|
|
|
|
|
01/02/2012
 Email to a friend
 Comment on this article
|
Tony Lewin reports on the most significant news from the recent CTI symposium
 The annual CTI Symposium on Advanced Transmissions in Berlin presents the ideal opportunity to test the temperature of the global driveline business in all its enormous breadth – everything from electric drives and the design of clutch bearings to the importance of having the right gear ratios for traffic conditions in the rapidly emerging market of India.
Most notably, there was talk in almost every quarter of the need to increase the gear ratio spread in everyday transmissions from today's 5 or 6 to at least 8, possibly 10, with the ratio count likely to increase, too.
The second focus to emerge was that of maximising efficiency at every stage of every process within the driveline. With some form of hybridisation likely to become a near-universal feature by 2020, energy now flows twice through every transmission, first under acceleration, and then when slowing down and recuperating kinetic energy. This means any parasitic losses impact twice as hard on the overall energy balance.
Will CVT stage another comeback?
A strong theme to emerge from 2011's symposium was that CVT can and will challenge other transmission types for overall efficiency honours.
Shigeo Ishida, until recently CEO of top CVT maker Jatco, surprised delegates when he stated that his firm's new CVT for 2012 would be 90% efficient and that, in recent Japan-mode emissions tests, it had equalled the efficiency performance of a wet clutch DCT. The CVT8, aimed at medium and large FWD vehicles of up to 350 Nm torque, retains the innovative auxiliary transmission of the smaller CVT7 for Micra-class models and claims a 10% improvement in fuel economy, thanks to its wide ratio span of 7.0.
"The key issue is to develop the engine and transmission together as a complete package," observed Ishida, pointing to the improvement in the new-generation Nissan Micra from 161 g/km CO2 to 115 g/km as evidence.
Revealing that Jatco would soon be producing more than half of its transmissions in emerging markets, Ishida forecast an annual output of
3 million CVTs and 2 million ATs; remarkably, Jatco now has manufacturing technology that allows both CVTs and conventional ATs to be made on the same line, at the same time.
Many in the transmissions hardware world had feared that the widespread adoption of electric vehicles could put them out of business: the wide torque spread from zero to maximum rpm of electric motors threatened effectively to render the gearbox and clutch redundant. Yet the past year has brought the realisation that such simple, single-speed drives impose uncomfortable compromises in efficiency, most notably when it comes to the most customer-sensitive aspect of EV performance – the issue of the driving range available on each full charge of the traction battery.
Multiple gears
This and several other issues point towards the need for multiple gears for maximum EV efficiency and performance; this also applies to electric assist axles, if they are to be able to operate over the whole of the vehicle's speed envelope.
Dr Uli Blessing, from Getrag, anticipated a 10% increase in mileage with a two-speed transmission, while Alex Tylee-Birdsall of Drive System Design made the case for a three-speed drivetrain as an enabler not only for greater efficiency, but also improved packaging through the use of smaller motors, lower in torque and cost.
As perhaps the most dramatic extension of this idea, Oerlikon Graziano showed, both in hardware and as a technical presentation, its eDCT transmission. As its name implies, this unit has some functional similarities with a conventional DCT – except that the C in this case stands for 'clutchless'.
In place of the clutches, explained Simone Bologna, senior designer at the Italian company, are twin electric motors; these allow torque interrupt-free shifting between the four ratios.
The choice of four ratios, said Bologna, was made on the grounds of efficiency. The normal 90+% efficiency of an electric motor can drop to 60 or 70 at lower rpm and simulations had shown that an overall improvement of 18% could be obtained through a multi-speed approach. Further gains are available through two distinct operating modes: fast-shifting power, where two gear pairs are engaged, as on a conventional DCT, and slower-shifting economy, with just one gear pair meshing. The configuration also allows for both motors to be used at the same time.
AMT-plus could threaten DCT
That was the provocative view of Ford transmission specialist Dr Patrick Kelly. Even with DCTs still firmly positioned in the premium segment at a typical on-cost of €2,300, AMTs have failed to seize the opportunity to fill the gap between MTs and DCTs. Kelly argued that the lessons learned from DCT, such as electronic clutch actuation and microslip control, could be used to provide partial torque fill and speed matching. This, though necessitating the addition of a small electric motor on non-hybrid versions, could give customers a much lower cost way of achieving the automation and shift comfort of an AT, if not the fast-shifting performance feel of a sophisticated DCT.
|
|
| |
Author
Tony Lewin
|
| |
| |
Copyright AD Media Europe.
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.
|
| |
|
|
| |
To access the whitepaper section you need to complete our 60 second registration process. Once completed this then allows you to download any and all white papers, register for e-zines and access our detailed supplier directory for FREE.
If you are all ready a registered user then enter your e-mail address and login.
You will need to have logged in prior to entering your comments in the boxes provided.
|
|
Engineering Recruitment Partner:
|