What is a hall sensor in a car
When American physicist Edwin Hall discovered his effect of interaction of electric current with magnetic field, he had no idea that his name would be most often used in car markets in Russia. Surprisingly, the fact is that a variety of people who are quite distant from physics and have no idea who Hall is, know what a Hall sensor is in a car, and even at one time suffered from their deficiency.
What is the Hall effect and how can it be used in technology
The magnetic field is widely used in automotive technology, despite its invisibility and intangibility. Even light, composed of electric and magnetic fields, is perceived due to its electrical component. Nevertheless, with the help of special magnetically sensitive sensors the field can be detected and even measured.
One of such sensors is based on the Hall effect, which consists in the appearance of a transverse potential difference on a semiconductor crystal, along which current flows. It is formed only when the crystal is placed in a magnetic field, everything else does not polarize the doped silicon wafer. This voltage is subject to fixation, which means that the sensor is in the zone of the magnetic field.
Actually, all this is not enough to use the crystal as a sensor. Magnetic field is present everywhere, it is necessary to determine its excess over the natural background and interference. To do this, a weak signal amplifier and an adjustable threshold element (comparator) are connected to the plate. The whole circuit outputs a logical “0” on the electrical level, if the field is present, and a logical one in all other cases. This negative logic is usually adopted in digital technology. And to prevent the output from “chattering” due to uncertainty when the signal changes, the device is equipped with a Schmitt trigger. This is a circuit that provides an amplitude delay of response (hysteresis), protecting against digital chattering and noise at the moment of switching, guaranteeing a single steep edge of the signal and unambiguous referencing in time.
Sensor Design and Operation
If all of the above were made with discrete elements, the sensor would be the size of a tape recorder, cost the same, work unreliably and consume a lot of power. In reality, the entire Hall sensor device is made by the methods of integrated microelectronics on the same semiconductor crystal, which, with a light hand of figures from Silicon Valley, has long been accepted to be called a chip.
The sensor itself is so tiny that its size can be neglected against the background of the size of the housing, electrical connector, supply wires and auxiliary permanent magnet. The crystal is completely encapsulated in plastic to protect against external influences, leaving only the connector and magnet pole outside. Depending on the application, the sensor may have a slot inside which the edge of the timing reference disc with grooves will run.
The principle of operation of the Hall sensor in automobiles is that when there is a change in the magnetic field in the working area, for example, the slit of the reference disc instead of its whole part, or a step on the pulley, or a mark on the camshaft flange, the signal at the output will change its value from zero to one or vice versa. Thus, the electronic block, which reads the sensor, learns about the onset of a certain moment in the rotation of the shaft, for example, the top dead center of the piston of a certain cylinder or any of its positions relative to this TDC, the necessary information is set by the engine designers. This is the basis for the engine control unit’s calculation of important information, such as ignition timing, injection intervals and injector opening sequence.
Different applications of Hall effect sensors
For the first time such a sensor was used on cars with carburetor engines to replace the ignition system contacts. Then other applications of magnetically sensitive sensors appeared.
Hall sensor in the ignition system of a carbureted engine
The classical battery ignition system operates on the principle of energy storage in the magnetic field of the ignition coil through current flow in its primary winding, followed by a sharp break in the circuit, which causes the secondary winding voltage to rise and spark discharge in the spark plug. The breaker contacts in this case work in extremely bad conditions, they burn out, wear out and do not live long. In addition, their capabilities limit the growth of the system power, and thus the engine operation with further depletion of the mixture for fuel economy.
The problem has been partially solved by the electronic contactless ignition system with a breaker based on the Hall sensor (DH). There are no more contacts that burn and require adjustment of the gap, there is only a reference disc that rotates in the slot of the sensor. While the solid wall of the disc passes the magnet, the ignition switch, which is a simple current amplifier controlled by the sensor signal, rests, that is, it waits for the moment of the beginning of energy accumulation. At the leading edge of the slot, the commutator output switch opens, and the energy accumulation in the coil begins.
The current increases not to infinity. Reaching the calculated nominal value of about half a dozen of amperes, it stabilizes, and at the moment of the second edge of the slot the sensor triggers, the key opens, the voltage on the coil windings begins to grow up to the breakdown of the spark gap.
The Hall sensor here fully justifies its abilities, it is very accurate and stable in setting the triggering moments of all the system elements, and hence the smooth operation of the engine without ignition skips and detonation. The magnetic choke itself does not wear out, and serves theoretically forever, saving the drivers and repairmen from all the troubles of a classical contact breaker-distributor (trambler). Only defective parts and suspiciousness made people buy the sensors for testing and for spare parts, creating a shortage, which was mentioned earlier.
As a crankshaft position sensor (CDPS)
Most often the simplest and most reliable inductive DPKV is used here. This is an ordinary coil with a thin wire wound on a permanent magnet. The gear of the crankshaft pulley, on which one tooth is missing, passes by it. The output signal is a sequence of alternating current pulses, one of which has increased duration and amplitude. The computer of the electronic engine control unit (ECU) will have no difficulty in linking all the processes in time to the phases of the crankshaft position with such a timing diagram.
However, some developers did not like this simplicity, perhaps they wanted more accuracy, so they used the same crankshaft position sensor. The principle is the same, the teeth of the master pulley close and open the magnetic flux through the sensor, changing its digital output signal. This produces a sequence of pulses, slightly different in form, but carrying exactly the same information and serving the same purpose. It’s the engine’s main sensor, the only one without which the engine won’t even start, so the Hall sensor is what’s needed here, increased reliability is very important.
Signalization of the camshaft position
Another job for which the Hall sensor is very well suited is another one for which it is often used. This is the synchronization of phased multipoint fuel injection.
In general, injection systems can be very different:
- Single-point, or mono-injection, not much different from a carburetor, there is one central module where the injector sprays gasoline into the intake manifold, from where it is evenly, or not so much, sucked up by the cylinders;
- multipoint, here each cylinder has its own injector, which is triggered after the end of the exhaust stroke to prepare the mixture for the intake;
- multi-point phased, for its implementation, just the Hall sensor is required.
The disadvantage of conventional injection is the lack of its precise synchronization with the moment of the start of injection into a particular cylinder. The fact is that the information for the ECU comes from the crankshaft sensor, and by its position it is impossible to accurately time a particular stroke in the cylinder, because the full cycle requires two revolutions of the shaft, which in terms of the BCI are exactly the same and do not differ. Therefore, injection will occur twice per cycle, and once is completely useless, on the intake valve closed before the stroke.
To improve the system, the camshaft position sensor was applied, of course, on the Hall effect. The design is already known, a disc repertory and a magnetic DC with an output to the ECU. Now the ECU knows exactly how to distinguish the compression TDC from the exhaust TDC and each injector will open strictly at the right moment. The gasoline will not have time to settle uselessly on the manifold walls.
How do you check the throttle valve in case of suspicion?
This device is very reliable, but there is no absolute protection against malfunction. Therefore, sometimes it is necessary to check these sensors as well.
- The simplest thing is to replace the sensor with a known good one. This will save you the trouble with probes, probes and oscilloscopes. And the sensor is inexpensive, it is always useful to have it in stock, if not for replacement, then just to check the faulty injection or ignition system.
- People who know how the Hall sensor works, can check it with simple and not so simple devices. For example, with a test probe with an LED. The output of the sensor is an open-collector cascade. This means that in the physical zero position the transistor is open, and if the probe is connected between the plus power supply and the DC output, the LED will light up. By moving the reverb in front of the sensor poles, you can make it blink, which will almost certainly indicate that the GC and the connected wiring circuits are working properly.
- The word “almost” was used in the sense that the only way to be sure is to use a digital oscilloscope, which many diagnosticians have as an attachment to a laptop. With it, you can check a parameter which is inaccessible with styli – the speed of the sensor. The voltage fronts should be steep enough, which the oscilloscope will show. A “clipped” front may be the very case where the sensor seems to work, and the probe or multimeter confirms it, but the system fails and lights up errors.
Almost all the cases explaining what a Hall sensor in a car is have been considered, it remains to mention the quite possible less obvious presence of these small devices in auto electronics. Many cars are equipped with fairly powerful electric motors, which also use Hall sensors to operate the power electronics, tracking the position of the rotor in the magnetic field. And even this, perhaps, is not the end of the penetration of the DC in the car. A compact, reliable and accurate device will always find an area of work in an increasingly electronics-enriched modern car.
How to Check a Hall Sensor in a Car
You will learn how Hall sensor works, where it is installed in your car and how to check it independently (by simple and available methods) from our article.
Any modern car is “stuffed” with a variety of sensors. Signals from them go to ECU, onboard computer or directly to instrument panel. In this article we will talk about the Hall sensor, its use in a car and ways to independently check the performance of this sensor.
Principle of operation
The principle of the Hall effect (it got its name after the scientist who first discovered it back in the second half of the XVIII century):
- If a DC voltage source is connected to a semiconductor rectangular plate (at points A and B), the electric current flowing through it will be a straight-line counter motion of negatively and positively charged particles (that is, electrons and “holes”).
- A voltmeter connected to points C and D shows “0” (this means no voltage).
- If a permanent magnet is brought to the plate, the field it creates deflects the movement of charged particles to the outer faces of the semiconductor rectangle. As a result, a potential difference arises between points C and D, that is, a voltage (Vh) is observed. This is recorded by a voltmeter.
Many sensors in cars work on the basis of the Hall effect described above. Naturally, the voltage on the semiconductor plate is minimal and not enough to directly feed it to the on-board computer. Modern technology has made it possible to create a chip based on the effect, consisting of several functional devices:
- The semiconductor Hall plate itself, which is made of gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs);
- A voltage amplifier;
- Schmidt trigger;
- voltage regulator (to prevent failure in case of sudden spikes in the onboard voltage);
- output switching transistor.
As a result, when the intensity of the magnetic field acting on the semiconductor plate changes, zeros and ones “understandable” to the onboard computer are obtained at the device output.
Technologically, modern Hall sensors are a microcircuit with three pins for:
- supply voltage connection;
- Detection of the signal converted by the sensor.
In modern automobiles, Hall sensors find quite a wide application. They are used:
- In distributors (or as it is popularly called trammlers) of contactless ignition systems of gasoline engines.
- To control the engine speed and output the readings directly to the tachometer of the dashboard.
- In diesel engines, as sensors to determine the position of the crankshaft and camshaft, so that the onboard computer “could” determine the position of the first cylinder and synchronize the work of injectors. More details about this is explained in the video below:
- In ABS systems.
- To synchronize the operation of individual components of automatic transmissions.
Hall sensor in the ignition system
In modern non-contact ignition systems, a Hall sensor is used instead of a mechanical separator. The sensor itself is mounted on the tumbler housing and has a special slot with a permanent magnet on one side and a chip with a sensing element on the other. A metal crown with rectangular teeth and slots (according to the number of engine cylinders) is fixed on the chopper axis. The principle of operation itself is quite simple. As the distributor rotor rotates, the metal teeth of the crown pass through the Hall sensor gap.
- When the slot between the permanent magnet and the chip is free (this occurs at the moment when the slot of the rotating crown passes through the sensor gap), there is no voltage at the sensor output (or it is minimal). ECU “perceives” such signal as a logical zero.
- And vice versa, when the metal plate enters the sensor gap and overlaps the magnetic flux, there is a significant voltage at the device output, which is fed to the ECU. The unit “turns on” the high-voltage coil and the air-fuel mixture is ignited in the desired cylinder.
For information! There are sensors (depending on car brand and its “brain” firmware), which algorithm of work looks “exactly the other way round” (compared to above described).
How to check independently
Quite a standard situation: the engine starts badly, runs unstable or periodically stalls. The described symptoms may well be caused by a malfunction of the Hall sensor installed in the ignition distributor. How to check its functionality? The most correct (from the technical point of view) is to do it with an oscilloscope. However, such an expensive measuring device is rarely found in the “household” of a motorist. But, almost everyone has a standard multimeter. It is with his help, you can easily check the performance of the sensor. To do this, first collect the circuit:
Then everything is simple:
- We turn on power supply (or just connect wires to the battery removed from the car): in this case voltmeter readings should be close to zero (as a rule, not more than 0,3÷0,4 V).
- Insert a flat metal object (a metal saw or a knife will do) into the slot in the sensor. If the instrument readings increase sharply (the voltage value depends on the brand of the sensor being tested), then the Hall sensor is faulty. Otherwise, you can conclude that the malfunctions of the engine were caused by it, and, therefore, it should be replaced with a new one.
If you do not have a multimeter, you can use an LED instead (designed for a direct voltage of about 12 V and costing about 10÷12 rubles) to check the sensor according to a similar algorithm.
A side note! As a power supply you can use a regulated laboratory unit or, in a pinch, a 9V Crone-type battery.
Checking crankshaft and camshaft position sensors
The sensors of camshaft and crankshaft position based on the Hall effect work in a slightly different way (in comparison to sensors that are installed in distributors of non-contact ignition systems).
- A special toothed ferromagnetic disc is mounted on the shaft. Moreover, one or two teeth are missing in a strictly defined place.
- In the immediate vicinity of the end of the disc, a Hall sensor (with minimum clearance) is mounted.
- As the shaft rotates, either a protruding tooth of the disk or a slot is consecutively opposite the sensor. As a consequence, the magnetic field acting on the sensing element is constantly changing, and voltage pulses of equal duration and duty cycle are generated at the sensor output.
- When a sector of the disk with a missing tooth passes by the sensor element, the device generates a pulse of greater duration. This moment is the “starting point” for the ECU to determine the shaft position.
Checking the position sensor (or as it is also called phase sensor) can also be done by yourself. You will learn the details from the video below: