Senzorul HALL Senzor Hall la arborele cu came. Descoperit de Edwin Hall in 1879, efectul Hall se referă la apariţia unui câmp electric atunci când un conductor strabatut de curent electric este poziţionat într-un câmp magnetic staţionar. Perpendicular pe fluxul de curent, precum şi pe câmpul magnetic, vectorul de tensiune pe conductor este numit tensiune Hall (U H ), după descoperitorul ei. Pin 1 + 5V Symbo l Pin 2 GND Pin 3 Sign al Scopul senzorului Hall este de a caracteriza exact primul cilindru (în termeni de: start injecţie de combustibil, bataie de control, aprindere de control), în coordonare cu senzorul arborelui cotit. Cu toate acestea, senzorul Hall poate efectua si alte funcţii: • de înregistrare a vitezei de transmisie de ieşire; • de detectare a vitezei active în sistemele ABS; • de inregistrare a parametrilor de aprindere.
Transcript
Senzorul HALL
Senzor Hall la arborele cu came.
Descoperit de Edwin Hall in 1879, efectul Hall se referă la apariţia unui câmp electric atunci când un conductor strabatut de curent electric este poziţionat într-un câmp magnetic staţionar. Perpendicular pe fluxul de curent, precum şi pe câmpul magnetic, vectorul de tensiune pe conductor este numit tensiune Hall (UH), după descoperitorul ei.
Pin 1 + 5V
Symbol Pin 2 GND
Pin 3 Signal
Scopul senzorului Hall este de a caracteriza exact primul cilindru (în termeni de: start injecţie de combustibil, bataie de control, aprindere de control), în coordonare cu senzorul arborelui cotit. Cu toate acestea, senzorul Hall poate efectua si alte funcţii:• de înregistrare a vitezei de transmisie de ieşire;• de detectare a vitezei active în sistemele ABS;• de inregistrare a parametrilor de aprindere.
senzor Hall
1. Rotating bell in a distributor with four sectors2. Magnet permanent 3. senzor Hall
FunctionareExemplu de sensor la arborele cu came: Rotorul realizat din material magnetic se roteste in jurul arborelui cu came. Senzorul Hall este situat între rotor şi un magnet permanent. În cazul în care un dinte trece peste elementul senzorului (o placă de semiconductor), se schimbă intensitatea câmpului magnetic perpendicular pe elementul Hall. Acest lucru produce o tensiune Hall în senzor.
A – Sensor housingB – Permanent magnetC – Evaluation circuitD - Hall IC
However, this voltage is very low, being in the order of a few millivolts. The sensor contains an integrated evaluation circuit which processes the signals and outputs them in square-wave form to the motor control unit.
Principle of a Hall sensor: I Plate current IH Hall current IV Input current UH Hall voltage / signal UR Reference voltage B Magnetic field a Deflection of electrons by the
magnetic fieldAs opposed to the inductive sensor, the signal voltage here does not depend on the relative speed of the sensor and rotor (i.e. engine speed).Put more simply: The rotation of the gear rim changes the Hall voltage of the Hall IC in the sensor head, the output comprising square-wave signals. The variable voltage is routed to the control unit where it is analyzed in order to acquire the necessary data.
De fiecare dată cand un dinte trece peste senzorul Hall, se generează o tensiune Hall, care este transmisa la unitatea de control a motorului. Împreună cu semnalul de la senzorul
arborelui cotit, semnalul senzorului Hall permite unitatii de control sa determine care cilindru nu functioneaza la parametrii prevazuti.
Experimente – sensor HallMotorul este echipat cu 2 senzori Hall, fiecare la capetele cilindrilor.
The engine with Hall sensors. The circuit diagram.
Realizati experimentul urmator: Pentru măsurătorile ulterioare, montaţi discul senzor Hall pe motor (stânga sus) şi lăsaţi motorul sa se roteasca. Nu uitati sa porniti sursa de alimentare.
Conectati senzorul Hall la bord conform listei:De la La
5V senzor Hall pin 1
Interfata A+ senzor Hall pin 3
Interfata A– senzor Hall pin 2Masurati semnalele conectate la senzor si tensiunea de alimentare utilizand Voltmetrul A:
Voltmetru A setari
Gama de masura: 5 V DC
Mod: P
Masurati tensiunea intre conexiunile senzorului Hall. Deschideti osciloscopul virtual meniul Instruments -> Measuring devices si setati ca mai jos:
Trigger: Channel A / Rising edge / Pre-trigger 25%
Măriţi viteza discului cu came utilizând potentiometrul rpm la o setare joasat. Copiaţi oscilograma rezultantă in tabelul prevăzut în acest scop:
Time base: ms / DIV Channel A:
Amplitude factor: V / DIV
Coupling: AC DC Channel B:
Amplitude factor: V / DIV
Coupling: AC DC
Cresteti rpm la o valoare medie, lăsând setările de osciloscoape cum sunt. Efectuaţi o măsurare la viteză maximă, cu potenţiometru rpm la limita din dreapta. Lasă setările de osciloscoape neschimbate. Determinati viteza maximă în rpm. Pentru aceasta, citiţi perioada de o rotaţie T, luând în considerare factorul de scala a osciloscopului. Lampa de control al motorului se aprinde si vehiculul intra in modul de operare de urgenţă. Într-un diagnostic iniţial cu tester, veţi găsi că un cod de eroare a fost eliberat, indicând un defect pe senzorul de arborele cotit. Un control vizual al senzorului nu dezvăluie defecte externe. Care ar putea fi cauza de defect
Senzorul inductiv functioneaza pe principiul inductiei, dupa care o tensiune este produsă într-o bobină atunci când se mişcă relativ sub un câmp magnetic. Senzorul inductiv utilizeaza acest fenomen, permitand masuratori de unghiuri, distante si viteze.
Pin 1 Signal
Symbol Pin 2 Signal
Scopul aplicatiei Masurarea vitezelor – ex. La arborele cotit, cutia de viteze sau ABS; Determinarea pozitiei arborelui cotit; Generarea de impulsuri pentru aprindere;
Description of a crankshaft sensor as an exampleComprising a permanent magnet and an induction coil with a soft iron core, a crankshaft sensor measures engine rpm. The pulse generator (motion-based) comprises a gear rim mounted on the flywheel, crankshaft or belt pulley. Only a narrow air gap separates the inductive sensor from the gear rim.
A – Electrical connections B – CoilC – Permanent magnetD – Soft iron core
The magnetic flux through the coil depends on whether a space or mark is in front of the sensor. A mark (i.e. cog) concentrates the magnetic field, while a space weakens the field.When the crankshaft and gear rim rotate, each passing cog changes the magnetic field. This change induces a voltage in the coil. The number of pulses per unit of time are a measure of the engine speed. Dedicated spaces on the gear rim also permit the control unit to identify the engine's instantaneous position.
Induced voltage and Magnetic field's intensity
The engine speed serves as a main control variable in calculating the injection and ignition points. This arrangement results in the signal shown next.
Inductive sensor's signal: 1 – cog; 2 – space; 3 – reference mark (large space)If the sensor fails:
the engine might misfire. the engine might stall. an error code is saved.
Possible causes: Winding short circuit Line interruption or short circuit Mechanical damage to the gear rim Heavy soiling Excessively large air gap
Fault localization Read out the error memory Check the connections Check for soiling and mechanical damage
Perform a check with an ohmmeterImportant: A direct check of the crankshaft sensor with an ohmmeter should be performed only after making sure that the sensor is inductive and not a Hall sensor, because the latter's electronics can get damaged by an ohmmeter. Sensors with 3 connections and even those with 2 connections might turn out to be Hall sensors. Active wheel speed (Hall) sensors forming part of the ABS also have a 2-pole connector. Caution should be exercised in all such cases.
Internal resistance: 200 - 1000 ohms (depending on the setpoint value)
Short circuit at 0 ohms; interruption at very high values Ground connection (pin to ground) – setpoint value: > 30 megohms.
Senzor inductiv - experimentThe sensor is positioned on the crankshaft housing near the flywheel.
The sensor. Identify the crankshaft sensor in the circuit diagram.
An inductive sensor can be connected to an oscilloscope, and the sensor's signal observed as the gear rim turns. Connect the inductive sensor appropriately on the board. Mount the accompanying toothed disc on the motor shaft at the top left.
Connection listFrom To
Interface A+ Inductive sensor pin 1
Interface A- Inductive sensor pin 2Open the virtual oscilloscope via the menu path Instruments -> Oscilloscope and set it as shown in the table below.
Oscilloscope settings
Channel A 200 mV / div
Channel B OFF
Time base 50 ms / div
Mode: X/T, DC
Trigger: Channel A / Rising edge / Pre-trigger 0%
Turn on the 12-V power supply and increase the crankshaft disc's speed by means of the "rpm" potentiometer to a low setting. Copy the resultant oscillogram to the placeholder provided for this purpose.
After that, conduct a measurement at maximum speed with the rpm potentiometer set to its right limit. Compare the two measurement results.If the voltage drops below a minimum level or a space is not detected, the control unit can no longer reliably evaluate the signal and assumes the emergency mode. Decide on the possible causes of the fault based on its description at the beginning of the exercise. As an aid, the fault is outlined once again below.
The engine control lamp comes on. The vehicle assumes the emergency operating mode. An initial diagnosis with the tester reveals that an error code has been issued. The code indicates a fault on the crankshaft sensor.
A visual check of the sensor reveals no external faults.A customer brings their car to the workshop with the complaint that the engine responds poorly and jerks on attempts to accelerate rapidly. Based on their long years of experience, the workshop supervisor assumes that this is due to a faulty throttle valve switch.
Design of a throttle valve switch unitA throttle valve switch unit serves to reflect the throttle valve's setting and is mounted directly on the valve axis. The switch settings are signalled to the motor control unit and used to help calculate the required fuel supply.
The throttle valve switch unit houses two switches operated via a shifter mechanism. Both switches provide the motor control unit with information on the engine's idle and full-load states to ensure precise calculations of the required fuel quantity and firing angle. In the idle state, the throttle valve switch unit essentially performs the function described next.
It permits fuel cut-off during self-propulsion, thus notably lowering the consumption of fuel injection engines compared with carburettor models. When the automobile is in the self-propulsion mode (i.e. rolling under its own momentum with the gas pedal closed), the switch notifies the motor control unit that the throttle valve is closed, so that the control unit stops fuel injection at an engine speed above 1800 rpm. When the speed drops below 1200 rpm, fuel injection is resumed again to prevent the engine from stalling. The precise threshold values depend on the fuel injection system. In the full-load state, the throttle valve switch unit performs the function described next.
It notifies the control unit that full load is being exerted, whereupon the control unit enriches the fuel mixture to ensure smooth acceleration.
Effects of failure:A defective throttle valve switch can have the effects described next.
The engine stalls in the idle state The engine jerks under full load
A defective throttle valve switch is attributable to the following causes: Mechanical damage (e.g. through vibrations) Faulty electrical contact (e.g. through corrosion, moisture) Faulty internal switch contact (e.g. through moisture, soiling)
VariantsA throttle valve switch unit's mechanical makeup varies according to its manufacturer, i.e. the two switches for the idle and full-load states can differ in design. A micro-switch and sliding contact are always used for indicating the idle and full-load states. Any possible combination of these components can be found in a throttle valve switch depending on the manufacturer.
Let's assume that our switch unit uses one micro-switch for the idle state and one sliding contact for the full-load state.Include the measures listed below when localizing faults.
1. Check the throttle valve switch unit for proper assembly. 2. Check whether the shifter mechanism is operable via the valve shaft
(when the engine is at a standstill, move the throttle valve from its idle limit to its full-load limit, listening whether the switches are actuated in this process).
3. Check whether the plug connection is firm and clean. 4. Check the switching contacts with a multimeter: o Idle switch closed: Measurement value = 0 ohms. o Idle switch open (important: slowly open the throttle valve until the idle switch opens): Measurement value = > 30 megohms. o Full-load switch open: Measurement value = >30 megohms. o Full-load switch closed: Measurement value = 0 ohms.
Experiment: Throttle valve switch unitSet up the experiment shown next and connect the throttle valve switch unit to the oscilloscope.
From To
Interface A+ Throttle valve switch unit pin 1
5V Throttle valve switch unit pin 2
Interface B+ Throttle valve switch unit pin 3
GND A- and B-Remember to turn on the board's power supply. Open the oscilloscope and perform the settings shown next.
Oscilloscope settings
Chan. A 2 V / div
Chan. B 2V / div
Time base: 1 s / div
Mode: X/T, DC, Single
Trigger: Chan. B/Rising edge/Pre-trigger 25%
Test the switch unit's response by turning the rotary knob from the centre leftward and rightward respectively to the limit, and copy the resultant oscillogram to the placeholder provided for this purpose.Interpret the measurement result.Detach the connection leads from the sensor board and use the multimeter to measure the resistance between the terminals on each switch setting. Left limit: Resistance between terminals 1, 2: Resistance between terminals 2, 3: Resistance between terminals 1, 3: Centre setting: Resistance between terminals 1, 2: Resistance between terminals 2, 3: Resistance between terminals 1, 3:
Resistance between terminals 2, 3: Resistance between terminals 1, 3:
Throttle valve potentiometerA customer's vehicle has been brought in with the following problem:The engine jerks during slow acceleration under partial load, but operates smoothly under full load. One of the suspected causes is a defective throttle valve potentiometer.
Throttle valve potentiometer theoryA throttle valve potentiometer serves the same purpose as a throttle valve switch, i.e. it indicates the throttle valve's current setting to the motor control unit. Being able to precisely determine valve's setting, the potentiometer is an advancement of the throttle valve switch. Furthermore, the potentiometer notifies the motor control unit of the rate at which the throttle valve is being opened / closed by the driver's actuation of the accelerator pedal. This information allows the motor control unit to adjust the fuel mixture's rich / lean level more accurately than using signals from a throttle valve switch.
Pin 1 + 5V
Symbol
Pin 2 GND
Pin 3 Signal
A potentiometer is a variable resistor comprising a sliding contact, or tap, which can be moved along a conductive track. The tap is linked to the throttle valve's shaft, so that a change in the sliding contact's position correspondingly changes the throttle valve's setting.
According to Ohm's law, the applied voltage of 5 V drops fully over the length of the resistor's path (i.e. the conductive track in this case). In other words: 5 V are present on the signal line if the sliding contact is at its left limit, 0 V if the contact is at its right limit, and 2.5 V if the contact is in the middle.In practice, the tap's travel is truncated by stops which restrict the effective voltage range to 0.7 – 4.3 V (this range can vary depending on design). The restriction is meant to facilitate an identification of short circuits and line interruptions.To calculate load, the throttle valve potentiometer's signal is used together with the signal from the lambda probe in the case of single-point fuel injection, and together with the signal from the air-mass meter or MAP sensor in the case of multi-point fuel injection.In the emergency mode, the potentiometer signal also serves to replace the signal from the air-mass meter if it is defective. In systems incorporating an electronic accelerator function (E-gas), the potentiometer signal is used for closed-loop control in conjunction with the servo motor for the throttle valve. It is important for a potentiometer to supply a continuous signal without any interruptions. As a potentiometer wears, gaps can occur in the conductive track. Such gaps lead to invalid signals which are not always identifiable during self-diagnostics. This happens when a normal voltage reading between 0.7 V and 4.3 V is obtained despite the presence of an invalid value.Such gaps in a potentiometer's conductive track can be detected by means of a noise test.During this test, the voltage values measured at the tap are visualized on an oscilloscope.
Experiment: Throttle valve potentiometerConnect the throttle valve potentiometer to the 5-V voltage supply.
Connections:From To
5V Throttle valve potentiometer pin 1
GND Throttle valve potentiometer pin 2
Interface A+ Throttle valve potentiometer pin 3
Interface A- GND
Remember to turn on the board's power supply (refer to the page on start-up). Voltmeter settings:
Voltmeter A settings
Measuring range: 5 V DC
Mode: AV
Measure the output voltage with the throttle valve on the open and closed settings.Noise test
Conduct a noise test in order to detect rifts in the potentiometer's conductive track. The test involves recording the voltage characteristic over the entire conductive path on an oscilloscope. The experiment configuration can remain unchanged here.
Oscilloscope settings
Channel A 2 V / div
Channel B Off
Time base: 1 s / div
Mode: X/T, DC, Single
Trigger: Channel A / Rising edge / Pre-trigger 25% / Level approx. 2 V
After turning on the oscilloscope, move the throttle valve from its fully open setting to its fully closed setting and back again. Evaluate the resultant oscillogram. Interpret the measurement result.
Air mass meterA customer comes to the workshop with the complaint that their car loses a lot of power and assumes the emergency operating mode. An initial diagnosis reveals a malfunction on the air-mass meter. The first symptoms appeared some time ago, when the car's starting and accelerating properties began to deteriorate on a regular basis.
Air mass-meter theoryAn air-mass meter or mass air-flow sensor (MAF) measures the amount of air flowing past per unit of time. Because the quantity of oxygen in the air stream is proportional to the measured mass flow, this variable can be used to control combustion processes, especially in internal combustion engines. The air-mass meter is installed between the air filter and the engine's intake pipe.
Pin 1 Air mass signalPin 2 +5 VPin 3 GNDPin 4 +12 V
Pin 5 Intake air temp. signal
The air drawn in by the engine flows through the air-mass meter. The motor control unit needs to know the intake air flow rate in order to calculate the required fuel injection quantities. Engine systems without an air-flow meter instead make use of a MAP sensor
Air-mass meter's installation point
Motor vehicles are usually furnished with a hot-film air-mass meter. In this case, a measuring surface (the hot film) is heated to a setpoint temperature by an internal circuit of the air-mass meter (PTC). When air flows past this surface, it is cooled. The film is then re-heated by the internal electronics to the setpoint temperature with the help of a Wheatstone bridge.
The value of the current needed to re-heat the film indicates the mass of air drawn in. This current value is converted by the air-mass meter's internal electronics into an output voltage signal.Advantages:
Very fast reaction Very precise measurements of flow rates, especially low ones (0 to 1
m/s) Cost-effective
Disadvantages: Susceptible to soiling Very susceptible to mechanical damage
To make the air-mass meter less susceptible to soiling and mechanical damage, a partial air flow is frequently employed. In this case, only a part of the air stream drawn in by the engine is routed past the air-mass meter's measuring surface, thus reducing the potential for damage / soiling.
A = Electrical connectionsB = HousingC = Air inletD = Measuring element
Most air-mass meters also incorporate an intake air temperature sensor which supplies its signal via a dedicated line to the motor control unit. When performing measurements on such air-mass meters, care must be taken not to mix up the two signals.How to differentiate:If the throttle valve is opened during engine operation, the voltage of the signal indicating the quantity of the intake air changes, whereas the voltage of the signal indicating the temperature of the intake air remains nearly constant.An air-mass meter accordingly has the following connections:
Ground +12 V (for the heating element) +5 V (supply voltage for the evaluation electronics) Air-mass signal line Air-temperature signal line
Experiment: Air mass meterOur air-mass meter has the following connections:
o Ground o +12 V (heating element) o +5 V (supply voltage for the evaluation electronics and temperature sensor) o Air-mass signal line
o Intake-air temperature signal lineTry to identify the air-mass meter's connections in the circuit diagram below.
The assignments of the remaining lines can only be determined with the help of appropriate legends. It must be pointed out that not all automobile manufacturers include such legends in their circuit diagrams. If the legends are missing, voltage measurements must be performed to ascertain the various line assignments.Set up the experiment shown next.
Connections:From To
Interface A+ Air-mass meter pin 1
5V Air-mass meter pin 2
Interface A-, GND Air-mass meter pin 3
12V Air-mass meter pin 4
Remember to turn on the board's power supply. Turn on the fan with the toggle switch (ON); open and close the valve several times and record the air-mass meter's signal response on the oscilloscope.
Trigger:Channel A / Rising edge / Pre-trigger 25% / Level approx. 1.5 V
Air mass meter summaryPossible faults on air-mass meters
Air-mass meters are very susceptible to dirt and moisture. If an air-mass meter gets soiled (e.g. by an oil filter whose replacement is overdue or by oil mist), it might start supplying deviant signals. Strong deviations are recognized by the motor control unit, when then activates the motor control lamp and the emergency mode in which the engine power usually drops significantly.A fault occurring on an air-mass meter does not necessarily generate a corresponding error code. If the signal output by the air-mass meter fluctuates within a plausible range (= considered normal by the motor control unit), no fault is assumed, no error code issued, and the motor control lamp remains off. In such situations, the engine performance also drops but the source of the problem is much more difficult to pinpoint.
