The automobile has met a world-wide demand for a personal or private means of rapid transportation of passengers. Running through the records of means of passenger transportation including the crude-wheeled vehicles drawn by domesticated animals of early ages down through the long list of the power-propelled vehicles such as the steam vehicles, steam trains, steamboats, airplanes, busses, electric cars, and electric trains, no other means has ever had the wide personal appeal of the private automobile.
The capacity of the privately owned and operated automobiles in the United States is hard to grasp. It is likely true that, as has been stated, if it ever became necessary to move every person in an area as large as the State of Ohio out of the state, it could be accomplished within three hours with the use of only those automobiles owned by the citizens of the state.
It is necessary to consider statements such as this and the following if one is to grasp the idea of the number and the influence of the automobiles owned and operated by private individuals. For instance, it is stated that all the people living in California could be moved to the Atlantic seaboard in less than a week's time by automobiles owned by residents of that western state. A further statement that all the people living in the United States could be moved at one time by automobiles owned by private individuals, is at least approximately correct.
No other means of transportation has ever caught the fancy of a whole people as has the automobile. It has served to change the entire social life of the nation. City, township, county, and state lines have disappeared insofar as they might be considered as limiting borders. School children are now as familiar with their neighbouring states and their outstanding characteristics as children of a few generations ago were with their neighbouring villages. The automobile has served to wipe out the restricting influences of distance and weld the nation into a unified group of people.
The question naturally arises in the mind of the student as to what is the fundamental thing which has allowed this unit of personal transportation to thus wield such a wide influence. Doubtless it is the fact that it is personal transportation, filled with a good measure of comfort and thrills. The thrill of a hundred-horsepower engine under the control of the least wish of the driver is the feel of power and strength. The comfort of the automobile is luxury beyond the fondest dreams of old-time princes and kings.
The romance of the building of the automobile to its modern state of high perfection is a Tatter which would fill many books. When the student studies his science lesson he finds the automobile there. When he studies commerce and industry he learns of its importance. When he studies history he sees there marks of its great influence. When he studies economics he finds the well-being of the nation tied up with the automobile in close step. The component parts of the automobile and the supplies it uses daily offer a study filled with thrills of knowledge of tremendous significance.
The stories of the Far East dealing with the transportation of mysterious articles of fabulous worth, by means of caravans through strange lands, have no more romance then the stories of the development of the great oil, fuel, rubber, fabric, chemical, steel, and other industries built up around the popularity of the private automobile. The student of automotive theory and design will find here and in many other studies interesting information dealing with the influence of parts and materials which combined make up the modern passenger car. This site deals primarily with the features of design and construction which have been combined to give us the modern passenger automobile. Appreciation of the maintenance care which every car requires, if it is to give its allotted measure of safe service, is developed.
The automobile is essentially a transportation unit having a frame supporting the body and certain power-developing and transmitting units, and being in turn supported by tires and wheels through the medium of springs and axles. The private automobile is a complete means of personal transportation within itself. The body affords protection and comfort. The engine supplies the motive power.
The transmission and rear axle deliver the power through the clutch, from the engine to the rear wheels, which in turn propel the car through the friction of their contact with the road. Brakes control the speed. The frame is used to hold all other units together in proper assembled arrangement. The usual method of classifying the several parts of the car is to divide it as to body and chassis units. While the frame serves to support the body, it is more definitely a part of the chassis except in cases where the frame is definitely a part of the body as well.
The automobile chassis
If a car chassis were purchased, it is likely that the instrument panel, hood, and possibly the cowl section would be included. This is usually the case in truck chassis, although the practice there as well as in passenger-car chassis varies somewhat.
Users of passenger cars are interested in the mechanical features of the chassis. They desire good performance which is typified by fast pickup, strength, safety, durability, dependability, ease of control, quietness, speed, power, accessibility, economy of operation, low centre of gravity, stability, road clearance, braking ability, good springing, simplicity of lubrication, and many other things incident to good chassis design.
Car bodies usually are designed as a separate part of the vehicle and, as a rule, are constructed in factories specializing in this feature. Bodies are of two general classes the open touring car or phaeton and the closed-car body type. The only points at which the body and the chassis designs interlock to a certain extent are the instrument panel and the dashboard, which may carry such items as the coil, or other accessories. As a rule, the dash and the instrument board are parts of the car body, and when the chassis is sold without the body, a dummy instrument board is run onto the job, to hold the instruments until the body can be mounted and the instruments permanently located on the boards provided in the body design.
Production of great numbers of automobile bodies has made it practical to spend large sums of money in providing dies which are used to stamp out all steel sections of bodies, which are joined with other sections by welding to form the all-steel bodies used by most manufacturers. Note that the coach-builder's art has carried over through a long period of time, and finds expression in such items as the decorative moulds and bands around the bodies and about the window openings which are formed, in the case of all-steel bodies, by the dies forming the metal from the inside of the sections.
The tendency of the all-steel body to drum or rumble is overcome by providing the panels with insulating and sound-deadening materials. In some bodies layers of heavy gummy material are sprayed or brushed onto the interior of the body panels. The materials used serve to make the car body less subject to temperature changes, since they act as heat insulators.
Dies required to form sections for this body are quite intricate. Bodies produced by these so-called production methods usually are quite attractive. Small irregularities are filled in with body metal, a cheap solder which serves to round out some imperfections left by the dies.
Form-fitting cushions, arranged for adjustment to the individual convenience of the driver or passengers, are usually provided in greater or less degree. Safe and easy operation of the car is assured when the seat is adjusted to the driver. Purchasers of automobiles should be careful that the car they select is so constructed that it may be adjusted to their needs. Cars which do not "fit" the driver are a source of danger on the highways. The driver with the car seat adjusted to his needs will find all controls ready to his hand or foot. He will not have to reach unduly for controls if the car fits, nor will he have to "crane" or stretch unduly in order to have good vision.
Centre of gravity
The higher the car speed the lower the centre of gravity has been a controlling factor in car design. In some instances the entire car has had to be redesigned to secure the desired result. Frames have been provided with a double drop. Engines have been lowered and the propeller shaft has been dropped down by making use of hypoid rear axle, or a shaft tunnel, where the advantages secured by that form of design are graphically illustrated in the relative low seating for the conventional rear-axle centre level.
Nothing can do more to promote safety on the highways than devices calculated to provide clear vision for the driver under all circumstances. Such a device is the sunshade. This device may be positioned out of the way under the roof or it may be used to keep the sun glare away from the eyes when in either the left door or windshield positions. Improper headlights on approaching cars are such a hazard that every driver should exercise concern that his car be not found at fault. Windshield wipers are necessary vision helps and should be maintained. Windshield defrosters are almost a necessity for vision in certain sections at certain seasons. Discoloured, cracked, or broken windshields are sources of danger and should be replaced.
The suspension is representative of good practice. Some tubular axles are used. Front-wheel brakes have influenced axle design. The front axle must carry the weight of the forward end of the car and part of the load. It must have sheer strength to do this. Aside from this, it is so designed as to allow the car to be steered with ease. The spindle and steering-knuckle assembly is an ingenious device, which, while carrying the load over all manner of roads, still allows ease of steering. Leaf springs are made rather short, as a rule, since this allows less play between the frame and the axle, consequently making the steering more accurate. Front-wheel brakes mean an increased load on the springs and on the other suspension parts. This has resulted in increasing the weight of parts and changes in the knuckle. Cars with independent, wheel suspension have no front axle beams, the parts being attached to the car frame.
The steering gear must be so designed in conjunction with the front axle, that the car may be directed quickly and easily along the roads and through traffic congestion. A car which is hard to steer is a dangerous vehicle on the streets.
Steering-gear failure is rare, considering the great strains placed on the system. It is true that gears and parts do fail occasionally. As a rule, these failures may be traced back to overloads or to accidents in which parts have suffered unusual strains. Failure may occur months later. Examination will show the initial start or break to have been made at an earlier date. This should suggest unusual care in renewing of parts after the steering system may have been damaged in an accident or otherwise. Manufacturers use the best grades of steel known in the manufacture of their steering gears and front-axle parts.
Power plants are assembled onto the frame of the car over the front axle or just back of it. There are a few variations from this rule, some power plants being built on the rear axle. Conventional practice places the engine under the hood just back of the radiator and front axle. Practically all power plants are what are termed unit power plants. That is, the transmission or gear box and clutch are mounted onto the engine. The matter of engine design is never ending.
Engineers are experimenting continuously in an effort to improve their product. The public is demanding more power, greater flexibility, economy, and smoother operation. All manner of designs are tried out in an effort to secure the desired results. It is a matter of record, however, that the engines after many years still embrace the fundamental principles which first made them a success. The four-stroke-cycle principle underlies all designing. Refinement of design is the great aim of the engineers.
The automobile is a self-contained machine. It carries fuel with it and converts that fuel into power. The power developed within the engine is used to drive the wheels, and so transport the car along the highways. It is arranged to develop or generate its own electrical energy which is used to ignite the fuel, start the engine by cranking, light the car, and light the way. The engine may be used as a brake as well as the means of developing power. Located under the hood of the motor car is a power plant, which, for completeness and for efficiency, is one of the greatest mechanical products of all times. The fact that power plants are so reliable that they may be handled by amateurs with success is their most remarkable feature.
The power developed by the engine must be available for use at the will of the operator of the car. It must be so applied that the starting of the car is gradual. The power plant is so designed that, at the pressure of the foot on the clutch pedal, the power is instantly disconnected. Engaging the clutch applies the power, when the engine is running, and disengaging by pressing down on the foot pedal, releases the power. The clutch consists of a driving plate or plates and driven plate or plates between the driving plates. The driving plates always turn with the flywheel and the driven plates turn the transmission shaft. The fluid flywheel sometimes is used to couple the engine to the transmission.
The transmission receives its driving power from the engine, through the clutch, and transmits or passes it on to the rear axle. On high speed or gear it passes the power directly through. On other speeds it steps down the car speed but delivers a greater torque (turning effort or power). In one instance (.reverse) the direction of drive is reversed within the transmission. Transmissions have been built integral with the rear axle, that is, with the transmission on the rear axle. They have been mounted amidships, that is, on the frame of the car, back of the clutch and flywheel. The practice which is nearest standard for all manufacturers is to mount the transmission on the engine flywheel housing. This is what is called the unit power-plant mounting.
Three speeds forward and one reverse is considered the standard practice. Brakes are sometimes placed just to the rear of the case and are called transmission brakes. These usually are connected with the hand-brake lever. The speedometer drive may be secured from the propeller shaft, back of the transmission case, or from gears within the case.
Propeller and universals
The drive or propeller shaft takes the power from the transmission, and delivers it to the rear axle. One or two universals may be used depending on the design of the rear axle. Common practice is to use two universals on exposed drive shafts and one universal on enclosed drive shafts.
Braking systems have long been an integral part of the rear system. Application of the brakes stops the wheels from turning, or tends to stop them, and this means just as great a strain on the axle parts as the actual driving of the car. The greatest strain, however, is on the axle shafts or axle drive shafts, as they are called. These must turn the wheels or turn the engine, depending on whether the engine is driving the car or the car is driving the engine. Besides these duties, they must in many cases carry the actual weight of the car and the load.
Other units in a chassis
Other items go into the make-up of the chassis. Some of the most important of these are the wheels, rims, tires, radiator, hood, fenders, mud aprons, gasoline tank, and so on. The larger and more important items have been pictured separately. In the final figures of the chapter, the important mechanical units are arranged in a chassis in their respective places. They will be taken up in detail in later chapters, but the student will want to hold in mind the purpose of the part being studied, and how the desired result has been attained by the designer and builder of motor cars.