Bi-stable contactor with permanent-magnet latching mechanism

Abstract

A bi-stable contactor assembly 100 which includes one or more fixed contacts 102, 104; a moveable contact 106; an actuator; a solenoid 120 configured to induce a first magnetic field that actuates movement of a plunger 108 within a plunger tube 110 to change the position of the moveable contact 106; and a permanent magnet 150 located outside of the arc chamber 152 and magnetically coupled to the plunger 108 through a top core 130 that defines an end of the plunger tube 110. The magnet 50 generates a second magnetic field that, together with the top core 130 and the plunger 108, forms a latching magnetic circuit configured to hold the plunger 108 in a position corresponding to the closed state in the absence of current in the coil. The latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

Description

BI-STABLE CONTACTOR WITH PERMANENT-MAGNET LATCHING MECHANISMBACKGROUND

[0001] Electromechanical switching devices, such as contactors and relays, are designed to carry a certain amount of electrical current for certain periods of time. Such devices are particularly important in electric vehicles. Typically, electric vehicles have multiple electromechanical switches, or contactors, that open or close high current paths between the battery packs and the electrical system. These contactors themselves require electrical energy for their operation, and thus increasing the energy efficiency of the contactors decreases the drain on the electric vehicle battery'. Typically, a solenoid must be powered to keep the contactor in a closed state.SUMMARY

[0002] The following summary is meant to help one skilled in the art understand the various presently disclosed combinations of features. It is not meant to unduly limit the scope of any- pending or future claims relating to the disclosure.

[0003] Embodiments of the present invention are directed to a bi-stable contactor that uses a permanent magnet and a solenoid-driven magnetic circuit arranged in parallel to achieve efficient, low-pow er sw itching of high-current electrical paths. Unlike traditional monostable contactors that require continuous coil power to maintain either the open or closed state, the disclosed design consumes energy only during transitions between states, thereby significantly reducing electrical losses in applications such as electric vehicles, battery systems, and power distribution equipment. By positioning the coil outside the arc chamber and configuring the permanent magnet to generate a latching force independent of the solenoid field, the actuator provides reliable holding performance without the need for hold current, as well as controlled release by applying reverse coil excitation. This improvement reduces thermal load, extends system operating life, and increases overall energy- efficiency, making the invention particularly valuable in systems where every- watt of conser ed power directly contributes to performance, safety, and range.

[0004] In a particular embodiment, a bi-stable contactor assembly includes one or more fixed contacts and a moveable contact disposed in an arc chamber of a housing and an actuator operable to change a position of the moveable contact betw een a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state. The actuator also includes a plunger and a plunger shaft that connects the plunger to the moveable contact. In this embodiment, the plunger is movable within a plunger tube. The assemblyalso includes a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube to change the position of the moveable contact. In addition, the assembly also includes a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube. In this embodiment, the permanent magnet generates a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to the closed state in the absence of current in the coil. The latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

[0005] In another embodiment, an electric vehicle is disclosed that includes one or more battery packs, an inverter, and a bi-stable contactor assembly operable to close an electrical circuit connecting the one or more battery packs to the inverter. In this embodiment, the bistable contactor assembly includes one or more fixed contacts, a moveable contact disposed in an arc chamber of a housing, and an actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact. In this embodiment, the plunger is movable within a plunger tube. The assembly also includes a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube. In addition, the assembly also includes a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube. In this embodiment, the permanent magnet generates a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to a closed state in the absence of current in the coil. The latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

[0006] In a particular embodiment, a method of operating a bi-stable contactor is disclosed that includes coupling a bi-stable contactor to a pow er source. In this embodiment, the bistable contactor includes one or more fixed contacts, a moveable contact, and an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state. The actuator includes a plunger and a plunger shaft that connects the plunger to the moveable contact. The assembly also includes a plunger tube within which the plunger moves: a solenoid configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet that generates a second magnetic fieldconfigured to hold the plunger in a position corresponding to the closed state. The method also includes closing the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has a same direction as a field generated by the permanent magnet, thereby causing the plunger to move into the closed state. In addition, the method also includes opening the bi-stable contactor by applying a second coil current to the solenoid in a direction such that a generated electromagnetic field has an opposite direction to the field generated by the permanent magnet, thereby causing the plunger to move into the open state.

[0007] The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular descriptions of exemplary embodiments of the invention as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts of exemplary embodiments of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0001] One or more aspects of the present disclosure are discussed below with reference to the accompanying Figures. It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components may be included in one functional block or element.

[0002] Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. For purposes of clarity, however, not every' component may be labeled in every drawing. The Figures are provided for the purposes of illustration and explanation and are not intended to be limiting. In the Figures:

[0003] FIG. 1 sets forth a sectional view of an example bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0004] FIG. 2A sets forth perspective view of an example bi-stable contactor in accordance with at least one embodiment of the present disclosure

[0005] FIG. 2B sets forth top plan view of the example bi-stable contactor of FIG. 2A.

[0006] FIG. 2C sets forth a sectional view of the bi-stable contactor of FIG. 2A.

[0007] FIG. 3 A sets forth an example magnetic flux measurement of an example bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0008] FIG. 3B sets forth another example magnetic flux measurement of an example bistable contactor in accordance with at least one embodiment of the present disclosure.

[0009] FIG. 4 sets forth an example graph of contactor force vs. plunger gap for an example bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0010] FIG. 5 A sets forth another sectional view of an example bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0011] FIG. 5B sets forth another example magnetic flux measurement of an example bistable contactor in accordance with at least one embodiment of the present disclosure.

[0012] FIG. 6 sets forth an example graph of contactor force vs. coil current for an example bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0013] FIG. 7 sets forth a flowchart of an example method for a bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0014] FIG. 8 sets forth a flowchart of another example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0015] FIG. 9 sets forth a flowchart of another example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure.

[0016] FIG. 10 sets forth a flowchart of another example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure.DETAILED DESCRIPTION

[0017] Connecting and disconnecting electrical circuits is as old as electrical circuits themselves and is often utilized as a method of switching power to a connected electrical device between “on” and “off7states. An example of one device commonly utilized to connect and disconnect circuits is a contactor, which is electrically connected to one or more devices or power sources. A contactor is configured such that it can change between “open” and “closed’' states to interrupt or complete a circuit to control electrical power to and from a device.

[0018] As society advances, various innovations have resulted in electrical systems and electronic devices becoming increasingly common. An example of such innovations includes recent advances in electrical automobiles, which are becoming the cncrgy-cfficicnt standard and will likely replace most traditional petroleum-powered vehicles. With a limited amount of stored energy available in the vehicle batteries, it is important that all devices in the vehicle are performing with the utmost energy efficiency so as to conserve the stored energy and extend the range of the vehicle.

[0019] Described herein are different embodiments of contact assemblies having certain components, or portions thereof, that are formed integral to one another to improve the operation characteristics and increase operational performance, reliability and safety. Thepresent disclosure also provides for new features of components of the contact assemblies, with these features providing the desired operational characteristics, performance, and safety. Embodiments of the disclosure are also directed to contactors (i. e. , electrical switching devices) utilizing the contactor assemblies according to the present disclosure, and to electrical circuits and systems utilizing the electrical switching devices according to the present invention.

[0020] The terminology used herein for the purpose of describing particular examples is not intended to be limiting for further examples. Whenever a singular form such as “a”, "an" and “the” is used and using only a single element is neither explicitly or implicitly defined as being mandatory, further examples may also use plural elements to implement the same functionality. Likewise, when a functionality is subsequently described as being implemented using multiple elements, further examples may implement the same functionality using a single element or processing entity7. It will be further understood that the terms “comprises”, “comprising”, “includes” and / or “including”, when used, specify the presence of the stated features, integers, steps, operations, processes, acts, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, acts, elements, components and / or any group thereof.

[0021] It will be understood that when an element is referred to as being “connected” or “coupled” to another element, the elements may be directly connected or coupled via one or more intervening elements. If two elements A and B are combined using an “or”, this is to be understood to disclose all possible combinations, i.e. only A, only B, as well as A and B. An alternative wording for the same combinations is “at least one of A and B”. The same applies for combinations of more than two elements.

[0022] Accordingly, while further examples are capable of various modifications and alternative forms, some particular examples thereof are shown in the figures and will subsequently be described in detail. However, this detailed description does not limit further examples to the particular forms described. Further examples may cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Like numbers refer to like or similar elements throughout the description of the figures, which may be implemented identically or in modified form when compared to one another while providing for the same or a similar functionality'.

[0023] In the design of hermetic electromechanical relays, referred to herein as "contactors," a solenoid coil is used to generate a magnetic field that actuates an armature to drive a moveable contact into contact with one or more fixed contacts, thus closing a circuit. Forexample, such a contactor may be used to connect a battery to an inverter in an electric vehicle. In traditional contactors, when the moveable contact is in contact with the fixed contacts, the contactor is said to be in ON or closed state; when the moveable contact is not in contact with the fixed contacts, the contactor is said to be in the OFF or open state. Continuous power is required to drive the coil to keep the contactor at least one of these states. For example, in many conventional contactors, continuous power is required to drive the coil to maintain the contactor in the closed state. Thus, while the contactor is ON, the coil used to actuate the contactor is continuously consuming power.

[0024] Unlike traditional contactors that require continuous power to maintain their state, a bi-stable contactor has two stable positions (open and closed) and only requires power momentarily to change its state. In some embodiments, a solenoid operated contactor is converted into a bi-stable contactor. In these embodiments, the actuation mechanism only consumes energy7during a state transition (from ON to OFF or OFF to ON). Compared to traditional mono-stable solenoid driven contactors, energy7consumption is reduced because the coil of a mono-stable contactor will always consume energy in one of the two (ON or OFF) states. According to embodiments, a latch magnet is used to retain the actuator in a closed position even when no power is supplied to the solenoid. Unlike conventional contactor designs, disclosed embodiments use an actuator that has the coil outside of the arc chamber environment (allowing more freedom in material choice of the permanent magnet) and the latching magnetic circuit acts in parallel to the electromagnetic circuit.

[0025] In accordance with some embodiments of the present disclosure, bi -stability is achieved by placement of permanent magnet (also referred to herein as a ‘latch magnet’) and a magnetic flux director in the magnetic actuator of the contactor. Together with the conventional actuator components, a second magnetic circuit is created in the actuator that acts in parallel to the magnetic circuit that is created by the actuator coil, magnetic cores, and plunger.

[0026] Using a bi-stable contactor increases the energy7efficiency of the contactor byreducing or eliminating the hold current supplied to the solenoid to keep the contactor in the closed state. The increased efficiency thus requires less electrical energy to function and can conserve battery utilization, for example, to extend electric vehicle battery range when used in an electric vehicle.

[0027] For further explanation, FIG. 1 sets forth a sectional view of a contactor 100 in accordance with at least one embodiment of the present disclosure. The example contactor 100 includes fixed contacts 102, 104. The contactor 100 also includes a moveable contact106 configured to move in and out of contact with the fixed contacts 102, 104. The moveable contact 106 and fixed contacts 102, 104 are disposed in an arc chamber 152 of a housing 116. The moveable contact 106 is actuated by an armature including a plunger 108 and a plunger shaft 112 that is coupled to the plunger 108 and the moveable contact 106. The plunger 108 is disposed in a plunger tube 110 and is actuated by a magnetic field induced by a solenoid 120. The plunger tube 110 is hermetically sealed to a base 130 (e.g., a top core) of housing 116 and is composed of a ferromagnetic material such as, for example, iron, steel, or martensitic stainless steel. The contactor 100 also include a contact spring 114 disposed around the plunger shaft 112 between the moveable contact 106 and the base 130 of the housing 116, and a return spring 118 disposed around the plunger shaft 112 between the base 130 of the housing 116 and the plunger 108.

[0028] The solenoid 120 includes a coil 124 in which a magnetic field is induced through a supply of current. When the magnetic field is induced, the plunger 108 is forced upward in response to the magnetic field acting on the plunger 108. Conventionally , the amount of current, supplied to the solenoid, that is needed to induce a magnetic field strong enough to hold the moveable contact 106 in contact with the fixed contacts 102, 104 is referred to as the hold current (also referred to as the magnetic hold current). In accordance with embodiments of the present disclosure, a permanent magnet 150 operating in parallel with the solenoid 120 and located outside of the arc chamber 152 is used to hold the moveable contact 106 in contact with the fixed contacts 102, 104, thus creating a bi-stable contactor.

[0029] For further explanation, FIGS. 2A-2C illustrate an example bi-stable contactor 200 in accordance with at least one embodiment of the present disclosure. FIG. 2A illustrates a perspective view of bi-stable contactor 200. FIG. 2B illustrates a top plan view of bi-stable contactor 200. FIG. 2C illustrates a sectional view of bi-stable contactor 200 taken along section A- A. As shown in FIG. 2C, bi-stable contactor 200 includes plunger 201, permanent magnet 202, magnetic flux director 203, top core 204, magnetic yoke 205, center yoke 206, contact spring 207, return spring 208, moveable contact 209, stationary contacts 210, shaft 211, tube 212, and coil 213.

[0030] In accordance with embodiments of the present disclosure, bi-stability is achieved by placement of permanent magnet 202 (also referred to herein as a ‘latch magnet’) and magnetic flux director 203 in the magnetic actuator of the contactor. Together with the conventional actuator components (e.g., the plunger 201, the top core 204), a second magnetic circuit is created in the actuator that acts in parallel to the magnetic circuit that is created by the actuator coil 213, magnetic cores, and plunger 201. The resulting force on theplunger 201 (that is mechanically coupled to the moveable contact 209) is dependent on the air gap between the plunger 201 and the top core 204. and the amplitude and sign of the coil current.

[0031] When the contactor is in the open position, the force generated by the return spring 208 keeps the plunger 201 in the down position and the magnetic forces generated by the permanent magnet 202 magnetic circuit are insufficient to move the plunger 201 to the closed position.

[0032] To close the contact, a coil current is applied in such direction that the generated electromagnetic field has the same direction as the field generated by the permanent magnet 202. At a defined current level this results in a force on the plunger 201 that overcomes the force of the return spring 208. Once the plunger 201 starts moving, the air gap between the plunger 201 and top core 204 decreases, which increases the efficiency of the magnetic circuit and thus increases the force on the plunger 201 as it travels upwards. When the two force opposing elements (return spring 208 and contact spring 207) are designed accordingly, the plunger 201 will always fully close once it starts moving.

[0033] Once the moveable contact 209 is fully closed, the magnetic circuit that encompasses the permanent magnet 202 has generated enough force to keep the contact closed, even without assistance of the electromagnetic field. The contact stays closed as long as the coil current is suppressed and the combined forces of the contact spring 207, return spring 208, and g-forces on the actuator are below the designed hold force of the permanent magnet 202 magnetic circuit.

[0034] To open the contact, a coil current is applied in such direction that the generated electromagnetic field has the opposite direction as the field generated by the permanent magnet 202. This results in reduced magnetic field strength in the actuator area between the plunger 201 and the top core 204. Beyond a certain threshold current level, the resulting magnetic force between the plunger 201 and top core 204 is insufficient to overcome the force generated by the contact spring 207 and return spring 208 and the plunger 201 is pushed downwards, thereby opening the contacts.

[0035] Thus, the bi-stable contactor 200 in accordance with the present disclosure does not use energy to keep the contacts closed. It only consumes energy while transitioning between the open state and the closed state. In some examples, the bi-stable contactor is implemented without using an outer flux core as part of the magnetic circuit of the permanent magnet 202.

[0036] The structural arrangement shown in FIGS. 2A-2C is significant because it enables a bi-stable actuator that provides reliable switching performance while greatly reducing theenergy required to operate a high-current contactor. By locating the permanent magnet and solenoid coil outside the arc chamber and configuring their magnetic circuits in parallel, the actuator can latch securely in the closed state without hold current and can be released in a controlled manner using a small reverse coil excitation. This architecture improves overall efficiency, reduces heat generation, expands material-selection freedom for the permanent magnet, and enhances long-term durability, making the contactor particularly advantageous in systems such as electric vehicles and battery-powered equipment where power conservation, reliability, and compact actuator design are critically important.

[0037] For further explanation, FIG. 3A illustrates a magnetic flux density diagram for the bistable contactor during the closed, latched state in accordance with embodiments of the present disclosure. The grayscale legend to the left indicates magnetic flux density values ranging from approximately 0.002 tesla to more than 2.6 tesla. As shown, the region between the permanent magnet 202 and the top core 204 exhibits the highest flux density, with the magnetic flux director 203 providing a preferential path that channels magnetic flux toward the plunger 201. The plunger 201 and adjacent ferromagnetic structures, including the center yoke 206, exhibit concentrated regions of elevated flux density, indicating that the permanent magnet produces a strong attractive force across the air gap. The coil 213 is shown in an unenergized state, and the flux distribution reflects that the permanent magnet alone establishes a continuous magnetic circuit through the top core 204, flux director 203, plunger 201, and the surrounding yoke components. The dense flux region in the upper portion of the actuator confirms that the permanent magnet generates sufficient force to hold the plunger in the latched, closed position without coil current.

[0038] For further explanation, FIG. 3B illustrates a magnetic flux density diagram for the bistable contactor during an opening event in which the solenoid coil 213 is energized with current in a direction that opposes the magnetic field of the permanent magnet 202. As shown by the shading distribution, regions that exhibited high flux density in FIG. 3A now display reduced intensity, particularly in the flux path between the magnetic flux director 203, the top core 204. and the plunger 201. This reduction indicates partial cancellation of magnetic flux caused by the reverse coil excitation. The flux density in the plunger 201 and center yoke 206 is correspondingly diminished, demonstrating that the opposing electromagnetic field weakens the permanent-magnet latching force across the air gap. The modified flux pattern in FIG. 3B shows that once the net magnetic force drops below the mechanical restoring force of the springs, the plunger can be driven downward into the open position. Together. FIGS. 3A and 3B illustrate how the actuator employs a permanent-magnet latching circuit and asolenoid-driven circuit in a parallel magnetic configuration, enabling selective reinforcement or cancellation of magnetic flux depending on the direction of the coil current. This behavior supports the disclosed bi-stable operation by demonstrating that the permanent magnet alone establishes the holding force in the closed position, and that energizing the coil in the opposite direction reduces the net force sufficiently to release the plunger.

[0039] For further explanation, FIG. 4 illustrates a graph 400 of magnetic force versus plunger gap for the bi-stable contactor in accordance with embodiments of the present disclosure. The horizontal axis shows the plunger gap, defined as the distance between the plunger and the top core, and extends from 0.0 mm to approximately 1.4 mm. The vertical axis represents the net axial magnetic force acting on the plunger in Newtons. The graph includes several force curves corresponding to different excitation conditions of the actuator. The curve labeled “1250 AT” (402) represents operation when the solenoid coil is energized in a direction that reinforces the magnetic field of the permanent magnet. In this condition, the magnetic force rises sharply at small gaps and remains greater than the combined force of the return spring and contact spring shown by the “spring forces” curve (408), allowing the plunger to be pulled upward and initiating closing of the contactor. The points labeled “0 AT” (406) represent the magnetic force produced solely by the permanent magnet with no coil current applied. At small gaps, these values remain above the spring-force curve, demonstrating that the permanent magnet alone supplies sufficient latching force to maintain the closed state without requiring hold current. As the gap increases, the magnetic force produced by the permanent magnet decreases and eventually falls below the spring-force curve at the region labeled “switch OFF,” corresponding to the natural drop-out point at which the plunger returns to the open state.

[0040] The curve labeled “-500 AT” (404) corresponds to operation when the solenoid is energized with current in a direction opposing the magnetic field of the permanent magnet. Under this reverse-excitation condition, the resulting magnetic force stays below the springforce curve over the entire stroke, allowing the mechanical springs to move the plunger downward and open the contactor. The force-gap behavior depicted in FIG. 4 shows how the disclosed actuator structure enables bi-stable operation: reinforcing coil excitation produces sufficient force to overcome spring loads and close the contactor, the permanent magnet alone maintains the closed state when the gap is small, and opposing coil excitation reduces the net magnetic force enough to allow the plunger to open. The different curves also demonstrate how the permanent magnet circuit and the solenoid drive circuit interact in a parallel configuration, with the plunger serving as their shared magnetic element, enablingthe magnetic forces to be selectively increased or decreased depending on the direction and magnitude of the coil current.

[0041] For further explanation, FIG. 5A sets forth a sectional perspective view of an upper portion of an actuator for a bi-stable contactor in accordance with at least one embodiment of the present disclosure. The actuator includes a plunger 201 positioned within a plunger tube and movable along a longitudinal axis. A permanent magnet 202 is located above the plunger 201 and is mechanically supported by a magnetic flux director 203. The flux director 203 is arranged to guide magnetic flux from the permanent magnet 202 directly into the plunger201. A top core 204 defines an upper end of the plunger tube and forms a magnetic pole surface that interfaces with the plunger 201 during the closed or latched condition. A magnetic yoke 205 surrounds the permanent magnet 202 and top core 204 and provides a structural and magnetic return path for flux generated by the permanent magnet 202.

[0042] As further shown in FIG. 5 A, a solenoid coil 213 is disposed around a lower region of the plunger tube and is spaced below the permanent magnet 202 and flux director 203. This arrangement positions the coil outside of the arc chamber and physically separates the coil’s drive magnetic circuit from the latching magnetic circuit formed by the permanent magnet202, flux director 203, plunger 201, top core 204, and yoke 205. The plunger 201 forms the only shared magnetic element between these two circuits, enabling the magnetic flux generated by the permanent magnet 202 to act in parallel with the magnetic flux generated by the solenoid coil 213.

[0043] The geometry illustrated in FIG. 5A provides a low-reluctance magnetic path from the permanent magnet 202 through the flux director 203, into the plunger 201, across a small air gap at the interface with the top core 204, and returning through the magnetic yoke 205. This arrangement creates a latching magnetic circuit capable of maintaining the plunger 201 in an attracted, closed position in the absence of applied coil current. Moreover, because the permanent magnet 202 and flux director 203 he outside of the arc chamber, the material selection and magnet geometry are not constrained by the conditions within the arc chamber. FIG. 5A therefore illustrates the structural features that provide the independent latching circuit used for bi-stable operation of the contactor.

[0044] For further explanation, FIG. 5B illustrates the magnetic flux density distribution in the actuator during the latched or closed state and demonstrates the specific configuration of the latching magnetic circuit used in the present invention. As shown in FIG. 5B. flux generated by the permanent magnet 202 is directed by the magnetic flux director 203 into the plunger 201 and across a small air gap into the top core 204 before returning through yoke205. This flux distribution forms a self-contained latching magnetic circuit that is structurally independent of the drive magnetic circuit generated by the solenoid. FIG. 5B shows that the permanent magnet circuit of the present invention closes entirely through the plunger, top core, flux director, and yoke without requiring any portion of the outer housing or coil structure to complete the magnetic loop.

[0045] The flux plot in FIG. 5B therefore provides direct evidence of the technical effect achieved by the disclosed actuator geometry: the permanent magnet circuit is isolated from the arc chamber environment, enabling the use of magnet materials and geometries not possible in designs where the magnet must share the same magnetic path or physical volume as the drive coil or arc chamber. Furthermore, because the permanent magnet flux does not flow through the outer housing or coil core, the latching circuit is arranged in parallel with the drive circuit, enabling independent control of pickup and release forces and allowing the contactor to remain latched without hold current. This configuration solves the technical problem of providing a bi-stable contactor with reduced energy consumption and improved design freedom over series-based permanent-magnet contactor designs. The magnetic behavior visible in FIG. 5B — specifically, the concentrated flux path limited to the permanent magnet 202, flux director 203, plunger 201, top core 204, and yoke 205 — could not be achieved in prior-art structures and results directly from the structural features disclosed herein. Accordingly, FIG. 5B demonstrates the technical advantage obtained over the closest prior art and supports the inventive step of the claimed actuator.

[0046] For further explanation, FIG. 6 sets forth a graph 600 representing the measured and simulated axial magnetic force acting on the plunger as a function of the magnetomotive force applied by the solenoid coil. The horizontal axis expresses coil excitation as current multiplied by the number of coil turns (ampere-turns, AT), and the vertical axis expresses the resulting axial force applied to the plunger in Newtons (N). Positive force values correspond to forces urging the plunger toward the closed position, and negative force values correspond to forces urging the plunger toward the open position. The force values shown in FIG. 6 therefore correspond to directly measurable actuator behavior resulting from the structural arrangement of the permanent magnet, the top core, the plunger tube, and the solenoid coil.

[0047] The graph includes several families of curves that correspond to different operating conditions of the bi-stable contactor. Curve 602, labelled ‘‘Hold (+0.1 A),” illustrates the condition in which the solenoid is supplied with only a minimal coil current of approximately +0.1 A, such that the flux generated by the solenoid substantially matches the latching flux generated by the permanent magnet 202. Because the latching magnetic circuit formed by thepermanent magnet, the top core, and the plunger is arranged in parallel with the magnetic circuit generated by the solenoid, the hold curve 602 represents the net force produced primarily by the permanent magnet. FIG. 6 therefore shows that the contactor can remain closed without any hold current, and that this result follows directly from the parallel permanent-magnet magnetic circuit disclosed herein.

[0048] Curve 604, labelled ‘“Pickup (+0.6A),” illustrates operation during a closing transition. In this mode, the coil current is applied in a direction that reinforces the magnetic field of the permanent magnet. Because the solenoid magnetic circuit and the latching magnetic circuit are arranged in parallel and share the plunger as a common flux path, their respective flux contributions add. Consequently, the axial force acting on the plunger increases sharply with additional coil excitation. The pickup curve shows that above a particular level, the net axial force exceeds the combined opposing forces of the return spring and contact spring, enabling the plunger to initiate upward movement and reduce the air gap between the plunger and the top core. Once motion begins and the air gap decreases, the reluctance of the magnetic circuit decreases and the resulting force increases further, as reflected in the steep upward slope of curve 604. This cooperative action between the electromagnetic field and permanent-magnet field is a direct consequence of the disclosed parallel magnetic circuit configuration and supports the method steps recited for initiating closure.

[0049] Curves 606 and 608 represent the force characteristics at two different plunger-to-core gaps. Curve 606 (“gap = 0. 1 mm”) corresponds to the plunger located very close to the top core. In this configuration, the magnetic reluctance of the latching circuit is minimal, and even modest coil excitation in the reinforcing direction yields a relatively large increase in net axial force. Curve 608 (“gap = 1.5 mm”) corresponds to a larger initial gap, such as during early stages of plunger movement. The force produced at this larger gap is significantly lower because the magnetic reluctance is greater. The presence of both curves in FIG. 6 demonstrates the dependency of magnetic force on plunger position, and FIG. 6 thereby provides a quantitative basis for the description of FIG. 4 relating to force versus gap. These curves collectively demonstrate that the disclosed geometry of the plunger tube, top core, and permanent magnet is sufficient to produce the force transitions necessary for bi-stable operation.

[0050] Curve 610, labelled “Return (-0.1 A),” illustrates operation during an opening transition. In this mode, a small coil current is applied in a direction opposite to the magnetic field of the permanent magnet. Because the latching magnetic circuit and the electromagnetic circuit are arranged in parallel, the opposing coil excitation reduces the net magnetic flux inthe latching circuit. With the magnetic attraction reduced below the combined forces of the return spring and contact spring, the plunger moves downward and the contactor transitions to the open state. FIG. 6 therefore quantitatively demonstrates the unlatching principle described in the method steps, in which the application of a reverse coil current unbalances the net magnetic forces sufficiently to permit mechanical opening.

[0051] The graph 600 also includes threshold markers indicating the minimum pickup and release forces. Because each curve is generated from a physically realizable actuator configuration, FIG. 6 provides written-description support for the relative magnitudes of the magnetic forces, the expected force profiles for different air-gap conditions, and the current polarities required to achieve pickup and release. A person skilled in the art can readily implement a bi-stable contactor having the characteristics shown in FIG. 6 using the structural features described herein, and FIG. 6 therefore provides enabling disclosure under §112(a) for the claimed bi-stable behavior, including hold- with -zero-current operation and state-transition control using current direction.

[0052] Accordingly, FIG. 6 demonstrates:(1) that the permanent magnet alone provides sufficient latching force to maintain the contactor in the closed state without applied coil current;(2) that reinforcement of the permanent magnet flux by the coil flux produces a pickup force exceeding spring loads; and(3) that applying coil current in the opposite direction reduces net magnetic attraction sufficiently to permit opening. These behaviors arise from the parallel magnetic circuit architecture of the actuator, which differs from series magnet configurations in conventional contactors and allows independent control of pickup and release characteristics.

[0053] For further explanation, FIG. 7 sets forth a flow chart of an example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure. The method includes closing 702 the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has the same direction as a field generated by a permanent magnet. To close the contact a coil current is applied in such direction that the generated electromagnetic field has the same direction as the field generated by the permanent magnet. At a defined current level this results in a force on the plunger that overcomes the force of the return spring. Once the plunger stats moving the air gap between the plunger and top core decreases, which increases the efficiency of the magnetic circuit and thus increases the force on the plunger as it travels upwards. When the two force opposing elements (return spring and contact spring) are designed properly theplunger will always fully close once it starts moving. Once the contact is fully closed the magnetic circuit that encompasses the permanent magnet generated enough force to keep the contact closed, even without assistance of the electromagnetic field. The contact stays closed as long as the coil current is suppressed and the combined forces of the contact spring, return spring and g-forces on the actuator are below the designed hold force of the permanent magnet magnetic circuit.

[0054] The method also includes opening 704 the bi-stable contactor by applying a second coil current to the solenoid in direction such that a generated electromagnetic field has the opposite direction as the field generated by the permanent magnet. To open the contact a coil current is applied in such direction that the generated electromagnetic field has the opposite direction as the field generated by the permanent magnet. This results in reduced magnetic field strength in the actuator area between the plunger and the top core. Beyond a certain threshold current level the resulting magnetic force between the plunger and top core is insufficient to overcome the force generated by the contact spring and return spring and the plunger is pushed downwards, thereby opening the contacts.

[0055] For further explanation, FIG. 8 sets forth a flow chart of an example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure. The method includes coupling 802 a bi-stable contactor to a power source, the bistable contactor including one or more fixed contacts and a moveable contact; an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state, the actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact; a plunger tube within which the plunger moves; a solenoid configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet that generates a second magnetic field configured to hold the plunger in a position corresponding to the closed state. Coupling 802 a bi-stable contactor to a power source may be carried out by electrically connecting the contactor’s input terminals to one or more battery packs or other suitable DC power sources within the system. This may include routing high-current conductors or busbars to the fixed contacts of the contactor and ensuring that the actuator control leads are connected to a controller configured to deliver the appropriate coil current for opening and closing operations. In some embodiments, coupling the contactor further includes mounting the contactor within the electrical architecture of the vehicle or device so that the moveable contact, once actuated, completes or interrupts the circuit between the power source and the downstream load.

[0056] The method of FIG. 8 also includes closing 804 the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has a same direction as a field generated by the permanent magnet, thereby causing the plunger to move into the closed state. Closing 804 the bi-stable contactor may be carried out by supplying a first coil current to the solenoid in a direction that reinforces the magnetic field produced by the permanent magnet. As this current is applied, the resulting electromagnetic field increases the net magnetic attraction across the plunger-to-top-core gap. overcoming the opposing forces of the return spring and contact spring. Once the plunger begins to move upward, the magnetic circuit becomes more efficient as the gap decreases, causing the plunger to accelerate into the fully closed position where the moveable contact engages the fixed contacts.

[0057] In addition, the method of FIG. 8 also includes opening 806 the bi-stable contactor by applying a second coil current to the solenoid in a direction such that a generated electromagnetic field has an opposite direction to the field generated by the permanent magnet, thereby causing the plunger to move into the open state. Opening 806 the bi-stable contactor may be carried out by applying a second coil current to the solenoid in a direction that opposes the magnetic field generated by the permanent magnet. The opposing electromagnetic field reduces the net magnetic attraction between the plunger and the top core, allowing the combined forces of the return spring and contact spring to overcome the diminished latching force. As a result, the plunger moves downward into the open position, separating the moveable contact from the fixed contacts and interrupting the electrical circuit.

[0058] The method depicted in FIG. 8 demonstrates how the bi-stable contactor can be actuated and controlled in a manner that minimizes energy usage while maintaining precise switching behavior. By relying on the permanent magnet to hold the plunger in the closed state and using directional coil current only when transitioning between states, the method reduces the need for continuous power delivery to the solenoid. This operational approach supports improved energy7efficiency, reduced thermal load on the actuator, and longer system service life in applications such as electric vehicles, battery systems, and other high-power electrical architectures.

[0059] For further explanation, FIG. 9 sets forth a flow chart of another example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure. The method of FIG. 9 is similar to the method of FIG. 8 in that the method of FIG. 9 includes all of the elements and steps of FIG. 8.

[0060] In the method of FIG. 9, closing 804 the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has a same direction as a field generated by the permanent magnet, thereby causing the plunger to move into the closed state includes discontinuing 902 the first coil current after the bi-stable contactor reaches the closed state, wherein the contactor remains in the closed state due to a latching force generated by the permanent magnet. Discontinuing 902 the first coil current after the bi-stable contactor reaches the closed state may be carried out by commanding the controller to cease supplying current to the solenoid once sensor feedback or predetermined timing indicates that the plunger has fully engaged the top core. When the current is removed, the solenoid field collapses, leaving only the magnetic field generated by the permanent magnet acting across the plunger-to-top-core interface. Because this permanent-magnet latching force exceeds the opposing spring forces at the closed position, the plunger remains held in place and the contactor stays closed without the need for any additional electrical power.

[0061] For further explanation, FIG. 10 sets forth a flow chart of another example method for operating a bi-stable contactor in accordance with at least one embodiment of the present disclosure. The method of FIG. 10 is similar to the method of FIG. 8 in that the method of FIG. 10 includes all of the elements and steps of FIG. 8.

[0062] In the method of FIG. 10, opening 806 the bi-stable contactor by applying a second coil current to the solenoid in a direction such that a generated electromagnetic field has an opposite direction to the field generated by the permanent magnet, thereby causing the plunger to move into the open state includes discontinuing 1002 the second coil current after the bi-stable contactor reaches the open state, wherein the contactor remains in the open state in the absence of coil current. Discontinuing 1002 the second coil current after the bi-stable contactor reaches the open state may be carried out by instructing the controller to stop supplying reverse-direction current to the solenoid once the plunger has moved fully away from the top core. When the reverse excitation is removed, the electromagnetic field opposing the permanent magnet dissipates, and the permanent magnet's residual attraction is no longer strong enough to pull the plunger upward from the open position. As a result, the return spring and contact spring maintain the plunger in the open state without requiring further electrical power, allowing the contactor to remain open in the absence of any coil current.

[0063] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, apparatuses, andmethods, according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

[0064] Advantages and features of the present disclosure can be further described by the following statements:

[0065] 1. A bi -stable contactor assembly comprising: one or more fixed contacts and a moveable contact disposed in an arc chamber of a housing; an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state, the actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact, the plunger being movable within a plunger tube; and a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube to change the position of the moveable contact; and a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube, the permanent magnet generating a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to the closed state in the absence of current in the coil; wherein the latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

[0066] 2. The bi-stable contactor assembly of statement 1, wherein a coil current is applied to the solenoid only during transitions between the open state and the closed state, and wherein coil current is not applied to the solenoid to retain the contactor in the open state or the closed state.

[0067] 3. The bi-stable contactor assembly of statements 1 or 2, wherein a lower end of the plunger tube is encompassed by the solenoid, and wherein an upper end of the plunger tube is encompassed by the permanent magnet.

[0068] 4. The bi-stable contactor assembly of any of statements 1-3, herein the top core defines one end of the plunger tube, and w herein the permanent magnet is mechanically and magnetically coupled to the top core.

[0069] 5. The bi-stable contactor assembly of any of statements 1-4, wherein the drive magnetic circuit includes the solenoid and the plunger, and wherein the latching magnetic circuit includes the permanent magnet, the plunger, and the top core, the latching magnetic circuit being magnetically in parallel with, and distinct from, the drive magnetic circuit, and wherein a return spring acting on the actuator applies a force opposing a latching force generated by the latching magnetic circuit.

[0070] 6. The bi-stable contactor assembly of any of statements 1-5, wherein a direction of the coil current during a transition from the open state to the closed state is selected such that the first magnetic field reinforces the second magnetic field, and wherein a direction of the coil current during a transition from the closed state to the open state is selected such that the first magnetic field opposes the second magnetic field.

[0071] 7. The bi-stable contactor assembly of any of statements 1-6, herein the permanent magnet is located outside of the arc chamber and is separated from the moveable contact and the fixed contacts by the top core and the plunger tube.

[0072] 8. The bi-stable contactor assembly of any of statements 1-7 further comprising a magnetic flux director positioned between the permanent magnet and the plunger and configured to guide magnetic flux from the permanent magnet into the plunger.

[0073] 9. An electric vehicle comprising: one or more battery' packs; an inverter; and a bistable contactor assembly operable to close an electrical circuit connecting the one or more battery packs to the inverter, the bi-stable contactor assembly comprising: one or more fixed contacts and a moveable contact disposed in an arc chamber of a housing; an actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact, the plunger being movable within a plunger tube; a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube, the permanent magnet generating a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to a closed state in the absence of current in the coil; wherein the latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

[0074] 10. The electric vehicle of statement 9. wherein a coil current is applied to the solenoid only during transitions between the open state and the closed state, and wherein coil current is not applied to retain the contactor in the open state or the closed state.

[0075] 11. The electric vehicle of statements 9 or 10, wherein a lower end of the plunger tube is encompassed by the solenoid and an upper end of the plunger tube is encompassed by the permanent magnet.

[0076] 12. The electric vehicle of any of statements 9-11, wherein the top core defines an upper end of the plunger tube and the permanent magnet is coupled to the top core.

[0077] 13. The electric vehicle of any of statements 9-12, wherein the permanent magnet generates the second magnetic field in parallel with the first magnetic field generated by the solenoid.

[0078] 14. The electric vehicle of any of statements 9-13, wherein the permanent magnet is located outside of the arc chamber and is separated from the moveable and fixed contacts by the top core and the plunger tube.

[0079] 15. The electric vehicle of any of statements 9-14 further comprising a magnetic flux director positioned between the permanent magnet and the plunger.

[0080] 16. A method comprising: coupling a bi-stable contactor to a power source, the bistable contactor including: one or more fixed contacts and a moveable contact; an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state, the actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact; a plunger tube within which the plunger moves; a solenoid configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet that generates a second magnetic field configured to hold the plunger in a position corresponding to the closed state; closing the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has a same direction as a field generated by the permanent magnet, thereby causing the plunger to move into the closed state; and opening the bi-stable contactor by applying a second coil current to the solenoid in a direction such that a generated electromagnetic field has an opposite direction to the field generated by the permanent magnet, thereby causing the plunger to move into the open state.

[0081] 17. The method of statement 16, wherein closing the bi-stable contactor by applying the first coil current to the solenoid in the direction such that the generated electromagnetic field has the same direction as the field generated by the permanent magnet further comprises discontinuing the first coil current after the bi-stable contactor reaches the closed state, wherein the contactor remains in the closed state due to a latching force generated by the permanent magnet.

[0082] 18. The method of statements 16 or 17, wherein opening the bi-stable contactor byapplying the second coil cunent to the solenoid in the direction such that the generated electromagnetic field has the opposite direction to the field generated by the permanent magnet further comprises discontinuing the second coil current after the bi-stable contactor reaches the open state, wherein the contactor remains in the open state in the absence of coil current.

[0083] 19. The method of any of statements 16-18, wherein the first coil cunent has a magnitude sufficient to generate an electromagnetic field that, in combination with the field generated by the permanent magnet, produces a force on the plunger that overcomes a force applied to the plunger by a return spring.

[0084] 20. The method of any of statements 16-19, wherein the bi-stable contactor further includes a magnetic flux director positioned between the permanent magnet and the plunger, and wherein at least a portion of the second magnetic field passes through the magnetic flux director to the plunger.

[0085] It will be understood from the foregoing description that modifications and changes may be made in vanous embodiments of the present disclosure without departing from its true spirit. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense. The scope of the present disclosure is limited only by the language of the following claims.

Claims

CLAIMSWhat is claimed is:1 . A bi-stable contactor assembly comprising: one or more fixed contacts and a moveable contact disposed in an arc chamber of a housing; an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state, the actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact, the plunger being movable within a plunger tube; and a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube to change the position of the moveable contact; and a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube, the permanent magnet generating a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to the closed state in the absence of current in the coil; wherein the latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

2. The bi-stable contactor assembly of claim 1 , wherein a coil current is applied to the solenoid only during transitions between the open state and the closed state, and wherein coil current is not applied to the solenoid to retain the contactor in the open state or the closed state.

3. The bi-stable contactor assembly of claim 1, wherein a lower end of the plunger tube is encompassed by the solenoid, and wherein an upper end of the plunger tube is encompassed by the permanent magnet.

4. The bi-stable contactor assembly of claim 1. herein the top core defines one end of the plunger tube, and wherein the permanent magnet is mechanically and magnetically coupled to the top core.

5. The bi-stable contactor assembly of claim 4, wherein the drive magnetic circuit includes the solenoid and the plunger, and wherein the latching magnetic circuit includes the permanent magnet, the plunger, and the top core, the latching magnetic circuit being magnetically in parallel with, and distinct from, the drive magneticcircuit, and wherein a return spring acting on the actuator applies a force opposing a latching force generated by the latching magnetic circuit.

6. The bi-stable contactor assembly of claim 1, wherein a direction of the coil current during a transition from the open state to the closed state is selected such that the first magnetic field reinforces the second magnetic field, and wherein a direction of the coil current during a transition from the closed state to the open state is selected such that the first magnetic field opposes the second magnetic field.

7. The bi-stable contactor assembly of claim 1, herein the permanent magnet is located outside of the arc chamber and is separated from the moveable contact and the fixed contacts by the top core and the plunger tube.

8. The bi-stable contactor assembly of claim 1 further comprising a magnetic flux director positioned between the permanent magnet and the plunger and configured to guide magnetic flux from the permanent magnet into the plunger.

9. An electric vehicle comprising: one or more battery’ packs; an inverter; and a bi-stable contactor assembly operable to close an electrical circuit connecting the one or more battery’ packs to the inverter, the bi-stable contactor assembly comprising: one or more fixed contacts and a moveable contact disposed in an arc chamber of a housing; an actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact, the plunger being movable within a plunger tube; a solenoid having a coil located outside of the arc chamber and configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet located outside of the arc chamber and magnetically coupled to the plunger through a top core that defines an end of the plunger tube, the permanent magnet generating a second magnetic field that, together with the top core and the plunger, forms a latching magnetic circuit configured to hold the plunger in a position corresponding to a closed state in the absence of current in the coil; wherein the latching magnetic circuit is arranged in parallel with a drive magnetic circuit that includes the coil and the plunger.

10. The electric vehicle of claim 9, wherein a coil current is applied to the solenoid only during transitions between an open state and the closed state, and wherein coil current is not applied to retain the contactor in the open state or the closed state.

11. The electric vehicle of claim 9, wherein a lower end of the plunger tube is encompassed by the solenoid and an upper end of the plunger tube is encompassed by the permanent magnet.

12. The electric vehicle of claim 9, wherein the top core defines an upper end of the plunger tube and the permanent magnet is coupled to the top core.

13. The electric vehicle of claim 9, wherein the permanent magnet generates the second magnetic field in parallel with the first magnetic field generated by the solenoid.

14. The electric vehicle of claim 9, wherein the permanent magnet is located outside of the arc chamber and is separated from the moveable and fixed contacts by the top core and the plunger tube.

15. The electric vehicle of claim 9 further comprising a magnetic flux director positioned between the permanent magnet and the plunger.

16. A method comprising: coupling a bi -stable contactor to a power source, the bi-stable contactor including: one or more fixed contacts and a moveable contact; an actuator operable to change a position of the moveable contact between a closed state, in which the moveable contact is in contact with the one or more fixed contacts, and an open state, the actuator including a plunger and a plunger shaft that connects the plunger to the moveable contact; a plunger tube within which the plunger moves; a solenoid configured to induce a first magnetic field that actuates movement of the plunger within the plunger tube; and a permanent magnet that generates a second magnetic field configured to hold the plunger in a position corresponding to the closed state; closing the bi-stable contactor by applying a first coil current to the solenoid in a direction such that a generated electromagnetic field has a same direction as a field generated by the permanent magnet, thereby causing the plunger to move into the closed state; and opening the bi-stable contactor by applying a second coil current to the solenoid in a direction such that a generated electromagnetic field has an opposite direction to thefield generated by the permanent magnet, thereby causing the plunger to move into the open state.

17. The method of claim 16, wherein closing the bi -stable contactor by applying the first coil current to the solenoid in the direction such that the generated electromagnetic field has the same direction as the field generated by the permanent magnet further comprises discontinuing the first coil current after the bi-stable contactor reaches the closed state, wherein the contactor remains in the closed state due to a latching force generated by the permanent magnet.

18. The method of claim 16, wherein opening the bi-stable contactor by applying the second coil current to the solenoid in the direction such that the generated electromagnetic field has the opposite direction to the field generated by the permanent magnet further comprises discontinuing the second coil current after the bi-stable contactor reaches the open state, wherein the contactor remains in the open state in the absence of coil current.

19. The method of claim 16, wherein the first coil current has a magnitude sufficient to generate an electromagnetic field that, in combination with the field generated by the permanent magnet, produces a force on the plunger that overcomes a force applied to the plunger by a return spring.

20. The method of claim 16, wherein the bi-stable contactor further includes a magnetic flux director positioned between the permanent magnet and the plunger, and wherein at least a portion of the second magnetic field passes through the magnetic flux director to the plunger.

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