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Chevy Volt Delivers Novel Two-Motor, Four-Mode Extended Range Electric Drive System; Seamless Driver Experience Plus Efficiency

by Mike Millikin and Jack Rosebro

Voltkinematics
The Volt drive unit combines two motors and three clutches to deliver four distinct operating modes to maximize efficiency and provide a seamless driving experience. Click to enlarge.

During the serial media launch events for the Chevrolet Volt, GM provided more detail (subsequent to the completion of related patent work) on the novel drive architecture applied in their first extended range electric vehicle to enhance the efficiency of both the battery electric and extended-range driving modes.

The complex system leverages GM’s learnings from its two-mode hybrid system in a number of areas, including the efficiency benefits of a multiple-motor approach to meeting the full range of electric drive operating requirements; synchronous clutches; and the vehicle’s control software and architecture.

The Volt is an electric-drive vehicle, powered by a 16 kWh Li-ion battery, incorporating an internal combustion engine and generator to serve as a range extender; an electrical plug is intended to be the primary source of stored energy used to deliver motive power. (The Volt could also be called a plug-in series hybrid, depending upon your taxonomic preference.)

Given that GM had committed to a combustion engine and a generator as a range extender for the battery, the engineering team set out to develop a drive system that could maximize the combined efficiency of all the components under the different driving modes (all battery electric, and extended range). Put another way, the GM team wanted to extend the range of the vehicle as efficiently as possible, while maintaining quality driving dynamics and experience.

The story of the electric drive is really a story about efficiency. How do we take all this battery energy...and very efficiently and effectively drive the wheels. That’s ultimately what the customer is looking for, is to maximize this notion of electric range, to maximize this notion of efficiency of the generator when we have to use it.

—Pam Fletcher, Global Chief Engineer for Volt and Plug-In Hybrid Electric Powertrains

Mechanical losses such as friction and windage dictate that the efficiency of an electric motor declines somewhat as motor speed increases. Recognizing the benefits derived from their two-mode approach in their earlier hybrids, the engineering team also observed that they had a second motor—the generator motor—“going along for the ride”, as Fletcher said during her presentation at the launch event in Detroit. They thus decided to exploit the generator motor more thoroughly than it would otherwise have been if used exclusively as a generator in extended-range driving.

The resulting Volt drive unit consists of two motors—a 111 kW main traction and 63 kW (at 4800 rpm) generator motor (55 kW generator output)—as well as three clutches and a planetary gear set tucked in the end of the traction motor that improve overall efficiency by reducing the combined rotational speed of the electric motors as needed.

This engine obviously has the capability of revving much higher and producing much more output. But this is really a study in rightsizing, rightsizing an internal combustion engine for this extended range capability. We’re almost repurposing an internal combustion engine to provide this very unique type of propulsion. That’s how much power output we determined we needed for this car that has a very large battery and almost a half-size engine in terms of displacement to provide you with the average power required to provide an urban and highway type commute.

—Pam Fletcher

This configuration reduces battery drain at steady state, cruising speeds in a window ranging from around 30 mph to more than 70 mph (48 to 113 km/h), adding up to two miles (3.2 km) of additional all-electric range. The Volt delivers a pure-electric range between 25 and 50 miles (40 and 80 km)—depending on terrain, driving techniques, driver comfort requirements (e.g., HVAC), and weather. The range extender pushes that to approximately 350 miles (563 km).

The Volt’s drive unit uses an on-axis configuration; motors and gear-set are mounted in an in-line with the range-extending internal combustion engine. Two of the clutches are used to either lock the ring gear of the planetary gear-set or connect it to the generator/motor depending on the mode. The third clutch connects the internal combustion engine to the generator/motor to provide range extension capability.

The 111 kW traction motor is permanently connected to the sun gear, and the final drive (gear reduction, differential) is permanently connected to the planetary carriers. The planetary carrier gears are used to modulate gearing ratios between the vehicle’s electric motors, its internal-combustion engine, and its 2:16 final drive.

The Volt has two primary driving modes:

  • All battery-electric (charge depleting), in which the battery is the sole source of power for the motors; and
  • Extended-range (charge sustaining), in which the battery and engine work together in different operating modes to power the traction motor and to improve overall efficiency.

Each of these two driving modes is supported by two drive unit operating modes: a low-speed, 1-motor mode, and a high-speed, 2-motor mode.

Mode1
Mode 1. Click to enlarge.

Mode 1: Low-speed EV Propulsion (Engine Off). In this mode, the ring gear is held (locked) by clutch C1. With clutch C2 and C3 disengaged, the generator-motor is decoupled from the engine as well as the planetary gearset. As the traction motor is permanently coupled to the sun gear, the planetary carriers must rotate when the traction motor rotates. Since the planetary carriers are permanently coupled to the final drive, the traction motor propels the vehicle. The generator-motor and the engine are idle during this mode, although the engine is free to start if necessary (example: engine maintenance mode).

Virtually all of the vehicle’s motive power is therefore delivered by the traction motor in this mode, including hard accelerations, using power supplied by the battery pack. With this configuration, the traction motor can produce up to 111 kW (149 hp) and deliver up to 370 N·m (273 ft-lb) of torque.

Mode2
Mode 2. Click to enlarge.

Mode 2: High-Speed EV Propulsion (Engine Off). As vehicle speed increases, motor speed and losses also increase. To engage both motors and preserve motor efficiency, clutch C1 is disengaged, allowing the ring gear to rotate. At the same time, clutch C2 is engaged, connecting the ring gear to the generator-motor. The generator-motor is then fed current from the inverter, and runs as a motor. The engine remains disengaged from the generator-motor.

This mode allows the two electric machines to operate in tandem at a lower speed than if the traction motor alone was providing torque. The speed of the traction motor in this mode drops to about 3250 rpm from 6500 rpm in the 1 motor mode, according to Fletcher.

This strategy allows the Volt to wring out as much as two extra miles of all-electric operation out of its battery pack, depending on operating conditions. However, switching from low-speed to high-speed EV mode requires the simultaneous operation of two clutches. GM’s experience with simultaneous clutch operation in their two-mode transmissions and transaxles was key to the development of the Volt’s transaxle control strategy.

Mode 3
Mode 3. Click to enlarge.

Mode 3: Low-speed Extended-Range Propulsion (Engine Running). Once the Volt’s battery pack has reached its minimum state of charge (SOC) (which varies depending on operating conditions), clutch C1 engages, locking the ring gear, and clutch C2 disengages, decoupling the generator-motor from the ring gear. At the same time, clutch C3 engages to couple the Volt’s 1.4 liter Ecotec range-extending engine to the generator-motor, so that it may be operated in generator mode.

During low speeds as well as hard accelerations, the traction motor propels the vehicle. The engine drives the generator-motor, and power to drive the traction motor is delivered by the generator-motor as well as the battery pack via the Volt’s inverter. Under most conditions, the generator will provide enough power to maintain minimum battery SOC, and therefore allow the vehicle to remain in this mode until it is plugged in.

Mode4
Mode 4. Click to enlarge.

Mode 4. High-Speed Extended-Range Propulsion (Engine Running). The blended two-motor electric propulsion strategy used at higher speeds in EV driving has also been adapted for extended-range driving. In this mode, the clutches that connect the generator/motor to both the engine and the ring gear are engaged, combining the engine and both motors to drive the Volt via the planetary gear set. All of the propulsion energy is seamlessly blended by the planetary gear set and sent to the final drive.

This novel mode—which GM calls “combined mode”—enables a 10-15% improvement in efficiency at steady state cruising speeds compared to a comparable single-motor mode, GM says. Under no circumstance can the Volt be propelled by engine torque alone; the traction motor must be operating if the vehicle is to move and the engine is to provide torque.

When we’re in this combination...on this planetary gearset we are driving the engine-generator combination onto the ring gear. We are utilizing the traction motor to provide the reactionary force so that we can ultimately drive the output. That is what happens in combined mode, that’s what allows us to get the 10-15% more efficiency.

—Pam Fletcher

In this mode, the generator still continues to produce electricity as well as deliver torque via the gearset, Fletcher said. The ratio of torque to power generation varies with operating conditions, and is, as the rest of the system, under the management of the control software, according to her. As noted earlier, the control software and architecture enabling this drive unit is critical to its overall success. We anticipate that additional information will be disclosed about the control mechanisms for Mode 4 as patents are awarded and SAE papers are approved for publication.

Packaging of the drive unit. The drive unit is quite compact, and includes the power electronics as well as the engine, motor generator, planetary gearset and traction motor. The power electronics unit includes three IGBT inverters: one for each motor, and one for the electric oil pump.

“If the Volt is in electric mode, we can accelerate the car wide open throttle to 100 mph—so you can have the full performance envelope of the car all electrically. That to me is a very important point.”
—Pam Fletcher

Driver experience. During the launch event (which GCC attended courtesy of GM), journalists paired off to drive pre-customer versions of the Volt on roads under different conditions for almost 200 miles. Based on that limited sampling, we can report that the transitions between modes are seamless and smooth; at one point, we had entered into range-extending mode without even knowing. The Volt accelerates crisply (and quietly), and handles snappily at moderately excessive interstate speeds—all on battery power.

The sole exception to the noise quality was on entering into mountain mode (driver-selected via the console); the engine races loudly.

The Volt offers three driver-selected modes: normal, sport, and mountain; mountain mode is designed to help the Volt traverse particularly steep and long grades—e.g., the Eisenhower Pass. This mode increases minimum battery SOC to around 45%. The driver will hear more engine noise during mountain mode, due to the higher rate of power generation required to maintain this mode. GM expects mountain mode to be required only under unusual power demand conditions.

GM engineers said that in the customer models, they are implementing a software fix to reduce the mountain mode noise somewhat. That said, GM wants the use of mountain mode to be exceptional—i.e., it doesn’t want customers running on mountain mode to recharge the pack. Power should come from the plug.

Comments

Roger Pham

@HarveyD,
You're a bit too pessimistic. PHEV's sale can take off like a rocket today, if all-out marketing is done. The Volt as is just unveiled has the installed power (of nearly 300 hp!) and performance and most amenities of a luxury sedan that would be priced at $40,000 to $60,000. No body would complain that a Cadillac or Lexus sedan is too expensive at $45,000 $60,000, and we see these luxo sedans everywhere in more affluent neighborhoods.

The Volt may also be rebadged as a Cadillac, and people with lesser means but who are good with a calculator would zap it up for both practicality and status!

At $41,000, the Volt is a real bargain in consideration of the $7,500 tax credit and potential saving of $10,000 of cost of gasoline for just the first 100,000 miles. You get the smoothness and the performance of a luxury high-performance sedan at the budget of an average midsize vehicle.

I've also just disclosed in earlier posting a version of PHEV having 8 kWh of battery, 1/2 the installed electrical power and 2/3 of the ICE power of the Volt, that is estimated to cost ~$10,000 less than the Volt. Charged twice daily, this inexpensive PHEV would cover 40-50 mile all electric driving range, and would have total cost of ownership a lot less than nearly all ICE cars of today. I'm sure that GM would consider this follow up low-cost PHEV once enough well-heeled early adopters have spoken with their wallets.

Bottom line: The key to high-performance and/or low-cost PHEV is serial-parallel architecture, like GM has smartly adapted here, that allows the Volt with nearly 300 hp of total power at the wheel...heck, this is equal to earlier versions of the legendary Chevy Corvette...
If GM would have stuck with the simple serial hybrid like many posters here have preferred, the Volt would have been stuck with just 111 kW of power ( a mediocre 150 hp)...not enough power to compete in the luxury high performance sedan market that will command a generous price tag!

Ben

Or they could have gone with an Atkinson cycle engine and not added all this extra complexity. If you think about GM's previous claims of wanting to be able to swap in different power sources (fuel cells, turbines, etc) than adding in a parallel hybrid system makes no sense!

Roger Pham

@Ben,
The Atkinson cycle will do nothing to provide nearly 300 hp on the tap in order to compete with the big boys luxo sedans that retails for $45,000 and up...

"All this extra complexity" is nothing in comparison to a modern 4-6-speed automatic transmission...or the new 8-speed transmission for high-end Lexus models.
The Volt's electrical CVT will be very reliable and will hardly required any service at all, for the entire life of the car.

Ben

The 300 hp total is only theoretical and not true in acceleration considering that the engine does not directly engage until the car is already going at high speed.

We were hoping for a complexity REDUCTION, not at par with. A system as promised by GM that could interchange with other power source options.

Roger Pham

True! The 300 hp is theoretical...but that's what will sell...along with the fast acceleration and the silky smoothness of the electric motors that even the V-12 Bentley can't match...that's all that will matter.

Having only a single planetary gear set is real reduction in complexity from cars with 4-8-speed transmission.

Ben

Considering its got 1 engine, 2 electric motors, 3 clutches, planetary gears and a huge battery pack its not exactly as simple as a 6 speed transmission on an engine. My problem with this is GM's broken promise of serial hybrid frame for future power plants.

HarveyD

Roger, you are very generous with GM's Volt. Hope that you will not be disappointed. Personally, I would prefer a PHEV with a much smaller simpler genset because I don't need 300 hp or have to tow anything.

Roger Pham

Well, I'm excited about green vehicles that can revolutionize existing paradigm. I'm pretty sure that more affordable versions will follow...the profit margin is a lot less for economy vehicles, and often, must be subsidized by higher profits from more upscale vehicles. Early adopters tend to be more affluent people who don't mind plunking down the bucks to get the latest in technology.

This may be GM's broken promise of serial hybrid frame, but it is a change for the better, as this makes the final product having much higher performance and efficiency so that they can sell it better, while no one is hurt in the process.

Ben

No the efficiency improvement is minor by their own emission, and many of the performance increase are purely hypothetical. If BEV or some other electric propulsion power plant is the future then going back to parallel hybrids is a waste of time and money on their part.

Engineer-Poet

Not only is parallel a step backwards, it's completely unnecessary for performance reasons. The AC150 drivetrain has been uprated to 200 kW (that's 268 HP) and even the original 150 kW, one-speed system was eating Ferraris for breakfast in 1/8 mile drag races.

Give the system an upgrade to 75 kW continuous and it will be capable of heavy-duty tasks like towing a ton of cargo up a mountain at 65 MPH. I should know; I've done it on about 70 kW.

Roger Pham

@Ben,

1) The efficiency improvement of a parallel connection is not minor. Let's recall that the efficiency of an electric motor or a generator is highly dependent on loads. At low load, the efficiency may be nearly 90%, but as one is nearly the maximum rated continous power level, the efficiency level will drop to about 60-70%, due to electrical resistance and eddie currents. If you try to cruise at high speed on engine power alone on a serial hybrid, whereby the engine is delivering close to maximum rating of the generator, the electrical conversion efficiency will be only ~60-70%. Multiply this loss to the ~80% efficiency of the motor running at 1/2 of rated power, 65% x 80%= 52% efficiency. This means that out of 50 kW power delivered by the engine, nearly 1/2 will be lost via the electrical route. By contrast, a direct mechanical connection via a very simple 2-speed transmission can be as much as 95%-efficient. Of course, one merely needs about 12-15 kW of power when cruising at 60 mph, so a serial hybrid will be OK for that purpose, but keep in mind that when you need higher power for climbing uphill or for passing, a lot of your rated power of the engine will be lost.

2) There is nothing hypothetical about the power improvement of the Volt from 111 kW power from the serial hybrid mode to a whopping 111 kW + 50 kW + 60 kW = 221 kW of a serial-hybrid arrangement. GM have just double the power output of the Volt from this simple power split single stage planetary gear and some inexpensive wet clutches. This power boost will raise the status of the Volt from a practical mediocre sedan of 150 hp rating to luxury high-performance sedan of 300 hp rating that will allow GM to justify the pricing of twice the $20,000 typical of a 150 hp vehicle, to $41,000 and thereby recouping development costs and make some profit, without hardly any increase in productin cost. A planetary gear set and 3 wet clutches will cost next to nothing in comparison to the cost of the electrical components and the huge battery.

Engineer-Poet
Let's recall that the efficiency of an electric motor or a generator is highly dependent on loads.
True. A 2-pole 60 Hz single-phase induction motor is typically rated at 3450 RPM shaft speed (150 RPM or 2.5 Hz slip). The slip will be lower at less than rated load, and a 3-phase motor will always have lower slip than a single-phase motor.
as one is nearly the maximum rated continous power level, the efficiency level will drop to about 60-70%, due to electrical resistance and eddie currents.
False. Large electrical machines have very high efficiency; the efficiency of the alternators used in powerplants is upwards of 98%. Even small motors achieve 90%.

Direct transmission of power from an alternator to an AC motor at a different frequency can be done with a cycloconverter; efficiencies can hit 95%. GM would use a mechanical transmission because they have people in-house they would prefer to employ, rather than creating a new

There is nothing hypothetical about the power improvement of the Volt from 111 kW power from the serial hybrid mode to a whopping 111 kW + 50 kW + 60 kW = 221 kW of a serial-hybrid arrangement.
This power is not being used, and it is probably not available. The Volt's 0-60 time is 8.53 seconds; the average power to the wheels is about 73 kW over that time. If it used the AC150 drivetrain it would go well under 6 seconds.

Engineer-Poet

... rather than creating a new department and laying off mechanical designers.

Roger Pham

Large stationary electrical machines have high efficiency due to the fact that they are oversized. In stationary application, who cares about power-to-weight ratio? Instead of a smallish 60 kW generator in the Volt, I can install a generator 3 times larger, and derate this generator to only 60 kW maximum, in order to achieve >90% efficiency...

Diesel-electric locomotives need plenty of weight on all its bogeys in order to have all the traction needed to pull a very long train. Due to the many axles involved in a locomotive, direct mechanical torque transfer from the engine would not be durable, and requires frequent maintenance. Locomotives are designed to run for millions of miles before overhaul, while a private automobile only needs to last for 100,000 to 200,000 miles. Trains accelerate very slowly, (who cares about 0-60 time when you have all the track to yourself?) while cars must accelerate fast in order that the cars can sell.

How fast can a Tesla accelerate with the AC 150 drive train (150 kW)? Answer: Very fast. How fast would the Volt accelerate with 170 kW of electrical power at low speeds? Not as fast, since the Volt weighs a lot more, and at low speeds, the ICE cannot contribute much power, since ICE do not have much torque at low rpm. However, after about 45 mph and up, the ICE's torque will come on board strong, and the Volt will accelerate like a rocket. If you would look at the time it takes from 0-100 mph, the 0-45 mph time is very little proportionally.
At any rate, I would predict that the Volt can be tweaked to get 0-60 time faster than 8.53 seconds, but no one should complain about 0-60 in 8.53 seconds...that is sport-car territory already!

Engineer-Poet

NEMA efficiency standards for induction motors exceed 91% at 50 HP.
AC-150 motor hits 91% peak at 50 kW and gets 86% at 8 kW road load.

Face it, Roger: you don't know anything about motors.

Roger Pham

What does the NEMA efficiency standards has to do with this discussion? Like I said, to get to above 91% efficiency for an electric motor, simply design it with larger gauge wires for the stator and rotor to reduce resistance, run it at higher voltages, and making a better core to reduce magnetic losses, or in PM motors, use very powerful NdFeB (Neodynum Iron Boron) magnet to reduce slippage, and voila, efficiency increase. At any rate, you will need a bigger motor for a rated maximum load if you want higher efficiency at maximum load.

For examples,
1) a R/C car motor, the Himax HC6332-250, has a power-to-wt. ratio (P/W) of 2.3 hp/lb, with efficiency during typical use of 60-80%, for racing purposes.
2) The Prius' AC PM motor is listed at .84 hp/lb, and can deliver 90% typical efficiency during use,
3) The Toshiba 660 MVA water cooled 23kV AC turbo generator for power plants can deliver only .3 hp/lb, but here, power plants owner wants ~98-99% efficiency!

You can see that in order to get the higher rated efficiency at maximum rated load, the electrical machinery has to get bigger and heavier...it's the law of physics!

AC-150 motor (150kW rated max power) hits 91% peak at 50 kW...but guess what? I'll bet that the AC-150 motor only can deliver 60-70% efficiency at 150 kW maximum rated output. So, in order to meet NEMA standard of 91% efficiency, I only to have to derate the AC-150 motor to 50 kW max output.
Why does it only get 86% at 8 kW road load? Probably friction and windage losses in the bearing and the rotor going thru the air become more predominant at lower loads...Ergo that's why GM opted for the planetary CVT system in order to reduce the rpm of the motor at lower loads, in order to optimize efficiency at a wider load range...

Engineer-Poet
What does the NEMA efficiency standards has to do with this discussion?
It has to do with you claiming "I can install a generator 3 times larger, and derate this generator to only 60 kW maximum, in order to achieve >90% efficiency...". As shown, this is not true. Since cars aren't restricted to operation at grid frequency, they can achieve much higher specific power (power of an induction motor is proportional to frequency).
I'll bet that the AC-150 motor only can deliver 60-70% efficiency at 150 kW maximum rated output.
Fine. You made the claim, now back it up with facts.
Roger Pham

True, either making the electrical machinery 3 times larger and run it at the same rpm, or making it a larger, enough to dissipate the heat, and run it 3 times faster, to obtain the same efficiency. Still, heat will be the problem with pushing a little motor (that can) real fast, as the rate of heat built up will still be faster, but efficiency remains the same, since 3 times of work will be done. Even though the current stays the same, the voltage needed to run the motor faster will have to be higher, at least for DC brushless motors, ergo the higher rate of heat built up. Heat is the limiting factor WRT specific power of electric machinery.

Let's say that a motor delivers 50 kW at 3000 rpm with 91% efficiency. To keep this level of efficiency at producing 150 kW, one must run it at ~9000 rpm! (But, you must find a way to cool it faster also, since 3x the output at the same efficiency will means 3x the heat production) So, yes, I can see your point.

But, imagine that in a fixed-gear BEV running up hill at 3000 rpm and 50 kW, and the driver floors the gas pedal in order to outrun the police! You can see that if the current flow is very high in order to triple the torque output, the motor can deliver 150 kW output for a many seconds before it will burn up, but the efficiency will be a lot less than 91%, until the motor (and the car) can accelerate to 9000 rpm.

This is the main thrust of the Stridsberg US patent 6740002 that MG had brought up. Even with electric machinery, an inexpensive and simple gear shift will still be needed to optimize efficiency for frequent city driving whereby one must accelerate and deccelerate all the times.

Engineer-Poet
making it a larger, enough to dissipate the heat, and run it 3 times faster,
You've got it backwards. The faster it runs, the smaller it can be and the lower the non-eddy current, non-windage losses are (because torque and slip are reduced).

Seriously, Roger, learn something about motors. There are a number of texts which address the physics and mathematical analysis of induction motors. Find one and read it.

Roger Pham

@E-P,
Well, then, you've got to correct GM's engineers on this too. The following is a direct quote from this very article:

"Mechanical losses such as friction and windage dictate that the efficiency of an electric motor declines somewhat as motor speed increases. Recognizing the benefits derived from their two-mode approach in their earlier hybrids, the engineering team also observed that they had a second motor—the generator motor—“going along for the ride”, as Fletcher said during her presentation at the launch event in Detroit. They thus decided to exploit the generator motor more thoroughly than it would otherwise have been if used exclusively as a generator in extended-range driving."

But, I was generous enough to assume with you that efficiency may remain constant even with tripling of the speed for a given torque level. But, you see, when you triple the speed at the same torque, you have tripled the output. When the output is tripled at the same efficiency level of say, 91%, then the heat to be rejected is also tripled, as well. Just a matter of bookeeping and arithmatic! How much heat can the stator reject will be key in the longevity of the motor and what kind of power-to-weight ratio an electric motor can have! Otherwise, you will be able to get insane power-to-weight ratio on an electric motor by just step-up the voltage insanely! Clearly, not possible. Just a matter of physics 101!

MG

Roger, E-P,

You seem to talk about different types of motors.
Volt uses PM motors (PMSM), and their efficiency drops somewhat with speed - as it it stated in the GM text.

On the other hand efficiency of AC induction motors appears constantly high (flat) once rpm goes above 1,000 or 1,500 rpm for motors that can work over 5,000 rpm.
(I'm talking about induction motors currently used for electric cars, like in Tesla roadster)

Maximum torque in induction motors (limited by max allowed current) is flat only in approximately first third of operating speed range, then goes down, more or less steeply.

Roger Pham

Thanks, MG, for the clarification.
BTW, after reviewing the Stridsberg patent and recalculating performance of a serial-parallel PHEV with just only two-speed transmission, it appears that your idea of upgrading to a 4-speed transmission would lend much better performance when a 35 kW engine is used.

Thanks, E-P, for correcting me that in a serial hybrid PHEV, a PM generator can deliver above 90% efficiency even when pushed to its maximum-rated capacity, since the engine is allowed to rev freely, and the rpm kept going up when higher power will be needed. The voltage output of the generator will be higher, but the inverter will handle that.

This topic has been quite educational and interesting.

MG

Thank you Roger for comments.
Here are links to specs and curves of some of the few available high speed induction motors for EVs (a picture tells a lot).
http://www.brusa.biz/index.php?id=128&L=1
Three motors there, some were used in hybrid racing cars. Less powerful and heavier than AC Propulsions' used in Tesla.
Its curve is here:
http://www.teslamotors.com/roadster/technology/motor

luis

toyota prius plug in will be on sale on 2012 ,next year,at a price around 25000.
and if toyota is smart enought theyll have a ethanol prius version ,which do it complete ecologic, 0 co2 emisions,.
volt hurry up ! if you want to compete with that.

Roger Pham

I think that the ultimate intention of GM is for the Volt to compete in high-end, high-power segment, in order to avoid direct competition with the Prius PHEV. (or that's how it should be). Diversification of product offering will be key to profitability, not direct competition in one market segment and leaving other market segments wide open.

Ethanol is not 0 CO2 emission. Grain ethanol has low return of invested energy...a lot of NG and diesel fuel is used in the fertilizer, irrigation, grow, harvesting, transportation, and distillation of the ethanol.

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