Hyrdaulic Systems Simulation Tool

 Contents

 

 

Pumps

There are two types of pumps: fixed displacement and variable displacement. In both the cases, into the dialog box, in addition to the pump parameters, the hydraulic fluid data are defined. These data will be used by all the other blocks. For this reason and due to a peculiar problem of Simulink, it is mandatory that the block name begins with the number 1 (‘1 Fixed displacement Pump’); if a pump block is closed inside a subsystem, also the subsystem name shall starts with the number 1. Should this rule not be applied, the fluid parameters are not correctly passed to the other blocks, at the first run.

 

The fixed displacement block has the following input and output:

angular speed [rpm]

supplied flow [m3/s]

 

The variable displacement block has the following inputs and output:

angular speed [rpm]

system pressure [Pa]; is the output of the Accumulator block; it is a two elements vector: the first element is the supply pressure, the second in the return pressure

supplied flow [m3/s]

 The internal leakage value [m3/s] is stored into the global variable 'pump_leak', that can be read by a 'From' block

 For the variable displacement motor, the displacement is evaluated as a function of the system pressure, on the basis of the following expression:

 

where

 

D is the displacement

D MAX is the maximum displacement

D MIN is the minimum displacement

ps is the system pressure

pMAX is the max compensation pressure corresponding to the max. displacement
pMIN is the min compensation pressure corresponding to the min. displacement

 

The result of this expression is then multiplied for a first order filter, to take into account a time lag.

In addition to these two kinds of pump blocks, there is the block ‘Hydraulic Supply’ that represents a constant pressure source. This block can be useful when the behaviour of the power generation system can be not considered. When this block is used, the accumulator, the reservoir and the pressure relief blocks shall not be introduced.

 

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