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21/05/2018
User friendly EVs with GKN eAxle

From engine to wheels

 

The EV revolution is close at hand and suppliers are quickly adapting. GKN, for example, unveiled its eAxle, an electric axle that can easily be integrated into future EVs

Nicodemo Angì

It may be hard to believe but at the end of the 19th century, electric cars were more common than fuel driven vehicles. In the United States, for example, EVs were particularly appreciated for their silence and lack of smelly fumes; furthermore, the absence of a hand-crank made electric cars particularly welcome to ladies. Another advantage, which may seem incredible nowadays, was the greater availability of charging stations: the widespread network of gas stations we are so accustomed to nowadays, was not even remotely imaginable. However, the discovery of large oil fields in Texas overturned the situation making the use of petrol driven vehicles more practical, thus relegating electric mobility to an insignificant role. However, recently things have been taking a different turn once again: Tesla, has broken the ice with its 2008 Roadster (a 2-seater sports car developed from a Lotus Elise) and then continued with expensive cars capable of delivering outstanding mileage.

 

“Electrified” components

Nowadays, it does seem rather logical to think that once the industry has decided to turn to electrically powered vehicles, thanks also to increasingly stringent emissions regulations, the scarce number of charging stations would likely grow considerably in the near future (just as it happened with fuel stations a century ago) reducing “mileage anxiety” to a thing of the past.

As manufacturers come up with original ideas and projects, and announcements follow one another, without a break, on specialized media, component producers are also preparing for the electric revolution.

GKN, a historic British steel company that turned to making automotive components back in the 60s, is the perfect example of this trend. And it doesn’t end here, the British giant, in fact, continues to look ahead: as early as the 80s it diversified into aerospace and today is looking with growing interest to the electric revolution sweeping through the automotive industry.

Its state-of-the-art eAxle solution, in fact, is perfect for a wide range of versions and applications. This compact unit boasts a shift mechanism that sits on the input shaft instead of the intermediate shaft in the middle of the transmission. To have an electric power-unit  just add a battery and an electronic management system. The limited volume of the unit makes it easy to place it somewhere under the body. Adopting a co-axial layout - meaning that transmission input and output are on the same axis - with a lay-shaft design, the volumes are comparable to that that of an electric motor or slightly larger.

The first version of the eAxle already equips the BMW Series 2 Active Tourer as well as the hybrid Volvo T8 Twin Engine, and can be used on all-wheel drive vehicles without the need for a bulky transmission shaft. The rear wheels are connected exclusively to the electric motor capable of providing 65 kW / 88 hp with 240 Nm of torque. The engine reaches 13,000 rpm (and no wonder, considering the perfectly balanced rotating parts) which allows the use of a simple gear reduction with a fixed ratio of 10: 1.

 

Smoke free cabs

The solution is very efficient (GKN declares a mechanical efficiency equal to 97.5%) and an electromagnetic coupling avoids dragging the motor when it is not needed; the overall dimensions are comparable to that of the conventional rear-wheel drive unit found on a  Volvo XC 90.

The versatility of the eAxle becomes even clearer when we look at another application: the eAxle, in fact, is made to motorize the new version of the classic and glorious London Black Cab.

The TX eCity architecture is optimized for urban traffic and uses the eAxle as its main engine: following this decision, a high-performance 120 kW / 163 hp unit was used. The batteries are not very large and, to reduce the number of unproductive stops to recharge the batteries, a solution was found: using a range extender. It is a small petrol engine, at the front end of the car, used only to charge the batteries. Reason why the power is rather limited (on the BMW i3x, for example, it’s only 28 kW) since the main engine will hardly ever be used to its full potential, and, when that happens, the battery pack will supply the needed power. The li-ion batteries, however, guarantee a range of about 130 km at zero emissions but the energy recovery braking system, if frequently used in the city, could increase this value; the range extender allows a total mileage of up to 600 km. The production of the third millennium Black Cab has already begun near Coventry. This vehicle meets the new and stringent requirements set by the Transport for London program which includes a range of 48 km with zero emissions and a maximum of 50 grams of CO2 / km at the most.

 

High electric performance

The potential of the eAxle does not end there, since the eTwinsterX version also features a GKN-designed two-speed transmission, as well as full torque vectoring capability.

The torque vectoring of the differential means that the system can precisely control the distribution of torque on all four wheels, which improves handling in all kinds of conditions besides providing additional aid to the ESP system. Adjusting the torque, for example, enhances the vehicle’s agility including its ability to over-speed the outside wheel in a corner to induce a yaw moment, helping to bring the car into a tighter line when turning. The GKN eTwisterX uses 2 electronically controlled multi-disc clutches, one for each axle shaft, so as to continuously vary the torque of each wheel. This solution is also suitable for off-road use and guarantees four-wheel drive safety and performance on hybrid systems (with an axle powered by petrol engines) and EVs, using one unit per axle.

The compact size of the unit stems from the same co-axial design already seen in the eAxle, and the exclusive 2-speed gearbox can be used also on Hi-performance electric cars, in which the motor’s inherent ability to guarantee high revs is not enough to overcome the limits of a single-speed gearbox.

The sporty soul of this solution (which offers great off-road traction too) is demonstrated by its use in hybrid supercars such as the Porsche 918 Spyder and the BMW i8.

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