Housing assembly and electrical switching device, in particular contactor or relay

Abstract

To provide a contactor improved in safety and reliability.SOLUTION: The present invention relates to a housing assembly for a contactor. The housing assembly includes: a frame (4) made of a ferromagnetic material and surrounding a contact chamber for separable contacts of the contactor; and an enclosure (6) made of an insulative material and at least partially covering the frame (4) internally and externally. The enclosure (6) includes at least one pocket (52) for receiving a blow-out magnet (50) of the contactor. The frame (4) is at least partially exposed for contact in the at least one pocket (52). The frame (4) improves the mechanical stability of the housing assembly and offers a suitable path for conducting a magnetic flux from the blow-out magnet (50).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a housing assembly for an electrical switching device, such as a contactor or relay. Furthermore, the present invention relates to an electrical switching device, in particular a contactor or relay, for high voltage automotive applications. However, the scope of application of the present invention extends to other fields of electrical engineering. [Background technology]

[0002] Generally, electrical switching devices such as contactors and relays are used in electrical engineering to open and close electrical circuits. The purpose is to affect the flow of a relatively strong electric current by means of a relatively weak control current. In particular, the control current is used to join or separate separable contacts which transmit the strong current flow.

[0003] Particularly in high voltage applications, interrupting the flow of strong currents can result in electric arcs, i.e. arcing between separable contacts, which can cause damage to components, such as melting of conductors, breakdown of insulation, and fire. To quickly extinguish arcs, so-called blow-out magnets are often placed near the separable contacts. These blow-out magnets are intended to generate a magnetic force that prolongs and ultimately interrupts the arc.

[0004] However, even with this or other types of arc quenching methods, electrical explosions, commonly known as arc flashes, can occur and explode electrical switching devices. For example, a short circuit in an electrical circuit in a high voltage application can cause excessive current flow. The resulting short circuit current often induces strong repulsive forces between the separable contacts. If the separable contacts are forced apart by the repulsive forces, the resulting arc discharge can create extremely high pressures and the arc flash described above. This is dangerous to personnel and equipment and must be prevented. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to improve contactors and other electrical switching devices with respect to safety and reliability. [Means for solving the problem]

[0006] This object is achieved by a housing assembly of the above-mentioned kind, which comprises a frame made of a ferromagnetic material, which surrounds a contact chamber for a separable contact of the contactor, and an enclosure made of an insulating material, which at least partially covers the frame inside and outside. The enclosure can also be called an enclosure or shell. The enclosure includes at least one pocket for receiving a blow-out magnet of the contactor, and the frame is at least partially exposed for contact in the at least one pocket.

[0007] The above solution is advantageous for at least two reasons.

[0008] First, the frame provides a mechanical reinforcement structure for the entire housing assembly. Therefore, even if the housing assembly according to the present invention is used in a contactor or other kind of electrical switching device and an arc flash occurs, the frame can effectively prevent or at least mitigate the explosion of the housing assembly. In particular, the housing assembly provides high safety in the event of a short circuit.

[0009] Second, the ferromagnetic material of the frame exhibits low magnetic resistance compared to the air, plastic, or ceramic that typically surrounds the blow-off magnet in conventional switches. Thus, in the present invention, the frame provides a suitable path for transmitting magnetic flux from the blow-off magnet when the blow-off magnet is received in at least one pocket. To this end, the frame is exposed in at least one pocket for contact by the blow-off magnet. In other words, the frame is accessible by the blow-off magnet in at least one pocket due to its exposure.

[0010] This allows the magnetic field of the blow-out magnet to better propagate in the contact chamber, resulting in improved arc quenching and shorter electric arcs, which contribute to safe and reliable operation of an electrical switching device using a housing assembly according to the present invention.

[0011] The invention can be further improved by the following embodiments, which are advantageous in themselves and can be combined in any combination with one another.

[0012] According to one possible embodiment, the at least one pocket may be adjacent to the frame, in other words a portion of the frame may define one side of the pocket, which results in a compact structure since the at least one pocket and the frame are directly adjacent to each other.

[0013] Alternatively, a separation wall may at least partially separate the frame from at least one pocket. In this case, the separation wall preferably includes an access window through which the frame is exposed for contact by the blow-off magnet. Optionally, the frame and / or the blow-off magnet may include a protrusion reachable through the access window. The access window allows the contact between the frame and the blow-off magnet to be concentrated in a specific location suitable for each application.

[0014] According to another embodiment that is easy to manufacture, the frame can have a polyhedral shape with at least one open side. For example, the frame can have an open box shape formed by five mutually perpendicular rectangular sides. Thus, the frame can be a deep-drawn metal part. Alternatively, the frame can be a stamped and bent part, a forged part, a die-cast part, or a 3D printed part.

[0015] The at least one pocket and the contact chamber may both open on one and the same side. In particular, the at least one pocket and the contact chamber may open on the same side of the polyhedral-shaped frame. This facilitates the assembly process of the switching device, where the blow-out magnet is received in the at least one pocket and the separable contact is placed in the contact chamber. Both assembly steps can be performed from the same direction and without the need to rotate or tilt the housing assembly.

[0016] According to a further embodiment, the housing assembly can comprise a lid for closing only a part of the contact chamber and at least one pocket. That is, the lid can have at least one relatively small opening through which the contact chamber communicates with the environment of the housing assembly. The size of the opening is selected so that the opening slows down the equalization of pressure between the inside and the outside of the contact chamber. Thus, when an electric arc occurs, the resulting high pressure is temporarily maintained in the contact chamber. Maintaining a high pressure for the duration of the arc discharge helps to extinguish the arc.

[0017] Optionally, at least one edge of the frame may protrude from the enclosure. Furthermore, the housing assembly may comprise a base plate weldable to the at least one protruding edge of the frame. The at least one protruding edge of the frame preferably surrounds the contact chamber and the at least one pocket. Correspondingly, the base plate may be welded to the at least one edge. The lid may be positioned between the frame and the base plate. The base plate may thus mechanically reinforce the lid in the same way that the frame reinforces the enclosure.

[0018] Alternatively, if a separate lid or base plate is not provided, the housing assembly may be welded directly to the housing of an actuator, such as, for example, a solenoid or other type of coil assembly.

[0019] According to another embodiment, the enclosure may include an inner wall that covers the contact chamber on the inside and an outer wall that encases the frame on the outside, the frame being positioned between the inner wall and the outer wall, in other words, the frame being sandwiched between the inner wall and the outer wall, which allows the frame to be effectively insulated from the separable contacts of the contact chamber and at the same time provides the frame with an external touch protection.

[0020] To simplify handling of the housing assembly, the frame and the enclosure together may form an integral structure. In particular, in this embodiment, the frame and the enclosure are a single unit, so that no additional separate parts are required. For example, the inner and outer walls may be overmolded onto the frame, whereby the inner wall is embodied by an inner layer of insulating material and the outer wall is embodied by an outer layer of insulating material.

[0021] Optionally, the frame can include at least one through hole leading to the contact chamber. During the overmolding process, a material stack of insulating material can be formed in the at least one through hole connecting the inner layer and the outer layer, thereby enhancing the bond between the frame and the enclosure.

[0022] Alternatively, the inner and outer walls may be prefabricated elements attached to the frame. In particular, the prefabricated elements may be precast from insulating material. This embodiment allows easier maintenance since the prefabricated elements can be replaced when necessary.

[0023] It is also contemplated that only the inner or outer wall may be a prefabricated element attached to the frame, with the respective other wall being overmolded to the frame.

[0024] The separation wall may be part of the enclosure, or may be embodied by a prefabricated element attached between the frame and the blow-off magnet, or by a separating layer of insulating material inserted between the frame and the blow-off magnet.

[0025] According to another embodiment, the at least one pocket can be defined by an inner wall, whereby the frame can surround a blow-out magnet received in the at least one pocket, and thus the frame can function, at least to some extent, as a shield against the magnetic field of the blow-out magnet.

[0026] To increase the number of blow-off magnets that can be accommodated by the housing assembly, the enclosure can preferably include at least two pockets, thereby improving arc quenching capabilities.

[0027] Optionally, the at least two pockets can be arranged opposite to each other with respect to the contact chamber. In other words, the contact chamber can be arranged between the at least two pockets. Thus, the blow-out magnet can be arranged at least on both sides of the contact chamber, thereby improving the arc-extinguishing effect.

[0028] The initially mentioned object can also be met by an electrical switching device, in particular a contactor, for example a DC or AC contactor, or a relay, comprising a housing assembly according to any one of the above embodiments and a contact assembly including separable contacts arranged in contact chambers of the housing assembly and at least one blow-off magnet positioned in at least one pocket of the enclosure and in direct contact with the frame.

[0029] The switching device benefits from the technical effects and advantages of the housing assembly described above, in particular the safety and reliability of the switching device is increased by the presence of the housing assembly.

[0030] According to one possible embodiment, the at least one blow-off magnet may be a permanent magnet, and the magnetic flux of the at least one blow-off magnet may be transmitted through the frame. In addition to improving the propagation of the magnetic field into the contact chamber, this embodiment is advantageous since no separate fixing means for the at least one blow-off magnet is required. The magnetic force between the permanent magnet and the ferromagnetic frame automatically assumes the fixing function. Preferably, one blow-off magnet is provided per pocket of the housing assembly.

[0031] Furthermore, the back and / or side of each blow-off magnet facing away from the contact chamber may be in direct contact with the frame. If two blow-off magnets are provided, the back and / or side faces away from the respective other blow-off magnet when the blow-off magnets are arranged on opposite sides with respect to the contact assembly. This results in a so-called magnetic reconnection of the blow-off magnets, connecting the respective back and / or side via the frame.

[0032] Optionally, the switching device may include a coil assembly for actuating the contact assembly. The housing assembly and the contact assembly may be disposed in the coil assembly. A plunger of the coil assembly may reach into the housing assembly. The plunger may transmit an actuation force and thus an actuation motion from the coil assembly to separable contacts of the contact assembly. Alternatively, manual actuation may be used.

[0033] Furthermore, the switching device can be optionally configured with a plurality of connections. A power cable can be provided for each connection and fixedly contact the associated connection. The switching device can in particular comprise a plurality of fixing elements, contact elements and / or current carrying elements at the connections. The connections are interconnected via a contact assembly and its separable contacts.

[0034] The present invention will be described in more detail below by way of example with reference to the drawings. The combination of features illustrated in the exemplary embodiments can be supplemented by further features according to the above description in accordance with the characteristics of the invention required for a particular application. If the effect of an individual feature is irrelevant to a particular application, that feature can also be omitted according to the above description of the described embodiment. The same reference numerals in the figures are always used for elements having the same function and / or the same structure. [Brief description of the drawings]

[0035] [Figure 1] 1 is a schematic perspective view of a housing assembly according to an exemplary embodiment; [Diagram 2] 2 is another schematic perspective view of the housing assembly of FIG. 1. [Diagram 3] 1 is a schematic perspective exploded cross-sectional view of a housing assembly according to a further exemplary embodiment; [Figure 4] 1 is a schematic cross-sectional side view of an electrical switching device in accordance with an illustrative embodiment; [Diagram 5] 1 is a schematic cross-sectional side view of a housing assembly according to another exemplary embodiment; [Figure 6] 1 is a schematic exploded cross-sectional side view of a housing assembly according to another exemplary embodiment; [Figure 7] 13 is a schematic perspective view of a frame and a bottom plate of a housing assembly according to a further exemplary embodiment; FIG. [Figure 8] 6 is another schematic cross-sectional view of the frame and base plate of FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Hereinafter, a schematic structure of a housing assembly 1 and an electrical switching device 2 according to the present invention will be described with reference to FIGS.

[0037] 1 and 2, the housing assembly 1 comprises a frame 4 and a surrounding body 6 that at least partially covers the frame 4 on the inside and outside. The surrounding body 6 may also be referred to as an enclosure or a shell.

[0038] The housing assembly 1 is for use with an electrical switching device 2, which may be, for example, an enclosure 6 or a relay 10. As described in more detail below, the housing assembly 1 can contribute to enhancing the safety and reliability of the electrical switching device 2.

[0039] In particular, the frame 4 provides a mechanical reinforcement structure for the entire housing assembly 1. That is, the frame 4 is formed from a ferromagnetic material, in particular a ferromagnetic metal. For example, the frame 4 may be a deep-drawn metal part 12 (see FIG. 6). Alternatively, the frame 4 may be a stamped and bent part, a forged part, a die-cast part, or a 3D printed part.

[0040] In the illustrated embodiment, the frame 4 may have an open box shape formed by five mutually perpendicular rectangular sides 14 (see FIG. 7 ). More generally, the frame 4 may have a polyhedral shape with at least one open side. Due to its shape, the frame 4 encloses contact chambers 16 for separable contacts 18 of a contact assembly 20 of the switching device 2.

[0041] The separable contact 18 includes at least one fixed contact 22 and at least one movable contact 24, all of which exhibit high electrical conductivity. For example, the movable contact 24 may be a contact bridge 26 spanning between two fixed contacts 22 disposed within the contact chamber 16 (see FIG. 4).

[0042] The switching device 2 may include a coil assembly 28 for actuating the contact bridge 26. The housing assembly 1 and the contact assembly 20 may be disposed in the coil assembly 28. A plunger 30 of the coil assembly 28 may reach into the housing assembly 1. The plunger 30 may transmit an actuation force and thus an actuation motion from the coil assembly 28 to the contact bridge 26. Alternatively, manual actuation may be used.

[0043] The enclosure 6 separates the frame 4 from the contact chamber 16. To this end, the enclosure 6 may include an inner wall 32 formed from an insulating material and lining the contact chamber 16. In particular, the inner wall 32 may be embodied by an inner layer 34 of insulating material overmolded onto the frame 4 (see FIG. 5).

[0044] Additionally, the enclosure 6 may provide external touch protection. Thus, the enclosure 6 may include an outer wall 36 that wraps the frame 4 on the outside. The outer wall 36 may thus be embodied by an outer layer 38 of insulating material. Again, the outer layer 38 may be overmolded onto the frame 4 (see FIG. 5).

[0045] In other words, both the inner wall 32 and the outer wall 36 can be overmolded to the frame 4. The frame 4 and the enclosure 6 can thus form a unitary structure 40. Optionally, the frame 4 can include at least one through hole 42 leading to the contact chamber 16. During the overmolding process, a material stack 44 of insulating material can fill the at least one through hole 42 connecting the inner layer 34 and the outer layer 38.

[0046] According to an alternative embodiment shown in Figure 6, the inner wall 32 may be a prefabricated element 46 attached to the frame 4. Similarly, the outer wall 36 may be a prefabricated element 48 attached to the frame 4. Here, the frame 4 is positioned, in particular sandwiched, between the inner wall 32 and the outer wall 36.

[0047] The ferromagnetic properties of the frame 4 can be further exploited in combination with the blow-off magnets 50 of the switching device 2. These blow-off magnets 50 are arranged close to the separable contacts 18 in order to rapidly extinguish any arc discharges that occur between the fixed contact 22 and the movable contact 24. In particular, the blow-off magnets 50 generate a magnetic force that stretches and ultimately interrupts the arc discharge.

[0048] Frame 4 provides a suitable path for transmitting magnetic flux from the blow-off magnet because frame 4 exhibits low reluctance compared to the air, plastic, or ceramic that typically surrounds the blow-off magnet in conventional switches (not shown). This allows the magnetic field of blow-off magnet 50 to better propagate in contact chamber 16, aiding in the extinguishing of the arc discharge.

[0049] To accommodate the blow-off magnets 50 of the switching device 2, the enclosure 6 includes one pocket 52 for each blow-off magnet 50. The frame 4 is at least partially exposed in these pockets 52 for contact by the corresponding blow-off magnets 50. In other words, the frame 4 is exposed and accessible by the blow-off magnets 50 in the respective pockets 52.

[0050] 2, the pockets 52 may be adjacent to the frame 4; that is, a portion 54 of the frame 4 may define one side of each pocket 52. Alternatively, a separation wall (not shown) may at least partially separate the frame 4 from the corresponding pocket 52. In this case, the separation wall preferably includes an access window through which the frame is exposed for contact by the blow-out magnet. Optionally, the frame and / or the blow-out magnet may include a protrusion that reaches through the access window.

[0051] 2, the pocket 52 and the contact chamber 16 may both open onto one and the same side. In particular, the pocket 52 and the contact chamber 16 may both open onto the same side as the frame 4.

[0052] The pockets 52 can preferably be formed by the inner walls 32 (see FIG. 6). Thereby, as can be seen in FIG. 4, the frame 4 can surround the blow-out magnets 50 received in the respective pockets 52. Furthermore, the pockets 52 can be arranged opposite to each other with respect to the contact chambers 16. In other words, the contact chambers 16 can be arranged between the pockets 52. Thus, the blow-out magnets 50 can be arranged on both sides of the contact chambers 16.

[0053] To close the contact chamber 16 and the pocket 52, the housing assembly 1 may include a lid 56 (see FIG. 3). The lid 56 may be configured to cover most of the contact chamber 16 and the pocket 52. Additionally, the lid 56 may have at least one opening 58 through which the contact chamber 16 communicates with the environment of the housing assembly 1. The size of the at least one opening 58 is selected to slow down pressure equalization between the inside and outside of the contact chamber 16.

[0054] The above-mentioned plunger 30 of the coil assembly 28 may reach into the contact chamber 16 through an opening 58 in the lid 56 and be connected in a force- and displacement-transmitting manner to the contact bridge 26 (see FIG. 4 ), so that an actuation force arising from the coil assembly 28 can be transmitted via the plunger 30 to move the contact bridge 26. If multiple contact bridges are provided, the plunger 30 of the coil assembly 28 can be connected to at least one of the contact bridges.

[0055] The lid 56 may be a prefabricated element 60 attached to the frame 4 and / or to the enclosure 6. The lid 56 is preferably formed from an insulating material. As a structural reinforcement for the lid 56, the housing assembly 1 may comprise a base plate 62 formed from a ferromagnetic material, in particular a ferromagnetic metal. The base plate 62 may be attached to the frame 4 and / or to the enclosure 6. The lid 56 may be positioned between the frame 4 and the base plate 62.

[0056] Optionally, at least one edge 64 of the frame 4 can protrude from the enclosure 6 (see FIG. 2). In this embodiment, the base plate 62 can be welded to the protruding edge 64 of the frame 4. The protruding edge 64 of the frame 4 preferably surrounds the contact chamber 16 and the pocket 52. Correspondingly, the base plate 62 can be welded to the protruding edge 64 along the entire periphery of the contact chamber 16 and the pocket 52. Thus, the frame 4 and the base plate 62 together form a high pressure resistant structure.

[0057] In an alternative embodiment (not shown), the housing assembly 1 can be welded directly to the housing of an actuator, such as, for example, a solenoid or other type of coil assembly, thereby eliminating the need for a separate lid or base plate.

[0058] Other methods of attaching the frame 4 to the base plate 62 or actuator housing can include techniques such as bending, pressing, riveting, screwing, gluing, etc. to establish a rigid connection.

[0059] As previously described, the switching device 2 comprises a housing assembly 1 and a contact assembly 20 including a separable contact 18 disposed in a contact chamber 16 of the housing assembly 1 and a blow-off magnet 50 positioned within a pocket 52 of the enclosure 6.

[0060] The blow-off magnets 50 are in direct contact with the frame 4. In particular, a back surface 66 of each blow-off magnet 50 facing away from the contact chamber 16 may be in direct contact with the frame 4. Additionally or alternatively, a side surface 68 of each blow-off magnet 50 may be in direct contact with the frame 4. The blow-off magnets 50 may be permanent magnets 70, preferably capable of transmitting their respective magnetic flux through the frame 4.

[0061] The base plate 62 may be positioned between the contact chamber 16 and the coil assembly 28 (see FIG. 4). As previously described, the base plate 62 is ferromagnetic, which allows the base plate 62 to transmit magnetic flux generated by the coil assembly 28, thereby improving the operation of the coil assembly 28.

[0062] 4, the switching device 2 can be optionally configured to have a plurality of connections 72. A power cable (not shown) can be provided for each connection 72 and fixed to the connections 72. For this purpose, a fixing element (not shown) can be present at each connection 72. Alternatively, each power cable can be welded or soldered to the connection 72.

[0063] The connection 72 can extend through the outer wall 36, the frame 4 and the inner wall 32 into the contact chamber 16 (see FIG. 4). For this purpose, suitable openings 74 can be provided in the outer wall 36, the frame 4 and / or the inner wall 32 (see FIG. 6).

[0064] The ends 76 of the connecting portions 72 that extend into the contact chambers 16 may function as the fixed contacts 22 described above. These fixed contacts 22 may be interconnected via contact bridges 26. This interconnection is broken when the contact bridges 26 are moved away from the fixed contacts 22 by the coil assembly. Any arcing that occurs during this separation process is extinguished by the blow-out magnets 50.

[0065] The electrical switching device 2, shown as an enclosure 6, may be a DC or AC contactor. Alternatively, the present invention may be used in a relay 10 or similar electrical switch. [Explanation of symbols]

[0066] 1 Housing Assembly 2. Switching Devices 4 Frames 6. Enclosure 8 Contactor 10 Relay 12 parts 14 sides 16 Contact Chamber 18 Separable Contacts 20 Contact Assembly 22 Fixed Contact 24 Movable Contact 26 Contact Bridge 28 Coil Assembly 30 Plunger 32 Inner wall 34 Inner layer 36 Exterior Wall 38 Outer layer 40 Monolithic structure 42 Through hole 44 Material Laminate 46 Assembled elements 48 Assembled elements 50. Blowout Magnet 52 Pocket 54 part 56 Lid 58 Opening 60 Assembled elements 62 Base Plate 64 Edge 66 Back side 68 Side 70 Permanent Magnets 72 Connection 74 Aperture 76 End

Claims

1. A housing assembly (1) for a contactor (8), said housing assembly (1) comprising: a frame (4) made of ferromagnetic material, surrounding contact chambers (16) for the separable contacts (18) of said contactor (8); an enclosure (6) made of insulating material, which at least partially covers said frame (4) inside and outside; Equipped with The enclosure (6) includes at least one pocket (52) for receiving a blow-off magnet (50) of the contactor (8); The frame (4) is at least partially exposed for contact in the at least one pocket (52).

2. The housing assembly (1) of claim 1, wherein the at least one pocket (52) is adjacent to the frame (4).

3. 3. A housing assembly (1) according to claim 1 or 2, wherein the frame (4) has a polyhedral shape with at least one open side.

4. The housing assembly (1) according to any one of claims 1 to 3, wherein the housing assembly (1) comprises a lid (56) for only partially closing the contact chamber (16).

5. 5. A housing assembly (1) according to any one of claims 1 to 4, wherein at least one edge (64) of the frame (4) protrudes from the enclosure (6), and the housing assembly (1) comprises a base plate (62) weldable to the at least one edge (64) of the frame (4).

6. The housing assembly (1) according to any one of claims 1 to 5, wherein the enclosure (6) includes an inner wall (32) that covers the contact chamber (16) on the inside and an outer wall (36) that wraps the frame (4) on the outside, the frame (4) being positioned between the inner wall (32) and the outer wall (36).

7. A housing assembly (1) according to any one of the preceding claims, wherein the frame (4) and the enclosure (6) form an integral structure (40).

8. The housing assembly (1) according to claim 6 or 7, wherein the inner wall (32) and the outer wall (36) are overmolded onto the frame (4).

9. 7. A housing assembly (1) according to claim 6, wherein the inner wall (32) and the outer wall (36) are prefabricated elements (46, 48) attached to the frame (4).

10. A housing assembly (1) according to any one of claims 6 to 9, wherein the at least one pocket (52) is defined by the inner wall (32).

11. The housing assembly (1) according to any one of the preceding claims, wherein the enclosure (6) comprises at least two pockets (52).

12. The housing assembly (1) according to claim 11, wherein the at least two pockets (52) are arranged opposite each other with respect to the contact chamber (16).

13. A switching device (2), A housing assembly (1) according to any one of claims 1 to 10, a contact assembly (28) including a separable contact (18) disposed in the contact chamber (16) of the housing assembly (1) and at least one blow-off magnet (50) positioned within the at least one pocket (52) of the enclosure (6) and in direct contact with the frame (4); A switching device (2).

14. 14. The switching device (2) of claim 13, wherein the at least one blow-off magnet (50) is a permanent magnet (70), and the magnetic flux of the at least one blow-off magnet (50) is transmitted through the frame (4).

15. 15. The switching device (2) according to claim 13 or 14, wherein a rear surface (66) of each blow-off magnet (70) facing away from the contact chamber (16) is in direct contact with the frame (4).

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