Oil mist detector for the detection and / or analysis of oil-air mixtures with bypass and associated method

Abstract

Oil mist detector (1) for the detection and / or analysis of potentially explosive oil-air mixtures, in particular designed for insertion into a crankcase (3) of an internal combustion engine, - with a measuring chamber (5) which forms at least one optical measuring section (6, 72, 73, 74, 75, 76) for the optical detection of an oil mist, - wherein the measuring chamber (5) is connected to an intake channel (7) by means of a gas supply (9), which opens into an intake opening (8), - wherein a gas outlet (10) is provided for the removal of gas from the measuring chamber (5), - wherein a bypass (11) is provided for diverting gas from the intake channel (7) bypassing the measuring chamber (5), wherein the intake channel (7) branches at a junction (12) into the gas supply (9) and the bypass (11), such that a first partial gas flow (14) is routed through the bypass (11) bypassing the measuring chamber (5), while a second, in particular remaining, partial gas flow (15) is routed through the gas supply (9) into the measuring chamber (5), characterized in that - that the intake duct (7) extends from a pre-chamber (50) to the gas supply (9) and the bypass (11), - that an acceleration section (17) is formed in the intake channel (7) before the branching point (12) for accelerating a gas flow (13) along an acceleration direction (18) after the gas flow (13) has passed the pre-chamber (50), and - that the pre-chamber (50) offers an increased flow cross-section compared to the subsequent acceleration section (17) of the intake channel (7), so that turbulence in the gas flow (13) within the pre-chamber (50) is reduced and an initial separation of larger oil particles can take place in the pre-chamber (50).

Description

[0001] The invention relates to an oil mist detector for detecting and / or analyzing oil-air mixtures. Such mixtures can be potentially explosive or (also sub-explosive) with a specific mixing ratio. These mixtures, which often occur as dispersions of fine oil droplets in air, are also referred to as oil mist or aerosol.

[0002] To detect and / or analyze the oil-air mixture, especially potentially explosive fine oil mist, the oil mist detector has a measuring chamber that forms at least one optical measuring path for the optical detection of oil mist. Using the measuring chamber, the oil mist detector can thus detect potentially explosive mixtures or oil mist, issue a corresponding warning signal, and thus ensure increased operational safety.

[0003] The oil mist detector can in particular be designed so that it can be inserted into a crankcase of a piston engine (such as an internal combustion engine or a compressor) in order to be able to detect fine oil droplets forming in the crankcase at an early stage, since these can form an explosive mixture with air in the crankcase.

[0004] The invention further relates to a piston engine, which can be designed in particular as a compressor or internal combustion engine, with a crankcase housing which delimits a crank chamber, and with an oil mist detector as described above.

[0005] Finally, the invention relates to a method for operating an oil mist detector as described above, in particular a method for detecting and / or analyzing oil-air mixtures in a monitored space such as an interior space, in particular a crankcase, of a piston engine (e.g. an internal combustion engine) with the aid of an oil mist detector having a measuring chamber forming an optical measuring path for the optical detection and / or analysis of an oil mist.

[0006] The detection and analysis of oil droplets in air using light is generally known. In particular, oil mist detectors are known that can detect oil mist using transmitted light and / or scattered light measurements, such as the oil mist described above. For example, US 2013 / 0 125 624 A1, DE 81 08 730 U1, and WO 97 / 25 611 A2 disclose such oil mist detectors. Measurement arrangements that enable scattered light and transmission measurements are also known from other technical fields, such as robotics, such as EP 2 659 260 B1. Furthermore, it is already known to design scattered light measurements redundantly, for example, to increase the reliability of an optical inspection of glass bottles, as described in US 4 050 824 A.

[0007] In the field of optical detection of particles in an aerosol, DE 10 2009 011 846 A1 explains the advantages for increasing operational reliability when particles are separated according to their size before the optical measurement is carried out.

[0008] EP 1 923 694 A2 discloses technical solutions for effectively preventing contamination of components of a light measuring device by oil deposits.

[0009] The formation or detection of small oil droplets within a monitored space, such as an engine compartment, is relevant because the presence of such oil droplets indicates that an engine failure is to be expected in the near future. In the worst case, this can lead to the

[0010] Oil droplets can ignite on surfaces heated by frictional heat or other ignition sources, thus triggering an explosion in the monitored space. Similar hazards also occur, for example, in process industry plants, and here, too, an oil mist detector according to the invention can be usefully used to monitor a space.

[0011] A distinction can be made between mechanically generated oil mist, which consists of relatively large oil droplets with diameters of 50 µm or more, and fine oil mist, which is generated by hot surfaces or other means of evaporation. This type of mist typically has a droplet size of less than 10 µm, for example, 1-5 µm. These small droplets are very dangerous because they can easily lead to the formation of potentially explosive mixtures in air.

[0012] However, in typical application situations, both these small droplets and the large oil droplets are formed and together form an inhomogeneous oil-air mixture that must be examined optically.

[0013] Against this background, the invention aims to improve the detection and / or analysis of smaller oil droplets in such oil-air mixtures, particularly for the reliable monitoring of the operation of piston engines, especially internal combustion engines. This is intended to increase the reliability of detecting potentially explosive oil-air mixtures. In particular, it is intended to enable safe operation of the oil mist detector over many years.

[0014] In an oil mist detector according to the invention, it can be provided, for example, that the measuring chamber has an optical measuring arrangement of light sources and light detectors and that this optical measuring arrangement is set up to carry out a simultaneous transmitted light measurement and a scattered light measurement, each on a gas sample located in the measuring chamber.

[0015] The advantage of such a design is that false alarms can be detected and suppressed if water droplets enter the measuring chamber. On the other hand, the presence of a dispersion of small oil droplets in the air in the measuring chamber can be reliably detected, even if water mist is also present. The use of an additional scattered light measurement provides additional measurement parameters that allow differentiation between signals originating from oil droplets and those caused by water mist. The reason for this is that water mist and oil mist scatter light to different degrees.

[0016] As explained at the beginning, it is precisely such dispersions of fine oil droplets with diameters of less than 10 µm in air that are responsible for a potential explosion hazard, so that precisely this type of fine oil mist must be reliably detected in order to ensure safety during operation.

[0017] For rapid optical characterization and correspondingly rapid detection of emerging, particularly potentially explosive, oil mists in a space monitored by the oil mist detector, it is advantageous according to the invention if the scattered light measurement and the transmitted light measurement are performed simultaneously, in particular using the same light source(s). In other words, both the transmitted light measurement and the scattered light measurement can be based on light emitted by a light source of the measuring arrangement at a specific time.

[0018] As will be explained in more detail below, both the transmitted light and the scattered light measurements can also be configured as redundant measurements, using at least two transmitted light paths or at least two scattered light paths, respectively. A redundant measurement can be understood here, in particular, as an optical measurement in which an identical portion of the total volume of a gas sample located in the measuring chamber is examined using light through at least two independent optical measurements.

[0019] If, for example, the optical measuring arrangement has two scattered light detectors, additional redundancy can be obtained so that, in particular, false alarms can be avoided by the oil mist detector carrying out a plausibility check of measurement results obtained in scattered light measurements carried out with the two scattered light detectors.

[0020] To suppress unwanted light reflections and the resulting false measurement signals, the measuring chamber can preferably be black anodized. Furthermore, the measuring chamber's interior can be designed, for example, by means of coatings or a suitable choice of material, to absorb infrared radiation, thus improving the quality of the measurement signals.

[0021] According to the invention, the object can also be achieved by further advantageous embodiments of the measuring arrangement, which are described below: The measuring arrangement can comprise a first functional pair and a second functional pair, each consisting of a light source and a light detector. The respective light source and the respective light detector of a functional pair can be formed by one and the same optical component (e.g., an LED that operates alternately as a light source and a light detector). Alternatively, the light source and the light detector of a functional pair can each be formed as a separate optical component. These alternatives can also be combined.

[0022] The design of separate optical components for the respective light source and the respective light detector has the advantage that the respective functional pair can emit and receive light not only alternately but also simultaneously.

[0023] Furthermore, if the light source and light detector are designed separately, the respective light source and light detector of a functional pair can be combined into a compact unit. This makes the functional pair particularly easy to replace and significantly simplifies adjustment during replacement.

[0024] In this case, the light source of each functional pair, in conjunction with the light detector of the other functional pair, can form an optical measuring path for a transmitted-light measurement. This means that the two components / functional pairs can form a bidirectional measuring pair, enabling two redundant, particularly simultaneous, transmitted-light measurements of an identical gas volume in the measuring chamber.

[0025] For example, the light source of the first functional pair can form a first optical measuring path with the light detector of the second functional pair, while the light source of the second functional pair forms a second optical measuring path with the light detector of the first functional pair. Furthermore, the first and second optical measuring paths can run in opposite directions, i.e., in particular, parallel to each other. Such a configuration makes it possible, in particular, for the first and second optical measuring paths to be evaluated simultaneously, which significantly increases measurement reliability.

[0026] This is particularly easy, for example, if the first and second functional pairs are arranged opposite each other and / or the first and second optical measuring paths extend through the measuring chamber. In such a measuring arrangement, the light source of the first functional pair can be aligned with the light detector of the second functional pair, while the light detector of the first functional pair can be aligned with the light source of the second functional pair.

[0027] For a simple design of the measuring arrangement and easy adjustment, it is further advantageous if the two functional pairs are each structurally designed as a single unit, each of which is inserted, preferably removably, into a receptacle of the measuring chamber. It is preferable if the two receptacles are positioned opposite each other and / or aligned with each other in such a way that the first and second optical measuring paths extend through the measuring chamber, preferably through a center of the measuring chamber.

[0028] These two functional pairs can thus realize two redundant transmitted-light measurements, namely using the first and second optical measuring paths. This is particularly easy to achieve if the two light sources and the two light detectors are each arranged axially symmetrically to a common axis of symmetry. This axis of symmetry can preferably run through the center of the measuring chamber.

[0029] For measuring scattered light, the optical measuring arrangement can further comprise at least one further light detector, preferably at least two further light detectors. These can function as scattered light detectors. The further light detector can each form a line of sight which encloses an angle of at least 10°, preferably of at least 30°, to the first and / or second optical measuring path. A line of sight can be understood here as a direction from which the respective light detector can receive light. This line of sight can therefore correspond precisely to the light path traveled by photons that are scattered by droplets in the measuring chamber and reach the respective further light detector.

[0030] To improve the reliability of the scattered light measurement and thus prevent false alarms, at least one additional light detector can be provided to perform at least one second scattered light measurement. This at least one second scattered light measurement can be redundant to a first scattered light measurement performed by the (first) additional light detector.

[0031] Preferably, two separate scattered light detectors can be provided, as well as two functional pairs, each consisting of a light source and a transmitted light detector. It is preferred if the two functional pairs are arranged diametrically opposite each other.

[0032] The oil mist detector can further comprise a calculation unit configured to evaluate two independent transmitted-light measurements using the first and second optical measuring paths, particularly simultaneously. This allows redundant measurement results to be generated with respect to a transmitted-light measurement of a gas sample located in the measuring chamber, thus ensuring a high degree of reliability for the transmitted-light measurement.

[0033] The oil mist detector can further comprise a calculation unit, in particular the one explained above, particularly in the form of an electronic unit configured to quantitatively determine light absorption based on the transmitted light measurement and scattered light intensity based on the scattered light measurement. This is because a measured transmission / light absorption in conjunction with scattered light intensity, each of which was determined, preferably simultaneously, on a gas sample in the measuring chamber, can be used to reliably characterize the gas sample and, in particular, to answer the question of whether the gas sample is water mist and / or oil mist.

[0034] More specifically, the calculation unit can be configured to distinguish, on the basis of the determined light absorption and the determined scattered light intensity, measurement signals that can be assigned to a water portion of a gas sample in the measuring chamber from measurement signals that can be assigned to a portion of an aerosol or dispersion of oil droplets, in particular of less than 10 µm in diameter, of the gas sample.

[0035] In this case, the calculation unit can also be configured to use the determined scattered light intensity to differentiate between the two measurement signals and / or to infer the presence of the aerosol or the dispersion of (small) oil droplets on the basis of the determined light absorption and / or the determined scattered light intensity and to issue a corresponding warning signal.

[0036] In other words, the oil mist detector can be configured to use measurement signals from the scattered light measurement and the transmitted light measurement to characterize a gas sample in the chamber to determine whether or not the gas sample contains an oil mist, which is particularly critical for operational safety, particularly in situations where the gas sample also contains a water component. The oil mist detector can be configured to use measurement signals from the scattered light measurement and the transmitted light measurement to differentiate between measurement signal components resulting from a water component in a gas sample in the measuring chamber and measurement signal components resulting from an oil component in the gas sample.

[0037] For this purpose, the calculation unit can be configured, in particular, to perform a plausibility check based on measurement data obtained with the second optical measuring path with respect to measurement data obtained with the first optical measuring path. This can thus increase the reliability of the measurement data from the transmitted-light measurement.

[0038] Alternatively or additionally, the calculation unit can also be configured to perform a plausibility check based on the measurement data obtained with the second scattered light measurement with respect to the measurement data obtained with the first scattered light measurement. This can thus increase the reliability of the measurement data from the scattered light measurement.

[0039] To achieve the object posed at the outset, the invention provides the features according to claim 1, which are explained in detail below. The following features of the oil mist detector can also be used in support of the features previously explained with regard to the design of the optical measuring chamber to achieve the object.

[0040] In the oil mist detector according to the invention according to claim 1, to achieve the object mentioned at the outset, the measuring chamber is connected by means of a gas supply to an intake duct which opens into an intake opening, a gas discharge is also provided for discharging gas from the measuring chamber, and finally a bypass is provided for discharging gas from the intake duct, bypassing the measuring chamber. For a compact design, it is preferable if the bypass connects the gas supply to the gas discharge. Furthermore, it should already be mentioned at this point that the intake opening, when the oil mist detector is installed, can preferably be arranged within a space monitored by the oil mist detector, for example an interior space being examined.

[0041] Furthermore, according to the invention, the oil mist detector is provided with the intake channel branching into the gas supply and the bypass at a branching point, so that a first partial gas flow is guided through the bypass, bypassing the measuring chamber, while a second, in particular remaining, partial gas flow is guided through the gas supply into the measuring chamber.

[0042] Finally, according to the invention, the oil mist detector is provided with the intake channel extending from an upstream pre-chamber to the gas supply and the bypass, with an acceleration section being formed in the intake channel upstream of the branching point for accelerating the gas flow along an acceleration direction after the gas flow has passed through the pre-chamber, and with the pre-chamber offering an enlarged flow cross-section compared to the subsequent acceleration section of the intake channel, so that turbulence in the gas flow within the pre-chamber can be reduced and a first separation of larger oil particles can take place in the pre-chamber.

[0043] The provision of such a bypass enables the efficient separation of the finest oil droplets from a gas sample captured by the oil mist detector into the measuring chamber, where they can then be optically measured precisely and reliably, thus achieving a high level of reliability in the detection of these small oil droplets. In this respect, a synergy exists in that the separation of the fine oil droplets enables differentiation between fine oil mist and water mist in the measuring chamber.

[0044] Bypassing the measuring chamber with the bypass has the particular advantage that heavier oil droplets, especially those with a diameter of more than 10 µm, can be diverted through the bypass, preventing them from entering the measuring chamber and hindering or even preventing the optical measurement of finer oil droplets. The bypass thus separates larger oil particles, especially larger liquid oil droplets, from entering the measuring chamber. This prevents such larger oil particles from settling on the light sources and light detectors in the measuring chamber and contaminating them, which would otherwise impair the optical measurement.

[0045] The bypass thus branches off a first partial gas stream from the intake duct and guides it out of the intake duct. The gas supply, in turn, branches off the second, particularly remaining, partial gas stream from the intake duct and guides it into the measuring chamber. The gas outlet, in turn, guides the second, particularly remaining, partial gas stream out of the measuring chamber after it has flowed through the measuring chamber. The first partial gas stream can contain predominantly heavier oil droplets, while the second partial gas stream can contain predominantly smaller oil droplets.

[0046] If the bypass connects the gas supply with the gas discharge, the bypass can combine the first partial gas flow and the second, in particular the remaining, partial gas flow in the gas discharge.

[0047] Alternatively or additionally, the bypass and the gas discharge from the measuring chamber can also be provided to open into a gas conveying device of the oil mist detector. Thus, the gas conveying device can convey gas both through the bypass and through the measuring chamber and the gas discharge adjoining the measuring chamber in the direction of gas flow. Thus, with the oil mist detector, a gas flow flowing in through the intake opening can be divided into at least two partial gas flows, with only one of the two partial gas flows being conveyed through the measuring chamber.

[0048] The bypass allows a portion of the gas flow flowing in through the intake port to be guided past the measuring chamber as a first partial gas flow. This allows the optical measurement in the measuring chamber to be performed unaffected by the first partial gas flow flowing through the bypass, which is advantageous for high measurement reliability.

[0049] In other words, the invention proposes - that the oil mist detector has an intake channel for sucking in a gas sample, for example directly from a crankcase of an internal combustion engine, through an intake opening; - a gas supply for guiding at least part of the gas sample from the intake channel into the measuring chamber; - a bypass, for example in the form of a connecting channel, through which a first part of the gas sample can be discharged directly from the intake channel, i.e. in particular bypassing the measuring chamber; - and a gas discharge means with which a second, in particular remaining, part of the gas sample can be discharged from the measuring chamber, preferably in a flow-through operation;

[0050] As already explained, the bypass can lead into this gas discharge.

[0051] Such an oil mist detector can therefore be designed, in particular with the aid of the previously described embodiments, to divide an inflowing gas sample, i.e. a specific volume of gas or a gas mixture, which is to be optically measured, into - a first partial gas flow passing through a bypass, bypassing the measuring chamber, and - a second, particularly residual, partial gas stream, which passes through a gas inlet and then through said optical measuring chamber. The oil mist detector can further be configured to subsequently combine the two partial gas streams into a common gas outlet.

[0052] By splitting the gas sample into two separate partial gas streams, the actual optical measurement can be significantly improved. This is because, during measurement, the bypass allows a portion of the gas stream flowing through the intake channel to be directed past the measuring chamber as a first partial gas stream into the gas outlet. This prevents this first partial gas stream from entering the measuring chamber.

[0053] In the installation situation, the intake opening can be arranged in particular within a crankcase housing, i.e. in particular in a crankcase, of an internal combustion engine which is monitored by means of the oil mist detector.

[0054] The previously described gas flow routing ensures that larger oil droplets, particularly those with a diameter of at least 10 µm, contained in the gas flow flowing through the intake port, flow preferentially through the bypass and only occasionally enter the measuring chamber or, in the best case, not at all. Furthermore, smaller oil droplets, particularly those with a diameter of less than 10 µm or even less than 5 µm—provided they are also contained in the gas flow flowing through the intake port—preferentially enter the measuring chamber through the gas supply for optical measurement.

[0055] In other words, the provision of a bypass designed according to the invention enables the separation of fine oil mist contained in the gas stream flowing through the intake opening from larger oil droplets. This separation significantly increases the reliability of the optical detection of potentially explosive mixtures, since the larger oil droplets can interfere with the accurate detection of smaller oil droplets.

[0056] According to the invention, the object can also be achieved by further advantageous embodiments, in particular in combination with the previously explained features in connection with the measuring arrangement according to the invention and / or the bypass according to the invention. These are described below: For example, one embodiment proposes that the bypass is branched off from the intake channel at a branching point in such a way that a first partial gas flow of a gas flow flowing through the intake opening and the intake channel can be guided through the bypass and past the measuring chamber into a gas discharge, in particular the previously explained gas discharge from the measuring chamber.

[0057] In such an embodiment, a second partial gas flow of the gas flow, which may in particular be a remaining part of the gas flow, can also be guided through the gas supply into the measuring chamber.

[0058] In such a configuration, as provided according to the invention, the gas flow flowing in through the intake opening can be divided into a first partial gas flow, which flows through the bypass, bypassing the measuring chamber, and a remaining partial gas flow, which enters the measuring chamber.

[0059] It is preferable for the gas supply to branch upwards at the branching point from the intake duct, based on the installation situation of the oil mist detector. This is because the smaller oil droplets can be sucked upwards, i.e., against gravity, by the gas supply from the gas stream flowing through the intake duct and thus separated from the larger oil droplets contained in the gas stream. The upward branch has the advantage that the heavier oil droplets tend to migrate downwards due to their greater inertia and therefore enter the gas supply and thus the measuring chamber less frequently or not at all.

[0060] In an installation situation, for example when the oil mist detector is inserted into the crankcase of an internal combustion engine, the gas supply can thus discharge the second, in particular the remaining, partial gas flow from the intake duct against gravity and / or against a flow direction of the first partial gas flow. It is understood that with such a configuration, the first partial gas flow can predominantly comprise larger oil droplets, in particular with a diameter of at least 10 µm. This is because these droplets have a comparatively small surface-to-weight ratio and will therefore sink more easily in the direction of gravity or fly further in the flow direction of the first partial gas flow than droplets of smaller diameter.

[0061] Furthermore, the discharge of the remaining part of the gas flow can be configured such that the second, in particular the remaining, partial gas flow entering the measuring chamber is low in larger oil droplets, preferably with a diameter of more than 10 µm, compared to the proportion of these larger oil droplets in the gas flow flowing in through the intake channel. In such a case, the second partial gas flow can thus, for example, predominantly comprise smaller oil droplets, preferably with a diameter of less than 10 µm.

[0062] For particularly efficient separation of oil droplets of different sizes, it is advantageous to have an acceleration section upstream of the branching point in the intake channel for accelerating a gas stream flowing through the intake opening along an acceleration direction. This acceleration section is useful for separating heavier oil droplets, especially those with a diameter of more than 10 µm, into the bypass, thus preventing them from entering the measuring chamber. This design ultimately results in the formation of an inertial separator that separates heavier oil droplets or other contaminants into the bypass, preventing them from entering the measuring chamber.

[0063] The separation according to the invention thus increases the relative proportion of smaller oil droplets in the measuring chamber relative to the relative proportion of these smaller oil droplets in the gas stream flowing in through the intake opening, which in typical application situations may also contain a significant proportion of larger oil droplets. Thus, the proportion of these larger oil droplets in the measuring chamber is reduced, which is advantageous for reliable measurement.

[0064] In other words, the separation according to the invention ensures that – after the smaller oil droplets have been separated into the gas supply line – the first partial gas stream flowing through the bypass has an increased relative proportion of larger oil droplets. In contrast, the second partial gas stream flowing into the measuring chamber has an increased relative proportion of smaller oil droplets, in particular with diameters of 10 µm and less. (This is in comparison to the incoming gas stream, which can contain both smaller and larger oil droplets.) In other words, the larger oil droplets are thus separated into the bypass. The efficiency of this separation increases significantly with the size of these oil droplets.

[0065] The acceleration section can be formed, for example, by a constriction of a flow cross-section. This can result in an increase in the flow velocity of the gas flow and thus in an increase in the kinetic energy of the individual oil droplets. Said acceleration section can thus, in particular, accelerate the previously explained first partial gas flow, which is passed through the bypass. At the same time, the acceleration section can also accelerate the second partial gas flow, which enters the measuring chamber. This acceleration improves the previously described separation of the larger oil droplets.

[0066] For efficient separation using gravity in the installation of the oil mist detector, it is advantageous if the acceleration section slopes upwards in the direction of the gas flow. For this purpose, the acceleration section can, for example, have a channel bottom that slopes downwards in the direction of acceleration.

[0067] The oil mist detector can also be designed so that the measuring chamber is at the highest point in an installation situation (compared to the gas inlet and gas outlet), while the gas inlet and gas outlet open into the measuring chamber from below. With such a design, the partial gas flow fed into the measuring chamber initially ascends through the gas inlet and then descends again through the gas outlet after passing through the measuring chamber.

[0068] The advantage of this design is that – especially when the gas flow decreases or dries up – liquid oil residues that have accumulated in the gas supply and / or gas discharge can flow back into the intake channel and / or an outlet channel due to gravity. This prevents these liquid residues from accumulating in the measuring chamber and interfering with the optical measurement.

[0069] Furthermore, oil residues can also flow away due to gravity in the opposite direction of acceleration and / or the previously explained ascent. Thus, both the acceleration and ascent sections can be used without problems, even if liquid oil residues occasionally accumulate in the oil mist detector.

[0070] The gas supply can now be designed in such a way that it discharges the second, in particular the remaining, partial gas flow of the gas flow counter to the direction of acceleration and / or counter to the direction of ascent from the gas flow. For this purpose, the gas supply can, in particular, open into the acceleration section at an acute angle.

[0071] Alternatively or additionally, it can be provided that the gas supply branches off from the acceleration section at an acute angle relative to the acceleration direction. This allows the smaller oil droplets to be separated from the acceleration section into the gas supply preferentially over larger oil droplets, particularly if these oil droplets experience a reversal of direction when branching off into the gas supply. These measures further improve the efficiency of the inventive separation of the smaller oil droplets.

[0072] For the same purpose, a flow cross-section can also be enlarged in the direction of the gas supply in the area of ​​the branching point. This significantly reduces the flow velocity, allowing the smaller oil droplets with lower inertia to distribute evenly across the acceleration direction. This allows the smaller oil droplets to enter the measuring chamber in greater numbers, while the heavier oil droplets, due to their greater inertia, initially fly further in the direction of acceleration and thus increasingly enter the bypass.

[0073] According to a further advantageous embodiment, a baffle surface can be formed upstream of the acceleration section in the gas flow direction. Such a baffle surface can cause the gas flow to initially reverse direction at the baffle surface as it passes through the acceleration section. During such a reversal of direction, the oil droplets can thus exhibit a zero velocity for a moment before subsequently being accelerated.

[0074] Furthermore, it is advantageous if a deflection surface is formed at one end of the acceleration section, forming an acute angle of less than 90° with the acceleration direction. This deflection surface can then form a collecting funnel for the first partial gas flow. In other words, the first partial gas flow, which has a higher proportion of larger oil droplets after the smaller oil droplets have been separated into the gas supply line, can be directed into the bypass at the deflection surface after passing through the acceleration section, with the deflection surface acting as a collecting funnel for heavier oil droplets.

[0075] As already mentioned, the bypass that discharges the first partial gas stream can flow into the gas discharge that discharges gas from the measuring chamber. More precisely, the bypass can flow into the gas discharge from the measuring chamber at a junction point in such a way that the first partial gas stream and the second, particularly remaining, partial gas stream are recombined at the junction point.

[0076] In such a configuration, it is preferable if the angle between the mean flow direction of the first partial gas flow and the mean flow direction of the second, particularly remaining, partial gas flow at the junction point is less than 60°. This prevents gas turbulence and thus a backflow of gas against the main flow direction, particularly back into the measuring chamber, thus increasing measurement reliability.

[0077] According to a preferred embodiment, a Venturi nozzle can be formed in the region of the junction, for example by means of a cross-sectional constriction in the area of ​​the bypass. This allows the second partial gas flow to be conveyed reliably, i.e., in particular, without interruption, through the measuring chamber by means of a pressure difference generated by the Venturi nozzle. The pressure difference is generated by a pressure drop that arises from the flow velocity of the first partial gas flow increasing at the point of the cross-sectional constriction, thereby reducing the static pressure at this point.

[0078] To ensure that the heavier oil droplets primarily enter the bypass and not the measuring chamber, it is also recommended that the gas supply leading into the measuring chamber has a higher flow resistance than the bypass. This allows the average flow velocity through the bypass to exceed the average flow velocity through the measuring chamber, which is advantageous for the intended separation, which should preferentially transport only the smaller oil droplets into the measuring chamber. The bypass thus forms a high-velocity pass for the first partial gas flow compared to the second partial gas flow through the measuring chamber.

[0079] This can be achieved particularly easily, for example, by ensuring that the first partial gas flow through the bypass is shorter than the second partial gas flow through the gas supply, the measuring chamber, and the gas discharge, each measured from the branching point to the junction point. For example, the length of the second partial gas flow can be at least twice as long as that of the first partial gas flow.

[0080] The use of a bypass, especially in combination with the aforementioned inertial separator and the Venturi nozzle, ensures reliable measurement results by reducing the ingress of dirt into the measuring chamber, prevents false alarms and also increases maintenance intervals.

[0081] The oil mist detector preferably has its own gas extraction device. This allows gas samples to be actively extracted from the oil mist detector through the intake port. It is advantageous if the gas extraction device is installed in the oil mist detector and is accessible from the outside.

[0082] Such a gas conveying device can be designed, in particular, as a gas conveying pump for conveying the gas stream, preferably in the form of a radial fan. It is further preferred to design the gas conveying pump as a suction pump rather than a pressure pump. The gas conveying device / gas conveying pump can thus be positioned downstream of the previously explained merging point. This prevents the original size distribution of the oil droplets in the gas stream from being distorted by interaction with a gas conveying device before entering the optical measuring chamber, which could result in incorrect measurement results.

[0083] To achieve the object mentioned at the outset, the features of claim 13 are further provided according to the invention for a piston engine, in particular designed as an internal combustion engine or compressor. Thus, to achieve the object in a piston engine of the type mentioned at the outset, it is proposed that the oil mist detector is set up to take gas samples from the crankcase and is designed according to the invention as described in claim 1. The oil mist detector can thus be designed in particular according to one of claims 2 to 12 directed to an oil mist detector. For high operational reliability, it is recommended that the oil mist detector be inserted tightly into the crankcase housing of the piston engine.

[0084] According to a preferred embodiment, a gas sampling device of the oil mist detector, such as an intake pipe, can be guided through the crankcase housing into the crankcase for taking the gas samples, wherein the oil mist detector, that is to say in particular the said measuring chamber and / or a gas conveying device of the oil mist detector, is accessible from the outside.

[0085] This design offers the advantage of simple maintenance and inspection of the oil mist detector, while also being easy to retrofit, since the piston engine / combustion engine itself does not require a device for conveying the oil mist to the oil mist detector. Rather, it is sufficient for the piston engine / combustion engine to have an opening, preferably one that can be easily closed, through which gas samples can be taken from the monitored interior using the oil mist detector. Furthermore, the measuring chamber or the gas conveying device can be serviced while the oil mist detector remains installed in the crankcase. This avoids the laborious disassembly of the entire oil mist detector.

[0086] To achieve the stated object, the invention further provides the features of independent method claim 14, wherein an oil mist detector configured according to the invention is used in accordance with claim 1. This method involves taking a gas sample from the monitored space, for example, from an interior of the previously described piston engine / combustion engine, through an intake opening of the oil mist detector using a gas conveying device of the oil mist detector and optically measuring it in the measuring chamber outside the monitored space / interior. In other words, in this method, the measuring chamber of the oil mist detector is thus arranged outside the monitored space / interior.

[0087] This method offers the significant advantage that the safe operation of an internal combustion engine can be ensured without major structural changes to the internal combustion engine itself, namely by simply retrofitting an oil mist detector according to the invention to the internal combustion engine. In particular, no complex modifications are required in the interior of the internal combustion engine. Instead, it is sufficient to use an existing opening for taking a gas sample from the interior with the oil mist detector, or to adapt it for this purpose, or - if none is available - to create one.

[0088] The method further provides for the gas sample and a resulting gas stream to be divided into at least two partial gas streams in the oil mist detector. For this purpose, a first partial gas stream is passed through the bypass, bypassing the measuring chamber, while a second, in particular remaining, partial gas stream is passed through a gas inlet into the measuring chamber of the oil mist detector.

[0089] In this case, it is particularly preferred if, with the aid of the gas supply, which can branch off from an intake channel opening into the intake opening, smaller oil droplets with diameters of less than 10 µm, which are contained in the gas sample, are separated from the first partial gas stream. As already described in detail above, this can achieve an increase in the relative proportion of these smaller oil droplets in the second partial gas stream compared to the relative proportion of these smaller oil droplets in the gas sample originally taken with the oil mist detector or in the resulting gas stream. This increase leads to a more reliable optical measurement of the gas volume in the optical measuring chamber and thus to an increase in measurement reliability.

[0090] The invention will now be described in more detail using an exemplary embodiment, but is not limited to this embodiment. Further developments of the invention can be derived from the following description of a preferred embodiment in conjunction with the general description, the claims, and the drawings.

[0091] In the following description, elements that are identical in function are given identical reference numbers even if they have different designs or shapes.

[0092] It shows: Fig. 1 shows an oil mist detector according to the invention with the housing dismantled, whereby the circuit boards otherwise installed in the housing and their fastening are not shown, Fig. 2 the oil mist detector Fig. 1 with attached housing, Fig. 3 a gas conveying device of the oil mist detector Fig. 1 in the form of a suction pump in removed condition (cf. Fig. 1, right illustration), Fig. 4 the oil mist detector Fig. 2 inserted into a crankcase of a piston engine designed as an internal combustion engine, Fig. 5 a gas sampling device of the oil mist detector Fig. 1 and Fig. 2 viewed from above, Fig. 6 the gas sampling device Fig. 5 viewed from below, Fig. 7 a front view of the gas sampling device from Fig. 5, Fig. 8 a longitudinal section through the gas sampling device from Fig. 5, Fig. 9 a view from the front of the oil mist detector Fig. 1 with separate housing, without circuit boards and with gas sampling device and service cover removed, Fig. 10 a view from the rear of the oil mist detector Fig. 9, Fig. 11 a plan view of the front of the oil mist detector with the cover removed, Fig. 12 a side view from below of the oil mist detector with remote housing, Fig. 13 a top view of the rear of the oil mist detector, with a detailed view at a lower level (hatched areas), Fig. 14 the detailed view Fig. 13 in an enlarged view with an illustration of various partial gas flows and a further enlarged detailed view of the gas flows in the area of ​​the bypass and the measuring chamber. Fig. 15 the oil mist detector Fig. 2 with clamping element removed, Fig. 16 a side view of the oil mist detector from Fig. 2 with a partial sectional view in the area of ​​the gas conveying device, Fig. 17 the gas conveying device from Fig. 3 in a sectional view with an opposite Fig. 3 cutting plane rotated by 90° around a longitudinal axis, Fig. 18 the gas conveying device Fig. 3 and Fig. 17 in a perspective view from the front and Fig. 19 another possible design of a gas sampling device of the oil mist detector.

[0093] The Fig. 2 shows an oil mist detector according to the invention with attached housing, while Fig. 1 shows the oil mist detector with the housing removed and without the circuit board(s), once with the gas conveying device 27 inserted (left) and once with the gas conveying device 27 removed (right).

[0094] As in Fig. 4, the oil mist detector 1 is designed to be inserted into a crankcase 3 of a (in Fig. 4 not further illustrated) designed as an internal combustion engine. For this purpose, the oil mist detector 1 has a gas sampling device 29 on a measuring part 70 (see the Fig. 4), which can be guided through the crankcase 3 into the crankcase 4 of the internal combustion engine in order to take a gas sample there. The measuring part 70 remains outside the crankcase 4, which is monitored by the oil mist detector 1.

[0095] As in the Fig. 15, the gas sampling device 29 is designed to be removable in order to be able to clean it. By means of an interface 58 formed on the housing 39 of the oil mist detector (see Fig. 9) and a separate clamping element 63 (see the Fig. 2 and Fig. 15) the gas sampling device 29 can be mounted securely and sealingly on the oil mist detector 1.

[0096] The advantage of this approach is that the oil mist detector 1, i.e. in particular the Fig. 11 shown measuring chamber 5 and the Fig. 1 and Fig. 3, are accessible from the outside. Furthermore, the oil mist detector 1 can be removed while the gas extraction device 29 remains inserted into the crankcase 3.

[0097] The gas conveying device 27 of the oil mist detector 1, which is shown in Fig. 4 shown installation situation is arranged outside in relation to the crank chamber 4, serves to take gas samples from the crank chamber 4. With the help of the gas conveying device 27, which is designed as a motor-driven gas conveying pump 28, as in Fig. 3, the oil mist detector 1 can thus actively take a gas sample from the crankcase 4 as required. The gas sample is drawn through the Fig. 4 can be seen, and through an intake channel 7 formed in an intake pipe 30 of the gas extraction device 29, which is in Fig. 8 is illustrated in more detail, from the crankcase 4 through the crankcase housing 3 into a measuring chamber 5 of the oil mist detector 1 arranged outside the crankcase 4, which Fig. 9 can be seen.

[0098] A return flow 65 is returned to the crankcase 4 through a return channel 67 via a return opening 66. The return opening 66 is facing away from the intake opening 8 to avoid a fluidic short circuit, i.e., the direct intake of the gas exiting from the return opening 66.

[0099] As the Fig. 1, Fig. 3 and Fig. 13, the gas feed pump 28 has a fan blade arrangement 31 for conveying the gas flow 13, which is driven by an electric drive motor 32. The gas feed pump 28 thus forms a radial fan together with a wall 68 of the receptacle 37. The gas feed pump 28 is also designed as a suction pump, since it is positioned downstream of the gas junction 24 and thus sucks the gas flow 13 from the crankcase 4 through the gas extraction device 29. This is advantageous since the gas flow 13 only comes into contact with the fan blade arrangement 31 after passing through the measuring chamber 5. This prevents the size distribution of the oil droplets from being distorted by interaction with the rotating fan blade arrangement 31.

[0100] This approach makes it possible to optically detect an oil mist 2, i.e., an aerosol of extremely fine oil droplets, forming in the crankcase 4 using the oil mist detector 1. This is because the oil mist 2 can be transported into the measuring chamber 5 as part of the gas sample using the gas sampling device 29 and optically measured there. Thus, the formation of fine oil mist 2 in the crankcase 4 can be monitored using the oil mist detector 1.

[0101] For this purpose, in the measuring chamber 5 of the oil mist detector 1, as shown in the detailed view of the Fig. 13, an optical measuring section 6 is designed for the optical detection of the oil mist 2 conveyed into the measuring chamber 5. More precisely, the measuring chamber 5 has an optical measuring arrangement 44. This comprises light sources 45 and light detectors 46 and is designed to carry out a transmitted light measurement and a scattered light measurement on the gas sample located in the measuring chamber 5. As can easily be seen in the detailed view of the Fig. 13, a first optical measuring section 6 is designed for a first transmitted light measurement, and a second optical measuring section 72 is designed for a second redundant transmitted light measurement of the same gas volume. In addition, as the Fig. As illustrated in Figure 14, four additional optical measuring sections 73, 74, 75, and 76 are provided, each of which is intended for a scattered light measurement. All six of these measuring sections 6, 72, 73, 74, 75, and 76 can be evaluated simultaneously.

[0102] For transmitted light measurement, the optical measuring arrangement 44 comprises a first functional pair 47 consisting of a light source 45 and a light detector 46, as well as a second such functional pair 48, which is designed analogously (cf. Fig. 13 and Fig. 14). The light sources 45 and light detectors 46 of the two functional pairs 47, 48 are each aligned such that the light source 45 of the first functional pair 47 forms the first optical measuring path 6 with the light detector 46 of the second functional pair 48, while the light source 45 of the second functional pair 48 forms the second optical measuring path 72 with the light detector 46 of the first functional pair 47. The two optical measuring paths 6 and 72 extend in opposite directions and cover the same measuring path through the measuring chamber 5. In other words, the first and second optical measuring paths 6 and 72, or the first functional pair 47 and the second functional pair 48, thus form a redundant bidirectional measuring pair.

[0103] The first and second optical measuring sections 6, 72 run in opposite directions and parallel to each other, as can be seen in the view of the Fig. 14 clearly recognizes. In Fig. 13 and Fig. 14, it can also be seen that the two functional pairs 47, 48 are each structurally designed as a single unit. Each of the units is inserted into a respective receptacle 49 of the measuring chamber 5. In Fig. 14 it can also be clearly seen that the two receptacles 49 of the functional pairs 47, 48 are positioned opposite each other in such a way that the first and second optical measuring sections 6, 72 run centrally through the measuring chamber 5.

[0104] By means of a Fig. The further light detector 52 illustrated in Figure 14, which forms a line of sight 53 at an angle of more than 10° with respect to the first optical measuring path 6, can detect scattered light, more precisely light emitted by the light source 45 of the left functional pair 47 and which is backscattered by oil droplets in the measuring chamber 5. A second scattered light detector 71 is also provided. This also forms a line of sight that forms an angle of more than 10° with the first optical measuring path 6. However, this second further light detector 71 receives forward-scattered light that was originally emitted by the light source 45 of the left functional pair 47.

[0105] With respect to the light source 45 of the second right-hand functional pair 48, the first further light detector 52 receives forward-scattered light (measurement section 73), and the second further light detector 71 receives backscattered light (measurement section 74). Conversely, the light detector 52 receives backscattered light from the left light source 45 (measurement section 75), and the light detector 71 receives forward-scattered light from the left light source 45 (measurement section 76). In other words, the light detectors 52 and 71 thus form a redundant measurement pair for (multiply) redundant scattered light measurements with forward and backward scattered light.

[0106] The second further light detector 71 is thus provided for performing a second scattered light measurement, namely using light emitted by the light source 45 of the second functional pair 48. This second scattered light measurement is redundant to the first scattered light measurement possible by means of the first further light detector 52 using light emitted by the light source 45 of the first functional pair 47. For example, with respect to light emitted by the left light source 45, the detector 71 can measure forward scattered light, and the further detector 52 can measure forward scattered light from the right light source 45.

[0107] To benefit from the redundancy provided by the measuring arrangement 44, the oil mist detector 1 has a calculation unit configured to evaluate two independent transmitted light measurements using the first and second optical measuring paths 6, 72, particularly simultaneously. Diode-specific contamination is constantly determined and taken into account in subsequent calculations. This function allows the maintenance / cleaning interval to be extended.

[0108] Alternatively, or in case of excessive contamination, the calculation unit rejects measurement results if the measurement signals from the first and second optical measuring sections 6, 72 deviate too greatly from each other.

[0109] In other words, the calculation unit thus performs a plausibility check of the transmitted light measurement based on measurement data obtained with the second optical measuring path 72, specifically with respect to measurement data obtained with the first optical measuring path 6. In addition, the calculation unit can also perform a plausibility check of one of the scattered light measurements in an analogous manner, for example, based on measurement data obtained with the second scattered light measurement 73 / 75, specifically with respect to measurement data obtained with the first scattered light measurement 74 / 76 (either for forward or backward scattered light).

[0110] The calculation unit, which is designed in the form of an electronic unit, is further configured to quantitatively determine light absorption based on the two redundant transmitted light measurements using the optical measuring sections 6 and 72, as well as scattered light intensity based on the multiple redundant scattered light measurements (using forward and backward scattered light) using the optical measuring sections 73 and 74. From such quantitative measurements, conclusions can be drawn about the concentration of the oil mist 2 in the measuring chamber 5. In particular, it can be determined at least indirectly whether the oil mist 2 contains oil droplets that can form a potentially explosive oil-air mixture in the monitored space 4, even if the exact size of the oil droplets remains unknown.

[0111] Furthermore, the calculation unit is capable of distinguishing, based on the determined light absorption and the determined scattered light intensity, measurement signals attributable to a water portion of the gas sample in the measuring chamber 5 from measurement signals attributable to an aerosol of oil droplets, in particular with a diameter of less than 10 µm, in the gas sample. To this end, the calculation unit uses the determined scattered light intensity to differentiate between the two measurement signals generated by the water portion and the oil aerosol portion, respectively.

[0112] To ensure safe operation of the internal combustion engine (as an example of a piston engine that can be monitored with the oil mist detector 1), the calculation unit issues a corresponding warning signal if it concludes the presence of said aerosol of oil droplets based on the determined light absorption and / or the determined scattered light intensity. In such a case, the operation of the internal combustion engine can be stopped.

[0113] The calculation unit thus implements a method according to the invention for detecting the oil mist 2 in the measuring chamber 5, in which the two measuring sections 6 and 72 are evaluated simultaneously or alternately for a redundant transmitted light measurement, while in addition a further scattered light measurement is carried out, either using light from the first measuring section 6 or 72 and one or both of the further light detectors 52 and 71, and wherein the detection of the oil mist 2 is based on the transmitted light measurement and the scattered light measurement.

[0114] As already described, diode-specific contamination is detected and taken into account in the measurement. This extends maintenance intervals, results in greater accuracy, and / or prevents false alarms.

[0115] In this method, the calculation unit also uses the two additional light detectors 52 and 71 simultaneously or alternately to make the scattered light measurement redundant. For this purpose, the additional optical measuring sections 73 and 74 are used, which are Fig. 14 and which each run at an angle of more than 10° to the first or second measuring section 6 / 72.

[0116] The oil mist detector 1 also has further features that may be of their own inventive quality. To enable the most accurate measurement of the critical small oil droplets with diameters of less than 10 µm in the measuring chamber 5, these droplets must be separated from larger oil droplets, which may also be present in the gas sample or may only form during the transport of the gas sample through the oil mist detector 1 due to condensation or agglomeration processes.

[0117] For this purpose, it is planned, as clearly shown by the Fig. 13 and Fig. 14 can be understood, a bypass 11 is formed, which guides a first part of the gas stream 13 flowing into the oil mist detector 1 via the gas sampling device 29 as a first partial gas stream 14 past the measuring chamber 5. This part of the gas sample or the gas stream 13 thus does not even enter the measuring chamber 5 and does not interfere with the optical measurement there.

[0118] A closer look at the Fig. 13 and Fig. Figure 14 shows that the measuring chamber 5 is connected to the previously explained intake duct 7 by means of a gas supply 9. The intake duct 7 extends from the intake opening 8 of the gas extraction device 29 located in the crankcase 4 (see Figure 1). Fig. 4) along the intake pipe 30 (cf. Fig. 8) by the Fig. 13 recognizable second intake opening 69 into a pre-chamber 50 and from there to the gas supply 9 and the bypass 11.

[0119] The pre-chamber 50 serves as a kind of calming zone in which turbulence in the gas stream 13 can be reduced. As a result, an initial separation of larger oil particles takes place in the pre-chamber 50. These can then be drawn back into the gas extraction device 29 via the intake opening 69, following the force of gravity, and from there via the Fig. 6 visible outlet openings 57 into the interior space 4 (monitored by the oil mist detector 1). Responsible for this calming of the gas flow 13 is the enlarged flow cross-section of the prechamber 50 - compared to the adjoining section of the intake duct 7.

[0120] Furthermore, a gas discharge 10 is designed as a channel for discharging gas from the measuring chamber 5. The gas discharge 10 extends from the measuring chamber 5 to the gas conveying device 27 (cf. Fig. 14). From there, the recombined gas stream 13 is further passed through the Fig. 11, Fig. 13 and Fig. 14 recognizable first outlet opening 54a into an outlet channel 55 of the gas extraction device 29 (see the Fig. 5 and Fig. 6) and from there to an opening 54b and 66 arranged in the crank chamber 4 in the installed situation, which in Fig. 6 are clearly visible. The outlet channel 55 also forms two further outlets 57 through which oil from the oil mist detector 1 can flow back into the crankcase 4 (cf. Fig. 6).

[0121] With the help of the oil mist detector 1, a gas flow circuit is thus formed which - driven by the gas conveying device 27 of the oil mist detector 1 - leads from the crankcase 4 through the gas extraction device 29 into the oil mist detector 1 and then again through the gas extraction device 29 - in the example via a separate return channel 67 - back into the crankcase 4.

[0122] The provided bypass 11 serves to discharge gas from the intake channel 7, bypassing the measuring chamber 5, into the outlet channel 55 and from there back into the crankcase 4. This can be realized particularly easily if - as shown in the embodiment of the figures - the bypass 11 connects the gas supply 9 to the gas discharge 10.

[0123] As can be seen from the illustration of the different gas flows within the oil mist detector 1 according to Fig. 14, the gas flow 13 flowing in through the gas sampling device 29 is thus divided into the first partial gas flow 14, which flows through the bypass 11, and a remaining partial gas flow 15, which flows through the gas supply 9 into the measuring chamber 5 and from there into the gas outlet 10. Shortly after the bypass 11, these two partial gas flows 14, 15 are then Fig. 13, before being conveyed back into the gas extraction device 29 as a common, recombined gas stream 13 by the gas conveying device 27. In order to minimize turbulence during this merging, the angle between the mean flow direction of the first partial gas stream 14 and the second partial gas stream 15 at the merging point 24 can, for example, be less than 60°.

[0124] The intake duct 7 branches off at the Fig. 13 and Fig. 14 illustrated branching point 12 thus into the gas supply 9 and the bypass 11. As a result, the first partial gas flow 14, which flows through the intake opening 8 and the intake channel 7, is guided through the bypass 11 and past the measuring chamber 5 into the gas discharge 10.

[0125] The second, remaining partial gas flow 15 of the gas flow 13 flowing through the intake channel 7, however, is guided through the gas supply 9 into the measuring chamber 5.

[0126] The aim of dividing the incoming gas stream 13 into the two partial gas streams 14 and 15 is to separate larger oil droplets into the bypass 11 and to direct primarily smaller oil droplets, which are relevant for the explosion hazard, into the measuring chamber 5 so that they can be precisely measured there - undisturbed by the larger oil droplets.

[0127] For this purpose, the gas supply 9 branches off from the intake duct 7 at the branching point 12, relative to the Fig. 4, upwards. As a result, oil droplets entering the measuring chamber 5 must migrate against gravity, which is more likely for smaller oil droplets than for larger oil droplets.

[0128] The separation of large oil droplets has the further advantage of reducing contamination of the measuring chamber / diodes, which significantly extends maintenance / cleaning intervals. In certain applications, this can ensure reliable operation of the Oil Mist Detector 1 for years.

[0129] In other words, in the installation situation, the gas supply 9 guides the second partial gas flow 15 against gravity and - upon closer inspection of the Fig. 14 - also opposite to a flow direction 16c of the first partial gas flow 14 from the intake channel 7. This ensures that the first partial gas flow 14 predominantly comprises larger oil droplets, in particular of at least 10 µm in diameter, while the second partial gas flow 15 predominantly comprises smaller oil droplets of less than 10 µm in diameter.

[0130] In order to improve the separation of the larger oil droplets from the smaller oil droplets, an acceleration section 17 is additionally formed in the intake channel 7 before the branching point 12 (cf. Fig. 10). How the Fig. 14 shows by means of the arrows of different strengths, which represent different flow velocities, the acceleration section 17 serves to accelerate the gas flow 13 along the Fig. 13, after it has passed through the prechamber 50. This also accelerates, in particular, the first part of the gas stream 13, which finally reaches the bypass 11.

[0131] The acceleration ensures that the larger oil droplets reach a high kinetic energy, so that they initially fly straight ahead until they reach the Fig. 14. The deflection surface 21 forms a kind of collecting funnel 22, which collects the heavy oil droplets and guides them into the bypass 11. For this purpose, the deflection surface 21 forms an acute angle of less than 90° with the acceleration direction 18.

[0132] The acceleration section 17 and the bypass 11 thus form an inertial separator which separates heavy oil droplets or other dirt into the bypass 11 and thus prevents them from contaminating the measuring chamber.

[0133] The small and thus lighter oil droplets, on the other hand, can change their direction more easily because they have a comparatively low kinetic energy and are therefore preferentially separated into the gas supply 9 before the deflection surface 21 and thus reach the measuring chamber 5.

[0134] Clearly visible in the Fig. 10 and Fig. 13 is that the acceleration section 17, in the installed situation, forms a rise 19 in the direction of the gas flow 13. Thus, the heavier oil droplets in the area of ​​the branching point 12 preferentially collect at the lower channel floor of the intake channel 7 and migrate along the rise 19 to the bypass 11.

[0135] In addition, it is advantageous for efficient separation of the smaller oil droplets if - as in Fig. 13, the gas supply 9 at the branching point 12 from the intake duct 7, relative to the Fig. 4, branches off upwards. For clarity, it should be mentioned again that the measuring chamber 5 is located at the highest point in the installation situation (cf. Fig. 4), so that the gas supply 9 and the gas outlet 10 open into the measuring chamber 5 from below (cf. Fig. 13), as a comparison of the Fig. 4, Fig. 11 and Fig. 13. This has the advantage, among other things, that when the gas flow 13 ceases, liquid oil residues that are deposited in the gas supply 9 and / or the gas discharge 10 can flow back into the intake channel 7 and / or the outlet channel 55 by gravity and thus do not accumulate in the measuring chamber 5. Fig. In the embodiment shown in Figure 13, the oil residues flow away due to gravity against the illustrated acceleration direction 18 and against the rise 19.

[0136] As in the Fig. 11, Fig. 13 and Fig. 14, the gas supply 9 thus leads the second partial gas flow 15 against the acceleration direction 18 and also against the direction of the rise 19 from the gas flow 13 flowing through the intake duct 7. Here, the gas supply 9 is branched off from the acceleration section 17 at an acute angle relative to the acceleration direction 18. As the flow arrows in Fig. As illustrated in Figure 14, this results in the oil droplets following the second partial gas flow 15 experiencing a reversal of direction relative to the original acceleration direction 18. However, this reversal of direction is very unlikely for heavier oil droplets with high kinetic energy, so they enter the gas supply 9 less frequently or not at all.

[0137] Furthermore, in the Fig. 11, Fig. 13 and Fig. 14 that a flow cross-section in the direction of the gas supply 9 in the area of ​​the branching point 12 increases, compared to the flow cross-section of the adjacent intake duct 7, as can be seen from the two double arrows in Fig. 13 is illustrated.

[0138] In Fig. 11 and Fig. 13 also shows that a baffle surface 20 is formed in the gas flow direction 16a upstream of the acceleration section 17, such that the gas flow 13 flowing through the prechamber 50 undergoes a reversal of direction 23 at the baffle surface 20 before passing through the acceleration section 17. As a result, all oil droplets experience a change of direction and are subsequently accelerated in the direction of the acceleration direction 18.

[0139] The conveyance of the second partial gas flow 15 through the measuring chamber 5 is carried out by means of a Venturi nozzle 25, which is formed by means of a cross-sectional constriction 26 in the area of ​​the bypass 11, as in Fig. 13 and Fig. 14. As a result, the second partial gas flow 15 is conveyed through the measuring chamber 5 by means of a pressure difference generated by the Venturi nozzle 25, because as in Fig. 14 can be seen from the flow arrows, the gas flow velocity is highest in the area of ​​the cross-sectional constriction 26.

[0140] To achieve this high flow velocity of the first partial gas stream 14 in the region of the bypass 11, the gas supply 9 is designed to have a higher flow resistance than the bypass 11. This ensures that the average flow velocity through the bypass 11 exceeds the average flow velocity through the measuring chamber 5.

[0141] The Venturi nozzle 25 interacts with the higher flow resistance to create a stable flow through the measuring chamber 5.

[0142] The device features explained above thus enable a method for detecting and / or analyzing potentially explosive oil-air mixtures in a monitored space 4, in particular in crankcases or other interior spaces of internal combustion engines, compressors, and other piston engines, in which a gas sample is taken from the monitored space 4 / interior space using the gas extraction device 27 of the oil mist detector 1 through an intake opening 8 of the oil mist detector 1 arranged in the monitored space 4 / interior space. The internal combustion engine does not require any additional, complex modifications for this purpose. The only prerequisite is that the piston engine, in particular the internal combustion engine or compressor, offers a passage through which the gas extraction device 29 of the oil mist detector 1 can be guided from the outside into the interior space and subsequently sealed.

[0143] If a bypass 11 as described above is implemented, the gas sample in the oil mist detector 1 can also be divided into at least two partial gas streams 14, 15, so that a first partial gas stream 14 is passed through the bypass 11, bypassing the measuring chamber 5, while a second, in particular remaining, partial gas stream 15 is passed through a gas supply 9 into the measuring chamber 5.

[0144] The measures described above can ensure that smaller oil droplets with diameters of less than 10 µm contained in the gas sample are separated from the first partial gas stream 14 or the incoming gas stream 13, respectively, in such a way that a relative proportion of these smaller oil droplets in the second partial gas stream 15 is increased compared to a relative proportion of these smaller oil droplets in the gas sample. In other words, the relative proportion of larger oil droplets in the measuring chamber 5 is lower than in the original gas sample taken from the interior, which is advantageous for precise measurement of said smaller oil droplets, since the larger oil droplets can no longer interfere with the transmitted or scattered light measurements.

[0145] Returning once again to the optical measuring arrangement 44 explained at the beginning, it can be said that the embodiment of the oil mist detector 1 shown in the figures provides: a first functional pair 47 consisting of a light source 45 and a detector 46 combined to form a first removable structural unit; an opposite second functional pair 48 consisting of a light source 45 and a detector 46 combined to form a second removable structural unit; and two separate, spaced-apart scattered light detectors 52 and 71, wherein the two functional pairs 47, 48 implement two redundant transmitted light measurements 6, 72 and the two scattered light detectors 52, 71 each implement a scattered light measurement 73 / 74 with light that was emitted by one of the functional pairs 47 / 48 and scattered by a gas sample located in the measuring chamber 5.Thus, two, in particular two redundant, scattered light measurements can be evaluated simultaneously, and the two opposing transmitted light measurements 6, 72 can also be evaluated simultaneously. Furthermore, it was explained that a respective line of sight 53 of the respective scattered light detector 52 / 71 can enclose an angle of at least 10° with a line connecting the first functional pair 47 with the second functional pair 48. This imaginary line forms an axis of the two transmitted light measurements 6 and 72.

[0146] In summary, to improve the measurement reliability and accuracy of an oil mist detector 1 for detecting and / or analyzing potentially explosive oil-air mixtures, it is proposed that the oil mist detector 1 internally have a bypass 11, by means of which a first partial gas stream 14, which has a higher relative proportion of larger oil droplets of at least 10 µm diameter compared to a gas stream 13 sucked in by the oil mist detector 1 through an intake opening 8, is guided past an optical measuring chamber 5, so that a second, in particular residual, partial gas stream 15, which is optically measured in the measuring chamber 5, primarily has smaller oil droplets of less than 10 µm diameter. This can increase the reliability and accuracy in the detection of these smaller oil droplets of less than 10 µm diameter, which can lead to the formation of potentially explosive mixtures.Furthermore, it is proposed to use a combination of a redundant transmitted light measurement (6, 72) and a multiple redundant scattered light measurement (73 / 74, 75 / 76) for the optical detection of smaller oil droplets. The bypass (11) reduces contamination. This significantly improves security against false alarms, improves measurement accuracy, and extends cleaning intervals.

[0147] How to Fig. 1, the gas conveying device 27 for actively taking gas samples is integrated into the oil mist detector 1. The gas conveying device 27, which is designed as an electric gas conveying pump 28 with an electric drive motor 32, has - as in Fig. 3 - a fan blade arrangement 31 for conveying the gas flow 13. This fan blade arrangement 31 is arranged in the intake duct 7, which in turn is connected to the measuring chamber 5 via the gas discharge 10. In other words, the intake duct 7 in the embodiment shown in the figures comprises the gas supply 9, the gas discharge 10, and the previously described bypass 11 and thus extends from the prechamber 50 to the fan blade arrangement 31.

[0148] As in Fig. 15, the electric drive motor 32 of the gas feed pump 28 is arranged outside the intake channel 7 in order to prevent sparks that may occur at the drive motor 32 from leading to a gas explosion within the oil mist detector 1.

[0149] In order to cause as little gas loss as possible from the intake duct 7, a first seal 33a is formed by means of an elastomer ring between the fan blade arrangement 31 and the drive motor 32 (cf. Fig. 3). This seal 33a thus seals the intake duct 7 from the drive motor 32. The seal 33a is designed as a shaft seal ring that is pushed over the shaft 64, which transmits the drive torque of the drive motor 32 to the fan blade arrangement 31 (see Fig. 3 and Fig. 17).

[0150] In the gas leakage direction behind the seal 33a, a gap 35 is formed (see also Fig. 16), that is, between the seal 33a and the drive motor 32. This intermediate space 35 is formed by a cartridge housing 36 of the gas delivery device 27 / the gas delivery pump 28. In addition, the intermediate space 35 is sealed from the drive motor 32 by means of a further seal 33b (see the Fig. 3 and Fig. 17), which prevents the gas that has passed through the first seal 33a, for example due to a defect in the seal 33a, from reaching the drive motor 32. The seal 33b is also designed as a shaft seal that is pushed over the shaft 64 (cf. Fig. 3 and Fig. 17).

[0151] The entire gas conveying device 27 / gas conveying pump 28 can be inserted with the cartridge housing 36 into a receptacle 37 provided for this purpose on the oil mist detector 1, as shown in Fig. 1. Furthermore, it is possible to replace the cartridge housing 36 and thus the drive motor 32 without disassembling the oil mist detector 1 and without removing the oil mist detector 1 from the crankcase housing 3, so that maintenance of the gas delivery device 27 can be carried out particularly easily and quickly.

[0152] Since it cannot be ruled out that during operation a leakage of gas from the intake duct 7 through the first seal 33a (or a seal 33c) into the intermediate space 35 occurs, this is vented to the outside by means of a vent 34, as shown in the Fig. 17 and Fig. 18 can be seen. The vent 34 is formed by means of a vent opening 38 of the cartridge housing 36, which is designed to correspond to a vent opening 60 of the receptacle 37 (cf. Fig. 16 and Fig. 18). The vent opening 60 in turn communicates with the Fig. 9, Fig. 11 and Fig. 15, which is covered but not closed by the clamping element 63, so that ventilation into the environment is realized, even when the gas extraction device 29 is attached. Thus, the intermediate space 35 is vented to the outside through the ventilation openings 38 and 60 when the gas delivery device 27 with the cartridge housing 36 is inserted into the receptacle 37.

[0153] The cartridge housing 36 thus also forms the ventilation of the intermediate space 35. Through the vent 34, gases which have passed through the first seal 33a (or the seal 33c) from the intake channel 7 are discharged outwards into the receptacle 37 and from there into the environment, as shown by the dashed line in Fig. 16. This prevents them from reaching the electric drive motor 32, thus ensuring explosion safety.

[0154] With these precautions, a very reliable method for detecting explosive oil-air mixtures in the interior of an internal combustion engine can be implemented using an oil mist detector 1. First, a gas sample is taken from the interior using the gas delivery device 27, with the gas sample being sucked in by a fan blade arrangement 31 arranged in the intake duct 7. The gas sample thereby reaches the measuring chamber 5 of the oil mist detector. Gas from the intake duct 7, which escapes in the direction of the drive motor 32 of the gas delivery device 27, in particular through the first seal 33a (or the seal 33c), is discharged to the outside by means of the previously described vent 34. This prevents an explosive mixture from forming in the immediate vicinity of the electric drive motor 32, in particular due to the second seal 33b (or a seal 33d).

[0155] In summary, in order to improve the handling and operational reliability of an optical oil mist detector 1 for the optical detection of fine oil mist 2, it is proposed that a gas sample to be optically examined be conveyed from the oil mist detector 1 into a measuring chamber 5 by means of an electric gas conveying pump 28 and that an electric drive motor 32 of the gas conveying pump 28 is decoupled from an intake channel 7 of the oil mist detector 1 by means of an outwardly vented intermediate space 35, through which intake channel the gas sample is conveyed by means of the gas conveying pump 28.

[0156] The oil mist detector 1 illustrated in the figures is not only designed for insertion into a housing 3 which defines an interior space 4, as in Fig. 4, but also to control a test gas supply 41 in order to introduce a test gas from the outside into the interior 4. As explained below, this functionality serves to enable a test measurement with the aid of which the correct functioning of the oil mist detector 1 can be reliably verified.

[0157] In the example shown in the figures, the oil mist detector 1, more precisely its gas sampling device 29, forms the test gas supply 41 itself, as can be seen from the Fig. 8 is clearly visible: The gas sampling device 29 provides a first channel 42, which serves as an inlet channel 51 for a test gas. By the oil mist detector 1 Fig. 5, Fig. 6 and Fig. 8, the oil mist detector 1 can thus trigger an inlet valve 56 for the test gas (with arrows in Fig. 8) through the inlet valve 56 and the inlet channel 51 into the interior 4. The inlet channel 51 ends precisely in the region of the inlet opening 8 of the gas sampling device 29. This causes the test gas to flow through the inlet opening 8 and a subsequent second channel 43, as part of the previously explained intake channel 7, and thus travels the same path to the measuring chamber 5 that a gas sample travels from the crankcase interior 4 to the measuring chamber 5 during normal measuring operation.

[0158] While the first channel 42 thus serves to supply a defined test gas flow 5 into the interior 4, the purpose of the second channel 43 is to discharge the test gas sample from the interior 4 into the external measuring chamber 5. The second channel 43 connects the intake opening 8 with the measuring chamber 5 and thus forms the previously explained intake channel 7. In Fig. 8 it can also be seen that the first channel 42 and the second channel 43 are separated by a partition wall 61, so that test gas can be flushed into the interior 4 through the test gas supply 41 at a predetermined volume rate, particularly in continuous operation.

[0159] As already explained, the oil mist detector 1 also has a gas conveying device 27 in the form of an electric gas conveying pump 28 for actively taking gas samples from the interior 4 as well as the said gas sampling device 29. With the Fig. The gas sampling device 29 illustrated in Figures 4 to 8, which is configured to take gas samples from the interior 4 and through the housing 3, allows the test gas flowing into the interior 4 through the test gas supply 41 to be removed again and transferred to the measuring chamber 5, where an optical test measurement can be performed on the test gas. The test gas is sucked in via the gas feed pump 28, in exactly the same way as a gas sample taken from the interior 4 using the gas sampling device 29 during normal operation.

[0160] How to see well in the longitudinal section of the Fig. 8, the test gas supply 41 designed by means of the inlet channel 51 and the inlet valve 56 is designed such that in a test measuring operation the test gas travels the same path from the interior 4 to the measuring chamber 5 through the gas sampling device 29 as a gas sample which is taken from the interior 4 by the oil mist detector 1 and optically measured in normal measuring operation.

[0161] The Fig. 19 shows a further possible embodiment of the gas sampling device 29, wherein in comparison to Fig. 8 in Fig. 19 the test gas flow 59 is guided from left to right into the interior 4. In contrast to the design according to Fig. 8 is in Fig. 19, it is provided that the first channel 42 of the gas sampling device 29 is connected to the intake opening 8 in such a way that the test gas stream 59, after passing through the intake opening 8, takes exactly the same path into the measuring chamber 5 that the gas stream 13 actually to be measured takes during normal operation of the oil mist detector 1. This ensures that the supply of the test gas and the test gas measurement carried out thereby check whether the path from the intake opening 8 to the measuring chamber 5 is completely clear.

[0162] The design of the Fig. 19 is thus characterized in that the test gas supply 41, more precisely its first channel 42, is formed by the intake opening 8. This ensures that the test gas flow 59, after passing through the intake opening 8, travels the same path into the measuring chamber 5 as a gas sample which, during normal operation, is taken from the monitored interior space 4 by means of the gas sampling device 29. If, for example, the intake opening 8 is blocked, this can be detected by a test gas measurement. In a configuration as in Fig. 8, however, there is a risk that the test gas flow 59 from the first channel 42 can still reach the measuring chamber 5 even if the intake opening 8 is blocked. In other words, a design as in Fig. 19 illustrates a higher level of safety regarding the verification of the functionality of the oil mist detector 1 achievable, compared to the design according to Fig. 8, in which a blockage within the second channel 43 (for example due to a liquid oil accumulation) can be detected but not necessarily a blockage of the intake opening 8.

[0163] As already explained, the measuring chamber 5 is connected to the intake channel 7, which - like the Fig. 5, Fig. 6 and Fig. 8 illustrate - opens into the intake opening 8, which in the installation situation is located inside the interior 4, while the measuring chamber 5 is arranged outside the interior 4. The test gas supply 41 now opens just in the area of ​​the intake opening 8, as can be seen in Fig.8 is clearly visible. At the outlet point, the test gas flow thus combines with the previously explained gas flow 13 (or replaces it in test measurement mode), which originates from the area around the intake opening 8. This design has the advantage that test gas fed into the interior 4 via the test gas supply 41, i.e. in particular the inlet channel 51, can be extracted from the interior 4 again through the intake opening 8 using the oil mist detector 1. This makes it possible to specifically check whether the gas sampling device 29 can actually pass a gas sample from the interior 4 to the measuring chamber 5. Unlike with only an external supply of test gas into the measuring chamber 5, in the said test mode not only the correct functioning of the measuring chamber can be checked, but also the correct functioning of the transport of gas samples from the interior through the gas sampling device 29 into the measuring chamber 5 can be checked. This thus increases the reliability of the check.

[0164] Because the test gas supply 41 is integrated into the gas sampling device 29, only one feedthrough 40 needs to be provided in the housing 3. The gas sampling device 29 is designed to fit through the opening 40 with a ¾ inch thread. Thus, the measuring arrangement can be easily retrofitted to an existing machine, since such access openings are common.

[0165] The oil mist detector 1 can also automatically perform a self-test of its functionality based on an optical measurement taken from a sample of the test gas in the measuring chamber 5. The oil mist detector 1 also outputs the result of the self-test in the form of a user message and stores it in an internal memory.

[0166] The design of the oil mist detector 1 shown in the figures thus allows a method for safety testing of the oil mist detector 1 to be implemented, in which the oil mist detector 1 introduces the test gas into the interior 4 monitored by the oil mist detector 1 by controlling the inlet valve 56 of the test gas supply 41. The oil mist detector 1 then withdraws test gas from the interior 4 using its gas delivery device 27 and subsequently optically measures it in the measuring chamber 5 as part of the previously discussed test measurement. In doing so, the oil mist detector 1 verifies its own correct functioning based on a measurement result of this test measurement. For example, the oil mist detector 1 can check whether a minimum quantity / minimum concentration of test gas can be detected in the measuring chamber for a volume rate of the test gas flow 59 that it has set.If this is the case, it can be concluded that the gas sampling device 29 allows a minimum volume flow of test gas to pass through, which is necessary for safe operation.

[0167] In this method, the gas conveying device 27 thus conveys test gas through the gas sampling device 29 into the measuring chamber 5 along the same path along which gas samples from the atmosphere of the interior space 4 reach the measuring chamber 5 during normal operation.

[0168] To improve the reliability of the optical detection of fine oil mist 2 with the aid of an oil mist detector 1, it is proposed that a test gas be flushed into an interior space 4 by means of a test gas supply 41 provided or at least controlled by the oil mist detector 1, and that a gas sample of the test gas be subsequently taken from the interior space 4 through a gas sampling device 29 of the oil mist detector 1 in order to optically measure it with the aid of the oil mist detector 1. In this case, the test gas preferably follows a flow path to an optical measuring chamber 5 of the oil mist detector 1, which a gas sample takes from the interior space 4 during normal operation of the oil mist detector 1, starting from an intake opening 8. List of reference symbols 1 oil mist detector 2 oil mist 3 Housing (especially crankcase) 4 monitored space, especially interior (e.g. crankcase) 5 Measuring chamber 6 optical measuring section 7 Intake duct 8 intake opening 9 Gas supply 10 Gas discharge 11 Bypass 12 branching point 13 Gas flow (through 7) 14 first partial gas flow (of 13, is passed past 5) 15 second partial gas stream (of 13, enters 5) 16a Flow direction (of 13) 16b Flow direction (of 13) 16c Flow direction (of 13) 16d Flow direction (of 13) 16e flow direction (of 13) 17 acceleration sections (of 7) 18 Acceleration direction (of 17) 19 increase 20 impact surface 21 Deflection surface 22 drogues 23 Reversal of direction 24 Association Office 25 Venturi nozzle 26 Cross-sectional narrowing 27 Gas conveying device 28 Gas pump 29 Gas sampling device 30 intake pipe 31 Fan blade arrangement 32 drive motors (of 27) 33a (first) seal 33b (second) seal 33c Seal 33d seal 34 Ventilation 35 Intermediate space (ventilated from the outside) 36 cartridge cases (out of 32) 37 recording (for 36) 38 vent opening (of 36) 39 housings 40 implementation (in 3 for 29) 41 Test gas supply 42 first channel (of 29) 43 second channel (of 29)5 44 optical measuring arrangement 45 Light source 46 Light detector 47 first pair of functions (from 45 and 46) 48 second pair of functions (from 45 and 46) 49 recording (for 47 / 48 / 52 / 71) 50 Antechamber 51 Inlet channel (for test gas) 52 additional light detector (for scattered light measurement) 53 Line of Sight (of 52 / 71) 54a (first) outlet opening 54b (second) outlet opening 55 Exit channel 56 Inlet valve (for test gas) 57 Outlet opening 58 interface (for 29) 59 Test gas flow 60 vent openings (of 37) 61 Partition wall 62 vent opening 63 clamping element 64 Wave 65 Return current 66 Return opening 67 Return channel 68 wall of 37 69 intake opening of 70 70 measuring part 71 additional light detector (for scattered light measurement) 72 optical measuring sections 73 optical measuring section 74 optical measuring sections 75 optical measuring section 76 optical measuring sections

Claims

[1] Oil mist detector (1) for detecting and / or analyzing potentially explosive oil-air mixtures, in particular designed for insertion into a crankcase (3) of an internal combustion engine, - with a measuring chamber (5) which forms at least one optical measuring section (6, 72, 73, 74, 75, 76) for the optical detection of an oil mist, - wherein the measuring chamber (5) is connected by means of a gas supply (9) to an intake channel (7) which opens into an intake opening (8), - wherein a gas discharge (10) is provided for discharging gas from the measuring chamber (5), - wherein a bypass (11) is provided for discharging gas from the intake duct (7) bypassing the measuring chamber (5), wherein the intake duct (7) branches at a branching point (12) into the gas supply (9) and the bypass (11), so that a first partial gas flow (14) is guided through the bypass (11) bypassing the measuring chamber (5), while a second, in particular remaining, partial gas flow (15) is guided through the gas supply (9) into the measuring chamber (5), characterized by , - that the intake channel (7) extends from an upstream pre-chamber (50) to the gas supply (9) and the bypass (11), - that an acceleration section (17) is formed in the intake duct (7) before the branching point (12) for accelerating a gas flow (13) along an acceleration direction (18) after the gas flow (13) has passed through the prechamber (50), and - that the pre-chamber (50) offers an enlarged flow cross-section compared to the adjoining acceleration section (17) of the intake duct (7), so that turbulence in the gas flow (13) within the pre-chamber (50) can be reduced and a first separation of larger oil particles can take place in the pre-chamber (50). [2] Oil mist detector (1) according to claim 1, wherein the bypass (11) is branched off from the intake duct (7) at the branching point (12) in such a way that the first partial gas flow (14) of the gas flow (13) flowing through the intake opening (8) and the intake duct (7) can be guided through the bypass (11) and past the measuring chamber (5) into the gas discharge (10), - in particular wherein the second, in particular remaining, partial gas flow (15) of the gas flow (13) can be guided through the gas supply (9) into the measuring chamber (5), - preferably wherein the gas supply (9) branches off upwards at the branching point (12) from the intake duct (7), relative to an installation situation. [3] Oil mist detector (1) according to claim 1 or 2, wherein in an installation situation the gas supply (9) leads the second partial gas flow (15) against gravity and / or against a flow direction (16c) of the first partial gas flow (14) from the intake channel (7), - in particular such that the first partial gas stream (14) predominantly comprises larger oil droplets of at least 10 µm diameter, while the second partial gas stream (15) is poor in such larger oil droplets. [4] Oil mist detector (1) according to one of claims 1 to 3, wherein in an installation situation the acceleration section (17) forms a rise (19) in the direction of the gas flow (13). [5] Oil mist detector (1) according to one of claims 1 to 4, wherein the oil mist detector (1) is designed such that the measuring chamber (5) is located at the highest point in an installation situation, while the gas supply (9) and the gas discharge (10) open into the measuring chamber (5) from below, - preferably so that liquid oil residues deposited in the gas supply (9) and / or the gas discharge (10) can flow back into the intake channel (7) and / or an outlet channel (55) independently due to gravity, - in particular, wherein oil residues can flow away due to gravity in the opposite direction to the acceleration direction (18) and / or in the opposite direction to the rise (19). [6] Oil mist detector (1) according to claim 4 or 5, wherein the gas supply (9) leads the second partial gas flow (15) away from the gas flow (13) against the direction of acceleration (18) and / or against the direction of rise (19) and / or - wherein the gas supply (9) branches off from the acceleration section (17) at an acute angle relative to the acceleration direction (18) and / or - wherein a flow cross-section increases in the direction of the gas supply (9) in the region of the branching point (12). [7] Oil mist detector (1) according to one of claims 4 to 6, wherein in the gas flow direction (16a) upstream of the acceleration section (17) a baffle surface (20) is formed such that the gas flow (13) undergoes a reversal of direction (23) at the baffle surface (20) when passing through the acceleration section (17), - preferably wherein at one end of the acceleration section (17) a deflection surface (21) is formed which forms an acute angle of less than 90° with the acceleration direction (18), - in particular wherein the deflection surface (21) forms a collecting funnel (22) for the first partial gas flow (14). [8] Oil mist detector (1) according to one of claims 1 to 7, wherein the bypass (11) opens into the gas discharge (10) at a junction point (24), - in particular so that the first partial gas stream (14) and the second partial gas stream (15) are combined at the junction point (24), - preferably wherein an angle between a mean flow direction of the first partial gas flow (14) and a mean flow direction of the second partial gas flow (15) at the junction point (24) is less than 60°. [9] Oil mist detector (1) according to claim 8, wherein a Venturi nozzle (25) is formed in the region of the junction point (24), in particular by means of a cross-sectional constriction (26) in the region of the bypass (11), - preferably so that the second partial gas flow (15) can be conveyed through the measuring chamber (5) by means of a pressure difference generated by the Venturi nozzle (25). [10] Oil mist detector (1) according to one of claims 1 to 9, wherein the gas supply (9) has a higher flow resistance compared to the bypass (11), - in particular so that an average flow velocity through the bypass (11) exceeds an average flow velocity through the measuring chamber (5). [11] Oil mist detector (1) according to one of claims 1 to 10, wherein the oil mist detector (1) comprises a gas conveying device (27) so that gas samples can be actively taken from the oil mist detector (1) through the suction opening (8). [12] Oil mist detector (1) according to one of claims 1 to 11, wherein the oil mist detector (1) has a gas conveying pump (28), preferably in the form of a radial fan, for conveying the gas stream (13), - preferably wherein the gas conveying pump (28) is designed as a suction pump and / or is placed downstream of the gas junction point (24). [13] Piston engine with a crankcase housing (3) delimiting a crankcase (4) and an oil mist detector (1) according to one of claims 1 to 12, wherein the oil mist detector (1) is arranged to take gas samples from the crankcase (4). [14] Method for detecting and / or analyzing oil-air mixtures in a monitored space (4) using an oil mist detector (1) designed according to one of claims 1 to 12, characterized by , - that a gas sample is taken from the monitored space (4) through a suction opening (8) of the oil mist detector (1) with the aid of a gas conveying device (27) of the oil mist detector (1) and is optically measured outside the monitored space (4) in the measuring chamber (5), - wherein the gas sample is divided into at least two partial gas streams (14, 15) in the oil mist detector (1) and - wherein a first partial gas flow (14) is guided through a bypass (11) bypassing the measuring chamber (5), while a second, in particular remaining, partial gas flow (15) is guided through a gas supply (9) into the measuring chamber (5). [15] Method according to claim 14, wherein with the aid of the gas supply (9), which branches off from an intake channel (7) opening into the intake opening (8), smaller oil droplets with diameters of less than 10 µm, which are contained in the gas sample, are separated from the first partial gas stream (14), - in particular such that a relative proportion of these smaller oil droplets in the second partial gas stream (15) is increased compared to a relative proportion of these smaller oil droplets in the gas sample or in the gas stream (13).

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