HST Pedal

   / HST Pedal #1  

Anonymous Poster

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Somewhere in the posts I had read that someone "needed to learn not to use the HST pedal as a gas pedal". Is this bad for some reason? Lots of times you need the RPM's to get over something but not speed or when you are using the FEL where you need the power but not speed, etc. etc...

This is the only tractor I have had with a HST so I don't have a lot of experience with it.

Matt
 
   / HST Pedal #2  
I think the message that is being conveyed is simply that as you press further on the HST pedal, your speed picks up but not the power to the engine (disregarding the compensation the governor plays). In other words, in situations where you need more power for a given range and engine RPM, pressing the HST pedal further down can actually result in less RPM's as the engine is loaded trying to meet the new demand for more hydraulic fluid to be pumped to the hydraulic motor that powers the output shaft that turns the wheels that makes you go. In the end I think those of us with HST tractors will all agree that practice with it will quickly get you quite proficient with its use.
 
   / HST Pedal #3  
The way I think of it is:

The HST acts mostly like a gear shifter. As the pedal is depressed, gear selection changes; to go faster. But the engine is still developing the same amount of power. In a car, the RPMs are changed and so are the gears.

Example: If climbing a steep embankment requires the equivalent of a low gear, then the tractor will stall if it is in too high a gear. A high gear can be selected if the pedal is mashed to the floor boards.

At least that's the basic idea. The pedal also regulates the amount of torque available. So naturally, there is a position where the pedal supplies 100% of the available torque. I'm not clear exactly where this position is.

If you can create a situation where high torque is required, like climbing or digging, then play with the HST pedal when you are in the High gear range (it's easiest to see the torque response).

If possible, try this out:
1) Put the FEL bucket firmly and slowly into the side of a large dirt pile (one where you won't be able to move the dirt a whole lot). This will set up a high torque requirement. Make sure the bucket is firmly stuck into the dirt!

2) Place the gear selector into High range and put the RPMs to about 1800. This will provide an amount of horsepower that is good for digging but won't cause a safety issue.

3) Now smoothly depress the HST pedal to its maximum position. This will supply all the torque available per the amount of horsepower made at 1800 RPM. It will also change the hydraulic gearing from low to high.

4) You should see the tractor begin to dig into the pile and then stop its forward progress. The tires will probably spin somewhat. The RPMs should drop dramatically; the engine may stall.

5) Now perform the same procedure with the manual gear selector in Low range. This time, you should notice the tires spin much more and the bucket should dig into the pile much better.
 
   / HST Pedal
  • Thread Starter
#4  
RaT & Pks,

I understand the differences between speed, power & RPM, I was just wondering if it could cause a problem by "feathering" the pedal, not all the way in or all the way out.

I just misundertand the posters comment about using it as a "gas pedal". I was thinking he meant ground speed and not RPM and didn't know why that was bad. But I guess you're right, he was talking about mistakenly pushing the pedal to increase RPM's.

Thanks

Matt
 
   / HST Pedal
  • Thread Starter
#6  
I hoping that is what you would say, that is the way I use it. /forums/images/graemlins/wink.gif
 
   / HST Pedal #7  
The HST pedal is supposed to be feathered. That's what makes having HST so wonderful. Mechanically, there is basically nothing to where out either (unless the clutch is used to perform the feathering).
 
   / HST Pedal #8  
Actually you can wear out a hydrostatic drive unit. The pistons and chambers in the both the variable displacement pump and the motor can have enough wear that the charge pump can no longer compensate for that great of internal fluid leakage. This results in loss of power and speed. This is why it is so important to keep the fluid in top condition, keep the suction screen clean, and replace the filter at regular intervals.
 
   / HST Pedal #9  
Yes, I quite agree with you. What I was tryning to refer to was the difference in a user's ability to wear out a clutch vs. wearing out the HST system.

But I think you stated it much better. Thank you.
 

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