JPH0326417Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a hot-wire flowmeter for an internal combustion engine that detects the intake air flow rate.

<Prior art> Conventional examples of hot wire flowmeters for internal combustion engines include those shown in Figures 3 to 6 (Utility Model No. 59-158031).
(see publication).

That is, as shown in FIG.
b, 4 (2 is a reference resistor, 3a is a temperature compensation resistor for compensating for fluctuations in the intake air amount detection characteristics due to changes in intake air temperature, 3b is for securing a potential between it and the first fixed resistor 4) A bridge circuit is constituted by the first fixed resistor 4 and the second fixed resistor placed under the same atmosphere. The power transistor 6 is controlled by the output of the differential amplifier 5 which inputs the unbalanced voltage of the bridge circuit, that is, the voltage between points a and b, and the current supplied to the bridge circuit is controlled based on the voltage change of the reference resistor 2, for example. This detects the amount of intake air. For example, if the intake air flow rate increases, the degree of cooling of the hot wire resistance 1 increases, and its resistance value tends to decrease. At this time, point a and b
The unbalanced voltage with respect to the point decreases, the output of the differential amplifier 5 decreases, the collector current of the power transistor 6 increases, and the current supplied to the bridge circuit increases.
This increases the amount of heat generated by the hot wire resistor 1 and controls the resistance value to be kept constant. Therefore, for example, by reading the flow velocity from the voltage Us of the reference resistor 2, the air flow rate can be calculated.

By the way, in order to increase the voltage at point a that is input to the differential amplifier 5 to a certain extent, the resistance value of the reference resistor 2 is increased, and a long thin wire is used in order to suppress and reduce the power consumption. However, in consideration of the installation of the reference resistor 2, conventional hot wire flowmeters are designed as shown in FIGS. 4 to 6.

That is, the support member 7 through which the intake air flows through the hot wire resistor 1 and the temperature compensation resistor 3a interposed in the intake passage.
Install it in the hollow part of. Then, the lead wire 8 connected to one end of the hot wire resistor 1 is passed through the inside of the cylindrical member 9 and connected to the collector terminal of the power transistor 6 provided in the control unit 10. Further, a reference resistor 2 connected to the other end of the hot wire resistor 1 is wound in a coil around the outer wall of the cylindrical member 9, and then its end is connected to a ground circuit (not shown) in the control unit 10. Here, the cylindrical member 9 is provided to penetrate an intake passage wall (not shown), and the reference resistor 2 is disposed inside the intake passage wall.

The first and second fixed resistors 3a, 3b are mounted within the control unit 10.

<Problems to be solved by the invention> However, in such a conventional hot wire flowmeter, since the reference resistor 2 is wound around the cylindrical member 9 in a coil shape, the reference resistor 2 has an inductance component. The control of the supply current is affected by the inductance component, and there is a risk that the current control may become unstable. Further, since the lead wire 8 is passed through the cylindrical member 9 and the reference resistor 2 is wound in a coil shape on the outer wall of the cylindrical member 9, electromagnetic induction occurs in the reference resistor 2 when the supplied current changes. There was a problem in that a noise current was generated in the lead wire 8 due to electromagnetic force.

The present invention has been developed in view of the above-mentioned circumstances, and even if the lead wire connected to the hot wire resistor is passed through a cylindrical portion in which a reference resistor connected in series with the hot wire resistor is wound into a coil, It is an object of the present invention to provide a hot wire flow meter for an internal combustion engine that is not influenced by each other.

<Means for Solving the Problems> For this reason, the present invention uses a cylindrical member, which is attached to a support member that supports the hot wire resistance disposed in the intake passage and is provided through the intake passage wall, as an electromagnetic shielding member. A reference resistor connected in series with the hot wire resistor is wound in a coil shape and attached to the outer wall of the electromagnetic shielding member, a capacitor is connected in parallel to the reference resistor, and a lead wire connected to the other end of the hot wire resistor is attached. The lead wire is passed through the cylinder of the electromagnetic shielding member, and the other ends of the lead wire and the reference resistor are taken out to the outside of the intake passage.

<Function> As a result, the reference resistor and the lead wire are electromagnetically shielded by the electromagnetic shielding member, and the influence of the inductance component of the reference resistor is suppressed by the capacitance of the capacitor.

<Example> An example of the present invention will be described below with reference to FIGS. 1 and 2. Incidentally, the same elements as those in the conventional example are given the same reference numerals as in FIGS. 3 to 6, and the explanation thereof will be omitted.

In the figure, a hot wire resistor 1 is supported by a support member (not shown) and disposed in an intake passage (not shown). This support member is attached to the end of a cylindrical member 11 made of an electromagnetic shielding member such as aluminum. A reference resistor 2 is connected in series to the hot wire resistor 1 . The reference resistor 2 is made of a long thin wire and is wound around the outer peripheral wall of the cylindrical member 11 in a coil shape. A lead wire 8 connected to the other end of the hot wire resistor 1 is provided to pass through the inside of the cylindrical member 11 . The other ends of the lead wire 8 and the reference resistor 2 are taken out to a control box (not shown) provided on the outer wall of the intake passage.

Further, a capacitor 12 is connected in parallel to the reference resistor 2 . Here, the capacitance of the capacitor 12 is shifted from the range where the capacitor 12 and the reference resistor 2 resonate in parallel.

According to this configuration, the reference resistor 2 and the cylindrical member 11 are connected to each other by the cylindrical member 11 made of an electromagnetic shielding member.
Since the lead wire 8 passing through the tubular member 11 is electromagnetically shielded, the lead wire 8 inside the cylindrical member 11 is not affected by the electromagnetic force generated in the coiled reference resistor 2, and no noise current is generated in the lead wire 8. . Also, since the capacitor 12 is connected in parallel to the reference resistor 2, the capacitance of the capacitor 12 is equal to the reference resistor 2.
Since the capacitor 12 repeats charging and discharging substantially in balance with the inductance, the current supplied to the bridge circuit is not affected by the inductance, and supply current control is stabilized.

<Effects of the invention> As explained above, the present invention uses an electromagnetic shielding member to cover a cylindrical member in which a reference resistor is coiled around the outer wall and through which a lead wire connected to a hot wire resistor passes through the cylinder. Since the capacitor is connected in parallel to the reference resistor, it is possible to suppress the generation of noise current due to the lead wire, and to stabilize the control of the current supplied to the bridge circuit.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a schematic diagram of the main parts of the same as above, FIG. 3 is a circuit diagram showing a conventional example of a hot wire flowmeter, FIG. FIG. 6 is a schematic diagram of the main parts of the same as above. 1... Hot wire resistance, 2... Reference resistance, 8... Lead wire, 11... Cylindrical member, 12... Capacitor.

Claims (1)

[Scope of utility model registration request] The supply current to a bridge circuit including a hot wire resistor disposed in the intake passage of the engine and a reference resistor connected to one end of the hot wire resistor and connected in series with the hot wire resistor is determined by the unbalanced voltage of the bridge circuit. In a hot-wire flowmeter for an internal combustion engine that outputs a voltage from a bridge circuit according to the intake air flow rate based on the
The reference resistor is wound in a coil shape and attached to the outer wall of a cylindrical electromagnetic shield member to which a support member for supporting the hot wire resistor is attached and is provided through the intake passage wall, and a capacitor is connected in parallel to the reference resistor. A lead wire connected to the other end of the hot wire resistor is passed through the cylinder of the electromagnetic shielding member, and the other end of the lead wire and the reference resistor is taken out to the outside of the intake passage. Hot-wire flowmeter for internal combustion engines.