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Operation principle of pulse generator
The crankshaft position sensor is one of the most important sensors in the electronic control system of the engine. It provides ignition time (ignition advance angle) and signals to confirm the crankshaft position, and is used to detect the piston top dead center, crankshaft angle and engine speed. The structure of crankshaft position sensor varies with different models, which can be divided into three categories: magnetic pulse type, photoelectric type and Hall type. It is usually installed at the front end of crankshaft, camshaft, flywheel or distributor.

The crankshaft position sensor is one of the most important sensors in the electronic control system of the engine. It provides ignition time (ignition advance angle) and signals to confirm the crankshaft position, and is used to detect the piston top dead center, crankshaft angle and engine speed. The structure of crankshaft position sensor varies with different models, which can be divided into three categories: magnetic pulse type, photoelectric type and Hall type. It is usually installed at the front end of crankshaft, camshaft, flywheel or distributor.

1. Detection of magnetic pulse crankshaft position sensor

1. Structure and working principle of magnetic pulse crankshaft position sensor

(1) Magnetic pulse crankshaft position sensor of Nissan Company

This crankshaft position sensor is installed behind the pulley at the front end of the crankshaft, as shown in Figure 1. A thin circular toothed disc with fine teeth (used to generate signals, called signal disc) is arranged at the rear end of the pulley, which is installed on the crankshaft together with the crankshaft pulley and rotates with the crankshaft. On the outer edge of the signal plate, there are teeth every 4 along the circumference. * * * There are 9 teeth, and one flange is arranged every 12, and there are ***3. The sensor box installed at the edge of the signal disk is a signal generator that generates electrical signals. There are three magnetic heads with induction coils wound around permanent magnets in the signal generator, of which magnetic head ② generates 12 signals, and magnetic head ① and magnetic head ③ * * * both generate 1 crank angle signals. The magnetic head ② faces the 12 flange of the signal disk, and the magnetic head ① and the magnetic head ③ face the gear ring of the signal disk, and are installed at a crank angle apart from each other. The signal generator has a signal amplification and shaping circuit inside, and a four-hole connector outside. Hole "1" is a 12 signal output line, hole "2" is a power supply line for the signal amplification and shaping circuit, hole "3" is a 1 signal output line, and hole "4" is a ground wire. The signal generated in the crankshaft position sensor is transmitted to the ECU through this connector.

when the engine rotates, the teeth and flanges of the signal panel cause the magnetic field passing through the induction coil to change, thus generating an alternating electromotive force in the induction coil, which is transformed into a pulse signal after filtering and shaping (as shown in Figure 2). When the engine rotates once, three 12 pulse signals are generated on magnetic head ②, and 9 pulse signals are generated on magnetic heads ① and ③ respectively (alternately). Since the magnetic head ① and the magnetic head ③ are installed at a crank angle of 3 degrees apart, and both of them generate a pulse signal every 4 degrees, the phase difference of the pulse signals generated by the magnetic head ① and the magnetic head ③ is exactly 9 degrees. After these two pulse signals are sent to the signal amplification and shaping circuit for synthesis, the signal of crankshaft rotation angle of 1 degree is generated (as shown in Figure 3).

the magnetic head ② that generates a 12 signal is installed at a position 7 before the top dead center (Figure 4), so its signal can also be called a 7 before the top dead center signal, that is, when the engine is running, the magnetic head ② generates a pulse signal at a position 7 before the top dead center of each cylinder.

(2) Toyota magnetic pulse crankshaft position sensor

Toyota TCCS system uses magnetic pulse crankshaft position sensor installed in the distributor, and its structure is shown in Figure 5. The sensor is divided into upper and lower parts. The upper part generates G signal and the lower part generates Ne signal. When the rotor with gear teeth rotates, the magnetic flux in the induction coil of the signal generator changes, thus generating alternating induced electromotive force in the induction coil, and then amplifying it and sending it to ECU.

Ne signal is a signal for detecting crankshaft angle and engine speed, which is equivalent to 1 signal of Nissan magnetic pulse crankshaft position sensor. This signal is generated by a rotor (N.2 timing rotor) with 24 teeth at equal intervals fixed in the lower half and an induction coil fixed on the opposite side (as shown in Figure 6(a)).

when the rotor rotates, the air gap between the gear teeth and the flange part (magnetic head) of the induction coil changes, resulting in the change of the magnetic field passing through the induction coil, resulting in induced electromotive force. When the gear teeth are close to and away from the magnetic head, there will be a change of increasing or decreasing magnetic flux. Therefore, when each gear tooth passes through the magnetic head, a complete AC voltage signal will be generated in the induction coil. N.2 There are 24 teeth on the timing rotor, so when the rotor rotates once, that is, the crankshaft rotates 72, the induction coil generates 24 AC voltage signals. As shown in fig. 6(b), the pulse of one cycle of the Ne signal is equivalent to 3 crank angle (72÷24 = 3). More accurate angle detection is to use the time of 3 angle to divide it into 3 equal parts by ECU, that is, to generate a signal of 1 crankshaft angle. Similarly, the engine speed is measured by ECU according to the elapsed time of two pulses (6 crank angle) of Ne signal.

G signal is used to judge the cylinder and detect the top dead center position of the piston, which is equivalent to the 12 signal of Nissan magnetic pulse crankshaft position sensor. G signal is generated by the flange wheel (No.1 timing rotor) located above the Ne generator and its two opposite symmetrical induction coils (G1 induction coil and G2 induction coil). Its structure is shown in fig. 7. The principle of signal generation is the same as that of Ne signal. The G signal is also used as a reference signal when calculating the crank angle.

G1 and G2 signals respectively detect the top dead center of cylinder 6 and cylinder 1. Because of the position of G1 and G2 signal generators, when the G1 and G2 signals are generated, the piston actually does not just reach the top dead center (BTDC), but is located 1 degrees before the top dead center. Fig. 8 shows the relationship between signals of crankshaft position sensors G1, G2 and Ne and crankshaft angle.

2. Detection of magnetic pulse crankshaft position sensor

Taking the magnetic pulse crankshaft position sensor used in electronic control system of 2JZ-GE engine of Crown 3. car as an example, the detection method is explained. The circuit of crankshaft position sensor is shown in Figure 9.

(1) Resistance check of the crankshaft position sensor

Turn OFF the ignition switch, unplug the wire connector of the crankshaft position sensor, and measure the resistance between the terminals on the crankshaft position sensor with a multimeter (Table 1). If the resistance value is not within the specified range, the crankshaft position sensor must be replaced.

table 1 resistance value of crankshaft position sensor

terminal conditional resistance value (ω)

G1-g-cold state 125-2

hot state 16-235

G2-G- cold state 125-2

hot state 16-235

ne-. Detection of output signal

unplug the wire connector of the crankshaft position sensor, and when the engine rotates, use the voltage range of multimeter to detect whether there is pulse voltage signal output between G1-G-, G2-G- and Ne-G- terminals of the crankshaft position sensor. If there is no pulse voltage signal output, the crankshaft position sensor must be replaced.

(3) Clearance inspection between the induction coil and the timing rotor

Measure the air gap between the timing rotor and the protruding part of the induction coil with a thickness gauge (Figure 1), and the gap should be .2-.4 mm.. If the clearance does not meet the requirements, the distributor housing assembly must be replaced.

ii. photoelectric crankshaft position sensor

1. Structure and work of photoelectric crankshaft position sensor

(1) Structure and work of photoelectric crankshaft position sensor of Nissan Company

The photoelectric crankshaft position sensor of Nissan Company is arranged in the distributor, which consists of a signal generator and a signal disk with a gap and a light hole (Figure 11). The signal panel is installed on the distributor shaft, and there are 36 gaps around it, generating a signal of 1 (crank angle); There are six light holes (at intervals of 6) slightly inside the periphery, which generate 12 signals, and one wide light hole generates 12 signals corresponding to the top dead center of the first cylinder, as shown in Figure 12.

the signal generator is fixedly installed on the distributor housing, and is mainly composed of two light-emitting diodes, two photosensitive diodes and an electronic circuit (fig. 13). The two light emitting diodes are opposite to the photodiode respectively, and the light emitting diodes take the photodiode as the irradiation target. The signal panel is located between the light-emitting diode and the photosensitive diode. When the signal panel runs with the engine crankshaft, because there are light holes on the signal panel, it produces alternating changes of light transmission and light shielding, which causes the signal generator to output pulse signals representing the position and rotation angle of the crankshaft. Fig. 14 shows the working principle of the photoelectric signal generator.

when the light beam of the light emitting diode irradiates on the photosensitive diode, the photosensitive diode is photosensitive and turned on; When the light beam of the LED is blocked, the photodiode is turned off. The pulse voltage signal output by the signal generator is sent to the electronic circuit for amplification and shaping, and then the crank angle 1 signal and the crank angle 12 signal are sent to the electronic control unit. Because of the installation position of the signal generator, the 12 signal is output 7 before the piston top dead center. For every two revolutions of the engine crankshaft and one revolution of the distributor shaft, the 1 signal generator outputs 36 pulses, with the high potential corresponding to 1 and the low potential corresponding to 1 in each pulse period, and * * * indicates that the crankshaft rotation angle is 72. At the same time, the 12 signal generator * * * generates six pulse signals.

(2) Structure and work of photoelectric crankshaft position sensor for modern SONATA automobile

The working principle of photoelectric crankshaft position sensor for modern SONATA automobile is similar to that of photoelectric crankshaft position sensor of Nissan Company, but the structure of its signal panel is slightly different, as shown in Figure 15. For an automobile with a distributor, the sensor assembly is installed in the distributor shell; For cars without distributor, the sensor assembly is installed at the left end of the camshaft (looking back from the front of the car). There are four holes in the outer ring of the signal panel, which are used to sense the crank angle and convert it into a voltage pulse signal. The electronic control unit calculates the engine speed according to this signal, and controls the gasoline injection timing and ignition timing. There is a hole in the inner ring of the signal panel for sensing the compression top dead center of the first cylinder (on some SONATA cars, there are two holes for sensing the compression top dead centers of the first and fourth cylinders in order to improve the accuracy), and it is converted into a voltage pulse signal and input to the electronic control unit, which calculates the gasoline injection sequence according to this signal. Its output characteristics are shown in Figure 16.

the line connection of the crankshaft position sensor is shown in fig. 17. There are two light-emitting diodes and two light-sensitive diodes in it. When the light-emitting diode irradiates a hole in the light hole of the signal panel, the light will irradiate the light-sensitive diode to make the circuit conductive.

2. Detection of photoelectric crankshaft position sensor

(1) Inspection of the wiring harness of crankshaft position sensor

Figure 18 shows the terminal position of the photoelectric crankshaft position sensor connector (plug) of Hyundai SONATA automobile in Korea. During the inspection, disconnect the wire connector of the crankshaft position sensor, turn the ignition switch to "ON", measure the voltage between the 4# terminal on the harness side and the ground with the voltage range of multimeter (Figure 19), the voltage between the 2# terminal and the 3# terminal on the harness side and the ground with 4.8-5.2V, and measure the voltage between the 1# terminal on the harness side and the ground with the resistance range of multimeter.

(2) Detection of output signal of photoelectric crankshaft position sensor

Connect the voltage of multimeter to the 3# terminal and 1# terminal on the sensor side. When starting the engine, the voltage should be .2-1.2V. During the idle running after starting the engine, the voltage of terminal 2 and terminal 1 should be 1.8-2.5V by using the multimeter voltage range. Otherwise, replace the crankshaft position sensor.

iii. detection of hall crankshaft position sensor

hall crankshaft position sensor uses the principle of hall effect to generate voltage pulse signal corresponding to crankshaft angle. It uses trigger blades or gear teeth to change the magnetic field intensity passing through the Hall element, so that the Hall element generates a pulsed Hall voltage signal, which is the output signal of the crankshaft position sensor after amplification and shaping.

1. Structure and work of Hall-type crankshaft position sensor

(1) Hall-type crankshaft position sensor with trigger blade

Hall-type crankshaft position sensor of American GM Company is installed at the front end of crankshaft and adopts the structure of trigger blade. At the front end of the crankshaft pulley of the engine, there are two inner and outer signal wheels with trigger blades, which rotate together with the crankshaft. 18 trigger blades and 18 windows are evenly distributed on the outer edge of the outer signal wheel, and the width of each trigger blade and window is 1 arc length; There are three trigger blades and three windows on the outer edge of the inner signal wheel. The widths of the three trigger blades are different, which are 1, 9 and 11 arc lengths respectively, and the widths of the three windows are also different, which are 2, 3 and 1 arc lengths respectively. Due to the installation position of the inner signal wheel, the leading edge of the trigger blade with 1 arc length is located 75 before the top dead center (TDC) of the first and fourth cylinders, 75 before the top dead center of the sixth and third cylinders with 9 arc length, and 75 before the top dead center of the fifth and second cylinders with 11 arc length.

Hall signal generator is composed of permanent magnet, magnetic conductive plate and Hall integrated circuit. A Hall signal generator is respectively arranged on the side surfaces of the inner and outer signal wheels. When the signal wheel rotates, whenever the blade enters the air gap between the permanent magnet and the Hall element, the magnetic field in the Hall integrated circuit is bypassed by the trigger blade (or called magnetic isolation), and no Hall voltage is generated at this time; When the trigger blade leaves the air gap, the magnetic relaxation of the permanent magnet 2 passes through the Hall element through the magnetic conductive plate 3, and a Hall voltage is generated at this time. After the Hall voltage signal intermittently generated by the Hall element is amplified and shaped by the Hall integrated circuit, the voltage pulse signal is transmitted to the ECU. The external signal wheel generates 18 pulse signals (called 18X signals) every revolution, and one pulse period is equivalent to the time for the crankshaft to rotate by 2 degrees. The ECU divides one pulse period into 2 equal parts, so that the time corresponding to the crankshaft rotating by 1 degree can be obtained, and the ignition time can be controlled according to this signal. The function of this signal is equivalent to the function of photoelectric crankshaft position sensor to generate 1 signal. The inner signal wheel generates three voltage pulse signals (called 3X signals) with different widths every revolution, and the pulse period is 12 crank angle. The rising edge of the pulse is generated at 75 before the top dead center of cylinders 1, 4, 3, 6 and 2, 5 respectively, which is used as the reference signal for ECU to distinguish cylinders and calculate the ignition time. This signal is equivalent to the 12 signal generated by the photoelectric crank position sensor mentioned above.

(2) Hall-type crankshaft position sensor with trigger teeth

The Hall-type crankshaft position sensor of Chrysler Company is installed on the flywheel housing and adopts the structure of trigger teeth. At the same time, a synchronous signal generator is set in the distributor to assist the crankshaft position sensor to distinguish the cylinder number. The Hall crankshaft position sensor of Beijing Cherokee car has eight slots on the flywheel of a 2.5L four-cylinder engine, which are divided into two groups. Every four slots are a group, and the two groups are separated by 18 degrees. The phases in each group