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?

 

[k0ua]

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

Here is a youtube video that might answer some questions about HST+

https://www.youtube.com/watch?v=hzO_-LCd838

 

[diesel lover]

Here is a youtube video that might answer some questions about HST+

https://www.youtube.com/watch?v=hzO_-LCd838

I remember now that the 50 horse power tractor I spent time operating had hst plus, auto throttle advance and all the features shown in this video. This is what got me sold onto hydrostatic tractors after operating this moving fallen trees, pulling them with a chain, etc the power out of this Kubota hst was very satisfactory. There was lots and lots of pulling torque. I know he had pulled some trucks, dead cars etc with this tractor and it really was a miniature backhoe!! This was an L series or grand L series tractor that was turbocharged.

So far I am sold on a 40 horse power hst plus Kubota. This way if my 25 horse tractor is unusable or I need to work in slightly smaller spaces this will be possible while having power to push snow, tow larger items etc

 

[DennisFolsom]

Both the newer Kubota and John Deere tractors, with the electronic control systems on their hydrostatic transmissions, have features which "muddy the waters" with respect to the traditional explanation of how a hydrostatic drive works. In addition to multiple "ranges" built into the hydro system, they sense torque and mix throttle control with the transmission control on the foot pedal. I have used a Kubota L39 with this kind of setup and it works very well. There are options in the controls to make the system behave in different ways, depending on user needs and preferences. Depending on the settings, you can use the foot pedal more like a "gas pedal" and the response is likely more like some of the heavy equipment.

Even though these new systems are great (when everything is working), I am glad that my John Deere 4600 has the older, simpler hydrosatic technology. There is less to go wrong. I have adjusted my techniques to the capabilities of the machine, and I don't expect the machine to adjust to me! I know that a lighter press on the pedal gives me a "lower gear." I can work with that, just fine.

 

[Arc weld]

There are many different hydrostatic configurations. TLB's and large loaders don't use hydrostatic transmissions. They use torque converters. There are a few smaller loaders and/or TLB's that are hydrostatic though. If a tractor is used for constant pullling under load like plowing, a gear transmission is much better. Getting back to hydrostatics there is constant torque, constant H.P., constant torque/constant H.P., variable torque, variable H.P., load sensing, pressure compensating and a host of other features. Modern track excavators are basically hydrostatic with cylinders instead of motors. Hydrostats are best run at full throttle.

 

[Redneck in training]

Automotive automatic transmission uses hydrodynamic torque converter while HST stands for hydrostatic transmission. The hydrodynamic torque converter has three parts: pump, guide vanes, turbine. The turbine and the pump are identical in design. The torques in hydrodynamic system is controlled by guide vanes between the pump and the turbine. The turbine might function as the pump and the pump becomes the turbine in example when going downhill and using engine as a brake. The pump and the turbine are very close together in the converter assembly.

In HST the pump and the hydraulic motor can be in single assembly (like in HST tractors) but often are distance away connected by piping (in example in combines)

The main difference between those two systems is that hydrodynamic torque converter uses dynamic pump and turbine while HST used positive displacement pump and motor.
Another difference is in power loading. HST has power loading limits around 50HP while hydrodynamic converters can be designed up to many thousand HP.
Hydrodynamic converter can be locked to prevent slippage and power loss. Then the trany works like pure mechanical transmission.

 

[oldnslo]

In HST the pump and the hydraulic motor can be in single assembly (like in HST tractors) but often are distance away connected by piping (in example in combines)

The main difference between those two systems is that hydrodynamic torque converter uses dynamic pump and turbine while HST used positive displacement pump and motor.
Another difference is in power loading. HST has power loading limits around 50HP while hydrodynamic converters can be designed up to many thousand HP.

All true except for the HST power limitations. Sauer Danfoss, Kawasaki, Bosch Rexroth, and probably others all make HST pumps that will stall 500 HP engines. Granted you won't see one of these on your 50 HP tractor but they are out there since the pump alone weighs over 300 lbs.

 

[CJONE]

All true except for the HST power limitations. Sauer Danfoss, Kawasaki, Bosch Rexroth, and probably others all make HST pumps that will stall 500 HP engines. Granted you won't see one of these on your 50 HP tractor but they are out there since the pump alone weighs over 300 lbs.

The HP limit like oldnslo said is wrong. I have personally built a unit that requires 400HP and it runs 24 hours a day, 7 days a week. I have plans for a unit that requires 975HP and the limiting factor is the hydraulic hoses will "only" handle 6000PSI. The 27 series Sauer Sundstrand pumps [I know "old school"] are capable of almost 7000PSI. So all this info on HP limits is wrong. A lot of new dozers at 150-200+ HP are hydrostats and they are a pleasure to run. CJ

 

[diesel lover]

Automotive automatic transmission uses hydrodynamic torque converter while HST stands for hydrostatic transmission. The hydrodynamic torque converter has three parts: pump, guide vanes, turbine. The turbine and the pump are identical in design. The torques in hydrodynamic system is controlled by guide vanes between the pump and the turbine. The turbine might function as the pump and the pump becomes the turbine in example when going downhill and using engine as a brake. The pump and the turbine are very close together in the converter assembly.

In HST the pump and the hydraulic motor can be in single assembly (like in HST tractors) but often are distance away connected by piping (in example in combines)

The main difference between those two systems is that hydrodynamic torque converter uses dynamic pump and turbine while HST used positive displacement pump and motor.
Another difference is in power loading. HST has power loading limits around 50HP while hydrodynamic converters can be designed up to many thousand HP.
Hydrodynamic converter can be locked to prevent slippage and power loss. Then the trany works like pure mechanical transmission.

Thank you for straightening that out! Good knew ledge to know off hand. The way the two drive lines connect from a stand still are different but when operated correctly I am 100% positive both can produce a lot of useable pushing and pulling power/ torque straight to the wheels

 

[Redneck in training]

While HST units can handle 1000 HP, hydrodynamic units can handle upto 200000 HP.