Cam phaser apparatus

Abstract

 The invention provides a cam phaser having a helical spline member (18) which is engageable with a cam shaft (12) and sprocket shaft (16) of a piston engine. In order to change the cam phase, a nut member (24) is rotated against a lead screw (22). The lead screw translates along the sprocket shaft thereby causing the spline and hence the cam shaft to rotate relative to the sprocket shaft. The rotation of the can shaft relative to the sprocket shaft allows the cam phase to be altered.

Description

[0001] The present invention relates to cam phaser apparatus, particularly, but not exclusively cam phaser apparatus used in valve trains of automobile engines.

[0002] It is desirable to be able to control the cam phase of engines in order to improve engine performance and / or emissions. Various types of cam phaser capable of achieving this exist. Such system are required to efficiently convert rotational movement from the drive shaft into rotational movement of the cam shaft whilst allowing dislocation between these rotational movements in order to allow variation of the cam phase. Current systems typically require a complex arrangement of planetary gears which have the disadvantage of producing large frictional losses in the conversion process. The complex arrangement of such systems can also introduce controllability and reliability problems.

[0003] An aspect of the present invention is described in claim 1, and preferable features of the invention are shown in the subsequent dependent claims.

[0004] An embodiment of the apparatus according to the present invention will now be described, with reference to the accompanying drawings, in which:-

Fig.1A is a partial transverse cross sectional view of cam phaser apparatus according to the present invention; and

Fig. 1B is a more detailed perspective view of a portion of the helical spline of the apparatus of Fig 1A.

[0005] As shown in Fig.1, cam phaser 10 is typically mounted on a driven member such as a cam shaft 12 which is connected to a sprocket 14 via a drive member such as a sprocket shaft 16. Coupling means provides a connection between the cam shaft 12 and sprocket shaft 16 and comprises a helical spline member 18 (shown in more detail in Fig. 1B) housed within a lead screw (or slide member) 22, a bearing 20 provided between the helical spline member 18 and the sprocket shaft 16, and actuating means comprising adjusting means in the form of a combined nut and rotor 24 positioned within a stator 26.

[0006] The helical spline member 18 is a cylindrical member fixed to the cam shaft 12 and has helical protrusions 28 around its outer surface.

[0007] The lead screw 22 has outer walls 22A provided with thread teeth 23, base portion 22B and inner walls 22C. The inner walls 22C project through the screw 22 such that a bore is provided there through. The inner walls 22C are also provided with protruding guide tongues 32 on their inner diameter; these engage with longitudinal grooves 34 provided along sprocket shaft 16. The lead screw 22 is engaged with the helical spline member 18 such that engagement members 30 on the internal diameter of walls 22A mate with the helical formations 28 on the outer diameter of helical spline member 18. The helical spline member 18 is free to rotate with respect to the sprocket shaft 16 by way of bearing 20; however, lead screw 22 is rotationally fixed relative to the sprocket shaft 16. Combined nut and rotor 24 is able to move longitudinally along shaft 16 by way of the guide tongues 32 and grooves 34 or alternatively by way of a straight spline system which would allow a higher torque to be transmitted.

[0008] The combined rotor and nut 24 has a head 36 provided with teeth 38 which engage with teeth 23 on the lead screw 22. The teeth 23, 38 can be regarded as screw threads. The remaining portion of the combined nut and rotor 24 comprises a rotor drum 40 which rotatably mounts the rotor on the sprocket shaft 16 by way of a bearing 42.

[0009] Stator 26 is provided around the combined nut and rotor 24 and its operation will be described subsequently.

[0010] During operation of the engine (not shown), when no current is supplied to the stator 26, the lead screw 22 will remain in its longitudinal position with reference to longitudinal axis L and rotate at the same speed as the sprocket shaft 16. When it is desired to adjust the cam phase, the stator 26 and combined nut and rotor 24 are actuated as an electric motor. In order to do this a suitable current is supplied to the stator 26 such that an electromagnetic torque is provided on the combined nut and rotor 24. This torque causes the combined nut and rotor 24 speed to increase (or decrease) relative to the rotating cam shaft 16 and hence the lead screw 22. This relative movement of the combined nut and rotor 24 causes the screw head 36 to move the lead screw 22 longitudinally along the shaft 16 due to the interaction between teeth 23 of the lead screw 22 and teeth 38 of the combined nut and rotor 24. This longitudinal movement of the lead screw 22 is assisted by guide tongues 32 which slide along the longitudinal grooves 34 of the shaft 16. The guide tongues 32 and grooves 34 also allow rotational force from the sprocket shaft 16 to be transmitted through the lead screw 22 to the helical spline 18.

[0011] As lead screw 22 moves longitudinal it will cause the engagement members 30 to act against helical protrusions 28 on the helical spline member 18. The helical arrangement of the protrusions 28 will cause the helical spline member 18 to rotate relative to the shaft 16 thereby converting the longitudinal axial movement of the lead screw 22 to rotational movement of the helical spline member 18. As previously mentioned, the helical spline member 18 is attached to the cam shaft 12 and will therefore rotate in direct correlation with the helical spline member 18.

[0012] Suitable components may be selected during manufacture to allow a sufficient torque to be supplied by the stator 26 and rotor 24. The torque force provided is converted into linear movement by the lead screw 22 and then back to a torque force by the helical spline member 18 on the cam side of the phaser 10. A portion of the torque force is used to overcome the cam friction and required valve actuation force of the engine to which it is connected. The remaining portion of the torque force, on the stator/rotor side of the apparatus 10, that is not needed to overcome cam friction and valve actuation forces, accelerates the lead screw and spline system with respect to the shaft 16.

[0013] The system described allows the phase of the cam shaft to be reliably altered whilst the engine is running. In this regard, it should be noted that the cam phase may be advanced or retarded depending upon the direction in which the rotor 24 is urged by the stator 26. Such adjustment may be controlled by the engine management system of typical automobiles. The system therefore effectively allows the rotational position of the cam shaft 12 to be varied relative to the rotational position of the sprocket shaft 16. Importantly, once the cam phase has been adjusted into the advanced / retarded position it will remain in that position (without any external forces from e.g. the rotor/stator being required) until it is positively re-adjusted by the engine management system.

[0014] Modifications and improvement may be made to the foregoing, without departing from the scope of the present invention, for example:-

[0015] Although the present invention has been described in relation to automobile engines, it could be used in similar engines used in other applications.

Claims

1. A variable cam phaser comprising coaxial drive and driven members drivingly connected by a coupling means, said coupling means enabling said drive and driven members to be relatively angularly adjusted while maintaining driving engagement there between, the coupling means comprising a slide member drivingly mated with one of said drive or driven members and capable of axial displacement with respect to said drive/driven member, the other of said drive or driven members being provided with a helical spline portion engageable with a cooperating portion provided on said slide member whereby axial displacement of said slide member relative to said drive/driven member causes relative angular rotation between said drive and driven members, actuating means being provided for selectively axially displacing said slide member with respect to said drive/driven member wherein said actuating means comprises an adjusting member rotatably mounted at a fixed axial location on one of the drive or driven members and engageable with the slide member such that rotation of the adjusting member relative to the slide member causes relative axial displacement of the slide member with respect to the drive/driven member with which it is mated.

2. A variable cam phaser as claimed in claim 1, wherein the adjusting member forms the rotor of an electromagnetic coil, a stator of the coil being energisable to apply a torque to the adjusting member to rotate the adjusting member relative to the slide member.

3. A variable cam phaser as claimed in any preceding claim, wherein the engagement means between the adjusting member and the slide member comprise corresponding screw threads.

4. A variable cam phaser according to any preceding claim, wherein the slide member is provided with a throughbore having a protrusion which assists maintenance of the driving engagement between the slide member and said drive or driven members whilst allowing axial displacement of said slide member with respect to said drive/driven member.

5. A cam phaser according to any preceding claim, wherein the drive or driven members are provided with bearings which allow them to rotate independently of one another.

6. A variable cam phaser according to any preceding claim, wherein said adjusting member comprises a nut.

7. A variable cam phaser according to any preceding claim, wherein said cooperating portion provided on said slide member comprises a cooperating helical spline portion.

Drawing