Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
1999-07-28
2001-02-20
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
Reexamination Certificate
active
06189379
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an air flow measuring instrument which forms an intake system of an internal combustion engine and measures an intake air flow of the intake system, and more particularly to a thermal type air flow measuring instrument suitable for measurement of an air flow taken in an engine of an automobile.
The prior art reference most relevant to the present invention includes U.S. Pat. No. 4,974,445 (corresponding to JP-A-2-1518). An air flow meter disclosed by the JP-A-02-1518 includes a substantially L-shaped auxiliary passage formed in a main passage by cast molding. An opened outlet surface of the auxiliary passage is provided in a plane parallel to the main passage. Thus, the disclosed air flow meter has not a construction in which the auxiliary passage is inserted into the main passage but a construction in which the main passage and the auxiliary passage are cast-molded simultaneously. Accordingly, there is an inconvenience that at least two complicated casts or molds are required and hence it is difficult to reduce the fabrication cost. In connection with this, the present invention is easy to reduce the fabrication cost since a main passage can be fabricated with a simple construction independently or by itself. The U.S. Pat. No. 4,974,445 includes a disclosure concerning the possibility of insertion of an auxiliary passage into the main passage but no disclosure concerning the detailed construction thereof. Also, in this prior art, since the length of a first path of the auxiliary passage is very large as compared with that of a second path thereof, there is an inconvenience that an error of the mounting position of the auxiliary passage including a heating resistor and so forth gives a great influence on the accuracy of measurement. To the contrary, in the present invention, since the length of a first path of the auxiliary passage is not very large as compared with that of a second path thereof or is about two times as large as that of the second path, the influence of the mounting position error on the accuracy of measurement can be reduced remarkably.
Also, an air flow measuring instrument disclosed by U.S. Pat. No. 4,709,581 (corresponding to JP-4-753853) is known. However, the U.S. Pat. No. 4,709,581 has no disclosure concerning a method for mounting and fixing a main passage, an auxiliary passage and circuit portions. Further, the air flow measuring instrument disclosed by the U.S. Pat. No. 4,709,581 has a structure in which the auxiliary passage is supported in a bridge form in the main passage with opposite ends of the auxiliary passage supported by the main passage so that a member forming the auxiliary passage completely goes across the inner diameter of the main passage. That is, the instrument disclosed by the U.S. Pat. No. 4,709,581 has not a structure, intended by the present invention, in which a circuit portion and an auxiliary passage portion are configured into a unitary module so that the module standardized independently of the size of the main passage is applicable to various internal combustion engines. Furthermore, the instrument disclosed by the U.S. Pat. No. 4,709,581 has not been put into practice because the deterioration of the accuracy of measurement is feared since the auxiliary passage has the above-mentioned bridge-like structure so that the auxiliary passage is complicatedly curved or bent and because the cost becomes high since the instrument must be formed by coupling several parts. The instrument disclosed by the U.S. Pat. No. 4,709,581 is not a structure in which sufficient consideration is given to a measure to counter the change of environment due to the arrangement of the main passage at different positions of an intake system and a measure to counter the variations of mounting of the module and the main passage.
SUMMARY OF THE INVENTION
An object of the present invention is to attain the reduction of the system cost of an internal combustion engine as the greatest subject of a thermal type air flow measuring instrument by making a unitary module of a circuit portion and an auxiliary passage portion have the most of the function of the thermal type air flow measuring instrument so that the module can be handled as one product. Another object of the present invention is to make it truly possible to put a thermal type air flow measuring instrument into practice by reducing the deterioration of the accuracy of measurement caused by the reduction in size and weight, the change of environment and the variations of mounting and by improving the handling operability.
For the purpose of the reduction of the system cost of an internal combustion engine, there are contemplated the reduction of the system cost of a thermal type air flow measuring instrument and the reduction of the number of parts of the system by the unification to other parts of an intake system. A circuit portion and an auxiliary passage portion are first united in a module, thereby enabling a great reduction in cost by constructing a flow meter body of a relatively high cost by a main passage which is a simple pipe passage, a hole which is provided in the wall surface of the main passage and a surface which is for fixing the circuit. Also, parts forming the auxiliary passage portion are simplified in form and reduced in size to facilitate the unification to the circuit portion, thereby attaining the unification of parts connecting the circuit portion and the auxiliary passage portion to achieve the reduction of the cost of the air flow measuring instrument. Further, since the form of the flow meter body is simplified, it becomes possible to form the flow meter body in a united form to other parts of the intake system without fabricating the flow meter body by a separate member, thereby reducing the number of parts of the system. Furthermore, the standardized module can be applied even if the setting position of the main passage or the size thereof is changed.
For the purpose of the reduction in size and weight, a member forming the auxiliary passage can be made small in size and light in weight with no damage of the function of the auxiliary passage not only by reducing the length of the auxiliary passage in a main flow direction in such a manner that the form of the auxiliary passage is simplified, the total path length is maintained by providing a bent passage, a temperature sensing resistor is arranged in an orthogonally bent portion of the auxiliary passage and the profile of a cross section of a second path of the auxiliary passage perpendicular to the main flow direction has a form in which a length in a direction perpendicular to the main flow direction is large as compared with that in the main direction but also by suppressing the length of the second path of the auxiliary passage perpendicular to the main flow direction. On the other hand, the main passage can be made small in size and light in weight by providing a construction which gets off with no enlargement of the cross section of the main passage by reducing the occupying proportion of the auxiliary passage forming member in the main passage and configuring the auxiliary passage so that it is hard to generate a pressure loss. Also, an insertion hole provided in the wall surface of the main passage for inserting the auxiliary passage can be formed with a small-diameter circle by selecting the ratio of the length of the auxiliary passage forming member to the width thereof so that it is not large. As a result, the formation of the insertion hole is facilitated, thereby making it possible to cope with the miniaturization of the circuit.
Measures to counter the change of environment include a measure to counter the change of the flow of a air in the main passage depending on the position of the intake system and a measure to counter a change in temperature depending on the position of the air flow measuring instrument at which it is placed. To cope with a measurement error caused by the generation of a pulsatio flow in the main passage, the auxiliary pas
Arai Nobukatsu
Hirayama Hiroshi
Igarashi Shinya
Kobayashi Chihiro
Saito Takayuki
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Fuller Benjamin R.
Hitachi , Ltd.
Thompson Jewel V.
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