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Article by: Suguru Nakajima, Project Manager, Braking Systems in Applus IDIADA
Read part one HERE
Benchmarking plays a crucial role in the automotive industry, allowing manufacturers to compare their vehicles with competitors, analyze performance, identify areas for improvement, and maintain competitiveness in an evolving market.
The first part of this article introduced the benchmarking activities performed by Applus IDIADA, with special interest in the state-of-the-art braking systems for EVs. That text covered the gathering of specifications for a particular example vehicle, as well as presenting some pedal feeling results. This new part continues with the testing program, dealing with brake blending, reaction time, stopping distance, etc.
2.1 Brake Blending / Effectiveness:
This analysis focuses on understanding the behavior of different driving modes during constant brake pedal application.
The benchmarking process evaluates blending under different conditions:
- Test conditions: Constant application, maintaining stroke after reaching the deceleration target, in DOW and GVW conditions, at two speeds, different IBTs, and different vehicle decelerations.
- Results:
- Metrics: Similar to those used in pedal feel analysis.
Key Findings and Observations:
- The blending between regenerative and friction braking is crucial for maintaining consistent pedal feel and deceleration performance.
- Different driving modes and regenerative braking levels affect the blending strategy and overall braking performance.
2.2 Stopping Distance
The objective of the stopping distance is to determine the distance that is needed to bring the vehicle to a halt, from a certain initial braking speed, on different surface / adhesion levels. It is important to emphasize that different methods exist to estimate the deceleration —namely ISO and MFDD.
- Results:
2.3 Reaction Time:
The benchmarking process assesses the responsiveness of the vehicle, primarily associated with the capabilities of the EMB (e-booster or equivalent) system:
- Test conditions: Constant application, maintaining stroke (equivalent to 0.3g deceleration) at different vehicle speeds and brake pedal application speeds.
- Results:
- Metrics: Percentage of achieved deceleration when full stroke is applied.
Key Findings and Observations:
- The responsiveness of the braking system, particularly the EMB system, is critical for ensuring safe and efficient deceleration.
- The benchmarking process evaluates the percentage of achieved deceleration when full pedal stroke is applied, providing insights into the system’s responsiveness.
2.4 Low-Mu Testing:
This section evaluates the behavior of regenerative brakes on low-friction surfaces and during transitions:
- Test conditions: Tests conducted on low-mu surfaces (wet asphalt and ceramic) during braking and coast-down scenarios. Mu-jumps in coast-down and braking are also analyzed.
- Results:
- Metrics: Engineering analysis of regenerative braking behavior during testing maneuvers.
Key Findings and Observations:
- Regenerative braking is typically disconnected when slip is detected on low-friction surfaces.
- The system may still use regenerative braking to decelerate the vehicle when no slip is detected.
- During mu-jump scenarios (transitions between different friction surfaces), the braking system must adapt quickly to maintain stability and deceleration performance.
2.5 Coast Down:
The benchmarking process analyzes the free-rolling deceleration of the vehicle:
- Test conditions: Analysis of vehicle deceleration from 100 km/h to low speeds in different driving modes and regenerative contribution levels.
- Results:
- Metrics: Vehicle deceleration in different speed intervals.
Key Findings and Observations:
- The analysis of free-rolling deceleration provides insights into the vehicle’s overall efficiency and the impact of regenerative braking on energy recovery.
- Different driving modes and regenerative braking levels significantly affect the coast-down behavior of the vehicle.
About Applus IDIADA
With over 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.
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