Here are some articles from Car & Driver on probably why 42 volts did not catch on.
Note the large Toyota 42 volt hybrid increased the city mileage by 15% while a turbo
compound engine would have 20% right from the get go without the weight
and expense.
Pete Lyon is an old friend of mine.
Paul Lamar
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-- Switching to 42 volts involves more than just shrinking wires and tallying up the cost saving. Faster corrosion of electrical components and sustained arcing
are two major reliability issues; the latter is a safety issue as well (see sidebar "Arc and the Angels Sing").
Electrical equipment has to be protected against much higher voltage spikes, such as when an alternator becomes disconnected from the battery, and many devices
in an automobile just prefer fewer volts.
Light-bulb filaments, for example, grow too long and flimsy to survive potholes if designed to handle more than 14 volts. Microchips sizzle if they see more
than 5 volts, and smaller, low-amp electric motors must be wound with special extra-thin wire that increases cost.
"What we learned is that if you go 42 volts, you want a dual-voltage vehicle," says Matouka.
Building a car with a 42-volt system and a 14-volt system is no simple feat. If 42 volts somehow barge their way onto the 14-volt system through accidental
contact, they'll go through the electronics like a cannonball through custard. What happens when an airbag module holds its party for 14 volts and 42 show up?
00 you want to be the first to find out?
Dual voltage also means conducting careful idiotproof engineering so the owner doesn't try to hook a
subwoofer to the wrong power supply or deep-fry somebody's 14-volt car with a 42-volt jump-start.
Says Matouka, "Right now the jury is out on cost savings. Everybody is finding out that there are some big trade-offs:' .
.Today'selectrical systems don't have the volts to sustain an arc. Air has high resistance. It takes roughly 1)0 to 200 volts to move electricity through .each
inch, so an arc in a 14-volt system can't be maintained aver even a tiny gap.
A 42"voltsystem, on the other hand, has 15 times the arcing potential. Says Matouka: "With 42 volts you can pull an arc and sustain it indefinitely while
dissipating a lot of power and not pulling enough current to blow the fuse:'
Arc and the Angels Si
Driving Toyota's 42-Volt Crown
(Pi ailed simply the Crown THS-M (for Toyota Hybrid 11 ... System-Mild), Toyota's third production hybrid (after ~) the Prius sedan and Estima minivan) is an
executive limo sporting a 3.0-liter direct-injection gasoline V-6 with a 42-volt electric motor lending assistance to reduce emissions and fuel consumption.
The Crown's hybrid system is tailored to Japan, a country where thousands of limousine drivers wait patiently for their clients with engines and air
conditioners running, pumping out copious exhaust gases.
When the Crown comes to a stop, the engine shuts down and the electric motor runs to operate the air conditioning and other electrical devices such as lights.
When the driver decelerates or brakes, the motor also acts as a generator, converting kinetic energy into electrical energy (regenerative braking) stored in the
battery.
In comparison to the normal Crown engine that averages 27 mpg, Toyota says the Mild system hits 31 mpg, or about a 15-percent improvement.
We drove a Crown THS-M for just 30 minutes around Tokyo and were surprised by how much of the time the car spent in its engine-off mode. Checking the meter on
the dash, the figure read 10 minutes, and the roads were not that crowded by Tokyo standards at least. During the hottest part of the day, the air conditioning
worked like a gem for all of those 10 quiet minutes. Well, it may seem quiet, but listening to the car in this "idle stop" mode from outside, you hear not just
the motor but also various small mechanical sounds from the electrical devices.
The Crown THS-M is set up mainly for transporting Japanese bigwigs around the Ginza in cool, soft comfort.
Dave Hermance, executive engineer of environmental engineering at Toyota Technical Center, USA, says it likely will never be sold in the U.S.
The Crown's hybrid system wouldn't make a dent in EPA-style fuel-economy cycles. "If you make a serious hybrid, it's not going to have 42 volts," says Hermance.
That's not enough. He notes that the Toyota Prius hybrid has a 33-kilowatt motor and a 300-volt battery pack. In Japan's grid-locked cities the Crown delivers
some fuel savings, but "we don't have [the Crown] in the U.S.
because it wouldn't make sense here:' -Peter Lyon
DECEMBER 2002
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