WO2007001230A1

WO2007001230A1 - A method and an apparatus for controlling an engine

Info

Publication number: WO2007001230A1
Application number: PCT/SE2006/050200
Authority: WO
Inventors: Mårten DAHLBÄCK
Original assignee: Scania Cv Ab (Publ)
Priority date: 2005-06-28
Filing date: 2006-06-16
Publication date: 2007-01-04
Also published as: SE528564C2; SE0501508L

Abstract

A apparatus for controlling the output torque of an engine (13) in a drive train of a motor vehicle having a transmission (9) coupled to the engine and having a plurality of engeageable gear ratios comprises a control unit (16) for controlling the fuelling of the engine and a device (17) adapted to determine a maximum engine output torque not to be exceeded through the control of the control unit while considering torques resulting from such a control upon components of said driver train. The device is adapted to calculate a maximum limit transmission output torque from the so called slip torque of the vehicle, and the control unit is adapted to control the fuelling of the engine so as to delimit the engine output torque to a value resulting in a transmission output torque below said maximum limit transmission output torque.

Description

A method and an apparatus for controlling an engine

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

[0001] The present invention relates to an apparatus for controlling the output torque of an engine in a drive train of a motor vehicle, said drive train comprising a transmission coupled to the engine and having a plurality of engageable gear ratios, said apparatus comprising a control unit for controlling the fuelling of said engine and a device adapted to determine a maximum engine output torque not to be exceeded through the control of the control unit while considering torques resulting from such a control upon components of said drive train, as well as a method according to the preamble of the appended independent method claim.

[0002] The invention is not restricted to any particular type of motor vehicle, but it is applicable to all types of motor vehicles rolling on wheels and especially, but accordingly not exclusively, directed to vehicles carrying heavy loads, such as busses or lorries. The invention will for this sake hereinafter be particularly discussed for such vehicles without limiting the invention thereto.

[0003] Said components of the drive train between the transmission and the wheels are dimensioned on the basis of a maximum torque to which they may be exerted during normal operation of the vehicle. Thus, an apparatus of the type defined in the introduction is used for ensuring that the engine output torque will never result in a torque which may be harmful to any of said components. The transmission and said components are normally dimensioned while considering the so called slip torque of the vehicle, i.e. the maximum torque applicable to the wheels of the vehicle before they start to slip on a certain ground resulting in a maximum friction coefficient, for a certain tyre dimension, for a maximum axle or bogie load pressure and for the highest transmission ratio of said transmission. During normal operation of the vehicle there is therefore no risk of overloading said components, since the torque applied to the wheels will never exceed said slip torque. However, the vehicle may by mistake or deliberately be overloaded or the wheels may get stuck, so that the wheels will not start to slip at a torque corresponding to said slip torque any longer, which makes it important to be able to control the engine output torque so as to protect said components against being damaged.

[0004] An apparatus according to the introduction is known through US

6 511 399, which calculates different engine torque limits while using different limit parameters in the drive train after the motor, and the lowest of these limits are determined to be the engine output torque for a certain speed of a vehicle.

[0005] US 5 738 606 describes an apparatus ensuring a restriction of the engine output torque to a maximum torque allowed in the transmission for exactly the gear ratio presently engaged. The maximum engine output torque allowed so as to consider the torque limit for the drive shaft further downstream in the drive train is also determined. The lowest of the two engine output torque limits is determined as the engine output torque limit not to be exceeded when controlling the fuelling of the engine.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide an apparatus and a method of the type defined in the introduction, which in a simple and reliable way ensures that said components of said drive train may never be overloaded.

[0007] This object is according to the invention obtained by providing such an apparatus with the further characteristics: said device is adapted to calculate a maximum limit transmission output torque from the so called slip torque of the vehicle, i.e. the maximum torque applicable to the wheels of the vehicle before they start to slip on a certain ground resulting in a maximum friction coefficient, for a certain tyre dimension, for a maximum axle or bogie load pressure and for the highest transmission ratio of said transmission, and the control unit is adapted to control the fuelling of the engine so as to delimit the engine output torque to a value resulting in a transmission output torque below said maximum limit transmission output torque. A corresponding method is defined in the appended independent method claim. [0008] Accordingly, the same maximum limit transmission output torque is set for all possible gear ratios of the transmission, so that it is in a very simple way ensured that the torque on any component in the drive train after said transmission may not be too high. This means that the engine output torque has only to be limited when there is a risk of exceeding said maximum limit transmission output torque on the transmission output.

[0009] Furthermore, by calculating said maximum limit transmission output torque from the so called slip torque of the vehicle and controlling the fuelling of the engine so that the engine output torque will not result in a transmission output torque exceeding said maximum limit transmission output torque, it may be guaranteed that torques harmful to said component may not occur. It is pointed out that the invention is based on the idea on using the so called slip torque of the vehicle when calculating said maximum limit transmission output torque, but it is not necessary to determine said maximum limit transmission output torque to be the transmission output torque resulting when said slip torque is applied on the wheels of the vehicle, but the transmission output torque so determined may be multiplied with a factor, such as for example 0.7, when determining said maximum limit transmission output torque. This factor is normally not higher than 1 , so that a transmission output torque exceeding the transmission output torque corresponding to the slip torque applied on the wheels may not be exceeded. This means that the fuelling of the engine is controlled so that the engine output torque may not result in a transmission output torque being harmful to said components even if the vehicle is overloaded or the wheels thereof get stuck and the slip torque is not valid any longer.

[0010] Said maximum limit transmission output torque is preferably determined when the vehicle is manufactured and the maximum engine output torques for each possible gear ratio may then be determined, i.e. it is determined how much fuel per time unit may be injected into the engine for each such gear ratio.

[0011] According to an embodiment of the present invention said device comprises means adapted to check whether information about the gear ratio presently engaged is available, and said device is adapted to use the result of said checking for determining the maximum engine output torque which is allowed to result from the control of the engine. Such checking is made with the aim of avoiding that the engine output torque is limited when there is no need to do that. Should such checking for instance result in information saying that the gear ratio presently engaged may not result in a transmission output torque exceeding said maximum limit transmission output torque for any engine output torque the fuelling of the engine may then take place without any limitations.

[0012] According to a further embodiment of the invention said device is adapted to determine that the control unit shall control said fuelling of the engine without any limitation in case that the checking indicates that there is a gear ratio presently engaged making it impossible to obtain a transmission output torque exceeding said maximum limit transmission output torque resulting in no unnecessary limitation of the engine output torque under such circumstances.

[0013] According to another embodiment of the invention said control unit is adapted to control the fuelling of the engine according to an individual limit of the engine output torque set for each gear ratio in case said checking results in a knowledge of the gear ratio presently engaged for all possible gear ratios of the transmission. This means that the fuelling of the engine is never limited more than necessary by having different limits of the engine output torque for each individual gear ratio by having a maximum limit transmission output torque in common to all gear ratios. Furthermore, no such limit will be set for the gear ratios with any possibility to result in a transmission output torque exceeding said maximum limit transmission output torque.

[0014] According to another embodiment of the invention the control unit is adapted to control the fuelling of engine according to the highest possible transmission ratio determined out of the information available with the limit for the engine output torque set by this transmission ratio in case said checking results in information not containing any exact indication of the gear ratio presently engaged, so that said maximum limit transmission output torque will not be exceeded. This ensures that said maximum limit transmission output torque will never be exceeded in spite of any exact information about the gear ratio presently engaged.

[0015] According to another embodiment of the invention constituting a further development of the embodiment last mentioned, said device is adapted to determine said highest possible transmission ratio to be the highest transmission ratio the gear ratios belonging to a group of gear ratios in case a checking results in information revealing that the gear ratio presently engaged belongs to a certain group of gear ratios and the control unit is adapted to control the fuelling of the engine according to that. This means that information about which group of gear ratios a gear ratio engaged belongs to is used to ensure that said maximum limit transmission output torque is not exceeded and that the engine output torque is not unnecessarily restricted should said group of gear ratios not be the group of gear ratios including the gear ratio with the highest transmission ratio of all the gear ratios.

[0016] In another embodiment of the invention said control unit is adapted to control the fuelling of the engine without setting any limit to the engine output torque in case said checking results in information stating that a gear ratio is presently engaged, which belongs to a group of gear ratios with a lower transmission ratio comparing to other groups of gear ratios of said transmission and having the highest possible transmission ratio below a predetermined transmission ratio. Thus, when it is determined that said maximum limit transmission output torque may not be exceeded irrespectively of the magnitude of the engine output torque no limit is set thereto.

[0017] According to another embodiment of the invention said apparatus is adapted to be arranged in a vehicle having a transmission with a possibility to select a high range or a low range of gear ratios. Information about to which of these ranges a gear range presently engaged belongs may then be used to set the limit to the engine output torque, and when said checking results in information stating that a gear ratio presently engaged belongs to said higher range such a limit may be omitted.

[0018] According to another embodiment of the invention said apparatus is adapted to be arranged in a vehicle having a transmission including a so called split position selector enabling selection of at least two different gear ratios for a gear engaged, said two different gear ratios being with respect to the transmission ratio located between the transmission ratios of the two gears next to the gear in question, and said device is adapted to consider information about the position of said split position selector when determining said highest possible transmission ratio for determining the upper limit for the engine output torque resulting from the control of the fuelling of the engine by said control unit. Information about said split position is another way of optimising the determination of the upper limit of the engine output torque when the exact gear ratio engaged is unknown.

[0019] According to another embodiment of the invention the apparatus comprises measuring means for measuring the speed of the vehicle, and said device comprises means adapted to compare the speed measured with a speed limit value and if the speed value measured is above this speed limit value make the control unit to control the fuelling of the engine without any limitation set to the engine output torque. It is impossible that the transmission output torque may exceed said maximum limit transmission output torque when the speed of the vehicle is above a certain value, so that there is no need to limit the fuelling of the engine in such a case.

[0020] Embodiments of the method according to the present invention are defined in the appended dependent method claims, and the features and advantages thereof appear from the above discussion of corresponding embodiments of the apparatus according to the invention.

[0021] The invention also relates to use of an apparatus according to the invention for controlling the output torque of an engine in a motor vehicle, for example in a bus or lorry.

[0022] The invention also relates to a computer program and a computer readable medium according to the corresponding appended claims. It is easy to understand that the method according to the invention defined in the appended method claims is well suited to be carried out through program instructions from a processor, which may be influenced by a computer program provided with the program steps in question. [0023] Further advantages as well as advantageous features of the invention will appear from the following description and the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] With reference to the appended drawings, below follows a specific description of an apparatus and a method according to the present invention cited as an example.

[0025] In the drawings:

Fig. 1 is a very schematic view illustrating a motor vehicle in the form of a lorry being heavily loaded and which has got stuck, this Fig. being used for illustrating the problem to be solved by the present invention,

Fig. 2 is a very schematic view illustrating a conventional gear shift lever in a motor vehicle of the bus or lorry type, Fig. 3 is a simplified block diagram illustrating an apparatus and a method according to an embodiment of the present invention, and Fig. 4 is a graph of the transmission output torque versus the engine output torque for different gear ratios of the transmission in a motor vehicle to which the apparatus and the method according to the present invention are applied, this graph being used for explaining the basic idea of the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE PRESENT

INVENTION

[0026] A heavily loaded lorry 1 , which gets stuck while digging into the ground through the rear wheels 2 when trying to go backwards, is schematically illustrated in Fig. 1. This means that the friction coefficient may be much higher than 1 , and if the fuelling of the engine is carried out without no limitation, so that the engine output torque for instance will be close to the maximum for this considerably high transmission ratio of the transmission the transmission output torque would be that high that components of the drive train located between the transmission and the wheels 2 may be harmed.

[0027] An apparatus according to the present invention is therefore arranged in said vehicle for delimiting the engine output torque to not exceed a maximum engine output torque while considering torques resulting therefrom upon components of said drive train. The risk of harming said components is the higher the higher the transmission ratio of a gear ratio engaged in said transmission of the vehicle is, so that it would favourable to be able to obtain an individual limitation of the engine output torque for different gear ratios. However, which one of them is presently engaged has for that sake to be known.

[0028] The different gear ratios normally engageable in a vehicle of the lorry or bus type will now be explained while making reference to Fig. 2 and 3. A gear shift lever 3 as it may look like in for example a lorry for changing the gear ratio in the gear box is illustrated in Fig. 2. This gear shift lever 3 has three different members for selecting a gear ratio of the gear box. These three members are acting upon gear elements connected in series in the gear box. One of these members is the very lever 3, through the movement of which in the direction of the arrow A for example three different gear ratios 1 , 3 and 5 may be selected. The lever has another member 4 in the form of a switch used for selecting two discrete gear positions of a so called split position selector. One of these gear positions is called low and means that the gear ratio selected by the lever 3 is valid, while the other position is called high and defines a gear ratio located one step higher in the direction of a decreased transmission ratio than the gear ratio indicated by the lever, but one step lower than the lever gear ratio which in the direction of a decreased transmission ratio follows upon the lever gear ratio selected. This means that when the switch is in the position last mentioned the gear ratios 2, 4 and 6 are obtained.

[0029] The third member for selecting the gear ratio is a selector member in the form of a member 5 displaceable according to the arrow B, which means a transfer of the gear box transmission between two different states through a so called range gear. The gear ratios 1-6 may in one of these states be selected by means of the lever 3 and the switch 4, while in the other state of the range gear the gear ratios 7-12 may be selected by means of the lever 3 and the split selector switch 4. This is conventional technique and the three selectors connected in series may for example have the following selectable factors, which shall be multiplied for obtaining the total transmission ratio of the gear box: the split selector: 1 and 1.233, the conventional gear (the lever): 1 , 1.549 and 2.461 , the range gear: 1 and 3.750. [0030] The lower the factor the higher the gear. Accordingly, the transmission ratio of the gear box for the highest gear, namely the gear 12, is defined to be 1. The twelve gears will in this case have the following relationship between the number of revolutions of the input shaft and the output shaft of the gear box:

1 : 11.379

2: 9.227

3: 7.166

4: 5.811

5: 4.625

6: 3.750

7: 3.034

8: 2.461

9: 1.911

10: 1.549

11 : 1.233

12: 1.000 [0031] There are normally some further possible gears of a gear box of this type, and in the present case there are four such gears, namely one high and one low reverse gear as well as one high and one low so called creep gear obtainable through a creep gear selector not shown and having a transmission ratio being even higher than the transmission ratio of gear 1. [0032] An apparatus used to control the output torque of an engine in a drive train of a motor vehicle of this type is illustrated in Fig. 3. It is illustrated how a split gear 6, a conventional gear 7 and a range gear 8 according to above are connected in series in an engine gear box 9 between the input shaft 10 and the output shaft 11 of the gear box. These are controlled by the switch

4, the lever 3 and a range gear ring 5 summarised by the box 12. An engine is schematically indicated by 13. The output shaft of the engine is directly or indirectly, usually indirectly through a fixed reduction of the number of revolutions, connected through a shaft 14 to a clutch 15 adapted to transmit the torque of the engine to the input shaft 10 of the gear box. Furthermore, a control unit for controlling the fuelling of said engine is indicated by 16.

[0033] Information about the gear ratio presently engaged may be sent from the box summarising gear shift lever, switch and range gear ring to a device 17 adapted to determine a maximum engine output torque not to be exceeded through a control of the control unit 16 while considering said information about the gear ratio presently engaged and the torques which may result from such a control upon components of said drive train.

[0034] The device 17 is in fact adapted to ensure that the transmission output torque, i.e. the torque on the transmission output shaft 11 , never exceeds a maximum limit transmission output torque. The device 17 is adapted to calculate this maximum limit transmission output torque from the so called slip torque of the vehicle, i.e. the maximum torque applicable to the wheels of the vehicle before they start to slip on a certain ground resulting in a maximum friction coefficient, for a certain tyre dimension for a maximum axle or bogie load pressure and for the highest transmission ratio of said transmission. This does not mean that said maximum limit transmission output torque is said to be identical to the transmission output torque which will result when the so called slip torque is applied on the wheels of the vehicle, although that could be suitable. It may just as well be decided to set said maximum limit transmission output torque to be for instance 70% or 50% of the transmission output torque that would result if the slip torque were applied on the wheels. Accordingly, the same value for the maximum limit transmission output torque is used for the control through the control unit irrespectively of which gear ratio is in fact engaged. This means that the control unit 16 is adapted to control the fuelling of the engine so as to delimit the engine output torque to a value resulting in a transmission output torque below said maximum limit transmission output torque. [0035] As already mentioned, the fuelling limit for each possible gear ratio of the transmission may have been determined in the production plant of the motor vehicle and may then be provided in a memory unit 18 providing said device 17 with information thereabout. It is also illustrated that the device 17 has a micro computer with a computer program 19 adapted to control the functions of the device.

[0036] It is illustrated in Fig. 4 how the transmission output torque TT is dependent upon the engine output torque TE. Furthermore, the maximum limit transmission output torque calculated by said device (possibly already in the production plant of the motor vehicle) is indicated by the dashed line M. It appears that this transmission output torque will never be obtained irrespectively of the magnitude of the engine output torque for most of the gear ratios, as for the high range gear ratios 7-12 indicated by H. Accordingly, would the gear ratio presently engaged always be known the fuelling of the engine could for most of the gear ratios be controlled without any limitation, and for the other gear ratios different limits may be put on the engine output torque for not limiting it unnecessary. Would at the contrary never any information about the gear ratio presently engaged be there, it would be necessary to always assume that the gear ratio with the highest transmission ratio of the transmission is engaged and never let the engine output torque exceed the value indicated by the vertical line L. This would then for nearly all the gear ratios result in a much lower upper limit of the engine output torque than would in fact be acceptable, so that there is of course a desire to avoid such unnecessary restrictions of the control of the fuelling of the engine.

[0037] It is for this sake checked by the member 12 whether information about the gear ratio presently engaged is available or not, so that the device 17 may use the result of this checking for determining the maximum engine output torque which is allowed to result from the control of the engine. It is then possible that no information about the exact gear ratio engaged, but still some information about the gear ratio engaged is available, such as to which group of gear ratios this belong. This information may then be used for not unnecessary delimiting the control of the engine with respect to the engine output torque.

[0038] The device is then adapted to determine that the highest possible transmission ratio is the highest transmission ratio of the gear ratios belonging to a group of gear ratios in case a checking results in information revealing that the gear ratio presently engaged belongs to a certain group of gear ratios, such as for instance the low range gear ratio group or the high range gear ratio group. In the case of the gear ratio presently engaged belonging to said high range gear ratio group, the device 17 may send signals to the control unit 16 to control the fuelling of the engine without any limitations.

[0039] It is also possible that the device 17 is provided with information about the position of said split position selector 4, so that the highest possible transmission ratio may be determined while considering this information. It is of course also possible that no information about the exact gear ratio presently engaged is available, but both the position of the split position selector and that of the range gear ring are known and may be considered for determining the highest possible transmission ratio of the gear ratio engaged for determining the upper limit for the engine output torque resulting from the control of the fuelling of the engine by the control unit 16. There are also sometimes sensors indicating that a particular gear ratio is engaged, which is often the case for the gears 5 and 6 indicated in the table above. Information from these sensors is then used for setting an upper limit to the engine output torque.

[0040] Another parameter to be used for avoiding unnecessary limitations of the control of the engine when there is no information available about the exact gear ratio engaged is the speed of the vehicle. It is shown in Fig. 3 that the apparatus may comprise measuring means 20 adapted to measure the speed of the vehicle by measuring the number of revolutions of the output shaft 11 of the gear box 9. Information about the speed of the vehicle is sent to the device 17 having means adapted to compare the speed measured with a speed limit value and if the speed value measured is above this speed limit value make the control unit to control the fuelling of the engine without any limitation set to the engine output torque. Thus, if the speed for example exceeds 60 km per hour, it may be decided that a gear ratio is presently engaged which do not require any limitation put on the engine output torque, since the transmission output torque may never exceed said maximum limit transmission output torque.

[0041] Thus, the same maximum limit transmission output torque is applied for all gear ratios of the transmission, so that individual limits may be put on the engine output torque when information about the gear ratio presently engaged is available, and this maximum limit transmission output torque is determined by using the so called slip torque of the vehicle ensuring that the components in the drive train between the transmission and the wheels of the vehicle may not be harmed.

[0042] The invention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.

[0043] There may for instance be different speed limit values resulting in different highest possible gear ratios engaged and being compared with the actual speed for being used for controlling the fuelling of the engine.

Claims

1. 1. A method for controlling the output torque of an engine (13) in a drive train of a motor vehicle, said drive train comprising a transmission (9) coupled to the engine and having a plurality of engageable gear ratios, in which the engine output torque is limited to not exceed a maximum engine output torque while considering torques resulting therefrom upon components of said drive train, characterized in that a maximum limit transmission output torque calculated from the so called slip torque of the vehicle, i.e. the maximum torque applicable to the wheels of the vehicle before they start to slip on a certain ground resulting in a maximum friction coefficient, for a certain tyre dimension, for a maximum axle or bogie load pressure and for the highest transmission ratio of said transmission, is used for controlling the engine to delimit the engine output torque to a value resulting in a transmission output torque below said maximum limit transmission output torque.

2. A method according to claim 1 , characterized in that it comprises the steps of:

- checking whether information about the gear ratio presently engaged is available, and

- using the result of said checking for determining the maximum engine output torque which is allowed to result from the control of the engine.

3. A method according to claim 2, characterized in that in the case that said information resulting from said checking indicates that there is a gear ratio presently engaged making it impossible to obtain a transmission output torque exceeding said maximum limit transmission output torque no limitation is set to the engine output torque when controlling the engine.

4. A method according to claim 2 or 3, characterized in that in case said checking results in a knowledge of the gear ratio presently engaged for all possible gear ratios of the transmission the engine is controlled according to an individual limit of the engine output torque set for each gear ratio.

5. A method according to claim 2 or 3, characterized in that in case the information resulting from said checking does not contain any exact indication of the gear ratio presently engaged the engine is controlled according to the highest possible transmission ratio determined out of the information available with the limit for the engine output torque set by this transmission ratio, so that said maximum limit transmission output torque will not be exceeded.

6. A method according to claim 5, characterized in that in case said checking results in information revealing that the gear ratio presently engaged belongs to a certain group of gear ratios said highest possible transmission ratio is determined to be the highest transmission ratio of the gear ratios belonging to said group.

7. A method according to claim 6, characterized in that in case said checking results in information stating that a gear ratio belonging to a group of gear ratios with a low transmission ratio comparing to other groups of gear ratios of said transmission and having a highest possible transmission ratio below a predetermined transmission ratio is presently engaged the engine is controlled without setting any limit to the engine output torque.

8. A method according to any of the preceding claims, characterized in that it is carried out for a vehicle having a transmission (9) with a possibility to select a high range or a low range of gear ratios.

9. A method according to claims 7 and 8, characterized in that when said checking results in information stating that a gear ratio presently engaged belong to said high range the engine is controlled without setting any limit to the engine output torque.

10. A method according to claim 5, characterized in that it is carried out for a vehicle having a transmission including a so-called split position selector (4) enabling selection of at least two different gear ratios for a gear engaged, said two different gear ratios being with respect to the transmission ratio located between the transmission ratios of the two gears next to the gear in question, and that information about the position of said split position selector is considered when determining said highest possible transmission ratio for determining the upper limit for the engine output torque when controlling the engine.

11. A method according to claim 5, characterized in that it comprises the step of measuring the speed of the vehicle, and that the speed measured is compared with a speed limit value and if the speed value measured is above this speed limit value the engine is controlled without any limitation set to the engine output torque.

12. An apparatus for controlling the output torque of an engine (13) in a drive train of a motor vehicle, said drive train comprising a transmission (9) coupled to the engine and having a plurality of engeagable gear ratios, said apparatus comprising a control unit (16) for controlling the fuelling of said engine and a device (17) adapted to determine a maximum engine output torque not to be exceeded through the control of the control unit while considering torques resulting from such a control upon components of said drive train, characterized in that said device (17) is adapted to calculate a maximum limit transmission output torque from the so-called slip torque of the vehicle, i.e. the maximum torque applicable to the wheels of the vehicle before they start to slip on a certain ground resulting in a maximum friction coefficient, for a certain tyre dimension, for a maximum axle or bogie load pressure and for the highest transmission ratio of said transmission, and that the control unit (16) is adapted to control the fuelling of the engine so as to delimit the engine output torque to a value resulting in a transmission output torque below said maximum limit transmission output torque.

13. An apparatus according to claim 12, characterized in that it comprises means (12) adapted to check whether information about the gear ratio presently engaged is available, and that said device (17) is adapted to use the result of said checking for determining the maximum engine output torque which is allowed to result from the control of the engine (13).

14. An apparatus according to claim 13, characterized in that said device (17) is adapted to determine that the control unit (16) shall control said fuelling of the engine without any limitation in case that the checking indicates that there is a gear ratio presently engaged making it impossible to obtain a transmission output torque exceeding said maximum limit transmission output torque.

15. An apparatus according to claim 13 or 14, characterized in that said control unit (16) is adapted to control the fuelling of the engine according to an individual limit of the engine (13) output torque set for each gear ratio in case said checking results in a knowledge of the gear ratio presently engaged for all possible gear ratios of the transmission.

16. An apparatus according to claim 13 or 14, characterized in that the control unit (16) is adapted to control the fuelling of the engine (13) according to the highest possible transmission ratio determined out of the information available with the limit for the engine output torque set by this transmission ratio in case said checking results in information not containing any exact indication of the gear ratio presently engaged, so that said maximum limit transmission output torque will not be exceeded.

17. An apparatus according to claim 16, characterized in that said device (17) is adapted to determine said highest possible transmission ratio to be the highest transmission ratio of the gear ratios belonging to a group of gear ratios in case a checking results in information revealing that the gear ratio presently engaged belongs to a certain group of gear ratios and the control unit (16) is adapted to control the fuelling of the engine (13) according to that.

18. An apparatus according to claim 17, characterized in that the control unit (16) is adapted to control the fuelling of the engine (13) without setting any limit to the engine output torque in case said checking results in information stating that a gear ratio belonging to a group of gear ratios with a low transmission ratio comparing to other groups of gear ratios of said transmission and having the highest possible transmission ratio below a predetermined transmission ratio is presently engaged.

19. An apparatus according to any of claims 12-18, characterized in that it is adapted to be arranged in a vehicle having a transmission (9) with a possibility to select a high range or a low range of gear ratios.

20. An apparatus according to claim 19, characterized in that said control unit (16) is adapted to control the fuelling of the engine (13) without setting any limit to the engine output torque when said checking results in information stating that a gear ratio presently engaged belongs to said high range.

21. An apparatus according to claim 16, characterized in that it is adapted to be arranged in a vehicle having a transmission (9) including a so-called split position selector (4) enabling selection of at least two different gear ratios for a gear engaged, said two different gear ratios being with respect to the transmission ratio located between the transmission ratios of the two gears next to the gear in question, and that said device (17 ) is adapted to consider information about the position of said split position selector when determining said highest possible transmission ratio for determining the upper limit for the engine output torque resulting from the control of the fuelling of the engine (13) by said control unit (16).

22. An apparatus according to claim 16, characterized in that it comprises measuring means (20) for measuring the speed of the vehicle, and that said device (17) comprises means adapted to compare the speed measured with a speed limit value and if the speed value measured is above this speed limit value make the control unit (16) to control the fuelling of the engine (13) without any limitation set to the engine output torque.

23. Use of an apparatus according to any of claims 12-22 for controlling the output torque of an engine in a motor vehicle, for example in a bus or lorry.

24. A computer program directly loadable into the internal memory of a computer, which comprises software code portions for controlling the steps of the method according to any one of claims 1-11 when said program is run on the computer.

25. A computer readable medium having a program recorded thereon adapted to make a computer control the steps of the method according to any one of claims 1-11.