Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2002-08-26
2004-01-20
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
C073S204260
Reexamination Certificate
active
06679113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow rate sensor for outputting a signal in response to a flow rate of a fluid being measured, and relates to a flow rate sensor suitable for measuring an intake air flow rate of an internal combustion engine in an automobile, for example.
2. Description of the Related Art
Generally, in an automotive engine, etc., an air-fuel mixture including fuel and intake air is burnt in a combustion chamber in the engine body, and rotational output from the engine is extracted from the resulting combustion pressure, requiring that the intake air flow rate be detected in order to calculate the injection rate, etc., of the fuel with high precision.
Thus, the flow rate sensor shown in Japanese Patent Non-Examined Laid-Open No. 2000-2572, for example, is known as a conventional technique of this kind.
FIG. 6
is a longitudinal section showing a conventional flow rate sensor such as described in Japanese Patent Non-Examined Laid-Open No. 2000-2572, for example, mounted to a main passage,
FIG. 7
is a partial perspective showing an assembly process for the conventional flow rate sensor,
FIG. 8
is an enlarged partial longitudinal section of the conventional flow rate sensor in
FIG. 6
, and
FIG. 9
is a cross section taken along line IX—IX in
FIG. 8
viewed from the direction of the arrows.
In the figures, a main passage
1
is formed into a cylindrical shape from, for example, a resin material, a metal material, etc., a small-diameter cylindrical mounting aperture
2
being disposed so as to project radially outward, and a passage forming body
3
having a vertically-aligned rectangular body being disposed so as to project radially inward from an inner wall surface of the main passage
1
. A bypass passage
4
is formed into a general U shape inside this passage forming body
3
, an inflow aperture
5
of the bypass passage
4
opening onto the vicinity of the axial center of the main passage
1
on a front surface of the passage forming body
3
, and an outflow aperture
6
of the bypass passage
4
opening onto the main passage
1
on a lower surface of the passage forming body
3
. In addition, an element insertion aperture
7
is formed in the passage forming body
3
at a position facing the mounting aperture
2
.
A flow rate sensor
10
is constituted by a casing
11
, a mount plate
18
, a circuit board
21
, a flow rate detecting element
23
, etc.
The casing
11
is formed into a stepped cylindrical shape from a resin material, for example, and is constituted by: a collar-shaped mount portion
12
formed on a base end portion of the casing; a circuit accommodating portion
13
formed into a generally rectangular overall box shape and is disposed so as to extend to a first side of the mount portion
12
; and a connector portion
14
formed on a second side of the mount portion
12
, the connector portion sending and receiving signals to and from an external portion. A circuit board mount recess portion
15
surrounded by a peripheral wall
15
a
forming a rectangular shape, a mount plate interfitting groove
16
formed by cutting away a portion of the peripheral wall
15
a
at an extremity of the casing
11
, and interfitting apertures
17
formed so as to be positioned on first and second sides of the mount plate interfitting groove
16
are disposed in the circuit accommodating portion
13
.
The mount plate
18
is formed into a plate-shaped body from a metal material, for example, being composed of: a circuit board mount portion
19
formed by bending edge portions of the mount plate
18
on the left and right in
FIG. 6
; and an element mount portion
20
formed integrally at an extremity of the circuit board mount portion
19
. A rectangular element accommodating recess portion
20
a
for accommodating the flow rate detecting element
23
is formed in this element mount portion
20
. This mount plate
18
is mounted to the casing
11
by housing the circuit board mount portion
19
inside the circuit board mount recess portion
15
such that the element mount portion
20
fits into the mount plate interfitting groove
16
. Here, an extremity of the element mount portion
20
projects from the casing
11
.
The circuit board
21
is disposed on the circuit board mount portion
19
, electronic components for sending and receiving electric signals to and from the flow rate detecting element
23
being mounted to the circuit board
21
. First circuit board terminals
21
a
of the circuit board
21
and connector terminals
14
a
of the connector portion
14
are each electrically connected by first bonding wires
22
a.
The flow rate detecting element
23
, as shown in
FIG. 7
, is provided with: a rectangular silicon substrate
24
; a heater resistor
25
formed on a surface of the silicon substrate
24
; a pair of temperature-detecting resistors
26
formed on the surface of the silicon substrate
24
so as to be positioned to the left and right of the heater resistor
25
; and a temperature-compensating resistor
27
formed on the surface of the silicon substrate
24
, the flow rate detecting element
23
being disposed inside the element accommodating recess portion
20
a
. Second circuit board terminals
21
b
of the circuit board
21
and element terminals
23
a
of the flow rate detecting element
23
are each electrically connected by second bonding wires
22
b.
Moreover, the heater resistor
25
, the temperature-detecting resistors
26
, and the temperature-compensating resistor
27
are electrically connected to each of the element terminals
23
a
by a wiring pattern (not shown) formed on the surface of the silicon substrate
24
. Furthermore, the electronic components mounted to the circuit board
21
constitute a heater control circuit for controlling the heater resistor
25
of the flow rate detecting element
23
, an amplifying circuit for amplifying detection signals from each of the temperature-detecting resistors
26
, a reverse-current sensing circuit, etc.
A stopper member
28
is constituted by a stopper main body
29
and an elastic protrusion
30
. The stopper main body
29
, as shown in
FIG. 7
, is formed by: an elongated plate portion
29
a
extending flatly so as to lie across the mount plate interfitting groove
16
; interfitting protrusions
29
b
positioned on left and right sides of the elongated plate portion
29
a
so as to project toward the interfitting apertures
17
of the circuit accommodating portion
13
and fit into the interfitting apertures
17
; a central protrusion
29
c
positioned between the interfitting protrusions
29
b
so as to fit into the mount plate interfitting groove
16
and, as shown in
FIG. 8
, extend to a position in proximity to the second bonding wires
22
b
; and a stopper recess portion
29
d
formed between the elongated plate portion
29
a
and the central protrusion
29
c
. The elastic protrusion
30
is composed of a flexible elastic material such as silicone rubber, for example, and is fixed to a leading edge portion of the central protrusion
29
c
. The stopper member
28
is mounted to the casing
11
such that the interfitting protrusions
29
b
fit into the interfitting apertures
17
. Here, the elastic protrusion
30
, as shown in
FIG. 8
, is placed in contact with a surface of the flow rate detecting element
21
in an elastically-deformed state.
A sealant
31
is formed from a silicone gel, for example, and is injected inside of circuit board mount recess portion
15
, as shown in
FIGS. 6 and 8
, so as to cover the surface of the circuit board
21
, the bonding wires
22
a
and
22
b
, and the connector and element terminals
14
a
and
23
a
. Hence, short-circuiting of the bonding wires
22
a
and
22
b
is prevented and the electronic components mounted to the circuit board
21
are protected.
A cover body
32
is mounted to the casing
11
such that a peripheral portion thereof is fixed by adhesive to the peripheral wall
15
a
of the circuit board mount recess portion
15
and the stopper main body
29
. Hence
Patel Harshad
Sughrue & Mion, PLLC
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