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Volt gains "Sport" mode and works out some of its noise issues

The 2011 GM Volt is generating unprecedented hype as the highest profile upcoming mass-market electric vehicle.  With the U.S. government and automakers worldwide all betting big on electric vehicles, General Motors has done perhaps the best job at promoting its upcoming vehicle.

The vehicle is currently in the pre-production testing phase, in which the final bugs in the prototypes are ironed out via minor changes, largely to the vehicle's software and mechanical settings.  A fleet of prototype Volts completed a long test-drive journey and engineers are now using the data collected to tweak the Volt.  They hope to minimize its problems in the process.

James Riswick, an editor with Edmunds.com, recently took one of the mules out for a test drive to measure their progress on this front.  He reports, "[The Volt] is sort of on the more fun to drive hybrid.  The suspension is a little firmer, than say, in the Prius, which is on the floaty, comfortable side.  This is not a sports car by any means, but actually the electric power steering is reasonably direct and well weighted."

In his opinion, the noise when driving under gasoline generator is minimal and seems like "white noise". However, when stopping, a more "rough" unpleasant sound was heard – GM says they're working on this issue.  Overall, Riswick says the car is "pretty darn normal" and that "It drives like a pretty nice car"

However, as many have noted a couple of pivotal unknowns remain -- the Volt's finalized real world gas mileage and cost.  The Volt will be available in all 50 states when it debuts, according to GM.  It will be available for around $40,000, plus a $7,500 federal tax credit, which brings it to approximately $32,500 (excluding additional hybrid tax breaks in certain states).  However, this price could be bumped significantly higher or lower still.

The vehicles will currently recharge in about 8 hours household 120-volt current, while special 240-volt charging stations can charge it in only 3 hours.  GM estimates the car's fuel economy to be 230 mpg, but this value has yet to be confirmed in real world independent testing.  One of GM's top priorities has been trying to tweak the gas mileage upwards during the testing cycle.

One detail that has not been widely publicized is the new vehicle's "sports mode".  Activated by a Sport button on the center stack, the feature makes the throttle more receptive and increases its ultimate limit, bumping 0 to 60 mph acceleration down to 9 seconds.  The Volt's urge to scoot increases in the mode, though.  Like most cars, the Volt also provides an electronic version of a "Low" gear similar to that found in normal cars, which allows faster deceleration.  GM recommends the Low mode for driving on slopes or in stop and go.

One disappointment is that the Volt and other Lithium-ion battery-powered electric vehicles may not be viable in hotter climates, such as some states in the American Southwest.  Despite the fact that Volts will be sold in these states, performance may be significantly undermined due to the heat.  Volt Chief Engineer Andrew Farah describes, "The Volt may not be right for everyone. If you live in the Southwest, depending on how you use your car, the Volt might not be right for you."



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RE: Where can you use the Volt?
By cvmaas on 12/1/2009 8:59:24 AM , Rating: 3
As an engineer I can tell you that efficiency chart is a crock under real world conditions. If an electric motor was 90% efficient they wouldn't need thermal controllers to shut them down when the core windings start to get too hot. An electric motor has a sweet spot at its designed RPM and torque output. As you move away from that point the efficiency drops like a rock and the motor starts to heat quickly. Thats why the acceleration ramp of the electric motor is so important.

As a comparison a small turbocharged gasoline engine is far more efficient, reaching nearly 90%.


RE: Where can you use the Volt?
By Ragin69er on 12/1/2009 10:36:04 AM , Rating: 4
Well surely as a fellow engineer you must know that the thermal efficiency of an internal combustion engine is related only to the compression ratio, and that turbocharging has no effect on the engines thermal efficiency. Turbocharging increases the density of air entering the engine, that is all. The maximum thermal efficiency of current internal combustion engines is closer to 30% under full throttle, and less when throttled. If you were referring to mechanical efficiency then you are closer to being correct, as at speeds below 40 rev/s its able to transfer 90% of the energy it has converted into useful work, but that drops off to 75% or so at higher revs.
However what they are comparing is the amount of energy inputted and how much work you can get out for that energy, which is thermal efficiency and electric motors are roughly 90% in that case compared with 35% max for ICE's.

Heywood, John "Internal Combustion Engine fundamentals". McGraw-Hill Toronto. 1988.


RE: Where can you use the Volt?
By randomly on 12/1/2009 11:05:36 AM , Rating: 2
Actually a properly implemented turbocharger can increase the engine efficiency. This is because the back pressure that the exhaust turbine creates is not seen inside the engine due to critical flow conditions at the exhaust valves. The turbocharger recovers some energy from the exhaust stream that would otherwise be lost and feeds it back into the engine by raising the intake manifold pressure.

A reality check on this can be observed by the fact that the exhaust temperature is lower on the turbocharged engine than the normally aspirated engine. The difference in heat output of the exhaust is the energy recovered from the exhaust stream.


RE: Where can you use the Volt?
By randomly on 12/1/2009 10:56:24 AM , Rating: 2
1) In the case of the motor systems used in vehicles like the Tesla and Volt you are wrong.

The efficiency only drops rapidly if there is no motor controller that controls the current into the motor. Those 'peaky' motor efficiency curves are only valid for simple motors running on a fixed supply voltage.

If you control both the rotor and stator currents you can achieve high efficiency over a broad range of torque and rpm. You are effectively changing the whole torque, rpm, efficiency curves on the fly allowing you to put the peak efficiency point where you want.

2) You are wrong again.
You would have to violate the laws of physics to get 90% efficiency out of a turbocharge gas engine. The maximum efficiency attainable under optimum conditions currently is in the mid 30 percent range.


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