GB299745A - Improvements relating to speedometers and other rate meters - Google Patents

Abstract

299,745. Farmer, C. D. July 27, 1927. Average speed, measuring directly. - Comprises a speedometer rate meter of the logarithmic cam type in which the cams employed are formed as multiple convolution cams, the time responsive cam being coaxial with and connected to the rotating case of the timing device while the other cam is driven at a constant gear ratio from its driving source. Logarithmic cam discs 14, 12 are driven according to distance travelled and to time respectively and engage arms on sectors 19, 17 on a common pivot 21; the algebraic sum of the angular movements of the sectors is represented by the position of an interengaging pinion 28 rotatably carried on a toothed sector 15 on the pivot 21 which sector gears with a pinion 29 on the spindle of the pointer 10. The disc .14 is driven by worm gear 22, 18<1>, worm gear 24 and a flexible shaft from the road wheel. The cam 14 provides for two and a half turns representing 250 miles. The initial part of the cam is smoothed out over an arc corresponding from 0 to 2.5 miles, and in the case of the cam 12 for a movement representing one quarter of an hour, and after this the instrument begins to read correctly. The time disc 12 is carried by the clock barrel 9 and rotates with it, a roller carries the arm on the sector 17 engaging the cam face. Similarly a roller 30 carried by the arm on the sector 19 engages the cam on the disc 14. The two sectors are urged towards one another by a spring (not shown). The clock may be rewound from the road wheels, but as shown a spring tongue 3 is pressed in to cause a pawl to engage ratchet teeth 13 on the rim of the disc 12 and by turning the tongue and bezel 2 the clock barrel is rotated to wind up the spring.