Patent Application
20100064996
The present invention relates to phasers for varying the phase of combustion valve actuation with respect to a crankshaft in an internal combustion engine; more particularly, to such a phaser employing a spring for biasing the rotational position of a phaser rotor with respect to an associated phaser stator through at least a portion of the rotor range of authority; and most particularly, to such a phaser wherein a helical bias spring has at least one linear portion (also referred to herein as a “flat” portion) accompanied by a region of radius of curvature smaller than that of the helix at an end convolution thereof replacing a prior art radial or axial tang for engaging either the stator or the rotor.
Camshaft phasers for varying the timing of combustion valves in an internal combustion engine transmit crankshaft torque to the engine camshaft, allowing varied timing of the camshaft relative to the crankshaft position.
It is known in some prior art phaser applications to employ one or more toroidal (also referred to herein as “helical”) torsional bias springs within a phaser, grounded at opposite ends to the stator and rotor, respectively, to counterbalance a portion of the friction torque of the camshaft due to the valve train components (lifters, cam journals, cam driven accessories, etc.).
Such a bias spring is especially useful in exhaust phasing applications because the friction torque from the exhaust camshaft acts to retard the camshaft in opposition to the timing advance default position. The bias spring helps the exhaust phaser to return to its default (locked) position on engine shutdown and allows more balanced control of the phaser at intermediate positions.
Intake phasers also may include a bias spring having a somewhat lower spring constant to provide more balanced advancing and retarding rates while not preventing the phaser from reaching the retard default position.
In some prior art phasers, it is known to utilize a flat, spiral wound spring having a squared inner end, similar to the long-standing application of such springs in watches and clocks. In these applications, the squared inner end is grounded by being wrapped around a square sided mandrel. A shortcoming of this design is that, when a torsional force is applied to the spring, the squared inner end spreads open as the flats of the square ramp up the mating flat surfaces of the mandrel.
More typically however, prior art cam phaser bias springs are helically wound, utilizing spring ends (tangs) that are bent either radially outward or axially and engage a slot to ground the spring to the phaser component. A shortcoming of such prior art phasers using helical bias springs is that the shape required in the rotor and/or stator to anchor and restrain a radial or axial tang is known to cause difficulties in forming powdered metal components.
In addition, an axially bent end increases the axial length of the phaser, which is undesirable.
Further, in pulley phaser applications wherein the phaser must be sealed to prevent oil leakage to the exterior of the part, packaging is difficult because a cover plug is required for plugging the access hole for the central cam bolt. The space required for the cover plug consumes the space otherwise usable for an axial or radial spring end.
Still further, a radially-outward spring end requires adding seal plates or significant increases in radial packaging volume of the entire phaser.
What is needed in the art is an improved bias system for a camshaft phaser wherein a helical bias spring is mechanically anchored to the rotor end without resort to an axial or radial tang.
It is a principal object of the present invention to reduce the size, complexity, and manufacturing cost of a camshaft phaser.
Briefly described, a helical phaser bias spring in accordance with the present invention includes at least one linear region and an adjacent region having a radius of curvature less than that of the helix. A mating channel in the phaser receives the flat portion of the spring and adjacent region to lock the spring to the phaser at either the rotor or the stator. Preferably, the spring includes two flat regions separated by a bend of about 90°. Additional flat regions, for example three (defined herein as a “square” end to a spring) are possible, separated by right and/or other angle bends. In a phaser rotor or stator, the geometric shape required to hold a spring end having a flat is easier to form with powdered metal tooling or diecasting than is a circular, radial, or axial shape for receiving a spring tang as in the prior art, and the packaging volume required for the spring is smaller.
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 exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring to
Referring to
Springs 10 and 16 are shown as examples of prior art springs used in prior art camshaft phasers. Note that prior art springs 10,16 employ tangs at both ends for being grounded to the stator and rotor of a phaser and further that the coils are circular and of unvarying radius.
Referring to
Referring to
There are three considerations addressed by a non-tang spring end: improved durability, improved packaging (minimal axial or radial space required), and improved performance.
A non-tang spring end presents a more distributed loading to the interfacing components. By applying the load to a larger area (across two or preferably three flats 110) and by fixing the last coil 104 and/or 106, wear rates of the bias spring interface to the rotor or stator decrease significantly.
A non-tang spring end minimizes packaging size and reduces complexity of interfacing components. Prior art helical bias springs employ axial, radial, and/or tangential tangs to ground the ends of a helical bias spring to the interfacing components. Each of these tangs increases overall package size in its respective direction, whereas a square-end spring incurs little or no increase in package size in any of those directions.
A non-tang spring end improves phaser performance by decreasing frictional hysteresis. In any bias spring, there are six vectors along which energy can be entered into the system via the spring (translational and rotational vectors about three orthogonal axes). A typical torsion spring produces excessive unwanted energy in more than one of the five undesired directions. A non-tang, square-end bias spring produces a more ‘pure’ moment (in the desired direction) than does a tang-end bias spring by being less prone to axial and radial force loading (“cocking”) of a phaser rotor and stator.
Referring to
A radial tang is often still the best option for grounding to a front cover (stator), while a square end generally is best for grounding to a rotor as shown in
Referring to
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.
