JPH03291528A - Hot wire type air flowmeter - Google Patents

Abstract

PURPOSE:To prevent a decrease in assembly accuracy and detection accuracy due to water stagnation by providing the exits of a by-pass passages on the upstream and downstream sides of a main air flow passage. CONSTITUTION:Air which is fetched from the air flow passage 5 is supplied to an engine by controlling the flow rate with a throttle valve 6 and a part of the air flow enters the by-pass passage 4 from an entrance 4c at a specific ratio. The passage 4 are provided with the main exit 4a and auxiliary exit 4b, the exit 4a is formed as an opening part in an upper member 3, and the exit 4b is formed as a notched part in the coupling surface between a throttle valve main body 8 and the member 3, thus, the rate of the air flow which returns to the passage 5 through the exit 4b is reduced passes through the exit 4a, so that a flow rate detecting element 2a provided on the passage 4 detects the air flow rate. Consequently, the accuracy of the position and shape of the exit 4a depends only upon the machining accuracy of the member 3 and is therefore high and the exit 4b is at the most downstream part of the passage 4, so water flowing in the passage 4 is discharged from the exit 4b immediately, so that an invariably stable air flow rate can be measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a bypass type hot wire air flowmeter,
In particular, the present invention relates to a hot wire air flow meter suitable for measuring the intake air flow rate of automobile engines.

[Conventional technology]

As intake flowmeters for automobile engines, bypass type hot wire air flowmeters have been known for a long time, examples of which are disclosed in Japanese Patent Application Laid-open No. 58-19510 and Japanese Patent Application Laid-Open No. 58-135917.
No. 59-652] No. 7, JP-A No. 58-1284
No. 12, and each publication of JP-A-60-185118,
and Utility Model Publication No. 63-38378.

[Problem to be solved by the invention]

By the way, in such a bypass type hot wire air flow meter, the outlet of the bypass passage is located at the lowest part of this passage (in the case of a downdraft type), and between the flow meter member and the throttle body member, or between these members. Some devices are made of a combination of at least two members, including a gasket inserted between them, but such conventional technology has problems in maintaining accuracy during assembly, resulting in variations in flow rate detection accuracy. Easy to occur.

On the other hand, with the conventional technology in which the above-mentioned bypass passage, including its outlet, is constructed only from flowmeter members, there is no particular problem in terms of maintaining accuracy, but this outlet cannot be formed at the lowest part of the bypass passage. Therefore, water tends to accumulate in the bypass passage, which poses a problem of lowering detection accuracy.

In addition, in recent years, there has been a strong demand for the integration of flowmeter components and throttle body components to simplify the configuration, and for reductions in length and radial dimensions to reduce size. The problem with this technology is that it is difficult to provide an intake flow meter with good characteristics because it does not take into account the decrease in detection accuracy due to the influence of turbulence caused by the throttle valve and the increase in intake resistance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hot-wire air flow meter that is free from the risk of deterioration in assembly accuracy or detection accuracy due to water accumulation, and can be sufficiently miniaturized.

[Means to accomplish the task]

In order to achieve the above object, the bypass passage has at least two outlets located on the upstream side and the downstream side in the air flow direction within the main air passage.

In addition, in order to achieve the above object, a folded passage section is provided in the bypass passage, and the dimension between the air inlet and the air outlet in the main air passage of the bypass passage is equal to that of the air inlet and the air outlet in the main air passage of the bypass passage. The maximum length dimension along the air flow direction is made smaller than the maximum length dimension along the air flow direction.

Furthermore, in order to achieve the above object, the air inlet of the bypass passage is formed into a tubular member projecting into the main air passage from the upstream end of the bypass passage.

[Effect]

By making the bypass passage have at least two outlets located on the upstream and downstream sides in the air flow direction within the main air passage, the flow rate can be detected using the upstream outlet without being affected by the throttle valve. At the same time, since the outlet on the downstream side can function as a water outlet, the flow rate can be detected with high accuracy.

In addition, by providing a folded passage in the bypass passage, even if the length dimension is reduced, the exit of the bypass passage can be installed at a position sufficiently far away from the throttle valve, which prevents deterioration in detection accuracy due to turbulent flow. It can be suppressed sufficiently.

Furthermore, by making the air inlet of the bypass passage a tubular member that protrudes from the upstream end of the bypass passage into the main air passage, the main air passage Since the diameter of the lens can be reduced and there is no offset, it can be easily miniaturized.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hot wire air flow meter according to the present invention will be explained in detail below using illustrated embodiments.

FIG. 1 shows an example in which the present invention is applied to a 5PI (single point injection) system, where 1 is a fuel injection valve, 2 is a flow rate measuring unit, and 2a is a flow rate consisting of a pair of hot wire and cold wire. Detection element, 3 is an upper member (member forming the main air passage), 4 is a bypass passage, 4a is a main outlet, 4b is an auxiliary outlet, 4C is an inlet, 5 is a main air passage,
6 is a throttle valve, 7 is an ISO (idle speed control) control valve, 7a is an ISO air inlet, 8 is a throttle body, and 9 is a gasket.

Air taken in from the main air passage 5 via an air filter (not shown) is controlled in flow rate by a throttle valve 6 and supplied to the engine. A part of the air flows into the bypass passage 4 from the inlet 4C at a predetermined rate, and flows into the main air passage 5 through the main outlet 4a.

Since there is a flow rate detection element 2a in the bypass passage 4, the flow rate is detected by this, and an intake flow rate signal is output from the flow rate measurement unit 2. This signal is input to a control device (not shown), and the engine The amount of fuel supplied is calculated. Then, the fuel injection valve 1 is controlled based on this calculation result, and fuel supply amount control is performed.

In this embodiment, the lower intake a of the air supplied to the engine through the ISO control valve 7 opens upstream from the injection port of the fuel injection valve 1, thereby controlling the ISC.
This prevents fuel from flowing into the air supplied to the engine through the control valve 7. In addition, at this time, the lower mantle a is located downstream of the opening position of the main outlet 4a of the bypass passage 4, so that the flow rate of air supplied to the engine through the ISO control valve 7 can also be measured. It looks like this.

By the way, in this embodiment, as is clear from FIG. 1, the bypass passage 4 is provided not only with the main outlet 4a but also with an auxiliary outlet 4b.

FIG. 2 is a developed view of the bypass passage 4. First, the main outlet 4
a is formed by an opening formed in the upper member 3, while the auxiliary outlet 4b is formed by a notch formed in the joint surface of the throttle valve body 8 with the upper member 3. .

Of course, correspondingly, the gasket 9 is also provided with a notch.

Therefore, according to this embodiment, since the accuracy of the position and shape of the main outlet 4a depends only on the processing accuracy of the upper member 3, high accuracy can be easily obtained. Since it is provided at the most downstream part, even if water flows into the bypass passage 4, this water will be immediately discharged from the auxiliary outlet 4b, so there is no risk of water puddles, and stable air is always provided. Flow measurements can be easily obtained.

In this case, in order to fully obtain the above-mentioned effects, it is necessary that most of the air flow rate passing through the bypass passage 4 be sufficiently dependent on the air flow rate passing through the main outlet 4a. This is because, otherwise, the positional accuracy of the auxiliary outlet 4b will affect the positional accuracy.

Here, Fig. 3 shows the pressure difference between the position downstream from the inlet position of the bypass passage 4 and the outlet part, and as is clear from this figure, the pressure P at the main outlet 4a located midway is shown. , the pressure P at the auxiliary outlet 4b at the most downstream end of the bypass passage 4.

is considerably smaller. In other words, P, > P.

Therefore, in this embodiment, the air flow rate returning from the bypass passage 4 to the main air passage 5 through the auxiliary outlet 4b is
The flow rate of the air flowing out from a is suppressed to a sufficiently low level, so that the above-mentioned effects can be reliably obtained.

Note that, as described above, the auxiliary outlet 4b only needs to have an opening area that is sufficient for the water that has flowed into the bypass passage 4 to be discharged. In this respect, the adverse effects of providing the auxiliary outlet 4b can be sufficiently suppressed.

Figure 4 shows the amount of water and measurement changes when water accumulates in the bypass passage 4. As is clear from this figure, as the amount of water increases, the error increases, and in extreme cases, measurement becomes impossible. It turns out that it becomes.

Next, other embodiments of the present invention will be described.

5 to 8 are sectional views taken along line A-All in FIG. 2. First, in the embodiment shown in FIG. 5, the auxiliary outlet 4b is
The bypass passage is formed by a notch provided in the joint surface of the upper member 3 with the throttle valve main body 8. Therefore, according to this embodiment, the entire bypass passage can be formed only by the upper member 3, and the structure is can be done easily and at low cost.

FIG. 6 shows the case of the embodiment shown in FIGS. 1 and 2. According to this embodiment, since the auxiliary outlet 4b is located at the lowest end of the bypass passage 4, the water removal effect is large. be.

FIG. 7 shows an embodiment suitable for cases where the gasket 9 is quite thick, and the auxiliary outlet 4b is formed by simply cutting out a part of the gasket 9.
This embodiment also has a simple configuration and can be made at low cost.

In the embodiment shown in FIG. 8, the shape of the auxiliary outlet 4b is such that the water that would have accumulated in the bypass passage 4 can easily flow out, and for this purpose, it is sloped toward the inside of the main air passage 5. Therefore, according to this embodiment, the drainage characteristics can be significantly improved with only simple shape processing.

Next, another embodiment of the present invention suitable for miniaturization will be described.

First of all, FIG. 9 shows that the dimensions of both the upper member 3 and the throttle valve body 8 in the main air flow direction (hereinafter referred to as the axial direction) can be made sufficiently small, which makes it possible to use a hot wire air flowmeter integrated with the throttle body. In the figure, 4d is the folded passage section of the bypass passage, 10 is the rotating shaft of the throttle valve, and 11 is the air flow chamber, and the other members are the same as in Figure 1. This is the same as the embodiment. That is, 2 is a flow rate measuring unit, 2a is a flow rate detection element consisting of a pair of hot wire and cold wire, 4 is a bypass passage, 4
a is a main outlet, 4C is an inlet, 5 is a main air passage, 6 is a throttle valve, and 9 is a gasket.

As is clear from FIG. 9, in this embodiment, the bypass passage 4 is not configured to immediately return to the main air passage 5 from the straight line portion following the inlet 4C through the main outlet 4a. , a folded passage section 4 facing opposite to the axial direction
d, proceed in the opposite direction and then take the main exit 4a.
, and is configured to return to the main air passage 5 with a further dimensional offset from the position of the flow rate detection element 2a.

As a result, according to this embodiment, even if the axial dimensions of the upper member 3 and the throttle valve main body 8 are reduced, the rotation axis of the throttle valve 6
0 and the main outlet 4a can have a sufficient value.

FIG. 10 is a characteristic diagram showing the relationship between dimension Q and air flow rate measurement error ΔQa. As is clear from FIG. If an attempt is made to reduce the size, this dimension 0 is insufficient, and sufficient measurement accuracy cannot be provided.For this reason, it has been difficult to reduce the size with the conventional technology, but according to the embodiment shown in FIG. Since the folded passage section 4d is provided, even if the axial dimensions of the upper member 3 and the throttle valve main body 8 are considerably reduced, the required dimension Ω can be sufficiently secured. An air flow meter can be easily obtained.

11 and 12 are developed views of the bypass passage in the circumferential direction. First, the embodiment shown in FIG. 11 has one main outlet 4a, which can be called a simple type. Not only is the passage easy to form, but the length of the bypass passage is short, and as a result, the amount of heat transferred from the air flow chamber 11 to the bypass air can be suppressed to a small level, even if the temperature difference between the intake air temperature and the air flow chamber 11 becomes large. , there is an advantage that there is little decrease in measurement accuracy and high accuracy can be obtained.

Next, in the embodiment shown in FIG. 12, a plurality of main outlets 4a, for example two, are provided, so that even if there is turbulence in the air flow in the main air passage 5, the engine is not affected much. This has the advantage that sufficient accuracy can be maintained even when there are many intake pulsations.

By the way, the overall layout of the bypass passage is different from that of the embodiment shown in FIG. 9, in which the folded passage part 4d and the main outlet 4a are provided on the opposite side of the straight pipe part where the detection element 2a is provided. However, it is also possible to create an embodiment in which the presence of obstacles such as the throttle valve opening axis 10 is taken into account, and such an embodiment will be described below.

13, 14, and 15 show the main air passage 5.
In each of these embodiments, the entire bypass passage is provided on one side of the rotating shaft 10 of the throttle valve, and as a simple structure, as in the embodiment shown in FIG. However, in either case, consideration must be given to providing the main outlet 4a in a position that is not affected by the intake pulsation of the engine as much as possible, but in order to do so, it is necessary to Since the increase is effective, in the embodiment shown in FIG. 13, if such a demand for increased volume cannot be met, the bypass passage can be lengthened as in the embodiments shown in FIGS. 14 and 15. . Here, the first
4 shows a case where there are two main outlets 4a, and FIG. 15 shows a case where there is one main outlet 4a, but in the embodiment shown in FIG. Since they are provided close to each other, the external dimensions are small, and there is an advantage that further miniaturization is possible.

Next, still another embodiment of the present invention will be described with reference to FIG. 16.

In this embodiment, as is clear from FIG. 16, the inlet of the bypass passage 4 is constituted by a pipe 4A, and other features are included.
The flow rate measuring unit 2, the upper member 3, the main air passage 5, etc. are the same as in the previously described embodiment.

According to this embodiment, since the pipe 4A is the only member that protrudes into the main air passage 5, the degree of reduction in the effective cross-sectional area of the main air passage 5 due to the installation of the bypass passage 4 can be reduced. As a result, the outer diameter of the upper 8IXs material 3 can be suppressed, resulting in miniaturization.

Furthermore, the shape of the tip of the pipe 4A is not limited to the right-angled cut shape as shown in FIG. 16, but may also be diagonally cut as in the embodiments shown in FIGS. It is possible to make the pipe 4B in the direction or the pipe 4C in the horizontal direction, and it is also possible to select the tip position Q+ of these pipes. As shown, it is possible to adjust the pressure difference Δp at the entrance of the bypass passage and the ratio between the main air flow velocity and the bypass air flow velocity, and it is possible to flexibly respond to changes in the flow measurement range.

Note that these pipes 4A and the like may be inserted into and attached to the bypass passage 4 of the upper member 3 as separate parts, or may be integrally formed by die-casting or the like. Here, if we use an integrated configuration, we can eliminate assembly errors, improve accuracy, and
This will also help reduce costs.

Further, the embodiment using these pipes 4A, 4B, and 4C may be combined with the embodiment described in FIGS. 1 to 15.

Next, FIGS. 21 and 22 show still another embodiment of the present invention configured as an integrated throttle body. For example, in the embodiment shown in FIG. 9, the upper member 3 and the throttle valve main body 8 are combined. The structure is integrated as a main body 12, and furthermore, in this embodiment,
A throttle valve opening sensor 13 is provided on the throttle valve opening moving shaft 10.

In addition, the flow rate measurement unit 2, bypass passage 4, main outlet 4
a, the main air passage 5, the pipe 5B, the throttle valve 6, the ISO control valve 7, the ISC air manifold lower a, etc. are the same as those in the embodiment explained in Figs. 1 to 18, and 7b is the ISC air bypass. It is a passage.

The ISC control valve 7 controls the engine rotational speed, such as the idle rotational speed, which is not dependent on the throttle valve 6. The ISC control valve 7 is a bypass passage 7 for ISC air that is provided to bypass the throttle valve 6.
The opening degree of b is controlled.

In this embodiment, since it is also necessary to measure the intake air flow rate supplied to the engine via the ISC air bypass passage 7b, the ISC air intake lower a measures the throttle valve 6 as shown in the figure. It is necessary to install it on the upstream side and on the downstream side of the main outlet 4a of the bypass passage 4. At this time, in order to measure the ISO air flow rate with high accuracy, it is necessary to install the ISO air lower a and the main outlet. 4a is required.

According to this embodiment, although not shown in the figure, the bypass passage 4 is provided with a turning passage part, and the pipe 4B is provided at the inlet thereof, so that high flow rate measurement accuracy can be achieved. While maintaining this, the axial length of the main body 12 can be sufficiently suppressed, and miniaturization can be achieved sufficiently.

〔Effect of the invention〕

According to the present invention, variations in bypass passage dimensions between products can be suppressed, and water accumulation in the bypass passage can be avoided, making it easy to create a high-performance hot wire air flow meter with good air flow measurement accuracy. can be provided.

Furthermore, according to the present invention, the exit position of the bypass passage can be arbitrarily selected without being affected by the installation position of the air flow rate detection element, so that the size can be sufficiently reduced without reducing the measurement accuracy due to the throttle valve. This has the effect of providing a greater degree of freedom in engine layout design.

Further, according to the present invention, there is no need to provide an offset to the center of the inlet or outlet of the main air passage, and the reduction in the effective cross-sectional area of the main air passage due to the bypass passage can be minimized. Therefore, the external shape can be made smaller, and the size can be sufficiently reduced.

In addition, according to the present invention, it is possible to change the bypass ratio as desired while keeping the same body, and as a result, the same body can be shared even if the measurement range is changed, and costs can be reduced sufficiently. can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the hot wire air flow meter according to the present invention, Fig. 2 is a developed view of a bypass passage, Figs. 3 and 4 are characteristic diagrams for explaining operation, Fig. 5, 6, 7 and 8 are sectional views showing various embodiments of the auxiliary outlet, FIG. 9 is a sectional view showing another embodiment of the present invention, and FIG.
FIG. 0 is a characteristic diagram for explaining the operation, FIGS. 11 and 12 are developed views of the bypass passage, FIGS. 13, 14, and 15 are sectional views showing various embodiments of the bypass passage, and FIG. The figure is a sectional view showing yet another embodiment of the present invention, Figures 17 and 18 are explanatory diagrams showing another embodiment of the bypass passage inlet, and Figures 19 and 20 are for explanation of operation. FIG. 21 is a top view showing an embodiment of the present invention as an integrated throttle body, and FIG. 22 is a sectional view. l...Fuel injection valve, 2...Flow rate measurement unit, 2a...Flow rate detection element consisting of a pair of hot wire and cold wire, 3...Upper member (main air passage ), 4...bypass passage, 4a...main exit, 4b...auxiliary exit, 4C...population, 5... ... Main air passage, 6 ... Throttle valve, 7 ... L5C (idle speed control) control valve, 7a ... I
SC air inlet, 8... Throttle valve body (throttle body), 9... Gasket. Figure jI2 Figure 1: Retirement I square 2: mf ↑ gradient t1 upper knit Figure 3 Nushi p's distance Sho Ryobori lJ figure 16 figure 17 figure 18 figure 19) (4) -j-Tsubome Yugo $20FA Main direct f Hyakuresho L

Claims (1)

[Scope of Claims] 1. A bypass type hot wire air flow meter that has a bypass passage provided in the main air passage upstream of the throttle valve and a sensor section for measuring the flow rate in a straight pipe portion of the bypass passage,
The air outlet of the bypass passage is comprised of at least two air outlets located upstream and downstream in the air flow direction within the main air passage. . 2. In the invention of claim 1, the air outlet located on the downstream side of the air outlet of the bypass passage is configured to be at the same position as the most downstream end of the straight pipe portion of the bypass passage. A hot wire air flow meter characterized by: 3. In the invention according to claim 2, the member forming the main air passage is configured separately from the member forming the throttle body, and at least a part of the air outlet located on the downstream side is connected to the main air passage. A hot wire air flowmeter characterized in that it is formed by a combination of a member forming an air passage and a member forming the throttle body. 4. In the invention of claim 2, the hot-wire air flow rate is characterized in that the air outlet located on the downstream side is provided with an inclined part facing downstream in the air flow direction in the main air passage. Total. 5. In a bypass type hot wire air flow meter that has a bypass passage in the main air passage upstream of the throttle valve and a sensor section for measuring the flow rate in the straight pipe part of the bypass passage,
A folded passage section is provided in the bypass passage, and the dimension between the air inlet and the air outlet in the main air passage of the bypass passage is the maximum along the air flow direction in the main air passage of the bypass passage. A hot wire air flow meter characterized by being configured to be smaller than its long dimension. 6. The hot wire air flow meter according to claim 5, wherein the air inlet of the bypass passage is constituted by a tubular member protruding from the upstream end of the bypass passage into the main air passage. . 7. The hot wire type according to claim 5, wherein at least the air inlet of the bypass passage is formed in a tubular shape that bulges out from the inner wall surface of the main air passage and opens in the upstream direction of the air flow. Air flow meter. 8. In the invention according to claim 5, the bypass passage has a passage portion extending along a side wall of the main air passage substantially perpendicular to the air flow direction in the main air passage, and the flow rate measurement device is provided in the passage portion. A hot wire air flow meter characterized by being configured such that a sensor section for use in the air is located. 9. In a bypass type hot wire air flow meter, which has a bypass passage in the main air passage upstream of the throttle valve and a sensor section for measuring the flow rate in a straight pipe part of the bypass passage,
A hot-wire air flowmeter characterized in that the air inlet of the bypass passage is constituted by a tubular member protruding from the upstream end of the bypass passage into the main air passage. 10. The hot wire air flow meter according to any one of claims 6 and 9, wherein the end face of the tubular member is at least one of a right angle cut state and an oblique cut state. 11. A hot wire air flowmeter according to any one of claims 5 and 9, wherein the member forming the main air passage is integrally constructed with a member forming a throttle body.