2001 TOYOTA PRIUS ABS

CHASSIS ± BRAKES
182CH44
Front
Brake ActuatorRear
Hydraulic
Brake
Differential
Gear
Stroke
Simulator
Hydraulic
Adjustment Area
ABS Function AreaHydraulic
Brake
MG2
MG1Inverter
EngineHV Battery
THS (TOYOTA Hybrid System) Regenerative
Brake
Switching
Valve
Power Splitting
Device
182CH45
Combination Meter
Brake ECU
Brake Warning Buzzer
Rear Wheel
Speed Sensors
and Rotors
Hydraulic Brake Booster
(Master Cylinder Portion)
Front Wheel Speed
Sensor and Rotor
Brake Actuator HV ECU
Hydraulic Brake
Booster
Power Supply
portion
Solenoid RelayReservoir
Tank
ECMPump
Motor Relays 104
BRAKE SYSTEM
1. General

A brake system, which uses brake fluid that is stored under high pressure to assist the brake pedal effort
and to operate the ABS with EBD control and the regenerative brake cooperative control, has been adopted.

A regenerative brake system, which uses the MG2 that is used for driving the vehicle as a generator to effi-
ciently convert the energy that is created during braking, has been adopted. This system enables to collect
more driving energy by having the control to cooperate the hydraulic brake and the regenerative brake.
2. System Diagram
3. Layout of Main Components

CHASSIS ± BRAKES105
4. Function of Main Components
ComponentsFunction
ABS Warning
LightLights up to alert the driver when the brake ECU detects the
malfunction in the ABS.
Combination
Meter
Brake System

Lights up together with the ABS warning light to alert the driver
when the brake ECU detects the malfunction not only in the ABS
but also in the EBD controlBrake System
Warning Lightbut also in the EBD control.

Lights up to alert the driver when the malfunction occurs in the
brake system.
Stop Light SwitchDetects the brake depressing signal.
Brake Warning BuzzerEmits a continuous sound to inform the driver that the ABS ECU
detects the malfunction in the hydraulic brake booster.
Speed SensorsDetect the wheel speed of each of the four wheels.
Brake ECU

Processes various sensor signals, regenerative brake signals, to
execute control of the ABS control, EBD control, regenerative
coordination control and hydraulic brake booster.

Communicates control data with the HV ECU.
HV ECUMaintains serial communication with the brake ECU to exchange
regenerative coordination control signals.
Hydraulic Brake Booster
Assists with the pedal effort applied to the brake pedal.

Supplies hydraulic pressure.
Brake ActuatorControls the brake fluid pressure to each brake wheel cylinder by
signals from the brake ECU.
Solenoid RelaySupplies power to the ABS's solenoid valve's in the brake actuator.
Pump Motor RelaysControl the pump motor operation in the hydraulic brake booster.

CHASSIS ± BRAKES
182CH46
SMC1
SMC2
SS
SLA
SLRSFRH
SFRR
SFLH
SFLR
SRrH
SRrRABS Solenoid Valves Switching Solenoid Valves
Linear Solenoid Valves
Hydraulic Brake BoosterAccumulator
Pump and
Pump
Motor
Pressure Switch PH
Pressure Switch PL
Master Cylinder and
Brake Booster
Brake Actuator
Pressure
Sensor
SLR
SLA
Reservoir
Pressure
Sensor
P & B Valve
Rear Wheel CylindersSRrH
SRrRSS
SMC1 SMC2
Pressure
Sensor
Front Wheel CylindersPressure
Sensor
Stroke
Simulator
SFRH
SFRR
SFLRSFLH 106
5. Hydraulic Circuit

CHASSIS ± BRAKES107
6. Construction and Operation
The brake system of Prius consists of the following components:
Components
Function
Pump and Pump Motor
Draws up the brake fluid from the reservoir tank
and provides high hydraulic pressure to the
accumulator.
Accumulator
Stores the hydraulic pressure that was generated
by the pump. The accumulator is filled with
highpressure nitrogen gas.
Power
Supply
PortionPressure Switches
Monitors the hydraulic pressure of the
accumulator and outputs control signals for the
pump motor.
There are two types: the pressure switch PH for
controlling the pump, and the pressure switch PL
for giving a warning when the pressure is low.
Hydraulic
Brake
Booster
Relief Valve
Returns the brake fluid to the reservoir tank to
prevent excessive pressure if the pump operates
continuously due to a malfunction of the pressure
switch.
Reservoir TankStores the brake fluid.
Brake Fluid Level
Warning SwitchDetects the low brake fluid level.
Master
Master Cylinder
Generates the hydraulic pressure in accordance
with the pedal effort that is applied to the brake
pedal.
Master
Cylinder
Portion
Brake Booster
Regulates the accumulator pressure in accordance
with the pedal effort that is applied to the brake
pedal and introduces this pressure to the boosterBrake Boosterpedal and introduces this pressure to the booster
chamber in order to provide a power assist to the
brakes.
Pressure SensorsDetects the pressure of the master cylinder,
regulator, and front and rear wheel cylinders.
Switching
Solenoid ValvesSwitches the hydraulic path between normal
braking and braking under control.
Brake
Actuator
ABS Control Solenoid
Valves
Pressure Holding
Valves
Pressure Reduction
Valves
Controls the hydraulic pressure that is applied to
the wheel cylinders during ABS control or EBD
control.
Actuator
Linear Solenoid Valve
Regulates the hydraulic pressure to the wheel
cylinders during braking in accordance with the
fluctuations in the regenerative brake force.
Reservoir
Temporarily stores the brake fluid when
regulating the hydraulic pressure to the wheel
cylinders in accordance with the fluctuations in
the regenerative brake force.
Stroke SimulatorGenerates a pedal stroke during braking in
accordance with the driver's pedal effort.

CHASSIS ± BRAKES
152CH17 182CH47
Reservoir Tank
Accumulator
Check
Valve
Pump and
Pump Motor To Master
Cylinder and
Solenoid
Valves
Pressure
Switch
PL
Relief
Valve
Pressure
Switch
PH
Brake ECUPump Motor
Relays
Brake Warning
BuzzerBrake System
Warning LightAccumulator
Pressure
Pressure
Switch PH
Pressure
Switch PLON
OFF
OFF
Time
Pump
Motor
Relief
ValveOpen
CloseBrake System
Warning Light
and Brake
Warning Buzzer
ON
OFF
ON
OFF
108
Hydraulic Brake Booster
1) General
Due to installation space constraints, a type of hydraulic brake booster that comprises two separate por-
tions has been adopted: the power supply portion (pump, pump motor, accumulator, pressure switches,
and relief valve) and the master cylinder portion.
Consisting of an pump and pump motor, accumulator, and hydraulic pressure switches, the hydraulic
brake booster performs the functions of both the booster and the master cylinder.
By optimizing the hydraulic circuits, the hydraulic pressure that is generated by the booster is applied
directly to the rear brakes. Thus, the hydraulic pressure from the master cylinder is used exclusively by
the front brakes.
2) Pump and Pump Motor, Accumulator, Pressure Switches and Relief Valve
If the accumulator pressure becomes lower than the pressure that is specified in the pressure switch PH,
which is used for detecting high pressure, the pressure switch PH turns OFF. Then, the brake ECU turns
ON the pump motor relays to operate the pump motor and the pump.
The brake fluid that is discharged by the pump passes through the check valve and is stored in the accumu-
lator. The hydraulic pressure that is stored in the accumulator is used for providing the hydraulic pressure
that is needed for normal braking, for operating the ABS, and for operating the EBD control, and for re-
generative brake cooperative controlling.
If the accumulator pressure becomes higher than the pressure that is specified in the pressure switch PH,
the pressure switch PH turns ON. Then, after several seconds, the brake ECU turns OFF the pump.
At this time, if the pressure switch PH malfunctions and causes the pump to operate continuously, the
relief valve opens to prevent excessive pressure from being generated.
Moreover, if the accumulator pressure becomes lower than the pressure that is specified in the pressure
switch PL, which is used for detecting low pressure, the pressure switch PL turns OFF. As a result, the
brake system warning light turns ON and the brake warning buzzer activates.
At this time, the ABS or EBD is prohibited from operating.

CHASSIS ± BRAKES
152CH29
From
Reservoir
To Front
Brake
182CH49
To Wheel Cylinders
From
Master
Cylinder
From Hydraulic
Brake Booster
To Front
Wheel
Cylinders
To Rear Wheel
Cylinders
SMC1 and SMC2 SS 11 2
v) During Power Supply Malfunction
If the accumulator pressure is affected due to some type of malfunction, no pressure will be supplied
by the regulator. Then, a power assist cannot be provided to the force that is applied via the brake pedal
and the pressure to the rear brakes cannot be increased.
The pressure to the front brakes will be increased by the master cylinder in accordance with the pedal
effort applied to the brake pedal.
Brake Actuator
1) Switching Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to switch the passages of the
brake fluid. There are 3 switching solenoid valves (SMC1, SMC2, and SS) and they switch the passages
to effect conventional brake control and ABS control.

CHASSIS ± BRAKES
182CH50
To Wheel Cylinder From Hydraulic
Brake BoosterFrom Wheel
CylinderTo Reser-
voir Tank
Pressure Holding Valve
(SFRH, SFLH, SRrH)Pressure Reduction Valve
(SFRR, SFLR, SRrR)
From Hydraulic
Brake Booster
Pressure Holding
Valve
To Wheel
Cylinder
Pressure
Reduction
Valve
Increase HoldingFrom
Wheel
Cylinder
To Reservoir Tank
Decrease
182CH51
To Wheel Cylinders
From
Hydraulic
Brake
Booster
To Built-In Reservoir
From
Wheel
Cylinders
SLA SLR
11 3
2) ABS Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to switch the passages of the
brake fluid. There are 2 (pressure holding valve, pressure reduction valve) ABS solenoid valves pro-
vided. The pressure increases if no current is applied to either valve. The pressure is held if current is
applied only to the pressure holding valve. The pressure decreases if current is applied to both the pres-
sure holding valve and pressure reduction valve. To effect control independently to the front wheels, si-
multaneously to both rear wheels, 6 solenoid valves are provided.
3) Linear Solenoid Valves
The control signals from the brake ECU cause the valves to open and close to regulate the volume of the
brake fluid that flows into the wheel cylinders. There are 2 types of linear solenoids, the SLA for pressure
increase and the SLR for pressure decrease, and they regulate the wheel cylinder pressure in accordance
with the fluctuations in the regenerative brake force. In addition, the SLA contains a relief function to
provide hydraulic pressure to the wheel cylinders in the event of a brake ECU failure.

CHASSIS ± BRAKES
182CH52
Spring
for 1st
Stage
Spring
for 2nd
StageTo
ReservoirStroke
Simulator
Full Stroke
Pedal Stroke 2nd Stage
Spring
Characteristics
1st Stage +
2nd Stage
Spring
Characteristics
Master Cylinder Hydraulic Pressure From
Master
Cylinder
182CH53
From wheel Cylinder (SLR)
182CH54
11 4
4) Stroke Simulator
The stroke simulator generates a pedal stroke in accordance with the driver's pedal effort during braking.
Containing 2 types of coil springs with different spring constants, the stroke simulator provides pedal
stroke characteristics in 2 stages in relation to the master cylinder pressure.
5) Reservoir
Temporarily stores the brake fluid to absorb
the pressure when regulating the wheel cylin-
der pressure.
6) Pressure Sensors
Mounted on the brake actuator, the pressure
sensor linearly detects the pressure that is gen-
erated in the master cylinder, regulator, and
the front and rear wheel cylinders and outputs
them to brake ECU.