Pressure problems when controlling a double acting actuator (IL) in Simscape

Hello, I am currently working on a simple hydraulic project using isothermal liquid components. What I`m essentially trying to do is to replicate a real hydraulic cylinder in Simscape and measure the maximum force it delivers. I put in the cylinder dimensions and tried to simulate. At a pressure of 210 bar a force of around 26kN are expected. My simulation shows however, that the force is only about 24kN. When looking at the pressure of the individual components I realised that the valve seems to be the troublemaker. The input pressure of 210bar drops to 202 bar at the connection P-A. Furthermore the pressure at B is not equal to the atmospheric pressure at T. When I looked at the valve characteristics plot I realised that at the valve position s=2 not only P-A and B-T are open, but also P-B to some extend. This would explain why the cylinder only delivers 24KN instead of 26KN.

To get the desired force I tried to change the parameters within the valve. For example I tried to change the spool travel distance so that P-A and P-B are not open at the same time. I also tried to change the discharge coefficient, to decrease the pressure drop between P-A. Doing so however, always resulted in the following error message:

An error occurred while running the simulation and the simulation was terminated

Caused by:

['Pruefmaschinenzylinder/Prüfmaschinenzylinder/Solver Configuration']: At time 0.118000, one or more assertions are triggered.

Pressure of liquid volume must be greater than or equal to Minimum valid pressure. The assertion comes from:

Block path: Pruefmaschinenzylinder/Prüfmaschinenzylinder/Double-Acting Actuator (IL)1

Apparently the pressure delivered by the pump is not big enough to move the cylinder properly.

My question now is: What makes this system so unstable? Why does changing the spool travel distance of the valve result in this error message? Is my system missing a component, or is there something else to it? I have attached the simscape file.

I would really appreciate any help.

Answer 1

[Sandro G]

I solved this problem by replacing the ideal pressure source with a fixed displacement pump, that is able to provide the system with the needed pressure and volumetric flow rate.

[Flávio Luiz]

This solution worked for me as well