ADELANTO, Calif. – The following is the third of three articles by: Fabio Squadrani, Senior Manager, Braking Systems of Applus IDIADA co-authored with Deaglán Ó Meachair, brake-engineering specialist of BrakeBetter.com.
This article suggests 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. It primarily shows how partial system failures (ESP, EPB, IEB) affect the general braking performance, mainly in terms of deceleration, stopping distance, front/rear modulation, on slope braking performance and finally time-to-lock.
In this 3rd and last part of the article, a series of test metrics for redundancy levels evaluation is finally presented.
- Test Metrics Evaluation
The analysis of multiple test data allows metrics to be compared with the reference values previously defined. The result of the comparison should serve to evaluate the behaviour of the system in a particular vehicle (the test vehicle) against the values previously defined as desirable.
This exercise allows measuring the level of demand of the primary metrics proposed on the one hand, and the necessary system improvements to be able to eliminate the gap to them on the other.
The different levels of requirements are detailed below to facilitate the understanding of the subsequent analysis:
- Full System: It considers the entire operation of the system and the expected level of response in this scenario.
- Partial System: It considers degraded system performance due to loss of primary actuation system and the expected level of response in this scenario
- Performance Floor: It defines the minimum acceptable response value for a system to be considered as redundant.
Thus, the metrics are defined as follows:
- Metric 1 – Deceleration Level (Type 0): Metric 1 correspond to the deceleration values obtained from the service brake test according to Type 0 R-13H
- Metric 2 – Stopping Distance (Type 0): The same analysis as for the level of deceleration applies to stopping distance given the direct relationship between them.
- Metric 3 – Stopping Distance Wet Asphalt (mu 0.8): The stopping distance on wet asphalt is calculated based on panic brake application, the results should meet the specified requirements either at full system or at partial system.
- Metric 4 – Steering Wheel Angle (Split Mu): The SWA values are within the specified requirements for vehicle controllability at full system but the maximum value achieved when ESP fails during braking is above 120 degrees.
- Metric 5 – EPB Stationary on Slope: The test is investigating the capability to hold the vehicle in 24% slope for 5 minutes in uphill and downhill scenarios having functional both EPB actuators, the same performance is achieved by generating failure in on caliper and holding the vehicle with one side functional EPB actuator.
- Metric 6 – Time to Lock: The TTL has been calculated based on panic brake application attempt, results should meet the defined requirements in both scenarios, at full and partial (iBooster failure) system performance.
This work is presenting a set of values, which allows the evaluation of redundant braking systems. The values and metrics are quite traditional and understandable. The engineering effort corresponds with the selection of simple reliable metrics and the definition of the target value when dealing with partial system failure (redundant braking systems). This target should be robust, reliable but also technically achievable.
An additional refinement work on this target value should be achievable and the increasing level of driving autonomy for standard passenger car vehicles should make it easier to benchmark it.
About Applus IDIADA
With more than 25 years’ experience and 2,450 engineers specializing in vehicle development, Applus IDIADA is a leading engineering company providing design, testing, engineering, and homologation services to the automotive industry worldwide.
Applus IDIADA is located in California and Michigan, with further presence in 25 other countries, mainly in Europe and Asia.
Deaglán Ó Meachair established Brakebetter.com to improve the efficiency of the planet’s electric vehicle fleet, by offering the automotive industry the insight and support required to move from legacy systems and grasp the vast potential available through electrification.