What is the function of the vehicle crankshaft sensor?
The crankshaft sensor (also known as the engine speed sensor) is the core sensor of the engine electronic control system. It is mainly used to detect the position of the crankshaft, the top dead center signal of the piston, and the engine speed, and transmits signals to the ECU to control ignition and fuel injection timing. This sensor is usually installed at the front end of the crankshaft, the front end of the camshaft, the flywheel, or the distributor. It needs to work in coordination with the camshaft position sensor.
According to its working principle, it can be classified into three types: magnetic pulse type, Hall type, and photoelectric type: The magnetic pulse type generates a sine wave signal by triggering a magnetic field change through a signal disc. The Hall type outputs a square wave signal by using a trigger blade. The photoelectric type generates a pulse voltage by using a light hole transmission. The Hall type requires an external 5V power supply, and the photoelectric type is susceptible to signal accuracy degradation due to oil contamination. Typical faults include signal interference caused by aging wiring, and difficulty starting due to dirty sensor. Abnormal situations may trigger the engine fault light and cause insufficient power or inability to start. The modern technology route shows an evolution trend from analog signals to digital detection.
The detection principle of the magnetic pulse type crankshaft position sensor
Nissan Company magnetic pulse type crankshaft position sensor
This crankshaft position sensor is installed behind the pulley at the front end of the crankshaft. At the rear end of the pulley, there is a thin circular disc with fine teeth (used to generate signals, called the signal disc), which is installed together with the crankshaft pulley on the crankshaft and rotates with the crankshaft. On the outer edge of the signal disc, there is a tooth every 4° along the circumference. There are a total of 90 teeth, and 3 protrusions are arranged at every 120°, totaling 3. The sensor box installed on the edge of the signal disc is a signal generator that produces an electrical signal. The signal generator has 3 magnetic heads wound around the permanent magnet on the induction coil, where magnetic head ② generates a 120° signal, and magnetic heads ① and ③ jointly generate a 1° crankshaft angle signal. Magnetic head ② is facing the 120° protrusion of the signal disc, magnetic head ① and ③ are facing the gear ring of the signal disc, with a phase difference of the crankshaft angle installation. The signal generator has signal amplification and shaping circuits, and an external four-hole connector, with hole "1" being the 120° signal output line, hole "2" being the power line for the signal amplification and shaping circuit, hole "3" being the 1° signal output line, and hole "4" being the ground line. Through this connector, the signal generated by the crankshaft position sensor is transmitted to the ECU.
When the engine rotates, the teeth and protrusions of the signal disc cause a change in the magnetic field passing through the induction coil, thereby generating an alternating electromotive force in the induction coil. After filtering and shaping, it becomes a pulse signal. After one rotation of the engine, magnetic head ② generates 3 120° pulse signals, and magnetic heads ① and ③ each generate 90 pulse signals (alternating). Since magnetic heads ① and ③ are installed at a 3° crankshaft angle interval and each generate a pulse signal every 4°, the phase difference between the pulse signals generated by magnetic heads ① and ③ is exactly 90°. These two pulse signals are sent to the signal amplification and shaping circuit for synthesis, and then a 1° crankshaft angle signal is generated.
The magnetic head ② that generates the 120° signal is installed at 70° before the top dead center, so its signal can also be called the 70° before top dead center signal, that is, during the engine operation, magnetic head ② generates a pulse signal at the top dead center of each cylinder.
Toyota Company magnetic pulse type crankshaft position sensor
Toyota Company's TCCS system installs the magnetic pulse type crankshaft position sensor in the distributor. The sensor is divided into upper and lower parts, the upper part generates G signal, and the lower part generates Ne signal, both using a rotor with teeth rotating to cause the signal generator's induction coil to have a magnetic flux change, thereby generating an alternating induced electromotive force in the induction coil, which is then amplified and sent to the ECU.
The Ne signal is the signal for detecting the crankshaft angle and engine speed, equivalent to the 1° signal of the Nissan Company's magnetic pulse type crankshaft position sensor. This signal is generated by a rotor (N0.2 timing rotor) fixed at the lower part with 24 evenly spaced teeth and an adjacent sensing coil.
When the rotor rotates, the air gap between the teeth and the flange part (magnetic head) of the sensing coil changes, causing a change in the magnetic field passing through the sensing coil and generating an induced electromotive force. When the teeth approach and move away from the magnetic head, there will be a change in the increase and decrease of magnetic flux, so that each tooth will generate a complete AC voltage signal in the sensing coil when passing through the magnetic head. The N0.2 timing rotor has 24 teeth, so when the rotor rotates one full circle (i.e., the crankshaft rotates 720°), the sensing coil generates 24 AC voltage signals. One pulse of the Ne signal in a cycle is equivalent to 30° of crankshaft rotation (720° ÷ 24 = 30°). More precise angle detection is achieved by dividing the 30° rotation time by the ECU into 30 equal parts, thus generating a 1° crankshaft rotation signal. Similarly, the engine speed is measured by the ECU based on the time elapsed between two pulses of the Ne signal (60° crankshaft rotation). The G signal is used to identify cylinders and detect the top dead center position of the piston, equivalent to the 120° signal of Nissan's magnetic pulse crankshaft position sensor. The G signal is generated by a flange rotor (No.1 timing rotor) above the Ne generator and its symmetrical two sensing coils (G1 sensing coil and G2 sensing coil). The principle of generating the signal is the same as that of the Ne signal. The G signal is also used as a reference signal for calculating the crankshaft angle.
The G1 and G2 signals respectively detect the top dead center of the 6th cylinder and the 1st cylinder. Due to the position of the G1 and G2 signal generator, when the G1 and G2 signals are generated, the piston is not exactly at the top dead center (BTDC), but at a position 10° before the top dead center.
Detection of magnetic pulse crankshaft position sensor
Take the magnetic pulse crankshaft position sensor used in the electronic control system of the 2JZ-GE engine of the Crown 3.0 sedan as an example to illustrate its detection method.
Resistance check of the crankshaft position sensor
Turn off the ignition switch, remove the connector of the crankshaft position sensor, and measure the resistance values between the terminals of the crankshaft position sensor with a multimeter's resistance setting (Table 1). If the resistance values are not within the specified range, the crankshaft position sensor must be replaced.
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