Issue: Jan 2018

Full integration of electric motor and intelligent axle provides “best of all worlds”

by Nick Palmen


Two-speed gearboxes for electric vehicles combined with an intelligent axle and torque delivery system put fun into the driving of battery-powered and hybrid vehicles, while at the same time extending the range.

Automotive Industries (AI) asked Dr Ray Kuczera, SVP of Technology and Engineering, GKN Driveline, to explain what eTwinsterX is.

Kuczera: GKN is a world leader in what we call eAxles and eTransmissions. We have over 400,000 in the market right now. eTwinsterX represents a big evolution of that. All the systems in the market today are single speed, with the exception of the one for the BMW i8, and GKN supplies that as well. eTwinsterX is a two-speed transmission, which also vectors torque output between the driven wheels.

We provide the optimum amount of torque to each wheel through our Twinster coupling which, combined with a two speed transmission and a very powerful electric motor, gives you the best of all worlds. You’ve got very high torque for launch because of the low ratio of the first gear, and you’ve got very high efficiency for regular vehicle driving because of the efficient layout put into the gearbox. It is very efficient in second gear, which is where you are going to do around 85% of your driving.

So you’ve got excellent power, maximum efficiency and you’ve also got the great dynamic handling characteristics from the Twinster, providing vectoring and differential locking.

AI: What are the advantages over conventional electric drivelines?

Kuczera: Let’s start with the differential first. The vast majority of vehicles use an open differential, which is not an intelligently controlled device. Torque goes to whatever wheel has the least resistance, which is generally not the best selection for the vehicle. With the Twinster we replace the differential with twin couplings in order to vector the torque.

The second advantage is the two speeds. The first is for excellent launch power, and the second for excellent efficiency to a maximum vehicle speed of 250kmph. With a conventional hybrid vehicle you would usually disconnect the rear axle above a certain speed. This system allows you to keep the axle turned on all the way to top speed.

AI: How do you combine an integrated e-motor, two-speed electrified transmission and torque vectoring within a complete eAxle system?

Kuczera: I would say through very clever and unique engineering. GKN has been at the forefront of integrated eAxle, which integrates the electric motor and the transmission for some time. When the first generation of vehicles came out the transmission and motor were fitted as separate sealed units.

If you look at the newer generation, like the Volvo SC90 eAxle, they share a common shield because one of those interfaces has been eliminated. It is a semi-integrated one. A completely integrated one is when they don’t even have a shield, so the shaft of the motor is essentially part of the gearbox. There is no separation between the motor and the transmission.

AI: Can the integrated eDrive system be adapted for use in both fully electric and in hybrid applications?

Kuczera: Absolutely. It was originally designed for hybrids, and that’s what it was first used for – as a supplement for the power provided by the internal combustion engine – but it is also is suitable for front and rear-driven battery electric vehicles.
AI: How does the new two-speed transmission maximise efficiency and increase performance? Kuczera: That is through the two different gear ratios. The first gear ratio allows maximum launch torque and also – if you wanted to – allows the vehicle to go off-road because with that low gear you can climb over rocks and go up hills. Second gear provides efficiency and higher speeds. You don’t have to do that single speed trade off that you see in all the current cars, where you have to have a certain ratio for both pull off and top speed.

AI: How does Intelligent Twinster torque vectoring technology improve driving dynamics and safety?

Kuczera: This is a great piece of technology. It is very exciting. We’ve used this for a while in normal drive vehicles. The Range Rover Evoque was the first application. This allows the vehicle to be very capable off-road as the Twinster coupling can act as either a locking differential or a limited slip differential. You can also use it for performance vehicles, as seen in the Ford Focus RS. Going into a turn I can send all the torque to the outside wheel and actually use the electric motor to vector the torque as well to try to oversteer the rear to give you much more dynamic cornering feel.

This overcomes a lot of problems you see with a lot of hybrid cars today. They feel heavy and not exciting to drive. On the safety side the Twinster can give you great straight line stability and obviously traction equals safety.

AI: When can we expect eTwinsterX on the market?

Kuczera: We have started demonstrating it to customers and there is a lot of interest. The Twinster is well known and very well accepted in the market, as are the other components. Introduction to the market will be based on the OEM production schedules.

AI: What is next for GKN Driveline? 

Kuczera: GKN is known as the world leader in CVJ technology, a world leader in eAxles, and a world leader in all wheel drive. We are also the world innovator in all those spaces. eTwinster is a great example of GKN innovation. We are not just resting on our laurels and saying today’s technology is good enough, let’s ride for the next several years.

We need to continue to make sure we push using new materials, leveraging our unique experience also as a system integrator and as a general driveline expert. By bringing that knowhow and technology to the OEMs we can really demonstrate our value and continue to push the technology forward. This two-speed transmission is a great example of it. We are doing it in a way that no one’s ever done it before and we are very proud of it.

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