SKF pioneered the introduction of smart hubs with integral electronic sensors to communicate wheel speed data to ABS and traction control systems (TCS). Now MEMS technology is opening up new possibilities for gathering data at a wheel hub.
Working closely with many of the world’s leading automakers SKF supports innovation in automotive design: corner assemblies that reduce weight, extend performance, and simplify assembly; integrated electronics that enhance safety and functionality; and sophisticated sealing solutions that reduce noise and vibration.
“The development of sensor-equipped bearings and communication of data from hub units to a vehicle’s CPU has helped to improve safety and performance,” explains Marchant Taylor, SKF South Africa’s Vehicle Service market manager.
The sophistication and availability of sensors have increased dramatically over the past few years. As a key element in the dynamic environment of a vehicle, the hub bearing is an ideal point to capture data for processing in vehicle performance and condition monitoring systems.
There are even more innovative and exciting developments around the corner – intelligent bearings that will monitor wheel-end temperature, measure vehicle loads, evaluate noise and vibration levels, and then process this data via embedded software before passing to the vehicle’s CPU.
The optimum wheel speed sensor solution is unique for each individual application. Sensors can be either integrated or non-integrated and may also be either passive or active. Passive sensors are capable of providing signals down to a speed of a few km/h, which is sufficient for ABS. Active sensors can provide signals down to zero speed – necessary for systems such as traction control or navigation.
Operating principle
A magnetic impulse ring divided into a sequence of north and south poles is attached to the inner ring of the bearing. The outer ring carries a sensor body with embedded Hall cells. When the inner ring rotates, the impulse ring moves past the stationary sensor ring, generating a magnetic field of changing polarity. The sensor outputs a pulse at a frequency dependent on the number of polarity changes per second.
The signal is then transmitted via a connection cable from the SKF sensor bearing unit to an electronic processing unit, which evaluates the signal and provides application-specific information.
Sensor bearings were first developed for anti-lock braking systems in passenger vehicles, when intelligent bearings were required to record the variations in the circumferential speed of the wheel.
MEMS technology
MEMS (micro-electro-mechanical systems) technology is opening up the possibility of more sophisticated measurements of temperature, vibration, strain and angular rotation.
MEMS are becoming increasingly important in military systems for instance, monitoring the condition, damage and serviceability at the level of individual components.
As an example, if a bearing starts to fail due to initial minor spalling, it will begin to vibrate and exhibit abnormal operating characteristics. Based on SKF’s bearing health knowledge and experience, this abnormal behaviour can be sensed, identified and diagnosed by a MEMS-based system. A failure-alert system then allows corrective action to be taken long before the bearing fails completely, causing other problems or safety issues.
Widespread use of MEMS as intelligent condition monitors is a key component in the transition from time-based maintenance (TBM) to condition-based maintenance (CBM). CBM is far more efficient and cost-effective than TBM. As such, the world’s military has embraced CBM as a key factor in improving the availability of all assets, while at the same time lowering the overall costs of ownership.
SKF will find the right solution and will assist with taking advantage of these developments and opportunities by offering a wide range of solutions for both passenger and heavy vehicle hub units.
For more information contact Marchant Taylor, SKF South Africa, +27 (0)11 821 3500, [email protected], www.skf.co.za
| Tel: | +27 11 821 3500 |
| Fax: | +27 11 821 3501 |
| Email: | [email protected] |
| www: | www.skf.co.za |
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