Abstract:
A transmission includes a first shaft connected to a differential transmission by a differential carrier. The differential transmission includes a first and a second differential shaft, wherein the second differential shaft is an output shaft. A shift element that includes a sliding element is used to couple the first differential shaft to the output shaft. The sliding element is connected in a torque-proof manner to the differential carrier and is axially movable relative to the differential carrier by a spring to produce a positive-locking connection between the first differential shaft and the output shaft. The first differential shaft has a movable area that moves axially with the shift element into a positive-locking connection with an area of the output shaft. The movable area of the first differential shaft is rotatable relative to the sliding element.

Description:
The invention relates to a transmission device and a vehicle drive train with a differential transmission device, which is in operative connection with a first shaft in the area of a differential cage, and with two differential shafts, of which at least one is able to be coupled with an output shaft through a shifting element that is able to be actuated through an actuator device. 
     BACKGROUND 
     A vehicle drive train with two drivable vehicle axles is known from WO 2009/127324 A2. The vehicle drive train comprises a transmission, coupled with a drive motor and/or a drive unit and designed as a gear wheel shift transmission, with several shiftable transmission stages, along with a first differential gear coupled with the gear wheel shift transmission, which is coupled with the wheels of a first drivable vehicle axle through two first drive shafts. The first drivable vehicle axle is constantly driven, and represents a driven front vehicle axle. Furthermore, a transfer gearbox and/or transfer device coupled with the first differential gear is provided, which is coupled through a connection shaft with a second differential gear, which is in turn in operative connection with the wheels of a second drivable vehicle axle through additional drive shafts. The operative connection between the first differential gear and the transfer gearbox can be separated at the wheels of the two drivable vehicle axles by means of a shiftable clutch for the interruption of a transfer fo the driving force and the turning moment. This shiftable clutch is arranged between the first differential gear and the transfer gearbox. 
     Depending on the operating state, uncoupling the part of the vehicle drive train leading in the direction of the second drivable vehicle axle uncouples in the immediate vicinity of the gear wheel shift transmission through the actuation of the shiftable clutch. In order to minimize the friction losses of the partial drive train that is uncoupled by means of the shifting clutch and, in this shifting position, is not in operative connection with the rest of the drive train, additional clutches are provided in the area of the drive shafts of the two drivable vehicle axles. In the open operating state of the additional clutches, the non-driven partial drive train between the transfer gearbox and the additional clutches comes to a standstill. 
     Disadvantageously, when the vehicle drive train is operated during an open operating state of the two additional clutches between the halves of the shifting element of the additional clutches designed as friction-locking clutches, there are differential rotational speeds that cause unwanted drag torques and impair the efficiency of the vehicle drive train and increase the fuel consumption of a drive motor designed as an internal combustion engine. 
     Furthermore, a four-wheel drive system with a drive unit, a main transmission for displaying different transmission ratios along with a differential gear provided in the area of a first drivable vehicle axle for distributing the drive force between the two drive wheels is known from DE 40 39 392 A1. A second drivable vehicle axle is able to be brought into operative connection with the drive unit through a decoupler. The turning moment (torque) value that is able to be led through the decoupler in the direction of the second drivable vehicle axle is diverted through a bevel gearbox in a vehicle transverse direction and is able to be led through wheel couplings in the direction of the drive wheels of the second drivable vehicle axle. 
     Depending on the respective operating status of the four-wheel-drive system, the decoupler for decoupling the second drivable vehicle axle is opened. In order to reduce friction losses in the area of the bevel gearbox, wheel couplings that are additionally arranged in the area between the bevel gearbox and the drive wheels of the second drivable vehicle axle are likewise opened. In turn, differential rotational speeds present between the halves of the shifting element of the opened friction-locking wheel couplings have drag losses. 
     For the further reduction of the power losses, positive-locking shifting elements instead of friction-locking shifting elements are provided in the area of vehicle drive trains, through which the side shaft separator known from the state of the art is possible in the area of a drivable vehicle axle. Moreover, with such vehicle drive trains, the supporting connection in the open operating state of the positive-locking shifting element is separated between a differential shaft of a differential gear and the associated wheel. Thus, the shutdown of a so-called “cardan drive” with the accompanying standstill of a cardan shaft and/or a shaft connected to a transfer box with the differential gear, a set of bevel wheels on the differential gear along with a crown wheel carrier and/or a differential carrier is enabled. 
     At vehicle speeds greater than zero, in the coupled condition and/or upon a rotational speed of a crown wheel and of the differential carrier connected with it of essentially zero, there is a rotational speed compensation in the area of the differential gear. During the rotational speed compensation, the two halves of the shifting element of the open positive-locking shifting element in the area between the differential shaft and an output shaft leading in the direction of the wheel rotates with the wheel rotational speed, whereas, the halves of the shifting element circulate with the opposing direction of rotation. Thereby, during a driving operation, a control sleeve of the positive-locking shifting element coupled to one of the shafts always undergoes a rotational movement. This leads to the fact that, for the actuation of the control sleeve between an open operating state of the positive-locking shifting element and a closed operating state of the positive-locking shifting element, stationary actuator devices are exposed to a high degree of mechanical wear based on the permanently present differential rotational speed between the rotating control sleeve and the actuator device. 
     In order to design a shiftable four-wheel drive of a vehicle with a desired long service life, a correspondingly high structural expenditure is to therefore be provided in the area of one or more shiftable shifting elements and the actuator devices allocated to each of them, yet, due to reasons of installation space and costs, this is not desired. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention is subject to the task of providing a transmission device and a vehicle drive train with at least two drivable vehicle axles, which are small, cost-effective, and operable with a high degree of efficiency over a desired duration. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. In accordance with the invention, the tasks are achieved with a transmission device and a vehicle drive train with the characteristics set forth herein. 
     The transmission device in accordance with the invention is designed with a differential transmission device, which is in operative connection with a first shaft in the area of a differential carrier. Furthermore, the transmission device includes two differential shafts, of which at least one is able to be coupled with an output shaft through a shifting element actuated by an actuator device. 
     In accordance with the invention, one shifting element half of the shifting element features a sliding element that is connected in a torque-proof manner to the differential carrier and is axially movable by the actuator device with respect to the differential carrier. Through axial movement of the sliding element on the side of the actuator device, a positive-locking connection is able to be coupled and uncoupled between the differential shaft and the output shaft between an area on the component configured on the differential shaft that is axially movable together with the sliding element, the component defining the movable area is connected in a torque-proof manner to the differential shaft, and an area of the output shaft, whereas the movable area component of the differential shaft is able to be rotated in respect of the sliding element. 
     During an operating state of the transmission device in accordance with the invention in which a rotational speed of the differential carrier is essentially equal to zero, the sliding element is at a standstill, and is able to be actuated by the actuator device without wear. The actuator device is preferably stationary. This is achieved in a structurally simple manner through the rotation decoupling provided in the area between the sliding element and the area of the differential shaft that is axially movable together with the sliding element. Through the rotation decoupling, with an active side shaft separator, the specified rotational speed compensation in the area of a differential gear is possible without an undesired high degree of mechanical wear in the area of an operative connection between the actuator device and the sliding element. 
     With an embodiment of the transmission device in accordance with the invention that engages a control cam of the sliding element. The sliding element rotates with the differential carrier and shifts counter to a spring force of a spring device applying at the sliding element into an axial end position, which is equivalent to a separate operating state of the positive-locking connection. 
     The spring device shifts the sliding element for an embodiment of the transmission device in accordance with the invention that is able to be actuated with a low control and governing effort with a control element arranged outside of the control cam into a further axial end position, which is equivalent to a closed operating state of the positive-locking connection. 
     If an axial bearing device is provided between the sliding element and the movable area of the differential shaft, actuating forces introduced by the actuator device into the sliding element are transferable in a desired extent with low power losses to the movable area of the differential shaft. 
     The transmission device is characterized by a low component count, if the movable area of the differential shaft is axially movable together with the differential shaft. 
     With an alternative embodiment of the transmission device in accordance with the invention, the movable area is movably connected to the differential shaft, by which shifting forces for shifting the positive-locking connection are themselves able to be generated essentially depending on the design of the differential shaft and the differential transmission device. 
     With a transmission device in accordance with the invention that is likewise favorable for installation space, the movable area of the differential shaft at least partially overlaps the differential carrier at least in the open operating state of the positive-locking connection between the differential shaft and the output shaft in a radial direction. 
     The transmission device in accordance with the invention is also characterized by a small installation space requirement if the movable area of the differential shaft is arranged radially within the sliding element, at least in areas. 
     In order to, in a simple manner, prevent or reduce shifting noise that impairs driver comfort in the operation of the transmission device, the transmission device in accordance with the invention is, with a further embodiment, designed with a stop dampening device between the movable area of the differential shaft and the output shaft, by means of which the one actuation movement of the movable area in the direction of the further axial end position is able to be dampened upon reaching the further axial end position. 
     Thereby, the actuator device, the sliding element with the control cam and the stop dampening device can be designed in the manner described in DE 10 2012 210 298.1. 
     For the vehicle drive train in accordance with the invention with at least two drivable vehicle axles, one drive unit, one transmission for displaying multiple transmission ratios and one transfer gearbox, the transmission connects with the vehicle axle through the gearbox. The transfer gearbox is arranged in the power flow between the transmission and at least one of the vehicle axles and is connected to a differential carrier of the described transmission device in accordance with the invention provided in the area of the vehicle axle shiftable through the transfer gearbox as a transverse transfer gearbox. 
     With a vehicle drive train in accordance with the invention the rotational speed of the differential carrier of the transmission device is essentially zero through the uncoupling of the vehicle axle designed with the transmission device in accordance with the invention from the power flow of the vehicle drive train. Thus, the positive-locking connection between the differential shaft of the transmission device and the output shaft of the transmission device is shiftable with low wear, and both the transmission device and the vehicle drive train are operable with low structural expense and low required installation space for a switched-off all-wheel drive with low power losses of the vehicle drive train. 
     With an embodiment of the vehicle drive train in accordance with the invention that is favorable for installation space, the transfer gearbox is designed with a friction-locking shifting element, whereas, in an open operating state of the friction-locking shifting element of the transfer gearbox, the shiftable vehicle axle is separated from the transmission and is present in its switched-off operating state. 
     Thus shifting the switched-on vehicle axle through a corresponding control and/or governing of the transfer capacity of the friction-locking shifting element of the transfer gearbox into an operating state necessary for the all-wheel operation, which corresponds at least approximately to a synchronous operating state, the positive-locking connection between the differential shaft and the output shaft is transferable, and thus shiftable with low shifting forces. 
     Both the characteristics specified in the patent claims and the characteristics specified in the subsequent embodiments of the transmission device and the vehicle drive train in accordance with the invention are, by themselves alone or in any combination with one another, suitable for providing additional forms for the object under the invention. In terms of the additional forms of the object under the invention, the particular combinations of characteristics do not represent a limitation; rather, they are essentially solely of an exemplary nature. 
     Additional benefits and advantageous embodiments of the transmission device in accordance with the invention and/or the vehicle drive train in accordance with the invention arise from the patent claims and the embodiments described below, with reference to the drawing in terms of principle, whereas, in the description of the various embodiments, in the interests of clarity, the same reference signs are used for structurally equivalent and functionally equivalent components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is shown: 
         FIG. 1  a schematic representation of a vehicle drive train with a transmission device with a differential transmission device and with an all-wheel drive that is able to be switched on; 
         FIG. 2  an enlarged individual view of an area II more specifically described in  FIG. 1 , with a first embodiment of the transmission device, with a shiftable positive-locking shifting element in an open operating state; 
         FIG. 3  a representation corresponding to  FIG. 2  of a second embodiment of the transmission device for a positive-locking shifting element present in an open operating state; and 
         FIG. 4  the transmission device according to  FIG. 3  with an open positive-locking shifting element. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein. 
       FIG. 1  shows a vehicle drive train  1  that is operable in the manner described below, either with one drivable vehicle axle  2  or with two drivable vehicle axles  2 ,  3  in an all-wheel operating mode. A drive unit  4  and a downstream transmission  5  and/or a main transmission are, in this case, installed in the vehicle in a “front longitudinal arrangement,” for driving drive wheels and/or front wheels  2 A,  2 B of the first drivable vehicle axle  2 , which in this case represents the permanently driven primary axle of the vehicle drive train  1 . The drive power of the drive unit  4 , designed in this case as an internal combustion engine, is correspondingly modulated in the downstream main transmission  5 , and is subsequently forwarded at least partially through a cardan shaft  6  in the direction of an axle differential transmission  7  of the vehicle axle  2 . In the area of the axle differential transmission  7 , in a known manner, the turning moment applied through the cardan shaft  6  is distributed between the two front wheels  2 A and  2 B in a vehicle transverse direction. 
     In addition, the vehicle drive train  1  features a transfer gearbox  8 , in the area of which a power flow is able to be produced or interrupted, depending on the request, in the direction of the vehicle axle  3  or the rear vehicle axle, as the case may be. In this case, the secondary axle represents the rear vehicle axle and is switched on according to need through a shifting element  9 . However, there is also the option that the rear vehicle axle is the primary axle, and the front vehicle axle of the vehicle drive train  1  is the secondary axle. 
     Through the shifting element  9 , the main transmission  5  is able to be brought into operative connection with a vehicle longitudinal shaft  10 , which is connected to a transmission device  11  in the area of the vehicle axle  3 , if there is a corresponding request for displaying the all-wheel operating mode. In order to disable the all-wheel distribution operation of the vehicle drive train  1 , the power flow between the drive unit  4  and the rear vehicle axle  3  in the area of the transfer gearbox  8  is interrupted by the opening of the shifting element  9 . In order to avoid the drag torques that arise during the continuous rotation of the components of the vehicle drive train  1  arranged in the power flow between the main transmission  5  and the drive wheels  3 A and  3 B of the rear vehicle axle  3 , the vehicle longitudinal shaft  10  and the components of the transmission device  11  shown in more detail in  FIG. 2  to  FIG. 4  are brought to a standstill in the described manner. 
     If the shifting element  9  is transferred into its open operating state in order to switch off the all-wheel operating mode, a positive-locking connection is opened between a differential shaft  12  of a differential transmission device  13  of the transmission device  11 , as presented in more detail in  FIG. 2  to  FIG. 4 , and an output shaft  14  of the transmission device  11 . The differential transmission device  13  is connected in the area of a differential carrier  15  to the vehicle longitudinal shaft  10  in a known manner (e.g., via a gear tooth system). For opening and closing the positive-locking connection between the differential shaft  12  and the output shaft  14 , in this case, a positive-locking shifting element  16  is provided, which is able to be actuated through an actuator device  17 . One shifting element half  18  of the positive-locking shifting element  16  features a sliding element  19  rotatably connected to the differential carrier  15  and axially movable by the actuator device  17  with respect to the differential cage  15 . Through axial movement of the sliding element on the side of the actuator device, a positive-locking connection is coupled and uncoupled between the differential shaft  12  and the output shaft  14 , particularly between an area  20  configured on the differential shaft  12  that is axially movable with the sliding element  19  and an area  21  of the output shaft  14 . The sliding element  19  is connected in a torque-proof manner to the differential shaft  12 . In this case, the sliding element  19  is also connected in a torque-proof manner to the differential carrier  15  through a spline shaft profile, and connected in an axially movable manner to the differential carrier. In this case, the movable area  20  is coupled in a torque-proof manner with a differential shaft  12  through a spline shaft profile, and designed in a movable manner in an axial direction with respect to the differential shaft  12 . In addition, the movable area  20  of the differential shaft  12  is formed in a manner that is able to be twisted with respect to the sliding element  19 , and arranged radially within the sliding element  19 . 
     In order to actuate the positive-locking shifting element  16 , in this case, the actuator device  17  comprises a control element  23  formed longitudinally in a housing  22  and designed essentially in a pin shape, which is movable by the electromagnet  17 A of the actuator device  17  into the axial position shown in  FIG. 2 , and in this position engages in a control cam  24  of the sliding element  19  provided on the external circumference of the sliding element  19 . 
     If the control element  23  engages in the control cam  24  of the sliding element  19 , and the sliding element  19  rotates together with the differential carrier  15 , the sliding element  19  is shifted counter to a spring force of a spring device  25  applied at the sliding element  19  into the axial end position shown in  FIG. 2 . This axial end position is equivalent to an open operating state of the positive-locking connection between the differential shaft  12  and the output shaft  14 , in which the spring device  25  exists in a preloaded operating state. The spring device  25  shifts the sliding element  19  when the control element  23  is moved away from of the control cam  24  in a further axial end position, which is equivalent to a closed operating state of the positive-locking connection or of the positive-locking shifting element  16 . Both the movable area  20  of the differential shaft  12  and the area  21  of the output shaft  14  are designed in front areas turned towards one another with claws  26  or  27 , as the case may be, in the areas of which the positive-locking connection is produced between the differential shaft  12  and the output shaft  14 , if the claws  26  and  27  are located in the overlap. 
     If there is a corresponding request to close the positive-locking shifting element  16 , the pin-shaped control element  23  is led from the engagement with the control cam  24  of the sliding element  19  by switching off the power supply of the electromagnet  17 A, and the sliding element  19  is transferred, together with the movable area  20  of the differential shaft  12 , from the spring device  25  into the axial end position equivalent to the closed operating state of the positive-locking shifting element  16 . 
     While the positive-locking shifting element  16  and the friction-locking shifting element  9  are both open, the differential carrier  15  is at a standstill. At the same time, the output shaft  14  turns with the rotational speed of the connected drive wheel  3 A. During such a driving operation, the coupled state of the output shaft  14  shifts the differential compensation in the area of the differential transmission device  13 . The differential shaft  12  connected in a torque-proof manner to the movable area  20  rotates with the wheel rotational speed and in a direction opposite the direction of rotation of the output shaft  14 . The doubled wheel rotational speed is the differential rotational speed in the area of the open positive-locking shifting element  16  The movable area  20  of the differential shaft  12  is a permanently rotating coupling element, while the sliding element  19 , the actuator device  17  designed as a pin actuator, the differential cage  15 , and an open positive-locking shifting element  16  with a rotational speed equal to zero are present in the housing  40  of the transmission device  11 . 
     In this case, the movable area  20  is formed in one piece with the differential shaft  12 . Upon an axial shifting of the sliding element  19 , in order to open or close the positive-locking shifting element, the entire differential shaft  12  is displaced with respect to the differential carrier  15  and a bevel wheel  28  connected in a torque-proof manner to the differential shaft  12 . To transfer the axial forces applied at the sliding element from the sliding element  19  to the movable area  20  of the differential shaft  12  with as little loss as possible, an axial bearing device  29 , which includes two spacer disks  30 ,  31 , is provided between the sliding element  19  and the movable area  20  of the differential shaft  12 . Thereby, the spacer disk  30  is arranged between a front surface  32  of the sliding element  19  and a first front surface  33  of the movable area  20  of the differential shaft  12 , while the second spacer disk  31  is held in an axial direction between a second front surface  34  of the movable area  20  and a radial spring washer  35  mounted in an internal groove  36  of the sliding element  19 . 
     A movement of the sliding element  19  and the movable area  20  of the differential shaft  12  in the direction of the further end position, which is equivalent to the closed operating state of the positive-locking shifting element  16 , is able to be braked in a damping manner in the area of a stop damping device  37 . In this case, the stop damping device  37  includes a damper element  38  designed in rubber-like form, which is spring-loaded through a spring device  39  at the output shaft  14 . 
       FIG. 3  and  FIG. 4  show a second embodiment of the transmission device  11 , which is essentially distinguished from the embodiment of the transmission device  11  shown in  FIG. 2  in that the movable area  20  of the differential shaft  12  is designed as a separate component, which is connected in a torque-proof manner to the differential shaft  12  and is axially movable with respect to the differential shaft  12  that is designed to be axially non-movable. 
     In the design of the transmission device  11  according to  FIG. 3  and  FIG. 4 , the movable area  20  of the differential shaft  12  at least partially overlaps the differential carrier  15  in a radial direction in an axial position equivalent to the open operating state of the positive-locking shifting element  16 , by which the transmission device  11  is designed in a vehicle transverse direction with a small installation space requirement. 
     For the design of the transmission device  11  according to  FIG. 2  and for the second embodiment of the transmission device  11  according to  FIG. 3  and  FIG. 4  the two-piece design of the first shifting element half  18  of the positive-locking shifting element  16  in the open operating state reduces mechanical stress of the actuator device  17 . The sliding element  19  and the differential carrier  15  are at a standstill in the open operating state of the shifting element  9 , and the positive-locking shifting element  16  is held in an open operating state by the actuator device  17  or by its control element  23  without a differential rotational speed. 
     Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.