Abstrict A mass air flow meter having smaller overall external dimensions
than prior devices to facilitate packaging within the engine compartment
of a vehicle. Contributing to this smaller size is the use of an
"inside-out" venturi in which the inside diameter of the
device body is relatively straight and an airfoil shaped body located
in the airflow causes the venturi effect. Advantages of this design
include high signal to noise ratio, lower manufacturing costs and
reduction of bulk.
Claims What I claim is:
1. In a mass air flow meter for internal combustion engines having
a hollow elongated body having a minimum cross-sectional area therein
forming a venturi, a sample duct associated with said elongated
body for receiving a flow of sample air therethrough, said sample
duct being tapered in decreasing area in the direction of the air
flow therethrough, the entire air source for the engine being split
into a main flow path through said elongated body and into a sampling
path through the sample duct, an air flow transducer disposed in
said sample duct near the minimum cross-sectional area thereof,
the flow through the sample duct downstream from said transducer
being accumulated in a collecting chamber and the flow exiting from
the latter passing through flow restriction means and then being
recombined with the main flow of air through said elongated body,
the improvement comprising:
(a) the collecting chamber being formed at the lower end of the
sample duct so as to receive direct in-line flow therefrom;
(b) both the sample duct and the collecting chamber being supported
within the interior of said elongated body centrally coaxially thereof;
(c) the exterior surface of said collecting chamber being an airfoil
surface having a maximum external dimension so as to form, with
the inside cross-sectional area of said elongated body, an inside-out
venturi having a minimum annular cross-sectional throat area;
(d) the principal internal volume of said collecting chamber (for
accumulation of sample air exiting from said sample tube) being
disposed downstream from the location of the minimum throat area;
and
(e) flow restriction means through the wall thickness of the collecting
chamber body at the location of said minimum throat area, said flow
restriction means serving as the outlet for the air accumulated
in said collecting chamber.
2. Improvement in a mass air flow meter for internal combustion
engines as claimed in claim 1 in which the exterior surface of the
collecting chamber (downstream from the location of the inside-out
venturi) is tapered in decreasing cross-sectional dimension (in
the direction of air flow through said elongated body) to enhance
recovery of pressure drop across said mass air flow meter.
3. Improvement in a mass air flow meter for internal combustion
engines as claimed in claim 2 in which the exit end of the flow
meter body extends downstream of the collecting chamber to further
enhance the recovery of pressure drop across said air flow meter.
4. Improvement in a mass air flow meter for internal combustion
engines as claimed in claim 1 in which said elongated body has a
straight taper (in decreasing cross-sectional area in the direction
of air flow therethrough).
5. Improvement in a mass air flow meter for internal combustion
engines as claimed in claim 1 in which the downstream end of the
sample tube is extended downstream of the upstream end of the collecting
chamber and internally thereof to a level below that of the flow
restriction means so as to isolate the flow of air exiting from
the sample tube from that which exits through the flow restriction
means.
6. Improvement in a mass air flow meter for internal combustion
engines as claimed in claim 1 in which the entering end of the sample
duct is disposed upstream from the entering end of said elongated
body to isolate the air entering the sample tube from the turbulence
at the entrance end of said elongated body.
Description By way of a trade name or trade mark for my present invention,
I prefer to describe it as the "ISOV" mass air flow meter.
The principal object of my present invention is to provide a different
embodiment of mass air flow meter than my "Pro-M-Dot"
mass air flow meter, but which has most of the advantages of my
"Pro-M-Dot" mass air flow meter together with additional
advantages including lower manufacturing costs and reduction of
bulk (to facilitate packaging of my "ISOV" mass air flow
meter within the engine compartment of the vehicle).
The foregoing object 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 a perspective view of my "ISOV" mass air flow
meter viewed so that a part of the sensing mechanism therefor is
shown;
FIG. 2 is a central vertical sectional view thereof;
FIG. 3 is a top plan view of the thereof;
FIG. 4 is a plan view thereof; and
FIGS. 5 and 6 are respective horizontal sectional views thereof
taken, respectively, through the lines 5--5 and 6--6 in FIG. 2.
Referring to the drawings in greater detail, my "ISOV"
mass air flow meter shown therein is generally designated 200. Same
has smaller overall external dimension than my prior Pro-M-Dot mass
air flow meter to facilitate packaging of my "ISOV" mass
air flow meter within the engine compartment of a vehicle. (In my
Pro-M-Dot mass air flow meter), the venturi for the main airflow
is provided by the main body thereof being formed to neck down to
a minimum cross sectional area at the level where the flow restriction
means 9 are located. Also the sample tube 12 is disposed laterally
of the path of flow for the main air flow through the meter body
#10. The meter body #10 has means for directly connecting to an
air filter and, preferably , has a bell shaped entrance). In contrast
thereto in my "ISOV" mass air flow meter 200 the venturi
is "inside-out" in that the I.D. of the body 210 is relatively
straight (actually a slight taper is provided which decreases in
cross-sectional area in the direction of air flow therethrough)
while a collecting chamber 208 having an upstream exterior surface
providing an airfoil surface having a maximum exterior dimension
is used to provide an annular cross sectional area 216. The "inside-out"
venturi is located at the level where equally circumferentially
spaced apart flow restriction apertures 209 are formed through the
wall thickness of the collecting chamber 208. The "ISOV"
mass air flow meter 200 does not directly connect with the engine
air filter as is the case within my prior Pro-M-Dot mass air flow
meter. However the "ISOV" mass air flow meter retains
most of the benefits of my "Pro-M-Dot" mass air flow meter
including a high signal to noise ratio and signal averaging via
an R.C. time constant the latter will always have a lower pressure
drop than my "ISOV" meter because of the superior job
it does in capturing entrance air(due to its being directly joined
to an air filter) and on account of its bell shaped entrance and
also because of the unimpeded path it provides for the main air
flow through the main body 210.
The internal cross section of the body 210 is generally cylindrical,
but has a slight internal taper 215 therein. The taper 215 is such
that the internal cross-sectional area of the body 210 decreases
in the direction of the air flow so as to aid in profiling or columnating
the main air flow through the body 210. The latter has a flange
structure 222 at the entrance end thereof for connecting to a conduit
(not shown) which, in turn, is connected to a remote air cleaner
assembly (not shown). Another flange structure 224 is provided at
the exit end of the body 210 for connecting to the entrance end
of an engine throttling device at the entrance end of the intake
vehicle for the vehicle. The tapered sample tube or duct 212 and
the collecting chamber 208 are disposed coaxially centrally in respect
to the longitudinal axis of the body 210. i.e. each is arranged
in a substantially straight line, as shown. The sample tube 212
and the collecting chamber 208 are supported, in the instance shown,
by a multi-leg spider structure 219 (having 3 legs, in this instance)
which, in turn, is supported by and upon the inside wall of the
body 210. One leg of the spider structure is hollowed out, as shown
in FIG. 5 to receive and hold therein both an air flow sensing
element 213 and an electrically insulated holder 214 for the latter.
A prior art signal amplifying and conditioning device 217 is affixed
to the outside wall of the body 210 and is electrically connected
to the flow transducer 213 as is well known in the art. Each leg
of the spider structure 219 is longer in axial length than in circumferential
width as can be seen by comparing FIGS. 2 and 5. The legs of the
spider structure 219 (though not shown herein) are each shaped as
an inverted teardrop (symmetrical in vertical cross-section) to
provide an airfoil surface in respect to the main air flow through
the body 210 so as to minimize air resistance.
Where the upstream end of the collecting chamber 208 joins the
downstream end of the sample duct 212 there is provided a steep
air foil shape, (on the exterior surface of said collecting chamber
208), which as previously mentioned, expands rapidly in diameter
to a maximum at the level where flow restriction apertures 209 are
located to create, with the interior of the body 210 an inside-out
venturi (annular area cross-sectional area) as shown in FIG. 2.
Downstream from the flow restriction apertures 209 the collecting
chamber 208 gradually decreases in diameter (by about 25 degrees
included angle) to provide an "inside-out" recovery cone
220 (annular area cross-section) to reduce the pressure drop across
the mass air flow meter 200. The ratio of the volume of the collecting
chamber 208 to that of the sample tube 212 and to the area of the
flow restriction means 209 is substantially the same as in my "Pro-M-Dot"
mass air flow meter. The maximum vacuum is created at the flow restriction
means (in the form of equally circumferentially spaced apertures
209 formed through the wall of the collecting chamber 208) to produce
maximum draw of the air flowing through the sample duct 212. The
tapered wall of the sample duct 212 is extended downwardly (internally
of the collecting chamber 208) below the level of the flow restriction
means 209 to isolate the flow of air exiting from the sample duct
212 from that which has accumulated in the collection chamber 208
and which exits therefrom outwardly through the flow restriction
means 209.
In this embodiment 200 the ambient temperature reference wire
218 for the flow transducer 213 is disposed on the tapered wall
215 above the hollow spider leg because of the space limitation
of the latter. This is different from the Pro-M-Dot mass air flow
meter in which the ambient temperature reference wire is incorporated
into the electronics of the sensing element 213.
The shape of the collecting chamber 208 below the flow restriction
means 209 is tapered in decreasing cross-sectional dimension (in
the direction of the air flow) to provide an "inside out"
recovery cone to reduce pressure drop across the mass air flow meter
200. It is preferred that the exit end of the body 210 extend below
the end of the collecting chamber 208 by at least 1 diameter (of
the collecting chamber 208; maximum diameter at the level of the
flow restriction apertures 209) to recover pressure drop. It is
preferred that the entering end of the sample duct 212 extend above
the entering end of the body 210 to isolate the former from turbulence
at the mechanical interface for the entering end of the body 210.
Nearly all of the advantages of the "Pro-M-Dot" mass
air flow meter as discussed in my prior patent application Ser.
No. 524581 are realized in my "ISOV" mass air flow meter
including that of signal to noise enhancement of the tapered sample
tube 212 and the low pass filter provided by the collecting chamber
208 and the flow restriction means 209. The descriptions and explanations
of the "Pro-M-Dot" mass air flow meter contained in my
prior patent application Ser. No. 524581 are also applicable to
my "ISOV" mass air flow meter. Likewise, the illustrations
(in FIGS. 12 and 13) of the signal to noise enhancement provided
by the tapered sample tube and the illustrations of the low pass
filter (in FIGS. 10 and 11A through 11D) are also applicable to
my "ISOV" mass air flow meter. |