Electromagnetic actuator

Abstract

Actuator apparatus is provided. The actuator apparatus comprises a first electromagnet switchable between a first on-state in which current flows through the first electromagnet in a first direction and a second on-state in which current flows through the first electromagnet in a second direction opposite the first direction. The actuator apparatus further comprises a second electromagnet operable in a first on-state in which current flows through the second electromagnet. The actuator apparatus further comprises a plunger movable between first and second positions, the actuator apparatus being configured to hold the plunger in the first position when the first and second electromagnets are in their respective first on-states depending on magnetic flux generated by the first and second electromagnets. The actuator apparatus further comprises switching circuitry for switching the first electromagnet from its first on-state to its second on-state to trigger movement of the plunger from the first position towards the second position. A switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from an off-state to its first on-state.

Description

[0001] ELECTROMAGNETIC ACTUATOR

[0002] BACKGROUND

[0003] Electromagnetic actuators convert electrical energy into mechanical energy in the form of movement of a plunger. Typical electromagnetic actuators comprise a moveable plunger and a single solenoid coil operable to selectively generate a magnetic field which attracts the plunger towards the solenoid coil. The plunger is typically biased by a spring such that it is urged towards and maintained at a nominal position away from the solenoid coil when the solenoid coil is not generating a magnetic field. Actuation of the plunger is typically effected by generating a potential difference across the solenoid coil, which causes current to flow through the solenoid coil and which in turn generates a magnetic field that attracts the plunger from the nominal position towards the solenoid coil to an end-stop position. When the potential difference is generated across the solenoid coil, current starts to flow through the solenoid coil and increases up to a steady state value at a rate depending on an electrical time constant, T, of the solenoid coil which is directly proportional to the inductance thereof. Movement of the plunger from the nominal position is triggered when the current flowing through the solenoid coil reaches a sufficiently high level that the magnetic field generated thereby is sufficient to exert an attractive force on the plunger which overcomes a biasing force of the spring. Accordingly, there is a delay between the time at which the potential difference across the solenoid coil is first generated and the time at which movement of the plunger commences. This delay may be referred to as a “triggering delay”. Once movement of the plunger commences, the plunger takes a certain amount of time to travel from the nominal position to the end-stop position. This time may be referred to as the “transit time”. The (i.e. total) actuation time taken from signalling the actuator to actuate (i.e. generating the potential difference across the solenoid coil) to the plunger reaching the end-stop position depends on the sum of the triggering delay and the transit time.

[0004] In some applications, electromagnetic actuators having relatively low actuation times may be particularly desirable. However, reducing the actuation time of known electromagnetic actuators such as those described above may be particularly challenging. For example, the transit time may depend on the (e.g. mean) force exerted on the plunger by the magnetic field of the solenoid coil during movement of the plunger from the nominal position to the end-stop position. This force may depend on the magnetic flux density generated by the solenoid coil, which may be increased by e.g. increasing the current flowing through the solenoid coil in an on-state or e.g. increasing the turn density of the solenoid coil. However, current cannot be increased in a solenoid coil instantaneously; rather the rate at which current can be increased in a solenoid coil is limited by its electrical time constant T. Accordingly, operating a given solenoid coil at a higher on-state current requires a longer time to fully energise the coil i.e. to allow the current to reach such a higher on-state value. Hence, increasing the nominal on-state current of a solenoid coil may have little effect on the force exerted on the plunger during its movement from the nominal position to the endstop position because movement of the plunger from the nominal position to the end stop position may be triggered, or indeed, completed, before the solenoid coil has had enough time to be fully energised i.e. for its current to reach its nominal on-state value. Furthermore, increasing the turn density of a solenoid typically increases its inductance (e.g. assuming constant solenoid length), and therefore, its electrical time constant T, which in turn may give rise to longer triggering delays and may increase the time required to fully energise the coil, and therefore, reduce the extent to which the coil is energised during movement of the plunger from the nominal position to the end-stop position.

[0005] Accordingly, there remains a need for an electromagnetic actuator having an improved actuation time.

[0006] BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Examples are further described with reference to the accompanying drawings, in which:

[0008] Fig. 1 schematically illustrates an example actuator;

[0009] Figs. 2A-B schematically illustrate first and second magnetic circuits of the actuator shown in Fig. 1 ;

[0010] Figs. 3A-D schematically illustrate an example sequence of states of the actuator shown in Fig. 1 ;

[0011] Fig. 4 graphically depicts various parameters of the actuator shown in Fig. 1 during an example sequence of states thereof;

[0012] Fig. 5 schematically illustrates an example electronically controllable valve;

[0013] Fig. 6 schematically illustrates an example fluid working machine;

[0014] Fig. 7 schematically illustrates a controller;

[0015] Fig. 8 is a flow diagram of a method for controlling an actuator; and

[0016] Fig. 9 is a flow diagram of a method of operating an actuator.

[0017] DETAILED DESCRIPTION

[0018] In accordance with the present disclosure, an actuator comprises a first (e.g. trigger) electromagnet, a second (e.g. primer) electromagnet, a plunger, and switching circuitry. The actuator may additionally comprise one or more magnetic conductors (e.g. which may be included in respective magnetic circuits of one or both of the first electromagnet and the second electromagnet). The actuator may additionally comprise a biaser. The actuator may additionally comprise a housing which may house any one or more of the components or features of the actuator disclosed herein, such as any one or more of: the first electromagnet; the second electromagnet; the plunger; the switching circuitry; the biaser; the one or more magnetic conductors.

[0019] Fig. 1 schematically shows a cross section of an example actuator 100 comprising a first (e.g. trigger) electromagnet comprising a first (e.g. solenoid) coil 110 of an electrically conductive wire, a second (e.g. primer) electromagnet comprising a second (e.g. solenoid) coil 120 of an electrically conductive wire, a plunger 130, an actuating member 135, switching circuitry 140, and one or more magnetic conductors 170. It is to be understood that the particular configuration of the example actuator 100 shown in Fig. 1 is merely for illustrative purposes and that the present disclosure is not so limited. For example, the magnetic conductor(s) 170 may be omitted in some examples.

[0020] The actuator 100 shown in Fig. 1 may be symmetrical about an axis 105. Fig. 1 shows the right-hand side of the cross section relative to the axis 105; the left-hand side of the crosssection of the actuator 100 may be a mirror image of the right-hand side of the actuator 100 reflected about the axis 105.

[0021] The first electromagnet may comprise a first electrical terminal and a second electrical terminal electrically coupled to the said first electrical terminal by way of the first coil 110, the first coil 110 comprising a first number of turns. It may be that the first electromagnet is configured to selectively operate in one or more of the following states (e.g. by way of the switching circuitry 140): a first on-state wherein current flows through the first coil 110 of the first electromagnet in a first direction (e.g. from the first electrical terminal to the second electrical terminal of the first electromagnet); a second on-state wherein current flows through the first coil 110 of the first electromagnet in a second direction, opposite the first direction (e.g. from the second electrical terminal to the first electrical terminal of the first electromagnet); a third on-state wherein current flows through the first coil 110 of the first electromagnet in the first or second direction (e.g., between the first and second electrical terminals of the first electromagnet); an off-state wherein a low (e.g., lower than in the on- states) or negligible amount of (e.g. substantially zero) current flows through the first coil 110 of the first electromagnet. It may be that the first electromagnet is switchable (e.g. by way of the switching circuitry 140) between any two of the said first on-state, second on- state, third on-state, off-state. It may be that the first coil 110 surrounds a first portion of the axis 105.

[0022] The third on-state of the first electromagnet may be identical to the first or second on-states of the first electromagnet, in which case the third on-state of the first electromagnet is the same as the first or second on-state (as the case may be). The second electromagnet may comprise a first electrical terminal and a second electrical terminal electrically coupled to the said first electrical terminal by way of the second coil 120, the second coil 120 comprising a second number of turns. It may be that the second electromagnet is configured to selectively operate in one or more of the following states (e.g. by way of driver circuitry, not shown): a first on-state wherein current flows through the second coil 120 of the second electromagnet in a first direction (e.g. from the first electrical terminal to the second electrical terminal of the second electromagnet); an off-state wherein a low (e.g., lowerthan in the on-state) or negligible amount of (e.g. substantially zero) current flows through the second coil 120 of the second electromagnet. It may be that the second coil 120 surrounds a second portion of the axis 105.

[0023] The plunger 130 of the actuator 100 is movable between a first (e.g. end-stop) position 150 and a second (e.g. end-stop) position 160. It may be that the plunger 130 is movable between the first and second positions 150, 160 along a (e.g. linear) axis. It may be that the first coil 110 of the first electromagnet and the second coil 120 of the second electromagnet are spaced apart with respect to the said axis. It may be that the said axis is substantially parallel to the axis 105.

[0024] The actuating member 135 may be mechanically coupled to (e.g. attached to or integrally formed with) the plunger 130. As will be discussed further below in relation to Fig. 5, the actuating member 135 may be mechanically couplable or coupled to e.g. a valve member of a valve comprising the actuator 100, in which case the actuating member 135 may act as a valve stem by which the position of the valve member may be controlled to open and close the valve.

[0025] Depending on operation states of the first and second electromagnets, the plunger 130 may be held in the first (e.g. end-stop) position 150, held in the second (e.g. end-stop) position 160 or moved between the first and second positions 150, 160. This is explained briefly as follows with reference to Fig. 1. A more detailed discussion is provided further below, for example in relation to Figs. 2-4.

[0026] When the plunger 130 is at the first position 150, the actuator 100 may be configured to hold the plunger 130 at that position depending on a magnetic field generated by the first electromagnet operating in the first on-state thereof (in which, as mentioned above, electrical current is caused to flow through the coil 110 of the first electromagnet in a first direction). While the plunger 130 is held in the first position 150 depending on the magnetic field generated by the first electromagnet operating in its first on-state, the second electromagnet can be energised from an off-state (e.g. in which substantially no electrical current flows through the coil 120 of the second electromagnet) to its first on-state in which electrical current is caused to flow through the coil 120 of the second electromagnet. The apparatus is configured to hold the plunger 130 in the first position 150 when the first electromagnet is in its first on-state and the second electromagnet is in its first on-state. That is, the magnetic field generated by the combination of the first electromagnet in its first on-state and the second electromagnet in its first on-state does not cause movement of the plunger 130 away from the first position 150 towards the second position 160. Indeed, it may be that some magnetic flux components generated by the first and second electromagnets in their respective first on-states positively combine with each other, whereby the plunger 130 is held in the first position 150. The second electromagnet can thus be (e.g. “fully”) energised (e.g. to a desired level) while the plunger 130 remains in the first position 150.

[0027] Once the second electromagnet has been energised, movement of the plunger 130 away from the first position 150 towards the second position 160 may be triggered by (e.g. while maintaining the second electromagnet in its first on-state) switching, by switching circuitry 140, the first electromagnet from its first on-state to its second on-state in which current flows through the second electromagnet in a second direction, opposite the first direction. This induces a gradient of magnetic flux across the plunger 130 (e.g. wherein a total flux received by a first surface of the plunger 130 nearest the first position 150, such as the first surface 130a described below, is less than a total flux received by a second surface of the plunger 130 nearest the second position 160, such as the second surface 130b described below) which causes a (e.g. relatively high) force to act on the plunger 130, moving the plunger 130 away from the first position 150 towards the second position 160. For example, the gradient of magnetic flux may be generated by the magnetic field generated by the first electromagnet operating in the second on-state at least partially cancelling a portion of the magnetic field generated by the second electromagnet in a vicinity of the first position 150. This at least partial cancelling of the portion of the magnetic field generated by the second electromagnet in the vicinity of the first position 150 may give rise to a greater gradient of magnetic flux across the plunger 130 relative to e.g. the case where the second electromagnet is in its first on-state and the first electromagnet is in its off-state. Hence, switching the first electromagnet from its first on-state to its second on-state to trigger movement of the plunger from the first position 150 towards the second position 160, as opposed to merely switching the first electromagnet from its first on-state to its off-state, may advantageously generate a greater force acting on the plunger 130 in a direction extending away from the first position 150 towards the second position 160, which may in turn provide for a reduced actuation time and more precise actuation timing.

[0028] The plunger 130 may accelerate as it moves away from the first position 150 towards the second position 160 as the magnetic flux gradient across the plunger 130 may increase as the plunger 130 moves towards the second position 160. The above-described holding and triggering mechanism may advantageously provide for particularly short actuation times for the plunger 130 moving from the first position 150 to the second position 160, and more precise actuation timing.

[0029] When the plunger 130 is in the second position 160, it may be held in the second position 160 by way of a magnetic field generated by the combination of the first electromagnet operating in its second on-state and the second electromagnet operating in its first on-state. The first electromagnet may be switched off once the plunger 130 reaches the second position 160, and the plunger 130 may be held in the second position 160 by the magnetic field generated by the second electromagnet. Alternatively, the first electromagnet may be switched to a third on-state once the plunger 130 reaches the second position 160, and the plunger 130 may be held in the second position 160 in the presence of the magnetic field generated by the combination of the first electromagnet operating in its third on-state and the second electromagnet operating in its first on-state.

[0030] The plunger 130 may be returned to the first position 150 by way of a magnetic field generated by the first electromagnet operating in the third on-state exerting a sufficiently attractive force on the plunger 130 to cause movement thereof from the second position 160 to the first position 150. Additionally or alternatively, the plunger 130 may be returned to the first position 150 from the second position 160 by way of a biaser, such as a spring. The second electromagnet may be switched from its first on-state to its off-state before the plunger 130 starts moving (e.g., to allow the magnetic field generated by the first electromagnet operating in its third on-state to cause movement of the plunger 130) away from the second position towards the first position.

[0031] It may be that the second electromagnet is configured to store more energy in its magnetic field than the first electromagnet when in their respective first on-states. The first and second electromagnets may be configured in any suitable manner to provide for such greater energy storage of the second electromagnet. For example, the second electromagnet may be configured to have a higher on-state current than the first electromagnet when in their respective first on-states, the second electromagnet may have a greater inductance than the first electromagnet, or the second electromagnet may both be configured to have a higher on-state current than the first electromagnet when they are in their respective first on- states and have a greater inductance than the first electromagnet. By virtue of the abovedescribed greater energy storage of the second electromagnet, it may be that the second electromagnet is, for a given distance to the plunger 130, operable to exert a greater attractive force on the plunger 130 than the first electromagnet when in their respective first on-states. It may be that for each of the first and second electromagnets, the attractive force which they can independently exert on the plunger 130 depends on a position of the plunger 130 relative to the first and second position 150, 160. For example, the attractive force which the first electromagnet can exert on the plunger 130 may depend on a (e.g. shortest) distance between the plunger 130 and the first position 150, and the attractive force which the second electromagnet can exert on the plunger 130 may depend on a (e.g. shortest) distance between the plunger 130 and the second position 160. Thus, it may be that the plunger 130 is held at the first position 150 when the first and second electromagnets are in their respective first on-states by virtue of a (e.g. shortest) distance between the first position 150 and the plunger 130 being less than a (e.g. shortest) distance between the second position 160 when the plunger 130 is at the first position 150.

[0032] References to the “off-states” of the first and second electromagnets may be references to states in which the first and second electromagnets are fully switched off (e.g., with substantially no electrical current flowing through them), or to states in which they are not fully switched off, but for example remain on with a relatively low level of electrical current flowing through them (e.g., relative to their “on-states”).

[0033] A time taken for the second electromagnet to transition from its off-state to its first on-state may be referred to as its “energising time”. The energising time of the second electromagnet may correspond to a time taken for electrical current flowing through the second electromagnet to increase from its off-state value (e.g. substantially zero), or some other default value, to its first on-state value. The energising time of the second electromagnet may depend on, for example, the electrical time constant of the second electromagnet (which may depend on the inductance of the second electromagnet). Additionally, the energising time of the second electromagnet may depend on a magnitude of the electrical current to flow through the coil 120 of the second electromagnet in its first on-state.

[0034] It may be that the first position 150 is defined by a first (e.g. magnetic insulator) end-stop (not shown) which may prevent the plunger 130 from sticking to the first electromagnet e.g. by way of preventing movement of the plunger 130 beyond the first position 150 e.g. in a direction extending away from the second position 160 towards the first position 150. It may be that the second position 160 is defined by a second (e.g. magnetic insulator) end-stop (not shown) which may prevent the plunger 130 from sticking to the second electromagnet e.g. by way of preventing movement of the plunger 130 beyond the second position 160 e.g. in a direction extending away from the first position 150 towards the second position 160.

[0035] As mentioned, movement of the plunger 130 between the first position 150 and the second position 160 may be caused by magnetic field(s) generated by one or both of the first electromagnet and the second electromagnet. Accordingly, the plunger 130 is configured such that a force is exerted thereon when the plunger 130 is in the presence of a magnetic field e.g. when there is a gradient of magnetic flux across the plunger 130. The greater the magnetic flux gradient across the plunger 130, the greater the force exerted on the plunger 130. It may be that the plunger 130 comprises a ferromagnetic material. As used herein, the term “ferromagnetic” may be used to refer to any material comprising a suitably high magnetic permeability to enable the plunger 130 to move under the influence of a magnetic field generated by one or both of the first and second electromagnets. It may be that the plunger 130 comprises a material comprising any one, or any combination of (e.g. as part of one or more alloys): iron; cobalt; nickel. For example, it may be that that plunger 130 comprises an iron-based alloy such as steel. It may be that the plunger 130 comprises a permanent magnet e.g. having magnetic dipole moment and associated magnetic field in the absence of an external magnetic field. It will be assumed in the following that, unless otherwise stated, the plunger 130 comprises ferromagnetic material but does not comprise a permanent magnet. However, as mentioned, it will be understood that the plunger 130 may alternatively comprise a permanent magnet.

[0036] As mentioned, the actuator 100 may comprise a biaser. When present, the biaser may be arranged to apply a biasing force to the plunger 130 to return the plunger 130 to, and hold (e.g. maintain) the plunger 130 at, a nominal position (e.g. the first position 150 or the second position 160) e.g. when neither the first electromagnet nor the second electromagnet are generating respective magnetic fields e.g. when the actuator 100 is an off-state. For example, the said nominal position may correspond to the second position 160 and the biaser may be arranged to apply a biasing force to the plunger 130 when the plunger 130 is at the first position 150, wherein the biasing forces acts in a direction extending away from the first position 150 towards the second position 160 to thereby return the plunger 130 to the second position 160 e.g. when neither the first electromagnet nor the second electromagnet are generating respective magnetic fields e.g. when the actuator 100 is an off-state. In such examples, when the plunger 130 is at the second position 160, the biaser may be arranged to hold (e.g. maintain) the plunger 130 at the second position 160 e.g. when neither the first electromagnet nor the second electromagnet are generating respective magnetic fields e.g. when the actuator 100 is an off-state. Alternatively, the said nominal position may correspond to the first position 150 and the biaser may be arranged to apply a biasing force to the plunger 130 when the plunger 130 is at the second position 160, wherein the biasing force acts in a direction extending away from the second position 160 towards the first position 150 to thereby return the plunger 130 to the first position 150 e.g. when neither the first electromagnet nor the second electromagnet are generating respective magnetic fields e.g. when the actuator 100 is an off-state. In such examples, when the plunger 130 is at the first position 150, the biaser may be arranged to hold (e.g. maintain) the plunger 130 at the first position 150 e.g. when neither the first electromagnet nor the second electromagnet are generating respective magnetic fields e.g. when the actuator 100 is an off-state.

[0037] The biaser may comprise a spring or any other suitable biaser. In examples where the biaser is not present, it may be that the plunger 130 is urged towards and held (e.g. maintained) at the said nominal position e.g. by way of generating suitable magnetic field(s) from one or both of the first electromagnet and the second electromagnet.

[0038] As discussed above, the switching circuitry 140 is operable to control respective states of the first electromagnet. The switching circuitry 140 may be operable to induce respective states of the first electromagnet responsive to a control signal e.g. received from a controller (not shown), such as the controller 700 described below in relation to Fig. 7. For example, the switching circuitry 140 may be operable to, in a first mode, induce the first on-state of the first electromagnet. Additionally, the switching circuitry 140 may be operable to, in a second mode, induce the second on-state of the first electromagnet. The switching circuitry 140 may be operable to, in a third mode, induce the third on-state of the first electromagnet. It will be understood that the third on-state of the first electromagnet may be identical to the first or second on-states, in which case the third mode of the switching circuitry is the same mode as the first or second mode (as the case may be) - i.e. it may be that there is no separate third mode of the switching circuitry and that the third on-state (when identical to the first or second on-states) is induced by operating the switching circuitry 140 in the first or second mode (as the case may be). Additionally, the switching circuitry 140 may be operable to, in a fourth mode, induce the off-state of the first electromagnet. A mode of the switching circuitry 140 (e.g. the first, second, third mode, or fourth mode of the switching circuitry 140) may be invoked responsive to a control signal e.g. received from a controller (not shown), such as the controller 700 described in relation to Fig. 7.

[0039] It may be that, in the first mode, the switching circuitry 140 is configured to selectively cause a flow of electrical current through the first coil 110 of the first electromagnet in a first direction (e.g. from the first electrical terminal to the second terminal of the first electromagnet e.g. by way of generating a first potential difference across the said first and second electrical terminals, the first potential difference having a first polarity) to induce the first on-state of the first electromagnet. As discussed, the first on-state of the first electromagnet may refer to a state of the first electromagnet wherein a magnitude of current flowing through the first electromagnet in the said first direction is at least sufficient to, when the second electromagnet is in its first on-state and when the plunger 130 is in the first position 150, generate a gradient of magnetic flux across the plunger 130 which exerts a net force on the plunger 130 sufficient to hold the plunger in the first position 150. It may be that, in the second mode, the switching circuitry 140 is configured to selectively cause a flow of electrical current through the first coil 110 of the first electromagnet in a second direction opposite the first direction (e.g. from the second electrical terminal to the first electrical terminal of the first electromagnet e.g. by way of generating a second potential difference across the said first and second electrical terminals, the second potential difference having an opposite polarity from the first polarity of the first potential difference) to induce the second on-state of the first electromagnet. As discussed, the second on-state of the first electromagnet may refer to a state of the first electromagnet where a magnitude of current flowing through the first electromagnet in the said second direction is at least sufficient to, when the second electromagnet is in its first on-state and when the plunger 130 is in the first position 150, change the gradient of magnetic flux induced across the plunger 130 by the combination of the first and second electromagnets to thereby exert a net force (by way of the magnetic flux generated by the first and second electromagnets) on the plunger 130 sufficient to trigger movement of the plunger 130 from the first position 150 towards the second position 160.

[0040] It may be that, in the third mode, the switching circuitry 140 is configured to selectively cause a flow of electrical current through the first coil 110 (by way of generating a third potential difference across the said first and second electrical terminals, the third potential difference having a suitable polarity) to induce the third on-state of the first electromagnet. The third on-state of the first electromagnet may refer to a state of the first electromagnet wherein a magnitude of current flowing through the first electromagnet is at least sufficient to, when the second electromagnet is in its off-state and when the plunger 130 is in the second position 160, generate a gradient of magnetic flux across the plunger 130 which exerts a net force on the plunger 130 sufficient to move the plunger 130 from the second position 160 to the first position 150.

[0041] It may be that, in the fourth mode, the switching circuitry 140 is configured to selectively (e.g. substantially) inhibit a flow of electrical current between the first and second electrical terminals of the first electromagnet (e.g. by way of generating a (e.g. substantially) zero potential difference across the said first and second electrical terminals) to induce the off- state of the first electromagnet.

[0042] The particular magnitude of electrical current flowing through the first electromagnet in each of its first, second and third on-states may depend on the particular configuration of the actuator 100. It may be that any one or more of the first, second and third on-states of the first electromagnet refer to respective states of the first electromagnet wherein electrical current flowing through the first electromagnet has e.g. reached a (e.g. substantially) steady- state, such as a corresponding steady-state value or a fraction of a corresponding steadystate value).

[0043] It may that the switching circuitry 140 is couplable to an electrical power source (not shown), such as a voltage source, and that the switching circuitry 140 is operable to selectively couple the first and second electrical terminals of the first electromagnet to the said electrical power source to thereby generate a potential difference having a selected polarity across the first and second electrical terminals of the first electromagnet. The switching circuitry 140 may include any suitable circuitry operable to selectively provide electrical current to, and to selectively reverse the direction of current through the first coil 110 (e.g. responsive to a control signal). It may be that the switching circuitry 140 comprises a so-called “H- bridge”, or any other suitable type of switching circuitry.

[0044] As mentioned above, driver circuitry (not shown) may be provided to control the operating state of the second electromagnet. The actuator 100 may comprise the driver circuitry. Alternatively, driver circuitry may be provided external to the actuator 100 and operably couplable or coupled to the second electromagnet.

[0045] The driver circuitry (not shown) may be arranged to induce the first on-state or the off-state of the second electromagnet (e.g. responsive to a control signal e.g. received from a controller (not shown), such as the controller 700 described in relation to Fig. 7). For example, the driver circuitry may be operable to, in a first mode, induce the first on-state of the second electromagnet. It may be that, in the first mode, the driver circuitry is configured to selectively cause a flow of electrical current through the second coil 120 of the second electromagnet (e.g. by way of generating a potential difference across the first and second electrical terminals of the second electromagnet) to induce the first on-on state of the second electromagnet. As discussed, the first on-state of the second electromagnet may refer to a state of the second electromagnet wherein a direction and a magnitude of electrical current flowing through the second electromagnet provide for a gradient of magnetic flux induced across the plunger 130 by the first and second electromagnets in their respective first on- states which, when the plunger 130 is in the first position 150, exerts a net force on the plunger 130 sufficient to hold the plunger in the first position 150. The first on-state of the second electromagnet may additionally refer to a state of the second electromagnet wherein the said direction and magnitude of the electrical current flowing through the second electromagnet provide for a gradient of magnetic flux induced across the plunger 130 by the first electromagnet in its second on-state and the second electromagnet in its first on-state which, when the plunger 130 is in the first position 150, exerts a net force on the plunger 130 sufficient to trigger movement of the plunger 130 from the first position 150 towards the second position 160. Additionally, the driver circuitry may be operable to, in a second mode, induce the off-state of the second electromagnet. It may be that, in the second mode, the driver circuitry is configured to selectively (e.g. substantially) inhibit a flow of electrical current between the first and second electrical terminals of the second electromagnet (e.g. by way of generating a (e.g. substantially) zero potential difference across the said first and second electrical terminals) to induce the off-state of the second electromagnet.

[0046] A mode of the driver circuitry (e.g. the first mode or the second mode of the driver circuitry) may be invoked responsive to a control signal e.g. received from a controller (not shown), such as the controller 700 described in relation to Fig. 7.

[0047] The particular magnitude of the current flowing through the second electromagnet in its first on-state may depend on the particular configuration of the actuator 100. It may be that the first on-state of the second electromagnet refers to a state wherein electrical current flowing through the second electromagnet has e.g. reached a (e.g. substantially) steady-state, such as a corresponding steady-state value or a fraction of a corresponding steady-state value.

[0048] It may that the driver circuitry is couplable to an electrical power source (not shown), such as a voltage source, and that the driver circuitry is operable to selectively couple the first and second electrical terminals of the second electromagnet to the said electrical power source to thereby generate a potential difference across the first and second electrical terminals of the second electromagnet to induce the first on-state of the second electromagnet. The driver circuitry 140 may include any suitable circuitry operable to selectively provide electrical current to the second coil 120 in the first direction (e.g. responsive to a control signal).

[0049] The first electromagnet may comprise a first magnetic circuit comprising at least one of the one or more magnetic conductors 170 (where provided). For example, it may be that magnetic flux generated by the first electromagnet is provided to influence the position of the plunger 130 through a path including the at least one of the one or more magnetic conductors 170. For example, as will be discussed further below, the first magnetic circuit of the first electromagnet may comprise the first coil 110, the at least one of the one or more magnetic conductors 170, the plunger 130, and one or more gaps, such as one or more air gaps (such as air gaps 155a-155c discussed further below).

[0050] Each of the one or more magnetic conductors 170 may comprise any material having a suitably high magnetic permeability. For example, each of the one or more magnetic conductors 170 may comprise a respective material having a relative magnetic permeability (e.g. at room temperature e.g. 20 degrees Celsius) greater than 1. It may be that one, some, or each of the one or more magnetic conductors 170 comprises a respective material comprising any one, or any combination of (e.g. as part of one or more alloys): iron; cobalt; nickel. For example, it may be that one, some, or each of the one or more magnetic conductors 170 comprises a respective iron-based alloy such as steel.

[0051] In the example illustrated in Figs. 1-5, a single magnetic conductor 170 is provided, portions of which form the magnetic circuits of the first and second electromagnets. However, it will be understood that a plurality of magnetic conductors may alternatively be provided to form the respective magnetic circuit(s). Alternatively, the magnetic conductor(s) may be omitted altogether (e.g., the first and second electromagnets may be “air-core” electromagnets).

[0052] In the example illustrated in Figs. 1-5, the plunger 130 has a first (e.g. upper) surface 130a which engages with the first end-stop when the plunger is in the first position 150, a second (e.g. lower) surface 130b which engages with the second end-stop when the plunger is in the second position 160, and third a (e.g. side) surface 130c extending between the first and second surfaces 130a, b.

[0053] In the example of Figs. 1-5, and as shown in Fig. 2A for example, the first electromagnet comprises a first magnetic circuit comprising a first magnetic circuit path 210 and a second circuit magnet circuit path 220 in parallel with the first magnetic circuit path 210.

[0054] The first magnetic circuit path 210 is illustrated in Fig. 2A by way of the bold dashed line, and extends through a first portion of the magnetic conductor 170 that is magnetically couplable or coupled to the first coil 110 of the first electromagnet i.e. the first portion of the magnetic conductor 170 is configured to receive at least some magnetic flux from the first coil 110 when the first electromagnet is in an on-state (such as its first, second or third on- state). The first portion of the magnetic conductor 170 has a first end 230a facing the first surface 130a of the plunger 130, and a second end 230b facing the third surface 130c of the plunger 130. The first magnetic circuit path 210 also extends through: a first air gap 155a between the first end 230a of the first portion of the magnetic conductor 170 and the first surface 130a of the plunger 130; (e.g. at least a portion of) the plunger 130; and a second air gap 155b between the second end 230b of the first portion of the magnetic conductor 170 and the third surface 130c of the plunger 130. It may be that the first air gap 155a extends axially in a direction (e.g. substantially) parallel to an axis of movement of the plunger 130 (e.g. substantially parallel to the axis 105). It may be that the second air gap 155b extends radially outwards from the third surface 130c of the plunger 130. For example, it may be that the second air gap 155b extends radially outwards form the third surface 130c of the plunger 130 (e.g. substantially) orthogonally to an axis of movement of the plunger 130 e.g. (e.g. substantially) orthogonally to the axis 105. When the first electromagnet is in an on-state (e.g. such as its first, second, or third on-state), magnetic flux generated by the first electromagnet “flows” around the first magnetic circuit path 210 i.e. flows through the first portion of the magnetic conductor 170, across the first air gap 155a, through the (e.g. at least the portion of) the plunger 130, and across the second air gap 155b. The magnitude of the said magnetic flux generated depends on a reluctance of the first magnetic circuit path 210, wherein the said reluctance includes respective reluctance components corresponding to the first air gap 155a, the (e.g. at least the portion of) the plunger 130, and the second air gap 155b.

[0055] The second magnetic circuit path 220 is illustrated in Fig. 2A by way of the dot-dash line and extends through a second portion of the magnetic conductor 170 that is magnetically couplable or coupled to the first coil 110 of the first electromagnet i.e. the second portion of the magnetic conductor 170 is configured to receive at least some magnetic flux from the first coil 110 when the first electromagnet is in an on-state (such as its first, second or third on-state). The second portion of the magnetic conductor 170 includes the first end 230a facing the first surface 130a of the plunger 130. The second portion of the magnetic conductor 170 has a third end 230c facing the second surface 130b of the plunger 130. The second magnetic circuit path 220 also extends through: the first air gap 155a between the first end 230a of the first portion of the magnetic conductor 170 and the first surface 130a of the plunger 130; (e.g. at least a portion of) the plunger 130; and a third air gap 155c between the third end 230c of the first portion of the magnetic conductor 170 and the second surface 130b of the plunger 130. It may be that the third air gap 155c extends axially in a direction (e.g. substantially) parallel to an axis of movement of the plunger 130. As will be discussed further below, when the first electromagnet is in an on-state (e.g. such as its first on-state or its second on-state), magnetic flux generated by the first electromagnet “flows” around the second magnetic circuit path 220 i.e. flows through the second portion of the magnetic conductor 170, across the first air gap 155a, through the (e.g. at least the portion of) the plunger 130, and across the third air gap 155c. The magnitude of the said magnetic flux generated depends on a reluctance of the second magnetic circuit path, wherein the said reluctance includes respective reluctance components corresponding to the first air gap 155a, the (e.g. at least the portion of) the plunger 130, and the third air gap 155c.

[0056] Considering, for the sake of illustration, the first electromagnet in isolation from the second electromagnet (i.e. in the case where no current flows through the second coil 120 of the second electromagnet), when current flows through the first coil 110 of the first electromagnet, a magnetomotive force is generated depending on the magnitude of the current flowing through the first coil 110 and the first number of turns of the first coil 110. This magnetomotive force gives rise to a respective magnetic flux “flowing” in the first and second magnetic circuit paths 210, 220 of the first electromagnet, the magnitude of which depends on the respective reluctances of the said first and second magnetic circuit paths 210, 220. It can be seen from Fig. 2A that the first air gap 155a is included in both the first and second magnetic circuit paths 210, 220, whereas the third air gap 155c is included in the second magnetic circuit path 220 and not in the first magnetic circuit path 210. Accordingly, the total magnetic flux “flowing” in the first and second magnetic circuit paths 210, 220 “flows” across the first air gap 155a, whereas only the magnetic flux “flowing” in the second magnetic circuit path 220 “flows” across the third air gap 155c. Thus, electrical current flowing through the first coil 110 of the first electromagnet gives rise to a magnetic flux in the first air gap 155a that is greater than a magnetic flux in the third air gap 155c, which in turn gives rise to a gradient of magnetic flux across the plunger 130 which generates a force acting on the plunger 130 in a direction extending away from the second position 160 towards the first position 150.

[0057] As discussed above, both the first air gap 155a and the third air gap 155c are included in the second magnetic circuit path 220. Accordingly, the reluctance of the second magnetic circuit path 220 may be substantially independent of plunger position 130 e.g. relative to the first position 150 and the second position 160. This is because the combined air gap size of the first and third air gaps 155a, 155c may remain substantially constant during movement of the plunger 130 between the first and second position 150, 160, and thus, a combined reluctance associated with the combination of the first and third air gaps 155a, 155c may remain substantially constant during movement on the plunger 130 between the first and second positions 150, 160.

[0058] In contrast to the second magnetic circuit path 220, the first magnetic circuit path 210 includes the first air gap 155a and does not include the third air gap 155c. Accordingly, the reluctance of the first magnetic circuit may depend on the position of the plunger 130 e.g. relative to the first position 150 and the second position 160. In particular, the smaller the first air gap 155a between the first end 230a of the magnetic conductor 170 and the first (e.g. upper) surface 130a of the plunger 130, the lower the reluctance of the first magnetic circuit path 210 and the greater magnetic flux across the first air gap 155a. Hence, for a given current flowing in the first coil 110 of the first electromagnet, the difference between the magnetic flux in the first air gap 155a and the third air gap 155c (i.e. the gradient of magnetic flux across the plunger 130) increases with decreasing size of the first air gap 155a. Thus, the magnitude of the force acting on the plunger 130 in the direction extending away from the second position 160 towards the first position 150 due to current flowing in the first electromagnet increases with decreasing size of the first air gap 155a.

[0059] The second electromagnet comprises a second magnetic circuit comprising a third magnetic circuit path and a fourth circuit magnet circuit path in parallel with the third magnetic circuit path. The third magnetic circuit path 270 is illustrated in Fig. 2B by way of the bold dashed line and extends through a third portion of the magnetic conductor 170 that is magnetically couplable or coupled to the second coil 120 of the second electromagnet i.e. the third portion of the magnetic conductor is configured to receive at least some magnetic flux from the second coil 120 when the second electromagnet is in an on-state (such as its first on-state). The third portion of the magnetic conductor 170 includes the second end 230b facing the third surface 130c of the plunger 130. The third portion of the magnetic conductor 170 also includes the third end 230c facing the second surface 130b of the plunger 130. The third magnetic circuit path 270 also extends through: the second air gap 155b, (e.g. at least a portion of) the plunger 130, and the third air gap 155c. When the second electromagnet is in an on-state (e.g. such as its first on-state), magnetic flux generated by the second electromagnet “flows” around the third magnetic circuit path 270 i.e. flows through the third portion of the magnetic conductor 170, across the second air gap 155b, through the (e.g. at least the portion of) the plunger 130, and across the third air gap 155c. The magnitude of the said magnetic flux generated depends on a reluctance of the third magnetic circuit path 270, wherein the said reluctance includes respective reluctance components corresponding to the second air gap 155b, the (e.g. at least the portion of) the plunger 130, and the third air gap 155c.

[0060] The fourth magnetic circuit path 260 is illustrated in Fig. 2B by way of the dot-dash line. The fourth magnetic circuit path 260 extends through a fourth portion of the magnetic conductor 170 that is magnetically couplable or coupled to the second coil 120 of the second electromagnet i.e. the fourth portion of the magnetic conductor 170 is configured to receive at least some magnetic flux from the second coil 120 of the second electromagnet when the second electromagnet is in an on-state (e.g. such as its first on-state). The fourth portion of the magnetic conductor 170 includes the first end 230a facing the first surface 130a of the plunger 130. The fourth portion of the magnetic conductor 170 also includes the third end 230c facing the second surface 130b of the plunger 130. The fourth magnetic circuit path 260 also extends through: the first air gap 155a between the first end 230a of the first portion of the magnetic conductor 170 and the first surface 130a of the plunger 130; (e.g. at least a portion of) the plunger 130; and the third air gap 155c between the third end 230c of the first portion of the magnetic conductor 170 and the second surface 130b of the plunger 130. When the second electromagnet is in an on-state (e.g. such as its first on-state), magnetic flux generated by the second electromagnet “flows” around the fourth magnetic circuit path 260 i.e. flows through the fourth portion of the magnetic conductor 170, across the first air gap 155a, through the (e.g. at least the portion of) the plunger 130, and across the third air gap 155c. The magnitude of the said magnetic flux generated depends on a reluctance of the fourth magnetic circuit path 260, wherein the said reluctance includes respective reluctance components corresponding to the first air gap 155a, the (e.g. at least the portion of) the plunger 130, and the third air gap 155c.

[0061] Considering, for the sake of illustration, the second electromagnet in isolation from the first electromagnet (i.e. in the case where no current flows through the first coil of the first electromagnet), it can be understood in view of the above description of the first electromagnet that when current flows through the second coil 120 of the second electromagnet, the resulting magnetic fluxes generated in the first and third air gaps 155a, 155c, respectively, give rise to a force acting on the plunger 130 in a direction extending away from the first position 150 towards the second position 160, wherein the magnitude of the said force increases with decreasing size of the third air gap 155c.

[0062] Thus, it may understood in view of the above description of Figs. 2A and 2B that each of the first and second electromagnets is operable to independently exert an attractive force on the plunger 130, wherein the magnitude of the said attractive force depends on the position of the plunger 130 relative to the first position 150 or the second position 160.

[0063] As discussed, the position of the plunger 130 may be controlled depending on the operating states of the first and second electromagnets. The following describes the operation of the actuator 100 in respect of a sequence of first to fourth states of the said actuator 100, which are schematically illustrated in Figs. 3A-3D, respectively. Fig. 4 corresponds to Figs. 3A-3D and graphically depicts, with respect to time: a position of the plunger 130 relative to the first position 150 and the second position 160 (as illustrated by the dotted line 422); a potential difference across the first coil 110 of the first electromagnet (as illustrated by the solid line 424) and a current through the first coil 110 of the first electromagnet (as illustrated by the dot-dash line 426); and a potential difference across the second coil 120 of the second electromagnet (as illustrated by the dashed lined 428) and a current through the second coil 120 of the second electromagnet (as illustrated by the dot-dot-dash line 430).

[0064] The following description assumes that the actuator 100 comprises a biaser configured to apply a biasing force on the plunger 130 to return the plunger 130 to, or at least hold the plunger 130 in, the second position 160 when each of the first electromagnet and the second electromagnet are in their respective off-states i.e. the second position 160 is the nominal position of the actuator 100. However, it will be understood that the biaser may alternatively bias the plunger to the first position 150, e.g. the first position 150 may be the nominal position of the actuator 100, or the biaser may be omitted altogether.

[0065] Fig. 3A schematically illustrates a first state (e.g. an off-sate) of the actuator 100 wherein each of the first and second electromagnets are in their respective off-states and the plunger 130 is held at the second position 160 by way of the biaser (not shown). This state is illustrated in the time period 410 shown in Fig. 4. When in the second position 160, the first electromagnet may be switched by the switching circuitry 140 to operate in its third on-state (e.g. responsive to a control signal received from a controller, such as the controller 700 described in relation to Fig. 7) by causing a flow of electrical current through the first coil 110, e.g. by way of generating a potential difference across the first coil 110 of the first electromagnet. The plunger 130 may be caused to move from the second position 160 to the first position 150 depending on a magnetic field generated by the first electromagnet in its third on-state, e.g. while the second electromagnet its maintained in its off-state. This subsequent second state of the actuator is schematically illustrated in Fig. 3B. This state is also illustrated in the time period 420 shown in Fig. 4, which also shows a transient response of the current 426 increasing in the first coil 110 of the first electromagnet at a rate dependent on an electrical time constant of the first coil 110 responsive to the generation of the above-mentioned potential difference.

[0066] The resulting magnetic flux “flowing” in the magnetic circuit of the first electromagnet in this state of the actuator 100 is schematically illustrated Fig. 3B by the arrows 310. It is to be understood that the magnetic flux arrows 310 are merely for illustrative purposes and are not e.g. indicative of any particular value of magnetic flux magnitude. Once the current flowing through the first coil increases to a sufficient magnitude, the flux flowing across the first air gap 155a relative to the flux flowing across the third air gap 155c gives rise to a gradient of magnetic flux across the plunger 130 which generates a sufficient force acting on the plunger 130 (which acts in a direction extending away from the second position 160 towards the first position 150) to overcome the biasing force applied by the biaser and cause movement of the plunger 130 from the second position 160 to the first position 150. Thus, Fig. 3B shows the plunger 130 at the first position 150.

[0067] Fig. 3C schematically illustrates a subsequent third state of the actuator 100, wherein, once in the first position 150, the plunger 130 may be held (e.g. maintained) at that position depending on a magnetic field generated by the first electromagnet in its first on-state while the second electromagnet is energised from its off-state to its first on-state. Hence, the second electromagnet can be (e.g. “fully”) energised to its first on-state before movement of the plunger 130 away from the first position 150 towards the second position 160 commences. The second electromagnet is energised from its off-state to its first on-state (e.g. its first on-state is induced) by causing a flow of electrical current through the second coil 120 of the second electromagnet, for example, by way of the driver circuitry (e.g. responsive to a control signal received from a controller, such as the controller 700 described in relation to Fig. 7). This state is illustrated in the time period 430 shown in Fig. 4, which also shows a transient response of the current 430 increasing in the second coil 120 of the second electromagnet at a rate dependent on the electrical time constant of the second coil 120. The energising time of the second electromagnet (e.g. the time taken for the second electromagnet to energise from its off-state to its first on state e.g. the time taken for the current through the second electromagnet to increase from its off-state value (e.g. substantially zero) to its first on-state value) is illustrated by the arrow 415.

[0068] Fig. 3C illustrates components of the resulting magnetic flux “flowing” in the respective magnetic circuits of the first and second electromagnets in this actuator state, wherein the solid arrows 310 indicate the magnetic flux components generated by the first electromagnet and the dashed arrows 320 indicate the magnetic flux components generated by the second electromagnet. The net magnetic flux in each of the first and third air gaps 155a, 155c in this actuator state will correspond to the sum of the flux components generated by the first and second electromagnets, respectively. In this actuator state, the flux components generated by the first and second electromagnets combine so as to hold (e.g. maintain or “latch”) the plunger 130 at the first position 150. For example, it may be that the said flux components combine such that a force acting on the plunger 130 resulting therefrom is greater than or equal to the biasing force, and hence, the net force acting on the plunger 130 holds the plunger 130 at the first position 150. For example, it may be that in this actuator state (e.g. as a result of the relatively low reluctance associated with the first air gap 155a due to the position of the plunger 130), the magnetic flux in the first air gap 155a is greater than the magnetic flux in the third air gap 155c, which may in turn give rise to force acting on the plunger 130 which holds the plunger 130 at the first position 150. Thus, Fig. 3C shows the plunger 130 in the first position 150.

[0069] When in the third state illustrated in Fig. 3C, the actuator 100 may be configured to trigger movement of the plunger 130 from the first position 150 towards the second position 160 (e.g. once the second electromagnet has been energised to its first on-state) by switching (e.g. by way of the switching circuitry 140) the first electromagnet from its first on-state to its second on-state, which may reverse a direction of current flowing through the first electromagnet and thereby reverse a polarity of a magnetic field generated by the first electromagnet relative to when operating in its first on-state. It may be that the second electromagnet is maintained in its first on-state (e.g. at least) during switching of the first electromagnet from its first on-state to its second on-state to thereby cause movement of the plunger 130 from the first position to the second position. For example, it may be that the actuator 100 is configured to (e.g. substantially) maintain the second electromagnet in its first on-state during switching of the first electromagnet from its first on-state to its second on-state and to (e.g. substantially) maintain the second electromagnet in its first on-state during movement of the plunger from the first position 150 to the second position 160. Fig. 3D schematically illustrates a subsequent fourth state of the actuator 100, wherein after the switching circuitry 140 switches the first electromagnet from its first on-state to its second on-state (e.g. responsive to a control signal received from a controller, such as the controller 700 described in relation to Fig. 7) to trigger movement of the plunger 130 from the first position 150 towards the second position 160, the plunger 130 is moved to the second position 160. As described herein, triggering movement of the plunger 130 in this way, as opposed to e.g. merely switching the first electromagnet from its first on-state to its off-state, may provide for particularly short actuation times, and more precise actuation timing, of the plunger moving from the first position 150 to the second position 160. As will be discussed further below, this may be because the respective magnetic fields generated by the first electromagnet in its second on-state and the second electromagnet in its first on-state combine in such a way so as to efficiently accelerate the plunger 130 from the first position 150 to the second position 160. For example, it may be that combined magnetic fields of the first electromagnet in its second on-state and the second electromagnet in its first on-state enable the energy stored in the magnetic field of the second electromagnet to be exploited so as to provide for a (e.g. relatively) high actuation force in moving the plunger 130 from the first position 150 to the second position 160, and thus, for a (e.g. relatively) short transit time and precise actuation time.

[0070] This is illustrated in the time period 440 shown in Fig. 4, which also shows a transient response of the current 426 in the first coil 110 changing direction at a rate dependent on the electrical time constant of the first electromagnet. The switching time for switching the first electromagnet from its first on-state to its second on-state (e.g. the time taken for the current through the first electromagnet to change from its first on-state value to its second on-state value) is illustrated by the arrow 425. It can be seen in Fig. 4, that the switching time illustrated by the arrow 425 is less than the energising time of the second electromagnet illustrated by the arrow 415.

[0071] Thus, a switching time for switching the first electromagnet from its first on-state to its second on-state is less than the energising time for energising the second electromagnet from its off-state to its first on-state. Hence, the triggering mechanism of switching the first electromagnet from its first on-state to its second on-state may advantageously provide for a triggering delay of the actuator 100 that is decoupled from the energising time for energising the second electromagnet to its first on-state, while enabling the energy stored in the magnetic field of the second electromagnet in its first on-state to be exploited for moving the plunger 130 from the first position 150 to the second position 160.

[0072] Also advantageously, the above-described holding and triggering mechanism of the actuator 100 may allow the second electromagnet to be (e.g. “fully”) energised to its first on-state prior to movement of the plunger 130 from the first position 150 towards the second position 160 being triggered, which may further enable reduce transit times.

[0073] In examples where the biaser is present and arranged to apply a biasing force to the plunger 130 acting in the direction extending away from the first position 150 towards the second position 160, the biaser may further enable a reduced transit time by increasing the net force on the plunger 130 acting towards the second position 160 during movement of the plunger from the first position 150 to the second position 160.

[0074] Fig. 3D illustrates components of the resulting magnetic flux “flowing” in the respective magnetic circuits of the first and second electromagnets in this actuator state, wherein the solid arrows 310 indicate the magnetic flux components generated by the first electromagnet and the dashed arrows 320 indicate the magnetic flux components generated by the second electromagnet. It can be seen from Fig. 3D that, when the first electromagnet is operating in its second on-state, the first electromagnet generates respective magnet flux components “flowing” across the first air gap 155a and the third air gap 155c in a direction opposite to the magnet flux components “flowing” across the first and third air gaps 155a, 155c by the second electromagnet in its first on-state. Advantageously, the magnetic flux components in the first air gap 155a generated by the first electromagnet in its second on-state may at least partially cancel the magnet flux components in the first air gap 155a generated by the second electromagnet in its first on-state such that a greater gradient of magnetic flux is generated across the plunger 130 when the second electromagnet is in its first on-state and the first electromagnet is in its second on-state than if the second electromagnet was in its first on- state and the first electromagnet was merely switched to its off-state. Hence, switching the first electromagnet from its first on-state to its second on-state in the manner described as opposed to e.g. merely switching the first electromagnet from its first on-state to its off-state, may advantageously enable reduce actuation times.

[0075] This can be understood as follows.

[0076] As can be understood from the description of the first electromagnet in Fig. 2A, the magnetic flux component “flowing” across the first air gap 155a due to the first electromagnet operating in its second on-state is less than the magnetic flux component “flowing” across the second third air gap 155c due to the first electromagnet operating in its second on-state. Hence, when the second electromagnet is in its first on-state and the first electromagnet is in its second on-state, the magnetic flux components generated by the first electromagnet cancel the magnetic flux components generated by the second electromagnet to a greater extent in the first air gap 155a compared to the third air gap 155c. Accordingly, operating the second electromagnet in its first on-state simultaneously with operating the first electromagnet in its second on-state gives rise to a greater gradient of magnetic flux across the plunger 130 relative to operating the second electromagnet in its first on-state alone (i.e. simultaneously with operating the first electromagnet in its off-state).

[0077] As described above, the switching time for switching the first electromagnet from its first on- state to its second on-state may be less than the energising time for energising the second electromagnet from its off-state to its first on-state. For example, it may be that the second electromagnet is configured to store more energy in its magnetic field in its first on-state than an energy associated (e.g. required to) switch the first electromagnet from its first on-state to its second on-state. This may be virtue of different inductances of the first and second electromagnets, by virtue of an electrical current magnitude of the second electromagnet in its first on-state relative to electrical current magnitudes of the first electromagnet in its first and second on-states, or by be virtue of both different inductances of the first and second electromagnets and by virtue of an electrical current magnitude of the second electromagnet in its first on-state relative to electrical current magnitudes of the first electromagnet in its first and second on-states. Advantageously, it may be that the transit time of the movement of the plunger from the first position 150 to the second position 16 depends on the energy stored in the second electromagnet in its first on-state, while the triggering delay depends on the switching time of switching the first electromagnet from its first on-state to its second on-state (which may depend on the energy associated (e.g. required to) switch the first electromagnet from its first on-state to its second on-state). Hence, the actuator 100 may enable the energy stored in the second electromagnet in its first on-state to be exploited for accelerating the plunger 130 from the first position 150 to the second position 160, while enable a triggering delay depending on the lower energy, and therefore faster, switching of the first electromagnet from its first on-state to its second on state.

[0078] Furthermore, because the second electromagnet can be energised independently from movement of the plunger 130 being triggered, the actuator 100 may provide for more optimal actuation forces (e.g. given the specification of the second electromagnet) by way of the second electromagnet being energised to a greater extent (e.g. fully energised), prior to movement of the plunger 130 being triggered.

[0079] When the plunger 130 is located at the second position 160 (e.g. having been caused to move from the first position 150 to the second position 160 in the manner described above), the plunger 130 may be returned to the first position 150 by attracting the plunger 130 to the first position 150 depending on a magnetic field generated by the first electromagnet, by way of the biaser (when present and when arranged to return to the plunger 130 to the first position 150), or both. In examples where the plunger 130 is caused to move from the second position 160 to the first position 150 depending on a magnetic field generated by the first electromagnet, it may be that the second electromagnet is switched (e.g. by driving circuitry) to its off-state and the first electromagnet is switched to its third on-state (e.g. by the switching circuitry 140) to thereby generate a sufficient magnetic field to attract the plunger 130 from the second position 160 to the first position 150.

[0080] In examples where the plunger 130 does not comprise a permanent magnet, it may be that the plunger 130 is attracted towards the first electromagnet in the third on-state irrespective of the polarity of the magnetic field generated thereby. Accordingly, it may be that, in the third on-state of the first electromagnet, current is caused to flow in either the first direction or the second direction of the first electromagnet. It may be that a current magnitude in the third on-state comprises any suitable current magnitude to cause movement of the plunger 130 from the second position 160 to the first position 150. It may be that the third on-state corresponds to (e.g. has a same current magnitude and direction as) the first on-state or the second on-state of the first electromagnet. Alternatively, it may be that the third on-state differs from each of the first and second on-states of the first electromagnet e.g. a current magnitude of the third on-state may be different from a respective current magnitude of the first and second on-states of the first electromagnet. In examples, where the plunger 130 comprises a permanent magnet, the third on-state of the first electromagnet may comprise any suitable polarity and current magnitude to cause movement of the plunger from the second position 160 to the first position 150.

[0081] In examples where the actuator 100 is configured to induce the third on-state of the first electromagnet to cause movement of the plunger 130 form the second position 160 to the first position 150, it may be that, by virtue of the above-described holding and triggering mechanism, a transit time of the movement of the plunger from the first position 150 to the second position 160 is less than a transmit time of the movement of the plunger from the second position 160 to the first position 150.

[0082] Hence, the actuator 100 may provide for actively driven (e.g. by way of the first and / or second electromagnets) bi-directional (e.g. from the first position 150 to the second position 160, and vice versa) movement of the plunger 130. This may advantageously be provide for more precise actuation control and greater flexibility relative to solutions which only actively drive actuation in one direction and rely on passive actuation in the other direction e.g. by way of biaser such as a spring.

[0083] The characteristics of the actuator 100 are particularly desirable in a variety of applications, including, for example, valve applications such as for fluid valves for selectively providing fluid to or receiving fluid from fluid working machines, automotive applications such as for electronic gear shifting, and robotics applications.

[0084] Fig. 5 shows an example electronically controllable valve 500 comprising the actuator 100 and a valve member 510 mechanically coupled to the actuating member 135 of the actuator 100, a fluid chamber 520, an inlet 530, and an outlet 540. The valve member 510 is configured to regulate the flow of fluid through the valve (e.g. between the inlet 530 and the outlet 540 by way of the fluid chamber 520) depending on the position of the plunger 130 (e.g. relative to the first and second positions 150, 160 of the actuator 100). The electronically controllable valve 500 may additionally comprise a housing (not shown) which may house any one or more of the components or features of the electronically controllable valve 500 disclosed herein disclosed herein.

[0085] The inlet 530 (which may extend through the housing, when present) is operable to provide fluid to the fluid chamber 520 by way of a fluidic coupling between the inlet 530 and the fluid chamber 520. The inlet 530 is fluidly couplable or coupled to a fluid source (such as a low pressure or high pressure fluid source) operable to provide fluid to the inlet port. The outlet 540 (which may extend through the housing, when present) is operable to receive fluid from the fluid chamber 520 by way of a fluidic coupling between the outlet port 540 and the fluid chamber 520. The outlet port 540 is fluidically couplable or coupled to a fluid sink (such as a low pressure or high pressure fluid sink) operable to receive fluid from the outlet port 540.

[0086] It may be that the electronically controllable valve 500 is configured to regulate the flow of fluid through the valve to thereby regulate the flow of fluid between the fluid source and the fluid sink. It may be that the flow of fluid through the electronically controllable valve 500 depends on a position of the valve member 510 (e.g., relative to a valve seat) which, in turn, depends on a position of the actuation member 135, and thus the plunger 130 (e.g. in relation to the first and second positions 150, 160).

[0087] It may be that the valve 500 has an open position in which fluid can flow through the valve from the inlet 530 to the outlet 540. It may be that the valve 500 has a closed position in which fluid is inhibited or prevented from flowing through the valve from the inlet 530 to the outlet 540. It may be that the open position of the valve 500 corresponds to the plunger 130 being at one of the first and second positions 150, 160, and that the closed position of the valve 500 corresponds to the plunger 130 being at the other of the first and second positions 150, 160. For example, it may be that the open position of the valve 500 corresponds to the plunger 130 being at the first position 150 (e.g., such that the valve member is spaced from the valve seat), and that the closed position of the valve 500 corresponds to the plunger 130 being at the second position 160 (e.g., such that the valve member sealingly engages a valve seat).

[0088] By comprising the actuator 100, the electronically controllable valve 500 may be able to switch from its open position to its closed position (or vice versa depending on the mapping between the first and second positions 150, 160 of the actuator 100 and the open and closed positions of the electronically controllably valve 500) in a particularly fast time, with precise timing.

[0089] For example, when the valve open position corresponds to the plunger 130 being at the first position 150 and the valve closed position corresponds to the plunger 130 being at the second position 160, a particularly short time for closing the valve 500 may be provided by way of the particularly short actuation time for moving the plunger 130 from the first position 150 to the second position 160.

[0090] Alternatively, when the valve closed position corresponds to the plunger 130 being at the first position 150 and the valve open position corresponds to the plunger 130 being at the second position 160, a particularly short time for opening the valve 500 may be provided by way of the of the particularly short actuation time for moving the plunger 130 from the first position 150 to the second position 160.

[0091] Furthermore, the above mentioned particularly short times for opening or closing the valve 500 may also provide for more precise timing control of the valve 500. For example, it may be that in opening or closing the valve 500, movement of the valve member 510 displaces fluid (e.g. in the fluid chamber 520 of the valve 500, or e.g. in the fluid source or fluid sink). It may be that when the valve member 510 moves at higher speed through the fluid that it is to displace, the time taken for valve member 510 moving through the said fluid is more consistent and less variable. Accordingly, the relatively high speed movement of the plunger 130 from the first position 150 to the second position 160 provided by the actuator 100 may enable the timing of opening or closing the valve 500 to be more consistent and predictable.

[0092] The electronically controllable 500 valve may comprise any suitable type of valve configuration. For example, the electronically controllable valve 500 may be configured as a poppet valve, wherein the actuating member 135 is part of a valve stem of the poppet valve to cause movement of a valve member attached to a distal end of the valve stem. As another example, while not shown in Fig. 5, the electronically controllable valve 500 may be configured as a spool valve, wherein the actuating member 135 is mechanically coupled to a spool of the spool valve to thereby cause movement of the said spool from an open position to a closed position, or vice versa. .

[0093] The electronically controllable valve 500 described above may be employed in a fluid working machine, such as a hydraulic or pneumatic pump (also referred to as a compressor herein), a hydraulic or pneumatic motor (also referred to as an expander herein) or a hydraulic or pneumatic fluid working machine operable as a pump in a first operating mode and as a motor in a second operating mode. For example, the electronically controllable valve 500 may be a low pressure valve configured to regulate a flow of fluid between a low pressure manifold and a working chamber of the fluid working machine, such as a working chamber of cyclically varying volume. Alternatively the electronically controllable valve 500 may be a high-pressure valve configured to regulate a flow of fluid between a high pressure manifold and a working chamber of the fluid working machine, such as a working chamber of cyclically varying volume. Valves which regulate the flow of fluid between a low pressure manifold and a working chamber are referred to herein as low pressure valves. Valves which regulate the flow of fluid between a high pressure manifold and a working chamber are referred to herein as high pressure valves.

[0094] Fig. 6 shows an example fluid working machine 600. The fluid working machine 600 comprises a working chamber 610 having an adjustable (e.g. cyclically varying) volume, and one or more electronically controllable valves 500. The fluid working machine 600 may comprise a number of such working chambers. Individual chambers are selectable (e.g. by a controller), on a cycle by cycle basis, to carry out an active cycle and displace a volume of fluid or to undergo an idle cycle with no net displacement of fluid, thereby enabling the net throughput of the machine to be matched dynamically to demand. The fluid working machine 600 may additionally comprise or may be communicatively couplable or communicatively coupled to a controller 615 of the fluid working machine.

[0095] The working chamber 610 may (e.g. selectively) function as a (e.g. positive displacement) compressor (e.g. a pump) operable to pressurise a working fluid (e.g. a gas or a liquid) provided thereto, or as an (e.g. positive displacement) expander (e.g. a motor) operable to depressurise a working fluid provided thereto. The fluid to be pressurised or depressurised may comprise a (e.g. substantially) non-compressible liquid (e.g. oil); alternatively, the fluid to be pressurised may be a gas. It may be that the fluid working machine is part of a heat pump system including but not limited to a pumped thermal energy storage system (PTES) such as the PTES system described in WO2021 / 069929A1 , which is incorporated in full herein by reference.

[0096] The one or more electronically controllable valves 500 are configured (e.g. controlled by the controller) to regulate a flow of working fluid into or out of the working chamber 610 e.g. to facilitate operation of the working chamber as a compressor or as an expander.

[0097] The working chamber 610 is configured to have a cyclically varying volume when the fluid working machine 600 is in use. For example, the fluid working machine 600 may additionally comprise or may be mechanically connectable to a rotatable shaft that when rotated causes the adjustable volume of the working chamber 610 to cyclically vary in a phased relationship with the rotation of the rotatable shaft. For example, as the rotatable shaft rotates through 360 degrees, the adjustable volume of working chamber 610 may be caused (e.g. by way of a mechanical linkage coupling the working chamber 610 to the rotatable shaft) to vary from a maximum volume to a minimum volume and back to a maximum volume (and so on). For example, the working chamber 610 may comprise a cylinder and a piston mechanically coupled to the rotatable shaft (e.g. by way of a cam mounted on the rotatable shaft), wherein rotation of the shaft may cause, by way of the said mechanical coupling, the piston to reciprocate within the cylinder such that the volume of the working chamber 510 cyclically varies (e.g. between a maximum volume e.g. when the piston is at a “top dead centre” position and a minimum volume e.g. when the piston is at a “bottom dead centre” position) in a phased relationship with the rotation of the rotatable shaft.

[0098] The fluid working machine 600 may comprise or may be connectable to a high pressure manifold 620, wherein the high pressure manifold 620 is e.g. connected to a high pressure side of a working fluid circulation pathway. The fluid working machine 600 may comprise a high pressure valve operable to regulate a flow of working fluid between the working chamber 610 and the high pressure manifold 620.

[0099] The fluid working machine 600 may comprise or may be connectable to a low pressure manifold 630, wherein the low pressure manifold is e.g. connected to a low pressure side of a working fluid circulation pathway. The fluid working machine 600 may comprise a low pressure valve operable to regulate a flow of working fluid between the working chamber 610 and the low pressure manifold 630.

[0100] It may be that one or both of the high pressure valve and the low pressure valve comprise or consist of an electronically controllable valve 500. That is, the one or more electronically controllable valves 500 of the fluid working machine 600 may comprise one or both of: an electronically controllable valve 500 configured to operate as the above-mentioned high pressure valve; and an electronically controllable valve 500 configured to operate as the above-mentioned low pressure valve. In examples where only one (e.g. and not the other) of the high pressure valve and the low pressure valve comprises an electronically controllable valve 500, the other of the high pressure valve and the low pressure valve may comprise any suitable alternative type of valve.

[0101] The controller may control each of the low and high pressure valves in a phased relationship with cycles of working chamber volume in order to time opening and closing of the high and low pressure valves so as to provide for compressor or expander functionality. It may be that the controller controls the timing of opening and closing the high and low pressure valves in phase with the cyclical variation of working chamber volume based on shaft position data (e.g. received from a shaft position sensor communicatively couplable with or communicatively coupled to the controller). When functioning as a compressor, the fluid working chamber 610 may selectively receive working fluid from the low pressure manifold through the low pressure valve, increase the pressure of the said working fluid, and output the working fluid at the increased pressure to the high pressure manifold through the high pressure valve. When functioning as an expander, the fluid working chamber 610 may selectively receive working fluid from the high pressure manifold through the high pressure valve, decrease the pressure of the said working fluid, and output the working fluid at the decreased pressure to the low pressure manifold through the low pressure valve.

[0102] During a compressor cycle, it may be that the low pressure valve is opened when the volume of the working chamber 610 is substantially at its minimum. As working fluid flows into the working chamber 610 from the low pressure manifold 630, the volume of the working chamber 610 may increase. When the volume of the working chamber 610 is substantially at its maximum, the low pressure valve may be closed. When the volume of the working chamber 610 starts to decrease, the pressure of working fluid in the working chamber 610 may increase. When the pressure of the working fluid within the working chamber 610 is substantially equal to the pressure of working fluid of the high pressure manifold, the high pressure valve may open and the pressurised working fluid may be forced out of the working chamber 610 through the high pressure valve into the high pressure manifold 620 by way of the volume of the working chamber 610 reducing back to its minimum value. The high pressure valve may be closed when the volume of the working chamber 610 has reduced back to its minimum value to prevent pressurised working fluid have been forced out of the working chamber 610 from returning to the working chamber 610.

[0103] As can be understood in view of the above, the net displacement of working fluid during a compressor cycle of the fluid working machine 600 operating as a compressor, the extent to which that fluid is pressurised, and the volumetric efficiency of the compressor (e.g., the ratio of the volume of working fluid entering the working chamber 610 through the low pressure valve during a compressor cycle to the volume of working fluid exiting the working chamber 610 through the high pressure valve during the compressor cycle) depends on the timing of the opening and closing of the low and high pressure valves relative to the cyclically varying volume of the working chamber 610. For example, the timing of closing the low pressure valve during a compressor cycle affects the volume of fluid entering the working chamber 610 during an intake stroke of the compressor cycle, which in turn affects the net displacement of working fluid during the compressor cycle, the extent of pressurisation of that fluid during a subsequent exhaust stroke, and the volumetric efficiency of the compressor. As another example, the timing of closing the high pressure valve during a compressor cycle affects the extent to which fluid in the working chamber 610 is ejected from the working chamber 610 during the exhaust stroke, and any deviation from closing the high pressure valve when the volume of the working chamber 610 has reduced back to its minimum value at the end of an exhaust stroke may negatively affect the net displacement of working fluid during a compressor cycle and the volumetric efficiency of the compressor. For example, closing the high pressure valve before the working chamber 610 has reduced back to its minimum value during an exhaust stroke may result in a significant volume of working fluid being undesirably retained in the working chamber 610 at the end of the exhaust stroke, thereby reducing the net displacement of working fluid during a compressor cycle and reducing the volumetric efficiency of the compressor. As another example, closing the high pressure valve after the volume of the working chamber 610 has reduced back to its minimum value at the end of an exhaust stroke may allow high pressure fluid having been ejected from the working chamber 610 during the exhaust stroke to return to the working chamber 610 during a subsequent intake stroke, thereby effectively reducing the net displacement of working fluid during a compressor cycle and reducing the volumetric efficiency of the compressor.

[0104] Accordingly, utilising an electronically controllable valve 500 for one or both of the low pressure valve and the high pressure valve of a fluid working machine operating as a compressor, configured such the valve is closed when the plunger 130 is in the second position 160, may be particularly advantageous. This is due to the increased speed of valve closure, and also due to the increased accuracy obtained in the timing of valve closure. The electronically controllable valve 500 also enables higher speed operation of fluid working machines operating as compressors, as the valve can operate (at least in one direction - e.g. from the first position 150 to the second position 160) more quickly.

[0105] During an expander cycle, it may be that the high pressure valve is opened when the volume of the working chamber 610 is substantially at its minimum. In order to open the high pressure valve, the pressure in the working chamber 610 should first be substantially equalised with the pressure in the high pressure manifold 620. Accordingly, the low pressure valve should be closed prior to the volume of the working chamber 610 reaching its minimum volume so as to pressurise remaining working fluid in the working chamber 610 to at least the pressure of the high pressure manifold 620. As working fluid flows into the working chamber 610 from the high pressure manifold 620, the volume of the working chamber 610 may increase. Prior to the volume of the working chamber 610 reaching its maximum value, the high pressure valve may be closed and the pressure of working fluid in the working chamber 610 may decrease while the volume of the working chamber 610 continues to increase up to its maximum value. When the pressure of the working fluid within the working chamber 610 is substantially equal to the pressure of working fluid of the low pressure manifold 630, the low pressure valve may open and the depressurised working fluid may be forced out of the working chamber 610 through the low pressure valve into the low pressure manifold 630 by way of the volume of the working chamber reducing back to its minimum value. As can be understood in view of the above, the net displacement of working fluid during a expander cycle, and the extent to which that fluid is depressurised, depends on the timing of the opening and closing of the high and low pressure valves relative to the cyclically varying volume of the working chamber 610. It is possible for such machines to fail if the timing of valve closure is not correct for the fluid pressure in the high pressure manifold. For example if, during an expander cycle, a low pressure valve closes too late in the exhaust stroke to compress the remaining working fluid in the working chamber to at least the pressure of the high pressure manifold, then the high pressure valve of the respective working chamber will not open in preparation for drawing fluid from the high pressure manifold in a subsequent expansion stroke. Thus the expansion cycle is not possible and the machine malfunctions. In a second example, if the high pressure valve closes too late in the expansion stroke of an expander cycle, this prevents the working chamber from sufficiently decompressing, thus preventing the respective low pressure valve from reopening to exhaust fluid from the working chamber and therefore causing fluid to be returned to the high pressure manifold on the compression stroke.

[0106] Accordingly, utilising an electronically controllable valve 500 for one or both of the low pressure valve and the high pressure valve of a fluid working machine operating as a compressor, configured such the valve is closed when the plunger 130 is in the second position 160, may be particularly advantageous. This is due to the increased speed of valve closure, and also due to the increased accuracy obtained in the timing of valve closure.

[0107] Fig. 7 schematically illustrates a controller 700 for controlling an actuator, such as the actuator 100 described above. The controller 700 comprises processing circuitry 710. The controller 700 may additionally comprise a memory 720 communicatively couplable or coupled to the processing circuitry 710. The processing circuitry 710 may comprise general purpose processing circuitry or special purpose processing circuitry. The functionality of the processing circuitry 710 described herein may be implemented in software, hardware or firmware, or a combination of any of software, hardware and firmware. For example, the processing circuitry 710 may be configured to retrieve and execute computer program instructions stored in the memory 720 to thereby provide its functionality described herein. The memory 720 may comprise any suitable memory such as cache memory, random access memory (RAM), read only memory (ROM), flash memory, magnetic or optical disk or any combination thereof.

[0108] The processing circuitry 710 may be configured to perform a method according to the method described below in relation to Fig. 8. It may be that the processing circuitry 710 is configured to perform the said method by way of controlling switching circuitry (such as the switching circuitry 140 described above) and driver circuitry (such as the driver circuitry described above). It may be that the processing circuitry 710 is communicatively couplable or coupled (e.g. by way of a wired electrical connection or e.g. a wireless connection) to the switching circuitry and the driver circuitry.

[0109] It may be that that the processing circuitry 710 is operable to induce a first on-state of a first electromagnet of the actuator by causing a flow of electrical current through the first electromagnet in a first direction. It may be that the processing circuitry 710 is operable to induce the said first on-state by way of providing a first control signal to the switching circuitry to thereby invoke a first mode of the switching circuitry in which the switching circuitry induces the first on-state of the first electromagnet. The first control signal may comprise e.g. one or more voltage pulses (e.g. having respective predetermined magnitudes and e.g. respective predetermined durations), one or more pulse width modulated voltage signals (e.g. having respective predetermined magnitudes, e.g. respective predetermined duty cycles, and e.g. respective predetermined durations), or any other suitable type of signal indicative of the first mode of the switching circuitry. In examples where the switching circuitry comprises an H-bridge, it may that the control signal comprises or is indicative of respective (e.g. gate) voltages for driving individual switches (e.g. transistors) of the H- bridge.

[0110] It may be that the processing circuitry 710 is operable to induce a first on-state of a second electromagnet of the actuator by causing a flow of electrical current through the second electromagnet. It may be that the processing circuitry 710 is operable to induce the said first on-state by way of providing a second control signal to the driver circuitry to thereby invoke a first mode of the driver circuitry in which the driver circuitry induces the first on-state of the second electromagnet. The second control signal may comprise e.g. a voltage pulse (e.g. having a predetermined magnitude and e.g. duration), a pulse width modulated voltage signal (e.g. having a predetermined magnitude, e.g. a predetermined duty cycle, and e.g. a predetermined duration), or any other suitable type of signal indicative of the first mode of the driver circuitry. It may be that the actuator 100 being controlled by the control 700 is configured to hold a plunger (such as the plunger 130 of the actuator 100 described above) at a first position (such as the first position 150 of the actuator 100 described above) when the first and second electromagnets are in their respective first on-state depending on magnetic flux generated by the first and second electromagnets. This may enable the second electromagnet to be (e.g. fully) energised before triggering movement of the plunger away from the first position, as described above with regard to the actuator 100.

[0111] It may be that the processing circuitry 710 is operable to induce a second on-state of the first electromagnet by causing the direction of current flow in the first electromagnet to change from the first direction to a second direction opposite the first direction. It may be that the processing circuitry 710 is operable to induce the said second on-state by way of providing a third control signal to the switching circuitry to thereby invoke a second mode of the switching circuitry in which the switching circuitry induces the second on-state of the first electromagnet. The third control signal may comprise e.g. one or more voltage pulses (e.g. having respective predetermined magnitudes and e.g. respective predetermined durations), one or more pulse width modulated voltage signals (e.g. having respective predetermined magnitudes, e.g. respective predetermined duty cycles, and e.g. respective predetermined durations), or any other suitable type of signal indicative of the second mode of the switching circuitry. In examples where the switching circuitry comprises an H-bridge, it may that the control signal comprises or is indicative of respective (e.g. gate) voltages for driving individual switches (e.g. transistors) of the H-bridge. It may be that the processing circuitry 710 is operable to (e.g. substantially) maintain (e.g. by way of the second control signal) the first on-state of the second electromagnet (e.g. at least) during switching of the first electromagnet from its first on-state to its second on-state. It may be that the actuator being controlled by the controller 700 is configured to trigger movement of the plunger from the first position towards the second position (such as the second position 160 of the actuator 100 described above) responsive to the first electromagnet switching from its first on-state to its second on-state. As described above in relation to the actuator 100, this triggering mechanism may advantageously enable short actuation times of the plunger from the first position to the second position.

[0112] It may be that, when the plunger 130 is in the second position, the processing circuitry 710 is configured to maintain the first electromagnet in its second on-state and maintain the second electromagnet in its first on-state to thereby hold the plunger in the second position. When the plunger is in the second position, the processing circuitry 710 may be configured to maintain the second electromagnet in its first on-state and to switch the first electromagnet off (i.e. to induce its off-state) to thereby hold the plunger in the second position. When the plunger is in the second position, the processing circuitry 710 may be configured to maintain the second electromagnet in its first on-state and to induce a third-on state (which may correspond to the third on-state of the actuator 100 described above) of the first electromagnet, thereby holding the plunger in the second position. The processing circuitry 710 may be configured to maintain or induce any of the respective states of the of first and second electromagnets in accordance with any example disclosed herein. For example, it may be that the processing circuitry 710 is operable to induce the said third on-state of the first electromagnet by way of providing a fourth control signal to the switching circuitry to thereby invoke a third mode of the switching circuitry in which the switching circuitry induces the third on-state of the first electromagnet. It may be that the processing circuitry 710 is configured to induce the third on-state of the first electromagnet to cause movement of the plunger from the second position to the first position (i.e. to return the plunger back to the first position) when the first electromagnet is in its third on-state. The current flowing through the first electromagnet in its third on-state may comprise any suitable magnitude and direction to cause movement of the plunger of the actuator being controlled by the controller 700 from the second position to the first position (e.g. at least when the second electromagnet is in its off-state). As mentioned, it may be that the processing circuitry 710 is operable to induce the said third on-state by way of providing a fourth control signal to the switching circuitry to thereby invoke the third mode of the switching circuitry. The fourth control signal may comprise e.g. one or more voltage pulses (e.g. having respective predetermined magnitudes and e.g. respective predetermined durations), one or more pulse width modulated voltage signals (e.g. having respective predetermined magnitudes, e.g. respective predetermined duty cycles, and e.g. respective predetermined durations), or any other suitable type of signal indicative of the third mode of the switching circuitry. In examples where the switching circuitry comprises an H-bridge, it may that the control signal comprises or is indicative of respective (e.g. gate) voltages for driving individual switches (e.g. transistors) of the H-bridge.

[0113] It may be that the processing circuitry 710 is configured to cause the second electromagnet to switch to its off-state to allow the plunger to move from the second position to the first position under the influence of the first electromagnet operating in the third on-state. For example the processing circuitry 710 may be configured to provide a fifth control signal to the driver circuitry to cause the second electromagnet to switch to its off-state. As discussed, the combination of the first electromagnet operating in its third on-state and the second electromagnet being in its off-state may cause the plunger 130 to move from the second position to the first position. The fifth control signal may comprise e.g. a voltage pulse (e.g. having predetermined magnitude and e.g. a predetermined durations), a pulse width modulated voltage signal (e.g. having a predetermined magnitude, e.g. a predetermined duty cycle, and e.g. a predetermined duration), or any other suitable type of signal indicative of the second mode of the driver circuitry.

[0114] Fig. 8 is a flow diagram 800 illustrating a method for controlling an actuator, such as the actuator 100 described above. The method 800 may be performed by, for example, the controller discussed in relation to Fig. 1 , the controller 700 discussed in relation to Fig. 7, or by any other suitable processing circuitry or apparatus. It is to be understood that any of the techniques or features discussed herein may be combined in any combination with any of the techniques or features discussed in the following in relation to the flow diagram 800. At block 810, a flow of electrical current through a first electromagnet of the actuator in a first direction is caused to thereby induce a first on-state of the first electromagnet. The said flow of electrical current through first electromagnet of the actuator to induce the first on-state of the first electromagnet may be caused in accordance with example disclosed herein. For example, it may be that the said flow of electrical current through the first electromagnet to induce the first on-state of the first electromagnet is caused by providing a first control signal to switching circuitry of the actuator (such as the switching circuitry 140 discussed above) to thereby invoke a first mode of the switching circuitry in which the switching circuitry induces the first on-state of the first electromagnet. The control signal may comprise e.g. one or more voltage pulses (e.g. having respective predetermined magnitudes and e.g. respective predetermined durations), one or more pulse width modulated voltage signals (e.g. having respective predetermined magnitudes, e.g. respective predetermined duty cycles, and e.g. respective predetermined durations), or any other suitable type of signal indicative of the first mode of the switching circuitry. In examples where the switching circuitry comprises an H-bridge, it may that the control signal comprises or is indicative of respective (e.g. gate) voltages for driving individual switches (e.g. transistors) of the H-bridge.

[0115] At block 820, a flow of electrical current through a second electromagnet of the actuator is caused to thereby induce a first on-state of the second electromagnet. The said flow of electrical current through second electromagnet of the actuator to induce the first on-state of the second electromagnet may be caused in accordance with example disclosed herein. It may be that the actuator being controlled by the method 800 is configured to hold a plunger (such as the plunger 130 of the actuator 100 described above) at a first position (such as the first position 150 of the actuator 100 described above) when the first and second electromagnets are in their respective first on-states depending on magnetic flux generated by the first and second electromagnets. This may enable the second electromagnet to be (e.g. fully) energised before triggering movement of the plunger away from the first position, as described above with regard to the actuator 100.

[0116] At block 830, the direction of electrical current flow in the first electromagnet is changed from the first direction to a second direction opposite the first direction to induce a second on- state of the first electromagnet. The said direction of the electrical current flow may be changed to induce the second on-state of the first electromagnet in accordance with any example disclosed herein. It may the first on-state of the second electromagnet is (e.g. substantially) maintained (e.g. by way of the first control signal) (e.g. at least) during switching of the first electromagnet from its first on-state to its second on-state. It may be that may be that the actuator being controlled by the method 800 is configured to trigger movement of the plunger from the first position towards a second position (such as the second position 160 of the actuator 100 described above) responsive to the first electromagnet switching from its first on-state to its second on-state when the second electromagnet is in its first on-state. As described above in relation to the actuator 100, this triggering mechanism may advantageously enable short actuation times of the plunger moving from the first position to the second position.

[0117] At block 840, when the plunger is in the second position, the first electromagnet may be maintained in its second on-state and the second electromagnet may be maintained in its first on-state to thereby hold the plunger in the second position. Alternatively, at block 840, when the plunger is in the second position, the second electromagnet may be maintained in its first on-state and the first electromagnet may be switched off (i.e. have its off-state induced) to thereby hold the plunger in the second position. Alternatively, at block 840, when the plunger is in the second position, the second electromagnet may be maintained in its first on-state and a third-on state (which may correspond to the third on-state of the actuator 100 described above) of the first electromagnet induced, again holding the plunger in the second position.

[0118] At block 850, a flow of electrical current through the first electromagnet of the actuator may be caused to thereby induce the third on-state of the first electromagnet to return the plunger to the first position 150. The said flow of electrical current through first electromagnet of the actuator to induce the third on-state of the first electromagnet may be caused in accordance with any example disclosed herein. It may be that may be that the actuator being controlled by the method 800 is configured to cause movement of the plunger from the second position to the first position (i.e. to return the plunger back to the first position) when the first electromagnet is in its third on-state. The current flowing through the first electromagnet in its third on-state may comprise any suitable magnitude and direction to cause movement of the plunger of the actuator being controlled by the controller from the second position to the first position. It may be that before, during or after inducing the third on-state of the first electromagnet, an off-state of the second electromagnet is induced. It may be that providing the second electromagnet in its off-state when the first electromagnet is in its third on-state advantageously reduces an attractive force acting on the plunger away from the first position towards the second position, thereby enabling the plunger to be returned from the second position to the first position more efficiently.

[0119] In the method 800, the various respective states of the first and second electromagnets discussed above may be induced in accordance with any example disclosed herein.

[0120] Fig. 9 depicts a flow diagram 900 of a method for operating an actuator, such as the actuator 100 discussed in relation to Fig. 1. It is to be understood that any of the techniques or features discussed herein may be combined in any combination with any of the techniques or features discussed in the following in relation to the flow diagram 900.

[0121] At block 910, a plunger of the actuator (such as the plunger 130 of the actuator 100 described above) is held in a first position (such as the first position 150 of the actuator 100 discussed above) by inducing a magnetic flux by energising a first electromagnet of the actuator (such as the first electromagnet of the actuator 100 discussed above) to a first on- state (such as the first on-state of the first electromagnet of the actuator 100 described above) in which current flows through the first electromagnet in a first direction and energising a second electromagnet (such as the second electromagnet of the actuator 100 described above) to a first on-state (such as the first on-state of the second electromagnet of the actuator 100 described above). The first and second electromagnets may be energised to their respective first on-states in accordance with any example disclosed herein.

[0122] At block 920, the first electromagnet is switched from its first on-state to a second on-state (such as the second on-state of the first electromagnet of the actuator 100 described above) while the second electromagnet is maintained in its first on-state to thereby trigger movement of the plunger from the first position towards a second position (such as the second position 160 of the actuator 100 described above), wherein current flows through the first electromagnet in a second direction opposite the first direction in the second on- state. The first electromagnet may be switched its first on-state to its second on-state in accordance with any example disclosed herein, wherein a switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from its off-state to its first on-state. Holding the plunger in the first position as described in relation to block 910, and triggering movement of the plunger towards the second position as described immediately above may provide for advantageously short actuation times for the plunger moving from the first position to the second position, as discussed herein.

[0123] At block 930, the plunger may be held in the second position. For example, when the plunger is in the second position, the first electromagnet may be maintained in its second on-state and the second electromagnet may be maintained in its first on-state to thereby hold the plunger in the second position, in accordance with any example disclosed herein. Alternatively, when the plunger is in the second position, the second electromagnet may be maintained in its first on-state and the first electromagnet may be switched off (i.e. have its off-state induced) to thereby hold the plunger in the second position, in accordance with any example disclosed herein. Alternatively, when the plunger is in the second position, the second electromagnet may be maintained in its first on-state and a third-on state (which may correspond to the third on-state of the actuator 100 described above) of the first electromagnet may be induced to thereby hold the plunger in the second position, in accordance with any example disclosed herein.

[0124] At block 940, the first electromagnet may be energised to a third on-state (such as the third on-state of the first electromagnet of the actuator 100 described above) to thereby return the plunger to the first position from the second position. The first electromagnet may be energised to its third on-state in accordance with any example disclosed herein. It may be that before, during or after inducing the third on-state of the first electromagnet, an off-state of the second electromagnet is induced to thereby cause the plunger to be (e.g. efficiently) returned from the second position to the first position, in accordance with any example disclosed herein.

[0125] The functionality of the processing circuitry described herein may be implemented in software, hardware or firmware or a combination of any of software, hardware and firmware. For example, the processing circuitry may be configured to retrieve and execute computer program instructions stored in memory to thereby provide its functionality described herein. The memory may comprise any suitable memory such as cache memory, random access memory (RAM), read only memory (ROM), flash memory, magnetic or optical disk or any combination thereof. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other components, integers or operations. Throughout the description and claims of this specification, the singular encompasses the plural unless the context demands otherwise. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context demands otherwise. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the elements of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or operations are mutually exclusive. Implementations are not restricted to the details of any foregoing examples.

[0126] The present disclosure also extends to the following numbered examples.

[0127] Example 1. Actuator apparatus comprising: a first electromagnet switchable between a first on-state in which current flows through the first electromagnet in a first direction and a second on-state in which current flows through the first electromagnet in a second direction opposite the first direction; a second electromagnet operable in a first on-state in which current flows through the second electromagnet; a plunger movable between first and second positions, the actuator apparatus being configured to hold the plunger in the first position when the first and second electromagnets are in their respective first on-states depending on magnetic flux generated by the first and second electromagnets; and switching circuitry for switching the first electromagnet from its first on-state to its second on-state to trigger movement of the plunger from the first position towards the second position (e.g. by changing the polarity of magnetic flux generated by the first electromagnet), wherein a switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from an off-state to its first on-state (e.g. the second electromagnet may have a higher energising time constant than the first electromagnet, e.g. the second electromagnet may have a higher inductance than the first electromagnet).

[0128] Example 2. A method of operating an actuator, the method comprising: holding a plunger in a first position by inducing magnetic flux by energising a first electromagnet to a first on-state in which current flows through the first electromagnet in a first direction and energising a second electromagnet to a first on-state; switching the first electromagnet from its first on-state to a second on-state (e.g. to change the polarity of magnetic flux generated by the first electromagnet) to thereby trigger movement of the plunger from the first position towards the second position, wherein current flows through the first electromagnet in a second direction opposite the first direction in the second on-state, wherein a switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from an off-state to its first on-state (e.g. the second electromagnet may have a higher energising time constant than the first electromagnet, e.g. the second electromagnet may have a higher inductance than the first electromagnet).

[0129] Example 3. The actuator apparatus of Example 1 or the method of Example 2, wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the plunger is operable to move between the first and second positions along an axis, and wherein the first coil and the second coil are spaced apart with respect to the axis.

[0130] Example 4. The actuator apparatus or method of any one preceding Example, wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the movement of the plunger from the first position towards the second position comprises a movement of the plunger away from the first coil and towards the second coil.

[0131] Example 5. The actuator apparatus or method of any one preceding Example, wherein the actuator apparatus is configured to (e.g. substantially) maintain, or the method comprises (e.g. substantially) maintaining the second electromagnet in its first on-state (e.g. at least) during switching (e.g. by the switching circuitry) of the first electromagnet from its first on-state to its second-on state to cause movement of the plunger from the first position to the second position.

[0132] Example 6. The actuator apparatus or method of any one preceding Example, wherein the actuator apparatus is configured to cause movement of, or wherein the method comprises moving, the plunger from the first position to the second position when the first electromagnet is switched from its first on-state to its second on-state depending on a magnetic field generated by the second electromagnet when the second electromagnet is in its first on-state.

[0133] Example 7. The actuator apparatus or method of any one preceding Example, wherein the switching circuitry is configured to induce (or wherein the method comprises inducing) a third on-state of the first electromagnet to cause movement of the plunger from the second position to the first position (e.g. after the plunger has moved from the first position to the second position, e.g. after switching the second electromagnet to an off-state).

[0134] Example 8. The actuator apparatus or method of any one preceding Example, wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the movement of the plunger from the second position to the first position comprises a movement of the plunger away from second coil towards the first coil.

[0135] Example 9. The actuator apparatus or method of any one preceding Example, wherein the actuator apparatus is configured such that (or wherein) a transit time of movement of the plunger from the first position to the second position is less than a transit time of movement of the plunger from the second position to the first position.

[0136] Example 10. The actuator apparatus or method of any one preceding Example, further comprising a biaser arranged to apply, or wherein the method comprises applying, a biasing force to the plunger when the plunger is in the first position, the biasing force acting in a direction extending away from the first position towards the second position.

[0137] Example 11. The actuator apparatus or method of Example 10, wherein the biaser comprises, or wherein the biasing force is applied by, a spring.

[0138] Example 12. The actuator apparatus or method of any one preceding Example, wherein the switching circuitry comprises, or wherein the switching is performed by, an H-bridge.

[0139] Example 13. The actuator apparatus or method of any one preceding Example further comprising a controller configured to control, or controlling by a controller, the switching circuitry to switch the first electromagnet between its first and second on-states.

[0140] Example 14. The actuator apparatus or method of Example 13, wherein the controller is further configured to selectively induce, or the method comprises the controller selectively inducing, the third on-state of the first electromagnet.

[0141] Example 15. An electronically controllable valve for regulating a flow of fluid therethrough, the electronically controllable valve comprising: the actuator apparatus of any one of Examples 1 , 3 to 14; and a valve member coupled to the plunger of the actuator apparatus, wherein the valve member is configured to regulate the flow of fluid through the valve depending on the position of the plunger.

[0142] Example 16. The electronically controllable valve of Example 15, wherein the electronically controllable valve is configured to be in an open state when the plunger is in the first position and to be in a closed state when the plunger is in the second position, wherein fluid can flow through the valve in the open state and fluid is inhibited or prevented from flowing through the valve in the closed state.

[0143] Example 17. A fluid-working machine comprising: a working chamber configured to have a cyclically varying volume; and an electronically controllable valve according to any one of Examples 15 to 16; wherein the electronically controllable valve is configured to regulate a flow of working fluid into or out of the working chamber.

[0144] Example 18. The fluid-working machine of Example 17, further comprising: a controller configured to control the electronically controllable valve to regulate the flow of working fluid into or out of the working chamber in a phased relationship to cycles of working chamber volume by way of one or more control signals to the switching circuitry.

[0145] Example 19. The fluid-working machine of Example 17 Example 18, wherein the fluidworking machine is operable as an expander, or wherein the fluid-working machine is operable as a compressor, or wherein the fluid-working machine is operable in a first operating mode as an expander and in a second operating mode as a compressor.

[0146] Example 20. The fluid-working machine of any one of Examples 17 to 19 wherein the valve is configured to regulate the flow of fluid between a high pressure manifold and the working chamber.

[0147] Example 21. The fluid-working machine of Example 20 wherein, when the plunger is in the second position, the valve is closed to inhibit or prevent fluid flow into the working chamber from the high pressure manifold through the valve.

[0148] Example 22. The fluid working machine of Example 21 as dependent on Examples 18 and 19, wherein the controller is configured to control the electronically controllable valve to inhibit or prevent flow of fluid into the working chamber through the valve at an intermediate portion of a cycle of working chamber volume between a minimum volume of the working chamber volume in the cycle of working chamber volume and a maximum volume of the working chamber in the cycle of working chamber volume.

[0149] Example 23. The fluid working machine of Example 21 as dependent on Examples 18 and 19, wherein the working chamber is defined by the interior of a cylinder and a piston which is configured to reciprocate within the cylinder between a top dead centre position and a bottom dead centre position to cyclically vary the volume of the working chamber, and wherein the controller is configured to control the electronically controllable valve to inhibit or prevent flow of fluid into or out of the working chamber through the valve at an intermediate position of the piston between the top dead centre position and the bottom dead centre position when the piston travels from the top dead centre position to the bottom dead centre position.

[0150] Example 24. Apparatus for controlling an actuator, the apparatus comprising processing circuitry to: induce a first on-state of a first electromagnet of the actuator by causing a flow of electrical current through the first electromagnet in a first direction; induce a first on-state of a second electromagnet of the actuator by causing a flow of electrical current through the second electromagnet; and induce a second on-state of the first electromagnet by causing the direction of current flow in the first electromagnet to change from the first direction to a second direction opposite the first direction.

[0151] Example 25. A method for controlling an actuator, the method comprising: inducing a first on-state of a first electromagnet of the actuator by causing a flow of electrical current through the first electromagnet in a first direction; inducing a first on-state of a second electromagnet of the actuator by causing a flow of electrical current through the second electromagnet; and inducing a second on-state of the first electromagnet by causing the direction of current flow in the first electromagnet to change from the first direction to a second direction opposite the first direction.

[0152] Example 26. The apparatus of Example 24 or the method of Example 25 wherein the processing circuitry is to induce the second on-state of the first electromagnet, or wherein the method comprises inducing the second on-state of the first electromagnet, by causing switching of the first electromagnet from the first on-state to the second on-state, and wherein the processing circuitry is to maintain, or wherein the method comprises maintaining, the second electromagnet in its first on-state during switching of the first electromagnet from its first on-state to its second on-state.

[0153] Example 27. The apparatus or method of any one of Examples 24 to 26 wherein the processing circuitry is to induce, or wherein the method comprises inducing, the first on- state of the first electromagnet by controlling switching circuitry to cause the flow of electrical current through the first electromagnet in the first direction.

[0154] Example 28. The apparatus or method of any one of Examples 24 to 27 wherein the processing circuitry is to induce, or wherein the method comprises inducing, the second on-state of the first electromagnet by controlling the switching circuitry to switch the flow of electrical current through the first electromagnet from the first direction to the second direction. Example 29. The apparatus or method of any one of Examples 24 to 28 wherein the processing circuitry is to induce, or the method comprises inducing, the first on-state of the second electromagnet by controlling driver circuitry to cause the flow of electrical current through the second electromagnet.

[0155] Example 30. A computer program product comprising computer program instructions which, when executed, cause processing circuitry to perform in accordance with the processing circuitry of the apparatus of any one of Examples 24, 26-29 or cause performance of the method according to any one of Examples 25, 26-29.

[0156] Example 31. One or more computer readable media comprising executable instructions for causing processing circuitry to perform in accordance with the processing circuitry of the apparatus of any one of Examples 24, 26-29 or to cause performance of the method according to any one of Examples 25, 26-29.

[0157] Example 32. Apparatus comprising: a fluid working chamber of adjustable volume; and an electronically controllable valve according to Example 15 or Example 16, wherein the electronically controllable valve is configured to control a flow of fluid into or out of the fluid working chamber.

[0158] Example 33. Apparatus comprising: the actuator apparatus of any one of Examples 1 , 3-14; or the electronically controllable valve of Example 15 or Example 16; or the fluid-working machine of any one of Examples 17-23; or the apparatus of Example 32; and the apparatus for controlling an actuator of any one of Examples 24, 26-29; wherein the apparatus for controlling the actuator is for controlling: the actuator apparatus of any one of Examples 1 , 3-14; or the actuator apparatus of the electronically controllable valve of Example 15 or Example 16; or the actuator apparatus of the fluid working machine of any one of Examples 17-23; or the actuator apparatus of the apparatus of Example 32.

Claims

CLAIMS1. Actuator apparatus comprising: a first electromagnet switchable between a first on-state in which current flows through the first electromagnet in a first direction and a second on-state in which current flows through the first electromagnet in a second direction opposite the first direction; a second electromagnet operable in a first on-state in which current flows through the second electromagnet; a plunger movable between first and second positions, the actuator apparatus being configured to hold the plunger in the first position when the first and second electromagnets are in their respective first on-states depending on magnetic flux generated by the first and second electromagnets; and switching circuitry for switching the first electromagnet from its first on-state to its second on-state to trigger movement of the plunger from the first position towards the second position, wherein a switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from an off-state to its first on-state.

2. The actuator apparatus of claim 1 , wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the plunger is operable to move between the first and second positions along an axis, and wherein the first coil and the second coil are spaced apart with respect to the axis.

3. The actuator apparatus of claim 1 or claim 2, wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the movement of the plunger from the first position towards the second position comprises a movement of the plunger away from the first coil and towards the second coil.

4. The actuator apparatus of any one of claims 1 to 3, wherein the actuator apparatus is configured to maintain the second electromagnet in its first on-state during switching, by the switching circuitry, of the first electromagnet from its first on-state to its second-on state to cause movement of the plunger from the first position to the second position.

5. The actuator apparatus of any one of claims 1 to 4, wherein the actuator apparatus is configured to cause movement of the plunger from the first position to the second position when the first electromagnet is switched from its first on-state to its second on-state depending on a magnetic field generated by the second electromagnet when the second electromagnet is in its first on-state.

6. The actuator apparatus of any one of claims 1 to 5, wherein the switching circuitry is configured to induce a third on-state of the first electromagnet to cause movement of the plunger from the second position to the first position.

7. The actuator apparatus of claim 6, wherein the first electromagnet comprises a first coil, wherein the second electromagnet comprises a second coil, wherein the movement of the plunger from the second position to the first position comprises a movement of the plunger away from second coil towards the first coil.

8. The actuator apparatus of any one of claims 1 to 7, wherein the actuator apparatus is configured such that a transit time of movement of the plunger from the first position to the second position is less than a transit time of movement of the plunger from the second position to the first position.

9. The actuator apparatus of any one of claims 1 to 8, further comprising a biaser arranged to apply a biasing force to the plunger when the plunger is in the first position, the biasing force acting in a direction extending away from the first position towards the second position.

10. An electronically controllable valve for regulating a flow of fluid therethrough, the electronically controllable valve comprising: the actuator apparatus of any one of claims 1 to 9; and a valve member coupled to the plunger of the actuator apparatus, wherein the valve member is configured to regulate the flow of fluid through the valve depending on the position of the plunger.

11. The electronically controllable valve of claim 10, wherein the electronically controllable valve is configured to be in an open state when the plunger is in the first position and to be in a closed state when the plunger is in the second position, wherein fluid can flow through the valve in the open state and fluid is inhibited or prevented from flowing through the valve in the closed state.

12. A fluid-working machine comprising: a working chamber configured to have a cyclically varying volume; andan electronically controllable valve according to any one of claims 14 to 15; wherein the electronically controllable valve is configured to regulate a flow of working fluid into or out of the working chamber.

13. The fluid-working machine of claim 12, further comprising: a controller configured to control the electronically controllable valve to regulate the flow of working fluid into or out of the working chamber in a phased relationship to cycles of working chamber volume by way of one or more control signals to the switching circuitry.

14. The fluid-working machine of claim 12 or claim 13, wherein the fluid-working machine is operable as an expander, or wherein the fluid-working machine is operable as a compressor, or wherein the fluid-working machine is operable in a first operating mode as an expander and in a second operating mode as a compressor.

15. The fluid-working machine of any one of claims 12 to 14 wherein the valve is configured to regulate the flow of fluid between a high pressure manifold and the working chamber.

16. The fluid-working machine of claim 15 wherein, when the plunger is in the second position, the valve is closed to inhibit or prevent fluid flow into the working chamber from the high pressure manifold through the valve.

17. The fluid working machine of any of claims 13 to 16, wherein the controller is configured to control the electronically controllable valve to inhibit or prevent flow of fluid into the working chamber through the valve at an intermediate portion of a cycle of working chamber volume between a minimum volume of the working chamber volume in the cycle of working chamber volume and a maximum volume of the working chamber in the cycle of working chamber volume.

18. A method of operating an actuator, the method comprising: holding a plunger in a first position by inducing magnetic flux by energising a first electromagnet to a first on-state in which current flows through the first electromagnet in a first direction and energising a second electromagnet to a first on-state; switching the first electromagnet from its first on-state to a second on-state to thereby trigger movement of the plunger from the first position towards the secondposition, wherein current flows through the first electromagnet in a second direction opposite the first direction in the second on-state, wherein a switching time for switching the first electromagnet from its first on-state to its second on-state is less than an energising time for energising the second electromagnet from an off-state to its first on-state.

19. The method of claim 18, further comprising maintaining the second electromagnet in its first on-state during switching of the first electromagnet from its first on-state to its second-on state to cause movement of the plunger from the first position to the second position.

20. Apparatus for controlling an actuator, the apparatus comprising processing circuitry to: induce a first on-state of a first electromagnet of the actuator by causing a flow of electrical current through the first electromagnet in a first direction; induce a first on-state of a second electromagnet of the actuator by causing a flow of electrical current through the second electromagnet; and induce a second on-state of the first electromagnet by causing the direction of current flow in the first electromagnet to change from the first direction to a second direction opposite the first direction.

21. The apparatus of claim 20, wherein the processing circuitry is to maintain the second electromagnet in its first on-state during switching of the first electromagnet from its first on-state to its second on-state.

22. The apparatus of claim 20 or claim 21 wherein the processing circuitry is to induce the first on-state of the first electromagnet by controlling switching circuitry to cause the flow of electrical current through the first electromagnet in the first direction.

23. The apparatus of any one of claims 20-22 wherein the processing circuitry is to induce the second on-state of the first electromagnet by controlling the switching circuitry to switch the flow of electrical current through the first electromagnet from the first direction to the second direction.

24. A method for controlling an actuator, the method comprising: inducing a first on-state of a first electromagnet of the actuator by causing a flow of electrical current through the first electromagnet in a first direction;inducing a first on-state of a second electromagnet of the actuator by causing a flow of electrical current through the second electromagnet; and inducing a second on-state of the first electromagnet by causing the direction of current flow in the first electromagnet to change from the first direction to a second direction opposite the first direction.

25. The method of claim 24, further comprising maintaining the second electromagnet in its first on-state during switching of the first electromagnet from its first on-state to its second on-state.

26. A computer program product comprising computer program instructions which, when executed, cause processing circuitry to perform in accordance with the processing circuitry of the apparatus of any one of claims 20 to 23 or cause performance of the method according to claim 24 or claim 25.

27. One or more computer readable media comprising executable instructions for causing processing circuitry to perform in accordance with the processing circuitry of the apparatus of any one of claims 20 to 23 or to cause performance of the method according to claim 24 or claim 25.

28. Apparatus comprising: a fluid working chamber of adjustable volume; and an electronically controllable valve according to claim 10 or claim 11 , wherein the electronically controllable valve is configured to control a flow of fluid into or out of the fluid working chamber.

29. Apparatus comprising: the actuator apparatus of any one of claims 1-9; or the electronically controllable valve of claim 10 or claim 11 ; or the fluid-working machine of any one of claims 12-17; or the apparatus of claim 28; and the apparatus for controlling an actuator of any one of claims 20-23; wherein the apparatus for controlling the actuator is for controlling: the actuator apparatus of any one of claims 1-9; or the actuator apparatus of the electronically controllable valve of claim 10 or claim 11; orthe actuator apparatus of the fluid working machine of any one of claims 12-17; or the actuator apparatus of the apparatus of claim 28.

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