MBD Simulation on a Piston Assembly
AIM – Design and MBD simulation of piston assembly
INTRODUCTION – A reciprocating engine is an engine that uses one or more pistons in order to convert pressure into rotational motion in particular system. Generally when piston going up and down that is called translatory motion and when this motion is transferred to crank it get converted to rotary motion.
Generally, in all types of engine have one or more pistons, which is follow the four-stroke cycle which is based on Otto cycle and diesel cycle. There are following engine that are available include a single row of cylinders (in-line), two rows (V-engine), a double zigzag (W-engine) and two horizontal rows (opposed engine).
Whether engine configuration is single type, V type or W type and other type they follow they follow same combustion cycle.
Intake: When , a fuel mixture is introduced inside the cylinder through the intake port, expanding the piston to the bottom of the cylinder.
Compression: The piston then gets pushed to the top, compressing the fuel mixture and igniting it by the spark plug.
Ignition: The ignition pushes the piston downwards providing useful work to the engine.
Exhaust: The waste chemicals get output through the exhaust port and the cycle repeats.
There are following parts of piston by which we made our assembly
Piston head
Connecting rod
End cap
Gudgeon pin
Crank
THEORY
So as we talk about the general piston assembly working in our introduction part. In our piston assembly is also working with same way as in our project we have single piston reciprocating engine that have a piston head, connecting rod, end cap, gudgeon pin and crank. When we made this part we assemble it and then run motion analysis so we could understand its working. There are following assumption also given before doing this work.
|
Sl.no |
Wrist pin offset |
Crank speed rpm |
|
1. |
0mm |
2000 rpm |
|
2. |
10mm positive |
2000 rpm |
|
3. |
10mm negative |
2000 rpm |
There are following steps to make a piston assembly
So first start from design
Piston head
- Open the soildworks and then select new part.
- First click on front plane and then click sketch. And then make a sketch with following dimension as give below in img.
3. Then use revolve boss/base feature for given sketch.
4. Then we have to make sleeve for piston ring fitting so for making the following sketch in front plane is given below.
5. Then make linear pattern of this cut sleeve make plane as top plane distance as 10 mm and pattern as 3.
6. Then we to make to make a hole in piston so that we can fit our wrist pin. So to make that first we select front plane then make following sketch as shown in img.
7. Then go on front plane and make sketch for piston skirt as shown in img.
8. Then extrude cut this part as condition as through all both sides and make sure the flip option is check.
9. Then following cut is look like this.
10. Then the circle which we have made for pin we offset that as 2.50mm and then extrude. And under extrude we offset geometry upto 30mm and then select direction as up to surface.
11. And then click on outside body of piston. And then click ok.
12. Now it look like this
13. We need also this part at other end so we mirror this particular part about it respected plane so then it look like this.
Now our piston head is done so save this part.
Connecting rod
So there are following steps to make connecting rod so let’s see
1. Open new window
2. Then select front plane and make a sketch of connecting rod as shown in img down below
Note – fillet radius = 20mm
3. Now extrude this part as select direction mid plane and distance as 30mm.
4. And now the highlighted area that seen on img. Just select it and choose option create sketch.
5. And then we make a circle of 20mm but make sure that circle mid point have align with origin. And then we mirror its about top plane as seen img down below.
6. And then extrude to 30 mm and select direction as reverse. And then it look like this.
7.Then we to make holes to extrude part as seen on img.
8. Then we have to make a circle of 11.50mm and make sure this align to orgin.
9. Then mirror this circle about top plane and then cut extrude this part. And then it seems like this as shown.
10. And then fillet edges upto 2.70mm.
Now connecting rod is ready and then save this.
Gudgeon pin
Now we make wrist pin so there are following steps so let’s see.
1. Open new in soildworks.
2. Then choose front plane and make sketch of circle a shown in img.
3. Then extrude this as mid plane upto 127mm.
Now the wrist pin is ready and then save it.
END CAP
Now we have to make wrist cap and there are following steps to make it.
So, let’s see.
1. Open new window in soildworks as a part.
2. Click on front plane a make a sketch that shown down below.
3. Then extrude this as direction mid plane and upto 30mm.
4. Then we to make a sketch on highlighted part of area to select that part and choose create sketch.
5. We draw a circle of 25.5mm and make sure is align with origin then we mirror the desired sketch.
6. Then we extrude it upto 30mm and direction choose as blind. As shown down below. And make sure the direction is reverse.
7. Now choose are to create sketch as seen highlighted on img.
8. Then create a circle on that of dimension of 11.25mm make sure is aligned to origin and concentric to outer circle. And then mirror it to other side also.
9. Then cut extrude as direction through all as shown in img.
10. Then fillet the edges that are necessary to fillet upto 2.75mm and then it look like this.
11. And make sure to fillet one side and other side also.
Now save this part.
CRANK
Now it is the time to make our final part crank so follow some steps to make that
So, let’s see
1. Open new as part in soildworks.
2. Then click on front plane and create sketch as shown below in img.
3. Then extrude as direction blind and distance upto 30mm.
4. Then we create sketch on highlighted that seen on img.
5. Now create this sketch as seen om img.
6. Then extrude this sketch direction as blind and distance upto 16 mm.
7. Now select this face to create sketch as highlighted area that is seen on img.
8. Then create this sketch as seen on img make sure is coincident with origin.
9. Extrude given sketch to direction as blind upto 20mm. As shown in img.
Then save this part.
ASSEMBLY
Now we are ready to do assembly of all this part.
So, there are following steps to do assembly so let’s see
1. First open window and select assembly
2. Then insert components and select crank and connecting rod.
3. Then select crank and make it axis concident with top plane and right plane.
4. Then select distance mate upto 36 mm between asssembly front plane and crank front plane.
5. Then insert end cap and make concident with connecting rod as highlighted their.
6. Then we make concident realtion between axis of connecting rod and axis of crank ans also done distance mate of 1mm with inner face of crank.
7. Then we insert piston head and make concident mate with axis of connecting rod and both front plane coincidence.
8. And to make piston head align properly with crank we use assembly of right plane and our respected plane to align the piston head.
Now assembly is done.
REPORTS ON MOTION ANALYSIS
Now we have come to motion analysis but before we done their some assumption to be given before motion analysis so let’s see.
But before doing motion analysis we set some settings of motion study properties
FRAME PER SECOND = 7200
USE PRECISE POINT MUST BE CHECK.
So assumptions are given-:
|
Sl.no |
Wrist pin offset (gudgeon pin) |
Crank speed rpm |
|
1. |
0mm |
2000 rpm |
|
2. |
10mm positive |
2000 rpm |
|
3. |
10mm negative |
2000 rpm |
So, let’s see
First case
Rpm =2000 offset= 0mm
As seen in img there is no offset.
Second case
Rpm = 2000 offset = 10 mm positive rotation = clockwise
As seen in img there is offset of 10mm positive.
Third case
Rpm = 2000 offset = 10mm negative rotation = clockwise
As seen in img there is offset of 10mm negative.
EXPLANATION
So, in our project we have
Piston head
Crank
Wrist pin
End cap
Connecting rod
And with all this parts we make our piston assembly and done our motion analysis
Now let’s see some calculation
As we know
Take as this 4 stroke engine.
1 stroke of piston = 180 degree
So, 4 stroke of piston = 720 degree
Means that engine completes 4 strokes of piston in two revolution of crankshaft.
We can calculate linear displacement by following formula
V = (Pi/4 *) sb^2n
So here,
V = engine displacement
S = stroke
B = bore diameter
N = no of cylinder in respected engine
So, by above formula we can calculate our linear displacement
So, talked about
First case
Rpm =2000 offset= 0mm rotation = clockwise
In this case the piston linear displacement is at maximum position when piston is travelled from TDC to BDC AT 2000 rpm
As we see in our plot also when we run our motion analysis upto 2 sec.
Second case
Rpm = 2000 offset = 10 mm positive rotation = clockwise
In this case the piston linear displacement is at minimum position because there is offset of 10mm is their so piston do not go maximum displacement from TDC to BDC.
Third case
Rpm = 2000 offset = 10 mm negative rotation = clockwise
This case also similar to above case like piston do not go as higher displacement as we compare to our 0mm offset case.
TO SEE PISTON MOTION ANALYSIS VIDEO CLICK/TAP THE VIDEO LINK