Dirt Moving An understanding on the age old debate of geared/hydro

[k0ua]

Here is another video from the German firm Linde. It shows a hydro in a fork truck, the only real difference is that with our tractors there is only one hydraulic motor instead of haveing a motor for each wheel, and we have a standard 3 speed transmission aft of the motor and also differential gearing.

 

[paulfun9]

For those that complain about a HST not going up a hill in high range... Would your gear machine make it up in high? I'm quite sure the answer is no. You'd stall the machine. On a HST the relief valve will usually pop open before stalling the tractor.

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This is an unfair statement. Its not the gear choice but the travel speed that is relevant! Simply stated no mater what gear choice the HST is lacking when any hill is in front of me compared to the same tractor in gear.

 

[Fallon]

This is an unfair statement. Its not the gear choice but the travel speed that is relevant! Simply stated no mater what gear choice the HST is lacking when any hill is in front of me compared to the same tractor in gear.

I don't think it's unfair at all. Yes a HST is 15% less efficient than a gear, giving the gear a bit of an edge there. But a HST is dynamic. I road my machine a lot. When I hit a hill I generally do so flat out in high range. As I start climbing the hill the RPMs start dropping, when they get below 2k RPM or so where my torque starts falling off I just ease off the go pedal enough to keep the RPMs in the sweet spot. More "work" & thought required, than just leaving it in a lower gear on a gear machine, but trivial to do.

The same goes for mowing, tilling & other stuff. I can stomp on the go pedal until RPMs start dropping me below 540 RPM on the PTO, then ease up. It lets me dynamically keep the engine tapped out for max power in varying conditions. You can't do that with a gear machine. You have to either stop & shift, or at least make some reasonably large jumps between gears on the fly if you have a GST, PowerShift or the like.

My L4060 is a hair underpowered (40hp, the same frame as a L6060, which has 60hp & several in between). With my HST I can ensure I'm always using all 40hp when mowing or roading despite changing conditions with virtually no lag. With a GST I could shift on the fly, but there is a bit of lag on the shift & there are only moderate jumps between gears, not the infinitely variable range of a HST.

 

[arrow]

The same goes for mowing, tilling & other stuff. I can stomp on the go pedal until RPMs start dropping me below 540 RPM on the PTO, then ease up. It lets me dynamically keep the engine tapped out for max power in varying conditions. You can't do that with a gear machine. You have to either stop & shift, or at least make some reasonably large jumps between gears on the fly if you have a GST, PowerShift or the like.

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This is the point. On a geared machine, there is no need for stopping or shifting. You pick a speed, select a gear and just go. This is why your statement would not fit all occasions for a geared tractor and thus not be relevant or fair or however one wishes to describe it. Many times the tractor is not decked to start off with so it is simply a matter of stepping harder on the go pedal. For road travel and in the highest gear (8th) on my tractor, I've yet to confront a road grade I could not go up. I think the reasons for this are several such as inertia and direct gear to gear involvement so energy losses are not as much.
It comes down to "conditions". I was skeptical or I should say complacent of why people are so enamored with hst only because of my experience with real smooth geared tractors. Now I know why as I longed for an hst on my last big tractor job with both an unsmooth and smoother geared tractor.
If I had to pick one tractor based on what Koua has shown and what others have stated, it would be an hst but a higher hp one of 40-60 and not the 28 hp of my Mahindra. This is coming from a previous , die hard geared guy. The negative is it would be a much more expensive tractor by at least a third or more over what I currently have.

 

[Crank Shaft]

If your tractor can spin the tires on the hill the transmission is putting all the torque it can down. Well, technically max torque would be just be before it lost traction. A transmission isn't going to affect traction unless it can't pass enough torque.

A HST will eat up 15% of the avalible torque compared to a gear. But neither will affect the point it looses traction, unless you consider the minor differences in weight.

Thanks Fallon but I cannot fully agree with the part of your statement that essentially says if the tires spin then you cannot blame the HST transmission. What I have learned from years of messing around with anything from old army jeeps and modern Jeep Wranglers to numerous modern 4WD and AWD vehicles is that many can spin their tires but only some can climb the steepest slopes. Success comes from not spinning the tires which can be accomplished by precisely controlling the power that goes to all 4 wheels and there are so many different ways to do this. In the best systems, power delivery is varied not only between front and rear axles, but also between left and right side wheels. When one wheel starts to spin, power is reduced and sent to the other side or to the other axle.
Its a balancing act between all four wheels.

Now I don't claim to know exactly how my HST operates internally, but it seems that the way it sends power to all 4 wheels is perhaps not as good as in my geared tractor. Now before I get flamed, please note I used the word "perhaps". This is a theory and as someone else pointed out it is a discussion and we have a lot of different opinions here. Wouldn't life be boring if we all agreed?

All I know for sure is that my 15 HP geared tractor can out-climb my 23 HP HST. But I cannot say for certain this is because of the HST. It could be something else, which I why I am on this forum learning as much as I can. Thanks to everyone for an interesting debate!

 

[Fallon]

Thanks Fallon but I cannot fully agree with the part of your statement that essentially says if the tires spin then you cannot blame the HST transmission. What I have learned from years of messing around with anything from old army jeeps and modern Jeep Wranglers to numerous modern 4WD and AWD vehicles is that many can spin their tires but only some can climb the steepest slopes. Success comes from not spinning the tires which can be accomplished by precisely controlling the power that goes to all 4 wheels and there are so many different ways to do this. In the best systems, power delivery is varied not only between front and rear axles, but also between left and right side wheels. When one wheel starts to spin, power is reduced and sent to the other side or to the other axle.
Its a balancing act between all four wheels.

Now I don't claim to know exactly how my HST operates internally, but it seems that the way it sends power to all 4 wheels is perhaps not as good as in my geared tractor. Now before I get flamed, please note I used the word "perhaps". This is a theory and as someone else pointed out it is a discussion and we have a lot of different opinions here. Wouldn't life be boring if we all agreed?

All I know for sure is that my 15 HP geared tractor can out-climb my 23 HP HST. But I cannot say for certain this is because of the HST. It could be something else, which I why I am on this forum learning as much as I can. Thanks to everyone for an interesting debate!

A transmission is not a transfer case. A transfer case sits after a transmission & splits the output to the front & rear axles. You also make the statement you don't know how it works, then describe multiple functions that aren't part of the transmission & don't exist on any geared or HST SCUT or CUT.

On all FWA (Front Wheel Assist, in the tractor world the term 4 wheel drive is reserved for machines with all 4 tires the same size, usually articulating monsters) CUTs the transfer case works exactly the same way. There is a mechanism to engage or disengage the output to the front axle, usually a lever. When engaged power goes equally out both ends. Wheel size differences & the fact that the front axle spins slightly faster than the rear to make turning easier.

There is no fancy torque biasing or limited slip anything like in modern cars. It's just brute force fixed gear output.

All tractors I'm aware of have a rear differential lock that liocks the rear wheels together to they both get equal power & spin at the same speed. Again, not the transmission. Some machines have locking or limited slip front differentials but those tend to be pushing 100hp. As far as traction control there is no automatic or electronic options like that on CUTs or SCUTs. There is just the left & right brake you can operate manually if needed.

And a HST can be operated much smoother & more dynamically than a geared machine. So again another advantage for HST in your scenario about precise control.

One other HUGE advantage for HST on hills is dynamic braking. Pull your foot off the go pedal & the machine stops, assuming gravity doesn't overcome traction. No need for brakes. I really only use my brakes for parking, turning really sharp or holding myself in position when doing something precise on unlevel ground. The rest of the time I just pull my foot off the go pedal & it takes care of business.

Geared machines do definitely have their place still, primarily due to their efficiency. But saying a gear machine is better at a given task because your gear machine that is completely different than a HST machine is better because of the transmission is just misguided.

 

[k0ua]

A transmission is not a transfer case. A transfer case sits after a transmission & splits the output to the front & rear axles. You also make the statement you don't know how it works, then describe multiple functions that aren't part of the transmission & don't exist on any geared or HST SCUT or CUT.

On all FWA (Front Wheel Assist, in the tractor world the term 4 wheel drive is reserved for machines with all 4 tires the same size, usually articulating monsters) CUTs the transfer case works exactly the same way. There is a mechanism to engage or disengage the output to the front axle, usually a lever. When engaged power goes equally out both ends. Wheel size differences & the fact that the front axle spins slightly faster than the rear to make turning easier.

There is no fancy torque biasing or limited slip anything like in modern cars. It's just brute force fixed gear output.

All tractors I'm aware of have a rear differential lock that liocks the rear wheels together to they both get equal power & spin at the same speed. Again, not the transmission. Some machines have locking or limited slip front differentials but those tend to be pushing 100hp. As far as traction control there is no automatic or electronic options like that on CUTs or SCUTs. There is just the left & right brake you can operate manually if needed.

And a HST can be operated much smoother & more dynamically than a geared machine. So again another advantage for HST in your scenario about precise control.

One other HUGE advantage for HST on hills is dynamic braking. Pull your foot off the go pedal & the machine stops, assuming gravity doesn't overcome traction. No need for brakes. I really only use my brakes for parking, turning really sharp or holding myself in position when doing something precise on unlevel ground. The rest of the time I just pull my foot off the go pedal & it takes care of business.

Geared machines do definitely have their place still, primarily due to their efficiency. But saying a gear machine is better at a given task because your gear machine that is completely different than a HST machine is better because of the transmission is just misguided.

What he said ^.

 

[pmsmechanic]

I'm going to add a bit here in that there is essentially no difference between an HST and a gear transmission power train after the transmission. The only difference is how the power gets transmitted through the transmission. After that they are essentially equal. Ie crown and pinion, diff lock, rear axle, gear train to the front wheels, and the front axle.

 

[k0ua]

I'm going to add a bit here in that there is essentially no difference between an HST and a gear transmission power train after the transmission. The only difference is how the power gets transmitted through the transmission. After that they are essentially equal. Ie crown and pinion, diff lock, rear axle, gear train to the front wheels, and the front axle.

Yep. When you look at how they are built, there are no mysteries.

 

[Crank Shaft]

A transmission is not a transfer case. A transfer case sits after a transmission & splits the output to the front & rear axles. You also make the statement you don't know how it works, then describe multiple functions that aren't part of the transmission & don't exist on any geared or HST SCUT or CUT.

Yes, I am aware of that but I was responding to your earlier statement of "If your tractor can spin the tires on the hill the transmission is putting all the torque it can down". In that statement you also ignore the rest of the drivetrain that is required in order to spin the wheels. We both should have been referring to the drivetrain.

I agree with you that there is no fancy torque biasing or limited slip on my HST. I came to that conclusion after carefully reviewing schematics of my geared drive train and schematics of my HST drive train. They do look very similar when one looks beyond the HST. I thought there might be some subtle differences that might explain my loss of traction but so far that theory looks unlikely.

So the reason for my traction loss, probably comes down to tires, tire pressure, weight distribution or some other reason and not the HST.