Powertrain and Transmission Technology

As the powertrain becomes more or less electrified, the tasks and requirements of the powertrain change.

Purely electric vehicles are today almost exclusively equipped with a single speed transmission. However, hybrid powertrains are equipped with automatic transmissions. The integration of at least one electric machine increases the complexity of the transmission architecture and the functional software. The development of dedicated hybrid transmissions seeks to reduce transmission complexity by taking over functions previously provided by the transmission from the e-machines.

This opens up many possibilities for novel powertrain systems. At the same time, new challenges arise in the design, integration and control of such systems. The IMS does research in the field of powertrain and transmission technology in order to meet the current challenges and thus to exploit the full potential of innovative systems. The focus is on the optimal design and control of the powertrain. The target criteria that are optimized are efficiency, driving performance, driving and shifting comfort as well as costs. Some completed and ongoing projects deal with different variants of the Two-Drive-Transmission. This innovative powertrain concept of the IMS provides a platform for exploring the diverse possibilities of dedicated, electrified transmission systems.

Current Projects Related to this Key Topic:

Period: 2018 – 2021

Cooperation: TU München (FZG), Leibniz Universität Hannover (IAL, IMKT), ATE, AVL, BMW, Fuchs, Lenze, Magna, Schaeffler

Support: see right

Speed4E is the follow-up project to the successfully completed research project Speed2E. As with in Speed2E, a purely electric drive train with two high-speed electric machines is to be designed and developed. The maximum speed should be raised from 30,000 to 50,000 rpm to further increase the power density. Another special feature is the multispeed sub transmission, which is realized by positive locking elements (dog clutches). For this purpose, a dedicated shift actuator and an innovative transmission control is developed. The integration of the drivetrain into a vehicle will enable the evaluation and optimization of shifting and driving comfort.

Contact: Daniel Schöneberger

Further informationen you can find on the Project homepage

Period: 2018 – 2021

Cooperation: BMW Group, FAI (TU Darmstadt)

The aim of this project is to investigate the perception of gear shifting processes in different powertrain configurations, taking into account different user groups. In this context, relationships between the physical effects of a gear shift sequence and the subjective evaluation of the driver are to be examined and suitable evaluation criteria for gear shifting processes are to be derived. As a test environment, the longitudinal dynamic driving simulator of IMS “Driveception” is available. The project is carried out in cooperation with the BMW Group and the Research Group for Work and Engineering Psychology (FAI) of TU Darmstadt.

Contact: Edward Kraft

Period: 2018 – 2022

Improvements in fuel economy and reductions in greenhouse gasses are common issues which drive the development of new technologies. Vehicle transmissions are vital components because their design directly impacts the engine operation and the power flow to the powertrain. As the focus, energy consumption in transmissions is analyzed in this project. The causes are not just the elements in the power flow path, but also the commonly used auxiliary systems. Based on the project “Modelling and analyzing the power losses in vehicle transmissions”, the energy consumption in the launch element, the hydraulic system and the open shift element is modeled. In order to accurately predict the total energy consumption, all important uncertain parameters are firstly determined by means of the parameter study. To identify these uncertain parameters in models, the isolated measurement for the individual energy consumption in the whole transmission system is conducted. For this, the experiments are designed by modifying the modules in the transmission and by intelligently operating the conditions. The validation of the models improved by parameter identification is carried out with the measurement data from other operational conditions.

The overall target of this project is to build the model of energy consumption which can be used to compare different vehicle transmissions in terms of total energy consumption.

Contact: Zhihong Liu

Selected publications: Theoretical and Experimental Investigation on Power Loss of Vehicle Transmission Synchronizers with Spray Lubrication

Completed Projects Related to this Key Topic:

Period: 2016 – 2018

Cooperation: Conti Temic Microelectronic GmbH

In the course of the project a dedicated hybrid transmission (DHT) was developed aiming for a cost-efficient alternative to existing hybrid powertrains. The electrification of the powertrain is used to omit or simplify cost-intensive transmission components of conventional powertrains. The use of dog clutches allows the use of a cost-efficient shift actuator, which was developed by Continental.

The main focus of the collaboration was the development of transmission layout including gearset concept and the arrangement of the components. Furthermore, a dedicated dog clutch was a purpose design for this powertrain developed at the IMS. The innovative dog clutch design allows fast and comfortable gear changes.

An efficient support of the entire development process from the initial idea to a powertrain layout was possible by using both, IMS-in-house tools and commercial software.


Period: 2015 – 2018

The power losses inside vehicle transmissions are related directly to the efficiency of vehicle systems. Hence, it is worth researching the overall power losses of transmissions, in order to develop the measures to reduce the overall energy consumption in vehicle powertrains. It is then necessary to put forward a general method to estimate the power losses in vehicle transmissions. In this project, a general overall power loss model of vehicle transmissions is established, based on component power loss models in the literature. Furthermore, a methodology concerning the analysis of the power losses inside vehicle transmissions is introduced. One part of the methodology is the calculation of component loads and speeds for the overall power loss model. To improve the estimation of the overall power losses, parameter sensitivity analysis and parameter identification strategy are employed in the methodology, with the help of experimental data from test rigs. The overall power loss model and the methodology are applied onto three different transmissions. In comparison with a standard model, the results of the overall power loss model have a better agreement with experimental data. Moreover, with the help of the methodology, accurate power loss distributions of these vehicle transmissions are possible to be obtained. It is expected that by means of the overall power loss model and the methodology in this project, a platform can be set up to investigate and benchmark different vehicle transmissions in terms of their efficiency in the future.

Selected publications: A method on modelling and analyzing the power losses in vehicle transmission

Period: 2015 – 2018

Cooperation: AKKA, Daimler AG, Magna Getrag

Support: see right

The „Two-Drive-Transmission with Range-Extender (DE-REX)“ is an innovative parallel-series hybrid powertrain concept. The DE-REX concept is characterized by coupling two identical electric motors and an internal combustion engine via an automated transmission with the drive shafts of the vehicle. Thereby, the transmissions consists of two subtransmissions with two speeds each. The powertrain offers high efficiency while pure electric and hybrid driving and performs gear shifts without interruption of traction force.

Based on the results of the completed project Doppel-E-Antrieb, in the publically fundet DE-REX project the electric motors and the transmission were designed, manufactured and set up as entire powertrain with an internal combustion engine at both a powertrain test bench and a demonstrator vehicle. All goals of the project were achieved and therefor, the project was successfully completed at June, 30th 2018.

Contact: Andreas Viehmann

Further informationen you can find on the project website.

Period: 2014-2017

Cooperation: TU München (FZG), Leibnitz Universität Hannover (IAL, IMKT)

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The overall goal of Speed2E was the development, optimization and test of a high-speed electric powertrain. Increasing the speed of the electric machine has the potential to significantly increase the power density of the electric machine and the overall efficiency of the vehicle. In order to meet requirements regarding drive-of-torque, top speed, efficiency and driving comfort, a powertrain with two electric motors was built, with a multispeed sub transmission. With the help of the operating strategy and transmission control developed for this innovative drivetrain by IMS, a safe, efficient and comfortable operation was realized and validated on a test bench.

Contact: Daniel Schöneberger

Further informationen you can find on the project website.

Period: 2013 – 2016

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From the customer's point of view there are two major obstacles to the electrification of the powertrain: costs and range. Although plug-in hybrid vehicles (PHEV) address the range problem they do not solve the cost issue. These solutions are only supplemented by specific and expensive electrical components and therefore they have a high price.

Subproject IMS „concept and simulation (operating strategy)“

Participating enterprises and research institutions strive to show that plug-in hybrid vehicles are feasible at attractive costs with the aid of a modular and scalable construction system.

The project part of TU Darmstadt focuses on simulative optimization topics, especially on the hybrid operating strategy.

The objective is to build up a simulation environment with which it is possible to perform optimizations with automated parameter variations. In addition to the important step of determining the cost reduction potential it especially is essential to develop a modular operating strategy, which enables a comparison of different variants of PHEVs. Among other investigations the simulations are used to determine, how a modular approach of the operating strategy affects the overall efficiency.

Further information you can find on the project website.

Selected publications: BEREIT: Optimization of Parallel Hybrid Electric Vehicle (HEV) Fleets

Period: 2012-2014

Cooperation: Institut für Elektrische Energiewandlung (TU Darmstadt)

The aim was to optimize a novel, highly efficient electric powertrain for a application as a traction drive in vehicles. The electric machines were designed as high speed drives with the highest possible torque and power density. The transmission should be designed to be as compact and efficient as possible with at least two stages and two gears per coupled electric machine.

Automated manual transmissions in a layshaft design are the simplest way for realizing multiple gears. With the Two-Drive-Transmission shown in the picture (an automated manual transmission (AMT) driven via two input paths) it is possible to avoid uncomfortable interruptions in tractive force during gear changes.

The use of two smaller electric motors also leads to an increase in efficiency compared to an electric vehicles with only one powerful electric motor. In partial load operation, only one of the two electric motors provides propulsion, resulting in higher specific load and thus better efficiency of the electric machine.

By coupling a combustion engine, a series-parallel hybrid architecture is created, which allows the operating modes “pure electric driving”, “series hybrid mode”, “parallel hybrid mode” and “pure combustion engine driving”.

First simulation results showed a considerable increase in efficiency and thus CO2 savings. In the New European Driving Cycle (NEDC), energy consumption is 17% lower than for an electric vehicle with only one electric motor and a 1-speed transmission.

Period: 2010-2013

Cooperation: TU Braunschweig (Institut für Fahrzeugtechnik)

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The development of modern vehicles and in particular of electrified drive systems is characterized by a high degree of complexity and a wide variety of variants with rising customer expectations. With a look at the design of the drives optimised to these boundary conditions, the focus is on legal requirements as well as specifications and customer requirements for the vehicle. In order to create an optimal vehicle concept, it is usually not appropriate to optimize the individual components with regard to the requirements, but to take a holistic view of the vehicle system requires a cross-component approach.

In this context, the so-called EVID method (Electric Vehicle Identification – identification of optimal powertrain configurations for electric vehicles) is used. The aim of the EVID method is to determine an optimal powertrain configuration for each of a selection of vehicle concepts that differ in their application profile (e.g. city vehicle or distribution vehicle in the city and overland traffic). If the input parameters are varied (design parameters of the components such as number of gears, ratio coverage, total system power, electric motor torque, battery capacity), the optimum solution is identified on the basis of the characteristic parameters relating to driving performance, energy balance and costs, which are taken into account in an evaluation function by means of different weightings. Mathematical models (MM) enable an evaluation with minimum computing time. These models are intended to represent the interrelationship of basic and characteristic parameters as accurately as possible. The MM and the computational models are then used in an optimization algorithm to identify the optimal concept, its components and the associated input and characteristic parameter values.

Project Structure graphic

Ausgewählte Veröffentlichungen: Antriebsstrangoptimierung von Elektrofahrzeugen