2001 TOYOTA PRIUS brakes

NEW MODEL OUTLINE
Gasoline engine + AC motor = TOYOTA Hybrid System (THS)
Tremendous improvement in fuel efficiency & clean achieved!
Inverter1NZ-FXE
engine
P111 Hybrid transaxleHV battery182MO11182MO12
Hybrid transaxle
13
TOYOTA Hybrid System (THS)
The TOYOTA hybrid system has two drive sources, one is the gasoline engine and the other, the AC motor.
The power train system selects the best combination of the different characteristics of both depending on
driving conditions. Also, through the adoption of a regenerative braking system, which recovers energy
during deceleration and ªidling stopº whereby the engine is stopped during idling, we have been able to
provide for maximum energy conservation. This has resulted in a vastly superior fuel economy compared
with that of gasoline A/T vehicles of the same displacement.
Features of the System
1. Optimum distribution of drive sources
The most efficient engine operating zone is automatically selected by controlling the optimum distribution of the engine and motor
drive energy sources.
2. Reduced energy loss
The engine is automatically stopped when starting and travelling at low load to reduce fuel consumption.*1
The kinetic energy that used to be lost through engine or foot braking is recovered by the regenerative braking system and used
for recharging, thereby contributing to improved fuel efficiency. When the driver applies the brakes, the hydraulic and regenera-
tive braking systems are coordinated. In order to recover more energy, a higher proportion of regenerative braking is used.
3. Not required for recharging from an external source
The system uses MG1 (Motor Generator No.1) and MG2 (Motor Generator No.2) to maintain a constant battery charge, so unlike
an electric vehicle, recharging from an external source is not required.
*1 : In some cases, the engine does not stop, depending on the air conditioner and HV battery (Hybrid Vehicle Battery) status.
System configuration
P111 HYBRID TRANSAXLE
Fitted with built-in THS transaxle MG1 (Motor Generator No.1), MG2 (Motor Generator No.2), power spliting device and reduction
gears for the hybrid system. These function to switch engine operation to MG2 assistance, HV battery charging and power generation
for driving MG2.
Inverter
This controls the current between MG1, MG2 and HV battery and converts DC/AC power.
HV Battery (Hybrid Vehicle Battery)
This supplies power to the motor at full load or on engine stopping and stores power recovered by regenerative braking or power
generation by MG1. 228 nickel-metal hydride batteries are connected in series to obtain a voltage of 273.6 V DC.

THS (TOYOTA HYBRID SYSTEM) 24

MAIN FUNCTIONS OF COMPONENTS
MG1Generates high-voltage electricity by being powered primarily by the engine.
Also functions as a starter to start the engine.
Hybrid
Trans-
axle
MG2
Primarily provide additional power to the engine in order to increase the
overall drive force. During braking, or when the accelerator pedal is not
depressed, it generates electricity to recharge the HV battery (Regenerative
brake system).
Planetary
Gear UnitDistributes the engine's drive force as appropriate to directly drive the vehicle
as well as the generator.
HV Battery
Supplies electric power to the MG2 during start-off, acceleration, and uphill
driving; recharged during braking or when the accelerator pedal is not
depressed.
InverterA device that converts the high-voltage DC (HV battery) into AC (MG1 and
MG2) and vice versa (Converts AC into DC).
Converter
Drops the high-voltage direct current (DC 273.6 V) into DC12 V in order to
supply electricity to body electrical components, as well as to recharge the
auxiliary battery (12 V).
HV (Hybrid Vehicle
Control) ECU
Information from each sensor as well as from the ECU (ECM, Battery ECU,
ABS ECU) is received, and based on this the required torque and output power
is calculated.
The HV ECU sends the calculated result to the actuators and controllers.
ECMSends a throttle open command to the electronically-controlled throttle in
accordance with the engine output request factor received from the HV ECU.
Battery ECUMonitors the charging condition of the HV battery.
Brake ECU
Controls the regenerative brake that is effected by the MG2 and the hydraulic
brake so that the total braking force equals that of a conventional vehicle that
is equipped only with hydraulic brakes.
Also, the brake ECU performs the ABS control conventionally.
Accelerator PedalConverts the accelerator angle into an electrical signal and outputs it to the HVAccelerator Pedal
Position Sensor
Converts the accelerator angle into an electrical signal and outputs it to the HV
ECU.
Shift Position SensorConverts the shift lever position into an electrical signal and outputs it to the
HV ECU.
SMR (System Main
Relay)Connects and disconnects the high-voltage power circuit through the use of
a signal from the HV ECU.
Service plugShuts off the high-voltage circuit of the HV battery when this plug is removed
for vehicle inspection or maintenance.

CHASSIS ± P111 HYBRID TRANSAXLE
182CH14
182CH13
HV Battery
Inverter
Drive
MG2 MG1
Discharge
Recharging
Electrical Path
Generation
Engine : Flow of
: motive force
: Flow of
: electrical force
Sun Gear Carrier Ring Gear
rpm
MG1 Engine MG2: Torque
: Driving Load
: MG2 Torque
Nomographic Chart of Planetary
Gear Unit
182CH18
182CH17
Inverter
HV Battery
MG2MG1
Speed
Control
Engine
Recharging
Electrical Path
Generation: Flow of
: electrical force
Sun Gear Carrier Ring Gear
MG1 Engine MG2: Driving
: Load
: MG2
: Torque
Nomographic Chart of Planetary
Gear Unitrpm Speed
Control : Flow of
: motive force 84
4) Normal Traveling
When the vehicle is being driven under normal traveling condition, the motive force of the engine is divided
by the planetary gears. A portion of this motive force is output directly, and the remaining motive force
is used for generating electricity through MG1. Through the use of an electrical path of an inverter, this
electrical force is sent to MG2 to be output as the motive force of MG2. Under further high-load conditions,
the electrical force from the HV batteries is also used as a motive force of MG2.
5) Deceleration Driving
If the SOC of the HV batteries is within the specified value during deceleration, electricity is generated
by MG2 to recharge the HV batteries. If the SOC is excessive, the apportionment of energy to the hydrau-
lic brakes is increased. However, if the shift lever is in position B, the engine is started by MG1 in order
to apply the engine brake.

CHASSIS ± BRAKES
182CH38
100
BRAKES
DESCRIPTION
The front brakes use ventilated disc brakes and the rear brakes use leading-trailing drum brakes.
To adjust the clearance between the shoes and drum, the rear drum brakes uses the incremental type hy-
draulic auto adjuster.
On the Prius uses a pedal type parking brake that is released by pressing the pedal further.
A hydraulic brake booster in which the master cylinder and booster are integrated has been adopted.
The Prius has adopted the ABS with EBD (Electronic Brake force Distribution) as a standard equipment.
A regenerative brake system, which uses the MG2 that is used for driving the vehicle as a generator to
efficiently convert the energy that is created during braking has been adopted. This system enables to col-
lect more driving energy by having the control to cooperate the hydraulic brake and the regenerative brake.

CHASSIS ± BRAKES
182CH39
182CH40
101

Specifications 
Master CylinderTypeSingleMaster CylinderDiameter mm (in.)22.22 (0.87)
Brake Booster TypeHydraulic
TypeVentilated Disc
Front BrakeCaliper TypePE54Front BrakeWheel Cylinder Dia. mm (in.)54.0 (2.13)
Rotor Size (D x T)* mm (in.)255 x 22 (10.04 x 0.87)
TypeLeading-Trailing Drum
Rear BrakeWheel Cylinder Dia. mm (in.)20.64 (0.81)
Drum Inner Dia. mm (in.)200 (7.87)
Brake Control Valve TypeP & B Valve
TypeDrum
Parking BrakeSize mm (in.)200 (7.87)g
Lever TypePedal
ABS with EBDSTD
*: D: Outer Diameter, T: Thickness
FRONT BRAKE
The PE54 type brake calipers and ventilated disc
rotor have been adopted. These brake calipers are
lightweight and compact to realize excellent brake
performance.
REAR BRAKE
General
The leading-trailing type drum brakes using
drums with a 200 mm (7.87 in.) inner diameter
have been adopted.
A hydraulic system that adjusts the clearance
between the shoes and the drum has been
adopted.

CHASSIS ± BRAKES
165CH33
Wheel Cylinder
Adjusting Bolt
Shoe
Strut
Auto
Adjust
Lever
Spring
A
C D
B
182CH41
PawlPawl SpringRelease
Intermediate
Lever
Sector
Parking Brake
Cable 102
Incremental Type Hydraulic Auto Adjuster
Ordinarily, when the rear brakes are applied, the
shoes expand until they come in contact with the
inner surface of the drum.
While the auto adjust lever remains in contact
with point A of the strut, the spring force causes
the auto adjust lever to rotate in direction C, with
adjust lever point B as the fulcrum. At this time,
if the shoe clearance exceeds a predetermined
amount, the tip of the auto adjust lever rotates the
adjusting bolt in direction D by 1 tooth, causing
the strut to move for a predetermined amount to-
wards the direction that expands the shoes. As a
result, by pushing and expanding the initial posi-
tion of the shoes, an appropriate amount of clear-
ance is maintained between the shoes and the
drum.
PARKING BRAKE
1. General
On the Prius uses a pedal type parking brake that is released by pressing the pedal further.
2. Construction
A pedal type parking brake pedal consists mainly
of a parking brake pedal, sector, pawl, release in-
termediate lever, pawl spring and pedal return
spring.
The parking brake pedal and sector are integrated,
and parking brake cable is attached to the parking
brake pedal.
The pawl and the release intermediate lever are
linked by the pawl spring and operate together
along with the movement of the pedal.

CHASSIS ± BRAKES
182CH42While Pressing Locked StateStroke
Reaction Force
of Parking
Brake Cable
182CH43
Press Again During Pedal Return Lift Portion of
Parking Brake Pedal103
3. Operation
During Applying
Pressing the parking brake pedal causes the sector's rachet to engage with the pawl. Then, when the pressure
on the brake pedal is released, the reaction force of the parking brake cable and the force of the pedal return
spring cause the pawl and sector, which remain engaged, to return (only for the stroke). As the result, the
parking brake becomes locked.
At this time, because the relative installed position of the pawl spring changes, the force of the pawl spring
that was applied to the intermediate release lever switches its direction and now pushes the intermediate
release lever down.
During Releasing
When the parking brake pedal is pressed again, as the reaction force of the parking brake cable and the force
of the pedal return spring will not be applied to the pawl, the action of the pawl spring causes the pawl to
lift. As a result, the pawl is released from the sector's ratchet.
Next, when the parking brake pedal returns to its initial point, the lift portion of the parking brake pedal
causes the intermediate release lever to lift. The pawl is then pushed down by the force of the pawl spring
and returns to its initial state.

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