Toyota Prius
Study case
Toyota Prius




Concept
Building
Operation
Electrical machines
The Toyota Hybrid System



The Prius evolved from 1997 to 2000
In 2003 Toyota increases the motor output by 50% (THS II)
The THS transmission is indicated by the dotted outline
The Toyota Hybrid System

The system’s main elements are:
 A power electronic unit
 A main processor
 HV battery
 MG1 and MG2
 Skid and break
control unit
The Toyota Hybrid System

The hybrid transaxle



MG1, MG2 and the engine are on one axle
A planetary unit ensures coupling of the
motors
A silent chain and a differential provide
motion transition to the wheels
The Toyota Hybrid System

This system controls the state of charge (SOC)


The SRMs control and limit the current
flow into and out from the battery
The target of the SOC is about 60%
controlled by the battery ECU
The Toyota Hybrid System

The power electronic of the THS is composed of:




The boost converter
Two inverters (one for each machine)
DC-DC converter
AC converter
The Toyota Hybrid System



The DC-DC converter ensures the charging of the auxiliary low
voltage battery of the machine
It has a H-bridge to invert the cc into high frequency ac
The transformer lower the ac voltage and rectify it to 12Vcc
The Toyota Hybrid System


The AC inverter ensures the ac for the air-conditioning compressor
This was introduced from 2004, changing the HV’s 201Vcc into
206Vac
The Toyota Hybrid System



The regenerative break system control
By this, the loss of kinetic force to heat and friction is diminished and
transformed into electrical energy
Distribution of force balance
The Toyota Hybrid System


The assisted break system was implemented in 2004
Is senses the speed and the force on of the pedal when it is pushed
and function of this, and of other sensor’s response it increases the
hydraulic pressure.
The Toyota Hybrid System

The EPS system assists the steering based on:



Torque sensors
Data from additional sensors regarding the machine condition
A DC motor
The THS operation
The THS operation
The THS operation
The THS improvements



Bus voltage 274V to 500V then to 650V
The torque is reduced and the speed is increased
Downsizing of the motor, reduced the motor weight, hence low
center of gravity offering the possibility of mounting on one shaft the
traction drive motor, the generator, the power distribution and the
engine
The THS improvements


Reducing the iron losses is mandatory
Losses were reduced with over 30%




10% due to improvement of reluctance
torque
20% due to using high grade steel
5% due to design considerations
The efficiency of the motor is 95%,
The THS improvements


The THD of the air-gap flux density must be decreased as much as
possible
The shape and the arrangement of the
permanent magnets is crucial
The THS improvements



The bridge is used to ensure mechanical stress and supports the
flux barrier
The bridge must be sized as small as possible
The number and size of the bridges reduces the mechanical stress
predicted for the manufacturing process and other final stage issues
The THS improvements

Experimental results of the 2005 motor design

Wise use of the reluctance torque
The THS improvements




The noise is due to the switching frequency that creates an AC field
in the core of the inductor
Frequency over 20kHz is recommended to be used in HEVs
The phenomenon is called “magnetostriction” (the core expands and
contracts)
More Si (from 4% to 6.5%) was added in the material for the core’s
lamination
The THS improvements

The noise given also by the power switches, the machine housing
and the vibration of different body parts, was diminished by
countermeasures, noise absorbing and insulation materials applied
to the body
Conclusions






The Toyota Prius has a complex system based on several sensors
all operating together to fulfill the control of the vehicle’s behaviour
A lot of improvements were added to increase the benefits of using a
Toyota designed HEV
The PMSM used for the Prius proved to fit all the requirements
perfectly reaching the desired output power and torque
The optimal structure is achieved testing several permanent magnet
arrangements, considering the solution to place them along the flux
paths
Using 3 bridges proved to fulfill the requirement of low air-gap flux
density THD
The noise due to switching and vibrations were reduced to a
convenient target
Thank you for your attention !