ADJUSTABLE CAMSHAFT

Abstract

An adjustable camshaft for an internal combustion engine includes an outer shaft and a support shaft defining at least one bore with a relief groove configured outside of the bore. The support shaft extends along a longitudinal axis. The outer shaft may include a cam element disposed on the support shaft such that the outer shaft is displaceable along the support shaft along the longitudinal axis wherein the outer shaft is latchable on the support shaft in at least two axial latching positions. A biasing means, a press-fit retainer, and a latching element are disposed within the bore such that the biasing means urges the latching element toward any one recess of the plurality of recesses defined in the outer shaft.

Description

TECHNICAL FIELD

The present disclosure relates to a valve operating device for an engine of a vehicle, particularly a valve operating device which switches a cam for opening and closing a valve.

BACKGROUND

Adjustable camshafts for internal combustion engines having a support shaft which extends in a longitudinal axis are known, and at least one outer shaft which is received on the support shaft such that it can be moved in the direction of the longitudinal axis. The outer shaft rotates with the rotation of the support shaft, for which purpose a splined structure between the support shaft and the outer shaft can serve, and a rotation of the outer shaft on the support shaft is prevented by way of the spline structure. In order to latch the outer shaft in discrete, reproducible axial positions on the support shaft, latching elements may be provided which can be prestressed by way of biasing a means, and the latching elements can latch into latching element receptacles, as a result of which, the axial position of the outer shaft on the support shaft may then be defined. The different axial positions of the outer shaft on the support shaft serve to bring the different cam elements of the outer shaft into connection with valves or tapping elements for actuating valves. The different cam elements can define different control times for opening and closing the valves of the internal combustion engine, or the valve stroke can be changed by way of different cam elements in operative connection with a tapping element or directly with a valve.

The change takes place by way of different, discrete axial positions of the outer shaft being assumed on the support shaft, and the displacement of the outer shaft takes place, for example, by way of a manipulation means which is received in a stationary manner in the cylinder head and can interact with an adjusting element which can likewise be included by the outer shaft.

For example, DE 10 2010 011 897 A1 discloses an adjustable camshaft for an internal combustion engine having a support shaft which extends in a longitudinal axis, and an outer shaft is received on the support shaft such that it can be moved axially. A latching element in the form of a ball which is loaded by way of a spring force of a biasing means serves to latch the outer shaft in discrete axial positions. The ball can latch into different profile grooves defined in lobe back as a result of the spring force, and the profile grooves are arranged with regard to the axial position in such a way that each profile groove corresponds to the contact of an associated cam track of a cam element against a tapping element.

However, a traditional adjustable camshaft as described above presents assembly issues in that the outer shaft must be installed on the support shaft adjacent to receptacle on the support shaft when the latching element and spring are assembled onto support shaft given that the outer shaft is used to prevent the ball and spring from falling out of the receptacle on the support shaft. As a result, the support shaft must have an extended length so as to accommodate the outer shaft on the support shaft when the ball and spring are installed onto the support shaft to enable the outer shaft to then immediately slide over the ball and spring in order to retain the ball and spring in the support shaft.

SUMMARY

The present disclosure provides an adjustable camshaft for an internal combustion engine. The adjustable camshaft includes an outer shaft and a support shaft which defines at least one bore with a relief groove configured outside of the bore. The support shaft extends along a longitudinal axis. The outer shaft may include a cam element disposed on the support shaft such that the outer shaft is displaceable along the support shaft along the longitudinal axis wherein the outer shaft is latchable on the support shaft in at least two axial latching positions. A biasing means, a press-fit retainer, and a latching element are disposed within the bore such that the biasing means urges the latching element toward any one recess of a plurality of recesses defined in the outer shaft. The latching element may or may not be provided in the form of a detent ball.

In various embodiments of the present disclosure, the relief groove may be configured as one of a straight groove, a semi-circle groove, and a full-circle groove. The relief groove defines a groove depth which may vary along the length of the relief groove or which may be fixed along the length of the relief groove. Regardless of whether the groove depth varies along the relief groove length or the groove depth is fixed along the relief groove length, the groove depth may fall in a depth range of about 1.5 mm to about 6 mm. Similarly, regardless of the fixed or varying nature of the relief groove depth, the relief groove may also define a groove width which falls in a width range of about 1.5 mm to about 6 mm. The groove width also may be fixed or may vary along the length of the relief groove. With respect to the aforementioned relief groove, the associated bore for the aforementioned relief groove may define a bore diameter which falls in a diameter range of about 8 mm to about 16 mm.

The manufacturing method includes the steps of: (1) providing a support shaft with a bore and a relief groove defined in the support shaft; (2) inserting a biasing means into a lower region of the bore: (3) inserting a latching element into the bore such that the latching element is adjacent to an upper end the biasing means: (4) press-fitting a press-fit retaining ring in an upper region of the bore so that the latching element is disposed in an aperture defined by the press-fit retaining ring; (5) positioning the outer shaft onto the support shaft so that the latching element may be disposed in one of a plurality of detent positions defined on the outer shaft.

The relief groove of the aforementioned support shaft is defined outside of the at least one bore such that the relief groove is configured to reduce cam shaft deflection along a longitudinal axis of the cam shaft when the press-fit retaining ring is inserted into the upper region of the at least one bore. The relief groove may be configured as one of a full-circle groove, semi-circle groove, straight groove and a circumferential groove.

The present disclosure and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present disclosure will be apparent from the following detailed description, best mode, claims, and accompanying drawings in which:

FIG. 1A is cross-sectional view of an example, non-limiting adjustable cam shaft according to various embodiments of the present disclosure.

FIG. 1B is a perspective view of the adjustable cam shaft of FIG. 1A.

FIG. 2A is a plan view of a full-circle relief groove defined in a support shaft.

FIG. 2B is a side view of the full-circle relief groove shown in FIG. 2A.

FIG. 2C is a plan view of a semi-circle relief groove defined in the support shaft.

FIG. 2D is a plan view of a straight relief groove defined in the support shaft.

FIG. 2E is a plan view of a circumferential relief groove defined in the support shaft.

FIG. 3 is an example, non-limiting cross-sectional view of the biasing means, a press-fit retainer, and a latching element disposed within the bore in the support shaft of the present disclosure

FIG. 4 is a stress diagram which shows the deflection in a traditional adjustable camshaft using a press-fit retainer.

FIG. 5 is a stress diagram which shows the decreased deflection in the support shaft of the present disclosure.

FIG. 6 is a flowchart which illustrates an example, non-limiting manufacturing method according to the present disclosure.

Like reference numerals refer to like parts throughout the description of several views of the drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present disclosure, which constitute the best modes of practicing the present disclosure presently known to the inventors. The figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the present disclosure that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the present disclosure and/or as a representative basis for teaching one skilled in the art to variously employ the present disclosure.

Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the present disclosure. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by weight; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the present disclosure implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.

It is also to be understood that this present disclosure is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present disclosure and is not intended to be limiting in any way.

It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.

The term “comprising” is synonymous with “including,” “having,” “containing,” or “characterized by.” These terms are inclusive and open-ended and do not exclude additional, un-recited elements or method steps.

The phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When this phrase appears in a clause of the lifter body 14 of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

The phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.

The terms “comprising”, “consisting of”, and “consisting essentially of” can be alternatively used. Where one of these three terms is used, the presently disclosed and claimed subject matter can include the use of either of the other two terms.

Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this present disclosure pertains.

The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

With reference to FIG. 1A, a vehicle engine (not shown) may include a shifting actuator 54 and an actuator pin 56 connected to the actuator 54. The actuator pin 56 may be cylindrical, as shown, or may be any other suitable shape. The shifting actuator 54 may move the actuator pin 56 into contact with the shifting feature 52 (FIG. 1B) when in an actuated state and may withdraw the actuator pin 56 from contact with the shifting feature 52 when in an unactuated state. The actuator pin 56 may cooperate with the shifting feature 52 to move the outer shaft 24 axially (longitudinal axis 14 arrow A) to the respective axial position 40A, 40B, 40C (FIG. 1A) that corresponds to the selected one of the plurality of selectable cams 36A, 366, 36C (FIG. 1B) when the shifting actuator 54 is in the actuated state. It is understood that, in FIG. 1A, the outer shaft 24 is in axial position 40A. There may be more than one shifting feature 52 and more than one actuator pin 56, as shown. The outer surface 34 of the outer shaft 24 is subjected to actuator loading in the region between the shifting feature 52 and the actuator pin 56.

The adjustable camshaft 10 is for shifting to a selected one or more selectable cam lobes 36A, 368, 36C (FIG. 1B). The adjustable camshaft 10 includes an inner shaft 22 and an outer shaft 24. The adjustable camshaft 10 may include one or more outer shaft 24. The inner shaft 22 has an external spline 26. The outer shaft 24 has an inner surface 28 (FIG. 1A) configured with an internal spline 30 (FIG. 1A) for transferring a torque from the external spline 26 of the inner shaft 22 and for sliding axially (longitudinal axis 14 arrow A) on the external spline 26 of the inner shaft 22.

Referring to FIG. 1B, the cam follower mechanism 44 of the engine (not shown) connects the valve 42 to the selected cam lobe shown as element 36 A in FIG. 1B so as to open and close the valve 42 according to the respective cam profile (shown as 38A in FIG. 1B). The cam follower mechanism 44 may be a roller finger follower, as shown and as understood to those skilled in the art, or may be any other suitable cam follower mechanism. The cam follower mechanism 44 includes a cam follower 46. The cam follower 46 may be a roller, as shown, or may be any other type of cam follower. A valve spring 48 may be connected to the valve 42 and may bias the valve 42 to urge the valve 42 toward a closed position (not shown) in an engine cylinder (not shown) and toward the selected cam lobe (shown as 36A). The outer surface 34 of the outer shaft 24 is subjectable to both wear and valve loading (arrow FV) at a second interface 50 between the cam lobes 36A, 36B, 36C and the cam follower 46.

As shown in FIG. 1A, the outer shaft 24 has an outer surface 34. As shown in FIG. 1B, the outer surface 34 is configured with the one or more selectable cam lobes 36A, 36B, 36C that have respective cam profiles 38A, 38B, 38C and that correspond to respective axial positions 40A, 40 B, 40C of the outer shaft 24 relative to the inner shaft 22. The selected cam lobe (shown as 36A in FIG. 1B) and its respective cam profile (shown as 38A in FIG. 1B) is selected by locating the outer shaft 24 at the respective axial position (shown as 40A FIG. 1B).

The inner surface 28 of the outer shaft 24 may be configured with a locating feature 74 in the form of a plurality of recesses 75 for temporarily locating the outer shaft 24 at the respective axial position 40A, 40B, 40C relative to the support shaft 22 that corresponds to the selected one of the plurality of selectable cam lobes 36A, 36B, 36C. The adjustable camshaft 10 may include a detent mechanism 60 which may further include a biasing means 70 (such as a spring) and a detent ball 72 (or latching element) 72.

With reference to FIG. 3, during the assembly process of the adjustable camshaft 10 of the present disclosure, it is understood that the biasing means 70, a press-fit retainer 18 ring, and a latching element 72 are inserted into the bore 12 of the support shaft 22 wherein the latching element (ball) is disposed in the press-fit retainer 18 ring at the upper region of the bore 12. The press-fit retainer 18 maintains the latching element (detent ball 72) in position within the bore 12 of the support shaft 22 during the assembly process. Accordingly, the use of the press-fit retainer 18 of the present disclosure obviates the need to install the outer shaft 24 on an end region of a support shaft before or during the installation process of the biasing means 70 and the latching element into the support shaft 22.

Under traditional adjustable camshaft 10 designs (not shown), the outer shaft 24 (having the cam pack) was immediately moved from its “stored” position on the end of the support shaft 22 to the region of the support shaft 22 which defined the bore 12 as soon as the detent ball 72 or latching element was assembled within the bore 12. This assembly step was necessary to prevent the detent ball 72 or latching element from inadvertently falling out of the bore 12 in the support shaft 22. In light of the present disclosure's implementation of the press-fit retainer 18 ring, the assembly process is improved given that there is no longer a risk of the detent ball 72 falling out of the support shaft 22 given that the detent ball 72 or latching element maintains position within the bore 12 during the assembly process without the aid of the outer shaft 24. As a further benefit, the support shaft 22 length may be shortened given that the region for only supporting the outer shaft 24 in the assembly process is no longer needed. Again, previously, the assembly process required that the outer shaft 24 be readily moved over the biasing means 70 and latching element upon inserting the detent ball 72 and biasing means 70 in the bore 12.

However, it is also understood that a traditional support shaft 22 may experience excessive shaft bending and axial run-out due to the stresses imposed on the support shaft 22 by the retainer 18 ring. Referring now to FIG. 4, the retainer ring 18′ imposes stresses 92′ on the traditional support shaft 22′ so as to cause the support shaft 22′ to bend or deflect as shown in FIG. 4. Under the undesirable condition shown in FIG. 4, the region of the support shaft 22′ which surrounds the press fit retainer ring 18′ absorbs the energy and deflects along the longitudinal axis 14 A-A of the support shaft 22′. The undesirable bending in the support shaft 22′ may then cause the support shaft 22′ to rotate off center.

Accordingly, in order to reduce shaft bending (shown in FIG. 4) and axial run out, the present disclosure provides for an improved adjustable camshaft 10 which experiences reduced deflection and reduced axial run-out. The adjustable camshaft 10 of the present disclosure may be implemented in an internal combustion engine wherein the adjustable camshaft 10 includes an outer shaft 24 with a cam pack and a support shaft 22 which defines a bore 12 with a relief groove 16 (FIGS. 2A-2E, FIGS. 3 and 5) configured outside of the bore 12. The support shaft 22 extends along a longitudinal axis 14 (A-A). The outer shaft 24 is displaceable along the length of the support shaft 22 (along the longitudinal axis 14) in example positions 40A, 40B, 40C wherein the outer shaft 24 is latchable on the support shaft 22 in at least two axial latching positions. A biasing means 70, a press-fit retainer 18, and a latching element may be disposed within the bore 12 such that the biasing means 70 urges the latching element (or detent ball 72) toward any one recess of a plurality of recesses defined in the outer shaft 24. The biasing means 70 may or may not be in the form of a spring as shown in FIG. 1. Moreover, as further shown in FIG. 1, each recess in the plurality of recesses enables the outer shaft 24 to move between three different positions.

As shown in FIGS. 1A and 3, the biasing means 70 may be disposed within the bore 12 of the support shaft 22. The biasing means 70 may be a coil spring, as shown, or any other suitable biasing means 70. As shown in FIG. 1A, the detent ball 72 may be disposed between the biasing means 70/support shaft 22 on one side of the detent ball 72 and the outer shaft 24 on the other side of the detent ball 72. The biasing means 70 applies a radially outward biasing force on the detent ball 72. The locating feature 74 (FIG. 1A) may be a circumferential detent groove with multiple recesses 75, as shown, which is formed on the inner surface 28 of the outer shaft 24. The locating feature 74 may be configured to temporarily locate the outer shaft 24 at the respective axial position 40A, 40B, 40C relative to the support shaft 22 by engaging the detent ball 72 of the detent mechanism 60.

With reference to the aforementioned relief groove 16 defined outside of the bore 12, the relief groove 16 is defined on the outer surface of the support shaft 22 and may be configured in different ways. Non-limiting example configurations for the relief groove 16 may be a full-circle relief groove 37 (FIGS. 2A-2B), a semi-circle relief groove 38 (FIG. 2C), a straight relief groove 40 (FIG. 2D) or a circumferential relief groove 40 (FIG. 2E). The circumferential relief groove shown in FIG. 2E may have a length which travels about the entire circumference of the support shaft or the circumferential relief groove may have a length which is less than the circumference of the support shaft thereby making such a groove a partial circle. It is understood that an intermediate region 80 is also defined on the support shaft 22 wherein the intermediate region 80 is defined as the region of the support shaft 22 which is disposed between the bore 12 and relief groove 16. The intermediate region 80 is therefore the region of the support shaft 22 which is defined between the upper end of the bore 12 and the relief groove 16 as shown in FIGS. 2A-2E, 3 and 5. Therefore, regardless of which form the relief groove 16 takes, the relief groove 16 and the intermediate region 80 associated with the relief groove 16 are configured to absorb structural loads imposed by the press-fit retainer 18 ring on the support shaft 22 such that the deflection of the support shaft 22 is significantly limited to the intermediate region 80 of the support shaft 22. It is understood that the intermediate region 80 of the support shaft 22 is the region of the support shaft 22 which is defined between the upper end of the bore 12 and the relief groove 16.

In the various embodiments of the present disclosure, the groove depth 20 of the relief groove 16 may vary or may be fixed along a length 27 of the relief groove 16. Regardless of whether the groove depth 20 is fixed or varies along the length 27 of the relief groove 16, the groove depth 20 may fall in a depth range of about 1.5 mm to about 6.0 mm. It is also understood that regardless of whether the groove depth 20 is fixed or varies along the length 27 of the relief groove 16, the relief groove width 31 may also be fixed or may vary along the length 27 of the relief groove 16. Regardless of whether the groove width 31 is fixed or varies, the relief groove 16 may define a groove width 31 which falls in a width range of about 1.5 mm to about 6 mm. Referring now to FIGS. 2A, 2C-2E, and 3, the support shaft 22 bore 12 of various example embodiments may, but not necessarily, have a bore diameter 32 which falls in a diameter range of about 8 mm to about 16 mm.

With reference to FIG. 6 of the present disclosure, a flowchart 90 is shown which illustrates an example, non-limiting method for manufacturing an adjustable camshaft 10 in accordance with the present disclosure. The manufacturing method includes the steps of: (1) providing a support shaft with a bore and a relief groove defined in the support shaft; step 44 (2) inserting a biasing means into a lower region of the bore; step 46 (3) inserting a latching element into the bore such that the latching element is adjacent to an upper end the biasing means; step 48 (4) press-fitting a press-fit retaining ring in an upper region of the bore so that the latching element is disposed in an aperture defined by the press-fit retaining ring; step 50 (5) positioning the outer shaft onto the support shaft so that the latching element may be disposed in one of a plurality of detent positions defined on the outer shaft 24. Step 51

It is understood that, in the aforementioned method to manufacture an adjustable camshaft 10, the relief groove 16 is defined outside of the at least one bore 12 such that an intermediate region 80 of the support shaft 22 is defined between the relief groove 16 and the bore 12. The relief groove 16 is configured to reduce the support shaft deflection along a longitudinal axis 14 of the cam shaft. The relief groove 16 may be provided in various forms. Example, non-limiting configurations include is configured as one of a full-circle 37 groove, semi-circle groove, a straight groove and a circumferential groove. The latching element 72 (detent ball 72) and the biasing means 70 for loading the latching element 72 with force may be arranged in a receiving bore 12 of the support shaft 22 as illustrated in FIG. 1A. Furthermore, as illustrated in FIG. 1A, recesses 75 or latching element receptacles 75 may be defined on the inner side in the outer shaft 24 in the form of the profile grooves.

If the camshaft 10 has to be assembled, first of all the biasing means 70 has to be inserted into the receiving bore 12 in the camshaft 10, and subsequently the latching element (ball) has to be inserted into the receiving bore 12 counter to the spring force before the outer shaft 24 is arranged on the support shaft 22. When the outer shaft 24 is subsequently pushed on, the difficulty arises that the latching element has to be pressed into the receiving bore 12 counter to the spring force of the biasing means 70, in order to prevent blocking of the outer shaft 24 when being pushed onto the support shaft 22 by way of the spherical latching element.

As previously described, the manufacturing process for the adjustable camshaft 10 has improved given that there is no longer a risk of the detent ball 72 falling out of the support shaft 22 given that the detent ball 72 or latching element maintains position within the bore 12 during the assembly process without the aid of the outer shaft 24. Also, as previously noted, the support shaft 22 length may be shortened given that the region for only supporting the outer shaft 24 in the assembly process is no longer needed.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.

Claims

1. An adjustable camshaft for an internal combustion engine, the adjustable camshaft comprising: a support shaft extending along a longitudinal axis;an outer shaft including a cam element disposed on the support shaft such that the outer shaft is displaceable along the support shaft along the longitudinal axis wherein the outer shaft is latchable on the support shaft in at least two axial latching positions; anda bore defined in the support shaft with a relief groove defined outside of the bore;wherein a biasing means, a press-fit retainer, and a latching element are disposed within the bore such that the biasing means urges the latching element toward a recess of a plurality of recesses defined in the outer shaft.

2. The adjustable camshaft as defined in claim 1 wherein the relief groove is configured as one of a full-circle groove, semi-circle groove, straight groove and a circumferential groove.

3. The adjustable camshaft as defined in claim 2 wherein the relief groove defines a groove depth which varies along a length of the relief groove.

4. The adjustable camshaft as defined in claim 2 wherein the relief groove defines a groove depth which is fixed along a length of the relief groove.

5. The adjustable camshaft as defined in claim 3 wherein the groove depth falls in a depth range of about 1.5 mm to about 6 mm.

6. The adjustable camshaft as defined in claim 3 wherein the groove depth falls in a depth range of about 1.5 mm to about 6 mm.

7. The adjustable camshaft as defined in claim 5 wherein the relief groove defines a groove width which falls in a width range of about 1.5 mm to about 6 mm.

8. The adjustable camshaft as defined in claim 6 wherein the relief groove defines a groove width which falls in a width range of about 1.5 mm to about 6 mm.

9. The adjustable camshaft as defined in claim 7 wherein the bore defines a bore diameter which falls in a diameter range of about 8 mm to about 16 mm.

10. The adjustable camshaft as defined in claim 8 wherein the bore defines a bore diameter which falls in a diameter range of about 8 mm to about 16 mm.

11. A method for manufacturing an adjustable camshaft for an internal combustion engine, comprising the steps of: providing a support shaft having a bore and a relief groove defined outside of the bore;inserting a biasing means into a lower region of the bore;inserting a latching element into the bore such that the latching element is adjacent to an upper end the biasing means;press-fitting a press-fit retaining ring in an upper region of the bore so that the latching element is disposed in an aperture defined by the press-fit retaining ring; andpositioning the outer shaft onto the support shaft so that the latching element may be disposed in one of a plurality of detent positions defined on the outer shaft.

12. The method for manufacturing an adjustable camshaft as defined in claim 11 wherein the relief groove is defined outside of the at least one bore.

13. The method for manufacturing an adjustable camshaft as defined in claim 12 wherein the relief groove is configured to reduce cam shaft deflection along a longitudinal axis of the cam shaft.

14. The method for manufacturing an adjustable camshaft as defined in claim 13 wherein the relief groove is configured as one of a full-circle groove, semi-circle groove, straight groove and a circumferential groove.