Air flow rate measuring device with integrated sensor module

The present disclosure provides an air flow rate measuring device disposed in an intake air passage. The air flow rate measuring device measures a flow rate of the intake air flowing through the intake air passage. The air flow rate measuring device includes a casing, a flow rate sensor, and a sensor module. The casing defines a bypass passage to take in a portion of the intake air. The flow rate sensor is disposed in the bypass passage. The flow rate sensor generates an output signal according to a flow rate of the intake air. The sensor module protrudes from an outer wall of the casing. The sensor module includes a multi-sensor unit that has a relative humidity sensor and a temperature sensor. The relative humidity sensor is exposed to an inside of the intake air passage to detect a relative humidity of the intake air flowing through the intake air passage. The temperature sensor detects a temperature of the intake air flowing through the intake air passage.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on reference Japanese Patent Application No. 2015-167708 filed on Aug. 27, 2015, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an air flow rate measuring device that measures a flow rate of an intake air used in an engine system.

BACKGROUND

Conventionally, there has been known an air flow rate measuring device that measures a flow rate of an intake air taking advantage of heat transfer with air while detecting a plurality of physical quantities of the intake air. In an engine system, advanced engine control has been required in order to achieve low fuel consumption. Thus, high accurate measuring of physical quantities of the intake air, such as an absolute humidity, a temperature, a pressure, or the like, is required in addition to measuring of a flow rate of the intake air. These physical quantities are important information involving combustion process of the engine system and are used to calculate, e.g., a fuel injection time.

For example, in a flow rate measuring device disclosed in Patent Literature 1 (JP 2011-075357 A) or Patent Literature 2 (JP 2015-004556 A), a humidity sensor is provided to calculate an absolute humidity of an intake air. The humidity sensor includes a relative humidity detector that detects a relative humidity and a temperature detector that calculates the absolute humidity based on the relative humidity. Furthermore, in addition to the temperature detector (in other words, a first temperature detector), a second temperature detector, which is dedicated to detect a temperature of the intake air, is disposed at a position where the intake air is directly brought into contact with the second temperature detector.

In the configuration described in Patent Literature 1 and Patent Literature 2, the humidity sensor includes the relative humidity detector and the first temperature detector to calculate an absolute humidity of the intake air. The first temperature detector of the humidity sensor takes in an intake air through a sub passage branching inside the air flow rate measuring device, and the first temperature detector is arranged at a position where the intake air is not directly brought into contact with the first temperature detector. Therefore, the first temperature detector is not able to detect a real temperature of the intake air, and thus the second temperature detector is additionally arranged at a position where the intake air is directly brought into contact with the second temperature detector. As a result, two temperature signals are output from the first and second temperature detectors. Hence, the second temperature detector is additionally necessary as an intake air temperature measuring device that dedicatedly a temperature of an intake air. As a result, the number of components such as terminals and harnesses is increased, which would lead to complexity to the device.

Furthermore, the relative humidity detector of the humidity sensor is arranged at a position where the intake air is not brought into contact with the relative humidity detector. Therefore, a relative humidity of the intake air cannot be detected accurately, and as a result, accuracy of calculation of the absolute humidity of the intake air would be deteriorated due to a measuring error of the relative humidity.

In view of the above, it is an objective of the present disclosure to provide an air flow rate measuring device that accurately performs calculation of an absolute humidity of an intake air and measuring of a temperature of the intake air without an additional temperature sensor dedicated to detect a temperature of the intake air.

SUMMARY

In an aspect of the present disclosure, an air flow rate measuring device is disposed in an intake air passage for intake air to be taken in an engine system. The air flow rate measuring device measures a flow rate of the intake air flowing through the intake air passage. The air flow rate measuring device includes a casing and a sensor module.

The casing defines a bypass passage to take in a portion of the intake air flowing through the bypass passage.

The flow rate sensor is disposed in the bypass passage. The flow rate sensor generates an output signal according to a flow rate of the intake air taken in the bypass passage.

The sensor module protrudes from the outer wall of the casing and includes the multi-sensor unit that detects a relative humidity and a temperature of an intake air flowing through the intake air passage. The multi-sensor unit is exposed to the inside of the intake air passage and is integrally connected to the sensor module. The multi-sensor is positioned away from the casing. Preferably, the relative humidity sensor and the temperature sensor of the multi-sensor unit are arranged to be close to each other. Furthermore, the sensor module is preferably integrally formed with the multi-sensor unit by resin-molding.

In the above-described aspect, the sensor module protruding from the outer wall of the casing includes the multi-sensor unit that has the relative humidity sensor and the temperature sensor, that is positioned away from the casing, and that is exposed to the inside of the intake air passage. Since the multi-sensor unit is exposed to the inside of the intake air passage, an intake air in the intake air passage is directly brought into contact with the multi-sensor unit. Furthermore, since the multi-sensor unit is arranged to be away from the casing, the multi-sensor unit is not in direct contact with the casing. Therefore, heat of the intake air is directly transferred to the multi-sensor unit, and an increase in a temperature of the intake air due to heat transfer from the casing to the multi-sensor unit can be prohibited. As a result, negative effects from the casing can be avoided, thereby accurately measuring a temperature of the intake air.

Furthermore, the multi-sensor unit including the relative humidity sensor and the temperature sensor can directly detect a temperature at the relative humidity sensor and a temperature at the intake air passage at the same time. Thus, calculation of an absolute humidity from a relative humidity and measuring of an intake air temperature can be accurately performed. As a result, an additional temperature sensor conventionally used for dedicatedly detecting a temperature in the intake air passage can be eliminated, while accurately performing calculation of an absolute humidity of an intake air from a relative humidity and measuring of an intake air temperature.

DETAILED DESCRIPTION

As follows, a plurality of embodiments of the present disclosure will be described in detail. It is needless to say that the embodiments are some examples of the present disclosure, and therefore the present disclosure is not limited to these embodiment. Furthermore, each of the substantially same structures among the embodiments will be assigned to the respective common referential numeral and the description of the substantially same structures will be omitted in the subsequent embodiments.

With reference toFIG. 1, a schematic configuration of an engine system will be described first.

As shown inFIG. 1, the engine system10includes a spark-ignition type engine13. The engine13is, for example, a multi-cylinder engine such as a four-cylinder engine, althoughFIG. 1only shows a cross-section of one of cylinders. The following description can be applied to other cylinders not shown inFIG. 1.

The engine system10ofFIG. 1does not include an EGR (Exhaust Gas Recirculation) system. Even if the EGR system is provided, the EGR system would not be illustrated because the EGR system has low relevancy to technical features of the present disclosure. Furthermore, a catalyst disposed in an exhaust passage is also not illustrated.

In the engine13, a mixed gas of an intake air supplied from an intake manifold15through an air cleaner112and a throttle valve14and a fuel injected from an injector16is combusted in a combustion chamber17. A piston18reciprocates due to an explosion power by the combustion. Exhaust gas is released into the atmosphere through an exhaust manifold20.

An intake valve22is disposed in an intake port of a cylinder head21that is an inlet of the combustion chamber17, whereas an exhaust valve23is disposed in an exhaust port of the cylinder head21that is an outlet of the combustion chamber17. The intake valve22and the exhaust valve23are operated to close or open the respective ports through valve driving mechanisms24. The valve timing of the intake valve22is adjusted by a variable valve mechanism25.

An ignition of the mixed gas in the combustion chamber17generates spark discharge in the combustion chamber17by applying high voltage to the ignition plug11from the ignition coil19.

The electric control unit27is formed of a microcomputer including a CPU, a ROM, a RAM and an input/output port, which is represented as “ECU” in the drawings.

As shown in the broken arrow, the electric control unit27inputs detection signals from a throttle opening degree sensor28and the air flow rate measuring device1. The electric control unit27uses the detection signals to calculate the fuel injection time, and then, as shown by the solid arrow, the electric control unit27controls operating condition of the engine13by operating the throttle valve14and the injector16. In this way, the detection signals from the air flow rate measuring device1are important information for controlling the operating condition of the engine system10with high accuracy.

Next, the configuration of the air flow rate measuring device according to a first embodiment will be described with reference toFIGS. 2 to 6.

The air flow rate measuring device1includes a casing7, a flow rate sensor80, and a sensor module40.

As shown inFIG. 2, the casing7includes a sensor connector90and the flow rate sensor80. The sensor connector90defines a bypass passage60through which an intake air flows, and the sensor connector90is integrally formed with the casing7. The flow rate sensor80generates an output signal according to a flow rate of the intake air by heat transfer with the intake air flowing through the bypass passage60. For example, the casing7is formed together with the sensor connector90by resin-molding. For example, an epoxy resin or a phenolic resin is used as the resin for the casing7.

As shown inFIG. 3, the casing7includes a bypass forming member30, a fitting portion12, and a fixing portion13. The bypass forming member30defines the bypass passage60and protrudes into the intake air passage2. The fitting portion12is a root portion of the bypass forming member30. The fixing member13is fastened to the air duct4by a screw.

With reference toFIG. 2, the bypass passage60includes an inlet61open toward an upstream side of the intake air passage2in a flow direction of the intake air. The bypass passage60further includes outlets62open toward a downstream side of the intake air passage2in the flow direction of the intake air. Further, the bypass passage60includes a straight path63that directs the intake air as a straight flow from the inlet61and a detour path64that directs the intake air from the straight path63to go around.

Therefore, the path length of the bypass passage60is longer than the path length of a straight passage where the intake air flows through the intake air passage2without being taken in the bypass passage60. The detour path64branches into two paths at a downstream side and the two outlets62are formed for the two paths. A dust discharging passage65to discharge dust is connected to the straight path63in a straight manner, and a lower end of the dust discharging passage65serves as a dust exhaust port66open toward a downstream side of the intake air passage2.

The fitting portion12has two end surfaces opposite to each other in an axial direction. The bypass forming member30extends from one of the two end surfaces of the fitting portion12in a direction perpendicular to the one of the two end surfaces of the fitting portion12. The bypass forming member30is inserted into the intake air passage2from an insert hole34formed in a wall3of the air duct4. The bypass forming member30forms a core portion of the casing7and takes in a portion of the intake air flowing through the intake air passage2into the bypass passage60.

The fitting portion12has a cylindrical shape, and an annular groove is formed in an outer wall of the fitting portion12. An O-ring35is fit into the groove. The fitting portion12is fit into the insert hole34in the wall3of the air duct4, whereby the intake air passage2is sealed from an outside by the O-ring35.

The fixing portion13is disposed on the other of the two end surfaces of the fitting portion12opposite to the bypass forming member30. The fixing portion13is fixed to the air duct4by a screw.

The sensor connector90includes a power terminal91, a ground terminal92, two sensor module terminals93,94, and a flow rate detecting terminal95. The sensor connector90is disposed in an end surface of the fixing portion13opposite to the fixing portion12. The terminals91,92,93,94,95are connected to an external terminal that is inside the sensor connector90and that is connectable to an external component.

The flow rate sensor80is disposed in the bypass passage60. The flow rate sensor80includes a flow rate detector81that detects a flow rate of an intake air by heat transfer with the intake air flowing through the bypass passage60. The flow rate sensor80further includes a signal processor82built in the flow rate detector81. The flow rate detector81is formed of, e.g., a heat resistor and a thermosensitive element that are made of film resistors on a surface of a semiconductor substrate.

The flow rate detector81is exposed to a space at a deepest position of the detour path64and furthest from the straight path63. A flow direction of an intake air at a position in the detour path64where the flow rate detector81is disposed is opposite from a flow direction of an intake air in the straight path63or in the intake air passage2.

The power terminal91is connected to a power source, and the ground terminal92is connected to a ground. Thus, the flow rate detector81is capable of detecting a flow rate of an intake air flowing through the intake air passage2. Output according to the flow rate of the intake air from the flow rate detector81is processed by the signal processor82to a signal according to the flow rate, then the signal is output to the electric control unit27outside of the flow rate measuring device1through the flow rate detecting terminal95.

The sensor module40protruding from an outer wall of the casing7includes a multi-sensor unit41that detects a relative humidity and a temperature of an intake air flowing through the intake air passage2. The sensor module40further includes a signal processing circuit55and a module connector50formed of a power terminal51, a ground terminal52, and output terminals53,54. The sensor module40may be formed by integrally resin-molding the multi-sensor unit41, the module connector50, and the signal processing circuit55.

As shown inFIG. 4, the sensor module40is inserted into the intake air passage2and protrudes from the fitting portion12toward the center of the intake air passage2. The direction in which the sensor module40protrudes from the fitting portion12is the same as a direction in which the bypass forming member30is exposed to the inside of the intake air passage2, in other words, a radial direction of the air duct4. Furthermore, the protruding direction of the sensor module40is parallel to an outer side surface of the bypass forming member30.

The multi-sensor detector41includes a relative humidity sensor42and a temperature sensor43. The relative humidity sensor42detects a relative humidity of an intake air flowing through the intake air passage2. The temperature sensor43detects a temperature of the intake air flowing through the intake air passage2. The relative humidity sensor42functions using, e.g., an electric permittivity change of a polymer membrane due to a change of a relative humidity. The relative humidity sensor42includes a polymer membrane such as polyimide that has a permittivity variable according to the relative humidity. The temperature sensor43includes, e.g., a thermistor (i.e., a ceramic semiconductor) having an electric resistance variable according to a temperature.

As shown inFIG. 5, the multi-sensor unit41is integrally formed with the sensor module40. In the first embodiment, the multi-sensor detector41is connected to an outer surface of the sensor module41such that the multi-sensor detector41is exposed to the inside of the intake air passage2. The multi-sensor unit41may be integrally formed with the sensor module40such that at least a portion of the multi-sensor unit41is exposed to the intake air passage2. The relative humidity sensor42and the temperature sensor43are away from each other in the multi-sensor unit41.

The multi-sensor unit41is away from the casing7through the sensor module40protruding from the outer wall of the casing7. The multi-sensor unit4is arranged at a tip end45of the sensor module40so that the multi-sensor unit41is positioned close to the center of the air duct4in a radial direction.

The module connector50is positioned at a rear end46of the sensor module40, in other words at an inserted side of the sensor module40. The power terminal51is connected to the power terminal91of the flow rate sensor connector90by wire bound. Similarly, the ground terminal52of the module connector50is connected to the ground terminal92of the flow rate sensor connector90by wire bound. Accordingly, the multi-sensor unit41is capable of detecting a relative humidity and a temperature of an intake air flowing through the intake air passage2.

Although the power terminal and the ground terminal are commonly used, additional terminals may be used to be connected to another power source or another ground.

The output terminal53of the module connector50is connected to the sensor module terminal93of the sensor connector90by wire bound. The output terminal54of the module connector50is connected to the sensor module terminal94of the sensor connector90by wire bound.

The signal processing circuit55is disposed between the multi-sensor unit41and the module connector50. The relative humidity and the temperature of the intake air flowing through the intake air passage2detected by the multi-sensor unit41are processed to signals by the signal processing circuit55. Then, the processed signals are output to the electric control unit27outside of the air flow rate measuring device1through the sensor module terminals93,94. In the present embodiment, the two sensor module terminals93,94are used, but only one sensor module terminal may be used. The relative humidity and the temperature of the intake air detected by the multi-sensor unit41may be directly output to the electric control unit27as an intake air relative humidity output and an intake air temperature output, respectively. In this case, the electric control unit27may perform processing as the signal processing circuit55. The intake air temperature output is used as information of the intake air temperature for the engine system10through the electric control unit27.

For example, a processing circuit is disposed between the output terminals53,54and the sensor module terminals93,94. The processing circuit may include an A/D converter and an interface circuit. The A/D converter is a multiplexer system or a simultaneously sampling system, and the ND converter converts the relative humidity and the temperature detected by the multi-sensor unit41into a digital signal. The interface circuit relates digital signals converted by the A/D converter to each other and stored the digital signals in one frame. The one frame stores a plurality of data.

The data stored in the frame is transmitted in a form of a pulse signal according to Society of Automotive Engineers Standards SAE-2716. That is, the relative humidity and the temperature detected by the multi-sensor unit41are transmitted in SENT protocol. SENT represents Single Edge Nibble Transmission. The processing may performed by the signal processing circuit55. With this, a single track can be used, whereby only one sensor module terminal93,94can be used.

With reference toFIG. 6, calculation of an absolute humidity of an intake air and measuring of a temperature of the intake air by the multi-sensor unit41will be described. The flow rate sensor80of the air flow rate measuring device1transfers the signal according to a flow rate Q of an intake air through heat transfer with the intake air to the electric control unit27. The relative humidity sensor42of the multi-sensor unit41detects a relative humidity U of an intake air flowing in from the intake air passage2and outputs an output signal according to the relative humidity U. The temperature sensor43detects a temperature T, and outputs an output signal according to the temperature T. The temperature T indicates an intake air temperature Tq and a temperature at the relative humidity sensor42. The signal processing circuit55calculates an absolute humidity D based on the relative humidity U using the temperature T.

The signal processing circuit55generates signals according to the absolute humidity D calculated and the intake air temperature Tq, and then transmits the signals to the electric control unit27. The electric control unit27transmits the signals as control signals to the throttle valve14and the injector16to control an intake air amount and a fuel injection amount.

In the present embodiment, the sensor module40protruding from the casing7includes the multi-sensor unit41exposed to the inside of the intake air passage2. The multi-sensor unit41includes the relative humidity sensor42that detects the relative humidity of an intake air in the intake air passage2and the temperature sensor43that detects a temperature of the intake air in the intake air passage2.

As described above, the sensor module40protrudes from the outer wall of the casing7, and therefore an intake air flowing through the intake air passage2is directly brought into contact with the multi-sensor unit41and the temperature sensor43. As a result, heat is directly transferred from the intake air to the temperature sensor43. Furthermore, the temperature sensor43is disposed to be away from the casing7, whereby an increase in a temperature of an intake air due to heat transfer from the casing7is prohibited. Therefore, effects by heat transfer from the casing7can be omitted. As a result, a temperature of an intake air can be accurately measured.

The multi-sensor unit41includes the relative humidity sensor42and the temperature sensor43. Therefore, the temperature sensor43can measure both an intake air temperature and a temperature at the relative humidity sensor42at the same time. When a temperature changes, a volume of air containing water vapor also varies. Thus, to achieve accurate calculation of an absolute humidity, temperature information is necessary in addition to a relative humidity. Thus, by using a temperature obtained from the temperature sensor43, it is possible to increase accuracy of the intake air temperature and to more accurately calculate an absolute humidity based on the relative humidity of an intake air.

In a Japanese patent literature (JP 2013-036892 A) discloses an air flow rate measuring device including a relative humidity sensor and a temperature sensor. However, in this configuration, the position of the temperature sensor is not specified. In the first embodiment, the relative humidity sensor42and the temperature sensor43of the multi-sensor unit41are integrally formed with the sensor module40. Therefore, it is possible to accurately calculate an absolute humidity of an intake air and accurately measure a temperature of the intake air. Because the calculation of the absolute humidity and the measuring of the temperature have an impact on control for an engine system, the accurate calculation of the absolute humidity and the temperature is of significance.

Above all, advanced control is required for the engine system to maintain combustion in a proper state in a combustion chamber under a condition where an environment for the air duct4and the intake air manifold15are significantly varying according to operational condition of a vehicle. Furthermore, constraints on a space for mounting the air flow rate measuring device and demand for reducing costs are high. Thus, the high accurate calculation of the absolute humidity of the intake air and the high accurate measuring of the temperature of the intake air are especially of significance for such a field.

The temperature sensor43integrally formed with the relative humidity sensor42is capable of calculating an absolute humidity from the relative humidity and of measuring the temperature of the intake air at the same time. Therefore, a conventional dedicated intake air temperature sensor can be eliminated. Therefore, the number of a connector terminal for the dedicated intake air temperature sensor and a harness for the engine ECU can be reduced.

With reference toFIG. 7, a second embodiment will be described. The multi-sensor unit41further includes a pressure detector44. The pressure sensor44is a sensor taking advantage of a change of an electric resistance of a metal or a semiconductor according to a change of a pressure. The pressure sensor44includes a silicon forming a diagram deformable by a pressure. The output terminal53,54of the module connector may be used as an output terminal of the pressure sensor44, or alternatively, an addition terminal may be used and connected to another terminal.

The pressure sensor44detects a pressure of an intake air flowing from the intake air passage2and outputs an output signal according to the pressure as detected. The pressure P of the intake air, together with the relative humidity U obtained from the relative humidity sensor42and the temperature T obtained from the temperature sensor43, is used for calculating the absolute temperature. The pressure P represents an intake air pressure Pq and a pressure at the relative humidity detector42. As with the first embodiment, the signal processing circuit55calculates the absolute humidity D based on the relative humidity U obtained using the temperature T and the pressure P obtained. Then, the signal processing circuit55processes the absolute humidity D calculated, the intake air temperature Tq, and the intake air pressure Pq into signals, and then transfers these signals to the electric control unit27. The electric control unit27performs a similar control as the first embodiment.

Since all air containing water vapor is affected by a partial pressure, calculation of an absolute humidity is affected by a pressure. When the air cleaner112is in normal operation, the pressure P of air introduced into the intake air passage2from the atmosphere is equal to the atmospheric pressure, there is no effect on accuracy of calculation of an absolute humidity when using a value of the atmospheric pressure. However, when the air cleaner112is clogged, a pressure loss generated when taking in an intake air increases, and therefore a pressure of the intake air in the intake air passage2is lowered as compared with the atmospheric pressure. In such a case, because the pressure has been changed, an error would generate when calculating an absolute humidity in the intake air passage2. Thus, by directly measuring a pressure of an intake air flowing through the intake air passage2by the pressure detector44, it is possible to accurately calculate the absolute humidity of an intake air flowing through the intake air passage2. Furthermore, the pressure detected by the pressure detector44may be used as the intake air pressure for the engine system10.

A Japanese patent literature (JP 2010-151795 A) discloses an air flow rate measuring device including a relative humidity sensor, a temperature sensor, and a pressure sensor. However, a sub passage branched in the air flow rate measuring device is used, and an intake air is not directly brought into contact with a sensor, and thus the air flow rate measuring device of the Japanese patent literature is not configured to accurately measure an intake air. Similar to the first embodiment, in the second embodiment, the pressure sensor44is exposed to the inside of the intake air passage2to be in direct contact with an intake air. Therefore, a pressure of an intake air in the intake air passage2can be accurately measured.

A pressure measured by the pressure sensor44can be used as information of an intake air pressure. Thus, it would be more effective when performing advanced control for an engine system. Furthermore, an additional sensor to detect a pressure of an intake air is not necessary for performing such advanced control of the engine system, and as a result, harnesses to the connector terminals and the electric control unit27can be eliminated.

The multi-sensor unit41may be arranged at the rear end46or a center portion47of the sensor module40. The same effects as those of the above-described embodiments can be achieved regardless of the position of the multi-sensor unit41.

The relative humidity sensor42, the temperature sensor43, and the pressure sensor44of the multi-sensor unit41may be arranged at the same position. By setting the sensors42,43,44at the same position, the temperature sensor43can further accurately measure the temperature at the relative humidity sensor42because the temperature sensor43is close to the relative humidity sensor42. The similar effects can be applied to the pressure sensor44.

The multi-sensor unit41and the signal processing circuit55can be arranged at the same position. By setting the same position, the size of the sensor module can be further reduced, leading to weight saving or low costs due to a decrease in material costs.

Three module connectors50can be used. The power terminal51and the ground terminal52are used while eliminating one of the output terminals53,54. Using the SENT protocol, outputs of physical quantities (an absolute humidity, a temperature, a pressure) detected by the multi-sensor unit41are processed to one signal. Accordingly, in addition to a reduction in the number of the terminals, wiring members such as harnesses can be eliminated, and therefore the configuration can be simplified.

The sensor module40may be integrally formed with the casing7together with the multi-sensor unit41, the signal processing circuit55, and the module connector50when resin-molding the casing7. Accordingly, molding process can be simplified, and thereby leading to a reduction in costs.