Valve device and method for current and position measurement on such a valve device

Abstract

Known valve devices comprise: a valve member (70); an actuator (12) which has an electronically commutated electric motor (14) comprising a stator (16) having a stator winding (18, 20), and which has a permanent-magnet rotor (22); a first coupling element (61) which can be set into rotation by means of the actuator (12); a valve rod (66) which is secured against twisting and on the first axial end (71) of which the valve member (70) is formed, and which has a second coupling element (69) that interacts with the first coupling element (61) in such a way that the rotary movement of the first coupling element (61) is converted into a translational movement of the second coupling element (69) and of the valve rod (66); and a magnetoresistive sensor (94) which interacts with a permanent magnet (98). The aim of the invention is to provide simplified position and current measurement. This aim is achieved in that the permanent magnet (98) is axially magnetised and fastened to the second axial end (100) of the valve rod (66), the central axis of which coincides with the central axis of the stator (16), and the magnetoresistive sensor (94) is arranged on this central axis opposite the second axial end (100) of the valve rod (66), and generates a voltage signal (96) which is proportional to the magnetic field acting thereon in the axial direction, wherein the voltage signal (96) of the sensor (94) can be supplied to an evaluation unit (102) which has a filter (106, 110) for generating a first, high-frequency voltage signal (112) and a second, low-frequency, voltage signal (108).

Description

[0001] DESCRIPTION

[0002] Valve device and method for current measurement and position measurement on such a valve device

[0003] The invention relates to a valve device with a valve member, an actuator which has an electronically commutated electric motor with a stator with a stator winding and a permanent magnet rotor, a first coupling element which can be set in rotation by means of the actuator, a valve rod which is secured against rotation and at the first axial end of which the valve member is formed, and which has a second coupling element which cooperates with the first coupling element in such a way that the rotary movement of the first coupling element is converted into a translatory movement of the second coupling element and the valve rod, and a magnetoresistive sensor which cooperates with a permanent magnet, as well as a method for current measurement and position measurement on such a valve device.

[0004] 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 circuits. These valves serve to reduce the pressure of the working fluid by throttling the available flow cross-section and to increase the volume of the working fluid, thus expanding it. By using controlled expansion valves, both the pressure drop and thus the volume increase can be controlled and the fluid flow can be almost completely interrupted. In refrigeration or air conditioning circuits, these valves are arranged upstream of the evaporators and downstream of the condensers. Due to the increase in volume, the working fluid is partially evaporated, while the still liquid working fluid absorbs heat in the evaporator, causing the liquid part to also evaporate.This now gaseous working fluid is fed to a compressor and compressed, before being converted back into the liquid state in the condenser, forming a closed circuit. Heat or cold can be extracted from this circuit in the evaporator and condenser areas.

[0005] In order to control the pressure drop across the expansion valve and the associated volume increase as precisely as possible, it is desirable to know the position of the valve element relative to the valve seat as precisely as possible and to be able to control it accordingly. Furthermore, it is desirable to measure the current flow in the stator, which is usually done via a shunt.

[0006] In order to determine the position of the valve member, EP 3 910 266 A1 proposes an electrically operated expansion valve driven by a claw-pole motor. The rotor of the can motor is connected to a spindle nut in which a spindle rod is rotatably arranged, which is moved axially when the rotor rotates. The angle of rotation of the rotor is detected by an angle sensor that interacts with the permanent magnets arranged in the rotor. A disadvantage, however, is that the stroke of the valve can only be calculated indirectly via the angle of rotation and the number of rotations. Accordingly, a voltage output from the sensor cannot be clearly assigned to a position of the spindle rod. A current measurement is not disclosed.The objective is therefore to provide a valve device and a method for position and current measurement that can determine the precise stroke position of the valve rod or the valve element formed on the valve rod without the need for conversions or inaccuracies, for example, due to changing play between the threads of the valve rod and the spindle nut. Furthermore, a current measurement should also be performed with the least possible effort. The component count and thus the cost of such a valve device should be minimized.

[0007] This object is achieved by a valve device having a valve member which serves as a valve member for changing a flow cross-section when performing a lifting movement. For this purpose, the valve member is either placed onto a valve seat, lifted off therefrom, or pushed into a corresponding flow cross-section. This displacement is effected by an actuator having an electronically commutated electric motor with a stator with a stator winding and a permanent magnet rotor. This rotor is either formed integrally with a first coupling element or this coupling element is fastened to it. Furthermore, the valve device has a valve rod which is secured against twisting and on the first axial end of which the valve member is formed, which can be formed integrally with the valve rod or can be fastened to it.The valve rod 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 rod. This can be achieved, for example, by interlocking threads or guides with pins running therein, with or without rollers. An axially magnetized permanent magnet is attached to the second axial end of the valve rod, i.e., the end of the valve rod opposite the valve member. The central axis of this permanent magnet and of the valve rod 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 rod.This generates a voltage signal proportional to the magnetic field acting on it in the axial direction. In addition, according to the invention, the valve device comprises an evaluation unit to which the voltage signal is fed and which has a filter through which the voltage signal is split into a first, high-frequency voltage signal and a second, low-frequency voltage signal. This can be achieved, for example, digitally by demodulation or analogically by known filter circuits.

[0008] Accordingly, in the method according to the invention, a low-frequency voltage signal is generated in the evaluation unit by filtering the voltage signal of the magnetoresistive sensor. This signal serves as a measure of the axial position of the valve stem, and a high-frequency voltage signal is generated, which serves as a measure of the current in the stator winding. The low-frequency signals are thus used for position determination, since the voltage signal of the sensor decreases with increasing distance of the permanent magnet from the sensor, as the magnetic field of the permanent magnet acting on the sensor becomes weaker. However, this voltage signal is superimposed by 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 recorded by the sensor as a high-frequency voltage signal, is directly dependent on the current flow in the stator, so it can be used to measure the current intensity. This high-frequency signal is generated by the rapidly changing magnetic fields during pulse-width modulation, but also 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. This reduces the number of components and the resulting costs.

[0009] Preferably, the first coupling element is a spindle nut with an internal thread, which is connected to the rotor, which also includes a one-piece construction, and the valve rod, as the second coupling element, comprises a spindle rod whose external thread engages the internal thread of the spindle nut. The valve rod 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 a rotary motion into a translatory motion.

[0010] The electric motor is advantageously designed as a claw-pole motor, which is cost-effective to manufacture and highly efficient. When using a double-claw-pole motor, the current is measured in the stator winding closest to the sensor.

[0011] The magnetoresistive sensor is preferably a linear Hall sensor. The output voltage of these sensors is proportional to the magnetic field strength acting on it 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 as well as to the distance between the magnet and the sensor, making it suitable for use as a current sensor and a position sensor.

[0012] In a preferred embodiment, the sensor is mounted on a circuit board, on the opposite side of which a second, stationary permanent magnet is located. This magnet has an opposite axial polarity to that of the permanent magnet on the valve stem. Such an additional magnet focuses the field lines of the first permanent magnet and accordingly improves the sensor's output signal, enabling more precise position determination.

[0013] The filter is preferably designed as a high-pass filter, allowing the high-frequency signals generated by the current flow in the stator to pass through, while filtering out the low-frequency signals from the permanent magnet used for position determination. Accordingly, this filtered voltage signal from the sensor is a direct measure of the current flow in the stator.

[0014] Such a high-pass filter can have a coupling capacitor through which DC voltage signals, such as those generated by the voltage output of the sensor due to the position of the permanent magnet, are filtered and the AC voltage signals, such as those generated at the sensor by the current supply to the stator, are passed through.

[0015] Alternatively or additionally, a low-pass filter can be used as a filter to filter out the high-frequency signals generated by the stator current flowing through 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 associated method, the sensor's voltage signal is advantageously 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. This low-frequency voltage signal is subtracted from the measured voltage signal, generating a high-frequency voltage signal that serves as a measure of the current in the stator winding.

[0016] Alternatively, the voltage signal from the sensor is fed to a high-pass filter, generating the 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 rod.

[0017] Thus, the filtered signal is generated by forming the difference between the original signal and the filtered signal, so that the signal which represents a measure of the current intensity is available for evaluation independently of the signal which represents a measure of the position of the valve element.

[0018] In an alternative embodiment 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 to a high-pass filter, generating the high-frequency voltage signal that serves as a measure of the current in the stator winding. Further conversions are then unnecessary. 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.

[0019] In a preferred embodiment of the valve device, the electric motor has a containment shell, which separates the rotor from the stator and has a base, which separates the sensor from the permanent magnet arranged on the valve stem. This allows the rotor chamber to be designed for fluid flow, since the sensitive windings of the stator and the electronics with the sensor are separated from the fluid-permeable interior by the containment shell.

[0020] Thus, a valve device and a method for measuring current and position on such a valve device are created, with which both the current strength of the electric motor and the position of the valve element can be determined using a single sensor, which can be inexpensively purchased, for example, as a linear Hall sensor. This simplifies the design of such a valve, as the number of electronic components can be reduced.

[0021] An embodiment of a valve device according to the invention is shown in the figures using the example of an expansion valve and is described below with the method according to the invention.

[0022] Figure 1 shows a side view of a valve device according to the invention in a sectional view.

[0023] Figure 2 shows a signal curve of the sensor during current and position measurement. The valve device shown in Figure 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.

[0024] The containment shell 28 has an axially defining base 30, from which a cylindrical outer surface extends axially. A stationary housing part 32 of the expansion valve 10 projects into the containment shell 28 or into its cylindrical outer surface. A radial groove 38 is formed on a radially outer wall 36 of the housing part 32, in which groove a sealing ring 40 is arranged, which bears radially against the outer surface of the containment shell 28. In addition, a shoulder 42 is formed on the radially outer defining wall 36, with which shoulder the housing part 32 bears against a collar 44 at the axial end of the containment shell 28, which, with its opposite axial side, bears against a shoulder 46 on an actuator housing part 50. Accordingly, the stator 16 is separated from the rotor 22 in a fluid-tight manner by the containment shell 28.

[0025] The actuator housing part 50 radially surrounds the stator 16 and the containment shell 28. On the side axially opposite 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 shell 28. This chamber 54 is closed by a cover 56 and serves as a receptacle for an electronics unit 58 arranged axially opposite the bottom 30 of the containment shell 28. The rotor 22 has a radially inner receiving opening 60 directed towards the open side of the containment shell 28, in which a spindle nut 62 is fastened, serving as a first coupling element 61. The spindle nut has an internal thread 63 that corresponds to an external thread 64 of a spindle rod 68 formed integrally with a valve rod 66, which correspondingly serves as a second coupling element 69.

[0026] At a first axial end 71 of the valve rod 66, remote from the bottom 30 of the containment shell 28, there is arranged a valve member 70 which interacts with a valve seat 72 which is formed on the housing part 32 of the expansion valve 10 and onto which the valve member 70 is placed when the rotor 22 rotates or from which the valve member 70 is lifted off, so that a precise control of a free flow cross-section between the valve seat 72 and the valve member 70 takes place depending on the rotational position of the rotor 22. For this purpose, the valve rod 66 is mounted via the valve member 70 in a plain bearing 74 so as to be axially displaceable, wherein axially extending webs 76 are formed on the valve member 70 outside the valve seat 72, which engage in grooves 78 of the plain bearing 74 and by means of which the valve rod 66 is secured 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 member 70.

[0027] The rotor 22 and the spindle nut 62 are supported on the one hand by a ball bearing 80, the outer ring 82 of which is pressed radially inward into an annular projection 84 of the housing part 32, which extends axially into the containment shell 28, and axially bears 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 end a shoulder 90 is formed, against which the inner ring 88 bears axially. At the axially opposite end, the unit comprising the spindle nut 62 and the rotor 22 is arranged on a hollow cylindrical pin 92 acting as a plain bearing, which is fixed to the bottom 30 of the containment shell 28 and into which the valve rod 66 can insert.

[0028] The hollow cylindrical pin 92 is made of a magnetizable material suitable for concentrating magnetic field lines. This is done to improve the signal of a magnetoresistive sensor 94, which is designed in particular as a linear Hall sensor and, in a known manner, generates a corresponding voltage signal 96 from an axially extending magnetic field, the strength of which increases and decreases with the strength of the magnetic field.

[0029] The sensor 94 is arranged on a circuit board 95 of the electronics unit 58 directly axially opposite the hollow cylindrical pin 92 in the outer space 24 of the containment shell 28 and interacts with a first axially magnetized permanent magnet 98 which is fastened to the second axial end 100 of the valve rod 66 opposite the valve member 70 and is moved accordingly with the valve rod 66.

[0030] By rotating the rotor 22 and thus the translational movement of the valve rod 66, the permanent magnet 98 is moved away from or closer to the sensor 94. The magnetic field acting on the sensor 94 changes accordingly, converting it in a known manner into an electrical voltage signal, which then forms a measure of the position of the valve member 70 relative to the valve seat 72.

[0031] Due to the ferromagnetic hollow cylindrical pin 92, the magnetic field lines are concentrated, thus amplifying the magnetic field, so that position detection can be achieved with high accuracy despite the distance between the permanent magnet 98 and the Hall sensor 94. Additional alignment and concentration of the magnetic field lines is achieved by arranging 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.

[0032] 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, which filters out higher-frequency signals from the voltage signal 96. This results in a low-frequency voltage signal 108, as shown in Figure 2, which represents a measure of the movement of the valve member 70.

[0033] However, in the present embodiment, in which 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 varying 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 generate any force to move the rotor.The resulting magnetic field lines have a high frequency corresponding to the current supply signal of the stator 16, which is reflected 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 to measure the current. When using the claw-pole motor 14 shown, the high-frequency voltage signal 112 is a measure of the current in the stator winding 18 located closer to the sensor 94.

[0034] Accordingly, a very precisely controllable actuator or a high-precision valve device is created that is easy to assemble and cost-effective to manufacture. Very precise control of the flow rate through the valve device 10 is enabled, with the sensor enabling complete functional monitoring of both the position of the valve element and the current intensity in the stator, without the need for additional electronic components.

[0035] It should be clear that the scope of the main claim is not limited to the described embodiment, but various modifications are possible. Thus, 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 respective other voltage signal can be generated by comparing the original voltage signal with the filtered signal.

[0036] Another electronically commutated electric motor can also be used instead of the claw-pole motor. Other design modifications are also conceivable.

Claims

PATENT CLAIMS Valve device with a valve element (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 element (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), characterized in that the permanent magnet (98) is axially magnetized and at the second is attached to the axial end (100) of the valve stem (66),whose central axis coincides with the central axis of the stator (16), and the magnetoresistive sensor (94) is arranged on this central axis opposite the second axial end (100) of the valve rod (66), and generates a voltage signal (96) which is proportional to the magnetic field acting on it in the axial direction, wherein the voltage signal (96) of the sensor (94) can be supplied to an evaluation unit (102) which has a filter (106, 110) for generating a first, high-frequency voltage signal (112), and a second, low-frequency voltage signal (108). Valve device according to claim 1, characterized in that 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) comprises a spindle rod (68) whose external thread (64) engages in the internal thread (63) of the spindle nut (62). Valve device according to claim 1 or 2, characterized in that the electric motor is a claw pole motor (14). Valve device according to any one of the preceding claims, characterized in that the magnetoresistive sensor (94) is a linear Hall sensor.Valve device according to one of the preceding claims, characterized in that 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, the magnet having an opposite axial polarity to the first permanent magnet (98) on the valve stem (66). Valve device according to one of the preceding claims, characterized in that the filter comprises a high-pass filter (110). Valve device according to one of the preceding claims, characterized in that the filter comprises a low-pass filter (106). Valve device according to one of the preceding claims, characterized in that the electric motor (14) comprises a containment shell (28) by which the rotor (22) is separated from the stator (16) and which has a base (30) by which the sensor (94) is separated from the first permanent magnet (98) arranged on the valve stem (66). Method for current and position measurement on a valve device according to one of the preceding claims, characterized in that in the evaluation unit (102) a low-frequency voltage signal (108) is generated by filtering the voltage signal (96) of the magnetoresistive sensor (94), which serves as a measure of the axial position of the valve stem (66), and a high-frequency voltage signal (112) is generated, which serves as a measure of the current in the stator winding (18).Method for current and position measurement according to claim 9, characterized in that 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 9, characterized in that 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).A method for current and position measurement according to claim 9, characterized in that 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). A method for current and position measurement according to any one of claims 9 to 12 on a valve device according to claim 3, characterized in that the high-frequency voltage signal (112) serves as a measure of the current in the stator winding (18) located closer to the sensor (94).