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EuroBrake 2022: Braking systems as part of the mobility agenda (Part 1) session overview

The Braking systems as part of the mobility agenda (Part 1) session will take place on Wednesday May 18th and will be chaired by Manfred Meyer of ZF Group and co-chaired by Thomas Bachmann of TU Ilmenau.

Topics and speakers for the session include:

Future Brake Systems: requirements and solutions

Alexander Gaedke, Robert Bosch GmbH

The automotive industry is undergoing a significant change mainly driven by the key drivers automation, electrification and environmental protection.

The brake system is affected in many ways, with highly automated driving (HAD) being the driver with the biggest impact.

  • Tasks that used to be performed by the driver are (partially) done by the brake system, depending on the degree of automation.

  • Brake redundancy must be ensured in accordance with the state of the art

Other requirements also need to be considered.

  • Expectations for time to lock are steadily increasing (NCAP)

  • Expectations towards NVH are increasing, driven by electric powertrains with less noise emission.

  • Any new brake system needs to ensure a high level of recuperation efficiency.

  • Further reduction of CO2 emission by zero drag brake systems.

  • Reduction of fine dust emission.

  • Cooperation with the electric power train, e.g. for traction control or stability control.

  • Reduction of vehicle assembly effort.

  • Variance within vehicle platforms requires optimal modularity of the brake system in order to achieve minimal cost.

Current solutions (combination of ESC with electric boost as well as some 1-box concepts) already provide answers to these requirements. In this presentation, we want to discuss these requirements and reflect in particular HAD L3 and L4 aspects at today's solutions, with special emphasis on Bosch's two main product lines for brake systems, iBooster plus ESP® on the one hand and IPB on the other hand. We will give an outlook to future systems such as brake-by-wire and new brake topologies.

Target setting and test metrics definition for redundant braking systems development for CAVs

Carlos Jose Sierra, Applus IDIADA

Braking systems development is currently facing a shift in the engineering and testing activities. Traditionally pedal feel tuning and performance refinement have been major issues, but along with electrification, the increasing level of driving automation is shifting development efforts into different directions.

For a brake system, the task of autonomous driving (with or without human presence) mandates redundancy in many subsystem elements. Therefore, a strong effort in understanding how to set targets is needed to correctly develop and validate reliable systems.

In this paper, the authors are initially defining a set of performance key factors, which will be used to define the global characteristics of the system. It is not necessary to deeply investigate the performance of the system to validate the operation of a vehicle equipped with a redundant braking system, but in the concept phase it is certainly useful to investigate how different architectures could potentially influence the vehicle performance.

Having investigated the structure of the system, the authors suggest how targets could be set for a vehicle equipped with a redundant braking system. This study is mainly focused on understanding and validating how failures affect the general performance of the vehicle. Primarily this paper shows how partial system failures (ESP, EPB, iBooster) affect the general braking performance, mainly in terms of deceleration, stopping distance, front/rear modulation, on slope braking performance and finally time-to-lock.

The main output of this study is the definition of a validation matrix (a so called Design Validation Plan), which is certainly a necessary step in order to perform a robust Vehicle Target Setting (VTS). A list of metrics is also proposed by the authors.

The target book generation needs to be as versatile as possible, in order to be adapted to the full range of available systems in the market, particularly when the systems allow automated driving levels higher than L3.

Investigation on the control of electromechanical brakes via wheel-speed-sensor feedback

Missie Aguado-Rojas, Hitachi Astemo

Motivation and objective

In recent years, electromechanical brakes (EMBs) have drawn significant attention from both research communities and automotive brake suppliers alike, as they are deemed to be a promising replacement for hydraulic brakes in the automotive industry. Compared to conventional hydraulic brakes, EMBs offer the potential for component, size, and weight reduction of the overall braking system, as well as faster response times, which result in shorter stopping distances and increased safety.

In the scientific literature, the control of EMBs has been commonly addressed through cascaded architectures with inner-loops for motor velocity and current/torque control, and outer-loops for clamping force control, thereby requiring an accurate measure of this variable. However, the use of load cells to measure the clamping force is too expensive to be installed on production vehicles; strain gauges need to be calibrated regularly, they have a high sensitivity to temperature variations, and their installation is complex and time-consuming.

With this in mind, we have investigated an alternative cascaded architecture with an outer-loop for deceleration control using wheel-speed-sensor (WSS) feedback. The objective is to study the benefits and drawbacks of such an approach in terms of technical performance and feasibility.

Methodology & results

For this study, a test vehicle was equipped with an EMB prototype and instrumented in order to have access to the WSS output. Firstly, a specific algorithm to process the WSS signal was implemented and tested under different driving conditions. The results show that by directly processing the WSS signal it is possible to obtain an accurate and smooth measurement of the wheel deceleration and eliminate the delay that would be obtained if these signals were retrieved from the CAN bus.

Once the measurement of the deceleration was available, the control algorithm for the EMB was tested on the vehicle, initially with the EMB actuating on a single wheel while the remaining three maintained the original hydraulic braking (for security concerns), and then with EMB actuation on the four wheels.

The algorithm’s inner-loops perform motor velocity and current control using field-oriented control techniques, whereas the outer-loop uses the wheel deceleration measurement to generate a velocity-equivalent reference for the actuator. The deceleration reference is generated as a function of the driver’s input/pedal stroke. The results so far show that, using deceleration feedback from the WSS, it is possible to achieve response times similar to those from conventional hydraulic braking, without compromising comfort.

Limitations & future work

One of the limitations encountered in this study concerns the accuracy of the deceleration measurement at low vehicle speeds. To overcome this constraint the deceleration-based control is switched to a (motor) position-based control at speeds lower than a certain threshold. Moreover, the tests conducted during this study considered only the use of the EMB for service braking. The use of deceleration-based feedback was not addressed during emergency braking or for parking brake.

Finally, during the initial stages of the study it was detected that the test vehicle has two different types of WSS at the front and rear axles (AK-protocol vs square-wave output), which made necessary to adapt some hardware and software components before being able to process the WSS signal, thus slightly increasing the complexity of the overall implementation.

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