System and method for sensing torque and angular position of a shaft

#The present invention relates to a system and method for measuring torque and angular position of a shaft, using for example position-dependent magnetic fields.

#Torque and position sensing systems are vital for electrical power steering systems in automobiles, among other applications. When a driver steers an automobile, electrical power steering systems may add energy during zero to low speeds when higher torque is required to adequately steer. Power steering systems may also provide feedback force to the driver during high speeds when less torque is required, ensuring that drivers are aware of the forces acting on the front wheel. Detecting the torque and position on the steering column is important to determine how much energy the power steering system should apply to aid the driver in steering.

#Prior methods for measuring torque may involve a torsion bar that twists with the amount of force applied to the steering column and a sensor that measures the amount of twisting occurring on the torsion bar. A separate mechanism for measuring angular position may involve a circular resistive tracking circuit with known linear resistance and a positive voltage applied to one end of the track. Voltage may be measured at an output contact moving with the shaft's rotation along the resistive track. The change in voltage may signify the shaft's position. Both of these methods may be expensive to assemble and maintain, and may enlarge the size of the steering column and power steering system.

#The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

#FIG. 1 is a diagram of a magnetic array according to an embodiment of the present invention.

#FIGS. 2A and 2B are schematic diagrams of systems measuring torque and angular position of a shaft, according to embodiments of the present invention.

#It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

#In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will however be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

#A sensing system according to embodiments of the present invention may include a shaft, a magnetostrictive ring affixed to the shaft, a first sensor for measuring a magnetic field that varies with angular position, and a second sensor for measuring a magnetic field that varies with torque. The rotation of a shaft may be represented by angular position, where a quarter turn of the shaft in a clockwise direction may be represented by, for example, 90 degrees or pi/2 radians. Other suitable ways of representing the shaft's rotation may be used. A first sensor may measure a magnetic field that varies with angular position when the first sensor registers a changing strength and direction in the magnetic field as the magnetostrictive ring rotates in the vicinity of the first sensor. When the shaft rotates, the shaft and magnetostrictive ring may experience torque, and the magnetostrictive ring's magnetic field may vary in strength and/or direction with the amount of torque. A method may involve rotating a shaft with a magnetostrictive ring affixed to the shaft, measuring a magnetic field that varies with the shaft's angular position and measuring magnetic field changes induced by torque applied to the shaft or ring. A magnetic field that varies with angular position may be generated by a magnetostrictive ring that includes magnetically differentiated areas arranged circumferentially around the magnetostrictive ring. Areas may be magnetically differentiated from the surface of the magnetostrictive ring if the magnetic field emitted by the areas have different strength and/or direction than the magnetic field emitted by the surface of the magnetostrictive ring. For example, if the surface of the magnetostrictive ring is magnetized in a circumferential direction, the areas may have magnetic differentiation if they are magnetized in a radial direction, or in a direction normal to the surface of the magnetostrictive ring. Other configurations may be used.