INTAKE AIR FLOW SENSOR

Abstract: The invention relates to an intake air flow sensor for internal combustion engines comprising a sensor main body (12) and a connection unit main body (14), the former consisting of a main passage (15) for passing intake air and a bypass passage (16) for bypassing part of the air flowing through the main passage (15) and joining it again to the air of the main passage (15). An intake air flow meter (26) is disposed in the bypass passage (16) to measure the intake air quantity. The bypass passage (16) has an outlet opening (20) which opens to the main passage (15). A ring (22) is fitted into the main passage (15) of the sensor main body (12) in such a manner as to close part of the outlet opening (20) of the bypass passage (16). An insulator (30) is clamped by the ring (22) and the connection unit main body (14). According to this construction, the area of the opening (20) of the bypass passage (16) to the main passage (15) is not changed due to the deformation of the insulator interposed between the sensor main body (12) and the connection main body (14) which are fixed together by bolts.

Description: This invention relates to an intake air flow sensor for measuring the quantity of intake air sucked by an internal combustion engine. Intake air flow sensors using a heat ray flow velocity meter are generally well known in the art and put into practical use as disclosed, for example, in Japanese Patent Laid-Open No. 162413/1984. In the intake air flow sensor described above, an insulator for heat insulation is interposed between a sensor main body where a heat ray sensor is disposed and a connection unit main body which is disposed downstream of the sensor main body. In this case, the insulator defines part of the outlet of a bypass passage. In the conventional intake air flow sensor described above, however, an opening of the bypass passage to the main passage is formed between the sensor main body and the insulator in order to guide the air flowing through the bypass passage into the main passage and moreover, the sensor main body and the connection unit main body are integrated with each other by pressure-caulking or bolt fixing. Accordingly, the opening to the main passage is not compressed but is closed by the insulator so that the area of the opening of the bypass passage to the main passage changes. The change in the area of the opening in turn changes the output characteristics of the intake air flow sensor disposed in the bypass passage when the intake air flow sensor is taken into consideration as a whole. It is an object of the present invention to provide an intake air flow sensor of the above-mentioned kind for internal combustion engines which prevents a change of the opening of the bypass passage due to the insulator. The above object is achieved according to claim 1. The dependent claims deal with preferred embodiments. In accordance with the present invention, a ring is disposed in such a manner that a part of the opening of the bypass passage to the sensor main body is closed and the insulator is clamped in cooperation with the connection unit main body. Further, a part of the outlet is formed by the ring, and the insulator is clamped by the ring and the connection unit main body so that the area of the opening is not changed by the insulator. The invention is now described with reference to the drawings. Fig. 1 is a sectional view of an intake air flow sensor in accordance with one embodiment of the present invention; Fig. 2 is a plan view taken along line II - II in Fig. 1; and Fig. 3 is a sectional view of principal portions of the sensor of Fig. 1 and shows the section of each component before assembly. In Figs. 1 through 3, the intake air flow sensor 10 consists of a sensor main body 12 and a connection unit main body 14. The sensor main body 12 has a main passage 15 and a bypass passage 16 formed therein, which has a bell mouth-like inlet 18 and a rectangular outlet opening 20. As can be seen from Fig. 3, the outlet 20 is formed in such a manner that three of its sides are positioned on the sensor main body 12 in a step form, and its remaining fourth side is formed by a ring 22. In other words, the outlet opening 20 is formed when the ring 22 is pushed into a corresponding hole 24 of the sensor main body 12. A sensor portion 28 of a heat ray air flow meter 26 is exposed at an intermediate portion of the bypass passage 16. An insulator 30 for heat insulation is interposed between the sensor main body 12, the ring 22 and the connection unit main body 14. A throttle valve 32 is disposed inside the connection unit main body 14 to control the air quantity. The quantity of air flowing through the connection unit main body 14 can be determined by measuring the quantity of the air flowing through the bypass passage 16 by the air flow meter 26. In the construction described above, the outlet 20 is formed by the sensor main body 12 and the ring 22, and the insulator 30 is clamped by the ring 22 and the connection unit main body 14 so that the area of the outlet 20 is not affected adversely by the insulator 30. In accordance with the present invention, the outlet opening 20 of the bypass passage 16 is formed by the sensor main body 12 and the ring 22, and the insulator 30 is interposed between the ring 22 and the connection unit main body 14, so that the outlet opening 20 of the bypass passage 16 is not affected by the insulator 30, and the outlet area does not change. Since the bypass passage 16 is bypassed from the bell mouth-like inlet 18 in such a manner as to encompass the main passage 15 up to the opening 20 of the main passage, pulsation of the air flow quantity can be prevented and the measuring accuracy of the intake air can be improved. Furthermore, the intake air system can be made compact by disposing the throttle valve 32 in the connection unit main body 14.

Claims: 1. An intake air flow sensor (10) for internal combustion engines comprising - a sensor main body (12) consisting of a main passage (15) for passing intake air and a bypass passage (16) for bypassing part of the air to be passed through said main passage and then joining it to the air of said main passage (15), - an intake air flow meter (26) for measuring the quantity of air flowing through said bypass passage (16) and - a connection unit main body (14) connected between the sensor main body (12) and the engine,characterized in that (a) the sensor main body (12) has a step portion disposed in such a manner as to face the connection surface to said connection unit main body (14) and the main passage (15), (b) a ring (22) is fitted into said step portion; (c) the sensor main body (12) has an outlet opening (20) for introducing the air flowing through the bypass passage (16) into the main passage (15) which is disposed on the inner peripheral surface of the bypass passage (16) in the proximity of the ring (22) fitted into the step portion of the main passage (15), and (d) an insulator (30) is interposed between the sensor main body (12) including the ring (22) and the connection unit main body (14)(Figs. 1, 3). 2. An intake air flow sensor according to claim 1, characterized in that the bypass passage (16) is formed in such a manner that it encompasses the main passage (15) and reaches the outlet opening (20) (fig. 1). 3. An intake air flow sensor according to claim 1 or 2, characterized in that the connection unit main body (14) is equipped with the throttle valve (32) controlling the quantity of the air flowing through the connection unit main body (14)(fig. 1).

Inventors: OSAWA, TADAO, USUI, TOSHIFUMI, YANAGISAWA, SHOZO
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: G01F1
IPC codes: G01F1, G01F5, F02D35