Group 6 - Toro CCR 2400 E GTS Snow-blower - Gate 3: Product Analysis

Introduction

Now that the group has dissected the snow-blower, we are ready to analyze its parts and systems. This report contains detailed information on the components of our product including part geometry, how it was manufactured, complexity as well as other characteristics. This report also includes 3-D models of several of the parts to better demonstrate their properties. Furthermore, this report will discuss possible engineering improvements to the snow-blower due to the shortcomings of a system or component.

Project Management

Progress Assessment

Throughout the process of Gate 3, our group has worked together well and now has a clear understanding of each member’s strengths and weaknesses. We posses the ability to proactively assign tasks to each member and work effectively to accomplish group goals. Several challenges have arisen during this section of the project that the group has successfully resolved. One of these aforementioned challenges appeared when group member Andrew Lyons required 3-D modeling assistance before he could begin work on the CAD drawings for this Gate. Andrew sought help from a senior Mechanical Engineering student in the UB Robotics club and received the aid required to begin work on the project. This action by Andrew reflects the proactive attitude amongst the group members and the willingness to look outside of its own resources to solve a problem. Another challenge that arose was determining the manufacturing processes used to create various parts from the snow-blower. For two of the parts, we could not as a group determine the processes used to create the part using our class notes and background knowledge. In order to find the required information, we took the crankshaft and the pull-start mechanism to Phil Cormier’s and Andrew Olewnik’s office during their office hours to discuss the classification of each part. As a result, we were able to accurately determine the manufacturing process that was used to create each part.

During the time window allotted for the completion of this gate, each group member unfortunately had many exams that took away from the time that could be devoted to the project with the group. In order to maximize the possible work that could be done before it became last minute, we assigned each group member tasks to complete so that the workload for the group would be decreased. For example, Tyler Salamone was assigned the completion of the Project Management: Coordination Review portion of the Gate as well as the component summary for the Crankshaft Connection Cup. Only one or two tasks for each group member was assigned due to the daunting amount of work required from each member to prepare for their respective exams. As a result, the amount of work needed for Gate 3’s completion was reduced drastically, leading to a more relaxed work environment when the rest of the project needed to be completed. Finally, upon receiving our graded Assignment 6 and realizing we did not perform as well on the assignment as we hoped, we decided that many changes needed to be made to it before it could be implemented into our Wiki for Gate 3. Joe Groele assessed the mistakes made in the assignment and worked to correct each one while the rest of the group revised his work upon completion. As a result, the group portion of Assignment 6 could be uploaded to the Wiki without the myriad of errors that could have caused point deductions to our grade.

Although we were able to successfully resolve many challenges throughout the course of Gate 3, a few challenges we have faced remain unsolved. One challenge that remains will occur during the reassembly of the snow-blower. As previously mentioned in Gate 2, several fasteners fell off the snow-blower during disassembly whose proper locations are still unknown. We plan to record the size of each part and take a step-by-step process of reassembly so that the proper locations of these pieces can be found. Another challenge also presented itself during disassembly when roller bearings fell out of a bearing piece on the crankshaft of the snow-blower. There are many of these and due to their size it will be difficult to place them back into the bearing for reassembly. We plan to put the bearings back with care so that parts are not lost and seek professional help with this task if needed.

Project Evaluation

Component Summary

Table 1: Component List

Component Number	Name	Image	Function	Material	Manufacturing Processes	Model Number	# of times used
1	Upper Handle	Figure 1: Upper handle	Provide user interaction between product and user	Steel	Forming and shaping	N/A	1
2	Lower Handle	Figure 2: Lower handle	Provide user interaction between product and user	Steel	forming and shaping	N/A	1
3	Engage Handle	Figure 3: Engage handle	Provide the method for human signal to engage auger rotation	Steel	Welding drawing forming	N/A	1
4	Top casing	Figure 4: Top casing	Protect internal components and subsystems	ABS Plastic	Injection Molding	N/A	1
5	Back casing	Figure 5: Back casing	Protect internal components and subsystems	ABS Plastic	Injection Molding	N/A	1
6	Ventilation Covering	Figure 6: Ventilation Covering	Provide ventilation for the engine exhaust	Steel	Forming and Shaping Milling	N/A	1
7	Chute top	Figure 7: Chute top	Direct the ejected material	ABS Plastic	Injection molding	N/A	1
8	Chute shaft	Figure 8: Chute shaft	Funnel the exported material	ABS Plastic	Injection molding	N/A	1
9	Chute base connector	Figure 9: Chute base connector	Connect the chute base to the chute shaft	ABS Plastic	Injection molding, drilling	N/A	1
10	Chute Base Connector Base	Figure 10: Chute base connector base	Fasten the chute base connector in place	Steel	Forming and shaping bending drilling for holes	N/A	1
11	Curved chute bracket	Figure 11: Curved chute bracket	Fasten the chute base connector in place	Steel	Forming shaping bending drilling for the holes	N/A	1
12	Chute Seal Ring	Figure 12: Chute Seal Ring	Seal the connection between chute and main casing	Rubber	Subtractive: stamping or drilling	N/A	1
13	Chute Base Brace	Figure 13: Chute Base Brace	Connect the chute base to the main casing	Steel	Forming drilling for the holes	N/A	1
14	Chute handle	Figure 14: Chute handle	Aim and rotate the chute to direct the snow	ABS Plastic	Injection molding	N/A	1
15	Inlet Scoop	Figure 15: Inlet Scoop	Scoop imported material into auger	steel	Formed and shaped drilling for the holes welding	N/A	1
16	Scoop wedge	Figure 16: Scoop wedge	Scrape material from ground	ABS Plastic	Injection molding Milling	N/A	1
17	Material channel	Figure 17: Material channel	Direct the material from the auger to the chute	ABS Plastic	Injection molding drilling for the holes	N/A	1
18	Engage cable	Figure 18: Engage cable	Transfer the signal from the engage handle to the pulley system	Plastic and Steel	Drawing forming injection molding	N/A	1
19	Auger axle	Figure 19: Auger axle	Provide rotational energy from axle pulley to the auger blade	Steel	Cutting from stock for the bar milling punching welding drilling/tapping	N/A	1
20	Auger blade	Figure 20: Auger blade	Collect snow from ground and pull into snow-blower	Laminated rubber	milling drilling riveting	N/A	2
21	Auger axle plate	Figure 21: Auger axle plate	Attach auger blades to auger axle	steel	Bending punching	N/A	2
22	Gear chamber casing	Figure 22: Gear chamber casing	House and protect the pulleys and belt system	steel	Forming shaping bending drilling	N/A	1
23	Auger axle pulley	Figure 23: Auger axle pulley	Transfer energy of the belt to the auger axel	ABS plastic and steel	Injection molding turning for the ridges die casting pressing milling for the center piece	60-9320	1
24	Pulley belt	Figure 24: Pulley belt	Transfer energy from the crankshaft pulley to the axle pulley	Rubber	Cut from stock then ends are formed together	N/A	1
25	Side panel	Figure 25: Side panel	Protect internal components	Steel	Forming shaping bending drilling for the holes	N/A	1
26	Main rear frame	Figure 26: Main rear frame	Provide support to the engine and other subsystems and a solid foundation for the wheels	Steel	Cut from stock welding bending shaping drilling for the holes	N/A	1
27	Wheel	Figure 27: Wheel	Allow translation of snowblower	Plastic	Injection molding drilling	N/A	2
28	Control panel casing	Figure 28: Control panel casing	Protect the components beneath the control panel	ABS plastic	Injection molding	N/A	1
29	Control panel	Figure 29: Control panel	contain the components that the user interacts with	Plastic	Injection molding	N/A	1
30	Key	Figure 30: Key	Send signal to turn snow-blower on or off	Plastic and brass	Milling for metal part then Injection molding with the metal part of the key in the mold so the plastic forms around it.	N/A	1
31	Engine shaft covering	Figure 31: Engine shaft covering	House and protect the pull start mechanism and the crankshaft	Steel	Forming shaping bending drilling punching	N/A	1
32	Pull start mechanism	Figure 32: Pull start mechanism	House the components of the pull start mechanism	Steel, plastic	Rolling stamping injection molding for the plastic	N/A	1
33	Pull start connection cup	Figure 33: Pull start connection cup	Allow for energy transfer from pull start to crankshaft	Steel	Die casting forming and shaping milling	N/A	1
34	crankshaft	Figure 34: crankshaft	Convert translational energy of piston	Steel	Turning tapping grinding milling slot cutting	N/A	1
35	Flywheel	Figure 35: Flywheel	Regulate energy from engine so it is continuous and consistent	Steel	Die casting milling drilling	N/A	1
36	Spark plug	Figure 36: Spark plug	Provide the spark to start the combustion reaction	Rubber, steel	Grinding die casting turning ceramic process	684048 19LV E	1
37	Piston	Figure 37: Piston	Provide translational energy from movement due to combustion reaction	Aluminum	Turning milling grinding	N/A	1
38	Engine block	Figure 38: Engine block	contains the combustion chamber, piston, and crankshaft	Cast iron	Die casting drilling tapping milling	94-5757	1
39	Flywheel housing	Figure 39: Flywheel housing	Encase and protect the crankshaft and flywheel	Cast iron	Die casting drilling	94-5759	1
40	Combustion chamber cap	Figure 40: Combustion chamber cap	Encloses the area where the combustion reaction occurs	Cast iron	Die casting drilling	94-5777	1
41	Roller bearing Containment piece	Figure 41: Roller bearing Containment piece	Contain all of the roller bearings	Steel	Die casting drilling	N/A	1
42	Roller bearings	Figure 42: Roller bearings	Decreases losses from friction, allows smoother rotation	Steel	Turning	N/A	32
43	Ball bearing	Figure 43: Ball bearing	Reduce friction to allow easier turning	Steel	Turning forming	N/A	2
44	Gas tank	Figure 44: Gas tank	Store the fuel	Plastic	Injection molding	N/A	1
45	Gas cap	Figure 45: Gas cap	Prevent fuel from leaving tank and anything else from entering tank	ABS plastic	Injection molding	N/A	1
46	Fuel line	Figure 46: Fuel line	Allow for transport of fuel from gas tank to engine	Rubber	Cut from stock tubing	N/A	1
47	Crankshaft pulley	Figure 47: Crankshaft pulley	allows for translation of energy from the crankshaft to the pulley belt	Steel	Turning	N/A	1
48	Engage spring	Figure 48: Engage spring	Move engage pulley into place so that crankshaft can transfer energy to the auger axle	Steel	Forming process: coiling	N/A	1
49	Electric motor and housing	Figure 49: Electric motor housing	The housing protects the motor. the motor turns the flywheel and crankshaft to start the engine.	ABS plastic is used for the housing	Injection molding is used for the housing	95-1799	1
50	Muffler	Figure 50: Muffler	Reduce noise output	Steel	Forming shaping bending welding	N/A	1
51	Nut, bolt, and washer	Figure 51: Nut, bolt, and washer	Fasten components to each other	Steel	Die casting turning forging	N/A	1

Product Analysis

Component Complexity and Interactions Scales

Each component assessment will conclude with a section discussing the component complexity. To analyze these components for their complexity on an equitable basis, we will split this section into discussions of four factors that affect the component complexity:

• Component functions
• Component geometry
• Manufacturing processes
• Physical Interactions

Component Functions will investigate the number and types of functions each component performs, as well as the importance of these functions to the overall product function. The most critical functions are those that are necessary for the product to achieve its purpose, for example, the transfers of energy from piston to auger would be considered of high functional importance.

Component Geometry involves the complexity of the shapes that the component consists of. An example of simple component geometry would be an axially symmetric part with few outcrops, slots, or holes.

Manufacturing Processes takes into account the number of manufacturing methods required to fabricate the finished component. The complexity of this category increases as the number of processes required increases.

Component Complexity Scale

The complexity scale is a numeric scale raging from 1 to 3 where:

• 1 is not complex
• 2 is complex
• 3 is the most complex

An increase in the complexity of any of the factors listed above would result in the rating being increased.

Interactions Scale

The Physical Interaction category examines the actual physical connections between the component and the adjacent components. A simple physical connection may just be a couple of bolts holding together two pieces. The complexity increases with the addition of washers or seals, and increases further as moving parts are introduced, as is the case in the engine block which has moving physical interactions with the piston and crankshaft. The number of these interactions also plays a role in the overall physical interaction complexity.

The interactions scale is a numeric scale ranging from 1 to 3:

• 1 is simple connection
• 2 is a complex connection
• 3 is a very complex connection

This rating is derived from the criteria stated directly above it.

Crankshaft

Component Function

Figure 52: A side view of the Crankshaft.

The primary function of the crankshaft is to convert the translational mechanical energy of the piston being driven back and forth by the pneumatic energy provided by pressure change as a result of the combustion reaction. The connection of the piston to the crankshaft via the connector pin provides for the transfer of this energy; the force of the connector pin to the small portion of crankshaft axel that is offset from the main axis causes the rotation about the main crankshaft axis. The crankshaft is also connected to the pull-start by the pull-start connection cup. When the pull-start chord is pulled, the energy is transferred to rotational energy of the crankshaft. Now that the crankshaft has converted the translational mechanical energy of the piston to rotational mechanical energy, its next function is to transfer this energy to the driver pulley of the pulley-belt system. This is a critical transfer of energy because it is the belt-pulley system that ultimately displaces this rotational mechanical energy to the auger, causing it to rotate and collect the snow and other material that is imported by the auger. The flow that is associated with the crankshaft is just this energy conversion. The crankshaft is located directly adjacent to the two-cycle gas engine, since it is connected to the piston by the connector pin. This location next to the engine is a hot environment that is caused by the convection of thermal energy off of the engine block’s heat sink. The high temperatures in this environment are cause for consideration when choosing the material for the crankshaft, which will be discussed in the following section, along with the geometry and appearance of the component.

Component Form

The general shape of the crankshaft is cylindrical. It is basically a cylindrical shaft with varying diameters to allow for bearings and other connections to be attached. The crankshaft is mostly axial symmetric with a few modifications that aid in its functionality. There is a smaller cylinder that is roughly two centimeters in diameter and is displaced from the main axis of symmetry that is for the connector pin to attach the piston to the crankshaft. The displacement of this cylinder from the main axis of symmetry is important to allow the translational mechanical energy to be converted to rotational energy. The component is primarily two dimensional, as a result of its general symmetry, but as mentioned, the crankshaft is not entirely axially symmetric.

• Length of 23 cm
• Minimum diameter of 1 cm, at the end with the external threads
• Maximum diameter of 8 cm, at the displaced axle
• Mass = 2 kg

The crankshafts cylindrical shape aids in its function of converting translational mechanical energy to rotational energy. The general axial symmetry of the component allows for smooth rotation without having large unnecessary shapes added on that would affect the rotational inertia and cause additional stresses along the length of the crankshaft as it rotates.

The crankshaft is made of steel, which was determined based on its appearance and by sticking a magnet to it. Another common material that is attracted to magnets is cast iron, but cast iron would be too brittle to be used as crankshaft material. This is an example of how the stresses that the crankshaft undergoes affected the chosen material. Plastic would have been a cheaper material, but would not have provided the strength necessary for a part that is subject to so much rotational stress. Additionally, the thermal energy given off by the engine needs to be considered. The crankshaft material must be able to maintain its integrity under the combination of the heat and rotation. For these reasons, steel was chosen for its strength and durability. Although fabricating the crankshaft out of steel might be more difficult to manufacture, as opposed to cast iron, the strength required for this component took precedence over manufacturability in choosing a material.

Of the Four Factors, the material of the crankshaft was influenced most by the economic factors. Choosing, while the snow-blower might be able to function properly with a less expensive and less durable material, Toro opted for a more expensive material option so that the retail price of the product could be higher. This would have been determined by calculating and weighing how much money could be saved by using a cheaper material against how much money could be made by selling the product for the respective prices.

The crankshaft does not have any notable aesthetic properties. This component is contained within the outer casing and cannot be seen without removing the covering, which requires the removal of four bolts before the casing can be rotated out of the way to reveal the engine block. Even with the casing out of the way, the crankshaft is still mostly concealed behind the engine casing. The crankshaft is a metallic gray color, that of ordinary steel. The color was left as it was, without painting or coloring. There would be no purpose to spending extra money to color the crankshaft since it will not be seen unless someone wanted to dissect the snow-blower.

The crankshaft has a very fine finish. However, this is not for aesthetic reasons. The crankshaft must be able to rotate smoothly; a fine surface finish aids in the smooth rotation, while the addition of lubrication and bearings work to further this effect.

Manufacturing Methods

The crankshaft would have started off as an ordinary steel ingot. The steel would have been attached to a fixture and by the process of turning, it would be made into the general cylindrical shape. Evidence that turning was used for the initial shape can be found in the axially symmetric nature of the crankshaft. The connector pin axle was probably turned separately once the basic shape was created. The segments of the crankshaft adjacent to the connector pin axle were milled down to their shape. These features are non-axially symmetric and would have to be done after the turning had been completed. Next, a slot cutter was used to create the key seats. The external threads were created by turning and the internal threads were made by tapping. It appears as if the surface of the crankshaft was then smoothed by grinding. This would not be necessary, but the refined finish does improve the quality of the component.

Material did not play a large role in the manufacturing process. The material choice was important for the stresses that the crankshaft would have to be able to endure. Alternative materials could have been easier to machine, but the necessity for strength in this component took precedence over the ease of machining for the crankshaft.

Shape definitely impacted the manufacturing procedures chosen. Since the shaft was to be a cylindrical shape, turning is an obvious subtractive process for manufacturing of the crankshaft. The non-axially symmetric features created the need for additional milling. The threads required turning and tapping, and the key seats needed to be created using a slot cutter since this feature could not be done by turning.

An economic factor that influenced the manufacturing process decision was the choice to improve the surface finish by grinding. From a functional standpoint, the snow-blower does not run noticeably better with a crankshaft that was finished with grinding than with a crankshaft that was merely turned to a high degree of smoothness. However, Toro would be able to sell the snow-blower for a higher price because of the improved quality that is offered by grinding. This was an economic consideration that had to be taken into account when the manufacturing methods of the crankshaft were chosen.

Component Complexity

Complexity: 3

The complexity of the crankshaft can be based on a number of factors. For example, the component function should be considered when analyzing the complexity of the component. How many functions does the component perform and how important are these functions to the overall product function. In the case of the crankshaft, the primary function is to transfer translational mechanical energy to rotational energy. An additional function is to transfer the rotational mechanical energy of the pull-start to translational energy of the piston.

The general component shape is fairly simplistic, just a solid cylinder with varying diameters along the length. The geometry is complicated by the addition of a displaced connector pin axle and by two key seats and threads for fastening the crankshaft to the pull-start connector cup and the driver pulley of the belt-pulley system.

The manufacturing methods also affect the complexity of the crankshaft. A number of techniques were required to obtain the end shape. Turning is the main process used, but milling, tapping, slot cutting, and grinding were also performed. The number of manufacturing steps required to produce the finished component adds to the complexity of the crankshaft.

Interactions: 2

The physical interactions with other components are complex. On the ends, the crankshaft is connected to the driver pulley and the pull-start connection cup by bolts. Additionally, each side had a key seat to lock the components in place during rotation. This is so no sliding occurs along the curved surface of the crankshaft. The crankshaft has a third connection with the connector pin, which provides for the energy transfer and conversion between the piston and the crankshaft. A scale of the complexity of these interactions takes into account the number of interactions, the significance of the interactions, the transfer of mass, energy, or signal across, and complexity of the physical connection between the two components that are interacting. In the case of the crankshaft, energy is being transferred, but this interaction is critical to the function of the snow-blower because without this connection, the pulley would not be driven and the auger would not rotate.

Crankshaft Connector Cup

Figure 53: Crankshaft Connector Cup

Component Function

This component acts as a transfer mechanism for rotational mechanical energy to travel from the wound pull-start cord to the crankshaft. This transfer induces the cycling of the engine upon the pulling of the cord. When the pull-start cord is pulled, metal teeth extend from a plastic cup in front of the cord housing and latch onto the grooves in the metal cup. This creates a physical attachment that holds when the piece rotates at a high speed upon actuation. The crankshaft attaches to the metal cup through the center hole of the cup and is tightened on through the use of a nut. This allows the crankshaft to rotate as the cup rotates due to the pulling of the cord. This flow of rotational mechanical energy from the pull-start cord to the crankshaft is the only function the connection cup performs.

The connection cup exists in a high temperature environment due to its proximity to the engine. It also is in a constant work environment and in turn must be reliable under mechanical stress. This is so because the part is constantly spinning at a high velocity while the engine is running.

Component Form

The cup takes on a hollow, cylindrical shape that has been bottomed out. It is a three-dimensional part that has an axis of symmetry through its center. It has been rounded along its edges and the “bottom” of the cup has a larger diameter than the rest of its shape due to a fanning out of its edge.

The part’s general dimensions have been listed below.

• Bottom Diameter D = 7.32 cm
• Outside Diameter D = 6.02 cm
• Inside Diameter 5.79 cm
• Height = 5.19 cm
• Center Hole Diameter = 1.12 cm
• Height of metal notch 0.50 cm
• Mass = 0.23 kg

The crankshaft connection cup has a circular hole down its axis to allow the entry of the crankshaft through the center of the part. This allows for the transfer of energy between the two systems. Also, the formed ridges on the inside of the cup allow the mechanism containing the pull-start cord to extend its teeth and latch onto the cup; thus causing the cup to rotate. Finally, its cylindrical shape was chosen to ensure that the part could rotate at high speeds with the least amount of air resistance. Any other shape would place too much drag force on the part and lower the efficiency of the engine.

The cup is made out of steel. The choice of this material was impacted by the manufacturing processes involved with the part. In order to make the shaped bottom and ridges along the outside of the cup, a material must be selected that is malleable. Steel also can be melted down and placed into a mold in a die cast process which was used to generate the cylindrical shape of the cup. In order for the part to function properly the material needs to be strong enough to withstand the shear force generated by the metal hooks that extend out and attach to the cup from the pull-start mechanism.

One engineering factor was taken into account upon the decision of steel as the material for the cup. Steel is a common material and inexpensive to work with. By using steel, manufacturing costs could be reduced which can lead to a price reduction of the overall product for the consumer.

Although it has no aesthetic purpose, the cup has a smooth surface finish which reduces the amount of drag on the surface of the cup; thereby allowing it transfer rotational mechanical energy more efficiently.

Manufacturing Methods

This part began as a steel ingot that was melted down for its insertion into a mold. During this die casting process, a manufactured mold defined the original shape of the hollow, cylindrical part. After it was molded, forming and shaping processes flattened and widened the bottom rim as well as defined the ridges on the inside of the cup. The small piece that has been lifted out of the component causing a second hole on the cup was created through forming and shaping as well. It can be seen that the material was heated for added manipulative capabilities in that area. A small section was then cut on three sides, bent, and lifted out of the surface. Finally milling created the hole in the center of the cup and a small, precisely shaped gear piece was welded on top of this created hole, inside the cup.

The general shape of the metal connection cup stands as evidence that it has been die cast. If the product were made using subtractive processes it would yield too much waste material and increase manufacturing costs. Also, its shape ensures sound structural integrity since the liquid metal can fill the mold uniformly. Since it would be very difficult to make a successful mold that accommodates a hole, ridges, and a gear shape, these features must have been added after the die cast process had been completed. The precision required for the ridges inside the metal cup could not have been created by a mill or other subtractive device. This is so because they have been indented into the part without the addition of extra material or the removal of metal. One can also come to this conclusion by looking at how smooth the surface finish is on these ridges.

The engineers chose steel as the material for this crankshaft cup. Factors that influenced this decision can be seen in the functionality requirements of the part. In order for it to function properly, the material needs to be strong and reliable through multiple cycles of the engine. The choice of steel as the material for the part then impacted which manufacturing processes would be used to create the cup. It would be too challenging to create the shape needed for the crankshaft cup with subtractive processes or forming and shaping due to the material properties of steel. Die Casting exists as the most cost-effective means for manufacturing the general cylindrical shape of the component since there is little to zero wasted material unlike subtractive processes. Also, die casting is optimal to create the small sized part in a high volume scenario since many of these parts will need to be manufactured. Secondly, the material choice affected the manufacturing process used to create the ridges on the inside of the cap. Steel can be easily manipulated when heated to very high temperatures so the engineers chose to use forming and shaping processes for these pull start lock ridges.

Various engineering factors were taken into account during the choice of material for the crankshaft connection cup. The choice of die casting the general shape of the cup accounted for economic factors such as production costs. The ability to create a high volume product in a time and cost-effective manner is crucial to cutting manufacturing costs. Die casting stands as the most efficient method for doing this as many parts can be generated out of one mold. If any other manufacturing process were used, manufacturing each part would take too much time and could possibly incur other costs such as wasted material and tooling maintenance costs.

Component Complexity

Complexity: 2

The connection cup has little structural complexity and performs one function. This part transfers rotational mechanical energy from the pull-start mechanism to the crankshaft. The importance of its function however does not lead to any complexity of the component as it consists of one piece.

Interactions: 1

This component has two interactions with other components. The first interaction is with the pull-start mechanism, which when spun, protracts clips which catch onto the grooves of the connection cup. This transfers the rotational energy generated by the pulling of the pull-start chord to rotational energy of the connection cup. The second interaction is with the crankshaft. The rotational energy of the spinning connection cup gets transferred to the crankshaft, thereby translating the piston for the initial cycles, until the engine can begin generating energy by itself to continue the engine cycle.

Engine Block

Component Function

Figure 54: Engine Block

The main function of the engine block is to encase the piston cylinder system and provide a channel for the crankshaft to rotate in. The combustion reaction occurs inside the piston cylinder system that is contained within the engine block. As a result, the engine block acts as a cooling jacket by the inclusion of a heat sink. The engine block itself is stationary, although it does transfer the flow of thermal energy through the walls where it can be transmitted to the environment.

Since the engine block contains the combustion chamber, it also has inlets for fuel and air, and a discharge opening which leads to the muffler. The surface with the open hole on the side opposite the crankshaft has screw threads that allow the spark plug cap to be fastened in place above the combustion chamber.

The engine block functions under very high temperatures. This is because the combustion reaction is occurring inside it. The engine block is not moving, but it houses two rapidly moving components: the piston and the crankshaft. The inside surfaces of the engine block are exposed to friction from these interactions, but this is reduced through the use of oil lubrication.

Component Form

Engine block is roughly a rectangular shape, but there are many circular geometric features included. The block has no overall symmetry, but the interior chamber is an axially symmetric hollow cylinder shape. The component is fully three-dimensional. Each view is different and all sides are important to the function.

The part’s general dimensions have been listed below.

• Piston chamber Diameter = 6.25 cm
• Piston chamber Height = 9 cm
• Mass = 3.5 kg

The engine block is approximately 13 cm from the crankshaft track surfaces to the surface where the spark plug cap would be screwed in and about 15 cm from the muffler discharge to the fuel valve intake.

The engine block’s shape is coupled to the function that it performs. The cylindrical void is required for the piston to translate in. The two curved slots are required to allow the crankshaft to smoothly rotate and be connected to the piston by the connector pin. The geometry of the inlet and discharge valves are such that pipes can be attached to transfer material between the components. The additional material that makes up the shape surrounding the cylindrical void is the geometry of the heat sink and acts to increase the surface area to allow for quicker rates of convection to transfer heat away from the engine block quicker.

It is made primarily of cast iron with a steel cylindrical shell that lines the combustion chamber. The decision for this material was chosen with consideration for impact that it would have on manufacturing. For the complexity of the geometry required, die casting would be an appropriate manufacturing process. Cast iron is often used for die casting because of its material fluidity, which is necessary for the material to effectively flow to all parts of the mold.

The steel cylindrical shell that lines the combustion chamber was chosen to provide for improved durability in the chamber which is exposed to large pressure changes and heat associated with the combustion of a two-cycle gas engine. This shell could have die casted itself, or possibly turned and then drilled to remove the inside. Steel was not required for the rest of the component because the high pressures and temperatures are most extreme within the combustion chamber. Due to the reduced stresses and heats found at other locations along the engine block, cast iron is sufficiently durable for use.

The choice to use cast iron for the majority of the engine block is an economic factor that influenced the decision. Although cast iron is more brittle than steel, the cost to produce a cast iron part is significantly less than if the entire part were to be cast out of steel. Toro must have decided that the cost of an entirely steel engine block was not made up for by the increased quality that an all-steel engine block would provide. In this way, economic factors influenced the decision to primarily use cast iron for the engine block material.

There are no aesthetic properties of the engine. It was designed to be encased by the outer snow-blower plastic casing. The color of the material is a dull gray. There is no reason for the engine block to be colored or shaped in any aesthetically appealing fashion because it is not meant to be seen. The engine block has a moderately fine surface finish, but it is still significantly rougher than finishes that can be achieved by grinding, for example, the surface of the crankshaft. The surface finish was chosen for functional and economic reasons. There would be no benefit in over machining the engine block to a fine surface finish because it just needs to perform the function of transferring excess heat from the combustion chamber to the surrounding environment.

Manufacturing Methods

The primary manufacturing method used to make the engine block is die casting. This involves the melting of cast iron ingots and injecting them into a mold of the general desired shape. From here, several subtractive processes were employed to further create the geometry. Holes were drilled for the air and fuel inlets, as well as for the exhaust outlet. There are seventeen threaded holes that were tapped along the surfaces of the engine block. These threads are to allow for the physical connections between this component, and those adjacent, and also to fasten the engine block in place along the main engine bracket that spans the width of the interior casing. Milling may have been used to touch up some of the geometry, particularly to clear out the grooves of the heat sink.

Evidence to support that the engine block was fabricated by die casting can be seen in the riser marks that are scattered across the surface of the piece. Part lines can also be seen along the surface that contains the crankshaft. Tapping is used to create the threads The cylindrical shell lining the combustion chamber is visibly a separate part and is axially symmetric itself, which may indicate that it was fabricated by turning. To permanently insert the shell into the cylindrical engine block void, the lining may have been cooled to shrink its size. Once small enough to slide into the cylindrical chamber, the lining was then heated so that it would expand to and permanently lodge itself into place.

The material choice played a significant role in the decision to fabricate the engine block by die casting. As discussed previously, the material cast iron was determined to be appropriate for the functions required. Cast iron is not as durable as steel, but because the engine block is subjected to intense pressures and heats mainly at the combustion chamber, this need could be met by the inclusion of a steel lining to provide increased durability in this location. With cast iron chosen for the material, die casting is a particularly appropriate manufacturing process. The material flows well into the edges of the mold and solidifies in a consistent manner.

Shape also impacted the manufacturing method chosen. The engine block is a component that requires good part detail. This is a feature that can easily be accommodated for by the process of die casting. This method also provides for high dimensional consistency, which is necessary for allowing the smooth movement of parts and the reduction of energy lost to friction at these contact surfaces. The thin ribs of the heat sink could also be created by die casting since they are not too long that the liquid metal would have difficulty flowing to the end. Regardless, this geometry may still require additional milling to result in the desired cooling jacket surface area.

The main factor that affected the decision of the manufacturing methods used is economic. Die casting is a process that is economical for high volume production. Although there is a high initial cost associated with die casting, Toro must have determined that they would be producing enough engine blocks to warrant the creation of a mold for this component. It is possible that this same engine block was used in variant models of snow-blowers that are also created by Toro. This would further the benefit of the die casting manufacturing process for the fabrication of the snow-blower engine block.

Component Complexity

Complexity: 3

The complexity of the engine block is affected by several factors. The number of functions and interactions are the most significant factors that affect the component complexity. The engine block is a very complicated piece, mostly in part to its numerous connections with other parts. The spark plug cap is fastened to the end of the combustion chamber. The muffler is attached to the exhaust discharge valve by a small angled pipe. The engine block also connects to the fuel injector valve. Lastly, the engine block provides the tracks for both the piston and the crankshaft, which are connected by the connector pin. All this takes place within the engine block.

The component shape of the engine block is also very complex. There is no general symmetry to be found. The inlet and discharge valves located on the sides of the combustion chamber have molded holes for screws to fasten the adjacent parts in place. There are seventeen threaded holes, which were tapped separately after the die casting procedure had been completed. The heat sink also adds to the geometric complexity by greatly increasing the surface area of the component through the addition of thin ribs that look almost like stacked plates running parallel to the circular surfaces of the cylindrical combustion chamber.

Although the method of die casting is a fairly simple process once the mold is created, there many more processes that need to be done before the finished engine block is created. As previously mentioned, seventeen threaded holes must be tapped. The additional processes required to permanently insert the steel combustion chamber liner also adds to the manufacturing complexity. The final milling to fine tune the heat sink adds complexity as well to this category.

Interactions: 3

The physical interactions with other components make the engine block an extremely complex component. There are threads for screws to attach the spark plug to the end of the combustion chamber as well as physical connections between the engine block and the muffler and between the engine block and the fuel injection valve. The crankshaft also rests in a cylindrical track adjacent to the combustion chamber. This is to allow for the physical interaction between the engine block, the piston, and the crankshaft. Each of these interactions is crucial for the overall product function. If one of the interactions is missing, the engine will not successfully produce the rotational energy at the crankshaft that is required to turn the driver pulley, and ultimately rotate the auger.

Pull Start Mechanism

Component Function

Figure 55: Pull Start Mechanism

The Primary function of the Pull Start Mechanism is convert translational energy form the user into rotational energy to be transferred to the pull start connection cup. The cord of the device is wound around the outer radius of the internal plastic wheel. When the cord of the mechanism is pulled two metal clips are extended out of the central axel of the device at a smaller radius which connects with the pull start connection cup. The force transferred by the user through the cord and wheel travels through these clips causing the crankshaft connection cup to rotate, which in turn rotates the cranks shaft.

After the human energy has been transferred to the crankshaft connection cup, the clips and the cord must be retracted and wound back into the device. This is accomplished by two springs in tension which are contained at the inner radius next to the metal clips. After the user releases the cord it is rewound around the external radius of the inner plastic wheel housed in the component. The springs in tension causes this to occur by rotating the wheel in the opposite direction of which it was pulled. The metal clips are simultaneously retracted back into the plastic housing which they are attached.

The pull start mechanism is adjacent to the crankshaft connection cup which is next to the engine. Thermal energy is given off as a result of the conduction through the various components throughout the engine. Some of this energy may reach the pull start mechanism. This component must also operate successfully under the force applied to it by the user through the pull cord. Both of these factors must be taken into account when choosing the materials used in this component.

Component Form

The general shape of the component is cylindrical. The outer metal casing and small plastic connection wheel are axially symmetric however the inner plastic wheel is not axially symmetric due to the angled edges extending from its center. The outer metal casing also has four holes that have been extended out from its outer diameter so it can attach to the engine shaft covering. It is a 3-Dimensional part whose general dimensions have been listed below.

• Outer Metal Casing Diameter = 14.05 cm
• Inner Plastic Wheel Diameter = 13.50 cm
• Small Plastic Connection Wheel Diameter = 4.92 cm
• Metal Casing Outer Hole Diameter = 0.50 cm
• Metal Casing Inner Hole Diameter = 0.30 cm
• Mass = .45 kg

This part has a cylindrical shape because it has to house the wound pull-start cable. The inner plastic wheel must also be cylindrical so that it can spin freely once the wound cord is pulled. The mechanism’s outer metal casing is made out of steel which, due to its high malleability, could be easily formed and shaped to gain the cylindrical shape. The inner wheel is made out of plastic which was chosen for its light weight and to save on manufacturing costs. Injection molding a plastic wheel is less expensive than custom making one made of steel since the mold can accommodate this high-volume, small size part. The small wheel is made out of plastic with steel teeth that extend from it to connect to the crankshaft connection cup. The teeth are made of steel because a material is needed to withstand the high amount of stress from the force due to the ridges on the cup when the two parts make contact. However, the wheel itself was injection molded with plastic to keep a low weight and also reduce manufacturing costs.

Aesthetics were not taken into account other than a main color scheme during the design of this part. This can be mainly attributed to the fact that this part is housed within the plastic casing of the snow-blower and therefore cannot be seen by the user. The Pull Start Mechanism is painted black to remain consistent with the red-black-white color scheme of the machine. The inner plastic wheel has a smooth surface finish to decrease the amount of friction between it and the metal casing to yield a more efficient pull-start.

Manufacturing Methods

The basic shape of the metal outer casing was made using forging. Then, milling cut and shaped the trapezoidal holes in the top of the casing. Drilling then cut the holes on the outside and inside of the casing. These conclusions were drawn on the basis that the combination of these methods is the most cost-effective means of producing this part. The shape of the casing is too intricate for a die cast model to work since the liquid metal would have trouble retaining a uniform structure as it traveled through the mold. Also, subtractive processes alone would yield too much waste material for the process to be cost-effective. The inner wheel was made from injection-molded plastic to create the complex design. This can be seen from the ejector and gate marks found across the components body. In the same manner as before, this method stands as the most efficient means of producing this part since injection molding is optimum for high volume parts.

Several economic factors were taken into consideration when designing the component. Since the component is made up of several parts, a material choice had to be made which reflected a functional decision as well as a cost efficient one as well. The inner plastic wheel could perform the same function if it were to be made out of a metal. However, the plastic chosen was able to perform the function at a cost efficient price. The outer metal casing of this component had to serve the function of protecting the mechanism as well as correctly positioning it outside of the engine. Both these material choices also had to factor in the most economic process possible to produce these parts.

Component Complexity

Complexity: 3

Each component of the pull start mechanism has a complex shape that requires various manufacturing steps to produce. Their geometry is complex although a few of the components are axially symmetrical. In terms of functions performed, the pull start mechanism is complex. The part involves two energy transfers and simultaneously latches on to another part of the snow-blower when pulled. It provides one of two ways for the engine to start by generating crankshaft rotation so it is thus complex.

Interactions: 2

It is also complex in its physical interaction because it is not only bolted to the engine housing but also latched on to the ridges in the crankshaft connection cup upon the pulling of the pull-start cord.

Auger Blade

Component Function

Figure 56: Auger Blade

The function of the auger blade is to break up and pull the snow from the ground into the snow-blower. Since this model is a single stage snow-blower, the auger blade also serves the purpose of discharging the snow, a function which would be performed by the impeller in a 2 stage snow-blower. The snow-blower is involved with the flow of snow and debris into and out of the machine. It also is involved with the flow of rotational mechanical energy since it receives its rotational energy from the auger axle. The auger blade comes in direct contact with the snow, and thus operates in a cold, wet environment. It must be durable enough to resist damage that could result from being forcibly driven into the snow. It must also be able to resist any damage that might arise as a result of getting wet from contacting the snow.

Component Form

The auger blade is a helical shape and encompasses a volume of approximately .022 cubic meters. When flattened out, each of the 2 auger blades is approximately:

• 55 cm long
• 20 cm wide
• 1 cm thick
• Mass = 1 kg

The helical shape of the auger is important to its function because this allows the blade to more effectively scoop the snow into the snow-blower.

The auger blade is made of laminated rubber. The primary reason for using this material was cost. The blade would be more effective it were made from metal, as many auger blades are, but the Toro CCR model we are examining is a low-end, relatively inexpensive snow-blower so high functionality was not as much of a concern. Not only is the material cost for rubber cheaper than it would be if the blade were made of metal, but the manufacturing process is cheaper as well. It requires more time, effort, and money to die cast a metal auger blade instead of cutting a rubber blade from stock. Also, since rubber is a very workable material, it can be formed into the helical shape much easier than steel.

This part is black and aesthetics were not considered during production. This is because the auger is contained beneath the external housing of the snow-blower and can therefore not be seen during use.

Furthermore, there is no evidence that anything was done to improve the surface finish of the auger blade. Again, this is because it is a low end product and altering the surface finish would not have a significant impact on functionality.

Manufacturing Methods

We believe that the auger blades were made using a subtractive process. The desired shape was most likely cut out of a stock piece of the rubber. This would account for the slightly rougher surface on the edges of the auger blade where the cut would have been made. One issue with this process is that it produces a significant amount of waste rubber.

Next, a drill would have been used to produce the holes through which the bolts which attach the blade to the axle pass. Finally, the rubber is flexible, so it can simply be bent into the final helical shape required.

The most important factor in determining the material and process for the auger blades was economic. This is meant to be a low cost product, and so it would be more important to keep manufacturing costs down than it would be to ensure the best functionality possible.

Component Complexity

Complexity: 1

The auger blade is not structurally complex as it is basically just a cut piece of rubber. The auger blade does serve 2 functions; it acts not only as the auger blade, but also as the impeller. This does not add to the complexity of the part or its interactions with other parts. Furthermore, there is little complexity in the manufacturing process. The auger is cut out of a piece of stock, and then rivets are added to it.

Interactions: 1

The only component the auger blade interacts with directly is the auger axle. The connection is very simple; it is just attached by nuts and bolts.

Solid Model Assembly

This section provides solid models of the crankshaft, the pull-start connection cup, and two cylindrical ball bearings. These components were chosen because they are central to the rotational energy that is essential to the overall product function. The pull-start connection cup is the device that captures the original human energy and transfers it as rotational energy to the crankshaft. From the crankshaft, the energy can then be directed either to the connection pin and piston to start the engine, or once the engine is cycling, the energy can be transferred to the driver pulley of the belt-pulley system. The cylindrical ball bearings were modeled because they are essential to the efficiency of the rotation of the crankshaft. Without these components, the significant amount of rotational energy could be lost to sliding friction.

Autodesk Inventor was chosen to be used to create the solid models because of its user-friendly interface, intuitive tools, and advanced modeling capabilities.

Figure 57: Crankshaft

Figure 58: Crankshaft Connection Cup

Figure 59: Ball Bearing

Figure 60: An exploded view of all the components.

Figure 61: A view of all the components assembled together.

A link to a folder containing the modeling files is provided below.

File:Group6CADParts.zip

Engineering Analysis

Energy Convection Calculation of the Engine

In this section, the convection of heat from the engine heat sink to the surrounding environment will be calculated. This is an important engineering analysis problem that would be used in the design or testing stages of the design process. The engineers designing the components that are adjacent to the engine would need to know how much thermal energy the components would be exposed to while the engine is cycling. This information would impact the material choice for those components. Certain plastics might have melting points below the temperature of the air surrounding the engine. This may be the reason that Toro opted for the metal ventilated component was chose to act as the casing near the engine.

Problem Statement

This will be done by using two equations that contain the variable Q, heat transfer (Eq. 1 and Eq. Using these equations, and by assuming that the temperature of the heat sink is the average temperature of the air (Eq. 3), the temperature of the final temperature of the air in the piston can be solved for. Then by plugging T₂ back into either Eq. 1 or Eq. 2, the heat transfer can be solved for. In order to determine the mass of air contained in the piston, one must only calculate the volume of the piston chamber and divide by the specific volume of air at atmospheric pressure. Using Eq. 4 and Eq. 5, the mass can be solved for.

Nomenclature:

System conditions given:

Solve for:

Diagram

Figure 62: Piston Chamber Diagram

Assumptions

Governing Equations

Calculations

This is the procedure that could be done to perform an engineering analysis to determine how much thermal energy was being given off by the engine to the surrounding air, allowing for design considerations to be made regarding the properties of the material chosen for the surrounding components. For certain components, this information would also have been considered when designing the placement of components. For example, since the gas tank was chosen to be made of plastic, it could not be positioned directly next to the engine so that the heat given off would not damage the tank.

Design Revisions

In this section, we will discuss three design revisions that we feel would improve our product. When considering our revisions, we took into account global, economic, environmental, and societal concerns.

Uniform Nut and Bolt Sizes

Figure 63: A bolt-nut pair used in the snow-blower

Our first change addresses an economic concern. While disassembling the Toro CCR snow-blower, we noticed that a wide variety of sizes of nuts and bolts were used. This requires the purchase of different parts, and the use of many different tools.

We recommend using as few sizes of nuts and bolts as is possible. In most cases, there would be no effect in altering the size of the nuts and bolts. Toro could likely cut back to 3 or 4 sizes without endangering or altering functionality or safety. If this change were implemented, Toro would be able to order or produce fewer sizes of the nuts and bolts and would save money as a result. It would also eliminate the need for several sizes of wrench or ratchet during the assembly process which would further reduce production cost.

Wheel Modification

Figure 64: An example of possible wheel replacement

Our second design revision to the Toro snow-blower addresses the poor functionality of the wheels. The current wheels are small, loosely fit, and have little traction rendering them inherently useless. The effect of poor wheel quality on the user is drastic and addresses a societal factor of engineering in regard to the ease-of-use and user demographic of the product. Without wheels that can allow for easy maneuvering of the snow-blower, users with less strength like women or teenagers will not be able to use the product to its fullest capabilities. In order to address this societal factor we propose the implementation of wheels with larger radii and a thicker tread. This will allow the user to maneuver the snow-blower through rougher terrain without over-exertion. Furthermore, the demographic of users of the snow-blower will increase due to the decreased amount of strength required to move the product.

Self Propulsion

Figure 65: An example of a self propelled snow blower

Our final revision to the snow-blower would be to add a self propulsion system to increase the product’s ease-of-use. Conventional snow-blowers today contain a system that allows the user to input a signal which induces movement in the wheels to drive the snow-blower forward. This allows a wider range of people to easily use the product and decreases the exertion experienced by the user during operation. In order to implement this system, another engage handle would be needed to transfer the signal from the user to the machine. From there, another system made from gears or pulleys would be needed to transfer the mechanical energy from the crankshaft to the wheels, causing them to move. By implementing a self-propulsion system, we take into account the societal factor of ease-of-use and thereby improve the user’s ability to operate the device.