MBD Simulation on a Piston Assembly
To model the piston assembly which consists of the piston head, gudgeon pin, connecting rod, end cap and the crank using solidworks and coplete the motion analsysi for the so modelled piston arrangement considering the 3 offset cases respectively and draw conclusions from the linear displacemnt vs time graphs from the 3 cases respectively.
Modelling
1. Piston head : The part was modelled using the predefined dimensions by the instructor usind the modelling options like revolved base where the sketch was rotated about an axis in order to have a hollow bottom and a sealed top portion. Grooves on the piston head were made to position the piston rings that help in preventing the leakage of the gases from the cylinder to the crank which might effect the efficiency and working. A hole was made with some support in order let the gudgeon pin connect the connecting rod and piston head.
2. Gudgeon Pin: Modelled by using the option of extrusion and chamfer as per the required dimensions.
3. Connecting Rod: Modelled using the options like extrusion and fillet. here the dimemnsions are to be satisfied by both the components i.e. gudgeon pin and also the crank where the connecting rod have to be as connection for the piston head and the crank. mostly preferred c/s is I section due to the loads acting on it are high at the ends when compared to the mid portion. Options like simple geometric shapes like cirlce, line are used along with the fillet radius. One end is made as complete hollow cylindrical extrusion where the gudgeon pin is attached and the otehr end only half part of the cylindrical part is made as the crank part should be inserted in it. It is made intentionally as the crank is a solid part where parts are attached to it rather than it being attached to the others.
4. End cap: Modelled to hold the connecting rod with the crank in position. Simple to model and only extrusion along with cut is involved. There by it joins the connecting rod to the crank using a nut and bolt assembly.
5. Crank: The crank is modelled as per the required dirmensions usint the extrusion option and also the mirror option as well. It has an axis about which the assembly is motored with power. The connecting rod and the end cap are bolted together to hold in position with the crank at the assembly.
Assembly is made by taking the crank as the reference i.e. by making the Assembly origin and the cranck origin as one along with the planes. Then the rest parts are assembled using the mate options like coincident, concentic and at times distance mate.
Simulation
Case 1: 0mm offset between the crank and the piston head central axes.
The right planes of the piston head and the crank are coincident in this case and then the analysis is done.
Case 2: 10mm positive offset between the crank and the piston head central axes.
The right planes of both are in a distance of 10mm where the piston head is behind the crank which rotates in the clockwise direction.
Case 2: 10mm positive offset between the crank and the piston head central axes.
The right planes of both are in a distance of 10mm where the piston head is ahead of the crank which rotates in the clockwise direction.
Following the above patterns, after assembly is done, motion analysis for every case is done the same by giving an motor rpm of 2000 to the axis of the crank to rotate the assembly. Giving the contact body pairs as 4 and then change the frames per second to 7200 with precise contact in order get the better view of the assembly and also the results would be very accurate and understandable.
Result:
For the cases after getting the plots for the linear displacement v/s time for the piston head we observe a sinusoidal wave showing the continuity in all the cases. It is observed that the case 2 and 3 i.e. the offset cases show the same variation with respect to time. It is also oberved that the linear displacement of the piston head without any offset has more cycle time when compared to the case of having an offset (either positive of negative).