GB2060339A

GB2060339A - Overload clutches

Info

Publication number: GB2060339A
Application number: GB8036418A
Authority: GB
Original assignee: C Van der Lely NV
Current assignee: C Van der Lely NV
Priority date: 1978-01-31
Filing date: 1979-01-29
Publication date: 1981-05-07
Also published as: NL7801079A; GB2013462A; IT1110607B; DE2902557A1; DE2902557C2; NL184534B; GB2013462B; GB2060339B; NL184534C; IT7919727A0; FR2415948A1; FR2415948B1

Abstract

An overload coupling (9) comprises a power input member (18), carrying spring-loaded balls (20), and a power output member (13) having formations (36, 37) Figure 4 (not shown) which interfit with similar formations in an intermediate coupling ring (27). The balls (20) engage recesses in the coupling ring (27) so transmitting drive from the input member (18). However, overload causes the balls (20) to move into deeper recesses, which allows the coupling ring (27) to move out of engagement with the output member. Braking of the coupling ring, which is achieved by reducing the speed of the input member 18, causes the balls (20) to return to the shallower recesses and re-establishes the engagement between the coupling ring (27) and the output member (13). The coupling ring (27) is braked by a shoe (49) when, on reducing speed, the centrifugal force on the shoe becomes less than that of a spring (56). <IMAGE>

Description

1

GB 2 060 339 A

1

SPECIFICATION

An overload coupling

5 This invention relates to an overload coupling. According to the present invention there is provided an overload coupling comprising two coupling members and a coupling ring which are rotatable about a common axis, the coupling ring being dis-10 posed between the two coupling members and being adapted to interconnect the two coupling members for rotation together in normal operation of the machine, the coupling ring being axially dis-placeable upon overload in to a position in which it is 15 freely rotatable relatively to at least one of the coupling members, whereby the coupling members are rotatable relatively to each other, means being provided for re-establishing the interconnection of the two coupling members after overload, this means 20 being responsive to the speed of rotation of one of the coupling members whereby the means is actuated to re-establish the interconnection when that speed of rotation is reduced to a value below the operating speed of the coupling.

25 An overload coupling in accordance with the present invention, in an agricultural machine, allows the machine to be used with any normal commercial tractor, without requiring a special control for reestablishing the interconnection.

30 For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 is a side elevation of an agricultural 35 implement attached to the lifting device of a tractor and provided with a coupling;

Figure 2 is a partly sectioned view of the coupling in Figure 1;

Figures 3,4 and 5 are views of parts of the coupl-40 ing shown in Figure 2;

Figure 6 shows an alternative construction for part of the coupling of Figure 2; and

Figure 7 shows another alternative construction for part of the coupling shown in Figure 2. 45 The agricultural implement of Figure 1 comprises, in this embodiment, a rotary harrow 1 which is attached by a three-point hitch 2 to a lifting device 3 of a tractor4. The agricultural implement may, however, be any machine. The lifting device 3 comprises 50 two lower carrier arms 5 and a top rod 6 of variable length. To drive the agricultural implement, the tractor has a powertake-off shaft 7 which is connected to an input shaft 8A of the machine by a universal auxiliary shaft 8. Shafts such as the auxiliary shaft 8 are 55 conventionally employed for driving agricultural implements; the shaft 8 comprises a terminal portion having a universal joint and comprising an overload coupling 9. This coupling 9 comprises a fork 10 which is part of the universal joint and a driven cou-60 pling member 11 which is rigidly connected to the fork 10 and comprises a flange 12, which is cast integrally with the fork 10, and a flange 13, the flanges 12 and 13 being interconnected by bolts 14. A driving coupling member 15 fits over the power 65 take-off shaft 7 and comprises a hub 16 provided on its inner surface with axial splines. The hub 16 and the driven coupling member 11 are rotatable relatively to each other but are axially fixed together by means of a ring 17. The hub 16 is rigidly connected 70 with a flange 18 having near its circumference three bores 19 spaced apart from one another by 120°. These bores 18 accommodate balls 20. The balls 20 are pressed by a stack of spring washers 21 which react against a retaining ring 22 fastened to the hub 75 16. The flange 18 has three further bores 23 which are also spaced apart by 120°. These further bores contain pins 24 which are pressed by springs 25 towards the driven coupling member 11, these springs 25 reacting against the cup spring 21. Bet-80 ween the coupling members 11 and 15 there is a coupling ring 27 which is shown in detail in Figure 3. The coupling ring 27 is coaxial with the rotary axis 26 of the coupling 9. The ring 27 has three identical guide paths 28 each having, as is shown in the 85 cross-sectional view of Figure 4, a depression 29 from which extends a ramp surface 30. Between a plateau 31 and the ramp surface 30 of each path 28 there is a generally part-spherical cavity 32 in which the ball 20 is situated in normal operation. The coupl-90 ing ring 27 has further recesses 33, each being next to a ramp surface 34, there being a flat surface 35 between each ramp surface and the next recess 33. On the side away from the spring stack 21 the coupling ring 27 has protuberances 36 which co-operate in 95 normal operation with recesses 37 in the flange 13. Between the flange 13 and the coupling ring 27 there is a spring 38 which presses the coupling ring away from the flange 13. At its circumference, the coupling ring 27 has a cylindrical contact surface 39, which 100 co-operates with three uniformly spaced brake shoes 49, each of which is connected by two ball-and-socket joints 50 and 51 with a carrier 52 fastened to the outer side of the flange 12. Each brake shoe 49 is in engagement with a substantially coaxial pres-105 sure face of a support 53, which is preferably of a somewhat heavier structure. The support 53 is pivotable about a substantially tangential shaft 54 and is connected with a carrier 55, the shaft 54 being surrounded by coils of a torsion spring 56, which 110 tends to turn the support 53 in the direction of the arrow C.

During operation the rotary elements of the harrow 1 are driven by the powertake-off shaft 7 of the tractor 4 through the auxiliary shaft 8. The overload 115 coupling 9 forming partof the auxiliary shaft 8 serves to protect the implement against overload. In normal operation, the balls 20 are held in the cavities 32 shown in Figure 4 underthe pressure of the spring stack 21. The pins 24 are pressed by the compression 120 springs 25 into the recesses 33 of the coupling ring 27 and are each in engagement with an end face 48 of the respective recess 33. Thus the coupling ring 27 and the flange 18 are interconnected for rotation together in the required direction of rotation. The 125 co-operation of the protuberances 36 with the corresponding recesses 37 also provides a driving connection between the coupling ring 27 and the flange 13. The brake shoe 49 is subjected to centrifugal force which holds it a short distance from the cylin-130 drical outersurface of the coupling ring 27. The cen

2

GB 2 060 339 A

2

trifugal force acting upon the support 53 overcomes the pressure exerted by the spring 56. Thus the brake constituted by the brake shoe 49 and the support 53 is released during normal operation.

5 If the maximum transmissible torque, determined by the characteristics of the various coupling parts 20,24,36 is transgressed due, for example, to jamming of one of the rotors of the harrow in the ground owing to obstruction by a stone, the balls 20 are 10 moved against the pressure of the spring stack 21 across the plateau 31 of the path 28 into the depression 29. The spring 38, acting as an overrun spring, biases the coupling ring 27 towards the spring stack 21 so that the protuberances 36 lift out of the reces-15 ses 37 and the coupling ring 27 can rotate freely with respect to the flange 13. In this way the drive ofthe driving member 15 can be continued, whereas the driven member 11 comes to a standstill, the agricultural implement being thus protected against over-20 load.

To re-establish the connection, it is sufficient for the tractor driverto reduce the speed ofthe power take-off shaft, for example, by disconnecting it, when the force ofthe spring 56 will overcome the cen-25 trifugal force exerted on the support 53. The spring 56 will then turn the support 53 in the direction ofthe arrow C to urge the brake shoe 49 in a radial direction against the coupling ring 27. The coupling ring 27 is thus engaged by the brake shoes 49, so that 30 relative rotation takes place between the coupling ring 27 and the flange 18. Braking ofthe coupling ring 27 continues until the balls 20 again snap into the cavities 32. At the same time the respective pins 24 slide up the associated ramp faces 34 and then 35 exert a pressure on the surfaces 35. Since the force ofthe springs 25 exceeds that ofthe spring 38, the coupling ring is moved axially towards the flange 13 until rotation ofthe coupling ring 27 with respect to the flange 13 causes the protuberances 36 to snap 40 into the recesses 37. Once this has occurred, the coupling is again ready for normal operation, the pins 24 again projecting into the recesses 33 under the pressure ofthe springs 25 and again engaging the end surfaces 48.

45 The pressure ofthe spring stack 21 is adjustable (in a manner not shown) so that the maximum transmissible torque can be adjusted. It will be understood that the device may have more than or fewerthan the three coupling members 20,24 and 50 36 shown, depending upon the maximum torque to be transmitted by the device.

In Figure 6, the coupling member 11 is shown to be connected with a support 57 having a part which extends axially and is provided nearthe end facing 55 the spring stack 21 with a spring-loaded, telescopi-cally extensible part 58. This terminal part 58 is urged by a spring 59 in the direction towards the spring stack 21. The terminal part 58 extends inwardly to near the flange 18 and is provided with 60 friction material 60 on the surface facing the coupling ring 27. The flange 18 is furthermore surrounded by a ring 61 having an internal screwthread 62 cooperating with a screwthreaded bushing 63 fitted to the flange 18. The ring 61 and the terminal part 58 65 are at least substantially in contact with one another in normal operation.

When the maximum transmissible torque ofthe coupling is exceeded and the coupling ring 27 runs freely with respect to the coupling member 11 in the manner described above, the tractor driver need only reduce the speed ofthe powertake-off shaft in the manner described with reference to Figure 2. He can do this, for example, by disconnecting it from the drive. The ring 61 will continue to rotate owing to its momentum, and so will be advanced by the screwthread 62 along the bushing 63 in the direction ofthe arrow D in Figure 6. This movement will cause the terminal part 58 to be moved towards the coupling ring 27 so that the friction material 60 brakes the coupling ring 27 with respect to the flange 18. In the same manner as described forthe first embodiment, the driving connection between the portions 15 and 11 is then re-established.

It should be noted that by omitting the brake formed by the friction material 60 and the terminal part 58, the fly-wheel effect is able in this embodiment to move the coupling ring 27 in the direction of the arrow D towards the coupling member 11.

When the coupling ring 27 moves in the direction ofthe arrow D, the balls 20 can snap in to the cavities 32 so that underthe action ofthe spring stack 21 the re-connecting operation described forthe first embodiment is performed.

In the embodiment shown in Figure 7, the coupling ring 27 has recesses 33, which are closed on the side nearer the portion 11 by a bottom 64. As shown in Figure 7, the free end ofthe pin 24 bears on the bottom 64. The pin 24 is provided with a shoulder 65 which fits in a cylindrical housing 66 provided with a supporting flange 67 engaged by the spring 25 of Figure 5. A terminal part 68 of a radially extending arm 69 engages the flange 67. The arm 69 is pivot-able about a tangentially extending shaft 70 lying in a fork 71, which is arranged on the outer circumference ofthe flange 18. The arm 69 is rigidly connected with an outwardly extending arm 72 provided at its end with a mass 73. Inside the housing 66, a compression spring 74 acts on the shoulder 65. In normal operation, with the normal speed ofthe power take-off shaft, the arm 72 occupies a substantially radial position, as illustrated, so that the terminal part 68 slightly compresses the spring 25 under the action of centrifugal force on the mass 73.

After overload, as before, the spring 38 overcomes the forces ofthe springs 25 and 74 and the extensions 36 leave the recesses 37 to allow the coupling ring 27 to run freely. When the tractor driver disengages the drive ofthe power take-off shaft, the centrifugal force acting on the mass 73 will decrease due to the speed reduction. At the same time the spring 74 will be compressed. As a result the spring 25 will urge the housing 66 and the pin 24 in the direction of the arrow E in Figure 7. Then the pin 24 will urge the coupling ring 27 towards the driven coupling member 11 and, owing to the disappearance ofthe compensation effect ofthe mass 73, the force ofthe spring 38 is overcome by the spring 25. Thus the projections 36 can snap into the recesses 37 and the ball 20 can move into the cavity 32 so that the coupling is again ready for normal operation. It should be

70

75

80

85

90

95

100

105

110

115

120

125

130

3

GB 2 060 339 A

3

noted that it is useful to dispose the speed-dependent coupling means so that only after an intentional reduction ofthe speed the connection between the two coupling members 11 and 15 can 5 be re-established. The speed concerned will preferably be chosen lower than the minimum speed at which, for example, a Diesel engine used as a prime mover of the tractor can drive the powertake-off shaft. Thus undesired coupling after overload with-" 10 out intentional disengagement ofthe drive is avoided.

Claims

1. An overload coupling comprising two coupling members and a coupling ring which are rotatable

15 about a common axis, the coupling ring being disposed between the two coupling members and being adapted to interconnect the two coupling members for rotation together in normal operation ofthe machine, the coupling ring being axially dis-20 placeable upon overload into a position in which it is freely rotatable relatively to at least one ofthe coupling members, whereby the coupling members are rotatable relatively to each other, means being provided for re-establishing the interconnection ofthe 25 two coupling members after overload, this means being responsive to the speed of rotation of one of the coupling members whereby the means is actuated to re-establish the interconnection when that speed of rotation is reduced to a value below the 30 operating speed ofthe coupling.

2. An overload coupling as claimed in claim 1, in which the re-establishing means causes the coupling ring to move in an axial direction upon reduction of the speed.

35 3. An overload coupling as claimed in claim 2, in which the axial displacement ofthe coupling ring is effected indirectly through one ofthe coupling members.

4. An overload coupling as claimed in claim 2 or 40 3, in which the re-establishing means comprises a brake, application of which causes relative rotation between the coupling ring and a driving one ofthe coupling members.

5. An overload coupling as claimed in claim 4, in 45 which the brake is disposed near the circumeference ofthe coupling ring.

6. An overload coupling as clamed in claim 5, in which the brake is disposed coaxially around the coupling ring.

50 7. An overload coupling as claimed in any one of claims 4 to 6, in which the brake comprises at least one brake shoe.

8. An overload coupling as claimed in claim 7, in which the or each brake shoe is mounted on a car-

55 rier.

9. An overload coupling as claimed in claim 8, in which the carrier is mounted for rotation with the driven coupling member.

10. An overload coupling as claimed in claim 9, 60 in which the carrier is movable radially with respect to the coupling ring.

11. An overload coupling as claimed in claim 9, in which the carrier is movable axially with respect to the coupling ring.

65 12. An overload coupling as claimed in claim 10

or 11, in which the movement ofthe carrier is effected as a result of a reduction in the speed of rotation ofthe said one ofthe coupling members.

13. An overload coupling as claimed in claim 12, 70 in which the movement of the carrier is effected by the action of centrifugal force.

14. An overload coupling as claimed in claim 12, in which the movement ofthe carrier is effected by an inertia member.

75 15. An overload coupling as claimed in any one of claims 1 to 3, in which the re-establishing means comprises resilient means for biassing the coupling ring in a direction to re-establish the interconnection, centrifugal means being provided for opposing the 80 action ofthe resilient means until the speed of rotation ofthe said one coupling member is reduced to a value below the operating speed.

16. A machine hitched to lifting means of a tractor, drive means being provided for transmitting 85 power from the tractor to the machine, this drive means including an overload coupling in accordance with any one ofthe preceding claims.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 7981.

Published at the Patent Office, 25 Southampton Buildings, London, WC2A1 AY, from which copies may be obtained.