MBD Simulation on a Piston Assembly
Aim :
To Study motion analysis on Piston displacement with 3 different configurations of Wrist Pin offset.
Introduction:
Motor Power given to Crank is transferred to Piston through Connecting Rod and Piston moves from TDC ( Top Dead Centre) to BDC ( Bottom Dead Centre ) which is called Stroke Length. Stroke Length can be adjusted by varying Connecting rod length. Piston is conected to Connecting Rod via Wrist pin which rest on Hole inside the piston. Wrist Pin Offset : Offset Distance of the Wrist Pin from centre of the Piston. Here motion analysis is performed to find out the impact on stroke length ( TDC to BDC & vice versa ) due to Wrist Pin offset. This is example of Slider-Crank mechanism. Power is given to Slider and output motion is cranking ( to and fro motion -- here up and down movement )
To perform motion study following components are designed:
1. Crank
2. End cap
3. Connecting rod
4. Piston
5. Wrist Pin /Gudgeon Pin
3D models :
Connecting rod
Crank
End cap
Wrist Pin /Gudgeon Pin
Piston
Simulation Conditions:
* Wrist Pin Offset : 0 mm , 10mm (positive) , 10mm ( negative )
1 . ZERO OFFSET : Line joining Motor axis and Wrist Pin axis Coincides
NEGATIVE OFFSET : Wrist Pin axis is at 10mm offset from Motor axis on the right side when motor rotates in clockwise direction
POSITIVE OFFSET : Wrist Pin axis is at 10mm offset from Motor axis on the left side when motor rotates in clockwise direction
Simulation Condition:
* Motor Speed : 2000 Rpm - Input condition
* Frames per Second : 7200 fps ( for better accuracy in result )
Video link :
SUPERIMPOSED PLOT:
RESULT & CONCLUSION:
From the result we can see that Wrsit Pin offset configuration does not seems to have applicable impact on Piston stroke length ( mm ). Zero Offset configuration has more cycles per second ( TDC - BDC ) comparing other two configuration despite same stroke length. As we know Piston travels from TDC to BDC, connecting rod undergoes enormous stress. At TDC , Connecting rod directly takes entire dynamic load (including weight of piston ) and at BDC Connecting rod requires more energy to lift the piston when directly in contact. So when Wrist Pin offset will reduce the load on Connecting rod when Piston at TDC and BDC during operation. Also wrist offset reduces angularity of the connecting rod which inturn reduces friction force on piston when moving from TDC to BDC and vice versa. Angularity refers to angle made by Rod with Piston axis when in rotation.