Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
1999-04-01
2001-05-22
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
C073S204220
Reexamination Certificate
active
06234015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for measuring the flow rate of a fluid comprising a constant flow, a pulsating flow or a pulsating flow with a backward current therein, in particular, a device suited for measuring the intake air flow rate of an internal combustion engine.
2. Discussion of Background
In
FIG. 31
is shown a cross-sectional view of the structure of an induction system for an automobile engine. In this Figure, reference numeral
1
designates an intake air flow rate measuring device for measuring the flow rate of intake air, reference numeral
2
designates a surge tank, reference numeral
3
designates an arrow to indicate the intake air, reference numeral
4
designates an air cleaner, reference numeral
5
designates a cleaning filter provided in the air cleaner
4
, reference numeral
6
designates a throttle valve for controlling the flow rate of the intake air
3
, reference numeral
7
designates an intake air passage, reference numeral
8
designates an engine combustion chamber, reference numeral
9
a
designates an intake manifold for introducing the intake air into the engine combustion chamber
8
, reference numeral
9
b
designates an exhaust manifold for taking out exhaust gas after combustion, reference numeral
11
designates a flow rate measuring duct, reference numeral
12
designates a flow rate detector, reference numeral
85
designates an air inlet, reference numeral
86
designates an intake valve, and reference numeral
87
designates an exhaust valve.
The intake air
3
which has entered through the air inlet
85
is cleaned through the filter
5
in the air cleaner
4
, passes through the intake air flow rate measuring device
1
and the throttle valve
6
in the intake air passage
7
, the surge tank
2
and the intake manifold
9
a
in this order, and is introduced into the engine combustion chamber
8
, being mixed with fuel. After combustion, the intake air is released to atmosphere through the exhaust manifold
9
b.
It has been known that the flow fashion of the intake air
3
passing through the intake air flow rate measuring device
1
in a series of intake/exhaust strokes depends on an operation state such as engine speed and opening degree of the throttle valve
6
so that a constant stable flow with a constant flow velocity is provided in some cases and a pulsating flow with a flow velocity thereof varied with time is provided in some cases.
In the intake/exhaust strokes of an engine, the intake valve
86
starts opening in the exhaust stroke to improve trapping efficiency. In some cases, not only a forward current from an air inlet
85
toward the combustion engine
8
but also a backward current is generated in the intake pipe
7
since the exhaust gas that remains in the cylinder enters the intake valve
86
as well as the exhaust valve
87
.
A conventional flow measuring device can not measure the flow rate of such a pulsating flow, in particular, a pulsating flow with a backward current therein, and the conventional device produces a considerable error in measurement of the flow rate of such a pulsating flow. Although the error has been reduced by software for correction in such a case, the measurement of the flow rate has a limited measuring accuracy, and the correction contributes to an increase in cost. From this viewpoint, it is extremely desirable that the intake air flow rate measuring device
1
basically has a function to detect a backward current, in terms of improvement in a measuring accuracy and a reduction in cost.
Now, explanation of the intake air flow rate measuring device
1
will be made. In order that the measurement of the intake air flow rate in an internal combustion engine becomes decreasingly less susceptible to drift or turbulence caused by a bent portion of the intake air passage
7
or the air cleaner
4
, the flow rate measuring duct, which is a size smaller than the intake air passage, has been provided in the intake air passage so as to have a longitudinal axis thereof extended substantially parallel to the flow of a fluid to be detected, and the flow rate detector
12
, such as a flow velocity sensor, has been in turn provided in the flow rate measuring duct to rectify the flow near to the detector, producing a stable output.
This arrangement has created a problem in that the flow rate detector
12
in the flow rate measuring duct
11
can not stably detect a flow rate of a fluid to be detected since the provision of the flow rate measuring duct
11
produces unstable vortexes or separation of the flow near to an inner wall of the flow rate measuring duct
11
to disturb the flow passing through the flow rate measuring duct
11
. If the flow separates at an inlet of the flow rate measuring duct
11
, the separation region has a thickness thereof increased toward a downstream direction. It is known that gas is irregularly disturbed by a shear force in the vicinity of the boundary between the separation region and a principal current portion since the separation region and the principal current portion have different flow velocities. The irregular disturbance has contributed to generation of an error in flow rate measurement.
In order to solve this problem, it has been proposed in JP-A-604813 that the flow rate measuring duct with the rectifying function stated above has small holes to reduce separation currents and vortexes caused at the inlet of the flow rate measuring duct so as to equalize the flow velocity distribution in the flow rate measuring duct. The details of this arrangement will be explained, referring to FIGS.
32
(
a
) and
32
(
b
). FIG.
32
(
a
) is a cross-sectional side view, and FIG.
32
(
b
) is a front view. In these Figures, reference numeral
100
designates an intake pipe, reference numeral
101
designates the flow rate measuring duct, reference numeral
102
designates an elastic heater element for measuring a flow rate, reference numeral
103
and
104
designate temperature-dependent elements, reference numeral
105
designates a first supporter, reference numeral
106
designates a second supporter, reference numeral
107
designates small holes, and reference numeral
108
designates a stay.
When the resistance wire
102
is energized and heated, and when air flows across the resistance wire in a forward direction, the temperature-dependent resistance wire
103
is cooled by the air flow supplied from an upstream direction. Since the air that has been heated by an upstream portion of the temperature-dependent resistance wire
103
passes across temperature-dependent resistance wire
104
at that time, a temperature difference due to heating of the intake air is provided between the temperature-dependent resistance wire
103
and the temperature-dependent resistance wire
104
. The temperature difference varies, depending on the caloric value of the resistance wire
102
and the mass flow rate of the intake air. The static pressure on an inner wall of the flow rate measuring duct
101
becomes smaller than the static pressure outside the flow rate measuring duct since the flow velocity in the flow rate measuring duct
101
is slower than that outside the flow rate measuring duct
101
because of the presence of friction loss against the inner wall in the flow rate measuring duct
101
. The difference in both static pressures creates currents which are directed into the flow rate measuring duct
101
from outside the flow rate measuring duct
101
through the small holes
107
. Since the gas that has flowed into the flow rate measuring duct
101
through the small holes
107
enters the separation region to reduce the velocity difference between the principal current portion and the separation region, a velocity boundary layer comes closer to the inner wall of the flow rate measuring duct
101
, decreasing the disturbance in the flow velocity. The publication states that this arrangement can transfer the heat from the heater
102
to the temperature-dependent element
104
in stable fashion to improv
Hamada Shingo
Kotoh Satoru
Oshima Takeharu
Uramachi Hiroyuki
Yamakawa Tomoya
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Patel Harshad
LandOfFree
Flow rate measuring device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flow rate measuring device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flow rate measuring device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2548311