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LucasVarity Control Systems Launches Wheel Speed Sensor

10 February 1999

LucasVarity Automotive Control Systems Launches Innovative Wheel Speed Sensor

    BIRMINGHAM, England, Feb. 10 -- LucasVarity Automotive
Control Systems has launched a new miniaturized wheel speed sensor for use
primarily in automotive applications. Employing active sensing technology, the
new sensor, named "Active Micro Sensor," promises significant benefits to
vehicle manufacturers in terms of compactness and reliability at competitive
cost.
    Current trends in vehicle safety and the increasing adoption of integrated
driver support systems, such as the LucasVarity Thomson-CSF Autocruise(R)
system, have defined a market need for wheel speed sensors which can generate
a robust signal over the full speed range.
    Mounted close to the car's wheel bearing seals, the LucasVarity Automotive
Control Systems "Active Micro Sensor" will use Hall Effect or Magneto
Resistive technology to determine wheel speed with associated conditioning
electronics to generate digital signals. This active sensing technology is
particularly suitable for applications where sensing at near zero is required,
such as traction and vehicle stability control, anti-lock braking and adaptive
cruise control, systems all marketed by LucasVarity. The sensor is also
expected to find use in other applications such as transmission and engine
rotation sensing.
    Measuring only 25.4 mm in length and 6.4 mm in diameter, the wheel speed
sensor can be mounted in locations where conventional flange or clip-mounted
sensors are difficult to fit, providing design freedom and space savings for
vehicle manufacturers and chassis system suppliers.
    The Active Micro Sensor's internal electrical/electronic assembly consists
of an Integrated Circuit chip and a capacitor welded to a lead frame. It is
terminated through a pre-molded connector or flying lead and is fully
overmolded using a unique encapsulation process, which seals out moisture
completely as well as protecting delicate internal parts, giving the sensor
enhanced reliability.
    The wheel speed sensor is triggered by a multi pole magnetic encoder,
normally molded onto the face of the wheel bearing oil seal, and generates a
robust current switched digital output at the standard 7mA/14mA level.
    "We are very pleased with this new development. This new Active Micro
Sensor overcomes a significant limitation found in passive sensors, where zero
speed sensing is not possible.  It therefore offers more precise system
control at very low speeds than is possible with passive sensors. For traction
control and ABS systems, sensing at near zero speed, i.e. below 7 km an hour,
is important because it contributes to the performance of these systems. The
fact that our new sensor is extremely small and compact as well as cost
competitive with passive sensors, offers vehicle manufacturers tremendous
advantages in terms of overall system cost and space savings," said Kim Smith,
principal engineer, LucasVarity Automotive Control Systems.
    Initially, LucasVarity Automotive Control Systems expects to supply the
new wheel speed sensors from its Birmingham, England, facility for use in
European designed vehicles with multi pole magnet targets incorporated into
wheel bearing oil seals. Future developments include incorporation of a
back-biased magnet to facilitate use with a toothed wheel rotating with the
road wheel, the approach adopted in North America.
    Control Systems is a business of LucasVarity Automotive, a division of
LucasVarity plc which designs, manufactures, and supplies advanced technology
systems, products and services in the world's automotive and aerospace
industries.