EP3227640A1

EP3227640A1 - Inductive position determination

Info

Publication number: EP3227640A1
Application number: EP15804761.3A
Authority: EP
Inventors: Thomas Erdmann; Ajoy Palit
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2014-12-04
Filing date: 2015-12-03
Publication date: 2017-10-11
Also published as: JP2017538937A; US20170310118A1; CN107003150A; DE102014224859A1; WO2016087562A1

Abstract

The invention relates to a device for inductive position determination comprising a signal generator, a coil connected to the signal generator, an element for influencing the inductance of the coil in accordance with the distance thereof to the coil and an evaluation device for determining the position of the element with respect to the coil, based on a voltage on the coil. Said signal generator generates a square-wave signal. Fig. 1 Nothing to translate

Description

Inductive position determination

The invention relates to an inductive position determination. In particular, the invention relates to the determination of a position of a device on board a motor vehicle.

In a motor vehicle position sensors are installed at different devices, which scan the position of a first element with respect to a second element, for example, to scan the position of a retractable window, a position of a seat or a shift position of a gear lever. A position sensor for detecting such a position may be constructed inductively, wherein a coil is attached to one of the elements and a conductive element is attached to the other. The coil can be acted upon by a sinusoidal voltage of a predetermined frequency, wherein the coil sets a complex voltage, which is dependent on the inductance of the coil. The closer the conductive element is to the coil, the stronger are the eddy currents induced in the conductive element which weaken the magnetic field in the region of the coil. The inductance of the coil is thereby adversely affected, so that the voltage drops across the coil. Thus, the position of the elements can be determined to each other on the basis of the coil voltage setting.

However, building a sine-wave generator usually requires either a sensitive analog circuit or a sophisticated digital circuit. In addition, the voltage at the coil usually has to be decoupled by means of an analog measuring amplifier in order to be able to be evaluated. Such amplifiers can bring about a pronounced temperature drift, a long settling time and an increased susceptibility to errors.

It is therefore an object of the present invention to provide an improved device for inductive position determination. The invention achieves this object by means of a device having the features of the independent claim. Subclaims give preferred embodiments again. An apparatus for inductive position determination comprises a signal generator, a coil connected to the signal generator, an element for influencing the inductance of the coil as a function of a distance to the coil and an evaluation device for determining the position of the element relative to the coil on the basis of a voltage on the coil , The signal generator provides a square wave signal. The signal generator provides the square wave signal to excite the coil. Thus eliminates all active electrical components that were traditionally necessary to allow an evaluation of the voltage across the coil. For example, it is no longer necessary to filter a signal from the signal generator with a low-pass filter, because a sinusoidal signal is no longer wanted. Furthermore, eliminates the need to reinforce the signal of the signal generator, because the conventional energy losses, which were due to the filtering, are thus eliminated. The square wave signal of the signal generator can thus act on the coil directly and / or by means of exclusively passive electrical components, and the production costs of such a device can thus be reduced. Furthermore, the scored coil voltage also does not necessarily have to be amplified. The square-wave signal can be realized for example by means of a digital logic circuit or by means of a programmable microcomputer. The voltage of the square wave signal can correspond to usual logic levels, for example, 0 volts and +5 volts, so that the square wave signal can be strong enough to cause a voltage on the coil, which can be clearly identified and detected by the evaluation. An amplifier for the square wave signal can be dispensed with as well as an amplifier for the voltage of the coil.

The fact that the number of active electrical components is reduced in this way reduces the start-up time or settling time until a stable measured value of the voltage of the coil is reached. In other words, when a square pulse is generated as part of the square wave signal from the signal generator, it takes a certain time until the voltage at the coil stabilizes.

By allowing a sample of this voltage to give a faulty sample when the voltage is sampled before the voltage is stable, it is advantageous if this settling time is as short as possible. The settling time is dependent, among other things, on the signal processing effort which is carried out between signal generation and signal arrival at the coil and on an ambient temperature. The elimination of a low-pass filter and a signal amplifier can be described as a reduction of the signal processing effort. Therefore, the inventive idea, the settling time is massively reduced, massive in this context, for example, a factor of ten may mean. Due to the fact that the temperature dependence of the settling time essentially depends on the temperature sensitivity of the active components, such as the amplifier, for example, the settling time is also shortened over the entire operating temperature range of the device by a reduction of the active components. The operating temperature range for electronics, which is used in automotive engineering, for example, between -40 degrees Celsius and +1 10 degrees Celsius.

The square wave signal may include a number of harmonics to a fundamental frequency, wherein the harmonics may each affect the voltage on the coil in the same way, so that the voltage signal on the coil with improved accuracy can point to the position of the element. The voltage may have a shortened rise or fall time, so that the position of the element can be determined more quickly. For example, a conventional measurement related to a sinusoidal voltage may require a measurement time of about 300 microseconds, while the proposed device may manage with a measurement time in the range of about 10 microseconds.

Furthermore, the elimination of electrical components enables a more compact design of the device. The reliability, as well as the expected service life are thereby also increased.

In one embodiment, a current limiting resistor is connected downstream of the signal generator in series with the coil. The current flowing through the coil can thus be limited to a predetermined maximum current value, and the life of the device can be increased. In a preferred embodiment, the coil is designed as a single-layer planar coil. By eliminating energy losses in the sensed voltage across the coil, it is no longer necessary to make the planar coil multilayer in such a device. Thus, the production costs can be further reduced, because the cost of producing multi-layer coils is considerably greater than the effort in the production of single-layer coils. For example, in the manufacture of multi-layer coils it is necessary to check each coil individually. In particular, it must be ensured that there is an electrical connection between the layers of the multilayer coil. In contrast, the integrity or functionality of a single-layer coil can be checked visually or visually automatically, because the entire coil is visible on a surface.

The voltage at the coil preferably comprises an alternating voltage with the frequency of the square wave signal and at least one further alternating voltage (harmonic wave) with an odd multiple frequency of the square wave signal. The further AC voltage usually has a lower amplitude than the first AC voltage. Generally, the square wave signal of infinitely many Sinusbzw. Cosine functions with frequencies that are multiples of the fundamental frequency, be composed. This synthesis is also known as Fourier series. The individual signals that make up the square-wave voltage can contribute to an increased voltage, which can be sampled as a measurement signal on the coil. The position of the element can thus be determined with greater sensitivity or greater speed. If an evaluation of the voltage by means of a programmable microcomputer, it may have a lower performance because of the shortened measurement time.

Preferably, an AC voltage applied to the coil is integrated by means of a low-pass filter into a DC voltage. This can in particular apply to the different AC voltages from which the square-wave signal is composed. Thus, the individual voltages can be easily and efficiently merged into a total voltage whose size can indicate improved the position of the element. It is further preferred that the coil is a planar coil. The planar coil may be formed, for example, as a printed circuit on the surface of a circuit board or other suitable carrier material. In one embodiment, the planar coil is multi-layered, in particular double-layered. The planar coil usually has only a few turns, for example in the range of about 9 to 30 turns. Accordingly, the basic inductance of the coil is relatively low. Due to the low inductance, the coil can influence voltage components of higher frequencies better, so that more harmonics of the fundamental can be evaluated. In addition, the planar coil can be easily handled, in particular in the area of the motor vehicle, due to its small thickness.

In a further embodiment, a controllable switching device is provided for connecting one end of the coil to a predetermined potential. The coil can be easily connected to the predetermined potential to perform a measurement with respect to the coil. Since the switching device leads to the predetermined potential, it does not have to be made suitable for high frequency, so that instead of a costly high-frequency transistor, for example, a low-cost low-cost transistor can be used as a switching device. The predetermined potential may in particular be a ground potential.

It is also possible to provide a plurality of coils, each with assigned switching devices. As a result, the signal generator, the evaluation device and possibly the low-pass filter can be used economically several times.

Preferably, a control device is provided, which is adapted to always close only one of the switching devices to perform a position determination with respect to the associated coil. The position of the element can thus be carried out successively with respect to a plurality of coils, so that an exact positioning is also possible over an enlarged range of movement of the element. It is further preferred that the evaluation device comprises an analog-to-digital converter and a microcomputer, wherein the microcomputer comprises a digital output, which is adapted to provide the square wave signal. In addition, the microcomputer may be configured to control one or more controllable switching devices. Thus, a simple and highly integrated assembly can be provided, which can be handled separately and is set up for easy and reliable position determination of the element.

In one embodiment, the element comprises an electrically conductive damping element. The inductance of the coil is reduced when approaching the damping element, as formed by the alternating magnetic field in the damping element eddy currents that reduce the energy of the alternating magnetic field.

In another embodiment, the element comprises a ferromagnetic and electrically insulating reinforcing element. The reinforcing element, when brought close to the coil, can increase the magnetic field strength in the region of the coil and thus increase the inductance of the coil.

In one embodiment, the device forms part of a switching device for selecting a gear stage of a motor vehicle.

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

Fig. 1 is a schematic representation of a device for inductive position determination; and

Fig. 2 is a schematic representation of an extended device according to the

Pattern of Fig. 1 represents.

FIG. 1 shows a device 100 for the inductive determination of the position of an element 105. The device can in particular be used on board a motor vehicle used to determine a position or position of a movable element. For example, the position of a selector lever for a gear ratio of a transmission can be scanned with respect to a console. In another embodiment, a steering angle between the motor vehicle and a trailer coupled by means of a trailer hitch can be determined. The magnetic element 105 is generally an element that affects an alternating magnetic field to which it is exposed. In this case, the element 105 may in particular be electrically conductive in order to weaken the alternating magnetic field in the region of the coil 15, or ferromagnetically and electrically insulating, in order to reinforce the magnetic alternating field in the region of the coil 15. In the first case, the element 105 may comprise, for example, copper or aluminum, in the second case, for example, iron, nickel or cobalt. The device 100 comprises in addition to the element 105 a signal generator 1 10 for providing a square wave signal, a coil 15 and an evaluation device 120, and a resistor R for current limiting, which is connected downstream of the signal generator 1 10 in series with the coil 15. The current flowing through the coil 15 can thus be limited to a predetermined maximum current value, and the life of the device can be increased.

The signal generator 1 10 provides at its output a square wave voltage with respect to a fixed potential, in the illustration of Figure 1 with respect to ground. The coil 15 is connected at a first end to the output of the signal generator 110 and at the other end to a further fixed potential, which may correspond to the other fixed potential. The evaluation device 120 is connected to the coil 15 and is adapted to sample a voltage which results at the coil 15 as a function of the rectangular signal of the signal generator 110. For this purpose, an integrator or low-pass filter 125 is preferably provided between the coil 15 and the evaluation device 120. Optionally, a diode 130 in the forward direction of the coil 1 15 lead to the low-pass filter 125. The low-pass filter 125 integrates high-frequency signals on the coil 15 for a predetermined period of time and provides the evaluation device 120 with a corresponding voltage. The position of element 105 with respect to coil 15 affects its inductance. Depending on the material of the element 105, the inductance of the coil 15 can be increased or decreased as the element 105 approaches the coil 15. The coil 15 is preferably designed as a flat coil, wherein it has a limited extent to remain manageable. The inductance of the coil 1 15 is therefore relatively low. The extent of the element 105 is usually in the range of the extent of the flat coil 1 15th

The square wave signal of the signal generator 1 10 can be regarded as a superposition of sine or cosine signals of different frequencies and amplitudes. A first sine signal has as a fundamental frequency the frequency of the square wave signal. Other sinusoidal signals have frequencies that correspond to integer multiples of the fundamental frequency. The higher the frequency, the lower is usually the amplitude of the frequency.

Odd multiples of the fundamental frequency are mutually reinforcing, so that the coil 1 15 - especially if its inductance is small - can react to several of the sinusoidal signals, so that the voltage dropping across it can be influenced several times by the position of the element 105. A voltage difference on the coil 15 with presence and absence of the element 105 can therefore be maximized. The measurement signal can have an improved signal-to-noise ratio and an amplifier for the measurement signal can be saved.

The evaluation device 120 may in particular comprise a digital-to-analog converter. This may provide a numerical value, for example, to a programmable microcomputer. However, another signal processing of the measuring voltage is also possible.

FIG. 2 shows a schematic representation of an expanded device 100 according to the pattern of FIG. 1. Here, a plurality of coils 1 15 are provided, one end of which is connected to the signal generator 1 10 via the resistor R. The respective other end can be connected by means of a switching device 205 with the predetermined, constant potential. The switching devices 205 can in particular be formed by transistors. Since the switching devices 205 do not have to transmit high frequencies regardless of the frequency of the rectangular signal of the signal generator 110, cost-effective low-frequency transistors, for example, can be used for this purpose.

The switching devices 205 are controlled by a control device 210, which may in particular comprise a programmable microcomputer. The control device 210 is configured to close only one of the switching devices 205 at any one time in order to carry out a measurement of the position of the element 105-or of several elements 105-with respect to the respective associated coil 15. The control device 210 can also carry out a further processing of the voltage determined by the evaluation device 120. In particular, when the controller 210 is implemented as a programmable microcomputer, the evaluation may include numerical or statistical operations.

In the illustrated embodiment, the control device 210 is also designed to provide the square-wave signal and thus also operates as a signal generator 1 10. For example, a serial or parallel interface of the controller 210 can be used, the rectangular signal with a relatively high amplitude, for example between 0 and 3, 3 volts or between 0 and 5 volts. For other voltages, limiters or amplifiers can be used.

By the above-described rectangular signal short settling times of the coils 1 15 can be effected. This means that a voltage which can be tapped on the coil 15 can indicate the presence or absence of the element 105 more quickly than with a sinusoidal signal. A measuring process with a single coil 15 can thereby be carried out relatively quickly, for example during a measuring phase of approximately 10 to 20 microseconds. Between individual measuring phases with different coils 15, one measuring interval can be inserted in each case, which may have a similar duration. Due to the short measuring times, many coils 1 15 can be interrogated successively by the control device 21 0, so that even with a low processing capacity of the control device 210 a safe and rapid positioning can be possible. The controller 210 may comprise a commercially available 8-bit microcomputer in a common application with up to about 20 coils 15. A 32-bit microcomputer, as required for sinusoidal-based measurement methods, can be saved.

The element 105 may be designed in its dimensions with respect to the arrangement of coils 1 15 so that it can affect several coils 1 15 simultaneously. Since the inductance of each coil 15 is more or less influenced depending on the spacing of the element 105, the exact position of the element 105 can then be estimated from ratios of the voltages provided by the affected coils 15 to the low-pass filters 125.

REFERENCE CHARACTERS

100 device

105 element

0 signal generator

1 15 coil

120 evaluation device

125 low pass filters

130 diode

205 switching device

210 control device

R resistance

Claims

claims

Device (100) for inductive position determination, comprising:

- a signal generator (1 10);

- One connected to the signal generator (1 10) coil (1 15);

- An element (105) for influencing the inductance of the coil (1 15) as a function of its distance from the coil (1 15);

- An evaluation device (120) for determining the position of the element (105) relative to the coil (1 15) on the basis of a voltage across the coil (1 15),

characterized in that

- The signal generator (1 10) provides a square wave signal.

Device (100) according to claim 1, wherein the voltage on the coil (1 15) comprises an alternating voltage with the frequency of the square wave signal and at least one further alternating voltage with an integer multiple frequency of the square wave signal.

Device (100) according to one of the preceding claims, wherein an AC voltage applied to the coil (1 15) is integrated by means of a low-pass filter (125) into a DC voltage.

Device (100) according to one of the preceding claims, wherein the coil (1 15) is a planar coil (1 15).

A device (100) according to any one of the preceding claims, further comprising controllable switching means (205) for connecting one end of the coil (15) to a predetermined potential.

Apparatus (100) according to claim 5, wherein a plurality of coils (1 15) are provided with respective associated switching means (205).

7. Device (100) according to claim 6, wherein a control device (210) is provided, which is adapted to always close only one of the switching means (205) to perform a position determination with respect to the associated coil (1 15).

8. Device (100) according to any one of the preceding claims, wherein the evaluation device (120) comprises an analog-to-digital converter and a microcomputer and the microcomputer comprises a digital output (1 10), which is adapted to provide the square wave signal.

9. Device (100) according to one of the preceding claims, wherein the element (105) comprises an electrically conductive damping element.

10. Device (100) according to one of the preceding claims, wherein the element (105) comprises a ferromagnetic and electrically insulating reinforcing element.

1 1. Device (100) according to at least one of the preceding claims,

characterized in that the signal generator (1 10) provides the square wave signal for exciting the coil (1 15).

12. Device (100) according to at least one of the preceding claims,

characterized in that the square-wave signal of the signal generator (1 10) can act on the coil (1 15) directly and / or by means of exclusively passive electrical components.

13. Device (100) according to at least one of the preceding claims,

characterized in that a resistor (R) for current limiting the signal generator in series with the coil (1 15) is connected downstream.

14. Device (100) according to at least one of the preceding claims,

characterized in that the coil (1 15) is designed as a single-layer planar coil.

15. Switching device for selecting a gear stage of a motor vehicle comprising a device according to at least one of the preceding claims.