Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-06-17
2003-07-29
Strecker, Gerard R. (Department: 2862)
Measuring and testing
Dynamometers
Responsive to torque
C324S207200, C324S207250
Reexamination Certificate
active
06598490
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for contact-less measuring the value of a difference angle between two parts rotating about a common axis.
BACKGROUND OF THE INVENTION
It is possible to reduce the task of detecting rotational variables between two rotating parts, like, for example torque, angle of rotation, rotational speed or rotational acceleration, to a measurement of the difference angle between these two parts. If a torque is to be measured, e.g. between a power take-in shaft and a power take-off shaft, a counter torsion force with a defined spring characteristic has to be provided between the two parts for transforming the torque into a corresponding difference angle. This can be affected by a spring or torsion element acting between the two parts.
U.S. Pat. No. 4,784,002 discloses a torque sensor measuring a torsion between two shafts rotating about a common axis and connected to each other via a torsion element. A stator connected to one of the shafts comprises permanent magnets each forming one magnetic pole, the magnetic poles being arranged at equal intervals and with alternating axial magnetization in the direction of rotation about the common axis. A rotor connected to the other shaft has two separate rotor parts each forming a set of pole ends for magnetically scanning the permanent magnets of the stator. All pole ends are arranged at equal intervals in the direction of rotation about the common axis, each pole end of the one rotor part being arranged between two pole ends of the other rotor part. The total number of pole ends of the rotor is equal to the total number of magnetic poles of the stator. An axial first air gap is formed between the permanent magnets of the stator and the pole ends of the rotor. Further, a rotationally symmetric radial second air gap is formed between the two rotor parts, the magnetic flux across the second air gap being changed according to the difference angle between the rotor and the stator. This change is determined by a magnetically sensitive element which is arranged at a stationary position within the second air gap. There is no other magnetic flux from the rotor to the stator and back than the flux between the magnetic poles and the pole ends.
DE 198 16 598 A1 discloses a sensor for measuring difference angles between two parts rotating about a common axis. Here, both a rotor and a stator have a same number of pole ends. The pole ends of the rotor face the pole ends of the stator across a radial first air gap. A magnetic flux through the stator towards the rotor is provided by a radially magnetized permanent magnet. The magnetic flux through the rotor varies with the position of the pole ends of the rotor with regard to the pole ends of the stator, i.e. with the difference angle between the two parts. This variation is measured in a radially accessible and rotationally symmetric axial second air gap between the rotor and the stator by means of a magnetically sensitive element. However, the signal of the magnetically sensitive element does not indicate the direction of the difference angle here.
Thus, a simple but highly sensitive apparatus for contact-less measuring the value, inclusive of the direction, of a difference angle between two parts rotating about a common axis is still needed.
SUMMARY OF THE INVENTION
The invention provides an apparatus for contact-less measuring the value of a difference angle between two parts rotating about a common axis, the apparatus comprising an annular shaped stator attached to one of the two parts, the stator having a permanent magnetization on an inner circumference thereof forming of a number of at least two magnetic pole pairs, each pole pair consisting of two magnetic poles of opposite signs, and the signs of the magnetic poles of all pole pairs alternating in the direction of rotation about the common axis; a cylindrically shaped ferromagnetic rotor attached to the other of the two parts and positioned inside the stator, the rotor having a number of at least two pole ends for magnetically scanning the stator, the poles being successive in the direction of rotation about the common axis, and the number of the pole ends being the same as the number of the pole pairs of the stator; a first air gap between the pole pairs of the stator and the pole ends of the rotor, each pole end of the rotor facing one pole pair of the stator over the first air gap, all conditions of arrangement of all pole ends and the corresponding pole pairs being the same; an accessible and rotationally symmetric second air gap of continuous dimensions between the stator and the rotor, the magnetic flux across the second air gap being changed according to the difference angle between the rotor and the stator; and at least one magnetically sensitive element for determining the magnetic flux across the second air gap, the magnetically sensitive element being arranged at a fixed position in the second air gap and not being rotated with one of the two parts about the common axis.
In a preferred embodiment of the invention, the first air gap is a radial air gap, the permanent magnetization of the stator and the pole ends of the rotor having a radial orientation with regard to the common axis. Further, it is preferred that the second air gap also is a radial air gap. The second air gap may then be arranged at an axial position along the common axis of rotation differing from the position of the first air gap. The provision of only radial air gaps makes this embodiment of the invention particularly insensitive to axial play between the two parts in the direction of the common axis with regard to the signal of the magnetically sensitive element obtained for a certain difference angle.
In a further preferred embodiment of the invention, the second air gap is provided between a stator yoke and a rotor yoke.
In a further preferred embodiment of the invention, the stator consists of permanent magnets forming the pole pairs and a stator yoke, the stator yoke being continuous from the pole pairs up to the second air gap.
In a further preferred embodiment of the invention, the rotor consists of a rotor yoke, the rotor yoke forming the pole ends and being continuous up to the second air gap.
In a further preferred embodiment of the invention, the pole pairs of the stator are arranged at the same intervals in the direction of rotation about the common axis as the pole ends of the rotor, the magnetic poles of opposite signs of each pole pair being arranged directly side-by-side.
In a further preferred embodiment of the invention, the magnetic poles of the pole pairs of the stator have the same dimensions in the direction of rotation about the common axis as the pole ends of the rotor.
In a further preferred embodiment of the invention, the magnetically sensitive element transforms the magnetic flux across the second air gap into an electrical signal. To this end, the magnetically sensitive element comprises a Hall probe. In a further preferred embodiment of the invention for measuring torque between the two parts, a spring having a defined spring characteristic over the difference angle is arranged between the two parts, the spring transforming a certain torque between the two parts into a certain difference angle. The spring may be a mechanical spring. As an alternative, the spring may be a magnetic spring. In this alternative, the magnetic spring may make use of an intrinsic magnetic holding force between the pole ends of the rotor and the pole pairs of the stator.
In a further preferred embodiment of the invention, the stator and the rotor are encapsulated by a housing made of a material which is selected from the group consisting of paramagnetic and diamagnetic materials. This housing may not encapsulate the magnetically sensitive element. Instead, this element may be placed outside the housing.
In a further preferred embodiment of the invention, at least one further magnetically sensitive element is arranged at a fixed position adjacent the rotating pole pairs of the stator but not rotating with one
Strecker Gerard R.
Thomas Kayden Horstemeyer & Risley
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