Insufficient information in datasheets referred by pre-parametrized Valves in Simscape Fluids (Isothermal Liquid)
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Manish Kumar Nayak on 1 May 2022
I have been trying to understand the various parametrization options used by different valves under Isothermal Liquid section of Simscape Fluids Toolbox, so that I can utilise the techniques in my own Hydraulic circuit project. However, it is evident that there are several assumptions made in the In-built examples, which may not be necessarily true for a realisitic model.
Specifically, let's consider the case of 3-Way Directional Valve (IL) Block. It has several predefined parametrizations available. I selected Eaton S229 example, and MATLAB populates the various parameters automatically based on the information from the corresponding datasheet. On a quick search, the corresponding datasheet can be found at - 82-83.pdf (hidraulines-sistemos.lt). As can be seen below, the orifice parametrization selected is Flow rate vs Spool travel and Pressure drop, which is logical, as per the curves in the datasheet.
Now, cross referencing this data with the corresponding datasheet, the only information available is Pressure vs Volume flow characteristics. There is no information of the spool distance.
Assumption 1 and 2 - Despite no information on spool travel in the datasheet, the default settings assume some value and also assume that the dp-dq curves available are at maximum spool position. (0.001m in this case)
Assumption 3 - Information about leakage is not evident in datasheet, but the flow output is simply reduced by a factor of 100. As seen below, flow values q(ds,dp); where the 2nd row (spool = 0.001m) is taken from the datasheet and the 1st row (spool = 0m) is 0.01*Val_Row2..All other spool values in between are linearly interpolated based on this.
Q. Although I have shown a specific case, these exact same assumptions have been made in all the predefined examples. My premise being the accuracy and thought process behind such assumptions. Even in the case of valves which I actually want to parametrize for my project, I can't find any information regarding the spool travel distances in the datasheets. I am unsure if I can use the same assumptions as used in these examples, especially the ones regarding spool distance.Or it doesn't have any relevance physically?
Any comments on this regard will be highly appreciated.
Yifeng Tang on 22 Jun 2022
These parameters for the pre-parametrized valves are found based on the information available in the datasheets. I've found that datasheets from different manufactures come in all kinds of different formats with different levels of details, so yes, assumptions, or more importantly assumptions based on some physical understanding of the valves, are often needed.
The particular assumptions in this case: max spool travel, linear change between fully open and closed, and leakage when fully closed, they are needed to fully describe the behavior of the valve in all s/dP/Q conditions. The max spool travel may not matter that much and you can easily change it if more info becomes available. You just need to make sure the input at the S port is consistent with this max travel, and if you have a controller outside, the control gains are set accordingly. For example, if the max travel is changed to 10mm, the control gains probably need to be larger to get similar valve response.