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EV WORLD EXCLUSIVE ARTICLE |
The new Opel/Vauxhall Insignia EcoFlex utilizes a 2.0 liter CDI diesel engine that produces 140g/km CO2. Its 0.26 CDi makes it extremely aerodynamic for a five-passenger sedan. The author suggests this would be a ideal platform for a parallel plug-in hybrid at less cost to GM and taxpayers.
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In an era of corporate bailouts, is the Chevy Volt just another boondoggle?
Open Access Article Originally Published: October 03, 2008
General Motors is enthusiastically promoting its recently announced Chevy Volt. The Volt is a plug-in series hybrid, which GM hopes to begin delivering towards the end of 2010. GM prefers to call the Volt an 'extended-range electric vehicle', but by launch it will probably be in direct competition with several other plug-in (parallel, rather than series) hybrids; one will be the official plug-in version of the Toyota Prius. This paper suggests why GM has chosen to adopt a design that is likely to prove more expensive to build and to run than those of most of its competitors.
The Volt is a series hybrid, unlike any of the other hybrid cars currently available. A series hybrid uses its engine solely to drive an electric generator. Consequently, all the power to the wheels, whether from the battery or the engine, is delivered electrically, via a large traction motor. In contrast, a typical parallel hybrid has a smaller electric motor driven only by the battery. Its engine drives the wheels via a conventional gear-based transmission. The Prius uses a transmission that combines both series and parallel features.
The production version of the Volt will use GM's Delta II platform, shared with the Chevrolet Cruze (due Spring 2009) and the next generation of the Astra. The Cruze is the replacement for the 4/5 seat Cobalt compact. The large battery mounted down the middle of the Volt will make it a four-seater only, impacting its appeal once the initial excitement wears off. It's a small car, internally.
The decision by GM to make the Volt a series hybrid means it needs a more powerful and expensive battery than an equivalent parallel hybrid, just to support the higher peak electrical power required. A claim often made is that using a generator rather than a conventional transmission to transmit engine power to the driving wheels will save money, but this is doubtful when the engine is radically downsized, requiring only a smaller, less expensive gearbox. A 50 kW generator and a more powerful traction motor (plus the inverters, etc, needed to control them) are likely to cost at least as much as one of the latest small Dual (dry) Clutch Transmissions (DCT), for example. Also note that an 'electric transmission' will inevitably produce higher losses than a DCT at cruising speeds, and therefore cause higher fuel consumption. If 'electric transmissions' for conventional cars were less expensive and/or more efficient, they would have been in wide use already. They were first tried more than a century ago, so the concept is far from novel.
A series hybrid can sometimes prove marginally more economical than a parallel hybrid in city driving (or running around a railroad marshalling yard in a 'diesel-electric' locomotive). However, once the requirement is for a mix of city and highway mileage in a 'fuel-only' hybrid, the balance tips the other way. And when the intention is to build a plug-in hybrid that results in most of the city driving being powered electrically, any remaining advantage of a series design effectively disappears. For a plug-in hybrid, cruising on the freeway will generally be where most of the fuel gets used. A direct mechanical connection between the engine and the wheels must be the most efficient solution under these conditions, as there are no ‘lossy’ energy transformations involved.
A 'fuel only' series hybrid would be at least as expensive to build as the equivalent parallel hybrid and it will generally have worse fuel consumption, which might explain why we can't buy one from any major manufacturer. Essentially, a Volt becomes a 'fuel-only' series hybrid once it has used its plug-in recharge of electricity. If, for some overriding reason, a manufacturer were to decide to offer a series hybrid with a range of plug-in options (say 10, 20 or 40 'electric miles'), the car would need the same increases in battery capacity to achieve each of its All-Electric Range (AER) increments as an equivalent parallel hybrid. Once both hybrids have gone beyond their AER and are running on fuel alone, the series hybrid will almost certainly use more fuel in highway driving.
The explanation GM gives for providing such a large battery (16 kWh and over 400 lbs) is to provide a sufficiently high AER to ensure most customers will be able to drive to work and back without the engine having to fire up. However, only 8kWh is theoretically needed to deliver ~40 miles of AER at ~200 Wh per mile. The other 8 kWh is there to provide the same surge capability as a 'fuel only' hybrid (both before and after the AER has been exceeded) and to help extend the life of the battery by keeping the typical 'state-of-charge swing' to less than 50%. As a general rule, and for most batteries, the lower the swing, the more 'deep' discharges the battery can sustain before its capacity drops below the '80% of nominal' level at which replacement becomes obviously desirable. As an example, the standard (i.e. fuel-only) Prius starts life with a 1.3 kWh (nominal) battery to provide sufficient excess capacity to 'comfortably' cover a swing usually less than 200 Wh and rarely as much as 400 Wh even when the car is several years old.
Most of the after-market plug-in offerings for the Prius retain the standard battery pack to buffer the additional high-capacity pack and leave it with only the relatively undemanding task of supplying a steady, one-way, flow of energy at relatively low power into the existing hybrid system. This also has the merit of allowing a modular approach to the provision of AER; a single model of car can be, at entry level, a fuel-only hybrid, leaving customers the option of paying for additional battery modules with AERs of, say, 10, 20 or 40 miles, installed by the dealer on day-one or years later, as batteries become cheaper and fuel more expensive. The Volt has a fixed nominal AER of 40 miles, but this would seem to apply only if it is used gently, on a cycle such as the federal UDDS. According to the NREL, on more demanding cycles hybrids may need to blend in engine power with battery power after only a few miles of each trip. For more on this, please visit:- http://www.nrel.gov/vehiclesandfuels/vsa/pdfs/39614.pdf This then suggests that the 'real world' fuel consumption of most plug-in hybrids will be higher than advertised, and that those users who choose a series over a parallel plug-in hybrid will probably find that their car's fuel consumption is higher than they may have been led to expect.
So why would GM choose to adopt an architecture that is likely to result in cars which will cost more to build and run than the alternative apparently preferred by most, if not all, of its competitors? One explanation, supported by a review of some of GM's concept projects, seems to be a desire to create a single platform capable of supporting the full spectrum of hybrid, fuel cell and battery-only vehicles. Take a look at:- http://www.evworld.com/article.cfm?storyid=1231
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8 comments so far...
03-Oct-2008
64185
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Chris,
You may be missing the appeal of a series hybrid. For the early adopters they are buying an EV with insurance. Your calculations are not valid, early adopters will be repalcing existing ICE vehicles used for mainly city driving with a vehicle that will NOT require gasoline for most driving, certainly most commuting. This may only appeal to 5 or 10% of the market, but that's lots of vehicles. Other segments of the market will prefer HEV or parallel PHEV's.
The commuter travelling 30 miles each way to work and similar distances on weekends will travel about 20,000 miles a year all electric. They will probably be replacing a 3-5 year old vehicle, getting 25-35 mpg, purchased when gasoline was $1-2 agallon, so the savings will be considerable.
I doubt that GM is betting its future on fuel cells being available in 5-10 years, but you can bet that many other models will have the basic Volt power train, thats the reason for the 16kWh battery capacity. As battery technology improves costs will come down and range will be increased. Have you ever seen a computer manufacture failing to sell because of too much memory? Only a year ago the Toyota president was ridiculing the plug-in concept, a 10 mile EV range plug-in Prius is going to be in a totally different market segment.
Posted by: Neil Howes
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03-Oct-2008
64186
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You'll notice that I censured his post and will do so from now. We don't object to constructive criticism, but this 'person' make little sense when 'he' does post, and certainly it can't be considered 'constructive.'
So, Ken, Keith, Kevin, or whatever your name is -- and anyone who comes across any future postings by this person, let us know -- you're on notice that your contributions to the dialogue are not welcome and will henceforth be removed.
Posted by: Bill Moore
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03-Oct-2008
64188
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The Volt is too heavy!
400lbs. of batteries in a 1500lb. EV will travel over 150 miles on a charge.
The car companies are still very blind when it comes to current lightweight construction technologies.
Look at the Karman delivery vehicle design.
www.fiberforge and www.alulight.com is all they need,but it is the blind leading the blind.
All of the technologies for a very lightweight and intelligent EV design has been around for a time.I will never buy another GM product.
Posted by: John Hurt
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04-Oct-2008
64210
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I mostly disagree with the author. The Volt is actually a PHEV, and the large battery pack is to supply the Electric Only driving range of 40 miles. The Volt battery pack is 50% utilized, thus the oversized 16 kwh battery pack. The Prius series/parallel hybrid has a 25% utilized 1.3 kwh battery pack. The reason is due to the extreme cycling requirements of the PHEV or the parallel HEV. The series HEV, the BEV or the extended range BEV have much lower cycling requirements. Note, however, that expired Volt battery packs will still be far superior to the Lead-Acid battery packs we are forced to use for energy storage applications, thus there is great interest in using expired BEV, PHEV or series HEV battery packs for that application. A BEV with a 50 kwh battery pack, and 1000 cycles will get about 200,000 miles – ample for a primarily city driving vehicle. The Volt PHEV will have to do almost a cycle every day to provide the average 30 miles commute travel, or 1800 cycles in 5 yrs. A series HEV requires only about a 5 kwh battery pack, which will be lightly used, 90% of the energy requirements being less than 1 kwh, with the balance only for extended bursts of high speed or travel in an unusually steep mountain environment at speed. As for surge, with a large100 kw motor, a 5 kwh battery pack only needs a 20C capability which is readily available in Li-Ion, LiPo, LiFePO4 or NiMH batteries, and also Ultra-capacitors or a parallel combination of the two. Note that the surge required to accelerate the vehicle is similar to the charging surge required to absorb the braking or downhill energy. See:
25C LiPo battery packs
The series hybrid is the most efficient way to build a vehicle. Unlike a BEV, the inherent ~15% charging loss is greatly reduced because much of the time the generator is directly supplying the PEM DC bus without charging the battery and if ultracapacitors are used on the DC Bus, the charging loss can be almost eliminated, all that is needed is a 1 kwh capacitor for all normal driving and about a 5 kwh battery bank connected through a DC-DC converter to the DC bus, which would supply energy only for sustained extreme speed travel or climbing mountains at speed or towing a trailer. Conversion efficiencies of generator, motor & PEM of > 90% have been achieved.
The series hybrid is much simpler in design & maintenance than the parallel hybrid. It does not need a clutch or transmission, no oil changes, spark plugs, fuel/oil filters except on the separate generator which can be removed or replaced easily. It does not need the complex control / interface between the gas engine & electric motor.
The series hybrid has better acceleration due to the superiority of the much larger electric motor to the gas motor in this respect.
A series hybrid recovers almost all the energy from braking, the parallel only a much smaller portion of the energy. The electric motor in a series hybrid supplies acceleration energy & recovers braking energy efficiently at all operating speeds. An Electric Motor delivers to the battery / ultracapacitor about the same current braking 60-0 in 8 secs, as it takes accelerating 0-60 in 8 secs, therefore a robust fully powered electric vehicle is necessary to recover the energy lost in deceleration, that is a fully electric drive. The partial electric drive in a parallel hybrid just won't do it.
The larger battery pack on a series hybrid is needed to store the potential energy lost by going downhill, so it can be used to power the uphill climb. The small battery pack on the parallel hybrid cannot do this, for example, the 0.25 kwh (utilized) battery on the Prius, is only capable of storing the energy for a small 1% grade hill for 1.5 km, anything more is thrown away, vs the series hybrid with a 4 kwh utilized battery pack, which could store the energy from a steep 12% grade for 2 km. Also the larger battery pack means lower charging currents / per cell, which leads to higher charging efficiency for braking energy recovery.
The generator engine on the series hybrid can be much smaller (typically 1/3 the size of a parallel hybrid’s), simpler and more efficient than on the parallel hybrid. It only needs to run at optimal charging speeds, does not need good torque or acceleration performance. It only needs to be large enough to supply average energy that the vehicle uses or even less if the vehicle is parked part of the time.
The generator module on the series hybrid can be easily be standardized for all electric vehicles, and mass produced as an interchangeable auto component. It could easily be replaced, exchanged or upgraded depending on requirements or the available technology. For instance, it could be a high efficiency diesel, a FlexFuel Turbine with up to 50% efficiency, a Fuel Cell or StarRotor’s Brayton cycle external combustion turbine (they are claiming 45% to 60% efficiency). The constant speed smaller engine on the series hybrid is much easier & cheaper to put pollution controls on. As examples of series HEV engines, some of which are totally unsuitable for ICEV’s or parallel HEV’s see:
The 50% efficient, low emissions, Liquid Piston HEHC engine
The Velozzi 200 mpg Series HEV with Micro-Turbine Engine/Generator
The Velozzi 200 mpg Ultra-Light High Performance Series HEV
The 45% efficient, ultra-lightweight, FreePistonPower Engine/Generator – MegaBucks Detroit couldn’t come up with this?
The RadMax Rotary Diesel Engine
The StarRotor 40-65% Efficient Brayton Cycle Engine
The series hybrid can readily be made a true all wheel drive vehicle, without the complexity of multiple drive shafts / differentials, by using wheel hub electric motors. Added benefit of zero turning radius by running wheels on one side backwards to wheels on the other side. Also the wheel motors run >90% efficient, with NO DRIVETRAIN LOSSES, which can amount to 50% of the I.C. Engine shaft horsepower output in a parallel hybrid or standard ICE powered vehicle (in particular at lower speeds – the Prius has 38% drivetrain losses at 45 mph and 51% at 5 mph). This cannot be done on the parallel hybrid.
Only the series hybrid can use wheel motors. The stability of the vehicle is greatly enhanced with wheel motors and the skateboard chassis of the series HEV, thus even SUV’s, notorious for deadly rollovers will be much more stable. Also since the wheel motors have no drive axle they can be moved vertically a large amount to provide much better traction and performance in rough terrain. As a matter of fact, they can be built with air shocks so the AWD vehicle can be raised high above the ground for rough terrain, and low to the ground for road travel. And in an accident the air can be exhausted causing the vehicle to skid safely to a stop, sliding on the belly plate. Another advantage is on cornering, the outboard and inboard wheel motors can be both powered at different speeds, resulting in improved stability on turns at speed. See:
The Crusher Series Hybrid Electric Vehicle with Wheel Motors video
The series hybrid avoids the problem of a patented custom built drivetrain, like the patented Synergy Drive Toyota uses.
The series hybrid can be mass produced with all drive components within the chassis of the vehicle, even the replaceable generator module can fit in chassis with some of the newer engine types (like the turbine or Reg Tech RadMax or Free Piston Power unit) This “Skateboard” Chassis has long been a goal of GM. With all the weight of the major components in or below the chassis, the series hybrid is inherently more stable than the typical ICE powered vehicle or parallel hybrid. With no heavyweight engine components in front of the driver, the vehicle can be made much more safe in a collision. Various bodies can be attached to the same frame. As such, the series hybrid would be less expensive to make.
The series hybrid drivetrain is essentially a pure EV architecture which can easily be made as any of four options, an all electric with no generator but expanded battery pack, the extended range BEV with a 30 kwh battery pack and a small 10-20 kw generator, the PHEV with a battery pack of about 10-15 kwh and a 30–60 kw generator, or as the series HEV with about a 5 kwh battery pack and a 30-80 kw generator. The generator would run typically 15 to 40 hp for a normal vehicle, and weigh around 200 lbs, as would the expanded battery pack. The unused space in the front of the vehicle, normally under the hood, could be made to contain either the battery pack expansion or the generator module. It would be a matter of unplugging two connectors (control cable & power cable) and swapping them according to the owner’s preference. Perhaps, battery pack for maximum all EV range in the city commuting, or the generator module for weekends extended range. A hydraulic lift on wheels, like they sell in hardware stores for $200 would easily allow swapping the modules.
The series hybrid can easily used as an emergency portable power generation system or to supply energy back to the grid for distributed power generation, a great advantage for utilities to supply emergency peak power after transmission line and/or power generating plant failure and/or major natural disaster or terrorist attack and/or extreme heat wave. This is called vehicle to grid or V2G.
The series hybrid has an inherently modular construction. Which enables it to be assembled from standard interchangeable mass produced components. These would include the battery pack, expansion battery pack, various interchangeable generator modules, operator interface (likely all electronic), PEM and Electric Drive Motors.
You can calculate the fuel economy of a Series Hybrid by using the Tesla Electric Car data, modified to assume an onboard fuel generator instead of a utility powered charger, which would replace 85% of the Tesla’s 44 kwh battery pack. At 7.85 km per kwh of utility energy, this would yield 68 miles per gal with a 35% mechanical efficiency diesel generator. This would be higher in actual fact because the generator would be substantially lighter than the replaced battery pack. Accounting for the generator energy directly supplying the DC bus, this would push the fuel economy up to about 73 mpg, using ultracapacitors this would increase to 78 mpg. The Tesla was designed for high speed (130mph), and so the 2 speed transmission. Using wheel motors to replace the transmission & rear differential should push the fuel economy up to at least 90 mpg. Replacing the Diesel Engine with a Fuel Cell, high efficiency turbine, Free Piston Power type engine/generator or the StarRotor type engine would push the fuel economy up to 115 to 155 mpg. Not bad for a 0-60 mph in 3.9 sec sports car.
The one place that I can see that a series/parallel architecture would be superior would be in Highway Transport Trucks. For them fuel cost is #1. It is most sensible to make them as efficient as possible. For this type of vehicle a standard series HEV chassis with the ICE / generator attached through a clutch to the electric drive motor might be more efficient. At highway speeds the clutch would be engaged and the engine would directly drive the wheels. Note however, that this would preclude the more efficient wheel motors, and would preclude certain types of generators such as fuel cells or free piston types, which may be more efficient as a series HEV than the series/parallel HEV design.
Posted by: Warren Heath
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03-Oct-2008
64189
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Thanks, Bill
This guy is a runaway attack dog!
Posted by: John Hurt
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05-Oct-2008
64228
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The author is not a fan of series hybrids, and he's right about series HEVs. HEVs get all of their energy from gasoline or diesel, and it is very important how efficiently that fuel is used.
The Volt is a PHEV, and it doesn't get all of its energy from gasoline. Once you get most of your energy from electricity, gasoline fuel efficiency becomes less important.
The series drivetrain provides full power EV operation. That's why GM calls the Volt an "EREV" instead of just PHEV. PHEV's like the Prius plug-in and Saturn Vue plug-in don't offer full power EV operation, so the Volt is truly more than just a PHEV.
I think the author has an ingrained "petrol" mindset, and concludes that the Volt is not a optimum gas car. He's right. However, if you have an EV mindset, the Volt is a great EV. It has all the EV advantages (except freedom from engine maintaince), and no range issues, and "fast recharge" at any gas station. You can drive it just like any other car, no compromises. The Volt also helps reduce the EV cost premium by substituting a relatively inexpensive gen set for a much larger and more expensive battery.
The Volt won't be as cost effective as an optimized HEV, but it will be more cost effective than pure EVs. It will be a great car.
Posted by: GS P
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06-Oct-2008
64242
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Sometimes it is hard to find an explanation to why that or that option is chosen, but in this case, as Mike point out, the answer is really straightforward. GM for once, is simply thinking ahead in terms of generator evolution. For the moment, they will stick to a standard ICE as range extender but next they will probably come up with something more efficient like a direct piston engine generator. Indeed, if the intention is only to produce electricity, which is the case in a series hybrid, then it is very interesting to “short circuit” the electric production by leaving the crank and shaft out of the loop. Those components are completely unnecessary, increasing the wear, demanding oil and above all decrease the yield. Of course, all the other options like turbines, or silent Thermo PhotoVoltaic (TPV) and Direct Ethanol Fuel Cell (DEFC) are still out there as well. The Volt platform creates flexibility like no other.
Now this being said, Toyota has enough resources to do both, the parallel Plug-in Prius III as long as they stick to a standard ICE and a free piston generator series Plug-in Prius IV, once they are ready for it on the market.
The obvious question then is rather what is the best strategy, to use the parallel system at first, while sticking to a standard ICE, or to directly start with a serial hybrid knowing that something comes next as more efficient generator.
Actually, history can give the answer.
Toyota started the hybrids first with the Prius, which was made a parallel system for a good reason; they had only NiMH batteries and didn’t know the market response so they wanted to reduce the changes to a minimum.
GM lost the hybrid train in the first place, so they now arrive at a later moment when Lithium batteries are more evolved and with a market in strong demand. They therefore prefer to jumpstart their hybrids by directly adopting the serial configuration so that they don’t have to redesign their platform from scratch all over again.
Two companies, two histories, two quiet logical decisions.
Posted by: Patrick Leonard
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03-Oct-2008
64182
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Has anyone noticed that our MR Beuchert,Beuchard or whatever the name is not spelled the same on his various posts? How often does a real person misspell their own name?
I agree with Juan that this is not a post from a real person. It's so poorly structured,with loosely related phrases and sentences and so poorly thought out it must be generated by a cut and paste program.Notice that even when we are critical of him he never replies. Maybe if we call him a really filthy name such as BUSH. How about the really foul name of Cheney? Had enough yet old Ken?
Just remember that anything proposed by anyone, that eventually becomes what is called a movement,especially a progressive movement is feared by our shadow government. They created an entire network called Fox News or better termed Fox opinion channel to try and crush any and all opposition to our being assimilated into the mindless so called conservative BORG. There is also the corporate whore known as Limbaugh. A most foul and perverted creature.This is just another of their many deranged tools. It's time to pick up pitchforks and clubs and put these remnant's of the so called Reagan Revolution where they belong. Deep sixed with a wooden stake in their hearts.
Posted by: lawrence elliott
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