HST Power Consumption

[brokenot]

My last point is if the hst doesn't do anything better, why have it?

I never said they "don't do anything better". As for 5% losses, that's optimistic to say the least. Any manufacturer of hydrostatic pumps and hydraulic motors has information readily available that shows the efficiency of the components across a range of speeds and loads. You *might* find a sweet spot in which the coupled losses of the pump and motor total 5%, but it most certainly will not be across the entire range of operation. And if we need to find such a "sweet spot" in the range of load and operation in order to *support* an argument about how efficient they are, then how relevant to an "efficiency comparison" discussion is that?

You don't need to rev it up if you have a 10 hp motor, it will happily chug at low rpm if the hst and aux gear box are sized right.

Once again, visit a manufacturer's website. Design a machine in your head or on paper, and come up with a pump you feel will be appropriate. (This is what equipment manufacturers do.) Now, see if the pump you have chosen, (based upon what it's capable of delivering to do the job you want it to do), has a recommended set of parameters its supposed to operate in. There WILL be a spec for an rpm range. And "sizing" the hydrostatic pump "right" need to take that into account. Minimum rpm is one of the most important considerations, but the possibility of overspeeding shouldn't be ignored either.

Do you understand the concept of drawbar hp and that it is limited by the weight of the tractor?

Yes I do. This thread topic though is about HST power consumption, and it simply cannot be argued that HST is as efficient at transferring available engine hp into useful work. Do the losses in a specific application make HST impractical? Probably not....never said they did. But that doesn't change the fact that they're less efficient. And in many applications that "built-in" inefficiency is made up for by up-sizing the powerplant.

I agree, a single stage roller chain drive at low speeds, is extremely efficient, one of the most efficient actually. Doesn't really have a place in the conversation about tractors.

I didn't *just* mention chains. There are also belts and gears. ANY of those simple things will transfer power more efficiently from the engine into useable work.

Unless we conveniently re-define what "efficiency" is, HST is less efficient. Debating it on a forum is hardly necessary when we can visit websites from manufacturers with hard numbers. Applications in which HST is not chosen, is NOT completely due to the cost. It's ridiculous to say that it is.

Some of these discussions kind of swerve into a ditch. Owners with *this* brand or *that* brand of something, or that have chosen *this* type of equipment over *that* type, seem to find it necessary to convince others that what they've chosen is the way to go. I don't understand it myself, it's not as if something I own is less satisfying to me if someone else has chosen something different to use....

 

[JDgreen227]

This discussion has turned "religious", and has strayed far from the OP's question, which had to do with why HST used more power.

As for the best choice in a piece of equipment, that depends on what you're doing. If you're going to run a tractor for long periods of time at constant speed then geared makes sense as even a gain of a couple percent in efficiency is worth while. If you're going to do shuttle type operations then Fwd/Rev using a single pedal makes sense. The tractors I use for haying are geared, never felt the need for anything else. The bobcat has HST w/ fwd/rev on a joystick, perfect for keeping the auger aligned when I've digging post holes. What it comes down to is the right tool for the job is the most efficient from a productivity point of view....

Excellent post and I agree with you, especially the last line. To owners like me, who almost never run at a constant speed, HST is well worth the small amount of extra power consumption. I was out mowing my smallest patch of yard last night, it's the one that has a lot of trees and obstructions so I need to change speed and direction constantly and I HATE the thought of having to do all the shifting and clutching a gear tractor would require.

 

[Redneck in training]

Let's put it this way.
Pros:
Very easy to operate even for inexperienced operator.
Brakes are rarely used.
PTO speed is independent of speed.
HST excels in many task common on hobby farms.
HST takes abuse (caused by inexperience) much better than gear.
Modern HSTs are very reliable.
Draw bar power is mute point. You will run out of traction before you run out of power.
Cons:
Hydraulic oil and filter are expensive and have to be changed regularly.
HST is less efficient than gear but not by a big margin.
Fuel consumption is marginally higher than gear.

 

[BeeferMan]

An old farmer once told me "When all you have is a hammer, everything looks like a nail."

The best thing to do is use the right tool for the job, and that implies you understand your tools and the requirements of job at hand...

[ame=http://www.youtube.com/watch?v=CwGrC0KicSo&NR=1]Hard On Equipment (Tool for the Job) - YouTube[/ame]

 

[JDgreen227]

Let's put it this way.
Pros:
Very easy to operate even for inexperienced operator.
Brakes are rarely used.
PTO speed is independent of speed.
HST excels in many task common on hobby farms.
HST takes abuse (caused by inexperience) much better than gear.
Modern HSTs are very reliable.
Draw bar power is mute point. You will run out of traction before you run out of power.
Cons:
Hydraulic oil and filter are expensive and have to be changed regularly.
HST is less efficient than gear but not by a big margin.
Fuel consumption is marginally higher than gear.

May be a dumb question and off topic but I am wondering: Does anybody have a gear tractor where it is recommended the hydraulic system fluid be changed at an interval? My Deere uses the same hydro fluid for the lifts and steering so when I change that, those systems are getting new fluid along with the transmission. I cannot find any mention in the owners manual for my tractor that mentions changing the hydraulic fluid for a gear tractor.

 

[mostly_gas]

JD I have the Ford 170 w 12X4 gear trannie. Hydraulics/rear axle is on a 300 hour change interval.

 

[Redneck in training]

May be a dumb question and off topic but I am wondering: Does anybody have a gear tractor where it is recommended the hydraulic system fluid be changed at an interval? My Deere uses the same hydro fluid for the lifts and steering so when I change that, those systems are getting new fluid along with the transmission. I cannot find any mention in the owners manual for my tractor that mentions changing the hydraulic fluid for a gear tractor.

I guess there is an interval for a change but I have no clue what it can be.

Typical time between changes for HST is 300 hours. There is about 10 gal of hydraulic fluid.

 

[k0ua]

May be a dumb question and off topic but I am wondering: Does anybody have a gear tractor where it is recommended the hydraulic system fluid be changed at an interval? My Deere uses the same hydro fluid for the lifts and steering so when I change that, those systems are getting new fluid along with the transmission. I cannot find any mention in the owners manual for my tractor that mentions changing the hydraulic fluid for a gear tractor.

My last 3 tractors the change interval for transmission/ hydraulic fluid is the same for gear or Hydrostat, no difference between the two. Just the extra expense of the Hydrostat filter (fairly expensive filter) Hydraulic fluid and transmission fluid is all the same..there is only one fluid. with the exception of the front axle/differential which is independent.

James K0UA

 

[JDgreen227]

I guess there is an interval for a change but I have no clue what it can be.

Typical time between changes for HST is 300 hours. There is about 10 gal of hydraulic fluid.

Deere recommends a 50 hour break in fluid change for my tractor, replace both filters for the system and all the hydraulic fluid, and replace both filters again at 200 hours, then at 400 hours replace filters and all hydraulic fluid.

AND I AM WRONG (BADLY WRONG) that my manual says nothing about changing fluid and filters on the gear transmission models, because it does say these service intervals apply to both gear and hydro models, the only difference is the amount of fluid you add after draining.

Redneck, you stated in an earlier post that hydro fluid and filters are expensive (for a HST) and yes they are, but in my case if the same service is required for both gear and HST models of the tractor that doesn't really add to the cost of HST maintenance vs gear maintenance.

BTW, my salesguy told me when I was at the dealership picking up my 50 hour break in filters and fluid, that he thought Deere's recommendation of changing them at 200 and 400 hour intervals was a lot of crap and to run mine 500 hours until the next fluid and filter change. I did, and the fluid I drained at 500 hours looked perfectly clean and the suction screen had no debris on it at all.

 

[Redneck in training]

Deere recommends a 50 hour break in fluid change for my tractor, replace both filters for the system and all the hydraulic fluid, and replace both filters again at 200 hours, then at 400 hours replace filters and all hydraulic fluid.

AND I AM WRONG (BADLY WRONG) that my manual says nothing about changing fluid and filters on the gear transmission models, because it does say these service intervals apply to both gear and hydro models, the only difference is the amount of fluid you add after draining.

Redneck, you stated in an earlier post that hydro fluid and filters are expensive (for a HST) and yes they are, but in my case if the same service is required for both gear and HST models of the tractor that doesn't really add to the cost of HST maintenance vs gear maintenance.

BTW, my sales guy told me when I was at the dealership picking up my 50 hour break in filters and fluid, that he thought Deere's recommendation of changing them at 200 and 400 hour intervals was a lot of crap and to run mine 500 hours until the next fluid and filter change. I did, and the fluid I drained at 500 hours looked perfectly clean and the suction screen had no debris on it at all.

My guess is the oil lasts much longer than manufacturer recommends. Manufacturer recommendation is apparently for worst scenario case. Our Grasshopper ZT has 1000 hours hydraulic oil change interval. Nevertheless I follow manufacturer recommendation.

 

[MHarryE]

If I uploaded this file correctly, it is a spreadsheet of real hydro numbers from the premium hydrostatic drive from one of the largest suppliers of hydros in the world. They ran the numbers for me for a proposed drive for a 27.5 ton machine. This system has a 6,000 psi top pressure which is higher than I have seen in any CUT - this is the high end series of hydros from this manufacturer and has better efficiency than most. the forst section is for the pump. Note that overall efficiency for the pump is at best 86.4%and can be as low as 78.9%. Then comes the motor. At best it is 93.1% and can be as low as 65.3%. Listed are normal operating conditions - I am sure there are conditions where things will be tougher.

Overall system, pump and motor together, therefore is 80% at best (max grade full displacement both pump and motor), 52% at worst (roading, minimum displacement for the motor, maximum displacement for the pump). This is before the final drive gearset.

Some people have thrown out numbers showing as high as 95% efficiency. Dream on. These are real world numbers. This particular class machine in the past used to have sliding gear transmissions, then switched to shuttle shift transmissions because it is a continuous back and forth operating machine. Now they are all hydros despite the loss of efficiency of the drivetrain because smooth operation is vital.

 

[schmism]

If I uploaded this file correctly, it is a spreadsheet of real hydro numbers from the premium hydrostatic drive

Pay attention peeps!

As an engineer working at Caterpillar right now in the building that actually does the testing for cats hydrualic pumps.

Those results, are the same type of results we list when testing pumps. IE i can look at that data and tell its the real deal, it wasnt just taken by billybob mechanic with a few pressure guages on some ports.

 

[JDgreen227]

Pay attention peeps!

As an engineer working at Caterpillar right now in the building that actually does the testing for cats hydrualic pumps.

Those results, are the same type of results we list when testing pumps. IE i can look at that data and tell its the real deal, it wasnt just taken by billybob mechanic with a few pressure guages on some ports.

I am just a retired old fart with a high school education, and I simply cannot fathom just how a spec chart for a 27.5 ton machine means anything in my real world situation where my 1.5 ton CUT only loses (according to Deere) 1 PTO hp going from gear drive to hydro drive. Not to belittle either yours or MHarryE's contributions, no offense meant to either of you.

 

[jenkinsph]

I am just a retired old fart with a high school education, and I simply cannot fathom just how a spec chart for a 27.5 ton machine means anything in my real world situation where my 1.5 ton CUT only loses (according to Deere) 1 PTO hp going from gear drive to hydro drive. Not to belittle either yours or MHarryE's contributions, no offense meant to either of you.

The reason your CUT only shows a loss of 1 hp is because the pto measurements are made with the machine parked. If it were moving up an incline at say 6mph running a brush hog it would lose alot more. That said I will gladly pay for more fuel for the convenience of an ehydro tranny.

 

[schmism]

That said I will gladly pay for more fuel for the convenience of an ehydro tranny.

For the record, I love my hydro and wouldnt change it for anything for the size tractor i have.

For those of you who think hydros are out of there element in tractors, all caterpillar wheel loaders smaller than a 938, are hydro exclusively now.

 

[schmism]

If it were moving up an incline at say 6mph running a brush hog it would lose alot more.

I can attest to this. There are some short STEEP hills on my new property that i can drive up in 4wd in med range at 2400rpm and i can hear the motor bog as i near the top and crest the hill.

If i try to drive up the same hill while running my 72" MMM (ie while im cutting grass) i stall out about half way up, unable to generate enough power even at high idle.

 

[JDgreen227]

I can attest to this. There are some short STEEP hills on my new property that i can drive up in 4wd in med range at 2400rpm and i can hear the motor bog as i near the top and crest the hill.

If i try to drive up the same hill while running my 72" MMM (ie while im cutting grass) i stall out about half way up, unable to generate enough power even at high idle.

Would be very interesting to see just how a comparable tractor and MMM like yours BUT with a gear tranny performed at same rpm and ground speed in the latter situation....bet the gear tractor would stall out also. BTW, what rpm is "high idle"?

 

[jenkinsph]

Would be very interesting to see just how a comparable tractor and MMM like yours BUT with a gear tranny performed at same rpm and ground speed in the latter situation....bet the gear tractor would stall out also. BTW, what rpm is "high idle"?

Maybe maybe not lots of variables, a gear tractor would be able to handle a slightly steeper grade at the same engine load compared to a hst.

One reason I increased the hp size when buying the 4520 was recognizing the 110 tlb with 43hp wasn't quite enough. Had a chance to buy a new 4320 cab tractor from the dealer and decided to move up to the 4520 for the extra power. I feel I made a good choice and tractors are relatively low powered machines any way, if you expect to move faster you would need double the hp.

 

[Jerry/MT]

I am just a retired old fart with a high school education, and I simply cannot fathom just how a spec chart for a 27.5 ton machine means anything in my real world situation where my 1.5 ton CUT only loses (according to Deere) 1 PTO hp going from gear drive to hydro drive. Not to belittle either yours or MHarryE's contributions, no offense meant to either of you.

If anything, the results for a 27.5 ton machine are optimistic relative to a 1.5 ton machine justdue to scaling laws. What I'm saying is the results for a CUT type machine will be even worse efficiency then the numbers quoted for big machinery in the table above.

Respectfully, I think you have misunderstood what the 1 pto hp difference really means.


from a retired aircraft propulsion engineer

 

[JDgreen227]

If anything, the results for a 27.5 ton machine are optimistic relative to a 1.5 ton machine justdue to scaling laws. What I'm saying is the results for a CUT type machine will be even worse efficiency then the numbers quoted for big machinery in the table above.

Respectfully, I think you have misunderstood what the 1 pto hp difference really means.


from a retired aircraft propulsion engineer

Thanks for your input, I stated I was just a high school graduate and therefore know little about engineering in general. I personally find this thread very informative and wish I could contribute more.