Group 11 - Dual Stage Snow Thrower (Gasoline Powered) - Gate 3

Introduction

In this section of our product dissection, we cataloged the different components, considered what decisions went into their design and manufacturing, and proposed some possible and currently used revisions.

Project Management

Previous Challenges Dealing with Procrastination: We resolved to get everything up two days before the due date, to have time to revise and cover.
Inconsistent English Skills: After putting everything up on the wiki page, more polished group members would look it over and edit.

Future Challenges Dealing with parallel responsibilities: All of us are now starting to feel crunch time between the different classes and requirements. We'll have to organize our efforts better in the future.

Product Analysis

Complexity Levels
1: Component has a straightforward function and presents little difficulty for manufacturing.
2: Component has a secondary purpose and/or poses some challenge to manufacturing.
3: Component is involved in multiple functions and is a very difficult piece to manufacture.

Starter Flywheel
Complexity: 2

-Component Function-
This component serves to preserve the internal momentum of the engine crank shaft in the brief moments that the piston is not in a power stroke. The power stroke effects movement, and the inertia due to the mass of the flywheel keeps it spinning while resisting friction. In this particular engine, the flywheel also serves another purpose. Fins on the part ensure the circulation of air while it is spinning, funneling clean air into the engine to burn and cool.
While in operation, the flywheel is in a high heat environment due to its proximity to the engine block. Its mounting is oiled to minimize energy lost due to friction. It is also positioned close to an open source of air.

-Component Form-
The flywheel is a circular part, with scooped fins all around the the "top" and gear teeth near the outer edge on the "bottom." There is a sizable chunk of the circle missing however. The fins are roughly 3/4s of an inch in height. It is primarily three-dimensional, since its secondary function involves the movement of a volume of air. The component is 5 inches in diameter and a total of 1.5 inches in height. It weighs 5 or 6 pounds.
Because it is used to preserve momentum and operate in a high heat environment, being composed of a dense material like steel is vital. It's high density and specific heat capacity allow it to weather the operating temperature of the engine. And while the density impedes the initial start-up of the engine, it afterwards is much more resistant to frictional forces and better preserves the rotational energy of the crankshaft when not on the power stroke. The flywheel could have been alternatively made from ceramics or heavy rubber/plastic. But ceramics are far more expensive and brittle than steel, and also less dense. Rubber or plastic would expand and contract during the operating cycle, squeezing against the central axle and impeding movement. They would also have a shorter lifespan, and upon degradation tend to pollute the environment. Knowing this, the manufacturers decided on using steel. There is no aesthetic purpose to the component, apart from the possibility of the color being strongly associated with the engine block to avoid parts confusion.

-Manufacturing-
The flywheel was most likely manufactured through investment casting. The surface is unrefined and rough, unlike the surface of a die-cast part. It is also devoid of ejector marks. There are no welding/fusion seams, so this was a single solid part. There are no flash marks and the shape is not conducive to being easily separated from a die, so no press-forging. And injection molding is not a viable method because this is a metal piece.

Chassis Shroud
Complexity: 1

-Component Function-
The shroud functions as a shell, protecting the internal components from the external elements. It also protects the operator from inadvertent contact with very hot metal during usage. It is intended to withstand the cold outside temperature and the thermal radiation from the engine.

-Component Form-
The shape of the shroud is very blocky, with several flat sides that don't always intersect at right angles. The component is the largest of all the parts of the snow blower, but also one of the simplest. It's about 3/8ths of an inch thick, and covers the entire top of the machine, over an area 32 inches by 24 inches. It would actually be more appropriate to refer to it as a shell because its sole function is to encapsulate. There is a cutaway section for the exhaust shroud to attach to , which is made of steel. Since plastic is not as heat resistant as steel, it would have been inadvisable to have a continuation of that section with ABS plastic. There is a central rise of 2 to 3 inches, a long rectangle that covers 3/4s the length of the machine. It connects to the discharge chute collar, and had to be a separate elevation from the lower section in order to conserve the space used by the machine. Finally, there is a "lip" near the front end of the shroud, that corresponds to the "mouth" of the machine, where the auger is.
The nature of the component, as stated, is that of a shell. Once linked to the other parts with nuts and bolts, it forms a, for all intents and purposes, weather-proof shell that protects the vitals from the outside elements. There are no holes that aren't used for linkage placement. The fact that it is also made with one of the cheapest materials usable for industrial applications, ABS plastic, is another clue. Why waste resources on something who's purpose merely requires a proper shape? The ABS plastic is also responsible for it's light weight: approximately 3 to 4 pounds. The color of the part is only for identification purposes. At the time it was developed, this model and its design family all had red coloring to signify its origins from the TORO company.

-Manufacturing-
The part was likely formed through Injection Molding. Casting, Forging and Welding can only be applied to metal components. This piece is plastic, and therefore subject to Extrusion, Forming or Molding. There is no axis where the part profile is the same throughout, so it cannot have been an extruded part. Therefore, Molding or Forming are the only choices. Injection Molding is the most likely, because the tapered geometry would be explained as well as the ejection marks on the bottom of the part. Since it is only a cover, the only requirements are that it should be cheap, easy to replicate, relatively clean environmentally, and have structural integrity.

Impeller Housing
Complexity: 2

-Component Function-
This component serves 2 functions. It is part of the frame for the Auger to attach to and operate with, and it is shaped to direct the incoming snow up and out of the machine.

-Component Form-
This piece is shaped like a semi-cylinder. There is a cutaway section with the sides sloping up to the hole in the center of the housing. It's more reminiscent of a snowplow shovel. It is 24 inches across, and about 18 inches high. The part is composed of black ABS plastic, and is about 1.5 inches thick all around. The component weighs about 4 to 5 pounds. It has a smooth face to prevent friction from affecting a buildup of snow and/or ice within the housing.
Since it's paired with the auger, which is a rotating part, its shape closely matches up with the radius of the auger. The auger sweeps snow first under it, and then up between itself and the housing. The slopes near the top are intended to force the snow to go through the outlet to be directed by the discharge chute. Due to the pressures and abuse from the snow, this plastic part is thicker than the shroud to better withstand the forces. The only thing needed of this part is structural integrity, and an immunity or resistance to chemical action from the snow or salt that may be in the way. Metal could be used, but it is more expensive. The ABS plastic is cheap, resistant, and has a good enough structural integrity, making it a perfect choice for material.

-Manufacturing-
In all likelihood, the component was manufactured through Injection Molding. Like the shroud, it is made of plastic, making Forging, Casting and Welding invalid. The component is too large for forming, and shows marks from the refining processes of smoothing out the surfaces. This part most likely used styrofoam to form the mold as shown by irregular patterns under the refining marks. The part is intended to be cheap, sturdy, universal, and clean.

Single Cylinder Engine
Complexity: 3

-Component Function-
The engine is what powers the entire machine, converting the chemical energy of the fuel into heat energy, and then into rotational mechanical energy. Incoming fuel from the fuel tank and oxygen introduced by the flywheel, reacts when the spark plug fires, producing heat and creating force on the piston. The piston is moved due to the expansion force of the ignition, and turns the crankshaft. The crankshaft sends out power through the pulley system to the auger. The engine block itself functions to contain the reactive process, and provide the framework for the piston and crankshaft to work.

-Component Form-
The piston is a cylinder connected to an intermediate lever. The lever links it to the crankshaft, which extends through the engine block. The spark plug "caps" the assembly. The engine block itself is a rectangular prism with fins on the side that serve to both radiate heat away and save weight as opposed to a solid block. The entire assembly is also the heaviest part of the machine at 20 pounds. It is roughly 8 inches long, 6 inches wide, and 12 inches high, not counting the protrusion of the crankshaft, and everything except the spark plug is made of cast iron. The inside chamber is cylindrical, to more evenly distribute the lateral force during reaction.
The block is designed to react the elements and contain the force while releasing the heat safely, as the machine may need to operate during extended periods of time. Cast iron is a very good heat conductor, and the block uses the highly increased surface area from the fine to vent the waste heat. It is also a very dense material for the purpose of this machine. Other metals could have been used, but they are either more expensive, or not quite as sturdy, or have too low of a melting point.

-Manufacturing-
Because the material is cast iron, very high heat methods are required to form the component, The engine block is actually two parts, initially formed through investment casting due to the shape complexity. They are welded together, as seen from the weld lines that go all around the part. The piston is formed from a die, and then machined on a lathe. The crankshaft and intermediate lever are die-cast parts. The block cannot be produced at high volume, while the piston and crankshaft can. This means that the piston and crankshaft can be produced locally, while the engine block may need to be shipped in from the main factory.

Fuel Tank
Complexity: 2

-Component Function-
The tank stores fuel, and due to its higher placement in relation to the engine ensures that fuel is constantly supplied to the engine.

-Component Form-
The fuel tank has a raised cylindrical opening at the top, and a hole at the bottom for the fuel to be respectively added and drained. Apart from the cylinder on top, its primary shape is rectangular. It is a 6 inch by 4 inch by 4 inch two-piece shell of ABS plastic fused together. This maximizes the fuel capacity that can be crammed into the machine. When dry, the tank weighs 2 to 3 pounds.
Due to its purpose of containing fuel, it is made of chemically resistant ABS plastic to avoid corrosion. The translucent yellow hue allows the owner to see the amount of fuel remaining when the user removes the gas cap. The use of ABS plastic makes it cheap and easy to make and replace locally, and the structural integrity ensures no fuel is lost to the environment.

-Manufacturing-
ABS plastic can only be worked with using Molding, Extruding, and Forming techniques. Since no axis presents consistent part symmetry and there are ejection marks present, the halves of the tank were produced using Injection Molding. The complex shape and internal cavity made it necessary to split it apart rather than use Blow Molding to construct it as one part. Again, because it is relatively cheap ABS plastic, it can be produced locally by relatively unskilled labor. This makes it inexpensive to purchase and replace.

Discharge Chute (upper)
Complexity: 2

-Component Function-
This part serves to direct the outgoing snow. It also directly shields the operator from getting snow to the face while operating the machine. The chute can be rotated, by virtue of being attached to a collar. The very "lip" of the chute can be swiveled up or down, changing the distance the snow flies.

-Component Form-
The chute consists of two pieces of plastic and two sets of nuts, washers, and bolts to hold them together. The discharge chute itself is shaped like a half-cylindrical shell, providing an effective shield. As such, it is primarily three-dimensional. Its shape ensures that all snow is discharged in the intended direction. It is fairly lightweight ABS plastic. This material was likely selected because it is relatively inexpensive, can withstand the cold, wet, snowy environment as well as the pressure of the snow coming out, and it is easy to move when redirecting the flow. From an aesthetic perspective, it is black, providing a sharp contrast with the snow and with the housing. This makes it easy to see where the snow is being directed even if used during a heavy snowstorm.

-Manufacturing-
The discharge chute was formed using injection molding, which is the most reasonable choice given the selected material. This is a fairly inexpensive and simple type of manufacturing, allowing for consistency of product regardless of where it was manufactured.

Engine Choke
Complexity: 3

-Component Function-
As starting the engine is the hardest part for the machine, this component makes it easier by altering the fuel-air ratio during start-up when engaged. With more oxygen, the ignition reaction is far more likely to take place. After starting, the choke is disengaged, returning the fuel-air ratio to normal operating parameters.

-Component Form-
The choke is a valve with inlets and an outlet. It must resist corrosion from the air and from the fuel and must be durable enough to withstand its proximity to the engine during both ignition and operation. It is made of some kind of hardy metal.

-Manufacturing-
The choke has to be precisely manufactured so that it allows the correct fuel-air ratio and opens and closes exactly as intended and exactly when intended. It was manufactured using a number of methods.

Modeled Assembly

We choose Siemens NX 8.0 CAD package to solid model the pair of gears,because of its user-friendly interface, intuitive tools, and advanced modeling capabilities. It is easier to draw 3-D graphs and one of our member is familiar with this software. This pair of gears is very important when operating the snowblower. It interacts to control the direction of snow blown. And also it is easier to solid.

It has 4 components. The bottom one is a bevel gear motivated directly be the handle. Then the bottom gear interacts with the two spur gears. One of the spur gear share the same axle with a worm gear. The spur gear rotates with the bevel gear and rotates the worm gear. Worm gear motivate the discharge chute to direct the snow's outlet. The single spur gear is used to make the whole gear system more stable.

Parts modeled: 1) Discharge Chute Handle

2) Spur Gear

3) Spur and Worm Gear

4) Central Gear

Assembly

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Design Revisions

1) Slider instead of hand crank
While the hand crank does the job, it takes longer than the slider currently implemented on modern Toro snow blowers to swivel the discharge chute in the desired direction. It is also less intuitive. With the slider, it would be more complex. Likely it would involve a toothed rail, wires, a small pulley system, and the slider itself. But it would be both faster and easier for the customer to use. And that is the main draw. There would be less overall material used as opposed to the gear set and crank handle, and there is sufficient space underneath the upper shroud to cover the altered arrangement.

2) Wider intake housing
This snow blower model favors compactness over efficiency. A wider mouth would allow it to remove more snow in one pass and save the customer time and fuel in operation. The auger may need to spin faster and be lengthened, and many other cover parts would need to be made wider. The wheel axles and handle bars would also need to be widened. There would be a higher material cost overall, but the cost difference would pay for itself after three or four times of cleaning a lot or driveway of snow with less time and fuel used compared to the model we disassembled.

3) Make it a Two-Stage
As previously mentioned, this snow blower is a single stage. It is inadequate for handling heavy snowfall or dense snow. Two-stage snow blowers have a wider and longer "mouth" and a second auger that serves to loosen up and slice through the snow, making it easier for the primary auger to remove it. This would be the most expensive revision, likely requiring a 2-cylinder engine rather than a single cylinder, and a much greater usage of steel for the front auger. It would require an additional pulley system and a higher engine output. It would also be heavier and consume more fuel. But ultimately, the revised snow blower would be capable of handling loads it currently cannot, and would be very useful in high snowfall regions such as Minnesota, Michigan, and states to the northeast of New York.

Parts Summary

 Name Number Used Function Manufacturing Method Material Part Number Figure:1 Upper handle 1 Help the user to handle the product Extrusion, forming and shaping Steel 12-4639 Figure:2 Lower handle 1 Connects the upper handle with the frame to make stability Extrusion, forming and shaping Steel 55-9120 Figure:3 Bar 1 Use to control the auger rotation Drawing, welding and forming Steel 55-9130 Figure:4 upper shroud 1 Protect the interior elements and subsystems.Example: rust, water Injection molding ABS plastic 12-4649 Figure:5 Lower shroud 1 Protect the interior elements and subsystems and to avoid harming userExample: rust, water Injection molding ABS plastic 55-8790 Figure:6 Chute Deflector 1 Throw the snow in a desired direction Injection molding ABS plastic 56-2680 Figure:7 Discharge chute 1 Transfer snow from rotor to the chute deflector Injection Molding ABS plastic 12-2919 Figure:8 Gear ring-chute 1 Join the chute base to the chute shaft and assist snow to run through the chute Injection molding and drilling ABS plastic 55-8720 Figure:9 Retainer –chute ring 1 Attach the chute base connector Forming, shaping and bending Steel 55-8910 Figure:10 Ring-chute support 1 Fasten the chute and fits the chute to shroud Die-casting Steel 55-8920 Figure:11 Shield 1 Offer Ventilation for the engine to reduce the heat Forming and milling Steel 55-9210 Figure:12 Left side panel 1 To protect and cover the pulleys and belt system from the external elements Forming bending, shaping and drilling Steel 55-8840 Figure:13 Pulley-rotor 1 Transmit energy to rotor from engine via belt Die-casting and Injection molding ABS plastic 60-9320 Figure:13 Belt 1 Transmit energy from pulley engine to pulley rotor Extrusion Rubber 55-9300 Figure:14 Engage cable 1 Connects to the bar and engages the pulley system Drawing Steel 55-9320 Figure:15 wheel 2 Allow the snow blower to move Injection molding ABS plastic 23-3250 Figure:16 Control panel casing 1 Protect the control panel and user interface functions Injection molding ABS plastic 23-3250 Figure:17 Control panel 1 Placed over the user interface function Injection molding ABS plastic 55-9350 Figure:18 Key 1 Enables the snow blower to be powered on or off Injection molding, milling Plastic and Brasｓ 12-4659 Figure:19 Flywheel 1 During combustion it helps to tune the momentum of the engine and maintains the crankshaft rotation Die-casting ,drilling Steel 33-2010 Figure:20 Fly wheel housing 1 Guards the flywheel and crankshaft Die-casting ,drilling Cast Iron 81-0320 Figure:21 Fuel Tank 1 It stores the gasoline which essential for the system Injection molding ABS plastic N/A Figure:22 Gas cap 1 It prevent gasoline from evaporating Injection molding ABS plastic 12-4669 Figure:23 Muffler 1 Reduce or alter the sound Forming, shaping ,welding ,drilling and bending Steel 55-3573 Figure:23 Fuel-Line 1 Connects the engine and fuel tank Extrusion Rubber 81-0490 Figure:24 Engine shaft cover 1 It prevent the recoil system and crankshaft from the external impacts Forming, shaping, welding and drilling Steel 49-2480 Figure:25 Engine 1 Drives the entire system Die casting, drilling, welding and milling Cast Iron N/A Figure:26 Spring 1 Transfer energy from crankshaft to auger axle Forming Steel 55-9620 Figure:27 Auger axle 1 Responsible for the rotation between auger pulley to auger blade Drilling, milling and bending Steel 55-9280 Figure:28 Auger blade 1 Pull the snow into the snow blower Milling and drilling Rubber N/A Figure:29 Main rear frame 1 Stable the whole snow blower system and connects with wheels Shaping ,welding, bending and drilling Steel 55-9250 Figure:30 Recoil handle 1 Connected to the Engage Cable, it is pulled to effect a recoil start Injection molding ABS plastic N/A Figure:31 Engine Pulle 1 Links the crankshaft and engine Die-casting Steel 81-1630 Figure:32 Cylinder Head 1 Cover the combustion chamber and compress the gasses Die-casting Aluminum 55-9180 Figure:33 Nuts ,bolts and washers Many Hold two or more objects together Die-casting and Threading Iron N/A