Working principle of throttle position sensor

Using the principle of magnetic induction

The working principle of the magnetic induction sensor is that the path through which the magnetic lines of force pass is the air gap between the stator and the rotor of the permanent magnet N pole, and the air gap between the rotor convex teeth and the stator magnetic head, magnetic head, magnetic conductive plate and the S pole of the permanent magnet. When the signal rotor rotates, the air gap in the magnetic circuit will change periodically, and the reluctance of the magnetic circuit and the magnetic flux passing through the signal coil head will also change periodically. According to the principle of electromagnetic induction, alternating electromotive force will be induced in the induction coil.

When the signal rotor rotates clockwise, the air gap between the rotor teeth and the magnetic head decreases, the reluctance decreases, the magnetic flux φ increases, the magnetic flux change rate increases (d φ/dt "0), and the induced electromotive force E is positive (e" 0), as shown in curve abc in Figure 2-24. When the rotor teeth are close to the edge of the magnetic head, the magnetic flux φ increases sharply, the magnetic flux change rate reaches the maximum [dφ/dt = (dφ/dt) max], and the induced electromotive force E reaches the maximum (E=Emax), as shown in curve B in Figure 2-24. After the rotor turns to point B, although the magnetic flux φ is still increasing, the change rate of magnetic flux decreases, so the induced electromotive force E decreases.

When the rotor rotates until the center line of the convex tooth is aligned with the center line of the magnetic head (see Figure 2-24b), although the air gap between the convex tooth of the rotor and the magnetic head is the smallest, the magnetic reluctance is the smallest, and the magnetic flux φ is the largest, the induced electromotive force E is zero because the magnetic flux cannot continue to increase, as shown in Curve C of Figure 2-24.

When the rotor continues to rotate clockwise and the convex teeth leave the magnetic head (see Figure 2-23c), the air gap between the convex teeth and the magnetic head increases, the magnetic resistance increases, and the magnetic flux φ decreases (dφ/dt "0"), so the induced electromotive force E is negative, as shown by curve cda in Figure 2-24. When the convex tooth deviates from the edge of the magnetic head, the magnetic flux φ decreases sharply, the magnetic flux change rate reaches the negative maximum [dφ/df =-(dφ/dt) max], and the induced electromotive force E also reaches the negative maximum (E=-Emax), as shown in point D on the curve of Figure 2-24.

It can be seen that every time the signal rotor rotates a convex tooth, a periodic alternating electromotive force will be generated in the induction coil, that is, the electromotive force will have a maximum value and a minimum value, and the induction coil will output an alternating voltage signal accordingly. The outstanding advantage of magnetic induction sensor is that it does not need external power supply, and the permanent magnet plays the role of converting mechanical energy into electrical energy, so its magnetic energy will not be lost. When the engine speed changes, the speed of rotor teeth will change, and the change rate of magnetic flux in the iron core will also change. The higher the rotating speed, the greater the change rate of magnetic flux and the higher the induced electromotive force in the induction coil. When the rotating speed is different, the changes of flux and induced electromotive force are shown in Figure 2-24.

Because the air gap between the rotor teeth and the magnetic head directly affects the reluctance of the magnetic circuit and the output voltage of the induction coil, the air gap between the rotor teeth and the magnetic head cannot be changed at will in use. If the air gap changes, it must be adjusted according to regulations, and the air gap is generally designed in the range of 0.2 ~ 0.4 mm