GB2580030A

GB2580030A - Engine valve actuation

Info

Publication number: GB2580030A
Application number: GB1820683.9A
Authority: GB
Inventors: Stone Roger
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-12-19
Filing date: 2018-12-19
Publication date: 2020-07-15
Anticipated expiration: 2038-12-19
Also published as: GB201820683D0; GB2580030B

Abstract

The present invention relates to an electromagnetic valve actuator 100 for at least one valve 300 of an internal combustion engine (40, Fig. 1), the electromagnetic valve actuator comprising: a rotor 102; a stator 101 for rotating the rotor; output means 104, 106 for actuating the valve in dependence on rotation of the rotor; and mechanical energy storage means 108, 110, 116, 118 arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor; The mechanical energy storage means comprises a cam means 108, the cam means having an asymmetric profile. The actuator 100 allows for continuously variable valve lift and improved engine efficiency.

Description

ENGINE VALVE ACTUATION

TECHNICAL FIELD

The present disclosure relates to engine valve actuation: and more particularly to rate of energy recovery and release by an energy recovery system of an engine valve actuator. In particular, but not exclusively it relates to rate of energy recovery and release by an energy recovery system of an electromagnetic valve actuator for an engine valvetrain of a vehicle.

Aspects of the invention relate to an electromagnetic valve actuator, a controller, a valve actuation system, an internal combustion engine, a vehicle, a method and a computer program.

BACKGROUND

Conventional camshaft-driven engine valvetrains suffer from limited or no adjustability of poppet valve ('valve' herein) timing and lift. Various systems have been derived to enable discrete variable valve lift (VVL) and even continuously variable valve lift (CVVL). CVVL systems enable improved engine efficiency.

Electromagnetic valve actuators (EVAs) can enable CVVL. Since the EVA is not physically coupled to the engine crankshaft, valves can be lifted at any time during a combustion cycle, to any target peak lift.

EVAs present various challenges, such as their parasitic energy consumption and difficulty to package within a vehicle.

SUMMARY OF THE INVENTION

It is an aim of the present invention to address disadvantages of the prior art.

Aspects and embodiments of the invention provide an electromagnetic valve actuator, a controller, a valve actuation system, an internal combustion engine, a vehicle, a method and a computer program as claimed in the appended claims.

According to an aspect of the invention there is provided an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means (output) for actuating the valve in dependence on rotation of the rotor; and mechanical energy storage means (mechanical energy storage device) arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor; wherein the mechanical energy storage means comprises a cam means (cam): the cam means having an asymmetric profile. In some examples, the cam means comprises an energy storage flank for enabling the mechanical energy storage means to store energy, and an energy release flank for enabling the mechanical energy storage means to release the energy, wherein the asymmetric profile comprises the energy storage flank having a different profile from the energy release flank.

The mechanical energy storage means defines a form of energy recovery system (ERS) which recovers energy from the inertia of the moving parts of the valvetrain. The energy is then released to assist with rotor acceleration, allowing a smaller stator rated at a lower torque. Valvetrain energy consumption is reduced. An advantage of asymmetric cam means is that the rotor deceleration during energy storage, and/or rotor acceleration during energy release, is optimized. This optimization could reduce the amount of stator torque required to achieve a required acceleration or deceleration. The power loss is reduced because less stator torque over a longer period consumes less power than more stator torque over a shorter period. Stator torque requires stator current and power loss is proportional to the square of current (I2R).

In some examples, the asymmetric profile comprises the energy storage flank having a lower average steepness than the energy release flank. An advantage is optimizing rotor deceleration during energy storage. This is because a situation may arise in which the stator is burdened with applying torque to fully charge the mechanical energy storage means. This situation may arise when inertia is too low for full energy recovery (e.g. low engine speed), causing the mechanical energy storage means to be a parasitic. By reducing the steepness, the parasitic effect is reduced because I2R losses are optimized. The energy release flank has a greater steepness, which may be adapted to the rate of energy release of the mechanical energy storage means. The greater steepness of the energy release flank may ensure that the cam means remains in continuous contact with the mechanical energy storage means during energy release. This improves efficiency because lost motion between the mechanical energy storage means and the energy release flank is avoided. If the steepness were insufficient, the stator may need to accelerate the rotor during the release of energy by the mechanical energy storage means to achieve a target rotor velocity for a valve lift event, so that the cam means would no longer be in contact with the mechanical energy storage means.

In some examples. the cam means comprises a single lobe having the energy storage flank and the energy release flank. An advantage is more space efficient packaging as the rotor does not have to be long enough to provide two lobes.

In some examples, the output means is desmodromic. A desmodromic application enables a target rotor velocity for closing the valve to be higher than a target rotor velocity for opening the valve, enabling skewed valve lifts which can improve combustion efficiency. Beyond the inherent advantages of desmodromic systems, an advantage of a shallower energy storage flank is to avoid a situation which can arise when the mechanical energy storage means is parasitic for the reason described above. In this situation, the stator is burdened with charging the mechanical energy storage means. If the stator has to do this while simultaneously accelerating the rotor to meet a target rotor velocity for closing the valve, the stator may be saturated such that the target rotor velocity cannot be satisfied, and the valve allows too much gas exchange. Therefore, a shallower energy recovery side of the cam means for a desmodromic application reduces the maximum in-service stator torque, allowing for a smaller and lighter stator.

In some examples the mechanical energy storage means is configured to supply X Nm of torque when releasing the energy to assist rotation of the rotor, wherein the stator is configured to supply up to Y Nm of torque for rotating the rotor, and wherein X is from the range 40% to 95% of Y. In some examples, X is from the range 60-95% of Y. An advantage is that net torque can be close to 2V without needing more stator windings contained in a larger stator housing. Since the mechanical energy storage means is smaller and lighter than the stator, the valvetrain is fighter and easier to package within a small engine bay such as an automobile engine bay.

In some examples, Y is less than a torque required to fully open the valve at an engine speed above 5000 rpm. An advantage is that there is no need for a larger stator housing. At high engine speeds the assistance from Ens is necessary and sufficient to meet target rotor velocity.

In some examples. the mechanical energy storage means comprises a resilient member. In some examples, the mechanical energy storage means comprises a cantilever spring. This is a highly space-efficient design, for system rightness and ease of packaging.

In some examples, the output means comprises an output cam means for actuating the valve. The output cam means may also be located on the rotor for space-efficiency.

In some examples, the cam means is oriented such that peak lift of the cam means occurs between closing of the valve and the next opening of the valve. The rotor could be held stationary at a park position while the cam means is at peak lift. The park position could be aligned with a detent location for minimal cogging torque.

According to another aspect of the invention there is provided a controller for an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means the cam means having an asymmetric profile, wherein the controller comprises: means to control the stator to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means. An advantage is to ensure that the cam means is at peak lift when the rotor settles in the park position. 25 According to a further aspect of the invention there is provided a controller as described above; wherein: said means to control the stator to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means comprises an electronic processor having one or more electrical inputs for receiving a parameter indicative of a requirement to perform said control; and an electronic memory device electrically coupled to the electronic processor and having computer program instructions stored therein; the processor being configured to access the memory device and execute the instructions stored therein such that it is operable to determine a requirement to perform said control, and perform said control in dependence on the determination.

In some examples. 'means to' perform a function comprises: at least one electronic processor; and at least one electronic memory device electrically coupled to the electronic processor and having instructions stored therein, the at least one electronic memory device and the instructions configured to; with the at least one electronic processor, perform the function.

In some examples; the controller comprises means to control the stator to provide torque for desmodromically closing the valve, while at the same time providing the assistive torque. An advantage is that a higher target rotor velocity for closing the valve is available while simultaneously providing the assistive torque, without exceeding maximum stator current.

According to a further aspect of the invention there is provided a valve actuation system comprising the electromagnetic valve actuator and the controller.

According to a further aspect of the invention there is provided an internal combustion engine comprising the electromagnetic valve actuator or the controller or the valve actuation system.

According to a further aspect of the invention there is provided a vehicle comprising the internal combustion engine.

According to a further aspect of the invention there is provided a method of controlling an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means the cam means having an asymmetric profile, wherein the method comprises: controlling the stator to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means.

According to a further aspect of the invention there is provided a computer program that, when run on at least one electronic processor: causes at least: controlling an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means the cam means having an asymmetric profile, such that: the stator is controlled to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means.

According to a further aspect of the invention there is provided a non-transitory tangible physical entity embodying a computer program comprising computer program instructions that, when executed by at least one electronic processor, enable a controller at least to perform any one or more of the methods described herein.

According to a further aspect of the invention the mechanical energy storage means as described above is not necessarily mechanical but could be any energy storage means, e.g. electrical or chemical.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or the any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

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 2A illustrates an example of a controller and Fig 2B illustrates an example of a computer-readable storage medium; Fig 3 illustrates an example of an electromagnetic valve actuator a mechanism and a poppet valve; and Fig 4 illustrates an example of asymmetric cam means.

DETAILED DESCRIPTION

Fig 1 illustrates an example of a vehicle 10 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 10 is a passenger vehicle, also referred to as a passenger car or as an automobile. Passenger vehicles generally have kerb weights of less than 5000 kg. In other examples, embodiments of the invention can be implemented for other applications, such as industrial vehicles, air or marine vehicles.

The vehicle 10 comprises an internal combustion engine (engine') 40. The engine comprises a valvetrain 20. The valvetrain 20 comprises the EVA 100 (not shown in Figure 1) embodying one or more aspects of the invention.

The vehicle 10 comprises a controller 50. An example implementation of the controller 50 is shown in Fig 2A. The controller 50 may consist of a single discrete control unit such as shown in Fig 2A and described below, or its functionality may be distributed over a plurality of such control units. The controller 50 may comprise an engine control unit and/or a dedicated valvetrain control unit and!or any other appropriate control unit(s). The controller 50 and EVA 100 may together define a valve actuation system when together.

The controller 50 includes at least one electronic processor 52; and at least one electronic memory device 54 electrically coupled to the electronic processor and having instructions 56 (e.g. a computer program) stored therein, the at least one electronic memory device and the instructions configured to, with the at least one electronic processor, cause any one or more of the methods described herein to be performed.

Fig 2B illustrates an example of a non-transitory computer-readable storage medium 58 comprising the computer program 56.

An example design of the EVA 100 is now described, with reference to Fig 3. Although the asymmetry of the cam means is not shown in Fig 3. an example underlying system to which the asymmetric cam means can be applied is shown.

Each EVA 100 may be for actuating a single valve 300 or for actuating a plurality of valves. In an engine 40 having a plurality of combustion chambers, each combustion chamber may be associated with one or more valves for allowing gas exchange to/from the combustion chamber, EVAs may be provided for at least one of the one or more valves. Therefore, the valvetrain 20 may comprise a plurality of EVAs.

Depending on implementation, EVAs may be provided for intake valves, for exhaust valves, or for a combination thereof.

The EVA 100 comprises an electric machine comprising a rotor-stator pair. Energy to the stator 101 can be supplied from any appropriate known energy source on the vehicle 10 such as a battery or the engine. The energy may be supplied via an alternator or inverter.

The rotor 102 opens the valve 300 via any appropriate means. In Fig 3 the rotor 102 comprises output means comprising an opening lobe 104. The opening lobe 104 may be coupled to the valve 300 via any appropriate mechanism 200 such as a conventional tappet. In Fig 3 the mechanism 200 is more complex than a conventional tappet. The mechanism 200 comprises an upper rocker 202,204 and a lower rocker 208 coupled to each other by a pushrod 206. Valve movement may be amplified relative to the lift of the opening lobe 104 by a multiple within the range 1.3 to 1.95. This range of mechanical advantage is for optimized tolerances, power consumption and system packaging. The EVA 100. mechanism 200 and valve 300 when supplied together may define a system.

The force required to close the valve 300 can be provided by a valve return spring (not shown) and/or by configuring the EVA 100 for desmodromic operation. In Fig 3. the EVA 100 is configured for desmodromic operation. In Fig 3, but not necessarily in all examples, the output means comprises a closing lobe 106. The opening lobe 104 actuates a clockwise portion 202 of the upper rocker (clockwise from perspective of Fig 3) and the closing lobe 106 actuates a counter-clockwise portion 204 of the upper rocker. The rocker 202, 204 pushes and pulls the pushrod 206. The pushrod 206 causes the lower rocker 208 to push and pull the stem of the valve 300. The lower rocker 208 grips the valve 300 like a claw to enable both opening and closing.

The stator 101 can apply positive and negative torque to accelerate and decelerate the rotor 102 and reverse its direction of rotation. The nominal output of the stator 101 may be capable of supplying up to Y Nm of torque for rotating the rotor 102. In one implementation, Y may be from the range approximately 0.5Nm to approximately 1.5Nm. The valve lift events that can be achieved is limited by the speed/acceleration/jerk of the rotor which is limited by Y and the derivative(s) of Y. To plan valve lift events and control stator current accordingly, the controller 50 may receive information indicative of one or more required properties of one or more upcoming valve lift events, such as valve opening time, peak valve lift, and valve closing time. The controller may determine a target rotor velocity (angular velocity) for achieving the valve lift curve. A relationship between target rotor velocity and stator current is stored in the controller 50. The stator current is determined and an output signal is transmitted which causes any appropriate power electronics to control the stator current. The controller 50 may be equipped to control stator current in various engine operating scenarios, including one or more of: * Perform a full valve lift event by rotating the rotor 102 in a first direction for the valve opening stage and continuing rotation in the first direction for the valve closing stage.

* Perform a partial valve lift event by rotating the rotor 102 in a first direction for the valve opening stage and in a second, opposite direction for the valve closing stage. The reversal occurs when a target peak lift less than the maximum peak valve lift is reached. The reversal requires negative stator current.

* Perform a skewed full or partial valve lift event wherein the target rotor velocity in the valve closing stage is different from the target rotor velocity in the valve opening stage.

* Perform multiple valve lifts in one stage of a combustion cycle. For example, the rotor may be rotated twice rather than once. Or, the rotor may be reversed twice or three times.

* -Park' the rotor 102 between valve lift events at a park position, in which the target rotor velocity is zero.

This requires negative 'braking' torque. The park position may correspond to a detent location for minimal cogging torque, so that little or no energy is required to hold the rotor 102 in the park position. The detent locations are specific to the permanent magnet arrangement of the stator 101.

In one implementation, the size of the stator 101 is constrained by engine bay space. It may be that Y is less than a torque required to fully open the valve 300 at an engine speed above 5000 rpm, e.g. for a gasoline engine. Therefore. the stator 101 may require assistance for achieving one or more of the above-described target rotor velocities. Therefore, as shown in Fig 3, the EVA 100 comprises a mechanical energy storage means, referred to as ERS (energy recovery system) herein. The nominal output of the ERS may be capable of supplying up to X Nm of torque for rotating the rotor 102, wherein X<Y and wherein X is approximately 80% of Y, or any other value from the range approximately 60% to approximately 95% of Y. Working together, the stator 101 and ERS can supply nearly X+Y torque to the rotor 102. If the stator can be larger, X could be from the broader range approximately 40% to approximately 95% because less assistance is required.

In Fig 3, but not necessarily in all examples, the ERS is cam-actuated. Cam means in the form of an ERS lobe 108 is shown on the rotor 102. The ERS lobe 108 directly or indirectly couples to a resilient member for storing elastic deformation energy. In Fig 3 the coupling is via an ERS rocker 110. In Fig 3, but not necessarily in all examples, the resilient member is a cantilever spring 116 which is deflectable about a fulcrum 118. The stiffness of the cantilever spring 116 can be configured to store elastic potential energy for X Nm of torque assistance when fully actuated by the nose of the ERS lobe 108. No elastic potential energy is stored when on the base circle of the ERS lobe 108. In other examples the resilient member could be a different type of resilient member such as a coil spring or other resiliently deformable component.

The operation of the ERS will now be described, with reference to a typical engine operating scenario. In this scenario, the ERS is charged during valve closing and the energy is released prior to the next valve opening. During the valve opening phase, the contact point between the ERS lobe 108 and the ERS rocker 110 is on the base circle of the ERS lobe 108, so that energy recovery does not commence while the valve 300 is opening. Then, during the valve closing phase the contact point between the ERS lobe 108 and the ERS rocker 110 ascends up a flank of the ERS lobe 108 to bias the cantilever spring 116 away from its equilibrium position. Once peak lift of the ERS lobe 108 is reached, the cantilever spring 116 is fully deflected (ERS fully 'charged'). It may be that the peak lift is aligned with a detent location as described above, so that the ERS is fully charged while the rotor 102 is in a park position. Fig 3 also shows that the ERS lobe 108 has a substantially flat top which is sufficiently flat to increase stability/reduce wobble. As soon as the rotor 102 starts to move for the next valve lift event, the contact point descends down a flank of the ERS lobe 108. If rotation is in the same direction the flank is the opposite flank from that which was ascended. If rotation is in reverse the flank is the same flank which was ascended. The cantilever spring 116 is no longer forced away from its equilibrium position so releases its energy to accelerate the ERS lobe 108. This accelerates the rotor 102. This extra acceleration torque assists the stator 101 in meeting the target rotor velocity for the next valve lift event.

The ERS of Fig 3 is also space-efficient for various reasons. One of the most significant packaging constraints for engine bays is the height of the EVA 100. The Ens lobe 108 is integrated into the rotor 102 and therefore does not increase the overall height of the system. The ERS rocker 110 is positioned lower than the top of the stator housing 122. The cantilever spring 116 comprises a coupling 120 at one end to the top of the stator housing 122. The axis of the cantilever spring 116 is substantially horizontal. In Fig 3 the fulcrum 118 is separate from the coupling 120 and located towards the free end of the cantilever spring, but in other examples the fulcrum 118 could be provided by the coupling 120. The fulcrum 118 is above the cantilever spring 116, but the top of the fulcrum 118 is only in the order of tens of millimetres higher than the top of the stator housing 122, for example from the range approximately lOmm to approximately 20mm.

Although the above design is space-efficient, it would be appreciated that various aspects of the invention relate to asymmetric cam means which can be achieved with a different implementation of the ERS and/or EVA 100 from that shown. In other examples the ERS may be implemented with different mechanical components, or even electronically, electromagnetically, hydraulically or pneumatically. Further, although one ERS lobe 108 is shown, more than one could be provided, or none if a different principle of actuation is provided such as a belt, chain or even an electric machine.

According to an aspect of the invention, the FRS lobe 108 is the cam means having an asymmetric profile. Fig 4 illustrates an example of the asymmetric profile.

The ERS lobe 108 comprises an energy storage flank 402 for enabling the ERS to store energy. The FRS lobe 108 comprises an energy release flank 404 for enabling the ERS to release the energy. When the ERS lobe 108 is rotated in a 'default' direction (for example clockwise in Figure 4) and performs a full rotation, the flank 402 charges the ERS. In some operating scenarios, the ERS lobe 108 may be operated in reverse such that the functions of the flanks 402 and 404 are reversed. Or, the ERS may be charged in the default direction and discharged in reverse, so one flank 402 or 404 performs both the energy storage and release functions. However, the flank 402 is for storage and the flank 404 is for release, when a default full valve lift event is scheduled.

Fig 4 also shows the optional substantially flat top 406, wherein this flatter lobe nose increases stability while the ERS is charged. The flatter lobe noses increases stability because, when the contact point between the ERS lobe 108 and ERS rocker 110 coincides with the flat top 406, the inwardly directed force provided by the spring bias does not induce rotation, and in fact slightly opposes it.

The asymmetric profile comprises the energy storage flank having a different profile from the energy release flank.

In Fig 4, but not necessarily in all examples, the asymmetric profile comprises the energy storage flank having a lower average steepness than the energy release flank. This is achieved in Fig 4 by the length of the energy storage flank 402 being longer than the length of the energy release flank 404. Since the lift of the energy storage flank 402 relative to the base circle 408 is the same as the lift of the energy release flank 404 relative to the base circle 408, the increased length of the energy storage flank 402 gives the energy storage flank 402 its lower steepness.

Steepness could be expressed in terms of distance per radian, for example. Distance represents the lift of the flank relative to the base circle 408, and radians represents a unit of angular change. Further. the lower steepness is a lower average steepness. The energy storage flank 402 could have a complex geometry such that some sections of the energy storage flank 402 have a higher instantaneous steepness than a section of the energy release flank 404, wherein the average steepness is still lower. In some examples, the steepness at any arbitrary point along the energy storage flank 402 is lower than the average steepness of the energy release flank 404. In some examples, the steepness at any arbitrary point along the energy storage flank 402 is lower than the steepness at any arbitrary point along the energy release flank 404.

This asymmetry can be utilised in various useful ways by a controller 50 planning valve lift events. For example, the controller 50 may be configured to provide torque for desmodromically closing the valve during a valve closing phase. This torque may be required for accelerating the rotor 102 to achieve a higher target rotor velocity in the valve closing phase than in the valve opening phase. The controller 50 may also be configured to provide the assistive torque needed to cause the stator to provide assistive torque to reach the ERS lobe nose, when the inertia is insufficient to charge the ERS. This assistance may be required at the same time as the higher target rotor velocity in the valve closing phase is required, depending on the phasing of the ERS lobe 108 relative to the output means. Without the asymmetry, the target rotor velocity for the valve closing phase may be low so that enough stator torque capacity is left to provide the assistive torque. Taking into account the asymmetry: the controller may be programmed so that the maximum available target rotor velocity for the valve closing phase is higher than would otherwise be possible for a system without the asymmetric cam means.

During release of energy from the mechanical energy storage means, the controller 50 may be configured to cause the stator 101 to apply a small amount of negative torque for slightly braking the descent of the energy release flank 404, therefore ensuring continuous contact between the energy release flank 404 and the ERS rocker 110.

Another way in which the asymmetry could be utilised is in planning whether to rotate the rotor 102 forward or in reverse. This could take into account the timing of the valve opening time and the valve closing time, to determine whether a short ramp (flank 404) or a long ramp (flank 402) is most efficient for acceleration or deceleration. For a partial valve lift event, the controller 50 could determine in which direction to rotate the rotor 102: based on whether the long ramp (flank 402) or the short ramp (flank 404) best achieves a target valve lift profile and/or is most efficient. For example: reversing the rotation of the rotor using the long ramp results in a flatter-topped valve lift profile, wherein the valve 300 remains at its target peak lift for longer. Reversing the rotation of the rotor using the short ramp results in a sharper-topped valve lift profile. The short ramp may be used below an engine-speed threshold and the long ramp above the threshold: the direction of rotation may be controlled such that the long ramp may be used for energy storage and the short ramp used for energy release, if rotor velocity for a preceding or later valve rift event is above a threshold.

For purposes of this disclosure, it is to be understood that the controller(s) described herein can each comprise a control unit or computational device having one or more electronic processors. A vehicle and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); 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 ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples. it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. An electromagnetic valve actuator for at least one valve of an internal combustion engine the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; and mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor; wherein the mechanical energy storage means comprises a cam means, the cam means having an asymmetric profile.
2. The electromagnetic valve actuator of claim 1, wherein the cam means comprises an energy storage flank for enabling the mechanical energy storage means to store energy, and an energy release flank for enabling the mechanical energy storage means to release the energy, wherein the asymmetric profile comprises the energy storage flank having a different profile from the energy release flank.
3. The electromagnetic valve actuator of claim 2, wherein the asymmetric profile comprises the energy storage flank having a lower average steepness than the energy release flank.
4. The electromagnetic valve actuator of claim 2 or 3, wherein the cam means comprises a single lobe having the energy storage flank and the energy release flank.
5. The electromagnetic valve actuator of any preceding claim, wherein the output means is desmodromic.
6. The electromagnetic valve actuator of any preceding claim, wherein the mechanical energy storage means is configured to supply X Nm of torque when releasing the energy to assist rotation of the rotor, wherein the stator is configured to supply up to Y Nm of torque for rotating the rotor, and wherein X is from the range 40% to 95% of Y.
7. The electromagnetic valve actuator of claim 6. wherein Y is less than a torque required to fully open the valve at an engine speed above 5000 rpm.
8. The electromagnetic valve actuator of any preceding claim, wherein the mechanical energy storage means comprises a resilient member.
9. The electromagnetic valve actuator of claim 8, wherein the mechanical energy storage means comprises a cantilever spring.
10. The electromagnetic valve actuator of claim 9, wherein the output means comprises an output cam means for actuating the valve.
II. The electromagnetic valve actuator of any preceding claim, wherein the cam means is oriented such that peak lift of the cam means occurs between closing of the valve and the next opening of the valve.
12. A controller for an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means the cam means having an asymmetric profile, wherein the controller comprises: means to control the stator to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means.
13. The controller of claim 12. comprising means to control the stator to provide torque for desmodromically closing the valve, while at the same time providing the assistive torque.
14. A valve actuation system comprising the electromagnetic valve actuator as claimed in any one or more of claims Ito 11 and the controller as claimed in claim 12 or 13.
15. An internal combustion engine comprising the electromagnetic valve actuator as claimed in any one or more of claims 1 to 11 or the controller as claimed in claim 12 or 13 or the valve actuation system as claimed in claim 14.
16. A vehicle comprising the internal combustion engine as claimed in claim 15.
17. A method of controlling an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means, the cam means having an asymmetric profile, wherein the method comprises: controlling the stator to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means.
18. A computer program that. when run on at least one electronic processor, causes at least: controlling an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising: a rotor; a stator for rotating the rotor; output means for actuating the valve in dependence on rotation of the rotor; mechanical energy storage means arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, wherein the mechanical energy storage means comprises a cam means, the cam means having an asymmetric profile, such that: the stator is controlled to provide assistive torque for the rotor to rotate past an energy storage flank of the cam means.