Speedometer and ratio testing apparatus

#This invention relates to testing apparatus, particularly a speedometer and like instrument testing apparatus of a portable type.

#While manufacturers of speedometers provide bench testing equipment and procedures and servicing and testing such instruments, it is necessary to remove the instrument from its working position to effect such servicing or testing. In the case of automotive vehicles the removal of such instruments from the instrument panel usually involves considerable time and labour. While a speedometer may be bench tested and prove accurate, this does not necessarily mean that the instrument is accurately recording the speed of the vehicle in which it is installed, since bench testing does not take into account other characteristics of the vehicle in which the instrument operates.

#The necessity of a speedometer to give an accurate reading of the speed of a vehicle is particularly important in commercial vehicles, since various speed restrictions are applied by the authorities to vehicles of different load capacities. For economic reasons and carriage time considerations it is necessary that commercial vehicles be driven at speeds closely within the limits set down for such vehicles in order to avoid the heavy penalties likely to be incurred for speed infringements. This same situation also applies in some degree to private vehicles in that driver normally relies on his speedometer to indicate his speed in order to insure that he is not infringing the limits applied in any speed limit zone.

#Reference will now to made to the accompanying drawings illustrating embodiments of testing apparatus in accordance with the invention.

#FIG. 1 is an elevation of the casing incorporating the testing apparatus diagramatically illustrated in FIG. 2, of one embodiment of the invention.

#FIG. 3 is a plan view of a casing incorporating the testing apparatus diagramatically illustrated in FIG. 4 of a second embodiment of the invention.

#As illustrated in FIGS. 1 and 2 a speedometer testing apparatus comprises a casing 5 having an inclined instrument supporting face 5a and having mounted thereon a master speedometer 6, a ratiometer 7, a polarity reversing switch 8 and a variable resistance control 9.

#Within the casing 5 and diagramatically illustrated in FIG. 2 there is supported an electric motor M, adapted to be operated from an automobile battery. Wiring is included to connect the motor to the battery through the polarity reversing switch 8 and the variable resistor 9 so that the motor may be rotated at a required speed and in the required direction as required by a particular speedometer to be tested.

#The Motor M is drive coupled to the input 10 of a gear box 11 (of known type) having two output shafts 12 and 13 adapted to rotate at the same speed. One output shaft 12 is drive coupled to a flexible drive assembly 14 extending from one side of the casing, the outer or free end of which is adapted to be coupled to a speedometer after the normal drive coupling is disconnected so that the speedometer may be coupled to the apparatus without the necessity of removing the speedometer from the vehicle instrument panel.