DESCRIPTION

Field of the invention.

The invention relates to a driving system for a vehicle, more particularly a lorry, comprising:

- a drive source with an output drive shaft,

- a transmission comprising:

- a plurality of gear trains,

- a plurality of gearings, which are capable of coupling the gear trains to each other and to the inputs and the output,

- two concentric inputs, of which a first input is formed by a first shaft and the second input by a hollow second shaft fitted around this first shaft on which second shaft a gear is fitted that forms part of one of the gear trains,

- an output which can be coupled to the driven wheels of a vehicle, where a first one of the gearings can be switched between a first state, in which the first input is coupled to the second input and a second state, in which the first input is not coupled to the second input or where the first input is coupled to a further gear of a further gear train, which first gearing is locked up and if it is not operated maintains its open or closed state, - a main clutch which is positioned between the drive shaft and the first input of the transmission and which is a friction clutch and if it is not operated is closed by a spring, and

- a further clutch which is positioned between the drive shaft and the second input of the transmission.

State of the art.

A driving system of this type is known from EP-A- 1869342. In this known driving system there is a further clutch installed outside the housing of the transmission and this is analogous to the main clutch as regards operation and this further clutch is closed if it is not operated. The second input and the further clutch make it possible in this driving system to change the speed transforming gear in the transmission for which it is necessary to open the main clutch, without interrupting the drive from the drive source to the wheels. For this purpose the further clutch is closed while the main clutch is being opened, so that the driving is effected via the second input. This second input is coupled to the output' via a different speed transforming gear than the first input, so that it is possible to switch from one speed transforming gear to the next without any interruption.

Summary of the invention.

It is an object of the invention to provide a driving system of the type defined in the opening paragraph having an improved further clutch and operation of this further clutch. For this purpose the driving system according to the invention is characterised in that the further clutch is a friction clutch which is open if it is not operated. By adjusting the manner of switching the speed transforming gear in an inventive way it is possible for a person to realize a driving system in which the further clutch needs to be opened only briefly for changing the speed transforming gear.

Since different demands are placed on a clutch that is to be open if it is not operated than a clutch that is to be closed if it is not operated, this embodiment of the further clutch makes it possible to accommodate the further clutch in the wet or dry space of the transmission. Besides, this provides that there is no longer a need for a torsion damper between the further clutch and the drive shaft of the combustion engine.

With the driving system according to the invention after each change of transmission ratio in the transmission by changing from one of the gearings to another the vehicle runs with the main clutch in closed position. Thus after is switched from the main clutch to the further clutch for changing of transmission ratio while drive torque is transferred (powershift), the drive system will be switched back to the main clutch (after the gearing is put into the first position). In combination with the embodiment in which the main clutch is closed when not actuated (normally closed) and the further clutch is open when not actuated (normally open), after switching the transmission ratio no external actuation force is needed for both clutches. This prevents high losses and wear in the actuation system (and cranckshaft) which is a problem that can occur at actuation of clutches of known drive systems having double clutches.

It is noticed that from DE 10 2008 001200 A a drive system is known in which the main clutch is open when not actuated (normally open), and the further clutch is closed when not actuated (normally closed). This in contradistinction to the clutches of the drive system according to the present invention.

Energy dissipation during powershifts occur mainly (for more than 90%) in the main clutch so that the further clutch doesn't have to dissipate significant energy and therefore can be less heavy. The further clutch of the drive system according to the invention doesn't have to be a full powershift clutch (lastschalt element).

Because in the drive system according to the invention the transmission (vehicle) is not driven during a long time via the further clutch, this further clutch can be operated in slip mode when torque has to be transferred (during a short time), so that no torsion damper is needed between the second output and the drive shaft of the combustion engine, or a more rigid and thus simpler torsion damper can be applied.

The further clutch is preferably arranged as a wet plate clutch having at least one plate or as a cone clutch having at least one cone.

In order to properly support the forces of the actuator of the further clutch, an embodiment of the driving system according to the invention is characterised in that the further clutch comprises two clutch halves of which a first clutch half is connected to the second input and the second clutch half is connected to a hollow intermediate shaft which also surrounds the first shaft, and the transmission comprises a housing with two wail portions remote from each other and between which the further clutch is positioned, where a first one of the wall portions is positioned between the further clutch and the first gearing, which wall portions are each provided with an opening through which the first input is projecting, which further clutch comprises an actuator for pressing the two clutch halves together, which actuator is positioned between the first and the second wall portions and is connected to either of these wall portions and is coupled to one of the clutch halves of the further clutch via a pressure bearing.

A further design of the embodiment mentioned earlier is characterised in that the actuator is connected to the second wall portion and the first clutch half of the further clutch is connected to the first wall portion via a further pressure bearing. The actuation force of the actuator is directly supported on the housing via the pressure bearing and the further pressure bearing.

Another design of the embodiment mentioned earlier is characterised in that the actuator is connected to the first wall portion and the intermediate shaft is bearing mounted in the second wall portion. The actuation force of the actuator is here supported by the housing via the pressure bearing, the intermediate shaft and the bearing.

The main clutch also comprises an actuator and the actuation forces of the actuators of the further clutch and of the main clutch are preferably generated pneumatically, hydraulically, electromechanically or electromagnetically.

This actuator of the main clutch is connected to the second clutch half of the main clutch via a further pressure bearing. Both pressure bearings are preferably subjected to pressure load or one of them is subjected to pressure load and the other one is subjected to tensile load.

The actuator of the further clutch is preferably concentric or coaxial to the actuator of the main clutch.

The invention likewise relates to a method of switching the first gearing of the driving system according to the invention from the second state to the first state. With respect to the method the invention is characterised in that the main clutch allows the drive source to rev up to a speed at which the two clutch halves of the further clutch are in synchronism or substantially in synchronism while the first gearing is present in the second state, after which the further clutch is closed, so that it transfers the drive torque of the drive source.

Subsequently, the main clutch is preferably opened completely.

Then, preferably the first gearing is switched from the second state to the first state.

Then, preferably the first gearing is closed again and the further clutch is opened.

As a result of this the further clutch needs to be closed only during the switching from one speed transforming gear to the next. After the change to the new speed transforming gear, the driving system again acts via the first input and the further clutch can be opened again. Since the driving system is operated via the further clutch only for a brief period of time, fewer demands need to be made on it than on the main clutch and a clutch may be used that is open if it is not operated. The invention further relates to a method of switching the first gear train of the driving system according to the invention from the first state to the second state. As regards this method the invention is characterised in that the further clutch is closed while the main clutch is still closed or is operated in slipping fashion and the first gearing is in the first state.

Subsequently, the main clutch is preferably opened completely.

Then, preferably the first gearing is switched from the first state to the second state.

In addition, after this the main clutch is preferably closed and the further clutch opened.

In the two methods described hereinbefore the further clutch needs to be operated only for a brief period of time (for only a few seconds), so that the actuation loss in the bearings and also the wear thereof is limited. The torque as a result of the further clutch can be limited by a limitation in the actuation force and the further clutch is preferably operated only when there is a minimum difference in speed between the two clutch halves.

Brief description of the drawings. The invention will now be described in more detail based on an example of embodiment of the driving system according to the invention while reference is made to the appended drawing figures, in which:

Fig. 1 gives a diagrammatic representation of the driving system according to the invention;

Fig. 2 shows a first concrete embodiment of the driving system according to the invention;

Fig. 3 shows a second concrete embodiment of the driving system according to the invention;

Fig. 4 shows a constructive design of the second embodiment of the driving system shown in Fig. 3;

Fig. 5 shows a third concrete embodiment of the driving system according to the invention; and

Fig. 6 shows a constructive design of the third embodiment of the driving system shown in Fig. 5. Detailed description of the drawings.

Fig. 1 gives a diagrammatic representation of the driving system according to the invention. The driving system 1 comprises a drive source 3 with an output drive shaft 5, which can be coupled via a main clutch 7 to a first input 11 of a transmission 9. The transmission 9 further has an output 13 which can be coupled to driven wheels 15. This main clutch is arranged as a lock-up clutch, which is closed if it is not operated and where a spring presses the two clutch halves 7A and 7B together.

The transmission 9 comprises a plurality of gear trains 17 - 23. Each gear train comprises a central gear fitted to a central shaft and two gears being in mesh with the central gear and positioned on two auxiliary shafts running parallel with the central shaft. The transmission 9 further includes a plurality of gearings 25 - 29 which can couple the central gears of the gear trains to the central shaft.

By having the clutches adopt various states, various speed-transforming gears between input and output may be obtained.

The transmission 9 further has a second input 31 which can be connected via a further clutch 33 to an intermediate shaft 35 which is connected to the drive shaft 5 of the drive source 3. This second input is connected to the central gear 37 of the gear train 17. The further clutch is present in a space which has an open connection to the oil-greased space in the housing of the transmission. This space in which the further clutch is located is in this case completely accommodated in the housing of the transmission. The further clutch is also a lock-up clutch, but is open if not operated and has a spring that pushes the two clutch halves 33A and 33B apart.

The first gearing 25 is arranged as a friction clutch and can be switched to a first state in which it connects the two inputs together and a second state in which it connects the first input to the central gear of the gear train 19. If this first gearing is not operated, it continues to be in the state into which it was switched before that.

Fig. 2 shows a first concrete embodiment of the driving system according to the invention. The first input 11 is formed by an input shaft and the output 13 is formed by an output shaft. The second input is formed by a hollow shaft which surrounds the input shaft. The first gearing 25 is arranged as a friction, synchromesh clutch. The first clutch half 7 A of the main clutch 7 is formed by a clutch housing which is fitted to an engine flywheel 39 which is connected to the drive shaft 5. The second clutch half 7B is formed by a clutch plate which is connected to the first input 11 by means of a spline connection. The first clutch half 7A further includes a pressure plate 41 which can clamp the clutch plate between the engine flywheel and the pressure plate via a lever 43 and an actuator 45. This actuator is connected to a wall 49 of the transmission housing 47.

The intermediate shaft 35 is connected via a connecting plate 51 coupled to the clutch housing to the drive shaft 5 of the drive source. The actuator 53 of the further clutch 33 is also connected to the wall 49. No torsion damper is present between the further clutch 33 and the drive shaft 5. A torsion damper 55 is present indeed between the second clutch half 7B and the main clutch and the first input 11.

A first pressure bearing 57 is present between the actuator 45 and the lever 43 and a second pressure bearing 59 is present between the actuator 53 and the first clutch half 33 A of the further clutch. The intermediate shaft 35 is bearing mounted via a first bearing 61 on the input shaft, which forms the first input 11, and bearing mounted via a second bearing 63 in the wall 49 of the housing 46. The hollow shaft which forms the second input 31 is bearing mounted on the input shaft via a third bearing 65. Seal rings 67 are positioned between the intermediate shaft 35 and the actuator 45 and between the intermediate shaft 35 and the input shaft

The actuation force of the actuator 45 of the main clutch 7 is supported on the housing of the drive source 3 via respectively the first pressure bearing 57, the first clutch half 7A, the engine flywheel 39 and the drive shaft 5. The actuation force of the actuator 53 of the further clutch 33 is supported on the wall 49 of the transmission housing 47 via respectively the second pressure bearing 59, the second input 33, the third bearing 65, the first input 11, the first bearing 61, the intermediate shaft 35 and the second bearing 63.

Switching the first gearing from the second state to the first state is effected as follows. First and foremost the main clutch allows the drive source to rev up up to a speed at which the two clutch halves of the further clutch are in synchronism or substantially in synchronism, while the first gearing occupies the second state. After this, the further clutch is closed so that it transfers the drive torque of the drive source. Then the main clutch is opened completely and the first gearing is switched from the second state to the first state. Then the main clutch is closed again and the further clutch is opened.

Switching the first gearing from the first state to the second state is effected as follows. First and foremost the further clutch is closed while the main clutch is still closed or is operated in slipping fashion and the first gearing is situated in the first state. Subsequently, the main clutch is opened completely. Then the first gearing is switched from the first state to the second state after which the main clutch is closed again and the further clutch is opened.

Fig. 3 shows a second concrete embodiment of the driving system according to the invention. In this Figure the wall 49 of the housing 47 of the transmission has a first wall portion 69 and a second wall portion 71 distant from it, between which the further clutch 33 is located. The actuator 53 of the further clutch is connected to the second wall portion 71 and via the second pressure bearing 59 to the first clutch half 33A of the further clutch. The second clutch half 33B of the further clutch is connected via a further pressure bearing 73 to the first wall portion 69. The actuation force of the actuator 53 is here supported directly on the housing 47 of the transmission via the second pressure bearing 59 and the further pressure bearing 73.

For illustrative purposes Fig. 4 shows a constructive design of this second embodiment of the driving system. In this concrete embodiment the clutch halves 33A and 33B have a conical shape so that the clutch halves can be pressed together with great force whereas only little actuation force is applied.

Fig. 5 shows a third concrete embodiment of the driving system according to the invention. The actuator 53 of the further clutch 33 is connected here to the first wall portion 69. The actuation force of the actuator 53 is then supported on the housing 47 of the transmission via the second pressure bearing 59, the intermediate shaft 35 and the second bearing 63.

For illustrative purposes Fig. 6 shows a constructive design of this third embodiment of the driving system.

Albeit in the foregoing disclosure the invention has been explained with reference to the drawing figures, it should be pointed out that the invention is by no means restricted to the embodiments shown in the drawing figures. The invention also pertains to all embodiments deviating from the embodiments shown in the drawing figures within the spirit and scope defined by the claims.