Hydrostatic pump vibration 1

[AntiqueGuy]

I have a hydraulic pump assembly mounted to a 4 cyl. engine which analysis shows 2nd order vibrations in excess of 5g at the pump CG.
Given this information, how can I determine how this affects pump duty cycle and durability.

 

[Artisi]

How is the pump connected to the engine?

 

[AntiqueGuy]

Thanks for replying.

The pump is bolted to a plate which is bolted to the engine flywheel housing so the two are inline.
There is no additional support for the pump, in hangs freely from the flywheel cover so the vibration accelerations from the engine are being amplified.

AntiqueGuy

 

[cb92]

If your motor is vibrating too much, you may have to remote mount the pump, drive it with a shaft with u-joints or flexible couplings. That's a pain. Is the pump connected to the flywheel with a solid or flexible joint? I used to mount marine clutches on auto flywheel housings. Getting it centered was always tough. We would connect them together with a machined shaft bolted to the flywheel that had a spline into the trans. Then I would move it up,down,left and right, marking as I went with a scribe. Then I would find the center of all the marks and transfer punch for the holes in the plate.
Why the heck is the motor vibrating so much?

 

[Artisi]

can you be sure that the connection between the flywheel and the pump shaft is running true- I very much doubt it with vibration numbers you are talking about.

 

[btrueblood]

" which analysis shows 2nd order vibrations in excess of 5g at the pump CG. "

What is the driving acceleration (I presume the engine itself), is this from measured real-world data?

"Given this information, how can I determine how this affects pump duty cycle and durability. "

Dunno about duty cycle, that would seem to be an operator-dependent term, "how hard does this get used?". Durability...another difficult term to assess, as it involves things not readily calculable (friction/wear on moving parts). You might be able to model the stresses occurring in the pump materials, and compare them to known fatigue life curves for the materials, adding on the stress due to pressure generated by the pump...which of course is dependent on how the pump is used...but maybe that answers the question?

 

[AntiqueGuy]

Just to give a little more information, the pump drive shaft is attached to the engine with a flexible coupler.
Its actually a tandem piston pump so it has two pumps in one housing which drives a set of ground drive motors in a mobile unit.

The engine vibration is the driving acceleration at the pump.
Accelerometer data collected at the pump shows high frequency accelerations at about 50 m/s2, of course this varies depending on engine rpm which rated is 2700.
I'm not too concerned with the low frequency vibrations like the ones seen when actually traveling.

The main thing I'm trying to determine is if accelerations are normally this high for this type of mobile application and how this affects the pump durability as well as efficiency.
I'm looking at replacing the pump which has pilot operated servos with one that is EH controlled and am trying specify the requirements I need in the area of durability and efficiency.

Thanks,
AntiqueGuy

 

[btrueblood]

Hm. Tandem piston as in two pistons? Could be quite a bit of pressure pulsation and "throb" if so, and that may add to the accel's you are seeing, but more importantly puts a heck of a lot of stress/fatigue on the plumbing. Consider a triplex (3 piston) pump, as they cut the pulsations down by more than half?

Yes, I could believe 5g accelerations for a heavily loaded engine, if there is not a lot of inertial load on it, and no torque converter or similar device to absorb the torque pulsations from the motor. We had similar trouble with a 2-cylinder motor driving a positive displacement (Roots) blower, turned out that the motor had been designed and delivered to us with a lighter flywheel than "normal", we had a lot of trouble with vibrations that we finally traced to the torque "ripple" from the motor. Are you seeing any fatigue damage on the flexible elements in the coupler; is the coupler a metallic flex, or a rubber-element type? Can you put a larger flywheel on the motor and retest?