The present invention relates to a brake assembly for slowing the rotational speed of a rotating component, such as a wheel. In particular, but not exclusively, the present invention relates to a brake assembly for automatically stopping a rail trolley.

A conventional rail trolley typically includes a load bed supported on four wheels for transporting material, plant and/or equipment from one location to another along a pair of spaced apart rails, e.g. a train track. The rail trolley typically includes a brake system comprising a removable handle which is manually-operated to urge a pair of brake pads away from their respective wheels to allow the trolley to freely roll along the track. The brake pads are spring-loaded to be urged against their respective wheels when the handle is not inserted to therefore apply a braking force to the two wheels as a default ‘fail-safe’ function.

However, this type of conventional brake system is susceptible to misuse, such as using a tubular pipe or the like for the brake-release handle which is not suitable for use on the rail trolley and adversely compromises the fail-safe function of the brake system in view of its excessive weight overcoming the spring force. Furthermore, the handle can easily be tied or the like in the ‘brake off position which can result in a runaway event. A number of unintentional runaway events have occurred as a result of such conventional brake systems being abused or failing which have resulted in significant damage, injuries and/or fatalities.

It is an aim of certain embodiments of the present invention to provide a brake assembly which automatically applies a braking force to a rotating component, such as a wheel, without any interaction from a person.

It is an aim of certain embodiments of the present invention to provide a brake assembly for automatically applying a braking force to a rotating component, such as a wheel, at a predetermined rotational speed of the component.

It is an aim of certain embodiments of the present invention to provide a brake assembly for automatically applying a braking force to a rotating component, such as a wheel, at a predetermined rotational speed of the component, and which is adjustable in terms of the rotational speed at which the braking force is applied to the rotating component.

It is an aim of certain embodiments of the present invention to provide a brake assembly for retrofitting to an existing rotational component, such as the hub of a wheel.

It is an aim of certain embodiments of the present invention to provide a brake system for a rail trolley which is less susceptible to misuse and/or abuse than conventional brake systems.

According to a first aspect of the present invention there is provided a brake assembly for reducing the rotational speed of a rotatable component, comprising: a brake drum member mounted on a shaft; at least one brake element axially moveable on the shaft and engageable with the brake drum member when in a brake engaged position; and a brake actuator configured to move the at least one brake element towards the brake engaged position responsive to a predetermined threshold rotational speed of the brake drum member or the shaft.

Optionally, the brake actuator comprises an axially moveable member mounted on the shaft configured to be disengaged from the at least one brake element when in a first axial position with respect to the shaft and engaged with the at least one brake element to apply an axial braking force thereto when in a second axial position with respect to the shaft.

Optionally, the brake actuator is configured to axially constrain the moveable member when in the first axial position.

Optionally, the movable member is selectively rotatable with respect to the shaft from a first rotational position corresponding to the first axial position to a second rotational position corresponding to the second axial position. Optionally, the brake actuator comprises at least one resilient element to axially urge the movable member towards the second axial position.

Optionally, the brake actuator comprises a trigger to rotationally urge the movable member from the first rotational position towards the second rotational position responsive to the predetermined threshold rotational speed.

Optionally, the trigger comprises a centrifugal element coupled to a rotatable carrier member and configured to move radially outwardly from a retracted position to a deployed position when subjected to a centrifugal force corresponding to the predetermined threshold rotational speed and engage an engagement surface of the movable member when in the deployed position to rotationally urge the movable member towards the second rotational position.

Optionally, the centrifugal element comprises an undercut region to define a tooth portion for positive engagement with the engagement surface of the moveable member.

Optionally, the centrifugal element is coupled to the carrier member by a screw and a spring is located between the screw and the centrifugal element.

Optionally, the carrier member is fixed to the brake drum member or the shaft.

Optionally, the shaft comprises at least one first engagement region to engage with a corresponding second engagement region associated with the movable member to axially and rotationally retain the same in the first axial position and the first rotational position.

Optionally, the first engagement region comprises at least one recess or projection and the second engagement region comprises at least one projection or recess.

Optionally, the first engagement region comprises a recessed surface for receiving a projection associated with the moveable member and at least one curved cam surface to guide the projection towards the recessed surface and to urge the moveable member from the second axial position to the first axial position when moved from the second rotational position to the first rotational position.

Optionally, the recessed surface is disposed between a pair of curved cam surfaces arranged in opposed rotational directions to each other with respect to an axis of the shaft.

Optionally, the second engagement region comprises at least one radially oriented and inwardly extending elongate member mounted to the movable member.

Optionally, the at least one elongate member comprises a plurality of circumferentially and equally spaced pins.

Optionally, the at least one brake element comprises a plurality of friction plates supported on the shaft.

Optionally, the friction plates are rotationally unconstrained with respect to the shaft.

According to a second aspect of the present invention there is provided a vehicle comprising a plurality of wheels and at least one brake assembly according to the first aspect of the present invention coupled to a one of the wheels.

Optionally, the one of the wheels comprises the brake drum member.

Optionally, the vehicle is a rail trolley.

According to a third aspect of the present invention there is provided a method of reducing the rotational speed of a rotatable component, comprising: axially moving at least one brake element towards a brake engaged position to engage a brake drum member mounted on a shaft responsive to a predetermined threshold rotational speed of the brake drum member or the shaft. Optionally, the method comprises axially moving a moveable member along the shaft from a first axial position to a second axial position to engage the at least one brake element and apply an axial braking force thereto.

Optionally, the method comprises axially urging the moveable member towards the second axial position by at least one resilient element.

Optionally, the method comprises axially constraining the moveable member in the first axial position wherein the moveable member is disengaged from the at least one brake element.

Optionally, the method comprises urging the movable member from a first rotational position corresponding to the first axial position on the shaft towards a second rotational position corresponding to the second axial position on the shaft responsive to the predetermined threshold rotational speed.

Optionally, the method comprises: radially deploying a centrifugal element coupled to a rotational carrier member when subjected to a centrifugal force corresponding to the predetermined threshold rotational speed; engaging the centrifugal element with an engagement surface associated with the moveable member; and rotationally urging the movable member from the first rotational position towards the second rotational position.

Optionally, the method comprises: moving the moveable member from the second rotational position to the first rotational position; guiding a projection associated with the moveable member along a cam surface towards a recessed surface associated with the shaft; urging the moveable member from the second axial position to the first axial position; and receiving the projection in the recessed surface to retain the moveable member in the first axial position and the first rotational position wherein the at least one brake element is in a brake disengaged position.

Description of the Drawings

Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an exploded isometric view of a brake assembly according to certain embodiments of the present invention;

Figure 2 illustrates a cross section through the brake assembly of Figure 1 when in an assembled state; and

Figure 3 illustrates the cam profiles on the end face of the splined portion of the shaft of the brake assembly of Figures 1 and 2.

Detailed Description

As illustrated in Figure 1 , a brake assembly 100 according to certain embodiments of the present invention includes a wheel 102 of, for example, a rail trolley, wherein the wheel is rotatably mounted at a hub region 104 thereof on the first end region 108 of a shaft 106. A first bearing 110 is provided between the shaft and the wheel hub at the first end region to aid rotation of the wheel with respect to the shaft. The first bearing 110 is aptly a deep groove ball bearing and the races thereof are axially constrained between a shoulder of the shaft and a shoulder of the wheel hub and respective circlips 116,118. Alternatively, the first bearing may be a roller bearing, thrust bearing, or the like, based on the technical application for the brake assembly.

An elongate splined portion 120 is provided between the first end region 108 and a second end region 122 of the shaft 106. The splined portion 120 of the shaft has a diameter which is greater than a diameter of the first and second end regions of the shaft. A plurality of brake elements 124 are mounted on the splined portion of the shaft 106, wherein each brake element has a substantially circular outer edge profile and has a central circular aperture to thereby define each brake element as an annulus or ring-shaped. The stack of brake elements 124 in the illustrated embodiment comprises nine friction plates and eight steel plates alternately arranged with respect to each other. The inner edge defined by the central aperture of the steel plates includes a plurality of circumferentially arranged teeth for corresponding engagement with the elongate teeth of the splined portion 120 such that the steel plates are constrained rotationally with respect to the stationary shaft but can move axially along the splined portion. The friction plates have a substantially continuous inner edge, i.e. the central aperture does not include teeth for engagement with the splined portion 120 of the shaft, and which is sized to allow the friction plates to rotate about, and axially translate along, the splined portion of the shaft. The outer edge of each friction plate has a plurality of spaced apart and outwardly extending lobed regions 125 for locating in corresponding regions of the wheel such that they rotate with the wheel and about the stationary shaft. During a braking operation, as described further below, the stack of brake elements 124 is compressed such that the friction plates are urged against the stationary steel plates to apply a rotational braking force to the rotating wheel. Instead of a splined portion on the shaft having multiple elongate projections, the steel plates may include at least one slot in their inner edge for engagement with at least one elongate projection extending along a portion of the shaft.

A substantially circular pressure plate member 126 having a central aperture is mounted on the shaft 106 between the splined portion 120 and the second end region 122. A plain bearing 121 is provided to aid rotation of the pressure plate member 126 on the shaft. The pressure plate member 126 includes a base portion 128 having an annular projecting region 130 extending towards the first end region 108 of the shaft 106 which provides an engagement surface 132 for engagement with the first brake element in the stack of brake element 124 mounted on the splined portion 120 of the shaft 106. The pressure plate member 126 is a moveable member which is automatically rotational and translatable with respect to the shaft to automatically apply the brake, as described below. As illustrated in Figure 1 , three circumferentially spaced pins 134 extend radially inwardly from the annular projecting region 130 of the pressure plate member 126. The free ends of the pins are spaced from the outer surface of the shaft 106. The side surface of each of these pins is engageable in a recessed surface 138 (see Figure 3) defined by a respective one of three engagement regions 136 disposed on an end face of the splined portion 120 of the shaft 106.

As illustrated in Figure 3, each engagement region 136 includes a pair of curved cam/ramp surfaces 140,142 arranged in opposed rotational directions to each other and the recessed surface 138 is disposed therebetween which is sized and shaped to at least partially accommodate one of the pins 134. The depth of the recessed surfaces 138 at least partially dictates the rotational force required to urge each pin 134 from the recessed surface 138 and rotate the pressure plate member 126, as described further below.

The pressure plate member 126 further includes an annular wall portion 144 extending from the base portion 128 towards the second end region 122 of the shaft 106 to define an interior space 146 at a second end region of the pressure plate member, wherein the annular projecting region 130 defines a first end region of the pressure plate member. As illustrated in Figure 2, a catch element 148 extends radially inwardly from the annular wall portion 144 into the interior space 146. The catch element 148 may be an integrally formed or machined projection, a pin, a countersink screwhead, or the like.

A substantially circular carrier plate member 150 is rotatably mounted on the second end region 108 of the shaft 106. A radially extending flange member 151 of the carrier plate member 150 is fixed to the inner face 152 of the wheel 102 by a plurality of fasteners 154, such as hex bolts, which locate through respective holes 155 in the flange portion 151. A second bearing 156 is provided between the shaft 106 and the carrier plate member 150 to aid rotation thereof with the wheel with respect to the shaft. The second bearing 156 is aptly a deep groove ball bearing and is axially constrained between a shoulder of the carrier plate member 150 and a circlip 160. Alternatively, the second bearing may be a roller bearing, thrust bearing, or the like, based on the technical application for the brake assembly.

A hub portion 164 of the carrier plate member 150 extends axially from the flange portion 151 towards the first end of the shaft 106. The hub portion 164 has an outer diameter which is less than an inner diameter of the annular wall portion 144 of the pressure plate member 126 to thereby allow the hub portion 164 to partially extend into the interior space 146 of the pressure plate member 126.

A centrifugal element 166 is mounted in a recess extending radially into the outer surface of the hub portion 164. The base of the recess includes a threaded bore.

The centrifugal element 166 includes a through bore 168 and is coupled to the hub portion 164 by a screw 170 engaged in the threaded bore. A compression coil spring 172 is located between the head of the screw 170 and a shoulder in the through bore 168 of the centrifugal element 166 to thereby urge the centrifugal element radially inwardly towards the hub portion 164. The centrifugal element 166 is urged against the base of the recess in the hub portion 164 by the spring 172 when the carrier plate member 150, and in turn the centrifugal element 166, are not rotating about the shaft 106, or when the spring force of the spring 172 has not been overcome by a centrifugal force acting on the centrifugal element 166 when the carrier plate member 150 and the centrifugal element 166 are rotating about the shaft 106. The centrifugal element 166 is in a retracted position when urged against the hub portion 164 by the spring 172.

The centrifugal element 166 includes a main portion 174 for accommodating the screw 170 and spring 172, and an engagement portion 176 defining a curved outer surface 178 having a radius which is less than the main portion 174 and substantially equal to a diameter of the outer surface of the hub portion 164. The reduced outer radius of the engagement portion 176 of the centrifugal element 166 allows the same to rotate within the interior space 146 of the pressure plate member 126 without engaging with the catch element 148 when the centrifugal element 166 is in the retracted position. The engagement portion 176 has an undercut region in each of its leading and trailing surfaces relative to a direction of rotation to define a tooth/hook portion for positive engagement with the catch element 148 of the pressure plate member 126.

The mass of the centrifugal element 166 and the spring force of the spring 172 determine at what rotational speed the centrifugal element will move from the retracted position to a deployed position. Therefore, the size of the main portion, for example, of the centrifugal element may be configured to obtain a desired mass of the centrifugal element relating to a desired rotational speed at which the centrifugal element moves from the retracted position towards the deployed position. As such, the centrifugal element 166 may be selected from a plurality of differently configured centrifugal elements having different masses based on a desired threshold rotational speed at which the centrifugal element moves from the retracted position towards the deployed position. Alternatively, or additionally, the spring 172 may be selected from a plurality of differently configured springs having different spring rates based on a desired threshold rotational speed at which the centrifugal element moves from the retracted position towards the deployed position. Furthermore, the screw 170 may be selectively adjusted to adjust the spring rate of the spring and in turn the threshold rotational speed at which the centrifugal element moves from the retracted position towards the deployed position.

As illustrated in Figure 2, an annular recess 180 is provided in the base of the interior space 146 of the hub portion 164 of the pressure plate member 126. A plurality of washers 182, including a thrust needle bearing located between a pair of plane washers, provide an annular support surface in the carrier plate member 150. The first ends of each of plurality of circumferentially spaced apart compression coil springs 186 are located in the annular recess 180 of the pressure plate member 126 and the second ends of the springs are located on the washers 182 mounted in the carrier plate member 150 such that compression springs 186 are disposed between the pressure plate member and the carrier plate member. The springs 186 urge the pressure plate member 126 axially away from the carrier plate member 150 and towards the stack of brake elements 124. The thrust bearing arrangement (the plane flat washers and the thrust needle bearing) withstands the thrust load from the compression springs and allows the wheel to rotate when the springs and pressure plate member are static before the device is triggered, as described further below. In normal use, i.e. when the brake is disengaged from the wheel, the pressure plate member 126 is in a rotational position such that each of the radial pins 134 is aligned with and engaged in the recessed surface 138 of a corresponding one of the engagement regions 136 provided on the end face of the splined portion 120 of the shaft 106. At least one hole or recess 188 may be provided in the annular wall portion 144 of the pressure plate member 126 to allow a tool, such as a lever, rod, screwdriver or the like, to extend through a slot (not shown) in the wheel and engage in the hole 188 to rotate the pressure plate member 126 and force each of the pins 134 up one of the curved cam surfaces 140,142 and into the recessed surface 138 of a respective one of the engagement regions 136. As each pin 134 is forced up the cam surface 140,142, the pressure plate member 126 is urged towards the carrier plate member 150 to thereby compress the compression springs 186. The brake assembly is now reset in a disengaged state. The cam surface/s 140,142 may be configured based on a desired axial distance of the pressure plate member to compress the springs when in the assembly in the brake disengaged state and/or a desired braking rate, i.e. the rate at which the pressure plate axially moves and compresses the stack of brake elements to apply the braking force to the wheel.

Aptly, a plurality of circumferentially spaced apart holes in the outer wall of the pressure plate member and a single through slot extending partially around the wheel, such as by around 45-90 degrees, would be provided to allow the brake assembly to be always capable of being reset irrespective of the rotational position of the pressure plate member. Alternatively, it may be desirable not to have means for the brake assembly to be reset after the same has been automatically actuated. For example, a resettable brake assembly may be reset by an unauthorised person.

The reduction in length of each compressed spring 186 equals the axial distance between the base of each recessed surface 138 and the end of the splined portion 120. The end face of the annular projecting region 130 of the pressure plate member 126 is spaced from the stack of brake elements 124 when in this ‘brake off position. The pressure plate member 126 is securely held rotationally and axially in the ‘brake off position by the pins 134, recessed surfaces 138 and compression springs 186 arrangement which is where it will remain during normal use of the rail trolley until emergency braking of the wheel is required by the brake assembly, such as in a runaway rail trolley situation.

When the rotational speed of the wheel 102, and in turn the carrier plate member 150, remains under a predetermined threshold rotational speed, such as around 265rpm for a wheel diameter (of the ‘working’ portion of the wheel engaged with the track) of around 160mm, which corresponds to a trolley speed along the track of, for example, around 8 km/h, the centrifugal element 166 will remain in the retracted position and rotate freely without engaging the catch element 148. For a wheel diameter of around 240mm, the predetermined threshold rotational speed is around 177rpm corresponding to a trolley speed along the track of around 8 km/h. The wheel will be free to rotate at speeds below the predetermined threshold rotational speed without the centrifugal element 166 being deployed and engaging the catch element 148 and in turn a braking force being applied. However, when the trolley speed along the track exceeds a predetermined track speed, and in turn the rotational speed of the wheel and the carrier plate member 150 reaches or exceeds the predetermined threshold rotational speed, the centrifugal force acting on the centrifugal element 166 will overcome the spring force of the compression spring 172 which otherwise urges the centrifugal element radially inwardly. The centrifugal element 166 will thus be forced radially outwardly by the centrifugal force acting thereon and will engage with the catch element 148 extending radially inwardly from the annular wall portion 144 of the pressure plate member 126. To ensure a positive engagement between the centrifugal element and the catch element, each element is aptly configured to interlock with each other, e.g. by way of an undercut or tooth like region on each element.

Positive engagement of the rotating centrifugal element 166 with the catch element 148 forces the pressure plate member 126 to rotate in the same direction as the carrier plate member 150 and the wheel 102. This rotational force applied to the pressure plate member 126 forces the radial pins 134 out of their respective recessed surfaces 138 and down one of the cam surfaces 140,142 dependent on the direction of rotation. The compression springs 186 acting on the pressure plate member 126 urge the pins down the cam surfaces and the pressure plate member axially towards the stack of brake elements 124. The pressure plate member 126 is axially moved along the shaft until the pins 134 engage the end face of the splined portion 120 of the shaft 106 and/or the pressure plate member engages the first brake element (a first one of the steel plates) in the stack of brake elements 124.

The compression springs 186 are configured to apply an axial force on the pressure plate member 126 to compress the stack of brake elements 124 together and against the hub portion 104 of the wheel 102 to rapidly and efficiently reduce the rotational speed of the wheel and in turn safely bring the trolley to a standstill within a safe distance. The wheel effectively acts like a brake drum. The centrifugal element 166 and the catch element 148 remain engaged during the braking operation. Alternatively, the axial distance may be sufficient for the catch element 148 to move axially away from and clear the rotating centrifugal element 166. Aptly, the brake assembly brings the rail trolley to a standstill within a distance of around 10m on a dry rail and around 14m on a wet rail on a gradient of around 4%.

Alternative embodiments can be envisaged without departing from the crux of the present invention. For example, the pressure plate member 126 may comprise at least one pin or other suitable projection which is engageable with a single engagement region or one of a plurality of engagement regions provided on the end face of the splined portion 120 or on the shaft itself. Alternatively, the pressure plate member may comprise at least one recess which is engageable with at least one projection on the shaft to provide the axial and rotational retainment when the pressure plate member is in the first axial and rotational position. Furthermore, the pressure plate member 126 may comprise a projection, such as a key, and the shaft may include a circumferential flange having a slot therein. During normal use, the key abuts the flange until the centrifugal element engages with catch element and the pressure plate member is rotated to align the key with the slot. At this point, the key is allowed to move through the slot and the compression springs acting on the pressure plate member move the same axially towards the brake elements to compress the same and apply a braking action to the wheel.

Alternatively, or additionally, the centrifugal ‘trigger’ element may take a different form to that described above and illustrated herein. For example, the centrifugal element comprise a lever element pivotally mounted at one end to the carrier plate member and urged towards a retracted position by a torsion spring or the like. When the centrifugal force acting on the centrifugal element exceeds the spring force of the torsion spring, the centrifugal element is rotated outwardly about the pivot axis towards the deployed position at which point it engages the catch element on the pressure plate member. Two centrifugal elements of this configuration would be required in opposed orientation if automatic braking in an emergency event was desired in both rotational directions. The pivot pin would also need to be relatively strong to withstand the impact force when the lever engages with the catch element. The centrifugal element as described above and illustrated herein desirably deploys in both rotational directions and forces acting on the centrifugal element during engagement with the catch element are transferred through the hub portion of the carrier plate member.

In an alternative embodiment of the present invention, the rotatable component requiring braking may be the shaft. In this embodiment, a rotationally fixed brake drum member (equivalent to the wheel of the embodiment described above and illustrated) is mounted to the first end region of the shaft and the carrier plate member is fixed to the second end region of the shaft to rotate therewith. In a normal state of operation, the axially moveable pressure plate member is stationary with respect to the rotating shaft, but when a rotational speed of the shaft and the carrier plate member exceeds a predetermined threshold rotational speed, the centrifugal element is deployed and engages with the catch element of the pressure plate member. The pressure plate member is then forced to rotate such that the radial pins are forced out of their respective recessed surfaces and down the cam surfaces to allow the pressure plate member to be urged axially towards the brake elements by the compression springs. The brake elements are compressed and engage an inner surface of the brake drum member by the action of the pressure plate member and compression springs, and in turn a rotational speed of the shaft is reduced until stationary. The rotating shaft in this alternative embodiment may be coupled by suitable means, such as a chain or belt or gears, or the like, to a rotational drive member, such as a wheel, roller, gear or the like.

The trolley wheel is aptly a metal material, such as an aluminium or steel alloy. The shaft, the pressure plate member and the carrier plate member are aptly a suitable steel material. As an example, the guide flange portion of the wheel may have an outer diameter of around 310mm, the splined shaft may have an outer diameter of around 48mm, the pressure plate member may have an outer diameter of around 108mm, the centrifugal element may have a mass of around 90g. Certain embodiments of the present invention therefore provide a brake assembly for a rail trolley wheel which is configured to automatically apply a braking force to the wheel in an emergency event. The brake assembly is non-complex and easy to maintain. It is not affected by vibrations subject thereon in use and is tamperproof. The brake assembly can be assembled with, or retrofitted to, a wheel of a rail trolley or other rotating components, such as wheels of other vehicles, conveyor pulleys or rollers, abseiling or fall protection equipment, devices for controlled acceleration or deceleration, winches, hoists, cranes, or the like, which may require automatic braking when the rotational speed of the rotating component exceeds a predetermined threshold. The brake assembly is selectively adjustable in terms of the rotational speed of the rotating component at which a braking force is to be applied to the rotating component.