Patent Publication Number: US-2022227371-A1

Title: Control device and method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition, computer program, computer-readable medium and vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage patent application (filed under 35 § U.S.C. 371) of PCT/SE2020/050452, filed May 5, 2020 of the same title, which, in turn claims priority to Swedish Patent Application No. 1950587-4 filed May 17, 2019 of the same title; the contents of each of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates in general to a method for controlling a vehicle powertrain and a control device configured to control a vehicle powertrain. The present disclosure further relates in general to a computer program and a computer-readable medium. Moreover, the present disclosure relates in general to a vehicle. 
     BACKGROUND OF THE INVENTION 
     Vehicles are driven forward by a propulsion unit torque produced by a propulsion unit, such as a combustion engine, in the vehicle. This propulsion unit torque is transmitted to the driving wheels of the vehicle through a powertrain of the vehicle. In addition to the propulsion unit, the powertrain comprises a gearbox adapted to selectively transfer torque between the propulsion unit and the driving wheels, at different gear ratios. 
     When shifting gears in a gearbox, cogwheels are often engaged and locked on shafts by means of axially displaceable coupling sleeves. Such a coupling sleeve generally comprises cogs, which are configured to mesh with corresponding spaces between cogs of the gear cogwheel to be engaged on the shaft. In order to engage the coupling sleeve with the cogwheel, the coupling sleeve and the cogwheel therefore need to have the same rotational speed. 
     A situation that may be encountered when seeking to engage an unsynchronized gear during a gear shifting step is that the cogs of the coupling sleeve and the cogs of the gear cogwheel end up in a cog-to-cog state, instead of intermeshing as intended. The time spent in this state is dependent of difference in angular velocity between the coupling sleeve and the cogwheel to be engaged. A lower difference in angular velocity increase the time spent in this state. This problem is especially pronounced when seeking to engage a start gear for starting propulsion of the vehicle, since in this situation the difference in angular velocity may be zero for a long time in view of the vehicle being at standstill. This can in turn lead to infinity long engagement time if no action is taken. 
     In addition to the fact that a slow gear shift may influence the operation of the vehicle, a slow gear shift performance may also cause irritation and thereby discomfort for a driver of the vehicle. 
     It has previously been proposed to use the clutch of the powertrain to overcome the problem. For example, US 2004/0118652 A1 discloses a strategy for overcoming a tooth butt condition wherein a controller selectively closes the clutch to provide limited engagement between the engine and the transmission in case a tooth butt condition exists. If the tooth butt condition is not resolved, the controller then changes the target closed clutch position to provide a different level of engagement between the engine and the transmission. The process is repeated until the tooth butt condition is resolved. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide fast and comfortable gear shifts during shift of an unsynchronized main gear. 
     The object is achieved by the subject-matter of the appended independent claims. 
     In accordance with the present disclosure, a method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting is provided. The vehicle powertrain comprises a propulsion unit and a gearbox. The gearbox comprises an input shaft, a lay shaft connected to the input shaft, and a main shaft connected to the lay shaft. The gearbox further comprises a first gear wheel configured to be engaged to the main shaft by a first coupling sleeve, the first coupling being axially movable and rotatably fixed to the main shaft. The gearbox further comprises a synchromesh arrangement comprising a second coupling sleeve. The synchromesh arrangement is configured to engage the first gear wheel and/or a second gear wheel to the input shaft. The method comprises a step of, when the input shaft is rotating, controlling the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft. The method is performed by a control device. 
     A difference in rotational speed between the first gear wheel and the first coupling sleeve increases the probability for proper engagement of the respective cogs of the first gear wheel and the first coupling sleeve. An increase of the difference in the rotational speed between the first gear wheel and the first coupling sleeve may further improve the probability for proper engagement. The difference in rotational speed may be increased up to a threshold value at which the probability for proper engagement is reduced again, for example due to the coupling sleeve risking bouncing against the cogs of the first gear wheel (a situation which also may be called gear grinding). 
     In view of the fact that the method according to the present disclosure overcomes or avoids a cog-to-cog condition, fast and accurate gear shifts may be achieved. Fast and accurate gear shifts also contributes to the comfort for the driver and potential passengers of the vehicle. 
     Furthermore, by means of the method according to the present disclosure, usage of the clutch (for example by engaging/disengaging the clutch a plurality of times) to overcome a cog-to-cog condition can be minimized, or even avoided. Thus, the wear of the clutch may be minimized by means of the present method. 
     The method may further comprise controlling the rotational speed of the input shaft to achieve a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. Thereby, a prevailing cog-to-cog condition may be quickly solved or, if not already present, be efficiently avoided. 
     The method may comprise controlling an actuator of the synchromesh arrangement so as to achieve a desired frictional force between constituent components in the synchromesh arrangement, thereby in turn obtaining a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. Thereby, a prevailing cog-to-cog condition may be quickly solved or, if not already present, be efficiently avoided. 
     Although the method according to the present disclosure may be used in conjunction of any gear shift of an unsynchronized main gear, the method is particularly suitable when engaging a starting gear. In such a condition, there is a high probability for a cog-to-cog condition to occur between the first gear wheel and the first coupling sleeve. Furthermore, since the main shaft of the gearbox in such a case is in a non-rotating state, the cog-to-cog situation may be difficult to solve without taking an active measure, such as achieved by the present method. Thus, according to one aspect, the main shaft may be in a non-rotating state at the initiation of the method. 
     The method may be performed in order to overcome a prevailing cog-to-cog condition of the first gear wheel and the first coupling sleeve during gear shifting. Thus, the method may further comprise an initial step of detecting a cog-to-cog condition between the first gear wheel and the first coupling sleeve. After the detection of the presence of the cog-to-cog condition, the synchromesh arrangement may be controlled so as to induce and/or increase the difference in rotational speed between the first gear wheel and the first coupling sleeve as described above. 
     The present disclosure further relates to a computer program comprising instructions, which when executed by a control device, cause the control device to perform the method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting as described above. 
     The present disclosure further relates to a computer-readable medium comprising instructions, which when executed by a control device, cause the control device to perform the method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting as described above. 
     Moreover, a control device configured to control a vehicle powertrain to overcome, or avoid a cog-to-cog condition during gear shifting is provided. The vehicle powertrain comprises a propulsion unit and a gearbox. The gearbox comprises an input shaft, a lay shaft connected to the input shaft, and a main shaft connected to the lay shaft. The gearbox further comprises a first gear wheel configured to be engaged to the main shaft by a first coupling sleeve, the first coupling being axially movable and rotatably fixed to the main shaft. The gearbox further comprises a synchromesh arrangement comprising a second coupling sleeve. The synchromesh arrangement is configured to engage the first gear wheel and/or a second gear wheel to the input shaft. The control device is configured to, when the input shaft is rotating, control the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft. 
     The control device has the same advantages as described above with regard to the corresponding method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting. 
     The control device may further be configured to control the rotational speed of the input shaft to achieve a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. 
     The control device may further be configured to control an actuator of the synchromesh arrangement in order to achieve a desired frictional force in the synchromesh arrangement, thereby in turn achieving a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. 
     The control device may also be configured to determine a cog-to-cog condition between the first gear wheel and the first coupling sleeve, and to perform the step of controlling the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve if a cog-to-cog condition has been determined. 
     Moreover, the present disclosure also relates to a vehicle comprising a propulsion unit and a gearbox. The vehicle further comprises a control device configured to control a vehicle powertrain to overcome, or avoid a cog-to-cog condition during gear shifting as described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates a side view of a vehicle; 
         FIG. 2  schematically illustrates an example of a powertrain; 
         FIG. 3  schematically illustrates a sectional view of an exemplifying synchromesh arrangement; 
         FIG. 4  represents a flowchart schematically illustrating an exemplifying embodiment of a method of controlling a vehicle powertrain; and 
         FIG. 5  schematically illustrates a device that may constitute, comprise or be a part of a control device configured to control a vehicle powertrain. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and/or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof. 
     In accordance with the present disclosure, a method for controlling a vehicle powertrain is provided. The vehicle powertrain comprises a propulsion unit, such as a combustion engine, and a gearbox. The gearbox comprises an input shaft, a lay shaft connected to the input shaft, and a main shaft connected to the lay shaft. The gearbox further comprises a first gear wheel configured to be engaged to the main shaft by a first coupling sleeve. The first gear wheel is unsynchronized in relation to the main shaft. In other words, there is no separate arrangement, associated with the first gear wheel, which is configured to synchronize the first gear wheel and the main shaft. The first coupling sleeve is axially movable and rotatably fixed to the main shaft. The gearbox further comprises a synchromesh arrangement comprising a second coupling sleeve. The second coupling sleeve may optionally be a split sleeve. The synchromesh arrangement is configured to engage the first gear wheel and/or a second gear wheel to the input shaft. The method is performed by a control device configured to perform the method. The method comprises a step of, when the input shaft is rotating, controlling the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partially engaging the first gear wheel or the second gear wheel to the input shaft. 
     Due to the at least partial engagement of the first gear wheel or the second gear wheel to the input shaft, at least a part of the rotational movement of the input shaft will be transferred to the first or second gear wheel being at least partially engaged. Thereby, there will be a change of the difference in rotational speed between the first gear wheel and the first coupling sleeve. This difference in rotational speed between the first gear wheel and the first coupling sleeve avoids, or overcomes, a cog-to-cog condition between the first gear wheel and the first coupling sleeve. 
     If the input shaft is not already rotating, the method may comprise controlling the powertrain so as to initiate rotation of the input shaft of the gearbox. This may for example be performed by controlling the propulsion unit, which may be a combustion engine, so as to initiate the rotational movement of the input shaft of the gearbox. In case the powertrain comprises a clutch arranged between the propulsion unit and the gearbox, the clutch may be controlled to be in a fully engaged or partly engaged state for this purpose. Rotation of the input shaft of the gearbox may alternatively be induced by means of an electrical machine, if such an electrical machine is present in the vehicle powertrain. 
     The method may be performed in order to overcome a cog-to-cog condition during gear shifting. Such a cog-to-cog condition may for example be detected or otherwise identified by a control device configured to control the vehicle powertrain. Thus, the method may for example be initiated upon detection of a prevailing cog-to-cog condition. Alternatively, the method may be performed in order to avoid a cog-to-cog condition during gear shifting. In such a case, the method may be performed without an actual detection of a prevailing cog-to-cog condition, but in a situation where there is a risk for a cog-to-cog condition to occur which may not be automatically solved sufficiently fast to avoid disturbance in the operation of the vehicle. In particular, the method may be performed in conjunction with engagement of a starting gear when the vehicle is at standstill since in such a situation, the risk for a cog-to-cog condition which cannot be solved other than by taking an active measure may occur. In such a case, the method may for example be initiated upon a request for engagement of a starting gear. The method is however not limited to a situation where a starting gear should be engaged, but could also be performed in conjunction with other gear shifts. 
     The fact that a difference in rotational speed between the first gear wheel and the first coupling sleeve is induced and/or increased facilitates the engagement of the first coupling sleeve and the first gear wheel. More specifically, an increase in the difference between the rotational speed of the first gear wheel and the rotational speed of the first coupling sleeve enables the respective cogs to intermesh such that the first gear wheel and the first coupling sleeve become engaged. 
     The method according to the present disclosure thus utilizes the synchromesh arrangement in the gearbox in contrast to previously known method where the clutch, arranged between the propulsion unit and the gearbox, is relied upon to solve the problem. This has the advantage of reducing the wear of the clutch which may otherwise occur as a result of multiple engagement/disengagement cycles of the clutch as proposed in previously discussed US 2004/0118652 A1. It should however be noted that the present method may in exceptional cases be supplemented with a step of using the clutch after having induced and/or increased the rotational speed between the first gear wheel and the first coupling sleeve, if desired. 
     The present method for controlling a powertrain also has the advantage of improving the accuracy when used in conjunction with engaging a starting gear. The reason for this is that speed sensors in a vehicle powertrain are normally designed to measure relative high rotational speeds. Therefore, when engaging a starting gear, there will normally be little or no information received from the sensor that is measuring rotational speed of the different shafts in the gearbox. By using the herein disclosed method, the input shaft can have a higher rotational speed to engage the main gear in case of cog-to-cog conditions or risk therefore. This possibility of a higher rotational speed of the input shaft is due to the gear ratios as well as gliding of the frictional surfaces in the synchromesh arrangement when engaging a split gear. The higher rotational speed of the input shaft increases the accuracy of the reading of a sensor configured to measure the rotational speed thereof, thereby better accuracy in the control of the powertrain may be achieved. This will lead to faster, more comfortable, and more accurate engagements of the starting gear as well as less mechanical wear of components in the gearbox. The rotational speed of the input shaft may be controlled by means of any previously known method therefore, for example by means of an electrical motor, a transmission brake associated with the input shaft or lay shaft of the gearbox, or by partial engagement of the clutch. 
     When the synchromesh arrangement has been controlled so as to induce and/or increase the difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft, the method may comprise a step of controlling the rotational speed of the input shaft to achieve a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. The desired amount of rotational difference may for example be a predetermined amount of rotational difference. Alternatively, the desired amount of rotational difference may be determined by progressively controlling the rotational speed of the input shaft and determining when the cog-to-cog condition has been overcome, i.e. when the first gear wheel and the first coupling sleeve are engaged. 
     Alternatively, the method may comprise a step of controlling an actuator of the synchromesh arrangement to achieve a desired frictional force in the synchromesh arrangement, thereby in turn obtaining the desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. 
     As mentioned above, the method may be performed when the vehicle is at standstill. In such a situation, the main shaft is in a non-rotating state at the initiation of the method. 
     The present disclosure further relates to a control device configured to control a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting. The control device is configured to control at least the gearbox of the vehicle powertrain. The vehicle powertrain comprises a propulsion unit, such as a combustion engine, and a gearbox. The gearbox comprises an input shaft, a lay shaft connected to the input shaft, and a main shaft connected to the lay shaft. The gearbox further comprises a first gear wheel configured to be engaged to the main shaft by a first coupling sleeve. The first coupling sleeve is axially movable and rotatably fixed to the main shaft. The gearbox further comprises a synchromesh arrangement comprising a second coupling sleeve. The synchromesh arrangement is configured to engage the first gear wheel and/or a second gear wheel to the input shaft. The control device is configured to, when the input shaft is rotating, control the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft. The control device may further be configured to perform any one of the steps described above with reference to the corresponding method for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition. 
       FIG. 1  schematically illustrates a side view of an example of a vehicle  1 . The vehicle  1  comprises a powertrain  3  comprising an internal combustion engine  2  and a gearbox  4 . A clutch (shown in  FIG. 2 ) may be arranged between the internal combustion engine  2  and the gearbox  4 . The gearbox  4  is connected to the driving wheels  5  of the vehicle  1  via an output shaft  6  of the gearbox  4 . The gearbox  4  is adapted to selectively transfer torque between the combustion engine  2  and the driving wheels  5  during operation of the vehicle. 
     The vehicle  1  may be, but is not limited to, a heavy vehicle, e.g. a truck or a bus. Furthermore, the vehicle may be a hybrid vehicle comprising an electric machine (not shown) in addition to the internal combustion engine  2 . 
       FIG. 2  schematically illustrates an exemplifying embodiment of a vehicle powertrain  3 , such as a powertrain of the vehicle  1  shown in  FIG. 1 . The powertrain  3  comprises a propulsion unit in the form of a combustion engine  2 . The powertrain  3  further comprises a gearbox  4  and a clutch  9  arranged between the combustion engine  2  and the gearbox  4 . The gearbox  4  may be an automated manual gearbox (AMT). The clutch  9  may be a friction clutch. The vehicle powertrain  3  furthermore comprises a control device  100 , as will be described in more detail below. The control device  100  is configured to control at least a part of the powertrain. More specifically, the control device may be configured to control the gearbox  4 . 
     The gearbox  4  comprises an input shaft  10  connected to the clutch  9  and an output shaft  6  connected to the driving wheels  5 . The gearbox  4  comprises a first gearbox unit  4 A and a second gearbox unit  4 B arranged downstream of the first gearbox unit  4 A. The first gearbox unit  4 A may be a split gearbox unit. The second gearbox unit  4 B may constitute a conventional main gearbox that can be set to a number of different forward gear ratios. The second gearbox unit  4 B is connectable to the first gearbox unit  4 A. Furthermore, while not shown in  FIG. 2 , the gearbox may optionally comprise additional gearbox units as known in the art, for example a range gearbox arranged downstream of the second gearbox unit. 
     The second gearbox unit  4 B comprises a lay shaft  20  with a plurality of gear wheels  12 B,  13 B,  14 B,  15 B that are rotatably fixed to the lay shaft  20 . For example, gear wheel  12 B may represent a first gear, gear wheel  13 B may represent a second gear, and gear wheel  14 B may represent a third gear. The second gearbox  4 B also comprises a main shaft  30  with corresponding gear wheels  12 A,  13 A,  14 A/ 14 A′ which rotate freely in relation to the main shaft  30 , but which can be selectively locked for rotation with the main shaft  30  in order to engage a gear. When each of the gear wheels  12 A,  13 A,  14 A/ 14 A′ rotate freely in relation to the main shaft  30 , the second gearbox unit  4 B is in neutral. Thereby, no torque is transmitted from the combustion engine  2  to the driving wheels  5 . The gear wheels  12 A,  13 A,  14 A/ 14 A′ on the main shaft  30  may be locked by means of corresponding coupling sleeves  16 ,  17 ,  18 . For example, the first gear in the second gearbox  4 B can be engaged by maneuvering the first sleeve  16 , arranged to rotate with the main shaft  30 , to a position where the gear wheel  12 A is engaged, i.e. to the left in the figure. The gear wheel  12 A will thereby rotate with the main shaft  30 , and the lay shaft  20  will thereby be connected to the main shaft  30  via gear wheel  12 B. Each pair of gear wheels on the lay shaft  20  and main shaft  30  represents a gear ratio. The second gear in the second gearbox unit  4 B may be engaged by disengaging the first sleeve  16  from the gear wheel  12 A and instead moving a second sleeve  17  to a position to the right in the figure where, instead, gear wheel  13 A is engaged. The gear wheel  13 A is thereby brought into rotation with the main shaft  30 . Correspondingly, the third gear in the second gearbox unit  4 B may be engaged by maneuvering the second sleeve  17  to the left in the figure where, instead, gear wheel  14 A/ 14 A′ is engaged. Each of the first through third gears in the second gearbox unit  4 B is used for a plurality of the total number of gears provided by the gearbox  4  as a whole. The second gearbox unit  4 B may further comprise one or more reverse gears (not shown) and a crawler gear (not shown). 
     In the method according to the present disclosure, any one of gear wheels  12 A,  13 A, and  14 A may constitute the herein denominated “first gear wheel”. 
     The lay shaft  20  further comprises an additional gear wheel  15 B that, similar to the above, is rotatably fixed to the lay shaft  20 . The first gearbox unit  4 A comprises a corresponding gear wheel  15 A rotating freely in relation to the input shaft  10 , but which may be selectively locked for rotation with the input shaft  10  through a split sleeve  18 . When the split sleeve  18  locks the gear wheel  15 A with the input shaft  10 , torque can be transferred to the lay shaft  20  via the corresponding gear wheel  15 B on the lay shaft  20 . The split sleeve  18  can further be used to connect the input shaft  10  to the gear wheel  14 A/ 14 A′ of the second gearbox unit  4 B directly. This way, depending on whether the gear wheel  14 A/ 14 A′ on the main shaft  30  is rotating freely in relation to the main shaft  30  or if it is locked on the main shaft  30 , torque can be transferred to the lay shaft  20  via the corresponding gear wheel  14 B on the lay shaft  20  or torque can be transferred from the input shaft  10  directly to the main shaft  30 . The gear wheel pair  15 A/ 15 B and the split sleeve  18  can thereby be used to provide two different split gear ratios for each gear of the second gearbox unit  4 B. The first gearbox unit  4 A may thus be controlled to engage a high-split gear or a low-split gear. For example, engaging the low-split gear may comprise to connect the input shaft  10  with the low gear wheel  14 A/ 14 A′ on the main shaft  30  by means of the split sleeve  18 . When e.g. the first gear is engaged in the second gearbox unit  4 B, the split sleeve  18  may be arranged to engage gear wheel  14 A/ 14 A′. This way, the input shaft  10  is directly connected to gear wheel  14 B, which via gear  14 B establishes a first gear ratio between the input shaft  10  and the lay shaft  20 . The gear wheel  14 A/ 14 A′, however, is not locked to the main shaft  20 , but the lay shaft  20  may be connected to the main shaft  20  through gear wheel pair  12 A/ 12 B. To engage the second gear, gear wheel pair  15 A/ 15 B is instead engaged, resulting in a second gear ratio between the input shaft and the lay shaft  20 . The gear wheel  12 A is still engaged by the coupling sleeve  16  according to the above, thereby extending the range of each gear. This split can be performed for each gear of the second gearbox unit  4 B. 
     Each of the coupling sleeves  16 ,  17 ,  18  described above may for example be operated by pneumatic actuators (not shown). Furthermore, the clutch  9  may be operated by a pneumatic actuator (not shown). 
     The second gearbox unit  4 B comprises unsynchronized gears. Thus, for the purpose of enabling a gear shift, it is important that the rotational speeds of the shaft and the gear wheel to be engaged are essentially the same. To achieve this, the gearbox  4  may for example comprise one or more transmission brakes, each transmission brake being connected to and configured to brake a corresponding shaft of the gearbox in order to control the rotational speed of such a shaft. In the figure, one example of a transmission brake is shown in the form of a lay shaft transmission brake  21 . 
     The first gearbox unit comprises a synchromesh arrangement comprising the coupling sleeve  18 . A synchromesh arrangement in a powertrain of a vehicle is in general used to synchronize the rotational speed between transmission elements, such as a gear wheel and a shaft, before the gear wheel is locked on the shaft. The synchromesh arrangement comprises an axially displaceable coupling sleeve, a latch cone ring and an inner cone ring arranged on the side of the gear wheel associated with the synchromesh arrangement. 
     As mentioned above, the vehicle powertrain  3  further comprises a control device  100 . The control device  100  may be configured to control one or more of the constituent components of the vehicle powertrain  3 . The control device may be configured to control at least the gearbox  4 . The control device  100  may comprise one or more control units. The responsibility for a specific function or control may be divided between two or more of the control units. One or more of the control units may be implemented in the form of a computer. The control device  100  may for example be connected to the power unit  2  and the gearbox  4 . The control device  100  may also be connected to any other constituent component of the vehicle powertrain  3 , for example the clutch  9 . The connections of the control device  100  to any constituent component of the vehicle powertrain  3  may be in the form of physical connection(s) and/or wireless connection(s). 
     The control of constituent components in the vehicle powertrain  3  may be governed by programmed instructions. These programmed instructions typically take the forms of a computer program which, when executed in a computer or control unit, causes the computer or control unit to effect desired forms of control action, for example the steps of the method disclosed herein. As described above, such a computer or control unit may be or constitute a part of the control device  100 . 
       FIG. 3  schematically illustrates a sectional view of an exemplifying synchromesh arrangement  40 , which may be comprised in the gearbox  4  of the powertrain  3  illustrated in  FIG. 2 . In the following, the synchromesh arrangement will be described in conjunction with the gear wheel  14 A/ 14 A″ and the input shaft  10 . It shall however be recognized that a synchromesh arrangement, such as the one described below, may be arranged at another position in the gearbox. 
     The synchromesh arrangement  40  comprises a latch cone ring  46  and an inner cone ring  48  arranged on a first side of a first transmission element, such as a gear wheel  14 A/ 14 A″. The synchromesh arrangement  40  further comprises a coupling sleeve, such as coupling sleeve  18 . In  FIG. 3  the coupling sleeve  18 , latch cone ring  46  and the inner cone ring  48  are depicted on a distance to each other for clarity reason. 
     The coupling sleeve  18  is axially displaceable by means of an actuator  54 . The latch cone ring  46  and the inner cone ring  48  are provided with interacting friction surfaces  56 A/ 56 B, which may be of a conical design. The actuator  54  is configured to transmit an axial force to the latch cone ring  46  via the coupling sleeve  18  in order to bring about contact between the friction surfaces  56 A/ 56 B on the latch cone ring  46  and the inner cone ring  48 , respectively, during gear shifting. This means that a film of lubricant formed between the friction surfaces  56 A/ 56 B is displaced and an initial torque between latch cone ring  46  and the inner cone ring  48  builds up. 
     The first transmission element, i.e. the gear wheel  14 A/ 14 A″, may be engaged and locked on a second transmission element, such as input shaft  10 , with the utilization of the axially displaceable coupling sleeve  18 . A hub  58  provided with splines  60  on the periphery is attached to the input shaft  10  and is configured to allow the coupling sleeve  18  to move axially. The hub  58  transmits torque between the input shaft  10  and the coupling sleeve  18 . However, the coupling sleeve  18  and gear wheel  14 A/ 14 A″ may have different rotational speeds during a gear shift when the gear wheel  14 A/ 14 A″ should be locked on the input shaft  10  by means of the coupling sleeve  18 . The normal purpose of the synchromesh arrangement  40 , when arranged as described here, is to synchronize the rotational speed between the sleeve  18  and the gear wheel  14 A/ 14 A″ before the gear wheel  14 A/ 14 A″ is locked on the shaft  10 . If the synchromesh arrangement is arranged at another position in the gearbox, the purpose would be to synchronize the respective transmission elements where it is arranged. 
     The latch cone ring  46  comprises latch teeth  62 . The surface of the latch teeth are designed to engage internal teeth  64  of the coupling sleeve  18  during synchronization. In order to obtain good synchronization properties, the surface of the latch teeth  62  are suitably angled relative to the axis of rotation of the latch cone ring  46 . The inner cone ring  48  comprises external teeth  74 . The internal teeth  64  of the coupling sleeve  18  are configured to engage with the external teeth  74  at the end of a synchronization process. 
     A number of balls  66 , each loaded with a spring  68 , may optionally be arranged in the coupling sleeve  18 . The purpose of such balls is to enable a so called pre-synchronization. The spring-loaded balls  66  may act on abutment means  70  arranged on the latch cone ring  46  to ensure that the latch teeth  62  of the latch cone ring  46  are in the correct axial position relative to the internal teeth  64  of the coupling sleeve  18  during pre-synchronization and the abutment means  70  press the spring-loaded balls  66  radially outwards when the coupling sleeve  18  moves axially in relation to the latch cone ring  46  when the pre-synchronization has ended and when the synchronization or main synchronization should start. The latch teeth  62  may extend in a direction parallel to the center line of the latch cone ring  46  and in a peripheral direction. The abutment means  70  may extend in a direction parallel to the center line of the latch cone ring  46  and in a peripheral direction. The abutment means  70  may have a larger extension than the latch teeth  62  in the direction parallel to the center line. 
     The synchromesh arrangement of the vehicle powertrain  3  is not limited to the synchromesh arrangement  40  described with reference to  FIG. 3 . Any previously known synchromesh arrangement may be used. 
       FIG. 4  represents a flowchart schematically illustrating a method for controlling a vehicle powertrain in accordance with one exemplifying embodiment of the present disclosure. The method may comprise a first step, S 105 , of detecting that at least one criterion associated with a cog-to-cog condition is fulfilled. The criterion may for example be that a cog-to-cog condition is present, or that there is a risk for a cog-to-cog condition, which cannot be solved sufficiently fast without taking an active measure. The method comprises a step, S 110 , of, when the input shaft is rotating, controlling the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft. The method may further, after step S 110 , comprise a step, S 115 , of checking whether a cog-to-cog condition is present between the first gear wheel and the first coupling sleeve. If not, the method may be terminated. If step S 115  reveals that a cog-to-cog condition is prevailing, the method may comprise a step, S 120 , of increasing the difference in rotational speed between the first gear wheel and the first coupling sleeve. This may be achieved by increasing the rotational speed of the input shaft. Alternatively, this may be achieved by controlling an actuator of the synchromesh arrangement to achieve another degree of engagement of frictional surfaces of the synchromesh arrangement, i.e. a different frictional force in the synchromesh arrangement. 
     In case the rotational speed of the input shaft should be too high to enable a desired difference in rotational speed between the first gear and the first coupling sleeve, the method may further comprise a step of reducing the rotational speed of the input shaft. This may for example be achieved by means of a transmission brake, an electrical motor or by means of the clutch, or any other previously known method therefore. Such a step of reducing the rotational speed of the input shaft may be performed prior to, or after, step S 110  described above. 
     In the following, the method according to the present disclosure for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting will be exemplified with reference to the powertrain  3  illustrated in  FIG. 2 . For ease of explanation, the method will be exemplified based on an initial condition wherein the vehicle is at standstill, and the main shaft  30  therefore is in a non-rotating state. However, the examples below apply in a corresponding manner during a gear shift even if the vehicle is not at standstill and the main shaft therefore is rotating at the initiation of the method. Furthermore, the examples below assume that the synchromesh arrangement comprises the coupling sleeve  18 . In the examples below, gear wheel  14 A/ 14 A′ is denominated  14 A when it represents the first gear wheel and is denominated  14 A′ when it represents the second gear wheel in the method disclosed herein. 
     According to a first example, a situation is considered where the main shaft  30  is not rotating as a result of the vehicle being at standstill, and the gear wheel to be engaged to the main shaft  30  constitutes the gear wheel  12 A. The gear wheel  12 A thus represents the “first gear wheel” and the coupling sleeve  16  represents the “first coupling sleeve” according to the method disclosed herein. When the input shaft  10  is rotating, the synchromesh arrangement is controlled such as to at least partly engage gear wheel  14 A′ to the input shaft  10 . The gear wheel  14 A′ is here functioning as the “second gear wheel” according to the method. As a result of the at least partial engagement of the gear wheel  14 A′ to the input shaft through the synchromesh arrangement while the input shaft is rotating, the gear wheel  14 B will start to rotate which in turn causes the lay shaft  20  to rotate. As a result of the lay shaft  20  rotating, a rotational movement of the gear wheel  12 A will be induced. Since the coupling sleeve  16  is not rotating as a result of the main shaft  30  being at standstill, a difference in rotational speed between the “first gear wheel”, i.e. gear wheel  12 A, and the “first coupling sleeve”, i.e. the coupling sleeve  16 , is thereby induced. By means of such a difference in rotational speed, a cog-to-cog condition may be avoided, or if already present, be overcome. 
     According to a second example, the gear wheel to be engaged to the main shaft  30  constitutes the gear wheel  13 A. In the method disclosed herein, the gear wheel  13 A thus represents the “first gear wheel” and the coupling sleeve  17  represents the “first coupling sleeve” according to this second example. In the same manner as described in the first example above, the synchromesh arrangement is controlled such as to at least partly engage gear wheel  14 A′ to the input shaft  10  when the input shaft is rotating. Thereby, the lay shaft  20  will start to rotate, which in turn causes a rotation of the “first gear wheel”, here gear wheel  13 A. Thereby, a difference in rotational speed between the “first gear wheel” and the “first coupling sleeve”, here coupling sleeve  17 , has been induced. By means of such a difference in rotational speed, a cog-to-cog condition may be avoided, or if already present, be overcome. 
     According to a third example, the gear wheel to be engaged to the main shaft constitutes the gear wheel  14 A and the gear shift to be performed is intended to be to a gear ratio 1:1 through the gearbox units  4 A and  4 B. Such a gear ratio is achieved when the input shaft  10  is directly connected to the main shaft  30 . According to this third example, the “first gear wheel” is represented by gear wheel  14 A and the “first coupling sleeve” is represented by coupling sleeve  17 . When the input shaft is rotating, the synchromesh arrangement is controlled so as to at least partly engage the “first gear wheel”, here gear wheel  14 A, to the input shaft  10 . The gear wheel  14 A will thereby start to rotate and a difference in rotational speed between the “first gear wheel” (i.e. gear wheel  14 A) and the “first coupling sleeve”, here coupling sleeve  17 , will thereby be induced. By means of such a difference in rotational speed, a cog-to-cog condition may be avoided, or if already present, be overcome. When the coupling sleeve  17  then successfully engages the first gear wheel  14 A, the input shaft  10  will be directly connected to the main shaft  30 . 
     According to a fourth example, the gear wheel to be engaged to the main shaft constitutes the gear wheel  14 A. Thus, here the “first gear wheel” is represented by gear wheel  14 A and the “first coupling sleeve” is represented by coupling sleeve  17 . According to this fourth example, the synchromesh arrangement is associated with gear wheel  15 A. When the input shaft  10  is rotating, the synchromesh arrangement is controlled so as to engage a “second gear wheel”, here gear wheel  15 A, to the input shaft  10  by means of the coupling sleeve  18 . Thereby, the lay shaft  20  will start to rotate, which in turn causes the gear wheel  14 A to rotate. Thereby, a difference in rotational speed between the gear wheel  14 A and the coupling sleeve  17  will be induced. By means of such a difference in rotational speed, a cog-to-cog condition may be avoided, or if already present, be overcome. 
     Naturally, gear wheels  12 A and  13 A may be selected as the “first gear wheel” according to the fourth example above in the same way as gear wheel  14 A. The “first coupling sleeve” will in such cases naturally be the corresponding coupling sleeve configured to engage such a “first gear wheel”. 
       FIG. 5  schematically illustrates an exemplifying embodiment of a device  500 . The control device  100  described above may for example comprise the device  500 , consist of the device  500 , or be comprised in the device  500 . 
     The device  500 , shown in the figure, comprises a non-volatile memory  520 , a data processing unit  510  and a read/write memory  550 . The non-volatile memory  520  has a first memory element  530  in which a computer program, e.g. an operating system, is stored for controlling the function of the device  500 . The device  500  further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory  520  has also a second memory element  540 . 
     There is provided a computer program P that comprises routines for controlling a vehicle powertrain to overcome, or avoid, a cog-to-cog condition during gear shifting. The powertrain comprises a propulsion unit and a gearbox. The gearbox comprises an input shaft, a lay shaft connected to the input shaft, and a main shaft connected to the lay shaft. The gearbox further comprises a first gear wheel configured to be engaged to the main shaft by a first coupling sleeve. The first coupling sleeve is axially movable and rotatably fixed to the main shaft. The gearbox further comprises a synchromesh arrangement comprising a second coupling sleeve. The synchromesh arrangement is configured to engage the first gear wheel and/or a second gear wheel to the input shaft. The computer program comprises routines for controlling the synchromesh arrangement so as to induce and/or increase a difference in rotational speed between the first gear wheel and the first coupling sleeve by at least partly engaging the first gear wheel or the second gear wheel to the input shaft. The computer program may further comprise routines for controlling the rotational speed of the input shaft to achieve a desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. The computer program may alternatively comprise routines for controlling an actuator of the synchromesh arrangement to achieve a desired frictional force in the synchromesh arrangement, thereby in turn obtaining the desired amount of difference in rotational speed between the first gear wheel and the first coupling sleeve. 
     The program P may be stored in an executable form or in a compressed form in a memory  560  and/or in a read/write memory  550 . 
     The data processing unit  510  may perform certain functions. For example, the data processing unit  510  may effect a certain part of the program stored in the memory  560  or a certain part of the program stored in the read/write memory  550 . 
     The data processing device  510  can communicate with a data port  599  via a data bus  515 . The non-volatile memory  520  may be intended for communication with the data processing unit  510  via a data bus  512 . The separate memory  560  may be intended to communicate with the data processing unit  510  via a data bus  511 . The read/write memory  550  may be adapted to communicate with the data processing unit  510  via a data bus  514 . 
     When data are received on the data port  599 , they may be stored temporarily in the second memory element  540 . When input data received have been temporarily stored, the data processing unit  510  may be prepared to effect code execution according to a computer program comprising program code for causing a control device to perform the method (or parts thereof) for controlling a braking system for a vehicle as described herein. 
     Parts of the methods herein described may be effected by the device  500  by means of the data processing unit  510  which runs the program stored in the memory  560  or the read/write memory  550 . When the device  500  runs the program, methods herein described are executed.