Patent Publication Number: US-2016230493-A1

Title: Connector

Description:
This application is entitled to the benefit of, and incorporates by reference essential subject matter disclosed in PCT Application No. PCT/GB2014/053013 filed Oct. 7, 2014, which claims priority to Great Britain Application No. 1317788.6 filed Oct. 8, 2013, which applications are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a connection arrangement, and in particular to a releasable connection arrangement. 
     2. Background Information 
     Connectors for providing a connection between components are common in many industries. For example, in the oil and gas industry connection between tubular components is often required. Further, in some applications a connection may be used to anchor one component inside a bore, such as anchoring a downhole tool within a casing tubular or within an open drilled bore. 
     In many cases a connector must be releasable to permit disconnection when necessary. Such disconnection may be provided in a controlled and user defined manner, such as when a user requires components to be separated. In some instances such disconnection may be necessary in an emergency situation, for example where disconnection is initiated to prevent damage to the connected components. For example, in marine environments involving the connection of a floating vessel with subsea infrastructure, excessive deviations of the vessel outside safe operational limits caused by wave motion, for example, may require the use of an emergency release connector. 
     Typical subsea connectors utilize a connection structure which includes engagement members such as dogs to engage with the part being connected to. However full and positive control of the position of the dogs at all stages of the engagement/disengagement procedures employed may not be achieved. Furthermore the available connectors are typically of relatively large diameter which can make deployment awkward. 
     SUMMARY OF THE INVENTION 
     According to a first aspect there is provided a connection arrangement for use in establishing a connection with an object, comprising a body; a connection member pivotally arranged relative to the body about a pivot axis and including an engagement feature, wherein the connection member is pivotal between an engaged configuration in which the engagement feature is engaged with the object to provide a connection thereto, and a disengaged configuration in which the engagement feature is disengaged from the object; and an actuator member, wherein the connection member and actuator member define a pair of complementary actuation surfaces which cooperate when the actuator member moves from a first to a second direction to cause the connection member to pivot from the engaged configuration towards the disengaged configuration. 
     The connection arrangement may establish a connection, e.g. a releasable connection, between the body and the object. 
     The pair of actuation surfaces may continuously cooperate during the movement of the actuator member from the first to the second direction or vice versa. 
     The pair of actuation surfaces may comprise a first actuation surface provided by or carried on the actuator member. 
     The pair of actuation surfaces may comprise a second actuation surface provided by or carried on the connection member. 
     Either or both of the actuation surfaces may be discontinuous. 
     The first and second actuation surfaces may be in continuous contact with one another such that movement of the actuator member actuates the connection member into either the engaged or disengaged configuration. The continuous contact between the first and second actuation surfaces may remain during the movement from the engaged or disengaged configuration, or vice versa. By remaining a continuous contact between the first and second actuation surfaces during movement of the actuator member jamming or backlashing of the connection member with respect to the actuator member may be prevented. Backlashing or jamming of the connection member may occur when, for example, loose particles, such as debris, interrupt the movement of the connection member. 
     The first actuation surface may include a first and second cam. Alternatively the first cam may be included on a first actuation surface of a first actuator member and the second cam may be included on a third actuation surface provided on a second actuator member. In this alternative both first and second actuator members may each define a pair of complementary actuation surfaces which cooperate when the actuator members move from a first to a second direction to cause the connection member to pivot from the engaged configuration towards the disengaged configuration. 
     The first and second cams of the actuator member or actuator members may define a cam-follower relationship with the second actuation surface of the connection member. The second actuation surface may exhibit a curved predetermined profile and may be on a spline or partially on a spline of the connection member. The first and second cams may move simultaneously along the profile of the second actuation surface. By providing a simultaneous movement of the first and second cams, a connection member may be actuated from the engaged to the disengaged, or vice versa, in a single movement of the actuation member. 
     The connection member may be arranged such that it is in contact with the body at a contact point. In use, the connection member may pivot with respect to the contact point, i.e. the contact point may define a pivot axis for pivotal movement of the connection member. For example, the connection member may comprise a protrusion or recess which cooperates with a corresponding recess or protrusion in the body. The protrusion or recess of the connection member and/or body may provide the contact point. Alternatively the connection member may be connected by a pivot member to the body. For example a pivot pin passing through the connection member and attached to the body. 
     In use, the first and second cams of the actuator member or members may follow the curved profile of the second actuation surface and cause pivotal movement of the connection member with respect to the body. The first and second cams may cause the connection member to radially pivot inward or outward with respect to a longitudinal axis of the object, i.e. to radially pivot into either the engaged or disengaged configuration. 
     In use, maintaining the actuator member in either the engaged or disengaged configuration may retain the connection member in either the engaged or disengaged configuration, respectively. 
     The object may further comprise an object engagement feature adapted to cooperate with the engagement feature of the connection member. The object engagement feature may be a recess or protrusion. For example, the object engagement feature may be an annular groove arranged on a peripheral surface of the object, e.g. an outer peripheral surface of the object. 
     The engagement feature of the connection member may comprise a recess or protrusion, adapted to cooperate with the object engagement feature. For example, the engagement feature may be a protrusion adapted to engage with the annular groove of the object. The engagement feature may be arranged on a surface opposing the second actuation surface of the connection member. 
     In some examples, engagement features of the connection member may have a profile, e.g. a serrated profile, which may match a corresponding profile of an object engagement feature. For example, a serrated profile on a protrusion engagement feature may engage with a corresponding serrated profile of an annular groove on an object. 
     The connection member may comprise a collet or a dog or a plurality of dogs. The plurality of dogs may be pivotally arranged relative to the body. The plurality of dogs may be arranged about a common axis of the body. The pivot points of the dogs may be arranged to be in the same plane. By arranging the dogs with the pivot points in the same plane, a simultaneous pivotal rotation of the plurality of dogs may be achieved. By arranging the dogs with, the pivot points in the same plane, that is normal to a common axis of the body, movement of an actuator member along that axis can achieve a simultaneous pivotal rotation of the plurality of dogs. A plurality of dogs circumferentially disposed about a common axis of the body and arranged for simultaneous pivotal rotation to engage/disengage with an object, can be considered to form a collet i.e. the dogs act as collet segments collectively engaging/disengaging with the object. 
     The/each dog(s) may comprise the second actuation surface which is in contact with the first and second cams of the actuator member. 
     The/each dog(s) may comprise the engagement feature. The engagement feature may be located on a free end of the/each dog on a surface opposing the second actuation surface. 
     The actuator member may be an annular piston. The annular piston may be movable along a longitudinal axis with respect to the object. The movement of the piston may be actuable by a hydraulic pressure. 
     The piston may comprise the first actuation surface which may comprise the first and second cams. The first actuation surface and/or the first and second cams of the piston may be in continuous contact with the second actuation surface of the/each dog(s). The second actuation surface of the/each dog(s) may comprise a curved profile. The second actuation surface may be on a spline of the dog(s) or the second actuation surface may include a spline of the dog(s). 
     In use, movement of the piston in the first longitudinal direction with respect to the object may cause the first and second cam to cooperate with the second actuation surface. For example, the first and second cams may move along the profile of second actuation surface in a first direction. The cooperation between the first and second cams and the profile of the second actuation surface may lead to pivotal movement of the dog(s) with respect to the body. For example, the cooperation between the first and second cam with the second actuation surface may cause each/the dog(s), or an end of the dog(s) including the engagement feature, to pivot inwardly. Inward pivotal movement of the dog(s) or an end of the dog(s) including the engagement feature, may cause the dog(s) to either engage or disengage with the object, i.e. the engagement feature of the/each dog(s) engages or disengages with the further engagement feature of the object. 
     In use, movement of the piston in the second longitudinal direction with respect to the object may cause the first and second cam to cooperate with the second actuation surface. For example, the first and second cams may move along the profile of second actuation in a second direction. The cooperation between the first and second cams and the profile of the second actuation surface may lead to pivotal movement of the dog(s) with respect to the body. For example, the cooperation between the first and second cam with the second actuation surface may cause each/the dog(s), or an end of the dog(s) including the engagement feature, to pivot outwardly. Outward pivotal moment of the dogs or an end of the dog(s) including the engagement feature may cause the dogs to either disengage or engage from the object. 
     Advantageously when the piston or other actuator member is in the engaged position the contact surfaces between the first and second cams and the second actuation surface on the dogs are parallel to and concentric with the common axis of the body. In such an arrangement radial forces acting on the contact surfaces will not produce a resultant force component tending to cause disengagement of the connection made. 
     In use, the first and second cams of the piston may remain in continuous contact with the second actuation surface of each/the dog(s) which may result in a unison movement of the dogs. By simultaneously engaging or disengaging the dogs with the object, sticking of the dog(s) to the object and/or damages to the connection arrangement or object may be prevented. 
     By providing first and second cams that remain in continuous contact with the with the second actuation surface during the engagement and disengagement with the object, the dogs may be kept under the control of the actuator member. A three point contact with the body and the actuator member is maintained. Both cams are in continuous contact with the second actuation surface or portion of the second actuation surface on each dog. The dog is also in contact with the body (via a pivot member or a contact point about which the dog pivots). This continuous three point contact can define (fix) the position of each dog at any given position of the actuator member i.e. the three point contact between dog(s), and the body and the first and second cams of the actuator member, can be fowled and arranged to fix the position of dog(s) relative to a given position of the actuator member. Thus dogs can be fully controlled at each point during movement of an actuator member and also held in fixed position at any point when the actuator member is not moving e.g. the fully engaged and fully disengaged positions of the dogs. 
     The holding of the dog(s) in a fixed position dependent on the position of the actuator member, by means of the three point contact of first and second cams and pivot point, can be achieved in various ways illustrated by embodiments described in more detail hereafter. For example, where the engagement feature is located on a free end of the/each dog on a surface opposing the second actuation surface, then the fixing of the dogs in position, depending on the actuator member position, can be achieved as follows. The first cam is located to one side of the pivot axis of the dog and the second cam is located to the other side of the pivot axis of the dog during movement of the actuator member, at least until the engagement feature has engaged with the object. 
     A different arrangement may be provided where the engagement feature is located on a free end of the/each dog and the first cam contacts a portion of the second actuation surface at the same side of the/each dog as the engagement feature. The second cam contacts a portion of the second actuation surface on a surface opposed to the side of the/each dog with the engagement feature and both the first and second cams are positioned at the end of the/each dog on the other side of the pivot axis from the engagement feature, at least until the engagement feature has engaged with the object. 
     The object may comprise a tubular part. The object engagement feature may be an annular groove on an outer periphery of the object, e.g. the tubular part of the object. In the engaged configuration the engagement features may be clamped into the groove by moving the annular piston in the first direction. In some examples, the groove of the object may be provided on an inner periphery of the object. In this example, the dogs may be inserted into the object. Movement of the piston in the first direction may pivot the dog(s), or at least an end of the dog(s) including the engagement feature, outwards towards the object so that their engagement features may engage with the groove of the object. 
     By maintaining the piston in the engaged configuration the dogs may be retained in the engaged configuration with the object, allowing for the hydraulic pressure to be switched off. 
     The connection arrangement may be retained in the disengaged configuration by de-activating the hydraulic pressure, allowing for the hydraulic pressure to be switched off. The hydraulic pressure may only be needed for operating the piston in the transition from either engaged to disengaged configuration or disengaged to engaged configuration. 
     The body may be a tubular or tubing, for example, an injection or production tubing. The body may comprise a wellhead, such as a subsea wellhead. 
     The object may comprise a subsea well unit, for example, a production tree or a subsea test tree. In use, the connection arrangement may provide a connection, e.g. a releasable connection, between the subsea well unit and the wellhead. 
     The connection arrangement may be a subsea connector, for releasable connection of subsea components in the oil and gas industry. It may be an emergency release connector for rapid disconnection when required. The connection arrangements described herein can be notably compact in diameter, allowing the possibility that they can be sized to pass through relatively small apertures, including that of rotary tables on oil drilling rigs which may be of 49.5 inches in diameter in many cases. Furthermore the positive and continuous control of engagement/disengagement that can be afforded by arrangements described herein can allow high angle release of a subsea connector i.e. in an emergency situation where the body and the object are being laterally displaced relative to each other reliable release may be achieved. Coupling members formed as described below can assist in high angle release. 
     The connection arrangement may comprise one or more coupling member(s) which may provide an inter-engaging coupling arrangement between the body and the object. The coupling members may be provided with seals for sealing engagement between parts of the body and the object, for example for sealing engagement between a tubular of the body and a tubular of the object. The coupling member(s) may act as guide members for connecting and/or disconnecting the body from the object. 
     Typically coupling members may be mounted on respective peripheries of the body and of the object. For example a first coupling member may be mounted on an end of the body and a second coupling member may be mounted on an end of the object. 
     The first and second coupling members may be tapered, for example conical or generally conical in form and may be formed to inter-engage by nesting one inside the other in a male-female connection. 
     Where the connection arrangement is for connecting tubulars, tubing, or tubular parts of a body and an object, conical coupling members are advantageous. During connection the nesting together of the conical first and second coupling members provides a degree of self-centering as the object and body approach each other. During disconnection any lateral forces between the conical surfaces will produce a resultant component tending to urge the object and body apart. 
     In a convenient arrangement the first coupling member may be a generally conical opening or mouth on the body. The first coupling member may comprise a set of annular members of increasing diameter towards the opening of the mouth. Each annular member is disposed about the same longitudinal axis. A corresponding second coupling member on the object, for nesting inside the first coupling member of the body, may be generally conical and may be formed for contact with the annular members of the first coupling member when the coupling arrangement is in the engaged configuration. The generally conical second coupling member may comprise a plurality of ribs, each projecting radially outwards about a longitudinal axis and forming a conical profile narrowing towards a free end to which the body connects. 
     As an alternative the conical feature of the second coupling member may comprise the annular members (narrowing in diameter towards the free end of the object) and the conical feature of the first coupling member may comprise ribs (projecting radially inwardly and fowling a conical opening). 
     The arrangements comprising annular rings and radial ribs provides good but discontinuous contact between the coupling members when the connection arrangement is engaged, with reduced friction compared to continuously surfaced cones for example. 
     The conical or generally conical form of either or both the first and second coupling members may comprise a curved profile. For example the first coupling member as a mouth on the body may have a radially inwardly convex profile and the second coupling member may have a complimentary concave profile 
     The first and second coupling members may roll off each other in case of an emergency disconnect between the body and the object. The rolling off movement provided by the coupling members may prevent damage to the connection arrangement and/or the object as described further hereafter with respect to an embodiment. 
     According to a second aspect there is provided a method for establishing and releasing a connection between a body and an object, comprising: positioning the body with respect to the object; moving a actuator member of the body in a first direction, wherein the actuator member cooperates with a connection member of the body causing the connection member to pivotally move into an engaged configuration in which an engagement feature is engaged with the object to provide a connection thereto; moving the actuator member in a second direction wherein the actuator member cooperates with the connection member causing the connection member to pivotally move into a disengaged configuration in which the engagement feature is disengaged from the object; and wherein the connection member and actuator member define a pair of complementary actuation surfaces which cooperate when the actuator member moves from a first to a second direction to cause the connection member to pivot from the engaged configuration towards the disengaged configuration. 
     The method may employ the connection arrangement of the first aspect of the invention as described herein. 
     It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilized, either alone or in combination with any other defined feature, in any other aspect or embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are schematic partial cross sectional views of a connector arrangement in an open position. 
         FIG. 2  is a schematic partial cross sectional view of a connector arrangement of the present invention in a locked position. 
         FIG. 3  is a schematic cross sectional view of a connector arrangement during connect or disconnect. 
         FIGS. 4A and 4B  are schematic cross sectional views of an individual dog and annular piston in the disengaged position and in the engaged position. 
         FIGS. 5A and 5B  show in cross section a connector arrangement in a closed position. 
         FIGS. 6A to 6D  show in cross section detail the operation of the connector arrangement of  FIG. 5 . 
         FIGS. 7A and 7B  show a connector arrangement in the open and closed positions. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  show a connector arrangement suitable for establishing a tubular connection suspended from a surface vessel to a subsea installation such as a wellhead.  FIG. 1A  is in partial cut away perspective and  FIG. 1B  in partial cross section elevation. 
     The connector arrangement  1  comprises a connector unit  2  to be mounted onto the subsea installation at a tube end  4  (rest of subsea installation not shown). The connector unit  2  includes as connection members  6  of a set of dogs  7  circumferentially mounted around a tubular body  8 . The individual dogs  7  are pivoted on pivot pins  10  all in the same plane, normal (at right angles) to the longitudinal axis of the connector unit  2  and tubular body  8 . As an alternative to pivot pins  10  a pivot ring could be provided, passing through all the dogs  7  at the same position as the pivot pins shown. 
     An annular piston (as actuator member)  12  encircles the dogs and is contained within outer cylinder  14 . The piston  12  is powered by hydraulics and is the actuator member for the arrangement. 
     The dogs  7  include engagement features  16 , inward projections  18  formed for engagement with annular groove  20  on the tube end  4 . 
     The piston  12  has first and second cams  22 , 24  as part of a first actuation surface that follow the curved profile of a second actuation surface  26  on dogs  7  that include a spline  28 . When the piston  12  moves downwards from the position shown in  FIG. 1B  as suggested by arrow A, the cams  22 ,  24  cause motion in unison of the dogs  7  about pivot pins  10 . If the extreme end  30  of tube  4  is positioned to abut or almost abut the extreme end  32  of the tubular body  8  then the action of the cams will be to cause the engagement features  16  of the dogs to engage the annular groove  20  thus connecting the tubular  8  and tube end  4 . 
     The connected and locked position that is obtained is shown in  FIG. 2 . Disengagement of the connection is performed by motion of the annular piston  12  in the opposite direction as suggested by arrow B in  FIG. 2 . The profile of the second actuation surface  26  when following cams  22  and  24  determines that contact between the cams  22 , 24  and the dogs  7  is always maintained during engagement and disengagement, of the connection. Together with the contact at the pivot pins  10  this means that the dogs  7  (connection members of the connection arrangement) are always held by three points of contact. Thus the position of the dogs  7  is always fixed by the position of annular piston  12  at any given moment. The first and second cams  22 , 24  are always one above the pivot pins  10  the other below the pivot pins  10 . In the arrangement shown in  FIGS. 1 and 2  engagement and disengagement is positively controlled at all times by the piston  12 , thus avoiding jamming or backlash that can occur if the dogs have free motion allowed at any point in the connection or disconnection procedure. 
     A feature of the arrangement shown in locked position  FIG. 2  is that the contact surfaces between cams  22 ,  24  and the dogs  7  (second actuation surface  26 ) are parallel to (and concentric with) the longitudinal axis. This arrangement of the profiling of the pair of actuation surfaces (when the connection arrangement is engaged) has an advantage. If a radially outwards or inwards force is experienced (as suggested by double headed arrow X) then there will be no resultant force component in the longitudinal direction urging the disengagement of the arrangement. 
     The connection arrangement of  FIGS. 1 and 2  also includes coupling members. The first coupling member (of connector unit  2 ) ends in a conical, inwardly convex profile, mouth  34 . The second coupling member (of tube end  4 ) is a corresponding conical concave profiled end portion  36 . The coupling members  34 , 36  aid in centering the connection arrangement when the connector unit  2  and tube end  4  are brought together for engagement and can also aid in disengagement as discussed below with respect to  FIG. 3 . The mouth  34  of the connector unit  2  comprises annular rings  38  of increasing diameter towards the mouth end that are held in radially inwardly projecting ribs  40 . The end portion  36  of tube end  4  comprises radially outwardly projecting ribs  42  narrowing towards the extreme end of the tube. 
     As can be seen in  FIG. 2  when the connection arrangement is engaged the end portion  36  nests inside mouth  34  with the rings  38  and ribs  42  (and/or ribs  40 ) in contact. There is less contact than there would be with continuous conical surfaces and so reduced friction on disengagement. Furthermore as the rings  38  are transverse to the ribs  42  connection can be made without the connector unit  2  having to be at any particular rotational orientation (about the longitudinal axis) to tube end  4 . 
       FIG. 3  shows a disconnection of the arrangements of  FIGS. 1 and 2  under a stressed condition, such as may occur subsea where a disengagement of a connection arrangement of the invention is being carried out in an emergency. For example, where a surface vessel connecting to a subsea installation is displaced from its holding position above the installation, by bad weather. As shown in  FIG. 3  the connection has been disengaged and connector unit  2  is at an angle to the tube end  4 . The curved profile and conical shape of the mouth  34  and tube end portion  36  allow relatively smooth completion of disconnection, with the connector unit  2  “rolling” upwards and away from the tube end  4  as indicated by curved arrow Y. 
       FIG. 4A  and  FIG. 4B  show in schematic cross section detail the operation of an annular piston  12  and dog  7  arrangements similar to that of  FIGS. 1 to 3  except with the annular piston operating inside the dogs  7 . Like parts are numbered the same as in the earlier figures. As in  FIGS. 1 and 2  the motion of piston  12  in the direction of arrow A causes the profiled surface  26  of dog  7  to follow the motion of cams  22  and  24 . This results in pivoting of dog  7  about pivot pin  10  giving, in this example, radially outwards motion of engagement feature  16  (protrusion  18 ). Starting from the disengaged position of  FIG. 4A  the protrusion  18  is directed into an annular groove  20  when moving to the fully engaged position shown in  FIG. 4B . 
     As in the example of  FIGS. 1 and 2  the contact between the cams  22 ,  24  and the second actuation surface  26  are parallel to (and concentric with) the longitudinal axis when the fully engaged position is attained. Radially directed forces indicated by double headed arrow X will not produce a resultant component tending to disengage the connection made. 
     A further embodiment of the invention is illustrated in cross section  FIGS. 5A and 5B . In  FIG. 5A  a connector unit  2  is shown fully engaged with a tubing end  4 . Engagement is by means of dogs  7  with the area shown in dashed line shown in more detail in magnified view  FIG. 5B . An outer annular ring  12  provided outside dogs  7  (only one dog  7  shown in the detail  FIG. 5B ). In the fully engaged and locked position shown, two cams  22  and  24 , provided on an actuation surface of the ring  12 , hold the dog in position by contact with second actuation surface  26  on the dog  7 . Engagement feature  16 , a protrusion  18  of the dog  7  is located in an annular groove  20  of tubing end  4 . A further contact  43  is made between the ring  12  and surface  26  at the end distal to the protrusion  18 , providing more security of fixing. Dog  7  can pivot about a contact point  44  but only when the annular ring  12  allows i.e. when the cams direct pivoting movement of the dog  7 . The contact point is provided by a protrusion  46  on the dog nesting in rotating contact with a recess  48  of the connector unit  2 . 
     Operation of this embodiment is illustrated in  FIGS. 6A to 6D . In  FIG. 6A  the connector unit  2  and tube end  4  are in contact ready for engaging together. Annular ring  12  is ready to move in the direction of arrow A. At this point the dog  7  is disengaged with protrusion  18  angled away from groove  20  by virtue of the action of cams  22  and  24  on actuation surface  26  which in concert with contact point  44  hold the dog  7  at three points, preventing movement. Movement in the direction A commences. 
     As shown in  FIG. 6B  the following of cams  22 , 24  by the profiled actuation surface  26  starts the pivoting of the of dog  7  about contact point  44 . 
     In  FIG. 6C  continued movement of ring  12  in direction A has caused further pivoting of the dog  7  to fully engage protrusion  18  in groove  20 . Up until this time the cams  22  and  24  have always been to either side of the pivot contact point  44 . However the ring  12  can now continue motion in direction A until the position of  FIG. 6D  is reached. In this position additional contact  43  provides further security of engagement. As with the embodiments discussed above the contact between the ring  12  (cams  22 ,  24  and in this case contact  43 ) and the second actuation surface  26  are parallel to (and concentric with) the longitudinal axis when the fully engaged position is attained. 
       FIGS. 7A and 7B  illustrate schematically a further embodiment. In this embodiment dog  7  pivots about pivot pin  10 . Motion of actuator member  50  in direction A causes the two cams  22  and  24  to interact with surface  26  of dog  7  to either side of its body, leading to the engaged position shown in  FIG. 7B  where protrusion  18  is in groove or slot  20 . As can be seen from  FIG. 7B  the cams  22 ,  24  are in constant contact with the surface  26  of the dog providing secure and controlled motion of the dog in accordance with the position of actuator member  50 . In this example the cams  22  and  24  are above the pivot point (pivot pins  10 ) at all times during engagement and disengagement (arrow B).