power control axial piston pump calculation

[RobertHasty]

Hello,

I would like to read some opinions regarding extension and/or retraction time calculation of a hydraulic cylinder when using axial piston pump with power controller (e.g. Rexroth DFLR) .

I have a pressure/stroke curve for a cylinder and a pump with fixed power value.

How can I calculate extension time with this data?

Thanks.

Best regards,
Robert

 

[HPost]

Hello Robert...

You can use integration to find the energy under the pressure / stroke curve. That will give you the total energy required to actuate the cylinder.

With a known power value for the pump controller, you can the divide the total energy by the power value for the controller. This will give you the time taken to move the cylinder with amount of the available power.

kJ/kW = T

Cheers

HPost CEng MIMechE

 

[RobertHasty]

Hello HPost, thanks for Your reply.

My wife gave me exactly the same answer.

Do you have some other tips, e.g. what else should I consider?

I assume the pressure, that a pump in a combination with a prime mover supplies, should be higher than the highest pressure in the system.

Any others?

Thanks.

 

[HPost]

Hi Robert...

Yes, the pressure at the pump outlet will be highest pressure in the system. The power you have available at the pump needs to include the pump efficiency losses so that the motor, power matched to the PQ controller does not stall. You also need to consider the system losses between the pump and the actuator. Depending on how you want the system to work and also how lean you want it to run, you may also want to consider the return flow restrictions.

You haven't stated how much power you are dealing with, so it's impossible to determine the power lost in the system as a percentage of total system power.

The total system power requirement needs to be added to motor and PQ controller, with some contingency to allow for higher pressure losses with cold oil etc...

If you trim the system too fine in terms power, you may find that your motor will stall if the controller doesn't respond quickly enough. Equally, you may see the actuator slow or stall.

I'm all for energy efficiency, but it's alwways important to allow enough room to wriggle.

Cheers

HPost Ceng MIMechE