Magnetoelastic torque sensor assembly

Details Magnetoelastic torque sensor assembly Magnetoelastic torque sensor assembly

2002-11-22

2004-07-06

Lefkowitz, Edward (Department: 2855)

Measuring and testing

Dynamometers

Responsive to torque

C073S862325, C073S862331

Reexamination Certificate

active

06758105

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to a magnetoelastic torque sensor assembly for measuring a torsion load applied to a shaft, such as an automotive steering column or the like. More particularly, this invention relates to such magnetoelastic torque sensor assembly comprising a molded plastic body defining a channel for receiving the shaft and magnetic sensors connected to a lead frame and embedded within the molded plastic body in a predetermined arrangement relative to the shaft.
BACKGROUND OF THE INVENTION
It is known to measure variations in a torsion load applied to a shaft using a magnetoelastic effect. The shaft is provided with a magnetic circumferential band. A magnetic flux sensor is positioned adjacent to the magnetic band and detects variations in the magnetic flux about the shaft when a torsion load is applied. Typically, multiple sensors are spaced circumferentially about the shaft to enhance sensitivity. Also, in order to distinguish variations in the magnetic flux due to lateral displacement of the shaft, it is desirable to arrange sensors in diametrically opposed pairs.
One proposed application of a magnetoelastic torque sensor is to measure torsion load applied to an automotive steering column on an automotive vehicle and to utilize the measurements during turning for adjusting an electronic power assist steering system. Careful arrangement of the sensors about the shaft is required for reliable sensing. Manual positioning of sensors is time consuming and not suited for mass production. It has been proposed to mount the sensors on a clamshell or other hinged bracket. However, sensor responsiveness is subject to variations in the closure of the bracket as well as in positioning of the bracket about the shaft. Fixed arrays have been proposed but cover only a portion of the shaft circumference, and do not position the sensors in diametrically opposed relationship.
Therefore, a need exists for a magnetoelastic torque sensor assembly that may be readily installed about a shaft, such as a steering column, to position an array of sensors in a fixed arrangement relative to the shaft and also to each other, including sensors that are diametrically opposed.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, a magnetoelastic torque sensor assembly is provided for sensing torsion load applied to a shaft. The assembly comprises a molded plastic body that defines a channel having an axis and an elongated axial opening for radially receiving the shaft to coaxially position the shaft within the channel. The molded plastic body includes a first side section and a second side section in spaced relationship about the axis. A U-shaped lead frame is embedded within the integrally molded plastic body. The lead frame includes a middle portion, a first side portion extending from the middle portion within the first side section of the molded plastic body, and a second side portion extending from the middle portion within the second side section of the molded plastic body. The middle portion includes electrical terminals adapted for external electrical connections to the channel lead frame. The magnetoelastic torque sensor also includes at least a first and a second magnetic flux sensor attached to the lead frame, with the first sensor embedded in the first section and the second sensor embedded in the second side section. Preferably, the first and second sensors are arranged in a plane parallel to the axis, either diametrically opposed or axially spaced. The magnetoelastic torque sensor is readily manufactured using the lead frame to position the magnetic flux sensors in the desired arrangement during molding and to provide electrical connections to the sensors once embedded. For use, the molded plastic body provides a robust assembly that may be readily installed about the shaft, while fixing the position of the magnetic flux sensors not only with each other, but also relative to the shaft.


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