Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
2001-04-23
2003-05-13
Williams, Hezron (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
Reexamination Certificate
active
06561021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a flow rate-measuring device and, more particularly, to a flow rate-measuring device suitable for measuring an intake air flow rate of an engine such as internal combustion engine.
2. Background Art
FIG. 13
is a front view of a conventional flow rate-measuring device disclosed in the Japanese Patent Publication (unexamined) No. 313318/1996.
FIG. 14
is a sectional view taken along the line XIV—XIV of FIG.
13
. In
FIGS. 13 and 14
, reference numeral
10
is a flow rate-measuring device, numeral
1
is a main body of the flow rate-measuring device, numeral
2
is a circuit substrate accommodation case, numeral
3
is an electric member for measuring the flow rate, numeral
5
is a duct where fluid to be an object of flow measurement (hereinafter referred to as fluid to be measured) flows, and numeral
6
is a honeycomb. An arrow A indicates the flow direction of the fluid to be measured (this is the same in the respective drawings described below). The circuit substrate accommodation case
2
is connected with the flow rate-measuring device body
1
, and the circuit substrate accommodation case
2
is attached to the duct
5
and holds the flow rate-measuring device body
1
in the duct
5
. The flow rate-measuring device body
1
is comprised of a terminal holding member
13
and a flow rate-measuring passage
11
consisting of a cylinder having a bell-mouthed inlet. The electric member
3
is comprised of a flow rate-detecting element
31
consisting of a flow rate-detecting resistance
311
, a temperature-compensating resistance
312
, a circuit substrate
34
accommodated in the circuit substrate accommodation case
2
, a terminal
35
, and a connector
36
. The flow rate-detecting element
31
and the temperature-compensating resistance
312
are electrically connected with the circuit substrate
34
through the terminal
35
, and the circuit substrate
34
is electrically connected with the connector
36
. In this manner, the flow rate-detecting element
31
and so on are operated by electric power supplied through the connector
36
. The flow rate of the fluid to be measured detected by the flow rate-detecting element
31
is transformed into an electric signal, and is inputted via the circuit substrate
34
to an external receiver (not shown in the drawings). The flow rate-detecting resistance
311
is formed by putting a platinum film in the form of teeth of a comb on a ceramic substrate. The temperature-compensating resistance
312
is also formed of platinum.
In such a conventional flow rate-measuring device
10
, a heating current flowing in the flow rate-detecting resistance
311
of the flow rate-detecting element
31
is controlled by a circuit (not shown in the drawings) formed in the circuit substrate
34
so that the average temperature of the flow rate-detecting resistance
311
is higher than the temperature of the fluid to be measured detected by the temperature-compensating resistance
312
by a predetermined value. The heating current supplied to the flow rate-detecting resistance
311
is detected from dependence of the resistance value of the flow rate-detecting resistance
311
on temperature and cooling effect of the flow rate-detecting resistance
311
based on the flow of the fluid to be measured, and this heating current value is inputted as a flow rate signal to the external receiver.
FIG. 15
shows a sectional view of an example of a pipe system in a case where the foregoing flowrate-measuring device
10
is used for measuring an air intake flow rate of an internal combustion engine for vehicles. In
FIG. 15
, numeral
6
is the honeycomb, numeral
7
is an air cleaner case, and numeral
71
is an air cleaner element arranged in the air cleaner case
7
. The air cleaner element
71
is a filter composed of a nonwoven fabric or filter paper. The air cleaner element
71
catches dust in the air sucked into the internal combustion engine (not shown) to prevent dust from coming into the internal combustion engine. In the pipe system as described above, the flow rate-measuring device
10
is arranged in the downstream of the air cleaner element
71
.
The air cleaner element
71
is plugged by accumulation of dust increasing with the increase of the air intake quantity due to operation of the internal combustion engine. Owing to the plugged air cleaner element
71
, eddy is generated or flow velocity distribution becomes uneven in the flow of the intake air having passed through the air cleaner element
71
. As a result, there is a great difference in the flow of the intake air in the upper stream of the flow rate-measuring device
10
depending upon whether it is before the air cleaner element
71
is plugged or after the element is plugged are greatly different. Even when the flow of the intake air is greatly changed, the change of the flow of the intake air is moderated by the honeycomb
6
arranged upstream from the flow rate-measuring device
10
and the bell-mouthed configuration of the flow rate-measuring passage
11
in the flow rate-measuring device
10
, and consequently, value of an error in the flow rate measured by the flow rate-measuring device
10
is lowered. In this situation, the honeycomb
6
functions to remove whirl flow components such as eddy. The bell-mouthed configuration functions to contract the flow of the air flowing into the flow rate measuring passage
11
to a certain degree and reduce unevenness in the flow velocity distribution. In addition, it is certain that the cylindrical flow rate measuring passage
11
has the bell-mouthed configuration, but the function of reducing eddies is not very large. Therefore, the flow rate-measuring device
10
having the flow rate-measuring passage
11
of such a cylindrical configuration is used generally in combination with the honeycomb
6
.
In recent years, under the background of increasing tendency of demanding for smaller engine rooms, the so-called plug-in type flow rate-measuring device, for example, a flow rate-measuring device disclosed in Japanese Patent Publication (unexamined) No. 219838/1996, being capable of easily attached to a duct has been proposed. However, the flow rate-measuring device disclosed in the foregoing official gazette is not provided with a special fluid passage for measuring the flow rate of the fluid to be measured like the flow rate-measuring passage
11
shown in
FIG. 14
as described above. Therefore, it is difficult to attach a rectifier like the foregoing honeycomb to the flow rate-measuring device itself. This causes a problem such that the error in measuring the flow rate is increased when the air cleaner element is plugged.
In order to reduce the error in the flow rate measured by the plug-in type flow rate-measuring device, in some cases, a rectifier is attached to the air cleaner case or an intake pipe. However, in such a case, when using a rectifier with small meshes to obtain a sufficient rectification performance, pressure loss is increased, and the quantity of air possible to be taken into the internal combustion engine is limited, whereby output of the internal combustion engine is lowered. There is another problem in that the rectifier is plugged by fine dust that has passed through the air cleaner element. On the other hand, when using a rectifier with large meshes is used to solve the problem of being plugged, not only the rectification effect is lowered but further problems such as increase in thickness of a boundary layer and unevenness in friction stress occur in a flow rate detecting portion of the foregoing flow rate-measuring device due to eddy generated in the downstream of the rectifier. As a result, there arises a turbulence in the signal of a detected flow rate, and the flow rate is not detected accurately in some cases. Moreover, there is a further problem in that due to the necessity of adding any rectifier such as honeycomb to the flow rate-measuring device, cost for manufacturing the flow rate-measuring device is increased.
A flow rate-
Hamada Shingo
Oshima Takeharu
Suetake Naruki
Tohyama Ryuji
Uramachi Hiroyuki
Mitsubishi Denki & Kabushiki Kaisha
Thompson Jewel
Williams Hezron
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