Rotary shear pin coupling

Abstract

 A shear pin coupling comprises a first coupling member (2) and a second coupling member (4), which members in normal operation are interconnected by a first shear pin (354). Fracture of that first shear pin (36A) due to overload of the coupling permits a relative rotation of the two coupling members (2,4). A second shear pin (30) is provided, which after fracture of the first shear pin (36A), is displaceable in a direction laterally of its length to re-establish the intercon- rection between the two coupling members (2,4).

Description

[0001] 

[0002] In this way the coupling is capable of traansmitting a high torque and provides protection from overload for a long- time, without needing to renew shear pins after each overloed.

[0003] For a better understanding of the present invention and to show how it may be carried into effect, reference will no be made, by way of example only, to the accompanying drawings in which:

Figure 1 is an elevational view of a shear pin coupling

Figure 2 is a sectional view taken on the line II-II in Figure 1;

Figure 3 is a sectional view taken on the lines III-III in Figure 2;

Figure 4 is a sectional view taken on the lines IV-IV in Figure 2;

Figure 5 is an elevational view taken in the direction of the arrow V in Figure 2;

Figure 6 is an exploded elevational view showing some component parts of the coupling of Figure 1 to 5; and

Figure 7 is an elevational view of a component part of the coupling in the direction of the arrow VII in Figure 6.

[0004] As shown in Figure 1, the shear pin coupling 1 comprises a first coupling member 2, which is mounted on a driving shaft 3, which may, for example, be the power take-off shaft of a tractor. The shear pin coupling also comprises a second coupling member 4, which has, on the side facing away from the first coupling member 2, fork prongs 6 of a universal coupling. This coupling may, for example, be one of a set of universal couplings of an auxiliary shuft (not shown), as is convem- tionally, employed between a power take-off shaft of a tractor and an input or driven shaft of an agricultural implement. The first coupling member 2 comprises a circular flange 6 (see Figure 3) and is provided on the side facing away from the coupling member 4 with a cylindrical boss 7. The boss 7 has at least one radial bore accommodating a ball 8, which is urged radially inwardly by a set screw 9 having a comical end into a groove 11 in the driving shaft 3. In this way the coupling is axially firmly connected with the driving shaft 3. The driving shaft 3 is provided with splines 12 which co-operate with corresponding splines in the first coupling member 2 to couple the driving shaft 3 and the first coupling member 2 for rotation together. On the side facing the second coupling member 4 the flange 6 has one or more (in this embodiment, twelve) guide slots 13 extending; radially from near the shaft to the periphery of the flunge 6. Each slot 13 is substantiall rectangular in tangential cross-section. The coupling member 2 also comprises a comparatively thin, circular disc 14, which has, near the shaft 3, a hub 15. The hub 15 fits coaxially with-



sure pin 38 each have a rectangular cross-section to match that of the slot 13. The pins 36 in the slot 13 preferably extend axially with respect to the rotary axis 3A. Each slot 13 may contain about 3 to 6 pins; in this embodiment, they each contain 4 pins.

[0005] The shear pin coupling described above operates as follows. During operation the shear pin coupling is provided between the output shaft of a power source and the shaft of mechanism to be driven. The shear pin coupling may be employed in many different situations, but in this embodiment it is arranged in the end portion of an auxiliary shaft ha- ving two universal couplings, in which, as stated above, the first coupling member 2 is connected with the power take-off shaft 3 of a tractor (not shown). The two coupling members 2 and 4 are interconnected for rotation together by a shear pin 36A. The part of this shear pin 36A which is disposed in the first coupling member 2 about the rear sidewall of the opening 18, as viewed in the direction of rotation A, this side wall ensuring by its concave shape a satisfactory transfer of forces from the sidewall to the adjacent part of the shear pin 36A. This part of the shear pin is retained against radially outward movement by the part 32 of the cover plate 30. The part of the shear pin 36A which is located in the second coupling member 4 lies in the opening 29 and is in contact with the leading sidewall of the opening 29, as viewed in the direction of rotation A, this sidewall comprising the side of the cutting plate 27, the surface of this side also matching the cylindrical surface of the shear pin. Preferably about one third of the length of the shear pin 36A is located in the opening 18 and the other two thirds are located in the opening 29. The openings 18 and 19 have, as viewed in a tangential direction, a larger dimension than the diameter of the shear pins 36 and 36A. This excess is preferably about 405. The part of the shear pin located in the opening 29 is not covered by the cover plate 30. As viewed in an axial direction, the length of the openings 18 and 29 is only slightly larger than the axial length of the shear pins 36 and 36A respectively. If the coupling is overloaded, which will occur at a torque depending upon the choice of characteristies for the shear pin 36 the cutting plate produces a sharply defined fracture and prevents damage of the rim 25, whilst damage of the ring 17 can be avoided by lading it from hardened material. After fracture of the shear pin 36A the coupling; mon- bor 4 will colle to a standstill, whilst the broken-off part of the shear pin 36A located in the opening 29 can emerge unhindered in a radial direction, The part of the shear pin remaining in the opening 18 will continue rotating with the first coupling member 2, which rotation results in relative rotation between the two coupling members 2 and 4. Thus the 18 Loves out from beneath the cover plate 30 so that the shear pin part can be ejected from the opening 18. This ejection is facilitated by the centrifugal force exerted on the shear pin. J oreover, since the rin 25 and the main portion 20 are a small distance apart from one another, any uneven fracture between the two parts of the broken-down shear pin should not result in jamming. The recess 22 located behind the opening 18, as viewed in the direction of rotation A, further facilitates the escape of the shear pin part. After the broken parts of the shear pin have been removed from the openings 18 and 29 respectively, a next-following shear pin 36 can move out of one of the slots 13 into a position for connecting the two coupling members. However, with the conventional speed of the power take-off shaft, which is about 540 rev/min. it is not possible for the next shear pin to be urged in a radial outward direction. This is because the tangential dimension of the opening 29 is intentionally chosen so that the sum of the force of the spring 35 and the centrifugal force exerted on the row of shear pins is not sufficient, at the normal operating speed of the power take-off shaft, to give the shear pin, having a known mass, an acceleration, sufficient to bridge the distance between the original position and the connecting position during the instant when the opening 29 is in register with the opening 10. It is important for the spring force to diminish proportionally to the reduced total mass of the row of shear pine as the shear pins are used up. The critical speed at which the spring is capable of displacing a new shear pin into a new connecting position is preferably chosen so that this speed is below the minimum speed of the power take-off shaft corresponding to idling of the driving engine. With a Diesel engine for example, this critical speed at which the connection is re-established. may be about 150 revolutions per minute. The movement of a shear pin into a new connecting position is limited in a radial direction by the part 32 of the cover plate 30 forming a stop. After the coupling is re-established, the shear pin coupling is again capable of transferring the driving power. In this way the construction according to the invention pre- vides protection from overload for a long time without nead-

be filled by removing the cover plate-30. By turning the rim 25 with respect to the main portion 20 the opening 29 can be brought into register with all of the openings 18 in suc=. cession, so that the shear pins can be inserted into the slots 13. After all the slots have been filled and the cover plate 30 is refitted, the shear pin coupling 1 is again ready for use.

[0006] Whilst various features of the shearn pin coupling that have been described, and that are illustrated in the drawing will be set forth in the following claims as inventive featur

Claims

1. A shear pin coupling comprising a first coupling member and a second coupling member which, in normal operation, are interconnected by a first shear pin, fracture of the first shear pin due to overload of the coupling permitting relative rotation of the two coupling members, characterized by a second shear pin which, after fracture of the first shear pin, is displaceable in a direction laterally of its length to re-establish interconnection between the two coupling members.

2. A shear pin coupling as claimed in claim 1, characterized by the second shear pin which,is displaceable in a direction. perpendicular to its length.

3. A shear pin coupling as claimed in claim 1 or 2, characterized by the first and second shear pins which are disposed in a group such that the plane containing their longitudinal axes also contains the axis of relative rotation of the coupling members, preferably a plurality of groups of shear pins, is provided, each group comprises at least four shear pins.

4. A shear pin coupling as claimed in any one of the preceding claims, characterized by the shear pins which are located in a guide slot, preferably at lest two guide slots for shear pins are provided, each guide slot extends fromnear the - axis of relative rotation up to the outer circumference of the coupling.

5. A shear pin coupling as claimed in claim 4, characterized the or each guide slot which accommodates,between the axis of relative rotation and the group of shear pins, means for displacing the shear pins, preferably the means for displacing the shear pins comprises a spring, the end of the spring facing the axis of relative rotation is located in a guide, a pressure pin is disposed between the spring and the adjacent shear pin.

6. A shear by pin coupling as claimed in claim 4 or 5, charac- terized/the or each guide slot which is provided in the first coupling member and the second coupling member has a radially extending opening which, in normal operation, accommodates- part of the shear pin which interconnects the two coupling member, preferably the first coupling member comprises at the circumference an annular element which has a respective radially extending opening in register with the or each guide slot, said openings have at least one concave, radial sidewall matching the shaped of the pin.

7. A shear pin coupling as claimed in claim 6,_' characterized by a recess which is provided in the annular element behind the opening, with respect to the intended direction of operative rotation of the coupling, preferably the recess has a circumfel ential dimension which is at least equal to the circumferential dimension of the opening.

8. A shear pin coupling as claimed in claim 6 or 7, characterized by a cover plate which is connected with the second coupling member and covers, in normal operation, only the opening in the annular element, preferably the cover plate is removable for filling the or each guide slot with shear pins", a cutting plate is arranged in the second coupling member radially inwardly of the cover plate, this cutting plate bearing, in normal operation, on the shear pin interconnecting the two coupling members, preferably the cutting plate projects beyond the axial end of the second coupling mem ber.

9. A shear pin coupling as claimed in any one of the preceding claims, characterized the adjacent surfaces of the

to A shear pin boupling substantielly as describes herein with reference to and as illustrated in the accompenying frawings.

Drawing