Patent Application
20090031974
The present invention relates to camshaft phasers for varying the valve actuation timing of compression valves in an internal combustion engine; more particularly, to an electromechanically-actuated camshaft phaser system having a worm gear drive; and most particularly, to such a phaser system wherein the worm gear is itself driven by a hypoid/ring gear train.
Camshaft phasers for controllably varying the actuation timing of engine compression valves are well known. At present, most prior art camshaft phasers in production by or for engine manufacturers are vane-type phasers having interlocked rotors and stators. The phase relationship between the rotor and the stator may be varied by varying the relative oil volume on one side or the other of interlocked vanes via a four-way oil control valve.
Vane phasers are compact and relatively inexpensive. However, they have difficulty operating rapidly or with precision at times of low oil pressure because phasers typically are powered by parasitic use of pressurized engine lubricating oil. When the engine is idling, or is very hot, or at engine start-up, or combinations of these conditions, engine oil pressure can be very low or substantially non-existent, resulting in poor phasing control and excessive engine emissions.
What is needed in the art is a camshaft phaser system wherein phasing is achieved electromechanically without reliance on engine oil pressures.
It is a principal object of the present invention to provide camshaft phasing without resort or regard to engine oil pressures to improve engine emissions control.
Briefly described, an electromechanical camshaft phasing system in accordance with the invention comprises a first pinion gear mounted on the end of an engine camshaft. The first pinion gear is engaged by a worm gear mounted on a transverse shaft extending from and journalled in a phaser drive sprocket for a drive chain or a toothed wheel for a toothed drive belt to rotate the camshaft in response to the engine crankshaft. The first pinion gear is surrounded by a ring gear driven by an armature or stator of a motor mounted on the engine coaxially of the camshaft and first pinion gear. A second pinion gear mounted on the worm gear shaft engages the ring gear such that motor rotation of the ring gear causes rotation of the second pinion gear, worm gear, first pinion gear, and thus the camshaft with respect to the sprocket, thus varying the phase of the camshaft with respect to the crankshaft.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
The present invention is directed to an electromechanical camshaft phaser comprising a phasing worm gear driven by a hypoid/ring gear drive train. The worm gear drive is an important improvement on prior art phasers as the worm/pinion gear is essentially self-locking: camshaft torque reversals cannot back-drive the worm gear as happens in oil-actuated prior art vane-type phasers, thus providing good positional stability of the phaser. Further, this arrangement minimizes the number of interfaces from which manufacturing and operational clearances and tolerances may accumulate to create angular lash, which lash results in audible noise. In the present invention, only lash in the worm/pinion gear and lash in the worm gear bearing support can contribute to lash noise. This arrangement further minimizes potential loading of the electric drive motor for the worm gear drive.
Referring to
In a presently preferred embodiment, sprocket 20 includes a tang 35 extending radially inwards into a gap 36 in the teeth of first pinion gear 12, defining first and second rotation limiting stops 38,40 for first pinion gear 12. Preferably, second pinion gear 32 is of the known “single-enveloping” type (not shown) wherein the diameter of the hypoid gear flights is progressive to enable greater contact area with the teeth of ring gear 24. Preferably, worm gear 16 is also a known enveloping-type (not shown) gear, either single-enveloping or double-enveloping, again to enable contact with the teeth of first pinion gear 12 over a broad central angle (number of teeth) of gear 12.
Note that in an alternative second embodiment (not shown), the shaft that supports worm gear 16 and second pinion gear 32 may be fixed in sprocket 20 rather than journalled for rotation, and worm gear 16 and second pinion gear 32 may be mounted on a sleeve that is rotatable upon the shaft, to equal effect as in the first embodiment described above. The overriding consideration is simply that worm gear 16 be rotationally coupled to second pinion gear 32, whatever the supporting structure.
Referring to
An electrically driven phaser in accordance with the invention may be applied to either an intake or an exhaust camshaft. It is most advantageous to apply the invention to the intake camshaft, as a major advantage is to enable repositioning of the intake cam during engine cranking (prior to any oil pressure being available) to obtain the optimal cam timing based on the temperature conditions of the engine. Once the engine fires, the cam timing can also be adjusted as needed during the first couple of seconds of engine run time to minimize emissions. This is a significant advantage over engines equipped with prior art oil-actuated phasers because a large portion of engine emissions occurs in the first few seconds of engine run time when the fuel/air mixture is quite rich and combustion is not yet running smoothly. As noted above, this is not possible to do with an oil-actuated phaser because sufficient oil pressure typically is not available for several seconds after engine start. Adjusting the intake cam during this period not only gives superior emissions control via valve timing overlap but also provides the additional advantage of influencing relative compression ratio.
Also, in accordance with the invention, the electric motor 30 can be operated in a motor mode, spinning the ring gear 24 faster (ahead of) than the rotational speed of the pinion gear 12, or in a generator mode (braking mode) spinning ring gear 24 slower (behind) than the rotational speed of pinion gear 12. Further, the hand (right or left hand) of the gearing can be reversed as suitable for either intake camshaft or exhaust camshaft applications so as to preferably move the phaser either towards advance or towards retard timing.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
