2001 TOYOTA PRIUS brake sensor

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
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.

CHASSIS ± BRAKES
182CH55
Speed Sensors
Combination Meter
Speedometer
ABS Warning Light
Brake System Warning
Light
Brake Warning Buzzer
Stop Light Switch
ECM
HV ECU
Inverter
Battery ECU
Brake
ECU
Solenoid Relay
Motor Relay
Brake Actuator
ABS Solenoid
Valves
Switching Solenoid Valve
Linear Solenoid Valve
Master Cylinder Pressure
Sensor
Regulator Pressure Sensor
Front Wheel Pressure Sensor
Rear Wheel Pressure Sensor
Pump Motor
High Pressure Switch
Low Pressure Switch
Reservoir Level Switch
Hydraulic Brake Booster11 5
Brake ECU
1) General
Based on the signals received from the sensors the communication it maintains with the HV ECU, the
brake ECU effects conventional brake control, ABS with EBD control, and regenerative brake coopera-
tive control.
2) Fail Safe
If a malfunction occurs in the brake ECU, in the input signals from the sensors, or in actuator system,
this function prohibits the current from flowing to the brake actuator.
As a result, the solenoids in the brake actuator turn off, enabling the braking force of the hydraulic brake
to take effect. Furthermore, by illuminating the ABS warning light or the brake system warning light,
this function alerts the driver that a malfunction exists in the system.
Only if the regenerative brake system cannot be used, such as in the case of a malfunction in the commu-
nication with the HV ECU, this function switches controls to enable the hydraulic brake to generate the
entire brake force.
3) Warning Light Check Function
The ABS warning light and brake system warning light turns on for about 3 seconds after the ignition
switch is turned on to check the circuit.

CHASSIS ± BRAKES
182CH79
Port A
Pressure
Holding
Valve
To
Wheel
Cylinder
Port B
Pressure
Preduction
ValveTo
Reservoir
and Pump
From Wheel Cylinder
182CH80 182CH81
11 6
4) Self-Diagnosis
If the brake ECU detects a malfunction in the brake system, the ABS warning light and brake system
warning light will light up and alert the driver that a malfunction has occurred. The ECU will also store
the codes of malfunctions. See the 2001 Prius Repair Manual (Pub. No. RM778U) for the DTC (Diagnos-
tic Trouble Code) check method, DTC and DTC clearance.
Brake System Control
1) ABS with EBD control
a. General
The EBD control utilizes ABS, realizing the proper brake force distribution between front and rear
wheels in accordance with the driving conditions. In addition, during cornering braking, it also controls
the brake forces of right and left front wheels, helping to maintain the vehicle stability.
The distribution of the brake force is performed under electrical control of the brake ECU, which pre-
cisely controls the brake force in accordance with the vehicle's driving conditions.
b. Operation
Based on the signals received from the 4 wheel speed sensors, the brake ECU calculates each wheel
speed and deceleration, and checks wheel slipping condition. And according to the slipping condition,
the ECU controls the solenoid valves in order to adjust the fluid pressure of each wheel cylinder in the
following three modes: pressure reduction, pressure holding and pressure increase modes.
Not Activated
Normal Braking±±
ActivatedPressure Increase ModePressure Holding ModePressure Reduction Mode
Hydraulic
Circuit
Pressure
Holding Valve
(Port A)OFF
(Open)ON
(Close)ON
(Close)
Pressure
Reduction Valve
(Port B)OFF
(Close)OFF
(Close)ON
(Open)
Wheel Cylinder
PressureIncreaseHoldReduction

CHASSIS ± BRAKES
182CH57
To Reservoir TankFrom Master Cylinder
Pressure
SensorPressure
Sensor
SLR
OFF
SLA
ON
SMC1
ON ONSMC2
Stroke
Simulator
ReservoirSS
ON
Pressure
SensorPressure
Sensor
SRrH
ONSFRH
ON
SRrR
ONSFRR
OFFSFLH
OFF
SFLR
OFF
Rear Wheel CylindersFront Wheel Cylinders P & B Valve11 7

Sample of ABS control