GEARBOX

Abstract: A known gearbox is modified to add a fifth gear ratio by using a lay shaft (24) of extended length with an additional gear (38) fixed to it. The driven shaft (12) is also of extended length and includes an additional gear (40) which meshes with the gear (38). A synchromesh assembly (42) slides on the driven shaft (12) to connect the gear (40) driveably to the driven shaft (12).

Description: GEARBOX This invention relates to a gearbox and to a gear ratio selector mechanism therefor. One object of the invention is to modify a known gearbox by adding means whereby a further gear ratio can be obtained. Another object is to provide a novel gear ratio selector mechanism. According to one aspect of the invention, a modification adding a further gear ratio to a multi-ratio constant mesh gearbox having a drive shaft with a gear fixed thereto, a co-axial driven shaft with x gears rotatable thereon, x+i interconnected gears on a parallel layshaft meshing respectively with the gears on the drive and driven shafts, and synchromesh means on the driven shaft for selectively driveably connecting to said shaft any one of the gears on the drive and driven shaft, comprises an additional gear on the layshaft interconnected to the other gears thereon, an additional gear rotatable on the driven shaft meshing with the additional gear on the layshaft, and additional synchromesh means on the driven shaft for selectively connecting thereto the additional gear on said shaft. Preferably the driven shaft and the layshaft are appropriately lengthened. Preferably the layshaft is rotatable and all the gears thereon are fixed thereto. Preferably, also, the layshaft is of increased diameter. A fifth gear ratio is preferably added to a four- ratio gearbox which has three gears on the driven shaft and synchromesh means comprising two synchromesh assemblies of double-ended type, the additional synchromesh means comprising a synchromesh assembly of single-ended type. Preferably in a modified gearbox according to the preceding paragraph, having a selector shaft with a radial projection which shaft is pivotable and slidable to enable said projection to actuate selectively one of two bell- crank levers pivoted about a common axis which levers slide respectively selector forks associated with the two synchromesh assemblies of double-ended type, and an interlock spool surrounding the selector shaft and pivotable but not slidable therewith, said spool being adapted to prevent the actuation of more than one bell- crank lever, the selector shaft has an additional radial projection which, when the first-mentioned radial projection is inoperatively located, can selectively actuate an additional bell crank lever pivoted about a different axis to the common axis of the aforesaid two bell-crank levers which additional lever slides an additional selector fork associated with the synchromesh assembly. The additional selector fork associated with the synchromesh assembly may be of single-ended type. Preferably, the first-mentioned radial projection and the additional radial projection are diametrically opposed to each other on the selector shaft, and said common axis and said different axis are disposed at opposite sides of the selector shaft. Preferably, also, the first-mentioned radial projection is inoperatively located by pivoting the selector shaft to align said projection with a spacer introduced between the two bell-crank levers on the common axis on the one hand and a reverse gear selector lever pivoted on said axis on the other hand. All the selector forks are preferably carried by a common selector fork shaft, the selector forks associated with the two synchromesh assemblies of double-ended type each being slidable on said shaft and the additional selector fork being fixed to said shaft which is slidable by the additional bell-crank lever. According to another aspect of the invention, a selector mechanism for a multi-ratio gearbox has a selector shaft with two radial projections which shaft is pivotable and slidable to enable one of said projections to actuate gear ratio selector means pivoted at one side of said shaft and to enable the other of said projections to actuate gear ratio selector means pivoted at the other side of said shaft, an interlock spool surrounding the selector shaft and pivotable but not slidable therewith being adapted, in conjunction with the relative disposition of both selector means, to prevent the selection of more than one gear ratio. The present invention also includes a method of modifying a gearbox and a method of operating a selector mechanism. The present invention includes any combination of the herein referred to features. The present invention may be carried into practice in various ways, but a preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which:- Figure 1 is a semi-diagrammatic plan view of the shafts, gears and synchromesh assemblies of a gearbox modified in accordance with the invention; Figure 2 is a semi-diagrammatic side elevation of the gear ratio selector mechanism for said modified gearbox; and Figures 3 and 4 show co-operating components of said selector mechanism. Referring to Figure l of the drawings, a known four- ratio constant-mesh gearbox comprises a casing (not shown) in which there are journalled a drive shaft 10 and a co- axial driven shaft 12. A gear 14 fixed to the drive shaft 10 meshes with a gear 16 forming part of an integral cluster comprising gears 18, 20 and 22. Said cluster is rotatably mounted on a layshaft 24 fixed to the casing. The gears 18, 20 and 22 mesh respectively with gears 26, 28 and 30 rotatably mounted on the driven shaft 12. Synchromesh assemblies 32 and 34 of double-ended type are slidable on splines (not shown) on the driven shaft 12. First (low) gear ratio is obtained by sliding the synchromesh assembly 32 to the left as seen in Figure 1 to connect the gear 30 driveably to the driven shaft 12 in well-known manner. Second gear ratio is obtained by sliding the assembly 32 to the right as seen in Figure 1 to connect the gear 28 driveably to the driven shaft 12. Third gear ratio is obtained by sliding the synchromesh assembly 34 to the left as seen in Figure 1 to connect the - 5 - gear 26 driveably to the driven shaft 12. Fourth (high) gear ratio is obtained by sliding the assembly 34 to the right as seen in Figure 1 to connect the gear 14 driveably to the driven shaft 12, that is to say to establish a direct drive between the drive shaft 10 and the driven shaft 12. A reverse gear ratio is provided by conventional means (not shown) of a reverse, idler gear rotatably mounted on a dead shaft fixed to the casing. Said idler gear meshes with the gear 22 and is slidable on the dead shaft so that it meshes with a gear 36 formed on the synchromesh assembly 32 whilst remaining in mesh with the gear 22. This known gearbox is modified to add a fifth gear ratio which may be an overdrive by employing a layshaft 24 of extended length and possibly of increased diameter which is journalled in a casing which has been strengthened and has the gears 16, 18, 20 and 22 together with an additional gear 38 fixed to it by splines or keys or formed integrally on it. There is also employed a driven shaft 12 of extended length on which an additional gear 40 meshing with the gear 38 is rotatably mounted. A synchromesh assembly 42 of single-ended type is slidable on splines (not shown) on the driven shaft 12, and fifth gear ratio is obtained by sliding the assembly 42 to the right as seen in Figure 1 to connect the gear 40 driveably to the driven shaft 12. Referring now to Figures 2 to 4, the gear ratio selector mechanism for the known four-ratio gearbox hereinbefore described comprises a selector fork shaft 44 • ixed to the casing upon which selector forks 46 and 48 are slidably mounted, the fork 46 co-operating in well- known manner with the synchromesh assembly 32 and the fork 48 co-operating likewise with the synchromesh assembly 34. The fork 46 is slidable by a bell-crank lever 50, and the fork 48 is similarly slidable by a bell-crank lever 52, the levers 50 and 52 being pivoted about a common axis 54 on a pin 56 fixed to the casing. A reverse gear selector lever 58 is also pivoted on the pin 56, the levers 50, 52 and 58, in the known four-ratio gearbox, being equally spaced apart by the same working clearance. The lever 58 carries a peg (not shown) which engages in an annular groove in the hub of a reverse idler gear so that pivoting of the lever 58 slides said idler gear into mesh with the gear 36. The levers 50, 52 and 58 are pivoted selectively by a selector shaft 60 with a radial projection 62 which shaft is surrounded by an interlock spool 64 rotatably mounted in the casing and having a slot 66 (as shown in Figure 4) which slidably accommodates the projection 62. The slot 66 bisects a flange 68 formed integrally on the spool 64, said flange being semi-circular in the known four-ratio selector mechanism. The selector shaft 60 is indirectly operated by a manual gear-change lever (not shown) so as to be rotatable together with the interlock spool 64 and also slidable through said spool. The working inter-relationship of the shaft 60 and the spool 64 is controlled by a spring-loaded ball 70 housed in a sleeve 72 fixed to the casing which sleeve passes through an actuate slot 74 in the spool 64 and permits said spool to rotate through a pre-determined angle but not to slide axially. The engagement of the projection 62 in the slot 66 constrains the shaft 60 to rotate with the spool 64, but said shaft is slidable axially between three positions determined by annular grooves 76 in its periphery which are engageable selectively by the ball 70, the intermediate groove defining the neutral position. The flange 68 can pass through forked projections on the levers 50, 52 and 58 when said levers are in their neutral positions. In operation, the selector shaft 60 and interlock spool 64 are turned until the projection 62 is aligned with the required one of the levers 50, 52 and 58, and as the slot 66 bisecting the flange 68 is also aligned with said one lever the latter can then be pivoted into an operative position by sliding the shaft 60 in the appropriate direction. Pivoting of said one lever slides the associated selector fork 46 or 48, or the reverse idler gear, into operative position whereby one of the available gear ratios is engaged. The flange 68 positively prevents pivoting of the other two of the levers 50, 52 and 58 by engaging in their forked projections. This known gear ratio selector mechanism is modified to enable the added fifth gear ration hereinbefore described to be engaged by employing a selector fork shaft 44 of int reased length which is slidable in the casing and has an additional selector fork 78 fixed to it. The selector forks 46 and 48 remains slidable on the selector fork shaft 44, said shaft has fixed to it a box 80 carrying a pin 82 which engages in a first forked projection on an additional bell-crank lever 84 pivoted about an axis 86 on a pin 88 fixed to the casing. The pin 82 may be formed by machining a block of metal to comprise the box 80 and pin 82. The selector shaft 60 is provided with an additional radial projection 90 diametrically opposite the projection 62, and the flange 68 is made circular instead of semi-circular, the slot 66 bisecting it at both sides. A spacer 92 is introduced on the pin 56, between the levers 52 and 58, the arrangement being such that when the selector shaft 60 and interlock spool 64 are turned, until the projection 90 is aligned with the lever 84 and engaged in a second forked projection thereon, the projection 62 is aligned with but clear of the spacer 92, as shown in Figure 2. As the slot 66 bisecting the flange 68 is also aligned with the lever 84, the latter can be pivoted into its operative position for sliding the shaft 60 in the appropriate direction. Pivoting of the lever 84 slides the selector fork shaft 44 and thus the selector fork 78 fixed thereto into operative position whereby fifth gear ratio is engaged. The flange 68 positively prevents pivoting of the levers 50, 52 and 58 by engaging in their forked projections. Conversely, when any one of the levers 50, 52 and 58 is actuated the flange 68 positively prevents pivoting of the lever 84. The disposition of the additional synchromesh assembly 42 on the driven shaft 12 rather than the layshaft 24 has the advantages that it minimises weight and stress on the layshaft 24, and that it enables the additional selector fork 78 to be accommodated on the same selector fork shaft 44 as the other selector forks 46 and 48. In an alternative embodiment (not shown) a sixth gear may be added on the shaft 12 on the opposite side of the synchromesh unit to the gear 40 with that sixth gear meshing with a further gear on the layshaft. The selector mechanism can operate the synchromesh 42 to engage either of the fifth or sixth gears. The present invention is particularly suitable to a Rover Group Mini/Metro A series and A+ series transverse gearbox.

Claims: CLAIMS 1. A modification adding a further gear ratio to a multi-ratio constant mesh gearbox having a drive shaft (10) with a gear (14) fixed thereto, a co-axial driven shaft (12) with x gears (26,28,30) rotatable thereon x+1 interconnected gears (16,18,20,22) on a parallel lay shaft (24) meshing respectively with the gears on the drive and driven shafts, and synchromesh means (32,34) on the driven shaft for selectively driveably connecting to said shaft any one of the gears on the drive (10) and driven shaft (12) , comprising an additional gear (38) on the lay shaft (24) interconnected to the other gears thereon, an additional gear (40) rotatable on the driven shaft (12) meshing with the additional gear (38) on the lay shaft (24) , and additional synchromesh means (42) on the driven shaft (12) for selectively connecting thereto the additional gear on said shaft. 2. A modification as claimed in Claim 1 in which the driven shaft (12) and the lay shaft (24) are appropriately lengthened. 3. A modification as claimed in Claim 1 or 2 in which the lay shaft (24) is rotatable and all the gears (16,18,20,22 and 38) thereon are fixed thereto. 4. A modification as claimed in any preceding claim in which the lay shaft (24) is of increased diameter. 5. A modification as claimed in any preceding claim in which a fifth gear ratio is added to a four gear ratio gearbox which has three gears (26,28 and 30) on the driven shaft and synchromesh means comprising two synchromesh assemblies of double-ended type (34,36), the additional synchromesh means comprising a synchromesh assembly (42) of single-ended type. 6. A modification as claimed in Claim 5 having a selector shaft (60) with a radial projection (62) which shaft (60) is pivotable and slidable to enable said projection to actuate selectively one of two bell-crank levers (50,52) pivoted about a common axis (54) which levers slide respectively selectors forks (46,48) associated with the two synchromesh assemblies (34,36) of double-ended type, and an interlock spool (64) surrounding the selector shaft (60) and pivotable but not slidable therewith, said spool (64) being adapted to prevent the actuation of more than one bell-crank lever, the selector shaft (60) having an additional radial projection (90) which, when the first-mentioned radial projection (62) is inoperatively located, can selectively actuate an additional bell-crank lever (84) pivoted about a different axis (86) to the common axis (54) of the aforesaid two bell-crank levers (50,52) which additional lever (84) slides an additional selector fork (78) associated with the synchromesh assembly. 7. A modification as claimed in Claim 6 in which the additional selector fork (78) associated with the synchromesh assembly is of single-ended type. 8. A modification as claimed in Claim 6 or 7 in which the first-mentioned radial projection (62) and the additional radial projection (90) are diametrically opposed to each other on the selector shaft (60) , and said common shaft (54) and said different axis (86) are disposed at opposite sides of the selector shaft (60) . 9. A modification as claimed in any of Claims 6 to 8 in which the first-mentioned radial projection (62) is inoperatively located by pivoting the selector shaft (60) to align said projection (62) with a spacer (92) introduced between the two bell-crank levers on the common axis (54) on the one hand and a reverse gear selector lever (58) pivoted on said axis (54) on the other hand. 10. A modification as claimed in any of Claims 6 to 9 in which all the selector forks are carried by a common selector fork shaft (44), the selector forks (46,48) associated with the two synchromesh assemblies of double- ended type each being slidable on said shaft and the additional selector fork (78) being fixed to said shaft which is slidable by the additional bell-crank lever (84) . 11. A method of modifying a gearbox comprising effecting any of the modifications as referred to in any of Claims 1 to 10. 12. A selector mechanism for a multi-ratio gearbox, the mechanism having a selector shaft (60) with two radial projections (62,90) which shaft (60) is pivotable and slidable to engage one of said projections (62) to actuate gear ratio selector means (50,52) pivoted at one side of said shaft (60) and to enable the other of said projections (90) to actuate gear ratio selector means (84) pivoted at the other side of said shaft (60) , an interlock spool (64) surrounding the selector shaft (60) and pivotable but not slidable therewith being adapted, in conjunction with the relative disposition of both selector means, to prevent the selection of more than one gear ratio. 13. A method of operating a selector mechanism as claimed in Claim 12 comprising controlling the selector shaft (60) to selectively enable one of the projections (62) to actuate the gear ratio selector means (50,52) or to enable the other of the projections (90) to actuate the other gear ratio selector means (84) .

Inventors: HARPER BRIAN, HARPER, BRIAN
Applicants: HARPER BRIAN, HARPER, BRIAN
Application year: 1992
Main classification: F16H63
IPC codes: F16H3, F16H63