Why no hydrostatic transmissions on larger tractors?

[MinnesotaEric]

I'm hearing the Payloaders referred to hydraulic drive but were they not actually torque converter drive? I suppose they would be hydraulic in the true sense of the word but not hydraulic as we normally think of it.

Three hydraulic pumps. All working.

 

[npalen]

Three hydraulic pumps. All working.

So what kind of a transmission is it, Eric? If you're referring to the torque converter as a pump, I get it.

 

[Bob Rooks]

I'm hearing the Payloaders referred to hydraulic drive but were they not actually torque converter drive? I suppose they would be hydraulic in the true sense of the word but not hydraulic as we normally think of it.

Yes. Similar to the Cat Powershift three speed which is not unlike a car automatic transmission with three speeds that is shifted manually (on a larger scale).

 

[MinnesotaEric]

So what kind of a transmission is it, Eric? If you're referring to the torque converter as a pump, I get it.

I cannot speak to other OEMs, but Hough refers to their torque converter as a pump. That said, the transmission is a selected gear power shuttle with a special air brake valve that can knock the transmission into neutral and back into gear when one of the brake pedals (of the two brake pedals) is depressed and released. The most likely point of failure is the torque converter.

 

[mo1]

There is little need for heavier tractors to be maneuverable, in terms of frequent changes from forward to reverse.

Some 90% of new compact tractors are sold with Loaders.
Once tractors reach 7,000 pounds bare weight, only a few are sold with Loaders.

Instead, the improved fuel efficiency of a geared tractor is important in field use raising crops for profit.

That is not true. A 7000 pound dry weight tractor is going to be about what the smallest cabbed full-sized utility tractors weigh. Loaders are very common on tractors up to about 150-160 HP around here, which typically have a dry weight in the 12,000-14,000 pound range and some type of a powered reverser transmission. Those are the machines people use for handling large round and square bales with a loader, sometimes two at a time, and the ability to go in reverse is certainly important.

Hydrostatic transmissions are not very efficient as they have significant pumping losses. An infinitely variable transmission gives the same type of speed control but is more efficient both in fuel and with transmitted power. I foresee IVTs coming to the smaller full-sized utility tractors rather than hydrostatic drives going to larger ones for this reason. I don't see hydrostatic drives leaving smaller tractors due to price, at least not for a long time.