Patent Application
20080078343
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
Rotor 20 includes an annular central well 24 surrounding a central arbor 26, defining an annular chamber 27 therebetween. A torsional coil spring 28 is disposed in chamber 27 for biasing rotor 20 into an extreme rotational position, typically a position wherein the valve overlap is minimized, at predetermined modes of operation such as engine shutdown and startup. In the cross-sectional view shown in
In the plan view shown in
Spring 28 is captured under torsional stress between rotor 20 and cover 16 during assembly of phaser 10. As noted above, such torsional stress causes a deformation of spring 28, creating contact points between the spring coils and the walls of the annular well and the arbor.
Referring now to
The first contact point at open triangle 34 is obvious. The body of spring 28 moves off center in this direction, as indicated by arrow 38. The second contact point at open diamond 36 typically occurs approximately ¾ of a turn from tang 30, as shown. Due to the contact occurring ¾ of a turn into the active coils, there is relative motion and thus friction occurring at this contact, which increases the frictional hysteresis of the torsional spring load. Note that the diameter of arbor 26 could be increased to change the second contact point to ¼ of a turn, near arrow 38, but this would provide insufficient operating clearance for the spring, effectively binding the spring as it tightens down on the arbor during deflection (spring diameter decreases). This would cause additional increases in frictional hysteresis.
Referring to
Referring now to
In the example shown, rotor 20 includes an annular well 24 surrounding an improved central arbor 126. Torsional coil spring 28 is disposed in well 24 and is connected to rotor 20 and cover 16 as in the prior art.
Improved arbor 126 provides the recommended 5% to 10% operating clearance to spring 28 as in the prior art, over the middle coils of the spring, at a radius 164 exemplary of the prior art arbor radius. However, over the first ¼ turn at each end of spring 28, arbor 126 is provided with a larger diameter angular region 160 having a radius 162 substantially equal to (but slightly less than, to permit assembly of the spring onto the arbor) the inner radius 129 of spring 28. Radius 162 thus is greater than the radius 164 of the intermediate portion of the arbor adjacent the intermediate spring coils between the innermost and outermost coils. Angular region 160 thus becomes the de facto inner bearing surface for spring 28 during rotation of the spring about the arbor with the rotor 20 and the cover 16 at the innermost and outermost spring ends, respectively. The radial deformation of the spring, seen at arrows 38,42 in
The present invention radially constrains end coils 28a,28x in a manner to avoid frictional contacts beyond the first ¼ turn at both spring ends, which minimizes frictional losses and functionally adds nearly a full turn to the spring. Also, the coils are supported in a manner to keep the deflected coil diameter centered on the phaser axis 146 during actuation of the phaser and minimizes phaser contact with the remainder of the coils.
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.
