hydrostatic trans - less pedal pressure = more power?

[wango tango]

i read that HST's are different from that of a car when you give it 'the gas'. i can only assume that HST's make peak power at very low pedal pressure?

i pushed a big tractor tonight in idle, with ease and was amazed.

 

[whistlepig]

i read that HST's are different from that of a car when you give it 'the gas'. i can only assume that HST's make peak power at very low pedal pressure?

i pushed a big tractor tonight in idle, with ease and was amazed.

The HST isn't making power. That's done by setting the RPM on the engine. The engine stays at peak power. The HST just makes it go faster or slower. The hydro petal is not a "gas" pedal. Just a forward or backward pedal.

 

[BobRip]

It's peak torque at low pedal travel.

 

[whistlepig]

It's peak torque at low pedal travel.

Kind of sounds like you ease up on the hydro pedal for more power to the ground here.

 

[kennyd]

Think of the Hydro pedal's as a variable gear control...the more you push the higher the gear so less torque/power to the ground. A very common mistake by new operators is to push the pedal further when digging or climbing a hill only to find out the engine bogs down and/or stalls-then they come here asking if their machine is broken

 

[TripleR]

What kennyd says and when I first started using them I made that mistake too. Keep your RPM's up and short pedal movement for best torque/power transfer to the ground.

 

[wango tango]

thats what i thought. thanks guys. i know its not a 'gas' pedal, thats why i said it in quotes. the throttle is a lever.

also, one could argue that HST's really do multiply power. of course they dont make it (the engine does).

 

[Ford tractor]

Remember when you were a kid with a 10 speed bike? The HST peddle can be thought of as the rear tire gears. Peddle up is the chain on the largest gear giving more torque multiplication. Peddle down is like the chain on the smallest gear giving least torque multiplication but highest speed.


Staying with the 10 speed analogy, when you start slowing down going up a big hill, you didn't move the chain down to the smaller gear, you moved it up to the bigger one. Do the same thing with the HST peddle.

 

[oldnslo]

How the HST works when combined with a gear train or trans axle is exactly as Kennyd stated.

In reality the HST tranny operating at 2000 PSI will create the same torque output over the whole range of speed. This is based on hydraulic motor torque formula of:

torque in/lbs = PSI x motor displace in cubic inches/rev(CIR) divided by 6.28

example: if you have a motor with 3 CIR displacement it creates 955 in/lbs of torque.

Roy

 

[ModMech]

^ Many (and mostly) good answers above.

Yes, yes, think of the travel pedal as the gear selector - after all it IS right? Higher gears = more ground speed but less Tq to the wheels at a given enigne speed.

No different than your car or pickup, you don't put the trans in 5th OD from 4th direct when you are going up a hill pulling a load so you should not push harder on the travel pedal as the tractor takes up a load or you will stall the engine.

Tractor HST / Automotive equivelant

Travel pedal = transmission gear

Throttle lever = accelerator pedal