JPS628358Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an air flow rate measuring device used in an electronic fuel control device installed in an internal combustion engine, and in particular uses a hot wire to measure the air flow rate based on changes in the degree of heat generated by the hot wire. The present invention relates to a type air flow rate measuring device.

The electronic fuel control device is a carburetor system that controls the air-fuel ratio (air amount/fuel amount) by changing the amount of air and fuel passing through the air bleed and jet of the carburetor using electrically driven solenoid valves. A fuel injection method that directs fuel maintained at positive pressure to a solenoid valve and controls the air-fuel ratio by changing the opening area or opening time of the solenoid valve.
Auxiliary air passage separate from the intake passage (bypass air passage)
The amount of air passing through this auxiliary air passage is controlled by an electric device, such as a pulse motor, to control the air-fuel ratio. It attempts to maintain the air-fuel ratio in an optimal state by electronically controlling the supplied air or fuel, or the supplied amounts of air and fuel.

The air flow rate is a typical parameter input to the control unit that makes up this electronic fuel control system.Currently, a movable vane is installed in a part of the intake passage to measure the air flow rate. The vane type, which measures the air flow rate using a corner, and the diaphragm-differential transformer type, which uses a diaphragm and a differential transformer to detect the pressure in the intake passage and measure the air flow rate, are in practical use. . However, these measuring devices have problems such as the presence of hysteresis because they have movable parts, and the fact that the device itself becomes large because its main structure is mechanical.

Therefore, unlike the above-mentioned measuring device, a hot wire type air flow meter has recently been proposed that does not have any moving parts or mechanical components. The principle of this hot-wire air flow meter is basically to install a temperature-dependent resistor in the middle of the intake path, and measure the air flow rate by detecting changes in the current or voltage flowing through this resistor as the air flow rate increases or decreases. An example of this is as disclosed in US Pat. No. 3,747,577.

The installation position of this hot wire air flowmeter is the throttle chamber where the throttle valve is installed, and it also bypasses the intake passage formed in the throttle chamber and connects the air cleaner and throttle directly above the throttle chamber. It was located in the middle of the bypass passage that connects upstream of the tutle valve. The reason for adopting this configuration is that the internal combustion engine has BACK FIRE.
This is to prevent the hot wires from coming into direct contact with the high temperature air generated by the backup fire, thereby preventing the hot wires from being burnt out.

However, when the hot wire is disposed in the bypass passage in this manner, the present inventors have confirmed the phenomenon that the hot wire output decreases when the internal combustion engine is continuously operated. For this reason, when the internal combustion engine is operated continuously, the degree to which the hot wire air flowmeter detects the true air amount decreases over time, resulting in unfavorable results in terms of exhaust gas characteristics and operating performance. It is presumed that this decrease in hot wire output is caused by the following reasons.

In other words, when an internal combustion engine produces a backfire, the flame or high-temperature air passes through the intake manifold that connects the throttle chamber and the engine combustion chamber, and the throttle chamber, and reaches the air cleaner directly above the throttle chamber. Due to the ventilation resistance of the filter installed in the air cleaner, the air does not drop in pressure and returns to the engine combustion chamber, and at this time, a portion of the air passes through the bypass passage where the hot wire is arranged. Therefore, the carbon grains and engine oil carried by the backfire adhere to the hot wire, and as a result of this return, the hot wire is covered with carbon grains and engine oil, and as a result, the amount of heat removed from the hot wire by the air flow increases. decreases, and the hot wire output decreases.

The purpose of this project is to provide a hot wire type air flow measuring device for an internal combustion engine that can prevent the reduction in hot wire output over time due to backfire and can detect an air flow rate close to the true value of the hot wire over a long period of time. It is.

The feature of this design is that a passage is provided between the throttle valve of the throttle chamber and the air cleaner to merge from another air cleaner, and by providing a hot wire in this passage, the backfire flows back toward the main air cleaner due to its directionality. This makes it difficult to access the passage where the hot wire is attached, and prevents carbon grains and engine oil from flowing into the hot wire.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an electronic fuel control system using a hot wire air flow rate measuring device according to an embodiment of the present invention, in which reference numeral 10 denotes a throttle chamber in which an intake passage 11 is formed. The intake passage 11 is 2 in the middle.
It is divided to form a primary side 12 and a secondary side 13, and a primary throttle valve 14 and a secondary throttle valve 15 are disposed on each side. The ventilation area of the primary side 12 is designed to be smaller than the ventilation area of the secondary side 13, and each throttle valve 14, 15 is designed so that the primary side throttle valve 14 is opened at a predetermined opening as in a general compound carburetor. The secondary throttle valve 15 is configured to open when opened. There is an air cleaner 16 on the upstream side of the throttle chamber, and a filter 18 inside the air cleaner
Air flows through the intake duct 17 to the intake passage of the throttle chamber 10. Further, a buffer chamber 19 having a larger volume per unit length than the duct 17 is formed in the middle of the suction duct 17.

Further, a bench lily 50 is formed in the throttle chamber, and a passage 51 separate from the intake passage leading to the air cleaner is provided in the bench lily portion, and an auxiliary air cleaner 52 is installed upstream of this passage.
Further, hot wires 21 and 22 are arranged in the middle of this passage 51, one hot wire 21 is for detecting air flow rate, and the other hot wire 22 is for detecting air temperature. The air temperature detection hot wire 22 detects the air temperature and compensates the output for changes in air temperature, taking into account the influence of air density. The outputs of the hot wires 21 and 22 are inputted to a control unit 24 via a lead wire 23, where they are subjected to arithmetic processing or program processing. In addition to the outputs of the hot wires 21 and 22, the control unit 24 also receives the output O ₂ sig from the oxygen concentration sensor installed in the exhaust system, the output Tesig from the temperature sensor, and the output θsig from the crank angle sensor. Comprehensive calculations and program processing are now possible. The control unit 24 performs analog or digital processing, and its output is sent to a fuel injection electromagnetic valve 25 to control the fuel flow rate by changing the opening area or opening time of the electromagnetic valve 25. The output of the control unit 24 is also used as an input signal IGsig to an ignition system (not shown) and a signal EGRsig to an exhaust gas flow control valve (not shown) of an exhaust gas recirculation system.

In a device using a hot-wire air flow measuring device for an internal combustion engine configured as described above, if a backfire occurs in the engine, most of the flames or high-temperature air containing carbon particles and engine oil will flow through the manifold and throttle. It reaches the air cleaner through the intake passage 11 of the chamber 10.

Since the passage 51 is oriented in a direction perpendicular to the flow of the backfire, it is difficult to enter the direction of the passage 51 even if a backup fire occurs. Therefore, there is little intrusion of high-temperature air, and it is possible to prevent carbon particles and engine oil from adhering to the hot wires 21 and 22. In particular, when backfire occurs continuously, the degree of adhesion of carbon particles and engine oil increases, but even in such cases, it was confirmed that the amount of adhesion of carbon particles and engine oil to the hot wire was significantly reduced.

Figure 2 shows the relationship between air flow rate and hot wire output of a conventional hot wire air flowmeter and the hot wire air flowmeter of the present invention, where the solid line represents the flowmeter of the present invention and the broken line represents the conventional flowmeter. There is. As can be understood from this figure 2, as the air flow rate increases, the amount of heat removed by the conventional type decreases due to the amount covered with carbon particles and engine oil, even though a large amount of air is flowing. First, the hot wire output is lower by △V. In other words, a signal indicating that the amount of supplied air is small is sent to the control unit 24. Therefore, the air-fuel mixture supplied to the engine tends to be lean, leading to problems such as deterioration of driving performance at high speeds and generation of large amounts of hydrocarbons due to misfires. On the other hand, in the flowmeter of the present invention, even if backfire occurs, the degree of adhesion of carbon grains and engine oil to the hot wire is small, so the hot wire output can output a value extremely close to the true air flow rate over a long period of time, and can be used at high speeds. It is possible to achieve the effects of improving operating performance and reducing hydrocarbon concentration.

On the other hand, in this embodiment, a heating wire 22 for detecting air temperature is provided in addition to the heating wire 21 for detecting air flow rate, but if the arrangement of the heating wires 21 and 22 is configured as in this embodiment, the following will occur. Effects such as this can also be achieved.

When two hot wires are installed in the passage that connects the air cleaner directly above the throttle chamber and upstream of the throttle valve as in conventional equipment, the hot wire for air temperature detection is affected by the high temperature air during backup. and begins to exhibit abnormal heat ray output. This state is shown in FIG. 3, and the broken line is the hot wire output at that time. As can be seen from this, when a backfire occurs, the hot wire output rises rapidly, and it takes 3 to 4 seconds to return to a steady state. Therefore, during this time the hot wire output provides a signal to the control unit that more air is flowing, and based on this signal the fuel injector will supply more fuel to the engine. As a result, extra fuel is supplied to the engine despite the fact that the air flow rate is small, causing the problem that the air-fuel mixture becomes extremely rich and the carbon monoxide concentration becomes abnormally high.

However, as in this embodiment, if the passage connecting between the upstream side of the throttle valve of the throttle chamber and the air cleaner is provided completely independently from the main air passage, and a hot wire is inserted in the middle, a backfire occurs. However, it was confirmed that the high temperature air at this time had almost no effect on the hot wire 22 provided in the air passage 51 for testing the air temperature. The solid line in FIG. 3 shows the hot wire output at that time, and even if there is only a small amount of backfire, the hot wire output is not so large compared to the steady state, and the time to return to the steady state is less than 1 second. Therefore, the amount of fuel supplied from the fuel injection valve 25 is in an amount that substantially ignores the influence of the backup fire due to the inertia of the fuel injection valve 25 and the processing time of the control unit 24, and it is possible to maintain a substantially constant air-fuel ratio. be.

As explained above, the present invention provides a passage that joins between the throttle valve of the throttle chamber and the air cleaner completely independently of the main air passage, and by incorporating a hot wire in the middle, it is possible to prevent backfire from occurring. , the high temperature flame or air reaches the direction of the main air cleaner and almost never reaches the passage where the hot wire is provided, and is substantially stopped, thus preventing carbon particles and engine oil from adhering to the hot wire. It is possible to obtain a practically extremely effective hot wire type air flow measuring device that can output a hot wire output that is extremely close to the true amount of air over a long period of time.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of an electronic fuel control device using a hot wire air flow rate measuring device which is an embodiment of the present invention, and Figure 2 is an air flow rate vs. hot wire output of the hot wire type air flow rate measuring device of the present invention and a conventional hot wire type air flow rate measuring device. FIG. 3 is a diagram showing the relationship between time during backup and hot wire output of the present invention and the conventional hot wire air flow measuring device. 10...Throttle chamber, 11...Intake passage, 12...Primary side, 13...Secondary side, 14...
Primary side throttle valve, 15...Secondary side throttle valve, 16...Air cleaner, 18...Filter, 21, 22...Heat wire, 23...Lead wire, 24...Control unit, 25...Solenoid valve .

Claims (1)

[Scope of utility model registration request] In a hot wire type air flow measuring device for an internal combustion engine that measures a portion of the air amount supplied to the engine via an intake passage in a throttle chamber using a hot wire for detecting air flow rate, a main air cleaner 1 through which main air flows is used.
6, a second air cleaner 52 and a passage 51 independent from the main air passage through which the main air flows from the second air cleaner 52 to the bench lily 50 upstream of the throttle valve of the throttle chamber.
A hot wire type air flow measuring device for an internal combustion engine, characterized in that the hot wire 21 is disposed within the passage 51 of the hot wire air flow measuring device.