HST Power Consumption

[Mark Page]

Why do HSTs consume so much power? I would think a geared trans would use more given the gears meshing.

[Baby Grand]

A properly designed gear system is the most efficient power transmission system available in terms of getting hp from point A to point B. Everything else is "lossy" in comparison. This is one of the reasons gear systems are still around, despite their cost of manufacture.

[MessickFarmEqu]

because your pumping fluid though tiny ports in an HST motor. Lots of restriction and heat.

I see your in MD. We do an open house @ Abbottstown, PA every year where they do service schools that show you how an HST works with torn down equipment.

[Baby Grand]

because your pumping fluid though tiny ports in an HST motor. Lots of restriction and heat.

I see your in MD. We do an open house @ Abbottstown, PA every year where they do service schools that show you how an HST works with torn down equipment.

That sounds like a very worthwhile way to spend a day - I would imagine just from the viewpoint of stressing the need for proper lubrication products, cleanliness and maintenance. There's nothing like hardware from a dirty teardown to demonstrate what can go wrong if you neglect proper maintenance or otherwise abuse equipment.

[CompactTractorFan]

We do an open house @ Abbottstown, PA every year where they do service schools that show you how an HST works with torn down equipment.

Really? Do you have a link for info?

[JDgreen227]

Why do HSTs consume so much power? I would think a geared trans would use more given the gears meshing.

A geared transmission has practically no slippage and although the gears meshing do have friction, so does a hydro and the hydro has far more slippage. My deere 4210 develops 28 gross hp, 23 pto hp with a manual transmission, and 22 pto hp with the hydro. When you say HSTs consume so much power, I don't know what tractors you are referring to. As for me, one hp difference at the pto on mine seems very low.

[brokenot]

A couple of years ago I was visiting back and forth with a guy online that was making some prototype hydrostatic vehicles for commuters. He'd thought he had stumbled upon the Holy Grail of vehicle transmissions, because the hydrostatic drives were infinitely variable, and as a result they could take advantage of the narrow "power band" of smallish diesel engines.

He matter-of-factly stated that CVTs were the most efficient types of transmissions available. What he failed to notice, were all of the inefficiencies of hydrostatic propulsion. Pumps have a finite amount of efficiency, and they send the fluid on to a hydraulic motor which has all of the same caveats. Additionally, there's the heat to not only contend with, but any heat built in the system is being generated at the expense of efficiency because some of the engine output has to be being used to produce that heat. If someone installs a hydrostatic system because the efficiency of a CVT is what they're after, it makes no sense. Any "efficiency" the CVT would have is offset by adding up all of the inefficiencies the individual components bring to the table.

Long story short, I simply asked him how long vehicles have been around....and how long hydros have been around. And why the oh-so-obvious hydraulically-driven vehicle wasn't already on the showroom floors 50 years ago or so....

[charleyfarmall]

CVT is not HST.

CVT is a mechanical transmission and is pretty efficient. It is as close to an infinitely variable geared transmission as you can get because that's basically what it is.

Although HST can be considered a form of CVT there is generally a distinction between the two as the HST is a hydraulic pump powering a hydraulic motor to provide continuously variable speeds. The conversion of mechanical energy to hydraulic pressure is what generates the heat and therefore the 1 to 1-1.5 hp loss in the HST.


It's a minimal loss so while he argument that gears put more power to the ground is technically true, the practical argument is pointless.

Spend some serious time on an HST, not just a demo or an hour or two. Then go back to a geared tractor and you'll appreciate just what an advantage HST really is. I have geared and HST tractors from small to Ag. sized. I get along fine with a hydraulic shuttle Ag tractor, but it it was an HST it would be even better.

[brokenot]

CVT is not HST

Ummm....no. CVT simply means "continuously variable transmission". CVTs are available in many forms, mechanical ones being just one of them.

From another site:

Hydrostatic CVTs:

Hydrostatic transmissions use a variable displacement pump and a hydraulic motor. All power is transmitted by hydraulic fluid. These types can generally transmit more torque, but can be sensitive to contamination. Some designs are also very expensive. However, they have the advantage that the hydraulic motor can be mounted directly to the wheel hub, allowing a more flexible suspension system and eliminating efficiency losses from friction in the drive shaft and differential components. This type of transmission is relatively easy to use because all forward and reverse speeds can be accessed using a single lever.

As for this:

It's a minimal loss so while he argument that gears put more power to the ground is technically true, the practical argument is pointless.

I think it all depends on your perspective really. While nobody can argue the ease of use of a hydro, it's silly to say "the practical argument is pointless". On some equipment, there's probably not much to gain or lose by comparing efficiencies and power losses. On the other hand, compare things like lawn and garden equipment available now in comparison to what was on the market and common years ago. Nowadays manufacturers will tell you, (and sell you), a riding tractor and claim that the 20 hp engine under the hood is "necessary" to get the job done. Then you turn the page in the sales brochure and see the available attachments for the particular model you're looking at. Tiny little spring-tine rakes and yard carts.

We can go to YouTube and watch the 10-12 hp tractors built years ago pulling single bottom plows...because the all gear drive is that much more efficient.

Try a hydro? I have.

Ever tried one of these?





EDIT:

Just read your entire post. I initially replied when I saw the first line, "CVT is not HST".

[Agent Blue]

If you have ever owned a hydro you would know instantly. I had a TC45DA with a hydro. Dig the buccket in the ground or get in soft earth. The hydro will get to a point of stop and whine. My gear drive 55 will grind those big tires til there is no more clearance and do it with little effort. On the hydro I wore ear muffs because of the tranny noise, not the diesel engine. My 4110 deere sub compact with mower / loader has a hydro and it is convenient. ( Same stopage with the loader ) Same old story... you pay for convenience, one way or another.