Single-acting hydraulic cylinder for modeling a fuel regulator system in Simulink

Good morning,

I am trying to build a mathematical model of an engine regulator using Simulink (with the SimHydraulics library). More exactly, I'm trying to reproduce the movement of the servo-pistons who, under varying pressure of the oil that surrounds them, open or close the doser. This consists basically of a variable volume of oil which is initially 4bar (simulated as a single-acting hydraulic cylinder) fed with high pressure oil at 8bar (simulated as a constant head tank) through a variable area hole ( variable orifice ).

My problem is that when I run the simulation, the pressure starts at 4bar at t=0 but it instantly drops to ambient pressure and I don't know why. I have checked the model several times specially taking care of:

- The "chamber initial pressure" of the single-acting hydraulic cylinder (set to 4 bar). - The "pressurization" of the constant head tank (set to 8 bar).

I was wondering that maybe there's something I'm missing in the solver initial conditions, but I'm running the R2011 and I can't find how to modify them.

Thanks in advance.

Answer 1

[Guy Rouleau]

It is very hard to determine a solution with those details.

My feeling is that the problem is not with the solver, but with how components are connected together. Try using the Simscape Explorer to visualize all the variables in the network:

http://www.mathworks.com/matlabcentral/fileexchange/28184-simscape-simulation-results-explorer

This should help identifying some path where the flow is leaking, leading to the pressure drop.

[Lucía]

Thank you very much, your suggestion is very interesting.

However, I'm going through some trouble with the Simscpae Explorer: when I plot the variables, it only displays 0.1s out of 10s (the whole time of the simulation). How could I solve this?

[Guy Rouleau]

In the model configuration, the default setting saves only the last 5000 points in "simlog", to avoid memory problems. Try disabling this option in the Simscape section of the model configuration.