WO2003036128A1

WO2003036128A1 - Automotive gearboxes

Info

Publication number: WO2003036128A1
Application number: PCT/GB2002/004795
Authority: WO
Inventors: Geoffrey Sedgwick
Original assignee: Ricardo Mtc Limited
Priority date: 2001-10-26
Filing date: 2002-10-23
Publication date: 2003-05-01
Also published as: GB0125792D0

Abstract

A gearbox comprises an input shaft (2), an output shaft (6) and a companion shaft (4) parallel thereto. The output shaft (6) carries a gearwheel (14) fixed thereto to rotate therewith and the input shaft (2) carries two or more gearwheels (8, 10, 12), each of which is in mesh with a respective gearwheel (38, 58) on the companion shaft. The gearwheel (8) at one end of the input shaft and the gearwheel (36) at the other end of the companion shaft are permanently fixed thereto to rotate therewith. The fixed gearwheel (36) on the companion shaft is in mesh with a gearwheel (14) on the output shaft. All the remaining gearwheels are rotatable with respect to the shaft on which they are carried. Axially movable clutch means (26, 52, 24, 50, 22, 48) are situated between each adjacent pair of gearwheels on both the input shaft and the companion shaft and between the fixed gearwheel (14) on the output shaft and the adjacent gearwheel (12) on the input shaft. Each of the clutch means is movable in a first direction parallel to the input shaft (2) to lock the adjacent pair of gearwheels so that they rotate together and in a second direction parallel to the input shaft to release the adjacent pair of gearwheels so that they may rotate independently.

Description

AUTOMOTIVE GEARBOXES

The present invention relates to automotive gearboxes, as are used in cars, motorcycles and other vehicles.

Numerous different types of automotive gearbox are known but one conventional type of gearbox used in cars includes an input shaft, an output shaft and a layshaft or compamon shaft parallel thereto. The input shaft carries a gearwheel, which is fixed to it and in mesh with a gearwheel fixed to the layshaft. The layshaft carries a number of further gearwheels, each of which is located on it and is in mesh with a respective gearwheel carried by the input shaft. Dog clutches situated between each adjacent pair of gearwheels on the output shaft and between the gearwheel on the input shaft and the adjacent gearwheel on the output shaft are selectively actuated to lock one of the output shaft gearwheels to the output shaft or to lock the input and output shafts together.

A further known type of gearbox, which is commonly used in motorcycles, includes an input shaft carrying a number of gearwheels, each of which is in mesh with a respective gearwheel carried by an output shaft parallel to the input shaft. A plurality of dog clutches may be selectively actuated to lock the gearwheels of any desired meshing pair of gearwheels to their associated shafts. A motorcycle gearbox of this type is disclosed in US 6021686 in which one gearwheel of each meshing pair is keyed to rotate with the shaft carrying them at all times and is selectively movable in the direction of the length of the associated shaft and constitutes one half of the dog clutch of an adjacent gearwheel, which is selectively rotatable with respect to the associated shaft. The torque may thus be directed to pass through a particular meshing pair of gearwheels by moving the gearwheel adjacent one or other of the pair into locking engagement with it, thereby locking it to the associated shaft.

It is inherent in both the types of gearbox referred to above that the number of meshing pairs of gearwheels must be equal to the number of gear ratios which the gearbox can provide.

There is a constant pressure to make gearboxes as small, light and refined as possible and it would, therefore, be desirable for a gearbox to provide a number of gear ratios in excess of the number of meshing pairs of gearwheels. Such a gearbox is disclosed in WO 01/11272 which relates to a gearbox including an input shaft carrying two gearwheels in mesh with respective gearwheels on a layshaft, which carries a number of further gearwheels in mesh with respective gearwheels carried on an output shaft coaxial with the input shaft. Certain of the gearwheels are permanently connected to the associated shaft whilst the remainder are selectively lockable thereto by means of a respective rotary lock situated between the outer surface of the shaft and the inner surface of the gearwheel. Whilst extremely effective, the provision of the relatively complex rotary locks within many of the gearwheels means that the gearbox has a relatively large part count and that each gearwheel is somewhat larger than would otherwise normally be the case. Whilst this is perfectly acceptable in connection with larger engines or vehicles, size is more important in connection with smaller vehicles, such as motorcycles.

It is, therefore, the object of the invention to provide a gearbox which has all the advantages of that disclosed in WO 01/11272 as regards its ability to provide a number of gear ratios in excess of the number of meshing pairs of gearwheels but which is particularly suitable for smaller vehicles, such as motorcycles.

According to the present invention a gearbox comprises an input shaft, an output shaft and a companion shaft parallel to the input shaft, the output shaft carrying a gearwheel permanently fixed thereto to rotate therewith and the input shaft carrying two or more gearwheels, each of which is in mesh with a respective gearwheel on the companion shaft, the gearwheel at one end of the input shaft and the gearwheel at the other end of the companion shaft being permanently fixed thereto to rotate therewith and the fixed gearwheel on the companion shaft being in mesh with the gearwheel on the output shaft and all the remaining gearwheels being rotatable with respect to the shaft on which they are carried, axially movable clutch means being situated between each adjacent pair of gearwheels on both the input shaft and the compamon shaft and between the fixed gearwheel on the output shaft and the adjacent gearwheel on the input shaft, each of the clutch means being movable in a first direction parallel to the input shaft to lock the adjacent pair of gearwheels so that they rotate together and in a second direction parallel to the input shaft to release the adjacent pair of gearwheels so that they may rotate independently.

The output shaft is preferably coaxial with or parallel to the input shaft, with the former being preferred since it gives a compact design. However, it is even possible to take the output directly from the companion shaft, i.e. the output shaft and the companion shaft are the same, although this will cause the output to rotate in the opposite direction to that shown in Figure 1. It is thus preferred that the output shaft is parallel to the companion shaft and coaxial with the input shaft. Thus the gearbox in accordance with the present invention is based on a principle radically different to those of known gearboxes in that apart from the gearwheels which are fixedly connected to the output shaft, one end of the input shaft and the other end of the companion shaft, all the other gearwheels are rotatable with respect to the associated shaft at all times. The selectively operable clutches associated with the gearwheels operate not to connect the gearwheels to the associated shaft but to connect adjacent pairs of gearwheels together. Thus when all the gearwheels on the input shaft and/or the companion shaft are connected together by operation of the clutches, they will rotate as a unit and the gearbox may therefore be thought of as actually comprising a total of four shafts, two of the shafts being in the form of hollow sleeves carrying external gearwheels coaxial with the two other shafts, respectively.

In order to connect two adjacent gearwheels to rotate together, it is not necessary that one or other of the gearwheels be moved but that the clutch between them is operated. This has a number of advantages including the fact that the clutches inherently have less inertia than the gearwheels with which they are associated which in turn means that when two gearwheels are locked together there is a smaller transfer of energy than conventional which means that gear changes are smoother than in the known gearboxes. Furthermore, it is no longer necessary for the gearwheels to have straight cut gear teeth but they can instead now have helical cut gear teeth which operate very much more quietly.

The clutch means and the manner in which the gearwheels are constructed to enable adjacent pairs of gearwheels to be connected together may take a variety of forms but it is preferred that on that side of each gearwheel carried by the input shaft, other than the gearwheel permanently fixed thereto, and on that side of the gearwheel on the output shaft, which is closest to the gearwheel fixed to the input shaft, there is a plurality of dogs and connected to the other side of each gearwheel carried by the input shaft there is a respective externally splined member which carries a respective dog clutch ring, which cooperates with a respective gear selector member arranged to move it between a locked position, in which it is in engagement with the dogs on the adjacent gearwheel and thus locks the two adjacent gearwheels and constrains them to rotate together, and an unlocked position, in which the two adjacent gearwheels may rotate with respect to one another and in which on that side of each gearwheel carried by the companion shaft, other than the gearwheel permanently fixed thereto, which is closest to the gearwheel permanently fixed thereto, there is a plurality of dogs and connected to the other side of each gearwheel carried by the companion shaft, other than the gearwheel furthest from the gearwheel permanently fixed thereto, there is a respective externally splined member, which carries a respective dog clutch ring, which cooperates with a respective gear selector member arranged to move it between a locked position, in which it is in engagement with the dogs on the adjacent gearwheel and thus locks the two adjacent gearwheels and constrains them to rotate together, and an unlocked position, in which the two adjacent gearwheels may rotate with respect to one another.

It is preferred that the splined portion connected to each gearwheel permanently fixed to the associated shaft is constituted by a splined portion of the surface of that shaft and each remaining splined portion constitutes an externally splined sleeve integrally connected to the associated gearwheel and extending around, and in the direction of the length of, the associated shaft.

Thus in the preferred embodiment there is a splined portion of the surface of the shaft adjacent to one side of the gearwheel permanently fixed to the input shaft and on the opposite side of the gearwheel permanently fixed to the companion shaft. Each of the remaining gearwheels carried by the input shaft is also associated with a splined portion afforded by an externally splined sleeve which extends around the shaft and is integral with the gearwheel on the side furthest from the gearwheel permanently fixed thereto. A similar integral splined sleeve is connected to each of the other gearwheels carried by the companion shaft, other than the gearwheel furthest from the gearwheel permanently fixed thereto, and this splined portion is again on the side of the associated gearwheel furthest from the gearwheel permanently fixed to the companion shaft. Situated between each adjacent pair of gearwheels on the splined portion between them there is a dog clutch ring which is movable selectively between a position in which the associated pair of gearwheels is locked to rotate together by engagement of the dogs on the one gearwheel with the dog clutch ring carried on the splined portion integral with the other gearwheel, and a position in which relative rotation of the associated pair of gearwheels is permitted.

It will be appreciated that, by virtue of selective operation of the clutches, the power transmitted through the gearbox may be constrained to follow a number of different complex routes and that the gearbox may therefore provide a number of gear ratios in excess of the number of pairs of meshing gearwheels. If there are three meshing pairs of gearwheels, a total of four gear ratios (excluding neutral) may be obtained. If there are four meshing pairs of gearwheels, a total of eight gear ratios may be obtained. If there are five gear pairs, at least sixteen gear ratios are possible.

It will therefore be appreciated that, for any given number of gear ratios, a gearbox in accordance with the present invention will be substantially smaller than known gearboxes. Due to the fact that the locking mechanisms for locking adjacent pairs of gearwheels together are situated between adjacent gearwheels rather than between each gearwheel and the associated shaft, the gearbox may be made even smaller and indeed smaller than in the gearbox disclosed in WO 01/11272.

It will be appreciated that the gearwheel splined sleeve units carried by the input shaft are "oppositely handed" to those carried by the companion shaft, that is to say that the splined sleeves associated with the input shaft are all on one side of the gearwheels carried by the input shaft whereas the splined sleeves associated with the companion shaft are all on the other side of the gearwheels carried by the companion shaft. It will be appreciated also that the dog clutch rings carried by the input shaft are associated in pairs with respective dog clutch rings carried by the companion shaft. This opens up the possibility of the two dog clutch rings of each associated pair being moved in synchronism and when this happens one dog clutch ring will lock together the two gearwheels between which it is situated whilst the other dog clutch ring will unlock the two gearwheels between which it is situated. Whilst it would be conventional for each dog clutch to be associated with a respective, independently actuable gear selector mechanism, it is preferred that the dog clutch rings of each pair cooperate with a respective common gear selector lever which will thus be generally of three pronged fork configuration. Further features and details of the invention will be apparent from the following description of two specific embodiments of a motorcycle gearbox in accordance with the invention which is given by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a highly schematic sectional view through a first embodiment of gearbox in accordance with the invention;

Figures 2 to 9 are views similar to Figure 1 showing the positions of the various dog clutch rings and the associated torque path in each of second to eighth gears respectively; and

Figure 10 is a highly schematic view similar to Figure 1 of a second embodiment.

The gearbox shown in Figures 1 to 9 includes an input shaft 2, a companion shaft 4 parallel to it and an output shaft 6, which is coaxial with the input shaft and is constituted by a sleeve mounted to rotate about the input shaft. Integral with the input shaft 2 at the end remote from the output shaft 6 is a gearwheel 8. Rotatably carried on the input shaft between the gearwheel 8 and the output shaft 6 are two gearwheels 10 and 12. Integral with the output shaft 6 is a gearwheel 14. Carried on the right-hand side, as seen in the Figures, of the gearwheels 10, 12 and 14 is a respective plurality of clutch dogs 16, 18 and 20. Cooperating with the dogs 16, 18 and 20 are respective, axially slidable dog clutch rings 22, 24 and 26. The dog clutch ring 22 situated between the gearwheels 8 and 10 is slidably received on a splined portion 28 of the surface of the input shaft on the left-hand side, as seen in the Figures, of the gearwheel 8. The dog clutch rings 24 and 26 are axially slidably carried by respective externally splined sleeves 30, 32 which are integral with the left-hand side, as seen in the Figures, of the gearwheels 10 and 12, respectively.

The gearwheel 8 is in mesh with a gearwheel 34, which is rotatably carried at one end of the companion shaft 4. Permanently fixed to the other end of the companion shaft 4 is a gearwheel 36, which is in mesh with the gearwheel 14 on the output shaft 6. Rotatably located on the companion shaft 4 between the gearwheels 34 and 36 are two further gearwheels 38 and 40, which are in mesh with the gearwheels 10 and 12, respectively, on the input shaft. Connected to the left-hand side, as seen in the Figures, of the gearwheels 34, 38 and 40 is a respective plurality of clutch dogs 42, 44 and 46. Cooperating with these clutch dogs 42, 44, 46 are respective clutch dog rings 48, 50 and 52 which extend around the companion shaft. The dog clutch ring 52 between the gearwheels 36 and 40 is accommodated on a splined portion 54 of the surface of the companion shaft 4 on the right-hand side, as seen in the Figures, of the gearwheel 36. The dog clutch rings 48 and 50 are axially slidably received on respective tubular sleeves 56, 58, which are integrally connected to the right- hand side, as seen in the Figures, of the gearwheels 38 and 40, respectively. Thus the input shaft and the companion shaft each carry a single gearwheel permanently fixed thereto at opposite ends thereof and two gearwheel/splined sleeve units, each comprising a gearwheel, integral with one side of which is a splined sleeve carrying a respective axially slidable dog clutch ring. It will be appreciated that the gearwheel/splined sleeve units on the companion shaft are "oppositely handed" to those on the input shaft, that is to say that the splined sleeves associated with the companion shaft are on the opposite side of the associated gearwheels to those associated with the input shaft. The dog clutch rings extending around the input shaft are associated in pairs with a respective dog clutch ring extending around the companion shaft. Each associated pair of dog clutch rings 26 and 52, 24 and 50 and 22 and 48 are acted on by a single respective gear selection lever 60, 62 and 64, respectively, which are shown only diagrammatically in Figure 1. Each gear selection lever is thus of generally three pronged shape, the two outer prongs engaging the two outer edges of the associated pair of dog clutch rings and the central prong engaging the two inner edges of the associated pair of dog clutch rings. The gear selection members or selector forks are moved axially by means of a barrel cam, which is of known type and is therefore not illustrated, to engage the desired gear ratio. It will be appreciated that each pair of dog clutch rings is thus moved in synchronism and that since the gearwheel/splined sleeve units on the input and companion shafts are oppositely handed, such movement in one direction will result in one of the dog clutch rings locking the two associated gearwheels together and the other dog clutch ring unlocking the two associated gearwheels and that movement in the opposite direction will have the opposite result. Since there are three pairs of dog clutch rings, each of which has two possible positions, the gearbox can produce a total of eight gear ratios, though not all of these may be required and it may be sufficient for e.g. only six of them to be used.

Figure 1 shows the gearbox in neutral gear, that is to say with all the dog clutch rings in a central position in which they are not in engagement with any of the series of dogs. However, it only takes one of the forks 60, 62, 64 to be in the central position to cut the torque transfer through the gearbox and so place it in neutral. The gaps between adjacent pairs of gearwheels in which two of the pairs of dog clutch rings 24, 50 and 26, 52 are accommodated will be sufficiently wide that the dog clutch rings have a central position in which the rings engage neither of their associated gearwheels, i.e. the position illustrated, so that, on changing gear, one gearwheel is disengaged before the other is engaged. However, for ease of manufacture of the selector mechanism, it is only required that one set of dog clutch rings are held in the central position to achieve neural gear and, in the illustrated example, it is dog clutch rings 22, 48 that are maintained in this central position by the selector to achieve neutral gear. In this condition, when the input shaft 2 is rotated, the gear 8 rotates also and this rotates the meshing gearwheel 34. However, the latter gearwheel is not connected to any further gearwheel and no torque is therefore transmitted to the output shaft. In order to engage a desired gear, each of the gear selector forks 60, 62 and 64 must be moved to a desired position. Each of them may be moved to the left (L) or the right (R) and the positions which each of the gear selector forks should adopt in each gear are shown in the table set forth below, which are a typical example but it will be understood that other permutations may be used to provide different gear ratios, that is to say the different gears (first, second third ...etc) may be achieved by different positions of the selector forks as compared to the positions stated in the table, [is this correct? I was not entirely sure what you meant since all the permutations of the illustrated gearbox are set out in the table]. The pairs of dog clutch rings are shown in the corresponding positions in Figures 2 to 9 which represent first to eighth gears, respectively, and show the associated torque path in each gear.

Figure 10 is a view similar to Figure 1 of a second embodiment. This embodiment is very similar to that illustrated in Figure 1 and differs from it only in that the output shaft 6, which is still coaxial with the input shaft 2, is at the opposite end of the input shaft 2 to that shown in Figure 1.

The ends of the input shaft 2 and companion shaft 4 at which the gearwheels 8 and 36 are permanently fixed to them, respectively, are also reversed with respect to Figure 1. In all other respects, however, the construction and operation of the gearbox shown in Figure 10 are the same as those of the gearbox shown in Figure 1 and further description is therefore unnecessary.

Instead of providing an output shaft 6 that is coaxial with the input shaft 2, it is possible for the output shaft to be driven from the final pair of meshed gears 36 and 14 and so provide an output shaft parallel to the input shaft.

Claims

1. A gearbox comprising an input shaft, an output shaft and a companion shaft parallel thereto, the output shaft carrying a gearwheel permanently fixed thereto to rotate therewith and the input shaft carrying two or more gearwheels, each of which is in mesh with a respective gearwheel on the companion shaft, the gearwheel at one end of the input shaft and the gearwheel at the other end of the companion shaft being permanently fixed thereto to rotate therewith and the fixed gearwheel on the companion shaft being in mesh with the gearwheel on the output shaft and all the remaining gearwheels being rotatable with respect to the shaft on which they are carried, axially movable clutch means being situated between each adjacent pair of gearwheels on both the input shaft and the companion shaft and between the fixed gearwheel on the output shaft and the adjacent gearwheel on the input shaft, each of the clutch means being movable in a first direction parallel to the input shaft to lock the adjacent pair of gearwheels so that they rotate together and in a second direction parallel to the input shaft to release the adjacent pair of gearwheels so that they may rotate independently.

2. A gearbox as claimed in claim 1 in which on that side of each gearwheel carried by the input shaft, other than the gearwheel permanently fixed thereto, and on that side of the gearwheel on the output shaft, which is closest to the gearwheel fixed to the input shaft, there is a plurality of dogs and connected to the other side of each gearwheel carried by the input shaft there is a respective externally splined member which carries a respective dog clutch ring, which cooperates with a respective gear selector member arranged to move it between a locked position, in which it is in engagement with the dogs on the adjacent gearwheel and thus locks the two adjacent gearwheels and constrains them to rotate together, and an unlocked position, in which the two adjacent gearwheels may rotate with respect to one another and in which on that side of each gearwheel carried by the companion shaft, other than the gearwheel permanently fixed thereto, which is closest to the gearwheel permanently fixed thereto, there is a plurality of dogs and connected to the other side of each gearwheel carried by the companion shaft, other than the gearwheel furthest from the gearwheel permanently fixed thereto, there is a respective externally splined member, which carries a respective dog clutch ring, which cooperates with a respective gear selector member arranged to move it between a locked position, in which it is in engagement with the dogs on the adjacent gearwheel and thus locks the two adjacent gearwheels and constrains them to rotate together, and an unlocked position, in which the two adjacent gearwheels may rotate with respect to one another.

3. A gearbox as claimed in claim 2 in which the splined portion connected to each gearwheel permanently fixed to the associated shaft is constituted by a splined portion of the surface of that shaft and each remaining splined portion constitutes an externally splined sleeve integrally connected to the associated gearwheel and extending around, and in the direction of the length of, the associated shaft.

4. A gearbox as claimed in claim 3 in which the dog clutch rings carried by the companion shaft are associated in pairs with respective dog clutch rings carried by the input shaft, the dog clutch rings of each pair cooperating with a common gear selector lever and thus being movable in unison out of the locked position into the unlocked position and out of the unlocked position into the locked position, respectively.

5. A gearbox as claimed in any one of claims 1 to 4, in which the output shaft lies parallel to or coaxial with the input shaft.

6. A gearbox as claimed in any one of claims 1 to 5, in which the companion shaft forms the output shaft or the output shaft lies parallel to the companion shaft.