Abstract:
The intake manifold assembly comprises three blocks each molded from a plastic material by injection molding, the three blocks consisting of a first block defining a half of the surge tank, a second block defining a half of the individual intake pipes and a third block defining a remaining half of the surge tank and a remaining half of the individual intake pipes. Thereby, the intake manifold assembly may be provided with various features for defining a pair of intake pipe sections arranged in a mutually parallel relationship while being made to be suitable for an injection molding process. Because the surge tank are defined by the first and third blocks while the individual intake pipes are defined by the second and third blocks, the intake manifold assembly essentially consisting of three blocks can internally define essential features required for a dual port intake device without requiring additional component members.

Description:
TECHNICAL FIELD 
     The present invention relates to a dual port intake device for an internal combustion engine provided with a pair of intake pipe sections arranged in a mutually parallel relationship for each cylinder, and in particular to a dual port intake device for an internal combustion engine adapted to be formed by injection molding a plastic material. 
     BACKGROUND OF THE INVENTION 
     There have been a number of proposals to form an intake manifold by molding plastic material primarily for the purpose of minimizing the weight of the engine. For instance, Japanese patent laid open publication (kokai) No. 2001-342918 discloses an intake manifold consisting of two pieces that are bonded to each other along a plane in parallel with the direction of the intake flow to define individual intake pipes that are commonly connected to a surge tank. 
     A number of dual port intake manifolds have also been proposed. According to the proposal disclosed in Japanese utility model publication (kokoku) H03-41056, each individual intake pipe includes a pair of intake pipe sections having different lengths branching off from the surge tank and connected to a same cylinder in a mutually parallel relationship and a butterfly valve for selectively closing one of the intake pipe sections depending on the load condition of the engine for the purpose of optimizing the intake volumetric efficiency of the engine over a wide operating range of the engine. 
     However, the aforementioned proposal to form an intake manifold by injection molding plastic material is not suitable for molding an intake manifold having a more complex configuration as is the case when the intake manifold is to be used as a part of a dual port intake device because of the limited freedom in design. In particular, the bearing arrangement for the selection valve for selectively closing one of the intake pipe sections tends to complicate the structure of the intake manifold. 
     Also, the selection valve for a dual port intake device is typically actuated by a vacuum actuator, and a negative pressure chamber for storing intake negative pressure is required. The need for a negative pressure chamber and the piping for communicating the negative pressure source to the negative pressure chamber and vacuum actuator also adds to the complexity of the intake device. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of such problems of the prior art, a primary object of the present invention is to provide an improved dual port intake device for an internal combustion engine which is adapted to be manufactured by injection molding plastic material. 
     A second object of the present invention is to provide an improved dual port intake device for an internal combustion engine which is simple and compact in structure. 
     A third object of the present invention is to provide an improved dual port intake device for an internal combustion engine including a negative pressure chamber provided integrally and internally in the intake manifold assembly for storing negative pressure for a vacuum actuator in a highly space saving manner. 
     A fourth object of the present invention is to provide an improved dual port intake device for an internal combustion engine which is provided with an intake manifold assembly having a curvature centered around a point on a side of the engine and allows an overall profile of the engine and intake device to be confined to a limited volume. 
     At least some of these objects of the present invention can be accomplished by providing an intake device for an internal combustion engine having an in-line cylinder bank, comprising: an intake manifold assembly defining a surge tank adjacent to a throttle valve end of the assembly and a plurality of individual intake pipes each including a pair of intake pipe sections branching off from each other and leading to a cylinder head end of the assembly; a selection valve rotatably supported by a selection valve supporting portion in one of the two intake pipe sections of each individual intake pipe for selectively closing the corresponding intake pipe section; and a vacuum actuator provided adjacent to the intake manifold assembly for actuating the selection valve by selectively supplying intake negative pressure thereto; wherein the intake manifold assembly comprises at least three blocks each molded from a plastic material by injection molding, the three blocks consisting of a first block defining a half of the surge tank, a second block defining a half of the individual intake pipes and a third block defining a remaining half of the surge tank and a remaining half of the individual intake pipes. 
     The intake pipe sections branching off from each other typically run substantially in parallel to each other, and merge with each other at the downstream ends thereof. 
     By thus forming the intake manifold assembly from the three blocks arranged and distributed in a favorable manner, the intake manifold assembly may be provided with various features for defining a pair of intake pipe sections arranged in a mutually parallel relationship while being made to be suitable for an injection molding process. In particular, each block may be given with a relatively simple shape which is suited to be molded by using a relatively simple molding die assembly that may include cores in addition to die members for defining the outer shape of the molded product. 
     Because the surge tank is defined by the first and third blocks (optionally with the aid of the second block) while the individual intake pipes are defined by the second and third blocks (optionally with the aid of the first block), the intake manifold assembly essentially consisting of three blocks can internally define essential features required for a dual port intake device without requiring additional component members. If necessary, each block may consist of a plurality of sub blocks without departing from the spirit of the present invention. 
     According to a preferred embodiment of the present invention, the intake device may extend along the outer contour of the engine so as to allow the engine assembly including the intake device to be fitted into a limited space. In such an embodiment, a downstream end of each individual intake pipe comprises an elbow section having an open outlet end defined by the third block in a plane extending substantially in parallel with a cylinder axial line and a lengthwise direction of the in-line cylinder bank, and an upstream end of the surge tank comprises an elbow section having an open inlet end defined by the first block in a plane extending substantially in parallel with a plane defined by a cylinder axial line and a lengthwise direction of the in-line cylinder bank. 
     The vacuum actuator may comprise a housing part which is integrally molded with a part of the intake manifold assembly such as the third block thereof so that this feature also may be integrally formed with the intake manifold assembly so as to eliminate a need for an additional component part. Such a vacuum actuator requires a solenoid valve for controlling the supply of negative pressure to the vacuum actuator, but the need for additional components can be minimized in this case also by integrally molding a stay member for supporting the solenoid valve with a part of the intake manifold assembly adjacent to the vacuum actuator. 
     The intake manifold assembly may further define a negative pressure chamber and a communication passage communicating the negative pressure chamber with the surge tank for minimizing the need for external or additional components. In such a case, a check valve may be fitted in the communication passage for storing negative pressure in the negative pressure chamber. Also, the support portion for rotatably supporting the selection valve may be provided in the intake manifold assembly, preferably between the first and third blocks thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Now the present invention is described in the following with reference to the appended drawings, in which: 
         FIG. 1  is a side view partly in section showing an outboard motor provided with an intake device embodying the present invention; 
         FIG. 2  is a sectional plan view of the outboard motor; 
         FIG. 3  is an exploded perspective view of the intake manifold assembly; 
         FIG. 4  is a sectional side view of the intake manifold assembly; 
         FIG. 5  is an enlarged fragmentary sectional view of a part of the intake manifold assembly; 
         FIG. 6  is a cross sectional view of the intake manifold assembly; 
         FIG. 7  is a fragmentary plan view of the vacuum actuator and the surrounding part of the intake manifold assembly; and 
         FIG. 8  is a fragmentary plan view of the intake manifold assembly showing the housing portion of the vacuum actuator integrally molded with the intake manifold assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show an engine of an outboard motor. This outboard motor  1  is of a per se known type adapted to be attached to a stern board  3  via a stern bracket  2  except for the novel arrangement for the intake device. The engine  4  of this outboard motor  1  is mounted on a mount case  7 , and the mount case  7  is substantially integrally provided with a swivel case  6  which is in turn connected to the stem bracket  2  so as to be freely vertically rotatable around a tilt shaft  5  extending horizontally. The engine  4  which is mounted on the mount case  7  is substantially entirely covered by a detachable engine cover  8 . 
     The mount case  7  is connected to an upper end of an extension case  9 , and a drive shaft  10  extending to a screw propeller (not shown in the drawings) is connected to a crankshaft  11  of the engine  4  in the mount case  7 . 
     The engine  4  consists of an in-line four-cylinder vertical crankshaft engine, for instance, and comprises a crankcase  12 , a cylinder block  13  and a cylinder head  14 . The engine  4  is oriented with respect to the boat so that the crankcase end of the engine  4  is directed forward. The cylinder head  14  defines combustion chambers  19  which are each selectively communicated with an intake port  15  and an exhaust port  16  via an intake valve  17  and exhaust valve  18 , respectively (see  FIG. 2 ). 
     An intake device  20  is provided opposite to a side (portside) surface of the engine defined by the crankcase  12 , cylinder block  13  and cylinder head  14 . The intake device  20  comprises an intake muffler chamber  21  and a throttle body  22  provided opposite to the forward end surface of the crankcase  12  and an intake manifold assembly  26  provided opposite to the portside surface of the engine. The intake manifold assembly  26  includes an elbow section  23  connected to an outlet end of the throttle body  22   a , surge tank portion  24  continuously extending from the elbow section  23  and individual intake pipes  25  each branching off from the surge tank portion  24  and individually connected to the intake port  15  of a corresponding one of the cylinders. This intake device  20  is attached to the engine  4  by securing the surge tank portion  24  to a side face of the crankcase  12  by threaded fasteners and the downstream end of each individual intake pipe  25  to a side face of the cylinder head  14  also by threaded fasteners. 
     The individual intake pipes  25  are arranged one next to another along the length of the cylinder bank on one side (portside) of the cylinder block  13 , and the upstream end of each individual intake pipe  25  adjacent to the surge tank portion  24  includes a short intake pipe section  27  located adjacent to the engine and a long intake pipe section  28  located remote from the engine in a mutually parallel relationship. These two pipe sections  27  and  28  commonly merge into a common pipe section C in the downstream end of the corresponding individual intake pipe  25 , and each individual intake pipe  25  further extends to a connecting end  25   c  that is connected to the cylinder head  14 . Each short pipe section  27  is provided with a butterfly valve  29  which moves jointly with the other butterfly valves  29  provided in the short pipe sections  27  of the other individual intake pipes  25 . 
     The intake manifold assembly  26  consists of three blocks as illustrated in  FIG. 3 . Each block is configured in such a manner that the individual intake pipes  25  each including the short intake pipe section  27  and long intake pipe section  28  arranged in parallel to each other in an intermediate part thereof and the surge tank portion  24  can be molded by using metallic die assemblies each essentially consisting of two pieces. As illustrated in  FIG. 4 , the first block or the inner block  31  includes a throttle body mounting portion  30  and a wall  24   a  of the surge tank portion  24  facing the engine, the second block or the outer block  32  includes an outer half  25   a  of each individual intake pipe  25  having a parting plane PI curving around a point on the side of the engine at a certain curvature along the flow line of the intake flow and a wall  24   b  of the surge tank  24  facing away from the engine, and the third block or the intermediate block  35  includes an inner half  25   b  of each individual intake pipe  25 , an end portion  25   c  of each individual intake pipe  25  adjacent to the cylinder head  14 , a butterfly valve support portion  33 , an open upstream end of each short intake pipe section  27  and an elbow portion  23  continuing from the wall  24   b  of the surge tank facing away from the engine. The inner block  31  and intermediate block  35  are separated from each other along a parting plane P 2  extending substantially in parallel with the wall  24   a  of the surge tank portion  24  facing the engine. 
     These three blocks  31 ,  32  and  35  are individually molded by injection a suitable molding plastic material, and are joined to each other, for instance, by vibration welding. Each pair of the bonding surfaces of these blocks are provided with a projection  36  and a complementary recess  37 , respectively, as illustrated in  FIG. 5 . Each projection  37  is provided with a suitable amount of overlap or excess material so that a part of the material of the projection  37  melts and fuses into the recess  37  as they are welded together. 
     Referring to  FIG. 6 , the four butterfly valves  29  are supported by a common shaft  40  which is rotatably supported by shaft holders  39   a  to  39   c  at two ends  40   a ,  40   b  and three intermediate parts  40   c  thereof. One end  40   b  of the shaft  40  is resiliently urged in a radial direction by a spring piece  41  provided on the corresponding shaft holder  39   b  (as an integrally molded piece thereof) so as to be smoothly rotatable without a play. The other shaft holder  39   a  integrally formed with the outer block  32  opposes the other end  40   a  of the shaft  40  while the three shaft holders  39   c  in the intermediate parts snugly receive the corresponding intermediate parts  40   c  of the shaft  40 . The intermediate parts  40   c  of the shaft  40  that are journaled on the three shaft holders  39   c  are each provided with annular ridges so as to form labyrinth seal for preventing the leaking of intake gas between adjacent intake passages and to provide friction-free journaling of the intermediate parts  40   c.    
     The other end  40   a  (upper end) of the shaft  40  for the butterfly valves  29  is connected to a per se known diaphragm actuator  42  which is adapted to be actuated by the intake vacuum. The four butterfly valves  29  are simultaneously opened and closed by intermittently actuating a solenoid valve  43  according to a prescribed control signal and thereby continually controlling the supply of the negative pressure to the diaphragm actuator  42 . 
     The atmospheric pressure chamber  44  of the diaphragm actuator  42  is defined by a wall portion that is integrally molded with the intermediate block  35  as illustrated in  FIG. 8  so that the necessary number of component parts can be minimized. 
     The inner block  31  is provided with a bulge  46   a  adjacent to the surge tank portion  24  that defines a negative pressure chamber  46  in cooperation with a recess  45  formed in the intermediate block  35  adjacent to the butterfly valves  29  as best illustrated in  FIG. 5 . More specifically, the negative pressure chamber  46  is located adjacent to the butterfly valves  29  on the downstream side thereof and on the inner circumferential part of the short intake pipe section  27  on the inner circumferential part of the individually intake pipes  25  that curve around a center of curvature located on the side of the engine. 
     As illustrated in  FIG. 5 , an intermediate part of the negative pressure chamber  46  along the direction of the cylinder bank is provided with a cylindrical hole  47  having a bottom end that communicates with the surge tank  24 . The cylindrical hole  47  is fitted with a negative pressure check valve  48 . The negative pressure check valve  48  comprises a valve member  49  having the shape of an inverted mushroom and made of relatively soft plastic material, and a valve support member  51  retaining the valve member  49  so as to be axially moveable by a prescribed stroke and formed with a valve seat  50  that cooperates with the valve member  49 . The valve support member  51  is fitted into the cylindrical hole  47  via a seal member  52  such as an O-ring. 
     Thus, a large part of the negative pressure chamber  46 , surge tank  24  and cylindrical hole  47  communicating these parts together and fitted with the negative pressure check valve  48  is integrally molded with the intermediate block  35  that forms the intake manifold assembly  26 . For this reason, no separate piping is required for conducting the intake negative pressure to the negative pressure chamber  46 . 
     The negative pressure valve  48  operates as follows. As the negative pressure in the individual intake pipes  25  increases, the valve member  49  is drawn toward the individual intake pipes  25  and moves away from the valve seat  50  with the result that the negative pressure prevails in the negative pressure chamber  46 . As the negative pressure in the individual intake pipes diminishes, the valve member  49  is urged against the valve seat  50  so that the negative pressure in the negative pressure chamber  46  is kept at the high level. 
     The negative pressure chamber  46  is connected to the negative pressure chamber  54  of the diaphragm actuator  42  via the solenoid valve  43  and rubber tubes  53  as best illustrated in  FIG. 7  so that the communication between the negative pressure chamber  54  of the diaphragm actuator  42  and negative pressure chamber  46  is selectively established by turning on and off the solenoid valve  43 . The solenoid valve  43  is attached to a stay portion  55  integrally formed on a side face of the intermediate block  35  adjacent to the atmospheric pressure chamber  44  of the diaphragm actuator  42  by using threaded fasteners. Also owing to the fact that the negative pressure chamber  46  is provided adjacent to the butterfly valve support portion  33 , the lengths of the rubber tubes  53  that connect the negative pressure chamber  46 , solenoid valve  43  and negative pressure chamber  54  of the diaphragm actuator  42  can be reduced even further. 
     Thus, when the diaphragm  57  is pushed toward the atmospheric pressure chamber  44  by the compressed coil spring  56  compressed in the negative pressure chamber  54  of the diaphragm actuator  42 , the butterfly valves  29  are open and the short pipe sections  27  leading to the cylinder head ends  25   c  from the open ends  34  immediately adjacent to the butterfly valves  29  communicate with the intake upstream ends of the long pipe sections  28  (in a high speed, high load operating range). When the negative pressure is introduced into the negative pressure chamber  54  of the diaphragm actuator  42  and the diaphragm  57  is pulled toward the negative pressure chamber  54 , the butterfly valves  29  are closed (as indicated by the double chain dot lines in  FIG. 4 ), and only the long pipe sections  28  having open ends  28   a  that are located more upstream than the open ends  34  of the short pipe sections  27  (in a low speed, low load operating range) are in communication. In this manner, the cross sectional area and length of the individual intake pipes  25  can be changed in two stages according to the operating condition of the engine  4 . 
     The downstream end of the pipe wall  58  that separates the upstream end of the long pipe sections  28  and short pipe sections  27  is located on a same plane D as the open end  34  of the short pipe sections  27  in the surge tank  24 . This plane D as well as the axial line of the cylinder head end  25   c  of the individual intake pipe portion  25  extends perpendicularly to the parting plane P 2  of the metallic die assembly so that the molded product may be removed from the intermediate block  35  without any problem. The axial line of the recess  45  defining the negative pressure chamber  46  and axial line of the cylindrical hole  47  fitted with the negative pressure check valve  48  also extend perpendicularly to the parting plane P 2  of the metallic die assembly for the convenience of separating the intermediate block  35  from the molded product. 
     The central axial line A of the atmospheric chamber  44  of the diaphragm actuator  42  may tilt with respect to the direction parallel with the plane D or the direction of separating the intermediate block  35  (as shown in  FIG. 8 ) because it is molded by using a separate slidable core  61  (indicated by the imaginary lines). It is also possible to do away with the separate slidable core  61  by directing the open end of the atmospheric chamber  44  upward in  FIG. 8  and orienting the central axial line in parallel with the plane D. 
     Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.