HELLA, the electrics and electronics specialist of choice

HELLA, the renowned original equipment (OE) manufacturer and system supplier, has more than 60 years of experience in the fields of electrics and electronics, stretching back to the introduction of the first flasher control units in 1957. Now an established supplier of innovative vehicle electronics globally, the company pioneered the 24 GHz radar sensor for rear end applications, paving the way for further automated driving functions, and was the first supplier to bring radar sensors into the aftermarket. This business segment now makes up 34% of its sales.

The HELLA electronics portfolio includes more than 45 product groups and covers vehicle functions such as emissions, comfort and safety. One of the company’s fastest growing aftermarket product lines is wheel speed sensors, or ABS sensors as they are otherwise known, reflecting the demand for replacements that come from independent workshops country wide.

Overview
Wheel speed sensors come in passive and active designs, but both are equipped with cables, with or without protective covers, in different lengths and with sensor angles at 90 degrees or straight.

Passive sensors
The wheel speed sensors are positioned directly above the impulse wheel, which is connected to the wheel hub or drive shaft. The pole pin, surrounded by a winding, connects to a permanent magnet whose magnetic effect extends to the pole wheel. The rotation of the impulse wheel and the resulting switching from tooth-to-tooth space brings about a change in the magnetic flow caused by the pole pin and winding. This changing magnetic field induces a quantifiable, or measurable, alternating voltage (AC) in the winding. The frequency and amplitudes of this AC voltage are in relation to the wheel speed, so inductive passive sensors do not require a separate power supply from the control unit. Since the range for signal detection is defined by the control unit, the amplitude level must be within a specific voltage range. The distance between the sensor and the pulse wheel is determined by the axis design.

Active sensors
The active sensor is a proximity sensor with integrated electronics that is supplied with a defined voltage from the ABS control unit. A multipole ring can be used as an impulse wheel while at the same time being integrated in a sealing ring of a wheel bearing and inserted in this sealing ring are magnets with alternating pole directions. The magneto-resistive resistors integrated in the electronic circuit of the sensor detect an alternating magnetic field when the multipole ring rotates. This sinusoidal signal is converted by the electronics in the sensor into a digital signal. It is then transferred to the control unit as a current signal using the pulse-width modulation method. The sensor is connected to the control unit via a two-pole electric connecting cable and the sensor signal is also transmitted at the same time over a power supply line. The other line is used as a sensor ground.
In addition to magneto-resistive sensor elements, nowadays Hall sensor elements are also fitted, which permit a larger air gap and respond to the smallest of changes in the magnetic field. If a steel impulse wheel is installed in a vehicle in place of a multipole ring, a magnet is also affixed to the sensor element. When the impulse wheel turns, the constant magnetic field in the sensor changes. The signal processing and IC are identical to the magneto-resistive sensor.

At-a-glance advantages
• Wheel speed detection from standstill that facilitates speed measurements down to 0.1 km/h, which is relevant to traction control systems as soon as the vehicle accelerates
• Hall sensors detect forward and backward movements
• The sensor is in design smaller and lighter
• The lack of impulse wheels simplifies the power transfer linkage
• Less sensitive to electromagnetic interference
• Changes in the air gap between the sensor and magnetic ring have no direct impact on the signal
• Virtual insensitivity to vibrations and fluctuations in temperature Quality and range

As wheel speed sensors are an integral part of the vehicle’s driving safety system, replacing a faulty sensor with one of OE quality should be the natural choice for the independent workshop and helpfully, HELLA provides the ideal solution with more than 340 12-volt part numbers, for multiple applications, including numerous models within the BMW and VAG line ups.
However, it's not just the passenger car sector to which HELLA’s range extends, as its 24-volt offering includes 48 part numbers that cater for several relevant truck, bus and trailer manufacturers, including BPW, DAF, Iveco, Kogel, Krone, Liebherr, MAN, Mercedes Benz, Renault, Scania, Schmitz Cargobull, Tata, and Volvo.

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