DE102017212050A1 - Inductive speed determination - Google Patents

Abstract

A first element (110) is rotatably mounted relative to a second element (115) with respect to a rotation axis (120). A device (105) for determining the rotational speed of the first element (110) relative to the second element (115) comprises a coil (135) adapted for attachment to the first element (110); an influencing element (140) which is set up for attachment to the second element (115) so that once per revolution of the first element (110) relative to the second element (115) a surface of the influencing element (140) of an end face (150) of the coil ( 135) and a gap (155) between the influencing element (140) and the coil (135) falls below a predetermined width; a determining device (130) for determining a change in the inductance of the coil (135); and processing means (185) arranged to determine the speed based on a time interval between successive changes in inductance.

Description

The present invention relates to an inductive speed determination. In particular, the invention relates to the speed determination on a shaft, for example an electric machine.

On an electric machine, a shaft is rotatably mounted relative to a housing with respect to a rotation axis. The electric machine may for example comprise an electric motor or a generator, for example a wind power plant. To monitor or control the electric machine, the speed of the shaft is to be determined relative to the housing. For this purpose, a rotatable pinhole can be mounted on the shaft, which can drop light of a light source onto a light sensor only in a predetermined rotational position of the shaft. The light sensor may provide a light signal that is output at the same rotational position of the shaft relative to the housing. Based on a time interval of successive pulses, the rotational speed of the shaft can be determined.

Often, however, dirt, oil, moisture or dust accumulates along the optical path, so the accuracy of the determination may be affected.

Another approach uses a permanent magnet mounted on the shaft and an integrated Hall sensor to determine a magnetic field. Magnetic sensor and magnet are aligned with each other so that the sensor can provide a signal indicative of a predetermined rotational position of the shaft with respect to the housing. The magnet or the magnetic sensor can be relatively expensive. In addition, an external magnetic field, which may arise, for example, in an industrial environment based on a large current flowing in a nearby cable, can impair the magnetic speed determination.

An object underlying the invention is to provide an improved technique for inductive speed determination. The invention solves this problem by means of the subjects of the independent claims. Subclaims give preferred embodiments again.

A first element is rotatably mounted relative to a second element with respect to a rotation axis. An apparatus for determining the rotational speed of the first member relative to the second member comprises a spool adapted for attachment to the first member; an influencing element, which is set up for attachment to the second element, so that once per revolution of the first element relative to the second element, a surface of the influencing element faces an end face of the coil and a gap between the influencing element and the coil falls below a predetermined width; a determining device for determining a change in the inductance of the coil; and a processing device configured to determine the speed based on a time interval between successive changes in the inductance.

The device can be made simple and inexpensive. The speed of the first relative to the second element can be determined easily and safely. For example, the device may be attached to an electric machine, an internal combustion engine, a powertrain, a transmission, or other arrangement in which a first element continues to rotate with respect to a second element. By determining the change in the inductance, an external influence, for example by a displacement of the influencing element or the coil with respect to the associated element can be compensated.

Preferably, the determination device is adapted to apply an AC voltage to the coil in order to generate an alternating magnetic field in the region of the coil. The influencing element is further configured to influence the alternating magnetic field differently depending on its distance from the coil. In this case, the determination device is set up to determine the change in the inductance on the basis of a change in the alternating voltage.

The detection of a predetermined rotational position of the first element relative to the second element can be carried out so easily and interference-proof. An external constant or variable magnetic field can usually affect the AC voltage applied to the coil only in a frequency range which is outside the rotational frequency of the elements against each other. In particular, a constant or very low-frequency magnetic interference signal can be filtered out so easily.

The coil is preferably formed as a flat coil. This allows the coil to be easily manufactured. The finished coil may be small and lightweight, so its attachment to the first or second element may have little or no side effects on the associated element.

The direction of extension of the coil is defined with respect to an axis about which the individual turns of the coil run. In a Embodiment are all turns of the coil in a position that can be particularly flat. In another embodiment, a plurality of layers are provided, which are preferably arranged parallel to each other. For this purpose, the turns of a layer can be applied to the surface of a carrier material. Electrical connections between turns of different layers can be realized by means of plated-through holes. It is preferred that the pancake comprises a plurality of turns in each ply. In a particularly simple embodiment, two layers are provided, which are arranged on the upper side and the lower side of a carrier material. Windings of the flat coil on the carrier material can be provided for example by means of methods of producing a printed circuit (printed circuit board, circuit board).

It is particularly preferred that the coil is made flexible. In particular, a flat coil can be designed to be flexible so that it can be attached to the cylindrical surface of a shaft or a housing in an improved manner. The flexibility of the coil can be effected by the fact that the carrier material, which separates turns on different layers, is also flexible.

The carrier material is preferably an electrical non-conductor and in one embodiment the coil is electrically insulated on one or both end faces by an additional layer. This layer may comprise, for example, a cover layer, a color layer or a dedicated insulating layer.

Similarly, the influencing element can be made flexible. The influencing element is preferably made flat and thin, as will be described in more detail below. Due to its flexibility, it can be improved adapted to a cylindrical lateral surface, which describes the associated first or second element. The influencing element can also be electrically isolated on one or both sides.

The influencing element can be set up in different variants to damp or amplify the magnetic alternating field of the coil. In a first variant, the influencing element comprises an electrical conductor in order to extract energy from an alternating magnetic field by forming eddy currents. As a result, the alternating magnetic field is weakened, so that the voltage applied to the coil AC voltage can be reduced. For example, a thin piece of metal, for example a sheet or a foil, can be used for the influencing element. The metal is preferably highly conductive and may include, for example, copper.

In a second variant, the influencing element comprises a soft magnetic and electrically insulating material, in particular to locally reinforce a magnetic alternating field. Local within the meaning of the invention means within a predetermined distance from the coil. The material may include, for example, a high permeability ferrite material. This material can help to direct the alternating magnetic field of the coil so that the inductance of the coil increases. The voltage applied to the coil AC voltage can increase in this variant, when the influencing element is approximated to the coil.

A system includes the above described apparatus and arrangement with the first and second elements. The coil is attached to one of the elements and the influencing element on the other element.

The arrangement may in particular comprise an electric machine and the device may be integrated in a control of the electric machine. For example, the electric machine may comprise a brushless DC motor and the control of individual phases of the electric motor may be performed against each other in dependence on a rotational speed and / or rotational position of the elements. In particular, the control can be performed in a field-oriented manner.

In general, it is preferred that the coil is attached to the rotatable element which is stationary with respect to an environment. The device described above can be fixed easier and possibly supplied with electrical signals or energy. The influencing element is fastened in this case to the element which rotates with respect to the environment.

In a variant of the system, the coil is aligned coaxially with the axis of rotation. To attach the coil or the influencing element to that rotatable element that does not stand still with respect to the environment, a disc or holder may be provided. In another variant of the system, the coil is aligned radially to the axis of rotation. This variant is particularly recommended when attaching a disc or holder on the rotatable element is undesirable.

The coil and / or the influencing element can be glued to the respectively associated rotatable element. For this purpose, the system may comprise an adhesive element for fastening the coil or the influencing element to the respectively associated rotatable element. In particular, in the second variant with radially extending to the axis of rotation coil, a surface of the coil and / or the influencing element to a Cylindrical surface adapted and fixed surface by means of the adhesive element.

• 1 ein System mit einer Vorrichtung zur Bestimmung der Drehzahl zweier gegeneinander drehbar gelagerter Elemente in einer ersten Ausführungsform;
• 2 ein System mit einer Vorrichtung zur Bestimmung der Drehzahl zweier gegeneinander drehbar gelagerter Elemente in einer zweiten Ausführungsform;
• 3 einen beispielhaften Zusammenhang zwischen der Induktivität einer Spule und dem Abstand eines Beeinflussungselements;
• 4 ein beispielhaftes zeitabhängiges Signal an einer Vorrichtung nach 1 oder 2;
• 5 beispielhafte Ausführungsformen einer Spule und eines Beeinflussungselements für eine Vorrichtung nach 1 oder 2

darstellt.The invention will now be described in more detail with reference to the attached figures, in which:

• 1 a system having a device for determining the rotational speed of two mutually rotatably mounted elements in a first embodiment;
• 2 a system comprising a device for determining the rotational speed of two mutually rotatably mounted elements in a second embodiment;
• 3 an exemplary relationship between the inductance of a coil and the distance of an influencing element;
• 4 an exemplary time-dependent signal to a device according to 1 or 2 ;
• 5 exemplary embodiments of a coil and an influencing element for a device according to 1 or 2

represents.

1 shows a system 100 with a device 105 attached to a first element 110 and a second element 115 are attached. The Elements 110 . 115 are with respect to a rotation axis 120 rotatably mounted against each other. The present is the first element 110 exemplary as a housing and the second element 115 as a wave of an electric machine 125 educated. In other embodiments, the elements may 110 . 115 but also serve other purposes or be executed differently.

The device 105 comprises a determination device 130 , a coil 135 and an influencing element 140 , Present is the coil 135 mechanically on the first element 110 and the influencing element 140 on the second element 115 appropriate; a reverse assignment is also possible. The sink 135 extends along an axis 145 that are radial to the axis of rotation 120 runs. An angle between the axis 145 and the axis of rotation 120 is preferably about 90 °, with the axes 120 . 145 cut or can be skewed to each other.

The sink 135 is preferably made flat, that is, that its outer diameter is preferably several times greater than its thickness along the axis 145 is. A front page 150 the coil 135 has radially on the second element 115 in the area of the influencing element 140 ,

The influencing element 140 is so on a circumference about the axis of rotation 120 attached it once at every turn of the elements 110 . 115 against each other the front side 150 the coil 135 is facing. A gap 155 between the coil 135 and the influencing element 140 has a width of d. Rotates the second element 115 in the presentation of 1 opposite the first element 110 further, the influencing element wanders 140 laterally out of the area opposite the front side 150 the coil 135 out. Lie the coil 135 and the influencing element 140 opposite each other, so their relative direction of movement in a plane that runs the gap 150 essentially contains.

The determination device 130 includes an AC voltage source 160 , which provides an AC voltage, for example, of sine or rectangular form, here by means of a resistor 165 to the coil 135 is coupled. In this case, the AC voltage has a predetermined frequency and amplitude, for example, the frequency may be in the range of about 10 to 15 MHz and the amplitude in the range of about 5 V. Due to the AC voltage is formed in the coil 135 and in particular its front side 150 an alternating magnetic field generated by the influencing element 140 can be influenced. The strength of the influence depends on the position of the influencing element 140 concerning the coil 135 and thus of the rotational position of the elements 110 . 115 up to today.

The determination device 130 further comprises a rectifier 170 which may include, for example, a Schottky diode and optionally a smoothing capacitor or low pass. The rectified voltage of the coil 135 can by means of a comparator 175 be compared with a predetermined threshold. At a first interface 180 Then a binary signal can be provided, the level of which indicates whether the elements 110 . 115 are in a rotational position in which the influencing element 140 close to the coil 135 is or not. This signal can be generated by means of a processing device 185 be further evaluated. In particular, time intervals between rising or falling edges of the binary signal can be determined and from this the rotational speed of the elements 110 . 115 be derived against each other. The specific speed can be at a second interface 190 to be provided.

2 shows a system 100 with a device 105 in a second embodiment. Unlike the in 1 illustrated embodiment is here the axis 145 , along which the coil 135 extends, substantially coaxially or parallel to the axis of rotation 120 , By way of example, the coil 135 again the first element 110 and the influencing element 140 the second element 115 assigned; a reverse mapping is also here possible. With the changed orientation of the coil 135 is also the orientation of the influencing element 140 changed. The gap 155 runs in the radial direction with respect to the axis of rotation 120 , its width d is dimensioned in the axial direction and the influencing element 140 is essentially in a plane of rotation about the axis of rotation 120 , Accordingly, the coil is located 135 essentially in a parallel plane of rotation.

To the influencing element 140 to arrange as described is on the second element 115 exemplarily a disc 205 appropriate. The disc 205 can be omitted if on the second element 115 another element is provided, opposite to the influencing element 140 can be fixed in the position shown. The free rotation of the elements 110 . 115 against each other should not be affected. The sink 135 can be right on the first element 110 or as shown by means of a support member to be attached thereto. Compared to the embodiment of 1 the carrier element can be designed simpler.

3 shows an exemplary relationship between the inductance of a coil 135 and the distance of an influencing element 110 , In the horizontal direction is a distance d between the coil 135 and the influencing element 140 and in the vertical direction, the inductance L the coil 135 plotted.

A first course 305 indicates how the inductance L decreases from a nominal value (horizontal axis) when the influencing element designed as a damping element 140 to the coil 135 is approximated and eddy currents in the influencing element 140 form. A maximum reduction in inductance L at minimum distance d can be about 20 to 30%. A second course 310 shows the increase in inductance L when approaching the designed as a reinforcing element influencing element 140 to the coil 135 at. The gain can reach about 40 to 50% at the smallest distance d.

For the present invention, alternatively, a reinforcing element or a damping element as an influencing element 140 are used, the absolute change of the inductance is crucial L the coil 135 upon approach of the influencing element 140 , The location of each meaningful thresholds can be determined from the representation of 3 be estimated approximately. To achieve hysteresis, two thresholds can also be used.

4 shows an exemplary time dependent signal applied to a device 105 one of 1 or 2 can be observed. It is assumed that the elements 110 . 115 rotate at a constant speed against each other. The influencing element 140 is preferably designed as a reinforcing element, so that a signal 405 at the first interface 180 logical 1 is when the influencing element 140 close to the coil 135 is, and otherwise logical 0 , The levels 0 and 1 are caused by different voltages in 4 represents.

At the time t1 the signal changes 405 from 0 on 1 and at a time t2 back on again 0 , A corresponding process will take place later at times t3 and t4 instead of. The time interval between t1 and t2 is like the between t3 and t4 a duration of tw. The time interval between t1 and t3 is T ,

The width of the approach to the influencing element 140 to the coil 135 indicative signal 405 , So the duration of tw is essentially dependent on how strong the rotation angle dependent influencing the inductance of the coil 135 through the influencing element 140 is and how large a threshold was chosen, the rectified voltage of the coil 135 must exceed to cause a signal change. Usually: tw << T.

Beträgt T beispielsweise 30 ms, so gilt $RPM=\frac{60.000}{30}=\mathrm{2.000.}$

Die Winkelgeschwindigkeit co bestimmt sich zu $\varpi =\frac{RPM\cdot 2\pi }{60}.$

The time T , which alternatively also between the falling edges too t2 and t4 can be determined, returns the time that passes, while the elements 110 . 115 describe a full turn against each other. From this, the RPM RPM can be determined as follows: $RPM=\frac{1}{T},$

For example, if T is 30 ms, then $RPM=\frac{\mathrm{60,000}}{30}=2000.$

The angular velocity co determines itself $\pi =\frac{RPM\cdot 2\pi }{60},$

5 shows exemplary embodiments of a coil 135 and an influencing element 140 for a device 105 or a system 100 after the 1 or 2 ,

5A shows a plan view of the coil 135 in one embodiment as a flat coil with angular windings. Round, oval or other shaped turns can also be used. The influencing element 140 , which is only shown as an outline, is hexagonal and big enough to hold the coil 135 cover at least approximately. Upon rotation of the elements 110 . 115 against each other becomes the influencing element 140 preferably in the drawing plane opposite the spool 135 postponed.

5B shows a similar embodiment, but in which the influencing element 140 is rhombus-shaped. The rhombus can be in an outline of the coil 135 inscribed so that the surface of the influencing element 140 smaller than that of the coil 135 is.

5C shows a side view (in longitudinal section) of an embodiment of the coil 135 as a print coil or printed circuit. Upon rotation of the elements 135 . 140 The influencing element is moved from left to right (or vice versa) or away from the observer (or towards it) in the illustration. On a carrier material 505 is the coil 135 in two layers 510 and 515 divided up. The carrier material may be, for example, polyimide, ceramic, glass or FR4 include. In every situation 510 . 515 are preferably several turns of the coil 135 arranged, such as in the top of 5A or 5B , Here are the layers 510 and 515 on opposite surfaces of the flat substrate 505 educated. In other embodiments, multiple layers of carrier material may also be used 505 alternating with layers 510 . 515 be used, it is also called a multilayer board.

5D shows an axial view of a further embodiment, in which the coil 135 and / or the influencing element 140 essentially have the shape of circle segments. This embodiment can in particular with axial alignment of the elements 135 . 140 as above with respect to 2 has been explained.

Both the coil 135 as well as the influencing element 140 are preferably made flat. This means that their thickness is at least an order of magnitude smaller than their edge length. The sink 135 and the influencing element 140 can each be on the surface of a substrate 505 to be appropriate. The carrier material 505 For example, by means of an adhesive element, that is to say an adhesive, an adhesive film or an adhesive carrier material, it can be attached to the surface of an element which is in contact with the respectively associated rotatable element 110 . 115 engaged. In other words, the coil can 135 and / or the influencing element 140 be attached by gluing. Especially with the radial alignment of the axis 145 referring to above 1 may be required, one of the elements may be required 135 . 140 to adapt to a cylindrical surface. In the presentation of 1 For example, the influencing element 140 directly on the shaft 115 be glued radially outward. This can be done by the coil 135 and / or the influencing element 140 be designed to be flexible accordingly. In particular, it is preferred that the carrier material 505 is flexible. A suitable flexible carrier material comprises, for example, polyimide.

The sink 135 and the influencing element 140 can be relatively small to the speed of an electric machine 125 safe to determine. In a purely exemplary embodiment according to 5A is an outer edge length of the square executed coil 135 about 10 mm, the individual turns have a thickness of about 35 microns and a width of about 0.12 mm. There are two layers 510 . 515 provided, in each case 20 turns of the coil 135 lie. The vertical distance between the layers 510 . 515 is about 70 microns. The distance d is about 3 mm. The sink 135 is operated at an AC voltage of about 5 V with a square wave signal of about 12 MHz. The inductance of the coil 135 is unaffected by approx. 9 μH and under the influence of an influencing element implemented as a damping element 140 from copper sheet or foil approx. 8.3 μH.

LIST OF REFERENCE NUMBERS

100

system

105

contraption

110

first element

115

second element

120

axis of rotation

125

electric machine

130

determiner

135

Kitchen sink

140

influencing element

145

axis

150

front

155

gap

160

AC voltage source

165

resistance

170

rectifier

175

comparator

180

first interface

185

processing device

190

second interface

205

disc

305

first course (damping element)

310

second course (reinforcing element)

405

signal

505

support material

510

first location

515

second location

Claims (12)

A device (105) for determining the rotational speed of a first element (110) which is rotatably mounted relative to a second element (115) about a rotation axis (120), wherein the device (105) comprises: a coil (135), the Attachment to the first element (110) is set up; an influencing element (140) which is set up for attachment to the second element (115) so that once per revolution of the first element (110) relative to the second element (115) a surface of the influencing element (140) of an end face (150) of the coil ( 135) and a gap (155) between the influencing element (140) and the coil (135) falls below a predetermined width; a determination device (130) for determining a change in the inductance of the coil (135); processing means (185) adapted to determine the speed based on a time interval between successive changes in the inductance. Device (105) according to Claim 1 wherein the determining device (130) is adapted to apply an AC voltage to the coil (135) in order to generate an alternating magnetic field in the region of the coil (135); the influencing element (140) is adapted to influence the alternating magnetic field differently depending on its distance from the coil (135); and the determining device (130) is configured to determine the change in the inductance based on a change in the AC voltage. Device (105) according to Claim 1 or 2 wherein the coil (135) is formed as a flat coil (135). Device (105) according to Claim 3 wherein the flat coil (135) comprises a plurality of mutually parallel layers (510, 515) each having a plurality of turns. Device (105) according to one of Claims 3 or 4 wherein the coil (135) is flexible. Device (105) according to one of the preceding claims, wherein the influencing element (140) is made flexible. Device (105) according to one of the preceding claims, wherein the influencing element (140) comprises an electrical conductor for drawing energy from an alternating magnetic field by forming eddy currents. Device (105) according to one of Claims 1 to 6 , wherein the influencing element (140) comprises a soft magnetic and electrically insulating material, in particular to locally amplify an alternating magnetic field. A system (100) comprising a device (105) according to one of the preceding claims and an arrangement having a first (110) and a second element (115) which are rotatably mounted relative to one another with respect to a rotation axis (120), wherein the coil (135 ) on one element (110, 115) and the influencing element (140) on the other element (110, 115) is mounted. System (100) after Claim 9 wherein the coil (135) is aligned coaxially with the axis of rotation (120). System (100) after Claim 9 wherein the coil (135) is aligned radially with respect to the axis of rotation (120). System (100) according to one of Claims 9 to 11 , further comprising an adhesive member for securing the coil (135) or the influencing element (140).

Images