Among the companies that have long been associated with diesel engines or the gearboxes that work with them and which are now starting to expand their reach into electric power is Allison Transmission.
As part of that shift, the American giant purchased AxleTech’s electric vehicle (EV) systems division and UK-based Vantage Power earlier this year. That signalled its intent to significantly build upon its existing experience in the diesel-electric hybrid sphere.
Those acquisitions have been key to the unveiling of a prototype of Allison’s ABE series heavy-duty electric drive axle.
In the first specific incarnation seen, the ABE130D, it has a dropped centre. That permits 700mm of low floor clearance between the wheels. It is also available in a conventional arrangement that will suit coaches.
The ABE series comprises an innovative system. It must if it is to compete in what is already a crowded marketplace. It has a 13,000kg maximum weight tolerance. Each motor has a nominal output of 123kW, and a peak rating of 200kW.
Notably, both gradeability and top speed are uncompromised. That has been accomplished using an individual two-speed transmission coupled to each of the two motors.
Not entirely new
While Allison’s association with full electrification is only beginning, its experience with diesel-electric hybrid drivelines, particularly in the US transit bus market, has seen over 8,500 units placed into service since 2003.
The ABE series will be available packaged in two ways: One as the axle on its own, the other as part of a full electric powertrain, including batteries and the control system, says Chief Commercial Officer, Electrification, Alex Schey.
That choice will allow vehicle OEMs to either leverage the knowledge of Allison to integrate electric power into their products with relative ease, or for those who already have developed componentry of their own to incorporate just the axle.
Key to making the ABE series suitable for a wide variety of applications are its two ratios. That element of the axle is what delivers excellent gradeability and a capability for higher-speed cruising. How it is applied is the clever bit.
“The two-speed transmission makes the axle up to 16% more efficient than comparable products that are not so equipped,” says Alex.
Shifts between the two speeds can be made by the Allison electric axle while traction power is maintained. As the axle has a motor and transmission for each wheel, changes can be strategically staggered. That ensures smooth operation throughout the speed range.
The greater efficiency that the two speeds bring gives the potential to benefit the most important thing in any EV: Range. Alternatively, OEMs will have the opportunity to offer a vehicle with a comparable range to their competitors, but with a substantially smaller battery pack.
A clever design
The axle is packaged in a compact manner. On the drop-centre ABE130D, shown publicly for the first time at Busworld recently, the power electronics are mounted within the axle ‘cradle’.
On this variant of Allison’s electric axle, the only high voltage electrical connections to the rest of the vehicle are the DC cables. That leaves the high voltage, three-phase cables and associated packaging and validation integrated directly into the axle from the manufacturer.
Mounting as much as possible as part of the axle is deliberate. It is to minimise the work needed from the vehicle OEM. Standard suspension pick-up points are used, further simplifying that process.
While locating the power electronics beneath the 700mm-wide drop centre may sound like it invites damage, Alex points out that the area has been well protected as part of the design process.
Additionally, as the axle is, by definition, unsprung, the central area should remain clear of speed humps.
Part of a family
Allison will first productionise its electric axle in a non-dropped centre form suited to truck applications. That line of products will be known as the AXE series.
The bus variant is the same in terms of motors and other electrical components. A timeline to production is currently being established.
“Allison already has a large footprint in the bus industry. We are speaking to many vehicle OEMs about the electric axle,” says Alex. He adds that Allison has also entered into early discussions with some coach manufacturers.
Allison has no plans to offer front axles. But it is working on a drive example with a 10,000kg weight tolerance to complement the ABE series. That will potentially suit lower GVW coaches and buses. One that is even lighter may follow that.
“The larger vehicle OEMs typically take on integration of electrical systems themselves. That is why we will offer the axle both as a ‘plug and play’ model and one that can work with components from other suppliers,” says Alex. “Smaller OEMs may prefer to take advantage of the full system.”
Allison is not the first transmission manufacturer to move into electrification. Its new axle has promise. With the growing Vantage Power business acting as an electrification centre of excellence, the ABE130D may be the first in a range of products for the zero-emission market.
