WO2007063412A2

WO2007063412A2 - Improved adaptor element

Info

Publication number: WO2007063412A2
Application number: PCT/IB2006/003497
Authority: WO
Inventors: Mario Antonio Morselli; Lorenzo Vignoli; Stefano Totti
Original assignee: Stm S.P.A.
Priority date: 2005-11-30
Filing date: 2006-11-29
Publication date: 2007-06-07
Also published as: WO2007063412A3; ITBO20050731A1

Abstract

An adaptor element for transmitting power between an output shaft of a motor and an input shaft of a driven machine comprises a substantially cylindrical body with a longitudinal hole on the surface of which is formed a longitudinally extending cavity for connection to the said output shaft, the said cavity in turn comprising a pair of substantially parallel lateral surfaces which can engage with corresponding bearing surfaces of a power transmission key. A distinctive feature of the invention is that the longitudinally extending cavity comprises substantially curved connecting surfaces between the said lateral surfaces , which are connected to each other to form a radial stop for the key, projecting towards the inside of the cavity. The main purpose of this is to decrease the maximum stresses on the cavity during power transmission, in order to eliminate risks of cracking and fatigue fracture of the body of the adaptor element.

Description

Improved adaptor element

The present invention relates to an adaptor element for transmitting power between an output shaft of a motor and an input shaft of a driven machine.

The present invention also relates to a driven machine and a motor/driven machine unit using the aforesaid adaptor element.

This adaptor element is designed particularly for application to driven machines comprising mechanical reduction units, such as reduction units using worms or gears such as cylindrical or bevel gears, or screw or geared pumps, which are driven by electric or hydraulic motors or internal combustion engines. For example, this adaptor element may be of the frontal engagement type as described in Italian patent application BO2004A000128.

More specifically, the improvement proposed by the present invention relates mainly to the architecture of a radial cavity with a longitudinal extension formed inside the adaptor element, and typically intended to house, when in use, a key for transmitting torque between the output shaft of a motor and the said adaptor element.

In the present state of the art it is common practice to use, in the key/cavity coupling of an adaptor element, standard keys of rectangular section which can engage in cavities which are also of substantially rectangular section, connected at the edges by connections having small radii of curvature .

With the increase in the cost of raw materials and machining and the increasing need to economize on materials, shorten production cycles and make the adaptor elements light and convenient to transport, handle and store, the dimensions of the adaptor elements are tending to become smaller and optimized with respect to the torque to be transmitted.

It is not uncommon for the adaptor elements, although usually made from heavy metallic materials such as ferrous alloys or brass, to be subject to problems of crack formation or even fatigue fracture in the edge areas or connection areas of the cavities of rectangular section. These problems become even more significant where synthetic plastics materials are chosen for use in the production of adaptor elements, as intended by the applicant for application to relatively low- powered motor/driven machine units .

The object of the present invention is to overcome the drawbacks of the known art, and in particular to provide an adaptor element which ensures reliability and durability in use.

One object of the invention is to provide an adaptor element which is easily made, light and economical, and which uses the smallest possible amount of material for a given torque transmission capacity..

Another object of the invention is to provide an adaptor element which as far as possible remains unaffected by crack formation and fatigue fracture during its use as a stressed element .

In order to achieve the above objects, the invention proposes an adaptor element for transmitting power between an output shaft of a motor and an input shaft of a driven machine, and a driven machine and a motor/driven machine unit comprising the said adaptor element, having the features indicated in the following claims . The adaptor element according to the invention comprises a substantially cylindrical body with a longitudinal, hole, on the surface of which is formed a longitudinally extending cavity for connection to the output shaft, the cavity comprising a pair of substantially parallel lateral surfaces which can engage with corresponding bearing surfaces of a power transmission key.

According to a first aspect of the invention, the longitudinally extending cavity comprises substantially curved connecting surfaces between the said lateral surfaces , which are connected to each other to form a radial stop for the key, projecting towards the inside of the cavity.

According to another aspect of the invention, the connecting surfaces extend from an edge or connection area of the cavity, particularly in order to form part of the base of the cavity.

According to a further aspect of the invention, the stop of the cavity is made to project prominently from the base of the cavity; in other words, the height of the stop with respect to the most distant end of the base of the cavity is of an order of magnitude comparable to the height of the lateral surfaces, for example in the range from 1/3 to 1/10 of the said height .

According to another aspect of the invention, the connecting surfaces comprise curved surfaces whose radius of curvature is of an order of magnitude substantially comparable to the width of the cavity.

In the present document, "radius of curvature of an order of magnitude substantially comparable to the width of the cavity" denotes a radius of curvature whose ratio to the width of the cavity is of the order of magnitude of several tenths or at least one tenth, and therefore of an order of magnitude greater than that of the customary edge connections of cavities of rectangular section.

Further features and advantages will be made clear by the following description of preferred embodiments of the invention, with reference to the attached drawings, provided by way of example and without restrictive intent, in which:

- Figures 1, 2 and 3 are front and side views of a first example of embodiment of an adaptor element according to the present invention,

Figure 4 shows a perspective view, in longitudinal section for greater clarity, of the adaptor element of Figures 1 to 3 ,

- Figure 5 shows a schematic sectional view taken along the plane A-A of Figure 2 , and

Figure 6 shows the same view as Figure 5, but in relation to a second example of embodiment of the adaptor element according to the invention.

With reference to Figures 1 to 5, an adaptor element for transmitting power between an output shaft of a motor and an input shaft of a driven machine, particularly of a frontal engagement type, is indicated as a whole by 1. It is composed of a substantially cylindrical body 2 provided with a through hole 10, on the surface of which a cavity 20 is formed radially, this cavity extending longitudinally along the whole length of the body 2. The cavity 20 is composed of a pair of lateral surfaces 21 parallel to each other and to a plane radial with respect to the cylindrical body 2 , and surfaces 22 for connection to the lateral surfaces 21, the connecting surfaces being joined or connected on the base of the cavity 20 to form a central stop 23. The stop 23 projects prominently towards the inside of the cavity 20, or, in other words, the base of the cavity 20 is composed of the stop 23, which represents the point of the cavity with the greatest inward radial extension. As shown in particular in Figure 5, the surfaces 21, 22 of the cavity 20 are shaped to receive, in use, a key 3 which bears laterally on the lateral surfaces 21 to transmit power between the output shaft of a motor and the input shaft of a driven machine.

It must be emphasized that the key 3 is a key of rectangular section of an entirely standard type, which is therefore easily made and has well-known technical and functional features. Advantageously, the use of standard keys for coupling to the cavity 20 of the adaptor element 1 means that the keys are readily available and savings can be made in the costs of forming the coupling between the motor shaft and the adaptor element .

The formation of the base of the cavity 20 according to the features of the present invention will now be detailed with particular reference to Figures 1, 4 and 5. In the first place, we define as the edge or connecting areas of the cavity 20 the parts of the cavity extending at the margins of the lateral surface portion 21 engaged by the key 3 when the latter is in its housing in the assembled condition, in other words in the configuration shown in Figure 5.

The connecting surfaces 22 originate substantially tangentially to the corresponding lateral surfaces 21 in the edge or connecting areas, extending symmetrically in the form of a double cradle or a double "U", with the concavities facing the inside of the cavity 20. These surfaces 22 are connected to each other to form part of the base of the cavity 20 and form a central stop 23, which projects prominently towards the inside of the cavity 20. The central stop 23 has the function of allowing a degree of radial play for the key 3 according to regulations , for the purpose of preventing the key from falling out of its assigned housing when in use.

Each of the U-shaped, portions of the connecting surfaces 22 has a substantially constant radius of curvature along its transverse extension, and the radius of curvature is equal to approximately 1/4 of the width of the cavity 20. The radius of curvature is therefore of an order of magnitude comparable to that of the width of the cavity, and of an order of magnitude greater than that of customary radii of curvature of connections of known cavities of rectangular section.

The said configuration of the cavity 20 advantageously makes it possible to limit the maximum tensile stress in the edge area. This stress is less than 50% of that which may be encountered in a conventional cavity of rectangular section having known connections. This decrease in stress reduces the risk of crack formation or structural failure due to fatigue, while enabling the design of the cylindrical body to be optimized in such a way as to decrease the thickness and therefore the quantity of material used and the overall weight of the adaptor element .

These advantages are most evident when synthetic plastics materials are used in the production of the body 2 of the adaptor element 1. The use of synthetic polymers is particularly advantageous in small and medium-sized power transmission applications, for example in worm or gear reduction units or in screw pumps driven by electric or hydraulic motors or internal combustion engines. This is because they offer an excellent compromise between power transmission behaviour, fatigue resistance, lightness and cheapness .

When made from the said synthetic polymers, and with reference in particular to Figures 2 and 4, the substantially cylindrical body 2 of the adaptor element 1 has lightening grooves 4 on its outer portion, formed circumferentially and longitudinally over the whole extension of the body 2. Their depth differs according to whether they are formed near the cavity 20, where they are shallower, or distant from it, where they are deeper.

Advantageously, the presence of the lightening grooves 4 permits not only a reduction in the use of material and the corresponding advantages, but also an optimal production of the adaptor elements, which are made from synthetic polymers by injection moulding. The presence of reduced thickness due to the lightening grooves 4 enables the moulds to be filled in an optimal and speedy way, for rapid and economical production of the adaptor elements .

The adaptor element 1 is of a frontal engagement type. As shown more fully in Figures 2 and 3 , the corresponding body 2 is provided with an annular frontal face 11 from which there extend axially teeth or projections 12 distributed uniformly over the perimeter of the frontal face 11, substantially adjacent to the outer peripheral edge. The projections 12 can engage with corresponding annular cavities formed on a cylindrical wall of a frontal end of the input shaft of a driven machine, as described and illustrated in Italian patent application BO2004A000128. The projections 12 and the said annular cavities thus form complementary frontally facing engagement means which can be engaged with each other to transmit a rotary motion, imparted in use by the output shaft of a motor to the input shaft of a driven machine by means of the interposition of the adaptor element 1. In greater detail, the projections 12 have a radially outer wall with a shape and size such as to substantially form, in the configuration of coupling between the input shaft and the adaptor element 1, the geometric complement of the cylindrical wall of the frontal end of the input shaft, in such a way that the wall is substantially continuous except for very small gaps between the lateral faces . Peripheral grooves 13 are formed on the radially outer walls of the projections 12, in such a way that, in the configuration of coupling to the input shaft, these peripheral grooves 13 are located on the extension of corresponding portions of annular cavity shaped on corresponding annular projections of the input shaft. In combination, the peripheral grooves 13 and the portions of annular cavity form, in the configuration in which the adaptor element 9 is coupled to the input shaft, a substantially continuous annular cavity intended to house a resilient split ring. The resilient ring has the function of keeping the two elements connected, while allowing them to be detached by a gentle pull, owing to its resilience, and, preferably, the rounded shape of the outermost edge of the peripheral grooves 13.

The cavity 20 also has an end portion 30, at the annular frontal face 11, with a substantially rectangular section. The base of the end portion 30 is at the same radial level as the stop 23, providing a continuity of the stop surface. This portion 30 is connected to the connecting surfaces 22 by longitudinally chamfered surfaces. In use, the lateral walls or surfaces of the portion 30 do not receive the corresponding lateral parts of the key, and therefore the key exerts no direct stress on them. Advantageously, this solution enables the cylindrical body 2 of the adaptor element 1 to be strengthened in an area likely to be particularly stressed by the presence of the projections 12, which can transmit torque to the input shaft of a driven machine .

Clearly, provided that the principle of the invention is retained, the forms of embodiment and the details of construction can be varied widely from what has been described and illustrated, without departure from the scope of the present invention.

For example, the location of the stop 23 on the base of the cavity 20 could be different. The stop could be located in a lateral rather than a central position, enabling a greater radius of curvature of the U-shaped portion of the corresponding connecting surface to be provided in the proximity of one of the lateral surfaces, in order to decrease further the maximum tensile stresses to be withstood by the cavity "in the proximity of the corresponding edge area. This configuration would be advantageous in cases in which the stresses exerted on the cavity by the key are markedly greater on only one of the lateral surfaces when in use.

The connecting surfaces of the cavity could have radii of curvature which vary along the transverse extension of the cavity, for example by decreasing their value as the distance from the edge or connecting area increases , in order to ensure lower maximum tensile stresses in the edge area.

Advantageously, the connecting surfaces 22 could be developed directly at the origin of the edge or connecting area of the cavity 20, or directly after the portion of lateral surface 21 which engages, in use, with corresponding contact surfaces of the key 3. Thus, for a given curvature of the connecting surfaces, and thus for given maximum stresses in the edge area, the cavity 20 would have a reduced depth, enabling the overall thickness of the cylindrical body 2 to be reduced for a given transmitted power, and therefore enabling less material to be used.

Figure 6 shows a possible variant of the adaptor element according to the invention. While retaining a body formation which is entirely similar to the example of Figures 1 to 5, the adaptor element differs in the shape of the connecting surfaces of the cavity 20, indicated by 32 in this figure. These surfaces 32 extend from the lateral surfaces 21 in such a way as to increase the width of the cavity 20, gently inverting their curvature immediately thereafter so as to bring the surfaces towards the central axis of the cavity 20, until they join each other to form a central stop 33, which clearly and substantially projects towards the inside of the cavity 20. The connecting surfaces 32 can be made with a cross-sectional shape resembling a "double loop", and the way in which they form part of the base of the cavity 20 is evident. According to one of the features of the invention, the connecting surfaces comprise substantially curved surfaces in which the ratio between the radius of curvature and the width of the cavity 20 is of the order of magnitude of several tenths, or at least one tenth.

Advantageously, the described variant makes it possible to have a cavity whose overall depth is less than that of the double U-shaped cavity, thus making it possible to use less material for the production of the body of the adaptor element, with a maximum stress approximately 40% lower than that found in the conventional cavity of rectangular section.

Claims

1. Adaptor element for transmitting power between an output shaft of a motor and an input shaft of a driven machine, comprising a substantially cylindrical body (2) with a longitudinal hole (10) , on the surface of which is formed a longitudinally extending cavity (20) for connection to the said output shaft, the said cavity (20) comprising a pair of substantially parallel lateral surfaces (21) which can engage with corresponding bearing surfaces of a power transmission key (3), characterized in that the said cavity (20) comprises substantially curved connecting surfaces (22; 32) between the said lateral surfaces (21) , which are connected to each other to form a radial stop (23; 33) projecting towards the inside of the cavity (20) .

2. Adaptor element according to Claim 1, characterized in that the said stop (23; 33) projects prominently from the base of the cavity (20) .

3. Adaptor element according to Claim 1 or 2 , characterized in that the said connecting surfaces (22; 32) extend from an edge area of the said cavity (20) .

4. Adaptor element according to any one of the preceding claims, characterized in that the said connecting surfaces (22; 32) comprise curved surfaces whose radius of curvature is of an order of magnitude substantially comparable to the width of the cavity (20) .

5. Adaptor element according to Claim 3 or 4, characterized in that the said connecting surfaces (22) originate substantially tangentially to the corresponding lateral surfaces (21) .

6. Adaptor element according to Claim 5, characterized in that the said connecting surfaces (22) extend symmetrically in the form of a double cradle or a double "U" , with the concavity facing the inside of the cavity (20) .

7. Adaptor element according to any one of Claims 1 to 5, characterized in that the said connecting surfaces (32) extend from the said lateral surfaces (21) in such a way as to increase the width of the cavity (20) , gently inverting their curvature immediately thereafter so as to bring the surfaces (32) towards the central axis of the cavity, until they connect to each other and form the said stop (33), particularly in a central location.

8. Adaptor element according to Claim 3, characterized in that the said connecting surfaces have radii of curvature which vary along the transverse extension of the cavity, for example by decreasing their value as the distance from the said edge area increases .

9. Adaptor element according to Claim 3, characterized in that the said connecting surfaces extend directly at the origin of the said edge or connecting area of the cavity (20) , in other words immediately after the lateral surface portion (21) which engages, in use, with corresponding surfaces of the key (3) .

10. Adaptor element according to any one of the preceding claims, characterized in that the said body (2) is made from synthetic polymers .

11. Adaptor element according to Claim 10, characterized in that the said body (2) comprises external lightening grooves (4) formed circumferentially and longitudinally, particularly along the whole extension of the body (2) .

12. Adaptor element according to Claim 11, characterized in that the said lightening grooves (4) vary in their depth according to whether they are formed near the said cavity (20) , where they are shallower, or distant from it, where they are deeper.

13. Adaptor element according to any one of the preceding claims, characterized in that it comprises engagement means (12) complementary to corresponding engagement means formed on the input shaft of a driven machine, facing each other frontally and engageable with each other to transmit a rotary motion, imparted in use by the output shaft of a motor to the input shaft of a driven machine.

14. Adaptor element according to Claim 13, characterized in that the said complementary engagement means comprise projections (12) which can engage with corresponding annular cavities formed on a cylindrical wall of a frontal end of the input shaft of a driven machine, the projections (12) having a radially outer wall with a shape and size such as to substantially form the geometrical complement of the cylindrical part of the frontal end of the input shaft, in such a way that this wall is substantially continuous with the exception of very small gaps between the lateral faces .

15. Adaptor element according to any one of the preceding claims, characterized in that the said hole (10) in the body (2) is a through hole, and the cavity (20) extends along the whole length of the hole (10) .

16. Adaptor element according to Claim 15, characterized in that the said cavity (20) comprises an end portion (30) with a substantially rectangular section, the base of the said cavity (20) being in particular at a depth equal to that of the stop (23; 33), the lateral surfaces (21) of this portion (30), in particular, not receiving the corresponding lateral walls of the key (3) in use.

17. Driven machine comprising, in the assembled configuration and associated with an input shaft of the driven machine, an adaptor element according to any one of the preceding claims .

18. Motor/driven machine unit, comprising an electric or hydraulic motor or an internal combustion engine with an output shaft which is coupled to an input shaft of a driven machine, characterized in that it comprises an adaptor element according to any one of Claims 1 to 16.