The invention relates to a camshaft, in particular for a motor-vehicle engine, having a first shaft and a second shaft that form a hollow outer shaft and an inner shaft that is coaxially mounted in the outer shaft and can be rotated relative to the outer shaft, including first cams that are rotationally fixed on the outer shaft and second cams that are rotatable on the outer shaft and are fixed to the inner shaft. In the context of the invention, depending on the particular embodiment, the first shaft may be the outer shaft or the inner shaft, and the second shaft will then correspondingly be the inner shaft or the outer shaft.
By adjusting the first shaft relative to the second shaft allows control of the valves of an internal combustion engine. Thus, for example, the ratio between the intake timing and the exhaust timing may be modified as a function of load and rotary speed, and the intake valves on the one hand and the exhaust valves on the other hand can be actuated using the respective groups of cams that can be adjusted relative to each other. Rotation of the inner shaft and the outer shaft relative to each other is generally carried out by adjusters that can also be referred to as phasers.
In order to enable a precise positioning of the shafts and at the same time easy adjustability of the inner shaft relative to the outer shaft, the two shafts need to be supported in a suitable manner for rotation relative to each other. Thus, it is known in a generic camshaft having the features described above according to DE 39 43 426 to provide sleeve bearings on the ends of the shaft elements lying inside of each other, which apart from a radial support also effect an axial fixing. The disadvantage arises that the axial support is provided by elements that are separated and are widely spaced from each other, and for this reason there is not only an increased production complexity, but also an increased risk of malfunction. For a precise axial support it is also advantageous if dimensionally stable materials are provided on the support surfaces that preferably also have a similar thermal expansion coefficient. An axial support via soft seals or the like is, as a rule, not sufficient.
In view of the above, the object of the invention is to provide an adjustable camshaft having an inner shaft and an outer shaft, where precise and reliable support axially is realized in a simple manner.
Starting from a camshaft having the features described above, according to the invention the object is achieved in that the first shaft and the second shaft are supported relative to each other axially by an interlocking formation, the first shaft having a first contact surface on one side, viewed axially, of the interlocking formation and a second contact surface for rotational support of the second shaft on the other side of the interlocking formation through the interlocking formation. In the context of the invention, a shaft is not just understood to mean a tubular or rod-shaped base body, but also a unit formed from one or more components connected to each other in a rotationally fixed manner. Depending on the embodiment, the interlocking formation may be provided for sliding or rolling support of the roller bearing type, and in this case several interlocking formations that are separate from each other will expediently be provided.
According to some of the embodiments according to the invention, the support location for axially supporting the inner shaft and the outer shaft is provided at one of the shaft ends. The interlocking formation is then usually part of the second shaft, so that the interlocking formation as a component of the second shaft cooperates with the contact surfaces of the first shaft that bear axially oppositely on it. In the context of such a view, the association of the first shaft and the second shaft with the outer shaft and the inner shaft has not yet been established.
According to a preferred development, it is provided on the basis of this that the inner shaft extends at one camshaft end beyond a tubular base body of the outer shaft and has there the interlocking formation that projects radially beyond the inner diameter of the base body of the outer shaft.
In the context of the described embodiment, a particularly simple design is achieved if the interlocking formation, for example a circumferential annular projection, is braced axially in one direction on an end face of the tubular base body of the outer shaft, and the second contact surface is then formed by a part of the outer shaft that is connected to the base body in an axially fixed manner. Such a part may for example have a region of enlarged diameter by which it is attached to the base body from the outside and can be fastened in a suitable manner.
The use of such an approach also brings with it the advantage that this part, which in principle may also be a functional element of the camshaft, is axially pushed onto the base body during installation using a force that allows on the one hand minimal play to be achieved and on the other hand also allows sufficient rotatability without jamming.
In the context of the invention it is of advantage if the surfaces cooperating with the axial support, which means the two contact surfaces as well as the associated faces of the interlocking formation, are provided with some surface finishing. Apart from fine grinding, additionally or alternatively also hardening, coating or the like come into consideration.
According to an alternative further embodiment of the invention, the interlocking formation as a component of the inner shaft, viewed axially, is supported on either side on opposite contact surfaces of a part that is axially fixed to the base body or on contact surfaces of two parts of the outer shaft that are connected to the base body. the interlocking formation is supported on one side on a part that is also a functional element of the camshaft, whereas on the other side, a simple end ring is inserted into this functional element to achieve an axial termination.
If the interlocking formation is formed as a radial projection of the inner shaft, then this interlocking formation may be formed either on a tubular or rod-shaped inner shaft base body or on a part that is connected to the inner shaft base body. The machining of the interlocking formation on the rod-shaped inner shaft base body is for example possible by casting or forging. Moreover, the interlocking formation may also be produced by machining, for example turning. If, according to a further described alternative, the interlocking formation is formed by a separate part that is axially fixed to the inner shaft base body, the advantage is achieved that the inner shaft base body itself may be very simply implemented as a straight rod, as a tube or the like, and in this case also a particularly cost-effective and simple production of the inner shaft base body is possible.
In case the interlocking formation of the inner shaft according to the particularly simple embodiment described above is provided between the end face of the base body of the outer shaft as well as a part that is connected to the base body in an axially fixed manner, then this part may also be a sleeve.
In the variant according to the invention as described above, the support is at a shaft end. However, an alternative concept according to the invention allows the camshaft to be axially supported in any desired position. According to this alternative concept according to the invention the inner shaft and the outer shaft each have, at a support location, starting from an annular gap between the inner shaft and the outer shaft, a recess in the form of an indent, a groove or an opening, and as an interlocking formation at least one separate interlocking member that engages in these recesses.
The interlocking element may be fixed to the inner shaft or the outer shaft. Even if the outer shaft and the inner shaft are formed from several parts that are connected to each other in a fixed manner, in the context of the invention the interlocking element is, even in the case of a fixed connection thereof to one of the shafts, regarded as a separate element that as a rule is exclusively used as an axial support.
According to a first variant of this alternative concept, the outer shaft has at the support location at least one opening and the inner shaft has a groove, and at least one interlocking element is inserted into the opening and engages in the groove. In the context of such an embodiment, the interlocking element may be retrospectively inserted, and in this case the interlocking element may be fixed to the inner shaft or the outer shaft. The interlocking element can, for example, be a small flat plate of the groove stone type; however, a certain way of securing this interlocking element has to be provided. The interlocking element may here be fastened to the inner shaft or the outer shaft, and in this case the other shaft provides the contact surfaces acting in the axial direction on either side of the interlocking element.
In order to achieve a uniform support, preferably a plurality of interlocking elements is provided and distributed around the circumference.
If the outer shaft is provided with a radially throughgoing opening, then this region can also be covered with a ring. The ring may be provided as protection from mechanical damage and contamination. Further, a ring may be used to prevent large amounts of oil from escaping through the opening of the outer shaft. In particular, in the context of the invention it is possible to apply oil to the annular gap between the inner shaft and the outer shaft, in order to ensure sufficient lubrication and free movement.
If the interlocking element has the form of a small plate, a sliding block or a groove stone, longitudinal angularly extending slots are as a rule provided as openings in the outer shaft.
If a simple ball or a plurality of balls is provided as interlocking elements, a simple, round hole in the outer shaft is sufficient to allow the ball to be inserted from the outside during the mounting process. This ball will then cooperate with the edges of the hole as well as with an indent in the inner shaft. The inner shaft may in particular include an indent in the form of a running surface having the shape of an arc of a circle, so that support can then be achieved in the manner of a ball bearing. In order to keep at least one ball or the balls in a predefined position and to secure it/them against falling out, a ring restricting the ball is provided in the outer shaft in the case of a continuous opening. A further advantage of this solution is moreover that the ring and the ball may then constitute also a radial support for the inner shaft.
According to an alternative embodiment the outer shaft has, starting from the annular gap, a recess in the form of a groove. In the context of such an embodiment, the outer shaft is closed to the side, so that the at least one interlocking element has to be inserted into the groove from the inside during the mounting process. To this end, the interlocking element is mounted on the inner shaft in a radially movable manner and an elastic pressure element is applied thereto. Thus, for example an interlocking element in the form of a ball with a spring provided underneath may be inserted into a blind bore of the inner shaft. Alternatively, also two opposite balls having a spring provided between them is possible.
During the mounting process, the balls are then pushed into the opening so far that the inner shaft can be inserted into the outer shaft. Once the groove has been reached, the balls will be pushed outward by the spring, as a result of which the desired fixing axially and, in the case of a suitable design, also radially is achieved. In order to enable support radially, in an arrangement having two balls, these have to be decoupled from each other. In the case of an embodiment with a continuous spring, such a spring has to be correspondingly fixed to the inner shaft at the center thereof.
According to a further variant, the inner shaft has an opening on the support location, and the outer shaft also has an elongate hole respectively on either side of the opening that extends in the circumferential direction, and a pin inserted into the opening is provided as an interlocking element. Unlike the simple fixing of the second shafts with a pin, the pin is here provided for a precise axial support. Apart from a simple round, cylindrical pin it is also possible for the pin to have lateral planar surfaces on at least one end that are provided for axial support. In this way, instead of a punctiform or linear support, a planar support is achieved, as a result of which the wear characteristics may be improved even in the case of prolonged use of the camshaft.
In the various described embodiments, not only an axial support but in principle also a radial support may be provided, if the interlocking formation cooperates with a corresponding radial contact surface of the first shaft also radially.
The invention will be explained below with reference to drawings that show only one embodiment. Therein:
The invention relates to an adjustable camshaft that according to its principal design comprises a first shaft and a second shaft that form a hollow outer shaft 1 and an inner shaft 2 that extends coaxially in the hollow outer shaft 1 and can rotate relative to the outer shaft.
The present invention deals with the axial support of the outer shaft 1 and the inner shaft 2 rotatable therein. In this regard, it is to generally accepted no axial play should be present between the inner shaft 2 and the outer shaft 1, but at the same time a sliding without jamming should be achieved.
To this end, according to the present invention an interlocking fixing and support in an axial direction x are provided. In general, the first shaft and the second shaft are braced against each other in the axial direction x by an interlocking formation 5, and the first shaft has, axially, a first contact surface 6a on one axial face of the interlocking formation 5 and a second contact surface 6b on the other axial face of the interlocking formation 5 for rotationally supporting the second shaft by means of the interlocking formation 5.
Starting from this basic principle according to the invention, the embodiment according to
According to
In
In the specific embodiments described above, during the manufacturing process, first of all the inner shaft 2 is inserted into the base body 8 of the outer shaft 1, before the functional element 9 (
It can in particular be seen especially from
While in the embodiment so far described the interlocking formation 5 is to be provided at a shaft end of the camshaft, the explanations following below relate to embodiments wherein the support location for the axial support may be in any desired position along the camshaft. However, for practical reasons, the axial support will preferably be at least in the vicinity of one end of the camshaft here as well.
According to
In order to reduce wear in connection with this, according to
In the embodiments of
Finally,
In the light of this,
Finally,
In this embodiment, the ring 19 is used as a counter bearing for the balls and can moreover prevent oil leaks.
Number | Date | Country | Kind |
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102011052822.9 | Aug 2011 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/065036 | 8/1/2012 | WO | 00 | 4/8/2014 |