This is only a preview of the December 2001 issue of Silicon Chip. You can view 28 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Build A PC Infrared Transceiver":
Items relevant to "100W RMS/Channel Stereo Amplifier; Pt.2":
Articles in this series:
|
Is there a
HYBRID
in your future?
By Ross Tester
6 Silicon Chip
www.siliconchip.com.au
With petrol prices approaching a dollar per litre in many areas of
Australia, motorists are starting to think “alternative”. Immediately
“electric” springs to mind but electric vehicles, especially cars, have
yet to prove commercially viable. Now though, there is another alternative: the hybrid – a passenger car driven by both internal combustion (petrol) AND electric engines. Hybrids made quite a splash
at October’s Sydney International Motor Show.
T
here were two (or was it three?)
hybrid vehicles on display at
the Sydney Exhibition Centre.
We went there specifically to look at
the hybrids.
Toyota’s Prius was launched with
much fanfare. Honda had their Insight
there – but being a year old, it wasn’t
given star treatment (in fact, it was
almost undersold – I had to ask if it
was actually there!). And since the
show, I’ve discovered that there was a
Toyota Tarago hybrid also on display
– at least according to the Toyota PR
people.
OK, so what exactly is a hybrid vehicle? To be more accurate with the
answer, we should say there are two
different types of hybrids – series and
parallel. Both are based on the same
theme: motive power is provided by
both hydrocarbon fuel (usually petrol)
and electric engines.
In a series hybrid, the whole of the
fuel engine output is devoted to driving a generator, which in turn supplies
the electric motor which turns the
wheels. It’s a similar arrangement to
a diesel-electric locomotive. The main
difference is that in most series hybrid
vehicles, there is also some form of
battery storage which can power the
vehicle independently of the fuel engine – to some degree, anyway.
In a parallel hybrid, the fuel engine
AND the electric motor can both drive
the wheels. They share the load (pun
intended!) according to the way the
vehicle is being driven, ranging from
100% fuel engine and zero electric
through to 100% electric and zero fuel.
For a lot of the time, the proportions
vary all over the place, under the management of one or several computers.
Why not all-electric?
As we mentioned before, while immense development has taken place
around the world on 100% electric
vehicles (ie, no fuel engine at all), there
have been very few vehicles actually
make it into production – and even
fewer which have been commercial
triumphs. In fact, the score to date
hovers marginally above the zero
mark!
Why is this? Quite simply, it is very
difficult – if not impossible – to cram
enough battery capacity into a vehicle to come even close to the energy
Above is the Honda Insight, while opposite is the Toyota Prius.
Both are now available in Australia; both use a combination of
petrol engine and electric motor.
www.siliconchip.com.au
December 2001 7
available from an equivalent volume,
and especially weight, of hydrocarbon
fuels – petrol, diesel, gas, etc.
Then there is the matter of energy
replenishment. Electric vehicles need
their discharged batteries recharged
(or swapped over) at even shorter intervals than you would normally fill
your petrol tank. Usually, this means
charging overnight. It also means you
cannot wander too far away from a
charger or source of power.
While a jerry-can and funnel can
get your petrol vehicle out of trouble
out in the sticks within a few minutes,
you’d need several hours and one
mighty long extension cord for an
electric vehicle!
Range is also a problem: 250-300km
is often quoted as the best that the very
best electric vehicles can achieve (and
then only under ideal conditions);
most petrol/diesel cars can achieve
double or even triple this.
While huge advances have been
made in batteries (and more recently
fuel cells) they still simply cannot
replace the easily-filled tank of fuel
feeding an internal combustion engine. That’s not to say it won’t happen
– somewhere down the track it (or
another development) most certainly
will. In fact, major manufacturers (including Toyota) are currently working
on electric and fuel cell electric hybrid
vehicles.
The Honda’s engine looks much like other modern engines – until you get inside
it! It’s actually two engines in one.
But don’t hold your breath for something this year or even next. Toyota
are talking “sometime in the next ten
years . . .”
Back to the hybrids . . .
Honda and Toyota have taken quite
different approaches to achieve quite
similar results. We’ll look at the Honda Insight first, mainly because it has
been around for the best part of a year.
The Insight is based on the Honda
Integrated Motor Assist (IMA) system.
This combines a highly efficient one
litre 3-cylinder lean-burn VTEC ULEV
(ultra low emission vehicle) engine
and ultrathin electric motor to produce
56kW of power. When we say “combines” we really mean it: an ultra-thin
(60mm thick!) permanent-magnet
electric motor is built into the engine,
residing between the flywheel and the
gearbox.
Electricity for the motor is stored
in a 144V, 6.5Ah nickel-metal hydride battery pack controlled by an
advanced electronic Power Control
Unit (PCU). You read that correctly:
At left is a cutaway of the Honda
hybrid engine – the blue parts are the
petrol driven while the red are the
electric. Above is a drawing of the
60mm wide 10kW electric motor.
8 Silicon Chip
www.siliconchip.com.au
It’s a very “conventional” looking dash and control layout, belieing the technology elsewhere in the car. The Honda has a 5-speed manual transmission.
the battery pack is rated at only 6.5Ah
and is in fact made up of 120 “D” cells!
Power for the system is primarily
sourced from regenerative braking,
eliminating the need for an external
power source for recharging.
The battery pack, PCU and electronics package are hidden under a
panel under the rear cargo area. The
PCU ensures the battery can be neither overcharged nor overdischarged,
resulting in much longer life than
you’d normally expect from a NiMH
unit.
Design features
combustion, low-emission engines,
variable valve timing, high-efficiency
electric motors, regenerative braking,
nickel-metal hydride battery technology and microproccessor control
help-ed engineers develop an efficient,
lightweight and compact hybrid drive
system.
The Insight’s primary power source
is a 1-litre, 12-valve, 3-cylinder
VTEC-E petrol engine. Although the
engine alone provides sufficient driving performance – even in sustained
uphill driving – a permanent-magnet
electric motor mounted between the
engine and transmission provides
additional power assistance under
certain conditions, such as initial
acceleration from a stop.
The electric motor’s role as power
assistance allows it to be made smaller
and lighter compared with the fullsized traction motors in other hybrid
systems.
As the IMA petrol engine enters its
mid-to-high-rpm operating range, the
electric motor assist ceases and power
is supplied solely by the engine, which
is operating in its high-rpm 4-valve
mode.
Power for the electric motor comes
mainly by recapturing energy from the
forward momentum and braking of the
vehicle, rather than from the petrol
engine. When the Insight is coasting
or the brakes are applied while the
vehicle is in gear, its electric-assist
motor becomes a generator, converting
forward momentum into electrical
energy.
When a normal vehicle brakes, this
energy is wasted as heat. But in the
Insight, on light “braking” the brakes
are not actually applied. Instead,
regeneration slows the vehicle. Only
on harder pressure do the brake pads
actually contact the discs in the conventional way.
IMA electric motor assist
The ultra-thin 10kW DC brushless
motor is highly efficient, light and
compact.
The IMA electric motor is capable of
There are many innovations in the
Insight design, not the least of which
is its aluminium body, weighing 40%
less than a comparable steel car but
having 13% greater rigidity. The vehicle also has a very low coefficient
of drag – 0.25 – which means it cuts
through the air with minimal friction.
Even the side mirrors and the skirts
around the rear wheels have been
designed for minimal drag and wind
turbulence.
The Insight features specially
designed 165/65 R14 low-rolling resistance tyres, mounted on 14 X 5.5 JJ
aluminium-alloy wheels, improving
fuel efficiency by 6%. The tyres have
40% less rolling resistance and a 5%
reduction in weight, compared with
conventional tyres.
The power plant
Technologies such as lean-burn
www.siliconchip.com.au
The battery pack – consisting of 120 “D” cells – and the control unit hide under
a panel roughly below the golf clubs. (The clubs are not standard equipment!).
December 2001 9
providing high torque at low speeds,
and assists the one-litre engine during
low-rpm acceleration for increased
efficiency during normal driving.
The IMA’s central rotor is manufactured using the “lost wax” casting
method to give a precise shape and
high strength for a 20 per cent weight
reduction. For the rotor magnet, Honda enhanced the neodymium magnet
originally used in the Honda EV Plus
for an improvement in magnetic flux
density or torque ratio by 8%. This also
improved heat resistance, eradicating
any need for a cooling system.
To create a thin motor, Honda used
a simple structure including a split
stator with compact salient-pole field
winding and centralised bus ring,
allowing a width of 60mm – 40% thinner than if conventional technologies
were used.
The motor also doubles as a generator for the IMA system and a high-rpm
starter, quickly spinning the engine
to its ideal speed. If the IMA system
battery charge is low or in the case
of extreme temperatures, a separate
(conventional) 12V battery and starter
motor will start the engine.
The Honda Insight is not a cheap
vehicle. At $52995 plus on-road costs
it would take a lot of savings in petrol
to make up the difference. And the
recommended fuel for the Insight is
the more expensive 95RON premium
Toyota wanted to get in on the golf-bag act, too. . . but it does show just how
roomy (and how “normal”) the Prius is. The little vents you can see behind the
rear doors are battery/controller excess heat vents.
unleaded. Fuel economy, by the way, is
3.6l/100km city cycle and 2.8l/100km
highway cycle – very good in anyone’s
language.
Toyota Prius
Again and again, the staff at the
Motor Show kept emphasising just
how “normal” the Prius was. Normal
to look at, normal to get into and out
of, normal to drive, normal in “just
about” every way.
And that’s how Toyota have marketed their new five-seat “baby”.
Admittedly, they believe a significant
proportion of their sales will be to
new technology junkies and more
than half will be sold to government
and fleet buyers wanting to reduce
running costs.
But the rest, they believe, will buy
the Prius because it is so normal.
Like the Honda Insight, it has a very
low drag coefficient (0.29) to help it
slip through the air. Standard equipment includes dual SRS airbags, ABS
brakes, front seatbelt pretensioners
with force-limiters, power windows
Under the lid of the Toyota things do look a little different to a conventional car engine bay. The petrol power plant is on
the left while one of the Prius’ two electric motors can be seen on the right. Notice the heavy (red) power cables in the rear
of the pic – they go off to the batteries and controller in the rear of the car.
10 Silicon Chip
www.siliconchip.com.au
and power mirrors, electric power
steering and climate control air conditioning with an economy mode.
There is only one “option” available for the Prius: an integral satellite
navigation system, based on DVDs.
Everything else (and the list is extensive) is built in. Oh, one other option
– it comes in various colours!
If it is so normal, what is different?
Well, for a start, the Prius has not two
engines but three.
Petrol engine
Main power is provided by an
advanced 1.5-litre Atkinson Cycle,
VVTi-equipped petrol engine which
delivers 53kW of power at 4500rpm
and 115Nm of torque at 4200rpm.
An Atkinson Cycle engine, by the
way, has smaller combustion chambers and a higher compression ratio
than a conventional (or “Otto cycle”)
engine. Compression ratio on the Prius
powerplant is a whopping (for a petrol
engine!) 13.5 – approaching that of
diesel engines.
The Atkinson cycle was proposed in
the 1880s by English engineer James
Atkinson, to enable the compression
stroke and expansion stroke to be
mechanically set independently of
each other.
The Atkinson cycle design makes
better use of combustion energy by
keeping the exhaust valves closed
until the end of the expansion stroke.
The expansion stroke is extended until
the expansion pressure has virtually
dissipated, converting more of the
combustion energy into torque on the
crankshaft.
Toyota has combined the Atkinson
cycle with a long-stroke engine design,
offset crankshaft, direct ignition and
variable valve timing with intelligence (VVTi), to further improve efficiency.
The Hybrid System in Prius
seam-lessly combines the power of
this engine and a 33kW electric motor.
In addition, the motor is part of
the regenerative braking system. It
converts the kinetic energy of the decelerating vehicle into electricity, for
storage in the battery.
Permanent-magnet generator
The Toyota Hybrid System (THS)
also has a high-efficiency AC permanent magnet synchronous generator,
to run the electric motor and charge
the battery. The generator also serves
www.siliconchip.com.au
Toyota have chosen a slightly different dash layout for the Prius.
Of partic-ular interest is the centre
console, shown enlarged at right,
which contains the engine management touch screen showing the status
and operation of the fuel and electric
sections. This doubles as the screen
for the only Prius option: a DVD-based
satellite navigation system. Below this
is a totally integrated entertainment
system (including CD stacker).
as a starter motor for the petrol engine.
In addition, the THS system uses the
generator to control the ratio of power distribution from the power-split
device.
Inverter/Converter
Energy that is not required to propel the car is stored in a sealed 274V
battery, for use when required.
The inverter turns direct current
from the battery into alternating
current for the drive motor, and the
converter takes alternating current
from the generator and motor (in regenerative braking mode) into direct
current for storage in the battery.
Environmentally friendly
The Prius uses up to 50% less petrol
than an equivalent-sized conventional
car and emits about half the carbon
dioxide on a typical city drive cycle. The petrol engine automatically
switches off when the car is stationary
and going downhill. When moving off,
initial power is provided by the electric motor but the petrol engine also
starts automatically with a virtually
seamless transition.
Emissions of carbon monoxide,
NOx and hydrocarbons are only one
thirteenth of legislated maximum permissible levels and one fifth those of
an equivalent sized conventional car.
Actual consumption figures for the
Prius are 4.6 l/100km city cycle and
4.2l/100km highway cycle – obviously
not as good as the Honda Insight but
the car is a lot cheaper!
Continuously variable transmission
Prius’ Toyota Hybrid System acts
as an electronically controlled CVT,
which can freely vary the engine
speed. It achieves this by controlling
the generator’s revolutions. Therefore,
the vehicle does not need a conventional transmission.
The power-split device operates
December 2001 11
via a planetary gear system, in which
the engine output shaft drives the
planetary gear carrier and uses a set
of pinion gears to simultaneously
transmit power to the outer ring gear
and the inner sun gear.
The shaft of the outer ring gear
connects directly to the electric motor
and (through the drive shaft) to the
reduction gears and hence the front
wheels. The shaft of the sun gear drives
the generator.
The use of one set of planetary gears
to achieve two roles provides a significant saving in weight and space under
the bonnet, compared with either a
traditional automatic transmission
or a belt and pulley type CVT. There
is no torque converter and hence no
loss of energy through slippage in the
driveline.
The Toyota Prius is significantly
cheaper than the Honda Insight at
$39,990 plus on-road costs. It is fully
imported and numbers available for
Australia are quite limited: we were
told each dealer can have a maximum
of one Prius per month.
Toyota Prius Vs Honda Insight Quick Comparison
TOYOTA PRIUS
HONDA INSIGHT
Main Engine
In-line 4 cylinder DOHC 4V
In-line 3cyl SOHC VTEC
Capacity
1497cc
995cc
Maximum Power
53kW<at>4500rpm
56kw<at>5700rpm
Maximum Torque
115nm<at>4200rpm
113nm<at>1500rpm
Compression ratio
13.0:1
10.8:1
91 RON (unleaded)
95RON (PULP)
4.6l/100km
3.6l/100km
Fuel
Consumption - City cycle
2.8l/100km
Permanent Magnet
33kW
10kW
274V 6.5Ah NiMH
144V 6.5Ah NiMH
Electronic Continuously Variable
5 speed manual
Electric Power Assisted
Electric Power Steering
9.4m
10.2m
4315 x 1695 x 1485mm
3955 x 1695 x 1355mm
1250kg
827kg
Steel
Aluminium
Output power
Battery
Transmission
Steering
Turning Circle
Vehicle Size
Weight
Body
Yes
Yes
ULEV standard
ULEV standard
Regenerative Braking
Emissions
Going for a drive . . .
Auto engine shutoff on idle
We didn’t get the opportunity to
drive the Honda but we did drive the
Toyota Prius, thanks to Bill Buckle
Toyota who, as luck would have it,
are just around the corner from the
SILICON CHIP office.
It takes a few minutes to get used
to the Prius because it behaves differently to other cars. That’s not to say
it behaves badly – far from it. It’s just
“different”. One of the main differences is due to the continuously variable
transmission. There is no change from
one gear to the next.
Similarly, there is no push-in-theseat acceleration, either. You plant
your foot and you think it’s taking off
rather sedately – until you glance at
the speedo and you’re doing 80 in a
50 zone. Woops! Sorry, officer.
But the major difference is in noise
or, to be more correct, lack of it. Sitting
at a set of lights you think “it’s stalled”
which in truth it has – but deliberately
so. Accelerate a little and you still hear
virtually nothing. You are still hardpressed to hear anything even when
the petrol engine starts. You certainly
don’t feel anything except, perhaps,
you are aware that you have more
power available.
The main reason you know that the
engine has cut in is that the LCD touch-
Price
12 Silicon Chip
4.2l/100km
2x high efficiency AC
Consumption - Highway cycle
Electric Motor(s)
Warranty
Yes
Yes
$39990 + ORC
$52990 + ORC
3 years/100,000km
3 years/100,000km
screen on the dashboard tells you so.
We’ll look at little more closely at that
LCD in a moment.
Another thing that the LCD tells
you is that power is being taken from,
or supplied to, the batteries. Driving
along, you are completely unaware
what is powering what unless you
look at that screen.
Regenerative braking, where the
electric motor becomes a generator
and starts recharging the battery, occurs whenever you lift your foot off
the accelerator or when you apply
the brakes.
Braking is quite normal, except for
one thing. Most of the time the brake
pads make no contact with the discs!
All of the braking effort (and you can
feel it) is courtesy of regenerative
braking. Only in an emergency stop,
or when you apply very hard pressure
to the brake pedal, will the mechanical
brakes actually come into play.
If you’re travelling down a long hill,
you can move the gear lever to “B” and
the engine forcibly brakes the vehicle
all the way down, supplying electricity
(and cutting off the fuel engine) as it
does, without you touching the brake
pedal.
Toyota maintain that brake pad wear
will be a tiny fraction of a normal
vehicle and tyre wear should also be
way down. It is virtually impossible
to “chuck a wheelie.”
We mentioned before the touchscreen LCD panel. As well as giving
a huge range of information about the
vehicle and being the input device for
a lot of user settings (eg, radio, air con,
etc), it also doubles as the display for
the optional $3800 satellite navigation system. I have to confess, techno
junkie that I am, this was the thing that
tickled my fancy most of all (forget the
impressive range of technology I was
driving . . .).
It tells you exactly where you are,
where you are going, how to get there,
even how to un-stuff a stuff-up (like
when it tells you to turn left and you
turn right instead!). It could even
direct me right to my door (and those
who know where my home is hidden
will be mightily surprised at that!).
Just in case you couldn’t tell, I’m
impressed with the Prius.
SC
www.siliconchip.com.au
|