HST Power Consumption

[Jerry/MT]

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.

I'm a big proponent of live long learning and I certainly don't claim to know it all. I learn a lot of things on these forums that are beyond my specialty area. They make me think more critically about some of the discussions and because of my background I am more skeptical of some of the statements that people make. I'm not trying to be a smart a** . We just recieve so much disinformation from the "media" daily and these forums offer the opportunity to civily and rationally discuss problems of common interest and come to pretty darn good conclusions. And it's OK to agree to disagree! We shoudn't be stroking egos here.

I know that's way off topic but I sensed a bit of "less than" in your response. The level of education should not be a barrier to good technical discussions. In fact the less you know about a topic the more your questions you will ask that will potentially challange a lot of the more technically trained people to think more critically about technical issues.
In my working life, I really liked, more like demanded, to have the more inexperienced people in our group be involved in the more complicated problems that we worked on. They didn't bring preconcieved ideas and solutions to the discussion. They asked questions that made the senior engineers look at the issue from first principals and we often found that some key assumptions weren't not applicable to the problem at hand. So it was win win. The young guys contribution was to challenge the old guys pat answers. Worked every time. It was also a confidence builder for the young guys and a reminder to the old guys to not be complacent in their thinking.

'nuff said.

 

[slowzuki]

I'll add a point, most CUT's can't achieve a drawbar hp rating anything close to their pto hp rating (gear or hst model) since they aren't heavy enough to do so, even in 4wd and ballasted up. This means even pulling at their maximum capacity, they are only transmitting a fraction of the available hp of the engine through the hst unit, and it is only this fraction that the hst losses are occuring from, not from the entire power output of the motor.

 

[IndyIan]

I'll add a point, most CUT's can't achieve a drawbar hp rating anything close to their pto hp rating (gear or hst model) since they aren't heavy enough to do so, even in 4wd and ballasted up. This means even pulling at their maximum capacity, they are only transmitting a fraction of the available hp of the engine through the hst unit, and it is only this fraction that the hst losses are occuring from, not from the entire power output of the motor.

In mid or high range though, you can put all the HP to the ground. But how many guys are running hay or grain wagons with a tractor like mine? Not many but there are some situations where 5-10% more in driveline losses would get annoying. Kind of like towing with an underpowered car, its easier on a manual trans than an automatic.

 

[yandeereguy]

look at pulling tractors, I'll bet you won't see any hydro trannys in those. I view Hydros the same way I view jet boats vs prop.. It takes alot more Hp with a jet drive compared to prop. My old 200hp rude bass boat would wipe the floor against a 400 hp jet boat no problem...
Still for snowplowing (and alot of other tasks) HST is the way to go, but I like my gear tractor just fine, reminds me of my great grandpas oliver 60

 

[brokenot]

I'll add a point, most CUT's can't achieve a drawbar hp rating anything close to their pto hp rating (gear or hst model) since they aren't heavy enough to do so, even in 4wd and ballasted up.

You're kind of hung up on this drawbar hp rating thing. Even if an HST or a gear tractor can't achieve its "drawbar hp rating" due to a lack of available traction, that's only one possible concern or issue. You're looking at it completely from that perspective. "I only have *X* amount of available traction, so I can ultimately only use that amount of available engine power anyway..."

As posted before, on something like a CUT, under most operating circumstances, the differences probably won't add up to make enough of a difference. That certainly doesn't mean the differences aren't there. The losses in an HST system aren't "only there" under certain conditions. It doesn't matter whether we're working the machinery to its maximum "traction potential" or not. A larger percentage of the engine's power IS converted to useable work with a more efficient powertrain.

When you're going down the road in a vehicle at the posted speed limit, are you using the maximum amount of power the engine has available? Of course not. Is the weight of your vehicle and its tire size right at the *tipping point* of having enough available traction? Of course not.

But does having a lower-loss powertrain make the vehicle more efficient even though the vehicle is operating at nowhere near its "power" or "traction" potential? Of course it does.

Unless of course....we try to re-define what "efficiency" means.

 

[crazyal]

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.

Would you happen to have a similar chart for a geared machine? I've read lots here and people seam to interchange the efficiency of HST in general (if I read it right is what you posted) and then switch to the efficiency difference between gear and HST. Just looking at Kubota's numbers my 4240 is about 79.5% efficient with HST and the geared version is 82%. Also if I read that pdf right it's saying the higher the pressure the less efficient it is.

Trying to go further into how much more loss there is when the tractors are moving is fruitless. There's just too many real world variables you can't account for. For example with gear your speed is limited by the pto speed. One gear could be a little too high forcing you to use one that's a little too low, that right their is HP loss (because it's unused).

Does anyone have any real world seat of the pants use with two identical tractors, one gear and one hst, doing the same job and can say the gear tractor got the job done 10% quicker? For example if you had a one acre field and it takes you one hour to brush hog it and you have been doing it for years with your geared tractor and then one day it breaks. Your father, being nice, offers to let you use his tractor that he bought the same day as you with the same engine, same model but his is hst for the rest of the season. After a dozen times using his tractor you find that it now takes you 1 hour 6 minutes then you could assume that gear is about 6% more efficient. Everything else is just paper math that means little in the real world.

 

[jenkinsph]

While I am sure that the hydro tractor uses more fuel than the gear tractor it isn't enough to get me concerned. In my "real world" use jockeying tractors around and in between obstacles of all kinds I would bet the fuel uses would be the same. With a hydro I can do the work alot faster and time is money. I doubt that using a gear tractor for my work would save any fuel either. I have lots of jobs where I change directions several times per minute.

 

[JDgreen227]

I honestly think it would be flat out impossible to compare gear vs. hst tractors as crazyal suggests using two identical tractors..."real world, seat of the pants"...In the course of an hour, even the way the operators handle the two tractors is going to skew the results, as is the density of the field being bush hogged, the sharpness of the blades, even the friction losses of the pto shaft and gearbox on the bush hog. What if the HST has a slightly more efficient engine than the gear model because of production differences? What if the operator of the gear model has slightly slower reflexes when turning his tractor? Too many variables involved that would skew the results.

 

[SPYDERLK]

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.

The HP figure not provided is that available at the wheels. While virtually all PTOs are gear drive [often thru a hydraulically activated clutch] the power transmission to the wheels is much different in a HST. The power is transmitted hydraulically at the 1st stage rather than strictly by gear. The 1st stage, being variable, is extremely convenient, but compared to gear it is lossy. Your wheel HP is likely to be about 18vs 20+ for gear.
larry

 

[US American]

Before I bought my 4320 power reverser I had the opportunity to run a 4320 hst at the local fairgrounds. I was working an arena for a barrel race. I was disappointed in the lack of drawbar power it had.

Before I bought my tractor I consulted with a very experiencesd farmer friend and told him that 75% of my work would be ground engaging or similar. His "small" tractor was a 5225 power reverser. He said to get the reverser hands down. The local JD salesmen said the same (experienced operators themselves).

So I got the reverser and I will tell you the power to the ground is night and day different (far more powerful) than the hst. With the hst I was limited by the tractor power. With the reverser I am only limited by the bumps.

I do not regret my choice one bit. Gear is better for what I do. Hst shines when surgical precision is needed (I had a 4200 hst before and it was great when played to its strength). Gear shines when brute force is needed. There is no debate, in my opinion based on same model/similar application experience. There is a reason why they make both. No tool excels at everything. Kinda like the reason why they make rifles, shotguns, and pistols. They all have their application.