GB2554713A

GB2554713A - Apparatus for a valve train

Info

Publication number: GB2554713A
Application number: GB1616958.3A
Authority: GB
Inventors: Stone Roger; tyrell Richard; Kelly David; Evans Owen
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-10-06
Filing date: 2016-10-06
Publication date: 2018-04-11
Anticipated expiration: 2036-10-06
Also published as: GB201616958D0; GB2554713B

Abstract

A desmodromic valve actuation system comprises a rocker 300 coupling a valve 400 and valve actuator and arranged to rotate about a fulcrum 302 in response to actuator pushing and pulling forces. The rocker has an input portion 308 to receive actuator forces and an output portion 312, spaced from the input, for coupling to the valve. The output portion comprises pushing 316 and pulling 314 contact surfaces. The pushing contact surface contacts a first curved surface 406 e.g. a dome, at a valve upper end portion 404, pushing the upper valve end portion along a first axis 418 and the pulling contact surface contacts a second curved surface 414, e.g. a cylinder affixed by a tapered and friction fit, at a lower valve end portion and pulling the valve end lower portion along the first axis. The curved surfaces may share a virtual circle circumference and enable relative slippage between the respective contact and second curved surfaces to minimise side forces. The actuator may be rotary hydraulic or electromagnetic and act on the rocker via cams and further rockers to provide mechanical advantage with a displacement ratio of 1.3 to 1.95.

Description

(71) Applicant(s):

Jaguar Land Rover Limited (Incorporated in the United Kingdom)

Abbey Road, Whitley, Coventry, Warwickshire,

CV3 4LF, United Kingdom (72) Inventor(s):

Roger Stone Richard Tyrell David Kelly Owen evans (74) Agent and/or Address for Service:

Jaguar Land Rover

Patents Department W/1/073, Abbey Road, Whitley, COVENTRY, CV3 4LF, United Kingdom (51) INT CL:

FOIL 1/30 (2006.01) FOIL 1/18 (2006.01) (56) Documents Cited:

GB 1230307 A US 20080110425 A

JPS6114410 (58) Field of Search:

INT CL FOIL

Other: Online: WPI, EPODOC, Internet (54) Title of the Invention: Apparatus for a valve train

Abstract Title: Curved surface at valve and rocker interface (57) A desmodromic valve actuation system comprises a rocker 300 coupling a valve 400 and valve actuator and arranged to rotate about a fulcrum 302 in response to actuator pushing and pulling forces. The rocker has an input portion 308 to receive actuator forces and an output portion 312, spaced from the input, for coupling to the valve. The output portion comprises pushing 316 and pulling 314 contact surfaces. The pushing contact surface contacts a first curved surface 406 e.g. a dome, at a valve upper end portion 404, pushing the upper valve end portion along a first axis 418 and the pulling contact surface contacts a second curved surface 414, e.g. a cylinder affixed by a tapered and friction fit, at a lower valve end portion and pulling the valve end lower portion along the first axis. The curved surfaces may share a virtual circle circumference and enable relative slippage between the respective contact and second curved surfaces to minimise side forces. The actuator may be rotary hydraulic or electromagnetic and act on the rocker via cams and further rockers to provide mechanical advantage with a displacement ratio of 1.3 to 1.95.

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APPARATUS FOR A VALVE TRAIN

TECHNICAL FIELD

The present disclosure relates to apparatus for a valve train. In particular, but not exclusively it relates to apparatus for a valve train for a cylinder head of an engine of a vehicle.

Aspects of the invention relate to a rocker apparatus, a valve, a system, a valve train, a cylinder head, an engine and a vehicle.

BACKGROUND

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

An example valve train comprises a camshaft. The camshaft comprises one or more lobes. Each lobe pushes on a valve directly or indirectly to displace the valve from a closed position to an open position. The valve train comprises valve return springs. Each valve return spring biases the valve to displace the valve from the open position to the closed position when the lobe is no longer pushing the valve. The shape of the lobe and design of the valve return springs dictates the resulting displacement over time of the valve from its closed position.

It is an aim of the present invention to provide an improved valve train.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a rocker apparatus, a valve, a system, a valve train, a cylinder head, an engine and a vehicle as claimed in the appended claims.

According to an aspect of the invention there is provided a rocker apparatus arranged to provide a coupling between a valve and a valve actuator for an engine, and arranged to 1 rotate about a fulcrum in response to pushing force from the valve actuator and in response to pulling force from the valve actuator, the rocker apparatus comprising:

an input portion for coupling to the valve actuator, arranged to receive the pushing force from the valve actuator and to receive the pulling force from the valve actuator;

an output portion, spaced from the input portion, for coupling to a valve, wherein the output portion comprises a pushing contact surface and a pulling contact surface, wherein the pushing contact surface is arranged to contact a first curved surface at an upper portion of an end of the valve, the contact enabling pushing of the upper portion of the end of the valve along a first axis, and enabling relative slippage between the pushing contact surface and the upper portion of the end of the valve, and wherein the pulling contact surface is arranged to contact a second curved surface at a lower portion of the end of the valve, the contact enabling pulling of the lower portion of the end of the valve along the first axis, and enabling relative slippage between the pulling contact surface and the lower portion of the end of the valve. Valves are engine valves for each combustion chamber, used to control internal combustion.

This provides the advantage of a rocker apparatus that exerts minimal side loading on a valve. This is due to the relative slippage.

The pushing contact surface and the pulling contact surface may be opposing and inwardly facing surfaces.

This provides the advantage of a rocker apparatus that retains the valve, because the rocker apparatus at least partially encloses the end of the valve.

The input portion and the output portion may be on a same side of the fulcrum.

This provides the advantage that more rockers can be installed in a valve train. This is because the rocker apparatus is analogous to a class two or a class three lever, which are more compact than an equivalent class one lever.

The input portion may be located between the output portion and the fulcrum.

This provides the advantage of minimising power consumption by the valve actuator for achieving a given valve lift. This is because the rocker apparatus is analogous to a class 2 three lever, so the displacement required from the valve actuator for exerting pushing and pulling forces is less than the required displacement of the valve. This reduces the inertia associated with the valve train, improving dynamics at high engine speeds.

The input portion may comprise a bearing for connection to a connecting rod.

This provides the advantage of a greater degree of design freedom for fitting a valve train into a cylinder head sized to meet the packaging constraints of a vehicle engine bay, because the bearing enables the connecting rod and the rocker apparatus to move along different paths upon application of the pushing and the pulling forces.

The pulling contact surface may be discontinuous and offset to either side of the first axis.

This provides the advantage that the rocker exerts minimal side loading on a valve despite the discontinuity, due to the symmetry of locating the pulling contact surface on either side of the first axis.

According to another aspect of the invention there is provided a valve for an engine, wherein:

a first curved surface at an upper portion of an end of the valve is arranged to contact a pushing contact surface of a rocker apparatus, the contact enabling pushing of the upper portion of the end of the valve along a first axis, and enabling relative slippage between the pushing contact surface and the upper portion of the end of the valve; and a second curved surface at a lower portion of the end of the valve is arranged to contact a pulling contact surface of the rocker apparatus, the contact enabling pulling of the lower portion of the end of the valve along the first axis, and enabling relative slippage between the pulling contact surface and the lower portion of the end of the valve.

This provides the advantage that the rocker apparatus exerts minimal side loading on the valve.

In at least one cross-section view, a portion of the first curved surface and a portion of the second curved surface may lie on the circumference of a same virtual circle. In the crosssection view, the rocker apparatus may comprise a fulcrum contact surface at the fulcrum, the fulcrum contact surface lying on the circumference of another virtual circle. The another virtual circle may have the same radius as the virtual circle.

This provides the advantage that the minimal stress is exerted on the rocker apparatus in use. This is because the matching curves of the first curved surface, the second curved surface and the circular portion results in minimal force attempting to separate the pulling contact surface and the pushing contact surface from each other, upon application of the pushing or the pulling.

The first curved surface may be domed.

This provides the advantage that the rocker apparatus exerts minimal side loading on the valve. This is because the dome enables relative slippage in more than one direction orthogonal to the first axis.

The second curved surface may be cylindrical.

The axis of a cylinder defined, at least in part, by the cylindrical second curved surface, may extend orthogonally to the first axis.

The second curved surface may be part of a retainer portion arranged to be retained in position with respect to a valve stem of the valve via at least friction upon application of the pulling of the lower portion of the end of the valve.

This provides the advantage of reduced manufacturing costs. This is because a manufactured valve can be adapted for use with the rocker apparatus by fitting the retainer portion.

An interface between the retainer portion and the valve stem may be tapered, the direction of the taper being arranged such that the taper further resists sliding of the retainer portion upwardly towards the upper portion of the end of the valve upon application of the pulling of the lower portion of the end of the valve.

This provides the advantage that the retainer portion is held robustly in use.

According to a further aspect of the invention there is provided a system for actuating valves of an engine, the system comprising:

a valve actuator as defined in any one the above statements; a rocker apparatus as defined in any one of the above statements for actuation by the valve actuator; and a valve as claimed in any one of the above statements for actuation by the rocker apparatus.

The valve actuator may comprise an electromagnetic actuator.

This provides the advantage that valve timing is independent from engine crank rotation, to allow optimisation of valve timing for increased power, increased efficiency or for other purposes. Valves can be opened then closed at any point during a combustion cycle, and can be opened for different durations.

The valve actuator may provide a rotational output.

This provides the advantage that the valve actuator is compact. In an example, the valve actuator is an electromagnetic valve actuator with a rotational output, which is compact and allows the system to fit into a cylinder head for a constrained vehicle engine bay.

The rotational output may be coupled to a further rocker, wherein the further rocker may be coupled to the rocker apparatus via a connecting rod. The further rocker may be a first rocker and the rocker apparatus may be a second rocker.

This provides the advantage of a greater degree of design freedom for packaging the system within a cylinder head.

Further still aspects of the invention provide a valve train comprising the system as described herein, a cylinder head comprising the valve train as described herein, an engine comprising the cylinder head as described herein, and a vehicle comprising the engine as described herein.

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 file 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 2 illustrates an example of a valve and a rocker apparatus;

Fig 3 illustrates an example of a system;

Fig 4 further illustrates the example system of Fig 3;

Fig 5 further illustrates the example system of Fig 3; and

Fig 6A illustrates an example of a first lift profile and a second lift profile and Fig 6B illustrates another example of a first lift profile and a second lift profile.

DETAILED DESCRIPTION

The Figures illustrate a rocker apparatus 300 arranged to provide a coupling between a valve 400 and a valve actuator 100 for an engine 40, and arranged to rotate about a fulcrum

302 in response to pushing force from the valve actuator 100 and in response to pulling force from the valve actuator 100, the rocker apparatus 300 comprising: an input portion 308 for coupling to the valve actuator 100, arranged to receive the pushing force from the valve actuator 100 and to receive the pulling force from the valve actuator 100; an output portion

312, spaced from the input portion 308, for coupling to a valve 400, wherein the output portion 312 comprises a pushing contact surface 316 and a pulling contact surface 314, wherein the pushing contact surface 316 is arranged to contact a first curved surface 406 at an upper portion of an end 404 of the valve 400, the contact enabling pushing of the upper 6 portion of the end 404 of the valve 400 along a first axis 418, and enabling relative slippage between the pushing contact surface 316 and the upper portion of the end 404 of the valve 400, and wherein the pulling contact surface 314 is arranged to contact a second curved surface 414 at a lower portion of the end 404 of the valve 400, the contact enabling pulling of the lower portion of the end 404 of the valve 400 along the first axis 418, and enabling relative slippage between the pulling contact surface 314 and the lower portion of the end 404 of the valve 400.

The Figures also illustrate a valve 400 for an engine 40, wherein: a first curved surface 406 at an upper portion of an end 404 of the valve 400 is arranged to contact a pushing contact surface 316 of a rocker apparatus 300, the contact enabling pushing of the upper portion of the end 404 of the valve 400 along a first axis 418, and enabling relative slippage between the pushing contact surface 316 and the upper portion of the end 404 of the valve 400; and a second curved surface 414 at a lower portion of the end 404 of the valve 400 is arranged to contact a pulling contact surface 314 of the rocker apparatus 300, the contact enabling pulling of the lower portion of the end 404 of the valve 400 along the first axis 418, and enabling relative slippage between the pulling contact surface 314 and the lower portion of the end 404 of the valve 400.

The Figures also illustrate a system 50 for actuating valves of an engine 40, the system 50 comprising: the valve actuator 100; the rocker apparatus 300 for actuation by the valve actuator 100; and the valve 400 for actuation by the rocker apparatus 300.

The Figures also illustrate a desmodromic valve train 20 for an engine 40, comprising: a first surface 206 arranged to be actuated by a valve actuator 100 arranged to actuate a valve 400 independently of the crank angle of the engine 40, causing the first surface 206 to move according to a first lift profile having a maximum displacement and a minimum displacement; a second surface 316 arranged to actuate directly the valve 400 in dependence on actuation of the first surface 206 by the valve actuator 100, causing the second surface 316 to move according to a second lift profile having a maximum displacement and a minimum displacement; and a load path arrangement for providing a load path from the first surface 206 to the second surface 316, wherein the load path arrangement comprises mechanical advantage means arranged such that the maximum-to-minimum displacement of the second lift profile is up to 1.95 times greater than the maximum-to-minimum displacement of the first lift profile.

The Figures also illustrate a desmodromic valve train 20 for an engine 40, comprising a valve actuator 100 arranged to actuate a valve 400 independently of the crank angle of the engine 40, wherein the desmodromic valve train 20 comprises: a load path arrangement comprising an input arranged to receive actuating force from the valve actuator 100, an output arranged to provide the actuating force to the valve 400, and mechanical advantage means arranged such that a first displacement, of the input, causes a second displacement, of the output, wherein the second displacement is a multiple of the first displacement, the multiple being within the range 1.3 to 1.95.

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 automobile. Passenger vehicles generally have kerb weights of less than 5000 kg. In other examples, embodiments of the invention can be implemented in engines for any application, for example engines for industrial vehicles, air or marine vehicles, or non-vehicle applications.

In Fig 1 the vehicle 10 comprises: an engine 40 (which may be an internal combustion engine); a cylinder head 30 of the engine 40; and a valve train 20 within the cylinder head 30.

Fig 2 illustrates a valve 400 and a mechanism 200 arranged to actuate the valve 400. The valve 400 and mechanism 200 are comprised in the valve train 20 when in use in the vehicle 10.

The function of the valve 400 is to block an aperture in a wall of a combustion chamber (not shown) of the engine 40 of Fig 1 when the valve 400 is closed and therefore seated on a valve seat (not shown), and to open the aperture when the valve 400 is open (in an open position) and therefore spaced from its valve seat. When the valve 400 is moved (lifted) in to an open position, the position of the open valve 400 controls gas flow into or out of the cylinder through the aperture, facilitating combustion.

In the example of Fig 2, but not necessarily all examples, the valve 400 is a poppet valve. The valve stem 402 of the poppet valve is arranged to couple with the mechanism 200.

The valve stem 402 is arranged to receive a pushing force and a pulling force from the mechanism 200, the forces being sufficient to overcome the inertia of the valve 400. Pushing force accelerates the valve 400 away from its closed position causing the valve 400 to open. Pulling force causes deceleration, slowing any movement of the valve 400 away from the closed position and increasing movement of the valve 400 towards the closed position.

In Fig 2, but not necessarily all examples, the valve 400 is arranged to displace along a first axis 418. In some examples the first axis 418 is coaxial with the long axis of the valve stem 402 over at least a portion of the length of the valve stem 402. Cycles of pushing and pulling forces cause the valve 400 to reciprocate along the first axis 418.

If the pushing and/or pulling force includes a force component that is normal to the first axis 418, the valve 400 will be subjected to side loading. Side loading can cause the valve 400 to deviate from its intended path and/or increases wear on the valve 400.

The valve 400 of Fig 2 is arranged to reduce, for example minimise, side loading. The valve 400 comprises a first curved surface 406 at an upper portion of an end 404 of the valve 400, and a second curved surface 414 at a lower portion of the end 404 of the valve 400. The end 404 of the valve 400 refers to the region of the valve 400, in particular the region of the valve stem 402, which is distal to a combustion chamber in use.

The first curved surface 406 is arranged to contact the mechanism 200 at a location on the mechanism 200 that provides pushing force to the valve 400. This location on the mechanism 200 is referred to as a pushing contact surface 316. The contact enables pushing of the upper portion of the end 404 of the valve 400 along the first axis 418 so that the valve 400 is opened. The contact also enables relative slippage between the pushing contact surface 316 and the upper portion of the end 404 of the valve 400. The relative slippage significantly reduces side loading on the valve 400 during valve pushing, so that any side loading would be negligible.

In some, but not necessarily all examples, the first curved surface 406 at the upper portion of the end 404 of the valve stem 402 is located at the furthest point (extremity) of the valve stem 402. At least part of the first curved surface 406 may define the extremity of the valve stem 402.

The convex curvature of the first curved surface 406, when it contacts the pushing contact surface 316, promotes the relative slippage during valve pushing. In some, but not necessarily all examples, the first curved surface 406 is domed. A domed surface refers to any surface that is curved in two dimensions. In other examples the first curved surface 406 is any other suitable curved shape, such as curved in one dimension (cylindrical).

In some, but not necessarily all examples, the diameter of the circumference of the first curved surface 406 is equal to the diameter of the valve stem 402. In other examples, these diameters are different. Similarly, the area defined by the circumference of the first curved surface 406 may be equal to or different from the area defined by the circumference of the valve stem 402 closest to the first curved surface 406.

In some, but not necessarily all examples, the radius of curvature of the first curved surface 406 is greater than the radius of the area defined by the circumference of the valve stem 402.

In some, but not necessarily all examples, the first curved surface 406 has rotational symmetry about the axis of the valve stem 402 (the first axis 418). In some, but not necessarily all examples, the first curved surface 406 has continuous curvature over its entire surface. In other examples the first curved surface 406 has discontinuous curvature and is defined by facets.

In some, but not necessarily all examples, the first curved surface 406 is a low friction surface for promoting the relative slippage. The low friction surface may result from an appropriate surface finishing process or from applying a low friction coating.

The second curved surface 414 is arranged to contact the mechanism 200 at a location on the mechanism 200 that provides pulling force. This location on the mechanism 200 is referred to as a pulling contact surface 314. The contact enables pulling of the lower portion of the end 404 of the valve 400 along the first axis 418 so that the valve 400 can be closed. The second curved surface 414 therefore enables desmodromic valve actuation. The contact also enables relative slippage between the pulling contact surface 314 and the lower portion of the end 404 of the valve 400. The relative slippage reduces side loading on the valve 400 during valve pulling.

The second curved surface 414 at the lower portion of the end 404 of the valve 400 is positioned along the end region of the valve stem 402 without being at the extremity of the valve stem 402. The second curved surface 414 is further from the extremity of the valve stem 402 than the first curved surface 406.

The convex curvature of the second curved surface 414, where it contacts the pulling contact surface 314, promotes the relative slippage during valve pulling. In some, but not necessarily all examples, the second curved surface 414 is cylindrical, but in other examples the second curved surface 414 could be any other suitable curved shape. The second curved surface 414 may define a non-enclosed cylinder, resulting in a U-shaped second curved surface 414. The cylinder is optionally hollow.

In some, but not necessarily all examples, the second curved surface 414 extends orthogonally to the valve stem 402. Therefore the second curved surface 414 extends orthogonally to the first axis 418. For example, if the second curved surface 414 is cylindrical, the effective axis of the cylinder would extend orthogonally to the first axis 418.

In some, but not necessarily all examples, the radius of curvature of a portion of the second curved surface 414 is the same as the radius of curvature of a portion of the first curved surface 406. The second curved surface 414 and the first curved surface 406 are however separated by a discontinuity 415. There is no surface-to-surface contact between the first curved surface 406 and the second curved surface 414.

In some, but not necessarily all examples, the second curved surface 414 has continuous curvature across its entire surface. In other examples the second curved surface 414 has discontinuous curvature and is defined by facets.

In some, but not necessarily all examples, the second curved surface 414 is a low friction surface for promoting the relative slippage. The low friction surface may result from an appropriate surface finishing process or from applying a low friction coating.

The valve 400 may be manufactured (e.g. moulded) to include the second curved surface 414 or the second curved surface 414 may be attached to a manufactured valve 400. Examples will be provided later.

In Fig 2, but not necessarily in all examples, the mechanism 200 comprises a rocker apparatus 300. The rocker apparatus 300 is arranged to provide a coupling between the valve 400 and a valve actuator 100 (not shown in Fig 2). A valve actuator 100 represents any suitable actuator in the cylinder head 30 that receives energy from one or more sources external to the cylinder head 30 and supplies that energy in the form of kinetic energy to the mechanism 200. Example valve actuators are mechanical, electrical, hydraulic and pneumatic actuators.

As shown in Fig. 2, the coupling between the rocker apparatus 300 and the valve 400 is direct. Therefore the valve 400 and the rocker apparatus 300 make direct contact with each other. However the coupling between the rocker apparatus 300 and the valve actuator 100 can be direct or indirect.

The rocker apparatus 300 is arranged to rotate about a fulcrum 302 in response to pushing force from the valve actuator 100 and in response to pulling force from the valve actuator 100. Application of alternating pushing and pulling forces to the rocker apparatus 300 causes the rocker apparatus 300 to rotate back and forth in a rocking motion.

The rocker apparatus 300 comprises an input portion 308 for direct or indirect coupling to the valve actuator 100. The input portion 308 is arranged to receive the pushing force from the valve actuator 100 and to receive the pulling force from the valve actuator 100. The input portion 308 is spaced from the fulcrum 302.

In some, but not necessarily all examples, the input portion 308 comprises a bearing for enabling relative rotation between the rocker apparatus 300 and the element providing the pushing and pulling forces.

The rocker apparatus 300 comprises an output portion 312, spaced from the input portion 308 and from the fulcrum 302, for coupling to the valve 400.

The output portion 312 comprises the aforementioned pushing contact surface 316 and pulling contact surface 314.

In some, but not necessarily all examples, the pushing contact surface 316 is arranged to provide only positive force (including pushing force) to the first curved surface 406 and 12 cannot provide any negative force (including pulling force). In some, but not necessarily all examples, the pulling contact surface 314 is arranged to provide only negative force (including pulling force) to the second curved surface 414 and cannot provide any positive force (including pushing force). Positive and negative are defined arbitrarily to represent forces of opposite signs.

In some, but not necessarily all examples, the pushing contact surface 316 and the pulling contact surface 314 are opposing and inwardly facing surfaces. The gap between the pushing contact surface 316 and the pulling contact surface 314 therefore defines a cavity 315 in which the end 404 of the valve 400 can be received. The gap is sized to enable the end 404 of the valve 400 to fit within the cavity. For example the size of the gap is equal to or slightly greater than the maximum separation of the first curved surface 406 from the second curved surface 414.

The pushing contact surface 316 and the pulling contact surface 314 can be straight or slightly curved. In some, but not necessarily all examples, at least a portion of the pushing contact surface 316 and at least a portion of the pulling contact surface 314 extend along parallel planes.

In the example of Fig. 2, but not necessarily in all examples, the input portion 308 is between the fulcrum 302 and the output portion 312. The distance of the input portion 308 from the fulcrum 302 is therefore less than the distance of the pushing contact surface 316 from the fulcrum 302, and is less than the distance of the pulling contact surface 314 from the fulcrum 302. The rocker apparatus 300 consequently has a mechanical advantage (of force applied) of less than one and is analogous to a class three lever. The rocker apparatus 300 therefore amplifies displacement of the input portion 308 into a greater displacement of the output portion 312 as it rotates about its fulcrum 302.

In another example, the output portion 312 is between the input portion 308 and the fulcrum 302, resulting in a class two lever and a mechanical advantage greater than one.

In the example of Fig 2, the input portion 308 and the output portion 312 are on a same side of the fulcrum 302. This means that the effective phase separation between the input portion

308 and the output portion 312 during rotation of the rocker apparatus 300 is less than π/2 radians. In other words, movement of the input portion 308 in a first direction (e.g. 13 downwards) results in displacement of both the input portion 308 and the output portion 312 in the first direction, and movement of the input portion 308 in a second opposite direction (e.g. upwards) results in displacement of both the input portion 308 and the output portion 312 in the second direction. However in an alternative example, the input portion 308 and the output portion 312 are on opposite sides of the fulcrum 302, resulting in a class one lever.

Although Fig 2 shows one rocker apparatus 300 for actuating one valve 400, in other examples the rocker apparatus 300 can comprise one or more additional pushing contact surfaces and pulling contact surfaces for actuating one or more additional valves in conjunction with the valve 400 shown in Fig 2.

Although Fig 2 shows the pushing contact surface 316 and the pulling contact surface 314 being opposed and facing each other, the first curved surface 406 and second curved surface 414 being located in the cavity 315 between the pushing contact surface 316 and the pulling contact surface 314, other arrangements are possible. For example the first curved surface 406 and second curved surface 414 could instead be opposed and facing each other, the pushing contact surface 316 and pulling contact surface 314 being located in a cavity between the first curved surface 406 and second curved surface 414.

A system 50 which implements the valve 400 and rocker apparatus 300 of Fig 2 will now be described, with reference to Figs 3 to 5. Each system 50 is associated with a single valve 400, so the system 50 can be replicated as many times as necessary for actuating all the valves of the engine 40. The system 50 is located in a cylinder head 30, and to save space the system 50 may be banked (angled) with respect to the direction of gravity.

Reference numerals in Figs 3 to 5 corresponding to reference numerals in Fig 2 refer to the same features as described in relation to Fig 2.

Figs 3 to 5 present an overview of the system 50. The system 50 comprises a valve actuator 100, a mechanism 200 including the rocker apparatus 300, and a valve 400.

Fig 4 presents additional more detailed views of the system 50, emphasising the end 404 of the valve 400 and the rocker apparatus 300. The end face of the valve stem 402 (at the extreme end of the valve stem 402) is domed to provide the first curved surface 406. A LJ14 shaped cylinder, extending orthogonally to the valve stem 402, comprises the second curved surface 414.

The cylinder comprising second curved surface 414 is mounted to the valve stem 402 by means of a retainer portion 412. The retainer portion 412 is a rigid hollow sleeve for fitting over the end face of the valve stem 402 and sliding into position along the valve stem 402.

The retainer portion 412 is arranged to be retained in position with respect to the valve stem 402 via at least friction upon application of the pulling by the pulling contact surface 314. In Fig 4, a collet 410 is also fitted over the valve stem 402. The collet 410 is fixed in place against the valve stem 402. The collet 410 comprises interlocking means 408 to interlock with the valve stem 402 and hold the collet 410 in place. The interlocking means 408 in Fig 4 are male circumferential grooves on an interior surface of the collet 410 that interlock with female circumferential grooves in an exterior surface of the valve stem 402. The collet 410 is inversely tapered, increasing in diameter with increasing proximity to the end face of the valve stem 402. The exterior surface of the collet 410 is frustro-conical in shape. Therefore upon application of pulling force to the second curved surface 414 (upwards in Fig 4), the retainer portion 412 and the collet 410 form a friction fit with one another at an interface 409 between them, the resulting friction and reaction force of the collet 410 at the interface 409 preventing the retainer portion 412 from being pulled off the end of the valve stem 402.

In some, but not necessarily all examples, the rocker apparatus 300 comprises a plurality of rocker arms. The rocker apparatus 300 of Fig 4 comprises a pushing rocker arm 304 and a pulling rocker arm 306. The pushing rocker arm 304 comprises the pushing contact surface 316. The pulling rocker arm 306 comprises the pulling contact surface 314.

The pushing rocker arm 304 and the pulling rocker arm 306 are both operably coupled to the input portion 308 and to the fulcrum 302.

The pushing rocker arm 304 and the pulling rocker arm 306 extend angularly away from one another with increasing distance from the fulcrum 302, defining a cavity between the pushing rocker arm 304 and the pulling rocker arm 306 at the output portion 312. The end 404 of the valve 400 is received within the cavity. The angular separation between the pushing rocker arm 304 and the pulling rocker arm 306 with respect to the fulcrum 302 does not change during rocker apparatus 300 rotation.

The pushing contact surface 316 on the pushing rocker arm 304 and the pulling contact surface 314 on the pulling rocker arm 306 are opposing and inwardly facing surfaces, each facing into the cavity.

The pushing rocker arm 304 and the pushing contact surface 316 are centrally located such that the axis of the valve stem 402 (which may be the first axis 418) intersects the pushing contact surface 316.

The pulling rocker arm 306 is offset to both sides of the first axis 418. Therefore the pulling contact surface 314 is discontinuous and offset to both sides of the valve stem 402. The discontinuity provides a gap through which the valve stem 402 can extend. The pulling contact surface 314 is arranged to contact the cylindrical second curved surface 414 of the valve 400 at both sides of the discontinuity. The discontinuity is between the two points of contact.

In the rocker arm of Fig 4, the input portion 308 comprises a bearing 310 (e.g. rose joint or roller bearing) between the fulcrum 302 and the output portion 312.

In the rocker arm of Fig 4, the geometric centre of the fulcrum 302 is illustrated. The geometric centre of the fulcrum 302 may define the axis of rotation of the rocker apparatus 300.

The rocker arm of Fig 4 comprises a fulcrum contact surface 320 arranged around the geometric centre of the fulcrum 302. The fulcrum contact surface 320 is a cylindrical or spherical surface arranged at a predetermined radial distance from the geometric centre of the fulcrum 302.

The fulcrum contact surface 320 is arranged to be supported by a support 322. The support 322 and the fulcrum contact surface 320 are arranged to resist unintended movement of the geometric centre of the fulcrum in use.

The support 322 may comprise adjusting means for adjusting the geometric centre of the fulcrum 302 in use. The adjustment ensures that operation of the system 50 remains within tolerances by accounting for component wear or other factors. The adjustment means may comprise a hydraulic lash adjuster.

The valve 400 and the rocker apparatus 300 as shown in Figs 3 to 5 have a special geometry that mitigates unsteady or imbalanced forces in use, for example mitigating forces pulling or pushing the pulling rocker arm 306 and the pushing rocker arm 304 away from each other. The special geometry is defined by any one or more of the following:

- The radius of curvature of at least a portion of the first curved surface 406 of the valve 400, at least a portion of the second curved surface 414 of the valve 400 and/or at least a portion of the fulcrum contact surface 320 are identical or substantially identical when the system 50 is viewed in a cross-section (SECTION E-E and DETAIL F of Fig 4). The viewing direction is orthogonal to the first axis 418;

In the cross-section, the portion of the first curved surface 406 and the portion of the second curved surface 414 lie on the circumference of a same virtual circle 416;

In the cross-section, portions of the curved fulcrum contact surface 320 at opposing quadrants of the fulcrum contact surface 320 lie on the circumference of another virtual circle 323 having the same radius as the virtual circle 416;

In the cross-section, a virtual line 318 extending from the centroid of the virtual circle 416 to the centroid of the another virtual circle 323 intersects the geometric centre of the input portion 308 (for example, through the axis of rotation of a bearing 310 at the input portion 308).

Fig 5 presents additional more detailed views of the system 50, emphasising the valve actuator 100 and other parts of the mechanism 200.

The mechanism 200 shown in Fig 5 includes intervening components between the rocker apparatus 300 of Figs 2 to 4 and the valve actuator 100. Therefore the rocker apparatus 300 is regarded as being indirectly coupled to the valve actuator 100.

The mechanism 200 in Fig 5 comprises two rockers 201,300 including the rocker apparatus 300 of Figs 2 to 4. The rockers are coupled in series. The two rockers of Fig 5 are coupled to each other by a connecting rod 214 of the mechanism 200. The connecting rod 214 is arranged to transfer the pushing and pulling forces from one rocker to the other. In other examples more or fewer rockers can be provided.

In the example of Fig 5 but not necessarily all examples, the mechanism 200, in particular the connecting rod 214, comprises compliant means 215. In Fig 5 the compliant means 215 comprises a helical spring. The compliant means 215 in Fig 5 transmits the pulling forces from one rocker to another. The compliant means 215 is arranged such that while the valve 400 is seated and is unable to be pulled any closer to its seat, the compliant means 215 will change length upon application of any undesired pulling force exerted by the valve actuator 100, therefore preventing damage while providing a greater degree of design freedom for the valve actuator 100.

The two rockers and the connecting rod 214 together form the mechanism 200 that defines a load path arrangement providing a load path for the pushing and pulling forces from the valve actuator 100 to the valve 400. In other examples the load path arrangement comprises more or fewer components.

The pushing and pulling forces are received by the rocker apparatus 300 after they have passed through the other rocker. Therefore the rocker apparatus 300 may be regarded as a second rocker and the other rocker as a first rocker 201.

The first rocker 201 is directly coupled to the valve actuator 100. Its design is dependent upon the design of the valve actuator 100.

In the example shown in Fig 5, the first rocker 201 is mounted on a shaft 202. The shaft 202 is a fulcrum for the first rocker 201, enabling the first rocker 201 to rotate about the shaft 202 in response to pushing force from the valve actuator 100 and in response to pulling force from the valve actuator 100.

The first rocker 201 comprises a first rocker arm 204 and a second rocker arm 208.

The first rocker arm 204 of the first rocker 201 extends from the shaft 202 to a first follower 206. The first follower 206 is a bearing acting as a roller follower for following a camming surface and receiving the pushing force (input).

The second rocker arm 208 of the first rocker 201 extends from the shaft 202 to a second follower 210. The second follower 210 is a bearing acting as a roller follower for following a camming surface and receiving the pulling force (input).

The angular separation between the first rocker arm 204 and the second rocker arm 208 of the first rocker 201 with respect to the shaft 202 does not change during rotation of the first rocker 201. In Fig 5 the angular separation is greater than zero but in other examples the angular separation could be zero - this depends on the design of the valve actuator 100.

The first rocker arm 204 and the second rocker arm 208 of the first rocker 201 are both operably coupled to the shaft 202 and to an output 212 (for example a bearing or rose joint) of the first rocker 201 that attaches to an end of the connecting rod 214.

In Fig 5, the first rocker arm 204 and the second rocker arm 208 of the first rocker 201 are separated from one another along the length of the shaft 202.

In the first rocker 201 of Fig 5, the first rocker arm 204 and the output 212 are on a same side of the shaft 202. This means that the effective phase separation between the first rocker arm 204 and the output 212 during rotation of the first rocker 201 is less than π/2 radians. In other words, movement of the first rocker arm 204 in a first direction (e.g. downwards) results in displacement of the output 212 in the first direction, and movement of the first rocker arm 204 in a second opposite direction (e.g. upwards) results in displacement of the output 212 in the second direction.

In the first rocker 201 of Fig 5, the second rocker arm 208 and the output 212 are on opposite sides of the shaft 202. This means that the effective phase separation between the second rocker arm 208 and the output 212 during rotation of the first rocker 201 is greater than π/2 radians. In other words, movement of the second rocker arm 208 in a first direction (e.g. downwards) results in displacement of the output 212 in a second opposite direction (e.g. upwards), and movement of the second rocker arm 208 in the second direction results in displacement of the output 212 in the first direction.

The valve actuator 100 shown in Fig 5 will now be described. The valve actuator 100 has a design that complements the above-described first rocker 201.

In Fig 5, the valve actuator 100 comprises an electromagnetic valve actuator 101. The electromagnetic valve actuator 101 in Fig 5 comprises a rotor-stator pair for providing a rotating output. However, in other examples the electromagnetic valve actuator 101 can be for providing a linear output (for example a solenoid that causes linear actuation of a plunger).

Fig 5 shows a rotor shaft 102 providing two functions. The rotor shaft 102 firstly acts as the rotor of the electromagnetic valve actuator 101. The rotor shaft 102 secondly acts as a camshaft for actuating the mechanism 200 by camming action, causing pushing and pulling forces to be transferred through the mechanism 200.

The electromagnetic valve actuator 101 is arranged to cause the rotor shaft 102 to perform a full rotation about the axis of the rotor shaft 102 (full rotation mode). In some, but not necessarily all examples, the electromagnetic valve actuator 101 is arranged to provide a ‘bounce mode’ that causes the rotor shaft 102 to perform a partial rotation in one direction of rotation (e.g. clockwise) followed by a partial rotation in the reverse direction of rotation (e.g. anti-clockwise). Bounce mode causes partial valve opening, while full rotation mode causes full valve opening.

The rotor shaft 102 (camshaft) in Fig 5 comprises an acceleration lobe 104 (for pushing forces) and a deceleration lobe 106 (for pulling forces). The acceleration lobe 104 is arranged to directly contact the first follower 206 on the first rocker arm 204 of the first rocker 201. The deceleration lobe 106 is arranged to directly contact the second follower 210 on the second rocker arm 208 of the first rocker 201.

The rotor shaft 102 is arranged such that when the acceleration lobe 104 pushes the first follower 206 on the first rocker arm 204 of the first rocker 201, the first rocker 201 rotates about the shaft 202 in a first direction of rotation (e.g. clockwise), and when the deceleration lobe 106 pushes the second follower 210 on the second rocker arm 208 of the first rocker 201, the first rocker 201 rotates about the shaft 202 in a second opposite direction of rotation (e.g. anticlockwise). In the example of Fig 5, this is achieved by locating the rotor shaft 102 between the first follower 206 and the second follower 210.

In full rotation mode, the switchover between the acceleration lobe 104 pushing the first follower 206 and the deceleration lobe 106 pushing the second follower 210 is determined 20 by the shapes and angular separations of the respective lobes 104, 106. The switchover enables pushing (acceleration) of the valve 400 to cease and pulling (deceleration) to commence, when in full rotation mode.

The amplitude of the valve lift is controlled by configuring the mechanical advantage in the load path arrangement.

Control of the mechanical advantage in the load path arrangement can provide advantages such as minimising power consumption by the system 50 and minimising errors in the final position of the valve 400.

The mechanical advantage in the load path arrangement determines the maximum-tominimum displacements of components at certain points along the load path.

Maximum-to-minimum displacement refers to the resultant displacement of a point being measured between a maximum displacement of the point and a minimum displacement of the point. In the context of the present disclosure, the point is a point on the mechanism 200. Valve opening over time follows a generally Gaussian-shaped curve, and the point along the mechanism 200 would move according to a similarly-shaped curve. Maximum displacement can be regarded as peak valve opening at which direction reversal occurs of the point being measured, i.e. while the point is momentarily static. The peak is a point of inflexion on a displacement-time plot. Minimum displacement occurs at the instant at which the point being measured is static, e.g. the time on a displacement-time plot at which a zero gradient becomes positive/a negative gradient becomes zero.

Referring to the system 50 shown in Figs 3 to 5 during pushing (opening) of the valve 400, the first follower 206 can be regarded as a first surface arranged to be actuated directly by the valve actuator 100 (e.g. actuated directly by the acceleration lobe 104 on the rotor shaft 102). The lobe cams the first surface, causing the first surface to move according to a first lift profile having a maximum displacement and a minimum displacement. The shape of first lift profile, when plotted as displacement (Pi_s) against normalised time (t) (e.g. Fig 6A, 602 and Fig 6B, 606), is near-representative of the shape of the lobe. Any differences would be down to tolerances and operating clearances. The relevant point on the first surface for accurately determining displacement is the contact point between the lobe and the first surface.

The pushing contact surface 316 of the rocker apparatus 300 can be regarded as a second surface arranged to actuate directly a valve 400 in dependence on actuation of the first surface by the valve actuator 100, causing the second surface to move according to a second lift profile having a maximum displacement and a minimum displacement. The shape of the second lift profile, when plotted as displacement (P_2s) against normalised time (t) (e.g. Fig 6A, 604 and Fig 6B, 608), is near-representative of the displacement of the valve 400. Any differences would be down to tolerances and operating clearances. The relevant location on the second surface for accurately determining displacement is the contact point between the second surface and the valve 400.

In this example and with reference to Figs 6A and 6B, the mechanical advantage in the load path arrangement is arranged such that during pushing (opening) of the valve 400, the maximum-to-minimum displacement of the second lift profile (AP_2s) is up to 1.95 times greater (Fig 6A, 604 compared to 602), and optionally no less than 1.3 times greater (Fig 6B, 608 compared to 606), than the maximum-to-minimum displacement of the first lift profile (APi_s).

Referring to the system 50 shown in Figs 3 to 5 during pulling (closing) of the valve 400, rather than pushing, the second follower 210 on the second rocker arm 208 of the first rocker 201 can be regarded as a first surface because it is actuated by the valve actuator 100 (e.g. camming of the second follower 210 by the deceleration lobe 106 on the rotor shaft 102). The pulling contact surface 314 of the rocker apparatus 300 can also be regarded as a second surface because it is arranged to actuate directly the valve 400. The first lift profile for pulling may be identical to or different from the first lift profile for pushing. In this example and with reference to Figs 6A and 6B, the mechanical advantage in the load path arrangement is arranged such that during pulling, the maximum-to-minimum displacement of the second lift profile (AP_2s) is up to 1.95 times greater (Fig 6A, 604 compared to 602), and optionally no less than 1.3 times greater (Fig 6B, 608 compared to 606), than the maximumto-minimum displacement of the first lift profile (AP_1s).

For convenience, these 1.3 and 1.95 ratios will be referred to respectively as a lower limit and an upper limit of a ‘lift ratio’. The lower limit and upper limit of lift ratio for pushing and/or pulling are applicable not only to the system 50 described in relation to Figs 2 to 5, but also to any other valve trains or desmodromic valve trains.

The upper limit and/or lower limit of lift ratio provides the advantage of optimizing error in the second lift profile, power consumption and system packaging. The error in the second lift profile arises from amplification of errors in the load path arrangement caused by a numerically high lift ratio. Errors can arise from design tolerances, elastic deflections of components or running clearances. Optimal error is achieved at a numerically low lift ratio. Optimal power consumption is however achieved at a numerically high lift ratio. This is because the displacement (cam lift) required from the valve actuator for exerting pushing and pulling forces is less than the required displacement of the valve, allowing the camshaft to have low rotational inertia, improving dynamics at high engine speeds. Optimal system packaging is also achieved at a numerically high lift ratio because the low cam lift displaces the first surface by a smaller swept angle, ensuring that adjacent mechanisms do not foul one another at a crowded location in the valve train.

In the system 50 illustrated in Figs 3 to 5, if the overall mechanical advantage of both the first rocker 201 and the rocker apparatus 300 is one, the lift ratio would be one. If the overall mechanical advantage of one or both of the first rocker 201 and the rocker apparatus 300 is less than one, the lift ratio would be greater than one. If the overall mechanical advantage of one or both of the first rocker 201 and the rocker apparatus 300 is greater than one, the lift ratio would be less than one. The mechanical advantages of the first rocker 201 and the rocker apparatus 300 can be identical or different. Differences may arise from packaging constraints and/or for achieving further reductions in inertia. In some, but not necessarily all examples, the mechanical advantage of the rocker apparatus 300 is less than the mechanical advantage of the first rocker 201, and may be less than one. This may be advantageous if the rocker apparatus 300 has more space to move than the first rocker 201 without fouling adjacent mechanisms, and the overall system inertia may be reduced. In some, but not necessarily all examples, the first rocker 201 has a mechanical advantage of one or greater than one for packaging reasons.

In some, but not necessarily all examples, there is provided a desmodromic valve train 20 for an engine 40. The desmodromic valve train 20 comprises a valve actuator 100 arranged to actuate a valve 400 independently of the crank angle of the engine 40. An example of a suitable valve actuator 100 is the electromagnetic valve actuator 101, because it is controlled by electrical current rather than by a belt or chain attached to the engine crank.

The desmodromic valve train 20 comprises: a load path arrangement comprising an input arranged to receive actuating force from the valve actuator 100, an output arranged to 23 provide the actuating force to the valve 400, and mechanical advantage means arranged such that a first displacement, of the input, causes a second displacement, of the output, wherein the second displacement is a multiple of the first displacement, the multiple being within the range 1.3 to 1.95.

In some, but not necessarily all examples, the input comprises the first follower 206 and/or the second follower 210. In some, but not necessarily all examples, the output comprises the pushing contact surface 316 and/or the pulling contact surface 314. In some, but not necessarily all examples, displacement of the pushing contact surface 316 (second displacement, pushing) is 1.3 to 1.95 times greater than displacement of the first follower 206 (first displacement, pushing), and/or displacement of the pulling contact surface 314 (second displacement, pulling) is 1.3 to 1.95 times greater than displacement of the second follower 210 (first displacement, pulling).

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. For example the rocker apparatus 300 can be the only rocker in the mechanism 200. Elements of the first rocker 201 can therefore be present in the rocker apparatus 300 for ensuring compatibility with the valve actuator 100.

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

1. A rocker apparatus arranged to provide a coupling between a valve and a valve actuator for an engine, and arranged to rotate about a fulcrum in response to pushing force from the valve actuator and in response to pulling force from the valve actuator, the rocker apparatus comprising:

an output portion, spaced from the input portion, for coupling to a valve, wherein the output portion comprises a pushing contact surface and a pulling contact surface, wherein the pushing contact surface is arranged to contact a first curved surface at an upper portion of an end of the valve, the contact enabling pushing of the upper portion of the end of the valve along a first axis, and enabling relative slippage between the pushing contact surface and the upper portion of the end of the valve, and wherein the pulling contact surface is arranged to contact a second curved surface at a lower portion of the end of the valve, the contact enabling pulling of the lower portion of the end of the valve along the first axis, and enabling relative slippage between the pulling contact surface and the lower portion of the end of the valve.

2. A rocker apparatus as claimed in any preceding claim, wherein the pushing contact surface and the pulling contact surface are opposing and inwardly facing surfaces.

3. A rocker apparatus as claimed in any preceding claim, wherein the input portion and the output portion are on a same side of the fulcrum.

4. A rocker apparatus as claimed in any preceding claim, wherein the input portion is located between the output portion and the fulcrum.

5. A rocker apparatus as claimed in any preceding claim, wherein the input portion comprises a bearing for connection to a connecting rod.

6. A rocker apparatus as claimed in any preceding claim, wherein the pulling contact surface is discontinuous and offset to either side of the first axis.

7. A valve for an engine, wherein:

8. A valve as claimed in claim 7, wherein in at least one cross-section view, a portion of the first curved surface and a portion of the second curved surface lie on the circumference of a same virtual circle.

9. A valve as claimed in claim 7 or 8, wherein the first curved surface is domed.

10. A valve as claimed in claim 7, 8 or 9, wherein the second curved surface is cylindrical.

11. A valve as claimed in claim 10, wherein the axis of a cylinder defined, at least in part, by the cylindrical second curved surface, extends extend orthogonally to the first axis.

12. A valve as claimed in any one of claims 7 to 11, wherein the second curved surface is part of a retainer portion arranged to be retained in position with respect to a valve stem of the valve via at least friction upon application of the pulling of the lower portion of the end of the valve.

13. A valve as claimed in claim 12, wherein an interface between the retainer portion and the valve stem is tapered, the direction of the taper being arranged such that the taper further resists sliding of the retainer portion upwardly towards the upper portion of the end of the valve upon application of the pulling of the lower portion of the end of the valve.

14. A system for actuating valves of an engine, the system comprising:

a valve actuator;

a rocker apparatus as claimed in any one of claims 1 to 6 for actuation by the valve actuator; and a valve as claimed in any one of claims 7 to 13 for actuation by the rocker apparatus.

15. A system as claimed in claim 14, wherein the valve actuator comprises an electromagnetic actuator.

16. A system as claimed in claim 14 or 15, wherein the valve actuator provides a rotational output.

17. A system as claimed in claim 16, wherein the rotational output is coupled to a further rocker, and wherein the further rocker is coupled to the rocker apparatus via a connecting rod.

18. A valve train comprising the system of any one of claims 14 to 17.

19. A cylinder head comprising the valve train as claimed in claim 18.

20. An engine comprising the cylinder head as claimed in claim 19.

21. A vehicle comprising the engine as claimed in claim 20.

22. A rocker apparatus, a valve, a system, a valve train, a cylinder head, an engine or a vehicle as hereinbefore described with reference to the accompanying drawings.

Intellectual

Property

Office

Application No: GB1616958.3