GB1581272A - Gear box - Google Patents

Description

(54) GEAR BOX (71) We, COSTELLO TRANSMIS SIONS LIMITED, a British Company of Oak Farm, Farnborough Hill, Green Street Green, Orpington, Kent do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a gear box.

Conventional gear boxes comprise within a casing, an input shaft, and a main or output shaft coaxial therewith, and a lay shaft alongside and parallel to the main and input shfats.

Power is transmitted from the input shaft through a pair of meshing gears to the lay shaft and thence to the main shaft through a selectable pair of gears.

The input and main shaft are mounted by bearing means within the casing and as the gears are normally of a helical type it will be understood that when drive is passing through the gear box there is developed an axial thrust in the various shafts. The gear box must clearly be constructed so as to be able to absorb these axial thrusts.

According to a first aspect, the invention provides a gear box comprising an input shaft carrying a helical input gear, a lay shaft carrying a helical gear meshing with said helical input gear and carrying further helical gears, a main shaft carrying helical gears for meshing with said further helical gears on the lay shaft, the helices on the gears being such that, when drive is applied to the input shaft, the input and main shafts are thrust axially towards one another, a grear box casing including means for mounting the input shaft and the main shaft coaxially and a thrust bearing acting between the input and main shaft for absorbing thrusts therebetween.

There are considerable advantages in this arrangement. In conventional gear boxes, thrusts tend to move the input shaft and main shaft apart and this thrust has to be absorbed by the opposite end walls of the casing of the gear box. In the present arrangement the thrusts are towards one another and these can be readily absorbed by means of the thrust bearing acting between the main and input shafts.

Preferably the casing is in two parts, the split between which is generally coplanar with the axes of the input, lay and main shafts.

The thrust bearing between the input and main shafts is preferably in the form of a taper roller bearing and may be mounted in a housing within the input shaft, the adjacent end of the main shaft extending into the housing.

A preferred arrangement of gear box incorporating the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a longitudinal section of a five speed gear box incorporating the invention, Figure 2 is a perspective diagrammatic view of the meshing gears on an input shaft and a lay shaft, and, Figure 3 is a perspective diagrammatic view of two meshing gears on the lay shaft and main shaft.

Referring to Figure 1, there is illustrated a gear box comprising a casing 10 which is in two halves (only one half being shown in Figure 1) which may be split lengthwise, and joined together by suitable connector means in the form of bolts passing through bolt holes 1 1 spaced around the mating surfaces 12 of the two halves. The casing 10 is of aluminium alloy for lightness. Projecting from the front end of the casing is an input shaft 14. The input shaft 14 is supported in the front wall 15 of the casing 10 by means of a taper roller bearing 16. Within the casing 10, the input shaft 14 carries a helical toothed input gear 17 which is in constant meshing engagement with a gear 18 carried by a lay shaft 19. The lay shaft 19 is arranged parallel to the input shaft 14 and is mounted in a taper roller bearing 20 in the front wall 15 of the casing 10, in a taper roller bearing 21 in an intermediate wall 22 of the casing, and in a conventional roller bearing 24 in a rear wall 25 of the casing 10.

The gear box in question is a five speed gear box and the lay shaft 19 carries five further gears 25 to 29. Gear 28 meshes with a reverse gear (not shown in Figure 1 behind the lay shaft) but gears 25, 26, 27 and 29 constantly mesh with respective gears 31 to 34 carried by a main shaft 35. As is clear from Figure 1, the main shaft 35 is supported by a normal roller bearing 36 in the rear wall 24 of the casing 10 by a taper roller bearing 37 carried by the intermediate wall 22 of the casing 10 and by a taper roller bearing 38 mounted in a housing within the helical input gear 17. It will be appreciated that the input shaft 14 and main shaft 35 are coaxial.

The gears 25 to 29 are fixedly mounted to the lay shaft 19 and rotate therewith but the gears 31 to 34 (or the input shaft 14) are selectively connected with the main shaft by generally conventional synchromesh assemblies 39 to 41. (Synchromesh assembly 41 in fact connecting the reverse gear cluster).

Details of the construction of the synchromesh assemblies will be readily apparent from the drawings and no further description is required. Similarly details of the method of mounting for example the bearings within the casing are also conventional and will not be described further.

The gears 17 and 25 to 34 are helical gears.

It will be further understood that because they are helical gears when drive is passed to the input shaft 14 then longitudinal thrusts will be exerted on the input shaft 14, the lay shaft 19 and the main shaft 35 as the drive passes through from the input shaft 14 to the main shaft 35. It will be understood from Figure 2 that the longitudinal thrust in the input shaft 14 is arranged so as to be directed inwardly of the gear box, that is towards the main shaft 35 and the longitudinal thrust in the main shaft 35 is arranged to be directed towards the input shaft 14. Thus whilst drive is passing through the gear box the taper roller bearing 38 is in compression and absorbs both thrusts. Such bearings can be readily designed so as to absorb large thrusts and to a certain extent, therefore, the thrust in the input shaft 14 and the main shaft 35 cancel each other out and are not passed to the gear box casing. This is in contradistinction to a conventional arrangement of gear box in which the helical teeth are arranged oppositely to that shown in Figure 3 in which the thrusts in the lay shaft and main shaft are in an outward direction and must be absorbed by the opposite walls of the casing.

Thus a lighter weight casing may be utilised in the arrangement of the present invention.

The thrust created by the two gears through which drive passes to and from the lay shaft 19 will tend to move the two gears on the lay shaft 19 in opposite directions but this is readily absorbed by the lay shaft 19 since the gears are rigidly mounted to the lay shaft 19. Clearly the lay shaft 19 is of such a diameter that it is able to absorb the thrust involved.

It is understood, of course, that during over-run, that is, when for example the vehicle to which the gear box is mounted is running downhill, the main shaft 35 will tend to drive the input shaft 14 and the thrusts will be in the opposite direction but the thrust created during such usage are generally less than those involved in normal operation whilst drive is passing from the input shaft to the main shaft.

WHAT WE CLAIM IS: 1. A gear box comprising an input shaft carrying a helical input gear, a lay shaft carrying a helical gear meshing with said helical input gear and carrying further helical gears, a main shaft carrying helical gears for meshing with said further helical gears on the lay shaft, the helices on the gears being such that, when drive is applied to the input shaft, the input and main shafts are thrust axially towards one another, a gear box casing including means for mounting the input shaft and the main shaft coaxially and a thrust bearing acting between the input and main shaft for absorbing thrusts therebetween.

2. A gear box as claimed in claim 1 in which the casing is in two parts, the split between which is generally coplanar with the axes of the input, lay and main shafts.

3. A gear box as claimed in claim 1 or claim 2 in which the thrust bearing between the input and main shaft is in the form of a taper roller bearing.

4. A gear box as claimed in any of claims 1 to 3 in which the thrust bearing is mounted in a housing within the input shaft, the adjacent end of the main shaft extending into the housing.

5. A gear box as claimed in any of claims 1 to 4 in which the casing of the gear box is of aluminium.

6. A gear box as claimed in any of the preceding claims including five forward speeds and one reverse speed.

7. A gear box substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. by a lay shaft 19. The lay shaft 19 is arranged parallel to the input shaft 14 and is mounted in a taper roller bearing 20 in the front wall 15 of the casing 10, in a taper roller bearing 21 in an intermediate wall 22 of the casing, and in a conventional roller bearing 24 in a rear wall 25 of the casing 10. The gear box in question is a five speed gear box and the lay shaft 19 carries five further gears 25 to 29. Gear 28 meshes with a reverse gear (not shown in Figure 1 behind the lay shaft) but gears 25, 26, 27 and 29 constantly mesh with respective gears 31 to 34 carried by a main shaft 35. As is clear from Figure 1, the main shaft 35 is supported by a normal roller bearing 36 in the rear wall 24 of the casing 10 by a taper roller bearing 37 carried by the intermediate wall 22 of the casing 10 and by a taper roller bearing 38 mounted in a housing within the helical input gear 17. It will be appreciated that the input shaft 14 and main shaft 35 are coaxial. The gears 25 to 29 are fixedly mounted to the lay shaft 19 and rotate therewith but the gears 31 to 34 (or the input shaft 14) are selectively connected with the main shaft by generally conventional synchromesh assemblies 39 to 41. (Synchromesh assembly 41 in fact connecting the reverse gear cluster). Details of the construction of the synchromesh assemblies will be readily apparent from the drawings and no further description is required. Similarly details of the method of mounting for example the bearings within the casing are also conventional and will not be described further. The gears 17 and 25 to 34 are helical gears. It will be further understood that because they are helical gears when drive is passed to the input shaft 14 then longitudinal thrusts will be exerted on the input shaft 14, the lay shaft 19 and the main shaft 35 as the drive passes through from the input shaft 14 to the main shaft 35. It will be understood from Figure 2 that the longitudinal thrust in the input shaft 14 is arranged so as to be directed inwardly of the gear box, that is towards the main shaft 35 and the longitudinal thrust in the main shaft 35 is arranged to be directed towards the input shaft 14. Thus whilst drive is passing through the gear box the taper roller bearing 38 is in compression and absorbs both thrusts. Such bearings can be readily designed so as to absorb large thrusts and to a certain extent, therefore, the thrust in the input shaft 14 and the main shaft 35 cancel each other out and are not passed to the gear box casing. This is in contradistinction to a conventional arrangement of gear box in which the helical teeth are arranged oppositely to that shown in Figure 3 in which the thrusts in the lay shaft and main shaft are in an outward direction and must be absorbed by the opposite walls of the casing. Thus a lighter weight casing may be utilised in the arrangement of the present invention. The thrust created by the two gears through which drive passes to and from the lay shaft 19 will tend to move the two gears on the lay shaft 19 in opposite directions but this is readily absorbed by the lay shaft 19 since the gears are rigidly mounted to the lay shaft 19. Clearly the lay shaft 19 is of such a diameter that it is able to absorb the thrust involved. It is understood, of course, that during over-run, that is, when for example the vehicle to which the gear box is mounted is running downhill, the main shaft 35 will tend to drive the input shaft 14 and the thrusts will be in the opposite direction but the thrust created during such usage are generally less than those involved in normal operation whilst drive is passing from the input shaft to the main shaft. WHAT WE CLAIM IS:

1. A gear box comprising an input shaft carrying a helical input gear, a lay shaft carrying a helical gear meshing with said helical input gear and carrying further helical gears, a main shaft carrying helical gears for meshing with said further helical gears on the lay shaft, the helices on the gears being such that, when drive is applied to the input shaft, the input and main shafts are thrust axially towards one another, a gear box casing including means for mounting the input shaft and the main shaft coaxially and a thrust bearing acting between the input and main shaft for absorbing thrusts therebetween.

2. A gear box as claimed in claim 1 in which the casing is in two parts, the split between which is generally coplanar with the axes of the input, lay and main shafts.

3. A gear box as claimed in claim 1 or claim 2 in which the thrust bearing between the input and main shaft is in the form of a taper roller bearing.

4. A gear box as claimed in any of claims 1 to 3 in which the thrust bearing is mounted in a housing within the input shaft, the adjacent end of the main shaft extending into the housing.

5. A gear box as claimed in any of claims 1 to 4 in which the casing of the gear box is of aluminium.

6. A gear box as claimed in any of the preceding claims including five forward speeds and one reverse speed.

7. A gear box substantially as hereinbefore described with reference to the accompanying drawings.