Where Mileage Begins (1949)

[music] [music] [bell] [music] [music] [music] [music] [music] [music] >> For over 250 years, man have dreamed and labored over an engine which would convert the heat of natural fuel into work in the cylinder of the engine itself. But not until the advent of gasoline was a successful internal combustion engine achieved. Even today, engineers writing specifications for a more ideal fuel. No ordinary explosive, in fact, can approach its potential energy. It is not unusual for a modern car to travel 18 miles on a gallon of gasoline. But with a like amount of TNT, the same car would make only 6 miles. An equal quantity of nitroglycerin would carry it barely 3 miles. Dynamite, about 2 and 1/3 miles. And black powder, less than two. Gunpowder was deemed the best available fuel for the internal combustion engine described by a Dutch scientist as long ago as the year 1680. The idea had merit. For yesterday's cannon and today's gasoline engine have much in common. Loading the cannon, for example, is a slow-motion counterpart of the intake stroke of the gas engine. Ramming or packing the powder charge serves the same purpose as the engine's compression stroke. Between the second and third operations or strokes, both the cannon and engine are fired. The burning powder results in expanding gases that force the shot up and out the barrel. Except for the ejection, the same thing happens in the power stroke of the engine. Then, like the cylinder of a motor, the cannon barrel must be cleaned before a new charge can be put in. This operation is the exhaust stroke in the engine. Using the cannon barrel as a cylinder, let us add the parts necessary to make a gasoline engine and see how simple it really is in principle. First, we'll change the ramrod into a closely fitting piston which slides up and down. But to propel a car, this vertical action must be converted into rotary movement. The moving parts of an ordinary grindstone and a man's arm will serve our purpose in a familiar form. The man's arm operates as a connecting rod and the hand crank makes a fair crankshaft. And the grindstone itself will do as a flywheel to keep our engine revolving smoothly between power strokes. Before we can make these power impulses, however, additions must be made to our engine so it can be supplied with a combustible mixture of gasoline and air. The necessary mixing device is called a carburetor, but it's nothing more than a glorified atomizer or spray gun. Air rushing at high speed past an open tube of correct size picks up the liquid fuel in the proper amount to form a combustible mixture. The pipe which carries the mixture from the carburetor to the engine is known as the intake manifold. The pipe on the opposite side is the exhaust manifold. And valves called intake and exhaust serve as the engine's doors to admit the fresh mixture and let out the burnt gases. Now, we add another set of parts, pushrods, rocker arms, cams, and a camshaft. And two gears which drive the camshaft at half the speed of the crankshaft. The task of the cams and camshaft is to make the valves open and close at the proper time. This is done simply by changing rotary into up and down movement. Unlike the cannon, the explosive mixture in our engine is ignited by a spark jumping the gap in a spark plug. The spark must start the mixture burning at the right instant, however, so we install a timing device called a distributor. The distributor is a switch driven by the engine which times the spark to occur as the piston nears the top of the cylinder. In the cannon, we observed its operation on the principle of a four-stroke cycle, namely the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. Our modern internal combustion engine also operates on a schedule known as the four-stroke cycle. The first stroke pulls the inflammable mixture from the carburetor in through the open intake valve to fill the cylinder. The second stroke compresses the mixture to approximately 125 lb per square inch. As the piston nears the top of the compression stroke, the spark plug ignites the mixture. The temperature in the chamber immediately jumps to as high as 4500° Fahrenheit. On the third or power stroke, the hot gases expand against the piston driving it downward with a pressure approaching a ton and a half on a 3-in piston. The fourth and final stroke of the cycle forces the burnt gases out through the exhaust valve and manifold. The four strokes come in rapid succession. Intake, compression, power, exhaust, intake, compression, power, exhaust, intake, compression, power, exhaust, intake, compression, power, exhaust. When an engineer says that an engine has a compression ratio of 6:1, he means that the mixture of gasoline and air is squeezed to 1/6 of its volume by the piston as it moves from the bottom to the top in the compression stroke. The higher the compression ratio, the more power the engine develops. One characteristic of gasoline limits the degree to which the compression can be raised. When the ratio is too high, the result is familiar to all of us, knock. Some idea of the complexity of the fuel problem may be obtained by looking in on research engineers as they photograph the air-gasoline mixture burning in a cylinder. This special combustion camera is capable of taking 5,000 photographs a second. To permit the filming of combustion, the top of the cylinder of a test engine has been made of quartz glass. Here, for example, is how a smooth combustion looks slowed down to 1/200 normal speed. A closer examination of these combustion pictures shows the spark. At the point of this spark, the mixture takes fire. The flame travels rapidly across the enclosed combustion chamber like fire in a field of dry grass. So rapidly, in fact, that the burning is completed in 3/1000 of a second. Now, for contrast, let us examine a knocking combustion. The beginning of the combustion is the same. The flame travels rapidly across the combustion chamber. But from here on, the burning is different. The instantaneous burning of the last part of the charge causes the trouble. This is the knocking zone. Here are the two combustion chambers side by side. The one on the right is using a gasoline containing an ant-knock fluid. Compare its smoothness with that of the knocking combustion on the left. Responsible for this imperfect combustion is the gasoline and the remedy is ant-knock fuels. Each time an automobile engine runs through its cycle of four strokes, the crankshaft makes two revolutions and the car moves ahead about a yard. If the car is ancient enough to have a single-cylinder motor, one power impulse does all this work. But as the number of cylinders increases, the flow of power becomes smoother for the power strokes begin to overlap more and more. It's a long step from the crude engine we built up from a cannon to the modern automobile motor. To appreciate the degree of perfection to which these power plants have been developed by automotive engineers, let's assemble one of today's internal combustion engines. The assembly parade starts with the pistons, rings, connecting rods, and wrist pins. Into the engine block they go, each piston fitting smoothly into its precision-ground cylinder. The backbone of any internal combustion engine is the crankshaft. For it converts the up-and-down movement of the pistons into the rotary movement that propels the car. And this one, followed by its squad of bearings and bolts, has been balanced both statically and dynamically on special machines. The >> The flywheel with the starter gear on its rim takes its place on the back end of the crankshaft. The camshaft of a modern engine runs in removable bearings which are lubricated from the oil pump and is driven at half engine speed by these timing gears. This group of parts is made up of the cam followers which ride on the cams, the springs which hold the followers against the cams, push rods which transmit the motion to the rocker arms, and retaining clips which hold the parts in place. This is the way the valves are assembled into the cylinder head. The valves which operate at red heat are made of special alloy steel. The valve springs hold the valves on their seats, keeping them tightly closed until lifted by the cams. The gasket is placed on the motor block and the cylinder head takes its position on top of the engine. The rocker arms are assembled in this fashion. Following the rocker arms to the motor are the oil feed and return lines, the side plate, and the top cover. Oil is circulated by a gear type oil pump and oil distributor to all the vital working parts. The crankcase now going on is the engine's oil reservoir. These parts are known as the oil filler and crankcase ventilator. The intake and exhaust manifolds goes where they belong. The air cleaner and intake silencer attaches itself to the carburetor. And here we see them secured to the top of the intake manifold. Next in order come the fuel pump and fuel line. The distributor and spark plugs. The self-starter assembles and bolts to the flywheel housing. The parts which follow operate and control the action of the self-starter. The job of the generator is to convert a small amount of mechanical energy from the engine into electrical energy to charge the battery and provide ignition and lighting current. The fan which pulls the air through the radiator, the pump which circulates the water, and the thermostat which controls the temperature are the backbone of the cooling system. Looking inside a cutaway model, we see the science of modern engineering exemplified in this marvel of powerful efficiency, the internal combustion engine, now complete and ready for a long life of fine service with a minimum of attention. So, we shall place it in position on the engine mountings in the car frame. Transferring the power or turning effort of the engine back to the road wheels is our next task. Moving back from the motor, we come first to the clutch, the device which connects and disconnects the power plant from the rear wheels. Next in line is the transmission, or as the English call it, the gearbox, which makes it possible to choose the relationship of the speed of the engine to that of the rear wheels. We join the large and small gears in various combinations to produce the speed ratio we want, namely low, intermediate, and high. This simple diagram shows what actually happens when we shift gears. To start the car, we need high turning effort and low speed at the rear wheels. A gear ratio which allows the engine to make almost 12 turns to one of the rear wheels is used for the first or low speed. When the car is in motion, we no longer need a great turning effort. A ratio which allows the engine to make about eight turns to one of the rear wheels gives second speed. The final shift is into high where the engine and the rear wheels are directly connected. This allows the engine to run at an economical speed. The problem in reverse is similar to that in low, great turning effort at low speed, with one exception. The rear wheels must turn in the opposite direction to that of the engine. A universal joint is installed between the transmission and the drive shaft to allow the rear axle to move up and down. The drive shaft transmits the power of the engine from the transmission to the rear axle. The rear axle is made up of two sets of gears. The first set, bevel drive gears, transmit power from the drive shaft to the rear axle shafts. The second set, the differential gears, allow independent rotation of either wheel as is necessary in going around corners. The chassis is now fitted with the entire power producing mechanism and the means of transmitting turning effort to the rear wheels. Just as important as a smooth-running car, however, is a smooth-stopping one. Our brake is made up of shoes lined with friction material and a drum of hard metal. The wheels are stopped by forcing the shoe against the rotating drum, which converts the mechanical energy of the moving car into heat. A modern 100 horsepower car has 500 horsepower brakes, and these are applied by a light pressure on the foot pedal through a hydraulic braking system. The steering mechanism must be strong, dependable, and easy to operate. When the steering wheel is turned, the steering gear causes an arm to move back and forth and change the direction of the front wheels. With the body, we have an automobile in which are crystallized the latest developments in automotive engineering, research, and styling. In it are built economy, safety, comfort, appearance, performance, and efficiency, everything, in fact, except the skill of the driver. >> [music] [music]