WO2008026993A1

WO2008026993A1 - A method for shifting gear in a gear-by-wire system in a vehicle, a vehicle equipped with a clutch, a computer program adapted for shifting gear in a gear-by-wire system in a vehicle and an electronic control unit

Info

Publication number: WO2008026993A1
Application number: PCT/SE2007/050562
Authority: WO
Inventors: Mikael Hanson; Samuel WICKSTRÖM
Original assignee: Scania Cv Ab (Publ)
Priority date: 2006-09-01
Filing date: 2007-08-21
Publication date: 2008-03-06
Also published as: BRPI0714851A2; DE112007002059T5; DE112007002059B4; BRPI0714851B1; SE0601805L; SE530294C2

Abstract

A method for shifting gear in a gear-by-wire system in a vehicle (1), comprising the steps of: determining if a reliable gear signal is obtainable from a gear shifting means (7), changing from a first mode for gear shifting in which a gear shift is initiated by manually actuating a clutch controlling means (21) and indicating a desired gear through the gear shifting means to a second mode for gear shifting if a reliable gear signal cannot be obtained, obtaining an appropriate gear in the second mode, and shifting to the appropriate gear if the clutch controlling means in the second mode is manually influenced and the appropriate gear is different from a currently engaged gear. A computer program (20), a computer program product (19), a vehicle and an electronic control unit for performing the method are also disclosed.

Description

A met o or s t ng gear n a gear- y-w re sys em n a vehicle, a vehicle equipped with a clutch, a computer program adapted for shifting gear in a gear-by-wire system in a vehicle and an electronic control unit.

Technical Field of the Invention

The invention relates to a method for shifting gear in a gear-by- wire system in case of an absent or abnormal gear signal from a manually influenced gear shifting means. The invention also relates to a computer program, a computer program product, a vehicle and electronic control unit for performing the method.

Background of the invention

Several different types of gearboxes and gear changing systems today exist on the market. One of them is a system enabling a driver to change gear manually through a gear-by-wire system, i.e. manually initiated gear changes, but the gear changes themselves being electrohydraulically, electropneumatically or electromechanically controlled via an electronic control unit and not by manual force on a gear-lever. Some gear-by- wire systems comprise a clutch pedal in addition to the brake pedal and the accelerator pedal in order to e.g. give the driver a feeling of shifting gear in substantially the same way as if the vehicle would have a manual gearbox system. Since the gear shift lever arrangement in a shift-by- wire system does not transmit a mechanical shifting force to the gearbox, the gear shift lever may not be as big and heavy as in e.g. heavy buses and trucks provided with a conventional, manual gear shifting system, but is usually small to save weight and space. One problem of shift- by- wire system is that normal operation of the transmission becomes impossible in case of gear shift lever signal failure. Such failure may result from e.g a broken gear shift lever/joystick, a faulty position sensor for sensing the position of the gear shift lever and a cable fault or connector fault between the position sensor and the ECU receiving the position sensor signal.

If the driver is unable to shift gear or put the gearbox in neutral the vehicle is immediately in practice not fit for driving, not even to a work shop, and especially not if the current gear is high and not suitable for lower vehicle speeds. Dangerous traffic situations may also arise from the driver's unability to initiate gearshifts.

Modern trucks and buses usually have an emergency mode, often called a limp home mode, which is intended to let the driver drive the vehicle with limited motion capacity to a workshop when certain predefined failures on the gear shifting system have been detected. US-5251733-A describes such a limp home mode for a tractor. In this limp home mode, which is manually activated by the driver, a gear is engaged by first moving the gear shift lever to its neutral position and then shifting the lever back into gear while depressing and releasing a clutch pedal. Hence, to shift gears in the limp home mode the gear shift lever must remain intact and the clutch pedal is used to modulate the engagement between the engine and the gearbox in a conventional way for manual gear shifting. EP-161521-A1 discloses a semi-automatic transmission system with a non- synchronous meshing mechanics, wherein the gearbox is set in the neutral position if any of the position sensors for the gear shifting actuators in the gearbox is found abnormal. Thus this document does not provide any limp home mode when e.g. a gear shift lever position signal is absent.

Summary of the invention

It is an object of the invention to enable a driver of a vehicle equipped with a shift-by- wire system and a clutch pedal to be able to change gear although a gear signal from a gear shifting means, such as a gear shift lever, is not available or abnormal in order to safely and efficiently drive the vehicle to e.g. a workshop or away from a position where it may cause hazardous traffic situations.

The invention relates to a method for shifting gear in a gear-by- wire system in a vehicle comprising a clutch, a gearbox, a clutch controlling means, e.g. a clutch pedal, for manually controlling engagement and disengagement of the clutch, and a gear shifting means, e.g. a gear shift lever, enabling a manual indication of a desired gear, comprising the steps of: determining if a reliable gear signal is obtainable from the gear shifting means, changing from a first mode for gear shifting in which a gear shift is initiated by manually actuating the clutch controlling means and indicating a desired gear through the gear shifting means, i.e. the usual way to manually change gear, to a second mode for gear shifting if a reliable gear signal cannot be obtained, obtaining an appropriate gear in the second mode, and shifting to the appropriate gear if the clutch controlling means in the second mode is manually influenced and the appropriate gear is different from a currently engaged gear. Hereby is achieved that e.g. in the case where the clutch controlling means is a clutch pedal the driver can change gear only by depressing the clutch pedal and thereby continue to drive the vehicle without losing the possibility to shift gear in an appropriate way although the ordinary gear signal showing the driver's intended gear is unavailable or determined not reliable. This way of shifting gear is very easy since the clutch usually has to be disengaged during the gear shift anyway to avoid excessive wear to the gearbox.

The method may comprise the step of causing a display means to show a first indication to a driver of the vehicle if the second mode is activated. Hereby is achieved that the driver is alerted that something is wrong with the gear signal and that he/she cannot select a gear through the gear shifting means and shift gear in a normal way, i.e. as in the first mode. In case of a visual fault on gear shifting means, such as an obvious gear shift lever breakage, the driver is informed that the vehicle has acknowledged the breakage.

The method may comprise the step of causing the display means to show a second indication associated with the currently engaged gear in the second mode. Hereby is achieved that the driver can see which gear that is engaged although he/she may not be able to see the engaged gear through the gear shifting means.

The method may comprise the step of causing the display means to, in the second mode, show a third indication associated with the appropriate gear if the appropriate gear is different from the currently engaged gear. Hereby is achieved that the driver is able to know which gear that will be engaged if he/she influences/presses down/touches the clutch controlling means.

In one embodiment the appropriate gear is a gear in which a motor speed, e.g. a diesel engine speed, is within a predetermined speed range, e.g. a speed range within which the fuel consumption is regarded as most efficient, while driving with a current vehicle speed. Hereby is achieved that the vehicle may be driven in an economical and ecological way also in the second mode provided that the predetermined engine speed range is adapted to a predetermined fuel efficient engine speed range such as the so- called green field normally being displayed on tachometers in e.g. modern trucks, buses and cars.

The method may comprise the step of enabling engagement of a reverse gear in the second mode, if the vehicle is considered substantially stationary during a first predetermined time and the clutch controlling means is manually influenced after the first predetermined time. Hereby is achieved that a reverse gear may be engaged in a safe way without unnecessary wear or damage to the gearbox.

The method may comprise the step of considering the vehicle to be substantially stationary by checking a hand/parking brake related sensor signal or a vehicle speed signal. Hereby is achieved that sensors usually already present in a modern vehicle may be utilised for a safe reverse gear engagement.

The method may comprise the step of enabling engagement of a reverse gear in the second mode only if also a brake pedal is affected more than the first predetermined time and is still affected when the clutch controlling means is manually influenced. Hereby an even safer way to engage a reverse gear is achieved.

The method may comprise the step of shifting the gearbox into neutral in the second mode if the clutch controlling means is influenced longer than a second predetermined time. Hereby is achieved that the gearbox in a very easy way can be thrown into neutral by the same means utilised for engaging driving gears irrespective of whether they are forward gears or reverse gears.

The invention also relates to a computer program adapted for shifting gear in a gear- by- wire system in a vehicle comprising a clutch, a gearbox, a clutch controlling means for manually controlling engagement and disengagement of the clutch, and a gear shifting means enabling a manual indication of a desired gear, wherein the computer program comprises computer readable code means, which when run on an electronic control unit in the vehicle causes the electronic control unit to perform the method.

Furthermore the invention relates to computer program product, comprising a computer useable medium and the computer program, the computer program being recorded on the computer useable medium.

Moreover the invention relates to an electronic control unit, comprising a storing means and the computer program being stored on the storing means.

In addition the invention relates to a vehicle equipped with a clutch, a clutch controlling means for manually controlling engagement and disengagement of the clutch and a gear-by- wire system comprising a gearbox and a gear shifting means enabling a manual indication of a desired gear, comprising at least one electronic control unit adapted to: determine if a reliable gear signal is obtainable from the gear shifting means, change from a first mode for gear shifting in which a gear shift is initiated by manually actuating the clutch controlling means and indicating a desired gear through the gear shifting means to a second mode for gear shifting if a reliable gear signal cannot be obtained, obtain an appropriate gear in the second mode, and shift to the appropriate gear if the clutch controlling means in the second mode is manually influenced and the appropriate gear is different from a currently engaged gear.

The vehicle may comprise a display means adapted to show a first indication to a driver of the vehicle if the second mode is activated. The display means may be adapted to show a second indication associated with the currently engaged gear in the second mode. The display means may be adapted to, in the second mode, show a third indication associated with the appropriate gear if the appropriate gear is different from the currently engaged gear.

The at least one electronic control unit may be adapted to determine the appropriate gear as a gear in which a motor speed is within a predetermined speed range while driving with a current vehicle speed.

The at least one electronic control unit may be adapted to enable engagement of a reverse gear in the second mode, if the vehicle is considered substantially stationary during a first predetermined time and the clutch controlling means is manually influenced after the first predetermined time. The at least one electronic control unit may be adapted to check a hand/parking brake related sensor signal or a vehicle speed signal in order to considered if the vehicle is substantially stationary. The at least one electronic control unit may be adapted to enable engagement of a reverse gear in the second mode only if also a brake pedal is affected more than the first predetermined time and is still affected when the clutch controlling means is influenced.

The at least one electronic control unit is adapted to initiate a gear shift in the gearbox into neutral in the second mode if the clutch controlling means is manually influenced more than a second predetermined time.

Brief Description of the Drawings The objects, advantages and effects as well as features of the present invention will be more readily understood from the following detailed description of embodiments, when read together with the accompanying drawings, in which: Fig. 1 schematically shows a vehicle according to an embodiment of the invention, Fig 2 schematically shows an ECU according to an embodiment of the invention, Fig 3 is a flow diagram of an embodiment according to the invention, Fig 4 is a flow diagram of an embodiment of a first loop according to the invention, Fig 5 is a flow diagram of an embodiment of a second loop according to the invention, and

Fig 6 is a flow diagram of an embodiment of a third loop according to the invention.

Detailed Description of Embodiments

While the invention covers various modifications and alternative constructions, embodiments of the invention are shown in the drawings and will hereinafter be described in detail. However it is to be understood that the specific description and drawings are not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended that the scope of the claimed invention includes all modifications and alternative constructions thereof falling within the spirit and scope of the invention as expressed in the appended claims.

Fig. 1 schematically shows a vehicle 1, such as a truck, bus or car, comprising a driveline with inter alia a motor, such as an internal combustion engine 2 or an electric motor, a clutch 3 between the engine 2 and a gearbox 4 and a propeller shaft 5 connected to an output shaft of the gearbox 4 in a conventional way. A first ECU 6 (Electronic Control Unit) is programmed to at least control the gear shifting in the gearbox 4 based on gear signals from a gear shifting means 7, which of course may be any kind of means that may be used by the driver of the vehicle 1 to indicate his/her selection of a certain gear. The gear shifting means 7 may be any kind of toggle switch or push button set, e.g. one pushbutton for every gear. Another alternative of a gear shifting means may be a voice-control system. However in the shown embodiment the gear shifting means 7 is a gear shift lever. At least one position sensor 8 indicating the position of the gear shift lever sends an associated gear signal to a second ECU 9, which forward the gear signal or a corresponding gear signal to the first ECU 6 via a vehicle internal network bus 10, e.g. a bus compatible with CAN (Controller Area Network), TTCAN (Time-triggered Controller Area Network), Byteflight and FlexRay. The signal received by the first ECU 6 shall thereby indicate which gear that is desired by the driver. The first ECU 6 also receives position signals directly from a clutch controlling means position sensor in the form of a clutch pedal switch and/or clutch pedal position sensor 11, and indirectly from an accelerator pedal position sensor 12, a brake pedal position sensor 13, a vehicle speed sensor 14 arranged at e.g. the propeller shaft 5, a crankshaft of the engine 2 or a flywheel, and a handbrake/parking brake lever position sensor 15 via the second ECU 9. All such sensors are as such known to a person skilled in the art and therefore not described more in detail. The first ECU 6 may also communicate with a display means 16, e.g. in the form of an LCD screen on a dashboard (not shown) via the second ECU 9. If the vehicle is equipped with a clutch-by-wire system, i.e. a system where there is no mechanical connection between a clutch pedal and the clutch, the first ECU 6 may also be adapted to control the actuation of the clutch 3. If the clutch system is a conventional manual clutch system with a mechanical link system between the clutch and the clutch pedal, with or without servo-mechanism, no such actuation control is necessary.

An example of an ECU according to the invention, in this embodiment the first ECU 6, is schematically disclosed in Fig. 2. The first ECU 6 here comprises a processing means 17 connected to a first port 181 in order to enable communication with other ECUs, such as the second ECU 9 via the vehicle internal network bus 10, a second port 182 for communications with possible actuator means (not shown) for the clutch 3 in case of a clutch-by- wire system, a third port 183 for communication with actuator means (not shown) for the gearbox 4, and a fourth port 184 for receiving signals from the clutch pedal position sensor. The processing means 17 is also connected to at least one computer program product in the form of a storing means 19, such as a hard disk, a flash memory, a ROM (Read-only memory), an EPROM (Erasable Programmable ROM) or an EEPROM (Electrically Erasable Programmable ROM). The storing means in this embodiment comprises inter alia a computer program 20 for gear shift control, which computer program 20 comprises several programme modules. A first programme module for a first mode for gear shifting controls the manually initiated gear shifts based on the gear signal received from the gear shift lever position sensor via the second ECU 9. In other words the first programme module controls gear changes during normal operation of the gearbox wherein a gear shift is made in a conventional way by first disengaging the clutch 3 by pressing down a clutch controlling means 21 in the form of a clutch pedal and then move the gear shift lever to a position corresponding to a gear or no-gear position (the neutral position) and last engaging the clutch 3 by releasing the clutch pedal. Such a programme module is the basis of a manual shift-by- wire system and is known to a person skilled in the art. Hence it is not described more in detail. A second programme module of the computer program 20 is run in order to activate a second mode in the form of a limp home mode in case the gear signal is not received by the first ECU 6 or is found erroneous by the first or the second ECU. An absent or erroneous gear signal may in the shown embodiment have been caused by e.g. a broken gear shift lever, a faulty gear shift lever position sensor 8, an error in the second ECU 9, and a cable fault or connector fault between the gear shift lever position sensor 8 and the second ECU 9 or between the first ECU 6 and the second ECU9. A third programme module of the computer program 20 causes the first ECU 6 to control gear shifts in the second mode.

Although the display means 16, the accelerator pedal position sensor 12, the brake pedal position sensor 13, the vehicle speed sensor 14, the gear shift lever position sensor 8 and the handbrake/parking brake lever position sensor 15 are all connected to the second ECU 9, some or all of them may in an alternative embodiment be connected directly to the first ECU 6 or any other ECU connected to the first ECU 6 via a vehicle internal network. Also, the clutch pedal position sensor 11 and/or a clutch pedal switch may be connected directly to the second ECU 9 or any other ECU connected to the vehicle internal network instead of the first ECU 6 as long as the first ECU is adapted to receive a signal associated with a current clutch pedal position. It must also be understood that, although a clutch pedal is an excellent choice as a clutch controlling means for manually influencing the engagement and disengagement of the clutch, other means such as physical or virtual buttons on a dashboard and display respectively, voice command means and or wireless remote controls are could be used as clutch controlling means in a vehicle provided with a clutch-by-wire system.

Having described embodiments of a system and a vehicle, some embodiments of a method according to the invention will now be described in conjunction with Fig 3-6. Fig 3 shows a schematic flow diagram of a loop/routine provided by the second programme module. In a first step S 1 it is checked whether a reliable gear signal indicative of a driver' s desire to drive with an indicated gear is present or not. A reliable gear signal shall be understood as a signal which is not absent or abnormal/faulty. Determination of whether a gear shift lever position signal is abnormal or not is known to a person skilled in the art and may comprise a check whether gear shift lever position sensors indicate that the gear shift lever is in two positions at the same time, which of course is impossible, a measured current level indicate that a circuit is short-circuited, and a bit configuration from switches for the gear shift lever position is considered as faulty. If the answer is yes, i.e. a reliable gear signal is present, a second step S2 follows, in which it is checked whether the present gear shifting mode is the second mode or not. If the answer is yes to the latter question, i.e. the second mode is activated, a third step S3 follows, in which the present mode is changed from the second mode to the first mode. After the third step S3, the loop returns to the first step Sl. If the answer is no in the second step S2, i.e. the first mode is activated, the loop returns to step S 1.

If it is determined in the first step S 1 that there is no reliable gear signal, a fourth step S4 follows after the first step S 1. In the fourth step S4 it is checked if the second mode is already activated. If the second mode is activated the loop returns to the first step S l. If the second mode is not already activated the loop continues with a fifth step S 5, in which the second mode is activated instead of the first mode by e.g. calling routines of the third programme module. In addition to activating the second mode, the fifth step S 5 may cause the first ECU 6 to generate diagnostic trouble codes. The loop returns to the first step S 1 upon completion of the tasks of the fifth step S 5. A person skilled in the art of course appreciate that the loop shown in Fig 3 is only exemplary and that alternative loops for changing into the second mode upon an absent or erroneous gear signal would be within the spirit of the present invention. For example, an alternative embodiment of the loop may comprise steps that delay the change into the second mode in order to see if a valid gear signal may be obtained within a certain time.

Fig 3 also shows the first step Ll of an exemplary routine in the second mode, in which step a first indication 22 in the form of a light or a symbol is displayed by the display means 16 to inform the driver that the second mode has been activated. Instead of or in addition thereto the driver may be informed by a sounding buzzer or another audio message. Since the gear signal is absent or abnormal the driver may not know which gear that presently is engaged. Therefore the engaged gear or neutral may also be indicated by a second indication 23 to the driver by the display means 16. After the first step Ll of the second mode, three parallel loops/sub-routines A, B and C according to the invention are run and separately described below in conjunction with Figs 4-6 respectively.

Fig 4 shows a flow chart of an embodiment of the loop A in the second mode. In a first step Al of loop A it is checked whether the currently engaged gear is considered as appropriate or not from an economical and/or ecological driving point of view, e.g. by checking if the current engine speed is within a predetermined engine speed range within which driving is considered especially economical and/or ecological. The speed range is conventionally marked as a green range in an engine speed indicator (not shown). If the current engine speed is below the engine speed range, a lower, appropriate gear within the engine speed range is calculated by the first ECU 6. If the current engine speed is above the engine speed range, a higher, appropriate gear within the engine speed range is calculated. Different methods to determine whether an engine speed is inappropriate from an economical and ecological point of view and to determine a better suited gear are known to a person skilled in the art and are therefore not described more in detail. It shall however be understood that these method may not only include the criterion of having the engine speed within a certain range, but also e.g. current driving conditions and road conditions as well as future driving conditions and road conditions calculated or retrieved from e.g. a look-ahead system. If the current gear is considered appropriate, a second step A2 is performed. If the current gear is considered as inappropriate the loop continues with a third step A3 in which it is checked whether a first predetermined time set by a first timer function has ended. The first predetermined time and the first timer function will be more thoroughly explained below in conjunction with Fig 6. If the predetermined time has ended the method continues with a fourth step A4 in which the first ECU 6 initiates a displaying of a third indication 24 in the form of a symbol, e.g. the letter "R" in the display means 16, which symbol is intended to show the driver that a reverse gear may be engaged by the driver by pressing down the clutch pedal. This symbol replaces a possible symbol or figure for a possible displayed appropriate gear decided in the first step Al (and not being already engaged). This symbol may preferably be displayed close to the symbols indicating that the second mode is activated and the currently engaged gear. The appropriate gear determined in the first step Al is furthermore replaced by a reverse gear as the appropriate gear. If the first predetermined time has not ended, a fifth step A5 is executed after the third step A3. In the fifth step A5 the first ECU 6 causes the display means 16 to indicate to the driver the appropriate gear, which is different from the currently engaged gear and determined in the first step Al. The indication is a symbol or a figure, e.g. "3" for the third forward gear, representing the appropriate gear. This symbol is displayed instead of a symbol associated with a reverse gear and caused to be displayed in a previous iteration of the fourth step A4. A sixth step A6 follows after both the fourth and the fifth step, A4 and A5. When the driver is notified by the third indication 24 representing either a reverse gear or an appropriate forward gear, the driver may choose to engage the displayed gear and in order to do that he/she has in this embodiment to substantially fully disengage the clutch 3 by pressing down the clutch pedal. By pressing down the clutch pedal at least a predetermined distance from a released clutch pedal position, which predetermined distance advantageously may be set to correspond to a fully depressed clutch pedal position or a position relatively close to the fully depressed clutch pedal position, the driver controls the clutch 3 in the same way as he/she would have done during a conventional, manual gear shift with or without a shift-by- wire system and with or without a clutch-by-wire system. Hence in the sixth step A6, the first ECU 6 checks whether the clutch pedal is pressed down the predetermined distance by monitoring the signals from the pedal switch and/or a clutch pedal position sensor 11. In addition thereto a clutch position sensor (not shown) for indicating whether a clutch really is disengaged or at least to some extent disengaged may be monitored. If the clutch pedal is pressed down the predetermined distance, a gear shift to the appropriate gear decided in the first step Al or, in case the fourth step A4 has been performed in the current iteration of the loop, the reverse gear decided in the fourth step A4 is initiated by the first ECU 6 in a seventh step A7. Suitably the seventh step A7 is not ended before the clutch pedal position signal indicates that the clutch pedal is released. After the seventh step A7 the loop returns to the first step Al . If the clutch pedal is determined in the sixth step A6 not being pressed down at least the predetermined distance the loop returns to the first step Al.

In the second step A2, it is determined if the display means 16 is displaying a third indication 24 of a gear considered appropriate in a previous iteration of the loop A and in that previous iteration not being the same as the engaged gear at that time. If such a symbol is displayed the loop continues with an eighth step A8 wherein the symbol is turned out. If no such third indication is displayed the loop returns to the first step Al after the second step A2. The method also returns to the first step Al after the eighth step A8. Although the embodiments of the first loop described above provides for a very suitable gear shifting strategy in case of an unreliable gear signal, there are of course other embodiments of the first loop according to the invention, such as, instead of obtaining an appropriate gear from an economical and ecological point of view, automatically selecting a gear which is one gear lower than the currently engaged gear in order to encourage the vehicle to a standstill since a lower gear gives a higher braking torque from the engine and e.g. a retarder. In other words, the appropriate gear can automatically be set as one gear lower than the currently engaged gear.

In other embodiments of the first loop, the first loop is started with a step corresponding to the third step A3, and if the first predetermined time is not ended a step corresponding to the first step Al is performed. If the first predetermined time has ended a step corresponding to A4 is processed without any calculation of an appropriate gear, i.e. a reverse gear is automatically selected as an appropriate gear by the gear shifting system.

Fig 5 shows a flow chart of an embodiment of the second loop B adapted to enable the driver to throw the gearbox in its neutral position also in the second mode and irrespective of whether the current gear is a forward or reverse gear. In a first step B 1 of the second loop B it is checked whether the clutch pedal is pressed down at least the predetermined distance or not. If the clutch pedal is not pressed down to the predetermined distance, step Bl is executed again. A second step B2 follows if the clutch pedal is pressed down at least the predetermined distance, wherein a second timer is started. After the second step B2, a third step B3 follows, in which it is determined whether or not the clutch pedal still is pressed down at least the predetermined distance. If the clutch pedal is no longer pressed down at least the predetermined distance, the loop continues with a fourth step B4, but if the clutch pedal still is pressed down at least the predetermined distance, the loop continues with a fifth step B 5. In the fourth step B 4 the second timer is reset to its initial value and the loop returns to the first step B 1 after the fourth step B4 has been executed. In the fifth step B 5 it is determined if a second predetermined time counted (down) by the timer has passed. If the second predetermined time has not passed the loop is returned to the third step B3. If the second predetermined time has passed, it is determined in a sixth step B 6 whether the gearbox already is in neutral or not. If the gearbox already is in a neutral position the loop continues with the fourth step B4, otherwise the first ECU 6 initiates a gear change into neutral position, i.e. no engaged gear, in a seventh step B7. Once the neutral position has been entered the loop continues with the fourth step B4.

In alternative embodiments, an additional criterion for shifting into neutral may be incorporated in the second loop. Such a criterion may be to also check if an accelerator pedal 25 is in its released position. This may be particularly relevant when a reverse gear is engaged.

Fig 6 discloses a schematic flow chart of an embodiment of the third loop C regarding the criteria for engaging a reverse gear in the second mode. In a first step Cl, the first ECU 6 determines if the handbrake/parking brake is applied by checking the corresponding signal from the handbrake/parking brake lever position sensor 15 via the second ECU 9. In an alternative embodiment the engagement of the handbrake/parking brake may alternatively or in addition thereto be checked by e.g. checking a hydraulic or pneumatic pressure or the position of a wheel brake cylinder associated with the parking brake. If the parking brake is not applied, the first step Cl is processed again. If the parking brake is applied the loop continues with a second step C2 in which the first ECU 6 determines whether service brakes (not shown) are applied or not. This is in this embodiment done by checking whether or not a brake pedal 26 is in a position forced to by the driver at least at a certain distance from the brake pedal's released position, i.e. the position where the brake pedal 26 is not pressed down, by checking the corresponding brake pedal position signal from the brake pedal position sensor 13 via the second ECU 9. If the brake pedal position signal shows that the brake pedal 26 is not moved from its released position, the loop returns to the first step C 1. If the brake pedal 26 is at least at a certain distance from the released position the loop continues with a third step C3 in which the first timer is started and is allowed to run until at least the first predetermined time has passed unless the first timer is reset to its start value. After step C3 a fourth step C4 follows in which it is determined if the parking brake is still applied. If the parking brake is not applied, the loop continues with a fifth step C5, in which the timer is reset and the loop then returns to the first step Cl. If the parking brake is determined to be still applied in the fourth step C4, the loop continues with a sixth step C6, in which it is checked if the service brakes are applied. If the service brakes are applied the loop returns to the fourth step C4, but if the service brakes are not applied the loop continues with the fifth step C5 after the sixth step C6. Due to the first and the third loop, A and C respectively, a reverse gear is only permitted to be engaged if the clutch pedal is pressed down at least the predetermined distance at substantially the same time as the vehicle is considered standing still and the brake pedal 26 is pressed down.

In alternative embodiments of the third loop C, a step corresponding to the second step C2 may of course be processed before a step corresponding to the first step Cl, i.e. as if the first step Cl and the second step C2 are changing places in an embodiment corresponding to Fig 6. In alternative embodiments a step corresponding to the fourth step C4 may naturally also change place with a step corresponding to the sixth step C6 of Fig 6, so that it is checked whether the service brakes are applied before it is checked if the parking brake is applied. In more simple embodiments one of the checks for the application of the parking brake and the service brakes may be omitted from the loop in order to e.g. save CPU allocation or memory space or to apply the invention in vehicles without a parking brake sensor or brake pedal position sensor. If for example the sixth step C6 of the embodiment described in conjunction with Fig. 6 is omitted, the fourth step C4 would loop back to itself as long as the parking brake is applied. In addition to or instead of all or one of the steps of checking the application of the parking brake or the service brake in the steps Cl, C2, C4 and C6, the first ECU 6 may in alternative embodiments check whether the vehicle is standing still or not by monitoring the vehicle speed signal from the vehicle speed sensor 14 sent to the first ECU 6 via the second ECU 9. A fourth loop/sub-routine (not shown) running in parallel with the three above loops A, B and C enables a driver to easily change between the neutral position and a forward gear provided that the vehicle is standing still. If it is determined in this loop that the gearbox is in neutral and the vehicle is standing still, a predetermined low gear is engaged when the clutch pedal is released.

It shall also be stated that a vehicle according to the invention may also be provided with additional limp home modes. An example of such a limp home mode is a mode activated if the signals from the clutch pedal position sensor for some reason becomes absent in the second mode or the first mode and the vehicle is equipped with a clutch- by-wire system. In such a limp home mode the gear shifts and the clutch engagement/disengagement may be controlled by another means which in the first and second mode is used by the driver to select and control other features of the vehicle.

Claims

1. A method for shifting gear in a gear-by- wire system in a vehicle (1) comprising a clutch (3), a gearbox (4), a clutch controlling means (21), e.g. a clutch pedal, for manually controlling engagement and disengagement of the clutch (3), and a gear shifting means (7), e.g. a gear shift lever, enabling a manual indication of a desired gear, comprising the steps of: determining if a reliable gear signal is obtainable from the gear shifting means (7), changing from a first mode for gear shifting in which a gear shift is initiated by manually actuating the clutch controlling means (21) and indicating a desired gear through the gear shifting means (7) to a second mode for gear shifting if a reliable gear signal cannot be obtained, obtaining an appropriate gear in the second mode, and shifting to the appropriate gear if the clutch controlling means (21) in the second mode is manually influenced and the appropriate gear is different from a currently engaged gear.

2. A method according to claim 1, comprising the step of causing a display means (16) to show a first indication (22) to a driver of the vehicle if the second mode is activated.

3. A method according to claim 2, comprising the step of causing the display means (16) to show a second indication (23) associated with the currently engaged gear in the second mode.

4. A method according to claim 3, comprising the step of causing the display means (16) to, in the second mode, show a third indication (24) associated with the appropriate gear if the appropriate gear is different from the currently engaged gear.

5. A method according to any one of the preceding claims, wherein the appropriate gear is a gear in which a motor speed is within a predetermined speed range while driving with a current vehicle speed.

6. A method according to any one of the preceding claims, comprising the step of enabling engagement of a reverse gear in the second mode, if the vehicle (1) is considered substantially stationary during a first predetermined time and the clutch controlling means is manually influenced after the first predetermined time.

7. A method according to claim 6, comprising the step of considering the vehicle (1) to be substantially stationary by checking a hand/parking brake related sensor signal or a vehicle speed signal.

8. A method according to claim 7, comprising the step of enabling engagement of a reverse gear in the second mode only if also a brake pedal (26) is affected more than the first predetermined time and is still affected when the clutch controlling means (21) is manually influenced.

9. A method according to any one of the preceding claims, comprising the step of shifting the gearbox (4) into neutral in the second mode if the clutch controlling means (21) is influenced longer than a second predetermined time.

10. A computer program (20) adapted for shifting gear in a gear-by- wire system in a vehicle (1) comprising a clutch (3), a gearbox (4), a clutch controlling means (21) for manually controlling engagement and disengagement of the clutch (3), and a gear shifting means (7) enabling a manual indication of a desired gear, wherein the computer program (20) comprises computer readable code means, which when run on an electronic control unit in the vehicle (1) causes the electronic control unit to perform the method according to claim 1.

11. A computer program product (19), comprising a computer useable medium and a computer program (20) according to claim 10, the computer program (20) being recorded on the computer useable medium.

12. An electronic control unit, comprising a storing means and a computer program (20) according to claim 10, the computer program (20) being stored on the storing means.

13. A vehicle (1) equipped with a clutch (3), a clutch controlling means (21) for manually controlling engagement and disengagement of the clutch (3) and a gear-by- wire system comprising a gearbox (4) and a gear shifting means (7) enabling a manual indication of a desired gear, comprising at least one electronic control unit adapted to: determine if a reliable gear signal is obtainable from the gear shifting means (7), change from a first mode for gear shifting in which a gear shift is initiated by manually actuating the clutch controlling means (21) and indicating a desired gear through the gear shifting means (7) to a second mode for gear shifting if a reliable gear signal cannot be obtained, obtain an appropriate gear in the second mode, and shift to the appropriate gear if the clutch controlling means (21) in the second mode is manually influenced and the appropriate gear is different from a currently engaged gear.

14. A vehicle (1) according to claim 13, comprising a display means (16) adapted to show a first indication (22) to a driver of the vehicle (1) if the second mode is activated.

15. A vehicle (1) according to claim 14, wherein the display means is adapted to show a second indication (23) associated with the currently engaged gear in the second mode.

16. A vehicle (1) according to claim 15, wherein the display means is adapted to, in the second mode, show a third indication (24) associated with the appropriate gear if the appropriate gear is different from the currently engaged gear.

17. A vehicle (1) according to any one of claims 13-16, wherein the at least one electronic control unit is adapted to determine the appropriate gear as a gear in which a motor speed is within a predetermined speed range while driving with a current vehicle speed.

18. A vehicle (1) according to any one of claims 13-17, wherein the at least one electronic control unit is adapted to enable engagement of a reverse gear in the second mode, if the vehicle (1) is considered substantially stationary during a first predetermined time and the clutch controlling means (21) is manually influenced after the first predetermined time.

19. A vehicle (1) according to claim 18, wherein the at least one electronic control unit is adapted to check a hand/parking brake related sensor signal or a vehicle speed signal in order to considered if the vehicle is substantially stationary.

20. A vehicle (1) according to claim 19, wherein the at least one electronic control unit is adapted to enable engagement of a reverse gear in the second mode only if also a brake pedal (26) is affected more than the first predetermined time and is still affected when the clutch controlling means (21) is influenced.

21. A vehicle (1) according to any one of claims 13-20, wherein the at least one electronic control unit is adapted to initiate a gear shift in the gearbox (3) into neutral in the second mode if the clutch controlling means (21) is manually influenced more than a second predetermined time.