HST - How Does It Work?

[DFB]

On the Deere there are directional control valves located in the valve block along with "valve plates" for both the pump and motor. Changing the position of the swash plate uncovers different slots in the valve plate.

In your drawing I would think those would be control valves. I see that your oil filter is located after the charge pump too.

DFB

 

[MossRoad]

The way I understand it is that when the plate is flat, you are not moving, even though the engine is spinning the shaft. If you move the plate in one direction, you go forward. As you bring it back towards flat, you slow down and stop. If you keep the plate moving past flat in the other direction, you go backwards.

Does that sound correct?

 

[hwp]

That's right, MossRoad. When the swashplate is in the neutral position. there is no stroke of the pump pistons, so no volume to the motor. I found the answer to my question. If you compare the attached diagram to the previous one I posted, you will see that the fluid follows a different direction depending on the tilt of the swashplate. What was the discharge stroke when the swashplate is tipped one way becomes the suction stroke when tipped the other. This changes the direction of the flow of the fluid which changes the direction of rotation of the hydraulic motor. No valves needed. Now that is neat!

 

[MossRoad]

Seems there have been a few questions about how HST works, so I thought it would be a good time to revive this post.

Also, there is a link to a military manual on hydraulics that does not work, so here is a link to the same thing at a differnt URL...

Click here for a link to Field Manual No. 5-499. Good reading for anyone interested in hydraulics.

 

[JustGary]

It's been a while since I did this, but you can grab an old automotive air conditioner compressor and take it apart. Most of them use a fixed-angle swash plate to drive three pistons for raising the pressure in three lower compression stages so they can use cheaper parts.

The clutch engages the driveshaft, the driveshaft turns the swash plate, and the turning plate pumps the pistons, which are mounted parallel to the driveshaft. Aside from a few reed valves to control the flow, they don't really have anything else in them.

It might be worth while to do a web search for how a car compressor works since it's similar and has a much larger audience.

Either way, an interesting thread on a fascinating device. I'm glad you brought it back for me to notice! Thanks.

- Just Gary