OCR Text |
Show SPEEDOMETERS OR SPEEO JNFORMERS One of Most Interesting and Important Chapters in Auto Development. The story of the development of the speedometer provides one ot the most interesting and Important chapters in the history of speed registering devices de-vices according to an engineering bulletin, which goes on, to say : "Speedometers, or speed indicators as they were called in the days before be-fore the automobile, were largely used on locomotives, street cars nnd bicycles. At that time none of them was considered very reliable and their development was slow. Came Out in 1906. "As an illustration of the prevailing prevail-ing situation, along about 1000 when automobiles began making their appearance ap-pearance in increasing numbers, a new speedometer came out. It was much larger than the present day speedometer and operated like a barograph baro-graph recording with an inked needle on a roll of paper the speedy time and even stops of a car. This was hailed as a promising improvement and caused quite a bit of interest in engineering circles. From that time on, the evolution of the instrument went through many stages, until today to-day we have speedometers as near perfect as it is possible to pake them. "The speedometer has two independent inde-pendent uuits, each driven from the same shaft a 'speed' unit to tell how fast you are going and, an 'odometer' unit to tell how far you have gone. The speed unit is driven directly by a flexible cable connected to the engine en-gine transmission. This cable drives a steel spider or rotor that s-pins around inside of an aluminum, cup which is mounted on a jeweled bearing bear-ing and is marked to read in miles per hour. This entire assembly is placed between the poles of a permanent perma-nent horse-shoe magnet. As the car moves, along the road, the rotor is driven by tlie flexible shaft, and a 'magnet drag' between the rotor and the horse-shoe magnet causes the aluminum cup to turn against a hair spring, the amount of turn being directly di-rectly proportional to the car speed. "The hair spring returns the cup to 'zero' when the car stops, and by offering a uniform, resistance against turning, keeps the readings steady at all speeds. "In order that the speedometer will accurately function at all speeds, it is checked at several intermediate speeds and the magnet adjusted to give the correct readings. This rakes the instrument accurate over its entire en-tire range. How It Operates. "The odometer unit that tells you how far you have gone is driven by a worm gear from a flexible cable and records both season and trip mileage. Every time the cable turns l.ODS times an additional mile is recorded on the first odometer wheel. Every ted miles on the first wheel, the second sec-ond wheel is moved one reading, and so on, the maximum reading being . 99,000 wiles. The 'trip' of the odometer odome-ter operates the same as the 'season' part but it can also he reset to zero or any mileage desired. It reads up to 99.9 miles and is used to measure the distance traveled on any trip. "All speedometer heads are geared aiii;e variations of size tires and nvi mi ins pic., are taken care .of by different combinations of speed drive gears in the transmission. L'n-der-inllation of tires, excessive load, and rough roads are conditions that will cause slight inaccuracies of speedometer speed-ometer indications." |