Patent Description:
A variable reluctance "VR" position sensor comprises excitation coils and detection coils in a first element and no coils in a second element which is movable with respect to the first element and whose position with respect to the first element is to be measured. Thus, there is no need to conduct electric current to the moving second element. A variable reluctance position sensor can be for example a variable reluctance resolver in which the above-mentioned first element is a stator and the above-mentioned second element is a rotor whose rotation angle with respect to the stator is to be measured. A significant advantage of a variable reluctance resolver is that there is no need to conduct electric current to the rotor. A stator of a variable reluctance resolver receives an alternating excitation signal to excitation coils and produces first and second alternating output signals by first and second detection coils, respectively, wherein amplitudes of the first and second alternating output signals are dependent on the rotational position of the resolver so that envelopes of the first and second alternating output signals i.e. curves outlining extremes of the first and second alternating output signals have a mutual phase shift.

The publication <CIT> describes a variable reluctance resolver that comprises a ring-like stator, a rotor, and a housing. The stator comprises a stator core and coils. The stator core is provided with plural salient poles. The coils are wound to the salient poles of the stator. The housing accommodates the stator. The rotor comprises an airgap surface having a profile formed with plural arc-like convex portions that deviate from a circular shape and are located at equal spaces in the circumferential direction. The number of the arc-like convex portions is the ratio of <NUM> degrees, i.e. a full circle, to the center angle of a measurement sector of the variable reluctance resolver. In a case where the variable reluctance resolver is used for measuring a rotational angle a rotor of an electric machine, the number of the above-mentioned arc-like convex portions can be e.g. the same as the number of pole-pairs of the electric machine, and thereby the variable reluctance resolver measures the rotational position of the rotor of the electric machine as electrical degrees. It is also possible that the number of pole-pairs of the electric machine is a multiple of the number of the arc-like convex portions. In this exemplifying case, the angle measured with the variable reluctance resolver is to be multiplied by this multiple number to obtain the rotational position of the rotor of the electric machine as electrical degrees of the electric machine.

A variable reluctance resolver of the kind described above is however not free from challenges. One of the challenges is related to cases in which a variable reluctance resolver is used for measuring a rotation angle of a rotor of an electric machine that has very many pole-pairs. In an exemplifying case where the number of the arc-like convex portions of the rotor of the variable reluctance resolver is the same as the number of pole-pairs of the electric machine, the center angle of a measurement sector of the variable reluctance resolver is small in mechanical degrees and thus the pole pitch in the stator of the variable reluctance resolver must be small in mechanical degrees to achieve a sufficient measurement accuracy in electrical degrees. This may lead to a situation in which the circumference of the stator of the variable reluctance resolver has very many stator teeth, and thereby the variable reluctance resolver is complex and expensive. In another exemplifying case where the number of pole-pairs of the electric machine is a multiple of the number of the arc-like convex portions, a sensing position error is increasing when the measured resolver angle is multiplied by this multiple number to obtain the rotational position of the rotor of the electric machine as electrical degrees of the electric machine.

<CIT>, <CIT> and <CIT> are further known examples of variable reluctance position sensors.

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments.

In this document, the word "geometric" when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a planar or non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new variable reluctance position sensor that can be for example a variable reluctance resolver for measuring a rotational angle of a rotating object. It is however also possible that a variable reluctance position sensor according to an embodiment of the invention is configured to measure a position of a linearly moving object.

A variable reluctance position sensor according to the invention comprises:.

The above-mentioned first ones of the magnetic sensor sections constitute a first group of successively placed magnetic sensor sections and the above-mentioned second ones of the magnetic sensor sections constitute a second group of successively placed magnetic sensor sections so that the second group is displaced with respect to the first group by C × the spatial meandering period, where C is a non-integer number. In exemplifying cases in which C = ¼ + an integer, the phase-shift between the envelopes of the first and second alternating output signals is <NUM> degrees, i.e. π/<NUM>.

In a variable reluctance position sensor according to an exemplifying and non-limiting embodiment, the first group of successively placed magnetic sensor sections covers less than the spatial meandering period, and correspondingly the second group of successively placed magnetic sensor sections covers less than the spatial meandering period.

In a variable reluctance position sensor according to an exemplifying and non-limiting embodiment, the first group of successively placed magnetic sensor sections covers less than <NUM> × the spatial meandering period, and correspondingly the second group of successively placed magnetic sensor sections covers less than <NUM> × the spatial meandering period.

In an exemplifying case where a variable reluctance position sensor according to an exemplifying and non-limiting embodiment is a variable reluctance resolver that is used for measuring a rotational angle of an electric machine having many pole-pairs, the stator of the variable reluctance resolver does not need to cover <NUM> mechanical degrees, but the first group of successively placed magnetic sensor sections covers advantageously less than one pole pair pitch, i.e. less than <NUM> electrical degrees, of the electric machine and correspondingly the second group of successively placed magnetic sensor sections covers advantageously less than one pole pair pitch of the electric machine.

Various exemplifying and non-limiting embodiments are described in accompanied dependent claims.

Exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in conjunction with the accompanying drawings.

Exemplifying and non-limiting embodiments and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which:.

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

<FIG> illustrates a variable reluctance position sensor according to an exemplifying and non-limiting embodiment. The variable reluctance position sensor comprises a first element <NUM> and a second element <NUM>. In this exemplifying case, the variable reluctance position sensor is a variable reluctance resolver for measuring a rotational angle θ of the second element <NUM> with respect to the first element <NUM>. The rotational axis of the second element <NUM>, i.e. a rotor, is parallel with the z-axis of a coordinate system <NUM>. The second element <NUM>, i.e. the rotor, comprises an air-gap surface <NUM> that has a periodically meandering profile with four spatial meandering periods. In this exemplifying case, the first element <NUM>, i.e. a stator, comprises a plurality of magnetic sensor sections that are placed along an arc of a geometric circle in a direction of movement of the airgap surface <NUM>. In <FIG>, two of the magnetic sensor sections are denoted with references <NUM> and <NUM>. As shown in <FIG>, the profile of the air-gap surface <NUM> meanders with respect to a geometric circle <NUM> so that a radius r is a periodic function of a center angle ϕ that is defined with respect to a reference direction fixed to the second element <NUM>. The radius r can be for example r(ϕ) = R<NUM> + R<NUM>sin(<NUM>(ϕ + γ), where R<NUM>, R<NUM>, and γ are constants. A part <NUM> of the second element <NUM> may comprise electrically insulated ferromagnetic sheets stacked in the axial direction of the second element <NUM>, i.e. in the z-direction of the coordinate system <NUM>. It is also possible that the part <NUM> is made of e.g. ferrite or soft magnetic composite such as e.g. SOMALOY®. A center part <NUM> of the second element <NUM> can be made of e.g. solid steel.

Each of the magnetic sensor sections of the first element <NUM> is configured to conduct a magnetic flux to and from the second element <NUM> via the airgap surface <NUM> of the second element. First ones of the magnetic sensor sections constitute a first group <NUM> of equidistantly successively placed magnetic sensor sections and second ones of the magnetic sensor sections constitute a second group <NUM> of equidistantly successively placed magnetic sensor sections. The first ones of the magnetic sensor sections comprise first excitation coils and first detection coils configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils. In <FIG>, one of the first excitation coils is denoted with a reference <NUM> and one of the first detection coils is denoted with a reference <NUM>. Correspondingly, the second ones of the magnetic sensor sections comprise second excitation coils and second detection coils configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils. In <FIG>, one of the second excitation coils is denoted with a reference <NUM> and one of the second detection coils is denoted with a reference <NUM>. Amplitudes of the first and second alternating output signals are dependent on the rotation angle θ of the second element <NUM> with respect to the first element <NUM> so that envelopes of the first and second alternating output signals, i.e. curves outlining extremes of the first and second alternating output signals, have a phase-shift with respect to each other.

The first group <NUM> of successively placed magnetic sensor sections and the second group <NUM> of successively placed magnetic sensor sections are mechanically arranged so that the second group <NUM> is displaced with respect to the first group <NUM> in a direction of movement of the airgap surface <NUM>, i.e. in the circumferential direction, by C × the spatial meandering period, where C is a non-integer number. In this exemplifying case, C = 1¼. With this exemplifying displacement between the first and second groups <NUM> and <NUM>, the phase-shift between the envelopes of the first and second alternating output signals is substantially <NUM> degrees. In the exemplifying variable reluctance position sensor illustrated in <FIG>, the second element has four mechanical poles, i.e. the meandering period is <NUM> mechanical degrees which corresponds to <NUM> electrical degrees. In this exemplifying case, the second group <NUM> is displaced with respect to the first group <NUM> by <NUM> electrical degrees + <NUM> electrical degrees = <NUM> electrical degrees, i.e. <NUM> mechanical degrees. In the exemplifying case illustrated in <FIG>, the first group <NUM> covers about <NUM> electrical degrees i.e. <NUM> mechanical degrees and correspondingly the second group <NUM> covers about <NUM> electrical degrees i.e. <NUM> mechanical degrees.

In the exemplifying variable reluctance resolver illustrated in <FIG>, the first and second groups <NUM> and <NUM> are circumferentially successive. In this case, the axial length i.e. the z-directional length of the variable reluctance resolver can be minimized. It is however also possible that the first and second groups <NUM> and <NUM> are axially successive and the first and second groups <NUM> and <NUM> are overlapping when seen along an axial direction i.e. along the z-axis of the coordinate system <NUM>. In this exemplifying case, the second group <NUM> can be circumferentially displaced with respect to the first group <NUM> by only <NUM> electrical degrees i.e. by <NUM> mechanical degrees, i.e. by ¼ × the spatial meandering period.

In a variable reluctance position sensor according to an exemplifying and non-limiting embodiment, the number of the magnetic sensor sections of the first group <NUM> of successively placed magnetic sensor sections is N, and: <MAT> where Ns0 is a predetermined integer, the absolute value of Ns(i) is the number of turns of the first detection coil in ith one of the magnetic sensor sections of the first group <NUM> and the sign of the Ns(i) is indicative of a winding direction of the first detection coil in the ith one of the magnetic sensor sections of the first group. The first detection coils are advantageously series connected. In this exemplifying case, the first excitations coils can be for example such that: <MAT> where Ne0 is a predetermined integer, the absolute value of Ne(i) is the number of turns of the first excitation coil in ith one of the magnetic sensor sections of the first group <NUM>, and the sign of Ne(i) is indicative of a winding direction of the first excitation coil in the ith one of the magnetic sensor sections of the first group. The first excitation coils are advantageously series connected. The magnetic sensor sections can be numbered for example so that the index i increases in the counterclockwise direction. The second group <NUM> of successively placed magnetic sensor sections is advantageously like the first group of successively placed magnetic sensor sections.

In a variable reluctance position sensor according to the above-described exemplifying and non-limiting embodiment, the envelope of the first alternating output signal produced by the first detection coils of the first group <NUM> is proportional to the sine of the rotation angle θ, i.e. sin(θ), and the envelope of the second alternating output signal produced by the second detection coils of the second group <NUM> is proportional to the cosine of the rotation angle θ, i.e. cos(θ).

In the exemplifying variable reluctance resolver illustrated in <FIG>: <MAT> <MAT>.

In the exemplifying variable reluctance resolver illustrated in <FIG>, the first and second excitation coils change the polarity in each next magnetic sensor section, which corresponds to the above-presented equations <NUM>-<NUM>, i.e. the part (-<NUM>)i in these equations. However, there can be any kind of orientation of the first and second excitation coils, while the orientation of the first and second detection coils is to be adjusted appropriately to obtain e.g. sine and cosine output signals. Below-presented equations correspond to an exemplifying case in which all the excitation coils have a same winding direction: <MAT> <MAT>.

The variables and parameters in equations <NUM> and <NUM> are the same as in equations <NUM> and <NUM>.

In the exemplifying variable reluctance resolver illustrated in <FIG>, the first element <NUM> comprises electrically and/or magnetically conductive elements <NUM> and <NUM> between the first and second groups <NUM> and <NUM> of successively placed magnetic sensor sections. The term "magnetically conductive" means that the relative magnetic permeability µ of material of the electrically and/or magnetically conductive elements is greater than one. The electrically and/or magnetically conductive elements can be for example electrically conductive and/or ferromagnetic. The exemplifying variable reluctance resolver illustrated in <FIG> comprises an electrically and/or magnetically conductive element <NUM> at an end of the first group <NUM> facing away from the second group <NUM>, and an electrically and/or magnetically conductive element <NUM> at an end of the second group <NUM> facing away from the first group <NUM>.

In the exemplifying variable reluctance resolver illustrated in <FIG>, each of the magnetic sensor sections has a magnetic core element that is separate with respect to magnetic core elements of other ones of the magnetic sensor sections, and each of the electrically and/or magnetically conductive elements <NUM>-<NUM> has the same shape as the magnetic core elements of magnetic sensor sections. It is also possible that the electrically and/or magnetically conductive elements have a different shape. <FIG> illustrates a variable reluctance resolver according to an exemplifying and non-limiting embodiment in which the first element <NUM> comprises electrically and/or magnetically conductive elements <NUM>, <NUM>, and <NUM> which have a shape different from the shape of the magnetic core elements of the magnetic sensor sections. It is to be noted that the electrically and/or magnetically conductive elements can be of any suitable shape that can be found e.g. with experiments and/or simulations.

According to experiments and simulations, an advantage of the electrically and/or magnetically conductive elements is that the electrically and/or magnetically conductive element <NUM> reduces unwanted magnetic interactions that would otherwise take place between those of the magnetic sensor sections of the first and second groups <NUM> and <NUM> which are nearest to each other. Once the electrically and/or magnetically conductive element <NUM> is placed between the first and second groups <NUM> and <NUM>, it is advantageous to place the other electrically and/or magnetically conductive elements <NUM> and <NUM> to the other ends of the first and second groups <NUM> and <NUM> to avoid asymmetry within each of the first and second groups <NUM> and <NUM>. Naturally, if the magnetic sensor sections of the first and second groups and are placed far enough from each other, there is no need to install electrically and/or magnetically conductive elements at all because the magnetic sensor sections belonging to different groups cannot interact with each other. Each of the electrically and/or magnetically conductive elements can be made of for example aluminum, solid or laminated steel, ferrite, soft magnetic composite such as e.g. SOMALOY®, or some other suitable electrically and/or magnetically conductive material.

In the exemplifying variable reluctance resolver illustrated in <FIG>, the airgap surface <NUM> of the second element <NUM>, i.e. the rotor, faces radially towards the first element <NUM>, i.e. the stator. <FIG> illustrate a variable reluctance resolver according to another exemplifying and non-limiting embodiment. <FIG> shows the variable reluctance resolver when seen along the negative z-direction of a coordinate system <NUM>, and <FIG> shows a section taken along a geometric arc A-A shown in <FIG>. The variable reluctance resolver comprises a first element <NUM> that is a stator of the variable reluctance resolver, and a second element <NUM> that is a rotor of the variable reluctance resolver. The rotational axis of the second element <NUM>, i.e. the rotor, is parallel with the z-axis of the coordinate system <NUM>. The stator comprises a plurality of magnetic sensor sections that are placed along an arc of a geometric circle. In <FIG>, two of the magnetic sensor sections are denoted with references <NUM> and <NUM>. The rotor comprises an air-gap surface <NUM> that has a periodically meandering profile with four spatial meandering periods. In this exemplifying case, the airgap surface <NUM> of the rotor faces axially towards the stator and the rotor and the stator are axially successive. As shown in <FIG>, the profile of the air-gap surface <NUM> meanders with respect to a geometric plane <NUM> that is perpendicular to the z-axis of the coordinate system <NUM>. A part <NUM> of the rotor may comprise a roll of electrically insulated ferromagnetic sheet so that the geometric axis of the roll coincides with the geometric axis of rotation of the rotor. It is also possible that the part <NUM> is made of e.g. ferrite or soft magnetic composite such as e.g. SOMALOY®. A center part <NUM> of the rotor can be made of e.g. solid steel.

First ones of the magnetic sensor sections constitute a first group <NUM> of equidistantly successively placed magnetic sensor sections and second ones of the magnetic sensor sections constitute a second group <NUM> of equidistantly successively placed magnetic sensor sections. The first ones of the magnetic sensor sections comprise first excitation coils and first detection coils configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils. Correspondingly, the second ones of the magnetic sensor sections comprise second excitation coils and second detection coils configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils. The first group <NUM> of successively placed magnetic sensor sections and the second group <NUM> of successively placed magnetic sensor sections are mechanically arranged so that the second group <NUM> is displaced with respect to the first group <NUM> in a direction of movement of the airgap surface <NUM>, i.e. in the circumferential direction, by C × the spatial meandering period, where C is a non-integer number. In the exemplifying case illustrated in <FIG>, C = 1¼.

<FIG> illustrate a variable reluctance position sensor according to an exemplifying and non-limiting embodiment. The variable reluctance position sensor comprises a first element <NUM> and a second element <NUM>. In this exemplifying case, the variable reluctance position sensor is a linear position sensor configured measure a position of the second element <NUM> with respect to the first element <NUM> in the x-direction of a coordinate system <NUM>. <FIG> shows the linear position sensor when seen along the negative z-direction of the coordinate system <NUM>, and <FIG> shows a section taken along a line A-A shown in <FIG>. The geometric section plane is parallel with the xz-plane of the coordinate system <NUM>. The first element <NUM> comprises a plurality of magnetic sensor sections that are placed along a geometric line. In <FIG>, two of the magnetic sensor sections are denoted with references <NUM> and <NUM>. The second element <NUM> comprises an air-gap surface <NUM> that has a periodically meandering profile with two spatial meandering periods. As shown in <FIG>, the profile of the air-gap surface <NUM> meanders with respect to a geometric plane <NUM> that is perpendicular to the z-axis of the coordinate system <NUM>.

First ones of the magnetic sensor sections constitute a first group <NUM> of equidistantly successively placed magnetic sensor sections and second ones of the magnetic sensor sections constitute a second group <NUM> of equidistantly successively placed magnetic sensor sections. The first ones of the magnetic sensor sections comprise first excitation coils and first detection coils configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils. Correspondingly, the second ones of the magnetic sensor sections comprise second excitation coils and second detection coils configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils. The first group <NUM> of successively placed magnetic sensor sections and the second group <NUM> of successively placed magnetic sensor sections are mechanically arranged so that the second group <NUM> is displaced with respect to the first group <NUM> in a direction of movement of the airgap surface <NUM> by C × the spatial meandering period, where C is a non-integer number. In the exemplifying case illustrated in <FIG>, C = 1¼.

<FIG> illustrates a variable reluctance position sensor according to an exemplifying and non-limiting embodiment. The variable reluctance position sensor comprises a first element <NUM> and a second element <NUM>. In this exemplifying case, the variable reluctance position sensor is a variable reluctance resolver for measuring a rotational angle θ of the second element <NUM>, i.e. a rotor, with respect to the first element <NUM>, i.e. a stator. The rotational axis of the second element <NUM>, i.e. the rotor, is parallel with the z-axis of a coordinate system <NUM>. The first element <NUM>, i.e. the stator, comprises a plurality of magnetic sensor sections that are placed along an arc of a geometric circle. The second element <NUM>, i.e. the rotor, comprises an air-gap surface <NUM> that has a periodically meandering profile with ten spatial meandering periods, i.e. the rotor comprises ten mechanical poles. First ones of the magnetic sensor sections constitute a first group <NUM> of equidistantly successively placed magnetic sensor sections and second ones of the magnetic sensor sections constitute a second group <NUM> of equidistantly successively placed magnetic sensor sections. The first ones of the magnetic sensor sections comprise first excitation coils and first detection coils configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils. Correspondingly, the second ones of the magnetic sensor sections comprise second excitation coils and second detection coils configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils. The first group <NUM> of successively placed magnetic sensor sections and the second group <NUM> of successively placed magnetic sensor sections are mechanically arranged so that the second group <NUM> is displaced with respect to the first group <NUM> in a direction of movement of the airgap surface <NUM>, i.e. in the circumferential direction, by C × the spatial meandering period, where C is a non-integer number. In the exemplifying variable reluctance resolver illustrated in <FIG>, C = 1¼. In other words, the second group <NUM> is displaced with respect to the first group <NUM> by <NUM> electrical degrees + <NUM> electrical degrees i.e. by <NUM> electrical degrees which is <NUM> mechanical degrees. With this displacement between the first and second groups <NUM> and <NUM>, the phase-shift between the envelopes of the first and second alternating output signals is substantially <NUM> degrees. Each spatial meandering period of the airgap surface <NUM> represents one full period of each of the above-mentioned envelopes.

In the exemplifying variable reluctance resolver illustrated in <FIG>, the first element <NUM> comprises electrically and/or magnetically conductive elements <NUM> between the first and second groups <NUM> and <NUM> of successively placed magnetic sensor sections. Furthermore, the exemplifying variable reluctance resolver comprises electrically and/or magnetically conductive elements <NUM> at an end of the first group <NUM> facing away from the second group <NUM>, and electrically and/or magnetically conductive elements <NUM> at an end of the second group <NUM> facing away from the first group <NUM>. Each of the magnetic sensor sections has a magnetic core element that is separate with respect to magnetic core elements of other ones of the magnetic sensor sections. In the exemplifying case shown in <FIG>, each of the electrically and/or magnetically conductive elements has the same shape as the magnetic core elements of magnetic sensor sections. The electrically and/or magnetically conductive elements can be made of e.g. aluminum, solid or laminated steel, ferrite, soft magnetic composite such as e.g. SOMALOY®, or some other suitable electrically and/or magnetically conductive material.

In the exemplifying variable reluctance position sensor illustrated in <FIG>, the first detection coils can be configured according to the earlier presented equation <NUM>: <MAT> where N is the number of the magnetic sensor sections in the first group <NUM>, Ns0 is a predetermined integer, the absolute value of Ns(i) is the number of turns of the first detection coil in ith one of the magnetic sensor sections of the first group <NUM>, and the sign of the Ns(i) is indicative of a winding direction of the first detection coil in the ith one of the magnetic sensor sections of the first group <NUM>. The magnetic sensor sections can be numbered for example so that the index i increases in the counterclockwise direction. In <FIG>, the index is presented with boldface numbers. The first detection coils are advantageously series connected. The first excitation coils can be configured according to the earlier presented equation <NUM>: <MAT> where Ne0 is a predetermined integer, the absolute value of Ne(i) is the number of turns of the first excitation coil in ith one of the magnetic sensor sections of the first group <NUM>, and the sign of Ne(i) is indicative of a winding direction of the first excitation coil in the ith one of the magnetic sensor sections of the first group <NUM>. The first excitation coils are advantageously series connected. The second group <NUM> of successively placed magnetic sensor sections is advantageously like the first group of successively placed magnetic sensor sections.

<FIG> show exemplifying first and second alternating output signals <NUM> and <NUM> simulated for the variable reluctance resolver illustrated in <FIG> when the variable reluctance resolver has the following parameters and operational data:.

material of the electrically and/or magnetically conductive elements: aluminum.

The winding dimensions are the following:.

<FIG> show an envelope <NUM> of the first alternating output signal <NUM> shown in <FIG> and an envelope <NUM> of the second alternating output signal <NUM> shown in <FIG>.

<FIG> shows a positioning error related to the variable reluctance position sensor illustrated in <FIG>. The peak-to-peak positioning error is about <NUM> electrical degrees.

<FIG> shows a positioning error related to a variable reluctance position sensor which is otherwise like the variable reluctance position sensor illustrated in <FIG>, but which does not comprise the electrically and/or magnetically conductive elements <NUM>-<NUM>. In this exemplifying case, the peak-to-peak positioning error is about <NUM> electrical degrees which is notably greater than the peak-to-peak positioning error related to the variable reluctance position sensor illustrated in <FIG>.

In the exemplifying variable reluctance position sensors illustrated in <FIG>, <FIG>, <FIG>, <FIG>, 3c, <FIG> and <FIG>, adjacent ones of the magnetic sensor sections within each of the first and second groups are displaced with respect to each other in the direction of movement of the airgap surface by the spatial meandering period/N, where N is the number of the magnetic sensor sections in each of the first and second groups. As illustrated below with reference to <FIG> and <FIG> this is however not the only possible choice.

<FIG> illustrates a variable reluctance position sensor according to an exemplifying and non-limiting embodiment. The variable reluctance position sensor comprises a first element <NUM> and a second element <NUM>. In this exemplifying case, the variable reluctance position sensor is a variable reluctance resolver for measuring a rotational angle of the second element <NUM>, i.e. a rotor, with respect to the first element <NUM>, i.e. a stator. The rotational axis of the second element <NUM>, i.e. the rotor, is parallel with the z-axis of a coordinate system <NUM>. The first element <NUM>, i.e. the stator, comprises a plurality of magnetic sensor sections that are placed along an arc of a geometric circle in a direction of the airgap surface of the rotor. The second element <NUM>, i.e. the rotor, comprises an air-gap surface that has a periodically meandering profile with ten spatial meandering periods, i.e. the rotor comprises ten mechanical poles. First ones of the magnetic sensor sections constitute a first group <NUM> of successively placed magnetic sensor sections and second ones of the magnetic sensor sections constitute a second group <NUM> of successively placed magnetic sensor sections. The first ones of the magnetic sensor sections comprise first excitation coils and first detection coils configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils. Correspondingly, the second ones of the magnetic sensor sections comprise second excitation coils and second detection coils configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils. The first group <NUM> of successively placed magnetic sensor sections and the second group <NUM> of successively placed magnetic sensor sections are mechanically arranged so that the second group <NUM> is displaced with respect to the first group <NUM> in the direction of movement of the airgap surface, i.e. in the circumferential direction, by C × the spatial meandering period, where C is a non-integer number. In the exemplifying variable reluctance resolver illustrated in <FIG>, C = 2¼. In other words, the second group <NUM> is displaced with respect to the first group <NUM> by <NUM> electrical degrees + <NUM> electrical degrees i.e. by <NUM> electrical degrees which is <NUM> mechanical degrees. With this displacement between the first and second groups <NUM> and <NUM>, the phase-shift between the envelopes of the first and second alternating output signals is substantially <NUM> degrees.

The arrangement of the magnetic sensor sections shown in <FIG> can be derived from the arrangement of the magnetic sensor sections shown in <FIG> so that the magnetic sensor sections indexed as <NUM>, <NUM>, and <NUM> in the first group <NUM> shown in <FIG> are shifted by one meandering period in the clockwise direction and the magnetic sensor sections indexed as <NUM>, <NUM>, and <NUM> in the second group <NUM> shown in <FIG> are shifted by one meandering period in the counterclockwise direction. The shifting is depicted with dashed line arrows in <FIG>. As a corollary, adjacent ones of the magnetic sensor sections of each of the first and second groups <NUM> and <NUM> shown in <FIG> are displaced with respect to each other in the direction of movement of the airgap surface by <NUM> × the spatial meandering period/N except that the displacement between the middle ones of the magnetic sensor sections within each of the first and second groups <NUM> and <NUM> is <NUM> × the spatial meandering period/N, where N is the number of the magnetic sensor sections in each of the first and second groups so that N = <NUM>, where M is an integer i.e. N is even. In this exemplifying case N = <NUM>.

In the exemplifying variable reluctance position sensor illustrated in <FIG>, the first detection coils can be configured according to the following equations: <MAT> <MAT> where Ns0 is a predetermined integer, the absolute value of Ns(i) is the number of turns of the first detection coil in ith one of the magnetic sensor sections of the first group <NUM> and the sign of the Ns(i) is indicative of a winding direction of the first detection coil in the ith one of the magnetic sensor sections of the first group <NUM>. The first detection coils are advantageously series connected. In <FIG>, the index i of each magnetic sensor section is presented with a boldface number.

In the exemplifying variable reluctance position sensor illustrated in <FIG>, the first excitation coils can be configured according to the following equations: <MAT> where Ne0 is a predetermined integer, the absolute value of Ne(i) is the number of turns of the first excitation coil in ith one of the magnetic sensor sections of the first group <NUM>, and the sign of Ne(i) is indicative of a winding direction of the first excitation coil in the ith one of the magnetic sensor sections of the first group <NUM>. The first excitation coils are advantageously series connected.

In the exemplifying variable reluctance position sensor illustrated in <FIG>, the first element <NUM> comprises an electrically and/or magnetically conductive element <NUM> between the first and second groups <NUM> and <NUM> of successively placed magnetic sensor sections. Furthermore, the first element <NUM> comprises electrically and/or magnetically conductive elements <NUM> and <NUM> at the other ends of the first and second groups <NUM> and <NUM>. Furthermore, the first element <NUM> comprises an electrically and/or magnetically conductive element <NUM> between the middle ones of the magnetic sensor sections within the first group <NUM> and an electrically and/or magnetically conductive element <NUM> between the middle ones of the magnetic sensor sections within the second group <NUM>.

<FIG> illustrates a variable reluctance position sensor according to an exemplifying and non-limiting embodiment. The variable reluctance position sensor illustrated in <FIG> is otherwise like the variable reluctance position sensor illustrated in <FIG>, but the first element <NUM> comprises electrically and/or magnetically conductive elements placed between the magnetic sensor sections so that the magnetic sensor sections and the electrically and/or magnetically conductive elements are alternately in the direction of movement of the airgap surface of the first element <NUM>. Furthermore, the first element <NUM> comprises electrically and/or magnetically conductive elements <NUM> and <NUM> at ends of the first and second groups <NUM> and <NUM> of magnetic sensor sections. In <FIG>, three of the magnetic sensor sections that are between adjacent ones of the magnetic sensor sections are denoted with references <NUM>, <NUM>, and <NUM>.

In the exemplifying variable reluctance position sensors illustrated in <FIG>, <FIG>, <FIG>, <FIG>, 3c, <FIG>, <FIG>, <FIG> and <FIG>, each of the magnetic sensor sections has a magnetic core element that is separate with respect to magnetic core elements of other ones of the magnetic sensor sections. Each magnetic core element comprises material whose relative magnetic permeability µ is greater than one. The material is advantageously ferromagnetic material. Each magnetic core element may comprise e.g. a stack of electrically insulated steel sheets, ferrite, or soft magnetic composite. In the exemplifying variable reluctance position sensors illustrated in <FIG>, <FIG>, <FIG>, <FIG>, 3c, <FIG>, <FIG>, <FIG> and <FIG> each of the magnetic sensor sections has a H-shaped magnetic core element. It is also possible that each magnetic sensor section has a U-shaped magnetic core element, a C-shaped magnetic core element, an E-shaped magnetic core element, or a magnetic core element having some other suitable shape. Furthermore, it is also possible that two or more of the magnetic sensor sections have a common magnetic core that has teeth and a yoke connected to the teeth.

Claim 1:
A variable reluctance position sensor comprising:
- a first element (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising a plurality of magnetic sensor sections (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), and
- a second element (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) moveable with respect to the first element and comprising an air-gap surface (<NUM>, <NUM>, <NUM>, <NUM>) having a periodically meandering profile with at least two spatial meandering periods,
wherein:
- each of the magnetic sensor sections is configured to conduct a magnetic flux to and from the second element via the airgap surface of the second element, and
- first ones of the magnetic sensor sections comprise first excitation coils (<NUM>) and first detection coils (<NUM>) configured to produce a first alternating output signal when alternating excitation signal is supplied to the first excitation coils, and
- second ones of the magnetic sensor sections comprise second excitation coils (<NUM>) and second detection coils (<NUM>) configured to produce a second alternating output signal when alternating excitation signal is supplied to the second excitation coils, amplitudes of the first and second alternating output signals being dependent on a position of the second element with respect to the first element so that envelopes of the first and second alternating output signals have a phase-shift with respect to each other,
characterized in that the first ones of the magnetic sensor sections constitute a first group (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of successively placed magnetic sensor sections and the second ones of the magnetic sensor sections constitute a second group (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of successively placed magnetic sensor sections so that the second group of successively placed magnetic sensor sections is displaced (α) with respect to the first group of successively placed magnetic sensor sections in a direction of movement of the airgap surface by C × the spatial meandering period, where C is a non-integer number.