Hybrid Car – More Fun with Less Gas

40 mpg Prius vs 50 mpg European Diesel cars - Page 29

register ::  Login Password  :: Lost Password?
Posted by DH on May 8, 2006, 8:41 pm
 



function.

It wasn't always so.  Time was that Mercedes charged a premium for the gas
engines.  If I remember correctly (always a chancy thing), the -D was, for
some years, the bargain basement Mercedes and a gasoline engine was $K
upgrade (might have brought along more features).

I can't think of any particular reason why a diesel should be significantly
more expensive than a gas engine - at least not any intrinsic reason.
Doesn't it have a similar part-count and similar fabrication methods?  Those
two items should pretty much determine the cost to produce, shouldn't they?
Fixed costs divided by unit production make a difference.  If the diesels
are low-volume production, the fixed-cost per unit would be higher but I
doubt this would justify a huge price difference in the motors.  Other
supply chain overhead might also drive up the cost of the lower-volume
engine a bit.



*** Posted via a free Usenet account from http://www.teranews.com  ***

Posted by Ray O on May 9, 2006, 4:22 am
 




<snipped>

I think that the lower volume of diesel engines for many automotive
applications is what drives up the cost, plus the additional battery
capacity.  The mechanical fuel injectors used to be very expensive, modern
electronic ones are probably in line with the cost of a gas engine.
--

Ray O
(correct punctuation to reply)



Posted by Scott on May 10, 2006, 1:19 am
 

DH wrote:

"I can't think of any particular reason why a diesel should be
significantly
more expensive than a gas engine - at least not any intrinsic reason."

The high compression ratios are the main reason.  Everything is hunkier
and heavier built, from the pistons to the connecting rods and the
crankshaft, bearings and crankcase, and the fuel metering system and
injectors must also accommodate high pressures and temperatures and
vibration.  Bearings and rings tend to be more sophisticated in their
design, requiring more machining and additional parts, and the
lubrication system is more sophisticated, with even the old VW Rabbit
having piston-cooling oil showers.  More noise-deadening padding and
baffling must be employed.  And since the ignition is by compression
rather than spark, the engines are less amenable to electronic control,
reducing the beneficial impact of one of the biggest savings drivers in
automotive design today.  Emissions are more difficult to clean up,
too.  Despite what you've read on this thread, modern European
automotive diesels are plenty stinky, though I admit they are improved.


Posted by Ken on May 10, 2006, 10:38 am
 

<The high compression ratios are the main reason.  Everything is
hunkier
and heavier built, from the pistons to the connecting rods and the
crankshaft, bearings and crankcase, and the fuel metering system and
injectors must also accommodate high pressures and temperatures and
vibration. >

I think you are wrong. Both diesel and petrol engines are built to the
same tolerances and, though engine management for diesels is even more
sophisticated than petrol, the impact on cost is negligible.

The only convincing reason I know of for diesel engines being more
expensive is that a much smaller number of them are made. Thus the
development costs must be recovered from a smaller throughput.

The things you mention might call for a few extra grams of steel -
chickenfeed.

If a diesel system is produced in similar numbers to petrol you will
find little difference in cost per engine.

And I have a theory that diesel engines last longer - because their
fuel has some lubricating properties, unlike petrol.

Thus a mass-produced diesel might well yield a whole of life cost less
than the petrol equivalent.


Posted by Scott on May 11, 2006, 3:18 pm
 

"I think you are wrong. Both diesel and petrol engines are built to the
same tolerances and, though engine management for diesels is even more
sophisticated than petrol, the impact on cost is negligible."

Horse... well, feathers.

Why "think" when you can "know"?  Google is your friend.  Here, let's
look at example parts costs:

===

http://www.drivewire.com/volkswagenparts/catalog/volkswagenjettapistonandcylinder.html

Mahle Piston Set - .50mm
Volkswagen Jetta GLI Piston Set: List price, $11.03, "our price"
$59.19

Mahle Piston Set - .50mm Turbo
Volkswagen Jetta Diesel Piston Set: List price, $04.68, "our price"
$20.56

===

http://www.thepartsbin.com/repsite/volkswagen~cylinder_head_gasket~reparts.html

Volkswagen Golf III GL 4 Cyl Cylinder Head Gasket, Reinz: Your Price
$1.43

Volkswagen Jetta Diesel Cylinder Head Gasket, Reinz: Your Price $9.92

===

These are typical, and reflect significant design, construction,
material and, yes, tolerance differences (especially in the fuel
injection system, where pressures can exceed 2000 psi even in
indirect-injection configurations).  If you'd ever seen even an economy
automotive diesel engine stripped down, you'd have an appreciation for
this.  And, worldwide, diesel engines are very popular; your conjecture
about relative volumes is incorrect, though certainly they hold in the
U.S.

If you'd look instead of "thinking", you'd find nuggets such as "The
cylinder head for the [VW] turbo diesel uses a different gasket [vs.
the gas model] and is cast from a special stronger alloy. Different
materials are also used for the turbo diesel cylinder head's valves,
valve seats, and combustion pre-chambers."
[http://ep0niks.ctech.ca/vw/eva2/GE01/ch1.3.1.html ] and "Although the
forged-steel connecting rods are similar to those used in the
spark-ignition engines, the pistons are of far more robust dimensions
and are totally different in design, since they must be capable of
attaining very high compression pressures and withstanding the loads of
compression ignition. As on other Volkswagen engines, full-floating
piston pins are secured by circlips. The connecting rods for the turbo
diesel engine have greater piston pin clearances, however, and the
piston skirts are notched for clearance with the piston-cooling oil
jets." [http://ep0niks.ctech.ca/vw/eva2/GE01/ch1.3.2.html ] and "Diesel
engines and high performance gasoline engines feature an oil cooler
attached to the filter housing through which engine coolant circulates
to help moderate oil temperature."
[http://ep0niks.ctech.ca/vw/eva2/GE01/ch1.1.6.html ]

You are correct, however, regarding the lubricity of diesel fuel and
the whole-life lower cost of diesel engines, at least mechanically
(although as I've noted from my experience, the rest of the car can be
just as crappy and have just as short a life as a gasoline model!).
Much depends, of course, on the relative costs of fuel.  That varies,
even in a given location.  In the '70s diesel fuel was usually
considerably cheaper than gasoline in the U.S.  Today it generally
isn't.  In Europe today, the relative prices of the two fuels depends
mostly on regional tax policies, since taxes are a much larger
component of fuel costs there than in the U.S. (where they're still
very high compared to, say, oil company profits per gallon).

And you neglect the fact that in conventional (non-hybrid)
installations, diesel engines need all the stuff a Prius doesn't:
alternator, power steering pump, belts and followers, clutch or torque
converter, transmission, shifter and linkage, and so on-- all of which
needs maintenance, the occasional repair, and periodic replacement of
significant components.  By comparison, the hybrids need their little
planetary-gear power-split gizmo, two electric motors, and a battery.


This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread