SE542091C2

SE542091C2 - A gearbox and a method for controlling a gearbox to achieve a freewheeling mode

Info

Publication number: SE542091C2
Application number: SE1751368A
Authority: SE
Inventors: Erik Kilsand; Rikard Dyrsch; Tomas Selling
Original assignee: Scania Cv Ab
Priority date: 2017-11-03
Filing date: 2017-11-03
Publication date: 2020-02-25
Also published as: SE1751368A1; DE112018005218T5; DE112018005218B4; WO2019088901A1

Abstract

The invention relates to a method for controlling a gearbox (4) of a vehicle powertrain (3), the gearbox (4) comprising: an input shaft (200) selectively connected to the propulsion unit (2); an output shaft (300) connected to the at least one driving wheel (8); a first gearbox unit (4A) connectable to the input shaft (200); and a second gearbox unit (4B) arranged downstream of the first gearbox unit (4A) connectable to the first gearbox unit (4A) and the output shaft (300); wherein the gearbox (4) comprises a coupling device (40) arranged downstream of the second gearbox unit (4B) for selectively disconnecting the second gearbox unit (4B) from the output shaft (300), the method comprising: controlling (s101) the coupling device (40) to disconnect the second gearbox unit (4B) from the output shaft (300) so as to achieve a freewheeling mode.

Description

A gearbox and a method for controlling a gearbox to achieve a freewheeling mode.

TECHNICAL FIELD The present invention relates to a method for controlling a gearbox, a control arrangement, a powertrain comprising such a control arrangement, a vehicle, a computer program and a computer-readable medium. The present invention more specifically relates to a method for controlling a gearbox of a vehicle powertrain to achieve a freewheeling mode.

BACKGROUND Vehicles today are often controlled to a so called freewheeling mode when travelling downhill in order to reduce the fuel consumption. Such freewheeling mode means that the internal combustion engine is allowed to run at idle speed or be completely shut off during downhill coasting instead of acting as a brake. This requires that the internal combustion engine is disconnected from the drive wheels of the vehicle. Traditionally, this is achieved by controlling the main gearbox to neutral. This is for example shown in document US20110015037 A1. Alternatively, a split gear arranged upstream of the main gearbox is disengaged. This is disclosed in US20040261557 A1. By controlling the main gearbox or the split gear to neutral, the main shaft of the gearbox, the output shaft and any components connected to these shafts will rotate, which will result in drag losses in the gearbox.

When the freewheeling mode is aborted, for example when the operator of the vehicle requests torque via the accelerator, it is important that the internal combustion engine and the drive wheels are quickly connected again. The connection is suitably achieved by engaging a gear but this can be achieved in different ways and it may be more or less complicated. For example, in gearboxes having unsynchronized main gears engaging a gear is more complicated and to achieve a fast and comfortable engagement of a gear the rotational speed of the main shaft and a lay shaft of the main gearbox must be precisely matched.

SUMMARY OF THE INVENTION Despite known solutions in the field, it would be desirable to develop a method for controlling a gearbox, which overcomes or at least alleviates the drawbacks mentioned above.

An object of the present invention is therefore to achieve a new and advantageous method for controlling a gearbox of a vehicle powertrain, which reduces fuel consumption and drag losses in the gearbox during a freewheeling mode. Another object of the invention is to achieve a new and advantageous method for controlling a gearbox of a vehicle powertrain, which results in a faster and more comfortable connection of the propulsion unit and the drive wheels of the vehicle to end a freewheeling mode.

Another object of the invention is to achieve a new and advantageous control arrangement, a powertrain, a vehicle, a computer program and a computerreadable medium which reduces fuel consumption and drag losses in the gearbox during a freewheeling mode.

The herein mentioned objects are achieved by a method for controlling a gearbox of a vehicle powertrain, a control arrangement, a vehicle, a computer program and a computer-readable medium according to the independent claims.

Hence, according to an aspect of the present invention a method for controlling a gearbox of a vehicle powertrain is provided, the gearbox being arranged to selectively transfer torque between a propulsion unit and at least one driving wheel. The gearbox comprising: an input shaft selectively connected to the propulsion unit; an output shaft connected to the at least one driving wheel; a first gearbox unit connectable to the input shaft; and a second gearbox unit arranged downstream of the first gearbox unit connectable to the first gearbox unit and the output shaft, wherein the gearbox comprises a coupling device arranged downstream of the second gearbox unit for selectively disconnecting the second gearbox unit from the output shaft. The method comprising: - controlling the coupling device to disconnect the second gearbox unit from the output shaft so as to achieve a freewheeling mode.

When no accelerating torque and no retarding torque is requested from the propulsion unit it is typically desired to enter a freewheeling mode and thus allow the propulsion engine to run at idle speed or to be completely shut off. Such situations typically occur when the vehicle is driving downhill or is about to drive downhill. This way, the fuel consumption is reduced. The method may thus comprise to determine that no accelerating torque and no retarding torque is requested from the propulsion unit, and then control the coupling device to disconnect the second gearbox unit from the output shaft. Determining that no accelerating torque and no retarding torque is requested may comprise identifying a request for freewheeling mode from a vehicle system, such as a cruise control system. That no accelerating torque and no retarding torque is requested from the propulsion unit may additionally and/or alternatively be identified based on data from various vehicle sensors. For example, this can be identified by determining the position of the brake pedal and the position of the accelerator pedal. The operator of the vehicle may determine to stop requesting torque and thereby initiate the method according to the invention. The operator of the vehicle may for example identify, while driving uphill, that the current vehicle speed is enough to get over the top and may thereby stop requesting accelerating torque. In such a situation the coupling device is suitably controlled to achieve a freewheeling mode.

As mentioned in the background a freewheeling mode requires that the propulsion unit is disconnected from the drive wheels of the vehicle. Disconnecting the propulsion unit from the drive wheels may be performed in various ways and the most common way is to control a main gearbox to neutral. This means that no gear in the main gearbox is engaged, whereby no torque can be transmitted from the main gearbox to the output shaft of the gearbox or vice versa. However, such solution typically involves drag losses in the gearbox since the output shaft and the main shaft will be rotated by the drive wheels when the vehicle is rolling downhill. By disconnecting the second gearbox unit from the output shaft by means of a coupling device according to the invention, the propulsion unit will be disconnected from the drive wheels and only the output shaft will be rotated by the drive wheels, thereby reducing the drag losses in the gearbox. The gearbox according to the invention is thus controlled to neutral at the output shaft instead of the main gearbox and thereby reduces fuel consumption and drag losses.

The first gearbox unit may constitute a main gearbox that can be set to a number of different forward gear rations, and the second gearbox unit may constitute a range gearbox. The second gearbox is suitably the last gearbox unit in the gearbox, meaning that no further gearbox unit is arranged downstream of the second gearbox unit. It is to be understood that downstream relates to the position in relation to the propulsion unit and thus in relation to the transfer of torque from the propulsion unit through the powertrain. The gearbox may also comprise a split gearbox arranged upstream of the first gearbox unit and connected to the first gearbox unit. The split gearbox may be connected to the input shaft and the first gearbox unit may thus be connected to the input shaft via the split gearbox.

The first gearbox unit suitably comprises a lay shaft and a main shaft, both connectable to the input shaft and/or the split gearbox. The lay shaft may be arranged in parallel with the main shaft. The main shaft may be connectable to the second gearbox unit. The first gearbox unit may comprise gear wheels that are rotatably fixed to the lay shaft. The main shaft may comprise corresponding gear wheels which rotate freely in relation to the main shaft, but which can be selectively locked for rotation with the main shaft in order to engage a gear.

Engaging a gear in the first gearbox unit comprises manoeuvring a sleeve, arranged to rotate with the main shaft, to a position where the gearwheel on the main shaft is engaged with the sleeve. Each pair of gearwheels on the lay shaft and the main shaft represents a gear ratio. When engaging a gear in the first gearbox unit the main shaft and the gear wheel on the main shaft should have synchronized rotational speeds to enable manoeuvring of the sleeve. The gear wheel on the main shaft is rotated by the corresponding gear wheel on the lay shaft and thus has a fixed relative speed to the lay shaft. The main shaft and the lay shaft should thus have essentially synchronized rotational speeds when engaging a gear.

The split gearbox suitably comprises a gear wheel rotating freely in relation to the input shaft but which can be selectively locked for rotation with the input shaft through a split sleeve. The lay shaft comprises a corresponding gear wheel rotatably fixed to the lay shaft. By locking the gear wheel on the input shaft by means of the split sleeve torque can be transferred from the input shaft to the lay shaft. The split sleeve may be provided with a split synchronising device. The split sleeve can further be used to connect the input shaft and thus the split gearbox to a gear wheel on the main shaft directly. The gear wheel on the main shaft may rotate freely in relation to the main shaft but can be selectively locked for rotation with the main shaft. The gear wheel on the main shaft is engaged with a corresponding gear wheel on the lay shaft. Thus, by controlling the split sleeve, such that the input shaft is directly connected to a gear wheel on the main shaft, torque can be transferred from the input shaft to the lay shaft or from the input shaft to the main shaft directly. The split gearbox may thus be engaged by being connected to the first gearbox unit, such that torque may be transferred directly from the input shaft to the main shaft or such that torque may be transferred from the input shaft to the lay shaft and from the lay shaft to the main shaft. The split gearbox may thus be arranged to provide, for each gear of the first gearbox unit, two gear steps with different gear ratios. The split gearbox may thus be controlled to engage a low-split gear or a high-split gear. The lowsplit gear has the highest gear ratio and the high-split gear has the lowest gear ratio. Controlling the split gearbox to engage the low-split gear may involve controlling the split sleeve to connect the input shaft with the gear wheel on the main shaft and engaging the high-split gear may involve controlling the split sleeve to lock the gearwheel on the input shaft. Alternatively, depending on the number of teeth on the respective gear wheels, engaging the low-split gear may involve controlling the split sleeve to lock the gear wheel on the input shaft and engaging the high-split gear may involve controlling the split sleeve to connect the input shaft with the gear wheel on the main shaft.

According to an embodiment of the invention controlling the coupling device suitably comprises to control a shift fork to axially displace a coupling sleeve. The coupling device may thus comprise an axially displaced coupling sleeve. The coupling sleeve may be arranged to, in a first position, connect the second gearbox unit and the output shaft. In a second position the coupling sleeve may be arranged to disconnect the second gearbox unit, and thus the whole gearbox, from said output shaft and thus the at least one drive wheel of the vehicle. The coupling sleeve is suitably attached to the output shaft. The axial displacement of the coupling sleeve may be provided with a shift fork of the coupling device. The shift fork may be arranged in engagement with an outside circumferential groove in the coupling sleeve. The shift fork may be influenced by an actuator. The actuator may be a pneumatic or hydraulic cylinder.

The method may also comprise to control the propulsion unit. The propulsion unit may be controlled to idle speed or be completely shut off when the coupling device has been controlled to disconnect the second gearbox unit from the output shaft. By turning off the propulsion unit all rotating parts except the output shaft can be brought to standstill, which will further reduce the fuel consumption and the drag losses in the gearbox.

According to an embodiment of the invention the second gearbox unit comprises a planetary gear arranged to provide a high range gear and a low range gear, and wherein disconnecting the second gearbox unit from the output shaft comprises to disconnect the planetary gear from the output shaft. In a first gear position corresponding to the low range gear a lower gear ratio than 1:1 is provided in the planetary gear. In a second gear position corresponding to the high range gear the gear ratio is 1 : 1 in the planetary gear. The second gearbox unit is thus used to double the number of gear ratios that are available from the first gearbox unit, and also, as an example, the number of gears available from the combination of the split gearbox and the first gearbox unit. The planetary gear is suitably connected to the main shaft of the first gearbox unit. The planetary gear may comprise 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. A number of planet gear wheels are rotatably arranged with bearings on the planet wheel carrier. The sun gear wheel is rotatably connected to the main shaft of the first gearbox unit and the planet gear wheels engage the sun gear wheel. The ring gear wheel surrounds and engages the planet gear wheels. The main shaft may be connected to the sun gearwheel by means of a splines connection.

The second gearbox unit may alternatively comprise a clutch arrangement adapted to transmit torque between the output shaft and the main shaft, instead of the planetary gear. The clutch arrangement may also be adapted to synchronize the rotational speed of the main shaft and the rotational speed of the output shaft, such that the coupling device can connect the second gearbox unit and the output shaft. The arrangement may comprise a disc clutch, cone clutch or similar.

The coupling device is suitably arranged to selectively connect/disconnect the planet wheel carrier and the output shaft of the gearbox. Thus, the step of disconnecting the second gearbox unit from the output shaft may comprise to control the coupling device, such that the planet wheel carrier is disconnected from the output shaft. The coupling sleeve may thus be arranged to, in the first position, connect the planet wheel carrier to the output shaft of the gearbox. The coupling sleeve may also in a third position couple the ring gear wheel with the output shaft and thus enable a reverse gear.

According to an embodiment of the invention the method further comprises to synchronize the rotational speed of the main shaft and the rotational speed of the output shaft; and controlling the coupling device to connect the second gearbox unit to the output shaft, to end the freewheeling mode. The coupling device is suitably unsynchronized. The coupling device is thus not controlled by means of a synchronization device and the components that are to be connected by means of the coupling sleeve should thus be controlled in some other way to achieve similar rotational speeds. The method may thus comprise to synchronize the rotational speed of the second gearbox unit and the rotational speed of the output shaft. By controlling the gearbox to synchronous speed between the two components to be connected by the coupling device, the axial displacement of the coupling sleeve, in order to connect the components, is facilitated. When the components should be disconnected the gearbox may be controlled, such that torque balance occurs between the components, whereby the coupling sleeve does not transfer torque. It then becomes possible to move the coupling sleeve axially in order to disconnect the components from each other.

According to an embodiment of the invention synchronizing the rotational speed of the main shaft and the rotational speed of the output shaft comprises controlling a clutch device arranged on the output shaft, such that the clutch device engages with the planetary gear of the second gearbox unit. When the clutch device is controlled to engage with the planetary gear the clutch device will start slipping and the torque from the rotating drive wheels will be transmitted via the clutch device to the planetary gear. The clutch device will thereby synchronize the rotational speed of the planetary gear and the output shaft. Suitably, the clutch device is arranged to engage with the planet wheel carrier of the second gearbox unit. The torque from the rotating drive wheels will thereby be transmitted via the clutch device to the planet wheel carrier, which will start rotating with the same rotational speed as the output shaft.

The method may be performed by a control arrangement in the vehicle powertrain. Such control arrangement may comprise one or a more control units and may also be adapted to control the gearbox and the propulsion unit. The method is suitably automatically performed when it has been identified that no accelerating torque and no retarding torque is requested from the propulsion unit, in order to achieve a freewheeling mode.

Each of the gears in the first gearbox unit is used for a plurality of the total number of gears provided by the gearbox as a whole. For example, a first gear of the first gearbox unit may be used for first and second gear of the gearbox, 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.

According to an aspect of the invention a control arrangement is provided for controlling a gearbox of a vehicle powertrain. The gearbox is arranged to selectively transfer torque between the propulsion unit and at least one driving wheel. The gearbox comprising: an input shaft selectively connected to the propulsion unit; an output shaft connected to the at least one driving wheel; a first gearbox unit connectable to the input shaft; and a second gearbox unit arranged downstream of the first gearbox unit connectable to the first gearbox unit and the output shaft, wherein the gearbox comprises a coupling device arranged downstream of the second gearbox unit for selectively disconnecting the second gearbox unit from the output shaft. The control arrangement comprising: - means for controlling the coupling device to disconnect the second gearbox unit from the output shaft so as to achieve a freewheeling mode.

The control arrangement may also comprise means for identifying that no accelerating torque and no retarding torque is requested from the propulsion unit. The means for identifying that no accelerating torque and no retarding torque is requested from the propulsion unit and the means for controlling the coupling device to disconnect the second gearbox unit from the output shaft may e.g. be different software modules/portions in the control arrangement, program code or similar.

According to an aspect of the invention a vehicle powertrain is provided, the powertrain comprising: a propulsion unit and a gearbox, wherein the gearbox is arranged to selectively transfer torque between the propulsion unit and at least one driving wheel. The gearbox comprising: an input shaft selectively connected to the propulsion unit; an output shaft connected to the at least one driving wheel; a first gearbox unit connectable to the input shaft; and a second gearbox unit arranged downstream of the first gearbox unit connectable to the first gearbox unit and the output shaft, wherein the gearbox comprises a coupling device arranged downstream of the second gearbox unit for selectively disconnecting the second gearbox unit from the output shaft. The powertrain further comprises a control arrangement comprising: means for controlling the coupling device to disconnect the second gearbox unit from the output shaft so as to achieve a freewheeling mode.

It will be appreciated that all the embodiments described for the method aspect of the invention are also applicable to the control arrangement aspect and the powertrain aspect of the invention. That is, the control arrangement may be configured to perform any one of the steps of the method according to various embodiments described herein.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas embodiments of the invention are described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of embodiments of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2 schematically illustrates a vehicle powertrain according to an embodiment of the invention; Figure 3 schematically illustrates a vehicle powertrain according to an embodiment of the invention; Figures 4a-b illustrate a flow chart for a method for controlling a gearbox according to an embodiment of the invention; and Figure 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a vehicle 1 according to an embodiment of the invention. The vehicle 1 includes a powertrain 3 comprising a propulsion unit 2, such as an internal combustion engine, a gearbox 4 and clutch (not shown) arranged between the propulsion unit 2 and the gearbox 4. The gearbox 4 is connected to the driving wheels 8 of the vehicle 1 via an output shaft of the gearbox 4. The gearbox 4 of the present invention may comprise a first gearbox unit 4A and a second gearbox unit 4B arranged downstream of the first gearbox unit 4A. Herein the term upstream refers to a position closer to the propulsion unit 2, and the term downstream refers to a position closer to the driving wheels 8.

Fig. 2 schematically illustrates a powertrain 3 according to an embodiment of the invention. The powertrain 3 comprises a propulsion unit 2, a gearbox 4 and a clutch 11 arranged between the propulsion unit 2 and the gearbox 4. The gearbox 4 comprises an input shaft 200 connected to the clutch 11 and an output shaft 300 connected to the driving wheels 8. The gearbox 4 further comprises a first gearbox unit 4A connectable to the input shaft 200; and a second gearbox unit 4B arranged downstream of the first gearbox unit 4A and connectable to the first gearbox unit 4A and the output shaft 300. The powertrain 3 may also comprise a split gearbox 4S arranged upstream of the first gearbox unit 4A and connected to the input shaft 200. The first gearbox unit 4A may thus be connected to the input shaft 200 via the split gearbox 4S. The first gearbox unit 4A may constitute a conventional main gearbox that can be set to a number of different forward gear ratios. The second gearbox unit 4B may constitute a range gearbox. The gearbox 4 further comprises a coupling device (not shown) arranged downstream of the second gearbox unit 4B for selectively disconnecting the second gearbox unit 4B from the output shaft 300. The second gearbox unit 4B and the coupling device are discussed further with reference to Figure 3.

The first gearbox unit 4A comprises a lay shaft 202 with gear wheels 203A, 204A, 205A that are rotatably fixed to the lay shaft 202. For example, gear wheel 203A may represent the first gear, gear wheel 204A the second gear and gear wheel 205A the third gear. The first gearbox unit 4A also comprises a main shaft 206 with 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. When the gear wheels 203B, 204B, 205B rotate freely in relation to the main shaft 206, the first gearbox unit 4A is in neutral. The gear wheels 203B, 204B, 205B on the main shaft 206 are suitably locked by means of sleeves 207, 208, 210. For example, the first gear in the first gearbox unit 4A can be engaged by manoeuvring a first 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. The gearwheel 203B will thereby rotate with the main shaft 206 and the lay shaft 202 will thereby be connected to the main shaft 206 via gear wheel 203A. Each pair of gear wheels on the lay shaft 202 and main shaft 206 represents a gear ratio. The second gear in the first gearbox unit 4A may be engaged by disengaging the first sleeve 207 from gear wheel 203B and instead moving a second sleeve 208 to a position to the right in the figure where, instead, gearwheel 204B is engaged. The gearwheel 204B is thereby brought into rotation with the main shaft 206. Correspondingly, the third gear in the first gearbox unit 4A may be engaged by manoeuvring the second sleeve 208 to a position to the left in the figure where, instead, gear wheel 205B is engaged. Each of the first through third gears in the first gearbox unit 4A is used for a plurality of the total number of gears provided by the gearbox 4 as a whole. The first gearbox unit 4A may further comprise a reverse gear (not shown) and a crawler gear (not shown).

The lay shaft 202 further comprises an additional gear wheel 209A that, similar to the above, is rotatably fixed to the lay shaft 202. The split gearbox unit 4S comprises a corresponding gear wheel 209B rotating freely in relation to the input shaft 200, but which can be selectively locked for rotation with the input shaft 200 through a split sleeve 210. When the split sleeve 210 locks the gear wheel 209B on the input shaft 200, torque can be transferred to the lay shaft 202 via the corresponding gear wheel 209A on the lay shaft 202. The split sleeve 210 may be provided with a split synchronising unit. The split sleeve 210 can further be used to connect the input shaft 200 to the gearwheel 205B of the first gearbox unit 4A directly. This way, depending on whether the gear wheel 205B on the main shaft 206 is rotating freely in relation to the main shaft 206 or if it is locked on the main shaft 206, torque can be transferred to the lay shaft 202 via the corresponding gear wheel 205A on the lay shaft 202 or torque can be transferred from the input shaft 200 directly to the main shaft 206. The gear wheel pair 209A-B and the split sleeve 210 can thereby be used to provide two different split gear ratios for each gear of the first gearbox unit 4A. The split gearbox 4S may thus be controlled to engage a high-split gear or a low-split gear. For example, engaging the low-split gear may comprise to connect the input shaft 200 with the gear wheel 205B on the main shaft 206 by means of the split sleeve 210. When e.g. the first gear is engaged in the first gearbox unit 4A, the split sleeve 210 may be arranged to engage gear wheel 205B. This way, the input shaft 200 is directly connected to gear wheel 205B, which via gear wheel 205A establishes a first gear ratio between the input shaft 200 and the lay shaft 202. The gear wheel 205B, however, is not locked to the main shaft 206, but the lay shaft 202 may be connected to the main shaft 206 through gear wheel pair 203A-B. To engage the second gear, gear wheel pair 209A-B is instead 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 first gearbox unit 4A.

The lay shaft 202 may be provided with a shaft brake mechanism 212, such as a lay shaft brake, in order to control the rotational speed of the lay shaft 202. It is to be understood that the gearbox 4 may comprise further shaft brakes not shown in the figure.

Figure 3 schematically illustrates a powertrain 3 according to an embodiment of the invention. The powertrain 3 may be configured as described in Figure 1 and in Figure 2. The powertrain 3 thus comprises a propulsion unit 2, a clutch 11 and a gearbox 4. The gearbox 4 comprises an input shaft 200 connected to the clutch 11 and an output shaft 300 connected to the driving wheels 8. The gearbox 4 further comprises a split gearbox 4S connected to the input shaft 200; a first gearbox unit 4A arranged downstream of the split gearbox 4S and connectable to the split gearbox 4S; and a second gearbox unit 4B arranged downstream of the first gearbox unit 4A and connectable to the first gearbox unit 4A and the output shaft 300. The second gearbox unit 4B comprises a planetary gear 14 which has a low and a high gear. The second gearbox unit 4B may thus be controlled between a high range gear position and a low range gear position. In 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. Figure 3 shows the second gearbox unit 4B in the low range gear position.

The second gearbox unit 4B may be accommodated in a gearbox housing 12 and comprises an input shaft, which may be the main shaft 206 of the first gearbox unit 4A. The planetary gear 14 comprises three main components which are rotatably arranged in relation to each other, namely a sun gearwheel 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 gear wheel 22, the relative gear ratio of the three components can be determined. The sun gearwheel 18 is rotatably connected to the main shaft 206 of the first gearbox unit 4A 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 may 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 main shaft 206 of the first gearbox unit 4A may be connected to a shaft 38 of the sun gear wheel 18 by means of a splines connection 34.

The second gearbox unit 4B may comprise a first axially displaceable coupling sleeve 42. The first coupling sleeve 42 may be arranged to, in a first position, connect the gearbox housing 12 with the ring gear wheel 22. This first position corresponds to the low range gear position. The first coupling sleeve 42 may be arranged to, in a second position, disconnect the gearbox housing 12 from the ring gear wheel 22 and to connect the main shaft 206 and the planet wheel carrier 20, such that the main shaft 206 and the planet wheel carrier 20 rotate with similar rotational speeds.

The gearbox 4 also comprises a coupling device 40 arranged downstream of the second gearbox unit 4B for selectively disconnecting the second gearbox unit 4B from the output shaft 300. The coupling device 40 may comprise a second axially displaceable coupling sleeve 43, which in a first position connects the planet wheel carrier 20 with the output shaft 300, and in a second position disconnects the planet wheel carrier 20 from the output shaft 300. Thus, in the first position the second axially displaceable coupling sleeve 43 may be arranged to connect said gearbox 4 to the driving wheels 8 of said vehicle 1. In the second position, the second coupling sleeve 43 is only connected to the output shaft 300 and not to the ring gear wheel 22 or the planet wheel carrier 20. In Figure 3, the coupling device 40 is in the second position where the planet wheel carrier 20, and thus the second gearbox unit 4B, is disconnected from the output shaft 300. Thus, in this figure, no torque may be transferred from the gearbox 4 to the output shaft 300 and the driving wheels 8 or vice versa.

The second axially displaceable coupling sleeve 43 may also, in a third position, connect the ring gear wheel 22 with the output shaft 300 and thus enable a reverse gear. In order to achieve a reverse gear the first coupling sleeve 42 is arranged to connect the planet wheel carrier 20 with the gearbox housing 12.

The first coupling sleeve 42 may be 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 may interact with corresponding first cooperating splines 50’ arranged on the shaft 38 of the sun gear wheel 18. The corresponding first cooperating splines 50’ disposed on the shaft 38 of the sun gear wheel 18 may be provided on the periphery of a first sprocket 46, which is mounted on the shaft 38 of the sun gear wheel 18. The first splines 50 on the inner periphery of the sleeve 42 may also be arranged to cooperate with corresponding first cooperating splines 50” arranged on the planet wheel carrier 20. The corresponding first cooperating splines 50” disposed on the planet wheel carrier 20 may be provided on the periphery of a second sprocket 44, which is mounted on the planet wheel carrier 20. The second splines 51 arranged on the an outer periphery of the sleeve 42 may interact with corresponding second cooperating splines 51’ arranged on a projection 52, which is fixedly connected to the gearbox housing 12.

The second axially displaceable coupling sleeve 43 of the coupling device 40 may comprise third splines 59 on an inner surface, which splines 59 are arranged to cooperate with corresponding third cooperating splines 59’, 59”, 59”’ arranged on the ring gear wheel 22, the planet wheel carrier 20 and the output shaft 300, respectively. The corresponding third cooperating splines 59” arranged on the planet wheel carrier 20 may be formed on the periphery of a third sprocket 49, which is mounted on the planet wheel carrier 20. The corresponding third cooperating splines 59’” provided on the output shaft 300 may be formed on the periphery of a fourth sprocket 53, which is mounted on the output shaft 300.

The axial displacement of the first and second coupling sleeves 42, 43 may be 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 may be actuated by a first actuator 66 and the second shift fork 61 may be actuated by a second actuator 67. The first and second actuator 66, 67 may be a pneumatic or hydraulic cylinder.

The powertrain 3 may also comprise a clutch device 80 arranged on the output shaft 300. The clutch device 80 may be referred to as a planetary clutch in the case where the second gearbox unit 4B comprises a planetary gear 14. The clutch device 80 is suitably arranged, such that it can be controlled to engage with the planetary gear 14 of the second gearbox unit 4B. Suitably, the clutch device 80 is movable between a first position in which the clutch device 80 engages with the planetary gear 14 and a second position in which the clutch device 80 does not engage the planetary gear 14. The clutch device 80 is suitably adapted to synchronize the rotational speed of the output shaft 300 and the rotational speed of the planet wheel carrier 20, such that the coupling device 40 can be controlled to connect the second gearbox unit 4B with the output shaft 300.

The powertrain 3 may further comprise an electronic control arrangement 70 connected to the gearbox 4, the propulsion unit 2 and the clutch 11. The control arrangement 70 may comprise a control unit 71 and a computer 72 may be connected to the control unit 71. The control unit 71 may be a transmission control unit, engine control unit or any other control unit of a vehicle. The control arrangement 70 may comprise a plurality of different control units. The control arrangement 70 may comprise means for controlling the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 so as to achieve a freewheeling mode. The control arrangement 70 may comprise means for synchronizing the rotational speed of the main shaft 206 and the rotational speed of the output shaft 300; and means for controlling the coupling device 40 to connect the second gearbox unit 4B to the output shaft 300 to end the freewheeling mode.

Figure 4a illustrates a flow chart for a method for controlling a gearbox 4 of a vehicle powertrain 3 according to an embodiment of the invention. The vehicle powertrain 3 and the gearbox 4 may be configured as disclosed in Figure 2 and 3. The method comprises: controlling s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 so as to achieve a freewheeling mode.

The method may be performed by means of the control arrangement 70 of the powertrain 3. The method may be referred to as a method for controlling a gearbox 4 for achieving a freewheeling mode. The method is suitably initiated when no accelerating torque and no retarding torque is requested from the propulsion unit 2. The method may thus comprise to determine that no accelerating torque and no retarding torque is requested from the propulsion unit 2, and then control s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300. Determining that no accelerating torque and no retarding torque is requested may comprise identifying a request for freewheeling mode from a vehicle system, such as a cruise control system.

Controlling s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 may comprise to disconnect the planetary gear 14 of the second gearbox unit 4B from the output shaft 300. Controlling s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 may comprise to control the coupling device 40, such that the planet wheel carrier 20 is disconnected from the output shaft 300.

Controlling s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 may comprise to control a shift fork 61 to axially displace a coupling sleeve 43. The shift fork 61 may be controlled to displace the coupling sleeve 43, such that the planet wheel carrier 20 is disconnected from the output shaft 300.

Figure 4b illustrates a flow chart for a method for controlling a gearbox 4 of a vehicle powertrain 3 according to an embodiment of the invention. The vehicle powertrain 3 and the gearbox 4 may be configured as disclosed in Figure 2 and 3. The method comprises: controlling s101 the coupling device 40 to disconnect the second gearbox unit 4B from the output shaft 300 so as to achieve a freewheeling mode as described in Figure 4a. The method further comprises: synchronizing s102 the rotational speed of the main shaft 206 and the rotational speed of the output shaft 300; and controlling s103 the coupling device 40 to connect the second gearbox unit 4B to the output shaft 300, to end the freewheeling mode. Since the main shaft 206 is connected to the second gearbox unit 4B the second gearbox unit 4B will rotate with the same rotational speed as the main shaft 206. In order to be able to connect the second gearbox unit 4B with the output shaft 300 by means of the coupling device 40 the rotational speeds must be essentially synchronized. The synchronization s102 and controlling s103 of the coupling device 40 to end the freewheeling mode is suitably performed when accelerating torque or retarding torque has been requested from the propulsion unit 2 once again.

Synchronizing s102 the rotational speed of the main shaft 206 and the rotational speed of the output shaft 300 may comprise controlling a clutch device 80 arranged on the output shaft 300, such that the clutch device 80 engages with the planetary gear 14 of the second gearbox unit 4B. When the clutch device 80 is controlled to engage with the planetary gear 14 the clutch device 80 will start slipping and the torque from the rotating drive wheels 8 will be transmitted to the planetary gear 14. The clutch device 80 will thereby synchronize the rotational speed of the planetary gear 14 and the output shaft 300. Suitably, the clutch device 80 is controlled to engage with the planet wheel carrier 20 of the second gearbox unit 4B.

Controlling s103 the coupling device 40 to connect the second gearbox unit 4B to the output shaft 300 may comprise to the control the coupling sleeve 43 to connect the planet wheel carrier 20 to the output shaft 300. The coupling sleeve 43 of the coupling device 40 may be controlled, such that the third splines 59 of the coupling sleeve 43 engages with the corresponding third cooperating splines 59”, 59”’ on the planet wheel carrier 20 and the output shaft 300.

Figure 5 is a diagram of a version of a device 500. The control unit 71 and/or computer 72 described with reference to Figure 2 and 3 may in a version comprise the device 500. The term “link” refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500.

The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer programme P which comprises routines for controlling a gearbox of a vehicle powertrain. The computer programme P comprises routines for controlling the coupling device to disconnect the second gearbox unit from the output shaft so as to achieve a freewheeling mode. The computer programme P comprises routines for synchronizing the rotational speed of the main shaft/planetary gear and the rotational speed of the output shaft. The computer programme P comprises routines for controlling the coupling sleeve to connect the second gearbox unit to the output shaft to end the freewheeling mode.

The programme P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the programme stored in the memory 560 or a certain part of the programme stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed.

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.

Claims

1. A method for controlling a gearbox (4) of a vehicle powertrain (3) for achieving a freewheeling mode, the gearbox (4) being arranged to selectively transfer torque between a propulsion unit (2) and at least one driving wheel (8), the gearbox (4) comprising: an input shaft (200) selectively connected to the propulsion unit (2); an output shaft (300) connected to the at least one driving wheel (8); a first gearbox unit (4A) connectable to the input shaft (200); and a second gearbox unit (4B) arranged downstream of the first gearbox unit (4A) connectable to the first gearbox unit (4A) and the output shaft (300); wherein the first gearbox unit (4A) constitutes a main gearbox, which can be set to a number of different forward gear ratios, and the second gearbox unit (4B) constitutes a range gearbox, and wherein the gearbox (4) comprises a coupling device (40) arranged downstream of the second gearbox unit (4B) for selectively disconnecting the second gearbox unit (4B) from the output shaft (300), the method comprising: - controlling (s101) the coupling device (40) to disconnect the second gearbox unit (4B) from the output shaft (300) so as to achieve a freewheeling mode.

2. The method according to claim 1, wherein controlling (s101) the coupling device comprises to control a shift fork (61 ) to axially displace a coupling sleeve (43).

3. The method according to any one of the preceding claims, wherein the second gearbox unit (4B) comprises a planetary gear (14) arranged to provide a high range gear and a low range gear, and wherein disconnecting the second gearbox unit (4B) from the output shaft (300) comprises to disconnect the planetary gear (14) from the output shaft (300).

4. The method according any one of the preceding claims, wherein the first gearbox unit (4A) comprises a main shaft (206) connectable to the second gearbox unit (4B), and wherein the method further comprises: - synchronizing (s102) the rotational speed of the main shaft (206) and the rotational speed of the output shaft (300); and - controlling (s103) the coupling device (40) to connect the second gearbox unit (4B) to the output shaft (300), to end the freewheeling mode.

5. The method according to claim 3 and 4, wherein synchronizing (s102) the rotational speed of the main shaft (206) and the rotational speed of the output shaft (300) comprises controlling a clutch device (80) arranged on the output shaft (300), such that the clutch device (80) engages with the planetary gear (14).

6. A computer program (P), wherein said computer program comprises programme code for causing a control unit (71 ; 500) or a computer (72; 500) connected to the control unit (71 ; 500) to perform the method according to any one of the preceding claims.

7. A computer-readable medium comprising instructions, which when executed by a control unit (71 ; 500) or a computer (72; 500) connected to the control unit (71 ; 500), cause the control unit (71 ; 500) or the computer (72; 500) to perform the method according to any one of claims 1-5.

8. A control arrangement (70) for controlling a gearbox (4) of a vehicle powertrain (3) for achieving a freewheeling mode, the gearbox (4) being arranged to selectively transfer torque between the propulsion unit (2) and at least one driving wheel (8), the gearbox (4) comprising: an input shaft (200) selectively connected to the propulsion unit (2); an output shaft (300) connected to the at least one driving wheel (8); a first gearbox unit (4A) connectabie to the input shaft (200); and a second gearbox unit (4B) arranged downstream of the first gearbox unit (4A) connectable to the first gearbox unit (4A) and the output shaft (300); wherein the first gearbox unit (4A) constitutes a main gearbox, which can be set to a number of different forward gear ratios, and the second gearbox unit (4B) constitutes a range gearbox; and wherein the gearbox (4) comprises a coupling device (40) arranged downstream of the second gearbox unit (4B) for selectively disconnecting the second gearbox unit (4B) from the output shaft (300), the control arrangement (70) comprising: - means for controlling the coupling device (40) to disconnect the second gearbox unit (4B) from the output shaft (300) so as to achieve a freewheeling mode.

9. A vehicle powertrain (3), comprising: a propulsion unit (2); and a gearbox (4); wherein the gearbox (4) is arranged to selectively transfer torque between the propulsion unit (2) and at least one driving wheel (8), the gearbox (4) comprising: an input shaft (200) selectively connected to the propulsion unit (2); an output shaft (300) connected to the at least one driving wheel (8); a first gearbox unit (4A) connectable to the input shaft (200); and a second gearbox unit (4B) arranged downstream of the first gearbox unit (4A) connectable to the first gearbox unit (4A) and the output shaft (300); wherein the gearbox (4) comprises a coupling device (4) arranged downstream of the second gearbox unit (4B) for selectively disconnecting the second gearbox unit (4B) from the output shaft (300), wherein the powertrain (3) further comprises a control arrangement (70) according to claim 8.

10. A vehicle (1) comprising a powertrain (3) according to claim 9.