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Double-acting hydraulic valve actuator driven by four pressures
The Hydraulic 4-Port Cartridge Valve Actuator block represents a double-acting hydraulic valve actuator driven by four pressures. Use it as a pilot actuator for cartridge valves, pilot-operated pressure and control valves, and similar devices. A schematic diagram of the 4-port cartridge valve actuator is shown in the following illustration.
The actuator drives a valve (spool, poppet, and so on) whose position depends on pressures at ports A, B, X, and Y and the spring force. Pressures at ports A and B tend to open the valve, while pressures at control ports X and Y, together with the spring force, act to close it. The model does not account for flow consumption and loading forces, except spring and pressure forces.
Inertial properties of the actuator are accounted for by adding a first order lag between the steady-state and actual valve displacements. The lag is simulated with the combination of the PS Gain and PS Integrator blocks, enveloped by the unity feedback.
The valve remains closed as long as the aggregate pressure force is lower than the spring preload force. The poppet is forced off its seat as the preload force is reached and moves up proportionally to pressure increase until it passes the full stroke.
The force acting on the poppet and the poppet displacement are computed with the following equations:
$${F}_{P}={p}_{A}\cdot {A}_{A}+{p}_{B}\cdot {A}_{B}-{p}_{X}\cdot {A}_{X}-{p}_{Y}\cdot {A}_{Y}$$
$${x}_{s}=\{\begin{array}{ll}0\hfill & \text{for}{F}_{P}={F}_{PR}\hfill \\ \left({F}_{P}-{F}_{PR}\right)/{k}_{spr}\hfill & \text{for}{F}_{PR}{F}_{P}{F}_{PR}+{k}_{spr}\cdot {x}_{\mathrm{max}}\hfill \\ {x}_{\mathrm{max}}\hfill & \text{for}{F}_{P}={F}_{PR}+{k}_{spr}\cdot {x}_{\mathrm{max}}\hfill \end{array}$$
$$x={x}_{s}\frac{1}{Ts+1}$$
where
F_{P} | Pressure force acting on the poppet |
p_{A}, p_{B}, p_{X}, p_{Y} | Pressures at ports A, B, X, and Y, respectively |
A_{A}, A_{B}, A_{X}, A_{Y} | Areas at ports A, B, X, and Y, respectively. Areas at ports A and Y are block parameters. Area at port X is specified by its ratio to that at port A, A_{A} / A_{X}. Area at port B is determined as A_{B} = A_{X} – A_{A}. |
x | Actual poppet displacement |
x_{s} | Steady-state poppet displacement |
x_{max} | Full stroke |
F_{PR} | Spring preload force |
k_{spr} | Spring rate |
Connections A, B, X, and Y are hydraulic conserving ports associated with the actuator ports. Connection P is a physical signal port whose output corresponds to poppet displacement. Pressures applied at ports A and B move the poppet in the positive or negative direction, depending on the value of the Actuator orientation parameter. Pressures at ports X and Y act in the opposite direction to pressures at ports A and B.
The flow consumption associated with the valve motion is assumed to be negligible.
The inertia, friction, and hydraulic axial forces are assumed to be small and are not taken into account.
Effective poppet area at port A. The parameter value must be greater than zero. The default value is 3.3e-4 m^2.
Ratio between poppet areas at port A and port X. The parameter value must be greater than zero. The default value is 0.66.
Effective piston area at port Y. The parameter value must be greater than zero. The default value is 1.65e-4 m^2.
Spring preload force. The default value is 26 N.
Spring rate. The default value is 1.4e4 N/m.
Maximum poppet stroke. The parameter value must be greater than zero. The default value is 5e-3 m.
Initial gap between the poppet and the seat. The parameter value must be greater than or equal to zero. The default value is 0.
Time constant of the first-order lag. The default value is 0.01 s.
Specifies actuator orientation with respect to the globally assigned positive direction. The actuator can be installed in two different ways, depending upon whether it moves the poppet in the positive or in the negative direction when pressure is applied at its inlet. If pressures applied at ports A and B move the poppet in the negative direction, set the parameter to Acts in negative direction. The default value is Acts in positive direction.
The block has the following ports:
Hydraulic conserving port associated with the valve inlet.
Hydraulic conserving port associated with the valve outlet.
Hydraulic conserving port associated with the valve control terminal.
Hydraulic conserving port associated with the valve control terminal.
Physical signal port that outputs poppet displacement.
For an example of using this block, see the Hydraulic Actuation System with Cartridge Valves example.