Documentation

Flow Divider-Combiner

Hydraulic two-path flow divider-combiner

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Flow Control Valves

Description

The Flow Divider-Combiner block models a hydraulic valve that divides incoming flow through port P (direct flow) between two outlets, and also maintains a specified proportion between return flows through ports A and B in the total flow rate through port P. In other words, the valve works in two distinctive modes: flow divider for direct flow and flow combiner for reverse flow.

The figure shows a schematic for the flow divider-combiner valve: a) in the divider mode, and b) in the combiner mode.

The valve works as a flow divider when fluid is pumped through port P to ports A and B (schematic figure a). In this mode, fluid passes through fixed orifices in pistons 2 and 5 and through variable orifices formed by round holes in the pistons and case. The pressure differential across pistons moves them apart from each other proportionally to the piston areas and the spring 1 and 6 forces. The spring-suspended pistons and the respective variable orifices work as pressure reducing valves maintaining constant pressure drop across fixed orifices and thus keeping flow rates through them practically constant. The flow divider-combiner valve is essentially a combination of two pressure-compensated flow control valves working in parallel.

For reverse flows (schematic figure b), the pressure differential across pistons forces them against each other until the gap in the hard stop is cleared. The pistons settle at a position where pressure drops across fixed orifices are equal, thus maintaining equal flow rates through branches.

The model of the flow divider-combiner uses the Fixed Orifice, Orifice with Variable Area Round Holes, Double-Acting Hydraulic Cylinder (Simple), Translational Hard Stop, Translational Spring, and Translational Damper blocks, as shown in the block diagram.

The table explains the purpose of each model component.

Name in the block diagramPurpose (numbers refer to the valve schematic)Name in the actual component file
Fixed Orifice AFixed orifice in piston 5fixed_orifice_A
Fixed Orifice BFixed orifice in piston 2fixed_orifice_B
Piston APiston 5piston_A
Piston BPiston 2piston_B
Hard Stop A-BHard stop between pistons 2 and 5hard_stop_A_B
Spring ASpring 6spring_A
Spring A-BSpring 4spring_A_B
Spring BSpring 1spring_B
Damper ASpring 6 dampingdamper_A
Damper A-BSpring 4 dampingdamper_A_B
Damper BSpring 1 dampingdamper_B
Orifice with Variable Area Round Holes AVariable orifice created by round holes in piston 5 and the casevariable_orifice_A
Orifice with Variable Area Round Holes BVariable orifice created by round holes in piston 2 and the casevariable_orifice_B
Ideal Translational Motion Sensor AMeasures piston 5 displacement and exports the measurement to the Orifice with Variable Area Round Holes Asensor_A
Ideal Translational Motion Sensor BMeasures piston 2 displacement and exports the measurement to the Orifice with Variable Area Round Holes Bsensor_B

The block orientations in the model are explained by the structure section of the underlying component file, reproduced below:

connections
    connect(P, fixed_orifice_A.A, fixed_orifice_B.A, piston_A.B, piston_B.B);
    connect(fixed_orifice_A.B, piston_A.A, variable_orifice_A.A);
    connect(fixed_orifice_B.B, piston_B.A, variable_orifice_B.A);
    connect(B, variable_orifice_B.B);
    connect(A, variable_orifice_A.B);
    connect(reference.V, piston_A.C, spring_A.C, damper_A.C, sensor_A.C, ...
        piston_B.C, spring_B.C, damper_B.C, sensor_B.C);
    connect(piston_A.R, spring_A.R, hard_stop_A_B.C, spring_A_B.C, ...
        damper_A.R, damper_A_B.R, sensor_A.R);
    connect(piston_B.R, spring_B.R, hard_stop_A_B.R, spring_A_B.R, ...
        damper_B.R, damper_A_B.C, sensor_B.R);
    connect(sensor_A.P, variable_orifice_A.S);
    connect(sensor_B.P, variable_orifice_B.S);
end

Assumptions and Limitations

The block does not account for inertia, friction, and hydraulic forces. For additional assumptions and limitations, see the reference pages of the underlying member blocks.

Parameters

Fixed Orifices Tab

Fixed orifice A area

The cross-sectional passage area of the fixed orifice in piston 5 (the P–A path). The default value is 1.5e-5 m^2.

Fixed orifice B area

The cross-sectional passage area of the fixed orifice in piston 2 (the P–B path). The default value is 1.5e-5 m^2.

Fixed orifice flow discharge coefficient

Semi-empirical coefficient for fixed orifice capacity characterization. The value depends on the orifice geometrical properties, and usually is provided in textbooks or manufacturer data sheets. The default value is 0.7.

Fixed orifice laminar transition specification

Select how the block transitions between the laminar and turbulent regimes for the fixed orifices:

  • Pressure ratio — The transition from laminar to turbulent regime is smooth and depends on the value of the Fixed orifice laminar flow pressure ratio parameter. This method provides better simulation robustness.

  • Reynolds number — The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches the value specified by the Fixed orifice critical Reynolds number parameter.

Fixed orifice laminar flow pressure ratio

Pressure ratio at which the flow transitions between laminar and turbulent regimes. The default value is 0.999. This parameter is visible only if the Fixed orifice laminar transition specification parameter is set to Pressure ratio.

Fixed orifice critical Reynolds number

The maximum Reynolds number for laminar flow in the fixed orifices. The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches this value. The default value is 10. This parameter is visible only if the Fixed orifice laminar transition specification parameter is set to Reynolds number.

Pistons Tab

Piston A area

The face area of Piston A (piston 5). The default value is 2e-4 m^2.

Piston A stroke

The full stroke of Piston A. The default value is 5 mm.

Piston A initial extension

The initial extension of Piston A. The default value is 0 m.

Piston B area

The face area of Piston B (piston 2). The default value is 2e-4 m^2.

Piston B stroke

The full stroke of Piston B. The default value is 5 mm.

Piston B initial extension

The initial extension of Piston B. The default value is 0 m.

Piston stop penetration coefficient

The penetration property of colliding bodies in the underlying cylinder blocks, which is assumed to be absolutely plastic. The default value is 1e12 s*N/m^2.

Springs/Dampers Tab

Spring A rate

Spring rate of Spring A (spring 6). The default value is 1e3 N/m.

Spring A preload

This parameter sets the initial high-priority target value for the Deformation variable in the underlying Spring A block. For more information, see Variable Priority for Model Initialization (Simscape). The default value is 0.1 m.

Damping coefficient A

Damping coefficient of Damper A (spring 6 damping). The default value is 150 N/(m/s).

Spring B rate

Spring rate of Spring B (spring 1). The default value is 1e3 N/m.

Spring B preload

This parameter sets the initial high-priority target value for the Deformation variable in the underlying Spring B block. For more information, see Variable Priority for Model Initialization (Simscape). The default value is -0.1 m.

Damping coefficient B

Damping coefficient of Damper B (spring 1 damping). The default value is 150 N/(m/s).

Spring A-B rate

Spring rate of Spring A-B (spring 4). The default value is 1e3 N/m.

Spring A-B preload

This parameter sets the initial high-priority target value for the Deformation variable in the underlying Spring A-B block. For more information, see Variable Priority for Model Initialization (Simscape). The default value is 0.1 m.

Damping coefficient A_B

Damping coefficient of Damper A-B (spring 4 damping). The default value is 150 N/(m/s).

Variable Orifices Tab

Variable orifice A hole diameter

Diameter of the holes in the underlying Orifice with Variable Area Round Holes A block. The default value is 0.0025 m.

Variable orifice B hole diameter

Diameter of the holes in the underlying Orifice with Variable Area Round Holes B block. The default value is 0.0025 m.

Number of hole pairs in the variable orifice

Number of holes in each of the Orifice with Variable Area Round Holes blocks. The default value is 4.

Variable orifice flow discharge coefficient

Semi-empirical parameter defining the orifice capacity of the Orifice with Variable Area Round Holes blocks. The value depends on the geometrical properties of the orifice, and usually is provided in textbooks or manufacturer data sheets. The default value is 0.7.

Variable orifice A initial center distance

Initial opening in the underlying Orifice with Variable Area Round Holes A block. The parameter value can be positive (underlapped orifice), negative (overlapped orifice), or equal to zero for zero lap configuration. The default value is 0.0025 m, which corresponds to the position of piston 5 in the valve schematic drawing.

Variable orifice B initial center distance

Initial opening in the underlying Orifice with Variable Area Round Holes B block. The parameter value can be positive (underlapped orifice), negative (overlapped orifice), or equal to zero for zero lap configuration. The default value is -0.0025 m, which corresponds to the position of piston 2 in the valve schematic drawing.

Variable orifice laminar transition specification

Select how the block transitions between the laminar and turbulent regimes for the variable orifices:

  • Pressure ratio — The transition from laminar to turbulent regime is smooth and depends on the value of the Variable orifice laminar flow pressure ratio parameter. This method provides better simulation robustness.

  • Reynolds number — The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches the value specified by the Variable orifice critical Reynolds number parameter.

Variable orifice laminar flow pressure ratio

Pressure ratio at which the flow transitions between laminar and turbulent regimes. The default value is 0.999. This parameter is visible only if the Variable orifice laminar transition specification parameter is set to Pressure ratio.

Variable orifice critical Reynolds number

The maximum Reynolds number for laminar flow through the variable orifices. The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches this value. The default value is 10. This parameter is visible only if the Variable orifice laminar transition specification parameter is set to Reynolds number

Variable orifice leakage area

The total area of possible leaks in each variable orifice when it is completely closed. The main purpose of the parameter is to maintain numerical integrity of the circuit by preventing a portion of the system from becoming isolated after the orifice is completely closed. The parameter value must be greater than 0. The default value is 1e-9 m^2.

Hard Stop Between Pistons Tab

Hard stop upper bound

Gap between the slider and the upper bound in the underlying Hard Stop block. The default value is 5.1 mm.

Hard stop lower bound

Gap between the slider and the lower bound in the underlying Hard Stop block. The default value is 1 mm.

Hard stop stiffness

The elastic property of colliding bodies in the hard stop. The default value is 1e8 N/m.

Hard stop damping coefficient

The dissipating property of colliding bodies in the hard stop. The default value is 150 N/(m/s).

Global Parameters

Parameters determined by the type of working fluid:

  • Fluid density

  • Fluid kinematic viscosity

Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.

Ports

The block has the following ports:

P

Hydraulic conserving port associated with the inlet port P.

A

Hydraulic conserving port associated with the outlet port A.

B

Hydraulic conserving port associated with the outlet port B.

Introduced in R2014b

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