Optical liquid sensor and electrical system for optical detection of liquids

Abstract

Optical liquid sensor (1) for detecting liquid (9) for an electrical system (10), comprising - a light source (2) for emitting light, - an optical detector (3) designed as a line detector (3a) with at least two light-sensitive photocells (6) for detecting the light emitted by the light source (2), and - a reflective surface element (5), wherein - the light source (2) and the surface element (5) are arranged such that the emitted light strikes the surface element (5) at an angle, - the light source (2) is designed to emit a parallel beam of light (4), - the light source (2) and the detector (3) are arranged such that the surface element (5) directs the light beam (4) onto the photocell (6), - the surface element (5) is movable in the direction of the surface normal of the surface element (5) and is mounted depending on the amount of liquid (9) present, and - the optical liquid sensor (1) has a beam splitter (12) which is configured to branch off a control beam (7) from the emitted light beam (4) and to direct the control beam (7) to the detector (3) independently of the surface element (5) and / or the liquid (9).

Description

[0001] The invention relates to an optical liquid sensor for detecting, in particular, electrically conductive liquids for an electrical system, comprising a light source for emitting a light beam, an optical detector with at least one light-sensitive photocell for detecting the light beam emitted by the light source, and a reflective surface element, wherein the light source and the surface element are arranged such that the emitted light beam strikes the surface element at an angle. The invention further relates to an electrical system for the optical detection of liquids.

[0002] The detection of a fluid, particularly an electrically conductive one, within an electrical system may be necessary, depending on the system's tightness and type of use, to identify potential malfunctions or safety hazards at an early stage. Examples of such electrical systems include high-voltage battery systems, high-voltage batteries, coolant reservoirs, fuel tanks, and other electrical systems where the fluid level is relevant.

[0003] Even small amounts of liquid can compromise system safety and must therefore be detectable. However, small amounts of liquid, such as condensation, do not pose a threat to the system and should not lead to its shutdown or repair. Shutting down the electrical system is sometimes necessary because protective measures are costly and rarely feasible within the system's technical limitations. For example, a high-voltage battery is not protected against an internal short circuit that can be caused by conductive liquids.

[0004] Typically, level sensors, film sensors, or insulation resistance measurements are used to detect liquids. However, level sensors are quite inaccurate for small quantities of liquid. Film sensors often have reduced reliability over their lifespan of several years in humid environments due to corrosion.

[0005] Insulation measurements only register a potential fault once it has already had an effect.

[0006] DE 1235191 discloses a liquid detector comprising a light source and a photosensitive cell. A space, delimited by two translucent walls and fillable with translucent leakage liquid, is arranged in the direct path of the light source between the light source and the photocell. The presence of liquid changes the illuminance on the photocell. However, the liquid detector can only detect liquid that has collected between the two translucent walls. The design with the two translucent walls is complex, especially if the quantity of liquid is also to be detected.

[0007] DE 10 2005 044 157 A1 discloses an optical liquid sensor with a radiolucent solid body, a portion of which projects into the liquid to be monitored. The radiolucent solid body has a recess designed such that part of the path of a light beam between a light source and a light detector passes through the liquid to be monitored only in the presence of liquid. The main part of the light beam thus reaches the light sensor only when liquid is present. The liquid sensor can only determine whether the recess is filled with liquid or not. Small quantities of liquid cannot be reliably detected.

[0008] US 2009 / 0153846 A1, WO 2007 / 049005 A1, WO 99 / 26044 A1, JP S62-138726 A and DE 10 2006 014 277 A1 each disclose optical liquid sensors in which light is emitted from a light source and reflected by a surface element. The reflected light is detected by an optical detector. This allows the presence of liquid to be inferred.

[0009] US Patent 2008 / 0 011 970 A1 discloses a non-contact optical measuring system that determines the liquid level using the triangulation principle and a float, whereby the point of impact of the reflected light beam on a position-sensitive detector shifts depending on the fill level. DD 239 864 A1 describes an optical level measuring system with fixed reflective prisms or mirrors. JP H10 - 300 558 A discloses an optical sensor with a float that carries a mirror for reflecting an emitted light beam, wherein the fill level is detected triangulatorily. JP H09 - 68 426 A describes a float with a reflective surface for water level detection, wherein the reflection is used for distance measurement.The CN 100 340 844 C refers to an optical method for measuring resin level in stereolithography using reflected laser radiation and position-sensitive detection, where the free liquid surface serves as the reflective surface.

[0010] The invention is based on the objective of providing a structurally simple, cost-effective and reliable detection method for any quantity of liquid.

[0011] The invention solves the problem with the features of the independent claim.

[0012] According to the invention, a light source is configured to emit a parallel beam of light. This allows the emitted light beam to be directed particularly effectively onto a surface element without spreading out. The emitted light beam strikes the surface element at an angle, meaning that the light beam and the surface form an angle of more than 0° and less than 90°. In the absence of liquid, the reflective surface element reflects the emitted light beam incident on the surface element essentially completely. The light source and a detector, designed as a line detector (3a), are arranged such that the surface element directs the light beam onto at least two photocells.In the absence of liquid, the light beam is directed as a parallel beam from the reflective surface element directly to the detector, wherein the surface element (5) is movable in the direction of the surface normal of the surface element (5) and is mounted depending on the amount of liquid (9) present, and the optical liquid sensor (1) has a beam splitter (12) which is configured to branch off a control beam (7) from the emitted light beam (4) and to direct the control beam (7) to the detector (3) independently of the surface element (5) and / or liquid (9).

[0013] The presence of liquid alters the path of the reflected light beam, for example, through the optical path the light beam travels before reflection on the surface of the reflective element, or through refraction, or it causes absorption or scattering of the light beam. The altered path of the beam, particularly due to refraction, in contrast to the absence of liquid, results in the photocell being less illuminated or not illuminated at all; that is, the signal strength is reduced and / or reduced to zero. The light beam, partially absorbed or scattered by the presence of liquid and directed from the reflective surface element to the photocell, exhibits a lower signal strength or intensity than the light beam directed to the photocell in the absence of liquid.In the presence of liquid, the signal strength measured by the detector is therefore reduced compared to a measurement in the absence of liquid.

[0014] Advantageously, the surface element is designed to float on any liquid that may be present. The mobility or floating of the surface element depends on the amount of liquid present and leads to a parallel offset of the light beam directed towards the detector, from which the amount of liquid present can be determined.

[0015] Due to the signal strength's dependence on the liquid, reliable detection of the liquid and an inference of the quantity present are possible. The proposed liquid sensor has the advantage of a very simple and cost-effective design. The light source and detector do not come into direct contact with the medium being detected, resulting in very low susceptibility to corrosion. Furthermore, embodiments without moving parts are conceivable, making them particularly robust against mechanical stress, especially vibrations. This ensures reliable liquid detection throughout the system's lifetime.

[0016] In a preferred embodiment of the invention, the optical liquid sensor comprises a housing, and the surface element is located on the inside of the housing to provide an embodiment with an efficient liquid sensor design. The reflective surface element can, for example, be a mirror bonded to the housing, or the surface of the housing can have a reflective section that forms the reflective surface element. In this embodiment, it is particularly advantageous if the reflective surface element is located on the inside of the housing such that any liquid present collects on the reflective surface element due to gravity. This means that, in the presence of liquid, the light beam must first pass through a surface of the liquid before reaching the reflective surface element.When the light beam strikes the surface of the liquid, a portion of it is reflected, and only a fraction, no longer possessing the full intensity of the emitted beam, reaches the reflective surface element and is then directed towards the detector. Additionally, further reflection can occur as the light beam exits the liquid, further reducing the signal strength of the beam reaching the detector. Thus, the reduced signal strength, or intensity, measured at the detector compared to the emitted beam allows for a reliable conclusion regarding the presence of liquid. The housing can also be the enclosure of the electrical system for which the optical liquid sensor is intended.

[0017] A line detector is advantageous for further improving the application possibilities of the liquid sensor. For example, a line detector can determine the deflection of the light beam caused by the presence of liquid. The line detector advantageously comprises multiple photocells. Based on the deflection of the light beam, which falls on a different photocell of the line detector depending on the amount of liquid present, the quantity of liquid can be determined.

[0018] In a preferred embodiment, the light source is configured to emit a polychromatic light beam, and the detector is configured to sensing a polychromatic light beam in order to determine, for example, what type of liquid is present, since a liquid exhibits characteristic absorption of at least one specific wavelength. This allows, for example, differentiation between water, conventionally colored coolant, oil, and / or at least one other liquid.

[0019] Advantageously, the light source is configured to emit at least two parallel light beams to increase the reliability of liquid detection. Emitting at least two parallel light beams allows, for example, spatial resolution, enabling the comparison of reflections on different sections of the surface element to detect local liquid or dirt deposits.

[0020] It is advantageous that the optical liquid sensor has a beam splitter which is designed to branch off a control beam from the emitted light beam and to direct the control beam to the detector independently of the surface element and / or liquid, in order to determine, for example, whether the light source and / or the detector has slipped or failed, or whether the beam path of the light beam directed over the surface element is blocked.

[0021] Advantageously, acceleration data can be input into the optical liquid sensor and evaluated for detection. The hydrodynamic behavior of a liquid present can be predicted based on its viscosity due to acceleration. For example, acceleration can cause the liquid to move into or out of the beam path between the light source and the detector via the surface element. If the hydrodynamic prediction matches the detected behavior, the type of liquid can be determined based on its viscosity. The acceleration data can be obtained, for example, by calculating the time derivative of the vehicle speed or transmitted from other sensors.

[0022] A method for the optical detection of liquid comprises the following steps: emitting light that strikes a reflective surface element at an angle and detecting the light emitted by the light source. It is proposed that a parallel light beam is emitted, and that in the absence of liquid, the reflective surface element directs the light beam at full signal strength onto a photocell, while in the presence of liquid, it directs the light beam at reduced signal strength onto the photocell. This method allows for simple and reliable detection of liquid based on the signal strength registered by the photocell.

[0023] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0024] Unless otherwise specified in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0025] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. The drawings schematically show: Fig. 1 an optical liquid sensor; Fig. 2 an optical liquid sensor with a line detector; Fig. 3 an optical liquid sensor with a polychromatic light source; Fig. 4 an optical liquid sensor with a floating reflective surface element; Fig. 5 an optical liquid sensor with a light source emitting two parallel beams of light; Fig. 6 an optical liquid sensor with a beam splitter; Fig. 7 an optical liquid sensor with a light source emitting two parallel beams of light; and Fig. 8 an electrical system with an optical liquid sensor.

[0026] Fig. Figure 1 shows an optical liquid sensor 1. The optical liquid sensor 1 comprises a light source 2 and a detector 3. The light source 2 is configured to emit a parallel light beam 4. The light source 2 can include a light source, in particular a light-emitting diode or laser, for generating light, as well as optics for parallelizing the light generated by the light source so that the parallel light beam 4 can be generated and selectively exit the light source. The light beam 4 is directed onto a reflective surface element 5, the light beam 4 striking the reflective surface element 5 at an angle of more than 0° and less than 90°, advantageously more than 15° and less than 85°, and further advantageously more than 30° and less than 60°, for example 45°, where the light beam 4 is reflected.

[0027] The optical liquid sensor 1 comprises a housing 11 in which the light source 2, the detector 3, and the reflective surface element 5 are arranged. The housing 11 also allows for the encapsulation of the liquid sensor. This enables the liquid sensor 11 to be used independently of the environment to be detected. The housing 11 contains a gas 8 in which the light source 2 and the detector 3 are located, and, in the absence of liquid 9, the reflective surface element 5 is also located.

[0028] The light source 2, the detector 3, and the reflective surface element 5 are arranged such that, in the absence of liquid 9, the light beam 4 is reflected and directed towards a photocell 6 of the detector 3 (lower beam path). When liquid 9 is present and collects on the reflective surface element 5, an additional reflection occurs at the interface between gas 8 and liquid 9, reducing the signal strength at the detector 3 (upper beam path). This allows the presence of liquid 9 to be detected. In a stationary system, the liquid 9 has a smooth surface, and therefore a constant reduction in signal strength due to reflection at the liquid 9 surface can be observed.When the surface of liquid 9 is moved, for example by acceleration or vibrations, the signal strength is variably reduced due to the changing reflection at the surface of liquid 9.

[0029] Fig. Figure 2 shows an optical liquid sensor 1 with a line detector 3a and is described with regard to the differences to the embodiment according to Fig. 1 described. In this embodiment, the detector or line detector 3a has a plurality of linearly arranged photocells 6. This allows, in particular, a detector 3 with a pixel matrix to be provided. The line detector 3a serves to detect the water level or the height h of the liquid 9 standing on the reflective surface element 5. The reflection at the interface between gas 8 and liquid 9 is used to calculate the height h. Thus, the reflective surface 5 serves, in particular, to detect the absence of liquid 9.

[0030] The light beam 4 strikes the surface of the liquid 9 at an angle α. Part of the light beam 4 is reflected at the surface of the liquid 9 and directed towards a photocell 6 of the line detector 3a. Another part of the light beam 4 passes through the surface of the liquid 9 and reaches the reflective surface element 5, where it is directed towards the line detector 3a. The light beam 4 reflected at the reflective surface element 5 strikes and passes through the surface of the liquid 9, forming an angle α between the light beam 4 and the surface of the liquid 9.Thus, the light beam 4, which is reflected at the surface of the liquid 9 (upper beam path), and the light beam 4, which is reflected at the reflective surface element 5 (lower beam path), are parallel to each other and strike photocells 6 of the line detector 3a, which are spaced at a distance d. From the distance d and the angle α, the height h of the liquid 9 located on the reflective surface element 5 can be calculated.

[0031] Fig. Figure 3 shows an optical liquid sensor 1 with a polychromatic light source 2 and is described with regard to the differences to the embodiment according to Fig. 1 described. In this embodiment, the optical liquid sensor 1 comprises a light source 2 configured to emit polychromatic light, that is, light with multiple wavelengths. For example, the light source 2 can comprise a plurality of light-emitting diodes that generate light beams with different wavelengths. Thus, polychromatic light with a specific spectrum is generated. The detector 3 is color-sensitive and comprises, for example, an RGB mosaic and / or a line detector 3a with a diffracting optical element 4, for example, a grating, positioned upstream to diffract the incident light beam 4.

[0032] The optical liquid sensor 1 can detect the quantity of a liquid 9 based on the reduction in signal strength. The liquid sensor 1 can also detect the type of liquid 9. The light beam 4 experiences characteristic absorption in the liquid 9, thus enabling spectral detection of the liquid 9's color and wavelengths.

[0033] Fig. Figure 4 shows an optical liquid sensor 1 with a floating reflective surface element 5 and is described with regard to the differences to the embodiment according to Fig. 2 described. The reflective surface element 5 is movably mounted in a guide 13 and can be moved perpendicular to its surface. The movement of the reflective surface element 5 depends on the amount of any liquid 9 present. If no liquid 9 is present, the light source 2 emits a light beam 4 that follows a path corresponding to the dotted line and falls on the reflective surface element 5 on the inside of the housing 11. From there, it is directed towards a photocell 6 of the line detector 3a and detected by it. If a liquid 9 is present, the buoyant force of the liquid 9 lifts the reflective surface element 5 to a height h. The light beam 4 emitted by the light source 2 is then reflected at a different location by the reflective surface element 5 and follows a path corresponding to the solid line in Figure 2. Fig. 4, which is parallel to the path of the light beam 4 in the absence of liquid 9. This means that in the presence of liquid 9, the light beam 4 is directed onto a different photocell 6 of the line detector 3a than in the absence of liquid 9.

[0034] Fig. Figure 5 shows an optical liquid sensor 1 with a light source 2 emitting two parallel light beams 4a, 4b and is described with regard to the differences to the embodiment according to Fig. As described in section 1, the light source 2 is configured to emit several parallel light beams 4a, 4b. Advantageously, the distance between, for example, two parallel light beams 4a, 4b is equal to the extent of the reflective surface element 5 and / or the distance between two photocells 6 of the detector 3. This allows for a spatial resolution sufficient to detect the presence of liquid 9 in different sections of the reflective surface element 5. In this example, a drop of condensation, acting as liquid 9, causes the light beams 4a, 4b to scatter, resulting in a reduction of the signal strength of the light sensed by the photocells 6.

[0035] Fig. Figure 6 shows an optical liquid sensor 1 with a beam splitter 12 and is described with regard to the differences to the embodiment according to Fig. 1 described. The beam splitter 12 is, for example, a semi-transparent mirror, wherein a light beam 4 incident on the beam splitter 12 is split into two partial beams. One partial beam is transmitted without significant change in direction, and another partial beam is reflected. The transmitted partial beam is treated as described with regard to Fig. 1 is directed towards the reflective surface element 5. The reflected partial beam serves as the control beam 7 and is directed directly, i.e., without being directed towards the reflective surface element 5, towards the detector 3. The power of the control beam 7 is determined by the output power of the light source 2 and the beam splitter 12. A deviation of the input power of the control beam 7 detecting at the detector 3 from the determined power of the control beam 7 can be used to diagnose malfunctions of the optical liquid sensor 1.

[0036] Fig. Figure 7 shows an optical liquid sensor 1 with a light source 2 emitting two parallel light beams 4a, 4b and has a setup as in Fig. Figure 5 illustrates that the optical liquid sensor 1 can also detect contaminants 9 located on the inside of the housing 11. An example of such a contaminant 9 could be corrosion, which affects the optical properties of the reflective surface element 5 and thus reduces the signal strength measured by the detector 3. Contaminants 9 of the electrical system 10 lead to a reduction in electrical clearances and creepage distances and are therefore also relevant to safety.

[0037] Fig. Figures 1 to 7 are merely schematic representations, in which refraction at an interface between a gas 8 and a liquid 9, as well as at an interface between a liquid 9 and a gas 8, is not shown in the path of the light beam 4. Furthermore, reflection of the light beam 4 at the interface between liquid 9 and gas 8 following reflection by the reflective surface element 5 is not shown. These reflections lead to a further reduction in the signal strength or intensity measured by the detector 3, or to a shift in the beam path, which a person skilled in the art can determine using optical geometry and standard laws of refraction.

[0038] Fig.Figure 8 shows an electrical system 10 comprising an optical liquid sensor 1 and an electronic control device 100. The electronic control device 100 is configured to control the optical liquid sensor 1. For example, the electronic control device 100 can send data regarding the acceleration of the electrical system 10 to the optical liquid sensor 1. The acceleration data can be used by the liquid sensor 1 to determine the presence of liquid 9 or its quantity. The electronic control device 100 can also be configured to control the electrical system 10 and, for example, control protective measures to protect the components of the electrical system 10 based on the liquid 9 detected by the optical liquid sensor 1.

[0039] Advantageously, the optical liquid sensor 1 is arranged within the electrical system 10 in such a way that, due to gravity, liquid 9 typically collects on the reflective surface element 5. Reference symbol list 1 optical liquid sensor 2 light sources 3 Detector 4, 4a, 4b Light beam 5 surface element 6 photocells 7 Control beam 8 Gas 9 Liquid 10 electrical system 11 cases 12 beam splitters 13 Leadership 100 electronic control devices

Claims

[1] Optical liquid sensor (1) for detecting liquid (9) for an electrical system (10), comprising - a light source (2) for emitting light, - an optical detector (3) designed as a line detector (3a) with at least two light-sensitive photocells (6) for detecting the light emitted by the light source (2), and - a reflective surface element (5), wherein - the light source (2) and the surface element (5) are arranged such that the emitted light strikes the surface element (5) at an angle, - the light source (2) is designed to emit a parallel beam of light (4), - the light source (2) and the detector (3) are arranged such that the surface element (5) directs the light beam (4) onto the photocell (6), - the surface element (5) is movable in the direction of the surface normal of the surface element (5) and is mounted depending on the amount of liquid (9) present, and - the optical liquid sensor (1) has a beam splitter (12) which is configured to branch off a control beam (7) from the emitted light beam (4) and to direct the control beam (7) to the detector (3) independently of the surface element (5) and / or the liquid (9). [2] Optical liquid sensor (1) according to claim 1, characterized by , that - the optical liquid sensor (1) has a housing (11), and - the surface element (5) is provided on an inside of the housing (11). [3] Optical liquid sensor (1) according to claim 1 or 2, characterized by , that - the light source (2) is designed to emit a polychromatic light beam (4) and the detector (3) is designed to sense the polychromatic light beam (4). [4] Optical liquid sensor (1) according to any one of the preceding claims, characterized by , that - the light source (2) is set up to emit at least two parallel light rays (4a, 4b). [5] Optical liquid sensor (1) according to any one of the preceding claims, characterized by , that - Acceleration data can be entered into the optical liquid sensor (1) and evaluated for detection. [6] Electrical system (10) comprising an optical liquid sensor (1) according to any of the preceding claims.

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