Patent Description:
Electrically controlled switches such as contactors or relays may experience a failure in which the contactor welds closed, caused by current flowing when a contactor is being opened or closed. As this effectively causes the contactor to fail with the contactor permanently closed, this is a potential hazard.

Conventionally, contactors are more resistant to welding with current flowing in one direction than in the other. The contactors are therefore installed in the circuit in the preferred direction, so that the current flows in the direction most resistant to welding. In many circuits this is a sufficient measure to protect against this failure as the current flows only in one direction. However, batteries may use the same circuit for charging and discharging and so the current will flow in both directions depending on the circumstance.

<CIT> discusses a system and method for charge contactor weld check. A power distribution system for a vehicle includes contactors that selectively electrically couple a charger to a high-voltage bus. The contactors are closed at the start of a charge event in an order that alternates for successive charge events. Upon completion of the charge event, the last closed contactor at the start of the charge event is opened first and a weld check is performed. If the weld check is indicative of a welded contactor, then the weld check is performed on the other contactor.

Against this background, there is provided a device according to claim <NUM>. The battery module is configured to be charged and discharged via a first circuit. The first circuit comprises the contactor assembly, the contactor assembly comprising a first contactor and a second contactor, wherein the first contactor is in series with the second contactor. Each of the first contactor and the second contactor is configured to have a higher resistance to welding for a switching current flowing in a preferred direction than in a nonpreferred direction. The first contactor is configured to have a preferred direction in a first direction and a nonpreferred direction in a second direction. The second contactor is configured to have a preferred direction in the second direction and a nonpreferred direction in the first direction. In response to an instruction to switch the contactor assembly, the battery management system is configured to determine whether the switching current direction is in the first direction or in the second direction. In an event that the instruction to switch comprises an instruction to open the contactor assembly the battery management system is further configured to first, open the contactor having a preferred direction in the switching current direction, and subsequently, open the contactor having a nonpreferred direction in the switching current direction. In an event that the instruction to switch comprises an instruction to close the series contactor assembly the battery management system is further configured to first, close the contactor having a nonpreferred direction in the switching current direction and subsequently, close the contactor having a preferred direction in the switching current direction.

There is also provided a method of switching a contactor assembly for a battery module of an electric work vehicle comprising a battery management system. The battery module is configured to be charged and discharged via a circuit. The circuit comprises the contactor assembly, the contactor assembly comprising a first contactor and a second contactor, wherein the first contactor is in series with the second contactor. Each of the first contactor and the second contactor is configured to have a higher resistance to welding for a switching current flowing in a preferred direction than in a nonpreferred direction. The first contactor is configured to have a preferred direction in a first direction and a nonpreferred direction in a second direction. The second contactor is configured to have a preferred direction in the second direction and a nonpreferred direction in the first direction. In response to an instruction to switch the contactor assembly, the method comprises using the battery management system to determine whether the switching current direction is in the first direction or in the second direction. In an event that the instruction to switch comprises an instruction to open the contactor assembly the method further comprises using the battery management system to first, open the contactor having a preferred direction in the switching current direction, and subsequently, open the contactor having a nonpreferred direction in the switching current direction. In an event that the instruction to switch comprises an instruction to close the contactor assembly the method further comprises using the battery management system to first, close the contactor having a nonpreferred direction in the switching current direction, and subsequently, close the contactor having a preferred direction in the switching current direction.

In this way, it is possible to either break or complete the circuit using the contactor that has a preferred direction in the same direction as the current, such that the contactor that breaks or completes the circuit (and therefore switches when current is flowing) is the contactor that has the highest resistance to welding for the current direction.

Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:.

Rechargeable batteries such as those used in electric work vehicles may use the same circuit for discharging (such as when the electric work vehicle is in use) and for charging. With reference to <FIG>, in an embodiment of the present disclosure, battery module <NUM> is configured to be charged and discharged via a first circuit. The first circuit comprises a contactor assembly <NUM>, the contactor assembly comprising a first contactor <NUM> and a second contactor <NUM>. The first contactor <NUM> is in series with the second contactor <NUM>. Each of the first contactor <NUM> and the second contactor <NUM> is configured to have a higher resistance to welding for a switching current flowing in a preferred direction than in a nonpreferred direction. The first contactor <NUM> is configured to have a preferred direction in a first direction, indicated by arrow <NUM>, and a nonpreferred direction in a second direction. The second direction is opposite to the first direction. The second contactor <NUM> is configured to have a preferred direction in the second direction, indicated by an arrow <NUM>, and a nonpreferred direction in the first direction.

It will be understood that the first and second directions refer to current flow through the first circuit and therefore through the first and second contactors <NUM> and <NUM>, and that the contactors may not be physically aligned with one another. For example, if a current is flowing through the first circuit in the first direction the current will flow through both the first contactor <NUM> and the second contactor <NUM> in the first direction, even if the first contactor <NUM> is physically at a finite angle with respect to the second contactor <NUM> (for example an angle that is neither <NUM> degrees nor <NUM> degrees).

The first contactor <NUM> and the second contactor <NUM> are shown as being on opposite sides of the battery module <NUM>. Alternatively, the first contactor <NUM> and the second contactor <NUM> may be arranged on the same side of the battery module <NUM>.

In response to an instruction to switch the contactor assembly <NUM>, a battery management system is configured to determine whether the switching current direction is in the first direction or in the second direction. In an event that the instruction to switch comprises an instruction to open the contactor assembly, the battery management system is configured to first open the contactor having a preferred direction in the switching current direction, and to subsequently open the contactor having a nonpreferred direction in the switching current direction. In an event that the instruction to switch comprises an instruction to close the series contactor assembly, the battery management system is configured to first close the contactor having a nonpreferred direction in the switching current direction, and to subsequently close the contactor having a preferred direction in the switching current direction.

In an embodiment, a method of switching a contactor assembly for a battery module of an electric work vehicle is provided, wherein the electric work vehicle comprises a battery management system. The battery module is configured to be charged and discharged via a first circuit. The first circuit comprises the contactor assembly, the contactor assembly comprising a first contactor and a second contactor, wherein the first contactor is in series with the second contactor. Each of the first contactor and the second contactor is configured to have a higher resistance to welding for a switching current flowing in a preferred direction than in a nonpreferred direction. The first contactor is configured to have a preferred direction in a first direction and a nonpreferred direction in a second direction. The second contactor is configured to have a preferred direction in the second direction and a nonpreferred direction in the first direction. In response to an instruction to switch the contactor assembly, the method comprises using the battery management system to determine whether the switching current direction is in the first direction or in the second direction. In an event that the instruction to switch comprises an instruction to open the contactor assembly, the method comprises first, opening the contactor having a preferred direction in the switching current direction and subsequently, opening the contactor having a nonpreferred direction in the switching current direction. In an event that the instruction to switch comprises an instruction to close the contactor assembly the method comprises first, closing the contactor having a nonpreferred direction in the switching current direction, and subsequently, closing the contactor having a preferred direction in the switching current direction.

<FIG> shows an example of the stages of opening a contactor assembly <NUM> with the current flowing in the first direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM> and the second contactor <NUM> are closed. In response to an instruction to open the contactor assembly, the first contactor to be opened is the contactor with a preferred direction in the same direction as the current. In this case the current is in the first direction so the first contactor <NUM> is opened first. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> has been opened, with the first contactor <NUM> open and the second contactor <NUM> closed. Opening the first contactor <NUM> breaks the first circuit, so the first circuit is broken by opening the contactor with the preferred direction in the same direction as the current (in the Figures, a dashed circle will be used to indicate opening the contactor that breaks the first circuit in response to an instruction to open the contactor assembly, or closing the contactor that completes the first circuit in response to an instruction to close the contactor assembly). The second contactor to be opened is the contactor with a nonpreferred direction in the same direction as the current, such that the contactor with a nonpreferred direction in the same direction as the current is opened when the current is no longer flowing. In this case the current is in the first direction so the second contactor <NUM> is opened second. <FIG> shows the contactor assembly <NUM> with both the first contactor <NUM> and the second contactor <NUM> open.

<FIG> (and <FIG>, described shortly) show the first contactor <NUM> and the second contactor <NUM> arranged on opposite sides of the battery module <NUM>. Alternatively, the first contactor <NUM> and the second contactor <NUM> may be arranged on the same side of the battery module <NUM>.

<FIG> shows an example of the stages of opening a contactor assembly <NUM> with the current flowing in the second direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM> and the second contactor <NUM> are closed. In response to an instruction to open the contactor assembly, the first contactor to be opened is the contactor with a preferred direction in the same direction as the current. In this case the current is in the second direction so the second contactor <NUM> is opened first. <FIG> shows the contactor assembly <NUM> after the second contactor <NUM> has been opened, with the second contactor <NUM> open and the first contactor <NUM> closed. Opening the second contactor <NUM> (as indicated by a dashed circle) breaks the first circuit, so the first circuit is broken by opening the contactor with the preferred direction in the same direction as the current. The second contactor to be opened is the contactor with a nonpreferred direction in the same direction as the current, such that the contactor with a nonpreferred direction in the same direction as the current is opened when the current is no longer flowing. In this case the current is in the second direction so the first contactor <NUM> is opened second. <FIG> shows the contactor assembly <NUM> with both the first contactor <NUM> and the second contactor <NUM> open.

<FIG> shows an example of the stages of closing a contactor assembly <NUM> with the current flowing in the first direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM> and the second contactor <NUM> are open. In response to an instruction to close the contactor assembly, the first contactor to be closed is the contactor with a nonpreferred direction in the same direction as the current, such that the contactor with a nonpreferred direction in the same direction as the current is closed when the current is not flowing. In this case the current is in the first direction so the second contactor <NUM> is closed first. <FIG> shows the contactor assembly <NUM> after the second contactor <NUM> has been closed, with the second contactor <NUM> closed and the first contactor <NUM> open. The second contactor to be closed is the contactor with a preferred direction in the same direction as the current. In this case the current is in the first direction so the first contactor <NUM> is closed second. <FIG> shows the contactor assembly <NUM> with both the first contactor <NUM> and the second contactor <NUM> closed. Closing the first contactor <NUM> (indicated by a dashed circle) completes the first circuit, so the first circuit is completed by closing the contactor with the preferred direction in the same direction as the current.

<FIG> shows an example of the stages of closing a contactor assembly <NUM> with the current flowing in the second direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM> and the second contactor <NUM> are open. In response to an instruction to close the contactor assembly, the first contactor to be closed is the contactor with a nonpreferred direction in the same direction as the current, such that the contactor with a nonpreferred direction in the same direction as the current is closed when the current is not flowing. In this case the current is in the second direction so the first contactor <NUM> is closed first. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> has been closed, with the first contactor <NUM> closed and the second contactor <NUM> open. The second contactor to be closed is the contactor with a preferred direction in the same direction as the current. In this case the current is in the second direction so the second contactor <NUM> is closed second. <FIG> shows the contactor assembly <NUM> with both the first contactor <NUM> and the second contactor <NUM> closed. Closing the second contactor <NUM> (indicated by a dashed circle) completes the first circuit, so the first circuit is completed by closing the contactor with the preferred direction in the same direction as the current.

With reference to <FIG> a contactor assembly <NUM> may further comprise a third contactor <NUM>, the third contactor <NUM> having a preferred direction (indicated by arrow <NUM>) in the first direction and a nonpreferred direction in the second direction. The third contactor <NUM> may be in parallel with the first contactor <NUM>, such that the parallel arrangement of the first contactor <NUM> and the third contactor <NUM> is in series with the battery module <NUM> and with the second contactor <NUM>. <FIG> shows the parallel arrangement on the opposite side of the battery module <NUM> to the second contactor <NUM>, but the parallel arrangement and the second contactor <NUM> may be arranged on the same side of the battery module <NUM>.

<FIG> shows an example of the stages of opening the contactor assembly <NUM> of <FIG> with the current flowing in the first direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> are closed. In response to an instruction to open the contactor assembly, the first contactor to be opened is a contactor with a preferred direction in the same direction as the current. In this case the current is in the first direction so either the first contactor <NUM> or the third contactor <NUM> may be opened first. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> has been opened, with the second contactor <NUM> and the third contactor <NUM> still closed. The second contactor to be opened is the other contactor with the preferred direction in the same direction as the current, so the third contactor <NUM> is opened second. Opening the third contactor <NUM> (as indicated by a dashed circle) breaks the first circuit, so the first circuit is broken by opening the contactor with the preferred direction in the same direction as the current. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> and the third contactor <NUM> have been opened, with the second contactor <NUM> still closed. The third contactor to be opened is the contactor with a nonpreferred direction in the same direction as the current, such that the contactor with a nonpreferred direction in the same direction as the current is opened when the current is not flowing. In this case the current is in the first direction so the second contactor <NUM> is opened third. <FIG> shows the contactor assembly <NUM> with the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> open.

<FIG> shows an example of the stages of opening the contactor assembly <NUM> of <FIG> with the current flowing in the second direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> are closed. In response to an instruction to open the contactor assembly, the first contactor to be opened is a contactor with a preferred direction in the same direction as the current. In this case the current is in the second direction so the second contactor <NUM> is opened first. <FIG> shows the contactor assembly <NUM> after the second contactor <NUM> has been opened, with the first contactor <NUM> and the third contactor <NUM> still closed. Opening the second contactor <NUM> (as indicated by a dashed circle) breaks the first circuit, so the first circuit is broken by opening the contactor with the preferred direction in the same direction as the current. The second contactor to be opened may be either of the contactors with the nonpreferred direction in the same direction as the current. In this example the first contactor <NUM> is opened second. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> and the second contactor <NUM> have been opened, with the third contactor <NUM> still closed. The third contactor to be opened is the other contactor with a nonpreferred direction in the same direction as the current. The third contactor <NUM> is opened third. <FIG> shows the contactor assembly <NUM> with the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> open. Both the contactors with a nonpreferred direction in the same direction as the current are opened when the current is not flowing.

<FIG> shows an example of the stages of closing the contactor assembly <NUM> of <FIG> with the current flowing in the first direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> are open. In response to an instruction to close the contactor assembly, the first contactor to be closed is the contactor with a nonpreferred direction in the same direction as the current. In this case the current is in the first direction so the second contactor <NUM> is closed first. <FIG> shows the contactor assembly <NUM> after the second contactor <NUM> has been closed, with the first contactor <NUM> and the third contactor <NUM> still open. The contactor with a nonpreferred direction in the same direction as the current is therefore closed when the current is not flowing. The second contactor to be closed may be either of the contactors with the preferred direction in the same direction as the current. In this example the first contactor <NUM> is closed second. Closing the first contactor <NUM> (as indicated by a dashed circle) completes the first circuit, so the first circuit is completed by closing a contactor with a preferred direction in the same direction as the current. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> and the second contactor <NUM> have been closed, with the third contactor <NUM> still open. The third contactor to be closed is the other contactor with a preferred direction in the same direction as the current. The third contactor <NUM> is closed third. <FIG> shows the contactor assembly <NUM> with the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> closed.

<FIG> shows an example of the stages of closing the contactor assembly <NUM> of <FIG> with the current flowing in the second direction (indicated by arrow <NUM>). In <FIG>, the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> are open. In response to an instruction to close the contactor assembly, the first contactor to be closed is one of the contactors with a nonpreferred direction in the same direction as the current. In this case the current is in the second direction so either the first contactor <NUM> or the third contactor <NUM> are closed first. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> has been closed, with the second contactor <NUM> and the third contactor <NUM> still open. <FIG> shows the contactor assembly <NUM> after the first contactor <NUM> and the third contactor <NUM> have been closed, with the second contactor <NUM> still open. Both contactors with a nonpreferred direction in the same direction as the current is therefore closed when the current is not flowing. The third contactor to be closed is the contactors with the preferred direction in the same direction as the current. Here, the current is in the second direction so the second contactor <NUM> is closed third. Closing the second contactor <NUM> (as indicated by a dashed circle) completes the first circuit, so the first circuit is completed by closing a contactor with a preferred direction in the same direction as the current. <FIG> shows the contactor assembly <NUM> with the first contactor <NUM>, the second contactor <NUM> and the third contactor <NUM> closed.

In an embodiment, a contactor assembly may comprise a plurality of battery modules arranged in parallel in a battery pack.

With reference to <FIG>, a contactor assembly <NUM> is shown with a battery pack <NUM> comprising four battery modules <NUM>, <NUM>, <NUM> and <NUM>. It will be understood that the battery pack <NUM> may comprise two, three or more than four battery modules. A first contactor <NUM> is arranged in series with the battery pack <NUM>. The first contactor has a preferred direction (indicated by arrow <NUM>) in the first direction and a nonpreferred direction in the second direction. The second contactor <NUM> is arranged in series with a first battery module <NUM>. The second contactor has a preferred direction (indicated by arrow <NUM>) in the second direction and a nonpreferred direction in the first direction. Each of a plurality of additional contactors are arranged in series with each of the remaining battery modules, wherein each additional contactor is equivalent to the second contactor <NUM>. In the example shown in <FIG>, a third contactor <NUM> is arranged in series with a second battery module <NUM>, a fourth contactor <NUM> is arranged in series with a third battery module <NUM> and a fifth contactor <NUM> is arranged in series with a fourth battery module <NUM>. The third, fourth and fifth contactors <NUM>, <NUM> and <NUM> each have a preferred direction (indicated by arrows <NUM>, <NUM> and <NUM>) in the second direction and a nonpreferred direction in the first direction. In response to an instruction to switch the contactor assembly <NUM>, the contactors will be opened or closed in the same way as described for the contactor assembly <NUM>, such that the contactors with a nonpreferred direction in the same direction as the current are switched when the current is not flowing. The contactor that breaks or completes the first circuit has a preferred direction in the same direction as the current.

With reference to <FIG>, a contactor assembly <NUM> is shown with a battery pack <NUM> comprising four battery modules <NUM>, <NUM>, <NUM> and <NUM>. It will be understood that the battery pack <NUM> may comprise two, three or more than four battery modules. A first contactor <NUM> is arranged in series with a first battery module <NUM>. The first contactor <NUM> has a preferred direction (indicated by arrow <NUM>) in the first direction and a nonpreferred direction in the second direction. A second contactor <NUM> is arranged in series with the battery pack <NUM>. The second contactor has a preferred direction (indicated by arrow <NUM>) in the second direction and a nonpreferred direction in the first direction. Each of a plurality of additional contactors are arranged in series with each of the remaining battery modules, wherein each additional contactor is equivalent to the first contactor <NUM>. In the example shown in <FIG>, a third contactor <NUM> is arranged in series with a second battery module <NUM>, a fourth contactor <NUM> is arranged in series with a third battery module <NUM> and a fifth contactor <NUM> is arranged in series with a fourth battery module <NUM>. The third, fourth and fifth contactors <NUM>, <NUM> and <NUM> each have a preferred direction (indicated by arrows <NUM>, <NUM> and <NUM>) in the first direction and a nonpreferred direction in the second direction. In response to an instruction to switch the contactor assembly <NUM>, the contactors will be opened or closed in the same way as described for the contactor assembly <NUM>, such that the contactors with a nonpreferred direction in the same direction as the current are switched when the current is not flowing. The contactor that breaks or completes the first circuit has a preferred direction in the same direction as the current.

Although the term contactor has been used, the contactors described above may comprise any switch for an electrical circuit that may be opened and closed by a controller. The contactors may comprise electrically controlled switches or relays.

In an embodiment, the contactors may comprise a moving arm and a plate, wherein the arm makes contact with the plate when the contactor is closed. For example, the first contactor may be configured such that current flowing in the first direction flows from the fixed plate to the movable arm, and current flowing in the second direction flows from the movable arm to the fixed plate. The second contactor may be configured such that current flowing in the first direction flows from the movable arm to the fixed plate, and current flowing in the second direction flows from the fixed plate to the movable arm. In another example, the first contactor may be configured such that current flowing in the first direction flows from the movable arm to the fixed plate, and current flowing in the second direction flows from the fixed plate to the movable arm, The second contactor may be configured such that current flowing in the first direction flows from the fixed plate to the movable arm, and current flowing in the second direction flows from the movable arm to the fixed plate.

Having more than one contactor in a circuit, for example as in the embodiments described herein, allows redundancies in the circuit such that in the event that a contactor does weld shut, the circuit can be broken by another contactor. This helps to prevent the circuit failing in a closed state.

Claim 1:
A circuit comprising a contactor assembly (<NUM>) for a battery module of an electric work vehicle and a battery management system, wherein in use, the battery module is configured to be charged and discharged via the circuit and wherein:
the circuit comprises the contactor assembly (<NUM>), the contactor assembly comprising a first contactor (<NUM>) and a second contactor (<NUM>), wherein the first contactor (<NUM>) is in series with the second contactor (<NUM>); and characterised in that:
each of the first contactor (<NUM>) and the second contactor (<NUM>) is configured to have a higher resistance to welding for a switching current flowing in a preferred direction than in a nonpreferred direction;
the first contactor is configured to have a preferred direction (<NUM>) in a first direction and a nonpreferred direction in a second direction; and
the second contactor is configured to have a preferred direction (<NUM>) in the second direction and a nonpreferred direction in the first direction;
in response to an instruction to switch the contactor assembly (<NUM>), the battery management system is configured to:
determine whether the switching current direction is in the first direction or in the second direction;
in an event that the instruction to switch comprises an instruction to open the contactor assembly (<NUM>):
first, open the contactor having a preferred direction in the switching current direction; and
subsequently, open the contactor having a nonpreferred direction in the switching current direction;
in an event that the instruction to switch comprises an instruction to close the series contactor assembly (<NUM>):
first, close the contactor having a nonpreferred direction in the switching current direction; and
subsequently, close the contactor having a preferred direction in the switching current direction.