Patent Application
20180003087
The invention relates to a method for producing a cam profile of a cam pack of a camshaft, said cam pack having at least two cam elements that can be adjusted in relation to each other. The invention further relates to a camshaft—in particular, a rotatable camshaft—advantageously having at least one cam pack comprising at least two cam elements that can be adjusted in relation to each other.
The use of camshafts is basically known in automotive engineering, by means of which camshafts a rotary motion can be converted into a longitudinal motion in order to operate intake valves and/or outlet valves of a combustion engine. These advantageously constructed camshafts comprise, for example, an outer shaft and an inner shaft arranged concentrically—in particular, coaxially—within the outer shaft in such a way that the inner shaft can be rotated, and at least one fixed cam element connected to the outer shaft for conjoint rotation and one adjustment cam element connected to the inner shaft for conjoint rotation. It is, further, basically known that at least some of these cam elements are ground and possibly also cured after the mounting of the camshaft.
Such a method for grinding cam elements is, for example, described in DE 10 2006 044 010 A1, which focuses on preventing an ingress of grinding dust into the camshaft—in particular, into an intermediate space between the outer shaft and the inner shaft—during the grinding process. For this purpose, a fluid, such as gas or oil, which acts as a barrier fluid, is pressed into the outer shaft under pressure. Particularly during the grinding process of the cam elements, manufacturing tolerances of the individual cam elements exist, wherein a play arising between the cam elements during their mounting onto the outer shaft or the inner shaft can also occur. These deviations bring about an undesired valve travel. In the cited publication, the processing—in particular, the grinding of the contour of the individual cam elements with respect to a desired cam profile—is not described. Rather, the topic of producing an advantageous cam profile in the individual cam elements, in order to allow for a cam profile of the cam pack that satisfies the required specifications, is omitted.
It is therefore the aim of the present invention to at least partially eliminate the disadvantages described above in a method for grinding cam elements in order to produce a cam contour. It is, in particular, the aim of the present invention to provide a method for producing a cam profile of an adjustable camshaft with an expandable cam pack, as well as a corresponding camshaft with at least one expandable cam pack, by means of which the occurrence of profile jumps is avoided during the contact change of a tapping element between the individual cam elements.
The aforementioned aim is achieved by a method for producing a cam profile of a cam pack of a camshaft, said cam pack having at least two cam elements that can be adjusted in relation to each other, wherein the camshaft comprises an outer shaft and an inner shaft arranged concentrically—in particular, coaxially—within the outer shaft in such a way that the inner shaft can be rotated, and at least one fixed cam element connected to the outer shaft for conjoint rotation and one adjustment cam element connected to the inner shaft for conjoint rotation, having the features according to claim 1. The aforementioned aim is further achieved by a camshaft comprising at least one outer shaft and one inner shaft arranged concentrically—in particular, coaxially—within the outer shaft, and a cam pack with at least one fixed cam element connected to the outer shaft for conjoint rotation and at least one adjustment cam element mounted rotatably in relation to the outer shaft and connected to the inner shaft for conjoint rotation, wherein the adjustment cam element and the fixed cam element can be rotated in relation to each other about a common central axis and together form a cam profile, which interacts with a tapping element for converting a revolving motion of the cam pack into a linear motion of valves, having the features according to claim 6. Additional features and details of the invention result from the dependent claims, description, and drawings. In this respect, features and details described in the context of the method according to the invention naturally also apply in connection with the camshaft according to the invention, and vice versa, so that mutual reference always is or can be made with respect to the disclosure of the individual aspects of the invention. In addition, the camshaft according to the invention—in particular, the cam profile of the cam pack of the camshaft according to the invention—can be produced with the method according to the invention.
The method according to the invention for producing a cam profile of a cam pack of a camshaft, said cam pack comprising at least two cam elements that can be adjusted in relation to each other, wherein the camshaft comprises an outer shaft and an inner shaft arranged concentrically within the outer shaft in such a way that the inner shaft can be rotated, and at least one fixed cam element connected to the outer shaft for conjoint rotation and one adjustment cam element connected to the inner shaft for conjoint rotation, comprises at least the following steps:
Advantageously, a processing of the cam elements by means of the method according to the invention allows for producing a cam profile in an assembled condition of the camshaft. During the processing of the cam pack—in particular, of individual cam elements—the adjustment cam is advantageously arranged rotatably, which means that it is not connected to the inner shaft for conjoint rotation, in order to ensure a spreading apart of the adjustment cam element toward the fixed cam element at least during the processing operation. Based upon the aforementioned processing of the adjustment cam element and the fixed cam element, jumps in the cam profile of the cam pack can be avoided, which jumps arise, for example, as a result of the functionally required play between the adjustment cam element and the outer shaft and the specific cam profiles required for the grinding process, and which jumps present themselves under the load of the camshaft by a strong acceleration occurring, for example, in the valve train during the transfer of the tapping element from the adjustment cam element to the fixed cam element or from the fixed cam element to the adjustment cam element. In addition, such profile jumps also bring about increased wear of the individual components, i.e., for example, of the tapping element or also of the cam elements and, in particular, of the cam element contour, etc.
In the adjustable camshaft, the outer shaft, which, for example, has the form of a hollow shaft, and the inner shaft, which is, for example, designed in form of a solid shaft, are arranged concentrically or coaxially in relation to each other so that the inner shaft extends through the outer shaft at least in sections. The cam pack advantageously consists of at least one fixed cam element and at least one adjustment cam element, which, as described above, are arranged for conjoint rotation with the outer shaft or the inner shaft, and movably in relation to one another, or rotatably about their common axis of rotation. The fixed cam element can therefore be steplessly spread apart in a defined angular range in relation to the adjustment cam element. It is, however, also conceivable for the cam pack to comprise more than two cam elements.
Advantageously, in the cam contour, the leading profile edge or profile flank is formed by means of the fixed cam element, and the trailing profile edge or profile flank is formed by means of the adjustment cam element. This means that the tapping element, which is, for example, a cam follower, such as a roller cam follower, contacts the fixed cam element if the tapping element is in contact with the region of the leading profile edge or profile flank. The tapping element contacts the adjustment cam element as soon as it is in the region of the trailing profile edge. Advantageously, the tapping element contacts the adjustment cam element in the region of the trailing flank shortly after passing over the cam tip.
The profile of the cam pack, which profile is to be formed or produced, advantageously comprises two transition points. At least in the regions of these transition points, a transfer of the tapping element from the fixed cam element to the adjustment cam element takes place, wherein this transition point is called the first transition point within the scope of the invention, or from the adjustment cam element to the fixed cam element, wherein this transition point is called the second transition point within the scope of the invention. Within the scope of the invention, the first transition point is advantageously formed in a region on the profile of the cam pack, which region extends between the beginning of the fixed cam elevation or the adjustment cam elevation and the end of the respective cam elevation, i.e., the adjustment cam elevation or the fixed cam elevation. The second transition point is advantageously formed in a region at the end of the fixed cam elevation or the adjustment cam elevation.
The processing point, which results from the processing of the fixed cam profile, is advantageously formed in the region of the base circle of the fixed cam element—preferably shifted a few angular degrees toward the end of the fixed cam elevation and, consequently, toward the second transition point formed with respect to the basically-known fixed cam elements. This means that the processing point is advantageously formed or shifted in comparison to the basically-known fixed cam elements such that the second transition point formed by means of the processing point is shifted into the fixed cam base circle region. Accordingly, the processing point advantageously forms the second transition point (new transition point), which marks the border region between the fixed cam elevation and the fixed cam base circle. The advantage thereof consists, in particular, in that a correspondingly small region of the base circle of the cam pack, which base circle is to be traversed by the tapping element, must be formed by means of the adjustment cam element—in particular, the adjustment cam base circle.
Within the scope of the invention, the term “base circle,” such as the fixed cam base circle or the adjustment cam base circle, refers to a region of the cam element, which extends, when viewed in the circumferential direction of the cam element, between the end of the cam elevation, i.e., the fixed cam elevation or the adjustment cam element, and the beginning of the respective cam elevation, wherein the first transition point is not formed in this named circumferential segment or cam contour region. The first transition point is advantageously formed in the region of the cam elevation, i.e., the cam contour segment in which the cam element has an elevation starting from the axis of rotation of the cam element.
According to the invention, the contour of the fixed cam element—in particular, a protrusion of this contour—advantageously a convex protrusion or a contour elevation of the fixed cam element—is reduced at least in a defined region. This means that at least some radii, which extend in this region of reduction of the contour protrusion, starting from a central point of the fixed cam element, radially outward, are at least partially reduced or decreased.
When using the method according to the invention, the camshaft—in particular, the cam elements—is therefore advantageously ground in a mounted condition. In this respect, it is conceivable that the adjustment cam element arranged rotatably in relation to the inner shaft and/or the outer shaft is spread apart from the fixed cam element connected to the outer shaft for conjoint rotation and is advantageously arrested—in particular, during the processing operation of the fixed cam contour. The inner shaft itself can—but does not need to—be mounted or arranged within the outer shaft during the processing of the cam elements. It is, additionally, also conceivable for the adjustment cam contour of the adjustment cam element to have already been processed—in particular, ground—prior to the mounting of the camshaft, so that the adjustment cam element is mounted onto the outer shaft in the processed condition, while the fixed cam element is processed after the mounting of the camshaft. It would, however, also be conceivable for both cam elements to be processed prior to the mounting and to thus be mounted onto the outer shaft in the ground condition. It is, consequently, also possible for both cam elements not to be processed until after the mounting of the camshaft and for their contours to accordingly be ground to form a cam profile avoiding profile jumps.
Within the scope of the invention, it is therefore conceivable that the processing of at least the adjustment cam contour or the fixed cam contour take place by means of a grinding process. In this respect, it is conceivable for the adjustment cam element to be spread apart from the fixed cam element and positioned on the outer shaft during the processing of the fixed cam contour and arrested, for example, such that the fixed cam element and, in particular, the contour of the fixed cam element can be processed. Advantageously, in the processing—in particular, the grinding process—the fixed cam element is processed in the transition region between the fixed cam elevation and the fixed cam base circle. Advantageously, material is removed in this region from the circumference of the fixed cam element.
Within the scope of the invention, it is conceivable that the adjustment cam contour be designed as a constant cam elevation at least one of the transition points. This constant adjustment cam contour advantageously extends in the region of the first transition point, where the tapping element is transferred from the fixed cam element to the adjustment cam element. A constant adjustment cam contour is understood in this respect to mean a region of the cam elevation of the fixed cam element, which region has no positive and/or negative slope. The adjustment cam contour is advantageously designed in this case such that, taking into consideration the desired adjustment angle, the adjustment cam profile of the adjustment cam element, when spread 0°, is covered by the fixed cam profile of the fixed cam element. It would also be conceivable that, instead of or in addition to forming a constant cam elevation in the adjustment cam element as described above, a correspondingly comparably-designed constant cam elevation be formed in the fixed cam element.
It is further conceivable that the adjustment cam contour of the adjustment cam element be reduced in the adjustment cam base circle at least in sections by about 0.02 mm per about 5° cam angle. This advantageously results in a continuous diameter reduction of the adjustment cam element. The adjustment cam profile, consequently, advantageously decreases starting from the second transition point down to the adjustment cam base circle, which, when viewed in relation to the fixed cam base circle, has a smaller diameter and is, consequently, advantageously formed in the form of a recess.
As a result, a recess is advantageously produced at least in sections in the adjustment cam base circle of the adjustment cam contour, which recess is reduced in relation to the fixed cam base circle at least by about a doubled profile tolerance of the adjustment cam base circle. This, advantageously, makes it possible for the cam tap in the base circle to be formed by means of the fixed cam element. This means that the tapping element explicitly contacts the fixed cam base circle only when traversing the base circle region of the cam pack.
According to a second aspect of the invention, a camshaft according to the invention comprises at least one outer shaft and one inner shaft arranged concentrically or coaxially within the outer shaft, and a cam pack with at least one fixed cam element connected to the outer shaft for conjoint rotation and at least one adjustment cam element mounted rotatably in relation to the outer shaft and connected to the inner shaft for conjoint rotation, wherein the adjustment cam element and the fixed cam element can be rotated in relation to each other about a common central axis and form a common cam profile, which interacts with a tapping element for converting a revolving motion of the cam pack into a linear motion of valve pistons. According to the invention, the cam profile has an adjustment cam contour of the adjustment cam element with an adjustment cam base circle diameter reduced at least in sections, which diameter is smaller than a fixed cam nominal circle diameter minus a doubled adjustment cam base circle tolerance, and a fixed cam contour of the fixed cam element with a fixed cam contour protrusion reduced at least in sections in at least one region between a first of at least two transition points, upon the reaching of which the tapping element can be transferred from the fixed cam element to the adjustment cam element, and a processing point, which is arranged at least in sections in the fixed cam base circle.
The camshaft can also comprise one or more cam packs with more than two cam elements and, in particular, three and more cam elements, wherein at least one of the cam packs comprises a fixed cam element and an adjustment cam element of the aforementioned design.
Within the scope of the invention, the nominal circle diameter is understood to be an ideal, mathematically calculable diameter of the processed cam element.
According to the invention, the adjustment cam comprises an adjustment cam base circle extending between the end of the adjustment cam elevation and the beginning of the adjustment cam elevation. The diameter of the adjustment cam base circle is advantageously less than the fixed cam base circle of the fixed cam element, which fixed cam base circle also extends between the end of the fixed cam elevation and the beginning of the fixed cam elevation. Accordingly, the adjustment cam element advantageously comprises, at least in sections, a recess in the region of the adjustment cam base circle, which recess is reduced at least by the doubled profile tolerance of the adjustment cam base circle in comparison to the fixed cam base circle.
It is furthermore conceivable that, at least at one of the transition points, the fixed cam contour have a constant cam elevation. Advantageously, this constant cam elevation is formed in the region of a first transition point, where the tapping element can be transferred from the fixed cam contour to the adjustment cam contour, and has, particularly advantageously, no—or a negligibly small—positive and/or negative slope. It is also conceivable that the adjustment cam element have a segment with a constant cam elevation, wherein this constant cam elevation advantageously extends in the region of the first transition point. It is advantageously also possible that both cam elements respectively have a segment with a constant cam elevation, wherein the constant cam elevations are, respectively, particularly advantageously formed in the region of the first transition point. Both constant cam elevation segments can in this case have an identical or a different design with respect to each other—for example, with respect to the length in the circumferential direction and/or with respect to the starting and/or end point, etc.
It is advantageously conceivable that the camshaft according to the invention be produced or manufactured using the method described in the first aspect of the invention. Accordingly, the contours of the individual cam elements, and consequently the profile of the entire cam pack, are advantageously produced using the aforementioned method.
All the advantages already described with respect to a method for producing a cam profile according to the first aspect of the invention result in the camshaft described.
Embodiments of the cam pack of a camshaft according to the invention—in particular, of the fixed cam element and the adjustment cam element—and embodiments of basically-known cam packs—in particular, their fixed cam elements and their adjustment cam elements—are explained in more detail below with reference to the drawings. They respectively show schematically:
Elements with the same function and mode of operation are respectively provided with the same reference symbols in
As can be seen in
With reference symbol 10 is illustrated a nominal cam contour for the entire cam pack 1 (cf., for example,
As shown in
As, for example, shown in
The transition points P1 and P2 are not points or regions that can be directly assigned to a cam element 2 or 3, but, rather, are formed as a result of the interaction of the two cam elements 2 and 3. When viewing the adjustment cam element 3, the transition points P1 and P2 can consequently also be specified as reference points for the description of the positioning of the individual design features of the adjustment cam element 3.
The transition points P1 and P2 are, therefore, also shown in
As shown in
The region of a cam elevation designed to be constant is denoted by reference symbol K in
Comparably to
Based upon the changed cam contours 2a and 3a of the fixed cam element 2 and the adjustment cam element 3 respectively, jumps in the profile of the cam pack, which is composed of at least one fixed cam element 2 and one adjustment cam element 3, are, advantageously, avoided. Particularly advantageously, the fixed cam contour 2a and/or the adjustment cam contour 3a, and consequently the cam profile of the cam pack 1, are, advantageously, ground circumferentially, after the mounting of the cam on the shaft.
In the illustration shown in
Independently of the desired adjustment angle of the camshaft (not shown here), and consequently of the spread of the cam pack 1, the design of the adjustment cam contour 3a and of the fixed cam contour 2a as described above results in an overlap in the regions of the transition points P1 and P2, such that jumps between the individual contours of the adjustment cam element 3 and the fixed cam element 2 are avoided in these regions, and an even cam profile with respect to the cam pack 1 consequently arises. Even a production of the cam elements 2 or 3 at the upper or lower tolerance limit does not have any negative influence upon the properties of the transition regions of the profile in the implementation of the method according to the invention. Thus,
Denoted by the reference symbol D is the direction of rotation of the entire cam pack 1, which is rotated about its axis of rotation A (cf.
In the illustration shown in
Independently of the desired adjustment angle of the camshaft (not shown here), and consequently of the spread of the cam pack 1, the design of the adjustment cam contour 3a and of the fixed cam contour 2a as described above results in an overlap in the regions of the transition points P1 and P2, such that jumps between the individual contours of the adjustment cam element 3 and the fixed cam element 2 are avoided in these regions, and an even cam profile with respect to the cam pack 1 consequently arises. Even a production of the cam elements at the upper or lower tolerance limit does not have any negative influence upon the properties of the transition regions of the profile. Thus,
The cam pack 1 comprises an adjustment cam element 3 and two fixed cam elements 2.1 and 2.2, which are arranged adjacently to the adjustment cam element 3 and in a manner enframing it between them. The fixed cam elements 2.1 and 2.2, as well as the adjustment cam element 3, have a common axis of rotation A and are advantageously arranged coaxially to each other.
Based upon the spread of the cam pack 1, i.e., as a result of the angular position of the adjustment cam element 3 in relation to the fixed cam elements 2.1 and 2.2, a variability in the valve elevation, and thus in the opening period of the control valve, of a combustion engine is, advantageously, made possible. The advantageously stepless opening period of the cam profile, which consists of the adjustment cam contour 3a and the respective fixed cam contours 2.1a and 2.2a of the fixed cam elements 2.1 and 2.2, is caused in this case by the spread of the cam pack 1 by, for example, a relative rotation of the inner shaft 5 in relation to the outer shaft 4. A rotation—in particular, the realization of an adjustment angle between the fixed cam elements 2.1, 2.2 and the adjustment cam element 3—advantageously takes place as a result of the arrangement of the adjustment cam element 3 on the inner shaft 5 for conjoint rotation and the arrangement of the fixed cam elements 2.1, 2.2 on the outer shaft 4 for conjoint rotation.
The described embodiments do not presuppose completeness. It is, furthermore, conceivable that the features described in the figures also be used in combination with each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 018 784.5 | Dec 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/073042 | 10/6/2015 | WO | 00 |
