METHOD FOR CONTROLLING A VALVE TRAIN

Abstract

A method (50) for controlling an electromagnetic valve actuator (400) having a rotatable camshaft (404) for actuating a valve (440) of an engine (20), the method (50) comprising: Scheduling a valve lift event comprising an opening phase from zero valve lift to a maximum valve lift and a closing phase from maximum valve lift to zero valve lift; Instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at constant or variable acceleration during at least one or more of: the opening phase; the closing phase; a section of the opening phase and a section of the closing phase; Instructing the electromagnetic valve actuator (400) to effect one of the following rotational behaviors of the rotatable camshaft (404) during a scheduled rotation of the rotatable camshaft (404), after the end of the closing phase and before the start of the next valve lift event associated with the valve (440), which results in the lowest overall effective acceleration of the rotation of the rotatable camshaft (404) when performing the scheduled rotation: Adjustment of the rotation of the rotating camshaft (404); Changing the acceleration of the rotating camshaft (404); or continuous constant accelerated rotation of the rotatable camshaft (404); the method further comprising: Instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at constant acceleration by one or more of: the entire opening phase; the entire closing phase; the entire opening phase and the entire closing phase.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for controlling a valve train. In particular, but not exclusively, it relates to a method for controlling a valve train of an engine of a vehicle.

[0002] Aspects of the invention relate to a method, a controller, a system, an engine, a vehicle and a computer program. BACKGROUND

[0003] A conventional reciprocating internal combustion engine uses valves (typically poppet valves) to control the flow of gas into and out of the cylinders, thus facilitating combustion. A valve train is a system that controls the operation of the valves.

[0004] An exemplary valvetrain includes a rotating camshaft. The camshaft consists of one or more cam lobes. Each cam lobe pushes on a valve, directly or indirectly through cam action, to shift (lift) the valve from a closed position to an open position. The valvetrain includes valve return springs. Each valve return spring biases the valve to shift the valve from the open position to the closed position when the cam lobe no longer pushes on the valve. The shape of the cam lobe and the design of the valve return springs determine the resulting displacement of the valve from its closed position over time.

[0005] In some cases, the camshaft can be controlled to vary valve timing or valve opening. For example, timing can be adjusted by changing the camshaft stagger with respect to a combustion cycle. Maximum valve lift can be adjusted by controlling the camshaft's separation from the valve. Known prior art is US 2007 / 0 068 473 A1. SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide an improved method for controlling a valve train.

[0007] Aspects and embodiments of the invention provide a method, a controller, a system, an engine, a vehicle and a computer program as claimed in the appended claims.

[0008] Rotational acceleration refers to the rate of change of angular velocity, not the rate of change of radial velocity. The ability to adjust and / or reverse camshaft rotation between valve lift events advantageously offers more opportunities to improve valvetrain efficiency.

[0009] The predetermined acceleration of the rotatable camshaft is at least constant during one or more of: the opening phase, the closing phase, a part of the opening phase and a part of the closing phase.

[0010] The constant acceleration command refers to the command of constant finite positive acceleration, constant finite negative acceleration, and, in some cases, constant zero acceleration. This offers the advantage of reducing the square root mean square (RMS) energy consumption of the electromagnetic valve actuator compared to, for example, a command of an instantaneous change in angular velocity at a given time. This is because the energy consumption is essentially proportional to the square of the required acceleration.

[0011] The specified acceleration of the rotating camshaft may be non-zero over one or more of the following ranges: the entire opening phase; the entire closing phase.

[0012] This offers the advantage of reducing RMS energy consumption when the average angular velocity required in the closing phase differs from the average angular velocity required in the opening phase.

[0013] The method includes: scheduling rotation of the rotatable camshaft prior to the opening phase to an operative position for lifting the valve at the beginning of the opening phase; and commanding the electromagnetic valve actuator to accelerate rotation of its rotatable camshaft at a constant acceleration during the scheduled rotation.

[0014] This has the advantage of reducing the RMS energy consumption in the situation (the "park-to-open" phase) in which the rotating camshaft has to be accelerated from a starting angular velocity (usually zero) in a park position to the angular velocity required for the opening phase in the operating position to lift the valve at the beginning of the opening phase.

[0015] The method comprises: instructing the electromagnetic valve actuator to cause, during the scheduled rotation prior to the opening phase, one of the following rotational behaviors of the rotatable camshaft that results in the lowest overall effective acceleration of rotation of the rotatable camshaft in performing the scheduled rotation: constant acceleration of rotation; constant acceleration of rotation preceded or followed by a constant rotational velocity (angular velocity); or constant positive acceleration of rotation followed by a constant negative acceleration of rotation.

[0016] This has the advantage of reducing RMS energy consumption during the "park-to-open" phase. The most efficient of the above-mentioned rotational behaviors for this "park-to-open" phase varies depending on the ratio of the required angular rotation of the rotating camshaft to the required angular rotation of the crank during the "park-to-open" phase.

[0017] The above characteristics of the park-to-open phase apply equally to a close-to-park phase in which the rotating camshaft must be accelerated from an angular velocity at the end of the closing phase to a final angular velocity (normally zero) at the park position.

[0018] In the close-to-park phase, the method may include: scheduling rotation of the rotatable camshaft after the close phase prior to a next valve lift event; and commanding the electromagnetic valve actuator to accelerate rotation of its rotatable camshaft at a constant acceleration during the scheduled rotation.

[0019] The method may comprise: instructing the electromagnetic valve actuator to cause one of the following rotational behaviors of the rotatable camshaft during the scheduled rotation that results in the lowest overall effective acceleration of rotation of the rotatable camshaft in performing the scheduled rotation: constant acceleration of rotation; constant rotational speed followed by constant acceleration of rotation; or constant acceleration of rotation followed by constant non-zero acceleration followed by constant varying acceleration of rotation.

[0020] The method may include: instructing the electromagnetic valve actuator to cease rotation of its rotatable camshaft after the closing phase prior to commencement of the next valve lift event associated with the valve.

[0021] Scheduling a “parking” of the rotating camshaft offers the advantage of reducing the probability that a closing phase of a first valve event will interfere with an opening phase of a next valve event.

[0022] In some examples, the rotation adjustment may be scheduled so that the rotatable camshaft adjusts rotation at one of several different angular positions depending on the detent positions of the electromagnetic valve actuator.

[0023] This has the advantage that the different angular positions can be specified, so that little or no energy is required to hold the camshaft in the parked position. The detent positions are specific to the permanent magnets of the electromagnetic valve actuator.

[0024] The method may include: instructing the electromagnetic valve actuator to change the rotational acceleration of its rotatable camshaft after the closing phase of the valve lift event or another valve lift event and before the start of the next valve lift event associated with the valve, comprising biasing the timing of the acceleration change to prevent unintended valve lift after the closing phase and before the start of a next valve lift event.

[0025] The temporal preload of the reversal point between the valve lift events offers the advantage of a compromise between the efficient operation of the valve train and the prevention of unintentional reopening of the valve.

[0026] The method may include: instructing the electromagnetic valve actuator to effect one of the following rotational behaviors of the rotatable camshaft during a scheduled rotation from the end of the closing phase of the valve lift event until the beginning of a next opening phase of a next valve lift event that results in the lowest overall effective rotational acceleration of the rotatable camshaft in performing the scheduled rotation: adjustment of the rotation of the rotatable camshaft; a change in the acceleration of the rotatable camshaft; or continuous constant acceleration of the rotation of the rotatable camshaft.

[0027] Allowing the choice between parking, a knee point, and continuous rotation between valve lift events advantageously provides more opportunities to improve valve train efficiency.

[0028] The method includes: commanding the electromagnetic valve actuator to accelerate the rotation of its rotatable camshaft at a constant acceleration closing phase over one or more of: the entire opening phase, the entire closing phase, the entire opening phase, the entire opening phase, and the entire.

[0029] This has the advantage of reducing RMS power consumption.

[0030] The method may include: instructing the electromagnetic valve actuator to reverse a direction of rotation of its rotatable camshaft, changing the angular velocity of the rotatable camshaft from a positive value during the opening phase to a negative value during the closing phase.

[0031] This makes the maximum valve lift a controllable variable. This offers the advantage of enabling continuous valve lift control.

[0032] The method may include receiving desired inputs indicative of a start time for the valve lift event, a duration of the valve lift event, a time of maximum lift, and optionally a lift amount of the valve at maximum lift, wherein scheduling of the valve lift event is dependent on the desired inputs.

[0033] Using only these target inputs to schedule valve events means the process can be performed in open-loop control. This has the advantage of requiring minimal to no feedback, thus avoiding fluctuations in the scheduled acceleration that can increase RMS energy consumption. In other examples, limited inputs from feedback sensors can be advantageous.

[0034] Constant acceleration can be a constant rate of change of the angular velocity of the camshaft over a time interval in a time range defined by the rotation of an engine crankshaft.

[0035] According to another aspect of the invention, there is provided a method of controlling an electromagnetic valve actuator having a rotatable camshaft for actuating a valve of an engine, the method comprising: scheduling a valve lift event comprising an opening phase from zero valve lift to maximum valve lift and a closing phase from maximum valve lift to zero valve lift; and commanding the electromagnetic valve actuator to rotate its rotatable camshaft at constant or variable acceleration during one or more of: the opening phase; the closing phase; a portion of the opening phase and a portion of the closing phase; and commanding the electromagnetic valve actuator to cease or reverse the rotation of its rotatable camshaft after the closing phase and before the start of the next valve lift event associated with the valve.

[0036] According to some, but not necessarily all, aspects of the disclosure, a method is provided for controlling an electromagnetic valve actuator having a rotatable camshaft to actuate a valve of an engine, the method comprising: scheduling a valve lift event including an opening phase from zero valve lift to maximum valve lift and a closing phase from maximum valve lift to zero valve lift; and commanding the electromagnetic valve actuator to accelerate the rotation of its rotatable camshaft at a constant acceleration during at least one or more of: the opening phase; the closing phase; a portion of the opening phase; and a portion of the closing phase.

[0037] According to some, but not necessarily all, aspects of the disclosure, a method is provided for controlling an electromagnetic valve actuator having an actuating element for actuating a valve of an engine, the method comprising: scheduling a valve lift event comprising an opening phase from zero valve lift to a maximum valve lift and a closing phase from maximum valve lift to zero valve lift; and commanding the electromagnetic valve actuator to accelerate its actuating element at a constant acceleration during one or more of: the opening phase; the closing phase; a portion of the opening phase; and a portion of the closing phase.

[0038] According to some, but not necessarily all, aspects of the disclosure, a method is provided for controlling an electromagnetic valve actuator having an actuating element for actuating a valve of an engine, the method comprising: scheduling a valve lift event comprising an opening phase from zero valve lift to a maximum valve lift and a closing phase from maximum valve lift to zero valve lift; and commanding the electromagnetic valve actuator to accelerate its actuating element at a constant acceleration during one or more of: the opening phase; the closing phase; a portion of the opening phase; and a portion of the closing phase.

[0039] According to some, but not necessarily all, examples of the disclosure, a method is provided for controlling a valve actuator having an actuating element for actuating a valve of an engine, the method comprising: instructing the valve actuator to accelerate its actuating element at a constant acceleration.

[0040] According to another aspect of the invention, a method is provided for controlling an electromagnetic valve actuator having a rotatable camshaft for actuating a valve of an engine, the method comprising: scheduling a first valve lift event having a first characteristic for a first combustion cycle associated with the valve; scheduling a second valve lift event having a second, different characteristic for a second combustion cycle associated with the valve; and in transition between the first valve lift event and the second valve lift event, commanding the electromagnetic valve actuator to accelerate the rotation of its rotatable camshaft to the speed required to activate the second valve lift characteristic using only finite acceleration.In some examples, the second characteristic corresponds to a different maximum valve lift and / or a different valve lift speed compared to the first characteristic.

[0041] This has the advantage of reducing the effective energy consumption of the electromagnetic valve actuator compared to, for example, an instantaneous change (“step”) of the angular velocity when the control changes from one valve lift characteristic (e.g., late valve opening) to another valve lift characteristic (e.g., early valve opening).

[0042] In some examples, the first valve lift event includes a valve opening phase and a valve closing phase, wherein the first characteristic is associated with a first speed of the rotatable camshaft at the beginning of the valve opening phase of the first valve lift event, and wherein the second valve lift event includes a valve opening phase and a valve closing phase, wherein the second characteristic is associated with a second different speed of the rotatable camshaft at the beginning of the valve opening phase of the second valve lift.

[0043] According to some, but not necessarily all, examples of the disclosure, a method is provided for controlling a valve actuator having an actuating member for actuating a valve of an engine, the method comprising: commanding the valve actuator to accelerate its actuating member without significant changes in acceleration.

[0044] According to a further aspect of the invention, a controller is provided that comprises means for carrying out the method. The means may comprise at least one processor; and at least one memory containing computer program code; the at least one memory and the computer program code are configured to cause the controller, together with the at least one processor, to at least carry out the method.

[0045] According to another aspect of the invention, a system is provided, comprising: the controller; and a desmodromic electromagnetic valve actuator controlled by the controller. According to another aspect of the invention, an engine is provided, comprising the controller. According to another aspect of the invention, a vehicle is provided, comprising the controller or the engine.

[0046] According to a further aspect of the invention, a computer program is provided which contains instructions which, when executed by one or more processors, cause a controller to carry out at least the method.

[0047] According to a further aspect of the invention, there is provided a method, a controller, a system, a cylinder head, an engine, a vehicle or a computer program as described with reference to the accompanying drawings.

[0048] For the purposes of this application, it is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, in the claims, and / or in the following descriptions and drawings, and in particular their individual features, may be adopted independently of one another or in any combination. This means that all embodiments and / or features of an embodiment may be combined in any manner and / or combination, unless these features are incompatible. The applicant reserves the right to amend an originally filed claim or to file a new claim accordingly, including the right to amend an originally filed claim so that it depends on another claim and / or incorporates a feature of another claim even though it was not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 illustrates an example of a vehicle; Fig. 2 illustrates an example of a controller; Fig. 3 illustrates an example of a computer-readable storage medium; Fig. 4 illustrates an example of an electromagnetic valve actuator; Fig. 5 illustrates an example of a method; Fig. 6 shows an exemplary representation of a planned valve lift event; Fig. 7 illustrates another exemplary representation of a planned valve lift event; and Fig. Figure 8 shows an exemplary representation of a planned camshaft rotation between valve lift events. DETAILED DESCRIPTION

[0050] The figures illustrate a method 50 for controlling an electromagnetic valve actuator 400 having a rotatable camshaft 404 for actuating a valve 440 of an engine 20, the method 50 comprising: scheduling 52 a valve lift event comprising an opening phase θC,O until θC,MOP from zero valve lift to a maximum valve lift and a closing phase θC,MOP until θC,C from maximum valve lift to zero valve lift; and instructing 54 the electromagnetic valve actuator 400 to accelerate the rotation of its rotatable camshaft 404 at constant acceleration during at least one or more of: the opening phase; the closing phase; a portion of the opening phase; and a portion of the closing phase.

[0051] Fig.Figure 1 illustrates an example of a vehicle 10 in which embodiments of the invention may be implemented. In some, but not necessarily all, examples, the vehicle 10 is a passenger car. Passenger cars typically have an unladen weight of less than 5,000 kg.

[0052] In Fig. 1, the vehicle 10 includes: an engine 20 (which may be an internal combustion engine); a cylinder head 30 of the engine 20; and a valve train 40, which may be located within the cylinder head 30 or elsewhere near the engine 20.

[0053] Fig. 2 shows an example of a control 200 of the engine 20 and / or the valve train 40.

[0054] For the purposes of this disclosure, it is understood that the controller(s) 200 described herein may each include a control unit or computing device having one or more electronic processors 202. A vehicle 10 and / or a system thereof may include a single control unit or electronic controller, or alternatively, different functions of the controller(s) may be embodied or housed in different control units or controllers. A set of instructions 208 may be provided that, when executed, cause the controller(s) or control unit(s) to implement the control techniques (including the method(s) described herein).The instruction set may be embedded in one or more electronic processors 202, or, alternatively, the instruction set may be provided as software 206 stored in at least one memory 204 and executed by one or more electronic processors 202. For example, a first controller may be implemented in software running on one or more electronic processors, and one or more other controllers may also be implemented in software running on one or more electronic processors, optionally on the same one or more processors as the first controller. However, it should be noted that other constellations are also useful, and therefore the present disclosure is not intended to be limited to a particular constellation. In any event, the set of instructions 208 described above may be embodied in a computer-readable storage medium 300 (e.g.,a permanent storage medium), as in . Fig. 3, which may include any mechanism for storing information in a form readable by a machine or electronic processor / computing device, including, but not limited to: a magnetic storage medium (e.g., floppy disk); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other type of media for storing such information / instructions.

[0055] Fig. shows an example of valve train hardware, illustrated in various cross-sectional views.

[0056] Fig.Figure 4 shows a valve 440. The valve 440 is a poppet valve. The valve 440 is arranged so that it can be opened as needed to control the flow of gas into and / or out of the cylinders.

[0057] In Fig.4, but not necessarily in all examples, the valve 440 is coupled to a mechanism 420. The mechanism 420 is arranged to push against the valve 440 to open the valve 440. In some, but not necessarily in all examples, the mechanism 420 is arranged to pull on the valve 440 to close the valve 440. The mechanism 420 is coupled to an actuating member in the form of a camshaft 404. The camshaft 404 includes a first cam 406 for locking the mechanism to cause compressive forces to be transmitted through the mechanism 420 to open the valve 440. The camshaft 404 includes a second cam 408 for causing tensile forces to be transmitted through the mechanism 420 to close the same valve 440, whereby the camshaft 404 enables desmodromic valve actuation. In further examples, other actuating elements can be used, e.g. linear actuators.

[0058] In other examples, the valve 440 is directly coupled to the camshaft 404, without an intermediate mechanism 420. The first cam 406 and the second cam 408 may be provided on different camshafts.

[0059] In Fig. 4, the camshaft 404 is coupled to an electromagnetic valve actuator 400. The electromagnetic valve actuator 400 in Fig. 4 includes a rotor-stator pair 402, with the rotor providing a rotating output. In other examples, the electromagnetic valve actuator 400 may provide a linear output.

[0060] The camshaft 404 from Fig.4 fulfills two functions. Camshaft 404 not only provides the cams, but also serves as the rotor of the electromagnetic valve actuator 400 to provide the rotating output. Camshaft 404 is rotatably mounted about its rotational axis 405, which extends the length of camshaft 404.

[0061] The angular velocity of camshaft 404 increases when the electromagnetic valve actuator 400 is supplied with sufficient drive current to overcome inertia. Sufficient positive drive current supplied to the electromagnetic valve actuator 400 produces a positive acceleration (a positive change in the angular velocity of camshaft 404), and sufficient negative drive current produces a negative acceleration (a negative change in the angular velocity of camshaft 404).

[0062] The drive current applied to the electromagnetic valve actuator 400 is controlled by the controller 200. The operation of the controller 200 is described in more detail below.

[0063] Fig. 5 shows a method for controlling the electromagnetic valve actuator 400 that may be performed by the controller 200. The method includes scheduling a valve lift event at block 52. The valve lift event includes an opening phase from zero valve lift to a maximum valve lift. With reference to the exemplary hardware of Fig. 4, the opening phase begins as soon as sufficient force is applied to the valve 440 so that the valve 440 begins to open. The opening phase ends when insufficient force is applied to the valve 440 to further raise the valve 440, and the valve 440 no longer rises for the remainder of the valve stroke.

[0064] The valve lift event also includes a closing phase from maximum valve lift to zero valve lift. Regarding the exemplary hardware of Fig. 4, the end of the opening phase is simultaneously the beginning of the closing phase. In some, but not necessarily all, examples, the closing phase begins when sufficient force is applied to valve 440 to cause valve 440 to move in the closing direction toward zero valve lift. The closing phase ends with the closing of valve 440 (zero valve lift).

[0065] In some, but not necessarily all, examples, a valve lift event consists only of the opening phase and the closing phase.

[0066] Example information that allows planning a valve lift event includes software models of one or more of the following properties: mechanical properties, shape properties, electrical properties, magnetic properties, or thermal properties of all or part of the Fig. 4. Examples of shape properties are the shape of the first cam 406 and the shape of the second cam 408.

[0067] In some, but not necessarily all, examples, one or more subsequent valve lift events are also scheduled before the start of the opening phase of the valve lift event.

[0068] In some, but not necessarily all, examples, termination is performed while the engine is running (combustion is taking place).

[0069] In some, but not necessarily all, examples, scheduling the valve lift event includes scheduling one or more of the following elements prior to the initiation of the opening phase of the valve lift event: the angular position; the angular velocity; or the rate of change of angular velocity (acceleration) of the camshaft 404 at a plurality of times during the valve lift event. The electromagnetic valve actuator 400 is controlled such that the camshaft 404 has the scheduled angular position, angular velocity, or rate of change of angular velocity at each of the plurality of times.

[0070] The scheduled valve lift event includes a period of time during which the acceleration of the camshaft 404 will be constant throughout the entire period. The period consists of one or more of: part or all of the opening phase; part or all of the closing phase; part of the opening phase and part of the closing phase; or the entire opening phase and the entire closing phase. The period or periods of constant acceleration ensure that the RMS energy consumption of the electromagnetic valve actuator 400 is reduced.

[0071] The method includes, at block 54, commanding the electromagnetic valve actuator 400 to accelerate the rotation of its rotatable camshaft 404 according to the scheduled period or periods of constant acceleration. In some, but not necessarily all, examples, block 54 includes commanding the electromagnetic valve actuator 400 to execute the entire scheduled valve lift event, not just the scheduled period or periods of constant acceleration.

[0072] Commanding the electromagnetic valve actuator 400 at block 54 includes at least transmitting a control signal that directly or indirectly controls, in whole or in part, the drive current supplied to the electromagnetic valve actuator 400 in accordance with the scheduled valve lift event. In some, but not necessarily all, examples, the control signal is transmitted after the scheduling of the valve lift event has occurred.

[0073] An example of a detailed control strategy that is wholly or partly part of Block 52 of the method according to Fig. 5 can be.

[0074] The control strategy begins by receiving target inputs. The target inputs represent high-level constraints that must be met. The target inputs can be determined, for example, by an engine control unit before being transmitted to the controller 200.

[0075] The target inputs include a first target indicating the target start time for the valve lift event. Based on this, it is possible to schedule the start of the opening phase. The time base refers to a combustion cycle associated with valve 440. The timing can be expressed as a crank angle position ("crank angle"); for example, 0 degrees crank angle represents the beginning of a four-stroke combustion cycle, and 720 degrees crank angle represents the end of the four-stroke combustion cycle. In an illustrative example, the target start time for the valve lift event can be 180 degrees crank angle.

[0076] The target inputs include a second target that indicates the duration of the valve lift event. It is possible to schedule the end of the closing phase by adding the duration (second target) to the start time of the target (first target). The start time and duration of the valve lift event are now known.

[0077] The target inputs include a third target indicating a target timing of maximum valve lift. In some, but not necessarily all, examples, the third target may be expressed as a percentage of the above-mentioned duration. In the absence of the third target, the default timing of maximum valve lift could be set to 50% of the above-mentioned duration. For values ​​below 50%, the closing phase is longer than the opening phase. For values ​​above 50%, the opening phase is longer than the closing phase.

[0078] In some, but not necessarily all, examples, the desired inputs include a fourth target indicating a desired lift amount of valve 440 at maximum valve lift. This may, for example, be specified as a percentage of the maximum achievable valve lift. In the absence of the fourth target, the default lift amount at maximum valve lift could be 100%. A full rotation of camshaft 404 would result in the maximum achievable valve lift. If the fourth target specifies a maximum valve lift below 100%, it would be necessary to reverse the direction of rotation of camshaft 404 before the maximum achievable valve lift is achieved.

[0079] Based on the target inputs, it is possible to determine the following constraints: Crank angle position ("crank angle") Rotor (camshaft 404) angular position Start of the opening phase i C,O i R,O End of opening phase / start of closing phase i C,MOP i R,MOP End of the closing phase i C,C i R,C

[0080] θ refers to an angle. The subscript MOP stands for "maximum open position," i.e., maximum valve lift. The subscript R stands for "rotor," which in this example is also camshaft 404. The subscript C stands for "crank."

[0081] The next stage of the control strategy involves determining a dimensionless angular velocity coefficient Ca for each phase: Ca = planned rotor (camshaft) angular rotation / planned crank angle rotation Ca=ΔθR / ΔθC

[0082] The angular velocity coefficient Ca represents the rate of change of the angular velocity of the rotor Δθ R with respect to a time range defined by the rotation of the crankshaft.

[0083] The mean angular velocity coefficient for the opening phase can be determined taking into account the limitations of Eq. 1: Ca1(opening phase)=(θR,MOP−θR,O) / (θC,MOP−θC,O)

[0084] For example, if the rotor is to rotate from 120 degrees to 200 degrees over the entire opening phase and the crank is to rotate from 270 degrees to 370 degrees over the entire opening phase, the average angular velocity coefficient is: Ca1(opening phase)=(200−120) / (370−270) Ca1(opening phase)=0.80

[0085] In this example, the average angular velocity coefficient of the rotor for the opening phase is 0.80 (i.e., the average angular velocity of the rotor must be 0.80 times the average crank angular velocity).

[0086] The mean angular velocity coefficient for the closing phase can also be determined taking into account the limitations of equation 1: Ca2(closing phase)=(θR,C−θR,MOP) / (θC,C−θC,MOP)

[0087] For example, if the rotor is to be rotated over the entire closing phase from 200 degrees to 300 degrees and the crank over the entire closing phase from 370 degrees to 450 degrees, the average angular velocity coefficient is: Ca2(closing phase)=(300−200) / (450−370) Ca2(closing phase)=1.25

[0088] In this example, the rotor's average angular velocity coefficient for the closing phase is 1.25 (i.e., the rotor's average angular velocity must be 1.25 times the average crank angular velocity).

[0089] Fig. 6 and Fig. 7 are graphs each having the angular velocity coefficient Ca as the y-axis, while the x-axis is time in a time range defined by the rotation of the crankshaft θC. The lines 601 in Fig. 6 and Fig. 701 in Fig.7 show different schedules for valve lift events.

[0090] Regarding the Fig. 6 and Fig. 7: A positive gradient of Ca over a time interval in the time domain indicates that the angular velocity of the rotor must increase relative to the angular velocity of the crank (positive acceleration). A negative gradient of Ca over the time interval indicates that the angular velocity of the rotor must decrease relative to the angular velocity of the crank (negative acceleration). A zero gradient of Ca over the time interval indicates that the angular velocity of the rotor must not change relative to the angular velocity of the crank (zero acceleration).

[0091] Different gradients of Ca (different accelerations) at different points in a valve lift event result in different angular velocities of the rotor (relative to the angular velocity of the crank) at different points in the valve lift event. This, in turn, determines the angular position profile of the rotor at different points in the valve lift event. The angular position profile of the rotor, in turn, determines the displacement behavior of valve 440 at different points in the valve lift event. For example, if changes in crank angular velocity are ignored (e.g., assuming a constant engine speed), when Ca2 is higher than Ca1, valve 440 will close faster than it opens. When Ca2 is lower than Ca1, valve 440 will close slower than it opens.

[0092] The advantage of scheduling a valve lift event using a dimensionless velocity coefficient Ca, which expresses the rate of change of the rotor angular position determined using a time domain defined by the rotation of the camshaft, is that Ca is independent of the crank angular velocity, and therefore the schedule does not need to be recalculated with changes in engine speed. The execution rate of the schedule can simply depend on information from a crank position / angle sensor. This reduces computational complexity and maintains the transient response of the valvetrain 40 to rapid changes in engine conditions.

[0093] It is possible to create a valve lift event as in the Fig. 6 and Fig. 7 schematically illustrated schedules 601 or 701 and instruct the electromagnetic valve actuator 400 to perform the scheduled valve lift event.

[0094] The schedule 601 of Fig. 6 includes: a constant Ca1 section 602, in which Ca=Ca1 throughout the entire opening phase; and a constant Ca2 section 604, in which Ca=Ca2 throughout the entire closing phase. Constant Ca for the entire duration of the opening phase means that a constant zero acceleration is provided for the entire opening phase. Constant Ca for the entire duration of the closing phase means that a constant zero acceleration is provided for the entire closing phase. In Fig. , but not necessarily in all examples, Ca2 and Ca1 are different.

[0095] The control strategy can be improved to further reduce energy consumption, as explained below.

[0096] One improvement involves scheduling the valve lift event to include a period in which the acceleration of the rotor is constant and non-zero over the entire period, i.e., Ca has a positive or negative gradient over the entire period. The period consists of one or more of: part or all of the opening phase; part or all of the closing phase; part of the opening phase and part of the closing phase; or the entire opening phase and the entire closing phase. The non-zero acceleration is scheduled to reduce or eliminate the magnitude of the marked changes in Ca, such as the marked change between Ca1 and Ca2 under θ C,MOP ( Fig. ). Plan 701 of Fig. 7 is determined according to the improved control strategy. Plan 701 of Fig. 7 includes phases with constant acceleration not equal to zero.

[0097] A process for creating a schedule such as Schedule 701 is described in more detail. For explanation, it is helpful to refer to points A through H in Schedule 701 of Fig. 7. Points A to H are represented at the following crank angles along the crank rotation axis: A. A starting point within an engine combustion cycle that represents the beginning of the Fig. 7. The crank angle at point A is θ C,A and the rotor angle at point A is θ R,A . B1 and B2. Between the start of the schedule and the start of the opening phase. C. The beginning of the opening phase that initiates the valve lift event. The crank angle at point C is θ C,O and the rotor angle at point C is θ R,O. In some, but not necessarily all, examples, valve 440 is an intake valve, and point C may represent the beginning of an intake stage in a combustion cycle. Alternatively, valve 440 may be an exhaust valve, and point C may represent the beginning of an exhaust stage in the combustion cycle. D. During the opening phase, optionally at 50% of the opening phase duration. E. The end of the opening phase. In this example, E is also the beginning of the closing phase. The crank angle at point E is θ C,MOP and the rotor angle at point E is θ R,MOP . F. During the closing phase, optionally at 50% of the closing phase duration. G. The end of the closing phase, which terminates the valve lift event. The crank angle at point G is θ C,C and the rotor angle at point G is θ R,CIn some, but not necessarily all, examples, valve 440 is an intake valve, and point G may represent the end of an intake stage in a combustion cycle. Alternatively, valve 440 may be an exhaust valve, and point G may represent the end of an exhaust stage in the combustion cycle. H. An endpoint that occurs after point A. In some, but not necessarily all, examples, the duration from A to H is the duration of a complete combustion cycle. Point H does not necessarily indicate a final point in the schedule. In some examples, the schedule may continue beyond point H. The crank angle of point H is θ C,H and the rotor angle of point H is θ R,H .

[0098] An exemplary scheduling process for determining a schedule, such as the schedule illustrated in 701, is described. Although a particular order of operations is provided below, this is not intended to limit the operations of the scheduling process to occur in any particular order.

[0099] First, a straight line is determined that intersects the point E. A “line” represents a vector of Ca on the graph of Fig. 7. If the line is straight, the line represents a phase of constant acceleration. If the gradient of the line is non-zero, the line represents a phase of constant non-zero acceleration. Although reference is made to lines, the process is not limited to line-adaptive, regression, or geometry-based algorithms and applies to any process or algorithm that plans for equivalent rotor acceleration behavior.

[0100] Line DE is straight during the opening phase. Line DE is extended to C to form line CDE. Line EF is straight during the closing phase. Line EF is extended to G to form line EFG. Lines CDE and EFG have equal or unequal gradients. If the control strategy permits, lines CDE and EFG have the same gradient and form a single line CDEFG.

[0101] In some, but not necessarily all, examples, the average Ca calculated from the area under the curve of line CDE must be equal to Ca1. The average Ca calculated from the area under the curve of line EFG must be equal to Ca2. This ensures that the resulting valve lift behavior substantially meets the requirements of the target inputs. In some, but not necessarily all, examples, the value of Ca at point D is Ca1 and the value of Ca at point F is Ca2.

[0102] In some, but not necessarily all, examples, it would be desirable for the value of Ca at point C to be positive and non-zero to avoid unnecessary reversal of the rotor rotation before the start of the opening phase. In this example, a minimum threshold value of Ca is required at point C. In some, but not necessarily all, examples, if Ca at point C is sufficient to meet the minimum threshold, it is still necessary to recalculate Ca at other points in the opening and closing phases to ensure that the average Ca calculated from the area under the curve of line CDE agrees with Ca1, as described above, and to ensure that the average Ca calculated from the area under the curve of line EFG agrees with Ca2, as described above. This recalculation may cause the gradient of line CDE to decrease and the gradient of line EFG to increase.

[0103] If the target inputs include a fourth target specifying a lift amount of <100% of the maximum achievable valve lift, it would be necessary to reverse the rotor rotation direction once the target lift amount is reached (referred to herein as "bounce mode"). This means that Ca2 would be negative.

[0104] To achieve bounce mode and meet the target inputs, scheduling is performed such that Ca is negative at points F and G. In some examples: point E is fixed at Ca=0; line DE is straight and has a negative slope; in some examples, line CDE is straight and has a negative slope; line EF is straight and has a negative slope; and in some examples, line EFG is straight and has a negative slope. As described above, it may be necessary for the average Ca calculated from the area under the curve CDE to coincide with Ca1 and the average Ca calculated from the area under the curve EFG to coincide with Ca2. In some, but not necessarily all, examples, the value of Ca at point D is Ca1 and the value of Ca at point F is Ca2.

[0105] So far, the process has determined the vector of the line Ca from points C to G. The entire opening and closing phases have been scheduled, which is why the valve lift event has been scheduled.

[0106] In some, but not necessarily all, examples, additional scheduling is required. For example, the value of Ca at point A may differ from the target value of Ca at point C (input Ca at point C). For example, the value of Ca at point A may be zero because the rotor is not rotating at all (it is "parked"). Therefore, it is necessary to schedule a change in Ca from point A to point C (referred to herein as a "park-to-open" phase). The value of Ca at points A and / or C represents schedule constraints. The required mean angular velocity coefficient Ca3 between points A and C is: Ca3(Park−to−open phase)=(θR,A−θR,O) / (θC,A−θC,O)

[0107] The most efficient Ca plan for the park-to-open phase is the one of the following lines that results in the lowest total RMS acceleration of the rotating camshaft 404 for the park-to-open phase: CV0. A straight line A to B2 with a constant first gradient non-zero, followed by a straight line B2 to C with a constant, different second gradient non-zero. Optionally, the first gradient and the second gradient have opposite signs; CV1. A straight line starting at A or beyond A (i.e., after an initial pause phase), having a constant positive gradient other than zero and extending to C; or CV2. A straight line A to B1 with a constant positive gradient other than zero, followed by a straight line B1 to C with a zero gradient.

[0108] In some, but not necessarily all, examples, line CV2 does not provide the lowest RMS acceleration of rotation when Ca3 is less than 1.1 or greater than two. Line CV1 does not provide the lowest RMS acceleration of rotation when Ca3 is less than two. Line CV0 does not provide the lowest RMS acceleration of rotation when Ca3 is less than zero or greater than four. A lower RMS acceleration of rotation is associated with lower RMS energy consumption.

[0109] In some, but not necessarily all, examples, point B2 is fixed along the crank rotation axis at 50% of the crank rotation from A to C. Point B1 is fixed along the crank rotation axis at 2 (S - R / Ca(C)), where Ca(C) is Ca(C) at point C, S is the crank rotation during the park-to-open phase (θ C,O -θ C,A ), and R is the rotor rotation during the park-to-open phase (θ R,O -θC,A ).

[0110] In some, but not necessarily all, examples, the mean Ca calculated from the area under the curve of the chosen line CV0, CV1 or CV2 must be equal to Ca3.

[0111] At points G and H, the value of Ca at point H differs in some, but not necessarily all, examples from the required value of Ca at point G (initial Ca at point G). For example, the value of Ca at point H may be zero because the rotor is not rotating at all (it is "parked"). Therefore, it is necessary to schedule Ca from point G to point H (referred to herein as the "close-to-park" phase). The value of Ca at points G and / or H represents schedule constraints. The required mean angular velocity coefficient Ca4 between points G and H is: Ca4(phase close-to-park)=(θR,C−θR,H) / (θC,O−θC,H)

[0112] The most efficient Ca plan for the close-to-park phase is the one of the following lines that results in the lowest RMS acceleration of the rotation of the rotatable camshaft 404 for the close-to-park phase: CV3. A straight line from G to a point between G and H (e.g., 50% of the crank revolution from G to H along the crank revolution axis) having a constant nonzero first gradient, followed by a straight line from that point to H having a constant, different, nonzero second gradient. Optionally, the first gradient and the second gradient have opposite signs; CV4 A straight line starting at G and having a constant negative non-zero gradient (or a positive gradient if Ca2<0) and extending to H or to a point between G and H (i.e. followed by a pause phase to H from zero Ca); or CV5. A straight line from G to a point between G and H (e.g., to a point along the crank rotation axis at 2 (S - R / Ca(G)), where Ca(G) is Ca at point G, S is the crank rotation during the close-to-park phase (θ C,H -θ C,C ), and R is the rotor rotation during the close-to-park phase (θ R,H -θ C,C )) with a zero gradient, followed by a straight line from this point to H, with a constant negative gradient (or a positive gradient if Ca2<0).

[0113] In some, but not necessarily all, examples, line CV5 does not provide the lowest RMS acceleration of rotation when the absolute value of Ca4 is less than 1.1 or greater than 2. Line CV4 does not provide the lowest RMS acceleration of rotation when the absolute value of Ca4 is less than 2. Line CV3 does not provide the lowest RMS acceleration of rotation when the absolute value of Ca4 is less than zero or greater than 4.

[0114] In some, but not necessarily all, examples, the mean Ca calculated from the area under the curve of the chosen line CV3, CV4 or CV5 must be equal to Ca4.

[0115] In some, but not necessarily all, examples, the adjustment of the rotation of the camshaft 404 is scheduled so that the camshaft adjusts its rotation at one of several different angular positions of the camshaft 404, which are known from the detent positions of the electromagnetic valve actuator. These positions may be predetermined, for example, based on a known distribution of the stator slots of the electromagnetic valve actuator 400.

[0116] The previous description has provided only one process for scheduling Ca from point A to point H. Ca at point H could define Ca at point A of a next schedule for a next valve lift event. In some, but not necessarily all, examples, scheduling may continue for multiple consecutive valve lift events. In this way, energy consumption can be further optimized. For example, scheduling "between valve lift events" (the close-to-park phase after the current valve lift event and the subsequent park-to-open phase for the next valve lift event) can be adapted to the requirements of the next valve lift event, which may be different.

[0117] The different requirements or "characteristics" of each valve lift event may, for example, relate to a different maximum valve lift and / or a different valve lift speed. In a non-limiting use case, if Ca at point C of the next valve lift event needs to be significantly faster than Ca at point C of the previous valve lift event, the camshaft 404 may need to accelerate before point H of the previous valve lift event to achieve good efficiency.

[0118] Examples of possible changes to meet different valve lift requirements are explained below.

[0119] For example, it may be more energy efficient to leave Ca non-zero at point H so that the rotor is not parked at point H. In this example, the value of Ca is not constrained to zero at point H and / or point A, so there is effectively no "parking" constraint.

[0120] If there is no parking restriction, the camshaft 404 may rotate continuously throughout the entire period between valve lift events ("continuous rotation"). The process may determine whether to schedule parking or continuous rotation, whichever provides the lowest RMS energy consumption. Continuous rotation with constant acceleration without parking may result in lower RMS energy consumption if the most efficient "close-to-park" phase overlaps the most efficient "park-to-open" phase.

[0121] It should be noted that the circumferential length of the camshaft base circle (e.g., 180 degrees) should not be exceeded between valve lift events to avoid unintended valve opening. The area under the curve of the Ca diagram for continuous rotation corresponds to the distance traveled with respect to the angular displacement of the camshaft 404. However, if a straight line of Ca is simply planned from point G of one valve lift event to the next point C of the next valve lift event, the angular displacement of the camshaft 404 may exceed the circumferential length of the base circle (>180 degrees), resulting in unintended premature valve opening.

[0122] Therefore, instead of scheduling continuous rotations with constant acceleration between valve lift events, it may be desirable to schedule at least one "knee point," that is, a point of change in the acceleration of the camshaft relative to the crankshaft, at some point between valve lift events. The knee point may, in some examples, result in a reversal of the camshaft's rotation direction. The knee point may have a positive or negative Ca, where negative Ca refers to a reversal of the camshaft's rotation direction.

[0123] Fig. 8 illustrates an example of a schedule between two valve lift events, ie, from point G of a first valve lift event to point A of the next valve lift event. Fig. Figure 8 illustrates a knee point at position I with negative Ca.

[0124] In the event that the knee point has a negative Ca, the camshaft rotates rearward for at least a portion of the time between valve lift events. It is important to prevent camshaft 404 from rotating rearward farther than it has rotated forward since point G, otherwise an inadvertent rearward reopening of valve 440 will occur between valve lift events.

[0125] It is also important to prevent the 404 camshaft from rotating too far forward before rotating backward, otherwise unintended valve lift will occur.

[0126] The Ca value of the knee point and timing can be controlled to ensure that the total rotation between valve lift events does not exceed the camshaft base circle, thus avoiding premature valve opening.

[0127] A knee point could be biased in time toward the previous valve lift event (toward point G) or toward the next valve lift event (toward point C), and does not necessarily have to be halfway between them. Allowing some distortion of the knee point timing without necessarily limiting the knee point's Ca value can be a good compromise between efficiency and the need to avoid unintended valve opening. Fig. 8, the knee point I is biased towards the first valve lift event, i.e. closer to point G of the previous valve lift event than to point A of the next valve lift event.

[0128] In some examples, the process may only allow a finite acceleration in the transition between valve lift events, i.e., not allowing any marked changes between valve events. This is particularly useful in the transition period between adjacent valve lift events with different characteristics. One could say that during this transition period, the system is transitioning from one valve lift mode to another, e.g., between high-lift mode and low-lift mode; between early valve opening and late valve opening; between early valve closing and late valve closing; between single valve opening and double valve opening (two openings in one combustion cycle); or between different skew modes (duration of the opening phase relative to the duration of the closing phase). Marked changes in Ca are avoided in the mode transition process to reduce energy consumption and improve reliability.Therefore, a process according to various, but not necessarily all, aspects of the present disclosure would be understood to include the following:. Scheduling a first valve lift event having a first characteristic for a first combustion cycle associated with valve 440; Scheduling a second valve lift event having a second, different characteristic for a (the next) second combustion cycle associated with valve 440; and in the transition between the first valve lift event and the second valve lift event, instructing the electromagnetic valve actuator 400 to accelerate the rotation of its rotatable camshaft 404 using only finite acceleration to the speed required to activate the second valve lift characteristic.

[0129] Once scheduling is complete using an efficient scheduling algorithm, the schedule is converted into a control signal format capable of directly or indirectly causing the electromagnetic valve actuator 400 to execute the scheduled valve lift event or events. The controller 200 transmits the control signal to control the electromagnetic valve actuator 400 in the manner described above.

[0130] In some, but not necessarily all, examples, the controller is configured to convert the schedule in real time from Ca to absolute angular velocity while determining a specific electrical drive current for the electromagnetic valve actuator. The conversion involves multiplying Ca by the real-time crankshaft speed, measured by a crankshaft position sensor or the like. This ensures that the implementation of the schedule adapts dynamically to accommodate changes in engine speed.

[0131] The conversion can be performed at high frequency, e.g. in steps of 0.5 milliseconds, or faster, e.g. 0.2 milliseconds or 0.1 milliseconds, depending on the performance of the processor.

[0132] Although the embodiments of the present invention have been described in the preceding paragraphs using various examples, it should be noted that modifications may be made to the examples mentioned without departing from the scope of the claimed invention. For example, although the rotor angular velocity was expressed as a dimensionless coefficient Ca, equivalent planning approaches based on the actual rotor angular velocity (dimensions: rad / s or m / s) and a real-time range (dimensions: s) are possible.

[0133] Although a valve lift event between θ C,A and θ C,H was planned, in other examples, several valve lift events between θ C,A and θ C,H be planned.

[0134] The features described in the above description may be used in combinations other than those expressly described.

[0135] Although functions have been described with reference to certain features, these functions can be performed by other features, whether described or not.

[0136] Although features have been described with reference to particular embodiments, these features may also be present in other embodiments, whether described or not.

[0137] Although the foregoing specification attempts to draw attention to those features of the invention which are believed to be of particular importance, it is to be understood that the applicant claims protection for any patentable feature or combination of features referred to and / or shown in the drawings, whether or not specifically emphasized.

Claims

[1] A method (50) for controlling an electromagnetic valve actuator (400) having a rotatable camshaft (404) for actuating a valve (440) of an engine (20), the method (50) comprising: Scheduling a valve lift event comprising an opening phase from zero valve lift to a maximum valve lift and a closing phase from maximum valve lift to zero valve lift; Instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at constant or variable acceleration during at least one or more of: the opening phase; the closing phase; a section of the opening phase and a section of the closing phase; Instructing the electromagnetic valve actuator (400) to effect one of the following rotational behaviors of the rotatable camshaft (404) during a scheduled rotation of the rotatable camshaft (404), after the end of the closing phase and before the start of the next valve lift event associated with the valve (440), which results in the lowest overall effective acceleration of the rotation of the rotatable camshaft (404) when performing the scheduled rotation: Adjustment of the rotation of the rotating camshaft (404); Changing the acceleration of the rotating camshaft (404); or continuous constant accelerated rotation of the rotatable camshaft (404); the method further comprising: Instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at constant acceleration by one or more of: the entire opening phase; the entire closing phase; the entire opening phase and the entire closing phase. [2] The method (50) of the preceding claim, wherein the predetermined acceleration of the rotatable camshaft (404) is constant while at least one or more of: the opening phase; the final phase; a section of the opening phase and a section of the closing phase. [3] The method (50) of any preceding claim, wherein the predetermined acceleration of the rotatable camshaft (404) is non-zero over one or more of: the entire opening phase; the entire closing phase. [4] Method (50) according to one of the preceding claims, comprising: Planning the rotation of the rotatable camshaft (404) into an operating position prior to the opening phase to lift the valve (440) at the beginning of the opening phase; and Commanding the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at a constant acceleration during the scheduled rotation. [5] Method (50) according to claim 4, comprising: Instructing the electromagnetic valve actuator (400) to effect one of the following rotational behaviors of the rotatable camshaft (404) prior to the opening phase during the scheduled rotation, which results in the lowest overall effective acceleration of the rotation of the rotatable camshaft (404) when performing the scheduled rotation: constant acceleration of rotation; constant acceleration of rotation preceded or followed by a constant rotational speed; or constant non-zero acceleration of rotation, followed by constant varying non-zero acceleration of rotation. [6] Method (50) according to one of the preceding claims, comprising: Instructing the electromagnetic valve actuator (400) to cease rotation of its rotatable camshaft (404) after the closing phase prior to the start of the next valve lift event associated with the valve (440). [7] The method (50) of claim 6, wherein the adjustment of the rotation is scheduled such that the rotatable camshaft (404) adjusts the rotation in one of a plurality of different angular positions that are dependent on the detent positions of the electromagnetic valve actuator (400). [8] The method (50) of any preceding claim, wherein changing the acceleration of the rotatable camshaft (404) causes a reversal of a direction of rotation of the rotatable camshaft (404) over at least a portion of the scheduled rotation after the end of the closing phase and before the start of the next valve lift event. [9] Method (50) according to one of the preceding claims, comprising: Instructing the electromagnetic valve actuator (400) to effect one of the following rotational behaviors of the rotatable camshaft (404) during the scheduled rotation, which results in the lowest overall effective acceleration of rotation of the rotatable camshaft (404) when performing the scheduled rotation: constant acceleration of rotation; constant rotational speed followed by constant rotational acceleration; or constant non-zero acceleration of rotation, followed by constant varying non-zero acceleration of rotation. [10] Method (50) according to one of the preceding claims, comprising: Instructing the electromagnetic valve actuator (400) to reverse a direction of rotation of its rotatable camshaft (404), changing the angular velocity of the rotatable camshaft (404) from a positive value during the opening phase to a negative value during the closing phase. [11] Method (50) according to one of the preceding claims, comprising: Receiving target inputs indicating a start time for the valve lift event, a duration of the valve lift event, a time of maximum lift, and optionally a lift amount of the valve (440) at maximum lift, and wherein the scheduling of the valve lift event is dependent on the target inputs. [12] The method (50) of any preceding claim, wherein the constant acceleration is a constant rate of change of the angular velocity of the camshaft (404) over a time interval in a time range defined by the rotation of an engine crankshaft. [13] A method (50) for controlling an electromagnetic valve actuator (400) having a rotatable camshaft (404) for actuating a valve (440) of an engine (20), the method (50) comprising: scheduling a first valve lift event having a first characteristic for a first combustion cycle associated with the valve (440); Scheduling a second valve lift event having a second different characteristic for a second combustion cycle associated with the valve (440); and in the transition between the first valve lift event and the second valve lift event, instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) using only finite acceleration to the speed required to activate the second valve lift characteristic; the method further comprising: Instructing the electromagnetic valve actuator (400) to accelerate the rotation of its rotatable camshaft (404) at constant acceleration by one or more of: the entire opening phase; the entire closing phase; the entire opening phase and the entire closing phase. [14] The method (50) of claim 13, wherein the second characteristic corresponds to a different maximum valve lift and / or a different lift speed of the valve (440) compared to the first characteristic. [15] The method (50) of claim 13 or 14, wherein the first valve lift event comprises a valve opening phase and a valve closing phase, wherein the first characteristic is associated with a first rotational speed of the rotatable camshaft (404) at the beginning of the valve opening phase of the first valve lift event, and wherein the second valve lift event comprises a valve opening phase and a valve closing phase, wherein the second characteristic is associated with a second different rotational speed of the rotatable camshaft (404) at the beginning of the valve opening phase of the second valve lift event. [16] Controller (200) comprising means for carrying out the method (50) according to one of claims 1 to 15. [17] System comprising: the controller (200) of claim 16; and the desmodromic electromagnetic valve actuator (400) controlled by the controller (200). [18] An engine (20) comprising the controller (200) of claim 16 or the system of claim 17. [19] A vehicle comprising the controller (200) of claim 16 or the system of claim 17 or the engine (20) of claim 18. [20] A computer program comprising instructions which, when executed by one or more processors (202), cause a controller (200) to perform at least the method (50) according to any one of claims 1 to 15.

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