Patent GB-149243-A (GB)
Title: Improvements in or relating to speed indicators
IPC: G01P3/04
Filed: 1920-07-12
Abstract: 149,243. Parker, F. W., (Assignee of Blackburn, G. W.). March 19, 1917, [Convention date]. Differential speed indicators; transmission mechanism.-In an instrument for motor-vehicles &c., a worm B<16>, Fig. 9, slidable along a shaft B<11> rotated by electrical means from the vehicle wheel, is in mesh with a threaded spindle F<9> which is rotated intermittently so as to reverse the endwise movement of the worm. The periods during which the spindle is stationary vary in length inversely with the speed so that the reciprocations of the worm in opposite directions are equalized at all speeds. A cam C' on the vehicle wheel C reciprocates a plunger C<2> which, through a pawl C<5>, drives step-by-step a threetoothed wheel C<7> provided with contact strips C", C<12>, C<13> arranged to engage contacts C<22>, C<20>, C" and thereby energize successively three magnets B', B', B<4>, the armatures B<5>, B<6>, B<7>, Fig. 3, of which are pivotally attached to a pin B<9> eccentrically mounted on the shaft B". In order to ensure breakage of the circuit to the battery C<15> when the vehicle is at rest, the shaft of the toothed wheel C' carries a paddle-wheel D, Fig. 11, adapted when in motion to raise mercury from the well D<3> into a cup D<4> communicating by a passage D<5> with the well, and containing a contact pin D<6> in circuit. The threaded spindle F<9> is geared with a parallel spindle F<5> and also constitutes the rotary shaft of a motor G similar to the one shown in Fig. 3, and electrically connected with a battery H<9> and with contact strips G<3>, G<4>, G<5> for engagement with contacts on the spindle F<5>. Also on this spindle is a tapering three-lobed cam F<4> cooperating with a contact roller F<2> pivoted to the piston F, Fig. 6, of a dash-pot E<8> which is supported in a carriage mounted on a rod E and connected so as to slide with the worm B<16>. The modus operandi is as follows. When the vehicle commences to move, the worm is rotated bv the motor B and owing to the threaded spindle F<9> being stationary, moves along the shaft B". The contact roller F<2>, which is in circuit with the other side of the battery H<9>, thereupon, by engagement with the cam F<4>, starts the motor G which consequently rotates the cam and spindle until the roller F<2> is disengaged by the cam. The roller is now free, subject to the restraining influence of the dash-pot E<8>, to fall into engagement with the next lobe of the cam, and the time it takes to do this depends upon the position the carriage occupies along the length of the cam, that is upon the speed under measurement. When the spindle rotates, it tends to return the worm B<16> towards zero position, but as soon as the roller F<2> is freed, the circuit to the motor is broken and the spindle F<9> again becomes stationary. The speed of descent of the roller F<2> may be varied manually by means of a needle valve which regulates the inlet of air to the dashpot E<8>. The position occupied by the worm and carriage is translated to the indicator by means of a rack and pinion. The spindle F<9> is braked, whenever the circuit to the motor G is broken, by means of an electro-magnet H<4>, the armature of which is connected with a leaf spring bearing upon a brake drum on the spindle. The distance traversed by the vehicle is registered by means of trip and total counters driven by worm and bevel gearing from the shaft B".