2 STROKE ENGINE

D.A.O PROJECT

Design of a two strokes engine

NilColomo Marina Flores

Fernando Carlos Rancao Carlos Rodriguez

Graphic expression

Professor: Jordi Torner December 2014

2

INDEX

Report

1. Purpose of the project... ... ... ... ... ... 3

2. Motivation... ... ... 4

3. Scope......... 5

4. Description of the machine. 6

4.1. Component parts.. 7

4.2. Main movements.. 9

4.3. Actual images of the machine 10

5. Pieces members..11

6. Hatch assembly.16

7. Main movements assembly.. 18

8. Exploded views 19

9. Study of the mechanical behavior ... 21

10. Conclusions..22

Drawings

1. General assembly ....25

2. Subassembly 1.. 26

3. Subassembly 2. 27

4. Subassembly 3.. 28

5. Pieces. 29

3

REPORT

1.PURPOSE OF THE PROJECT

Our group is going to make an assembly of an engine using SolidWorks. The

engine belongs to a pocket bike; so firstly, we want to dismount it to see in

detail each piece. Once we have done this, we will design each piece of the

engine with the software, making all the parts in 3D and then doing the draws.

Finally, having all the pieces in SolidWorks, we will be able to show the

movement of the engine on a screen and we will see how each piece is fixed to

another and how it moves making the engine run.

Our intention is to be able to elaborate the entire project satisfactory and to

learn a lot using SolidWorks, a useful tool for our future.

4

2. MOTIVATION

We started by telling one idea each of the members of the group, which we call

"Brainstorming", between them we got:

Clock Wall

2T Motor

Water Tap

Finally, after each one defending its idea and making a vote, we decided to

choose the 2T Motor. One of our first motivations for our decision was that in

this group we have got two "Mechanical Engineer students", and also because

we count with a physical motor as an example and it would be more illustrative

and handful.

We took the motor and we got all the pieces in order to watch them all. From

here on we saw the Pros and Cons of our project:

Facilities (Pros):

We got the physical motor in order to study and observe it.

Motivation for the study and explanation of the motor.

Difficulties (Cons):

Creation of the pieces, due to the large amount of forms and angles.

Assembly of the different pieces, due to the measures and the

exactitude.

5

3. SCOPE

Since the very beginning, we agreed to simplify the radii of the every rounding

to appear while modelling, due to the hardness of its measurement and the poor

significance.

We also agreed not to build screws since in the engine to build there is none,

and the ones used to attach the engine to the outer shell would not be

necessary since we were not going to build any further from the engine itself.

While modelling with Solidworks, we found some difficulties that we used to

simplify our pieces, as we can see, for example, in pieces 9 and 10 (see way

further to know the nomenclature of the engine pieces) where we can observe a

pretty hard to measure (and to build) setoff that we simplified, since it does not

play any role in the movement of the engine.

Same happened in piece 14, where with the circular entry at the bottom, two

'wings' were supposed to be modelled to drill the part. Since the depth were

hard to measure and it does not play any role in the movement of the engine,

we skip it (building the entry just as a circular one) simplifying our piece.

Finally, while drawing the pieces, we skipped the material involved fields, since

all the engine would be build in aluminium (note than rubber could be used for

deterioration protection).

6

4. DESCRIPTION OF THE MACHINE

The machine we are drawing in this project is an engine, in particular a two-

stroke engine. A two-stroke engine is an internal combustion machine and it is

called two-stroke because it completes a power cycle in only one crankshaft

revolution, an up and down movements of the piston which differs from four-

stroke engines. Our engine is from a pocket bike so it is quite small and light.

However, it is really similar to the ones used by mopeds or lawnmowers.

This type of engine has some

advantages, though it also has

some disadvantages. On the

one hand, two-stroke engines

do not need valves or any

similar mechanism so they are

lighter and cheaper. Also, as

there is an explosion in every

cycle of the crankshaft these

type of engines have more

power than four-stroke engines,

which only make an explosion every two cycles of the crankshaft. On the other

hand, two-stroke engines consume oil to lubricate the parts that are in

movement. Oil is mixed with petrol so when petrol is burned, oil too. That

pollutes quite a lot and produces a white smoke. Moreover, two-stroke engines

are less efficient than four-stroke engines or Otto engines.

7

4.1.COMPONENT PARTS

Here there is a short explanation of the different parts of the engine:

Piston:is one of the most important parts of the engine

but at the same time it is one of the simplest ones. The

piston moves up and down the cylinder when the

engine is working.

Cylinder head: its interior is a cylinder, and here is

where the piston moves and in the exterior there are

thin metal sheets. It has got these metal sheets to

dissipate the heat of the interior of the engine.

Glow plug: is simply like a screw and in its end there are two thin pieces of

metal that are really close. The glow plug receives electricity and it produces

a spark which makes the mix of petrol and air explodes.

Connecting rod:is a part that is quite long and has a hole in each end. One

of the holes is attached to the piston whereas the other is attached to the

crankshaft.

Crankshaft: as it is said before it is attached to the connecting rod, and this

part is quite heavy in order to have the sufficient inertia to make sure the

engine does not get still in any moment. The crankshaft and the connecting

rod make a crank-rod mechanism which transforms rectilinear motion to

circular motion.

8

Crankcase: it is formed by two symmetric parts which must match perfectly

because it has to be totally hermetic. The petrol is mixed with oil before

entering in the crankcase to lubricate all parts that are moving.

Centrifugal clutch: is a type of automatic clutch that has some springs. It

uses the centrifugal force: when the engine is turning fast then the clutch

transmits the movement to the wheel and when it is idling the clutch does

not transmit the movement.

9

4.2. MAIN MOVEMENTS

Our engine has two main movements inside it:

The piston moves in an alternative rectilinear way inside the cylinder. It

follows this movement because the petrol is mixed with the air and explodes

in the combustion chamber when the spark is produced. This explosion

makes the piston go down the cylinder.

The piston is attached to the connecting rod. The connecting rod is attached

to the crankshaft this is called rod-crank mechanism. This mechanism

makes the crankshaft have a circular. Then this circular movement allows

the motorbike to work matching the gear and the chainring through a chain.

10

4.3. ACTUAL IMAGES OF THE MACHINE

11

5. PIECES MEMBERS

Piece 1:

Piece 2:

Piece 3:

12

Piece 4:

Piece 5:

Piece 6:

13

Piece 7:

Piece 8:

Piece 9:

14

Piece 10:

Piece 11:

Piece 12:

15

Piece 13:

Piece 14:

16

6.HATCH ASSEMBLY

SUBASSEMBLY 1:

17

SUBASSEMBLY 2:

SUBASSEMBLY 3:

18

7. MAIN MOVEMENTS ASSEMBLY

We have made the assembly by adding many mates in order that the engine

moves properly. The mates we have used to join all the parts are concentricity,

coincident and parallel. The engine has some parts that move and we had to

add some mates so that the exterior parts move at the same time as the ones of

the interior. In the assembly you can see that piece 11 has a circular motion and

then the crankshaft starts moving. Moreover, the connecting rod and the piston

also move. We add a mate to the center of the cylinder and the center of the

cylinder head.

To show clearer the movement of the interior of the engine we have made 3

subassemblies that only show the parts that cannot be seen in the general

assembly.

19

8. EXPLODED VIEWS

EXPLODED VIEW SUBASSEMBLY 1:

20



21

9. STUDY OF THE MECHANICAL BEHAVIOR

It is a type of internal combustion engine which completes a power cycle in only

one crankshaft revolution and with two strokes, or up and down movements of

the piston.

This is done by the end of the combustion stroke and the beginning of the

compression stroke happening in the same stroke and the intake and exhaust

also together.

22

10. CONCLUSIONS

- Final conclusions of the Project.

Our conclusions as a group are mainly positive. As in each Project group there

are things that could be improved, sometimes there are also problems between

the group members, because there are always different ways of doing the

things, each of them wants the project to be done in his way and that produces

some problems, but after talking the points all the members should reach a

solution.

This project has been really useful in order to improve our teamwork and also to

see a positive result of our classes, after doing the tutorials and assisting the

different sessions that we have done, we were able to create the different parts

in SolidWorks, and also to draw them with the measures correctly.

The 2T Motor has been a really good choice to our group, we have studied it

physically and it was great to know what the result should be and if we were

doing a good job, just comparing it to reality.

We have met many times in order to do the work together, so the measures

were the same for all of us and also the way to do it. It is also true that some of

the work had to be done individually, due to other exams or exercises that we

had from other subjects.

To sum up, this experience, with this group has been really positive for all of us,

we have agreed in the way to do things and that was very helpful.

- Aspects that could be improved.

It is hard to tell by ourselves the things that could be improved, we think that all

the work that we have done and the way that we have done it is fine, we

followed the instructions that we had in Atenea and then we just met sometimes

and tried to do the work by ourselves.

Maybe some aspects that could be improved are:

23

Time organization: The deadline coincides with some exams, but also

sometimes is our fault to let it passing until the end, however, we have done the

work periodically and it was not a big problem.

We do not really think that there are more things that can be improved at the

moment.

- Concrete aspects that we think that are important to write down.

The most important thing for us has been the fact that we could reproduce our

final project physically and whenever that we had any problem, we just saw the

real motor and correct errors or change the way of doing things.

Also the motivation that we got in order to do this project was really helpful, we

knew how a motor works and we had the chance to reproduce it as a project, it

was great.

- Difficulties that we got and the way we solved them.

The first difficulty that we saw was the SolidWorks part, when we had to create

the pieces into de computer program. Because they are really complicated and

the assembly has to be really exact in order not to have a bad end result.

We solved this part by working together and putting the measures together, with

that we could evade the final problem of a bad assembly. But with this solution

another problem came:

We were four people in the group and sometimes it is hard to meet all together,

in order to do a little step in our project we had to meet all and sometimes it was

difficult so we also did some work individually and after a while meet in order to

sum it all.

- Project analysis. Good and bad things.

The end analysis as we told before is positive, we agreed since the beginning

and all ran pretty fine.

The good things of this project are:

The improvement of teamwork.

24

The use of new systems, such as SolidWorks.

The motivation of doing something that we knew and we were interested

in.

The bad things of the project are:

Find the time to meet us all.

The difficulty of many pieces, we had to simplify some of them.

- Extra things that we would like to say about the project.

There is not much that we can tell before we do the defense in front of the class

and that someone evaluates us and told us our errors.

It has been interesting to do this project, it was not something boring or that we

had to do as an obligation, and that was really helpful.

25

DRAWINGS

1.GENERAL ASSEMBLY

26

2. SUBASSEMBLY 1

27

3. SUBASSEMBLY 2

28

4.SUBASSEMBLY 3

29

5.PIECES

Documents

2 STROKE ENGINE