Abstract:
An arrangement for shifting a gearbox. The arrangement having first and second transmission components ( 14 ) and an axially movable shifting sleeve ( 17 ) such that the shifting sleeve ( 17 ) and the second transmission component ( 14 ) each have respective drive teeth ( 14   a,    17   a ) that can be brought into engagement with one another. The drive teeth are in the form of beveled teeth ( 14   a,    17   a ).

Description:
[0001]    This application claims priority from German patent application serial no. 10 2011 075 775.9 filed May 13, 2011. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns an arrangement for shifting a gearbox. 
       BACKGROUND OF THE INVENTION 
       [0003]    The invention starts from a shifting arrangement of the type known as a claw shifting element. By means of this, a first transmission component is connected by an axially displaceable shifting or sliding sleeve to a second transmission component. The shifting sleeve and the transmission component to be connected have drive or shifting teeth, namely outer teeth and inner teeth, which by being pushed one inside the other form a rotationally fixed connection so that a torque can be transmitted or supported. The shifting sleeve must be engaged when the rotational speed difference is minimal, preferably zero. Due to the steep rotational speed gradient only a short amount of time is available for this. Thus, with conventional drive or claw teeth a relatively large tooth flank clearance must be provided to enable the claws to engage within the given time window. However, too large a tooth flank clearance is undesirable. 
         [0004]    Drive teeth as used in known claw shifting elements have a relatively simple tooth profile, for example a trapezoidal or triangular profile. In the case of running gears in which the gearwheels mesh with one another by a rolling action, other tooth profiles such as involute profiles are used. The known running gears also have beveled teeth, i.e. teeth for conical spur gears whose rotational axes intersect, cross, or can also be parallel to one another. 
         [0005]    From DE 103 06 935 A1 by the present applicant a spur gear stage with beveled gearwheels is known, which have equal-sized but oppositely directed cone angles. To reduce the rotational flank clearance the beveled gearwheels are adjusted in the axial direction by a temperature-dependent element. Thus, the known gearwheel transmission has beveled running gears for conical spur gearwheels with parallel axes. 
         [0006]    Beveled running gears are also known for driving so-termed lateral shafts in motor vehicle transmissions for an all-wheel drive system. From DE 10 2008 042 038 A1 by the present applicant a bevel drive with intersecting or crossing rotational axes for a drive-train of a motor vehicle is known. 
       SUMMARY OF THE INVENTION 
       [0007]    The purpose of the present invention is, with a shifting arrangement of the type described at the start, to enable a shifting process to take place even with larger rotational speed differences. 
         [0008]    According to the invention, the drive teeth are formed as beveled teeth, also called shifting teeth. According to the invention, the beveled teeth until now known only as running gearing is used as shifting teeth. Beveled teeth are involute teeth in which the profile displacement varies over the tooth width. The result is that the teeth of the shifting gears become thicker in the tooth width direction, so the flank clearance becomes smaller. At the beginning of the shifting displacement, i.e. when the sliding sleeve engages in the shifting teeth, the teeth—as viewed in the circumferential direction—are relatively narrow so the flank clearance is relatively large. In contrast, at the end of the shifting displacement the teeth are relatively thick, resulting in a small flank clearance. Thus, the flank clearance decreases along the direction of the shifting displacement. This has the advantage that engagement and disengagement are possible even with higher rotational speed differences. Bevel gears have the advantage of being produced by continuous machining, which therefore also brings cost advantages compared with known drive gears. 
         [0009]    In a preferred embodiment the beveled teeth are in the form of straight teeth, i.e. without any obliqueness. The straight teeth enable the shifting gears to be symmetrical, i.e. to have a symmetrical tooth profile. 
         [0010]    In another preferred embodiment the beveled teeth are oblique teeth with an angle of inclination β which is within a preferred range larger that 0° and smaller than 3°, particularly preferably 2°. The oblique teeth make it possible to have asymmetrical shifting gears, i.e. with an asymmetrical tooth profile. 
         [0011]    In a further preferred embodiment the tooth flanks of the beveled teeth have flank angles of inclination β L  and β R  which are equal for both flanks in the case of straight teeth. Thus, as viewed in the circumferential direction the thickness of the tooth profile increases symmetrically in the tooth width direction. 
         [0012]    According to another preferred embodiment only one tooth flank of a tooth profile has a flank angle of inclination &gt;0°, so that the tooth profile is asymmetrical. Preferably, the one tooth flank has a flank angle of inclination of about 4° and the other tooth flank a flank angle of inclination of 0°. 
         [0013]    In a further preferred embodiment the shifting sleeve has inner shifting teeth, also called claws, whereas the second transmission component has outer shifting teeth. Thus, by axial displacement, the claws can be pushed over the shifting teeth of the second transmission component and the shifting process is carried out thereby. In this case the flank clearance is at a maximum at the beginning of the shifting displacement and at a minimum at the end of the shifting displacement. 
         [0014]    According to another preferred embodiment the second transmission component is an element of a planetary gearset. Preferably the element is the sun gear, but it can also be the carrier or the ring gear of the gearset. In this way the planetary gearset element concerned can be connected by the shifting sleeve in a rotationally fixed manner to the first transmission component. 
         [0015]    In a further preferred embodiment the shifting sleeve is supported in a rotationally fixed manner, for example on a transmission housing. In this way a planetary gearset element can be braked. 
         [0016]    In another preferred embodiment the transmission is in the form of an automatic variable-speed transmission of a motor vehicle. Compared with conventional automatic transmissions this means that the known shifting elements in the form of disk clutches and/or brakes can be omitted in favor of shifting elements with beveled shifting teeth. This saves fitting space, weight and costs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Example embodiments of the invention are illustrated in the drawing and described in more detail below, whereby further characteristics and/or advantages can emerge from the description and/or the drawings, which show: 
           [0018]      FIG. 1 : A conical spur gear with beveled teeth, 
           [0019]      FIG. 1   a : A single tooth, shown in perspective, 
           [0020]      FIG. 1   b : Tooth profile of the beveled teeth shown in  FIG. 1 , 
           [0021]      FIGS. 2   a ,  2   b : Radial sections through shifting teeth according to the invention, at different shifting displacements, 
           [0022]      FIGS. 3   a ,  3   b : Symmetrical shifting teeth in the form of straight teeth with equal flank angles of inclination, 
           [0023]      FIGS. 4   a ,  4   b : Asymmetrical shifting teeth in the form of oblique teeth with different flank angles of inclination, and 
           [0024]      FIGS. 5 ,  6 : A shifting element with shifting teeth according to the invention for a planetary gearset, in different shifting positions. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]      FIG. 1  shows a conical spur gear  1  with beveled teeth  1   a  and a tooth width  1   b , viewed in semi-section. The beveled teeth  1   a  have a profile displacement that varies over the tooth width b. This is indicated in  FIG. 1   b  by different tooth profiles  2 ,  3 ,  4  which correspond to the radial section planes at the points of the beveled teeth  1   a  identified by the arrows A, B, C. From this representation it can be seen that the tooth profile becomes thicker from the front face (arrow A) to the rear face (arrow C), the tooth thickness being measured in the circumferential direction. 
         [0026]      FIG. 1   a  shows a perspective view of a single tooth  5  of the beveled teeth  1   a . The front end of the tooth  5  is called the toe  5   a  and the rear end of the tooth  5  is called the heel  5   b . The result of the thickness variation is a tooth flank angle of inclination, as explained in more detail below. 
         [0027]      FIGS. 2   a ,  2   b  show shifting teeth for a transmission component  6  and a sliding or shifting sleeve  7 . The transmission component  6 , which for example can be in the form of the sun gear of a planetary gearset (see  FIGS. 5 ,  6 ), has outer teeth  6   a  whereas the shifting sleeve  7  has inner teeth  7   a , which are in tooth engagement with one another and can be displaced axially, i.e. in the shifting direction. The two sets of teeth  6   a ,  7   a  are in the form of beveled teeth with flank angles of inclination that extend in opposite directions.  FIG. 2   a  shows the shifting teeth  6   a ,  7   a  at a shifting displacement point that corresponds to the middle of the total shifting displacement. The flank clearance between the two sets of teeth  6   a ,  7   a  is represented by the dimension j 1 . 
         [0028]      FIG. 2   b  shows the same shifting teeth  6   a ,  7   a  at a different shifting, namely two millimetres before the position shown in  FIG. 2   a . In this case the flank clearance is denoted j 2  and it can be seen that j 2  is larger than j 1 . Owing to the chosen flank obliqueness angle of the beveled teeth the flank clearance varies as a function of the shifting displacement (see also  FIGS. 5 ,  6 ), being relatively large at the beginning of the shifting displacement and relatively small at the end of the shifting displacement. This enables engagement and disengagement to take place even at higher rotational speed differences between the transmission component  6  and the shifting sleeve  7 . Furthermore, a larger flank angle of inclination also assists disengagement, i.e. the release of the shifting sleeve  7 . 
         [0029]      FIGS. 3   a  and  3   b  show an example embodiment of the invention for shifting teeth  8   a ,  9   a  according to the invention, which are in the form of straight teeth with a symmetrical tooth profile. The outer teeth  8   a  of the transmission component  8  have flank angles of inclination denoted β L  and β R . From  FIG. 3   b  in particular it can be seen that the flank angles of inclination β L  and β R  of the two tooth flanks are equal. In a preferred example embodiment they are both equal to 2°. The flank angles of inclination β L  and β R  of the outer teeth  8   a  of the transmission component  8  and of the inner teeth  9   a  of the sliding sleeve  9  extend in opposite directions. 
         [0030]      FIGS. 4   a  and  4   b  show a further example embodiment of the invention with asymmetrical shifting teeth  10   a ,  11   a  of the transmission component  10  and the shifting sleeve  11 . The shifting teeth  10   a  have an angle of inclination β, preferably 2°. The tooth flanks have on one side a flank angle of inclination β R  of 0° and on the other side a flank angle of inclination β L  preferably of 4°. In this case the flank angle of inclination β R  of 0° is on the thrust flank whereas the flank angle of inclination β L  or 4° is on the trailing side of the shifting teeth. 
         [0031]      FIG. 5  illustrates a section of an automatic variable-speed transmission of a motor vehicle, showing a planetary gearset  12  and a bearing support  13  fixed to the housing. The planetary gearset  12  has a sun gear  14  that meshes with a planetary gearwheel  15  which rolls around a ring gear  16 . On the sun gear  14  are arranged shifting teeth  14   a . In the bearing support  13  is arranged a sliding sleeve  17 , also called a shifting sleeve  17 , which is connected in a rotationally fixed manner by means of drive teeth  18  to the bearing support  13 , i.e. to a transmission housing (not shown). The shifting sleeve  17  is actuated hydraulically or pneumatically and has inner teeth in the form of beveled shifting teeth  17   a . The shifting teeth  17   a  are generally referred to as claw teeth or claws and, by displacing the shifting sleeve  17  axially, they can be brought into or out of engagement with the shifting teeth  14   a  of the sun gear  14 . In the position shown in  FIG. 5  the shifting teeth  17   a  are in their open, i.e. disengaged position so there is no rotary connection between the sun gear  14  and the shifting sleeve  17 . 
         [0032]      FIG. 6  shows the shifting sleeve  17  in its engaged position, i.e. with the shifting teeth  17   a  fully engaged with the shifting teeth  14   a  of the sun gear  14 . Thus, the shifting sleeve  17  produces a rotationally fixed connection between the sun gear  14  and the bearing support  13  fixed to the housing, i.e. the sun gear  14  is braked and supported relative to the transmission housing. The shifting teeth  14   a ,  17   a  correspond to the above-described beveled teeth according to the invention with flank angles of inclination β L , β R , with a taper of about 2°. By an appropriate choice of the flank angles of inclination β L , β R  the flank clearance along the shifting displacement of the shifting sleeve  17  can be adjusted optimally, and at the same time the disengagement of the shifting teeth is assisted. 
       INDEXES 
       [0000]    
       
           1  Conical spur gear 
           1   a  Beveled teeth 
           2  Tooth profile 
           3  Tooth profile 
           4  Tooth profile 
           5  Tooth 
           5   a  Toe 
           5   b  Heel 
           6  Transmission component 
           6   a  Outer teeth 
           7  Shifting sleeve 
           7   a  Inner teeth 
           8  Transmission component 
           8   a  Outer teeth 
           9  Shifting sleeve 
           9   a  Inner teeth 
           10  Transmission component 
           10   a  Outer teeth 
           11  Shifting sleeve 
           11   a  Inner teeth 
           12  Planetary gearset 
           13  Bearing support 
           14  Sun gear 
           14   a  Shifting teeth 
           15  Planetary gearwheel 
           16  Ring gear 
           17  Shifting sleeve 
           17   a  Shifting teeth 
           18  Drive teeth 
         b Tooth width 
         β Angle of inclination 
         β L  Flank angle of inclination of the left flank 
         β R  Flank angle of inclination of the right flank 
         j 1  Tooth flank clearance 
         j 2  Tooth flank clearance 
         A Arrow (front side) 
         B Arrow (middle) 
         C Arrow (rear side)