ELECTROMAGNETIC ACTUATOR AND METHODS OF OPERATION THEREOF

Abstract

A rotary electromagnetic actuator includes a biasing assembly for applying a torque to its rotor. Such an actuator may be used to operate a poppet valve of an internal combustion engine. The biasing assembly is switchable between (a) a first configuration in which the biasing assembly exerts a torque on the rotor over at least part of the range of rotation of the rotor, wherein the torque exerted varies with the rotational position of the rotor according to a torque profile, and (b) a second configuration in which the biasing assembly exerts substantially no torque on the rotor over the range of the rotor.

Claims

1. An electromagnetic actuator comprising: a stator; a rotor which is rotatable relative to the stator over a range of rotation of the rotor; and a biasing assembly for applying a torque to the rotor, wherein the biasing assembly is switchable between: (a) a first configuration in which the biasing assembly exerts a torque on the rotor over at least part of the range of rotation of the rotor, wherein the torque exerted varies with the rotational position of the rotor according to a torque profile; and (b) a second configuration in which the biasing assembly exerts substantially no torque on the rotor over the range of rotation of the rotor.

2. The actuator of claim 1, wherein the biasing assembly is a mechanical assembly and comprises a resilient mechanical component.

3. The actuator of claim 2, wherein the biasing assembly comprises a constraining member, and, in the first configuration of the biasing assembly, the constraining member is in a first orientation and constrains movement of part of the resilient mechanical component and, in the second configuration, the constraining member is in a second orientation and does not constrain movement of the resilient component, as the rotor rotates over its range of rotation.

4. The actuator of claim 2, wherein the rotor defines a cam surface and the biasing assembly includes a cam follower in engagement with the cam surface, and the magnitude of the torque exerted on the rotor by the biasing assembly is dependent on the magnitude of the displacement of the cam follower by the cam surface.

5. The actuator of claim 4, wherein a first part of the resilient mechanical component forms or is coupled to the cam follower and moves in response to movement of the cam follower.

6. The actuator of claim 5, wherein a second part of the resilient mechanical component is more constrained in the first configuration of the biasing assembly than in the second configuration.

7. The actuator of claim 6, wherein the resilient mechanical component is a leaf spring which is pivotably mounted.

8. The actuator of claim 6, wherein the biasing assembly comprises a constraining member, and wherein movement of the second part of the resilient mechanical component is constrainable by reducing the distance between an engagement surface of the constraining member and the resilient mechanical component.

9. The actuator of claim 3, wherein the constraining member is a rotatable member which is rotated between its first orientation and its second orientation when the biasing assembly moves between its first configuration and its second configuration, respectively, wherein an engagement surface of the constraining member moves in a direction towards the resilient mechanical component when the rotatable member moves from its first orientation to its second orientation.

10. A control mechanism in combination with the actuator of claim 3, wherein the control mechanism comprises: a controller which is moveable between first and second controller positions; and a coupling between the controller and the biasing assembly, wherein the coupling is arranged such that when the controller is in the first controller position, the coupling urges the constraining member towards its first orientation.

11. The combination of claim 10, wherein the controller is able to move from its second controller position to its first controller position even if the constraining member is not initially able to move into its first orientation.

12. The combination of claim 11, wherein the coupling comprises a resilient component which enables the controller to move from its second controller position to its first controller position even if the constraining member is not initially able to move into its first orientation.

13. The combination of claim 10, wherein the controller comprises a rotatable controller member which is rotatably mounted and/or the constraining member is rotatably mounted.

14. The combination of claim 12, wherein the resilient component is a torsion spring.

15. A control mechanism in combination with a plurality of actuators according to claim 3, wherein the control mechanism comprises a controller which is moveable between first and second controller positions; wherein the combination further includes a plurality of couplings, with each coupling provided between the controller and the biasing assembly of a respective one of the actuators; and wherein each coupling is arranged such that when the controller is in the first controller position, the coupling urges the constraining member of the respective one of the actuators towards its first orientation.

16. An internal combustion engine including at least one cylinder having at least one valve and the actuator of claim 1, wherein the actuator is arranged to actuate the at least one valve.

17. An internal combustion engine of claim 16, including: a plurality of cylinders each having at least one valve; a plurality of actuators according to claim 3, wherein each of the actuators is arranged to actuate a respective valve; a control mechanism, wherein the control mechanism comprises a controller which is moveable between first and second controller positions; and a plurality of couplings, with each coupling provided between the controller and the biasing assembly of a respective one of the actuators, wherein the each coupling is arranged such that when the controller is in the first controller position, the coupling urges the constraining member of the respective one of the actuators towards its first orientation.

18. An internal combustion engine including: a plurality of cylinders each having at least one valve; a plurality of actuators according to claim 3, wherein each actuator is coupled to a respective valve of the plurality of valves; a plurality of control mechanisms, wherein each control mechanism comprises a controller which is moveable between first and second controller positions, wherein each controller is moveable independently of the other controllers; and a plurality of couplings, wherein each coupling is provided between a respective controller of the plurality of control mechanisms and the biasing assembly of a respective one of the plurality of actuators, and wherein each coupling is arranged such that when the respective controller is in its first controller position, the coupling urges the constraining member of the respective one of the actuators towards its first orientation.

19. An internal combustion engine, including: a plurality of cylinders each having at least two valves, with one valve of each cylinder belonging to a first set of valves and a second valve of each cylinder belonging to a second set of valves; a plurality of actuators according to claim 3, wherein the plurality of actuators comprises a first set of actuators arranged to actuate respective ones of the first set of valves and a second set of actuators arranged to actuate respective ones of the second set of valves; first and second control mechanisms, each comprising a respective controller which is moveable between first and second controller positions, wherein the controller of each control mechanism is moveable independently of the other controller; and first and second sets of couplings, with each coupling of the first set provided between the controller of the first control mechanism and the biasing assembly of a respective one of the first set of actuators and each coupling of the second set provided between the controller of the second control mechanism and the biasing assembly of a respective one of the second set of actuators, and wherein each coupling is arranged such that when the respective controller is in its first controller position, the coupling urges the constraining member of the respective one of the actuators towards its first orientation.

20. A method of operating an electromagnetic actuator comprising: a stator; a rotor which is rotatable relative to the stator over a range of rotation of the rotor; and a biasing assembly for applying a torque to the rotor, the method comprising the step of switching the biasing assembly between: (a) a first configuration in which the biasing assembly exerts a torque on the rotor over at least part of the range of rotation of the rotor, wherein the torque exerted varies with the rotational position of the rotor according to a torque profile; and (b) a second configuration in which the biasing assembly exerts substantially no torque on the rotor over the range of rotation of the rotor.

21. The method of claim 20, wherein the actuator is arranged to actuate a valve of a cylinder in an internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings, wherein:

[0040] FIG. 1 is a perspective front view of a pair of rotary electromagnetic actuators, with one of the actuators embodying the invention;

[0041] FIG. 2 is a plan view of part of an internal combustion engine including a set of actuators according to an embodiment of the invention;

[0042] FIGS. 3 and 4 are end and side views, respectively of the assembly shown in FIG. 2 with the biasing assemblies of the actuators in their first, activated configuration, with FIG. 3 being a cross-sectional end view along line A-A marked in FIG. 4;

[0043] FIGS. 5 and 6 are end and side views, respectively of the assembly shown in FIG. 2 with the biasing assemblies of the actuators in their second, deactivated configuration, with FIG. 5 being a cross-sectional end view along line B-B marked in FIG. 6;

[0044] FIG. 7 is a perspective rear view of the pair of actuators shown in FIG. 1;

[0045] FIG. 8 is an enlarged perspective view of one end of the assembly shown in FIG. 3;

[0046] FIG. 9 is a cross-sectional end view of the assembly shown in FIG. 2 along line C-C;

[0047] FIG. 10 is a plan view of part of an internal combustion engine according to another embodiment of the invention; and

[0048] FIG. 11 is a perspective end view of part of the assembly shown in FIG. 10.

DETAILED DESCRIPTION OF THE DRAWINGS

[0049] A rotary electromagnetic actuator 2 embodying the invention is shown in FIG. 1. It includes a rotor 4 which is rotatably mounted in a stator 6. In the embodiment shown, the stator 6 is shared with a second actuator 8. The stator includes eight coils 10 which are evenly circumferentially spaced around the rotor, with respect to the rotational axis 12 of the rotor. In operation of the actuator, a magnetically generated torque is exerted on the rotor by selectively energising the stator windings. The rotor of actuator 8 is omitted for clarity in the drawing.

[0050] A cam surface 14 is formed on the rotor. A cam follower in the form of a roller 16 is in engagement with the cam surface. The cam follower 16 is rotatably mounted at one end of an arm 18. The other end of the arm is rotatably mounted on a shaft 20. Shaft 20 is supported by a bearing housing for the rotor 4. This bearing housing is omitted for clarity in FIG. 1. The exposed part of the shaft 20 is a press fit into a bore in the bearing housing.

[0051] The cam follower 16 is urged into engagement with the cam surface 14 by a biasing assembly 30. This assembly includes a leaf spring 32. The leaf spring is pivotably mounted on the stator 6 at a first end 34. A second, opposite end 36 of the leaf spring bears against the cam follower arm 18, urging it downwardly, towards the cam surface 14. The leaf spring, cam follower and cam surface are arranged such that the biasing assembly can exert a force on the rotor which acts to one side of the rotor axis, rather than towards it, so that it generates a torque around this axis.

[0052] Preferred cam surface configurations are disclosed in a co-pending UK patent application filed by the present applicants.

[0053] The biasing assembly also includes a constraining member in the form of a locking cylinder 40. The locking cylinder 40 is mounted in use for rotation about its central, longitudinal axis 42, by means not shown in FIG. 1. When the locking cylinder is orientated as shown in FIG. 1, its cylindrical circumferential surface 44 is in engagement with the upper surface of a part of the leaf spring 32 located towards first end 34 and so constrains upward movement of the leaf spring. The circumferential surface of the locking cylinder also includes a flattened, planar portion 46, which extends in a plane parallel to the rotational axis 42 of the locking cylinder and perpendicular to a plane containing that axis.

[0054] The biasing assembly 30 is switchable between a configuration (as shown in FIG. 1) in which upwards movement of the leaf spring in response to the interaction between the cam surface 14 and cam follower 16 is constrained by the constraining member 40, and a second configuration in which the upwards movement of the leaf spring is unconstrained when its second end 36 is moved in response to the interaction between the cam surface 14 and the cam follower 16. This will be described in further detail with reference to FIGS. 2 to 8.

[0055] FIG. 2 shows a plan view of an assembly for fastening to an actuator housing which is in turn fastened to the cylinder head of an internal combustion engine. It comprises a supporting framework 50 which carries two control mechanisms for controlling two sets of biasing assemblies, each biasing assembly being associated with a corresponding rotary actuator.

[0056] Each of the control mechanisms comprises a controller in the form of a rotatable shaft 52,54. Each shaft is coupled to a set of four actuators by respective couplings 56 and 58. More particularly, the couplings comprise torsion springs connected between each shaft and a constraining member of each actuator biasing assembly. Each shaft is rotatable by a respective actuator (not shown) which is connected to a respective crank arm 60,62.

[0057] FIGS. 3 and 4 show the control mechanisms in their activated configuration and FIGS. 5 and 6 show the control mechanisms in their deactivated configuration.

[0058] In the activated configuration, it can be seen in FIG. 3 that the circumferential surface 44 of the locking cylinder 40 is in contact with an upper surface of the leaf spring 32. This corresponds to the orientation shown in FIG. 1. Upwards movement of the leaf spring at the location in contact with the constraining member is blocked by the locking cylinder. Accordingly, when the distal end 36 of the leaf spring is pushed upwards by the cam follower arm 18, the leaf spring is therefore deformed and will exert a resilient biasing force on the arm 18. It will also store energy in the form of mechanical strain energy. This energy will then be transferred back to the rotor as and when the end 36 of the leaf spring is allowed to move downwards, causing the cam follower 16 to exert an accelerating torque on the rotor.

[0059] In the deactivated configuration shown in FIGS. 5 and 6, the locking cylinder 40 has been rotated by the associated switching shaft 52. The cylinder has rotated such that its planar face 46 is facing towards the leaf spring. As a result, the surface of the locking cylinder adjacent to the leaf spring is spaced from the leaf spring when the leaf spring is in its non-deflected position. When the distal end 36 of the leaf spring is then displaced upwards by the cam follower arm 18, this movement is not constrained (at least initially) by the locking cylinder 40. The leaf spring is able to pivot upwards about a pivot 64 to the position shown in FIG. 5. The upwards movement of the distal end 64 does not therefore deform the leaf spring and so it does not exert a biasing force on the cam follower arm 18 or, in turn, the rotor 4. Accordingly, in this configuration, the biasing assembly 30 does not have a material effect on the rotation of the rotor.

[0060] In a preferred configuration shown in FIG. 7, the cam follower arm 18 and leaf spring 32 are biased upwards by a coil spring 48. The spring may keep the cam follower arm, the leaf spring and the locking cylinder in contact with each other to avoid rattling of loose parts which may generate noise and wear of the parts. One end 47 of the spring may be held in a fixed position by engagement with a bearing housing (not shown in the Figures), whilst the other end 49 may be coupled to the distal end of the cam follower arm.

[0061] The configuration of the coupling present between each switching shaft 52,54 and the associated locking cylinders is more clearly visible in FIGS. 8 and 9. FIG. 9 shows a coupling associated with switching shaft 52. One end 70 of the torsion spring 56 is connected to an arm 72 mounted on switching shaft 52. The other end 74 of the torsion spring is located in a radial hole in the locking cylinder 40. In FIG. 9, switching shaft 52 is in its activated configuration. Clockwise rotation of the shaft when viewed in the direction shown in FIG. 9 has moved the arm 72, displacing the associated end 70 of the torsion spring 56, and causing the spring to exert a biasing force on the locking cylinder 40 which urges the cylinder to rotate in an anti-clockwise direction. This urges the locking cylinder towards the orientation shown in FIG. 3.

[0062] When the switching shaft is subsequently rotated anti-clockwise from the orientation shown in FIG. 9, this in turn displaces the associated end 70 of the torsion spring 56 so as to generate a biasing force urging the locking cylinder to rotate clockwise towards the configuration shown in FIG. 5.

[0063] When the distal end 36 of the leaf spring has been deflected upwards by the cam follower arm 18, it can be seen that the leaf spring may resist or block rotation of the locking cylinder from one orientation to another. Accordingly, the locking cylinder is not then able to immediately respond to switching of the switching shaft. However, the movement of the switching shaft is accommodated by deformation of the torsion spring 56 which stores mechanical strain energy in the torsion spring. As and when the leaf spring then moves downwards, the biasing force exerted to the locking cylinder by the torsion spring then rotates the locking cylinder into its other orientation.

[0064] A modified embodiment of the configuration shown in FIG. 2 is illustrated in FIGS. 10 and 11. In this embodiment, each locking cylinder has its own switching shaft 80. Each switching shaft in turn has its own actuator 82 for selectively switching the respective shaft. In such a configuration, each biasing assembly can be switched from one configuration to another independently of the others to give greater flexibility of operation of multiple actuators.