Abstract:
The present disclosure relates to a connection system for connecting a component to a gear wheel, wherein the gear wheel comprises helical gearing having a tooth helix angle and a first connecting section, and the component comprises a second connecting section by way of which the component can be connected or is connected to the first connecting section, wherein the component, in the second connecting section, comprises at least one depression or elevation that is operatively connected to the first connecting section when the component is connected to the first connecting section, wherein the depression has a connection helix angle, and the connection helix angle is defined as follows: 0°≦α≦β. The disclosure furthermore relates to a device for transmitting a rotational movement, comprising a rotatable component and a gear wheel, wherein the gear wheel and the component are connected by way of such a connection system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application No. 16 181 746.5, filed Jul. 28, 2016, which is incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a connection system for connecting a component, in particular a shaft, hub, bushing or the like, to a gear wheel, wherein the gear wheel comprises helical gearing. The disclosure furthermore relates to a device for transmitting a rotational movement, comprising a rotatable component such as a rotatable shaft, hub, bushing or the like, and a gear wheel, wherein the gear wheel and the rotatable component are connected by way of such a connection system. The connection system can be used to non-rotatably connect the gear wheel to the component, so that torque can be transmitted. 
       SUMMARY 
       [0003]    Compared to spur gearing, helical gearing has the following advantages, among other things. Improved running smoothness and lower noise development can be achieved by way of helical gearing since every gear wheel pair engages one another in a continuous transition, and thus torque transmission takes place more uniformly than with spur gearing. Compared to a straight-toothed gear wheel pair having comparable dimensions and the same number of teeth, moreover the tooth root and tooth flank load-bearing capacities are slightly higher. 
         [0004]    In the case of helical gearing, not only tangentially acting, but also axially acting forces are transmitted, relative to the rotational axis. Electrical steering devices of motor vehicles especially are often subjected to very high axially acting forces, which is why the gear wheel experiences accordingly high axial loads. As a result of the axial load, a tilting moment is introduced into the gear wheel, whereby the gear wheel becomes deformed and the running smoothness and the noise development are adversely affected. Moreover, faulty engagements occur, and the service life of the gear wheel is reduced. 
         [0005]    One known example for such connection systems are shaft/hub connections, in which axial loads are frequently transmitted at least partially by the component surrounded by the gear wheel, and in particular the shaft, being provided with a projection against which the hub of the gear wheel is seated. This, however, creates a point load on the connection system, resulting in a tilting moment, whereby the gear wheel is able to detach from the component, such as from the shaft, hub, bushing or the like. Depending on the design of the gear wheel, what is known as lift-off may occur, or skipping of the gear wheel may take place in relation to the hub. While poorer running smoothness and increased noise development do not have any significant influence on the function of the torque transmission from the component to the gear wheel and the gear wheel pair, torque transmission is no longer possible when the connection system fails. 
         [0006]    So as to reduce the load on the connection system, the tooth helix angle of the helical gearing may be reduced. This, however, to a large extent cancels out the advantage of helical gearing mentioned at the outset, in particular the uniform torque transmission and the low noise development. The load on the connection system can be reduced through the use of very stiff materials, for example through the use of steel; however, this increases the manufacturing costs, the weight and the noise development compared to soft materials such as plastic. 
         [0007]    In one embodiment of the present disclosure, a connection system is provided that, regardless of the material used for the component, and in particular for the shaft, hub, bushing or the like, and for the gear wheel, has an increased load-bearing capacity compared to known connection systems. 
         [0008]    The present disclosure provides a connection system having the features and structures disclosed herein. Advantageous embodiments of the present disclosure are also disclosed herein. 
         [0009]    One embodiment of the disclosure relates to a connection system for connecting a component, and in particular a shaft, hub, bushing or the like, to a gear wheel, wherein the gear wheel comprises helical gearing having a tooth helix angle β and a first connecting section, and the component comprises a second connecting section by way of which the component can be connected or is connected to the first connecting section, wherein the component, at least in the second connecting section, comprises at least one depression or elevation that is operatively connected to the first connecting section when the component is connected to the first connecting section, wherein the depression or the elevation has a connection helix angle α, and the connection helix angle α is defined as follows: 0°&lt;α≦β. 
         [0010]    Both the connection helix angle α and the tooth helix angle β are based on the rotational axis about which the component and the gear wheel rotate. Due to the fact that the at least one depression or elevation has the connection helix angle α, it is possible, for example, to also transmit axial forces between the gear wheel and the component along the entire depression or elevation, in contrast to frequently used splined shaft connections. The resulting more uniform load at least considerably reduces a point load, and considerably decreases the tilting moment, which results in the above-mentioned failure occurrences such as lift-off and skipping, whereby the risk of a failure of the connection system decreases. Moreover, it is also possible to transmit higher torque and axial forces via the connection system designed according to the disclosure. Consequently, both the component and the gear wheel can have smaller dimensions, and consequently a more material-saving design, at a particular torque to be transmitted and a particular axial load. 
         [0011]    In a further embodiment, the connection helix angle α and the tooth helix angle β have the same sense of rotation. The sense of rotation is based on the rotational axis and is derived from the direction in which a straight line, proceeding from the rotational axis, must be rotated about a fulcrum extending through the rotational axis by the magnitude of the connection helix angle or the tooth helix angle so as to run parallel to the depression or elevation or the helical gearing. When the connection helix angle and the tooth helix angle have the same sense of rotation, it is possible to achieve a particularly uniform load on the connection system, whereby the tendency of the connection system to fail can be reduced further. 
         [0012]    A further embodiment is characterized in that the component, in the second connecting section, comprises a number of depressions or elevations, and the helical gearing of the gear wheel comprises the same number of teeth. This embodiment is in particular an obvious choice when the diameter of the component in the second connecting section, or the diameter of the gear wheel in the first connecting section, is only slightly smaller than the diameter of the helical gearing. In this case, the wall thickness of the gear wheel is relatively thin, so that, if the number of depressions or elevations and the number of the teeth are selected to be the same, fluctuations in the wall thickness of the gear wheel can be minimized. In a cutting plane perpendicular to the rotational axis, the gear wheel then approximately has the shape of an undulated circular ring surrounding the rotational axis. Due to the substantially constant and uniform wall thickness of the gear wheel, stress peaks and failure spots are avoided, whereby the strength of the gear wheel is increased. 
         [0013]    According to a further embodiment, the first connecting section comprises protrusions corresponding to the depression or depressions. In contrast to a gear wheel molded around the component, in this way a detachable, form-locked connection can be achieved, yielding in particular the advantage that, if the gear wheel or the component, and in particular the shaft, hub, bushing or the like is damaged during operation, either only the gear wheel or only the component has to be replaced, but not both parts simultaneously. This decreases the material consumption, and moreover the costs incurred during replacement can be minimized. The same applies analogously if the second connecting section comprises a number of elevations, and the first connecting section comprises recesses corresponding to the elevations. 
         [0014]    According to a further embodiment, the gear wheel is made of a softer material than the component. When the gear wheel is made of a soft material, such as plastic, the noise development can be reduced compared to one that is made of a hard material, such as steel. Moreover, the softer material can be selected such that the loads occurring during operation can be absorbed particularly well, and the production of the gear wheel can be kept particularly simple. It may also be an obvious choice for this purpose to produce the gear wheel by way of an injection molding method and to insert mold the component during production. In this case, a separate step for producing the connection system is dispensed with, which shortens production and thus makes it more cost-effective. 
         [0015]    It is an obvious choice that the gear wheel comprises a toothed ring, in which the helical gearing is disposed, and a connecting part, which comprises the first connecting section, and that the toothed ring is made of a softer material than the connecting part. The toothed ring located on the outside surrounds the connecting part. As mentioned above, the noise development may be reduced, for example, by producing the gear wheel from a softer material than the component. In many cases, however, the axial loads mentioned at the outset result in major deformations of the gear wheel when soft materials are used, so that the softer the material, the greater is the tendency toward lift-off and skipping. In this embodiment, it is possible to produce the toothed ring of a softer material than the connecting part, so that the noise development can be minimized, without having to tolerate excessive deformation of the gear wheel. Consequently, it is possible for the connection system to absorb higher axial forces, without the noise development increasing. 
         [0016]    The component can furthermore include a hub part, which comprises the second connecting section, wherein the connecting part is disposed between the toothed ring and the hub part, and the toothed ring is made of a softer material than the connecting part ( 34 ), and the connecting part is made of a softer material than the hub part ( 36 ). In this embodiment, the connection system comprises a total of three different materials, so that it is particularly easily possible to take the respective requirements in regard to the particular parts of the gear wheel into consideration in the material selection. As was already mentioned above, the noise development may be reduced by using a particularly soft material for the toothed ring. The deformation of the gear wheel in total can be decreased by using a harder material for the connecting part compared to the toothed ring. The torque and forces transmittable by the connection system can be increased by producing the hub part from a material that is harder than the material of the connecting part. 
         [0017]    One embodiment of the disclosure relates to a device for transmitting a rotational movement, comprising a rotatable shaft, hub, bushing or the like, and a gear wheel, wherein the gear wheel and the component are connected by way of a connection system according to one of the preceding embodiments. The technical effects and advantages that can be achieved by way of the embodiment of the device as proposed correspond to those that were described for the various embodiments of the connection system. In summary, it shall be pointed out that, in contrast to splined shaft connections, for example, it is also possible to transmit axial forces between the gear wheel and the component along the entire depression. As a result of the more uniform loading thus achieved, the tilting moment, which results in the above-mentioned failure occurrences such as lift-off and skipping, is considerably reduced, whereby the risk of a failure of the connection system decreases. 
         [0018]    A further embodiment of the disclosure relates to an electrical steering device for a motor vehicle, comprising a device according to the above-described embodiment. The technical effects and advantages that can be achieved by way of the design of the electrical steering device as proposed correspond to those that were described for the various embodiments of the connection system. A further embodiment of the disclosure moreover relates to the use of a connection system according to one of the above-described embodiments for steering devices, and in particular for electrical steering devices, of motor vehicles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Exemplary embodiments of the disclosure will be described in more detail hereafter with reference to the accompanying drawings. In the drawings: 
           [0020]      FIG. 1  shows a first exemplary embodiment of a device according to the disclosure for transmitting a rotational movement, comprising a component and a gear wheel; 
           [0021]      FIG. 2 a   ) shows a developed view of a second connecting section of the component shown in  FIG. 1 ; 
           [0022]      FIG. 2 b   ) shows a developed view of the gear wheel shown in  FIG. 1 ; 
           [0023]      FIG. 3  shows a second exemplary embodiment of a device according to the disclosure for transmitting a rotational movement, comprising a component and a gear wheel; 
           [0024]      FIG. 4  shows a third exemplary embodiment of a device according to the disclosure for transmitting a rotational movement, comprising a component and a gear wheel; 
           [0025]      FIG. 5  shows a fourth exemplary embodiment of a device according to the disclosure for transmitting a rotational movement, comprising a component and a gear wheel; 
           [0026]      FIG. 6 a   ) shows a developed view of the second connecting section of the component shown in  FIG. 5 ; and 
           [0027]      FIG. 6 b   ) shows a developed view of the gear wheel shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows a first exemplary embodiment of a device  10   1  for transmitting a rotational movement based on a schematic sectional illustration. The device  10   1  comprises a component  12 , for example a shaft, a hub or a bushing, which can be rotated about a rotational axis T. In the illustrated example, the component  12  shall be a shaft. Furthermore, the device  10   1  comprises a gear wheel  14 , which is non-rotatably connected to the component  12  by way of a connection system  16 , so that torque can be transmitted from the component  12  to the gear wheel  14 . In the illustrated embodiment, the connection system  16  is designed as a shaft/hub connection. 
         [0029]    So as to form the connection system  16 , the gear wheel  14  comprises a first connecting section  18 , and the component  12  comprises a second connecting section  20 . The second connecting section  20  has a smaller diameter than the remaining component  12 , whereby a projection  22  is created by way of which the first connecting section  18 , and consequently the gear wheel  14 , is axially positioned with respect to the component  12 . The gear wheel  14  comprises a number of teeth  24 , which form helical gearing  26 . For the sake of illustration, the teeth  24  and the helical gearing  26  are symbolically identified by a hatched area. 
         [0030]      FIG. 2 a   ) shows a developed view of the second connecting section  20  of the component  12  shown in  FIG. 1 , and  FIG. 2 b   ) shows a developed view of the gear wheel  14 . In both instances, the view is onto the outer circumference of the second connecting section  20  of the component  12  or of the gear wheel  14 . The teeth  24  of the helical gearing  26  of the gear wheel  14  form a tooth helix angle β with the rotational axis T. A number of depressions  28  or elevations  28  are disposed on the second connecting section  20  of the component  12 , which form a connection helix angle α with the rotational axis T. In the illustrated example, the connection helix angle α and the tooth helix angle β have the same size. According to the disclosure, the connection helix angle α is either equally as large as the tooth helix angle β or smaller than the tooth helix angle β, but larger than 0°. Both the tooth helix angle β and the connection helix angle α have the same sense of rotation R with respect to the rotational axis T. 
         [0031]    Not shown is one embodiment in which the depressions  28  are designed so as to form a stop for the component  12 , whereby the projection  22  is not required. 
         [0032]    The gear wheel  14  shown in  FIG. 1  is made completely of one material, for example steel or plastic. Regardless of whether the gear wheel  14  is made of steel or plastic, the first connecting section  18  can comprise protrusions  30  corresponding to the depressions  28 , whereby the connection system  16  can have a form-locked and releasable design. The depressions  28  and the protrusions  30  corresponding thereto are identified by way of a hatched area for illustration purposes. In the case where the second connecting section  20  comprises a number of elevations  28 , the first connecting section  18  can comprise a number of recesses  30  corresponding thereto. In this way, a releasable form-locked connection can be provided between the gear wheel  14  and the component  12 . In the case where the gear wheel  14  is made of plastic material, the gear wheel  14  can be molded around the component  12  already during production. In this case, no connection system  16  that can be non-destructively released is created between the gear wheel  14  and the component  12 . 
         [0033]      FIG. 3  shows a second exemplary embodiment of the device  10   2  according to the disclosure for transmitting a rotational movement, likewise based on a schematic sectional illustration. The essential composition of the device  10   2  according to the second exemplary embodiment of corresponds to that of the first exemplary embodiment  10   1 . In this exemplary embodiment, however, the gear wheel  14  comprises a separate toothed ring  32 , in which the helical gearing  26  is disposed. Furthermore, the gear wheel  14  comprises a connecting part  34 , which forms the first connecting section  18 . The toothed ring  32  is made of a softer material than the connecting part  34 . 
         [0034]      FIG. 4  shows a third exemplary embodiment of the device  10   3  according to the disclosure, again based on a schematic sectional illustration. Once again, the essential composition of the device  10   1  is similar to that of the above-shown exemplary embodiments. As in the second exemplary embodiment, the gear wheel  14  comprises the toothed ring  32  and the connecting part  34 . In addition to the shaft, the component  12  also comprises a hub part  36 , which forms the first connecting section  18 . The toothed ring  32  is made of a soft material, while the connecting part  34  is made of a harder material in relation to the material of the toothed ring  32 , and the hub part  36  is made of the hardest material. In the exemplary embodiment shown in  FIG. 4 , the hub part  36  is made of steel and connected to the shaft  12  by way of a known press fit connection. The hub part  36  can serve as an adapter between the gear wheel  14  and the shaft of the component  12 , for example so as to compensate for differences in diameter. 
         [0035]    Both in the second and in the third exemplary embodiment, it is an obvious choice to produce the gear wheel  14  from plastic material, wherein the differing materials are selected such that the functions of the toothed ring  32  of the connecting part  34  and of the hub part  36  can be optimally satisfied. The component  12 , which is implemented in particular as a shaft, hub or bushing, is usually made of steel, but may also be made of plastic material. It may be an obvious choice to produce the hub part  36  and the shaft or other elements of the component  12  from the same material, making joining the same simpler. If the shaft and the hub part  36  are made of the same steel, they may be welded to one another or joined to one another by way of a press fit. 
         [0036]    In the developed view, the second connecting sections  20  correspond to the component  12  shown in  FIG. 3 , or the hub part  36  shown in  FIG. 4 , and the gear wheels  14  shown in  FIGS. 3 and 4  correspond to  FIGS. 2 a   ) and  2   b ). In particular, both the connection helix angle α and the tooth helix angle β have the same sense of rotation R with respect to the rotational axis T. 
         [0037]      FIG. 5  shows a fourth exemplary embodiment of the device  10   4  according to the disclosure, again based on a schematic sectional illustration. The fourth exemplary embodiment essentially corresponds to the third exemplary embodiment shown in  FIG. 4 , however the tooth helix angle β and the connection helix angle α have a different, opposite sense of rotation with respect to the rotational axis T, which is also symbolized by the hatched areas used for the helical gearing  26  and depressions  28  or elevations  28 , which do not run parallel, but perpendicularly to one another. 
         [0038]      FIG. 6 a   ) shows a developed view of the second connecting section  20  of the hub part  36  shown in  FIG. 5 , and  FIG. 5 b   ) shows a developed view of the gear wheel  14  shown in  FIG. 5 , each being shown in accordance with the fourth exemplary embodiment of the device  10   4  according to the disclosure. The selected representation corresponds to that from  FIGS. 2 a   ) and  2   b ). In contrast to the exemplary embodiments, which relate to  FIGS. 2 a   ) and  2   b ), the tooth helix angle β and the connection helix angle α according to the fourth exemplary embodiment  10   4  have a different, opposite sense of rotation R with respect to the rotational axis T. 
         [0039]    Hereafter, it is deduced why the connection helix angle α is to be selected smaller than, or at most equal to, the tooth helix angle β. The helical gearing  26  allows not only tangentially, but also axially acting forces and torque to be transmitted. The resulting axial forces F aS  acting on the helical gearing  26  (running gear teeth) act counter to the axial forces F aV  (synchronization teeth) acting between the two connecting sections  18 ,  20 . It is to be achieved that the axial forces acting on the helical gearing, in terms of magnitude, are not greater than the forces acting between the two connecting sections  18 ,  20 . The relationship of the axial forces F aS  and F aV  can be expressed by the following formula: 
         [0000]        F   aV   =F   tV  tan α≦ F   aS  
 
         [0040]    F aV : axial force acting between the connecting sections  18 ,  20   
         [0041]    F tV : tangential force acting between the connecting sections  18 ,  20   
         [0042]    F aS : axial force acting on the helical gearing  26   
         [0043]    The tangential force F tV  is calculated from the torque to be transmitted and the diameter on which the force engages: 
         [0000]        F   t   v= 2 M   z   /D   v    
         [0044]    M z : moment acting on the gear wheel 
         [0045]    D v : diameter or pitch circle of the connecting sections  18 ,  20   
         [0046]    D v : diameter or pitch circle of the helical gearing  26   
         [0047]    This reduces deformation and increases the performance capability of the gear wheel  14 . Ideally, 
         [0000]    
       
      
       F 
       aV 
       =F 
       aS  
      
     
         [0048]    Since the moment acting on the helical gearing  26  is identical to the supporting torque in the connecting sections  18 ,  20 , the ideal tooth helix angle β is derived as follows: 
         [0000]      tan β=tan α D   v   /D   s  
 
         [0049]    Since D v /D s  is always &lt;1, the connection helix angle α is to be selected smaller than the tooth helix angle β or at most approximately the same. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 List of Reference Numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10, 10 1 , 10 3   
                 device 
               
               
                   
                 12 
                 component 
               
               
                   
                 14 
                 gear wheel 
               
               
                   
                 16 
                 connection system 
               
               
                   
                 18 
                 first connecting section 
               
               
                   
                 20 
                 second connecting section 
               
               
                   
                 22 
                 projection 
               
               
                   
                 24 
                 tooth 
               
               
                   
                 26 
                 helical gearing 
               
               
                   
                 28 
                 depression, elevation 
               
               
                   
                 30 
                 protrusion, recess 
               
               
                   
                 32 
                 toothed ring 
               
               
                   
                 34 
                 connecting part 
               
               
                   
                 36 
                 hub part 
               
               
                   
                 R 
                 sense of rotation 
               
               
                   
                 T 
                 rotational axis 
               
               
                   
                 α 
                 connection helix angle 
               
               
                   
                 β 
                 tooth helix angle