How does an HST compare in pulling power with the same tractor and a gear trans?

[jimglassford]

This conversation is entertaining but the two tractor drive technologies were designed for different purposes. The hydrostatic transmission allows better close quarter control. You set the engine RPM on a diesel engine and the governor adjusts the fuel delivery based on load to maintain the same RPM. So saying a gear transmission tractor can idle up a hill, the governor is increasing the fuel as the incline increases. Now on the hydrosatic transmission, you can set the engine RPM and the operator is controlling a fluid flow. The benefit of the hydrostatic drive is that you can maintain the engine RPM in the sweet spot of torque while the operator adjust speed. Mowing a lawn or using a loader, the HST shines while you have to constantly slip a clutch on a GST. As for which pulls better, given a fixed load and both spinning tires, they should be equal. If you want to know which will pull more of a load with the same HP, the gear drive will. Time is also a factor, pulling a heavy load with a HST builds heat and you lose more efficiency.

Construction equipment use hydrostatic because besides the drive system, there are a lot of other hydraulic functions on the vehicle as well As for the large tractors, the premium ones use CVT transmission to get the benefits of the hydrostatic with less power loss.

 

[Industrial Toys]

Lawn tractors have gone that way. Perhaps hydro is just a more consumer friendly platform.

 

[Waffles]

I used a 33 HP NH and LS that are virtually the same.

I tested both in a mid range gear that put them at equal speed. The HST would bog down and stop when working up steep hills. The gear didn't even notice the hill and could almost idle up it.

They are both have the same max pull force in low range as they are traction limited, even on flat concrete.

HST will do the same work, just slower than gear.

I still bought HST since I don't have enough hands and feet to: steer, shift, brake, clutch, operate loader, change throttle while navigating my constantly changing terrain.
I have mowed tall grass and brush up a steep hill with a 6 ft cutter behind a 32 pto hp hst mahindra without the slightest bog.In fact i have dug tons of dirt out of a tall bank and never came close to it bogging way down.

My hills are 20-30 degrees.

 

[4570Man]

My hills are 20-30 degrees.

A 30 degree hill is a heck of a hill. Assuming it’s workable at all I’d much rather use a HST. You’re more in control if something starts to go wrong and direction changes would be easier.

 

[milkman636]

I’ve owned a 35hp tractor with a geared transmission and draft control, and currently own a 38 hp HST tractor. In my experience, plowing and disking are better performed with the geared transmission. My plow and disks run better at 4-5 mph, and draft control keeps the hitch loading uniform at that speed. At low speed I feel my HST out-pulls my previous geared one, but the HST loses efficiency as the transmission oil flow increases with ground speed. My 38hp hydro can pull the same plow as my 35 hp manual did, but does it slower and sucks more fuel and creates more heat. The lack of draft control also makes it harder to regulate tillage depth as I traverse contours of the ground. But, I made the jump to the HST for all the other tasks I do. Plowing is the only time I ever miss the geared transmission, but it’s something I do for only a couple hours each year, every other task is better with HST.

Part of what makes the HST feel like it pulls better at low speed is the way you can gradually apply power and creep to a start while you’re right on the edge of breaking traction. The HST is actually at its peak of efficiency at that crawl speed. Unless you have some real creeper gears, the geared transmission requires some slip of the clutch to get that the same effect. That clutch slippage effectively reduces the engine torque that can be applied to the wheels off the start. So, I’ll pick my HST for just tugging on something heavy too.

 

[MHarryE]

Skid steers or compact track loaders often have 2 ranges. It’s done with a dual displacement motor. I have a Kubota SVL75. Pressing a button opens a valve pressurizing a piston that shifts the motor swash plate angle. Same thing with my Caterpillar mini-excavator. Doubles travel speed but halves maximum torque. Same thing with my Kubota L6060 CUT. It also has dual displacement motor in effect giving 6 speed ranges.

The design guide for gears is 3% loss through each gear set. Figure that the transmission, differential, and final drives each eat up 3% - the result is 91% at the wheels. Hydro has the same 3 gear sets, plus hydro efficiency that varies greatly depending on swash plate angle, and add in the power consumed by the charge pump and it will put less power to the ground.

First half of my career was with self propelled combines. When I started all used v-s belt drives which really sucked. By the time I moved to construction equipment they had all changed to hydros. Precise speed control, end row turning, cover twice as much ground in a day. My first project in construction was large cold planers - milling asphalt. 250 HP from 2 pumps to 4 track drives, 90,000 pound machine, precise speed control required so the 750 HP going to the cutters was running close to 100% all the time. Couldn’t imagine how to do it with gears.

 

[CobyRupert]

If both transmissions can transmit enough power to overcome the tire’s traction (/friction), that seems like a different issue than OP’s comparison question.

IMHO, to me the answer seems simple, perhaps if rephrased.

Two tractors have the same exact engine. One tractor’s transmission can transmits 97% of the engine’s power to the tires, and the other transmits 83% (max) of the engines’s power to the tires.....which has more pulling power?

 

[K5lwq]

A good(fun) test would be to take two tractors of the same size, weight, HP and tires, one HST the other gear and chain them together rear to rear. Which one would over power the other one in a pull off?

If any of you decides to do this, sell tickets because I want to watch! :laughing:

I almost would put my money on the HST winning that contest but who knows. :confused3:

 

[sixdogs]

Skid steers or compact track loaders often have 2 ranges. It痴 done with a dual displacement motor. I have a Kubota SVL75. Pressing a button opens a valve pressurizing a piston that shifts the motor swash plate angle. Same thing with my Caterpillar mini-excavator. Doubles travel speed but halves maximum torque. Same thing with my Kubota L6060 CUT. It also has dual displacement motor in effect giving 6 speed ranges.

The design guide for gears is 3% loss through each gear set. Figure that the transmission, differential, and final drives each eat up 3% - the result is 91% at the wheels. Hydro has the same 3 gear sets, plus hydro efficiency that varies greatly depending on swash plate angle, and add in the power consumed by the charge pump and it will put less power to the ground.

First half of my career was with self propelled combines. When I started all used v-s belt drives which really sucked. By the time I moved to construction equipment they had all changed to hydros. Precise speed control, end row turning, cover twice as much ground in a day. My first project in construction was large cold planers - milling asphalt. 250 HP from 2 pumps to 4 track drives, 90,000 pound machine, precise speed control required so the 750 HP going to the cutters was running close to 100% all the time. Couldn稚 imagine how to do it with gears.

MHarryE--Thank you for your reply. I'm the OP on this. Take your HST L6060, put R-1's on it and pull some secondary tillage tools like cultivators or harrows through a worked field. Maybe a heavy planter. Now get the exact same tractor with a gear transmission. How would it perform or how would you expect it to perform? What would you notice, or expect to notice as differences? At the end of the day, how would you feel about the two tractors?

If a cultivator was almost too much for one secondary tillage task would the gear transmission also be maxed out or would it be able to take up the slack and keep going?

 

[art]

I am that old I worked with the IH tractors quite a bit and my thoughts are if they ever built them in three range they would have been a bigger success sooner. Smarter sales people would not have sold as many into tillage work and would have stressed them for the PTO work which was their gravy on the farm. One important part is anyone could drive them and never grate a gear!!!

There is about a 15 percent loss either way on drive trains! For the bad on a hydro there is about a 15 percent loss on pull with those tractors on identical ground and conditions from what I have witnessed. There is about a 15% increase in productivity in PTO work with a hydro and I'd say it goes right into loader work as well. While the comparisons of pto work was being done both tractors were dyno'd and ballasted identical and the forage harvesters were also set-up identical right down to model and knives sharpened and cut length of the hay. Plowing was with five bottom plows in a sandy type sod and again with 100 horsepower at the pto tractors as well as an 85pto horsepower. Not quite the same horsepower's we are used to talking about here and there are variables in all testing or demo's but they both have there place. For most people the hydro is the most efficient at this point including the hydraulic shuttle for the benefit of the gear drivers.