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The GM Silverado/Sierra
hybrid is a full-sized pickup truck. Unlike the Toyota
Crown, it doesn’t use an
electric motor as a traction
motor or for mechanically
powering accessories
when the engine is not
running. Instead, it uses
a conventional 5.3-litre
V8 and 4-speed automatic
transmission with a 14kW,
3-phase induction AC starter/
generator sandwiched
between the transmission
and the engine. Energy
storage is by a 36V lead-acid
battery. [GM]
The New Era in Car
Electrical Systems
The first cars using the new 42V standard
are now being released. So why the move
from 12V and what are the implications for
the design of higher voltage car electrical
systems?
By JULIAN EDGAR
B
ACK IN OUR JULY 2000 issue, we
briefly looked at the way in which
vehicle electrical systems are changing. The use of high-output alternators
and 42V electrical systems were being
mooted as technical solutions to the
ever-increasing electrical power demands in cars. What’s happened since?
Well, in a few words – a lot!
Toyota in Japan currently sells a car
with a 42V electrical system, while
GM in the US is this year releasing a
42V pickup truck – and some organisations are already using pre-delivery
vehicles. New technical standards are
being developed to cover everything
from 42V battery terminal and fuse
20 Silicon Chip
design to the colour-coding of 42V wiring. Automotive component suppliers
have developed 42V alternators, starter motors, circuit breakers and other
components. Some are predicting that
by 2010 as many as half of all vehicles
will use 42V electrical systems. In 20
years, the forecasts suggest that all cars
will use this voltage.
Even more interesting is the relationship developing between “mild”
petrol/electric hybrids and 42V electrical systems. Throw in the increasing
availability of mains power in cars
(yes, that’s right – in the USA you
can now have a factory-fitted mains
power socket in your car!) and the
whole area of car electrical systems is
undergoing a change of a magnitude
never seen before.
Power-hungry cars
The trends in automotive technology can be summarised as:
• Better fuel economy
• Reduced exhaust emissions
• Improved safety
• Better comfort and convenienc
Each of these has implications for
the load placed on car electrical systems. For example, improvements in
fuel economy can be gained by applying systems such as automatic engine
stop/start capabilities, electricallyassisted acceleration from a standstill,
electric engine cooling pumps and
fans, and electric power steering and
air-conditioning.
Also being thoroughly investigated
is the electromechanical operation of
engine valves. While it could bring
about significant increases in engine
power and efficiency, this approach
looks likely to be electrically power
hungry, with estimates of up to 2.4kW
peak loads on a six-cylinder engine.
siliconchip.com.au
Table 1
•
•
•
•
•
Daimler Chrysler
Renault/Nissan
General Motors
Peugeot/Citroen
Ford
•
•
•
•
•
Fiat
BMW
Toyota
VW/Audi
Honda
Car manufacturers in North America,
Europe and Japan currently developing
42V cars
Reductions in emissions can come
from electrically heated catalytic
converters (some cars already have
these), while dynamic safety can be
improved by the use of active electric
power steering, active suspension
and high-powered electric de-icing
of glass. Finally, increasing comfort
and convenience can lead to the use
of electrically heated and cooled seats,
electrically heated steering wheels,
high-end sound systems, in-car computers, navigation systems and the
provision of mains-power sockets.
Even without including electrical
propulsion, components supplier
Delphi expects the growth in electrical
loads in cars to be 5% per year over
the next 20 years. If electric propulsion is included, that estimate rises
to 8% per year. Fig.1 shows the past
and estimated future increases in car
power demands.
The consumer acceptance of the
latest model Toyota Prius – this year
Toyota expects to sell 50,000 in the
USA alone – has given car manufacturers the confidence to start thinking
seriously about incorporating electricassist into otherwise conventional designs. These so-called “mild hybrids”
use electric assistance only in certain
conditions. For example, in a mild
hybrid, the petrol engine is turned off
whenever the vehicle is stationary. The
electric motor then helps the car accelerate as the petrol engine re-starts.
The gains in fuel economy are not as
great as in high-voltage full hybrids but
the manufacturing and development
costs are much lower.
This acceptance of mild hybrids
makes the rate of growth in electrical
power demand likely to be close to
Delphi’s 8% per year estimate.
42V systems
Prior to 1955, vehicles used 6V elecsiliconchip.com.au
Fig.1: past and estimated future increases in car power demands (note the
logarithmic vertical axis). The massive increase in electrical power loads is
seeing a move to 42V systems. [Delphi]
ACCESSORIES
BELT
STARTER
(INITIAL START)
PULLEY
MAGNETIC
CLUTCH
ENGINE
GEAR
MOTOR/GENERATOR (MG)
INVERTER
36V BATTERY
DC/DC CONVERTER
DRIVE WHEELS
12V BATTERY
ECU
CONTROL UNIT
Fig.2: the mild hybrid Toyota Crown is the first car in the world to feature
the new 42V standard. It uses a 3kW 3-phase AC synchronous motor/
generator in conjunction with a 147kW petrol engine. The transmission is
a conventional 5-speed automatic. The motor/generator, which is larger
than a conventional starter motor but not as large as the traction motor
used in a full hybrid, charges a 20Ah 36V battery via a water-cooled
inverter. [Toyota]
trical systems. However, recognition
in the US that higher ignition energy
would be required for the high compression V8s then being introduced
prompted the adoption of a higher
voltage system. In addition, the introduction of higher power headlights,
radios and higher-powered starter
motors were all showing the limitations of the 6V system. 12V systems
– using 13.8V regulation – were then
introduced, with most manufacturers
achieving the transition within two
years.
November 2004 21
STARTER
MOTOR/
GENERATOR
CONTROL
UNIT
12V BATTERY
OIL PUMP
36V BATTERY
Fig.3: in the Toyota Crown, the 12V battery is charged via a DC/DC converter
and the 36V battery from the generator inverter. Both batteries are mounted
over the rear axle of the car in the forward section of the boot. [Toyota]
36V VALVE REGULATED LEAD ACID BATTERY
INVERTER, ECU
DC-DC CONVERTER
MG
AT OIL PUMP
ELECTROMAGNETIC CLUTCH
Fig.4: the use of an electromagnetic clutch allows the Toyota’s motor/generator
(MG) to drive the accessory belt even when the engine is off. By engaging the
clutch, the motor generator can start the engine and even help propel the car.
[Toyota]
The increasing power demand of
current cars has now caused a similar
situation to develop – a higher voltage is needed. However, the situation
isn’t quite the same – there are far
more devices of vastly greater sophistication working on the current 12V
standard than there were working on
22 Silicon Chip
6V in 1955.
The new standard is termed a 42V
system. That is, battery voltage is 36V
with the bus regulated at 42V. Basing
the standard on the 42V running-car
voltage, rather than the 36V lead-acid
battery voltage, was done to cater
for future developments that might
displace lead-acid batteries and traditional charging systems.
One benefit of increasing the voltage
to 42V is a reduction in wiring gauges.
A current mid-size car has a wiring
loom that weighs 35kg or more and
contains 2km of wire, 1000 cut leads
and 300 connectors. With the potential
for loads of many kilowatts (the catalytic converter heating in the BMW
750iL requires a short-term power
of 17kW!), the current flow required
at 13.8V becomes very high indeed.
As a result, conductor sizes are large,
adding cost and weight. Increasing the
voltage reduces the current flow and
so smaller conductors can be used.
In addition to reducing conductor size, adopting a 42V standard
allows the development of powerful
combined starter/generators, more
compact and powerful electric motors,
and other actuators that are smaller,
have a lower mass and improved
performance. Table 3 shows some of
the benefits of adopting 42V systems.
Another advantage of the higher
voltage is in the field of semiconductors. The cost of semiconductor
switches, which are expected to be
used very widely in cars, depends on
the current and voltage ratings of the
device. The current-handling capability is related to the semiconductor’s
area, while the voltage rating is tied
to the device’s thickness and doping
profile. A reduction in required current capability results in a smaller chip
area, decreasing costs.
For example, an electric powersteering controller may need to handle a power of 600W. At 14V with
an assumed electronic efficiency of
85%, the switch is required to handle
50A. However, at 42V the required
current handling drops to less than
17A, reducing the cost of the powerdependent components by 60%.
But why just 42V? If reductions in
conductor and electric motor size are
the criteria, why not use 500V, say, as
does the current model Toyota Prius?
There was widespread consensus that
the new voltage standard should be
sufficiently low to ensure the personal
safety of those that come in contact
with it. During the development of the
new standard, the Society of Automotive Engineers performed an in-depth
study of the research that had been
carried out on human tolerance to electrical shocks. The society concluded
that protection against direct contact
siliconchip.com.au
Toyota Crown Running Modes
The petrol engine switches off whenever the car is
stationary. On restart, the electric motor/generator
drives the car and starts the engine.
In normal driving the petrol engine propels the vehicle.
If battery charge is low, the electric motor/generator is
used to charge the battery.
During braking or any other time that the fuel supply
to the engine is cut, the electric motor/generator
regeneratively brakes and so charges the battery.
When the vehicle is stopped, the engine is turned off and
the electric motor/generator powers the accessories such
as the air-conditioning compressor. [Toyota]
was not required if the voltage did
not exceed 65V DC, including ripple.
Subsequently, the German standards
body VDE reduced this to 60V. The
specification of 42V systems suggests
that a maximum bus voltage of 55V
is permitted during dynamic overvoltage conditions.
Table 1 shows car manufacturers
in North America, Europe and Japan
currently developing 42V cars, while
Table 2 lists the automotive component suppliers currently developing
42V components.
The first 42V cars
The first two cars featuring 42V
technology are mild hybrids that run
dual 12/42V electrical systems. The
Toyota Crown mild hybrid has been
produced in small numbers in Japan
siliconchip.com.au
since 2001 and initial deliveries of
the General Motors Silverado/Sierra
hybrid twins are occurring now, with
full sales to begin later this year.
(1). The Toyota Crown Mild Hybrid:
the Crown uses what Toyota dubs
a “Toyota Hybrid System – Mild”,
or THS-M. Fig.2 shows its layout. A
belt-driven motor/generator comprising a 3kW 3-phase AC synchronous
motor is used in conjunction with
a 147kW 3-litre in-line 6-cylinder
petrol engine. The transmission is a
conventional 5-speed automatic. The
motor/generator, which is larger than
a conventional starter motor but not
as large as the traction motor used in
a full hybrid, charges a 20Ah 36V battery via a water-cooled inverter. The
motor/generator is used to:
• restart the stopped engine (initial
starting is by a conventional 12V
starter motor).
• help drive the vehicle when moving away from a standstill.
• generate all electrical power.
• provide regenerative braking on
deceleration.
• drive engine auxiliaries when the
engine is stopped.
The 12V battery is charged via a
DC/DC converter. Both batteries are
mounted over the rear axle of the car in
the forward section of the boot (Fig.3).
The motor/generator, which is located
where a conventional belt-driven alternator normally would be, is able to
drive the accessories with the petrol
engine stopped because in this mode
a magnetic clutch is used to decouple
the accessory belt drive system from
the engine.
November 2004 23
Just some of the parts developed for the mild hybrid Toyota Crown (clockwise
from top left): the engine; 36V battery; inverter & electronic control unit; and
electric motor/generator.
Fig.4 shows an overview of the
engine bay. In stop/start urban conditions, fuel consumption is improved
by about 15%.
(2). GM Silverado/Sierra hybrid
the GM Silverado/Sierra hybrid is a
full-sized pick-up truck. Unlike the
Toyota Crown, the GM mild hybrid
does not use the electric motor as a
traction motor or for mechanically
powering accessories when the engine
is not running. It uses a conventional
5.3-litre V8 and 4-speed automatic
transmission – the design criteria
required that an existing GM engine
be used and that the transmission had
only minor modifications for its new
hybrid vehicle role. Overall driveline
length also needed to remain the same
as non-hybrid versions.
In order that these criteria could be
met, the starter/generator (GM call it
simply the ‘electric machine’ - EM) is
inserted between the engine and the
transmission, with the torque converter being reduced in diameter to create
the space. To overcome problems of
excessive heat resulting from a smaller
torque converter, the transmission
control strategy is revised to allow
Table 2
•
•
•
•
•
•
•
•
•
Bosch
Motoral SPS
Aisin
Motoral AIEG
Continental Teves
Siemens VDO
Delco Remy America
Infineon
Delphi
Table 1
•• Daimler
•
Yazaki Chrysler
•• Renault/Nissan
•
Denso
•• General
Motors
•
Valeo
•• Peugeot/Citroen
JCI (Johnson Controls)•
•• Ford
•
Visteon
Fiat
BMW
Toyota
VW/Audi
Honda
• Lear
Car
manufacturers in North America,
Europe
and Japan currently developing
• Varta
42V cars
• Magneti Marelli
Some of the automotive component suppliers currently developing 42V components. Delphi,
for example, state that they can now provide a complete 42V generation, conversion,
storage, distribution and usage system.
24 Silicon Chip
earlier-lock-up of the torque converter
clutch. The EM is then used to reduce
poor driveability resulting from this
early lock-up.
The EM is a 14kW, 3-phase induction motor. The rotor is bolted to the
engine’s crankshaft and surrounds
the torque converter. This approach
allows the crankshaft’s bearings to
support the rotor.
The stator is located around the rotor and is supported by an assembly
positioned by existing dowels projecting from the rear of the engine block. It
is clamped between the transmission
and the engine. The stator is watercooled via a thermostat-controlled
feed from the engine coolant system.
Changes made to the transmission
included the use of a unique bellhousing and flex-plate and an alteration to the hydraulic valve body that
allows the transmission to drive the
engine (and so the EM) on over-run in
second and third gears. In addition, a
small electric pump is used to provide
hydraulic pressure within the transmission until the transmission pump
is rotating quickly enough to provide
normal working pressures.
The GM mild hybrid uses these
strategies to reduce fuel consumption:
• deceleration fuel cut-off much more
frequently used, with the EM smoothing the resulting torque fluctuations.
• automatic engine stop during stationary and very low speed vehicle
operations.
• lower speed torque converter lockup clutch engagement.
• regenerative braking.
A 42V electro-hydraulic power
steering pump replaces the traditional
engine-driven unit, while air conditioning requirements with the engine
stopped are met by “careful management of refrigerant capacity already
in the system prior to the stop”. The
traditional starter motor is deleted.
42V challenges
The change in such a universal and
long-standing car standard as 12V has
some major challenges – technical and
financial. Taking the latter first, why
should customers feel any urge to pay
more for a car that has a 42V electrical
system?
General Motors puts it like this: “A
42V system is only an enabler. It is
not something that consumers will
be willing to pay for directly – so it
absolutely must deliver the capabilisiliconchip.com.au
MAINS OUTLETS
General Motors see the inclusion of
110VAC power sockets in their mild
hybrid pick-up truck as a major
selling point of hybrid technology. The
circuits are protected by ground fault
detection and up to 14kW is available.
ties and features that customers desire
and value.”
The company suggests examples
of such customer-desirable features
are mains-power outlets, new entertainment systems, electrically heated
windscreens, fast heating and cooling
systems and “by-wire” chassis and
engine controls. They also suggest
the thinner wiring looms and smaller
components will provide space for
more features likely to appeal to the
consumer.
The fuel economy achieved by 42V
combined starter/generator systems
will also have immediate consumer
appeal. It’s for customer justification
reasons that GM has highlighted the
availability of mains power (there are
four outlets!) in its promotion of the
Silverado/Sierra hybrid.
General Motors delivered its first hybrid pick-up truck on May 3, 2004. The
mild hybrid uses a combined electric motor/generator and boasts 10-12%
improved fuel economy. The car is only the second to use the new 42V standard.
[GM]
12V/42V possibilities
What about cars where a 42V electrical system is introduced in conventional engine form? As with the two
hybrid cars that we’ve looked at, it’s
very likely that cars will continue to
have both 42V and 12V systems for
some time to come. In fact, it is suggested that incandescent lighting will
stay at 12V because of bulb durability
issues associated with the automotive
use of higher voltages.
Three 12V/42V architectures are
likely to be used:
• Single voltage generation and
single voltage energy storage – a 42V
alternator charges a 36V battery which
services 36V loads, with a DC/DC
converter used to charge a 12V battery
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The GM mild hybrid control system incorporates an inverter to generate
110VAC mains power (four mains power outlets are provided on the truck),
a DC/DC converter to operate the 12V loads and an inverter that operates the
starter/generator. [GM]
that services 12V loads;
• Dual voltage generation and single voltage energy storage – a dual
14V/42V alternator charges two
separate systems, one 12V and the
other 36V;
• Dual voltage generation and dual
voltage energy storage – a dual
14V/42V alternator charges a dual
12/36V battery.
In all cases the inclusion of 42V car
systems poses challenges in controlNovember 2004 25
Table 3
Current Technology
Benefits of 42V Architecture
Electric power steering
More power, improved fuel economy
Electric brakes
Redundant power supplies
Power windows, power seats, power
hatchback lifts
Reduced size and mass of motors; more
efficient operation
Heated catalytic converter
Lower emissions; quicker light-off time
Heating, ventilation, air-conditioning
blower motors and cooling fans
Greater efficiency; smaller/lighter units;
flexible packaging
Mobile multimedia
More power available for video, mobile
phones, navigation systems, audio amplifiers, fax machines
Water pumps
Improved efficiency; longer service life
Selected engine management system
components (eg, exhaust gas recirculation valves, ignition systems, control
actuators)
Reduced size and mass; increased
performance
Fuel pumps
Reduced size and mass
Heated seats
Faster heating, more efficient operation;
increased power
The benefits to current automotive electrical technology of adopting a 42V
system. [Delphi]
ling arcing and corrosion, especially
in the presence of contaminants like
salt water. (An example? – consider
a boat trailer’s electrical system that
can be under water quite frequently!)
Another “real-world” problem is the
use of jumper leads. To prevent people
with 42V cars attempting to jump-start
12V vehicles, 42V vehicles will have
non-accessible batteries and use a
dedicated jump-starting connection
with a unique, fused connector. 42V
jumper leads will be specific to the
application and incorporate microprocessor control. One proposal sees the
use of 42V jumper-leads occurring in
the following manner:
• Connect terminations to each car or
car and boost pack.
• Units activates (wakes up) and
checks polarity – both LEDs flash.
• LED flashes red if either or both
batteries are reversed.
• Low current circuit is activated and
checks for conductivity.
• If all is OK then green LED flashes.
• Switch is pushed and internal relay
is activated – green LED on.
• Relay is opened if either battery is
disconnected – green LED flashes.
• If both batteries are below 36V or
either battery is below 18V, relay will
Super-Capacitors For 42V Systems
Super-capacitors suitable for 42V automotive systems are being developed.
These capacitors can be used to meet peak loads and then be recharged
over a period from an existing battery or at a fast rate through regenerative
braking.
A 10kJ, 42V super-capacitor has sufficient energy to operate the combined
starter/generator of the 5.7-litre V8 GM Silverado/Sierra hybrid for two
consecutive engine starts (the engine starts in 0.3–0.5 seconds). Compared
with a lead-acid battery, a combined super-capacitor-battery prolongs battery
service life with its ability to handle high recharge/discharge events typical of
a mild hybrid car.
However, at this stage super-capacitor costs remain high when compared
with traditional battery technology.
26 Silicon Chip
Suppliers have already developed a
complete range of 42V automotive
components. Here are two 42V
compatible bimetallic circuit
breakers, available in 5 - 30 amp
ratings. [First Technology]
not activate – red LED on.
Fuses also need redesigning. Testing was carried out of normal 12V
blade-type fuses on 42V and it was
discovered that when subjected to
overload, terminals could melt away
(probably through arcing) and the
plastic fuse housing was subjected to
intense heat, resulting in carbonisation
and melting. New 42V fuses use polyamide housings and feature a slightly
different shape to 12V fuses, preventing 12V/42V fuse inter-changeability.
Circuit breakers suitable for 42V operation are already available.
Wiring standards also need to be upgraded. The current proposal is that all
42V wiring is coloured amber. Because
of the potential problems of arcing, all
42V terminal connections will need to
be correctly seated and locked. More
sealed connectors will be used.
Note that not all wiring will be
reduced in conductor size – in many
cases those wires that are 0.35mm2
will remain that size even when working on 42V, as this is the minimum size
for mechanical durability.
Conclusion
While it was initially thought that
the first 42V cars would be luxury
cars with very high electrical power
loads, mild hybrids have beaten them
to the punch. In addition, a report that
Daimler Chrysler has put 42V system
development on hold appears to be a
temporary setback for that company.
However, over the next few years a
wide range of cars will appear with
12V/42V systems and as they become
common, it won’t be long before dediSC
cated 42V cars appear.
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