BACKGROUND AND PRIOR ART

The present invention pertains to a braking device for a gearbox according to the preamble of claim 1, a gearbox according to the preamble of claim 9, a vehicle according to the preamble of claim 11 and a method to start a vehicle according to the preamble of patent claim 12.

Vehicles, and in particular heavy goods vehicles, e.g. trucks, are usually equipped with a gearbox connected to the combustion engine, which gearbox may be automatic, manual or a combination thereof. In an automated manual transmission, a so-called AMT gearbox, the gearbox is controlled by an electronic control device. Such a gearbox may be equipped with a main shaft and a side shaft parallel thereto. The gearbox may also be equipped with a range gearbox, which may constitute a separate device or be integrated in the gearbox. The main shaft is connectible to an input shaft via the side shaft and to an output shaft in the gearbox via the range gearbox, if this is integrated in the gearbox. The gearbox may also be equipped with a split gear unit, via which the side shaft is connectible via the input shaft. A brake mechanism is arranged to retard the side shaft in connection with change of gears in the gearbox, in order to achieve synchronous rotation speeds in the side shaft and the main shaft, so that the new gear may be engaged without any greater torque existing between those transmission parts in the gearbox which are brought to engage with each other at the moment the new gear is engaged. The brake mechanism is thus used to retard the side shaft in relation to the main shaft at a stage during a shifting operation when the main shaft is in the neutral position, while the side shaft is disconnected from the main shaft.

In gearboxes of this type, the synchronisation devices, comprising conical synchronisation rings and coupling rings, are replaced by toothed operating sleeves, which are dis- placed axially in order to engage with cogwheels placed on the main shaft. Each cogwheel placed on the main shaft is engaged with corresponding cogwheel elements, which are anti-rotationally connected with the side shaft. On shifting, the operating sleeve is displaced axially in order to engage with coupling teeth arranged on a select- able cogwheel, in order to connect the cogwheel to, and rotation lock it, on the main shaft.

Under certain operational conditions it is, however, difficult to engage the starting gear, since the geometry of the operating sleeve's teeth and the coupling teeth in the cogwheel for the starting gear entails that the operating sleeve is prevented from being displaced axially and thus engaging with the coupling teeth on the cogwheel for the starting gear. In order for the operating sleeve to be displaced axially, the cogwheel for the starting gear must be offset at an angle in relation to the operating sleeve, so that the toothing of the operating sleeve may be inserted in the hatches created between the coupling teeth in the cogwheel for the starting gear. If the cogwheel for the starting gear and the operating sleeve are so offset at an angle in relation to each other that the coupling teeth in the cogwheel for the starting gear and the toothing of the operating sleeve coincide axially, wholly or partly, the axial end surfaces of the coupling teeth of the cogwheel for the starting gear and the axial end surfaces of the toothing of the op- erating sleeve abut against each other, and prevent the toothing of the operating sleeve from being inserted in the hatches between the coupling teeth of the cogwheel for the starting gear.

In order to facilitate engaging the starting gear, the axial displacement of the operating sleeve is carried out when there is a small speed difference between the main shaft and the side shaft. This may be achieved when the vehicle is slowing down and comes to a standstill and the gearbox is prepared for engagement of the starting gear. The braking device is then used to retard the side shaft in relation to the main shaft, while the side shaft is disconnected from the main shaft. The engagement of the starting gear takes place with a certain speed difference between the main shaft and the side shaft. If the speed difference between the main shaft and the side shaft is too big, the driver and passengers in the vehicle will experience a disruption to their comfort in the form of a shock in the vehicle. If the speed difference is too small, however, the operating sleeve may not be displaced axially for the reasons described above and the result is a missed gear selection, entailing that a new gear manoeuvre must be carried out in the gearbox, which leads to long shifting time. It is thus very difficult to use the braking mechanism of the side shaft in order to brake down the side shaft to the optimal speed difference between the main shaft and the side shaft for gear selection.

The document WO2011/062544 shows a gearbox, which is equipped with a main shaft and a side shaft parallel thereto. A range gearbox is integrated in the gearbox. The main shaft is connectible to an input shaft to the gearbox via the side shaft and to an output shaft in the gearbox via the range gearbox. The gearbox is also equipped with a split gear unit, via which the side shaft is connectible via the input shaft. A brake mechanism is arranged to retard the side shaft in relation to the main shaft at a stage during a shifting operation when the main shaft is in the neutral position, while the side shaft is disconnected from the main shaft.

The document US2010044183 shows a transmission brake, which is controlled to prevent a tooth-to-tooth situation. An extra brake pulse is emitted during a synchronisation process in order to bring the toothing of the transmission parts into engagement.

SUMMARY OF THE INVENTION

Despite prior art, there is a need to develop a brake mechanism for a gearbox, which facilitates the engagement of the starting gear, eliminates comfort disruptions when the starting gear is engaged and requires a short time for engagement of the starting gear.

The objective of the present invention is to provide a brake mechanism for a gearbox, which facilitates the engagement of the starting gear. Another objective of the present invention is to provide a braking mechanism for a gearbox, which eliminates comfort disruptions in connection with engagement of the starting gear. Another objective of the invention is to provide a braking mechanism for a gearbox, which requires a short time for engaging the starting gear. These objectives are achieved with a braking mechanism for a gearbox of the type mentioned above, which is characterised by the features specified in patent claim 1.

These objectives are further achieved with a gearbox of the type mentioned above, which is characterised by the features specified in patent claim 9.

These objectives are achieved also with a vehicle of the type specified above, which is characterised by the features specified in patent claim 11.

These objectives are achieved also with a method of the type specified above, which is characterised by the features specified in patent claim 12.

By activating the braking mechanism, a turning motion is achieved in the side shaft, which turning motion facilitates the engagement of the starting gear. The turning is achieved by the at least one second disc in the braking mechanism, which disc is ar- ranged to abut against the control means, interacting with the at least one first disc, which is anti-rotationally arranged to the brake shaft via splines. The first as well as the second disc are axially moveable between a compressed braking position and a pulled apart non-braking position. The second disc's ability to rotate around the central axis of the brake shaft when the braking mechanism is activated, is achieved through a design of the second disc with a number of radially protruding lugs, which interact with the guide surface on the control means. The lugs' and the guide surface's interaction facilitates the turning motion when the braking mechanism is activated at the axial displacement of the second disc along the guide surface.

The first disc lacks radially projecting lugs and will, when the braking mechanism is activated, be dragged along with the second disc's turning motion through friction. When the braking mechanism is activated, both the first and second disc will thus be turned while they simultaneously are displaced axially along the braking shaft, which leads to the first disc turning the braking shaft around its central axis.

In order to achieve the turning motion of the braking shaft according to the invention when the braking mechanism is activated, the radially projecting lugs on the second disc must thus interact with the guide surface on the control means, so that the second disc and thus the first disc turn in relation to the housing. The guide surface is there- fore, according to the invention, designed to be oblique or slanting in the axial direction of the brake shaft, which, when the braking mechanism is activated, produces a turning movement of the second disc, which transfers the turning movement through friction to the first disc which is compressed together with the second disc, and which in turn forwards the turning movement to the brake shaft. This facilitates engagement of the starting gear and leads to quick gear selection with good comfort.

The starting gear selection is thus achieved by braking the gearbox's side shaft to a standstill by activating the braking mechanism, and subsequently deactivating the braking mechanism, then activating the actuator for the actuating fork, so that the op- erating sleeve for gear selection may be displaced axially, and simultaneously activating the braking mechanism to turn the side shaft, as described above, in order to thus facilitate that the operating sleeve's toothing may be displaced into the hatches between the coupling teeth of the cogwheel for the starting gear. Other advantages of the invention are set out in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, preferred embodiments of the invention with reference to the enclosed drawings, in which: shows schematically a vehicle in a side view, with a braking mechanism according to the present invention, shows a sectional view of a gearbox with a braking mechanism according to the present invention, shows a sectional view from the side of a braking mechanism according to a first embodiment of the present invention, shows a sectional view of the braking mechanism according to the first embodiment of the present invention, shows a sectional view of a braking mechanism according to a second embodiment of the present invention, and

Fig. 6 shows a flow chart of a method to start a vehicle, comprising a gearbox with a braking mechanism according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a side view of a vehicle 1, e.g. a truck, which comprises a braking mechanism 2 according to the present invention. A combustion engine 4 is connected to a gearbox 6, which is further connected to the vehicle's 1 driving wheels 8 via a transmission, which comprises a propeller shaft 10.

Fig. 2 shows a sectional view of the gearbox 6 with the braking mechanism 2 according to the present invention. The gearbox 6 is equipped with a main shaft 12 and a side shaft 14 parallel thereto. The gearbox 6 is equipped with a range gearbox 16, which is integrated in the gearbox 6. The main shaft 12 is connectible to an input shaft 18 to the gearbox 6 via the side shaft 14, and to an output shaft 20 in the gearbox 6 via the range gearbox 16. The gearbox 6 is equipped with a split gearbox device 22, via which the side shaft 14 is connectible via the input shaft 18. The brake mechanism 2 is connected with the side shaft 14 and is arranged to retard the side shaft 14 in connection with change of gears in the gearbox 6, in order to achieve synchronous rotation speeds in the side shaft 14 and the main shaft 12, so that the new gear may be engaged without any greater torque existing between those transmission parts in the gearbox 6 which are brought to engage with each other at the moment the new gear is engaged. The brake mechanism 2 is thus used to retard the side shaft 14 in relation to the main shaft 12 at a stage during a shifting operation, when the main shaft 12 is in the neutral position and the side shaft 14 is disconnected from the main shaft 12. The braking mecha- nism 2 may be arranged directly on the side shaft 14 or via a gear which is not displayed.

The gearbox 6 comprises operating sleeves 24a- 24c, which are equipped internally with toothing 26. The operating sleeves 24a- 24c are displaced axially through an oper- ating fork 28 to be brought into engagement with the cogwheels 30a-30e placed on the main shaft 12. The operating forks 28 are activated through the operating element 29, which may consist of pneumatic or hydraulic cylinders. Only one operating fork 28 and one operating element 29 are shown schematically in Fig. 2. Each cogwheel 30a- 30e, placed on the main shaft 12, is engaged with corresponding cogwheel elements 32a-32f, which are anti-rotationally connected with the side shaft 14. On shifting, the operating sleeve 24a- 24c is displaced axially in order to engage with coupling teeth 34 arranged on a selectable cogwheel 30a-30e in order to connect the cogwheel 30a-30e to, and rotation lock it, on the main shaft 12. Fig. 3 shows a sectional view from the side of a braking mechanism 2 according to a first embodiment of the present invention. The brake mechanism 2 comprises at least one first disc 36 and at least one second disc 38. According to the embodiment displayed, the brake mechanism 2 is equipped with four first discs 36 and five second discs 38. The first discs 36 are equipped with a friction coating 40, which, when the braking mechanism 2 is activated, abuts the second discs 38 in order to achieve a braking torque. A power element 42 in the form of a pneumatically or hydraulically operated piston 44 is arranged to compress the first and second discs 36, 38 against each other. The first discs 36 slide axially on a rotatable brake shaft 46, which is designed to be connected to the side shaft 14. The brake shaft 46 shows a central axis 47. The first discs 36 are anti-rotationally arranged on the brake shaft 46 through a spline joint 48. It is possible to design the brake shaft 46 and the side shaft 14 as one connected unit, where the first discs 36 are arranged directly on the side shaft 14 and axially sliding through a spline joint on the side shaft 14. In this case, the side shaft 14 functions like a brake shaft 46 in the brake mechanism 2. The first and second discs 36, 38 are surrounded at least partly by a brake housing 50. The brake mechanism 2 is equipped with at least one control means 52 with a guide surface 54, against which the second discs 38 are arranged to abut. According to the first embodiment, the control means 52 consists of wall sections 56 connected with the brake housing 50.

As shown in Fig. 3, the guide surface 54 is arranged to slope in the shaft's axial direction, so that the second discs 38 are turned around the brake shaft's 46 central axis 47 when the power element 42 compresses and axially displaces the first and second discs 36, 38. The guide surface 54 has an inclination which entails that the radial distance to the shaft changes linearly in the axial direction of the brake shaft 46. The radial distance of the guide surface 54 to the brake shaft 46 is reduced in the same direction as the one in which the second discs 38 are displaced, when the power element 42 compresses the first and the second discs 36, 38. Preferably, the inclination of the guide surface 54 is adapted to turn the brake shaft 46 and thus the side shaft 14 at an angle of rotation corresponding to the angular spread of a coupling tooth 34 of a start cogwheel 30 in the gearbox 6.

Fig. 4 shows the braking mechanism 2 according to the first embodiment in a sectional view. Three control means 52 are arranged essentially symmetrically in the brake housing 50, around the second discs 38. The second discs' 38 ability to rotate around the brake shaft's 46 central axis when the braking mechanism 2 is activated is achieved through the second discs 38 being designed with a number of radially protruding lugs 58, which interact with the guide surface 54 on the control means 52. The interaction of the lugs 58 and the guide surfaces 54 facilitates a turning of the second discs 38 when the braking mechanism 2 is activated at the axial displacement of the second discs 38 along the guide surface 54. The first discs 36 lack radially protruding lugs and will, when the braking mechanism 2 is activated, be dragged along with the turning of the second discs 38 due to friction. When the braking mechanism 2 is activated, the first and second discs 36, 38 will be turned at the same time as they are displaced axially along the brake shaft 46, which leads to the first discs 36 turning the brake shaft 46 around its central axis 47, since the first discs 36 are anti-rotationally arranged on the brake shaft 46 through the spline joint 48.

In order to achieve the turning of the brake shaft 46, according to the invention, when the braking mechanism 2 is activated, the radially protruding lugs 58 on the second discs 38 must thus interact with the guide surface 54 on the control means 52, so that the second discs 38, and thus the first discs 36, turn in relation to the brake housing 50. The guide surfaces are therefore, according to the invention, designed to be oblique or slanting in the axial direction of the brake shaft 46, which, when the braking mechanism 2 is activated, produces a turning movement of the second discs 38, which trans- fers the turning movement through friction to the first discs 36, which are compressed together with the second discs 38, and which in turn forward the turning movement to the brake shaft 46. This facilitates engagement of the starting gear and leads to quick gear selection with good comfort. Fig. 5 shows a section view from the side of a braking mechanism 2, according to a second embodiment of the present invention. The second embodiment differs from the first, in that the control means 52 is a conical mandrel 60, which is connected with the brake housing 50. The mandrel 60 may be equipped with a screw thread 62 and connected with the brake housing 50 through a nut 64. Fig. 6 shows a flow chart of a method to start a vehicle 1, comprising a gearbox 6 with a braking mechanism 2 according to the present invention. The method according to the invention to start the vehicle 1, comprises the steps:

a) to brake the side shaft 14 in the gearbox 6 to a standstill, by activating the braking mechanism 2,

b) to deactivate the braking mechanism 2,

c) to activate the operating element 29 for the operating fork 28 arranged for the operating sleeve 24, so that the operating sleeve 24 may be displaced axially for gear selection, and

d) to activate the braking mechanism 2 to turn the side shaft 14, so that the toothing 26 arranged on the operating sleeve 24 may be displaced into the hatches between the coupling teeth 34 of the starting gear's cogwheels 30.

The components and features specified above may within the framework of the inven- tion be combined between the different embodiments specified.