Arizona republican., 1918-04-21
MOTORISTS SHOULD KNOW HOW ID CARE
 FOR SPEEDOMETER

Among the subsidiary mechanical units of the modern motor car, which only gives trouble on occasion, must be included the speedometer. In spite of the delicate nature of this instru- n1ent, it is not often that the motorist has occasion to attempt repairs of it. However, when such an occasion does arise, some knowledge of the device is essential.
 At the present time there are in ser vice four definite types of speedome- ters, magnetic, centrifugal, hydraulic md that driven by air current. The magnetic type of speedometer is prob lbly the most popular type, as far as the number of makes of car son which 1t finds a place. A typical construc- lion in this class employs but one nov ng part, circular magnet Over the magnet. but not touching it. is an in verted metallic cup. on the rim of which are q TOW of figures. indicating he miles per hour. The magnet is evolved by means of a flexible shaft, t5 field acting on the dial cup. As the speed of the magnet increases, so does the magnetic pull and the dial cup is drawn around to indicate the increasing speed. The dial is mount ed on a steel shaft with a jeweled bear ing at the top. A hairspring is fitted to resist the pull of the magnet and this also serves to return the cup to zero when the car stops. In general temperature con pensator is fitted in this type, to prevent the hairspring being effected by climatic changes.
 Within the past year or so the air current type of speedometer has been achieving a considerable popularity. This type of instrument employs a stream of air to turn the dial which indicates the mileage. A typical con- struction in this class has a flexible shaft driving an air circulator, con- sisting of two elongated aluminium gears, placed in the head of the in- strument and opening into an air chamber. This latter has two open ings. one an entrance for the air, the other an exit. A dial fitted with a vane is pivoted in the chamber. A cur rent of air is forced into the chamber by the revolutions of the gears and this stream striking the vane, revolves the dial to show appropriate figures A hairspring is used to return the dial 70 zero when the car stops.
 The centrifugally operated speedo- meter, is actuated on the same prin- ciple found in the flyball governor Weights are mounted on the moving shaft by means of lever or cranks, SC that the movement of the weights by centrifugal force is communicated through the shaft to the dial Wheu the car speed increases these weights end to fly out and being connected with the dial through the shaft, pull the former around to the right and display the correct figures for the miles per hour.
 The hydraulic type of speedometeI has not gained any considerable fol- lowing as yet though it's many excel lent qualities may eventually win il recognition.
 All speedometers have certain char Rcteristics in common; the variations in type generally refer to the mean. amployed of actuating the mileag, 1ial. All these instruments have ; connection in the shape of a rotating shaft that is flexible and is housed il a flexible housing, running to som, running part of the mechanism, usually front wheel. On the end Of this Shaf IS a gear, which meshes with geal ln the moving part employed. Thi shaft is driven from the cars mechan ism and in turn it drives the mechan ism of the speedometer through som, sort of joint It has in the past beer practically universal custom to con meet the speedometer with a iron wheel, but recently the idea of utilizing the propeller shaft has come int, marked favor. Now some makers ar beginning to connect the speedomete with the transmission unit and claim of maximum quiet, perfect lubricatio and protection are made for this To cation.
 When something goes wrong wit he internal economy of the speedome ger itself, the car owner can do noth