Electromagnetic switch with stable moving contact

Abstract

Electromagnetic switch comprising: at least two stationary electrical contacts; and a movable contact (102, 604, 702-706, 1002), wherein the electromagnetic switch (100, 600, 1000, 1100, 1200, 1300) is configured for a reciprocating movement of the movable contact (102, 604, 702-706, 1002) into and out of contact with the stationary electrical contacts, wherein the movable contact (102, 604, 702-706, 1002) is configured such that at least three contact points (a, b, c) are created during the reciprocating movement, and such that a triangle (300, 910) defined by the at least three contact points (a, b, c) encloses a center of force of the movement, wherein a first and a second stationary electrical contact and at least one non-conductive mechanical contact are present, and wherein the movable contact (102, 604, 702-706, 1002) is configured to form a first contact point (a) with the first stationary electrical contact (602, 1306), a second contact point (b) with the second stationary electrical contact (602, 1306), and a third contact point (c) with the non-conductive mechanical contact (616).

Description

background

[0001] A number of applications, such as electric vehicles, require the use of contactors and relays to control the opening and closing of various power lines. Under certain conditions, electric vehicles and / or other electrical devices may generate audible noise and / or vibration.

[0002] WO 2012 / 128072 A1 discloses a contact device having a structure in which all three movable contacts can be brought into secure contact with a fixed contact. The contact device is provided with: a fixed terminal having a fixed contact; a movable terminal that comes into contact with and separates from the fixed terminal and has three movable contacts that come into contact with the fixed contact; and a contact pressure spring that presses the movable terminal and causes the fixed contact to come into contact with the movable contacts at a predetermined contact pressure. The contact device is characterized by a structure in which an operating point of the contact pressure spring is located within a triangular region formed by internal tangent lines of the three movable contacts.

[0003] The invention is defined in the claims. Brief description

[0004] In a first aspect, an electromagnetic switch comprises: at least two stationary electrical contacts and one movable contact, wherein the electromagnetic switch is configured for a reciprocating movement of the movable contact into and out of contact with the stationary electrical contacts, wherein the movable contact is configured such that at least three contact points are created during the reciprocating movement and such that a triangle defined by the at least three contact points encloses a center of force of the movement.There are a first and a second stationary electrical contact and at least one non-conductive mechanical contact, wherein the movable contact is configured to form a first contact point with the first stationary electrical contact, a second contact point with the second stationary electrical contact, and a third contact point with the non-conductive mechanical contact.

[0005] Embodiments may include one or all of the following features. There are first and second stationary electrical contacts, and the movable contact is configured to form the three contact points with the stationary electrical contacts: a first and second contact point formed at the first stationary electrical contact, and a third contact point formed at the second stationary electrical contact. The electromagnetic switch is formed from a rectangular metal block having at least one flat surface, the metal block having a first recess in the flat surface to form the first and second contact points, and a second and third recess to form the third contact point. A hole for a shaft passes through the metal block at the center of force, the shaft driving movement of the movable contact.

[0006] The non-conductive mechanical contact is positioned so that the third contact point occurs at one end of the reciprocating motion and not during any other portion of the reciprocating motion. The electromagnetic switch further includes a heat sink in thermal contact with the non-conductive mechanical contact. The electromagnetic switch further includes another non-conductive mechanical contact that is in contact with the movable contact at the beginning of the reciprocating motion. The non-conductive mechanical contact is positioned so that the third contact point occurs throughout the reciprocating motion. The electromagnetic switch further includes a heat sink in thermal contact with the non-conductive mechanical contact.The electromagnetic switch further comprises another non-conductive mechanical contact, wherein the movable contact is limited throughout the reciprocating movement between the mechanical contacts. The non-conductive mechanical contact has a mounting of the movable contact to the electromagnetic switch. The mounting has a flexure that allows for the reciprocating movement. The electromagnetic switch further comprises a heat sink in thermal contact with the mounting.

[0007] The movable contact has a triangular shape corresponding to the three contact points. The triangular shape has at least one blunt corner. There are a first, a second, and a third stationary electrical contact, the movable contact being configured to make at least one contact point with each of the first, second, and third stationary electrical contacts. The first, second, and third stationary electrical contacts are positioned so that the contact points occur at one end of the reciprocating movement and not during any other part of the reciprocating movement. The movable contact is spring-loaded.

[0008] The center of force of the movement is far from the center of gravity of the triangle, which is defined by at least three contact points.

[0009] Designs can offer one or all of the following advantages. A contactor within a switch can provide mechanically stable electrical contact by incorporating a triangular contact point geometry. Electrodynamic movement or oscillatory instability resulting from large-amplitude currents can be eliminated or reduced. Short description of drawings Fig. 1A-B show an elevation and a cross-section of an electromagnetic switch, respectively. Fig. 2 shows a contact according to the state of the art. Fig. Figure 3 shows schematically a triangle defined by contact points enclosing a center of force of a movement. Fig. 4 shows a perspective view of the movable contact in Fig. 1AB. Fig. 5 shows a side view of the movable contact in Fig. 1A-B. Fig. 6 shows an example of an electromagnetic switch with an additional contact. Fig. Figure 7 shows an example of a movable contact with a triangular shape. Fig. Figure 8 shows another example of a movable contact with a triangular shape. Fig. Figure 9 shows another example of a movable contact with a triangular shape. Fig. 10 shows another example of an electromagnetic switch with an additional contact. Fig. 11 shows an example of an electromagnetic switch in which a movable contact is fixed by a ball joint. Fig. 12 shows an example of an electromagnetic switch in which a movable contact is fixed by a flexure. Fig. 13 shows an example of an electromagnetic switch in which a movable contact is fixed by a hinge. Detailed description

[0010] This document describes examples of electromagnetic switches, each comprising a moving contact subject to reciprocating motion, with at least three points of contact during the reciprocating motion. In some embodiments, the moving contact forms at least three points of contact with the stationary contacts that are also part of the electromagnetic switch. In some embodiments, two points of contact may be formed with the stationary contacts, and a third point of contact may be formed with another contact, such as a non-conductive mechanical contact. The triangle defined by the three contact points encloses the center of force driving the movement of the moving contact. For example, such configurations may eliminate or reduce noise caused by unwanted resonance that may arise in a moving contact during use.

[0011] Fig. 1A-B show an elevational view and a cross-section, respectively, of an electromagnetic switch 100. In some implementations, the switch is part of the power electronics of an electric motor. For example, an electric vehicle may have electromagnetic switches in an inverter, where they are used to convert direct current from a battery to alternating current to drive the motor. In the present example, only one electromagnetic switch is shown, and some of its components are omitted for clarity. Nevertheless, the electromagnetic switch may operate similarly or identically to conventional switches with respect to characteristics or aspects not explicitly mentioned herein.

[0012] The electromagnetic switch 100 has a movable contact 102 configured to move into and out of contact with stationary contacts 104A-B. For example, the stationary contacts can be thought of as the positive (+) and negative (-) terminals of an electrical circuit, respectively. In a closed position, the movable contact forms an electrical path between the stationary contacts. This allows, for example, current to flow from one of the stationary contacts to the other.

[0013] The electromagnetic switch 100 has a solenoid 106 that actuates a shaft 108. Specifically, the solenoid interacts with an armature 110 connected to the shaft 108 inside the solenoid, thus causing the shaft to reciprocate. The movable contact 102 is attached to the shaft. For example, an opening 112 for the shaft is formed in the movable contact. The opening may be a hole extending through the entire thickness of the movable contact, as in the present example.

[0014] The reciprocating movement of the shaft and the movable contact can be facilitated by one or more springs. In some embodiments, the movable contact is spring-loaded. For example, here a coil spring 114 is arranged around the shaft 108 on the outside of the solenoid coil, between the movable contact 102 and the top of the solenoid coil. As another example, here a spring 116 is arranged around the shaft on the inside, between the armature 110 and the top of the solenoid coil.

[0015] Fig. Figure 2 shows a prior art contact 200. Contact 200 is shown here in a closed position, with the contact closing a path between respective stationary contacts 202A-B. Each of the stationary contacts may have an uneven surface facing the contact, such as a cylindrical surface with a radius of curvature greater than the dimensions of the contact. The contact is spring-loaded and can be moved into and out of contact with the stationary contacts by a shaft 204.

[0016] When contact 200 is used, some undesirable effects may occur. The contact may experience resonance or other vibration for numerous reasons, which may produce undesirable noise or increased resistance, to name a few. For example, the contact may vibrate about a longitudinal axis 206 passing through shaft 204. Such vibration may be caused or increased by a torque acting on the contact about the longitudinal axis.

[0017] With further reference to Fig. 1, the movable contact 102 is configured to form multiple contact points with the stationary contacts 104A-B. For example, the movable contact may have a surface 118A for the stationary contact 104B and surfaces 118B-C for the stationary contact 104A. The surfaces 118A-C are positioned such that the respective contact points are located around the shaft 108 in a particular manner. Examples of this will now be described.

[0018] Fig. Figure 3 schematically shows a triangle 300 defined by contact surfaces 302A-C, which are defined between the stationary contacts 104A-B on the one hand and the movable contact (not shown for clarity) on the other hand. That is, when the movable contact 102 ( Fig. 1A-B) is in the closed position, it forms contact points with the stationary contacts within areas 302A-C, respectively. Each of the contact points is associated with a current flowing between that stationary contact and the moving contact. In this example, triangle 300 is an isosceles triangle. In other implementations, the contact points may form a different type of triangle. In some implementations, some or all of the moving contacts and the stationary contacts have a finite radius of curvature.

[0019] A center point 304 indicates where the force acts on the movable contact. The center point 304 is not directly between surfaces 302B-C, but rather is offset toward surface 302A. In some embodiments, when the reciprocating motion of the contact is driven by a shaft (not shown), the center point 304 coincides with the shaft. As another example, if the driving force acts on the contact at more than one location, the center point 304 indicates the center of the force driving the contact.

[0020] The center point 304 is enclosed by the triangle 300. This means that the movable contact is configured such that when it forms contact points with the stationary contacts within the surfaces 302A-C, these contact points form a triangle enclosing the center of force that drives the movement of the contact. This means that no two contact points are collinear with the center point 304.

[0021] In some embodiments, the center point 304 coincides with a centroid of such a triangle formed by the contact points. In other embodiments, the center point is located away from the centroid (but is enclosed by the formed triangle).

[0022] Fig. 4 shows a perspective view of the movable contact 102 in Fig. 1A-B. The movable contact is formed from a rectangular metal block 400 having a flat surface 402. Furthermore, the metal block has recesses 402A-C formed in the flat surface. Recesses 402A-B are located at respective corners at one end of the block, thereby forming contact surface 118A. Recess 402C, in turn, lies along the short end of the metal block, between the other corners, thereby forming contact surfaces 118B-C. For example, the recesses can be formed by machining the metal block. As another example, the metal block can be cast into the desired shape. Here, the shaft is not currently located in opening 112.

[0023] Fig. 5 shows a side view of the movable contact 102 in Fig. 1A-B. Here, one side of the rectangular metal block is shown, with the recess 402A visible. The recess 402B and the opening 112 are shown in phantom.

[0024] The movable contact can be manufactured with selected properties depending on the planned design. In an exemplary design, the contact is made of a conductive material (e.g., metal), has a certain length, width, and height, and the recesses have specific dimensions. One or all of the properties just mentioned can be selected based on one or more factors relevant to the design. For example, such factors can include, without limitation: The magnitude(s) of the voltage and / or current expected to be used in the switch The speed rate and / or force of the reciprocating movement of the contact The size and / or shape of the upper surfaces of the stationary contacts The manufacturing and / or material costs

[0025] Fig. Figure 6 shows an example of an electromagnetic switch 600 with an auxiliary contact. Generally, the switch includes at least two stationary electrical contacts 602 with terminals connected to the external circuit to be closed / opened. In the perspective shown, one of the stationary electrical contacts is positioned behind the other and is therefore not currently visible. A movable contact 604 is driven into reciprocating motion by an actuator 606, such as a solenoid coil acting on a magnet connected to a piston attached to the movable contact. The components are mounted on or contained within a housing 608, such as an enclosure made of a non-conductive material that provides electrical insulation from the outside and protects the interior from liquid and particles. The actuating force is denoted by f aand acts on the moving contact at a point sometimes referred to as the center of force.

[0026] The electromagnetic switch 600 includes at least one auxiliary contact 612 intended to mechanically stabilize the movable contact. In some embodiments, this is a non-conductive mechanical contact. The mechanical contact may, for example, be made of the same material as the housing 608 (e.g., as a projection formed integrally on its surface) or of a different insulating material. At the end of the reciprocating movement, the movable contact is at a position 614 where it contacts the auxiliary contact 612 as well as both stationary electrical contacts 602. Therefore, this creates an electrical connection between at least the stationary electrical contacts 602. The presence of the at least three contact points creates increased rigidity, which prevents the occurrence of vibrations in the movable contact.

[0027] When the actuator 606 moves the movable contact 604 away from the contacts 602, the electrical connection thus created should be broken. The movable contact 604 can be connected to the actuator 606 in a manner that is more or less rigid or constrained. For example, if the movable contact is attached to a shaft, the applicable manufacturing tolerances and / or the properties of the materials involved may provide some play in attaching the contact. As a result, the movable contact may be capable of tilting slightly away from the horizontal plane during one or more phases of the reciprocating movement. However, should the contact tilt too far, it is possible that the point of contact with one or both of the stationary electrical contacts may remain (or re-occur) as the contact 604 moves away.If this is the case, the electrical connection may not be completely broken and the switch may not work satisfactorily.

[0028] The movable contact 604 can be limited in various ways during at least part of the reciprocating movement. In some implementations, a contact 616 may be provided that limits one end of the movable contact from moving too far away from the auxiliary contact 612. This may, for example, prevent the other end of the movable contact from contacting one of the stationary electrical contacts 602. The contact 616 may be attached to the housing 608 or may be formed integrally therewith.

[0029] As another example, the movable contact 604 may be configured so that one of its ends rests on the contact 616 during substantially the entire reciprocating movement. In some such embodiments, the auxiliary contact 612 may be formed to protrude less or be completely absent.

[0030] The auxiliary contact 612 and / or the mechanical contact 616 may be used for one or more other purposes in addition to providing a contact point for the movable contact 604. For example, current flow in the movable contact 604 results in ohmic heating of the contact and the rest of the electromagnetic switch 600. In some implementations, the switch includes one or more heat sinks 618 connected to the housing 608 that are used to dissipate heat from the switch. This may provide an additional path for thermal contact between the movable contact and the surrounding environment of the switch.

[0031] Any suitable type of heat sink may be used, including, but not limited to, an uninsulated heat fin extending into the immediate vicinity of the switch. For example, if the auxiliary contact 612 is integrated into the wall of the housing 608, it may be made of a relatively thin-walled material so that heat is conducted from the moving contact to the heat sink. That is, the conductor, ground, or heat sink, etc., comprising the heat sink may be brought into close thermal contact with the side of the auxiliary contact opposite the moving contact by a thermally conductive grease, paste, soldered joint, adhesive, etc. Because, in some implementations, the heat sink is electrically isolated from the stationary contacts 602, fluid cooling may be facilitated.For example, heat exchange channels may be incorporated into the auxiliary contact(s) to transfer heat from the contact directly into a cooling fluid.

[0032] In some examples, contact 612 and / or 616 is a non-conductive mechanical contact. For example, the contact may be made of any suitable material that is sufficiently insulating given the electrical and other properties of the particular implementation.

[0033] In other implementations, however, contact 612 and / or 616 may be an electrical contact. This may increase the number of materials available for implementation, for example, such that the selected material is tougher, has lower friction, is more (or less) thermally conductive, and / or more impact resistant. The movable contact 604 then makes contact with at least three separate electrical contacts at the end of the reciprocating motion. This may, for example, allow one contact to serve as an input and two others to serve as outputs. As another example, two of the electrical contacts may be electrically connected (e.g., auxiliary contact 612 to one of stationary electrical contacts 602). The electrical contact may, in some implementations, be affixed to an insulating housing material.In other embodiments in which the housing comprises a conductive material, an insulating spacer, a fastener or another layer (e.g., adhesive) may be disposed between the electrical contact and the conductive housing.

[0034] Fig. Figure 7 shows an example of a movable contact 700 with a triangular shape. Here, the movable contact is shown together with stationary contacts 702, 704, and 706, such that at least contact points a, b, and c are formed when the movable contact is driven by an actuator (not shown for clarity) at a center of force 708. For example, the stationary contact 702 may be a non-conductive mechanical contact, and the other two may be electrical contacts. As another example, all three of the contacts 702-706 may be electrical.

[0035] Normally, the center of force 708 is fixed relative to the movable contact 700 due to the way the shaft is attached to it. However, it should be noted that the movable contact may have some freedom of rotation. For example, if the movable contact rotates about an axis parallel to the line bc between the contact points b and c, this causes the contact points b and c on the surface of the movable contact to move in a direction perpendicular to both bc and the driving force f. a (e.g. Fig. 6). This rotational movement in combination with the driving force f agenerates a torque or moment at the movable contact, where the torque is measured by a distance 710 between the center of force 708 and the line bc. For example, the generated force may be a monotonic function of the angular displacement of the movable contact and may be directed so that it tends to restore the angular equilibrium of the movable contact. When zero-slip conditions of surface contact exist between the movable contact and the stationary contacts 704-706, translational movement of the movable contact in a direction perpendicular to both bc and the driving force f a occur as a result of this rotation.

[0036] In some situations, passing a large current between the stationary electrical contacts 704 and 706 via the moving contact results in a self-sustaining electromechanical excitation of the pivoting movement. This has been observed when the current is direct current, and it is believed that similar behavior can occur when the current is alternating current. This movement is detrimental to the performance and life expectancy of the contactor. For example, temporary voltage drops across the contacts and power losses in the contactor can degrade the component materials, and temporary arcing can lead to redistribution of contact material and deterioration of the contact geometry.

[0037] Here, contact point a, formed with contact 702, provides rigidity about the rotational axis of the movable contact defined by line bc, which can prevent or reduce undesired rotational and / or translational movement. The movable contact can be configured such that contact points a, b, and c form any suitable triangle shape, including, but not limited to, an equilateral or isosceles triangle. Here, center of force 708 lies inside triangle abc. These and other configurations correspond to a rigid body system that is mechanically stable, with all three points a, b, and c making contact with a positive normal force. For example, center of force 708 is separated from line bc by a distance 710; similarly, the center of force is separated from contact point a by a distance 712.The distances 710 and 712 may be relatively small compared to the distance the movable contact moves during reciprocating motion. In some implementations, the distances 710 and 712 may have different proportions relative to each other.

[0038] At the respective corners of contact points a, b, and c, the movable contact 700 has blunt sides. For example, the blunt sides corresponding to contact points b and c are parallel to each other and perpendicular to the blunt side of contact point a. The movable contact may have rounded edges between two or more of the blunt sides.

[0039] In the previous example, the movable contact has two angular degrees of freedom: rotation about the axis parallel to line bc and passing through the center of force 708, and rotation about an axis connecting contact point a to the center of force 708. In some implementations, the required limitations on the movement of the movable contact can be translated into degrees of freedom of the movable contact itself. For example, the permissible rotation in the above-mentioned axes can be restricted by a suitable connection of the movable contact to the actuator. If the movable contact is attached to the actuator by a drive rod limited to purely linear movement, and this drive rod passes through a hole in the movable contact, an appropriate choice of the dimensional fit tolerance between the movable contact and the drive rod can serve as a constraint.Due consideration should be given to the effect of mechanical abrasion on these tolerances.

[0040] It may also be necessary or desirable to limit the rotational movement of the movable contact around the axis defined by f a is defined. For example, if the moving contact has a triangular shape, a limit can be used to ensure that the contact points between the moving contact and the stationary contacts are correctly formed. For example, a + / - 60° rotation of the moving contact around the f aaxis renders the movable contactor inoperative. In this embodiment, some form of limitation may be provided by features incorporated into one or more additional (mechanical or electrical) contacts, or auxiliary features located near the contacts (such as rods). On the other hand, if the movable contact is sufficiently rotationally symmetrical about the center of force, the contactor will operate correctly in any rotational position. For example, with complete rotational symmetry, the movable contact is a disk and not a triangle.

[0041] Fig. Figure 8 shows another example of a movable contact 800 with a triangular shape. The movable contact is shown together with stationary contacts 802, 804, and 806, and the contact points are again labeled a, b, and c. The movable contact is actuated at the force center 808 by a driving force f adriven. Here, the corner of the movable contact, where the contact point a is formed, is limited between the stationary contacts 802A-B. For example, the degree of separation between the stationary contacts 802A-B can be selected based on the relevant thickness of the movable contact so that its other side (with the contact points b and c) moves due to the driving force f a can move up and down a certain amount. In this example, the movable contact has a substantially uniform thickness and forms an isosceles triangle. In some embodiments, contact 802 may be non-conductive, and the others may be electrical contacts. In other embodiments, all of contacts 802-806 may be electrical contacts.

[0042] Fig. Figure 9 shows another example of a movable contact 900 with a triangular shape. Stationary contacts 902, 904, and 906 are shown. Contact points a, b, and c, and a force center 908 are also shown.

[0043] At the respective corners of contact points a, b, and c, the movable contact has 900 blunt sides. For example, here, the blunt sides corresponding to contact points b and c are parallel to each other and perpendicular to the blunt side of contact point a. Likewise, the movable contact has straight edges connecting the corresponding blunt sides.

[0044] Mechanical wear and deformation of a contact during use can tend to cause contact points to deviate from their intended, or original, locations. For example, here, contact point a is offset from the centerline of the movable contact and is closer to contact point b than c. Contact points b and c, in turn, are offset in opposite directions, so that they are closer to each other than before. That is, even if each of the contact points was originally centered relative to its corresponding contact, the contact points have since migrated to the locations shown. However, the movable contact is configured such that, despite such wear / deformation, a triangle 910 formed by the contact points still encloses the center of force 908. This helps maintain the stability and rigidity of the movable contact.

[0045] Fig. Figure 10 shows another example of an electromagnetic switch 1000 with an additional contact. Here, a driving force f a a reciprocating movement of a movable contact 1002 into and out of contact with stationary electrical contacts 1004. Another end of the movable contact is defined by an auxiliary contact 1006. In this example, the auxiliary contact includes portions 1006A-B, both of which are formed as part of the switch housing. The switch may define a heat sink 1008 near the auxiliary contact. In some implementations, the auxiliary contact 1006 is an electrical contact.

[0046] Fig. Figure 11 shows an example of an electromagnetic switch 1100, wherein a movable contact 1102 is attached by a ball joint 1104. Similar to the previous examples, an actuator exerts a driving force f ato move the movable contact against stationary electrical contacts 1106. In this example, one end 1102A of the movable contact has a rounded shape that at least partially corresponds to the shape of the socket of the joint, which allows one or more other ends 1102B of the movable contact to reach the stationary contact(s) during reciprocating movement. The socket of the ball joint 1104 may be manufactured as a separate component that is then attached to the housing of the switch, or may be an integral part formed during housing manufacture. In some implementations, the ball joint has the opposite orientation, such that the movable contactor forms the socket portion, and the ball portion is formed by the housing. In some implementations, the ball joint is an electrical contact. A heat sink 1108 may be provided proximate the ball joint.

[0047] Fig. Figure 12 shows an example of an electromagnetic switch 1200, wherein a movable contact 1202 is fixed by a flexure 1204. The movable contact is actuated by a driving force f a against stationary electrical contacts 1206. In this example, the flexure 1204 is attached to one end 1202A of the movable contact so that another end or ends 1202B of the movable contact can reach the stationary contact(s) during the reciprocating movement. The flexure may be made of any suitable material, such as metal (e.g., steel or bronze). The flexure may be attached to a base 1206 on the housing. The base 1206 may be a non-conductive protrusion on the housing or may be an electrical contact. A heat sink 1208 may be provided near the flexure.

[0048] Fig.Figure 13 shows an example of an electromagnetic switch 1300, wherein a movable contact 1302 is attached by a hinge 1304. The movable contact is actuated by a driving force f a driven against stationary electrical contacts 1306. In this example, the joint is formed integrally with the movable contact. That is, one end 1304A of the joint is fixed to the housing, and the other end 1304B extends a certain length to form the movable contact. Any suitable material can be used for the joint, such as steel, and the material dimensions (e.g., thickness) are selected based on the specific design. In some embodiments, the joint 1304 is an electrical contact. A heat sink 1308 may be provided near the joint.

[0049] In some embodiments, thermal contact between the movable contact and one or more auxiliary contacts may be enhanced in one or more ways. Such ways include, but are not limited to: providing complementary surface radii; allowing a small gap among the permissible directions of movement (e.g.,as in ball-and-socket features); providing a retained grease, liquid, or paste that allows performance or enhanced convection between the surfaces; providing small, repeating lands, pockets, channels, or the like that allow convective exchange through the contactor fill gas by confining convection to defined length dimensions; providing flexible joints, such as a spring, made of a thermally conductive material; and inserting a phase-change fluid into the joint between the movable contact and one or more other contacts to create a heat pipe effect, to name a few examples.

[0050] When an electromagnetic switch is opened under load, electrical arcs may occur. It may be necessary or desirable to incorporate one or more permanent magnets into the switch so that its field tends to blow these electrical arcs away from the conductors through Lorentz force. In some designs, one or more such magnets can be arranged so as not to interfere with the operation of the moving contact.

Claims

[1] Electromagnetic switch comprising: at least two stationary electrical contacts; and a movable contact (102, 604, 702-706, 1002), wherein the electromagnetic switch (100, 600, 1000, 1100, 1200, 1300) is configured for a reciprocating movement of the movable contact (102, 604, 702-706, 1002) into and out of contact with the stationary electrical contacts, wherein the movable contact (102, 604, 702-706, 1002) is configured such that at least three contact points (a, b, c) are created during the reciprocating movement, and such that a triangle (300, 910) defined by the at least three contact points (a, b, c) encloses a center of force of the movement, wherein a first and a second stationary electrical contact and at least one non-conductive mechanical contact are present, and wherein the movable contact (102, 604, 702-706, 1002) is configured to form a first contact point (a) with the first stationary electrical contact (602, 1306), a second contact point (b) with the second stationary electrical contact (602, 1306), and a third contact point (c) with the non-conductive mechanical contact (616). [2] Electromagnetic switch according to claim 1, wherein a first and a second stationary electrical contact are provided and the movable contact (102, 604, 702-706, 1002) is configured so that the three contact points (a, b, c) are formed with the stationary electrical contacts: a first and second contact point (a, b) is formed at the first stationary electrical contact (602, 1306) and a third contact point © is formed at the second stationary electrical contact (602, 1306). [3] An electromagnetic switch according to claim 2, formed from a rectangular metal block (400) having at least one flat surface (402), the metal block having a first recess in the flat surface (402) to form the first and second contact points, and a second and third recess to form the third contact point. [4] An electromagnetic switch according to claim 3, wherein a hole for a shaft (108, 204) passes through the metal block at the center of force, the shaft (108, 204) driving the movement of the movable contact (102, 604, 702-706, 1002). [5] The electromagnetic switch of claim 1, wherein the non-conductive mechanical contact (616) is positioned such that the third contact point is formed at one end of the reciprocating movement and not at another part of the reciprocating movement. [6] The electromagnetic switch of claim 5, further comprising a heat sink (1008, 1108, 1208, 1308) in thermal contact with the non-conductive mechanical contact (616). [7] An electromagnetic switch according to claim 5, further comprising another non-conductive mechanical contact (616) that comes into contact with the movable contact (102, 604, 702-706, 1002) at the beginning of the reciprocating movement. [8] The electromagnetic switch of claim 1, wherein the non-conductive mechanical contact (616) is positioned to provide the third contact point throughout the reciprocating movement. [9] The electromagnetic switch of claim 8, further comprising a heat sink (1008, 1108, 1208, 1308) in thermal contact with the non-conductive mechanical contact (616). [10] The electromagnetic switch of claim 8, further comprising another non-conductive mechanical contact (616), wherein the movable contact (102, 604, 702-706, 1002) is confined between the mechanical contacts (616) throughout the reciprocating movement. [11] The electromagnetic switch of claim 1, wherein the non-conductive mechanical contact (616) comprises an attachment of the movable contact (102, 604, 702-706, 1002) to the electromagnetic switch (100, 600, 1000, 1100, 1200, 1300). [12] An electromagnetic switch according to claim 11, wherein the attachment comprises a flexure (1204) that allows for reciprocating movement. [13] The electromagnetic switch of claim 11, further comprising a heat sink (1008, 1108, 1208, 1308) in thermal contact with the mount. [14] An electromagnetic switch according to claim 1, wherein the movable contact (102, 604, 702-706, 1002) has a triangular shape corresponding to the three contact points (a, b, c). [15] An electromagnetic switch according to claim 14, wherein the triangular shape has at least one blunt corner. [16] The electromagnetic switch of claim 1, wherein there are first, second, and third stationary electrical contacts, and wherein the movable contact (102, 604, 702-706, 1002) is configured to form at least one contact point with each of the first, second, and third stationary electrical contacts (602, 1306). [17] An electromagnetic switch according to claim 16, wherein the first, second and third stationary electrical contacts (602, 1306) are positioned such that the contact points (a, b, c) are formed at one end of the reciprocating movement and not during any other part of the reciprocating movement. [18] An electromagnetic switch according to claim 1, wherein the movable contact (102, 604, 702-706, 1002) is spring-loaded. [19] Electromagnetic switch according to claim 1, wherein the center of force of the movement is located away from a center of gravity of the triangle (300, 910) defined by the at least three contact points (a, b, c).

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