WO2015010155A1

WO2015010155A1 - Self-adjusting calliper

Info

Publication number: WO2015010155A1
Application number: PCT/AU2014/000743
Authority: WO
Inventors: Barry WHITAKER
Original assignee: Custom Fluidpower Pty Ltd
Priority date: 2013-07-23
Filing date: 2014-07-22
Publication date: 2015-01-29
Also published as: AU2014295804B2; AU2014295804A1

Abstract

A self-adjusting caliper (10) includes a housing (12), an actuator rod (20) substantially located within the housing (12) and adapted to apply a brake force against a friction pad (180); the friction pad (180) being locatable adjacent to a brake disc (4DD)f an air gap being located between the friction pad (ISO) and the brake disc (400) when the calliper (10) is in a brake release configuration. The calliper (10) includes a shaft (60) adapted to urge the actuator rod (20) toward the friction pad (180) and an extension mechanism (17) adapted to urge the actuator rod (20) away from the shaft and toward the friction pad. When the air gap exceeds a predetermined size due to wear of the friction pad (180), the extension mechanism (17) resets a location of the actuator rod (20), thereby reducing the air gap, such that the air gap is self adjusting within a range of wear of the friction pad (180).

Description

Self-adjusting calliper

Field of the Invention

The present invention relates to a self-adjusting calliper. In particular, the present invention relates to a self-adjusting brake calliper for use with conveyers, wind turbines, winches, train unloaders, ship loaders and other industrial applications, providing a fail-safe feature.

However, it will be appreciated by those skilled in the art that the self-adjusting calliper can be applied to various other applications.

Background of the Invention

Callipers are used in various brake applications. A calliper is generally used to slow the rotation of a brake disc or other component by applying a frictional force against the rotating disc. The frictional force may be applied by one or more springs. The disc is generally coupled to a shaft, such as an axle.

Conventional brake callipers generally require regular servicing and adjustment. Adjustment is required to ensure that the brake pad maintains the correct spacing from the rotating component, to ensure the correct braking force is maintained, and this parameter changes over time due to various factors, but predominantly as a result of wearing of the brake pad. Servicing and adjustment needs to be conducted by a skilled technician. However, this can result in several potential problems. A first problem is the risk of human error which can result from incorrect adjustment. A further problem is the cost associated with down time, which can be considerable in some industrial applications. This is especially problematic where other machinery in a production line cannot be operated while a component of that line undergoes maintenance.

One problem that is common in brake assemblies is the variability of the brake force applied to the brake disc. As the brake pad wears over time, the brake force applied varies, even within the intended operational range of brake pad wear that occurs between a new pad being fitted and the pad being removed at the end of its service life. This can cause complications for automatic control systems, as the distance that the pad needs to move relative to the rotating disc varies over the life of the brake pad.

Object of the Invention

It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or at least to provide a useful alternative.

Summary of the Invention

In a first aspect, the present invention provides a self-adjusting calliper including:

a housing;

an actuator rod substantially located within the housing and adapted to apply a brake force against a friction pad, the friction pad being beatable adjacent to a brake disc, an air gap being located between the friction pad and the brake disc when the calliper is in a brake release configuration;

a shaft adapted to urge the actuator rod toward the friction pad; and

an extension mechanism adapted to urge the actuator rod away from the shaft and toward the friction pad;

wherein when the air gap exceeds a predetermined size due to wear of the friction pad, the extension mechanism resets a location of the actuator rod, thereby reducing the air gap, such that the air gap is self adjusting within a range of wear of the friction pad.

The extension mechanism preferably includes a collet nut, the collet nut having a first truncated conic surface further wherein the shaft includes a second truncated conic surface, adapted to abut the first truncated conic surface,

a floating sleeve located within the actuator rod, the floating sleeve having a first engagement formation, the nut including a corresponding second engagement formation; wherein the nut is radially retractable to disengage the first and second engagement formations.

The extension mechanism preferably includes a friction ring seated within the housing and frictionally engaged with a side wall of the actuator rod,

wherein a frictional force applied by the friction ring against the actuator rod is smaller than a force applied by a resilient biasing means against the actuator rod.

In a second aspect, the present invention provides a self-adjusting calliper including:

a housing; an actuator rod adapted to apply a force to a friction pad, the actuator rod having a proximal abutment surface and a side wall defining a receptacle, an internal portion of the receptacle having a first engagement formation, the proximal abutment surface extending through a hole formed in the housing;

a nut located within the receptacle, an outer portion of the nut including a

corresponding second engagement formation adapted to engage the first engagement formation,

a shaft having a proximal end adapted to abut against the nut and a distal end, a piston coupled to the shaft;

a first resilient biasing means adapted to urge the actuator rod, nut, shaft and piston toward the friction pad;

wherein the nut is radially retractable to disengage the first and second engagement formations,

further wherein a second resilient biasing means is located in the receptacle between the proximal abutment surface and the nut, the second resilient biasing means being adapted to urge the nut towards the shaft when the first and second engagement formations are disengaged.

In a third aspect, the present invention provides a self-adjusting calliper including:

a housing;

an actuator rod adapted to apply a force to a friction pad, the actuator rod having a proximal abutment surface and a side wall defining a receptacle;

a floating sleeve located within the receptacle, an internal portion of the sleeve having a first engagement formation,

a nut located within the receptacle, an outer portion of the nut including a

a first resilient biasing means adapted to urge the actuator rod, floating sleeve, nut, shaft and piston toward the friction pad;

The first and second engagement formations preferably each include corresponding sawtooth shaped projections.

The nut preferably includes a hole, and a portion of the hole defines a first truncated conic surface, further wherein the shaft proximal end includes a second truncated conic surface, adapted to abut the first truncated conic surface.

The self-adjusting calliper preferably further comprises a friction ring seated within the housing and frictionally engaged with an outer portion of the actuator rod side wall,

wherein a frictional force applied by the friction ring against the actuator rod is smaller than a force applied by the first resilient biasing means against the actuator rod.

The self-adjusting calliper further preferably comprises an abutment element located in the hole formed in the housing, the abutment element adapted to abut against the friction ring to prevent the actuator rod from moving toward the first resilient biasing means.

The nut is preferably divided into a plurality of segments, the segments being radially secured by a torsion spring.

The first resilient biasing means preferably comprises a plurality of belleville springs.

The self-adjusting calliper further preferably comprises one or more oil flow apertures formed in the housing, the oil flow apertures being in fluid communication with a proximal side of the piston for applying a brake release force which operates in a longitudinally opposing direction to a force applied by the first resilient biasing means.

The friction pad is preferably secured to the housing with a plurality of screws, each screw having a friction pad retraction spring adapted to urge the friction pad toward the housing.

The shaft preferably includes a longitudinally extending through hole adapted to receive a rod for locking the actuator rod in a fully extended position.

When the air gap exceeds about 2.5mm, the extension mechanism preferably resets a location of the actuator rod, thereby reducing the air gap to about 1mm. Brief Description of the Drawings

A preferred embodiment of the invention will now be described by way of specific example with reference to the accompanying drawings, in which:

Fig. 1 is a cross-sectional side view depicting a self adjusting calliper;

Fig. 2 is a detail showing a portion a nut and shaft of the self adjusting calliper of Fig. i;

Fig. 3 depicts the calliper of Fig. 1 in a retracted, starting position;

Fig. 4 depicts the calliper of Fig. 1 in a brake applied position;

Fig. 5 depicts the calliper of Fig. 1 in a brake release position;

Fig. 6 is a first end view of a nut of the self adjusting calliper;

Fig. 7 is an opposing, second end view of the nut of Fig. 8;

Fig. 8 is a further embodiment of the self adjusting calliper including a floating sleeve;

Fig. 9 is a partial sectional detail of the portion labelled X in Fig. 8;

Fig. 10 is a front view depicting a self adjusting calliper assembled with a brake disc; and

Fig. 11 is a side view of the self adjusting calliper and brake disc of Fig. 10. Detailed Description of the Preferred Embodiments

Fig. 1 is a cross-sectional view of a self-adjusting brake calliper assembly 10. The brake calliper assembly 10 can be used in applications such as wind turbines, conveyors, winches, train unloaders, ship loaders and other such instances where a rotating mass requires stopping, slowing or speed regulation.

The calliper assembly 10 includes a main housing 12, which houses the internal components of the calliper assembly 10. A circular hole 14 is formed in a proximal, leading end of the main housing 12. The hole 14 is adapted to receive an actuator rod 20. In the embodiment depicted in the drawings, the actuator rod 20 is cup shaped and includes a proximal abutment surface 22, and an annular side wall 24 defining a receptacle. The abutment surface 22 extends partially through the circular hole 14. A first engagement formation 27 is defined by a saw-tooth profile formed on the inner, annular side wall 24 of the actuator rod 20.

The calliper assembly 10 includes a piston 40. The piston 40 has a disc like body 42, and an annular flange 44 which extends into an annular groove located between the annular side wall 24 of the actuator rod 20, and the main housing 12. The piston 40 is seated within a circular recess 46 formed in the trailing side of the main housing 12. The circular recess 46 is coaxial with and in communication with the circular hole 14, but of a larger diameter.

The piston is sealed with two ring seals 50 which provide an oil seal.

The calliper assembly 10 includes a shaft 60. The shaft 60 has a threaded portion 62 which engages with a corresponding threaded hole which is formed in the centre of the piston 40. Accordingly, the shaft 60 and piston 40 are coupled to each other, and move uniformly together along the longitudinal axis XX.

A spring housing 80 is secured to the trailing side of the main housing 12. The spring housing 80 may be secured to the main housing 12 with screws 52, or alternatively with corresponding male and female threaded portions, as depicted in Fig. 1.

An annular void 100 is defined by the inner wall of the spring housing 80 and a trailing portion 64 of the shaft 60. A resilient biasing means in the form of a first spring 120 (or set of springs) is located in the annular void 100. In the embodiment depicted in the drawings, the first spring 120 is provided by a plurality of belleville disc springs 120. However, it will be appreciated that other types of spring such as coil springs may be utilised. The belleville springs 120 provide the braking force.

One or more oil flow apertures 16 are formed in the main housing 12. The oil flow apertures 16 are in fluid communication with a leading face of the piston 40. A force can be applied against the piston 40 by increasing the oil pressure delivered through the oil flow apertures 16. The oil is sealed between the two seals 50. If the force is greater than the spring force applied by the first spring 120, the piston 40 and the shaft 60 translate along the longitudinal axis XX away from the actuator rod 20, to a brake released position.

Alternatively, if the spring force provided by the first spring 120 is greater than the force generated by the oil, the brake is applied. Accordingly, the pressure generated by the oil provides the brake release force.

An adjusting nut or collet nut 140 is located within the actuator rod 20. The adjusting nut 140 is shown in isolation in the end views of Figs 8 and 9, and the adjusting nut 140 can be seen in situ in Fig. 2. The adjusting nut 140 is shown in the detail of Figs. 2 and 8. The nut

140 has an outer circumferential surface which has a second engagement formation 141 in the form of a saw-tooth profile 141, which engages with the first engagement formation 27 defined by the saw-tooth profile 27 formed on the inner, annular side wall 24 of the actuator rod 20.

The corresponding saw-tooth profiles 27, 141 are sized with a pitch of approximately 2mm between teeth. The profile of the teeth is directed such that each tooth has a generally perpendicular surface (which is generally perpendicular to the longitudinal axis XX) and an angled surface which is angled at about 45°. The orientation of the saw-tooth profiles 27,

141 is such that movement of the nut 140 toward the belleville spring 120, parallel to the axis XX results in contact between the angled surfaces. In contrast, movement of the nut 140 away from the belleville spring 120, parallel to the axis XX, is inhibited by meshing of the perpendicular surfaces of the teeth.

The adjusting nut 140 includes a central hole having a step 142, which defines an annular seat 144 which is generally perpendicular to the longitudinal axis XX. A second spring 150 in the form of a coil spring 150 extends between the seat 144 and the engagement surface 22 (or alternatively between the seat 144 and a spring capsule 250 (discussed below)), and urges the nut 140 axially away from the engagement surface 22 along axis XX.

The central hole of the nut 140 includes a first truncated conic surface 146 which engages with a corresponding second truncated conic surface 148 located at or near a leading end of the shaft 60. The two conic surfaces 146, 148 each taper at an angle of about 45°.

As depicted in the embodiment of Fig. 1, the nut 140 has three conic surfaces 146. However, it will be appreciated that the nut may be formed with one, two, four or more conic surfaces 146. This also applies to the shaft 60. In the embodiment of Fig. 1, the shaft 60 has three conic surfaces 148. However, it will be appreciated that the shaft 60 may be formed with one, two, four or more conic surfaces 148.

By adjusting the nut 140 relative to the actuator rod 20, as a result of movement of the nut 140 relative to the actuator rod 20, the first and second truncated conic surfaces 146, 148 (or sets of truncated surfaces) move the shaft towards the belleville springs 120, a direction which is parallel to the longitudinal axis XX.

The nut 140 is manufactured as a single component, and it is subsequently cut into separate segments 143. There are six independent segments 143, which are cut along planes which extend parallel to the longitudinal axis XX. Typically each of the six pieces 143 of the nut 140 are equal in size. However, the nut 140 can be manufactured with a different number of segments such as 3, 4, 5 or more. The nut 140 is able to radially expand or contract, depending the interaction between the first and second truncated conic surfaces 146, 148. It will be appreciated that the nut 140 may also be manufactured by casting or another suitable process.

Two circumferential grooves 147, 149 are formed in the outer wall of the nut 140, best seen in Figs. 1 and 2. The grooves 147, 149 provide a seat for light torsion springs, such as gator springs, which hold the nut segments 143 together.

The calliper assembly 10 includes a brake or friction pad 180. The friction pad 180 is mounted to a backing plate 182 which is located external to the main housing 12. The backing plate 182 being in abutment with the proximal engagement surface 22 of the actuator rod 20. Accordingly, movement of the actuator rod 20 along the longitudinal axis XX, away from the first spring 120, causes the friction pad 180 to also move parallel to the longitudinal axis XX, towards a brake disc.

A plurality of pad 180 retraction screws 200 are secured to the pad 180 and/or backing plate 182 and extend through holes 202 formed in an annular flange 204 located on an outer circumference of the main housing 12. Each pad retraction screw 200 includes a screw head 206. Each retraction screw 200 includes a friction pad retraction springs 210 which is located between the screw head 206 and the flange 204. The retraction springs 210 bias the friction pad 180 and backing plate 182 against the proximal engagement surface 22 of the actuator rod 20.

The operation of the nut 140, the spring 150 the shaft 60, friction ring 212 together provide an automatic extension mechanism 17 once the friction pad has worn down by a predetermined amount, which is typically 2 mm. As depicted in Fig 2, a spring retainer 200 is located within the actuator rod 20. The spring retainer 200 acts to mount the coil spring 150 to the shaft 60. The spring retainer 200 is housed within a spring capsule 250. The spring capsule 250 is best seen in Fig. 2, and sits between the nut 140 and the actuator rod 20. The Spring retainer 200 abuts against a spring plate 252, which is held in position with the spring retainer 200 with a cirdip 254. As best shown in Fig. 2, the coil spring 150 applies a force between the spring capsule 250 and the spring retainer 200.

The shaft 60 is hollow and the spring retainer 200 is also hollow. This permits a rod (not shown) or other such tool to be inserted through the shaft 60 to contact the spring plate 252, to retract the coil spring 150 and in turn collapse the adjusting nut 140 to allow the actuator rod 20 to be retracted i.e. This permits resetting of the self adjusting brake assembly 10.

The assembly may include two proximity switches or sensors 203, 205, located at a trailing end of the shaft 60. One of the switches 203, 205 is used to indicate if the brake is applied or not, and the other of the switches 203, 205 indicates if the friction pad 180 has worn.

The actuator rod 20 is radially seated against a friction ring 212, as shown in Figs. 1 and 3 The friction ring 212 is manufactured from a brass alloy, it is machined to one size initially and then there is a cut made in the diameter that allows it to collapse further as it wears out. There are two springs 213 placed around the friction ring 212 that apply a predefined force to generate the desired amount of resistance between the actuator rod 20 and the friction ring 212.

A cirdip 220 or other such retaining element is located adjacent to the friction ring 212. The cirdip 220 prevents the friction ring 212 from moving axially beyond a certain axial position.

The operation of the calliper assembly 10 will now be described. The belleville springs 120 provide the braking force to urge the friction pad 180 against the object to be slowed or stopped, such as a brake disc 400. In order to release the friction pad 180, oil at a pressure of up to 250 bar enters the oil flow apertures 16 formed in the main housing 12. The oil pressure acting on the piston 40 is larger than the pressure applied by the belleville springs 120. Accordingly, the oil pressure acts to compress the belleville springs 120. As the springs 120 compress, the shaft 60, which is coupled to the piston 40, moves axially along the axis XX, away from the friction pad 180. As this occurs, the retraction springs 210 retract the friction pad 180. The actuator rod 20 is prevented from moving further once the friction ring 212 comes into abutment with the circlip 220.

The calliper assembly 10 includes an extension mechanism 17 which urges the actuator rod 20 away from the shaft 60 and toward the friction pad 180. When the air gap exceeds a predetermined size due to wear of the friction pad 180, the extension mechanism 17 resets a location of the actuator rod 20, thereby reducing the air gap, such that the air gap is self adjusting within a range of wear of the friction pad 180.

When the brake is applied, the oil pressure is permitted to dissipate, by opening a valve in fluid communication with the oil flow apertures 16. The oil pressure returns to zero, or at least significantly less than when the brakes are released. As the oil pressure reduces, the pressure applied by the belleville springs 120 becomes greater than the force applied by the oil. Accordingly, the shaft 60, the nut 140, and actuator rod 20 move parallel to axis XX, against the backing plate 182 of the friction pad 180. The clamping force is determined by the spring force provided by the belleville springs 120.

As the friction pad 180 wears over time, the belleville springs 120 will provide less braking force, around 3 - 6% less force per millimetre of pad wear. Eventually the calliper assembly 10 needs to be adjusted to compensate for this wear factor. The callipers are automatically adjusted back to approximately 1mm of clearance (i.e. air gap between the friction pad 180 and the disc brake 400) when the brakes are not applied. The adjustment is typically conducted when the clearance has reached around 3mm when the brakes are not applied, although this may vary depending on the particular application.

The calliper assembly 10 provides automatic adjustment of the brake clearance. Automatic adjustment preferably occurs when the friction pad 180 has been worn by about 2mm - 2.5mm.

The second truncated conic surface 148 of the shaft 60 is in abutment with the

corresponding nut 140 truncated conic surface 146. As the shaft 60 advances in the direction of the friction pad 180, the segments of the nut 140 are forced to expand radially outwardly. The saw-tooth profile 141 formed on the circumferential outer wall of the nut 140 meshes with the corresponding saw-tooth profile 27 formed on the annular side wall 24 of the actuator rod 20. The meshing ensures that the actuator rod 20 always advances with the shaft 60 when the shaft moves axially toward the friction pad 180.

The belleville springs 120 provide enough force to slide the actuator rod 20 relative to the friction ring 212. However, the pad retraction springs 212 do not provide enough force to push the actuator rod 20 relative to the friction ring 212 in the opposing direction. Therefore the actuator rod 20 can extend freely toward the friction pad 180, but can only retract about 1mm, which is the distance between the friction ring 212 and the circlip 220.

As the friction pad 180 wears down, the actuator rod 20 is forced through the friction ring 212, which is interferingly but not permanently secured to the outer wall of the actuator rod 20. The actuator rod 20 is not coupled to the piston 40. In contrast, the engagement between the shaft 60 and the actuator rod 20 only occurs as the braking force is applied. When the shaft 60 moves in the opposing direction, away from the friction pad 180, the shaft does not also withdraw the actuator rod. As such, the shaft 60 only engages the actuator rod 20 in one direction of movement along the axis XX. When the shaft moves in the opposing direction, back toward the belleville springs 120, the actuator rod 20 is only driven by the backing plate 182 which is pushed by the friction pad retraction springs 210.

However, as the actuator rod 20 retracts, the circlip 220 eventually comes into abutment with the friction ring 212, and this defines the stopping point at which the actuator rod 20 axially stops moving. The. friction ring 212 prevents the actuator rod 20 from retracting more than about 1mm.

Once the wear on the friction pad 180 has reached around 2mm, as the shaft 60 retracts (i.e. moves toward the belleville springs) the spring 150 inside the actuator rod 20 pushes the nut 140 in the same direction, and the gator springs seated on the grooves 147, 149 pull the segments of the nut 140 radially inwardly. As the shaft 60 withdraws, the nut 140 eventually moves on account of the force applied by spring 150. Movement of the nut 140 relative to actuator rod 20 results in meshing of the adjacent set of teeth relative to the actuator rod 20. At this point, the air gap (in the non-applied brake position) between the brake friction pad 180 and the brake disc is reset to approximately 1mm. This process repeats continuously within the range of wear of the friction pad 180, until the friction pad 180 requires replacement.

Different stages of the brake application and wear process are depicted in Figs. 3 to 5. In particular, Fig. 3 depicts a starting position, prior to the friction pad 180 being applied. Fig. 4 depicts the calliper assembly 10 when the brake is applied. Fig. 5 depicts the friction pad 180 being released.

When the pad 180 is worn, then the travel of the piston 40 will be greater than 1mm. In this situation, the brake still functions normally, but the friction ring 212 comes into operation. As previously described, the friction ring 212 allows the actuator rod 20 to pass through as the force from the belleville springs 120 is sufficiently large.

When the brakes are released, the shaft 60 and piston 40 retract due to the hydraulic pressure. As before, the friction pad 180 is withdrawn back by the pad retraction springs 210 which in turn pushes the actuator rod 20 back. The difference now is that the friction ring 212 only allows the actuator rod 20 to retract about 1mm. This is because the force required to slide past the friction ring 212 it is greater than the force applied by the retraction springs 210.

As the shaft 60 and piston 40 move back away from the adjusting nut 140, the adjusting nut is able to radially shrink, and the force applied by the spring 150 causes the nut 140 to move toward the belleville springs 120, and causes the saw-teeth of the nut 140 to shift by one tooth relative to the saw teeth of the actuator rod 20.

Fig. 8 depicts an alternative embodiment of the self-adjusting brake calliper assembly 10. This embodiment is similar to the self-adjusting brake calliper assembly 10 of Figs. 1 and 2. The main difference concerns the inclusion of a floating sleeve or bush 300. The floating sleeve 300 is preferably manufactured from AS4340 high tensile steel or another suitable material. The floating sleeve 300 is fitted within a cylindrical bore formed within the actuator rod 20. The floating sleeve 300 includes a first engagement formation defined by a sawtooth profile 304 formed on an inner, annular side wall of the floating sleeve 300. The sawtooth profile 304 engages with a second engagement formation defined by the saw-tooth profile 141 of the nut 140 as described above. The inclusion of the floating sleeve 300 simplifies the process of installing the adjusting nut 140 within the actuator rod 20. In addition, the floating sleeve 300 distributes the pressure evenly around the nut 140, preventing or at least reducing the likelihood of binding (unintentional locking) of the nut 140 during operation.

The floating sleeve 300 is held in position by a wear spring or washer 310, depicted in Fig. 8.

Fig. 9 discloses a detail of the trailing end of the adjusting brake calliper 10, and in particular the proximity switches or sensors 203, 205.

The self-adjusting brake calliper assembly 10 includes a lockout feature. This enables a technician to change the brake pads in-situ without any risk of the brake unexpectedly moving. The lockout is achieved by removing the sensors and inserting a rod (not shown) through the trailing end of the brake calliper assembly 10, through a central hole 312 formed in the shaft 60. The rod may then be secured to the shaft 60 or the spring housing 80 by a threaded connection. This permits the technician to lock the brake calliper assembly 10 at a desired location, thereby preventing the calliper assembly 10 from retracting the brake.

Fig. 10 is a front view depicting a self adjusting calliper assembled with a brake disc 400 and Fig. 11 is a side view of the self adjusting calliper and brake disc 400 of Fig. 10. As shown in Fig. 11, the air gap located between the friction pad 180 and the brake disc 400 is approximately initially 1mm when the calliper is in a brake release configuration. Once the friction pad 180 wears to a predetermined amount, typically when the air gap reaches about 2mm - 2.5mm, then resetting occurs, thereby reducing the air gap back to approximately 1 mm.

Advantageously, the self-adjusting brake calliper assembly 10 increases the time frame between required servicing/maintenance shut-downs. This typically results in both time and cost savings.

Although the invention has been described, with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

The claims defining the invention are as follows:

1. A self-adjusting calliper including:

a housing;

an actuator rod substantially located within the housing and adapted to apply a brake force against a friction pad, the friction pad being locatable adjacent to a brake disc, an air gap being located between the friction pad and the brake disc when the calliper is in a brake release configuration;

a shaft adapted to urge the actuator rod toward the friction pad; and

2. The self adjusting calliper of claim 1, wherein the extension mechanism includes a collet nut, the collet nut having a first truncated conic surface further wherein the shaft includes a second truncated conic surface, adapted to abut the first truncated conic surface,

3. The self adjusting calliper of claim 2, wherein the extension mechanism includes a friction ring seated within the housing and frictionally engaged with a side wall of the actuator rod,

4. A self-adjusting calliper including:

a housing;

an actuator rod adapted to apply a force to a friction pad, the actuator rod having a proximal abutment surface and a side wall defining a receptacle, an internal portion of the receptacle having a first engagement formation, the proximal abutment surface extending through a hole formed in the housing;

a nut located within the receptacle, an outer portion of the nut including a

5. A self-adjusting calliper including:

a housing;

a nut located within the receptacle, an outer portion of the nut including a

wherein the nut is radially retractable to disengage the first and second engagement formations, further wherein a second resilient biasing means is located in the receptacle between the proximal abutment surface and the nut, the second resilient biasing means being adapted to urge the nut towards the shaft when the first and second engagement formations are disengaged.

6. The self-adjusting calliper of claim 4 or 5, wherein the first and second engagement formations each include corresponding saw-tooth shaped projections.

7. The self-adjusting calliper of any one of claims 4 to 6, wherein the nut includes a hole, and a portion of the hole defines a first truncated conic surface, further wherein the shaft proximal end includes a second truncated conic surface, adapted to abut the first truncated conic surface.

8. The self-adjusting calliper of any one of claims 4 to 7, further comprising a friction ring seated within the housing and frictionally engaged with an outer portion of the actuator rod side wall,

9. The self-adjusting calliper of claim 8, further comprising an abutment element located in the hole formed in the housing, the abutment element adapted to abut against the friction ring to prevent the actuator rod from moving toward the first resilient biasing means.

10. The self-adjusting calliper of any one of claims 4 to 9 wherein the nut is divided into a plurality of segments, the segments being radially secured by a torsion spring.

11. The self-adjusting calliper of any one of claims 4 to 10 wherein the first resilient biasing means comprises a plurality of belleville springs.

12. The self-adjusting calliper of any one of claims 4 to 11 further comprising one or more oil flow apertures formed in the housing, the oil flow apertures being in fluid communication with a proximal side of the piston for applying a brake release force which operates in a longitudinally opposing direction to a force applied by the first resilient biasing means.

13. The self-adjusting calliper of any one of claims 4 to 12, wherein the friction pad is secured to the housing with a plurality of screws, each screw having a friction pad retraction spring adapted to urge the friction pad toward the housing.

14. The self-adjusting calliper of any one of claims 4 to 13, wherein the shaft includes a longitudinally extending through hole adapted to receive a rod for locking the actuator rod in a fully extended position.

15. The self-adjusting calliper of any one of claims 1 to 3, wherein when the air gap exceeds about 2.5mm, the extension mechanism resets a location of the actuator rod, thereby reducing the air gap to about 1mm.