WO1995034765A1

WO1995034765A1 - Helical spring coupling device between two shafts made by means of an axial cylindrical slider

Info

Publication number: WO1995034765A1
Application number: PCT/IT1994/000111
Authority: WO
Inventors: Vittorio De Michele
Original assignee: La Bottega Del Giardinaggio S.A.S. Vittorio Demic Hele & C.
Priority date: 1994-06-10
Filing date: 1994-07-14
Publication date: 1995-12-21
Also published as: AU7274594A; ITMI941221A1; EP0765442A1; IT1270209B; ITMI941221A0

Abstract

Device for a coupling between mechanical shafts (21, 25) with a helical spring (50) placed around two cylindrical components (30, 40) fixed to the two shafts, the ends being fixed to two collars (60, 70) that surround said spring (50) and a control collar (80) on which are triangular radial tabs (81) which, by an axial movement engaging or disengaging themselves between the raised pieces (72) on the first collar (70) and the teeth (62) on the second collar (60), cause rotations to be made in opposite directions for winding or unwinding the spring (50) and so for determining adherence or detachment, to said cylindrical components (30, 40).

Description

Helical spring coupling device between two shafts made by means of an axial cylindrical slider

The invention concerns couplings between mechanical shafts . These couplings are generally used to connect the ends of two aligned shafts so as to transmit a torque with possibility of making or breaking the connection even during operation. In one clutch type the coupling is formed of a helical spring that surrounds two opposing axial cylindrical com¬ ponent parts fixed to the two shafts, the drive shaft and the driven shaft .

The ends of said spring are respectively coupled to two collars that surround the spring. By causing the two collars to rotate in the direction op¬ posite that in which the spring is wound, the inner dia¬ meter of the spring is increased thus reciprocally freeing the spring from the two cylindrical components and these latter from each other, and this breaks the connection between the drive shaft and the driven shaft.

3y leaving the collars idle the spring rewinds and once more adheres to the cylindrical components, this adher¬ ence becoming stronger with increase in pulling force set up by the drive shaft when rotating in the direction in which the spring is wound. Rotation of the two collars is caused by transversal pressure applied to arms for the purpose and on the parts that project from them.

This produces vibrations, leads to lack of precision, to rapid wear and implies a coupling of considerable bulk. The above invention greatly improves both structure and operation of these couplings as will be explained below. Subject of the invention is a coupling device between mechanical shafts with a helical spring under tension around two opposing axial cylindrical transmission com¬ ponents fixed to the two shafts. The ends of said spring are tied to two collars, that form a pair, in contact at the front and surrounding the spring. The spring is wound up or unwound according to whether re¬ lative rotation of the two collars goes in the winding direction of the spring or in the opposite direction. The two collars are made to rotate in opposite directions by a third controlling collar which is round the first collar of the pair, said third collar comprising a number of triangular radial tabs whose apexes face towards the second collar of the pair. A number of raised trapezoidal-shaped pieces are placed close to the edge of the first collar with the smaller side indwards while a number of trapezoidal-shaped teeth project from the edge of the second collar of the pair, their smaller side facing towards the first collar. Therefore by sliding the third collar towards the point of contact between the pair of collars each tab will fit in between one side of a raised piece on the first collar and one side of a tooth on the second collar, thus caus¬ ing the two collars to rotate in opposite directions unwinding the spring and making the two mechanical shafts independen . If, however, the control collar is made to slide in the opposite direction, the spring, then allowed to contract, adheres to the cylindrical components on the ends of the shafts and the driven shaft will be drawn along by the drive shaft. The angles of the sides of the raised piaces and of the teeth on the pair of collars correspond with those of the tabs on the third control collar.

The raised pieces and the teeth, respectively above the pair of collars, consist of substantially equal bodies each one being approximately hexagonal.

Said hexagonal body comprises raised trapezoidal projec¬ tions on the cylindrical surface of^" the edges and is fixed by its longer side to the longer sides of the teeth. Said collars are therefore practically reversable and the third control collar can be mounted, as preferred, on the first or on the second collar of the pair. The control collar is made to slide by a second-class traction lever, power being applied to one end of the lever wtrrje its intermediate part makes contact with the back of the control collar.

This action, produced by contact only, therefore permits said control collar to make free axial rotation and con¬ sequently the coupling as well. The traction lever is controlled by a second lever, this being a first class control lever whose power is determined by the pull of a spring that puts the device in the released position. To determine the engaged position of the coupling pres¬ sure must be applied to an arm mounted on the resistance end of said second lever.

The coupling is used here for a lawn mower. The engine is mechanically connected by a wormscrew and a toothed gear wheel fixed to one of the cylindrical trans¬ mission components. The second cylindrical component is fixed to the driven shaft onto which a gear is fitted that transmits the motion to the mower's drive wheels. The arm fixed to the second control lever is connected to a short bar articulated on the end of a front rod, for guiding the mower, by means of a metal wire that slides inside a sheath covering said rod.

By pressing this short bar the coupling is engaged while when left idle the coupling is released. The invention evidently offers many advantages.

As action on the controlling part that engages or disen¬ gages is made by means of a contact on which the coupling slides freely, any vibration or irregularity is avoided, operation is smooth, precise and therefore quiet. A highly compact and sturdy structure is created since collar rotation on the spring is determined by substan¬ tially axial inclined planes round the axis of the device. The actual coupling in practice consists of a cylindrical block making the best use of available space. When released the driven shaft rotates in either direction, As traction force increases, with the coupling engaged, there is an automatic increase of tension and adherence of the spring round the drive and driven shafts.

The fact that the transmission collars are substantially equal with consequent possibility of reversing them, makes it possible to use the coupling in many applications. The lawn mower on which the coupling is mounted becomes a highly practical machine, easy to drive and manoeuvre, qualities which are of great benefit to the user.

Characteristics and purposes of the invention will become still clearer from the following example of its execution illustrated by diagrammatically drawn figures.

Fig.1 The invented coupling mounted on a lawn mower.

Fig.2 Detail of a transmission box with the invented coupling in the 'released' position ', longitudinal section. Fig.3 Detail as in Fig. 2 in the 'engaged' position.

Fig. Perspective view of the 'released' coupling.

Fig.5 Detail of the coupling in Fig.4, in perspective.

Fig.6 The coupling in the 'engaged position', perspective.

Fig.7 Detail of the coupling in Fig.5, in perspective. Fig.8 An exploded perspective view of the coupling.

Figure 1 shows a lawn mower 10 on which is mounted the coupling device 20 subject of the invention.

The lawn mower has a chassis 11, front free wheels 12, rear drive wheels 13 and a central handlebar 14. The internal engine, not seen in the drawing, drives the wheels 13 by means of a transmission box 15.

From this box emerges the transmission shaft 21 carrying the gear wheel 22 that transmits movement to the drive wheels through mechanisms such as 23. Connection between the engine and the shaft 21 is made by a coupling 20 illustrated in Figures 2 to 8. The shaft 25 of the engine, not shown in the figures, has a wor screw 26 fixed to it and this meshes with the idling spiral bevel gear 27 on the shaft 21 but fixed by means of the transversal pins 32 to the cylindrical com- ponent 30 with shoulder 31 similarly idling on the shaft 21 Also fixed to the shaft 21, by the transversal pin 42, is the cylindrical component 40 with shoulder 41 substan¬ tially the same as the cylindrical component 30 but facing in the opposite direction. As seen in Figures 2-4 said components make contact lat¬ erally and therefore have a coinciding geometrical cylin¬ drical surf ce .

Around said components is the helical cylindrical spring 50 with outwardly turning radial ends 51 and 52 and whose inner diameter is slightly smaller than the outer diameter of said cylindrical components 30 and 40 so that,when idle, there is reciprocal adherence between said spring and said cylindrical components. Collars 60 and 70 are placed round said spring 50, their equal inner diameter being slightly greater than the outer diameter of the spring 50, their length being equal, about half the length of the. spring 50 whose ends 51 and 52 re¬ main lodged in the notches 61 and 71 respectively, cut in the outer edges of said collars 60 and 70. On the collar 60 there are three trapezoidal teeth 62, set at equal angular distance, projecting above the cylindri¬ cal surface and having at least one side 63 at an angle in relation to the axis of said collar. On the collar 70 are three trapezoidal raised pieces Z2: set at an equal angular distance, having -at least 'one side ^' 73 at an angle in relation, to the axis of said collar. Around collar 70 a third collar 80 is placed, its inner diameter being slightly greater than the outer diameter of the collar 70, and there being three triangular tabs 81 set at an equal angular distance, substantially crea¬ ted within the geometrical cylindrical walls defined by said collar 70.

The tabs 81 fit, under pressure, between the raised pie¬ ces 72 on the collar 70 and the teeth 62 on the collar 60 (Figures 2, 4, 5). In particular, one side of each tab 81 presses against

_> the side 73 of a raised piece 72 on the collar 70 while the other sides press against the sides 63 of teeth 62 on the collar 60.

This pressure is supplied by the helical spring 85 hooked to one end of the pin 86 in the box 15 while the other end is hooked to the end 91 of a first class lever 90 pivoted at 95, and to which is fixed an orthogonal arm 93 that acts on the end 101 of a second class ringwise traction lever 100 that surrounds the collar 80 pivoted at the other end 102 of said lever in the seat 104 of said box 15.

The central portion 103 of said lever 100 is in contact with the back of the collar 80.

It follows that on account of the pull exerted by the spring 85, insertion of the tabs 81 between the raised pieces 72 on the collar 70 and the teeth 61 on the collar 60 determines rotation of said collars 60 and 70 in op¬ posite directions as indicated by the arrows A and B in Figure 4. Bearing n mind the direction in which the spring 50 turns, said rotation causes said spring to unwind sufficiently to break adherence between said spring 50 and the cylin^¬ drical components 30 and 40. In Figure 5 arrows A and B indicate the forces working on the spring 50 whose turns are partially wound and whose inner diameter is therefore greater than the outer diame¬ ter of the cylindrical components 30 and 40. The device is therefore in the 'released' position (Figures 2,4,5). The arm 92 of the lever 90 is connected to the control bar 110 articulated on the pin 113 at the upper end of the central handlebar 14 of the lawn mower 10, by means of the wire 111 that slides inside the sheath 112 covering said handlebar 14.

Therefore to connect the engine to the drive wheels 13 it is merely necessary to move the control bar which then pulls on the free end of the lever 90. By so pulling, the collar 80 is left free and the pair of collars 60 and 70 remain free to rotate in the opposite direction to that previously described, due to the effect of the pull on the ends 51 and 52 of the spring 50 that tends to resume its idle position. In said position there is a reduction of the inner diame- ter of the spring 50 which adheres to the cylindrical com¬ ponents 30,40. The cylindrical component 30 thus pulls on the cylindrical component 40 and, by means of the gear wheel 22, works the drive wheels 13 (Figures 3,6,7). In Figure 7 the diameter of the spring 50 has reached that of the cylindrical components 30 and 40.

As the above invention has been described and explained solely as an example of its use in no way confined to the present one, and in order to show its essential features, numerous variations may be made to it in compliance with industrial, commercial or other requiremen s, while other systems and means may be included in it without thereby implying a daparture from its sphere of operation. It is therefore understood that the application to patent the invention comprises any equivalent use of the concepts and any equivalent product executed and/or in operation ac¬ cording to any one or more of the characteristics set forth in the following claims.

Claims

C l a ims l. Device for a coupling (20) between mechanical shafts (21,25) with a helical spring (50) placed under tension around two opposing axial cylindrical transmission compo- nents (30,40) fixed to the two shafts (21,25), their ends (51,52) being attached to a pair of transmission collars (60,70) in- frontal contact that surround the spring (50) causing said spring (50) to wind or unwind according to whether relative rotation of the two collars (60,70) is made in the direction for winding the spring (50) or in that for unwinding it, characterized in that rotation of the two collars (60,70) relatively in opposite directions is obtained by means of a third, control, collar (80) that surrounds the first (70) of the pair of transmission collars, said third col¬ lar comprising a number of radial triangular tabs (81) whose apexes lie towards the other collar (60) and by means of a number of radial trapezoidal raised pieces (72) situated near the edge of said first collar (70) their smaller base lying towards the inside of the collar and by means of a number of trapezoidal teeth (62) projecting on the edge of said second collar (60) whose base lies to¬ wards the first collar (70), the third collar (80) is made to slide towards the area of contact between the pair of collars (60,70), each of the tabs (80) becoming inserted between one side (73) of one raised piece (72) on the first coller (70) and one side (63) of a tooth (62) on the second collar (60), determining rotation in opposite directions of the two collars (60,70), and therefore unwinding of the spring (50), and independence of the two mechanical shafts while, when the collar (80) is made to slide in the oppo¬ site direction, the spring (50) remaining free contracts and adheres to the two cylindrical components (30,40) at the ends of the shafts and so causes the driven shaft

(21) .to be drawn along by the drive shaft (25).

2. Device for a coupling (20) as in claim 1, ^• characterized in that the angle of the sides (73,63) of the raised pieces (72) and of the teeth (62) on the col¬ lars (60,70) as a pair, corresponds to the angle of the tabs (81) on the third control collar (80).

3. Device for a coupling (20) as in claim 1, characterized in that the raised pieces (72) and the teeth (62) respectively upon the.:the two collars (70,60) in a pair, are obtained from substantially equal bodies each formed by a kind of hexagonal structure comprising the trapezoidal raised pieces (72) projecting from, the cylin- drical surfaces of the edges of the collars (60,70) and whose greater base is fixed to the greater base of the trapezoidal teeth, in such a way that said collars (60,70) are substantially exchangeable and the third collar (80) for control can be mounted, as preferred, on the first (70) or the second (60) of the pair of collars.

4. Device for a coupling (20) as in claim 1, characterized in that the sliding movement made by the con¬ trol collar (80) is determined by a second-class traction lever ( 100) power being applied at one end of the lever ( 100) while the intermediate portion acts against the back of the control collar (80) said action consisting merely of contact so that said control collar (80), and therefore the coupling (20), can make free axial rotation.

5. Deviee- for a coupling (20) as in claim 4, characterized in that the traction lever ( 100) is subjec¬ ted to action by a second lever (90) this being a first- class control lever whose power is created by the pull from a spring (85) that puts the device (20) into the re¬ lease position while, to determine the engaged position action must be taken on an arm (93) applied to the re¬ sistance end of said second lever (90).

6. Device for a coupling (20) as in claims 1 to 5, characterised in that the coupling (20) is mounted on a lawn mower ( 10), mechanical connection to the engine being provided by a wor screw (26) and a bevel gear(27) fixed to one of the cylindrical transmission components (30) while the second cylindrical component (40) is fixed to the driven shaft (21) onto which is mounted a gear(22) that transmits motion to the drive wheels ( 13) of the lawn mower ( 10), the second control lever (90) being connected to a short bar ( 110) articulated at the end of a front handlebar ( 14),with which to guide the lawn mower ( 10), by means of a metal wire ( 111) that slides inside a sheath ( 112) fixed onto said handlebar ( 14) so that moving the short bar ( 110) engages the device while, by leaving said bar idle the device is released.