Patent ID: 7392145
Filing Date: 2008-06-24
Classification: G01P

Abstract:
1. A speed determining apparatus for a vehicle having a set of road wheels and a mechanical speedometer, the apparatus comprising: a motor mounted to the mechanical speedometer; a shaft encoder operatively fitted to the motor to facilitate the measurement of rotation by the motor; a sensor capable of sensing rotation of one of the road wheels; an electronic control circuit electronically connected to the shaft encoder and the sensor, where the electronic control circuit is capable of; monitoring the sensor and determining road wheel speed; monitoring the shaft encoder and controlling the speed of the motor in response to the determined wheel speed; displaying visual indicia based upon a location of a mechanical pointer on the face of the speedometer instrument combined with the measured rotation of the motor by the shaft encoder; and where the shaft encoder receives a first positive encoder pulse edge signal and a second positive encoder pulse edge signal from the electronic control circuit to determine an elapsed time of about 1/32 revolutions of the motor.