1. Field of the Invention
The present invention relates to steering angle sensor assemblies and, more particularly, steering angle sensor assemblies that transmit steering angle information to a vehicle control module.
2. Description of the Related Art
A wide variety of steering angle sensor assemblies are known in the art for providing steering angle data to vehicle systems such as vehicle stabilizing systems. Such conventional steering angle sensor assemblies may be broadly classified as either “dumb” sensor assemblies or “smart” sensor assemblies. Dumb sensor assemblies typically transmit raw analog signals to the electronic control unit (ECU) of the vehicle which then analyzes the signals to determine the steering angle of the vehicle. Smart sensor assemblies, in contrast, typically include a microprocessor for processing the raw sensor signals and determining the steering angle value.
Both dumb sensor assemblies and smart sensor assemblies may include one or more sensing devices. For example, between one and three light emitting diodes (LEDs) and a corresponding number of photosensitive sensors may be positioned on opposite sides of a rotating tone ring that has slots therein. As the tone ring is rotated along with the steering wheel, the slots in the tone ring allow the LEDs to illuminate the sensors. The signals generated by the photosensitive sensors in response to the light are then analyzed to determine the steering angle position. Other forms of sensing devices may also be employed within the sensor assemblies. For example, a potentiometer-like sensing device may output an analog voltage that is indicative of which of the several possible revolutions that the tone ring is positioned in.
A drawback associated the dumb analog sensor assemblies is that each of the individual sensing devices used in the sensor assembly has a wire leading to the ECU. These wires may pick up noise or become broken. If only one of the wires is broken, the ECU may still receive signals from the remaining sensing devices and, as a result, the ECU may compute an erroneous steering angle position. Another drawback is that analog signal transmission may require a digital-to-analog converter on the sensor side, and an analog-to-digital converter at the ECU. In addition to their expense, these converters may introduce sources of error into the system.
A drawback associated with the smart sensor assemblies is that they are relatively expensive. The cost is driven up by the expense of the microprocessor located in the sensor assembly as well as the controller area network (CAN) bus that is required in order to communicate data computed by the microprocessor in the sensor assembly to the ECU.
What is needed in the art is a cost effective steering angle sensor assembly that can reliably transmit steering angle information over a single wire, or over another single conduit, to a vehicle controller.