MBD Simulation on a Piston Assembly
The Piston Assembly Consist of mainly five parts such as Piston itself, Gudgeon pin, Connecting Rod, Endcap, and Crank. it is used in the different mechanical machines such as Internal/External combustion engines, compressors, pumps, and etc. based on Applications such as power-producing device (or) power-consuming device it is used to transfer the power.
Our Main Objective is to do motion analysis of piston assembly by Designing different Parts of the Piston Assembly and Assemble them in SolidWorks. Where our analysis is carried out in using three different conditions as follows.
| SR. NO. | Wrist Pin Offset | Crank Speed (RPM) |
| 1. | 0 mm | 2000 |
| 2. | 10 mm Positive | 2000 |
| 3. | 10 mm Negative | 2000 |
Before going to do motion analysis of piston assembly we need to design parts individually, after that we assemble them together and use a motion analysis tool in SolidWorks to analyze linear displacement of the piston.
Piston Design:
i. The piston is a component used is many mechanical machines piston transfers power from combusting fuel to the crank with the help of a connecting rod. To design Piston, we are going to design a 2D sketch on the front plane in SolidWorks. after that, by using the Revolve option we get our primary 3D piston part.
ii. Create slots for piston ring (2.2*5 mm) at 5 mm upward from the x-axis. and by using the Revolve Cut option we cut the slot.
iii. By using a Linear Pattern option in Features and taking the top plane as a reference plane we created more slots in the piston.
iv. Crating hole for Gudgeon pin with 25.4 mm diameter and Extruding it to 127 mm from the midplane.
v. Creating a curve cut in the piston by using a three-point arc. with 45 mm as diameter and distance between two curve points as an 84 mm (i.e 42 mm on one side from y-axis).
vi. Using Convert Entities with 2.5 mm and selecting a circular hole sketch, we are creating a mount for the Gudgeon pin. Extruding the mount to 30 mm up to surface in the reverse direction. To create the same mount we used a mirror tool.
At last, Saving the part in our computer directory and naming as a piston and our first part is now completed.
Gudgeon Pin:
Gudgeon pin is used to connect the connecting rod and piston to transfer power. to design it we are going to use a circle tool from the menu and draw a 2D circle with a diameter 25.4mm (for internal circle), 5.5mm offset circle as an External circle, and extrude it to 127 mm on both sides from the midplane.
Connecting Rod
the connecting rod connects one side piston with another side crank and helps to convert linear motion into rotational motion of the crank. the connecting rod based on the parameters shown below. which has mount for the nut.
EndCap:-
The Endcap is an extension of the connecting rod which helps to mount the connecting rod on the crank. Designing the Endcap with similar parameters of the connecting rod.
Crank
The crank is used to convert linear motion into rotational motion and transfers the power to do work in a power-producing device and vice versa in a power-consuming device. To design crank, we draw the following sketch and after that we extruded it and on extrusion, we remove material to make the curve on it. when this process is completed we mirror the crank to get the final output.
Assembly:-
To do assembly we are going to import different parts of piston assembly in SolidWorks. the first part imported is always fixed in Solidworks, so by right click on the component, we can make it float. first, we are imported Crank, which is used as a basis for our assembly. after that, we are using a mate option to align crank properly in a 3D plane. similarly, we imported all the components of the piston assembly and assemble them with the help of the Mate option.
In our study, we are going to offset the wrist pin in three different ways and analyze its effect on the linear displacement of the piston.
Wrist Pin Offset:- The position of the wrist pin is going to be varied as followed. But the center of the axis of the piston head and the crank are coincident to each other (i.e) They are on the same plane in all the three cases.
To do Motion studies in all the three cases we are using the crank axis as input to the motor with 2000 rpm. similarly, we are using 7200 frames per second and used precise contact option to get a more clear result.
CASE 1 - 0 mm Offset:-
In this study wrist pin plane and Rotation axis of Crank coincides with each other in the same plane by using the coincident option as shown below.
In the above plot, we can see that the linear displacement of piston starts between the 2.0000E+02 and 3.0000E+02. The smooth constant curve indicates that the constant linear displacement of piston with respect to time.
CASE 2 - 10 mm Positive Offset:-
In this study, we provided a 10mm offset in (positive direction) between the wrist pin plane and the Rotation axis of Crank in the same plane. the crank rotation is in the clockwise direction as shown below.
In the above plot, we can see that the linear displacement of piston starts near to the 2.0000E+02, Which caused due to the positive offset provided. The smooth constant curve indicates that the constant linear displacement of piston with respect to time similar to the previous plot of case-1.
CASE 3 -10 mm Negative Offset:-
In this study, we provided a 10mm offset in (negative direction) between the wrist pin plane and the Rotation axis of Crank in the same plane. the crank rotation is in the clockwise direction. to get 10mm offset in a negative direction we are using flip direction option as shown below.
In the above plot, we can see that the linear displacement of piston starts near to the 3.0000E+02, Which caused due to the negative offset provided. Similar to the previous studies the smooth constant curve indicates that the constant linear displacement of piston with respect to time.
From three studies we get nearly the same plot for all. For comparing the results of all the three plots of different analysis results, we are using a superimposed graph. with the help of a superimposed graph, we can plot all the three graphs in a single graph which helps to understand the difference between plots. the superimposed graph is as follows.
In all the above three plots of different cases, we can see that the linear displacement of the piston is nearly the same in all cases but the starting position, as well as the path at some duration, is different for each study which is due to the 10mm offset provided in the second and third study. without offsetting the line of action of power transmission is caused impact load on the assembly which is harmful during operation. to get rid of this, offsetting the piston from crank so that the axis of the piston and connecting rod are aligned vertically at the moment of combustion - when the pressure in the cylinder is at its peak.
Due to the offset provided between the piston and crank the impact load is reduced. Doing this greatly reduces the stress acting on the connecting rod and friction from the diagonal force pushing the piston against the cylinder wall. At the same time, this enables more effective use of the energy produced by combustion which causes more efficient mechanisms in real-life applications.
Animation:-