13th International Munich Chassis Symposium 2022

Ambient light is becoming more and more a common feature in the cars of not only the premium, but also the middle-class market. From the first beginnings of illuminating door handles and door compartments, ambient illumination is proceeding to become a design feature ubiquitous within a car’s interior. The Back Ring Light Element (BRLE) incorporates this trend for the steering wheel. Apart from mitigating the distraction potential of these design features, the upper steering wheel rim is usually recommended through various studies as a perfect warning location for forward-collision warnings or takeover requests; but if this is a valid use case for an ambient lighting technology remains unclear. Therefore, a study in a static driving simulator was conducted. The results of this study seem to be promising in terms of using multiple use cases within the same feature, the BRLE with ambient lighting technology in the steering wheel.

As the automotive industry continues its rapid evolution to fully autonomous driving, automakers and suppliers are working to develop safe and advanced autonomous features while maintaining costs that are acceptable to the consumer. Efficiently integrating multiple sub-systems to support this transformation provides opportunities for optimizing performance and cost.

A stowable steering column assembly integrated with a steer-by-wire handwheel actuator is one example of such an integration opportunity. While a traditional power-actuated steering column enhances driver comfort by providing relatively minor adjustments to the steering wheel location, a stowable steering column transforms a vehicle cockpit during an autonomous steering mode by significantly moving the steering wheel out of a driver’s way. This transformation is further enhanced when integrated with a steer-by-wire handwheel actuator, which enables technology like Quiet Wheel™ Steering, where the steering wheel does not rotate during vehicle lateral motion.

While there are significant benefits of implementing a stowable steering column with a steer-by-wire system, it comes with many challenges. These challenges include creating a mechanical design to provide the large movements required for stowing the steering wheel, maintaining typical steering column performance constraints such as natural frequency, stiffness, and acoustic performance, achieving the desired stow path and speeds, and fitting the steering column assembly hardware within a vehicle’s packaging space environment. Other electrical design challenges include thermal management, system packaging, fail-operational performance, pinch detection, software function partitioning, diagnostics, software throughput, and safety. These challenges provide additional opportunities for hardware cost reduction, optimized validation effort, and implementation of advanced software features. Strategic planning between an OEM and a supplier helps mitigate and address these challenges.

In the automated, driverless, electric vehicle concept U-Shift, a novel type of mobility is created by separating a vehicle into a drive module and a transport capsule. The autonomous driving module, known as a driveboard, is able to change the transport capsules independently and thus serves to transport both people and goods. In order to be able to use the vehicle sensibly, especially in urban areas, the space required for manoeuvring and loading or unloading the capsules must be kept to a minimum. This poses special challenges for the steering system.

In this contribution, a new type of steering system is presented, which enables both same-direction and opposite-direction wheel steering. During normal cornering, there is a mechanical coupling between the wheels. This means that occurring forces and moments are mutually supported by the wheels, which minimises the energy requirement of the steering system. The mechanical coupling of the wheels can be separated for manoeuvring the vehicle. By turning the front wheels in opposite directions towards the centre of the vehicle, the centre of rotation of the vehicle can be shifted to the centre of the rear axle. The vehicle can thus be rotated around the centre of the rear axle which allows to reduce the space required for manoeuvring to a necessary minimum.

Extended, specific safety requirements are necessary for the future technology Steer-by-Wire. For this purpose, an industry-wide standard is to be developed as part of a DIN standard.

The focus here is on questions of general interest such as item definition, safety goals, error categories, controllability in the case of a first fault, operational behavior after a first fault and the associated degradation concept.

The following explanation provides an overview of how these questions could be answered in the intended DIN standard.

As digitalization plays in increasing role within automotive development projects the terminology “Digital Twin” becomes more and more prominent. The paper describes the Digital Twin approach that is used in ZF steering development including model build up, model validation, capabilities and potential use cases in development of robust steering systems.

By using some subsystems of a steering system as an example it is shown that the tolerance chains, system wear and environmental conditions play a very dominant role especially in steering system characteristics. When developing any kind of simulation model for a steering system those influences need to be considered when validating the model. For this purpose, the concept of Digital Twins is used at ZF as a digital representation of system characteristics of an individual system including the influence of noise factors.

After the description of ZF’s concept of Digital Twins, a typical 1-D model build up is shown including validation using specially designed test rigs. In addition, the statistical validation using the Monte-Carlo method is described. For this, main tolerances and the effects of environmental conditions are set randomly within the given range of tolerance bands and environmental conditions to generate a statistical distribution of model responses. This distribution is then compared with measured responses, allowing model validation against systems where not all noise factors are known. In the last part of this paper the potential and a certain use case of a Digital Twin is described on more detail. It includes a design study of a mechanical system and the validation of robust system behavior in closed loop conditions.

With the increasing use of virtual models and driver in the loop simulators for vehicle development the traditional activities of automotive companies and suppliers are having to adapt. Previously OEM’s would drive early prototypes and use competitor vehicles as a comparative benchmark, however, this can be replaced with the use of a digital twin of a competitor vehicle to allow a virtual comparison to be performed. Additionally Tier 1 suppliers who traditionally developed their physical prototype products using the ‘best in class’ vehicle as a test bed require a representative vehicle model to enable them to make the transition to software-based development. Although representative chassis models can be produced from objective data, the key interaction the driver has in a static simulator is via the steering feedback and if this is not adequate it has a detrimental effect on the driver’s subjective opinion of the entire vehicle model behaviour and makes it difficult to carry out any comparisons or detailed development.

In this paper HORIBA MIRA explains the process of determining the key steering system parameters that influence feedback with particular focus on use in static simulators. A range of steering systems have been measured and assessed and the data is used to provide a reference for the model parameterisation and to define the key parameters that influence the subjective feel. The steering feedback is generated using the Pfeffer steering model, available within commercial low degree of freedom software packages, and, where required, a secondary controller system with additional and tuneable functionality has been developed.

Driving simulators can help to understand the driving performance of virtual vehicle prototypes, especially to evaluate with human inputs if they are feasible and are meeting the expectations of the development team. The representation of steering feel is one of the essential characteristics to deliver a realistic driving experience besides other feedback channels like visual, audible or vestibular, which are equally important to be represented in a driving simulator environment. The representation of steering feel, more specifically torque/force feedback is typically achieved through a Model-in-the-Loop or a Software-in-the-Loop setup with the help of an e-motor drive unit. For this approach it is necessary to simulate the whole chain of components up to the driver’s hand, e.g. the tire-road interaction, the suspension and the steering system including the mechanical and electrical components. A different approach is implementing the steering system hardware and ECU in the loop with a rack force actuator on the steering rack and a bus simulation. Both approaches are analyzed in terms of steering feel on driving simulators. The benefits of the presented Hardware-in-the-Loop implementation for closed-loop assessment on a dynamic driving simulator are presented. Subjective evaluation results from an expert study are discussed.

The regenerative braking functionality of electric vehicles significantly reduces the use of friction brakes. This can offer a potential for downsizing or, in extreme cases, even elimination of the friction brakes particularly on the rear axle due to the reduced brake torque demand. However, the elimination of wheel individual brake torque interventions of electronic stability control (ESC) on the driven axle makes acceleration on gradients with inhomogeneous surface (\(\mu \)-split) impossible, jeopardising state-of-art vehicle safety. Limited slip differentials that can support in such situation may negatively affect the driving comfort, efficiency and tyre wear. This study investigates the impact of locking differentials with different operating principles in a representative driving cycle for typical everyday use utilising a dynamic simulation environment.

The current massive changes in the electrification of vehicles are also causing a lot of new challenges for the foundation brake development.

New considerations and tools necessary, which allow the development of new techniques for the brake development processes.

Due to the heavy battery packages in BEV (battery electric vehicle), the GVW (gross vehicle weight) increases, which requires larger brake systems. But at the same time, due to the kinetic energy recuperation, the usage of the foundation brake decreases significantly.

The effects to the braking system are varied, due to the different blending algorithms, which are available from car manufacturer to car manufacturer and even vary from vehicle to vehicle.

The topic of this paper is to address this problem. The aim is to develop new approaches and testing techniques for standard brake shaft dynamometers to consider all those effects and make the dyno much smarter in order to close the gap between dyno-level and vehicle-level tests.

The implementation of a real time HiL (hardware in the loop) system into the dyno would allow users to simulate different vehicle components models, which typically impact the brake in real vehicles and allow new maneuvers and brake applications.

As a results this approach, a wider variety of brake maneuvers could be simulated. Maneuver variations could be based on tire models, road surface models, battery management models, etc.

The above described is an addition in the ALPHA project, which is a consortium of some European vehicle manufacturers, brake system suppliers, test equipment manufacturers, and vehicle simulation providers.

Residual drag torque of disc brakes is caused by unintended contacts between brake-disc and -pads when the brake is not applied. Brake drag opposes the current efforts for BEV range improvement as well as prospective restrictions for brake dust emission. Since every unnecessary friction contact dissipates kinetic energy and emits additional particles. State of the art for brake-drag-analysis is based on component level measurement primarily performed on brake dynamometers. Tough under real driving conditions in-vehicle the brake is exposed to different and additional influencing factors like wheel forces known to potentially affecting drag torque significantly. Therefore, using component-test results to forecast brake drag behavior in-vehicle on the road is to some degree uncertain, evoking the provocative question: Is drag optimization, on brake dynamometer effective or maybe even overengineered for in-vehicle use? A related comprehensive answer is currently prevented by a lack of appropriate brake drag measurement data in-vehicle. In this light the following research first defines the requirements for in-vehicle brake drag measurement under real driving conditions. Based on a categorization and assessment of existing measurement technology as well as related patents, an approach using 3-axis piezo-force-sensors is identified and subsequently implemented. After evaluating sufficient functionality on the brake dynamometer, a vehicle is equipped with the measurement system at each (fixed caliper) brake. According to the RDE-categorization real-driving tests are performed on urban, rural and highway-road-sections and additionally on the roller dyno. The results point out certain differences (theoretical presumed in literature) between component- and in-vehicle brake drag behavior motivating further investigation to expand the understanding under real driving conditions.

The first approach towards a regulation of Brake Emissions by PMP (Particle Measurement Program) under the United Nations Economic Commission for Europe (UNECE) is ongoing – with a dedicated cycle, defined indicators to be measured and a procedure to be confirmed within a Round Robin end of 2021. The results of the participating laboratories shall be analyzed latest in April 2022.

Next big steps shall then be the consideration of xEVs with their capability to recuperate (TF4) and thus reduce the use of the friction brake, which shall be included in the first draft of an upcoming legal regulation.

This will subsequently increase the complexity of the measuring procedures as recuperation strategies shall be included. PMP shall then release a first draft in June 2022.

In the end all measures and vehicle systems that contribute to a reduction of Brake Emission shall be taken into account, which means a huge peak of development on this topic with a respective high demand on test bench capacity.

Affected components will not only be software and functions, but also new brake system hardware like Electro Mechanical Brakes, that shall also reduce emissions by e.g. “true zero drag” or better controllability for brake blending.

Adapted simulation will be introduced and optimized to enable respective measurement campaigns at the test rigs.

As the availability of brake test rigs is limited the industry is requested to flexibly provide affordable testing solutions to cover this accumulation in testing.

The test rigs themselves might evolve from inertia dynos to inertia simulation – increasing the degrees of freedom.

After the actual focus on – also electrified – passenger cars and light commercial vehicles up to 3.5 t also heavy commercial vehicles will be considered.

Electrification of vehicles and increasing level of automation of the driving task are driving factors for true by-wire technologies – braking being on of the domains where conventional mechanical fallbacks are to be replaced with electronic redundancy. The paper will define and motivate these technologies. It will furthermore discuss the concept of an electric brake pedal as a building block for true brake-by-wire. The electric brake pedal will be discussed as a component but also its integration in a redundant brake system will be presented.

While electro-mechanic brake actuators are already seen on the roadmap of brake-by wire systems, electro-hydraulic brake systems are a near-term solution and share key features of the true by-wire technology. The paper will present architectures of such electro-hydraulic brake systems consisting of separate brake control units as well as integrated solutions.

Driving range and efficiency are two of the major influencing factors on current electric vehicle development efforts. While the focus is obviously on battery and powertrain technology, an optimized braking system can greatly contribute to achieving range and efficiency goals. Significant negative torque generation by the electric powertrain adds an important degree of freedom to modern electrified brake systems. It not only influences range and efficiency in general but also requires the engineers to tune the electric driving experience according to the specific OEM’s vehicle DNA.

This interdisciplinary challenge between brake, chassis and powertrain systems has to be continuously incorporated into the development process and solved by a cross-domain team collaboration. A full vehicle simulation environment is able to support these activities. Early on, virtual vehicle prototypes can be built up and used in a MIL/SIL environment to evaluate the performance regarding relevant optimization criteria. Further on in the process, component prototypes can be included for calibration and testing on HIL test systems. Later in the process, this is also possible for full powertrain and chassis prototypes.

In an application example, the energy efficiency and vehicle stability of an EV with a rear-wheel drive (RWD) powertrain are analyzed and optimized for different real driving scenarios. Due to the RWD architecture, the amount of regenerative braking (recuperation) directly influencing the energy efficiency is limited depending on the dynamic driving situation. The results from the MIL testing environment indicate that a careful calibration is necessary to ensure the vehicle’s driving stability, but also allow for the highest amount of recuperation at the rear axle. Future studies will take the driver behavior as well as driving and brake pedal force calibration into account.

This paper presents a new methodology to evaluate the Emission Factors for PM10 and PM2.5 from tire wear using an on-road driving collecting device to capture the Tire Road Wear Particles (TRWP) directly at the source. Special attention was paid to ensure a maximal reduction of the usual biases associated to this kind of approach: the test track was systematically cleaned prior to all the tests, only one vehicle was allowed during the tests, the design of the collector was made to maximize the collection of TRWP of the tested tire.

The results show emission factor values significantly lower compared to those commonly reported in the literature. The discrepancy calls for further tests to confirm the results.

At the Institute of Vehicle System Technology at the Karlsruhe Institute of Technology (KIT) a new inner drum test bench had been build up and put into operation in 2022. This test bench allows the analysis of PLT (passenger and light truck) and truck tires under realistic quasi-stationary and dynamic loads on different real track surfaces. The test bench consists of a rotating drum and a load unit based on a servo-hydraulic hexapod unit, which allows almost any setting of the operating conditions of the tire with frequencies of up to 30 Hz. An electric wheel drive unit allows the tire to be loaded with respective drive and braking torques. In addition, the test bench construction principle allows the investigation of chassis systems, which can be attached to the Hexapod and be operated as a quarter vehicle.

Initially, the authors discuss the future demands on the experimental analysis of tires and identify major research fields for the usage of the new test bench. After this introduction, the authors present and describe details of the construction and the main technical specifications of the new test bench. The technical specifications will be compared to requirements resulting from the operation of PLT and truck tires, so that the operation field of the new test bench is more precisely described. Finally, first experimental results will be presented, that demonstrate the functionality of the test bench and give a first impression of future applications of the test bench.

New mobility, battery electric vehicles (EVs) and vehicle manufacturer strategies to achieve climate neutrality are transforming car design and automotive engineering. As an important styling element and an essential part of emissions-reduction strategies, wheel design is undergoing significant change.

Advances in simulation tools, supercomputing and increasingly diverse engineering capabilities are enabling advances in wheel design. These investments and advances are enabling Maxion to deliver on its objective of offering customers the most sustainable wheel option for every vehicle segment.

To achieve substantial carbon footprint reductions, however, major innovations are required: replacing aluminum with less energy-intensive materials is a key part of the challenge. With a carbon footprint that is 70% less than aluminum, steel wheels represent a significant opportunity for life cycle CO2 savings.

As vehicle manufacturers adjust to the evolving demands of new mobility, the need for improved aerodynamics and changing perceptions of what creates additional value for EV buyers are prompting a shift in attitudes toward steel wheels by program managers. Long overlooked, the industry’s commitment to carbon neutrality, sustainability and new mobility, is encouraging a fundamental rethink of the role of steel wheels.

This paper relates the experimental analysis carried out to obtain a quantitative grasp of the influence of wheel stiffness on driving stability, which up to now had been inferred through a reliance on rule of thumb. For the disk section and the rim section, stiffness alternatives with additional wheel reinforcement were prepared, and comparative testing of the influence that wheel stiffness has on tire contact patch characteristics, tire lateral force, and driving stability was carried out by bench and driving tests. Wheel stiffness was divided into the disk section, the rim section, and the hub fixing section for evaluation.

Disk reinforcement has an influence that reduces change in the camber angle of the disk. Rim reinforcement has an influence that reduces the displacement to the ground of the rim. The disk stiffness and rim stiffness have different respective influences on tire contact patch characteristics. Disk stiffness is related to tire contact patch length, and rim stiffness is related to tire contact patch area. Tire contact patch length is related to the maneuverability of driving stability. Tire contact patch area of the tire is related to the stability of driving stability.

The balance between maneuverability and stability was successfully enhanced by optimizing the proportion between disk stiffness and rim stiffness. In addition, the amount of additional wheel reinforcement necessary to achieve the objective of enhanced balance between maneuverability and stability was successfully minimized. The substance of the report follows.

The transformation from vehicles with combustion engines to electric drives influences the wheel development of OEMs. This paper shows how the “optimal compromise” between engineering, design and cost is changing due to the relatively heavy batteries and the recuperation possibility of kinetic energy.

Higher wheel loads and significantly higher aerodynamic demands also change the design of the wheels. However, since wheels are one of the most important design elements of a vehicle, it is necessary to develop concepts to make these wheels more attractive without significantly increasing the wheel weights.

Visible genuine alloy, in which the machining process may also be visible, e.g. in the case of polished wheels, still stands for high-priced wheels. Bright machined casting-wheels with good aerodynamic properties are usually extremely heavy. Therefore, plastic panels are increasingly being used, which are either screwed, glued, or clamped. With panels made of formed aluminum sheets, which are back injected with plastic, one comes a good step closer to this goal. However, the forming possibilities and the surface design are very limited, since aluminum sheets tend to crack during forming in the case of large deformations.

The company Ulbrichts GmbH in Austria has developed a process that uses generic alloy with extremely precisely manufactured wheel panels with real alloy in such a way that they are no longer distinguishable from classically mechanically manufactured parts. As a result, high-quality, acceptable priced, lightweight wheels can be produced. At the end wheels with this panels fulfill the highest requirements for premium OEMs and contribute significantly to increasing the range of electric vehicles.

Vehicle performance enhancement is one of the thorniest challenges that motorsport teams and car manufacturers face every day. In order to optimize the car dynamic behavior, it is fundamental to make tires work in temperature, pressure and setup conditions which can let them exhibit their maximum potential. For this reason, in recent years, great efforts have been made towards both indoor and outdoor novel tire characterization methodologies and increasingly complex mathematical models able to reproduce the tire physical behavior, accounting for all the interlinked physical phenomena involved.

In the presented work three different physical models, developed by the UniNa research group and its spin-off MegaRide, are coupled within a co-simulation framework, allowing to investigate the tire performance sensitivities and to optimize the vehicle behavior in the widest possible range of tire working conditions.

To this purpose, a vehicle model called T.R.I.C.K. (Tire/Road Interaction Characterization and Knowledge) has been developed to process data acquired from outdoor test session, adopting standard vehicle data to obtain interaction curves and time-by-time tire kinematics and dynamics. The output “virtual telemetry” is employed as an input for a tire thermodynamic model, called thermoRIDE, able to evaluate the local temperatures of all the different tire external and internal layers, not reachable by sensors. Finally, to take into account the effects due to energy, temperature, tread viscoelasticity and road roughness on tire wear and degradation, an additional physical model, weaRIDE, has been implemented and parameterized.

Analyzing the enriched dataset, it is possible to obtain fundamental information concerning tire behavior to define an optimal setup to increase and to govern the overall vehicle performance, both in design and pre-race phases.

The lateral dynamic response of passenger cars is highly influenced by the interaction between the vehicle’s suspension system and tire characteristics. One important task in the development of vehicle dynamics performance is the design of the tire characteristics to the needs of the vehicle and its suspension system. Optimizing the whole system is possible in an interactive process between OEM customer and tire supplier.

On the tire side we will be discussing the use of modern simulation methods to predict tire force and moment characteristics based on tire simulation methods and on the vehicle side we will be going into the integration of virtual tire characteristics into the vehicle performance simulation. Furthermore, target setting and target fulfillment will be discussed along with taking other criteria than vehicle handling, e.g., rolling resistance requirements, into account.