Abstract:
Gas sensors are provided that are fashioned such that there is an increased flow over the sensor element. In this way, a good measurement dynamic is achieved even when these gas sensors are exposed to exhaust gases having a low flow speed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is based on a gas sensor for determining at least one state variable of a measurement gas, in particular the particle concentration in the exhaust gas of a burner or of an internal combustion engine, as known for example from German Published Patent Application No. 102008041038 A1. 
       BACKGROUND INFORMATION 
       [0002]    The exhaust gas sensors shown there have, on their end exposed to the exhaust gas, an outer and an inner protective tube that surround a ceramic sensor element. The protective tubes are shaped so that a guide flow occurs in which the sensor element is protected on the one hand from the impact of liquid components of the exhaust gas, such as water drops, and on the other hand there takes place a flow over a measurement area of the sensor element, essentially in the longitudinal direction of the sensor. 
         [0003]    Due to the long path of the exhaust gas inside the protective tubes, and due to the rather low interaction of the exhaust gas with the measurement area of the sensor element when flowing over it in the longitudinal direction, such exhaust gas sensors are provided in particular for installation in exhaust gas trains of internal combustion engines and burners in which there is a relatively high flow speed, and/or in applications in which the demands on the dynamics of the measurement devices are rather low. 
         [0004]    On the other hand, however, there is a need for exhaust gas sensors that can also perform measurements with good dynamic behavior even in the exhaust gas trains of internal combustion engines and burners in which there is only a low flow speed. For example, such sensors, fashioned as soot sensors and installed in an exhaust gas box of a commercial vehicle, are intended to collect a minimum quantity of soot within a specified time period, so that a precise measurement of the quantity of soot emitted by the internal combustion engine of the commercial vehicle is possible. 
       SUMMARY 
       [0005]    The gas sensors according to the present invention are therefore designed such that there is an increased flow past the sensor element. Even when these gas sensors are exposed to exhaust gases having low flow speed, in this way a good measurement dynamic is achieved. 
         [0006]    The embodiment of the gas sensors according to the present invention can in principle take place according to one or more of three embodiments. 
         [0007]    According to a first embodiment, according to the present invention one or more, for example two, gas inlets are provided that are situated on the jacket surface of the outer protective tube and are fashioned in particular as swirl valves. According to this embodiment, it can be provided in particular that the outer protective tube is closed at its end face, i.e. does not have any gas inlets. 
         [0008]    According to a second embodiment, according to the present invention it is provided that the inner protective tube has one or more gas inlets in its jacket surface. 
         [0009]    It can in particular be provided that the inner protective tube has only one gas inlet, and this gas inlet is made up of a single opening. The flow of the gas into the internal chamber of the inner protective tube, i.e. its flow to the sensor element, is then possible only via this one gas inlet. This can be realized in such a way that there is a directional flow onto the sensor element inside the inner protective tube. In this case, it is preferable that the gas sensor be fashioned as a soot sensor, and that the one gas inlet be oriented toward an interdigital electrode of the sensor element. 
         [0010]    Exhaust gas sensors according to the second embodiment can have in particular an inner protective tube whose gas inlet or gas inlets are situated only downstream relative to the situation in the exhaust gas train of an internal combustion engine or of a burner. Alternatively or in addition, it can be provided that exhaust gas sensors according to the second embodiment have outer protective tubes that have one or more, for example two, gas inlets, and this gas inlet or inlets is/are fashioned in particular as swirl valves, these gas inlets being situated only upstream in particular relative to the situation in the exhaust gas train of an internal combustion engine or of a burner. 
         [0011]    For the directional installation of the sensor in an exhaust gas train, corresponding means can always be provided, which can include for example markings, locking means, cap nuts, bayonet couplings, and/or similar devices. 
         [0012]    According to a third embodiment, exhaust gas sensors are provided that have only a one-part protective tube, i.e. an inner protective tube, but no outer protective tube. It can in particular be provided that the inner protective tube has only one gas inlet, and this inlet is made up of a single opening. The flow of the gas into the interior of the inner protective tube, i.e. its flow to the sensor element, is then possible only via this one gas inlet. This can be realized in such a way that there is a directional flow onto the sensor element inside the inner protective tube. In this case, it is preferable that the gas sensor be realized as a soot sensor, and that the one gas inlet be oriented toward an interdigital electrode of the sensor element. 
         [0013]    Exhaust gas sensors according to the third embodiment can in particular have an inner protective tube whose gas inlet or gas inlets are situated only upstream relative to the situation in the exhaust train of an internal combustion engine or of a burner. In addition or alternatively, the sensor element and/or the gas outlet hole can be eccentrically offset relative to a mid-axis of the inner protective tube, in particular relative to the situation in the exhaust tract of an internal combustion engine or of a burner in the downstream direction. 
         [0014]    For the directional installation of the sensor in an exhaust gas train, corresponding means can always be provided, which can for example include markings, locking means, cap nuts, bayonet couplings, and/or similar devices. 
         [0015]    Sensors according to the present invention having the first, the second, and/or the third embodiment can for example be installed in those devices within an exhaust gas train of a burner or of an internal combustion engine in which the flow cross-section is increased and/or the flow speed is reduced. Sensors according to the present invention having the first, the second, and the third embodiment can for example be installed in bypass lines of an exhaust gas train. For example, sensors according to the present invention can be installed in an exhaust gas box, in particular of a commercial vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows an exhaust gas sensor according to the first embodiment of the present invention. 
           [0017]      FIG. 2  shows an exhaust gas sensor according to the second embodiment of the present invention. 
           [0018]      FIG. 3  shows an exhaust gas sensor according to the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows a segment, oriented toward the exhaust gas, of a gas sensor according to the first embodiment of the present invention. This is a sensor for determining the particles, in particular the concentration of soot, in the exhaust gas of an internal combustion engine, also referred to as a particle sensor or soot sensor. It is indicated here as an example of a general gas sensor for determining at least one state variable of a measurement gas. Other gas sensors of this type include gas sensors for determining the oxygen concentration in the exhaust gas of an internal combustion engine, so-called lambda probes, or gas sensors for determining the nitrogen oxide concentration in the exhaust gas of an internal combustion engine. Temperature measurement probes for measuring the exhaust gas temperature can also be such a gas sensor. 
         [0020]    The gas sensor shown in  FIG. 1  has a metallic housing  11  that is provided for installation in a flow duct (not shown here) for the measurement gas, in particular in the exhaust gas tube of a burner or of an internal combustion engine, having a threaded segment  12  and a hexagonal key head  13 . In housing  11 , a sensor element  14  is installed in such a way that an end segment  141  protrudes from housing  11 . The installation in housing  11  takes place using a sealing element  15  that in the exemplary embodiment is formed by a sealing packing made up of an elastic seal  16  pressed axially between two ceramic shaped parts, the seal pressing radially on sensor element  14  and on the inner wall of housing  11 . In  FIG. 1 , only ceramic shaped part  17  situated on the end of housing  11  at the measurement gas side is shown; this shaped part has a central rectangular opening  171  for admitting sensor element  14  and is supported axially on a radial shoulder  111  formed in housing  11 . On the gas-sensitive end segment  141  of sensor element  14 , which for example has a rod-shaped ceramic body, on a large surface of the ceramic body there is situated a so-called interdigital electrode  18  for measuring a soot deposit brought about on end segment  141 . Interdigital electrode  18  has two electrode segments that are fashioned in the manner of combs and whose comb teeth mesh together. The manner of functioning and the design of such an interdigital electrode for determining the quantity of soot deposited thereon as a measure for the concentration of soot in the exhaust gas is described in German Published Patent Application No. 10 2004 028 997 A1. 
         [0021]    Gas-sensitive end segment  141  of sensor element  14  is covered by a protective tube module  20  that is provided with means for allowing the gas to pass through so that the measurement or exhaust gas flowing in the measurement gas flow channel, or in the exhaust gas pipe of the internal combustion engine, can reach gas-sensitive end segment  141 . The direction of flow of the measurement or exhaust gas is indicated in  FIG. 1  by flow arrows  19 . Protective tube module  20  is made up of an inner protective tube  21  that is cap-shaped and that surrounds end segment  141  of sensor element  14  with a radial and axial spacing, and an outer protective tube  22  that is cap-shaped or pot-shaped and that surrounds the inner protective tube with a radial spacing. Cap-shaped inner protective tube  21  has a cap floor  211 , a cap opening  212 , and a cap brim  213  that surrounds cap opening  212 . Cap floor  211  and cap brim  213  are connected via cap sheath  214 , which is shaped as a cylindrical sheath. Outer edge  213   a  of cap brim  213  is bent off at a right angle, and grasps a fastening support  112  that is integrally formed in one piece on the end face of housing  11 , the fastening support having an outer diameter that is reduced relative to the outer diameter of housing  11 . Pot-shaped outer protective tube  22  has a pot floor  221  having a central circular opening  23  and a pot sheath  222  that is pushed over bent-off edge  213   a  of cap brim  213  of inner protective tube  21 , so that an annular space  33  is present between inner protective tube  21  and outer protective tube  22  whose radial width matches the width of cap brim  213 . The axial length of outer protective tube  22  is significantly smaller than the axial length of inner protective tube  21 , so that the latter passes through circular opening  23  in the pot floor and extends significantly past pot floor  221 . Protective tube module  20  is fastened with a material fit on fastening support  112  of housing  11 , for example by a circumferential weld seam. 
         [0022]    The means provided in protective tube module  20  for allowing the gas to pass through include a gas outlet  24  in inner protective tube  21  that is formed for example by a central hole  25  in cap floor  211  of inner protective tube  21 , a gas inlet  26  in outer protective tube  22 , and a gas inlet  27  in inner protective tube  21 . Gas inlet  26  in outer protective tube  22  is realized by one or more openings formed in pot sheath  222 , in particular as one or more holes and/or as one or more swirl valves. Gas inlet  27  in inner protective tube  21  is situated in cap brim  213 , and in the direction of flow of the measurement gas flowing into protective tube module  20  behind cap brim  213 , i.e. toward housing  11 , there is provided an open space  29  extending underneath cap opening  212 . Gas inlet  27  is realized with openings  30  in cap brim  213  that are situated at a distance from one another in the circumferential direction of cap brim  213 . Preferably, openings  30  are fashioned as circular holes. In open space  29  there are situated flow means that divert the flow of measurement gas passing through openings  30  toward cap opening  212 . 
         [0023]    The openings or swirl valves formed in the pot sheath have the effect that even in the case of slow-flowing exhaust gas, exhaust gas can move with a high dynamic behavior into the interior of the sensor and to sensor element  14 , even if a protection of sensor element  14  against the impact of liquid components of the exhaust gas, such as water droplets, is also present. 
         [0024]      FIG. 2  shows a segment, oriented toward the exhaust gas, of a gas sensor according to the second embodiment of the present invention. This is a sensor for determining the particles, in particular the concentration of soot, in the exhaust gas of an internal combustion engine, also called a particle sensor or soot sensor. It is indicated here as an example of a general gas sensor for determining at least one state variable of a measurement gas. Other gas sensors of this type include gas sensors for determining the oxygen concentration in the exhaust gas of an internal combustion engine, so-called lambda probes, or gas sensors for determining the nitrogen oxide concentration in the exhaust gas of an internal combustion engine. Temperature measurement probes for measuring the exhaust gas temperature can also be such a gas sensor. 
         [0025]    The gas sensor shown in  FIG. 2  has a metallic housing  11  that is provided for installation in a flow duct (not shown here) for the measurement gas, in particular in the exhaust gas tube of a burner or of an internal combustion engine, having a threaded segment  12  and a hexagonal key head  13 . In housing  11 , a sensor element  14  is installed in such a way that an end segment  141  protrudes from housing  11 . The installation in housing  11  takes place using a sealing element  15  that in the exemplary embodiment is formed by a sealing packing made up of an elastic seal  16  pressed axially between two ceramic shaped parts, the seal pressing radially on sensor element  14  and on the inner wall of housing  11 . In  FIG. 2 , only ceramic shaped part  17  situated on the end of housing  11  at the measurement gas side is shown; this shaped part has a central rectangular opening  171  for admitting sensor element  14  and is supported axially on a radial shoulder  111  formed in housing  11 . On the gas-sensitive end segment  141  of sensor element  14 , which for example has a rod-shaped ceramic body, on a large surface of the ceramic body there is situated a so-called interdigital electrode  18  for measuring a soot deposit brought about on end segment  141 . Interdigital electrode  18  has two electrode segments that are fashioned in the manner of combs and whose comb teeth mesh together. The manner of functioning and the design of such an interdigital electrode for determining the quantity of soot deposited thereon as a measure for the concentration of soot in the exhaust gas is described in German Published Patent Application No. 10 2004 028 997 A1. 
         [0026]    Gas-sensitive end segment  141  of sensor element  14  is covered by a protective tube module  20  that is provided with means for the passage through of the gas so that the measurement or exhaust gas flowing in the measurement gas flow channel, or in the exhaust gas pipe of the internal combustion engine, can reach gas-sensitive end segment  141 . The direction of flow of the measurement or exhaust gas is indicated in  FIG. 1  by flow arrows  19 . Protective tube module  20  is made up of an inner protective tube  21  that is cap-shaped and that surrounds end segment  141  of sensor element  14  with a radial and axial spacing, and an outer protective tube  22  that is cap-shaped or pot-shaped and that surrounds the inner protective tube with a radial spacing. Cap-shaped inner protective tube  21  has a cap floor  211 , a cap opening  212 , and a cap brim  213  that surrounds cap opening  212 . Cap floor  211  and cap brim  213  are connected via cap sheath  214 , which is shaped as a cylindrical sheath. Outer edge  213   a  of cap brim  213  is bent off at a right angle, and grasps a fastening support  112  that is integrally formed in one piece on the end face of housing  11 , the fastening support having an outer diameter that is reduced relative to the outer diameter of housing  11 . Pot-shaped outer protective tube  22  has a pot floor  221  having a central circular opening  23  and a pot sheath  222  that is pushed over bent-off edge  213   a  of cap brim  213  of inner protective tube  21 , so that an annular space  33  is present between inner protective tube  21  and outer protective tube  22  whose radial width matches the width of cap brim  213 . The axial length of outer protective tube  22  is significantly smaller than the axial length of inner protective tube  21 , so that the latter passes through circular opening  23  in the pot floor and extends significantly past pot floor  221 . Protective tube module  20  is fastened with a material fit on fastening support  112  of housing  11 , for example by a circumferential weld seam. 
         [0027]    The means provided in protective tube module  24  for admitting the gas include a gas outlet  24  in inner protective tube  21 , formed for example by a central hole  25  in cap floor  211  of inner protective tube  21 , a gas inlet  26  in outer protective tube  22 , and a gas inlet  27  in inner protective tube  21 . Gas inlet  26  in outer protective tube  22  is realized by one, two, or more than two openings formed in pot sheath  222 , in particular as one, two, or more than two holes and/or as one, two, or more than two swirl valves  55 . In particular, two swirl valves  55  can be provided that conduct a flow in directions that are tangentially opposite one another. Gas inlet  27  in inner protective tube  21  is placed in cap sheath  214 , in particular in the half of the cap sheath facing away from the exhaust gas-side end of the gas sensor; this is at the bottom in  FIG. 2 . Gas inlet  27  in inner protective tube  21  is realized as a single opening  51  of cap sheath  214 . Outer protective tube  22  can have, in the region of this single opening  51  of cap sheath  214 , a bulge inward  50  so that the volume, or the width, of annular space  33  between protective tubes  21 ,  22  is reduced at this point. 
         [0028]    Advantageously, at the edge of gas inlet  27 , in cap sheath  214  there is provided an inwardly inclined flow-guiding element  52  that additionally diverts the flow of gas into the interior of inner protective tube  21 . 
         [0029]    It is in particular provided that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , and gas inlet  26  in outer protective tube  22  are fashioned on radially opposite sides of protective tube module  20 , no gas inlet  26  being provided in outer protective tube  22  at the side of gas inlet  27 , in the present case the single opening  51  of cap sheath  214 . 
         [0030]    It is in particular provided that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , and interdigital electrode  18  situated on the surface of sensor element  14  are situated such that they are oriented in the same radial direction. 
         [0031]    Preferably, the sensor includes means for its directional installation, such as markings, locking means, cap nuts, bayonet couplings, and/or similar devices, so that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , can be installed at a downstream-situated side in an exhaust gas train. 
         [0032]      FIG. 3  shows a segment, oriented toward the exhaust gas, of a gas sensor according to the third embodiment of the present invention. This is a sensor for determining the particles, in particular the soot concentration, in the exhaust gas of an internal combustion engine, also called a particle sensor or soot sensor. It is indicated as an example of a general sensor for determining at least one state variable of a measurement gas. Other gas sensors of this type include gas sensors for determining the oxygen concentration in the exhaust gas of an internal combustion engine, so-called lambda probes, or gas sensors for determining the nitrogen oxide concentration in the exhaust gas of an internal combustion engine. Temperature measurement probes for measuring the exhaust gas temperature can also be such a gas sensor. 
         [0033]    The gas sensor shown in  FIG. 3  has a metallic housing  11  that is provided for installation in a flow duct (not shown here) for the measurement gas, in particular in the exhaust gas tube of a burner or of an internal combustion engine, having a threaded segment  13  and a hexagonal key head  13 . In housing  11 , a sensor element  14  is installed in such a way that an end segment  141  protrudes from housing  11 . The installation in housing  11  takes place using a sealing element  15  that in the exemplary embodiment is formed by a sealing packing made up of an elastic seal  16  pressed axially between two ceramic shaped parts, the seal pressing radially on sensor element  14  and on the inner wall of housing  11 . In  FIG. 3 , only ceramic shaped part  17  situated on the end of housing  11  at the measurement gas side is shown; this shaped part has a central rectangular opening  171  for admitting sensor element  14  and is supported axially on a radial shoulder  111  formed in housing  11 . On gas-sensitive end segment  141  of sensor element  14 , which for example has a rod-shaped ceramic body, on a large surface of the ceramic body there is situated a so-called interdigital electrode  18  for measuring a soot deposit brought about on end segment  141 . 
         [0034]    Interdigital electrode  18  has two electrode segments that are fashioned in the manner of combs and whose comb teeth mesh together. The manner of functioning and the design of such an interdigital electrode for determining the quantity of soot deposited thereon as a measure for the concentration of soot in the exhaust gas is described in German Published Patent Application No. 10 2004 028 997 A1. 
         [0035]    Gas-sensitive end segment  141  of sensor element  14  is covered by a protective tube module  20  that is provided with means for the passage through of the gas so that the measurement or exhaust gas flowing in the measurement gas flow channel, or in the exhaust gas pipe of the internal combustion engine, can reach gas-sensitive end segment  141 . The direction of flow of the measurement or exhaust gas is indicated in  FIG. 1  by flow arrows  19 . Protective tube module  20  is made up of an inner protective tube  21  that is cap-shaped and that surrounds end segment  141  of sensor element  14  with a radial and axial spacing. A further, outer, protective tube that surrounds the inner protective tube is not provided. Cap-shaped inner protective tube  21  has a cap floor  211 , a cap opening  212 , and a cap brim  213  that surrounds cap opening  212 . Cap floor  211  and cap brim  213  are connected via cap sheath  214 , which is shaped as a cylindrical sheath. Outer edge  213   a  of cap brim  213  is bent off at a right angle, and grasps a fastening support  112  that is integrally formed in one piece on the end face of housing  11 , the fastening support having an outer diameter that is reduced relative to the outer diameter of housing  11 . 
         [0036]    The means provided in protective tube module  20  for admitting the gas include a gas outlet  24  in inner protective tube  21  that is formed for example by a hole  25  in cap floor  211  of inner protective tube  21 . Gas inlet  27  in inner protective tube  21  is placed in cap sheath  214  and is realized as a single opening  51  of cap sheath  214 . It is situated in the half of cap sheath  214  oriented toward cap brim  213 , preferably in the one-third or one-fourth of cap sheath  214  oriented toward cap brim  213 ; in  FIG. 3  this is at the bottom. 
         [0037]    It is provided in particular that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , is fashioned on a radial side of protective tube module  20 , while sensor element  14  is situated toward the opposite side, radially eccentrically, in housing  11  and/or in protective tube module  20 . 
         [0038]    It is in particular provided that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , is fashioned on a radial side of protective tube module  20 , while gas outlet opening  24  is fashioned, radially eccentrically, as hole  25  in cap floor  211 , oriented toward the opposite side. In particular, radially eccentrically situated sensor element  14  and radially eccentrically situated gas outlet opening  24  are situated one over the other, in a radial top view. 
         [0039]    It is in particular provided that gas inlet  27 , in the present case single opening  51  of cap sheath  214 , and interdigital electrode  18 , which is situated on the surface of sensor element  14 , are configured in such a way that they are oriented in the same radial direction. 
         [0040]    Preferably, the sensor includes means for its directional installation, such as markings, locking means, cap nuts, bayonet couplings, and/or similar devices, so that gas inlet  27 , in the present case the single opening  51  of cap sheath  214 , can be installed at the downstream side.