RJ285

I talked to my friend and they don't have any problems with heat. He said they don't even use an oil cooler. He couldn't go into it because of intellectual property rights, but these hydraulic transmissions I spoke of earlier and the hydrostatic transmissions found in tractors are different in a number of ways.

This is all information from him and none of this I know first hand. I have not seen a scematic for a hydrostatic transmission and therefore cannot tell you the differences between the two. Just trying to inform those here about what technology is being developed.

bhaugen

Is it more of a CVT style transmission? Because those are proving to be more and more efficient at tranfering power, and they are not a hydraulic system. John Deere has been putting them in tractors for a few years now and there are some cars coming out with them. They are a blend of mechanical and some hydraulic.

You cannot efficiently transfer power with the conventional Hydraulic motor/pump setup.

RJ285

Do hydrostatic transmissions use accumulators to store pressure?

GJTJ

Based on the posts following mine on page three, it doesn't look like anyone bothered to read the articles I linked to.

bhaugen

I did, There is a lot of Speculation and "testing", but no real world use on it yet. I could see on the Garbage truck where there is a lot of start and stop it shows potential, but there is still all that friction and heat loss. I am not sure its going to be any better/worse than electric hybrid in that situation. If you want to go out on the open road with it, I believe it will be worse milage than a conventional drivetrain.

GJTJ

Actually the fleet testing is the real world use . It seems that they are past the "speculation" or product idea phase of their development process. The testing that is going on is used to validate the gains that the engineers expect from their calculations. Once the gains are validated, the system will move one step closer to production (2008). See new links discussing two particular types of hydraulic hybrid and a third with presentation explaining both in detail.

http://www.eaton.com/EatonCom/Produc...cHLA/index.htm

http://www.eaton.com/EatonCom/Produc...ulic/index.htm

http://www.aqmd.gov/tao/conferencesw...mannSlides.pdf

The first system maintains a normal drivetrain and uses hydraulic pressure created during braking to assist in acceleration. The second system is pure hydraulic and replaces a traditional drivetrain with standard hydraulic components used for decades. The third link is a company slide show which shows real world fuel economy gains of 26% for a garbage truck using the first type of "HLA" system while the the pure hydraulic system achieved a real world gain of 45-50% on a UPS delivery truck. Don't forget the increase in brake lining life too!

Both systems above capture energy during braking and store it as energy used to accelerate the vehicle from a stop. This basically dictates that the benefit of a hybrid comes with stop and go driving cycles rather than constant speed driving such as on the highway. I believe that the electric hybrid vehicles really show their benefit in the same way. The Ford Escape hybrid has a better EPA city mileage rating than highway. I agree that a manual transmission would be more efficient than a pure hydraulic system on the highway. But obviously, in the cases outlined in the articles such as garbage, delivery, fleet, etc. the benefit of storing the braking energy outweighs the losses from the hydraulic system to provide an overall efficiency improvement and therefore a fuel savings.

Any mechanical system will have friction and therefore create heat which will be a loss of energy. Don't be too concerned though. I'm guessing that the engineers at Eaton understand the friction and heat generated by the hydraulics and have taken that into account. I'm fairly confident that they have wisely selected the correct components in their system to deal with all types of operating conditions.

bhaugen

That is all fine and dandy, but a Mechancal system is more efficient at transfering power than a hydraulic. The problem is you cannot store with a mechanical drive. They have come up with a very good well thought out system for storing energy, but I think you would be surprised at how much energy is truely lost and not captured in a pure physics sense. The parallel system would be the best all around, but the series looks to be a hydrostatic drive with an accumulator on it. I would also be concerned about cold weather. The hydraulics on my tractor don't work very well below zero I wonder how well this system will do at those temps. Don't get me wrong, what they are doing is great, but it only works for a specific driving style. Stop and go traffic/delivery. Same as where the Gas/electric hybrid shows its stuff. It will be interesting to see if it stands the test of time or if its just another system that falls to the wayside due to it being a novelty or by mechanical failures.