Help Text for variable displacement motor block

This block is the model of a fixed displacement hydraulic motor.

The inputs to the block are:

  1. the motor flows from the lines (is a two elements vector)
  2. the external force acting on the actuator (a constant) [Nm]
  3. the system pressure (accumulator output)
  4. the motor displacement in [m3/rev]
  5. the torque transmitted by the a second mass connected to the actuator output through a link, having a defined stiffness [Nm/rad].

The input 5 shall be connect to the output of a 'Stiffness & Inertia' block or to a 'Ground' block if the second inertia is not present.

The outputs are:

  1. the actuator position [rad]
  2. the pressures into the two actuator chambers (it a two elements vector)
  3. the motor speed

The motor drag torque is represented by the following equation:

DragTorque = Displ*(rkm*omg^1.4 + Ploss + (p1 + p2)*Cf)

where

Displ is the motor displacement

omg is the angular speed

p1 and p2 are the input and output pressure

rkm, Ploss and Cf are constant input data that shall be set to match the efficiency curve of the motor.

The motor displacement is an input and shall be expressed in m3/rev. The displacement variation system can be modelled by means of a servovalve and a actuator and considering the displacement linearly dependent from actuator position. Generally it is more convenient not consider the valve and actuator dynamic, to avoid too low simulation speed, and consider the relation between the displacement command and motor displacement only as a lag.

Together with the Variable Displacement Motor block shall be used the Lines Resistance block instead of a valve block.

 


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