METHOD OF MAKING A PROJECTOR FOR A VEHICLE HORN

Abstract: A method of making a sound projector of unitary construction for a vehicle horn. A projector body (12) and projector cover (14) are molded of heat weldable plastic material as complementary parts to provide a unitary structure when the parts are joined together. The body (12) is molded with a spiral wall member (28) which defines an open channel (18) extending from a central opening (22) in the body (12) to a bell (24) at the outer peripheral turn. The wall member (28) is formed with one or more wall edges which are of substantially uniform thickness and which are adapted to be engaged by flat surfaces (52, 54) on the cover (14). The cover (14) is placed on the body (12) and the parts are subjected to relative rectilinear vibration to friction weld the parts together at the interface.

Description: METHOD OF MAKING A PROJECTOR FOR A VEHICLE HORN FIELD OF THE INVENTION This invention relates to vehicle horns; more particularly, it relates to an improved method of making the sound projector of a vehicle horn. BACKGROUND OF THE INVENTION Automotive vehicle horns typically comprise, in general, a linear electromagnetic motor coupled with a sound generator which is acoustically coupled with the air column of a sound projector. The sound generator is either a diaphragm or a percussion plate. The sound projector comprises a generally flat body with a spiral passage of several convolutions extending from a central opening adjacent the sound generator to a peripheral opening to the atmosphere. The spiral passage provides an air column having a length related to the wave length of the sound to be generated by the horn. The passage has a varying cross-sectional area which is generally smaller at the central portion and which flares into a much larger bell portion at the peripheral opening. A horn of this type is disclosed in U.S. Patent 4,433,750 which was granted on February 28, 1984 and assigned to the same assignee as the invention disclosed and claimed herein. In the manufacture of the horn projector, it has been a common practice to mold it of plastic material in two complementary parts, a projector body and a projector cover. Because of the spiral passage in the projector and the molding dies required, the interface between the two complementary parts is such that a flat surface on the cover overlies and spans several wall edges in the body and also a pair of wall edges on the body are engaged by complementary wall edges on the cover. It is desired to seal the spiral passage through the projector so that it is air tight, i.e. without leakage to the atmosphere or between adjacent turns of the spiral passage. Efforts to achieve an air tight passage have not been successful. Precise dimensional control and surface flatness at the interface of the complementary molded parts does not result in a satisfactory degree of air tightness. The use of a separate gasket interposed between the parts is not satisfactory because of material and production costs. The use of an adhesive at the interface has not provided a satisfactory solution to the problem. One reason for this is that the plastic materials suitable for the projector cannot be satisfactorily bonded by an adhesive. Polypropylene is used in most car horn projectors and is the preferred material for reasons including weight, durability and cost and yet it cannot be adhesively bonded in a satisfactory manner. One commercial vehicle horn projector is made of polypropylene parts which are riveted together and an adhesive material is applied to the interface in an attempt to produce an air tight seal. A projector of this construction is unsatisfactory because a durable air tight seal is not achieved and because of manufacturing costs. A general object of this invention is to provide an improved horn projector which overcomes certain disadvantages of the prior art. SUMMARY OF THE INVENTION In accordance with this invention, a plastic horn projector is made from two separate complementary molded parts which are formed into a projector of unitary structure. Thus, a permanent air tight seal of the passage is achieved in a rugged durable structure without the need for separate fasteners to hold the parts together. Further, there is no need to maintain precise dimensional and flatness control in the manufacture of the molded parts. While various plastic material may be used, polypropylene is preferred in the practice in the invention. In accordance with the invention, it has been found that even with the wall configuration at the interface of the complementary part that the parts can be welded together as a unitary body by a method of friction welding. In accordance with this invention, a projector body and a projector cover are separately molded of heat weldable plastic material. The body is molded with an open spiral channel extending from a central opening to a peripheral opening with a bell portion in the peripheral turn of the spiral channel. The projector cover is molded with the channel portion complementary with the bell portion and with a flat portion which is complementary with the remainder of the spiral channel on body. The wall members of the channels are formed with free edges of substantially uniform thickness. The body and cover are held in engagement and subjected to relative vibratory motion in the plane of the interface to produce a heat weld throughout the interface. The vibratory motion is rectilinear motion preferably in a direction generally parallel to the bell. The stroke length of the vibratory motion is preferably less than the thickness of the wall edges. Preferably, the plastic material is polypropylene. A more complete understanding of this invention may be obtained from the detailed description that follows taken with the accompanying drawings. DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of the horn projector in accordance with this invention; FIGURE 2 is an exploded view of the parts of the horn projector; FIGURES 3 and 4 show friction welding apparatus; and FIGURE 5 shows a detail of construction of the horn projector. BEST MODE FOR CARRYING OUT THE INVENTION An illustrative embodiment of the invention will now be described with reference to the drawings. It will be appreciated as the description proceeds that the invention may be realized in different embodiments. As shown in FIGURE 1, the horn projector 10 comprises, in general, a projector body 12 and a projector cover 14. The projector is provided with a metal mounting flange 16 which is molded into the body 12 as described in the above-identified patent 4,433,750. The metal mounting flange is not a part of this invention. The horn body 12 and the cover 14 are shown in an exploded view, prior to assembly, in FIGURE 2. The projector body 12 is molded as a unitary body, preferably from polypropylene. It comprises, in general, a spiral passage 18 which extends from a central opening 22 which communicates with a sound generator of the horn to a bell 24 which opens to the atmosphere. The projector body includes a flat plate or outer wall member 26 and a unitary upstanding spiral wall member 28 which defines the spiral passage 18 as an open channel in the body. It is noted that the spiral path and width of the passage 18 is determined in part by the thickness of the wall member 28. In particular, the wall member 28 is provided with a thick lobe 32 at its starting point, a thick portion 34 at an intermediate location and a thick portion 36 at the end of the bell. For reasons to be described subsequently, the wall member 28 is provided with upper wall edges of substantially uniform thickness throughout its length. For this purpose, the wall member and the thick lobe 32 is provided with a recess 38 such that the wall edges surrounding the recess and extending therefrom are of substantially the same thickness as the remainder of the wall member 28. Similarly, the thick portion 34 is provided with a recess 42 and the thick portion 36 is provided with a recess 44such that the wall edges are of substantially the same thickness as the remainder of the wall member 28. The recesses 38, 42 and 44 may be molded into the body member 12 or may be formed after molding. The wall edges of the wall member 28 lie in substantially the same plane but it is not necessary to maintain precise flatness or dimensional control with respect to the wall edges. The projector cover 14 is molded as a single piece and is made of the same heat weldable plastic material as the projector body 12. The cover 14 comprises a flat central circular portion 52, a flat peripheral portion 54 and a bell portion 56. The lower surface of the flat portions 52 and 54 is flat and is complementary with and adapted to engage all of the wall edges of the wall member 32 except for the bell portion 24. The bell portion 56 comprises an arcuate plate or outer wall 58 and a pair of divergent walls 62 and 64 which, together with the outer wall 58, form an open channel. The bell portion 56 complements the bell portion 24 with the walls 62 and 64 adapted to engage the wall member of the bell portion 24. Thus, with the projector cover 14 in place on the projector body 12 the open channel formed by the wall member 28 is closed to provide an air tight spiral passage from the opening 22 to the end of the bell portion 24, provided that the interface between the body and cover is properly sealed. The method of providing such an air tight seal will be described presently. The projector body 12 and cover 14 are joined together by a method of friction welding, suitably in apparatus as shown in FIGURES 3 and 4. The friction welding apparatus comprises a support member 72 which supports a clamp plate 74 by a pair of clamp actuating cylinders 76. A lower part fixture 82 is mounted on the clamp plate 74 and is adapted to receive the projector body 12. An upper part fixture 84 is mounted on a vibratory platen 86 and is adapted to receive the projector cover 14. A vibratory platen 86 is supported from the support member 72 by a set of springs 88. A drive motor 92 is supported by a bracket 94 from the support member 72 and is drivingly coupled with the vibratory platen 86. The drive motor 92 is adapted to impart rectilinear vibration to the platen 86 with a predetermined stroke length and a predetermined frequency. Friction welding of the projector body 12 and cover 14 in the apparatus 70 is carried out as follows. The projector body 12 is placed in the fixture 82 and the projector cover 14 is placed on top of the body 12 in the approximate location of the final assembly. The clamp actuators 76 are energized to raise the clamp plate 74 until the cover 14 is accurately positioned in the close fitting recess of fixture 84. The actuators 76 clamp the projector body 12 and the cover 14 into engagement with each other under a controlled load. In this condition, the drive motor 92 is energized and the vibratory motion of the platen 86 is imparted to the projector cover 14 in a rectilinear direction as indicated on FIGURE 4. This vibratory motion causes heat of friction to be developed at the interface of the projector body and cover causing a melting or fusion of the contact surfaces. The vibratory motion is preferably in a direction generally parallel to the walls of the bell portion 24 to minimize the flexing of the walls. The stroke length is limited to a distance less than the wall thickness. The vibratory motion is stopped after the contact surfaces have melted sufficiently and the load is maintained between the parts. After a holding period long enough for the material at the interface to get hard, the clamp plate 74 is lowered and the finished projector 10 is removed from the fixture 82. The friction welding provides a welded joint, as shown for example in FIGURE 5, along the entire interface between the projector body 12 and cover 14 so that the projector 10 becomes a unitary body. By reason of the substantially uniform thickness of the wall edges, the contact surfaces at the interface are heated and melted at substantially the same rate and thus a uniform weld is provided throughout the extent of the interface. Although the description of this invention has been given with reference to a particular embodiment, it is not to be construed in a limiting sense. Many variations and modifications will now be occur to those skilled in the art. For a definition of the invention reference is made to the appended claims.

Claims: What is claimed is: 1. The method of making a projector for a vehicle horn comprising the steps of: molding a projector body of heat weldable plastic material with an open spiral channel therein extending from a central opening to a peripheral opening and having a bell portion extending through at least part of the peripheral turn of the spiral channel, molding a projector cover of said plastic material for covering said channel and having an open channel portion therein which is complementary with said bell portion of said spiral channel, said cover also having a flat portion which is complementary with the remainder of the spiral channel, said spiral channel and channel portion each being defined by respective wall members having at least one free edge at the open side of the respective channel, forming said wall members with free edges of substantially uniform thickness, placing the cover on the body with the edges of the walls of the bell portion in engagement with the edges of the walls of the bell portion on the cover and with the flat portion of the cover in engagement with the edges of the walls of the remainder of the spiral channel. subjecting the body and cover to relative vibratory motion in the plane of the interface between the body and the cover while they are pressed into engagement, and stopping the vibratory motion after fusion of said material at said interface, whereby the body and cover are heat welded together throughout said interface. 2. The method of making a projector for a car horn comprising the steps of: molding a projector body of heat weldable plastic material with an open spiral channel therein extending from a central opening to a peripheral opening, molding a projector cover of said plastic material for covering said channel and having a flat portion thereon which is complementary with at least a portion of said spiral channel, said channel being defined by a wall member having at least one free edge at the open side of the channel, forming the wall member with free edges of substantially uniform width. placing the cover on the body with the flat portion in engagement with the edges of the wall member, subjecting the body and cover to relative vibratory motion in the plane of the interface between the body and the cover while they are pressed into engagement, and stopping the vibratory motion after fusion of said material at said interface, whereby the body and cover are heat welded together throughout said interface. 3. The invention as defined in Claim 1 wherein said vibratory motion is in a direction generally parallel with the wall members of said bell portion. 4. The invention as defined in Claim 1 wherein said material is polypropylene. 5. The invention as defined in Claim 2 wherein said material is polypropylene. 6. The invention as defined in Claim 3 wherein the stroke length of said vibratory motion is less than the thickness of -said wall members. - 13 - 7. The invention as defined in Claim 1 wherein the step of molding a projector body includes molding said wall member of the projector body with a thick portion which is substantially thicker than said uniform thickness, and wherein said step of forming said wall members includes the step of forming said thick portion into two or more free edges of said substantially uniform thickness. 8. The invention as defined in Claim 2 wherein the step of molding a projector body includes molding said wall member of the projector body with a thick portion which is substantially thicker than said uniform thickness, and wherein said step of forming said wall members includes the step of forming said thick portion into two or more free edges of said substantially uniform thickness.

Inventors: SMITH ROBERT E, SMITH, ROBERT, E.
Applicants: SPARTON CORP, SPARTON CORPORATION
Application year: 1986
Main classification: B29C35
IPC codes: B29C65, G10K11