2001 TOYOTA PRIUS wheel torque

2001 PRIUS (EWD414U)
EMPS
In this system, the controller determines the direction and the amount of the assistant force based on the signals from the
vehicle speed sensor and the torque sensor that is built in the gear box. The controller then assists the operation of the
steering wheel by controlling the DC motor installed in the steering gear box.
E5 (C), E6 (D) EMPS ECU
(D) 5±GROUND : Approx. 12 volts with the ignition SW at ON position
(C) 2±GROUND : Always continuity
: PARTS LOCATION
CodeSee PageCodeSee PageCodeSee Page
B1136E5C36J18A37
C1036E6D36J19B37
D134J14A37J2237
D236J15B37J2637
E3A36J1637S135
E4B36J1737
: RELAY BLOCKS
CodeSee PageRelay Blocks (Relay Block Location)
324Engine Room R/B No.3 (Engine Compartment Right)
: JUNCTION BLOCK AND WIRE HARNESS CONNECTOR
CodeSee PageJunction Block and Wire Harness (Connector Location)
2A30Instrument Panel Wire and Instrument Panel J/B (Cowl Side Panel LH)2B30Instrument Panel Wire and Instrument Panel J/B (Cowl Side Panel LH)
2G31Engine Room Main Wire and Instrument Panel J/B (Cowl Side Panel LH)
2I31Cowl Wire and Instrument Panel J/B (Cowl Side Panel LH)
: CONNECTOR JOINING WIRE HARNESS AND WIRE HARNESS
CodeSee PageJoining Wire Harness and Wire Harness (Connector Location)
IA242Engine Room Main Wire and Cowl Wire (Cowl Side Panel LH)
ID142Instrument Panel Wire and Cowl Wire (Left Kick Panel)
IM144Engine Room Main Wire and Cowl Wire (Right Kick Panel)
IO144Engine Wire and Cowl Wire (Right Kick Panel)
IP144Instrument Panel Wire and Cowl Wire (Right Kick Panel)
: GROUND POINTS
CodeSee PageGround Points Location
IG42Cowl Side Panel RH
IH42Right Kick Panel
: SPLICE POINTS
CodeSee PageWire Harness with Splice PointsCodeSee PageWire Harness with Splice Points
I744Engine Wire
SYSTEM OUTLINE
SERVICE HINTS

THS (TOYOTA HYBRID SYSTEM)
HV ECUGO
ECM
Engine
Throttle Control
Motor
SPDO
EF1
HTE, ETH
ESA
VVT-i
W
MESTP
Brake Actuator
(Brake Master
Cylinder)
BRAKE ECUBrake Actuator
(Solenoid Valves)
Pressure Sensors
Signal
HV ECU Pressure
BTH
Total Brake Force
RequestedHTB
Regenerative Brake
Force Transmitted29
3. ECM Control
The ECM receives the demand torque and the target rpm which were sent from HV ECU (THE, ETH), and
controls the degree of throttle valve opening, fuel injection timing, ignition time and VVT-i.
In addition, the actual rpm is sent to the HV ECU with GO, and the speed signal from the hybrid transaxle
is received through HV ECU with SPDO.
When the vehicle is stopped, the HV ECU may send an engine stop (ESTP) command to the ECM to reduce
fuel used.
When a malfunction occurs in the system, the ECM activates MIL via the directions from the HV ECU.
4. BRAKE ECU Control
The brake ECU calculates the total braking force needed, based on the master cylinder pressure in the brake
actuator generated when the driver depresses the brake pedal, and sends this valve to the HV ECU.
The HV ECU computes a part for the regeneration brake force from the total braking force, and sends the
result to the brake ECU.
The HV ECU executes to the minus torque to MG2, and carries out the regenerative brake functions.
The brake ECU controls the brake actuator solenoid valves and generates the wheel cylinder pressure, which
is the regenerative brake force subtracted from the total braking force.

THS (TOYOTA HYBRID SYSTEM)
182TH33
31
± REFERENCE ±
The MG1 and the MG2 are generally shut down when the shift lever is in the N position.
However, the shut-down function is canceled under the following exceptions:

During driving, if the brake pedal is depressed and a wheel locks up, the ABS is activated. After this, low
torque is requested from the MG2 to provide supplemental power in order to restart the rotation of the wheel.
Even if the shift lever is in the N position at this time, the shut-down function is canceled to allow the wheel
to rotate. After the wheel rotation has been restarted, the system resumes its shut-down function.

When the vehicle is driven in the D or B position and the brake pedal is depressed, the regenerative brake
operates. At this time, as the driver moves the shift lever to the N position, the brake hydraulic pressure in-
creases while the request torque of the regenerative brake decreases gradually so as not to create a sluggish
brake feel. After this, the system effects its shut-down function.
When any of the conditions described below is pres-
ent, the message prompt as shown appears in the
multi information display, accompanied by the illu-
mination of the master warning light and the continu-
ous sounding of the buzzer.

The ªREADYº light is illuminated, the shift lever
is in the N position, and the HV battery is dis-
charged.

The ªREADYº light is illuminated, the shift lever
is in the N position, and the driver's door is open.

The ªREADYº light is illuminated, the parking brake is engaged, the shift lever is in the B or D position, and
the driver's door is open.

CHASSIS ± P111 HYBRID TRANSAXLE
182CH20
182CH19
Inverter
HV Battery
MG2MG1
Engine
Discharge
Electrical Path
Recharging
GenerationDrive: Flow of
: motive force
: Flow of
: electrical force
Sun Gear Corrier Ring Gear
rpm
MG1 Engine MG2: Driving Load
: MG2 Torque
Nomographic Chart of Planetary
Gear Unit
NOTICE
Because it is not possible for this transaxle to separate the MG2 output force from the drive wheels when
the shift lever is in position N, the generation of electricity is disabled. In this condition, the generation
of electricity could cause the motive force to be transmitted, which creates a hazardous situation. There-
fore, beware that the HV batteries could become discharged in this state.85
6) Reverse Driving
The vehicle drives in reverse powered only by MG2. If the SOC of the HV batteries exceeds the specified
value, the vehicle drives powered only by MG2. If the SOC is below the specified value, the engine starts,
and the electrical force generated by MG1 passes through the electrical path function of the inverter in
order to be used as the motive force of MG2.

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.

CHASSIS ± STEERING
182CH68
Rear Wheel
Speed SensorsBrake ECU
Torque Sensor Signal 1
Torque Sensor Signal 2
EMPS
ECUMeter ECU
Gateway ECUDLC3
Display ECU
Multi-information
Display
123
EMPS (Electric Motor-assisted Power Steering)
1. General
In accordance with sensor information such as that provided by the rear wheel speed sensors, the torque sen-
sor that is mounted on the steering gear, and the EMPS ECU determines the direction and the force of the
power assist and actuates the DC motor that is mounted on the steering gear to provide power assist to the
steering effort.
The EMPS in the Prius the following features:
This system can provide power assist even when the engine is stopped.
This system offers excellent fuel economy characteristics because power assist is provided by the DC mo-
tor that is mounted on the steering gear, and this motor consumes energy only when power assist is re-
quired.
Unlike the conventional hydraulic power steering system, this system excels in serviceability because it
does not require pipes or the power steering fluid.

System Diagram 

CHASSIS ± STEERING
182CH69
Meter ECU
EMPS ECU
Relay
DC MotorRear Wheel Speed
Sensors and Rotors
Brake ECU Multi-information Display 124
2. Layout of Main Components
3. Function of Main Components
ComponentsFunction
St i
Torque Sensor
Detects the twist of the torsion bar, converts the torque that is applied
to the torsion bar into an electrical signal, and outputs this signal to
the ECU.
Steering
Gear
DC MotorGenerates power assist in accordance with a signal received from the
EMPS ECU.
Reduction
MechanismReduces the rotation of the DC motor and transmits it to the pinion
shaft.
EMPS ECU
Actuates the DC motor mounted on the steering gear for providing
power assist, based on the signals received from various sensors and
the rear wheel speed signal.
Meter ECUOutputs a signal for displaying the PS warning on the center display
in case of a malfunction in the system.
Brake ECURear wheel speed signals are outputted to EMPS ECU.
RelaySupplies power to the DC motor for power assist.
Multi-information DisplayDisplays the PS warning in case of a malfunction in the system.

CHASSIS ± STEERING
182CH70
182CH71
182CH72
Torque
Sensor
Rack and
PinionDC Motor
Reduction Mechanism
Motor
Shaft
Stator
Rotor
Pinion Gear
Motor Shaft
DC Motor
Ring Gear
Pinion Shaft125
4. Construction and Operation of Main Components
Steering Gear
1) General
The steering gear consists of the rack and pin-
ion, DC motor, reduction mechanism, and
torque sensor. The front suspension compo-
nents have been optimized to reduce the load
on the DC motor. Also, the components have
been optimally allocated to ensure ample rack
travel and wheel turning angle, resulting in
excellent cornering performance.
2) DC Motor
The DC motor is mounted on the gear hous-
ing. The DC motor consists of the motor shaft
that is integrated with the hypoid pinion to
transmit the torque that has been generated by
the drive force of DC motor to the pinion
shaft, the rotor and stator.
3) Reduction Mechanism
A reduction mechanism that transmits the
rotation of the motor to the pinion shaft has
been mounted on the steering gear. The reduc-
tion mechanism consists of the ring gear that
is secured to the pinion shaft and the pinion
gear that is integrated with the motor shaft.
The power assist of the motor is transmitted
by the reduction mechanism to the pinion
shaft, which provides power assist to the
steering effort.