Abstract:
A seal for an electrical connector having a housing with at least one chamber for an electrical contact and a pressure plate with at least one through hole corresponding to the chamber where a seal is located between the pressure plate and the housing and the seal is formed of an insulating foam whose cells are filled with a grease where the foam can be an open-cell foam with a film at its outer walls or a closed-cell foam.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a seal for an electrical connector, which seal has at least one opening for the introduction of an electrical contact that is connected to a conductor. Furthermore, the invention relates to a method for manufacturing a seal and a use of this seal in an electrical connector. 
     2. Summary of Prior Art 
     For electrical connectors with electrical contacts it is often necessary to seal the contact-making area of the connectors with respect to the housing. Basically two different methods are specified for this. It is possible to seal each individual contact, or each individual conductor, with respect to the connector housing, or a family seal can be used. The application of a family seal has considerable advantages particularly if the connector has a very large number of contacts which are packed very tightly. 
     A disadvantage of family seals is that they can easily be damaged. Family seals are firstly introduced into the connector housing and are then penetrated by the individual contacts when the contacts are introduced into the connector housing. If the contacts do not have a very smooth surface without corners and edges, the problem arises of either the seal being cut into or even material from the seal being carried out when the contact is introduced through the seal into the connector housing. If it is necessary to replace a contact, and the latter is repeatedly moved through a seal in different directions, this can lead to substantial damage of the family seal and also to the contamination of the contact surface of the contacts with particles of the seal. 
     U.S. Pat. No. 4,875,870 discloses an electrical connector in which a layer of gel is used as family seal. The connector housing is of two-part design here and has a first part in which a layer of gel and the chambers for the contacts are located, and a second part which can assume two different positions in relation to the first part. In a second position, the second part presses onto the gel like a cap and, by this compression, causes the gel to have a sealing effect. 
     GB 2 101 420-A discloses an underwater electrical connector having contacts disposed in a grease chamber sealed with a resilient diaphragm. A rigid plate member having openings according to the contacts is mounted adjacent the diaphragm. The plate member protects the diaphragm against damage. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to specify a seal for an electrical connector, that can be used as a family seal and leads to a good sealing effect. Furthermore, an object of the invention is to specify a method for manufacturing such a seal, and a use of such a seal. 
     The object is achieved with respect to the seal by means of a seal which has at least one opening or the introduction of an electrical contact that is connected to a conductor, the seal being formed by an insulating foam whose cells are filled with a grease. 
     With regard to the method for manufacturing a seal, the object is achieved by means of a method with the following method steps: the material for the foam and the grease are mixed, the mixture is then introduced in a mould, the mould is closed with a cover and then the expansion and the curing of the foam take place. 
     A further solution is specified by means of a method in which a mat in the form of a plate having openings and made of an open-cell foam is impregnated with a grease and then provided with a closed surface. 
     Furthermore, a use of such a seal is specified in an electrical connector which comprises a housing with at least one chamber for the electrical contact, and has a pressure plate with at least one through hole, the seal being provided between the housing and pressure plate. 
     Advantageous developments are specified for each main claim in the subclaims. 
     A seal according to the invention has at least one opening for the introduction of an electrical contact, connected to a conductor, into an electrical connector, that is to say actually an opening for leading through an electrical contact; the seal comprises an insulating foam whose cells are filled with a grease. This foam can be an open-cell or closed-cell foam which has a closed surface at its outer walls. In the case of an open-cell foam, this surface can be formed by a film. In the case of a closed-cell foam, a closed surface is already available. In addition, the foam can have in the region of the surface, at least in the region of the top and bottom surface and advantageously also around the openings, a layer in which the cells are very small. The cells are substantially smaller in this layer in comparison with the rest of the foam. 
     The described structure proves particularly advantageous if the seal is damaged when the opening is penetrated by an electrical contact. As a result, the outer surface of the seal is cut into and the cells of the foam are correspondingly cut into. These cells are however filled with the grease. Since the seal is used in an electrical connector which has a pressure plate which correspondingly exerts a pressure on the seal, the grease will, as a result of this pressure, flow out of the cells which have been cut into and will have a sealing effect at the damaged points of the actual seal. The grease also acts as a lubricant and reduces the insertion forces. 
     If the contacts used are configured in such a way that the seal is not damaged, then no grease will leave the seal if it has a closed surface. 
     The term grease is to be understood for example as a mineral or synthetic oil which contains a thickening agent. It is particularly advantageous to use a silicone-based compound as grease. The use of a synthetic hydrocarbon grease is also possible. The cone penetration of the grease should be between 150 and 500{fraction (1/10)} mm (measured after DIN 51580). 
     For the characterization of the term foam: it will be a mixture of the polymer material with a gas. In this context, the gas produces cells or pores whose diameter is between 0.1 mm and 1 mm. The term foam does not necessarily mean that it is manufactured by “expansion”. 
     The insulating foam is for example a material with the following properties in the expanded state: tensile strength 0.03 MPa-0.9 MPa, elongation 40%-100%. 
     It is particularly advantageous to use, for example, a two-component silicone foam as closed-cell foam and a polyurethane foam as open-cell foam. 
     By using these materials, it is possible to manufacture a hybrid foam/grease system which has the properties necessary for the seal. 
     Owing to the particular features of the seal, it is suitable in particular for use as a family seal. 
     The seal can be manufactured in a plurality of ways. A first possibility is to proceed as follows: firstly, the material for the foam and the grease are mixed together. The mixture is then introduced into a mould which is closed with a cover. Then, the mixture is expanded and the foam is cured. 
     It is particularly advantageous that the mould already has pins by means of which the openings of the seal are manufactured. The openings are therefore not manufactured by the introduction of the contacts. 
     A particular advantage is also obtained if the mixture is introduced into a housing of an electrical connector in whose chambers there are pins which appropriately project into the opening into which the mixture is introduced. Then, a cover is fitted onto the housing, which cover is in contact with the pins so that a seal with openings is produced. Instead of the introduction into the housing, introduction of the mixture into a depression in the pressure plate is also possible, the through holes in the pressure plate being closed by pins. 
     Another possibility is the introduction of the mixture in to a mould, which is closed by the pressure plate. The pressure plate includes integrated pins instead of through openings for the contacts. The pressure plate further includes holes for the mixture to expand in. The mixture is then foamed and cured. The seal is integrated into the pressure plate. The pressure plate is cut so that pins are cut out by a punch and through openings are so created. The cut pins are removed from the pressure plate with the integrated seal. 
     Another possible manufacturing method is to manufacture a relatively large mat having through-holes in the foam filled with grease, from which mat seals of the appropriate size are cut out or punched out. If the mat comprises a closed-cell foam, closed surfaces are also produced at the interfaces. The grease of the cells which are cut into in the region of the interfaces will emerge from them but the sealing effect is not impaired by this. 
     A further possible manufacturing method for a seal according to the invention is to impregnate a mat having openings and made of an open-cell foam with a grease, and then to provide it with a closed surface, that is to say for example to coat it with a film. 
     In order to initiate the process of expansion and curing and to achieve uniform expansion, the mould or the housing with the mixture should be placed in an oven. The appropriate temperatures and the curing time are essentially dependent here on the materials used. 
     If the mixture has already been expanded in the housing of the electrical connector, all that is then necessary is to remove the cover which has been put on, to remove the pins from the chambers of the housing and then to close the housing again with a pressure plate which has corresponding through holes for the contacts. It is particularly advantageous here if the pressure plate has a first engagement and a final engagement position with respect to the housing. In the final engagement position, the seal is then compressed, while there is no such compression, or only a smaller compression, in the first engagement position. As a result, contacts can be easily introduced in the first engagement position and the good sealing can be achieved in the final engagement position. If the seal were to be damaged during the introduction of the contacts, that is to say the outer closed surface were to be damaged, this causes cells, which are filled with grease, to be cut into. The engagement of the pressure plate in the final engagement position will now exert a pressure on the seal. This means that the grease will emerge from the damaged cells and, as a result, a seal is formed around the conductor, which is connected to an electrical contact. 
     The main advantages of the foam and grease seal are: 
     1. An equal force distribution of the insertion force as the grease acts as a liquid. The force distribution is due to the “hydraulic effect” of the grease. 
     2. The insertion forces are low as the grease acts as a lubricant (&lt;5N). 
     3. Small damages in the seal are recovered and the compression force necessary for a good sealing does not increase after several insertions of contact through the same opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a connector housing with introduced pins, into which the mixture is introduced; 
     FIG. 2 shows the connector housing with cover fitted on after the expansion of the foam/grease mixture; 
     FIG. 3 shows the connector housing with introduced seal and pressure plate fitted on in the first engagement position; 
     FIG. 4 shows the connector housing with pressure plate in the final engagement position; 
     FIG. 5 shows the steps of filling a mould; 
     FIG. 6 shows a pressure plate with an integrated seal; 
     FIG. 7 shows a first step of the punching of the pressure plate; 
     FIG. 8 shows a second step of the punching of the pressure plate; 
     FIG. 9 shows a first step of the removal of the pins from the pressure plate; 
     FIG. 10 shows a second step of the removal of the pins from the pressure plate; 
     FIG. 11 shows a first view of the pressure plate with integrated seal, and 
     FIG. 12 shows a second view of the pressure plate with integrated seal. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 clearly shows the housing  1  of the electrical connector which, in the illustrated cross-section, has three chambers  2 . Electrical contacts can be introduced into these chambers. Furthermore, a cover  3  which can be fitted onto the housing is provided. This cover is a blind cover which is only fitted on in order to foam the seal onto the connector and it does not have any through holes. It is in principle also possible to use the pressure plate of the connector for expansion of the seal. In that case, the pins which are introduced into the connector housing must also close the through holes in the pressure plate. The pins  4  which are each located in the chambers  2  of the housing  1  are also illustrated in FIG.  1 . The foam/grease mixture is injected into the opening  6  of the housing and dosed appropriately by means of an injection nozzle  5 . Then, the cover  3  is fitted onto the housing. For this purpose, the cover can have two engagement arms which engage with corresponding engagement hooks  8  on the housing. However, it is also possible to provide a different temporary means of securing the cover  3  on the housing  1 . 
     It is advantageous if depressions are provided in the cover  3  at each of the points at which the pins  4  are located, in order to ensure that the pins are satisfactorily guided. 
     After the cover  3  has been appropriately fitted onto the housing  1 , as illustrated in FIG. 2, the system is introduced into an oven for heating as a result of which the expansion of the mixture and the curing of the foam take place. Then, the cover  3  and the pins  4  can be removed from the housing  1  and from the expanded foam. The foam is a closed-cell, insulating foam. The cells are filled with the grease. The seal is plate-shaped with openings. The cover  3  is now replaced by the pressure plate  9 . The pressure plate  9  has through holes  10  for the introduction of electrical contacts which are connected to corresponding conductors. Furthermore, the pressure plate  9  has two engagement arms  11  and  12  which engage on the corresponding engagement hooks  8  and  13  of the housing  1 . The seal  14  is located between the pressure plate  9  and the housing  1 . As a result of the two engagement hooks  8  and  13  on the housing  1 , the pressure plate  9  can assume a first engagement and a final engagement position. In the final engagement position, the seal  14  is compressed between the pressure plate and the housing (see FIG.  4 ). 
     As is illustrated in FIG. 3, the contacts  15  (illustrated schematically) should be introduced into the housing when the pressure plate  9  is located in the first engagement position. 
     As is illustrated in FIGS. 1 to  4 , a diaphragm  16 , which securely surrounds the pins  4 , whose diameter can be smaller than that of the chambers  2 , can be arranged between the housing  1  and seal  14 . The diaphragm  16  therefore prevents the penetration of the mixture into the chambers  2  in the liquid state. 
     Instead of the use of a separate diaphragm a very thin layer with small openings may be moulded integrally with the housing. The layer closes the chambers portly on the pressure plate side. 
     In the FIGS. 5 to  12  a further possibility is shown how the seal could be produced. 
     FIG. 5 shows the steps of filling the mould and foaming and curing the seal. The letter “a” points to an empty mould  20 . The letter “b” points to a mould  20  which is already filled with the mixture of the foam with the grease  21 . Letter “c” points to a mould  20  which is filled with the seal material  21  and the pressure plate  22  is placed over the mould. It further has openings  24  on the inner side on the pressure plate  22  the openings  24  are closed with a very thin layer of plastics material and a pin is fixed to this layer. The pressure plate  22  further comprises engagement arms  25  which engage on corresponding engagement hugs of the housing of the connector. Letter “d” points to the pressure plate  22  being fixed to the mould  20 . The process of foaming and curing the seal mixture can now take place. This can be seen under letter “e”. The pressure plate  22  with the integrated seal can be removed from the mould. 
     FIG. 6 shows a view from the lower side on the pressure plate  22  with the seal  26 . What can be seen are integrated pins  27  of different diameter. The holds which are created in the seal also do have different diameters. Depending on the wire sizes to achieve a good sealing the diameters of the openings in the seal  26  should be appropriately chosen. The pins  27  must now be removed before the seal can be used. As the pins  27  are fixed to a very thin layer of the material a punch may be used as shown in FIGS. 7 and 8 to cut this very thin layer of material from the pressure plate  22 . The punch  28  is inserted through the openings  24  and cuts lose the thin layer closing the openings where the pins  27  are attached to. 
     After the pins are cut lose they should be removed from the pressure plate  22  and the seal  26 . To do that, a pin  29  is inserted from the seal side into the openings of the seal. Doing that the pins  27  with the thin cut layer  30  are removed from the pressure plate  27  with the seal  26 . 
     FIGS. 11 and 12 show now the finished product, a pressure plate  22  with openings  24  to insert contacts which are fixed to conductors and with engagement arms  25  to fix the pressure plate  22  to a connector housing, the pressure plate being integral with a seal  26  having through holes  31 .