Practically all modern gasoline motor cars may be divided, in a mechanical sense, into six groups of parts or units. These are: (1) The engine or power producing group; (2) the clutch group, needed, as will be explained later on, with all forms of explosion motor; (3) the transmission, or gearset, for producing the various car speeds and different powers, while the engine gives a practically constant speed and power output; (4) the final drive group, which connects the speed variator or transmission with the rear wheels, and thus propels the car. Of a necessity, this includes the rear axle, while the front axle is usually grouped with the rear;
(5) the steering device, for controlling the direction of motion; and:
(6) the frame, upon which all these and their various accessories are hung, with the springs for suspending the frame upon the axles of the car. There is, of course, a seventh group, the body, but that need not be discussed here, since reference is now had only to the mechanical parts.
In the large diagram of a modern motorcar, Fig. 1, the sectional side view is shown above and the plan view below. In this, note that the engine is placed at the front of the outfit. This is now the general position, practically all modern motorcar manufacturers using it. A few cars have the motor located on the rear axle to save the parts necessary for connecting the two, while formerly the middle position was a favorite one. The purpose of the engine is to generate the power. This is done by the drawing in, compressing, and exploding of gas produced from gasoline.
The production of the gas necessitates what is called a carbureter; carrying the liquid gasoline necessitates a good-sized fuel tank, piping is needed to connect the two; the fuel is not always pure and must be filtered, necessitating a strainer; means for turning on and of! the supply of liquid must be provided in the form of a cock, while the gas produced is taken into the engine through an inlet manifold. These and other parts, the functions and construction of which will be explained in full later on, constitute the carburetion subgroup.
In order to get the gas, which is produced by the carburetion group, into the motor cylinders at the proper time and in the proper quantity, there are needed inlet valves, and, for their operation, cams, which are placed on a camshaft, which, as will be explained in detail, is driven from the crankshaft of the engine. In addition, after the gas has been admitted into the cylinders, compressed, and exploded, thus producing its power, it is of no further use and must be removed from the cylinders. As this must be done at the proper time, and as the proper quantity must be removed, additional valves known as the exhaust valves are needed, these also being operated by cams on a camshaft, driven from the crankshaft.
Further, in passing out, the exhaust gases pass through a particular pipe, known as the exhaust manifold, and thence to the back of the car. As there remains considerable pressure in these gases, when allowed to escape freely, they make much noise and considerable smoke, so that all cars are required by law to carry and use a muffler. The name explains the purpose of this - it muffles the noise. The exhaust gases pass through this and thence out into the atmosphere. This whole group of parts might be called the exhausting system, for the purpose of removing the gases after use, as contrasted with the carburetion system, for producing and supplying the gases.
In an intermediate stage comes the explosion. This is done by means of an electric spark, which is produced within the cylinders by means of a spark plug. The electric current which is the original source of this spark may be produced by means of a form of rotary current producer, known as a magneto, or it may be taken from a battery. In any case, such current must be brought up to a proper strength and the various sparks must be produced at the exact time they are needed. All this calls for auxiliary apparatus. Moreover, the current producer, if it be a magneto, must be driven from some rotating shaft; there must be a suitable place provided on the engine for it, with means for holding it there, as well as for quick and easy removal. All this, as a complete unit, is called the ignition system.
In the production of the gas for use, and in its explosion and subsequent expanding and exhausting, a great amount of heat is created. Some idea of this may be gained from the two simple statements that the explosion temperature often runs up as high as 3000° F., and the exhaust temperature frequently is as high as 1500° F. In order to take away this heat, which communicates itself to the walls and parts of the engine wherever it contacts with them, and by conduction, to other parts with which it does not contact, the parts which are exposed to the greatest heat are surrounded by hollow passages, called jackets, through which water is forced or allowed to flow. This might be called a collector of the heat, for it is then conducted to the radiator, a device for cooling the water, which is there cooled off and then used again. In order to circulate the water, a pump is used, driven from some rotating shaft, supported, removable, accessible, etc. All this, with the necessary piping to connect the various parts, is called the cooling system.
Moreover, as the various parts rotate within one another, bearings, or parts specially designed to facilitate easy and efficient rotation, must be used. Furthermore, in and on all such bearings a form of lubricant is necessary, as it is also between all sliding parts. In order to have a copious supply at certain points, various forms of lubricators or oil pumps are needed to circulate it; pipes must be provided to carry it; a sight feed, or visible indication that the system is working, must be placed in sight of the driver (usually on the dashboard); an oil tank for carrying the supply must be provided; and a location found for the lubricator or pump and means for driving, removing, adjusting, and cleaning it. All this as a whole comes under the head of the lubrication system. This system covers in addition isolated points requiring lubrication, and the different ways used to supply them.
In order to start the engine, a starting handle is provided on all older cars, with possibly a primer working on the carbureter, and other parts. On modern cars, this work of starting is done by electricity, which requires a starting motor, a battery, a switch for connecting the two, wiring, buttons, and other parts. All this combined is called the starting system.
At one end of the engine shaft, there is provided the flywheel. This is a large, wide-faced member of metal, comparatively heavy, the function of which is to store energy (by means of rotation) as the engine produces it, and to give it back to the engine at other parts of the cycle when energy is needed and none is being produced. In short, it is a storehouse of energy, absorbing the same from the engine, and giving back the excess when it is needed. In general, this effect is greatest when the mass of metal is farthest from the center, consequently flywheels are made of as large a diameter as is possible considering the frame members. Note this in the illustration, Fig. 1.
Within the flywheel the clutch is located, generally. This is a device, by means of which a positive connection can be made with the engine, or disconnection from it effected at the driver's will. A moment's consideration will show that when such disconnection is made with the engine running, it will continue to run idly, and will not drive the car, which, perforce, must stand still. Similarly, when the positive connection is made the motor will drive the clutch and such parts beyond it as are connected-up at the time. This arrangement is necessary because of a peculiarity of the gas or gasoline engine - it cannot start with a load but must be started and allowed to get up speed before any load is thrown upon it. This is the function of the clutch, for at all starting times it is thrown out, disconnecting the balance of the driving system from the engine, so that the latter may speed up. When this has been done, the proper gear is engaged, and the clutch is thrown in so that the engine picks up this load.
Like other parts, this must have a means of connecting and disconnecting, a proper place, proper fastenings, means for adjustment and removal, other means for lubrication, as well as other parts. All this, collectively, is called the clutch group.
As has just been pointed out, the engine cannot start with a load; it must get up speed first. Furthermore, it must be started under a light load. This necessitates certain gearing, so that, when starting, the power of the engine may be multiplied many times before reaching the wheels, and, therefore, before it is applied to the propulsion of the car. Furthermore, it has been found convenient to have a series of such reductions or multiplications. These correspond to the various speeds of the car, for obviously, if the power is multiplied by means of gearing, it is reduced in speed in the same ratio. This whole group of gearing is the transmission or gearset, and the various reductions are the low speed, intermediate, and high in a three-speed gearbox; and low, intermediate, second, and high in & four-speed gearbox. A gearbox is always spoken of by its number of forward speeds, but there is in all of them, in addition to the forward speeds, a reverse speed for backing the car.
In the usual form, these gears are moved or shifted into and out of mesh with one another, according to the driver's needs. For this purpose, shifting gears must be provided within the gearbox, that is, the arrangement must be such that the proper gears can be moved back and forth, with a shifting lever outside for the driver's use, and proper and accurate connections between the two. The gears must be mounted on shafts, these in turn on bearings, the bearings must be supported in the gear case, and this must be supported on the frame. In addition, there must be suitable provision in the gear case cover for inspection, adjustments, and repairs; all the moving parts must be lubricated; all parts must be protected from the dust, dirt, and moisture of the road, etc. All this comprises the transmission or gearing group, which properly ranks second to the engine group in importance. That is, next to producing the power quickly, efficiently, and cheaply, it is important to use it with equal quickness, efficiency, and cheapness.