BACKGROUND OF THE INVENTION A conventional drum brake system comprises a brake drum having an inner circumferential surface and a pair of brake shoes each provided with a lining of friction material which faces the inner circumferential surface of the brake drum. The brake shoes are rotationally fixed and pivotally coupled at one end to a stationery support.

A single double-acting piston is located between the adjacent ends of the brake shoes opposite the pivotally coupled ends. When the piston is activated, the brake shoes are pivoted towards the braking surface of the brake drum.

The park brake of a conventional drum brake system generally comprises a lever coupled between the brake shoes and attached at one end to a cable, an opposite end of the cable is attached to a hand or foot operated park brake actuator located within the cabin of a vehicle.

When the actuator is pulled or depressed, the lever forces the brake shoes apart to provide a park or emergency brake effect.

SUMMARY OF THE INVENTION According to the present invention there is provided a drum brake system with an integrated park brake comprising: a brake drum having an inner circumferential surface;

at least one brake shoe having an outer circumferential surface facing the inner circumferential surface; a layer of friction material attached to one of the inner and outer circumferential surfaces, a remaining one of the inner and outer circumferential surfaces forming a braking surface; a service brake actuator having an applied state in which the service brake actuator moves the at least one brake shoe towards the inner circumferential surface and holds the braking surface against the friction material, and an unapplied state where the service brake actuator allows the at least one brake shoe to move away from the inner circumferential surface; and, a park brake having an ON state which, when the service brake actuator is in said applied state, holds the braking surface against the friction surface whereby when the service brake actuator is in a subsequent unapplied state, the park brake maintains the braking surface against the friction surface to provide a park brake effect.

Optionally the park brake comprises at least one member for engaging each of the at least one brake shoe and a park brake actuator associated with the at least one member the park brake actuator causing engagement of the at least one member with a corresponding brake shoe when the park brake is in an ON state and disengagement of the at least one member with a corresponding shoe when the park brake is in an OFF state.

Optionally the park brake actuator comprises an electrically operated device.

Optionally the electrically operated device comprises a solenoid having a movable core wherein each member comprises or is attached to a corresponding core, and bias

means for biasing each member in a manner to hold or urge the braking surface against or towards the friction surface when said solenoid is de-energised corresponding to the park brake being in the ON state, each member being held by its core against the bias means in a position enabling the braking surface to be spaced from the friction surface when the solenoid is energised corresponding to the park brake being in the OFF state.

Each member may comprise a tapered end that engages a corresponding brake shoe when the park brake is in the ON state.

In one embodiment the park brake comprises two of the members for each brake shoe.

Optionally each of the brake shoes comprises an axially extending post for engagement with the member.

Optionally each post is provided with a hole or recess in which the tapered end is received when the park brake is in the ON state.

Optionally each of the brake shoes is mounted to lineally slide towards the inner circumferential surface when acted upon by the service brake actuator.

Optionally the friction material is attached to the inner circumferential surface of the brake drum.

In one embodiment the friction material comprises a plurality of pads of friction material disposed about the inner circumferential surface.

Optionally the pads are circumferentially spaced.

However in an alternate embodiment, the friction material comprises a single ring of friction material attached to the inner circumferential surface.

Optionally a surface of the friction material facing the braking surface is provided with a plurality of grooves.

Optionally the said grooves open onto axially opposite edges of said friction material.

The grooves may follow a spiroidal path.

Optionally the service brake actuator operates substantially simultaneously at two diametrically opposed locations on each of the brake shoes.

Optionally each brake shoe is provided with a fluid inlet, a fluid outlet, and one or more internal fluid flow paths in fluid communication between the fluid inlet and the fluid outlet and extending beneath at least a portion of the braking surface through which a cooling fluid flows.

According to the present invention there is further provided a wet drum brake system comprising: a substantially sealed housing; a drum brake system with integrated park brake in accordance with the first aspect of the present invention; the substantially sealed housing encasing the brake drum, brake shoes and service brake actuator; and, a volume of lubricating liquid retained within the housing.

According to the present invention there is further provided a park brake for a drum brake system having one

or more brake shoes adapted for motion toward and away from an adjacent surface of a brake drum, the park brake comprising : at least one solenoid having a coil and a moveable core, the core coupled to one of said brake shoes, said solenoid arranged so that when in an energised or ON state, a magnetic field created by said coil acts on said core to urge said one of said brake shoes toward said adjacent surface or said brake drum.

According to the present invention there is further provided a park brake for a drum brake system having one or more brake shoes adapted for motion toward and away from an adjacent surface of a brake drum, said park brake comprising: at least one solenoid having a coil, a moveable core and bias means acting on said core, said core coupled to one of said brake shoes, said solenoid arranged so that: when in an energised or ON state, a magnetic field created by said coil acts on said core and against said bias means to allow said brake shoes to move away from said adjacent surface of said brake drum; and when in a de-energised or OFF state said magnetic field ceases to exist and said bias means acts on said core to urge said one of said brake shoes toward said adjacent surface of said brake drum.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation showing the section view from the side of an embodiment of the drum brake

system with integrated park brake in accordance with the present invention; Figure 2 is a plan view of the drum brake system depicted in Figure 1 with a cover of an associated housing removed; Figure 3 is a plan view of the brake shoes incorporated in the drum brake system depicted in Figures 1 and 2; and, Figure 4 is a view of section A-A of a shoe depicted in Figure 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Figures 1 and 2 depict an embodiment of a drum brake system 10 with an integrated park brake. In this particular embodiment the drum brake system 10 is in the form of a wet brake system although as will be explained in greater detail below, embodiments of the present invention are equally applicable to a dry drum brake system. The drum brake system 10 comprises a brake drum 12, brake shoes 14, and a service brake actuator in the form of hydraulic pistons 16. The brake shoes 14 have an outer circumferential surface 18 which faces an inner circumferential surface 20 of the drum 12. A layer of friction material 22 is attached to the inner circumferential surface 20 of the drum 12. The surface 18 constitutes a braking surface 18, while the surface of the friction material provides a friction surface 23. In this particular embodiment, the friction material 22 is in the form of a continuous ring or annulus of friction material which is attached to the inner circumferential surface 20.

The general form of the drum brake system 10 is the same as that described in Applicants corresponding International application No. PCT/AU2004/001159 the contents of which is incorporated herein by way of

reference. Specifically, the shoes 14 are arranged to slide lineally toward and away from a facing portion of the drum 12 rather than pivot at one end as is the case with conventional drum brake systems. In order to facilitate this sliding motion, each shoe 14 is provided with a pair of elongate slots 24 on their respective support webs 26 through which respective pins 28 extend.

The pins 28 are screwed into or otherwise attached to a stationery component or member of the drum brake system 10. The pins 28 are typically provided with flat heads or intermediate transverse flanges which prevent the shoes 14 from lifting. The pistons 16 act between the adjacent opposite ends of the shoes 14 causing them to slide away from each other and into contact with the drum 12 when an associated brake pedal is depressed.

Tension springs 30 are provided with hooks 32 at the opposite ends which engage respective pins 34 extending from the webs 26 of each shoe 14. The tension springs 30 bias the shoes 14 so as to move toward each other and away from the inner circumferential surface 18 of the drum 12.

Thus when the service brake is not applied, the tension springs 30 effectively retract the shoes 14 from contact with the friction material 22.

A park brake 36 is incorporated in the system 10 having an OFF state which, when the service brake actuator (i. e. pistons 16) is in an applied state holds the braking surface 18 against the friction surface 23 so that when the service brake actuator is subsequently released or placed in an unapplied state, the park brake 36 maintains the braking surface 18 against the friction surface 23 to provide a park brake effect.

The park brake 36 comprises, for each shoe 14, two members 38 which engage each shoe 14 and associated park brake actuators in the form of solenoids 40. Each member 38

comprises a pin 42 with a tapered head 44 which is seated in corresponding posts 46 that extend axially from the webs 26 of the corresponding shoes 14. The pins 42 may be directly fixed to a sliding core (not shown) of a corresponding solenoid 40. The solenoid also comprises a bias means in the form of a solenoid spring (not shown) that acts to urge the members 38 to push the braking surface 18 (ie brake shoe 14) toward the friction surface 23 when the solenoid is de-energised, which corresponds to the park brake 36 being in the ON state. Thus in the event of a loss of electrical power the park brake 36 will be automatically deployed. When the solenoid is energised (corresponding to the park brake 36 being OFF) the bias means is held by the core of the solenoid allowing the braking surface 36 to be spaced or pulled away from the friction surface 23 by the springs 30.

More particularly, when the park brake 36 is in an OFF state, the solenoids 40 are energized and the pins 42 are withdrawn from the posts 46 against the bias of the solenoid springs. When the park brake is ON the solenoids are de-energised and the pins are urged into the posts 46 that are disposed substantially in alignment with the pins 42. The taper on the pins 42 accommodates for wear of the friction material 22. As the friction material wears, the shoes 14 will be lineally displaced further in the direction of the inner circumferential surface 20 of the drum 12, thus displacing the posts 46 further in the same direction. By appropriately tapering the pins 42 this displacement due to wear is accommodated ensuring proper operation of the park brake 36 during the normal operational life of the shoes 14.

When system 10 is in use, a driver of a vehicle in which the system 10 is installed, would ordinarily use the brake pedal to activate the pistons 16 to bring a moving vehicle to stop. Prior to releasing the brake pedal, the driver

would then push a button to turn the park brake 36 to the ON state where the solenoids 40 are de-energised so that the members 38 biased by the solenoid springs enter and engage the posts 46 preventing the brake shoes 14 from moving inwardly away from the drum 12, countering the bias applied by the springs 30. The brake pedal can now be released relieving the hydraulic pressure on the pistons 16. Nevertheless, the shoes 14 are held in contact with the drum 12 and in particular the friction material 22 thereby providing a park brake effect.

In order to release the park brake, an appropriate button or switch within the vehicle is operated to energise the solenoids 40 thereby retracting the pins 42 against the solenoid springs and allowing the springs 30 to retract the shoes 14 from contact with the friction material 22.

In the above described embodiment, it is a requirement that the service brake be initially activated to place the brake shoes 14 in the braking position where the braking surface 18 is in contact with the friction surface 23, prior to actuation of the park brake 36. However, alternate embodiments are envisaged wherein the park brake 36 is configured to apply sufficient force to overcome the bias of the springs 30 and physically move the shoes 14 and associated braking surfaces 18 into contact with the friction material 22 and friction surface 23.

The brake shoes 14 are modified over conventional brake shoes to facilitate fluid cooling of a braking interface between the braking surface 18 and friction material 22.

With particular reference to Figures 3 and 4, each shoe 14 is provided with a fluid inlet 48, a fluid outlet 50, and a plurality of fluid flow paths 52 extending there- between, through which a cooling fluid can flow. As the brake shoes 14 do not rotate, hoses can be coupled with the inlet 48 and outlet 50 to a cooling circuit which may

comprise a reservoir of cooling fluid such as water or glycol, a pump, and a radiator or heat exchanger. This enables heat to be drawn from the braking interface between the braking surface 18 and the friction material 22.

The fluid flow paths 52 are formed as a plurality of parallel channels 54 which extend in the circumferential direction of the surface 18. Each of the channels 54 is open at its opposite ends leading to a common distributor channel 56 at one end which is in communication with the inlet 48, and a common distributor channel 58 at its opposite end which is in fluid communication with the outlet 50. In order to create the fluid flow paths 54, the shoes 14 comprise two curved plates 60 and 62. The curved plate 60 is welded or otherwise attached to the webs 26 and is machined, cast or otherwise formed so as to provide the channels 54. The plate 62 covers and seals the channels 54 to create the fluid flow paths 52. The braking surface 18 is formed on the outer circumferential surface of the plate 62.

When the shoes 14 are incorporated in a wet drum brake system of the type shown in Figures 1 and 2, the shoes 14 are provided with a pair of scrapers 64. The scrapers 64 are used for wiping lubricating oil from the surface of the friction material 22 during a braking operation. The scrapers 64 may be made from many different types of material including PTFE. The scrapers 64 are biased so as to extend radially beyond the braking surface 18 so that they contact the friction material 22 before the braking surface 18. As the shoes 14 are advanced further toward the friction material 22, the scrapers 64 are retracted inwardly to ultimately lie flush with the friction surface 18. Further structural and functional details of the scrapers 64 are described in Applicants International

Publication Number WO 02/23060, the contents of which are incorporated herein by way of reference.

In the embodiment depicted in Figures 1 and 2, the system 10 is part of a wet brake system 66 which is characterised by a sealed housing 68 which encloses the drum 12, the brake shoes 14 and the pistons 16. However the solenoids 14 are on the outside of the housing 68. The housing 68 includes an opening 70 at one end through which a rotating component such as a hub 72 can extend for coupling by way of mounting bolts 74 to the drum 12. Seals 76 are provided about the opening 70 supported by the housing 68 to prevent the escape of lubricating oil used in the wet drum brake system. The housing 68 includes a circumferential wall 78 which extends about the outside of the drum 12, and is closed by a front plate 80 which is sealed about its inner circumferential edge to the wall 78. The front plate 80 is further provided with an opening 82 through which a mounting plate 84 which is coupled to the hub 72 can extend. The mounting plate 84 is provided with a plurality of studs 86 to enable coupling to a wheel (not shown). Seals (not shown) are provided between the front plate 80 and the opening 82 to form a seal against the mounting plate 84. The lubricating fluid within the wet brake system 66 is completely separate from the fluid flowing through the fluid flow paths 52.

To assist in the dispersion of lubricating fluid during a braking action, the friction material 22 can be provided with a plurality of grooves, in particular spiroidal grooves, on their surface. Opposite ends of the grooves open onto axial edges of the friction material 22 to channel oil across the face of the friction material 22.

Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the pins 42 may be coupled via mechanical linkages or gears to a core of corresponding solenoid 40. In addition, the pins 42 may engage an outside of the posts 46. Further, the posts 46 may be removed and the pins 42 arranged to engage directly with the web 26 of the shoes 14. In addition, the friction material 22 may be attached to the outer surfaces 18 of the brake shoes 14 so that the inner circumferential surface 20 of the brake drum 12 constitutes the braking surface. Further, the park brake 36 may be applied to a conventional dry drum brake system where a single piston is used to cause the shoes to pivot about respective pins into contact with the brake drum.

In addition, in the above described embodiment solenoid springs are utilised so that when the solenoids are de- energised the park brake is ON and when the solenoids are energised the park brake is OFF. This arrangement provides the benefit that if electrical power is lost, the park brake is automatically deployed. However, if this feature is not required or not desired, the solenoid springs can be removed and the solenoids arranged to hold the brake shoes (braking surface) in contact with the friction surface 23 when the solenoids are energised (corresponding to the park brake being in the ON state); and to allow the brake shoes to be retracted by spring 30 when de-energised (corresponding to the park brake being in the OFF state).

All such modifications and variations together with others that would be obvious to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.