How to model a vertically mounted gas-sprung hydraulic height-controlled piston in Simscape?

I’m trying to model a vertically mounted piston system in Simscape where the piston supports a variable weight (parameter-controlled). The system consists of a gas-sprung hydraulic actuator that uses a floating piston to separate the gas volume from the hydraulic oil volume. The purpose is to maintain a pressure-balanced condition to support the load while allowing controlled height adjustment.

Key features of the system:

• The piston is mounted vertically to the ground.
• The upper chamber contains compressible gas (e.g., nitrogen), acting as a spring.
• The lower chamber contains hydraulic oil.
• A floating piston separates the gas and oil, maintaining pressure equilibrium.
• The supported load is a variable parameter.
• The system includes height (position) control of the main piston.

I need guidance on:

• How best to model the gas/oil separation with a floating piston in Simscape.
• Incorporating the gas spring behavior.
• Implementing height control in the model.
• Handling the variable load and its interaction with the system.

Any help, component suggestions, or example models would be greatly appreciated.

Answer 1

[Yifeng Tang]

Something similar to this should work:

Be careful with the direction of the force and motion though. Pointing up to down on the canvas doesn't imply the direction of motion.

If you have Simscape Fluids, there is a block that I think does nearly exactly what you have in mind

https://www.mathworks.com/help/hydro/ref/doubleactingactuatorgil.html

For the other two topics:

• Implementing height control in the model.
• Handling the variable load and its interaction with the system.

It's hard to discuss in general without further details. It may be a good idea to reach out to your MathWorks sales rep and ask to be connected to an application engineer for further guidance.

[Raphael]

Hi Yifeng,

Thank you for your clear and quality response - This makes sense to me !

I can see that in your example the hydraulic manifold (ride height control) would sit between the pump and the oil piston and the ideal force source would act as the force induced by the weight of the vehicle on the oil volume (lower) and gas volume (upper).

Consdering your point on direction of force I gather we would we handle the direction of force within the ideal force source block ?

Note : The number of moles of gas is constant in the gas volume and has an intial pressure under static load so perhaps an alternative double acting piston. There is also a damper between the oil volume piston and the floating piston seperating the oil and gas volume.

Additional;

I am curious to better understand the use of To-Workspace blocks for controlling valves and sharing sensor readings between the model and the written control logic. Please could you provide a simple example ?