A ROPE BLOCK

Abstract: A rope block (1) comprising a sheave (2), a sheave housing (3) with fixedly mounted radial bearings (4) supporting said sheave (2), and a ratchet mechanism (5) situated inside the sheave housing (3). The ratchet mechanism (5) comprises a ratchet (6) pivotally arranged inside the housing (3) and co-operating with an inner toothed rim (7) on the sheave (2), whereby said ratchet in the use position is prestressed by a spring means (8) connected to an outer pin. When the ratchet (6) engages the toothed rim (7) and the rope exerts a strong pull in the block, the spring means (8) can move from one position (S) to another position (F) by simply turning the outer pin. Subsequently, when the rope is slightly hauled in, the ratchet (6) disengages the toothed rim (7) and the sheave (2) can rotate freely. The rope block (1) comprises in this manner a reliable and safe ratchet mechanism (5) showing a long life. The sheave (2) is furthermore advantageously provided with throughgoing openings (23) along the periphery. As a result, a particularly good retaining of the rope in the guide of the sheave (2) is obtained.

Description: Title: A rope block Technical Field The invention relates to a rope block comprising a sheave, a sheave housing with fixedly mounted radial bearings supporting said sheave, and a ratchet mechanism situated inside the sheave housing, said ratchet mechanism compris¬ ing a r≤-tchet pivotally arranged inside the housing and co-operating with an inner toothed rim on the sheave, whereby said ratchet in the use position is prestressed by a spring means in a direction substantially radially outwards into engagement with the toothed rim. Background Art Rope blocks of the above type are mainly used on board sailing boats and especially on board racing sailing boats where the block is usually mounted as the last block of a rope tackle, such as for instance in connection with a mainsail sheet. When for instance the helmsman is holding on to the so-called hauling member of the rope in the tackle, said rope member extends from the hand of the helmsman and directly to the above block mounted as the last block of the rope tackle. When the ratchet mechanism is activated the sheave can only follow the rotation when the helmsman hauls in the hauling member of the rope in the tackle, i.e. when he is hauling the rope towards himself. When the helmsman slackens the hauling member of the rope, the sheave cannot rotate in the opposite direction because of the friction between the rope and the sheave, and conse¬ quently the helmsman need only hold on. to the hauling member of the rope by a force substantially weaker than the one by which the rope tackle is hauling in the block so as to avoid a slackening of the rope. In periods it is, however, often necessary to deactivate the ratchet mechanism such that the sheave can rotate freely in both directions, such as for instance when it is necessary quickly to slacken or haul in the rope. The latter procedure necessitates that the helmsman by one hand activates a ratchet, a slide means or the like situat¬ ed on the outside of the block. By all conventional types of rope blocks the above procedure is difficult to carry out when the rope tackle exerts a strong haul in the block. The latter is inter alia due to the fact that the ratchet can only be forced into the free wheel position with great difficulty by the helmsman simultaneously hauling in the rope in such a way that the high pressure in the ratchet mechanism is simultaneously relieved. It is therefore necessary to use both hands for carrying out the above procedure, which in turn unfortunately necessitates the assistance of an additional person. Attempts at carrying out the procedure repeatedly without hauling in the rope result in a ratchet mechanism being quickly worn or dam¬ aged. Conventional types of rope blocks are often encumbered with the unfortunate drawback that the ratchet mechanism fails when subjected to a repeated hauling in and slacken¬ ing of the rope with the result that during such periods it is necessary for the helmsman to hold on to the rope by the same force as the one by which the rope tackle hauls in the block. The groove of the sheaves of the known rope blocks is provided with various types of grooves or teeth in order to increase the friction between the rope and the sheave. The effect aimed at is, however, not quite satisfactory, and often the rope is worn very quickly. The sheaves of the conventional rope blocks are manufac¬ tured either by injection molding of an article of plastics or by assembling two identical, die cast, anodised alumi- nium articles. In both cases the surface of the groove is often quickly worn, and as far as the aluminium is con¬ cerned the anodic coating on the teeth in the groove is often quickly worn off in such a manner that the surface of said teeth is particularly vulnerable to corrosion, especially when said teeth come into contact with salt water. Disclosure of Invention The object of the invention is to provide a rope block of the above type, whereby it is possible also under high loads of the rope block to deactivate or reactivate the ratchet mechanism by using one hand only and by involving a mimimuin force. The grooves of the sheave must furthermore present a high friction against the rope without wearing said rope or said groove, and furthermore present a long life. The rope block according to the invention is characterised in that the spring means is manually activatable from the outside of the housing so as to be in a first position in which said spring means prestresses said ratchet in a di¬ rection towards the toothed rim or in a second position in which said spring means prestresses said ratchet in a direction away from and out of the engagement with the toothed rim. As a result it is possible also in connection with high loads on the rope block to deactivate the ratchet mechanism by means of one hand and without necessitating a hauling in of the rope by means of the other hand. When the ratchet mechanism is activated and the ratchet engages the toothed rim, the spring means can be manually activated from the outside so as to be in a first posi¬ tion or in a second position in which it prestresses the ratchet in a direction away from the engagement with the toothed rim but without said ratchet thereby disengaging the toothed rim. As a result the ratchet remains in the engagement with the toothed rim until, optionally at a later stage, the rope is slightly hauled in in such a manner that the sheave is slightly angularly turned. The latter angular turning is sufficient for the ratchet to disengage the toothed rim because of the above prestressing in a direction away from the toothed rim, whereby the ratchet mechanism is deactivated. According to the invention the spring means may be pivot- ally mounted about an axis of rotation extending parallel to the axis of rotation of the ratchet, and the spring means may furthermore comprise a member engaging the ratchet such that when the spring means is turned about its axis of rotation between the two positions the member is moved from a position in which the ratchet is influenced by a torque counter-clockwise about the axis of rotation of the ratchet into a position in which said ratchet is influenced by a torque clockwise about the axis of rotation of the ratchet. As a result, the spring means can be activated from the outside by way of a mere rotation. According to a particularly simple embodiment the member of the spring means may be a spring-loaded bar, one end of which engages the ratchet, and said bar may be axially displaceably mounted in a guide forming part of a manually operatable rotation body which is activatable from the outside of the housing. Furthermore the bar may advantageously extend diametrically relative to the rotation body. Moreover according to the invention the rotation body may be centrally mounted in a guide in the sheave housing, whereby the sheave housing in a particularly advantageous manner can be formed by only two identical halves . In addition the opposite end of the bar may engage the surface of a flat spring, which in the relaxed state extends substantially perpendicular to the plane extending between the axes of rotation of the rotation body and the ratchet, the ends of said flat spring . being releasably connected to the sheave housing. As a result, a particular¬ ly advantageous load progress of the bar is obtained when the rotation body is turned from the first position into the second position or vice versa. Moreover according to the invention the member may engage a substantially planar surface such that when the ratchet is in a position between the two outer positions of said ratchet said planar surface extends perpendicular to the plane extending between the axes of rotation of the spring means and the ratchet. As a consequence thereof the bar is in the above intermediary position disposed as much as possible against the force of the spring which implies that the rotation body retains the ratchet in the two outer positions in a very reliable manner. According to the invention stop means may advantageously be provided at both ends of the planar surface, said stop means stopping the spring means in the two positions. Furthermore according to the invention the rope-receiving groove of the sheave may be a surface smooth per se and provided with recesses at regular intervals along the periphery of the sheave. At high loads, the rope is pressed into the recesses and retained therein in a particularly reliable manner. As a result, neither the rope nor the sheave guide are significantly worn. Moreover according to the invention the recesses may be formed as throughgoing openings extending parallel to the axis of rotation of the sheave from one side of said sheave to the other, whereby the sheave can be manufactured in an easy and inexpensive manner. By a method of- producing a sheave to be used in a rope block of the above type, cylindrical sectional bodies may be extruded, said bodies being provided with an inner toothing and identical recesses extending at regular intervals along the outer periphery of said sectional bodies, whereafter said sectional bodies are cut into radial planes interspaced a distance corresponding to the thickness of the sheave followed by a circumferential groove finally being shaped in the outer circumferential surface of the sheave. As a result the sheaves can be manufactured in an easier and less expensive manner com- pared to previous methods, and in addition the sheaves possess a higher strength and higher resistance to corro¬ sion than the sheaves manufactured by the conventional methods . Brief Description of Drawings The invention is described in greater detail below with reference to the accompanying drawing, in which Fig. 1 is a side view of a particularly preferred embodi¬ ment of the rope block according to the invention, Fig. 2 is a side view of the sheave and the sheave housing of the rope block of Fig. 1, whereby both side plates of the block and one half of the sheave housing have been removed in order to show the ratchet mechanism, Fig. 3 is an axial, sectional view taken along the line III-III of Fig. 2 through the sheave and both halves of the sheave housing, Fig. 4 is a side view of a portion of a sheave of another embodiment, and Fig. 5 i s an axial, sectional view taken along the line V-V of Fig. 4. Best Mode for Carrying Out the Invention Fig. 1 illustrates a particularly preferred embodiment of a rope block 1 comprising a sheave housing 3 fixedly mounted between two side plates 26. The block 1 comprises furthermore a sheave 2 supported by means of radial bear- ings fixedly mounted inside the sheave housing 3. A ratchet mechanism 5, cf. Fig. 2, is situated inside the sheave housing 3. The side plates 26 of the rope block 1 are assembled about the sheave housing 3 by means of screws 25 screwed into bushings (not shown) provided with threads. A swivel member 27 is mounted at the head 32 of the rope block 1, said swivel member 27 comprising a transverse opening 28 for the mounting of a so-called shackle, whereby the block can be secured in a suitable fitting fixedly mounted for instance on a sailing boat. The rope block 1 is particularly used on racing sailing boats and then often as the last block of a rope tackle, such as for instance in connection with a mainsail sheet, where the hauling member of the sheet extends directly from the rope block 1 and to for instance the helmsman, i.e. such that the hauling member of the rope extends from the block 1 to the hand of the helmsman. The rope block 1 is often used as the last block too in connection with a spinnaker sheet, where said sheet extends from the hand of an assisting person. The block may, however, also advantageously be provided with more than one sheave and one sheave housing (with or without the ratchet mechanism) in such a manner that so-called double blocks, triple blocks or fiddle blocks are provided. When the ratchet mechanism 5 situated inside the sheave housing 3 is to be activated, the helmsman or the assisting person simply turns a pivot 24 from the outside of the sheave housing and by the fingers of one hand either from the position S in which the ratchet mechanism is activated and into the position F in which said ratchet mechanism 5 is deactivated and the sheave 2 is consequently free wheeling or rotating in the opposite direction. The latter procedure can be followed under all loads of the block even when a possible rope in the tackle exerts a strong pull in the block 1 and without necessitating that the helmsman or the assisting person hauls in the hauling member of the sheet rope during said procedure. The structure and function of the sheave 2, the sheave housing 3 and the ratchet mechanism 5 are explained in greater detail below with particular reference to Figs. 2 and 3. The description of the function refers to the si¬ tuation where a helmsman or an assisting person activates the ratchet mechanism from the outside by turning the pivot 24 between the two positions S and F. The radial bearings supporting the sheave wheel 2 against the sheave housing 3 are preferably two ball bearings, the balls 4 running in circumferential grooves 30 shaped in the sheave wheel 2 and the two halves of the sheave housing 3. Fig. 2 only illustrates a few of the balls 4. The sheave 2 is furthermore provided with an outer circum¬ ferential groove 22 receiving the rope. The sheave housing comprises advantageously two identical halves assembled, by means of screws 33, cf. Fig. 3, said screws being screwed into openings 29 provided with threads. The two halves of the sheave housing 3 are fur¬ thermore provided with throughgoing openings 28 in such a manner that they can be mounted between the two side plates 26 . The ratchet mechanism 5 situated inside the sheave housing comprises a ratchet 6 pivotally mounted about an axis of rotation 0 p , said ratchet co-operating with an inner toothed rim 7 on the sheave 2 and being prestressed by a spring means 8. The ratchet 6 is preferably pivotally mounted about a shaft pin 34 in the halves of the sheave housing 3. The spring means 8 comprises a rotation body 12 pivotally mounted about an axis of rotation Op in a guide 13 in the halves of the sheave housing 3. The guide 13 is centrally situated in the halves of the sheave housing 3 in such a manner that the axis of rotation Op of the rotation body 12 coincides with the axis of rotation Og of the sheave 2. An axially displaceable and spring-loaded bar 9 is situated in a guide 11 in the rotation body 12, said bar 9 extending diametrically through said centrally situated rotation body 12. One end 10 of the bar 9 engages a substantially planar surface 19 on the ratchet 6. The ratchet 9 can be situated in two outer positions Sp and Fp corresponding to the situations in which the ratchet 6 engages the toothed rim 7 and in which said ratchet 6 disengages said toothed rim 7. The planar surface 19 of the ratchet 6 extends in a position between the two outer positions Sp anf Fp of said ratchet 6 perpendicular to a plane P extending between the axis of rotation Op of the rotation body 12 and the axis of rotation 0 p of the ratchet 6. Stop means 20, 21 are preferably provided at both ends of the surface 19, said stop means stopping one end 10 of the bar 9. The opposite end 14 of the bar 9 engages the contact surface 16 of a flat spring 15. The ends 17 and 18 of the flat spring 15 are preferably loosely connected to the halves of the sheave housing 3. The spring 15 is preferably situated in a cavity 35 in each half 3 of the sheave housing in such a manner that it is compressed therein at the ends 17 and 18 preferably by means of pins 36. In the relaxed state the contact surface 16 of the flat spring 15 extends substantially perpendicular to the plane P in turn extending between the axis of rotation Op of the rotation body 12 and the axis of rotation 0 p of the ratchet 6, the centre of said flat spring 15 in addition being intersected by said plane P. The above outer pivot 24 is pressed into a recess 37 in the half of the sheave housing 3 by means of the side plate 26 of the rope block 1. The pivot 24 engages furthermore the rotation body 12, one portion 38 of said pivot 24 extending into a recess 39 in the rotation body 12. The block 1 may be provided with a pivot 24 on both sides or arbitrarily only on one side, such as for instance when the block is to be mounted on the deck of a ship. When the pivot 24 is in the position S, the ratchet mecha- nism 5 is activated and the sheave 2 can only rotate clockwise in a direction T. In this position of the pivot 24, the rotation body 12 and consequently also the bar 9 are in the position S too, whereby the bar 9 of the flat spring 15 is prestressed in the direction F s towards the ratchet 6. In other words, the bar 9 actuates the ratchet 6 by a torque Mg in a direction counter-clockwise so as to rotate about its axis of rotation 0 p . The position S of the rotation body 12 causes the bar 9 to reciprocate in the guide in said rotation body 12 against the effect of the spring 15 when said ratchet 6 is moved forward and backwards about its axis of rotation 0 p by the teeth of the toothed rim 7 flushing with said ratchet. The latter procedure is a consequence of a hauling in the rope, whereby the sheave 2 rotates in the direction T clockwise about its axis of rotation Og . When the outer pivot 24 is turned into the position F while the rope block 1 is subjected to a high load, i.e. a high load is exerted on the engagement of the ratchet 6 with the toothed rim 7, the rotation body 12 and conse- quently also the bar 9 are turned too into the position F. As a result, the rotation body 12, the bar 9 and the spring 15 enter the positions indicated by dotted lines. During the latter turning of the rotation body 12, the ratchet 5 remains in its position Sp due to its engagement with the toothed rim 7. In the position F, the bar 9 subjects the ratchet 6 to a prestressing by way of the flat spring 15 in the direction F , which means that the bar 9 subjects the ratchet 6 to a torque Mp in a direction clockwise about the axis of rotation O p of the ratchet 6. Not until the rope is subjected to a slight hauling in again in such a manner that the sheave 2 rotates slightly about its axis of rotation Og in a direction T clockwise and the ratchet 6 can disengage the toothed rim 7 and consequently rotate about its axis of rotation O p , the prestressed bar 9 in the position F can be freely disposed in the direction Fp and consequently move the ratchet 6 into the position F p , in which said ratchet 6 no longer engages the toothed rim 7. As a result, the sheave wheel 2 can rotate freely in both directions. A further consequence of the above is that it is also possible to deactivate the ratchet mechanism 5 under high loads of the rope block 1 and consequently also of said ratchet mechanism 5 without thereby causing a fast wearing out or damaging of the toothed rim 7 and the ratchet 6. When the pivot 24 is returned from the position F back into the position S, the ratchet 6 and the toothed rim 7 cannot be damaged either, because by being spring-loaded during the entire turning said ratchet 6 is not forced back . Unintentional attempts at turning the pivot 24 out of one of the positions, for instance if a rope fouls the block or a person kicks said block, the pivot 24 is rela- tively well secured against turning because the bar 9 is subjected to a substantial increase of the prestressing in a direction towards the ratchet 6 when attempts at turning the rotation body 12 are made. In other words, a position including a "dead centre" for the bar 9 exists between the two positions S and F, said bar 9 being sub¬ jected to the highest possible prestressing by the spring 15 in said "dead centre". The halves of the sheave housing 3, the ratchet 6 and the rotation body 12 are preferably made of Delrin. Combined with the bar 9 , the flat spring 15, the shaft pin 34 and the pinε 36 being made of stainless steel, the Delrin provides a particularly strong and reliable ratchet me¬ chanism resistant to salt water. The sheave 2 is according to the invention preferably made of an aluminium extrudate . The extrudate is a cylin¬ drical sectional body with an inner toothing and identical - recesses at regular intervals along the inner periphery. The aluminium extrudate is cut in radial planes interspaced a distance corresponding to the thickness of the sheave 2. Finally a circumferential groove 22 is shaped in the surface of the outer periphery of the sheaves 2. According to a particularly advantageous embodiment the rope-receiving groove 22 of the sheave 2 may as shown in Fig. 3 be a surface smooth per se and provided with throughgoing openings 23 at regular intervals along the periphery of the sheave 2. The throughgoing openings 23 extend parallel to the axis of rotation Og of the sheave 2. from one side of said sheave 2 to the other, i.e. the recesses are shaped as circular cavities during the ex¬ trusion. As a result, a particularly good retaining of the rope in the guide 22 of the sheave 2 is obtained, said rope being squeezed out into the openings at an increasing pull, whereby neither the rope nor the prefer¬ ably anodised aluminium sheave 2 are worn significantly. In the embodiment of the sheave 2 shown in Fig. 3, the bottom 22g of the groove 22 thereof extends more inwards towards the centre of the sheave 2 than the openings 23. This embodiment is particularly advantageous in connection with some types and dimensions of rope. Fig. 4 illustrates another advantagoeus embodiment of the sheave 2, where the recesses have been shaped during the extrusion as channels at the periphery. In this manner a sheave 2 is provided with a periphery interrupted by notches 31 extending from the outside and radially inwards towards the centre of the sheave 2. In this embodiment the bottom 22g of the guide 22 does not extend as far towards the centre of the sheave 2 as the notches 31, such a feature being advantageous in connection with other types and dimensions of rope.

Claims: Claims : 1. A rope block comprising a sheave, a sheave housing with fixedly mounted radial bearings supporting said sheave, and a ratchet mechanism situated inside the sheave housing, said ratchet mechanism comprising a ratchet pivotally arranged inside the housing and co-operating with an inner toothed rim on the sheave, whereby said ratchet in the use position is prestressed by a spring means in a direction substantially radially outwards into engagement with the toothed rim, c h a r a c t e r ¬ i s e d in that the spring means (8) is manually ac¬ tivatable from the outside of the housing so as to be in a first position (S) in which said spring means (8) pre¬ stresses said ratchet (6) in a direction (Fg) towards the toothed rim (7) or in a second position (F) in which said spring means (8) prestresses said ratchet (6) in a direc¬ tion (Fp) away from and out of the engagement with the toothed rim (7) . 2. A block as claimed in claim 1, c h a r a c t e r - i s e d in that the spring means (8) is pivotally mounted about an axis of rotation (Op) extending parallel to the axis of rotation (0 p ) of the ratchet (6), and that the spring means comprises a member (9) engaging the ratchet (6) such that when the spring means (8) is turned about its axis of rotation (Op) between the two positions (S and F) the member (9) is moved from a position in which the ratchet (6) is influenced by a torque (Mg) counter¬ clockwise about the axis of rotation (0 p ) of the ratchet (6) into a position in which said ratchet (6) is influenced by a torque (Mp) clockwise about the axis of rotation Op) of the ratchet (6). 3. A block as claimed in claim 2, c h a r a c t e r ¬ i s e d in that the member of the spring means (8) is a spring-loaded bar (9), one end (10) of which engages the ratchet (6), and that said bar (9) is axially displaceably mounted in a guide (11) forming part of a manually operat- able rotation body (12) which is activatable from the outside of the housing. 4. A block as claimed in claim 3, c h a r a c t e r ¬ i s e d in that the bar (9) extends diametrically relative to the rotation body (12). 5. A block as claimed in claim 3 or 4, c h a r a c ¬ t e r i s e d in that the rotation body (12) is centrally mounted in a guide (13) in the sheave housing (3) . 6. A block as claimed in claim 3, 4 or 5, c h a r a c¬ t e r i s e d in that the opposite end (14) of the bar (9) engages the surface (16) of a flat spring (15), which in the relaxed state extends substantially perpendicular to the pλane (P) extending between the axes of rotation (Op and Op) of the rotation body (12) and the ratchet (6), the ends (17 and 18) of said flat spring (15) being releas- ably connected to the sheave housing (3). 7. A block as claimed in one or more of the preceding claims 2 to 6, c h a r a c t e r i s e d in that the member (9) engages a substantially planar surface (19) such that when the ratchet (6) is in a position between the two outer positions (Sp and Fp) of said ratchet said planar surface (19) extends perpendicular to the plane (P) extending between the axes of rotation (Op and 0 p ) of the spring means (8) and the ratchet (6). 8. A block as claimed in claim 7, c h a r a c t e r ¬ i s e d in that stop means (20, 21) are provided at both ends of the surface (19) , said stop means stopping the spring means (8) in the two positions (S, F) . 9. A block as claimed in any of the preceding claims, c h a r a c t e r i s e d in that the rope-receiving groove (22) of the sheave (2) is a surface smooth per se and provided with recesses (23) at regular intervals along the periphery of the sheave (2) . 10. A rope block comprising a sheave and a sheave housing with fixedly mounted radial bearings supporting said sheave, c h a r a c t e r i s e d in that the rope- receiving groove (22) of the sheave is a surface smooth per se and provided with recesses (23) at regular intervals along the periphery of the sheave (2) . 11. A block as claimed in claim 9 or 10, c h a r a c ¬ t e r i s e d in that the recesses are formed as through- going openings (23) extending parallel to the axis of rotation (Og) of the sheave (2) from one side of said sheave (2) to the other. 12. A block as claimed in claim 11, c h a r a c t e r¬ i s e d in that the openings (23) are of a circular cross section. 13. A block as claimed in claim 11, c h a r a c t e r- i s e d in that the openings are formed as notches (31) extending from the outside like a U and radially inwards towards the centre of the sheave (2) in such a way that the periphery of the sheave (2) is interrupted. 14. A method of producing a sheave to be used in a rope block according to one or more of the preceding claims 1 to 13, c h a r a c t e r i s e d by extruding cylindrical sectional bodies provided with an inner toothing and identical recesses extending at regular intervals along the outer periphery of said sectional bodies, whereafter said sectional bodies are cut into radial planes inter¬ spaced corresponding to the thickness of the sheave (2), and by finally shaping a circumferential groove in the outer circumferential surface of the sheave (2).

Inventors: FREDERIKSEN GERT HANS, FREDERIKSEN, GERT, HANS
Applicants: FREDERIKSEN GERT HANS, FREDERIKSEN, GERT, HANS
Application year: 1989
Main classification: F16H55
IPC codes: B66D3, F16D43