GB2593102A

GB2593102A - Engine valve actuation

Info

Publication number: GB2593102A
Application number: GB2107306.9A
Authority: GB
Inventors: Tyrrell Richard
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-12-19
Filing date: 2018-12-19
Publication date: 2021-09-15
Anticipated expiration: 2038-12-19
Also published as: GB201820684D0; GB2593102B; GB2580031B; GB202107306D0; GB2580031A

Abstract

An electromagnetic valve actuator 100 for at least one valve 300 of an internal combustion engine (40, Fig. 1), comprising: a rotor 102; a stator 101 for rotating the rotor; 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, wherein the mechanical energy storage means comprises cam means 108, the cam means having a staged profile (1082, 1084, 1085, 1086, 1087, 1088, 1083, Fig. 5).

Description

ENGINE VALVE ACTUATION

TECHNICAL FIELD

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

Aspects of the invention relate to 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 a first 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; 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 control means (control device) to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction: between a first positive amount and a second positive amount.

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 control means is that the mechanical energy storage means is controllable based on the amount of inertia available to most efficiently capture the energy and mitigate a scenario in which the mechanical energy storage means could become parasitic. The mechanical energy storage means could become parasitic if there is insufficient inertia, requiring the stator to instead -charge' the mechanical energy storage means.

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 spring arrangement provides a highly space-efficient design, for system lightness and ease of packaging.

In some examples the control means is configured to change a characteristic of a fulcrum of the resilient member to vary the quantity of energy storable in the mechanical energy storage means. This 'active fulcrum' can advantageously tune the mechanical energy storage means to the amount of available inertia.

In a first example implementation the control means comprises staging means (staging device) for controlling staged actuation of the mechanical energy storage means. In some examples the staging means controls the relative duration of a flrst stage of actuation of the mechanical energy storage means and a second stage of actuation of the mechanical energy storage means, wherein in the first stage of actuation less energy is stored in the mechanical energy storage means. In some examples the first stage is a lost motion stage in which no energy is stored in the mechanical energy storage means. In some examples the staging means comprises a fulcrum, wherein the fulcrum comprises a cylinder having a plurality of cross-sectional radii. The fulcrum could therefore be described as an active fulcrum. In some examples the staging means comprises a deactivated position, e.g. deactivated cross-sectional radius, allowing no energy to be stored in the mechanical energy storage means. An advantage is that the mechanical energy storage means can be controlled with few moving parts such as a rotary actuator, to tune the mechanical energy storage means (e.g. spring) to the available inertia.

In a second example implementation the control means comprises lever arm length adjusting means (lever arm length adjuster) for adjusting the length of a lever arm of the mechanical energy storage means, the length of the lever arm controlling energy storable by the mechanical energy storage means. In some examples the lever arm length adjusting means is configured to adjust the length of the lever arm by adjusting fulcrum location, using an active fulcrum which can be translationally moved relative to the lever arm. In some examples the lever arm length adjusting means is substantially continuously movable between two locations. An advantage is that the mechanical energy storage means can be controlled with few moving parts such as a rotary actuator, to tune the mechanical energy storage means (e.g. spring) to the available inertia.

In a third example implementation other than the active fulcrum described above, the control means comprises cam means (cam), the cam means having a staged profile. In some examples the staged profile comprises a first stage of the cam means defining a first park position in which the rotor can cease rotation at the end of a period of rotation of the rotor such that the amount of energy stored in the mechanical energy storage means corresponds to the first positive amount, and a second stage defining a second park position in which the rotor can cease rotation at the end of a period of rotation of the rotor such that the amount of energy stored in the mechanical energy storage means corresponds to the second positive amount. In some examples the first stage comprises a plateau in a flank of the cam means, and the second stage comprises the nose of the cam means. An advantage is that the energy storage can be controlled simply by stopping the rotor at the first park position before reaching the lobe nose. when available inertia is low. Therefore, a parasitic region between the first park position and the lobe nose can be avoided. The stator can then rotate the rotor in reverse to perform the next valve lift event or can climb the remaining parasitic region when there are no other higher priority demands on the stator, such as achieving a particular target rotor velocity for a valve lift event.

In some examples two or more of the first implementation, the second implementation or the third implementation can be combined to enable a finer level of control.

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, 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 2Y 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 lighter 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 greater than 5000 rpm. An advantage is that there is no need for a larger stator housing. At high engine speeds the assistance from ERS is necessary and sufficient to meet target rotor velocity.

In some examples the electromagnetic valve actuator is desmodromic. The output means may comprise an opening lobe and a closing lobe. 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 phasing the ERS in a desmodromic application is to avoid the situation described above in relation to the first example operating scenario, to enable the target rotor velocity for closing the valve to be achieved.

According to a further 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; 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 cam means, the cam means having a staged profile. This relates to at least the third example implementation.

According to a further aspect of the invention there is provided a controller configured to control 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; 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 control means to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction, between a first positive amount and a second positive amount, wherein the controller comprises: means to cause the control means to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction, between at least the first positive amount and the second positive amount. This enables tuning of the mechanical energy storage means to the amount of available inertia.

According to a further aspect of the invention there is provided a controller as described above, wherein: said means to cause the control 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 in dependence on the parameter, 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 control means in dependence on a parameter indicative of kinetic energy. In some examples the parameter is engine speed-dependent. For example the engine-speed dependent parameter could be engine speed or target rotor velocity. In some examples the controller comprises means to control the control means to increase the quantity of energy stored to the second positive amount when the parameter increases above a threshold. Low engine speed or rotor velocity is an example parameter for identifying when the mechanical energy storage means is parasitic.

In some examples the controller comprises means to reverse the direction of rotation of the rotor for a subsequent period of rotation of the rotor. This relates to at least the third example implementation. An advantage is there is no need to climb the parasitic region to the lobe nose.

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.

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; 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 control means to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction: between a first positive amount and a second positive amount, wherein the method comprises: causing the control means to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction, between at least the first positive amount and the second positive amount.

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; 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 control means to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction, between a first positive amount and a second positive amount, such that: the control means is caused to control the amount of energy stored in the mechanical energy storage means by the end of a period of rotation of the rotor in a first direction, between at least the first positive amount and the second positive amount.

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 28 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; Fig 4 illustrates an example of staging means; Fig 5 illustrates an example of cam means with a staged profile; and Fig 6 illustrates an example of lever arm length adjusting 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 some specific aspects of the control means are not shown in Fig 3, an example underlying system to which the control 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 tappet. In Fig 3 the mechanism 200 is more complex. 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 phase and continuing rotation in the first direction for the valve closing phase.

* Perform a partial valve lift event by rotating the rotor 102 in a first direction for the valve opening phase and in a second: opposite direction for the valve closing phase. 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 phase is different from the target rotor velocity in the valve opening phase.

* Perform multiple valve lifts in one phase 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 greater than 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 Ens 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 FRS lobe 108 to bias the cantilever spring 116 away from its equilibrium position. Once peak lift of the FRS 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 ERS 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 at the location of coupling 120. The fulcrum 118 could provide the function of the coupling. 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 controlling energy stored by the ERS 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.

Fig 4 relates to the first example implementation discussed earlier. Fig 4 is an illustration of the principle of staging means for controlling staged actuation of the ERS. and a possible implementation.

The implementation of Fig 4 relies on an active fulcrum. The active fulcrum in Fig 4 is a cylinder configured to be actuated (rotated). While referred to herein as a cylinder, it should be understood that the active fulcrum is only generally cylindrical, since it does not have a uniform cross section. The fulcrum 118 and the cantilever spring 116 are in contact at a contact point preferably at all times. To maintain contact between the fulcrum 118 and the cantilever spring 116. the ERS rocker 110 may be permanently biased against the underside of the cantilever spring 116 [distal from the pivot point of the cantilever spring]. For the embodiment of Figure 4 the contact point between the fulcrum 118 and the cantilever spring 116 is static, although in other embodiments (see for example Figure 6) the contact point is not static. The fulcrum 118 is rotatable about an axis of rotation in a manner which varies (with angular positon) the distance between the axis of rotation and the contact point. As a result, the cantilever spring 116 moves towards the axis of rotation of the fulcrum 118 when the distance between the axis of rotation of the fulcrum 118 and the contact point decreases, and moves away from the axis of rotation of the fulcrum 118 (and towards the ERS rocker 110) when the distance between the axis of rotation of the fulcrum 118 and the contact point increases. In some embodiments, for at least one position of the fulcrum 118, a gap exists between the ERS lobe 108 and the ERS rocker 110 when the ERS rocker 110 is aligned with (but not in contact with) the base circle of the ERS lobe 1108. The size of this gap is controlled to vary the duration of a lost motion stage during which the cantilever spring 116 is not deflected and no energy is stored therein.. In Fig 4, but not necessarily in all examples, the size of the gap is controlled by rotating the fulcrum 118 using an actuator (not shown) from a first stage (position) in which a contact point formed when the fulcrum 118 and the cantilever spring 116 contact is at a first cross-sectional radius from the cross-sectional centre of the equivalent circle defined by the cylinder, to a second stage (position) in which the contact point is at a second different cross-sectional radius from the centre. Each stage is defined as a different cross-sectional radius.

The illustrated active fulcrum has four stages, but more or fewer stages could be provided in other implementations.

When the fulcrum 118 is in a first deactivated stage (deactivated position), the gap between the ERS rocker 110 and the ERS lobe 108 is such that even when the cantilever spring 116 is deflected to its maximum extent (nose of ERS lobe 108 contacts ERS rocker 110), the cantilever spring 116 does not deform about the fulcrum 118. The cantilever spring 116 is physically deflected but its connection to the stator housing allows free rotation, so the spring 116 is not resiliently deformed away from its neutral equilibrium position. Consequently no elastic potential energy is stored in the cantilever spring 116.

In a flrst activated stage (1s] stage' in Fig 4), the gap between the ERS lobe 108 and the ERS rocker 110 (when the ERS rocker 110 is aligned with the base circle of the ERS lobe 108) is smaller than in the first deactivated stage such that the ERS lobe 108 exerts a force on the cantilever spring 116 (via the ERS rocker 110) before the cantilever spring 116 is deflected to its maximum extent. In other words, the duration of the lost motion stage is reduced. Subsequent deflection of the cantilever spring 116 to the maximum extent stores elastic potential energy.

In a second activated stage (-2'16 stage' in Fig 4), the gap between the ERS lobe 108 and the ERS rocker 110 (when the ERS rocker 110 is aligned with the base circle of the ERS lobe 108) is smaller than in the first activated stage. The duration of the lost motion stage is further reduced and the amount of elastic potential energy stored increases further.

In a third activated stage ('3E6 stage' in Fig 4), the gap is smaller than in the second activated stage or is eliminated. The duration of the lost motion stage is further reduced or lost motion is eliminated. The third stage may be the final 'fully engaged' stage, for which lost motion is reduced to substantially zero, i.e. within manufacturing tolerances. This provides the maximum amount of stored elastic potential energy.

The third activated stage is most suitable for when inertia is high, such as when rotor velocity is high, e.g. engine speed is high (>6000rpm). The first activated stage is most suitable for when inertia is low, such as when rotor velocity/engine speed is low (e.g. engine speed <3000rpm). The intermediate first and second stages enable fine tuning for intermediate rotor velocities/engine speeds. The controller 50 can implement the required stage in dependence on a parameter such as rotor velocity or engine speed. Rotor velocity is engine speed dependent when not normalised by crankshaft rotation. Threshold engine speeds could be defined in the controller 50 for switching from one stage to the next. For example, the active fulcrum 118 could be controlled to increase the quantity of energy stored when a parameter such as engine speed increases above a threshold, such as by increasing the amount of lost motion. The amount of lost motion could be decreased when the parameter falls, for example when the parameter falls below the threshold or another threshold.

The fulcrum 118 of Fig 4 is rotated by a rotary actuator (not shown). The fulcrum 118 is a cylinder having an asymmetric/irregular surface, i.e. variable lift positions corresponding to different radii. The fulcrum 118 of Fig 4 has: a first (smallest) cross-sectional radius 1181 for enabling the deactivated stage; a second larger cross-sectional radius 1182 for enabling the first stage; a third larger cross-sectional radius 1183 for enabling the second stage; and a fourth largest cross-sectional radius 1184 for enabling the third stage.

Although Fig 4 illustrates rotary actuation, it would be appreciated that the fulcrum 118 could alternatively be controlled by linear actuation or any other appropriate form of actuation.

Although Fig 4 illustrates an example in which there are provided various different lost motion stages, it would be appreciated that in another variation, there may be no lost motion. For example the staging means could be deformable to a different extent in each stage, without introducing lost motion. In another variation, there could be another variable gap in the mechanical energy storage means, instead of the gap between the ERS lobe 108 and the ERS rocker 110.

Fig 5 relates to the third example implementation discussed earlier. Fig 5 is an illustration of the principle of a cam means such as the ERS lobe 108 having a staged profile. The staged profile can enable intermediate 'park' positions in which little to no stator energy is required to keep the rotor stationary.

Fig 5 illustrates plateaus 1084, 1088 in the ERS lobe 108, each plateau providing a park position. The ERS lobe 108 can therefore be 'climbed' up from one stage (park position) to the next, or can be climbed up to a lower stage.

A first plateau 1084 is provided on a first flank 1082 of the ERS lobe 108. The flrst plateau 1084 enables a first park position labelled 'a' in Fig 5. Park position a requires the least amount of energy to be input into the cantilever spring 116 to reach the position, because the position is the closest to the base circle 1081 out of all the positions.

The nose 1086 of the ERS lobe 108 defines a second park position on the lobe, labelled '0' because it could represent a default. As described earlier, the nose 1086 can define a substantially flat top to increase stability. The second park position requires the most amount of energy to be input into the cantilever spring 116 to reach the position, because the position is furthest from the base circle 1081 out of all the positions.

A third plateau 1088 is provided, which is on a second flank 1083 of the ERS lobe 108 and labelled 'U. In other examples the third plateau 1088 is on the first flank 1082. The third plateau 1088 requires more energy to be input into the cantilever spring 116 than the first plateau 1084, because the position is further from the base circle 1081 than the first plateau 1084. However: the third plateau 1088 requires less energy to be input into the cantilever spring 116 to reach the position than the second park position at the nose 1086.

Park position 0 is most suitable for when inertia is high such as when rotor velocity/engine speed is high (>6000rpm). Park position a is most suitable for when inertia is low, such as when rotor velocity/engine speed is low (e.g. <3000rpm). The intermediate park position b enables fine tuning for intermediate rotor velocities/engine speeds. The controller 50 can implement the required park position in dependence on a parameter such as rotor velocity/engine speed. Threshold rotor velocities/engine speeds could be defined in the controller 50 for switching from one target park position to the next, to minimise a requirement for stator assistance.

In one example, the controller 50 could cause the rotor 102 to reach park position a after a low-speed valve lift event and rotate no further because travelling up the rest 1085 of the flank 1082 to position 0 would require parasitic stator energy consumption. In dependence on planning a higher-speed valve rift event, the controller 50 could rotate the rotor 102 in reverse from park position a because the inertia will be sufficient for park position b to be reached without stator assistance. If an even higher speed valve lift event is planned subsequently: the rotor 102 could be rotated forward or in reverse for reaching park position 0.

When at an intermediate position a or b, the controller 50 may determine whether to 'charge' up the rest 1085 or 1087 of the flank 1082 or 1083 to position 0. This may be permissible when the stator 101 does not have any higher priority loads such as meeting a target rotor velocity. For example. climbing from position a or b to 0 may not be achievable during the valve closing phase of a fast-valve closing event. However, the climb may be achievable between valve lift events.

Although Fig 5 illustrates the ERS lobe 108 having a staged profile, the same principles could be applied to a different component in the force path to the cantilever spring 116, such as a roller on the ERS rocker 110 or any other suitable component. Further, although three park positions are shown, more or fewer could be provided.

Fig 6 relates to the second example implementation discussed earlier. Fig 6 is an illustration of the principle of adjusting the amount of energy storable in the mechanical energy storage means, similar to Fig 4, and a possible implementation.

The difference from Fig 4 is that there is no lost motion, and instead a characteristic of the resilient means (e.g. cantilever spring 116) itself is changed. Fig 6 shows that the length of the lever arm can be adjusted in operation. The lever arm is defined as the distance of the contact point of the input (e.g. Ens rocker 110) to the fulcrum 118. By moving either the location of the input or the fulcrum 118 or both, the lever arm length can be adjusted. Fig 6 illustrates an example of moving the fulcrum 118 but the same principles apply to moving the input, e.g. the contact point of the FRS rocker 110.

Once the lever arm length has been adjusted, a given amount of deflection defined by the lift of the ERS lobe 108 results in a different amount of elastic potential energy being stored in the cantilever spring 116.

Fig 6 illustrates that the fulcrum 118 is movable between two positions. This defines two lengths of the lever arm. The diagram on Fig 6 through which section A-A is cut shows a first position of the fulcrum 118 defining a first lever arm length, and the diagram on Fig 6 through which section B-B is cut shows a second position of the fulcrum 118 defining a second longer lever arm length increasing the effective spring rate.

Fig 6 shows that the position of the fulcrum 118 is also adjustable between the two extreme positions. The five upper cross-sections of Fig 6 illustrate five positions of the fulcrum 118, although more or fewer positions could be provided in various examples. In some implementations, the fulcrum position is continuously adjustable to enable a fine level of control of lever arm length.

According to Fig 6. the fulcrum 118 is adjusted by sliding the fulcrum 116 without necessarily breaking contact between the fulcrum 118 and the cantilever spring 116. This can be achieved with any appropriate actuator, although Fig 6 illustrates a double eccentric mechanism to give an example.

The double eccentric mechanism comprises an outer eccentric 602 and an inner eccentric 604. The fulcrum is fixed to (or integral with) the inner eccentric 604 off-center from its axis of rotation. The outer diameter of the larger outer eccentric 602 can be caused to rotate in a housing (not shown), and the inner eccentric 604 contained within the outer eccentric 602 can be caused to rotate in the opposite direction, such that the shaft of the fulcrum 118 through the inner diameter of the inner eccentric 604 slides in a straight line along the direction of the cantilever spring 116. The five relative orientations of the fulcrum, inner eccentric 604 and outer eccentric 602, and the resulting positioning of the fulcrum while it moves horizontally (generally parallel to the longitudinal axis of the spring 116) can be seen at the top of Figure 6.

The second (longer) lever arm length (upper configuration in Figure 6) is most suitable for when inertia is high such as when rotor velocity/engine speed is high (>6000rpm), to maximise energy recovery. The first lever arm length (lower configuration in Figure 6) is most suitable for when inertia is low, such as when rotor velocity/engine speed is low (e.g. <3000rpm). An intermediate lever arm length could be determined for intermediate rotor velocities/engine speeds. As with the other examples, the controller 50 can implement the required park position in dependence on a parameter such as rotor velocity/engine speed. Threshold rotor velocities/engine speeds could be defined in the controller 50 for switching from one lever arm length to the next, to minimise a requirement for stator assistance. Rotor velocities/engine speeds could even be mapped to lever arm length in a continuously variable manner if the lever arm length is continuously adjustable.

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; 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 cam means, the cam means having a staged profile.
2. The electromagnetic valve actuator of claim 1, wherein the staged profile comprises a first stage of the cam means deflning a first park position in which the rotor can cease rotation at the end of a period of rotation of the rotor such that the amount of energy stored in the mechanical energy storage means corresponds to the first positive amount, and a second stage defining a second park position in which the rotor can cease rotation at the end of a period of rotation of the rotor such that the amount of energy stored in the mechanical energy storage means corresponds to the second positive amount.
3. The electromagnetic valve actuator of claim 2, wherein the first stage comprises a plateau in a flank of the cam means, and the second stage comprises the nose of the cam means.
4. 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, wherein X is from the range 40% to 95% of Y.
5. The electromagnetic valve actuator of claim 4. wherein Y is less than a torque required to fully open the valve at an engine speed above 5000 rpm.
6. A controller configured to control an electromagnetic valve actuator according to any preceding claim for at least one valve of an internal combustion engine.
7. The controller of claim 6, comprising means to control the cam means in dependence on a parameter indicative of kinetic energy.
8. The controller of claim 7. wherein the parameter is engine speed-dependent.
9. A valve actuation system comprising the electromagnetic valve actuator as claimed in any one or more of claims 1 to 5 and the controller as claimed in any one or more of claims 6 to 8.
10. An internal combustion engine comprising the electromagnetic valve actuator as claimed in any one or more of claims 1 to 5 or the controller as claimed in any one or more of claims 6 to 8 or the valve actuation system as claimed in claim 9.II. A vehicle comprising the internal combustion engine as claimed in claim 10.