EAxles Gain Traction for Truck Electrification
OEMs are developing and testing axles with integrated electric powertrains to electrify trucks of all sizes.
Development of electrified drivelines is rapidly ramping up at OEMs and tier one suppliers. With a wide variety of vehicles suddenly in need of electrified drivelines capable of matching or surpassing the capabilities of the existing ICE powertrains, suppliers are providing an array of solutions to meet customer needs.
For the electrification of light and medium duty trucks, one of the technologies rapidly gaining interest is electric axle or eAxles. An eAxle is a traditional axle housing and differential incorporating an electric motor, an inverter and a thermal management system. Most eAxles are also equipped with a multi-speed transmission for high and low torque demands. While the basic concept is similar across the industry, suppliers are taking varying approaches to put these axles on the roads depending on their target vehicle segment, required power output, and desired vehicle range.
The benefit of an eAxle from the OEM standpoint is that they offer the capability to electrify new and legacy chassis with minimal engineering changes, which in turn provides a shorter lead to bring such a vehicle to market. The scalability of eAxles also enables suppliers to develop a single design which can be easily adapted for use in light and heavy-duty applications. The following is a look at several companies currently developing and testing eAxles for existing and future trucks.
ZF’s scalable design
ZF recently demonstrated their prototype truck eAxle at their Next Generation Mobility event at M1 Concourse in Pontiac, Michigan. ZF’s unit is a solid axle with an integrated electric motor, inverter and transmission. It is scalable for 400 V and 800 V architectures with a power output range of 180 to 350 kW. Max torque output is reportedly 15,000 Nm (11,063 lb-ft). ZF states that an integrated inverter in transmission housing is an option and that customers have a choice of various differentials. Rear wheel steering is also available.
The axle is designed to be packaged into legacy and future chassis as a complete unit so that OEMs can upfit vehicles with very few engineering changes. ZF packaged a prototype version of their eAxle into a current generation Chevrolet Silverado 2500 which was used as a demonstrator for SAE Media and other journalists. The eAxle in the demonstrator was rated at 300 kW and 10,200 Nm (7,376 ft-lb).
The batteries powering the demo vehicle were supplied by CATL. They operate on an 800V architecture and can also operate with a 400V system). In the demo vehicle, there were four battery packs positioned under the floor and two more in the bed. ZF noted that this would not be the production configuration and their placement was purely for prototype purposes. Each pack had a rated capacity of 35 kWh for a system total of 210 kWh.
From inside the cabin and behind the wheel, the axle’s operation is quiet and seamless. Though the motor, inverter, and other components do add unsprung weight, handling was not adversely affected in a noticeable manner even combined with the additional weight of the battery packs. Though SAE Media did not get to drive the demo truck with a trailer or a load, the benefits in instant torque when towing or hauling would be a welcome attribute.
It’s clear that the acceleration capabilities of ZF’s eAxle aren’t meant to pin occupants in their seats. Rather it is designed to match the hauling capabilities of today’s current crop of light and medium-duty diesel powertrains. The ZF did not give specific towing ratings for this prototype, but it expects that a production eAxle fitted to a similar truck would be capable of hauling 10,000 lb (4,536 kg) or more. Range estimates were also not provided as they would depend largely on application and battery pack configuration.
“Our focus was to build and integrate a highly efficient drive unit for a 3/4-ton pickup truck that gives the vehicle the same capabilities as its ICE counterpart,” said Jörg Trampler, program director-Electrified Powertrain Technology. “Our first prototype already has a peak efficiency of 95 percent.” ZF also stated that their eAxle is scalable for up to class vehicles up to Class 6 with power ranges and that four-wheel drive systems could also be implemented. The prototype eAxle was reportedly built utilizing many off-the-shelf ZF components, including the motor, transmission, and inverter. Though no OEMs have currently stepped up to the plate to implement ZF’s eAxle offering, the company has stated that it will begin production of the unit by 2026.
Schaeffler keeps it cool
Schaeffler has also announced an electric drive axle of their own design. The company states that eAxles are “a key element of our electric mobility strategy,” and that their unit is suitable for both light and medium-duty applications. The company is also claiming a major technological advancement with their unit, the integration of the thermal management system into the axle along the electric motor, power electronics, and transmission. The upside is that packaging all four components into the axle drive results in a more compact and lighter assembly.
The company is targeting North America as its main point of sale for its eAxle and will sell it as a “ready-to-fit unit” for both light and medium duty vehicles. Schaeffler also detailed the benefits of their eAxle’s thermal management system, particularly in extreme climates which can negatively affect battery performance. “The thermal management system has a significant influence on the efficiency and comfort of the vehicle,” says Dr. Jochen Schröder, head of Schaeffler’s E-Mobility business division. “(This) creates a highly integrated and compact complete system which requires significantly less space than non-integrated solutions.”
Schaeffler engineers assert that their design also reduces the number of required hoses and cables, meaning less energy is lost due to heat transfer. “The greatest advantage of the (integrated) system is the optimized interaction of the individual subsystems,” Schröder explained. The control system efficiently transfers heat from components which need to be kept at a stable temperature, such as drive system electronics and motors, and utilizes it for tasks such as warming the interior. The system also regulates the temperature of the battery to maximize vehicle range and reduce charge times.
The thermal management system is charged with natural carbon dioxide refrigerant. Schaeffler states that carbon dioxide refrigerant has less environmental impact than conventional refrigerant and that its physical properties are more efficient for heating and cooling. The company claims that up to a 96% overall efficiency rating is possible for this system, which translates into increased range. Schaeffler manufactures components for electric axles at locations in Hungary and China. A production facility is being set up in Massachusetts for where hybrid modules are already being manufactured and a new lead plant for electric motors is now being built in Bühl, Germany.
Allison powers-up commercial trucks
On the commercial end of the eAxle spectrum, Allison Transmission has begun exhibiting their eGen Power axle at trade shows across Europe and North America. Allison’s eAxle lineup consists of three units, the 100S, 100D, and 130D. These axles are intended to cover the needs of the global medium- and heavy-duty truck and bus markets with a range of weight ratings and power outputs.
The 100S is the lightest duty axle and features a single electric motor rated at 227 kW @ 650V for continuous operation and 326 kW of peak output. The 100s has a maximum wheel torque of 26,177 Nm (19,307 lb-ft) and a GAWR of 23,000 lb (10,433 kg). The 100S was designed principally for medium and tandem-axle heavy-duty vehicles in North American markets.
The 100D carries the same weight rating as the 100S but is a dual motor design with a max torque output of 47,018 Nm (34678 lb-ft) and a 454-kW continuous/652-kW peak power rating. The 130D maintains the same core components, kW rating and peak output as the 100D, but a greater GAWR of 28,660 lb (13,000 kg). The 130D was specifically designed for the European and Asia Pacific markets, where many commercial vehicles require a heavier axle weight rating than North American applications.
All three of Allison’s eAxles have a recommended voltage range of 550-850V with a min/max of 400 and 900V respectively. Each axle can also be upfitted with either drum or air actuated discs and are reportedly compatible for most on-highway applications. Each axle also features a two-speed gearbox integrated into the central housing, which enables high torque operation when needed as well as efficiency at cruising speeds. Differential lock functionality is also a feature across Allison’s eAxle range.
Allison states that several commercial truck OEMs have already integrated their eAxle into existing chassis. Emergency One, a U.K.-based manufacturer of fire and rescue vehicles, has implemented the eGen Power 100D into their E1 EV0 platform on a MAN TGM chassis. The vehicle was presented at Interschutz in Hannover, Germany. Allison has also stated that Hino Trucks has been validating its eAxle in its XL series heavy duty BEVs. Allison and Hino demonstrated an 100D-equipped Hino XL tractor NTEA Work Truck Week in Indianapolis, Indiana.
Allison is marketing their eGen Power axles as a bolt-in solution compatible with current commercial frame designs. “The next generation of our eGen Power 100D are now being built at our Auburn Hills, MI, electric axle development and manufacturing facility,” said Rohan Barua, VP, North America Sales for Allison Transmission. “Allison’s extensive investments and experience in electric hybrid technology allow us to be well positioned to commercialize a broad portfolio of fully electric propulsion solutions, including electric axles.”
Shorter lead times benefit
Suppliers ZF, Schaeffler, and Allison are well on their way to bringing electrified drive axles into the light and heavy-duty truck electrification space. For OEMs, the benefit of an eAxle is the capability to electrify new and legacy chassis with minimal engineering changes, which in turn provides a shorter lead to bring such a vehicle to market. The scalability of eAxles also enables suppliers to develop and single design whin can be easily adapted for use in light and heavy-duty applications.