AU2375992A - Improved blade shaft drive for machines having rotary cutting or abrading tools - Google Patents

Description

IMPROVED BLADE SHAFT DRIVE FOR MACHINES HAVING ROTARY CUTTING OR ABRADING TOOLS

This invention relates to machines having rotary cutting or abrading tools. It is particularly, but not exclusively concerned with machines for cutting or sawing concrete paving or like material such as asphalt, of the type comprising at least one cutting blade, means for driving the cutting blade and a wheeled support structure for supporting the cutting blade and its drive means. Such machines will hereinafter be referred to as "concrete cutting machines".

The invention is particularly applicable for use in concrete cutting machines of the kind which are adapted to be used by one person who operates and manoeuvres the machine from its rear as it moves forwardly with a rotatable cutting blade at the front end of the machine to cut a pavement or a slab of concrete beneath the front end of the machine. Conventional concrete cutting machines of this kind typically have a pair of front wheels and a pair of rear wheels which may be driven by a motor to move the machine rearwardly or forwardly and a cutting blade located on either side of the machine forwardly of the front wheels, the or each cutting blade being adapted to be rotatably driven from an internal combustion engine or electric engine mounted on the support structure via a single belt and pulley drive system. A disadvantage associated with conventional concrete cutting machines results from cutting blades of different diameters being required to cut concrete slabs of different thicknesses; different diameter blades having different optimum operating speeds. In conventional machines, a direct belt and pulley drive system at one side of the machine is used to transmit drive from the engine to the drive shaft of the cutting blade or blades. Such machines are usually arranged to carry only blades within a small range of sizes, because replacement of pulleys to provide different operating speeds for different cutting blades can be a laborious and time-consuming operation. It is therefore desirable to provide a concrete cutting machine which can operate efficiently with a wider range of blades and to provide a drive arrangement for the cutting blades in a concrete cutting machine that facilitates interchange of components for different cutting requirements.

Furthermore, excessive vibration is a problem commonly experienced in the use of concrete cutting machines, and hitherto this problem has generally caused petrol engines to be used as the source to drive the cutting blades in conventional machines because they do not vibrate as much as diesel engines. It would thus be desirable to provide a concrete cutting machine in which the cutting blade could be driven by a diesel engine without the machine suffering from excessive vibration of the cutting blades which tends to reduce the working life of a blade..

According to one aspect of the invention there is provided a machine comprising at least one rotatable cutting blade, a motor or engine and blade drive transmission means to rotate the at least one cutting blade, and a wheeled support structure on which the motor or engine and the at least one cutting blade is supported, wherein the blade drive transmission means comprises a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted at one end of a transverse idler shaft, a third pulley means mounted on the transverse idler shaft at an inward position relative to the sides of the support structure and a second drive belt arrangement extending downwardly from the third pulley means to an inwardly located fourth pulley means mounted on a blade shaft for the at least one cutting blade. In a preferred embodiment the first and second pulley means comprise toothed pulleys or sprockets and the first drive belt arrangement is a toothed drive belt or a drive chain engageable with the sprockets whilst the second drive belt arrangement comprises a V-belt or a series of V-belts extending around the third and fourth pulley means which are located substantially centrally relative to the sides of the support structure.

The "indirect" blade drive transmission arrangement of this aspect of the invention provides several advantages over the usual direct drive arrangement of conventional concrete cutting machines which consist of a V-belt or assembly of V- belts at one side of the machine extending around an upper pulley mounted on the power output shaft from the motor or engine and downwardly to another pulley mounted on the driven shaft which carries a cutting blade on either side of the machine.

One advantage of the blade drive transmission system of the invention is that variation of the system to provide different required cutting speeds for different diameter blades is greatly facilitated. Generally speaking, cutting blades of larger diameters should be operated at lower speeds than smaller diameter blades and so the drive transmission system needs to be changed for a different cutting application, e.g. thicker or harder concrete. In the present invention, it is a relatively simple operation to change the first and second toothed pulleys at the side of the machine for pulleys of different diameter and teeth to vary the rotational speed of the transverse idler shaft, without the third and fourth V-belt pulleys requiring adjustment, whereas in conventional "direct" drive systems it is a time consuming operation to change the V-belt pulleys and to re-adjust the tension of the V-belt arrangement. In addition, the width of a machine can be reduced by the provision of a toothed belt drive and the substantially central location of the V-belt drive. Also, a further advantage provided by the blade drive arrangement of the invention is that there is minimal power loss from the output of the engine to the blade shaft.

In accordance with a further advantageous feature of the invention, vibration throughout the machine, particularly the blade shaft, can be significantly reduced by supporting the motor or engine on a support platform with a plurality of suitable vibration dampening mountings, such as rubber isolators, at the edges or corners of the platform. The mounting of the engine on a platform supported by vibration dampening mountings combined with inward, central location of the third and fourth pulleys provides a positive V-belt drive to the blade shaft which is ideally suited to the use of diesel engines as the power source. This is achieved because essentially the engine is set-up to move freely in the horizontal plane without affecting the V-belt pulley system so that the distance between the idler shaft and blade shaft remains substantially constant.

According to a further aspect of the invention there is provided a concrete cutting machine comprising a support structure carrying a pair of ground-engaging rear wheels and a front wheel or wheels, at least one rotatable cutting blade, a motor or engine, and blade drive transmission means to transmit drive from the motor or engine to rotate the at least one cutting blade, the blade drive transmission comprising a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted at one end of a transverse idler shaft, a third pulley means mounted on the transverse idler shaft and a second drive belt arrangement extending downwardly from the third pulley means to a fourth pulley means mounted on a blade shaft for the at least one cutting blade, wherein the motor or engine is supported on a support platform of greater horizontal dimensions than that of the motor or engine, the platform being connected to the support structure by a plurality of vibration-absorbing mountings distributed around the periphery of the platform and the third and fourth pulley means being located in such positions that the centre of the second drive belt arrangement lies substantially on the longitudinal axis of the machine.

A single front wheel or a pair of front wheels may be provided disposed at a central location on the longitudinal axis of the machine at a position close to but slightly rearwardly of the blade shaft. In this case, the third and fourth pulley means and second belt drive arrangement may comprise pulleys and pulley belts on both sides of the longitudinal axis of the machine, preferably disposed outwardly of the central front wheel or front wheels. Alternatively, the third and fourth pulley means may comprise a number of pulleys mounted on the transverse idler shaft and blade shaft at a central location on the longitudinal axis of the machine, with front wheels of the machine being provided on both sides of the centrally located third and fourth pulley and second drive belt arrangement. In this alternative embodiment, the front wheels are preferably located inwardly of the rear wheels. A concrete cutting machine incorporating the various aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a side view of a concrete cutting machine in accordance with the invention with the cutting blade in a raised position and the front and auxiliary wheels arranged for manoeuvering the machine;

Figure 2 is a partial side view of the machine in a position with the blade about to enter a pavement or concrete slab for cutting;

Figure 3 is a plan view of the undercarriage of the concrete cutting machine of Figures 1 and 2; and

Figure 4 is a section through the attachment means for securing a pulley on the power output shaft of the motor or engine of the cutting machine.

Referring to Figures 1 to 3 of the drawing there is illustrated a concrete cutting machine 10 comprising a support frame 12, a pair of front wheels 14, -a pair of rear wheels 16 adapted to be driven by an hydraulic motor of an hydraulic system (not shown) housed within a rear housing 17 of the machine to move the concrete cutting machine forwardly or rearwardly, and a rotatable cutting blade 20 disposed at either side of the machine slightly forwardly of the front wheels 14. The blade 20 can be rotatably driven from an engine 18 mounted on the support structure 12 via an improved blade drive transmission system 19 which will be described in more detail later on. The engine 18 is also used to drive an hydraulic pump 21 for the hydraulic system via a belt drive 23.

As shown in Figure 3, the support frame 12 comprises a substantially rectangular frame having longitudinal side members 22, a front frame member 24, a rear frame member 26 and an intermediate frame member 28 extending transversely between the side members 22. Located in front of the intermediate frame member 28 is a transversely extending shaft 30 which forms a pivot for the front pair of wheels 14 and for a pair of auxiliary intermediate wheels 32. The auxiliary wheels 32 are provided on a transverse axle 34 which is connected by a pair of longitudinally extending support arms 36 to the shaft 30 in such a manner that the arms 36, the axle 34 and the auxiliary wheels 32 are pivotally movable relative to the support frame structure 12 about the axis of the shaft 30.

The front wheels 14 are likewise mounted on a transversely extending front axle 38 connected to the transverse shaft 30 by longitudinally extending support members 40 which are also pivotally movable relative to the support frame structure about the axis of the shaft 30. Pivotal movement of the longitudinal members 40, front axle 38 and front wheels 14 relative to the support frame structure 12 is achieved by extension or contraction of a first hydraulic piston and cylinder assembly

42, one end of which is connected to the rear frame members 26 and the other end of which is connected to a rod 44 extending transversely between the rear ends of the longitudinal members 40 at a position above and slightly to the rear of the transverse shaft 30.

A second hydraulic piston and cylinder assembly 46 is provided which has an upper end connected to a transverse element 50 extending between the front axle support members 40 and a lower end connected to a transverse member 48 connected to and extending between the longitudinal support arms 36. Alternatively, the lower end of the piston and cylinder assembly may be connected to a flange on the axle 34. Extension or contraction of the second piston and cylinder assembly 46 causes the support arms 36 and axle 34 of the auxiliary wheels 32 to move relative to the support members 40, front axle 38 and front wheels 14. Control levers 52 are preferably provided at the rear of the machine to effect actuation of the first and second hydraulic piston and cylinder assemblies 42 and 46.

Figure 1 of the drawings shows the machine in a manoeuvering position in which the operator can grasp a pair of handles 51 extending rearwardly and substantially horizontally from the rear of the machine and use the handles 51 to lift the rear wheels clear of the ground or pavement to manoeuvre the machine easily into the required position for cutting. When the machine is in the required position for cutting the operator actuates one of the control levers 52 to contract the second piston and cylinder assembly 46 to move the front wheels 14 downwardly into engagement with the ground. Further contraction of the piston and cylinder assembly 46 raises the auxiliary wheels 32 above the ground into the position shown in Figure 2.

Figure 2 of the drawings shows the concrete cutting machine 10 in a cutting mode just prior to the blade entering a pavement or a slab of concrete beneath the front end of the machine. In this position the front and rear wheels 14 and 16 are in engagement with the ground indicated by line A and the auxiliary wheels 32 are raised slightly above ground level. In this position the operator stands at the rear of the machine where he can control the engine 18 and the blade drive transmission system 19 to cause the cutting blade 20 to rotate. The operator can also control the blade penetration into the pavement by actuating another of the control levers 52 to contract the hydraulic piston and cylinder assembly 42 so that the support structure 12 pivots relative to the support members 40 to move the cutting blade 20 into engagement with the pavement or concrete slab to the desired depth of cut and can control drive to the rear wheels 16 to move the machine forwardly or rearwardly. The concrete cutting machine may have a pair of cutting blades, one on each side of the machine, so that the operator can choose which of the blades he wishes or needs to use when cutting a slab of concrete. It will, however, be appreciated that the present invention is equally applicable to a machine having one concrete cutting blade 20 which may be located on either the left or right side of the machine. When the operator has finished cutting, he can then operate the said other control lever to actuate the hydraulic piston and cylinder assembly 42 to lift the blade clear of the pavement into the position shown in Fig. 2. From the position shown in Figure 2, extension of the second piston and cylinder assembly 46 then moves the auxiliary wheels 32 downwardly into engagement with the ground and raises the front wheels 14 and the front end of the support frame structure 12 above the ground into the manoeuvering position shown in Figure 1 in which the machine is supported by the auxiliary wϋeels 32 and the rear wheels 16. In this position, the centre of gravity of the machine is located at a position almost vertically above the auxiliary wheel axle 34 thereby greatly enhancing manoeuvrability of the machine as compared with some conventional concrete cutting machines which have no auxiliary wheels and the front wheels disposed well in advance of the centre of gravity.

The drive transmission system 19 for driving the cutting blade 20 will now be described with particular reference to

Figure 1 of the drawings. The cutting blade 20, which is preferably diamond tipped, may be carried at either end of a transverse blade shaft 54 which is rotatably driven from the engine 18 via an indirect belt drive transmission system. The transmission system 19 comprises a first toothed pulley 56 mounted on the power output shaft 58 of the engine

18, a toothed drive belt 60 preferably of the type known as

"POLY-CHAIN G.T." drive belt which extends around the first toothed pulley 56 in a generally horizontal direction to a second toothed pulley 62 mounted on a transverse "idler" shaft

64 disposed at a level above the blade shaft 54, a third pulley

66 mounted substantially centrally on the idler shaft, and a multiple V-belt 68 which extends around the third pulley 66 and downwardly to a fourth pulley 70 mounted on the blade shaft 54 for the cutting blade 20. An advantage of this type of toothed pulley and drive belt system is that it can transmit the power in approximately half the width required by a V-belt drive system, thereby reducing the width of the machine.

The multiple V-belt drive system, 66, 68 and 70 allows for slippage whenever the cutting blade 20 locks up in the cut. An improved mounting arrangement for the engine 18 is also shown in Figure 1 in which the engine and idler shaft 64 are mounted upon a support platform 72 of greater horizontal dimensions than that of the engine, the platform being connected to the main support frame structure 12 by a plurality of vibration- dampening mountings 74 at the periphery of the support platform 72. Conveniently, the support platform 72 is of generally rectangular shape with its front end disposed forwardly of idler shaft 64, and the platform 72 is supported upon rubber mountings 74 distributed at the edges or corners of the platform 72 on each side of the central longitudinal axis of the machine. In a preferred embodiment, four rubber mountings 74 (only two or which are shown in Figure 1) are provided at the corners of the rectangular support platform 72. It will, however, be appreciated that the platform could be of any desired shape and the number and location of rubber mountings may vary according to the shape or size of the platform provided that the rubber mountings are distributed around the periphery of the platform well outside the area covered by the engine 18 in contrast to conventional engine mountings. Preferably, the type of rubber mountings which are used are those which give approximately the same deflection for the same vertical and horizontal shear loads. The mounting arrangement of the invention has been found to be very effective in reducing the vibration transmitted from the engine to the support frame structure 12 and particularly to the blade shaft 54 for the cutting blade 20 thereby improving the blade performance and efficiency.

Whilst this arrangement may be used on a concrete cutting machine with a petrol engine, it is particularly suitable for supporting a diesel engine, the use of which has not previously been seriously contemplated in concrete cutting machines of the general type described above, owing to larger vibrations experienced during operation of diesel engines.

Another advantage of the above-described drive transmission of the invention is that it facilitates changing of the toothed pulley drive system to provide different operating speeds for the blade shaft 54 because different diameter cutting blades are required to be operated within predetermined ranges of cutting speeds for safe and effective operation to cut concrete slabs of different thicknesses. For instance, cutting blades having diameters between 16 inches an 36 inches are suitable for most applications, but a 36 inc diameter cutting blade should be rotated within a speed rang of between 900-1200 r.p.m. and the recommended optimum speed o rotation for a 16 inch diameter blade is within the range 2100- 2800 r.p.m. Use of the "POLY-CHAIN G.T." drive system or othe similar toothed belt and pulley drive system enables toothe pulleys having dif erent diameters and/or numbers of teeth to be used to vary the speed of the idler shaft 64 from an engine of particular maximum power output so as to provide di erent speeds of revolution for the blade shaft 54 whilst the engine is being run at maximum power. For example, only three interchangeable toothed pulleys, having 28, 30 and 36 teeth, are required for use with an engine of particular maximum power output to provide the appropriate revolutionary speeds for cutting blades of six different diametrical sizes from 16 inches to 36 inches.

Interchange of the toothed pulleys may be further facilitated in accordance with another advantageous feature of the invention which will be described with particular reference to Figure 4. Instead of a semi-permanent method of fixing a pulley to a keyed shaft which is often conventionally used to secure pulleys to shafts. Figure 4 shows the first toothed pulley 56 secured to the power output shaft 58 by a single locking nut 78 located in a recess 79 in the pulley 56 and received on a screw-threaded extension 80 of the output shaft 58. A drive pin or spigot 82 extending outwardly from a flange 83 on the shaft 58 and received in a complementary aperture 84 in the pulley 56 enables a drive transference from the shaft 58 to the pulley 56. The second toothed pulley 62 may be secured on the transverse idler shaft 64 in similar fashion. This fastening arrangement permits rapid replacement or interchange of the first and second toothed pulleys 56 and 62 when required and locating the nut 78 in the recess 79 also enables a reduction in width to be achieved.

A further advantageous feature of the mounting arrangement for the blade drive transmission system will now be described with particular reference to Figure 1. When it is desired to change the toothed pulleys 56 and 62, the tension on the toothed drive belt 60 is slackened by undoing a tensioning bolt 86 so that a mounting plate 88 for the second toothed pulley 62 and the idler shaft 64 pivots about pivot point 90. As shown in figure 1 the pivot point 90 is located substantially in a plane joining the centres of the third and fourth pulleys 66 and 70. This arrangement has the benefit that the tension of the V-belt drive system 66, 68 and 70 is not substantially affected by interchange of the toothed pulleys 56 and 62, because the distance between the centres of the toothed pulleys 56 and 62 does not change appreciably when the pulleys are changed, and only a small amount of adjustment, is required to re-tension the toothed drive belt 60. Also, only one toothed belt is required, thereby simplifying the interchange operation.

If adjustment of the tension of the V-belt arrangement is required, this may be achieved by adjusting the position of an adjustable pin 92 received in a slot 94 at the front end of the support structure 12 below the platform 72 so that the idler shaft 64 and third, pulley 66 can pivot about a further pivot point 96 on the support structure below the rear rubber mounting 74 of the platform 72. For a particular machine, the load of the engine may not be uniform, and so the location of the rubber mountings 74 to support the load and the location of the V-belt pulleys are chosen so that the idler shaft 64 is parallel to the blade shaft 54 when the V-belts 68 are fully tensioned so that all V-belts are under uniform tension.

From the above description it will be apparent that the present invention provides a concrete cutting or sawing machine which has several advantages over conventional machines. An important advantage is that reduced vibration is transmitted to the blade shaft whilst allowing a positive V-belt drive to the blade shaft. Also, the toothed pulleys 56 and 62 may be readily changed to allow for different toothed pulley belts to be used to provide different operational speeds for different sizes of cutting blades 20. The blade drive arrangement can be set up to drive any blade size at its optimum speed whilst the engine is able to be run at its maximum torque output. The operator can easily change the blade shaft speed when changin to a different blade diameter. Power is transmitted from th engine to the blade shaft with minimal power loss.

It will be appreciated that various modifications may b made to the machine as described above without departing fro the scope or spirit of the invention as defined in th accompanying claims which form part of the disclosure of thi specification. For example, the improved drive arrangemen and/or the engine mounting arrangement may be used with othe types of machinery having rotary parts, such as garde cultivators.

Claims (14)

CLAIMS :

1. A machine comprising a wheeled support structure, a drive motor or engine supported on the support structure, a rotatable blade means mounted on the support structure at a front end thereof, and blade drive transmission means for transmitting drive from the motor or engine to the rotatable blade means, characterized in that the blade drive transmission means comprises a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted on a transversely extending shaft, a third pulley means mounted on the transverse shaft in an inward position relative to the sides of the support structure, and a second drive belt arrangement extending downwardly from the third pulley means to an inwardly located fourth pulley means mounted on a blade shaft for said rotatable blade means.

2. A machine according to claim 1 wherein the first pulley means comprises a first toothed pulley, the second pulley means comprises a second toothed pulley and said first drive belt arrangement comprises a toothed drive belt.

3. A machine according to claim 1 wherein said second drive belt arrangement comprises a plurality of V-belts.

4. A machine according to claim 1 wherein the third and fourth pulley means and the second drive belt arrangement are located substantially centrally relative to the sides of the support structure.

5. A machine according to any one of the preceding claims wherein the drive motor or engine is supported on a support platform connected to the support structure by a plurality of vibration-dampening mountings at the periphery of the support platform.

6. A machine comprising a support structure carrying a pair of ground-engaging rear wheels and a front wheel or wheels, at least one rotatable cutting blade, a motor or engine, and blade drive transmission means to transmit drive from the motor or engine to rotate the at least one cutting blade characterized in that the blade drive transmission comprises a first pulley means mounted on a power output shaft of the motor or engine. a first drive belt arrangement connecting the first pull means to a second pulley means mounted at one end of transverse idler shaft, a third pulley means mounted on t transverse idler shaft and a second drive belt arrangeme extending downwardly from the third pulley means to a four pulley means mounted on a blade shaft for the at least o cutting blade, the machine being further characterized in th the motor or engine is supported on a support platform greater horizontal dimensions than that of the motor or engin the platform being connected to the support structure by plurality of vibration-absorbing mountings distributed arou the periphery of the platform, and the third and fourth pull means being disposed in such positions that the centre of t second drive belt arrangement lies substantially on t longitudinal axis of the machine.

7. A machine according to claim 6 wherein the third a fourth pulley means comprise a plurality of pulleys mounte respectively on the transverse idler shaft and on the blad drive shaft at a central location on the longitudinal axis o the machine.

8. A machine according to claim 7 wherein the machine has pair of front wheels, each of which is located outwardly of th third and fourth pulley means.

9. A machine according to claim 6 wherein the machine has on or more front wheels disposed at a central location on th longitudinal axis of the machine in close proximity to an slightly rearwardly of the blade drive shaft, and the third an fourth pulley means and second drive belt arrangement comprise a number of pulleys and pulley belts on each side of th longitudinal axis of the machine, disposed outwardly of th centrally located front wheel or wheels.

10. A machine according to claim 6 wherein the first pulle means comprises a first toothed pulley and the second pulle means comprises a second toothed pulley and said first driv belt arrangement comprises a toothed drive belt.

11. A machine comprising a wheeled support structure, a driv motor or engine supported on the support structure, a rotatabl blade means mounted on the support structure at a front en thereof, and variable speed blade drive transmission means for transmitting drive from the motor or engine to the rotatable blade means, characterized in that the blade drive transmission means comprises interchangeable first and second toothed pulleys, one of which is mounted on a power output shaft of the motor or engine and the other toothed pulley being mounted at one end of a transversely extending idler shaft, a toothed drive belt extending around the first and second toothed pulleys, a third V-belt pulley means mounted on the transverse idler shaft at an inward position relative to the sides of the support structure, and a V-belt arrangement extending downwardly from the third V-belt pulley means on the transverse idler shaft to an inwardly located fourth V-belt pulley means mounted on a blade drive shaft for said rotatable blade means. 12. A machine according to claim 2, claim 10 or claim 11 wherein the second toothed pulley and the idler shaft are pivotally movable relative to the support structure about a pivot point located substantially in a plane joining the centres of the third and fourth pulley means. 13. A machine according to claim 2, claim 10 or claim 11 wherein at least one of the first and second toothed pulleys is connected to its respective shaft by a locking nut received on a screw-threaded extension of the shaft, drive being transferred between the shaft and the pulley by a drive pin provided on the shaft or the pulley receivable in a complementary aperture in the pulley or shaft. 14. A machine according to claim 13 wherein the locking nut is located in a recess provided in the outwardly facing surface of the toothed pulley.

AMENDED CLAIMS

[received by the International Bureau on 7 December 1992 (07.12.92); original claim 2 cancelled; original claim 1 amended; new claim 3 added; claim 3 renumbered as claim 2; other claims unchanged (4 pages)]

1. A machine comprising a wheeled support structure, a drive motor or engine supported on the support structure, a rotatable blade means mounted on the support structure at a front end thereof, and blade drive transmission means for transmitting drive from the motor or engine to the rotatable blade means, the blade drive transmission means comprising a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted on a transversely extending shaft, a third pulley means mounted on the transverse shaft in an inward position relative to the sides of the support structure, and a second drive belt arrangement extending downwardly from the third pulley means to an inwardly located fourth pulley means mounted on a blade shaft for said rotatable blade means, characterized in that the first pulley means comprises a first toothed pulley, the second pulley means comprises a second toothed pulley and said first drive belt arrangement comprises a toothed drive belt. 2. A machine according to claim 1 wherein said second drive belt arrangement comprises a plurality of V-belts. 3. A machine comprising a wheeled support structure, a drive motor or engine supported on the support structure, a rotatable blade means mounted on the support structure at a front end thereof, and blade drive transmission means for transmitting drive from the motor or engine to the rotatable blade means, the blade drive transmission means comprising a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted on a transversely extending shaft, a third pulley means mounted on the transverse shaft in an inward position relative to the sides of the support structure, and a second drive belt arrangement extending downwardly from the third pulley means to an inwardly located fourth pulley means mounted on a blade shaft for said rotatable blade means, characterized in that the third pulley means comprises a set of V-belt pulleys, the fourth pulley means comprises a second set of V-belt pulleys and said second drive belt arrangement comprises a plurality of V-belts. 4. A machine according to claim 1 wherein the third and fourth pulley means and the second drive belt arrangement are located substantially centrally relative to the sides of the support structure. 5. A machine according to any one of the preceding claims wherein the drive motor or engine is supported on a support platform connected to the support structure by a plurality of vibration-dampening mountings at the periphery of the support platform. 6. A machine comprising a support structure carrying a pair of ground-engaging rear wheels and a front wheel or wheels, at least one rotatable cutting blade, a motor or engine, and blade drive transmission means to transmit drive from the motor or engine to rotate the at least one cutting blade characterized in that the blade drive transmission comprises a first pulley means mounted on a power output shaft of the motor or engine, a first drive belt arrangement connecting the first pulley means to a second pulley means mounted at one end of a transverse idler shaft, a third pulley means mounted on the transverse idler shaft and a second drive belt arrangement extending downwardly from the third pulley means to a fourth pulley means mounted on a blade shaft for the at least one cutting blade, the machine being further characterized in that the motor or engine is supported on a support platform of greater horizontal dimensions than that of the motor or engine, the platform being connected to the support structure by a plurality of vibration-absorbing mountings distributed around the periphery of the platform, and the third and fourth pulley means being disposed in such positions that the centre of the second drive belt arrangement lies substantially on the longitudinal axis of the machine.

7. A machine according to claim 6 wherein the third and fourth pulley means comprise a plurality of pulleys mounted respectively on the transverse idler shaft and on the blade drive shaft at a central location on the longitudinal axis of the machine.

8. A machine according to claim 7 wherein the machine has a pair of front wheels, each of which is located outwardly of the third and fourth pulley means. 9. A machine according to claim 6 wherein the machine has one or more front wheels disposed at a central location on the longitudinal axis of the machine in close proximity to and slightly rearwardly of the blade drive shaft, and the third and

5 fourth pulley means and second drive belt arrangement comprises a number of pulleys and pulley belts on each side of the longitudinal axis of the machine, disposed outwardly of the centrally located front wheel or wheels.

10. A machine according to claim 6 wherein the first pulley Q means comprises a first toothed pulley and the second pulley means comprises a second toothed pulley and said first drive belt arrangement comprises a toothed drive belt.

11. A machine comprising a wheeled support structure, a drive motor or engine supported on the support structure, a rotatable blade means mounted on the support structure at a front end thereof, and variable speed blade drive transmission means for transmitting drive from the motor or engine to the rotatable blade means, characterized in that the blade drive transmission means comprises interchangeable first and second toothed pulleys, one of which is mounted on a power output shaft of the motor or engine and the other toothed pulley being mounted at one end of a transversely extending idler shaft, a toothed drive belt extending around the first and second toothed pulleys, a third V-belt pulley means mounted on the transverse idler shaft at an inward position relative to the sides of the support structure, and a V-belt arrangement extending downwardly from the third V-belt pulley means on the transverse idler shaft to an inwardly located fourth V-belt pulley means mounted on a blade drive shaft for said rotatable blade means.

12. A machine according to claim 1, claim 10 or claim 11 wherein the second toothed pulley and the idler shaft are pivotally movable relative to the support structure about a pivot point located substantially in a plane joining the centres of the third and fourth pulley means.

13. A machine according to claim 1, claim 10 or claim 11 wherein at least one of the first and second toothed pulleys is connected to its respective shaft by a locking nut received on a screw-threaded extension of the shaft, drive being transferred between the shaft and the pulley by a drive pin provided on the shaft or the pulley receivable in a complementary aperture in the pulley or shaft.

14. A machine according to claim 13 wherein the locking nut is located in a recess provided in the outwardly facing surface of the toothed pulley.