1. Function and Identification of Crankshaft Position Sensor
The crankshaft position sensor, also known as the engine speed sensor, is one of the most important sensors in the engine centralized control system. It is used to detect the signals of piston top dead center and crankshaft angle and input them into the engine ECU for controlling ignition timing and fuel injection timing. It is also a signal source for measuring engine speed.
2. Electromagnetic induction crankshaft position sensor
(1) Installation location
Electromagnetic induction crankshaft position sensors are typically installed at the front end of the crankshaft or on the engine flywheel housing, as shown in the figure below.
(2) Structural principle
Electromagnetic induction sensors, also known as magnetic pulse sensors, are mainly composed of a signal rotor made of magnetically conductive material, a permanent magnet, and a signal coil. The sensor's position is fixed, and a certain gap must be maintained between the soft magnetic core and the teeth of the signal rotor.
Sensor connectors are mainly wired in two ways: two-wire and three-wire. In a two-wire system, the two wires are the signal return lines, with the signal alternating between positive and negative. In a three-wire system, the additional wire is the shielding wire.
(3) Detection
① Toyota Models: The 2016 Toyota Camry Hybrid (engine model 6AE-FSE) uses an electromagnetic induction crankshaft position sensor. Sensor terminal #1 provides a 5V reference power to terminal 110 of the engine control unit connector E81; sensor terminals #3 and #2 are the positive and negative signals, respectively, and are connected to terminals #76 and #109 of the engine control unit connector E81.
Sensor resistance testing: Turn off the ignition switch, unplug the sensor connector, and check the resistance between terminals 1 and 2 of the sensor connector. The standard resistance is 1.6–2.7 kΩ at -10℃ to 50℃; and 2.0–3.2 kΩ at 50℃ to 100℃. If the resistance is infinite, it indicates an open circuit in the signal coil, and the sensor should be replaced.
② Volkswagen Series: The diagram below shows the G28 circuit of the crankshaft position sensor in the FAW-Volkswagen New Magotan. Terminal T2yf/1 is one pole of the sensor, connected to terminal T60ya/51 of the ECU; terminal T2yf/2 is the other pole of the sensor, connected to terminal T60ya/36 of the ECU.
The detection method of the electromagnetic induction crankshaft position sensor is as follows:
a. Fault symptom detection: When the crankshaft position sensor malfunctions during engine operation, it will cause signal interruption, engine failure to start, or immediate shutdown during operation. At this time, the electronic control unit can diagnose the fault and store the code.
b. Crankshaft position sensor resistance check: Turn off the ignition switch, unplug the sensor connector, and check the resistance between terminals 1 and 2 on the sensor. It should be 980~1600Ω. If the resistance is infinite, it indicates an open circuit in the signal coil, and the sensor should be replaced.
c. Output voltage measurement: Using the AC voltage setting of a multimeter, with the circuit properly connected and the engine running, measure the voltage between terminal #1 and terminal #2. The voltage value should fluctuate between 0.2 and 2V.
3. Hall effect crankshaft position sensor
The Hall effect refers to the phenomenon where a thin metal or semiconductor sheet is placed perpendicularly in a magnetic field with magnetic induction intensity B. When a current I flows through it perpendicular to the magnetic field, an electromotive force UH is generated between the opposite sides of the sheet. This generated electromotive force is called the Hall electromotive force, and such a sheet (usually semiconductor) is called a Hall plate or Hall element. Based on the different structures of the signal triggers, they can be divided into two types: trigger blade type and trigger wheel type.
(1) Trigger blade type
The Hall effect crankshaft position sensor mainly consists of a trigger impeller, a Hall integrated circuit, and a permanent magnet, as shown in the figure below.
Each of the inner and outer signal wheels has a signal generator mounted on its side. When the signal wheel rotates, whenever a blade enters the air gap between the permanent magnet and the Hall element, the magnetic field in the Hall integrated circuit is blocked, and no voltage is generated. When the blade leaves the air gap, the magnetic flux in the permanent magnet passes through the magnetic guide plate and into the Hall element, generating a voltage. This voltage is amplified by the integrated circuit and sent as a pulse signal to the control unit. The outer signal wheel generates 18 pulse signals per revolution, known as the 18X signal. One pulse corresponds to a 20° crankshaft rotation angle. The engine control unit calculates the time corresponding to a 1° crankshaft rotation. Based on this signal, the engine control unit can precisely control the ignition timing.
(2) Trigger gear type
The structure of the Hall crankshaft position sensor is similar to that of the electromagnetic induction crankshaft position sensor, consisting of a signal rotor with protruding teeth and a Hall signal generator.
The flywheel of a four-cylinder engine has eight toothed grooves on its outer edge, divided into two groups, spaced 180° apart. Each toothed groove in each group is 2° wide, and the two grooves are 18° apart.
The flywheel of a six-cylinder engine has 12 toothed grooves on its outer edge, divided into three groups, each group spaced 120° apart. Each toothed groove in each group is 2° wide, and there is also an 18° gap between two toothed grooves.
When the flywheel tooth passes through the sensor's magnet, the Hall sensor outputs a 5V high level; when the flywheel tooth leaves the magnet, the Hall sensor outputs a 0.3V low level. Each time a flywheel tooth passes the sensor, the sensor generates a high or low level signal.
4. Photoelectric crankshaft position sensor
Photoelectric crankshaft position sensors were used in early engines with distributors.
(1) Nissan's photoelectric crankshaft position sensor
Nissan's photoelectric crankshaft position sensor is located inside the distributor. It consists of a signal generator and a signal disk (shielding disk) with optical apertures, as shown in the diagram. The signal disk is mounted on the distributor shaft and has 360 slots on its outer perimeter. Adjacent slots generate a 1° crankshaft angle signal. Slightly inward from the outer perimeter, six optical apertures (for six cylinders) are distributed at 60° crankshaft angle intervals, generating a 120° crankshaft angle signal. One of these apertures, which is wider, generates the 120° crankshaft angle signal corresponding to the top dead center of the first cylinder's compression stroke.
Nissan vehicles feature photoelectric crankshaft position sensor signal discs.
The pulse signal generator is fixed to the distributor housing and mainly consists of two light-emitting diodes (LEDs), two photodiodes, and electronic circuitry. The two LEDs face the two photodiodes, with the LEDs using the photodiodes as their illumination targets. A signal disk is located between the LEDs and the photodiodes. As the signal disk rotates with the engine crankshaft, the presence of apertures on the disk creates alternating light transmission and blocking, causing the signal generator to output pulse signals corresponding to the crankshaft position and rotation angle.
(2) Photoelectric crankshaft position sensor for Hyundai Sonata
The working principle of the photoelectric crankshaft position sensor in the Hyundai Sonata is similar to that of Nissan's photosensitive crankshaft position sensor, although the structure of its signal disc differs slightly, as shown in the diagram below. The outer ring of the signal disc has four arc-shaped slots used to detect the crankshaft angle and convert it into voltage pulse signals. The electronic control unit (ECU) uses these signals to calculate the engine speed and control the fuel injection timing and ignition timing. The inner ring of the signal disc has a hole used to detect the compression top dead center (TDC) of cylinder 1 (some Sonatas have two holes to detect the TDC of cylinders 1 and 4 for improved accuracy), and converts this into a voltage pulse signal which is then input to the ECU. The ECU uses this signal to calculate the fuel injection sequence.
Hyundai vehicles feature photoelectric crankshaft position sensor signal discs.
