Cylinder

Description

Model of a differential cylinder with Stribeck friction and volumetric losses.

The fundamental geometrical properties of the differential cylinder are the piston and rod diameters (pistonDiameter and rodDiameter) as well as the lengths of the cylinder and the rod (cylinderLength and rodLength). By using the parameter angle, the inclination of the cylinder with respect to the horizon can be adjusted. The resulting forces due to gravity are taken into account automatically, however without inclusion of static fluid masses.

For dynamic calculations, the masses of the piston and the cylinder are required. These can be provided by specifying the parameters massPiston and massCylinder. The dynamic mass of the fluid, which acts as an additional inertia, is automatically taken into account by the model.

The parameters fBreakaway, fCoulomb, fProp and vM (velocity parameter of Stribeck friction at which the friction force begins to grow linearly) characterize the velocity dependence of the friction force between piston and cylinder. Instead of using the Stribeck friction model, a simplified friction calculation can be enabled by setting the check mark relFric. In this case, the friction force equals the net force acting on the interface between piston and cylinder multiplied by the parameter relFricFactor. Regardless of which friction model is used, the friction force is not influenced by the inclination of the cylinder or the system pressure. The parameter vSmall is used by the internal state machine of the cylinder model and determines the velocity below which the piston is considered stuck.

The pressure in both cylinder chambers can be initialized by assigning start values to pA (bore side) and pB (rod side). The parameter deadVolume determines the size of the parasitic volume which remains even if the piston has reached the mechanical stops at the cylinder ends.

Cylinder ends are modeled as bumstops whose stiffness, damping and stiffness exponent can be tuned in the appropriate Bumpstops parameter tab. Alternatively, the stroke limits can be enforced by means of hard constraints (through useHardBumpstops) thus strictly impeding the cylinder to overextend.

The volumetric losses due to internal and external leakage are parameterized by providing the respective flow rates (Internal leakage: volume flow and External leakage: volume flow), associated pressure drops (Internal leakage: pressure difference and External leakage: pressure difference) and the fluid density Reference density for volume flow and pressure difference for which these values were obtained.

The fluid properties can be propagated between the two hydraulic ports by setting the parameter forwardFluidProperties to "true".