GB2566489A

GB2566489A - Actuation assembly and methods of operation thereof

Info

Publication number: GB2566489A
Application number: GB1714840.4A
Authority: GB
Inventors: Stone Roger; Kelly David
Original assignee: Camcon Auto Ltd
Current assignee: Camcon Auto Ltd
Priority date: 2017-09-15
Filing date: 2017-09-15
Publication date: 2019-03-20
Also published as: GB201714840D0

Abstract

A valve actuation assembly for an inlet or exhaust valve 92 of an internal combustion engine, wherein the assembly comprises an actuator 76 including a connector 80 for coupling to a valve stem 74 of the valve. The actuator is operable to move the connector between a first position and a second position, and the assembly includes a fail-safe mechanism 100,102,106 which is selectively operable to prevent the actuator from moving the connector more than a predetermined distance away from its first position. The fail-safe mechanism may urge the connector towards a first position if it is not in that position, or may prevent the connector from moving away from that position. The fail-safe mechanism may include a blocking member which impedes the movement of the connector in a deployed configuration. Also claimed is an internal combustion engine fitted with this valve actuation assembly.

Description

Title: Actuation Assembly and Methods of Operation thereof

Field of the Disclosure

The present disclosure relates to a valve actuation assembly for a poppet valve of an internal combustion engine. The assembly is intended to be used instead of a rotating camshaft to control the valve movement profile and/or timing independently of crankshaft motion.

Background of the Disclosure

It is well known to operate inlet and exhaust valves of an internal combustion engine by means of a rotating camshaft. If the camshaft is rotated by a mechanical connection with the crankshaft of the engine, the range of valve movement profile and/or timing adjustments that can be made in relation to the engine speed or loading is limited. However, greater efficiency can be achieved by removing the mechanical connection between crankshaft and camshaft.

In order to give greater control over the valve actuation, it has been proposed to operate the valves using actuators governed by a computer-controlled engine management system. W02004/097184 relates to an electromagnetic actuator having a driven rotor which is coupled to a valve by a suitable linkage. This system provides valve events that are controlled separately from the crankshaft motion.

Summary of the Disclosure

The present disclosure provides a valve actuation assembly for an inlet or exhaust valve of an internal combustion engine, the assembly comprising:

an actuator including a connector for coupling to a valve stem of the valve, the actuator being operable to move the connector between a first position and a second position; and a fail-safe mechanism which is selectively operable to prevent the actuator from moving the connector more than a predetermined distance away from its first position.

In many engine configurations, the volumes swept by an inlet valve, exhaust valve and/or piston of a cylinder may overlap. When these engines are operated as intended, the timing of the motions of these components is such that they do not come into contact. However, in the event of failure or malfunctioning of part of a valve actuation assembly or associated control systems, there is the risk that the head of a valve could come into contact with another valve or the piston, causing damage to the valve and/or other parts of the engine. To reduce the risk of such damage, according to the present disclosure, a valve actuation assembly includes a fail-safe mechanism which is selectively operable to restrict the motion of the actuator and therefore the travel of a valve coupled to it.

The fail-safe mechanism may be arranged to prevent selectively the actuator from moving the connector more than a predetermined distance away from its first position, with the predetermined distance being selected so as to restrict movement of the connector and therefore a valve coupled to it to a range over which the volume swept by the valve does not overlap with those swept by other valves and/or the piston. Thus, once the fail-safe mechanism has been deployed, the valve is prevented from coming into contact with other valves and/or the piston.

With the valve actuation assembly coupled to a valve stem via the connector in an assembled engine, the first position of the connector may correspond to a closed position of the valve and the second position of the connector may correspond to a fully open position of the valve.

In a preferred example, the fail-safe mechanism is configured such that, when the mechanism is deployed and the connector is more than the predetermined distance away from its first position, the fail-safe mechanism exerts a force on the actuator which urges the actuator towards a configuration in which the connector is the predetermined distance or less from its first position. Under these circumstances, the assembly is arranged to urge the actuator towards a configuration in which the connector is within the safe range of travel defined by the predetermined distance from its first position. The mechanism therefore acts to move the connector and a valve coupled to it away from a region where there may be a risk of contact with another valve and/or the piston of the associated cylinder. The safe configuration can therefore be reached even if the actuator is no longer able to move the connector.

The fail-safe mechanism may include a blocking member, and the fail-safe mechanism may be operable to switch between a non-deployed configuration in which the blocking member does not impede operation of the actuator, and a deployed configuration in which the blocking member prevents the actuator from moving the connector more than the predetermined distance away from its first position. When the fail-safe mechanism is in its deployed configuration, the blocking member may form a stop preventing movement of the connector beyond the predetermined distance away from its first position. In doing so, the blocking member may come directly into contact with part of the actuator.

The fail-safe mechanism may be configured such that, when the fail-safe mechanism is deployed and the connector is more than the predetermined distance away from its first position, the blocking member exerts a force on the actuator which urges the actuator towards a configuration in which the connector is the predetermined distance or less from its first position.

In some implementations, the fail-safe mechanism is operable to prevent the connector from moving away from its first position. This may correspond to the mechanism holding a valve in its closed position.

The valve actuation assembly may include a controller for governing the operation of the actuator and the fail-safe mechanism.

In further examples of the disclosure, a valve actuation assembly may include a controller for governing the operation of the actuator and the fail-safe mechanism, wherein the controller is arranged to monitor the status of the actuator and deploy the fail-safe mechanism when the controller detects a failure mode of the actuator.

The controller may be operable to cause the actuator to move the connector towards its first position when the controller detects a failure mode of the actuator. Accordingly, in a scenario where the fail-safe mechanism has been deployed due to a risk of contact within a cylinder and the actuator is still operable to move the connector, the controller may cause the actuator to move the connector and the valve coupled to it to a safe range of travel.

The controller may be operable to de-energise the actuator when the controller detects a failure mode of the actuator. In some configurations and/or failure scenarios, it may be preferable to de-energise the actuator and rely on the associated fail-safe mechanism to prevent the connector moving more than the predetermined distance away from its first position and possibly also to move the actuator and connector to within its safe range of travel defined by the predetermined distance.

In an example of the present disclosure, the actuator comprises a stator, a rotor which is rotatable relative to the stator about an axis of rotation by energising the stator, and a linkage which is coupled to the rotor at one end and to the connector at its other end, and arranged to convert rotary motion of the rotor into motion of the connector between its first and second positions. The linkage may be a mechanical linkage for example.

The assembly may include a set of actuators, each actuator includes a connector for coupling to a valve stem of a respective valve, and each actuator is operable to move its connector between a first position in which the respective valve is in its closed position and a second position in which the respective valve is in its fully open position. The assembly may include a controller arranged to govern the operation of the set of actuators and the fail-safe mechanism.

In preferred examples, the controller may monitor the status of the actuators and deploy the fail-safe mechanism when the controller detects in response to input signals that one of the actuators has developed a fault and should therefore be deemed to be in a failure mode.

In some implementations, the fail-safe mechanism is configured such that when it is deployed, it prevents all of the actuators of the engine from moving the respective connectors more than the predetermined distance away from their first positions. The controller may be arranged to de-energise all of the actuators when the fail-safe mechanism is deployed.

Once the fail-safe mechanism has been deployed and therefore restricts the range of motion of each actuator connector, the controller may be operable to reciprocate the connectors over a limited range of travel (other than the failed actuator) thereby allowing the engine to continue to function, albeit in a restricted manner.

In some configurations of the present disclosure, the set of actuators consists of a plurality of sub-sets of actuators, and the fail-safe mechanism is operable to prevent a selected sub-set of actuators from moving their connectors more than a predetermined distance away from their first positions. For example, each set of actuators may actuate the inlet and exhaust valves of a respective cylinder. Each fail-safe mechanism associated with a corresponding sub-set of actuators may be deployable independently of the other fail-safe mechanisms, so that individual cylinders may be independently switched to a more restricted mode of operation when the respective fail-safe mechanism has been triggered.

The controller of the assembly may be arranged to detect when an actuator is in a failure mode, to determine which sub-set of actuators a failed actuator belongs to, and deploy the fail-safe mechanism in relation to that sub-set of actuators only.

The engine may therefore be configured to continue to operate using the unaffected cylinders only, or the unaffected cylinders together with the affected cylinder operating with its valves restricted to a safe range of travel (apart from the failed actuator).

In examples of the present disclosure, the fail-safe mechanism is operable to prevent a selected actuator from moving its connector more than a predetermined distance away from its first position. The assembly may include a controller arranged to govern the operation of the set of actuators and the fail-safe mechanism. The controller may monitor the status of the actuators, detect when an actuator is in a failure mode and deploy the fail-safe mechanism in relation to that actuator only. In such a configuration, the controller may be arranged to continue to operate the other actuators which actuate the other inlet and exhaust valves of the same cylinder. Thus, in an engine in which each cylinder has more than one inlet valve or more than one exhaust valve, other valves of the same type as the valve associated with the failed actuator may continue to operate allowing the associated cylinder to continue to function.

The present disclosure further provides an internal combustion engine including at least one cylinder having at least one inlet or exhaust valve, a piston and a valve actuation assembly as described herein, wherein the at least one valve is operable by an actuator of the assembly independently of rotation of the engine crankshaft, and the connector of the actuator is coupled to the at least one valve to enable the actuator to actuate the at least one valve.

The present disclosure also provides a method of operating an assembly or an engine as described herein, comprising a step of deploying a fail-safe mechanism to prevent a connector of a valve actuator from moving more than the determined distance away from its first position.

Brief description of the Drawings

Examples of the present disclosure will now be described by way of example and with reference to the accompanying schematic drawings, wherein:

Figure 1 is a block diagram of an engine control system, including a valve actuation assembly of the present disclosure;

Figure 2 is a cross-sectional side view of the upper portion of a cylinder in a known internal combustion engine; and

Figures 3 to 5 are side views of a valve actuation assembly according to the present disclosure in different configurations.

Detailed Description of the Drawings

Figure 1 shows an engine control system including a valve actuation assembly according to the present disclosure. In this example, both the inlet valve and the exhaust valve are individually electronically controllable, independently of the rotation of the engine crankshaft. An actuator 30 is provided to operate the inlet poppet valve 12 and actuator 32 operates the exhaust poppet valve 14.

A piston 2 is arranged to reciprocate up and down within a cylinder block 4. The flow of charge air (or an air and fuel mixture, depending on the engine configuration) from an inlet port 6 within cylinder head 8 into the combustion chamber is controlled using the inlet poppet valve. The exhaust valve allows exhaust gases to escape from the combustion chamber after combustion has taken place, with the exhaust gases being carried away via exhaust port 16.

The overall operation of the engine is governed by an engine control unit 34. It controls the fuel injection and ignition of a spark ignited engine, or the fuel injection of a compression ignition engine. Control unit 34 is responsive to signals from various transducers monitoring the operating conditions of the engine. For example, they may monitor the crankshaft position, the coolant temperature, the oil temperature, the engine speed, the engine’s cranking mode, and so on.

A bi-directional communication link 38 is provided between the engine control unit 34 and a valve control unit 40. In practice, control units 34 and 40 may be physically separate units or integrated into a single controller. Valve control unit 40, together with an actuator power electronics module 42 and the actuators 30 and 32 are part of a valve actuation assembly controlling the operation of the inlet and exhaust valves 12, 14.

Having regard to control signals from the engine control unit, the valve control unit in turn generates inlet actuator and exhaust actuator drive signals 44, 46 which are sent to the actuator power electronics module 42. In response to these input signals, module 42 generates inlet actuator and exhaust actuator drive currents along respective conductive lines 48 and 50.

To enable the operation of the actuators to be responsive to changes in their operating conditions, feedback signals 52 and 54 are communicated to the valve control unit from the inlet valve and exhaust valve actuators, respectively. These feedback signals may provide information relating to one or more operating conditions of the respective valve actuator, such as its position, the temperature of electromagnetic windings, current flow in the windings, and the like. The information conveyed by the signals may of course vary depending on the type of actuation employed, whether electromagnetic, hydraulic or pneumatic, for example. From analysis of the feedback signals 52 and 54, the valve control unit may be able to determine when an actuator is operating abnormally or has failed, such that there is a risk that the associated valve may come into contact with another valve and/or the piston 2. The valve control unit may therefore determine that a particular actuator should enter a failure mode.

During normal operation of an engine, the timing of the valve actuations is such that any contact between valves or a valve and the piston is avoided. Areas of potential interference between these components in the event of some form of malfunction are indicated in Figure 2. It can be seen that in this example there is an area of potential piston-to-inlet valve interference 60, an area of potential piston-to-exhaust valve interference 62, and an area of potential valve-to-valve interference 64.

An example of a valve actuator in combination with a fail-safe mechanism according to an example of the present disclosure will now be described with reference to Figures 3 to 5.

The actuator includes a rotatable push cam 70. The cam is rotatable about an axis 71 which is perpendicular to the plane of the drawing. A pull cam 73 rotates with push cam 70 about the axis 71. The actuator also includes a drive arrangement for rotating the cams as required by the valve control unit. This drive arrangement may be electromagnetic, hydraulic or pneumatic, for example. It is not shown in Figures 3 to 5 for the purposes of clarity in the drawings. A desmodromic mechanism 72 is provided to form a linkage between the cams 70, 73 and a valve 74. The mechanism 72 comprises a rocker 76, a link arm 78 and a pivotable connector 80.

Rocker 76 is mounted in the valve actuation assembly so as to be pivotable about an axis 82, which extends perpendicular to the plane of the drawing. The body of the rocker is rigid and includes three arms. A first arm 84 carries a push cam follower 86 at its distal end. The push cam follower is maintained in engagement with the push cam 70. A second arm 85 carries a pull cam follower 87 at its distal end. The pull cam follower is maintained in engagement with the pull cam 73. The body of the rocker includes a third arm 88 which is pivotably connected to the rigid link arm 78 at its distal end by a pivot 89.

The other end of the link arm 78 is pivotably connected to the body of the connector 80 by a pivot 91. The connector 80 is adapted to be coupled to one end 93 of a valve stem. Connector 80 is mounted in the valve actuation assembly so as to be pivotable about an axis 90, which extends perpendicular to the plane of the drawing. The pivot axis 90 is disposed towards one end of the body of the connector. Towards the other end of the body of the connector, it forms a pair of jaws for receiving the end of the stem of the valve 74. The head 92 of the valve 74 is received by a valve seat 94. The valve is shown in its closed configuration in Figure 3.

Each of the pivotal axes 71, 82, 90 and 104 are located at fixed positions relative to each other in the valve actuation assembly.

The valve is shown in its fully open configuration in Figure 4. It can be seen that the valve head has moved away from the valve seat. This displacement may be around 8mm for example. In Figure 4, the cams 70, 73 have rotated about axis 71 relative to their orientation in Figure 3. The profile of the push cam 70 has caused the push cam follower 86 to be lifted away from the axis of rotation 71 of the cam. This has in turn resulted in clockwise rotation of the rocker 76 about axis 82. This caused the link arm 78 to exert a torque on the connector 80, causing it to rotate around axis 90, resulting in the connector 80 exerting a force on the valve stem which moved the valve head 92 away from its seat 94.

Rotation of the cams 70,73 in the same (or opposite) direction reduces the lift of the push cam 70 at the point of contact of with the push cam follower 86, and increases the lift of the pull cam 73 at the point of contact with the pull cam follower 87. This causes the rocker to rotate anti-clockwise about its axis of rotation 82. This in turn causes the link arm to exert a torque on the connector 80 in an opposite direction to that generated during opening of the valve, resulting in the connector exerting a force on the valve stem which moves the valve head back towards its seat. Eventually, this action returns the valve to the closed configuration shown in Figure 3.

A fail-safe mechanism is provided in combination with the actuator of Figures 3 to 5. It comprises a rotary actuator 100 which is operable to rotate actuation member 102 about an axis of rotation 104 which extends perpendicular to the plane of the drawing. A blocking member 106 is rigidly mounted on the actuation member. The rotary actuator 100 is arranged to rotate under the control of control signals generated by the valve control unit 40 and/or the engine control unit 34.

During normal operation of the valve actuator as depicted in Figures 3 and 4, the actuator is operable to reciprocate the valve between closed and open positions without being impeded by the fail-safe mechanism.

Figure 5 depicts a configuration in which the fail-safe mechanism has been deployed. Rotary actuator has been rotated anti-clockwise such that the blocking member 106 is in contact with the body of the connector 80. In this configuration, the valve head 92 has been lifted only part way towards is fully open position and the blocking member prevents the valve head from lifting any further than a predetermined distance from the valve seat 94 by blocking further movement of the connector towards the valve seat. For example, the valve lift may be restricted to no more than 5mm.

The fail-safe mechanism may be configured to exert a biasing force on the actuator such that it urges the actuator towards its valve closed configuration. Alternatively, the fail-safe mechanism may be controlled to hold the blocking member at a position which defines the maximum range of travel of the actuator, thereby allowing the actuator and valve to operate within a limited range of travel.

The fail-safe mechanism may be arranged to act simultaneously on all of the actuators of the engine when deployed. Alternatively, the fail-safe mechanism may be arranged to act on each actuator independently or in groups of actuators independently.

Each cylinder of an engine will have multiple valves and an engine having multiple cylinders will have multiple sets of valves. Depending on the degree of flexibility required, the engine may include a fail-safe mechanism which, when deployed, restricts the movement of all valves of the engine. In a further example, a fail-safe mechanism is provided which may be deployed in order to restrict the actuators of a selected cylinder only. In a further implementation, the fail-safe mechanism may be independently deployable in relation to each actuator to provide greater versatility.

In the event of failure of an actuator, in an engine having multiple independently controllable valves, the engine may continue to operate using the functioning actuators, allowing a vehicle to continue its journey in a reduced power mode.

In an engine in which the operation of all actuators is restricted when the fail-safe mechanism is triggered, the operational actuators may continue to run but with reduced valve lift. If the cylinder of the failed valve has more than one valve of the same type (inlet or exhaust) as the failed valve, that cylinder may still continue to operate using the remaining functioning valves.

In an engine in which deployment of the fail-safe mechanism is able to restrict the motion of a set of valves associated with a particular selected cylinder, the remaining cylinders may continue to operate using the full range of valve lift. The valve actuators of the affected cylinder may be de-energised so that the engine continues to run using the other cylinders only. If the affected cylinder has more than one valve of the same type as the failed valve, then it may continue to run, but with the range of travel of the actuators restricted to be within the range allowed by the fail-mechanism.

An engine in which deployment of the fail-safe mechanism is controllable independently for each valve, following the failure of an actuator, the actuators of the other cylinders and the other actuators of the affected cylinder may continue to operate with the full valve lift available. Again, the affected cylinder could be deenergised or, if there is more than one of the valve type of the failed actuator, the cylinder may continue to run using the operational actuators.

The blocking member may be arranged to selectively restrict the range of motion of another part of the linkage between the cam and the valve in other examples. For example, when deployed, it may contact part of the rocker 76, such as one of its arms 84 or 88, to restrict its range of travel.

In the event of the fail-safe mechanism being deployed, the controller may be operable to determine which actuator connectors are more than the predetermined distance away from the first positions and actively drive the associated actuators so as to move their connectors to be no more than the predetermined distance away from their first positions. This is facilitated by the desmodromic nature of the actuator, with the rotation of the respective pull cam being used to exert a pulling force on the corresponding connector via rocker 76 and link arm 78.

In some examples, the controller is configured to de-energise all the actuators when the fail-safe mechanism is triggered. This makes sure that the mechanism is able to move all the actuators to safe configurations without being resisted by operation of the actuators themselves.

The fail-safe mechanism may comprise a mechanical potential energy store. When the fail-safe mechanism is deployed, energy from this store may be used to generate the force used to drive the fail-safe mechanism. The energy store may be a resilient device such as a coil spring for example.

In other examples, the fail-safe mechanism may include an electromagnetic actuator which is operable to switch the fail-safe mechanism from its non-deployed configuration to its deployed configuration. The actuator may be a bistable device. It may be able to hold either stable state without consuming electrical power. For example, it may be a bistable linear actuator as described in United Kingdom Patent Publication Nos. 2342504 and 2380065, International Patent Publication No.

io W02010/067110, or US Patent No. 6598621, the contents of which are incorporated herein by reference.

Claims

1. A valve actuation assembly for an inlet or exhaust valve of an internal combustion engine, the assembly comprising:

2. An assembly of claim 1, wherein the first position corresponds to a closed position of the valve and the second position corresponds to a fully open position of the valve.

3. An assembly of claim 1 or claim 2, wherein the fail-safe mechanism is configured such that, when the mechanism is deployed and the connector is more than the predetermined distance away from its first position, the fail-safe mechanism exerts a force on the actuator which urges the actuator towards a configuration in which the connector is the predetermined distance or less from its first position.

4. An assembly of any preceding claim, wherein the fail-safe mechanism includes a blocking member, and the fail-safe mechanism is operable to switch between a non-deployed configuration in which the blocking member does not impede operation of the actuator, and a deployed configuration in which the blocking member prevents the actuator from moving the connector more than the predetermined distance away from its first position.

5. An assembly of claim 4 when dependent on claim 3, wherein the fail-safe mechanism is configured such that when the fail-safe mechanism is deployed and the connector is more than the predetermined distance away from its first position, the blocking member exerts a force on the actuator which urges the actuator towards a configuration in which the connector is the predetermined distance or less from its first position.

6. An assembly of any preceding claim, wherein the fail-safe mechanism is operable to prevent the connector from moving away from its first position.

7. An assembly of any preceding claim including a controller for governing the operation of the actuator and the fail-safe mechanism, wherein the controller is arranged to monitor the status of the actuator and deploy the fail-safe mechanism when the controller detects a failure mode of the actuator.

8. An assembly of claim 7, wherein the controller is operable to cause the actuator to move the connector towards its first position when the controller detects a failure mode of the actuator.

9. An assembly of claim 7, wherein controller is operable to de-energise the actuator when the controller detects a failure mode of the actuator.

10. An assembly of any preceding claim, wherein the actuator comprises:

a stator;

a rotor which is rotatable relative to the stator about an axis of rotation by energising the stator; and a linkage which is coupled to the rotor at one end and to the connector at its other end, and arranged to convert rotary motion of the rotor into motion of the connector between its first and second positions.

11. An assembly of any preceding claim, wherein the assembly includes a set of actuators, each actuator includes a connector for coupling to a valve stem of a respective valve, and each actuator is operable to move its connector between a first position in which the respective valve is in its closed position and a second position in which the respective valve is in its fully open position.

12. An assembly of claim 11 when dependent on claim 7, wherein the controller is arranged to govern the operation of the set of actuators and the fail-safe mechanism, to monitor the status of the actuators, and to deploy the fail-safe mechanism when the controller detects a failure mode of one of the actuators.

13. An assembly of claim 11 or claim 12, wherein the set of actuators consists of a plurality of sub-sets of actuators, and the fail-safe mechanism is operable to prevent a selected sub-set of actuators from moving their connectors more than a predetermined distance away from their first positions.

14. An assembly of claim 13 when dependent on claim 7, wherein the controller is arranged to govern the operation of the set of actuators and the fail-safe mechanism, to monitor the status of the actuators, to detect when an actuator is in a failure mode, to determine which sub-set of actuators the failed actuator belongs to, and to deploy the fail-safe mechanism in relation to that sub-set in response to detection of the failure mode.

15. An assembly of claim 13 or claim 14, wherein each sub-set of actuators is arranged to actuate the inlet and exhaust valves of the same cylinder.

16. An assembly of claim 11, wherein the fail-safe mechanism is operable to prevent a selected actuator from moving its connector more than a predetermined distance away from its first position.

17. An assembly of claim 16 when dependent on claim 7, wherein the controller is arranged to govern the operation of the set of actuators and the fail-safe mechanism, to monitor the status of the actuators, to detect when an actuator is in a failure mode, and to deploy the fail-safe mechanism in relation to that actuator in response to detection of the failure mode.

18. An assembly of claim 17, wherein when an actuator is in failure mode, the controller is arranged to continue to operate the other actuators which actuate the other inlet and exhaust valves of the same cylinder.

19. An internal combustion engine including at least one cylinder having at least one inlet or exhaust valve, a piston and an assembly of any preceding claim, wherein the at least one valve is operable by an actuator of the assembly independently of

5 rotation of the engine crankshaft, and the connector of the actuator is coupled to the at least one valve to enable the actuator to actuate the at least one valve.

20. A method of operating an assembly of any of claims 1 to 18 or an engine of claim 19 comprising a step of deploying a fail-safe mechanism to prevent the io connector from moving more than a predetermined distance away from its first position.