Abstract:
A retaining formation defined on a brake lever of an air disc brake includes a push fit/snap fit connection for releasably securing a push rod to a brake lever. The retaining formation can include a pinned connection and a ball and socket joint, and a main axis of the pinned connection is coincident with a center of rotation of the ball and socket joint. The retaining formation can include a concave formation on one of the push rod and the brake lever and a corresponding convex formation on the other of the push rod and the brake lever. The concave formation at least partially surrounds the convex formation to prevent axial separation of the push rod and the brake lever. A method of assembling a brake subassembly includes the steps of assembling a push rod and a brake lever including a retaining formation such that at least a portion of the retaining formation deforms during assembly and resiles when the push rod is assembled to the brake lever to provide a snap fit connection therebetween. Another method of manufacturing a retaining formation includes the steps of providing one of a push rod and a brake lever with a concave formation, providing the other of the push rod and the brake lever with a convex formation able to receive the concave formation, assembling the concave formation and the convex formation, mechanically working the one of the push rod and the brake lever with the concave formation such that the concave formation at least partially surrounds the convex formation to prevent axial separation of the push rod and the brake lever.

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims priority to United Kingdom Patent Application No. 0725225.7 filed Dec. 24, 2007. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a retaining formation for the connection of components in a brake. Specifically, the present invention relates to a retaining clip for the connection of a push rod in an actuator to a lever of an air disc brake. 
     It is known in brake applications to operate levers such as op-shafts and adaptors with push rods. The push rods act in compression when an actuating force is applied (e.g., by the activation of the brake) and transmit compressive forces in an actuation stroke, for example, between: an actuator and an op-shaft for actuation of a brake, an actuator and an adaptor lever for rotation of the adaptor lever, and an adaptor lever and an op-shaft for actuation of a brake. 
     The push rod then returns via a return stroke as air pressure is released and a return spring takes over. In brake applications, the return stroke occurs as a result of the actuating force being removed (e.g., by release of the brake by a driver) and additionally the lever providing a return force on the push rod (as most brakes provide a return mechanism to prevent the brake from remaining engaged). 
     Levers such as op-shafts and adaptor levers rotate in use. The end of the lever on which the push rod acts is positioned away from a pivot axis of the lever, and the contact point at which the push rod contacts the lever will tend to have a component of motion in a plane perpendicular to a main axis of the push rod. 
     If the push rod is to be attached to the lever, the end of the push rod that contacts the lever needs to be able to articulate in the plane perpendicular to the main axis of the push rod at the same time as the lever. This may be achieved by rotatably mounting the push rod about both ends, i.e., both at the contact point and at and end distant from the contact point. In the instance of an actuator push rod, the actuator lever itself may be rotatably mounted to achieve this. 
     The push rod may be rotatably mounted to the lever at the contact point by simply providing a socket on the lever and a ball on the end of the push rod. The push rod is constrained from movement away from the contact point on the lever (by the walls of the cup), but is able to slide rotationally providing the desired motion in use. 
     This solution is problematic, as in certain situations, the push rod can return before the lever. This may occur if, for example, the brake is operating in cold weather conditions. If the brake actuator is released, the brake push rod returns. However, the brake mechanism may be slow to respond due to the low temperature causing increased viscosity in the lubricant. The push rod and the lever can become disengaged and misaligned such that on a subsequent actuation stroke, the push rod either contacts the lever at the incorrect position, or does not contact it at all. 
     Alternatively, a pinned joint is known. A pin is then inserted through a corresponding series of bores in the lever and push rod to pin the push rod to the lever, allowing relative rotation about an axis parallel to a lever rotation axis. However, this arrangement requires modifications to the manufacture of both the lever and the push rod (i.e., the formation of the bores) and increases part count (in the need for a pin). The complexity and cost of assembly and servicing the brake is also increased due to the need to fit and remove the pin in a confined space. 
     Additionally, one of the corresponding bores is often of relatively large diameter compared to the pin to allow free movement of the push rod relative to the lever at the extreme ends of the range of motion of the lever. This may result in misalignment of the push rod and lever and jamming of the brake. 
     It is an aim of the present invention to overcome or at least mitigate one or more of these problems. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a retaining formation for retaining a push rod on a brake lever, the retaining formation including a pinned connection and a ball and socket joint. A main axis of the pinned connection is coincident with a center of rotation of the ball and socket joint. In one example, the retaining formation is part of a brake subassembly including a push rod and a brake lever, the brake subassembly being located in a transmission path from a brake actuator to a brake op-shaft. The brake lever may be a lever of an op-shaft or a lever of a brake adaptor. 
     Alternatively, or in addition, the pinned connection may include a pin defined in one of the push rod and the brake lever, and a bore defined in the other of the push rod and the brake lever, the bore receiving the pin. The pin and the bore are relatively sized to permit relative rotational movement of the push rod and the brake lever about a pivot axis transverse to a main axis of the pin. A pinned joint permits retention of the push rod against the lever in tension, and the ball and socket joint helps to mitigate misalignment between the components. 
     According to a further aspect of the present invention, there is provided a retaining formation defined on a brake lever of an air disc brake including a push fit/snap fit connection for releasably securing a push rod to a brake lever. The push rod may be retained against the lever, and no separation will be seen in use as the lever can exert a tension force on the push rod to return it to its initial position. The snap fit feature allows for ease of assembly and servicing. 
     In one example, the formation includes a resilient clip having a substantially U-shaped member to at least partially surround a brake lever. In one example, each arm of the substantially U-shaped member includes an orifice configured to receive a projecting pin of a push rod. In one example, an arm of the U-shaped member includes an outwardly projecting lip at a free end to guide the push rod into the U-shaped member. 
     Alternatively, the resilient clip may include a substantially hollow cuboid having an open face to receive a lever. Alternatively, the substantially hollow cuboid has an orifice defined in a sidewall to receive at least a part of a push rod, the orifice positioned to be proximate a recess in a brake lever for receiving a push rod in use such that assembly of the push rod into the recess prevents removal of the resilient clip from a brake lever. In one example, the push rod includes a pair of opposed, co-axial projecting pins projecting from a first end thereof for engagement with the orifices in use to form the snap fit. 
     According to a still further aspect of the present invention, there is provided a retaining formation for retaining a push rod on a brake lever, the retaining formation including a concave formation on one of the push rod and the brake lever and a corresponding convex formation on the other of the push rod and the brake lever. The concave formation at least partially surrounds the convex formation to prevent axial separation of the push rod and the brake lever. 
     According to a yet still further aspect of the present invention, there is provided a method of assembling a brake subassembly including the steps of providing a brake lever including a retaining formation as described above, assembling a push rod and the brake lever such that at least a portion of the retaining formation deforms during assembly and resiles when the push rod is assembled to the brake lever to provide a snap fit connection therebetween. 
     According to another aspect of the present invention, there is provided a method of manufacturing a retaining formation as above including the steps of providing one of a push rod and a brake lever with a concave formation, providing the other of the push rod and the brake lever with a convex formation able to receive the concave formation, assembling the concave and the convex formation, mechanically working the one of the push rod and the brake lever with the concave formation such that the concave formation at least partially surrounds the convex formation to prevent axial separation of the push rod and the brake lever. The step of mechanically working may include the step of peening. 
     In this manner, the potential problems caused by separation of the push rod and the lever are alleviated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of a retaining clip in accordance with the present invention will now be described with reference to the accompanying Figures, in which: 
         FIG. 1  is a partial section view of a brake assembly incorporating an adaptor subassembly according to a first aspect of the present invention; 
         FIG. 2  is a section view of a part of the brake assembly of  FIG. 1 ; 
         FIG. 3  is a section view along line III-III of  FIG. 2 ; 
         FIG. 4  is a partial section view of an adaptor subassembly and a retaining clip according to a second aspect of the present invention; 
         FIG. 5  is a partial section view of the adaptor subassembly and the retaining clip of  FIG. 4  in an assembled condition; 
         FIG. 6  is a perspective section view of the retaining clip of  FIG. 4 ; 
         FIG. 7  is a perspective view of the retaining clip of  FIG. 4 ; 
         FIG. 8  is an end view of a third embodiment of a retaining clip in accordance with the present invention; 
         FIG. 9  is a side section view of a brake assembly including a retaining clip according to a fourth embodiment of the present invention; 
         FIG. 10  is a side section view of a part of the brake assembly of  FIG. 9 ; 
         FIG. 11  is a perspective view of a part of the brake assembly of  FIG. 9 ; 
         FIG. 12  is a perspective view of a part of the brake assembly of  FIG. 9  in an assembled condition; 
         FIG. 13  is a perspective view of a brake assembly including a retaining clip according to a fifth embodiment of the present invention; 
         FIG. 14  is a side section view of a part of the brake assembly of  FIG. 13  in a brakes-off condition; and 
         FIG. 15  is a side section view of a part of the brake assembly of  FIG. 13  in a brakes-on condition. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A brake assembly  100  is shown in  FIG. 1 . The brake assembly  100  includes a brake subassembly  102  and an adaptor box subassembly  104 . The brake subassembly  102  includes a brake caliper  106  slidably mounted with respect to a brake carrier  107  and a pair of opposed brake pads  108  for actuation and engagement with a brake disc or rotor  109  to provide a braking force for retarding rotation of a wheel (not shown) of a vehicle (not shown). The basic layout and purpose of an adaptor box is shown in our earlier application EP1348882. 
     The brake pads  108  are pushed into engagement with the brake disc or rotor  109  via an op-shaft  110  of the brake subassembly  102  (see  FIG. 2 ) via an actuation force in a direction A. The op-shaft  110  converts a relatively high displacement, low force input from an air actuator into a low displacement, high force output to the brake pads  108  in a known manner. 
     The adaptor box subassembly  104  includes an adaptor box housing  112 , an adaptor subassembly  114 , and an attachment feature  116  to attach the adaptor box housing  112  to the brake subassembly  102 . The adaptor box subassembly  104  allows an air actuator to be positioned with its main axis at an angle to the direction of force applied to the op-shaft  110 . This is achieved via a pivotable lever as will be described below. 
     The adaptor subassembly  114  includes an adaptor lever  118  with a first arm  120  and a second arm  122  radially projecting from a pivot axis B, with an angular spacing of approximately 90 degrees between them. The adaptor lever  118  defines a bore  124  through which a pin  125  is inserted and fixed to the adaptor box housing  112 . With reference to  FIG. 3 , a distal end of the first arm  120  includes a recess  131  flanked by a pair of sidewalls  133 . A pair of bores  134  are defined through a distal end of the first arm  120  through both the pair of sidewalls  133 . Each of the pair of bores  134  have a diameter D. 
     The adaptor box subassembly  104  also includes a push rod  126 . The push rod  126  has an elongate cylindrical body  127  with a generally hemispherical first end  128  and a generally hemispherical second end  130 , as can be seen in  FIGS. 2 and 3 . The hemispherical second end  130  has a bore  132  defined therethrough of a diameter C. The adaptor box subassembly  104  also includes a pin  136 , as will be described below. 
     When assembled, the adaptor lever  118  is rotatably mounted on the pin  125  to rotate about the pivot axis B. The hemispherical second end  130  of the push rod  126  is inserted into the recess  131  such that the pair of bores  134  and the bore  132  are coaxial. The pin  136  is then inserted through the assembled push rod  126  and the adaptor lever  118 , as shown in  FIG. 3 . The pin  136  is sized to be of slightly larger diameter than the diameter D, thus providing an interference fit and retaining the pin  136  in place. The pin  136  may be a roll pin. The hemispherical first end  128  of the push rod  126  is located in a recess on the op-shaft  110 . 
     In use, a brake actuation force E is applied (by an air actuator or similar) to the second arm  122  of the adaptor lever  118 , as shown in  FIG. 2 . This causes counter-clockwise (as shown in  FIG. 2 ) rotation of the adaptor lever  118  about the pivot axis B. This in turn pushes the push rod  126  in the direction A against the op-shaft  110  to provide braking force. 
     The coexistence of the pin  136  joint and the recess  131  provides retention between the push rod  126  and the adaptor lever  118  in addition to permitting stable sliding rotation in use. Misalignment of the push rod  126  and the adaptor lever  118  is therefore made less likely. 
     The motion of the push rod  126  is not entirely axial (i.e., not entirely in the direction A). Rather, due to the rotation of the adaptor lever  118 , some articulation in the direction of actuation force E is also observed. This movement is accounted for by the ability of the push rod  126  to rotate about the pin  136  mounted in the adaptor lever  118  and rotate in the recess provided on the op-shaft  110 . 
     Additionally, some movement is experienced in the direction of the pivot axis B at the first end  128  due to the rotation of the op-shaft  110 . To account for this, the bore  132  is made of a significantly larger diameter than the pin  136  to allow rotation of the push rod  126  in the plane of  FIG. 3 ; i.e., about a tilt axis. The tilt axis is generally transverse to the pin  136 . In the example, the tilt axis (when viewing  FIG. 2 ) is parallel to the brake actuation direction E, but passing through the pin  136 . When viewing  FIG. 3 , the tilt axis is perpendicular to the plane of the page and passes through the pin  136 . The degree of freedom of rotation of the push rod  126  about the tilt axis may be controlled by the relative diameters of the pin  136  and the bore  132 . In the example, the push rod  126  can rotate ±4 degrees relative to the first arm  120 , as this has been found to be sufficient to account for tilting due to normal motion of the op-shaft  110 . Even though such movement is permitted, the pin  136  continues to retain the push rod  126  relative to the adaptor lever  118 . 
     Forming the recess  131 , the pair of sidewalls  133 , the pair of bores  134  and the bore  132  is evidently more complex, and hence time consuming and expensive than forming a simple ball and socket joint (e.g., the joint between the push rod  126  and the op-shaft  110 ). Furthermore, an extra assembly operation of inserting the pin  136  is required. Additionally, it is necessary to assemble the push rod  126  onto the adaptor lever  118  prior to mounting the adaptor lever  118  in the adaptor box housing  112 , which reduces the flexibility of the assembly process and hence may be undesirable. 
     The pin  136  can move in the large diameter bore  132 , and as such the push rod  126  has a large range of movement relative to the adaptor lever  118 . In the event that extreme cold weather hinders the op-shaft  110  from returning with the push rod  126  ( FIG. 2  shows the op-shaft  110  and the push rod  126  beginning to disconnect), the op-shaft  110  and the push rod  126  become disconnected and may not relocate properly due to the significant permitted range of movement of the push rod  126 . 
       FIGS. 4 and 5  show a push rod  202 , the head  204  of an adaptor lever and a retaining clip  206  in accordance with a second embodiment of the present invention.  FIGS. 6 and 7  show the retaining clip  206  in isolation. 
     The push rod  202  has a generally cylindrical body  203  with first and second hemispherical ends  208  and  210 , respectively. The second hemispherical end  210  is adapted to mate with an op-shaft, as shown in  FIGS. 1 to 3 . A circumferential neck  212  is defined on the push rod  202  proximate the first hemispherical end  208  delimited by a first shoulder  214  and a second shoulder  216 . The head  204  is generally rectangular in section, and defines a hemispherical recess  218 . 
     The retaining clip  206  includes a generally cuboidal body  220 . The generally cuboidal body  220  is preferably shaped to conform to the profile of the head  204 . One wall of the generally cuboidal body  220  is open to define an opening  222 . A further wall of the generally cuboidal body  220  adjacent to the opening  222  defines a circular mouth  224 , the periphery of which is coincident with a smaller diameter end of a frustroconical projection  226 , which projects outwardly from the generally cuboidal body  220 . The diameter of the circular mouth  224  is sized to be less than the diameter of the generally cylindrical body  203  of the push rod  202 , but greater than the diameter of the circumferential neck  212 . 
     The retaining clip  206  is constructed from a resilient material, such as plastics material, or sheet metal material. The retaining clip  206  is preferably molded in the case of a plastics material, or sheet metal formed in the case of sheet metal material. 
     To use the retaining clip  206 , the retainer clip  206  is placed over the head  204  by inserting the head  204  into the opening  222  such that the circular mouth  224  is adjacent to the hemispherical recess  218  in the head  204 , as shown in  FIG. 4 . The first hemispherical end  208  of the push rod  202  is then inserted in a direction F into the frustroconical projection  226 . As the diameter of the circular mouth  224  is sized to be less than the diameter of the generally cylindrical body  203 , the retaining clip  206  deforms to allow the first hemispherical end  208  to pass through the circular mouth  224 . The circular mouth  224  then resiles back to its original diameter once the push rod  202  has been inserted sufficiently that the circumferential neck  212  is coincident with the circular mouth  224 . During this operation, the frustroconical projection  226  acts as a guide to guide the push rod  202  towards the circular mouth  224  and hence the hemispherical recess  218 . The frustroconical projection  226  also reduces the amount of free movement of the push rod  202  should it lose contact with the op-shaft at the second hemispherical end  210 . The sides of the frustrocone reduce the amount that the push rod  202  can rotate about the head  204  as the generally cylindrical body  203  will abut them. 
     The push rod  202  has been inserted sufficiently once the hemispherical head  208  mates with the hemispherical recess  218 , as shown in  FIG. 5 . In use, the push rod  202  can rotate relative to the head  204 . Rotation of the push rod  202  is permitted due to the difference in diameters between the circular mouth  224  and the circumferential neck  212 . Alternatively, or additionally, the circular mouth  224  may be a relatively tight fit around the circumferential neck  212  with rotation being permitted due to the resilient nature of the retaining clip  206 . 
     The head  204  may be of any relevant lever in a brake assembly. For example, it may be the head of an adaptor lever (as shown), or the head of an op-shaft. Equally, the push rod  202  may be the push rod of an actuator or an adaptor. Thus, in other embodiments, the push rod  202  may have the circumferential neck  212  at both the first and second hemispherical ends  208  and  210 , respectively, to be releasably secured to both an adaptor lever and an op-shaft lever. 
     The push rod  202  can be disassembled from the head  204  by axially pulling it with sufficient force to widen the circular mouth  224  to pass over the hemispherical head  208 . The force required to disassemble the push rod  202  from the head  204  is significantly higher than the tension forces that the joint between the two will experience in use, thus making it extremely difficult for the components to become separated accidentally. 
       FIG. 8  shows part of an alternative retaining clip  300  substantially similar to the retaining clip  206 , but with projecting fingers  302  spaced circumferentially around an orifice  304  at the base of a frustroconical projection  306 . An orifice outer periphery  308  has a diameter larger than a push rod cylindrical portion diameter (not shown), whereas an inner periphery  310  defined by distal ends of the projecting fingers  302  has a diameter less than the push rod cylindrical portion diameter. As such, the projecting fingers  302  must resile to allow insertion of a push rod (substantially similar to the push rod  202 ). 
       FIG. 9  shows a brake assembly  400  including a pair of opposed brake pads  402  configured to be moved together to clamp a disc or rotor (not shown) by counter-clockwise rotation of an op-shaft  404  (best viewed in  FIGS. 10 to 12 ). 
     The op-shaft  404  includes a body portion  406  and a lever arm  408  projecting radially outwardly therefrom. The op shaft  404  is carried on needle roller bearings  410  to rotate about an axis G to actuate the brake in a known manner. The end of the lever arm  408  describes a circular path H (see  FIG. 10 ) in use. The lever arm  408  has a cylindrical socket formation  409  defined at its distal end, with the main axis of the cylindrical socket formation  409  being parallel to the axis G. 
     The brake assembly  400  further includes an air actuator  412  having an actuator housing  414  with a piston  416  disposed therein. The piston  416  is connected to a push rod  418 . The air actuator  412  further includes a return spring  420  positioned between the actuator housing  414  and the piston  416  to return the piston to the position shown in  FIG. 9  following actuation. The air actuator  412  is configured to allow a small amount of rotational movement of the push rod  418 , either by use of a flexible seal  413 , or alternatively by inclusion of a rotational joint (not shown) connecting the push rod  418  to the piston  416 . 
     The distal end of the push rod  418  includes a foot  424  having a generally cuboidal body  426  and a cylindrical end  428 . A pair of opposing pins  430  (shown in  FIG. 11 ) extend coaxially from the foot  424 . 
     The brake assembly  400  further includes a retaining clip  432 . The retaining clip  432  includes a substantially U-shaped sheet formation having a back  434  connected to two parallel opposing sidewalls  436 . A pair of mutually divergent lips  438  are defined on free ends of the two parallel opposing sidewalls  436  and extend outwardly. A bore  440  is defined in each of the two parallel opposing sidewalls  436 . The bores  440  are co-axial. 
     The retaining clip  432  is constructed from a resilient material, such as plastics material or sheet metal material. The retaining clip  432  is preferably molded in the case of a plastics material, or sheet metal formed in the case of sheet metal material. 
     To assemble the brake assembly  400 , the cylindrical end  428  of the push rod  418  is inserted into the cylindrical socket formation  409 , as shown in  FIG. 10 . The retaining clip  432  is then pushed over the assembled push rod  418  and the op-shaft  404  from a direction opposite to the direction of insertion of the push rod  418 . The back  434  of the retaining clip  432  abuts the lever arm  408 . 
     As the retaining clip  432  is pushed, the pair of mutually divergent lips  438  contact the pair of opposing pins  430  and slide such that the two parallel opposing sidewalls  436  spread. As the bores  440  come into engagement with the pair of opposing pins  430 , the two parallel opposing sidewalls  436  resile to the position shown in  FIG. 12 . The retaining clip  432  is a “snap fit” component. Alternatively, the retaining clip  432  is secured to the op-shaft  404 , e.g. by welding or adhesive prior to inserting the push rod  418 , which may be advantageous during assembly. 
     Actuation of the air actuator  412  occurs by the supply of compressed air to an inlet  422  formed in the actuator housing  414 . The piston  416  is then actuated to the left in  FIG. 9  such that the push rod  418  extends from the actuator housing  414 . The motion of the push rod  418  causes the op-shaft  404  to rotate about the axis G and activate the brake. As the op-shaft  404  rotates and describes the circular path H, the flexible seal  413  and the rotational joint formed by the interaction of the pair of opposing pins  430  and bores  440  allow rotational movement of the push rod  418 . Therefore, the component of motion of the end of the op-shaft  404  perpendicular to the direction of motion of the push rod  418  is accounted for. 
     Without the retaining clip  432 , the push rod  418  and the op-shaft  404  can easily become separated. Once air is no longer supplied to the inlet  422 , the return spring  420  returns the piston to the position shown in  FIG. 9 . In normal working conditions, the end of the op-shaft  404  will return with the push rod  418  as the braking forces act to disengage the brake. However, in extreme cold conditions, the brake mechanism may become stiff, and the op-shaft  404  may return at a slower rate than the push rod  418 . Without the retaining clip  432 , this may cause disengagement and misalignment of the two components. 
     The retaining clip  432  acts to retain the push rod  418  against the op-shaft  404  and prevent such disengagement while still allowing rotational motion. This results from the engagement of the pair of opposing pins  430  with the bores  440 . 
     The “snap-fit” nature of the retaining clip  432  simplifies the assembly process over the pin  136 . In other embodiments, an attachment may be provided to retain the retaining clip  432  on the op-shaft  404 . For example, a bolt may be provided to attach the back  434  to the lever arm  408 . Alternatively, the retaining clip  432  may be configured to surround the end of the lever arm  408  like the retaining clip  206 . 
       FIGS. 13 to 15  show an op-shaft  502 , a piston  504  and a push rod  506  of a brake assembly  500  substantially similar to the corresponding components of the brake assembly  400 . In addition, the brake assembly  500  includes a retaining clip  508 . 
     The op-shaft  502  includes a head  510  with a hemispherical recess  512 . A bore  514  extends from the hemispherical recess  512  to a rear face  516  of the head  510 . 
     The push rod  506  includes a cylindrical portion  516  and a spherical head  518 . A neck  520  is disposed between the cylindrical portion  516  and the spherical head  518 . The neck  520  is substantially circular in cross-section and of a smaller diameter than the cylindrical portion  516  and the spherical head  518 . 
     The retaining clip  508  includes a cup-shaped hollow body  521  and defines an orifice  522  over less than half of the surface of the neck  520 . An arm  524  extends from the cup-shaped hollow body  521  and is opposed from the orifice  522 . The arm  524  includes a pair of barbed projections  526  with a slit defined therebetween. 
     In one example, the retaining clip  508  is constructed from engineering plastics material and is resilient. In other embodiments, the retaining clip  508  may be overmolded onto the op-shaft  502  to hold it in place rather than being secured by arm  524  to the op-shaft  502 . 
     In use, the retaining clip  508  is secured to the head  510  by inserting the arm  524  into the bore  514 . The retaining clip  508  can then be pushed home such that the barbed struts resile to their normal position and secure the retaining clip  508  in the hemispherical recess  512  as shown in  FIGS. 14 and 15 . In other embodiments, the retaining clip  508  may be overmolded onto the op-shaft  502  to hold it in place rather than being secured by arm  524  to the op-shaft  502 . 
     The push rod  506  is secured to the retaining clip  508  by inserting the spherical head  518  into the orifice  522 . The diameter of the spherical head  518  is slightly smaller than the diameter of the inner surface of the cup-shaped hollow body  521 , but larger than the diameter of the orifice  522 . The cup-shaped hollow body  521  deforms upon insertion of the spherical head  518  and resiles to surround the spherical head  518  as shown in  FIGS. 14 and 15 . 
     The assembly sequence may be in either order, with the retainer clip  508  either being assembled to the op-shaft or the push rod first. In one example, the retainer clip  508  is assembled to the op-shaft first because the spherical head  518  and the cup-shaped hollow body  521  can be aligned in a number of relative positions and as such is easier than the alignment of the retaining clip  508  and the head  510 , which can only be aligned in a single position. This is advantageous as the assembly may have to take place within e.g., an adaptor box where visibility and the ability to maneuver the components are low. As can be seen in  FIGS. 14 and 15 , the hemispherical recess  512  is hemispherical to allow the cup-shaped hollow body  521  to deform upon insertion of the spherical head  518 . 
     In use, the spherical head  518  can rotate in the retaining clip  508 , but is translationally retained by the fact that the cup-shaped hollow body  521  defines a portion of a sphere larger than a hemisphere. The abutment between a part  528  of the cup-shaped hollow body  521  proximate the orifice  522  and a part  530  of the spherical head  518  proximate the neck  520  ensures that translational motion is constrained. 
     In an alternative embodiment, a cup-shaped recess may be provided in a lever, the push rod end inserted, and the lever subsequently formed to retain the push rod end, for example, by mechanically deforming the lever. This mechanical deformation may take place using peening. 
     The embodiments shown in  FIGS. 4 to 15  secure a push rod to a lever arm via a “snap fit.” The term “snap fit” is intended to cover connections in which a resilient body deforms during and/or after the assembly process to inhibit subsequent unintentional disassembly (by requiring a predetermined degree of force to disassemble). It should be noted that the “snap fit” enables simple disassembly, although that force required to part the retaining clip and the push rod or lever is substantially higher than the force required to fulfil the function of retaining the components together in use. Additionally, it should be noted that adaptor levers may define a range of angles between the first and second arms, ranging from 0 to 180 degrees. 
     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.