Advanced Brakes Benchmarking for EVs (Part 1 of 3)

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Article by: Suguru Nakajima, Project Manager, Braking Systems in Applus IDIADA

1.0. Introduction

The automotive industry is experiencing a significant shift towards electric vehicles (EVs), which has necessitated changes in various aspects of vehicle design and performance, including braking systems. This article focuses on advanced brake benchmarking for EVs, highlighting the differences between traditional internal combustion engine (ICE) vehicles and EVs in terms of braking technology and performance evaluation.

1.1. Background

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. Applus IDIADA, a company with extensive experience in benchmarking activities, has been working closely with customers to define new processes for EV brake benchmarking.

The transition to EVs has brought about significant changes in braking systems, necessitating an evolution in benchmarking processes. The increasing market share of EVs has prompted the need for updated methodologies and metrics to evaluate braking performance effectively.

1.2. Key Differences in EV Braking Systems

• Regenerative Braking: EVs utilize regenerative braking as a primary means of deceleration, converting kinetic energy into electrical energy to recharge the battery.
• Blended Braking Systems: EVs combine regenerative and friction braking, requiring sophisticated control systems to balance both types and ensure a seamless transition between regenerative and mechanical brakes.
• Brake System Design: EVs often require smaller friction brakes due to the presence of regenerative braking. They also have different brake force distribution due to higher vehicle weight.
• Maintenance: EVs generally experience less wear on brake pads and rotors, resulting in different service intervals due to reduced friction brake usage.
• Safety Systems: EVs incorporate additional fail-safe mechanisms for regenerative braking systems and backup systems for power loss scenarios.

2.0. Benchmarking

This article outlines a new approach to benchmarking for EVs, focusing on several key areas. The test program is as follows:

2.1. Specifications

The example vehicle used in the article has the following specifications:

1. Vehicle

• All-Wheel Drive (AWD)
• 200 kW power output
• 180 km/h top speed
• 100 kWh battery capacity
• Kerb weight: 2000 kg (Front/Rear: 1100/900 kg)
• Gross Vehicle Weight (GVW): 2800 kg (Front/Rear: 1400/1400 kg)
• Wheelbase: 2800 mm

2. Brakes

3. Tyres & Wheels

• Dimensions: 205/55 R18
• Code: 93W
• Brand: Bridgestone
• Model: Turanza
• Rim size: 18 x 6.5J
• Offset: ET 50

4. Driving Modes: The vehicle features various driving modes, including

• Drive: Sport, Standard, Comfort
• Regenerative Braking: High, Standard, ECO
• Brake Assist: Always On
• Creep: Not available
• Off-brake to a halt: Normal

2.2. Pedal feel

The objective of the pedal feel test is to understand the main difference in behavior between different driving modes during a ramp application of the brake pedal.

The benchmarking process evaluates pedal feel under different conditions:

• Test conditions: Linear acceleration increase at 0.25 ±0.05 g/s, with an initial brake temperature (IBT) of 100 ±10°C.
• Test matrix: Includes various combinations of weight (DOW + 1P, GVW), brake assist modes, speeds (100 km/h), and regenerative braking levels.

Results:

Metrics: Travel and effort at 0.2g, 0.5g, and at the deadband; Pedal Stiffness (N/mm between 0.2 and 0.5g); Force Linearity (N/g between 0.2 and 0.5g).

Key Findings and Observations:

• The regenerative braking contribution varies significantly with vehicle speed and deceleration demands.
• Higher efficiency is observed at moderate deceleration rates (0.2-0.4g).
• In the example vehicle, regenerative braking is disconnected when slip is detected during low-mu surface testing, demonstrating advanced safety integration between regenerative and conventional braking systems.

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.

www.applusidiada.com