Crankshaft sensor

The crankshaft sensor records the speed and position of the crankshaft . It is the special application of an induction encoder or incremental encoder that z. B. an internal combustion engine is used.

Structure and measuring principle

The sensor essentially consists of a magnet and a coil . It is usually mounted near the outer edge of the flywheel , which is firmly attached to the crankshaft. The flywheel has steel or iron teeth on the edge. When the crankshaft rotates in the crankshaft sensor, they change the magnetic field and induce a voltage in its coil according to the induction law . The frequency of this alternating voltage is a measure of the speed and is evaluated as a speed value in a motor controller. From this, not only is the ignition point determined, but the value also flows into the control of the injection duration and the start of injection. To determine the ignition point, the sensor must also recognize the crankshaft position. Therefore, the impulse wheels are missing a single tooth. The reference mark is preferably the top dead center of the first cylinder. Due to the missing pulse, the control unit can determine when the first cylinder is in top dead center and determine both the ignition point and the ignition sequence. In the past, this was determined by the ignition distributor, but today it is common to have individual ignition coils for each cylinder or a pair of cylinders (" wasted spark ") that are controlled by the engine electronics.

The induced voltage reaches 1 to 2 volts at a speed of 100 revolutions per minute (for example when the starter cranks the engine when starting). With increasing speed, the voltage increases proportionally. The electrical resistance of the coil is approximately one kiloohm.

literature

• Robert Bosch GmbH (Ed.): Autoelectrics Autoelectronics. 5th edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8 .