1. ME240/107S: Product Dissection ME240/107S: Engine Dissection You are dissecting a 3.5 HP single cylinder, 4 cycle engine, made by Briggs & Stratton in Milwaukee, WI These engines are typically used in lawn mowers, snow blowers, go-carts, etc (ref. 2, Used by permission of Briggs and Statton, ©1992, all rights reserved)

2. ME240/107S: Product Dissection Lecture 2 n Carburetor n Ignition System n Drivetrain Components

3. ME240/107S: Product Dissection Session 1: Carburetor and Ignition n In small groups, discuss your answers to the following questions from Session 1 Carburetor: n What are the components of the Pulsa-Jet Carburetor and how do they work? n How many jets are used? What is their function?

4. ME240/107S: Product Dissection Session 1: Carburetor and Ignition Ignition: n What is the purpose of the starter clutch? n Why is the flywheel comprised of different materials? What are those materials? n How does the ignition system work? n How is ignition timing achieved in the engine?

5. ME240/107S: Product Dissection Carburetor n Purpose of the carburetor is to produce a mixture of fuel and air on which the engine can operate n Uses a venturi nozzle to reduce air pressure in the carburetor to create suction to “pull” fuel into air

6. ME240/107S: Product Dissection Pulsa-Jet Carburetor n Incorporates a diaphragm type fuel pump and a constant level fuel chamber

7. ME240/107S: Product Dissection Pulsa-Jet Carburetor Operation n Intake stroke of piston creates a vacuum in carburetor elbow n Pulls cap A and pump diaphragm B inward and compresses spring n Vacuum thus created on “cover side” of diaphragm pulls fuel up suction pipe S into intake valve D

8. ME240/107S: Product Dissection Pulsa-Jet Carburetor Operation n When engine intake stroke is complete, spring C pushes plunger A outward n Gasoline in pocket above diaphragm to close inlet valve D and open discharge valve E n Fuel is then pumped into fuel cup F

9. ME240/107S: Product Dissection Pulsa-Jet Carburetor Operation n Venturi in carburetor is connected to intake pipe I which draws gasoline from fuel cup F n Process is repeated on the next stroke, keeping the fuel cup full n Since fuel cup level is constant, engine gets constant air-fuel ratio

10. ME240/107S: Product Dissection Ignition System Consists of: n Spark plug n Armature n Coil (primary and secondary) n Flywheel n Magnet

11. ME240/107S: Product Dissection Ignition System - Electric Circuit n Uses a changing magnetic field to generate current in primary and secondary circuits

12. ME240/107S: Product Dissection Ignition System - Magnetic Flux n As magnet approaches, induces magnetic flux in armature n Breaker points close and current dissipates through primary circuit

13. ME240/107S: Product Dissection Ignition System - Spark Fires n After magnet rotates past armature flux reverses direction, and the breaker points open n Change in magnetic flux produces 170 volts in primary circuit n Induces 10,000 volts in secondary circuit, firing spark plug

14. ME240/107S: Product Dissection Ignition System - Breaker Point n Crankshaft rotation causes mechanical actuation of breaker

15. ME240/107S: Product Dissection Ignition System - Magneto System n In Magnetron ignition system, magnetic flux induced by flywheel magnet also actuates primary circuit and spark timing n Capacitor helps regulate current (i.e., serves as condenser)

16. ME240/107S: Product Dissection The Drivetrain n As a group, brainstorm as many drivetrain components as you can. You have 3 min.

17. ME240/107S: Product Dissection Drivetrain Provide power via rotating crankshaft

18. ME240/107S: Product Dissection Drivetrain: Piston-Rod Assembly n Piston is connected to the crankshaft by the connecting rod n Vertical motion of piston rotates the crankshaft n What is purpose of compression rings?

19. ME240/107S: Product Dissection Drivetrain: Valves Valves regulate air-fuel flow mixture into and out of piston cylinder

20. ME240/107S: Product Dissection Drivetrain: L-Valve Actuation Camshaft drives actuation and timing of intake and exhaust valves in L-head configuration

21. ME240/107S: Product Dissection Drivetrain: Valve Actuation In overhead or I -head, camshaft actuates a tappet (lifter) which forces a push rod upward, causing the rocker arm to rotate to actuate the valves n What is the purpose of the valve spring? Push rod Rocker arm Tappet

22. ME240/107S: Product Dissection Intake Stroke Intake valve opens, admitting fuel and air. Exhaust valve closed for most of stroke Compression Stroke Both valves closed, Fuel/air mixture is compressed by rising piston. Spark ignites mixture near end of stroke. Intake Manifold Spark Plug Cylinder Piston Connecting Rod Crank Power Stroke Fuel-air mixture burns, increasing temperature and pressure, expansion of combustion gases drives piston down. Both valves closed - exhaust valve opens near end of stroke 1 2 3 4 Exhaust Stroke Exhaust valve open, exhaust products are displaced from cylinder. Intake valve opens near end of stroke. Crankcase Exhaust Manifold Exhaust Valve Intake Valve 4 Stroke Cycle

23. ME240/107S: Product Dissection Parts of an IC Engine CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE Name as many parts as you can Your name:_________________