HST, not an automatic according to some

[Bob_Skurka]

</font><font color="blue" class="small">( Volfandt, you must be an engineer. You are the first to actually explain it correctly and in a way I (also an enginner) can undersand. The problem with everyone elses analogy . . . )</font>

The problem with engineers talking is that us regular folk have no darn clue what you are talking about. And when an engineer talks to another engineer, then the rest of us just pretend and nod our heads like we do when our wives talk to us. /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif

 

[Charlie_in_TX]

/forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
Ya I know what you mean. At least he didn't try to explain it using a Laplac (sp?) transform, a forrier series or a series of differental equations.

It happens in all professions thought. My wife works for HP. She trys to find parts for portable computers that are nearing end of life. Now I know computers but listining to her talk to one of her co-employees in the same field, well my eyes glass over and I get an empty look on my face.

BB_TX posted this link. How Trannys Work . It is a much easier to understand explanation.

 

[jinman]

</font><font color="blue" class="small">( The problem with everyone elses analogy is they all give a torque multiplication thru gear reduction in the HST. As you stated, "There is no gear reduction in the hydraulic assembly of an HST." No gear reduction, no torgue multiplication. )</font>

Ooow... You "stepped in it and got a little on you" there Charlie. /forums/images/graemlins/smirk.gif /forums/images/graemlins/wink.gif

If an engine turns the input to a HST tranny pump at 2000 rpm and the output hydraulic motor speed is 50 rpm, you mean to tell me you think there is no torque multiplication? You are correct to say there is no gearing providing torque multiplication, but the output shaft of the motor has much more torque than the input from the engine. It has torque multiplication the same way a hydraulic jack converts the easy movement of its handle over a long distance and multiple cycles to the short but but very strong stroke of the ram. Agreed? /forums/images/graemlins/smile.gif

 

[3RRL]

Correct-o-mundo Jim, me engineer two. /forums/images/graemlins/grin.gif

 

[MossRoad]

The way conventional HST was explained to me was...

The engine turns the pump.
The pump pushes the hydraulic fluid.
The hydraulic fluid turns a motor.
The motor turns a gearbox(on most tractors, two or three ranges).
The gearbox turns the differential.
The differential turns the axles.

On my current tractor there isn't a gearbox or differential, sooo...
The engine turns the pump.
The pump pushes hydraulic fluid.
The hydraulic fluid pushes four motors(one at each corner of the tractor).
Seems simpler! /forums/images/graemlins/tongue.gif

With either one, though, the operation is the same....
If the engine starts dogging out, let off the pedal a bit to get more power to the wheels. Stomping on it usually results in a stalled engine or hydraulic bypass valves opening. If you have a range selector, choose a lower range and try it again.



An interesting discussion from the past on HST and how it works...

Unfortunately, many of the links in the discussion no longer work, but it was still a great discussion. /forums/images/graemlins/wink.gif

 

[jinman]

</font><font color="blue" class="small">( ...let off the pedal a bit to get more power to the wheels. )</font>

So if your foot pushes the pedal, what does the pedal push? Perhaps a swashplate in the pump that pushes pistons?

Sorry, MossRoad. I'm just being a bit pushy here. /forums/images/graemlins/wink.gif /forums/images/graemlins/laugh.gif

 

[Volfandt]

Nah Charlie, I'm just an old telephoneman /forums/images/graemlins/grin.gif
But I did cutover a Holiday Inn the other day /forums/images/graemlins/grin.gif

Thanks for the compliment tho /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif

Volfandt

 

[DaveNay]

OK....here's my take on it.

The function of a hydrostatic transmission is separated into two very distinct functions.

Pressure and Flow

The RPM (actually, more correctly the peak Torque/H.P. point) of the engine controls the maximum available pressure in the system, while the hydrostatic pump controls the flow rate to the hydraulic motor. The foot pedal controls the flow rate, with a higher flow rate delivering more fluid to the drive motor, and thus "going faster". If you bog down the tractor, the flow rate is reduce and approaches zero. Since hydraulic fluid is an incompressible fluid, one of two things will happen....either you will pop off a bypass valve, and the engine and hydrostatic pump will continue to circulate, but you will have no forward motion, or there is no bypass valve, and the engine will stall.

Question of my own.....is the physical gear reduction between the IC engine and the hydrostatic pump, or is it between the hydraulic motor and the differential? I can see it working in either place.

 

[KiotiJohn]

Okay, here's my take on this /forums/images/graemlins/grin.gif

You push the pedal and it goes. If it doesn't, make sure you don't still have the clutch latched, or the parking brake on. That's enough to know.
John

 

[john_bud]

KiotiJohn,


GOOD ONE!