Crankshaft and Camshaft Position Sensors, Engine Speed Sensors

Basic Description

Crank or camshaft position sensors and engine speed sensors are similar devices that operate based on pulse detection and counting. The fundamental components of these sensors include a tooted disc mounted on the shaft, a stationary detector and electronic circuitry (Fig-1). The disc has teeth or marks distributed evenly around the circumference. When the shaft spins, teeth or marks pass by the stationary detector and generate a series of electrical pulses. The frequency of these pulses is detected and converted to the corresponding shaft rotation speed. The relative angular position can be obtained by counting the number of pulses. Additional reference markers are required to sense the absolute position of the crank or camshaft. Some sensors have two sets of discs with a constant phase shift in order to determine the direction of the rotary motion.

Generally, there are four types of crankshaft or camshaft position sensors: magnetic pick-up coils, Hall-effect sensors, magneto-resistive element (MRE) sensors and optical sensors. The first three utilize metal teeth to generate a series of pulse signals based on changes in the magnetic field as the teeth come into the proximity of the sensor. Optical position sensors use a light-emitting diode (LED) light source and a photodiode to detect optical marks on the shaft or slots in the disk as they move past the detector. Optical sensors have good accuracy and are suitable for both high- and low-speed applications, but the optical components and disc must be kept clean to ensure an accurate reading.

Manufacturers

Bosch, Continental, Delphi, Denso, Hella

For More Information

[1] Rotary Encoder, Wikipedia

[2] Crankshaft Position Sensor, video clip from "www.youtube.com"

[3] Crank and Camshaft Sensor, video clip from "www.youtube.com"