GB2082695A

GB2082695A - Torque limiting clutch

Info

Publication number: GB2082695A
Application number: GB8041596A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-27
Filing date: 1980-12-31
Publication date: 1982-03-10
Also published as: GB2082695B; IT1154855B; IT8009525A0

Abstract

A torque limiting clutch comprises an inner member (16) carrying a pair of sliders (26) biased by spring-loaded plungers (36) and weak springs (52) to operative positions in which their ends (46) engage in recesses (9) in an outer member (7) to transmit torque between the members. On torque overload, the sliders are cammed radially inwards to inoperative positions in which only the springs (52) provide a resulting bias, so that the sliders can only re-engage the member (7) when the relative angular speed of the two members (7, 16) falls to a low value. In their inoperative positions, the sliders engage member (7) via rollers (50). <IMAGE>

Description

SPECIFICATION Torque limiting coupling The invention relates to a torque limiting coupling for preventing damage due to overloading in mechanical transmissions, of the automatic re-engagement type, i.e. arranged to restore torque transmission. These couplings comprise a drive member and a driven member, one of which comprises movement seats for mobile members provided with entrainment teeth, whereas the other of said members comprises engagement seats for said entrainment teeth, said entrainment teeth being resiliently urged towards said seats, whereas an opposing thrust is generated by reaction as a result of the torque transmitted by the coupling.

The object of the invention is to provide a coupling in which a substantial reduction is obtained in the thrust on the entrainment teeth towards the engagement seats, the coupling thus having a more suitable operation from the kinematic and dynamic aspects with respect to known couplings.

These and further objects and advantages will be apparent to experts of the art from reading the description given hereinafter.

According to the invention, said torque limiting coupling comprises resilient retention means arranged to urge said mobile members and thus said entrainment teeth into the entrainment position, and able to be neutralised when the entrainment teeth are disengaged from their respective engagement seats by excess transmission torque; means being provided for ensuring that the resilient thrust on said mobile members, and thus on said entrainment teeth towards their respective engagement seats is limited.

Said resilient retention means can be constituted by pawls arranged to act on surfaces inclined to the directions of movement of the mobile members when the entrainment teeth are in their engaged position, but said pawls being arranged to act on surfaces which are parallel, or at least less inclined than said surfaces, to said directions of movement of the mobile members, when the entrainment teeth are disengaged from their engagement seats, in order to nullify - or at least reduce - the resilient thrust of said pawls on the mobile members.

Advantageously, several pawls acting in parallel cooperate with each mobile member, their actions being added. Said pawls can be selectively neutralised in order to vary the maximum transmissible torque.

Although the mobile members can be pivoted, in order to obtain a rational construction said mobile members are slide members. More particularly, the slide members can be two in number, in sliding contact with each other along a substantially diametrical plane and with their entrainment teeth in diametrically opposite positions. The pawls are accommodated in seats formed in the slide members. The pawls carried by one of said slide members cooperate with inclined surfaces of the other of said slide members.

Advantageously, the pawls of each slide member have transverse stepped surfaces arranged to cooperate with corresponding stepped surfaces of the pawls of the other slide, or of the other slide itself, when in the disengaged position, in order to prevent rotation of the pawls about their respective axes when in the disengaged state; the facing surfaces of the two slides being slightly spaced apart in the pawl zone.

The means for urging the entrainment teeth into their respective engagement seats can be constituted by springs which act on a projection extending in each slide member from the side opposite the surface of contact with the other slide member. Said springs can be multiple and acting in parallel, and can be partially dispensed with or replaced in order to vary the thrust of the entrainment teeth in the direction of the engagement seats.

In one advantageous embodiment, cooperating profiles of the entrainment teeth and of the respective seats comprise correspondingly inclined surfaces, in order to transmit the torque with a component in the direction of movement of the mobile members, and comprise further surfaces which are more greatly inclined to the direction of movement of the mobile members in order to repel the entrainment teeth when they have carried out only a first part of their path of travel involved in engaging in the engagement seats.

That member of the coupling which carries the mobile slide members provided with the entrainment teeth can comprise an approximately diametrical seat for the two slide members, and opposing cavities originating from said seat for the projections and the springs acting on them.

The invention will be more apparent from the description and the accompanying drawings which shows a non-limiting embodiment of the invention, and in which: Figure 1 is a partly sectional side view on an axial plane, taken on the line I-I of Figure 2; Figure 2 is a cross-section on the line Il-Il of Figure 1; Figure 3 is a section taken approximately on the line Ill-Ill of Figure 2; Figure 4 is a diagrammatic isolated perspective view of an internal mobile member of the coupling; Figures 5 and 6 are two orthogonal isolated views of one of the pawls; Figure 7 is a separate detailed exploded view of an engagement seat and the relative entrainment tooth which cooperates with it; and Figures 8, 9 and 10 are views, enlarged with respect to Figure 2, of a detail of Figure 2 to illustrate an entrainment tooth in its engaged position, in its disengaged position and in a position in which its path of travel has been insufficient for engagement.

As shown on the accompanying drawing, the reference numeral 1 illustrates a discoidal member from which two fork appendices 3 project for pivoting a transverse cross pin forming part for example of a conventional cardan joint. The discoidal member 1 is joined peripherally by means of an annular weld 5 to a tubular casing 7, which can be formed from a tubular section. The tubular casing 7 is cylindrical over two substantial portions of its periphery, these being equal to each other and bounded by two opposing profiles 7A designed to constitute two internal engagement seats 9.As can be seen in particular from Figures 7 to 10, the engagement seat 9 comprises a base portion 9A between a side wall 9B and a transmission profile 9C inclined in an accentuated manner to the corresponding tangential direction of the inscribed cylindrical profile, which is defined by the inner surface 7B of the casing 7. The transmission profile 9C is followed by a connection portion 9E which is slightly inclined to the geometrical surface bounded by the inner cylindrical surface 7B. The engagement seat 9 cooperates by way of its described profile 9B, 9A, 9C, 9E, with a corresponding entrainment tooth described hereinafter, there being provided two engagement seats 9 and thus two entrainment teeth in diametrically opposite positions in the torque limiting coupling illustrated in the example.

The components 1, 3, 7, 7A constitute one of the members of the coupling.

The other member of the coupling is constituted substantially by a member 10 formed by casting (as is the member 1, 3), which in the example illustrated is in the form of an engagement sleeve 12 with a splined axial seat 1 2A for a splined transmission shaft into which the torque limiting coupling is connected. The reference numeral 14 indicates a pin for retaining the shaft in the splined seat 1 2A. The member 10 also comprises a cylindrical expansion 1 6 which has an outer diameter approximately corresponding to that of the inner surface 7B of the tubular casing 7. The cylindrical expansion 16 is accommodated in the tubular casing 7 between the discoidal member 1 and a resilient retention ring 18 by way of an annular spacer 20, which can be of hardened and/or antifriction metal, and which is engaged in the two recesses 9.The cylindrical expansion 1 6 is diametrically provided with a channel in the form of a slide seat 22 which extends in a substantially diametrical direction and has a substantially rectangular cross-section. In said cylindrical expansion 1 6 there are also provided two cavities 24 originating from the slide seat 22 and extending as far as the periphery of the cylindrical expansion 1 6.

Two mobile slide members 26, which are equal to each other and can be formed from a single section, can slide independently in the slide seat 22. Each slide member 26 (see Figure 4 in particular) comprises two side portions 26A which are guided one by the base of the slide seat 22 and the other by the opposing surface of the discoidal member 1. A third wall of each slide 26 comprises an appendix 26B which extends in one of the cavities 24, for the purpose described hereinafter.

The fourth wall of each slide 26 comprises relief surfaces 28 and depressed surfaces 30, which are connected on at least one side to inclined surfaces 32. The surfaces 28 of the two slides are slightly spaced apart. The reference numeral 33 indicates sliding contact surfaces.

Cylindrical seats 34 (three in the example) for a like number of cylindrical bodied pawls 36 open into the fourth wall, i.e. at the surfaces 28, 30.

Each pawl 36 is recessed internally to constitute a seat 38 open at one end for springs 40 of two types, which as shown on the drawing operate in parallel and are designed to act between the pawl and the base of the respective seat 34. At the closed end of the cylindrical body of each pawl 36, a prismatic profile is formed, i.e. parallel to a diameter, and comprises in particular a transverse portion 42 and an inclined portion 44 in addition to further stepped connection portions. The inclined portions 44 have an inclination which corresponds to that of the inclined surfaces 32 which connect together the relief surfaces 28 and depressed surfaces 30 of said fourth wall of the mobile slide members 26.When accommodated in the seats 34 of each slide 26, the prismatic profiles of the pawls 36 are parallel to those of the opposing pawls and to the bounding edges of the surfaces 28, 32 and 30 of the other slide 26, with which each pawl cooperates. By this means, by cooperating with each other and with the edges of the slides when in the disengaged position, the pawls remain always with their profiles parallel to each other and transverse to the direction of movement of the slides.

Each slide 26 has one end profiled to constitute an entrainment tooth 46 comprising an inclined surface 46A, the inclination of which corresponds to that of the profile 9C of the engagement seat 9, a second surface 46B with a different inclination, and a third surface 46C with a shape substantially corresponding to that of the base 9A of the engagement seat. The end of each slide 26 in the form of an entrainment tooth 46, as heretofore defined, also advantageously comprises a recess 48 in which there is mounted, by means of a pin 49, a rolling means 50 which just emerges from the surface 46C and is designed to cooperate with the inner surface 9B of the casing 7 and with the surfaces 9A, 9C, 9E of the engagement seats 9.

The two slides 26 of the described torque limiting coupling are accommodated in the slide seat 22 and are in sliding contact with each other the surfaces 33 of one being in contact with the surfaces 33 of the other slide, so that limited sliding can be carried out both relative to each other and to the cylindrical expansion 1 6 of the member 10. The amount of sliding required for each slide relative to the expansion 1 6 is of an extent substantially corresponding to the radial depth of the engagement seat 9 with respect to the inner surface 78 of the casing 7.

On assembly, the two slides 26 have their respective entrainment teeth 46 in opposing positions, and the appendices 268 of the two slides extend into their respective cavities 24 and are subjected to the thrust of springs 52 arranged to exert a relatively limited resilient thrust on the respective slides 26, in order to urge the respective entrainment tooth 46 towards the casing 7 and thus into the engagement seats 9 and against the inner surface 7A. In the example illustrated, three springs 52 can act on the same appendix 26B, these being housed in three seats in the form of dead bores in a block 54, which can be constructed of synthetic resin or the like. The resilient thrust on the slides 26 in the sliding direction can be adjusted either by changing the springs 52 or varying their number.

The resilient thrust of each pawl 36 can also be changed by replacing or dispensing with some of the springs 40.

The two members of the described torque limiting coupling can rotate one relative to the other because of the facility for angular relative movement between the member 10, 12, 16 (together with that combined therewith) relative to the tubular casing 7 and the discoidal member 1. The entrainment teeth 46 of the slides 26 and the engagement seats 9 cooperate in order to oppose the relative rotation and thus determine torque transmission between the two members of the coupling.

In the position shown in Figures 2 and 8, the slides 26 are urged to project from the cylindrical expansion 1 6 by way of their entrainment teeth 46, which enter the engagement seats 9, by the effect both of the resilient thrust of the springs 25 and of the longitudinal component of the resilient reaction which can be exerted between the two slides 26 by the springs 40 of the group of pawls 36 by way of the inclined surfaces in contact with each other, constituted by the inclined portions 44 of the prismatic profiles of the pawls 36 and by the surfaces 32 of the slides.In this respect, the pawls 36 of each slide are urged towards the other slide and in particular towards the depressed surface 30 of the other slide such as to rest by way of the inclined portion 44 on the corresponding inclined surface 32 of the other slide, the mutual force giving rise to resilient thrusts on each slide in such a direction that their respective entrainment tooth 46 is moved into the engagement seat 9.

The thrust on the entrainment teeth 46 in the engagement seats 9 is thus determined by the sum of the reactions of the springs 40 of the pawls 36 (the active components of these reactions), to which the relatively much smaller resilient thrust of the springs 52 is added. During transmission, contact can occur between the pawl surfaces 42 and the surfaces 30 of the opposing slide, until the limiting torque value is reached, which then determines disengagement. Under these conditions, the driven member is entrained by the drive member by means of the thrust reaction between the inclined profile 9C of the engagement seat 9 and the inclined surface 46A of the entrainment tooth 46.This reaction has a tangential component, and a component parallel to the sliding direction of the respective slide 26 and acting on the slide 26 in opposition to the resilient thrusts of the pawls 36 and springs 52.

As the torsional torque transmitted through the coupling increases, a value of the reaction between the profile 9C and the surface 46A can be attained such that the resilient thrust on the teeth 46 is overcome, and thus the two slides 26 each slide in such a direction as to re-enter the cylindrical expansion 1 6. The pawls 36 thus slide into the seats 34,with the inclined portions 44 along the inclined surfaces 32, until the transverse portions 42 of the pawls 36 of each slide correspond with the relief surfaces 28 of the other slide, this happening when the amount by which the slides have re-entered the cylindrical expansion 1 6 is equal to the depth of the engagement seats 9.Under these conditions (see Fig. 9) the thrust reactions of the pawls 36 in the same direction as the thrust of the springs 52 cease, this latter thrust being the only resilient reaction tending to cause the entrainment teeth 46 to again project in the centrifugal direction, apart from a possible centrifugal force which is very low because of the generally low rotational speed of these couplings and because of the small determining distance of the centre of gravity of the slides 26 from the axis of rotation when the drive member is represented by the member 10.The consequence of this is that whereas the disengagement between the two members is determined by a relatively high limiting torque, the thrust exerted on the slides 26 in the centrifugal direction tending to re-engage them is very low, and the pressure exerted by the entrainment teeth 46 is also very low against the inner surface 7B of the tubular casing 7, and along which the entrainment teeth 46 slide or rather the rolling means 50 roll.

When the coupling is in its disengaged state, the pawls 36 project slightly from their respective seats 34 because of the short distance between the surfaces 28 of the two slides; the stepped profiles of said pawls cooperate with the stepped profiles of the opposing slide or with the stepped profiles of the opposing pawls respectively, because of which any spontaneous rotation of the individual pawls from the position in which their profiles are transverse to the direction of movement of the slides is prevented.

The two members of the coupling are kept in their relative disengaged state until the relative angular speed of the two members reaches a relatively very low value, almost zero, this being an advantage in most applications of such torque limiting couplings. The reason for this is that after the two members have become disengaged from each other, the engagement thrust on the entrainment teeth 46 towards the engagement seats 9, as already stated, is very small and thus the acceleration which can be imposed on the slides 26 in the engagement direction is very low.

Thus, when the entrainment teeth 46 and the engagement seats 9 correspond with each other during the relative rotation of the two members, the movement of penetration of the teeth 46 into the seats 9 is relatively slow. Provided the relative speed of the two members exceeds a certain limit, the entrainment teeth 46 are able to penetrate only partially into the seat 9, and then each tooth 46 rises again along the respective connection portion 9E before the inclined surface 46A makes contact with the profile 9C. Re-engagement and thus entrainment takes place only when the relative speed of the two members of the coupling is very low, and such as to give sufficient time to the teeth 46 to penetrate into the seats 9 under the thrust of the springs 52 alone.This thrust is increased only during the final portion of the centrifugal travel path by the reactions of the pawls, under the action of the springs 40, by way of the inclined surfaces 44 and 32, the sliding friction of the slides having been overcome.

A residual thrust such as that of the springs 52-in addition to or in replacement of that of said springs -- could also be obtained by slightly inclining the surfaces of the transverse portions 42 of the pawls 36 and the depressed surfaces 30 which cooperate with them, in order to obtain a reaction by the pawls which is less than that obtained with the more greatly inclined surfaces of the portions 44 and of the surfaces 32.

The drawing shows only one embodiment of the invention given by way of example only, and modifications can be made to the shapes and arrangements without leaving the scope of the inventive idea.

The purpose of any reference numerals given in the accompanying claims is to facilitate the reading of the claims with reference to the description and drawing, and therefore does not limit the scope of the protection represented by

Claims

the claims. CLAIMS

1. A torque limiting coupling for preventing damage due to overloading in mechanical transmissions, of the automatic re-engagement type, i.e. arranged to restore torque transmission, comprising a drive member and a driven member, one of which comprises movement seats for mobile members provided with entrainment teeth, whereas the other of said members comprises engagement seats for said entrainment teeth, said entrainment teeth being resiliently urged towards said seats, whereas an opposing thrust is generated by reaction as a result of the torque transmitted by the coupling, characterised by comprising resilient retention means (36, 40) arranged to urge said mobile members (26), and thus said entrainment teeth (46), into the entrainment position, and able to be neutralised when the entrainment teeth (46) are disengaged from their respective engagement seats (9) by excess transmission torque; means being provided for ensuring that the (resilient) thrust on said mobile members (26), and thus on said entrainment teeth (46) towards their respective engagement seats (9) is limited.

2. A torque limiting coupling as claimed in claim 1, characterised in that said resilient retention means are constituted by pawls (36) arranged to act on surfaces (32) inclined to the directions of movement of the mobile members (26) when the entrainment teeth (46) are in their engaged position, but said pawls (32) being arranged to act on surfaces (28) which are parallel, or at least less inclined than said surfaces (32), to said directions of movement of the mobile member (26) when the entrainment teeth (46) are disengaged from the engagement seats, in order to nullify - or at least reduce - the resilient thrust of said pawls (36) on the mobile members (26).

3. A torque limiting coupling as claimed in claim 2, characterised in that several pawls (36) acting in parallel cooperate with each mobile member (26), their actions being added; said pawls (36) being able to be selectively neutralised in order to vary the maximum transmissible torque.

4. A torque limiting coupling as claimed in the preceding claims, characterised in that the mobile members are slide members (26).

5. A torque limiting coupling as claimed in claim 4, characterised in that the slide members (26) are two in number, in sliding contact with each other along a substantially diametrical plane and with their entrainment teeth (46) in diametrically opposite positions; and the pawls (36) are accommodated in seats (34) formed in the slide members; the pawls (36) carried by one of said slide members cooperating with inclined surfaces (32) of the other of said slide members.

6. A torque limiting coupling as claimed in the preceding claims, characterised in that the pawls (36) of each slide member have transverse stepped surfaces arranged to cooperate with corresponding stepped surfaces of the pawls (36) of the other slide, or of the other slide itself, when in the disengaged position, in order to prevent rotation of the pawls about their respective axis when in the disengaged state; the facing surfaces of the two slides being slightly spaced apart in the pawl zone.

7. A torque limiting coupling as claimed in the preceding claims, characterised in that the means for urging the entrainment teeth into their respective engagement seats (9) are constituted by springs (52) which act on a projection (54) extending in each slide member (26) from the side opposite the surface (28, 30) of contact with the other slide member (26).

8. A torque limiting coupling as claimed in claim 7, characterised in that said springs (52) am, multiple and act in parallel, and can be partially dispensed with or replaced in order to vary the thrust on the entrainment teeth (46) in the direction of the engagement seats (9).

9. A torque limiting coupling as claimed in at least some of the preceding claims, in which cooperating profiles of the entrainment teeth (46) and of the respective seats (9) comprise correspondingly inclined surfaces (46A, 9C), in order to transmit the torque with a component in the direction of movement of the mobile members (26), characterised in that said profiles comprise further surfaces (9E and possibly 46B) which are more greatly inclined to the direction of movement of the mobile members (26) in order to repel the entrainment teeth (46) when they have carried out only a first part of their path of travel involved in engaging in the engagement seats (9).

10. A torque limiting Coupling as claimed in the preceding claims, characterised in that the entrainment teeth (46) comprise rolling means arranged to slide on surfaces (78) concentric to the axis of rotation of the member (7, 1) comprising the engagement seats (9).

11. A torque limiting coupling as claimed in the preceding claims, characterised in that the member(l0, 16) which carries the mobile slide members (26) provided with the entrainment teeth (46) comprises an approximately diametrical seat (22) for the two slide members, and opposing cavities (24) originating from said seat (22) for the projections (268) and the springs (52) acting on them.

12. A torque limiting coupling with automatic re-engagement; all as heretofore described and represented by way of example on the accompanying drawing.