Patent Publication Number: US-2018038817-A1

Title: Sensor

Description:
TECHNICAL FIELD 
     The present invention relates to a sensor for detecting an amount of particular matter (hereinafter, referred to as PM) contained in exhaust gas. 
     BACKGROUND ART 
     Sensors for detecting an amount of PM contained in exhaust gas to be discharged from an internal combustion engine are known. As the sensors, a sensor is also known, in which sensor electrode portions are arranged in an exhaust pipe and PM is detected based on an electrostatic capacitance change amount occurred as the PM is adhered on the sensor electrode portions (e.g., see Patent Reference 1). 
     In the sensor, determination on failure of the sensor is performed using a change in peak shape of an electrostatic capacitance appearing if condensate water, which is created by condensation of moisture contained in exhaust gas, is adhered on the sensor electrode portions. 
     PRIOR ART REFERENCE 
     Patent Reference 
     Patent Document 1: JP-A-2010-275917 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved 
     In terms of protection of various sensors and the like, it is preferable to reliably detect the condensate water. Also, water is likely to be infiltrated into the exhaust system of the internal combustion engine from the outside, and for the same reason, it is preferable to reliably detect water infiltrated from the outside. However, the sensor as described above is configured to determine a failure of the sensor itself and thus does not take into account detection of water present in the exhaust system of the internal combustion engine, such as condensate water or water infiltrated from the outside. 
     An object of the present disclosure is to provide a sensor in which it is possible to detect water present in the exhaust system of the internal combustion engine. 
     Means for Solving the Problems 
     A sensor according to the present disclosure includes: a sensor unit arranged in an exhaust system of an internal combustion engine and including: a filter member having a plurality of cells divided by porous partition walls and collecting a particulate matter in exhaust gas, and at least one pair of electrode members arranged to face each other with the cell interposed therebetween so as to form a capacitor and a controller estimating an amount of the particulate matter in the exhaust gas and detecting water present in the exhaust system of the internal combustion engine, based on an electrostatic capacitance between the pair of electrode members. 
     Further, a sensor according to the present disclosure includes: a sensor unit arranged in an exhaust system of an internal combustion engine and including: a filter member having a plurality of cells divided by porous partition walls and collecting a particulate matter in exhaust gas, and at least one pair of electrode members arranged to face each other with the cell interposed therebetween so as to form a capacitor, and a control unit, wherein the control unit is operated to execute an estimating process of estimating an amount of the particulate matter in the exhaust gas based on an electrostatic capacitance between the pair of electrode members; and a detecting process of detecting water present in the exhaust system of the internal combustion engine based on the electrostatic capacitance between the pair of electrode members. 
     Advantageous Effects of Invention 
     According to the sensor of the present disclosure, it is possible to detect water present in the exhaust system of the internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration view showing an example of an exhaust system to which a PM sensor of a first embodiment is applied. 
         FIG. 2  is a schematic partially sectional view showing the PM sensor of the first embodiment. 
         FIG. 3A  is a partially enlarged sectional view explaining collecting of PM. 
         FIG. 3B  is a partially enlarged sectional view explaining a water-infiltrated state. 
         FIG. 4A  is a chart explaining a change over time in electrostatic capacitance change amount of a PM sensor as an amount of PM is increased. 
         FIG. 4B  is a chart explaining a change over time in electrostatic capacitance change amount of the PM sensor due to water infiltration. 
         FIG. 4C  is a chart explaining a change over time in electrostatic capacitance in a case where water infiltration is occurred while PM is being collected. 
         FIG. 5  is a schematic partially sectional view showing a PM sensor of a second embodiment. 
         FIG. 6A  is a schematic perspective view of each of sensor units according to a third embodiment. 
         FIG. 6B  is a schematic exploded perspective view of each of sensor units according to the third embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, sensors according to respective embodiments of the present invention will be described with reference to the accompanying drawings. The same components will be designated by the same reference numerals, and the names and functions thereof are the same. Therefore, the detailed descriptions thereof will not be repetitively made. 
     First Embodiment 
       FIG. 1  is a schematic configuration view showing an example of an exhaust system of a diesel engine (hereinafter, simply referred to as engine)  100 , to which a PM sensor  10 A according to the first embodiment are applied. In an exhaust pipe  110  of the engine  100 , an oxidation catalyst  210 , a diesel particulate filter (DPF, hereinafter, simply also referred to as filter)  220 , a NOx purification catalyst  230 , a NOx/lambda sensor  240  and the like are provided in this order from an upstream side in an exhaust direction. 
     The oxidation catalyst  210  is configured to oxidize unburned fuel (hydrocarbon (HC)) and to increase a temperature of the exhaust gas when the unburned fuel is supplied thereto. The filter  220  is formed so that a plurality of cells divided by porous partition walls are arranged along exhaust gas flow direction and are alternately plugged at upstream and downstream sides of the cells. The filter  220  is configured so that PM in the exhaust gas is collected by micro-holes or surfaces of the partition walls and if an estimated amount of PM accumulated thereon reaches a predetermined amount, a so-called filter forced regeneration of combusting and removing the accumulated PM thereon is executed. The filter forced regeneration is performed, for example, by supplying unburned fuel to the oxidation catalyst  210  upstream of the filter  220  and thus increasing a temperature of the exhaust gas to be introduced into the filter  220  to a PM combustion temperature. The NOx purification catalyst  230  is configured to reduce and purify NOx in the exhaust gas, and the NOx/lambda sensor  240  is configured to detect a NOx concentration and excess air ratio in the exhaust gas. The PM sensor  10 A of the present embodiment is provided in the exhaust pipe  110 , for example, downstream of the DPF  220  and also upstream of the NOx purification catalyst  230 , but may be provided in the exhaust pipe  110  downstream of the NOx purification catalyst  230 . 
     Next, the detailed configuration of the PM sensor  10 A according to the first embodiment will be described with reference to  FIG. 2 . The PM sensor  10 A includes a case member  11  inserted in the exhaust pipe  110 , a pedestal portion  20  configured to attach the case member  11  to the exhaust pipe  110 , a sensor unit  30  accommodated in the case member  11  and a control unit  40 . 
     The case member  11  has a shape of a bottomed cylinder, of which a bottom side (a lower end side in the shown example) is closed. A length L of the case member  11  in a cylinder axis direction is substantially the same as a radius R of the exhaust pipe  110  so that a cylindrical wall portion at the bottom side protrudes to a location near to a center axis CL of the exhaust pipe  110 . Meanwhile, in the following descriptions, the bottom side of the case member  11  is referred to as a distal end side, and an opposite side to the bottom side is referred to as a base end side of the case member  11 . 
     A cylindrical wall portion of the case member  11  at the distal end side is provided with a plurality of inflow ports  12  arranged to be spaced from each other in a circumferential direction. Also, a cylindrical wall portion of the case member  11  at the base end side is provided with a plurality of outflow ports  13  arranged to be spaced from each other in the circumferential direction. A total opening area S 12  of the inflow ports  12  is smaller than a total opening area S 13  of the outflow ports  13  (S 12 &lt;S 13 ). That is, an exhaust flow velocity V 12  in the vicinity of the inflow ports  12  becomes slower than an exhaust flow velocity V 13  in the vicinity of the outflow ports  13  (V 12 &lt;V 13 ), so that a pressure P 12  at the inflow ports  12  becomes higher than a pressure P 13  at the outflow ports  13  (P 12 &gt;P 13 ). Thus, the exhaust gas smoothly flows into the case member  11  through the inflow ports  12 , and the exhaust gas in the case member  11  smoothly flows out through the outflow ports  13  into the exhaust pipe  110 . 
     The pedestal portion  20  has a male screw portion  21  and a nut portion  22 . The male screw portion  21  is provided on a base end portion of the case member  11  and is configured to close an opening of the case member  11  at the base end side. The male screw portion  21  is screwed with a female screw portion of a boss portion  110 A formed on the exhaust pipe  110 . The nut portion  22  is, for example, a hexagonal nut and is fixed to an upper end portion of the male screw portion  21 . The male screw portion  21  and the nut portion  22  have through-holes (not shown) formed therein, through which conductive wires  35 ,  36  and the like as described below are to be inserted. 
     The sensor unit  30  has a filter member  31 , a plurality of pairs of electrode members  32 ,  33 , and an electrical heater  34 . 
     The filter member  31  is formed so that a plurality of cells, which form lattice-shaped exhaust flow paths divided by partition walls of, for example, porous ceramics, are alternately plugged at upstream and downstream sides thereof. The filter member  31  is held on an inner peripheral surface of the case member  11  via a cushion member CM in a state where a flow path direction of the cells is arranged to be substantially parallel to an axial direction (an upward and downward direction in the figure) of the case member  11 . 
     As enlargedly shown in  FIG. 3A , PM  310  in the exhaust gas introduced in the case member  11  through the inflow ports  12  is collected by surfaces or micro-holes of partition walls as the exhaust gas flows from cells C 1  plugged at the downstream side thereof into cells C 2  plugged at the upstream side thereof as shown by broken line arrows. Meanwhile, in the following description, the cell plugged at the downstream side thereof is referred to as a measurement cell C 1  and the cell plugged at the upstream side thereof is referred to as an electrode cell C 2 . 
     As shown in  FIG. 2 , the electrode members  32 ,  33  are, for example, conductive metal wires and are alternately inserted into the electrode cells C 2 , which face each other with the measurement cell C 1  interposed therebetween, from the downstream side (unplugged side) thereof, thereby forming a capacitor. The electrode members  32 ,  33  are respectively connected to an electrostatic capacitance detection circuit (not shown) embedded in the control unit  40 , via the conductive wires  35 ,  36 . 
     The electrical heater  34  is, for example, an electric heating wire and is configured to generate heat by being energized and thus to directly heat the sensor filter  31 , thereby executing a so-called filter regeneration of combusting and removing the PM accumulated in the measurement cells C 1 . Accordingly, the electrical heater  34  is formed to be bent into a continuous S-shape, and linear portions thereof parallel to each other are inserted in the respective measurement cells C 1  along the flow paths thereof. 
     The control unit  40  is an example of the controller of the present invention and has a filter regeneration control unit  41 , a PM amount estimating calculation unit  42 , a water infiltration determination unit  43  and a sensor protection control unit  44  as individual functional elements. The functional elements are described as being contained in the control unit  40 , which is a unitary hardware, but may be provided in separate hardware. 
     The filter regeneration control unit  41  is configured to determine whether or not a filter regeneration condition is satisfied, based on an electrostatic capacitance Cp between the electrode members  32 ,  33 , which is detected by an electrostatic capacitance detection circuit (not shown), and then to execute filter regeneration control of turning on (energizing) the electrical heater  34  in a case where the filter regeneration condition is satisfied. The electrostatic capacitance Cp between the electrode members  32 ,  33  is expressed by the following equation 1, where ∈ is a dielectric constant of a medium between the electrode members  32 ,  33 , S is a surface area of the electrode members  32 ,  33 , and d is a distance between the electrode members  32 ,  33 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   Cp 
                   = 
                   
                     Σ 
                      
                     
                       ( 
                       
                         ɛ 
                         × 
                         
                           S 
                           d 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In the equation 1, the surface area S of the electrode members  32 ,  33  is constant, and when the dielectric constant s and the distance d are changed by the PM collected in the measurement cells C 1 , the electrostatic capacitance Cp is correspondingly changed. That is, the electrostatic capacitance Cp between the electrode members  32 ,  33  and an amount of the PM accumulated in the sensor filter  31  have a proportional relation. 
     In the example shown in  FIG. 4A , the electrostatic capacitance between Cp the electrode member  32 ,  33  is increased at a change amount per unit time θ 1  (ΔCp/Δt) as the PM is accumulated in the measurement cells C 1 . If the electrostatic capacitance Cp reaches a predetermined electrostatic capacitance upper threshold C P   _   max , which indicates an upper limit amount of the accumulated PM, the filter regeneration control unit  41  determines that the filter regeneration condition is satisfied and thus starts filter regeneration of turning on the electrical heater  34 . The filter regeneration continues until the electrostatic capacitance Cp is lowered to a predetermined electrostatic capacitance lower threshold C P   _   min , which indicates that the PM is completely removed. 
     The PM amount estimating calculation unit  42  is configured to estimate a total PM amount m PM  in the exhaust gas discharged from the filter  220 , based on an electrostatic capacitance change amount ΔCp of the PM sensor  10 A during a regeneration interval period (from the end of the filter regeneration to the start of the next filter regeneration). The PM amount m PM  collected in the filter member  31  during the regeneration interval period is obtained by the following equation 2, in which the electrostatic capacitance change amount ΔCp of the PM sensor  10 A is multiplied by a linear coefficient β. 
       [Equation 2] 
         m   PM   =β·ΔCp   (2)
 
     The water infiltration determination unit  43  is configured to determine whether or not water is present in the exhaust system, based on a peak value of the electrostatic capacitance Cp or an electrostatic capacitance change amount per unit time θ (ΔCp/Δt) of the PM sensor  10 A. Then, when water is present in the exhaust system, the water infiltration determination unit  43  is configured to estimate an amount of the water. 
     If water is present in the exhaust system, as shown in  FIG. 3B , some of the water is held in the filter member  31 . Specifically, the water is held in the measurement cells C 1  and electrode cells C 2  equipped in the filter member  31 . Since the measurement cells C 1  and electrode cells C 2  are a lattice-shaped elongated space, the water  320  is smoothly introduced and held in each of the cells C 1 , C 2 . 
     If the water  320  is held in the filter member  31 , the peak value of the electrostatic capacitance Cp in the PM sensor  10 A is significantly higher than that of a case where PM is accumulated therein, and also the electrostatic capacitance change amount θ until reaching the peak value is steeper (greater in gradient) than that of the case where PM is accumulated therein. Further, as an amount of water  320  held in the filter member  31  is increased, the peak value of the electrostatic capacitance Cp becomes higher, and also as the amount of water  320  held in the filter member  31  is increased, the electrostatic capacitance change amount per unit time θ (ΔCp/Δt) becomes steeper. 
     As shown by a one-dot chain line in  FIG. 4B , if a certain amount of water  320  is held in the filter member  31 , the electrostatic capacitance Cp is increased at a change amount θ 2 , which is significantly steeper than a change amount θ 1  of the case when PM is accumulated therein, during a period until the electrostatic capacitance Cp reaches a peak value C pw   _   pk1  (times t 0  to t 1 ). As shown by a broken line in  FIG. 4B , if more water  320  is held in the filter member  31 , the electrostatic capacitance Cp is increased at a change amount θ 3 , which is even steeper than the change amount θ 2 , until reaching a peak value Cp w   _   pk2 . In both the cases, if the water  320  is evaporated from the filter member  31  due to flowing of exhaust gas therethrough, the electrostatic capacitance Cp is decreased to C p   _   min  (times t 3  to t 4 ). 
     Therefore, the water infiltration determination unit  43  determines that water  320  is present in the exhaust system, if at least one of determination conditions, including a case where the peak value Cp w   _   pk  of the electrostatic capacitance is equal to or higher than a predetermined upper threshold and a case where the change amount θ in the electrostatic capacitance Cp is equal to or greater than a predetermined upper threshold is satisfied. Also, the water infiltration determination unit  43  determines an amount of water present based on a value of the peak value Cp w   _   pk  of the electrostatic capacitance. Determining the amount of water can be performed, for example, by using a map for determination. The map can be created by changing an amount of water held in the filter member  31  and then measuring a corresponding peak value Cp w   _   pk  of the electrostatic capacitance. 
       FIG. 4C  shows an example of a case where water is infiltrated from the outside while PM is being collected. As shown in  FIG. 4C , the electrostatic capacitance Cp is increased at a change amount θ 1  corresponding to an amount of accumulated PM during a period from time t 0  to time t 1 . Thereafter, the electrostatic capacitance is steeply increased from Cp —bs  to Cp —pk  at the time t 1  and then returns to Cp —bs  at a time t 2 , and then based thereon, the water infiltration determination unit  43  determines that during a period from time t 1  to time t 2 , the predetermined determination condition is satisfied and thus water  320  is infiltrated into the exhaust system from the outside. 
     The sensor protection control unit  44  is configured to protect various sensors by prohibiting energization to the sensors, when the water infiltration determination unit  43  determines that water is present in the exhaust system. In the present embodiment, the sensor protection control unit  44  protects the NOx/lambda sensor  240  by prohibiting energization to a heater (not shown) equipped in the NOx/lambda sensor  240 . 
     As such, the water infiltration determination unit  43  can detect water (condensate water or infiltrated water) present in the exhaust system of the engine  100 , based on the change amount per unit time θ (ΔCp/ΔT) in electrostatic capacitance Cp between the electrode members  32 ,  33  or the peak value Cp —pk , thereof. In this way, since water is detected based on the electrostatic capacitance Cp between the electrode members  32 ,  33 , water present in the exhaust system can be detected. In addition, detection of water is performed by the PM sensor  10 A, which is intended to detect an amount of PM. That is, the PM sensor  10 A is used both for detecting an amount of PM and for detecting water present in the exhaust system. Accordingly, it is unnecessary to separately provide a dedicated sensor, thereby achieving a simplified configuration. 
     Further, the sensor protection control unit  44  prohibits energization to various sensors during a period in which the water infiltration determination unit  43  is determining that water is present in the exhaust system. Therefore, the various sensors can be protected. 
     Second Embodiment 
     Next, a PM sensor  10 B according to the second embodiment will be described in detail with reference to  FIG. 5 . The PM sensor  10 B of the second embodiment is configured so that the case member in the PM sensor  10 A of the first embodiment has a double pipe structure. The other components have the same structures, and accordingly the detailed descriptions thereof will be omitted. Also, some components, such as the control unit  40  and the like, are not shown. 
     The case member of the second embodiment has a cylindrical bottomed inner case portion  11 A and a cylindrical outer case portion  15  surrounding a cylindrical outer peripheral surface of the inner case portion  11 A. 
     The inner case portion  11 A is formed to have an axial length greater than that of the outer case portion  15  so that a distal end side thereof protrudes relative to the outer case portion  15 . Also, a bottom portion of the inner case portion  11 A is provided with an outflow port  13  for allowing exhaust gas in the inner case portion  15  to flow into an exhaust pipe  110 . Further, a cylindrical wall portion of the inner case portion  11 A at a base end side thereof is provided with a plurality of passage ports  14  arranged to be spaced with each other in a circumferential direction. The passage ports  14  are configured to allow exhaust gas in a flow path  16  defined between an outer peripheral surface of the inner case portion  11 A and an inner peripheral surface of the outer case portion  15  to flow into the inner case portion  11 A. 
     On a downstream end of the flow path  16 , a circular ring-shaped inflow port  12  defined between the cylindrical wall portion of the inner case portion  11 A at the distal end side thereof and the distal end portion of the outer case portion  15  is formed. An opening area S 12  of the inflow port  12  is formed to be smaller than an opening area S 13  of the outflow port  13  (S 12 &lt;S 13 ). 
     That is, the exhaust gas flowing through the exhaust pipe  110  collides with the cylindrical wall surface of the inner case portion  11 A protruding distally relative to the outer case portion  15  and thus is smoothly introduced into the flow path  16  through the inflow port  12  arranged near to a center axis CL of the exhaust pipe  110 . Then, the exhaust gas flowing through the flow path  16  is introduced into the inner case portion  11  through the passage ports  14 , passes through the filter member  31 , and then smoothly flows out through the outflow port  13  arranged near to the center axis CL of the exhaust pipe  110  into the exhaust pipe  110 . As such, in the PM sensors  10 B of the second embodiment, the inflow port  12  and the outflow port  13  are arranged near to the center axis CL where an exhaust flow velocity is highest in the exhaust pipe  110 , so that it is possible to effectively increase a flow rate of the exhaust gas passing through the sensor filter  31 . 
     Third Embodiment 
     Next, a PM sensor according to the third embodiment will be described in detail with reference to  FIG. 6 . The PM sensor of the third embodiment is configured so that the sensor unit  30  of the first embodiment is a stack type. The other components have the same structures, and accordingly the detailed descriptions and illustrations thereof will be omitted. 
       FIG. 6A  is a perspective view of the sensor unit  60  of the third embodiment and  FIG. 6B  is an exploded perspective view of the sensor unit  60 . The sensor unit  60  has a plurality of filter layers  61  and a plurality of electrode plates  62 ,  63 . 
     The filter layer  61  is formed so that a plurality of cells, which are divided by partition walls of, for example, porous ceramics or the like and form exhaust flow paths, are alternately plugged at upstream and downstream sides thereof and the cells are arranged in parallel in one direction in a cuboid shape. PM contained in the exhaust gas is collected by surfaces or micro-holes of the partitions walls of the cells C 11  as the exhaust gas flows from the cells C 11  plugged at the downstream side thereof into the cells C 12  plugged at the upstream side thereof as shown by broken line arrows in  FIG. 6B . Meanwhile, in the following description, a flow path direction of the cells is referred to as a longitudinal direction (an arrow L in  FIG. 6A ) of the sensor unit  60 , and a direction perpendicular to the flow path direction of the cells is referred to as a width direction (an arrow W in  FIG. 6A ) of the sensor unit  60 . 
     The pair of electrode plates  62 ,  63  are conductive members having, for example, a flat plate shape, and external dimensions thereof in the longitudinal direction L and the width direction W are substantially the same as those of the filter layer  61 . The pair of electrode plates  62 ,  63  are alternately stacked with the filter layer  61  interposed therebetween and are respectively connected to an electrostatic capacitance detection circuit (not shown) embedded in the control unit  40  via conductive wires  64 ,  65 . 
     That is, the pair of electrode plates  62 ,  63  are arranged to face each other and the filter layer  61  are interposed between the electrode plates  62 ,  63 , so that the entire cells C 11  form a capacitor. As such, in the PM sensor of the third embodiment, the entire cells C 11  are configured as the capacitor due to the electrode plates  62 ,  63  having a flat plate shape, so that it is possible to effectively secure an electrode surface area S and to increase an absolute value of a detectable electrostatic capacitance. Also, the distance d between the electrodes corresponds to a pitch of the cells and is uniform, so that it is possible to effectively suppress the non-uniformity of an initial electrostatic capacitance. 
     Meanwhile, when combusting and removing the PM accumulated in the cells C 11 , a voltage may be directly applied to the electrode plates  62 ,  63  or a heater board or the like (not shown) may be provided between the filter layer  61  and the electrode plates  62 ,  63 . 
     [Others] 
     The present invention is not limited to the foregoing embodiments and changes thereof can be appropriately made without departing from the spirit and scope of the present invention. 
     This application is based on Japanese Patent Application No. 2015-031525 filed on Feb. 20, 2015, the entire contents of which are incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     The sensor of the present invention has the effect that it is possible to detect water present in an exhaust system of an internal combustion engine and thus is useful in that sensors therein can be protected. 
     REFERENCE SIGNS LIST 
     
         
           10 A,  10 B PM sensor 
           11  Case member 
           12  Inflow port 
           13  Outflow port 
           20  Pedestal portion 
           21  Male screw portion 
           22  Nut portion 
           30  Sensor unit 
           31  Filter member 
           32 ,  33  Electrode member 
           34  Electrical heater 
           40  Control unit 
           41  Filter regeneration control unit 
           42  PM amount estimating calculation unit 
           43  Water infiltration determination portion 
           44  Sensor protection control unit