Electronic lock for VCT phaser

Abstract

A lock mechanism for a phaser of a variable cam timing system is actuated by an electromagnetic force. Since the lock mechanism is not dependent upon engine oil pressure, it is actuatable at any time from engine startup to engine shutdown. A lock solenoid is preferably used to actuate a lock pin, which is otherwise urged toward a lock hole and a locked position by a spring force, to an unlocked position. The lock solenoid preferably acts on a pin lock plate that is coupled to the lock pin. A preferred startup method and a preferred shutdown method are also described.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of variable camshaft timing phasers. More particularly, the invention pertains to an electronically actuated lock for a variable camshaft timing phaser.

2. Description of Related Art

Various mechanisms have been employed with internal combustion engines to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phaser has a rotor with one or more vanes, mounted to the end of the camshaft, surrounded by a housing with the vane chambers into which the vanes fit. The vanes may also be mounted to the housing, and the chambers may be in the rotor. The housing's outer circumference forms the sprocket, pulley, or gear-accepting drive force through a chain, belt, or gears, usually from the camshaft, or from another camshaft in a multiple-cam engine.

A variety of lock mechanisms are known in the art for locking a phaser in a predetermined position. Commonly a lock pin is biased toward a lock hole by a spring for locking the phaser and away from the lock hole by engine oil pressure for unlocking the phaser. Thus, when oil pressure is reduced, such as upon shutdown of the engine, the lock pin engages the lock hole to lock the rotor with respect to the housing. On many cam phasers there is a piston-style lock that uses oil pressure to move the lock pin to let the phaser actuate. This style of lock mechanism requires oil pressure to release the lock pin from engagement with the lock hole and thus may be delayed from releasing after the engine starts while the oil pressure builds up. Many oil pressure actuated (OPA) phasers do not unlock at hot engine start up because the oil pressure is too low for the phaser to be stable or actuate consistently.

With the ever increasing need to improve fuel efficiency, original equipment manufacturers (OEMs) are exploring advanced combustion strategies that benefit from a cam phaser with an extended range of motion (>60° ), fast actuation, and operability immediately after the engine starts. A cam torque actuated (CTA) phaser utilizes the torsionals of the engine to meet these needs. In order for the CTA phaser to move, the lock pin must be able to release prior to the engine pump providing oil to the phaser.

One such means for actuating a lock mechanism is an electromagnetic force. Electromagnetic braking is known in the art. In U.S. Pat. No. 4,754,727, several brake mechanisms are shown for providing a retarding force, including several electromagnetic brake configurations. U.S. Pat. No. 5,031,585 shows a wet brake mechanism electromagnetically actuated for retarding phase changes. In U.S. Pat. Nos. 6,250,265, 6,382,155, and 6,883,479, a locking plate is electromagnetically actuated for locking a VCT phaser. However, none of these patents use an electromagnetic force to actuate a lock pin.

In many situations a lock pin mechanism for a phaser is preferable over a locking plate mechanism or a braking mechanism. Therefore, there is a need in the art for a lock pin mechanism that is not dependent upon engine oil pressure.

SUMMARY OF THE INVENTION

The lock mechanism for a phaser of a variable cam timing system is actuated by an electromagnetic force. Since the lock mechanism is not dependent upon engine oil pressure, it is actuatable at any time from engine startup to engine shutdown. A lock solenoid is preferably used to actuate a lock pin, which is otherwise urged toward a lock hole and a locked position by a spring force, to an unlocked position. The lock solenoid preferably acts on a pin lock plate that is coupled to the lock pin. A preferred startup method and a preferred shutdown method are also described.

The variable cam timing phaser for an internal combustion engine includes a housing with an outer circumference for accepting drive force, a rotor for connection to a camshaft coaxially located within the housing, and a lock mechanism. The housing and the rotor define at least one vane separating a chamber into an advance chamber and a retard chamber. The rotor is capable of rotation within the housing to shift the relative angular position of the housing and the rotor. The lock mechanism includes a lock solenoid, a lock plate in proximity to the lock solenoid, a lock plate spring biasing the lock plate toward the second position, and a lock pin coupled to the lock plate for movement therewith. The lock plate moves between a first position when the lock solenoid is in an energized state and a second position when the lock solenoid is in a de-energized state. When the lock plate is in the first position, the lock pin is in an unlocked state such that the lock pin does not prevent rotation of the rotor within the housing. When the lock plate is in the second position, the lock pin is in a locked state such that the lock pin extends into a lock hole, thereby preventing rotation of the rotor within the housing.

In one embodiment, the lock pin is located within the housing in the unlocked state and the lock hole is located in the rotor. In this embodiment, the lock pin may be located such that the vane is in a mid position when the phaser is in the locked state or such that the vane is in an end position when the phaser is in the locked state.

In another embodiment, the lock pin is located within the rotor in the unlocked state and the lock hole is located in the housing on a side opposite to the lock solenoid. Preferably, the lock pin is urged toward the lock plate by a lock pin spring opposing the lock plate spring. In this embodiment, the lock hole may be located such that the vane is in a mid position when the phaser is in the locked state or such that the Vane is in an end position when the phaser is in the locked state.

In a preferred embodiment, the phaser further includes a variable force solenoid, wherein the lock solenoid is mounted with and around the variable force solenoid and a spool valve actuated by the variable force solenoid to regulate a position of the phaser.

In another embodiment, the phaser further includes a linear actuator and a spool valve actuated by the linear actuator to regulate a position of the phaser. The linear actuator is preferably a stepper motor, a vacuum actuator, a differential pressure controller, or a regulated pressure controller.

The lock pin and the lock plate are preferably coupled to move together.

A method of controlling a variable cam timing phaser during startup of an internal combustion engine includes energizing the lock solenoid to move the lock plate coupled to the lock pin to a position wherein the lock pin is removed from a lock hole such that the lock pin does not prevent rotation of the rotor within the housing. The. method preferably further includes determining if conditions have been met to move the phaser, and if conditions have been met, energizing a variable force solenoid to move a spool in a spool valve, thereby moving the phaser.

A method of controlling a variable cam timing phaser during shutdown of an internal combustion engine includes de-energizing the lock solenoid to release the lock plate coupled to the lock pin, thereby allowing the lock pin to extend into a lock hole to prevent rotation of a rotor within a housing. In one embodiment, the method further includes moving the phaser to a locked position when the engine is at idle such that the lock pin is aligned with the lock hole. In another embodiment, the method further includes determining the position of the phaser when the engine is turned off and moving the phaser to a locked position as the engine is slowing down such that the lock pin is aligned with the lock hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross section of an electromechanical lock mechanism of the present invention in an unlocked state.

FIG. 2 shows the mechanism of FIG. 1 in a locked state.

FIG. 3 shows a cross section of a first embodiment of the present invention in an unlocked state.

FIG. 4 shows the embodiment of FIG. 3 in a locked state.

FIG. 5 shows a cross section of a second embodiment of the present invention in an unlocked state.

FIG. 6 shows the embodiment of FIG. 5 in a locked state.

FIG. 7 shows an elevated view of lock pin and lock hole positions of a phaser of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In a preferred embodiment, an electronic coil is mounted on the outside of the phaser to magnetize a plate coupled to a lock pin. The coil is stationary and is preferably mounted with and around a variable force solenoid (VFS) that is used to move the VCT spool valve. The lock solenoid is energized upon command from an electronic control unit that also controls the cam phaser solenoid. Inputs that help determine when to energize the solenoid and release the lock pin include, but are not limited to, engine speed, engine temperature, time, exhaust temperature, manifold air pressure (MAP), and throttle position.

Referring to FIGS. 1 and 2, a lock mechanism 10 of the present invention includes a lock solenoid 12, a pin lock plate 14, a lock pin 16, and a lock hole 18. In an unlocked state, as shown in FIG. 1, the lock coil 20 of the lock solenoid 12 is energized, thereby attracting the lock plate 14, which pulls and holds the lock pin 16 clear of the lock hole, 18, allowing the rotor 28 to rotate with respect to the housing 24. In a locked state, as shown in FIG. 2, the lock solenoid 12 is not energized, and a spring 22 force urges the lock pin 16 into the lock hole 18, thereby preventing the rotor 28 from rotating with respect to the housing 24. In the embodiment shown in FIGS. 1 and 2, the lock pin 16 sits primarily within the housing 24 of the phaser 26 in an unlocked state and extends into the lock hole 18, which is located in the rotor 28, in a locked state. The lock hole 18 is preferably in a vane of the rotor 28. A camshaft 30 is also shown in FIGS. 1 and 2. In an alternate embodiment discussed below, the lock pin sits primarily in the rotor in an unlocked state and extends into a lock pin hole in the housing in a locked state.

In a first preferred embodiment of the present invention, as shown in FIG. 3 in an unlocked state, a lock solenoid 40 is located annularly around the variable force solenoid (VFS) 42, which is used to control the position of a spool 44 of a spool valve. The position of the spool 44 regulates whether the phaser 46 moves toward an advance position, moves toward a retard position, or remains in its present position. A solenoid stem 48 extends from the VFS 42 to actuate the spool 44 in conjunction with an opposing spool spring 50. The spool valve preferably sits near the end of the camshaft 52. The lock solenoid 40 preferably has a recessed surface 54 complementary to and for receiving the lock plate 56 when the electromagnetic coil 58 of the lock solenoid 40 is energized.

In this embodiment, the lock pin 60 is located in the housing 62, when the lock solenoid 40 is energized and the lock mechanism is in an unlocked state. In this state, the lock pin 60 does not prevent the rotor 64 from rotating with respect to the housing 62. As shown in FIG. 4, when the lock solenoid 40 is de-energized, a spring 66 urges the lock pin 60 into the lock hole 68 located in the rotor 64, thereby preventing the rotor 64 from rotating with respect to the housing 62.

In a second preferred embodiment of the present invention, as shown in FIG. 5 in an unlocked state, a lock solenoid 70 is located annularly around a variable force solenoid 72, which is used to control the position of a spool 74 of a spool valve. The position of the spool 74 regulates whether the phaser 76 moves toward an advance position, moves toward a retard position, or remains in its present position. A solenoid stem 78 extends from the VFS 72 to actuate the spool 74 in conjunction with an opposing spool spring 80. The spool valve preferably sits near the end of the camshaft 82. The lock solenoid 70 preferably has a recessed surface 84 complementary to and for receiving the lock plate 86 when the electromagnetic coil 88 of the lock solenoid 70 is energized.

In this embodiment, the lock pin 90 is located in the rotor 92, when the lock solenoid 70 is energized and the lock mechanism is in an unlocked state. In this state, the lock pin 90 does not prevent the rotor 92 from rotating with respect to the housing 94. A lock pin spring 96 urges the lock pin 90 away from the lock hole 98 and toward the lock plate 86. As shown in FIG. 6, when the lock solenoid 70 is de-energized, a lock plate spring 100 urges the lock plate 86 toward the lock pin 90, pushing the lock pin 90 into the lock hole 98 located in the housing 94, thereby preventing the rotor 92 from rotating with respect to the housing 94. Although the lock mechanism is preferably in a locked state when the lock solenoid is in a de-energized state and in an unlocked state when the lock solenoid is in an energized state, an unlocked state when the lock solenoid is in a de-energized state and a locked state when the lock solenoid is in an energized state is within the spirit of the present invention.

The lock pin hole may be located either in a mid position or a normal position as shown in FIG. 7, which shows the phaser in an unlocked position. A rotor 110 is mounted in a housing 112 and on top of an end plate 114. Sprocket teeth 116 surround the housing 112. The housing 112 includes recesses which are each divided into a pair of chambers by vanes extending from the rotor 110. A lock pin is located in one of the vanes on the side facing the end plate 114. In a mid position strategy, the lock pin hole is located such that in a locked state the vane is located significantly far away from both sides of the chambers. In a normal strategy, the lock pin hole is located such that in a locked state the vane is rotated to one extreme with respect to the housing. In the embodiment of FIG. 3 and FIG. 4, the lock pin hole 118 is in the vane and the lock pin is in a first position 120 for the mid position strategy and in a second position 122 in the normal strategy. In the embodiment of FIG. 5 and FIG. 6, the lock pin 118 is in the vane and the lock pin hole is in a first position 120 for the mid position strategy and in a second position 122 in the normal strategy.

In an embodiment of the present invention, the following start method is preferably used. During the cranking of the engine the phaser is preferably locked in mid position, and as soon as the engine starts the phaser is preferably commanded to move to a new position for improved emissions or idle stability. The electronic control unit (ECU) determines if conditions have been met to move the phaser. If the conditions have been met, the VFS is energized so that the phaser is allowed to move to a new position. The lock pin release solenoid is energized to allow the phaser to move to the new position. This is operated under closed loop control.

In an embodiment of the present invention, the following shut down method is preferably used. When the engine is at idle, the phaser is commanded to the locked position. Then the lock pin in released and the phaser is locked. The phaser is controlled under closed loop control to a desired position at idle, and the lock solenoid is de-energized to allow the lock pin to insert into the lock hole. This position may be at the positional end stops of the phaser or in a mid position. The electronic control unit then verifies that the phaser is at the commanded set point prior to engine shutdown.

In another embodiment, the phaser is at a position away from the locked position, and when the engine is turned off and is. slowing down, the phaser is commanded to move to the locked position and the lock pin is released. In this embodiment, it is preferable to release the lock pin when the key is turned off so that the lock starts to release when the phaser is moving to the locked position. Thus, when the phaser reaches the locked position, the lock pin simply drops into the lock pin hole.

Although the invention is described and shown in FIG. 3 through FIG. 6 in combination with a variable force solenoid for controlling the spool valve of the phaser, other controllers including, but not limited to, a stepper motor, a vacuum actuator, and a pressure controller such as a differential or a regulated pressure controller may be used within the spirit of the present invention.

The lock mechanism of the present invention may be used with any system with a lock mechanism including, but not limited to, an oil pressure actuated (OPA) phaser, a torsion-assist (TA) phaser and a cam-torque actuated (CTA) phaser within the spirit of the present invention.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Claims

1. A variable cam timing phaser for an internal combustion engine comprising: a housing with an outer circumference for accepting drive force; a rotor for connection to a camshaft coaxially located within the housing, the housing and the rotor defining at least one vane separating a chamber into an advance chamber and a retard chamber, the rotor being capable of rotation within the housing to shift the relative angular position of the housing and the rotor; and a lock mechanism comprising: a lock solenoid; a lock plate in proximity to the lock solenoid such that the lock plate moves between a first position when the lock solenoid is in an energized state and a second position when the lock solenoid is in a de-energized state; a lock plate spring biasing the lock plate toward the second position; and a lock pin coupled to the lock plate for movement therewith; wherein when the lock plate is in the first position, the lock pin is in an unlocked state such that the lock pin does not prevent rotation of the rotor within the housing; and wherein when the lock plate is in the second position, the lock pin is in a locked state such that the lock pin extends into a lock hole, thereby preventing rotation of the rotor within the housing.

2. The variable cam timing phaser of claim 1, wherein the lock pin is located within the housing in the unlocked state and the lock hole is located in the rotor.

3. The variable cam timing phaser of claim 2, wherein the lock pin is located such that the vane is in a mid position when the phaser is in the locked state.

4. The variable cam timing phaser of claim 2, wherein the lock pin is located such that the vane is in an end position when the phaser is in the locked state.

5. The variable cam timing phaser of claim 1, wherein the lock pin is located within the rotor in the unlocked state and the lock hole is located in the housing on a side opposite to the lock solenoid.

6. The variable cam timing phaser of claim 5, wherein the lock pin is urged toward the lock plate by a lock pin spring opposing the lock plate spring.

7. The variable cam timing phaser of claim 5, wherein the lock hole is located such that the vane is in a mid position when the phaser is in the locked state.

8. The variable cam timing phaser of claim 5, wherein the lock hole is located such that the vane is in an end position when the phaser is in the locked state.

9. The variable cam timing phaser of claim 1 further comprising: a variable force solenoid, wherein the lock solenoid is mounted with and around the variable force solenoid; and a spool valve actuated by the variable force solenoid to regulate a position 5 of the phaser.

10. The variable cam timing phaser of claim 1 further comprising: a linear actuator selected from the group consisting of: a) a stepper motor; b) a vacuum actuator; c) a differential pressure controller; and d) a regulated pressure controller; and a spool valve actuated by the linear actuator to regulate a position of the phaser.

11. The variable cam timing phaser of claim 1, wherein the lock pin and the lock plate are coupled to move together.

12. A method of controlling a variable cam timing phaser having a housing with an outer circumference for accepting drive force, a rotor for connection to a camshaft coaxially located within the housing, a lock solenoid, a lock plate in proximity to the lock solenoid, a lock plate spring biasing the lock plate toward the second position, and a lock pin coupled to the lock plate for movement therewith, during startup of an internal combustion engine comprising the step of: a) energizing the lock solenoid to move the lock plate coupled to the lock pin to a position wherein the lock pin is removed from a lock hole such that the lock pin does not prevent rotation of the rotor within the housing.

13. The method of claim 12 further comprising the steps of: b) determining if conditions have been met to move the phaser; and c) if conditions have been met, energizing a variable force solenoid to move a spool in a spool valve, thereby moving the phaser.

14. A method of controlling a variable cam timing phaser having a housing with an outer circumference for accepting drive force, a rotor for connection to a camshaft coaxially located within the housing, a lock solenoid, a lock plate in proximity to the lock solenoid, a lock plate spring biasing the lock plate toward the second position, and a lock pin coupled to the lock plate for movement therewith, during shutdown of an internal combustion engine comprising the step of: a) de-energizing the lock solenoid to release the lock plate coupled to the lock pin, thereby allowing the lock pin to extend into a lock hole to prevent rotation of a rotor within a housing.

15. The method of claim 14 further comprising the step of: b) moving the phaser to a locked position when the engine is at idle such that the lock pin is aligned with the lock hole.

16. The method of claim. 14 further comprising the steps of: b) determining the position of the phaser when the engine is turned off; and c) moving the phaser to a locked position as the engine is slowing down such that the lock pin is aligned with the lock hole.