13th International Munich Chassis Symposium 2022

The ongoing and strong transition to electrified powertrain systems and by-wire technology gives rise to new potentials for the control of vehicle dynamics and at the same time imposes new requirements to the control system. Thus, modern vehicle dynamics control systems need to be capable of managing cross-domain actuator control, keeping system complexity low, creating synergies, and unlocking the full potential of each single actuator in any driving situation. Further, the ongoing trend to more centralized and zone-oriented vehicle E/E architectures is another major technological challenge in developing a future-proof vehicle dynamics control system.

The Electrification of the powertrain, digitalization of the vehicle and automated driving are the major drivers of the transformation in the automotive industry. The implementation of the resulting requirements is taking place at the level of the E/E and the vehicle architecture in parallel.

Requirements such as easy scalability, fast upgradeability and learning ability as well as reduced complexity call for fundamental changes in the E/E architecture. The key concepts are centralization and zonalization as well as a standardized abstraction layer between the hardware and the vehicle functions/software. Legacy control units - especially for safety-critical functions such as braking, steering - are maintained at this stage of evolution. This creates the foundations for the long-term goal of creating a standardized central server architecture.

At the same time, there is a similar development in the vehicle architecture. More and more companies are showing studies and, in some cases, production-ready implementations of so-called rolling chassis and corner modules.

In this lecture, important aspects will be highlighted that are not only relevant for the rolling chassis. The electrification of the brake is shown with the associated development. Another topic is the central control of all vehicle motion actuators - brakes, steering, propulsion and chassis. This is also the case with the introduction of the rolling chassis, which requires a clearly defined, electrical and mechanical interface to easily separate the cabin and chassis.

In modern vehicle development, proof of functional safety represents a crucial aspect since the software content in vehicles and the significance of automated driving functions are continuously increasing. While humans can act as a fallback level for conventional systems, algorithms take over this role for automated driving functions. They depend on the complete and correct recognition of the vehicle’s environment at all times and on the error-free communication of the vehicle’s components, such as sensors, actuators and ECUs, with each other.

To ensure functional safety in all traffic situations, the focus on the full vehicle needs to be strengthened in development. Integration and system tests enable investigations of the interaction between all components. Due to the variety of possible traffic situations, an extremely large number of tests is required to achieve maximum test coverage for proof of safety. This is the only way to ensure accurate handling of any situation.

For every stage of the development process, there are suitable test methods that offer support to achieve the required test coverage with simulation: software-in-the-loop (SIL), hardware-in-the-loop (HIL) and vehicle-in-the-loop (VIL). The targeted test strategy resembles a funnel. The early development stage starts with high levels of virtualization, automation, parallelization and, derived from this, many possible tests. Over the course of the development process, the scope of every aspect mentioned before decreases continuously while the tests remain entirely reproducible at any time.

An open integration and test platform (e.g. CarMaker) offers the possibility to implement tests automatically and safely as well as in an unlimited number of critical scenarios, and thus ensures functional safety. Combined with agile software development, virtual vehicle development lays an ideal foundation for coping with said requirements for functional safety and for enabling assurance of the necessary quality.

By wire systems in vehicles are increasingly used for driver assist and automated driving mainly for steering and braking. Fail operational actuators with FIT rates below 10FIT are the typical challenge.

This paper is about what we learned, what we observe and about basic considerations on a systematic approach of how to optimize the efforts for implementation based on experience from real applications.

The increasing autonomy levels of modern vehicles require the accommodation of advanced driver assistance systems (ADAS) but also the revision of previously well-established domains. This study examines the recently introduced demands placed on chassis-relevant domains to partially transfer control from the driver to the vehicle. Essential aspects include, but are not limited to, fail-safe strategies for the steering system and practices to increase the reliability of the braking system. Within the scope of this work, solutions deployed by Ford Motor Company, General Motors, Tesla and Lucid Motors on their most recent releases claiming level 2.0 or higher autonomy are considered and compared.

With Vision EQXX, Mercedes-Benz brings a highly efficient electric vehicle on the road to show the ultimate performance of its new EV-platforms.

This presentation will give an insight in the development of the chassis for this unique project.

Stepping into the electric-only future with rear-wheel drive makes a complete new chassis system necessary. Main point is the all-new compact rear axle that fits perfectly to the electric powertrain and brings the efficiency to the road.

Just like the entire vehicle, also the chassis with its sub-systems pulls all the major efficiency levers to boost the overall performance of the vehicle. Ultra-low rolling resistance tyres, innovative aluminium brake discs and a lightweight rear-axle subframe (developed in close cooperation with Mercedes-Benz Formula1 Team) are only some examples of the efficient solutions.

Beside the innovative solutions throughout all the chassis sub-systems, the agile working model in this project is remarkable, too. In only a short development-period the whole chassis must be designed, realized and tuned to bring EQXX on the road in time.

Future steering systems must not only be compatible with automated driving systems, but also allow for improved driving space flexibility. To address these needs, we are currently developing a Steer-by-Wire system with no mechanical link. This paper proposes a fully redundant configuration, the state transition and, a control method of variable steering gear ratio and reaction force to achieve natural steering feel in a Steer-by-Wire vehicle assuming driver doesn't change hand position on the steering wheel. Moreover, taking advantage of the characteristics of Steer-by-Wire system, we also demonstrate the effectiveness of a control method to transmit only necessary road information to the driver.

As the automotive market continues to welcome autonomous technologies, the development of the corresponding features and system redundancies is becoming critical to the successful adaptation of these advanced innovations. As vehicle manufacturers invest in these critical technologies, the ability to engineer and properly execute the products in a cost-effective manner is a valued concern. CNXMotion has worked closely with its partner companies, Nexteer and Continental Automotive, to develop autonomous system redundancies and safety concepts to better facilitate an affordable transition to the autonomous future. Brake-to-Steer is one such technology that has been developed as a redundancy to allow lateral control of the vehicle when the steering system is unavailable.

This paper will discuss the methods by which CNXMotion approached the concept and testing methods used to identify the main chassis and environmental parameters contributing to the performance of Brake-to-Steer. The team began by using Design-for-Six-Sigma (DFSS) principles. DFSS studies were used to understand the main factors contributing to lateral vehicle movement using brakes. Although the vehicles were limiting the success of this method, the factors identified laid a path to allow for high-fidelity vehicle testing methods made possible by the addition of autonomy.

Once the team understood the main contributing factors to steering the car with brakes, creating a testing method to allow repeatable and consistent results was necessary. By automating a straight path, the team was able to manipulate varying brake inputs to augment the vehicle’s path and compare the lateral movement to the known straight path. This method created a basis for analysis and allowed for metrics to be created. Once the metrics were established, braking algorithm designs commenced and evolved into several iterated designs.

The paper will explain in order:

In summary, the team has extensively tested the interactions of the braking, powertrain, and surface mu and their individual and combined effects on the lateral movement of the vehicle through applying brakes.

The chassis of a passenger vehicle has a long history of development and seems to have reached its optimum in the cost-benefit ratio. On the one hand, the cost pressure is increasing, because the raw materials are becoming more expensive; on the other hand, high-end systems must clearly demonstrate the necessity of their use from a functional, weight, consumption, cost and strategic point of view. Caused by this reasons a large field opens between conventional, passive and fully active stabilizers.

As a new technical concept is presented an adaptive stabilizer, whereby a frequency-selective damping valve is connected in parallel to the torsion bar,see Fig. 1. The operating principle describes the use of the difference in angle of rotation of the two halves of the stabilizer to adjust a hydraulic piston, whereby a volume of oil is passed through a valve system and generates a frequency-selective damping. The stabilizer halves are connected on the one hand to the housing on the other hand to the shaft. The internal, passive application torsion bar connected to both sides is always engaged. The concept has been developed and prototype parts have been installed into a BMW X4. Due to the first positive driving impressions the basic concept could therefore be confirmed.

In times of increasing electrification in all vehicle segments, one of the main challenges is to provide high driving range in combination with a smart battery pack design. Especially for A and B Vehicle-segments the torsion beam of the twist beam axle (TBA) is the main limiting factor regarding package space in the rear end.

Based on this problem, a new axle concept, the so called Multi Link Torsion Axle (MLTA), was developed as a part of a research project in collaboration with Ford, VW and other project partners. The basic idea is to reverse the installation direction of the TBA to create additional package for the battery. To compensate the kinematic drawbacks caused by reversed installation, namely anti-lift and wheel recession behavior, the twist beam structure was integrated in a longitudinally oriented Watt’s linkage. This new arrangement leads to a battery volume increase of up to 30%. At the same time, the longitudinal kinematic behavior can be varied nearly independently from the torsion beam position by modifying the Watt’s linkage hard points.

The basic kinematic concept and design process was presented at Chassis.Tech 2021. Based on this prior work, the elasto-kinematic design was carried out further. To achieve the elasto-kinematic performance close to a conventional TBA, the orientation and stiffness of the toe-correcting bushings were optimized using a method developed in this work. Furthermore, a new bushing for the Watt’s Linkage was developed in collaboration with Vorwerk-Autotec. Additionally, side-force springs developed by Mubea were implemented to further improve the lateral compliance and the steering response behavior.

Following the concept development, the CAD was conducted. The design process was mainly driven by structural stiffness and strength performance, evaluated with CAE Methods. Finally, the whole axle-module was manufactured and mounted by CP Auto to a modified Ford Fiesta body, which was done with a tubular frame work design. To rate the overall performance, handling, ride and KnC Test with the full-vehicle were performed by Ford and finally compared to the original and a mass modified Ford Fiesta.

The chassis is one of the most or even the most important assembly group of a vehicle as it is the main support structure. It is the load bearing framework and stabilizing the vehicle against external impacts. Therewith, the chassis is crucial for the safety but also for the optimum driving comfort. For battery electric vehicles, it needs to provide maximum space for the batteries which are usually placed in the sub-structure. Thus, chassis applications are facing several technical and sustainability challenges.

The omni-present topic of lightweight does not stop for chassis applications. Weight reductions mean more energy efficiency but also the possibility of weight compensation due to further equipment for passenger comfort and safety or due to heavy batteries.

Stainless steel is a traditional but also innovative material, continuously developing according to human and industry needs. This paper presents the latest material development of temper rolled 1.4376 for use in chassis applications. It offers a combination of high strength and high elongation, which can solve several safety and design aspects. Finally, cost-competitive and sustainable lightweight solutions can be achieved. All this makes this stainless steel pioneering and extremely interesting for chassis concepts.

The topics of automated driving and digitization are becoming increasingly important and have the potential to shape the future of mobility. Concurrently, manufacturers want to continue to differentiate themselves through driving characteristics typical of their brands. Rapid developments regarding technological changes as well as legal regulations combined with short development times present new challenges for the entire automotive industry. In this context, virtualization and front-loading methods play a major role within the vehicle development. There has been a clear trend of pushing virtual development via simulation to reduce the number of necessary prototypes. However, since both engineers and management still rely heavily on the crucial insights gained by real road tests, subjective closed-loop assessment must remain a part of this virtual process. Driving simulators have the potential to bridge these gaps, allowing engineers and test drivers to subjectively experience and assess new systems in an early virtual phase of development.

Kempten University of Applied Sciences is working with technology partners to research and further develop their dynamic driving simulator. With the goal to develop use-case specific methods for virtual vehicle development, the simulator’s novel motion platform is used specifically for research projects in areas requiring high dynamic performance such as vehicle dynamics and ride. This paper describes the methods and solutions developed in an R&D project investigating the simulator’s capabilities for ride comfort evaluation, such as primary & secondary ride. With the goal to enable experienced test drivers to perform a subjective ride evaluation in a very early development phase, the simulator’s real-time environment was extended with the highly sophisticated tire model FTire. This paper provides an overview of the system’s performance regarding subjective ride assessment. It presents a brief insight into the detailed road modelling and describes the measures taken to ensure real-time capability of the individual model interfaces. Objective performance evaluation shows the benefit of this work for comfort evaluation in early phases of virtual development.

The assessment of driving simulator immersiveness and realism is a relevant problem. Driving simulators are reputed to be professional development tools only, but their use by a large sample of subjects is, however, crucial for automated vehicles development or for Human-Machine-Interface studies.

At Politecnico di Milano, engineers and psychologists from Vita-Salute San Raffaele University, have completed an assessment of a cable driven driving simulator to check immersiveness and realism. Both subjective and objective measurements have been made testing ordinary (non-professional) drivers in presence of other road users during an immersive experience.

The main focus was on motorway running conditions since UN-ECE Regulation 157 (Level 3 automated vehicles) refers to such a scenario.

Before starting the driving experience, driving styles and emotions were assessed. Biological signals referring to eye tracking, gaze tracking, skin potential response, heart rate variability, forces and moments applied by each hand at the steering wheel were recorded during the driving (objective assessment). The DiM400 provided good immersiveness and allows a large experimental test campaign with ordinary drivers in a scenario relevant for UN-ECE 157 Regulation. After the driving simulation experience on the simulator, non-professional drivers reported average or above-average values of realism.

The key trends in the automotive world demand for a highly integrated, validated and applicable digital development process. In this vehicle dynamics development process, several models for hardware & software development and evaluation need to be available. Key factor in the usage of these models is the ability to not only set targets, but also to follow up on these targets throughout the development process. Since not all characteristics of vehicle behavior can be completely described through objective measures, the integration of test drivers as subjective evaluators in driving simulators is evident. Validated models available for vehicle dynamics are not only needed for the development of the core behavior, but also in other use cases like software-in-the-loop (“SiL”) test clusters or drivetrain test benches. This article discusses the possibility of reusing existing models in multi-domain simulation environments. The advantage of this integral approach concentrates the efforts on optimizing models and products, instead of communicating data and understanding external models.

The present contribution introduces a systematic approach to the development of optimal attributes of Lane Keeping Assist Systems. An Active Lane Departure Warning (ALDW) with corrective steering interventions was the specific use case.

Firstly, a subjective evaluation baseline was created from a proband study involving five different ALDW implementations and a catalogue of attribute related subjective rating criteria. Afterwards the respective vehicles were characterized by conducting designated driving maneuvers and computing objective performance indicators from the measurements taken. By correlating the subjective ratings with the performance indicators, a set of descriptive key performance indicators (KPIs) with corresponding target values was identified.

Based on the objective targets an optimized calibration variant was prepared and implemented in a test vehicle. By repeating and evaluating the initial driving maneuvers, the coverage of targets was ensured. Conclusively proving the effectiveness of the introduced approach, a verification study under comparable conditions delivered significant subjective improvement as well.

Along with the electrification and connectivity of vehicles, the automation of the driving task represents one of the main trends in the automotive industry. With the increasing capabilities of Advanced Driver Assistance Systems (ADAS) and Automated Driving Systems (ADS), the number of driving scenarios that must be handled by the systems in road traffic is constantly increasing. Drivers expect the vehicle to act safely, comfortably and efficiently, which is why ADAS/ADS must successfully perform a calibration and validation process during vehicle development. While this process is nowadays accomplished on proving grounds or in road traffic, a variety of new approaches will be required in the future to deal with the increasing scope of the systems. One of these approaches is the use of simulation tools to perform virtual calibration and validation. The main challenge of this approach is the multitude of components, such as a scenario catalog, the simulation itself, evaluation metrics and more, that are required in high quality to generate usable results. To meet this challenge, the paper presents a modular framework for both virtual calibration and validation of ADAS/ADS. The focus is on the presentation of the modules required for a combined approach as well as their structure and interfaces. The paper first presents the framework in a generalized structure that can be applied to a wide variety of ADAS/ADS, and then shows the exemplary implementation for virtual calibration and validation of an adaptive cruise control. Finally, the results of a virtual calibration and validation run are shown and discussed.

Virtual methods utilization is increasing during vehicle development phases, to speed up the process, explore broader design space and increase the design detail before producing the first physical prototype. For complex systems like ADAS, which are inherently multidisciplinary, the use of multi-domain simulation environment is advisable: therefore, the utilization of test benches to integrate the virtual development with the first physical prototypes can increase opportunities in development and validation phases.

This work focuses on the development of a test bench and a test scenario for testing the Lane Centering system in all its components. Using a steering bench, capable of reproducing forces on the real steering system, and a camera in the loop bench, the LCA system has been entirely implemented on the static simulator and validated in virtual high-fidelity scenarios, reproducing a real test track.

Firstly, the testing apparatus construction and calibration is described. Secondly, the scenario creation procedure is shown. Lastly, various evaluation tests are carried out on the simulator, following the same methodologies as if the system is mounted on a real vehicle.

The proposed bench and testing methodologies has resulted capable of accurately reproduce the key performance index of the real system, allowing its complete assessment on the static simulator, thus broadening the design space, allowing for development time and cost reduction.

Vehicle automation is still one key trend in the vehicle industry where nowadays just a few advanced series projects barely reach SAE Level 3, and even less series projects achieve SAE Level 4 (and only in very limited conditions).

Modern autonomous driving algorithms focus mainly on situation recognition and automated driving decisions. This essentially includes the planning and implementation of trajectories based on environmental sensor data coming from cameras, LiDAR, radar- or ultrasonic-sensors.

Currently, one important aspect of automation which is overlooked is the responsibility to monitor the overall technical condition of the vehicle and the road.

Even if all relevant vehicle systems have suitable monitoring functions, there are still malfunctions or critical conditions which may not be covered, which a human driver can detect or even handle intuitively. This is also of great importance when considering functional safety in “controllability” (manageability of a fault).

Automated and autonomous vehicles must be able to continuously track the overall condition of the vehicle and the immediate environment to ensure that not only faults but also risks can be detected reliably in time.

The increasing digitization of vehicles leads to a continuously increasing number of wireless interfaces between the vehicle and components outside. These additional functionalities and interfaces lead to an increasing vulnerability and probability of a cybersecurity attack by third parties. IAV has implemented a process standard to develop and maintain cybersecurity relevant electrical components in accordance with ISO/SAE 21434 Road vehicles—Cybersecurity engineering. Due to the large proportion of safety-relevant and networked electrical components in the chassis, automotive cybersecurity must be widely applied. IAV´s Cybersecurity Management System offers the possibility to perform security analyses during the development phase and support phase of the vehicle. The primary objective of the security analysis is to identify threats, to evaluate them in terms of impact for the considered item and to identify appropriate mitigation measures. In this paper, excerpts of the IAV process standard are presented and the security analysis (TARA—Threat Analysis and Risk Assessment) is discussed exemplary based on the steering functionality of an autonomous shuttle. The focus is put on a safety goal as an asset by means of cybersecurity. Furthermore, possibilities for mitigating the identified risks are shown. As an addition, interfaces between functional safety and cybersecurity are illustrated.

The aim of this paper is to present a model predictive control strategy for autonomous vehicles with capabilities to handle trajectory planning (trajectory optimization) and trajectory tracking. In addition, with the content presented in 2019, current development of the trajectory planner has been updated and now is obtained in an online fashion using a linearized vehicle model.

For the trajectory planning, a set of boundaries have been given in terms of road limits, reference path with lateral limits and speed limitations for each section. In relation to vehicle dynamics performance boundaries have been given such as maximum lateral acceleration and sideslip angle. In addition, the trajectory planner integrates an ACC logic in the MPC formulation to maintain an adequate distance to the vehicle in front. With this set up, a model predictive algorithm calculates a dynamically feasible trajectory which is the input to the second MPC algorithm working in series. This second MPC is the trajectory tracker that aims to follow closely the reference given. By using a dynamic model of the vehicle, predictions of the future states of the vehicle helps to anticipate the actions to be performed within a defined horizon.

The work presented has been developed under the scope of a European research project in the field of autonomous driving acceptance: SUaaVE project which will be introduced in the 1^st chapter. In the 2^nd chapter a detailed description of the controllers is given. In 3^rd chapter a description of the tests is disposed followed by the results of the motion comfort survey performed have been analyzed using advanced machine learning techniques with the aim of being able to predict passenger feelings and be able to influence on vehicle behavior accordingly.

Coordinated control (i-LEED: The trademark of Hitachi Astemo, Ltd.) provides performance evolution for vehicle dynamics response and stable steering feel. The system only adds a unique control logic module to the existing control logic and requires no additional hardware in the vehicle. A prominent aspect of innovation is that it uses the steering effort information from the EPS. This allows a very quick response for pre-conditioning the steering and shock absorbers at an earlier phase of the turning maneuver, enabling remarkably stable steering feel.

First, the coordinated control for semi active shock absorber improve turning feel, which is response and feel of unity by optimizing the pitch movement in accordance with the roll motion at earlier timing using the steering effort from the EPS (Electric Power Steering) system. Then, the coordinated control for EPS improves stable steering effort by compensating the SAT (Self Aligning Torque), which is the cause of an unstable steering effort using the roll rate from the semi active shock absorber system. As a result, comfortable turning feel during turning transient is realized by applying both controls coordinated and in defined succession.　A welcome effect from not requiring additional hardware is the cost and weight saving, as well as the elimination of failure sources.

The automotive software development industry is undergoing a major shift as more and more SAE Level 4 and SAE Level 5 autonomous features are being developed. Many high-tech companies, OEMs, suppliers, IT services, government agencies, contract houses, etc., have invested billions of dollars into software for autonomous features. Automotive software has become much more complex, and OEMs are looking at non-traditional suppliers such as start-ups as sources for these new applications. This has led to the need for improved interaction between electronic control units (ECUs) and the increased use of domain controllers. Developing features such as road surface detection, brake-to-steer, etc. in this new environment presents numerous new challenges and hurdles.

Road Surface Detection software is an example that can provide a safer driving experience for the driver. Knowing the road surface such as icy, gravel, or wet could be used by many systems in a vehicle to improve safety. The road surface detection algorithm is designed to reside in any ECU or domain controller in the vehicle. The feature classification of the algorithm & target ASIL development requires multiple signals from multiple systems. This presents challenges to the authenticity and accuracy of the data, standardization of the interface, and validation of signals. When systems are provided by different suppliers within vehicles, it becomes difficult to exchange information across ownership silos.

This paper will take a deeper dive into the challenges and potential recommendations of providing an algorithm such as road surface detection in the form of software as a product – as well as solving these challenges while understanding the OEMs’ desire to source software functions from diverse suppliers, justify costs and meet safety requirements and launch timing. We will present our solutions in the context of what is currently being considered in the industry – not only focusing on the technical aspects of vehicle implementation, but it does also consider the technical aspects of software delivery concepts such as an automotive software marketplace or consumer enabled to purchase and update.

A semi-active suspension system is often used to allow a broad spread between ride comfort and handling ability. The performance of the chassis system is directly related to the high responsive hydraulics control as well as the control strategy. This control software is using information from the vehicle applying through the CAN connection and other functions developed by the suspension supplier to assure driving safety, handling control and riding comfort independent on the road solicitation by controlling electro-magnetic valves at each shock absorber.

Upon the physics there are existing borders for those systems in regards of possible noise impacts in case of high frequency or high amplitude road inputs which can be solved by passive systems using mechanical rubber stops at the rebound or compression side. Such a system requires additional package and increases the cost of the shock absorber.

The proper use of a software solution can avoid the implementation of hydraulic rebound or compression stoppers and thus reduce the dimensions of mechanical rubber stoppers keeping the overall shock absorber length on an equal level and furthermore avoid additional cost for additionally required components.

New software functions can be implemented into the same ECU as for the semi-active suspension system providing a higher damping robustness for extreme road input. Furthermore, it is possible to adapt the damping force progressivity by modifying the gradient and activation point for rebound and compression conditions.

The paradigm change from the classical development of mechanical components towards the finding of numerical solutions of solving a big variety of vehicle drivability issues is the key item for the future enablement of moving towards the virtual development of shock absorbers and chassis systems.

Improving the behavior of the suspension purely by the adjusting of the related application software, allows the adaption of different control strategies according to the requirements of the applied vehicle reducing the variants of shock absorbers and thus the overall development effort just by software map definition.

Finally, the focus on software solutions will reduce cost and shorten the lead time both at OEM and supplier side by reducing loops of bench and vehicle validation during the setting definition.