Abstract:
The invention relates to a hub ( 1 ) with a hub opening ( 2 ) in the front face ( 8 ), for press-fitting to a base body, whereby the hub ( 1 ) comprises a insertion region (A 2 ), tapering in the pressing direction, characterized in that a cylindrical section is arranged between the front face and insertion region (A 2 ), viewed in the pressing direction. Furthermore, a hub ( 1 ) with a tapering insertion region (A 2 ) is disclosed, whereby said insertion region (A 2 ) has a length of 40% to 96% of the total length (L) of the hub ( 1 ). The invention further relates to a camshaft with at least one cam ( 9 ), associated with said hub ( 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is an U.S. national phase application under 35 U.S.C. §371 based upon co-pending International Application No. PCT/EP2003/008130 filed on Jul. 24, 2003. Additionally, this U.S. national phase application claims the benefit of priority of co-pending International Application No. PCT/EP2003/008130 filed on Jul. 24, 2003 and European Application No. 02017216.9 filed on Jul. 31, 2002. The entire disclosures of the prior applications are incorporated herein by reference. The international application was published on Feb. 12, 2004 under Publication No. WO 2004/013507 A1. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hub and a cam with a hub for pressing onto a base body and a camshaft with at least one pressed-on hub, in particular, a cam. 
     2. Description of Related Art 
     It is known to make camshafts by pressing cams onto a shaft. On the respectively provided positions for the cam, the shaft is machined, such that a material aggregate exists, whose diameter exceeds that of the shaft. Upon pressing on, this material is deformed by the cam, so that the cam is fixed by a lateral pressing onto the shaft. 
     Cams for such a manufacturing method of camshafts are described in documents EP-A2 1058033 and WO-A1 01/94802. 
     The hub opening of a hub or a cam according to document EP-A2 1058033 is designated by two conically formed sections of the hub. These two hub sections connect successively to the front face of the cam, forward in the press-on direction. The two conical sections each have a different incline. With this profile structure, the disadvantage exists in that with pressing on of the cam onto the shaft, already at the beginning of the cam opening, a force effect acts on the cam, and so tensioning in the cam material can occur. This tensioning leads to microscopic tears in the structure and can cause a weakening or collapse of the attachment operation, and likewise, can cause functional destruction of the camshaft based on the deformation. 
     WO-A1 01/94802 shows a cam with an inlet area, which takes up approximately half of the cam or hub width. The profile of this inlet area is described as conical and goes continuously over into a hub region, which takes up the remaining width of the hub and is either conical or cylindrical. With this structure of the hub, a shifting of the connection tensioning in the center of the hub width should be possible. However, it should be noted that already after the beginning of the inlet region, a deformation of the material aggregate on the shaft takes place. Therefore, in this region, damage of the material connection with the result of microscopic tears in the outer region of the cam hub with the previously described effects is to be expected. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to avoid the disadvantages of the known hubs and to make an alternative hub for pressing onto a base body. 
     The object is solved by a hub for pressing onto a base body, whereby the hub has a hub opening, which is defined by hub front faces, and whereby the hub has an insertion area A 2  tapering in the press-on direction P, and the hub opening is characterized by a cylindrical section A 1 , which is arranged between the front face and insertion area A 2  as viewed in the press-on direction. 
     With the term “hub” in the sense of the present invention, a section with a through-going opening within a component is to be understood, for example, those required with cams, wheels, cog wheels, eccentric rings, sensor rings, curved disks, or the like and for the mounting of cams, cogwheels, eccentric rings, sensor rings, curved disks onto a base body. Although the description relates substantially to hubs in cams, the invention is not limited thereto. Cams can be formed as a separate element, for example, tube-shaped. As a base body, also shafts, tubes, or also bearings (for example, ball bearings or bushings) can be used. Such cams are generally attached to or in the component, by which the hub is supported. Cams can be formed also integrally as an opening in a component. 
     A cylindrical embodiment of the section A 1  of the hub avoids a direct effect of force between a component or a base body on which the hub is to be placed and the hub in the region of the front face, since the deformation of the material aggregates on the shaft begins upon pressing-on of the hub on the base body first in the tapered insertion region. Any connection strains occur, therefore, first in the insertion section A 2 ; they act on the fixed seat of the hub on the base body. The base body can be a shaft, which can comprise solid material as well as a hollowed-out tube, or the like. 
     By avoiding the connection strains in the cylindrical section A 1 , the formation of weak points, such as microscopic tears or deformations or material distortions in the body, which supports the hub, for example, the running surfaces of a tire or a cam, are avoided. Damage to the function of the cam, as well to the material stability of the cam, is prevented. 
     Generally, the sequence of sections or areas of the hub are to be understood, in that, respectively, a lesser number lie forward in the press-on direction. The press-on direction is that in which, for example, the cam is guided over the base body. The cam front face is the surface of the cam, whose normal is oriented parallel to the press-on direction. 
     Advantageously, the hub of the present invention has a cylindrical section A 1  of the hub opening, whose diameter is at least the same size as the largest diameter of the base body. Such a diameter D 1  permits a simple placing of the hub on the base body and makes possible upon pressing on, the avoidance of existing connection strains in the region of the front face. A force effect between the base body and the hub in the cylindrical section A 1  is not formed. 
     Likewise advantageously, a hub is formed, which has a hub opening with a second cylindrical section A 3 . This second cylindrical section A 3  is arranged on the opposite side of the insertion area A 2 , with reference to the first cylindrical section A 1 . This section A 3  also avoids the formation of weak points upon pressing-on of the hub, in particular, on the second front side of the hub, since the diameter of the base body already is reduced in the insertion area or insertion section A 2  to the mass of the unmachined base body, in particular, the shaft. No substantial force transmission between the shaft and the hub takes place in section A 3 . 
     Essentially, the diameter D 1  of the first cylindrical section A 1  is greater than the diameter D 2  of the cylindrical section A 3 . 
     One embodiment of the hub of the present invention is distinguished by an insertion section A 2 , which has a curved profile. This profile corresponds to circular segments arranged on one another, whereby these circulate segments have different radii. The length as well as the radius of the individual circular segments are directed toward the desired profiled structure. Of course, the profile also can be formed by sections of other curved shapes. The radii of the circular segments, which are adjacent to the first cylindrical section A 1 , are small. 
     The curve progression to the third section A 3  is based on circular segments with a respectively increasing and greater radius. The continuous curvature of the curved profile permits an avoidance of a maximum connection strain and a force-fit connection extending over a larger area. 
     The curved segments cross over preferably continuously on another; that is, they connect tangentially to one another, respectively. The curved segments, however, also can discontinuously cross over one another; that is, on the respective transition points, a transition edge is provided. In addition, the first curved segment can continuously or discontinuously connect to the section A 1 . 
     The same is true for the last curved section, which can run continuously or discontinuously into the section A 3 . With a particularly simple embodiment, the curve between the sections A 1  and A 3  are formed by a radius, which, for example, connects discontinuously with the formation of the transition edge E 1  to the section A 1 , and for example, continuously, that is, without formation of a transition edge in the section A 3 . 
     In a preferred embodiment, the insertion area (section) A 2  of the hub is divided into two subsections, which are formed along the longitudinal axis of the hub in the form of a truncated cone. Therefore, both truncated cone-shaped subsections have different conical angles. The conical angle K 1  of the subsection A 2 ′ adjacent to section A 1  is greater than the conical angle K 2  of the subsection A 2 ″ adjacent to section A 3 . The different conical angle permits, on the one hand, an improved centering of the hub upon pressing onto the base body and, on the other hand, a sufficient force-locking ability between the hub and the base body. In particular, in view of the frictional connection ability, it is important that this is provided over a sufficient longitudinal area of the hub, in order to permit a permanent connection also under operating conditions. Preferably, in addition, the cone with the conical angle K 1  is opened in the same direction as the cone with the conical angle K 2 . Thus, a substantially continuous transition from a larger diameter to a smaller diameter can be assured. At the same time, the frictional connection between the hub and the base body is created over a wider region. 
     As “conical angle”, the angle which is determined viewed from the fictional vertex of the truncated cone to the widening of the fictional cone is intended. The half value of a conical angle, therefore, provides the increase or incline of the conical surface with reference to the height of the truncated cone. The spatial orientation of the truncated cone to the hub is such that the truncated cone vertex coincides with the longitudinal axis of the hub. 
     In a preferred embodiment, the insertion area A 2  of the hub  1  is formed by an individual truncated cone (cone), which tapers originating from the diameter D 1  to the diameter D 2 . 
     In this manner, the edges E 1  and E 2  are formed on the transition points. 
     In a further preferred embodiment, the cam has a diameter D 1  in the first section A 1 , which is at least the same size at a diameter W 1  of the base body. The diameter W 1  corresponds with the diameter of the material aggregate existing on the base body from a machining of the base body. These material aggregates are in the form of coils or bars. The material aggregates can extend either in the circumferential direction of the base body or parallel to the longitudinal axis of the hub. Based on the selection of the diameter D 2  as at least the same size as the diameter W 1 , the hub can slide upon pressing-on first over the material aggregate, without material deformation. The hub is guided opposite to the hub and makes possible an improved centering of the hub on the base body. At the same time, as previously described, also a shifting of possible connection strains takes place in the central region (insertion section A 2 ) of the hub and a related avoidance of weak points on exposed points of the cam. As exposed points, the front face or the region of the cam lying directly thereunder is to be understood. 
     Likewise, it is advantageous to form a hub, in which the diameter D 2  is at least the same size or bigger than the diameter W 2  of the base body. The diameter W 2  corresponds with the diameter of the unmachined base body. The suitable selection of the diameter D 2  makes possible, likewise, a guiding of the hub onto the base body during pressing-on. 
     At the same time, the formation of substantial connection strains in this second cylindrical section A is avoided, and therewith, likewise, the formation of weak points with possibly negative effects on the longevity of the hub-base body-connection. The diameter D 2  relative to the diameter W 2  is preferably selected, such that a clearance fit between the hub and base body is achieved. 
     In one embodiment, the hub of the present invention has a first section A 2 , which includes 2% to 30% of the entire length L of the hub. With such a length, it is assured that, on the one hand, a sufficient guiding of the hub is achieved, and on the other hand, possible connection strains are removed far enough from the front face and exposed points of the hub, in order to avoid the initially disclosed disadvantageous. Preferably, the section A 2  has a length of 5% to 15% of the entire length of the hub. 
     It is likewise advantageous if the hub has a third section A 3  with a length of 2% to 30% of the entire length L of the hub. Such a length ensures that no substantial connection strains exist in the region of the section A 3 , which could lead to weak points on the exposed points. 
     Also, a sufficiently good centering of the hub on the base body is made possible. Preferably, in addition, a length of the section A 3  is from 5% to 15% of the entire length L of the hub. 
     In a further embodiment, the second insertion section A 2  of the hub includes a length of 40% to 96% of the entire length L of the hub. This length of the insertion area A 2  forms the region of the hub, which accommodates the frictional connection of the hub and shaft. This is important, in order to ensure an adequate functioning of the manufactured camshaft also under conditions of long-term use. Preferably, the insertion section has a length between 70% and 90% of the entire length L of the hub. 
     A further aspect of the hub of the present invention is the longitudinal ratio of the two subsections of the insertion section A 2 . The ratio of the subsection A 2 ′ to the subsection A 2 ″ lies between 0.1 and 10. By means of a suitable selection, the development of the frictional connection between the hub and the base body is controlled advantageously. Preferably, a longitudinal ratio between a first subsection and section subsection is from 0.1 to 5. 
     Furthermore, it is advantageous if the hub has a first conical angle K 1  of 10° to 40°. This conical angle region permits driving the material deformation up to the point that a frictional connection between the hub and base body can be achieved directly. 
     A hub according to the present invention advantageously has a second conical angle K 2  between 1° and 15°. This conical angle range leads to an expanded contact area between the hub and the shaft, which creates an approximately uniform frictional connection between the hub and base body. Based on such a structure, a possible maximum of connection strains is substantially reduced or avoided, and therewith, non-uniform and damaging loads are reduced. 
     In a further embodiment, a hub of the present invention has at least one recess, which extends at least over the length of the section A 2  and A 3  of the hub. Under the term “recess”, a material demarcation, which defines a small part of the circumference of the hub and which extends radially outward at a maximum to the diameter D 2  originating from the longitudinal axis of the hub, is to be understood. Such a recess, for example, is viewed as a narrow channel parallel to the longitudinal axis of the hub, which continues in a small circumferential region of the hub from the first section A 2  through the sections A 2  and A 3 . Such a recess ensures that additionally, from a frictional connection, a form fit between the hub and the base body is achieved, and thereby, a rotation of the cam in the circumferential direction is avoided. 
     The invention, in addition, includes a system having a base body, in particular, a shaft, and a cam, whereby the hub penetrates the cam or its front faces. The hub has a tapered insertion area A 2 . The hub and shaft are formed, such that upon pressing-on of the cam, the distance of the point for a first contact between the largest outer diameter of the shaft and the insertion area A 2  amounts to at least 2% to 40% of the entire length L of the hub. 
     Distance values of at least 3% to 20% are preferred, and further preferred is at least 5% to 15% of the entire length L of the hub. 
     In addition, the present invention relates to a camshaft, on which at least one of the previously described inventive hubs, in particular, a cam, is pressed. 
     As the exemplary embodiment for a hub, in the following description of the invention, a cam for constructed camshafts is described. The invention, however, is not limited only to cams for constructed camshafts. Hubs, for example, can be formed as cogwheels, eccentric rings, sensor rings, curved disks, or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The schematic representations of the hub of the present invention show: 
         FIG. 1 : a view of the pressing-on side of a cam. 
         FIG. 2 : cross section Q-Q′ of the cam of  FIG. 1 . 
         FIG. 3 : cam cross section and shaft with material aggregate before pressing on. 
         FIG. 4 : cam cross section and material aggregate of the shaft after pressing on. 
         FIG. 5 : further embodiment of the cam with an axial running recess. 
         FIG. 6 : further embodiment of the insertion section A 2  with an axially running recess. 
         FIG. 7 : further embodiment of the insertion section A 2 . 
         FIG. 8 : further embodiment of the insertion section A 2 . 
         FIG. 9 : cam cross section and shaft with longitudinally parallel material aggregate before pressing on. 
     
    
    
     The figures show embodiments of hubs and cams with the features of the invention in a schematic representation; they do not represent exact proportions or dimensions and serve purely for clarification of the principle structure of a hub according to the present invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     According to  FIGS. 1 and 2 , a cam  9  has a hub  1  with a hub opening  2  in the front surface  8 . The cylindrical section A 1  with the diameter D 1  is closed off by the edge E 1  (not recognizable in the figure). The first subsection A 2 ′ of the second section (insertion area A 2 ) connects thereto. The surface of this subsection A 2 ′ corresponds to a truncated cone with the conical angle K 1 . This is recognizable in  FIG. 2 , which shows a section along Q-Q′ of  FIG. 1 . The following subsection A 2 ″ likewise is formed to be a truncated cone, but has a smaller conical angle K 2 , which is smaller than K 1 . Section A 3  of the hub opening  2  has a cylindrical shape with the diameter D 2 . 
     Likewise, the transition edges E 1 , E 2 , and E 3  can be recognized, which clarify the subdivision of the nub  1  into the individual sections A 1 , A 2 ′, A 2 ″, and A 3 . 
     Both  FIGS. 3 and 4  show a base body  3  formed as a shaft with corresponding material aggregates  5 . The arrow P, therefore, shows the pressing-on direction of the hub opening  2 . In  FIG. 3 , the cam  9  is displaced or pressed onto the based body  3  to such a point that the material aggregates  5  are located in section A 1  of the hub opening. 
     It can be recognized clearly that still no material deformation has occurred. This is visible in  FIG. 4 , which shows the cam  9  after pressing on. The material aggregates  5  lying behind in the pressing on direction are located already in subsection A 2 ″ of the hub opening  2  and have already been substantially deformed (material deformation  6 ). The section A 3  takes up the shaft ridges in section A 2 , without deformation of this additionally in section A 3 . The base body  3  has a diameter W 2  in the unmachined region and in the region of the material aggregates  5 , has a diameter W 1 . 
     A recess  7  in the hub opening  2  of the hub  1  of the cam  9  is shown in  FIG. 5 . In the view of the front face  8 , it can be seen how the recess  7  extends only into a part of the radial circumference of the hub  1 . The radially most outward point of the recess  7  from the longitudinal axis  4  coincides with the surface of section A 1 . Therefore, the recess  7  can be designated as a narrow channel, since it extends over the length A 2  and A 3 . This recess  7  affects no material deformation upon pressing-on of the cam  9  onto a base body  3 . Therefore, the cam  9  performs a circumferential-side fixing onto a base body  3 . Also, more than one recess  7  can be located in the hub  1 . The profiling of such a recess also can be adapted to the necessary specifications.  FIG. 6  shows a further embodiment of the section A 2  of the hub  1 . This section A 2  here is formed by a single cone, which connects sections A 1  and A 3  by the interior edges E 1  and E 2 . In  FIG. 6 , the recess  7  is shown in cross section. In addition, also the half conical angle K 1  for the section A 2  as well as the diameter D 1  and D 2  of sections A 2  or A 3  can be recognized. 
     A further embodiment of the section A 2  of the hub  1  according to the present invention is shown in  FIG. 7 . In addition to the two sections A 1  and A 3  of the hub opening  2 , the cam  9  has a one-part section A 2 . The profile of the section comprises a continuously changing curve progression. The curve progression can be described as a succession of circular segments, whereby the radius of these circular segments enlarges progressively. The circular segment connecting directly to section A 1  has the smallest radius of all of the circular segments, which form the curve progression, that is, the profile of section A 2 . 
     The largest radius, which opens directly into the section A 3 , can connect by means of a transition edge E 2  discontinuously, as shown in  FIG. 7 , to section A 3 . This transition in region A 3 , however, also can take place continuously, that is, without formation of an edge E 2 . In this case, the largest radius of the section A 2  runs tangentially in the section A 3  (analogous to  FIG. 8 ). The curve progression in section A 2  also can be formed by a single radius R, which connects discontinuously to section A 2  with formation of the edge E 1  and opens tangentially, that is, continuously, without edge E 2  into the region A 3 . 
     Based on the increasingly flattened profile progression in section A 2  in the direction of section A 3 , the connection strains are distributed over a larger area, without causing excessively large load maximums. The connection strains, however, are simultaneously displaced into the interior of the cam  9 . Thus, structure defects, such as microscopic tears in the outer regions A 1  and A 3  of the hub opening  2 , are avoided. The functionality, in particular, the long-term stability, is therefore improved: in addition, it is conceivable that the curve profile is divided into two or more subsections with respective individual curve profiles, such as that described for the embodiment with truncated cone-shaped sections. 
     An embodiment of the cam  9  of the present invention is based on a cam body made of ball bearing steel with a cam width of 15 mm. The length of the individual sections A 1  and A 3  as well as the insertion section A 2  of the hub opening  2  amounts to 1 mm, 1 mm as well as 13 mm. The diameter D 1  of the section A 1  amounts to 25.6 mm, whereas the diameter D 2  of section A 3  amounts to 25.0 mm. The insertion section A 2  is subdivided into the subsections A 2 ′ and A 2 ″ with, respectively, lengths of 2 mm and 11 mm. The subsection A 2 ′ has a conical angle of 30°, and the subsection A 2 ″ has a conical angle of 15°. The rotating surface of the cam  9  as well as the surface of the hub  1  is hardened, in order to reduce the operating loads and to increase longevity. 
     With the making of a camshaft, on the corresponding points of the shaft (base body  3 ), a material aggregate  5  is produced by machining, whose length corresponds approximately to the cam width, that is, 15 mm and its diameter difference W 1  minus W 2  amounts to approximately 0.6 mm. A cam  9  according to the present invention is placed on the shaft  3  and pressed with a pressing force of approximately 20,000 Newton over this material aggregate. 
     In this manner, the correct pressing-on must be attended to, in particular, in view of the positioning of the hub center, that is, of the insertion section A 2  over this material aggregate. After completion of pressing on of the first cam  9 , the further cams  9  are successively pressed on with the correspondingly predetermined distance onto the respectively, individually produced material aggregates  5 .