TECHNICAL FIELD

[0001] The field to which the disclosure generally relates to includes mechanical power transmission devices and related components.

BACKGROUND

[0002] Some types of mechanical power transmission devices include synchronizers to couple one rotatable component to another. For example, an automotive dual-clutch transmission typically includes two input shafts that receive power input from an engine flywheel via two input clutches, which selectively couple the flywheel to one or the other of the two input shafts. The two input shafts are coupled to a counter shaft via various pairs of meshed gears carried by the shafts.

[0003] At any given moment, the dual-clutch transmission conveys power in a synchronous fashion, wherein only one of the two input clutches is fully applied to couple the engine flywheel to only one of the two input shafts. Accordingly, power flows from the flywheel through only one fully applied clutch and its corresponding input shaft, and through only one of the pairs of meshed gears. The one input shaft is selected by applying its respective input clutch, and the one pair of meshed gears is selected with a synchronizer to couple one or the other of the pair of meshed gears to its respective shaft. BRIEF SUMMARY

[0004] According to one illustrative embodiment, a freewheeling synchronizer for a power transmission device includes a clutch race rotationally fixable to a component of the power transmission device, and a synchronizer hub disposed radially outwardly of the clutch race and unidirectionally rotatable relative to the clutch race. The clutch race and synchronizer hub are freewheelable relative to one another.

[0005] According to another illustrative embodiment, a power transmission device includes a shaft, a gear freely rotatable on the shaft, and a freewheeling synchronizer having a clutch race coupled to the shaft, a synchronizer hub selectively connectable to the gear, and at least one unidirectional clutching element disposed between the clutch race and the synchronizer hub.

[0006] According to a further illustrative embodiment, a dual-clutch transmission includes a first input shaft coupled to a first input clutch, a second input shaft coupled to a second input clutch, and an input gear coupled to the first input shaft. A counter shaft is offset from the input shafts, and a counter shaft gear is freely rotatable on the counter shaft and in constant mesh with the input gear. The transmission further includes a freewheeling synchronizer including a clutch race coupled to the counter shaft, a synchronizer hub selectively connectable to the counter shaft gear, and at least one unidirectional clutching element disposed between the clutch race and the synchronizer hub. The counter shaft and clutch race are freewheelable relative to the synchronizer hub during a transmission upshift to allow both input clutches to be simultaneously fully applied. [0007] Other illustrative embodiments will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing illustrative embodiments of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Illustrative embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0009] FIG. 1 is a fragmentary cross-sectional view of an illustrative power transmission device including an illustrative freewheeling synchronizer;

[0010] FIG. 2 is an end view of a portion of the freewheeling synchronizer of FIG. 1 ;

[0011] FIG. 3 is a diagrammatic view of a portion of another illustrative freewheeling synchronizer; and

[0012] FIG. 4 is an enlarged view of the synchronizer of FIG. 1 .

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0013] The following description of the embodiments is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0014] In general, the present disclosure includes a synchronizer having freewheeling clutch functionality, for example, to enable non- synchronous or overlapping application of dual clutches in a dual-clutch type of layshaft transmission. Those skilled in the art will recognize that such a freewheeling synchronizer can be applied in any other type of transmission, or any other suitable power transmission device where it is desired to selectively rotatably couple one component to another using a synchronizer. For example, the freewheeling synchronizer of the present disclosure may be used with an automatic transmission, manual transmission, continuously variable transmission, hybrid or electric motorized transmission, automotive transfer case, or the like.

[0015] As used herein, the term synchronizer includes a device to gradually equalize speed, or achieve common rotation, of two rotatable components before the components are positively coupled to one another by the synchronizer. As also used herein, the terminology freewheeling clutch is synonymous with overrunning clutch and one-way clutch, and includes a device that disengages a drive component from a driven component when the driven component rotates faster than the drive component.

[0016] Referring now to FIG. 1 , an illustrative freewheeling synchronizer 10 is illustrated in conjunction with a portion of an illustrative dual-clutch transmission T having a counter shaft S and gears G1 , G3. As shown in FIG. 2, the freewheeling synchronizer 10 includes an integrated freewheeling clutch 12. The freewheeling clutch 12 may include a clutch race 14 that may include an inner spline diameter 16 for positive coupling to corresponding splines of another component, for example, the input shaft S (FIG. 1 ) and may also include an outer ratchet diameter 18 defining a plurality of notches 20. The freewheeling clutch 12 may also include one or more unidirectional clutching elements, for example, pawls 22 for engagement with the notches 20 of the clutch race 14 and corresponding springs 24 for urging the pawls 22 into such engagement. The freewheeling clutch 12 may further include a portion of a synchronizer hub 26 disposed radially outwardly of the clutch race 14 and unidirectionally rotatable with respect thereto. The synchronizer hub 26 may include pawl pockets 28 for housing the pawls 22 and spring recesses 30 for housing the springs 24. An illustrative freewheeling clutch is described and illustrated in U.S. Patent 6,745,881 , which is assigned to the assignee hereof and is hereby incorporated by reference herein in its entirety in accordance with the teachings herein.

[0017] Although the illustrated freewheeling clutch 12 is a pawl-and- ratchet driving mechanism, any suitable type of freewheeling clutch mechanism may be used. For example, as shown in FIG. 3, a generic freewheeling clutch 1 12 may include a clutch race 1 14, a synchronizer hub 126, and any suitable type of unidirectional clutching element(s) 122 therebetween. For example, the element(s) 122 may include pivoted pawls, slidable pawls, balls or rollers, wedging pawls or blocks, two-point grippers, springs, cams, sprags, or other like devices as well as related components, for example, springs, cages, guides, or the like.

[0018] In addition to the freewheeling clutch 12, the freewheeling synchronizer 10 may also include the rest of the synchronizer hub 26, which may also include an axially splined outer diameter 32, and strut pockets 34 radially disposed therein. The freewheeling synchronizer 10 may further include an axially movable sleeve 36 including an axially splined inner diameter 38 for slidable splined engagement with the splined outer diameter 32 of the hub 26, and a circumferentially grooved outer diameter 40 to accept a shift fork (not shown) to axially move the sleeve 36. Gear selection may be performed by an actuator (not shown) that moves the shift fork to move the sleeve 36 of the freewheeling synchronizer 10. The freewheeling synchronizer 10 may also include a detent mechanism, which may include a ring spring 42 carried between the hub 26 and the sleeve 36 for yieldable engagement with a spring groove 43 of the sleeve 36. The freewheeling synchronizer 10 may also include reaction rings 46 fixed to the respective gears G1 , G3, blocker rings 48 positioned between the reaction rings 46 and the hub 26 and sleeve 36, and friction material 50 carried between corresponding conical surfaces of the rings 46, 48. One illustrative synchronizer is described and illustrated in U.S. Patent 5,269,400, which is assigned to the assignee hereof and is hereby incorporated by reference herein in its entirety in accordance with the teachings herein.

[0019] Like the hub 26, the reaction and blocker rings 46, 48 include splined outer diameters 52, 54 adapted for cooperation with the splined inner diameter 38 of the sleeve 36 when the sleeve 36 is axially moved. But before the splined diameters 38, 52, 54 can engage, axial movement of the sleeve 36 initiates frictional contact between corresponding conical surfaces of the reaction and blocker rings 46, 48 to bring the speeds of the gear G1 or G3 and shaft S together. For example, struts 44 may be disposed in the strut pockets 34 for axial engagement of the blocker rings 48 upon axial movement of the sleeve 36. Once the speeds are substantially synchronized, the sleeve 36 can pass over the blocker and reaction rings 48, 46. Accordingly, the sleeve splined inner diameter 38 interengages the ring splined outer diameters 54, 52, while still being partially engaged with the hub splined outer diameter 32, so as to positively couple the shaft S to the gear G1 or G3 through the freewheeling synchronizer 10.

[0020] The freewheeling clutch 12 may lock the rest of the freewheeling synchronizer 10 to the shaft S in one rotational direction, and may permit freewheeling of the freewheeling synchronizer 10 relative to the shaft S and vice-versa. More specifically, the freewheeling clutch 12 may enable the clutch race 16 and synchronizer hub 26 to be freewheelable relative to one another. In other words, using the freewheeling clutch 12, the shaft S may rotate faster than the hub 26 of the freewheeling synchronizer 10, for example, to permit the freewheeling synchronizer 10 to remain engaged to its respective gear G1 or G3 while some other synchronizer (not shown) is engaged to some other gear (not shown) to increase the speed of the shaft S.

[0021] In locked operation, rotation of the gear G1 or G3 is transmitted through the splined diameter 52 of the reaction ring 46, through the splined sleeve 36, through the splined synchronizer hub 26, through the pawl(s) 22, through the splined clutch race 14, and into the splined shaft S. In freewheeling operation, the shaft S and clutch race 14 may rotate faster than the hub 26 such that the pawls 22 come out of engagement with the notches 20 of the clutch race 14. Accordingly, a respective one of the dual input clutches (not shown) associated with the freewheeling synchronizer 10 and gear G1 or G3 does not slip and its load is automatically released or at least reduced when the shaft S rotates faster than the synchronizer hub 26.

[0022] Generally, a multiple input clutch transmission may receive power input from an engine flywheel through multiple input clutches coupled respectively to multiple input shafts. For example, a dual-clutch transmission may include two input clutches that receive power from a flywheel and may include two input shafts coupled to a lay shaft or counter shaft with several pairs of meshed gears therebetween. One illustrative dual-clutch transmission is described and illustrated in U.S. Patent 7,219,571 , which is assigned to the assignee hereof and is hereby incorporated by reference herein in its entirety in accordance with the teachings herein.

[0023] The dual-clutch transmission multiplies the received power between one or the other of the two input shafts and the counter shaft using one of the pairs of meshed gears therebetween at any given moment. The dual-clutch transmission may transmit the multiplied power from the counter shaft to an output shaft, which may be coupled to some downstream device like a vehicle axle.

[0024] Each input shaft carries different gears thereon in either a fixed manner, or in a selectively fixable manner. In one example, the first input shaft may carry odd gears and the second input shaft may carry even gears. More particularly, in a 6-speed dual-clutch transmission one input shaft may include forward gears 1 , 3, and 5, and the other input shaft may include forward gears 2, 4, and 6 as well as a reverse gear.

[0025] Similar to the input shafts, the counter shaft may carry different fixed and/or selectively fixable gears for meshed engagement with the corresponding input shaft gears on the input shafts. Accordingly, the transmission includes several different pairs of meshed gears between the input shafts and the counter shaft to define different gear ratios.

[0026] The synchronizers are carried on the input shafts and/or counter shaft next to respective gears so that the synchronizers can selectively fix a selectively fixable gear to its respective shaft. The synchronizers ensure that the rotational speed of the selected gear closely matches that of its respective shaft to enable smooth gear ratio shifting amongst the different pairs of meshed gears.

[0027] Uniquely, the synchronizers are carried on their respective shafts in such a manner so that they can freewheel in one direction about the shafts. This configuration enables particularly good shift feel and shift timing by enabling smooth release of an off-going one of the input clutches as the other, on-coming input clutch gains torque capacity and engages. In other words, the off-going input clutch need not be entirely disengaged when the oncoming input clutch becomes fully engaged.

[0028] In fact, both input clutches may be simultaneously fully engaged. In a specific example, the synchronizers may be arranged such that when the first input clutch is transmitting power, the power path of the second input clutch is free to permit synchronous selection of a gear of different gear ratio. Then, by gradually disengaging the first input clutch and gradually engaging the second input clutch, the power path is changed from the first input shaft to the second input shaft and through the selected gear.

[0029] With reference to FIG. 1 of the incorporated U.S. Patent 7,319,571 , the freewheeling synchronizer 10 may be substituted for the synchronizers 74, 76, 78, 80 disclosed therein. For example, the freewheeling synchronizer 10 may be substituted for the synchronizers 78, 80 on the counter shaft 18 so that the counter shaft 18 may freewheel with respect to the freewheeling synchronizer hubs 26. [0030] For instance, if the freewheeling synchronizer 10 is substituted for first/third gear synchronizer 78, the resulting synchronizer 10/78 as well as the first input clutch 32 may remain engaged during and even after an upshift from first gear to second gear. In this scenario, when the reverse/second gear synchronizer 80 becomes engaged to its selectable second gear 54, the counter shaft 18 will increase in speed and will freewheel with respect to the engaged freewheeling synchronizer 10/78.

[0031] Similarly, if the freewheeling synchronizer 10 is substituted for reverse/second gear synchronizer 80, the resulting synchronizer 10/80 as well as the second input clutch 34 may remain engaged during and even after an upshift from second gear to third gear. In this scenario, when the third/fifth gear synchronizer 76 becomes engaged to its selectable third gear 42, the counter shaft 18 will increase in speed and will freewheel with respect to the engaged freewheeling synchronizer 10/80.

[0032] Accordingly, the counter shaft 18 and clutch races 14 of the synchronizers 10/78, 10/80 are freewheelable relative to the synchronizer hubs 26 thereof during a transmission upshift to allow both input clutches to be simultaneously fully applied. Therefore, the engagement and disengagement of the input clutches need not be synchronized to achieve an upshift. Rather, both input clutches may be fully applied for an overlapping period of time.

[0033] The freewheeling synchronizer 10 also may be substituted for the synchronizers 74, 76 on the input shafts 16, 14 so that the freewheeling synchronizer hubs 26 may freewheel with respect to the shafts 16, 14. [0034] In any case, use of the freewheeling synchronizer 10 may enable faster shifting because selection of both odd and even gear ranges can be carried out with little to no impact on system drag. In contrast, selection of both odd and even gear ranges in a conventional system would necessarily result in higher system drag at least for the time that both odd and even ranges are selected. Such drag in the conventional system may be attributed to forced slip across one or more open clutches in order to select both an odd and even gear range. But use of the freewheeling synchronizer reduces or eliminates the need for forced slip across the clutch(es), thereby reducing or eliminating drag.

[0035] The above description of embodiments of the invention is merely illustrative in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.