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Antonov study of multi-speed transmission for EVs finds improved efficiency over different drive cycles

Antonov
Antonov’s study found that its multi-speed electric vehicle transmission can deliver 10% better efficiency compared with a single speed gearbox. Click to enlarge.

Automatic transmission specialist Antonov reports that its comparative studies of an electric vehicle equipped with its multi-speed transmission over eight different drive cycles suggest that the transmission delivers typically 10% better cycle efficiency than a single-speed solution. (Earlier post.)

Antonov has been invited by the Technology Strategy Board (TSB) to present its findings at the LCV2011 event being hosted by Cenex this week at the Rockingham Motor Speedway in Corby, Northamptonshire. The TSB has helped fund several transmission research and development projects with the company’s involvement.

The majority of electric vehicles are currently equipped with a single speed, so there are clear implications for the next generation of electric vehicles. Our analysis shows that with a single speed gearbox there is significant variation in drive cycle efficiency, whereas a multi-speed transmission tends to be more consistent with better overall cycle efficiency.

The results are consistent with the multi-speed transmission keeping an electric motor operating in its peak efficiency range. Inevitably, there is a compromise with a single speed gearbox particularly in terms of low speed acceleration, hill climbing and high speed cruising. The 10 per cent step change improvement in efficiency can be achieved with just two ratios, but technical compromises remain in other areas. Three or more ratios are better, delivering additional improvements in performance and refinement as well as efficiency, with each additional ratio providing small incremental gains in cycle efficiency.

— Antonov’s business development manager David Paul

Antonov has developed its latest modeling tools to help demonstrate the performance and efficiency benefits of its powershift multi-speed transmission to electric vehicle manufacturers. The company can determine the ideal motor and transmission combination, as well as optimizing the gear ratios and final drive ratio for any given electric vehicle application. The analysis supports real world vehicle trials.

Antonov is supplying Smith Electric Vehicles with a prototype of its multi-speed transmission for a TSB funded research and development project. The ‘E-Van’ electric vehicle demonstrator is based on Smith’s Edison 3.5 tonne delivery van, with Antonov’s 3-speed transmission currently being installed for test and evaluation.

Antonov’s multi-speed transmission was first evaluated in a Jaguar Limo-Green research vehicle as part of a consortium project with Jaguar Land Rover and MIRA. This research and development project was also part funded by the TSB.

Now looking at a wide range of vehicle applications, particularly commercial vehicles, Antonov says the technology with its seamless shift quality has strong potential for further development as a 4 or 5-speed transmission, with virtually the same packaging. The design of Antonov’s powershift electric vehicle transmission is such that additional ratios can be easily added. It is also scalable to different classes of vehicle ranging from family cars to light commercial vehicles, taxis, delivery trucks and public transport buses.

Comments

DaveD

GEEZ, look at the difference in efficiency on the motorway! Going from 40% efficiency up to about 85% would be worth it's weight in gold...or batteries in this case :-)

It won't literally double the mileage because aerodynamic losses dominate at freeway speeds, but it sure couldn't hurt anything to have the motor itself over twice as efficient there.

Dave R

If you look at this earlier post on GCC regarding multi-speed EV transmissions, the graphic shows that motor efficiencies don't drop much below 70% except at very low motor speeds.

On-road testing of new multi-speed transmission for EVs from Oerlikon Graziano/Vocis begins; potential for increased range or reduced pack size

At higher speeds efficiency is in the 80-90% range except at very low torque values or near top speed.

So I have a very hard time believing that efficiency is as low as 40% on the motor way.

If for some crazy reason they are right, It sure would be nice to double my LEAFs highway range from 70 miles to 140! This would allow some serious downsizing of batteries or increase in range for perhaps a couple thousand dollars in added cost. I would happily pay that to double my highway range! Even if the improvement in range was only 25% it would be worth it, especially if the improvement came with additional acceleration performance.

MG

It depends a lot on the efficiency curve of the motor itself - some motors are inefficient at low rpm, some at high rpm. Induction motors are inefficient at low rpm. For drivetrains using them, it would be beneficial to shorten time spent in that area, i.e. during frequent starts (after stops) - a two-speed gearbox would help if it could be made very reliable, inexpensive and lightweight.
Another thing to be taken into consideration is that the e-motors used in current single speed transmission were designed to cover broad speed range, and in that process some trade-offs must have been made.
Nissan Leaf acceleration time 0-60 mph is about 11 sec.
Not good selling point, many people (especially young) like good acceleration. With a 2-speed it would probably be close to 8 sec (just my guesstimate).
The UK's Zeroshift seem to offer the simplest 2-speed transmission. If used with e-motors, the dumper would IMHO suffer far less stress than with an ICE engine during quick shifts, as it's possible, far easier, to quickly match rpm's in electric drives. I don't know anything about reliability of Zeroshift system.

ChrisL

BMW i3 goes from 0-100 kph (62 mph) in 7.9 seconds with single speed transmission. 0-60 acceleration times are perhaps not too meaningful, however, since in my experience in everyday traffic very few people press throttle to the floor, certainly not all the way to 60 (or do they?). E-cars do very well off the line because they develop full torque at zero RPM.

That said, I'm sure BEV manufacturers have explored the option of using multi-speed transmissions in their designs, and I'm assuming the likes of Tesla, BMW, Nissan, etc. have competent engineers on staff. As technology evolves, their choices may change, but for now, they seem to think one-speed is the way to go.

The article mentioned commercial vehicles more than once; that segment may be the focus of their research, and of course, as always, they're looking to sell a product.

HarveyD

Not much difference in efficiency between 2, 3 and 4 speed transmission. Wouldn't the major difference between 1 and 2-3-4- speeds depend, to a great extend, on the type of e-motor used or compared with? Not so sure that the indicated difference would be as much with improved variable torque e-motors and appropriate control system.

Herm

Perhaps this simulation applies to heavy duty trucks, but the Leaf is already 85% efficient from 38mph to about 80mph, and peaks around 95% over a wide range (that includes battery-inverter-motor losses, not sure about the single gear reduction and differential/halfshafts).. there is just not enough room for that kind of improvement to then put up with a transmission cost and maintenance.

ChrisL

I just saw the video of Toyota's electric race car breaking the lap record at the Nurburgring-Nordschleife race course at the end of August. It's really wild, and the car uses a one-speed transmission. Video is at the end of this article on the record-breaking lap: http://www.motorauthority.com/news/1065448_toyota-smashes-nurburgring-electric-car-lap-record-video

ToppaTom

I think they purposely eliminated the stop and go city cycle from the Nurburgring-Nordschleife speed trial.

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