Two sorts of wheel velocity sensors are at present in use: magnetic inductive, extra generally often known as passive sensors, and magneto-resistive or energetic wheel velocity sensors. Each sensors do the identical job, however they work in utterly other ways. Each work successfully in their very own methods, however the extra fashionable energetic wheel sensor is usually thought-about extra dependable.
Passive sensors have been round because the early days of anti-lock braking system (ABS). These sensors work in response to the generator precept. The velocity sensors work together with the cogwheels to watch the anti-lock braking module (ABM) and supply wheel velocity info. The actuator is a toothed tone wheel that rotates with the person wheel. Every tooth on the tone wheel acts as an actuator for the wheel velocity sensor. Because the tonewheel rotates, the tooth transfer out and in of proximity to the sensor. The result’s an alternating present (AC) voltage generated within the sensor coil by magnetic strains of drive that fluctuate because the tone passes the magnetic sensor.
Wheel velocity sensor output could fluctuate from car to car on account of: winding sort, air hole, sensor magnetic energy, tone wheel metallic properties, and wheel velocity. Sadly, a majority of these passive methods are liable to false biking, which is the time period used to explain an ABS cycle, regardless that street situations don’t dictate the necessity for this cycle. This situation may be very liable to happen at decrease speeds. This often occurs due to injury to the wheel or rust on the tonewheel. An incorrect air hole of the sensor causes this situation, as does dust on the tip of the wheel velocity sensor.
Energetic wheel sensors have been in use since 1999. Any such velocity sensor helps enhance low velocity efficiency, sturdiness and accuracy. Energetic sensors do not appear to have the identical false cycle downside as passive sensors. Most automobiles with energetic sensors nonetheless use a toothed tone wheel that acts as a set off mechanism for the sensor. Some automobiles use a magnetic encoder as an alternative of a conventional tone wheel. The encoders have north/south pole magnets embedded within the ring. The ring is then pressed onto the thru-axle similar to a tone wheel. In each instances, the result’s a digital sq. wave sign.
On this technique, the ABM sends the battery voltage to the velocity sensor to start out it up. The sensor, in flip, supplies the ABM with a continuing 7 milliamps (mA) sign on a sign return circuit. Relying on the place of the tone ring or magnetic encoder, this 7 mA sign is switched on or off. The output from the sensor despatched to the ABM is a direct present (DC) voltage sign with alternating voltage and present ranges. The ABM displays the altering digital sign from every wheel velocity sensor and interprets it as wheel velocity.