Sorry, we have no pictures of swoopy new cars coming your way, but perhaps a multi-speed transmission for electric vehicles is newsworthy enough to post with just a simple graphic.
You see, if this innovation from Vocis – or ones like it – come to production, they stand to improve any EV’s range and/or speed capability. Smaller batteries could be used, if desired, or more performance could be baked in without need for larger motors and batteries.
Until now, multi-speed transmissions have been seen as added cost, weight and complexity that most EV makers have said they can get by without.
This was because electric motors produce maximum torque from zero rpm, so single-speed output ratios have been enough to give an electric vehicle acceptable acceleration and top speed.
But as the graphic helps to show, efficiency does suffer, so maybe it’s time they learned what petrol vehicle makers have known for over one hundred years.
“Electric motor efficiency drops off at low load levels and towards the extremes of speed,” said Vocis technical director, Richard Taylor. “Multiple gear ratios with electronic control allow the motor to be kept in the region of greatest efficiency for a much higher proportion of the time, allowing significant range extension.”
The Vocis (company part owned by Oerlikon Graziano) transmission is designed and manufactured in Italy, with UK engine controls.
Company engineers have begun road testing their innovative multi-speeders with a European vehicle manufacturer.
A couple years ago the company also developed a two-speed EV transmission which was shown to improve efficiency by 5-10 percent on the European drive cycle.
The ultra-smooth multispeed does even better, and is similar in concept to a dual-clutch transmission which the company is also adept at making – albeit, the EV trans does not actually use clutches.
The Vocis differs from most EV powertrains which use a single motor/generator, by using two small “e-machines” (motor/generators), each on its own independently controlled shaft.
The result is balanced distribution of drive and recovered energy and seamless gear changing thanks to torque infill from each shaft.
Shifting is so imperceptible, one test driver asked to be shown that he was not driving a one-speed, said Taylor.
The technology is scalable for auto or truck usage, and electronically controlled for full driveline integration. Multiple available ratios can be selected by a manufacturer to optimize acceleration, top speed, torque output, or match brand characteristics, as needed.
“The priority for a passenger car application is to increase the performance to that of a conventional car by improving acceleration and top speed,” Taylor said, “The priority for a delivery van would be to improve fully laden performance during pull away or hill climbing. And both will benefit from the significant improvement in range.”
As mentioned, the Vocis multi-speed would increase cost, weight, and complexity, but these are being presented as a worthwhile trade-off, just as they are for internal combustion machines.
The company says because the system requires no clutch or synchronizers, its cost and weight compete well against a conventional gearbox.
Both the multi-speed and two-speed EV transmission will be on display Sept. 7-8 at the LCV2011 (Low Carbon Vehicle show) at Rockingham Motor Speedway in the UK.
“Our two-speed transmission demonstrated the benefits of EVs moving beyond a single speed. We are now extending those gains by using multiple ratios to make EVs more competitive in a variety of applications, said Vocis Managing Director, Mike Everitt. “ This gives us single, twin and multi-speed EV transmissions, all of which are already in running vehicles. We believe this to be one of the most comprehensive ranges available anywhere.”
The twin-speed transmission will be demonstrated in an electric minibus that was co-developed with powertrain supplier, Zytek.
Whether EV transmissions will catch on remains to be seen, but their need at this point seems obvious.
Examples of EV manufacturers that have seen the value include ALTe, which will retain the OE transmissions in its converted extended-range electric truck conversions, and Brammo, which is readying a six-speed for its all-electric motorcycles.