Two-stroke internal combustion engine with improved air intake system

Abstract

A two-stroke internal combustion engine comprising an engine block, a plurality of crankcases and including a mounting surface having therein a plurality of inlet openings each communicating with a respective one of the crankcases, a throttle housing defining a throttle passage and including a plenum mounting surface, a throttle valve in the throttle passage, and a plenum member which is separable from both the engine block and the throttle housing and which defines a plurality of intake passages each having an outlet end communicating with a respective one of the inlet openings and each having an inlet end communicating with the throttle passage such that the intake of the engine can be tuned solely by modifying the configuration of the plenum member.

We claim: 
     
       1. A two-stroke internal combustion engine comprising a cylinder block including a generally planar crankcase mounting surface having therein a crankcase recess, a crankcase cover including a generally planar cylinder block mounting surface mating with said crankcase mounting surface and having therein a crankcase recess aligned with said crankcase recess in said cylinder block and defining therewith a crankcase, and air intake means for supplying a flow of air to said crankcase, said air intake means defining a U-shaped.Iadd., generally horizontal, .Iaddend.air intake path having a downstream leg directed toward and generally perpendicular to said crankcase mounting surface .Iadd.and affording air flow in the rearward direction toward said crankcase .Iaddend.and having an upstream leg .Iadd.extending .Iaddend.generally parallel to and directed opposite said downstream leg .Iadd.and affording air flow in the forward direction.Iaddend.. 
     
     
       2. An engine as set forth in claim 1 wherein said intake path has a plurality of downstream legs. .[.3. An engine as set forth in claim 1 wherein said upstream and downstream legs define a generally horizontal 
     
     
        plane..].4. An engine as set forth in claim 1 wherein said crankcase mounting surface and said cylinder block mounting surface lie in a 
     
     
        generally vertically extending plane. 5. An engine as set forth in claim 1 wherein said crankcase cover includes an intake manifold mounting surface 
     
     
        having therein an inlet opening communicating with said crankcase. 6. An engine as set forth in claim 5 wherein said air intake means includes an intake manifold including a crankcase cover mounting surface mating with 
     
     
        said intake manifold mounting surface. 7. An engine as set forth in claim 6 wherein said intake manifold includes a plenum mounting surface opposed to said crankcase cover mounting surface and an intake passage extending from said plenum mounting surface to said crankcase cover mounting surface 
     
     
        and communicating with said inlet opening. 8. An engine as set forth in claim 7 wherein said intake manifold includes a throttle passage extending from said plenum mounting surface parallel to said intake passage, said throttle passage being laterally offset from said intake manifold mounting 
     
     
        surface. 9. An engine as set forth in claim 8 wherein said intake means further includes a plenum cover including an inner surface mating with said plenum mounting surface, said plenum cover cooperating with said intake manifold to define an intake chamber communicating with said 
     
     
        throttle passage. 10. An engine as set forth in claim 9 wherein said plenum cover also cooperates with said intake manifold to define an intake runner passage communicating between said intake chamber and said intake 
     
     
        passage. 11. A two-stroke internal combustion engine comprising an engine block defining a crankcase including an intake manifold mounting surface having therein an inlet opening communicating with said crankcase, an intake manifold having a crankcase cover mounting surface mating with said intake manifold mounting surface, a plenum mounting surface spaced from and extending in parallel relation to said crankcase cover mounting surface, and an intake passage extending from said plenum mounting surface to said inlet opening and generally perpendicularly to said plenum mounting surface, and a plenum cover including an inner surface mating with said plenum mounting surface, and an intake runner passage communicating with said intake passage and extending from said intake 
     
     
        passage in lateral relation to said plenum mounting surface. 12. An engine as set forth in claim 11 wherein said plenum cover also cooperates with said intake manifold to define an intake chamber, and wherein said intake runner passage communicates between said intake chamber and said intake 
     
     
        passage. 13. An engine as set forth in claim 11 wherein said engine block means includes a cylinder block including a crankcase mounting surface having therein a crankcase recess, and a crankcase cover including a cylinder block mounting surface mating with said crankcase mounting surface and having therein a crankcase recess aligned with said crankcase recess in said cylinder block to define said crankcase, and wherein said 
     
     
        crankcase cover includes said intake manifold mounting surface. 14. An engine as set forth in claim 11 wherein said engine block means defines a plurality of crankcases, wherein said intake manifold mounting surface has therein a plurality of inlet openings each of which respectively communicates with a respective crankcase, and wherein said plenum cover and said intake manifold cooperate to define a plurality of intake runner passages each of which respectively communicates with a respective inlet 
     
     
        opening. 15. An engine as set forth in claim 14 wherein said engine block means includes a V-type cylinder block, and wherein all of said inlet 
     
     
        openings are in-line. 16. A two-stroke internal combustion engine comprising a cylinder block including a generally planar crankcase cover mounting surface having therein a crankcase recess, a crankcase cover including a generally planar cylinder block mounting surface mating with said crankcase cover mounting surface and having therein a crankcase recess aligned with said crankcase recess in said cylinder block to define a crankcase, air intake means for supplying air to said crankcase and including a throttle housing and a wall located intermediate said throttle housing and said crankcase and partially defining an air passageway communicating between said throttle housing and said crankcase, said wall having therein an opening communicating with said passageway, an electronic control unit mounted on said wall, and means for cooling said electronic control unit including a plurality of cooling fins extending from said electronic control unit and through said opening and into said 
     
     
        passageway. 17. A two-stroke internal combustion engine comprising an engine block means defining a crankcase and including an intake manifold mounting surface having therein an inlet opening communicating with said crankcase, an intake manifold including a crankcase cover mounting surface mating with said intake manifold mounting surface, a plenum mounting surface opposed to said crankcase cover mounting surface, an intake passage extending from said plenum mounting surface to said crankcase cover mounting surface and communicating with said inlet opening, and a throttle passage extending from said plenum mounting surface and parallel to said intake passage, said throttle passage being laterally offset from said intake manifold mounting surface, and means for conducting air from 
     
     
        said throttle passage to said intake passage. 18. An engine as set forth in claim 17 wherein said intake manifold supports at least one of any of an electronic control unit, a plurality of reed boxes, a throttle linkage which is connected to a throttle plate, a cable mount which supports a 
     
     
        throttle control cable, a timing pointer, and an alternator. 19. An outboard motor having forward and rearward ends and comprising a propulsion unit adapted to be mounted on the transom of a boat, said propulsion unit including a propeller shaft with a rearward end adapted to have mounted thereon a propeller, and said propulsion unit also including a two-stroke internal combustion engine drivingly connected to said propeller shaft, said engine including engine block means defining a crankcase and air intake means for supplying air to said crankcase, said air intake means defining a U-shaped.Iadd., generally horizontal, .Iaddend.air intake path having a rearwardly directed downstream leg .Iadd.affording air flow in the rearward direction toward said crankcase .Iaddend.and having a forwardly directed upstream leg .Iadd.extending .Iaddend.generally parallel to said downstream leg .Iadd.and affording air 
     
     
        flow in the forward direction.Iaddend.. 20. A two-stroke internal combustion engine comprising an engine block including a cylinder block including a crankcase cover mounting surface having therein a crankcase recess, and a crankcase cover including a cylinder block mounting surface mating with said crankcase cover mounting surface and having therein a crankcase recess aligned with said crankcase recess in said cylinder block to define a plurality of crankcases, said crankcase cover also including an intake manifold mounting surface having therein a like plurality of inlet openings respectively communicating with said crankcases, a throttle housing defining a throttle passage and including a plenum mounting surface, a throttle valve in said throttle passage, an intake manifold including a crankcase cover mounting surface mating with said intake manifold mounting surface, a plenum mounting surface opposed to said crankcase cover mounting surface, and a like plurality of inlet passages respectively communicating between said plenum mounting surface and said inlet openings of said crankcase cover, and a plenum member which is mounted on said plenum mounting surfaces of said throttle housing and said intake manifold, which is separable from both said intake manifold and said throttle housing and which defines a like plurality of intake passages having respective outlet ends communicating respectively with said inlet passages of said intake manifold and having respective inlet ends communicating with said throttle passage such that the intake of said engine can be tuned solely by modifying the configuration of said plenum member.