GB2086496A

GB2086496A - Improvements in or relating to a mechanical drive mechanism for rotary cultivators

Info

Publication number: GB2086496A
Application number: GB8010372A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-03-27
Filing date: 1980-03-27
Publication date: 1982-05-12
Also published as: GB2086496B

Abstract

A variable ratio transmission utilises a double expanding VEE-belt pulley 15a 15b, 16 the shaft 14 of which is driven in use to transmit drive to two respective VEE-belts 17a, 17b. Each belt in turn drives one input 19a, 19b of a corresponding differential 11a, 11b, so that the rates of rotation of the output shafts (not shown) of these latter will depend upon, inter alia, the adjustment of the common member 16 of the double VEE-belt pulley. The other inputs 10a, 10b of the differentials are driven by belts 8a, 8b from a shaft 6 which also drive the shaft 14 through gearing 12, 13 and itself driven by a prime mover 1 through a belt 4. Reversal of relative rotation of the two output shafts may be achieved. The transmission is illustrated in use in a rotary cultivator. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a mechanical drive mechanism for rotary cultivators This invention relates to a mechanical drive mechanism for rotary cultivators.

The invention is concerned with the provision of differential drive to two members, such as the ground wheels and the rotor of a rotary cultivator. In the past this has been achieved by fixed ratio gearing, butthis restricts the ratios which can be obtained.

The basic feature of the drive mechanism is the provision of a variable ratio transmission device consisting of two VEE-belt pulleys mounted on a drivable shaft and having a common member slidable on the shaft in such manner that the effective radii of the two pulleys may be simultaneously varied in opposite directions to vary the driven speeds of belts engaging the pulleys.

The variable ratio transmission device finds its initial application in a drive mechanism suitable for a rotary cultivator in which two rotary output members are driven by the output from two corresponding differential units which have respective first input shafts driven by a prime mover in a fixed ratio and respective second input shafts driven by the prime mover via a variable ratio transmission device such as that set out above.

The selection of the various drive ratios in the drive mechnism may be selected to permit reversal of the relative movement between the two output members.

The invention will now be explained in greater detail with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic plan view of a drive mechanism embodying the present invention, Figure2 is a diagrammatic side elevation of the mechanism of Figure 1, and Figure 3 is a diagrammatic view of a differential unit suitable for use in the embodiment illustrated in Figures 1 and 2.

In Figures 1 and 2 a prime mover 1, having an output shaft 2 and drive pulley 3, acts through a driving belt 4 and pulley 5 to drive a layshaft 6. This layshaft carries two further pulleys 7a and 7b of diameters such that the drive ratios between the pulley 5 on the one hand and the respective further pulleys 7a and 7b are 8:5 and 8:3 approximately. The pulleys 7a and 7b act through respective driving belts 8a and Sb and pulleys 9a and 9b to transmit drive to the respective first input shafts 1 0a and lOb of a pair of differential drive units 1 1a and lb. The pulleys 9a and 9b are identical and provide drive ratios of 10:7 and 6:7 between the parts of the transmission path identified by the suffixes "a" and "b" respectively.In addition to the pulleys 7a and 7b, the layshaft 6 carries a first pinion 12 which meshes with an identical pinion 13 on a second layshaft 14.

This layshaft constitutes the drivable shaft of the variable ratio transmission device of the invention and carries the component parts of the two VEE-belt pulleys. These components are a pair of identical frusto-conical discs 15a and 1 sub fixed to the shaft 14 at spaced positions with their conical surfaces facing inwards, and a disc 16 carried on the shaft 14 between the discs 15a and 15b for sliding movement axially of the shaft. The two opposed surfaces of the disc 16 are both frusto-conical and define annular VEE-grooves together with the adjacent discs 1 spa and 15b. It will be understood that the axial position of the disc 16 on the shaft 14 defines the effective axial width of those VEE-grooves, and thus the relative radii of the pulleys defined by the three discs.Belts 17a and 17b couple the two parts of the variable pulley 15/16tofurther pulleys 18a and 18b mounted on the respective second input shafts 1 9a and 19b of the differential drive units 1 1a and 1 1b.

The variation of the ratios of the radii of the variable pulley 15/16 permit variation of the drive ratio to the shafts 19a and 19b to varyfrom 4:9to 4:3. The shaft 14 is journalled in one end of a link 20 which in turn is journalled on to the shaft 6. Arcuate movement of the link 20 about the shaft 6 acts to cause corresponding changes in the distances between the shaft 14 and the shafts 19a, 19b respectively, and when the mechanism is in operation, these changes are accomodated by a consequent axial movement of the disc 16 which relieves the tension in that belt 17 which has to span the increasing inter-shaft distance, and incidentally takes up the slack in the other belt.Thus, means (not shown, but which could be a simple hand-operated lever) provided to cause the swinging of the link 20 about its pivot on the shaft 6 will produce the variation of ratio referred to above.

In the configuration shown in Figure 1 the ratio between the radii of the parts of the pulley 15/16 is approximately 1 :4, and axial adjustment of the disc 16 can reverse this ratio to 4:1.

With the ratios quoted above, the output from differential unit 1 it, which is connected to drive the ground wheels of the cultivator, will vary from +0.47 to -0.42 revolutions relative to each revolution of the input shaft 6, while at the same time the output from the differential unit 1 lea, which is connected to drive the rotor of the cultivator, will vary from -0.99 to -0.10 revolutions relative to each revolution of the input shaft 6. This gives a wide range of ratios between the relative speeds of the ground wheels and rotor of the cultivator, and in fact permits the ground wheels to produce a reverse drive without reversal of rotor direction, and with the possibility of stopping the rotor rotation altogether while maintaining the reverse drive to the wheels.In practice, this wide variation of ratio permits the cultivator to be operated to produce a correct tilth in a corres pondinglywide range of soil conditions.

Further advantages result from the derivation of the drive to both rotor and ground wheels through respective differential units. Firstly, the prime mover can be run at its optimum speed for any task, since the actual output speeds are determined by the differential units 11. Secondly, if the operator lets go of the controls, the double pulley 15/16 will adopt a position in which the minimum mechanical work is done, and if the machine is simply standing on a hard surface, it will come to rest. Thirdly, by releasing the tension in either of the belts 8a or Sb the output speed of the respective differential units will fall to zero as the pully 9a or 9b is permitted to slip freely. This may be achieved by reducing the action of respective jockey pulleys 20a, 20b.

It is to be understood that the transmission ratios described above relate only to one specific embodiment of the mechanism, and that any different embodiment will be designed to have appropriate transmission ratios. This will vary not only between different designs for rotary cultivators, but also when considering powered devices for other tasks, whether horticultural or not. Thus, for example, small scale snow-clearing machinery could be powered by such a transmission unit, quite apart from its use in relation to crop-harvesting machines or similar devices.

In the above description, it has been assumed that each of the differential units is of the crown and bevel type, with equality of ratio between the two input shafts. Figure 3 shows an epicyclic differential which could be used in place of this type.

In Figure 3, the unit is housed in a casing 21 journalled to accept the input shafts 1 Oa and 19a.

The latter extend nearly to the centre line of the housing and carry needle-roller races 21a and 22a which support the planet cage 23 of the unit. A planet ring 24 is keyed to the shaft 1 9a while a sun wheel 25 is keyed to the shaft 10a. A planet pinion shaft 26 is carried in needle-roller bearings 27 in the planet cage, the shaft carrying two planet pinions 28a, 28b at its ends. Planet pinion 28a engages the planet ring 24 while the planet pinion 28b engages the sun wheel 25. It will be readily understood that the rate of rotation of the planet cage 23, which is toothed at 23' to engage a drive chain 29, depends on the relative rates of rotation of the shafts 10a and 19a. The chain 29 engages a sprocket 30 keyed to an output shaft 31 through which drive may be transmitted to the wheels or rotor of the cultivator. It will be appreciated that the two input shafts are geared to the planet pinion 28a, b in different ratios, but this can be compensated for if necessary by varying the transmission ratios elsewhere in the fixed-ratio part of the unit. Finally, although the above description refers to the reversal of the direction of rotation of the output shaft 1 it, it is possible, by using double pulleys 9a, 9b, to permit the belts Ba, Sb to be transposed and thus interchange the output ratios of thetwo shafts 11a,11b of Figures 1 and 2 or the corresponding shafts 31 when differential units of the type illustrated in Figure 3 are used.

Claims

1. A variable ratio transmission device consisting of two VEE-belt pulleys mounted on a drivable shaft and a common member slidable on the shaft in such manner that the effective radii of the two pulleys may be simultaneously varied in opposite directions to vary the driven speeds of respective belts engaging the pulleys.

2. Avariable ratio transmission device according to Claim 1 in which at least one of the said respective belts also engages a pulley mounted on one input shaft of a differential drive unit the other input shaft of which is driven independently of the said one belt.

3. A variable ratio transmission device according to Claim 2 in which the said other input shaft is arranged to be driven by the same prime mover which drives the said drivable shaft.

4. Avariable ratio transmission device according to Claim 2 or Claim 3 in which both respective belts are coupled to corresponding differential drive units as set out in Claim 2.

5. A variable ratio transmission device according to any one of Claims 2 to 4 in which each of the said respective belts forms part of the transmission path to a corresponding output member and in which the range of variation of the effective radii of the said two pulleys includes a point on opposite sides of which the relative sense of rotation of the two output members is reversed.

6. A rotary cultivator in which power from a prime mover is transmitted via a variable ratio transmission device as claimed in any one of Claims 1 to 5.

7. A rotary cultivator as claimed in Claim 6 in which one of the respective belts is coupled to the ground wheels of the cultivator and the other of the respective belts is coupled to its rotor.

8. A rotary cultivator as claimed in Claim 7 when dependent upon Claim 5 in which the sense of rotation of the rotor is constant while that of the ground wheels is reversible.