Axial piston motors and oscillation 3

[hydroman247]

Hi guys, another question for you.

4 wheel drive mobile machine.
Main pump is a gear pump
Electro proportional spool control
4 axial piston motors. (2 motors on each side hosed in series).
Please note, there is no flow divider, just the drive spool direct to the wheel motors with a cross line anti-cavitation valve in between.

When driving normally it is fine, but when I select low speed which is ~20L/min through the drive valve and am at full lock I get lurching oscillations. This also seems to only happens when going forwards at full lock, either left or right.

The only other little issue is at very low speed, I mean <0.5km/h, the whole chassis shakes and the wheels twitch a lot. Like something is opening and closing very rapidly causing pressure spikes. When I checked the pressures between both side pairs of wheel motors, I could see this oscillation clearly.

Does anyone have any idea what could be causing this? The fact that it only happens going forward has to be a big clue. The steering angle is very sharp but this problem did not occur to the same extent with the previous wheel motors from a different brand, although they were also axial piston.

Thanks,

Hydroman

 

[Compositepro]

Since you have wheels that turn to steer, the motors should all be piped in parallel. The ground will keep them all turning at the appropriate speed and flow will divide automatically. There would only be a problem if you lose traction on one wheel, as Mike said. Your piping arrangement would be suitable for skid steer, where the wheels do not turn to steer.

 

[hydroman247]

Whilst this is the obvious solution, current production machines use this set up and the only things we have changed are the wheel motors. There is an anti cavitation valve which should be supplying oil in case of a drop in pressure and it also has a relief valve but in the scenario I am talking about, pressure spiked at 120bar which is nowhere near the 350 bar relief setting.

More testing today so hopefully sort it by the tonight.