New 3-speed EV powertrain to offer 10-15% improvement in EV range
19 February 2014
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| Compared to a single-speed EV or HEV transmission, DSD’s MSYS 3-speed system provides a 40% weight saving and 10-15% lower energy consumption. Click to enlarge. |
UK-based Drive System Design is developing a new EV powertrain based on an alternate approach to powershifting (no torque interrupt) achieved by separating the existing functions of a synchronizer. The integrated design of an axial flux YASA motor (earlier post) with the multi-speed transmission contributes to simplification of the motor cooling system, electrical architecture and powertrain control system.
The MSYS system can mean a 10-15% improvement in the range of electric vehicles, the company says. (Earlier post.) The company was recently showcased at the Cleantech Innovate 2014 event by the UK’s LowCVP organization (Low Carbon Vehicle Partnership), along with 7 other companies. DSD was the winner of a LowCVP commendation as the most impressive of the road transport-focused entries.
(DSD is participating in the Evoque_e research program (earlier post) to develop new modular hybrid, plug-in hybrid, and battery-electric vehicle (BEV) technology. The pure electric research vehicle will the MSYS multi-speed traction system developed.)
The company’s Technical Director, Alex Tylee-Birdsall, is presenting a paper entitled “High efficiency electric vehicle powertrain” at the Future Powertrain Conference (FPC2014) at the National Motorcycle Museum in Solihull, UK tomorrow.
MSYS supplies 55 kW of continuous power (100 kW peak for 60 seconds) and more than 2,000 N·m (1,475 lb-ft) of torque at the wheels in an extremely compact package with more than 91% total electric powertrain efficiency (98% transmission efficiency). MYSYS weighs just 55 kg (121 lbs).
MSYS offers 3-speed gearing with powershifting; the ratios are:
| 1st — | 10.01:1 |
| 2nd — | 7.15:1 |
| 3rd — | 5.42:1 |
Rapid ratio shifting using DSD Overlap Shift Technology minimize torque interruption. The powershift elements in the MSYS transmission separate the two basic synchronizer functions of friction and latching and use the enhanced friction capacity of multi-cone clutch assemblies to provide an uninterrupted flow of torque to the wheels while using no energy to hold the transmission in gear.
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| Each ratio of the MSYS transmission uses its own multi-cone friction clutch to transmit drive during shifting and a separate dog clutch to latch the assembly in gear. Click to enlarge. |
The increased friction capacity allows the powershift cone clutch to temporarily drive the vehicle during shift events while latching in gear is achieved by dog clutches with self-locking teeth, similar to a conventional synchronizer.
There is growing recognition of the benefits of multiple ratios for EV transmissions. DSD has taken a unique approach by developing a reliable, highly efficient, seamless gearshift in order to make such transmissions acceptable to the user.
MSYS avoids the disadvantages inherent in other transmission options. A DCT consumes energy continually to maintain clutches in the open or closed position (depending on clutch type); an AMT suffers from torque interruption during shift events, and automatics based on epicyclic gear sets add complexity, cost and drag.
By using proven technologies in a unique arrangement, i.e. synchronizer-derived cone clutches and dog clutches, DSD has been able to seek patent protection for the system while minimizing the technical risks during development and enabling system suppliers to make use of their existing expertise.
Enhanced friction levels have been achieved in the multi-cone clutches by using forced lubrication with variable flow through the clutch packs. Flow variation permits good thermal management at times of high slip with maximum efficiency at times of lower demand.
Characterization testing of the cone clutches has shown good linear engagement properties (torque vs applied pressure), enabling the clutch-to-clutch shifting that is an essential part of the MSYS design. The next phase of development will include installation of a prototype transmission in a demonstrator vehicle, allowing calibration to commence. The vehicle will be ready for demonstration to customers during the summer of 2014.
MSYS will be ready for series production during Q4 2016, to support the growing demand from vehicle manufacturers needing to comply with increasingly tight CO2 emissions regulations. A family of MSYS powertrains with different power and torque outputs is planned, to suit the requirements of different target sectors.
Good news for future extended range PHEVs, FCEVs and BEVs. Tesla could be looking at this approach for their future Model E?
Posted by: HarveyD | 19 February 2014 at 10:30 AM
Use a planetary gear CVT.
Posted by: SJC | 19 February 2014 at 11:52 AM
Keep in mind Tesla did have a 2 gear transmission made, and then decided to drop it as not worth it.
Transmissions can be expensive. This is very likely not worth it.
Posted by: NewtonPulsifer | 19 February 2014 at 12:53 PM
Good news for car mechanics: One of the reasons GM killed their EV-1 was that it was so mechanically simple they knew their service department wouldn't be making any profit. That's the real reason their new EV has a range extender.
Posted by: ai_vin | 19 February 2014 at 12:56 PM
I think there is a mistake here. I don't think this device is intended for pure EV powertrains.
Posted by: T2 | 19 February 2014 at 07:10 PM
Well, I'm all for simplicity. But considering the state of batteries and their expense, this may be worth it in the short to medium run. I think I'll wait and reserve judgement before panning this one.
Posted by: DaveD | 19 February 2014 at 07:27 PM
Well, I'm all for simplicity. But considering the state of batteries and their expense, this may be worth it in the short to medium run.
Oh absolutely, we just have to keep in mine the trade-offs and know when perfect become the enemy of good (or best becomes the enemy of better).
Posted by: ai_vin | 19 February 2014 at 10:40 PM
Another solution in search of a problem. The Yasa-750 weighs only 27 kg and has 800 Nm of peak torque. If you want more torque, use 2 Yasa-750 motors and you'll get 1600 Nm of torque, twice the power (150 KW continuous power total) for only 54 kg of mass versus the 55 kg for this monstrosity. Like I said, a stupid solution in search of a dumb problem.
Posted by: Freddy Torres | 19 February 2014 at 10:51 PM
A solution in search of a problem. Just use two Yasa-750 electric motors: 150 kW of continuous power, 1600 Nm of torque for only 54 Kg of mass. Like I said, a solution in search of a problem.
Posted by: Freddy Torres | 19 February 2014 at 10:59 PM
@Freedy @ ai vin,
Perhaps gears are cheaper than copper, magnet, and power inverter. For tasks that require high torque and slow speed, perhaps higher gear ratio would provide higher efficiency by having less ohmic loss, since the single smaller motor is operating at higher voltages.
I think that there is merit in this design even for pure BEV application. Even more wonderful for PHEV.
Posted by: Roger Pham | 20 February 2014 at 12:21 AM
If 3 speeds are better than one, why not a 6, 7 or 8-speed transmission? Then old school engineers would also recognize themselves when they lift the hood of an EV.
Posted by: Peter_XX | 20 February 2014 at 01:02 AM
Generally speaking, it's not the transmission that the service department sees as the moneymaker. Don't get me wrong, when they break they are a big source of cash for your dealer but they just don't break that often. If they did people would complain and buy another make next time. No, the real moneymaker for dealerships is routine maintenance: Changing the fluids, belts and filters. I know I know, it sounds simple - too simple - but it's true. Even if you can do the maintenance yourself you still have to buy the parts from them.
Posted by: ai_vin | 20 February 2014 at 01:30 AM
Using variable ratios for the gearing can keep the motor running in its most efficient rpm range, i.e., where the motor draws the least current for the applied load. In the 2011 Nissan Leaf this is about 4000 to 6000 rpm and is beyond the knee of the torque curve which occurs about 3000 rpm.
I, like others, believe a CVT would work. Perhaps the Versa CVT could be modified.
Posted by: Lad | 20 February 2014 at 08:49 AM
Elon Musk was right in the initial concept of the Roadster and his 2-speed trans. Despite having a much flatter efficiency curve than ICE counterparts, all electric motors have a sweet range. It's broader than the ICE; hence the 5, 6, or more ratios don't really do anything for you, but 2 or 3 can be a significant benefit.
There are two tricks, neither unsolvable but harder than they look. The first is obvious: get the highest mechanical efficiency you can. This is more critical with the EV than the ICE, and compromises may show up in weight, noise, and shift operability. The second is more of a system issue. High-speed rotor inertia is extremely high, and goes up with the square of speed. Shifting successfully, especially during rapid acceleration, will take some fairly advanced control of motor speed. (That issue, plus the fact that the young Tesla business had very little ability to push its supplier to make engineering adjustments/fixes, probably made the initial Roadster two-speed quite prone to breakage.)
My only real question about the design shown in the article is weight. Yikes. It's a horse compared to modern automotive equivalents.
Posted by: Herman | 20 February 2014 at 11:20 AM
There is no need to make it any harder than it should be. Electric motor only need a 2-speed gear shift transmission for powerful passenger cars, or perhaps 3-5 speeds for trucks and buses. No need for automatic transmission.
A very simple and very low-cost and very light-weight 2-speed synchromesh manual tranny is all that's needed for the likes of Tesla or Leaf, etc. No pedal clutch will be needed, since there will be no idling. The car is already engaged in fist gear to start out, then at cruise, just move the shift lever to the second gear while working the gas pedal to lower the rpm of the motor to roughly match the desired rpm prior to final engagement of the synchromesh, while the synchroclutch will do the final rpm matching prior to complete gear shift. Extremely easy and fun to upshift and downshift...this is what the fun of driving is all about. Of course, those who don't want to shift gear can drive at hwy speeds on first gear, the car will still run, though a little less efficient and not as fast, but it will still run...
Perhaps, Tesla should consider a simple 2-speed pedal-clutchless manual synchromesh tranny for the next model. The sport-car enthusiasts will love it, and perhaps will extend the range and the top speed of the car somewhat, perhaps the gain will much outweigh the slight added cost and weight.
Posted by: Roger Pham | 21 February 2014 at 12:48 PM
That's funny, Roger. I assume you realize that Tesla originally used a 2-speed transmission on the Roadster. Unfortunately, the 2-speed version gave lots of trouble and they switched to a 1 speed design. Given how well their 1-speed powertrain works on the Model S, I doubt they will be too interested in going back.
Posted by: Kevin Cameron | 21 February 2014 at 04:31 PM
@Kevin,
Manual Synchromesh transmission is very simple, and in a BEV or PHEV that does not require a large dry clutch, it will be even easier and simpler and lighter. A 2-speed is even much simpler than a 5-6 speed manual transmission commonly available for even entry-level cars that retails for under $13,000. Now, a reversing gear is not necessary in a PEV because the motor can turn backward, and that ought to reduce the complexity level down another notch. So, let's see, a 2-speed manual transmission without a clutch to wear out, only 1/3 the number of gears change, and no reversing gear...AND gear shifting is NOT REQUIRED in frequent stop-and-go city traffic...in fact, gear shifting IS NOT REQUIRED AT ALL !
No gear shifting required! A gentle driver can start the car in 2nd gear and drive the entire time gently on 2nd gear, except in hilly countries, then he/she can elect to remain in 1st gear all the time. A lead-footed driver will wanna keep the vehicle in 1st gear for most of the time, except when he/she need to stretch the range of the vehicle a bit.
But, being able to shift gears will bring back the FUN FACTOR in driving, for motor enthusiasts. Driving is no longer a chore...it is a fun thing to do...in your dream vehicle...a Tesla, no less!!! Being able to be in touch with the motor and the road!
So, Tesla, please bring back the FUN in motor sport and give back the ability to shift gears. Hard-core drivers may opt for a 3-speed transmission...
NO NEED TO DEVELOP THE 2-SPEED TRANSMISSION IN HOUSE! Just outsource to a transmission specialist, and all problems will be gone! The smooth power of the e-motor will put much less stress on the gears and the shafts, in comparison to that of an ICEV, with torsional resonnance to deal with.
Posted by: Roger Pham | 21 February 2014 at 05:16 PM
Roger, have you ever driven a Model S? It's hard to imagin arguing for a return to a manual shifting gearbox because it's "fun". Outsourcing rarely means no trouble. Just somebody else's trouble, you can't fix, as pointed out correctly by so many others above.
Posted by: electric-car-insider.com | 22 February 2014 at 10:00 AM
For the 416 hp that the 85-kWh version has, it ought to do 180 mph top speed, not 125 mph. 125mph is for cars of well under 200 hp, something a Toyota Cressida (160hp) or Nissan Maxima can easily do with sub-200hp engine. Corvettes can do 190-200 for 450 hp. Bragging rights is everything for sport car enthusiasts!
So, by having a higher top gear of 1.5:1 in comparison to existing ratio, the car can do ~180 mph, and can cruise at 60-75 mph using less power. Remember that induction AC motor has lousy efficiency at below 20% load, and with that kind of power, when cruising at 60-70 mph, the load will be well below 20%, since the car is so aerodynamic.
But, if you don't wanna shift when offered with an additional 1.5 ratio gear, fine with me. Kept reving at 14,000 rpm at 125 mph. Other will prefer driving 125 mph while on second gear, with 1.5:1 ratio, the rpm can drop down to below 10,000 rpm, and the motor bearing will thank you for that, and the gyroscopic force and motor inertia will drop to 1/2.
Posted by: Roger Pham | 22 February 2014 at 04:27 PM
Well, thank you for laying out your rationale for incorporating a heavy, expensive, failure prone component into the car. Bragging rights for speeds over 125mph.
I was going to suggest that if you haven't actually driven a Model S, you look me up next time your in San Diego but now I'll have to let the opportunity pass.
Posted by: electric-car-insider.com | 23 February 2014 at 09:19 AM
Actually, Tesla made a smart decision for using a single-speed transmission, because early models will need to be as simple as possible.
However, there is such a thing as "Planned Obsolescence" in hardwares and softwares design and marketing, in order to spur continual high demand for your product. A 2-speed transmission can be developed for later models when manual-tranny enthusiasts will be looking for something extra. Those who don't want to gear shift don't have to do any shifting!
Actually, a 2-speed transmission can allow reduction in motor and inverter size as well as battery pack size for the same performance and range, hence will help address both the weight and cost gain associated with the 2-speed transmission. Actually, since steel gears are cheaper than copper, Lithium and power electronics, perhaps more profit can result!
Posted by: Roger Pham | 23 February 2014 at 02:00 PM