The brake pedal anti-lock braking system (antilockbrakesystem) of the car is collectively referred to as ABS. The function is to control the force of the braking system of the braking system when the car is braking, so that the wheels are not locked by the wheels and are in a situation of rolling and slipping (the mobility rate is about 20%), so as to ensure the adhesion of the wheels and the ground. The knot force is at the maximum value.
The function of the wheel speed sensor in the ABS is to accurately measure the wheel transmission ratio of the car. The wheel speed sensor detects the frequency signal (transmission ratio signal) of each wheel rotation, and then sends this signal to the ABS electronic computer. When the speed is guaranteed to the rated value, the emergency brake pad brakes the system and the ABS system starts to work. When the ABS computer controls the wheel to loosen for a moment, the wheel speed sensor sends the interval signal that detects the rotation of the tire from braking to rotating to the ABS electronic computer, so that the ABS controls the brake pad to achieve the best braking distance. A wide range of wheel speed sensors mainly include magnetoelectric wheel speed sensors and Hall-type wheel speed sensors.
The magnetoelectric wheel speed sensor is designed by applying the magnetic effect scheme of electric current. It is simple in structure, low in cost, not afraid of mud stains, and does not require power distribution equipment, and is widely used in ABS anti-lock braking systems. But there are also some disadvantages, such as the phase-frequency characteristic is not high, when the speed is too high, the phase-frequency characteristic of the sensor cannot keep up, which can easily lead to false signals. There is also a poor ability to resist electromagnetic interference. The waveform accurately measured by the analog oscilloscope is in the shape of a sine function wave, and the higher the wheel transmission ratio, the larger the output signal working standard voltage intensity value.
The Hall-type wheel speed sensor is made by applying the basic concept of the Hall effect. Its output signal is not easily damaged by the speed of the standard voltage and strength value. It has high phase-frequency characteristics and strong anti-electromagnetic wave interference ability, but it must have power distribution equipment. Guys, so the sensor makes precise measurements for the example:
At first, connect a BNC to banana head cable to a safety outlet of the analog oscilloscope. The red head is connected to the needle as the positive level, and the signal line of the sensor is connected. The black head of the acne can be connected to the alligator clip or the needle as the negative grounding system.
Open the safety exit toolbar of the analog oscilloscope, set the safety exit loss ratio to 1X, adjust the vertical car gear to 1V/div, and enter the time base to about 10ms, then you can adjust it according to the details.
Since the Hall-type wheel speed sensor has switching power supply circuit power distribution equipment, there should be a DC regulated power supply of about 11-12V to observe the waveform at this time.
Lift the vehicle with a jack, turn the wheel, and accurately measure the output waveform of the sensor signal with an automotive analog oscilloscope.
Hall effect sensors consist of a permanent magnet or a closed circuit with the electromagnetic field almost completely switched off, a magnetic tile fan impeller flips the gap between the magnet and the electromagnetic field, and is not harmed when the tip box on the fan impeller allows the magnetic field When the ground is transmitted to the Hall effect sensor, the magnetic field is interrupted (because the blade is the mainstream medium that transmits the magnetic field to the sensor), the fan impeller allows the magnetic field basis and the total wind magnetic field when the prompt box is opened and closed, resulting in Hall effect. The effect sensor is connected and turned off like a power switch, which is why some car companies refer to the hall effect sensor and some other similar electronic devices as the hall power switch, this machine device is actually a high voltage Switchgear. Therefore, the signal waveform of the Hall effect sensor is actually one pulse after another, that is, the waveform.
The faster the wheel transmission ratio is, the faster the frequency of the signal waveform becomes, but the AC current of its communication remains the same, all from 0V to 1V. Slowing down the speed of the wheel rotation, you can see that the frequency of the signal waveform also decreases.
If the digital display ABS sensor has only a 0 volt working standard voltage output, it should be checked first to determine whether it has a switching power supply circuit supply. It is then determined whether the signal frequency of the sensor closely follows the wheel ratio, otherwise it is indicative of a common problem.
Post time: Apr-27-2022