Abstrict A flow meter for metering the air quantity aspirated by an internal
combustion engine including a metering valve element constructed
as a box-like cylindrical segment pivotably mounted in a flow tube
of the engine. The valve element has a radial transverse wall oriented
transversely relative to the direction of the air stream in the
flow tube, side walls oriented parallel relative to the direction
of the air stream and a curved cylinder wall connected to the radial
transverse wall and the side walls. The transverse, side and curved
cylinder walls define a recess which opens in a direction opposing
the direction of the air stream. The flow meter thus constructed
possesses the advantage of producing a nearly linear characteristic
curve.
Claims What is claimed is:
1. A flow meter for metering the air quantity aspirated by an internal
combustion engine through an air flow tube, the flow tube defining
an air stream which is directed as the aspirated air quantity into
the engine comprising:
(a) a metering valve element constructed as a box-like cylindrical
segment pivotably mounted in the flow tube in opposition to a restoring
force and transversely relative to the direction of the air stream;
and
(b) means connected to the valve element for providing the restoring
force to the valve element, and wherein:
(i) the box-like cylindrical segment includes: a radial transverse
wall oriented transversely relative to the direction of the air
stream; side walls oriented parallel relative to the direction of
the air stream; and a curved cylinder wall connected to the radial
transverse wall and the side walls, said walls defining a recess
which opens in a direction opposing the direction of the air stream;
and
(ii) the deflection of the valve element against the restoring
force represents a measure of the air quantity flowing through the
flow tube.
2. The flow meter as defined in claim 1 further comprising:
(c) a baffle plate guide located in the flow tube upstream of the
valve element, said baffle plate guide having a section which extends
into the recess.
3. The flow meter as defined in claim 2 wherein the baffle plate
guide section which extends into the recess forms as small a gap
as possible with the inner surfaces of the side walls and curved
cylinder wall of the valve element.
4. The flow meter as defined in claim 3 wherein the gap is less
than 1 millimeter.
5. The flow meter as defined in claim 3 wherein the baffle plate
guide section which extends into the recess is oriented in such
a manner as to be near the transverse wall when the valve element
is in its rest position.
Description BACKGROUND OF THE INVENTION
The invention relates to a flow meter, and in particular to a flow
meter for metering the air quantity aspirated by an internal combustion
engine.
Flow meters are known in which a force directed in opposition to
the meter opening force exists, which opposing force leads to a
non-linear characteristic flow metering curve due to the vacuum
produced by the flow constriction associated with the meter. The
flow metering curve defines a relationship between the angular deflection
of a metering valve of the flow meter and the throughflow quantity
of the medium passing the flow meter.
The non-linear characteristic referred to is undesirable, so that
corrective measures to produce linearization would be desirable.
OBJECT AND SUMMARY OF THE INVENTION
It is, therefore, a principle object of the invention to provide
a flow meter of the type disclosed above in which the non-linear
characteristic noted above is effectively corrected.
This object is achieved by the provision of a flow meter comprising
a metering valve constructed as a box-like cylindrical segment open
in the direction opposing the air flow, with the metering valve
including a radial transverse wall oriented transversely relative
to the direction of flow.
The flow meter preferably also comprises a baffle plate guide located
upstream of the metering valve and including a section extending
into the segment opening.
Such a flow meter possesses the advantage of producing a nearly
linear characteristic curve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view taken along the line I--I of FIG.
2 and illustrates details of the flow meter according to the invention.
FIG. 2 is a partial cross sectional view taken along the line II--II
of FIG. 1 with further details of the fuel supply and control system
used with the flow meter of the invention.
FIG. 3 is a cross sectional view taken along the line III--III
of FIG. 2.
FIG. 4 is a cross sectional view taken along the line IV--IV of
FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning to FIG. 1 there is shown a flow meter 2 which serves for
metering the air quantity aspirated by an internal combustion engine.
The flow meter is located, for example, in the air intake tube of
the engine. The combustion air flows in the direction of the arrows
within a section 1 of the air intake tube, past the flow meter 2
and then through a section 3 of the intake which contains an arbitrarily
pivotal throttle valve 4 to one or several cylinders (not shown)
of the engine. The flow meter 2 includes a valve element 21 pivotably
mounted on a stationary bearing axle 5. The axle 5 is oriented transversely
relative to the longitudinal axis of the air intake tube. The valve
element 21 is constructed as a rotary slider in the form of a box-like
cylindrical segment transversely penetrating the air intake tube.
The cylindrical segment presents a face surface 6 remote from the
axle 5 and this face surface sweeps past an aperture 7 leading
into the section 3 of the air intake tube. The box-like segment
is open on the side opposing the direction of flow and defines a
recess 8 terminating in a radial transverse wall 9 oriented transversely
relative to the flow direction. The recess 8 is also defined by
side walls 10 oriented in the plane of the flow direction, and with
a curved wall 11 bounded by the surface face 6. An edge 12 facing
the air flow opens the aperture 7 defining the cross-sectional area
of the air intake tube more or less as a dependent function of the
aspirated air quantity by means of its control edge 13 remote from
the fixed axle or shaft 5.
The valve element 21 penetrates the air intake tube section 1 with
a narrow radial circumferential clearance. The transverse wall 9
of the valve element 21 during an opening motion thereof swings
into a damping chamber 14 connected with the air intake tube section
3 downsteam of the aperture 7 via a line 15 containing a damping
throttle 16. This achieves the result that suction tube pressure
fluctuations evoked by the suction strokes have practically no influence
upon the given angular position of the valve element 21. Thus, the
valve element 21 moves within the correspondingly fitted induction
tube 1 according to a nearly linear function of the air quantity
flowing through the induction tube, wherein for a constant air pressure
prevailing upstream of the valve element 21 the pressure prevailing
between the valve element 21 and the throttle valve 4 likewise remains
constant. As shown in the drawings, (FIG. 2), the valve element
21 can be one of the elements of a fuel injection system and can
serve for the direct actuation of a fuel apportioning valve.
Turning now to FIG. 2 it will be seen that fuel is supplied to
the system by a fuel pump 26 driven by an electric motor 25. The
pump 26 aspirates fuel from a fuel container 27 and delivers it
via a line 28 to a chamber 29 within a pressure control valve 30.
From the chamber 29 fuel flows through a line 31 into a chamber
32 which is defined by the end face of the fixed shaft 5 and its
guide bore 33 in an extension of the induction tube wall. A bore
34 shown in broken lines in FIG. 2 establishes communication of
the chamber 32 with a notch 35 machined into the fixed shaft 5.
The wall 9 is formed integrally at one end with a sleeve 36 which
is fixedly attached to a bushing 37 rotating on the fixed shaft
5. The bushing 37 has a control slot 38 machined therein, which
terminates in an annular groove 39. The control slot 38 cooperates
with a control edge 40 (see FIG. 3) which is formed by the end surface
of the notch 35 in the bearing shaft 5. Depending on the position
of the valve element 21 the control edge 40 opens the control slot
38 to varying degrees for metering out a fuel quantity proportional
to the aspirated air flow rate. Thus, the control edge 40 and the
control slot 38 together form a fuel metering valve 41 within the
fixed shaft 5 of the valve element 21. The metered fuel flows from
the annular groove 39 through a groove 44 in the fixed shaft 5.
The annular groove 44 communicates with a line 44 (FIG. 1) disposed
within the face portion of the valve element 21 and the line 45
opens in the vicinity of the aperture-controlling edge 12 e.g.
at the end face of the valve element 21 through an injection nozzle
46 into the portion of the passage 7 opened by the face 6 as best
seen in FIG. 1.
Fuel is metered out at the metering valve 41 at a constant pressure
differential. For this purpose a chamber 49 separated from a chamber
29 of the pressure control valve 30 by a diaphragm 50 is connected
by a line 48 on bore 47 with the induction tube section 1 upstream
of the valve element 21. The pressure control valve 30 is urged
to close by a spring 51 within the chamber 49. The force of the
spring 51 may be changed in dependence on operational parameters
of the engine. This can be accomplished, for example, by an electromagnet,
not shown, which acts on the spring 51. Also, a supplementary force
functionally dependent on known operating characteristics alternatively
can act directly upon the diaphragm 50 in parallel with the spring
51. The pressure control valve 30 is embodied as a flat seat valve
whose diaphragm 50 is its movable valve member which cooperates
with a fixed valve seat 57 over which fuel may flow into a return
line 58 which terminates in the fuel container 27. The pressure
control valve serves at the same time as a system pressure control
valve. The excursion of the valve element 21 takes place in opposition
to the force of a spiral spring 17 one end of which is connected
to the bushing 37 while the other end is attached to a stop member
on the air induction tube.
The basic setting of the fuel metering valve 41 may be adjusted
by rotating the fixed shaft 5 with respect to the valve element
21 by means of a lever 18 and a screw 19 abutting a stop 20.
A favorable feature of the invention is that the metered-out fuel
is mixed with air prior to injection in the air induction tube.
For this purpose, as shown more clearly in FIG. 4 the annular groove
44 communicates with an air hole 62 in the face 8 via a groove 60
and an annular groove 61. The air hole 62 leads to the interior
of the air induction tube 1 upstream of the valve element 21. The
annular groove 61 is preferably so embodied that it covers the groove
60 only when the engine runs at least at minimum idling rpm. This
feature prevents the admission of an incombustible fuel-air mixture
during engine start up. The same purpose could be achieved by placing
the terminus of the injection nozzle 46 a small distance upstream
of the edge 12 or by placing it so as to be very close to the induction
tube wall. The admixture of air to the metered fuel prior to injection
in the induction tube results in an improved mixture preparation.
The valve element 21 includes a recess 8 that is directed upstream
thus providing a nearly linear characteristic quantity metering
curve; e.g. a nearly linear relationship exists between the angular
deflection of the valve element 21 and the air quantity throughflow
since the flow stagnates in the recess 8 so that pressure upstream
of the valve element can build up unhindered. In contrast thereto,
a force directed in opposition to the opening force that acts on
the valve element will also act on a corresponding valve element
closed on all sides, wherein the opposing force is caused by the
subpressure evoked as a result of the flow constriction at the aperture,
and in turn, produces a non-linear characteristic quantity metering
curve.
The linearity of the characteristic quantity metering curve can
be improved by means of the placement of a sheet metal guide means
65 into the induction tube section 1 upstream of the valve element
21. The sheet metal guide means 65 is installed with a predetermined
side clearance between it and the air intake tube wall, and it containes
a section 66 which is arranged to extend into the recess 8 of the
valve element 21 and thus form as small a gap as possible, in particular
one under 1 millimeter, between it and the bounding walls of the
recess 8. The wall 66 of the sheet metal guide 65 is arranged in
such a manner as to be near the transverse wall 9 as shown when
the valve element is in its position at rest, and arranged so as
not to effect a throttling of the air flow in the induction when
the valve element is fully opened. The flow influence effects which
would be detrimental to the linearity of the characteristic quantity
metering curve are largely avoided by means of the utilization of
the sheet metal guide 65. |