S11 Brake System

S11 Brake System Introduction

ABS warning lampRight brake lamp

Left brake lamp

Brake switch

Left rear wheel speed sensor

ABS wheel speed sensor

ABS control moduleABS master

cylinder

Brake lamp switchVacuum booster

ABS electronic control module

ABS hydraulic control unit

Composition of Ordinary Brake System

Brake booster

Parking brake control lever

Disc brake

Brake master cylinder

Disc brakeBrake pedal

Proportioning valveParking brake cable

Brake Booster

1. Usually, the brake booster can increase the braking force two to

four times.

2. Brake booster's performance varies with the actual atmospheric

pressure, vacuum degree and its active area. The bigger its active

area is, the stronger its boosting force is.

Brake Booster not in Braking

Variable-pressure chamber- chamber A

Relationship between Fb + Fsand Fa

Fb=FaFs pushes the piston to the right.

Brake master cylinder

SpringPiston

Valve

Cylinder sleeve

Vacuum

To brake wheel

cylinder

Constant-pressure chamber- chamber B

Relationship between Fb + Fsand Fa

Fb + Fs < FaFa pushes the piston to the right

Vacuum

Brake master cylinder

Hydraulic pressure

Air

Valve

Brake Booster in Braking

Brake Booster Structure

Vacuum Check valve

Constant-pressure chamber

Diaphragm

Power piston

Reaction disc

Valve body

Air

Variable-pressure chamberBooster housing

Push rod

Brake master cylinder

Diaphragm spring

Booster housing sealing member

Booster housing sealing member

Air filter

Valve control lever

Opened vacuum valve & control valve

A is connected with B

1. Brake Booster not in Braking

Piston

Passage A

Passage B

Constant pressure chamber

Variable pressure chamber

Air valve (closed)

Air valve return spring

Air filter element

Valve control lever

Valve body

Control valve spring

Control valve

Vacuum valve (opened)

When not in braking

2. Brake Booster in Braking

C

Closed vacuum valve & control valve

A is not connected with BB is connected with C

Piston

Passage B

Constant pressure chamber

Variable pressure chamber

Air valve (opened)

Air filter element

Control valve

When not in braking

Air

Reaction disc

Booster push rod

3. Brake Booster in the Retained Position

Closed vacuum valve & control valve

A is not connected with B or C

Piston

Constant pressure chamber

Air valve (closed)

Control valve

When in the retained position (brake force)

Valve control lever

Control valve spring

Vacuum valve (closed)

Stop

Variable pressure chamber

4. Brake Booster in the Released Position

Opened vacuum valve & control valve

A is connected with B and C

Piston

Air valve (closed)

Control valve

When in the released position (brake)

Valve control lever

Vacuum valve (opened)

Variable pressure chamber

Air valve return springPassage B

Passage A

Purpose of Brake Master Cylinder

Brake master cylinder

Drum brake

Brake pedalFront/rear brakes

Brake Master Cylinder Structure

Tandem brake master cylinderPrimary pistonSecond pistonRubber piston cup

Reservoir

Liquid lever sensor

RR/LF brake cylinders

RF/LR brake cylinders

Piston cup is located between inlet port and compensating port

1. Brake Master Cylinder not in Braking

Secondary return springPrimary return spring

Compensating port

Inlet port

Primary piston cup

Secondary piston cup

Stopper bolt

When not in braking

进油孔

Secondary piston

Both inlet port

and

compensating

port are closed

with the oil

pressure

increased

2. Brake Master Cylinder in Braking

When in braking

Primary piston

Inlet port

Compensating port

Piston cup

3. Brake Master Cylinder when Released (1)

Inlet portOrifice

Piston cup

When brake pedal is released (1)

The orifice in the

piston is opened

and the brake

fluid flows back

to the piston-cup

side

4. Brake Master Cylinder when Released (2)

The

compensating

port allows

surplus fluid to

flow back to

the reservoir

Compensating port

When brake pedal is released (2)

5. Rear-end Leakage

In contact

Primary pistonSecondary piston

Rear-end leakage

6. Front-end Leakage

Piston contacts cylinder wall

Primary pistonSecondary piston

Front-end leakage

Proportioning valve

Proportioning Valve

Importance of Proportioning Valve

1. Loads on front and rear wheels are differentThe front wheels of the vehicle bear more of the vehicle weight than its rear wheels. In addition, its center of gravity will move forward when in braking, resulting in increased load on front wheels and reduced load on rear wheels. The bigger the braking force is, the more obvious this change is.

2. The risk of too early locking of rear wheelsWhen in braking, the load on rear wheels is light, and this causes them to be easily locked too early, thereby resulting in lateral sway of the vehicle body's rear half.

3. Measure to prevent the above problem from happeningProportioning valve: to automatically reduce hydraulic pressures delivered from brake master cylinder to rear-wheel brake wheel cylinders. Pressure reduction is in proportion to the stepping force on the brake pedal.

Bifurcation point

Pressure in brake master cylinder

Pres

sure

in re

ar b

rake

whe

el c

ylin

der

Requirements on Rear-wheel Brake Force

LF wheel

Proportioning Valve

RR wheel

RF wheel

RF wheel

Working Principle of Proportioning Valve—When the Pressure is zero

Spring

Control valve

Proportioning valve

Rear

Piston

Working Principle of Proportioning Valve—When the Pressure is Low

Spring

Piston

Cha

mbe

r A si

de

Cha

mbe

r B si

de

Piston

Small area Large areaFa+Fs=Fb

Working Principle of Proportioning Valve—When the Pressure is high

Fa+Fs<Fb

When the pressure is higher than some point, the difference between chambers A and B will overcome the spring's elastic force to make the piston move until the port C is closed.

1.When the Braking Pressure is Low

Cylinder cup

Spring To rear-wheel brake wheel cylinders

Piston

From brake master cylinder

2.When the Braking Pressure is High

In contact

Piston

3.When the Brake Pedal is Released

Cylinder cup

Piston

Spring

When the brake pedal is released, the pressure drop in the left chamber will cause the piston to move to the left.

Floating caliper

Disc Brake

Fixed caliper

Brake disc

Motion

Rotor disc

Brake lining

Floating-caliper type

Hyd

raul

ic p

ress

ure

Piston

Friction disc thickness sensor

Stee

ring

knuc

kle

Front-wheel Brake

Rear-wheel Brake