Prius loses out to VW on Autoweek mileage test

<div class='quotetop'>QUOTE(vikingrob @ May 29 2006, 04:51 PM) [snapback]262341[/snapback]</div>

Why do you think that Diesel=VW? Toyota definetely doesn't need VW for that. They have some very fine diesels themselves that sell like hot cakes in Europe. For example, the Corolla has a diesel version that only consumes 4.8 Liter/100 km in mixed cycle (city/highway combined). Not far away from a Prius (4.3 Liter/100km). The most fuel-efficient Golf diesel is at 5.0 Liter/100km.

It sounds like a very nice idea indeed to combine a fuel-sipping small diesel engine with the advanced hybrid technology. But there might be practical complications. For example, I don't think that you can shut down and restart a diesel engine as fluently as a gasoline engine.

 

For the U.S. market, there are some problems right now for diesel hybrids - the states which comprise the biggest "green" markets mostly use the California Air Resources Board (CARB) emissions standards, which penalize diesels heavily because of the Nox output. Currently I cannot buy a new TDI in California. I must agree with those who perceive VW as having some quality issues right now, at least in the U.S. market - I have several friends and relatives who are unhappy with their VWs but thrilled with sundry Hondas, Toyotas, and even Chryslers. While not scientific sampling, such anecdotal evidence has a powerful effect on individual buyers when they are making a purchasing decision. I entertained the idea of finding a used TDI for a high-mileage commuter vehicle but discarded it when I heard from those VW owners.

Some manufacturers are preparing a new generation of cleaner diesels to possibly bring into this market after the phase-in of Ultra Low Sulpher Diesel is complete. One of the lubricity additives to offset the loss of the sulphur is biodiesel. I personally believe that it would be good for my country to maximize the use of a domestically produced energy source. I also perceive biodiesel to be a better option from a greenhouse gas perspective as well as other emissions with the exception of Nox - which I understand can be dealt with using after-treatment of the exhaust. Obviously that's not a unanimously-held opinion here. Anybody care to educate me?

I think we are a few years away, but it looks like clean diesel hybrids are coming to the American market. I have no idea whether the idle shutdown would be a showstopper, but I think that might be at least partly offset by the higher volumetric efficiency of the diesel. And there may be a way to allow shutdown in a clean-sheet design - maybe one with a very capable EV mode able to give the diesel time to warm.

Anyway, I think that one magazine article should not inspire concern. The Prius is doing extremely well in the marketplace, it is saving all of us fuel and generating extremely low emissions in the process, and for many of us represents a way to tread a little lighter on the environment. Obviously those factors were worth the cost of the car to all of us. Why worry about a single driving report? We as owners probably effect the buying decisions of those around us far more than a single issue of Autoweek. Those who revel in the results of that article may harbor a dislike of the Prius for some reason, but what is BAD about people buyng a different high-efficiency vehicle? Still better than a hog of an SUV!

Jim

 

<div class='quotetop'>QUOTE(Tideland Prius @ May 29 2006, 07:45 PM) [snapback]262389[/snapback]</div>

Perhaps, but that doesn't mean it can be easily adopted to the Prius HSD. A diesel engine gives much more resistance when spinned, so the "warp stealth" mode might not work well.

Also, frequently shutting down a modern turbo diesel is very bad for the turbo. It can easily be damaged by heat deformation because it lacks cooling at that moment. Actually, the manuals of these cars typically recommend you to have your engine run on idle for a few minutes before shutting it down, if you have put some load on the engine (e.g. highway driving). Recently however, other solutions to this problem have become available. For example, the turbo in my Volvo XC70 diesel is water cooled, and the cooling continues to run for a while after the engine has been shut down. But I'm not sure if this technology is easily scalable to a much smaller engine. Anyway, I don't think that the dynamic shutdown of the engine is the biggest saver in the Prius. I believe that the regenerative braking is more important.

Another complication might be the fact that a turbo diesel delivers its power in a much smaller band of revs/min. The combo MG1/MG2 + the planetary gear system acts like a reduction regulator, but is it flexible enough to keep the diesel engine in such a narrow range? For example, even at 180km/h, you don't want the engine to spin faster than approx. 3300 revs/min. Maybe MG2 would have to spin too fast to achieve this.

I'm sure diesel hybrids will come, but there might be some clever engineering work needed. I don't think it's just a matter of putting a turbo diesel engine in the existing HSD.

 

<div class='quotetop'>QUOTE(vtie @ May 30 2006, 04:03 AM) [snapback]262659[/snapback]</div>

Nissan diesel already sells a diesel hybrid truck in Japan, using an ultracapacitor it gets 50% better mileage than the standard diesel truck.

Diesel hybrids from mainstream manufacturers can't be that far off, as VW/Audi had the diesel hybrid Duo on sale about 10 years ago in Europe (nobody wanted it back then).

Since then, VW have put the 1.4L TDi together with a hybrid system and see about 75 mpg (US) in the Golf. It looks fairly production ready (see here for some pictures), but no word as to when we'll get it.

Peugeot and Citroen are developing diesel hybrids too, the C4 gets about 70 mpg (US). Some pictures and discussion here.

By the way, regarding the issue of stop-starting a diesel engine - there does not seem to be a problem with doing this. The Ford HyTrans delivery van uses a mild hybrid setup to allow automatic stop start of an ordinary diesel engine. On typical delivery driving runs, it leads to a cut in fuel consumption of 20%.

 

<div class='quotetop'>QUOTE(clett @ May 30 2006, 12:55 PM) [snapback]262661[/snapback]</div>

I know that many manufacturers are working on diesel hybrids (including mercedes).

But once more, I guess, a lot of confusion comes from the fact that "hybrid" is not well defined... If it's just a fact of combining a diesel engine with an electromotor (some would call this a mild hybrid), this is perhaps rather straightforward indeed. And this is perhaps what most manufacturers are looking for. But I was thinking about the concept of plugging a diesel into the advanced HSD system of the Prius (which was the original suggestion in this thread).

Shutting down the engine at a stop and restart it may not be a big problem indeed. In addition, most modern diesels will stop the fuel injection if the engine is spinning sufficiently fast and not delivering any torque. However, as every diesel driver will observe, this causes the car to decellerate quite rapidly. So, I'm not sure whether the Prius planetary gear system would be well suited for a diesel configuration, because you don't have much freedom what to do with the engine (the revs of MG2 being the limitation). Maybe a configuration with an electronic clutch would solve it.

 

A diesel hybrid would work very well even if the engine has to run all the time. Hybrids are efficient for much more than just auto-stop.

In the case of IMA, the electric motor improves acceleration which allows the engine to be scaled down to a weaker but more efficient variant. It's not great at very high speeds but it's good otherwise.

In the case of HSD, the engine can run at its optimum speed all the time, for maximum efficiency. And imagine an Atkinson-cycle diesel engine...

 

<div class='quotetop'>QUOTE(Potential Buyer @ May 30 2006, 11:00 PM) [snapback]262978[/snapback]</div>

Of course. I actually think that the dynamic shutdown of the engine only accounts for a small fraction of the fuel saving. But it has a big wow factor...

<div class='quotetop'>QUOTE(Potential Buyer @ May 30 2006, 11:00 PM) [snapback]262978[/snapback]</div>

I'm really not an expert in this, but would that be beneficial? Diesels can have a higher compression factor anyway, because of the fuel is less combustible. Especially with the common rail injection technology at extremely high pressures. Or am I wrong?

 

I disagree with your statement about babying the Prius to get good mileage. Ihave made several tripe to Newport RI from Boston in the last month driving at speeds between 75 - 80 on the highway and I commute 30 miles each way to Boston weekdays. My overall mileage for the first 4,000 miles on my 2006 Prius running synthetic oil has beem 50.5 MPG. I would assume if I wanted to baby the car I could increase this to the mid 50's, but 50MPG is good enough for me and I am able to drive the car like I would any other.

 

I drove the '06 Jetta TDI, and I did the mileage research. The car definitely drove and handled like a dream, for a diesel. But here's what it came down to, and why I went back to the Prius, and then eventually bought one: the diesel emissions-- there is no comparison here between the TDI and Prius, as we all know--and let's face it, even today, VW's reputation is not the best--read some online forums about the TDI, and many people have been left stranded out on the road, or at the dealership--when the thing just craps out, as VW's are well known to do, even brand new, for no apparent reason. All that being said, it was a very easy decision to me. Besides, I can't stand the dirty, sticky, stinky diesel pumps at the gas station--you need a HAZMAT suit on just to use the pump!

 

<div class='quotetop'>QUOTE(judibob @ Apr 22 2006, 10:52 AM) [snapback]243620[/snapback]</div>

With capability and role of the Prius ECU, I wonder if the Prius ECU is programmed with a precalculated optimal solution to the long established EPA test courses. I suspect manufacturers would like to do this with most of their cars. A full hybrid drivetrain simply expands the flexibility of power options and the role of the ECU.

Autoweek said "The Vette paced the group at 75 to 80 mph." This test reminds me of the German test of fuel efficiency at autobahn speeds. http://priuschat.com/index.php?showtopic=19900&hl=german or http://www.greencarcongress.com/2006/05/fuel_consumptio.html, http://bioage.typepad.com/.shared/image.ht...d/autobild1.png
In that test, cars that might seem overpowered, certainly at EPA test speeds, did admirably above 100 mph. Most car engines operate at an inefficiently low load most of the time. Hybrid systems enable automakers to use weaker engines that operate closer to efficient loads more of the time, by using only the battery under very low loads and using a smaller engine that operates efficiently at typical speeds. The larger engine required for passing power in non-hybrid cars is inefficiently powerful at low speeds but may be more efficient at high speeds. On the other hand, smaller engines like the 76 hp Prius engine may be operating at inefficiently high loads at 80 mph.

If I planned to drive 75 to 80 mph most of the time, personally I'd buy a Civic or a Corolla for efficiency or a Mazda3 for fun. I wouldn't want to have to calculate the fuel cost of trips to the repair shop for the Volkswagen.

 

I've no problems with 75-80 MPH and STILL get better mileage than a Civic or Corolla or Mazda3. Where does this myth of high speed in a Prius come from?

It does fine...way better than most cars out there. My opinion.

cheers,

Curt.

 

I absolutely agree that the Prius is more fuel efficient than a Mazda3, Civic, or Corolla at 80 mph. I simply don't expect the savings at high speed to compare with the savings in the city and at moderate speeds.

I expect to get 50 mpg in the Prius or 33 mpg in one of the compacts with my mixed usage. I expect to save 1,030 gallons over 100,000 miles. If I were to always drive at 75-80 mph, I'd expect 43 mpg in the Prius or 36 mpg in one of the others, saving 452 gallons. I bought the Prius expecting to save around a 1,000 gallons of gas. I wouldn't have bought it had I expected to save less than half that.

 

<div class='quotetop'>QUOTE(clett @ May 30 2006, 12:55 PM) [snapback]262661[/snapback]</div>

Kind of.... Toyota was first on the market with production diesel hybrid, sold in Japan since 2004 in an Van (probably what Nissan is using).

As to the VW, and PSA, they are research vehicles, shown to make PR's. When Autobild tested Hybrid TDI they were not impressed. When 4car tested hybrid PSA vehicle, engineers admitted they had long way to go to make it production ready - it is using manual transmission for god sakes, which means engine and motor are working completly independant from each other.

It is really a lot of PR's, rather like vaporware. Until they have product on the market, it is all vaporware.