FR2466666A1 - Torque governing shaft coupling - uses blade spring catch effect to permit relative rotation at specific torque - Google Patents

Abstract

The torque governing shaft coupling is used on kitchen appliances e.g. electric food mixer, connecting a revolving shaft drive (1) to a driven component (9), and protecting the motor in the event of accidental jamming of the component. An elastic component (3) connects the two parts and is capable of radial elastic deformation to permit relative rotation when a definite torque is reached. A 'W' shaped spring steel clip (3) may be used, being secured to the shaft by a pin (10), and fitting snugly (4,5) inside a square spigot (2). The clip deforms until its diagonal dimension is less than that of spigot to permit relative rotation. Alternatively a square shaft may house in spigot which has corner splits.

Description

SAFETY DEVICE FOR THE TRANSITION OF A TDUVENtENT FROM
ROTATION
The invention relates to a safety device for the transmission of a rotational movement (continuous or alternating).

A certain number of apparatuses (such as household appliances) have a movable member in continuous or alternating rotation, at low speed; for example, a swinging system is known such as that described in French patent application No. 79 01169 of January 9, 1979, which in particular comprises a tank movable around a horizontal axis and driven in a rocking movement; this is ensured by an oscillating motor axis whose movement is transmitted to the tank by means of a square secured to the engine axis which fits into a female ear secured to the tank and which envelops the square on three sides.

In such devices, a certain number of more or less abnormal forces may be printed on the receiving member and transmitted entirely to the drive system and to the motor itself.

The normal forces and torques required to drive this type of equipment are relatively low, of the order of 10 daN.m because, in general, the loads are at least partially balanced.

On the other hand, accidental efforts can be considerable; this is the case, for example, of the mobile member being blocked by hand during various operations either for inspecting the content, or for adding seasoning, or for removing the removable mobile member.

In another case, you can inadvertently leave a spoon or fork in the removable bowl; during the movement, this cover can become wedged against a fixed part of the apparatus, which blocks the movement.

For obvious economic reasons, it is not possible to build the motors and various drive members in such a way that they resist such abnormal forces. It is therefore important to provide the kinematic chain with a security system.

 There are many known devices of this type: for example friction systems, snap-fastening such as a ball held by a spring, which is pushed out of its housing in the event of abnormal resistance, etc.

The device according to the invention is characterized by great simplicity, therefore a moderate cost price and high operating reliability. It consists in providing the motor shaft (or the receiving member) animated by an oscillating or rotary movement with an elastic device which normally ensures the transmission of the movement to the receiving member (or the driving shaft) and which , under the action of sufficient external forces, deforms so as to break the initial kinematic chain.

When the overload disappears, the initial kinematic chain is automatically restored to an elastic connecting device resuming its initial shape. The device therefore plays the role of a mechanical "torque limiter". The elastic element secured to an element of the kinematic chain is supported by at least part of its lateral surface on a rigid conjugate surface of identical shape, secured to the other movable part. In a preferred embodiment, the external surface of the elastic device consists of (or is inscribable into) a pyramid-based polygonal surface which fits into the rigid conjugate part. In its simplest form, the pyramidal form reduced to a prismatic surface whose generatrices are parallel to the axis of rotation and whose directrix is all or part of a regular convex polygon (possibly rounded angles). The actual shape of the coupling system optionally allows for the easy installation and removal of the removable receiving member; for this purpose, the pyramidal surface can be opened on one or more sides. The elastic member can be made of any suitable material, such as rubber, plastics, metals and alloys, etc., in the form of blocks, ribbons, wires, strips, etc., which are suitably arranged.

The invention will be better understood from the embodiments given below although these are not exhaustive of all the possible embodiments of the invention.

EXAMPLE 1
FIG. 1 represents a perspective view of the connection system as ensuring the transmission of an alternating rotational movement (<1 turn) between the motor shaft (1) and the receiving member (9) which carries a rigid ear ( 2) having the shape of a square prism, open downwards.

 Uh metal spring (3), in the form of a ribbon having the general shape of an M (or a W), is, on the one hand, secured to the motor axis (1) using a pin transverse (10) and is supported essentially by its two external faces (4 and 5) against the two opposite faces of the internal surface of the ear (2). In case of accidental overload, the spring (3) is deformed so that its maximum diagonal becomes equal to the internal length of the square of the ear (2), which separates the movements. Of course, the shapes and dimensions of the spring (s) are adapted to the maximum value of the torque which must transmit the device before "hanging up".

Figures 2, 3 and 4 show end views of alternative embodiments of the device shown in Figure 1.

In Figure 2, the spring has the general shape of a Z (or an N); it is fixed to the shaft (1) by passing through a longitudinal slot in the axis; in normal operation, it rests on the two faces (4 and 5) of the closed ear (5). This device is particularly intended for a continuous rotary movement in one direction (arrow).

In FIG. 3, the springs (3) consist of metallic wires with rounded ends which rest on said ends on two opposite cylindrical surfaces of the ear (2). The contact area is therefore limited to a small extent (4 ′, 5 ′) in the vicinity of the support generators.

In FIG. 4, the leaf springs are fixed to the axle using a rivet (11); the areas of contact with the ear (2) are limited to the generators (4 ', 5', 6 ', 7').

EXAMPLE 2
FIG. 5 represents a perspective view of the device relating to a rocking movement which comprises the motor shaft (1) provided at its ex-tremat with a prism with a rigid square base (13).

The ear (2) integral with the receiving member (9) has notches (12) which delimit three elastic elements (17, 18, 19) which, normally, are supported respectively on the three faces (14, 15, 16) from the prism (13).

In the event of an overload, the prism spreads the elastic elements (17, 18, 19) up to a distance equal to its diagonal and the rocking movement is no longer transmitted to the receiving member (9).

When the cause of blockage has disappeared, the prism continuing to rotate returns to its usual position and the entire device again functions normally.

The advantage of this version lies in the fact that it does not require any intermediate part between the drive shaft and the receiving member, the ear (2) performing both the roles of connecting part (or support) and elastic element. It therefore presents great simplicity.

EXAMPLE 3
Figures 6 and 7 show a cross-sectional and longitudinal view of another alternating swing device comprising the drive shaft (1) and the receiving member (9) secured to an ear (2) which rests on a stirrup (20) surrounding the shaft (1). The spring (3) has a middle part (4) in the form of a dihedral which rests on a corresponding notch (21) formed at the end of the motor shaft (1).

The invention is mainly applicable to household appliances, but can be used in any other mechanical device where the torque must not exceed a relatively low value (of the order of 50 daN.m).

In addition to the simplicity of the device, the invention also provides the following advantage: in normal operation, the elastic element constantly cancels the clearances which would necessarily exist between two rigid members; this has the effect of regularizing the rocking (or rotational) movement and attenuating the "peak" forces at each alternation, during the reversal of the direction of rotation.

Claims (6)

R E V E N D T C A T T .0 N S 10 / - Safety device for the transmission of a rotational movement (uniform or reciprocating) along a kinematic chain comprising: the drive shaft, an elastic connecting piece and the receiving member, characterized in that, under the effect of '' an accidental overload, the connection piece deforms and breaks the kinematic chain, this connection being re-established automatically as soon as the overload disappears. 20 / - Device according to claim 1, characterized in that the elastic connecting piece, integral with the drive shaft or with the receiving member, is supported by at least part of its lateral surface on a conjugate surface of identical shape, linked to the other movable member of the kinematic chain. 30 / - Device according to claim 2, characterized in that the lateral bearing surface consists of (or inscribed in) a pyramidal surface with a polygonal base which fits into the conjugate part. 40 / - Device according to claim 3, characterized in that the pyramidal surface is open on one or more sides. 50 / - Device according to one of claims 3 or 4, characterized in that the pyramidal surface is a prismatic surface whose edges are parallel to the axis of rotation, and whose base is a regular convex polygon, whose angles are possibly rounded. 60 / - Device according to one of claims 1 to 5, characterized in that the elastic piece consists of rubber, plastic or elastic metal alloy, in one or more parts.