GB2069073A

GB2069073A - Overload clutch for transmitting limited torque

Info

Publication number: GB2069073A
Application number: GB8100088A
Authority: GB
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1980-02-11
Filing date: 1981-01-02
Publication date: 1981-08-19
Also published as: JPS56120828A; IT1135174B; ES264745Y; ES264745U; NL8006796A; FR2475658A1; DE3004991A1; SE8100461L; IT8119322A0

Abstract

A motor driven hand tool such as a hammer drill incorporates an overload clutch, for minimising the idling torque transmitted to its handle should the working tool jam, comprising two disc-shaped drive parts (2, 3) mounted on a shaft 1, the drive part (3) having a cage (5) retaining balls (4), at different radial spacings relative to the centre of the shaft (1), which register with respective detent openings (14) on the drive part (2). In the event of a predetermined torque being exceeded, the balls (4) move out of the detent openings (14) to move the drive parts (2, 3) apart against the action of compression spring (9) uncoupling the clutch and thereby allowing the drive parts (2, 3) to rotate freely relative to each other subject only to the rolling friction of the balls which are also at different angular spacings so that they reengage the detent openings only once per revolution. <IMAGE>

Description

SPECIFICATION Overload clutch for transmitting limited torque This invention relates to an overload clutch for transmitting limited torque between two substantially disc-shaped drive parts which are arranged coaxially with respect to one another, wherein there are mounted on a first of these drive parts balls which project beyond an end surface thereof, adjacent to a second of these drive parts, and which each engage under a spring force into a corresponding detent opening in an end surface of the second driving part.

In motor-driven hand tools, for example hammer drills, for safety reasons a clutch has to be provided in the rotary drive between the motor and the working tool, which clutch is intended to interrupt the transmission of power between the motor and the tool in the event of blocking of the tool.

In hand tools, ball catch clutches are mostly used for this purpose. One such known clutch consists, for example, of two disc-shaped driving parts which are mounted on the same axis as one another and may be rotationally locked together by means of spring-loaded balls. The balls also provide for mutual axial support of the driving parts. Therefore, to achieve a uniform pressure distribution it is customary to use a great number of balls. In this way the specific pressure per ball can be reduced, which has a positive effect on clutch wear.

The balls are mounted on the first drive part along a prescribed circular path and at regular angular spacings. Each ball is independently, spring-loaded and projects, in the coupled state, into correspondingly arranged detent (or catch) openings in the end face of the other driving part.

If the limited torque, defined by the engagement of the balls into the detent openings, is exceeded, for example in the event of blocking of the tool as a result of jamming in the material being drilled, the balls are urged, contrary to the spring force, out of the detent openings, whereupon the drive parts rotate mutually. This mutual rotation is effected under an idling moment, which is relatively high in comparison with the release moment of the clutch, since all the balls drop, on relative rotation of the drive parts, successively into all the detent openings. This causes rapid and consecutive clutch impulses. These impulses are transmitted by way of the handle of the tool to the operator. Therefore, the operator is exposed to considerable risk, for example where he or she is standing on a ladder when using the tool.

The problem underlying the invention is to provide an overload clutch for transmitting torque which is distinguished by a low idling moment.

To solve this problem the present invention provides an overload clutch for transmitting limited torque between two substantially discshaped drive parts which are arranged coaxially with respect to one another, wherein there are mounted on a first of these drive parts balls which project beyond an end surface thereof, adjacent to a second of these drive parts, and which each engage under a spring force into a corresponding detent opening in an end surface of the second drive part, characterised in that the balls, and their corresponding detent openings, are arranged at different radial spacings relative to the centre of the drive parts.

In the coupled state of the drive parts, each of the balls has plunged into the detent opening associated with it. Upon the exceeding of the limited torque between the driving parts defined by the stop engagement of the balls with the detent openings all of the balls, as in the case of known overload clutches, are disengaged from the detent openings contrary to the spring force, so that subsequently the drive parts can rotate freely relative to one another. Upon the mutual rotation of the drive parts, after each complete relative rotation there is a renewed catch engagement of all the balls since the balls and the detent openings are disposed at the same radial spacings relative to the centre of the respective drive parts.

To achieve a powerful clutch engagement with slight wear, it is, for example, also possible to arrange balls or detent openings in pairs or in groups at the same radial spacings relative to the centre of the drive parts. In comparison with known ball catch clutches, however, the idling moment is in each case smaller by a multiple and thus not dangerous for the operator.

To solve the previously defined problem, with the invention it is alternatively possible to arrange the balls and their corresponding detent openings so as to be staggered at different angles relative to one another along a single circular path. This solution is distinguished above all by the possibility of the construction of the overload clutch being limited radially to a minimum.

This difference in angular displacement between the balls and the detent openings ensures that the balls can plunge into the detent openings only in one particular rotary position of the driving parts relative to one another. As a result of appropriately non-uniform angle selection a very low idling moment can be achieved in that during each relative rotation of the driving parts only one ball at a time plunges into one detent opening thus leading to very small clutch impulses in idling.

Where the balls and detent openings are arranged at different radial spacings relative to the centre of the drive parts it is advantageous to space-apart the balls, and analogously also the corresponding detect openings, by different angular amounts. In this way one-sided loading of the driving parts by the spring-loaded balls can be avoided. For this purpose, the angle between the balls or detent openings respectively having a large radial spacing is advantageously to be selected to be greater the angle between the balls having in contrast thereto a small radial spacing.

As a result of the said angular displacement, with an arranging of balls or detent openings in pairs or groups respectively at identical radial distances relative to the centre of the driving parts during the relative rotation thereof the balls can arrive only singly in the region of a relevant detent opening. This arrangement makes it possible to use a high number of balls with a relatively compact type of construction of the overload clutch, in which respect a significantly low idling moment is achievable.

In accordance with a further proposal of the invention, a particularly simple and functionally advantageous overload clutch is achieved if, to produce the spring force for the balls, a compression spring is provided which is supported against a pressure disc which rests against all of the balls. Basically it is, however, also possible to a pressure disc which is itself a disc-shaped compression spring. In order to make possible a disengagement of the balls from the detent openings, the pressure disc is either mounted so as to be axially displaceable (relative to the driving part having the detent openings) or, in the case of the design as a compression spring, so as to be elastically yieldable (relative to the driving part having the detent openings).The balls are, for their part, preferably mounted so as to be axially displaceable in passage bores of the one driving part and protrude beyond the two end surfaces thereof, so that on the one hand each ball is able -to project into a detent opening and on the other hand is capable of being acted upon for this purpose by the pressure disc.

The constructional simplicity of the clutch of the invention is above all achieved in that only one compression spring acts on all the balls, whilst in the case of known clutches a separate compression spring is associated with each ball. It proves to be a decisive functional advantage that only upon each complete relative rotation of the drive parts through 3600 does the compression spring bring all of the balls into engagement with the detent openings. In each relative intermediate rotary position at least some of the balls are, along their circular path, out of alignment with the detent openings and thus keep the pressure disc remote from the drive part containing the detent openings.Thus, if during the relative rotation of the two drive parts, one ball comes into the region of a detent opening, which lies along its circular path, then the pressure disc, since it also rests on the other disengaged balls, cannot move said one ball into the detent opening.

Preferably the rolling resistance of the balls upon relative rotation of the drive parts is reduced by rotary mounting of the pressure disc relative to the drive parts. The rotary mounting contributes also to the reduction of the idling moment.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a part sectional side view illustrating a preferred embodiment of the clutch of the present invention in its engaged condition; and Fig. 2 is a sectional elevation of the clutch of Fig. 1 , the section having been taken on the line Il-Il of Fig. 1.

The preferred embodiment of the overload clutch of the invention, as shown in Fig. 1 comprises a disc-shaped driving drive part 2, having a toothed rim 2a, and a drive part, to be driven, designated as a whole by 3. The drive part 2 and the part 3 are mounted coaxially on a shaft 1. The drive part 3 consists of a disc 5 which serves as a cage for several balls 4 and which is secured by way of a threaded connection 10 on a hub disc 6. The hub disc 6 is connected to the shaft 1, by way of a slide spring 7, in torsionallyfast manner and so as to be axially displaceable.

Also seated on the shaft 1, so as to be axially nondisplaceable, is a shoulder bush 8, on which bus 8 is supported a compression spring 9 which is a cup spring. The compression spring 9 presses against an intermediate ring 11, which for its part butts against the hub disc 6. A pressure disc 12 is seated rotationally on the hub disc 6 by means of a roller bearing 13 which can roll on a circularring-shaped surface 6a of the hub disc 6. The force produced by the compression spring 9 is transmitted to the pressure disc 12, by way of the roller bearing 13, and from the pressure disc 12 to the balls 4, whereby the latter are forced against inner end surface 2b of the driving drive part 2.In the coupled state, the balls 4 project into conical detent openings 14 in the drive part 2 and thus bring about a rotation-tocking connection of the two drive parts 2, 3 under a rotary or clutch moment which is limited by the spring force.

In order to achieve a rotary mounting of the drive parts 2, 3 which is as restraining-free as possible, the drive part 2 is supported frontally on a shoulder of the shaft 1 by way of a bearing disc 1 5. Furthermore, the drive part 2 is seated, along with interpolation of a bearing bush 16, on the hub disc 6.

As can be gathered from Fig. 2, in the disc 5 six balls 4 are retained in passage bores 17, in which respect the balls 4 are arranged at a different radial spacing, for example r, r1, and staggered at different angles for example a al, from the centre of the shaft 1. Likewise, six detent openings 14 are disposed, in the same arrangement as the balls 4, in the end surface 2b of the drive part 2.

If, for example, as a result of jamming of the tool in the material being drilled, the drive part 3 is too severly braked or blocked, then this results in the said limited torque between the drive parts 2, 3 being exceeded whereupon the balls 4 are forced, upon commencement of the mutual rotation of the drive parts 2, 3 Gut of the detent openings 14. In this respect, the pressure disc 12, the roller bearing 13, the drive part 3 and the intermediate ring 11 are displaced axially against the compression spring 9 by the balls 4, by an amount which corresponds to the depth of the detent openings 14.

Upon further relative rotation of the drive parts 2, 3 the balls 4 run on the end surface 2b in circular paths which correspond to the radial spacings of the balls from the centre of the shaft 1. Only after each complete relative rotation of the drive parts 2, 3 are all of the balls 4 in register with all of the detent openings 14, in order that they can engage therein once more. In contrast to known clutches, with the clutch of the invention only after each complete relative rotation does it lead from an overload clutch which is in idling to a clutch coupling. Thus a very low idling moment is achievable, in which respect also the roller bearing 13 contributes thereto, in that said roller bearing 1 3 makes possible an approximately free rotation of the pressure disc 12 relative to the drive part 3.

In this way classical rolling-off of the balls 4 between the end surface 2b and the pressure disc 12 is effected.

Claims

1. An overload clutch for transmitting limited torque between two substantially disc-shaped drive parts which are arranged coaxially with respect to one another, wherein there are mounted on a first of these drive parts balls which project beyond an end surface thereof, adjacent to a second of these drive parts, and which each engage under a spring force into a corresponding detent opening in an end surface of the second drive part, characterised in that the balls, and their corresponding detent openings, are arranged at different radial spacings relative to the centre of the drive parts.

2. An overload clutch as claimed in claim 1, characterised in that the balls together with their corresponding detent openings are arranged so as to be staggered at different angles relative to one another.

3. An overload clutch as claimed in claim 1 or 2, characterised in that a compression spring is provided to produce the spring force for the balls, which compression spring is supported on a pressure disc which rests on all the balls.

4. An overload clutch as claimed in claim 3, characterised in that the pressure disc is mounted for rotation relative to the drive parts.

5. An overload clutch for transmitting limited torque substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.