ELECTRONICALLY CONTROLLED BRAKE UNIT

id042000002200


Electronically Controlled Brake Unit


Outline

•  A highly reliable, reduced size and weight electronically controlled brake unit, integrating both the HU part and CM part, has been adopted.


HU part purpose, function

•  The HU part of the electronically controlled brake unit controls each solenoid valve and the hydraulic pressure generation equipment by the signal from the CM part, adjusts the fluid pressure applied to the caliper pistons, and executes each function of the DSC system (ABS, EBD (Electronic Brake Force Distribution), TCS, DSC, brake assist control, vehicle roll prevention function, Hill Launch Assist (HLA) control, and the secondary collision reduction system control).
•  When the vehicle is decelerated using the brakes, the braking force of the hydraulic brakes is controlled according to the change in the vehicle deceleration (regenerative braking force) by the resistance of the integrated starter generator.


HU part construction

•  The HU part of the electronically controlled brake unit consists of the master cylinder, stroke simulator, linear actuator, pressure feed valve, TMC cut valve, inlet side/outlet side solenoid valve, simulator valve, and the diagnosis valve.


Main component parts and functions

Part name

Function
Master cylinder
•  Converts the brake pedal depression amount by the driver to brake fluid pressure and sends it to the stroke simulator.
Stroke simulator
•  Generates a brake pedal stroke and brake pedal depression response according to the brake pedal depression amount by the driver.
Linear actuator
•  Generates the necessary brake fluid pressure according to the control signal from the CM part.
Pressure feed valve
•  Sends the brake fluid pressure generated by the linear actuator to each caliper piston.
•  If a malfunction occurs in the system, it blocks the hydraulic passage from the linear actuator to each caliper piston.
TMC cut valve
•  During normal operation, it blocks the hydraulic passage from the master cylinder to each caliper piston.
•  If a malfunction occurs in the system, the brake fluid pressure generated by the master cylinder is sent directly to each caliper piston.
Inlet solenoid valve
•  Increases and maintains the brake fluid pressure by connecting/blocking the brake circuit according to the control signal from the CM part.
Outlet solenoid valve
•  Decreases the brake fluid pressure by connecting/blocking the brake circuit according to the control signal from the CM part.
Simulator valve
•  Sends the brake fluid pressure generated by the master cylinder to the stroke simulator.
•  If a malfunction occurs in a system, it blocks the hydraulic passage from the master cylinder to the stroke simulator.
Diagnosis valve
―


Hydraulic Circuit Diagram

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Master Cylinder


Purpose, function

•  The master cylinder generates brake pedal pressure according to the amount of brake pedal depression.
•  During normal operation, the master cylinder generates brake fluid pressure according to the brake pedal depression amount by the driver, and transmits the brake fluid pressure to the linear actuator.
•  If a malfunction occurs in the system, the TMC cut valve opens. As a result, the brake fluid pressure generated by the master cylinder is transmitted directly to the brake caliper.
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Construction

•  The master cylinder is integrated in the electronically controlled brake unit and it cannot be disassembled and serviced.


Operation

•  When the brake pedal is depressed, the push rod moves and presses in the master cylinder piston. By pressing in the piston, the brake pedal force is transmitted to the brake fluid.


Stroke Simulator


Purpose, function

•  During normal operation, the stroke simulator generates the brake pedal depression response according to the brake pedal depression amount by the driver.
•  If a malfunction occurs in the system, the simulator valve closes. As a result, the brake fluid line to the stroke simulator is closed off and the stroke simulator cannot generate a brake pedal depression response.
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Construction

•  The stroke simulator is equipped in the electronically controlled brake unit.
•  The stroke simulator consists of the following parts and it is equipped with a hydraulic passage leading to the master cylinder.
―  Piston
―  Pressure piece
―  Compression ring
―  Rubber spring
―  Closing cover
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Operation

•  A natural brake pedal depression response according to the brake pedal force is generated by introducing the brake fluid pressure from the master cylinder to the stroke simulator when the brake pedal is depressed.
―  Initial brake pedal depression
•  The brake fluid pressure from the master cylinder is applied to the piston which depresses the spring. Because the spring force of the spring is small, the counterforce relative to the brake pedal depression is hardly perceptible.
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―  Midway brake pedal depression
•  When the brake pedal is further depressed from the initial depression condition, the brake fluid pressure from the master cylinder overcomes the spring force of the spring, further depressing the spring, and the piston and pressure piece come into contact.
•  When the piston and the pressure piece come into contact, the pressure piece depresses the compression spring. As a result, the counterforce relative to the brake pedal depression is larger in proportion to the brake pedal depression amount.
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―  Ending brake pedal depression
•  When the brake pedal is further depressed from the midway brake pedal depression condition, the rubber spring is further depressed and the pressure piece contacts the closing cover. Under this condition, the brake pedal reaches full stroke and the counterforce relative to the brake pedal depression reaches the maximum.
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Stroke Sensor


Purpose/function

•  Detects the brake pedal depression amount (amount of master cylinder piston movement) and sends it to the electronically controlled brake unit.


Construction

•  The stroke sensor is integrated in the electronically controlled brake unit. Therefore, if a stroke sensor malfunction occurs, replacement of the electronically controlled brake unit is required.


Brake Fluid Pressure Sensor


Purpose/function

•  The brake fluid pressure sensor detects the fluid pressure from the master cylinder and transmits it to the electronically controlled brake unit.


Construction

•  The brake fluid pressure sensor is built into the electronically controlled brake unit. Therefore if there is any malfunction of the brake fluid pressure sensor, replace the electronically controlled brake unit.


Linear Actuator

•  The linear actuator pressurizes the brake fluid according to the signal from the CM part of the electronically controlled brake unit to generate the brake fluid pressure amount required for each control the electronically controlled brake system.
•  The linear actuator is integrated in the electronically controlled brake unit.

HU Part Operation


During normal braking

•  The HU energizes the pressure feed valve, TMC cut valve, and simulator valve. The TMC cut valve closes, and the pressure feed valve and simulator valve open. When the brake pedal is depressed, the brake fluid pressure is introduced to the stroke simulator from the master cylinder, and the pump motor generates brake fluid pressure according to the brake fluid pressure and brake pedal depression amount (amount of master cylinder piston movement) detected by the brake fluid pressure sensor (master cylinder side). The brake fluid pressure generated by the pump motor is transmitted to the caliper pistons passing through the pressure feed valve and the inlet solenoid valve.

Solenoid valve operation table

Pressure feed valve

TMC cut valve

Inlet solenoid valve

Outlet solenoid valve

Simulator valve

Linear actuator

LF―RR

RF―LR

LF―RR

RF―LR

LF

RF

LR

RR

LF

RF

LR

RR
ON (open)
ON (closed)
OFF (open)
OFF (closed)
ON (open)
Operation

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During ABS and EBD control

•  If the wheels are about to lock during braking, the brake fluid pressure is adjusted by controlling the 3 pressure modes (increase, decrease, or maintain pressure) to energize the inlet solenoid valve and outlet solenoid valve, and prevented wheel-lock. The brake fluid during pressure decrease is returned directly to the reserve tank (figure below shows right front wheel pressure increase, left front wheel maintenance, left/right rear wheel pressure decrease condition).

Solenoid valve operation table

Pressure feed valve

TMC cut valve

Inlet solenoid valve

Outlet solenoid valve

Simulator valve

Linear actuator

LF―RR

RF―LR

LF―RR

RF―LR

LF

RF

LR

RR

LF

RF

LR

RR
Pressure increase mode
ON (open)
ON (closed)
OFF (open)
OFF (closed)
ON (open)
Operation
Hold mode
ON (open)
ON (closed)
ON (closed)
OFF (closed)
ON (open)
Operation
Pressure decrease mode
ON (open)
ON (closed)
ON (closed)
ON (open)
ON (open)
Operation

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During DSC control (oversteer tendency suppression) and during TCS control

•  When a large oversteer tendency is determined, the inlet solenoid is energized, switching the hydraulic circuits. At the same time, by activating the hydraulic pressure generating equipment, the brake fluid pressure applied to the caliper piston of the outer front wheel or the front and rear wheels is increased.
•  After the pressure increase, the brake fluid pressure is adjusted using the 3 modes of pressure decrease, pressure maintain, or pressure increase so that the yaw rate reaches the target value (figure below shows control condition during a left turn (while in pressure increase mode)).

Solenoid valve operation table

Pressure feed valve

TMC cut valve

Inlet solenoid valve

Outlet solenoid valve

Simulator valve

Linear actuator

LF―RR

RF―LR

LF―RR

RF―LR

LF

RF

LR

RR

LF

RF

LR

RR
Pressure increase mode
ON (open)
ON (closed)
ON (closed)
OFF (open)
ON (closed)
OFF (closed)
ON (open)
Operation
Hold mode
ON (open)
ON (closed)
ON (closed)
OFF (closed)
ON (open)
OFF
Pressure decrease mode
ON (open)
ON (closed)
ON (closed)
OFF (closed)
ON (open)
OFF (closed)
ON (open)
OFF

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During DSC control (understeer tendency suppression)

•  When a large understeer tendency is determined, the inlet solenoid valve is energized, switching the hydraulic circuits. At the same time, by activating the linear actuator, the brake fluid pressure is applied to the caliper piston of the inner rear wheel.
•  After the pressure increase, the brake fluid pressure is adjusted using the 3 modes of pressure decrease, pressure maintain, or pressure increase so that the yaw rate reaches the target value (figure below shows control condition during a left turn (while in pressure increase mode)).

Solenoid valve operation table

Pressure feed valve

TMC cut valve

Inlet solenoid valve

Outlet solenoid valve

Simulator valve

Linear actuator

LF―RR

RF―LR

LF―RR

RF―LR

LF

RF

LR

RR

LF

RF

LR

RR
Pressure increase mode
ON (open)
ON (closed)
ON (closed)
OFF (open)
ON (closed)
OFF (closed)
ON (open)
Operation
Hold mode
ON (open)
ON (closed)
ON (closed)
OFF (closed)
ON (open)
OFF
Pressure decrease mode
ON (open)
ON (closed)
ON (closed)
OFF (closed)
ON (open)
OFF (closed)
ON (open)
OFF

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System malfunction

•  If a malfunction occurs in the electronically controlled brake system, all of the solenoid valves are turned off. Because the pressure feed valve and simulator valve close and the TMC cut valve opens, the brake fluid pressure is transmitted directly to the caliper pistons from the master cylinder when the brake pedal is depressed.

Solenoid valve operation table

Pressure feed valve

TMC cut valve

Inlet solenoid valve

Outlet solenoid valve

Simulator valve

Linear actuator

LF―RR

RF―LR

LF―RR

RF―LR

LF

RF

LR

RR

LF

RF

LR

RR
OFF (closed)
OFF (open)
OFF (open)
OFF (closed)
OFF (closed)
OFF

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CM Part Purpose, Function

•  The CM part of the electronically controlled brake unit calculates the input signals from each sensor, and to execute each function of the electronically controlled brake system, it outputs the brake fluid pressure control signal applied to each wheel to the HU part of the electronically controlled brake unit, and it also outputs the engine output control signal to the PCM.

Function Table

Function

Content
Regenerative brake coordinated control
•  Controls the brake fluid pressure according to the difference between the deceleration speed by the ISG resistance (regenerative braking) and the deceleration speed requested by the driver.
Normal brake control
ABS control
•  Maintains the directional stability during braking, assures steerability, and reduces the stopping distance by controlling the brake fluid pressure during braking.
EBD control
•  Prevents the rear wheels from locking first during braking by constantly and optimally controlling the distribution of brake fluid pressure of the front and rear wheels according to the vehicle load, road conditions and the vehicle speed.
TCS control
•  Improves acceleration from starts, acceleration performance, and safety by controlling the drive force so that the drive force is within the limits of the road surface friction according to the road and driving conditions.
DSC control
•  Controls strong oversteer tendency and strong understeer tendency while turning by controlling the engine output and the brakes on each wheel to assure vehicle stability.
Electronic control brake assist function
•  After determining emergency braking, hydraulic pressure higher than the normal brake hydraulic pressure is supplied to each wheel by controlling the brakes on each wheel.
•  If a condition is detected in which emergency braking is anticipated by the change in speed of the accelerator pedal position, the gap between the brake pad and disc plate is reduced to enhance the response during braking.
AUTOHOLD
•  Maintains the vehicle in a stopped condition using the brake fluid pressure hold function of the electronically controlled brake unit even if the brake pedal is released while the vehicle is stopped.
Vehicle roll prevention function
•  Prevents the vehicle from moving during i-stop control (engine off) by drive torque transmission from engine revving when the foot is released from the brake pedal and the engine is restarted.
Hill Launch Assist (HLA) function
•  When the vehicle is held at a stop by depressing the brake pedal on a slope with a grade of 6% (ATX vehicle), or 3% (MTX vehicle) or more, the brake fluid pressure is maintained to prevent the vehicle from rolling backwards even after the driver's foot is released from the brake pedal.
Secondary collision reduction system control function
•  If the vehicle is hit by another vehicle and it is moved by the force of the collision, the brakes on the vehicle are automatically applied to mediate secondary collision damage, and the hazard lights are flashed at the same time to caution surrounding vehicles.
CAN communication function
•  Information such as the wheel speed signal and DSC system warning control is output via CAN communication.
On-board diagnostic system
•  A main component of the electronically controlled brake system includes the on-board diagnostic function. In case a malfunction occurs, warning lights or warning indicators turn on to alert the driver and, at the same time, a DTC is stored in the electronically controlled brake unit.
•  As a result of the on-board diagnostics, if a malfunction is determined, it performs control to prevent loss of drive safety.
Automatic configuration function
•  When the ignition is switched ON after the electronically controlled brake unit has been replaced, the electronically controlled brake unit reads data from the instrument cluster via CAN communication to perform automatic configuration.


Block diagram

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