Alternative Engine Speed Sensing Using the Electric Signals of the Alternator

In the low-cost segment for 2-Wheelers legislative, economic and ecologic considerations necessitate a reduction of the emissions and further improvement in fuel consumption. To reach these targets, the commonly used carburetors are being replaced by engine management systems (EMS). One option to provide these systems for acceptable and attractive system costs is to save a sensor device and to substitute its measure by an estimation value. In many motorcycles the rotor of the vehicle's alternator is rigidly attached to the crankshaft. Therefore, the voltage and current signals of the alternator contain information about the engine's speed, which can be retrieved by evaluating these electric signals. After further processing of this information inside the electronic control unit (ECU), the absolute crankshaft position can be obtained. A high-resolution speed signal without mechanical distortions like tooth errors is gained, whose signal quality equals the one of a common speed sensor. Hence, it can be used for the timing of injection and ignition and for calculations of more elaborate speed based control functions. Because the existing alternator signals are used to determine the speed and no extra installations inside the crankcase are necessary, this method may ease the transition from carburetors to EMS.Cross Reference: