Crankshaft and camshaft position sensors
1, function and type
Crankshaft position sensor (CPS), also known as engine speed and crank angle sensor, is used to collect crank angle and engine speed signals and input them into electronic control unit (ECu) to determine ignition time and fuel injection time.
Camshaft position sensor (CPS) is also called cylinder identification sensor (CIS). In order to distinguish it from the crankshaft position sensor (CPS), the camshaft position sensor is generally represented by CIS. The function of camshaft position sensor is to collect the position signal of valve camshaft and input it to ECU, so that ECU can identify the compression top dead center of 1 cylinder, and then carry out sequential fuel injection control, ignition timing control and deflagration control. In addition, the camshaft position signal is also used to identify the first ignition time when the engine is started. Because the camshaft position sensor can identify which cylinder piston is about to reach the top dead center, it is called cylinder identification sensor.
2. Photoelectric crankshaft and camshaft position sensors
Structural characteristics of (1)
The photoelectric crankshaft camshaft position sensor produced by Nissan Company is improved from the distributor, which is mainly composed of signal panel (i.e. signal rotor), signal generator, distributor, sensor housing and wire harness plug.
The signal panel is the signal rotor of the sensor and is press-fitted on the sensor shaft, as shown in Figure 2-22. An inner circle and an outer circle of light holes with evenly spaced radians are made near the edge of the signal disk. Among them, the outer ring is made of 360 light-transmitting holes (gaps) with an interval radian of 1. (0.5% of light holes. , sunshade hole accounts for 0.5. ) for generating crank angle and speed signals; The inner ring is made of six light-transmitting holes (rectangular L) with an interval of 60 radians. , used to generate the top dead center signal of each cylinder, in which the rectangle with a slightly longer width is used to generate the top dead center signal of 1 cylinder.
The signal generator is fixed on the sensor housing and consists of Ne signal generator (rotation speed and rotation angle signal), G signal generator (top dead center signal) and signal processing circuit. The Ne signal and G signal generators are composed of light emitting diodes (LEDs) and phototransistors (or photodiodes), and the two LEDs are opposite to the two phototransistors respectively.
(2) Working principle
The working principle of photoelectric sensor is shown in Figure 2-22. The signal panel is installed between the light emitting diode (led) and the phototransistor (or photodiode). When the light hole on the signal panel rotates between the LED and the phototransistor, the light emitted by the LED will shine on the phototransistor, at this time, the phototransistor is turned on, and its collector outputs a low level (0.1~ 0.3v); When the light shielding part on the signal panel rotates between the LED and the phototransistor, the light emitted by the LED cannot shine on the phototransistor. At this time, the phototransistor is turned off, and its collector outputs a high level (4.8 ~ 5.2V).
If the signal panel rotates continuously, the light-transmitting hole and the light-shielding part will alternately rotate around the LED to transmit light or shield light, and the collector of the phototransistor will alternately output high level and low level. When the sensor shaft rotates with the crankshaft and the valve camshaft, the light-transmitting hole and the light-shielding part on the signal board rotate between the LED and the phototransistor, and the light emitted by the LED will alternately illuminate the phototransistor of the signal generator under the light-transmitting and light-shielding effects of the signal board, and the signal sensor will generate pulse signals corresponding to the positions of the crankshaft and the camshaft.
Because the crankshaft rotates twice and the sensor shaft drives the signal to rotate once, the G signal sensor will generate six pulse signals. The Ne signal sensor will generate a 360 pulse signal. Because the interval radian of G signal lamp holes is 60. , each crankshaft rotation 120. A pulse signal is generated, so the G signal is usually called 120. Signal. Design and installation guarantee 120. The signal is 70 before TDC. (BTDC70.), the signal generated by rectangular smooth hole with slightly longer width corresponds to engine cylinder 1 70 before TDC. So that ECU can control the fuel injection advance angle and the ignition advance angle. Because the interval radian of Ne signal lamp holes is 1. (0.5% of light holes. , sunshade hole accounts for 0.5. ), so in each pulse period, the high and low levels account for 1 respectively. The crankshaft angle of 360 indicates that the crankshaft rotates 720. . Every crankshaft rotation is 120. The G signal sensor generates one signal, and the ne signal sensor generates 60 signals.
3. Magnetic induction crankshaft and camshaft position sensors
Working principle of (1) magnetic induction sensor
The working principle of magnetic induction sensor is shown in Figure 2-23. The paths through which the magnetic lines of force pass are the air gaps between the N-pole stator and the rotor of the permanent magnet, and the air gaps between the rotor teeth and the stator magnetic head, the magnetic head, the 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 flux φ increases, the flux change rate increases (dφ/dt > 0), and the induced electromotive force E is positive (e >；). 0), as shown in figure 2-24 curve abc. 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
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
2) Magnetic induction crankshaft position sensor for Jetta and Santana cars.
1) Structural features of crankshaft position sensor: The magnetic induction crankshaft position sensor of Jetta AT, GTX and Santana 2000GSi cars is installed on the cylinder block near the clutch side in the crankcase, and is mainly composed of a signal generator and a signal rotor, as shown in Figure 2-25.
The signal generator is fixed on the engine block by screws and consists of permanent magnets, induction coils and wire harness plugs. Induction coil is also called signal coil. The permanent magnet has a magnetic head, which is opposite to the toothed signal rotor installed on the crankshaft. The magnetic head is connected with the yoke (magnetic plate) to form a magnetic conduction loop.
The signal rotor is a toothed disc with 58 convex teeth, 57 small backlash and a large backlash evenly distributed on its circumference. Output reference signal with large backlash, corresponding to a certain angle before compression top dead center of engine 1 cylinder or cylinder 4. The radian occupied by a large backlash is equivalent to that occupied by two convex teeth and three small backlash. Because the signal rotor rotates with the crankshaft, the crankshaft rotates once.
(360。 ), the signal rotor also rotates once (360. ), so the crank angle occupied by the convex teeth and backlash on the circumference of the signal rotor is 360. The crank angle of each convex tooth and small backlash is 3. (58×3。 +57×3。 =345。 ), the crankshaft angle occupied by large backlash is 15. (2×3。 +3×3。 = 15。 )。
2) Working condition of the crankshaft position sensor: When the crankshaft position sensor rotates with the crankshaft, according to the working principle of the magnetic induction sensor, 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 coil will output an alternating voltage signal accordingly. Because the signal rotor is provided with a large backlash to generate a reference signal, when the large backlash rotates around the magnetic head, the signal voltage needs a long time, that is, the output signal is a wide pulse signal, corresponding to a certain angle before the compression top dead center of 1 cylinder or cylinder 4. When the electronic control unit (ECU) receives the wide pulse signal, it can know that the top dead center position of 1 cylinder or cylinder 4 is coming soon. Whether 1 cylinder or cylinder 4 is coming soon needs to be determined according to the signal input by the camshaft position sensor. Because there are 58 teeth on the signal rotor, every time the signal rotor rotates (the engine crankshaft rotates), the induction coil will generate 58 AC voltage signals and input them to the electronic control unit.
Whenever the signal rotor rotates with the engine crankshaft, the sensor coil will input 58 pulse signals to the ECU. Therefore, every time the ECU receives 58 signals from the crankshaft position sensor, it can know that the engine crankshaft has turned once. If the ECU receives the 116000 signal from the crankshaft position sensor within1minute, the ECU can calculate the crankshaft speed n as 2000 (n = 1 16000/58 = 2000) r/rain; If the ECU receives 290,000 signals from the crankshaft position sensor every minute, the ECU can calculate that the crankshaft speed is 5000 (n = 290,000/58 = 5000) r/min. By analogy, ECU can calculate the rotational speed of engine crankshaft according to the number of pulse signals received by crankshaft position sensor per minute. Engine speed signal and load signal are the most important and basic control signals of electronic control system. Based on these two signals, ECU can calculate three basic control parameters: basic fuel injection advance angle (time), basic ignition advance angle (time) and ignition conduction angle (ignition coil primary current conduction time).
Jetta AT, GTx, Santana 2000GSi car magnetic induction crankshaft position sensor signal as reference signal, ECU controls fuel injection time and ignition time according to the signal generated by large backlash. When ECu receives the signal generated by large backlash, it controls the ignition time, fuel injection time and primary current conduction time (i.e. conduction angle) of the ignition coil according to the signal of small backlash.
3) Toyota TCCS magnetic induction crankshaft and camshaft position sensor.
The magnetic induction crankshaft camshaft position sensor used in Toyota Computer Control System (1FCCS) is improved from the distributor and consists of upper and lower parts. The upper part is a generator for detecting crankshaft position reference signal (i.e. cylinder identification and top dead center signal, called G signal); The lower part is divided into the crankshaft speed and angle signal of the generator (called Ne signal).
1) structural features of the Ne signal geNerator: the ne signal generator is installed under the g signal generator, and is mainly composed of No.2 signal rotor, ne induction coil and magnetic head, as shown in figure 2-26a. The signal rotor is fixed on the sensor shaft and driven by the valve camshaft. The upper end of the shaft is sheathed with a fire head, and 24 convex teeth are made outside the rotor. The sensing coil and the magnetic head are fixed in the sensor housing, and the magnetic head is fixed in the sensing coil.
2) Generation principle and control process of speed and angle signals: When the engine crankshaft rotates, the valve camshaft drives the sensor signal rotor to rotate, the air gap between the rotor teeth and the magnetic head changes alternately, and the magnetic flux of the sensor coil changes alternately. According to the working principle of magnetic induction sensor, alternating electromotive force will be induced in the sensor coil, and the signal voltage waveform is shown in Figure 2-26b. Because the signal rotor has 24 convex teeth, the induction coil will generate 24 alternating signals every time the rotor rotates. Every rotation of the sensor shaft (360. ) is equivalent to two revolutions of the engine crankshaft (720. ), so the alternating signal (that is, one signal period) is equivalent to the crankshaft rotating 30. (720。 ÷24=30。 ), equivalent to rotor rotation 15. (30。 ÷2= 15。 )。 Every time ECU receives 24 signals from Ne signal generator, it can know that the crankshaft has turned twice and the ignition head has turned once. The internal program of ECU can calculate and determine the engine crankshaft speed and ignition head speed according to the time occupied by each ne signal cycle. In order to accurately control the ignition advance angle and fuel injection advance angle, it is necessary to adjust the crankshaft angle (30. Angle) is smaller. It is very convenient for the microcomputer to complete this work. Every Ne signal (crank angle 30. ) is divided into 30 pulse signals, each pulse signal is equivalent to the crank angle of 1. (30。 ÷30= 1。 )。 If each Ne signal is divided into 60 pulse signals, each pulse signal is equivalent to 0.5 crank angle. (30。 ÷60=0.5。 )。 The specific setting is determined by angle accuracy requirements and program design.
3) Structural features of the G signal generator: The G signal generator is used to detect the top dead center position of the piston and determine which cylinder is about to reach the top dead center position. Therefore, G signal generator is also called cylinder identification and TDC signal generator or reference signal generator. G signal generator consists of signal rotor 1, induction coils G 1, G2 and magnetic head. The signal rotor has two flanges, which are fixed on the sensor shaft. Induction coil G 1 and G2 are separated 180. When installed, the signal generated by G 1 coil corresponds to 10 before the compression top dead center of the sixth cylinder of the engine. The signals generated by the coils G2 and G2 correspond to the lO before the compression top dead center of the first cylinder of the engine. .
4) Principle and control process of cylinder identification and TDC signal generation: The working principle of G signal generator is the same as that of Ne signal generator. When the engine camshaft drives the sensor shaft to rotate, the flange of the G signal rotor (signal rotor 1) alternately passes through the magnetic head of the induction coil, and the air gap between the rotor flange and the magnetic head alternately changes, and alternating electromotive force signals are induced in the induction coils Gl and G2. When the flange of the G signal rotor approaches the magnetic head of the induction coil G 1, a forward pulse signal is generated in the induction coil G 1 because the air gap between the flange and the magnetic head decreases, the magnetic flux increases, and the magnetic flux change rate is positive. When the flange of the G signal rotor approaches the induction coil G2, the air gap between the flange and the magnetic head decreases, the magnetic flux increases, and the magnetic flux change rate is positive, so a positive pulse signal is also generated in the induction coil G2, which is called G2 signal. When the flange part of the G signal rotor passes through the magnetic heads of G 1 and G2, the induced electromotive force in the induction coils G 1 and G2 is zero because the air gap between the flange and the magnetic head is constant, the magnetic flux is constant and the magnetic flux change rate is zero. When the flange part of the G signal rotor leaves the magnetic heads G 1 and G2, the air gap between the flange and the magnetic head increases, the magnetic flux decreases, and the magnetic flux change rate is negative, so the induction coils G 1 and G2 will induce negative AC electromotive force signals. Every time the sensor rotates (360. ) is equivalent to two revolutions of the crankshaft (720. ), because the induction coil G 1 and G2 are separated by 180. G 1 and G2 each generate a forward pulse signal. G 1 signal corresponds to the sixth cylinder of the engine and is used for detecting the top dead center position of the sixth cylinder; G2 signal corresponds to the first cylinder and is used to detect the top dead center position of the first cylinder. The corresponding position detected by the electronic control unit is actually the position when the front end of the G rotor flange is close to and aligned with the magnetic heads of the induction coils G 1 and G2 (at this time, the magnetic flux is maximum and the signal voltage is zero), which corresponds to 10 before the piston compression top dead center. (BT-DCl0.) location.