Group 1 - Product Name Here
Tecumseh Two-Stroke Engine Stored revision Line 1: Line 1:
ed. For example, elderly people can cut their lawn just as children can, both of which need little technical skill or experience.
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There are four main controls on a two stroke engine that need to be known for proper use. These controls include the pull start, the throttle, the choke and the fuel tank. The choke, throttle and fuel tank are clearly labeled, resulting in a simple user interface for these components. The throttle allows the user to determine how hard the engine is working or how power it is outputting. The operation of the throttle is significantly simple, if the user simply pushes the throttle lever, shown in Figure 1, to one side the engine will increase power output, and if the user pushes the throttle lever the opposite direction the engine will decrease power output. The choke determines the ratio of fuel to air the engine is receiving which allows the user to easily start and stop the engine. For the proper use of the choke the user must, before the use of the engine, fill the fuel tank full of an oil and gasoline mixture, of which a ratio is clearly labeled on top of the fuel tank cover. Once this is completed the user can start the engine, with the choke increase the carburetor will increase the amount of fuel/air mixture that is entering the combustion chamber which will ultimately make it easier to initially start the cycle. Once the engine is running the user must return the choke to its intermediate state to avoid spending any fuel that is not needed. The choke is an initially difficult input to understand for an inexperienced user but once understood the user will find ease in starting the engine. The pull cord is the easiest task the user must do to get the two-stroke engine running, since it is as simple as pulling the cord, but without a label or instruction, may cause a bit of confusion at first. To start the engine all that the user must do is to increase the choke and pull hard on the pull cord until the engine starts. The pull cord requires a quick and firm pull in order to start the engine which might necessarily be difficult for inexperienced users, but with multiple uses the starting process becomes quick and simple. Overall, the two-stroke engine is a quite simple tool for just about anyone to use.
As with any product with moving parts, there is maintenance required to keep the engine operating properly and efficiently. Since there is such interchangeability with engine components, keeping a two-stroke in a proper working condition isn’t necessarily hard, but may require previous knowledge about engines depending on the issue. The mixing of oil directly into the gasoline means that the engine is lubricating itself just by running. This self lubrication process means less maintenance for the owner. This is a great advantage over other engines that only run gasoline or diesel because with those other engines the oil must be changed frequently. Like other internal combustion engines, the spark plug will become dirty and wear out over time, so it must be changed. The user will be able to tell if the spark plug needs replacing if the engine starts to become more difficult to start. The life cycle of the spark plug depends greatly on the amount of time the engine is being run. The replacement of a spark plug is a simple process to any two-stroke engine owner with the proper tool, which is typically a 3/4 inch wrench. Another important task that must be done to keep an engine in the proper working condition is the cleaning of the air filter. This most likely has to be done less frequently than replacing the spark plug, depending on the environmental conditions the engine is running in. Having a proper fuel filter is another maintenance requirement because damage to the engine can be caused by debris entering it either through the air taken in or the fuel. Cleaning or replacing the fuel filter is more of a difficult task because it is located inside the fuel tank.
Gate 2: Group 1 Product Dissection
Preliminary Project Review
Project Review Completion Date: 10/18
Product Dissection Completion Date: 10/23
Wiki Due Date: 10/26
Project Review Completion Date: 10/26
Product Dissection Completion Date: 10/17
Wiki Due Date: 10/31
The alteration of the Project Review changed from 10/18 to 10/26 because of the content required in the section. The Project Review asks to assess the work and management plans of Gate 2 which needs to be done after the actual dissection of the engine.
The alteration of the Product Dissection changed from 10/23 to 10/17 due to a common free time between all group members as well as a realization of the amount of work entailed in the dissection and dissection assessment.
10/14: Group meeting to determine a set date and time for the Product Dissection as 10/17 at 5:00 p.m.
10/17: Product Dissection began at 5:30 p.m. and was completed at 7:00 p.m.
10/21: Group meeting to compile, format and organize the pictures and videos taken during the Product Dissection. We also established a meeting date and time for the Product Dissection Assessment as 10/26 at 5:00 p.m.
10/26: Group meeting to work on the Product Review and Product Dissection Assessment.
Our Management Proposal originally stated “We plan to do the majority of work away from each other, then the next time we meet each of us will revise everyone’s sections to get five different perspectives on the analysis at hand so that everything is covered that needs to be.” This plan worked for the most part as we split up the research and profiles along with the management and work proposals evenly between the five group members. We then established a group meeting to compile and format all of the work from each group member and we each revised each members section to gain five separate perspectives.
In Gate 1 we encountered for the most part only one major challenge which was the time constraint. This challenge was due to poor time management by the group and we resolved this problem in Gate 2 by establishing dates in our Management Proposal for completion of each section of the Gate.
Our Management Proposal originally stated, “We plan to do the majority of work away from each other, then the next time we meet each of us will revise everyone’s sections to get five different perspectives on the analysis at hand so that everything is covered that needs to be.” Our management process altered so we did all of the work together due to the difference in work processes of Gate 1 and Gate 2. Gate 1 required a sufficient amount of research for completion which made it logical to divide the work between the group members, while Gate 2 required a group dissection and an assessment that requires analysis and discussions between group members.
We followed our Work Proposal exactly as it is stated in Gate 1 and it worked perfectly as planned. Our plan worked because of the previous knowledge of gas-powered engines by our technical expert; this made the dissection of the engine go smoothly without any problems. Our work plan was also successful due to the fact of precise recording and documentation of every step of the dissection as well as details for each step.
During the Product Dissection we encountered three challenges: (1) stripped bolt, (2) chipped fan guard, and (3) lack of and accessibility of tools. To resolve these challenges, and avoid problems in the future, especially during reassembly of the product, we will: (1) replace the bolt with an equivalent; (2) even though the chip on the fan guard is irrelevant to the operation of the engine we will repair the chipped piece using an industrial grade adhesive; and (3) since we documented the size and type of each tool used during the dissection we can collect all tools needed for the reassembly before we begin which will reduce the time it takes to put the engine back together.
During the Product Dissection we addressed two challenges: (1) difficulty in the removal of the fly wheel bolt, and (2) a dead battery in the intended video camera. We immediately addressed these challenges during the dissection by: (1) increasingly used more force, and changed directions repeatedly; (2) used alternative recording devices (phones).
- Takes a relatively short period of time, fasteners are easily visible and removable no prior knowledge of engine construction is required.
- Fasteners may be harder to remove due to corrosion, still little or no prior knowledge of the engine is needed for part removal.
- Fasteners may be harder to remove due to corrosion and obscure location. Some mechanical knowledge and or knowledge of engine construction may be needed here.
- Fasteners may be hard to remove due to a significant amount of corrosion and or significant damage to fastener. Mechanical knowledge is required for removal of these parts along with some prior knowledge of engine construction is required.
- Fasteners may be mostly or completely obscure. High difficulty in removing fasteners due to high corrosion and or damage to fastener. Mechanical knowledge and prior knowledge to engine construction is required. These steps would require the most amount of time due to their complexity.
- Note: Fasteners refer to any bolt, screw, nut, that is holding a part to the engine.
Is that intended to be disassembled?
Carburetor: As the carburetor is seen as a system of its own, then it is technically intended to be disassembled but not for the intentions of this project. The carburetor is not intended to be disassembled in our Product Dissection because it is seen as a separate system/product from the engine. Evidence that the carburetor is intended to be disassembled is the fact that there are screws and and small bolts all over it. It would seem that the carburetor was meant to be disassembled by professional dues to its small component size and complexity. An example of the complexity of the carburetor is the complex spring-valve system visible from the side.The process and detailed system analysis of a carburetor are well-documented and easily accessible on the internet. A disassembly of the carburetor in our Product Dissection would be seen as a waste of work time as well as unnecessary work to determine information that can be easily found outside of the lab.
Engine: The engine is intended to be disassembled in order to repair broken parts and components as well as determine the series of subsystems that it entails for analysis to ensure proper and efficient operation. Evidence that the engine is intended to be disassembled is the fact that it is built using bolts, screws and gaskets and doesn’t have any welded connections which give the user the option to disassemble it in the occurrence that replacement parts or system analysis is needed.
Subsystem Connection Table
The human energy inputted by the user into the pull start is needed to create rotational momentum in the fly wheel which the magneto is in close proximity to. Once the fly wheel rotates, a magnet sends a signal to the magneto which sends a pulse of electricity to the spark plug at the exact moment necessary for the combustion. The carburetor controls the throttling of the engine by controlling the amount of fuel/air mixture going into the combustion chamber when the spark is fired and the combustion starts converting electrical energy from the spark to chemical energy from the combustion then to mechanical energy in the translational motion of the piston to the rotation of the crankshaft.
- Availability of Resources: The connections include basic components that are universal to most two-stroke engines around the globe making it easier for the user to locate interchange the appropriate parts if necessary
- Cultural Attributes: The materials used give the engine the capability to withstand both hot and cold weather conditions and maintain the same amount of work production, so the external conditions do not affect the performance of the engine
- Safety: Connections from the pull start to the fly wheel include a strong casing over the connection to ensure safety from high speed systems of the engine as well as any foreign debris that threatens to enter the engine during the cycle
- Aesthetics: Every object that is purposely visible is black
- Ease of Use: The handle of the pull start is shaped from the comfort of the user
- Safety: Controlled combustion within a chamber made of sufficiently durable material
- Safety: A rubber casing from the magneto to the spark plug ensures safety of the user to avoid electrical energy escaping the system when it is unnecessary
- Cost: Connections that don’t require a lot of force onto them are made out of plastic or sheet metal to reduce nonessential cost
- Cost: Uses cheap, unleaded fuel
- Cost: Uses a pull start rather than an electric start
- Emissions: The engine meets applicable emission regulations
- Less Waste: Use of reusable material such as the metal from the piston cylinder that can be melted down and reused
Gate 3: Product Analysis
Cause for Corrective Action
Our biggest challenge as a group has been time management, we tend to leave a bulk of the work until just before the gates are due. To resolve this for the current gate we started with the majority of the work a week in advance and have more frequent, longer, and productive meetings. In doing so we believe that we will be more successful in this gate and in future assignments by allotting a more sufficient amount of time to each task.
Steel: This material of some of these components was determined by its magnetic property. A magnet was held up to each component, those that were magnetic were concluded as steel. This material is ideal for the components that it was used for, such as the Piston Rings, Connecting Rod and Crank Shaft, because of its strength, durability and low cost.
Aluminum: This material was determined through its non-magnetic property as well as metallic color. The group determined that if the material was metallic silver then it was either Steel or Aluminum which could then be differentiated using a magnet. Aluminum is ideal for the components that its used for, such as the Piston, Combustion Chamber and Crank Case, because of its thermal resistance and low cost.
|Function(RIGHT) Component(DOWN)||Mounting/ Protection||Import Human Energy||Import Chemical Energy||Sense Throttle Signal||Sense On/Off Signal||Convert Chemical Energy to Pneumatic Energy||Convert Pneumatic Energy to Mechanical Translational Energy||Convert Mechanical Translational Energy to Mechanical Rotational Energy|
|Pull Start Mechanism||0||1||0||0||0||0||0||0|
|Pull Start Lock Mechanism||0||1||0||0||0||0||0||0|
|Pull Start Cover||1||0||0||0||0||0||0||0|
|Crank Case Cover||1||0||0||0||0||1||0||0|
|Relief Valve Cover||0||0||0||0||0||1||0||0|
Figure 1.2: Note: 1 = Component is involved in the function, 0 = Component is uninvolved in the function
Component FunctionThe fly wheel performs four functions, consistency, timing, performance and cooling. The first function fly wheel is to resist changes in speed and maintain consistency, for example if the piston is exerting an uneven torque through the engine, the fly wheel is responsible for evening it out. The rotational inertia of the fly wheel is critical to the timing of the engine, which is the reason why design revisions of most engines do not involve the fly wheel. Another function that the fly wheel performs is to send an electrical signal to the spark plug through the magneto after every rotation using the attached magnet.
The fly wheel is meant to function through a high vibration, high heat, and variable speed environment. The high vibrations come from the piston moving quickly up and down inside the cylinder. The fly wheel is rotating just as fast as the piston is moving up and down, therefore, the fly wheel is rotating extremely fast thus creating a high amount of heat transfer at its center. This is combated by using oil to decrease the amount of friction produced, however the center will still be extremely hot. The fly wheel is therefore made of steel which has a high melting point thus allowing it to operate in such an environment. The variable speeds originate from the combustion sent to the piston. Initially the piston will be forced down with a significant amount of force, but as it bottoms out, the volume increases, and the combustion decreases in magnitude thus decreasing the force, this rapid and repeating increasing and decreasing of force cause high vibrations throughout the cycle. The fly wheel combats this by keeping the cylinder rotating at a near constant frequency.
Component FormThe general shape of the fly wheel is basically a disk. If looked at straight on it would be a circle with a hole in the middle.
The fly wheel’s diameter at its largest distance is 16.75 cm, its largest thickness is 4.5 cm and it weighs approximately 1.0 kilograms.
The fly wheel’s shape allows it to rotate faster with less air resistance. Since it is a thin disk, it has small edges that would create a higher air resistance at the corners. Its shape allows it to cut through the air and reduce the air resistance resulting in more potential momentum that the fly wheel can hold.
A stock fly wheel is typically made of steel. This fly wheel appears to be made of steel due to the amount of rust and the heavy weight. I do not think that manufacturing processes influenced this. The decision to use a steel fly wheel is usually based on performance or economics. A steel fly wheel will hold inertia better as well as last longer due to durability, while an aluminum fly wheel will not allow as much inertia and will throw off the timing of the cycle. This engine was made for a snow blower, so faster revolutions are not an issue, the work output is the issue. The only specific material property that a fly wheel will need is a high melting point. It not only spins extremely fast creating significant friction, but it is also close in proximity to the combustion chamber which will also heat it up.
The four factors of design did influence the material used to build the fly wheel. The first major factor is an economic design consideration. Steel was used as the material not only because it carries momentum better, but also because it is less expensive to manufacture. It is cheaper to manufacture because there was more abundance of steel than there was aluminum when the engine was made, which leads to the global factor. The United States has a very large steel production as does Russia and China which is where most of the parts are made for this engine, the fly wheel is no exception. There is no societal design factor because it is inside the engine and is not meant to be taken off or visible, therefore there are no aesthetics or safety features.
The color of the fly wheel is dirty silver, much like the cylinder and combustion chamber. Its surface finish is smooth, however it is not as smooth as the piston cylinder which may not have been finished, just molded. This characteristic is neither functional or aesthetic. The fly wheel does not need a smooth surface finish in order for it to perform its function. The choice of steel for the flywheel is purely performance and cost-based.
Manufacturing MethodsThe fly wheel is manufactured by die-casting and machining processes.
There are only three factors of design that impacted this decision. They were global, societal, and economic. Manufacturing process was influenced globally because there are only certain places that have the sufficient population to make this component in bulk quickly. Societal impacted this process, because production does not require people who have knowledge of the machines or prior experience in factories. The people working in the factories must only know when something is hot and not to touch it, otherwise they are probably performing the same task every day. This process was influenced by economics because die-casting the fly wheel is the cheapest and efficient process to make a component of this shape.
Based on a 1-5 scale, a 1 being a part with simple geometries and requiring only one manufacturing process, and a 5 being a part with complex geometries and requiring multiple manufacturing processes, the fly wheel is fairly non-complex. The fly wheel is ranked as a 1. The most complex part of the fly wheel is the ridges. The function of the fly wheel is simple, and it is simple to carry out. The form of the fly wheel is the most complex part. Its ridges are of a more complex geometry. The interactions it makes are simple as well. It keeps the crankshaft rotating consistently and sends an electrical signal every rotation. A more complex interaction would by the piston cylinder sucking in air and blowing out exhaust.
The piston and the piston rod transfer the potential chemical energy contained in the combustion of the fuel-air mixture into mechanical translational energy through its movement in the cylinder to the crankshaft. The initial pull of the pull start moves the piston towards the bottom of the cylinder, creating a low pressure system inside and drawing the fuel-air mixture from the carburetor. The piston rings around the outside of the piston head create a seal so that the explosive force from the combustion of the fuel is directly translated to the piston and through the piston rod into the crankshaft. The piston is directly related to conversion functions as seen in. These functions include the conversion of chemical energy to pneumatic energy, conversion of pneumatic energy to mechanical translational energy and conversion of mechanical energy to mechanical rotational energy. For the conversion of chemical energy to pneumatic energy the piston is influenced by both the human and potential chemical energy being input.
The throttle, start and stop signals all affect whether or not the piston is used and if so, how fast it cycles. The piston is exposed to the most extreme heat of the engine processes because it is inside the combustion chamber. Due to the high frequency of rotation and motion, the piston is exposed to friction forces from the cylinder walls and the crankshaft connection.
The piston head is made from aluminum. This can be determined by the weight of the piston and the lack of magnetism.
Since both the piston head and the piston rod are only seen if the engine needs serious work done to it, aesthetics do not apply to this component. For this reason, paint or other coloring agents are not used on the piston. Although the piston head is not designed to “look good”, it is designed to work well. The smooth surface finish of the piston head allows for less friction on the cylinder walls and in turn means higher efficiency. There is also a smooth surface finish on the area of the piston rod that connects to the crankshaft and on the area that attaches to the piston head, again for creating the least amount of friction. The surface finish on the rest of the piston rod is rough, but for no particular purpose.
Manufacturing MethodsThe piston head and piston rod were both made by die casting.
Since die casting is a relatively cheaper manufacturing process of high volumes of the same part, the die casting of the piston rod and head are the most economical choices for the manufacturer. Also, the use of aluminum for the piston head is much more economical than using a more expensive metal, such as steel. The material choice of steel for the piston rod is a societal design factor. If a weaker metal was used for this component, the safety of both the engine and the user would be at risk because there would be an increased chance of breaking. The breakage of the piston rod would cause serious damage to the engine and could result in user injury.
Based on a 1-5 scale, a 1 being simple geometries and requiring only one manufacturing process and a 5 being a part with complex geometries and multiple manufacturing process needed, the piston head would be a 3 and the piston rod would be a 1. The piston rod has simple geometries and is made with only die casting. The piston head is fairly simple as well, but it requires die casting, drilling and turning, so it is a bit more complex.
The piston interacts with the components it is attached to rather simply. It gets forced either up or down inside a cylindrical chamber from both the crankshaft it is attached to and the explosive forces of the combustion of the fuel and air mixture. On a scale of 1-5, a 1 being a component that is only used once in a process, such as the pull start mechanism, and a 5 being a component that requires multiple functions, such as the carburetor, the piston would be a 2.
Component FunctionThe magneto is an electric generator which has been tuned to create periodic high voltage pulses.
The magneto is designed to function in harsh weather conditions such as severe winter. It wouldn’t function if submerged in water (except pure water), hence it functions in non–aquatic environments.
The magnet on the flywheel induces a magnetic field on the armature when it flies past. This magnetic field induces current into the primary and secondary coil. It is for this reason the armature faces the flywheel. The case is attached to one leg of the armature; I deduce this is where the primary coil is connected to the armature.
The weight of the magneto is estimated to be less than 1 lb. The armature is made of steel, the magnetic property of steel is necessary to create the magnetic field the magneto converts to electrical energy. Economic factors such as cost were considered in choosing the material used in the armature. The case in is made of high density rubber and the coils enclosed in the case are made of copper. The copper is used for its high conductivity. Economic factors such as cost were taking into consideration in choosing copper. The case is present and made of high density rubber for safety reasons which are influenced by societal factor.
The case is black for aesthetics, but the armature has no aesthetics in its present state. The armature since its enclosed has little or no aesthetic purpose. The armature is presently in a rusted state with no sign of a finishing.
The primary and secondary coils were extruded. The armature consists of multiple sheets that were cut and shaped from a larger sheet of steel; the each individual layer has a clip that fits into another sheet. When put together this individual clip holds them together all the sheets together. The clip doesn’t incur any extra cost since it is cut out into that shape from the larger sheet; hence it is a very cheap way to hold the sheets together. The decision for using clips is influenced by economic factors.
Based on a 1-5 scale, a 1 being simple geometries and requiring only one manufacturing process and a 5 being a part with complex geometries and multiple manufacturing process needed, the magneto has a complexity rank of 3. The magneto is ranked intermediately on this complexity scale due to its very simple parts and multiple manufacturing processes. The simple parts of the magneto include the armature and a black case containing the primary and secondary coils and the electronic control unit, while the manufacturing processes include extrusion and shaping.
Component FunctionThe function of the carburetor is to sense user input by way of the choke and throttle settings, then mixes the fuel and air accordingly.
The carburetor is designed to work in a snow blower based on model number that was found on the engine block. Evidence that this carburetor was meant to be used in a cold wet environment can be found in the use of materials. The butterfly valves on the inside of the carburetor have been made of brass to prevent corrosion in addition the intake and most of the fasteners have also been made of brass for the same purpose.
The carburetor for this small engine is fairly complex and is made up of several different shape components however in general it is made up of cylindrical and square parts. The carburetor does not have a true axis of symmetry due to the complex function of the carburetor. The carburetor measures 7.62 x 6.03 x 7.0 cm. The carburetor does have a noticeable cylindrical chamber where fuel appears to be stored just before mixing of the fuel and air. There is also a couple of butterfly valves to control the flow of air into the carburetor. The carburetor is primarily 3 dimensional. The main body of the carburetor is shaped like a box and is hollowed out on the inside into a circular shape, the reason for this is to allow efficient function of the butterfly valves inside the carburetor to allow either complete or no flow of air into the component.
The component roughly weighs 0.23 kg and is made of a combination of steel and brass. The main body is made from cast steel, this was determined not to be aluminum because of its magnetic property. The cast steel was then machined on the inside to allow airflow and optimal performance of the butterfly valves. The carburetor is mounted directly to the engine and would have to be resistant to fatigue due to heat. Aluminum is used for the reservoir. The use of brass on the valves would most likely be for reduced friction and spark resistant material property. Given the reservoir of fuel in the carburetor and its function of creating an optimal ratio of air and fuel for combustion this is a very important material property. Societal factors play a lot into this decision to ensure safe operation by the user. With brass producing less friction than steel an environmental factor can be found with its use in the butterfly valves and the intake, with less friction the efficiency of the carburetor is improved and could result in better fuel economy and lower emissions. The only global design consideration would be the design of the carburetor to use normal gasoline. This also plays into the economical factor by using a combination of both brass and steel, brass is more expensive than steel so only using in sparingly saves cost and its spark resistance prevents law suits.
This component has no aesthetic purpose, it is purely functional. The component is made up of a couple shades of metallic silver and some dull gold pieces. Supporting the fact that this is a purely functional component all of the colors on the carburetor are there just because of the color of the materials used there is bright silver for the aluminum reservoir brass for the valves, intake and some fasteners and steel for the rest. The main body is cast and has been left with a non-machined surface finish on the exterior, however on the interior it has been machined for functional purposes. The finish on the rest of the component is smooth due to the method used for production. The only component that really has an aesthetic property is the lever for the choke which has been formed not just for strength but for appearance with a clearly defined handle and valley pressed into the structure.
The main body of the carburetor has been cast from steel this is apparent from the rough exterior of the component, inside the casting it has been machined, could even just have been milled out due to the fact that the portion machined is completely round and just increments in sizes from one end to the other. Another manufacturing method that was used on the valves, reservoir and intake is forming. It appears that the parts have a simple shape and all the edges are very rounded and have most likely been stamped over a die to form the shape. Some edges would have had to been ground to achieve their edges. Then all the fasteners would have been extruded and rolled to get the threads. Material wouldn’t have been as much of a factor as shape with the material. The body of the carburetor has a pretty complex shape which would make it hard to impossible to actually shape and form it in the way that most of the other components were made. Material choice did aid the process of forming the butterfly valves, intake, and reservoir however. The reservoir is aluminum which is soft and easy to bend. The valves and intake are made of brass which is even softer and makes stamping the parts out much easier. The stamping method used to make the reservoir, valves and intake the process of stamping out the parts works into the economical factor along with the choice of casting and machining the body of the carburetor.
Given a 1-5 scale, a 1 being simple geometries and requiring only one manufacturing process and a 5 being a part with complex geometries and multiple manufacturing process needed. The carburetor is a complex component. It is made up of several different parts and performs a complex process of mixing air and fuel. Individually the parts that make up the carburetor are simple, the most complex of which being the butterfly valve. On a scale from 1-5 for the carburetor complexity 1 being few machining operations and consisting of few parts when assembled, and 5 meaning the part was made using many machining operations and consists of many different parts. For complexity the carburetor is definitely a 5, it is its own subsystem and performs a very important task. The carburetor also interacts with other components. The carburetor acts as an interface between the user and the engine, controlling the amount of air and fuel that is forced into the cylinder head on the down stroke of the piston. The carburetor controls combustion and directly controls the movement of the piston, the crankshaft and the flywheel which also controls the magneto’s production of electricity.
For complexity of the interactions given a scale of 1 to 5 where 1 is a small amount of interactions and interactions aren’t complex to a max of a five where there is a number of different interactions and the interactions are very complex. The interactions of the carburetor would rank at a 4, it impacts the whole combustion process but the interactions are simple. Fuel and air are mixed and then sucked into the cylinder head. The biggest interaction is the one between the carburetor and the user.
Choice of CAD Package
For the process of solid modeling we selected Autodesk Inventor 11. It was determined that for this challenge inventor was best suited for the job, being very versatile when it comes to creating 3D components. Inventor also makes it easy to create several different views of a part after it is finished.
Choice of Components For Modeling
For our small engine the components chosen for #D modeling were the piston, crank shaft, connecting rod, and the pin the joins the connecting rod to the piston head. These are the components responsible for converting the downward force from the pressure of combustion to translational mechanical energy and then into rotational mechanical energy, which is the intended output for the small engine used to power a snow thrower.
A key function that an engine performs is converting Mechanical Translational Energy into Mechanical Rotational Energy. This is done by igniting an air/fuel mixture in the Combustion Chamber, which increases pressure and pushes down on the top of the cylinder head. The Piston head is attached to a Crank Shaft via a Connecting Rod which is in turn connected to the Crank Shaft in an offset position, so when the cylinder is pushed down, the Crank Shaft rotates. An engineering analysis can be performed to calculate the singular velocity of the Crank Shaft.
The first step in calculating the angular velocity is determining the initial velocity of the Piston head right after the mixture is ignited. The piston moves a small distance, so we assume that the velocity is constant and equal to the initial velocity. The velocity can be measured by an experiment using a Piston not connected to the Crank Shaft, and the normal amount of air/fuel mixture that is used for one rotation. Using a flag/gate system, one can ignite the mixture in a Piston cylinder, and as the Piston moves through the gate, one can measure the time in which it takes for the Piston to move through the gate. From this, the velocity can be measured as:
After multiple trials, the average velocity can be calculated. The Mechanical Translational Energy can be measured as:
After the Translational Energy is calculated, the Rotational Energy can be calculated by making a number of assumptions. The first assumption made is that no energy is lost due to heat or friction when converting from Translational to Rotational Energy. The second assumption is that the Crank Shaft is not attached to anything. The third assumption is that all of the air/fuel mixture will be used every time. From these assumptions, we get that:
- KE(rotational)=1/2Iw^2 (1)
We will assume that w is the angular velocity, the Crank Shaft is hollow and the inertia (I)is given by the following equation:
- I = mr^2 (2)
Where m is the mass of the Crank Shaft, and r is the radius of the Crank Shaft. We can then substitute equations (1) and (2) to solve for the angular velocity (w):
- w = √(2(KE(rotational))/(mr^2 ))
Increase of Piston RingsSince the piston rings are a key component in the efficiency of the potential chemical energy being converted into mechanical rotational energy, a revision in this area would be appropriate. An addition to the number of piston rings would result in more of the combustion force being transferred through the piston rod and into the crankshaft.
Piston Head Material
The amount of force that is required to move the piston up and down negatively impacts the engines power output. For this reason the current piston head is made out of a fairly light and cheap metal, aluminum. A lighter piston head with the same or better strength characteristics would increase the engines power output even further. The use of titanium for the piston head would give this result. The use of titanium would be expensive for the manufacturer, as well as the buyer.
This design revision would positively impact environmental factors and in the long run would positively affect economical factors for the user. The greater efficiency of the engine means less emission into the atmosphere. With greater engine efficiency comes less fuel needed to be purchased, which means it costs the user less in a winter season to snow blow their driveway. The use of a high quality metal such as titanium means less wear on the piston head which in turn results in less service of the engine and less maintenance cost for the user.
Fly Wheel Form
Two of the fly wheel’s functions mentioned in the component analysis are to increase the power output of the engine, and help with the engine cooling. Since the current flywheel is completely solid, the fly wheel needs ridges that act like fan blades to help cool off the engine. The ridges increase the airflow over the engine, but they also increase the air resistance.
One of the design revisions that we would consider making, is changing the design of the fly wheel.
The final design revision to be made to the flywheel will be done to the remaining ridges. On our current fly wheel, the ridges are straight. The design revision to the ridges would encompass angling the ridges so that they will push more air towards the engine as opposed to pushing it perpendicular to their face. Increasing the air flow across the engine will keep it operating between larger temperatures, and thus increase its efficiency. The performance of the engine is increased by this design revision. It is a economic design revision, because it will be able to be put on a wider variety of engines, thus increasing part changeability between models.
Gate 4: Product Explanation
Cause for Corrective Action
At this point in the project, the group is having no conflicts that call for corrective action. Each member is understanding the workload that is upon them in order to complete each gate with organization and professionalism.
Although the group is interacting very well, we find that there is one action that can be taken to further better our grade, and that is revision. We have found a trend in each of our grading sheets for each gate that we are losing points on minor mistakes that can easily be avoided with constant revisions. Up to this point in the project all four group members have not been completely revising each section which in turn has cost the group points. Throughout the remainder of the project we will conduct organized revisions that will catch mistakes that we have made and ultimately save us valuable points.
- Takes a relatively short period of time, component is easily assembled with no prior knowledge of engine construction is required.
- Fasteners may be harder to attach due to corrosion, still little or no prior knowledge of the engine is needed for part reassembly.
- Fasteners may be harder to attach due to corrosion and obscure location. Some mechanical knowledge and or knowledge of engine construction may be needed here.
- Fasteners may be hard to attach due to a significant amount of corrosion and or significant damage to fastener. Mechanical knowledge is required for reassembly of these parts along with some prior knowledge of engine construction is required.
- Fasteners may be mostly or completely obscure. High difficulty in attaching fasteners due to high corrosion and or damage to fastener. Mechanical knowledge and prior knowledge to engine construction is required. These steps would require the most amount of time due to their complexity.
- Note: Fasteners refer to any bolt, screw, nut, that is holding a part to the engine.
|Step||Description of Step||Tools Used in Step||Procedure Taken||Time Taken||Observations||Difficulty (Scale Defined Below)|
|1||Crank Shaft Assembly||None||Crank Shaft is attached to the Fly Wheel Seat||20 sec||N/A||1|
|2||Piston Assembly||5 mm Socket Wrench & 7/16 in Wrench||The parts of the Piston are fitted together inside the Crank Case||90 sec||One of the Piston Rings got damaged in the process||3|
|3||Fly Wheel Seat Placement||Star Driver Torx T30||The Fly Wheel Seat is screwed to the Crank Shaft||55 sec||N/A||1|
|4||Addition of Head Cover||Husky Star Driver T30||Head Cover is screwed into place on top of the Combustion Chamber||92 sec||N/A||2|
|5||Addition of Mounting Plate||1/4 in Wrench||The Mounting Plate is screwed into place on the side of the Crank Case||240 sec||Difficulty finding appropriate tool||3|
|6||Fly Wheel Placement||18 mm Wrench & 3/8 in Husky Driver||The Fly Wheel was slid into place on the Fly Wheel Seat in the correct orientation, then fastened with the Fly Wheel nut||252 sec||The threads of the nut had been stripped which made screwing it on exceptionally difficult||5|
|7||Magneto Placement||1/4 in Wrench||The Magneto is screwed into place facing the Fly Wheel||157 sec||N/A||3|
|8||Exhaust Placement||7/16 in Wrench||Exhaust is screwed into place on the side of the Combustion Chamber||33 sec||N/A||1|
|9||Addition of Crank Case Cover||Husky Star Driver T25||Crank Case Cover is screwed into place on the bottom of the Crank Case||50 sec||N/A||1|
|10||Placement of the Fly Wheel Cover||3/4 in Wrench||Fly Wheel Cover is screwed into place covering the Fly Wheel||240 sec||The chipped fragment of the Fly Wheel Cover was glued back in place. Difficulty finding the appropriate tool||4|
|11||Placement of the Pull Start Mechanism||1/4 in Wrench||Pull Start Mechanism is screwed into place onto the Fly Wheel Cover||260 sec||It was very loud when pulled due to lack of lubrication||3|
|12||Placement of the Spark Plug||3/4 in Wrench||The Spark Plug is screwed into its slot on top of the Combustion Chamber||5 sec||N/A||1|
|13||Addition of Carburetor||Allen Wrench||The Carburetor is screwed into place on the side of the Combustion Chamber||240 sec||N/A||4|
Conflicts During Reassembly
- Fly Wheel Nut: During disassembly we discovered that the end of the crankshaft that the fly wheel is bolted onto was stripped along with the nut that held the fly wheel in place which ultimately increased the difficulty in disassembly of that component. We encountered this problem during the reassembly as well. To resolve this we bought a new nut identical to the one originally in the engine, while this increased ease of reassembly of this component this task still was not as easy as it should be because the fact of the slightly stripped threads on the end of the crankshaft. We did end up tightening the nut completely onto the crank shaft to hold the fly wheel in place but it was difficult to screw on.
- Fly Wheel Cover: As stated in Gate 2 we encountered the conflict of the chipped piece on the fly wheel cover. This conflict was easily resolved using industrial strength adhesive to replace the chipped piece back onto the fly wheel cover.
Ease of Reassembly
Most engines, unless built yourself, are assembled in a factory that passes it down a line of people or machines that perform one task on it. A traditional assembly of a two-stroke engine starts off with the bare engine block, and each component is then systematically attached and added. A few of the steps that go into assembly of this simple two-stroke engine can be done in parallel with each other. Here is the traditional method of assembly for an engine.
- Attach crankshaft/mounting plate to engine block.
- Attach connector rod to crankshaft using a latch and screws.
- Snap on piston rings to piston head.
- Attach the piston head to the connector rod using rod that fits through the top of the connector rod and the middle of the piston head.
- Insert the piston-crankshaft assembly into the engine block.
- Attach the flywheel to mounting plate using nuts and screws.
- Add the head cover to the top of the engine using screws.
- Add the crank case to the side of the engine using screws.
- Attach Magneto using screws.
- Attach spark plug by screwing it on to its mount.
- Attach carburetor using screws.
- Attach exhaust port using screws.
- Attach pull start and pull start cover using screws.
As stated above, a few of the steps can be done in parallel with each other, so the steps for reassembly and dis-assembly can be different depending on who is performing the work. The assembly and dis-assembly are therefore almost identical. The ease or difficulty of each step is listed in the above table.
Direct InjectionThe Tecumseh HSK635 is a conventional two-stroke engine that uses a carburetor to monitor the intake of the fuel/air mixture entering the crank case. Though this throttling system does simplify the system of the engine, it does have disadvantages that affect the efficiency and emissions of the engine. With conventional two-stroke engines, a large share of the fuel/air mixture that enters the cylinder from the crank case goes through the intake port as intended but escapes out the exhaust port before the piston rises and covers it up.
To counteract this loss in efficiency and increase in emissions, a 'Direct Injection' system can be added to the engine to monitor the injection of fuel instead of the carburetor. With direct injection only air is transferred from the crank case into the cylinder and the fuel is not injected into the combustion chamber until the piston completely rises and closes all of the ports that the fuel could escape through. A direct injection system is intended to be mounted at the top of the combustion chamber to inject the fuel down into the chamber, this is a successful alternative to a carbureted system also because it evenly distributes the fuel, due to its placement at the top of the chamber, ultimately balancing the combustion pressure on the piston which is meant to sustain a pressure evenly throughout its surface. This can also increase fuel efficiency of the engine because it can slightly increase the energy being transfer through the piston from the combustion which will increase the rotations per minute (rpm) of the crank shaft and in turn increase the power output for the same amount of fuel input. Although these direct injection system may increase fuel efficiency of the engine it may have a somewhat high initial cost in comparison to a carburetor. Along with the initial cost of the injection system maintenance cost for the engine may increase due to the complexity of the regulator device as well as the need for alternative lubrication for the crank case due to the void of oil passing through which originally lubricated it.
The addition of a direct injection system will ultimately keep the ease of use of the engine about the same for the user because of two factors. The first being the less user input necessary for throttling and choking the engine because of the removal of the carburetor. While the second is the fact that the user must input a lubrication into the crank case as a form of additional maintenance because oil is no longer passing through it. These two factor will ultimately balance each other out since one increases user input while the other decreases user input. An additional societal factor is the idea of advanced technology, in our society today the carburetor is seen to be almost outdated and the alternative direct injection can be seen as a way to keep up with the advanced technological world.
One of the major advantages of adding a direct injection system into the engine is the increase in fuel efficiency and power output. With a reduction of fuel loss in the engine more fuel is used per each injection than with a carbureted system which will increase the strength of the combustion in the chamber, produce more power per stroke and ultimately increase the efficiency of the engine. But this advancement in the engine has a downside of initial cost and increased maintenance cost. The injection system will have a comparatively high initial cost to install into the engine and in addition to the original maintenance the user must also add an alternative lubrication to the crank case due to the void in oil passing through it.
The second major advantage of switching from a carbureted system to a direct injection system is the decrease in emission levels of the engine. With the fuel being directly added to the combustion chamber, with no chance of escaping, that lowers the amount of unburnt fuel exiting through the exhaust port and decreases the emission levels that are harmful to the environment.
Fuel AtomizationAs the Tecumseh HSK635 two-stroke engine stands now the fuel is injected through the carburetor, flows into the crank case which in turn flows into the combustion chamber. This flow of the fuel into the combustion chamber just before ignition can cause an undistributed combustion. This undistributed combustion can cause strain on different components of the engine such as the piston. The piston head was design to sustain an even combustion pressure across the whole surface and when the balance is off then that will cause problems internally in the engine system and affect the output.
In order to resolve this internal offset in the engine the use of a 'Fuel Atomizer' is ideal. A fuel atomizer is a device that can be inputted into the engine at the intake port to take the fuel entering the combustion chamber and force it through a small jet opening under high pressure to break it into a fine misted spray as shown in Figure 2. This spray of fuel into the combustion chamber will result in an even distribution of fuel throughout causing a balanced combustion and combustion pressure onto the piston head. This sustaining of balance in the combustion chamber will result in higher fuel efficiency and power output of the engine. Not only will the atomizer increase the outputs of the engine but it will also help to keep the engine running smoothly to minimize maintenance.
The addition of a fuel atomizer will decrease strain on the engine due to any unbalanced forces which will in turn keep the engine continuously running smoothly in the aspect of the combustion and transfer of energy to the crank shaft. This will minimize maintenance for the user and ultimately decrease user input over the long term.
With the fuel atomizer system keeping a balanced distribution of fuel throughout the combustion chamber it ensures that the piston is receiving the maximum amount of energy possible from the combustion. This maximization will increase the fuel efficiency of the engine due to the fact that the piston is getting the full potential of the combustion and converting that to mechanical rotational energy that can be transferred to the crank shaft to be outputted. Although the atomizer may ensure smooth running of the engine, this may also have a comparatively high initial cost and additional maintenance cost due to the addition of a more complex component. These costs will ultimately be canceled out due to the reduction of maintenance cost of the engine overall because of the systematic balanced that the atomizer helps to provide.
Filtration SystemThe Tecumseh HSK635 engine was designed to be put into a snow blower and would have then been used in a low dust environment, for that reason it would appear as though the engine was not designed with an air or fuel filter. Schematics of the engine support this theory. By not including a filtration system for incoming fluids everything is drawn into the engine and could result in damage to the combustion chamber of the engine. When the engine was disassembled there was carbon build up which was to be expected, however there were also easily distinguishable particles mixed in with the carbon that almost looked like very small rocks. This provides proof then that a filtration system would aid in protecting internal engine components. The proposed revisions would include the addition of both a fuel filter that would be placed on the intake fuel line, leading from the fuel tank and into the carburetor. A whole air filter assembly would also be added utilizing a foam sponge filter encased in a plastic housing that would take in air through the filter and then would be drawn into the carburetor.
These two components would not make the product much more complex however the maintenance required would increase as the fuel and air filters would need to be replaced over a regular period of time. However given these changes would prevent the intake of debris into the engine the proposed maintenance would be much simpler than having to take apart the whole engine to clean the cylinder head and piston.
By adding these components the cost of building the engine would be increased and therefore either the purchase price would increase or the potential profit would decrease. However, being a small engine manufacturer, an air filter assembly could most likely be lifted from another existing engine line and fitted to this engine so engineering costs would be greatly reduced. In addition, a small plastic fuel filter with a screen inside to keep debris out of the cylinder head would be very simple to produce and therefore very cheap.
More material would be needed to make the product and the process of manufacturing would take slightly longer so the initial production may put more of a strain on the environment, however by extending the engine life, fewer engines would be tossed into a scrap yard. So while the initial manufacturing may use more resources the filtration counteracts that by prolonging the engine life.
Gate 5: Delivery
As Group # 1 of this product analysis project, we completed and documented a very thorough analysis of the Tecumseh HSK635 Two-Stroke Engine. The purpose of this analysis was to conduct a series of tasks that will teach each member of the group the precise system and cycle of this specific two-stroke engine as well as general knowledge on the principles of how internal combustion engines work. Most of our group had never worked on any engine, because of this our group felt it would be a good idea to start small with some sort of two stroke engine. Besides knowledge related to the engine this project had also given us experience in technical communication that is an essential tool to engineers. It also gave us a chance to work in a project group, giving us the opportunity to organize and manage ourselves.
- The group began by determining Work and Management Proposals that would be sufficient in planning the project process and ensuring the complete efficiency of work throughout the group. In addition more specific roles were given to each group member, this ensured that if there were any questions the person covering that topic was easy to find for the answer.
- Precise research of the background, alternatives, material, energy and applications of a two-stroke engine was then conducted. The purpose of this research was to acquire the basic information that is necessary to be known before the engine can be disassembled.
- Following the research the group conducted the dis-assembly of the Tecumseh two-stroke engine. This process included extremely precise documentation of the tools used, the time taken, description and pictures of each component that needed to be removed. This information aided in our product assessment.
- The next task was the assessment of the product. The group conducted multiple individual assessments on each component, their complexity, their interactions, the manufacturing processes needed to produce them and most importantly, their functions.
- The group then produced multiple design revisions for different components of the engine that could possibly increase product efficiency, ease of use, versatility, or decrease cost
- Once assessments were done the reassembly step was necessary. Similar to the dis-assembly, this step included the same precise documentation for a comparison between the two. Original documentation was very useful during this step. Essentially follow the original steps in reverse was all it took to re-assemble the engine. We also had the benefit of knowing what tools were used for which parts.
- Once the reassembly was completed the group produced three more design revisions at the system level. These revisions would need to improve the engine by increasing efficiency,versatility, decreasing cost or decreasing user input meaning making the product easier for the consumer to use.
Throughout these tasks the group came to multiple conclusions about the cycle of the engine. Through the use of physical dis-assembly it was determined that not only the components, but also the component functions are interdependent. For example, the rotation of the fly wheel signals the combustion, which in turn causes the compression of the piston which then, causes rotation of the crankshaft to be outputted. The interdependence of components is a reoccurring theme as seen in this technical report and proves the extreme importance of precise timing and motions of each component in the engine or ultimately it will fail. The interdependence of this two-stroke allows energy to be transferred efficiently while at the same time being converted. It was found that energy is produced by the conversion of potential chemical energy to mechanical translational energy and from there to rotational mechanical energy which is the usable form of energy or in other terms the combustion and compression is a crucial step in powering the engine. For the components to operate in a smooth fashion most must be manufactured dimensionally consistent through an efficient process with a very tight tolerance, such as die casting/machining. To conclude, this project was performed to provide a deep and thorough understanding for the combustion cycle of most common two-stroke engines or specifically this Tecumseh HSK635. Concluding this process the group has learned everything necessary for the system and cycle of a two-stroke engine and look forward to using this information in future applications.