21 replies to this topic

[Wuzak]

I was thinking about electric vehicles which have rang extenders included.

 

As far as I know, the only two production cars of this type are the Fisker Karma, which is no longer in production, and the Chevy Volt.

 

The Karma had a 20kWh battery and a 2.0l 4 cylinder engine rated at 260hp. The range was 230 miles, with an electric only range of 32 miles.

 

The current Volt has a 18.4kWh battery and a 1.4l 4 cylinder engine with 84hp. The range is 420 miles, electric only is 23 miles.

 

From those figures it would seem that they are less range extended electric vehicles than petrol vehicles with electric transmission.

 

For comparison, the Tesla S (similar size to the Karma) has a range of 240 miles with a 70kWh battery and 265 miles with the 85kW battery.

 

I would have thought that it would be better to have a larger battery and a smaller range extender. For cruising it may only need to be 20 or 30hp?

Edited by Wuzak, 22 June 2016 - 23:53.

[MatsNorway]

You can also get the i3 with a range extender just as you think is better. I agree btw. i think it is the future.  http://www.caranddriver.com/bmw/i3

Edited by MatsNorway, 22 June 2016 - 12:05.

[Canuck]

The current Volt has a 18.4kWh battery and a 1.4l 4 cylinder engine with 84hp. The range is 420 miles, electric only is 523 miles.

That's a range shortener then.

[Greg Locock]

Officially the Volt is good for 36 miles in EV mode.

 

 

The problem with making the range extender less powerful is that it doesn't get /that/ much lighter, I guess. I think there is a good argument that perhaps the petrol engine only needs to be say 30-40 hp, which would permit cruising and light acceleration. Anything more would need electric 'assist'. Various companies are (or have been) working on compact range extenders, but nothing much seems to be happening at the pointy end of things.

 

 

This very poor paper is discussing this sort of thing http://onlinepresent...l53_2014/11.pdf

 

and this one is a bit better http://tra2014.traco...paper_18329.pdf as is https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwiny_7Y_rvNAhWJKJQKHcd2CFcQFggqMAE&url=https%3A%2F%2Fcore.ac.uk%2Fdownload%2Fpdf%2F19542636.pdf&usg=AFQjCNE0DIm3pT8YwFmZPAUegRlOMdOgMw&sig2=nbxkzpqLlohI-4of-oL68g

 

SAE  2014-01-1105 is also relevant.

 

I guess the crucial question is, what is the mass of the EREV system (including generator ) as a function of its maximum power? And how does its efficincy at typical operating points affect that tradeoff?

[BRG]

I was thinking about electric vehicles which have range extenders included.

 

Aren't all hybrids just EVs with range extenders, only given a fancy name to fool the public?

Edited by BRG, 22 June 2016 - 20:14.

[saudoso]

The plugin hybrids maybe? I think I remember that being a new thing some time ago.

[J. Edlund]

I was thinking about electric vehicles which have rang extenders included.

 

As far as I know, the only two production cars of this type are the Fisker Karma, which is no longer in production, and the Chevy Volt.

 

The Karma had a 20kWh battery and a 2.0l 4 cylinder engine rated at 260hp. The range was 230 miles, with an electric only range of 32 miles.

 

The current Volt has a 18.4kWh battery and a 1.4l 4 cylinder engine with 84hp. The range is 420 miles, electric only is 523 miles.

 

From those figures it would seem that they are less range extended electric vehicles than petrol vehicles with electric transmission.

 

For comparison, the Tesla S (similar size to the Karma) has a range of 240 miles with a 70kWh battery and 265 miles with the 85kW battery.

 

I would have thought that it would be better to have a larger battery and a smaller range extender. For cruising it may only need to be 20 or 30hp?

 

A more powerful range extender and a smaller capacity battery is a better combination, which is why most manufacturers have chosen that combination.

 

Battery cost will increase roughly linear with battery capacity, fuel cost saving will however drop off rapidly once the electric range is greater than what is needed to cover most of your driving. If the circa 10 kWh of usable energy available in the Volt battery will cover 80% of your driving twice the capacity will only increase this with maybe 5 to 10% while doubling battery cost. With a plug in hybrid, you simply have no need for a battery electric range of a Tesla.

 

A small range extender will have other implications as well. With only 20 or 30 hp your range extender will be outside the most efficient operating points in many cases, and during for instance extended highway driving the driver may have to slow down to reduce power consumption if the battery state of charge is low.

 

In my opinion the mixed hybrid configuration is a better compromise between fuel saving and performance for a car fitted with a combustion engine.

[J. Edlund]

Aren't all hybrids just EVs with range extenders, only given a fancy name to fool the public?

 

From a technical standpoint, these can use different solutions as to how the motors/engine are used to power the wheels, and how they are sized..

[Wuzak]

That's a range shortener then.

 

Thanks for pointing out my mistake!

[Wuzak]

The problem with making the range extender less powerful is that it doesn't get /that/ much lighter, I guess. I think there is a good argument that perhaps the petrol engine only needs to be say 30-40 hp, which would permit cruising and light acceleration. Anything more would need electric 'assist'. Various companies are (or have been) working on compact range extenders, but nothing much seems to be happening at the pointy end of things.

 

Take the Volt's range extender - 4 cylinder, 1.4l, 84hp.

 

We could change that to a 2 cylinder, 42hp motor and save some weight in the engine. The savings won't be half, but will be significant. 

 

The other side to the equation is that the generator required would be half the capacity as well. So some more weight is saved there.

[Wuzak]

A small range extender will have other implications as well. With only 20 or 30 hp your range extender will be outside the most efficient operating points in many cases, and during for instance extended highway driving the driver may have to slow down to reduce power consumption if the battery state of charge is low.

 

For highway driving the power required is generally quite low.

 

I thought that sizing the range extender to the average highway power required, plus a little bit, would allow the EV to run directly off the range extender, allow some charging of the battery, which would be used for the periods where the range extender power is not enough. 

 

I would think that a range extender would be designed to operate at a fixed rpm point, and generate the required power. This would be its most efficient point.

Edited by Wuzak, 23 June 2016 - 00:17.

[Wuzak]

Aren't all hybrids just EVs with range extenders, only given a fancy name to fool the public?

 

I think most are petrol/diesel cars with electric assistance.

 

That is, the engine drives the wheels most of the time, but can be assisted by an electric motor or, in some cases, the vehicle can be driven by the electric motors alone for short distances.

 

An EV with a range extender I think of a car which is only driven by electric motors, where the range extender petrol/diesel engine cannot drive the wheels directly.

[desmo]

Yes, I had made the same distinction whether rightly or wrongly. It makes sense.

[Greg Locock]

Strictly speaking you are describing a series hybrid, where the only way to power the wheels is electric. That is in contrast to the parallel architecture used by some mild hybrids, or series/parallel as used by most of the modern hybrids, which was identified as the best architecture in the early 1970s by TRW. Dr. Baruch Berman, Dr. George H. Gelb and Dr. Neal A. Richardson. They even built a car to demonstrate it. Strictly speaking the Volt is series/parallel, since in one narrow operating range it operates as a parallel hybrid, but most of the time it is series.

 

However due to GMs rather annoying marketing we aren't allowed to call the Volt a PHEV, instead it is supposed to be an EREV and by default that name seems to have got attached to all series hybrids.

[imaginesix]

To repeat what Greg just said, "EV" designates the fuel type, in this case electricity. As opposed to gas, diesel, or whatever. Add a range extender, and it's no longer an EV, it's a hybrid. The only way you could get a range extended EV would be by adding extra battery capacity, as Tesla offers.

 

The range extenders described by the OP are series hybrids, where all power is eventually routed through the batteries to the electric motors. As far as I know they always have a charging plug. The more common hybrids are the parallel hybrids that use either the combustion engine and/or electric motor to drive the wheels. They come with or without charging plugs, so that isn't really a distinguishing factor between the two types of hybrids.

 

Now that we know that, we can answer the original questions

 

The range extended electric-driven cars are not EVs, they are as you put it "petrol vehicles with electric transmissions". AKA series hybrids.

 

As for the ideal combination of engine power/battery size, that's an improper equivalency as one develops power and the other stores energy. The correct approach would be to determine what performance is desired and work your way from their. In practical terms, it seems that battery cost is the biggest constraint for much larger dependency on electricity for motive power, judging by the price of various hybrids and EVs versus their battery range.

[Greg Locock]

Oh, and for the pendants, yes you could use flywheels or hydraulics or air or any number of less plausible options, not just electricity. 

[scolbourne]

Does anyone know the difference in efficiency when comparing series  driven vehicles like the Volt (engine charges battery ,to power motors for wheels) with something like the Prius which can drive the wheels directly from the engine ?

 

I would guess the Prius should come out much better once the initial EV distance has been taken out of the equation.

[Greg Locock]

Good question. Our solar car wheel motors had an optimum efficiency of 98.4%, so if you used one as a gen and the other as a wheel motor you'd be lucky to see 97% overall, at best.

 

Each gear tooth interface loses you about 2%, and conventional diffs are a whole lot worse than that, so the Prius drivetrain is probably 92% or so. Priuschat seem to think 87%, but that includes some electrical losses, the Prius driveline uses motors all the time (sometimes just stationary). Bob Wilson works back to 93% mechanical, http://priuschat.com...-60-mph.115094/

 

Incidentally when discussing the Volt it may be very confusing as  the second generation has some significant differences to the first production model. Gen 2 always uses an epicyclic between the motors and the wheels, so I'd guess 93% at best.

 

It is very interetsting to see how much hard won engine efficiency is trashed in the driveline.

 

Incidentally, re diffs, at best 85% efficient, and a lot worse round town.

[Wuzak]

How much variation in the thermal efficiency over the operating range of the ICE in the Prius?

 

And it seems that the Volt engine doesn't run at constant speed either.

 

http://gm-volt.com/f...hp/t-18037.html

 

The OP in that thread is suggesting that the ICE run at peak efficiency constantly (2200rpm) in certain modes. He suggests that:

1. If the demand would be equal than what the ICE would provide at 2200 RPM, than the battery would be at the constant SOC. 
2. If the required power would be higher than what the ICE could provide at 2200 RPMs, the rest of the electric power would come out of the battery, resulting in a slow decrease of SOC.
3. If the required power would be lowert than what the ICE could provide at 2200 RPMs, the ICE generator would simply be turned off and the car would be driving on pure battery power.
4. In no case would the ICE replenish the battery (like MM does)

I would suggest that in situation 3 the engine would remain running directly powering the motors with any surplus power being used to replenish the battery. Only after the battery reach a suitable state of charge (probably close to 100%) would the ICE be stopped.

[Greg Locock]

I do have a bsfc map for the first gen Prius overlaid with the operating band of the engine. Basically it doesn't idle. You get 1500 rpm or more,depending on the demand power. At1500 it is about 30% efficient,rising to a maximum of 42% and then falling at higher rpm.

[manolis]

Hello all.

With an engine-less and transmission-less base-car-structure having in each wheel a, say, 20kW electric motor and the wiring / circuitry to a central box, various electric cars could be made.

With a lot of batteries somewhere in the car, the base-car-structure turns to a plug-in electric.

With batteries and a small REM (Range Extender Module) it turns to a plug-in electric wherein a small internal combustion engine is used in emergency (say, when the battery is empty).

With fewer batteries and a bigger REM, the car is less plug-in and more internal-combustion-engine dependent.

Without batteries, but with a big REM, the car is closer to a conventional car but rid of gearbox, of transmission, of differentials, of drive shafts, of CVJ’s etc.


A control box / program is the mind / brain of the car.


Reasonably, soon the carmakers will provide such base-car-structures. Initially the customer will have to pick his desirable battery pack and his desirable REM from the same carmaker.
Latter, the carmakers will agree to make compatible base-car-structures so that the customer will be able to combine any compatible battery pack and any compatible REM from the market with his base-car-structure.

Say like what happens with the Desktop computers wherein the customer picks his favorite compatible subunits (video card, DVD, hard disk etc) to complete the basic structure.


It seems that the REM’s will become more and more important in the auto industry.

The REM will be the heart of the car.

The REM comprises one or more electric generators and an internal combustion engine driving the electric generator(s).

The characteristics and design of the internal combustion engine of a REM are substantially different than those of a conventional internal combustion engine of a car.


For instance,
think of a substantially over-square design (like, say, the Ducati Panigale 1299: 60.8mm stroke, 116mm bore) wherein the crankshaft is small relative to the cylinder head.

What if instead of combining two big cylinder heads with a common (and compact) crankshaft / crankcase (as happens in the Ducati Panigale), a unique cylinder head were combined with two crankshafts?

Here is a 4-stroke even-firing Opposed-Piston PatRoVa rotary valve engine, wherein a unique rotary valve serves two cylinders:



Think of a REM having an electric generator at each crankshaft of the above engine.

Or think of the balancing / vibration-free-quality of such a solution (perfectly balanced).

Or think how much the crankshaft balance webs can be reduced without affecting the balancing quality.

Or think about the NVH properties of such a unit; without poppet valves to hit on their seats, the engine runs quieter; without free inertia vibrations the engine runs smoother; without combustion vibrations the overall NVH improves.

Or think how much simpler the intake and exhaust plenums can be made. Etc.


Thanks
Manolis Pattakos

[imaginesix]

To repeat what Greg just said, "EV" designates the fuel type, in this case electricity. As opposed to gas, diesel, or whatever. Add a range extender, and it's no longer an EV, it's a hybrid. The only way you could get a range extended EV would be by adding extra battery capacity, as Tesla offers.

 

The range extenders described by the OP are series hybrids, where all power is eventually routed through the batteries to the electric motors. As far as I know they always have a charging plug. The more common hybrids are the parallel hybrids that use either the combustion engine and/or electric motor to drive the wheels. They come with or without charging plugs, so that isn't really a distinguishing factor between the two types of hybrids.

 

Now that we know that, we can answer the original questions

 

The range extended electric-driven cars are not EVs, they are as you put it "petrol vehicles with electric transmissions". AKA series hybrids.

 

As for the ideal combination of engine power/battery size, that's an improper equivalency as one develops power and the other stores energy. The correct approach would be to determine what performance is desired and work your way from their. In practical terms, it seems that battery cost is the biggest constraint for much larger dependency on electricity for motive power, judging by the price of various hybrids and EVs versus their battery range.

This issue of nomenclature for EVs, hybrids, seems to have stuck in my craw as I've noticed different application of the words in common usage.

 

'EV' in non-technical lingo seems to be used to refer to any car that has a charging plug. I guess the notion is that if they contain so much battery capacity that they justify a plug, then they can be used to meaningfully replace some gas-powered trips. They're also more expensive, and subject to more gov't rebates.

 

In fact I tried to find a legal definition of 'EV' in my province (Ontario) but there seems to simply be a list of vehicles that are eligible for the rebate. As best I can tell, they follow the principle I just described and define all cars with a charging plug as "eligible EVs".

 

EDIT:

Confirmed: "An electric vehicle (EV) is any vehicle that is partially or entirely powered by electricity and plugs in to recharge." They then go on to distinguish BEVs (Battery Electric Vehicles) from PHEV (Plug-in Hybrid Electric Vehicles), which I've always just called hybrids.

 

A manufacturer can't just put a charging plug on one of its cars to *charge* its standard 12V 6-cell lead acid battery and expect to be eligible for rebates, as battery capacity is figured into the calculation of the rebate amount.

Edited by imaginesix, 02 July 2016 - 05:39.