Transmission system for a motor vehicle

Abstract

A transmission system for a motor vehicle includes two input shafts (11, 12), a mainshaft (15), an output shaft (5), a clutch arrangement (40) for connecting alternately the input shafts (11, 12), to a driveshaft, a first power transmission shaft (A1) provided with at least a first gearwheel (K1b) which is in engagement with a gearwheel (K17a) situated on either of the input shafts, and a second gearwheel (K3a) which is in engagement with a gearwheel (35b) situated on the mainshaft, and a second power transmission shaft (A1) provided with at least a first gearwheel (K4b) which is in engagement with a gearwheel (K4a) situated on either of the input shafts, and a second gearwheel (K5a) which is connected or connectable to the gearwheel (K35b) on the mainshaft via an intermediate gearwheel (K5c) to allow the establishment of a power transfer path for a reverse gear via these gearwheels (K5a, K5c, K35b).

Claims

1. A transmission system for a motor vehicle, comprising: first and second input shafts which are mutually coaxial, a mainshaft, an output shaft connected to the mainshaft, a clutch arrangement for connecting alternately said input shafts to a driveshaft, a first power transmission shaft provided with at least a first gearwheel, a second gearwheel situated on either of the input shafts, and in engagement with the first gearwheel, a third gearwheel in engagement with a fourth gearwheel situated on the mainshaft, a second power transmission shaft parallel with the first power transmission shaft, the second power transmission shaft is provided with at least a fifth gearwheel, a sixth gearwheel situated on either of the input shafts, the fifth and sixth gearwheels being engaged; the second power transmission shaft is provided with a seventh gearwheel which is connected or connectable to said fourth gearwheel on the mainshaft via an eighth intermediate gearwheel to allow the establishment of a power transfer path for a reverse gear via these gearwheels; and a movable intermediate wheel shaft on which the eighth intermediate gearwheel is fixed axially, wherein the eighth intermediate gearwheel is movable with the movable intermediate wheel shaft relative to the seventh gearwheel on the second power transmission shaft and the fourth gearwheel on the mainshaft, to and fro between a disconnecting state in which the eighth intermediate gearwheel is disconnected from the seventh gearwheel on the second power transmission shaft and/or from the fourth gearwheel on the mainshaft, and a connecting state in which the eighth intermediate gearwheel is in engagement with the seventh gearwheel on the second power transmission shaft and with the fourth gearwheel on the mainshaft.

2. A transmission system according to claim 1, further comprising: an operating device configured to move the eighth intermediate gearwheel to and fro between the disconnecting state in which the eighth intermediate gearwheel is disconnected from the seventh gearwheel on the second power transmission shaft and/or from the fourth gearwheel on the mainshaft, and the connecting state in which the eighth intermediate gearwheel is in engagement with the seventh gearwheel on the second power transmission shaft and with the fourth gearwheel on the mainshaft.

3. A transmission system according to claim 2, wherein the eighth intermediate gearwheel is movable axially between the states thereof.

4. A transmission system according to claim 3, wherein the operating device is configured to move in axial directions for moving the eighth intermediate gearwheel between the states thereof.

5. A transmission system according to claim 4, further comprising the operating device comprises a pneumatic or hydraulic cylinder including a piston rod, and the intermediate wheel shaft is connected to the piston rod of the hydraulic cylinder.

6. A transmission system according to claim 3, further comprising the eighth intermediate gearwheel is movable on an axially fixed intermediate wheel shaft along which the operating device is configured to move the eighth intermediate gearwheel in axial directions to effect movement of the eighth intermediate gearwheel between the states thereof.

7. A transmission system according to claim 1, further comprising the seventh gearwheel is journalled for rotation on the second power transmission shaft, and the seventh gearwheel is connectable for joint rotation with the second power transmission shaft; a clutch device situated on the second power transmission shaft and the clutch device is configured for connecting the seventh gearwheel with the second power transmission shaft.

8. A transmission system according to claim 1, further comprising a range gear unit connecting the mainshaft to the output shaft.

9. A transmission system according to claim 8, further comprising: the first power transmission shaft comprises a countershaft of the transmission system, and the second power transmission shaft comprises a bypass shaft via which at least one of the input shafts can be connected to the output shaft to establish a power transfer path from the at least one input shaft to the output shaft without passing through the range gear unit.

10. A transmission system according to claim 9, further comprising the second power transmission shaft is provided with a ninth gearwheel which is in engagement with a tenth gearwheel situated on the output shaft.

11. A transmission system according to claim 9 further comprising: the range gear unit comprises a planetary gear including a sunwheel and a planet wheel carrier, the mainshaft is connected, for joint rotation with the sunwheel of the planetary gear, the output shaft is connected for joint rotation with the planet wheel carrier of the planetary gear, and the second power transmission shaft extends past, and radially externally to, the planetary gear.

12. A transmission system according to claim 1, further comprising a third power transmission shaft, the first and the third power transmission shafts each comprise a countershaft of the transmission system.

13. A transmission system according to claim 1, further comprising the first and second power transmission shafts each comprise a countershaft of the transmission system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in more detail below on the basis of embodiment examples with reference to the attached drawings, in which

(2) FIG. 1 is a schematic diagram of a transmission system according to a first embodiment of the present invention, showing the aforesaid intermediate gearwheel in a connecting state,

(3) FIG. 2 is a schematic diagram corresponding to FIG. 1, but showing the intermediate gearwheel in a disconnecting state,

(4) FIG. 3 is a schematic front view of parts of a transmission system according to FIG. 1,

(5) FIG. 4 is a section along the lines A-A in FIG. 3,

(6) FIG. 5 is a section along the lines B-B in FIG. 3,

(7) FIG. 6 is a schematic diagram of a transmission system according to a second embodiment of the present invention,

(8) FIG. 7 is a schematic diagram of a transmission system according to a third embodiment of the present invention, and

(9) FIG. 8 is a schematic diagram of a transmission system according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(10) FIGS. 1, 2 and 6-8 illustrate very schematically a transmission system 1 for a motor vehicle according to various embodiments of the present invention. Some of the parts of the transmission system in the embodiment illustrated in FIGS. 1 and 2 are depicted in more detail in FIGS. 3-5.

(11) The transmission system 1 comprises a twin-clutch main gear unit 10 and a range gear unit 30. The range gear unit can be put into a low-range state and a high-range state by means of a clutch arrangement 31 which may be provided with synchronising means of known type. The main gear unit 10 comprises a first input shaft 11 and a second input shaft 12 which are mutually parallel and coaxial. The first input shaft 11 extends axially through the second input shaft 12, which is thus situated externally to the first input shaft. The main gear unit 10 comprises also a mainshaft 15 connected via the range gear unit 30 to an output shaft 5 of the transmission system. In the example illustrated the mainshaft 15 and the first input shaft 11 are mutually coaxial.

(12) The transmission system 1 comprises a clutch arrangement 40 for alternate connection of the input shafts 11, 12. This clutch arrangement can be used to connect the input shafts alternately to a driveshaft 2 of a prime mover 3. It comprises a first clutch device 41 by means of which the first input shaft can be put into power-transmitting communication with and be disconnected from the driveshaft 2, and a second clutch device 42 by means of which the second input shaft 12 can be put into power-transmitting communication with and be disconnected from the driveshaft.

(13) In the embodiments illustrated, the range gear unit 30 comprises a planetary gear 32 with a sunwheel 33, planet wheels 34 and a ring gear 35. The planet wheels surround and are in engagement with the sunwheel, while the ring gear surrounds and is in engagement with the planet wheels. The sunwheel is connected to, for joint rotation with, the mainshaft 15. The planet wheels are journalled for rotation in a planet wheel carrier 36 which is connected to, for joint rotation with, the transmission's output shaft 5. The ring gear 35 has internal teeth via which it engages with the planet wheels. The ring gear is movable axially and serves as a connecting means which can be used to put the range gear unit into a low-range state and a high-range state.

(14) By being moved in a first direction the ring gear 35 can be connected to, for joint rotation with, a first clutch means 37 which is connected to, for joint rotation with, a gearbox housing 7, thereby preventing rotation of the ring gear. In this low-range state the planet wheels 34 rotate jointly with the planet wheel carrier 36 relative to the sunwheel 32 and the ring gear 35, and the output shaft 5 rotates at a slower speed than the mainshaft 15.

(15) By being moved in an opposite second direction the ring gear 35 can be connected to, for joint rotation with, a second clutch means 38 which is connected to, for joint rotation with, the mainshaft 15, causing the ring gear to rotate jointly with the mainshaft. In this high-range state the planet wheels 34 and the planet wheel carrier 36 are prevented from rotating relative to the sunwheel 33 and the ring gear 35, and the output shaft 5 consequently rotates at the same speed as the mainshaft 15.

(16) As an alternative, the ring gear 35 might be fixed axially and be in engagement with a coupling sleeve surrounding it which is movable axially for change of gear position in the range gear unit 30 between said low-range state and high-range state.

(17) The transmission system 1 comprises a first power transmission shaft A1 and a second power transmission shaft A2 each configured to convey power from at least one of the first and second input shafts 11, 12 to the mainshaft 15. The first and second power transmission shafts A1, A2 are mutually parallel and are also parallel with the first and second input shafts 11, 12 and the mainshaft 15.

(18) In all the embodiments illustrated the transmission system 1 comprises a first gear combination K1 to convey power from the second input shaft 12 to the first power transmission shaft A1, a second gear combination K2 to convey power from the first input shaft 11 to the first power transmission shaft A1, a third gear combination K3 to convey power from the first power transmission shaft A1 to the mainshaft 15, a fourth gear combination K4 to convey power from the first input shaft 11 to the second power transmission shaft A2, and a fifth gear combination K5 to convey power from the second power transmission shaft A2 to the mainshaft 15.

(19) In the embodiments in FIGS. 1-6 and 8 the first gear combination K1 comprises a second gearwheel K17a, K17a″ situated on, for joint rotation with, the second input shaft 12, and a first gearwheel K1b journalled for rotation on the first power transmission shaft A1. This latter gearwheel K1b is in engagement with said second gearwheel K17a, K17a″ and can be connected to, for joint rotation with, the first power transmission shaft A1 by means of a clutch device C1 situated on this shaft.

(20) In the embodiment in FIG. 7, the first gear combination K1 comprises a second gearwheel K1a situated on, for joint rotation with, the second input shaft 12, and a first gearwheel K1b situated on, for joint rotation with, the first power transmission shaft A1. This latter gearwheel K1b is in engagement with said second gearwheel K1a.

(21) The second gear combination K2 comprises in the embodiment in FIGS. 1-6 a gearwheel K28a, in the embodiment in FIG. 7 a gearwheel K2a and in the embodiment in FIG. 8 a gearwheel K24a situated on, for joint rotation with, the first input shaft 11, and a gearwheel K2b journalled for rotation on the first power transmission shaft A1. This latter gearwheel K2b is in engagement with said gearwheel K2a in the embodiment in FIG. 7. In the embodiments in FIGS. 1-6 and 8 the gearwheel K2b can be connected to, for joint rotation with, the first power transmission shaft A1 by means of the aforesaid clutch device C1, and in the embodiment in FIG. 7 it can be connected to, for joint rotation with, the first power transmission shaft A1 by means of two clutch devices C2, C3 situated on this shaft.

(22) The third gear combination K3 comprises a third gearwheel K3a situated on, for joint rotation with, the first power transmission shaft A1, and the fifth gear combination K5 comprises a seventh K5a situated on the second power transmission shaft A2. In the embodiments in FIGS. 1-5, 7 and 8 this latter gearwheel K5a is situated on, for joint rotation with, the second power transmission shaft A2. In the embodiment in FIG. 6 this latter gearwheel K5a is journalled for rotation on the second power transmission shaft A2 but can be connected to, for joint rotation with, said shaft by means of a clutch device C4 situated on this shaft. The third and fifth gear combinations K3, K5 further have in common a fourth gearwheel K35b which is situated on the mainshaft 15 and in engagement with the third gearwheel K3a of the third gear combination K3. In the embodiments in FIGS. 1-6 the fourth gearwheel K35b is situated on, for joint rotation with, the mainshaft 15. In the embodiments in FIGS. 7 and 8 it is journalled for rotation on the mainshaft 15 but can be connected to, for joint rotation with, the mainshaft by means of a clutch device C5, C6 situated on this shaft. The fifth gear combination K5 comprises also an eighth intermediate gearwheel K5c via which the seventh gearwheel K5a of the fifth gear combination K5 is in engagement with said fourth gearwheel K35b. The eighth intermediate gearwheel K5c is arranged for rotation by being journalled for rotation on a shaft 17 which is connected to, for joint rotation with, the gearbox housing 7, or by being situated on, for joint rotation with, a shaft which is journalled for rotation relative to the gearbox housing. The fifth gear combination K5 constitutes a reverse gear. The gearwheels of the third gear combination K3 and those of the fifth gear combination K5 are arranged in a common row R. This gearwheel row R may be used both to establish a power transfer path for a forward gear via the third gear combination K3 and to establish a power transfer path for a reverse gear via the fifth gear combination K5.

(23) In the embodiments in FIGS. 1-7, the fourth gear combination K4 comprises a sixth gearwheel K4a journalled for rotation on the first input shaft 11, and a fifth gearwheel K4b situated on, for joint rotation with, the second power transmission shaft A2. This sixth gearwheel K4a is in engagement with the fifth gearwheel K4b and can be connected to, for joint rotation with, the first input shaft 11 by means of a clutch device C7 situated on this shaft.

(24) In the embodiment in FIG. 8, the fourth gear combination K4 and the second gear combination K2 have in common a sixth gearwheel K24a situated on, for joint rotation with, the first input shaft 11. In this case the fourth gear combination K4 further comprises a fifth gearwheel K4b journalled for rotation on the second power transmission shaft A2. This latter gearwheel K4b is in engagement with said sixth gearwheel K24a and can be connected to, for joint rotation with, the second power transmission shaft A2 by means of a clutch device C8 situated on this shaft.

(25) In the embodiments in FIGS. 1-7, the first power transmission shaft A1 takes the form of a countershaft of the main gear unit 10, while the second power transmission shaft A2 takes the form of a bypass shaft via which at least one of the input shafts 11, 12 can be connected to the output shaft 5 to establish a power transfer path from the respective input shaft to the output shaft without passing through the range gear unit 30 during changes of gear position in the range gear unit from the low-range state to the high-range state or from the high-range state to the low-range state. The transmission system comprises in this case a sixth gear combination K6 to convey power from the second power transmission shaft A2 to the output shaft 5. This sixth gear combination comprises a ninth gearwheel K6a situated on, for joint rotation with, the second power transmission shaft A2, and a tenth gearwheel K6b journalled for rotation on the output shaft 5. This latter gearwheel K6b is in engagement with said ninth gearwheel K6a and can be connected to, for joint rotation with, the output shaft by means of a clutch device C15 situated on this shaft. In the embodiments illustrated in FIGS. 1-7, the second power transmission shaft A2 extends past, and radially externally to, the planetary gear 32.

(26) In the embodiments in FIGS. 1-6, the transmission system comprises also a third power transmission shaft A3 to convey power from at least one of the input shafts 11, 12 to the mainshaft 15. This third power transmission shaft A3 takes the form of a second countershaft of the main gear unit 10 and is parallel with first and second power transmission shafts A1, A2. The second power transmission shaft A2 and the other two power transmission shafts A1, A3 do not extend in a common plane, so the second power transmission shaft A2 is represented by broken lines in FIGS. 1, 2 and 6.

(27) In the embodiments in FIGS. 1-6, the transmission system comprises not only the aforesaid gear combinations K1-6 but also a seventh gear combination K7 to convey power from the second input shaft 12 to the third power transmission shaft A3, an eighth gear combination K8 to convey power from the first input shaft 11 to the third power transmission shaft A3, a ninth gear combination K9 to convey power from the third power transmission shaft A3 to the mainshaft 15, and a tenth gear combination K10 to convey power from the third power transmission shaft A3 to the mainshaft 15.

(28) The seventh gear combination K7 and the first gear combination K1 have in common a second gearwheel K17a situated on, for joint rotation with, the second input shaft 12. The seventh gear combination K7 further comprises a gearwheel K7b journalled for rotation on the third power transmission shaft A3. This latter gearwheel K7b is in engagement with said second gearwheel K17a and can be connected to, for rotation with, the third power transmission shaft A3 by means of a clutch device C9 situated on this shaft.

(29) The eighth gear combination K8 and the second gear combination K2 have in common a gearwheel K28a which is situated on, for joint rotation with, the first input shaft 11. The eighth gear combination K8 further comprises a gearwheel K8b journalled for rotation on the third power transmission shaft A3. This latter gearwheel K8b is in engagement with said gearwheel K28a and can be connected to, for rotation with, the third power transmission shaft A3 by means of a clutch device C10 situated on this shaft.

(30) The ninth gear combination K9 comprises a first gearwheel K9a situated on, for joint rotation with, the third power transmission shaft A3, and a second gearwheel K9b journalled for rotation on the mainshaft 15. This latter gearwheel K9b is in engagement with said first gearwheel K9a and can be connected to, for joint rotation with, the mainshaft 15 by means of a clutch device C11 situated on this shaft.

(31) The tenth gear combination K10 comprises a gearwheel K10a situated on, for joint rotation with, the third power transmission shaft A3, and a gearwheel K10b journalled for rotation on the mainshaft 15. This latter gearwheel K10b is in engagement with said gearwheel K10a and can be connected to, for joint rotation with, the mainshaft 15 by means of the aforesaid clutch device C11.

(32) In the embodiment illustrated in FIG. 7, the transmission system comprises not only the aforesaid gear combinations K1-K6 but also a seventh gear combination K7′ to convey power from the first power transmission shaft A1 to the mainshaft 15. This seventh gear combination comprises a gearwheel K7a′ journalled for rotation on the first power transmission shaft A1, and a gearwheel K7b′ journalled for rotation on the mainshaft 15. This latter gearwheel K7b′ is in engagement with the gearwheel K7a′ and can be connected to, for joint rotation with, the mainshaft 15 by means of a clutch device C12 situated on this shaft. The gearwheel K7a′ can be connected to, for joint rotation with, the first power transmission shaft A1 by means of the previously mentioned clutch device C3. The gearwheel K7a′ can also be connected to, for joint rotation with, the gearwheel K2b of the second gear combination K2 by means of the previously mentioned clutch device C2.

(33) In the embodiment illustrated in FIG. 8, the first power transmission shaft A1 takes the form of a first countershaft of the main gear unit 10, while the second power transmission shaft A2 takes the form of a second countershaft of the main gear unit. In this embodiment the transmission system comprises not only the aforesaid gear combinations K1-K5 but also a sixth gear combination K6″ to convey power from the first power transmission shaft A1 to the mainshaft 15, a seventh gear combination K7″ to convey power from the second input shaft 12 to the second power transmission shaft A2, and an eighth gear combination K8″ to convey power from the second power transmission shaft A2 to the mainshaft 15.

(34) The sixth gear combination K6″ comprises a gearwheel K6a″ situated on, for joint rotation with, the first power transmission shaft A1, and a gearwheel K6b″ journalled for rotation on the mainshaft 15. This latter gearwheel K6b″ is in engagement with said gearwheel K6a″ and can be connected to, for joint rotation with, the mainshaft 15 by means of a clutch device C13 situated on this shaft.

(35) The seventh gear combination K7″ and the first gear combination K1 have in common a second gearwheel K17a″ situated on, for joint rotation with, the second input shaft 12. The seventh gear combination K7″ further comprises a gearwheel K7b″ journalled for rotation on the second power transmission shaft A2. This latter gearwheel K7b″ is in engagement with said second gearwheel K17a″ and can be connected to, for rotation with, the second power transmission shaft A2 by means of a clutch device C9 situated on this shaft.

(36) The eighth gear combination K8″ comprises a gearwheel K8a″ situated on, for joint rotation with, the second power transmission shaft A2, and a second gearwheel K8b″ journalled for rotation on the mainshaft 15. This latter gearwheel K8b″ is in engagement with said gearwheel K8a″ and can be connected to, for joint rotation with, the mainshaft 15 by means of the aforesaid clutch device C13.

(37) In the embodiments illustrated, the main gear unit 10 and the range gear unit 30 are enclosed in a shared gearbox housing 7 but each of them might alternatively be enclosed in a gearbox housing of its own. The first input shaft 11 is journalled for rotation relative to the second input shaft 12, while the second input shaft 12 and the output shaft 5 are journalled for rotation relative to, and protrude from opposite ends of, the gearbox housing 7. The power transmission shafts A1-A3 and the mainshaft 15 are also journalled for rotation relative to the gearbox housing 7. For the sake of clarity, the bearings via which the various shafts are journalled for rotation are not depicted in FIGS. 1, 2 and 6-8.

(38) In the embodiments illustrated in FIGS. 1, 2, 7 and 8 the intermediate gearwheel K5c is movable relative to the other two gearwheels K5a, K35b of the fifth gear combination K5. The transmission system comprises in this case an operating device 50 which can be used to move the eighth intermediate gearwheel K5c axially to and fro between a disconnecting state (see FIG. 2) in which the eighth intermediate gearwheel K5c is disconnected from the seventh gearwheel K5a on the second power transmission shaft A2 and/or from the fourth gearwheel K35b on the mainshaft 15, and a connecting state (see FIGS. 1, 7 and 8) in which the eighth intermediate gearwheel K5c is in engagement with the seventh gearwheel K5a on the second power transmission shaft A2 and the fourth gearwheel K35b on the mainshaft 15. In the embodiments illustrated in FIGS. 1, 2, 7 and 8 the eighth intermediate gearwheel K5c is fixed axially on a movable intermediate wheel shaft 17 which the operating device 50 is arranged to move in axial directions and thereby move the eighth intermediate gearwheel K5c between the aforesaid states. In this case the operating device comprises with advantage a pneumatic or hydraulic cylinder 51 and the intermediate wheel shaft is connected to a piston rod 52 of this cylinder. The operating device might alternatively comprise an electric motor for moving the intermediate wheel shaft, e.g. via a ball screw which is rotatable by the electric motor. As a further alternative (not illustrated) the intermediate gearwheel might be movable on an axially fixed intermediate wheel shaft, in which case the operating device would be arranged to move the eighth intermediate gearwheel K5c in axial directions along the intermediate wheel shaft in order thereby to effect movement of the intermediate gearwheel between the aforesaid states.

(39) In the embodiment illustrated in FIG. 6 the second power transmission shaft A2 is disconnectable from the mainshaft 15 by means of the clutch device C4 situated on the second power transmission shaft.

(40) In the embodiments illustrated a direct connection can be set up between the first input shaft 11 and the mainshaft 15 by means of one of the clutch devices C6, C7, C14.

(41) Each of the clutch devices C1-C16 may for example take the form of a conventional synchronising clutch or claw clutch of known type or some other suitable type of clutch.

(42) The transmission system according to the invention might of course comprise a main gear unit with fewer or more gear combinations than as depicted in FIGS. 1-8.

(43) To engage a reverse gear, a reversing power transfer path between the driveshaft 2 of the engine and the mainshaft 15 of the main gear unit is established via, in this order, the first input shaft 11, the fourth gear combination K4, the second power transmission shaft A2 and the fifth gear combination K5. In the embodiments in FIGS. 1-6 it is possible to establish not only this first reversing power transfer path but also a second reversing power transfer path between the engine's driveshaft and the mainshaft of the main gear unit via, in this order, the second input shaft 12, the seventh gear combination K7, the third power transmission shaft A3, the eighth gear combination K8, the first input shaft 11, the fourth gear combination K4, the second power transmission shaft A2 and the fifth gear combination K5. These two reversing power transfer paths may be employed alternately by connecting the two input shafts 11, 12 alternately to the engine's driveshaft 2 via the first and second clutch devices 41, 42. Dimensioning the seventh and eighth gear combinations K7, K8 in such a way that the gear ratio on the second reversing power transfer path differs from that on the first reversing power transfer path makes it possible, when reversing, to change between a low reverse gear and a high reverse gear. As the clutch devices 41, 42 are used to effect the change between these reverse gears, this change can take place with no torque interruption.

(44) In the embodiments in FIGS. 1-6 a first set of power transfer paths for forward gears with mutually different gear ratios can be established between the driveshaft 2 of the engine and the mainshaft 15 of the main gear unit via the first input shaft 11 and the gear combinations K2, K3, K8, K9 and K10, and a second set of power transfer paths for forward gears with mutually different gear ratios can be established between the engine's driveshaft and the mainshaft via the second input shaft 12 and the gear combinations K1, K3, K7, K9 and K10. In the embodiment in FIG. 7 a first set of power transfer paths for forward gears with mutually different gear ratios can be established between the driveshaft of the engine and the mainshaft of the main gear unit via the first input shaft 11 and the gear combinations K2, K3 and K7′, and a second set of power transfer paths for forward gears with mutually different gear ratios can be established between the engine's driveshaft and the mainshaft via the second input shaft 12 and the gear combinations K1, K3 and K7′. In the embodiment in FIG. 8 a first set of power transfer paths for forward gears with mutually different gear ratios can be established between the driveshaft of the engine and the mainshaft of the main gear unit via the first input shaft 11 and the gear combinations K2, K3, K4, K6″ and K8″, and a second set of power transfer paths for forward gears with mutually different gear ratios can be established between the engine's driveshaft and the mainshaft via the second input shaft 12 and the gear combinations K1, K3, K6″, K7″ and K8″. The two different sets of power transfer paths may be employed by alternately connecting the first and second input shafts 11, 12 alternately to the engine's driveshaft via the first and second clutch devices 41, 42. It thus becomes possible to effect stepped upshifts and downshifts in the main gear unit 10 with no torque interruption, i.e. without interrupting the power transfer between the engine's driveshaft 2 and the transmission's output shaft 5.

(45) The transmission system according to the invention is particularly intended for use in a heavy motor vehicle, e.g. a bus, a tractor unit or a truck.

(46) The invention is of course in no way confined to the embodiments described above, since a multiplicity of possibilities for modifications thereof are likely to be obvious to one skilled in the art without thereby deviating from the invention's basic concept such as defined in the attached claims.