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)

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

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?

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?

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

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

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

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

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

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

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

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

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

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

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)

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

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

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?

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

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

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

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 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

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:_________________