2001 TOYOTA PRIUS Service Repair Manual

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 

CHASSIS ± BRAKES
Battery
Acceptance
Capacity
182CH58
Braking
Force
Regenerative
Braking ForceHydraulic
Braking Force
Vehicle SpeedRegenerative
Braking ForceHydraulic
Braking Force
Time
Changes in Regenerative Braking Force Changes in Braking Force Apportionment
Braking
Force
Driver's DemandDriver's Demand 11 8
2) Regenerative Brake Cooperative Control
a. General
The regenerative brake cooperative control uses the switching valves and linear solenoid valves to regu-
late the hydraulic pressure that is supplied to the wheel cylinders. It also operates cooperatively with
the regenerative braking force that is generated in the MG2 in accordance with the master cylinder pres-
sure.
b. Apportioning of the Brake Force
The apportioning of the brake force between the hydraulic brake and the regenerative brake varies by
the vehicle speed and time.
The apportioning of the brake force between the hydraulic brake and the regenerative brake is con-
trolled so that the total brake force of the hydraulic brake and the regenerative brake matches the brake
force that the driver requires.

Imagery Drawing 
c. Operation
Regenerative brake cooperative control is executed when the vehicle is driven in the shift position ªDº
or ªBº.
The master cylinder pressure that is generated when the driver presses on the brake pedal is detected
by the pressure sensor, and the brake ECU calculates the brake force request factor. A portion of the
brake force request factor is transmitted to the HV ECU in the form of a regenerative brake activation
request factor. The HV ECU executes generative braking by commanding the electric motor to generate
negative torque.
The brake ECU controls the opening of the linear solenoid valves, which are used for increasing / de-
creasing the hydraulic pressure, to regulate the wheel cylinder hydraulic pressure in relation to the mas-
ter cylinder hydraulic pressure, thus compensating for the brake force that is not provided sufficiently
by the regenerative brake.
While the regenerative brake cooperative control is being prohibited due to an abnormality in the sys-
tem, or when the shift lever is in a position other than D or B, the regenerative braking force is not gener-
ated. At this time, only the hydraulic braking force is applied by turning ON (opening) the linear sole-
noid valve SLA and turning OFF (closing) the SLR.