Induction transmitter
Induction sensors (inductive sensors ) are used to transmit counting pulses and are often part of speed sensors . They are used in many different ways in machines and vehicles. They are located on the wheels as ABS speed sensors, as speed and reference mark transmitters on the flywheel ring gear and as non-contact pulse transmitters in electronic ignition systems .
In the past, they were also used to generate sine waves in electromechanical tone generators.
functionality
In the housing of the induction generator there is a coil with an iron core, at the end of which there is a permanent magnet . A magnetic field is generated in the induction winding via the iron core . By turning an incremental wheel, the magnetic field strength in the coil changes constantly and an alternating voltage is induced. The frequency of the alternating voltage changes with the speed. The voltage level depends, among other things, on the size of the air gap between the encoder and the incremental wheel. With a uniform tooth sequence, the voltage curve corresponds to a sine curve. Additional signals are superimposed on the voltage curve through gaps or permanent magnets used in the incremental wheel. These signals are used, for example, to determine the position.
Applications
Hammond organ
Passive induction generators were already the buyers in the electromechanical tone generator of the Hammond organ . For her, it was not a question of measuring the position of the toothed pulley increment wheels (the tonewheels ), but of the waveform and amplitude of the output signal. In order to bring this closer to the sinusoidal shape , low-pass filters were added. The number of turns of the coils varied accordingly. A tonewheel with 192 teeth required fewer turns. The bobbin is like the bobbin thread on a household sewing machine . While the tonewheel only had two teeth for the lowest notes and was actually cut oval, the same amplitude required a multiple of turns, which in turn required a longer coil body. Bumps on the cut surface were audible because they acted like a tape on a playback head . The fine adjustment of the amplitude and thus the volume of the individual fundamental tones was adjusted by the distance from the core to the toothed disc.
automatic transmission
In automated manual transmissions , the gear wheel speeds of the motor and transmission shafts are measured inductively in order to protect the clutch. This is done with a phase short circuit . The gearbox control units accelerate the manually initiated downshift in order to adapt the engine speed to the geared vehicle speed. For cost reasons, the mass-produced ABS sensor, which is also suitable, is sometimes used here . These can be used for the following functions:
- Digital speedometer
- Cruise control
Anti-lock braking system
In the anti-lock braking system, they are used to record the wheel speed within a few degrees of rotation angle. In older vehicles, a ring gear was mounted as an incremental wheel on the constant velocity joints to record the wheel speed. The distance between the induction sensor and the incremental wheel is decisive for the signal quality. The drive slip control (also called traction control ) also needs the wheel speeds to compare them with each other and with the speed of the drive shaft on which the speedometer measures.
Inductive ignition triggering and engine timing
With inductive ignition triggering, control units scan a toothed disk or gear wheel that has a fused pair of teeth or a missing tooth for zero point detection to determine the precise angle of the motor. Alternatively, a permanent magnet is worked into a tooth, which induces a higher voltage. By counting the pulses and recording their frequency, the start of injection and ignition can be triggered according to map values .
Wear-free switches on a camshaft in mechanical engineering
In mechanical engineering, machine states are also recorded in this way. Camshaft switches can be replaced by a respective induction transmitter or an incremental wheel with a single induction transmitter and a digital counter without wear. However, if the parts to be detected do not move or move only slowly, or if the switch-on state has to be detected before the machine starts, the inductive proximity switches that are more frequently used in this area are used.
See also
literature
- Robert Bosch (Ed.): Autoelectronics Autoelectronics. 5th completely revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8 .