JPH0337687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a hot wire type air amount detection device, and particularly to an air amount detection device used in a fuel supply system for an internal combustion engine.

[Prior Art] Various air amount detection devices for internal combustion engines have been proposed in the past. For example, in the air amount detection device disclosed in Japanese Patent Laid-Open No. 55-37555, air taken from an air cleaner is passed through an intake passage. It passes through the bench lily and is supplied to the engine via a throttle valve. A bypass air passage is further provided in parallel with this intake passage, and a heat sensitive resistor (hot wire) is provided within this bypass passage. The output signal appearing on the heat-sensitive resistor provided in this bypass passage indicates the total air flow rate supplied to the engine through the air passage, and this signal is inputted to, for example, a control unit to determine the optimal required fuel flow rate. Used for calculations. Then, based on the optimal required fuel flow rate calculated by this control unit, the injector is controlled and fuel is supplied to the engine.

However, in the air amount detection device as described above, when the air enters the air passage from the air cleaner, it collapses to generate a vortex and draw a complicated streamline. Such airflow turbulence also affects the airflow in the bypass air passage, which has the disadvantage of tampering with the output of the heat-sensitive resistor, indicating a false airflow rate.

In addition, due to phenomena such as blowback in internal combustion engines,
Carbon and oil droplets enter the air passage and further enter the bypass passage. Another drawback is that the carbon and oil droplets adhere to the surface of the heat-sensitive resistor, that is, the heat wire, provided in the bypass passage, thereby disturbing the detection output.

In order to solve the above-mentioned problems, the present applicant has proposed an air amount detection device having a structure as shown in FIGS. 1 and 2.

First, an air amount detection device proposed by the present applicant will be explained based on FIGS. 1 and 2.

In FIG. 1, an air cleaner 1 is disposed above an air passage 2 having a bench lily portion 3 at the center of its inner surface. Below this air passage 2,
Throttle valve 4 and fuel injector 6
is installed. Air that has passed through the filter 5 of the air cleaner 1 passes through the bench lily portion 3 of the air passage 2, is mixed with fuel injected from the injector 6, and is guided to the cylinders of the engine (not shown).

As is generally known, the fuel supplied to the engine is set to an optimal value calculated by the control unit 7 based on the detected air flow rate Q _A supplied to the engine. The fuel injection time of the injector 6 is then controlled according to this optimum fuel.

A throttle body including an air passage 2 having a bench lily portion 3 is formed of, for example, aluminum die casting, and a bypass air passage 8 is further formed within the throttle body. The entrance of this bypass passage is the air passage 2
It opens in a land part 10 formed on one side of the air horn part 9 at the upper part of the air horn part 9, and its outlet is led to an air passage 11 through a slit 11 formed in the narrowest part of the bench lily part 6.

Furthermore, in the upper part of this bypass air passage 8,
For example, a metal pipe 12 is attached. Inside this bypass air passage 8,
A heat-sensitive hypobody, ie, a heat wire 13, whose resistance value changes depending on the air flow rate is provided.

Hot wire 1 arranged in bypass air passage 8
3 usually consists of two hot wires. These hot wires form the bipods of the bridge circuit.

Air flow rate flowing through air passage 2 of the throttle body
_A is generally defined by the bench lily portion 3;
An air flow proportional to this air flow rate, that is, the air flow rate supplied to the engine, flows into the bypass air passage 8. A hot wire whose resistance value changes in response to the air flow rate flowing through the bypass passage 8 will therefore generate an output signal proportional to the air flow rate supplied to the engine.

Generally, in an air flow rate detection device having an air passage and a bypass air passage provided in parallel to the air passage, the air flow particularly in the upstream portion of the bypass passage is likely to be disturbed by swirls or the like if the air flow falls. The air flow rate detection device proposed by the applicant is based on the following experimentally discovered facts. That is, the length l of the upstream portion of the hot wire 13 of the bypass passage 8
This is the fact that by making D at least twice as large as the diameter D of the bypass passage 8, it is possible to reduce the adverse effects of turbulence in the surrounding airflow. On the other hand, since the length of the bypass passage, especially the length of the upstream portion of the hot wire, is determined by the size or structure of the throttle body, it is difficult to set it to a desired length.

A pipe 12 bent at a predetermined curvature is attached to the upstream entrance of the air passage 8 in order to make the length of the hot wire upstream portion of the bypass passage a desired length. This pipe 12 is a metal pipe when folded down, and a flange portion 14 is attached by welding or the like. This bent pipe 12 having a flange portion 14 is firmly fixed to a land portion 10 of the throttle body by screws 15. Further, a metal support member 16 is attached to this land portion by screws 17 when it is folded down, and this support member 16 supports the bent pipe 12 more firmly.

As is clear from the figure, the inlet opening of this bent pipe 12 is opened inside the upper projection part of the bench lily part 3 and along a plane substantially perpendicular to the axial line of the bench lily part 3, and the outlet The opening is opened to a bypass passage upstream of the hot wire 13.
By providing such a bent pipe 12, air with low inertia is guided into the bypass passage 8 through the pipe 12, but on the other hand, carbon and oil droplets with large inertia compared to air enter the pipe 12. It becomes difficult to do. Therefore, it is possible to prevent carbon and oil droplets from adhering to the hot wire 13 due to phenomena such as blowback.

In the air amount detection device proposed by the applicant as described above, the length upstream of the hot wire in the bypass passage can be made sufficiently long, so that air turbulence does not occur in the bypass passage, and carbon and oil droplets are removed in the axial direction of the bench lily. Since it uses a bent pipe that opens at right angles to the line, it is difficult to enter the bypass passage.

By the way, after actually manufacturing the air amount detecting device proposed by the present applicant as a product, a problem arose in that when the output of the air amount detecting device was measured, the output varied between individual devices. When I considered why this problem occurred, I found that bent pipe 1
It has been found that this is due to the fact that the inlet opening of No. 2 does not open exactly at right angles to the axial line of the bench lily portion 3.

As described above, the reason why the inlet opening of the bent pipe 12 does not open at right angles to the axial direction of the bench lily part 3 is that firstly, the bending angle of the bent pipe 12 cannot be made constant for all individual pipes (usually ± (There is an error of 5 degrees.).Secondly, it is considered that the installation error when the bent pipe 12 is fixed to the land portion 10 is not constant.

In particular, when the inlet opening of the bent pipe 12 opens in the direction of air flow and receives the dynamic pressure of the intake air flow, the air flow rate detection device produces an extremely large output, and the degree of reception of this dynamic pressure As a result, the output will vary greatly.

[Purpose of the invention]

The purpose of the present invention is to ensure that the output representing the intake air amount of each air amount detection device does not vary from one air amount detection device to another, and that each air amount detection device can obtain almost the same output under the same conditions. It is to make it.

[Summary of the invention]

A feature of the present invention is that the inlet opening of the bent pipe is opened in a direction that does not receive the dynamic pressure of the intake air flow relative to the axis of the bench lily, thereby introducing static pressure to the inlet opening of the bent pipe. It made me tremble.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

In FIG. 3, the inlet opening 18 of the bent pipe 12 has a relief angle θ as shown by a cutting line D with respect to the axial direction C of the bench lily portion 3 (translated parallel to the central axis of the bench lily portion 3). It has an opening. That is, with respect to the distance L from the central axis M of the bypass passage 8 to the uppermost end 18u of the inlet opening 18, the lowermost end 18 of the inlet opening 18
The distance l to d is getting shorter.
Therefore, the flow of intake air flows along the axial line of the bench lily portion 3, but the inlet opening 18 of the bent pipe 12 has a clearance angle θ in any air flow rate detection device. It is designed not to be affected by the dynamic pressure of airflow. Therefore, both air flow rate detection devices can obtain substantially the same output under the same conditions.

In FIG. 4, the relationship between the clearance angle θ and the rate of change in the output of the air amount detection device will be explained. The horizontal axis is the relief angle θ
, and Odeg is the value of bent pipe 12
The figure shows when the inlet opening 18 and the axial line of the bench lily part 3 are perpendicular to each other. As shown in Figure 3, this shows when the opening is open so as not to receive dynamic pressure. The vertical axis shows how much the output fluctuates based on the output value when the clearance angle θ is Odeg while keeping the amount of air taken into the internal combustion engine constant (20 kg/h).

As can be understood from FIG.
8 is subjected to the dynamic pressure of the intake air flow, the output fluctuates greatly, and the inlet opening 18 of the bent pipe 12
It can be seen that if the clearance angle θ is on the tenth side, and the clearance angle θ varies among individual air amount detection devices, the output thereof will also vary greatly. On the other hand, when the relief angle θ of the bent pipe 12 is on one side, that is, when the inlet opening 18 of the bent pipe 12 is not subjected to the dynamic pressure of the intake air flow, the output remains almost constant, although there may be slight fluctuations. If the inlet opening 18 of the bent pipe 12 has a relief angle θ on one side, the output can be kept almost constant even if the relief angle θ varies between individual air amount detection devices. I understand.

In this way, the inlet opening 1 of the bent pipe 12
If the clearance angle of 8 is made to be on one side in all air quantity detection devices, as long as the clearance angle of the inlet opening of the bent pipe 12 of each air quantity detection device varies on one side, as shown in FIG. As explained in
The output of the air amount detection device is kept approximately constant.

The above was proposed taking into consideration the influence of dynamic pressure on the intake airflow, but when considering the output of the air flow rate detection device, it is possible to improve the accuracy of the output by considering the following. Become.

That is, the inlet opening 18 of the bent pipe 12
If the clearance angle θ is increased unnecessarily to one side, turbulence of airflow will occur in the area of clearance angle θ, and this turbulence may have an adverse effect on the bypass passage 8.

In Fig. 5, the horizontal axis shows the clearance angle θ of the inlet opening 18 of the curved pipe 12, and the vertical axis shows the median output value and the rate of change in output swing width under the condition of constant intake air amount (20 kg/h). It shows. As can be understood from FIG. 5, when the relief angle θ is set to -15 degrees or more, there is a problem in that the rate of fluctuation of the output increases rapidly. This is thought to be because when the clearance angle θ becomes -15 degrees or more, air turbulence rapidly occurs in this part. Therefore, it is desirable that the relief angle θ is around −15 degrees at maximum.

FIG. 6 shows how to determine the clearance angle θ of the bent pipe 12.

Now, the error range of the bending angle of the bent pipe 12 is normally 5 degrees. Therefore, if the installation error when attaching the bent pipe 12 to the land 10 of the air horn section 9 is ±2 degrees, the overall error in the clearance angle θ is ±7 degrees. Conventionally, this ±
Inlet opening 1 of bent pipe 12 in the range of 7 degrees
8 varied with respect to the axial direction C of the bench lily portion 3. In the present invention, the inlet opening 18 of the bent pipe 12 is cut at a cutting angle θ ₁ so that the tip of the bent pipe 12 becomes the inlet opening 18. This cutting angle θ ₁ is set to 8 degrees. Then, when the total error reaches the maximum of +7deg on the tenth side, the clearance angle θ becomes θ=+7deg−8deg=−1deg, and on the other hand, when the total error reaches the maximum of one side of −7deg, , the relief angle θ is θ=−7deg−8deg=−15deg, which falls within the limit range shown in the experimental results of FIGS. 4 and 5.

As described above, in the example shown in FIG. 6, only the tip of the bent pipe is simply cut at a predetermined cutting angle θ ₁ , so the work is extremely simple.

Next, another embodiment of the present invention will be described based on FIG.

FIG. 7 shows another embodiment of the present invention, which differs from FIG. 6 in that the inlet opening 18 at the tip of the bent pipe 12 is not cut at a cutting angle θ ₁ ; Bending angle θ ₂ as corresponding to cutting angle θ ₁
has become a predetermined value.

That is, the inlet opening 18 of the bent pipe 12
The opening is perpendicular to the axis of the bent pipe 12, which is similar to the embodiment shown in FIG. However, the bending angle θ ₂ of the bent pipe 12 is 90° or less and is bent at 82 degrees. Therefore, when the bent pipe 12 is fixed to the land 10, the inlet opening 18 has a relief angle θ similar to that shown in FIG. Therefore, the dynamic pressure of the air flow no longer acts on the inlet opening 18, as in FIG.

The reason why the bending angle θ ₂ of the bent pipe 12 was decided to be 82 degrees is as follows.

As mentioned above, the overall installation error of the bent pipe 12 is ±7 degrees. Therefore, when the mounting error reaches +7deg at the maximum on one side, the relief angle θ becomes θ = +7deg + 82deg = 89deg (=-1deg). On the other hand, when the mounting error reaches -7deg at the maximum on one side , the clearance angle θ is θ=-7deg+82deg=75deg (=-15deg), which falls within the limit range shown in the experimental results of FIGS. 4 and 5.

In this manner, in the example shown in FIG. 7, the work is extremely simple because the bending angle θ ₂ of the bent pipe is simply selected to a predetermined value and bent.

What is common to the embodiments shown in FIGS. 6 and 7 is that the relief angle θ is on one side and its maximum is in the range of −15 degrees, so that the dynamic pressure of the air flow is not applied to the inlet opening 18. , no significant air turbulence occurs in the area of the inlet opening 18.

〔Effect of the invention〕

As described above, according to the present invention, the inlet openings of the bent pipes are opened in a direction that does not receive dynamic pressure in all of the individual air amount detection devices.
The output of each air amount detection device can be kept almost constant under the same conditions.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an air amount detecting device proposed by the applicant, FIG. 2 is a view taken along the - arrow in FIG. 1, and FIG. 3 is an air amount detecting device according to an embodiment of the present invention 4 and 5 are cross-sectional views of main parts, diagrams showing the relief angle of the bent pipe and changes in the output of the air amount detection device,
FIG. 6 is a sectional view of a bent pipe, and FIG. 7 is a sectional view of a main part of an air amount detection device according to another embodiment of the present invention. 2... Air passage, 3... Bench lily section, 4...
Throttle valve, 8... Bypass passage, 9...
Air horn part, 10...Land part, 11...Slit, 12...Bent pipe, 13...Hot wire, 1
8...Inlet opening, θ... Relief angle, θ ₁ ... Cutting angle, θ ₂ ... Bending angle.

Claims (1)

[Claims] 1. A bench lily portion formed in the middle of an air passage that supplies air to the internal combustion engine, a bypass passage that opens upstream of the bench lily portion and bypasses the air passage and opens into the bench lily portion, and a portion in the middle of the bypass passage. and a bent pipe having an inlet opening opening into the air passage and an outlet opening opening into the bypass passage upstream of the air quantity detection means; In the air amount detection device in which the inlet opening is opened toward the axial direction of the bench lily, a distance L from the uppermost end of the inlet opening of the bent pipe to the central axis of the bypass passage; The distance l from the lowermost end of the inlet opening of the bent pipe to the central axis of the bypass passage has a relationship of L>l, and a line connecting the uppermost end and the lowermost end and the uppermost end The maximum angle between the axial line of the bench lily and the
An air amount detection device characterized by 15deg.