SE2051501A1

SE2051501A1 - Control device and method for engaging a start gear in a gearbox

Info

Publication number: SE2051501A1
Application number: SE2051501A
Authority: SE
Inventors: Jonas Lindström; Richard Rosander
Original assignee: Scania Cv Ab
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2022-06-19
Also published as: DE102021130319A1; DE102021130319B4; SE544598C2

Abstract

A control device (100) and a method for engaging a start gear in a gearbox (4) of a vehicle powertrain (2) are provided. The gearbox (4) comprises a first transmission shaft (20, 40) comprising a first set (SI) of gear wheels (12B, 13B, 14B), and a main shaft (30) comprising a second set (S2) of gear wheels (12A, 13A, 14A). Each gear wheel of the second set (S2) cooperates with a corresponding gear wheel of the first set (S1) of gear wheels. The method comprises a step (S101) of locking the main shaft (30) in a non-rotating state by means of a brake device (25) connected to a housing (26) of the gearbox (4); a step (S102) of, when the main shaft (30) is in the non-rotating state and the first transmission shaft (20, 40) is rotating, locking a predetermined gear wheel of the second set (S2) of gear wheels to the main shaft (30); and a step (S103) of releasing the main shaft (30) from the non-rotating state.

Description

CONTROL DEVICE AND METHOD FOR ENGAGING A START GEAR IN A GEARBOX TECHNICAL FIELD The present disclosure relates in general to a method for engaging a start gear in a gearbox of avehicle powertrain. The present disclosure further relates in general to a control device configured toengage a start gear in a gearbox of a vehicle powertrain. The present disclosure also relates ingeneral to a computer program and to a computer-readable medium. The present disclosure also relates in general to a vehicle.

BACKGROUND A gearbox of a vehicle powertrain may have many different configurations formed of a plurality oftransmission shafts and gear wheel pairs connecting said transmission shafts. Each gear wheel paircomprises one gear wheel which is rotatably fixed to one transmission shaft, and another gear wheelwhich is arranged on a second transmission shaft such that it may rotate freely in relation theretobut may also be locked to said second transmission shaft for rotation therewith. For the purpose oflocking a gear wheel to a transmission shaft, an axially displacea ble coupling sleeve, which may berotatably fixed to the transmission shaft, may be used. Such a coupling sleeve generally comprisescogs, which are configured to mesh with corresponding spaces between cogs of the gear wheel to beengaged on the transmission shaft. ln order to engage the coupling sleeve with the gear wheel, thecoupling sleeve and the gear wheel therefore generally need to have essentially the same rotationalspeed. lt may therefore be necessary to synchronize the rotational speed of the transmission shaftwith the rotational speed of the gear wheel to be locked thereto. This may be achieved by thecoupling sleeve comprising a synchronizing device. However, there are also unsynchronizedgearboxes wherein the rotational speeds of the transmission shafts are synchronized by means of the propulsion unit and/or a transmission brake.

The cogs of the coupling sleeves and the corresponding cogs of the gear wheels may often have arounded configuration allowing them to be pressed against each other such that they end up in anengaged state where the respective cogs intermesh. ln other words, the cogs have a geometrical configuration assisting in the engagement of the coupling sleeve with the gear wheel.

However, in some cases it may be desirous to have a more flat configuration of the cogs of thecoupling s|eeve (and the corresponding gear wheel), for example for increasing the cog surface ableof transmitting torque and/or for more cost effective production. Such a configuration of the cogshowever requires a somewhat different strategy when seeking to engage a gear by means of thecoupling s|eeve since it is not sufficient to simply press the coupling s|eeve against the gear wheel. lfsimply pressing the coupling s|eeve against the gear wheel, there is a risk of ending up in a so-calleddog-on-dog condition, especially in case of unsynchronized gears. Therefore, the strategy is insteadto allow the mating cogs to slide against each other until the cogs of the coupling s|eeve reach therespective corresponding space between the cogs of the gear wheel such that the cogs of thecoupling s|eeve and the gearwheel can intermesh. ln order to achieve this, a difference in rotationalspeed of the coupling s|eeve and the gear wheel is required. Said difference in rotational speed willresult in a change in angular momentum when engaging the gear, which may in turn result in animpulse which will be propagated through the powertrain. This is especially pronounced when thevehicle is standing still since the impulse will be the only driving force acting upon the vehicle. Theimpulse force will also be amplified with the gear ratio seen from the shaft where the coupling s|eeveis arranged to the driving wheels of the vehicle. The above described impulse may cause considera ble discomfort to a driver or any other person present in the vehicle.

SUMMARY The object of the present invention is to provide a more comfortable engagement of a start gear in a gearbox of a vehicle powertrain.

The object is achieved by the subject-matter of the appended independent claim(s). ln accordance with the present disclosure, a method for engaging a start gear in a gearbox of avehicle powertrain is provided. The method is performed by a control device. The gearbox comprisesa first transmission shaft comprising a first set of gear wheels rotata bly fixed to the first transmissionshaft. The gearbox further comprises a main shaft comprising a second set of gear wheels. Each gearwheel of the second set of gear wheels cooperates with a corresponding gear wheel of the first set ofgear wheels, and is selectively lockable to the main shaft for rotation therewith. The second set ofgear wheels comprises unsynchronized gear wheels. The method comprises the steps of: locking the main shaft in a non-rotating state by means of a brake device connected to a housing of the gearbox, when the main shaft is in the non-rotating state and the first transmission shaft is rotating,locking a predetermined gear wheel of the second set of gear wheels to the main shaft for rotationwith the main shaft, and releasing the main shaft from the non-rotating state. ln view of the main shaft being locked in the non-rotating state by means of the brake device, whenthe predetermined gear wheel is locked to the main shaft, the impulse generated is not propagatedthrough the powertrain to the drive wheels but absorbed by the gearbox housing. Furthermore, theimpulse will not be amplified by the gear ratio of from example additional gearbox units arrangeddownstream of the gear wheel to be engaged. Therefore, by means of the present method, theengagement of a start gear will be much more comfortable to a driver or any other person on-board the vehicle.

Moreover, the present method may be used when a coupling sleeve comprising cogs having anessentially flat configuration is used for locking a gear wheel to the main shaft. By locking thepredetermined gear wheel to the main shaft when the main shaft is in a non-rotating state but thefirst transmission shaft is rotating, the desired difference in rotational speed between the gear wheelto be locked to the main shaft and the main shaft is ensured. lt should however be noted that thepresent method may also be used in case of using a coupling sleeve comprising cogs of other configurations than essentially flat for locking a gear wheel to the main shaft.

The first transmission shaft may be a layshaft, and the gearbox may further comprise an input shaft connectable to the layshaft.

The method may further comprise a step of, in response to a request for engagement of a start gear,initiating rotation of the first transmission shaft if the first transmission shaft is not already rotating.Thereby, the ability to obtain a desired difference in rotational speed between first transmission shaft and the main shaft, at the point in time desired, may be achieved.

The method may further comprise a step of controlling the rotational speed of the first transmissionshaft to be within a predetermined rotational speed interval before locking the predetermined gearwheel of the second set of gear wheels to the main shaft. Thereby, the ability for a comfortableengagement of the start gear may be further improved. lt may furthermore enable a fast and smooth engagement of the start gear.

Moreover, the step of releasing the main shaft from the non-rotating state may be performed inresponse to a determination that the predetermined gear wheel has been locked to the main shaftfor rotation therewith. Thereby, it may be ensured that the main shaft remains locked in the non-rotating state until the start gear has been engaged, thereby further minimizing the risk for an impulse propagating through the powertrain to the drive wheels.

The brake device may be arranged downstream of the predetermined gear wheel of the second setof gear wheels. Thereby, the ability of absorbing the impulse may be improved, and the risk for the impulse to propagate through the powertrain to the drive wheels may be further reduced.

The gearbox may further comprise a range gearbox unit connected to the main shaft. The presentmethod is particularly advantageous for use in such vehicle powertrains, comprising a range gearboxunit, because the amplification of a generated impulse may be even greater in such cases due to the high gear ratio provided by the powertrain from the main shaft to drive wheels of the vehicle.

The present disclosure further relates to a computer program comprising instructions which, when executed by a control device, cause the control device to carry out the method as described above.

The present disclosure further relates to a computer-readable medium comprising instructionswhich, when executed by a control device, cause the control device to carry out the method as described above.

Furthermore, the present disclosure provides a control device configured to engage a start gear in agearbox of a vehicle powertrain. The gearbox comprises a first transmission shaft comprising a firstset of gear wheels rotata bly fixed to the first transmission shaft. The gearbox further comprises amain shaft comprising a second set of gear wheels. Each gear wheel of the second set of gear wheelscooperates with a corresponding gear wheel of the first set of gear wheels and is selectively locka bleto the main shaft for rotation therewith. The second set of gear wheels comprises unsynchronizedgear wheels. The control device is configured to: lock the main shaft in a non-rotating state by means of a brake device connected to a housing ofthe gearbox; when the main shaft is in the non-rotating state and the first transmission shaft is rotating,locking a predetermined gear wheel of the second set of gear wheels to the main shaft for rotationwith the main shaft, and release the main shaft from the non-rotating state.

The control device provides the same advantages as described above for the corresponding method for engaging a start gear in a gearbox of a vehicle powertrain.

The control device may further be configured to, in response to a request for engagement of a startgear, initiate rotation of the first transmission shaft if the first transmission shaft is not already rotating.

The control device may further be configured to control the rotational speed of the first transmissionshaft to be within a predetermined rotational speed interval before locking the predetermined gear wheel of the second set of gear wheels to the main shaft.Moreover, the control device may be configured to release the main shaft from the non-rotatingstate in response to a determination that the predetermined gear wheel has been locked to the main shaft for rotation therewith.

The brake device, utilized by the control device for locking the main shaft in the non-rotating state, may be arranged downstream of the predetermined gear wheel of the second set of gear wheels.

The present disclosure further relates to a vehicle comprising the control device as described above.

The vehicle may be a heavy vehicle, such as a truck or a bus.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 schematically illustrates a side view of an example of a vehicle; Fig. 2 schematically illustrates a first exemplifying embodiment of a vehicle powertraincomprising a gearbox; Fig. 3 schematically illustrates a second exemplifying embodiment of a vehicle powertrain comprising a gearbox; Fig. 4 represents a flowchart schematically illustrating a method for engaging a start gear ina gearbox of a vehicle powertrain according to one exemplifying em bodiment of thepresent disclosure; Fig. 5 schematically illustrates a device that may constitute, comprise or be a part of a control device configured to engage a start gear in a gearbox of a vehicle powertrain.

DETAILED DESCRIPTION The invention will be described in more detail below with reference to exemplifying embodimentsand the accompanying drawings. The invention is however not limited to the exemplifyingembodiments discussed and/or shown in the drawings, but may be varied within the scope of theappended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.

When used in the present disclosure, the term "downstream" is considered to mean in relation tothe direction of which driving torque may be transferred from a propulsion unit to drive wheels of the vehicle powertrain.

The present disclosure provides a method for engaging a start gear in a gearbox of a vehiclepowertrain. ln addition to the gearbox, a vehicle powertrain typically comprises at least onepropulsion unit configured to provide the propulsion torque. The gearbox comprises a firsttransmission shaft comprising a first set of gear wheels rotata bly fixed to the first transmission shaft.The gearbox further comprises a main shaft comprising a second set of gear wheels. Each gear wheelof the second set of gear wheels cooperates with a corresponding gear wheel of the first set of gearwheels. Furthermore, each gear wheel of the second set of gear wheels is selectively locka ble to themain shaft for rotation therewith. More specifically, each gear wheel is selectively lockable to themain shaft by means of a corresponding coupling device. Such a coupling sleeve may comprise cogs,when the gear wheel is locked to the main shaft, configured to intermesh with corresponding cogs ofthe gear wheel. Such cogs may for example comprise essentially flat cogs (such as essentiallyrectangular cogs), but the present disclosure is not limited thereto. Moreover, the second set of gearwheels comprises unsynchronized gear wheels. This means that no synchronization device (such as asynchromesh), which may be used to synchronize the rotational speed of the gear wheel with the rotational speed of the coupling sleeve during gear shifting, is present at the gear wheel of the second set of gear wheels. The first set of gear wheels and the second set of gear wheels may bepresent in a main gearbox unit of the gearbox. The gearbox may comprise further gearbox units, such as a split gearbox unit and/or a range gearbox unit, if desired.

The present method comprises a step of locking the main shaft in a non-rotating state by means of abrake device connected to a housing of the gearbox. The step of locking the main shaft in a non-rotating state may be performed in response to a request for engagement of a start gear. Themethod further comprises a step of, when the main shaft is in the non-rotating state and the firsttransmission shaft is rotating, locking a predetermined gear wheel of the second set of gear wheelsto the main shaft for rotation with the main shaft. Said predetermined gear wheel corresponds tothe start gear to be engaged. The method then comprises a step of re|easing the main shaft from thenon-rotating state. By re|easing the main shaft from the non-rotating state, the vehicle may be put in motion (with the start gear engaged) from a standsti|| condition.

The first transmission shaft may be a |ayshaft and the gearbox may further comprise an input shaftconnectable to the |ayshaft. Such an input shaft may be connectable to a propu|sion unit, such as acombustion engine and/or an electric machine. A c|utch may be arranged between the propu|sion unit and the input shaft of the gearbox.

Alternatively, the first transmission shaft may be an input shaft of the gearbox. ln such a case, the input shaft may typically be connected to a propu|sion unit in the form of an electric machine.

The method may further comprise a step of, in response to a request for engagement of a start gear,initiating rotation of the first transmission shaft if the first transmission shaft is not already rotating.By initiating rotation of the first transmission shaft in response to a request for engagement of a startgear, a difference in rotational speed between the first transmission shaft and the main shaft may beachieved before the predetermined gear wheel should be locked to the main shaft. Rotation of thefirst transmission shaft may be initiated by any previously known method. For example, a propu|sionunit of the vehicle powertrain may be used for this purpose. By way of example only, in case thevehicle powertrain comprises a combustion engine connecta ble to an input shaft of the gearbox bymeans of a c|utch, a rotation of a first transmission shaft constituting a |ayshaft may be effected bythe combustion engine whereafter the gearbox is disconnected from the combustion engine by opening the c|utch such that the gearbox may be shifted.

The method may further comprise a step of controlling the rotational speed of the first transmissionshaft to be within a predetermined rotational speed interval before locking the predetermined gearwheel of the second set of gear wheels to the main shaft. Thereby, it may be ensured that thedifference in rotational speed between the main shaft (which is stationary by being locked in a non-rotating state by means of the brake device) and the first transmission shaft is suitable for achievinga fast and comfortable engagement of the start gear. The rotational speed of the first transmissionshaft may be controlled by any previously known method therefore. By way of example, therotational speed of the first transmission shaft may be controlled by means of a transmission brake connected to the first transmission shaft.

The step of releasing the main shaft from the non-rotating state may be performed in response to adetermination that the predetermined gear wheel has been locked to the main shaft for rotationtherewith. Thereby, it may be ensured that the main shaft remains in the non-rotating state and thatan impulse generated during engagement of the gear wheel to the main shaft will not propagatethrough the powertrain to the drive wheels. Alternatively, the step of releasing the main shaft fromthe non-rotating state may be performed after a preselected time has elapsed from the point in timeat which the main shaft was locked in the non-rotating state. Such a preselected time may correspond to the time expected to be needed for engagement of the start gear.

The brake device used for locking the main shaft in the non-rotating state is connected to a housingof the gearbox, and is thereby grounded. An impulse generated when locking the predeterminedgear wheel to the main shaft will thus, via the brake device, be transferred to the housing of thegearbox. The housing of the gearbox may thus absorb the impulse. Thereby, the risk of the impulsepropagating through the powertrain, and being amplified by the gear ratio provided by thepowertrain from the location of the predetermined gear wheel to the drive wheels of the vehiclepowertrain, is reduced. The impulse will thus be essentially absorbed by non-rotating parts of thevehicle and the engagement of the start gear will be considerably more comfortable to a personpresent in the vehicle, such as a driver. The brake device may be configured to directly brake themain shaft or indirectly brake the main shaft, as long as it may be used for locking the main shaft in anon-rotating state. The brake device may be arranged downstream of the predetermined gear wheelof the second set of gear wheels. Thereby, the ability of absorbing the impulse may be improved, andthe risk for the impulse to propagate through the powertrain to the drive wheels may be further reduced.

The method of the present disclosure is especially suitable for use in vehicle powertrains providingthe possibility for high gear ratios. This may be typical for heavy vehicles, such as trucks or buses. Byway of example, such vehicle powertrains may comprise a range gearbox unit (which may be aplanetary gear) connected to the main shaft. ln such cases, there is an even greater risk of theimpulse causing discomfort for being amplified by the gear ratio provided by the range gearbox unit and any additional devices, such as a differential, arranged downstream thereof.

The performance of the method for engaging a start gear in a gearbox of a vehicle powertrain asdescribed herein may be governed by programmed instructions. These programmed instructionstypically take the form of a computer program which, when executed in or by a control device, causethe control device to effect desired forms of control action. Such instructions may typically be stored on a computer-readable medium.

Furthermore, the present disclosure provides a control device configured to perform the hereindescribed method for engaging a start gear in a gearbox of a vehicle powertrain. The control devicemay be configured to perform any one of the steps of the method described herein. Morespecifically, the control device is configured to engage a start gear in a gearbox (as described above)of a vehicle powertrain. The control device is configured to lock the main shaft in a non-rotating stateby means of a brake device connected to a housing of the gearbox. The control device is furtherconfigured to, when the main shaft is in the non-rotating state and the first transmission shaft isrotating, locking a predetermined gear wheel of the second set of gear wheels to the main shaft forrotation with the main shaft. The control device is further configured to release the main shaft from the non-rotating state.

The control device may comprise one or more control units. The responsibility for a specific functionor control may be divided between two or more of the control units. One or more of the controlunits may be implemented in the form of a computer. The control device may be a control device ofa vehicle powertrain. The control device may be present in a vehicle. Alternatively, parts of thecontrol device may be arranged remote from the vehicle, such as at a remote control center, if desired.

The present disclosure further relates to a vehicle comprising the above described control device.The vehicle may comprise a vehicle powertrain comprising at least one propulsion unit and agearbox. The gearbox may comprise a first transmission shaft and a main shaft. The first transmission shaft may comprise a first set of gear wheels rotata bly fixed to the first transmission shaft. The main shaft may comprise a second set of gear wheels. Each of the gear wheels of thesecond set of gear wheels may be configured to cooperate with a corresponding gear wheel of thefirst set of gear wheels and may be selectively locka ble to the main shaft for rotation therewith, forexample by means of a corresponding coupling device (such as an axially displaceable coupling sleeve).

Figure 1 schematically i||ustrates a side view of an example of a vehicle 1. The vehicle 1 comprises apowertrain 2 comprising a propulsion unit, such as an internal combustion engine 3, and a gearbox 4.The gearbox 4 may be connected to the driving wheels 5 of the vehicle 1 via an output shaft 6 of thegearbox 4. The vehicle may be a heavy vehicle, such as a truck or a bus. The vehicle may be a hybridvehicle and thus further comprise a second propulsion unit in the form of an electric machine.Alternatively, the vehicle may be a fully electric vehicle. ln such a case, the vehicle 1 does not comprise a combustion engine.

Figure 2 schematically i||ustrates a first exemplifying embodiment of a vehicle powertrain 2, whichmay be incorporated in the vehicle 1 shown in Figure 1. The method for engaging a start gear asdescribed herein may be used in the vehicle powertrain 2 shown in Figure 2. The powertrain 2comprises a propulsion unit, in the form of an electric machine 11, and a gearbox 4. The gearbox 4 isconfigured to transfer propulsion torque at various gear ratios, from the electric machine 11 todriving wheels 5 of the vehicle powertrain 2. The gearbox 4 may be connected to the driving wheels via a differential 8 and a drive wheel shaft 7.

The gearbox 4 may comprise a first transmission shaft 40 and a main transmission shaft 30. The firsttransmission shaft 40 may be connected to the electric machine 11 and thus may be considered toconstitute an input shaft of the gearbox 4. The first transmission shaft comprises a first set of gearwheels, illustrated in the figure as S1. The first set S1 of gear wheels may comprise two or more gearwheels. Said first set S1 of gear wheels may for example comprise three gear wheels 12B, 13 B, 14B asillustrated in Figure 2. The gear wheels 12B, 13B, 14B of the first set S1 of gear wheels are rotatablyfixed to the first transmission shaft 40 and will thus rotate with the first transmission shaft. The mainshaft 30 comprises a second set of gear wheels, illustrated in the figure as S2. The second set S2 ofgear wheels may for example comprise three gear wheels 12A, 13A, 14B. Each gear wheel of thesecond set S2 of gear wheels cooperates with a corresponding gear wheel of the first set S1 of gearwheels. ln other words, the gear wheel 12A cooperates with gear wheel 12B. This may be achievedby the peripheral teeth of the respective gear wheels intermeshing with each other. Thus, upon rotation of the gear wheel 12B, gear wheel 12A will also rotate. Likewise, gear wheel 13A cooperates 11 with gear wheel 13B, and gear wheel 14A cooperates with gear wheel 14B. Each gear wheel 12A,13A, 14A of the second set of gear wheels, S2, may be selectively locked to the main shaft 30 forrotation therewith. More specifically, the gear wheel 12A may be locked to the main shaft 30 bymeans of a first coupling s|eeve 16. The first coupling s|eeve 16 may be an axially displaceablecoupling s|eeve, and may be rotatably fixed to the main transmission shaft 30. Such a coupling s|eevemay comprise cogs configured to, when the gear wheel is locked to the main shaft, intermesh withcorresponding cogs of the gear wheel. Similarly, the gear wheel 13A may be locked to the main shaft30 by means of a second coupling s|eeve 17. The second coupling s|eeve 17 may also be an axiallydisplaceable coupling s|eeve. The second coupling s|eeve 17 may also be used for locking the gearwheel 14A to the main shaft 30. Alternatively, a third coupling s|eeve may be used for locking the gear wheel 14A to the main shaft.

The gearbox 4 exemplified in Figure 2 is a three-speed gearbox in view of comprising only two shafts,i.e. the first transmission shaft 40 and the main shaft 30, and three gear wheel pairs 12A/12B,13A/13B and 14A/14B. lt should however be noted that the gearbox 4 may comprise only two gearwheel pairs and thereby have a two-speed configuration. Alternatively, the gearbox 4 may further comprise a lay shaft, and thereby also have for example a four-speed configuration.

The vehicle powertrain 2 further comprises a brake device 25 configured to brake the main shaft 30.The brake device 25 may be arranged downstream of the second set S2 of gear wheels. The brakedevice 25 may be connected to a housing 26 of the gearbox 4 and thereby grounded. By way ofexample, the brake device 25 may comprise a brake shaft 25a connected to the main shaft 30 bymeans of a gear wheel pair comprising a gear wheel 27A, rotatably fixed to the main shaft, and gearwheel 27B rotatably fixed to the brake shaft 25a. By means of the brake device 25, a rotational speedof the main shaft 30 may be controlled. Furthermore, the main shaft 30 may, when desired, be locked in a non-rotating state by means of the brake device 25.

The vehicle powertrain 2 further comprises a control device 100. The control device 100 may beconfigured to control one or more of the constituent components of the vehicle powertrain 2, suchas the gearbox 4 and the brake device 25. The control device 100 may further be configured to control the electric machine 11.

Figure 3 schematically illustrates a second exemplifying embodiment of a vehicle powertrain 2, suchas a powertrain of the vehicle 1 shown in Figure 1. The method for engaging a start gear as described herein may be used in the vehicle powertrain 2 shown in Figure 3.The powertrain 2 according to the 12 second exemplifying embodiment comprises a propulsion unit in the form of a combustion engine 3.The powertrain 2 further comprises a gearbox 4 and a clutch 9 arranged between the combustionengine 3 and the gearbox 4. The gearbox 4 may comprise an automated manual gearbox (AMT). The clutch 9 may for example be a friction clutch.

Although Figure 3 illustrates a powertrain comprising a combustion engine, it should be noted thatthe combustion engine may be replaced by an electric machine. ln such a case, the clutch may beomitted, if desired. Alternatively, the powertrain 2 may comprise both a combustion engine and an electric machine, if desired.

The vehicle powertrain 2 furthermore comprises a control device 100, as will be described in moredetail below. The control device 100 is configured to control at least a part of the powertrain 2. More specifically, the control device may be configured to control the gearbox 4.

The gearbox 4 comprises an input shaft 10 connected to the clutch 9 and an output shaft 6connected to the driving wheels 5 via a differential 8 and a drive wheel shaft 7. The gearbox 4comprises a first gearbox unit 4A and a second gearbox unit 4B arranged downstream of the firstgearbox unit 4A. The first gearbox unit 4A may be a split gearbox unit. The second gearbox unit 4Bmay constitute a conventional main gearbox that can be set to a number of different forward gearratios. The second gearbox unit 4B is connectable to the first gearbox unit 4A. Furthermore, thegearbox 4 may optionally comprise additional gearbox units as known in the art, for example a range gearbox unit 4C arranged downstream of the second gearbox unit 4B.

The second gearbox unit 4B comprises a lay shaft 20. The layshaft 20 comprises a first set S1 of gearwheels, here exemplified by gear wheels 12B, 13B, 14B. The gear wheels 12B, 13B and 14B are eachrotatably fixed to the lay shaft 20. For example, gear wheel 12B may represent a first gear, gearwheel 13B may represent a second gear, and gear wheel 14B may represent a third gear. The secondgearbox unit 4B also comprises a main shaft 30. The main shaft 30 comprises a second set S2 of gearwheels, here exemplified by gear wheels 12A, 13A, 14A. Each gear wheel 12A, 13A, 14A of thesecond set S2 of gear wheels is arranged to rotate freely in relation to the main shaft 30, but can beselectively locked for rotation with the main shaft 30 in order to engage a gear. When each of thegear wheels 12A, 13A, 14A rotate freely in relation to the main shaft 30, the second gearbox unit 4Bis in neutral. Thereby, no torque is transmitted from the combustion engine 3 to the driving wheels5. The gear wheels 12A, 13A, 14A may each be locked to the main shaft 30 by means of corresponding coupling sleeves 16, 17. For example, the first gear in the second gearbox 4B can be 13 engaged by maneuvering the first sleeve 16, arranged to rotate with the main shaft 30, to a positionwhere the gear wheel 12A is engaged, i.e. to the left in the figure. The gear wheel 12A will therebyrotate with the main shaft 30, and the lay shaft 20 will thereby be connected to the main shaft 30 viagear wheel 12B. Each pair of gear wheels on the lay shaft 20 and main shaft 30 represents a gearratio. The second gear in the second gearbox unit 4B may be engaged by disengaging the first sleeve16 from the gear wheel 12A and instead moving a second sleeve 17 to a position to the right in thefigure where, instead, gear wheel 13A is engaged. The gear wheel 13A is thereby brought intorotation with the main shaft 30. Correspondingly, the third gear in the second gearbox unit 4B maybe engaged by maneuvering the second sleeve 17 to the left in the figure where, instead, gear wheel14A is engaged. Each of the first through third gears in the second gearbox unit 4B is used for aplurality of the total number of gears provided by the gearbox 4 as a whole. The second gearbox unit 4B may further comprise one or more reverse gears (not shown) and a crawler gear (not shown).

The lay shaft 20 further comprises an additional gear wheel 15B that, similar to the above, is rotata bly fixed to the lay shaft 20. The first gearbox unit 4A comprises a corresponding gear wheel15A rotating freely in relation to the input shaft 10, but which may be selectively locked for rotationwith the input shaft 10 through a split sleeve 18. When the split sleeve 18 locks the gear wheel 15Awith the input shaft 10, torque can be transferred to the lay shaft 20 via the corresponding gearwheel 15B on the lay shaft 20. The split sleeve 18 can further be used to connect the input shaft 10to the gear wheel 14A of the second gearbox unit 4B directly. This way, depending on whether thegear wheel 14A on the main shaft 30 is rotating freely in relation to the main shaft 30 or if it is lockedon the main shaft 30, torque can be transferred to the lay shaft 20 via the corresponding gear wheel14B on the lay shaft 20 or torque can be transferred from the input shaft 10 directly to the mainshaft 30. The gear wheel pair 15A/15B and the split sleeve 18 can thereby be used to provide twodifferent split gear ratios for each gear of the second gearbox unit 4B. The first gearbox unit 4A maythus be controlled to engage a high-split gear or a low-split gear. For example, engaging the low-splitgear may comprise to connect the input shaft 10 with the low gear wheel 14A on the main shaft 30by means of the split sleeve 18. When e.g. the first gear is engaged in the second gearbox unit 4B,the split sleeve 18 may be arranged to engage gear wheel 14A. This way, the input shaft 10 is directlyconnected to gear wheel 14B, which via gear 14B establishes a first gear ratio between the inputshaft 10 and the lay shaft 20. The gear wheel 14A, however, is not locked to the main shaft 20, butthe lay shaft 20 may be connected to the main shaft 20 through gear wheel pair 12A/12B. To engagethe second gear, gear wheel pair 15A/15B is instead engaged, resulting in a second gear ratio between the input shaft and the lay shaft 20. The gear wheel 12A is still engaged by the coupling 14 sleeve 16 according to the above, thereby extending the range of each gear. This split can be performed for each gear of the second gearbox unit 4B.

Each of the coupling sleeves 16, 17, 18 described above may for example be operated by pneumaticactuators (not shown). Furthermore, the clutch 9 may be operated by a pneumatic actuator (not shown).

The second gearbox unit 4B may comprise unsynchronized gears, which means that there is nosynchronization device (such as a synchromesh) present for synchronizing rotationa| speeds whengear wheels are to be locked to the main shaft 30. The first gearbox unit 4A may however comprise asynchromesh arrangement comprising the coupling sleeve 18. A synchromesh arrangement in apowertrain of a vehicle is in general used to synchronize the rotationa| speed between transmission elements, such as a gear wheel and a shaft, before the gear wheel is locked on the shaft.

The vehicle powertrain 2 comprises a brake device 25 configured to brake the main shaft. The brakedevice 25 may also be used for locking the main shaft 30 in a non-rotating state, when desired. Thebrake device 25 is connected to a housing 26 of the gearbox 4. Thereby, the gearbox housing 26 maybe able to absorb energy from the brake device 25 when the brake device is activated. The brakedevice 25 may be arranged downstream of the second set S2 of gear wheels, as shown in Figure 3.The brake device 25 may be configured to act directly on the main shaft 30 or act indirectly on themain shaft 30, as long as it is capable of directly or indirectly lock the main shaft 30 in a non-rotatingstate. The brake device 25 may for example be arranged in the main gearbox unit 4B or in the range gearbox unit 4C.

The gearbox may also comprise one or more additional transmission brakes. For example, thegearbox may comprise a lay shaft transmission brake 21 configured to control the rotationa| speed of the lay shaft 20.

As mentioned above, the vehicle powertrain 2 further comprises a control device 100. The controldevice 100 may be configured to control one or more of the constituent components of the vehiclepowertrain 2. The control device may be configured to control at least the gearbox 4 and the brakedevice 25. The control device 100 may further be configured to control the combustion engine 3. Thecontrol device 100 may also be connected to any other constituent component of the vehicle powertrain 2, for example the clutch 9.

Figure 4 represents a flowchart schematically illustrating a method for engaging a start gear in agearbox of a vehicle powertrain according to one exemplifying em bodiment of the presentdisclosure. As previously mentioned, the gearbox comprises a first transmission shaft comprising afirst set of gear wheels rotata bly fixed to the first transmission shaft. The gearbox further comprises amain shaft comprising a second set of gear wheels. Each gear wheel of the second set of gear wheelscooperates with a corresponding gear wheel of the first set of gear wheels, and is selectively locka bleto the main shaft for rotation therewith. The method comprises a step S101 of locking the main shaftin a non-rotating state by means of a brake device connected to a housing of the gearbox. Step S101may be performed in response to a request for engaging a start gear. The method further comprisesa step S102 of, when the main shaft is in the non-rotating state and the first transmission shaft isrotating, locking a predetermined gear wheel of the second set of gear wheels to the main shaft forrotation with the main shaft. After step S102, the method comprises a step S103 of re|easing themain shaft from the non-rotating state. Step S103 may be performed in response to a determinationthat the start gear has been engaged or after a predetermined time has e|apsed since the main shaftwas locked in the non-rotating state. By re|easing the main shaft from the non-rotating state, the main shaft is able to rotate and the vehicle can thus be put in motion.

Figure 5 schematically i||ustrates an exemplifying embodiment of a device 500. The control device100 described above may for example comprise the device 500, consist of the device 500, or be comprised in the device 500.

The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/writememory 550. The non-volatile memory 520 has a first memory element 530 in which a computerprogram, e.g. an operating system, is stored for controlling the function of the device 500. The device500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, atime 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 program P that comprises instructions for engaging a start gear in agearbox of a vehicle powertrain. Said gearbox comprises a first transmission shaft comprising a firstset of gear wheels rotata bly fixed to the first transmission shaft. The gearbox further comprises amain shaft comprising a second set of gear wheels. Each gear wheel of the second set of gear wheelscooperates with a corresponding gear wheel of the first set of gear wheels and is selectively locka ble to the main shaft for rotation therewith. The computer program comprises instructions for locking 16 the main shaft in a non-rotating state by means of a brake device connected to a housing of thegearbox. The computer program further comprises instructions for, when the main shaft is in thenon-rotating state and the first transmission shaft is rotating, locking a predetermined gear wheel ofthe second set of gear wheels to the main shaft for rotation with the main shaft. The computer program further comprises instructions for re|easing the main shaft from the non-rotating state.

The program 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.

The data processing unit 510 may perform one or more functions, i.e. the data processing unit 510may effect a certain part of the program P stored in the memory 560 or a certain part of the program P 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 bus512. The separate memory 560 is intended to communicate with the data processing unit 510 via adata bus 511. The read/write memory 550 is adapted to communicate with the data processing unit510 via a data bus 514. The communication between the constituent components may beimplemented by a communication link. A communication link may be a physical connection such asan optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.

When data are received on the data port 599, they may be stored temporarily in the second memoryelement 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 dataprocessing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, methods herein described are executed.

Claims

1. A method, performed by a control device (100), for engaging a start gear in a gearbox (4) of avehicle powertrain (2),the gearbox (4) comprising: a first transmission shaft (20, 40) comprising a first set (S1) of gear wheels (12B, 13B,14B) rotatably fixed to the first transmission shaft (20, 40), and a main shaft (30) comprising a second set (S2) of gear wheels (12A, 13A, 14A), eachgear wheel (12A, 13A, 14A) of the second set (S2) of gear wheels cooperating with acorresponding gear wheel of the first set (S1) of gear wheels and being selectively locka ble tothe main shaft (30) for rotation therewith, the second set (S2) of gear wheels comprising unsynchronized gear wheels;the method comprising the steps of: locking the main shaft (30) in a non-rotating state by means of a brake device (25)connected to a housing (26) of the gearbox (4), when the main shaft (30) is in the non-rotating state and the first transmission shaft(20, 40) is rotating, locking a predetermined gear wheel (12A, 13A, 14A) of the second set(S2) of gear wheels to the main shaft (30) for rotation with the main shaft, and releasing the main shaft (30) from the non-rotating stateThe method according to claim 1, wherein the first transmission shaft comprises a layshaft (20), and the gearbox further comprises an input shaft (10) connectable to the layshaft (20)The method according to any one of claims 1 or 2, further comprising step of:in response to a request for engagement of a start gear, initiating rotation of the first transmission shaft (20, 40) if the first transmission shaft is not already rotatingThe method according to any one of the preceding claims, further comprising a step of:controlling the rotational speed of the first transmission shaft (20, 40) to be within apredetermined rotational speed interval before locking the predetermined gear wheel (12A, 13A, 14A) of the second set (S2) of gear wheels to the main shaft (30)The method according to any one of the preceding claims, wherein the step of releasing the main shaft (30) from the non-rotating state is performed in response to a determination thatthe predetermined gear wheel (12A, 13A, 14A) has been locked to the main shaft (30) for rotation therewithThe method according to any one of the preceding claims, wherein the brake device (25) isarranged downstream of the predetermined gear wheel (12A, 13A, 14A) of the second set (S2) of gear wheelsThe method according to any one of the preceding claims, the gearbox (4) further comprising a range gearbox unit (4C) connected to the main shaft (30)A computer program comprising instructions which, when executed by a control device(100), cause the control device (100) to carry out the method according to any one of the preceding claimsA computer-readable medium comprising instructions which, when executed by a controldevice (100), cause the control device (100) to carry out the method according to any one of claims 1 toA control device (100) configured to engage a start gear in a gearbox (4) of a vehiclepowertrain (2),the gearbox (4) comprising: a first transmission shaft (20, 40) comprising a first set (S1) of gear wheels (12B, 13B,14B) rotatably fixed to the first transmission shaft (20, 40), and a main shaft (30) comprising a second set (S2) of gear wheels (12A, 13A, 14A), eachgear wheel (12A, 13A, 14A) of the second set (S2) of gear wheels cooperating with acorresponding gear wheel (12B, 13B, 14B) of the first set (S1) of gear wheels and beingselectively lockable to the main shaft (30) for rotation therewith, the second set (S2) of gear wheels comprising unsynchronized gear wheels;the control device (100) configured to lock the main shaft (30) in a non-rotating state by means of a brake device (25)connected to a housing (26) of the gearbox; when the main shaft (30) is in the non-rotating state and the first transmission shaft(20, 40) is rotating, locking a predetermined gear wheel (12A, 13A, 14A) of the second set(S2) of gear wheels to the main shaft (30) for rotation with the main shaft (30), and release the main shaft (30) from the non-rotating state.The control device (100) according to claim 10, further configured to:in response to a request for engagement of a start gear, initiate rotation of the first transmission shaft (20, 40) if the first transmission shaft (20, 40) is not already rotatingThe control device (100) according to any one of claims 10 or 11, further configured to:control the rotational speed of the first transmission shaft (20, 40) to be within apredetermined rotational speed interval before locking the predetermined gear wheel (12A, 13A, 14A) of the second set (S2) of gear wheels to the main shaft (30)The control device (100) according to any one of claims 10 to 12, wherein the control device(100) is configured to release the main shaft (30) from the non-rotating state in response to adetermination that the predetermined gear wheel (12A, 13A, 14A) has been locked to the main shaft (30) for rotation therewithThe control device (100) according to any one of claims 10 to 13, wherein the brake device(25) is arranged downstream of the predetermined gear wheel (12A, 13A, 14A) of the second set (S2) of gear wheelsA vehicle (1) comprising the control device (100) according to any one of claims 10 to 14.