HST Power Consumption

[slowzuki]

The charge pump on the Kubota must shuttle to a neutral port or something at rest, at normal temps no discernible change in load from pushing the clutch in. The engine reacts quite noticeably to the a/c clutch engaging or lighting loading on the alternator.

In -30 weather, there is quite a load though until up to temp.

 

[Mark Page]

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.

http://www.masseyferguson.us/Library/upload/MF1600-Series-Brochure.pdf
Check out page 41. Almost across the board hydros loose almost 20% of their engine horse power.

 

[Baby Grand]

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.

Exactly.
My tractor (with HST) is rated at 25.0 hp from a 32.0 hp engine .
My tractor (with gear) is rated at 26.5 hp from that same engine
(6% more PTO hp).

32.0 - 26.5 = 5.5 hp lost to heat.
32.0 - 25.0 = 7.0 hp lost to heat (27% more heat rejection).
This additional heat is created in the HST and must be convected, conducted or radiated away at a sufficient rate to prevent overheating the oil and losing film thickness under load.

 

[CJONE]

The charge pump on the Kubota must shuttle to a neutral port or something at rest, at normal temps no discernible change in load from pushing the clutch in. The engine reacts quite noticeably to the a/c clutch engaging or lighting loading on the alternator.

In -30 weather, there is quite a load though until up to temp.

No the excess flow just travels over a relief. Not much heat will develop at 300psi.CJ

 

[brokenot]

50 years or so ago the tech was not around or affordable to develop a system that would operate ar 5000psi and hold together....

Okay, so fast-forward to a couple of years ago when we were having the discussion. The guy designing /building prototypes was unable to achieve the huge gains he thought possible. Why? He was using currently available components, and was attempting to take advantage of the fuel efficiency of small diesels in a vehicle application. He'd done the "engine math" and thought that's all there was to it basically. All he had to do, was come up with a CVT to take advantage of the engine's power and efficiency by allowing the engine to stay at or near his rpm target as much as possible.

The engine lived up to its efficiency expectation, but those gains were lost due to the losses of the pumps and motors. The most modern hydrostatic components are more efficient than their counterparts from a few years ago, but what about cost?

Not "against" hydrostatic power transmission, nor am I unfamiliar with it. We have about 90 boom lifts and 30 rough terrain scissor lifts in the fleet with variable displacement pumps driving hydraulic motors. There are also 10 full-size and mini skid steers as well. The hydrostatic propulsion is user friendly and relatively trouble free, BUT....the prime mover under the hood typically carries a rating of 15-20% more than it would have to if it weren't for losses.

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

I've never thought they were unreliable, (and I'm about 25 years into it), I'm just realistic about expectations and results. If I view a manufacturer's spec sheets for components I'm considering using for a project and I see that a given pump, (for example), is 90% efficient, AND the motor I'm going to drive with it is also 90% efficient, then those losses need to be totaled up and taken into consideration. For one application, it may not matter....for another it might.

There may very well be uber-efficient systems available now or in the very near future. But how common are they, or will they be....unless the higher cost is offset enough by the increase in efficiency that the expense is justified?

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.

It's not just a "weight thing". There are also plenty of clips with walk-behind tractors plowing for us to enjoy. Look at some of the old David Bradleys, or Simplicities, or Graveleys. (There are many other brands as well.)

Here's an old Simplicity, with something like 7 hp. Watch it work with the engine running at a lower-than-the-rated-hp rpm. Now imagine this same machine, pulling this same load....via a hydrostat. This old belt-drive/gear-drive combination is just more efficient at transferring the engine power to the work that needs to be done:

Simplicity VB Garden Tractor Plowing & Disking - YouTube

Two-wheel tractors like the one in the video aren't nearly as popular as they used to be, but they are still available from companies like BCS. The method of choice for getting the power to the ground is still gear drive. Simply stated, hydrostatic components are readily available, but in order to net the same amount of work output, they'd have to drop on a 10 hp engine instead of an 8 hp if they went with a hydrostat....

 

[IndyIan]

So does anyone have any numbers or links on how much wheel hp is lost in a HST vs. geared? The 1 or 1.5hp pto loss isn't really big deal to me atleast, but I have been loading up my box blade lately and the tractor is actually throwing some heat from the hyd fluid cooler.
Anyways the tractor pulls very well and always has more power than traction in low range, so I have no complaints about the functionality of the HST and I'd probably pay more of a premium for it now that I've used it alot.

 

[Redneck in training]

My HST tractor doesn't whine even at load. No matter what I do the tractor runs out of traction before it runs out of power. I can stall the tractor only when I run the engine below 2000 rpm.

 

[slowzuki]

Its complicated, the hp loss from leakage in the pump motor combination increases with pressure but not linear, so in high range at low speed gives you high loss. On the flip side, you start losing power via friction of pumping the fluid and the movement of the parts in the hydro at high pump speeds / low pressures, ie in low range with pedal to the floor. If the charge pump runs always against the relief valve as said above, its power loss is just a function of speed.

Add them all together and the answer is, its complicated.

So does anyone have any numbers or links on how much wheel hp is lost in a HST vs. geared?

 

[slowzuki]

A) two wheel tractors aren't popular so doing things like retooling an established respected model that you have long recovered your development costs from, is only going to increase the already high price of your niche product.

B) You aren't going to notice a change of power output from hst on a 2 wheel tractor. I've got a simplicity, it had a 2 hp motor on it, it doesn't even have enough weight to put the 2 hp to the ground, it just spins out. It might have the weight to develop 1 drawbar hp in perfect conditions, but I doubt it. The hst would only have to be sized to transmit the drawbar hp, so even your very high 20% of 1 hp, is something less than 200 watts. If you plunk an 8 hp motor on there for the pto type loads of a mower etc, it becomes even less significant.

I'm not a die hard hst fan but it would make a fine transmission for powered wheels. We've got one in an old Ford 120 garden tractor from 1965 or so. Still works, wasn't a problem pulling plows etc back then either. The 12 hp Kohler would spin those tires even with chains on and 400 lb of lead in the rear weight box.

Two-wheel tractors like the one in the video aren't nearly as popular as they used to be, but they are still available from companies like BCS. The method of choice for getting the power to the ground is still gear drive. Simply stated, hydrostatic components are readily available, but in order to net the same amount of work output, they'd have to drop on a 10 hp engine instead of an 8 hp if they went with a hydrostat....

 

[brokenot]

two wheel tractors aren't popular so doing things like retooling...

Retooling would be expensive, but that alone isn't why they don't do it. Two wheel tractors are just one example I brought up because someone mentioned that the older garden tractors were capable of doing what they do because they're "heavy". Weight isn't the only issue. It's also how efficiently the engine's power is put to the ground.

You aren't going to notice a change of power output from hst on a 2 wheel tractor. I've got a simplicity, it had a 2 hp motor on it

Which is what I'm saying. Would, (or could), a 2 hp engine powered HST tractor be practical? The 2 hp non-HST example you gave that would spin its wheels under load illustrates what I mean. Put that same 2 hp engine on a machine and couple it to a hydrostat and see if the results are even remotely similar. They won't be. You'll have to have the engine revved up higher to efficiently drive the pump. Then once you add up the associated losses along the way, you'll end up with a lot less power being transmitted to the wheels.

The larger the equipment is, the less it all matters. If you're designing a machine to do a job, and that job is going to require 50 hp, then upsizing a powerplant to 55-60 hp to compensate for losses in a hydrostatic system is no big deal.

The smaller something is, the more it matters. Consider a smaller and simpler "machine" designed to transport you from point A to point B using the power you can provide manually. You can hop on a normal bicycle and do the job easily. Now imagine someone designed a bicycle that you propelled by pedaling a pump, that in turn sent power to the wheel via a hydraulic motor. In that situation, the losses and inefficiencies would be greatly magnified. You would expend a LOT more energy to travel the same speed or distance.

Machines that are gear-driven, (or chain-driven, or belt-driven), are not only built that way because it would be costly to re-tool to a different type of power-transmission. It's simply that what the machines could be re-tooled to use instead of the gears, chains, or belts costs more than just the $$ spent for the bits and pieces. Efficiency falls off as well.