CHAPTER XIIIAUTOMOBILE ACCESSORIES
Self-starting devices are the latest permanent addition to a perfect car equipment. Two general types are being made, one purely mechanical in its character, and the other operated by the engine itself.
The mechanical devices usually have some connection with the forwardly-projecting end of the crank shaft, where the present cranking shaft is located, and some of the inventions in this respect have an arrangement whereby the driver is able manually to operate the starter from his seat.
The actual work of turning the shaft is now performed by compressed air which actuates mechanism that gives from one to two turns to the shaft, sufficient to ignite the fuel in several of the cylinders.
Simple Type of Starter.—The simplest type of starter is that which utilizes the cylinders themselves to give the initial turns. To illustrate the matter we have given some sketches of the engine cycle, in Fig. 95. The four positions of the pistonin a four-cylinder engine are so placed that the spark cannot ignite the charge in either cylinder.
Cylinders 1 and 2 are descending, and 3 and 4 are ascending. The charge in 4 is partially compressed, but it must reach the position indicated by the dotted lines A before it can be ignited.
Fig. 95. Starting Mechanism.
Fig. 95. Starting Mechanism.
The sparking mechanism was cut off before the cylinder 1 reached its highest point, at the previous stopping of the car, so that it still has an unexploded charge; and piston 3 is now discharging the gas from that cylinder.
As the engine is now at rest, the problem is to supply a charge to cylinder 1, or a pressure ofsufficient strength to turn the engine shaft so that the piston in 1 will be brought up to the explosion line A. It is accomplished in the following manner:
One or more of the engine cylinders is connected up by a small pipe with a storage tank, located at any convenient point, so that at each explosion a portion of the charge in the cylinders goes into the tank, where it is held by a check valve.
The Distributer.—This tank is connected with a distributer, which controls the pressure flow to the different cylinders. In Fig. 91 the distributer would send this pressure to cylinder No. 1. The opening of a valve readily accomplishes this, and if the charge in No. 4 should not explode, the next in order to get the compressed gas from the tank, would be cylinder 4, which would bring cylinder 3 into position for firing.
As soon as ignition takes place, the driver merely shuts off the valve, and no further attention is required to operate it.
Lighting.—Most cars depend for illumination on the use of compressed gas usually, some form of acetylene, which makes a brilliant light, and is not expensive.
The best cars, however, are also equipped with electricity, some depending on storage batteries,and others on current generated on the car itself. There is nothing in either system that requires any special explanation, nor are they difficult to care for and operate.
Signaling.—It has been the custom for drivers, in approaching corners, or street intersections, to hold out the right hand as a sign that a turn is to be made to the right, or the left hand for a turn in the other direction.
Car Signals.—Numerous devices are now on the market designed to be located both in front and in rear of the vehicle, which are intended to indicate direction, as well as to impart other information.
These signals are under control of the driver, and have signs on them which indicate “stop,” “right,” “left,” or other words which conspicuously display the intention of the driver.
All machines have signaling horns of some character, operated, usually, by some mechanical arrangement connected with the gearing or by compressed air, and others are connected up with the engine exhaust. Chime whistles are so operated.
Speed Signals.—Other inventions are designed to indicate, by automatic mechanism, the speed of the car, in which color displays the relative speed. Thus, a car going at the normal speed, say 10miles per hour, would show a white light; from 10 to 15 miles, blue; from 15 to 20 miles, green; and above that speed, red.
The foregoing colors and speeds are arbitrarily selected, merely to show the ideas involved. The device in question has nothing whatever to do with the regular speed registering mechanism of the car, but is designed to show pedestrians and police officials the actual running speed at a glance.
Mufflers.—There is really no excuse for noisy automobiles. Mufflers are now made which absolutely eliminate all noise from the exhaust. The great difficulty in the past has been to make them sufficiently large for the engine. If too small they do not take care of the exhaust properly, and they also serve to check the flow of the exhaust gases from the engine, and thus greatly decrease the power of the engine.
Exhaust.—All racing engines are made without exhausts, so there will be nothing to retard the flow of the exhaust.
The function of the muffler is to receive the exhaust gas and permit it to expand as nearly as possible down to atmospheric pressure before delivering it to the air. Fig. 96 shows the simplest form in which it can be made.
Construction of Muffler.—The inner pipeA, from the engine exhaust, passes axially through a cylinder B, the pipe, however, being closed at its inner end where it is attached to the head C. Numerous small holes D are formed through this pipe for the escape of the burnt gases.
Within the cylinder B is a smaller cylinder E, surrounding the inner tube. This has one end attached to the head C, and its other end is open so as to provide a passage way F from the interior of the cylinder. The discharge ports are at G, through the head C.
Fig. 96. Muffler.
Fig. 96. Muffler.
Almost any design of muffler is serviceable, if it has sufficient area. However large it may be it is always advisable to have a valve in the pipe A from the engine manifold, so the muffler can be cut out going up steep hills.
Ball and Roller Bearings.—All running gears are provided with either ball, or roller bearings. For heavy vehicles roller bearings are most serviceable, but for light vehicles and forspeed most manufacturers prefer ball-bearings.
Race Ways.—The object in the use of balls, is to provide two, three, or four points of contact, which should be so arranged as to have the paths of the bearings of equal lengths, as nearly as possible, and thus prevent the balls from wearing by creeping along the contact walls, and also thereby wearing the paths on which they travel.
Fig. 97. 3-Point Roller Bearing.
Fig. 97. 3-Point Roller Bearing.
The Three-Point Contact.—To understand the full importance of this, examine Fig. 97, in which A is the roller, or shaft, and B the hub having the raceway C designed to hold the balls D, and gives two points of contact, the third point being the shaft A.
Fig. 98. Wrong Bearing.
Fig. 98. Wrong Bearing.
Compare the foregoing figure with the illustration given in Fig. 98, where the contact points A, B, C, represent the three bearing circles, which differ in their circumference, and it is obvious that a ball in traveling around must slip somewhere on one or more of the paths A, B, C.
Fig. 99. Improper Alinement.
Fig. 99. Improper Alinement.
Wrong Construction.—Another sample of wrong construction is shown in Fig. 99. In this diagram the three bearing points A, B, C, also represent circles of different diameters, which are sure to wear grooves in the three paths made by the balls.
Fig. 100. Correct Raceways.
Fig. 100. Correct Raceways.
The most ideal form of bearing is shown in Fig. 100, which represents the four-point contact, and this also provides against longitudinal thrust of the shaft or axle.
Roller Bearings.—This type of bearing is ideal because of the large surface which is available. The difficulty is to keep the rollers parallel, with the shaft. Furthermore, they should not roll in contact with each other. To obviate this the rollers are put into a cage.
Fig. 101. Cage for Roller Bearing.
Fig. 101. Cage for Roller Bearing.
Form of Roller Bearing.—Fig. 101 shows a side and a cross section of a set of rollers held within a cage formed of two end rings A A, each roller B having at its end a reduced bearing C, and intermediate the rollers are tie rods D, which keep the rings in proper relation to each other, and also prevent them from alining themselves diagonally along the shaft, or against the bearing within the boxing.
To provide means for utilizing roller bearings so they will take up end thrust, taper rollers are employed, as shown in Fig. 102.
Fig. 102. Roller Bearing.
Fig. 102. Roller Bearing.
The shaft, or axle, A, has two runways, B, C, which are conically-formed, and inclined toward each other. The rollers D are tapering, and have their small ends pointed towards each other so that the outer ends of the bearing surfaces E of the hub are at a considerable angle to the axis of the shaft.
These rollers are also mounted in cages which turn around the shaft. This structure, in a modified form, is largely used in automobile construction.