Drivetrain Concept Research Articles

Novel modular powertrain proposal for e-bicycle

Bicycles with electric pedal assist systems are becoming increasingly popular, with increasing versatility, a range of intended areas of use, and different design approaches for system realization. This paper deals with the proposal for a novel modular drivetrain concept based on a friction driving wheel, for which a brief design outline is given. Desired performances based on law constraints and average bicycle driving experience analysed, and basic powertrain properties required for their realization assessed.

Techno-economic analysis of power smoothing solutions for pumping airborne wind energy systems

In pumping airborne wind energy (AWE) systems, the kite is operated in repetitive crosswind patterns, pulling the tether from a winch that drives a generator on the ground. During the reel-out phase of its operation, it produces power, whereas, during the reel-in phase, it consumes a small fraction of the produced power. This leads to an oscillating power profile that requires smoothing before it can be supplied to the electricity grid. This paper proposes three drivetrain concepts as a solution to this power smoothing challenge. The three concepts are based on three different types of storage technologies: electrical, hydraulic and mechanical. Techno–economic models of the drivetrains were developed and a case-study on sizing and costing of the three drivetrain concepts for a MW–scale AWE system was performed. Conclusions were drawn that provide guidance to AWE developers for choosing a suitable drivetrain concept for their systems.

Method for holistic wind turbine drivetrain comparison exemplarily applied to geared and direct drive systems

The drivetrain as an important part of wind turbines needs to be improved in order to deal with today’s high development and cost pressure. One important step towards enhanced drivetrains is to identify the most suitable concept for a targeted onshore application in an early design stage. With this purpose, a holistic lifecycle system evaluation approach relying on minimum input information is presented. In order to identify a dominant solution, an additive target system is defined taking cost, ecological sustainability, and supplied energy into account. This multi-criteria decision is aggregated by defining a macrosocial evaluation criterion: “drivetrain specific energy supply effort”. A physics- and empirically-based model is developed to quantify the targets for different onshore drivetrain concepts. The validity of the model results is shown by a comparison to meta-analysis findings. Being utilized on a drivetrain concept comparison between geared and direct drive the approach’s value is showcased. Both concepts score on a comparable level slightly differing in weak and strong wind regimes. An exemplary trade-off between investment- and operational effort shows, that for both concepts the investment effort is higher than the operational. The comparison furthermore shows how robust decision support can be provided by parameter variation and finally it stresses, that the decision maker’s preferences need to be incorporated in the decision. Concluding, this analysis shows that physics- and empirically-based model approaches enable holistic wind turbine drivetrain concept comparisons in an early design stage.

Current experimental developments in 48 V-based CI-driven SUVs in response to expected future EU7 legislation

AbstractIn this paper, we describe experimental developments in an Exhaust Aftertreatment System (EAS) used in a four-cylinder Compression Ignition (CI) engine. To meet the carbon dioxide (CO$$_\mathrm {2}$$ 2 ) fleet limit values and to demonstrate a clean emission concept, the CI engine needs to be further developed in a hybridized, modern form before it can be included in the future fleet. In this work, the existing EAS was replaced by an Electrically Heated Catalyst (EHC) and a Selective Catalytic Reduction (SCR) double-dosing system. We focused specifically on calibrating the heating modes in tandem with the electric exhaust heating, which enabled us to develop an ultra-fast light-off concept. The paper first outlines the development steps, which were subsequently validated using the Worldwide harmonized Light-duty vehicles Test Cycle (WLTC). Then, based on the defined calibration, a sensitivity analysis was conducted by performing various dynamic driving cycles. In particular, we identified emission species that may be limited in the future, such as laughing gas (N$$_\mathrm {2}$$ 2 O), ammonia (NH$$_\mathrm {3}$$ 3 ), or formaldehyde (HCHO), and examined the effects of a general, additional decrease in the limit values, which may occur in the near future. This advanced emission concept can be applied when considering overall internal engine and external exhaust system measures. In our study, we demonstrate impressively low tailpipe (TP) emissions, but also clarify the system limits and the necessary framework conditions that ensure the applicability of this drivetrain concept in this sector.

Reducing cost uncertainty in the drivetrain design decision with a focus on the operational phase

Abstract. In order to identify holistically better drivetrain concepts for onshore wind turbine application, their operational behavior needs to be considered in an early design phase. In this paper, a validated approach for estimating drivetrain-concept-specific unplanned operational effort and risk based on open-access data is presented. Uncertain influencing factors are described with distribution functions. This way, the poor data availability in the early design phase can be used to give an indication of the concept's choice influence on the unplanned operational wind turbine behavior. In order to obtain representative comparisons, a Monte Carlo method is applied. Technical availability and drivetrain-influenced unplanned operational effort are defined as evaluation criteria. The latter is constituted by labor, material and equipment expenses. By calculating the range of fluctuation in the evaluation criteria mean values, this approach offers an indication of the inherent risk in the operational phase induced by the drivetrain concept choice. This approach demonstrates that open-access data or expert estimations are sufficient for comparing different drivetrain concepts over the operational phase in an early design stage when using the right methodology. The approach is applied on the five most common state-of-the-art drivetrain concepts. The comparison shows that among those concepts the drivetrain concept without a gearbox and with a permanent magnet synchronous generator performs the best in terms of absolute drivetrain-influenced unplanned operational effort over the drivetrain's lifetime as well as in terms of the inherent risk for the assumptions made. It furthermore makes it possible to give insights into how the different drivetrain concepts might perform in future applications in terms of unplanned operational effort. Exemplarily the impacts of higher torque density in gearboxes, a change to moment bearings and adjusted coil design in electrically excited generators have been analyzed. This analysis shows that the superiority of synchronous-generator concepts manifested in historic data is not entirely certain in future applications. Concluding, this approach will help to identify holistically better wind turbine drivetrain concepts by being able to estimate the inherent risks and effort in the operational phase.

Design, Production, and Verification of a Switched-Reluctance Wheel Hub Drive Train for Battery Electric Vehicles

This contribution deals with the topic of the consistent further development of a wheel hub motor for battery electric vehicles (BEV) based on the principle of an outer rotor switched reluctance machine (SRM). The research work presented in this paper was founded by the ERDF.NRW program, Investment for Growth and Employment and the European Regional Development Fund. The R&D project was named Switched-Reluctance fo(u)r wheel (SR4Wheel). Based on the experience made by first prototype Evolution 0 (EVO 0), developed in the Laboratory for Automation Engineering, Power Electronics and Electrical Drives of the Cologne University of Applied Sciences (CUAS), the test results of EVO 1, as well as the redesign, EVO 2 is presented in this paper. The prototype EVO 0, a first proof of concept leads to several optimizations and lessons learned for the predecessor model EVO 1. The overall target of developing such a gearless outer rotor wheel hub motor is the full integration of the complete machine including its power electronics into the given space between the original friction brake and the rim. Furthermore, due to the additional integration of the power electronics, great opportunities in terms of new vehicle design as well as retrofitting capabilities of already existing vehicle platforms can be achieved. Thereby, further drive train assembly space like the engine compartment is no longer necessary. The SRM does not require magnets for torque production which leads to independence from the changeable commodity prices on the rare earth element markets. This paper presents the developing process, testing, and verification of the innovative drive train concept starting with the final CAD of EVO 1. During the testing and verification process a machine characteristic mapping is performed on a drive train test bench and subsequently the results of a finite element analysis (FEA) are plausibility checked by the test bench results. The process continues with energy conversion test scenarios of the project demonstrator vehicle on a roller test bench focused on noise vibration harshness (NVH) behavior and efficiency. As a conclusion, the gained knowledge by evaluating two EVO 1 prototypes on the rear axle of the test vehicle, and the design for the front axle drive train EVO 2 will be presented. As a major task on the front axle, the limited space due to the large disc brake can be identified and solved.

A generic transmission model for hybrid electric drives

The design problem of hybrid electric drivetrains has a large design space, especially, when complex dedicated hybrid transmissions that combine an internal combustion engine with multiple electric machines are considered. To evaluate a drivetrain design over a driving cycle, a transmission model is needed. To avoid the need of modeling every drivetrain concept individually, a generic transmission model for hybrid electric drives is developed. The developed model integrates the dynamic behavior of all conventional-, electric-, and hybrid- transmission mode types. Mode types and mode type dependent control variables are defined. The outputs of the model are the torque and rotational speed of all power sources of the drivetrain. The inputs of the model are the torque and speed of the wheels, and the control variables. As a practical example, the model is used to compare the energy efficiency of two complex dedicated hybrid transmissions by optimizing the control for both over a driving cycle.

Improvement of grid frequency dynamic characteristic with novel wind turbine based on electromagnetic coupler

A synchronous generator is directly coupled to grid in the novel wind turbine drive train concept based on electromagnetic coupler (WT-EMC). Similarly to conventional power plants, WT-EMC has inherent (inertial) grid frequency support capability, albeit rather limited due to its configuration. Additional power should be generated in response to a grid frequency drop in order to improve the dynamic characteristic of the grid frequency. In this paper, a novel control strategy for WT-EMC to improve the dynamic characteristic of grid frequency is proposed. The principle is to detect active power imbalance in the grid and then rapidly regulate the output power of WT-EMC. Based on the calculated electromagnetic torque of the synchronous generator in WT-EMC—acquired faster than the calculated grid frequency—the synchronous generator mechanical torque is controlled to track its electromagnetic torque to stabilize the rotor speed, therefore directly improving the grid frequency. The proposed control strategy effectiveness is firstly tested through simulations and then validated on a specially built experimental platform.

New Drive Train Concept with Multiple High Speed Generator

In the research project RapidWind (financed by the German Federal Ministry for Economic Affairs and Energy under Grant 0325642) an alternative 6 MW drive train configuration with six high-speed (n = 5000 rpm) permanent magnet synchronous generators for wind turbine generators (WTG) is designed. The gearbox for this drive train concept is assembled with a six fold power split spur gear stage in the first stage, followed by six individual 1 MW geared driven generators. Switchable couplings are developed to connect and disconnect individual geared generators depending on the input power. With this drive train configuration it is possible to improve the efficiency during partial load operation, increasing the energy yield about 1.15% for an exemplary low-wind site. The focus of this paper is the investigation of the dynamic behavior of this new WTG concept. Due to the high gear ratio the inertia relationship between rotor and generator differs from conventional WT concepts, possibly leading to intensified vibration behavior. Moreover there are switching procedures added, that might also lead to vibration issues.

Optimal gearshift control for a novel hybrid electric drivetrain

Torque-fill capability during gearshifts is an important customer requirement in automated transmission systems. This functionality can be achieved through transmission system layouts (e.g., based on dual-clutch technology) characterized by significant mechanical complexity, and hence with relatively high cost and mass. This paper describes a parallel hybrid electric drivetrain concept, based on the integration of an electric motor drive into a relatively simple six-speed automated manual transmission. The resulting hybrid electric drivetrain actuates the torque-fill function through control of the electric motor torque during the gearshifts on the engine side of the drivetrain. An optimal controller, based on the off-line computation of the control gain profiles, is presented for the clutch re-engagement phase. The novel controller allows computationally efficient consideration of clutch energy dissipation during the clutch re-engagement phase of the gearshift. The performance with the optimal controller is contrasted with that of two conventional clutch engagement controllers, along a set of gearshifts simulated with an experimentally validated vehicle model.

EcoTrain: The Erzgebirgsbahn's New Hybrid Railway Vehicle

Climate change is one of the greatest challenges of the 21th century. To counteract increasing temperatures and to decrease the dependency on fossil fuels various projects are currently conducted aiming at the private and all the different industrial sectors. One of them is the EcoTrain project which is an undertaking of a consortium of several project partners lead by Deutsche Bahn. Working closely with DB RegioNetz Verkehrs GmbH, the Erzgebirgsbahn, the TU Dresden, the Fraunhofer IVI as well as the TU Chemnitz, these partners explore and work on new approaches to finding solutions for an energy-efficient mass transit vehicle. The EcoTrain project aims at developing a hybrid railcar for the Erzgebirgsbahn: A standard class 642 rail vehicle is going to be converted to a cutting-edge and innovative hybrid railcar. Later on, this prototype will serve as basis for converting the entire Erzgebirgsbahn railcar fleet. This paper deals with the development of a drive train concept for the EcoTrain. Three different approaches to hybridization are explained in conjunction with their respective advantages and disadvantages. The hybridization concepts are assessed and the drive train concept of the EcoTrain is introduced. Furthermore the simulation tool IVIsion which was used to dimension the drive train components is explained along with the achieved simulation results. The paper concludes with an introduction to the so-called energy management module which is developed by Fraunhofer IVI. This module predicts the vehicle's movement along the track and calculates recommendations for energy flow and driving style based on the schedule and current position.

A low-cost hybrid drivetrain concept based on compressed air energy storage

This paper introduces a new low-cost hybrid drivetrain concept based on compressed air energy storage. In contrast to most contemporary approaches to pneumatic hybridization, which require modification to the primary power plant, this concept is based on a stand-alone pneumatic system that could be readily integrated with existing vehicles. The pneumatic system consists of an air tank and a compressor–expander that is coupled to the rest of the drivetrain via an infinitely variable transmission. Rather than incorporating more expensive technologies such as variable valve timing or a variable compression ratio compressor, a fixed valve system consisting of a rotary valve and passive check valves is optimized to operate efficiently over a range of tank pressures. The feasibility of this approach is established by thermodynamic modeling and the construction of a proof-of-concept prototype, which is also used to fine tune model parameters. While the proof-of-concept system shows a round trip efficiency of just under 10%, modeling shows that a round trip efficiency of 26% is possible with a revised design. If waste heat from the engine is used to maintain an elevated tank temperature, efficiencies of nearly 50% may be possible, indicating that the concept could be effective for practical hybridization of passenger vehicles.

Driving Torque Control for a Nacelle Test Bench

Recently wind industry paid a lot of attention to ground testing facilities in order to improve reliability of wind turbines by undergoing overall system tests at an early stage of development. Some experience has been gained during the last years with drive train test benches, that allow for pure mechanical and electrical tests of the turbine's components. Since the loads occurring inside a wind turbine significantly depend on its control strategy, the natural extension of drive train test benches are so-called nacelle test benches, which also include the wind turbine's controller. The worldwide first nacelle test bench was installed and launched at RWTH Aachen University in 2013. This nacelle test bench was set up as a demonstrator and has a rated power of 1 MW.For the demonstrator test bench a gearbox-based drive train concept, which does not intrinsically meet the high dynamic requirements of the real-time aerodynamics simulation, was chosen. In this paper the mechanical concept is reviewed from a control engineering point of view and a detailed control model is presented and validated using measurement data. In order to minimize the impact this mechanical limitations have and to achieve the dynamics and accuracy required, a driving torque controller is proposed. Due to the communication layout at the nacelle test bench, time delay in data transfer cannot be omitted for controller design.Experiments confirm that the driving torque controller allows to operate a wind turbine at the nacelle test bench and suppresses unrealistic, test bench-related torque dynamics.

Safe Torque Vectoring function for an electric vehicle

A safe Torque Vectoring function is applied to an electric vehicle with a two front motors drivetrain concept. The function has been embedded in a lean and scalable functional architecture adaptable to various drivetrain concepts. The Torque Vectoring function comprises an LPV control algorithm with good performance even in extreme test cases. The controller can be parameterised for case specific performance. The implementation of functional safety requirements is presented for one safety goal.

Optimal Operation of a Turbocharged Diesel Engine during Transients

Recent development has renewed the interest in drivetrain concepts which give a higher degree of freedom by disconnecting the engine and vehicle speeds. This freedom raises the demand for active control, which especially during transients is not trivial but of which the quality is crucial for the success of the drivetrain concept. In this work the fuel optimal solution for a turbocharged diesel engine connected to a load which does not restrict the engine speed is derived, analysed and utilized for finding a suboptimal operating point trajectory. We use a Willan s efficiency model for the engine, expanded with a first order delay dependent torque reduction representing the turbocharger pressure, and study different output power transients. The analysis is made with dynamic programming, Pontryagin’s maximum principle and a suboptimal strategy based on the static optimal operating points. We present a method for using Pontryagin’s maximum principle for deriving the optimal operating point trajectory. The time needed for computation was reduced a factor >100 compared to dynamic programming, but this method is only applicable to load cases with steps between different high output powers. We also present a suboptimal method which shows a 1000 compared to dynamic programming.

Fuel savings through steering and braking technologies

Technical discussions about effective means of addressing reduction in fuel consumption and lower CO2 emissions are often centred on elaborate and costly drive train modifications. The automotive supplier TRW shows how, independent of the selected drive train concept, steering solutions and leading-edge braking technologies can help to optimise consumption levels. For example, TRW can quickly adapt the electro-mechanical and electro-hydraulic steering system, the electronic stability control with a regenerative braking function ESC-R and the electro-hydraulic braking system SCB to different models and platforms.