Relay

Abstract: A relay comprising a first part of a control circuit via a movement creating arm (12) and a transmission mechanism (18,20) influences a contact means (23) in order to switch on or switch off a main circuit. The arm comprises two elongated parallel parts (12a, 12b) which are separated by a thermally insulated layer and which at one of their ends are fastened to a holder (10). The other ends of said parts (12a, 12b) are fixed to each other to form a movable end of the arm. One or both parts (12a, 12b) of the arm are provided with a heat creating element (15), which constitutes the first part of the control circuit and which when a control current flows through the element heats one of the two parts of the arm thereby causing a movement of the movable end of the arm. The transmission mechanism comprises a finger (18) extending mainly perpendicular to the length direction of the arm the finger acting on a leaf spring (20) which is parallel to the arm the spring supporting said contact means (23).

Description: This invention relates to a relay comprising a first part of a control circuit which via a movement creating arm and a transmission mechanism influences a contact means in order to switch on or switch off a main circuit, the arm comprising two elongated parallel parts which are separated by a thermally insulated layer and which at one of their ends are fastened to a holder the other ends being fixed to each other to form a movable end of the arm, one or both parts of the arm being provided with a heat creating element which constitutes the first part of the control circuit and which when a control current flows through the element heats one of the two parts of the arm thereby causing a movement of the movable end of the arm. A device of the abovementioned type is previosly known, see EP-A-0 403453. The device shown in this publication has however certain shortcomings since the transmission mechanism requires relatively large movements of the arm in order to work properly which means that the device achieves a rather large height. At the same time the transmission mechanism and the position of the contact means contribute to that the complete arrangement also achieves a rather large extension in the length direction of the arm. Relays having an arm which is provided with a heating element and acting on a flat spring which is parallel to the arm for switching on or switching off a circuit are also previously known, see US-A-3842382. The purpose of this invention is to achieve a device of the type mentioned above but with a more compact layout than before the device also beeing suited for massproduction. This purpose is achieved, according to the invention, by a relay with the features of claim 1. An embodiment of the invention will now be decribed with reference to the attached drawing on which Fig. 1 shows a vertical section through the device according to the invention wheras Fig. 2 is a section on the line II-II in Fig. 1. As appears from the figures the relay comprises a holder 10 preferably consisting of an electrically insulating plastic material and which serves as a protecting shell for the electro-mechanical arrangement. The holder has a side wall 11 in which an elongated arm 12 is fixed, the arm comprising two parallel parts 12a, 12b, separated by a thermally insulating layer i.e. an air gap, each having one end extending through the side wall 11 to a recess 13 at the outside of the shell. The other ends of the parts 12a, 12b are fixed to each other to form a vertically movable free end of the arm 12. Preferably the parts 12a, 12b are made of sheet metal and are at the major part of the free length of the arm provided with side flanges 12c, 12d serving as reinforcing means for the arm and preventing that the arm is bent at other places than at the part 14 adjacent the sidewall 11 where it is weakened with respect to bending influences. One or both parts 12a, 12b of the arm 12 are equipped with a heat creating element 15 which is activated by current flowing from a circuit card 16 via outer parts 12e, 12f of the arm which are placed in the recesses 13 and via electric conductors 17 between the lastmentioned parts and the circuit card 16. Preferably the arm 12 consists of an oxidized aliminium plate which is folded at the free end of the arm and on which the heat creating element is fastened as a thin layer by means of a printing method known per se. The free end of the arm 12 has a finger 18 arranged mainly perpendicular to the length direction of the arm and the finger has an opening 19 with an upper and a lower abutting surface 19a and 19b resp for a leaf spring 20. The finger 18 has such a length that the demands for air- and creep insulation distance between the control circuit and main circuit is fulfilled. The spring 20 is clamped between the side wall 11 and an opposite side wall 21 and has bent end parts 20a resting in recesses 22 in the walls 11 and 21 resp the spring 20 thus being clamped mainly moment free in the walls. The spring preferably consists of sheet metal and has a length which is somewhat larger than the free length of the arm and also larger than the distance between the two recesses 22 which means that the spring achieves a bent shape according to Fig 1. At the center of the spring 20 there is a contact means 23 having two contact surfaces 23a, 23b which are electrically connected to each other and which each cooperate with a contact surface 24a of two pins 24 which are fastened to the holder 10 and via conduits not shown are connected to a main circuit. Since the contact means have a more central position with respect to the finger 18 a positive transmission ratio is created when the arm moves. The holder 10 also has angular openings 25 through which a profile not shown can be inserted. This arrangement admits several holders to be positioned beside each other in order to form comlete relay packages. Above the spring 20 there is a shaft 26 extending through the complete relay package the shaft being provided with one or several cams 27 so that the cams when the shaft is turned act on the spring 20. The device operates in the following manner. At the position shown in fig 1 the main circuit which is connected to the pins 24 is closed since the contact means 23 with its contact surfaces 23a, 23b by means of the spring 20 are urged towards the contact surface 24a of the pins 24. In order to switch off the main current a control current is guided from the circuit card 16 via the conduit 17 to the heat creating element 15 at the part 12a of the arm 12. This means that the part 12a is heated and elongated wheras the part 12b mainly keeps its length. The outer part of the arm with the finger 18 will now move downwards in the figure so that the abutting surface 19a urges the leef spring 20 downwards. At a certain spring deflection the spring snaps over to the position shown by dashdotted lines in fig 1, which means that the contact surfaces 23a, 23b of the contact means 23 are disengaged from the contact surfaces of the pins 24a the main current thus being switched off. At the same time the circuit card switches off the current to the heating element 15 whereby the arm returns to its original position in which the surface 19b now abuts the spring 20. In order to close the main circuit a current is in a corresponding way guided to the heat creating element at the lower part 12b of the arm 12 which means an upwardly directed movement of the finger 18 whereby the spring 20 by means of the abutting surface 19b is returned to its original position. If the main current should be switched off without being influenced by from the circuit card it is possible to turn the shaft 26 by means of a handle, not shown, which means that the cam 27 presses the spring downwards in Fig. 1 so that the contact means disengages the contact surfaces of the pins 24. Thereby a manual main switch off function is achieved which is a demand in many applications. The arrangement described above is a bistable arrangement but it is of course possible also to design the relay as a monostable arrangement i.e. by putting a heat creating element solely on one of the parts of the arm i.e. the upper in fig 1 and by means of some kind of abutting surface below the spring 20 prevent that it snaps over to its lower stable position. Such an arrangement means that the main switch is open solely during the time when a current flows through the heat creating element.

Claims: Relay comprising a first part of a control circuit which via a movement creating arm (12) and a transmission mechanism (18,20) influences a contact means (23) in order to switch on or switch off a main circuit, the arm (12) comprising two elongated parallel parts (12a, 12b) which are separated by a thermally insulated layer and which at one of their ends are fastened to a holder (10) the other ends being fixed to each other to form a movable end of the arm (12), one or both parts of the arm (12) being provided with a heat creating element (15), which constitutes the first part of the control circuit and which when a control current flows through the element heats one of the two parts (12a,12b) of the arm (12) thereby causing a movement of the movable end of the arm (12), caracterized in that the transmission mechanism comprises a finger (18) extending mainly perpendicular to the length direction of the arm (12) and acting on a blade shaped spring (20) which is parallel to the arm (12) the spring (20) being provided with said contact means (23) and being mainly moment free clamped between two fastening points (22) the free length of the spring (20) being larger than the distance between the fastening points (22), and in that the contact means (23) is positioned on the spring (20) between said fastening points (22) more centrally than the abutting point of the finger (18).. Relay according to claim 1 caracterized in that the length of the spring (20) is somewhat larger than the free length of the arm (12). Relay according to any of the preceding claims, caracterized in that the finger (18) has an opening (19) through which the spring (20) extends. Relay according to claim 3, caracterized in that the spring (20) is fastened free of moment in the opening (19). Relay according to claim 4, caracterized in that the opening (19) has a first and a second abutting surface (19a, 19b) for the spring (20) the two abutting surfaces (19a,19b) being positioned at each side of the spring (20) and at a distance from each other which is larger than the thickness of the spring (20). Relay according to any of the preceding claims, caracterized in that it comprises a cam mechanism (27) which is placed adjacent the spring (20) and when being turned acts on the spring (20) to switch off or swich on the main circuit.

Inventors: BERGQUIST PER-MARCUS, TROBERG HENRIK EVALD, BERGQUIST, PER-MARCUS, TROBERG, HENRIK EVALD
Applicants: ELECTROLUX RES & INNOVATION, ELECTROLUX RESEARCH & INNOVATION AB
Application year: 1992
Main classification: H01H61
IPC codes: H01H61