SE539177C2 - Method and system for changing gear in a vehicle gearbox comprising first and second gearbox units - Google Patents

Abstract

Abstract The present invention relates to a method for changing gearratio in a gearbox (103) of a vehicle (100). The gearbox (103)comprises a first gearbox unit (103A, 103B, 103C) and at leastone second gearbox unit (103A, 103B, 103C), forming a combinedgear ratio of said gearbox (103). The method includes, when changing gear ratio of said gearbox (103): - disconnecting said gears of the gearbox units (103A, 103B,103C) of said gearbox (103) from said power source (101) and from said at least one drive wheel (113, 114); - when said gears of the gearbox units (103A, 103B, 103C) aredisconnected from said power source (101) and from said atleast one drive wheel (113, 114), changing gear ratio of at least one of said gearbox units (103A, 103B, 103C). Fig. 4

Description

lO METHOD AND SYSTEM FOR CHANGING GEAR IN A VEHICLE GEARBOXCOMPRISING FIRST AND SECOND GEARBOX UNITS Field of the invention The present invention relates to vehicle gearboxes, and inparticular to a method and system for changing gear ratio in avehicle gearbox. The present invention also relates to avehicle, as well as a computer program and a computer program product that implement the method according to the invention.Background of the invention There exist various kinds of vehicle transmissions. Forexample, a vehicle gearbox can be of a fully automatic kind,where a vehicle control system controls completely gearchanging operations. The gearboxes being used in these systemsmay consist of conventional automatic gearboxes, butoftentimes consist of an automated manual gearbox where thevehicle control system automatically controls change of gear in the gearbox.

With regard to, in particular, commercial vehicles, a largernumber of gears than normally is present in passenger cars areoften required to provide a desired driveability. However, apassenger car type gearbox providing a large number of gearswould be relatively complex and space requiring. In addition,if gear change is to be performed manually, the conventional "H"-type pattern would get rather complicated.

Commercial vehicles requiring a relatively large number ofgears, therefore, often utilises a gearbox consisting of twoor more gearbox units. A first gearbox unit may constitute aconventional main gearbox being controllable to a plurality offixed gear ratios, e.g. in the order of 3-6 gears, and one ormore additional gearbox units can be used to provide additional gear changing possibilities. In this way, the lO number of gear ratios provided by the main gearbox can bemultiplied with the number of gear ratios provided by additional gearbox units.

For example, it is common to use a, commonly denoted, rangegear which can be set to a low range gear ratio and a highrange gear ratio. Each of the gear ratios of the main gearboxcan be used in low range and high range, respectively, the useof a range gear thereby resulting in a gearbox providing twicethe number of gear ratios being available through the main gearbox.

For example, if the main gearbox has three forward gears,first through third gear are accessed when the range gear isset to low range. A change of range to high range providesthree additional gears, where the first gear of the main gearbox becomes fourth, the second gear becomes fifth, etc.

The gearbox may further be provided with a splitter gear,which essentially splits each gear of the main gearbox intotwo. That is, first gear of the vehicle gearbox corresponds tofirst gear of main gearbox/low split, second gear correspondsto first gear of main gearbox /high split, third gear beingsecond gear of main gearbox/low split, fourth gear being second gear of main gearbox/high split, etc.

Consequently, if both a range gear portion and a splitter gearportion are used, the initial three gears are doubled both bythe splitter gear and by the range gear, thereby providing l2 gears in total.

Transmissions of the kind where different gearbox units are used can be manufactured in a cost-efficient manner, and alsobe made more compact in comparison to a single gearbox with acomparable number of gears. These advantages, however, come at the expense of at least certain changes of gear requiring lO simultaneous changes of gear ratios in different gearboxunits, hence rendering the gear changing operation relatively complex and time consuming.Summary of the invention It is an object of the present invention to provide a methodand system for facilitating a change of gear ratio of agearbox in a vehicle. This object is achieved by a method according to claim l.

According to the present invention, it is provided a methodfor changing gear ratio in a gearbox of a vehicle, saidgearbox being arranged to transfer torque between a powersource and at least one drive wheel of said vehicle. Thegearbox comprises a first gearbox unit and at least one secondgearbox unit, each of said first and second gearbox unitsbeing individually controllable to at least two gears havingdifferent gear ratios to form a combined gear ratio of saidgearbox. The method includes, when changing gear ratio of said gearbox: - disconnecting said gears of the gearbox units of saidgearbox from said power source and from said at least one drive wheel; and - when said gears of the gearbox units are disconnected fromsaid power source and from said at least one drive wheel, changing gear ratio of at least one of said gearbox units.

As mentioned above, vehicle gearboxes, in particular withregard to commercial vehicles, can be relatively complex innature and comprise a plurality of gearbox units that arearranged in sequence, assembled as a single unit, to form agearbox that is capable of exhibiting a relatively large number of gear ratios. lO A change of gear ratio in gearboxes of this kind furtherrequires that the powertrain is essentially relieved fromtorque when a change of gear occurs. Consequently, there is aninterruption of the transmission of torque from the powersource to the vehicle's drive wheels when the power train isrelieved from torque. Oftentimes, the clutch is opened duringa change of gear so that the power source is completelydisconnected from the vehicle's drive wheels during the gear changing operation.

This interruption in the transmission of torque is oftentimeshighly undesirable, in particular when a heavily loadedvehicle is being driven in an uphill section of a road. Aninterruption in torque when going uphill will result in anundesired retardation of the vehicle. Longer torqueinterruptions may also be seen as negative from a driverperspective for various reasons. For example, longerinterruptions with associated retardations may bediscomfortable to the driver. Also, a vehicle exhibitinglonger interruptions in the transmission of torque may beperceived as a less powerful vehicle in comparison to vehiclesexhibiting shorter interruptions in the transmission of torque.

It is, consequently, desirable that automatic changes of gearin gearboxes that can be set to a number of fixed gear ratioscan be performed with minimum interruptions in thetransmission of torque from power source to the vehicle's drive wheels.

According to the present invention, the duration of torqueinterruptions when changing gears can be reduced by means of amethod where the gearbox is disconnected from both powersource, such as e.g. a combustion engine, and vehicle's drive wheels. At least in some situations an efficient change of lO gears can be accomplished by disconnecting the gearbox, andthereby the gearbox units making up the gearbox from the powersource and the vehicle's drive wheels. Since the gearbox, andthereby the various gears of the gearbox units, isdisconnected from the power source and the drive wheels,rotating parts of the gearbox are allowed to rotate completelyindependent from e.g. rotation that otherwise is caused by thevehicle's drive wheels. This has the advantage that nosynchronization to speeds being dependent from current drivingconditions, such as current vehicle speed, is required at theactual change of gear ratio. Instead, such synchronization canbe arranged to be performed when the changes of gear ratio inthe one or more gearbox units have been carried out and thegearbox again is to be connected to the vehicle's drive wheels.

The gearbox can, for example, be disconnected from said atleast one drive wheel by disconnecting said gearbox from a propeller shaft of said vehicle.

Furthermore, according to one embodiment rotating parts, suchas shafts etc. can be subjected to a braking force, applied bya transmission brake, e.g. a shaft brake, to reduce therotational speed of rotating parts to a speed where change ofgear ratio can be performed without the risk for wear due tohigh-speed miss-meshing. A powerful shaft brake can be used,since all changes of gear can be arranged to be performed atlow rotational speeds, or standstill, of gearbox internalcomponents due to the independence of the speed of the power source and the speed of the vehicle's drive wheels.

The braking force can be applied prior to disconnecting any ofthe engaged gears of said gearbox units. This has theadvantage that when the gears are still engaged, a braking force applied to one rotating member will automatically brake lO the other rotating members of the gearbox being involved inthe transmission of torque between power source and drive wheels.

The gearbox can advantageously be of a kind where one of thegearbox units constitutes a range gearbox, arranged to providea high range gear and a low range gear. In particular, therange gearbox can be of a kind comprising a planetary gear,and it can be the gearbox unit arranged closest to the vehicle's drive wheels.

In particular, according to one embodiment, the planetary gearcomprises a sun wheel being connected to an output shaft ofsaid first gearbox unit, and a planet wheel carrier carrying aplurality of planet wheels engaging said sun wheel, where saidplanet wheel carrier is selectively connectable to an outputshaft of said second gearbox unit. Since the output shaft isconnected to the vehicle's drive wheels via e.g. a propellershaft the planetary gear is connected to the drive wheels whenconnected to the output shaft. The planetary gear isdisconnected from said at least one drive wheel bydisconnecting said planet wheel carrier from said output shaft of said second gearbox unit.

For example, an axially displaceable coupling sleeve may bearranged to, in a first position, connect the planetary gearto the output shaft, and in a second position be arranged todisconnect said planetary gear from the output shaft and thereby also from the vehicle's drive wheels.

When the change of gear ratio has been performed in one ormore of the gearbox units the torque transmitting shaftsthrough the gearbox are again connected to the power source,and can be accelerated by the power source, e.g. by partially or fully closing the clutch. In this way, the rotational speed lO of the gearbox shafts can be synchronized, by conventionalcontrol of the power source speed, to the speed prevailingdownstream the gearbox, e.g. a propeller shaft speed, so thatthe gearbox can be connected to the drive wheels, e.g. byconnection to a propeller shaft, without large shaft speed differences, thereby reducing the risk of excessive wear.

According to one embodiment, the torque transmitting shaftsare accelerated to a speed such that a rotational speeddifference at the position for connecting said gearbox to said at least one drive wheel is at most a first speed difference.

Further characteristics of the present invention andadvantages thereof are indicated in the detailed descriptionof exemplary embodiments set out below and the attached drawings.Brief description of the drawings Fig. lA illustrates a powertrain of an exemplary vehicle in which the present invention advantageously can be utilized; Fig. lB illustrates an example of a control unit in a vehicle control system; Fig. 2 illustrates an example of gearbox units of the gearbox of fig. 1A.Fig. 3 illustrates a gearbox unit of fig. 2 more in detail.

Fig. 4 illustrates an exemplary method according to one embodiment of the present invention.

Fig. 5 illustrates shaft speeds at an exemplary change of gearoperation according to one embodiment of the present invention.

Detailed description of exemplary embodiments Fig. 1A schematically depicts a powertrain of an exemplaryvehicle 100. The powertrain comprises a power source, in thepresent example a combustion engine 101, which, in aconventional manner, is connected via an output shaft of thecombustion engine 101, normally via a flywheel 102, to agearbox 103 via a clutch 106. A propeller shaft 107 connectsthe gearbox 103 to drive wheels 113, 114 via a final drive108, such as a common differential, and drive axles 104, 105 connected to said final drive 108.

The combustion engine 101 is controlled by the vehicle controlsystem via a control unit 115. The clutch 106 and gearbox 103are also controlled by the vehicle control system by means of a control unit 116.

As mentioned above, vehicles in general comprise a gearboxthat can be set to a number of gear ratios, whereheavy/commercial vehicles often comprise a gearbox comprisinga plurality of individually controllable gearbox units to form a combined gear ratio of the gearbox.

The present invention relates to gearboxes comprising at leasttwo gearbox units, and an exemplary gearbox 103 comprising aplurality of (in this example three) gearbox units is disclosed in fig. 2.

Fig. 2 discloses the combustion engine 101 and clutch 106. Thefigure further discloses the gearbox 103, comprising threegearbox units 103A, 103B, 103C. The gearbox unit 103Aconstitutes a conventional main gearbox that can be set tothree different forward gear ratios and a reverse gear. Thefigure further discloses a gearbox unit 103B constituting arange change gearbox, or simply range gearbox, arranged downstream of the main gearbox unit 103A. The range gearbox unit l03B is discussed further with reference to fig. 3. Thethird gearbox unit l03C is located upstream the main gearboxl03B in the direction of torque from combustion engine 101 todrive wheels 113, 114. The gearbox unit l03C constitutes asplitter gear which divides each gear of the main gearbox intotwo gear steps with different gear ratios in order to provide more gear ratios of the gearbox 103.

With regard to the main gearbox, a layshaft 202 comprises gearwheels 203A, 204A, 205A that are rotatably fixed to thelayshaft 202 and each representing a gear ratio. For example,gear wheel 203A represents the first gear, gear wheel 204A thesecond gear and gear wheel 205A the third gear. A main shaft206 comprises corresponding gear wheels 203B, 204B, 205B whichrotate freely in relation to the main shaft 206, but which canbe selectively locked for rotation with the main shaft 206 inorder to engage a gear. For example, the first main gearboxgear can be engaged by manoeuvring a dog clutch 207, arrangedto rotate with the main shaft 206, to a position where thegear wheel 203B is engaged (i.e. to the left in the figure),thereby bringing the gear wheel 203B into rotation with themain shaft 206 and thereby also engaging the layshaft 202 to the main shaft 206 via gear wheel 203A.

The second main gearbox gear can be engaged by disengaging dogclutch 207 from gear wheel 203B and instead moving dog clutch208 to a position (to the right in the figure) where, instead,gear wheel 204B is engaged, thereby bringing the gear wheel204B into rotation with the main shaft 206. Correspondingly,the third main gearbox gear can be engaged by manoeuvring dogclutch 208 to a position (to the left) where, instead gearwheel 205B is engaged, thereby setting the main gearbox tothird gear. Each of the first through third gears are used for a plurality of the total number of gears provided by the gearbox as a whole. For example, the first gear of the maingearbox will be used for first and second gear of the gearbox103 (low and high split, low range) and also for seventh andeighth gear (low and high split, high range), in a manner well known to a person skilled in the art.

Further, with regard to the splitter gear, the layshaft 202comprises an additional gear wheel 209A that, similar to theabove, is rotatably fixed to the layshaft 202. An input shaft201 comprises a corresponding gear wheel 209B rotating freelyin relation to the input shaft 201 but which can beselectively locked for rotation with the input shaft 201through a coupling unit 210, e.g. a synchronising unit, in amanner known per se. It is also contemplated that unit 210consists of or comprises a dog clutch. The coupling unit 210can further be used to connect the gearbox input shaft 201 togear wheel 205B directly. The gear wheel pair 209A-B andcoupling unit 210 can thereby be used to split each gear of the main gearbox into two parts.

When e.g. the first gear is engaged, the coupling unit 210 isarranged to engage gear wheel 205B. This will have the resultthat the input shaft 201 is directly connected to gear wheel205B, which via gear wheel 205A establishes a first gear ratiobetween input shaft 201 and layshaft 202. Gear wheel 205B,however, is not connected to the main shaft 206, but thelayshaft 202 is connected to main shaft 206 through gearwheel pair 203A-B. Consequently, the first gear is obtainedthrough input shaft 201 -> gear wheel 205B -> gear wheel 205A-> layshaft 202 -> gear wheel 203A -> gear wheel 203B -> main shaft 206.

When the second gear is engaged (i.e. high split of first maingearbox gear), the vehicle is, instead, driven with gear wheel pair 209A-B engaged, resulting in a second gear ratio between 11 input shaft and layshaft 202. The gear wheel 203B is stillengaged by dog clutch 207 according to the above, thereby extending the range of each gear.

This split can be performed for each gear, where, whencoupling unit 210 engages gear wheel 205B and also dog clutch208 engages gear wheel 205B a 1:1 gear ratio through thegearbox units l03C, l03A is obtained. Finally the main gearboxl03B comprises a reverse gear, which is engaged by gear wheelpair 2l2A-B through dog clutch 207 being moved to the right inthe figure, and where the change of direction of rotation ofthe main shaft 206 is accomplished by means of an intermediate gear wheel 2l2C.

So far, gearbox units l03A, l03C have been described. It is tobe understood that fig. 2 merely discloses an example of adesign of such gearbox units, and that the present inventioncan be utilised for various different designs of such gearboxunits. For example, the splitter gear can be omitted. As isexplained below, the invention can be utilized for any gearboxcomprising a plurality of gearbox units that can bedisconnected both from the power source and the vehicle'sdrive wheels. However, the invention is perhaps particularlywell suited for use in a system where a range gearbox, e.g.comprising a planetary gear, is used and can be disconnected from the vehicle's drive wheels.The gearbox unit l03B is described with reference to fig. 3.

The gearbox unit l03B constitutes a gearbox unit of a kindthat commonly is denoted range gearbox. As mentioned above,the range gearbox is used to double the number of gear ratiosthat are available from the main gearbox, and also, as in this case, the number of gears available from the combination of 12 gearbox units 103A, 103C. Hence the gearbox 103 provides, intotal, 2*3*2=12 gear ratios.

The gearbox unit 103B is, as shown in the figures, arrangeddownstream of the main gearbox 103A as seen from thecombustion engine 101, and comprises an input shaft 316 thatmay be formed by the main shaft 206 extending into gearboxunit 103B. The gearbox unit 103B is housed in a gearboxhousing 312 which may be separate from the housing of the main gearbox 103A, although in general being affixed to the main gearbox housing.

Gearboxes of this kind oftentimes comprises a planetary gear314 having a low gear and a high gear by means of which thegear changing possibilities of the main gearbox is dividedinto a low range set of gears and a high range set of gears.According to the disclosed example, there is a downshiftthrough the planetary gear 314 in the low range mode. In thehigh range mode the gear ratio is 1:1 through the planetary gear 314 according to the present example.

The planetary gear 314 comprises three main components thatare rotatable in relation to each other. These components consist of a sun wheel 318, which may be rotatably fixed tothe input shaft 316, a planet wheel carrier 320 carrying a plurality of planet wheels 324 and a ring gear 322.

The planet wheels are rotatably attached to the planet wheelcarrier 320, e.g. by means of bearings, and meshes with thesun wheel 318 in a manner known per se. The ring gear 322, inturn, surrounds and meshes with the planet wheels 324. Theplanet wheel carrier 320 is, as explained below, arranged tobe selectively engaged for rotation with an output shaft 328,which is rotatably fixed to the propeller shaft 107 and hencethe vehicle's drive wheels 113, 114. 13 The gearbox unit 103B further comprises a first axiallydisplaceable coupling sleeve 340 that is arranged todisconnect the input shaft 316 and thereby sun wheel 318 fromthe planet wheel carrier 320 in a first (low range) position,and which is, in a second (high-range) position, arrangedconnect the input shaft 316 / sun wheel 318 for rotation withthe planet wheel carrier 320. The connecting/disconnecting isaccomplished by the sleeve selectively engaging coupling hubsor discs 346, 348 that are rotatably fixed on the sunwheel/input shaft and planet wheel carrier, respectively. Thefirst coupling sleeve 340 is displaced by any suitable means, such as e.g. a pneumatic or hydraulic cylinder 364.

A second axially displaceable coupling sleeve 342 is, in afirst position, arranged to lock the ring gear 322 to thegearbox housing 312, the ring gear 322 thereby being heldstationary. In a second position of the second coupling sleeve342, the ring gear 322 is allowed to rotate freely in relationto the gearbox housing 312. The second coupling sleeve 342 is displaced by, e.g., a pneumatic or hydraulic cylinder 366.

Finally, a third axially displaceable coupling sleeve 343 isarranged to selectively connect the planet wheel carrier 320to the output shaft 328. That is, in a first position, shownin fig. 3, the coupling sleeve 343 locks the planet wheelcarrier 320 for rotation with the output shaft 328, andthereby propeller shaft 107 and vehicle's drive wheels 113,114, via a coupling hub or disc 353 that is locked forrotation with the output shaft 328. In the second position,the coupling sleeve 343 disconnects the planet wheel carrier320 from the output shaft 328 so that the planetary gear canrotate completely independent from rotation of propeller shaft 107 and vehicle's drive wheels 113, 114. The third coupling 14 sleeve is displaced by, e.g., a pneumatic or hydraulic cylinder 367.

The low range mode is obtained by positioning the firstcoupling sleeve 340 to disconnect the planet wheel carrier 320from the input shaft 316 and positioning the second couplingsleeve 342 such that the ring gear 322 is rotatably locked tothe gearbox housing 312, while the third coupling sleeve locks the planet wheel carrier to the output shaft.

In the high range mode, which is shown in fig. 3, the firstcoupling sleeve 340 is positioned to connect the input shaft316 to the planet wheel carrier 320. The second couplingsleeve 342 is further positioned to the position fordisconnecting the ring gear from the gearbox housing. Thetransfer of torque from the input shaft to the output shaftis, in the high range mode, performed by means of the inputshaft 316, the planet wheel carrier 320 and further to theoutput shaft 328 by means of the third coupling sleeve, thegear ratio through the planetary gear 314 thereby being 1:1.

The planetary gear 314 disclosed in fig. 3 is exemplified froma functional point of view and does not disclose particularconstructional features. The planetary gear is, however,thoroughly described in the Swedish patent applicationSE1450626, which is incorporated herein in its entirety. Forthis reason, reference is made to the application SE1450626with regard to particular advantages and features of thisgearbox, and in the present application functionality is onlydescribed insofar is required for explanation of the invention. Further details are disclosed in said application.

In difference to the referenced application, the thirdcoupling sleeve is, according to the present example, used to disconnect the planetary gear from the output shaft. In the referenced application, instead, the third coupling sleeve isarranged to connect the ring gear to output shaft instead ofdisconnecting the planetary gear from the output shaft. Inthis way, a reverse gear is obtained by the planetary gear.

This is thoroughly described in the referenced application.

It is also contemplated that the third coupling sleeve can beset to three different positions to provide also for a reversegear. Alternatively it is contemplated that an additionalcoupling sleeve is used. Solutions where the planetary gear isarranged to be disconnected from the vehicle's drive wheelsare described in a parallel application SE1550665. This application is also incorporated herein in its entirety.

By means of the possibility of disconnecting the planetarygear from the output shaft, the present invention provides amethod that allows for time-efficient changes of gear withminimum wear. An exemplary method 400 of the present inventionis shown in fig. 4, where the method can be implemented atleast partly e.g. in the control unit 116 for controllingoperation of the clutch 106 and gearbox 103. The functions ofa vehicle are, in general, controlled by a number of controlunits, and control systems in vehicles of the disclosed kindgenerally comprise a communication bus system consisting ofone or more communication buses for connecting a number ofelectronic control units (ECUs), or controllers, to variouscomponents on board the vehicle. Such a control system maycomprise a large number of control units, and the control of a specific function may be divided between two or more of them.

For the sake of simplicity, Fig. 1A depicts only control units115-116 but vehicles 100 of the illustrated kind are often provided with significantly more control units, as one skilledin the art will appreciate. Control units 115-116 are arranged to communicate with one another and various components via 16 said communication bus system and other wiring, partly indicated by interconnecting lines in fig. 1A.

The present invention can be implemented in any suitablecontrol unit in the vehicle 100, and hence not necessarily inthe control unit 116. The control of a change of gearaccording to the present invention will usually depend onsignals being received from other control units and/or vehiclecomponents, and it is generally the case that control units ofthe disclosed type are normally adapted to receive sensorsignals from various parts of the vehicle 100. The controlunit 116 may, for example, receive signals e.g. from theengine control unit 115 or any other control unit that achange of gear is to be carried out. The control unit 116 mayfurther be arranged to receive signals from various sensorswith regard to the control of the gearbox, e.g. signalsindicating positions of coupling sleeves, dog clutches etc.Control units of the illustrated type are also usually adaptedto deliver control signals to various parts and components ofthe vehicle, e.g. to actuators of coupling sleeves, dogclutches etc. of the gearbox, and/or e.g. to control unit 115to request particular engine control before, during and/orafter a change of gear. All this is known to the person skilled in the art.

Control of this kind is often accomplished by programmedinstructions. The programmed instructions typically consist ofa computer program which, when executed in a computer orcontrol unit, causes the computer/control unit to exercise thedesired control, such as method steps according to the presentinvention. The computer program usually constitutes a part ofa computer program product, wherein said computer programproduct comprises a suitable storage medium 121 (see Fig. IB) with the computer program 126 stored on said storage medium 17 121. The computer program can be stored in a non-volatilemanner on said storage medium. The digital storage medium 121can, for example, consist of any of the group comprising: ROM(Read-Only Memory), PROM (Programmable Read-Only Memory),EPROM (Erasable PROM), Flash memory, EEPROM (ElectricallyErasable PROM), a hard disk unit etc, and be arranged in or inconnection with the control unit, whereupon the computerprogram is executed by the control unit. The behaviour of thevehicle in a specific situation can thus be adapted by modifying the instructions of the computer program.

An exemplary control unit (the control unit 116) is shownschematically in Fig. 1B, wherein the control unit cancomprise a processing unit 120, which can consist of, forexample, any suitable type of processor or microcomputer, suchas a circuit for digital signal processing (Digital SignalProcessor, DSP) or a circuit with a predetermined specificfunction (Application Specific Integrated Circuit, ASIC). Theprocessing unit 120 is connected to a memory unit 121, whichprovides the processing unit 120, with e.g. the stored programcode 126 and/or the stored data that the processing unit 120requires to be able to perform calculations. The processingunit 120 is also arranged so as to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit 116 is equipped with devices122, 123, 124, 125 for receiving and transmitting input andoutput signals, respectively. These input and output signalscan comprise waveforms, pulses or other attributes that thedevices 122, 125 for receiving input signals can detect asinformation for processing by the processing unit 120. Thedevices 123, 124 for transmitting output signals are arrangedso as to convert calculation results from the processing unit 120 into output signals for transfer to other parts of the 18 vehicle control system and/or the component (s) for which thesignals are intended. Each and every one of the connections tothe devices for receiving and transmitting respective inputand output signals can consist of one or more of a cable; adata bus, such as a CAN bus (Controller Area Network bus), aMOST bus (Media Oriented Systems Transport) or any other bus configuration, or of a wireless connection.

Returning to the exemplary method 400 illustrated in fig. 4,the method starts in step 401, where it is determined whethera change of gear is to be performed. This change of gear maybe arranged to be performed, for example, by changing the gearratio of one or more from main gearbox l03A, range gearboxl03B and splitter gear l03C. Consequently, it can, accordingto one embodiment, be determined in step 401 if any kind ofchange of gear is to be performed. The method remains in step401 for as long as this is not the case. The method continuesto step 402 when it is determined that a change of gear according to the invention is to be performed.

The transition from step 401 to step 402 may also, forexample, be initiated only according to various criteria andnot at all times for any change of gear. For example, controlaccording to the invention can be arranged to be performede.g. only when particular changes of gear is to be performed,such as when a change of gear ratio is to be performed in therange gearbox l03B, or both range gearbox l03B and maingearbox l03A. Other suitable criteria for performing thetransition from step 401 to step 402 may also be applied. Thedetermination of whether a change of gear is to be performedcan be performed in any suitable and conventional manner and does not form part of the present invention.

According to the present example, the gearbox is changed from sixth gear to seventh gear. The sixth gear, in this example, 19 corresponds to the main gearbox 103A being set to thirdposition (gear wheel 205B engaged), the splitter gear 103Cbeing set to high (i.e. engaging gear wheel 209B) and therange gearbox 103B being set to low range. When changing gearto the seventh gear, the main gearbox 103A is changed fromthird position to first position, the range gearbox 103B ischanged from low range to high range, and the splitter gearfrom high to low. Consequently, the present example involveschanges of gear in all three gearbox units 103A-C. The changeof gear will also be illustrated with reference to FIG. 5,which discloses corresponding speeds of the gearbox inputshaft 201, the layshaft 202 and main shaft 206. At time T0the vehicle 100 is being propelled at a gearbox input shaftspeed, solid line 501, of approximately 1500 RPM. When theclutch 106 is closed the speed of the gearbox input shaft 201corresponds to the speed of the combustion engine 101, andhence the combustion engine speed is also approximately 1500 RPM prior to the change of gear.

The gearbox main shaft 206, connected to the input shaft 201via the gear wheels 209A-B and gear wheels 205A-B, is rotatingat a higher speed than the gearbox input shaft 201,dash/dotted line 503. Furthermore, the layshaft 202, dashedline 502, is rotating at a speed in the order of the inputshaft speed. At time T1, a change of gear is initiated according to step 401, and the method continues to step 402.

In step 402, a reduction of the torque being transmitted viathe gearbox 103 is commenced. That is, the torque produced bythe combustion engine 101 is reduced in order to relieve thepowertrain from transmission of torque. When the torque hasbeen reduced to a desired extent the clutch 106 is opened instep 403. As is known to the person skilled in the art, the reduction of transmitted torque through the gearbox 103 can partially be accomplished by reducing the transmittable torqueusing the clutch 106, and hence opening of the clutch can bearranged to be performed at least partially simultaneouslywith the reduction of torque being produced by the combustionengine. The reduction of torque can be performed in any suitable manner.

Furthermore, when the torque being transmitted through thegearbox 103 has been reduced to a desired extent and theclutch has been opened, the planetary gear 314 isdisconnected, step 404, from the vehicle's drive wheels bymanoeuvring the third coupling sleeve 343 to the positionwhere the planet wheel carrier 320 no longer is connected to the output shaft 328.

With regard to FIG. 5, this corresponds to time T2.Consequently, at time T2, the gearbox is disconnected bothfrom the combustion engine 101 as well as from the vehicle'sdrive wheels 113, 114. This means that any rotational parts ofthe gearbox units 103A-C rotate completely independent fromboth combustion engine speed and propeller shaft (drive wheel)rotational speed.All the gearbox units 103A-C are stillengaged as before the gear change is initiated. That is, inputshaft 201 is still rotationally locked to the planet wheelcarrier via gear wheels 209A-B, main gearbox third gear, sun wheel and planet wheels.

In step 405 one or more shaft brakes acting on any suitableshaft or shafts is/are activated. Since the gearbox is stillin gear e.g. any of gearbox input shaft 201, layshaft 202,main shaft 206, sun wheel 318, planet wheel carrier etc. canbe subjected to a braking action which simultaneously willbrake all rotating parts being in operation on the currentgear. According to the invention, a powerful brake can be used, which is capable of reducing shaft speeds to zero and/or 21 low rotational speed in a short period of time. This isbecause, in difference to prior art solutions, gearbox speedsneed not be synchronised with rotating output shafts whenchanging gears since the gearbox 103 has been disconnected in both ends.

According to the present invention, therefore, the speeds ofthe rotating parts are braked to zero, or substantially zero,speed, or at least a speed that is lower than a first speed,speed_lim, which can be arranged to depend on the particularshaft for which it is defined. If for example the gear in therange gearbox is to be changed, the first speed speed_lim willbe adapted and applied to the main shaft. In particular, thefirst speed speed_lim is chosen so that dog clutches andcoupling sleeves can be manoeuvred without being subjected to excessive wear.

Consequently, according to the invention, the speeds ofrotating parts of the gearbox are reduced to such low speedsthat essentially no moments of inertia remain in the gearbox,and change of gear thereby can be performed smoothly andwithout the risk of undesired miss-meshing. By way of examplethe first speed, speed_lim, can be 100 rpm or preferably 50 rpm.

According to the present example, braking is accomplished by alayshaft brake 211, and in step 406 it is determined if therotational speed of the rotating parts of the gearbox has beenreduced at least to the first speed speed_lim. Braking iscontinued via step 405 for as long as this is not thecase.When the first speed speed_lim has been reached, time T3in fig. 5, the method continues to step 407 where gears arechanged when gearbox components are non-rotating or rotatingat low speeds. That is, according to the present example, dog clutch 208 disengages gear wheel 205B (third main gearbox 22 gear) while instead dog clutch 207 engages gear wheel 203B(first main gearbox gear). Further, coupling unit 210 disengages gear wheel 209B and engages gear wheel 205B tochange the splitter gear from high to low. Also, the first coupling sleeve 340 is manoeuvred to engage the planet wheel carrier with the sun wheel/input shaft 316 to change the rangegearbox into high range, and the second coupling sleeve 342 isdisplaced to the position for disconnecting the ring gear fromthe gearbox housing. That is, the first and second coupling sleeve are displaced to be positioned as shown in fig. 3.

In step 408 it is determined whether all requested changeshave been carried out, which e.g. can be determined by meansof position sensors, such as e.g. inductive sensors, of dogclutches and coupling sleeves, or by means of any othersuitable means for determining the position of gearboxelements. The method remains in step 408 for as long as thisis not the case. When all changes of gear ratios have beenmade, and the gearbox 103 thereby has been set to seventhgear, a closing of the clutch 106 is commenced, step 409. Whenthe clutch engages, time T4 in fig. 5, the input shaft 201will accelerate, and since all gears are engaged, layshaft202, main shaft 206, planet wheel carrier etc. will also be accelerated. This is illustrated between T4 and T5 in fig. 5.

Preferably the speed of the combustion engine 106 iscontrolled in the time period starting at time T2 to thetarget speed at the new gear, which in this example is 1180RPM, so that, when the clutch 106 has been closed to aposition where it is no longer slipping, time T5, the planetwheel carrier 320 will rotate at a speed substantiallycorresponding to the rotational speed of the output shaft 328.In step 410 it is determined whether the output shaft 328 can 23 be engaged, e.g. by determining whether the speed differencebetween planet wheel carrier and output shaft 328 is withinsome suitable speed difference, An, within which the thirdcoupling sleeve 343 safely can be operated without the risk ofexcessive wear on components. The speed difference, An, can insome embodiments be 50 rpm. The method can remain in step 410for as long as this is not the case, where e.g. appropriatecontrol of the combustion engine speed can be carried out/requested upon necessity.

When it is determined that the output shaft can be engagedthis is performed in step 411 by manoeuvring the couplingsleeve 343 to engaging position, thereby closing thepowertrain so that torque again can be transmitted from powersource to drive wheels. The torque is then increased todesired level in a conventional manner, step 412, and themethod can return to step 401, waiting for a following changeof gear. The invention has been described in fig. 5 for achange of gear to a higher gear (although, as disclosed, theremay actually be changes of gears to lower gears in individualgearbox units). The invention is, however, equally applicablefor any kind of change of gear, e.g. also changes from highergears to lower gears. The invention is, however, particularly suitable for changing range in the range gearbox.

The present invention, consequently provides a solution wherechange of gear can be performed with gearbox components thatare standing still, or rotating at low speeds, andindependently from rotational speeds of power source and drivewheels. That is, no synchronisation is required during theactual manoeuvring of gearbox components such as dog clutches,coupling sleeves and the like. This has the advantage that e.g. powerful shaft brakes can be used, since no precision lO 24 control of shaft speeds is required. This, in turn, allows for fast changes of gear.

In addition, a solution according to the invention reduces therisk of undesired oscillations in gear changes of theplanetary gear which otherwise may arise caused by reactiontorques arising e.g. from planet wheel bearings when theplanet wheels are accelerated and planet wheel carrier is connected to the output shaft as in the prior art.

Finally, the present invention has been exemplified for aparticular kind of range gearbox, where disconnection frompropeller shaft is performed in a particular manner. Theinvention is, however, applicable for any kind of gearbox, inparticular any kind of range gearboxes, that can besimultaneously disconnected from vehicle's drive wheels and vehicle power source.

Claims (1)

1. Claims ld Method for changing gear ratio in a gearbox (103) of a vehicle (100), said gearbox (103) being arranged totransfer torque between a power source (101) and at leastone drive wheel (113, 114) of said vehicle (100), saidgearbox (103) comprising a first gearbox unit (103A,103B, 103C) and at least one second gearbox unit (103A,103B, 103C), each of said first and second gearbox unitsbeing individually controllable to at least two gearshaving different gear ratios to form a combined gearratio of said gearbox (103), the method beingcharacterised in, when changing gear ratio of saidgearbox (103): - disconnecting said gears of the gearbox units (103A,103B, 103C) of said gearbox (103) from said power source(101) and from said at least one drive wheel (113, 114);and - when said gears of the gearbox units (103A, 103B, 103C)are disconnected from said power source (101) and fromsaid at least one drive wheel (113, 114), changing gearratio of at least one of said gearbox units (103A, 103B, 103C). . Method according to claim 1, further comprising, when said gearbox units (103A, 103B, 103C) are disconnectedfrom said power source (101) and from said drive wheels(113, 114): - applying a braking force to a rotating member of any ofsaid gearbox units (103A, 103B, 103C), so as to reducethe rotational speed of rotating members of said gearbox(103), and - when the rotational speed of said rotating member has been reduced at least to a first speed (speed_lim), l0 26 changing gear ratio of at least one of said gearbox units (l03A, l03B, l03C). . Method according to claim 2, further comprising: - reducing the rotational speed of said rotating member substantially to zero. . Method according to claim 2 or 3, further comprising: - applying said braking force prior to disconnecting atleast one of the engaged gears of said gearbox units (l03A, l03B, l03C). . Method according to any one of the claims l-4, wherein said second gearbox unit (l03B) is a range gearbox,arranged to provide a high range gear and a low range gear. . Method according to claim 5, said second gearbox unit (l03B) comprising a planetary gear, the method furthercomprising:- disconnecting said planetary gear from said at least one drive wheel (ll3, ll4). . Method according to claim 6, wherein said planetary gear comprising a sun wheel (318) being connected to an outputshaft of said first gearbox unit (l03A), and a planetwheel carrier (320) carrying a plurality of planet wheels(324) engaging said sun wheel (318), said planet wheelcarrier (320) being selectively connectable to an outputshaft (328) of said second gearbox unit (lO3B), and, - disconnecting said planetary gear from said at leastone drive wheel (ll3, ll4) by disconnecting said planetwheel carrier (320) from said output shaft (328) of said second gearbox unit (l03B). . Method according to claim 6 or 7, wherein an axially displaceable coupling sleeve (343) in a first position is 10. 11. 12. 27 arranged to connect said planetary gear to said at leastone drive wheel (113, 114) of said vehicle (100), and ina second position is arranged to disconnect saidplanetary gear from at least one drive wheel (113, 114) of said vehicle (100). Method according to any one of claims 1-8, wherein saidgearbox (103) comprises said first (103A), said second(103B) and a third (103C) gearbox unit being controllableto at least two gears having different gear ratios, themethod further comprising, when said gearbox units aredisconnected from said power source (101) and from saidat least one drive wheel (113, 114): - changing gear ratio of at least one of said first, second and third gearbox units. Method according to claim 9, further comprising:- changing gear ratio of at least two of said first, second and third gearbox units. Method according to any one of the claims 1-10, furthercomprising, following said change of gear ratio of saidat least one of said gearbox units (103A, 103B, 103C): - by means of said power source (101), acceleratingtorque transmitting shafts of said gearbox units prior toconnecting said gearbox (103) to said at least one drive wheel (113, 114). Method according to claim 11, further comprising:-accelerating said torque transmitting shafts such that arotational speed difference at a position for connectingsaid gearbox, downstream said engaged gears, to said atleast one drive wheel (113, 114) is at most a first speed difference (An). 13 14. 15. 16. 28 .Method according to any of the preceding claims, further comprising:- connecting said gearbox (103) to said at least onedrive wheel by connecting said gearbox (103) to a propeller shaft (107) of said vehicle. Computer program comprising program code that, when saidprogram code is executed in a computer, causes saidcomputer to carry out the method according to any of claims 1-13. Computer program product comprising a computer-readablemedium and a computer program according to claim 14,wherein said computer program is contained in said computer-readable medium. System for changing gear ratio in a gearbox (103) of avehicle (100), said gearbox (103) being arranged totransfer power between a power source (101) and at leastone drive wheel (113, 114) of said vehicle (100), saidgearbox (103) comprising a first gearbox unit (103A,103B, 103C) and at least one second gearbox unit (103A,103B, 103C), each of said first and second gearbox unitsbeing individually controllable to at least two gearshaving different gear ratios to form a combined gearratio of said gearbox (103), the system beingcharacterised in: - means for disconnecting said gears of the gearbox units(103A, 103B, 103C) of said gearbox (103) from said powersource (101) and from said at least one drive wheel (113,114); - means for, when said gears of the gearbox units (103A,103B, 103C) are disconnected from said power source (101) and from said at least one drive wheel (113, 114), 29 changing gear ratio of at least one of said gearbox units (lO3A, lO3B, lO3C). l7.Vehicle, characterised in that it comprises a system for changing gear ratio in a gearbox according to claim 16.