I swear I read that after the battery runs out the car uses an engine to generate electricy for the motors. And it gets 50 MPG doing this. How can this be true? If it can get 50 MPG by generating electricy then why don't other small cars use electricy generated by a motor to get 50 MPG? What am I missing here?

Below is what I posted to a similar question on the Home threads, hope this helps:

Because the engine needs to be made for relatively low power delivery and gradual changes in power output to achieve 50mpg. This would not result in acceptable performance. A powerful battery or other power source is needed for peak power demands in order to have acceptable performance. Once this “large” power source is added, the additional for enough storage to achieve 40 miles AER is not that great.

GM is by no means beyond reproach, but they have made a VERY, VERY, VERY good choice in developing EFLEX EREVs. The Volt is the first iteration of this drivetrain. In allnlikelihood, it will be improved and implemented accross all of their brands and many other platforms. One of the few iterations they have mentioned is a 20 mile AER version. This will probably be the first “affordable” EREV solution, but if batteries alone continue as the eletrical storage technology of choice then I doubt we’ll see less than a 20 mile EREV anytime soon.

Like Koz said, you need the battery as a buffer to get the engine that efficient. The engine can run at its most efficient rate all the time that way.

Thanks for the help! Makes sense now!

you also get the benefits of regenerative breaking when you use a series hybrid this way. recovering power that would otherwise be wasted without a battery.

main difference is that he GM version charges the batteries, and does not drive he car, therefore it can be set to optimum RPM for efficiency. Other hybrids use the ICE to drive the car, and an electric assist. The Volt is electric drive with ICE assist. Other hybrids do not have a disconnect from the ICE to the drive wheels.

This lack of requirement to vary the engine rpm improves the efficiency as the motor can possibly be simply idling at cruising speed if there is sufficent charge being prduced. Imagine driving 55mph with a 1.4 liter engine idling!!!

That is the beauty and difference that is VOLT!:D

“I read that after the battery runs out the car uses an engine to generate electricity for the motors. And it gets 50 MPG doing this. How can this be true? If it can get 50 MPG by generating electricity then why don't other small cars use electricity generated by a motor to get 50 MPG? What am I missing here?”

Or to put it more succinctly:
So how can a Series Hybrid get much better mileage if it still uses an old-fashioned internal combustion engine to generate electricity?

The Answer lies in the difference between the *average* power draw of a vehicle, and the *burst* power requirement that is the standard for determining vehicle performance.

First, THE BACKGROUND:
A standard internal combustion engine (ICE) vehicle is sized for its *maximum* power production -- think of top-end hp and torque numbers. Those top numbers represent the "oomph" the car depends on for those brief seconds of maximum (or ‘burst’ torque) acceleration. Carmakers are aware that customers want to have a car that is fast off the mark for merging into highway traffic and other situations, and are wary of downsizing the engine and making a car's performance anemic despite efficiency gains from a smaller and lighter engine. They’ve learned this painfully from the hostile reviews to very inexpensive, and underpowered cars like some of the old (and >40mpg) Honda Civics, or the Geo Metro. Therefore standard ICE vehicle engines have to be made for that "burst" requirement.

If a typical sedan requires perhaps 25-35 kW of power, but in order to gain market acceptance it needs to apply 4-6 times that power (150kW or more) for a several seconds at a time, then the ICE has to be over-engineered, heavier, and more expensive. Additional efficiency is lost since every ICE has a particular speed where it is most efficient, and this overpowered engine is constantly shifting its rpm which occasionally takes it out of that maximum efficiency zone, which results in poorer gas mileage.

Second, THE FACTS:
From a mileage perspective, a *small* gasoline or diesel motor can give superb performance , as long as excess energy for that ‘burst’ requirement is stored in a battery or capacitor. A Series Hybrid, like the Volt, ICE motor would be optimized and tuned for a limited speed and power range, which gives better efficiency (and lower emissions) than today’s automotive engines that must operate from 500 to 5000 rpm. Therefore a smaller motor, sized like the 50-60hp of a Geo Metro, would easily generate 40+ mpg, yet still throw a medium or large car around with impunity either using the ‘burst’ torque from either over-sizing the 3-Phase AC induction electric motors on the Volt, OR using a multiphase AC induction motor/drive such as Chorus Meshcon. However, The Chorus Meshcon inverter/drive is presently found only in aerospace at the moment (Wheeltug.com (http://www.Wheeltug.com)/ChorusMotors.com (http://www.ChorusMotors.com)).

Since the alternative, Chorus Meshcon, can provide TEN TIMES the ‘burst’ torque of any conventionally sized and hp rated motor, a Volt using this motor wouldn’t need to oversize the electric motors as they do now and the volt would further gain from the weight savings. And since the power draw during those rare 10-15 seconds of (up to) 10x ‘burst’ torque can come from a capacitor bank or an ultracapacitor, the number of batteries can be reduced as the batteries would not need to be configured to provide that much short term power (which would come from capacitors.)

Also, Chorus Meshcon Motor/Drive is particularly good at low speed-high torque operations, which is why Delta Airlines will be installing it (in the ‘Wheeltug’ configuration) on their fleet of 737NGs in 2010 (after FAA certification is completed in 2009) to drive their planes forwards and backwards without the use of tugs or the planes own engines: that’s a lot of torque for an electric motor that will fit within the hub of the planes nosewheel. I would expect that if the Volt incorporated Chorus Meshcon, the power train gearing of the vehicle would be simpler as well since Chorus Meshcon can operate both as a low speed-high torque motor and high speed motor.

The Series Hybrid car approach of the Volt is fundamentally correct in terms of the power train; using a small ICE to gain fuel efficiency by operating at a single peak efficiency speed. In comparison, insisting on the "plug-in" approach that requires batteries that do not exist (and if they did would not be affordable) represents numerous limitations, including infrastructure changes and recharge time, plus those additional batteries add hundreds of pounds of extra weight. GM admits that the Volt is likely to top a sticker price of $45k -- and a lot of that is the battery.

I really think that the Volt would experience a radical price drop if it used the Multi-Phase Chorus Motor instead of the historical standard 3-phase AC Electric Motor since a Chorus Meshcon Inverter/Drive would be smaller and sized more directly to the ‘average’ power draw for the motors while providing the exact ‘burst’ torque that is needed for those rare 10-15 seconds when you have to go from a stop to merging onto the highway. At present the ‘over-powering’ of the ICE in a standard vehicle (causing mileage inefficiency) has been transferred slightly to the Volt by over-sizing the 3-Phase AC electric motors. Again, mileage is being lost by having to use a motor that is more powerful than needed, by designing it for the occasional ‘burst’ requirements. The next step is to go with a motor that can do this at a 10x ‘burst’ torque without having to change the size/weight of the motor to be anything other than what you need for the ‘average’ power draw, and that step can only be Chorus Meshcon. They even have a site with information on how their motor can be applied to Series Hybrids (ChorusCars.com (http://www.ChorusCars.com)) and outperform on both price and performance either Permanent Magnet or 3-Phase AC Induction electric motors on both PRICE and PERFORMANCE.

Can the Chorus Meshcon Inverter/Drive provide regen power as well as traction power?

A PM (Permanent Magnet) motor can provide regenerative power.

In a PM, whenever there is movement in relation to the magnets, you have electron flow, which is both a blessing and problem.

An AC induction motor, whether 3-phase or Multi-Phase (12 ,18, or higher) would be the same when it comes to regenerative power.

You can find out more from contacting www.ChorusMotors.com (http://www.ChorusMotors.com)

Can you please elaborate on

An AC induction motor, whether 3-phase or Multi-Phase (12 ,18, or higher) would be the same when it comes to regenerative power.

Are you saying the Chorus solution has the same problem as PMs or as other AC motors?

"Can you please elaborate on

An AC induction motor, whether 3-phase or Multi-Phase (12 ,18, or higher) would be the same when it comes to regenerative power.

Are you saying the Chorus solution has the same problem as PMs or as other AC motors? "

PM motors can do regenerative braking because current is generated (due to there being permanent magnets) whenever the wheel spins freely. AC induction motors can’t do regenerative braking like a PM motor.

I’m not sure what problem you are talking about since both PM motors and AC motors have ‘different’ problems which make them a critical decision in the development path of a hybrid. In the Volts case, the early decision was to go in the ‘other’ direction from the Prius, which has a PM motor (which fails at high temperatures and requires liquid cooling, adding weight, complexity, and cost). I’m glad that GM went with an induction motor which can be air cooled, even though it was at a tradeoff.

In this case, the Volt has a 3-Phase AC induction motor which requires a ‘larger’ motor than the equivalent powered PM motor. It also needs to be larger for that ‘burst’ torque I mentioned earlier even though that burst torque is rarely needed. By over designing the electric motors (like they do on a standard ICE vehicle) you are getting less mileage than you might otherwise get.

Chorus Meshcon has none of the drawbacks of PM’s (failing at high temperatures, requiring rare earths, etc.) and none of the draw backs of an AC (low-speed/high-torque problems, require larger motor for ‘burst’ requirements.). It simply is a new motor that goes beyond the first three phases that a 3-Phase AC Induction motor uses, and is the first to do it successfully. The company (http://www.chorusmotors.com) that designed it has found the ‘ideal’ application for it by applying it to the aerospace (http://www.WheelTug.com)industry and saving them close to 20lbs of fuel per minute that the planes burn while taxing, and all in a 100lb package to move a 737.

I just hope that they can get the Volt engineers to look at Chorus Meshcon before those same engineers ride on the 737’s with Chorus Meshcon installed on the planes nosewheel. It simply seems like the perfect ‘improvement’ that will provide better mileage and a longer range for the Volt.

A PM (Permanent Magnet) motor can provide regenerative power.

In a PM, whenever there is movement in relation to the magnets, you have electron flow, which is both a blessing and problem.


Not exactly true. There must be a closed-loop circuit in order for the current to flow.

Closed loop faults in PM motors happen. Akin to an arc welder....

I would call that a problem, especially with fuel & passengers near by.

Such faults can occur when motor windings overheat, if the magnets haven't degraded first.

AC motors fail to open circuit.

--------

Aaron, I extracted the word 'problem' from your #2 post looking for elaboration,
In a PM, whenever there is movement in relation to the magnets, you have electron flow, which is both a blessing and problem.

Very little has changed in basic motor design for many decades. Looks like Chorus might shake that up some what. Lighter / denser / cheaper / safer.

It's not the 'same' problem. They have different weaknesses and strengths.

PM motors fail at higher temperatures and need a cooling solution. The Volt avoids that added complexity with a 3-phase AC electric motor. And PM motors perform better at low speed-high torque applications.

The Multi-phase Chorus Motor (http://www.ChorusMotors.com)is able to provide the extra torque even at low speeds, and can literally have a ‘Virtual Transmission’ for shifting between high speed and low speed operation such that you don’t need complex and/or heavy gearing. It is literally the best of both worlds, without the respective weaknesses of both PM and 3-phase AC electric motors.

A Volt with Chorus Meshcon could probably have smaller electric motors because they would be able to deliver 10x the torque on those rare occasions, and that extra torque wouldn’t need to be built into the electric motors by ‘oversizing’ them as is likely the case at present. You just get more ‘burst’ torque out of a Chorus Meshcon inverter/drive without needing a complex solution for cooling it or dealing with the current that comes from having a permanent fixed magnet motor.

“PM motors fail at higher temperatures and need a cooling solution… ” – Aaron Bianco

??? Are you talking about the Curie temperature? If so, it is about 590 degrees F (310C) for neodymium variety of magnets (much higher for samarium-cobalt type). Before you reach this temperature the motor itself will fry. I do not think the Prius motor is force-cooled either by water or air.

“The Volt avoids that added complexity with a 3-phase AC electric motor… ” – Aaron Bianco

Although I could not find information as to what kind of motor the Volt will be using, I think it will be a kind of permanent magnet synchronous motor, since this type of motor can be switched easily to a generator (for energy regeneration). Unless the ICE-driven generator is also mechanically connected to a wheel, it would be more practical to trun the drive motor into a generator when braking and coasting. The Chorus Meshcon motor is essentially a VVVF (variable voltage, variable frequency) controlled AC induction motor. Nothing special. Modern electric trains all use the VVVF system.

“… or dealing with the current that comes from having a permanent fixed magnet motor… ” – Aaron Bianco

To deal with the counter-electromotive force generated by the permanent magnet motor you do either of the following:

1) keep increasing supply voltage above the self-generated voltage
2) weaken (in effect) the generator magnetism
3) keep the motor speed low (in-wheel motors help since their max speed is around 800 – 1000rpm)

“PM motors fail at higher temperatures and need a cooling solution… ” – Aaron Bianco

??? Are you talking about the Curie temperature? If so, it is about 590 degrees F (310C) for neodymium variety of magnets (much higher for samarium-cobalt type). Before you reach this temperature the motor itself will fry. I do not think the Prius motor is force-cooled either by water or air.

I'm looking up that information now. I know that there is a critical performance drop for the Prius, which is why they went with liquid cooling instead of the Air Cooling that would be required for an standard 3-phase AC induction motor or with a Multi-phase (more than 3 phases) AC induction motor like the Chorus Motor (http://www.ChorusMotors.com).


“The Volt avoids that added complexity with a 3-phase AC electric motor… ” – Aaron Bianco

Although I could not find information as to what kind of motor the Volt will be using, I think it will be a kind of permanent magnet synchronous motor, since this type of motor can be switched easily to a generator (for energy regeneration). Unless the ICE-driven generator is also mechanically connected to a wheel, it would be more practical to trun the drive motor into a generator when braking and coasting. The Chorus Meshcon motor is essentially a VVVF (variable voltage, variable frequency) controlled AC induction motor. Nothing special. Modern electric trains all use the VVVF system.

You can find it at autobloggreen (http://www.autobloggreen.com/2007/01/07/detroit-auto-show-general-motors-e-flex-platform).

The Prius uses a PM motor, and the Volt will be using a 3-Phase AC induction motor. At this time, there have been no announcements regarding using "Multi-Phase" AC induction motors in the transportation industry other than in Aerospace applications (see Delta Airlines (http://http://news.delta.com/article_display.cfm?article_id=10647)) where Delta will be using Chorus Meschon (http://www.ChorusMotors.com)on 'Wheeltugs' (http://www.Wheeltug.com)so that their fleet of Boeing 737NGs can drive themselves around with their engines off.




“… or dealing with the current that comes from having a permanent fixed magnet motor… ” – Aaron Bianco

To deal with the counter-electromotive force generated by the permanent magnet motor you do either of the following:

1) keep increasing supply voltage above the self-generated voltage
2) weaken (in effect) the generator magnetism
3) keep the motor speed low (in-wheel motors help since their max speed is around 800 – 1000rpm)

All good techniques, and all require some 'additional' engineering, which adds to the cost/weight. These additional complexities/costs can be shaved off by switching to a 3-Phase AC induction motor, but that only shifts to 'different' complexities/costs as 3-phase AC induction motors have other issues that need to be dealt with on an engineering level.

There is only one other motor option that has a unique set of characteristics that 'solves' the need for the 'engineering' solutions, and that is the Chorus Motor, but at present it isn't being used in Automotive industry but it is being implemented in the Aerospace industry and is undergoing FAA certification at them moment. The topics regarding these complexities/costs that come from the two main types of electric motors (PM & 3-phase AC) are addressed at www.ChorusCars.com (http://www.ChorusCars.com)

The Chorus Meshcon motor is essentially a VVVF (variable voltage, variable frequency) controlled AC induction motor. Nothing special. Modern electric trains all use the VVVF system.

You are correct that VVVF systems have been commonly available in motors for years. But that is like saying that words on a page have been around for millenia, so Hamlet is nothing special. :)

I think the question is a simpler one: does Chorus do something that other VVVF motors do not, and if so, is it a technological and/or commercial advantage that should be used in hybrid vehicles?

If the claims of much higher peak torques are correct, then it would appear that Chorus might have something?

It does have higher peak torque, this is one of the reasons Delta wants it on their planes, to back them out of the gate (from a dead stop) AND to run them around on the tarmac.

And Chorus does do things that VVVF motor cannot do, and if implemented in a Series Hybrid, it will help achieve the 50mpg+ that "KansasGuy" was doubtful about in his first post, due to reducing complexity and providing tremendous 'burst torque' from a small package.

And I'm awaiting some information regarding PM motors suffering performance problems to answer G35X's question. I should have bookmarked the info, but I didn't.

http://www.osti.gov/bridge/product.biblio.jsp?osti_id=885987

Looks like the Prius cuts out ENTIRELY at 170C, and is weakened at lower temperatures. Presumably Toyota knows what they are doing, so these thermal limits are there for a reason.

As the Oak Ridge report says, the Prius motor is entirely unsuitable as a sole drive motor because of thermal limits. So this part of the Chorus story seems to check out.

Thanks, you beat me to it. :)

Chorus Motors has definitely done their research on PM & (3-phase) AC electric motors. They've come to the firm conclusion that thier motor is a perfect fit for Series Hybrids in that they overcome the individual problems inherent to each motor with regards to Series Hybrids (www.ChorusCars.com (http://www.ChorusCars.com)). And the 'burst' torque (weight savings as a result) will be instrumental to getting the gase mileage up as per my previous post on the topic in response to Kansasguy

Aaron, I found the following description in the article in the autobloggreen you mentioned:
“The first E-flex iteration, as implemented in the Volt, is a front wheel drive vehicle with a compact AC electric motor mounted low between the front wheels.”

This motor still can be a PM type as the Prius motor is also an AC (3-phase, synchronous) type. Anyway, we need more info on the Volt motor. Still I think the Volt will be using a PM type since it is easier to turn it into a generator for energy recovery.

Re cooling of the Prius motor, sorry I was wrong. It is cooled by water. I speculate that it is to protect insulation materials and not so much to maintain magnetic strength. 170C mentioned in the Oak Ridge report is much below the Curie temperature. (If necessary, the magnets embedded in the rotor can be cooled with the air drawn by a rotary fan.)

Re the Chorus Motor (as well as the Raser Tech motor with similar claims), I could not find any detailed info and I speculate it is a VVVF AC induction variety. There is not much “aerospace” about it other than the fact it flies with the aircraft, thence the requirement of FAA certification. What you need for this application is a lightweight, high torque motor system that can be “soft” started without frying itself.

"If the claims of much higher peak torques are correct, then it would appear that Chorus might have something" – Treetop

Higher torque can only be obtained by stronger attraction and repulsion of magnetism, read; higher amount of current (in addition to such mechanical design considerations as choice of core material, narrower gap between the stator and rotor and larger diameter of the rotor). Since the heat generated at the motor windings increases as the current increases (@ square of the rate of increase) heat management becomes very important. Maybe Chorus found a new way to control the heat… The Volt’s 53kW motor draws 177 amps of current if the supply voltage is 300 volts, for example. Compare this to our kitchen-stove element, which draws less than 10 amps at 220 volts. 177 amps through even a 0.5-ohm load is a lot of heat (current*current*resistance).

“The first E-flex iteration, as implemented in the Volt, is a front wheel drive vehicle with a compact AC electric motor mounted low between the front wheels.”


This motor still can be a PM type as the Prius motor is also an AC (3-phase, synchronous) type.

Synchronous motors are "built-field" machines that are brushless permanent magnet motors. Asynchronous motors are induction machines, that use electromagnets. Toyota uses the former; the Volt the latter.



Still I think the Volt will be using a PM type since it is easier to turn it into a generator for energy recovery.

It is no challenge to make an inverter-fed AC induction machine a generator. Just spin the rotor faster than the magnetic field.



Re the Chorus Motor (as well as the Raser Tech motor with similar claims), I could not find any detailed info and I speculate it is a VVVF AC induction variety.

That is really strange, since I found a LOT of information at http://www.chorusmotors.com . It is different from 3 phase AC induction machines in that it uses more phases (one reference was to 18 phases), and the company claims that the higher phase count allows the helpful use of harmonics. This is apparently what allows for higher power density in overload conditions. There seems to be something called "Meshcon" that allows for more current from the inverter by using harmonics on purpose. That is the big money-saver claim, since I know inverter electronics cost more than the motors do.


"If the claims of much higher peak torques are correct, then it would appear that Chorus might have something" – Treetop


Higher torque can only be obtained by stronger attraction and repulsion of magnetism, read; higher amount of current (in addition to such mechanical design considerations as choice of core material, narrower gap between the stator and rotor and larger diameter of the rotor). Since the heat generated at the motor windings increases as the current increases (@ square of the rate of increase) heat management becomes very important. Maybe Chorus found a new way to control the heat… The Volt’s 53kW motor draws 177 amps of current if the supply voltage is 300 volts, for example. Compare this to our kitchen-stove element, which draws less than 10 amps at 220 volts. 177 amps through even a 0.5-ohm load is a lot of heat (current*current*resistance).

That is toasty indeed! I don't disagree that higher magnetism allows for higher torque densities. I think the company is claiming that precisely in *overload* conditions (or "saturation"), much more power can be driven through the motor.

That said, heat is, as you point out, an absolute. I would be surprised if the Chorus motor has a significantly higher *continuous* rating for the same cooling -- if they make that claim, then I would be skeptical overall. But if the claims are only for intermittent operation, then it may all hold together. Cars use power in a highly intermittent fashion, after all. 0-60 is a LOT more work than cruising down the highway!

If this is right, then the question is whether the Volt's motor/drive is sized for their continuous or overload conditions. If the latter, then Chorus may indeed have a big money/space/weight saver.

Treetop

High temperature magnets are expensive now. Supply is limited & localised too. The automotive market is vast. Doubt this could be the solution. If the geography of oil is an issue now, the geography of such magnet supply will be far more contentious.

Power Electronics are VERY expensive. If the lower capacity PEs needed by Chorus can provide the low speed torque, that too will be a major factor.

When the market matures, the word PROFIT will be an issue. Subsides, both by the industry & governments will not continue for ever....


Cars need to cost a lot less to make than currently, not a lot more.

I haven't thought about motors for quite some time (decades), so I can't comment on those details. I do understand semiconductors quite well though. Power electronics are only expensive because of the lack of volume. Three years of volume and those expensive electronics are dirt cheap commodities. Copper windings will be WAY more expensive, but they are a recoverable resource.

Power electronics are only expensive because of the lack of volume. Three years of volume and those expensive electronics are dirt cheap commodities. Copper windings will be WAY more expensive, but they are a recoverable resource.

I thought it was the other way around. *Logic* is dirt cheap in quantity. But Power electronics require a considerable amount of high purity material, and that is never a giveaway.

There IS a lot of volume in power electronics already, but the prices remain steady. In some applications I understand the electronics cost 2-3x the motor -- and that is in automotive, where volumes are already very high!

Treetop

“Synchronous motors are "built-field" machines that are brushless permanent magnet motors. Asynchronous motors are induction machines, that use electromagnets. Toyota uses the former; the Volt the latter… ” – Treetop

Pardon my ignorance… but, I could not find any info re type of the motor GM is going to use for the Volt. Is it really an induction type? By the way the PM synchronous motors also use electromagnets.

“It is no challenge to make an inverter-fed AC induction machine a generator. Just spin the rotor faster than the magnetic field… ” – Treetop

Are you talking about slip rings on the rotor, whch require periodic maintenance? Besides, rotor speed in the regeneration mode is dictated by the rotational speed of the wheels. Isn’t it much simpler to use a PM motor/generator, which does not require exciter current?

“ I found a LOT of information at http://www.chorusmotors.com … ” – Treetop

I found it more an advertising brochure than a scientific paper worthy of peer scrutiny.
In essence it seems the motor system simply distributes the burden of heat generated in coil windings among higher number of coils. Besides, I think higher frequency (harmonics) means higher hysteresis and eddy current losses… right?

“ …then the question is whether the Volt's motor/drive is sized for their continuous or overload conditions… “ – Treetop

Being the serial design the Volt’s motor must have the strength for continuous duty at 45kW, while the motor for the parallel design can be of part-time duty (although as automakers tries to prolong the duty time of the parallel motor, it too must become more heat resistant).

Chorus is a commercial entity.

However I think you missed one of it's major features re harmonics & heat.

Where you say
In essence it seems the motor system simply distributes the burden of heat generated in coil windings among higher number of coils. Besides, I think higher frequency (harmonics) means higher hysteresis and eddy current losses… right?

They say
Technical Summary
Introduction
The Chorus concept utilizes concentrated, high phase order windings which allows the beneficial use of harmonics (temporal, spatial, and overload). Rather than harmonics running against the main drive (creating heat), they run with the main drive, creating more power. Consequently, a Chorus machine can achieve much higher torque densities than a traditional 3-phase motor, but with no cost penalty.

...

Isn't one of the main issues that others are forced to use a parallel design because of the limitations of their motor? Otherwise would anybody choose to go to the expense of duplicating everything?

I thought it was the other way around. *Logic* is dirt cheap in quantity. But Power electronics require a considerable amount of high purity material, and that is never a giveaway.

There IS a lot of volume in power electronics already, but the prices remain steady. In some applications I understand the electronics cost 2-3x the motor -- and that is in automotive, where volumes are already very high!

Treetop

Hard to discuss this without data. What kind of volume numbers are you talking about?

Mike

“Synchronous motors are "built-field" machines that are brushless permanent magnet motors. Asynchronous motors are induction machines, that use electromagnets. Toyota uses the former; the Volt the latter… ” – Treetop

[QUOTE]Pardon my ignorance… but, I could not find any info re type of the motor GM is going to use for the Volt. Is it really an induction type?

I see other posts that say so, such as
http://gm-volt.com/forum/showthread.php?p=11239
But I don't see confirmation from GM. The EV1 used an induction motor, and others in the industry tell me GM is using a 3 phase induction machine.

“It is no challenge to make an inverter-fed AC induction machine a generator. Just spin the rotor faster than the magnetic field… ” – Treetop


Are you talking about slip rings on the rotor, whch require periodic maintenance? Besides, rotor speed in the regeneration mode is dictated by the rotational speed of the wheels. Isn’t it much simpler to use a PM motor/generator, which does not require exciter current?

No slip rings. A PM is MORE complicated and more sensitive than an induction machine, because it has to have a speed and rotor position sensor in order to work. An induction machine can be run "open loop", and the position of the rotor is not needed for motoring or generation.

While excitation current may seem complicated, there are millions of induction machines with inverters that are installed and run beautifully. Inexpensive, and rugged.

“ I found a LOT of information at http://www.chorusmotors.com … ” – Treetop


In essence it seems the motor system simply distributes the burden of heat generated in coil windings among higher number of coils. Besides, I think higher frequency (harmonics) means higher hysteresis and eddy current losses… right?

That is how I understand it. The thing is, a car may run an average load of 25 kW, but at 0-60 mph it pushes 150kW. So brief inefficiency in operation, if it means running a much smaller and less expensive motor, makes a lot of sense.

In other words, in overload an induction machine is not optimally efficient. But car motors run in overload only a small percentage of the time, so a little extra heating at those times makes no real difference.

“ …then the question is whether the Volt's motor/drive is sized for their continuous or overload conditions… “ – Treetop


Being the serial design the Volt’s motor must have the strength for continuous duty at 45kW, while the motor for the parallel design can be of part-time duty (although as automakers tries to prolong the duty time of the parallel motor, it too must become more heat resistant).

I agree that a Series design requires the motor to do all the heavy lifting, all the time. Still, getting rid of the dual (mechanical) drivetrain has a lot of savings all around.

Treetop

There's been a long standing solution to converting electrical energy to mechanical energy and vice versa. It is called a Motor-generator (http://en.wikipedia.org/wiki/Motor-generator).

Problem:
Use two motor generators, an ICE, clutches, and an electrical energy storage/supply system to produce a series hybrid propulsion system.

Answer:
Closer to the Volt than the Chorus motor.

Thank you Treetop for the explanation. All in all I think it boils down to heat management. Although electric motors are much more efficient than ICE, still they loose some energy as heat while in operation. Take the Volt’s 45KW (continuous) motor, for example. To obtain this much of mechanical energy at the spindle, the battery pack (plus the ICE/generator sometimes) will be supplying 47KW or so of power. The 2KW difference turns into heat. This heat is more than that of a cooking stove coil going at the max setting. (The generator also heats up in the same manner.) The electric motor is not made entirely of metal. You have to use some kind of insulation material, which can be damaged by the intense heat. Also, unlike the metal-to-water heat transfer of ICE, the heat generated at the motor coil goes through the insulation material making forced cooling inefficient. Therefore, you want to limit the amount and/or duration of current that flows through the motor so that it won’t fry itself. If because of this limitation you cannot obtain necessary torque, you want to use a reduction gear or transmission to get higher torque in exchange for speed. A larger motor will be more heat resistant, but there are limitations in size, weight and cost to be put in a car.

The parallel hybrid design is a compromise in this regard by using smaller motor with part-time duty.

Thank you Treetop for the explanation. All in all I think it boils down to heat management. Although electric motors are much more efficient than ICE, still they loose some energy as heat while in operation. Take the Volt’s 45KW (continuous) motor, for example. To obtain this much of mechanical energy at the spindle, the battery pack (plus the ICE/generator sometimes) will be supplying 47KW or so of power. The 2KW difference turns into heat. This heat is more than that of a cooking stove coil going at the max setting. (The generator also heats up in the same manner.) The electric motor is not made entirely of metal. You have to use some kind of insulation material, which can be damaged by the intense heat. Also, unlike the metal-to-water heat transfer of ICE, the heat generated at the motor coil goes through the insulation material making forced cooling inefficient. Therefore, you want to limit the amount and/or duration of current that flows through the motor so that it won’t fry itself. If because of this limitation you cannot obtain necessary torque, you want to use a reduction gear or transmission to get higher torque in exchange for speed. A larger motor will be more heat resistant, but there are limitations in size, weight and cost to be put in a car.

The parallel hybrid design is a compromise in this regard by using smaller motor with part-time duty.

Remember that a car only needs its maximum output when accelerating as fast as possible. Even most hill-climbing doesn't require maximum output, and the bulk of most vehicles' operation is steady-state cruise, which only requires enough energy to overcome aerodynamic drag and mechanical friction. You design for the maximum output, but apply reasonable estimations of how often/for how long you'll need to produce that output, and with a computer-controlled electrical drive system you can program the system to prevent damage to the motor by limiting the length of time it can be asked to generate maximum torque, and dialing back the torque if the motor's temperature exceeds specs.

GearheadGeek,

Your point about limited use of the 'maximum' output is quite correct. It is why most engines are overpowered or overdesigned.

The ability of an electric motor to provide up to 1,000% of it's standard torque is unique to Chorus Meshcon (which can provide up to 10x its torque for 'startup' or 'burst' conditions). For use in a Series Hybrid, the electric motor chosen can be chosen based on its “steady state cruise” requirements needed to cover aerodynamic drag and mechanical friction

Besides, an AC motor is much better able to be air cooled while a Permanent Magnet motor in the volt would require a more complex solution for liquid cooling. PM motors simply can’t operate efficiently at high temperatures like AC induction motors can.