eS4500i: Highly Integrated Electric Drive Unit for Multiple Applications

Marco Silvestri, Chief Engineer, Dana Incorporated

Across all our actions, we never lose sight of a guiding vision toward a zeroemissions future. This has powered our first-mover advantage in electrification.

At Dana, we strategically invest in technical competence − designing, engineering, and manufacturing the components of a complete e-Propulsion system in-house. These innovations include efficient EV systems and new electrodynamic products like motors, inverters, controls and software, battery cooling systems, and metallic bipolar plates for fuel cell applications.

The legislation for pollutants and emissions is driving OEMs to design their reduction programs to align with aggressive timelines — accelerating the adoption of electrification. These mandates, coupled with corporate commitments from OEMs, will significantly increase the demand for electrified vehicle architectures, the main components of a Battery Electric Vehicle.

Dana’s solution is the Spicer® Electrified eS4500i e-Drive Unit − a highly versatile 3-in-1 electric drive unit (EDU) that converts the stored electrical energy from the battery into mechanical power to the wheels.

eS4500i Platform

Utilizing competencies from Dana’s global network of technology centers, the highly integrated eS4500i comprises an inverter, motor, one-speed geartrain, open differential, and optional park-lock.

The thinking behind the eS4500i was really to provide more than a single EDU. What was needed was a versatile platform offering multiple ratios and integrated design of motor and gearbox while also taking into consideration efficiency, optimized packaging space, and lower weight.

To cover multiple applications, five different ratios were designed (macrogeometry) with the same center distances, same gear width, and similar envelopes diameters also recombining the same gears to reach five different ratios.

In this way, with a unique design of the housing and bearings, the eS4500i can host five different gear-trains to be able to match different vehicle requirements in terms of maximum torque and speed. From figure 2, it’s appreciable the spread of torque and speed that the system can cover with the five different ratios options. A limitation of around 4,500 Nm (as max nominal output torque value) has been decided for ratio 15.1 and 13.1 because of match with other Dana products but useful in case of demanding vehicle gradeability and high continuous torque.

Highly Integrated Layout

The design of the gearbox and the motor was improved by integrating the components as much as possible to provide a light, compact, and power-dense EDU.

For the eS4500i, it has been decided to have a highly integrated design between the motor and gearbox to save weight and to improve the power density.

Only three housings compose the structure of the EDU and shape two separate environments: a dry one for the motor and a wet one for the oil-lubricated gearbox.

Referring to figure 3, from right to left:

The motor back-case supports the rear motor bearing and becomes the seat for the stator and the internal side of the motor cooling jacket. The helical cooling path is made by die-cast molding for manufacturing efficiency.

A carrier housing supports the front motor bearing and becomes one of two gearbox housings as well as the external side of the motor cooling jacket to complete the sealed channel.

The cover housing enclosures the gearbox components.

One of the main characteristics of the highly integrated layout is the over-hanged pinion gear directly mounted on the head of the rotor shaft. Between the pinion gear and the motor front bearing, there is a parking gear.

The layout is completed by an intermediate shaft and an open differential, both supported by taper roller bearings.

This new layout reduces the interfaces between the gearbox and the motor to achieve a precise axial centering of the gearbox with the output shaft of the motor. This also allowed a significant reduction of components like having only two bearings on the input axis, a reduction of the number of housings and a significant a reduction of fasteners.

The EDU is completed by the inverter that is direct-mounted on top of the motor with the high voltage connections passing through the back housing.

The park-lock adds another degree of flexibility because it can be added or removed on customer request. This park-lock option is already patented and in series production, with a mechanism layout now upgraded with a new smart actuator.

Motor and Inverter

The eS4500i is powered by a propulsion system composed of an asynchronous dry 450V motor and with a Dana 2nd generation directmounted inverter.

The propulsion system is cooled by water-glycol and the theoretical performance curves are shown in fig. 5 at 65°C coolant temperature.

Since this propulsion system is for a medium voltage (450V) application, Dana decided to use the latest IGBT module technology for this inverter over the newer SiC MOSFET technology. This allows the use of our proprietary Reflex gate driver technology to achieve the most cost-effective solution for this voltage range.

Conclusion

As a Tier 1 supplier, Dana offers its new eS4500i EDU, an off-the-shelf solution on the path to electrification, with a compact and light package for a wide range of applications.

The eS4500i is equipped with the well-known Dana differential from a robust off-road heritage, with an optional park lock system.

Dana is offering its all-new configurable off-the-shelf eS4500i EDU to a multitude of segments and applications. This work is the result from the synergy between the different technical centers and other global Dana branches, putting together different competencies. With its power density, reliability, and cost competitiveness, this product will contribute to our customers’ success on the path to electrification.

JJE 2-Speed Electric Beam Axle for Medium Duty Truck

Ping Yu, CEO, Chief Engineer, Founder, Jing-Jin Electric
Dr. Yang Cao, Transmission Senior Supervisor, Jing-Jin Electric

The electrification of medium duty truck grows rapidly. JJE’s newest electric beam axle family can cover up to 11T (or class 6 in North America) trucks, including single-speed and  2-speed systems. Multiple advanced technologies are integrated into the electric beam system, such as bi-stable electromagnetic bi-directional shifting clutch, bi-stable eLocker, linear park lock system, and active cooling and lubrication. These functions’ control is all in the electric beam axle’s inverter, which is mounted on the axle. 800V, high power hairpin motor and SiC inverter are used to produce strong capacity, and high efficiency across wide operating range.

The 2-speed axle features a high efficiency hair-pin electric motor, a 400kW SiC inverter with “safe towing” feature, electro-magnetic shifted 2-speed gearbox, with neutral position that also serves as a disconnect, bi-stable differential eLocker, linear park lock system. With 2-speed gearbox, the beam axle’s wheel-end torque is up to 15,000Nm, and the maximum vehicle speed is over 160km/h. Integrated design for motor and gearbox reduces the axial length of the system.

JJE’s 2-speed beam axle features high performance and high output speed, with little power degradation at high speed. Its efficiency is high over a wide speed range – especially in comparison to a single speed axle thanks to the 2-speed gearbox.

Fig. 2 JJE Electric Beam at the Rear of a Truck Demonstrator

Fig. 3 JJE 2-speed Electric Beam Performance

Electric Motor

JJE has a mature hairpin motor designs to cover performance requirement of wide range of vehicles. For this electric beam axle system, the electric motor’s peak power reaches 420kW at 650Vdc, with 97.4% maximum efficiency, and over 90% of the efficiency map is above 88%. The water-oil combined cooling allows the electric motor to produce high continuous power.

2-speed Gearbox

The 2-speed gearbox provides high launch torque, high vehicle speed and high efficiency over broad duty conditions, and helps contain motor’s top speed for better reliability and durability. It also broadens high efficiency operating range, and significantly reduces thermal loading in the system at high speed. A 2-way, bi-stable electromagnetic clutch is used for shifting between 1st gear and 2nd gear, with neutral position. The neutral position is a natural “disconnect”. Combining this rear axle with neutral with a constantly powered front eAxle, the vehicle efficiency can be improved. JJE’s patented DirectFluxTM Bi-stable eLocker enhances functional safety of the locker and eliminate the power consumption. Proven park lock system is implemented on the motor shaft, or the “lowest torque” point of the system. An oil pump provides active oil lubrication, which allows low oil level in the gearbox, reduces gear churning loss.

SiC Inverter

The electric beam axle has an 850V SiC inverter integrated on it, with functional safety level up to ASIL D. Multiple functions − such as motor control, differential locker control, 2-speed transmission control, park lock control − are integrated in the inverter, taking advantage of inverter’s high functional safety control platform. With backup power supply, the inverter enables “safe towing”, a feature highly desired by customers. It is a critical safety redundancy in the event of 12V power supply loss.

DirectFluxTM Bi-stable Electromagnetic Clutch

Patented bi-stable electromagnetic clutch is JJE’s one of the most advanced technologies. It is used for gears shifting and locking the differential in the electric beam axle system. This technology has been successfully used as a differential locker in JJE’s 300kW SiC EDM and as a disconnect in JJE’s new AWD EDM.

DirectFluxTM electromagnetic clutch takes advantages of its innovative magnetic circuit design. Compared to the more conventional reluctance flux magnetic circuit design, the DirectFluxTM design greatly reduces flux leakage, and therefore utilizes magnetic flux more effectively to generate force. However, the conventional reluctance flux design cannot avoid magnetization of parts near flux circuit, or “flux leakage”, which causes less effective utilization of magnetic flux. As a result, DirectFlux acts 2-3 times faster than a reluctance flux design.

The bi-stable clutch is inherently fail-safe as it won’t change state in the event of loss of power. This feature gives bi-stable clutch a higher safety level than mono-stable clutch. For differential locker, it will prevent sudden locker release due to the loss of power or control failure. For transmission shift, it will prevent gear unexpected back to neutral which will lead the vehicle loss of traction. On energy consumption side, the bi-stable clutch’s feature of “zero holding current” eliminates holding current and in turn achieves zero power consumption.

In the development stage of an electromagnetic clutch, a software platform based on several simulation tools is built for more precise simulation result. This platform covers signal, electric, electromagnetic, and mechanical aspects. It addresses almost every detail, including software control, PCB layout, electromagnetic transient simulations, multi-body dynamic simulations, and strength. It provides strong support to the clutch’s development.

Electric beam axles are designed for pickup trucks, light duty trucks, or medium trucks. As the beam axles get electrified, a lot of traditional technologies no longer fit. JJE takes advantage of its knowledge in electric drive, strong R&D capabilities on motor, inverter, transmission and clutches and expertise in system integration, creating the 2-speed electric beam axle for the large medium truck segment.

Overcoming Challenges to High-Speed Electric Motors

Craig Renneker, Vice President Innovation, AAM

While the EV growth rate remains uncertain, there is little doubt that the use of automotive electric drive units must drastically increase to meet global climate objectives. This requires mass market acceptance across the full range of vehicles − size and price. A major enabler to reaching more customers is to reduce the cost, size and mass of Electric Drive Units (EDUs), as well as the quantity of natural resources required in manufacturing.

The power produced by an EDU is a product of its torque and rotational speed. Increasing the rotational speed enables power to be achieved at a lower torque. Simply put, spinning the motor faster reduces its size, mass and cost (Figure 1). The result: fewer costly materials are required, such as copper windings, magnetic steel and, in some cases, rare-earth magnets.

Traditional electric motors rarely spin to 20,000 rpm. Exceeding this level requires careful motor, gearbox and inverter design. This article discusses the approach AAM is taking to overcome various design obstacles to enable speeds up to 30,000 rpm – the speed needed to make a real impact in clean mobility and customer acceptance of EVs.

The Integrated Approach

An accessible EDU with a 30,000 rpm motor requires an integrated motor, gearbox and inverter. Each area presents specific challenges to execution and opportunities for new designs:

• Motor: pole count, rotor centrifugal forces, cooling, sealing and bearings
• Gearbox: pitch line velocity of the gear teeth
• Inverter: Switching losses

The Motor

Most electric motors employ stators with 3-phase copper windings driven by sinusoidal alternating current. As the frequency of these sinusoidal currents increase, parasitic power losses in both the magnetic steel laminations and copper conductors increases. These are commonly called iron and copper AC losses. The required frequency for a 3-phase motor is determined by the motor pole count and rotational speed. Most motors today are 8-pole designs with interior permanent magnets. AAM uses a 4-pole architecture which requires half the sinusoidal current frequency of an 8-pole design. This significantly reduces iron and copper AC losses. (Figure 2)

Reducing the diameter of the rotor enables higher speeds. Fortunately, higher-speed motors require less torque for a given power level, allowing a smaller diameter. As an example, the tangential speed of an 87 mm OD rotor at 24,000 rpm is lower than a much larger rotor spinning at 15,000 rpm (Figure 3). Using stress analysis of the lamination and magnet geometry, high speeds can be attained.

Smaller, fast turning motors have basic geometric challenges in removing heat. To effectively remove this heat AAM uses forced oil cooling of both the stator and rotor. A series of stamped holes in the stator laminations are arranged to form helical cooling passages around the copper windings. Oil is also pumped into the hollow rotor shaft with special heat sink features to increase surface cooling. This method reduces the heat generated in both the stator and rotor without the need for a glycol-cooled motor jacket.

AAM is employing a completely different approach to cooling highspeed rotors. Instead of pumping glycol coolant through the hollow center of the rotor requiring radial lip seals, AAM is cooling the stator, rotor and inverter with the same low-viscosity oil used to lubricate the gears and bearings. With this arrangement, no sealing is required between the rotor and gearbox elements.

In most EDUs, a simple 2-stage helical-gear reduction is used to step motor speed down to the vehicle wheel speed. The pressure angle of the gear teeth generates a radial load proportional to gear torque that must be carried by bearings on the rotor axis. With a typical singlemesh, 2-stage helical gear reduction, bearing capability limits motor speeds to 20,000 rpm. AAM uses a dual-layshaft gearbox arrangement to balance these gear separation loads, which enables traditional small bearings to be used. (Figure 4).

Gearbox

Higher motor speeds require higher gear ratios to maintain normal wheel speeds. Any ratio can be accommodated with enough successive reduction stages. However, each additional stage adds cost, mass, package space and parasitic loss to the gearbox. Typical low-speed drive units employ a 2-stage reduction. As such, it is desirable for a high-speed motor to avoid the penalty of adding a third reduction stage. The critical enabler for high ratio (up to 22:1) is keeping the first stage drive gear very small. By keeping the motor off the wheel axis AAM enables the rotor shaft drive gear pitch diameter to be very small to provide a large reduction in the first stage and reduce pitch line velocity (Figure 5)

Inverter

The inverter converts DC battery voltage into multi-phase AC that drives the stator of the electric motor. The frequency of the required sinusoidal current is directly proportional to the  motor’s rotational speed and its number of magnetic poles. The inverter induces this sinusoidal AC to flow in the stator windings using pulse-width modulation (PWM) of the battery voltage (Figure 6). Pulse-width modulation involves solidstate switching devices that can turn on and off very quickly. Each on/off cycle results in a small amount of energy being lost within the switching device. As such, higher sinusoidal frequencies require faster switching, which increases inverter losses.

AAM’s 4-pole motor design operates at half the sinusoidal frequency of a traditional 8-pole motor. This enables the motor to spin at twice the speed with equivalent inverter switching losses.

Conclusion

AAM continues to push the limits of electric motor speed in EDUs. The company has several demonstration vehicles and one pre-production application running at 24,000 rpm, with an additional development unit producing 30,000 rpm. These designs can be produced at low cost in high volume using practical engineering solutions overcoming previously perceived limiting factors. These designs can enable the growth of EDUs into a wide variety of vehicle applications, thus creating a broader impact on carbon reduction and clean transportation. Innovations at AAM are creating efficiencies for our customers, satisfaction for consumers and an increased opportunity to positively impact our environment.