Vocis is road testing a multi-speed EV transmission
Published September 6, 2011
By Jeff Cobb
A multi-speed transmission could help an EV stay in its motor's optimal powerband.
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.
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24 weeks ago
That is the one minor downside to eventually getting an EV, I'll miss the stick. I've always had a stick. They are fun to drive, they keep me engaged, I feel that I have more control. Even is EVs get multiple gears, there won't be a clutch or stick.
Can one have too much torque? I think about how easy it is to peel out in the snow sometimes. With all of that torque all of the time, it would be nice to have a way to control it. Oddly enough, not ask for more, but ask for less.
24 weeks ago
Is this why the gas engine goes on when driving the Volt above 72 mph? The battery is less efficient at higher speeds?
MrEnergyCzar
24 weeks ago
The graph shows a single motor's efficiency rating. I wonder if 2 electric motors - a larger one to handle acceleration and higher torque efficiently and a smaller motor to handle higher speeds more efficiently might work better than a transmission. Electric motors are so compact that the there may be weight savings by avoiding the transmission by replacing it with a smaller motor. I am not an engineer so I really wouldn't know. I understand that there would be some kind of transmission to run the drivetrain between the two motors, bit it might be a lot simpler. Just pondering...
24 weeks ago
The Volt can go from 1 - 100 mph using battery alone. Only when the battery is depleted and the car is generating electricity and in low torque demands (i.e. cruising at ~72 mph) is the engine used along with the main traction motor. One of the reasons it's used is because the Volts main traction motor and the second motor/generator are used basically as a CVT when cruising for efficiency.
When the battery is depleted and the ICE is turning the motor/generator (second motor) to generate electricity for the main traction motor, if traveling at cruising speed once again the second motor/generator is clutched in (just happens to be clutch to the ICE as well). But, if the battery is depleted and you stepped on the accelerator the Volt will still go from 1 - 100 using just the main traction motor because the ICE isn't used for high torque since the ICE is only ~ 80 hp.
Basically the Volt is an EV, serial hybrid and parallel hybrid. It can go from 1 - 100 mph in EV and serial hybrid modes. Parallel mode is reserved for constant speeds at higher speeds when the main traction motor is less efficient and there isn't sufficient battery power to be in EV mode.
Youtube video that talks about this whole subject:
http://www.youtube.com/watch?v=IWSK8BR6LT8
23 weeks ago
Quote "That is the one minor downside to eventually getting an EV, I'll miss the stick. I've always had a stick. They are fun to drive, they keep me engaged, I feel that I have more control. Even is EVs get multiple gears, there won't be a clutch or stick."
Amen to that. But is there a technical reason a transmission in an EV can't have a clutch and stick? Or does it have more to do with the fact that most Americans never developed the necessary coordination to drive a manual transmission car?
23 weeks ago
The Volt gas engine does not come on at an y particular speed. It comes on when they battery charge becomes to low.
The volt has a sun gear that the primary EV traction motor and it can take the car as fast as the limiter allows (100mph). There is a second electric motor(and/or generator). The second motor can drive, in electric mode, the ring of the planetary gear (which can be clutched by the computer). This provides more EV efficiency at higher speeds.
The ICE (gas) engine only is used when the buffer is to low, which is called charge sustaining mode (CS-mode). The ICE is clutched to the the second "generator" motor to produce electric to drive the Traction EV motor (then it looks like 1-motor series hookup). When in CS mode its only 1-motor electric drive with lots of toque. When in high speed (low HP demand really), and in CS-mode, the ICE can clutch to the generator motor and the generator motor is clutched into to the ring of the planetary, providing 10-15% more efficiency. This improves MPG in range extended mode (i.e. a more efficient use of the ICE engine.
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