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Print 53 comment(s) - last by shiftypy.. on Jan 28 at 8:51 AM

Formula XL1 can travel up to 22 miles on battery power alone

We don't usually think of the Qatar Motor Show as a place where major automotive product announcements/advances are made, but Volkswagen used the show to unveil the latest in its line of vehicles aimed at extracting the ultimate mileage out of a single gallon of gasoline.

The German company today announced its Formula XL1 concept car that makes use of a two-cylinder turbodiesel engine, hybrid electric motor (with a lithium-ion battery pack), and a seven-speed dual-clutch transmission. The Formula XL1 has enough juice from its lithium-ion pack to travel for 22 miles on battery power alone, and gets a total combined fuel efficiency rating of 260 mpg.

When the subject of gasoline electric hybrids is brought up on DailyTech, there quite often is chatter from our European readers stating that they have been getting similar -- if not better -- mileage from turbodiesel engines for years in similar vehicle types. So it's nice to see that VW is taking the best of both worlds with this new vehicle concept. 

And it's not just the turbodiesel-electric hybrid powertrain that gives the Formula XL1 its impressive fuel economy; the vehicle also makes use of lightweight carbon fiber reinforced polymers for the body panels to further reduce weight. The driver and passenger also sit in a tandem arrangement -- the passenger sits slightly aft of the driver and behind the driver's seat (think McLaren F1) -- which allows the Formula XL1's body to cut through the wind more efficiently, which also improves overall fuel efficieny. 

There is no word if or when such a vehicle will be put into production, but we're sure that there are more than a few hypermilers here in the United States that wouldn't mind getting their hands on one.



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By Suntan on 1/26/2011 12:47:53 PM , Rating: 2
I don’t want to rain on anyone’s parades, but at the same time, let’s look at some of the practical aspects of this situation without getting too bogged down in the technical minutia.

Namely, let’s have a look at this idea that 1) Diesels get good mileage, 2) hybrids get good mileage put 1+2 together and you get great mileage!

First off, let’s look at the traditional car with a spark ignition engine. One of the drawbacks of this design is that the spark engine makes relatively weak torque/power at low RPMs. This requires two things a an engine that is sufficiently large so that it can actually get the car moving, and a sufficiently complex transmission to allow the engine to stay out of the low RPM/low torque operating area as much as possible. This “overly large” engine then is normally working at a fraction of its optimum efficiency for the remainder of its working cycle once the car has finished accelerating up to speed and the engine is running at a high RPM where it normally develops much more torque. As such, most of the time you end up with much more engine than you need (and much more transmission) just to accommodate the periods where the vehicle must accelerate from a stand still. On their own, they tend to be a little cheaper than diesels (without needing the relatively expensive emissions components of a diesel) and obviously benefit (in the States anyway) from a much better public image.

Now let’s look at the diesel equipped car. Diesel engines tend to make substantially more torque at much lower RPMs than a spark engine of the same category, while the torque tends to peter out quickly as RPMs raise. This allows for a smaller engine that can be more effective at speed, but still allows a person to accelerate away from a standstill. They do tend to be more “efficient” overall than a sparker, so it isn’t just a matter of the smaller the engine the better the MPGs, but the main point is that for a given vehicle, a diesel can roughly do the job with less size, and less fuel. However, they tend to cost more for a couple of technical reasons (higher combustion pressures require more steel/aluminum, etc.) but mainly because they require expensive after treatment of their exhaust gases to meet the strict emissions requirements in the Sates (these requirements are much more lax in Europe, and as such European diesels do not get burdened with as much cost for emissions treatment.) Further, the transmission can be simpler (although it needs to have more substantial gearing in the first stage) in that it never really has to cope with the loads produced by running at higher RPMS, but it still needs a fair amount of gear ratios to keep the diesel engine running in its narrow powerband. All that said, as the TDI offerings clearly show, a carmaker can successfully make a small market out of charging more for a car that gets the better mileage when a more expensive diesel is used.

In comes the conventional hybrid (with spark engines.) The current hybrids are a complimentary design with an electric motor and a spark engine. As discussed above, the spark engine is weak at low RPM. As all these hybrid articles always point out, the electric motor works best at the low RPMs, petering out as RPMs rise. Put the two together and you can have a smaller, less thirsty engine for most operation, with the motor helping it get going at low RPMs. You also get a more uniform torque output (from both the engine and motor combined) across a broader RPM range. That allows you to have a simpler/cheaper transmission that doesn’t need a vast amount of gears to keep the drive train happy as the vehicle moves from standstill to normal speed. So even though you have to eat the cost of an added motor and battery, you recoup a bit of that in having a smaller engine and simpler transmission. That said, they still tend to cost a fair deal more than a comparable vehicle with just a spark engine, but they get more mileage while doing it.

Now let’s look at the diesel hybrid. As discussed, the diesel likes to make a lot of torque down in low RPMs… The electric motor also likes to make a lot of torque down low in the RPMs… Neither of them like to operate up in the high RPM range. So now you have a drive train that makes stump-pulling torque down in low RPMs, but quickly runs out of juice as RPMs rise. This means you still need a transmission with many gears, but now they also have to cope with substantial torque input, which does add cost. So now you have a diesel engine, which tends to cost more than its spark cousin, an extra motor/battery and a more expensive/high gear transmission that can handle prodigious torque. Those three components add up to a lot of cost that is hard to balance out, even with high MPG numbers. People would likely have a severe case of sticker shock if they saw the price of a production hybrid diesel and how much more of a premium it was over a hybrid with a traditional sparker (and that’s long after the CF skins and ceramic brakes were cut in the journey from concept to production.)

There’s a reason VW keeps making “prototype” and “concept” vehicles centered around the hybrid diesel. But I’d wager it has much less to do with looking forward to production, and a lot more to do with trying to get hybrid crazy Americans to start looking at their traditional TDI lineup.

-Suntan


By drewsup on 1/26/2011 2:46:00 PM , Rating: 2
There is one flaw in your argument, this is a 2 cylinder tdi, the cost and weight issues of a 4 cylinder do not apply.


By Suntan on 1/26/2011 4:44:28 PM , Rating: 2
This is a one-off prototype with carbon fiber panels and all the regular car show jazz. Don’t look to far into the specifics of this concept car and try to extrapolate it to what a real world diesel hybrid would look like.

In any case, the above comments hold for any model of car, 2 cyl vs 4 cyl doesn’t change the fact that hybrid spark ignition cars have a much more complimentary layout than hybrid diesel cars.

-Suntan


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