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Rotational Pneumatic-Mechanical Converter

Interface between pneumatic and mechanical rotational domains

Library

None (example custom library)

  • Rotational Pneumatic-Mechanical Converter block

Description

Note

As of Release R2016b, the Gas block library replaces the Pneumatic library as the recommended way of modeling pneumatic systems. The former Pneumatic library is now included in the product installation as an example custom library. The pneumatic domain definition is still provided with the software, and all the pneumatic blocks in your legacy models continue to work as before. However, these blocks no longer receive full production support and can be removed in a future release.

The Rotational Pneumatic-Mechanical Converter block provides an interface between the pneumatic and the mechanical rotational domains. Use it as a building block for modeling pneumatic pumps and motors.

The pneumatic flow rate and mechanical rotation are related by the following equations:

Q=D·ω

T={D·(pApB)·ηfor (pApB)·ω >= 0D·(pApB)/ηfor (pApB)·ω < 0 

where

QVolumetric flow rate flowing from port A to port B
pAPressure at port A
pBPressure at port B
ωShaft angular rotational speed
TMechanical torque
DVolumetric displacement per unit rotation
ηConverter efficiency

The torque equation depends on the direction of power flow, and is always such that the conversion results in some thermal losses.

From considering energy flow, the heat flow out (qo) of the converter must equate to the heat flow in (qi) minus mechanical work done. Therefore, the heat equations are:

qi=|G|·cp·Ti

qo={qiD·(pApB)·ω·ηfor (pApB)·ω >= 0qiD·(pApB)·ω/ηfor (pApB)·ω < 0 

where G is the mass flow rate.

If the pneumatic pressure drops from port A to port B, then the resulting torque is positive acting from the mechanical port C to port R.

Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Basic Assumptions and Limitations

  • Conversion efficiency is constant, that is, it does not depend on torque or speed.

  • Gas flow rate is linearly dependent of pump speed.

  • The process is adiabatic, that is, there is no heat transfer with the environment.

  • Gravitational effects can be neglected.

Parameters

Displacement

Specify the effective piston displacement, as volume per unit angle. The default value is .001 m^3/rad.

Efficiency

Specify the converter efficiency. The default value is 0.2.

Ports

The block has the following ports:

A

Pneumatic conserving port associated with the converter inlet.

B

Pneumatic conserving port associated with the converter outlet.

R

Mechanical rotational conserving port associated with the piston (rod).

C

Mechanical rotational conserving port associated with the reference (case).

Version History

Introduced in R2009b