Abstract:
The present invention relates to a transmission having a housing, having a first drive output shaft, having a second drive output shaft and having a clutch system for distributing a torque between the drive output shafts. At least two transmission components are operatively connected between the drive output shafts and generate lubricating oil pressure. A separate tube extends within the housing from the at least two transmission components to the clutch system in order to supply lubricating oil to the clutch system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 U.S. National Stage of International Application No. PCT/EP2007/005453, filed Jun. 20, 2007. This application claims the benefit of German Patent Application No. DE 10 2006 034 153.8, filed Jul. 24, 2006. The disclosures of the above application are expressly incorporated herein by reference. 
     FIELD 
     The present invention relates to a transmission having a housing, a first output shaft, a second output shaft as well as a clutch system for the distribution of a torque between the output shafts, wherein at least two transmission components are operatively connected between the output shafts and generate lubrication oil pressure. 
     BACKGROUND 
     This section provides background information related to the present disclosure and which is not necessarily prior art. 
     Transfer cases are used in all-wheel drive vehicles for the distribution of the torque to a plurality of axles. The distribution takes place by a multi-disk clutch which is made such that the torque transmission between a first output shaft and a second output shaft can be controlled. On engagement by means of a controllable multi-disk clutch, one speaks of “torque on demand”. 
     The lubrication of transfer cases whose multi-disk clutch above all has a high cooling oil requirement in slip operation usually requires a separate oil supply. In addition, in particular on a blocking of the multi-disk clutch, the bearings which support the components of the multi-disk clutch are fully loaded, with the friction between the bearings and the components being at a maximum. 
     EP 0 268 904 B1 describes a transfer case having a transmission with a pump-less oil lubrication of a planetary gearset, wherein gears act as an oil pump to build up a specific pressure and wherein the lubrication oil is supplied to the planetary gearset through a passage and a gap between concentric shafts. The passage is integrated in the transmission housing. The transmission of EP 0 268 904 B1 thus does not have any direct oil lubrication of the multi-disk clutch and requires a complex and/or expensive housing design to form the passage. 
     SUMMARY 
     It is the object of the present invention to provide a transmission having improved efficiency, a simpler structure and improved oil lubrication properties. 
     Since the transmission of the invention delivers a pump-less oil lubrication, the transmission does not require any additional oil pump. In addition, the direct oil lubrication of the multi-disk clutch and of the supporting bearings improves the efficiency, in particular when the components are temperature loaded. The separate pipe additionally extends within the housing without the necessity of integrally forming a passage in the transmission housing. The transmission housing is simpler in this manner and requires less material and is thus lighter and cheaper. 
     In a first preferred embodiment of the invention, the pipe is coupled to the clutch system via a distributor element, with the distributor element conducting lubrication oil between the parts of the clutch system. The components of the clutch system are thus lubricated directly to improve the efficiency. 
     In a second preferred embodiment of the invention, one of the transmission components is a gear having cut-outs which are provided at at least one side surface of the gear. The lubrication oil is conducted through the cut-outs into the toothed arrangements of the gear to increase the lubrication oil pressure and thus to improve the lubrication oil supply. 
     In a third improved embodiment of the invention, a lubrication oil shield plate is provided which shields the transmission components with respect to the lubrication oil. The lubrication oil shield plate prevents the respective transmission components from permanently churning in the oil sump, whereby churning losses are reduced to a minimum. The temperature of the lubrication oil is reduced in this manner and the service life of the lubrication oil is extended. In addition, the viscosity of the lubrication oil is maintained for the better lubrication of the clutch system. 
     In a fourth preferred embodiment of the invention, a lubrication oil supply is provided with a pan, with the pan having a lubrication oil reservoir. The lubrication oil reservoir delivers additional lubrication oil to the transmission components. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific example in this summary section are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The invention will be described in the following only by way of example with reference to the drawings; in which are shown: 
         FIG. 1  shows a schematic representation of a motor vehicle powertrain equipped with a transfer case; 
         FIG. 2  illustrates a first sectional representation of a first embodiment of the transfer case; 
         FIG. 3  illustrates a second sectional representation of the first embodiment of the transfer case; 
         FIG. 4  shows a perspective representation of a housing a gear and a first embodiment of an oil shield plate of the transfer case; 
         FIG. 5  shows a perspective representation of the housing, the gear and a second embodiment of the oil shield plate of the transfer case; 
         FIG. 6  shows a perspective representation of a third embodiment of the oil shield plate; 
         FIG. 7  shows a perspective representation of a fourth embodiment of the oil shield plate; 
         FIG. 8  shows a perspective representation of a fifth embodiment of the oil shield plate; 
         FIG. 9  illustrates a sectional representation of a second embodiment of a transfer case; 
         FIG. 10  shows a perspective representation of a housing, a gear, an output shaft and a clutch lubrication arrangement of the second embodiment of the transfer case; 
         FIG. 11  shows a perspective representation of a lubrication oil supply of the clutch lubrication arrangement of  FIG. 10 ; 
         FIG. 12  shows a sectional representation of a first embodiment for the clutch lubrication arrangement of  FIG. 10 ; and 
         FIG. 13  shows a sectional representation of a second embodiment of the clutch lubrication arrangement of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     A schematic representation of a vehicle powertrain  10  is shown in  FIG. 1  which includes a drive  12  which includes a first power transmission path  14 , a second power transmission path  16 , an internal combustion engine  18 , a manual transmission  20  and a transfer case  22 . The internal combustion engine  18  generates a driving torque which drives the transfer case  22  via the manual transmission  20 . The transfer case  22  distributes the output torque of the manual transmission between the first and second power transmission paths  14 ,  16 . 
     The first power transmission path  14  includes a Cardan shaft  24  which is driven by the transfer case  22 , a pair of half-shafts  26  connected to a pair of wheels  28  and a differential unit  30  which is operative to transmit a driving torque from the Cardan shaft  24  to one or both half-shafts  26 . In a similar manner, the second power transmission path  16  includes a Cardan shaft  32  which is driven by the transfer case  22 , a pair of half-shafts  34  connected to a pair of wheels  36  and a differential unit  38  which is operative to transmit a driving torque from the Cardan shaft  32  to one or both half-shafts  34 . 
     A control unit  40  controls the operation of the transfer case  22  on the basis of a plurality of vehicle parameters. The control unit  40  is electronically connected to at least one sensor and preferably to a plurality of further sensors. Exemplary sensors include a yaw rate sensor  42  and/or wheel speed sensors  44 . The sensors  42 ,  44  detect a plurality of operating states, e.g. the yaw rate of the vehicle, the speed of each wheel and/or the speed of the vehicle. The control unit  40  processes the signal or signals and generates a control signal, with at least one actuator of the transfer case  22  being controlled on the basis of the control signal to distribute a torque between the power transmission paths  14 ,  16 . 
     The components of a first embodiment of the transfer case  22  will now be described with reference to  FIG. 2  and  FIG. 3 . The transfer case  22  includes a transmission housing  50 , a first output shaft  52 , a second output shaft  54 , a multi-disk clutch  56 , an actuator  58  and torque transmission components  60 ,  62 ,  64 . The first output shaft  52  rotates around a first axis A and is driven directly by an output shaft, not shown, of the manual transmission  20 . The second output shaft  54  rotates around a second axis B. The multi-disk clutch  56  is controllable to control a torque transmission between the first output shaft  52  and the second output shaft  54 . 
     The transfer case  22  furthermore includes a clutch lubrication arrangement for the lubrication of the components of the multi-disk clutch  56  and of the supporting bearings. The clutch lubrication arrangement has a pressure chamber  66  integrally shaped in the transmission housing  50 , a pipe  68  and a distributor element  70 . The pipe  68  extends from the pressure chamber  66  to the multi-disk clutch  56  to supply lubrication oil from the pressure chamber  66  to the multi-disk clutch  56 . The distributor element  70  conducts the lubrication oil to the different components and to the supporting bearings of the multi-disk clutch  56 . The transfer element  70  in particular includes a plurality of openings  71  which distribute the supplied lubrication oil in different directions. The pipe  68  is preferably shaped of plastic and the distributor element  70  is preferably an injected molded part. As  FIG. 3  shows, converging free spaces are formed with a spacing X and Y respectively in each case between the idler gear  62  and the second gear  64  as well as the transmission housing  50 . The spacings converge in the direction of rotation of the respective gear and serve to regulate the lubrication oil conveying amount. The converging free spaces in particular act as nozzles to increase the lubrication oil pressure. 
     The torque transmission takes place by the torque transmission components which include a first gear  60 , an idler gear  62  and a second gear  64 . The first gear  60  is rotationally fixedly connected to a component of the multi-disk clutch  56  and is rotationally journaled around the first output shaft  52 . The second gear  64  is rotationally fixedly connected to the second output shaft  54 . The idler gear  62  is rotationally journaled within the transmission housing  50  and meshes with each of the first and second gears  60 ,  64 . The idler gear  62  and the second gear  64  dip partly into the lubrication oil which is located in the transmission housing and whose level is indicated by the line SN. 
     With respect to  FIG. 2 , the multi-disk clutch  56  includes a clutch hub  73  which is rotationally fixedly connected to the first output shaft  52 . The clutch hub  73  can be coupled with friction locking via respective friction disks  72  to a clutch basket  74  which is rotationally journaled around the first axis A of the multi-disk clutch  56  or of the first output shaft  52 . The friction locking for the transmission of a torque between the clutch hub  73  and the clutch basket  74  is effected by means of a pressure plate  76  which is axially displaceable against the pre-stress of a plate spring arrangement  78  and hereby presses the respective friction disks  72  of the clutch hub  70  and the clutch basket  74  toward one another. 
     To selectively displace the pressure plate  76  against the pre-stress and to hereby actuate the multi-disk clutch  56 , the actuator  58  includes a support ring  80  and an adjustment ring  82  which are arranged coaxially to one another and with respect to the axis A. The support ring  80  is rotationally fixed and held fixedly axially. For this purpose, the support ring  80  is supported at the first output shaft  52  or a section  88  by means of a radial bearing  84  and of an axial bearing  86  and the support ring  80  is held rotationally fixedly by shape matched connection to a securing section of the transmission housing (not shown). The adjustment ring  82  is rotationally and axially displaceably journaled and it is supported at the pressure plate  76  by means of an axial bearing  90 . 
     The support ring  80  and the adjustment ring  82  each have a plurality of ball grooves  92  and  94  respectively at the mutually facing sides. Said ball grooves extend along the respective peripheral direction with respect to the axis A. A respective ball groove  92  of the support ring  80  and a ball groove  94  of the adjustment ring  82  stand opposite one another and hereby each surround an associated ball  96 . The ball grooves  92 ,  94  are inclined with respect to the normal plane of the axis A, i.e. the ball grooves  92 ,  94  have a varying depth along the named peripheral extent. It is hereby achieved that a rotational movement of the adjustment ring  82  relative to the rotationally fixedly held support ring  80  results in an axial displacement of the adjustment ring  82  so that the pressure plate  76  is axially offset by such a rotational movement of the adjustment ring  82  and the multi-disk clutch  56  can hereby be actuated. The pre-stress effected by the plate spring arrangement  78  in this respect ensures that the respective ball  96  remains captured in the associated ball grooves  92 ,  94  in every rotational position of the adjustment ring  82  relative to the support ring  80 . 
     To be able to bring about the explained rotational movement of the adjustment ring  82 , it is coupled to an electric drive motor  100  via a gear drive  98 . A toothed segment  102  which is made as an angular segment is shaped radially outwardly along a angular range of approximately 90° at the adjustment ring  82 . This toothed segment  102  forms, together with a worm gear  104  of the drive motor  100 , the gear drive  98 . The teeth of the toothed segment  102  of the adjustment ring  82  can have a pitch angle with respect to the axis A of between 5° and 15°, for example. An axis C of the helical gear shaft  104  of the drive motor  100 , on the one hand, and the axis A or the axis of rotation of the adjustment ring  82  with the toothed segment  102 , on the other hand, intersect one another and form an axial angle of 90°. 
     The actuation of the shown multi-disk clutch  56  for the transmission of the torque between the first output shaft  52  and the second output shaft  54  takes place as follows: 
     By actuation of the drive motor  100 , a corresponding rotational movement of the worm gear  104  around the axis C is effected. This results due to the gear drive  98  in a rotational movement of the adjustment ring  82  around the axis A. The slanted position of the teeth of the toothed segment  102  of the adjustment ring  82  is in this connection aligned such that the axial forces of the helical gear pair caused by the slanting toothed arrangement on the adjustment rig  82  in the direction of the desired movement of the adjustment ring  82  act to bring about the pressing actuation of the multi-disk clutch  56 . The cooperation of the ball grooves  94  of the adjustment ring  82  via the respective ball  96  with the associated ball groove  92  of the support ring  80  has the effect during the rotational movement of the adjustment ring  82  that the adjustment ring  82  moves away axially from the support ring  80  and displaces the pressure plate  76  axially against the bias of the plate spring arrangement  78 . The respective friction disks  72  of the clutch hub  70  and the clutch basket  74  are hereby pressed toward one another such that an increasing torque can be transmitted from the clutch hub  70  to the clutch basket  74 . The release of the friction locking hereby effected takes place in the reverse order, i.e. the drive motor  100  causes the adjustment ring  82  to make a rotational movement in the reverse sense, with the corresponding axial movement of the adjustment ring  82  and the pressure plate  76  being supported in the direction of the support rig  80  by the plate spring arrangement  78 . 
     On the torque transmission by the multi-disk clutch  56 , the first gear  60  rotates around the axis A and drives the idler gear  62 . The idler gear  62  thus drives the second gear  64  around the axis B. Normally, the gears  62 ,  64  have the direction of rotation reproduced by the arrows so that their portions dipping into the lubrication oil sump move with respect to one another. Pressure is generated in the toothed engagement by the conveying effect of the gears  62 ,  64  to effect a conveying of the lubrication oil via the pressure chamber  66 , the pipe  68  and the distributor element  70  up to and into the actuator and the multi-disk clutch. In this connection, the components of the actuator  58 , in particular the supporting bearings  84 ,  86 ,  90 , and the components of the multi-disk clutch  56  are directly lubricated. 
     As  FIG. 4  shows, radially extending cut-outs  122  are provided in an end face  120  of the idler gear  62 . Furthermore, a lubrication oil shield plate  124  is provided which approximately surrounds the lower half of the idler gear  62 . The pan-shaped lubrication oil shield plate  124  has side walls  126  and a peripheral section  128  between the side walls  126  and serves for the reduction of temperature development and for the regulation of the lubrication oil conveying amount. The lubrication oil shield plate  124  in particular prevents the idler gear  62  from constantly churning in the oil sump in the transfer case  22 . An unwanted foaming of the lubrication oil is hereby caused and the resulting churning losses result in an unwanted temperature increase specifically in the higher speed range and thus have to be reduced to a minimum. 
     In the embodiment of the lubrication oil shield plate  124  shown in  FIG. 4 , openings are provided in the side walls  126 , with lubrication oil flowing in via a curved elongate hole  130  which is formed in the side wall  126  and being conducted into the toothed arrangement of the gears via the cut-outs  122 . In another embodiment shown in  FIG. 5 , the elongate holes  130   a  are formed at the edge between the side walls  126   a  and the peripheral section  128   a . The lubrication oil shield plate  124   a  includes additional openings  132   a  in the side walls  126   a  which serve for the holding tight of the lubrication oil shield plate  124   a  within the transmission housing  50 , with the openings  132   a  taking up projections, not shown, of the transmission housing  50 . 
       FIGS. 6 to 8  show additional embodiments of the lubrication oil shield plate. The lubrication oil shield plate  124   b  of  FIG. 6  is similar to the lubrication oil shield plate  124   a  of  FIG. 5 , but the elongate holes  130   b  are formed at the bottom between the side walls  126   b  and the peripheral portion  128   b , with the elongate holes  130   b  lying completely within the lubrication oil sump. The lubrication oil shield plate  124   c  of  FIG. 7  is similar to the lubrication oil shield plate  124  of  FIG. 4 , but made without openings in the side walls  126   c . Instead, an opening  134   c  is provided in peripheral section  128   c . The lubrication oil shield plate  124   d  of  FIG. 8  is similar to the lubrication oil shield plate  124   b  of  FIG. 6 . Instead of openings in the side walls  126   d , however, an intermediate opening  130   d  is provided in the peripheral section  128   d.    
     The components of a second embodiment of a transfer case  22 ′ will now be described with reference to  FIG. 9  and  FIG. 10 . The transfer case  22 ′ includes a transmission housing  50 ′, a first output shaft  52 ′, a second output shaft  54 ′, a multi-disk clutch  56 ′, an actuator  58 ′ and torque transmission components  60 ′,  62 ′,  64 ′. The first output shaft  52 ′ rotates around a first axis A′ and is driven directly by an output shaft, not shown, of the manual transmission  20 . The second output shaft  54 ′ rotates around a second axis B′. The multi-disk clutch  56 ′ is controllable to control a torque transmission between the first output shaft  52 ′ and the second output shaft  54 ′. In accordance with the second embodiment, the transfer case  22 ′ is made as a chain gear, with the torque transmission component including gears  60 ′,  64 ′ which are rotationally operatively connected by a chain  62 ′. The chain  62 ′ has a plurality of chain links  140  which form teeth  142  ( FIGS. 12 and 13 ). The teeth  142  mesh with the teeth of the gears  60 ′,  64 ′. The multi-disk clutch  56 ′ and the actuator  58 ′ each include components like the multi-disk clutch  56  and the actuator  58 ′ respectively. 
     With reference to  FIGS. 10 to 13 , the transfer case  22 ′ furthermore includes a clutch lubrication arrangement  150  for the lubrication of the components of the multi-disk clutch  56 ′ and of the supporting bearings. The clutch lubrication arrangement  150  has a lubrication supply  152  and at least one pipe  154   a ,  154   b . Although it is not shown, the clutch lubrication arrangement  150  can furthermore have a distributor element which distributes the supplied lubrication oil in different directions. The lubrication oil supply  152  is preferably an injection molded part and has a pan  156  having two arms  158  extending laterally. The pan  156  includes side walls  160 , end walls  162 ,  162 ′ and a base  164 . The side walls  160  as well as the arms  158  form a chain path  165  through the chain  62 ′ runs. The arms  158  and an arcuate surface  166  of the end wall  162 ′ form a pocket which partly encloses the gear  60 ′. 
     The lubrication oil collects within the trough  156 , whereby an additional lubrication oil sump is formed. The base  164  includes passages, not shown, through which lubrication oil is supplied to the chain  62 ′. The pan  156  has the task of catching the lubrication oil drawn up from the lubrication oil sump by the chain  62 ′ and of immediately supplying it to the chain  62 ′ again. That lubrication oil is thus captured again which is not immediately conveyed into the multi-disk clutch  56 ′ through the pipe  154 ,  154   b . The pan  156  thus serves for the improvement of the conveying power of the transfer case  22 ′. 
     In a first embodiment of the clutch lubrication arrangement  150 , a passage  170  is formed through the end wall  162 ′ and the surface  166 . The pipe  154   a  is connected to a connection pipe  172  ( FIG. 12 ) to establish flow communication between the lubrication oil supply  152  and the multi-disk clutch  56 ′ and the actuator  58 ′. In a second embodiment of the clutch lubrication arrangement  150 , a passage  174  is formed by an arm  158  with the pipe  154   a  being connected to a connection pipe  176  to establish flow communication between the lubrication oil supply  152  and the multi-disk clutch  56 ′ and the actuator  58 ′. 
     The chain  62 ′ carries lubrication oil upwardly out of the lubrication oil sump within the transfer case  22 ′. Normally, the gear  60 ′ and the chain  62 ′ have the direction of rotation reproduced by the arrows. Pressure is generated in the tooth engagement region ZB by the conveying effect of the gear  60 ′ and of the chain  62 ′ to effect a conveying of the lubrication oil via the pipe  154   a  and/or the pipe  154   b  up to and into the actuator  58 ′ and the multi-disk clutch  56 ′. In accordance with the first embodiment of the clutch lubrication arrangement  150 , the lubrication oil is conducted through the passage  170  and the connection pipe  172  up to the pipe  154   a . In accordance with the second embodiment of the clutch lubrication arrangement  150 , the lubrication oil is conducted through the passage  174  and the connection pipe  176  up to the pipe  154   b.    
     Since the transfer case  22 ,  22 ′ of the invention provides a pump-less oil lubrication, the transfer case  22 ,  22 ′ does not require any additional oil pump. In addition, the direct oil lubrication of the multi-disk clutch  56 ,  56 ′ and of the supporting bearings improves the efficiency, in particular when the components are temperature loaded. Individual parts of the oil lubrication system, for example the pipe  68 ,  154   a ,  154   b , the distributor element  70  and the lubrication oil supply  152 , can be made of plastic. The parts are thus easy and cheap to make. In addition the pipe  68 ,  154   a ,  154   b  extends within the housing  50 ,  50 ′ without the need of forming a passage integrally in the transmission housing. 
     REFERENCE NUMERAL LIST 
     
         
         
           
               10  vehicle powertrain 
               12  drive 
               14 ,  16  power transmission path 
               18  internal combustion engine 
               20  manual transmission 
               22 ,  22 ′ transfer case 
               24 ,  32  Cardan shaft 
               26 ,  34  half-shafts 
               28 ,  36  wheels 
               30 ,  38  differential unit 
               40  control unit 
               42 ,  44  sensors 
               50 ,  50 ′ transmission housing 
               52 ,  52 ′,  54 ,  54 ′ output shaft 
               56 ,  56 ′ multi-disk clutch 
               58 ,  58 ′ actuator 
               60 ,  60 ′,  64 ,  64 ′ gear 
               62  idler gear 
               62 ′ chain 
               66  pressure chamber 
               68 ,  154   a ,  154   b  pipe 
               70  distributor element 
               71  opening 
               72  friction disks 
               73  clutch hub 
               74  clutch basket 
               76  pressure plate 
               78  plate spring arrangement 
               80  support ring 
               82  adjustment ring 
               84 ,  86 ,  90  bearing 
               88  portion 
               92 ,  94  ball groove 
               96  ball 
               98  gear drive 
               100  drive motor 
               102  toothed segment 
               104  worm gear 
               120  end face 
               122  cut-outs 
               124 ,  124   a - d  lubrication oil shield plate 
               126 ,  126   a - d  side walls 
               128 ,  128   a - d  peripheral section 
               130 ,  130   a - d  elongate hole/opening 
               132   a - d  opening 
               140  chain links 
               142  teeth 
               150  clutch lubrication arrangement 
               152  lubrication oil supply 
               156  pan 
               158  arms 
               160  side walls 
               162 ,  162 ′ end walls 
               164  base 
               165  chain path 
               166  surface 
               170 ,  174  passage 
               172 ,  176  connection pipe 
           
         
       
    
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.