Abstract:
In relation to a humidity sensor sensitive to water and contamination, a sensor implementation structure that achieves both protection performance against water and contaminants and measurement performance such as humidity responsiveness is provided. A sensor structure has a mass airflow measurement element that measures a mass airflow flowing in an intake pipe, a humidity sensing element that senses humidity of air flowing in the intake pipe, a housing structural component having a connector that carries out input/output to/from outside and a terminal component of the connector, and a bypass passage that is composed by using part of the housing structural component and takes in part of the air that flows in the intake pipe, the mass airflow measurement element being mounted in the bypass passage; wherein space is provided in the housing structural component in the vicinity of the bypass passage, the humidity sensing element is mounted in the space.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sensor structure suitable for physical quantity measurement about intake air of an internal combustion engine and to an internal combustion engine control device using the structure. 
     2. Background Art 
     As a physical quantity measuring technique about intake air for an internal combustion engine, for example, about a flow rate measuring technique, a mass airflow measurement device of a heating resistor type is known (see JP Patent No. 3523022). This utilizes the fact that the heat quantity taken away from the heating resistor has a correlation with an inflow flow rate, and this is widely used particularly as a flow meter for air-fuel ratio control of automobiles since the mass flow rate required in combustion control of an engine can be directly measured. 
     Furthermore, as other physical quantity measuring techniques about the intake air for internal combustion engines, a sensor having a plurality of measurement functions integrating a flow rate measurement device, a pressure measurement device, a humidity detection device, etc. is shown as publicly known techniques as examples in which an airflow sensor, a humidity sensor, and a pressure sensor are integrated in JP Patent Publication (Kokai) No. 2008-304232 and JP Patent Publication (Kokai) No. 2010-43883. 
     SUMMARY OF THE INVENTION 
     An automobile using an electronic control fuel injection system has become common, and further enhancement in the performance and functions thereof have been recently developing. In that case, various sensors and control devices are densely disposed in an engine room, and wire harnesses which mutually connect various sensors, control devices, and control units, etc. for controlling them are also complex. 
     Under such circumstances, reduction in the number of parts and improvement of the appearance in the engine room achieved by integrating the plurality of sensors and control devices are desired. For example, a measure of integrating a flow rate measurement device, a temperature detection device, a semiconductor-type pressure measurement device, a humidity detection device, etc. and sharing a connector is an example thereof, and, by virtue of this, the number of steps of parts assembly with respect to a vehicle can be reduced, and wire harnesses can be simplified. 
     Conventionally, the above described structure that integrates the flow rate measurement device and the temperature detection device has been a mainstream. However, as described above, as the pressure measurement device, the humidity detection device, etc. are also integrated in the future, various technical problems emerge. 
     Normally, the intake air of an automobile is configured to be taken in after removing the substances floating in the air by an air filter element provided in an air cleaner box. However, since large pressure loss generated by the air filter element that causes engine output reduction and fuel consumption rate deterioration is not desired, for example, a paper filter that captures fine carbon, etc. contained in an exhaust gas is not used, and fine floating substances, etc. in the air pass through the paper filter and are taken into the engine. 
     After the engine is stopped, the engine oil exposed to high temperature becomes vapor and sometimes flows back to the air cleaner box side. Therefore, the air that exists in or passes through the intake air pipe in the downstream of the air cleaner box is not always clean. Moreover, recently, the electronic control of a diesel engine has been advancing, and a diesel engine is harsher than a gasoline engine system as an environment for installing sensors. 
     The sensors in such an environment are densified as described above, and the demands for higher accuracy are further increasing in the future. In order to increase accuracy, the capability of maintaining the accuracy as long as possible is very important, and so consideration for anti-contamination property is required. Conventionally, an intake air flow meter, an intake air temperature meter, an intake air pressure meter, etc. have been widely used as intake sensors. However, in the future, the tendency that measurement of intake air humidity is also used in the control of an internal combustion engine is strong. Particularly, the humidity sensor is a sensor that has high sensitivity to contamination, therefore, an implementation structure that achieves all of measurement accuracy, measurement responsiveness, and anti-contamination property will be a problem. 
     JP Patent Publication (Kokai) No. 2010-43883 shows a second bypass air passage which bypasses a bypass passage. However, although JP Patent Publication (Kokai) No. 2010-43883 assumes that obstructing intake of contaminants is an effect, there is basically a presupposed condition that the contaminants and water droplets are taken in together with air. Furthermore, there is no measure even against the case in which a small amount of contaminants are actually taken in. 
     It is an object of the present invention to provide a sensor structure capable of measuring humidity with good accuracy and preventing entry of contaminants, water droplets, etc. 
     In order to solve the above described problems, a sensor structure has a mass airflow measurement element that measures a mass airflow flowing in an intake pipe, a humidity sensing element that senses humidity of air flowing in the intake pipe, a housing structural component having a connector that carries out input/output to/from outside and a terminal component of the connector, and a bypass passage that is composed by using part of the housing structural component and takes in part of the air that flows in the intake pipe, the mass airflow measurement element being mounted in the bypass passage; wherein space is provided in the housing structural component in the vicinity of the bypass passage, the humidity sensing element is mounted in the space, and the part of the space does not have a structure sealed by an adhesive, a seal material, or the like. 
     According to the present invention, a sensor structure capable of measuring humidity with good accuracy and preventing entry of contaminants and water droplets can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sensor structure drawing showing an embodiment of the present invention. 
         FIG. 1B  is an A-A cross sectional view of  FIG. 1A . 
         FIG. 2  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 3  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 4  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 5  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 6  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 7  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 8  is a sensor structure drawing showing another embodiment of the present invention. 
         FIG. 9A  is a sensor structure drawing showing an embodiment in which the present invention is configured to be a multifunction sensor. 
         FIG. 9B  is a B-B cross sectional view of  FIG. 9A . 
         FIG. 10  is an embodiment in which a product of the present invention is applied to an internal combustion engine of an electronic fuel injection type. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A specific configuration example of the present invention will be explained by using  FIG. 1 . 
     An installation hole  4  in which part of a mass airflow measurement device  3  is installed is provided in part of a main air flow passage component (intake pipe line component)  2  constituting a main air flow passage (also referred to as “intake pipe line” or simply “intake pipe”)  1 , and the mass airflow measurement device  3  is installed thereat via a seal material  6 . 
     The mass airflow measurement device  3  is composed of: a base plate  8 ; a cover  10  for protecting an electronic circuit board  9 ; a heating resistor  11  for measuring the mass airflow; a temperature compensation resistor  12  used in mass airflow measurement; an intake air temperature sensor  13  used in the vehicle side; a bypass air passage  14  in which the heating resistor  11 , the temperature compensation resistor  12 , etc. are mounted; a bypass air passage structural component  15  for constituting the bypass air passage  14 ; and so on in addition to a housing structural component  7 . Each of the parts is fixed by using an adhesive  65 , and particularly the region in which the electronic circuit board  9  is mounted is sealed so that exhaust gases and water from outside do not enter. 
     The heating resistor  11 , the temperature compensation resistor  12 , and the intake air temperature sensor  13 , which detect the intake mass airflow and intake air temperature, are connected to the electronic circuit board  9  via bonding wires  16 . Furthermore, the electronic circuit board  9  is similarly electrically connected to connector terminals  17  via bonding wires  16 , and inputs/outputs to/from the outside are carried out via the connector terminals  17 . 
     A humidity sensing element  5  is installed on the electronic circuit board  9  of the mass airflow measurement device  3 , and the humidity sensing element  5  is positioned in open space  18  formed in the housing structural component  7 . The open space  18  is composed only of the combination of the base plate  8  and the housing structural component  7  in the vicinity of the bypass air passage  14 , and gas exchange can be carried out therein without using a seal agent, an adhesive, or the like. By virtue of this configuration, humidity can be measured with good accuracy, and complete isolation from contaminants and water droplets floating in the air is enabled. 
       FIG. 2  is a sensor structure drawing showing another embodiment of the present invention. The humidity sensing element  5  is installed on the electronic circuit board  9  of the mass airflow measurement device  3 , and the humidity sensing element  5  is mounted in the open space  18  formed in the housing structural component  7 . An air communication channel-A  19 , which communicates between the open space  18  and the upstream side of the main air flow passage  1 , and an air communication channel-B  20 , which communicates between the open space  18  and the downstream side of the main air flow passage  1 , are provided to enable ventilation to the open space  18 . By virtue of the present configuration, responsiveness of humidity detection can be improved. However, isolation from the contaminants and water droplets floating in the air becomes difficult in this configuration, and, in that case, anti-contamination property is improved by removing the air communication channel-B  20  and causing only the air communication channel-A  19  to function. 
       FIG. 3  is a sensor structure drawing showing another embodiment of the present invention. The humidity sensing element  5  is installed on the electronic circuit board  9  of the mass airflow measurement device  3 , and the humidity sensing element  5  is mounted in the open space  18  formed in the housing structural component  7 . 
     An air communication channel-C  21 , which communicates between and connects the open space  18  and the bypass air passage  14  to each other in the upstream side of the bypass air passage  14 , and an air communication channel-D  22 , which communicates between and connects the open space  18  and the bypass air passage  14  to each other in the downstream side of the bypass air passage  14 , are provided. Furthermore, air communication openings  23  of the air communication channel-C  21  and the air communication channel-D  22  in the bypass air passage  14  are parallel to the flow of the air in the bypass air passage  14 , thereby significantly reducing the risk of taking in the contaminants and water droplets floating in the air. 
     The inner pressures of the air communication channel-C positioned in the upstream side and the air communication channel-D positioned in the downstream side have the relation of “air communication channel-C&gt;air communication channel-D” because of the influence of pressure loss caused by pipe line friction, etc. of the bypass air passage  14 . Therefore, the air communication channel-C  21  is an air introduction channel  24  having the function of taking in part of the air flowing in the bypass air passage  14 , the air communication channel-D  22  is an air discharge channel  25  having the function of discharging the air in the open space  18  by the inner pressure difference of the bypass air passage  14 , and the air flows in the path from the air communication channel-C  21  to the open space  18  and from the open space  18  to the air communication channel-D  22 . 
       FIG. 4  is a sensor structure drawing showing another embodiment of the present invention. Compared with the configuration shown in  FIG. 3 , structures such as the heating resistor  11  for measuring the mass airflow, the temperature compensation resistor  12  used in the mass airflow measurement, the intake air temperature sensor  13  independently used in the vehicle side, and terminal members  26 , which support and fix them, are disposed between the air communication openings  23  of the air introduction channel  24  and the air discharge channel  25  in the bypass air passage  14 . By virtue of these structures, pressure loss in the bypass air passage  14  is further increased, in other words, a larger pressure difference is generated between the two air communication openings  23  related to the air introduction channel  24  and the air discharge channel  25 . Therefore, the effect of discharging the air is increased, and sufficient air can be sent to the part of the humidity sensing element  5 . 
       FIG. 5  is a sensor structure drawing showing another embodiment of the present invention. The terminal members  26  which are integrally molded with the housing structural component  7  and support and fix the heating resistor  11 , the temperature compensation resistor  12 , and the intake air temperature sensor  13  are disposed so as to avoid the open space  18  in the housing structural component  7 , and the open space  18  is characterized by being installed in the upper side of the stream than the heating resistor  11 . 
     The mass airflow measurement device  3  is used by being installed in the flow of the main air flow passage  1  and serves as a resistance to the flow. The pressure loss in the main air flow passage  1  serves as a direct cause of reduction in the engine output or deterioration of fuel cost. Therefore, the front projected area of the mass airflow measurement device  3  is desired to be smaller, and the configuration shown in  FIG. 5  is one means for reducing the thickness (width) size of the mass airflow measurement device  3 . 
     Humidity measurement and air temperatures have a close relation, and relative humidity is a physical quantity that varies in accordance with the temperature of air. Therefore, the temperature environment around the humidity sensing element  5  is important. In the configuration shown in  FIG. 5 , the open space  18  is mounted in the upstream of the heating resistor  11  to avoid the thermal influence from the heating resistor  11 . By virtue of the configuration thereof, a compact and highly-accurate multifunction sensor can be provided. 
       FIG. 6  is a sensor structure drawing showing another embodiment of the present invention. Compared with the configuration shown in  FIG. 5 , this is an example in which the humidity sensing element  5  and the open space  18  are installed in the downstream side of the heating resistor  11 . In the case in which the air communication opening  23  of the air introduction channel  24 , which introduces measurement air to the humidity sensing element  5 , is installed in the upstream side of the heating resistor  11 , the humidity sensing element  5  is not much affected by the heat-release influence exerted on the downstream of the heating resistor  11 . In this case, the positions of the humidity sensing element  5  and the open space  18  are not limited, and the degree of freedom of design is increased. 
       FIG. 7  is a sensor structure drawing showing another embodiment of the present invention. The humidity sensing element  5  is installed on the electronic circuit board  9  of the mass airflow measurement device  3 , and the humidity sensing element  5  is mounted in the open space  18  formed in the housing structural component  7 . 
     The air introduction channel  24 , which communicates between and connects the open space  18  and the bypass air passage  14  to each other in the upstream side of the bypass air passage  14 , and the air discharge channel  25 , which communicates between and connects the open space  18  and the bypass air passage  14  to each other in the downstream side of the bypass air passage  14 , are provided. The humidity sensing element  5  is mounted at a position away from a streamline  27  (path of a main flow) formed at this point. An object thereof is to reduce the contamination density and prevent direct adhesion of contaminants by increasing the air volume of the open space  18 . Even if contaminants flow into the open space  18 , the contamination density can be reduced at the position of the humidity sensing element  5 , and the risk that the contaminants may adhere to the humidity sensing element  5  can be reduced. When the humidity sensing element is mounted at the position deviated from the streamline  27  in the open space  18 , the risk that the humidity sensing element  5  may be directly contaminated can be further reduced. 
       FIG. 8  is a sensor structure drawing showing another embodiment of the present invention. The periphery of the open space  18  is sealed with a material having moisture absorbency such as a silicone adhesive  30  to further improve the resistance to the contaminants and water droplets floating in the air. If quick humidity measurement responsiveness is not required, humidity measurement can be sufficiently carried out with the present configuration. 
       FIGS. 9A and 9B  show an embodiment in which the present invention is applied to a multifunction sensor integrated with a mass airflow meter and a pressure measurement device and show a B-B cross section thereof. The pressure measurement device  28  is mounted on the housing structural component  7 , and a pressure intake port  29  communicating between the mounted location of the pressure measurement device  28  and the interior of the main air flow passage  1  is provided so that at least three physical quantities, i.e., the mass airflow, air humidity, and air pressure can be detected and output. 
     In the end, an embodiment in which the present invention is applied to an internal combustion engine of an electronic fuel injection type is shown by using  FIG. 10 . Intake air  51  taken in from an air cleaner  50  is taken into an engine cylinder  56  through the main air flow passage component  2  in which a multifunction sensor  64  is installed, an intake air duct  52 , and an intake manifold  55  provided with a throttle body  53  and a fuel injector  54  to which fuel is supplied. Meanwhile, an exhaust gas  57  generated in the engine cylinder  56  is discharged through an exhaust manifold  58 . 
     A mass airflow signal, a humidity signal, a pressure signal, and a temperature signal output from the multifunction sensor  64 , a throttle valve angle signal output from a throttle angle sensor  59 , an oxygen concentration signal output from an oxygen meter  60  provided in the exhaust manifold  58 , an engine speed signal output from an engine speed meter  61 , etc. are input to an engine control unit  62 . The engine control unit  62  sequentially calculates these signals to obtain an optimum fuel injection amount and optimum output torque and controls the fuel injector  54  and the throttle valve  63  by using the values thereof. 
     DESCRIPTION OF SYMBOLS 
     
         
           1  MAIN AIR FLOW PASSAGE 
           2  MAIN AIR FLOW PASSAGE COMPONENT 
           3  MASS AIRFLOW MEASUREMENT DEVICE 
           4  INSTALLATION HOLE 
           5  HUMIDITY SENSING ELEMENT 
           6  SEAL MATERIAL 
           7  HOUSING STRUCTURAL COMPONENT 
           8  BASE PLATE 
           9  ELECTRONIC CIRCUIT BOARD 
           10  COVER 
           11  HEATING RESISTOR 
           12  TEMPERATURE COMPENSATION RESISTOR 
           13  INTAKE AIR TEMPERATURE SENSOR 
           14  BYPASS AIR PASSAGE 
           15  BYPASS AIR PASSAGE STRUCTURAL COMPONENT 
           16  BONDING WIRE 
           17  CONNECTOR TERMINAL 
           18  OPEN SPACE 
           19  AIR COMMUNICATION CHANNEL-A 
           20  AIR COMMUNICATION CHANNEL-B 
           21  AIR COMMUNICATION CHANNEL-C 
           22  AIR COMMUNICATION CHANNEL-D 
           23  AIR COMMUNICATION OPENING 
           24  AIR INTRODUCTION CHANNEL 
           25  AIR DISCHARGE CHANNEL 
           26  TERMINAL MEMBER 
           27  STREAMLINE 
           28  PRESSURE MEASUREMENT DEVICE 
           29  PRESSURE INTAKE PORT 
           30  SILICONE ADHESIVE 
           50  AIR CLEANER 
           51  INTAKE AIR 
           52  INTAKE AIR DUCT 
           53  THROTTLE BODY 
           54  FUEL INJECTOR 
           55  INTAKE MANIFOLD 
           56  ENGINE CYLINDER 
           57  EXHAUST GAS 
           58  EXHAUST MANIFOLD 
           59  THROTTLE ANGLE SENSOR 
           60  OXYGEN METER 
           61  ENGINE SPEED METER 
           62  ENGINE CONTROL UNIT 
           63  THROTTLE VALVE 
           64  MULTIFUNCTION SENSOR 
           65  ADHESIVE