JPH01257221A - Hot-wire type air flow rate detector for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable highly accurate detection of a flow rate at a high accuracy over a wide range of flow rate, by arranging a mobile flap within a main intake path so that it is energized with a return spring in the direction of being closed while being turned in the direction of being opened according to a flow rate or air. CONSTITUTION:In an operation range with a relatively small intake air flow rate of an internal combustion engine 1, a mobile flap 11 energized in the direction of being closed with an unillustrated return spring is almost fully closed so that the most of intake air passes to a bypass path 8 to increase a diversion ratio on the side of the path 8. Therefore, a flow velocity in a host wire 9 becomes higher though the flow rate as a whole is small to improve detection accuracy at a low flow rate area. On the other hand, in an operation range relatively large in the intake air flow rate, the flap 11 is opened against an energizing force of the return spring and air also passes to a main intake path 7 to lower the diversion ratio on the side of the path 8. Then, the flap 11 is almost fully opened near the largest output of the engine 1. Thus, increase in a pressure loss is made almost negligible thereby enabling detection of a flow rate in a wide range avoiding a drop in the largest output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a hot wire air flow rate detection device that detects the intake air flow rate of an internal combustion engine by utilizing heat dissipation from a wire or foil heating element. Regarding improvements.

BACKGROUND ART A hot wire type is known as a type of air flow rate detection device for an internal combustion engine (for example, see "Service Bulletin No. 484" published by Nissho Jidosha Co., Ltd. in June 1988).

This method measures the flow velocity by placing a hot wire such as a platinum wire or Ni foil in the air flow path and controlling the current to keep it at a constant temperature. As the amount of heat dissipated increases, the temperature of the hot wire decreases and the resistance of the hot wire decreases, so by detecting the change in resistance using a bridge circuit or the like, an output voltage corresponding to the air flow rate is obtained.

FIG. 5 schematically shows the configuration of a conventional bypass type hot wire air flow rate detection device, in which a part of the intake passage 23 leading from the air cleaner 21 to the internal combustion engine 22,
Specifically, a part of the upstream side of the throttle valve 24 is connected to the main intake passage 25.
and a bypass passage 26, and a hot wire 27 serving as a detection section is disposed within the bypass passage 26.

In this configuration, the hot wire 27 actually detects the flow velocity in the bypass passage 26, that is, the air flow rate on the side of the bypass passage 26, but the main intake passage 27
5 and the bypass passage 26, air always flows at a constant division ratio regardless of the size of the air flow rate, so the air flow 'it of the entire internal combustion engine 22 is detected based on the flow velocity on the side of the bypass passage 26. It is possible.

Problems to be Solved by the Invention However, in the hot wire type air flow rate detection device as described above, in a region where the air flow rate is low such as when the engine is idling, the flow velocity near the hot wire 27 decreases due to the pressure loss generated in the bypass passage 26. becomes too small,
Detection accuracy decreases.

In other words, in a low flow rate region where the output voltage is below a certain value, the influence of errors due to various factors increases, and the detection accuracy cannot be guaranteed.

Incidentally, if the cross-sectional area of the main intake passage 25 is set small and the flow division ratio on the bypass passage 26 side is increased, the detection accuracy in the low flow rate region will be improved accordingly, but this will also reduce the pressure loss in the high flow rate region. increases, resulting in a decrease in the maximum output of the internal combustion engine.

In addition, hot wire air flow rate detection devices sensitively detect pulsation of intake air, and the output voltage changes with a large amplitude, so countermeasures for this are a major technical issue.

Means for Solving the Problems The present invention has been made to solve the above-mentioned conventional problems, and includes separating a part of the intake passage of an internal combustion engine into a main intake passage and a bypass passage, and also forming a part of the intake passage of an internal combustion engine into a main intake passage and a bypass passage. In the hot wire type air flow rate detection device for an internal combustion engine, the hot wire type air flow rate detection device for an internal combustion engine is provided with a movable member in the main intake passage that is biased in the closing direction by a return spring and rotates in the opening direction depending on the air flow rate. It is characterized by a flap.

Function: The movable flap above opens and closes naturally depending on the air flow rate.
For example, the degree of opening is small in the low flow 'rt region. Therefore, the branching ratio on the bypass passage side increases, and the detection accuracy using the hot wire improves. Furthermore, since the opening degree of the movable flap naturally increases in the high flow rate range, the pressure loss near the maximum output becomes small. Incidentally, since the opening degree of the movable flap and thus the flow division ratio are uniquely determined by the air flow rate of the entire engine, the relationship between the output voltage and the air flow rate is also given as a fixed characteristic as in the conventional case.

Embodiment FIG. 1 shows an embodiment of a hot wire type air flow rate detection device according to the present invention.

In the figure, I indicates an internal combustion engine, 2 indicates an air cleaner, and 3 indicates an intake passage leading from the air cleaner 2 to the internal combustion engine I.A throttle valve 4 is interposed in the intake passage 3, and a throttle valve 4 is interposed in the intake passage 3. An air flow meter 5 is interposed on the upstream side of the throttle valve 4.

The air flow meter 5 has a casing 6 that constitutes a part of the intake passage 3, and within the casing 6, a main intake passage 7 and a bypass passage 8 are formed separately. The main intake passage 7 has a substantially rectangular cross section as shown in FIG. Further, the bypass passage 8 has a substantially circular cross section, and is set to have a considerably smaller cross-sectional area than the main intake passage 7.

A hot wire 9 made of platinum wire, Ni foil, or the like and serving as a detection section is disposed in the center of the bypass passage 8.

IO indicates a control circuit section that controls the temperature of the hot wire 9 to be kept at a constant temperature and outputs an output voltage VQ according to the flow velocity, and this is attached to the upper surface of the casing 6.

Further, a movable flap 11 is provided in the main intake passage 7 and is rotatable about a valve shaft 11a at the upper end. The movable flap 11 has a rectangular plate shape large enough to close the entire main intake passage 7, and can be rotated 6 points upstream from the fully closed position (Δ position) of the main intake passage 7 by a stopper (not shown). It is now impossible to do so. In other words, it is configured to be rotatable only toward the downstream side. And a valve with one casing 6 passed through! +h 11 a is linked to the inner circumferential end of a spiral return spring 12 attached to the side surface of the casing 6, thereby constantly biasing the movable flap 11 in the closing direction.

Reference numeral 13 indicates a control unit that calculates the air flow rate from the output voltage VQ of the control circuit +"a<t o. This control unit 13 uses, for example, a digital microcomputer, and is configured to calculate the detected air flow rate. Based on this, air-fuel ratio control, ignition timing control, etc. of the internal combustion engine 1 are simultaneously performed.

Next, the operation of the above structure will be explained with reference to the characteristic diagram shown in FIG. First, in an operating range where the intake air flow rate of the internal combustion engine I is relatively small, the movable flap 11 biased in the closing direction by the return spring 12 is in a substantially fully closed state, and most of the intake air is directed to the bypass passage 8 side. Flow through. In other words, the branching ratio on the bypass passage 8 side becomes extremely large. Therefore, even if the overall flow rate is small, a high flow velocity can be obtained in the hot wire 9 portion, and as shown in FIG. 3, a correspondingly high output voltage VQ is ensured. Therefore, detection accuracy in low flow areas such as when idling is improved, and the minimum flow rate (Takigawa corresponding to the lower limit voltage ■) for which detection accuracy is guaranteed is smaller than the conventional one (see broken line). - Detection is possible on the low flow rate side of the layer. Furthermore, as shown in ``-'', when the movable flap 11 closes, the force loss yF increases (see Figure 4), but since the overall air flow rate is small in this operating range, this increase in pressure loss poses no problem. Not.

On the other hand, in the operating region where the intake airflow (the hold is relatively large),
-3 Self FiJ dynamic flap I! or return spring 12
Since it is pushed open against the urging force of , air also flows to the main intake passage 7 side, which means that the division ratio on the bypass passage 8 side decreases. In the vicinity of the maximum output of the internal combustion engine 1, the movable flap 11 is substantially fully open, so that the increase in pressure loss caused by this can be almost ignored. That is, as shown in FIG. 4, the pressure loss can be maintained at approximately the same level as that of the conventional type (indicated by the broken line) that does not include the movable flap 11, and a decrease in the maximum output can be avoided.

Here, the opening degree of the movable flap II is maintained at a position where the pressing force by the air flow and the biasing force of the return spring 12 are balanced, so that the intake air flow rate of the internal combustion engine 1 is increased as shown in FIG. It is uniquely determined depending on. Since the diversion ratio is determined by the degree of opening of the movable flap If, the relationship between the output voltage VQ and the air flow rate shown in FIG. 3 has a fixed characteristic. The relationship between the output voltage VQ and the air flow rate is provided in advance in the control unit 13, for example, as a data map, and based on this, the air flow rate is detected from the output voltage VQ of the control circuit section IO. That is, the movable flap 11
There is no need to detect the degree of opening of the valve or to make corrections according to the degree of opening.

Further, according to the above configuration, the movable flap 11 supported by the return spring 12 acts as a damper against changes in intake pulsation, so intake pulsation is suppressed and the amplitude of pulsation in output voltage VQ is extremely small. Become. Therefore, there is an advantage that detection accuracy can be improved to a certain extent and high-resolution sampling is not required.

As is clear from the explanation in Section 2 of ``Effects of the Invention'', the hot wire air flow rate detection device for an internal combustion engine according to the present invention can improve the detection accuracy in the low flow rate range, Highly accurate flow rate detection becomes possible. Also, the movable flap is pushed naturally by the airflow. Since it is an open configuration and there is no need to control the opening degree or detect the opening degree, the configuration does not become complicated. .

At the same time, the movable flap can alleviate the intake pulsation, thereby avoiding a decrease in detection accuracy due to the intake pulsation.

[Brief explanation of the drawing]

Fig. 1 is a configuration explanatory diagram showing an embodiment of the hot wire type air flow rate detection device according to the present invention, Fig. 2 is a cross-sectional view taken along the line ■ - A characteristic diagram showing the relationship between the air flow rate and the relationship between the movable flap opening and the air flow rate. Figure 4 is a characteristic diagram also showing the relationship between pressure loss and air flow rate. Figure 5 is a conventional hot wire air flow rate detection. FIG. 2 is an explanatory diagram of the configuration of the device. 3... Intake passage, 5... Air flow meter, 7...
Main intake passage, 8... bypass passage, 9... hot wire, If
...Movable flap, 12...Return spring.

Claims (1)

[Claims] (1) In a hot-wire type air flow rate detection device for an internal combustion engine, in which a part of the intake passage of the internal combustion engine is separated into a main intake passage and a bypass passage, and a hot wire is arranged in the bypass passage, A hot-wire type air flow rate detection device for an internal combustion engine, characterized in that a movable flap is disposed in an intake passageway, the flap being biased in the closing direction by a return spring and rotating in the opening direction depending on the air flow rate.