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HST and PTO HP

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2005-12-11          120880


Can anyone tell me why there is such a large difference in loss of PTO HP with hydrostatic drive? Is there a large difference in the hydrostatic pumps? For example~30HP tractors; Kubota L3130 8.1HP, L2800-6.5HP, B7800-8.0HP; JD 4210-6HP, 3120-7.5 HP; NH/IH -TC29DA-5.4HP, MF 1528 -6HP; Kioti CK30-8HP; CubCadet 6228 7HP. From the lowest to the highest is 2.7 HP.




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Murf
Join Date: Dec 1999
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2005-12-12          120892


There is a fair amount of parasitic losses with any HST system, that then has a 'trickle down' effect on the rest of the system, PTO included.

Different manufacturers also rate their units differently as we already know, when it gets to HST's it gets even more convoluted. Some advertise "theoretical" power outputs, some bench-tested engines & TX's, but with the pump idling in neutral, which is still not really a true measure either.

I've even seen examples where a particular engine, including like spec. numbers, are rated differently in various applications.

Best of luck. ....


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DRankin
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2005-12-12          120898


This is what I kept yelling about when I had an RTV 900.

I figured that thing had about 9 HP by the time it got to the wheels. You can get away with that in a tractor but not in a unit that is also designed to achieve 25 mph top speed.

I wish someone with a dynometer(Sp?) would put some popular models to the test and tell the rest of us what actually gets to the ground. ....


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Chief
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2005-12-12          120905


I agree with the above. From what I have observed and this is just my personal observation/theory/speculation.......the HST system does create parasitic hp loss with respect to pto hp output but I think the amount of hp loss is dependent upon how much of a load is placed on the HST sytem. The only time I have seen the engine struggle to maintain rpm is when I have place a large load or resistance on the HST system. Otherwise I have not noticed much if any hp loss running implements such as my pto tiller. My thinking is that the HST consumes a variable amount of pto hp dependent upon how much demand for power is placed upon the HST system. I suspect the pto hp losses specified by each manufacturer is arrived at a little differently and more than likely a worst case max. hp. loss. ....


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Peters
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2005-12-12          120906


The stats are all for similar sized tractors and HST. You have Kubota with 2.5 HP difference with a similar engine and HST? Deere has a 1.5 HP difference. Remember 30 HP so you are talking a difference of near 10% and 5% loss of total HP by single companies. You would hope they would measure the HP the same.
What is more confusing for me is that the more resent designs are worse than the older ones? Is there any difference in the design basics? ....


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Murf
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2005-12-12          120910


I think the differences between the older stuff and the newer designs has more to do with the marketing department than the engineering people.

;-> ....


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DRankin
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2005-12-12          120911


In general I have noted that Kubota HST's, especially the 3 speed models, seem to suffer more loss at the PTO than than the Deere two speeds.

I don't know if the extra gearing plays into it. ....


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Peters
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2005-12-12          120930


What started me looking at this was the description of the new efficient HST pump on the Kioti CK 30 HST and the poor numbers on the PTO.
Maybe the new tractors just have larger altenators for the roll up window and the beer coolers? ....


Link:   Kioti CK30 HST

 

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Art White
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2005-12-14          121081


I've run both the two range and three in many different applications and I'll take a three range any day. As far as the new higher performance most often in many companies means better then they had before. Still might not be the highest or best but new to them! ....


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DRankin
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2005-12-14          121090


I would rather have three ranges too......

Maybe next time. ....


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Peters
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2005-12-14          121092


Art; Kioti did not have any until a few years ago. I guess it would be a bit like buying a Duramax with an Allison the first year or two.
I doubt the 3 range HST would make a difference on the PTO HP do you? ....


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Murf
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2005-12-15          121099


Any time you optimise the efficiency of the drivetrain that actually moves the tractor, you have more power left to do other things, like run the PTO.

In this case, if low range was too low, and high range made it lug, yes, running in the middle range would certainly render more PTO HP, assuming travel speed didn't change.

Best of luck. ....


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kthompson
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2005-12-15          121103


Realizing I know very little here, a few years ago looking at different tractos this was pointed out by one salesperson. He said part of it came into how much importance "A" company placed on the hyd oil needs. Not just for the HST but also the rest of they system. The best I can remember he said something along the line with the more HP drop you are seeing more gallons per minute of capicity. I did notice at that time what he said did hold up with the companies specs being looked at.

From my experience it does seem the load placed on the HST might affect the PTO hp. Of coures anytime an engine has extra load placed on it in one area of use it has to affect the total output. If you stall your tractor with pulling, it stalls the same engine powering your PTO.
kt ....


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Art White
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2005-12-15          121142


To look at the hydro in a different way if you had a four speed main transmission and a high and low range and reverse. Just think to be able to adjust your ground speed with out depressing a clutch or shifting a gear and not changing your engine speed! That is were the third range comes in to fit the job or conditions better. For PTO work the hydro will always be the winner with chores like mowing or blowing driveways. It makes it more like a 4 by 3 gear for torque and power with the three range. The bulk of two range keep it about to 3 or 4 mph in low and you have to around 9 or 10 in high range. The three range is still to about 4 mph in low but the middle is good to about 7 or 8 mph! That means to be able to carry lighter loads with a flexible range of 0 mph to 8 depending on conditions with out shifting! High range is for going down the road and not in a field. ....


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DRankin
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2005-12-16          121150


Art is absolutely right. On my 4115 I have a "work" range and a "transport" range.

A middle gear would come in handy once in a while. ....


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Peters
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2005-12-16          121152


OK, Art am I understanding what you are saying?
The older HST designs only had 2 speeds one for working and the other for transport. The new designs have 3 speeds, one for transport, one for slow work and the other for faster work. The number they are publishing is for the worse case senario when considerable power is being used to push the tractor in the high gear therefore the PTO HP is lower. In reality it would be the same for the slow working range? ....


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Art White
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2005-12-17          121222


Not really correct. When you talk horsepower the test is done stationary not while the tractor is moving! The larger the pumps for the drives alone the more power you use just to run them! The second or medium range will give you nearly the power as in low to load or scrape or even to mow in! This leaves the high range a for good ground speed normally in to the teens. When IH first introduced the hydro it was nearly thirty years ago and a far more complacated system then todays and they were only a two range. I often thought that if they would have had a three range they would have sold far more then they did but they made a place on many farms but were limited to PTO and loader work for efficency. ....


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Toolin
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2005-12-17          121232


I have been following this post for a while and tend to agree with just about everything that Art has said. The way I see it, PTO horsepower is a measure of the usable horsepower available to do work with the tractor. It doesn't matter if it is gear drive or HST. The number of gears and or ranges in the transmision does not add or take away horspower, rather it gives the operator more options when choosing the most efficient ground speed for the job at hand. If you can keep a full load on the engine at all times when doing any kind of work, be it PTO or ground engaging, you will get more work done in a given amount of time. Given that a HST draws a little more power from the engine than a gear drive due to the extra oil pumps I believe that that power loss is offset by the HSTs abilty to easily adjust the ground speed on the fly to keep the engine fully loaded as conditions change. Now as to why there is a difference at all in the HP figures from advertised engine HP to PTO HP, in my opinion, that is just marketing and should never be considered when comparing one tractor to another. The only HP that matters is PTO HP as that is what you can use. Say you are looking at a tractor that is rated at 30 HP, yet it's PTO HP is 23. Since you can't really use the lost 7 HP then in reality you are looking at a 23 HP tractor. 30 HP sure sounds better though, doesn't it. As to why there is such a wide variance between these numbers when comparing similiar tractors, it could be that different engineers use different methods to arrive at those numbers. More likely it is because some systems are more eficient than others. Anyway, this is just my .02 to add to this interesting discussion. ....


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Art White
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2005-12-17          121238


It isn't that different engineers rate all things different. The PTO horsepower is done on a dyno and engines are run for gross horsepower numbers. Different systems get different results! Different pump sytems are better at one thing then another and there might be another type of parasite power loss. ....


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Peters
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2005-12-17          121240


OK. I guess I am still confused as to why the newer HST systems seem to be worse. ....


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agriman
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2005-12-19          121389


Well, In todays world all the manu- are up against the fence with engine hp. With the new Tier 2 standards for 2003 and Tier 3 for 2007 their trying to Balance HP and Emissions.

Most Manu- are meeting PTO hp by the skin of their teeth and when you throw Hydro into the mix your asking for trouble.

Some Hydro trans of the same make can vary as much as 5% from one trans to the next so, when your talking about a 30 hp tractor they have to be careful about advertised hp.

This is also the reason you can see differences in return to neutral between two tractors of the same make.

By having three gear ranges you basically have three different gear ratios to make better use of your engine torque curve.


....


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Art White
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2005-12-19          121392


I've often found when working them on steep inclines that those with the most loss on the PTO horsepwer more often then not would out perform those with less loss. Another words before the relief valves would say no more up hill! This is a test that I often like to do and you'd be suprised with the results from manufacturer to manufacturer. ....


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