SE1551339A1 - Method and system for selecting gear in a vehicle - Google Patents

Abstract

The present invention relates to a method for selecting gear ratio in a gearbox (103) of a vehicle (100), said gearbox (103) being arranged for transmitting power from a power source (101) to at least one drive wheel (113, 114) of said vehicle (100), said gearbox (103) comprising a plurality of selectable gear ratios, a change of gear ratio being controlled by a vehicle control system, said change of gear being dependent on a rotational speed of said power source (101). The method includes, when to change from a first gear ratio to a second gear ratio, said second gear ratio being higher than said first gear ratio:. - determining a decelerationof said vehicle (100), and. - controlling the dependency of the rotational speed of said power source (101) when selecting gear ratio at least partly on the basis of said determined deceleration. Fig. 2

Description

lO METHOD AND SYSTEM FOR SELECTING GEAR IN A VEHICLEField of the invention The present invention relates to vehicles, and in particular to a method and systemfor selecting gear in a vehicle. The present invention also relates to a vehicle, as wellas 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 powertrains. For example, vehicle transmissionscan be of an automatic kind, where a vehicle control system completely controls gearchanging operations. The gearboxes being used in these systems can, for example,include conventional automatic transmissions comprising torque converters, but mayalso include automated manual transmissions where the vehicle control system automatically controls gear shifting in “manual” gearboxes.

Automatic gear shifting in commercial (heavy) vehicles, in particular long-haulvehicles, often includes a control system controlled gearshift of manual gearboxes,i.e. automatic control of gearboxes comprising a discrete number of fixed gear ratios(i.e. gears). During operation of vehicles of this kind, the gearbox is often controlledby the vehicle control system in a manner in which the gear ratio is selected in dependence of the current driving conditions. ln general, it is often desirable to propel the vehicle using as high a gear as possible(i.e. the lowest possible gear ratio given the circumstances), in order to reduce therotational speed of the power source, oftentimes a combustion engine, therebyreducing fuel consumption. Consequently, when selecting gear ratio, fuelconsumption is often a matter of concern, but at the same time the vehicle should, ingeneral, be driven using a gear ratio that is capable of propelling the vehicle in a desired manner.

For example, when going uphill, in particular when the vehicle is heavily loaded, it isoften required that the gearbox of the vehicle is set to a gear ratio that is capable of providing enough power to propel the vehicle without undesired retardation. lO Summary of the invention lt is an object of the present invention to provide a method and system that improvesthe control of a selection of gear ratio when to change from a lower gear ratio to ahigher gear ratio in situations when the vehicle is decelerating, i.e. is subjected to anacceleration in a direction opposite a direction of travel of the vehicle. This object is achieved by a method according to claim 1.

According to the present invention, it is provided a method for selecting gear ratio in agearbox of a vehicle, said gearbox being arranged for transmitting power from apower source to at least one drive wheel of said vehicle, said gearbox comprising aplurality of selectable gear ratios, a change of gear ratio being controlled by a vehiclecontrol system, said change of gear being dependent on a rotational speed of saidpower source. The method includes, when to change from a first gear ratio to asecond gear ratio, said second gear ratio being higher than said first gear ratio: - determining a deceleration of said vehicle, and - controlling the dependency of the rotational speed of said power source whenselecting gear ratio at least partly on the basis of said determined deceleration.

With regard to vehicles in general, gearboxes of the kind that historically has beenused in vehicles having a manual transmission, but where a change of gear isperformed automatically by means of the vehicle control system, are presently oftenused. This applies, e.g., both to heavy vehicles and passenger cars. Such gearboxesare usually arranged to comprise a discrete number of distinct gear ratios (gears),where the gear ratios of gearboxes in heavy vehicles often are distributed such thatone or more of the lowest gear ratios (highest gears) are capable of propelling thevehicle at a constant speed when the vehicle is travelling on substantially levelground.

When vehicles of this kind, at least when being heavily loaded, are travelling uphill, achange of gear to a higher gear ratio (lower gear) is often required in order to provideenough power to properly overtake the uphill section of road in a desired manner. lnparticular, when travelling uphill, there is often a minimum gear ratio below which thevehicle will lose speed due to lack of power for propelling the vehicle. lO lf a change of gear is not performed at least to the highest gear (the lowest gearratio) where this criterion is fulfilled, the vehicle will continue to decelerate due to thepropelling force being less than the driving resistance. The highest gear whereenough power is obtained can, for example, be denoted as “Gear With Power toAccelerate”, in the following referred to as GWPA gear.

For this reason, a change of gear ratio to a gear ratio being equal to or above theGWPA gear ratio is common in order to be capable of overtaking the uphill section ofroad without losing vehicle speed other than what is required to fulfil criteria forengaging the GWPA gear. For this reason, when a heavy vehicle enters an uphillsection of road, the vehicle is often allowed to decelerate as a change of geartowards the GWPA gear is performed, e.g. through intermediate changes of gear to intermediate gear ratios.

A change of gear is often performed when one or more criteria”s are fulfilled. Forexample, a change of gear to a lower gear (higher gear ratio) can be arranged to beperformed when it is determined that the rotational speed of the combustion enginefollowing the change of gear will not exceed some predetermined calibrated speedlimit that is not to be exceeded, possibly by the further criterion that the vehicle isexpected to be propelled on the new gear for at least a minimum period of timebefore the rotational speed of the combustion engine has reached a rotational speedthat again requires a change of gear to a lower gear. The calibrated power source speed can, for example, be different for different gears and/or vehicle speeds.

This strategy for changing gear, however, may result in changes of gear to lowergears in situations where the change of gear in reality may not be motivated. Forexample, the deceleration of the vehicle on a current gear may be relatively low, i.e.the vehicle may only slowly be losing speed. lf a change of gear is performed in asituation of this kind, this may seem unnecessary and discomforting to the driver, andthe change of gear may also be disadvantageous from a fuel consumption point of view.

According to the present invention, situations of this kind can be avoided or at leastbe reduced in occurrence. This is accomplished by means of a method where a deceleration of the vehicle is determined, and where the dependency of the rotational lO speed of the power source when changing gear is controlled at least partly on thebasis of said deceleration. For example, the maximum allowed rotational speed ofsaid power source following the change of gear can be controlled in dependence ofthe determined deceleration.

Consequently, selection of gear is made dependent of the deceleration of the vehicle.When the vehicle is travelling in an uphill section of road, different road inclinationswill result in different decelerations, where lower inclinations will result in lessdeceleration than higher inclinations for a similarly loaded vehicle, and vice versa.According to the present method, the vehicle can be arranged, for example, tocontinue on a current gear for a longer period of time than previously, therebyallowing propulsion on lower power source rotational speeds when the vehicle deceleration is below e.g. a predetermined deceleration.

This means that selection of gear, and thereby change of gear, for a same vehiclespeed can be different for different situations in which the vehicle is decelerating dueto insufficient power to overcome the current driving resistance. For example, thevehicle can be arranged to be propelled longer on a current gear for lower uphillinclinations than for higher inclinations. ln this way, for example, changes of gear thatnormally occur also when the vehicle is only slowly losing speed may be avoided or at least postponed. lt is also possible to increase the maximum allowed rotational speed on the basis ofthe deceleration. For example, the maximum allowed rotational speed of the powersource can be increased to a value exceeding the calibrated maximum allowedrotational speed when the deceleration exceeds some predetermined value, whichcan be similar to the predetermined deceleration mentioned above or a higherdeceleration, and where the increase can be dependent on the magnitude of thedeceleration.

Consequently, the vehicle can be arranged to automatically adapt to the currentdriving conditions in a manner that may be perceived as logical to a driver of thevehicle. lf the deceleration is higher, selection of gear can be performed such thatchange of gear occurs earlier, while if the deceleration is lower operation on a current lO gear can be prolonged. Vehicle load may also be taken into account, since different vehicle loads will result in different decelerations.

For example, the maximum allowed rotational speed of the power source followingthe change of gear can be arranged to be reduced more for lower decelerations thanfor comparatively higher decelerations. Consequently, the lower the deceleration, thelonger the vehicle may be allowed to continue on a current gear before a change ofgear is performed.

According to one embodiment, the vehicle is, in addition or alternatively, forced tomaintain propulsion on a current gear for as long as the rotational speed of the powersource has not fallen below a minimum speed limit. For example, change of gearratio from said first gear ratio to said second gear ratio may be prohibited for as longas the rotational speed of said power source when said first gear ratio is engaged isabove said rotational speed limit.

This minimum speed limit may also be arranged to be dependent on the determineddeceleration, where lower limits of the rotational speed can be applied forcomparatively lower decelerations. Basically this has the same effect as theembodiment exemplified above, since the difference in rotational speed of the powersource before and after a change of gear is linked through the difference in gear ratiobetween the gears.

Further characteristics of embodiments of the present invention and advantagesthereof are indicated in the detailed description of exemplary embodiments set outbelow and the attached drawings.

Brief description of the drawingsFig. 1A illustrates a powertrain of an exemplary vehicle;Fig. 1B illustrates an example of a control unit in a vehicle control system; Fig. 2 illustrates an exemplary method according to an embodiment of the present invenfion; Fig. 3 illustrates a gear changing scenario according to the prior art; lO Fig. 4 illustrates a gear changing scenario according to an embodiment of the present invenfion.Detailed description of exemplary embodiments Fig. 1A schematically depicts a powertrain of an exemplary vehicle 100. Thepowertrain comprises a power source, in the present example a combustion engine101, which, in a conventional manner, is connected via an output shaft of thecombustion engine 101, normally via a flywheel 102, to a gearbox 103 via a c|utch106. An output shaft 107 from the gearbox 103 propels drive wheels 113, 114 via afinal drive 108, 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 control system via a controlunit 115. The c|utch 106 and gearbox 103 are also controlled by the vehicle control system by means of a control unit 116.

The gearbox 103 can be set to a plurality of distinct (discrete) gear ratios, where asuitable gear ratio is selected for each driving situation by means of the vehiclecontrol system. As was mentioned above, there exist situations where the controlsystem selection of a particular gear ratio may not be perceived as being motivatedby the vehicle driver. Embodiments of the invention provide a method for changinggear ratio in a decelerating vehicle that may seem more appropriate from a driver perspective.

An exemplary method 200 according to embodiments of the present invention isshown in fig. 2, which method can be implemented at least partly e.g. in the controlunit 116 for controlling the c|utch 106 and gearbox 103. As indicated above, thefunctions of a vehicle are, in general, controlled by a number of control units, andcontrol systems in vehicles of the disclosed kind generally comprise a communicationbus system including one or more communication buses for connecting a number ofelectronic control units (ECUs), or controllers, to various components on board thevehicle. Such a control system may comprise a large number of control units, and the control of a specific function may be divided between two or more of them. lO For the sake of simplicity, Fig. 1A depicts only control units 115-116, but vehicles 100of the illustrated kind are often provided with significantly more control units, as oneskilled in the art will appreciate. Control units 115-116 are arranged to communicatewith one another and various components via said communication bus system and other wiring, partly indicated by interconnecting lines in fig. 1A.

Embodiments of the present invention can be implemented in any suitable controlunit in the vehicle 100 and hence not necessarily in the control unit 115. The controlof the gearbox 103 according to embodiments of the present invention will usuallydepend on signals being received from other control units and/or vehiclecomponents, and it is generally the case that control units of the disclosed type arenormally adapted to receive sensor signals from various parts of the vehicle 100. Thecontrol unit 116 will, for example, receive signals from the engine control unit 115.Control units of the illustrated type are also usually adapted to deliver control signalsto various parts and components of the vehicle, e.g. to control the clutch 106 and gearbox 103.

Control of this kind is often accomplished by programmed instructions. Theprogrammed instructions typically include a computer program which, when executedin a computer or control unit, causes the computer/control unit to exercise the desiredcontrol, such as method steps according to embodiments of the present invention.The computer program usually constitutes a part of a computer program product,where said computer program product comprises a suitable storage medium 121 (see Fig. IB) with the computer program 126 stored on said storage medium 121. Thecomputer program can be stored in a non-volatile manner on said storage medium.The digital storage medium 121 can, for example, include any of the groupcomprising: ROIVI (Read-Only l\/lemory), PROIVI (Programmable Read-Only l\/lemory),EPROIVI (Erasable PRONI), Flash memory, EEPROIVI (Electrically Erasable PRONI),a hard disk unit etc, and be arranged in or in connection with the control unit,whereupon the computer program is executed by the control unit. The behaviour ofthe vehicle in a specific situation can thus be adapted by modifying the instructions ofthe computer program. lO An exemplary control unit (the control unit 116) is shown schematically in Fig. 1B,wherein the control unit can comprise a processing unit 120, which can include, forexample, any suitable type of processor or microcomputer, such as a circuit for digitalsignal processing (Digital Signal Processor, DSP) or a circuit with a predeterminedspecific function (Application Specific lntegrated Circuit, ASlC). The processing unit120 is connected to a memory unit 121, which provides the processing unit 120, withe.g. the stored program code 126 and/or the stored data that the processing unit 120requires to be able to perform calculations. The processing unit 120 is also arrangedso as to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit 112 is equipped with devices 122, 123, 124, 125 forreceiving and transmitting input and output signals, respectively. These input andoutput signals can comprise waveforms, pulses or other attributes that the devices122, 125 for receiving input signals can detect as information for processing by theprocessing unit 120. The devices 123, 124 for transmitting output signals arearranged so as to convert calculation results from the processing unit 120 into outputsignals for transfer to other parts of the vehicle control system and/or the component(s) for which the signals are intended. Each and every one of the connections to thedevices for receiving and transmitting respective input and output signals can includeone or more of a cable; a data bus, such as a CAN bus (Controller Area Networkbus), a l\/IOST bus (l\/ledia Oriented Systems Transport) or any other bus configuration, or of a wireless connection.

Fïeturning to the exemplary method 200 illustrated in fig. 2, the method starts in step201, where it is determined whether there is a control system initiated request for achange of gear. This can, for example, be determined by determining whether somesuitable function in the vehicle control system determines that the current state ofdriving has reached a situation where a gear changing operation should beperformed. This can be determined e.g. according to any suitable function fordetermining when a gear change is to be performed. Embodiments of the inventionrelate to changes of gear to higher gear ratios (lower gears), and hence, according toone embodiment, it can be determined in step 201 whether the request for change of gear is a request for a change of gear to a lower gear (higher gear ratio). According lO to one embodiment, it is also determined whether there is an ongoing deceleration that is due to driving resistance of the vehicle.

When it is determined that a change of gear is to be performed, the methodcontinues to step 202, where a current deceleration dec of the vehicle 100 isdetermined. The vehicle deceleration dec can be determined by means of anysuitable means as is known per se, such as e.g. by the use of an accelerometer, orby determining a reduction in speed between two consecutive points in time. ln step203 it is determined whether the vehicle deceleration dec is below a decelerationlimit decfim. lf this is not the case, i.e. when the vehicle deceleration dec is above thedeceleration limit dechm the method continues to step 204 where e.g. a normal gearchanging operation is initiated. This change of gear can be arranged to be carried outaccording to the criteria that normally are applied in the propulsion of the vehicle 100,e.g. with regard to restrictions regarding combustion engine speed before/after achange of gear etc.

However, if it is determined in step 203 that the vehicle deceleration dec is below said deceleration limit decmn, the method continues to step 205. ln step 205 gear changing criteria regarding combustion engine speed n are adapted such that thechange of gear is delayed, i.e. the vehicle 100 is forced to be propelled on the currentgear for a longer period of time than normally is the case. This can, for example, beaccomplished by reducing the highest rotational speed nlim of the combustion engine101 that is allowed following the change of gear. ln this way the criteria for performingthe gear changing operation will not be fulfilled until the vehicle 100 has deceleratedfurther and the vehicle 100 thereby being propelled for a longer period of time on thecurrent gear. The effect of embodiments of the invention is explained further withreference to figs. 3-4.

Fig. 3 exemplifies a normal scenario during a gear changing operation. Fig. 3 showsthe combustion engine 101 rotational speed n as a function of time t. The figurefurther discloses the change in combustion engine speed n for two differentscenarios, the dash-dotted line 301 representing the change in combustion enginespeed n in a situation where the vehicle 100 loses vehicle speed, and hence lO lO combustion engine rotational speed n, relatively fast. This can be the case, forexample, when the vehicle 100 is being driven in a steep uphill section of a road, in particular when being heavily loaded.

The solid line 302 represents the change in combustion engine speed n for asituation where the vehicle 100 is being driven in a relatively less steep uphill sectionof road and/or being loaded to a lesser extent. The dashed line 303 represents the combustion engine speed limit nfim that is not to be exceeded following a change of gear to a lower gear (i.e. change of gear ratio to a higher gear ratio).

Starting from time to, in the situation being represented by dash-dotted line 301, thevehicle 100 is continuously losing speed (decelerating) and hence the rotationalspeed n of the combustion engine 101 is also continuously reducing.

At time t1 the combustion engine 101 speed n reaches a speed n representing change 1a time/speed where conditions for a change of gear to a lower gear (higher gearratio) are fulfilled. As was mentioned above, a condition for performing a change ofgear is often that the speed of the combustion engine following a completed change of gear is not allowed to exceed some speed limit nlim, which often is a calibrated maximum engine speed that is not to be exceeded. This maximum calibrated enginespeed nüm can, for example, be different for different gears and/or vehicle speeds. Asa consequence, a change of gear to a lower gear is, in general, performed when it isdetermined that the speed of the combustion engine on the new gear will not exceed said speed limit nmn. This has the result that, following the change of gear, the speed of the vehicle combustion engine is increased to a speed limit equal to or less than nüm at time t2.

Oftentimes, when changing gears, a further condition regarding the change of gear isalso utilized. This, too, is illustrated in fig. 3, where a further determination is madeprior to the actual change of gear. Specifically it is determined whether the vehicle100 is expected to be driven on the new (lower) gear at least for a time tx before afurther change of gear is initiated. That is, it is determined whether the vehicle isexpected to be driven on the new gear at least for the time tX until the speed n of the combustion engine 101 again reaches e.g. the speed nchang, at which a change of lO ll gear to a lower gear is again initiated. When this is the case, a change of gear isperformed to the intended gear, while otherwise a change of gear to an even lowergear may be evaluated instead.

According to the prior art, this change of gear is performed irrespective of the rathersubstantial differences in driving conditions that in reality may prevai| when a changeof gear is to be carried out. When the speed of the vehicle is dropping relatively fast,as is e.g. the case with the situation represented by dashed line 301, a change ofgear according to fig. 3 is often highly desirable in order to reduce the deceleration.The change of gear makes available higher drive wheel power, so that the vehicle will be losing speed more slowly, or even be capable to accelerate.

However, as is illustrated by solid line 302, the situation can also be different. ln thesituation being represented by solid line 302 the vehicle 100 is decelerating moreslowly, i.e. loses speed more slowly than in the situation represented by dashed line301. Still the vehicle 100 is subjected to the same combustion engine 101 speedcriteria regarding change of gear. Hence it will be determined at time t1 that a changeof gear is to be performed in this situation as well. A change of gear in a situation ofthis kind, however, may seem highly uncalled for, at least from a driver perspective.

According to embodiments of the invention, it is provided a method that distinguishesbetween situations of this kind through the use of the determination of a decelerationaccording to the above. This is illustrated in fig. 4, which shows a similar situation asin fig. 3, where the dash-dotted line 401 is similar to the dashed line 301 in fig. 3.With regard to the situation represented by dash-dotted line 401 it is determined instep 203 that the deceleration dec of the vehicle 100 determined in step 202 is above the limit decfim. Therefore, similar to the above, a change of gear is still performed attime ta in this case.With regard to the scenario represented by solid line 402 in fig. 4, on the other hand, the situation is different. ln this case, it is determined in step 203 that the deceleration dec of the vehicle is below said limit decfim. Therefore, even though the requirements for a change of gear in principle are fulfilled at time ti, the change of gear is notperformed but delayed. This is accomplished by lowering the maximum allowed lO 12 combustion engine speed nüm following a change of gear to a second speed limitnümjec, step 205. The speed limit nfimßc can be determined, for example, in dependence of the current deceleration of the vehicle 100. That is, the difference An between the speed limit nhm and the new limit unde, can be arranged to be different for different decelerations. Consequently, in the situation according to the solid line402, when the vehicle 100 reaches time t2, no change of gear is performed since thenew gear changing criteria are not fulfilled. lnstead, the vehicle 100 is allowed tocontinue on the current gear while the vehicle speed, and thereby combustion enginespeed n, continues to reduce. At time te, it is determined that the speed of thecombustion engine 101 following a change of gear to a lower gear will be below the second speed limit nfimfdec _ A change of gear is then performed at time t4. ln step 206 it is determined whether the new criteria for changing gear are fulfilled, and themethod can be arranged to remain instep 206 for as long as this is not the case oruntil the method of fig. 2 is aborted, e.g. due to a change of gear no longer beingrequired, and controlled by some other vehicle function. Otherwise a change of gearis performed in step 207 and the method can then return to step 201 waiting for anew request for change of gear.

Consequently, according to embodiments of the invention, the vehicle 100 is allowedto continue on a current gear for a longer period of time than otherwise is allowed.This means that the vehicle 100 in at least some situations may behave moreaccording to the expectations of the driver and not perform changes of gear e.g. in situations where this may not be necessary.

For example, the vehicle 100 may be only very slowly losing speed. According to theprior art a change of gear will still take place when the set criteria are fulfilled. Suchvehicle behaviour can be difficult to comprehend, in particular when the vehicledeceleration is so low that it may appear as if the vehicle 100 is travelling atessentially constant speed. The road may also e.g. be about to level out. A change ofgear to a lower gear in a situation of this kind may even seem contradictive to anexpected change of gear, since a change of gear to a higher gear may be more appropriate when the road levels out. lO 13 Furthermore, instead of, or in addition to, reducing the maximum allowed combustionengine speed following the change of gear, a further/other criterion can be set. Forexample, the criterion can instead be set such that the vehicle is forced to continue on a current gear until the speed n of the combustion engine 101 has reduced to a speed n see fig. 4, that is lower than the combustion engine speed n at change _ dec I change which change of gear normally is carried out.

According to embodiments of the invention, consequently, the occurrence ofundesired changes of gear can be reduced. Embodiments of the invention furtherhas the advantage that the vehicle may be perceived as being more powerful sincethe vehicle, on average, will be driven at lower combustion engine speeds. The reduction in average combustion engine speed also reduces fuel consumption.

There may exist, however, situations where it can be desired that this aspect of theinvention is not carried out. According to one embodiment of the present invention,therefore, a further criterion is applied in order to allow the reduction of the maximumallowed engine speed of the combustion engine. That is, the maximum allowed combustion engine speed is only reduced if this further criterion is fulfilled.

This further criterion can, for example, include a requirement that the total reductionin speed exhibited by the vehicle 100 since the reduction in speed began must notexceed some suitable speed difference. When a heavily loaded vehicle enters e.g. asteep hill and/or an uphill section of road of some length a change of gear withassociated required reduction in speed is often inevitable. This reduction in speedcan be substantial for a heavily loaded vehicle, at least in longer uphill sections ofroad. lt is, therefore, sometimes desirable, from a driver point of view, that the vehicleis being propelled using the maximum deliverable power from the combustion enginein order to reduce the loss in vehicle speed as much as possible.

Embodiments of the invention have the effect that the vehicle on average is propelledat lower combustion engine speeds, and hence at a lower average combustionengine power. Embodiments of the invention may therefore cause the vehicle tosuffer an additional reduction in speed that is not desired. lO 14 Consequently, there may exist situations where a delay of a change of gear to alower gear by a continued propelling of the vehicle on a current gear according to theabove is not desirable since this increases further an already substantial reduction inspeed when overtaking the uphill section of road. ln order to avoid such situations from occurring, therefore, according to oneembodiment of the invention, a determination is made of the total loss in speed thatthe vehicle has suffered since the loss in speed began. This can be determined, e.g.,by some suitable function in the vehicle control system. For example, vehicle speed,at least with regard to heavy vehicles, is, in general, logged throughout the journeyand hence available, both present value and past, on the vehicle communication bussystem. lt is also possible to use a dedicated function that monitors the vehicle speed andgenerates a signal, e.g. when the vehicle speed starts reducing, and/or when thevehicle speed has reduced to a suitable extent where the delayed change of gear should no longer be utilised.

According to one embodiment, it is also determined if the reduction in speedcorresponds to a corresponding increase driving resistance and not through the useof a vehicle braking system. Also this can be determined in any suitable manner as isknown per se and as oftentimes already is determined for use in various other existing vehicle functions. lt can be determined whether the vehicle speed has been reduced by some suitablespeed difference, such as e.g. a percentage of the vehicle speed prevailing when thereduction in speed began or some suitable number of km/h. Other criteria can also beused. lf the vehicle speed has been reduced to such an extent that a furtherreduction in speed is not desirable, the use of the delayed change of gear accordingto the above can be prohibited.

Above, embodiments of the invention have been described where the deceleration isused to lower e.g. the maximum allowed rotational speed of a power source followinga change of gear. According to embodiments of the invention, e.g. the maximumallowed rotational speed can also be increased on the basis of the deceleration. For example, in correspondence to the above, the calibrated maximum allowed rotational lO speed of the power source can be increased when the deceleration exceeds somepredetermined value, which can be the same or higher than the deceleration at whichthe maximum allowed rotational speed is lowered. Also the increase can bedependent on the magnitude of the deceleration. Consequently, a maximum allowedrotational speed that has already been lowered can be increased when the deceleration increases, and vice versa.

Furthermore, embodiments of the invention can be used in combination with thesolution described in the parallel Swedish patent application having the same filingdate as the present application, the same inventor and the title “METHOD ANDSYSTEM FOR CONTROLLING SELECTION OF GEAR RATIO IN A VEHICLE”.

This parallel application relates to a method and system where undesired losses invehicle speed due to the driving resistance exceeding the available propelling powercan be reduced. This is accomplished by means of a method where, when it isdetermined that the vehicle e.g. has lost speed to some extent, caused by the drivingresistance exceeding the propelling force, the dependency of the rotational speed ofthe vehicle power source when selecting gear is controlled on the basis of the loss inspeed of the vehicle.

For example, the rotational speed of the power source at which a change of gear iscarried out, and/or the resulting rotational speed of the power source following thechange of gear, can be increased irrespective of whether the deceleration is low. Thisallows the vehicle to be propelled at higher rotational speeds of the power source,and thereby higher power to reduce the deceleration and continued loss in vehiclespeed. The increase in allowed rotational speed of the power source can bearranged to depend on the reduction in speed that the vehicle has suffered, and alsoon the deceleration of the vehicle. Consequently, the higher the loss in speed, thehigher rotational speeds of the power source may be allowed.

Embodiments of the invention can be used in combination with the solution describedin the parallel application, so that the allowed power source rotational speeds whenchanging gear can be adapted according to current conditions. For example, controlcan e.g. be performed according to the present application for as long as the loss in vehicle speed does not exceed some suitable speed difference. When the vehicle lO 16 has lost too much in speed, the vehicle can, instead be controlled according to thesolution described in the parallel application to reduce negative impact of loss in speed.

According to the combined solution, the vehicle can be propelled at lower combustionengine speeds, and hence at a lower average combustion engine power, whenpossible, but where it may be ensured that the vehicle does not lose too much speed.Further according to the combined solution, e.g. the maximum allowed rotationalspeed may be arranged to increase and decrease according to the current drivingconditions, so that the vehicle behaviour can be adapted to prevailing conditions.

Finally, embodiments of the invention have been exemplified above for a particularexample of a vehicle, but is applicable for any vehicle in which the vehicle controlsystem controls gear change. The invention also encompasses a vehicle comprising a system implementing the invention.

Claims (1)

1. lO 17 Claims 1. Method for selecting gear ratio in a gearbox (103) of a vehicle (100), saidgearbox (103) being arranged for transmitting power from a power source(101) to at least one drive wheel (113, 114) of said vehicle (100), said gearbox(103) comprising a plurality of selectable gear ratios, a change of gear ratiobeing controlled by a vehicle control system, said change of gear beingdependent on a rotational speed (n) of said power source (101), the methodbeing characterised in, when to change from a first gear ratio to a secondgear ratio, said second gear ratio being higher than said first gear ratio: - determining a deceleration (dec) of said vehicle (100), and - controlling the dependency of the rotational speed (n) of said power source(101) when selecting gear ratio at least partly on the basis of said determined deceleration (dec ). l\/lethod according to claim 1, further including:- in dependence of said determined deceleration (dec ), controlling a maximumallowed rotational speed (nümñdec) of said power source (101) following said change of gear ratio in relation to a predetermined maximum allowed rotational speed. l\/lethod according to claim 1 or 2, further including:- in dependence of said determined deceleration (dec ), reducing themaximum allowed rotational speed (nümßc) of said power source (101) following said change of gear ratio in relation to a predetermined maximum allowed rotational speed. l\/lethod according to claim 2 or 3, further including: - controlling the maximum allowed rotational speed (nfimjec) of said powersource (101) following said change of gear ratio in relation to a predeterminedmaximum allowed rotational speed such that the maximum allowed rotational speed (nümídec) is reduced compared to said predetermined maximum allowed rotational speed to a first rotational speed for a first deceleration and a second rotational speed for a second deceleration, said first rotational speed being lO 18 lower than said second rotational speed when said first deceleration is lower than said second deceleration. _ Method according to any one of the preceding claims, further including: - on the basis of said determined deceleration (dec ), determining a maximumallowed rotational speed (nümjec) of said power source (101), to be caused ifsaid second gear ratio is engaged, and - initiating said change of gear ratio only when the rotational speed of saidpower source (101) will be below said maximum allowed rotational speed (nfimídgc) upon engagement of said second gear ratio. _ l\/lethod according to any one of the preceding claims, further including: - initiating a change of gear from said first gear ratio to said second gear ratiowhen the rotational speed (n) of said first power source (101) when said firstgear ratio is engaged falls to a minimum rotational speed limit (nChange/dec ), said minimum rotational speed limit (nchangeídec) being determined in relation to a predetermined minimum rotational speed limit at least partially on the basis of said determined deceleration (dec )_ _ l\/lethod according to claim 6, further including: - controlling said minimum rotational speed limit (n such that said change _ dec ) minimum rotational speed limit (nchangeídec) is reduced compared to said predetermined minimum rotational speed limit to a third rotational speed for afirst deceleration and a fourth rotational speed for a second deceleration, saidthird rotational speed being lower than said fourth rotational speed when saidfirst deceleration is lower than said second deceleration. _ l\/lethod according to any one of the preceding claims, further including: - controlling the dependency of the rotational speed of said power source(101) when selecting gear ratio at least partly on the basis of said determineddeceleration (dec) only when said determined deceleration (dec) is below a first deceleration limit (declim). lO 9. 19 Method according to any one of the preceding claims, further including, prior tosaid selection of gear ratio: - determining a first vehicle speed at which a deceleration of said vehiclebegins, and - initiating said change of gear ratio to said second gear ratio only when thedifference in speed of said vehicle (100) in relation to said first vehicle speed isbelow a first speed difference.

   10. l\/lethod according to any one of the preceding claims, further including: 11. - determining whether said determined deceleration (dec) of said vehicle iscaused by an increase in driving resistance, and - controlling the dependency of the rotational speed of said power source(101) when selecting gear ratio at least partly on the basis of said determineddeceleration (dec) only when said determined deceleration (dec) of said vehicle (100) is caused by an increase in driving resistance. l\/lethod according to any one of the preceding claims, further including: - controlling the maximum allowed rotational speed (nfimjec) of said powersource (101) to follow said change of gear ratio in relation to a predeterminedmaximum allowed rotational speed such that the maximum allowed rotational speed (nümídec) is reduced compared to said predetermined maximum allowedrotational speed when said determined deceleration (dec) is below a firstdeceleration, and such that the maximum allowed rotational speed (nümßc) is increased compared to said predetermined maximum allowed rotational speedwhen said determined deceleration (dec) is above a second deceleration, the second deceleration being higher than the first deceleration.

   12. Computer program comprising program code that, when said program code is executed in a computer, enables said computer to carry out the methodaccording to any one of the preceding claims 1-11.

   13. Computer program product comprising a computer-readable medium and a computer program according to claim 12, wherein said computer program iscontained in said computer-readable medium.

   14. System for selecting gear ratio in a gearbox (103) of a vehicle (100), saidgearbox (103) being arranged for transmitting power from a power source(101) to at least one drive wheel (113, 114) of said vehicle (100), said gearbox(103) comprising a plurality of selectable gear ratios, a change of gear ratiobeing controlled by a vehicle control system, said change of gear beingdependent on a rotational speed of said power source (101), the system beingcharacterised in that the system includes means for, when to change from afirst gear ratio to a second gear ratio, said second gear ratio being higher thansaid first gear ratio: - determining a deceleration (dec) of said vehicle (100), and- controlling the dependency of the rotational speed of said power source(101) when selecting gear ratio at least partly on the basis of said determined deceleration (dec ). 15.Vehicle, characterised in that it comprises a system according to claim 14.