Background of the Invention A conventional drum brake system comprises a drum which is fixed to a rotating body such as a hub, and a pair of brake shoes each of which is rotationally fixed and pivotally coupled at one end to a stationary support located within the drum. Each shoe has an outer circumferential surface to which is attached a lining of friction material. A double acting piston is located between adjacent opposite ends of the shoes for the purposes of causing the shoes to pivot outwardly to bring the friction material into contact with a braking surface on the drum.

A wet drum brake system is of the same basic design as the conventional dry drum brake system but with the inclusion of a sealed housing which encloses the drum and the shoes, and contains a volume of lubricating fluid such as oil.

To maintain effective braking it is desirable to maintain the temperature at the braking drum and shoe interface (the"braking interface") in the region of 70°C to 80°C.

In existing dry drum brake systems, the temperature generated at the braking interface typically reaches 350°C to 400°C although this range can be exceeded in some instances.

Surprisingly the lubricating oil in the conventional wet braking system does not reduce the temperature at the braking interface to the above-mentioned desired range. A seemingly obvious way to address this would be to pump the

FLUID COOLED DRUM BRAKE SYSTEM Field of the Invention The present invention relates to a drum brake system.

Background of the Invention A conventional drum brake system comprises a drum which is fixed to a rotating body such as a hub, and a pair of brake shoes each of which is rotationally fixed and pivotally coupled at one end to a stationary support located within the drum. Each shoe has an outer circumferential surface to which is attached a lining of friction material. A double acting piston is located between adjacent opposite ends of the shoes for the purposes of causing the shoes to pivot outwardly to bring the friction material into contact with a braking surface on the drum.

A wet drum brake system is of the same basic design as the conventional dry drum brake system but with the inclusion of a sealed housing which encloses the drum and the shoes, and contains a volume of lubricating fluid such as oil.

To maintain effective braking it is desirable to maintain the temperature at the braking drum and shoe interface (the"braking interface") in the region of 70°C to 80°C.

In existing dry drum brake systems, the temperature generated at the braking interface typically reaches 350°C to 400°C although this range can be exceeded in some instances.

Surprisingly the lubricating oil in the conventional wet braking system does not reduce the temperature at the braking interface to the above-mentioned desired range. A seemingly obvious way to address this would be to pump the

oil of the wet brake system through a radiator or other heat exchanger. However in order to provide optimum performance, the volume of oil within the wet brake system is only a fraction of the volume defined by the housing containing the braking system. The remainder of the volume is occupied by air. The presence of air creates enormous difficulties in pumping oil through a heat exchanger. In theory, this could be rectified by completely filling the housing with oil. However were this to occur, then it would not be possible to expel the oil between the brake shoes and braking surface during a braking operation thereby drastically reducing stopping power.

Throughout this specification, except where the context requires otherwise due to express language or necessary implication, the word"comprise"or variations such as "comprises"or"comprising"is used in an inclusive sense, i. e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Summary of the Invention It is an-object of the present invention to provide a drum brake system in which heat is more effectively transferred from the braking interface.

According to one aspect of the present invention there is provided, a fluid cooled drum brake system comprising: a brake drum having an inner circumferential surface; a set of brake shoes rotationally fixed within the drum each shoe in the set having an outer surface facing the inner circumferential surface, a fluid inlet, a fluid outlet, and one or more fluid flow paths in fluid

communication between the fluid inlet and the outlet and extending beneath at least a portion of the outer surface and through which a cooling fluid flows ; a layer of friction material attached to one of the inner circumferential surface and the outer surface, the other of the inner circumferential surface and outer surface forming a braking surface; and, an actuator for selectively applying a force to the set of brake shoes to force respective braking surfaces against the friction material.

According to a further aspect of the present invention there is provided a fluid cooled wet drum brake system comprising : a sealed housing containing a volume of lubricating liquid; a drum brake disposed in the housing and having an inner circumferential surface; a set of brake shoes rotationally fixed within the drum, each shoe in the set having an outer surface facing the inner circumferential surface, a fluid inlet, a fluid outlet, and one or more fluid flow paths in fluid communication between the inlet and the outlet and extending beneath at least a portion of the outer curved surface through which a cooling fluid flows; a layer of friction material attached to one of tge inner circumferential surface and the outer curved surface, the other of the inner circumferential surface and the outer curved surface forming a braking surface ; and,

an actuator for selectively applying a force to the brake shoes to force respective braking surfaces against the friction material.

Preferably the layer of friction material is attached to the inner circumferential surface and the outer surface forms the braking surface.

Preferably the friction material comprises a plurality of pads of friction material disposed about the inner circumferential surface.

Preferably the pads are circumferentially spaced apart from each other.

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

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

Preferably the grooves open onto axially opposite edges of the friction material.

Preferably the grooves follow a spiroidal path.

Preferably the set of brake shoes comprises two brake shoes and the actuator selectively applies a force to each of the two brake shoes to urge the braking surfaces into contact with the friction material.

Preferably each brake shoe comprises a first curved plate provided with a plurality of channels on one side and a second curved plate attached to the first curved plate for covering the channels, the covered channels forming the internal fluid flow paths.

Preferably each brake shoe is mounted in the drum to slide linearly toward said friction material when the actuator is operated to urge the braking surface into contact with the friction material.

Preferably the actuator operates simultaneously at opposite ends on the brake shoes.

Preferably the actuator comprises a pair of pistons each piston acting between the ends of the brake shoes at respective opposite ends of the brake shoes.

Brief Description of the Drawings An embodiment of the present inventions will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a front view of a fluid cooled drum brake system in accordance with the present invention; Figure 2 is a representation of a pair of brake shoes incorporated in the fluid cooled drum brake system; Figure 2A is a view of section A-A of the brake shoes depicted in Figure 2; Figure 2B is a view of section B-B of the brake shoes depicted in Figure 2; Figure 3 is a section view of a wet drum brake incorporated in an embodiment of the fluid cooled drum brake system; and, Figure 4 is a front view of a second embodiment of the fluid cooled drum brake system.

Detailed Description of Preferred Embodiments With reference to the accompanying drawings an embodiment of the fluid cooled drum brake system 10 in accordance with the present invention comprises a brake drum 12 (see Figure 3) having an inner circumferential surface 14 to which is attached a layer of friction material formed as three circumferentially spaced arcuate sections of friction material 16a-16c (hereinafter referred to generally as"friction material 16"). A set of two brake shoes 18a and 18b (hereinafter referred to in general as "brake shoes 18") is rotationally fixed within the drum 12. Each brake shoe 18 has: an outer (convexly curved) surface which forms a braking surface 20 facing the friction material 16; a fluid inlet 22 (see Figures 2 and 2A); fluid outlet 24; and, a number of fluid flow paths 26 in fluid communication between the fluid inlet 22 and fluid outlet 24 and extending beneath at least a portion of the braking surface 20. An actuator 27 in the form of a pair of double-acting hydraulic pistons 28 is provided for selectively applying force to the brake shoes 18 to urge their respective braking surfaces 20 against the friction material 16.

Each brake shoe 18 is formed with first and second curved plates 30 and 32 of a curvature which is coaxial with the inner surface 14 of the drum 12. The curved plate 32 has an outer surface which constitutes the braking surface 20.

The curved plate 30 is radially inside of the plate 32 and has a radially inner surface 34 to which is coupled the brake shoe web 36. The fluid inlet 22 and fluid outlet 24 are formed through the surface 34 of the plate 30 and provide fluid communication to the fluid flow paths 26 which are confined between the curved plates 30 and 32.

The fluid flow paths 26 are formed as a plurality of parallel channels 38, machine, cast or otherwise formed on

a radially outer surface 40 of the curved plate 30. The channels 38 are separated by parallel spaced-apart walls or ridges 41 that are created in the process of forming the channels 38. Opposite ends of the channels 38 lead to common feed channels 42 and 44 which provide fluid communication with the inlet 22 and outlet 24 respectively. The fluid flow paths 26 are effectively created by covering the channels 38 with the curved plate 32 and sealing the plate 32 to the plate 30.

Scrapers 46, typically made from PTFE are provided on each brake shoe 18 at opposite ends of the curved plates 30 and 32. The purpose of the scrapers 46 is to wipe lubricating oil from the surface of the friction material 16 when the brake shoes 18 are used in a wet brake system. The scrapers 46 are resiliently biased so as to protrude radially beyond the braking surface 20. As the shoes 18 are advanced toward the friction material 16, the scrapers 46 will initially contact the friction material 16 to wipe off the lubricating oil. As the pistons 28 continue to advance the shoes 18 toward and into contact with the friction material 16, the scrapers 46 retract radially inwardly. Further details of the operation and structure of the scrapers 46 can be derived from Applicant's International Publication No. WO 02/23060, the contents of which are incorporated herein by way of reference.

A substantial departure in the structure of the brake system 10 in comparison with conventional drum brakes is that the shoes 18 and actuator 27 (ie pistons 28) are arranged to ensure that the shoes 18 move linearly toward the friction material 16 rather than move in an arcuate path. To this end, the webs 36 of the shoes 18 are provided with elongated slots 47 through which guide pins 48 extend. The pins 48 are on a stationary mounting plate (not shown, but of a form similar to the stationary plate used in conventional drum brakes to support the brake

shoes) located within or adjacent the drum 12. The actuator 27 operates at opposite ends of the shoes 18 to cause the shoe to slide linearly into contact with the friction material 16. More particularly, respective pistons 28 act between the ends of adjacent shoes 18.

Upon release of an associated brake pedal, springs 50 which are coupled between the webs 36 of the shoes 18, slide the shoes 18 linearly toward each other and out of contact with the friction material 16 thereby releasing the brake. The springs 50 may be coupled to the webs 36 in any conventional manner including by the provision of hooks 52 on opposite ends of the springs 50 which engage pins 54 extending axially from one side of the webs 36.

Since the shoes 18 are rotationally fixed and move linearly only a short distance, hoses (now shown) can be attached to the inlet 22 and outlet 24 to couple the fluid flow paths 26 to a cooling circuit which can include a reservoir of cooling fluid such as water or glycol, a pump and if desired or required, a radiator or heat exchanger.

By flowing fluid through the fluid flow path 26 heat is transferred from the immediate vicinity of the braking interface thereby providing a mechanism to maintain temperature at the locking interface in the region of 70°C to 80°C.

Embodiment of the drum brake system 10 may be utilised as either a dry brake system or alternately as part of a wet brake system.

Figure 3 depicts an embodiment of a wet brake system 56 in which the fluid cooled from brake system 10 may be incorporated. The wet brake system 56 is in substance the same as the dry brake system illustrated in Figures 1 and 2 but with the addition of an outer sealed housing 58 which contains the drum 12, friction material 16 and brake shoes 18 (not shown). The housing 58 is a stationary

component and is provided with an opening 60 at one end through which a rotating body in the form of a mounting hub 62 passes. The drum 12 is attached to the mounting hub by mounting bolts 64. Thus the drum 12 rotates with the mounting hub 62.'Circumferential seals 65 are provided within the housing 58 to form a fluid seal against an outer surface of the hub 62. The housing 58 includes a circumferential wall 66 which extends about the outside of the drum 12, and a cover plate 68 which is attached about its outer circumferential edge to the wall 66 and defines a central opening 70 through which a mounting plate 72 extends. A rotary seal (not shown) is provided between the cover plate 68 and mounting plate 72.

The mounting plate 72 rotates with the drum 12 and hub 62.

A wheel (not shown) can be fastened to the mounting plate 72 via axially extending studs 74. The housing 58 contains a volume of lubricating oil which acts to reduce wear of the friction material 16 and the braking surfaces 20.

To assist in the dispersion of lubricating fluid during a braking action, the friction material 16 can be provided with a plurality of grooves, and in particular spiroidal grooves 76 on their surface. Opposite ends of the grooves 76 open onto opposite axial edges of the friction material 16 to channel the oil across the face of the friction material 16. The friction material 16 is supported on a steel backing 78 which is attached by screws or bolts 80 to the drum 12.

A minor variation of the fluid cooled drum brake system 10 is depicted in Figure 4. The system in Figure 4 differs from that depicted in Figure 1 solely by the provision of friction material 16 as a single continuous layer about the entire circumference of the inner circumferential surface 14 of the drum 12.

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, while the set of brake shoes is depicted as comprising two brake shoes 18a and 18b, the set may contain different numbers of shoes.

All such modifications and variations 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.