Capacitor, assembly comprising a capacitor and a busbar and method of manufacturing a capacitor

Abstract

A capacitor, an assembly comprising a capacitor and a busbar and a method for manufacturing a capacitor are disclosed. In an embodiment a capacitor includes a winding element and a terminal having a first part of a first material and a second part of a second material, the second material being different than the first material, wherein the first part is electrically contacted to the winding element, and wherein the second part is an external contact of the capacitor.

Claims

1. A capacitor comprising: a winding element; and a terminal comprising a first part of a first material and a second part of a second material, the second material being different than the first material, wherein the first part is electrically contacted to the winding element, wherein the second part is an external contact of the capacitor, wherein the second part forms a sleeve and comprises an inner thread and an outer thread, wherein the inner thread is configured to receive a screw, wherein the second part is screwed into the first part, and wherein manufacturing tolerances are adjusted for by setting a depth by which the second part is screwed into the first part.

2. The capacitor according to claim 1, wherein the first part comprises an opening, and wherein the second part is arranged in the opening of the first part.

3. The capacitor according to claim 2, wherein the second part is screwed into the opening of the first part.

4. The capacitor according to claim 1, wherein the second part comprises a self-tapping thread and is mechanically connected to the first part by the self-tapping thread.

5. The capacitor according to claim 1, wherein the winding element does not abut the second part.

6. The capacitor according to claim 1, wherein the second part comprises the inner thread configured to be contacted to a busbar.

7. The capacitor according to claim 1, wherein the second material has a higher Young's modulus than the first material.

8. The capacitor according to claim 1, wherein the first material comprises aluminum.

9. The capacitor according to claim 1, wherein the second material comprises copper or a copper based alloy.

10. The capacitor according to claim 1, wherein the second part is covered by a coating.

11. The capacitor according to claim 1, wherein the second part is movable relative to the first part so that a height of the terminal is adjustable.

12. The capacitor according to claim 1, further comprising a second terminal comprising a first part of the first material and a second part of the second material, wherein each of the terminals comprises a top face which faces away from the winding element, and wherein the top faces of the terminals are co-planar.

13. The capacitor according to claim 12, further comprising a cover disc, wherein each of the terminals is arranged in an opening of the cover disc.

14. The capacitor according to claim 13, wherein the cover disc forms a part of a housing of the capacitor.

15. An assembly comprising: the capacitor according to claim 1; and a busbar, wherein the busbar is mechanically fixed and electrically contacted to the second part of the terminal.

16. A method for manufacturing a capacitor, the method comprising: electrically contacting and mechanically connecting a winding element to a first part of a terminal, wherein the first part comprises a first material, impregnating the winding element and the first part of the terminal; and electrically contacting and mechanically connecting a second part of the terminal to the first part of the terminal, wherein the second part comprises a second material different from the first material, wherein the second part forms a sleeve and comprises an inner thread and an outer thread, wherein the inner thread is configured to receive a screw, wherein the second part is screwed into the first part, and wherein manufacturing tolerances are adjusted for by setting a depth by which the second part is screwed into the first part.

17. The method according to claim 16, wherein the capacitor comprises more than one terminal, each terminal comprising a first part and a second part fixed to the first part, wherein each of the second parts comprises a top face which faces away from the winding element, and wherein the method further comprises adjusting a position of each of the second parts with respect to the first part such that the top faces of the second parts are co-planar.

18. The capacitor according to claim 8, wherein the second material comprises copper or a copper based alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the present invention is described in further detail with respect to the figures.

(2) FIG. 1 shows a part of a capacitor before a final assembly step;

(3) FIG. 2 shows a second part of a terminal of the capacitor;

(4) FIG. 3 shows an enlarged view of a part of the second part;

(5) FIG. 4 shows the part of the capacitor after the final assembly step; and

(6) FIG. 5 shows an assembly comprising the capacitor and two busbars.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(7) FIG. 1 shows a part of a capacitor. In particular, FIG. 1 shows a part of a capacitor during the manufacturing process of the capacitor before a final assembly step.

(8) The capacitor comprises a cover disc 1 which forms a part of a housing of the capacitor. Further, the capacitor comprises two terminals 11, 12 wherein each of the terminals 11, 12 is arranged in an opening of the cover disc 2. The terminals 11, 12 are configured to electrically contact a winding element arranged inside the housing of the capacitor to an external busbar 8, 13 which is not part of the capacitor. One of the terminals 11 is a plus terminal and the other terminal 12 is a minus terminal.

(9) Each of the terminals 11, 12 comprises a first part 2 and a second part 3. The second part 3 has not yet been assembled to the capacitor before the final assembly step as shown in FIG. 1.

(10) The first part 2 forms receptacle. The first part 2 comprises an opening 2a. In particular, the opening 2a is a bore hole. The opening 2a of the first part 2 is configured to receive the second part 3. The first part 2 further comprises a pen-shaped protrusion 14 which faces into the inside of the housing of the capacitor. The protrusion 14 is configured to be directly contacted to a tab 15 of the winding element.

(11) The first part 2 consists of a first material. The first material has a low Young's modulus. The first material is determined by the electrochemical nature of the capacitor. For example, wet aluminum electrolytic capacitors require internal contacts of high purity aluminum, for example of aluminum having a purity of at least 99.5%. The first material is aluminum. In particular, the first material is aluminum having a purity of at least 99.5%.

(12) FIG. 2 shows the second part 3 which is configured to be mounted into the opening 2a of the first part 2. The second part 3 is an insert which can be received in the opening 2a. FIG. 3 shows an enlarged view of a part of the second part 3. This part is marked by a circle in FIG. 2.

(13) The second part 3 is made of a second material which has a higher Young's modulus than the first material. The second part 3 is configured to provide the outer contact of the capacitor to the busbar 8, 13. Further, in the assembled capacitor, the second part 3 is mechanically fixed and electrically connected to the first part 2.

(14) The second part 3 forms a sleeve. The second part 3 comprises an inner thread 4 and an outer thread 5. The inner thread 4 is configured to receive a screw 9 wherein the second part 3 can be fixed to a busbar 8, 13 by the screw 9 and by a washer 10.

(15) The outer thread 5 is configured to mechanically connect the second part 3 to the first part 2 of the terminal. The outer thread 5 is a self-tapping thread. During the final assembly step of the capacitor, the second part 3 is screwed into the first part 2. As the second material is harder than the first material, the self-tapping outer thread 5 of the second part 3 carves a groove 7 or thread into the inner surface of the first part 2.

(16) Further, the second part 3 comprises a top plate 3a which defines a top face of the second part 3 which faces away from the first part 2 of the terminal. The top plate 3a of the second part 4 abuts the busbar 8, 13 when the capacitor is assembled to the busbar 8, 13. The top plate 3a comprises a hole. When the terminal is fixed to a busbar 8, 13 by the screw 9, the screw 9 can pass through the hole.

(17) Each of the sleeve having the inner thread 4 and the outer thread 5 and the top plate 3a consists of the second material. The second material is harder than the first material. The second material has a higher Young's modulus than the first material. The second material is preferably copper or comprises copper. The second material may be a copper based alloy or may comprise a copper based alloy.

(18) The second part 3 provides the outer contact of the capacitor, i.e. the contact to the busbar 8, 13. Due to the use of the second material, multiple disadvantages of an outer contact of aluminum can be overcome:

(19) The busbar 8, 13 typically consists of copper. The contact surface of the second material and the busbar 8, 13 has a higher ripple current capability than a connection of the busbar 8, 13 to aluminum. For example, in case that the second material is copper or a copper based alloy, a contact surface of either copper to copper or copper to a copper based alloy is provided, both resulting in a ripple current capability that is significantly higher than the ripple current capability of a copper to aluminum contact surface and both resulting in a contact resistance that is more than an order of magnitude smaller than the contact resistance of a copper to aluminum contact surface.

(20) Further, aluminum is very prone to oxidization. Thus, thick oxide layers form on components made of aluminum. As the second material a material is chosen that is less prone to oxidization. For example, copper and copper based alloys are less likely to oxidize compared to aluminum. Accordingly, the use of the second material can prevent the formation of a thick oxide layer at the contact surface of the terminal 11, 12 and the busbar 8, 13. Such a thick oxide layer would deteriorate the allowed ripple current capability. The second part 3 of the second material shows a reduced surface corrosion compared to aluminum.

(21) Moreover, as the second material a material is chosen that has a higher mechanical strength than aluminum, e.g. that has a higher Young's modulus than aluminum. Accordingly, the connection of the second part 3 to the busbar 8, 13 has a higher mechanical strength and can therefore tolerate an increased mounting torque compared to a connection of the busbar 8, 13 with an aluminum component.

(22) The second material has a reduced surface roughness compared to the surface roughness of aluminum. The surface roughness of the state of the art manufacturing of aluminum terminals, e.g. by cold forming, is inferior compared to a machined surface of the second material.

(23) Further, the second part 3 is fixed to the first part 2 of the terminal by the outer thread 5. As the outer thread 5 is self-tapping a very tight connection between the second part 3 and the first part 2 can be formed during the assembly of the second part 3 to the first part 2. Thus, the contact surface of the second part 3 to the first part 2 is not prone to oxidation. No oxide layer, or at least no thick oxide layer, is formed at the contact surface of the two parts 2, 3 and, therefore, the contact resistance is not significantly increased.

(24) The connection of the second part 3 to the first part 2 is so tight that it can be considered as being self-sealing. In other words, a corrosion of the contact surface and an entrance of moisture into the contact surface of the second part 3 and the first part 2 is prevented.

(25) FIG. 4 shows the part of the capacitor shown in FIG. 1 after the last assembly step of the capacitor has been completed. The second part 3 has been arranged inside the opening 2a of the first part 2.

(26) In FIG. 4, the two second parts 2, 3 are arranged such that their respective top plates 3a are co-planar. By arranging the second parts 3 in the first part 2, it is possible to adjust for manufacturing tolerances of the first part 2 of the terminal. For example, one second part 3 may be screwed deeper into the respective first part 2 than the other second part 3 in order to adapt for manufacturing tolerances. Thus, the second parts 3 allow to increase the co-planarity of the terminals 11, 12 as the second parts 3 allow to balance out and re-correct any previously generated and often unavoidable distortions of the co-planarity of the terminals 3.

(27) In other words, the terminals 11, 12 have the same height. The height of terminal 11 is marked as H11 in FIG. 4 and the height of terminal 12 is marked as H12.

(28) FIG. 5 shows an assembly comprising the previously described capacitor and two busbars 8, 13. One of the busbars 8 is fixed to the first terminal 11 by a conventional screw 9 and a washer 10 wherein the screw 9 is screwed into the inner thread 4 of the second part 3. The other busbar 13 is fixed to the other terminal 12 by a second screw 9. The busbars 8, 13 are in direct contact only to the top plates 3a of the second part 3, i.e. to the second material. The two busbars 8, 13 are separated by an insulator 16.

(29) Furthermore, FIG. 5 shows a part of the winding element. In particular, the winding element comprises tabs 15 which are fixed to the protrusion 14 of the first part 2 of the terminal. The tabs 15 comprise holes wherein the protrusion 14 is arranged inside the hole. Afterwards, the protrusion 14 is riveted to the tabs 15, thereby permanently fixing the tabs 15 to the terminal 11, 12. The winding element, i.e. the tabs 15, are in direct contact only to the first part 2, i.e. to the first material.