motors analyses the wide range of opportunities for this kind of interaction between CVTs and fixed gearsteps with various specifications. The aim is to find the most efficient solution.
Intelligent electronic control systems are optimising transmissions further still. These make sure the optimal ratio is always selected, in keeping with the driver’s wishes and the respective driving scenario. Modern CVTs are also perfect for integration into hybrid drive automobiles.
Leonardo would love it!
Leonardo da Vinci is said to have sketched the principle of a continuously variable transmission more than 500 years ago. Today, engineers are again thinking hard about innovative build shapes, and developing them for mass production.
Dana is turning heads with its VariGlide® planetary transmission. The rings of the input and output shaft roll on ball bearings arranged in planetary form; by tilting the ball bearings, the transmission ratio can be varied steplessly.
In the off-highway segment, this system has been proven for years. Now the aim is to get progress rolling in automobiles too.
The GIF Development Company presents its Cone Ring Transmission (CRT) at CTI Symposia. Power is transferred by a metal ring that rotates between two opposite cones. With the aid of a shifter mechanism, the ring can be pushed along the cones to vary the transmission ratio.
The CRT is an all-mechanical system that requires no hydraulics for the shifter mechanism. Designed for smaller automobiles, CRTs are set to enter serial production next year.
CVTs are an option for active drivers too
Many modern CVTs can now do something that doesn’t
come naturally, namely select a fixed gear! Actually, they
only simulate the process. The feature is a concession to drivers who are used to shifting from previous automobiles, and to active drivers who enjoy giving shift commands. The pioneers are Audi (Multitronic) and Subaru (Lineartronic); both systems enable drivers to select various shift programs, and to up- or downshift manually to their heart’s content.
A thrilling contest between systems
ATs, DCTs and CVTs are three equally strong transmission concepts competing for market share in conventionally powered automobiles.
With numerous expert talks, eight parallel sessions and a comprehensive exhibition, the CTI Symposium China is the perfect forum for this and other hot topics.
Welcome to Shanghai, 21 – 23 September 2016!