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Power Unit with Fixed-Displacement Pump

This example shows a typical power unit consisting of a fixed-displacement pump driven by a motor through a flexible transmission, a pressure-relief valve, and a variable orifice, which simulates system fluid consumption. The motor model is represented as an Ideal Angular Velocity Source block, which rotates the shaft at 188 rad/s at zero torque. The load on the shaft decreases the velocity with a slip coefficient of 1.2 (rad/s)/Nm. The pump driving shaft load is measured with the torque sensor. The shaft between the motor and the pump is assumed to be compliant and is simulated with a rotational spring and damper.

The simulation starts with the variable orifice open, which results in a low output pressure and the maximum flow rate going to the system. The orifice starts closing at 0.5 s and is closed completely at 3 s. The output pressure builds up until it reaches 75e5 Pa, and is maintained at this level by the pressure-relief valve. At 3 s, the valve starts opening, thus returning the system to its initial state.

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