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Engine speed sensors. Measuring the motor speed with a hall sensor Speed ​​sensor motor control

Crankshaft (crankshaft)- this is a node of parts, a part of a rather complex shape. It has necks that serve to fasten the connecting rods, and already from these elements the part perceives all efforts, converting them into torque. The crankshaft is an integral part of the crank mechanism.

The sensor has many different names, starting with the name "DPKV" - the crankshaft position sensor (synchronization sensor), and ending with the name "TDC sensor".

It is the crankshaft sensor (crankshaft speed sensor) that is a unique sensor. This is due to the fact that the malfunction of this electronic system is the only one of its kind that causes a complete engine shutdown.

But why does it happen that if there is a problem with the crankshaft sensor, the internal combustion engine stops working? This is due to the fact that the crankshaft sensor itself is designed to synchronize the operation of the ignition system and fuel injectors. This means that a malfunction of such a sensor will inevitably lead to a failure of the fuel injection system.


The crankshaft sensor itself, during its operation, gives certain signals to the electronic control unit about the immediate position at this moment of the crankshaft, the direction of its rotation and its frequency. The principle of operation of the crankshaft sensor is very often different, since it entirely depends on the type of sensor used on a particular make and model of car.

There are several types of crankshaft speed sensor:

-Magnetic sensors inductive type do not require a special separate power source for their consumption. For the signal of the electronic control unit, the voltage is displayed at a certain moment when the synchronization tooth passes through the magnetic field. This magnetic polo is formed around the sensor. In addition to the fact that the sensor controls the crankshaft speed, it is also often used as a speed sensor.

- Hall Sensor based on the Hall effect. This means that the movement of current begins at the moment when a constantly changing magnetic field approaches the sensor. Synchronization disc blocking the magnetic field, with the help of its teeth interacts with the magnetic field that has formed around the sensor. This type of crankshaft speed sensor is also used for ignition distribution.

- Optical sensor. In this type of sensors, the synchronization disk is made with teeth or holes. The disk itself blocks the flow of light that passes between the LED and the receiver. The receiver processes the received light flux into a voltage pulse, which, in fact, is transmitted to the electronic control unit.

The electronic control unit receives all the input signals that are generated by the crankshaft frequency sensor. After that, it determines the positions of the crankshaft relative to the top dead center in the fourth and first engine cylinders, and also determines the frequency and direction with which the crankshaft rotates.

Thanks to the results that the electronic control unit receives, signals are created for controlling: ignition timing, injectors, regulation of the electric fuel pump, tachometer readings.


The synchronization sensor has an identical housing to the various other sensors. There is only one difference between the appearance of these sensors - a long wire with a connector through which it is connected to the onboard target.

The location of the crankshaft sensor is very inconvenient. It is because of this that a long wire with a connector is connected to the sensor. The sensor itself is attached to a bracket next to the alternator drive pulley.

When installing the crankshaft sensor directly, the gap must be set between the toothed pulley and the sensor itself. The position of the sensor is correct when the gap that is between its core and the synchronization disk ranges from 0.5 mm to 1.5 mm, and the distance of the gap itself can be adjusted using gaskets (washers) between the sensor and its seat.

During direct operation, malfunctions of the crankshaft speed sensor may occur, although this is a rather rare occurrence. All mechanical damage to the sensor often occurs when indirect repairs are made under the hood, or if various foreign objects are between the pulley teeth and the sensor.

1. What is DPKV


Before proceeding with the determination of malfunctions and breakdowns in the crankshaft sensor (alarm indicator), you need to find out what exactly this sensor is and what it is for. So here it is its main purpose is to enable the fuel injection system of the vehicle to perform synchronous operation of the ignition system and fuel injectors.

The crankshaft sensor device is quite simple and consists of: a nylon frame wrapped with copper wire, which is mounted on a steel core. The wire itself is insulated with enamel. The hermetic role is played by the compound resin. During its direct operation, the sensor sends signals to the electronic control unit about the position and the entire operation of the crankshaft.

Problems and breakdowns with the crankshaft position sensor make it impossible for the fuel system to establish all the most important characteristics mentioned above. That is why you should know how to independently check the health of the crankshaft sensor.

2. Crankshaft sensor - signs of malfunction

To begin with, you need to highlight The most understandable and obvious signs of malfunctions of the crankshaft sensor:


In addition, the fact that the crankshaft position sensor has become unusable and has become faulty may be indicated by the banal impossibility of starting the car engine. Therefore, a car enthusiast does not have to be a professional in various matters about the design of car electronic systems in order to identify and determine a malfunction.

3. How to check the crankshaft position sensor


The performance of the entire node of a given device can be analyzed in several ways. First you need to stock up on all the necessary devices, and remove the synchronization sensor from the engine. After that, you need to inspect it and proceed to a direct check.

When viewed from the outside, you can identify and install various damage to the core, terminal block or the crankshaft sensor housing itself. Sometimes a simple cleaning of contacts and cores from various contaminants can be a sufficient action. If, during an external examination, no obvious problems were identified, then you need to start checking the “hidden threats”.

First way this kind of inspection will ring the crankshaft sensor with an ohmmeter. This elementary option makes it very easy to solve the problem, which is to check the crankshaft position sensor for serviceability. Thus, it is necessary to measure the resistance of the winding of the crankshaft sensor. The normal value variation is from 550 ohms to 750 ohms.

Second way more difficult than the first, as it involves more time and resources. Initially, it is necessary to measure the resistance of the winding of the crankshaft sensor, as in the first case, using an ohmmeter and megohmmeter. After that, it is necessary to measure the inductance using a specific device. A normal indicator would be an inductance from 200 to 400 MHz.


As a result, a digital voltmeter and a mains transformer must be used. It is the results of all the above measurements that will indicate to the motorist whether the crankshaft position sensor is serviceable or defective.

Let's summarize. The crankshaft position sensor is one of the most important elements of the car's electronic system. This is the only device that can completely stop the operation of the engine. That is why many experienced motorists give practical and useful advice: always have a spare crankshaft position sensor in the trunk. It is quite cheap, but the value of this device for engine operation is invaluable.

Engine speed sensors are used in engine management systems for:

  • engine speed measurement
  • determining the position of the crankshaft (position of the engine piston)

The number of revolutions is calculated from the interval between the signals of the speed sensor.

Inductive speed sensors

Rice. Inductive rotation speed sensor (design):

  1. Permanent magnet
  2. Sensor housing
  3. Engine housing
  4. Pole contact pin
  5. Winding
  6. Air gap
  7. Gear wheel with reference point

Design and function The sensor is mounted directly opposite the ferromagnetic gear (item 7) with a defined air gap. It has a soft magnetic steel core (pole pin, pos. 4) with winding (5). The pole contact pin is connected to the permanent magnet (1). The magnetic field propagates through the pole contact pin, passing into the gear wheel. The magnetic flux passing through the coil depends on whether the location of the sensor falls against the cavity or tooth of the wheel. The tooth connects the magnetic scattering flux emanating from the magnet into a beam. Through the coil there is an amplification of the network flow. The depression, on the contrary, weakens the magnetic flux. These changes in magnetic flux as the gear rotates induce a sinusoidal output voltage in the coil, proportional to the rate of change and the speed of the motor. The amplitude of the alternating voltage increases intensively with an increase in the number of revolutions (several mV ... > 100 V). Sufficient amplitude is present, starting from a minimum speed of 30 per minute.

Rice. Inductive engine speed sensor signal:

  1. depression
  2. Reference signal

Active speed sensors

Active rotation speed sensors work according to the magnetostatic principle. The amplitude of the output signal is independent of the speed. This makes it possible to measure the speed even at very low speeds (quasi-static speed detection).

Hall differential sensor

On a conductive plate, along which the magnetic induction B passes vertically, a voltage UH (Hall voltage) proportional to the direction of the current can be removed transversely to the direction of the current.

Rice. The principle of operation of the differential Hall sensor:

  • a Sensor location
  • b Hall sensor signal
  • high amplitude with small air gap
  • small amplitude with large air gap
  • with output signal
  1. Magnet
  2. Hall sensor 1
  3. Hall sensor 2
  4. Gear

In the differential Hall sensor, the magnetic field is generated by a permanent magnet (pos. 1). Between the magnet and the impulse ring (4) there are two Hall sensor elements (2 and 3). The magnetic flux that passes through them depends on whether the rotational speed sensor is located against a tooth or a groove. By creating a signal difference from both sensors, a reduction in magnetic disturbance signals and an improved signal-to-noise ratio is achieved. The side surfaces of the encoder signal can be processed without digitization directly in the control unit.

Instead of a ferromagnetic gear wheel, multi-pole wheels are also used. Here, a magnetizable plastic is mounted on a non-magnetic metal carrier, which is alternately magnetized. These north and south poles take on the function of the teeth of the wheel.

AMR sensors

Rice. Principle of speed detection with AMP encoder:

  • a Placement
  • at various points in time
  • b AMP sensor signal
  • with output signal
  1. Impulse (active) wheel
  2. touch element
  3. Magnet

The electrical resistance of a magneto-resistive material (AMP, anisotropic magnetoresistive) is anisotropic. This means that it depends on the direction of the magnetic field that affects it. This property is used in the AMP sensor. The sensor is located between the magnet and the impulse ring. The field lines change their direction when the impulse (active) wheel is rotated. As a result, a sinusoidal voltage is formed, which is amplified in the data processing circuit and converted into a square wave signal.

GMR sensors

The improvement in active rotation speed sensors is reflected in the use of GMR (GMR) (Giant Magneto-Resistance) technology. Due to the high sensitivity compared to AMP sensors, large air gaps are possible here, which makes it suitable for difficult applications. Higher sensitivity produces less edge noise.

All two-wire ports previously used in Hall speed sensors are also possible in GMR sensors.

When motorists have certain problems with the engine, they begin to wonder which sensor is responsible for engine speed, since the first suspicion often falls on these devices.

However, this is not always the case, because revolutions can “float” for various reasons. It is best to first make sure that there are no other breakdowns, and check the meters after. One way or another, if you want to find the right sensor, you need to know what it looks like and where to look for it.

Basic concepts

To synchronize the operation of the ignition and injection systems, a speed sensor is provided, or, as it is called, a speed meter. It is he who transmits to the electric unit that controls the motor the necessary data about what rotations the crankshaft supports at the moment.

This power unit meter is the most important element of the car, without which the interaction of many systems is indispensable, because it helps to ensure the correct functioning of the entire machine as a whole.

The electronic control unit of the car processes the special signals that this meter sends to find out:

  • the amount of injected fuel at the moment;
  • moment of injection;
  • the time required to activate the adsorber valve;
  • ignition timing (for gasoline engines);
  • the angle of rotation of the camshaft during the operation of the system for changing the phases of the gas distribution mechanism.

To determine the performance of the meter, you need to know its location.

Location

The speed sensor, or inductive meter, is usually located above the vehicle's marker disc.

The disk, in turn, can be located:

  • on the flywheel;
  • on the crankshaft inside the cylinder block - this happens with Ford, Opel, etc .;
  • in front of the engine compartment on the crankshaft, together with the drive pulley for additional units (Jaguar, BMW, VAZ, etc.).

It is best when the flywheel marker teeth are intended only for measuring engine speed. It is a little worse if the marker teeth are starter teeth: this feature is present in cars of the Audi and Volvo brands.

A slight curvature of a flywheel tooth or a small chip present on it can often cause a malfunction in the ignition system, due to which the power unit cannot operate at higher speeds. In this case, chaotic sparking often occurs, since the control unit incorrectly determines the number of teeth.

Important Features

It should be noted that on some vehicles, the speed sensor replaces the Hall meter: this device can transmit to the main control unit not only a signal about the phases of the gas distribution mechanism, but also engine speed. If you have just such a situation, then you can find the device near the camshaft.

In the event that the crankshaft speed meter fails, you will not be able to start your car: after a thorough check of the ignition and fuel supply system, during which no significant deviations will be found, it is recommended to check the performance of the speed sensor.

Conclusion

"Floating" motor rotations are not uncommon: this condition can occur due to several reasons, so all options must be carefully checked.

26 . Sensorsspeed

Speed ​​sensors are used to determine the number of revolutions of the motor shaft per unit of time and are used in controlled drive systems.

Speed ​​sensors are used in tachometers - devices that measure the speed or angular speed of rotating parts. Tachometers are magnetic, vibration, hourly integrating, stroboscopic, electronic integrating, magnetic-induction, magnetic-electric, frequency-pulse, ferrodynamic and others.

In industry, it is now widely used magnetic induction speed sensors(tachogenerators), generating electrical voltage pulses of approximately sinusoidal shape. The frequency of this signal is proportional to the rotational speed of the motor shaft where the inductor is installed.

Design and principle of operation of a non-contact magnetic induction speed sensor

Sensor design example. The magnetic induction sensor consists of an inductor, inside which is a mild steel core connected to a permanent magnet. The steel core is located through a small air gap directly above the edge of a ferromagnetic toothed ring (gear) located in the magnetic field of a permanent magnet. If a ring tooth hits directly opposite the sensor, then it concentrates the magnetic field and enhances the flux of magnetic induction in the coil, and if the gear notch becomes opposite the sensor, then the magnetic flux weakens. These two states of the sensor constantly alternate during the rotation of the impulse gear together with the shaft, the rotational speed of which, in fact, is the measured characteristic. AC voltage pulses are induced in the coil, the frequency of which indicates the frequency of rotation of the shaft.

Purpose. Non-contact inductive speed sensors are widely used to control and record the speed of various engines, incl. on vehicles.

Tachogenerators

A typical tachogenerator is a low power electrical machine that converts mechanical rotation into an electrical signal. The design of an asynchronous tachogenerator is no different from an asynchronous motor with a hollow non-magnetic rotor. Like a motor, one of the stator windings is connected to the AC network (excitation winding), and the other - the generator winding - serves to remove the output voltage. The windings of an asynchronous generator are located at an angle of 90º to each other. The output power of the tachogenerator can reach several watts. In addition to asynchronous, synchronous tachogenerators and DC tachogenerators are produced.

Tachogenerator example

Tachogenerator GT 3 manufactured by Huebner, Germany

Main technical characteristics

Output voltage: 5mV/rpm

Temperature coefficient: -0.035%/ºС

uneven characteristics: no more than 1.2%

Time constant: 2 µs

Power: 0.025W

Operating temperature range: from -30 ºС to +130 ºС

Hollow shaft diameter: 6mm

The highest speed: 10000 rpm

Moment of inertia: 9gsm2

Rotor weight: approx. 20 g

Case Diameter: 34mm

Protection class: IP00; IP54

DC tachogenerator is a DC machine with independent excitation or excitation by permanent magnets, operating in generator mode. By design, it almost does not differ from DC machines.

DC tachogenerators are used to measure the rotational speed by the value of the output voltage, as well as to obtain electrical signals proportional to the shaft rotational speed in automatic control circuits.

The main requirements for tachogenerators are: a) linearity of the output characteristic; b) large steepness of the output characteristic; c) a small effect on the output characteristic of changes in ambient temperature and load; d) minimum voltage ripple on the collector.

On the. rice. 9.5 shows schematic diagrams of DC tachogenerators with electromagnetic excitation (a) and excitation with permanent magnets (b).

(1)

where ra is the resistance of the armature winding, Ohm; Rn - internal resistance of the device connected to the tachogenerator, Ohm.

From (1) it follows that the greater the resistance of the device Rn, the greater the steepness of the output characteristic Cu. The highest steepness of the output characteristic corresponding to the idling mode of the tachogenerator, when the armature winding is open "(RH = ∞).

With an increase in the load current (decrease in RH), the steepness of the output characteristic decreases (Fig. 9.6, a). Modern DC tachogenerators Cu = (6÷260).10¯³V/(rpm), which exceeds the steepness of asynchronous tachogenerators.


The output characteristic of the DC tachogenerator is a straight line. However, experience shows that the output characteristic is rectilinear only in the initial part (at low relative speeds), and with increasing speed it becomes curvilinear (Fig. 9.6, a). The curvilinearity of the characteristic increases with a decrease in the load resistance RH and an increase in the rotational speed n. This is due to the demagnetizing effect of the armature reaction in the tachogenerator. To reduce the curvilinearity of the output characteristic, do not use the tachogenerator at its maximum speeds and use devices with low internal resistance as a load.

Wheel speed sensors
Application
Wheel speed sensors are used to determine the speed of rotation of the wheels of the vehicle (the number of revolutions of the wheel). The speed signals are transmitted via cable to the vehicle's ABS, ASR or ESP control unit, which individually controls the braking force of each wheel. This control loop prevents the wheels from locking (with ABS) or spinning (with ASR or ESP) and guarantees vehicle stability and control. Navigation systems also need wheel speed signals to calculate the distance traveled (for example, in tunnels or in the absence of satellite signals).

Design and principle of operation
Signals for the wheel speed sensor are generated using a steel pulse sensor rigidly connected to the wheel hub (for passive sensors) or a multipole magnetic pulse sensor (for active sensors). This encoder has the same rotational speed as the wheel and passes through the non-contact sensitive area of ​​the encoder head. The sensor "reads" without direct contact through an air gap of up to 2 mm (Fig. 2).
The air gap (with small tolerances) serves to ensure that the process of obtaining a signal without interference. Possible disturbances such as oscillations, vibrations, temperature, humidity, installation conditions on the wheel, etc. are excluded.

Since 1998, instead of passive (inductive) speed sensors, the latest developments have almost exclusively used active wheel speed sensors. Passive (inductive) speed sensors consist of a permanent magnet (fig. 2, pos. 1) and a magnetically soft pole contact pin (3) connected to it, which is inserted into the coil (2). Thus, a constant magnetic field is created.
The pole contact pin is located directly above the impulse wheel (4), a gear wheel rigidly connected to the hub. During the rotation of the impulse wheel, the existing constant magnetic field is "disturbed" due to the constant change of tooth and cavity. This changes the magnetic flux passing through the pole contact pin, and with it the magnetic flux passing through the turns of the coil. The change in magnetic fields induces an alternating voltage in the winding, which is removed at the ends of the winding.
Both the frequency and the amplitude of the alternating voltage are proportional to the number of revolutions of the wheel (rotation speed) (Fig. 3). When the wheel is not moving, the induced voltage is also zero.
The shape of the teeth, the air gap, the steepness of the power surge and the input sensitivity of the control unit determine the minimum measurable vehicle speed, as well as the lowest possible response sensitivity and switching speed for ABS use.

Since mounting conditions on the wheel are not the same everywhere, there are various forms of pole contact pins and various mounting options. The most common are the incisal pole contact pin (Fig. 1a, also called a flat inductor) and the diamond-shaped contact pin (Fig. lb, also called a cruciform inductor). Both pole contact pins must be exactly directed towards the impulse ring during installation.

Active rotation speed sensor
Touch elements
Modern brake systems almost exclusively use active speed sensors (fig. 4). They usually consist of a silicon integrated circuit hermetically sealed with plastic, located in the sensor head.
In addition to magnetoresistive integrated circuits (change in electrical resistance with a change in magnetic field), Bosch still uses Hall sensor elements in large quantities, which react to the slightest changes in the magnetic field and can therefore be used with larger air gaps compared to passive speed sensors. rotation.
Active (pulse) ring
A multi-pole wheel is used as the pulse ring of the active rotation speed sensor. We are talking about alternately arranged permanent magnets arranged in the form of a ring on a non-magnetic metal carrier (Fig. 6 and Fig. 7a). The north and south poles of these magnets act as the prongs of the impulse ring. The sensor IC is exposed to a constantly changing magnetic field. Therefore, the magnetic flux passing through the integrated circuit also changes as the multipole ring rotates.

Figure #4 Active RPM Sensor

As an alternative to the multi-pole ring, a steel gear can be used. In this case, a magnet is installed on the Hall integrated circuit, which generates a constant magnetic field (Fig. 7b). During the rotation of the impulse ring, the existing permanent magnetic field is subjected to "interference" due to the constant change of the tooth-notch. Otherwise, the principle of measurement, signal processing and integrated circuit are identical to those in the sensor without a magnet.

Characteristics
A typical phenomenon for an active rotation speed sensor is the integration of the Hall measuring element, signal amplifier and signal preparation in an integrated circuit (Fig. 8). The rotational speed data is transmitted as an input current in the form of rectangular pulses (Fig. 9). The frequency of the current pulses is proportional to the number of revolutions of the wheel, and readings are possible almost until the wheel stops (0.1 km/h).

The supply voltage is between 4.5 and 20 volts. The square wave output level is 7 mA (low) and 14 mA (high). With this form of digital signal transmission, for example, an inductive interference voltage is inefficient compared to a passive inductive sensor. Communication with the control unit is carried out by a two-wire cable.

The compact design and light weight allow the active speed sensor to be mounted on or in a wheel bearing (Fig. 10). Various standard sensor head shapes are suitable for this.

Digital signal processing allows coded additional information to be transmitted using a pulse-width modulated output signal (Fig. 11).
Determination of the direction of rotation of the wheels: this is especially necessary for the "Hill Hold Control" function, which prevents the car from rolling back while climbing a hill. Determining the direction of rotation is also used for vehicle navigation.
Stop state definition: this data is also processed in the "Hill Hold Control" function. Further data processing is included in the self-diagnosis section.
Sensor signal quality: it is possible to transmit data on the quality of the sensor signal. This way, in the event of an error, the driver can be informed about the need to contact the service department in a timely manner.

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