GB2079877A

GB2079877A - Multi-ratio gearbox

Info

Publication number: GB2079877A
Application number: GB8022137A
Authority: GB
Original assignee: Rolls Royce Motors Ltd
Current assignee: Bentley Motors Ltd
Priority date: 1980-07-05
Filing date: 1980-07-05
Publication date: 1982-01-27
Also published as: GB2079877B

Abstract

A multi-ratio gearbox for a vehicle comprises an input shaft (10), an output shaft (11) and two intermediate shafts (12, 13). The shafts, (10, 11, 12, 13) carry a plurality of gears (14, 15, 16, 17, 18, 19, 20, 21, 22, 23). Some of the gears (15, 16, 17, 18, 22) are free to rotate on the shafts whilst others are fixed (19, 20, 21, 23) and dog or friction clutches (33, 34, 38, 41) are associated with the rotatably mounted gears (15, 16, 17, 18, 22) so that they may be fixed rotatably with respect to their associated shafts. A gear (14) on the input shaft (10) meshes with gears (18, 22) on the intermediate shafts (12, 13) and gears (19, 20, 21) on the intermediate shafts (13 and 14) mesh with respective gears (15, 16, 17) on the output shaft (11) so that depending on whether the gears on the intermediate shaft are free to rotate or not a different gear ratio is provided. An additional ratio is provided by allowing for input and output shafts (10 and 11) which are coaxial to be directly connected and provision may be made for reverse ratios. In an alternative form (Figure 3, not shown), the input shaft is in the form of a sleeve and coaxially surrounds one of two intermediate shafts which both carry gears on the output shaft. In a further embodiment (Figure 5, not shown), the dog clutches have synchronizers. <IMAGE>

Description

SPECIFICATION A multi-ratio gearbox The present invention relates to a gearbox.

In our co-pending application No. 31496/78 there was disclosed a multi-ratio Countershaft type gearbox in which a gear wheel free to rotate on a shaft may be connected to drive that shaft b a sliding dog clutch or alternatively may serve as an idler gear to drive another shaft in order to provide an additional ratio without increasing the length of the gearbox.

The present invention extends the use of this principle of using a gear wheel in two alternative roles to provide a plurality of additional ratios wil minimal additional complexity and size and particularly without increasing the length of the gearbox. These additional ratios may be either forward or reverse.

According to the present invention there is provided a gearbox comprising an input shaft, output shaft, first and second intermediate shaft; two gears mounted for rotation on the output shaft, means for preventing rotation of each gear relative-to the output shaft such that each gear may be employed to drive the output shaft, disconnectable means enabling the first intermediate shaft to be driven from the input shaft, two gears fixedly mounted on the first intermediate shaft and meshing with respective gears on the output shaft, disconnectable means enabling the second intermediate shaft to be driven from the input shaft and a gear fixedly mounted on the second intermediate shaft meshing with one of the gears on the output sha The-effect of this arrangement is that the first intermediate shaft may be driven either by its ow disconnectable driving means or alternatively at different speed ratio through the second intermediate shaft and the output shaft gear which then functions as an idler. Compared with the conventional arrangement, the total number ratios availabie is therefore increased by the number of gear pairs connecting the first intermediate shaft to the output shaft.

A preferred embodiment of the invention may comprise any one or more of the following advantageous features:- (a) The means enabling the first intermediate shaft to be driven from the input shaft includes a sliding dog clutch.

(b) The means enabling the second intermediate shaft to be driven from the input shaft includes a sliding dog clutch.

(c) The means enabling the first intermediate shaft to be driven from the input shaft includes a friction clutch.

(d) The means enabling the second intermediate shaft to be driven from the input shaft includes a friction clutch.

(e) There are more than two gears on the first intermediate shaft meshing respectively with a plurality of gears freely rotatably mounted on the output shaft with individual means for preventinc rotation of each gear on the output shaft.

(f) The input and output shafts are coaxial and means are provided for drivably connecting both shafts.

(g) The means for drivably connecting the input and output shafts is a friction clutch.

(h) The means for drivably connecting the input and output shaft is a dog clutch.

(i) Means are provided for reverse gear ratios.

(j) There are a plurality of gears on the output shaft and a plurality of respective gears on both the first and second intermediate shafts with which the gears on the output shaft mesh.

(k) The input shaft is sleeve shaped and concentrically surrounds the first intermediate shaft.

In order that the invention may be more clearly understood, several embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a longitudinal section through one form of gearbox according to the invention, Fig. 2 shows a cross section of the gearbox shown in Fig. 1 taken along the line A-A, but with the gearbox shafts differently arranged, Fig. 3 shows a longitudinal section through another form of gearbox according to the invention, Fig. 4 shows a cross section of the gearbox shown in Fig. 3, Fig. 5 shows a longitudinal section through a gearbox similar to that shown in Fig. 1 but in which speed synchronising means are provided for the dog clutches, and Fig, 6 shows a longitudinal section through a gearbox similar to that shown in Fig. 1 but in which the dog clutches are replaced by friction clutches.

Referring to Figures 1 and 2, the gearbox comprises an input shaft 10 and an output shaft 11. These shafts 10 and 11 are coaxial. A gear 14 is fixed to input shaft 10 and extended to provide dog clutch teeth 24. The output shaft 11 carries gears 1 5, 1 6 and 17 which are extended to provide dog teeth 25, 26 and 27 respectively and are free to rotate on bearings 28, 29 and 30 respectively. Toothed hubs 31 and 32 are splined to output shaft 11 and carry dog clutches members 33, which may be moved axially to engage teeth 24 or 25, and 34 which may be moved axially to engage teeth 26 or 27. First and second intermediate shafts 1 2 and 1 3 are arranged parallel to the coaxial input and output shafts 10 and 11.Input shaft 10 is mounted for rotation in bearing 1, output shaft 11 in bearings 2 and 3, intermediate shaft 12 in bearings 4 and 5 and intermediate shaft 13 in bearings 6 and 7. The whole gearbox is disposed in a housing 8. Gears 19, 20 and 21 are fixed on the first intermediate shaft 12 and mesh with gears 15,16 and 17 respectively on the output shaft 11. A gear 1 8 is carried on first intermediate shaft 12, is free to rotate on a bearing 35, and is extended to provide dog clutch teeth 36. The toothed hub 37 is splined to shaft 12 and carries dog clutch member 38 which may be moved axially to engage teeth 36. A gear 23 is fixed on the second intermediate shaft 13, and meshes with gear 16 on the output shaft 11.A gear 22 is carried on the second intermediate shaft 13, is free to rotate on bearing 39, and is extended to provide dog clutch teeth 40. The dog clutch member 41 is mounted on teeth 42 formed on intermediate shaft 13 and may be moved axially to engage teeth 40. Gears 22 and 23 have fewer teeth than gears 13 and 19 respectively.

When the dog clutch member 38 is in engagement with the teeth 36 the gearbox functions in the same manner as a conventional four speed gearbox. The input shaft 10 drives the first intermediate shaft 12 through gears 14 and 18 and dog clutch member 38. The gears 19, 20 and 21 drive the gears 15, 16 and 17 which may be selectively connected to the output shaft 11 by movement of the dog clutch members 33 or 34 to engage teeth 25, 26 or 27 as described above, providing three transmission ratios. Alternatively the dog clutch member 33 may be moved to engage teeth 24 to connect the input and output shafts 10 and 11 together to provide a direct drive.

When the dog clutch member 38 is disengaged from teeth 36 and the dog clutch member 41 is in engagement with teeth 40, the second intermediate shaft 13 is driven from the input shaft 10 through gears 14 and 22 and dog clutch member 41, and drives the first intermediate shaft 12 through gears 23, 16 and 20. Because gears 22 and 23 have fewer teeth than gears 18 and 19 respectively, the first intermediate shaft 12 rotates at a lower speed than when driven through the dog clutch 38 and lower output shaft speeds are therefore obtained when gears 1 5, 16 or 17 are connected to the output shaft 11. With dog clutch member 34 in engagement with teeth 26 of gear 1 6 the second intermediate shaft 13 drives the output shaft 11 through gears 23 and 16 and dog clutch member 34.With dog clutch member 34 in engagement with teeth 27, or dog clutch member 33 with teeth 25, the second intermediate shaft 13 drives the first intermediate shaft 1 2 through gear 1 6 which then acts as an idler gear and gear 20. The second intermediate shaft 13 then drives the output shaft through gears 21 and 17, or 19 and 15.

A total of seven forward transmission ratios is obtained with the arrangement shown in Figure 1, which may be considered as providing 'high' and 'low' ratios in first second and third ranges, according to whether dog clutch 38 or dog clutch 41 is engaged, and a direct drive. A conventional arrangement to provide a reverse ratio may be used but is not shown. 'High' and 'low' reverse ratios will be available according to whether dog clutch 38 or dog clutch 41 is engaged.

Figure 2 shows that arranging the shafts in one plane as shown for convenience in Figure 1 is probably not the best arrangement. In Figure 2 the intermediate shafts 12 and 13 are positioned so that the gears 18 and 22 just miss each other.

This arrangement results in a gearbox of convenient shape and when the ratios are engaged in which the gear 1 6 functions as an idler the equal tooth loads 'a' and 'b' imposed upon gear 1 6 from gears 23 and 20 respectively, are as nearly as possible in opposite directions and the resultant load on bearing 29 is minimised.

The gearboxes of Figures 1 and 2 would be particularly suitable for heavy commercial vehicles requiring a large number of speed ratios in a short axial length.

A further form of gearbox is illustrated in Figures 3 and 4 which is intended for use in a tracked vehicle in which a plurality of reverse ratios is necessary to achieve the required performance. As with the gearboxes of Figures 1 and 2, the gearboxes of Figures 3 and 4 comprise an input shaft 110, output shaft 111 and first and second intermediate shafts 112 and 11 3. Input shaft 110 is mounted for rotation in bearings 80 and 81, output shaft 111 in bearings 82 and 83, intermediate shaft 112 in bearings 84 and 85 and intermediate shaft 11 3 in bearings 86 and 87. In this case the input shaft 110 is sleeve form, surrounds part of the first intermediate shaft 112 and is driven from the engine through a friction clutch, not shown, a shaft 107 and bevel gears 108 and 109.The output shaft 111 is connected at both ends through final drives, not shown, to the track driving sprockets for respective tracks of the tracked vehicle. No direct drive is provided in the gearbox.

The first intermediate shaft 112 may be driven from the sleeve 110 by moving a dog clutch member 114, which is driven by a toothed hub 11 5 fixed to the sleeve 11 0, into engagement with teeth 11 6 on a member 117 which is fixed to theshaft112.Gears 118,119,120and 121 fixed to shaft 112 and gear 122 fixed to sleeve 110 mesh with gears 123, 124, 125, 126 and 127 respectively which are extended to provide clutch teeth 128,129,130,131 and 132 respectively and are supported on the output shaft 111 by bearings 133,134,135,136 and 137 respectively.Toothed members 138,139 and 140 are fixed to shaft 111 and carry axially, movable dog clutch members 141,142 and 143 respectively which may be moved axially to connect gears 133, 134, 135, 136 or 137 to drive the output shaft 111.

The second intermediate shaft 113 is driven from gear 122 fixed to sleeve 110 which meshes with gear 144 as shown in Figure 4. Gear 1 44 is supported on shaft 113 by bearing 145 and is extended to provide dog clutch teeth 146. A toothed member 147 is fixed to shaft 113 and carries dog clutch member 148 which may be moved axially to drive shaft 113 from gear 144.

Gear 149 is fixed to shaft 113 and meshes with gear 125 on output shaft 111.

When dog clutch 114 is in engagement with teeth 11 6 the sleeve 110 and the shaft 112 rotate together and gears 118,119,120,121 and 122 drive gears 123,124,125,126 and 127 on the output shaft at different speeds. Five different forward speed ratios are therefore available by engaging dog clutches 141, 142, or 143 on output shaft 111 with teeth 128, 129, 130, 131 or 132. A sixth forward ratio is provided by gear 1 50 supported on bearing 1 52 on sleeve 110 and extended to provide dog clutch teeth 1 53 which may be engaged by dog clutch member 114 to drive gear 1 51 which is fixed to shaft 111.

When dog clutch 114 is not in engagement with teeth 116 or 1 53 the dog clutch member 148 may be moved to engage teeth 146 on gear 144. The second intermediate shaft 11 3 is then driven from the sleeve 110 by gears 122 and 144 and the first intermediate shaft 112 is driven from shaft 113 by gears 149, 125 and 120, causing it to rotate in the opposite direction from sleeve 110. Engagement of dog clutch members 141 or 142 with teeth 128,129, or 131 will thus engage one of four available reverse ratios. When dog clutch member 142 is engaged with teeth 1 30 the output shaft 111 is driven from the sleeve 110 through gears 122, 144, 149 and 125.In the other reverse ratios shaft 11 2 is driven by shaft 110 through gears 122, 144, 149, 125 and 120, and the output shaft 111 is driven through gears 118 and 123, or 119 and 124 or 121 and 126.

The gear 1 25 is then employed as an idler.

Figure 4 shows the true relative positions of the shafts and shows that the equal loads represented by the arrows 'C' and 'D', applied to teeth of gear 125 by gears 149 and 120 is functioning as an idler, are in approximately opposite directions and the load on bearing 135 is therefore low.

Referring to Fig. 5, a longitudinal section of a gearbox similar to that shown in Fig. 1 is shown, but in which speed synchronising means are provided for all the dog clutches. In the Fig. 5 gearbox parts equivalent to the part of the Fig. 1 gearbox are given the same reference numeral as in Fig. 1 but prefixed by the numeral 5. Thus, for example, input shaft 10 in Fig. 1 is equivalent to input shaft 510 in Fig. 5.

Speed synchronising means are provided between gears 514 and 515, gears 516 and 517 and adjacent to gears 518 and 522. Those between gears 514 and 515 consist of a synchronising sleeve 1 52 surrounding and supported by a sliding dog clutch member 1 53 and surrounded by a ring 1 54 which is fixed to the sliding member 1 53 by a plurality of pins 1 55 passing through axial slots 1 56 in the sleeve 1 52.

The ring 1 54 is engaged by a selector fork 1 57.

Spring loaded balls or plungers 1 58 engage a circumferential groove 1 59 formed in the internal wall of sleeve 1 52. The axial slots 1 56 are widened locally at the centre to provide baulking surfaces. The sleeve 1 52 has internal conical surfaces 160 and 161 which coact with surfaces 162 or 1 63 on gears 514 and 51 5 respectively to produce the synchronising torque when fork 1 57 is moved from the central position shown.

The dog clutch and synchronising assembly shown diagrammatically at 164 for the gears 516 and 51 7 is as described above but is larger in size to provide the higher synchronising torques required for changes into the lower gears.

The synchronising assembly for gears 522 and 51 8 are also of the design described above but are "single-ended" and have discs 1 65 and 1 66 attached to the respective shafts to position synchronising sleeves 1 67 and 1 68 correctly when the dog clutches are disengaged. The dog clutch for gear 522 is re-positioned compared with Fig. 1 because of space limitations. Parts equivalent to parts of the above described synchronising assembly have been given the same reference numerals but with the prefix numeral 1 replaced by numeral 2.

Other known designs of synchroniser could be used, but the type illustrated is preferred because it permits large diameter cones within a restricted space.

Referring to Fig. 6, a version of the embodiment of gearbox shown in Fig. 1 is illustrated, in which dog clutches are replaced by friction clutches. In similar fashion to Fig. 5, parts equivalent to parts of the gearbox of Fig. 1 are given the same reference numberal as in Fig. 1 but prefixed by the numeral 6.

Referring to the clutch associated with gear 622, the gear hub is extended and has fixed to it (by splines) a clutch housing 1 70 having internal teeth 1 71 which support the driven clutch plates.

A hub 172 is fixed (also by splines) to the shaft 613 and has external teeth 173 supporting the driving clutch plates which are assembled alternately with the driven plates. An annular piston 1 74 is free to move axially in a housing 1 75 fixed to the clutch housing 1 70 and has sliding seals 1 76 and 1 77. Oil under pressure supplied by a pump (not shown) and directed by a control valve (not shown) is fed through a stationary bobbin 178 having rotating seals 179 and 180, and through passage 181 into an annular space 182 and acts upon the piston 174 to clamp the clutch plates together.

The intermediate shaft 613 and the gear 622 together with its clutch are supported by roller bearings 183 and 184.

The clutch 185 for the gear 618 is as described above except that it is larger, to transmit the higher torque through this gear. Parts equivalent to parts of the above described clutch have been given the same reference numerals except that the numeral 1 prefix has been replaced by numeral 2.

The clutch unit 1 86 consists of two clutches having a common housing 1 87 for two pistons 188 and 189 which is fixed (by splines) to the shaft 611 and has fixed to it two clutch housings 1 90 and 191 which support the driven clutch plates. The driving clutch plates are supported by externally toothed extensions of the gears 614 and 615 respectively. The clutch for the gear 61 5 has more plates because it has to transmit a higher torque.

The clutch unit shown diagrammatically at 1 92 for the gears 616 and 61 7 is of essentially the same design as the unit 1 86 but is larger in diameter because these clutches have to transmit high, torques.

Oil under pressure and directed by control valves is fed to the clutches in the units 186 and 192 by four ducts 193,194,195 and 196 to circumferential grooves in a rotating sleeve 1 97 having seals 198 and then through drillings in output shaft 611, one of which is illustrated at 199,200 and 201.

A further embodiment which might be found advantageous would be to use friction clutches to engage gears 1 8 and 22, as shown in Fig. 6 and dog clutches, with or without synchronisers, as shown in Fig. 1 or Fig. 6 to engage gears 1 5, 1 6 and 1 7 and direct drive.

Claims

1. A gearbox comprising an input shaft, output shaft, first and second intermediate shafts, two gears mounted for rotation on the output shaft, means for preventing rotation of each gear relative to the output shaft such that each gear may be employed to drive the output shaft, disconnectable means enabling the first intermediate shaft to be driven from the input shaft, two gears fixedly mounted on the first intermediate shaft and meshing with respective gears on the output shaft, disconnectable means enabling the second intermediate shaft to be driven from the input shaft and a gear fixedly mounted on the second intermediate shaft meshing with one of the gears on the output shaft.

2. A gearbox as claimed in Claim 1 in which the means enabling the first intermediate shaft to be driven from the input shaft includes a sliding dog clutch.

3. A gearbox as claimed in Claims 1 or 2, in which the means enabling the second intermediate shaft to be driven from the input shaft includes a sliding dog clutch.

4. A gearbox as claimed in Claim 1, in which the means enabling the first intermediate shaft to be driven from the input shaft includes a friction clutch.

5. A gearbox as claimed in Claim 1 or 2, in which the means enabling the second intermediate shaft to be driven from the input shaft includes a friction clutch.

6. A gearbox as claimed in any preceding claim, in which there are more than two gears on the first intermediate shaft meshing respectively with more than two gears freely rotatably mounted on the output shaft with individual means for preventing rotation of each gear in the output shaft.

7. A gearbox as claimed in any preceding claim, in which the input and output shafts are coaxial and means are provided for drivably connecting both shafts.

8. A gearbox as claimed in Claim 7, in which the means for drivably connecting the input and output shafts is a friction clutch.

9. A gearbox as claimed in Claim 7, in which the means for drivably connecting the input and output shaft is a dog clutch.

10. A gearbox as claimed in any preceding claim, in which means are provided for reverse gear ratios.

11. A gearbox as claimed in any preceding claim, in which there are a plurality of gears on the output shaft and a plurality of respective gears on both the first and second intermediate shafts with which the gears on the output shaft mesh.

12. A gearbox as claimed in any of Claims 1-6, in which the input shaft is sleeve shaped and concentrically surrounds the first intermediate shaft.

13. A gearbox substantially as hereinbefore described with reference to Figure 1 or Figure 2 or to Figures 3 and 4 of the accompanying drawings.