The invention refers to a housing consisting of two housing parts made of plastic that are braced against one another with a force that acts along a housing axis or parallel to it. In this case, the direction of the force or the housing axis extends transversally to a joint or parting plane existing between the housing parts. The housing parts lie either directly beside one another or there are structural parts (e.g. additional housing parts and seals) squeezed between the housing parts. A bracing of the type described here is required, for example, when an interior space enclosed by housing parts towards the surroundings should be sealed, which is the case in pump housings.
Metallic screws are used frequently for bracing housing parts. When temperature conditions change, as occurs during the construction of motor vehicles, for example, the considerably different thermal expansion of metal and plastic becomes a problem. Thus, plastics such as PPM or HDPE have a much higher thermal expansion coefficient than metallic tools. The relative longitudinal expansion of the plastic material in the direction of the screw axis under higher temperatures causes the areas of materials impinged by a screw head or screw nut of housing parts to be stressed above the intended screw pre-stressing force. The plastic material starts to flow, and settling phenomena in the areas of the materials mentioned above start occurring. After the housing cools off again, the housing parts are no longer pressed against one another with the intended force so that a secure connection—and therefore a hermetic sealing towards the exterior—is no longer ensured.
Taking this into account, the task of the invention is to suggest a housing of the type mentioned in the beginning and a method for assembling such a housing to help solving the problems described above.
With regard to the housing, this task is solved in accordance with claim 1. According to it, the two housing parts of the housing that have a joint running transversally to a housing axis between them are braced against one another with the help of at least one connecting element made of plastic firmly bonded to housing parts, with a force acting along the housing axis of the housing.
During the assembly process according to claim 15, the solution to the task consists in that the housing parts are pressed against each other with the help of a clamping device under impingement with a pressing force (if need be, by placing an intermediate layer of additional structural parts), in which case a firmly bonded connection between the at least one connecting element and a housing part takes place while force is being applied.
The force needed for a secure mutual bracing depends almost entirely on the elastic retraction forces of the housing parts and, if necessary, on the structural parts squeezed in between, which are the result of a preceding elastic deformation of the material of the parts mentioned above (that are preferably, and at least partially, made of plastic material) carried out with the help of the clamping device. Since the plastics possibly considered for the manufacturing of housing parts have very similar thermal expansion coefficients, the firmness of the connection between housing parts and other structural parts arranged in between changes only insignificantly, if at all. Settling phenomena, which reduce the firmness of the connection or the clamping force of the connecting element(s) acting on the connection, are ruled out. This occurs when the housing parts and the connecting element are made from a plastic with the same thermal expansion coefficient. In this case, it can be the same or a different plastic.
The firmly bonded connection between the at least one connecting element and the housing parts is not critical with regard to a load of the connecting joints that leads to the settling of material, particularly when the connecting element and the housing part are welded together, preferably laser welded—as is the case with an especially preferred design variant.
The at least one connecting element can be executed as a separate part, in which case a welding with every one of the two housing parts would be necessary. Twofold welding can be avoided when one end of the connecting element is connected as one piece to a housing part. Moreover, this method reduces the number of parts needed.
An especially advantageous design variant from the point of view of assembly technique foresees that at least one connecting element and one housing part are executed in such a way that they are firmly held against one another in a state of pre-assembly in which the connecting element is not yet firmly bonded to a housing part. The housing—and if need be, the structural parts arranged sandwich-like between the housing parts—can in this case be already mounted to the extent that all housing components are aligned in exact position to one another so that easy handling during transportation to the clamping device mentioned above, for example, is possible and, apart from the pressing process taking place in the clamping device, no more manipulations are necessary. Because the form closure is designed to be ineffective against the direction of assembly (i.e. the direction in which the housing parts are joined together during assembly), the housing parts—and, if need be, structural parts arranged in between—can be pressed together in the direction of assembly and then joined together with at least one connecting element while being braced in the direction of assembly.
An easily produced holding together of the housing parts and the possibly structural parts arranged in between can be accomplished in an especially easy way if the connection between the at least one connecting element and a housing part is executed as a snap connection. This opens up the possibility that the parts to be joined together can be brought closer to one another with a direction of assembly running along the housing axis until the snap connection becomes effective when it creates a form closure and the individual parts of the housing are held together as a result of that.
So the connecting element does not protrude from the outer side of the housing when the latter is placed in an installation space and can interfere, there is a recess on the outer side of a housing part that contains in it an overlapping section of the connecting element, at least partially, preferably entirely. So the latter can be accomplished, it is proposed that the depth of the recess should be the same or greater than the thickness of the overlapping section.
In an especially advantageous design variant, there are several connecting elements spaced apart above the circumference of the housing parts, executed preferably as arms with their one end connected as one piece to one of the two housing parts. The form closure mentioned above in a state of pre-assembly can easily, with the help of the free end of an arm (i.e. the end not connected as one piece with a housing part), a cross leg formed transversally to its longitudinal extension.
The invention will now be explained in more detail with the help of the enclosed drawings, which show:
FIG. 1: A schematic lateral view of a housing clamped in a pressing device,
FIG. 2: A lateral view of a pump with a motor flanged-mounted on the pump housing,
FIG. 3: A perspective, partially pried open exploded view of the pump shown in FIG. 2.
FIG. 1 shows the generalized form of a pump 1. It includes two housing parts, namely a first housing part 2 and a second housing part 3. The two housing parts have roughly square contours and are largely executed in the shape of disks. Regardless of their respective design, they have a contact surface 4, 5. In a simple embodiment, the contact surfaces 4, 5 are directly beside one another (not shown.). In the embodiment shown in FIG. 1, however, additional structural parts 6a, b, c have been arranged between the first and second part of the housing 2, 3. In this example, the housing parts 2, 3 are braced against one another with four connecting elements 7, with a force F acting in direction of the housing axis 8, and as a result of this the structural parts 6a-6c are squeezed or pressed together between the structural parts 2, 3. The direction of the force and the housing axis 8 extend transversely to the contact surfaces 4, 5 of the housing parts 2, 3.
In the example shown in FIG. 1, there are four connecting elements 7 on the first housing part 2 spaced apart in its circumferential direction. The connecting elements are not executed here as separate parts, but are connected as one piece to the first housing 2. The connecting elements 7 are arms 9 executed in form of strips of material or brackets. They are formed peripherally as one piece on the first housing part 2 and extend parallel to the housing axis 8. They overlap the outer side 13 of the second housing part 3 with an overlapping section 10. The overlapping section 10 is firmly bonded to the second housing part 3, namely by means of laser welding. To make such welding possible, the first housing part 2 or at least the overlapping section 10 of the arms 9 allows laser light to go through. The second housing part 3 or at least a section of the second housing part 3 covered by the overlapping section 10 is made of plastic material that absorbs laser light. Such plastic material can contain embedded soot particles, for example. Once the laser beam impinges on the overlapping section 10, the material of the second housing part 3 lying underneath starts melting and a dot-like joint 14 is created, for example, between the arms 9 and the second housing part 3.
For assembling the housing 1, a force F acting in the direction of the housing axis 8 applies pressure on the two housing parts 2, 3 with the help of a clamping device 16. The clamping device encompasses, for example, a stamp 16 movable in the direction of the housing axis 8 and a fixed counter holder 17, in which case the two housing parts 2, 3 are arranged between stamp and counter holder. By advancing the stamp, the first housing part 2 supporting the arms 9 or connecting elements 7 is pressed against the corresponding other housing part 3 together with the structural parts 6a-6c. In doing so, an elastic deformation or compression of the housing parts 2, 3 and structural parts 6a-6c occurs in the direction of the housing axis 8. While pressure is being applied with a given force F, the firmly bonded joint between the overlapping section 10 of the arms 9 and the second housing part 3 is carried out. As soon as the melted material on the joint 14 has cooled and solidified, the stamp 16 is moved back and the housing 1 taken out of the clamping device 15. The elastic deformation of the housing parts 2, 3 and of the structural parts 6a-6c done with the help of the stamp 16 results in an elastic retraction force that acts in the direction of the housing axis 8 and is initiated in the connecting elements 7 or arms 9.
A structural part 6c arranged between the housing parts 2, 3 can be a membrane 19 made of an elastic (i.e. rubber-like) material clamped between two structural parts 6a, 6b.
The pump shown in FIGS. 2 and 3 is a membrane pump such as a pneumatic pump, for example. As with the embodiment described above, the housing 1a of the pump has a first housing part 2 and a second housing part 3. A motor 24 has been flanged onto the underside 23 of the second housing part 3 that extends transversally to a housing axis 8. The first housing part 2, on which an inlet connection piece 15 for air has been arranged, also comprises four connecting elements 7 or arms 9 formed as one piece spaced apart in circumferential direction of the housing part 2a.
Each one of the overlapping sections 10 of the arms 9, with which they overlap the second housing part 3 on its outer side 13, are inserted in a recess 26 of the outer side 13. The thickness 27 of the arms 9 or of the overlapping sections corresponds to the depth 28 of the recesses, so that the overlapping sections 10 do not protrude from the outer side 13 of the second housing part 3 or are fully contained therein.
A form closure acting against the direction of assembly 35 has been executed between the free ends 29 of an arm 9 and the second housing part 3. Such a form closure is not restricted to the housing 1a in accordance with FIGS. 2 and 3, but can also be present in any housing shapes such as those shown in FIG. 1. The form closure is effective in a state of pre-assembly because the housing parts 2, 3 are not yet joined together with the help of at least one connecting element 7 (thus, in the case of the example shown in FIGS. 2 and 3, the arms 9 are not yet firmly bonded to the second housing part 3). Generally speaking, the form closure is executed in such a way that the free end 29 or one arm 9 has a rear grip element 30 that acts together with a counter face 33 facing away from the first housing part 2. Thus, the first housing part 2 and the structural parts 6 lying in between cannot therefore be removed from the second housing part 3 in the direction of the arrow 34 (i.e. against the direction of assembly 35). In other words, when the individual components of the housing are being put together in the direction of assembly 35, the form closure is not effective. When the housing parts 2, 3 and the structural parts 6 are pressed together in the clamping device 15, the arms 9 can therefore move in the direction of assembly 35 with regard to the second structural part—hence, they do not interfere with the axial pressing together of the housing components. In the final state of assembly according to FIG. 2, this can be recognized in that there is a gap or axial separation 36 between the rear grip element 30 and the counter face 33. In the specific example of the membrane pump shown in FIGS. 2 and 3, a cross leg 37 has been formed on the free end 29 on two arms 9′ located opposite one another for creating the form closure. The upper edge sticking out laterally from its arms 9 pointing towards the first housing part 2 forms the rear grip element 30. The recess 26 has been designed to complement the cross leg 37 and has an area 38 that widens and extends transversally to the housing axis 8 for containing the cross leg 37. In this area, the recess 26 has a wall 39 that forms the counter face 33 acting together with the rear group element 30 forms and extends transversally to the housing axis 8 or in circumferential direction of the second housing part. The housing axis 8 mentioned above extends very generally parallel to the direction of assembly 35.
The membrane pump in question also comprises, in addition to the two housing parts 2, 3, the structural parts 6d to 6g arranged in between. The structural part 6 is a pot-shaped housing part that contains the structural part 6e that forms the pump membrane 39, which comprises four pump chambers 40 protruding from the structural part 6d with cogs 43 on the underside. The cogs 43 serve for actuating the pump membrane (i.e. for enlargement or reduction) and the pump chambers 40 when air is suctioned and driven out. The pump membrane 39 has an edge bulge 35 squeezed between structural part 6d and disk-shaped structural part 6f. Finally, the structural part 6g is a valve membrane squeezed between the first housing part 2 and structural part 6f that comprises freely cut valve elements (not shown) that control the valve openings.