Abstract:
A mass fluid flow sensor for determining the amount of fluid inducted into an internal combustion engine, for example, is disclosed. The mass fluid flow sensor includes an external intake fluid temperature element which improves the accuracy of the mass fluid reading. An external cold wire element is further provided which improves response time. The mass fluid flow sensor has an improved aerodynamic design which provides a lower system pressure drop. A molded one-piece isolated jet nozzle having a hot element disposed therein is included in a fluid sampling portion. The fluid sampling portion has a tubular sampling channel, wherein the sampling channel has one bend having a constant bend radius. Consequently, an improved lower internal flow passage pressure drop is achieved. Additionally, an improved signal to noise ratio, as well as a larger dynamic range is an advantageous consequence of the present invention. A three surface contact seal is provided between the sensor housing and an intake duct to further enhance the vibrational characteristics of the sensor.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to devices and methods for measuring the mass of a fluid flowing in a duct.  
         BACKGROUND OF THE INVENTION  
         [0002]    Internal combustion engines today include electronic controls to provide optimal engine operation. Typically, the electronic control systems include a primary control unit for processing control algorithms and a variety of sensors for providing control signals to the primary control unit. One critically important sensor for achieving optimal engine control is a mass fluid flow sensor for measuring air intake into the internal combustion engine.  
           [0003]    It is critical that the mass fluid flow measurement is accurate in order to provide optimal engine operation. One significant problem affecting the mass fluid flow measurement, is reverse flow or back flow in the direction opposite of fluid intake. Typically, mass fluid flow sensors detect the flow of air in both the forward and reverse directions relative to air intake, therefore reverse flow causes an inaccurate mass fluid flow reading.  
           [0004]    Prior art mass fluid/air flow devices have attempted to address this problem by providing mass air flow sensor configured as disclosed in U.S. Pat. No. 5,556,340 issued to Clowater et al. In Clowater, a mass air flow sensor having a U-shaped air passage and a longitudinally converging elliptical inlet configuration is disclosed, and hereby incorporated by reference. This configuration increased measurement efficiency and reduced the effect of back flow on the measurement of air flow into the internal combustion engine. Further, such a configuration produces advantageously low signal to noise ratio, as well as high velocity across the mass fluid flow sensor element.  
           [0005]    While prior art mass fluid flow sensors, such as the one disclosed in Clowater, significantly improved the accuracy of the mass fluid flow measurement. Improvements are still needed to address other problems.  
           [0006]    For example, it would be advantageous to provide a mass fluid/air flow sensor having an improved housing configuration. The improved housing should provide enhanced structural stability, be able to withstand harsh vibration environments, and reduce manufacturing complexity, for example.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    In an embodiment of the present invention, a mass fluid flow sensor is provided for determining the amount of air inducted into an internal combustion engine, in accordance with the present invention. The mass fluid flow sensor of the present invention includes an external intake air temperature element which improves the accuracy of the mass air reading. An external cold wire element is further provided which improves response time. The mass fluid flow sensor of the present invention has an improved aerodynamic design which provides a lower system pressure drop.  
           [0008]    Moreover, a molded one-piece isolated jet nozzle having a hot element disposed therein is provided in a tubular flow passage of the sampling portion of the housing. Consequently, an improved lower internal flow passage pressure drop is achieved. Additionally, an improved signal to noise ratio, as well as a larger dynamic range is an advantageous consequence of the present invention. The present invention further provides improved electromagnetic interference performance.  
           [0009]    In an embodiment of the present invention, a mass fluid flow sensor having a circular opening or inlet of the nozzle is provided.  
           [0010]    In another embodiment of the present invention, control electronics are located in a longitudinally extending section of the mass fluid flow sensor housing above the sampling portion. Thus, the present invention provides an integrated circuit cavity and sampling portion in one package.  
           [0011]    In another aspect of the present invention, a U-shaped flow passage is provided having one constant radius bend r for capturing a sample of the intake air.  
           [0012]    In yet another embodiment of the present invention, an outlet of the U-shaped flow passage is provided to allow the fluid to exit and flow out of the bottom of the flow passage, as well as, the sides of the housing.  
           [0013]    In yet another embodiment of the present invention, a measuring element is located within the flow passage at the exit or outlet of the jet nozzle, in accordance with the present invention.  
           [0014]    In yet another aspect of the present invention, the measuring element is centered at the exit of the converging nozzle.  
           [0015]    In still another embodiment of the present invention, the control electronics are located adjacent the flow passage within the circuit cavity.  
           [0016]    Further objects, features and advantages of the invention will become apparent from consideration of the following description and the appended claims when taken in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is an exploded view of a mass fluid flow sensor in accordance with the present invention;  
         [0018]    [0018]FIG. 2 is a perspective view of a mass fluid flow housing in accordance with the present invention;  
         [0019]    [0019]FIG. 3 is a perspective view of a mass fluid flow housing cover, in accordance with the present invention;  
         [0020]    [0020]FIG. 4 a  is an inside perspective view of a mass fluid flow housing cover, in accordance with the present invention;  
         [0021]    [0021]FIG. 4 b  is an outside perspective view of the housing with the housing cover installed thereon, in accordance with the present invention;  
         [0022]    [0022]FIG. 4 c  is a perspective view of the housing with the housing cover installed thereon, in accordance with the present invention;  
         [0023]    [0023]FIG. 5 is a perspective inside view of an electronics cover for a mass fluid flow sensor, in accordance with the present invention;  
         [0024]    [0024]FIG. 6 is an outside view of an electronics cover of a mass fluid flow sensor, in accordance with the present invention;  
         [0025]    [0025]FIG. 7 a  is a fully assembled perspective view of a mass fluid flow sensor in accordance with the present invention;  
         [0026]    [0026]FIG. 7 b  is a cross-sectional view through the mass fluid flow sensor as indicated in FIG. 7 a  in accordance with the present invention;  
         [0027]    [0027]FIG. 8 is cross-sectional view through an automotive fluid intake manifold and further illustrated in exemplary location of the mass fluid flow sensor, in accordance with the present invention;  
         [0028]    [0028]FIGS. 9 a - 9   d  are perspective and cross-sectional views through an alternate embodiment of a mass fluid flow sensor, in accordance with the present invention;  
         [0029]    [0029]FIG. 9 e  is a computational fluid dynamics diagram illustrating the fluid flow direction and velocity through the mass fluid flow sensor;  
         [0030]    [0030]FIG. 10 is a perspective view of the mass fluid flow sensor having an improved sensor housing, in accordance with the present invention;  
         [0031]    [0031]FIG. 11 a  is a perspective view of the mass fluid flow sensor and further illustrating the mounting configuration of the present invention;  
         [0032]    [0032]FIG. 11 b  is a cross-sectional view through the mass fluid flow sensor and the duct interface of the fluid carrying duct illustrating a three surface contact seal, in accordance with the present invention;  
         [0033]    [0033]FIG. 12 is a cross-sectional view of the sensor housing and the heat sink cover, in accordance with the present invention; and  
         [0034]    [0034]FIG. 13 is a perspective magnified view of the nozzle exit and heating element disposed in the housing, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    Referring now to FIGS. 1 and 2, exploded and perspective views of a mass fluid flow sensor  10  for calculating the amount of fluid flowing in a duct is illustrated, in accordance with the present invention. One application or use for sensor  10  is for measuring the amount of air inducted into an internal combustion engine (not shown). However, the present invention contemplates other uses and application for sensor  10 . For example, sensor  10  may be used to calculate the amount of fluid (other than air) flowing through a duct (other than an air intake duct of an internal combustion engine). Mass fluid flow sensor  10  includes a housing  12 , housing cover  14 , a secondary housing cover  16 , an electronics cover  18 , and a gasket  20 .  
         [0036]    Housing  12  includes an integral connector  30  having connector terminals (not shown) that are in electrical communication with engine operation control electronics external to mass fluid flow sensor  10  and in electrical communication with a circuit module  32  disposed within a central housing portion  34 . Adjacent to central housing portion  34 , housing  12  further provides an integrally attached fluid sampling portion  36 . Fluid sampling portion  36  includes an inlet  38  that opens into a nozzle  39 . Nozzle  39  communicates with a substantially U-shaped flow passage  40 . U-shaped flow passage  40  terminates at an outlet  42 .  
         [0037]    Nozzle  39  has, generally, a jet nozzle configuration or shape. As will be further illustrated and described, nozzle  39  is defined by a generally circular opening or inlet  38  that meets longitudinally converging elliptical side surfaces (as shown in FIG. 7 b ). The longitudinally converging elliptical side surfaces of the nozzle create a relatively high pressure at an exit  41  of nozzle  39 . Further, the jet nozzle configuration of nozzle  39  creates a critical area  43  located at exit  41  having a uniform fluid flow velocity across the critical area. This critical area created by the nozzle provides enhanced fluid flow detection and measurement as will be described hereinafter. To further enhance the flow of fluid through passage  40  a wedge deflector  45  is positioned on an end of housing  12  upstream of outlet  42 . Wedge deflector  45  has a surface that is tilted to create an advantageously low pressure area adjacent outlet  42 . If the angle of the surface of deflector  45  (indicated by the letter α in FIG. 7 b ) is too small with respect to the direction of fluid flow an insufficient pressure drop is created at outlet  42 . Conversely, if the angle of the surface of deflector  45  is too large with respect to the direction of fluid flow an insufficient pressure drop is created at outlet  42 . Preferably, the angle a of the surface of deflector  45  is between 47° and 60° with respect to a horizontal line.  
         [0038]    As illustrated in FIG. 2, a plurality of resistive elements are operatively disposed and supported by housing  12  and are in electrical communication with circuit module  32  via electrical conductors, such as integrally molded leads or terminals. The resistive elements include a hot wire element  44 , a cold wire element  46  and an internal fluid temperature (IAT) element  48 . Generally, these elements change resistance as a function of temperature.  
         [0039]    Circuit module  32  senses a fluid, such as, air flowing through passage  40  by monitoring the power dissipated by the elements. Circuit module  32  may be a single integrated circuit chip or a substrate having discrete, as well as, integrated circuits mounted thereon. The sensed resistance change in the elements is converted to an output signal that is received by the electronic engine control system (not shown). Typically, the electronic engine control system regulates the quantity of fuel injected into the engine by controlling the air to fuel ratio.  
         [0040]    The IAT or element  48  is generally a thermistor or similar device. Element  48  is located on housing  12  to insure an accurate reading of the temperature of the air charge during the induction cycle of the internal combustion engine. As shown in FIG. 2, element  48  is located, preferably, external of passage  40  to minimize the fluid heating effects caused by the heat dissipation from hot element  44 .  
         [0041]    In a preferred embodiment of the present invention, a fluid flow sensor  10  is provided having elements  44  and  46  made of platinum wire wound resistors. Generally, these elements have a positive temperature coefficient. Thus, any resistive changes in the elements will correspond with a temperature change in the same direction. That is, if the temperature increases, the resistance will increase, and if the temperature decreases, the resistance will decrease. Preferably, hot element  44  is located at exit  41  of nozzle  39  and within the critical area  43 . The location of the hot element within the critical area insures that fluid, having a uniform velocity profile, flows over the hot element causing heat to dissipate from the entire surface of the element. Thus, the present invention provides enhanced fluid flow detection.  
         [0042]    In an embodiment of the present invention, hot element  44  may for example have a resistance of 20 Ohms at 21.1° C. Thus, if the temperature increases by +17.2° C. the resistance of the hot wire will increase by approximately 0.025 Ohms. The hot element  44  is used primarily for detecting the velocity of the fluid flowing through passage  40  from which the mass of fluid flowing through passage  40  may be derived.  
         [0043]    The cold wire element  46 , may for example have a nominal resistance of 500 Ohms at 21.1 ° C. If the temperature of the cold wire is increase by ±17.2° C. the resistance of cold wire will increase by approximately 0.5 Ohms. The primary purpose of the cold wire element  46  is to provide temperature correction.  
         [0044]    In operation hot wire element  44  is held at approximately 200° C. above the ambient temperature. This is accomplished by placing the hot wire element in a voltage divider circuit. With reference to FIG. 3, an exemplary voltage divider circuit  500  for fixing hot wire element  44  at a desired constant resistance and temperature is illustrated, in accordance with the present invention. In an embodiment of the present invention circuit  500  is disposed in integrated circuit  32 , along with other control circuitry. Exemplary circuit  500  includes two voltage divider networks  502  and  504  in communication with an operational amplifier  506 . Voltage divider network  502  generally has two 500 Ohm resistors  508  and  510  which form a 50% voltage divider network and force plus pin  512  of op-amp  506  to half the output voltage on line  518 . The other voltage divider network  504  includes generally a 25 Ohm resistor  514  in series with the hot wire element  44 . The minus pin  516  of op-amp  506  is connected between resistor  514  and hot wire element  44 . Thus the ratio of this network starts with a ratio of 20 Ohms to 45 Ohms, so minus pin  516  is forced to 20/45 th  of the output voltage. For example, the op-amps output voltage on output line  518  will increase if the voltage on plus pin  512  is greater than the voltage on the minus pin  516 . Likewise, the output voltage on line  518  will decrease if the voltage on plus pin  512  is less than the voltage on minus pin  516 . Accordingly, the op-amp&#39;s output voltage on line  518  will increase or decrease by a voltage amount necessary to force the voltage on plus pin  512  to equal the voltage on minus pin  516 .  
         [0045]    Since resistor network  502  provides a greater voltage on plus pin  512  that is 50% of the output voltage as compared to 44% on minus pin  516 , the op-amps output voltage will increase on line  518 . As the voltage increases, the power dissipated by the hot wire element  44  causes an increase in resistance of the hot element. It takes approximately one quarter watt of power in still air to increase the temperature of hot element  44  by 93.3° C. A 93.3° C. increase in temperature raises hot wire element  44 &#39;s resistance by 5 Ohms. The ratio of the hot wire resistance at the increased temperature to the total resistance in resistor network  504  forms a 50% voltage divider network. Thus, the plus and minus pins  512  and  516  of op-amp  506  are at the same voltage since both networks  502  and  504  form 50% voltage divider networks. Thus the temperature of hot wire element  44  is forced to approximately 132.2° C.  
         [0046]    The circuit  500  provides an output on line  518  to an electronic engine control module (not shown) which determines the proper air fuel ratio for optimal engine operation, as well known in the art. Since it takes a quarter watt as disclosed above for voltages on plus and minus pins  512  and  516  to be equal, the voltage across the hot wire element  44  and resistor  514  can be calculated using the equation: Power=(voltage) 2 /resistance and then solving for voltage (V): V=(power×resistance) 1/2  or (0.25×25) 1/2 . Since the voltage across resistors in series add the nominal output of the circuit is 5 volts for no air flow. Obviously, more circuitry would be used to level shift and amplify the output of the circuit  500 .  
         [0047]    As air flows over hot wire element  44 , power in the form of heat is transferred from the hot wire element to the air. Heat removed from the hot wire element  44  causes the resistance of element  44  to decrease. Decreasing resistance causes the voltage applied to the minus pin  516  to decrease. Accordingly, the output voltage on line  518  would increase causing more power to be dissipated by the hot wire element  44 . Thus, the increase in power dissipated by the hot wire element causes the temperature of element  44  to increase and return to 132.2° C. When this temperature is reached, the voltage on pins  512  and  516  of op-amp  506  will be at equilibrium.  
         [0048]    Accordingly, since the circuit regulates the resistance of hot wire element  44  the output of the circuit on line  518  is proportional to the square root of the power removed from the hot wire times two minus 5 volts, for example. Nominal power dissipated by the hot wire element  44  is one-quarter of a watt which is the amount of power needed to keep the hot wire element  44  at 132.2° C. Any heat removed from the hot wire is replaced by applying more power to element  44 . Resistance of the hot wire is regulated to 25 Ohm thus resistance is considered to be constant. Power removed equals the power applied minus the amount needed to maintain the hot wire at 132.2° C. Solving the power formula for voltage: v=(power×resistance)½, any increase in power applied to the hot wire element  44  is also applied to the 25 Ohm resistor. Therefore, the voltage necessary to compensate for power removed from element  44  is doubled.  
         [0049]    For proper operation of sensor  10 , the temperature of hot wire element  44  needs to be maintained at 200° C. above ambient temperature. If the ambient temperature is constant there is no need for temperature correction. That is, a constant difference in temperature guarantees the same amount of power will be removed from the hot wire element  44  for a given air flow. However, when a fluid flow sensor is placed in an automobile (as shown in FIG. 8), ambient air temperature is not constant. Typically, sensor  10  will be exposed to temperatures below freezing and above boiling. Thus, air flow temperatures lower than expected will cause a larger than desired output voltage and temperatures higher than expected will cause a lower than desired output voltage.  
         [0050]    The present invention provides temperature correction to compensate for the variable ambient temperature environment present in an automobile. Temperature correction is achieved through the use of the cold wire element  46 . The cold wire element  46  is placed in resistor network  502  in place of resistor  510 , as illustrated in FIG. 3. Circuit  500  uses cold wire element  46  for temperature compensation. Element  46  is supported by housing  12  and is placed in the air stream outside of flow passage  40 . Placing cold wire element  46  in the air stream allows the circuit to quickly respond to changes in the ambient air temperature. The temperature of cold wire element  46  will follow the temperature changes of the incoming air. Since the resistance of the cold wire element (500 Ohms) is relatively large compared to the voltage drop across the element, the power dissipated is very small. For example, at 21.1° C. the resistance of element  46  is 500 Ohms with a voltage drop of 2.5 volts. Moreover, the power dissipated by element  46  is 0.0125 watts which results in a temperature increase of about +12.2° C.  
         [0051]    Accordingly, the resistance of the cold wire element  46  would increase by 5 Ohms and resistor network  502  resistance ratio would change. For example, the voltage applied to plus pins  512  would equal 505/1005 or 50.25% of the output voltage on line  518 . In turn resistor network  504  will also have to form a ratio equal to 50.25% of the output voltage. Thus, to form the same ratio, the hot wire resistance would need to be maintained at 25.25 Ohm to develop the same resistance ratio of 50.25% thus the hot wire element  44  will be maintained at 200° C. above the cold wire element 46 or 137.7° C. if the ambient temperature is 21.1° C. Cold wire element  46  is +12.2° C. above the ambient temperature of 21.1° C. Thus, the temperature difference that is necessary for handling environmental extremes is maintained. The nominal output of this circuit is still five volts. It takes ¼ watt of power to raise the temperature of the hot wire element by 93.3° C. Solving the power equation for current (i), i=(power/resistance) 1/2 . Thus, current in the hot wire network equals 0.099503 amps ((0.25/25) 1/2 ). The output voltage is then (0.099503×50.25), which is approximately five volts. The circuit in FIG. 3 can dynamically adjust to ambient air temperature changes because the change in the cold wire network is directly proportional to the properties of the hot wire network.  
         [0052]    The values for resistance and changes in resistance are solely for explanatory purposes and other values certainly may be used.  
         [0053]    Referring now to FIGS. 4 a  and  4   b , a perspective view of housing cover  14  is further illustrated, in accordance with the present invention. FIG. 4 a  is an inside view of housing cover  14  and FIG. 4 b  is an outside view of housing cover  14 . Housing cover  14  is fixedly joined to housing  12  (as shown in FIG. 4 c ) along a protruding ridge  60  and  62 . Ridge  60  protrudes from an inside surface  64  of housing cover  14  and matingly seals with channel  50  disposed on an inside surface  52  of housing  12 . Ridge  62 , protruding from an inside surface  64  of housing cover  14 , matingly seals with channel  54  disposed within surface  52  and around the perimeter of flow passage  40 , thus creating an enclosed and sealed flow passage  40 . Housing cover  14  further includes a window aperture  66  for providing access, during manufacture, to integrated circuit  32  (as shown in FIG. 4 c ). For example, window aperture  66  provides access to integrated circuit  32  during the calibration step in the manufacturing process. Further, as shown in FIG. 4 c , integrated circuit  32  is wire bonded using wire bonds to various terminal and/or bonding pads disposed on housing  12 .  
         [0054]    As shown in FIG. 4 b  a channel  68  is provided around a perimeter of window  66  to matingly seal the secondary housing cover  16  to housing cover  14 . Further, a side opening  70  allows air exiting flow passage  40  to flow out of both side surfaces  72  and of cover  14 . A ramped portion  75  is included in surface  72  to funnel and direct air passing over the surface toward cold wire element  46   
         [0055]    A perspective inside view of secondary housing cover  16  is illustrated in FIG. 5. Cover  16  includes a perimeter ridge protrusion  80  which matingly seals with housing cover  14  along the perimeter of window  66  and within channel  68 . Secondary housing cover  16  is substantially flat and maybe constructed of a heat conductive material, such as a metal for dissipating heat generated by integrated circuit  32 . As shown in FIG. 1, secondary housing cover  16  has a generally planar outside surface  84 . After cover  16  is positioned on housing cover  14 , both the cover  14  and the secondary housing cover  16  create a longitudinally extending and generally planar surface to insure minimal disturbance of the air flowing around sensor  10 .  
         [0056]    A perspective inside view of electronics cover  18  is illustrated in FIG. 6. In an embodiment of the present invention integrated circuit  32  is bonded to cover  18  and the resulting circuit and cover assembly is loaded into and matingly seals against housing  12 . Cover  18  has a protruding ridge  83  rising from a surface  85  of cover  18 . Protruding ridge  83  sealingly mates with a corresponding channel (not shown), disposed on housing  12 , to create a weather resistant sensor housing. Preferably, cover  18  functions as a heat sink to draw heat emanating from circuit module  32 . In an embodiment of the present invention, heat sink  18  is made from a metallic material or other material having similar thermal conductive properties.  
         [0057]    A perspective view of a fully assembled mass fluid flow sensor  10  is illustrated in FIG. 7 a , in accordance with the present invention. A flange  90  is integrally formed in housing  12  and includes a plurality of mounting apertures  92  and  94 . Mounting apertures  92  and  94  receive fasteners (not shown) such as screws for securing sensor  10  to a mounting surface. Further, flange  90  has a mating surface  96  for matingly engaging an engine air intake duct  304  (shown in FIG. 8) as will be described below. Gasket  20  is configured to engage a flange ledge or shelf  98 . Gasket  20  is positioned between engine intake duct  304  and flange  90  to provide an air tight seal between mass fluid flow sensor  10  and air intake duct  304 .  
         [0058]    As illustrated in FIG. 7 a , air flows into inlet  38  of mass fluid flow sensor  10  in a direction, as indicated by arrow i, and out of outlet  42  in a direction, as indicated by arrows O. Inlet  38  is generally circular and as illustrated in FIG. 7 b  has a generally elliptical cross-section.  
         [0059]    With specific reference to FIG. 7 b , elliptical surfaces  200  which define the perimeter of inlet  38  and nozzle  39 . Moreover, as shown, elliptical surfaces  200  converge along a longitudinal axis  202 , creating an inlet and nozzle having a longitudinally converging elliptical surface. This inlet and nozzle configuration is known as a jet nozzle. Further, it is known that this jet nozzle configuration creates a critical area, at the exit of the nozzle, having a uniform fluid flow velocity. As stated above the present invention has improved accuracy as compared to the prior art because, for example, the hot element  44  is located in the critical are and therefore is evenly cooled by incoming fluid.  
         [0060]    Referring now to FIG. 8, an exemplary automotive environment in which a mass fluid flow sensor may be operatively disposed is illustrated, in accordance with the present invention. Typically, an automotive vehicle has an air intake manifold  300  for supplying fresh air to the vehicle&#39;s engine (not shown). Generally, air intake manifold  300  includes a filter  302  for filtering the intake air and extract contaminants from the air drawn into manifold  300 .  
         [0061]    Air intake manifold  300  is typically attached to an air duct  304  for communicating the clean air to the vehicle&#39;s engine. As illustrated, mass fluid flow sensor  10  is positioned and fixedly secured to air duct  304  through an aperture  306  in air duct  304 . Outside air is drawn into intake manifold  300  in a direction indicated by arrow A and flows through manifold  300  as indicated by arrows A′ and A″. When the intake air reaches air duct  304 , a portion of the intake air flows into the mass air flow sensor, as indicated by arrow i, and then out of the mass fluid flow sensor as indicated by arrow o. All of the intake air eventually exits air duct  304  and enters the vehicle&#39;s engine, as indicated by arrow e. Electrical control signals containing information regarding the amount of air flowing through the air duct  304 , derived from measurements and processing carried out on integrated circuit  32 , is communicated to the vehicle&#39;s electronic control systems through a connector  308  and wire harness  310 .  
         [0062]    The present invention contemplates an assembly and/or manufacturing method or process for constructing mass fluid flow sensor  10 . In an initial step the resistive elements are electrically connected to the housing using solder or other like material or other bonding process (i.e. resistance welding). At a next step, the electronics cover  18  and integrated circuit assembly  32  is mounted to the housing  12 , using an adhesive or similar material. At a next step, the housing cover  14  is mated to housing  12  and bonded thereto using an adhesive or similar material. At a next step, the assembly is placed in an oven or other environment suitable for curing the adhesive. At a next step, the integrated circuit  32  is wire bonded to terminals and/or bonding pads on housing  12 . At a next step, the integrated circuit  32  is calibrated and/or adjusted and/or resistors disposed within circuit  32  are trimmed. At a next step, the secondary housing cover  16  is mated to housing  12  and bonded thereto using an adhesive or similar material. At a final step, sensor  10  is tested to insure proper function at different operating states and environmental conditions.  
         [0063]    Referring now to FIGS. 9 a - e , an alternate embodiment of a mass air flow sensor housing  412  is illustrated, in accordance with the present invention. As in the previous embodiments, housing  412  has a connector end  414  having electrical terminals  415  for communicating electrical signals from the mass air flow sensor to external circuitry (not shown), as illustrated in perspective view of FIG. 9 a  and in the cross-sectional view of FIG. 9 b . Connector end  414  further has a flange  416  that enables housing  412  to be mounted to an air duct  304  of an air intake of an engine (see FIG. 8), for example.  
         [0064]    Additionally, housing  412  has a central portion  418  and an air sampling end  424 . Central portion  419  includes an aperture  420  for receiving a circuit module  422 . At air sampling end  424 , an air sampling passage  426  is disposed. Air sampling passage  426  includes an inlet  428 , a sampling channel  430 , and an outlet  432 . Sampling channel  430  is in-molded or integrated into air sampling end  424 . More specifically, sampling channel  430  has two portions a housing portion  430   a  and a housing cover portion  430   b , as shown in FIGS. 9 a  and  9   c . The housing portion  430   a  is in-molded or integrated into housing  412  and housing cover portion  430   b  is in-molded or integrated into housing cover  414 . When the housing cover  414  is bonded to housing  412  the two portions, housing portion  430   a  and housing cover portion  430   b  mate to form a uniform tubular sampling channel  430 .  
         [0065]    To further enhance the flow of fluid through channel  430  a wedge deflector  445  is positioned on an end of housing  412  upstream of outlet  442 . Wedge deflector  445  has a surface that is tilted (with respect to a horizontal) to create an advantageously low pressure area adjacent outlet  432 . If the angle of the surface of deflector  445  (indicated by the letter a in FIG. 9 b ) is too small with respect to the direction of fluid flow an insufficient pressure drop is created at outlet  432 . Conversely, if the angle of the surface of deflector  445  is too large with respect to the direction of fluid flow (and horizontal line h) an insufficient pressure drop is created at outlet  432 . Preferably, the angle α of the surface of deflector  445  is between 47° and 60° with respect to the horizontal line h.  
         [0066]    In a preferred embodiment channel  430  includes an expansion tube portion  431 , a re-directional portion  433  and channel exit portion  435 . Expansion tube portion has a length I e  (see FIG. 9 e ) and extends from the nozzle exit to the entrance of re-directional portion  433 . The re-directional portion  433  is semi-circular in shape and extends from the expansion tube portion to the channel exit portion. Further, re-directional portion  433  has an inner wall having a constant inner radius r l  and an outer wall having a constant outer radius r o  (see FIG. 9 e ). Thus, the present invention provides a sampling channel  430  having reduced turbulent flow.  
         [0067]    Disposed within the fluid sampling passage  426  is a thermal sensor  434 . Thermal sensor  434  is in communication with circuit module  422  for detection and signal processing of electrical signals indicative of a change in power dissipation of thermal sensor  434 . Processed and/or conditioned signals are then communicated through an electrical lead frame to terminals  415  for communication to external circuitry.  
         [0068]    Inlet  428  of fluid sampling passage  426  is configured to have elliptically converging interior surfaces  436  that define a jet nozzle  437 , as shown in FIG. 9 b . Thermal sensor  434  is positioned at an exit  438  of jet nozzle  437 . Again, channel  430  of fluid sampling passage  426  is preferably tubular in shape. Further, the jet nozzle exit  438  has a diameter e that is less than a diameter t of tubular channel  430 , as shown in the partial-expanded view of fluid sampling end  424  of FIG. 9 d . The different diameters of jet nozzle exit  438  and tubular channel  430  create a transitional section  460  at the interface of nozzle exit  438  and channel  430 . A fully annular vortices is created in transitional section  460 . Such a controlled fully annular vortices spins within transitional section  460  creating a fluid bearing  502  which extends circumferentially around the nozzle exit  438  (see FIG. 9 e ). Fluid bearing  502  creates a substantially frictionless area at transitional section  460  that promotes (enhances) fluid flow through sampling channel  430 .  
         [0069]    With specific reference to FIG. 9 e , a computational fluid dynamics diagram indicating the direction and velocity of fluid flowing through channel  430  is illustrated. As shown, fluid enters inlet  428  and the velocity and pressure of the fluid rises as the fluid moves toward nozzle exit  438 . At the transition from the nozzle exit to channel  430  opening the pressure and velocity of the fluid drops dramatically due to the channel diameter t being larger than the diameter e of the nozzle exit (shown in FIG. 9 d ). As previously stated, channel  430  includes expansion tube portion  431  having an expansion tube length I e . The expansion tube has generally straight walls and runs between nozzle exit  438  and an entrance  514  of re-directional portion  433  of channel  430 . The length of the expansion tube is predetermined such that at a maximum fluid flow velocity the fluid contacts or “attaches” to a wall  510  of the expansion tube before reaching an end  512  of expansion tube  431 . The Fluid bearing  502  creates a low pressure at nozzle exit  438 . Thus, fluid is pulled through the nozzle and into the sampling channel  430  to wall  510  of the channel and prevents fluid from re-circulating backward in the channel. Therefore, the present invention has many benefits over the prior art. For example, the present invention has increased dynamic range, such that the mass fluid flow may be determined at very low fluid intake speeds as well as at very high fluid intake speed.  
         [0070]    Referring now to FIGS. 10 and 11 a - b , an alternative sensor housing  600  is illustrated, in accordance with the present invention. Housing  600  includes a connector portion  602 , a mounting portion  604 , a circuit portion  606 , and a fluid flow sampling portion  608 . Connector portion  602  cooperates with a mating connector portion (not shown), in a conventional manner, to produce a secure mechanical as well as electrical connection.  
         [0071]    Mounting portion  604  includes a plurality of mounting apertures  610  for mounting sensor housing  600  to a fluid flow duct  622  (shown in FIG. 11 a ). Further, mounting portion  604  is configured to reduce movement of sensor housing  600  especially in an x-direction where the x-direction is perpendicular to a fluid flow direction fd. To that end, a sealing ledge  612  is provided in mounting portion  604  to receive a gasket  614  (shown in FIG. 11 a ). Gasket  614  seats against a side surface  611  of ledge  612  and an underside surface  616  of mounting portion  604 . Further, when housing  600  is mounted to a duct interface  620  of fluid carrying duct  622 , gasket  614  is compressed against an inclined surface  624  of mounting interface  620 . Thus, a three surface contact seal is achieved where gasket  614  contacts side surfaces  611 , underside surface  616  and inclined surface  624  (as shown in FIG. 11 b ). This three surface contact seal provides enhanced sealing between housing  600  and duct  622  as well as dampen lateral and transverse movement of the housing within the duct. Preferably, inclined surface  624  is inclined at an angle between 40 and 70 degrees with respect to a top surface  626  of mounting interface  620 .  
         [0072]    Housing  600  is mounted to mounting interface  620  through mechanical attachment of mounting portion  604  to mounting interface  620 . For example, by fastening means such as screws or bolts through apertures  610  and mounting interface apertures  628  in mounting interface  620 .  
         [0073]    With continuing reference to FIG. 11 a , improved housing  600  is further illustrated. Improved housing  600  provides ribs and/or gussets  650  at a transition area  652  that connects circuit portion  606  with fluid flow portion  608 . Gussets  650  are configured to reduce torque effects on fluid flow portion  608 . More specifically, gussets  650  are angled toward the mass moment of inertia of housing  600  about a longitudinal axis of the housing. This configuration reduces movement of fluid flow portion  608  with respect to circuit portion  606 . Further, advantageously housing  600  has enhanced virbrational characteristics to reduce twisting or torquing of the circuit portion  606  for example corner ribbing  654  as provided in circuit chamber  656 . Corner ribbing  654  is preferable over square ( 90 ° corners) or radius corners for enhancing the structural stability of the circuit chamber.  
         [0074]    Referring now to FIG. 12, a cross-sectional view through housing  600  is illustrated, in accordance with the present invention. Heat sink cover  700  as illustrated in FIG. 10 is mounted to circuit portion  606  of housing  600 . An inside view of cover  700  is further illustrated in FIG. 11 a  as viewed through circuit chamber  656 . Heat sink cover  700  includes a plurality of ribs/fins  702 . Ribs/fins  702  serve at least two purposes provide enhanced (1) structural stability to the cover and (2) heat dissipation through the cover. Cover  700  mates with housing  600  by the cooperation of a tongue  706  protruding from a peripheral surface  704  of cover  700 . Tongue  706  mates with a groove  708  and is sealed using an epoxy or similar material.  
         [0075]    With respect to assembly, a circuit module or integrated circuit (not shown) is placed adjacent to cover  700  to allow heat buildup in the circuit to dissipate through cover  700  and ribs/fins  702 . Heat sink cover  700  further provides a grounding plane for the circuit module. For this purpose, a grounding post  710  is formed in cover  700 . The circuit module is wire bonded to grounding post  710  to achieve an electrical ground reference.  
         [0076]    Referring now to FIG. 13, an exploded view of fluid flow sampling portion  608  is illustrated, in accordance with the present invention. As previously described, a hot element  800  is mounted at an outlet of the fluid flow nozzle. A pair of hot element posts  802  and  804  are provided on either side of the outlet for mounting wire leads  806  and  808  of hot element  800 . Hot wire posts  802  and  804  facilitate the mounting of hot wire element  800  thereto by providing a flat surface that extends into the fluid flow sampling chamber. Moreover, this mounting scheme does not interfere with fluid bearing  502  shown in FIG. 9 e . Thus, the present housing  600  configuration provides reduced manufacturing complexity, for example.  
         [0077]    The foregoing discussion discloses and describes a preferred embodiment of the invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the true spirit and fair scope of the invention as defined in the following claims.