SE1451510A1

SE1451510A1 - An actuator for a synchronizing unit in a gearbox

Info

Publication number: SE1451510A1
Application number: SE1451510A
Authority: SE
Inventors: Häggström Daniel; Norberg Peer
Original assignee: Scania Cv Ab
Priority date: 2014-12-10
Filing date: 2014-12-10
Publication date: 2016-06-11
Also published as: WO2016093760A1; DE112015005078T5; SE538562C2

Abstract

14 Abstract The present invention relates an actuator for a synchronizing unit in a gearboX. Theactuator (21) comprises a cylinder (30), a piston (31) movably arranged into an innerspace of the cylinder (30) such that it divides the inner space into a first chamber (32)and a second chamber (33) and a piston rod (35) adapted to transmit movements fromthe piston (31), via a shift mechanism (15, 25), to the first component (16) of thesynchronizing unit (14). The actuator (21) comprises a valve mechanism (36-42)configured to provide a restricted ﬂoW area and a restricted compressed medium ﬂoWfrom a compressed medium source (22) to the first chamber (32) during a displacementof the first component (16) from a neutral position to a synchronizing position and toprovide a larger ﬂoW area and a larger compressed medium ﬂoW from the compressedmedium source (22) to the first chamber (32) When the first component (16) has reached the synchronizing position. (Pig. 2)

Description

An actuator for a synchronizing unit in a gearbox BACKGROUND OF THE INVENTION AND PRIOR ART The invention relates to an actuator for a synchronizing unit in a gearboX according to the preamble of claim 1.

Conventional gearboxes comprise a main shaft, a counter shaft, a plurality ofgearwheel pairs each comprising a primary gearwheel fiXedly arranged on thecountershaft and a secondary gearwheel rotatably arranged on the main shaft. Theprimary gearwheel and the secondary gearwheel of the gearwheel pairs are constantlyin meshing engagement with each other. The main shaft may support synchronizingunits arranged at the vicinity of the secondary gearwheels of the respective gearwheelpairs. Each synchronizing unit is used to selectively synchronize and lock one of the secondary gearwheels on the main shaft when a gear is to be engaged in the gearbox.

Each synchronizing unit comprises a displaceable coupling sleeve and a synchronizingring which are rotationally fiXedly arranged on the main shaft such they rotate at thesame speed as the main shaft. The synchronizing ring is provided with a conicallyshaped friction surface adapted to come in contact with a correspondingly conicallyshaped friction surface of a coupling ring which is fiXedly connected to a secondarygearwheel on the main shaft. When a gear is to be engaged in the gearbox, an actuatorprovides a movement, via a shift fork, which displaces the coupling sleeve in an aXialdirection from a neutral position to a synchronization position. During this movementthe pre-synchronizing process takes place, where the coupling sleeve is temporarilyhalted by e. g. a spring system to allow for removal of the oil present between theconical friction surfaces, to allow indexing of the synchronizing ring which willprevent the coupling sleeve to pass the synchronizing position until a synchronousspeed between the synchronizing ring and the coupling ring is achieved, as well as toallow mechanical contact between the conical friction surfaces resulting in a torquethat seeks to synchronize the rotational speed of the synchronizing ring and thecoupling ring. The synchronizer ring and the coupling ring relatively quickly obtain asynchronous speed. When the synchronous speed has been reached, the couplingsleeve is displaced further in the aXial direction to a locking position in which it comes in engagement with a locking element of the coupling ring. ln the locking position, the coupling sleeve provides a rotary locking of the coupling ring and the secondary gearwheel on the main shaft.

Usually a pneumatic actuator is used to displace the coupling sleeve from the neutralposition to the synchronizing position and from the synchronizing position to thelocking position. The last part of the movement towards the synchronizing position canbe defined as a pre-synchronizing process. During the pre-synchronizing process, oil isto be evacuated from the friction surfaces of the synchronizing ring and the couplingring before they come into contact with each other. In order to provide a favourablepre- synchronizing process in which the oil is evacuated in a robust manner, the e. g.spring system needs to be able to halt the coupling sleeve for a sufficiently long time, aprocess which is aided by a low force and a slow increase of the force generated fromthe actuator. The synchronizing process starts when the friction surfaces have comeinto contact with each other. In order to achieve a favorable synchronizing process, theactuator has to act with a large force on the synchronizing ring such that the frictionsurfaces are pressed together with a large force. Consequently, it is difficult to designan actuator having the property of providing a favorable pre-synchronizing process and a favorable synchronizing process.

SUMMARY OF THE INVENTION The object of the present invention is to achieve an actuator of a synchronizing unit ina gearboX having a simple design and a reliable function at the same time as it provides a favorable pre-synchronizing process and a favorable synchronizing process.

The above mentioned objects are achieved by the actuator defined in the characterizedpart of claim l. Thus, the actuator comprises a valve mechanism configured to providea restricted ﬂow area for a compressed medium ﬂow to the first chamber when thefriction surface of the first component is moved towards the friction surface of thesecond component. The restricted compressed medium ﬂow to the first chamber of theactuator results in movement of the piston with a relatively slow speed. Since thevolume of the first chamber successively expands during the movement of the piston,the pressure acting on the first piston will be low. Consequently, the piston obtains amovement with a low force. The movement of the piston is transmitted to the firstcomponent of the synchronizing unit such that it is moved towards the second component of the synchronizing unit with a correspondingly low speed and force. The low speed and force of the first component allows a robust evacuation of oil locatedbetween the friction surfaces of the first component and the second component duringa pre-synchronizing process just before the contact surfaces come into contact with each other.

The movement of the piston is stopped at least temporarily when the contact surface ofthe first component has come into contact with the contact surface of the secondcomponent of the synchronizing unit. The expansion of the first chamber ceases whenthe movement of the piston is stopped. However, the restricted compressed mediumflow to the first chamber continuous resulting in a pressure raise in the first chamber.In order to provide a faster pressure raise in the first chamber, the valve mechanism isconfigured to provide a larger ﬂow area and a larger compressed medium ﬂow to thefirst chamber when the first component has reached the synchronizing position. Thelarger medium ﬂow to the first chamber results in a fast pressure raise in the firstchamber. As a consequence, the piston provides a large force pressing together thefriction surfaces of said components substantially immediately after the firstcomponent has reached the synchronizing position. The larger supply of the compressed medium ﬂow to the first chamber results in a fast synchronizing process.

According to an embodiment of the invention, the valve mechanism comprises a firstinlet passage, a second inlet passage and a valve member configured to provide therestricted compressed medium ﬂow to the first chamber via the first inlet passage andto provide the larger compressed medium ﬂow to the first chamber via the first inletpassage and the second inlet passage. The first inlet passage and the second inletpassage may receive a compressed medium ﬂow from a common line. The ﬂow areasof the first passage and the second passage are dimensioned such that the first chamberreceives a suitable restricted compressed medium ﬂow during the pre- synchronizingprocess and a suitable larger compressed medium ﬂow during the synchronizing pfOCCSS.

According to an embodiment of the invention, the first inlet passage is connected to acompressed medium source in the form of a compressed air source comprising acompressed air line provided with a valve configured to connect the first inlet passagewith the compressed air source or air with ambient pressure. When the valve connectsthe first chamber with air of ambient pressure, the actuator is in an inactivated state and the synchronizing unit in a neutral position. When the valve connects the first chamber With the compressed air source, compressed air is supplied to the firstchamber, via the first inlet passage, Which moves the first component of thesynchronizing unit from the neutral position to the synchronizing position. When thefirst component has reached the synchronizing position the valve mechanism supplycompressed air to the first chamber via the first inlet passage and the second inletpassage Which provides a fast synchronizing process. HoWever, it is possible to use another medium than compressed air such as, for example, a hydraulic oil.

According to an embodiment of the invention, the second inlet passage is connected tothe compressed medium source via an opening, Wherein the valve member isconfigured to close the opening When the restricted compressed medium is to besupplied to the first chamber and to eXpose the opening When the larger compressedmedium ﬂoW is to be supplied to the first chamber. The valve member may beconfigured to be moved from the closed position to the open position When thepressure in the first chamber eXceeds a predetern1ined pressure. When the contactsurfaces of the components come into contact With each other, the piston is stoppedand the restricted compressed medium ﬂoW to the first chamber results in a pressureraise in the first chamber. The pressure raise in the first chamber indicates that thecontact surfaces have come into contact With each other. Preferably, said increasedpressure in the first chamber is used to initiate adjustment of the valve member from the closed position to the open position.

According to an embodiment of the invention, the valve member comprises a movablyarranged valve body Which in the closed position closes the opening and in the openposition eXposes said opening to the second inlet passage. Such a valve body may begiven a very simple design. The valve body may comprise a surface to be in contactWith the pressure in the first chamber and an opposite surface in contact With a valvespring. In this case, the valve spring moves the valve body to the closed position Whenthe pressure in the first chamber is lower than the predeterrnined pressure value. Whenthe pressure in the first chamber eXceeds the predetern1ined pressure value, the valvebody is moved by the pressure in the first chamber from the closed position to the openposition against the action of the valve spring. In this case, the valve mechanism isautomatically set in the open position When the contact surfaces of the componentscome into contact With each other and the pressure in the first chamber starts to rise.

No control units needs to be used controlling the valve member.

According to an embodiment of the invention, said opening to the second inletpassage is formed between a wall element dividing the first inlet passage from thesecond inlet passage and a wall of a valve housing enclosing the valve spring and atleast a part of the valve body. In this case, the first inlet passage and the secondpassage may be arranged in parallel divided by the wall element. To define the openingby means of an already existing wall of the valve housing allows a simple design of the valve mechanism.

According to an embodiment of the invention, the ﬂow area of the first inlet passage issmaller than the ﬂow area of a line conducting the compressed medium from thecompressed medium source to the actuator. This is a prerequisite for supplying arestricted compressed medium ﬂow to the first chamber, via a compressed media line,from a compressed medium source containing the compressed medium with asubstantially constant pressure. The ﬂow areas of the first inlet passage and the secondinlet passage are dimensioned in a suitable manner. The total ﬂow area of the first inletpassage and the second inlet passage may correspond to the ﬂow area in the compressed medium line.

According to an embodiment of the invention, the shift mechanism is a shift fork and acoupling sleeve transmitting a movement from the actuator to a first component in theform of a synchronizing ring and a second component in the form of a coupling ring.The actuator displaces the coupling sleeve in an aXial direction from a neutral positiontowards a synchronizing position via the shift fork. The coupling sleeve brings thesynchronizing ring to the synchronizing position in which the friction surface of thesynchronizing ring comes in contact with the friction surface of the coupling ring.When the synchronizing ring and the coupling ring have reached a synchronous speed,the coupling sleeve is displaced further in the aXial direction to a locking position withthe coupling ring in which the coupling ring and the secondary gearwheel are rotary locked on the main shaft.

According to an embodiment of the invention, the actuator comprises a spring memberconfigured to brake the movement of the piston in a pre-synchronizing position. In thiscase, the speed of the first component will be reduced in a pre-synchronizing positionjust before the contact surfaces come into contact with each other. Such a springmember ensures a low speed of the first component during the pre-synchronizing process allowing a robust evacuation of oil located between the friction surfaces of the first component and the second component during the pre- synchronizing process. Thepiston rod may comprise a protruding portion configured to come in contact with thespring member in the pre-synchronizing position. In this case, the spring memberbrakes the movement of the first component when it moves from the pre- synchronizingposition to the synchronizing position. Thus, the first component is able to move fromthe neutral position to the pre-synchronizing position without being braked by thespring member and from a synchronizing position to a locking position without beingbraked by the spring member. The spring member may be designed to be compressed in a radially outward direction by the protruding portion of the piston rod.

BRIEF DESCRIPTION OF THE DRAVVINGS In the following, a preferred embodiment of the invention is described as an example with reference to the attached drawings, on which: Fig. l shows a gearboX comprising an actuator according to the invention,Fig. 2 shows the actuator in Fig. l in a first position Fig. 3 shows the actuator in a second position and Fig. 4 shows the actuator in a third position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THEINVENTION Fig. l shows a part of a gearboX 2 in a vehicle l. The vehicle l can be a heavy vehicle.The gearboX 2 comprises a housing and an input shaft 3 driven by a not shown engine.The gearbox 2 comprises further a counter shaft 4 provided with a plurality ofgearwheels 5-7 of different sizes. The gearwheels 5-7 are fiXedly mounted on thecounter shaft 4. The gearboX 2 comprises a main shaft 8 provided with a plurality ofgearwheels l0- ll of different sizes. The gearwheels 6-7 on the counter shaft 4 are inconstant meshing engagement with a gearwheel l0-ll on the main shaft 8 so that theyform a number of gearwheel pairs in the gearboX 2. Each gearwheel pair includes aprimary gearwheel 6-7 fiXedly attached on the counter shaft 4 and secondary gear wheel l0-ll rotatably arranged on the main shaft 8 or the input shaft 3.

The gearboX 2 is equipped with a split gear which in a first split position connects the input shaft 3 with the counter shaft 4 via a first gearwheel pair 5, 9 and which in a second split position connects the input shaft 3 With the counter shaft 4 via a secondgearWheel pair 6, 10. The gearWheel pair 6, 10 provides a ratio that defines a gear inthe gearboX 2 and the gearWheel pair 7, 11 defines another gear in the gearboX 2.

The secondary gearWheels 9-11 are rotatably arranged on the main shaft 8 or the inputshaft 3 by means of bearings 12 that can be needle bearings. A first synchronizing unit13 and a second synchronizing unit 14 are disposed adjacent to the secondary gearWheels 9-11 of the main shaft 8 and on the input shaft 3. Each synchronizing unit 13,14 is configured to synchronize and lock at least one of the secondary gear Wheels 9-11on the main shaft 8 or on the input shaft 3. The first synchronizing unit 13 has the taskto establish the different split positions. The first synchronizing unit 13 is able toconnect the input shaft 3 With the countershaft 4 in the gearbox, via the firstgearWheels pair 5, 9 in the first split position and, via the second gearWheels pair 6 10,in the second split position. The second synchronization device 14 is configured to synchronize and lock the secondary gearWheels 10, 11 on the main shaft 8.

Each synchronizing unit 13, 14 comprises one displaceable coupling sleeves 15 andtWo synchronizing rings 16. The coupling sleeves 15 and the synchronizing rings 16are rotationally fiXedly connected to each other. The coupling sleeves 15 of the firstsynchronizing unit 13 is connected to the input shaft 3 by a driver 17. Thus, thecoupling sleeve 15 and the synchronizing rings 16 of the first synchronizing unit 13rotate With the same speed as the input shaft 3. The coupling sleeves 15 of the secondsynchronizing unit 14 are connected to the main shaft 8 by tWo drivers 17, 18. Thus,the coupling sleeve 15 and the synchronizing rings 16 of the second synchronizing unit14 rotate With the same speed as the main shaft 8. ln this case, the synchronizing units13, 14 are double acting. Thus, each synchronizing unit 13, 14 comprises tWosynchronizing rings 16 and tWo coupling rings 19. Each synchronizing ring 16 isprovided With a conically shaped friction surface 16a adapted to come in engagementWith a correspondingly conically shaped friction surface 19a of a coupling ring 19. Thecoupling rings 19 are fiXedly connected to a secondary gearWheel 9-11 on the mainshaft 8.

A control unit 20 controls the activation of the second synchronizing unit 14 during agear exchange processes in the gearbox 2. The control unit 20 controls the activation ofthe synchronizing unit 14 by means of a schematically shoWn pneumatic actuator 21.The actuator 21 is connected to a compressed air source 22 via a compressed air line 23. The compressed air source 22 contains compressed air With a substantially constant pressure. The compressed air line 23 comprises a three way valve 24. The control unit20 is able to adjust the three way 24 valve to a first position in which the actuator 21 isconnected to ambient air of atmospheric pressure and to a second position in which theactuator 21 is connected to the compressed air source 22. The actuator 21 is connected,via a schematically shown shift fork 25, to the coupling sleeve 15 of the secondsynchronizing unit 14. The actuator 21 is, via the shift fork 25, able to displace thecoupling sleeve 15 of the second synchronizing unit 14 in an aXial direction in relationto the main shaft 8. In this case, the actuator 21is single-acting and it has the task to synchronize and lock the secondary gearwheel 10 on the main shaft 8.

Figs. 2 and 3 show the actuator 21 more in detail. The actuator 21 comprises a cylinder30 provided with an inner space. A piston 31 is movably arranged in the inner space ofthe cylinder 30. The piston 31 divides the inner space of the cylinder 30 into a firstchamber 32 and a second chamber 33. The second chamber 33 comprises a springmember 34 compressive in a radial direction. The spring member 34 is provided with acenter opening. The piston 31 is fiXedly connected to a piston rod 35 which transmitmotions from the piston 31, via the shift fork 25, to the coupling sleeve 15 of thesynchronizing unit 14. The piston rod 35 eXtends through the center opening of thespring member 34. The piston rod 35 comprises a protruding portion 35a having alarger diameter than the center opening of the aXial spring member 34. Thecompressed air line 23 comprises a first inlet passage 36 and a second inlet passage 37connected the first chamber 32 of the cylinder 30. A wall element 38 is arrangedbetween the first inlet passage 36 and a second inlet passage 37. The compressed airline 23 is connected to the second inlet passage 37 via an opening 39. A valve member40-42 controls the compressed air ﬂow through the opening 39 to the second inletpassage 37 of the inlet passage. The valve member 40-42 comprises a valve housing 40enclosing a valve spring 41 and a valve body 42. The valve housing 40 and the wallelement 38 define the opening 39 to the second inlet passage 37. The cylinder 30comprises at least one opening 43 through which the second chamber 33 is in constant contact with ambient air.

Fig. 2 shows the piston 31 in a first end position in the cylinder 30. The three-wayvalve 24 has connected the actuator 21 to ambient air of atmospheric pressure. A stopelement 44 defines the first end position of the piston 31which is located at a distancefrom en end wall of the cylinder 30. The second inlet passage 37 has an opening located at a distance from the opening of the first inlet passage 36 in the first chamber 32. When atmospheric pressure prevai1s in the first chamber 32, the va1ve spring 41 isable to move the va1ve body 42 to a closed position in which it covers the opening 39 to the second in1et passage 37 of the in1et passage.

When the secondary gearwhee1 10 is to be engaged in the gearboX 2, the contro1 unit20 moves the three-way 24 va1ve from the first position to the second position suchthat compressed air is conducted from the compressed air source 22 to the firstchamber 32 of the actuator 21 via the compressed air 1ine 23. Since the va1ve body 42covers the opening 39 to the second in1et passage 37, the compressed air ﬂow entersthe first chamber via the first in1et passage 36. Due to the fact that the first in1etpassage 36 has a restricted ﬂow area in re1ation to the compressed air 1ine 23, arestricted compressed air ﬂow is supp1ied to the first chamber 32. The supp1iedcompressed air raises the pressure in the first chamber 32 to a 1eve1 such that itprovides a movement of the piston 31 from the first end position. The movement of thepiston 31 is transmitted, via the piston rod 35 and the shift fork 25, to a correspondingmovement of the coup1ing s1eeve 15 of the synchronizing unit 14. The actuator 21 moves the coup1ing s1eeve 15 and the synchronizing ring 16 from a neutra1 position.

The protruding portion 35a of the piston rod 35 comes in contact with the aXia1 springmember 34 in a pre-synchronizing position which is shown in Fig. 3. The protrudingportion 35a of the piston rod 35 comprises an inc1ined contact surface to come incontact with an inc1ined contact surface of the spring member 34. In the pre-synchronizing position, the protruding portion 35a presses the wa11 defining the centeropening of the spring member 34 in a direction radia11y outward1y. The restrictedcompressed air in the first chamber 32 acts with a re1ative1y 1ow force on the piston 31.As a consequence the speed of the piston 31 wi11 s1owed down to a 1ow speed when theprotruding portion 35a of the piston rod 35 comes in contact with the spring member34.The friction surface 16a obtains a corresponding movement with a 1ow speed and a1ow force towards the friction surface 19a of the coup1ing ring 19. Such a movementresu1ts in an efficient evacuation of oi1 from the space between the friction surfaces16a, 19a.

When the friction surfaces 16a, 19a have come in contact with each other, the actuator21 has moved the coup1ing s1eeve 15 to the synchronizing position. The contactbetween the friction surfaces 16a, 19a stops the movement of the coup1ing s1eeve 15 and the piston 31. Since the movement of the piston 31 has stopped, the fo11owing supply of Compressed air inCreases the pressure in the first Chamber 32. The increasedpressure in the first Chamber 32 eXerts on a front surface of the va1ve body 42 with asuCCessive1y higher pressure. When the pressure in the first Chamber 32 has reaChed apredeterrr1ined va1ue, the va1ve body 42 is forCed to an open position against the aCtionof the va1ve spring 41. In the open position, the opening 39 is exposed and theCompressed air in the Compressed air 1ine 23 is a1so direCted to the first Chamber 32 viathe seCond in1et passage 37. It is now possib1e for the Compressed air to ﬂow into thefirst Chamber 32 via the ﬂow areas of the first in1et passage 36 and the seCond in1etpassage 37. The supply of Compressed air to the first Chamber 32, via the two in1et passages 36, 37 resu1ts in an inCreased Compressed air ﬂow to the first Chamber 32.

The inCreased Compressed air ﬂow to the first Chamber 32 and the faCt that themovement of the piston 31 has stopped resu1ts in a very rapid pressure rise in the firstChamber 32. The high pressure in the first Chamber 32 aCts on the piston 31with a highforCe whiCh is transmitted, via the piston rod 35, the shift fork 24 and the Coup1ings1eeve 15, to the synChronizing ring 16 suCh that the friCtion surfaCe 16a of thesynChronizing ring 16 is pressed against the friCtion surfaCe 19a of the Coup1ing ring 19with a Corresponding1y high forCe. The high forCe aCting on the friCtion surfaCes 16a,19a resu1ts in a fast synChronizing proCess of the speed of the shaft 8 and the seCondarygearwhee1 10. When the synchronizing ring 16 and the Coup1ing ring 19 has reaChed asynChronous speed, the Coup1ing s1eeve 15 is disp1aCed by the aCtuator 21 to a 1oCkingposition in whiCh the Coup1ing s1eeve 15 Comes in engagement with a 1oCking e1ementof the Coup1ing ring 19. Fig. 4 shows the aCtuator 21when the piston 31 has reaChed aseCond end position Corresponding to a 1oCking position of the Coup1ing s1eeve 15. Inthe 1oCking position, the Coup1ing s1eeve 15 provides a rotary 1oCking of the Coup1ingring 19 and the seCondary gearwhee1 15 on the main shaft 8. The movement of theCoup1ing s1eeve 15 to the 1oCking position is provided with a re1ative1y high speed anda re1ative1y high forCe sinCe Compressed air is supp1ied to the first Chamber 32 via boththe first in1et passage 36 and the seCond in1et passage 37.The protruding portion 35a ofthe piston rod 35 has moved through the Center opening of the spring member 34.Thus, the spring member 34 does not brake the movement of the Coup1ing s1eeve 15 from the synChronizing position to the 1oCking position.

The invention is not restriCted to the desCribed embodiment but may be varied free1y within the sCope of the C1aims.

Claims

11 Claims

1. An actuator for a synchronizing unit in a gearboX, Wherein the actuator (21) isconfigured to move a first component (16) of the synchronizing unit (14) from anneutral position to a synchronizing position in Which a friction surface (16a) of the firstcomponent (16) comes in contact With a friction surface (19a) of a second component(19) of the synchronizing unit (14), Wherein the actuator (21) comprises a cylinder(30), a piston (31) movably arranged into an inner space of the cylinder (30) such thatit divides the inner space into a first chamber (32) and a second chamber (33), and apiston rod (35) adapted to transn1it movements from the piston (31), via a shiftmechanism (15, 25), to the first component (16) of the synchronizing unit (14),characterised in that the actuator (21) comprises a valve mechanism (36-42) configuredto provide a restricted ﬂoW area and a restricted compressed medium ﬂoW from acompressed medium source (22) to the first chamber (32) during the displacement ofthe first component (16) from the neutral position to the synchronizing position and toprovide a larger ﬂoW area and a larger compressed medium ﬂoW from the compressedmedium source (22) to the first chamber (32) When the first component (16) has reached the synchronizing position.

2. An actuator according to claim 1, characterised in that the valve mechanismcomprises a first inlet passage (36), a second inlet passage (37) and a valve member(40-42) configured to provide the restricted compressed medium ﬂoW to the firstchamber (32) via the first inlet passage (36) and to provide the larger compressedmedium ﬂoW to the first chamber (32) via the first inlet passage (36) and the secondinlet passage (37).

3. An actuator according to claim 1, characterised in that the first inlet passage (36) isconnected to a compressed medium source (22) via a compressed medium line (23)provided With a valve (24) configured to connect the first inlet passage (36) With the compressed medium source (22) or air With ambient pressure.

4. An actuator according to claim 2 or 3, characterised in that the second inlet passage(37) is connectable to the compressed medium source (22) via an opening (39),Wherein the valve member (40-42) is configured to close the opening (39) When the restricted compressed medium ﬂoW should be supplied to the first chamber (32) and to 12 eXpose the opening (39) When the larger compressed medium ﬂoW should be suppliedto the first chamber (32).

5. An actuator according to claim 4, characterised in that the valve member (40-42) isconfigured to be moved from the closed position to the open position When the pressure in the first chamber (32) eXceeds a predetermined pressure.

6. An actuator according to claim 5, characterised in that the valve member (40-42)comprises a movably arranged valve body (42) Which in the closed position closes theopening (39) and in the open position eXposes said opening (39) to the second inlet passage (37).

7. An actuator according to claim 6, characterised in that the valve body (42)comprises a surface to be in contact With the pressure in the first chamber (32) and thatthe valve member (39) comprises a valve spring (41) acting on an opposite surface ofthe valve body (42).

8. An actuator according to any one of the preceding claims, characterised in that saidopening (39) to the second inlet passage (37) is formed between a Wall element (38)dividing the first inlet passage (36) from the second inlet passage (37) and a Wall of avalve housing (40) enclosing the valve spring (41) and at least a part of the valve body(42).

9. An actuator according to any one of the preceding claims, characterised in that theﬂoW area of the first inlet passage (36) is smaller than the ﬂoW area of a compressedmedium line (23) conducting the compressed medium from a compressed mediumsource (22) to the actuator (21).

10. An actuator according to any one of the preceding claims, characterised in that theshift mechanism (15, 25) is a shift fork and a coupling sleeve (15) transn1itting amovement from the actuator to a first component in the form of a synchronizing ring (16) and a second component in the form of a coupling ring (19).

11. An actuator according to any one of the preceding claims, characterised in that itcomprises a spring member (34) configured to brake the movement of the piston (31) When the first component (16) arrives to a pre-synchronizing position. 13

12. An actuator according to c1aim 11, characterised in that the piston rod (35)comprises a protruding portion (35a) Which is configured to come in contact With the spring member (34) When the first component (16) arrives to a pre-synchronizingposition.

13. An actuator according to c1aim 12, characterised in that the spring member (34) is designed to be compressed in a radia11y outWard direction by the protruding portion(35a) of the piston rod (35).

14. A gearboX comprising an actuator according to any one of the preceding c1aims 1-13.

15. A Vehic1e comprising a gearbox according to c1aim 14.