Group 35 - Leaf Blower Engine
The leaf blower engine discussed below underwent a multitude of dissection, analysis, and reconstruction. A seamless flow of inter-working component precision allows for this seemingly simple devise to function in a useful way. Our dissection of the product enforced our basic understanding of the engine. Through diligent dissection, the engine was completely stripped down to its individual key components. Each part was thoroughly examined and studied thereby completing our mental picture of the system as a whole. With an excellent understanding of the engine and its real world functionality, several constructive suggestions were informally proposed as design revisions. In accordance with our technical knowledge of the engine and the leaf blower system researched on its Homelite consumer website (see Reference), it is believed that our ideas for improvement could make for a more ideal product.
Request for Proposal
Preliminary Design Review
Causes for Corrective Action
Essentially our work proposal and management proposals have gone according to the plan. All of our group members have contributed evenly, including meeting regularly and working in a timely fashion. The work is divided evenly according to each group members’ strengths. As far as our disassembly process as described in our work proposal, we were mostly accurate. Some of the tools outlined were not required. “The tools required for this are flathead and Phillips head screw drivers of various sizes, metric sockets and wrench set, needle nose pliers, hex (torx) keys, and allen keys, all of various sizes.” What we used were the metric sockets and wrench set, need nose pliers and torx wrenches, and Phillips head screw driver. We didn’t use the allen keys, or the flat head screwdriver. The time we proposed it would require was a slightly over estimated. “The whole process of disassembly should not take longer than one to two hours, as it is a small engine.” The process was only around 45 minutes, for disassembly and reassembly.
Product Dissection Plan
|System||Parts||Disassembly Description (Est. Time)||Difficulty||Tools Used|
|Exhaust System||- Muffler Cover/Body,- Internal Packing,- Exhaust Gasket||The exhaust is held on with two t25 torx bolts. The exhaust system itself was missing the internal packing used for sound muffling. (3 min)||1||T25 torx|
|Gas Tank||Tank and the Cap||Held on by crank case cover (4 short T25 torx bolts)||1||T25 torx|
|Air Filter Assembly||Cover/Body,Air Filter,Gasket||The air filter is directly mounted to the carburetor with two 10mm bolts. No air filter material found inside the casing. (5 min)||1||10mm wrench|
|Carburetor System||Float Bowl,Primer,Main Body,Spacer||The float bowl of the carburetor is held on with two Phillips head screws, as is the primer bulb. The spacer between the carburetor and the cylinder, and the carburetor itself is held on with two T25 torx bolts. (15 min)||1||Phillips head screw driver|
|Flywheel Cover||Body Cover,Rope,Spring||There was no pull start assembly/flywheel cover present. If it were present, it would be held on with 4 T25 torx bolts that were provided. (5 min)||1||T25 torx|
|Ignition System||Spark Plug,Spark Plug Wire,Solenoid||One T25 torx bolt held the magnetic solenoid to the crank. (3 min)||1||T25 torx|
|Flywheel Assembly||Flywheel,Bushing,Key||The flywheel is held by a large aluminum nut that is easy to unscrew, however a torque wrench is required to tight it back up. The bushing slides of the flywheel with ease.
|Cylinder||The top cylinder block is only held by 3 long screws which must be torque wrenched during assembly process.(5 min)||1||T25 torx|
|Piston Assembly||Piston,Piston Ring,Connecting Rod,Wrist Pin||To remove the connecting rod from the piston, snap ring pliers are needed, which are not provided in the dissection lab. Also, the piston ring was absent. (10 min)||1,5,3,5,5|
|Block Assembly||Main Block,Open Bearing,Sealed Bearing||We left the crank in the crank case; we needed a small press to remove the bearings to retrieve the crank assembly, without rendering the bearings useless.||1,1,5,5|
|Part Name||Quantity||Material||Function||Manufacturing Process||Model/Part Number||Applied Force||Complexity||Functional or Cosmetic||Image|
|Exhaust||1||Aluminum||exit point for the burnt gases from the engine and also lower the sound output||Metal Stamping||not provided||N/A||2||Functional|
|Gas tank with cap||1||Plastic||Holds gasoline and delivers it to the carburetor||Injection Molding||not provided||N/A||2||Functional|
|Air filter||1||Plastic||Provide clean air to the carburetor||Die Casting||not provided||N/A||1||Functional|
|Carburetor||1||Aluminum||Supply fuel and air mixture to the engine||Investment Casting||not provided||N/A||5||Functional|
|Fly wheel||1||Aluminum||Produce electricity for the engine||Die Casting||not provided||Centripetal||3||Functional|
|Ignition system||1||Combination of Metal and Plastic||Convert the electricity generated from the fly wheel to a spark for the spark plug.||assembled by hand||not provided||N/A||5||Functional|
|Cylinder||1||Aluminum||The cylinder is a where the combustion takes place of the air and gas mixture, from the pressure provided by the piston and the spark provided by the ignition system.||Die Casting||06825||Compressive||3||Functional|
|Gaskets||1||Paper||Provide sealing for different components. There are gaskets between the cylinder and block, the carburetor and the cylinder, and exhaust||stamped||not provided||N/A||1||Functional|
|Piston||1||Aluminum||Reciprocate up and down inside the cylinder providing pressure for the combustion process||Die Casting||not provided||Compressive||3||Functional|
|Connecting rod||1||Aluminum||Connects the piston to the crank and provides the up and down motion||Die Casting||not provided||Tensile||3||Functional|
|Block||1||Aluminum||Houses the main engine components. All of the other components either bolt to or go inside the block||Die Casting||not provided||Compressive||4||Functional|
|Bearings||2||Steel||Provide less resistance in the spinning shafts of the crank||not provided||Centripetal||3||Functional|
|Bolts||25||Steel||Attach different components of the engine to one another||Die Casting||not provided||Shear and Compressive||2||Functional|
1. A slight increase in engine displacement would be increase power, resulting in a more powerful leaf blower. With more blowing power, the user will be more satisfied in the product because of it's increased efficiency. This would be done in the beginning of the design process, and would not be overly expensive addition. The slight increase in cost would be made up for an increase in sales due to a more capable leaf blower.
- Advantages: Increased power
Increased efficiency Higher sales
- Disadvantages: Higher initial cost
2. A higher quality exhaust would not only be a good improvement for the user, but any one in the vicinity of the leaf blower. The current exhaust system is a simple aluminum shell, that is supposed to have a packing material inside, however ours is missing. To replace this with a tubed exhaust with a silencer would greatly decrease the sound output of the motor. The addition of a higher quality exhaust could be fairly expensive in comparison to the current design, due to the current design being so primitive, but having a more muffled engine is in the interest of users and neighbors alike.
- Advantages: Decrease sound output
More satisfied customer Higher sales
- Disadvantages: Higher initial cost
Increased complexity (capacity to result in decreased reliability)
3. There is a plastic spacer between the carburetor and the cylinder. It could easily be eliminated by making a slight design revision in the carburetor. Doing this would decrease production costs because the part would no longer be necessary. Having a less complex product, is in the interest of the manufacturer because it eases in the manufacturing and design process, and also cuts down on cost.
- Advantages: Fewer parts
Less Complexity Higher sales
- Disadvantages: Design revisions on carburetor has potential to be costly
In a leaf blower engine the piston should support a maximum temperature, compression and a maximum pressure. If the piston ring is broken in some way the gas volume will change and a significant compression loss will be there. Determining that compression loss.
The combustion chamber is where our initial volume and clearance volume is calculated. Our engine is a Homelite two stroke with a displacement of 26 cc which can be converted to .026 liters. Clearance volume is when the piston is at the top of the stroke.
- The initial volume to be V_i=400CMF. (cubic feet per minute) http://www.cpohomelite.com/products/zr08550.html
- The leaf blower engine is 26cc.
- If there is a compression lose, the clearance volume would be higher than the usual.
- Calculations are based only according to the above diagram, which is considering only the piston system.
- Compression ration 10:1 = V_i: V_C
- C_r= compression ratio
- V_i= initial volume
- V_C= clearance volume
- d= diameter of the cylinder
- l= length of the piston
|System||Parts||Reassembly Description (Est. Time)||Difficulty||Tools Used||Image|
|Block Assembly||Main Block,Open Bearing,Sealed Bearing||Begin with main block and insert the base gasket onto the top being sure to align the holes.||1,5,5||no assembly required|
|Crank Shaft||No reassembly required. The crank shaft is already installed inside the main block.||1||already assembled|
|Piston Assembly||Piston,Piston Ring,Connecting Rod,Wrist Pin||Place the connecting rod with the piston attached onto the crank shaft. Do this by aligning the hole on the lower end of the connecting rod onto the round crank shaft.||1,5,3,5||already assembled|
|Cylinder||Place the cylinder over the piston and bolt to the main block and base gasket using the 3 long bolts which must be torque wrenched during assembly process.(5 min)||1||T25 Torx|
|Carburetor System||Float Bowl,Primer,Main Body,Spacer||The carburetor was not completely disassembled. The float bowl of the carburetor is held on with two Phillips head screws, as is the primer bulb. Include the black spacer between the cylinder and the carburetor which is held on with two T25 torx bolts. Also place the gasket between the carburetor itself and the cylinder.||1||T25 Torx, Phillips head screw driver|
|Flywheel Assembly||Flywheel,Bushing,Key||Bolt the flywheel to the crank shaft using an aluminum bushel and the nut provided. The flywheel must be aligned with the key way on the crank shaft as shown in the image.||1,1,5||10mm wrench|
|Ignition System||Spark Plug,Spark Plug Wire,Solenoid||Screw a single T25 torx bolt which holds the magnetic solenoid to the cylinder. Press the spark plug cap onto the spark plug.||1||T25 Torx|
|Flywheel Cover||Body Cover,Rope,Spring||There was no pull start assembly/flywheel cover present. If it were present, it would be held on with 4 T25 torx bolts that were provided.||1||T25 torx|
|Air Filter Assembly||Cover/Body,Air Filter,Gasket||The air filter is directly mounted to the carburetor with two 10mm bolts. No air filter material found inside the casing. Include the gasket between the aif filter assembly and the carburetor.||1||10mm wrench|
|Gas Tank||Tank and the Cap||Use 4 T25 torx bolts to hold the gas tank to the block. Also make sure that the small, black, rubber stoppers are intact to the gas tank to hold it more securely in place.||1||T25 Torx|
|Exhaust System||- Muffler Cover/Body,- Internal Packing,- Exhaust Gasket||The exhaust is bolted to the cylinder using two T25 Torx bolts. The exhaust system itself was missing the internal packing used for sound dampening.||1||T25 Torx|