NexxtDrive DualDrive e-CVT Prototype Promises Fuel Savings, Hybrid Capability
14 September 2005
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| NexxtDrive’s DualDrive Transmission |
NexxtDrive (formally DriveTec UK), a UK-based design and development company, used the Frankfurt IAA to promote its prototype DualDrive, a power-split electronic Continuously Variable Transmission (e-CVT) with dual motor-generators.
NexxtDrive claims that the DualDrive can provide potential fuel and CO2 emissions savings of up to 20% even in non-hybrid applications. With the addition of a more robust energy storage and management system enabling full hybrid capabilities, NexxtDrive projects savings of up to 35%.
The two motors are assembled concentrically, which, combined with an extremely compact planetary gear set, allows the whole system to be engineered into a drivetrain with minimal impact on configuration. NexxtDrive says the DualDrive can be packaged in the same space as a conventional manual gearbox.
The DualDrive is based on an input split design (such as used in the Toyota and Ford hybrid powertrains), in which the single planetary gear set serves as the power split device. The system works without the need for clutches, torque converters or any form of mechanical gear change. In use, the majority of power is transferred through the mechanical path with very low losses, while a small fraction (never more than 25%) is transferred electrically between the motor-generators.
(A compound split approach, such as that being taken notably by GM/DaimlerChrysler/BMW, uses dual planetary gear sets, and dual disconnect clutches in addition to the dual motors.)
In plain CVT mode, controlling the relative speed of the two electric motors gives full control of the gearbox ratio, allowing the vehicle’s engine to operate at its most efficient speed in all conditions, delivering potential fuel and CO2 emissions savings of up to 20% even in a non-hybrid application, according to the company.
The electric motors can also replace the vehicle’s conventional starter motor and alternator to deliver stop-start functionality for further fuel savings in traffic along with a further reduction in total package cost.
Additional battery storage and energy management systems can provide support for a hybrid application, without altering the DualDrive gearbox in any way. In such applications, the company looks for CO2 reductions of up to 35%.
NexxtDrive has a completed detailed prototyping and simulation of the DualDrive system. In its portfolio of designs is a solution for rear-wheel drive passenger vehicles of up to 200 kW and extremely compact designs for front-wheel drive vehicles.
In studies currently underway for an unnamed OEM, NexxtDrive has demonstrated that the compact design of DualDrive can provide automatic transmission capabilities in vehicles where it has hitherto been impossible to package an automatic transmission to date. The system can also be scaled up for use in four-wheel drive, truck and bus applications.
DualDrive substantially reduces the risks for car makers looking at hybrid and CVT technology. With a similar unit cost to conventional automatic transmissions and straightforward integration into existing vehicle platforms, it will eliminate the daunting costs associated with development of vehicle-specific transmission solutions.
—Rod Keech, Chairman of NexxtDrive
NexxtDrive is also working with Integral Powertrain on SuperGen2, a supercharger technology. (Earlier post.)
It's like a Prius in a box! To bad there is no info here (or on the linked website) on what power the generator and the motor are capable of. It would be great if this became available as an aftermarket clutch/gearbox replacement for regular manual / automatic cars.
Posted by: Kweksma | 15 September 2005 at 05:09 AM
Let me see if I understand this correctly. This uses a set of motor/generators to provide smooth and consistent power and torque output for ICEs. When used on an ICE alone, replacing the standard clutch or transmission, it provides up to 20% improvement in efficiency, and when used in conjunction with battery storage, it can do up to 35% improvement?
I don't quite understand how this works to improve the output torque of an ICE at low RPM, if you don't have energy storage in batteries (which could be used to provide additional torque at low vehicle speeds). I understand that they're saying that the engine can run at a more efficient speed, which would hint that the ICE never runs at a low RPM, but that seems wasteful.
Kweksma: The article says it can do up to 200kW of power (= 268 HP).
Posted by: Caoimhan | 15 September 2005 at 08:20 AM
Yes, they’re basically saying that they have produced a highly efficient electronic CVT--that on its own merits will save up to 20% (which seems rather high compared to what other CVT systems deliver.)
Improvements on the CVT front come not from an external supplement to the drive torque, but just from the more efficient operation of the engine and transmission (e.g., precisely the right gear for the right speed, condition, etc.)
Then if you begin to add in battery storage and energy management system, you increase your efficiency through stop-start, power boosting, regen braking, etc. The 35% theoretical gain is going to be limited by the motor capability and energy storage.
Or to look at it from another perspective, they designed a mild-hybrid transmission--but without the battery and energy storage systems, and hence the hybrid functionality--which serves to replace a conventional CVT and delivers what they claim will be a significant increase in efficiency relative to a conventional transmission.
All those figures, though, are the result of simulations, not actual production or road testing. So, we'll see.
Posted by: Mike | 15 September 2005 at 10:05 AM
First, I want to compliment Green Car Congress for the fine job of reporting on these types of cutting edge technologies. I really think this drive system is a brilliant breakthrough.
As near as I can tell, the electric motors/generators between the internal combustion engine (ICE) and output drive shaft are connected by a planetary gear arrangement. The planetary gear speed is adjusted by varying the relationship between the three componets (sun gear, planetary gear and ring gear). I assume that there is a motor/generator connecting the sun and ring gear, and another motor generator on the output shaft. The output speed of the drive shaft is varied by changing the torque/speed relationships between the two motor/generators inside the planetary gear. The end result is that the ICE can run at one speed, while the drive shaft speed can be varied at will. The planetary gear relationship transmits most of the power, while the motor/generators transmit a maximum of 25% of the power. The two motor generators have a combined efficiency of about 80% (=90%x90%). But they only transmit a maximum of 25% of the power, so the electrical portion of total transmission losses are only 5% (25% x (1-80%)).
The beauty of this compact design is that it not only has all of the hybrid car benefits, but it also can run in an all-electric mode as a plug-in hybrid, and is compact enought to fit in almost any vehicle, including retrofitting existing cars.
Posted by: James White, PE | 15 September 2005 at 10:17 AM
Thanks for the clarification. It sounds like a great idea. The main thing holding back technologies like this, however, is patent greediness. If the promises this transmission makes hold true, this should be installed in every new car coming out of the factory. But the automakers won't do it, unless the price is competitive with current transmission technologies, because they won't want to add to their costs. If the technology licensing costs are too high, it will price the end product out of the OEM market.
Posted by: Caoimhan | 15 September 2005 at 01:14 PM
I wonder if this design will have the low speed limit in pure EV mode as the Escape and Prius have, with regard to the sun gear's motor-generator having to spin in reverse at a higher speed than the motor is rated for, such as 10,000 RPM in the Prius II? If they have solved that with the motor design, then they really do have something special.
Posted by: Schwa | 17 September 2005 at 01:42 AM
I don't think there's any big patent issue here. This is exactly the same concept that Toyota uses with the Prius, but when I checked into it, I found that even Toyota did not own the basic patent. The concept seems to have been around long enough to be public domain. Naturally, Toyota owns a bunch of patents on various refinements and implementation methods. But the specific configuration implemented here may be different enough to avoid any infringement on Toyota's patents. (Caveat: I'm not a patent lawyer, and my research has been superficial.)
As to cost, one would hope that when it enters volume production, the cost of the two motor-generators will not be significantly more than the cost of the clutch and gear box that it replaces.
I'm a little surprised by the statement that no more than 25% of the power flow from engine to wheels ever goes through the motor-generators. With a single mechanical gear ratio, I'm not sure that's possible. Having two mechanical gear ratios, controlled by clutches, does enable the power flow through the motor-generators to be kept small, but at considerable added expense in mechanical components. It may be that the 25% they're refering to is actually 25% of the maximum engine output. That I could believe.
Posted by: Roger Arnold | 23 September 2005 at 07:19 PM
Go to the Antonov discussion forum: http://www.antonovforum.com
It is the biggest discussion forum there is. We talk about all kind of possibilties about this future automatic transmission technology. It is a Dutch forum, but we all speak English so do not hasite to start a discussion or te be an member.
We hope te meet you all on our Antonov discussion forum
Regard Warren2
We have also an Antonov-Clubsite.
http://www.antonovforum.com
http://www.antonov-clubsite.nl
Posted by: Ron Froger | 24 September 2005 at 03:43 AM
I've studied both the Prius and GM/DC 2-mode systems and one weakness I've identifed is that all these systems rely on battery power alone to drive in reverse - if you've driven the Prius you'll know. I wonder how this system copes with reverse - a brake on the ring gear perhaps?
Check out www.torotrak.com for information on mechanical IVT.
Posted by: JB | 24 September 2005 at 12:13 PM
This is a great idea, but what are the cost compared to existing systems?
Posted by: Doug | 20 January 2006 at 10:08 AM
i want working of revers gear of dual clutch transmision
Posted by: anil | 07 April 2006 at 01:30 AM