WO2000054569A1

WO2000054569A1 - Gear box housing

Info

Publication number: WO2000054569A1
Application number: PCT/GB2000/000842
Authority: WO
Inventors: Georg Agertoft Lauritzen
Original assignee: Kverneland Kerteminde A/S; Orr, William, Mclean
Priority date: 1999-03-16
Filing date: 2000-03-13
Publication date: 2000-09-21

Abstract

An elongate gearbox housing (100) comprising an assembly of intermeshing gear wheels (2a, 2b) spaced apart in a horizontal plane along its length, wherein each gear wheel is adapted to apply driving rotation to a rotary mower disc (200) and comprises a main annular body (12) supported by a plurality of bearings and a plurality of gear teeth (13a, 13b) extending outwardly from the annular body, wherein the outer edge profile of one or more of the gear teeth has a peripheral portion (14a, 14b) of maximum radial extent from the annular body and at least one chamfered portion (15a, 16a; 15b, 16b) of lesser radial extent, to give meshing engagement with another gear wheel with reduced noise generation.

Description

GEAR BOX HOUSING

The present invention relates to a gear box housing (eg a cutter bar housing for a disc mower) .

An agricultural disc mower may be used to cut a standing crop of grass and to deposit the mown crop in a swath where it is allowed to dry. The cutter bar of a disc mower extends substantially perpendicularly to the mowing direction and has a number of rotary mower discs arranged along its length. These rotary mower discs are typically driven to rotate in alternate directions by a gear drive tram powered from the PTO shaft of a tractor used to propel the disc mower. The drive train typically comprises a plurality of mtermeshmg gear wheels mounted internally of the cutter bar and arranged along its length. The power input is generally applied to an input gear wheel at one end of the cutter bar and transferred through adjacent mtermeshmg gear wheels along the length of the cutter bar. Each rotary mower disc is associated with and driven by a respective gear wheel of the drive tram.

In a conventional installation, the cutter bar is formed from metal plate of generally rectangular cross- section and of relatively shallow depth to house a plurality of gear wheels which are located in a generally horizontal plane so as to rotate about substantially vertical axes. Adjacent rotary mower discs are rotatably mounted on respective gear wheels and spaced along the length of the cutter bar. One such arrangement is described m International Patent application no. PCT/GB98/03048 (Kverneland) . A disadvantage of the conventional cutter bar is that it cannot be manufactured as accurately as a normal gearbox housing which may lead to the mesh between adjacent gear wheels being unsatisfactory. This may cause a conventional cutter bar to exhibit a high level of noise during use. More generally, where gear wheels m a gear box housing are mounted on ball bearings there is a certain degree of sideways slackness such that when the gear wheel mesh is misaligned, it may tilt from side to side to a degree permitted by the bearing. A high level of noise has been measured at the tooth frequency and at double the tooth frequency.

The present invention is based on the recognition that reducing the radial extent of the peripheral portion of intermeshing gear wheels provides a gear drive train m which high levels of noise may be reduced.

Thus viewed from one aspect the present invention provides an elongate gear box housing comprising an assembly of mtermeshmg gear wheels spaced apart m a horizontal plane along its length, wherein each gear wheel is adapted to apply driving rotation to a rotary mower disc and comprises a ma annular body supported by a plurality of bearings and a plurality of gear teeth extending outwardly from the annular body, wherein the outer edge profile of one or more of said gear teeth has a peripheral portion of maximum radial extent from the annular body and at least one chamfered portion of lesser radial extent.

In accordance with the invention, the chamfered portion of the teeth provides a portion of lesser radial extent which has been found to lead to reduced levels of noise in the gear box housing. An added benefit of the invention is that the chamfering reduces the bearing load.

Preferably the elongate gear box housing comprises an elongate cutter bar housing for use in a disc mower. The chamfering may be added during manufacture in accordance with conventional practices.

Preferably, the outer edge profile of one or more teeth comprises a peripheral portion located substantially midway between the axially spaced apart ends of the profile. Preferably two chamfered portions diverge from the peripheral portion towards the axially spaced apart ends . Typically each tooth is axially symmetrical.

In the preferred embodiment, it would appear that it is essentially the mid-portion of the tooth which is meshed first and not the corners of the tooth thereby advantageously preventing the gear wheel being thrown from side to side.

The peripheral portion is typically reduced to about one-third or less of its full axial extent in accordance with the invention. For example, the peripheral portion is about one-third or less of the distance between the axially spaced-apart ends of the tooth.

Preferably, the assembly of intermeshing gear wheels comprises a ma drive gear wheel at or near one end of the cutter bar housing. Additional drive gear wheels may be provided. Preferably, the assembly of mtermeshmg gear wheels comprises a plurality of intermediate gear wheels forming a gear drive train receiving rotary drive from the mam drive gear. Typically, the elongate cutter bar housing of the invention comprises 10 or more gear wheels, typically 10 to about 28 gear wheels m mtermeshmg relationship. Viewed from a further aspect the present invention provides a gear wheel comprising a main annular body and gear teeth extending outwardly therefrom, wherein the outer edge of each tooth has a peripheral portion of maximum radial extent from the annular body and at least one chamfered portion of lesser radial extent. Preferably each tooth comprises upper and lower chamfered portions diverging from a substantially central peripheral portion.

Viewed from a yet further aspect the present invention provides a gear drive tra comprising a plurality of gear wheels as hereinbefore defined in mtermeshmg relationship. Preferably, the gear drive train comprises at least one mam drive gear and a plurality of intermediate gears.

The invention will now be described m a non-limitative sense with reference to examples shown in the accompanying Figures in which:

Figure 1 represents a schematic representation of a disc mower assembly;

Figure 2 represents a perspective view of a cutter bar and disassembled, partial drive train;

Figure 3 represents a mam drive gear wheel of a first embodiment of the invention;

Figure 4 represents an intermediate gear wheel of a second embodiment;

Figure 5 represents a comparison of noise levels of the invention vis a vis the prior art;

Figure 6 represents a perspective view of mtermeshmg gear wheels of the invention;

Figure 7 is a sectional view of a third embodiment of gear wheel; and, Figure 8 is a sectional view of a fourth embodiment of gear wheel.

Figure 1 illustrates schematically a disc mower assembly comprising a cutter bar (housing 100 m truncated form along the top surface of which are mounted a plurality of mower discs 200 m spaced apart arrangement. As indicated by the respective arrows, the mower discs are rotated m opposite directions. The direction of cutting is indicated by arrow 300.

With reference to Figure 2, a mam drive gear wheel 1 and intermediate gear wheel 2a, 2b are shown disassembled from cutter bar housing 3. Additional intermediate and/or drive gear wheels may be provided as required for the number of desired rotary cutter discs (not shown . Drive is applied at one end of the housing 4 and transmitted through the gear wheels along the length of the cutter bar housing. The mam drive gear wheel 1 is mounted tc the housing using conventional components of a bearing asse~-bly 5 as will be apparent to the skilled man. The intermediate gear wheel 2b is shown mounted to the housing using cor"entιonal components of a bearing assembly 6 as wιl_ be apparent to the skilled man.

Figure 3 shows in cross-section a rram drive gear wheel m a preferred embodiment of the inventic- designated generally by reference numeral 10. The ma_n drive gear wheel 10 comprises a ma annular body 12 and a plurality of gear teeth ba, 13b. Each tooth 13a, 13b comprises a peripheral portion 14a, 14b of maximum radial extent from which diverge chamfered portions 15a, 16a and 15b, 16b respectively which are of lesser radial extent. Figure 4 illustrates in cross-section an intermediate gear wheel in a preferred embodiment of the invention designated generally by reference numeral 20. The intermediate gear wheel comprises a substantially annular body 22 from which extend outwardly a plurality of teeth 23a, 23b. Each tooth 23a, 23b comprises a peripheral portion 24a, 24b located substantially midway between the axially spaced ends of the tooth and two chamfered portions diverging therefrom 25a, 26a and 25b, 26b. Cut-away portions 27a, 28a and 7b, 8b may be provided to reduce the overall weight of the gear wheel.

Figure 5 illustrates a comparative measurement of the noise level for a cutter bar housing of the invention (5a) and of the prior art (5b) . The number of revolutions is relatively high (3000 rpm) and there are 31 teeth corresponding to a frequency of 1550 Hz. The reduction m noise at this frequency is clearly seen.

Figures 6a, b and c illustrate various arrangements of gear wheels according to a preferred embodiment of the invention. If alignment is poor, there is a risk that the corners of the gear wheel teeth 61 a, 61b will contact the normal working surface 62 on an mtermeshed gear wheel. By removing these corners to provide a peripheral portion 64a of maximum radial extent and chamfered portions 65a, 66a of lesser radial extent, this problem may be alleviated and noise problems reduced. This will be seen from the mtermeshmg arrangement shown schematically m Figure 6a.

Figure 6d shows a further arrangement, also with chamfered portions on the tooth edge to reduce noise generation. However, this shows that it is not essential to reduce the radial extent of the tooth edge throughout the width of the tooth edge.

Thus, the tooth edge has a main portion 70 of maximum radial extent, and in which the main portion extends axially throughout the length of the tooth edge. Chamfered portions 71 of reduced radial extent are formed by grinding along the shoulders only of the axially outer ends 70a of the main portion 70.

It should be understood that a gear wheel according to the invention is particularly suitable for use in a gear box of a gear drive mechanism for rotating mower discs of a disc type mower. However, it should be understood that a gear wheel according to the invention may be utilised in gear boxes which form part of a drive train to operate other types of mechanism, than a disc mower.

Furthermore, while a gear wheel according to the invention is particularly suitable for transmission of rotation to an adjacent gear which is located in substantially the same plane, it should be understood that a gear wheel according to the invention may transmit drive, via its teeth, to an adjacent gear wheel meshing therewith, and which is not located in the same plane i.e. in which the axes of the two gears are non-parallel. This still gives advantage of less reduction of noise, even when the angle between the axes is not the theoretical required angle.

Figure 7 of the drawings shows further example or embodiments of gear box 30 according to the invention, and in which drive can be transmitted from one gear wheel 31 to an intermeshing gear wheel 32, in which the axes of the gear wheels are non-parallel e.g. in which the gear wheels are bevel gears . Figure 8 shows another embodiment of gearbox 40 having intermeshing gearwheels 41 and 42, and level gearwheel 43, and each of which also embody the noise-reducing features of the invention.

Claims

1. An elongate gear box housing (100 comprising an assembly of mtermeshmg gear wheels (2a, 2b) spaced apart m a horizontal plane along its length, wherein each gear wheel is adapted to apply driving rotation to a rotary mower disc (200) and comprises a main annular body (12) supported by a plurality of bearings and a plurality of gear teeth

(13a, 13b) extending outwardly from the annular body, wherein the outer edge profile of one or more of said gear teeth has a peripheral portion (14a, 14b) of maximum radial extent from the annular body and at least one chamfered portion (15a, 16a; 15b, 16b) of lesser radial extent.

2. A gear box according to claim 1, and comprising an elongate cutter bar housing (1) for use in a disc mower.

3. A gear box according to claim 1 or 2 , in which the outer edge profile of one or more teeth comprises a peripheral portion (64a) located substantially midway between the axially spaced-apart ends (65a, 66a) of the profile .

4. A gear box according to claim 3, m which two chamfered portions (65a, 66a) diverge from the peripheral portion (64a) towards the axially spaced apart ends.

5. A gear box according to claim 4, in which each tooth is axially symmetrical.

6. A gear box having an assembly of ter-meshmg gear wheels according to any one of claims 1 to 5, and comprising a mam drive gear wheel (1) at or near one end of tne gear box housing (100) .

7. A gear wheel (10) comprising a main annular body (12) and gear teeth (13a, 13b) extending outwardly therefrom, wherein the outer edge of each tooth has a peripheral portion (64a) of maximum radial extent from the annular body and at least one chamfered portion (65a, 66a) of lesser radial extent .

8. A gear wheel according to claim 7, m which each tooth comprises upper and lower chamfered portions diverging from a substantially peripheral portion.

9. A gear wheel according to claim 7, m which each tooth edge has a mam portion 70 and chamfered portions 71 formed by grinding away parts of the axially outer ends 70a of the mam portion.