Hyrdaulic System Simulation Tool |
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Into the hydraulic module block there are 5 blocks relevant to accumulators, the pressure relief, the pressure reducer, the filter. An accumulator block shall be present in each model otherwise some errors can arise, with the exception of the models where the ‘Hydraulic Supply’ block is utilised. The pressure relief shall be introduced in case of fixed displacement pump, to regulate the pressure. The pressure reducer can be used in case some actuation systems operate at a lower pressure with respect to the pump pressure; this block includes a pressure reducer and an accumulator.
The hydraulic accumulator blocks have the following inputs and output:
the flow supplied from the pump
the output flows to the valves; it is a two elements vector, composed by supply and return pressures. In case of more then one actuation system, this signal shall be the output of a 'sum' block having each valve flow as input.
the relief flows
the single acting actuators flow of the uncontrolled pressure side
the accumulator pressure [Pa]; it is a two elements vector: the first element is the supply pressure, the second is the return pressure
The flow coming from the single acting actuators shall be connected only if the pressure of the side not controlled by the valve is the supply pressure, otherwise this input shall be connected to a ground block (from Utility sub-library).
One of the two accumulator blocks takes into account the effect of the thermal exchange between the hydraulic fluid and the gas. If the heat exchange coefficient are not known, the adiabatic accumulator block can be used.
In the first type of block, the accumulator is modelled considering that the input and the output of the fluid produce a compression or an expansion of the gas and that there is a heat exchange between fluid and gas. Thus, the first principle of thermodynamic can be written for a perfect gas as:
where
H is the thermal flux from liquid to gas = h(Tl - Tg)
h is the heat exchange coefficient (a good value for small accumulator is suggested in the dialog window)
Tl is the liquid temperature
Tg is the gas temperature
pg is the gas and liquid pressure
U is the internal energy = cvTgM
cv is the constant volume specific heat
M is the gas mass
If the pressure is lower than the precharge pressure, the accumulator acts like a hydraulic compliance.
The Relief Valve has the following inputs and output:
The pressure reducer has the following inputs and output:
the system pressures (output of the accumulator block) (is a two elements vector)
the valve flows (is a two elements vector)
the downstream pressure of the reducer (is a two elements vector)
The Filter has the following inputs and output:
the system pressures (output of the accumulator block) (is a two elements vector)
the pump flow
the reduced pressure (is a two elements vector)