Self Study Program 861213

The ID.4 Electromechanical Brake Servo (eBKV)
Tablet Format

Volkswagen Group of America, LLC
Volkswagen Academy
Published in U.S.A.
2/2021
SSP 861213

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Table of Contents
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Design of the Electromechanical Brake Servo Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
How the Electromechanical Brake Servo Works. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Brake Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Introduction
Due to the increasing number of electric vehicles and the low vacuum produced in the intake manifolds on modern combustion engines, a method to enhance
braking force is needed. The Electromechanical Brake Servo (eBKV) provides a solution to these concerns.
In addition to enhancing braking force, this system also reduces the total weight of the brake system, allowing further CO2 emission reduction for vehicles with
combustion engines.

1

Introduction
Technical features of the Electromechanical Brake Servo (eBKV):
• Parallel axis electric drive
• Weight-saving gear unit
• Weight saving control unit housing
• Vacuum-free brake force boosting
• No additional pressure accumulator
• Up to 5.3 kN power assistance
• Weight of approx. 9.7 lb (4.4 kg)
• Motor output 370 W
• Voltage range 9.8–16 V
• Maximum torque of 2.4 lb/ft (3.3 Nm)

Advantages of the eBKV
• Particularly fast brake pressure build-up for driver assist functions
• High safety advancement
• Reduced wheel brake drag torque
• Comfortable pedal feel
• CO2 savings due to weight reduction and omission of vacuum pump
• Long service life
• Redundant brake system for Electronic Stability Control (ESC)

2

Introduction
Safety Increases due to the eBKV
The eBKV increases the effectiveness of driver assist systems, such as Front Assist, in potential accident conditions that require extremely high pressure braking
increases. This cannot be performed using conventional vacuum-based systems.
This results in a shorter stopping distances than conventional systems:
• A reduced emergency braking distance of up to 4.2 ft (1.3 m) with deceleration from 18.5 mph (30 km/h) to a stop
• Collision speeds can be reduced by approximately 1.8 mph (3 km/h) due to the shorter stopping distance
This also allows pedestrian accident avoidance to be improved by 10%.
Reducing collision speed decreases the energy that the body has to absorb during the impact, improving occupant protection.

Vehicle Speed 18.5 mph (30.0 km/h)

Emergency Braking Distance with ESC

Emergency Braking Distance with eBKV

3

4.2 ft (1.3 m)

Introduction
What is Reduced Brake Drag Torque?
Brake drag torque occurs with disc brakes after a braking event. Brake drag
torque leads to higher fuel consumption and increased CO2 emissions.

Brake Caliper

After a braking event, the brake pads retract to their starting position as brake
pressure decreases. Due to slight wobbling of the brake disc in relation to
the brake caliper, combined with tight clearance, the whole brake pad does
not immediately lose contact with the brake disc. There is still transitional
frictional contact between the brake disc and the brake pad. By using a clip in
the brake caliper, the pads can be mechanically retracted faster.

Brake Pad

Clip

4

Introduction
Conventional, Vacuum-based Brake Systems
Vacuum-based brake systems create vacuum using multiple methods:

Brake Servo

• Intake manifold evacuation while the combustion engine is running
• A mechanical vacuum pump
• An electric vacuum pump

These methods have some partial disadvantages:

Brake Fluid Reservoir

Tandem Brake
Master Cylinder

• Poor CO2 figures
• Heavy weight
• High production costs
ESC Unit

Vacuum Pump

Brake Caliper

5

Introduction
Current Brake Systems for Electric Vehicles
This is the 1st Generation eBKV. It is used in high-voltage vehicles.
Electromechanical Brake
Servo Generation 1

Its distinguishing feature is a special pressure accumulator for the brake
system. It stores brake fluid during recuperation, reducing the brake pressure
in the system.
The disadvantages are:
• The space required

Brake Fluid
Reservoir

• The separate drive for the active accumulator
• Its weight

Tandem Brake
Master Cylinder

ESC Unit

Brake System
Pressure Accumulator

Brake Caliper

6

Introduction
Electronic Brake Servo
Electromechanical Brake Servo

The eBKV has an accumulator integrated into the ESC unit that holds brake
fluid during recuperation, instead of an external brake system pressure
accumulator.
The advantages of this system are:
• No additional space required for additional components
• Weight reduction

Brake Fluid
Reservoir

• Lower CO2 emissions
• Reduced costs

Tandem Brake
Master Cylinder

ESC Unit

Brake Caliper

7

Design of the eBKV
Exterior Design
The eBKV has the following components:
• The housing
• The push rod with boot

J539

• The motor/gear unit
• J539 Brake Booster Control Module

Housing

• The brake fluid reservoir
• The tandem brake master cylinder

Push Rod with Boot

Motor/Gear Unit

8

Design of the eBKV
Function
When the driver presses on the brake pedal, the push rod introduces this movement into the assembly. This movement is sensed by the transferred by the
Brake Pedal Position Sensor G100, which is part of the Brake Booster Control Module J539.
The G840 Brake Booster Motor Position Sensor is also intgral to the J539, and relays the current motor position.
The J539 uses the information about the driver’s brake request and the motor position to calculate the brake servo movement required.
To initiate movement, the reinforcing sleeve is
moved to the left by the pinion shafts, located
on either side of the reinforcing sleeve.

G840

As the reinforcing sleeve moves, the push
rod also moves. The braking force is
increased by seven to eight times when the
electromechanical brake servo is used.

G100

Reinforcing Sleeve

When the braking request is removed, the
spring located between the master cylinder and
the reinforcing sleeve pushes the reinforcing
sleeve/push rod back to its original position.

Tandem Brake
Master Cylinder

Push Rod

Spring
Push Rod
Gear Mechanism

9

Pinion Shaft

Design of the eBKV
Spring

Released and Engaged Positions

Released Position

These overhead images illustrate the released and engaged
positions as described on the previous page.

Released position:
• The spring is relaxed
• The parallel pinion shafts are on the left side of the
reinforcing sleeve

Engaged position
• The reinforcing sleeve has moved the left
• The spring is compressed

Engaged Position

10

Pinion Shafts

Reinforcing Sleeve

Design of the eBKV
Design in Detail - Pressure Accumulator in the ESC Unit
When compared to the 1st Generation eBKV, the active pressure accumulator has been removed. The pressure accumulator function is now integrated into the
ESC unit. The ESC unit has a larger volume to accommodate this function.

ESC Unit

J104 ABS Control Module
Accumulator

11

Design of the eBKV
G100 Brake Pedal Position Sensor - Design and Failure Effects
Design
The brake pedal position sensor has two Hall sensor
elements on the boost body and a slide with four Hall
magnets. The magnets are connected to the input push rod.
When the driver presses the brake pedal, the Hall magnets
move over the Hall sensors. This movement is interpreted
as a braking request by the brake servo system

Failure Effects
If the G100 fails, the brake function is taken over by the ESC
unit. If the electromechanical brake servo and ESC fail at
the same time, purely mechanical braking is still possible.

12

Brake Management
Network System
The eBKV is connected to the engine and transmission control modules using CAN-Bus.

Key
G85

Steering Angle Sensor

J104 ABS Control Module
J285 Instrument Cluster Control Module
J428 Control Module for Adaptive Cruise Control
J500 Power Steering Control Module
J519 Vehicle Electrical System Control Module
J533 Data Bus On Board Diagnostic Interface
J539 Brake Booster Control Module
J623 Engine/Motor Control Module
J775 Drivetrain Control Module
R242 Driver Assistance Systems Front Camera
U31

13

Diagnostic Connection

Powertrain CAN-bus
Running Gear CAN-bus
Drivers Assist System CAN-bus
Convenience CAN-bus
Diagnostic CAN-bus
Analogue Connection

Brake Management
What is Brake Blending?
The term “brake blending” comes from high-voltage vehicles. The three phase current drive of a high-voltage vehicle can be used in regenerative mode to
brake (decelerate) the vehicle speed. Part of the vehicle’s kinetic energy is converted into electrical energy and thermal energy during the process and the
vehicle speed decreases.
Depending on the battery charge level and the temperature of the high-voltage battery, it is not always possible to use the high-voltage system for
deceleration. Any fluctuations in deceleration are covered by the hydraulic brake system.
Since the eBKV responds much faster than vacuum-based systems, this collaboration between hydraulic braking and high-voltage braking is very efficient.

ESC Unit
Wheel Brakes

Three-phase
Current Drive
Driver's Braking
Demand

14

Situation-based interaction between braking effect
from three-phase current drive and braking effort
from eBKV

eBKV

Brake Management
Brake Blending Process - Deceleration Requirement
When brake pedal actuation occurs, which is detected by the J539 Brake Booster Control Module, the eBKV will build up pressure.

ESC Unit
Wheel Brakes

Three-phase
Current Drive
Driver's Braking
Demand

eBKV

15

Brake Management
Brake Blending Process - Frictional Deceleration
The brake pressure built up in the hydraulic brake system presses the brake pads against the brake disc. Due to the resulting friction, part of the vehicle’s
kinetic energy is converted into thermal energy and radiated. This energy is lost.

Required Brake Pressure is
Built Up
ESC Unit
Braking Intervention

Driver's Braking
Demand

Braking Support from eBKV

16

Brake Management
Brake Blending Process - Recuperative Deceleration
If the charge level of the high-voltage battery and its temperature are suitable, a large part of the frictional deceleration can happen using the regenerative
mode of the three-phase current drive.
The vehicle’s kinetic energy is converted into electrical energy, stored in the high-voltage battery and can be used for acceleration. In this process, which is
known as recuperation, a small amount is lost as thermal energy due to bearing friction and the heat occurring during induction.
Since the braking effect happens using the high-voltage drive, brake pressure in the hydraulic system and the electrical brake force boosting are reduced.
Electrical energy is saved by the not using the hydraulic brake system.

Low Brake Pressure is Built Up
ESC Unit
Braking Intervention

Main Braking Effect
Through Three-phase
Current Drive

Driver's Braking
Demand

Braking Support from eBKV

17

Brake Management
Brake Blending Process - Supporting Deceleration
If the charge level of the high-voltage battery and its temperature do not allow recuperative deceleration to be used, hydraulic braking must be used to slow
the vehicle. The eBKV and the hydraulic brake system intervenes and supplies the required braking force using the wheel brake cylinders.
The driver does not notice any of this interaction since the eBKV acts autonomously and will automatically build up the brake pressure without driver
intervention.

High Brake Pressure is Built Up
ESC Unit
Braking Intervention

Small Braking Effect
Through Three-phase
Current Drive

Driver's Braking
Demand

Braking Support from eBKV

18

Service
Service - Work After the Electromechanical Brake Servo is Replaced
If defective, eBKV must be replaced as a complete unit. Once the new eBKV has been installed, the brake system needs to be checked for free movement and
also bled by means of a pressure test:
• A free movement test is performed first. This involves testing the mechanical functions of the brake servo
• The pressure test is then performed with the vehicle diagnostic tester using “Guided Functions”

The individual steps for changing a new electromechanical brake servo vary according to model.

19

Volkswagen Group of America
2200 Ferdinand Porsche Drive
Herndon, VA 20171
February 2021