Abstract:
Improvement in a mass air flow meter having a static pressure manifold disposed upstream from an air flow path for sample air and capable of accumulating a volume of air therein, the flow path constructed to receive an air flow transducer, the static pressure manifold having an inlet arrangement in communication with the kinematic main air flow traveling through the meter so as to be capable of sensing different static pressures thereof, the static pressure manifold having a single outlet serving as the sole inlet for the sample air to be measured by the air flow transducer, the static pressure of the air accumulated in the static pressure manifold being such that it functions as a resultant average of the different static pressures sensed at its inlet arrangement, the static pressure manifold providing substantial immunity for the meter in respect to turbulent air flow upstream therefrom.

Description:
My invention relates to mass air flow meters of the type shown and described in my prior U.S. Pat. No. 5,048,327 issued Sep. 17, 1991 which I refer to as my “PRO-M-Dot” mass air flow meter. 
    
    
     One object of my present invention is to provide an improved mass air flow meter which is neutral or universal in respect to turbulent air flow caused by air flow devices immediately upstream from the meter such as elbows, remote air cleaners, superchargers, super-chargers with inter-coolers and other such upstream structure that contribute to turbulent air flow. 
     Another object of my invention is to provide a unique and advantageous venturi construction for a mass air flow meter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     By way of a trade name for my new mass air flow meter, I prefer to designate same as the “UNIVER” mass air flow meter. 
     The foregoing objects of my invention and the advantages thereof will become apparent during the course of the following description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is perspective view of my “UNIVER” mass air flow meter viewed so that the exterior housing for the electronic elements therefor can be seen; 
     FIG. 2 is a vertical sectional view thereof; 
     FIG. 3 is top plan view thereof; 
     FIG. 4 is a bottom plan view thereof; 
     FIG. 5 is a front elevational view thereof with parts in section; 
     FIG. 6 is a top plan view of a portion of the structure of FIG. 5 with a portion of the structure thereof removed; 
     FIG. 7 is a fragmentary vertical sectional view similar to that of FIG. 2 of another embodiment of my invention; 
     FIGS. 8A through 8D are respective schematic views of a prior art meter shown having an upstream elbow connected directly thereto in different orientations thereof; 
     FIG. 9 is another schematic view of said prior art meter further illustrating such different orientations of such upstream elbow; 
     FIG. 10 is a graph showing the effect upon such prior art mass air flow meter at the different orientations of said elbow; and 
     FIG. 11 is a similar graph showing the effect upon my “UNIVER” mass air flow meter of a directly connected elbow at the same orientations thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings in greater detail and particularly to FIGS. 1-6, reference numeral  300  designates my “UNIVER” mass air flow meter which will be described as in use for internal combustion engines though same has wider uses. The mass air flow meter  300  has a main body  310 , in cylindrical form in the instance, through which the main air flow travels on its way to the intake manifold of such an engine. One or both ends of the body  310  may be provided with flanges (not shown) for connecting to external ducting (not shown). The venturi for mass air flow meter  300  is provided by a venturi member  318  of shorter axial length and smaller diameter than that of the body  310 . The venturi member  318  has two axially spaced apart maximum outside diameter (O.D.) portions  314  and  316  thereof forming respective mounting surfaces therefor. The O.D. portions  314  and  316  each have a diameter substantially equal to the inside diameter (I.D.) of the body  310  so that the venturi member  318  can be disposed inside of the body  310  and be made fast thereto by any suitable means known in the art. For example, the O.D. portions  314  and  316  can be made slightly larger in diameter than the I.D. of the body  310  so that the latter must be heated to expand it circumferentially in order to insert the venturi member  318  thereinto. The body  310  can then be cooled while the venturi member  318  is correctly positioned and held stationary inside thereof during such cooling to contract the body  310  circumferentially, whereby to bond it to the venturi member  318  by hoop strength. 
     The venturi member  318  is necked-down as shown to form a minimum I.D. portion thereof where it is provided with flow restriction means in the form of equally circumferentially spaced apart slits  320  through the wall thickness thereof. In the instance, the through-slits  320  are 35 thousandths of an inch in axial length though these may vary from 20 to 50 thousandths of an inch depending upon the particular application. There are three such slits  320  of approximately 105 degrees in circumference each in the instance. Two of the three remaining wall portions of the venturi member  318  (each of which is 15 degrees in circumference) are shown at the throat of the venturi and indicated at  322 . 
     The air-flow surface of the venturi member  318  is formed, as shown, into a convergent air foil  315  above the venturi throat (where said flow restriction means  320  are located) and into a divergent recovery cone therebelow. The non-air-flow surface of the venturi member  318  forms, with the I.D. wall of the body  310 , an axially extending cavity  319  between its opposite ends  314  and  316  where these bear against the I.D. of the body  310 , as shown and described above. Such annular cavity  319  serves as a collection chamber as will be mentioned below. 
     Upstream from the venturi  318 , a static pressure manifold  324  is provided which has a sole outlet therefor serving as the sole inlet for the sample tube  328 . In the instance, the manifold  324  is an annular chamber having, as an inside wall thereof, a portion of the body  310 . The outside wall of the manifold  324  is designated  340 , the bottom wall or floor thereof  342  and the top wall or roof thereof  344 . The inlet for the manifold  324  is in the form of a plurality of circumferentially aligned equally spaced apart through-apertures  326  extending through the wall thickness of the body  310 . The axes of the apertures  326  are perpendicular to the axis of the main body  310  in order to correctly sense the static pressure of the kinematic air flow traveling through the body  310  toward the venturi. In the instance, the apertures  326  are eight in number and, for the 8 inch nominal size meter shown, each is approximately ¼ inch in diameter. For a 3 inch nominal size meter, the apertures  326  would still be eight in number, but approximately ⅛ inch in diameter. The static pressure of the sample air flow path through the sample tube  328  is thus controlled by the static pressure of the air accumulated in the manifold  324  which, in turn, produces a resultant average of the plurality of individual static pressures sensed at the apertures  326  (of the kinematic air flow traveling through the body  310  toward the venturi  318 ). A dam  325  is provided at the inlet  327  to surround same which upstands from the floor  342  of the manifold  324 , as shown, for damming that portion of the air mass which hugs said manifold floor  342  while moving into the inlet  327 . Thus, the air entering the inlet  327  of the sample tube  328  is more axially directed and produces less noise in the signal output than without such damming. The top wall of the dam  325  is formed with a convergent taper, as shown, to assist moving the dammed air into the inlet  327  of the sample tube  328 . The sample tube  328  is formed in an exterior mounting structure  329  which is fastened by well known means to the outside wall of the body  310  beneath the manifold  324 , as shown. The sample tube  328  is provided with a taper, as shown, which decreases in diameter in the direction of the air flow therethrough. Slightly upstream from the exit end of the sample tube  328 , the mounting structure  329  is counterbored, as at  332 , to receive and hold therein two sensing elements (not shown), as is well known in the art. One is an air flow sensing element and the other an ambient temperature sensing element which are both housed in an electrically insulated holder  334  which also houses a prior art signal amplifier (not shown). Projecting laterally from the holder  334  is an electrical connector  334 a for supplying electrical power to said elements and amplifier and for serving as an electrical connection for the signal out from said amplifier (to the engine process controller which meters fuel to the engine). The holder  334  is made fast to the mounting structure  329  externally thereof by well known means so that the sensing elements therein protrude through said counterbore  332  into the interior of the sample tube  328  to carry out their respective sensing functions, as is well known in the art. A transverse expansion chamber  330  is provided at the outlet of the sample tube  328  which is greater in cross-section than that of the largest cross-section of the sample tube  328  to allow for immediate expansion for the sample air flow exiting from the sample tube  328 . Downstream from the expansion chamber  330  is the aforementioned annular collection chamber  319  surrounding the flow restriction means  320  which chamber  319  is of greater volume than that of the sample tube  328  and the expansion chamber  330  combined. The collecting chamber  319  accumulates the sample air flow transferred from the expansion chamber  330  and distributes it substantially equally to the plurality of flow restriction means  320 . 
     Referring now to FIG. 7, the embodiment of my “UNIVER” mass air flow meter shown therein is designated  400  which has a main hollow body  410 . The venturi (not shown) for the mass air flow meter  400  is identical to the venturi  318  previously described. Upstream from such venturi  318  (not shown), the body  410  is provided with a static pressure manifold  424  having a sole outlet which serves as the sole inlet  427  for the sample tube  428 . As in the prior embodiment, the manifold  424  is an annular chamber having as an inside wall thereof a portion of the body  410 . The outside wall of the manifold  424  is designated  440 , the bottom wall or floor thereof  442 , and the top wall or roof thereof  444 . The sole inlet for the manifold  424  is a 360 degree circumferential slit  426  through the wall thickness of the body  410  which divides the latter into two separate portions thereof. The axial length of the through-slit  426  can vary from approximately 50 thousandths of an inch to ¼ of an inch depending upon the size of the mass air flow meter  400 . The larger the size of my UNIVER mass air flow meter, the smaller is the axial length of the through-slit  426 . In the instance, for the 8 inch nominal size meter shown, the axial length of the through-slit  426  is 90 thousandths of an inch. For a 3 inch nominal size meter, the through-slit  426  is ⅕ of an inch in axial length. For the same reason as in the prior embodiment, the axis of the through-slit  426  is perpendicular to the axis of the body  310 . It is essential that the portion of the body  410  above the through-slit  426  and the portion below have matching annular cross-sections and that they be aligned axially of each other (so that the two portions of the body  410  have no radial offset between them). The i static pressure of the sample air entering the sample tube  428  is thus controlled by the static pressure of the air accumulated in the manifold  424  which, in turn, produces a resultant average of the plurality of individual static pressures sensed through the slit  426  [of the kinematic air flow traveling toward the venturi  318  (not shown)]. As in the prior embodiment, a dam  425  having a convergently tapered top wall, as shown, is provided at the inlet  427  to surround same which dam  425  upstands from the floor  442  of the manifold  424  for damming that portion of the air mass which hugs said manifold floor  442  while moving into the inlet  427 . The sample tube  428  is formed in a mounting structure  429  with a taper, as shown (decreasing diameter in the direction of the air flow therethrough), the same as for the sample tube  328  and mounting structure  329 . As in the prior embodiment  300 , a transverse expansion cavity (not shown) is provided at the outlet of the sample tube  428  to allow for expansion for the sample air flow exiting from the sample tube  328 . Immediately downstream from the expansion chamber is a collecting chamber (not shown) provided by a venturi member (not shown) identical to the venturi member  318 . In those uncommon instances where the mass air flow meter  400  is not connected into an air intake system, but is used with a free air inlet, same can be provided in the form of an inlet air horn  411  which attaches to the body  410  by well known means. The horn  411  is provided with a divergent air surface structure, as shown. The downstream cross section of the air horn  411  should match that of the upstream end of the body  410 , as shown. 
     In operation of my UNIVER mass air flow meter  300 , the air accumulated in the manifold  324  has a resultant static pressure, as mentioned, from averaging of the plurality of static pressures of the kinematic flow through the body  310  sensed at the apertures  326 . Said manifold  324  feeds the inlet  327  of the sample tube  328 . As is well known, the maximum vacuum is created at the throat of the venturi (where the flow restriction means  320  are located) to produce maximum draw of the air flowing through the sample tube  328 . The sample air flow exiting from the sample tube  328  enters the expansion chamber  330  to insure no back pressure for such flow of sample air through the sample tube  328 . The sample air flow exiting from the expansion chamber  330  enters the collecting chamber to likewise insure no back pressure for such sample air flow and to accumulate and distribute such sample air flow substantially equally to the flow restriction means  320 . 
     As mentioned, the major advantage of my UNIVER mass air flow meter is its immunity in respect to turbulent air flow caused by upstream elbows and the like. Virtually the same output for an elbow immediately in front of the meter is realized as with an ideal upstream inlet condition for the particular engine as discussed below. Reference is made to FIGS. 8-11 wherein FIGS. 8A through 8D are front elevation views of a typical prior art meter PA showing the electrically insulated holder H affixed to the front face thereof, as is usual. The prior art meter PA has affixed thereto an elbow E at four different orientations therefor as shown in FIGS. 8A through 8D, respectively, so that the inlet air flow for said meter PA enters same from four different directions (corresponding to 0, 90, 180 and 270 degrees) as illustrated in FIG. 9, namely, at the respective locations A, B C and D therein. As is well known in the art, most such meters have their sample tubes affixed internally close by an I.D. wall of t h e main body of the mass air flow meter so as to be laterally offset from the center of the main flow path through the venturi, as shown in FIG. 9 for the prior art meter PA and for the sample tube therefor s h o w n and indicated at ST. In the case of my UNIVER meter, the sample t u b e  328  is likewise laterally offset, but, as has been described and shown, is disposed externally of the main body  310  of the mass air flow meter  300  and so as to be fed with air exclusively from that which accumulates within the static pressure manifold  324 . The sample tube  328 , in such instance, receives a representative flow of the intake air flow which is both repeatable and reliable no matter that it is laterally offset. My UNIVER meter thus functions as though the air intake system is near an ideal upstream configuration for air flow devices irrespective of necessarily crowded conditions in engine compartments. To duplicate the function of my UNIVER meter, the upstream configuration would have to be near ideal conditions meaning that such flow is established by a long straight path (of at least ten times the diameter of the meter body). In such instance, the air flow takes on a centered parabolic flow pattern. In the case of prior art air flow meters, this near ideal condition can never be realized because most air intake systems need to closely couple elbows to the mass air flow meter inlet for connecting to other upstream devices within the engine compartment. An elbow immediately in front of the air meter is quite common though it represents a worst case scenario because it causes the inlet air to pack against the far side of the closely coupled elbow. In prior art meters this condition adversely affects their sensing accuracy so much so that it is necessary to separately calibrate the meter for that particular air intake system. The manufacturer has to carry separate part numbers for each air intake system that has to be calibrated, whereas with my UNIVER meter same is universal for all air intake systems. For the after market, where meters are replaced in ageing vehicles, the number of calibrations (and separate part numbers) required will greatly be reduced. In the case of my UNIVER mass air flow meter, the aforementioned near ideal condition can be realized in actual effect in spite of any and all turbulent air flow caused by most air intake systems that need to closely couple elbows thereto (to my UNIVER mass air flow meter inlet) for connecting to other upstream devices within the engine compartment. This is due to the function of the static pressure manifold  324  which accumulates therein the air source for the sample air tube  328  to insure the aforementioned repeatable and reliable represenative sample air flow irrespective of the turbulence of the actually encountered upstream air flow profiles. 
     FIG. 10 illustrates flow curves (A through D, respectively) of the prior art meter PA in the four different positions of the elbow E (positions A through D of FIG.  9 ). The four curves A through D represent voltage response outputs (at the voltage amplifier) versus absolute air flow in kilograms per hour (National Bureau of Standards specifications for certified mass air flow). The curves A through D are different from each other over the whole range of flow of the meter PA. In most cases, this difference is as much as 40% in output voltage values, but can be as much as 60%. 
     FIG. 11 shows the results with my “UNIVER” meter  300  which, for each of the four orientations of the same elbow E (locations A through D in FIG.  9 ), yields but a single curve (labeled A-D) wherein the voltage response outputs are substantially the same (i.e., differing from each other by no more than 3% to 5%) over the whole range thereof (of the meter  300 ). Comparable results were realized with the meter  400 . 
     It will thus be seen that there has been provided by my invention improvements in a mass air flow meter in which the objects hereinabove set forth, together with many thoroughly practical advantages, have been successfully achieved. While preferred embodiments of my invention have been shown and described, it is to be understood that variations and changes may be resorted to without departing from the spirit of my invention as defined by the appended claims.