Method for current and position measurement on a valve device

Abstract

Method for current and position measurement on a valve device comprising: a valve member (70), an actuator (12) comprising an electronically commutated electric motor (14) with a stator (16) having a stator winding (18, 20) and a permanent magnet rotor (22), a first coupling element (61) which can be rotated by means of the actuator (12), a valve rod (66) secured against rotation, at the first axial end (71) of which the valve member (70) is formed, and which has a second coupling element (69) which interacts with the first coupling element (61) in such a way that the rotational movement of the first coupling element (61) is converted into a translational movement of the second coupling element (69) and the valve rod (66), and a magnetoresistive sensor (94) which interacts with a permanent magnet (98), wherein the permanent magnet (98) is axially magnetized and attached to the second axial end (100) of the valve stem (66),the central axis of which coincides with the central axis of the stator (16), wherein the magnetoresistive sensor (94) is arranged on this central axis opposite the second axial end (100) of the valve stem (66) and generates a voltage signal (96) which is proportional to the magnetic field acting on it in the axial direction, wherein the valve device has an evaluation unit (102), wherein the voltage signal (96) of the sensor (94) is supplied to the evaluation unit (102), and wherein the evaluation unit (102) has a filter (106, 110) for generating a first, high-frequency voltage signal (112) and a second, low-frequency voltage signal (108), wherein, according to the method, a low-frequency voltage signal (108) is generated in the evaluation unit (102) by filtering the voltage signal (96) of the magnetoresistive sensor (94),which serves as a measure for the axial position of the valve stem (66) and generates a high-frequency voltage signal (112) which serves as a measure for the current in the stator winding (18).

Description

The invention relates to a method for a valve device comprising a valve element, an actuator comprising an electronically commutated electric motor with a stator having a stator winding and a permanent magnet rotor, a first coupling element which can be rotated by means of the actuator, a valve rod secured against rotation, at the first axial end of which the valve element is formed, and which comprises a second coupling element which interacts with the first coupling element in such a way that the rotational movement of the first coupling element is converted into a translational movement of the second coupling element and the valve rod, and a magnetoresistive sensor which interacts with a permanent magnet, as well as a method for current measurement and position measurement on such a valve device. Such valve devices can be used in the automotive sector, for example, as exhaust gas recirculation valves or expansion valves for refrigeration or air conditioning systems. Their purpose is to reduce the pressure of the working fluid by throttling the available flow cross-section and to increase the volume of the working fluid, i.e., to expand it. By using controlled expansion valves, both the pressure drop and thus the volume increase can be regulated, and the fluid flow can be almost completely interrupted. In refrigeration or air conditioning systems, these valves are positioned before the evaporators and after the condensers. The increase in volume causes some of the working fluid to evaporate, while the remaining liquid fluid in the evaporator absorbs heat, causing the liquid portion to also evaporate. This now gaseous working fluid is fed to a compressor and compressed, before being converted back into a liquid state in the condenser, thus completing the closed cycle. Heat or cooling can be extracted from this cycle at the evaporators and condensers. To precisely control the pressure drop across the expansion valve and the associated increase in volume, it is desirable to know the position of the valve element relative to the valve seat as accurately as possible and to be able to adjust it accordingly. Furthermore, it is desirable to measure the current flow in the stator, which is usually done using a shunt. To determine the position of the valve element, EP 3 910 266 A1 proposes an electrically actuated expansion valve driven by a claw-pole motor. The rotor of the canned motor is connected to a spindle nut in which a spindle rod is rotatably mounted. This spindle rod moves axially when the rotor rotates. The rotor's angle of rotation is detected by an angle sensor that interacts with permanent magnets located in the rotor. However, a disadvantage is that the valve stroke can only be calculated indirectly via the angle of rotation and the number of rotations. Consequently, a voltage output from the sensor cannot be unambiguously assigned to a specific position of the spindle rod. Current measurement is not disclosed. Another valve device is known from JP 2005 - 321 029 A. DE 10 2017 108 654 A1 discloses a signal evaluation via a filter, by which the sensor signal is divided into a low-frequency and a high-frequency component. The challenge, therefore, is to provide a method for position and current measurement that allows for the precise determination of the stroke position of the valve stem or the valve element mounted on the valve stem, without requiring conversions or accepting inaccuracies, for example, due to changing play between the threads of the valve stem and the spindle nut. Furthermore, current measurement should be performed with minimal effort. The number of components and thus the cost of such a valve device should be minimized. This problem is solved by a method using a valve device comprising a valve element that serves to change the flow cross-section during a stroke movement. For this purpose, the valve element is either placed on or lifted from a valve seat, or pushed into the corresponding flow cross-section. This displacement is effected by an actuator comprising an electronically commutated electric motor with a stator having a stator winding and a permanent magnet rotor. This rotor is either formed integrally with a first coupling element or this coupling element is attached to it. Furthermore, the valve device has a valve rod secured against rotation, at the first axial end of which the valve element is formed, which can be formed integrally with the valve rod or attached to it.The valve stem has a second coupling element which interacts with the first coupling element in such a way that the rotational movement of the rotor, and thus of the first coupling element, is converted into a translational movement of the second coupling element, and thus of the valve stem. This can be achieved, for example, by interlocking threads or cams with pins running therein, with or without rollers. An axially magnetized permanent magnet is attached to the second axial end of the valve stem, i.e., the end of the valve stem opposite the valve member. The central axis of this permanent magnet and of the valve stem simultaneously forms the central axis of the stator and the axis of rotation of the rotor. Furthermore, according to the invention, a magnetoresistive sensor is arranged on the central axis opposite the second axial end of the valve stem.This generates a voltage signal that is proportional to the axially directed magnetic field acting upon it. Additionally, according to the invention, the valve device includes an evaluation unit to which the voltage signal is fed and which has a filter that splits the voltage signal into a first, high-frequency voltage signal and a second, low-frequency voltage signal. This can be achieved, for example, digitally by demodulation or analogously by known filter circuits. According to the inventive method, a low-frequency voltage signal is generated in the evaluation unit by filtering the voltage signal of the magnetoresistive sensor. This low-frequency signal serves as a measure of the axial position of the valve stem, while a high-frequency voltage signal is generated as a measure of the current in the stator winding. The low-frequency signals are thus used for position determination because the sensor's voltage signal decreases with increasing distance of the permanent magnet from the sensor, as the magnetic field acting on the sensor weakens. However, this voltage signal is superimposed on a signal generated by the stray field of the stator.It has been shown that this axially acting magnetic stray field of the stator, which is detected by the sensor as a high-frequency voltage signal, has a direct dependence on the current flow in the stator, so that it can be used to measure the current. This high-frequency signal is generated by the rapidly changing magnetic fields during pulse-width modulation as well as during sinusoidal control. Accordingly, both the current measurement and the position determination of a valve device according to the invention can be performed with just one sensor. In this way, the number of components and the resulting costs are reduced. Preferably, the first coupling element is a spindle nut with an internal thread, which is connected to the rotor (this can also be achieved by manufacturing it in one piece), and the valve stem, as the second coupling element, comprises a spindle rod whose external thread engages the internal thread of the spindle nut. The valve stem can thus either be designed as a spindle rod with an external thread itself or be connected to it. Such a motion coupling provides a particularly simple conversion of rotary motion into translational motion. The electric motor is advantageously designed as a claw-pole motor, which is inexpensive to manufacture and has a high efficiency. When using a double-claw-pole motor, the current is measured in the stator winding located closer to the sensor. The magnetoresistive sensor is preferably a linear Hall sensor. The output voltage of these sensors is proportional to the magnetic field strength acting on them in the selected direction, in this case, the axial direction. Thus, there is a proportionality to the magnetic field generated by the current flow in the winding and to the distance between the magnet and the sensor, making it suitable as both a current and position sensor. In a preferred embodiment, the sensor is arranged on a circuit board, on the side of which opposite the sensor a second, stationary permanent magnet is arranged, having an opposite axial polarity to the permanent magnet on the valve stem. This additional magnet focuses the field lines of the first permanent magnet and thus improves the sensor's output signal, enabling more precise position determination. Preferably, the filter is designed as a high-pass filter, so that the high-frequency signals present due to the current flow in the stator are passed through, while the low-frequency signals from the permanent magnet used for position determination are filtered out. Accordingly, this filtered voltage signal from the sensor is a direct measure of the current flow in the stator. Such a high-pass filter can have a coupling capacitor that filters out DC voltage signals, such as those generated by the sensor's voltage output signal due to the position of the permanent magnet, and allows AC voltage signals, such as those generated at the sensor by the energizing of the stator, to pass through. Alternatively or additionally, a low-pass filter can be used to filter out the high-frequency signals generated by the current flowing to the stator at the sensor, so that the filtered output signal is a measure of the position of the permanent magnet relative to the sensor and thus of the position of the valve element. According to the method, the voltage signal of the sensor is advantageously fed to a low-pass filter, thereby generating the low-frequency voltage signal, which serves as a measure of the axial position of the valve stem, and this low-frequency voltage signal is subtracted from the measured voltage signal, thereby generating a high-frequency voltage signal, which serves as a measure of the current in the stator winding. Alternatively, the sensor's voltage signal is fed to a high-pass filter, generating a high-frequency voltage signal that serves as a measure of the current in the stator winding, and this high-frequency voltage signal is subtracted from the measured voltage signal, generating a low-frequency voltage signal that serves as a measure of the axial position of the valve stem. Thus, the respective filtered signal is generated by taking the difference between the original signal and the filtered signal, so that the signal representing a measure of the current intensity is available for evaluation independently of the signal representing a measure of the position of the valve element. In an alternative implementation of the method, the sensor's voltage signal is fed to a low-pass filter, generating the low-frequency voltage signal that serves as a measure of the axial position of the valve stem, and then to a high-pass filter, generating the high-frequency voltage signal that serves as a measure of the current in the stator winding. No further conversions are then necessary. When using a claw-pole motor, the high-frequency voltage signal serves as a measure of the current in the stator winding located closer to the sensor. It can be assumed that the current in the more distant winding is the same. In a preferred embodiment of the method, the electric motor has a containment shell that separates the rotor from the stator and has a base that separates the sensor from the permanent magnet arranged on the valve stem. Thus, the rotor chamber can be designed to allow fluid flow, since the sensitive stator windings and the electronics with the sensor are separated from the fluid-filled interior by the containment shell. This provides a method for measuring current and position in such a valve device, enabling the determination of both the electric motor's current and the valve element's position using only one sensor, such as a cost-effective linear Hall sensor. This simplifies the design of such a valve, as the number of electronic components can be reduced. An embodiment of the method according to the invention, using a valve device according to the invention, is illustrated in the figures using the example of an expansion valve and is described below. Fig. 1 shows a side view of a valve device in a sectional view. Fig. 2 shows the signal waveform of the sensor during current and position measurement. The valve device shown in Fig. 1 is designed as an expansion valve 10 for a refrigerant or air conditioning circuit and has an actuator 12 in the form of a brushless electric motor designed as a claw-pole motor 14. This claw-pole motor 14 consists of a radially outer, wound stator 16 with an upper stator winding 18 and a lower stator winding 20, and a radially inner permanent magnet rotor 22. An outer chamber 24, in which the stator 16 is arranged, is separated from an inner chamber 26, in which the rotor 22 is arranged, by a containment shell 28. The containment vessel 28 has an axially bounding base 30 from which a cylindrical outer surface extends axially. A stationary housing part 32 of the expansion valve 10 projects into the containment vessel 28, or rather into its cylindrical outer surface. A radial groove 38 is formed on a radially outer wall 36 of the housing part 32, in which a sealing ring 40 is arranged, bearing radially against the outer surface of the containment vessel 28. Additionally, a shoulder 42 is formed on the radially outer wall 36, with which the housing part 32 abuts a collar 44 at the axial end of the containment vessel 28. The opposite axial side of the collar abuts a shoulder 46 on an actuator housing part 50. Accordingly, the containment vessel 28 provides a fluid-tight separation between the stator 16 and the rotor 22. The actuator housing part 50 radially surrounds the stator 16 and the containment pot 28. On the side axially opposite to the housing part 32, the actuator housing part 50 projects beyond the stator 16 and forms a chamber 54 beyond the bottom 30 of the containment pot 28, which is closed by a cover 56 and serves as a receptacle for an electronic unit 58, which is arranged axially opposite to the bottom 30 of the containment pot 28. The rotor 22 has a radially inner receiving opening 60 directed towards the open side of the containment pot 28, in which a spindle nut 62 serving as the first coupling element 61 is fastened, which has an internal thread 63 which corresponds to an external thread 64 of a spindle rod 68 formed integrally with a valve rod 66, which accordingly serves as the second coupling element 69. A valve element 70 is arranged at a first axial end 71 of the valve stem 66, located remote from the bottom 30 of the containment vessel 28. This valve element 70 interacts with a valve seat 72, which is formed on the housing part 32 of the expansion valve 10. The valve element 70 is placed onto or lifted from the valve seat 72 when the rotor 22 rotates, thus enabling precise control of the free flow cross-section between the valve seat 72 and the valve element 70 as a function of the rotor 22's rotational position. For this purpose, the valve stem 66 is axially displaceable over the valve element 70 in a sliding bearing 74. Axially extending webs 76 are formed on the valve element 76 outside the valve seat 72. These webs engage in grooves 78 of the sliding bearing 74 and secure the valve stem 66 against rotation.Accordingly, the rotation of the rotor 22 and with it the spindle nut 62 is converted into a translational movement of the valve rod 66 and the valve element 70. The rotor 22 and the spindle nut 62 are supported on one side by a ball bearing 80, the outer ring of which is pressed radially inside an annular projection 84 of the housing part 32, which extends axially into the containment shell 28, and bears axially against a shoulder 86 from which the annular projection 84 extends. An inner ring 88 of the ball bearing 80 bears against an end of the spindle nut 62 facing the valve member 70, on which a shoulder 90 is formed against which the inner ring 88 bears axially. At the axially opposite end, the assembly consisting of the spindle nut 62 and rotor 22 is arranged on a hollow cylindrical pin 92, which acts as a sliding bearing and is fixed to the bottom 30 of the containment shell 28, and into which the valve stem 66 can engage. The hollow cylindrical pin 92 consists of a magnetizable material suitable for focusing magnetic field lines. This is done to improve the signal of a magnetoresistive sensor 94, which is in particular designed as a linear Hall sensor and generates a corresponding voltage signal 96 from an axially extending magnetic field in a known manner, the strength of which increases and decreases with the strength of the magnetic field. The sensor 94 is arranged on a circuit board 95 of the electronic unit 58 directly axially opposite the hollow cylindrical pin 92 in the outer space 24 of the split pot 28 and interacts with a first axially magnetized permanent magnet 98, which is attached to the second axial end 100 of the valve rod 66 opposite the valve element 70 and is moved accordingly with the valve rod 66. By rotating the rotor 22 and thus by the translational movement of the valve stem 66, the permanent magnet 98 is moved away from or closer to the sensor 94. Accordingly, the magnetic field acting on the sensor 94 changes, which it converts in a known manner into an electrical voltage signal. This signal then provides a measure of the position of the valve element 70 relative to the valve seat 72. Due to the ferromagnetic hollow cylindrical pin 92, the magnetic field lines are focused, thus amplifying the magnetic field, enabling highly accurate position detection despite the distance between the permanent magnet 98 and the Hall sensor 94. Further alignment and focusing of the magnetic field lines is achieved by the addition of a second, stationary permanent magnet 99, which is also axially magnetized and located on the side of the circuit board 95 opposite the Hall sensor 94. The voltage signal 96 generated at sensor 94 is fed to an evaluation unit 102, which feeds this voltage signal 96 to at least one filter. This is, in particular, a low-pass filter 106, by which higher-frequency signals are filtered out from the voltage signal 96. A low-frequency voltage signal 108 is thus generated, as shown in Fig. 2, and represents a measure of the movement of the valve element 70. However, in the present embodiment, where the sensor 94 and the first permanent magnet 98 share a common central axis with the stator windings 18, 20, the voltage signal 96 also contains a high-frequency changing voltage signal component. The pure high-frequency voltage signal 112 can be generated by using a high-pass filter 110, which filters out the low-frequency components from the voltage signal 96. This high-frequency voltage signal is generated by energizing the stator windings 18, 20 with alternating current or pulse-width modulated current. This current generates a stray field that runs axially inside the stator 16 and thus does not produce a force to move the rotor.The resulting magnetic field lines have a high frequency corresponding to the current signal of the stator 16, which manifests itself in a correspondingly changing magnetic field and ultimately also in a correspondingly high-frequency voltage signal 112 at the sensor 94. The resulting voltage signal 112 is proportional to the current in the stator 16 and is used according to the invention for current measurement. When using the illustrated claw-pole motor 14, the high-frequency voltage signal 112 is a measure of the current in the stator winding 18 located closer to the sensor 94. Accordingly, a highly precisely controllable actuator or a high-precision valve device is created, which is easy to assemble and cost-effective to manufacture. Very precise control of the flow rate through the valve device 10 is enabled, in which the sensor allows for complete functional monitoring with regard to both the position of the valve element and the current in the stator, without the need for additional electronic components. It should be clear that the scope of protection of the main claim is not limited to the described embodiment, but rather that various modifications are possible. For example, the separation of the low-frequency signal from the high-frequency signal can be achieved either by analog filters with capacitors and resistors or by purely digital demodulation. Furthermore, after high-pass or low-pass filtering, the other voltage signal can be generated by comparing the original voltage signal with the filtered signal. Alternatively, a different electronically commutated electric motor can be used instead of the claw pole motor. Further design modifications are also conceivable.

Claims

Method for current and position measurement on a valve device comprising: a valve member (70), an actuator (12) comprising an electronically commutated electric motor (14) with a stator (16) having a stator winding (18, 20) and a permanent magnet rotor (22), a first coupling element (61) which can be rotated by means of the actuator (12), a valve rod (66) secured against rotation, at the first axial end (71) of which the valve member (70) is formed, and which has a second coupling element (69) which interacts with the first coupling element (61) in such a way that the rotational movement of the first coupling element (61) is converted into a translational movement of the second coupling element (69) and the valve rod (66), and a magnetoresistive sensor (94) which interacts with a permanent magnet (98), wherein the permanent magnet (98) is axially magnetized and attached to the second axial end (100) of the valve stem (66),the central axis of which coincides with the central axis of the stator (16), wherein the magnetoresistive sensor (94) is arranged on this central axis opposite the second axial end (100) of the valve stem (66) and generates a voltage signal (96) which is proportional to the magnetic field acting on it in the axial direction, wherein the valve device has an evaluation unit (102), wherein the voltage signal (96) of the sensor (94) is supplied to the evaluation unit (102), and wherein the evaluation unit (102) has a filter (106, 110) for generating a first, high-frequency voltage signal (112) and a second, low-frequency voltage signal (108), wherein, according to the method, a low-frequency voltage signal (108) is generated in the evaluation unit (102) by filtering the voltage signal (96) of the magnetoresistive sensor (94),which serves as a measure for the axial position of the valve stem (66) and generates a high-frequency voltage signal (112) which serves as a measure for the current in the stator winding (18). Method for current and position measurement according to claim 1, wherein the voltage signal (96) of the sensor (94) is fed to a low-pass filter (106), thereby generating the low-frequency voltage signal (108), which serves as a measure of the axial position of the valve stem (66), and this low-frequency voltage signal (108) is subtracted from the measured voltage signal (96), thereby generating a high-frequency voltage signal (112), which serves as a measure of the current in the stator winding (18). Method for current and position measurement according to claim 1, wherein the voltage signal (96) of the sensor (94) is fed to a high-pass filter (110), thereby generating the high-frequency voltage signal (112), which serves as a measure of the current in the stator winding (18), and this high-frequency voltage signal (112) is subtracted from the measured voltage signal (96), thereby generating a low-frequency voltage signal (108), which serves as a measure of the axial position of the valve stem (66). Method for current and position measurement according to claim 1, wherein the voltage signal (96) of the sensor (94) is fed to a low-pass filter (106), thereby generating the low-frequency voltage signal (108), which serves as a measure of the axial position of the valve stem (66), and is fed to a high-pass filter (110), thereby generating the high-frequency voltage signal (112), which serves as a measure of the current in the stator winding (18). Method for current measurement and position measurement according to one of the preceding claims, wherein the electric motor (14) is designed as a claw pole motor with two stator windings (18, 20), and wherein the high-frequency voltage signal (112) serves as a measure of the current strength of the stator winding (18) located closer to the sensor (94). Method for current measurement and position measurement according to one of the preceding claims, wherein the first coupling element (61) is a spindle nut (62) with an internal thread (63) which is connected to the rotor (22) and the valve rod (66) as a second coupling element (69) has a spindle rod (68) whose external thread (64) engages in the internal thread (63) of the spindle nut (62). Method for current measurement and position measurement according to one of the preceding claims, wherein the magnetoresistive sensor (94) is a linear Hall sensor. Method for current and position measurement according to one of the preceding claims, wherein the sensor (94) is arranged on a circuit board (95) on the side of which opposite the sensor (94) a second stationary permanent magnet (99) is arranged, which has an opposite axial polarity to the first permanent magnet (98) on the valve rod (66). Method for current measurement and position measurement according to one of the preceding claims, wherein the electric motor (14) has a containment pot (28) by which the rotor (22) is separated from the stator (16) and which has a bottom (30) by which the sensor (94) is separated from the first permanent magnet (98) arranged on the valve rod (66).

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