What makes cars fuel efficient?

[monroe74]

"WEIGHT is a bigger problem than HP"

I agree that weight is very important.

"Although HP has skyrocketed, it has really not outpaced weight by very much over the years."

I don't think that's true. I think our standards have shifted.

"170HP sounds like alot for a small car.... But a 3000 pound car needs this kind of HP just to be able to accelerate somewhat decently."

Here's an example of what I'm talking about. The Chevy Impala was (and still is) one of the best-selling cars in the US. Let's pick the 1980 model, just for the heck of it. That car weighed 3,344-3,924 lbs. The base engine had 115 hp. The optional engines had 120-155 hp.

Assuming the lightest Impala (3344 lbs) and the biggest engine (155 hp), that's 21.6 lbs/hp (and of course that's an overly generous assumption). 3000 lbs with 170 hp is 17.6 lbs/hp. That's what you're claiming is needed. But in 1980 lots of American buyers were willing to accept 21.6 lbs/hp, or something even worse than that.

A 2008 Impala weighs 3555 lbs, and has 211 hp. That's 16.8 lbs/hp. So the car weighs about the same as it did in 1980, but the stock engine is now 36% bigger (in hp) than the biggest optional engine that was offered in 1980.

Here's another interesting comparison. A stock 1980 Corvette had a 0-60 time of 7.1-7.7 seconds. The 2006 Impala has a 0-60 time of 5.7-8.4 sec. So the family sedan now has performance comparable to the 1980 Corvette.

"I think that performance/acceleration is not really the issue."

I've explained why I don't really agree. We have a problem because cars have gotten heavier, but we also have a problem because we've become greedy for hp. And cars with big motors still have relatively bad FE, even if you try to drive them efficiently and slowly.

The car companies don't have much incentive to sell small, light cars with small motors, because those cars also have smaller profits. And selling a hybrid is a lot more profitable than selling a car like a VX.

"even a VX looks sleek and aerodynamic compared to the overly tall small cars you see today"

The VX looks sleek and aerodynamic because it actually is. Its coefficient of drag is 0.32. That's pretty low.

"small cars tend to be MUCH less sleek these days than larger offerings"

I don't see any evidence of this. The new Civic and Prius (for example) are exceptionally sleek.

references:

http://auto.howstuffworks.com/1980-corvette.htm
http://auto.howstuffworks.com/chevrolet-impala23.htm
http://www.motortrend.com/roadtests/...ecs_price.html
http://www.edmunds.com/new/2008/chev...162/specs.html
http://en.wikipedia.org/wiki/Automob...g_coefficients

[VetteOwner]

dont forget those old boats were ment to be towing a camper going 80 on the interstate. While they didnt have much HP those boats had a buttload of torque.

nowadays its a virtual race to see who can get to walmart fastest, who can show off to their neighbors, and bragging rights about hp and 0-60 times, etc...

also something we haven't touched on is rim sizes, nowadays its who can have the biggest rims on your car. Back in the 80's- early 90's cars had narrow small tires. Nowadays a 12-14" rim is unheard of. The public is expecting a ride quality liek sitting on a lazyboy. Only way to do that is increase the tire size and width...Not to mention the interior layout(width, number of armrest, cupholders, etc) hell my chevette doesnt even have cup holders! had an AM only radio with ONE speaker(could get it without the radio) no ac, no power anything...Nowadays if you try to get a car without AC they look at you like your crazy...

i blame todays society really, were all expecting a Cadillac ride out of a pinto sized car, it just aint gonna happen!

[froggy81500]

I don't think cars in general have gotten heavier than what they used to be. They've gone to use a lot more lighter materials, like aluminum, plastics and composites. The difference between a complete cast iron motor and an aluminum one could be several hundred pounds.

The horsepower aspect of it goes with American culture. Its cool, hot and sexy, while econo boxes and ecofriendly cars traditionally aren't. Sure, I'd love to get back into another Mustang, but having a family, I'll stick with the two Saturn Ions we have now. If people bought vehicles that actually suited their needs and not their wants, you might actually see a different picture of vehicles on the road, and fuel costs accordingly. But as is the case with Americana, its always bigger, better, faster that sells. The automakers have known this all along, which is why fuel economy standards, the CAFE standards, hadn't increased in decades. No one will built cars that people won't buy. When you see gas hit $5/gallon just for regular 87, then you might actually see people change their minds about what they drive.

[monroe74]

"I don't think cars in general have gotten heavier than what they used to be."

It's true that certain lighter materials are used, but I think cars in general are heavier. For example, take into account that in many households, the family vehicle is now a pickup or SUV. These are obviously heavy. Minivans are popular, and heavy.

And lots of individual models have gained weight. A Civic now weighs more than an Accord used to weigh. A '77 Accord weighed about as much as my '95 VX. And it got by with 68 hp.

The original Civic (1973) weighed 1500 pounds, and had 50 hp. Civics today start at about 2600 pounds.

Makers have a large profit incentive to only sell cars loaded with toys. And buyers have been happy to go along with this.

[samandw]

I'm kinda surprised no-one has touched on the other important reason for low mpg's in modern cars: Ever tightening emissions regs.

People often equate low emissions with high efficiency, but that is simply not true. Lean burn technology like the Civic VX used is much much harder to do, due to tightening of NOX regulations.

Also, weight HAS gone up significantly in spite of the improvements in technology. Just compare the 2008 Challenger to the 1970 Challenger. The 1970 had drum brakes, steel body, cast iron V8, etc etc, and yet weighed 700-800 lbs LESS than the 2008. Safety regs and extra features are definitely a part of it, but I also wonder if modern automakers just aren't placing much value on weight reduction. . .

[dosco]

Originally Posted by samandw

Also, weight HAS gone up significantly in spite of the improvements in technology. Just compare the 2008 Challenger to the 1970 Challenger. The 1970 had drum brakes, steel body, cast iron V8, etc etc, and yet weighed 700-800 lbs LESS than the 2008. Safety regs and extra features are definitely a part of it, but I also wonder if modern automakers just aren't placing much value on weight reduction. . .

I would disagree. Cost drivers in fabrication are materials and labor. Big companies always seek to reduce costs, and thus I think the carmakers have a very strong incentive to reduce weight.

Of course balanced with this is the need to meet safety requirements.

I do know that many carmakers make extensive use of modern CAE tools to predict crash performance of new car designs. One use of the tools are optimization routines to figure out ways to reduce weight but maintain crash performance.

[froggy81500]

Originally Posted by dosco

I would disagree. Cost drivers in fabrication are materials and labor. Big companies always seek to reduce costs, and thus I think the carmakers have a very strong incentive to reduce weight.

Of course balanced with this is the need to meet safety requirements.

I do know that many carmakers make extensive use of modern CAE tools to predict crash performance of new car designs. One use of the tools are optimization routines to figure out ways to reduce weight but maintain crash performance.

It cuts both ways. Automakers will reduce costs IF people won't buy at the selling price. So long as people keep paying, there really is no incentive to reduce anything. Basic supply and demand. We keep paying they keep making. People keep buying freighter sized SUV's they'll keep building them.

[R.I.D.E.]

here is some info from the EPA hydraulic hybrid document:

Losses of energy:

Fuel conversion-engine

25.56 in-7.788 out

Powertrain

7.788 in-6.359 out

Wheel slip

6.359 in-5.507 out

at wheel losses

4.965 Aero and Rolling out
Resist Energy .0962

This is for a military HMMWV but the figures are fairly close for most vehicles

Figures for vehicles (overall averages-passenger car)
EPA city cycle
Brakes-40%
Aero drag-29%
Rolling resistance-31%

EPA highway cycle
Brakes-9%
Aero drag-62%
Rolling resistance-29%

The esitmated potential for improvements
Mild hybrid-20-40%
Full hybrid (series) with conventional engine-60-80%
Future full series (advanced engines,improved aero, LRR tires)-100-120%

They have a test vehcile that weighs 3800 pounds that gets 80 MPG.

I have spent a considerable time over the last 8 years to develop a hybrid drive system that addresses all of the issues with the exception of aerodynamics and tire rolling resistance.

As you can see from these figures the greatest room for improvement is in the engines conversion of fuel energy into output power. The most obvious improvement would be to utilize the wasted heat energy in the engine itself.

From the first figures you can see that a 1% (from negative to positive) improvement at the engine translates to a 15% improvement at the wheels. The engine is where the greatest potential improvement would be possible, and this has been the focus of most R&D, which is really sad. I say this because the 60-80% quoted improvement could be accomplished with no change in the engine.

The simplest improvement would be to use the exhaust heat to generate energy, especially when the catalist needs to operate at 900 degrees to function properly. Put a small self contained steam turbine immediately behind the cat and use the power generated to run all the accessories, including those driven by belts directly from the engine.

My focus is on the powertrain, where the extreme improvements demonstrated by radical hypermiling prove a 100 % improvement over current EPA ratings is not just possible but completely doable. The present record for an Insight is 180MPG, at an average speed in the mid 30s MPH. With a truely infinitely variable transmission (my design incorporates the components in the wheels themselves (replacing the brakes on an equal weight basis- selective 4wheel drive) you have the potential for neck snapping acceleration as well as all wheel regeneration, without sacrificing efficiency). Another major advantage is a significant reduction in per vehicle manufactured components.

In summary I am trying to describe a car that cost less to produce than anything currently available in the US market, while providing acceleration that could reach the limit of the tires ability to maintain traction with the road. That right, acceleration equal to the 4 wheel drive rally cars on dry pavement. Accleeration superior to any 2 wheel drive vehicle on the planet.
In fact the rate of acceleration could be identical to the shortest braking distance of the same vehicle, with every acceleration event reusing over 85%of the energy consumed in braking from the high speed to a stop.

After six years of rejections by 100s of organizations, 6 trips to my congressman, etc,etc,etc,etc, I finally got one person to listen and this fall Va Tech will be building a prototype that will demonstrate the design . The threshold of efficiency is 82% wheel to storage to wheel regeneration. That is about 3 times the efficiency of current electric hybrids. The current state of the art is in the low to mid 70% range.

My design is not an adaptation of anything existing, it's purpose from the beginning was to allow the techniques of hypermiling to be applied in such a way that the engine is hypermiling (no idle-no low efficiency running) while the powertrain stores the engine produced energy to be applies gradually or virtually instantly to the vehicle depending on the operators desires.

How about 0-6 in twenty revolutions of the wheels, about 120 feet. hte weight of the vehicle is relatively insignificant (not totally of course) because you are utilizing that same weight to accumulate more energy storage , every time you decelerate.

In hypermiling you must sacrifice energy to reach your higher pre coast speed, due to the exponential increase in aero drag. This system allows you to select any desired speed, and the engine only needs to run to maintain suffecient reserves of energy to provide on rapid acceleration event.

No idling
No low efficiency operation
85%+regeneration capability

Combine this with minimal weight, reduced manufacturing costs, a much simpler and more reliable powertrain, and of course every possible aero and rolling resistance refinement and you can see the potential.

The perfect machine (of course unobtainable) would get 5 TIMES the current mileage. What I see is about half of that when the potential is fully realized.

regards
gary

[GasSavers_RoadWarrior]

Hey R.I.D.E. I like the idea of flywheels too, realised how much more efficient they are than batteries. I wanna build a storage flywheel that fits in a spare tire well, that works as a homopolar motor and generator, and fit two homopolar motor/generators to the rear wheels of FWD cars (Or use the wheel rims heh) brake and it dumps energy to the flywheel, then tap it again for acceleration. Thinking of using a simple mechanical commutator modulation device for power control. Also thinking that low voltage pyroelectric generators could be added to the system and could keep the "charge" topped up on long highway runs... such that you might be able to cut the IC motor for 10 minutes in the hour, cruise off the flywheel, then let it suck up waste heat again for 50 mins. Also there's some low voltage pyroelectric-solar tech that might make enough power to keep the flywheel spinning while you're parked... i.e. park at 9 AM with 6000RPM in the flywheel and at 5pm it's still got 6000RPM to get you going, 'coz it sucked up enough sun to overcome frictional losses. Having auto vehicles though, I might be more inclined to set it up to make enough HHO to run the motor off for a short period of time at highway speed, coz that's easier than killing the motor and figuring out how to run the accessories and transmission pump. (Could make for some interesting P+G variations, like accelerate up to 70 at most efficient BSFC, flywheel brake down to 55, HHO "coast", repeat.)

[R.I.D.E.]

The simplest bidirectional path from linear inertia (vehicle motion) to storage (flywheel or accumulator) and back is your ideal goal, as long as you dont loose much energy in the storage and return cycles.

Launch assist means taking the unused wheels, like the rear in a FWD car, and replacing the brakes with hydraulic pumps that slow the car down by pressurizing an accumulator or spinning up a flywheel. Those of us who are older might remember the toy flywheel cars.

I like the sapre tire area for storage, in either a flywheel or accumulator. Accumulators are hard to beat because their efficency is in the 95%+ range. Any flywheel will eventually run out of energy, while an accumulator can store it for months with no loss. Run flat tires mean you need no spare.

Hypermiling has many similarities to a roller coaster, but if you have enough internal storage you have the ability to dampen the inertial differences in normal operation. Its like eliminating the hills (hypermileing) in the roller coaster

Its like having two guages one for speed one for pressure, you trade energy states between speed and pressure, the speedometer goes down (deceleration) while pressure rises, on acceleration it's the reverse, depleting stored pressure while accelerating the vehicle. All during a deceleration and acceleration cycle you are reusing stored energy with no need for engine power 90% of the time. The engines only job is to keep pressure reserves in between a specific minimum and maximum, unless you are climbing a steep grade for a sustained period. This is when the engine would have to work the hardest. If that requires a larger engine then the total operation time of that engine would be proportionatelly less, when full power was not needed.

Another way to think of it is to be able to toss a bungee cord out and hook it on a telephone pole to stop, then move the pole in front of you to launch yourself back to almost the same speed. Stopping by climbing a hill, then using the grade to get back to speed is exactly the same. Like the skateboarder in the U shaped track who only has to apply energy at the beginning of his run to do many cycles of the ramps.

When your storage system has the same efficiency as a conventional powertrain in the complete cycle of pressurize-store-release, you have passed the threshold where there is no trade off. Now you add an engine or electric motor (or both of course) and you can used electricity or combustible fuel without having to have two vehicles, one ofr local and one for high speed distances. The vehicle could operate on either system independently of the other .

I am hoping to get 85% but it would really be unbeatable if it could hit 90%. There are only two stages of energy conversion, which by carnots law are the minimum possible. As long as each stage is above 90 % including the storage you would be at 81% total efficiency.

The problem with an electric storage hybrid is the stages are at least 3 or more in and the same out, so the losses multiply.

This doesnt mean there is no place for an electric drive, it means that regeneration probably should not be electric. Remember when they got the astounding mileage out of the Insight, they really didn't use the electric portion of the hybrid, for this exact reason. The wheel to wheel efficiency of electric storage has too many steps and the compounding of individual losses makes it substantially less efficient.

A 500 hp hydraulic pump is not very heavy, and the present ones are good a low speeds but their efficiency dies off at high speeds. Put the pump in the wheel and it is never really high speed. It can use the same bearings as the wheel itself, and the wheel can function as a portion of the pump. With 4 pistons rotating around an offset journal set in the hub, you have a drive. If the journal is adjustable you have an infinitely variable transmission.

A launch assist regenerative axle option would have another advantage few understand. Instead of driving at 55 MPH and accelerating to hypermile, you can add the regenerative "drag" to add pressure at constant speed, and then use the "launch assist" to drive the vehicle while the engine is shut off, without changing speed. Now you are hypermiling the vehicle, with absolutely no driver imput necessary, and you are not paying the higher drag penalty of adding 10 mph to your speed. Short term capacitive storage allows you to run the engine at a higher (less fuel per hp) load, while the pressure launch allows you to use a smaller engine.

My grandfather was a fisherman who couldn't read or write. They had a Model A Ford. On Monday they put the car engine into the Chesapeake deadrise and used it to fish all week, then put the motor back in the car for weekends. Later on they could afford two motors and didn't have to switch them around.

My concept would also have a similar capability, the person who needs no more than a 50 mile range could use only electric drive, while another person with different circumstances migh use only IC drive. It depends on many circumstances.

regards
gary