What makes cars fuel efficient?

[R.I.D.E.]

Monroe, UPS is using delivery trucks with hydraulic hybrid powertrains and has been for a year.

If you google UPS hydraulic hybrid, or EPA hydraulic hybrid. You can get volumes of information about their research and the potential for a big SUV getting 40 MPG, a sedan the size of a Taurus getting 80 MPG.

Replacement cost of electric hybrid batteries and motors (the electric motor) for a Prius is about $14,000. That is what the dealer told me when I test drove one some years ago.

The current Prius will certainly need at least one battery to reach 200K miles, the mileage that seems about average for the Civic VX's people are driving who post on this forum. Electric hybrid mileages will not stay as high as they are as wear on components reduces their efficiency. My brother bought a Prius and left it in his garage for a week, the battery went dead (12 v batt). The dealer told him he needed to drive it more often, that there was nothing wrong with the car. Hmmm, I cant park my car for a week without a dead battery!

The EPA document gives a lot of good data on accumulators, there is a lot of R&D using composites and my estimate was conservative. The UPS delivery truck uses 82 gallons of fluid in it's accumulator, but thats for a 7 ton truck not a 1 ton car. They are working with pressures of 5000 psi. The Americas cup racers use accumulators operating at 12000 PSI which would reduce the volume of the fluid by 60% with a corresponding reduction in weight.

This additional weight would be offset by reduced weight in the fuel tank. My basic calculation would require about 1 gallon per wheel motor for a full displacement acceleration event to 60 MPG with no engine powered recovery of pressure. That would be a total of 20 revolutions of each wheel in less than 5 seconds, at maximum displacement, the worst case scenario.

Charles Gray of the EPA made this statement. The hydraulic hybrid will be as revolutionary to the auto industry as the assembly line was many years ago.
He has been involved in the research for many years.

Understand I am not against electric cars. The current problems are potentially solveable, but battery capacity is a huge negative, fuel cells are nowhere near practical economically and 20 billion dollars in R&D still has us talking about ranges of 50 miles. Sure you can put several thousand laptop batteries in one and do a lot better, butis that a realistic vehicle for the common citizen?

Certainly you could retrofit one (a launch assist axle) in the rear end of a FWD car, but you would sacrifice the advantage of being able to use a smaller engine in the same vehicle. That being said if you combined the radical aerodynamics of one of this forums members cars (Basjoos, I think), with a small displacement diesel engine with turbocharging for sustained grade climbing, and the hydraulic launch capability, you would be very close to a real 100 MPG car that would hypermile itself without the driver having to be the brains of the system.

You could park your hydraulic hybrid for a year and the battery might go dead, but your pressure reserve would still be there.

regards
gary















regards
gary

[monroe74]

"If you google UPS hydraulic hybrid"

I just did. Very interesting. Thanks.

This means the public will be learning more about this kind of approach, which should make it easier for people to grasp what you're talking about.

"Certainly you could retrofit one (a launch assist axle) in the rear end of a FWD car, but you would sacrifice the advantage of being able to use a smaller engine in the same vehicle"

Good point. But I was thinking that you could create a product that is positioned for enhancing performance, not economy. If this had some success, it would be a foundation for further product and market development.

[dosco]

Originally Posted by StorminMatt

Even if steel is more expensive than it was in the past, it is still cheap in comparison to the cost of trying to reduce the amount used.

I disagree. While steel is relatively cheap (particularly in comparison to what one *could* make a car from) I can assure you that several automakers make extensive use of crash simulations to minimize the body weight while still protecting the occupants.

During the initial product design cycle, it is quite simple to use modeling and simulation to study and then optimize the car's crash performance (among other things). It's a natural extension of using a CAD system. As a matter of fact, a whole host of analyses and optimization steps take place when a car is designed.

Secondly, modeling and simulation codes are now taking advantage of parallel processing capabilities to rapidly run analysis jobs. With such parallel systems made from commodity parts, it is easy to setup a powerful system that isn't uber-expensive - the days of the kabillion-dollar Crays are largely over. Rapid compute times are the norm. The crash codes run overnight, in a week the enigneering team can have a lot of runs under their belt.

Thirdly, these codes are now setup with "templates" that allow a stress analyst (highly paid) to setup an analysis routine that can be populated and executed by junior engineers (not as highly paid). Crash analysis and optimization projects might take a month, which doesn't translate into huge dollars when amortized across a production run of cars.

Lastly, these engineers aren't sitting around with their thumbs up their keisters waiting for an analysis to complete. The guy kicks off the analysis and then works on something else.

As far as manufacturing techniques, car guys don't drastically change what they're doing - they build manufacturing considerations into their design and analysis methods. Usually when they do change, they perform a range of trade studies to figure out when the change will "pay for itself." As stupid as they may seem with some of their product offerings, when it comes to manufacturing they aren't dummies.

[R.I.D.E.]

I figured out how to resize these photos so I could post them.

This is a demonstration model, only the outer rim rotates (the part outside the shaded black mark).

You can see the three different stroke positions, foreward neutral and reverse. Look at the exposed portions of the pistons and you can see the different displacements when the journal is in foreward or reverse. In neutral the piston positions are the same.

In neutral this is a spinning wheel with no displacement changes. In foreward pressure drives the rim in on rotational direction, while in reverse it is driven in the opposite direction.

Thats it, the hydraulic fluid passes through ports in the center hub (obviously of a larger diameter than this simple model. The journal is externally adjustable and that same adjustment acts as a valve allowing fluid into the hub or restricting fluid from the hub (for neutral).

The journal adjustment amount controls the variable displacement which is the key to infinitely variable operation.

Use one connected to the accumulator with supply and return lines and you have just built a complete powertrain, replacing all of the powertrain components including the brake system on a conventional vehicle.

regards
gary