HST Power Consumption

[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.