HST Power Consumption
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Baby Grand
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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.
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MessickFarmEqu
Super Member
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.
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
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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
Super Member
Really? Do you have a link for info?
JDgreen227
Super Member
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.
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....
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
Platinum Member
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.
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.
Ummm....no. CVT simply means "continuously variable transmission". CVTs are available in many forms, mechanical ones being just one of them.
From another site:
As for this:
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
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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.
slowzuki
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To quote your saying, uhm no. Old 10-12 hp tractors could pull one bottom because they were heavy and therefore could develop adequate drawbar pull to pull a plow. Actually some really old steam tractors pulled 10 bottoms or more on just a few hp, but they didn't do it very fast.
slowzuki
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You're not quite right, many hst's when sized right spin their tires or stall the motor if you drop the loader into the ground and don't back off the pedal. The whine is proportional to the load on the hst, so if you use the low range on most hst's you can reduce the load on the hst unit and use the appropriate gearing.
If I try to drive my gear tractor into a high load situation, it will just stall out or spin, the same as an hst. I need to use a lower gear or range, just like an hst.
If I try to drive my gear tractor into a high load situation, it will just stall out or spin, the same as an hst. I need to use a lower gear or range, just like an hst.
rsewill
Veteran Member
Use the right tool for the job. For a mower I wouldn't have anything but a hydro anymore. But for row crops, a gear tractor.
k0ua
Epic Contributor
That has not been my experience with the last 2 hydro tractors I have owned, unless you were in HI maybe. In LO they will spin all 4 tires and dig to China if you say put it up against a tree or other imoveable object. My new Kioti has practically no whine at all in LO and very Little in Med.Range. My last Kubota had some.. Some of the Kubota Bx's seem to whine quite a bit. Of course if you run around in a higher range and put big loads on them they will whine more.
James K0UA
MHarryE
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The PTO power difference quoted is with the tractor standing still hooked to a dyno through the PTO. The hydro is transmitting no power but a hydro does have an additional hydraulic pump needed to charge the hydrostatic system. The piston pump in a hydro needs this oil for its control, to make up for leakage, and for cooling. The charge pump on my Kubota L5740 pumps continuously at 350 psi. The book doesn't give the flow rate but at a reasonable 4 gpm it is close to one HP. They don't publish drawbar horsepower ratings which would tell the real difference during operation but remember the hydro is in series with a gear transmission so you have the losses of gears (we estimate 3% loss per gear set) plus pump and motor. Pump and motor efficiency is dependent on pressure, displacement and oil viscosity.
radrock
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Agent Blue said:
Aw. But why would you take a good tractor and spin the tires right off of the rims? My hydro will stop when it can't make the dig. It's time to get rid of the load and come back for a second cut. The d-8 Dozer I operate does the same thing. You make to big of a cut it will stop in its tracks and it's time to pick up and get a little less of a load. There is a place for both
BeeferMan
Gold Member
There's 99% of the answer in one word. Do the same job using a geared tranny and an HST - check the temp of each. Heat coming off a transmission (or any other part of the machine) means efficiency lost as that heat energy came from fuel and isn't doing any useful work.
CJONE
Veteran Member
50 years or so ago the tech was not around or affordable to develop a system that would operate ar 5000psi and hold together. Now it is common to see systems at 6000psi and pumps to almost 7000psi. If the customer I am designing a system pulls the trigger we will start on a skid mounted pump package that can develop just shy of 7000psi and 250GPM. More and more equipment is going to Hydrostat and granted the % of loss will always be there but the gains of durability and less damage for operator error far surpass the added HP and coolers needed. If your Hydrostatic system is loud then it is either a poor design or something is wrong. Yes when they go to relief at 5k they make noise,[as to be expected] but on my Kioti the gear pump makes more noise than the stat does. 15 years ago before I started doing this I used to believe they were unreliable but when a stat system is set up correctly and filtered with good oil they will last a LONG time. Improper repair and not knowing the systems have give Hydrostats a bad rep. CJ
oldnslo
Super Member
There are also different grades of HST's.
Example: Your low end throw away HST's used on inexpensive riding mowers are far less efficient than than the HST's used on skid loaders etc. They are also doing very little work compared to skid steer. The HST used on SCUT's like the Kubota BX falls some where between these two extremes.
general rule of thumb is a good quality HST will around 85 - 90% efficient at rated load. As MrHarryE stated: all true HST's have a charge pump that is 100% pure power loss when the HST is stationary like when doing a PTO HP dyno test. This charge pump is usually sized to be around 15 -20% of full rated flow of the HST pump.
Example: Your low end throw away HST's used on inexpensive riding mowers are far less efficient than than the HST's used on skid loaders etc. They are also doing very little work compared to skid steer. The HST used on SCUT's like the Kubota BX falls some where between these two extremes.
general rule of thumb is a good quality HST will around 85 - 90% efficient at rated load. As MrHarryE stated: all true HST's have a charge pump that is 100% pure power loss when the HST is stationary like when doing a PTO HP dyno test. This charge pump is usually sized to be around 15 -20% of full rated flow of the HST pump.
