let's talk about hydrostatic

[diesel lover]

Hey guys. I'm more firmilar with hydrostatic systems on payloaders and backhoes than on newer tractors. I really like how all newer tractors have different ranges in order to lower/increase speed and build torque as well. For instance on a komatsu WA180 pay loader I have a lot of experience with there are forward and reverse with 1,2,3, and 4. For heavy snow I always use 1 and 2 to build engine rpm and torque. I don't know why the guys at work don't understand that. They try and try to use 4 to push snow when all that does is heat up the trans! Plus not to mention they are revving on the engine and the wheels are not even turning!

I'm very firmilar with automatics and torque convertors as the torque convertor can multiply torque 2 to 3 times from the engine crankshaft and then planetary gears are used to create different gear ratios. A built automatic is stronger than a manual trans because you remove the clutch and the helical or spur gears which cannot hold as much torque as a planetary gear set. Upon pulling a load with an automatic you are building torque and not slipping a clutch causing torque loss.

Alright so are farm tractor hydrostatic transmissions designed to build torque as well? I know this is true of construction equipment. Can you rev on the engine and apply the hst drive for forward motion? That's the first thing that bothers me when you com pair farm tractor hst and construction hst. On construction hst you engage the drive in forward or reverse than you use the throttle to start moving as these type of hst have a stall below a certain rpm.

Does a farm tractor and construction hst work the same way mechanically?

His does hst work? I understand it as a hydraulic pump that causes fluid flow and this is stopped by a valve. The valve leads to a hydraulic "motor" that takes hydraulic pressure and turns it into a rotary motion which causes torque building and increase due to the muliplycation and speed ratios between high engine rpm to a lower transmission output speed and yes the low geared rear end. Thank you

 

[V1Rotate]

I think you understand the hydrostatic system pretty well. One thing some people don't understand is that the farther down you push the pedal to make the tractor go faster, the less torque you get.
When pushing into a dirt pile, for instance, as the machine starts to bog down you must ease up on the pedal, which actually puts more torque to the ground.

 

[RLstangs]

Hydrostatic transmissions | Hydraulics content from Hydraulics & Pneumatics

 

[FredH]

My 2003 New Holland TC 30 has 3 ranges for speed selection . But you manually set the throttle rpm , ( say I am mowing , then I set it some were around 2200 ?? , what ever brings up the PTO speed to 540 rpm's ) , select your range , press the forward / reverse motion lever on floorboard ( mine is on right side ) and go . Depending upon how far you press the pedal for that range you selected , it goes up to it's maximum speed in that range .

On mine , Low range is the most torque , medium range has some torque but with speed also , while high range has very little torque but all speed . Thus most of your implement pulling is done in low range or maybe medium range if flat ground .

Example : I have a 6.5' king kutter 3 point disk . Weighs over 1,100# now with the added weight I put on it . Going downhill , I can bury it up to the axle's , 6" + , and go any were from a crawl to hauling the mail in medium range . But once I turn around and start back up , Have to either partly raise the disk to half that depth or shift to low range as it will stall regardless of how slow I try to go , based upon directional pedal position .

The directional pedal is much like the " Mono " pedals on electric hysters I use to run in the '80's . Step on one side go forward , step on other side and go backwards .

Now , How does it all work , While I do understand the process of the pumps , valves , etc... , Somebody like J.J. in the Hydraulic forums or somebody with a higher pay grade than me , would have to answer that . While I could likely tear mine apart and fix if needed , the process in which it all works is beyond my feeble mind .:thumbsup:


Fred H.

 

[arlen4720]

The Hydro transmission is usually a variable displacement pump coupled with a fixed displacement motor. There is no valve between the 2 to stop fluid flow. Your directional pedals control the stroke of the piston pump via the swashplate angle. If no pedals are pressed, then the swashplate is at an angle of zero, so the pump has a stroke of zero, hence no fluid is moved. The pump is directly coupled to the engine, so whenever the engine spins, so does the pump. You get torque multipication just like a variable set of gears...if the engine is screaming, and you just press down a little on a pedal, then the machine will just creep along just like being in a low gear. You would have maximum torque at that point. As you apply more pedal, the pump stroke increases, so your speed increases, and your torque goes down. There is a system relief valve (set at 5800psi on my 4720) to prevent applying too much torque to the hydraulic motor. The manual range transmission is between the hydraulic motor and the final drive.
It is a closed loop system, in other words, it's the same fluid circulating between the pump and motor, except that the charge pump exchanges a portion with fresh fluid and runs it through the cooler and filter.
A torque converter is totally different. It doesn't have the solid link that a hydro has. It has blades that "fling" fluid onto a different set of driven blades. Depending on how fast the the blades are spinning, the fluid impacts the driven blades at different points giving you your torque conversion.

 

[DK35vince]

Hey guys. I'm more firmilar with hydrostatic systems on payloaders and backhoes than on newer tractors. I really like how all newer tractors have different ranges in order to lower/increase speed and build torque as well. For instance on a komatsu WA180 pay loader I have a lot of experience with there are forward and reverse with 1,2,3, and 4. For heavy snow I always use 1 and 2 to build engine rpm and torque. I don't know why the guys at work don't understand that. They try and try to use 4 to push snow when all that does is heat up the trans! Plus not to mention they are revving on the engine and the wheels are not even turning!

I'm very firmilar with automatics and torque convertors as the torque convertor can multiply torque 2 to 3 times from the engine crankshaft and then planetary gears are used to create different gear ratios. A built automatic is stronger than a manual trans because you remove the clutch and the helical or spur gears which cannot hold as much torque as a planetary gear set. Upon pulling a load with an automatic you are building torque and not slipping a clutch causing torque loss.

Alright so are farm tractor hydrostatic transmissions designed to build torque as well? I know this is true of construction equipment. Can you rev on the engine and apply the hst drive for forward motion? That's the first thing that bothers me when you com pair farm tractor hst and construction hst. On construction hst you engage the drive in forward or reverse than you use the throttle to start moving as these type of hst have a stall below a certain rpm.

Does a farm tractor and construction hst work the same way mechanically?

His does hst work? I understand it as a hydraulic pump that causes fluid flow and this is stopped by a valve. The valve leads to a hydraulic "motor" that takes hydraulic pressure and turns it into a rotary motion which causes torque building and increase due to the muliplycation and speed ratios between high engine rpm to a lower transmission output speed and yes the low geared rear end. Thank you

It sounds to me like you are using/describing a torque converter power shift type transmission. Common in commercial backhoes and front loaders.
The hydrostat type used in a tractor are not the same.

 

[diesel lover]

Arlen 4720 Thanks for separating the differences between automotive/ large truck automatics and hydrostatic. I was only com pairing the two with what I know and how they both use fluid to mulitply torque.

Very good explanation guys!!! Everyone that I haven't talked to doesn't know. Well bingo!!!! So the slightest press on the pedal and medium throttle provides maximum torque for pulling power!! I will need to know because I am shopping for a 4 WD tractor for my needs in a year or two. Only have owned manual trans tractors. I'm highly considering a hst tractor after all this cooperation of construction equipment. I want something with a fel and maybe to work in short small spaces completing task.
It makes perfect sence that highest torque is at the lowest spot on the pedal and as speed increases on the pedal torque decreases as will most drive train applications.

I understand hydraulics quite well because we have 115 forklifts at work and their hydraulic systems need repaired. Steering is acomplised by an orbitor- a motor/ rotational valve that transfers the rotational movement from the steering wheel to a hydraulic cylinder that controls steering wheels.

Also our highway plow trucks are hydraulicly powered. Our top kick has a conver belt in the bed that feeds a spredder. Both of these are powered by a fixed displacement motor

 

[diesel lover]

It sounds to me like you are using/describing a torque converter power shift type transmission. Common in commercial backhoes and front loaders.
The hydrostat type used in a tractor are not the same.

Oh so backhoes and pay loaders do use a torque convertor? Must be a very large and strong torque convertor such as large truck allisons

What is the drive train in a payloader/ backhoe behind the torque convertor? Is it made of large planetary gears like an automatic and that's why you are able to shift between 1,2,3 and 4 on the fly at any time you want ?

 

[diesel lover]

Must be why construction equipment actually has stall while engaged in gear due to the nature of a torque convertor.

 

[Gary Fowler]

The way I visualize a HST transmission is it is like a multi speed bicycle where you can change drive chain to the sprockets from small at the power end (pedals) to large at the drive wheels(transmission). Small for maximum power and large for maximum speed. The power to the pedals depends on the speed of the engine turning the pump to an extent, the more RPM, the more pressure (up to the set pressure relief limit )and volume the pump will flow so you can go faster and have more power with higher RPM until you stall the motor and the pressure goes to bypass relief. When you put pressure on the go pedal, it starts out with small sprocket in front and large in rear for maximum torque and as you continue to push down on the pedal the ratio changed till it has a large sprocket pulling a small one for maximum speed but less torque. CUT Tractors have a 2 or 3 range transmission, unlike HST lawnmowers that only have one speed, so operating in L range gets you the most power but least speed and on up to H where mostly you have speed but very little power. They are no way similar to the heavy equipment that you are used to using with torque converter where more RPM= more power and speed with shift on the go powershift transmissions. Also MOST CUT tractors have to be at dead stop in order to shift transmission ranges.