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Rotational Hydro-Mechanical Converter

Interface between hydraulic and mechanical rotational domains

Library

Hydraulic Elements

Description

The Rotational Hydro-Mechanical Converter block models an ideal transducer that converts hydraulic energy into mechanical energy, in the form of rotational motion of the converter shaft, and vice versa. Physically, the converter represents the main component of a single-acting rotary vane actuator. The compressibility option makes the converter account for dynamic variations of the fluid density.

Using this block as a basic element, you can build a large variety of rotary actuators by adding application-specific effects, such as leakage, friction, hard stops, and so on.

The converter is simulated according to the following equations:

where

qFlow rate to the converter chamber
DConverter displacement, or fluid volume needed to rotate the shaft per angle unit
ωSConverter shaft angular velocity
ωCConverter case angular velocity
TTorque on the shaft
pGauge pressure of fluid in the converter chamber
VPiston volume
αRelative amount of trapped air
ρl0Fluid density at atmospheric conditions
ρg0Gas density at atmospheric conditions
p0Atmospheric pressure
γSpecific heat ratio
βlBulk modulus at atmospheric conditions and no gas
εConverter orientation with respect to the globally assigned positive direction. If pressure applied at port A generates torque in positive direction, ε equals 1. If pressure applied at port A generates torque in negative direction, ε equals –1.

The piston volume is computed according to

where

VdeadChamber dead volume
θ0Shaft initial angle
θShaft rotation from initial position

Port A is a hydraulic conserving port associated with the converter inlet. Ports S and C are mechanical rotational conserving ports associated with the shaft and the case of the converter, respectively. Pressure at port A generates torque in the direction specified by the Converter orientation parameter.

The block dialog box does not have a Source code link. To view the underlying component source, open the following files in the MATLAB® editor:

  • For incompressible converter implementation — matlabroot\toolbox\physmod\simscape\library\m\+foundation\+hydraulic\+elements\rotational_converter_incompressible.ssc

  • For compressible converter implementation — matlabroot\toolbox\physmod\simscape\library\m\+foundation\+hydraulic\+elements\rotational_converter_compressible.ssc

where matlabroot is your root folder.

Basic Assumptions and Limitations

The block simulates an ideal converter, with an option to account for fluid compressibility. Other effects, such as hard stops, inertia, or leakage, are modeled outside of the converter.

Dialog Box and Parameters

Displacement

Effective converter displacement. The default value is 1.2e-4 m^3/rad.

Converter orientation

Specifies converter orientation with respect to the globally assigned positive direction. The converter can be installed in two different ways, depending upon whether it generates torque in the positive or in the negative direction when pressure is applied at its inlet. If pressure applied at port A generates torque in negative direction, set the parameter to Acts in negative direction. The default value is Acts in positive direction.

Compressibility

Specifies whether fluid density is taken as constant or varying with pressure. The default value is Off, in which case the block models an ideal transducer. If you select On, the block dialog box displays additional parameters that let you model dynamic variations of the fluid density without adding any extra blocks.

Shaft initial angle

Initial offset of the piston from the cylinder cap. The default value is 0.

Chamber dead volume

Volume of fluid in the chamber at zero piston position. The default value is 1e-4 m^3.

Specific heat ratio

Gas-specific heat ratio. The default value is 1.4.

Initial pressure

Initial pressure in the chamber. This parameter specifies the initial condition for use in computing the block's initial state at the beginning of a simulation run. The default value is 0.

 Restricted Parameters

Ports

The block has the following ports:

A

Hydraulic conserving port associated with the converter inlet.

S

Mechanical rotational conserving port associated with the shaft of the converter.

C

Mechanical rotational conserving port associated with the case of the converter.

See Also

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