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steering arm at the lower end of the steering column. The steer. ing arm is coupled to one of the steering knuckles of the front axle by a connecting link and the movement imparted to the one steering knuckle is transferred to the other one by means of the tiebar which joins them so they must move in unison.

Electric Starting and Lighting Systems. One of the greatest improvements made in the modern automobile is the use of an

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electric motor to start the gasoline engine, which relieves the driver of the hand cranking necessary on early models. As elec tric current is used for this purpose it is very easy to use it for lighting as well, which is another great convenience. Cars of several years ago used kerosene oil lamps and searchlights burning acetylene gas. The modern cars have more powerful lighting systems and at the same time the lights can be obtained by the simple act of turning of a switch. While electric lighting and starting systems are made in numerous forms, all of these may be arranged in two main classifications. The one-unit sys. tem is the simplest because in this a combined motor-dynamo

Padding

Fabric Body

Inner Tube

Bead Filler

Rim Channel

Bead

| Felloe

-Valve Inside

-Valve Cap

Fig. 23.-Outlining Construction of Pneumatic Tire Fitted to Simple

Clincher Rim.

answers for generating current when the engine is running and for starting the engine when it is stopped. In the two-unit system, the main parts of which are shown at Fig. 21, the generator and starting motor are independent and uni-functional. The generator is used only to supply current to the storage battery. The starting motor is employed exclusively for turning over the engine crankshaft. This is easily accomplished by means of a small pinion carried by the armature shaft of the motor, which automatically engages a large gear cut in or attached to the flywheel rim.

It is not within the scope of work of this character to discuss electric starting or lighting systems at length. It is sufficient to explain that all the while the engine is running above a certain predetermined speed that the generator is delivering current to the storage battery. Some method of governing the current output is always provided to prevent the generation of too much electricity at high engine speeds and a consequent overcharging of the battery. Similarly a cut-out device is interposed between the storage battery and the generator to prevent the battery from discharging through the current producer when that was turning so slowly that it was generating the current weaker than that of the battery and therefore unable to oppose the flow of the stronger current. All that is necessary to bring the starting motor into action is to close the circuit between the storage battery and the motor windings by means of a foot-operated switch. If the ignition switch is closed so the spark takes place in the engine cylinders the engine will start after the flywheel has been turned over several times by the electric motor. The lights are supplied from the storage battery and are controlled by an independent switch.

Detachable Wire Wheel.—Many recent models of automobiles will be found equipped with wire wheels of some form or other. Improvements have been made in the method of lacing wire wheels so that the forms used for automobiles are very strong. This is due to a method known as triple spoke lacing as this provides a combination that permits the wheel to support radial, torsional, side thrust, and shock stresses in a much superior manner to the old double spoke lacing formerly used on light automobiles and widely applied on bicycles and motorcycles.

A typical triple spoke wheel of Houk manufacture is shown at Fig. 22 A, while the method by which it is fastened to the master hub is clearly shown at Fig. 22 B. Most wire wheels are made so as to be easily detachable from a master hub which is not removed from the wheel spindle or axle and which is supported by the bearings or axle shafts. The wire wheel is built up with an auxiliary pressed steel hub as a basis which is provided with a series of holes to fit over driving pins attached to

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Fig. 24.-Quick Detachable Demountable Rim for Straight Side Tires.

the flange of the master hub and which is formed on the inside with two tapered seats, the angle of the tapers being opposed to each other. One of the male tapers forms part of the master hub which is shown at B in place on the front wheel spindle while the other male taper is on the locking nut. When the lock nut is screwed onto the threaded end of the master hub, which is sometimes termed the inner or fixed hub, it forces the female taper on the inside of the pressed steel wheel hub against the male taper on the master hub. The torsional force is applied to the wheel through substantial driving pins which engage with registering holes in the hub flanges. A spare wheel with fully inflated tire may be carried and a quick change made in event of a puncture.

Pneumatic Tires and Rims. The pneumatic tire of the present day is invariably of the double tube type and is composed of two members, the inner tube and the shoe or carcass. The inner member is utilized to retain the air and is made of a very pure rubber, about an eighth of an inch thick for cars of average weight. While this tube is very elastic and is air-tight, it would not be strong enough or have adequate resistance to be run directly in contact with the road surface; therefore it is necessary to protect it by a shoe composed of layers of fabric and rubber composition. The shoe member is provided with beads on its inner periphery designed to interlock with the rim channel, as shown at Fig. 28. The air is introduced into the tire through a simple form of automatic valve which is securely attached to the inner tube. As the inner tube becomes distended by the air pumped into it, it forces the beads of the tire outward and clinches the shoe so firmly in the rim channel that it will be impossible to dislodge it without the use of special tire irons, and then only when the air pressure is relieved from the inner tube.

In order to reduce the time occupied in changing tires, which is needed to adjust the shoe properly and blow up the inner tube, a number of demountable rims have been devised. The wheel felloe carries a metal rim, and to this is attached a second member on which the tire is mounted. The tire-carrying rim may be securely attached to the wheel by means of suitable and quickly operated clamping bolts, rings or wedges. When demountable rims are fitted, instead of carrying the usual deflated spare outer casing, fully inflated tires are carried on rims similar to the demountable portions, and when the tire is punctured the damaged one and its rim are removed as a unit and a new, fully inflated member replaced. When it is necessary to remove the shoe, as in the ordinary single-rim construction, the operation of replacing a tire will take from ten to fifteen minutes under favorable conditions, but with quickdemountable rims the operation of changing a tire will take

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