Abstract:
A vehicle, in particular a motorcycle, having an engine with a crankshaft extending transversely to a travel or longitudinal direction of the vehicle, a transmission, and a clutch, which may assume an open state and a closed state. The clutch, which allows a torque transmission from the crankshaft to the transmission in the closed state, is situated coaxially to the crankshaft. The engine and transmission may be arranged such that the vehicle&#39;s rearswing arm may be located coaxially with an axis of a transmission output shaft.

Description:
This application is a Continuation of PCT/EP2006/006478, filed Jul. 4, 2006, and claims the priority of DE 05015290.9, filed Jul. 14, 2005, the disclosures of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     In typical motorcycles having a chain or belt drive, the pinion, which drives the chain or the drive belt, is typically situated at least approximately 65 mm offset in relation to the axis to which the rear wheel swing arm is linked. The clutch is commonly situated on the transmission input shaft in typical motorcycles. Seen in a side view of the motorcycle, the clutch thus “overlaps” the transmission output shaft. In the following, the transmission output shaft is understood as the shaft on which the pinion is situated, which drives the chain or the belt, which in turn drives the rear wheel. The transmission output shaft is typically located in front of the swing arm axis. 
     Typical motorcycle concepts of this type have a whole array of disadvantages. Because of the offset between the chain pinion and the swing arm axis, a certain chain sag is necessary. In particular for off-road motorcycles, which have a spring range of 150 mm or more, a significant chain sag is required. In a motorcycle having a spring range of 300 mm, for example, a chain sag of approximately 70 mm is required. 
     A greater chain sag results in relatively strong friction losses and requires a special chain guide. Greater chain wear also results with a large chain sag. A further result of the large chain sag may be strong running noises due to “chain whipping.” “Encapsulation” of the chain is constructively complex, in particular in the event of large chain sag. 
     A further problem of typical motorcycle concepts may be seen in that the pinion diameter is limited in relation to the swing arm mounting by the clearance required for a pivot movement of the swing arm. Furthermore, it is problematic that the swing arm spar is situated adjacent to or below the driving strand of the chain, which implies a relatively large gauge of the swing arm spars and, in the case of a single-arm swing arm, makes the construction very complex, because the engine housing and the swing arm mounting must also be housed having an offset in relation to the transmission output shaft between the rear wheel and the output shaft of the transmission. Because in typical motorcycles, the swing arm spars must always lie between the top and bottom chain strands, the bottom spring strut attachment is located at a relatively low level, which in turn has an unfavorable effect on the spring strut progression. 
     As already noted, the clutch is typically situated on the transmission input shaft in normal motorcycles. Quite high torques occur on the transmission input shaft. To be able to transmit these high torques continuously, the clutch must be relatively large or run in an oil bath. Oil-bath clutches have the disadvantage that they may result in a relatively rapid contamination of the oil. 
     In normal motorcycles, the frame is also typically designed relatively complexly. The frame connection between the steering head and the swing arm axis lying behind the transmission output shaft must be guided past the clutch basket, which has a relatively large construction. In typical motorcycles, in which the swing arm axis is situated behind the drive pinion, the frame typically has frame tubes which extend below the engine past the clutch housing to the swing arm linkage points. Frame constructions of this type imply an unfavorable force flow and are also relatively heavy and costly to produce. The engine mounting is also relatively difficult with frames of this type, because the engine and the transmission are “embedded” very tightly in the frame. 
     It was already recognized many decades ago that it would be advantageous if the drive pinion which is provided for driving the chain or the drive belt was situated coaxially to the swing arm axis. Concept approaches are described, for example, in U.S. Pat. No. 6,755,272 B2, GB 558 387, FR 2370 625, WO 02/094649 A1, or EP 592 655 B1. However, in the motorcycles described therein, the drive pinion is not seated on the transmission output shaft, but rather on a separate shaft which is driven by the transmission output shaft via a chain or belt drive. This is a relatively cumbersome design and has therefore also not been successful. 
     In the textbook “Motorradtechnik [Motorcycle Technology],” 5th edition, Vieweg-Verlag, ATZ MTZ-Fachbuch, pages 295-298, edited by Jürgen Stoffregen, the basic idea of situating in the chain pinion coaxially to the pivot axis is also described. However, Stoffregen does not provide a concrete description of how the chain pinion may be driven and how the chain pinion is to be situated in relation to the transmission. 
     FR 1038 140 may also be included in the technical background. 
     The object of the present invention is to provide a completely novel vehicle concept which may be implemented in a simple design, which allows the problems described at the beginning to be avoided, as well as providing an engine/transmission unit as a basis for such a vehicle. 
     The starting point of the present invention is the consideration of providing a novel engine/transmission unit, which allows a correspondingly novel vehicle concept, in particular a novel motorcycle concept. Such an engine/transmission unit has an engine having a crankshaft which extends transversely to the travel direction of the vehicle, as well as a transmission and a clutch which may assume an open state and a closed state, the clutch allowing a torque transmission from the crankshaft to the transmission in the closed state. A central feature of this novel engine/transmission unit is that the clutch is situated coaxially to the crankshaft. The rotational axis around which the clutch disks rotate is thus transverse to the travel direction of the vehicle or the motorcycle. 
     The advantage results due to the coaxial configuration of crankshaft and clutch that the clutch-in contrast to typical vehicle engine/transmission units, in which the clutch is typically situated on the transmission input shaft-operates at higher speeds and lower torques and may thus be implemented more compactly. The clutch may thus have a comparatively small diameter, which in turn has the advantage that it does not extend up into the area of the transmission output shaft. The reason why this is so advantageous in regard to the overall vehicle concept will be explained in greater detail below. 
     It is expressly noted that the present invention is not restricted to the use of such an engine/transmission unit in motorcycles, but rather is applicable very generally in connection with vehicles. The following description and the claims are also to comprise multiwheel vehicles in addition to motorcycles, such as three-wheeled vehicles or four-wheeled vehicles, in particular so-called “quads.” 
     According to a refinement of the present invention, the vehicle has a frame and a rear wheel swing arm, which is situated so it is pivotable on a swing arm axis in relation to the frame, and a transmission having a transmission housing and a transmission output shaft projecting out of the transmission housing. A “transmission output pinion” is situated on the transmission output shaft, which is coupled to a chain wheel, which drives a rear wheel or rear wheels of the vehicle situated in the rear wheel area of the vehicle via a traction mechanism, such as a chain or a toothed belt. 
     According to a refinement of the present invention, the transmission output pinion situated on the transmission output shaft is situated coaxially to the swing arm axis. A coaxial configuration of the transmission output pinion, i.e., the pinion which drives the chain or the belt, and the swing arm axis has the advantage that practically no sag of the “traction mechanism,” i.e., the drive chain or the drive belt, has to be maintained for the spring compression of the rear wheel swing arm, as is the case for typical motorcycles having a chain or belt drive. The problems connected with a chain sag are thus avoided from the beginning. 
     According to a refinement of the present invention, the swing arm axis, i.e., the pivot axis around which the rear wheel swing arm pivots, extends through the transmission/engine housing. When “engine/transmission housing” or “transmission housing” or “engine housing” are discussed in the following, these terms are each to be understood broadly. The terms “engine/transmission housing” or “transmission housing” or “engine housing” are to be understood very generally in the following description and in the patent claims as the housing of the transmission and/or the housing of the engine. 
     The swing arm axis extending through the transmission housing projects out of the transmission housing on opposite sides of the transmission housing. Ends of the swing arm axis may then be mounted in the frame of the vehicles so they are pivotable. The swing arm axis may be mounted in the frame by roller bearings or friction bearings. For example, taper roller bearings may be used for mounting the swing arm axis in the frame. The taper roller bearings may be situated in an O configuration, for example. 
     It is expressly noted that the swing arm does not necessarily have to be mounted in the frame. The swing arm may also be mounted to or on the transmission output shaft using bearings, e.g., needle bearings, if the transmission output shaft and the engine/transmission housing are implemented as sufficiently stable to support the forces introduced via the swing arm. 
     The rear wheel swing arm may be permanently connected to the swing arm axis. A simple possibility is to clamp the rear wheel swing arm to the swing arm axis using a clamp connection. 
     The transmission output shaft on which the transmission output pinion is situated is preferably mounted in the transmission housing by roller bearings. 
     According to a refinement of the present invention, the transmission output shaft is implemented as a hollow shaft. This has the advantage that the swing arm axis may be inserted very simply through the transmission output shaft, which allows very simple mounting and dismounting of the rear wheel swing arm. 
     As already noted, the engine/transmission unit may be installed in a vehicle in such a way that the crankshaft of the engine extends in a transverse direction, i.e., parallel to the swing arm axis of the vehicle. In contrast to most normal vehicles and/or motorcycles, in which the clutch is situated on the transmission input shaft, according to the present invention, the clutch is situated coaxially to the crankshaft and preferably on the crankshaft itself. Because higher speeds and smaller torques arise on the crankshaft than on the transmission output shaft, the clutch may be implemented smaller, i.e., having a smaller diameter, than in typical motorcycles. 
     In typical motorcycles, in which the clutch is situated on the transmission input shaft, the clutch overlaps the transmission output shaft seen in a side view of the vehicle. In typical motorcycles, a coaxial configuration of swing arm axis and transmission output pinion would not be possible at all, because the swing arm axis would penetrate the clutch. 
     In contrast, a configuration of the clutch on the crankshaft has the advantage that the clutch may be implemented more compactly and, seen in a side view of the vehicle, the clutch does not overlap the transmission output shaft and thus allows “through insertion” of the swing arm axis. Because smaller torques arise on the crankshaft than on the transmission input shaft, different types of clutches may be used, e.g., single-disk clutches, multiple disk clutches, dry clutches, wet clutches, etc. 
     A “drive element” of the clutch is preferably connected rotationally fixed to the crankshaft. An “output element” of the clutch is situated so it is rotatable in relation to the crankshaft and is connected to a primary pinion which is mounted so it is rotatable on the crankshaft. The output element may be a clutch basket which may be connected in one piece to the primary pinion. Alternatively thereto, the clutch basket and the primary pinion may also be implemented in two pieces. The primary pinion may be mounted on the crankshaft using a roller bearing or a friction bearing. The primary pinion is preferably mounted on the crankshaft using a needle bearing. 
     The torque may be transmitted from the primary pinion seated on the crankshaft via an intermediate wheel situated on an intermediate shaft to the transmission input shaft. The intermediate wheel or another gearwheel seated on the intermediate shaft engages with a gearwheel of the transmission input shaft, which is situated offset in relation to the intermediate shaft in the direction of the rear wheel swing arm. Multiple shiftable gearwheel stages which are permanently engaged are situated adjacent to one another on the transmission input shaft and on the transmission output shaft, via which the individual gears of the transmission may be engaged. 
     The basic principle of the present invention described above also allows, in contrast to the prior art, an optimum design of the frame, in particular an optimum design of the motorcycle frame in the case of a motorcycle. 
     According to a refinement of the present invention, the frame has at least two left and two right frame tubes. The left frame tubes are essentially mirror-identical to the right frame tubes. The frame tubes of each frame side intersect one another. “Intersect” in this context means that they run together and are connected to one another. The frame is preferably designed in such a way that the swing arm axis extends through the “intersection point” of the left frame tubes and through the intersection point of the right frame tubes. The engine and the transmission of the vehicle may be situated in the area between the left and the right frame tubes. 
     The left and the right frame tubes may each be differentiated by terms into a left and a right bottom frame tube and a left and a right top frame tube. Seen in a side view of the vehicle, the two bottom frame tubes may be essentially linear and extend forward up into an area below handlebars of the vehicle from the swing arm axis and be connected there to a steering head bearing tube. In a top view of the vehicle, the two bottom frame tubes are not necessarily linear, but rather may also be curved. 
     The two top frame tubes are situated above the bottom frame tubes and extend from an area below the handlebars or from a steering head bearing tube backward down to the pivot axis. 
     A frame designed in this way has multiple advantages. The engine, the transmission, and a radiator of the motorcycle may be inserted from below as a prefinished assembly into the area between the left and the right frame tubes, which significantly simplifies the mounting and/or dismounting. 
     While in typical motorcycles having a chain drive the frame tubes extend from the handlebars area below the engine and/or the transmission to the swing arm bearing of the rear wheel swing arm, according to the present invention, the left and the right frame tubes of the frame run laterally past the engine and/or the transmission from the handlebars area diagonally downward to the swing arm axis. This has the advantage in turn that a continuous radiator may be situated in an area below the bottom frame tubes and forward of the engine. 
     An air filter of the engine may be situated in a very space-saving way which is protected from sprayed water in the area proximal to the handlebars between the top and bottom frame tubes above the engine. 
     An onboard battery of the motorcycle may be situated in an area proximal to the swing arm axis between the top and bottom frame tubes above the transmission. The center of gravity of the vehicle is preferably located in this area. Situating the relatively heavy onboard battery in the area of the center of gravity of the vehicle very significantly improves the handling of the vehicle. 
     The frame described above also has significant advantages in regard to the configuration of a spring strut. The spring strut may be situated between the frame and the rear axle swing arm. It has the object of springing and damping movements of the spring strut occurring during travel. A bottom end of the spring strut may be connected in an articulated way to the swing arm. A top end of the spring strut may be connected in an articulated way to the frame. The spring strut extends from bottom rear diagonally to top forward. 
     In the frame design described above, it is advantageous to situate the spring strut in such a way that, seen in a side view of the motorcycle, it is in an essentially linear extension of the forward sections of the top two frame tubes. In a configuration of this type, the forces exerted by the spring strut on the frame are essentially introduced into the frame in the longitudinal direction of the forward sections of the top frame tubes. The top frame tubes function as “compression bars” and are primarily loaded with pressure and only slightly with bending upon spring compression of the rear wheel swing arm. In contrast to typical motorcycles, the frame thus allows a significantly flatter installation of the spring strut supports, which allows a high progression during spring compression of the spring strut. 
     The fuel tank may also be situated in a more favorable position closer to the center of gravity in the vehicle concept described above than is the case in most normal vehicles and/or motorcycles. According to a refinement of the present invention, the fuel tank is situated in an area above the spring strut and below the seat of the vehicle. The tank cover of the fuel tank may be situated on the top side of the fuel tank below the seat. The seat then only has to be removed for filling. In comparison to typical motorcycles, in which the fuel tank is situated forward of the seat, a configuration in the area above the spring strut has the advantage that the center of gravity of the vehicle may thus be lowered, which further improves the handling. 
     Alternatively thereto, an access opening or a “hole” may also be provided in the seat, via which the tank connecting piece of the fuel tank is accessible. Filling is then also possible without removing the seat. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a motorcycle according to an embodiment of the present invention. 
         FIG. 2  shows the crankshaft and the clutch of the motorcycle of  FIG. 1 . 
         FIG. 3  shows a side view of the engine and the transmission of the motorcycle of  FIG. 1 . 
         FIG. 4  shows a section along section line A-A shown in  FIG. 3 . 
         FIG. 5  shows a cross-section through the swing arm axis, the transmission output shaft, and the rear axle swing arm of the motorcycle of  FIG. 1 . 
         FIG. 6  shows a perspective view of a schematically illustrated motorcycle according to an embodiment of the present invention. 
         FIG. 7  shows a side view of the schematically illustrated motorcycle of  FIG. 6 . 
         FIG. 8  shows a top view of the motorcycle of  FIG. 1 . 
         FIG. 9  shows the rear wheel swing arm and the rear wheel mounted therein of the motorcycle of  FIG. 1 . 
         FIG. 10  shows an embodiment according to the present invention in the area of the crankshaft and/or clutch in a sectional illustration. 
         FIG. 11  shows a sectional illustration of the clutch of the exemplary embodiment from  FIG. 10 . 
         FIG. 12  shows a detail drawing of area X of  FIG. 11 . 
         FIG. 13  shows an embodiment of a clutch according to the present invention, a hydraulic attachment connected to the slave cylinder being integrated in the clutch cover. 
         FIG. 14  shows a detail drawing of a clutch situated on the crankshaft according to an embodiment of the present invention. 
         FIG. 15  shows a sectional illustration of an engine/transmission unit according to an embodiment of the present invention. 
         FIGS. 16-19  show the intermediate drive situated between the primary pinion and the transmission input shaft in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a motorcycle  1  having a front wheel  2  and a rear wheel  3 . The front wheel  2  is connected via a telescoping fork  4  to a frame  5  of the motorcycle  1 . In the side view shown in  FIG. 1 , a top left frame tube  6  and a bottom left frame tube  7  of the frame  5  may be recognized. The top left frame tube  6  may be divided into a forward section  6   a  and a rear section  6   b . The top left frame tube  6  is curved in the transition area between the frame tube sections  6   a ,  6   b . The forward section  6   a  is essentially linear in the side view shown in  FIG. 1 . The bottom left frame tube  7  is also essentially linear in the side view shown in  FIG. 1 . The two frame tubes  6 ,  7  extend from an area below handlebars  8  from a steering head bearing  9  diagonally downward to the rear. The section  6   b  of the top left frame tube  6  “intersects” the bottom left frame tube  7 . 
     As may be seen best from  FIG. 8 , the frame  5  is constructed essentially symmetrically in relation to a middle longitudinal axis of the motorcycle. The frame thus has a top right frame tube  6 ′ corresponding to the top left frame tube  6  and a bottom right frame tube  7 ′ corresponding to the bottom left frame tube  7 . A swing arm axis  10 , which is shown by dashed lines in  FIG. 8 , extends through the “intersection points” of the frame tubes  6 ,  7  or  6 ′,  7 ′. The swing arm axis  10  is visible best in  FIG. 5 . The rear wheel swing arm  11  (cf.  FIG. 5 ) is fastened to the swing arm axis  10 . The rear wheel swing arm  11  is thus situated so it is pivotable in relation to the frame  5  via the swing arm axis  10 . As is also best visible from  FIG. 5 , a transmission output pinion  12 , which drives a chain  13  of the motorcycle, is situated coaxially to the swing arm axis  10 . The transmission output pinion  12  is coupled via the chain  13  to a chain wheel  14 , which drives the rear wheel  3 . 
     As is obvious from  FIG. 1 , the top bar  11   a  of the rear wheel swing arm is hollow. A driving strand  15  of the chain  13  extends through the top bar  11   a  of the rear wheel swing arm  11 . The top bar  11   a  is also used simultaneously as a chain protector. A bottom strand  16  of the chain  13  runs through a casing  17  and is thus also protected. 
     It is expressly noted that the chain does not necessarily have to be guided through the top bar of the rear wheel swing arm, but rather may also be situated “outside.” 
     A spring strut  18  is situated between the frame  5  and the rear wheel swing arm  11 . As is obvious from  FIG. 1 , the spring strut  18  is situated relatively flat in comparison to typical motorcycles. A bottom rear end  18   a  of the spring strut  18  is connected in an articulated way to the rear wheel swing arm  11 . A top front end  18   b  of the spring strut  18  is connected in an articulated way to a transverse tube of the frame  5  (not shown here). As is obvious from  FIG. 1 , the spring strut  18  is essentially in a linear extension of the top frame tube  6  in the side view of the motorcycle shown here. A very favorable force introduction into the frame  5  thus results. The top frame tubes  6 ,  6 ′ (compare  FIG. 8 ) are thus primarily loaded with pressure. Because of the relatively “flat” configuration of the spring strut  18 , a relatively high spring progression also results upon spring compression of the rear wheel  3 , which also has a favorable effect on the driving behavior of the motorcycle  1 . The spring progression is significantly higher than in typical motorcycles, in which the spring strut is installed more steeply. 
     As is obvious from  FIG. 1 , the frame  5  of the motorcycle  1  is essentially open on the bottom. This has the advantage that the engine  19 , the transmission  20 , and a radiator  21  may be inserted from below into the frame  5  easily as a “prefinished power unit” during the assembly of the motorcycle  1 , which significantly simplifies the assembly effort in comparison to typical motorcycles, in which frame tubes extend below the engine and/or the transmission. 
     The frame conception described above in connection with the coaxial configuration of the swing arm axis  10  and the transmission output pinion  12  allows an installation position of the engine  19  and the transmission  20  in which the engine  19  is situated further to the rear than in typical motorcycles and the cylinder of the single-cylinder engine shown in  FIG. 1  extends forward and outward comparatively flatly. 
     A so-called “air box”  23 , which contains an air filter, via which the engine  19  is supplied with intake air, is situated in the area below the handlebars  8 , behind the steering head bearing  9 , and between the top frame tubes  6 ,  6 ′ and the bottom frame tubes  7 ,  7 ′. Because the air box is relatively light and thus only slightly impairs the handling of the motorcycle, it is situated relatively far upward on the motorcycle  1 , approximately where the tank is located in typical motorcycles. 
     Because of the relatively flat position of the spring strut  18 , the fuel tank may be situated in a favorable position closer to the center of gravity than is the case in most typical motorcycles. The fuel tank  24  is located in a position above the spring strut  18  and below a seat  25  of the motorcycle  1 . The fuel tank  24  is thus situated relatively close to the center of gravity of the motorcycle, which is approximately in the area of the spring strut  18 . The handling of the motorcycle  1  improves due to the configuration of the fuel tank  24  in proximity to the center of gravity. 
     A further relatively heavy vehicle component is the onboard battery  26 . The onboard battery  26  is situated in an area diagonally above and/or forward of the swing arm axis  10  between the top frame tubes  6 ,  6 ′ and the bottom frame tubes  7 ,  7 ′ and thus also in proximity to the center of gravity of the motorcycle, which further improves the handling. The onboard battery may particularly be situated “behind” the engine/transmission unit. In this context, “behind” generally means in the area between the engine/transmission unit and the rear wheel or the rear wheels of the vehicle. The onboard battery may particularly be situated below the fuel tank. 
     The engine  19  of the motorcycle  1  is installed in such a way that the crankshaft  27  (cf.  FIG. 2 ) extends in the transverse direction of the motorcycle, i.e., perpendicularly to the plane of the drawing of  FIG. 1  and parallel to the swing arm axis  10 . The term “transverse direction” may also be interpreted so that the crankshaft is transverse to the main travel direction and thus transverse to the longitudinal direction of the motorcycle. The crankshaft  27  is best visible from  FIG. 2 . In  FIG. 2 , the crankshaft of a single-cylinder engine is shown. The present invention is also suitable for transversely installed multi-cylinder engines, of course. The piston (not shown) of the engine transmits a piston force and thus causes a rotation of the crankshaft  27 . The torque is transmitted from the right end of the crankshaft  27  shown in  FIG. 2  to a drive element  28  of a multi-disk clutch  29 . 
     In contrast to typical motorcycles, in which the clutch is typically situated on the transmission input shaft, the clutch  29  is situated on the crankshaft  27 . When the clutch  29  is closed, the torque is transmitted from the drive element  28  to a clutch basket  30  functioning as an “output element,” which is connected to a primary pinion  31  in one piece here. The clutch basket does not necessarily have to be connected in one piece to the primary pinion, of course. A riveted connection is also conceivable at this point. The clutch basket  30  and/or the primary pinion  31  is/are mounted via a needle bearing  32  on the crankshaft  27 . 
     In comparison to typical motorcycles, in which the clutch is situated mounted on the transmission input shaft, a configuration on the crankshaft has the advantage that lower torques are to be transmitted there, which allows a more compact construction of the clutch. 
       FIG. 3  shows a side view of the engine/transmission unit, from the side opposite to the side shown in  FIG. 1 , i.e., seen from the “right” side of the motorcycle  1 . The position of the clutch  29 , an intermediate shaft  33 , a transmission input shaft  34 , and the transmission output shaft  35  situated coaxially to the swing arm axis  10  may be recognized. Furthermore, a section line A-A is shown. 
       FIG. 4  shows a section through the engine/transmission unit along section line A-A. As is obvious from  FIG. 4 , the torque is transmitted from the crankshaft  27  via the clutch  29  to the primary pinion  31  and from the primary pinion  31  to an intermediate gearwheel  35 ′, which is situated on the intermediate shaft  33 . A gearwheel  80  connected rotationally fixed to the intermediate wheel  35 ′ engages with a transmission input pinion  36  is a gear wheel, which is situated on the transmission input shaft  34 . Multiple shiftable gearwheel stages  37 - 40  are situated on the transmission input shaft  34  and on the transmission output shaft  35 , via which individual gears of the transmission  20  may be engaged. The torque is transmitted via one of these gearwheel stages  37 - 40  to the transmission output shaft  35  and from there via the transmission output pinion  12  to the chain  13  coupled to the rear wheel  3  as a function of the engaged gear.  
     As is visible best from  FIGS. 4 and 5 , the transmission output shaft  35  is a hollow shaft. The swing arm axis  10  is inserted through the transmission output shaft. The transmission output shaft  35  extends out of the transmission housing  41  on one side of the transmission housing  41 . The transmission output pinion  12  is situated on the projecting section of the transmission output shaft  35 . The transmission output shaft  35  is mounted in the transmission housing  41  using two roller bearings  42 ,  43 . 
     As is visible best from  FIG. 5 , the swing arm axis  10  extends through the transmission output shaft  35  and thus also through the transmission housing  41 . Ends  44 ,  45  of the swing arm axis  10  project out of the transmission housing  41  and are mounted in the frame  5  of the motorcycle  1  using two taper roller bearings  46 ,  47 , which are installed here in an O configuration. The swing arm axis  10  is thus an “insert axis,” which allows simple mounting and dismounting of the rear wheel swing arm  11 . 
     The rear wheel swing arm  11  is clamped using a clamp connection  48  to the swing arm axis  10  and is thus positioned fixed in relation to the swing arm axis  10 . Since the swing arm axis  10  is mounted in the frame  5  via the taper roller bearings  46 ,  47 , the rear wheel swing arm  11  may be pivoted around the swing arm axis  10  in relation to the frame  5 . 
       FIG. 6  shows a very schematic illustration of a motorcycle  1  according to the present invention in a perspective illustration. In this illustration, the flat installation of the spring strut  18  may be recognized especially well. The forward end  18   b  of the spring strut  18  is connected in an articulated way to the frame  5  via a transverse strut  49  which connects the two top frame tubes  6 ,  6 ′ to one another. As already noted, a strong spring strut progression results due to the flat configuration of the spring strut  18 , which significantly improves the driving behavior of the motorcycle in comparison to typical motorcycles, in which the spring strut is installed more steeply. 
       FIG. 7  shows the motorcycle of  FIG. 6  in a side view. The flat installation position of the spring strut  18  and the very simple construction of the frame  5  may again also be recognized very well here. It may also be recognized very well from  FIGS. 6 ,  7  that the engine  19 , the transmission  20 , and the radiator  21  may be inserted from below into the frame  5  during the assembly of the motorcycle  1  as a prefinished “power unit,” because in contrast to typical motorcycles, no frame tubes extend “to the rear” below the engine  19  and/or the transmission  20  to the linkage point of the rear wheel swing arm. 
     As is obvious from  FIGS. 6 and 8 , this frame conception also allows the positioning of a continuous, i.e., one-piece radiator  21  below the bottom frame tubes  7 ,  7 ′. 
       FIG. 9  shows a side view of the rear wheel swing arm  11  of the rear wheel  3  in an enlarged illustration. 
       FIG. 10  shows an exemplary embodiment of a vehicle engine  19  in the area of the clutch. The engine  19  has an engine housing  50 , in which the crankshaft  27  is mounted by roller bearings  51 . A clutch  29 , which is implemented as a lamellar (or “multi-plate”) clutch in the exemplary embodiment shown here, is situated in the area of the right end of the crankshaft  27 . The lamellar clutch  29  has a drive element, which is also referred to in the following as an “internal part” or “driver element”  28 , and is connected rotationally fixed to the crankshaft  27  via wedge teeth and/or a serrated profile in the exemplary embodiment shown here. Multiple lamellae (or “drive plates”)  52  suspended radially inward (i.e., at their radially-inner edges) are connected rotationally fixed to the drive element  28 , which engage between external lamellae (or “driven plates”)  53 , which are situated rotationally fixed in an output element  30  of the clutch. The output element  30  is also referred to in the following as a “clutch basket.” 
     The clutch basket  30  is connected in one piece to the primary pinion  31 . The clutch basket  30  is mounted so it is rotatable on the crankshaft  27  in the area of the primary pinion  31  using needle bearings  32 . In the axial direction, i.e., in the longitudinal direction of the crankshaft  27 , the lamellar clutch  29  is fixed as follows. The drive element or the internal part  28  is tensioned against a shoulder  55  of the crankshaft using a shaft nut  54 . 
     In contrast, the clutch basket  30  is fixed in the axial direction by a disk  56 , which is clamped between the internal part  28  and the shoulder  55 . In the opposite direction, the clutch basket  30  and/or the primary pinion connected in one piece thereto is/are supported via axial needle bearings  57  and an intermediate plate or intermediate disk  58  on the housing  50  of the engine  19 . This is a significant difference in relation to many typical clutch configurations, in which the clutch is frequently supported via shaft bearings in the axial direction. In contrast thereto, in the exemplary embodiment of  FIG. 10 , the forces which arise upon actuation of the clutch are not transmitted to the crankshaft  27  and thus not to the roller bearings  51 . The lamellar clutch  29  thus exerts practically no influence on the running of the engine  19  and/or the crankshaft  27 . 
     A further special feature of the exemplary embodiment shown in  FIG. 10  is that the force flux is not introduced, as in most lamellar clutches, via the clutch basket and transmitted via the lamellae to the clutch internal part, but rather the reverse. In the exemplary embodiment of  FIG. 10 , the torque is transmitted from the crankshaft to the internal part  28  and via the lamellae  52 ,  53  outward to the clutch basket and the primary pinion  31  connected thereto in one piece. The primary pinion  31  in turn engages with the intermediate wheel  35 ′ of an “intermediate drive” situated on the intermediate shaft  33 , via which the torque is transmitted to the transmission input shaft. 
     As is obvious from  FIG. 10 , a clutch cover  59  which covers the lamellar clutch  29  is flanged onto the housing  50  of the engine  19  and screwed to the housing  50  using fastening screws  60 . A cylindrical recess  61  is provided in the clutch cover  59 , which is also referred to in the following as a “slave cylinder.” A slave piston  62  is situated so it is displaceable in the cylindrical recess  61 . The slave cylinder  61  has a peripheral grooved recess  63 , in which a seal  64 ′ is inserted, which seals the slave cylinder  61  in relation to the slave piston  62 . 
     The configuration of the seal  64 ′ in the grooved recess  63  of the slave cylinder  61  has the advantage that the seal may be implemented more cost-effectively than in typical systems, in which the seal is typically integrated in the piston. In typical configurations, in which the seal is integrated in the piston, the external part, i.e., the slave cylinder has to be coated to avoid wear. A coating of this type of the slave cylinder is relatively costly. In the exemplary embodiment shown in  FIGS. 1 through 13 , in contrast, the slave cylinder  61  does not need to be coated, but rather only the slave piston  62 , which is significantly more cost-effective. 
     The slave piston  62  is held in a defined position using a spring  64 , in which a ball  65  inserted in the slave piston  62  presses against a disengaging element  66 . Using the slave piston  62 , a pressure force acting in the axial direction may be transmitted to a disengaging ring  68 , which is provided for opening the lamellar clutch  29 , via the ball  65 , the disengaging element  66 , and an axial bearing  67 . 
     If the slave piston  62  is not impinged with pressure, the lamellar clutch  29  is held closed by a disk spring  69 . The disk spring  69  has a radial external area  70 , which presses against a pressure plate  71 , which presses the lamellar assembly together in the closed state of the clutch and thus couples the internal part  28  and the clutch basket  30  friction-locked to one another. The disk spring  70  is supported by a ring  72  extending around the circumference of the clutch basket  30 . 
     A constructive feature of the exemplary embodiment shown in  FIG. 10  which is particularly to be cited is that the disk spring  69 , the ring  72 , and the disengaging ring  68  are fixed and centered in a way having a very simple design, namely via multiple collar screws situated distributed around the circumference, of which only two collar screws  73 ,  74  may be seen in  FIG. 10 . 
     As is visible best from  FIG. 12 , the collar screws  73 ,  74  are screwed to a cover-like element  75  of the clutch basket  30 . The collar screws have a peripheral collar or a shoulder  76  on their end facing toward the interior of the clutch basket  30 . The ring  72  is supported on the shoulders  76  of the collar screws. The disk spring  69 , the ring  72 , and the disengaging ring  68  are centered using the collar screws  74 . 
     To open the clutch, i.e., to relieve the disk spring assembly of the lamellar clutch  29 , the slave piston  62  is impinged with pressure and displaced to the left. The opening force exerted by the slave piston  62  is transmitted to the disengaging ring  68 , which is also displaced to the left. As is visible best from  FIG. 12 , a radial external area  77  of the disengaging ring  68  comes into contact with a radial internal area of the disk spring  69 . The axial force exerted by the disengaging ring  68  on the disk spring  69  displaces the radial internal area of the disk spring in  FIG. 12  somewhat to the left, which, because of the contact of the disk spring on the ring  72 , has the result that the radial external area of the disk spring  69  lifts off of the pressure plate  71 , which results in relief of the disk spring assembly and thus in opening of the lamellar clutch  29 . 
       FIG. 13  shows a section through the lamellar clutch  29  in another sectional plane. It is clearly visible from this illustration that a hydraulic channel  78  is integrated in the clutch cover  29 , which opens into a chamber  79 , in which the spring  64  is situated. The slave piston  62  may be impinged with pressure via the hydraulic channel  78 , which is connected to an actuating apparatus (not shown in greater detail here), e.g., a manual valve situated on the motorcycle handlebars, which functions as a “sensor.” 
       FIG. 14  shows the overall configuration of the crankshaft  27  and the lamellar clutch  29  situated on the crankshaft  27 . 
       FIG. 15  shows a section through the entire engine/transmission unit similar to that of  FIG. 4 , but having the clutch configuration described in  FIGS. 10 through 14 . With closed lamellar clutch  29 , the torque is transmitted from the crankshaft  27  to the internal part  28  and via the lamellar assembly to the clutch basket  30  and the primary pinion  31  connected thereto. The primary pinion  31  engages with the intermediate wheel  35 ′, which is connected rotationally fixed to a gearwheel  80 . The gearwheel  80  is in turn connected in one piece to the intermediate shaft  33 . The gearwheel  80  engages with the transmission input pinion  36 , which is situated on the transmission input  34 , from which the torque is transmitted via one of the gearwheel stages  37 - 40  to the transmission output shaft  35  and/or the transmission output pinion  12 . 
       FIG. 16 through 19  show details of the intermediate drive  81 . The intermediate drive  81  is essentially formed by the intermediate wheel  35 ′ engaging with the primary pinion  31  and the gearwheel  80  connected in one piece to the intermediate shaft  33 . The intermediate wheel  35 ′ is pressed onto the intermediate shaft  33  and additionally welded thereto. A sheet-metal pot  82  is inserted between the gearwheel  80  and the intermediate wheel  35 ′, which is used for oil separation. A cavity  83  is implemented between the sheet metal pot  82  and the wheel  35 ′, which is fluidly connected via radial holes  84  to a cylindrical recess or hole  85  provided in the intermediate shaft  33 . The cylindrical recess  85  is in turn fluidly connected to a ventilation channel  87  provided in the transmission housing  86 , which is used for engine ventilation. 
     Air admixed with engine oil penetrates into the cavity  83 . The engine oil distributed dispersed in the air is separated using the sheet-metal pot  82 . The exhaust gases may be exhausted outward from the cavity  83  via the radial holes  84  into the cylindrical recess  85  and from there via the ventilation channel  87  outward from the engine and/or transmission housing  86  to the outside. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modification of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.