Surge tank structure in intake manifold

Abstract: A surge tank structure in an intake manifold has a surge tank to which a plurality of branch tubes are joined at one end. The branch tubes are joined at the other end to a cylinder head mounting flange, and one end of each branch tube in the surge tank is enlarged to have a horn-like shape. The surge tank comprises a main body and a top plate. The main body has through holes provided therein for accepting the branch tubes and has its top side opened. The top plate is joined in a plane to the top of the main body. The main body has a bottom which has engagement recesses formed by raised portions, so that each engagement recess has a horn-like surface that conforms to the horn-like shape of one end of each branch tube.

Description: Background of the Invention Field of Industrial Applications The present invention relates to a surge tank structure in an intake manifold. Related Art In general, an intake manifold for use in an automobile gasoline or diesel engine has such a structure as shown in Fig. 9, where a plurality of branch tubes 2 are joined at one end to a cylinder head mounting flange 4 provided for installation on a cylinder head and at the other end to a surge tank 3. Fig. 10 illustrates an enlarged cross sectional view of the joint between the branch tubes 2 and the surge tank 3 where each branch tube 2 is connected as inserted into the surge tank 3, which inner wall for accepting the leading end of the branch tube 2 has a horn-like region 51 formed by changing the diameter for the purpose of moderating a change of the cross section so that the load of a suction caused by abrupt change in the cross section can be reduced. The surge tank 3 is fabricated by casting with the use of a core for shaping the horn-like regions 51 and will hence be increased in the production cost because of the use of the core in the casting. For compensation, a modification has been proposed, as shown in Fig. 11 as well as Fig. 12 that is a cross sectional view taken along the line XII-XII of Fig. 11, where the leading end of each branch tube 2 is flared or enlarged in its diameter to have a horn-like flared or enlarged region 2a and is then mounted to a surge tank 3. The surge tank 3 comprises two separable components, a lower member 52 and an upper member 53. More specifically, after the branch tubes 2 having the horn-like flared or enlarged regions 2a have been set in their position, the upper member 53 is joined to the lower member 52 to complete the serve tank 3. With this structure, the joint between the branch tube 2 and the two tank members 52 and 53 includes semi-circular and straight regions, thus requiring higher degrees of the roundness of the overall dimensions of the branch tubes 2 and of the machining accuracy on the joining portions of the lower member 52 and the upper member 53 to the branch tubes 2. In addition, there are needed a set of pins 54 for positioning the lower member 52 and the upper member 53, thereby increasing the manufacturing cost. Moreover, there may be very likely developed positional discrepancy between the branch tubes 2 and the two tank members 52 and 53, causing the problem that condensed liquid or blow-by oil is deposited on the bottom of the lower member 52 is hardly sucked up into the branch tubes 2 and thus tends.to be left on the bottom of the lower member 52. Such an intake manifold is disclosed in DE 1 576 402. Summary of the Invention The present invention has been developed in view of the above problems and its object is to provide an intake manifold which allows condensed water or blow-by oil deposited in a surge tank to be favorably discharged and can be fabricated at lower cost without use of cores in the casting molds. According to the present invention, there is provided a surge tank structure in an intake manifold having a surge tank to which a plurality of branch tubes are joined at one end. The branch tubes are joined at the other end to a cylinder head mounting flange, and one end of each branch tube in the surge tank is flared or enlarged to have a horn-like shape. The surge tank comprises a main body and a top plate. The main body has through holes provided therein for accepting the branch tubes and has its top side opened. The top plate is joined in a plane to the top of the main body. The main body has a bottom which has engagement recesses formed by raised or raised portions, so that each engagement recess has a horn-like surface that conforms to the horn-like shape of one end of each branch tube. Because the main body and the top plate are joined to each other in a plane, the surge tank is tightly sealed off with the joint. Also, the branch tube is precisely positioned in the engagement recess provided in the bottom of the main body so that the horn-like shape of the end of the branch tube closely contacts the horn-shape surface of the bottom, hence facilitating its function of sucking up a pool of condensed water or blow-by oil deposited on the bottom of the surge tank. In other words, the structure of the surge tank is improved as hardly fouled with condensed water or blow-by oil. Also, the surge tank can be fabricated at less cost since no core in the molds is used. After each branch tube have been inserted into the respective through holes and have been positioned in the respective engagement recesses in the main body of the surge tank, an enlarging tool is inserted from above into the main body so as to urge one end of each branch tube against the corresponding horn-like surface and to enlarge the same to have the horn-like shape. Accordingly, the process can be implemented at a lower cost by removing the top plate, setting the branch tubes to the through holes in the main body, inserting the dice into the main body, and performing an enlarging or flaring process with the end of each the branch tube closely contacting the horn-shaped surface. The invention also provides a method of making such a surge tank. Brief Description of the Drawings Fig. 1 is a cross sectional structural view showing branch tubes joined to a surge tank; Fig. 2 is a cross sectional structural view taken along the line II-II of Fig. 1; Fig. 3 is a cross sectional structural view showing engagement recesses formed to have a shallow depth; Fig. 4 is a perspective structural view of a separable structure of the surge tank; Fig. 5 is a cross sectional structural view showing the surge tank with a separate bottom plate; Fig. 6 is an exploded perspective view of the structure shown in Fig. 5; Fig. 7 is an explanatory view showing an enlarging process of the leading end of the branch tube by using a die; Fig. 8 is an explanatory view showing a process of removing the bottom plate and of enlarging the tube by using a die when the top opening is small; Fig. 9 is a perspective structural view of a conventional intake manifold; Fig. 10 is a cross sectional enlarged structural view showing the joint between a conventional surge tank and branch tubes; Fig. 11 is a cross sectional structural view showing the joint between a conventional separable type surge tank and branch tubes; and Fig. 12 is a cross sectional view taken along the line XII-XII of Fig. 11. Detailed Description of the Invention One preferred embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross sectional structural view showing branch tubes 2 joined to a surge tank 3. Fig. 2 is a cross sectional structural view taken along the line II-II of Fig. 1. In this embodiment, the surge tank 3 comprises a main body 31 and a top plate 32. The main body 31 has a bottomed box-like structure with the top side opening and includes a side wall 31b that extends upwardly from a bottom 31a. The side wall 31b has through holes 31d for accepting the branch tubes 2 from the outside. The top of the side wall 31b is smoothed to develop a horizontal joining surface 31c. The top plate 32 is joined to the joining surface 31c so as to be placed thereon from above, thus completing the overall structure of the surge tank 3. As the interface between the top plate 32 and the main body 31 is flat, the top plate 32 and the main body 31 can be joined to be reliably sealed up. Also, the bottom 31a of the main body 31 has thickened or raised portions 33 arranged beside the through holes 31d. The raised portion 33 also has, as best shown in Fig. 2, semi-circular engagement recesses 33b provided therein to conform to the outer configuration of the branch tubes 2, so that the leading ends of the branch tubes 2 are positioned precisely to their joining locations. In particular, an inner end portion of each the engagement recess 33b defines a horn-shape surface 33a which curves down to the bottom 31a of the main body 3. Each engagement recess 33b is tailored in an arc shape that is less than half the circumferential length of the branch tube 2. This allows no use of a core in making the main body 31 with the raised portion 33 and with the horn-shape surfaces 33a and the engagement recesses 33b, hence minimizing the cost of casting the main body 31. Also, the top plate 32 is tightly joined to the top of the main body 31, ensuring a higher sealing effect of the overall structure while requiring no use of pins as employed in the prior art. Accordingly, the manufacturing cost of the overall surge tank structure can further be reduced. As shown in Fig. 3, the raised portion 33 may be lowered as closer to the bottom 31 and its engagement recess 33b may be shallowly recessed to contact only a lower side of the outer periphery of the branch tube 2 positioned therein. Even if the surge tank structure is of a type with a throttle chamber mount 5 joined laterally to the main body 31 for introducing a flow of air into the interior of the surge tank 3, as shown in Fig. 4, the surge tank 3 may also have a separable structure comprising the main body 31 and the top plate 32, and the raised portions 33 with the engagement recesses 33b and the horn-shape surfaces 33a may also be provided on the bottom of the main body 31. Further, as shown in Fig. 5 by a cross sectional view and in FIG. 6 by an exploded perspective view, the bottom 31a of the main body 31 may be formed by a separate bottom plate 34 which can be removed from the main body 31. More specifically, for joining the branch tubes 2 to the main body 31 of the surge tank 3, as shown in FIG. 7, the leading end of each branch tube 2 is inserted from the outside into the through hole 31a in the main body 31 with the top plate 32 being removed. The leading end of the branch tube 2 is then set to be positioned in the engagement recess 33b, and the branch tube 2 is fixed in position by a clamp C from the outside. This is followed by inserting a die D from above into the main body 31 and pressing the leading end of the branch tube 2 with the die D until the leading end of the branch tube 2 is bent to closely contact the horn-shape surface 33a of the raised portion 33 of the main body 31 and then yielded to form a horn-like flared or enlarged portion 2a which conforms to the horn-shape surface 33a. Because the leading end of the branch tube 2 closely contacts the horn-shape surface 33a, no positional discrepancy may be caused. Therefore, any condensed water or blow-by oil deposited on the bottom of the main body 31 can favorably be sucked up by the branch tubes 2. In other words, condensed water or blowby oil is hardly accumulated on the bottom of the main body 31. The die D is withdrawn when it have forced the loading end of the branch tube 2 to turn to the horn-like enlarged portion 2a and then, the top plate 32 is mounted to the top of the main body 31. In case that the top opening of the main body 31 is rather small, the structure shown in Figs. 5 and 6 is employed. Thus, as shown in FIG. 8, with the separate bottom plate 34 being removed, the leading end of the branch tube 2 can be effectively flared or enlarged by a die D that has a lower portion projecting downwardly from the lower opening K of the main body 31. After the leading end of the branch tube 2 has been shaped to the horn-like enlarged shape to closely contact the horn-shape surface 33a, the dice D is withdrawn and the separate bottom plate 34 is mounted to the bottom of the main body 31 to close the lower opening K. Then, the top plate 32 is mounted to the top of the main body 31 to complete the surge tank 3. While the leading end of the branch tube 2 is being shaped by the die D to have the horn-like enlarged portion 2a, the branch tube 2 is positioned in the engagement recess 33b and its inward end is pressed against the horn-shape surface 33a. Therefore, the engagement recess 33b and the horn-shape surface 33 serve as a backup tool, thus contributing to the better performance of the horn-shape forming action.

Claims: A surge tank structure for an intake manifold having a surge tank (3)to which a plurality of branch tubes (2) are joined at one end, the branch tubes (2) being for connection at their other ends to a cylinder head mounting flange (4), the end of each branch tube (2) in the surge tank being enlarged to have a horn-like shape, the surge tank comprising a main body (31) and a top plate (32), the main body (31) having through holes (31d) provided therein for accepting the branch tubes (2) and having its top side open, the top plate (32) being joined in a plane to the top of the main body (31) characterized by the main body (31) having a bottom (31a) which has engagement recesses (33b) formed therein, so that each engagement recess (33b) has a horn like surface (33a) that conforms to the horn-like shape of one end of each branch tube (2). A structure according to claim 1, wherein the engagement recesses (33b) are formed by raised portions (33). An intake manifold including a surge tank structure according to claim 1 or 2. An internal combustion engine including an intake manifold according to claim 3. A method of making a surge tank structure according to claim 1 or 2 comprising the steps of: providing a surge tank (3) having a main body (31) having its top side open and a top plate (32), providing a plurality of branch tubes (2), providing the main body (31) with through holes (31d) therein for accepting the branch tubes (2), providing the main body (31) with a bottom (31a) which has engagement recesses (33b) therein, wherein after the branch tubes (2) have been inserted into the respective through holes (31d) and have been positioned in the respective engagement recesses (33b) in the main body (31) of the surge tank (3), an enlarging tool (D) is inserted from above into the main body (31) so as to urge one end of each branch tube (2) against the corresponding horn-like surface (33a) and to enlarge the same to have the horn-like shape after which the top plate (32) is joined in a plane to the top of the main body (31) to form a closed structure.

Inventors: HADA MASATOSHI, SUNAGA YASUO, HADA, MASATOSHI, SUNAGA, YASUO, Hada, Masatoshi, c/o Aichi Kikai Kogyo K.K.
Applicants: AICHI MACHINE IND, SAN O IND CO, AICHI KIKAI KOGYO KABUSHIKI KAISHA, SANOH KOGYO KABUSHIKI KAISHA
Application year: 2000
Main classification: F02M35
IPC codes: F02M35