Cylinder Cushion (IL)
Hydraulic cylinder damper in an isothermal liquid network.
Description
Unit Cylinder Cushion (IL) is a throttle-braked hydraulic cylinder damper in an isothermal liquid network. The damper slows the cylinder rod as it approaches the end of its stroke, limiting the flow of fluid exiting the piston cavity. The figure below shows a typical damper design [1].
As the piston moves toward the cap, which is on the left in the figure, the damper sleeve, or plunger, enters a mating hole in the cap (damper cavity) and provides additional resistance to the fluid leaving the cylinder working cavity. Piston deceleration begins when the plunger enters the damper cavity in the cap and blocks the main fluid outlet. In this condition, fluid flows through the throttle valve and the minimum clearance. The valve limits the flow of fluid exiting the operating cavity and brakes the piston.
The hydraulic cylinder damper consists of two orifices, variable and constant cross-sections, and a check valve. The variable bore represents the variable clearance between the plug and the notch in the end cap. The constant cross-section port is a throttle in the channel connecting the damper cavity to the piston cavity. The check valve allows flow between the damper cavity and the piston cavity only when the piston is extended.
Block Cylinder Cushion (IL) - is a composite component consisting of the following blocks:
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Block Orifice (IL) models the throttle valve.
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Block Check Valve (IL) models the check valve.
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Block Orifice (IL) models the variable clearance between plug and end cap.
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Block Absolute Translational Motion Sensor converts the distance between the plug and the cavity in the end cap into a physical signal. This signal controls the degree of opening of the variable clearance.
The block Cylinder Cushion (IL) can be used to model hydraulic actuators. A single-acting or double-acting hydraulic actuator can include dampers to slow the piston near the ends of the stroke. The damper prevents hard shocks when the piston is stopped by the end caps.
Ports A and B are non-directional isothermal liquid ports associated with the fluid supply and piston cavity, respectively. Port R is a mechanical non-directional port associated with the piston plunger. Port C is a mechanical non-directional port associated with the clamping structure of the cylinder. The block dampens the flow from port B to port A. The check valve in the block is orientated from port A to port B.
Variable port area
In a variable orifice block, it is assumed that when the plunger is away from the cap, the cross-section of the main fluid path is open and its area is , where is the diameter of a round plunger. As the plunger moves towards the cap, fluid passes through the radial gap from the cylinder cavity into the reciprocating orifice on the cap. It is assumed that the orifice area varies linearly with piston movement between the maximum area and the leakage area. The orifice area for a given piston position is
where
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- is the bore area for the given piston position;
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- is the leakage area between plunger and cushion sleeve, the value of the Leakage area between plunger and cushion sleeve parameters;
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- maximum bore size, which is equal to the value of the Cushion plunger cross-sectional area parameter;
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- piston position. Piston initial displacement ; the value of the Actuator piston initial displacement parameters;
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- has a value of
1when the Actuator mechanical orientation parameter is set toPressure at A causes positive displacement of R relative to C, and-1when the Actuator mechanical orientation parameter is set toPressure at A causes negative displacement of R relative to C; -
- length of the cushioning plunger, the value of the Cushion plunger length parameters;
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- cushion plunger diameter, the value of the Cushion plunger diameter parameter.
Numerical smoothing of area and pressure values
You can maintain numerical stability in simulation by adjusting the Smoothing factor parameters. If the Smoothing factor parameters are not zero, the orifice area and check valve control pressure are smoothed. The orifice area between parameters Leakage area between plunger and cushion sleeve and Cushion plunger cross-sectional area is smooth. The control pressure of the valve is infinitely variable between the parameters Check valve cracking pressure differential and Check valve maximum pressure differential.
Ports
Non-directional
A - inlet port
isothermal liquid
Isothermal liquid port corresponding to the inlet to the damper cavity.
B - outlet port
`isothermal liquid'.
Isothermal liquid port corresponding to the outlet to the piston cavity.
R - rod
translational mechanics
Mechanical progressive port corresponding to the piston of a hydraulic cylinder.
C - housing
` translational mechanics`.
Mechanical progressive port corresponding to the support structure of the hydraulic cylinder.
Parameters
Cushion Plunger
Cushion plunger cross-sectional area - cushion plunger cross-sectional area
1e-4 m² (by default) | Positive scalar
The cross-sectional area of the shock absorber plunger. The area is equal to , where is the diameter of the circular plunger.
Cushion plunger length - cushion plunger length
1e-3 m (by default) | `positive scalar'.
Cushion plunger length.
Initial actuator piston displacement - initial piston displacement
0 m (by default) | scalar
The displacement of the piston in the cylinder at the start of the simulation. This displacement defines the initial area of the variable bore, which models the variable clearance between the ram and the end cap.
Dependencies
If the Actuator mechanical orientation parameters are set to `Pressure at A causes positive displacement of R relative to C', the value of the initial piston displacement must be greater than or equal to zero.
If the Actuator mechanical orientation parameters are set to `Pressure at A causes negative displacement of R relative to C', the value of the initial piston displacement must be less than or equal to zero.
Actuator mechanical orientation - direction of piston displacement
Pressure at A causes positive displacement of R relative to C (by default) | Pressure at A causes negative displacement of R relative to C.
Direction of piston displacement of the connected drive unit. If this parameter is set to Pressure at A causes positive displacement of R relative to C, the piston extends at positive displacement of R to C. If this parameter is set to Pressure at A causes negative displacement of R relative to C, the piston retracts at positive R to C.
Valves
Cushion orifice area - throttle valve orifice area
1e-6 m² (by default) | positive scalar
Constant throttle valve orifice area through which fluid flows from the piston cavity when the plunger is inside the damper cavity.
Leakage area between plunger and cushion sleeve - total leakage area when the plunger is inside the cover bore
1e-7 m² (by default) | Positive scalar
Total area of possible leakage when the plunger is inside the damper cavity. When the piston movement is less than or equal to the value of the Cushion plunger length parameters, the area of the variable orifice modelling the gap between the plunger and the cover is equal to the value of this parameter.
Check valve cracking pressure differential - pressure differential at which the check valve starts to open
0.01 MPa (by default) | `positive scalar'.
The minimum differential pressure across the check valve at which the valve starts to open. The check valve allows fluid to flow freely from the damper cavity to the piston cavity, but does not allow fluid to flow in the opposite direction.
Check valve maximum pressure differential - pressure differential required to fully open the check valve
0.1 MPa (by default) | `positive scalar'.
Pressure drop across the check valve required for the check valve to fully open. The value of this parameter must be greater than the value of the Check valve cracking pressure differential parameter. The check valve allows fluid to flow freely from the damper cavity to the piston cavity, but does not allow fluid to flow in the opposite direction.
Check valve maximum area - area of fully open check valve
1e-4 m² (by default) | Positive scalar
The cross-sectional area of the check valve orifice in the fully open position.
Check valve leakage area - total leakage area when the check valve is fully closed
1e-10 m² (by default) | Positive scalar
Total possible leakage area with fully closed check valve.
Smoothing factor - numerical smoothing factor
0.01 (by default) | positive scalar
A continuous smoothing factor that provides smooth opening by correcting the valve characteristic in the nearly open and nearly closed positions. Set a non-zero value less than one to increase the stability of the simulation in these modes.