Rotationally Balanced Camshaft Assembly

Abstract

A method for intentionally imbalancing one or more mass elements of a camshaft assembly to provide overall rotational balance to the assembly, also referred to herein as “zero balance”. Such intentional imbalance may be imparted to any element of a camshaft assembly. In a currently-preferred embodiment, one or more components of an improved camshaft phaser assembly are manufactured as rotationally unbalanced, either by intentionally forming an unbalanced component such as a sprocket wheel having added material or by removing non-functional material from an otherwise standard component. Because the camshaft phaser assembly has a unique and fixed angular relationship to the camshaft, zero balance can be readily and repeatedly achieved for all camshaft assemblies by correct manufacture of parts without requiring separate balancing for each individual camshaft assembly as manufactured.

Description

RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS

This application claims the benefit of U.S. Provisional Application No. 61/203,895, filed Dec. 30, 2008.

TECHNICAL FIELD

The present invention relates to rotational balancing of an internal combustion engine; more particularly, to rotational balancing of a camshaft assembly; and most particularly, to a rotationally balanced camshaft assembly manufactured by using an intentionally unbalanced element of the camshaft assembly, and especially a component of a camshaft phaser, to achieve rotational balance of the overall assembly.

BACKGROUND OF THE INVENTION

It is well known in the engine arts to achieve overall rotational balance of the crankshaft assembly of an internal combustion engine by strategic removal of material from one or more rotational elements of the crankshaft assembly, such as a flywheel, a balancer, and/or the crank throws. Heretofore, comparable rotational balancing of an engine camshaft has not been disclosed. In the prior art, the diameter and rotational mass of a camshaft assembly has not been sufficiently great to cause unacceptable wear and vibration in an engine to warrant balancing.

However, in some modern applications, it has been found that engine idle quality can be seriously impaired by camshaft rotational imbalance, especially for relatively small engines having two camshafts. In current cam phaser applications, the design metric for cam phaser assembly imbalance is typically lower than an OEM specified threshold value. This value varies by OEM. Other than the cam phaser itself, various other components directly fixed to camshafts, including cam lobes, fuel pump lobes, and target wheels, can create additional overall rotational imbalance in a complete camshaft assembly. Lastly, various drillings and machined features, such as those for oil feeds, sensors, or tapped holes on the camshaft itself can create further rotational imbalance. The combined effects of these factors can result in camshaft assemblies that are imbalanced above the threshold value.

Optimum system design would dictate that auxiliary components should be placed along the camshaft in an orientation that favors better system balance; however there are oftentimes overriding design considerations that do not favor camshaft balance. Imbalance of the camshaft assembly, as a rotating mass, can lead to excessive engine vibration. This vibration can lead to various end effects including premature cam bearing wear, excessive wear on other mating valvetrain components, and excessive engine noise. All of these effects are a concern over the entire engine RPM range, but the last effect is primarily a concern at idle condition when a vehicle is stationary and engine vibration and noise can be easily perceived by occupants of the vehicle.

What is needed in the art is a method and apparatus for readily balancing a camshaft assembly to reduce engine vibration and noise.

It is a principal object of the present invention to reduce engine vibration and noise, and to extend engine operating life.

SUMMARY OF THE INVENTION

Briefly described, a method in accordance with the present invention intentionally imbalances one or more mass elements of a camshaft assembly to provide overall rotational balance to the assembly, also referred to herein as “zero balance”. Such intentional imbalance may be imparted to any element of a camshaft assembly, including any new element (counterweight) or plurality of elements provided expressly for that purpose. In a currently-preferred embodiment, one or more components of a camshaft phaser assembly are manufactured as rotationally unbalanced, either by intentionally forming an unbalanced component such as a sprocket wheel having added material or by removing non-functional material from an otherwise balanced component. Because the camshaft phaser assembly has a unique and fixed angular relationship to the camshaft, zero balance can be readily and repeatedly achieved for all camshaft assemblies by correct manufacture of parts without requiring separate balancing for each individual camshaft assembly as manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an exploded isometric view of a prior art vane-type camshaft phaser;

FIG. 2 is an isometric view of a prior art camshaft assembly;

FIG. 3 is an isometric view of the prior art camshaft phaser shown in FIG. 1, partially in cutaway, showing the oil passages in the camshaft phaser, a basis for inherent rotational imbalance;

FIG. 4 is an isometric view of first embodiment of an unbalanced phaser sprocket wheel in accordance with the present invention, showing addition of material to cause the intentional imbalance;

FIG. 5 is an isometric view of a camshaft phaser including the sprocket wheel shown in FIG. 4;

FIG. 6 is an isometric view of a second embodiment of an unbalanced phaser sprocket wheel in accordance with the present invention, showing azimuthally progressive removal of material in the tooth root area; and

FIG. 7 is an isometric view of a third embodiment of an unbalanced phaser sprocket wheel in accordance with the present invention, showing removal of material by machined features in the wheel hub area.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The object of the present invention is to rotationally balance (zero-balance) a camshaft assembly using components within the camshaft assembly, preferably by intentional imbalancing of an incorporated camshaft phaser assembly. Re-balance can be accomplished using any of the non-functional areas of such components and/or by adding material as counterweights. Both adding mass features and removing mass can affect imbalance and a combination of the two can be used to achieve the end result. A secondary objective of the present invention is to accomplish the abovementioned without an increase in part count, complexity, or cost. Because of its relatively large mass and diameter, the camshaft phaser assembly is a preferred site for creation of such component imbalance.

Referring to FIG. 1, a typical prior art vane-type camshaft phaser assembly 10 includes a pulley or sprocket wheel (pulley/sprocket) 12 for engaging a timing chain or belt (not shown) operated by an engine crankshaft (not shown). The upper surface 14 of pulley/sprocket 12 forms a first wall of a plurality of hydraulic chambers in the assembled phaser. A stator 16 is disposed against surface 14 and is sealed thereto by a first seal ring 18. Stator 16 is rotationally immobilized with respect to pulley/sprocket 12. Stator 16 is provided with a plurality of inwardly-extending lobes 20 circumferentially spaced apart for receiving a rotor 21 including outwardly extending vanes 22 which extend into the spaces between lobes 20. Hydraulic advance and retard chambers (not visible in exploded drawing) are thus formed between lobes 20 and vanes 22. A thrust washer 24 is concentrically disposed against rotor 21, and cover plate 26 seals against stator 16 via a second seal ring 28. Bolts 30 extend through bores 32 in stator 16 and are received in threaded bores 34 in pulley/sprocket 12, immobilizing the stator with respect to the pulley/sprocket. In installation to an engine camshaft, phaser 10 is secured via a central bolt (not shown) through thrust washer 24 which is covered by cover plug 36 which is threaded into bore 38 in cover plate 26.

A locking pin mechanism 40 comprises a hollow locking pin 42 having an annular shoulder 43, return spring 44, and bushing 46. Spring 44 is disposed inside pin 42, and bushing, pin, and spring are received in a longitudinal bore 48 formed in an oversize vane 22′ of rotor 21, an end of pin 42 being extendable by spring 44 from the underside of the vane. A pin seat 47 is disposed in a well 49 formed in pulley/sprocket 12 for receiving an end portion of pin 42 when extended from bore 48 to rotationally lock rotor 21 to pulley/sprocket 12 and, hence, stator 16. The axial stroke of pin 42 is limited by interference of shoulder 43 with bushing 46. A shallow channel 51 formed in pulley/sprocket 12 extends from below seat 47 and intersects surface 14 in a region of that surface which forms a wall of a selected advance chamber in the assembled phaser. Thus, when oil is supplied to advance the rotor with respect to the stator, oil also flows through channel 51 to bring pressure to bear on the end surface (axial face) 53 of pin 42, causing the pin to be forced from seat 47 and thereby unlocking the rotor from the stator. Conversely, the pin defaults to the locked position whenever oil pressure is below a threshold level.

Referring to FIG. 2, a prior art camshaft assembly 100 comprises at least a camshaft 102 having a plurality of eccentric cam lobes 104, a plurality of shaft bearing surfaces 106, and a camshaft phaser assembly 108 that may or may not be identical with camshaft phaser assembly 10. Camshaft phaser assembly 108 is mounted to the end of camshaft 102 in a unique and fixed azimuthal relationship. Assembly 100 may further include a target wheel 110 mounted on either the camshaft phaser assembly 108 (not shown) or on the opposite end of the camshaft as shown in FIG. 1.

Referring to FIG. 3, the oil passages 150 in a typical vane-type camshaft phaser 108 are shown. Since oil is distributed to and within the cam phaser through oil galleries which are not symmetrically distributed about the rotational axis 152 of the phaser, oil galleries, when filled with oil rather than the metal which is removed by their creation, can create significant imbalance in a phaser.

Referring to FIGS. 4 and 5, in a first embodiment of an unbalanced camshaft assembly element in accordance with the present invention, a phaser sprocket wheel 212 is formed having two asymmetrically-positioned radial ribs 260, causing wheel 212 to be unbalanced in direction 262 with respect to axis 152. The mass and shape of ribs 260 is predetermined as by modeling and/or experimentation to be just sufficient to offset a rotational imbalance in opposite direction 264 in a camshaft assembly in which a sprocket wheel 212 is an element, thereby producing a net zero rotational imbalance in the camshaft assembly. FIG. 5 shows an improved camshaft phaser assembly 208 incorporating unbalanced sprocket wheel 212 for substitution for prior art camshaft is phaser 108 in prior art unbalanced camshaft assembly 100 (FIG. 2), in accordance with the present invention, to yield an improved rotationally-balanced camshaft assembly.

Presently-known embodiments utilize a powdered metal (sintered steel) sprocket with an added mass feature 260 to zero-balance a camshaft assembly. By utilizing powdered metal modified die features to form ribs 260, overall zero balance in a camshaft assembly can be achieved without added complexity, part count or cost.

Referring now to FIG. 6, in a second embodiment of an unbalanced camshaft assembly element in accordance with the present invention, a phaser sprocket wheel 312 includes a progressive removal channel 370 formed in the root area 372 of sprocket teeth 374, either by machining or by casting, the net effect of removal channel 370 being to unbalance sprocket wheel 312 in direction 262 as in first embodiment 212 (FIGS. 4 and 5).

Referring now to FIG. 7, in a third embodiment 412 of an unbalanced camshaft assembly element in accordance with the present invention, a phaser sprocket wheel includes one or more machined features 470 in the hub 472 of sprocket wheel 412, the net effect of machined features 470 being to unbalance sprocket wheel 412 in direction 262 as in first embodiment 212 (FIGS. 4 and 5) by removal of material in a net opposite direction.

Further, it will be appreciated by those of ordinary skill in the art that rotational balancing of an otherwise unbalanced camshaft assembly may be achieved by addition of one or more eccentrically-placed counterweights (not shown) at any convenient point along the camshaft or within the camshaft phaser assembly.

The disclosed specific embodiments are only demonstrative of the invention. Any component of a camshaft assembly, including but not limited to a counterweight and the camshaft phaser assembly and furthermore including but not limited to the sprocket wheel, stator, rotor, cover plate, and target or timing wheel, may be used for re-balancing, and many possible locations for mass addition/removal are available. Embodiment 212 (FIGS. 4 and 5) is zero-balanced with the cam phaser in the default position such as is experienced at idle condition. Rotational mass balance or unbalance can also be achieved if so desired with the cam phaser in advance position, retard position or at any intermediate position. In addition, the rotor assembly and the stator assembly of a camshaft phaser assembly can be mass-balanced or unbalanced independently, causing the phaser assembly to be mass balanced in all positions.

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.

While the embodiments as described are shown in a single camshaft arrangement, the invention is equally applicable in multiple camshaft arrangements and on intake or exhaust camshafts.

Claims

1. A method for forming a rotationally balanced camshaft assembly for an internal combustion engine, the camshaft assembly including at least a camshaft having at least one eccentric cam, and a camshaft phaser, the method comprising the steps of:

a) determining the magnitude of rotational imbalance of an unbalanced camshaft assembly; and

b) adjusting the magnitude of rotational imbalance of at least one component of said unbalanced camshaft assembly to compensate for said magnitude of rotational imbalance of said unbalanced camshaft assembly to yield said rotationally balanced camshaft assembly.

2. A method in accordance with claim 1 wherein said at least one component is an element of said camshaft phaser.

3. A method in accordance with claim 2 wherein said element is selected from the group consisting of sprocket wheel, stator, rotor, cover plate, and target wheel.

4. A method in accordance with claim 1 wherein said adjusting step includes the step of forming said at least one component in a predetermined unbalanced arrangement.

5. A method in accordance with claim 4 wherein said forming step includes addition of material to said at least one component to cause said predetermined unbalanced arrangement.

6. A method in accordance with claim 4 wherein said forming step includes subtraction of material from said at least one component to cause said predetermined unbalanced arrangement.

7. A method in accordance with claim 1 wherein said component is a counterweight added eccentrically to said camshaft assembly expressly to rotationally balance said camshaft assembly.

8. A camshaft assembly comprising a plurality of components wherein at least one of said components is intentionally rotationally unbalanced such that said camshaft assembly is rotationally balanced.

9. A camshaft assembly in accordance with claim 8 comprising at least a camshaft having at least one eccentric cam, and a camshaft phaser, wherein said at least one component is an element of said camshaft phaser.

10. A camshaft assembly in accordance with claim 9 wherein said element is selected from the group consisting of sprocket wheel, stator, cover plate, and target wheel.

11. A camshaft assembly in accordance with claim 9 wherein said at least one component is formed in a predetermined unbalanced arrangement.

12. A camshaft assembly in accordance with claim 11 wherein said predetermined unbalanced arrangement includes addition of material to said at least one component.

13. A camshaft assembly in accordance with claim 11 wherein said predetermined unbalanced arrangement includes removal of material from said at least one component.

14. A camshaft assembly in accordance with claim 8 wherein said at least one component is a counterweight added eccentrically to said camshaft assembly expressly to rotationally balance said camshaft assembly.

15. An internal combustion engine having at least one camshaft assembly wherein at least one component of said camshaft assembly is intentionally rotationally unbalanced in a predetermined unbalanced arrangement such that the overall camshaft assembly is rotationally balanced.