MULTI-RATIO POWER TRANSMISSION

Abstract: A preselected multi-ratio power transmission has three friction clutches (l6,l8,20) and one mechanical synchroniser clutch assembly (34) to provide five forward speed ratios, and an additional mechanical clutch assembly (48) to provide a reverse ratio. The clutches are combined with a gearing arrangement (22,24,26,28,30,38,40,44) such that either sequential shifting or skip-shifting is possible.

Description: This invention relates to preselected multi-ratio power transmissions as specified in the preamble of claim 1, for example as disclosed in US-A-4 488 446. US-A-4 513 631 also discloses a preselected multi-ratio power transmission that permits both sequential and skip-shifting patterns, but achieves the skip-shifting patterns by the use of duplicate ratio gearing. The present invention is concerned with the provision of a preselected multi-ratio power transmission that permits ratio skip-shifting without the need for duplicate ratio gearing, and specifically with the use of only one mechanically synchronised clutch assembly for the forward gear ratios. To this end a preselected multi-ratio power transmission in accordance with the present invention is characterised over US-A-4 488 446 by the features specified in the characterising portion of claim 1. In a preselected multi-ratio power transmission in accordance with the present invention, the number of forward gear ratios can if required be increased in pairs by the addition of, in respect of each pair, a single friction clutch and the appropriate ratio gear elements. However, even with the addition of two forward ratios, only the one mechanically synchronised clutch is required for the forward ratios. It is thus within the scope of the present invention for an improved preselected multi-ratio power transmission to have three selectively engageable friction clutches, one mechanically synchronised clutch assembly and four pairs of ratio gears which are selectively operable in combination to provide five forward gear ratios. It is also within the scope of the present invention for an improved preselected multi-ratio power transmission to have three selectively engageable friction clutches, two mechanically synchronised clutch assemblies, four pairs of ratio gears and a reverse idler gear which are selectively operable in combination to provide five forward gear ratios and one reverse ratio. It is further within the scope of the present invention for an improved preselected multi-ratio power transmission to have a plurality of selectively engageable friction clutches, one mechanically synchronised clutch assembly and a plurality of pairs of ratio gears sufficient to provide forward ratios equal in number to one less than twice the number of the friction clutches, wherein the components are selectively operable in combination to provide an odd number of forward gear ratios in a manner which permits shifting to and across the centremost (central) forward ratio. In the drawing: Figure 1 is a schematic representation of a preferred embodiment of a preselected multi-ratio power transmission in accordance with the present invention; and Figure 2 is a diagrammatic representation of an end view of a portion of the ratio gearing of the preselected multi-ratio power transmission shown in Figure 1. With reference now to the drawing, in which like characters represent like or corresponding parts in the respective views, there is seen in Figure 1 a preselected multi-ratio power transmission, generally designated 10, having an input shaft 12 and an output shaft 14. The input shaft 12 has operatively connected thereto three rotary friction clutches 16, 18 and 20. The clutch 16 has drivingly connected thereto a pair of gear members 22 and 24; the clutch 18 has connected thereto a gear member 26; and the clutch 20 has drivingly connected thereto a gear 28. The gear member 22 meshes with a gear 30 that is rotatably disposed on the output shaft 14 and is drivingly connected to one portion 32 of a mechanical synchroniser clutch 34. Another portion 36 of the synchroniser clutch 34 is connected to a pair of gears 38 and 40 that mesh with the gear members 24 and 26 respectively. The output member 42 of the synchroniser clutch 34 is drivingly connected to the output shaft 14 and to a gear member 44 which meshes with the gear 28 and with a reverse idler gear 46. The reverse idler gear 46 is operatively connected by way of a single-sided mechanical synchroniser clutch 48 to another reverse idler gear 50 which meshes with the gear member 24. The reverse idler gears 46 and 50 are connected to respective idler shafts 52 and 54. The friction clutches 16, 18 and 20 may be constructed in accordance with any of the well-known selectively engageable friction-type clutches, and may be engaged hydraulically, electrically or mechanically. The synchroniser clutches 34 and 48 may be constructed in accordance with the known synchroniser-type clutches, and may be actuated mechanically, electrically or hydraulically. Controls for such devices are well-known. The friction clutches 16, 18 and 20 and the synchroniser clutch 34 can be selectively engaged in combination to provide five forward-drive speed ratios, as follows. For first-ratio operation, the synchroniser clutch 34 is actuated to provide a drive relationship between the portion 32 thereof and the output shaft 14, thereby connecting the gear 30 to the output shaft 14. Selective engagement of the friction clutch 16 will then transmit driving torque from the input shaft 12 by way of the gear member 22 and gear to the output shaft 14, so providing the first, lowest forward drive ratio of the transmission. For second-ratio operation, the friction clutches 16 and 18 are interchanged, by the use of any of the well-known clutch control mechanisms, such that drive torque from the input shaft 12 will be transmitted by way of the gear member 26 and gear 40, the gear member 38 and gear 24, and the gear member 22 and gear 30 to the output shaft 14. For third-ratio operation, this being the centremost (central) drive ratio, the friction clutches 18 and 20 are interchanged such that the input torque at the input shaft 12 is delivered by way of the gear 28 and gear member 44 to the output shaft 14. During third-ratio operation, the synchroniser clutch 34 is torque-unloaded, such that free manipulation thereof is possible. During third-ratio operation, also, the synchroniser clutch 34 provides disengagement between the portion 32 thereof and the output shaft 14, and is moved into engagement to provide a driving connection between the portion 36 therof and the output shaft 14. For fourth-ratio operation, after manipulation of the synchroniser clutch 34 the fourth-ratio drive is established by simultaneously interchanging the friction clutches 16 and 20. With the friction clutch 16 engaged, input torque is delivered by way of the gear member 24 and gear 38 to the output shaft 14. For fifth-ratio operation, this being the highest forward gear ratio, the friction clutches 16 and 18 are interchanged. With the friction clutch 18 engaged, the input torque on the input shaft 12 is directed by way of the gear member 26 and gear 40 to the output shaft 14. A reverse gear ratio is engaged with the vehicle stationary and the synchroniser clutch 34 in neutral by engaging the synchroniser clutch 48 and thereafter controllably engaging the friction clutch 16 such that forwardly directed input torque on the input shaft 12 is connected by way of the gear member 24 and the reverse idler gear 50, and the reverse idler gear 46 and gear member 44, to the output shaft 14. The reverse idler gears 50 and 46 provide for reversal of the direction of rotation between the input shaft 12 and the output shaft 14. From the above description it will be evident that sequential shifting of the forward gear ratios, namely the first to the fifth ratio, is easily accomplished. This is a conventional shifting pattern. However, with the present invention, it is also possible to provide skip-shifting from the first ratio to the third ratio and to the fifth ratio in the following manner. The synchroniser clutch 34 is actuated to engage the portion 32 thereof, and thereafter the friction clutch 16 is engaged to provide first-ratio operation. Selective interchange of the friction clutches 16 and 20 will then permit a skip-shift ratio change from first to third ratio. During third-ratio operation, the synchroniser clutch 34 can be manipulated to engage the portion 36 thereof, after which the friction clutches 20 and 18 may be interchanged to provide a skip-shift ratio change from third to fifth ratio. Downshifting direct from fifth ratio to third ratio, and then direct from third ratio to first ratio, can be accomplished by reversing the clutch interchanges. In some instances it may be desirable to provide additional forward speed ranges. Additional forward speed ranges can be provided in pairs by the addition of a single friction clutch and gear member and an additional gear member that is made drivingly connectible to the synchroniser portion 36. The additional gear ratios may be obtained by selective engagement of the added friction clutch; depending on the position of the synchroniser clutch 34, the additional ratio will be either lower or higher than the centremost (central) ratio provided by the friction clutch 20 and the gear 28 and gear member 44. The addition of a friction clutch will not inhibit the skip-shifting from a ratio below the central ratio to the central ratio and then skip-shifting above the central ratio. For example, in a seven-speed transmission, skip-shifting from first to fourth to sixth or seventh ratio may be accomplished, as may skip-shifting from second to fourth to sixth or seventh ratio. From the above description it will be evident that the five speed-ratio transmission described is a basic element in providing a preselected skip-shifting multi-ratio power transmission. The addition of gear ratios to the transmission is readily accomplished, such that the overall transmission ratios can be expanded from five to seven to nine or more. The limiting factor of adding transmission ratios is in fact a physical one, determined by the volume (space) required for the transmission to fit into the vehicle. Thus a family of transmissions can be provided by expanding the basic five-speed transmission described herein.

Claims: A preselected multi-ratio power transmission in which input means (12) for transmitting drive forces; output means (14); first, second and third friction clutch means (16,18,20) each selectively engageable with the input means (12) for accepting drive forces therefrom; first input gear means (22,24) drivingly connected to the first friction clutch means (16); second input gear means (26) drivingly connected to the second friction clutch means (18); third input gear means (28) drivingly connected to the third friction clutch means (20); first output gear means (30) meshing with the first input gear means (22,24); second output gear means (38,40) meshing with the first (22,24) and second (26) input gear means; third output gear means (44) meshing with the third input gear means (28) and drivingly connected to the output means (14); and a synchroniser clutch (34) for selectively engaging the first output gear means (30) with the output means (14); the first friction clutch means (16) and the synchroniser clutch (34) co-operating during engagement to establish two drive ratios between the input (12) and output (14) means; the third friction clutch means (20) being engageable to provide another drive ratio between the input (12) and output (14) means which is numerically central of the said two drive ratios; characterised by reverse gear means (46,50) drivingly connected between the first input gear means (22,24) and the third output gear means (44) and including a selectively engageable mechanical clutch means (48); in that the synchroniser clutch (34) is alternately actuable to selectively engage the second output gear means (38,40) with the output means (14); in that the second friction clutch means (18) and the synchroniser clutch (34) when engaged co-operate to establish two other drive ratios between the input (12) and output (14) means, with said another drive ratio being numerically central of the said two other drive ratios; and in that the first friction clutch means (16) and the mechanical clutch means (48) are simultaneously engageable to establish a reverse drive ratio between the input (12) and output (14) means. A preselected multi-ratio power transmission according to claim 1, characterised in that during the engagement of the third friction clutch means (20) the synchroniser clutch (34) is relieved of transmitting drive forces. A preselected multi-ratio power transmission according to claim 1 or 2, characterised in that the third friction clutch means (20) is engageable to provide a numerically central drive ratio between the input means (12) and the output means (14), and the transmission ratio is arranged to be interchanged from first to second ratio by interchange of the first (16) and second (18) friction clutches without manipulation of the synchroniser clutch (34).

Inventors: POLAK, JAMES CASIMIR
Applicants: GENERAL MOTORS CORPORATION
Application year: 1986
Main classification: F16H3
IPC codes: F16H61, F16H3, F16H63, F16H1