I. Field of the Invention
The present invention relates generally to torque sensors and, more particularly, to a torque sensor which detects the deflection angle between the input and output shaft, such as a steering column for an automotive vehicle.
II. Description of Related Art
In steering systems of the type used in automotive vehicles, the steering system typically includes an input shaft connected to the steering wheel. The input shaft is then connected to an output shaft through a torsion bar and the output shaft, in turn, is mechanically or otherwise connected through linkage to the vehicle wheels. Consequently, rotation of the steering wheel pivots the wheels of the automotive vehicle through the torsion bar, output shaft, and steering linkage.
In many situations, it is highly desirable to determine the angular deflection between the input shaft and the output shaft of the steering mechanism. The degree of angular deflection between the input shaft and output shaft, i.e. the angular deflection of the torsion bar, is then utilized by the vehicle management system to determine the steering wheel torque and the amount of assist provided by the power steering. For example, when the vehicle is stopped or nearly stopped, e.g. during a vehicle parking situation, rotation of the steering wheel typically creates a relatively high angular deflection between the input shaft and the output shaft thus requiring increased power assistance from the power steering system in order to turn the vehicle wheels. This deflection, furthermore, rarely exceeds 4 degrees for automotive vehicles.
There have been previously known systems that are capable of monitoring the angular deflection between the input and output shafts of the steering column. These previously known systems typically employ a transducer which measures the angular torque between the steering input and output shafts. However, since the steering output shaft can rotate up to three or four full revolutions, it has been previously necessary for these previously known devices to provide a long length of electrical cable, typically a ribbon cable, within and around the steering column. Sufficient ribbon cable was necessary so that the ribbon cable could wind around the steering column two or three times to accommodate multiple rotations of the steering wheel.
This previously known solution, however, has not proven wholly satisfactory in use. For example, it is possible for the electrical connector to become entangled after extended use which can compromise or even destroy the electrical connection between the cable and the angle sensor between the steering input and output shafts. When this occurs, the overall operation of the torque sensor for the steering system is compromised.
There have been other types of systems which require multiple magnets, but these previously known systems require high manufacturing tolerances for accurate measurements.