FIELD OF TH E INVENTION The present invention relates to a low-voltage contactor for controlling an electric power or control circuit of an electrical device such as a motor, a lighting unit, a heating apparatus or a capacitor bank. The range of the low-voltage is up to 1000 V AC or 1500 V DC. PRIOR ART

A low-voltage contactor comprises an actuating unit, a stationary contact, and a contact carrier including a movable contact that is operated by the actuating unit, a spring acting on the movable contact to produce a force that reduces the electrical resistance between the contacts and a connecting means for connecting the contact carrier to the actuating unit. The contactor controls power connection and disconnection of an electrical device by closing/connecting and opening/disconnecting the contacts. When connecting contacts, the contact carrier is driven by the actuating unit and thereon carries the movable contact moving from an initial rest position to a final working position towards the stationary contact. On the other hand, when disconnecting the contacts, the contact carrier will be moving back from the working position to the rest position by a restoring mechanism. This means that the contact carrier is constantly exposed to the mechanical wear and tear. Furthermore, an electric arc is produced between the contact surfaces when they are being electrically disconnected. The electric arc results in an exceedingly high temperature in a surrounding area of the contacts within the contact carrier. It therefore is required that the material used for making the contact carrier must pos- sess a good thermal and electrical insulation property and be tolerant to mechanical stresses as well. For the above-mentioned reasons, thermosetting plastic materials are conventionally used for manufacturing contact carriers. However, for molding thermosetting plastics into the final form of a contact carrier, an exceedingly long machine processing time is needed, which increases the costs of manufacturing contactors. Therefore, a reduced manufacturing process time and cost is desired.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a contactor which requires a reduced manufacturing time and therefore reduces the cost for manufacturing contactors. This object is achieved by a contactor as defined in claim 1 .

Such a contactor comprises an actuating unit, a stationary contact, and a contact carrier which further comprises a framework part made of a first thermal and electrical insulation material and including a connecting means for connecting the contact carrier to the actuating unit, a holder part made of a second thermal and electrical insulation material that is different from the first thermal and electrical insulation material and comprising a holding member adapted to hold a movable contact and a spring, and the holder part and the framework part are arranged to be detachably connected to each other.

Due to the fact that the contact carrier is composed of two separate physical parts, the framework part and the holder part, the invention makes it possible to use different thermal and electrical insulation materials with different thermal, mechanical and molding properties to make the framework part and the holder part, respectively. It is advantageous to manufacture the framework part and the holder part using different thermal and electrical materials, since it is then possible that the framework part is made of a thermal and electrical material that is easily molded during the manufacturing so the machine processing time of contact carriers is shortened. The object of a reduced manufacturing time and cost of contactors is therefore achieved.

According to an embodiment of the invention, the second thermal and electrical insulation material is thermosetting plastic material. It is advan- tageous to make the holder part of thermosetting plastics since they possess properties of strong resistance to heat and good electrical insulation. Therefore, the holder part is able to withstand to thermal stresses constantly loaded on the holder part. Thermosetting plastics or thermosets are polymer materials that irreversibly cure.

According to an embodiment of the invention, the first thermal and electrical insulation material is thermoplastic material. A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. It is advantageous to make the framework part of a thermoplastic material, because such a thermoplastic can go through melting/freezing cycles repeatedly, which makes it more easily handled during the manufacturing compared to thermosetting plastic materials. Therefore, the manufacturing time of contactors is can be shortened considerably and the cost for producing the contactors is therefore reduced. Furthermore, a contactor is often used to control an electric power to another electrical device, for example, a motor. The motor, during its lifetime, will be connected and disconnected to the electric power up to 10 million times. In each such connecting and disconnecting operation, the contact carrier carries the movable contact moving forwards or backwards between an initial position and a final working position to enable a contact or disable a contact with a stationary contact, which means that the contact carrier is constantly exposed to a mechanical deterioration during each connection and disconnection of contacts. By making the framework part using thermoplastic materials which possess the properties of durability and mechanical stiffness, the contact carrier is able to withstand mechanical deterioration. Yet another advantage is that thermoplastic material is re-moldable and recyclable, which therefore is beneficial for the sus- tainability of contactors.

According to an embodiment of the invention, the holder part and the framework part are designed so that the first end of the spring is acting on the movable contact held by the holder part and the second end is acting on the framework part when the framework part and the holder part are connected to each other. The framework part and the holder part further respectively comprise a linking means, which are designed to be connected to each other. To be able to retain the spring in a stable position with respect to the framework part and the movable contact without gliding aside, the framework part and the movable contact further respectively comprise a spring positioner, which are adapted to position the first and second ends of the spring. In this way the spring is able to produce a desired force on the movable contact so that the contact area is maximized. Therefore, the electrical resistance between the movable and stationary contacts is reduced when they are in contact with each other.

Due to the fact that the assembling/mounting steps can be performed sequentially in one direction, it is easier to automate assembling of the contact carrier. An automated assembling may comprise the following steps: placing the movable contact on the holding member of the holder part, placing the spring to the spring positioner of the movable contact so that the first end of the spring is positioned by the spring positioner, pressing the spring down against the movable contact and, as a last step, connecting the framework part and the holder part by the connectors so that the second end of the spring is positioned by the positioner of the framework part, which results in the first end of the spring acting on the movable contact held by the holder part and the second end of the spring acting on the framework part so that the spring is able to produce a force that reduces the electrical resistance between the contacts when they are in contact with each other. All the above steps except the last one may be carried out sequentially in a top-down direction.

According to another embodiment of the invention, the holder part further comprises a casing enclosing the movable contact and the spring, the cas- ing being adapted to be detachably connected to the framework. The advantage of this embodiment is modularity of the casing, which means that the casing may be manufactured in one place or a factory and assembled with the framework part in another place or factory. The casing comprises a container to receive the spring and the movable contact and the container is designed so that the first end of the spring is acting on the movable contact held by the holder and the second end of spring is acting on the casing. The casing may be made of thermosetting plastic material to withstand thermal stresses.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures.

Fig. 1 illustrates a partial cross-sectional view of an uncovered contactor having a contact carrier, according to a first embodiment of the invention. Fig. 2 shows a detailed isometric view of the contact carrier illustrated in Fig. 1 .

Fig. 3a illustrates an assembling procedure of the contactor carrier shown in Fig. 2.

Fig. 3b illustrates the assembled contact carrier shown in Fig.2.

Fig. 4a illustrates a perspective view of a contact carrier, according to a second embodiment of the invention.

Fig. 4b show a perspective view of the assembled contact carrier illustrated in Fig. 4a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a partial cross-sectional view of a contactor having a contact carrier, according to a first embodiment of the invention. The contactor 2 includes an actuating unit 60, a stationary contact 70, and a contact car- rier 1 having a framework part 20 and a holder part 10 including a movable contact 30 and a spring 40. In this embodiment, the contactor is a three- pole low-voltage contactor. It is understood that the view is a portion of the contactor, and therefore not all the elements of the contactor are illustrated in the figure. The number of the movable contacts depends on the number of the poles. In this embodiment, three movable contacts have been provided.

The stationary contact 70 is sited on a housing 80 of the contactor 2. In this embodiment, two stationary contacts 70, 70' are arranged aligned with for each movable contact 30. Each stationary contact 70, 70' includes a contact surface 72, 72'.

The movable contact 30 includes two movable contact surfaces 34, 34' sited respectively on each end of the movable contact on the same side of the movable contact.

The function of the actuating unit 60 is to drive the contact carrier 1 moving towards the stationary contacts 70, 70' so that contacts are made between surfaces 72, 72' and 34, 34' of the stationary contacts 70, 70' and the movable contact 30. Such an actuating unit may be an electromagnet apparatus electrically connected to an electrical circuit arranged for supplying electric power to energize the electromagnet. An electromagnetic force is then produced for driving the contact carrier 1 moving, from a rest position, downwards to the stationary contact and eventually an electrical contact is made between the contact surfaces 72, 72', 34, 34' of the stationary and movable contacts 70, 70', 30 at a working position.

The contact carrier 1 includes the framework part 20 and the holder part 10 positioned so that the stationary contacts 70, 70' are aligned with the movable contact 30 in an opening position.

A detailed isometric view of the contact carrier is further illustrated in Fig. 2, according to the first embodiment of the invention. In this figure, the other two movable contacts and springs have been removed for a better illustration. The framework part 20 includes an elongated body 21 , a connecting means for mechanically connecting the contact carrier 1 to the actuating unit 60 and a linking means for coupling the framework part 20 to the holder part 10.

In this embodiment, the connecting means includes two connectors 26', 26" protruding from the ends of the body 21 . Each of the connectors 26', 26" is provided with a connection mechanism 27', 27", for example a snap hooking mechanism. The linking means includes four coupling elements 23', 23", 24', 24" for coupling the framework part and the holder part in a stable position with respect to the Z- and X-axes. The first and second coupling elements 23', 23", protruding from the ends of the body in a direction opposite the two connectors, include respectively hooking ele- ments 25', 25" arranged at the free end of the coupling elements 23', 23" and protruding inwardly to cooperate with corresponding hooking means of the holder part. The third and fourth coupling elements 24', 24", protruding in the same direction as the first and second coupling elements, are arranged between the first and second coupling elements 23', 23". Each of the third and fourth coupling elements 24', 24" including two protruding bars arranged on each side is therefore in the form of a criss-cross for cooperating with corresponding coupling elements of the holder part. Preferably, the framework part 20 is made in one piece and of an electrical insulation material having such stiff and strong mechanical properties so as to withstand mechanical wear caused by movements of the contact carrier, for example, a thermoplastic material. A suitable thermoplastic may be any type of polyamide, polyethylene, polybutylene terephthalate, polycarbonate or polypropylene. They may be either fiberglass-filled or without filled fiberglass.

The holder part 10 includes a frame 12 provided with holding members 15, 15', 15" in the form of recesses for receiving the movable contacts and the springs. The number of the recesses depends on the number of the movable contacts. In this embodiment, three recesses are provided on the frame 12. Each recess has a ring-shaped wall provided with an inlet opening in the direction of the Z-axis for receiving a movable contact and thereon a spring, and two opposite openings in the direction of the Y-axis for allowing the movable contact surfaces 34, 34' extending beyond the recess. A movable contact retainer 17, 17', 17" is provided by each recess for receiving and retaining a movable contact. In this embodiment, on the opposite side of the recesses, two other spring holding elements 16', 16" are provided in the form of recesses for holding restoring springs to enable the contact carrier to move back to the rest position from the working position when a disconnecting operation is conducted. The frame is provided with four coupling elements 13', 13", 14', 14" to cooperate correspondingly with the coupling elements 23', 23", 24', 24". The first and second coupling elements 13', 13" are formed to be hooked with the hooking elements 25', 25" of the first and second coupling elements 23', 23" of the framework part. The third and fourth coupling elements 14', 14" have grooves in the form of a criss-cross for matching the criss-cross-shaped third and fourth coupling elements 24', 24" provided on the framework part. Preferably, the holder part 10 is made in one piece and of an electrical insulation material having such thermal properties so as to withstand thermal stresses, for example thermosetting plastic material. A suitable thermosetting plastic may be any type of melamine formaldehyde, epoxy or phenol formaldehyde and is normally used together with a type of fiber such as fiberglass, carbon fiber, cotton fiber or Kevlar.

In this embodiment, the movable contact 30 further includes a spring positioner 32 for retaining the first end of the spring. The spring positioner is arranged on one side of the movable contact in the middle of the movable contact. The spring positioner 32 is formed in the same shape as the mov- able contact retainer 17, so a groove formed on the other side matches the shape of the movable contact retainer.

In this embodiment, The framework part further includes three spring positioners 22, 22', 22" arranged between the coupling elements 23' and 24', 24' and 24" and, 24" and 23", respectively. Each spring positioner 22, 22', 22" is formed to retain the second end of the spring.

Fig. 3a illustrates an assembling procedure of the contactor carrier shown in Fig. 2.

The arrow A represents an assembling direction for the first three steps as the following: 1 ) mounting the movable contact 30 on the holding member 15 of the holder part 10, 2) mounting the spring 40 on the spring positioner 32 of the movable contact 30 and 3) pressing the spring down. The last step is mechanically connecting the framework part 20 with the holder part 10 in the direction of the Y-axis shown as the arrow B. This means that the assembling directions are simplified along firstly a longitudinal Z-axis, followed by a latitudinal Y-axis; it is therefore easier to automate the assem- bling steps.

When the contact carrier 1 is assembled as shown in Fig. 3b, the movable contacts 30, 30', 30" are placed on the movable contact retainer 17, 17', 17" provided by the corresponding holding member 15, 15', 15", then the spring 40, 40', 40" are placed on the movable contact 30 with the first end positioned by the spring positioner 32, 32', 32". The spring 40, 40', 40" are pressed downwards to the movable contact 30, 30', 30" and the holder part 10 is coupled with the framework part 20 by the coupling elements provided by the framework part and holder part, respectively. The coupled framework part 20 and holder part 10 is in a stable position with respect to the Z- and X-axes, while the pressed spring 40, 40' 40" retained by the spring positioners 22, 22', 22', 32, 32', 32" on each end results in the contact carrier 1 now also being in a stable position with respect to the Y-axis. Therefore, all parts in the assembled contact carrier are stable with re- spect to the X-, Y- and Z-axes as the framework part and holder part were built in one piece. A pressed spring generates a force on the movable contact to enable a maximum contact area between the movable and stationary contacts to reduce the electrical resistance. Fig. 4a shows a conceptual perspective view of a contact carrier, accord- ing to a second embodiment of the invention. The contact carrier 1 ' comprises a framework part 20' and three holder parts 1 1 , 1 1 ', 1 1 ". The number of the holder parts depends on the number of poles of the contactor. In this embodiment, the contact carrier 1 ' is designed for a three-pole low- voltage contactor. Three holder parts are therefore provided. The figure also shows an assembly process in which two of the holder parts 1 1 ', 1 1 " have been assembled into the framework part 20' and the third one 1 1 is about to be assembled. The holder part 1 1 includes a casing 50 for enclosing a spring 40 and a movable contact 30. In this embodiment, the holder part 1 1 is designed as the casing 50 including a container 18 in the form of three openings. The casing 50 is adapted to be detachably connected to the framework part 20'. In this embodiment, the casing 50 is formed as a rectangular cube. It should however be understood that it is possible to form the casing in any other applicable form rather than a rectangular cube. To form the container 18, on one side of the rectangular cube of the casing 50, the first inlet opening is provided for receiving the spring 40 and, on two other opposite sides, two opposite, the second and third, openings are provided for receiving the movable contact 30 and allowing the movable contact surfaces 34, 34' extending beyond the framework part 20'. In this embodiment, the inlet opening is formed as a ring-shaped wall and the other two openings are formed as rectangles. It is however possible to form the openings in any other applicable forms.

The framework part 20' comprises a frame 90 and a connecting means for mechanically connecting the contact carrier 1 to the actuating unit 60. In this embodiment, the frame 90 is provided with three openings 29, 29' and 29" for receiving the casings 50, 50', and 50", respectively. Each opening 29, 29', 29" is formed correspondingly to the casing. The connecting means includes two connectors 28', 28" protruding from the ends of the frame 90. Each of the connector elements 28', 28" may be provided with a connection mechanism, for example, a snap hooking mechanism as shown in Fig. 2. To enable a stable mechanical connection between the frame- work part 20' and the casing 50, a snapping mechanism may be optionally designed on an inner wall of each opening 29, 29', 29" and an outer wall of the casing 50, 50' 50". In this embodiment, on the opposite side of the connectors 28', 28", two spring holding elements 91 ', 91 " are provided in the form of recesses for holding restoring springs to enable the contact carrier to move back to the rest position from the working position when an electrically disconnecting operation is conducted.

Preferably, the casing 50 is made in one piece and of thermosetting plastic material and the framework part 20' is made in one piece and of thermo- plastic material.

The lines with the numbers and arrows represent assembling orders and directions for assembling the contact carrier, which is as follows: ® inserting the spring 40 into the casing 50 through the inlet opening, (2) while pressing the spring 40, inserting the movable contact 30 through the second and third openings and placing it on the container 18 of the casing so that one end of the spring is retained by the spring positioner 32 of the movable contact, and (3) coupling the casing with the framework part. An assembled contact carrier is illustrated in Fig. 4b.

Although, in the above embodiments, a contact carrier is designed for a three-pole low-voltage contactor, it is understood that it may also be designed for a four-pole low-voltage contactor. It is also applicable to an AC or a DC power supplier.