Gear arrangement and dual-clutch transmission provided therewith

Abstract

A gear arrangement includes a first and a second gearwheel where the first and second gearwheels are arranged next to each other upon a first shaft such that the first and second gearwheels can rotate relative to the first shaft. At least one gearwheel of the first and second gearwheels is arranged upon the first shaft such that it can be axially displaced between a distanced axial position and a contact axial position upon the first shaft, and whereby in the distanced axial position, the first and second gearwheels are distanced from each other and in the contact axial position, an axial contact between the first and second gearwheel is enabled.

Claims

1. A gear arrangement comprising a first and a second gear wheel, whereby the first and second gearwheels are arranged next to each other upon a first shaft such, that the first and second gearwheels can rotate relative the first shaft, wherein at least one gearwheel of the first and second gearwheels is arranged upon the first shaft such, that it can be axially displaced between a distanced axial position and a contact axial position upon the first shaft, and whereby in the distanced axial position, the first and second gearwheels are distanced from each other and in the contact axial position, an axial contact between the first and second gearwheel is enabled, wherein both the first and the second gearwheel are provided with helical gear teeth, whereby the helical gear teeth of the first gearwheel are cut in the same direction as the helical gear teeth of the second gearwheel, wherein the at least one gearwheel is mounted upon a first and a second roller bearing such that the at least one gearwheel can slide thereupon, and the at least one gearwheel is provided with an inwardly directed protrusion arranged such between the first and second roller bearing such that axial displacement is allowed.

2. The near arrangement according to claim 1, wherein the at least one gearwheel is displaced into the contact axial position when it transfers a torque load.

3. The gear arrangement according to claim 1, wherein the gear arrangement is provided with a synchronisation mechanism or a dog clutch enabling a rotational connection between the first and the second gearwheel.

4. The gear arrangement according to claim 1, wherein the gear arrangement is provided with a second synchronisation mechanism or a dog clutch enabling a rotational connection between one of the first and second gearwheel and the first shaft.

5. The gear arrangement according to claim 1, wherein the axial displacement of the at least one gearwheel, from the distanced axial position to the contact axial position, is actuated when the at least one gearwheel transfers a torque load to another gearwheel.

6. A transmission provided with a gear arrangement according to claim 1.

7. The transmission according to claim 6, wherein the transmission is a dual-clutch transmission.

8. The transmission according to claim 6, wherein the transmission is provided with a centre shaft and a countershaft and wherein the first shaft is the countershaft and the gear arrangement is provided upon the countershaft.

9. The transmission according to claim 8, wherein the first gearwheel meshes with first primary gear teeth of the transmission and the second gearwheel meshes with a gearwheel arranged upon the centre shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in detail with reference to the figures, wherein:

(2) FIGS. 1 a and b shows an inventive gear arrangement with one axial displaceable gearwheel;

(3) FIG. 2 a to 2d shows an inventive gear arrangement with two axial displaceable gearwheels

(4) FIG. 3 shows a transmission provided with a gear arrangement according to the invention.

DETAILED DESCRIPTION

(5) In the following only one embodiment of the invention is shown and described, simply by way of illustration of one mode of carrying out the invention.

(6) The term bearing is considered to encompass all different kinds of bearings which could be suitable to use in the gear arrangement, wherein the most common are roller bearing, however plain bearings or other form of bearings also would be possible. In the figures, the gearwheels 333, 535, 335 in the gear arrangement are provided with helical gear teeth, which are directed such that the first and the second gearwheel 333, 535 are pressed against each other during a transfer of the torque load T in one of the directions. Obviously gearwheels 130, 132 meshing with any of these gearwheels 333, 335, 535 are also provided with helical gear teeth.

(7) FIGS. 1 a and b discloses a first preferred embodiment of the invention. The gear arrangement comprises a first shaft 223 upon which said first and second gearwheel 333, 535 is arranged. Both gearwheels are arranged upon a pair of bearings comprising a first and second beating 33b, 33c; 35b, 35c respectively. The first gearwheel 335 however, is mounted such upon its pair of bearings 33b, 33c that it can be axially displaced thereupon. The axial displacement is defined by an inwardly directed protrusion (a shoulder) 333s upon the first gearwheel 333 and which protrusion 333s is arranged between the first and the second bearing 33b, 33c. The axial displacement of the first gearwheel 333 is thereby limited by the position and width of the inwardly directed protrusions 333s between the first and the second bearing 33b, 33c. Also the second gearwheel 535 is provided with an inwardly directed protrusion 535s. The inwardly directed protrusion 535s is however arranged such between the first and second bearing 35b, 35c of the second gearwheel 535, that it does not allow any significant axial displacement of the second gearwheel 535.

(8) In the figures, the bearings are shown as being axially fixed to the shaft 223, and the first gearwheel 333 may have a relative axial motion that is limited by the inwardly directed Protrusion 333s. In an alternative arrangement the first bearing 331 is axially fixed on the gearwheels 33b, 33c and the axial relative motion being limited by shoulders on or axially fixed to the shaft 223.

(9) The first gearwheel 333 is provided with a contact surface 33 in axial direction towards the second bearing 535. Second bearing 535 is provided with corresponding contact surface 35 in direction towards the first gearwheel 333.

(10) In FIG. 1a, the synchronisation mechanism 148 has locked the first and second gearwheel 333, 535 to each other, which thereby rotate in the same direction and with the same speed. The first and the second gearwheel 333, 535 are disconnected from the first shaft 223, whereby there is a relative rotation between the two gearwheels 333, 535 and the first shaft 223. A torque load T is transferred from a gearwheel 130, which meshes with the first gearwheel 333, and further from the first to the second gearwheel 333, 535 over the synchronisation mechanism 148 and there from to a gearwheel 132, which meshes with the second gearwheel 535. The gearwheels 130, 132, 333, 535 are provided with helical gear teeth, which are directed such that the first and the second gearwheel 333, 535 are pressed against each other during a transfer of the torque load T in the direction shown.

(11) Due to the helical gear teeth of the gearwheels 130, 132, 333, 535 the transfer of the torque load T thereby causes oppositely directed axial gear mesh forces F1, F2 upon the first and the second gearwheel 333, 535 respectively. The axial gear mesh force F1 upon the first gearwheel 333 causes the first gearwheel 333 to be axially displaced such that the axial contact surface 33 of the first gearwheel 333 comes in contact with the axial contact surface 35 of the second gearwheel 535.

(12) Due to the axial displacement of the first gearwheel 333 during the torque transfer, the axial gear mesh forces F1, F2 are cancelled out and only the net axial force Fn needs to be transferred to the bearings, i.e. to the first bearing 235b of the second gearwheel 535. Because the bearings 33b, 33c, 35b, 35c not are subjected to any or essentially any axial load during the rotation, the wear of the bearings 33b, 33c, 35b, 35c is decreased, whereby the lifecycles of the bearings 33b, 33c, 35b, 35c are increased.

(13) In FIG. 1b torque T is transferred from the first gearwheel 333 to the first shaft 223 over the first and second synchronisation mechanism 148, 149 and the second gearwheel 535. The axial gear mesh force F1 upon the first gearwheel 333 causes the first gearwheel 333 to be displaced such that the axial contact surface 33 of the first gearwheel 333 comes in contact with the axial contact surface 35 of the second gearwheel 535. The axial gear mesh force F1 on the first gearwheel 333 is thereby reacted via direct contact to the second gearwheel 535 and further to the first shaft 223 over the second bearing 35c of the bearing pair 35b, 35c of the second gearwheels 535. The bearings 33b, 33c and 35b are thereby relieved from axial forces. Because there are no relative motion between the two gearwheels 333, 535 and the first shaft 223, the axial load Fr upon the second bearing 35c of the second gearwheel 535, does not cause any additional wear upon the second bearing 35, because there are no relative rotation between the second gearwheel 535 and the first shaft 223.

(14) In the embodiment shown in FIGS. 1a and 1b, the bearings 35b, 35c of the second gearwheel 535 is preferably tapered roller bearings. Tapered roller bearings have a comparably high axial load capacity, whereby they are able to handle the additional axial load from the first gearwheel in the state shown in FIG. 1b. Other types of bearing would also be possible, e.g., cylindrical roller bearings, as known by a person skilled in the art.

(15) Further, for the embodiments disclosed in FIGS. 1a and 1 b, it can be noted that it is required that the first gearwheel 333 transfers power, thereby being subjected to gear mesh forces, only when it is rotationally locked to the second gearwheel 535. Otherwise, there would be a sliding contact between the first and the second gearwheels 333, 535.

(16) The FIGS. 2 a to 2d disclose an alternative embodiment of the invention, in which both the first and second gearwheel 333 and 335 are arranged such that they can be axially displaced. First gearwheel 333 is arranged in the same manner as for the embodiment disclosed in FIG. 1. The second gearwheel 335 is arranged in a correspondently manner, i.e. is provided with an inwardly directed protrusion (a shoulder) 335s upon the first gearwheel 333 and which protrusion 333s is arranged between the first and the second bearing 235b, 235c.

(17) In the figures, the bearings 33b, 33s, 235b, 235c are shown as being axially fixed to the shaft 223, and each of the gearwheels 333, 335 may have a relative axial motion that is limited by the protrusions 333s, 335s. An alternative arrangement is that the bearings 33b, 33s, 235b, 235c are axially fixed on the gearwheels 333s, 335s and the axial relative motion being limited by shoulders on or axially fixed to the shaft 223.

(18) Now the function of the inventive gear arrangement will be explained when torque T is transferred in different directions and to/from different gearwheels.

(19) In FIG. 2a the same torque transfer as in FIG. 1a is disclosed, i.e. the torque T is transferred from a gearwheel 130, which meshes with the first gearwheel 333 and further from the first to the second gearwheel 333, 335 over the synchronisation mechanism 148 and there from to a gearwheel 132, which meshes with the second gearwheel 335.

(20) The gearwheels 130, 132, 333, 335 are provided with helical gear teeth, which are directed such that the first and the second gearwheel 333, 335 are pressed against each other during a transfer of the torque load T in the direction shown.

(21) Due to the helical gear teeth of the gearwheels 130, 132, 333, 335 the transfer of the torque load T thereby causes oppositely directed axial gear mesh forces F1, F2 upon the first and the second gearwheel 333, 335 respectively. The axial gear mesh forces F1, F2 upon the first and second gearwheel 333, 335 correspondently causes the first and the second gearwheel 333, 335 to be axially displaced such that the axial contact surface 33 of the first gearwheel 333 comes in contact with the axial contact surface 35 of the second gearwheel 335.

(22) Due to the axial displacement of the first and second gearwheel 333, 335 during the torque transfer, the axial gear mesh forces F1, F2 cancel each other out and only the net axial force Fn needs to be taken up by the bearings. Dependent on which of the axial gear mesh forces F1, F2 that is the largest, the net axial force Fn will be taken up by either one of the second bearing 33c of the first gearwheel 333 or the first bearing 235b of the second gearwheel 335. In the situation shown in FIG. 2a, the axial gear mesh force upon the second gearwheel 335 is larger than the axial gear mesh force F1 upon the first gearwheel 333, whereby the first bearing 235b of the second gearwheel 335 must take up the net resulting force Fn.

(23) The situation shown in FIG. 2a is preferably a situation in which the gear arrangement is commonly used, whereby the benefit of the axial force cancellation is as large as possible over time. A typical example is in a forward speed of a vehicle transmission.

(24) In FIG. 2b the torque load T is transferred in the opposite direction compared to FIG. 2a. Whereby the axial gear mesh forces F1, F2 also is directed away from each other. Hence, the first and the second gearwheel 333, 335 is axially displaced away from each other. Obviously, in this situation there will be no cancellation of the gear mesh forces F1, F2. The size of the axial net forces Fn1, Fn2 will thereby correspond to the corresponding axial gear mesh force F1, F2 and will be taken up by the outer bearings 33b, 235c.

(25) The situation shown in FIG. 2b leads to that the full axial gear mesh loads F1, F2 must be taken up by the first bearing 33b of the first gearwheel 333 and the second bearing 235c of the second gearwheel 335 correspondently. Further, because the two gearwheels 333, 335 are not locked to the first shaft 223, the is a relative motion between the two gearwheels 333, 335 and the first shaft 223, whereby the wear of the bearings 33b, 235c will be higher in this situation. It is therefore preferred that the inventive gear arrangement is installed such that the situation in FIG. 2b occurs as little as possible, e.g. during engine braking of a vehicle.

(26) FIG. 2c shows a condition in which torque load T is transferred from the first shaft 223 to a gear wheel 132 that meshes with the second gearwheel 335, whereby the synchronisation clutch 149 locks the second gearwheel to the first shaft 223. No torque transfer occurs in the first gearwheel 333 in the situation shown. The first gearwheel 333 is idling and rotating with a different speed than the first shaft 223. In this situation there is no relative rotation between the second gearwheel 335 and the first shaft 223, however between the first gearwheel 333 and the first shaft 223, and the first gearwheel 333 and the second gearwheel 335 there is as relative rotation

(27) Due to the axial gear mesh force F2 between the second gearwheel 335 and the therewith meshing gearwheel 132, the second gearwheel 335 is axially pressed against its first bearing 235b. The first bearing 235b must thereby take up the axial net force Fn2, which is essentially equal to the axial gear mesh force F2 upon the second gearwheel 335. However, because there is no relative rotation between the first shaft 223 and the second gearwheel 335 there is no additional wear of the bearing 235c that is subjected to the axial load Fn2.

(28) The inwardly directed protrusion 333s of the first gearwheel 333 is adapted to allow an axial displacement of the first gearwheel 333 such that the axial contact surfaces 33, 35 of the first and the second gearwheel 333, 335 are not in contact with each other. If the first gearwheel 333 is in a position that its axial contact surface 33 comes in contact with the second gearwheels 335 axial contact surface 35, when the second gearwheel is axially displaced by the gear mesh force F2, the first gearwheel 333 will be pushed away from the second gearwheel 335. Interference between the first and the second gearwheel 333, 335 is thereby avoided.

(29) FIG. 2d shows a condition in which a torque load T is transferred from a gearwheel 130 meshing with the first gearwheel 333 to the first shaft 223 over the first gearwheel 333, the first synchronisation mechanism 148, the second gearwheel 335 and the second synchronisation mechanism 149. No torque is transferred from the second gearwheel 335 to the gearwheel 132 meshing therewith, whereby the second gearwheel 335 is not subjected to any axial gear mesh forces. There is no relative rotation between the two gearwheels 333, 335 and the first shaft 223, whereby an axial load Fn1 upon the bearings does not influence the lifecycle of the bearings.

(30) The first gearwheel 333 is however subjected to an axial gear mesh force F1, which presses the first gearwheel 333 towards the second gearwheel 335. The first gearwheel 333 is thereby axially pressed against its second bearing 333c. The second bearing 333c of the first gearwheel 333 must thereby take up the axial net force Fn1, which is essentially equal to the axial gear mesh force F1 upon the first gearwheel 335. The inwardly directed protrusion 335s of the second gearwheel 335 is adapted correspondently to the inwardly directed protrusion 333s such that a contact between the contact surfaces 33, 35 can be avoided, and thereby jamming of the gearwheels with each other will not occur.

(31) There are some relevant distances between the different parts of the inventive gear arrangement. The following distances are defined in the FIGS. 1a, b and 2 a-d:

(32) Distances upon the first gearwheel 333; 333d1: from the contact surface 33 to beginning of the downwardly directed protrusion 333s of the first gearwheel 333, 333d2: from the contact surface 33 to the end of the downwardly directed protrusion 333s of the first gearwheel 333.

(33) Distances upon the second gearwheel 335, 535; 335d1: from the contact surface 35 to beginning of the downwardly directed protrusion 335s of the second gearwheel 335, 535, 335d2: from the contact surface 35 to the end of the downwardly directed protrusion 335s of the second gearwheel 335, 535.

(34) Distances between the bearings 33b, 33c; 35b, 35c; 235b, 233c; 233bd: Between the first and second bearing 33b, 33c of the first gearwheel 333 235bd: Between the first and second bearing 35b, 35c; 235b, 235c of the second gearwheel 335 2335bd: Between the inner surface of the second bearing 33c of the first gearwheel 333 and the inner surface of the first bearing 35b; 235b of the second gearwheel 335, 535.

(35) For the situation disclosed in FIG. 2a, the following must be fulfilled in order to enable the axial gear mesh forces to cancel each other out:
333d1+335d1>2335bd.(a)

(36) To make sure that the net axial force is transferred by bearings 235b, the following applies:
233bd+2335bd>333d2+335d1b)

(37) If b) not is fulfilled, the net axial force Fn would be transferred by the first bearing 33b of the first gearwheel 333. More importantly, in the situation shown in FIG. 2c, the first gearwheel 333 would not be able to be axial displaced far enough to avoid that the contact surfaces 33, 35 are in contact with each other.

(38) A general conclusion is found for situations as in FIG. 2a, where axial forces are cancelled out between the gearwheels 333, 335 that are locked rotationally to each other: The net axial force Fn shall not be transferred by the bearings of a gearwheel 333 that transfers power only when it is rotationally connected to other gearwheels 335 in the in the gear arrangement.

(39) In order to avoid jamming of the second gearwheel 335 in FIG. 2d, the following inequality is valid:
2335bd+235bd>333d1+335d2c)

(40) In order to allow just one gearwheel 333 to be axially displaceable the following inequality must be valid:
2335bd+235bd<333d1+335d2d)

(41) FIG. 3 discloses a dual-clutch transmission 300 provided with a gear arrangement according to the invention. The gear arrangement is provided upon the countershaft 223 and has two gearwheels 333, 335, which both are axially displaceable according to the invention.

(42) The first gearwheel 333 is meshing with the first primary gear teeth 130 of the transmission 300. The second gearwheel 335 is meshing with a secondary loose gearwheel 134 upon a central shaft 171 of the transmission 300.

(43) In the transmission in FIG. 3, the torque is transmitted from an engine in the third gear, and the second gear is preselected. The situation in FIG. 3 corresponds to the situation shown in FIG. 2a, i.e. the gear mesh force F2 upon the second gearwheel 335 is larger than the axial gear mesh force F1 upon the first gearwheel 333. The resulting net force Fn is taken up by the first bearing 235b of the second gearwheel 335. The resulting net force Fn is reduced and ideally close to zero, due to that the axial gear mesh forces F1 and F2 cancel each other out.

(44) The axial loads upon the bearings 33b, 33c; 35b, 35c; 235b, 235c are thereby reduced and the lifecycle of the bearings 33b, 33c; 35b, 35c; 235b, 235c are increased because the bearings are not subjected to axial loads during rotation. The robustness of the transmission 300 is thereby increased.

(45) The situation shown in FIG. 2b in the transmission shown in FIG. 3 corresponds to an engine braking in the third gear when second gear is preselected.

(46) The situation shown in FIG. 2c in the transmission shown in FIG. 3 corresponds to that torque is transmitted from an engine in a fourth forward gear when the fifth gear is preselected.

(47) The situation shown in FIG. 2d in the transmission shown in FIG. 3 corresponds to that torque is transmitted in the first gear and the second gear is preselected.

(48) As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims.

(49) Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.