Abstract:
A shifting arrangement for a dual clutch transmission as a change-speed transmission for motor vehicles, with two coaxially arranged input shafts, each of which can be activated via a respective clutch, an axially parallel output shaft and gear sets arranged on the shafts and shiftable by means of synchronous clutches to form a plurality of forward gears and one reverse gear, wherein the gear sets are subdivided into a first subtransmission with one of the input shafts and a second subtransmission with the other input shaft. A pre-shifting unit and/or post-shifting unit shiftable into at least two transmission ratio stages is associated with the first subtransmission and/or the second subtransmission.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2013/003186, filed Oct. 23, 2013, which designated the United States and has been published as International Publication No. WO 2014/067634 and which claims the priority of German Patent Application, Serial No. 10 2012 021 293.3, filed Oct. 30, 2012, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a switching device for a dual clutch transmission as change-speed gearbox for motor vehicles. 
     Such twin clutch transmissions can be used automated switching transmissions with good transmission efficiency, and due to the division into two subtransmissions and two separating clutches can be shifted fast and without interruption of traction. In order to optimally adjust such change speed transmissions to the drive power of the drive aggregate or internal combustion engines, a great transmission spacing is desired, which can be realized for example by providing a higher number of forward gears (in the absence of excessive transmission steps). 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to set forth a dual clutch transmission of the generic type which enables great transmission spacing and in an increased number of forward gears, while at the same time being of compact construction and well manageable in terms of control. 
     The object is solved with the features of the independent patent claim. Advantageous embodiments and refinements of the invention are set forth in the dependent claims. 
     According to the characterizing part of claim  1  at least one a pre-shifting unit and/or a post-shifting unit is assigned to the subtransmission A and/or the subtransmission B, which pre-shifting unit and post-shifting unit can be shifted between two different transmission stages. The integrated pre- and/or post-shifting unit makes it possible to multiply the forward gears in the subtransmissions A and B, wherein in spite of the realizable greater transmission spacing the number of gear wheel sets can be reduced. This is possible without increasing the overall length of the transmission and the additional costs can be kept relatively low. 
     For example assignment of a pre- and or post shifting unit to the subtransmission A results in twice the number of gears of the subtransmission A. in addition in this case a greater transmission spacing can also be achieved n the subtransmission A. 
     The pre- an/or prost shifting unit can generally be configured in a layshaft design, for example as performer stage, a pre- or post-shifting group or in another appropriate design. Particularly preferably the pre- and post shifting unit can be realized as planetary transmission. 
     In the following, optional refinements of the invention are described in particular in connection with a shifting unit which is configured as a planetary transmission. It is understood, however, that the generally achieved advantages can also be achieved with differently constructed shifting units. Insofar the following discussion also applies to shifting units that are not constructed as planetary transmission. 
     Thus in a first preferred embodiment the one planetary transmission can be positioned adjacent the dual clutch K 1 , K 2  on the input hollow shaft of the subtransmission A and the second planetary transmission can be positioned in force flux direction downstream of the gearwheel sets of both subtransmissions A, B on the output shaft. With this both planetary transmissions are advantageously spatially situated outside the gear wheel sets of the two subtransmissions. The transmission stages that are formed by the gear wheel sets can be quadrupled for the subtransmission A and doubled for the subtransmission B, which allows generating defined gear steps. 
     In a further alternative embodiment of the invention the one planetary transmission can be arranged adjacent the dual clutch on the input hollow shaft of the subtransmission A and the other planetary transmission can be arranged coaxially on the input shaft of the subtransmission B. this enables a doubling of the transmission stages of both subtransmissions A and B while enabling a particularly compact construction of the transmission. 
     In a third alternative embodiment of the invention both planetary transmissions can be arranged directly behind each other and arranged on the input hollow shaft of the subtransmission A. this enables depending on the circumstances the integration of both planetary transmissions in a single structural and mounting unit. Further the transmission stages of the subtransmission A can be quadrupled while the transmission stages of the subtransmission B, however can only be used singularly. 
     As mentioned above the pre- and/or post shifting unit can generally be shifted between two different transmission stages. Especially in the configuration as a planetary transmission the two transmission stages can be a first 1:1 transmission stage and a second lower (or higher) transmission stage. Such a planetary transmission has an input element, an output element and a transmission element which can be blocked via a brake B for shifting the lower transmission stage. Further, the planetary transmissions can be shiftable into the higher 1:1 transmission stage via a clutch K 3 , wherein the clutch respectively connects two elements of the planetary transmissions with each other. The clutch can be a conventional hydraulically controlled multi-disc clutch and the brake can be a hydraulically operable disc brake or can be configured similar to a multi-disc clutch, so that comfortable, jolt fee shifting without interruption of traction is possible. 
     In a preferred transmission configuration which is advantageous in terms of construction, the input element of the planetary transmissions can be a ring gear, the output element a planet gear carrying web and the transmission element a sun gear which meshes with the planet gears, and which can be blocked via the brake B or can be connected with one of the other elements via the clutch K 3 . The clutch K 3  can be provided between the driving ring gear and the sun gear. 
     Further the brake B and the clutch K 3  can be constructively simple arranged on a common hollow shaft with the sun gear. 
     In an advantageous refinement of the invention it is proposed that the two planetary transmissions are of essentially the same construction, optionally however have different transmission ratios in the lower transmission stage in order to realized targeted gear steps which are adjusted to the transmission stages by the gear wheel sets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the following multiple exemplary embodiments of the invention are explained in more detail by way of the included schematic drawing. It is shown in: 
         FIG. 1  a block diagram of a dual clutch transmission for a motor vehicle with subtransmissions A and B which have gear wheel sets, wherein a pre-shift unit is arranged upstream of to the subtransmission A, for example a planetary transmission, and a post shifting unit for example a planetary transmission is arranged on the output shaft downstream of the subtransmission A; 
         FIG. 2  the schematic representation of the upstream arranged planetary transmission according to  FIG. 1  with ring gear, a web with planet gears and a sun gear, and a clutch and a brake for shifting between the transmission stages. 
         FIG. 3  the planetary transmission of the dual clutch transmission integrated on the output shaft which is essentially constructed identical to that of  FIG. 2 ; 
         FIG. 4  an alternative shifting arrangement of the dual clutch transmission with a pre-shifting unit arranged upstream of the subtransmission A and subtransmission B; 
         FIG. 5  a further alternative shifting arrangement with two shifting units arranged directly behind each other and arranged on the input shaft. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows very schematically a dual clutch transmission  12  as change-speed transmission for motor vehicles, with two coaxial transmission input shafts  14 ,  16  which can be drivingly connected with a driving drive aggregate or an internal combustion engine (not shown) via two separating clutches K 1 , K 2 . The input shaft  14  is configured as hollow shaft. The dual clutch K 1 , K 2  can be assigned a rotation damper for example a two-mass flywheel  10 . 
     Arranged axially parallel to the input shafts  14 ,  16  is an output shaft  18 , which outputs onto a front axle differential  22  (only schematically indicated) which is attached to the transmission housing  20 . 
     The mentioned shafts  14 ,  16 ,  18  are rotatably supported in the housing  20  via only schematically indicated rolling bearings (without reference signs). 
     The dual clutch transmission  12  is divided into a subtransmission A and a subtransmission B, wherein the input hollow shaft  14  only extends within the subtransmission A while the input shaft  16  extends through the input shaft  14  into the subtransmission B up to its end wall  20   a.    
     In the subtransmission A three forward-gear gearwheels I, III, V and a reverse gear gearwheel set with integrated reversing gear (not shown) is arranged, which are formed in a manner known per se by fixed gears and idler gears, wherein the idler gears can be shifted via synchronizing clutches (generally designated  28 ). 
     In the subtransmission B two forward gear gearwheel sets II and IV are provided which are also formed by fixed gears and idler gears which can be shifted via synchronizing clutch  28  and which form the forward gears in the corresponding transmission configuration. 
     A first planetary transmission  30  is arranged upstream of the subtransmission A adjacent the dual clutch K 1 , K 2 , which planetary transmission is configured coaxial to the input hollow shaft  14  and which can be shifted between two transmission stages or between a lower transmission stage and a higher 1:1 transmission stage. 
     Further a second planetary transmission  32  as a post shifting unit of essentially the same construction is integrated in the output shaft  18  in force flux direction downstream of the mentioned gear wheel sets I to V and R. 
       FIGS. 2 and 3  show schematically the planetary transmissions  30  or  32  whose corresponding transmission elements are provided with the same reference signs. 
     The planetary transmission  30  ( FIG. 2 ) which is mounted to the dual clutch K 1 , K 2  has a ring gear as input element which is drivingly connected to the clutch K 1 , a web  36  with rotatably supported planet gears  38  as output element and a sun gear  40  as transmission element. 
     The web  36  is directly drivingly connected with the input hollow shaft  14  of the subtransmission A, while the sun gear  40  is connected to the housing fixed brake B via a further hollow shaft  42 . The brake B is preferably constructed similar to a multi-disc clutch or a s disc brake and cam be hydraulically actuated. 
     Further a multi-disc clutch K 3  is provided between the ring gear  34  and the hollow shaft  42  or the sun gear  40 , which clutch K 3  when hydraulically actuated connects the ring gear  34  with the sun gear  40  and with this forms the 1:1 transmission ration of the planetary transmission  30 . The clutch K 1  then drives the hollow shaft  14  of the subtransmission A via the blocked planetary transmission  30 . 
     The planetary transmission can be shifted to the lower transmission stage in that the clutch K 3  is disengaged and the brake B is actuated. Then the engaged clutch K 1  drives the input hollow shaft  14  via the planet gears  38 , the ring gear  34  and the web  36 , while the sun gear  40  is braked fixed as support element. 
     The planetary transmission  32  differs form the planetary transmission  30  described above only in that it is integrated in the output shaft  18 , wherein the section  18   a  of the output shaft  18  which carries the fixed gears ( FIG. 1 ) is connected with the ring gear  34  and the outputting web  36  is drivingly connected with the continuing section  18   b  of the output shaft  18 . 
     As a result of the arrangement of the planetary transmission  30  in the subtransmission A each gear wheel set I, III, V and the reverse gear gearwheel set R can be driven in two transmission ratios, and thus forms eight gears of defined transmission ratio configurations. 
     The gear wheel sets II and IV can also be driven via the planetary transmission  32  integrated in the output shaft  18  in two transmission ratios, correspondingly thus further four forward gears. 
     Further in cooperation of the two planetary transmissions  30 ,  32  further transmission ration configurations can be driven so that here theoretically the number of the gears is quadrupled. 
     This enables achieving a great transmission spacing, by using optionally not all theoretically possible gears, a great transmission spacing at defined transmission ratio steps. The transmission control (not shown) hereby preferably shifts, without interruption of traction, the gear wheel sets of the subtransmission A or the subtransmission B by coupling the synchronizing clutch  28  active and controls the two planetary transmissions  30 ,  32  depending on the driving situation, into the lower or the higher 1:1 transmission ratio. 
       FIGS. 4 and 5  show alternative dual clutch transmissions  12 ′,  12 ″ which are only explained insofar as they differ from the ducal clutch transmission  12  according to  FIG. 1 . Functionally same parts are provided with the same reference signs. 
     According to  FIG. 4 , the second planetary transmission  32  is not integrated into the output shaft  18  but into the second input shaft  16  of the subtransmission B. 
     As a consequence the gear wheel sets II, IV (according to  FIG. 1 ) of the subtransmission B can already be shifted in two transmission stages on the input side; an interaction (serial connection) of the two planetary transmissions  30 ,  32  is not possible in this case. 
       FIG. 5  shows an embodiment of the dual clutch transmission  12 ″ in which the two planetary transmissions  30 ,  32  are directly coupled one after the other and arranged on the input hollow shaft  14  of the subtransmission A. 
     This has ion one hand the advantage in terms of construction and production, that the two planetary transmissions  30 ,  32  can be configured as a single structural unit. 
     Via the two planetary transmissions  30 ,  32  then each of the gears of the subtransmission A shifted via the synchronizing clutches  28 , can be driven in four possible transmission sages by shifting the clutches K 3  and/or the brakes B. the forward gears of the gear wheel sets II and IV (according to  FIG. 1 ) then form non modifiable simple transmission stages. 
     Beside the possible multiplication of the transmission stages via the individual gear wheel sets I to V fast and comfortable shifting processes can be performed by preferably hydraulic control of the clutches K 3  and the brakes B. via the separating clutches K 1 , K 2  the drive moment is in a common manner conducted to the gear wheel sets I, III, V, R and II, IV of the subtransmission A and B. 
     The invention is not limited to the shown exemplary embodiments. 
     Depending on the required transmission spacing and the desired number of, forward gears and reverse gears a higher or lower number of gear wheel sets can be arranged in the subtransmission A and in the subtransmission B of the dual clutch transmission  12 . Also the constructive circumstance may be important for the arrangement of the two planetary transmissions  30 ,  32 . 
     The transmission ratios of the two planetary transmissions  30 ,  34  can be configured different in the lower transmission stage, in order to accomplish defined greater and smaller gear steps. For constructive or spatial reasons the planetary transmissions  30 ,  34  may also be configured differently (for example without ring gear and with a web with multi-stage planet gears, which mesh with two axially neighboring sun gears). 
     The dual clutch transmission  12  can also be configured for all wheel drive of the motor vehicle. For this the output shaft  18  can for example be configured as hollow shaft which outputs onto the differential housing of an integrated interaxle differential. Its output shafts can then drive a rear axle differential and through the hollow shaft the front axle differential  22 .