WO2015163805A1

WO2015163805A1 - Arrangement for an upshift process in a gearbox

Info

Publication number: WO2015163805A1
Application number: PCT/SE2015/050432
Authority: WO
Inventors: Daniel HÄGGSTRÖM; Daniel Norberg; Nichlas FLORÉN
Original assignee: Scania Cv Ab
Priority date: 2014-04-23
Filing date: 2015-04-13
Publication date: 2015-10-29
Also published as: DE112015001338T5; SE1450481A1; SE537975C2; DE112015001338B4

Abstract

The present invention relates to an arrangement to provide an upshift process in a gearbox. The arrangement comprises a braking device (16) that comprises two spaces (19a, 19b), adapted to receive a pressurised medium, and two pistons (18a, 18b), which are adapted to be shifted by the pressurised medium in said spaces (19a, 19b) and to transfer a force to a braking component (20), so that it acts with a braking torque (M) on the countershaft (5) during an upshift process in the gearbox. The arrangement comprises connecting means (24, 26, 28, 29), adapted to connect the pressurised medium source (25) with the first space (18a), so that the countershaft (5) is decelerated with the first braking torque (Mi), or with the second space (18b), so that the countershaft (5) is decelerated with the second braking torque (M2), or with both the spaces (19a, 19b) simultaneously, so that the countershaft (5) is decelerated with a third braking torque (M3).

Description

ARRANGEMENT FOR AN UPSHIFT PROCESS IN A GEARBOX

BACKGROUND OF THE INVENTION AND PRIOR ART The invention relates to an arrangement for an upshift process in a gearbox according to the preamble of claim 1.

Conventional gearboxes comprise a countershaft, a main shaft, several gear sets, each one of which comprises a primary cogwheel which is rotatably arranged on the

countershaft and a secondary cogwheel which is rotatably arranged on the main shaft. Synchronisation devices are used to synchronise the secondary cogwheels' rotational speed with the rotational speed of the main shaft, and to lock the cogwheel on the main shaft when a synchronous rotational speed is obtained. The synchronisation devices generally comprise conically shaped friction surfaces, which are in charge of the synchronisation of the cogwheels' rotational speed on the main shaft. The

synchronisation devices' friction surfaces are subjected to great stress and are exposed to a huge wear.

One alternative to using synchronisation devices is to use a brake that brakes the countershaft during an upshift process. The brake may also be used in combination with synchronisation devices. In cases where no synchronisation devices are used, locking devices may be used, which only provide a rotational locking of the secondary cogwheels on the main shaft. During an upshift process, the brake provides a

deceleration of the countershaft until a secondary cogwheel obtains a synchronous rotational speed with the main shaft, following which a locking device provides a rotational locking of the secondary cogwheel on the main shaft. During a downshift process, a drive engine is activated, which provides an acceleration of the countershaft, via an input shaft to the gearbox, until a secondary cogwheel obtains a synchronous rotational speed with the main shaft, following which a locking device provides a rotational locking of the secondary cogwheel on the main shaft.

Conventional brakes for the countershaft brake the countershaft with a fixed braking torque. Some types of gearboxes, which comprise, for example, a split gear, have a countershaft with varying moments of inertia, depending on the state of the split gear during a shifting process. It is a problem to dimension brakes for countershafts with different moments of inertia. If a brake is dimensioned for the countershaft's greatest moment of inertia, problems will arise when it brakes the countershaft on occasions when this has a smaller moment of inertia. In this case, the countershaft provides a very fast deceleration, which makes it difficult to disconnect the brake when a synchronous rotational speed has been achieved. If the braking device is dimensioned for the countershaft's smallest moment of inertia, problems will arise when it brakes the countershaft on occasions when this has a greater moment of inertia. In this case, the countershaft provides a slow deceleration, resulting in a long shifting time.

US 5172797 shows a braking device for a countershaft in a gearbox. The braking device comprises a shiftable piston, which activates a disc brake. The braking device comprises a first chamber for supply of a pressurised fluid to activate the disc brake when the countershaft must be braked during an upshift process, and a second chamber for supply of a pressurised fluid for activation of the disc brake when the countershaft must be braked in order to prevent that the vehicle rolls backwards when starting on an uphill slope. When the pressurised fluid is supplied to the second chamber, it acts on a larger surface of the piston than when the pressurised fluid is supplied to the first chamber. Thus, a larger moment of inertia is obtained when the braking device is used to prevent that the vehicle rolls backwards during start on an uphill slope, than when it is used during an upshift process.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide an arrangement and a method for an upshift process in a gearbox, wherein a countershaft may substantially always provide a fast braking to a desired engine speed with good precision.

This objective is achieved with the arrangement of the type specified at the beginning, which is characterised by the features specified in the characterising portion of claim 1. A gear in the gearbox may obtain an upshift to substantially all higher gears in the gearbox. In a gearbox with many gears, the number of upshift alternatives is relatively great. The arrangement thus comprises a braking device, is adapted to brake the countershaft. The braking device comprises a first space in connection with a first piston, transferring a power to a braking component that brakes the countershaft with a first braking torque, and a second space in connection with a second piston, transferring a power to the braking component that brakes the countershaft with a second braking torque. With a suitable dimensioning of the pistons and the pistons' contact surfaces with the pressurised medium, each of these may provide its force, which is transferred to the braking components in such a way that it brakes the countershaft with a first braking torque when the first piston is activated, and a second braking torque when the second piston is activated. When both pistons are activated, they simultaneously supply their forces s to the braking components, which in this case brake the countershaft with a third braking torque, which is greater than the first torque and the second torque. The braking device may thus brake the countershaft with three alternative braking torques. It is thus possible, for each of the different upshift alternatives that occur in the gearbox, to activate the braking device in such a way that the countershaft is decelerated with the most suitable of the three braking torques.

Accordingly, a fast deceleration of the countershaft to a desired rotational speed may thus substantially always be provided, and with a good precision.

According to one embodiment of the present invention, said connecting means comprises conduits extending between the pressure medium source and said spaces in the braking device, at least one valve with which the pressure medium source is alternatingly connected with said spaces, and a control device, which is adapted to control the valve. The two spaces are connected with the pressure medium source via at least partly separate conduits. A joint valve may be in charge of which of said spaces that is connected with the pressure medium source. Such a joint valve may be set in three different states, namely a first state, in which the first space is connected with the pressure medium source, a second state, in which the second space is connected with the pressure medium source, and a third state, in which none of the spaces is connected with the pressure medium source. Alternatively, each of the two conduits may comprise a valve, which may be set in an open state and a closed state.

According to one embodiment of the present invention, stored information comprises information that defines which of said spaces must be connected with the pressure medium source at different upshift alternatives in the gearbox. As a rule, it is possible to store information in advance, defining which of the three alternative braking torques that is the most suitable to use, in order to brake the countershaft at the different upshift alternatives in the gearbox. Said stored information may be comprised in a memory in the control device, or be stored in another location where the control device has access to said information. The information defining which space or spaces that must be connected with the pressure medium source at different upshift alternatives in the gearbox, and thus the braking torque which must be applied on the countershaft, need not be the same throughout the entire braking process of the countershaft. It is not excluded to use one braking torque during one phase of the braking process and another braking torque during another phase of the braking process. Said stored information may also comprise terms defining different operating occasions, at which the different braking torques must be used. A control device that has access to this information controls the valves, so that the countershaft is decelerated with the defined braking torque for each one of the different upshift alternatives. Thus, at substantially all upshift alternatives, a fast shifting process with good precision may be provided. Wear caused by insufficient synchronisation of the secondary cogwheel's rotational speed in relation to the main shaft's rotational speed may thus be substantially eliminated at all upshift alternatives.

According to one embodiment of the present invention, the countershaft has at least two different moments of inertia in connection with different upshift alternatives in the gearbox, and said stored information defining one of said spaces is to be connected with the pressure medium source when the countershaft has one of said moments of inertia, and the second space is to be connected with the pressure medium source when the countershaft has another moment of inertia. In this case, it is thus possible to provide a greater braking torque when the countershaft has a greater moment of inertia, and a smaller braking torque when the countershaft has a smaller moment of inertia. Thus, the countershaft may provide a braking time corresponding to a desired rotational speed with good precision, when the countershaft has different moments of inertia. According to one embodiment of the present invention, the arrangement comprises pressure reducing means, adapted to connect said spaces with an area that has an ambient atmospheric pressure, when a braking process of the countershaft is to be ended. In order to obtain a good synchronisation of the secondary cogwheel's rotational speed in relation to the main shaft's rotational speed, the applied braking torque must cease substantially exactly when the synchronous rotational speed is achieved. It is also important that the control device interrupts the connection with the pressure medium source at the same time as it connects the pressurised space or spaces with atmospheric pressure. Said pressure reducing means may comprise venting passages, which are arranged between said spaces and said area having an ambient atmospheric pressure, as well as venting valves which are arranged in the venting passages. The venting passages may be set in a closed state when they maintain the pressure prevailing in the respective spaces, and in an open state when the

overpressure in the respective spaces is eliminated and the braking device is deactivated. According to one embodiment of the present invention, said area having an

atmospheric pressure is located in a silencer. When compressed air is released from the spaces to said area, pulsing sounds arise. For this reason, it is suitable that said area with atmospheric pressure is located inside a silencer, where the noise arising is attenuated. Accordingly, the arrangement provides no disturbing noise to any significant degree, which is propagated to the surroundings.

According to one embodiment of the present invention, the gearbox comprises a split gear arranged in connection with an input shaft in the gearbox. In gearboxes with split gears, the countershaft is generally connected with the input shaft via two different gearings. The countershaft in this case provides different moments of inertia, depending on the gearing between the input shaft and the countershaft. The split gear may be set in two split states, in which the countershaft obtains two separate moments of inertia, and in a neutral state, in which the countershaft obtains a third moment of inertia. In the neutral state the countershaft may be entirely disconnected from the input shaft. The countershaft thus has a significantly smaller moment of inertia in the neutral state than in the two split states. In this case, the countershaft thus has three different moments of inertia at the different gearing alternatives that may occur in the gearbox. It is therefore suitable that the largest braking torque is applied on the countershaft when it has the greatest moment of inertia, that the intermediate braking torque is applied on the countershaft when it has the intermediate moment of inertia and that the smallest moment of inertia is applied on the countershaft when it has the smallest moment of inertia.

According to one embodiment of the present invention, the braking device comprises a house, and the first piston and the second piston are arranged in a substantially joint plane as well as shiftably arranged in parallel directions in said house facing the braking component. The pistons are thus separately shiftable towards the braking component. In case the braking components consist of a disc brake, the brake discs may be compressed by the respective pistons, so that the disc brake provides a braking torque on the countershaft. The second piston may extend annularly around the first piston. Accordingly, a compact construction with a centrally arranged circular piston and a peripherally arranged annular piston is obtained.

According to one embodiment of the present invention, the arrangement comprises locking devices, adapted to provide a rotational locking of the secondary cogwheels on the main shaft when the secondary cogwheels have obtained a synchronous rotational speed with the main shaft during an upshift process. In this case, no synchronisation devices are thus required on the main shaft, having friction surfaces providing a synchronisation of the secondary cogwheels' rotational speed with the main shaft. Locking devices may thus have a significantly simpler design than the synchronisation devices.

According to one embodiment of the present invention, said medium is compressed air. Compressed air is an existing power source in heavy goods vehicles, and may also advantageously be used to activate the braking device.

According to one embodiment of the present invention, the control device is adapted to have access to information relating to a suitable gear in the gearbox during different operating states, and to initiate shifting in the gearbox, in such a way that a suitable gear is engaged in the gearbox during different operating states. The different operating states are defined by several operating parameters such as the vehicle's speed, the engine's engine speed etc. Such a gearbox, acting entirely automatically based on current values of a number of operating parameters, may be referred to as an AMT gearbox (Automatic Manual Transmission). The arrangement according to the invention may, however, be used also for other types of gearboxes. The control device may, for example, receive information from a shifting control, relating to the shifting alternative that should be carried out in the gearbox. With the shifting control the driver thus indicates disengagement of an existing gear in the gearbox and engagement of a new gear. The control device in this case receives information relating to the requested shifting alternative, and initiates necessary shifting movements to carry out the requested shifting alternative.

BRIEF DESCRIPTION OF THE DRAWING

Below is a description, as an example, of preferred embodiments of the invention with reference to the enclosed drawing, on which: Fig. 1 shows a gearbox, which is equipped with an arrangement according to the present invention, and

Fig. 2 shows the braking device in Fig. 1 in more detail.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 shows a gearbox that may be arranged in a heavy goods vehicle. The gearbox is attached inside a house 1. The gearbox comprises an input shaft 2, which is operated by a non-displayed combustion engine. The gearbox comprises a split gear, which, in a first split state, connects the input shaft 2 with a countershaft 5 in the gearbox via a cogwheel 3, which is in constant engagement with a cogwheel 4 on the countershaft 5. In a second split state, the input shaft 2 is connected with the countershaft 5 via a cogwheel 7c, which is in constant engagement with a cogwheel 6c on the countershaft 5. The countershaft 5 thus provides a rotation movement of the input shaft 2. The countershaft 5 is equipped with several additional cogwheels 6a-e of various sizes. The cogwheels 6a-e are separate units, which are fixedly fitted on the countershaft 5, or constitute a homogeneous part of the countershaft 5. Each one of the cogwheels 6a-e on the countershaft 5 is in constant engagement with a corresponding cogwheel 7a-e on a main shaft 8. The gearbox thus contains several gear sets in constant engagement with each other. Each one of the gear sets comprises a primary cogwheel 6a-e, which is fixedly arranged on the countershaft, and a secondary cogwheel 7a-e which is rotatably arranged on the main shaft 8. One gear set, comprising a primary cogwheel 6a and a secondary cogwheel 7a, provides a gearing that defines the first gear in the gearbox. One gear set, comprising a primary cogwheel 6b and a secondary cogwheel 7b, provides a gearing that defines the second gear in the gearbox. One gear set, comprising a primary cogwheel 6c and a secondary cogwheel 7c, provides a gearing that defines the third gear in the gearbox. A gear set comprising a primary cogwheel 6d and a secondary cogwheel 7d defines a creeper gear. A gear set, comprising a primary cogwheel 6e and a secondary cogwheel 7e defines a reverse gear. The gear set 6e, 7e for the reverse gear comprises an interim cogwheel, which provides a reverse rotational direction of the main shaft 8. The secondary cogwheels 7a-e are rotatably arranged on the main shaft 8 with the help of a bearing 9, which may be a needle bearing. Locking devices lOa-c are arranged in connection with the secondary cogwheels 7a-e on the main shaft 8. The task of each of the locking devices lOa-c is to provide a rotational locking of at least one of the secondary cogwheels 7 in relation to the main shaft 8, in connection with engaging a gear. A locking device 10a is adapted to be responsible for rotational locking of the secondary cogwheel 7a for the first gear. A locking device 10b is adapted to be responsible for rotational locking of the secondary cogwheels 7b, 7c for the second and third gears. A locking device 10c is comprised in the split gear, whose task it is to set the different split positions in such a way that it in the first split state connects the input shaft 2 with a countershaft 5 in the gearbox via the cogwheels 3, 4, and via the cogwheels 7c, 6c in the second split state.

Each one of the locking devices lOa-c is attached on the main shaft 8 with a rotatable connection, so that it rotates with the same rotational speed as the main shaft 8. Each one of the locking devices lOa-d comprises a shiftably arranged clutch sleeve with a dog clutch or similar, which on the main shaft 8 is shiftable in an axial direction between a neutral state and at least one locked state, in which the dog clutch provides a rotational locking of a secondary cogwheel 7a-e on the main shaft 8. The gearbox also comprises a range gear 11, which is arranged between the main shaft 8 and an output shaft 12 in the gearbox. With the help of a range gear 11, all gearings in the gearbox may be given a high and a low gearing, respectively. Accordingly, the gearbox may obtain twice as many gears.

A control device 14 is adapted to have access to stored information 14a, relating to a suitable gear in the gearbox at different operating states that are defined by a number of operating parameters 13, such as the vehicle's speed, the combustion engine's engine speed etc. The control device 14 is adapted to receive information relating to the current values of said operating parameters 13 during operation, and to initiate shifts in the gearbox with the help of this information. The control device 14 is adapted to create shifting movements of the locking devices lOa-c with the help of a schematically displayed manoeuvring element 15, which may comprise an actuator and a movement transferring mechanism for each of the locking devices lOa-c. With the help of such a manoeuvring element 15, the locking devices lOa-c may be moved from a locked state to a neutral state during a disengagement process of a gear in the gearbox and, from the neutral state to the locked state during an engagement process of a gear in the gearbox. During an upshift process, the secondary cogwheel 7a-c, which defines the higher gear to be engaged in the gearbox, has a higher rotational speed than the main shaft 8. The countershaft 5 must thus be decelerated, in order for the secondary cogwheel 7a-c to obtain a synchronous rotational speed with the main shaft 8. The control device 14 thus activates a braking device 16, which reduces the countershaft's engine speed, so that the secondary cogwheel 7a-c obtains a synchronous rotational speed with the main shaft 8. When a synchronous rotational speed has been achieved, the locking device lOa-c is shifted from the neutral state to the locked state, in which it provides a rotational locking of the secondary cogwheel 7a-c on the main shaft 8. During a downshift process, the secondary cogwheel 7a-c, which defines the lower gear to be engaged in the gearbox, has a lower rotational speed than the main shaft 8. The countershaft 5 must thus be accelerated, in order for the secondary cogwheel 7a-c to obtain a synchronous rotational speed with the main shaft 8. In this case the control device 14 activates the drive engine, which is connected with the gearbox via the input shaft 2. With the help of the drive engine the countershaft 5 provides an acceleration, until the secondary cogwheel 7a-e obtains a synchronous rotational speed with the main shaft 8. When a synchronous rotational speed has been achieved, the locking device lOa-c is shifted from the neutral state to the locked state, in which it provides a rotational locking of the secondary cogwheel 7a-c on the main shaft 8.

When a shifting process occurs between a low split state and a high split state in the gearbox, the locking device 10c is in a neutral state. The locking device 10c may also be in a neutral state when the shift occurs between the gears that are defined by the secondary cogwheels 7a-c. When the locking device 10c is in a neutral state, the countershaft 5 is disconnected from the input shaft 2. In the disconnected state, the countershaft 5 has a first moment of inertia Ji, which is relatively small. Braking the countershaft 5 during a synchronisation process with the split gear in the neutral state requires a relatively small braking torque. When a shifting process occurs with an engaged split gear, the countershaft 5 is connected with the input shaft 2. The countershaft 5 thus has a larger moment of inertia than in the disconnected state. When a shifting process occurs with the split gear in the high split state, the countershaft 5 is connected with the input shaft 2 via a high gearing, and it therefore has a second moment of inertia J₂, which is larger than the first moment of inertia Ji . In this case a larger braking torque is required in order to decelerate the countershaft 5 within a time corresponding to the time when the split gear is in a neutral state. When a shifting process occurs with the split gear in the low split state, the countershaft 5 is connected with the input shaft 2 via a low gearing, and it therefore has a third moment of inertia , which is larger than the second moment of inertia J₂. In this case an even larger braking torque is required to brake the countershaft 5 within a corresponding time. Fig. 2 shows the braking device 16 in more detail. The braking device 16 comprises a house 17 with a moveably arranged first piston 18a. The first piston 18a has a first side 18ai that defines a wall in a first space 19a inside the house 17, and an opposite second side, which is adapted to come into contact with a disc brake 20. The braking device 16 comprises a moveably arranged second piston 18b. The second piston 18b has a first side 18bi that defines a wall in a second space 19b inside the house 17, and an opposite second side, which is adapted to come into contact with the disc brake 20. The first piston 18a and the second piston 18b are arranged in a substantially joint plane, and shiftably arranged in parallel directions facing the braking component 20. The second piston 18b extends annularly around the first piston 18a. The second space 19b extends in a similar manner around the first space 19a. The disc brake 20 comprises alternating non-rotatable brake discs, which are attached in the house 17, and rotatable brake discs, which are attached on a central section 21 of the countershaft 5. With the help of the pistons 18a, 18b the brake discs may be compressed, in such a way that the countershaft 5 is decelerated with a braking torque related to the pressure prevailing in the respective spaces 19a, b and to the pistons' contact surfaces 18ai,

18bi with the pressurised medium in the respective spaces 19a, 19b. The countershaft 5 extends through a wall 1 of the gearbox. The countershaft 5 is rotatably attached with a bearing 22 in an attachment element 23, which also supports the house 17. The first space 19a in the braking devices 16 is, via a first conduit 24, connected with a compressed air source 25, where the compressed air has a substantially constant pressure pi. The compressed air source 25 may consist of an existing compressed air system in a vehicle. The first conduit 24 comprises a first valve 26, which by the control device 14 may be set in an open state and in a closed state of. In the open state, the compressed air source 25 is connected with the first space 19a. When this happens, the first piston 18a is shifted with a force, related to the pressure pi prevailing in the first space 19a and to the first piston's area 18ai, which is in contact with the compressed air in the first space 19a. By the disc brake 20 this force is converted to a first braking torque Mi, which acts on the countershaft 5. The first conduit 24 comprises a venting section 24a, equipped with a first venting valve 27. When the first venting valve 27 is set in an open state, the first space 19a is connected with an area 31, comprising air with an atmospheric pressure. This eliminates the overpressure that acts on the first piston 18a, and the first braking torque Mi on the countershaft 5 ceases. The second space 19b of the braking devices 16 is connected, via a second conduit 28, with the compressed air source 25. The second conduit 24 comprises a second valve 29, which by the control device 14 may be set in an open state and in a closed state. In the open state, the compressed air source 25 is connected with the second space 19b of the braking device 16. When this happens, the second piston 18b is shifted with a force related to the pressure pi prevailing in the second space 19b and to the second piston's area 18bi, which is in contact with the compressed air in the second space 19b. By the disc brake 20 this force is converted into a second braking torque M₂, which acts on the countershaft 5. The second conduit 28 comprises a venting section 28a, which is equipped with a second venting valve 30. When the second venting valve 30 is set in an open state, the second space 19b is connected with an area 31, comprising air with an ambient atmospheric pressure. This eliminates the overpressure acting on the second piston 18b, and the second braking torque M₂ on the countershaft 5 ceases. Said area 31 may be located in a silencer. When compressed air is released from the spaces 19a, 19b to said area 31, pulsing sounds arise. Since said area 31 is located inside a silencer, substantially no such disrupting noise arises.

The first braking torque Mi, which the countershaft 5 obtains when the first piston 18a is activated, is thus related to the first piston's contact surface 18ai and the pressure in the first space 18a. The second braking torque M₂, which the countershaft 5 obtains when the second piston 18b is activated, is thus related to the second piston's contact surface 18bi and the pressure in the second space 18b. In this case, the same pressure pi is thus obtained in the two spaces 19a, 19b when the respective pistons 18a, 18b are activated. The difference in obtained braking torque, between the first braking torque Mi and the second braking torque M₂, thus becomes related to the size of the respective pistons' contact surfaces 18a_l5 18b₁. In cases where the second piston's contact surface 18a₂ is larger than the first piston's contact surface 18ai, the second braking torque M₂ is larger than the first braking torque Mi. If both the first valve 24 and the second valve 28 are set in an open state, both the first space 19a and the second space 19b are filled with compressed air with the pressure pi. Both the first piston 18a and the second piston 18b thus provide a force which acts on the disc brake 20. The disc brake in this case provides a third braking torque M₃, which is larger than the first braking torque Mi and the second braking torque M₂. The control device 14 is adapted to control the valves 26, 27, 29, 30 with information from said operating parameters 13, and information from a sensor 33 or similar that detects or estimates the main shaft's 8 rotational speed, and a sensor 34 or similar that detects or estimates the countershaft's 5 rotational speed, as well as stored information 14a.

During operation, the control device 14 receives substantially continuously

information from said operating parameters 13. The control device thus controls whether the most suitable gear in the prevailing operating occasion, according to the stored information 14a, corresponds to the existing gear in the gearbox. If this is not the case, the control device 14 activates the manoeuvring device 15, which moves the locking device lOa-c for the existing gear from the locked state to the neutral state, so that the secondary cogwheel 7a-c for the existing gear is disconnected from the main shaft 8. The control device 14 determines whether the shifting process relates to an upshift process or a downshift process. If the shifting process relates to an upshift process, the braking device 16 is activated, so that it supplies a braking torque on the countershaft 5, until it obtains a rotational speed at which the secondary cogwheel 7a-c for the new gear has a synchronous rotational speed with the main shaft 8. If the shifting process relates to a downshift process, the drive engine provides an activation of the countershaft 5, so that it is accelerated to an engine speed at which the secondary cogwheel 7a-e for the new gear has a synchronous rotational speed with the main shaft 8.

In cases where the shifting process relates to an upshift process, the control device 14 determines which upshift alternative is to be carried out. The upshift alternative is defined by the gear that is disengaged from the gearbox and the gear that is engaged in the gearbox. The number of upshift alternatives may be relatively large in a gearbox with many gears. The control device 14 subsequently decides, with the help of the stored information 14a, whether one or both the spaces 19a, 19b must be connected with the compressed air source 2 for the relevant upshift alternative. The stored information 14a may define which of the three braking torques Mi, M₂, M₃ that are to be applied on the side brake 5 for each one of the upshift alternatives existing in the gearbox. The countershaft 5 thus has a first moment of inertia Ji when the locking device 10c is in a neutral state during an upshift process, a second higher moment of inertia J₂ when the locking device 10c is in a locked state, in which the split gear is in a high split state, and a third moment of inertia J₃ when the locking device 10c is in a locked state, in which the split gear is in a low split state. In this case, said stored information 14a may define that at all upshift alternatives, wherein the countershaft 5 has the first moment of inertia Ji, the first piston 18a must be activated, so that the countershaft 5 is decelerated with the first braking torque Mi, at all upshift alternatives, wherein the countershaft 5 has the second moment of inertia J₂, the second piston 18b must be activated, so that the countershaft 5 is decelerated with the second braking torque M₂, and at all upshift alternatives, wherein the countershaft 5 has the third moment of inertia J₃, both the first piston 18a and the second piston 18b must be activated, so that the countershaft 5 is decelerated with the third braking torque M₃.

When the stored information defines that the countershaft 5 will have the first moment of inertia Ji during the synchronisation process, the control device 14 sets the first valve 26 into an open state. The other valves 27, 29, 30 are in the closed state. The compressed air source 25 is thus connected with the first space 19a. The first piston 18a is shifted toward the disc brake 20, which therefore brakes the countershaft with the first braking torque Mi. During the braking process, the control device 14 receives information from the sensors 33, 34 relating to the countershaft's 5 and the main shaft's 8 rotational speeds. When the control device 14 receives information indicating that the relevant secondary cogwheel 7a-e has obtained a synchronous rotational speed with the main shaft 8, the control device 14 closes the valve 26, at the same time as it opens the valve 27, so that the overpressure in the first space 19a is eliminated.

Accordingly, the braking device 16 is deactivated. The control device 14 subsequently activates the manoeuvring device 15, which moves the relevant locking device 10a, b from the neutral state to a locked state, in which the relevant secondary cogwheel 7a-c obtains a rotational locking on the main shaft 8. Subsequently, the split gear may be set in a low or high split state, following synchronisation and locking, with the help of the locking device 10c.

When the stored information defines that the countershaft 5 will have the second moment of inertia J₂ during the synchronisation process, the control device 14 sets the second valve 29 in an open state. The other valves 24, 27, 30 are in the closed state. The compressed air source 25 is thus connected with the second space 19b. The second piston 18b is shifted towards the disc brake 20, which accordingly brakes the countershaft with the second braking torque M₂. The control device 14 receives information from the sensors 33, 34 relating to the countershaft's 5 and the main shaft's 8 rotational speeds during the braking process. When the control device 14 receives information, which indicates that the relevant secondary cogwheel 7a-c has obtained a synchronous rotational speed with the main shaft 8, the control device 14 closes the valve 29 at the same time as it opens the valve 30, so that the overpressure in the second space 19b is eliminated. Accordingly, the braking device 16 is deactivated. The control device 14 subsequently activates the manoeuvring device 15, which moves the relevant locking device 10a, 10b from the neutral state to a locked state, in which the relevant secondary cogwheel 7a-c obtains a rotational locking on the main shaft 8.

When the stored information defines that the countershaft 5 will have the third moment of inertia J₃ during the synchronisation process, the control device 14 sets the first valve 24 and the second valve 29 in an open state. The other valves 27, 30 are in the closed state. The compressed air source 25 is thus connected with both the first space 19a and the second space 19b. The first piston 18a and the second piston 18b are shifted towards the disc brake 20, which accordingly brakes the countershaft 5 with the third moment of inertia M₃. The control device 14 receives information from the sensors 33, 34 relating to the countershaft's 5 and the main shaft's 8 rotational speeds during the braking process. When the control device 14 receives information, which indicates that the relevant secondary cogwheel 7a-c has obtained a synchronous rotational speed with the main shaft 8, the control device 14 closes the valves 26, 29 at the same time as it opens the valves 27, 30, so that the overpressure in the first space 19a and the second space 19b is eliminated. Accordingly, the braking device 16 is deactivated. The control device 14 subsequently activates the manoeuvring device 15, which moves the relevant locking device 10a, 10b from the neutral state to a locked state, in which the relevant secondary cogwheel 7a-c obtains a rotational locking on the main shaft 8.

The invention is not limited to the embodiment described above, but may be varied freely within the scope of the patent claims. It is possible to use more than two pistons, providing different braking torques on the countershaft, and to combine the activation of two or more pistons in any manner in order to create additional alternative braking torques acting on the countershaft. The information 14a, which defines the piston or pistons 18a, 18b to be activated, need not be related to the countershaft's moment of inertia. Several different braking torques may also be used during different phases of a braking process of the countershaft. The stored information 14a may also comprise conditions defining braking torque that must act on the countershaft in different operating states. Such terms may be related to suitable operating parameters.

Claims

1. Arrangement for an upshift process in a gearbox, wherein the gearbox comprises a countershaft (5), a main shaft (8), and several gear sets, each of which comprises a primary cogwheel (6a-e), which is rotatably arranged on the countershaft (5), and a secondary cogwheel (7a-e), which is arranged on the main shaft (8), wherein the arrangement comprises a pressurised medium source (25) comprising a pressurised medium with a substantially constant pressure (p , and a braking device (16) comprising a first space (19a), which is adapted to receive a pressurised medium, and a first piston (18a), which is adapted to be shifted by the pressurised medium in said first space (19a) and to transfer a force to a braking component (20), so that it acts with a first braking torque (Mi) on the countershaft (5) during an upshift process in the gearbox, characterised in that the braking device (16) comprises a second space (19b), adapted to receive a pressurised medium, and a second piston (18a), which is adapted to be shifted by the pressurised medium in said second space (19b) and to transfer a force to the braking component (20), so that it acts with a second braking torque (M₂) on the countershaft (5) during an upshift process in the gearbox, and connecting means (24, 26, 28, 29) adapted to connect the pressurised medium source (25) with the first space (18a), so that the countershaft (5) is decelerated with the first braking torque (Mi), or with the second space (18b), so that the countershaft (5) is decelerated with the second braking torque (M₂), or with both the spaces (19a, 19b) simultaneously, so that the countershaft (5) is decelerated with a third braking torque (M₃).

2. Arrangement according to claim 1, characterised in that said connecting means comprises conduits (24, 27), extending between the pressurised medium source (25) and said spaces (19a, b) of the braking device (16), at least one valve (26, 29) with which the pressurised medium source (25) is alternately connected with said spaces (19a, 19b), and a control device (14) adapted to control the valves (26, 29).

3. Arrangement according to claim 1 or 2, characterised in that the arrangement comprises stored information (14a), which defines which of said spaces (19a, 19b) is to be connected with the pressurised medium source (25) at different upshift alternatives in the gearbox.

4. Arrangement according to claim 3, characterised in that the countershaft (5) has at least two different moments of inertia (Ji, J₂, J₃) in connection with different upshift alternatives in the gearbox, and in that said stored information (14a) defines one of said spaces (19a, 19b) to be connected with the pressurised medium source (25) when the countershaft has one of said moments of inertia, and in that the second space (19a, 19b) is to be connected with the pressurised medium source (25) when the countershaft (5) has another moment of inertia (Ji, J₂, J₃).

5. Arrangement according to any of the previous claims, characterised in that the arrangement comprises pressure reducing means (24a, 27, 28a, 30), adapted to connect said spaces (19a, 19b) with an area (31) having an ambient atmospheric pressure when a braking process of the countershaft is to be ended.

6. Arrangement according to claim 5, characterised in that said pressure reducing means comprises venting passages (24a, 28a), arranged between said spaces (19a, 19b) and said area (31) having an ambient atmospheric pressure, and venting valves (27, 30), arranged in the venting passages (24a, 28a).

7. Arrangement according to claim 5 or 6, characterised in that said area (31) with an atmospheric pressure is located in a silencer.

8. Arrangement according to any of the previous claims, characterised in that the gearbox comprises a split gear, arranged in connection with an input shaft (2) in the gearbox.

9. Arrangement according to claim 8, characterised in that the split gear may be set in two split states, in which the countershaft (5) obtains two different moments of inertia

(Ji, J₂), and in a neutral state in which the countershaft (5) obtains a third moment of inertia (J₃).

10. Arrangement according to any of the previous claims, characterised in that the braking device 16 comprises a house (17), and in that the first piston (18a) and the second piston (18b) are arranged in a substantially joint plane, and shiftably arranged in parallel directions in said house (17) towards the braking component (20).

11. Arrangement according to claim 10, characterised in that the second piston (18b) extends annularly around the first piston (18a).

12. Arrangement according to any of the previous claims, characterised in that the arrangement comprises locking devices (lOa-c), adapted to provide a rotational locking of the secondary cogwheels (7a-c) on the main shaft (8), when the secondary cogwheels (7a-c) have obtained a synchronous rotational speed with the main shaft (8) during an upshift process.

13. Arrangement according to any of the previous claims, characterised in that said medium is compressed air.

14. Arrangement according to any of claims 2 - 13, characterised in that the control device (14) is adapted to have access to information (14a), relating to a suitable gear in the gearbox during different operating states, and to initiate shifting in the gearbox so that a suitable gear is engaged in the gearbox during different operating states.

15. Gearbox comprising an arrangement according to any of claims 1 to 14.

16. Vehicle comprising a gearbox according to claim 15.