The present invention relates generally to a tachometer used to detect engine speed, and more particularly, to a universal tachometer operative to measure the speeds of engines with different numbers of cylinders.
Tachometers have been broadly applied to measure the angular velocity, typically measured in units of revolutions per unit (RPM). Among various tachometers, the contactless magnetic pickup tachometers are particularly popular for measuring the engine speed of automobiles. For measuring the engine speed, the magnetic pickup tachometer is typically disposed near an ignition timing wheel made of ferromagnetic material. When each tooth of the ignition timing wheel passes through the magnetic pickup tachometer, a pulse is generated. Normally, either the period of the pulse is measured, or the number of pulses per unit time is counted. According to the number of the teeth for the ignition timing wheel and the measured period or counted pulse, the speed can be obtained.
As the above tachometer has to be installed near the crankshaft of the engine, the installment is difficult and laborious. Therefore, companies have developed tachometers with inductor pickup coupled to coil wires of the engine, avoiding the need to measure the magnetic field induced by the rotation of the crankshaft. However, as the coil wires are not readily accessible in the engines in many new vehicles, the installation may remain difficult.
Further, conventional tachometers are designed for the engine with a specific number of cylinders. To measure the speed of engines with different numbers of cylinders, different tachometers are required. Moreover, in many newer engines, two sparks are generated for each operation cycle for each cylinder. Using the conventional tachometer may incorrectly read the second spark as a separate cycle, doubling the reported engine speed.