High frequency switching variable cam timing phaser

Abstract

A variable cam timing phaser arrangement is disclosed, comprising: a rotor having at least one vane; a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor, wherein the at least one vane divides the at least one recess into an first chamber and a second chamber; and a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa. The control assembly comprises a central on/off piloted valve for allowing or preventing fluid communication between the first and second chambers, and a remotely located solenoid-controlled actuator for controlling the on/off piloted valve. The present disclosure further relates to a method of controlling the timing of a camshaft in an internal combustion engine. The disclosure also relates to an internal combustion engine and a vehicle comprising the disclosed variable cam timing phaser arrangement.

Claims

1. A variable cam timing phaser arrangement for an internal combustion engine comprising: a rotor having at least one vane, the rotor arranged to be connected to a camshaft; a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor and allowing rotational movement of the rotor with respect to the stator, the stator having an outer circumference arranged for accepting a drive force, wherein the at least one vane divides the at least one recess of the stator into a first chamber and a second chamber, the first chamber and the second chamber being arranged to receive hydraulic fluid under pressure wherein introduction of hydraulic fluid into the first chamber causes the rotor to move in a first rotational direction relative to the stator and introduction of hydraulic fluid into the second chamber causes the rotor to move in a second rotational direction relative to the stator, the second rotational direction being opposite the first rotational direction; and a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa, said control assembly comprising: an on/off piloted valve located centrally within the rotor or camshaft, the piloted valve comprising a pilot port, a first flow port and a second flow port, the first flow port being in fluid communication with the first chamber and the second flow port being in fluid communication with the second chamber, wherein the piloted valve is switchable between an open state and a closed state by regulation of a pressure of a pilot fluid at the pilot port, wherein in the open state the piloted valve allows fluid communication between the first chamber and second chamber, and in the closed state the piloted valve prevents fluid communication between the first chamber and the second chamber; and a solenoid-controlled actuator located remotely from rotating components of the variable cam timing phaser arrangement and in fluid communication with the pilot port of the piloted valve, the solenoid-controlled actuator having at least two states, a primary state and a secondary state, wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the open state to the closed state when the solenoid-controlled actuator switches from the primary state to the secondary state, and wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the closed state to the open state when the solenoid-controlled actuator switches from the secondary state to the primary state, by regulating the pressure of the pilot fluid at the pilot port, i. wherein the solenoid-controlled actuator in the secondary state provides the piloted valve in the closed state, thereby preventing fluid communication between the first chamber and the second chamber; ii. wherein the solenoid-controlled actuator may be switched from the secondary state to the primary state so as to coincide with a camshaft torque acting in a chosen direction, thereby switching the piloted valve to the open state and allowing fluid to flow between the first chamber and the second chamber in a direction in accordance with the chosen direction of camshaft torque, thus rotating the rotor relative to the stator; iii. wherein the solenoid-controlled actuator may be switched from the primary state to the secondary state prior to the camshaft torque changing to a non-chosen direction, thereby switching the piloted valve to the closed state and preventing fluid flowing between the first chamber and the second chamber in an opposite direction to the direction of state ii; iv. wherein states ii and iii may be repeated until a desired angle of the rotor relative to the stator is obtained; and v. wherein the solenoid-controlled actuator may be maintained in the secondary state, thereby providing the piloted valve in the closed state, thus preventing fluid communication between the first chamber and the second chamber, and thereby maintaining the desired angle of the rotor relative to the stator.

2. The variable cam timing phaser arrangement according to claim 1, wherein the hydraulic fluid and/or pilot fluid used in the arrangement is hydraulic oil.

3. The variable cam timing phaser arrangement according to claim 1, wherein the pilot fluid is air.

4. The variable cam timing phaser arrangement according to claim 1, wherein the piloted valve is a 2/2 way on/off valve, arranged to be normally in the open state, and actuated by increased fluid pressure at the pilot port to switch to the closed state.

5. The variable cam timing phaser arrangement according to claim 1, wherein the solenoid-controlled actuator is a 3/2 way on/off solenoid valve having an inlet port in fluid communication with a source of increased fluid pressure, an outlet port in fluid communication with the pilot port of the piloted valve, and a vent port, wherein the primary state of the solenoid valve is a de-energized state preventing fluid communication from the source of increased fluid pressure to the pilot port of the piloted valve and allowing fluid communication from the pilot port of the piloted valve to the vent port, and wherein the secondary state of the solenoid valve is an energized state allowing fluid communication from the source of increased fluid pressure to the pilot port of the piloted valve and actuating the piloted valve.

6. The variable cam timing phaser arrangement according to claim 1, wherein the solenoid-controlled actuator comprises a solenoid-driven piston arranged in a cylinder, the cylinder being arranged in fluid communication with the pilot port of the piloted valve, wherein the primary state of the solenoid-driven piston is a retracted de-energized state and the secondary state of the solenoid-driven piston is an extended energized state, the extended state increasing the pressure of the pilot fluid at the pilot port of the piloted valve and actuating the piloted valve.

7. The variable cam timing phaser arrangement according to claim 1, wherein the piloted valve is a 2/2 way on/off valve, arranged to be normally in the closed state, and actuated by decreased fluid pressure at the pilot port to switch to the open state.

8. The variable cam timing phaser arrangement according to claim 7, wherein the solenoid-controlled actuator comprises a solenoid-driven piston arranged in a cylinder, the cylinder being arranged in fluid communication with the pilot port of the piloted valve, wherein the primary state of the solenoid-driven piston is an retracted energized state and the secondary state of the solenoid-driven piston is an extended energized state, the retracted state decreasing the pressure of the pilot fluid at the pilot port of the piloted valve and actuating the piloted valve.

9. The variable cam timing phaser arrangement according to claim 8, wherein the solenoid-controlled actuator further comprises a normally open 2/2 way solenoid valve having an inlet port in fluid communication with a source of increased fluid pressure and an outlet port in fluid communication with the cylinder, wherein the primary state of the solenoid valve is a closed energized state and the secondary state of the solenoid valve is an open energized state, allowing fluid communication from the source of increased fluid pressure to the pilot port of the piloted valve.

10. The variable cam timing phaser arrangement according to claim 1, wherein a source of increased fluid pressure is arranged in fluid communication with the first chamber and the second chamber via a first refill channel and a second refill channel respectively, the first refill channel and second refill channel each having a check valve arranged to prevent fluid flow from the first chamber or second chamber to the source of increased fluid pressure.

11. The variable cam timing phaser arrangement according to claim 10, wherein a pilot check valve having a first flow port arranged in fluid communication with the piloted valve, a second flow port arranged in fluid communication with the second chamber and a pilot port arranged in fluid communication with the second refill channel, wherein the pilot check valve is arranged to be in a first state allowing flow between the piloted valve and the second chamber in any direction when a fluid pressure in the second refill channel is greater than a predetermined pressure, and to be in a second state when the fluid pressure in the second refill channel is lower than the predetermined pressure, wherein when in the second state the pilot check valve allows fluid flow only from the second chamber via the piloted valve to the first chamber, and prevents flow from the first chamber to the second chamber.

12. A method for controlling a timing of a camshaft in an internal combustion engine comprising a variable cam timing phaser arrangement, wherein said variable cam timing phaser arrangement comprises: a rotor having at least one vane, the rotor arranged to be connected to a camshaft; a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor and allowing rotational movement of the rotor with respect to the stator, the stator having an outer circumference arranged for accepting a drive force, wherein the at least one vane divides the at least one recess into a first chamber and a second chamber, the first chamber and the second chamber being arranged to receive hydraulic fluid under pressure wherein introduction of hydraulic fluid into the first chamber causes the rotor to move in a first rotational direction relative to the stator and introduction of hydraulic fluid into the second chamber causes the rotor to move in a second rotational direction relative to the stator, the second rotational direction being opposite the first rotational direction; and a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa, said control assembly comprising: an on/off piloted valve located centrally within the rotor or camshaft, the piloted valve comprising a pilot port, a first flow port and a second flow port, the first flow port being in fluid communication with the first chamber and the second flow port being in fluid communication with the second chamber, wherein the piloted valve is switchable between an open state and a closed state by regulation of a pressure of a pilot fluid at the pilot port, wherein in the open state the piloted valve allows fluid communication between the first chamber and second chamber, and in the closed state the piloted valve prevents fluid communication between the first chamber and the second chamber; and a solenoid-controlled actuator located remotely from rotating components of the variable cam timing phaser arrangement and in fluid communication with the pilot port of the piloted valve, the solenoid-controlled actuator having at least two states, a primary state and a secondary state, wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the open state to the closed state when the solenoid-controlled actuator switches from the primary state to the secondary state, and wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the closed state to the open state when the solenoid-controlled actuator switches from the secondary state to the primary state, by regulating the pressure of the pilot fluid at the pilot port, wherein the method comprises: i. providing the solenoid-controlled actuator in the secondary state, thereby providing the piloted valve in the closed state, thus preventing fluid communication between the first chamber and the second chamber; ii. timing a switching of the solenoid-controlled actuator from the secondary state to the primary state to coincide with a camshaft torque acting in a chosen direction, thereby switching the piloted valve to the open state and allowing fluid to flow between the first chamber and the second chamber in a direction in accordance with the chosen direction of camshaft torque, thus rotating the rotor relative to the stator; iii. switching the solenoid-controlled actuator from the primary state to the secondary state prior to the camshaft torque changing to a non-chosen direction, thereby switching the piloted valve to the closed state and preventing fluid flowing between the first chamber and the second chamber in an opposite direction to the direction of step ii; iv. repeating steps ii and iii until a desired angle of the rotor relative to the stator is obtained; and v. maintaining the solenoid-controlled actuator in the secondary state, thereby providing the piloted valve in the closed state, thus preventing fluid communication between the first chamber and the second chamber, and thereby maintaining the desired angle of the rotor relative to the stator.

13. The method according to claim 12, wherein the switching of the solenoid-controlled actuator in step ii. is timed to coincide with the camshaft torque increasing over a threshold value and the switching of the solenoid-controlled actuator in step iii. is timed to coincide with the camshaft torque decreasing under a threshold value.

14. An internal combustion engine comprising a variable cam timing phaser arrangement, wherein said variable cam timing phaser arrangement comprises: a rotor having at least one vane, the rotor arranged to be connected to a camshaft of the combustion engine; a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor and allowing rotational movement of the rotor with respect to the stator, the stator having an outer circumference arranged for accepting a drive force, wherein the at least one vane divides the at least one recess into a first chamber and a second chamber, the first chamber and the second chamber being arranged to receive hydraulic fluid under pressure wherein introduction of hydraulic fluid into the first chamber causes the rotor to move in a first rotational direction relative to the stator and introduction of hydraulic fluid into the second chamber causes the rotor to move in a second rotational direction relative to the stator, the second rotational direction being opposite the first rotational direction; and a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa, said control assembly comprising: an on/off piloted valve located centrally within the rotor or camshaft of the combustion engine, the piloted valve comprising a pilot port, a first flow port and a second flow port, the first flow port being in fluid communication with the first chamber and the second flow port being in fluid communication with the second chamber, wherein the piloted valve is switchable between an open state and a closed state by regulation of a pressure of a pilot fluid at the pilot port, wherein in the open state the piloted valve allows fluid communication between the first chamber and second chamber, and in the closed state the piloted valve prevents fluid communication between the first chamber and the second chamber; and a solenoid-controlled actuator located remotely from rotating components of the variable cam timing phaser arrangement and in fluid communication with the pilot port of the piloted valve, the solenoid-controlled actuator having at least two states, a primary state and a secondary state, wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the open state to the closed state when the solenoid-controlled actuator switches from the primary state to the secondary state, and wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the closed state to the open state when the solenoid-controlled actuator switches from the secondary state to the primary state, by regulating the pressure of the pilot fluid at the pilot port, i. wherein the solenoid-controlled actuator in the secondary state provides the piloted valve in the closed state, thereby preventing fluid communication between the first chamber and the second chamber; ii. wherein the solenoid-controlled actuator may be switched from the secondary state to the primary state so as to coincide with a camshaft torque acting in a chosen direction, thereby switching the piloted valve to the open state and allowing fluid to flow between the first chamber and the second chamber in a direction in accordance with the chosen direction of camshaft torque, thus rotating the rotor relative to the stator; iii. wherein the solenoid-controlled actuator may be switched from the primary state to the secondary state prior to the camshaft torque changing to a non-chosen direction, thereby switching the piloted valve to the closed state and preventing fluid flowing between the first chamber and the second chamber in an opposite direction to the direction of state ii; iv. wherein states ii and iii may be repeated until a desired angle of the rotor relative to the stator is obtained; and v. wherein the solenoid-controlled actuator may be maintained in the secondary state, thereby providing the piloted valve in the closed state, thus preventing fluid communication between the first chamber and the second chamber, and thereby maintaining the desired angle of the rotor relative to the stator.

15. A vehicle comprising a combustion engine and a variable cam timing phaser arrangement, wherein said variable cam timing phaser arrangement comprises: a rotor having at least one vane, the rotor arranged to be connected to a camshaft of the combustion engine of the vehicle; a stator co-axially surrounding the rotor, having at least one recess for receiving the at least one vane of the rotor and allowing rotational movement of the rotor with respect to the stator, the stator having an outer circumference arranged for accepting a drive force, wherein the at least one vane divides the at least one recess into a first chamber and a second chamber, the first chamber and the second chamber being arranged to receive hydraulic fluid under pressure wherein introduction of hydraulic fluid into the first chamber causes the rotor to move in a first rotational direction relative to the stator and introduction of hydraulic fluid into the second chamber causes the rotor to move in a second rotational direction relative to the stator, the second rotational direction being opposite the first rotational direction; and a control assembly for regulating hydraulic fluid flow from the first chamber to the second chamber or vice-versa, said control assembly comprising: an on/off piloted valve located centrally within the rotor or camshaft of the combustion engine of the vehicle, the piloted valve comprising a pilot port, a first flow port and a second flow port, the first flow port being in fluid communication with the first chamber and the second flow port being in fluid communication with the second chamber, wherein the piloted valve is switchable between an open state and a closed state by regulation of a pressure of a pilot fluid at the pilot port, wherein in the open state the piloted valve allows fluid communication between the first chamber and second chamber, and in the closed state the piloted valve prevents fluid communication between the first chamber and the second chamber; and a solenoid-controlled actuator located remotely from rotating components of the variable cam timing phaser arrangement and in fluid communication with the pilot port of the piloted valve, the solenoid-controlled actuator having at least two states, a primary state and a secondary state, wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the open state to the closed state when the solenoid-controlled actuator switches from the primary state to the secondary state, and wherein the solenoid-controlled actuator is arranged to switch the piloted valve from the closed state to the open state when the solenoid-controlled actuator switches from the secondary state to the primary state, by regulating the pressure of the pilot fluid at the pilot port, i. wherein the solenoid-controlled actuator in the secondary state provides the piloted valve in the closed state, thereby preventing fluid communication between the first chamber and the second chamber; ii. wherein the solenoid-controlled actuator may be switched from the secondary state to the primary state so as to coincide with a camshaft torque acting in a chosen direction, thereby switching the piloted valve to the open state and allowing fluid to flow between the first chamber and the second chamber in a direction in accordance with the chosen direction of camshaft torque, thus rotating the rotor relative to the stator; iii. wherein the solenoid-controlled actuator may be switched from the primary state to the secondary state prior to the camshaft torque changing to a non-chosen direction, thereby switching the piloted valve to the closed state and preventing fluid flowing between the first chamber and the second chamber in an opposite direction to the direction of state ii. iv. wherein states ii and iii may be repeated until a desired angle of the rotor relative to the stator is obtained; and v. wherein the solenoid-controlled actuator may be maintained in the secondary state, thereby providing the piloted valve in the closed state, thus preventing fluid communication between the first chamber and the second chamber, and thereby maintaining the desired angle of the rotor relative to the stator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For the understanding of the present invention and further objects and advantages of it, the detailed description set out below can be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

(2) FIG. 1 illustrates schematically one embodiment of a variable cam timing phaser arrangement according to the present disclosure.

(3) FIG. 2 illustrates schematically another embodiment of a variable cam timing phaser arrangement according to the present disclosure.

(4) FIG. 3 illustrates schematically yet another embodiment of a variable cam timing phaser arrangement according to the present disclosure.

(5) FIG. 4 illustrates schematically a further embodiment of a variable cam timing phaser arrangement according to the present disclosure.

(6) FIG. 5 illustrates schematically yet a further embodiment of a variable cam timing phaser arrangement according to the present disclosure.

(7) FIG. 6 shows a process chart for a method for controlling the timing of a camshaft in an internal combustion engine according to the present disclosure.

(8) FIG. 7 illustrates schematically the periodic variation in camshaft torque as a function of camshaft angle.

(9) FIG. 8 illustrates schematically a vehicle comprising an internal combustion engine comprising a variable cam timing phaser arrangement according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(10) The present invention is based on the realization that cam torque actuated cam phasing can be achieved by utilizing a centrally-mounted on/off piloted valve instead of the multi-positional spool valve known in the prior art. The on/off valve controls fluid passage between a first chamber of the cam phaser and a second chamber. The switching of the piloted valve can be timed to allow flow during each period the camshaft torque acts in the desired direction and to prevent flow when the camshaft torque acts in the opposite direction. In this manner, the rotor is shifted rotationally in in the desired direction relative to the stator.

(11) The cam timing phaser arrangement of the present invention comprises a rotor, a stator co-axially surrounding the rotor, and a control assembly.

(12) The cam phaser rotor is arranged to be connected to a camshaft of the internal combustion engine. This can be an intake valve camshaft, exhaust valve camshaft, or any other camshaft in the engine such as a combined intake/exhaust camshaft. The rotor has at least one vane, but may preferably have a plurality of vanes, such as three, four, five or six vanes. Separate oil channels for channelling oil to and from the piloted valve of the control assembly are provided at each side of at least one of the vanes, but preferably at each side of each of the vanes.

(13) The stator is arranged for accepting drive force. This may for example be by connecting the stator to a cam sprocket, which takes up drive force from the crankshaft via the timing belt. The stator may also be constructionally integrated with the cam sprocket. The stator co-axially surrounds the rotor and has at least one recess for accepting the at least one vane of the rotor. In practice, the stator has the same number of recesses as the number of rotor vanes. The recesses in the stator are somewhat larger than the rotor vanes, meaning that when the rotor is positioned in the stator with the vanes centrally positioned in the recesses, a chamber is formed at each side of each rotor. These chambers can be characterized as first chambers, rotating the rotor in a first direction relative to the stator when filled with hydraulic oil, and second chambers, rotating the rotor in a second direction relative to the stator when filled with hydraulic oil.

(14) The control assembly comprises a piloted valve and a remotely-located solenoid-controlled actuator for actuating the piloted valve.

(15) Where valves are referred to as “on/off” this refers to a valve having only two states: an open state and a closed state. Such valves may however have more than two ports. For example, a 3/2 way on/off valve has three ports and two states. Such a valve often connects two flow ports when open and connects one of the flow ports to a vent/exhaust port when closed.

(16) Where valves are referred to as “normally closed/open/on/off”, this refers to the state of the valve when non-actuated. For example, a normally open solenoid valve is held in the open position when not actuated/energized, commonly using a return such as a spring return. When the normally open solenoid valve is actuated/energized the solenoid acts with a force sufficient to overcome the force of the return holding the valve open, and the valve is therefore closed. Upon de-actuation/de-energization, the return returns the valve to the open state.

(17) Where components are stated to be in “fluid communication” or flow is allowed or prevented “between” components, this flow is to be interpreted as not necessarily directional, i.e. flow may proceed in either direction. Directional flow in a single direction is denoted as flow “from” a component “to” another component.

(18) The piloted valve may be a 2/2 way on/off valve, i.e. a valve having two flow ports, i.e. a first and second port, and two positions (open or closed). The piloted valve is in fluid communication with the oil channels leading to the first chambers at the first port and is in fluid communication with the oil channels leading to the second chambers at the second port. Therefore, fluid communication between the first and second chambers is established when the valve is open. The pilot valve also has a pilot port connected to the pilot fluid feed. The switching of the on/off piloted valve is regulated by the pressure of the pilot fluid at the pilot port; the pressure of the pilot fluid being regulated by a remotely-placed solenoid actuator. The pilot fluid may be air, i.e. the piloted valve may be pneumatically actuated. However, it is preferable that the pilot fluid is hydraulic oil since this considerably simplifies the system design, due to hydraulic oil already being used in the cam phaser arrangement. The pilot valve may be normally closed, i.e. be closed when non-actuated. However it may also be normally open, i.e. open and allowing fluid communication between the first chamber and the second chamber when non-actuated. The piloted valve may be any suitable valve type known in the art, including but not limited to a poppet valve, sliding spool valve and rotary spool valve. The valve may have a return spring. The piloted valve is located centrally, such as in the rotor or camshaft.

(19) The solenoid actuator is located remotely from the rotating components of the cam phaser arrangement and may instead placed on a stationary component of the internal combustion engine such as the cam bearing holder. The solenoid actuator regulates the pilot fluid pressure in order to actuate the piloted valve. This may be done by increasing the pressure to actuate the piloted valve by “pushing”. However the piloted valve may also be actuated by a “pulling” effect using decrease pilot fluid pressure. The solenoid actuator may be an on/off solenoid valve that increases fluid pressure by connection to a source of fluid pressure, such as the main oil gallery if oil is used as the pilot fluid. It can, for example be a 3-port, 2-position on/off solenoid valve being connected to an oil gallery at the inlet port, at the outlet port being connected to an oil channel leading to the pilot port of the pilot valve, and having a vent port for release of oil pressure from the channel leading to the pilot port when in the “off” position. It may normally be in the “off” position when the solenoid is not actuated, and switch to the “on” position upon activation of the solenoid. The solenoid valve may be any suitable valve type known in the art, including but not limited to a poppet valve, sliding spool valve and rotary spool valve. The use of a poppet valve virtually eliminates the risk for valve jam.

(20) The solenoid actuator may also be an oil-filled cylinder in fluid connection with the pilot port of the piloted valve. An on/off solenoid-actuated piston is provided in the cylinder. The solenoid-actuated piston may push down on the volume of oil in the cylinder upon actuation, leading to increased pressure at the pilot port. Alternatively, the solenoid-actuated piston may retract in the cylinder upon actuation, leading to decreased oil pressure at the pilot valve, and therefore a “pull” effect.

(21) The oil pressure may be maintained in the cam phaser system by connection to a source of oil pressure, such as the main oil gallery. For example, such connection points may be arranged on the fluid channels leading from the first and/or second chambers to the piloted valve. Such connection points may also be arranged in conjunction with the solenoid actuator, for example as a connection to the inlet port of a solenoid valve (as previously mentioned), or in conjunction with an oil-filled cylinder. The channel(s) connecting to the source of oil pressure may be provided with a check valve(s) to prevent backflow of oil from the cam phaser assembly to the source of oil pressure.

(22) The cam phaser assembly may also be provided with a number of failsafe features. For example, a pressure-actuated lock pin may be arranged in at least one of the vanes of the rotor, together with a corresponding recess in the stator for receiving the lock pin. The recess for receiving the locking pin is located at a base position, i.e. either fully advanced or fully retarded. A torsion spring may be provided in order to bias the rotor towards the base position in the event of system failure. The lock pin is normally in the deployed (locking) position, and is actuated to the retracted (unlocked) position when the pressure in a component of the cam phaser arrangement exceeds a threshold pressure. For example, the lock pin may be in fluid connection with one or more channels leading from a chamber to the piloted valve. The lock pin may alternatively be in fluid connection with a channel leading from the solenoid actuator to the piloted valve. This means that the lock pin may deploy in the event of solenoid failure. In such a case, a constriction may be provided in the channel leading to the lock pin so that transitory dips in oil pressure at the pilot port when performing cam phasing do not lead to the lock pin deploying momentarily.

(23) Another failsafe feature that can be utilized is a pilot check valve arranged in a channel leading from a chamber to the piloted valve. This pilot check valve is normally allows flow in either direction whenever the pressure in the channel exceeds a threshold level. However, if the pressure in the channel is reduced below the threshold level, e.g. in the event of system failure, the pilot check valve prevents flow in one direction. This results in a “hydraulic ratchet” effect being achieved, provided that the piloted valve is open, and the rotor is directed towards locking base position by the action of the camshaft torque. Thus, by using such a pilot check valve failsafe measure, the need for a failsafe torsional spring in the rotor is removed, thus allowing the cam phaser to utilize more of the camshaft torque.

(24) When camshaft phasing is desired, the switching of the solenoid actuator is timed so that the piloted valve is opened to coincide with camshaft torque in the desired direction and the piloted valve is closed to coincide with camshaft torque in the direction opposite to the desired direction. So, for example positive camshaft torque resists cam rotation and retards the variable cam timing. If retardation of the camshaft timing is desired, actuation of the solenoid actuator is timed so that the piloted valve is open during periods of positive torque and closed during periods of negative torque. Likewise, if advancement of the camshaft timing is desired, actuation of the solenoid actuator is timed so that the piloted valve is open during periods of negative torque and closed during periods of positive torque. The switching of the solenoid actuator may also be controlled so that the piloted valve is open only when the torque exceeds a certain (positive or negative) magnitude.

(25) The invention will now be further illustrated with reference to the figures.

(26) FIG. 1 shows a one embodiment of the variable cam timing phaser arrangement 1 of the invention. A rotor 3 comprises at least one vane 5. A stator 7 having at least one recess 9 co-axially surrounds the rotor 3. The stator is fixed to a cam sprocket (not shown). The vane 5 divides the recess 9 into a first chamber 13 and a second chamber 15. A 2/2 way on/off piloted valve 17 is arranged centrally in the rotor 3. A first oil channel 19 is arranged at the side of the vane 5 and leads from the first chamber 13 to a first port of the piloted valve 17. A second oil channel 21 is arranged at the side of the vane 5 and leads from the second chamber 15 to a second port of the piloted valve 17. A pilot oil channel 23 leads from the pilot port of the pilot valve 17 to an outlet port of a 3/2 way on/off solenoid valve 25. The solenoid valve 25 is located on a stationary component of the internal combustion engine such as the cam holder bearing, remote from the rotating components of the combustion engine such as the rotor 3, stator 7, cam sprocket and camshaft (not shown). The inlet port of the solenoid valve 25 is connected to a source of oil pressure 27, and the remaining port of the solenoid valve 25 is a vent port. Oil refill channels 29, 31 leading from a source of oil pressure 27 adjoin the first oil channel 19 and second oil channel 21 respectively. Each of the oil refill channels 29, 31 is fitted with a check valve (30, 32) preventing oil backflow from the first and second oil channels 19, 21. A lock-pin 33 is arranged in the vane 5 of the rotor 3. The lock-pin 33 is in fluid communication with the pilot oil channel 23 though a lock oil channel 35. A restricting orifice 37 is arranged in the lock oil channel 35.

(27) The piloted valve 17 is open when not actuated by increased fluid pressure and the solenoid valve 25 is closed (leads the pilot oil channel 23 to vent) when not actuated. To set the cam timing phaser arrangement 1 in a holding state, i.e. a state where no phasing takes place, the piloted valve 17 must be closed by actuating the solenoid valve 25 to increase the oil pressure in the pilot oil channel 23. Once in the holding state, the cam timing phaser arrangement 1 can be advanced by timing the switching of the solenoid valve 27 so that the piloted valve 17 is open to coincide with periods of negative torque on the camshaft and closed to coincide with periods of positive torque. Alternatively, the cam timing phaser arrangement 1 can be retarded by timing the switching of the solenoid valve 27 so that the piloted valve 17 is open to coincide with periods of positive torque on the camshaft and closed to coincide with periods of negative torque. When the desired degree of timing advancement or retardation is obtained, the phasing can be held (maintained) by actuating the solenoid valve 25.

(28) Oil refill channels 29, 31 ensure a constant supply of oil to the cam phaser arrangement 1. The lock pin 33 is retracted (unlocked) when the solenoid valve 25 provides oil pressure to the pilot oil channel 23, which it must do in order to hold phasing. During phasing the pressure will fluctuate in the pilot oil channel 23, but due to the high frequency of the switching and the restricting orifice 37, the lock pin 33 will not experience these pressure fluctuations and will not deploy. However, if the oil system pressure becomes too low or the solenoid is deactivated for a significant period of time, the lock pin 33 will deploy and the rotor will be rotated to base (locking) position by a torsional spring (not shown).

(29) The embodiment shown in FIG. 2 is similar to that of FIG. 1 except that the lock oil channel 35 is in fluid communication with the oil refill channel 29 instead of the pilot oil channel 23. In this embodiment, the lock-pin will be retracted when the system pressure is sufficiently high and will deploy when the system pressure sinks below a threshold level, irrespective of the functioning of the solenoid valve.

(30) The embodiment shown in FIG. 3 is similar to that of FIG. 2 except that a pilot check valve 39 is arranged in the second oil channel 21 in proximity to the piloted valve 17. If the system oil pressure is above a threshold level the pilot check valve 39 will allow oil flow in both directions. However, if the pressure falls below this threshold, the pilot check valve 39 will allow only flow from the second chamber 15 to the first chamber 13. This means that upon failure of the oil system, the rotor will move to base (locking) position by cam torque actuation, without the need for a torsional spring. The pilot check valve may instead be arranged in the first oil channel 19 if the locking position at the opposite rotational extremity is desired.

(31) The embodiment shown in FIG. 4 is similar to that of FIG. 2, except that a cylinder 41 with solenoid-actuated piston 43 replaces the solenoid valve 25 as the solenoid actuator. The source of oil system pressure 27 is coupled to the pilot oil channel 23 by a check valve 44 to prevent backflow. Pressure is increased at the pilot port of the piloted valve 17 by actuating the solenoid-actuated piston 43, whereby it presses down upon the column of oil in the cylinder, thereby raising pressure in the cylinder 41 and pilot oil channel 23 in fluid communication with the cylinder 41.

(32) The embodiment shown in FIG. 5 is similar to that of FIG. 2 but utilizes a different control assembly. The cam phaser arrangement is shown with no system oil pressure and therefore the piloted valve 17 is open. During operation at normal system pressure, the piloted valve 17 is a normally closed 2/2 way valve. The piloted valve 17 may then be actuated (opened) by a pressure reduction at the pilot port, i.e. the valve is “pulled” open by reduced oil pressure. The solenoid actuator is a cylinder 41 with a solenoid-actuated piston 43. However, in contrast to the cylinder of the embodiment of FIG. 4, the solenoid-actuated piston 43 is normally in an extended position, pressing down upon the column of fluid in the cylinder 41 due to the presence of a spring return on the solenoid-actuated piston 43. When actuated, the solenoid-actuated piston 43 retracts, reducing the pressure in the cylinder 41 and pilot oil channel 23, thereby “pulling” the piloted valve 17 open. A separate on/off 2/2 way solenoid valve 45 provides a fluid connection from a source of oil pressure 27 to the cylinder 41 and pilot oil channel 23. This solenoid valve 45 is in open when non-actuated, meaning that the pilot oil channel 23 is subject to oil pressure when the solenoid valve 45 is non-actuated. Solenoid-actuated piston and solenoid valve 45 work in tandem and are switched simultaneously. When both are non-actuated, the pressure in the pilot oil channel is elevated due to the open connection to the source of oil system pressure 27. When both are actuated, fluid communication with the source of oil system pressure 27 is ended and the retraction of the solenoid-actuated piston 43 decreases oil pressure in the pilot oil channel 23, thus actuating the piloted valve 17. In this embodiment, there is a lesser need for a spring return in the piloted valve 17. Instead, the solenoid-actuated piston and solenoid valve 45 are both fitted with spring returns. Since these components are positioned remotely from the rotating cam phaser components, larger, more robust springs may be used, thus increasing the robustness of the cam phaser arrangement.

(33) The embodiment of FIG. 5 is therefore in a holding state when non-actuated. In order to obtain phasing, the solenoid actuator (solenoid valve 27 and solenoid-actuated piston 43) is energized in order to open the piloted valve 17 during periods when the camshaft torque is acting in the desired direction.

(34) The variable cam timing phaser arrangements described above are used to control the timing of a camshaft in an internal combustion engine. The control method comprises the following steps, as shown in FIG. 6:

(35) The method of controlling the camshaft phasing starts in an initial state whereby the current timing is held. This is achieved when the piloted valve is closed, which in turn is achieved by switching the solenoid actuator to the secondary state, if it is not already in the secondary state. In the holding state, fluid flow between the first chamber and second chamber is not permitted, and therefore rotation of the rotor relative to the stator is not possible.

(36) In order to initiate phasing, the piloted valve is opened by switching the solenoid actuator to the primary state. This switching is performed to coincide with the camshaft torque acting in the direction desired for phasing. Positive camshaft torque retards timing and negative camshaft torque advances timing. FIG. 7 shows a schematic representation of how the camshaft torque (y-axis) may vary depending on crank angle (x-axis). For example, in order to achieve retardation of timing, the piloted valve may be opened to coincide with points 47 on the camshaft torque curve.

(37) To obtain a uni-directional flow from one chamber to the other, the piloted valve must be closed when camshaft torque acts in the opposite direction to that desired. This is achieved by switching the solenoid actuator to the secondary state. For example, to achieve timing retardation the piloted valve may be closed to coincide with points 49 on the camshaft torque curve.

(38) Steps ii and iii are repeated until the desired degree of timing advancement or retardation is obtained; i.e. until the desired angle of the rotor relative to the stator is obtained. The rotor is gradually rotated relative to the stator for each time an on/off switching cycle is performed.

(39) One the desired timing has been achieved, the timing is held by maintaining the solenoid actuator in the secondary position.

(40) It should be noted that the solenoid primary state may be a non-actuated state as shown in the embodiments of FIGS. 1-4, or it may be an actuated state as shown in FIG. 5. That is to say that in some embodiments opening of the piloted valve is achieved by energizing the solenoid actuator, and in some embodiments opening of the piloted valve is achieved by de-energizing the solenoid actuator.

(41) There may be barriers to initiating and propagating rotation of the rotor relative to the stator, due to for example frictional effects. Therefore it may in some instances be desirable to open the piloted valve only when the camshaft torque exceeds a value sufficient to initiate rotation and close the piloted valve when the camshaft torque is no longer sufficient to maintain rotation. The torque required for initiation and propagation of rotation may be the same, but are not necessarily the same. For example, in order to achieve retardation of timing, the piloted valve may be opened at points 51 on the camshaft torque curve shown in FIG. 7, and closed at points 53.

(42) The present invention also relates to an internal combustion engine and a vehicle comprising a variable cam timing phaser arrangement as described above. FIG. 8 shows schematically a heavy goods vehicle 100 having an internal combustion engine 103. The internal combustion engine has a crankshaft 105, crankshaft sprocket 107, camshaft (not shown), camshaft sprocket 109 and timing chain 111. The variable cam timing phaser arrangement 1 is located at the cam sprocket/camshaft. An engine provided with such a variable cam timing phaser arrangement has a number of advantages such as better fuel economy, lower emissions and better performance as compared to a vehicle lacking cam phasing.