Hot-wire type air flow meter and an internal combustion engine with the same

Abstract

A compact hot-wire type air flow meter for an internal combustion engine with a high measuring accuracy is provided with a primary flow path forming an intake air passage and an auxiliary flow path incorporating therein a hot-wire element for measuring the intake air. The auxiliary flow path is defined by a flow path in an axial direction of the primary flow path and a flow path in a radial direction of the primary flow path.

We claim: 
     
       1. A hot-wire type air flow meter comprising a primary flow path constituting an intake air passage of an internal combustion engine, a hot-wire element for measuring intake air, and an auxiliary flow path provided substantially entirely within said primary flow path and having mounted therein said hot-wire element, said auxiliary flow path having an L-shaped configuration including a flow path portion formed in an axial direction of said primary flow path and a flow path portion formed in a radially inward direction of said primary flow path and extending at least half way across said primary flow path, and wherein said auxiliary flow path portion in the axial direction of said primary flow path is provided eccentrically with respect to said primary flow path. 
     
     
       2. A flow meter according to claim 1, wherein said hot-wire element is provided in the flow path portion formed in the axial direction of said primary flow path. 
     
     
       3. The flow meter according to claim 1, wherein a throttle for throttling air flow is provided at an inlet portion of said auxiliary flow path. 
     
     
       4. The flow meter according to claim 1, wherein a member for forming said primary flow path is integral with a member for forming said auxiliary flow path. 
     
     
       5. The flow meter according to claim 1, wherein the auxiliary flow path portion formed in the radial direction of said primary flow path comprises a plurality of outlet openings at the end thereof opposite said auxiliary flow path portion formed in the axial direction. 
     
     
       6. A hot-wire type air flow meter according to claim 1, said auxiliary flow path portion defined in an axial direction of said primary flow path having a check valve for preventing a counter flow back to said auxiliary flow path, said check valve being located in an outlet portion of said auxiliary flow path. 
     
     
       7. An internal combustion engine comprising the hot-wire air flow meter; an rpm sensor for sensing an rpm of the internal combustion engine; a fuel injection means for injecting fuel into the sucked air; and a controlling means for determining the corresponding fuel injection amount on the basis of the sucked air-flow rate detected by said hot wire type air flow sensor and the rpm detected by said rpm sensor, and for outputting a command signal for the determined fuel injection amount to said fuel injection means, wherein said hot-wire type air flow meter comprises a primary flow path constituting an intake air passage of an internal combustion engine, a hot-wire element for measuring intake air, and an auxiliary flow path provided substantially entirely within said primary flow path and having mounted therein said hot-wire element, said auxiliary flow path having an L-shaped configuration including a flow path portion formed in an axial direction of said primary flow path and a flow path portion formed in a radially inward direction of said primary flow path and extending at least half way across said primary flow path, and wherein said auxiliary flow path portion in the axial direction of said primary flow path is provided eccentrically with respect to said primary flow path. 
     
     
       8. A hot-wire type air flow meter comprising a hollow body forming a primary flow path constituting an intake air passage of an internal combustion engine; a hot wire element for measuring intake air; and an auxiliary flow path formed in a radial arm disposed in said primary flow path within said hollow body and having said hot-wire element mounted therein; said radial arm having a bore extending therethrough in the direction of said primary flow path, a groove in the downstream surface thereof and communicating with said bore, and a cover plate secured over said groove to form said groove into a channel having an opening into said primary flow path serving as an outlet for said auxiliary flow path. 
     
     
       9. A hot-wire type air flow meter as claimed in claim 8, wherein said bore communicates with said groove intermediate the ends of said groove and said cover plate covers said groove so as to provide a pair of outlets for said auxiliary flow path at opposite ends of said groove. 
     
     
       10. A hot-wire type air flow meter as claimed in claim 8, wherein said radial arm extends completely across said primary flow path within said hollow body. 
     
     
       11. A hot-wire type air flow meter comprising a hollow body forming a primary flow path constituting an intake air passage of an internal combustion engine; a hot wire element for measuring intake air; and an auxiliary flow path formed in a circumferential projection extending into said primary flow path within said hollow body and having said hot wire element mounted therein; said circumferential projection having a bore extending therethrough in the direction of the primary flow path, a circumferential groove in the downstream surface thereof and communicating with said bore, and a cover plate secured over said downstream surface to form said groove into a channel having an opening into said primary flow path and serving as an outlet for said auxiliary flow path. .Iadd. 
     
     
       12.  A thermal type air-flow meter, comprising a body member forming a primary flow path constituting an intake air passage of an internal combustion engine, a thermal resistor for measuring an intake air, an auxiliary flow path provided in said primary flow path and having said thermal resistor mounted thereon, a projecting portion integrated with said body member forming said primary flow path and having the auxiliary flow path formed thereon, said primary flow path having in the neighborhood of an outlet of the auxiliary flow path, a cross-sectional area which is less than the cross-sectional area at the inlet of the auxiliary flow path, with the formation of said projecting portion changing between said outlet said inlet. .Iaddend. .Iadd.13. A thermal type air flow meter as claimed in claim 12, further comprising a circuit unit mounted on a outer portion of said body forming said primary air flow path for taking out as an electrical signal a measure of heat released from said thermal resistor to the air flowing in said auxiliary path, a molding member containing a wiring element for electrically connecting said circuit unit to said thermal resistor, and said projecting portion integrated with said body forming with said body a reducing cross-sectional area portion of said primary flow path. .Iaddend. .Iadd.14. A thermal type air flow meter as claimed in claim 12, wherein said projecting portion formed in said primary flow path connects an inner wall of the primary flow path at the location of the circuit unit mounted on the outer portion of the body forming the primary flow path to the inner wall opposite thereto through a center portion of the primary flow path, thereby dividing the primary flow path into two sections. .Iaddend. 
     
     
        .Iadd.15.  A thermal type air flow meter as claimed in claim 13, wherein said molding member containing the wiring element passes through said projecting portion and is integrated with said circuit unit, thereby allowing the thermal resistor to be disposed in said auxiliary flow path coincident with a central axis of the primary flow path. .Iaddend. .Iadd.16. A thermal type air flow meter as claimed in claim 12, wherein said projecting portion in which said auxiliary flow path is formed is provided in a central portion of the primary flow path through a rib integrated with the body forming said primary flow path, and a portion of said auxiliary flow path downstream of said thermal resistor is formed by part of a wall surface of said projecting portion and a cover member serving as a counter flow member. .Iaddend. .Iadd.17. A thermal type air flow meter, comprising a body forming a primary flow path constituting an intake air passage of an internal combustion engine, a projecting member formed integral with said body and disposed in said primary flow path so as to restrict the cross-sectional area of said primary flow path by amount which vary along the length of said projecting member according to a predetermined curvature of said projecting member. .Iaddend. .Iadd.18. An air flow meter comprising a primary flow path constituting an intake air passage of an internal combustion engine, a thermal-type element for measuring intake air, and an auxiliary flow path provided substantially entirely within said primary flow path and having mounted therein said element, said auxiliary flow path having an L-shaped configuration including a flow path portion formed in an axial direction of said primary flow path and a flow path portion formed in a radially inward direction of said primary flow path and extending at least half way across said primary flow path, and wherein said auxiliary flow path portion in the axial direction of said primary flow path is provided eccentrically with respect to said primary flow path. .Iaddend. .Iadd.19. A flow meter according to claim 18, wherein said element is provided in the flow path portion formed in the axial direction of said primary flow path. .Iaddend. .Iadd.20. The flow meter according to claim 18, wherein the throttle for throttling air flow is provided at an inlet portion of said auxiliary flow path. .Iaddend. .Iadd.21. The flow meter according to claim 18, wherein a member for forming said primary flow path is integrated with a member for forming said auxiliary flow path. .Iaddend. .Iadd.22. The flow meter according to claim 18, wherein auxiliary flow path portion formed in the radial direction of said primary flow path comprises a plurality of outlet openings at the end thereof opposite said auxiliary flow path portion formed in the axial direction. .Iaddend. .Iadd.23. A flow meter according to claim 18, said auxiliary flow path portion defined in an axial direction of said primary flow path having a check valve for preventing a counter flow back to said auxiliary flow path, said check valve being located in an outlet portion of said auxiliary flow path. .Iaddend. .Iadd.24. An internal combustion engine comprising an air flow meter; an rpm sensor for sensing an rpm of the internal combustion engine; a fuel injection means for injecting fuel into the sucked air; and a controlling means for determining the corresponding fuel injection amount on the basis of the sucked air flow rate detected by said air flow meter and the rpm detected by said rpm sensor, and for outputting a command signal for the determined fuel injection amount to said fuel injection means, wherein said air flow meter comprises a primary flow path constituting an intake air passage of an internal combustion engine, a thermal-type element for measuring intake air, and an auxiliary flow path provided substantially entirely within said primary flow path and having mounted therein said element, said auxiliary flow path having an L-shaped configuration including a flow path portion formed in an axial direction of said primary flow path and a flow path portion formed in a radially inward direction of said primary flow path and extending at least half way across said primary flow path, and wherein said auxiliary flow path portion in the axial direction of said primary flow path is provided eccentrically with respect to said primary flow path. .Iaddend. .Iadd.25. A air flow meter comprising a hollow body forming a primary flow path constituting an intake air passage of an internal combustion engine; a thermal-type element for measuring intake air; and an auxiliary flow path formed in a radial arm disposed in said primary flow path within said hollow body and having said element mounted therein; said radial arm having a bore extending therethrough in the direction of said primary flow path, a groove in the downstream surface thereof and communicating with said bore, and a cover plate secured over said groove to form said groove into a channel having an opening into said primary flow path serving as an outlet for said auxiliary flow path. .Iaddend. .Iadd.26. A air flow meter as claimed in claim 25, wherein said bore communicates with said groove intermediate the ends of said groove and said cover plate covers said groove so as to provide a pair of outlets for said auxiliary flow path at opposite ends of said groove. .Iaddend. .Iadd.27. A air flow meter as claimed in claim 25, wherein said radial arm extends completely across said primary flow path within said hollow body. .Iaddend. .Iadd.28. A air flow meter comprising a hollow body forming a primary flow path constituting an intake air passage of an internal combustion engine; a thermal type element for measuring intake air; and an auxiliary flow path formed in a circumferential projection extending into said primary flow path within said hollow body and having said element mounted therein; said circumferential projection having a bore extending therethrough in the direction of the primary flow path, a circumferential groove in the downstream surface thereof and communicating with said bore, and a cover plate secured over said downstream surface to form said groove into a channel having an opening into said primary flow path and serving as an outlet for said auxiliary flow path. .Iaddend.