"two unit" system. The same designation applies to a system when the current generating and ignition functions are performed by one appliance, and where a separate starting motor is used. The three unit system is that in which a magneto is employed for ignition, a generator for supplying the lighting and starting cur rent, and a motor for turning over the engine crankshaft. Before describing the individual systems it would be well to review briefly the various components common to all systems.

The actual appearance of a motor fitted with a two unit motor starting ignition and lighting system is shown at Fig. 355. It will be observed that the generator is driven from the pumpshaft extension by a leather universal joint, while the starting motor is mounted at the back end of the crankshaft in such a position that the automatic sliding pinion may be brought into engagement with the flywheel driving gear.

Q. What voltage current is usually employed in connection with electric starting and lighting systems?

A. Electrical starting systems are usually operated on either six or twelve volt current, the former being generally favored because the six-volt lamps use heavier filaments than those of high voltage, and are not so likely to break, due to vibration. It is also easier to install a six volt battery, as this is the standard voltage that has been used for several years for ignition and electric lighting purposes before the starting motors were applied. Some systems in which the motor-generator is part of the flywheel use twenty-four volt or twelve cell batteries.

Q. What is the purpose of the generator?

A. The generator, as is apparent from its name, is utilized for producing current. This is usually a miniature dynamo patterned largely after those that have received wide application for generating current for electric lighting of our homes and factories. The generators of the different systems vary in construction. Some have a permanent magnetic field, while others have an excited field. In the former case permanent horseshoe magnets are used as in a magneto. In the other construction the field magnets, as well as

the armature, are wound with coils of wire. In all cases the dynamo or generator should be mechanically driven from the engine crankshaft either by means of a direct drive, by silent chain, or through the medium of the timing or magneto operating gears. Belts are apt to slip and are not reliable.

Q. What is the storage battery for?

A. All the current produced by the generator and not utilized by the various current consuming units such as the lamps, ignition system, electric horn, etc., is accumulated or stored in the storage

Fig. 357.-One Type of Westinghouse Starting Motor and Parts Comprising the Assembly.

battery, and kept in reserve for starting or lighting when the engine is not running or for lighting and ignition when the car is being run at such low speed that the generator is not supplying current. Storage batteries used in starting systems must be of special design in order to stand the high discharge and to perform efficiently under the severe vibration and operating conditions incidental to automobile service. The storage battery may be installed on the running board of the automobile, under the body, or under the front or rear seat, the location depending upon the design of the car and the degree of accessibility desired. The best practice is to set the storage battery in a substantial carrying case held by rigid braces attached to the frame side and cross members. If the battery should be set under the tonneau floor boards, a door must be provided in these to give ready access to the battery.

Q. How does the starting motor differ from the generator?

A. The starting motor, which takes the place of the common hand crank, is operated by current from the storage battery, and the high speed armature rotation is reduced to the proper cranking speed by reduction gears of the different forms to be described in proper sequence. The construction, of the starting motor is practically the same as that of the dynamo, and it operates on the same principle, except that one instrument is a reversal of the other.

Q. What is the "cut-out" or automatic circuit breaker?

A. In order to secure automatic operation of a lighting and starting system several mechanical and electrical controls are needed, these including the circuit breaker, the governor, which may be either mechanical or electrical, and the operating switches. The circuit breaker is a device to retain current in the storage battery under such conditions that the battery current is stronger than that delivered from the generator. If no circuit breaker was provided the storage battery could discharge back through the generator winding. The circuit breaker is sometimes called a "cutout." The circuit breaker is usually operated by an electro magnet, and may be located either on the generator itself or any other convenient place on the car, though in many cases the circuit breakers are usually mounted on the back of the dashboard. This device is absolutely automatic in action and requires but little attention.

Q. How is the current output of the generator controlled?

A. The governors are intended to prevent an excessive output of current from the generator when the engine runs at extremely high speed. Two types are used: one mechanical, operated by centrifugal force as at Fig. 356, and the other electrical as depicted at Fig. 358. The former is usually a friction drive mechanism mounted in the generator shaft which automatically limits the speed of the dynamo armature to a definite predetermined number of revolutions per minute. The maximum current output is thus

held to the required amount independently of the speed at which the car is being driven. The use of this device minimizes the pos

sibility of overheating the generator or overcharging the battery at high car speeds. The electrical system of governing does not affect the speed of the armature, but controls the output of the