Patent Application
20180087411
The present disclosure relates generally to electric cam phasing systems and more specifically to electric cam phasing systems including locks.
EP 1813783 B1, U.S. Pat. No. 8,677,961 B2, and U.S. Pat. No. 7,377,245 B2 disclose electric cam phasing systems.
An electric cam phasing system is provided. The electric cam phasing system includes an electric motor including a center shaft; a camshaft; a center fastener extending into a center of the camshaft and a gearbox including a sprocket and a drive unit. The drive unit includes an input shaft coupling connected to the center shaft. The drive unit is configured for coupling the camshaft to the sprocket in a manner such that relative phasing of the camshaft with respect to sprocket is adjustable via the electric motor driving the drive unit. The electric cam phasing system also includes a lock positioned axially between the center shaft and the camshaft, the lock being configured for selectively engaging the center fastener to lock the gearbox.
A method of constructing an electric cam phasing system is also provided. The method includes nonrotatably fixing an input shaft coupling of a drive unit of a gearbox to a center shaft of an electric motor, the drive unit coupling a camshaft to a sprocket in a manner such that relative phasing of the camshaft with respect to the sprocket is adjustable via the electric motor driving the drive unit; fixing the drive unit to the camshaft via a center fastener extending into a center of the camshaft; and providing a lock positioned axially between the center shaft and the camshaft, the lock being configured for selectively engaging the center fastener to lock the gearbox.
The present invention is described below by reference to the following drawings, in which:
The present disclosure provides a locking device that is activated by a locking pin inside of the gearbox central bolt to provide a locking of the gearbox input shaft coupling to the gearbox central bolt head. The locking pin is actuated by oil pressure that is supplied from the engine's oil circuit through the cam bearing and into a center passage of the bolt. The locking device includes a bias spring and is arranged to be pressurelessly locked, such that an inherent decrease in oil pressure during engine shutdown will facilitate engagement of the locking device with the head of the central bolt; the locking device inner diameter has the form of a socket tool to engage the shape of the head of the central bolt. The locked position is maintained during engine shutdown and also during engine start-up until enough oil pressure is provided to an end of the locking pin to overcome the force of the bias spring of the locking device and any inherent friction between mating components. Another feature of the lock is that any position can be chosen between the range of authority (within the angular resolution of the locking positions) to lock the phaser movement. Locking is not limited to one or two positions.
End stop disk 32 is sandwiched axially between an end of camshaft 16 and a radially extending section 33 of output unit 28b, which integrally fixed to second outer spline 28b, and is held axially against the end of camshaft 16 by a center fastener, which in this embodiment is a center bolt 34. Center bolt 34 includes a shaft 34a extending axially into a hollow bore within camshaft 16 such that a first end of bolt 34 is positioned within camshaft 16 and nonrotatably fixed to camshaft 16. A second end of bolt 34 includes a head 34b positioned within input shaft coupling 22 and abutting a radially extending surface of output unit 33.
Rotating the input shaft coupling 22 via motor 12 is the means by which camshaft 16 is rotated relative to sprocket 14 to change the valve timing. A gear ratio exists between input shaft coupling 22 and camshaft 16 that allows for relatively small rotations of the camshaft 16 when there are many rotations of the input shaft coupling 22. In normal operation with constant valve timing relative to the crankshaft, motor shaft 20 rotates at the same speed as camshaft 16. When valve timing is adjusted to either advance or retard the position of the camshaft 16, motor 12 either speeds up or slows down. During this adjustment, center bolt 34 and input shaft coupling 22 are no longer rotating at the same speed, but instead there is a relative rotation between bolt 34 and coupling 22. In order to prevent this relative rotation during engine shut down and engine start up, when there is a natural increase and decrease of oil pressure, system 10 is configured to lock gearbox 17 using this natural increase and decrease of oil pressure.
For this purpose, cam phasing system 10 is configured in substantially the same manner as conventional system 100, but with a modified paddle forming a connector 18 and the addition of an activatable lock 36. Connector 18 includes a disc-shaped radially extending section 18a extending radially outward from shaft 20 and a cylindrically-shaped axially extending section 18b extending axially from a radially outer end of radially extending section 18a, with axially extending section 18b being provided with radially extending pins 18c that each extend radially outward from an outer circumferential surface of axially extending section 18b into a respective slot 22a formed in coupling 22, as shown in
More specifically, lock 36 is formed by an engager 38 configured for selectively engaging bolt head 34b, a compression spring 40 for acting axially on engager 38 and a movable element 42 received in an axially extending bore hole 44 formed in bolt 34. In this embodiment movable element 42 is a pin, but in other embodiments movable element may have another shape such as a sphere. In other embodiments, the movable element may be part of a check valve, as described further below with respect to
Engager 38 is fixed to the end of shaft 20 by spring 40 and is positioned axially between radially extending section 18a of connector 18 and bolt head 34b. Engager 38 is axially slidable within connector 18 with an outer diameter surface of engager 38 contacting an inner diameter surface of axially extending section 18b of connector 18. In order to engage an outer diameter surface of bolt head 34b, engager includes an axially extending section 38b protruding at the outer diameter of a radially extending base 38a, which formed as a plate. Radially extending base 38a and axially extending section 38b together have cup shape configured for receiving bolt head 34b.
An inner diameter surface of axially extending section 38b is contoured to match the outer diameter surface of bolt head 34b such that when the inner diameter surface of axially extending section 38b engages the outer diameter surface of bolt head 34b, engager 38 is nonrotatably connected to bolt head 34b. In other words, the inner diameter surface of axially extending section 38b is in the form of a socket too for engaging the pattern of the outer diameter surface of bolt head 34b. In one preferred embodiment, the inner diameter surface of axially extending section 38b of engager 38 and the outer diameter surface of bolt head 34b have corresponding hexagonal shapes. In other embodiments, such surfaces can have other corresponding shapes, for example rectangular or octagonal, or the surfaces can include intermeshing teeth. In further embodiments, such as in the embodiment shown in
Bolt 34 also includes a fluid feed channel 46 formed therein for providing pressurized oil to bore hole 44 to force pin 42 axially into protrusion 38c of engager 38. Channel 46 includes at least one radially extending section 46b extending from an outer diameter surface of bolt shaft 34a and an axially extending section 46a extending axially from radially extending section 46b. Oil pressure supplied from the engine's oil circuit is provided to channel 46 from the cam bearing via a channel 48 extending radially through a cam shaft 16. In another embodiment, the center bolt can be configured for an axial oil feed from the center of camshaft 16.
In contrast,
At engine shut down, the oil pressure drops below the predetermined threshold and compression spring 40 overcomes the oil pressure behind pin 42 in channel 46 and, via engager 38, pushes pin 42 further into bore hole 44 in bolt 34, causing the inner diameter surface of axially extending section 38b of engager 38 to engage with the outer diameter surface of bolt head 34b.
At engine start up, gearbox 17 remains locked in the same exact position it was in at engine shut down via lock 36 until the oil pressure in channel 46 increases enough to overcome compression spring 40 and push pin 42 axially such that the inner diameter surface of axially extending section 38b of engager 38 is disengaged from the outer diameter surface off bolt head 34b. This disengagement allows input coupling shaft 22 to once again freely rotate relative to center bolt 34 when commanded to do so by motor 12 and a controller. Lock 36 remains in the unlocked orientation during the engine operation until the oil pressure falls below the predetermined threshold.
The control strategy for motor 12 requires gearbox 17 to be held in the desired lock position until engager 38 can be engaged with center bolt head 34b. This may require the control strategy to slowly adjust the rotation of input coupling 22 until the pattern of the inner diameter surface of axially extending section 38b of engager 38 can align with the pattern of the outer diameter surface of bolt head 34b and engage with bolt head 34b. The controller can determine this by monitoring electrical input (i.e., current) versus cam position. If a change in cam position is not detected when current is increased then the controller can consider the engager 38 engaged with the bolt head 34b and gearbox 17 locked. Likewise for the startup routine. The controller can apply a small torque in both directions until the oil pressure increases enough to push pin 42 out to compress spring 40 and disengage engager 38 from bolt head 34b. The release of torque can signal the controller that gearbox 17 is no longer locked and drive input shaft coupling 22 accordingly to the desired valve timing position.
Once engager 38 engages bolt head 34b and the phasing movement is locked, motor 12 is coasting and is driven by gearbox 17 and camshaft 16, as motor 12 is then being driven by camshaft 16. Once the controller senses that the gearbox phasing is prevented, the power can be cut to the motor 12 to allow such coasting.
Spring 140 has a greater diameter than spring 40, and is not fixed to shaft 20 as in the embodiment shown in
In the disengaged or unlocked orientation, the oil pressure from the engine circuit causes the oil pressure in channel 46 to reach a predetermined threshold that forces pin 142 axially toward engager 138 to such a degree that spring 140 is compressed and the outer diameter surface 138d of protrusion 138c of engager 38 is disengaged from inner diameter surface 134c of bolt head 134b.
In the engaged or locked orientation, the oil pressure from the engine circuit is such that the oil pressure in channel 46 is below the predetermined threshold and the force of spring 140 is greater than the force of the oil pressure in channel 46 and protrusion 138c of engager 138 forces pin 142 axially toward channel 46 while outer diameter surface 138d of protrusion 138c of engager 38 engages inner diameter surface 134c of bolt head 134b.
Check valve 250 functions to relieve the oil in bore 244 through head 234a of bolt 234 to make it easier for the spring 40 (
In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.
