JPH0321456Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tamper-proof structure of a hot wire flowmeter for detecting the intake air amount, etc. of an electronically controlled fuel injection type internal combustion engine.

<Prior art> For example, as shown in Fig. 5, in a hot wire flowmeter,
A hot wire R _H made of platinum wire or the like is connected in series to a reference resistor R ₃ , and a temperature compensation resistor R _K arranged in a fluid passage in the same atmosphere as the hot wire R _H is connected to a fixed resistance.
After connecting R ₁ and R ₂ in series, these two series circuits are connected in parallel to form a bridge circuit.

Then, the potential U _S (terminal voltage of the reference resistor R ₃ ) at the branch point a on the side where the hot wire R _H and the reference resistor R ₃ of the bridge circuit are connected in series, the temperature compensation resistor R _K , and the fixed resistor R Potential at branch point b on the side where ₁ and R ₂ are connected in series (terminal voltage of fixed resistor R ₂ )
is supplied to the differential amplifier 1, and the transistors 2 and 3 are controlled according to the output of the differential amplifier 1 to control the current supplied to the bridge circuit, so that the unbalanced voltage of the bridge circuit is always maintained. I'm trying to make it zero.

Therefore, if the bridge circuit is in equilibrium and the flow rate of fluid increases, thereby cooling the hot wire R _H and decreasing its resistance value, the bridge circuit becomes unbalanced and the resistance R ₃ increases. The terminal voltage U _S increases, and the output of the differential amplifier 1 decreases. Then,
The current supplied to the bridge circuit (hot wire R _H ) controlled by transistors 2 and 3 increases, which causes the temperature of the hot wire R _H to rise and its resistance value to increase to its original value, causing the bridge circuit to close. unbalanced voltage is returned to zero.

Also, when the temperature of the fluid changes, the ambient temperature around the hot wire R _H changes and its resistance value changes, but the resistance value of the temperature compensation resistor R _K placed in the same atmosphere as the hot wire R _H also changes. The supply current to the bridge circuit does not change as it changes to maintain the balance of the bridge circuit. In this way, the flow rate of the fluid and the current supplied to the bridge circuit always correspond, regardless of the temperature of the fluid, so that, for example, the terminal voltage U _S of the reference resistor R ₃
By measuring this, the flow rate of the fluid can be measured.

By the way, when using a hot wire flow meter with such a configuration as an intake air amount sensor for an internal combustion engine,
When the flow rate characteristics of intake air are changed to adjust emissions (CO), it is necessary to correct the measurement value by the hot wire flowmeter (value of measurement data of intake air flow rate supplied to the controller) accordingly. For example, as shown in FIGS. 6 and 7, a potentiometer 5 is housed in a case 4 of a hot wire flowmeter, and a valve is rotatably attached to the bottom of a hole 6 provided in the case 4. 7 and the shaft of the potentiometer 5 through an S-shaped spring 8, the potentiometer 5 is adjusted through the valve 7 and the spring 8 to open a fluid passage (intake passage). The relationship between the flow rate of the flowing fluid (intake air) and the flow rate measured by the hot wire flowmeter can be changed.

Conventionally, as a tamper-proof structure that prevents the control characteristics of the fuel supply amount from being destroyed due to the relationship between the flow rate and its measured value being changed by a general user, for example, the structure shown in Fig. 8 has been proposed. As shown, a method was adopted in which a disc-shaped plate 10 made of metal such as aluminum was press-fitted into an insert fitting 9 that formed a hole 6 for mounting the valve 7 to cover the valve 7. 11 is a heat sink made of copper or the like, 12 is a ceramic HIC board that holds elements 13, 14 is a connector, and 15 is a receiver used when press-fitting the plate 10, which is not shown in the case 4. A cover is applied.

<Problems to be solved by the invention> By the way, in order to press fit the plate 10 into the insert metal fitting 9, the plate 10 must be pressed by an external force such as vibration.
It is necessary to make the pressing force sufficiently large to prevent the material from accidentally falling off. However, since the case 4 is usually made of a resin material, the heat sink 11 is deformed by the force during press-fitting, and the HIC board 11 adhered to the heat sink 11 is
may be damaged. Also, something like this
In order to prevent damage to the HIC board 12 (deformation of the heat sink 11), it is conceivable to glue the plate 10 to the hole 6, but in this case, it would take a lot of effort to remove the plate 10 at a maintenance shop, etc. Otherwise, there is a problem that not only the plate 10 but also the insert fitting 9 may be damaged, which is impractical.

The present invention was developed in view of the above circumstances, and although it is difficult for general users to remove the plate 10, it is possible to easily remove the plate 10 when readjusting it at a repair shop or the like. Can be removed and housed in a case
The purpose is to provide a tamper-proof structure for hot wire flowmeters that can prevent damage to HIC boards, etc.

<Means for Solving the Problems> To this end, the present invention includes a plate that is inserted into the hole in which the valve is mounted, a spring washer that is partially cut out, and an inner peripheral surface of the hole. A tamper-proof structure of the hot-wire flowmeter is achieved by providing a ring groove recessed in the flowmeter.

<Function> As a result, after inserting the plate into the hole and covering the valve, the spring washer is inserted into the hole in a reduced diameter state and elastically engaged with the ring groove, so that the plate is inserted into the hole. It is designed to be locked so that it does not come off.

<Example> An example of the present invention will be described below in detail based on FIGS. 1 to 4. Note that parts having the same functions as those of the conventional example shown in FIGS. 5 to 8 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

Fig. 1 is an enlarged cross-sectional view of the main parts showing an embodiment of the present invention, and Fig. 2 is a plan view of Fig. 1.Inserts are installed in case 4 of a hot wire flowmeter made of resin material. A hole 6 is provided with a metal fitting 9, and a valve 7 rotatably attached to the bottom of the hole 6 is rotated by a driver or the like inserted into the hole 6 from outside the case 4 to adjust a potentiometer (not shown). What is possible is the same as before.

In this embodiment, a ring groove 16 is formed in the inner peripheral surface of the metal insert 9. and,
The aluminum plate 17 that covers the valve 7 is inserted into the hole 6 with a loose fit, and the spring washer 18 having a partially cutout is elastically engaged with the ring groove 16. As a result, the plate 17 is held in the hole 6 in a non-slip engagement to provide a tamper-proof structure.

Therefore, according to such a tamper-proof structure, after adjusting the valve 7, the hole 6 is connected to the plate 17.
is inserted to cover the valve 7, and then the spring washer 18 is reduced in diameter using a suitable tool and inserted into the hole 6. When the spring washer 18 is elastically engaged with the ring groove 16 by releasing this diameter reduction operation force and pushing the spring washer 18 into the ring groove 16, the plate 17 is engaged with the inside of the hole 6 to prevent it from coming off. Therefore, the valve 7 cannot be operated from the outside.

Further, when it is necessary to readjust the potentiometer (valve 7) at a maintenance shop or the like, the plate 17 can be easily removed by breaking the spring washer 18.

That is, the basic shape of the spring washer 18 is, for example, a C-shape with a portion cut out, as shown in FIGS. 3A and 3B. Then, the end portions of the spring washers 18 are moved closer to each other to reduce the width of the opening portion 18a (notch portion). It is desirable to provide an engagement hole 18b with a tool (not shown) at the end forming the opening portion 18a. Further, in order to make it impossible for a general user to remove the spring washer 18, it is preferable to provide the engagement hole 18b in a portion that is recessed into the ring groove 16.

On the other hand, when the plate 17 is removed for readjustment at a maintenance shop or the like, the spring washer 18 is cut using a drill or the like, but in order to facilitate this cutting, the opening portion 18 is
By providing a cutout portion 18c deeper than the depth of the ring groove 16 at a position facing a, it is possible to indicate the cutting position with a drill or the like and at the same time reduce the cutting width (shaving width). Further, as a means for instructing the cutting position in this way, for example, a fourth
As shown in FIG. B, a portion of the spring washer 18 may be recessed toward the center.

<Effects of the invention> As explained above, according to the invention, when readjusting the potentiometer of a hot wire flowmeter, it is necessary to destroy the spring washer installed in the ring groove by cutting it with a drill or the like. This property prevents general users from readjusting the potentiometer. Further, since there is no need to press-fit the plate with a large force as in the conventional case, the case and the heat sink are not deformed, and damage to the internal mechanism can be avoided.

[Brief explanation of the drawing]

Fig. 1 is an enlarged sectional view of the main parts showing an embodiment of the present invention, Fig. 2 is a plan view of Fig. 1, and Figs. 3 A and B are plan and front views showing the basic shape of the spring washer. , Figures 4A and 4B are plan views showing modified examples of the spring washer, Figure 5 is a circuit diagram showing the principle of the hot wire flowmeter, and Figure 6 is a front view showing the internal mechanism of the hot wire flowmeter. FIG. 7 is a cross-sectional view taken along the line shown in FIG. 6, and FIG. 8 is an enlarged cross-sectional view of main parts showing a conventional example. 4... Case, 5... Potentiometer, 6... Hole,
7...Valve, 9...Insert fitting, 16...Ring groove, 17...Plate, 18...Spring washer, 18a...Opening (notch) part, R _H ...Hot wire, R _K
…Temperature compensation resistance, R ₁ , R ₂ , R ₃ …Resistance.

Claims (1)

[Scope of utility model registration request] A bridge circuit is configured including a hot wire arranged in a fluid passage, a current value supplied to the bridge circuit is controlled so as to always maintain the temperature of the hot wire at a predetermined value, and a flow rate of the fluid is determined from the supplied current value. On the other hand, a valve is rotatably attached to the bottom of a hole provided in the case, and a potentiometer linked to the valve is adjusted by rotating the valve from the outside, thereby controlling the fluid passage. A hot wire flowmeter configured to adjust the relationship between the flow rate of fluid flowing through the hole and its measured value, the hot wire flowmeter comprising: a plate that is inserted into the hole with a clearance fit; a spring washer with a portion formed with a cutout; A ring groove is provided in the inner circumferential surface of the spring washer, and after the plate is inserted into the hole to cover the valve, the spring washer is inserted into the hole in a reduced diameter state and elastically engaged with the ring groove. A tamper-proof structure for a hot wire flowmeter, characterized in that the plate is fixed inside the hole to prevent it from coming off.