All about the Toyota Prius

Part 2 -- Description

Images are linked to larger versions.



Review of other hybrid topologies

Series Parallel


THS/HSD system topology

Series/Parallel hybrid topology
    More direct (and efficient) path to wheels
    Electric-only drive capability -- "full hybrid"
    Downsized components -- engine & motors can help push

MG1 and MG2 interchangeably power each other
    "Closes the loop" for power transfer

Linked via the Power Split Device
    PSD is a single planetary gearset -- nothing new here
    Model T Ford
    Almost any modern A/T is full of them

Essentially, it's a differential -- just lopsided!


Driveline basics

Another view of the same thing

"Generator" and "Motor" really are misnomers
    Both can perform either function
    "Motor/generator" is the accurate term

Yes, the axles have their own differential too
    (Just not shown in many of these diagrams)


Driveline implementation

Toyota's trade-show transaxle cutaway

Two electric motor/generators
    MG1 == "generator", charging, starter, and torque-balance
    MG2 == "motor", traction and regen

Mnemonic: 2 is larger than 1

(And they're both smaller than the engine!)


Driveline mechanical schematic

Engine shaft through center
    Connects to planet carrier (inner black line)
    Runs a small fluid pump at far end

MGs run on sleeves around that
    MG1 is sun gear
    MG2 is ring and road (outer black lines)
       ...that's a little hard to see here -- there are
       THREE concentric parts where the chain takes off

Engine torque splits 72% to wheels, 28% to MG1

NO mechanical shifting, except park

"Continuously variable" is done electrically


Driveline output coupling

This tech stole the show!
    Lacey, WA alternative fuel fair
    A whole Classic transaxle to play with
    He's holding the engine shaft / carrier

Final drive from ring multiplies torque
    Chain take-off reduces side loading
    The Prius has a "4.11 rear"

Engine shaft, sun gear, ring turn independently


Transaxle (another view)

Rotors are strongly magnetic!
    Keep laptops, cards, etc away

This unit is *heavy*
    As you might imagine, with all that iron inside

Toyota considers this a FRU
    Simple and (hopefully) reliable
    And yet there are complete overhaul instructions
    Independents can maybe rebuild them?
    Opportunities will be rare

MG2 slings a little oil
    Maybe makes up for pump not turning?
    Gen 2 rotors are smoother



Here's the 72/28% split again

Simplest graph of torque/RPM relationship
    Read RPM (for all) down left side
    Read road speed (for MG2 only) down right
    MG2 RPM has direct correspondence with MPH
    Useful engine (ICE) RPM 1000-5000, or OFF

Gears treated as levers/pivots
    Hold back MG1, and the car moves
    Just like sand under the spinning tire...

Two shopping carts and a broomstick?
    It's all about balancing loads


Demo time!

Play with the models

Understand torque-transfer




Meet "Torquey the Muppet"
    Rework of 1.5L Echo plant
    This is good for 50+ MPG by itself
    Closely matches ASE composite type 3

Many efficiency hacks...
    Offset crank
    Narrow bearing surfaces
    Low-tension rings
    5w30 or lower oil
    Belt only drives primary water pump
    Low friction in general (can turn with one hand!)

VVTi with Atkinson/Miller intake


Atkinson / Miller cycle

Lower compression, higher expansion
    Nominal 13:1 turns into 8:1 on intake
    Extracts more net energy from gases
    Significantly better FE, slightly less torque

Original Atkinson linkage changed piston stroke
    see excellent animation at

Miller simplified w/ delayed intake close
    Pushes a little mixture back into plenum

Compression tests *will* be lower...


VVTi modes

Several operation modes/ranges
    Variable intake, fixed exhaust
    Range 4 yields high MPG!
    Full retard during fuel-cut "warp stealth"

Internal EGR via valve overlap
    No external plumbing to fool with
    This is becoming typical in VVT systems

How to monitor valve timing?? Scantool lies


Valve train

Chain cam drive
    Direct bucket lifters
    Adjustment rarely needed if ever

34 tooth CKP (2 missing)

3 tooth CMP (1 missing)

No scantool "CMP learn" needed

VVTi actuator driven by oil pressure
    Control solenoid nudges spool valve back and forth
    Vanes inside sprocket hub set relative cam angle
    cam/crank timing discussion:


Electric throttle

ETCS (not just in Prius now)

1st gen repair: fix/adjust
    manual describes TPS R&R

2nd gen repair: throw it away?!
    Manual doesn't even get into it...
    But it's the same $750 of serviceable parts!

TPS angle must be restored
    There's apparently no auto-learn
    But no IAC to fool with, either

Diagnostic: listen/feel the motor PWM
    It actively fights you when it's working

Failsafe rest position via return springs
    Two springs set a default 15% TPS, slightly open


Throttle/intake features

Dual-wiper pot for redundancy-checking
    VTA1 used as main input

Two PCV hoses
    One above plate, one below

Coolant loop around throat

Clean/lube butterfly is useful service item
    Can clean/service without disconnecting coolant lines

MAF only, no MAP or BARO

Air box has charcoal HC filter


Intake issues

Oil sump in intake is very common
    Several theories on why -- PCV, blowback, ...
    May also include fuel distillates
    Oil overfill seems to exacerbate it

P3191 "engine does not start"? Look here
    Especially in cold weather
    Oil viscosity may be a factor
    Throttle-butterfly edge crud could cause sticking

More 1st-gens having problems now


Oil overfill?

3.7 quarts does not mean 4 quarts
    1/4 inch BELOW full mark is about right


Fuel system

Bladder inside metal gas tank
    (US/CAN market only)
    Reduces vapor volume and loss
    Stiffer and hard to fill in cold weather
    Gauge sender is off to side, parallel plumbing

Returnless fuel system
    Single-speed pump & regulator (in tank)
    Nominal pressure 48 psi
    No rail pressure feedback (would have been nice)

EVAP tests include bladder leak detection
    Tank air pulled to intake and tested by A/F sensor
    More pix and teardown/discussion:


Fuel system

    14 ohm saturation injectors
    Easy injector-wire access at ECM
    Fuel supply tube & fittings under cowl
    Scantool pump activation
    No FP fuse, and "C/OPN" relay is semi-buried
    Best pump-power access is under driver's kick-panel

Test adapters are hard to find
    Toyota says "purchase new fuel tube"

<Insert whiney "fuel systems WTF" rant here...>



1st gen: O2 sensors
    And HCAC adsorber (see next slide)

2nd gen: Wideband A/F at B1S1
    Differential output -- both sides 3.something volts
    Current-based, can't really scope it
    Some scantools confused about its "voltage"

Post-cat is normal O2
    Sits low, somewhat vulnerable...


HC adsorber cat

1st-gen special second cat

Vacuum-actuated valve
    Closed for warmup
    Open for HC purge later

Problem: it rusts and sticks
    Esp. in the Salt Belt...
    P1430, P1431

Can possibly lube and work it loose
    But it requires frequent attention


HCAC Vacuum line

Vacuum fitting still present in '04+
    Not used in 2nd-gen but still on the manifold
    Convenient vacuum-gauge takeoff!

Some throttle-body hoses visible here
    Note front PCV wear pattern from air box


Cooling system

Heat storage and retrieval system
    (US/CAN only, not JP/EU)
    Hot coolant "put away" in insulated tank
    Used to preheat head/cylinders at next startup

Three-way valve directs coolant flow
    Preheat is reverse of normal flow into head
    Warms right around combustion area, lowers emissions

Normal radiator and cabin heater
    With the addition of an electric circulation pump
    (Remember that "furnace" thing?)

Scantool-driven bleeding procedure
    Hex bleed tap semi-hidden under LHS radiator brace


Thermos bottle

Vacuum dewar bottle
    Holds about 3 liters

Frequent collision victim

Has one of three engine coolant drains

Fairly easy access past fender liner
    But don't mangle it (or its clips)

Bug: wasted preheat
    Pump-in happens on most power-ups
    But what if you're not going anywhere?


Other engine features

Which sensor is which here?
    The manual may mislead

Oil pressure: switch only
    Pressure transducer would be a nice hack...

Coil-on-plug ignitors
    Iridium plugs, 100K
    Pull and anti-seize them well before then!

Hole for electric block heater
    (see "heatgames" webpage for many details)

The inverter blocks easy access to here
    The ... what? Is that a car part?


Demo time!

Look around the engine
    Examine throttle area
    Find sensors (or difficulty of access)

Find my block heater
    (do NOT remove it -- thermal grease)

Find the fuel pump power
    Under the LHS kick panel is easiest



The battery

This is what everyone asks about
    Answer: "lasts the life of the car"

Charge management is the key
    40% - 80% limits, seeks 60%

NiMH best present chemistry right now
    High charge/discharge currents
    But lithium is rapidly gaining ground

Note service-plug wiring!
    Also contains battery ECU, relays, prechage resistor...
    Hall-effect current-sensor donut is what I tapped

Tour de Sol hack-job charging experiment
    ... not particularly safe, but proof of concept
    We don't need Toyota's magic charger


Battery facts

Prismatic modules
    6 cells at 1.2V each = 7.2V
    6 or 6.5 Amp-hours
    Thermistor cavity

Classic pack: 6 Ah
    38 modules == 273V
    50A max charge/discharge

2nd-gen pack: 6.5 Ah
    28 modules == 201V
    100A max charge/discharge
    Secondary cell interconnect for more current
    Better cooling surfaces


Battery facts

    [Quiz: Why is this pack okay to touch without gloves?]

Modules are all series-connected
    String voltage monitored every 2 modules
    ONE weak cell can ruin your day
    Can read block voltages on scantool [~16V]

Real-life operational voltage is higher
    273 --> 300, 201 --> 220

Compression rods hold the pack together
    Otherwise, cells can easily bulge out

Warmed/cooled from cabin air
    Batteries are happy at human "comfort zone" temps

Not sized for distance -- ~600Wh avail
    Used for energy bouncepad, not the day's commute
    1.5 or 2 miles max on "full" charge


HV system safety

Entire HV system is isolated
    Battery, relays, wires, inverter, motors
    Any chassis leak detected as a ground-fault
    P3009 and system shutdown

Coaxial cable and shielded connectors
    Penetration/damage likely to cause ground-fault

WARNING: Battery ECU sense leads still hot??
    That ECU plug is orange for a reason

Components can be megger tested
    But read the manual on how:
       500V max, and all low-voltage electronics disconnected
    Can track down ground-faults piece by piece


Motors 101?

Do we know what we're looking at here?
Study the basics on motors and inverters


Original system

1st-gen electrical system
    One of about 300 patents covering the car

Basic MG1, MG2, inverter shown here
    Many lessons from industrial motor-control
    Toyota had to design their own semis --
       off-the-shelf wasn't good enough!

Analog position resolvers for commutation
    Tamagawa-Seiki "singlsyn" type, quadrature output
    Feedback loop includes the computer
    Bridge PWM control sent straight from ECU


Updated system -- THS II

2nd-gen system has several improvements
    Buck/boost converter, steps up to 500V
    Push motors faster, regulate charging
    Higher efficiency motors
    Updated IGBT power modules

Same position resolvers

Electric A/C with its own inverter
    Variable speed, saves energy...
    Run from HV battery, lots of power

Single bleed resistor drains all caps
    And it's a funky one; see next slide



My clear cover for the "naked" exhibit

Not a whole lot to see up top
    Major interconnects (200V, 500V, motors)
    Capacitor module (separate cans in 1st-gen)
    Green card is 64K bleed resistor assy
    See "ginv" teardown webpage for in-depth detail

Water-cooled, separate radiator section
    Middle layer is a cold-plate
    Pink tank is coolant reserve

Inverter can be shifted aside w/o draining
    Some items accessible underneath
    AirLift works well to refill if drained
    Listen to the pump, look it up ...

Coolant drain in-line w/ transaxle hoses


Inverter details ('04+)

Oak Ridge 890029.pdf shots
    Capacitor module removed


Inverter details

PWM chop frequencies 5K and 10K
    You can hear this while driving
    Funky modulation schemes, based on speed

ECU sends 3 control leads + "gate"
    Turned into six for 3-phase bridge
    Gate disables control, such as for Neutral

Interlocks on covers/lid
    And on 2nd-gen service plug, too
    Easy enough to bypass...


Inverter details ('04+)

DC/DC converter and A/C control
    If both fail, might be that 30A fuse

Your tax dollars at work
    Argonne/Oakridge papers are all public


Motor/Generator notes

MG1: ~12-15 kW, MG2: 50 kW
    1st-gen slightly less

295 ft-lb @ 0-1200 RPM
    ~ 150 lbf tangential per pole at air gap -- times eight!
    and that's *before* final reduction

Three-phase permanent-magnet synchronous AC
    Eight poles, four electrical revs per rev

1st-gen motors are parallel-wound

2nd-gen motors are series-wound
    Higher voltage, but less current

Motor windings can be a boost converter
    Argonne/Oakridge *missed* that very important fact
    We can demo this easily -- crank-n-spark
    Waveform very similar to injector pulse
    I have a webpage up about it...


Demo time!

"Exploded" sub-pack

Pull spare inverter apart, ID parts

Electrical experiments
    Play with 3-phase
    Be the inverter -- can you keep up?

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