Abstract:
A dog clutch operative to provide shiftably connection. A first clutch element includes a plurality of dogs selectively engagable with a plurality of counterdogs coupled to the second clutch element for selectively coupling primary and secondary rotatable parts. The second clutch element further includes a bush coupled to the secondary rotatable part and an intermediate part containing the counterdogs. The intermediate part can be selectively coupled to the bush for selectively coupling the second clutch element and the secondary part.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a clutch for the shiftable connection of a primary part to a secondary part, said clutch comprising a dog clutch consisting of a first and of a second clutch half. 
   Positive clutches of this type are used in the drive train of motor vehicles for the cutting in of drive axles or for the blocking of differential gears. Engagement and disengagement take place by means of the axial displacement of one of the clutch parts, the dogs or teeth provided on their end faces being brought into engagement or out of engagement. Thus, with a minimal installation space, a very high torque can be transmitted positively. The displacement of one clutch part may take place by means of an actuator acting in both directions or, as described in DE-C-4113 128, by means of an actuator acting in only one direction. This requires teeth or dogs with undercut flanks and with a spring acting in the opening direction between the two clutch halves, so that the clutch opens automatically when the torque lapses. 
   The term “undercut flanks” is to be understood to mean that the dogs of the clutch have, in circumferential section, essentially the form of a trapezium, of which the shorter of the two parallel sides faces away from the counterdogs. 
   During disengagement and engagement, frictional forces act between the flanks of the clutch dogs, and these frictional forces delay disengagement and have to be overcome by the actuator. If the clutch is designed in such a way that it is disengaged automatically when the torque lapses, this then also means that it cannot be disengaged under load. Both must be avoided when a rapid opening of the clutch in the drive train of a motor vehicle is required, for example for cooperation with electronic action on the brake system (for example, ABS). 
   The object of the invention is to ensure a rapid opening of a generic clutch even under load. 
   SUMMARY OF THE INVENTION 
   According to the invention, this is achieved in that, between the primary part and the secondary part, an intermediate part is provided, which has the counterdogs on its side facing the dogs and, on its side facing away from the dogs, can be positively connected fixedly in terms of rotation to the secondary part via radially displaceable elements (sliding blocks or sliding pieces), the position of these being determined by the position of a shift sleeve. 
   Thus, the frontal-dog clutch is followed in series by a further positive clutch. The intermediate part belongs with one side to one and the other side to the further positive clutch. However, in the latter, the force-transmitting teeth are not oriented radially, but axially. Thus, high circumferential forces can be transmitted, without an axial force component occurring in this case. The reaction forces of the sliding pieces distributed uniformly on the circumference of the clutch act radially, of course, and therefore cancel one another. The deflecting coupling toothing can therefore be designed with a very large deflection angle, this initially being conducive to a rapid release of the further clutch and consequently ensuring a rapid opening of the dog clutch. Moreover, the centrifugal force can thus also be incorporated into or taken into account in the mode of action. Engagement and disengagement accordingly take place in each case in two phases. 
   Various embodiments are to be preferred, depending on requirements and on the installation situation. In a first embodiment, the radially displaceable sliding pieces are guided in the intermediate part and can be connected fixedly in terms of rotation via a deflecting coupling toothing to a bush displaceable on the secondary part. For actuation, the shift sleeve has a conical inner face which cooperates with the sliding pieces and which holds these inward on to the deflecting coupling toothing. 
   The sliding pieces may also be guided in a bush connected fixedly in terms of rotation to the secondary part and be connectable fixedly in terms of rotation to the intermediate part via a deflecting coupling toothing. In a further embodiment, the shift sleeve has a conical outer face which cooperates with the sliding pieces and which moves and holds these outward on to the deflecting coupling toothing, and the bush is displaceable. In yet a further embodiment, the shift sleeve has a conical inner face which cooperates with the sliding pieces and which moves and holds these inward on to the deflecting coupling toothing. 
   In further embodiments, the sliding pieces have a deflecting coupling toothing on their side nearer to the axis of rotation and, on their side further from the axis of rotation, cooperate with a conical inner face of a shift sleeve. Thus, at higher rotational speeds, the centrifugal force ensures a particularly rapid opening of the further positive clutch. 
   In a development of the invention, the sliding pieces are sliding blocks which are guided between parallel radial faces and which engage with a tooth or a plurality of teeth into the countertoothing, and a common spring is looped around the sliding pieces. 
   In a particularly advantageous development of the invention, the dogs and counterdogs have undercut flanks, and, between the primary part and the intermediate part, a spring is provided which endeavors to push these apart from one another. As a result, when the torque lapses, the clutch opens automatically, without an actuator having to be activated, and therefore virtually without delay. Even during disengagement under load, the clutch opens instantaneously as soon as the further clutch is opened. 
   Finally, the invention also relates to a differential gear having a dog clutch as a differential lock, in which the primary part of the dog clutch is the differential cage and the secondary part is one of the output shafts. Thus, while having the smallest possible installation space, an arrangement satisfying all the requirements to be met by a differential lock is provided. Both an axle differential and a longitudinal differential may be concerned in this context. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described and explained below by means of depictions of various embodiments in which: 
       FIG. 1  illustrates a longitudinal section through a first embodiment in a first position, 
       FIG. 2  illustrates the same as  FIG. 1  in a second position, 
       FIG. 3  illustrates an end face view according to III in  FIG. 1 , 
       FIG. 4  illustrates the same as  FIG. 1  in a third position, 
       FIG. 5  illustrates an end face view according to V in  FIG. 4 , 
       FIG. 6  illustrates a longitudinal section through a second embodiment in a first position, 
       FIG. 7  illustrates the same as  FIG. 6  in a second position, 
       FIG. 8  illustrates an end face view according to VIII in  FIG. 7 , 
       FIG. 9  illustrates the same as  FIG. 6  in a third position, 
       FIG. 10  illustrates an end face view according to X in  FIG. 9 , 
       FIG. 11  illustrates a longitudinal section through a third embodiment, 
       FIG. 12  illustrates a section according to XII in  FIG. 11 . 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , the housing of a differential gear is indicated only partially by broken lines and is designated by  1 . A differential gear, designated as a whole by  3 , is mounted in said housing in rolling bearings  2  (only one can be seen). The differential gear consists of the rotatably mounted differential cage  4  and of a shaft  5  to the differential pinions  6  and output pinions  7 , of which only that connected to an output shaft  8  via a first spline toothing  9  can be seen. The differential gear  3  can be blocked by means of a clutch unit designated as a whole by  10 . In the blocked state, the differential cage  4  is connected fixedly in terms of rotation to the output shaft  8 . 
   The clutch unit  10  consists of a first clutch half  11  with dogs  12 , of a second clutch half  13  with counterdogs  15 , of an intermediate part  14 , of sliding pieces  17  and of a bush  18  connected fixedly in terms of rotation to the output shaft  8 . The first clutch half  11  is formed on the differential cage  4  and the second clutch half  13  on the intermediate part  14 . The dogs  12  and the counterdogs  15  are frontal dogs, that is to say lie approximately in an axially normal plane or in the outer surface area of a very obtuse cone and, in the exemplary embodiment shown, are provided with undercut flanks. That is to say, the torque-transmitting flanks of the dogs are inclined in such a way that the dogs are trapezoidal in circumferential section and, when a torque is transmitted, generate axial force components which endeavor to bring the first clutch half  11  and the second clutch half  3  nearer to one another. Within the scope of the invention, however, the dogs may also be rectangular in circumferential section. Thus, the primary part of the clutch unit consists of the differential cage and of the first clutch half  11  with the dogs  12 , and the secondary part consists of the output shaft  8 . 
   The intermediate part  14  has the counterdogs  15  on its side facing the first clutch half  11  and, on the side facing away from the first clutch half, a number of radial guides  16  distributed uniformly over the circumference and having parallel walls, between which a sliding piece is in each case guided displaceably in the radial direction. The bush  18  is connected to the output shaft  8  via a second spline toothing  19  fixedly in terms of rotation, but displaceably in the longitudinal direction. Torque transmission from the intermediate part  14  to the bush  18  takes place via the sliding pieces  17  having a conical face  17 ′. These are taken up by the intermediate part  14  via the guides  16  and, in the engaged position, are connected to the bush via a deflecting coupling toothing oriented axially. For this purpose, the bush  18  has a coupling toothing  20  running all round in the manner of a gearwheel, and the sliding pieces  17  have only a few coupling teeth  21 , three of these in  FIG. 3 . In an extreme case, a single tooth is sufficient. 
   The whole of the sliding pieces  17  distributed uniformly over the circumference is held together and pressed outward by a looping spring  22  which is a closed bent ring consisting of a spring wire. A shift sleeve  23  is displaceable in the axial direction on the bush  18 . For this purpose, said shift sleeve has, for example, a peripheral groove  24  for the engagement of a shift fork or other actuator, not illustrated. The shift sleeve  23  has a part  26  which diverges in a bell-shaped manner and the inner face  25  of which is designed conically. The inner face  25  cooperates with the sliding pieces  17 . For the engagement of the sliding pieces  17 , the shift sleeve  23  is displaced in the axial direction in such a way that the conical inner face  25  pushes the sliding pieces  17  inward, with the result that their teeth  21  are pressed into the coupling toothing  20  of the bush. 
   Between the output pinion  7  and the intermediate part  14  is arranged a compression spring  27  which endeavors to push the intermediate part  14  away from the first clutch half  11 . The bush  18  is limited in its axial displaceability by a stop shoulder  28  and a stop  29 . 
   As regards the mode of operation: in the position of  FIG. 1 , the clutch is engaged and the differential gear  3  is therefore blocked. The sliding pieces  17  are held by the conical inner face  25  of the shift sleeve  23  in their inner position, in which the deflecting coupling toothing  21  of the sliding pieces is in engagement with the coupling toothing  20  of the bush  18 . The radially directed deflection forces occurring during the transmission of a torque are absorbed by the bell-shaped part  26  of the shift sleeve  23 . The conical inner face  25  even has a cylindrical step, against which the sliding pieces  17  bear in order to relieve the actuator of axial holding forces. 
   When the clutch device  10  is to be disengaged, a first step leads to the position of  FIG. 2 and 3 . This is reached by means of the displacement of the shift sleeve  23  to the left, with the result that the conical inner face  25  of the latter releases a larger diameter and the sliding pieces  17  are forced outward by the force of the looping spring  22 , by the radially outward-acting force exerted by the deflecting coupling toothing  20 ,  21  and, where appropriate, also by the centrifugal force, so that the teeth  21  of the sliding pieces  17  come out of engagement with the deflecting coupling toothing  20  of the bush  18 . As a result, the intermediate part  14  becomes load-free, and, as a result of further movement of the shift sleeve  23  to the left, can be drawn with its counterdogs  15  out of the dogs  12  of the first clutch half  11 ; or the compression spring  27  present in the exemplary embodiment shown pushes the intermediate part  14  out of engagement. This leads to the position depicted in  FIGS. 4 and 5 . 
   The position of  FIG. 4  is reached, in a second phase of movement, in that the spring  27  pushes the intermediate part  14  together with the sliding pieces  17  and with the bush  18  to the right. Since the shift sleeve  23  has not in this case been moved, the sliding pieces  17  slide inward with their chamfered conical faces  17  on the conical inner face  25  of the shift sleeve  23 , with the result that the deflecting coupling toothing  20 ,  21  is brought into engagement again. The clutch can be brought into engagement again from this position by means of the displacement of the shift sleeve  23  to the right. 
   In the embodiment of  FIG. 6 , identical parts bear the same reference symbols and similar parts bear reference symbols increased by 100. It differs from the preceding embodiment in that the sliding pieces  117  are not guided radially displaceably in the intermediate part  114 , but, instead, in the bush  118 , and in that the sliding pieces  17  have their deflecting coupling toothing  121  on the outside, where it cooperates with the deflecting coupling toothing  120  which is designed, here, as an inner toothing on the intermediate part  114 . For actuation, the sliding pieces  117  have on their inside a conical face  117 ′ which cooperates with a conical face  125  of the shift sleeve  123 . Here, the conical face  125  is on the outside of the shift sleeve  123 . The phases of movement during engagement and disengagement, illustrated in  FIGS. 7 ,  8  and  9 ,  10  do not differ from those of the preceding exemplary embodiment. 
   In the embodiment of  FIG. 11 , the specific parts are given reference symbols increased by 200. This differs from that of  FIG. 1  in that the bush  218  is connected to the output shaft  8  not only fixedly in terms of rotation, but also fixedly in terms of sliding, and in that the deflecting coupling toothing  221  of the intermediate part  214  is so much longer than that of the sliding pieces  217  that axial displacement is possible between these. Here, too, the shift sleeve  223  can cooperate with the intermediate part  214 . Its cooperation with the sliding pieces  17  is the same as in  FIG. 1 .