April 14, 2021

The core of e-mobility - Electric Drive Units

New vehicle models rely on efficient electric drive solutions to make sustainability strategies of OEMs more effective while providing comfort and a superior driving experience to their consumers.
The core of e-mobility - Electric Drive Units

The number of electrified vehicles on our roads continues to grow year by year. OEMs' new models need efficient electric drive solutions to meet growing CO2 requirements while offering consumers a comfortable driving experience along with optimal performance and a high level of usability. Meanwhile, industry developments show a growing need for experts who specialize in electric drive units (EDUs) and bring the required depth of expertise and experience to the table. Additionally, highly adaptable and rapidly deployable system solutions are essential to shorten the overall development times, enabling accelerated realization of new electric vehicle concepts.

What are EDUs and why are they important for powertrain electrification?

Electric Drive Unit - a highly modifiable solution for every development need

An Electric Drive Unit (EDU) consists of 3 main modules: the power electronics, the gearbox and the electric motor. All three must work in perfect harmony to get the vehicle moving.

EDUs deliver dynamic driving behavior, driving fun and comfort as well as cost savings and efficiency in the overall system.  The main purpose is the effective conversion of electrical energy into motion. The type of energy source used can vary on a case-by-case basis - from conventional electricity from charging stations or power outlets, stored in batteries, to fuel cells - anything is possible.

The power electronics of an EDU

The power electronics are responsible for the overall control of the e-drive and convert the DC voltage of high-power batteries into a three-phase AC voltage. This subsystem carries the logic of the entire EDU system and regulates the current to the motor. For electric and hybrid drive systems, achieving maximum efficiency is considered more important than maximum power. The inverter is expected to achieve high flexibility, durability, power availability and allow variable and maximum voltage utilization at the same time. In order to deliver steady torque even at the highest performance levels, strict safety requirements and compliance with ISO standards must be met, including the highest safety classification of ASIL Level D for some high-risk safety-relevant system functions.

Other prominent topics are charging times and charging speed. Demands for high charging capabilities require a new generation of inverters that keep losses as low as possible during the charging process while also coping with extremely high voltages. Because power electronics manage the flow of current between the battery and the motor, its design must be able to handle these high currents effectively. For this reason, 800 V inverter, allowing twice the charging speed of 400 V inverter, are gaining popularity. Quicker charging rates are achieved using new technologies such as silicon carbide-based semiconductors, which can withstand even higher reverse voltages. SiC technology loses less heat than conventional silicon semiconductors, taking power electronics to a whole new level.

The e-motor of an EDU

The E-motor is a key focus for electric vehicle powertrains' future, since it is needed in both hybrid and pure electric vehicles (read more about the different vehicle types here). It converts electrical energy into mechanical energy. Depending on the continuous and peak power, electric motors can be classified into different power ranges. Some new vehicle models already belong to the 800V category. Depending on the overall performance requirements set by OEMs, the decision is made whether a single electric motor can provide the desired power or whether multiple electric motors are needed. In our most popular EDU variants, the power of the e-motor is transmitted to the half-shafts by means of a multi-stage spur gear or a planetary gear and a differential.

The transmission on an EDU

The transmission is ultimately responsible for the torque transfer from the motor to the wheels with the most effective gear ratio. When choosing an EDU, the number of gears in transmission has a significant impact on the design complexity, functionalities, overall performance and efficiency of the system, influencing other factors such as the size of the e-motor and the system costs. The main focus lies on 2 performance aspects in particular: the acceleration power and the driving range. For a wide range of applications the 1-2 gear transmissions are the most effective. In contrast to the 1-gear transmission, a 2-gear transmission allows an increase in driving range and top speed with the same acceleration power. With multi-gear transmissions, the transmission must be capable of changing gears to ensure acceleration without traction interruption, which is known to be typical for electric vehicles.  

EDU transmissions tend to have additional functions, such as an electrically activated Park-Lock inside the electric drive unit, which contributes to the vehicle´s safety and prevents a parked car from moving.

The control software

An overarching functional element, particularly relevant in this highly connected and digital time, is the control software. It includes the functions for regulating and monitoring the drive unit of the vehicle. The control unit, located in the power electronics, communicates with the high-level vehicle systems. In vehicles, the demand for software is skyrocketing. Drive units need to be controlled in a manner that ensures the highest possible efficiency. However, since the inverter has a limit depending on its power capacity, it is the control software's job to reach this edge to fully utilize the potentials and deliver maximum performance.

The efficiency of electric drive systems benefits enormously from advances in software control. Excellent accuracy in the recording of currents, voltages and temperatures is required. After all, precise control software reduces the amount of hardware and materials required within a vehicle.

Algorithms are used to optimize the range, always determining the most efficient driving characteristics. High-grade software design is essential. Beginning in the development phase, the models must be able to represent all desired software functions in detail and take them into account at an early stage.

More and more expectations concerning safety are imposed upon control technologies. Monitoring and protective functions, that identify vehicle malfunctions fast and resolve them smartly, are needed. Removing power in time if an unexpected, unintended acceleration is detected, or activating the brake if the vehicle is accelerating too fast and losing control are only some examples of such functions. All these functions ensure that consumers have greater confidence and trust in electric vehicles, thereby accelerating the progressive adoption of e-mobility.

The engineers' overarching goal is to eliminate as much hardware as possible and replicate software functionality without sacrificing quality to achieve greater cost efficiency and functionality for customers. Software and application engineers with a systems approach and strong know-how are indispensable for implementing the desired functions in various vehicle concepts.

An integrated system approach of an EDU allows high level of multi-functionality

Multi-functionality is in demand in the automotive industry and significantly linked to Electric Drive Units. Depending on individual preferences, manufacturers have a wide range of architectures and configuration options to choose from. The advantage of an integrated system approach of an EDU is the possibility to make quick, marginal adjustments and adaptations.

Existing E-motor and PEU power variants offer a great deal of flexibility as elements of an EDU and can be configured for variable power levels. This minimizes development complexities and costs and lets manufacturers incorporate their desired solutions into their vehicle concepts in a short time frame, making it possible to get them on the road as quickly as possible.

Most Electric Drive Units differ in their hardware, whereas our control software is flexible and can cope with all EDUs regardless of their power ranges due to its flexible configuration.

Most popular EDU variations - characteristics and application possibilities

All our EDU variants are compact in design. The Electric Drive Units differ in their power capacities, drive torque, transmission ratios. They can accommodate everything from 12V systems to high power categories of up to 300 / 400 / 500 kW. Based on the electric machines used, they deliver different degrees of torque, ranging from 220 Nm to 300 Nm to 450 Nm and more. These specifications of an EDU depend on the vehicle's requirements, weight, size, and available installation space - SUVs require a larger electric drive unit than small vehicles. Whether coaxial, axially parallel or double-axially parallel, with or without a disconnect clutch, hofer powertrain offers these solutions as standard solutions as well as customized high-performance versatile solutions.

In the next segment of this EDU article series, we will present the most popular drive units along with their technical parameters. We shed light on interesting application scenarios of EDUs on the market and take a look at the latest developments from hofer powertrain engineering teams.


Want to know how our customers achieve maximum efficiency through standardized and customized electric drive solutions in their vehicles? Stay tuned and let your peers benefit from our Electrification Weeks as well. Register here to receive exclusive expert insights.

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