SE541436C2

SE541436C2 - A method and a system for controlling a synchromesh arrangement

Info

Publication number: SE541436C2
Application number: SE1651705A
Authority: SE
Inventors: Daniel Häggström; Peer Norberg
Original assignee: Scania Cv Ab
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2019-10-01
Also published as: BR102017026776B1; SE1651705A1; DE102017011429A1; DE102017011429B4; BR102017026776A2

Abstract

The invention relates to a method for controlling a synchromesh arrangement (8) of a transmission (4) of a vehicle (1).The method comprising the step of controlling displacement of the sleeve (50) of the synchromesh arrangement (8) from a first position (A1) to a second position (A2) such that the axial velocity of the sleeve (50) decelerates at a third position (A3) between the first and second positions (A1 , A2) and before a position (AS) where the synchronization is initiated, and then accelerates towards the second position (A2). The invention also relates to a system for controlling a synchromesh arrangement (8), a transmission (4), a vehicle (1), a computer program (P), and a computerreadable medium.

Description

A METHOD AND A SYSTEM FOR CONTROLLING A SYNCHROMESH AR-RANGEMENT TECHNICAL FIELD The invention relates to a method for controlling a synchromesh arrangement in a transmission of a vehicle, a system for controlling a synchromesh arrangement, a transmission comprising a synchromesh arrangement, a vehicle comprising such a transmission, a computer program, and a computerreadable medium.

BACKGROUND AND PRIOR ART A synchromesh arrangement in a powertrain of a vehicle is 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 sleeve, a latch cone ring and an inner cone ring arranged on the side of the gear wheel. The shaft may be a shaft in a gearbox.

Peripheral latch teeth on the latch cone ring face the sleeve and are designed to engage internal teeth in the sleeve during synchronization. In order to obtain good synchronization, the surface of the peripheral latch teeth is angled relative to the axis of rotation of the latch cone ring. The angle is balanced against the braking torque that the latch cone ring transmits to the sleeve in order to achieve synchronous speed. This means that said angle must be designed so that the latch teeth on the latch cone ring engage with that portion of the internal teeth in the sleeve that is at said angle and act on the sleeve sufficiently to achieve synchronous speed and then disengage from the portion of the internal teeth in the sleeve at said angle when the sleeve is to engage with the inner cone ring when synchronous speed has been obtained. In the engaged position between the sleeve and the inner cone ring, the internal teeth in the sleeve engage with peripheral coupling teeth of the inner cone ring. The inner cone ring is attached to the gear wheel and the sleeve is axially displaceable in relation to the shaft but is rotationally engaged with the shaft. To ensure that synchronous speed is reached before the sleeve passes the latch cone ring axially, the teeth of the latch cone ring must disengage from internal teeth at the right moment. This is achieved by a torque balance where the friction torque, also defined as the synchronizing torque, seeks to increase the overlap between the latch cone teeth and the inner cone teeth, while the torque arising from the teeth-teeth contact seeks to reduce the overlap between the teeth. When the peripheral latch teeth on the latch cone ring have disengaged from the internal teeth in the sleeve when synchronous speed has been obtained between the sleeve and the inner cone ring, the sleeve will be axially displaced so that the latch cone ring is moved inwards into the sleeve and stops in an axial position relative to the sleeve, said axial position being determined by the position at which the sleeve meets and engages with the inner cone ring on the gear wheel.

Pre-synchronization occurs before the synchronization process occurs. During pre-synchronization, the lubricant, such as oil, present between the conical surfaces must be evacuated so that a sufficiently high friction torque is developed, effectively blocking the engagement of the gear wheel during asynchronous speed.

During the pre-synchronization and the following synchronization process the axial position of the latch cone ring is defined by the axial force from the sleeve acting on the latch cone ring. After the synchronization process the sleeve is coupled to the inner cone ring and also the gear wheel. In this position the sleeve, the latch cone ring, the inner cone ring and the gear wheel rotate together with the shaft of the powertrain as one unit.

The axial force from the sleeve acting on the latch cone ring may be generated by an actuating element. The axial force and also the axial movement of the sleeve may be controlled by means of a control unit.

The evacuation of lubricant between the conical surfaces during the presynchronization is critical and depends mainly on a spring force from springs restricting the axial movement of the sleeve, the force and speed of the sleeve generated by the actuating element and controlled by means of a control unit, the viscosity of the lubricant and on the overall geometrical design of the components in the synchromesh arrangement. The springs temporarily prevent engagement of gears, so that the lubricant between the conical surfaces will have enough time to be evacuated. The time for evacuation of the lubricant is determined by means of the spring force, the time for the actuating element to build up power, and the velocity and momentum of the sleeve when the sleeve abuts the spring and is temporarily prevented from being displaced axially.

The springs are normally installed in a very space limited areas and can for that reason not be designed strong enough to restrict the axial movement of the sleeve under certain circumstances. The lubricant between the conical surfaces that should be evacuated during the pre-synchronization normally has certain properties in order to correctly lubricate the synchromesh arrangement and also the rest of the gearbox. The geometry of the synchromesh arrangement is dependent on all of the different functions and properties needed by the synchromesh arrangement and is difficult to optimize solely for the evacuation of the lubricant. Thus, it is difficult to optimize the parameters above to achieve a satisfied evacuation of lubricant during the pre-synchronization. Also, there are counteracting demands on the actuator system. On one hand a robust and good pre-synchronization is sought, but on the other hand a short total synchronization process in time, which demands high force and a quick force build up from the actuating element, is sought.

In some situations, such as cold weather or worn components in the synchromesh arrangement, there is a risk of a failed pre-synchronization, which may result in a clash. A clash is a situation where the rotational speed of the sleeve and the rotational speed of the gearwheel are not synchronized when engaging. The pointed teeth of the sleeve will be pushed out by the pointed teeth of the inner cone ring and the sleeve will start to oscillate between a disengaged and a partly engaged position. This results in severe wear of the components in the synchromesh arrangement and also to a discomforting noise.

The document JP2006153235 discloses an automatic gear change control device for synchronous meshing a transmission gear. The control device comprises a gear clashing judging means which judges whether or not the gear clashing occurs when the actuator displaces the sleeve based on a gear change demand in order to engage the synchronous meshing mechanism; and a control means for changing the way of carrying out the engagement motion according to the judgement result of the gear clashing judging means so as to perform the engagement motion.

The document EP0976955 discloses a shifting device for synchromesh-type transmission. An accurate change of the input rotation at each area of the shifting operation is detected, and the applied load to the shifting fork based on the change of input rotation is set. The shifting device for the synchromeshtype transmission comprises a detecting means for detecting a rotation change rate of an input shaft, a judging means for judging a balk point based on the rotation change rate of the input shaft detected by said detecting means, and a transmission controlling mechanism including an electric-controlled driving means for actuating a shift actuator to influence the shift fork. The driving means is arranged to control a drive current to the shift actuator when the balk point is detected by the judging means.

SUMMARY OF THE INVENTION Despite prior art, there is a need to develop a method for controlling a synchromesh arrangement in order to reduce the risk of a clash to occur. There is also a need to develop a method for controlling a synchromesh arrangement in order to achieve a more robust and improved pre-synchronization with a reduced total synchronization process time.

The object of the invention is thus to provide a method for controlling a synchromesh arrangement in order to reduce the risk of a clash to occur.

A further object of the invention is to provide a method for controlling a synchromesh arrangement in order to achieve a more robust and improved presynchronization with a reduced total synchronization process in time.

These objects are achieved with a method for controlling a synchromesh arrangement in a transmission, a system for controlling a synchromesh arrangement, a transmission comprising a synchromesh arrangement, a vehicle comprising such a transmission, a computer program, and computer-readable medium according to the appended independent claims.

According to the invention, a method for controlling a synchromesh arrangement of a transmission of a vehicle is provided. The synchromesh arrangement comprises a sleeve, which is axially displaceable between a first and second position, wherein, as the sleeve moves from the first position to the second position, a synchronization between a rotational speed of a first transmission element of the transmission and a rotational speed of a second transmission element of the transmission is accomplished. The method comprises the step of controlling displacement of the sleeve from the first position to the second position such that the axial velocity of the sleeve decelerates at a third position between the first and second positions and before a position where the synchronization is initiated, and then accelerates towards the second position.

When the axial velocity of the sleeve decelerates at the third position, between the first and second positions, but before a position where the synchronization is initiated, the axial force and speed of the sleeve is decreased. Thereafter, the axial force and speed of the sleeve increases when the sleeve accelerates towards the second position. However, the axial force and speed of the sleeve are both reduced when the sleeve reaches the position where the synchronization is initiated compared to a situation when the sleeve is not decelerated at the third position. As a result, there will be more time to evacuate lubricant present between the components in the synchromesh arrangement in order to achieve synchronous speed, whereby the risk of a clash to occur is reduced.

The invention allows a design that when everything is in normal working conditions an improved performance regarding total synchronization time is achieved. It also enables use of less powerful and thereby smaller presynchronization springs, which means that the complete synchronizer can be reduced in size which will give a smaller total gearbox size, lower gearbox weight and lower cost.

The invention will also allow a design of the synchromesh arrangement not having to cope with the most extreme situations that happens very rarely but which could damage the synchromesh arrangement or gearbox permanently.

It could also prolong the life of a gearbox where the synchronizer starts to get worn with a somewhat prolonged total synchronization time as the result.

This solution do not require any additional hardware components, thereby reducing the complexity of the product.

According to an embodiment of the invention, the axial velocity of the sleeve is decelerated to zero at the third position.

When the sleeve is accelerated from a stand still condition at the third position towards the second position the axial force and speed of the sleeve are both reduced when the sleeve reaches the second position, which eliminates or reduces the risk of any clash situation.

According to an embodiment of the invention, the third position is a neutral positon between the first transmission element and the second transmission element.

The first and second transmission elements are not engaged at the neutral positon and there will not be a transmission of torque between the first and second transmission elements at the neutral position. The neutral position may be situated at a position between the first position and the position where the synchronization is initiated. Thus, the axial velocity of the sleeve may be decelerated and even decelerated to zero at the third position where no torque is transferred between the first and second transmission elements.

According to an embodiment of the invention, the controlling of the sleeve is performed if receiving an indication that a clash occurs or is expected to occur in the synchromesh arrangement.

During conditions when a clash is not expected to occur in the synchromesh arrangement the sleeve may be displaced directly from the first position towards the second position without decelerating the axial velocity of the sleeve at the third position. When displacing the sleeve directly from the first position towards the second position, when a clash is not expected and without decelerating the axial velocity of the sleeve at the third position, the total time for performing the synchronization process may be kept to a minimum. However, if an indication is received that a clash occurs or is expected to occur in the synchromesh arrangement the displacement of the sleeve from the first position to the second position is controlled such that the axial velocity of the sleeve decelerates at a third position between the first and second positions but before a position where the synchronization is initiated and then accelerates towards the second position. However, the synchronization takes place before the second position and therefore the sleeve decelerates at the position where the synchronization is initiated and the acceleration of the sleeve towards the second position will be reduced and stopped at the position where the synchronization is initiated.

According to an embodiment of the invention, the occurrence of a clash is detected by monitoring the axial position of the sleeve.

If the first and second transmission elements have different rotational speed when the sleeve is at the second position or reaches the second position a clash may be expected to occur. Synchronization occurs when there is substantial no change in the axial position of the sleeve, but when there is a substantial change in rotational speed of a transmission element in the synchromesh arrangement. A rapid displacement of the sleeve from the first position to the second position and when the rotational speed of one of the transmission elements is not changed indicates that no synchronization occurs. Thus, a clash may occur. Also, the occurrence of a clash may be detected if the sleeve oscillates in the axial direction between a disengaged and a partly engaged position.

According to an embodiment of the invention, the expected occurrence of a clash is determined by: monitoring the rotational speed of the sleeve and an inner cone ring of the synchromesh arrangement, and/or monitoring the temperature of a lubricant which is in contact with the synchromesh arrangement, and/or monitoring the ambient temperature of the transmission.

If the rotational speed of the sleeve and an inner cone ring of the synchromesh arrangement are different when the sleeve is in the vicinity of the second position a clash may occur. If the temperature of a lubricant which is in contact with the synchromesh arrangement is below a threshold temperature, the viscosity of the lubricant may have increased to a certain level, which increases the time for evacuating lubricant present between the surfaces of the synchromesh arrangement. Thus, the synchronization may not take place before the sleeve reaches the second position and therefore a clash may occur. If the ambient temperature of the transmission is below a threshold temperature a clash may occur due to the increased viscosity of the lubricant which is in contact with the synchromesh arrangement.

The object mentioned above is also achieved with a system for controlling a synchromesh arrangement of a transmission of a vehicle. The synchromesh arrangement comprises a sleeve, which is axially displaceable between a first and second position, wherein, as the sleeve moves from the first position to the second position, a synchronization between a rotational speed of a first transmission element of the transmission and a second transmission element of the transmission is accomplished. The system comprises at least one control unit, the at least one control unit comprising means for controlling displacement of the sleeve from the first position to the second position such that the axial velocity of the sleeve decelerates at a third position between the first and second positions and before a position where the synchronization is initiated, and then accelerates towards the second position.

The axial force and speed of the sleeve are both reduced when the sleeve reaches the second position comparing to a situation when the sleeve is not decelerated at the third position. Thus, there will be enough time to evacuate lubricant present between the components in the synchromesh arrangement in order to achieve synchronous speed and to avoid a clash.

According to an embodiment, the synchromesh arrangement may further comprise a latch cone ring with a (at least substantially) circular first friction surface, an inner cone ring with a (at least substantially) circular second friction surface, which inner cone ring is attached to a transmission element.

The synchromesh arrangement may further comprise a hub attached to a shaft. The transmission element is connectable to the shaft by means of the synchromesh arrangement.

Further, the synchromesh arrangement may comprise at least one control unit, the at least one control unit comprising means for controlling displacement of the sleeve from the first position to the second position such that the axial velocity of the sleeve decelerates at a third position between the first and second positions and before a position where the synchronization is initiated, and then accelerates towards the second position.

Such synchromesh arrangement comprising the above features may result in that the axial force and speed of the sleeve are both reduced when the sleeve reaches the second position comparing to a situation when the sleeve is not decelerated at the third position. Thus, there will be more time to evacuate lubricant present between the components in the synchromesh arrangement in order to achieve synchronous speed and to reduce the risk of a clash to occur.

BRIEF DESCRIPTION OF THE DRAWINGS Below is a description of, as examples, preferred embodiments of the invention with reference to the enclosed drawings, in which: Fig. 1 shows schematically a vehicle in a side view, with a synchromesh arrangement, which is controlled by the method according to an embodiment, Fig. 2 shows a sectional view of a synchromesh arrangement, which is controlled by the method according to an embodiment, Fig. 3 shows a sectional view along line I - I in fig. 2 of the latch cone ring in a synchromesh arrangement, which is controlled by the method according to an embodiment, Fig. 4 shows a sectional view of a synchromesh arrangement in fig. 2 in a presynchronizing position, Fig. 5 shows a sectional view of a synchromesh arrangement in fig. 2 in a synchronizing position, Fig. 6 shows a sectional view of a synchromesh arrangement in fig. 2 in a position when the synchronizing process has ended, Fig. 7a shows a graph over the axial position of the sleeve and the rotational speed of the inner cone ring in relation to time where a clash in the synchronization process has been detected, Fig. 7b shows a graph over the axial position of the sleeve and the rotational speed of the inner cone ring in relation to time where a correct synchronization process has been detected, and Fig. 8 shows a flow chart of a method for controlling a synchromesh arrangement according to an embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows a side view of a vehicle 1 , e.g. a truck, which comprises an engine 2 and a transmission 4, such as a gearbox, provided with a synchromesh arrangement 8, which is controlled by a method according to an embodiment. The engine 2 is connected to the transmission 4 and the transmission 4 is further connected to driving wheels 10 of the vehicle 1 via a propeller shaft 12. Preferably, the engine 2 is an internal combustion engine but another type of engine 2 is also applicable, such as an electrical engine. The transmission 4 may e.g. be a manual transmission, an automated transmission, an automated manual transmission, a dual-clutch transmission or a continuously variable transmission.

Fig. 2 shows a sectional view of the synchromesh arrangement 8 which is controlled by the method according to an embodiment. The synchromesh arrangement 8 may comprise a latch cone ring 46, an inner cone ring 48 arranged on the side of a first transmission element, such as a gear wheel 40, and a sleeve 50, which is axially displaceable e.g. by means of a shifter fork 52. The shifter fork 52 is axially displaceable by means of an actuating element 54. The latch cone ring 46 and the inner cone ring 48 are provided with interacting friction surfaces 56, which preferably are of a conical design. The shifter fork 52 transmits axial force from the actuating element 54 to the latch cone ring 46 via the sleeve 50 in order to bring about contact between the friction surfaces 56 on the latch cone ring 46 and the inner cone ring 48 during gear shifting. This means that a film of lubricant formed between the friction surfaces 56 is displaced and an initial torque between latch cone ring 46 and the inner cone ring 48 builds up.

The gearwheel 40 is engaged and locked on a second transmission element, such as a shaft 14, by means of the axially displaceable sleeve 50. A hub 58 provided with splines 60 on the periphery is attached to the shaft 14 and allows the sleeve 50 to move axially. The hub 58 transmits torque between the shaft 14 and the sleeve 50. However, the sleeve 50, gearwheel 40 and shaft 14 may have different rotational speeds when the gear should be shifted and when the gear wheel 40 should be locked on the shaft 14 by means of the sleeve 50. The synchromesh arrangement 8 is therefore used to synchronize the rotational speed between the sleeve 50, gear wheel 40 and shaft 14 before the gear wheel 40 is locked on the shaft 14.

The shifter fork 52 transmits axial force from the sleeve 50 to the latch cone ring 46 in order to bring about contact between the friction surfaces 56 on the latch cone ring 46 and the inner cone ring 48 during gear shifting. This means that a film of lubricant formed between the friction surfaces 56 is displaced and an initial torque between latch cone ring 46 and the inner cone ring 48 builds up. The actuating element 54 is connected to the electronic control unit 76 and the computer 78 is connected to the electronic control unit 76.

Peripheral latch teeth 62 on the latch cone ring 46 face the sleeve 50 and are designed to engage internal teeth 64 in the sleeve 50 during synchronization. In order to obtain good synchronization in the transmission 4, the surface of the latch teeth 62 is angled relative to the axis of rotation of the latch cone ring 46. The angle is balanced against the braking torque that the latch cone ring 46 generates in order to achieve synchronous speed without clashing.

A number of balls 66, each loaded with a spring 68, are arranged in the sleeve 50. The purpose of the balls 66 is to ensure that pre-synchronization occurs. The spring-loaded balls 66 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 sleeve 50 during pre-synchronization and the abutment means 70 press the spring-loaded balls 66 radially outwards when the sleeve 50 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. In Fig. 2 the sleeve 50, latch cone ring 46 and the inner cone ring 48 are depicted on a distance to each other for clarity reason. However, before the gearwheel 40 should be engaged on the shaft 14, the sleeve 50 is situated at a distance from the inner cone ring 40, which represents a first position A1 (see also fig. 7a). In Fig. 2 the gear wheel 40, shaft 14 and hub 58 are schematically disclosed. The latch teeth 62 extend in a direction parallel to the centre line of the latch cone ring 46 and in a peripheral direction. The abutment means 70 extend in a direction parallel to the centre line of the latch cone ring 46 and in a peripheral direction. The abutment means 70 have a larger extension than the latch teeth 62 in the direction parallel to the centre line. A circumferential groove 49 is arranged in the peripheral surface of the latch cone ring 46 adjacent to the abutment means 70.

Fig. 3 shows a sectional view along line I - I of the latch cone ring 46. In the disclosed embodiment four abutment means 70 are arranged on a substantially equally distance on the periphery 72 of the latch cone ring 46. Also, the latch teeth 62 are arranged on a substantially equally distance on the periphery 72 of the latch cone ring 46.

Fig. 4 shows a sectional view of the synchromesh arrangement 8 in a presynchronizing position. The shifter fork 52 acts with an axial force on the sleeve 50 and displaces the sleeve 50 and also the latch cone ring 46 axially in relation to the hub 58 in direction towards the inner cone ring 48. The springloaded balls 66 are pressed into the direction of the circumferential groove 49 so that the axial position of the latch cone ring 46 in relation to the sleeve 50 will be defined. For this reason the groove 49 has a design which interacts with the spring-loaded ball 40. As mentioned above, the spring-loaded balls 66 also act on the abutment means 70 arranged on the latch cone ring 46, so that the latch cone ring 46 will be displaced axially by the force from the spring-loaded balls 66 when the sleeve 50 is displaced by means of the shifter fork 52. As the sleeve 50 and the latch cone ring 46 are displaced axially the friction surfaces 56 on the latch cone ring 46 and the inner cone ring 48 will be brought to an adjacent position to each other. However, as the transmission 4 is filled with lubricant a thin film 29 of lubricant is created between the friction surfaces 56 on the latch cone ring 46 and the inner cone ring 48. The axial force from the latch cone ring 46 acting on the inner cone ring 48 results in that the film of lubricant formed between the friction surfaces 56 is displaced.

The latch teeth 62 and the abutment means 70 are preferably situated at the side of each latch cone ring 46 that is closest to the inner cone ring 48 to allow the movement of the latch cone ring 46 in the sleeve 50 during the synchronization process. The abutment means 70 have a smaller radial extension than that of distance between the internal teeth 64 in the sleeve 50. This allows the movement of the latch cone ring 46 in the sleeve 50 during the synchronization process.

Fig. 5 shows a sectional view of the synchromesh arrangement 8 in a synchronizing position in which the film of lubricant formed between the friction surfaces 56 has been displaced during pre-synchronization, the friction surfaces 56 have contact with each other and an initial torque between latch cone ring 46 and the inner cone ring 48 is building up. The latch teeth 62 on the latch cone ring 46 engage with and rest against internal teeth 64 in the sleeve 50 during synchronization. Therefore, the surface of the latch teeth 62 on the latch cone ring 46 which engage with and rest against the surface of the internal teeth 64 in the sleeve 50 must be angled relative to the axis of rotation of the latch cone ring 46, and said angle must balance against the braking torque that the latch cone ring 46 transmits to the sleeve 50 in order to achieve synchronous speed. During the synchronization the sleeve 50, gearwheel 40 and shaft 14 have different rotational speeds. However, when a synchronous speed has been reached between the sleeve 50, gear wheel 40 and shaft 14 the angled surface of the latch teeth 62 on the latch cone ring 46 disengage from the angled surface of the internal teeth 64 in the sleeve 50, so that the sleeve 50 passes the latch cone ring 46 axially. To ensure that synchronous speed is reached before the sleeve 50 passes the latch cone ring 46 axially, the teeth 62 of the latch cone ring 46 must disengage from internal teeth 64 at the right time. This is achieved by a torque balance where the friction torque, also defined as the synchronizing torque, seeks to increase the overlap between the latch cone teeth 62 and the inner cone teeth, while the torque arising from the teeth-teeth contact seeks to reduce the overlap between the teeth. When the sleeve 50 moves axially in relation to the latch cone ring 46, the spring-loaded balls 66 are pushed radially outwards due to a radially directed force from an inclined surface on the abutment means 70. Since the surface on the abutment means 70 is inclined the spring-loaded balls 66 are gradually pushed radially outwards when the sleeve 50 moves in the axial direction.

Fig. 6 shows a sectional view of the synchromesh arrangement 8 in a position when the synchronizing process has ended and when the peripheral latch teeth 62 on the latch cone ring 46 have disengaged from the internal teeth 64 in the sleeve 50 when the rotational speed is synchronous between the sleeve 50 and the inner cone ring 48. In this position the sleeve 50 has been axially displaced to a second position A2 (see also fig. 7a), so that the latch cone ring 46 has been moved inwards into the sleeve 50 and stopped in an axial position relative to the sleeve 50, said second position A2 is an axial position being determined by the position at which the sleeve 50 meets and engages with the inner cone ring 48 on the gear wheel 40. In this second position A2 the gear shifting operation has ended and the gear wheel 40 is engaged on the shaft 14. Also, in this second position A2 the spring-loaded balls 66 has been pushed even more radially outwards and rest on an outer surface of the abutment means 70, depicted as a forth surface 76 of the abutment means 70.

When disengaging the gear wheel 40 from the shaft 14, the sleeve 50 is displaced to the first, initial position by means of the shifter fork 52. Since no axial force from the sleeve 50 is acting on the latch cone ring 46, it will be retracted from the inner cone ring 48 and be ready for synchronization the next time the gear wheel 40 should be engaged to the shaft 14.

It may also be possible to arrange a further gear wheel (not shown) on the shaft 14 at the other side of the hub 58 and sleeve 50. The further gear wheel may be engaged on the shaft 14 by means of the sleeve 50 and a further synchromesh arrangement (not shown). A neutral position of the sleeve 50 may be achieved when the sleeve 50 is in a position between the both gearwheels and when both gearwheels are disengaged from the shaft 14.

Fig. 7a shows a graph over the axial position of the sleeve 50 in relation to time. The sleeve 50 is axially displaced from a first position A1 towards a second position A2. In the first position A1 two transmission elements 40, 14 are disconnected. In the second position A2 the two transmission elements 40, 14 are connected and may transfer torqu Between the first and second positions A1 , A2 a synchronization process should be initiated at a position AS. In this synchronization process (as illustrated in fig. 7a) a clash has occurred. A clash is a situation where the rotational speed of the sleeve 50 and the rotational speed of the gearwheel 40 are not synchronized when engaging. The pointed teeth of the sleeve 50 will be pushed out by the pointed teeth of the inner cone ring 48 and the sleeve 50 will start to oscillate between a disengaged and a partly engaged position. This results in severe wear of the components in the synchromesh arrangement 8 and also to a discomforting noise. A clash is a result of a failed pre-synchronization and may occur in situations such as cold weather or worn components in the synchromesh arrangement.

Fig. 7b shows a graph over the axial position of the sleeve 50, the rotational speed of the inner cone ring 48 and the rotational speed of the gear wheel 40 in relation to time where a correct synchronization process takes place. The graph over the axial position of the sleeve 50 is shown with an unbroken line, the graph over the rotational speed of the inner cone ring 48 is shown with a broken line and the graph over the rotational speed of the sleeve 50 and the shaft 14 is shown with dots. In order to connect the the gear wheel 40 to the shaft 14 the sleeve is displaced from the first axial position, at A1 in fig. 7b, towards a second axial position A2. In the first position A1 the two transmission elements 40, 14 are disconnected. In the second position A2 the two transmission elements 40, 14 are connected and may transfer torque. Between the first and second positions A1 , A2 a synchronization process should be initiated at a position AS. The gear wheel 40 initially rotates with a speed that is different from the shaft 14, which depends on the difference in gear rate before and after gear shifting. The shaft 14 rotates and also the sleeve 50 rotates when the vehicle 1 moves. The synchronizing process starts at a second point of time t2, when the sleeve 50 has been displaced to an intermediate axial position AS. The rotational speed of the gear wheel 40 starts to change at the second point of time t2 since the torque and the rotational motion of the shaft 14 are transferred to the gear wheel 40 by means of the synchromesh arrangement 8. When the synchronizing process starts at the time t2, the axial displacement of the sleeve 50 stops, so that the synchronizing process may take place under a certain synchronizing period. At a third point of time t3 the synchronizing process is completed and the shaft 14 and the gear wheel 40 have the same rotational speed n1. Finally, the sleeve 50 is displaced to the second axial position A2, so that the internal teeth 64 in the sleeve 50 engage with external teeth 74 of the inner cone ring 48 at the point of time t4. Thus, fig. 7b represents a functional synchronizing process.

In order to avoid a clash, a system for controlling the synchromesh arrangement 8 of the transmission 4 of the vehicle 1 is suggested according to an embodiment. The synchromesh arrangement 8 comprises the sleeve 50, which is axially displaceable between the first and second positions A1 , A2, wherein, as the sleeve 50 moves from the first position A1 to the second position A2, a synchronization between a rotational speed of the first transmission element represented by the gearwheel 40 of the transmission 4 and a second transmission element represented by the shaft 14 of the transmission 4 is accomplished. The system comprises at least one control unit 76, which comprises means for controlling displacement of the sleeve 50 from the first position A1 to the second position A2 such that the axial velocity of the sleeve 50 decelerates at a third position A3 between the first and second positions A1, A2 and before the position AS where the synchronization is initiated, and then accelerates towards the second position A2.

The dash dotted line in fig. 7b represents the axial velocity of the sleeve 50 in relation to time and also in relation to the axial position of the sleeve 50. At the position A1 the axial velocity of the sleeve 50 is zero. At time t1 the sleeve starts to accelerate towards the position A2 by means of the actuating element 54. However, at the time tx the sleeve 50 reaches the third position A3. At the third position A3 the actuating element 54 controls the sleeve 50 to decelerate to zero velocity. At time ty the sleeve 50 again starts to accelerate towards the second position A2 by means of the actuating element 54. However, the axial force and speed of the sleeve 50 are both reduced when the sleeve 50 reaches the position AS at time t2 where the synchronization is initiated. During synchronization the axial displacement of the sleeve 50 is zero, or substantially zero. When the two transmission elements 40, 14 have reached synchronous rotation speed at time t3, the sleeve 50 again starts to accelerate towards the second position A2 by means of the actuating element 54. At time t4 the sleeve 50 has reached the second position A2 and the two transmission elements 40, 14 are connected and may transfer torque.

Fig. 8 shows a flow chart of the method for controlling the synchromesh arrangement 8 of a transmission 4 of a vehicle 1. The synchromesh arrangement 8 comprises a sleeve 50, which is axially displaceable between a first and second position A1 , A2, wherein, as the sleeve 50 moves from the first position A1 to the second position A2, a synchronization between a rotational speed of a first transmission element 40 of the transmission 4 and a second transmission element 14 of the transmission 4 is accomplished.

The method comprises the step of controlling s101 displacement of the sleeve 50 from the first position A1 to the second position A2 such that the axial velocity of the sleeve 50 decelerates s102 at a third position A3 between the first and second positions A1 , A2 and before a position AS where the synchronization is initiated, and then accelerates s103 towards the second position A2.

When the axial velocity of the sleeve 50 decelerates at the third position A3 between the first and second positions A1 , A2, but before a position AS where the synchronization is initiated, the axial force and speed of the sleeve 50 is decreased. Thereafter, the axial force and speed of the sleeve 50 increases when the sleeve 50 accelerates towards the second position A2. However, the axial force and speed of the sleeve 50 are both reduced when the sleeve 50 reaches the position AS where the synchronization is initiated compared to a situation when the sleeve 50 is not decelerated at the third position A3. Thus, there will be enough time to evacuate lubricant present between the components in the synchromesh arrangement in order to achieve synchronous speed and to avoid a clash.

As a further step of the method, the axial velocity of the sleeve 50 may be decelerated s104 to zero at the third position A3.

When the sleeve 50 is accelerated from a stand still condition at the third position A3 towards the second position A2 the axial force and speed of the sleeve 50 are both reduced when the sleeve 50 reaches the position AS where the synchronization is initiated, which eliminates or reduces the risk of any clash situation.

The third position A3 may be a neutral positon between the first transmission element 40 and the second transmission element 14.

The first and second transmission elements 40, 14 are not engaged at the neutral positon. Thus, the axial velocity of the sleeve 50 may be decelerated and even decelerated to zero at the third position A3 where no torque is transferred between the first and second transmission elements 40, 14.

As a further step of the method, the controlling of the sleeve 50 may be performed s105 if receiving an indication that a clash occurs or is expected to occur in the synchromesh arrangement 8.

During conditions when a clash is not expected to occur in the synchromesh arrangement 8 the sleeve 50 may be displaced directly from the first position A1 to the second position A2 without decelerating the axial velocity of the sleeve 50 at the third position A3. However, if an indication is received that a clash occurs or is expected to occur in the synchromesh arrangement 8 the displacement of the sleeve 50 from the first position A1 to the second position A2 is controlled such that the axial velocity of the sleeve 50 decelerates at a third position A3 between the first and second positions A1 , A2 and then accelerates towards the second position.

As a further step of the method, the occurrence of a clash may be detected by monitoring s106 the axial position of the sleeve 50.

If the first and second transmission elements 40, 14 have different rotational speed when the sleeve 50 is at the second position A2 or reaches the second position A2 a clash may be expected to occur. Synchronization occurs when there is substantial no change in the axial position of the sleeve 50, but when there is a substantial change in rotational speed of a transmission element 40, 14 in the synchromesh arrangement 8. A rapid displacement of the sleeve 50 from the first position A1 to the second position A2 and when the rotational speed of one of the transmission elements 40, 14 are not changed indicates that no synchronization occurs. Thus, a clash may occur.

As a further step of the method, the expected occurrence of a clash may be determined by monitoring s107 the rotational speed of the sleeve 50 and an inner cone ring 48 of the synchromesh arrangement 8, and/or monitoring (s108) the temperature of a lubricant which is in contact with the synchromesh arrangement 8, and/or monitoring the ambient temperature of the transmission 4.

If the rotational speed of the sleeve 50 and an inner cone ring 48 of the synchromesh arrangement 8 are different a clash may occur. If the temperature of a lubricant which is in contact with the synchromesh arrangement 8 is below a threshold temperature, the viscosity of the lubricant has increased to a certain level, which increases the time for evacuating lubricant present between the surfaces of the synchromesh arrangement. The increased period of time for evacuation results in that the lubricant will not be evacuated before the force from the actuating element exceeds the spring force, which may result in that the synchronization process never will be performed. Thus, the synchronization may not take place before the sleeve 50 reaches the second position A2 and therefore a clash may occur. If the ambient temperature of the transmission 4 is below a threshold temperature a clash may occur due to the increased viscosity of the lubricant which is in contact with the synchromesh arrangement 8.

According to an embodiment also a computer program P and computerreadable medium are present for performing the method steps. The computer program P controls the method for controlling a the synchromesh arrangement 8, wherein said computer program P comprises program code for making the electronic control unit 76 or a computer 78 connected to the electronic control unit 76 to performing the method steps according to an embodiment as mentioned herein, when said computer program P is run on the electronic control unit 76 or computer 78 connected to the electronic control unit 76. In fig. 2 the actuating element 54 is connected to the electronic control unit 76 and the computer 78 is connected to the electronic control unit 76.

The computer-readable medium comprises a program code stored on the electronic control unit 76 or computer 78 connected to the electronic control unit 76 readable, media for performing the method steps according to an embodiment as mentioned herein, when said computer program P is run on the electronic control unit 76 or the computer 78 connected to the electronic control unit 76. Alternatively, the computer-readable medium is directly storable in the internal memory M into the electronic control unit 76 or the computer 78 connected to the electronic control unit 76, comprising a computer program P for performing the method steps according to an embodiment, when said computer program P is run on the electronic control unit 76 or the computer 78 connected to the electronic control unit 76.

In the above described embodiments, the first and second transmission elements are exemplified as a gearwheel and a shaft of the gear box, respectively. However, it will be appreciated that the first and second transmission elements may be other transmission elements, such as a chain transmission with a sprocket wheel and a shaft.

The components and features specified above may be combined between the different embodiments specified.

Claims

1. A method for controlling a synchromesh arrangement (8) of a transmission (4) of a vehicle (1), which synchromesh arrangement (8) comprises: a sleeve (50), which is axially displaceable between a first and second position (A1 , A2), wherein, as the sleeve (50) moves from the first position (A1) to the second position (A2), a synchronization between a rotational speed of a first transmission element (40) of the transmission (4) and a rotational speed of a second transmission element (14) of the transmission (4) is accomplished, the method comprising the step of: controlling (s101) displacement of the sleeve (50) from the first position (A1) to the second position (A2) such that the axial velocity of the sleeve (50) decelerates (s102) at a third position (A3) between the first and second positions (A1 , A2) and before a position (AS) where the synchronization is initiated, and then, from the third position (A3), accelerates (s103) towards the second position (A2).

2. The method according to claim 1 , wherein the axial velocity of the sleeve (50) is decelerated (s104) to zero at the third position (A3).

3. The method according to any one of the preceding claims, wherein the third position (A3) is a neutral positon between the first transmission element (40) and the second transmission element (14).

4. The method according to any one of the preceding claims, wherein said controlling of the sleeve (50) is performed (s105) if receiving an indication that a clash occurs or is expected to occur in the synchromesh arrangement (8).

5. The method according to claim 4, wherein the occurrence of a clash is detected by monitoring (s106) the axial position of the sleeve (50).

6. The method according to claim 4 or 5, wherein the expected occurrence of a clash is determined by: monitoring (s107) the rotational speed of the sleeve (50) and an inner cone ring (48) of the synchromesh arrangement (8), and/or monitoring (s108) the temperature of a lubricant which is in contact with the synchromesh arrangement (8), and/or monitoring the ambient temperature of the transmission (4).

7. A computer program (P), wherein said computer program comprises programme code for causing a control unit (76) or a computer (78) connected to the control unit (76) to perform the method according to any one of the preceding claims.

8. A computer-readable medium comprising instructions, which when executed by a control unit (76) or a computer (78) connected to the control unit (76), cause the control unit (76) or the computer (78) to perform the method according to any one of claims 1 -6.

9. A system for controlling a synchromesh arrangement (8) of a transmission (4) of a vehicle (1), which synchromesh arrangement (8) comprises: a sleeve (50), which is axially displaceable between a first and second position (A1 , A2), wherein, as the sleeve (50) moves from the first position (A1) to the second position (A2), a synchronization between a rotational speed of a first transmission element (40) of the transmission (4) and a second transmission element (14) of the transmission (4) is accomplished, wherein the system comprises at least one control unit (76), the at least one control unit (76) comprising: means for controlling displacement of the sleeve (50) from the first position (A1) to the second position (A2) such that the axial velocity of the sleeve (50) decelerates at a third position (A3) between the first and second positions (A1 , A2) and before a position (AS) where the synchronization is ini tiated, and then, from the third position (A3), accelerates towards the second position (A2).

10. A transmission (4) comprising a synchromesh arrangement (8), a first and a second transmission element (40, 14), and a system according to claim 9.

11. A vehicle (1), comprising a transmission according to claim 10.