fluid transfer transmissions

[olds88]

hey do any of you know if any of the major manufacuers are going to put this type of transmission in a production vehical any time soon? from what i have herd it is a very strong and durable consept. i also think it is curently being used in trains

[texan]

If you are talking about hydrostatic drive systems, which I just spent a good long time trying to find info on , I'm not sure how well suited they would be to use in cars. First, there is now a hydrolic pump which must be powered by something, and with the current limitation in vehicle elecrtical systems that would mean it's crank driven. Which would definitely sap some power from the motor, in addition to the inefficient nature of fluid based drive systems (we all know how automatics are less efficient than manuals, but the hydrostatic tranny is even worse than an auto). So right off the bat you take a big hit in efficiency and power transmission, of course having an infinitely variable drive ratio would make up for a good portion of that. You would now be able to hold the engine at a specific RPM point, thus allowing the engineers to focus on a very small range of ultra efficient power production from the motor (in contrast to current engine tuning).

Another problem would likely be noise, at current the only thing these transmissions are used on are commercial vehicles were NVH levels are not an issue. I suspect a hydrolic pump and motor would make considerable noise at low speeds, possibly this is another reason why you don't see them in anything else.

Finally, the newer CVT transmission designs which are direct couplers adress all these points. They can infinitely vary transmission ratio wihtout the big hit in efficiency of possibly NVH the hydrostatic has. Furthermore, the newest CVT's being designed are capable of handling much larger torque outputs without breaking, so there's one more thing the hydrostatic doesn't possess as an advantage. Designs like Audi's Multitronic CVT and Nissan's Extroid CVT show pretty clearly which way the manufacturers are leaning, we may soon have CVT's in all our cars, but I don't think we'll be seeing any hydrostatic tranmissions.

[olds88]

well all a hydrostatic transmission is basicly a groupe of touqe converter as for the inificentsy problem could be easaly fixed with simle lockup clutch like in a modern touqe converter. but thanks for the info and i did read your last post on cvts

[Hudson]

I'm currently driving a Honda Civic HX coupe. It has got to be one of the best automatic-transmissioned cars in its class. It's quiet and VERY smooth. The only complaints I have are the relative lack of power from a stop and the high-revving when coasting down a long hill. Other than that, it's great.

By the way, the HX has a CVT.