SE540153C2

SE540153C2 - Changing Gear Ratio in a Gearbox of a Vehicle

Info

Publication number: SE540153C2
Application number: SE1650701A
Authority: SE
Inventors: Selling Tomas; Arnelöf Per; Norberg Peer
Original assignee: Scania Cv Ab
Priority date: 2016-05-23
Filing date: 2016-05-23
Publication date: 2018-04-17
Also published as: BR102017008772A2; SE1650701A1; DE102017004637A1; DE102017004637B4

Abstract

The invention relates to a method for changing gear ratio in a gearbox (2) of a vehicle (1), said gearbox (2) being arranged to transfer torque between a power source (4) and at least one drive wheel (8) of said vehicle (1), said gearbox (2) comprising a first gearbox device (15A, ) and at least one second gearbox device (15B), each of said first and second gearbox devices (15B) being individually controllable to engage at least two gears having different gear ratios to form a combined gear ratio of said gearbox (2), said second gearbox device (15B) being arranged between said first gearbox device (15B) and said at least one drive wheel (8). The method comprising steps of:- disconnecting said first and second gearbox devices (15A, 15B) of said gearbox (2) from said at least one drive wheel (8);- changing gear ratio of said second gearbox device (15B) when said first and second gearbox devices (15A, 15B) of said gearbox (2) are disconnected from said at least one drive wheel (8); and- synchronizing the rotational speed between a rotating member (20, 22) of said second gearbox device (15B) and said at least one drive wheel (8) when said gear ratio of said second gearbox device (15B) has been changed.The invention also relates to a computer program comprising program code, a system for changing gear ratio in a gearbox (2) of a vehicle (1), and a vehicle (1).

Description

Changing Gear Ratio in a Gearbox of a Vehicle BACKGROUND AND PRIOR ART The invention relates to a method for changing gear ratio in a gearbox of a vehicle, a system for changing gear ratio in a gearbox of a vehicle, a computer program, a computer program product and a vehicle according to the appended claims.

Vehicles, and in particular heavy goods vehicles, e.g. trucks, are usually equipped with a gearbox connected to a power source such as an internal combustion engine, an electric engine or a combination thereof. The 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 gearbox device provided with a main shaft. A lay shaft is arranged in parallel with the main shaft. The main shaft is connectible to an input shaft via the lay shaft and to an output shaft in the gearbox via a range gearbox device, if such a range gearbox device is integrated in the gearbox. The range gearbox device may constitute a separate device instead of being integrated in the gearbox. The gearbox may also be equipped with a split gear device, arranged between the input shaft and the lay shaft.

A brake mechanism may be arranged to retard the lay shaft in connection with change of gears in the gearbox, in order to achieve synchronous rotational speeds between the lay shaft and the main shaft, so that the new gear may be engaged without any difference in rotation speed 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 lay shaft in relation to the main shaft at a stage during a shifting operation when the main gearbox is in the neutral position, while the lay shaft is disconnected from the main shaft. Also, a similar brake mechanism may be arranged to retard the main shaft in connection with change of gears in the gearbox.

In gearboxes of this type, the synchronization devices, comprising conical synchronization rings and coupling rings, may be replaced by coupling sleeves provided with splines, which are displaced axially in order to engage with gearwheels placed on the main shaft. Each gearwheel placed on the main shaft is engaged with corresponding gearwheel elements, which are firmly attached to the lay shaft. On shifting, the coupling sleeve is displaced axially in order to engage with coupling teeth arranged on a selectable gearwheel, in order to connect the gearwheel to, and rotation lock it, on the main shaft. The synchronization device in the split gearbox device and in the range gearbox device may also be replaced by coupling sleeves.

The synchronization between gearwheels and shafts in the gearbox is for some gear shifting provided by the power source. The power source accelerates the gearwheel or the shaft to be connected with each other. When synchronization has been reached the gearwheel and the shaft are connected by means of the coupling sleeve.

The range gearbox device is usually provided between the main gearbox device and a propeller shaft coupled to the drive wheels of the vehicle. The range gearbox device is accommodated in a gearbox housing and comprises an input shaft coupled to the main gearbox device, an output shaft and between the input shaft and the output shaft is a planetary gear of the range gearbox device disposed. The planetary gear usually comprises three components, which are rotatably arranged relative to each other namely, a sun gear wheel, a planet wheel carrier with planet gear wheels and a ring gear wheel. With knowledge of the number of teeth of the sun gear wheel and the ring gear wheel the relative speed of the three components can be determined during operation. In a range gearbox device the sun gear wheel can be rotatably connected to the input shaft, a number of planet gear wheels which engage said sun gear wheel, which planet gear wheels are rotatably mounted on the planet wheel carrier which is fixedly connected to the output shaft, and an axially displaceable ring gear wheel which surrounds and engages the planet gear wheels. The teeth of the sun gear wheel, planet gear wheels and ring gear wheel can be helical, that is, they are arranged at an angle to a common rotation axis of the sun gear wheel, planet wheel carrier and ring gear wheel.

There are range gearboxes in which the synchronization devices are replaced with coupling sleeves provided with splines. By controlling the transmission to synchronous speed between the two components to be engaged, an axial displacement of the coupling sleeve is made possible in order to connect them. When the components should be disengaged the transmission is controlled so that torque balance occurs between the components so that the coupling sleeve is not transmitting torque. It then becomes possible to move the coupling sleeve axially in order to disengage the components from each other.

The document US6196944 shows a planetary gear comprising a sun gear wheel, a planet wheel carrier with planet gear wheels and a ring gear wheel. The sun gear wheel may be connected to the input shaft by means of a coupling sleeve in a low range gear position and disengaged from the input shaft in a high range gear position. In the high range gear position the input shaft is connected to the planet wheel carrier by means of the same coupling sleeve. The ring gear wheel is firmly connected to a gearbox housing. The known planetary gear is arranged in an auxiliary gearbox, having only two gear positions.

The document US6196944 shows a gearbox for motor vehicles comprising a planetary gear comprising a first and a second sleeve acting on the planet wheel carrier, the ring gear wheel, the gearbox housing and the output shaft. The first and second sleeves are controlled as one connected unit.

The synchronous speed and torque balance between the components that should be engaged and disengaged when shifting gears may be achieved by controlling the power source in the powertrain. However, when the power source is an internal combustion engine, the period of time for synchronizing when shifting gears may be too long depending on the inertia in controlling the engine. As a result, the internal combustion engine will not reach the final speed for synchronous shifting of gears in the gearbox.

SUMMARY OF THE INVENTION Despite the known solutions there is a need to further develop a gearbox which is less dependent of the power source when shifting gears. There is also a need to further develop a gearbox in which the period of time for shifting is short.

An object of the invention is therefore to provide a gearbox which is less dependent of the power source when shifting gears.

Another object of the invention is to provide a gearbox in which the period of time for shifting is short.

The herein mentioned objects and other objects are achieved by a method for changing gear ratio in a gearbox of a vehicle, a system for changing gear ratio in a gearbox of a vehicle, a computer program, a computer program product and a vehicle according to the independent claims.

According to an aspect of the present invention a method for changing gear ratio in a gearbox of a vehicle is provided. The gearbox is arranged to transfer torque between a power source and at least one drive wheel of said vehicle. The gearbox comprises a first gearbox device and at least one second gearbox device, each of said first and second gearbox devices being individually controllable to engage at least two gears having different gear ratios to form a combined gear ratio of said gearbox. The second gearbox device is arranged between said first gearbox device and said at least one drive wheel. The method comprises steps of: - disconnecting said first and second gearbox devices of said gearbox from said at least one drive wheel; - changing gear ratio of said second gearbox device when said first and second gearbox devices of said gearbox are disconnected from said at least one drive wheel; and - synchronizing the rotational speed between a rotating member of said second gearbox device and said at least one drive wheel when said gear ratio of said second gearbox device has been changed.

The step of disconnecting said first and second gearbox devices of said gearbox from said at least one drive wheel comprises to disconnect rotatable parts of the first and second gearbox devices from said at least one drive wheel, so that no torque or speed may be transferred to the first and second gearbox devices from said at least one drive wheel. The step of changing gear ratio of said second gearbox device when said first and second gearbox devices of said gearbox are disconnected from said at least one drive wheel comprises to make an upshift or a downshift in the second gearbox device depending on the driving conditions of the vehicle. The step of synchronizing the rotational speed between a rotating member of said second gearbox device and said at least one drive wheel when said gear ratio of said second gearbox device has been changed comprises to accelerate the rotating member of said second gearbox device in order to synchronize the rotational speed between the rotating member of said second gearbox device and said at least one drive wheel to prepare for a connection between the second gearbox device and the at least one drive wheel.

The method steps may be performed and/or controlled by means of a control unit connected to the power source and the gearbox.

According to an aspect of the present invention, the step of changing gear ratio of said second gearbox device when said first and second gearbox devices of said gearbox are disconnected from said at least one drive wheel further comprises steps of: - disconnecting said second gearbox device from said first gearbox device by shifting said first gearbox device to a neutral gear position; - applying a braking force to the rotating member of said second gearbox device by means of a first braking element; - changing gear ratio of said second gearbox device when said rotating member of said second gearbox device is in a standstill condition.

The step of disconnecting said second gearbox device from said first gearbox device by shifting said first gearbox device to a neutral gear position comprises to disconnect rotatable parts of the second gearbox device from the first gearbox device, so that no torque or speed may be transferred from the first gearbox device to the second gearbox device. The step of applying a braking force to the rotating member of said second gearbox device by means of a first braking element comprises to retard the speed of the rotating member of said second gearbox device to a standstill condition. The step of changing gear ratio of said second gearbox device when said rotating member of said second gearbox device is in a standstill condition comprises to make an upshift or a downshift in the second gearbox device depending on the driving conditions of the vehicle.

According to an aspect of the present invention the method further comprising steps of: - accelerating a rotating member of said first gearbox device by means of said power source after connecting said gearbox to said at least one drive wheel; - changing gear ratio of said first gearbox device when the rotational speed of said rotating member has been accelerated at least to a first speed.

The step of accelerating a rotating member of at least one of said first gearbox device by means of said power source when changing gear ratio of said second gearbox device or after connecting said gearbox to said at least one drive wheel comprises to synchronizing the speed between rotating members within said first gearbox device. The step of changing gear ratio of at least one of said first gearbox device when the rotational speed of said rotating member has been accelerated at least to a first speed comprises to make a downshift in said first gearbox device.

According to an aspect of the present invention the method further comprising steps of: - applying a braking force to a rotating member of said first gearbox device by means of a second braking element, after connecting said gearbox to said at least one drive wheel; - changing gear ratio of at least one of said gearbox devices when the rotational speed of said rotating member has been reduced at least to a second speed.

The step of applying a braking force to a rotating member of said first gearbox device by means of a second braking element, when changing gear ratio of said second gearbox device or after connecting said gearbox to said at least one drive wheel comprises synchronizing the speed between rotating members within said first gearbox device. The step of changing gear ratio of said first gearbox device when the rotational speed of said rotating member has been reduced at least to a second speed comprises to make a upshift in said first gearbox device.

According to an aspect of the present invention said second gearbox device is a range gearbox comprising a planetary gear, arranged to provide a high range gear and a low range gear. The step disconnecting said first and second gearbox devices of said gearbox from said at least one drive wheel, further comprises a step of: - disconnecting said planetary gear from said at least one drive wheel.

The step of disconnecting said planetary gear from said at least one drive wheel comprises to disconnect rotatable parts of the planetary gear from said at least one drive wheel, so that no torque or speed may be transferred to the planetary gear from said at least one drive wheel.

According to an aspect of the present invention the planetary gear comprises a sun wheel being connected to an output shaft of said first gearbox device, and a planet wheel carrier carrying a plurality of planet gear wheels engaging said sun wheel, said planet wheel carrier being selectively connectable to an output shaft of said second gearbox device. The step disconnecting said planetary gear from said at least one drive wheel, further comprises a step of: - disconnecting said planet wheel carrier from said output shaft of said second gearbox device.

The step of disconnecting said planet wheel carrier from said output shaft of said second gearbox device comprises to disconnect the rotatable parts of planet wheel carrier from said output shaft, so that no torque or rotation from the at least one drive wheel may be transferred to the planet wheel carrier from said output shaft.

According to an aspect of the present invention an axially displaceable coupling sleeve in a first position is arranged to connect said planetary gear to said at least one drive wheel of said vehicle, and in a second position is arranged to disconnect said planetary gear from said at least one drive wheel of said vehicle. The method further comprising a step of: - synchronizing the rotational speed between said planetary gear and said at least one drive wheel by means of a synchronizing element, and thereafter - connecting said planetary gear to said at least one drive wheel.

The step of synchronizing the rotational speed between said planetary gear and said at least one drive wheel by means of a synchronizing element comprises to accelerate the rotating member of said planetary gear from a standstill condition in order synchronize the rotational speed between the rotating member of said planetary gear and said at least one drive wheel which rotates when the vehicle moves. The step of connecting said planetary gear to the at least one drive wheel comprises to displace the coupling sleeve to the first position in order to connect the planetary gear to said at least one drive wheel.

According to an aspect of the present invention the method further comprising a step of: - connecting said gearbox to said at least one drive wheel by connecting said gearbox to a propeller shaft of said vehicle.

The step of connecting said gearbox to said at least one drive wheel by connecting said gearbox to a propeller shaft of said vehicle comprises to make a connection for transfer torque and rotation from the gearbox to the at least one drive wheel by connecting said gearbox to a propeller shaft arranged between the gearbox and the at least one drive wheel.

A control unit may be connected to the powertrain, such as the power source, a clutch and the gearbox to achieve the gear shifting above. The control unit may be the engine control unit or may comprise a plurality of different control units. A computer may be connected to or form part of the control unit.

According to an aspect of the invention a system for changing gear ratio in a gearbox of a vehicle is provided. The gearbox being arranged to transfer torque between a power source and at least one drive wheel of said vehicle, said gearbox comprising a first gearbox device and at least one second gearbox device, each of said first and second gearbox devices being individually controllable to engage at least two gears having different gear ratios to form a combined gear ratio of said gearbox, said second gearbox device being arranged between said first gearbox device and said at least one drive wheel. The system comprises: - means for disconnecting said first and second gearbox devices of said gearbox from said at least one drive wheel; - means for changing gear ratio of said second gearbox device when said first and second gearbox devices of said gearbox are disconnected from said at least one drive wheel; and - means for synchronizing the rotational speed between a rotating member of said second gearbox device and said at least one drive wheel when said gear ratio of said second gearbox device has been changed.

The means for disconnecting said first and second gearbox devices of said gearbox from said at least one drive wheel may comprise a second displaceable coupling sleeve. The second displaceable coupling sleeve may be displaced by means of a second pneumatic, hydraulic or electric actuator.

The means for changing gear ratio of said second gearbox device, when said first and second gearbox devices of said gearbox are disconnected from said at least one drive wheel, may comprise a first displaceable coupling sleeve. The first displaceable coupling sleeve may be displaced by means of a first pneumatic, hydraulic or electric actuator.

The means for synchronizing the rotational speed between a rotating member of said second gearbox device and said at least one drive wheel when said gear ratio of said second gearbox device has been changed accelerates the rotating member of said second gearbox device, so that the rotating member of said second gearbox device will reach the same rotational speed as a propeller shaft connected to said at least one drive wheel. The means for synchronizing the rotational speed between a rotating member of said second gearbox device and said at least one drive wheel may comprise a synchronizing element.

According to an aspect of the invention said second gearbox device is a range gearbox comprising a planetary gear, arranged to provide a high range gear and a low range gear and wherein an axially displaceable coupling sleeve in a first position is arranged to connect said planetary gear to said at least one drive wheel of said vehicle, and in a second position is arranged to disconnect said planetary gear from at least one drive wheel of said vehicle. The system further comprises: - a synchronizing element for synchronizing the rotational speed between said planetary gear and said at least one drive wheel before connecting said planetary gear to said at least one drive wheel.

The synchronizing element may accelerate the planetary gear of said second gearbox device, so that the rotating member of said second gearbox device will reach the same rotational speed as the propeller shaft connected to said at least one drive wheel. The synchronizing element may be provided with friction surfaces arranged on the planetary gear and on an output shaft connected to the propeller shaft. A friction force between the friction surfaces will urge the planetary gear to rotate with the same speed as the propeller shaft connected to said at least one drive wheel. The friction surfaces may have a conical shape. However, another shape of the friction surfaces is also possible.

According to an aspect of the invention the synchronizing element is a friction clutch arranged between said planet wheel carrier and an output shaft of said second gearbox device, which output shaft is connected to the propeller shaft. The system further comprises: - means for synchronizing the rotational speed between said planetary gear and said output shaft of said second gearbox device by engaging the friction clutch.

The means for synchronizing the rotational speed between said planetary gear and said output shaft of said second gearbox device by engaging the friction clutch comprises pneumatic, hydraulic or electric controlled actuators.

According to an aspect of the invention the synchronizing element is an electrical machine arranged to rotate said planet wheel carrier. The system further comprises: - means for synchronizing the rotational speed between said planetary gear and said at least one drive wheel by activating the electrical machine to a speed that rotates the said planetary gear with a speed that substantially correspond to the speed of said output shaft of said second gearbox device.

The electrical machine may be connected to the planetary gear so that it is able to rotate said planetary gear with a speed that substantially correspond to the speed of said output shaft of said second gearbox device.

Further advantages of the invention appear from the following detailed description.

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: Fig. 1 schematically illustrates a vehicle according to an embodiment of the invention, Fig. 2 schematically illustrates a powertrain according to an embodiment of the invention, Fig. 3 schematically illustrates a powertrain according to an embodiment of the invention in a low range gear position, Fig. 4 schematically illustrates a powertrain according to an embodiment of the invention in a low range gear position, Fig. 5 schematically illustrates a powertrain according to an embodiment of the invention in a high range gear position, Fig. 6 schematically illustrates a powertrain according to an alternative embodiment of the invention, Fig. 7 schematically illustrates a flow chart for a method for changing gear ratio in a gearbox of a vehicle according to a first embodiment of the invention, and Fig. 8 schematically illustrates a flow chart for a method for changing gear ratio in a gearbox of a vehicle according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 schematically illustrates a vehiclel according to an embodiment of the invention. The vehicle 1 includes a powertrain 3, which comprises a power source 4, such as an internal combustion engine, a gearbox 2 and a propeller shaft 10. The combustion engine 4 is coupled to the gearbox 2. The gearbox 2 is further connected to the drive wheels 8 of the vehicle 1 via the propeller shaft 10. The gearbox 2 of the pre sent invention comprises a range gearbox. Herein reference is made to various positions in/of the powertrain 3. In this context, the term upstream referes to a position towards the power source 4, and the term downstream refers to a position towards the drive wheels 8.

Fig. 2 shows schematically a part of the powertrain 3 comprising the combustion engine 4 and a clutch 11. The figure further discloses the gearbox 2, comprising three gearbox units 15A, 15B, 15C. A first gearbox unit 15A constitutes a conventional main gearbox that can be set to three different forward gear ratios. The figure further discloses a second gearbox unit 15B constituting a range gearbox, arranged downstream the main gearbox unit 15A. The range gearbox unit 15B is surrounded by a gearbox housing 12 and is discussed further with reference to figures 3 - 5. A third gearbox unit 15C is located upstream the main gearbox 15B in the direction of torque from combustion engine 4 to drive wheels 8. The third gearbox unit 15C constitutes a split gearbox which provides for each gear of the main gearbox into two gear steps with different gear ratios in order to provide more gear ratios of the gearbox 2.

Instead of a disengageable clutch 11, an arrangement with first and second electrical machines (not disclosed) may be arranged to rotate and brake a planetary gear (not disclosed) arranged in the powertrain 3 and located upstream the gearbox 2. In such an arrangement the first electrical machine should be arranged at a sun gearwheel (not disclosed) of the planetary gear, and the second electrical machine should be arranged at the first ring gearwheel (not disclosed) of the planetary gear. The first and second electrical machines may be the power source or may form part of the power source.

With regard to the main gearbox 15A, a lay shaft 202 comprises gearwheels 203A, 204A, 205A that are rotatably fixed to the lay shaft 202. For example, gear wheel 203A represents the first gear, gear wheel 204A the second gear and gear wheel 205A the third gear. A main shaft 206 comprises corresponding gear wheels 203B, 204B, 205B which rotate freely in relation to the main shaft 206, but which can be selectively locked for rotation with the main shaft 206 in order to engage a gear. For example, the first main gearbox gear can be engaged by manoeuvring a first main sleeve 207, arranged to rotate with the main shaft 206, to a position where the gear wheel 203B is engaged, i.e. to the left in the figure, thereby bringing the gear wheel 203B to rotate the main shaft 206 and thereby also engaging the lay shaft 202 to the main shaft 206 via gear wheel 203A. Each pair of gear wheels on the lay shaft 202 and main shaft 206 representing a gear ratio.

The second main gearbox gear can be engaged by disengaging the first main sleeve 207 from gear wheel 203B and instead moving a second main sleeve 208 to a position to the right in the figure where, instead, gear wheel 204B is engaged, thereby bringing the gear wheel 204B to rotate the main shaft 206. Correspondingly, the third main gearbox gear can be engaged by manoeuvring the second main sleeve 208 to a position to the left in the figure where, instead gear wheel 205B is engaged, thereby setting the main gearbox to third gear. Each of the first through third gears is used for a plurality of the total number of gears provided by the gearbox 2 as a whole. For example, the first gear of the main gearbox 15A will be used for first and second gear of the gearbox 2, low and high split, low range, and also for seventh and eighth gear, low and high split, high range, in a manner well known to a person skilled in the art.

Further, with regard to the split gearbox 15C, the lay shaft 202 comprises an additional gear wheel 209A that, similar to the above, is rotatably fixed to the lay shaft 202. An input shaft 201 comprises a corresponding gear wheel 209B rotating freely in relation to the input shaft 201 but which can be selectively locked for rotation with the input shaft 201 through a split sleeve 210, which may be provided with a split synchronising unit. The split sleeve 210 can further be used to connect the gearbox input shaft 201 to gear wheel 205B directly. The gear wheel pair 209A-B and coupling unit 210 can thereby provide two different split gear ratios for each gear of the main gearbox into two parts.

When e.g. the first gear is engaged, the split sleeve 210 is arranged to engage gear wheel 205B. This will have the result that the input shaft 201 is directly connected to gear wheel 205B, which via gear wheel 205A establishes a first gear ratio between input shaft 201 and lay shaft 202. Gear wheel 205B, however, is not connected to the main shaft 206, but the lay shaft 202 is connected to main shaft 206 through gear wheel pair 203A-B.

When the second gear is engaged, i.e. high split of first main gearbox gear, the vehicle 1 is, instead, driven with gear wheel pair 209A-B engaged, resulting in a second gear ratio between an input shaft 201 and lay shaft 202. The gear wheel 203B is still engaged by the first main sleeve 207 according to the above, thereby extending the range of each gear.

This split can be performed for each gear of the main gearbox 15A, where coupling unit 210 engages gearwheel 205B and also the second main sleeve 208 engages gearwheel 205B a 1:1 gear ratio through the gearbox units 15C, 15A is obtained.

Also, the main shaft 206 may be provided with a first braking element 212, such as a main shaft brake, which is used to brake the main shaft 206 and also a planetary gear 14 (fig. 3) in the range gearbox 15B to a standstill condition when shifting gears in the range gearbox 15B. The lay shaft 202 may be provided with a second braking element 211, such as a lay shaft brake in order to decrease the speed of the lay shaft 202 during upshifting in the gearbox 103.

So far, gearbox units 15A, 15C have been described. It is to be understood that fig. 2 merely discloses an example of a design of such gearbox units, and that the present invention can be utilised for various different designs of such gearbox units. For example, the split gearbox 15C can be omitted. As is explained below, the invention can be utilized for any gearbox 2 comprising a plurality of gearbox units that can be disconnected both from the power source 4 and the drive wheels 8 of the vehicle 1. However, the invention is perhaps particularly well suited for use in a system where a range gearbox 15B, e.g. comprising a planetary gear 14, is used and can be disconnected from the drive wheels 8 of the vehicle 1.

Fig. 3 schematically illustrates a powertrain 3 according to an embodiment of the invention in a low range gear position. The gearbox 2 comprises a planetary gear 14 which has a low and a high gear, so that the switching capability of the main gearbox 15A can be divided into a low range gear position and a high range gear position. In a first gear position corresponding to the low range gear position a lower gear ratio than 1:1 is provided in the planetary gear 14. In the high range gear position the gear ratio is 1:1 in the planetary gear 14. Fig. 3 shows the gearbox 2 in the first gear position, corresponding to the low range gear position. The range gearbox 15B is used to double the number of gear ratios that are available from the main gearbox 15A, and also, as in this case, the number of gears available from the combination of gearbox units 15A, 15C. The gearbox unit 15B is, as shown in the figures, arranged downstream of the main gearbox 15A as seen from the combustion engine 4.

The gearbox 2 is accommodated in the gearbox housing 12 and comprises an input shaft 16 which may be a main shaft 26 of the main gearbox 15A. The planetary gear 14 comprises three main components which are rotatably arranged in relation to each other, namely a sun gear wheel 18, a planet wheel carrier 20 and a ring gear wheel 22. A number of planet gear wheels 24 are rotatably arranged with bearings on the planet wheel carrier 20. With knowledge of the number of teeth 32 of sun gear wheel 18 and the ring gearwheel 22, the relative gear ratio of the three components can be determined. The sun gear wheel 18 is rotatably connected to the input shaft 16 and the planet gear wheels 24 engage the sun gear wheel 18. The ring gear wheel 22 surrounds and engages the planet gear wheels 24. The teeth 32 of the sun gear wheel 18, the planet gear wheels 24 and the ring gear wheel 22 can be bevelled, so that they have an angle relative to a common axis of rotation 30 of the sun gear wheel 18, the planet gear carrier 20 and the ring gear wheel 22. The input shaft 16 may be connected to the sun gearwheel 18 by means of a splines connection 34.

A first axially displaceable coupling sleeve 42 is in a first gear position arranged to connect the gearbox housing 12 with the ring gear wheel 22 and in a second gear position arranged to disconnect the gearbox housing 12 from the ring gear wheel 22. The first axially movable coupling sleeve 42 is in the first gear position arranged to disconnect the input shaft 16 from the planet wheel carrier 20.

An engaging element in the form of a second axially displaceable coupling sleeve 43 is in a first position arranged to disconnect the planet wheel carrier 20 from an output shaft 28 of the gearbox 2, which output shaft 28 is coupled to the propeller shaft 10 of the vehicle 1. In a second position the second axially displaceable coupling sleeve 43 is arranged to connect said gearbox 2 to said at least one drive wheel 8 of said vehicle 1.

In that position, disclosed in fig. 3, the second axially displaceable coupling sleeve 43 transfers torque from the planet wheel carrier 20 to the propeller shaft 10 and also to the driving wheels of the vehicle 1. The second axially displaceable coupling sleeve 43 thus forms an engaging element between the gearbox 2 and the driving wheels 8.

The second axially displaceable coupling sleeve 43 may in a third gear position couple the ring gear wheel 22 with the output shaft 28 of the gearbox 2 and thus achive a reverse gear. In the third gear position, corresponding to the reverse gear, the first axially displaceable coupling sleeve 42 is arranged to disconnect the input shaft 16 from the planet wheel carrier 20 and instead is arranged to interconnect the planet wheel carrier 20 with the gearbox housing 12.

The first coupling sleeve 42 is provided with first splines 50 on an inner periphery of the sleeve 42 and second splines 51 on an outer periphery of the sleeve 42. The first splines 50 arranged on the inner periphery of the sleeve 42 interact with corresponding first cooperating splines 50’ arranged on the input shaft 16. Corresponding first cooperating splines 50’ disposed on the input shaft 16 are made on the periphery of a first sprocket 46 which is mounted on the input shaft 16. The first splines 50 on the inner periphery of the sleeve 42 are also arranged to cooperate with corresponding first cooperating splines 50” arranged on the planet wheel carrier 20. Corresponding first cooperating splines 50” disposed on the planet wheel carrier 20 are made on the periphery of a second sprocket 44 which is mounted on the planet wheel carrier 20. The second splines 51 arranged on an outer periphery of the sleeve 42 interact with corresponding second cooperating splines 51’ arranged on the projection 52 which is fixedly connected to the gearbox housing 12.

The second axially displaceable coupling sleeve 43 is on an inner surface provided with third splines 59 which are arranged to cooperate with corresponding second cooperating splines 59’, 59”, 59’” arranged on the ring gear wheel 22, the planet wheel carrier 20 and the output shaft 28, respective. The corresponding second cooperating splines 59” arranged on the planet wheel carrier 20 are formed on the periphery of a third sprocket 49 which is mounted on the planet wheel carrier 20. The corresponding second cooperating splines 59’” provided on the output shaft 28 are formed on the periphery of a fourth sprocket 53 which is mounted on the output shaft 28.

An axial stop 54 arranged on the planet wheel carrier 20 is adapted to abut against the ring gear wheel 22, which axial stop 54 prevents the ring gear wheel 22 to be moved axially. The axial stop 54 may comprise a disc-shaped plate, which by means of a first thrust bearing 56 is mounted on the planet wheel carrier 20. The axial stop 54 is rotatable relative to the planet wheel carrier 20 and the input shaft 16, and follows the rotation of the ring gear wheel 22. The axial stop 54 fixes the ring gear wheel 22 axially, and leads to that an axial bearing of the input shaft 16 is subjected to less stress when the gears 18, 22, 24 are provided with helical teeth. However, instead of, or in combination with the axial stop 54 a pair of thrust bearings 56 may be arranged on both axial surfaces connected to the ring gear wheel 22. Thus, the thrust bearings 56 are arranged between the ring gear wheel and the planet wheel carrier 20. A second thrust bearing 57 may be disposed between the shaft 38 of the sun gear wheel 18 and the planet wheel carrier 20 to accommodate axial forces generated by the sun gear wheel 18.

The low gear in the gearbox 2 is obtained by displacing the second coupling sleeve 42, so that the ring gearwheel 22 is connected to the transmission housing 12. The axial displacement of the first and second coupling sleeves 42, 43 are provided with a first and second shift fork 60, 61 arranged in an outside circumferential groove 62 in the respective coupling sleeve 42, 43. The first shift fork 60 is influenced by a first actuator 66 and the second shift fork 61 is influenced by a second actuator 67. Each of the first and second actuators 66, 67 may be a pneumatic or hydraulic cylinder. The shift forks 60, 61 and actuators 66, 67 are schematically shown in Fig. 3.

Fig. 4 schematically illustrates a powertrain 3 according to an embodiment of the invention in a low range gear position and with the second coupling sleeve 43 in the first position. In this position the output shaft 28 is disconnected from the planetary gear 14, and thus no torque may be transferred from the gearbox 2 to the output shaft 28, the propeller shaft 10 and the driving wheels 8. The second coupling sleeve 43 is in this position only connected to the output shaft 28 and not to the ring gear wheel 22 or the planet wheel carrier 20. When the output shaft 28 is disconnected from the planetary gear 14 and the clutch 11 is disengaged, so that no torque is transferred from the internal combustion engine 4 to the gearbox 2, gears may be shifted in the gearbox 2.

Fig. 5 schematically illustrates a powertrain 3 according to an embodiment of the invention in a high range gear position. When the output shaft 28 was disconnected from the planetary gear 14 and the clutch 11 was disengaged, the first coupling sleeve 42 was axially displaced to the second gear position in order to disconnect the gearbox housing 12 from the ring gear wheel 22, and instead connect the sun gear wheel 18 with the planet wheel carrier 20. Thereafter the second coupling sleeve 43 was axially displaced to its first position so that the second coupling sleeve 43 transfers torque from the planet wheel carrier 20 to the output shaft 28. The transmission of torque from the input shaft 16 to the output shaft 28 is in the high range gear position via the input shaft 16 and planet wheel carrier 20 and further to the output shaft 28 via the second coupling sleeve 43, so that the gear ratio through the planetary gear 14 becomes 1:1. The second axially movable coupling sleeve 43 may in another gear position be arranged to engage the ring gear wheel 22 with the output shaft 28. Thus, another gear ratio over the planetary gear is achieved in this position.

However, since the planet wheel carrier 20 is in a standstill position during gearshifting and the output shaft 28 is rotating due to the rotation of the driving wheels 8, the speed between the planet wheel carrier 20 and the output shaft 28 must be synchronized before the second coupling sleeve 43 is axially displaced in order to connect the planet wheel carrier 20 with the output shaft 28. Therefore, a synchronizing element 74 is arranged between the planet wheel carrier 20 and the output shaft 28. According to an embodiment of the invention the synchronizing element 74 is a friction arrangement, which comprises first and second friction surfaces 76, 78, which may be engaged and disengaged by means of an actuation arrangement 80. The actuation arrangement 80 comprises an electric, a pneumatic or a hydraulic controlled cylinder 82, wherein a piston 84 in the cylinder 82 is axially displaceable in order to engage and disengage the first and second friction surfaces 76, 78. The first friction surface 76 may be arranged on the planet wheel carrier 20 and the second friction surface 78 may be arranged axially displaceable by the piston 84. According to the embodiment in fig. 5 and also in figures 3 and 4 the first and second friction surfaces 76, 78 may be conical in order to increase the friction force between the friction surfaces 76, 78. According to another embodiment the cylinder 82 and piston 84 may be circular and arranged substantially concentric to the common axis of rotation 30. The second friction surface 78 is arranged on a circular sleeve 86. The actuation arrangement 80 may be mounted at the gearbox housing 12. For that reason the actuation arrangement 80 is not rotatable, which simplifies the connection of wires and fluid pipes to the actuation arrangement 80. A radial bearing 90 is arranged between the circular sleeve 86 and the piston 84, so that the axial displacement of the circular sleeve 86 and the second friction surface 78 can be made without rotating the actuator 82 and the piston 84. The first and second friction surfaces 76, 78 may be conical in order to increase the friction force between the friction surfaces 76, 78 and therefore also transfer enough torque for accelerating the planet wheel carrier 20 when synchronizing the speed between the output shaft 28 and the planet wheel carrier 20.

Fig. 6 schematically illustrates a powertrain 3 according to an alternative embodiment of the invention. According to this alternative embodiment the the synchronizing element 74 is an electrical machine arranged to rotate said planet wheel carrier 20 when synchronizing the rotational speed between said planetary gear 14 and said at least one drive wheel 8. Synchronizing is achieved by activating the electrical machine to a speed that rotates the said planetary gear 14 with a speed that substantially correspond to the speed of said output shaft 28 of said second gearbox device 15B.

An electronic control unit 70 is coupled to the gearbox 2, the combustion engine 4 and the clutch 11 to achieve the gear shifting above. Speed sensors in the gearbox 2, in the main gear box 6 and in the internal combustion engine 4 may be connected to the control unit 70. A computer 72 may also be connected to the control unit 70. The control unit 70 may be a computer with appropriate software for this purpose. The control unit 70 and/or the computer 72 comprise a computer program P, which can include routines to control the gearbox 2 of the invention. The program P may be stored in an executable form or compressed form in a memory M and/or in a read/write memory. A computer program product may be provided, which comprises a program code stored on a, by a computer readable medium for performing the gear shifting above, when said program is run on the control unit 70 or the computer 72 connected to the control unit 70. Said code may be non-volatile, stored in said computer readable medium.

Figure 7 shows a flowchart for a method for changing gear ratio in a gearbox 2 of a vehicle 1 according to a first embodiment. The gearbox 2 may be configured as described in Figure 2. The method comprises the steps of; - disconnecting s101 said first and second gearbox devices 15A, 15B of said gearbox 2 from said at least one drive wheel 8; - changing s102 gear ratio of said second gearbox device 15A, 15B, 15C when said first and second gearbox devices 15A, 15B of said gearbox 2 are disconnected from said at least one drive wheel 8; and - synchronizing s103 the rotational speed between a rotating member 20, 22 of said second gearbox device 15B and said at least one drive wheel 8 when said gear ratio of said second gearbox device 15B has been changed.

Before disconnecting said first and second gearbox devices 15A, 15B of said gearbox 2 from said at least one drive wheel 8 the torque of the power source is decreased and the clutch 11 is disengaged.

If there is a gear arrangement, such as a differential, between the rotating member 20, 22 of said second gearbox device 15B and said at least one drive wheel 8 care must be taken to any gear ratio in such a gear arrangement when synchronizing the speed between the rotating member 20, 22 and said at least one drive wheel 8.

The step of changing s102 gear ratio of said second gearbox device 15B when said first and second gearbox devices 15A, 15B of said gearbox 2 are disconnected from said at least one drive wheel 8 may further comprises the steps of:: - disconnecting s104 said second gearbox device 15B from said first gearbox device 15A by shifting said first gearbox device 15A to a neutral gear position; - applying s105 a braking force to the rotating member 20, 22 of said second gearbox device 15B by means of a first braking element 212; - changing s106 gear ratio of said second gearbox device 15B when said rotating member 20, 22 of said second gearbox device 15B is in a standstill condition.

The step of disconnecting s101 said first and second gearbox devices 15A, 15B of said gearbox 2 from said at least one drive wheel 8 further comprises a step of: - disconnecting s111 said planetary gear from said at least one drive wheel 8.

The step disconnecting s111 said planetary gear from said at least one drive wheel 8, further comprises a step of: - disconnecting s112 said planet wheel carrier 20 from said output shaft 28 of said second gearbox device 15B.

A second axially displaceable coupling sleeve 43 is in a first position arranged to connect said planetary gear 14 to said at least one drive wheel 8 of said vehicle 1, and in a second position is arranged to disconnect said planetary gear 14 from said at least one drive wheel 8 of said vehicle 1, and wherein the step of synchronizing s103 the rotational speed between a rotating member 20, 22 of said second gearbox device 15B and said at least one drive wheel 8 when said gear ratio of said second gearbox device 15B has been changed may further comprise steps of: - synchronizing s113 the rotational speed between said planetary gear 14 and said at least one drive wheel 8 by means of a synchronizing element 74, and thereafter - connecting s114 said planetary gear 14 to said at least one drive wheel 8.

The method further comprises a step of: - connecting s115 said gearbox 2 to said at least one drive wheel 8 by connecting said gearbox 2 to a propeller shaft 10 of said vehicle 1.

After the second gearbox device 15B has been disconnected from the first gearbox device 15A by shifting the first gearbox device 15A into a neutral state the method further comprises steps of: - accelerating s107 a rotating member 202 of said first gearbox device 15A, by means of said power source 4 after connecting said gearbox 2 to said at least one drive wheel 8; - changing s108 gear ratio of said first gearbox device 15A when the rotational speed of said rotating member 201, 202 has been accelerated at least to a first speed.

In steps s107 and s108 a downshift takes place in the first gearbox device 15A.

Figure 8 shows a flowchart for a method for changing gear ratio in a gearbox 2 of a vehicle 1 according to a second embodiment. The gearbox 2 may be configured as described in Figure 2. The method steps s101 - s106 and s111 — s115 in the first embodiment are also performed in the second embodiment. However, in the second embodiment the method further comprises the steps of: - applying s109 a braking force to a rotating member 202 of said first gearbox device 15A by means of a second braking element 211, after connecting said gearbox 2 to said at least one drive wheel 8; - changing s110 gear ratio of said first gearbox device 15A when the rotational speed of said rotating member 202 has been reduced at least to a second speed.

In steps s109 and s110 an upshift takes place in the first gearbox device 15A.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use. The components and features specified above may within the framework of the invention be combined between the different embodiments specified.

Claims

1. A method for changing gear ratio in a gearbox (2) of a vehicle (1), said gearbox (2) being arranged to transfer torque between a power source (4) and at least one drive wheel (8) of said vehicle (1), said gearbox (2) comprising a first gearbox device (15A, 15C) and at least one second gearbox device (15B), each of said first and second gearbox devices (15A, 15B) being individually controllable to engage at least two gears having different gear ratios to form a combined gear ratio of said gearbox (2), said second gearbox device (15B) being arranged between said first gearbox device (15A) and said at least one drive wheel (8), the method comprising steps of: - disconnecting (s101) said first and second gearbox devices (15A, 15B) of said gearbox (2) from said at least one drive wheel (8); - changing (s102) gear ratio of said second gearbox device (15B) when said first and second gearbox devices (15A, 15B) of said gearbox (2) are disconnected from said at least one drive wheel (8); and - synchronizing (s103) the rotational speed between a rotating member (20, 22) of said second gearbox device (15B) and said at least one drive wheel (8) when said gear ratio of said second gearbox device (15B) has been changed - connecting (s115) said gearbox (2) to said at least one drive wheel (8) by connecting said gearbox (2) to a propeller shaft (10) of said vehicle (1).

2. The method according to claim 1, wherein the step of changing (s102) gear ratio of said second gearbox device (15B) when said first and second gearbox devices (15A, 15B) of said gearbox (2) are disconnected from said at least one drive wheel (8) further comprising the steps of: - disconnecting (s104) said second gearbox device (15B) from said first gearbox device (15A) by shifting said first gearbox device (15A) to a neutral gear position; - applying (s105) a braking force to the rotating member (20, 22) of said second gearbox device (15B) by means of a first braking element (212); - changing (s106) gear ratio of said second gearbox device (15B) when said rotating member (20, 22) of said second gearbox device (15B) is in a standstill condition.

3. The method according to claim 2, further comprising steps of: - accelerating (s107) a rotating member (202) of said first gearbox device (15A) by means of said power source (4) after connecting said gearbox (2) to said at least one drive wheel (8); - changing (s108) gear ratio of said first gearbox device (15A) when the rotational speed of said rotating member (202) has been accelerated at least to a first speed.

4. The method according to claim 2, further comprising steps of: - applying (s109) a braking force to a rotating member (202) of said first gearbox device (15A) by means of a second braking element (211), after connecting said gearbox (2) to said at least one drive wheel (8); - changing (s110) gear ratio of said first gearbox device (15A) when the rotational speed of said rotating member (202) has been reduced at least to a second speed.

5. The method according to any of the preceding claims, wherein said second gearbox device (15B) is a range gearbox comprising a planetary gear (14), arranged to provide a high range gear and a low range gear, wherein the step of disconnecting (s101) said first and second gearbox devices (15A, 15B) of said gearbox (2) from said at least one drive wheel (8), further comprises a step of: - disconnecting (s111) said planetary gear (14) from said at least one drive wheel (8).

6. The method according to claim 5, wherein said planetary gear (14) comprises a sun gear wheel (18) being connected to an output shaft (28) of said first gearbox device (15A), and a planet wheel carrier (20) carrying a plurality of planet gear wheels (24) engaging said sun gear wheel (18), said planet wheel carrier (20) being selectively connectable to an output shaft (28) of said second gearbox device (15B), wherein the step of disconnecting (s111) said planetary gear (14) from said at least one drive wheel (8), further comprises a step of: - disconnecting (s112) said planet wheel carrier (20) from said output shaft (28) of said second gearbox device (15B).

7. The method according to claim 6, wherein a second axially displaceable coupling sleeve (43) in a first position is arranged to connect said planetary gear (14) to said at least one drive wheel (8) of said vehicle (1), and in a second position is arranged to disconnect said planetary gear (14) from said at least one drive wheel (8) of said vehicle (1), and wherein the step of synchronizing (s103) the rotational speed between a rotating member (20, 22) of said second gearbox device (15B) and said at least one drive wheel (8) when said gear ratio of said second gearbox device (15B) has been changed further comprising steps of: - synchronizing (s113) the rotational speed between said planetary gear (14) and said at least one drive wheel (8) by means of a synchronizing element, and thereafter - connecting (s114) said planetary gear (14) to said at least one drive wheel (8).

8. A computer program comprising program code that, when said program code is executed in a computer (70, 72), causes said computer (70, 72) to carry out the method according to any of claims 1-7.

9. A computer program product comprising a computer readable medium and a computer program according to claim 8, wherein said computer program is contained in said computer readable medium.

10. A system for changing gear ratio in a gearbox (2) of a vehicle (1), said gearbox (2) being arranged to transfer torque between a power source (4) and at least one drive wheel (8) of said vehicle (1), said gearbox (2) comprising a first gearbox device (15A) and at least one second gearbox device (15B), each of said first and second gearbox devices (15A, 15B) being individually controllable to engage at least two gears having different gear ratios to form a combined gear ratio of said gearbox (2), said second gearbox device (15B) being arranged between said first gearbox device (15A) and said at least one drive wheel (8), the system being characterised in: - means for disconnecting said first and second gearbox devices (15A, 15B) of said gearbox (2) from said at least one drive wheel (8); - means for changing gear ratio of said second gearbox device (15B) when said first and second gearbox devices (15A, 15B) of said gearbox (2) are disconnected from said at least one drive wheel (8); and - means for synchronizing the rotational speed between a rotating member (20, 22) of said second gearbox device (15B) and said at least one drive wheel (8) when said gear ratio of said second gearbox device (15B) has been changed.

11. The system according to claim 10, wherein said second gearbox device (15B) is a range gearbox comprising a planetary gear (14), arranged to provide a high range gear and a low range gear and wherein a second axially displaceable coupling sleeve (43) in a first position is arranged to connect said planetary gear (14) to said at least one drive wheel (8) of said vehicle (1), and in a second position is arranged to disconnect said planetary gear (14) from at least one drive wheel (8) of said vehicle (1), the system further being characterised in: - a synchronizing element (74) for synchronizing the rotational speed between said planetary gear (14) and said at least one drive wheel (8) before connecting said planetary gear (14) to said at least one drive wheel (8).

12. The system according to claim 11, wherein the synchronizing element (74) is a friction arrangement arranged between said planet wheel carrier (20) and said output shaft (28) of said second gearbox device (15B), the system further being characterised in: - means for synchronizing the rotational speed between said planetary gear (14) and said output shaft (28) of said second gearbox device (15B) by engaging the friction clutch.

13. The system according to claim 11, wherein the synchronizing element (74) is an electrical machine arranged to rotate said planet wheel carrier (20), the system further being characterised in: - means for synchronizing the rotational speed between said planetary gear (14) and said at least one drive wheel (8) by activating the electrical machine to a speed that rotates the said planetary gear (14) with a speed that substantially correspond to the speed of said output shaft (28) of said second gearbox device (15B).

14. A vehicle, characterised in that it comprises a system for changing gear ratio in a gearbox (2) according to claim 10.