Inductive sensors in the car. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Inductive sensors in the car. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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Among the variety of non-contact sensors, due to their unpretentiousness to external conditions, ease of manufacture and durability, induction (or generator) sensors are the most attractive.

On their basis, various devices were created - from the simplest, registering linear movements, to complex ones, such as digitally controlled ignition systems, fuel injection systems, anti-lock brake control systems, etc.

Let us dwell on the process taking place in the generator sensor. In the simplest case, the sensor consists of a coil with a winding, a core of soft iron and a magnet. These three components make up the stator of the sensor. The rotor interacts with the stator in the form of a toothed disk or a toothed rack with the number of teeth determined by the conditions for using the sensor (Fig. 1).

Inductive sensors in the car
Ris.1

When the rotor rotates, an alternating voltage appears in the stator winding. When one of the teeth of the rotor approaches the winding, the voltage in it increases rapidly and, when coinciding with the middle line of the winding, reaches a maximum, then, when the tooth is removed, it quickly changes sign and increases in the opposite direction to a maximum. The graph shown (Fig. 2) clearly shows the steepness of the voltage change, so the transition between the two maxima can be used to control electronic systems.

Inductive sensors in the car
Ris.2

The amount of voltage generated by the sensor depends on the speed of the rotor, the number of turns of the coil and the amount of magnetic flux created by the permanent magnet. Since the last two values are constant, the magnitude of the induced voltage reaches a maximum at maximum speed. When designing, special attention should be paid to the amplification of pulses at a low repetition rate.

The scope of such sensors is extensive, let us dwell on some examples.

Swing or shock sensor (fig. 3)

A small piece of magnetically soft iron is fixed on a spiral spring made of thin wire; when swinging or pushing, it interacts with the sensor stator, which produces a series of aperiodic pulses.

Inductive sensors in the car
Ris.3

Rotometer (tachometer)

In the engine crankshaft speed sensor (Fig. 4), the sensor stator is mounted on the flywheel housing or on the inspection hatch plug - in the immediate vicinity of the flywheel ring gear. The device provides the most accurate determination of the speed without intrusion into the circuits of the ignition system.

Inductive sensors in the car
Ris.4

Speedometer

To measure vehicle speed, the toothed rotor is mounted on the output shaft of the gearbox or on the gearbox block instead of a flexible shaft. The system allows you to abandon the expensive tachometer or mechanically unreliable flexible shaft (Fig. 5).

Inductive sensors in the car
Ris.5

Odometer

The vehicle path is measured using a toothed disk mounted on a non-drive wheel (Fig. 6). Similar sensors are also used in the automatic braking system (ABS - AntiBlockSystem), which prevents the car's wheels from blocking and skidding.

Inductive sensors in the car
Ris.6

Wiper

The gear sector is fixed on the gearbox. Readable pulses allow you to smoothly adjust the stroke frequency of the brushes depending on weather conditions.

Ignition system

The generator sensor (Fig. 1) is the basis of the BOSH ignition system.

Dr. Hartig's "Impulse-Technic" digital ignition system uses an engine flywheel ring gear with an extra tooth to produce a reference signal (Fig. 7). This system allows very precise control of the ignition timing.

Inductive sensors in the car
Ris.7

If we return to the design of the inductive sensor, it should be noted that if the parameters of the medium being measured affect the rotor speed, then the question arises about the braking torque exerted by the magnetic field of the permanent magnet. In this case, measures are taken to increase the starting moment (increase the impeller area). If, according to operating conditions, it is not required to control a small rotational speed, the core can be made of a hard magnetic material without an additional magnet, and a sufficient signal value can be obtained due to residual magnetism.

As an example, we can cite the parameters of sensors that have found application in various devices.

For example, the sensor core is made of steel (St1, St2, St3) 03...8 mm (Fig. 1). Coil cheeks 012...20 mm are pressed onto the core at a distance of 10...15 mm from each other. The core under the winding is insulated with a fluoroplastic film. The coil is wound in bulk, until the space between the cheeks is filled. Wire - PEV-1 00,06 ... 0,1 mm. The number of turns is approximately 2500 ... 4000.

The length of the core ranges from 12 to 35 mm. On one side of the core there is a platform for attaching an anisotropic magnet. Magnets from reed keyboards turned out to be convenient. The free end of the core is removed from the housing. The sensor housing is made of non-magnetic material. If the application conditions require, the sensor is filled with a compound.

The rotor, if it needs to be specially made, is made of a soft magnetic material. The number of teeth is determined from the operating conditions. The gap between the stator and the rotor should be as small as possible.

The signal from the sensor is fed to the input of a simple electronic circuit (Fig. 8), which amplifies and generates a signal for further use in analog or digital form.

Inductive sensors in the car
Ris.8

Another feature of such sensors should be mentioned. They can read not only a signal from a special rotor, it can be gear teeth or even mounting bolts on a rotating part.

Literature

1. Bun B. Electronics on the car. - M.: Transport, 1979.
2. Digital and analog microcircuits. Directory. - M.: RiS, 1989.
3. 750 electronic practical circuits. Collection, 1987.

Author: I.Semenov; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Automobile. Electronic devices.

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