Another HST question

[farmacist]

I have used my TC35D for 4 years and love the HST transmision, BUT I still do not understand the workings. Does the motor or transmission work any harder or send more power to the wheels if I use Range 1 turtle with a FULL foot pedal or Range 2 turtle with a LITTLE foot pedal? Will the transmission oil heat up more if I use Range 2 with a little pedal? I note the manual referes to the foot pedals, the HST range lever, and the turtle/rabbit ALL as speed control devices. Do these 3 speed control devices simply allow us to "feather" the foot pedal at a speed/power that fits the task? Thanx Frank

 

[beenthere]

I think of it as two transmissions, or one main transmission and a 3 speed rear end. Within any range of the 3 selectable speeds, you have infinite range of 'gears' with the HST pedal. The further down the pedal is pushed, the higher the gear you are selecting. At higher gears, you increase speed but will lose power to the wheels.

Stomping down on the HST (as is the tendancy) will not give more power. However, increasing the throttle speed will give more power. If pulling a load, and the tractor starts moving slower, it means one has to back off the HST pedal (picking a lower range) or shift into a lower range, NOT push down harder on the pedal thus picking a higher range that will mean even less power from the engine (not more).

 

[thcri]

Run with her the way you feel most comfortable. Transmission heat or oil flow is no different from a low hear with pedal down low versus high gear with pedal up high. When using the loader I keep mine in second gear but keep the pedal up high, this way when taking product to the place I want to I can just lower the pedal and get there faster. And when diggin into the pile you still have the power you need by keeping the pedal up high.

murph

 

[jinman]

</font><font color="blue" class="small">( I have used my TC35D for 4 years and love the HST transmision, BUT I still do not understand the workings. Does the motor or transmission work any harder or send more power to the wheels if I use Range 1 turtle with a FULL foot pedal or Range 2 turtle with a LITTLE foot pedal? Will the transmission oil heat up more if I use Range 2 with a little pedal? I note the manual referes to the foot pedals, the HST range lever, and the turtle/rabbit ALL as speed control devices. Do these 3 speed control devices simply allow us to "feather" the foot pedal at a speed/power that fits the task? Thanx Frank )</font>

Unlike many tractors in the New Holland line of TCs, the Class III Boomers only have two ranges (High and Low). Both of those ranges are gear ranges. When you shift the lever, you are changing gears in the transmission similar to the guys with a regular gear transmission. So like a gear transmission, the lower gear has more mechanical advantange and requires less input power, but the output is slower. The high range requires much more power in, but your output is faster.

The hydrostatic transmission in your tractor sits in front of this mechanical transmission. Therefore, it's output to the mechanical transmission requires more or less power depending on the selection of high or low range.

In a hydro transmission, there is a hydraulic pump and a hydraulic motor. The pump is attached to the engine and spins at a constant rate, but the amount of fluid it pumps is determined by the position of the hydro footpedal. There is a part of the pump called a swashplate that pumps more or less fluid based on the angle of the pedal.

So when you just barely move the pedal, the pump doesn't pump much fluid does it? In high gear, to move the transmission, that small amount of fluid must be under very high pressure. Of course the maximum pressure inside your transmission is 5000 psi, so when that is reached, the relief valve lfts and your tractor stalls.

When you go to the lower range, your pump has to pump much more fluid, but it doesn't require as much pressure because the transmission is in low range. You may be able to used the whole pedal moverment (swashplate angle) to vary the speed without reaching relief pressure.

So, both flow friction and high pressure cause heat. I'm not sure which of these methods produces more, but I do know that it's much easier to control the full range of speed within a gear range while in low range. High range goes from creep to relief very quickly. I only use high range as a road gear or for mowing on flat ground.

Now... Are you ready for that rabbit-turtle function? That's a unique feature to NH. Remember I said the hydro tranny has both a pump and a motor? Well, just like you can change the swashplate angle in the pump with the pedals, when you push the rabbit-turtle buttons, you change a swashplate angle in the motor section of the hydro. So the footpedals and rabbit-turtle switches change the hydro transmission, but the range selector changes the output gears of the the mechanical transmission.

Clear as mud? I hope I helped a little. /forums/images/graemlins/smile.gif