let's talk about hydrostatic

[oldnslo]

HST torque output:
On all HST transmissions with fixed displacement motors the operating pressure dictates the torque available they do not care if the pump is at 1/4, 1/2, or full stroke it will still produce the same torque with the same pressure what does change is the motor output speed and the pump input torque required. That is why you must let up on the pedal to prevent stalling the drive engine since rarely will the drive engine be large enough to run the HST at full speed and pressure.

For speed control the HST pedal is similar to an accelerator pedal where pressing down further does increase your travel speed.

 

[corl]

I have a Kubota MX5100HST that I got last summer. For the previous 35 years I had manual transmission tractors (JD 60, IH574RC) and used them as utility tractors and for haying. The HST Kubota is smaller than the IH but with 4WD it does great. Recently I had 225 cubic yards of mushroom compost delivered for my market garden. Two of the 10 wheel dump trucks (25 cubic yards each) got stuck after dumping and with them spinning their wheels and me pushing with the HST both got out of the field safely. The HST was terrific as you can just touch the truck and start pushing in low range with very little pedal. I use the tractor for tilling the gardens and it works great. I got a bigger bucket for the FEL (.76 cu yd stacked) and it is really quick and takes a lot less physical effort than the IH for doing FEL work. After living in both worlds I would never go back to a manual transmission for my needs. The only big difference between the old and the new tractor is weight. The Kubota is lighter and I use it with weight in the rear tires and keep the 750 lb tiller attached when doing serious FEL work. I usually run the FEL work at between 1500 and 2000 RPM and it is fine in the middle range.

 

[DeereMann]

Piston,
Torque Convertors don't multiply power, they only multiply torque. Power is time rate of work = rpm x torque. Power is always lost through power transmission devices - it is never gained or multiplied.

You increase torque (work) in general by slowing speed over the same time period. The big difference between the HST & Torque Converter is that the Torque Converter has no neutral position - it is ALWAYS in forward fluid motion, whereas the HST has a true neutral position where no fluid is being pumped to the hydraulic motor. This is why you have to hold the brakes on a T.C. equipped machine or it will creep forward. And HST machine in neutral will sit still without brakes (on a flat surface).

The T.C. multiplies torque by accelerating fluid from the engine/impeller to the fluid motor unitl the motor starts to move. Simple as that.

 

[MHarryE]

Not sure about other CUT's but Kubota Grand L's have a 2 position variable displacement motor. Since torque = pressure x displacement, they it is like having a 6 speed transmission (the displacement shift is electrical and can be on the go).

Some of the largest torque converter transmissions I know of are a Cat D11 with 850 HP and a 3 speed transmission and Cat 797 truck with 4,000 HP and a 7 speed transmission. Totally different drive than a hydro; however, Cat for one uses a semi-hydrostatic drive for steering. The differential steer will speed up one track while slowing the other drive.

Many of the larger ag tractors use a combination hydrostatic drive manipulating planetary gearsets resulting in an IVT or Infinitely Variable Transmission.

 

[arlen4720]

Not sure about other CUT's but Kubota Grand L's have a 2 position variable displacement motor. Since torque = pressure x displacement, they it is like having a 6 speed transmission (the displacement shift is electrical and can be on the go).

It seems like that is a unique feature to Kubota. I think that is the HST "plus" that everybody seems to like.

 

[diesel lover]

It seems like that is a unique feature to Kubota. I think that is the HST "plus" that everybody seems to like.

I keep meaning to ask what is the large difference from kubotas hst to its hst plus?

 

[MHarryE]

I keep meaning to ask what is the large difference from kubotas hst to its hst plus?

part of the difference is the 2 displacement motor but the other part is that in heavy pull applications it will also destroke the pump to maintain engine speed. For example I have a 2 acre garden plot that varies from rich black loose soil to heavy clay. When plowing I can put the pedal to the metal so to speak, the ground speed will vary from 2.3 mph to 4.4 mph, but the engine speed won't vary more than 200 rpm. It destrokes the pump to maintain engine power. Take it out of HST plus and I have to watch the tach continuously as the soil conditions change and feather the pedal accordingly. Heavy drawbar pull is where I notice it the most but it may be helping out other places and I just don't recognize it.

 

[Industrial Toys]

The Hydro I hava in my small Kubota wheel loader is a little different again. It operates like a machine with a torque converter, in that is it has a foot throttle that both operates the swash plate angle but also throttle.

Not that there is much available HP to operate a demanding attachment, but the problem is that you can't turn up the RPMs while going really slow.

EDIT: Possibly the thing I like most about this machine is that there is not a single transistor, never mind a micro computer to be found anywhere on board! Gotta love that!

 

[RickB]

It seems like that is a unique feature to Kubota. I think that is the HST "plus" that everybody seems to like.

New Holland used a two speed motor in their Class III Shibaura built hydro tractors (TC45D, etc)

 

[oldnslo]

Does the new "E" series JD's have dual speed motors?