Double-clutch Transmission For Vehicles

Abstract

A double-clutch transmission (DCT) includes, but is not limited to two input shafts that are connected to two clutch discs respectively. The DCT also has three parallel layshafts. One or more of the layshafts includes, but is not limited to a pinion as a final drive. The DCT also includes, but is not limited to seven gearwheel groups for providing seven sequentially increasing forward gears. Each gearwheel group includes, but is not limited to a fixed gearwheel on one of the input shafts, meshing with an idler gearwheel on one of the layshafts. A third fixed gearwheel meshes with a third gear idler gearwheel and a fifth gear idler gearwheel. Especially, a reverse gearwheel group of the DCT includes, but is not limited to a reverse fixed gearwheel on one of the input shafts, meshing with a reverse gear idler gearwheel on one of the layshafts for providing a reverse gear. A second fixed gearwheel meshes with a second gear idler gearwheel and a fourth gear idler gearwheel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a U.S. National-Stage entry under 35 U.S.C. .sctn.371 based on International Application No. PCT/EP2009/002356, filed Mar. 31, 2009, which was published under PCT Article 21(2) and which claims priority to European Application No. 08006645.9, filed Mar. 31, 2008, and which claims priority to European Application No. 08006638.4, filed Mar. 31, 2008, and which claims priority to European Application No. 08006639.2, filed Mar. 31, 2008, and which claims priority to European Application No. 08006640.0, filed Mar. 31, 2008, and which claims priority to European Application No. 08006641.8, filed Mar. 31, 2008, and which claims priority to European Application No. 08006642.6, filed Mar. 31, 2008, and which claims priority to European Application No. 08006635.0, filed Mar. 31, 2008, and which claims priority to European Application No. 08006643.4, filed Mar. 31, 2008, and which claims priority to European Application No. 08006644.2, filed Mar. 31, 2008, and which claims priority to European Application No. 08006486.8, filed Mar. 31, 2008, and which claims priority to European Application No. 08006606.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006607.9, filed Mar. 31, 2008, and which claims priority to European Application No. 08006608.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006646.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006616.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006617.8, filed Mar. 31, 2008, and which claims priority to European Application No. 08006609.5, filed Mar. 31, 2008, and which claims priority to European Application No. 08006610.3, filed Mar. 31, 2008, and which claims priority to European Application No. 08006611.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006612.9, filed Mar. 31, 2008, and which claims priority to European Application No. 08006621.0, filed Mar. 31, 2008, and which claims priority to European Application No. 08006622.8, filed Mar. 31, 2008, and which claims priority to European Application No. 08006623.6, filed Mar. 31, 2008, and which claims priority to European Application No. 08006624.4, filed Mar. 31, 2008, and which claims priority to European Application No. 08006569.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006637.6, filed Mar. 31, 2008, and which claims priority to European Application No. 08006615.2, filed Mar. 31, 2008, and which claims priority to European Application No. 08006636.8, filed Mar. 31, 2008, and which claims priority to European Application No. 08006625.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006626.9, filed Mar. 31, 2008, and which claims priority to European Application No. 08006627.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006628.5, filed Mar. 31, 2008, and which claims priority to European Application No. 08006629.3, filed Mar. 31, 2008, and which claims priority to European Application No. 08006630.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006631.9, filed Mar. 31, 2008, and which claims priority to European Application No. 08006619.4, filed Mar. 31, 2008, and which claims priority to European Application No. 08006620.2, filed Mar. 31, 2008, and which claims priority to European Application No. 08006618.6, filed Mar. 31, 2008, and which claims priority to European Application No. 08006614.5, filed Mar. 31, 2008, and which claims priority to European Application No. 08006613.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006634.3, filed Mar. 31, 2008, and which claims priority to European Application No. 08006633.5, filed Mar. 31, 2008, and which claims priority to European Application No. 08006632.7, filed Mar. 31, 2008, and which claims priority to European Application No. 08006649.1, filed Mar. 31, 2008, and which claims priority to European Application No. 08006648.3, filed Mar. 31, 2008, and which claims priority to European Application No. 08006647.5, filed Mar. 31, 2008, which are all hereby incorporated in their entirety by reference.

TECHNICAL FIELD

[0002] The present application relates to a double-clutch transmission for vehicles, such as cars.

BACKGROUND

[0003] A double-clutch transmission comprises two input shafts that are connected to and actuated by two clutches separately. The two clutches are often combined into a single device that permits actuating any of the two clutches at a time. The two clutches transmit driving torque from an engine to the two input shafts of the double-clutch transmission.

[0004] U.S. Pat. No. 6,634,247 B2 discloses a six-gear double clutch transmission with an electric unit. The double clutch transmission has not been widely used in the cars for street driving. Problems that hinder the wide application of double clutch transmissions comprise of providing a compact, reliable and fuel-efficient double clutch transmission. Therefore, there exists a need for providing such a double clutch transmission that is also affordable by consumers.

SUMMARY

[0005] The present application provides a double-clutch transmission that comprises an inner input shaft and an outer input shaft. The outer input shaft surrounds a portion of the inner input shaft. The outer input shaft surrounds the inner input shaft in a radial direction. The radial direction indicates regions that surround a longitudinal axis of the inner input shaft. The outer input shaft can be a hollow input shaft and the inner input shaft can be a solid input shaft. Alternatively, the inner input shaft can also be a hollow input shaft.

[0006] A first clutch disc is non-rotatably connected to the inner input shaft and a second clutch disc is non-rotatably connected to the outer input shaft. The non-rotatable connections ensure that a connection between two joined shafts causes simultaneous rotation of the two shafts. For example, the two shafts can be fused together to make the non-rotatable connection. Alternatively, the non-rotatable connection can be provided by a universal joint.

[0007] The DCT has a first layshaft, a second layshaft and a third layshaft that are spaced apart from the input shafts and arranged in parallel to the input shafts. That is, longitudinal axes of these shafts are parallel to each other, including overlapping axes. One of more of the layshafts comprises a pinion as a final drive. The pinion can mesh with an output gear wheel on an output shaft for outputting a drive torque to a drive train of a vehicle. The drive train can alternatively be referred as powertrain or powerplant that comprises the group of components for generating power and delivering it to the road surface, water, or air. The drive train can include an engine, a transmission, drive shafts, differentials, and a final drive. The final drive can be drive wheels, continuous track like with tanks or caterpillar tractors, propeller, etc. Sometimes "drive train" refers simply to the engine and the transmission, including the other components only if they are integral to the transmission.

[0008] Gearwheels of the DCT are arranged on the first layshaft, on the second layshaft, on the third layshaft, on the inner input shaft and on the outer input shaft. These gearwheels comprise a first gearwheel group, a second gearwheel group, a third gearwheel group, a fourth gearwheel group, a fifth gearwheel group, a sixth gearwheel group, a seventh gearwheel group for providing seven sequentially increasing forward gears. A gear of the DCT can refer to an output speed of the output gear wheel. The sequentially increasing gears describe an escalating order that members of the order follow each other. Gears of a car can be arranged in a sequentially increasing manner from a first gear to a seventh gear. Gear ratios of the DCT decrease from the first gear to the seventh gear correspondingly. For example, in a car having a DCT of seven gears, a first gear has a gear ratio of 2.97:1; a second gear has a gear ratio of 2.07:1; a third gear has a gear ratio of 1.43:1; a fourth gear has a gear ratio of 1.00:1; a fifth gear has a gear ratio of 0.84:1; a sixth gear has a gear ratio of 0.56:1; and a seventh gear has a gear ratio of 0.32:1. The seven gears provide an increasing order of output speeds of the transmission for driving a car with the DCT.

[0009] The first gearwheel group comprises a first fixed gearwheel on the outer input shaft, meshing with a first gear idler gearwheel on one of the layshafts for providing a first forward gear. The third gearwheel group comprises a third fixed gearwheel on the outer input shaft, meshing with a third idler gearwheel on one of the layshafts for providing a third forward gear. The fifth gearwheel group comprises a fifth fixed gearwheel on the outer input shaft, meshing with a fifth gear idler gearwheel on one of the layshafts for providing a fifth forward gear. The seventh gearwheel group comprises a seventh fixed gearwheel on the outer input shaft, meshing with a seventh gear idler gearwheel on one of the layshafts for providing a seventh forward gear.

[0010] The second gearwheel group comprises a second fixed gearwheel on the inner input shafts, meshing with a second gear idler gearwheel on one of the layshafts for providing a second forward gear. The fourth gearwheel group comprises a fourth fixed gearwheel on the inner input shafts, meshing with a fourth gear idler gearwheel on one of the layshafts for providing a fourth forward gear. The sixth gearwheel group comprises a sixth fixed gearwheel on the inner input shafts, meshing with a sixth gear idler gearwheel on one of the layshafts for providing a sixth forward gear.

[0011] One or more gearwheel groups comprises a coupling device which is arranged on one of the layshafts to selectively engage one of the gearwheels for selecting one of the seven gears. The third fixed gearwheel further meshes with the fifth gear idler gearwheel.

[0012] Especially, the gearwheels further comprises a reverse gearwheel group that comprises a reverse fixed gearwheel on one of the input shafts, meshing with a reverse gear idler gearwheel on one of the layshafts for providing a reverse gear. The reverse gearwheel group further comprises a coupling device on one of the layshafts to engage the reverse gear idler gearwheel for providing the reverse gear. The second fixed gearwheel further meshes with the fourth gear idler gearwheel.

[0013] The DCT provides seven forward gears through a dual clutch. The DCT makes gear switching between odd and even ratios to be swift and efficient because the gearwheels of the odd and even gears are driven by different clutch discs or different clutches respectively. One double meshing feature is provided by the third fixed gearwheel that meshes with the third gear idler gearwheel and the fifth gear idler gearwheel. Another double meshing feature is provided by the second fixed gearwheel that meshes with the second gear idler gearwheel and the fourth gear idler gearwheel. The two double meshing features make the DCT to be compact and lightweight at low cost because two fixed gearwheels are avoided on the input shafts.

[0014] In the application, the first forward gear and the reverse gear can be provided by the two different input shafts. Dual clutches of the DCT enables that the switching between the two input shafts can be achieved quickly. As a result, a driving scheme that the DCT engages the two input shafts alternatively can drive the vehicle back & forth rapidly. This scheme is useful for moving the vehicle out of a muddy puddle because the vehicle can simply be driven back & forth to get out the puddle. Less loss of momentum of the gearwheels and the layshafts of the DCT can be achieved. Alternatively, the back and forth movements can be provided by a second forward gear and a first reverse gear on different input shafts.

[0015] In the application, the DCT can comprise a second reverse gearwheel group that comprises a fixed gearwheel on one of the input shafts, meshing with a second reverse gear idler gearwheel on one of the layshafts. The meshing can be provided directly between the two gearwheels or indirectly via other gearwheels. The second reverse gearwheel group can further comprise a coupling device which is arranged on the layshaft mounted with the second reverse gear idler gearwheel to selectively engage the second reverse gear idler gearwheel for proving a second reverse gear. The second reverse gear enables dual speeds for reversing a vehicle, which can be useful driving different applications of a multi-purpose vehicle. For example, the first reverse gear can be used as a faster reverse operation, whilst the second reverse gear can be used as a slower and silent reverse operation, or vice versa.

[0016] The reverse gearwheel group can provide a first reverse gear and a second reverse gear that are driven by the different input shafts respectively. This scheme makes the interchange between the two reverse gears to be fast, just by alternatively engaging one of the two clutches of the DCT. One of the two reverse gears provides a powerful and slower reverse gear. In contrast, the other reverse gear provides a faster reverse gear with less strength. The two reverse gears at different speeds enable some special vehicles, such as a Leopard II Main Battle Tank, to increase their maneuverability and operation efficiency.

[0017] The double-clutch transmission device can comprise a park-lock. The park-lock can comprise a fixed gearwheel on one of the layshafts that has the pinion as a final drive. The layshaft with the park-lock comprises a final drive pinion for engaging and locking a differential of the DCT. The differential comprises the output gearwheel on the output shaft. The park-lock enables a vehicle with the park-lock to park at a place in a secure manner, even on a slope. The park-lock is easy to implement and beneficial for the vehicle and passengers' safety.

[0018] The double-clutch transmission device can comprise two pinions that are mounted on two of the layshafts respectively. The two pinions can mesh or comb with one relatively big output gearwheel on an output shaft. The output gearwheel can be integrated into a transmission differential device without providing an intermediate output shaft of the transmission gearbox. This allows a very dense packaging situation for the DCT.

[0019] According to the application, two or more of the first gear idler gearwheel, the second gear idler gearwheel, and the third gear idler gearwheel are mounted on the same layshaft. Putting idler gearwheels of low gears, such as idler gearwheels of the first, second and third gears, on the same shaft require the layshaft to be strong and sturdy. Remaining layshafts of the double-clutch transmission can thus be made slim at low cost for carrying gearwheels of high gears, except the layshaft carrying reverse gear idler gearwheel. For example, two or more the fourth gear idler gearwheel, the fifth gear idler gearwheel, the sixth gear idler gearwheel and the seventh gear idler gearwheel are mounted on the same layshaft.

[0020] The double-clutch transmission can further comprise bearings for supporting the layshafts. One or more of the bearings is provided next to the pinion. The pinion that outputs torque of its carrying layshaft is better supported by immediately adjacent bearing for reducing deflection the layshaft under load. The supporting bearing thus can improve torque transmission efficiency and reduce cost of the DCT.

[0021] One or more the bearings are provided next to one of the driven gearwheels of low gears. Gearwheels of low gears transmit larger torques as compared to the gearwheels of high gears. Close support of the bearings help to reduce excessive deflection and weight related cost of their carrying shafts.

[0022] In the application, these can be a gearbox that comprises the double-clutch transmission and an output gearwheel on an output shaft. The output gearwheel meshes with the pinion for outputting a drive torque to a torque drain. The output gearwheel can even mesh with each of the pinions. The output gearwheel provides a single source of torque output so that the construction of the DCT is made simple and neat.

[0023] The application provides a power train device with the gearbox. One or more of power source generates a driving torque. The power train device usually has the gearbox and the power source onboard so that a vehicle with the power train device can be mobile without being physically attached to an external stationary power source.

[0024] The power source can comprise a combustion engine. The power train with the combustion engine and the DCT is easy to manufacture. The combustion engine can consume less petrol for environmental protection. Furthermore, a combustion engine usable for other types of fuel can have even less polluting emission, such as hydrogen fuel.

[0025] The power source can comprise an electric motor. Electric motor used in a hybrid car, or in an electrical car enables reduction of pollution, as compared to typical combustion using petrol. The electric motor can even recuperate brake energy in a generator mode.

[0026] The application also provides a vehicle that comprises the power train device. The vehicle having the power train device is efficient in energy usage by using the DCT.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and

[0028] FIG. 1 illustrates a front view of a first embodiment of a double clutch transmission of the application;

[0029] FIG. 2 illustrates the path of torque flow of a first gear transmission ratio;

[0030] FIG. 3 illustrates the path of torque flow of a second gear transmission ratio;

[0031] FIG. 4 illustrates the path of torque flow of a third gear transmission ratio;

[0032] FIG. 5 illustrates the path of torque flow of a fourth gear transmission ratio;

[0033] FIG. 6 illustrates the path of torque flow of a fifth gear transmission ratio;

[0034] FIG. 7 illustrates the path of torque flow of a sixth gear transmission ratio;

[0035] FIG. 8 illustrates the path of torque flow of a seventh gear transmission ratio;

[0036] FIG. 9 illustrates the path of torque flow of a first reverse gear transmission ratio;

[0037] FIG. 10 illustrates the path of torque flow of a second reverse gear transmission ratio;

[0038] FIG. 11 illustrates an assembly of a double-sided coupling device with its neighboring gearwheels for engagement;

[0039] FIG. 12 illustrates an assembly of a single-sided coupling device with its neighboring gearwheel for engagement;

[0040] FIG. 13 illustrates an assembly of an idler gearwheel that is rotatably supported by a shaft on a bearing;

[0041] FIG. 14 illustrates an assembly of a fixed gearwheel that is supported on a shaft;

[0042] FIG. 15 illustrates a cross-section through a detail of a crankshaft of an internal combustion engine according to embodiment of the double-clutch transmission;

[0043] FIG. 16 illustrates a front view of a further embodiment of a double clutch transmission of the application;

[0044] FIG. 17 illustrates an expanded side view of the double clutch transmission of FIG. 16;

[0045] FIG. 18 illustrates a front view of a further embodiment of a double clutch transmission of the application;

[0046] FIG. 19 illustrates an expanded side view of the double clutch transmission of FIG. 18;

[0047] FIG. 20 illustrates a front view of a further embodiment of a double clutch transmission of the application;

[0048] FIG. 21 illustrates an expanded side view of the double clutch transmission of FIG. 20;

[0049] FIG. 22 illustrates an alternative expanded side view of the double clutch transmission of FIG. 16; and

[0050] FIG. 23 illustrates an alternative front view of a further embodiment of a double clutch transmission in FIG. 19.

DETAILED DESCRIPTION

[0051] The following detailed description is merely exemplary in nature and is not intended to limit or the application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description.

[0052] In the following description, details are provided to describe the embodiments of the application. It shall be apparent to one skilled in the art, however, that the embodiments may be practiced without such details.

[0053] FIGS. 1-15 provide detailed description of an embodiment of a double clutch transmission (DCT) of the application. FIGS. 1-15 comprise similar parts that have similar reference numbers. Relevant description of the similar parts is incorporated where necessary.

[0054] FIG. 1 illustrates a front view of an embodiment of a double clutch transmission 1 of the application. The DCT 1 comprises a reverse pinion 55 on a reverse gear shaft 38, a relatively large output gearwheel 12 on an output shaft 14, an upper pinion 41 on an upper layshaft 40, an inner input shaft 20 inside an outer input shaft 22, and a lower pinion 51 on a lower layshaft 50. The inner input shaft 20 is a solid input shaft 20 (i.e. K1) and the outer input shaft is a hollow input shaft 22 (i.e. K2). The solid input shaft 20 and the hollow input shaft 22 share the same longitudinal axis of rotation. The three pinions 41, 51, 55 are fixed to right ends of the upper layshaft 40, the lower layshaft 50 and the reverse gear shaft 38 respectively. The output gearwheel 12 is also fixed to the output shaft 14 along its longitudinal axis. The three pinions 41, 51, 55 mesh with the output gearwheel 12 separately at different positions of the output gearwheel 12.

[0055] The reverse gear shaft 38, the upper layshaft 40, and the lower layshaft 50 are parallel to the coaxial input shafts 20, 22 with predetermined distances in-between. The distances are provided in radial directions of these shafts respectively, which is better seen in FIG. 2. Other gearwheels are mounted on these shafts that mesh with each other according to predetermined manners. These manners are better seen in some of the following figures.

[0056] FIG. 1 further shows a cutting plane A-A for illustrating an expanded cross-section view through the DCT 1, which is shown in FIGS. 2 to 10. The cutting plane A-A passes through the rotational axes of the reverse gear shaft 38, the upper layshaft 40, the input shafts 20, 22, the lower layshaft 50, and the output shaft 14. One of the goals of FIGS. 2 to 10 is to further illustrate structure and torque flows of the DCT 1.

[0057] FIG. 2 illustrates the expanded view of the DCT that shows the manners of the gearwheels mounting, which corresponds to FIG. 1.

[0058] According to FIG. 2, the DCT 1 comprises the following shafts, from top to bottom, the reverse gear shaft 38, the upper layshaft 40, the hollow input shaft 22, the solid input shaft 20, the lower layshaft 50, and the output shaft 14. The solid input shaft 20 is partially disposed inside the hollow input shaft 22. The solid input shaft 20 also protrudes outside the hollow input shaft 22 at two ends. The hollow input shaft 22 is mounted onto the solid input shaft 20 by a pair of solid shaft bearings 71 that are disposed between the solid input shaft 20 and the hollow input shaft 22 at two ends of the hollow input shaft 22. As a result, the two input shafts 20, 22 are coupled together such that the solid input shaft 20 is free to rotate inside the hollow input shaft 22. The hollow input shaft 22 surrounds a right portion of the solid input shaft 20, and a left portion of the solid input shaft 20 is exposed outside the hollow input shaft 22. The assembly of the input shafts 20, 22 is supported by the solid shaft bearing 71 at a protruding end of the solid shaft 20 on the left and by the hollow shaft bearing 72 on the hollow input shaft 22 on the right.

[0059] According to FIG. 2, a portion of the solid input shaft 20 is surrounded by the outer input shaft 22 in a radial direction of the solid input shafts 20. The radial direction is perpendicular to the common longitudinal axes of the input shafts 20, 22. There are two gearwheels fixed on the left exposed portion of the solid input shaft 20. These gearwheels are a fixed wheel second gear 30 and a fixed wheel sixth gear 32 from right to left sequentially. The fixed wheel second gear 30 also serves as a fixed wheel fourth gear 31. Each of the fixed wheel second gear 30 and the fixed wheel sixth gear 32 is mounted onto the solid input shaft 20 coaxially. On the hollow input shaft 22, which is mounted on the right portion of the solid input shaft 20, there are attached with a fixed wheel third gear 25, a fixed wheel seventh gear 27, and a fixed wheel first gear 24 from left to right. The fixed wheel third gear 25 also serves as a fixed wheel fifth gear 26. Each of the fixed wheel third gear 25, the fixed wheel seventh gear 27, and the fixed wheel first gear 24 is fixed onto the hollow input shaft 22 coaxially.

[0060] The upper layshaft 40 is provided above the input shafts 20, 22. There are gearwheels, coupling devices and bearings provided on the upper layshaft 40, which includes, from right to the left, an upper pinion 41, a layshaft bearing 73, a idler first gear 60, a double-sided coupling device 80, a idler third gear 62, an idler second gear 61, a single-sided coupling device 81, and a layshaft bearing 73. The idler first gear 60, the idler third gear 62, and the idler second gear 61 are mounted on the upper layshaft 40 by bearings respectively such that these gearwheels are free to rotate around the upper layshaft 40. The double-sided coupling device 80 can move along the upper layshaft 40 to engage any of the idler first gear 60 and the idler third gear 62 to the upper layshaft 40. Similarly, the single-sided coupling device 81 can move along the upper layshaft 40 to engage the idler second gear 61 to the upper layshaft 40. The idler first gear 60 meshes with the fixed wheel first gear 24. The idler third gear 62 meshes with the fixed wheel third gear 25. The idler second gear 61 meshes with the fixed wheel second gear 30.

[0061] The reverse gear shaft 38 is provided further above the upper layshaft 40. A reverse gear idler wheel 37, a double-sided coupling device 84, a second reverse gear idler wheel 35 and a park-lock gearwheel 39 are mounted onto the reverse gear shaft 38 at a left side of the reverse pinion 55 from right to left. One idler shaft bearing 74 is mounted at a left end of the reverse gear shaft 38 next to the park-lock gearwheel 39. Another idler shaft bearing 74 is installed on the reverse gear shaft 38 between the reverse gear idler wheel 37 and the reverse pinion 55. The reverse gear idler wheel 37 and the second reverse gear idler wheel 35 are mounted on the reverse gear idle shaft 38 by bearings such that the reverse gear idler wheel 37 and the second reverse gear idler wheel 35 are free to rotate around the reverse gear shaft 38. The park-lock gearwheel 39 is fixed onto the reverse gear shaft 38 coaxially. The reverse gear idler wheel 37 meshes with the idler first gear 60. The second reverse gear idler wheel 35 meshes with the idler second gear 61.

[0062] The park-lock gearwheel 39 comprises a park-lock on the reverse gear shaft 38. The park-lock is the park-lock gearwheel 39 which is provided with a ratchet device, with a click device having a rack element, a pawl or similar. The park-lock keeps the reverse gear shaft 38, the reverse pinion 55 and the output shaft 14 from rotating, which stops a vehicle with the DCT 1 from running when parked. Detailed structure of the park-lock is not shown in FIG. 2.

[0063] The DCT 1 with the park-lock is controlled by a gearshift lever located in a driving compartment and movable by a vehicle operator between positions corresponding to transmission gear ranges such as Park, Reverse, Neutral, Drive, and Low. A linear actuation cable is attached at its first end to the gearshift lever, and movement of the gearshift lever alternatively pushes or pulls on the cable to move a transmission mode select lever attached to the other end of the cable. The mode select lever is mechanically connected to a shift valve within a DCT housing, and movement of the shift valve effects shifting between different gears.

[0064] When the gearshift lever is placed in the Park position, two related mechanical actuations take place within the DCT 1. First, the mode select lever is moved to disengage the input shafts 20, 22 from an engine. Second, the park-lock pawl is moved into locking engagement with the park-lock gearwheel 39 on the reverse gear shaft 38 to thereby lock the output shaft 14 against rotation. A linear actuation cable that actuates the mode select lever moves the lock pawl.

[0065] The lower layshaft 50 is provided below the input shafts 20, 22. There are a number of gearwheels, coupling devices and bearings mounted on the lower layshaft 50, which include, from right to the left, the lower pinion 51, a layshaft bearing 73, an idler seventh gear 66, a double-sided coupling device 83, an idler fifth gear 64, an idler fourth gear 63, a double-sided coupling device 82, an idler sixth gear 65, and a layshaft bearing 73. The lower pinion 51 is fixed onto the lower layshaft 50 at its longitudinal axis. The idler seventh gear 66, the idler fifth gear 64, the idler fourth gear 63 and the idler sixth gear 65 are mounted on the lower layshaft 50 by bearings separately such that these gearwheels become idlers, being free to rotate around the lower layshaft 50. The double-sided coupling devices 83 can move along the lower layshaft 50 such that it can engage either the idler seventh gear 66 or the idler fifth gear 64 to the lower layshaft 50. The double-sided coupling device 82 can also move along the lower layshaft 50 such that it can engage either the idler sixth gear 65 or the idler fourth gear 63 to the lower layshaft 50 respectively. The idler seventh gear 66 meshes with the fixed wheel seventh gear 27. The idler fifth gear 64 meshes with the fixed wheel fifth gear 26. The idler fourth gear 63 meshes with the fixed wheel fourth gear 31. The idler sixth gear 65 meshes with the fixed wheel sixth gear 32.

[0066] In other words, there are four double-meshing features provided in the DCT 1. A first double-meshing feature comprises that the idler first gear 60 meshes with both the reverse gear idler wheel 37 and the fixed wheel first gear 24. A second double-meshing feature comprises that the fixed wheel third gear 25 meshes with both the idler third gear 62 and the idler fifth gear 64. A third double-meshing feature comprises that the fixed wheel second gear 30 meshes with the idler second gear 61 and the idler fourth gear 63. A fourth double meshing feature comprises that the idler second gear 61 meshes with both the second reverse gear idler wheel 35 and the fixed wheel second gear 30.

[0067] A distance 56 between the input shafts 20, 22 and the upper layshaft 40 is measured from a common longitudinal axis of the input shafts 20, 22 to a longitudinal axis of the upper layshaft 40. Similarly, a distance 58 between the input shafts 20, 22 and the lower layshafts 50 is measured from the common longitudinal axis of the input shafts 20, 22 to a longitudinal axis of the lower layshaft 50.

[0068] The output shaft 14 is further provided further below the lower layshaft 50. Two output shaft bearings 75 are installed at two opposite ends of the output shaft 14 respectively for supporting. The output gearwheel 12 is fixed onto the output shaft 14 coaxially in the middle. The output gearwheel 12 meshes with the reverse pinion 55, the lower pinion 51 and the upper pinion 41.

[0069] In the present specification, the expressions "mesh" and "comb" with respect to geared wheels or engaged gearwheels are provided as synonyms. The solid input shaft 20 is alternatively termed as an inner input shaft 20, while the hollow input shaft 22 is alternatively termed as an outer input shaft 22. The solid input shaft 20 is alternatively replaced by a hollow shaft and disposed inside the hollow input shaft 22. The term "coupling device" is alternatively termed as "shifting mechanism" or "synchronizer" for engaging or disengaging gearwheels on its carrying shaft. The double-clutch transmission (DCT) is alternatively termed as a double-clutch, a double clutch transmission or a dual clutch transmission (DCT).

[0070] The fixed wheel first gear 24 is also known as the first fixed gearwheel 24. The fixed wheel third gear 25 is also known as the third fixed gearwheel 25. The fixed wheel fifth gear 26 is also known as the fifth fixed gearwheel 26. The fixed wheel seventh gear 27 is also known as the seventh fixed gearwheel 27. The fixed wheel second gear 30 is also known the second fixed gearwheel 30. The fixed wheel fourth gear 31 is also known as the fourth fixed gearwheel 31. The fixed wheel sixth gear 32 is also known as the sixth fixed gearwheel 32. The second reverse gear idler wheel 35 is also known as the second reverse idler gearwheel 35. The reverse gear idler wheel 37 is also known as the reverse idler gearwheel 37. The idler first gear 60 is also known as the first gear idler gearwheel 60. The idler second gear 61 is also known as the second gear idler gearwheel 61. The idler third gear 62 is also known as the third fixed gearwheel 62. The idler fourth gear 63 is also known as the fourth gear idler gearwheel 63. The idler fifth gear 64 is also known as the fifth gear idler gearwheel 64. The idler sixth gear 65 is also known as the sixth gear idler gearwheel 65. The idler seventh gear 66 is also known as the seventh gear idler gearwheel 66. The output gear wheel 12, the park-lock gearwheel 39, the upper pinion 41, the lower pinion 51, the reverse pinion 55, the fixed wheel first gear 24, the fixed wheel third gear 25, the fixed wheel fifth gear 26, the fixed wheel seventh gear 27, the fixed wheel second gear 30, the fixed wheel fourth gear 31, the fixed wheel sixth gear 32 are also known as fixed gearwheels or gear wheels. The upper pinion 41, the lower pinion 51, and the reverse pinion 55 are alternatively known called final drive pinions or final drives. The park-lock on the park-lock 39 can alternatively be provided on any of the layshafts 38, 40, 50 that has a final drive pinion. Any of the input shafts 20, 22 or layshafts 38, 40, 50 can be supported by more than two bearings.

[0071] In the drawings of the present application, dash lines indicate either alternative positions of illustrated parts or combing relationship between gearwheels.

[0072] The application provides the DCT 1 that permits gearshift operations with less loss of driving torque. This is because the gearshift operations can be achieved by selectively connecting one of the two clutch discs 8, 10 of the DCT 1. Therefore, an associated additional main drive clutch can be avoided. Selective connections between the two clutch discs 8, 10 also enable the realization of an automatic transmission that can be operated without interruptions in propulsive power. The propulsive power comprises momentum derived from the rotating gearwheels and shafts of the DCT 1. Such a transmission is similar in design to a mechanical manual transmission and it has correspondingly very low friction losses. The DCT 1 further provides a parallel manual transmission that can be used for transverse installation in a front-wheel drive vehicle.

[0073] The DCT 1 according to the application can be connected similar to a known manual transmission, such as a parallel manual transmission. In the know manual transmission, a drive shaft for the front axle of a vehicle extends outward from its DCT case, and parallel to the output shaft 14 of the main DCT 1. The arrangement of the known manual transmission provides little space left for actuation of the manual transmission and clutch, and also for an optional electric motor. The optional electric motor can act as a starter device for a combustion engine, as an energy recuperation device for brake operation or as an additional drive means in hybrid vehicles. Having such little space presents difficulties that are solved or at least alleviated by the application. The application provides a DCT 1 that has two clutches for connecting to an electrical motor and the manual transmission respectively in a compact manner.

[0074] The application provides a compact structure of a parallel transmission. The parallel transmission includes two input shafts 20, 22, each of which can be non-rotatably coupled to a shaft via its own clutch that is powered by a drive engine of a vehicle. The DCT 1 of the application further provides the output shaft 14 that is parallel to the input shafts 20, 22.

[0075] The DCT 1 according to the application is particularly well suited for transverse installation in front-wheel drive vehicles, in which the front differential, for example, is positioned below the pinions 41, 51, 55. A short overall length of the power train for transmitting torques can be achieved.

[0076] The application provides at least three relatively small pinions 41, 51, 55 on intermediately arranged layshafts 38, 40, 50 that comb with one relatively big output gearwheel 12. The output gearwheel 12 in turn is fixed onto the output shaft 14. This arrangement provides a compact and lightweight DCT 1.

[0077] The application further enables a design in which the output gearwheel 12 is integrated into a transmission differential device without providing an intermediate output shaft of the DCT 1. This allows a very dense packaging situation for the DCT 1.

[0078] It is further not only of advantage to provide the even gearwheels fixed onto one input shaft, but also fix the odd gears onto another input shaft. This arrangement provides the above-mentioned power-shift operation in a smooth and efficient manner when gearshift is performed sequentially. This is because the DCT 1 can alternatively engage one of the two clutch discs 8, 10 in the process of increasing or decreasing gear. For example, the power-shift operation from the third gear to the fourth gear causes the solid input shaft 20 and the hollow input shaft 22 being engaged alternatively, which is energy efficient and fast.

[0079] Some idler gearwheels of the low gears (e.g. 1st, 2nd, & 3rd gears) provided on the same layshaft are advantageous. In FIG. 2, the idler first gear 60, the idler second gear 61, and the idler third gear 62 are installed on the same upper layshaft 40. In contrast, idler gearwheels of high gears (e.g. 4th, 5th, 6th, & 7th gears) provided on another layshaft. According to FIG. 2, the idler fourth gear 63, the idler fifth gear 64, the idler sixth gear 65, and the idler seventh gear 66 are provided on the same lower layshaft 40. The lower layshaft 50 has higher rotational speed with smaller diameter for lower torque transmission, as compared to that of the upper layshaft 40. This arrangement eliminates the need of providing multiple layshafts with large size for carrying those heavily duty idler gearwheels 60, 61, 62 of low gears (e.g. 1st, 2nd, & 3rd gears) on many shafts respectively. These arrangements offer the feasibility of making the DCT 1 lightweight and compact at less cost.

[0080] The layshaft bearings 73, 74 of the DCT 1 are next to the pinions 38, 41, 51. The layshaft bearings 73, 74 offer strong support to the pinions 38, 41, 51 carrying layshafts 38, 40, 50 for reducing unwanted shaft deflection. Excessive shaft deflection can lower gear transmission efficiency or cause gearwheels' early worn out. The idler shaft bearings 74 next to the reverse gear idler wheel 37 also provide strong support to the reverse gear shaft 38. In a like manner, the output shaft bearings 75 at two opposite ends of the output shaft 14 offer sturdy support to the output shaft 14.

[0081] In fact, it is also beneficial to provide the idler first gear 60, the idler second gear 61, and the reverse gear idler wheel 37 close to the bearings 73, 74, 75 for supporting. As shown in FIG. 2, the layshaft bearing 73 is immediately adjacent to the idler first gear 60 for giving strong support to the upper layshaft 40. The pinions 38, 41, 51 and especially these gearwheels of low gears (e.g. 1st and 2nd gears) undergo heavier load than those of the higher gears (e.g. 6th & 7th gears) because their drive ratio is higher for the lower gears and reverse gears. Therefore, a carrying shaft of low gears (e.g. upper layshaft 40) must take up stronger driving torques and carry heavier gearwheels with larger sizes. If those loads are taken up close to the supporting bearings of the shafts, their load-carrying shafts' bending will be reduced.

[0082] FIG. 2 illustrates the path of torque flow of a first gear transmission ratio. In FIG. 2, an input torque of the first gear is received from a crankshaft 2 of a combustion engine (not shown). According to FIG. 2, the input torque of the first gear is received by the hollow input shaft 22 from the double-clutch 6 of the DCT 1. A torque of the first gear is transmitted from the hollow input shaft 22, via the fixed wheel first gear 24, via the idler first gear 60, via the double-sided coupling device 80, via the upper layshaft 40, via upper pinion 41, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 80 is engaged the idler first gear 60 to the upper layshaft 40 when transmitting the torque of the first gear, which provides the first gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the first gear is two.

[0083] FIG. 3 illustrates the path of torque flow of a second gear transmission ratio. In FIG. 3, an input torque of the second gear is received from the crankshaft 2 of the combustion engine (not shown). According to FIG. 3, the input torque of the second gear is received by the solid input shaft 20 from the double-clutch 6 of the DCT 1. A torque of the second gear is transmitted from the solid input shaft 20, via the fixed wheel second gear 30, via the idler second gear 61, via the single-sided coupling device 81, via the upper layshaft 40, via the upper pinion 41, via the output gearwheel 12, to the output shaft 14. The single-sided coupling device 81 engages the idler second gear 61 to the upper layshaft 40 when transmitting the torque of the second gear, which provides the second gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the second gear is two.

[0084] FIG. 4 illustrates the path of torque flow of a third gear transmission ratio. In FIG. 4, an input torque of the third gear is received from the crankshaft 2 of the combustion engine (not shown). According to FIG. 4, the input torque of the third gear is received by the hollow input shaft 22 from the double-clutch of the DCT 1. A torque of the third gear is transmitted from the hollow input shaft 22, via the fixed wheel third gear 25, via the idler third gear 62, via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 80 engages the idler wheel third gear 62 to the upper layshaft 40 when transmitting the torque of the third gear, which provides the third gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the third gear is two.

[0085] FIG. 5 illustrates the path of torque flow of a fourth gear transmission ratio. In FIG. 5, an input torque of the fourth gear is received from the crankshaft 2 of the combustion engine (not shown). According to FIG. 5, the input torque of the fourth gear is received by the solid input shaft 20 from the double-clutch 6 of the DCT 1. A torque of the fourth gear is transmitted from the solid input shaft 20, via the fixed wheel fourth gear 31, via the idler fourth gear 63, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 82 engages the idler fourth gear 63 to the lower layshaft 50 when transmitting the torque of the fourth gear, which provides the fourth gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the fourth gear is two.

[0086] FIG. 6 illustrates the path of torque flow of a fifth gear transmission ratio. In FIG. 6, an input torque of the fifth gear is received from the crankshaft 2 of a combustion engine (not shown). According to FIG. 6, the input torque of the fifth gear is received by the hollow input shaft 22 from the double-clutch 6 of the DCT 1. A torque of the fifth gear is transmitted from the hollow input shaft 22, via the fixed wheel fifth gear 26, via the idler fifth gear 64, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 83 engages the idler fifth gear 64 to the lower layshaft 50 when transmitting the torque of the fifth gear, which provides the fifth gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the fifth gear is two.

[0087] FIG. 7 illustrates the path of torque flow of a sixth gear transmission ratio. In FIG. 7, an input torque of the sixth gear is received from the crankshaft 2 of a combustion engine (not shown). According to FIG. 7, the input torque of the sixth gear is received by the solid input shaft 20 from the double-clutch 6 of the DCT 1. A torque of the sixth gear is transmitted from the solid input shaft 20, via the fixed wheel sixth gear 32, via the idler sixth gear 65, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 41, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 82 engages the idler sixth gear 65 to the lower layshaft 50 when transmitting the torque of the sixth gear, which provides the sixth gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the sixth gear is two.

[0088] FIG. 8 illustrates the path of torque flow of a seventh gear transmission ratio. In FIG. 8, an input torque of the seventh gear is received from the crankshaft 2 of a combustion engine (not shown). According to FIG. 8, the input torque of the seventh gear is received by the hollow input shaft 22 from the double-clutch 6 of the DCT 1. A torque of the seventh gear is transmitted from the hollow input shaft 22, via the fixed wheel seventh gear 27, via the idler seventh gear 66, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 83 engages the idler seventh gear 66 to the lower layshaft 50 when transmitting the torque of the seventh gear, which provides the seventh gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the seventh gear is two.

[0089] FIG. 9 illustrates the path of torque flow of a first reverse gear transmission ratio. In FIG. 9, an input torque of the first reverse gear is received from the crankshaft 2 of a combustion engine (not shown). According to FIG. 9, the input torque of the first reverse gear is received by the hollow input shaft 22 from the double-clutch 6 of the DCT 1. A torque of the first reverse gear is transmitted from the hollow input shaft 22, via the fixed wheel first gear 24, via the idler first gear 60, via the reverse gear idler wheel 37, via the double-sided coupling device 84, via the reverse gear idle shaft 38, via the reverse pinion 55, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 84 engages the reverse gear idler wheel 37 to the reverse gear idle shaft 38 when transmitting the torque of the first reverse gear, which provides the first reverse gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the first reverse gear is three.

[0090] Alternative paths for transmitting some of the above-mentioned torque flow paths of the DCT 1 are possible to be provided.

[0091] FIG. 10 illustrates the path of torque flow of a second reverse gear transmission ratio, which provides an alternative to the first reverse gear. In FIG. 10, a second reverse gear idler wheel 36 and a single-sided coupling device 85 have been added onto the reverse gear idle shaft 38 at its left end. The second reverse gear idler wheel 36 meshes with the idler sixth gear 65. In FIG. 10, an input torque of the second reverse gear is received from the crankshaft 2 of a combustion engine (not shown). According to FIG. 10, the input torque of the second reverse gear is received by the solid input shaft 20 from the double-clutch 6 of the DCT 1. A torque of the second reverse gear is transmitted from the solid input shaft 20, via the fixed wheel second gear 30, via the idler second gear 61, via the second reverse gear idler wheel 35, via the double-sided coupling device 84, via the reverse gear idle shaft 38, via the reverse pinion 55, via the output gearwheel 12, to the output shaft 14. The double-sided coupling device 84 engages the second reverse gear idler wheel 35 to the reverse gear shaft 38 when transmitting the torque of the second reverse gear, which provides the second reverse gear of the DCT 1. The number of tooth engagements or engaged gear pairs for the torque transfer of the second reverse gear is three.

[0092] FIG. 11 illustrates an assembly 100 of a double-sided coupling device 102 with its neighboring gearwheels 101, 103 for engagement. The assembly 100 comprises a shaft 104 with the two coaxially mounted idler gears 101, 103 on two bearings respectively. The coupling device 102 is provided between the idler gear 101 on the left and the idler gear 103 on the right. The coupling device 102 is configured to move along the shaft 104 to selectively engage any of the idler gears 101, 103 at one time. In other words, the idler gears 101, 103 can alternatively be brought into non-rotating engagement with the shaft 104 by the coupling device 102. Symbols for showing the assembly 100 is provided at the right hand side of FIG. 11.

[0093] FIG. 12 illustrates an assembly 110 of a single-sided coupling device 112 with its neighboring gearwheel 113 for engagement. The assembly 110 comprises a shaft 114 with the one coaxially mounted idler gear 113 on a bearing. The coupling device 112 is provided next to the idler gear 113 on the left side. The coupling device 112 is configured to move along the shaft 114 to engage or disengage the idler gears 113. In other words, the idler gear 113 can be brought into non-rotating engagement with the shaft 114 by the single-sided coupling device 112. Symbols for showing the assembly 110 are provided at the right hand side of FIG. 12.

[0094] FIG. 13 illustrates an assembly 120 of an idler gearwheel 121 that is rotatably supported by a shaft 122 on a bearing 123. The idler gearwheel 121 is coaxially mounted onto the shaft 122 via the bearing 123. The bearing 123 enables the idler gearwheel 121 to be freely rotated around the shaft 122. Symbols that represent the assembly 120 are provided at the right hand side of the FIG. 13.

[0095] FIG. 14 illustrates an assembly 130 of a fixed gearwheel 132 that is supported on a shaft 131. The fixed gearwheel 132 is coaxially mounted onto the shaft 131 such that the gearwheel 132 is fixed to the shaft 131. The fixed gearwheel 132 and the shaft 131 are joined as one single body such that torque of the fixed gearwheel 132 is transmitted to the shaft 131 directly, and vice versa.

[0096] A number of fixed gearwheels are rigidly connected to the input shafts 20, 22 and other shafts 14, 38, 40, 50 in a manner that is similar to the assembly 130. A symbol as used in the previous figures for such a fixed gearwheel is provided on the left side in FIG. 14. The more commonly used symbol for such a fixed gearwheel is provided on the right side in FIG. 14.

[0097] FIG. 15 illustrates a cross-section through a detail of a crankshaft 2 of an internal combustion engine according to the embodiment of the DCT 1. According to FIG. 15, the crankshaft 2 of the internal combustion engine, which is not shown here, is non-rotatably connected to a housing 4 of a double clutch 6. The double clutch 6 includes an inner clutch disc 8 and an outer clutch disc 10, which can be brought into non-rotating engagement with the housing 4 via control elements that are not illustrated here. The solid input shaft 20 can be non-rotatably connected to the inner clutch disc 8, and extends all the way through the hollow shaft 22. Similarly, the hollow input shaft 22 can be non-rotatably connected to the outer clutch disc 10. The inner clutch disc 8 is also known as the inner clutch, whilst the outer clutch disc 10 is also known as the outer clutch.

[0098] The clutch housing 4 has a larger outer diameter around the inner clutch disc 8 than that around the outer clutch disc 10. Correspondingly, the inner clutch disc 8 has a larger outer diameter than that of the outer clutch disc 10 inside the clutch housing 4. The fact that the larger inner clutch disc 8 on the solid input shaft 20 drives the first gear makes the DCT 1 robust.

[0099] The above-mentioned nine torque flow paths not only provide viable solutions to generate nine gears of the DCT 1, but also offer possibilities of switching from one gear to another efficiently. The gear switching can be achieved by switching between the two input shafts, between gearwheels of a double meshing feature, or in combination of both.

[0100] For example, the DCT 1 can provide odd gears (i.e. 1st, 3rd, 5th & 7th gears) by driving the gearwheels of the DCT 1 using the hollow input shaft 22. The DCT 1 also can provide even gears (i.e. 2nd, 4th & 6th gears) by driving the gearwheels of the DCT 1 using the solid input shaft 20. Gear switching between the odd and the even can simply be obtained by alternating between the two input shafts 20, 22.

[0101] One double meshing feature provides efficient and fast gear switching between gears of two driven gearwheels that comb with a shared driving gearwheel. For example, the DCT 1 provides the convenience of selecting the third gear or the fifth gear without stopping their shared driving gearwheel, namely the fixed wheel third gear 25. The selection can be achieved by engaging either the driven idler third gear 62 or the driven idler fifth gear 64.

[0102] The double-meshing feature of the fixed wheel third gear 25 reduces the number of driving gearwheels, which is commonly engaged by the driven gearwheels idler third gear 62 and the driven gearwheel idler fifth gear 64. For example, the fixed wheel third gear 25 and the fixed wheel fifth gear 26 as driving gear wheels become one single gearwheel that is shared by the idler third gear 62 and the idler fifth gear 64. As a result, the number of gearwheels on the hollow input shaft 22 has been reduced and less space is required on the hollow input shaft 22 so that the DCT 1 can be made cheaper and lighter.

[0103] The other double-meshing feature of the fixed wheel fourth gear 31 also reduces the number of driving gearwheels, which is commonly engaged by the driven gearwheel idler second gear 61 and the driven idler fourth gear 63. For example, the driving fixed wheel fourth gear 31 and the driving fixed wheel second gear 30 become one single gearwheel that is shared by the idler fourth gear 63 and the idler second gear 61. As a result, the number of gearwheels on the solid input shaft 20 has been reduced and less space is required on the solid input shaft 20 so that the DCT 1 can be made cheaper and lighter.

[0104] The park-lock gearwheel 39 comprises a park-lock on the reverse gear shaft 38 that carries a final drive pinion 55. The park-lock is a wheel which is provided with a ratchet device, with a click device having a rack element, a claw or similar. The park-lock keeps the reverse gear shaft 38, the reverse pinion 55, the output gear wheel 12, and the output shaft 14 from rotating, which stops a vehicle with the DCT 1 from running when parked. Detailed structure of the park-lock is not shown.

[0105] In providing gear meshing or combing for torque transmission, less number of gear tooth engagement (i.e. gear engagement) is preferred. The less number of gear tooth engagement provides lower noise and more efficient torque transmission. Examples of the less gear tooth engagement are provided in FIGS. 2-10.

[0106] The DCT 1 drives the gearwheel groups of the first gear and the second reverse gear by different input shafts 20, 22. A vehicle with the DCT 1 can move between a slow forward mode and a slow backward mode by engaging and disengaging the respective clutch discs 8, 10, which are connected to the two input shafts 20, 22 respectively. The DCT 1 enables the vehicle to move back and forth quickly with little loss of the transmission power or gearwheels momentum. This scheme helps in many situations in which a wheel of the vehicle is stuck in a hostile environment such as a snow hole or a mud hole. The vehicle can then be swayed free just by switching between the two clutch discs 8, 10. Alternatively, the vehicle cam move back and forth by switching between the second forward gear and the first reverse gear.

[0107] The DCT 1 provides two reveres gears so that a vehicle can be maximized in engine output capacity. The DCT 1 can also be more fuel efficient when having the two reverse gears. The DCT 1 with the two reverse gears is especially useful for maneuverability of some specialized vehicles, such as main battle tanks.

[0108] Moreover, the fact that two reverse gears are provided by two different input shafts respectively are convenient because any of the two reverse gears can be swiftly chosen by engaging one of the clutch discs 8, 10 of the DCT 1.

[0109] FIGS. 16-17 illustrate a further embodiment of the application. The embodiment includes parts that are similar to the parts of previously described embodiment. The similar parts are labeled with the same or similar part reference number. Descriptions related to the similar parts are hereby incorporated by reference.

[0110] FIG. 16 shows a front view of the gearbox of the application. A relatively big output gearwheel 12 on an output shaft 14 meshes with a lower pinion 51 which is provided on a lower layshaft 50. The output gearwheel 12 further meshes with an upper pinion 41 which is provided on an upper layshaft 40. A reverse gear shaft 38, a solid input shaft 20, and a hollow output shaft 22 are provided in parallel with the layshafts 40, 50. In some variants of the application, at least one a further layshaft with a further pinion can be provided but this is not shown here. Such a further pinion would then also mesh or comb with the output gearwheel 12.

[0111] FIG. 16 further comprises a cutting plane A-A for illustrating the cross-section through the gearbox which is shown in FIG. 17. For an embodiment which has more than two layshafts or an additional idler shaft, a cutting plane which leads through all shafts is applied similarly. One of the goals of FIG. 17 is to further illustrate the structure and the torque flows through the embodiment of the gearbox.

[0112] FIG. 17 illustrates a simplified cross-section through the double clutch transmission gearbox 1 of FIG. 16. It illustrates structure and various torque flows for the several gears of the double clutch transmission gearbox 1.

[0113] The double clutch transmission gearbox 1 comprises the following shafts, from top to bottom, the reverse gear shaft 38, the upper layshaft 40, the solid input shaft 20, the hollow shaft 22, the lower layshaft 50 and the output shaft 14.

[0114] The above-mentioned shafts are provided parallel to each other at predetermined mutual distances inside the gearbox 1. The hollow shaft 22 is arranged concentrically around the solid shaft 20. The solid input shaft 20 protrudes outside the hollow input shaft 22 at both ends.

[0115] The solid input shaft 20 comprises, from the right end to the left end, a solid shaft bearing 71, a hollow shaft bearing 72, which serve also as solid shaft bearing 71, a fixed wheel second gear 30, which serves also as a fixed wheel fourth gear 31, a fixed wheel sixth gear 32, and a solid shaft bearing 71.

[0116] The hollow input shaft 22 comprises, from the right end to the left end, a hollow shaft bearing 72, a fixed wheel first gear 24, a fixed wheel seventh gear 27, and a fixed wheel third gear 25, which serves also as a fixed wheel fifth gear 26.

[0117] The upper layshaft 40 comprises, from the right end to the left end, the upper pinion 41, a layshaft bearing 73, an idler first gear 60, an attached idler first gear 60' which is attached to the idler first gear 60, a double-sided coupling device 80, an idler third gear 62, an idler second gear 61, a single-sided coupling device 81, a park-lock gearwheel 39, and a layshaft bearing 73. The idler first gear 60 meshes with the fixed wheel first gear 24. The idler third gear 62 meshes with the fixed wheel third gear 25. The idler second gear 61 meshes with the fixed wheel second gear 30. The double-sided coupling device 80 is configured to move the along the upper layshaft 40 for engaging either attached idler first gear 60' or the idler third gear 62 to the upper layshaft 40. The single-sided coupling device 81 is also configured to move along the upper layshaft 40 for engaging or disengaging the idler second gear 61 to the 40.

[0118] The reverse gear shaft 38 comprises, from the right end to the left end, the reverse pinion 55, a reverse gear idler wheel 37, a double-sided coupling device 85, a second reverse gear wheel 36 as an idler, and an idle shaft bearing 74. The reverse gear idler wheel 37 meshes with the attached idler first gear 60'.

[0119] The lower layshaft 50 comprises, from the right end to the left end, the lower pinion 51, a layshaft bearing 73, an idler seventh gear 66, a double-sided coupling device 83, an idler fifth gear 64, an idler fourth gear 63, a double-sided coupling device 82, an idler sixth gear 65, and a layshaft bearing 73. The idler seventh gear 66 meshes with the fixed wheel seventh gear 27. The idler fifth gear 64 meshes with the fixed wheel fifth gear 26. The idler fourth gear 63 meshes with the fixed wheel fourth gear 31. The idler sixth gear 65 meshes with both the second reverse gear wheel 36 and the second reverse gear wheel 36.

[0120] Torque flow of the first gear according to FIG. 17 starts from the hollow input shaft 22, via the fixed wheel first gear 24, via the idler first gear 60, via the attached idler first gear 60', via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0121] Torque flow of the second gear according to FIG. 17 starts from the solid input shaft 20, via the fixed wheel second gear 30, via the idler second gear 61, via the single-sided coupling device 81, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0122] Torque flow of the third gear according to FIG. 17 starts from the hollow input shaft 22, via the fixed wheel third gear 25, via the idler third gear 62, via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0123] Torque flow of the fourth gear according to FIG. 17 starts from the solid input shaft 20, via the fixed wheel fourth gear 31, via the idler fourth gear 63, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0124] Torque flow of the fifth gear according to FIG. 17 starts from the hollow input shaft 22, via the fixed wheel fifth gear 26, via the idler fifth gear 64, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0125] Torque flow of the sixth gear according to FIG. 17 starts from the solid input shaft 20, via the fixed wheel sixth gear 32, via the idler sixth gear 65, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0126] Torque flow of the seventh gear according to FIG. 17 starts from the hollow input shaft 22, via the fixed wheel seventh gear 27, via the idler seventh gear 66, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0127] Torque flow of the first reverse gear according to FIG. 17 starts from the hollow input shaft 22, via the fixed wheel first gear 24, via the idler first gear 60, via the attached idler first gear 60', via the reverse gear idler wheel 37, via the double-sided coupling device 85, via the reverse gear layshaft 38, via the reverse pinion 55, via the output gear wheel 12, to the output shaft 14.

[0128] Torque flow of the second reverse gear according to FIG. 17 starts from the solid input shaft 20, via the fixed wheel sixth gear 32, via the idler sixth gear 65, via the second reverse gear wheel 36, via the double-sided coupling device 85, via the reverse gear layshaft 38, via the reverse pinion 55, via the output gear wheel 12, to the output shaft 14.

[0129] FIGS. 18-19 illustrate a further embodiment of the application. The embodiment includes parts that are similar to the parts of previously described embodiments. The similar parts are labeled with the same or similar part reference number. Descriptions related to the similar parts are hereby incorporated by reference.

[0130] FIG. 18 shows a front view of the gearbox of the application. A relatively big output gear wheel 12 on an output shaft 14 meshes with a lower pinion 51 which is provided on a lower layshaft 50. The output gearwheel 12 further meshes with an upper pinion 41 which is provided on an upper layshaft 40. A reverse gear idler shaft 38, a solid input shaft 20, a hollow input shaft 22 are provided in parallel with the two layshafts 40, 50. In some variants of the application, at least one a further layshaft with a further pinion can be provided but this is not shown here. Such a further pinion would then also mesh or comb with the output gear wheel 12.

[0131] FIG. 18 further comprises a cutting plane A-A for illustrating the cross-section through the gearbox which is shown in FIG. 19. For an embodiment which has more than two layshafts or an additional idler shaft, a cutting plane which leads through all shafts is applied similarly. One of the goals of FIG. 19 is to further illustrate structure and torque flows through the embodiment of the gearbox 1.

[0132] FIG. 19 illustrates a simplified cross-section through the double clutch transmission gearbox 1 of FIG. 18. It illustrates structure and various torque flows for the several gears of the double clutch transmission gearbox 1.

[0133] The double clutch transmission gearbox 1 comprises the following shafts, from top to bottom, the reverse gear idler shaft 38, the upper layshaft 40, the solid input shaft 20, the hollow input shaft 22, the lower layshaft 50, and the output shaft 14.

[0134] The above-mentioned shafts are provided parallel to each other at predetermined mutual distances inside gearbox 1. The hollow shaft 22 is arranged concentrically around the solid input shaft 20. The solid input shaft 20 protrudes outside the hollow input shaft 22 at the right end.

[0135] The solid input shaft 20 comprises, from the right end to the left end, a solid shaft bearing 71, a hollow shaft bearing 72, which serves also as a solid shaft bearing 71, a fixed wheel fourth gear 31, which is at the same time a fixed wheel second gear 30, a fixed wheel sixth gear 32, and a solid shaft bearing 71.

[0136] The hollow input shaft 20 comprises, from the right end to the left end, a hollow shaft bearing 72, a fixed wheel first gear 24, a fixed wheel seventh gear 27, and a fixed wheel third gear 25 which is at the same time a fixed wheel fifth gear 26.

[0137] The upper layshaft 40 comprises, from the right end to the left end, the upper pinion 41, a layshaft bearing 73, an idler first gear 60, combing with the fixed wheel first gear 24, a attached idler first gear 60' which is attached to the idler first gear 60, a double-sided coupling device 80, an idler third gear 62, combing with the fixed wheel third gear 25, an idler second gear 61, combing with the fixed wheel second gear 30, a single-sided coupling device 81, a park-lock gearwheel 39, and a layshaft bearing 73.

[0138] The lower layshaft 50 comprises, from the right end to the left end, a lower pinion 51, a layshaft bearing 73, an idler seventh gear 66, combing with the fixed wheel seventh gear 27, a double-sided coupling device 83, an idler fifth gear 64, combing with the fixed wheel fifth gear 26, an idler fourth gear 63, combing with the fixed wheel fourth gear 31, a double-sided coupling device 82, an idler sixth gear 65, combing with the fixed wheel sixth gear 32, and a solid shaft bearing 71.

[0139] The reverse gear shaft 38 comprises, from the right end to the left end, an idle shaft bearing 74, a reverse gear idler wheel 37, combing with the attached idler first gear 60', a second fixed wheel reverse gear 35, combing with the fixed wheel reverse gear 34, and an idle shaft bearing 74.

[0140] Torque flow first gear according to FIG. 19 starts from the hollow input shaft 22, via the fixed wheel first gear 24, via the idler first gear 60, via the attached idler first gear 60' via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0141] Torque flow second gear according to FIG. 19 starts from the solid input shaft 20, via the fixed wheel second gear 30, via the idler second gear 61, via the single-sided coupling device 81, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0142] Torque flow third gear according to FIG. 19 starts from the hollow input shaft 22, via the fixed wheel third gear 25, via the idler third gear 62, via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0143] Torque flow fourth gear according to FIG. 19 starts from the solid input shaft 20, via the fixed wheel fourth gear 31, via the idler fourth gear 63, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0144] Torque flow fifth gear according to FIG. 19 starts from the hollow input shaft 22, via the fixed wheel fifth gear 26, via the idler fifth gear 64, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0145] Torque flow sixth gear according to FIG. 19 starts from the solid input shaft 20, via the fixed wheel sixth gear 32, via the idler sixth gear 65, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0146] Torque flow seventh gear according to FIG. 19 starts from the hollow input shaft 22, via the fixed wheel seventh gear 27, via the idler seventh gear 66, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gear wheel 12, to the output shaft 14.

[0147] Torque flow a reverse gear according to FIG. 19 starts from the solid input shaft 20, via the fixed wheel reverse gear 34, via the first reverse gear wheel 35, via the reverse gear idler shaft 38, via the single-sided coupling device 85, via the reverse gear idler wheel 37, via the attached idler first gear 60' via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gear wheel 12, to the output shaft 14.

[0148] FIGS. 20-21 illustrate a further embodiment of the application. The embodiment includes parts that are similar to the parts of previously described embodiments. The similar parts are labeled with the same or similar part reference number. Descriptions related to the similar parts are hereby incorporated by reference.

[0149] FIG. 20 shows a front view of the gearbox 1 of the application. A relatively big output gear wheel 12 on an output shaft 14 meshes with a lower pinion 51 which is provided on a lower layshaft 50. The output gear wheel 12 further meshes with an upper pinion 41 which is provided on an upper layshaft 40. The output gear wheel 12 also meshes with a reverse pinion 55 which is provided on a reverse gear shaft 38. In some variants of the application, at least one a further layshaft with a further pinion can be provided but this is not shown here. Such a further pinion would then also mesh or comb with the output gearwheel 12.

[0150] FIG. 20 further comprises a cutting plane A-A for illustrating the cross-section through the gearbox 1 which is shown in FIG. 21. For an embodiment which has more than two layshafts or an additional idler shaft, a cutting plane which leads through all shafts is applied similarly. One of the goals of FIG. 21 is to further illustrate structure and torque flows through the embodiment of the gearbox 1.

[0151] FIG. 21 illustrates a simplified cross-section through the double clutch transmission gearbox 1 of FIG. 20. It illustrates structure and various torque flows for the several gears of the double clutch transmission gearbox 1.

[0152] The double clutch transmission gearbox 1 comprises the following shafts, from top to bottom, the reverse gear shaft 38, the upper layshaft 40, the solid input shaft 20, the hollow input shaft 22, the lower layshaft 50, and the output shaft 14. The above-mentioned shafts are provided parallel to each other at predetermined mutual distances inside gearbox 1. The hollow shaft 22 is arranged concentrically around the solid input shaft 20. The solid input shaft 20 protrudes outside the hollow input shaft 22 at its two ends.

[0153] The solid input shaft 20 comprises, from the right end to the left end, a solid shaft bearing 71, a hollow shaft bearing 72, which serves also as a solid shaft bearing 71, a fixed wheel fourth gear 31 which serves also as a fixed wheel second gear 30, a fixed wheel sixth gear 32, and a solid shaft bearing 71.

[0154] The hollow input shaft 20 comprises, from the right end to the left end, a hollow shaft bearing 72, a fixed wheel seventh gear 27, and a fixed wheel third gear 25, which also serves as a fixed wheel fifth gear 26.

[0155] The upper layshaft 40 comprises, from the right end to the left end, the upper pinion 41, a layshaft bearing 73, an idler first gear 60, a double-sided coupling device 80, an attached idler third gear 62', an idler third gear 62, combing with the fixed wheel third gear 25, an idler second gear 61, combing with the fixed wheel second gear 30, a single-sided coupling device 81, and a layshaft bearing 73.

[0156] The reverse gear shaft 38 comprises, from the right end to the left end, the reverse pinion 55, an idler shaft bearing 74, a first reverse gear wheel 35 on the reverse gear hollow shaft 39, combing with the idler first gear 60, a second reverse gear wheel 36 on the reverse gear hollow shaft 39, combing with the attached idler third gear 62', a single-sided coupling device 85, and an idler shaft bearing 74.

[0157] The lower layshaft 50 comprises, from the right end to the left end, the lower pinion 51, a layshaft bearing 73, an idler seventh gear 66, combing with the fixed wheel seventh gear 27, a double-sided coupling device 83, an idler fifth gear 64, combing with the fixed wheel fifth gear 26, an idler fourth gear 63, combing with the fixed wheel fourth gear 31, a double-sided coupling device 82, an idler sixth gear 65, combing with the fixed wheel second gear 30, a 34, and a solid shaft bearing 71.

[0158] Torque flow first gear according to FIG. 21 starts from the hollow input shaft 22, via the 25, via the idler third gear 62, via the attached idler third gear 62', via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gearwheel 12, to the output shaft 14.

[0159] Torque flow second gear according to FIG. 21 starts from the solid input shaft 20, via the fixed wheel second gear 30, via the idler second gear 61, via the single-sided coupling device 81, via the upper layshaft 40, via the upper pinion 41, via the output gearwheel 12, to the output shaft 14.

[0160] Torque flow third gear according to FIG. 21 starts from the hollow input shaft 22, via the fixed wheel third gear 25, via the idler third gear 62, via the attached idler third gear 62', via the double-sided coupling device 80, via the upper layshaft 40, via the upper pinion 41, via the output gearwheel 12, to the output shaft 14.

[0161] Torque flow fourth gear according to FIG. 21 starts from the solid input shaft 20, via the fixed wheel fourth gear 31, via the idler fourth gear 63, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14.

[0162] Torque flow fifth gear according to FIG. 21 starts from the hollow input shaft 22, via the fixed wheel fifth gear 26, via the idler fifth gear 64, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14.

[0163] Torque flow sixth gear according to FIG. 21 starts from the solid input shaft 20, via the fixed wheel sixth gear 32, via the idler sixth gear 65, via the double-sided coupling device 82, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14.

[0164] Torque flow seventh gear according to FIG. 21 starts from the hollow input shaft 22, via the fixed wheel seventh gear 27, via the idler seventh gear 66, via the double-sided coupling device 83, via the lower layshaft 50, via the lower pinion 51, via the output gearwheel 12, to the output shaft 14.

[0165] Torque flow first reverse gear according to FIG. 21 starts from the hollow input shaft 22, via the fixed wheel third gear 25, via the idler third gear 62, via the attached idler third gear 62', via the second reverse gear wheel 36, via the reverse gear hollow shaft 39, via the single-sided coupling device 85, via the reverse gear shaft 38, via the reverse pinion 55, via the output gearwheel 12, to the output shaft 14.

[0166] FIG. 22 illustrates an alternative expanded side view of the double clutch transmission of FIG. 16. FIG. 22 comprises parts that are similar to that of FIGS. 16-17. The similar parts have similar or same part reference numbers. Descriptions of the similar or the same parts are hereby incorporated.

[0167] FIG. 23 illustrates an alternative front view of a further embodiment of a double clutch transmission in FIG. 19. FIG. 23 comprises parts that are similar to that of FIGS. 18-19. The similar parts have similar or same part reference numbers. Descriptions of the similar or the same parts are hereby incorporated.

[0168] Although the above description contains much specificity, these should not be construed as limiting the scope of the embodiments but merely providing illustration of the foreseeable embodiments. Especially the above stated advantages of the embodiments should not be construed as limiting the scope of the embodiments but merely to explain possible achievements if the described embodiments are put into practice. Thus, the scope of the embodiments should be determined by the claims, rather than by the examples given.

[0169] While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

Claims

1. A double-clutch transmission, comprising: an inner input shaft and an outer input shaft, at least a portion of the inner input shaft being surrounded by the outer input shaft; a first clutch disc connected to the inner input shaft and a second clutch disc connected to the outer input shaft; a first layshaft, a second layshaft and a third layshaft spaced apart from the input shafts and arranged in parallel to the input shafts; at least one of the layshafts comprises a pinion; gearwheels arranged on the first layshaft, on the second layshaft, on the third layshaft, on the inner input shaft and on the outer input shaft, the gearwheels comprising a first gearwheel group, a second gearwheel group, a third gearwheel group, a fourth gearwheel group, a fifth gearwheel group, a sixth gearwheel group, a seventh gearwheel group for providing seven sequentially increasing forward gears, the first gearwheel group comprising a first fixed gearwheel on the outer input shaft, meshing with a first gear idler gearwheel on one of the layshafts for providing a first forward gear, the third gearwheel group comprising a third driving gearwheel on the outer input shaft, meshing with a third driven gearwheel on one of the layshafts for providing a third forward gear, the fifth gearwheel group comprising a fifth fixed gearwheel on the outer input shaft, meshing with a fifth gear idler gearwheel on one of the layshafts for providing a fifth forward gear, the seventh gearwheel group comprising a seventh fixed gearwheel on the outer input shaft, meshing with a seventh gear idler gearwheel on one of the layshafts for providing a seventh forward gear, the second gearwheel group comprising a second fixed gearwheel on the inner input shafts, meshing with a second gear idler gearwheel on one of the layshafts for providing a second forward gear, the fourth gearwheel group comprising a fourth fixed gearwheel on the inner input shafts, meshing with a fourth gear idler gearwheel on one of the layshafts for providing a fourth forward gear, the sixth gearwheel group comprising a sixth fixed gearwheel on the inner input shafts, meshing with a sixth gear idler gearwheel on one of the layshafts for providing a sixth forward gear, and each gearwheel group comprising a coupling device which is arranged on one of the layshafts to selectively engage one of the gearwheels for selecting one of the seven gears, and the third fixed gearwheel further meshing with the fifth gear idler gearwheel, wherein the gearwheels further comprises a reverse gearwheel group that comprises a reverse fixed gearwheel on one of the input shafts, meshing with a reverse gear idler gearwheel on one of the layshafts for providing a reverse gear, the reverse gearwheel group further comprises a coupling device on one of the layshafts to engage the reverse gear idler gearwheel for providing the reverse gear, and the second fixed gearwheel further meshes with the fourth gear idler gearwheel.

2. The double-clutch transmission according to claim 1, wherein the first forward gear and the reverse gear are provided by the different input shafts.

3. The double-clutch transmission according to claim 1, wherein the reverse gearwheel group provides a first reverse gear and a second reverse gear that are driven by the different input shafts respectively.

4. The double-clutch transmission device according to claim 1, comprising a park-lock.

5. The double-clutch transmission device according to claim 4, wherein the park-lock comprises a fixed gearwheel on one of the layshafts that has the pinion as a final drive.

6. The double-clutch transmission device according to claim 1, further comprising: two pinions mounted on two of the layshafts respectively.

7. The double-clutch transmission device according to claim 1, wherein at least two of the first gear idler gearwheel, the second gear idler gearwheel, and the third gear idler gearwheel are mounted on the same layshaft.

8. The double-clutch transmission device according to claim 1, wherein at least two of the fourth gear idler gearwheel, the fifth gear idler gearwheel, the sixth gear idler gearwheel and the seventh gear idler gearwheel are mounted on the same layshaft.

9. The double-clutch transmission according to claim 1, further comprising bearings for supporting the layshafts, at least one of the bearings being provided next to the pinion.

10. The double-clutch transmission according to claim 8, wherein at least one of the bearings is provided next to one of the driven gearwheels of low gears.

11. A gearbox, comprising; an inner input shaft and an outer input shaft, at least a portion of the inner input shaft surrounded by the outer input shaft; a first clutch disc connected to the inner input shaft and a second clutch disc connected to the outer input shaft; a first layshaft, a second layshaft and a third layshaft spaced apart from the input shafts and arranged in parallel to the input shafts; at least one of the layshafts comprises a pinion; gearwheels arranged on the first layshaft, on the second layshaft, on the third layshaft, on the inner input shaft and on the outer input shaft, the gearwheels comprising a first gearwheel group, a second gearwheel group, a third gearwheel group, a fourth gearwheel group, a fifth gearwheel group, a sixth gearwheel group, a seventh gearwheel group for providing seven sequentially increasing forward gears, the first gearwheel group comprising a first fixed gearwheel on the outer input shaft, meshing with a first gear idler gearwheel on one of the layshafts for providing a first forward gear, the third gearwheel group comprising a third driving gearwheel on the outer input shaft, meshing with a third driven gearwheel on one of the layshafts for providing a third forward gear, the fifth gearwheel group comprising a fifth fixed gearwheel on the outer input shaft, meshing with a fifth gear idler gearwheel on one of the layshafts for providing a fifth forward gear, the seventh gearwheel group comprising a seventh fixed gearwheel on the outer input shaft, meshing with a seventh gear idler gearwheel on one of the layshafts for providing a seventh forward gear, the second gearwheel group comprising a second fixed gearwheel on the inner input shafts, meshing with a second gear idler gearwheel on one of the layshafts for providing a second forward gear, the fourth gearwheel group comprising a fourth fixed gearwheel on the inner input shafts, meshing with a fourth gear idler gearwheel on one of the layshafts for providing a fourth forward gear, the sixth gearwheel group comprising a sixth fixed gearwheel on the inner input shafts, meshing with a sixth gear idler gearwheel on one of the layshafts for providing a sixth forward gear, and each gearwheel group comprising a coupling device which is arranged on one of the layshaft to selectively engage one of the gearwheels for selecting one of the seven gears, and the third fixed gearwheel further meshing with the fifth gear idler gearwheel, wherein the gearwheels further comprises a reverse gearwheel group that comprises a reverse fixed gearwheel on one of the input shafts, meshing with a reverse gear idler gearwheel on one of the layshafts for providing a reverse gear, the reverse gearwheel group further comprises a coupling device on one of the layshafts to engage the reverse gear idler gearwheel for providing the reverse gear, the second fixed gearwheel further meshes with the fourth gear idler gearwheel; and an output gearwheel on an output shaft that meshes with the pinion for outputting a drive torque to a torque drain.

12. A power train device, comprising: an inner input shaft and an outer input shaft, at least a portion of the inner input shaft surrounded by the outer input shaft; a first clutch disc connected to the inner input shaft and a second clutch disc connected to the outer input shaft; a first layshaft, a second layshaft and a third layshaft spaced apart from the input shafts and arranged in parallel to the input shafts; at least one of the layshafts comprises a pinion; gearwheels arranged on the first layshaft, on the second layshaft, on the third layshaft, on the inner input shaft and on the outer input shaft, the gearwheels comprising a first gearwheel group, a second gearwheel group, a third gearwheel group, a fourth gearwheel group, a fifth gearwheel group, a sixth gearwheel group, a seventh gearwheel group for providing seven sequentially increasing forward gears, the first gearwheel group comprising a first fixed gearwheel on the outer input shaft, meshing with a first gear idler gearwheel on one of the layshafts for providing a first forward gear, the third gearwheel group comprising a third driving gearwheel on the outer input shaft, meshing with a third driven gearwheel on one of the layshafts for providing a third forward gear, the fifth gearwheel group comprising a fifth fixed gearwheel on the outer input shaft, meshing with a fifth gear idler gearwheel on one of the layshafts for providing a fifth forward gear, the seventh gearwheel group comprising a seventh fixed gearwheel on the outer input shaft, meshing with a seventh gear idler gearwheel on one of the layshafts for providing a seventh forward gear, the second gearwheel group comprising a second fixed gearwheel on the inner input shafts, meshing with a second gear idler gearwheel on one of the layshafts for providing a second forward gear, the fourth gearwheel group comprising a fourth fixed gearwheel on the inner input shafts, meshing with a fourth gear idler gearwheel on one of the layshafts for providing a fourth forward gear, the sixth gearwheel group comprising a sixth fixed gearwheel on the inner input shafts, meshing with a sixth gear idler gearwheel on one of the layshafts for providing a sixth forward gear, and each gearwheel group comprising a coupling device which is arranged on one of the layshaft to selectively engage one of the gearwheels for selecting one of the seven gears, and the third fixed gearwheel further meshing with the fifth gear idler gearwheel, wherein the gearwheels further comprises a reverse gearwheel group that comprises a reverse fixed gearwheel on one of the input shafts, meshing with a reverse gear idler gearwheel on one of the layshafts for providing a reverse gear, the reverse gearwheel group further comprises a coupling device on one of the layshafts to engage the reverse gear idler gearwheel for providing the reverse gear, the second fixed gearwheel further meshes with the fourth gear idler gearwheel; and an output gearwheel on an output shaft that meshes with the pinion for outputting a drive torque to a torque drain; and at least one power source for generating a driving torque.

13. The power train device according to claim 12, wherein the power source comprises a combustion engine.

14. The power train device according to claim 12, wherein the power source comprises an electric motor.

15. (canceled)