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(11) | EP 1 455 373 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Relay contact assembly |
| (57) A relay contact assembly having a contact spring 13 and an actuator 11 comprises at least one rib 23 which extends towards the contact spring 13 and which restricts the freedom of motion of the contact spring 13 in the open contact state in case of spring breakage. Thereby, the contact spring
13 is held in a safety distance from the counter contact 16 and/or the spring terminal 14. |
[0001] In a safety relay it must be ensured that normally closed (NC) and normally open (NO) contacts cannot be closed at the same time, even in case of an abnormal incident, such as a breakage of the contact spring. According to EN 50205, the contact spacing for a single interruption has to be at least 0.5 mm, and for a double interruption at least 0.3 mm.
[0002] Possible incidents to be analysed are the breakage of the contact spring and its loosening from the rivet. It is assumed that a potential breakage of the spring occurs at the position of highest material stress, that is essentially at the clamping site or at the location where the contact spring is riveted or welded to a terminal or spring support. Breakage at other sites is prevented by systematic and careful design and placement of the contact spring.
[0003] It has to be prevented that a spring which is vagabonding after a breakage at the predestined site exceeds the prescribed safety distance to the counter contact in the open contact state.
[0004] The problem arises in conventional contact assemblies and will be explained referring to Figs. 5A to 6.
[0005] In the position shown in Fig. 5A, the actuator 11 holds the contact spring 13 extending through the actuator slit 12 in an open state, in which the contact piece 15 located at the free end of the contact spring 13 is held in a distance from the counter contact 16. The contact spring 13 is a mechanically biased flat spring, the foot of which is riveted, or fixed otherwise, to a terminal 14.
[0006] In contact assemblies of this type, there is the danger that a loose contact spring 13 comes in the open state too close to the counter contact. The loosening of the contact spring 13 is particularly dangerous, since in this case the contact spring 13 persists in its complete length so that the danger that a spacing below the prescribed minimum or even a contact is reached, becomes particularly high.
[0007] Fig. 5B illustrates such an incident. The loose and relaxed contact spring 13 has moved to the other face of the terminal 14 and is contacting there. This means a single interruption in the contact region for which the required minimum distance of 0.5 mm to the counter contact 16 is not observed, as indicated by 17.
[0008] Fig. 5C shows a case in which the loose contact spring 13 is displaced in its longitudinal direction. Again, the foot of the spring 13 has contact to the terminal 14. In this position, a recess 18 of the contact spring 13 is located within the actuator slit 12 and the contact spring 13 can rotate about its longitudinal axis such that the required minimum distance to the counter contact 16 is again not observed at the sites 19.
[0009] A known measure to avoid the case described with reference to Fig. 5C is shown in Fig. 6. Therein, the freedom of motion of the spring is restricted by a mushroom-shaped spacer 20 opposite to the free end of the spring. The spacer 20 prevents the recess 18 of the contact spring 13 from reaching the region of the actuator 11, i.e. the position which allows a maximum rotation of the contact spring 13.
[0010] The presence of such a spacer 20 close to the counter contact 16 has, however, the drawback of metallic deposit on the spacer 20 resulting from contact wear. Consequently, the electric characteristic of the relay is deteriorated and the electric lifetime may be shortened.
[0011] EP-B-1 121 701 discloses a relay in which the actuator comprises a window for the contact spring and a blocking wall, which effect that in case of a breakage, the spring is caught by the actuator. This avoids the danger of a short circuit potentially produced when the broken spring falls into the neighbouring chamber.
[0012] The present invention has the general object to avoid at least partially the drawbacks of conventional contact assemblies, and particularly to provide a relay contact assembly which ensures a safety contact spacing in case of a spring breakage without impairing the lifetime. It is further desired to keep the constructive and manufacturing expenditure as small as possible.
[0013] The object is met by the invention defined in claim 1 according to which the freedom of motion of a vagabonding contact spring is restricted in such a way that it cannot exceed the prescribed safety spacings. The subclaims relate to advantageous modifications of the invention.
[0014] According to claim 2, the element restricting the freedom of motion of the broken or loose contact spring has the form of a rib positioned to tilt the loose spring in such a way that it moves away from the counter contact.
[0015] The modification of the invention according to claim 3 relates to the case that the contact spring is operated by the actuator in a slit and hence from two sides. The actuator slit and the rib cooperate to restrict the freedom of motion of the broken or loose contact spring in the intended manner.
[0016] The modifications of the invention according to claims 4 and 5 provide ribs on both sides of the contact spring which further restrict the freedom of motion with respect to rotations about the spring's longitudinal axis.
[0017] According to claim 6, the rib extends transversely to the contact spring and across the complete width thereof such that the contact spring cannot evade.
[0018] The modification of the invention according to claims 7 and 8 relate to a contact assembly in which the contact spring is operated by the actuator only from one side.
[0019] In the following, the invention will be explained in more detail with reference to the accompanying drawings, in which Figs. 1A to 4B show cross-sections through contact assemblies according to four embodiments.
[0020] The embodiment according to Figs. 1A to 2B corresponds in its general assembly to the state of the art explained with reference to Figs. 5A to 5C, such that the description of corresponding parts is not repeated.
[0021] According to Figs. 1A and 1B, two ribs 22, 23 are provided in the region between the terminal 14 of the contact spring 13 and the actuator 11. The ribs are located at the side which is not facing the counter contact 15 and extend towards the contact spring 13. The ribs 22, 23 are preferably made of plastics and integrally formed with the relay base or the housing cap.
[0022] Fig. 1A shows an operative contact assembly in the open state. The ribs 22, 23 protrude towards the contact spring 13 but do not contact it in any moment of the switching movement.
[0023] Fig. 1B shows a contact assembly in the same actuator state which correspond to the open contact state in case of an abnormal incidence. The loose contact spring 13 is in a position which shows a double interruption. In this state, the ribs 22, 23 prevent the loose contact spring from reaching the other side of the terminal 14.
[0024] Further, the rib 23 and the actuator slit 12 effect that the contact spring 13 is kept in a distance from the terminal 14 as well as from the counter contact 16. At each interruption site, the minimum distance of 0.3 mm is observed, even if the contact spring 13 is rotated about its longitudinal axis as indicated in Fig. 1B.
[0025] The embodiment according to Figs. 2A and 2B provides two further ribs 24, 25 in addition to the ribs 22, 23 on the opposite side of the contact spring 13. The ribs 24, 25 protrude towards the contact spring 13 without actually contacting it in any moment of the switching movement.
[0026] In Fig. 2A, the operative contact spring 13 is shown simultaneously in closed and open state without actuator so that the bending behaviour of the contact spring 13 is visible for both states. It is shown that the position of the contact spring 13 close to the terminal 14 hardly differs in the two states. Therefore, the spacing between ribs 22 and 24 can be made smaller than between ribs 23 and 25 which hinders a rotation of the contact spring 13 (as in Fig. 1B).
[0027] Fig. 2B shows a possible state of a loose contact spring 13 in an abnormal incidence with double interruption. As in Fig. 1B, the rib 23 and the actuator slit 12 effect that the minimum distance of 0.3 mm is observed between the foot of the contact spring 13 and the terminal 14 as well as between the contact piece 15 and the counter contact 16.
[0028] The embodiment according to Figs. 3A and 3B shows that a single rib 23 located in the middle between the terminal 14 and the actuator 11 is sufficient for effectively keeping the relay in fail safe condition in case of a spring breakage.
[0029] In Fig. 3A a single rib 23 is positioned on the side of the contact spring 13 which is not facing the contact piece 15. The upper part of Fig. 3B shows a possible state of a broken contact spring 13 in an abnormal incidence with single interruption. The rib 23 cooperates with the actuator 11 to ensure that the minimum distance of 0.5 mm is observed between the contact piece 15 and the counter contact 16, while the broken end of the spring contacts the terminal 14.
[0030] The lower part of Fig. 3B shows a contact assembly which is axially symmetric to the one in the upper part. The lower contact is in open state when the upper contact is in closed state and vice versa. It can be seen that the rib 23 does not affect the normal switching operation and has no influence on the contact spring 13 in the closed state.
[0031] The embodiment according to Figs. 4A and 4B relates to a relay contact assembly in which the contact spring 13 is forcibly operated by the actuator 11a with the contact spring 13a and by the actuator 11b with the contact spring 13b, as it is principally known from DE-C-101 01 751. Fig. 4A illustrates the open state and Fig. 4B the closed state of the relay.
[0032] It is shown that in the forced operation, the NC-contact spring 13 cannot be operated in a narrow actuator slit as this has been the case with the NO-contact springs 13a, 13b or with the contact spring 13 in the assemblies according to Figs. 1A to 2B. Therefore, the freedom of motion of the contact spring 13 in longitudinal or rotational direction is not sufficiently restricted by the actuator 11a and 11b.
[0033] To obtain nevertheless the required distance with respect to the counter contact 16 in the energised relay state (Fig. 4B), a shoulder 26 is integrally formed with the basis of the relay. In this case, the shoulder 26 practically replaces the missing side of the actuator slit.
[0034] The shoulder 26 and the actuator 11a confine the position of the potentially loose contact spring 13 to avoid any undesired contact closure by the loose spring. A rib 23 integrally formed with the housing cap may enhance the safety in the way known from Figures 1B, 2B and 3B.
[0035] The shown assembly of the shoulder 26 provides the additional advantage that a vagabonding contact spring 13 faces the rib 23 with a broad portion even if the spring is displaced in the direction of the counter contact 16, with the effect that the rotation about the longitudinal axis is further restricted.
List of reference characters
1. A relay contact assembly comprising:
a contact spring (13) which is mounted with its foot to a terminal (14) and which comprises a contact piece (15) close to its free end which cooperates with a fixed counter contact (16);
an actuator (11) acting on the contact spring (13) between the terminal (14) and the contact piece (15); and
at least one element (23; 26) fixedly mounted with respect to the counter contact (16) and positioned in immediate proximity to the contact spring (13) in the region between the terminal (14) and the spring end in the open contact state without contacting the contact spring (13),
characterised in that the actuator (11) and the element (23; 26) restrict the freedom of motion of a broken or loose contact spring (13) in such a way that the spring is held in a security distance from the counter contact (16) and/or the terminal (14).2. The contact assembly of claim 1, wherein the element is a rib (23) which is integrally formed with the base or a housing cap of the relay.
3. The contact assembly of claim 1 or 2, wherein the contact spring (13) is operated in a slit (12) of the actuator (11), and the rib (23) is positioned on the side of the contact spring (13) which is not facing the contact piece (15).
4. The contact assembly of claim 2 or 3, wherein one further rib (24, 25) is provided on the side of the contact spring (13) which is opposite to the rib (23).
5. The contact assembly of claim 4, wherein two ribs (22, 23; 24, 25) are provided on each side of the contact spring (13).
6. The contact assembly of any of claims 2 to 5, wherein the rib extends essentially
transversal to the contact spring (13) across the full width of the spring.
7. The contact assembly of claim 1 or 2, wherein the contact spring (13) is operated by the actuator (11a, 11b) only on one side, the element (23) is positioned on the opposite side of the contact spring (13), and a further element (26) is provided, which is fixedly mounted with respect to the counter contact (16), restricts the freedom of movement of a broken or loose contact spring (13) and is located in immediate proximity to the contact spring (13) in the region of the actuator (11a, 11b) in the open contact state.
8. The contact assembly of claim 7, wherein the further element is a shoulder (26) integrally formed on the relay base.