Technical Field This specification discloses a disc brake system, and in particular, but not exclusively, to a wet disc brake system that is suitable for vehicles which undergo a large number of braking events.

Background Art

The disclosed brake system was developed to provide a solution to the high cost in servicing and maintaining conventional brakes of a garbage truck. As an example, one municipal authority indicated that a typical single front axle, tandem rear axle, garbage truck having a tare weight of over 1 1 ,500kg, with 419 mm x 152mm (6") S-cam brake drums on the front axle, and 419mm x 178mm (7") S-cam brake drums on the rear axle, requires a rear brake overhaul every six months, and a front brake overhaul every 12 months. This maintenance schedule incurs an annual cost in the order of

US$6,000 - US$9,000. While the disclosed brake system was developed to reduce braking system

maintenance costs for a garbage truck or heavy trailer, embodiments of the brake system are not limited to such applications. Embodiments of the brake system may be applied to: other vehicles including other types of truck or heavy vehicle such as buses, vehicle trains (road and rail) and haul packs used in mining irrespective of whether the operating profile for the vehicle comprises a relatively large number of braking events or use in a contaminated environment; and to non-vehicular machines such as winches and conveyors.

Summary of the Disclosure

In the first aspect there is disclosed an enclosed brake system for a vehicle having one or more axles that each support one or more rotational units the brake system comprising;

a rotor defining a braking surface of a diameter between 375mm and 450mm the rotor being capable of being coupled to rotate with a rotational unit;

one or more brake calipers that are selectively operable to bring one or more friction surfaces in contact with between 30% to 90% of the area of the braking surface; and a housing enclosing the rotor and calipers and retaining a volume of liquid brake lubricant to both: lubricate the rotor and the one or more friction surfaces; and, transfer heat from at least the rotor, the one or more friction surfaces and the housing. In the second aspect there is disclosed a brake system comprising:

a rotor defining a rotor braking surface;

one or more calipers arranged in a radial array, the calipers selectively operable to apply brake pads to instantaneously contact between 30% to 90% of the rotor braking surface;

a housing enclosing the rotor and calipers and partially filled with a volume of a liquid brake lubricant; and

a heat exchanger located within the housing and arranged so as to extract heat from the liquid brake lubricant. In the third aspect there is disclosed a brake system comprising:

a rotor;

one or more brake calipers each being selectively operable to apply one or more brake pads to the rotor;

a housing enclosing the rotor and brake calipers and partially filled with a volume of a liquid brake lubricant; and

a heat exchanger disposed in the housing and arranged to transfer heat from the liquid brake lubricant via circulation of a coolant which is isolated from contact with the liquid brake lubricant, the heat exchanger configured to transfer heat by a combination of natural heat convection, forced heat convection and conduction.

In the fourth aspect there is disclosed a brake system for a vehicle having two or more axles each axle having two wheel ends and having a gross axle load rating of at least 6000kg, the brake system being provided for each wheel end and comprising:

a rotor;

one or more brake calipers each being selectively operable to apply one or more brake pads to the rotor;

a housing enclosing the rotor and brake calipers and partially filled with a volume of a liquid brake lubricant; and

a cooling system capable of transferring heat from the liquid brake lubricant contained within the brake housing.

In the fifth aspect there is disclosed a brake system for a vehicle having two or more axles, each axle having two wheel ends and a gross axle load rating of at least 6000kg, the brake system for each wheel of each axle comprising:

a rotor;

one or more brake calipers each being selectively operable to apply one or more brake pads to the rotor;

a sealed housing enclosing the rotor and brake calipers and partially filled with a volume of a liquid brake lubricant; and

a pressurised cooling system operable to cool the liquid brake lubricant by circulating fluid between inside and outside of the sealed housing through a fluid circuit, the cooling system including a liquid brake lubricant temperature monitor providing a signal indicative of liquid brake lubricant temperature .

In the sixth aspect there is disclosed a brake system comprising:

a rotor;

one or more calipers, each caliper being selectively operable to apply one or more brake pads to the rotor;

a sealed housing enclosing the rotor and calipers and partially filled with a volume of a liquid brake lubricant; and

an operator feedback system arranged to provide feedback to an operator of a vehicle fitted with the wet disc brake system on the basis of liquid brake lubricant temperature exceeding a threshold temperature.

In the seventh aspect there is disclosed a brake system comprising:

a housing configured to form a liquid sealed cavity about a body rotating relative to the housing the cavity being vented to atmosphere;

one or more brake calipers disposed in the housing, the brake calipers provided with one or more cylinders, the housing being provided with an opening for each of the cylinders, wherein each cylinder is seated in a respective opening. In the eighth aspect there is disclosed a brake system comprising a service and park brake caliper provided with at least two cylinders wherein at least one of the cylinders houses a hydraulic operated service piston to facilitate service braking, and at least one cylinder housing a park piston which is applied by a spring and released by air pressure to facilitate park and emergency braking.

In the ninth aspect there is disclosed a vehicle with at least one axle having a gross axle load rating of at least 6000kg, the vehicle comprising: a receptacle configured to transport material;

an air compressor;

a braking system driven by compressed air from the air compressor to brake motion of the vehicle the brake system comprising a service brake and a park brake, the service brake being a wet air over hydraulic actuated disc brake, and the park brake being a spring applied and air released.

In one embodiment the wet brake system that may be actuated by an air over hydraulic or electric over hydraulic method.

In the tenth aspect there is disclosed a method of overhauling an air operated drum brake system on a vehicle having an air compressor, at least one axle with a gross axle load rating of at least 6000kg, the axle having a hub at each end and a respective drum brake assembly associated with each hub, the method comprising:

removing the hub and associated drum brake assembly from respective axles; and,

fitting a brake system according to the seventh or eighth aspect to the respective axles together with a corresponding hub. In the eleventh aspect there is disclosed a brake housing for a vehicle brake system having a rotor and one or more brake calipers capable of selectively applying braking force to the rotor, each caliper having one or more cylinders and associated pistons: the housing configured to circumferentially surround the rotor and the or each caliper, and provided with one or more openings for seating the cylinders.

In the twelfth aspect there is disclosed a brake system for a vehicle comprising:

a rotor;

one or more brake calipers capable of selectively applying braking force to the rotor, each caliper having one or more cylinders and associated pistons;

a housing configured to circumferentially surround the rotor and the or each caliper, and provided with one or more openings for seating the cylinders;

a structural component coupled to the vehicle and wherein the housing is coupled to the structural component; and,

one or more fasteners which couple the one more calipers to the structural component wherein load generated by operating the calipers to apply braking force to the rotor is transferred directly through the fasteners to the structural component. Brief Description of the Drawings

An embodiment of the brake system will now be described in by way of example only with reference to the accompanying drawings in which:

Figure 1 is a section view of an embodiment of the disc brake system mounted on an axle;

Figure 2 is a rear view of the brake system shown in Figure 1 ;

Figure 3 is a plan view of the brake system shown in Figures 1 and 2;

Figure 4 is a front view of the brake system;

Figure 5a is a front view of an outer casing of a housing assembly incorporated in the brake system;

Figure 5b is a view of section A-A of the outer casing shown in Figure 5a;

Figure 5c is a perspective view from the front of outer casing;

Figure 5d is a perspective view from the rear of the outer casing;

Figure 6a is a rear view of an inner plate incorporated in the housing assembly;

Figure 6b is a front view of the plate shown in Figure 6a;

Figure 6c is a side view of the inner plate;

Figure 6d is a view of section A-A of the inner plate shown in Figure 6a;

Figure 7a is a representation of seal carrier incorporated in the housing assembly; Figure 7b is a view of section A-A of the seal carrier shown in Figure 7a;

Figure 7c is an enlargement section view showing the coupling together of outer casing of Figs 5a-5e and the seal carrier of Fig 7a and 7b

Figure 8a is a perspective view of a service and park brake caliper incorporated in the brake system;

Figure 8b is a side view of the caliper shown in Figure 8a;

Figure 8c is a plan view from the bottom of the caliper shown in Figure 8a;

Figure 8d is a view of section A-A of the caliper shown in Figure 8b;

Figure 8e is a view of detail B shown in Figure 8b;

Figure 8f is a view of section C-C of the caliper shown in Figure 8b;

Figure 9a is a perspective view of a two piston caliper incorporated in an embodiment of the brake system;

Figure 9b is a side view of the caliper shown in Figure 9a;

Figure 9c is a plan view from the bottom of the caliper shown in Figure 9a;

Figure 9d is a view of section A-A of the caliper shown in Figure 9b;

Figure 9e is a view of detail B shown in Figure 9d;

Figure 9f is a view of section C-C of the caliper shown in Figure 9b; Figure 10a is a perspective view of a three piston caliper incorporated in an

embodiment of the brake system;

Figure 10b is a side view of the caliper shown in Figure 10a;

Figure 10c is a plan view from the bottom of the caliper shown in Figure 10a;

Figure 10d is a view of section A-A of the caliper shown in Figure 10b;

Figure 10e is a view of detail B of the caliper shown in Figure 10d;

Figure 1 1 is a perspective view of a spacer incorporated in the calipers shown in Figures 8a - 10e;

Figure 12a is a perspective of a park piston incorporated in the service and park brake caliper shown in Figures 8a - 8e;

Figure 12b is a side view of the piston shown in Figure 12a;

Figure 12c is a view of one end of the park piston shown in Figure 12a;

Figure 12d is an opposite end view of the park piston shown in Figure 12a;

Figure 12e is a view of section A-A of the park piston shown in Figure 12c;

Figure 13 is a section view of a second embodiment of the brake system;

Figure 14 is a representation of a garbage truck fitted with a brake system in accordance with the present brake system;

Figure 15a is an elevation view of an inner plate incorporated in a second embodiment of the braking system;

Figure 15b is a view of section A-A of the inner plate shown in Figure a;

Figure 15c is a perspective view of the inner plate shown in Figure 15a from the rear; Figure 15d is a perspective view of the inner plate shown in Figure 15a from the inside; Figure 16 is a schematic representation of a cooling circuit which may be incorporated in an embodiment of the brake system;

Figure 17 is a schematic representation of an embodiment of the brake system incorporating an alternate lubricant fluid cooling system;

Figure 18 is a front elevation of one plate incorporated in a heat exchanger of the cooling system shown in Figure 17;

Figure 19 is a view of an inside surface of a panel used to construct the plate shown in Figure 18;

Figure 20a is a side elevation of a portion of the heat exchange incorporated in the cooling system shown in Figure 17;

Figure 20b is a side elevation of the heat exchanger fitted with scoops to enhance heat transfer efficiency;

Figure 21 is an end view of an assembled portion of the brake system incorporating brake calipers, a rotor, and a heat exchanger of the cooling system depicted in Figure 17; and

Figure 22 is a front elevation of a portion of the brake system depicted in Figure 17.

Detailed Description of Preferred Embodiments

With reference to the accompanying Figures and in particular Figure 1 an embodiment of the brake system 10 comprises a number of interacting components and assemblies including a housing assembly 12 and brake calipers 14. The housing assembly 12 forms a liquid tight seal between an axle housing 16 and a wheel hub 18 to enclose and retain a volume of liquid brake lubricant (not shown) for the brake system 10. When the housing contains liquid brake lubricant the brake system constitutes a wet brake system. While the housing is sealed to prevent leakage of the liquid brake lubricant (or indeed ingress of foreign liquid) it may nonetheless be vented to atmosphere. This can be achieved by a breather hose which extends to a condenser located above the housing. A vent line is plumbed to an upper part of the condenser terminates in an air permeable filter. The condenser enables lubricant vapours to condense and flow back to the housing. Thus reference to a "sealed housing" in the context of this specification insofar as a wet brake system is concerned means that the housing is sealed at least to the extent to retain the liquid brake lubricant and/or prevent ingress of other liquid. A rotor 20 is splined onto and thus rotates with the hub 18. The rotor 20 and spline are lubricated by the lubricant as it rotates within the housing 12 and brake calipers 14. A portion of the brake calipers 14, and in particular cylinders 22, extends into and is seated in openings 24 formed in the housing assembly 12. O rings 26 are provided in the opening 24 to form a seal between the housing assembly 12 and the cylinders 22.

Seating the cylinders 22 in the openings 24 enables coupling to mechanical, hydraulic or pneumatic actuators, or electrically assisted variations of the aforementioned for operating the calipers 14. The calipers 14 are directly coupled to a structural component in the form of flange 28 extending about the axle housing 16. Accordingly reactive forces created during a braking operation are transmitted via the calipers 14 to the flange 28 and axle housing 16 rather than being transferred to or through the housing assembly 12. This enables the housing assembly 12 to be made of a relatively light weight construction and/or materials such as aluminium because housing assembly 12 that bears minimal load. The housing assembly 12 comprises an outer casing 30 shown in Figures 1 and 5a - 5d which extends circumferentially about the calipers 14; an inner plate 32 shown in Figures 6a - 6d and a seal carrier in the form of a second plate 34 shown in Figures 1 , 7a and 7b. With particular reference to Figures 5a - 5d, the outer casing 30 comprises a circumferential wall 36 of constant inner diameter and provided, on an outside surface near one end 38, with a plurality of axially extending spaced apart and integrally formed ribs 40. The ribs 40 provide additional strength and thickness to the wall 36 for supporting threaded studs 41 to enable fastening of the inner plate 32. An opposite end 42 of the outer casing 30 is formed with an inwardly directed

circumferential lip 44. The second plate 34 is fastened to the outer casing 30 by screws 46 (Figs 1 , 3, 4) that pass through the lip 44.

With reference to Figures 6a - 6d, the inner plate 32 is provided with a central opening 48 through which an axle housing 16 extends and which aids to centralise the brake housing relative to the hub 18. Surrounding the opening 48 is a fixing ring 52 by which the inner plate 32 and indeed the housing assembly 12 is coupled to the flange 28 on the axle housing 16. The fixing ring is provided with a plurality of holes 54 that register with holes formed in the brake calipers 14 as well as holes in the flange 28 enabling attachment of the calipers 14 to the flange 28. Further holes 56 are provided in the fixing ring 52 to couple the inner plate 32 to the flange 28. Additional smaller diameter holes 57 are formed in the fixing ring 52 to locate the inner plate 32 to the calipers 14.

The inner plate 32 is formed with a portion 58 radially outward of the fixing ring 52 in which is formed the openings 24 for the caliper cylinders 22. The openings 24 are, in this embodiment, arranged in two banks 62 each comprising three openings 24. The banks 62 are raised in relation to the portion 58 of the inner plate 32. The centres of the two end openings 24 in each bank 62 are separated by approximately 66°. A plurality of bosses 64 is formed about the outer circumferential surface of the inner plate 32 which align with the studs 41 on the outer casing 30. The bosses 64 are formed with holes for receiving the threaded end of the studs 41. Nuts are screwed on the studs 41 to fasten the inner plate 32 to the outer casing 30.

With reference to Figures 1 , 7a, 7b and 7c, the second plate 34 is in the general form of an annular plate having: a central opening 68 through which fits the hub 18; and, an outer circumferential edge 70. The outer edge 70 has a diameter greater than the diameter of the lip 44 on the outer casing 30. When assembling the housing assembly 12, the plate 34 is inserted into the outer casing 30 from end 38. Radially inboard of outer edge 70 is formed an annular seat 74 in plate 34 which abuts on inside of the lip 44 of outer casing 30. The seat is provided with a circumferential groove 75 for seating an O-ring 77 (Fig 7c). Radially inward of seat 74 there is a right angle circumferential shoulder 76 which forms one edge of annular seat 74. Shoulder 76 abuts lip 44 of outer case 30 to centrally locate plate 34 with outer case 30. The seat 74 is provided with a plurality of blind holes 80 to threadingly engage the screws 46 which fasten the plate 34 to the lip 44 of the outer casing 30. The plate 34 is also provided with an inner circumferential seat 84 having blind holes 86 to facilitate the attachment of a flange seal support 88 (shown in Figure 1 ). The seat 84 is rebated with respect to the seat 74.

The plate 34 also comprises an axially projecting boss 89 having an inner

circumferential surface 90 adjacent the inner band 84 of constant diameter. The free axial end of the boss 89 defines the opening 68. A cassette seal 100 (see Figure 1 ) is seated in the boss 89 on the surface 90 to form a rotary seal between the housing assembly 12 and an outer surface of the hub 18.

To provide some physical context embodiments to the brake system 10 for a vehicle having an axle with a gross axle load rating of say 6-12 tonnes and providing an average in service braking effort of about 60kW per wheel end the rotor 20 may have a diameter of between about 375 mm to 450 mm and thickness of between about 15 mm and 50 mm. The housing assembly 12 in such embodiment may have an inner diameter of between about 385mm and 460 mm. Liquid brake lubricant occupies about 20% to 50% of the height of the housing when the axis of the housing lies in a horizontal plane. In some instances this may also equate to a volume of about 20% to 50% of the gross housing volume (i.e. exclusive of the volume occupied by the brake components, e.g. calipers and rotor).

Embodiments of the brake system 10 incorporate three similar but different brake calipers. These comprise a service/park brake caliper 14a shown in Figures 8a - 8f; a two piston brake caliper 14b shown in Figures 9a - 9f; and a three piston caliper 14c shown in Figures 10a - 10f. The three forms of calipers are referred to in general, i.e. when describing common features, as "calipers 14". Referring to Figures 8a - 8f, the park/service brake caliper 14a comprises an inner shell 104 and outer shell 106 which are coupled together to define a cavity 108 in which the rotor 20 rotates. The calipers 14a also house opposing brake pads 1 10a and 1 10b (referred to in general as "pads 1 10") as shown in Figure 1. The cavity 108 opens onto an outer circumferential surface 109 of the caliper 14a forming a central gap 1 1 1 between the shells 104 and 106. The brake pad 1 10a is seated in a recess 1 12 formed on an inside of the outer shell 106.

The inner shell 104 is formed with three cylinders 1 14a, 1 14b and 1 14c (hereinafter referred to in general as "cylinders 1 14"). Each of the cylinders 1 14a and 1 14c is provided with holes 1 18 to allow connection to hoses providing hydraulic fluid to respective service brake pistons 120 retained in the cylinders 1 14a and 1 14c.

Extending transversely between the holes 1 18 on each cylinder 1 14a and 1 14c is a land 122 to facilitate connection of a spring canister 124 (shown in Figure 1 ). The spring canister is pneumatically operated to provide the park brake aspect of the service/park brake caliper 1 14a. Seated on the inside of the outer shell 104 is a reaction plate 126 (shown in Fig 13) which is in the form of a steel plate of a shape and configuration similar to the brake pad 1 10a. The reaction plate 126 extends across each of the pistons 120 held in the cylinders 1 14a and 1 14c as well as a park brake piston 128 (shown in Figures 1 and 12a - 12e) disposed within the cylinder 1 14b.

The inner and outer shells 104 and 106 are coupled together by sets of bolts 130 that extend from the shell 106 into the shell 104. The bolts 130 are located near the ends of the shells 104 and 106 on the side of the service brake cylinders 1 14a and 1 14c distant the cylinder 1 14b. In addition, metal spacers 132 bridge the cavity 108 and are coupled to both of the shells 104 and 106 to provide bracing to the caliper 14a. Bolts 130 also fix the spacers 132 to the shells 104 and 106.

A mounting flange 142 is formed integrally with the inner shell 104 to facilitate attachment of the caliper 14a to the flange 28 on the axle housing 16. To this end the mounting flange 142 is provided with holes 144 and 145 that register with the holes 54 and 57 respectively in the fixing ring 52 of the inner plate 32.

The park brake piston 128 (see Figures 1 , 8a, 8c, 8d and 12a - 12e) is housed within the cylinder 1 14b and is acted upon by the spring canister 124 via a wear

compensating mechanism 146 which includes a rod 147 (see Figure 1 ). One end 148 of the piston 128 is formed with an axially projecting ring 150. Inside of the ring 150 the piston 128 is provided with a radial face 152 which is formed with a central raised land 154. A slot 156 extends axially on the piston 128 from the ring 150 to a distance approximately one third of the way toward an opposite end 158 of the park piston 128. A circumferential groove 160 is formed about the park piston 128 between the slot 156 and the end 158 for seating an O-ring 162 (shown in Figure 1 ). The slot 156 accommodates a pin 163 which extends from a face 164 of the rod 147. The face 164 abuts the raised land 154 and is located within the ring 150 of the piston 128.

The land 154 provides a pivot between the rod 147 and the interface piston 128. This provides a means of self-alignment between the rod 147 and the piston 128, allowing lateral movement or rocking at the face due to: the length of the rod 147; and, the mechanism 146 which multiplies the force of the canister 124 comprising a pivoted lever arrangement.

Wear of the brake pads 1 10 is compensated for in relation to application of the park brake by the mechanism 146 which causes a housing of the rod 147 to rotate about a longitudinal axis of the rod 147 as the rod 147 is advanced linearly by application of force by the spring canister 124. This rotation maintains the rod 147 in a linearly advanced position relative to its position prior to application of force by the spring canister 124 to provide wear compensation.

The two piston caliper 14b is shown in Figures 9a - 9f. Each feature of the caliper 14b which is identical to corresponding features of the caliper 14a is denoted with the same reference number. The caliper 14b differs from the caliper 14a in the following two aspects. Firstly, the central cylinder 1 14b in the caliper 14b is closed and does not house any piston. Thus, braking force is applied only via the pistons 120 in the cylinders 1 14a and 1 14c applying pressure to associated brake pads 1 10. Secondly, as the caliper 14b does not have a park brake function, it does not require and therefore does not have the lands 122 depicted on the caliper 14a for mounting of the spring canister 124. In the embodiment of the braking system 10 shown in Figures 1 - 4, one piston caliper 14b is used together with a service/park brake caliper 14a to form a rear brake assembly for braking a wheel coupled to the hub 18.

Figures 10a - 10f depict the three piston caliper 14c. Features of the caliper 14c which are identical to features of the calipers 14a and 14b are denoted with the same reference number. The three piston caliper 14c differs from the caliper 14b by the provision of a service piston 120 in the central cylinder 1 14b and the provision of holes 1 18 in the cylinder 1 16 to allow the application of hydraulic pressure to the piston 120. The calipers 14 selectively apply brake pads 1 10 onto opposing surfaces of the rotor 20. In one embodiment the brake pads 1 10 are arranged to collectively contact between about 30% - 90% of the friction surface area of a corresponding rotor 20. Conversely about 10% - 70% of the friction surface area of the rotor 20 is left uncovered, i.e. not disposed within a caliper 14 at any one time. In one embodiment the calipers are evenly spaced about the rotor 20. In this or an alternate embodiment the brake system 10 may have two calipers 14 that are diametrically opposed. The two diametrically opposed calipers may each extend for the same arc length. In that case the calipers are arranged to have an equal spacing between their respective adjacent ends. As a result of this the area of the braking surfaces of the rotor 20 swept by friction surfaces (i.e. the pads 1 10) is 0.87 times the square of the outer rotor diameter within plus or minus 10%.

The above stated range of 30% - 90% is intended to cover every single value and any every sub-range in this range. For example this range includes, but is not limited to, for example the sub ranges 30%-70%; 60%-90%; and 60%-70%.

Figure 13 depicts an embodiment of the brake system 10b comprising a housing assembly 12 and two of the three piston calipers 14c held within the housing assembly 12 to brake a rotor 20 mounted on a wheel hub 18b. In this particular embodiment, the wheel hub 18b mounted on a stub axle 50b. The calipers 14c and thus the brake system 10b provide service brakes only with no park (or emergency) braking facility. In one further minor modification the brake pads 1 10 are provided with surface grooves 1 13. The grooves 1 13 facilitate the flow of the lubricant to form a lubricant film on the friction surface of the rotor 20. The spacing of the grooves 1 13 may be used to control the thickness of the film. The grooves may extend between adjacent edges of a pad or between opposite edges of a pad. The grooves may follow an arcuate and in particular a spirodal path. Figure 14 depicts a garbage truck 170 having a receptacle 172 for holding and transporting waste matter, and mounted on a chassis having a single front axle and a tandem rear axle. The truck 170 in its original form is provided with drum brakes on each of the hubs on each of the axles. The brakes are pneumatically operated. To this end, the truck 170 is provided with an air compressor (not shown) for activating the brakes. Embodiments of the brake system 10 may be retrofitted to the truck 170 by first removing the original equipment hubs and drum brakes and retrofitting

embodiments of the brake system. For example, a brake system 10b as shown in Figure 13 comprising two calipers 14b with a hub 18b may be fitted on the front axles of the truck 170. On each of the rear axles, a brake system 10 shown in Figures 1 - 4, each provided with a service/park brake caliper 14a and a two piston service brake caliper 14b with a hub 18 can be fitted. In order to provide hydraulic pressure to the service brakes, one or more air over hydraulic actuators (not shown) is provided between the air compressor and the cylinders of calipers that house the service brake pistons 120. Thus the service brakes are hydraulically operated. The parking brake facility provided by the service/park brake caliper 14a is a spring applied air release park brake. The supply of compressed air to the canister 124 operates against the spring within the canister to release the park brake. When either the park brake is actuated, or is there is a loss in air pressure, the spring within the canister 124 is released so that the bias of the spring is applied through the rod 146 to the park piston 144 to apply the park brake. Due to the configuration of the brake system 10, complete brake and hub assemblies for any axle can be preassembled on a work bench and coupled as a single unit to the axle. For example, consider the brake assembly 10 illustrated in Figure 1. This assembly comprises a service and park brake caliper 14a, a two piston service brake caliper 14b. When assembling the brake assembly 10, the calipers 14a and 14b are first assembled with the spring canister 124 and associated wear compensating rod system 145 not being attached to the caliper 14a. The rotor 20 is then placed centrally between the calipers with a portion of the rotor extending between the brake pads 1 10a and 1 10b in each of the calipers 14a and 14b. Next, the second plate 34 is passed into the outer casing 30 from the end 38 so as to abut with the inside of the lip 44. The outer casing 30 and second plate 34 are connected together by screws that pass through the lip 44 into the holes 80 in the band 78 of the plate 34. The hub 18 is now inserted into the opening 68 of plate 34. The inner plate 32 is located over the calipers 14a and 14b so that the cylinders of the calipers pass through the openings 24. O-rings 26 seal the cylinder of each of the carriers 14a and 14b to the inner plate 32. Screws which extend through holes 57 into holes 157 connect the inner plate 32 to the calipers 14a and 14b, with the rotor 20 retained within and between the calipers 14a and 14b. The seal 100 is seated in the plate 34 and the calipers 14a and 14b which are attached to the plate 32 are now lowered into the outer casing 30 with the rotor 20 orientated to slide onto splines on the hub 18. The inner plate 32 is now fastened to the outer casing 30.

The entire assembly comprising the calipers 14a and 14b held within the housing 12, and the hub 18 can now be fitted onto an axle assembly. The hub 18 is allowed to rotate on the axle housing 16 via two tapered roller bearings 1 1 , 13 (see Figure 1 ) which are seated on the axle housing 16. Axle shaft 50 which extends through the axle housing is attended to the face of the hub 18 by axle studs 15. The wet disc brake assembly is attached to the flange 28 on the axle housing using bolts that pass through the holes 54 and threadingly engage with holes 144 in the mounting flange 142 of the calipers 14a and 14b. Thus load applied during a braking operation on the calipers 14a and 14b is transferred via the fasteners to the flange 28 and axle housing 16 rather than being born by the housing assembly 12. Next, hydraulic hoses can be coupled to the cylinders 22 of the calipers 14a and 14b and the canister 124 connected with the caliper 14a.

Figures 15a-15d illustrate an inner plate 32a of a further embodiment of a wet brake system 10. The inner plate 32a differs from the inner plate 32 depicted in Figures 6a- 6d by the provision of a finned sump 180 which protrudes in an axial direction away from the seal carrier or second plate 34. The purpose of the sump 180 is to increase the volume of lubricating oil inside the brake without increasing the level of the oil. Further, the sump 180 lies substantially below the level of the O-ring seals 26 provided in the openings 24 which seat the caliper cylinders 22. Thus the positioning of the sump 180 reduces the likelihood of lubricant leakage about the seals.

The sump 180 is also provided with a plurality of cooling fins 182 to an outside surface of the inner plate 32. The sump 180 and the fins 182 may be dimensioned to protrude beyond the wheel and rim associated with the braking system to increase heat rejection from the braking system 10. A sump fill hole 184 and sump drainage hole 186 is formed on the outside of the inner plate 32a to allow filling and drainage of the sump 182. The holes 184 and 186 may be closed by conventional plugs.

As an addition or an alternative to the fins 182, the brake system 10 may also incorporate a cooling system 200 depicted in Figure 16 for cooling the lubricant sealed within housing assembly 12 used for lubricating the rotor 20. Cooling system 200 comprises an oil cooling circuit 202 comprising an oil filter 204, radiator 206, and pump 208, which are connected in a closed series loop with the housing 12 by a conduit 210. Conduit 210 is connected at an outlet 212 in a lower portion of housing 12 and returns via an inlet 214 at a spaced apart location in an upper region of housing 212. While one circuit 202 is shown, it is envisaged that each brake system 10 will include a separate fluid circuit although the conduit for each circuit may pass through a common radiator 206 in a manner where the fluid for each brake system 10 is kept separate. The order of the filter 204, radiator 206 and pump 208 in the circuit 202 is of no significance and may change or be varied to suit the chassis and structure of the vehicle to which the brake system 10 is fitted.

Figures 17 - 21 depict an alternate brake cooling system 300 that may be incorporated with the brake system 10. The cooling system 300 comprises a heat exchanger (also known as an intercooler) 302 that is disposed in the housing 12 and arranged to extract heat from the liquid brake lubricant 304. In the cooling system 300 the exchange of heat is via the circulation of a coolant that is isolated from contact with the liquid brake lubricant 304. The coolant is pumped through the heat exchanger 302 by a pump 306 and subsequently through one or more radiators 308. The coolant is circulated back to the heat exchanger 302. The flow of coolant through the heat exchanger 302, pump 306 and radiator 308 is via a fluid circuit 310 which comprises: a conduit 312 extending between the heat exchanger 302 and pump 306; a conduit 314 extending between the pump 306 and the radiator 308; and a conduit 316 extending from the radiator 308 to the heat exchanger 302. The heat exchanger 302 is provided with an inlet port 318 and an outlet port 320 to provide fluid coupling with the fluid circuit 310. The ports 318 and 320 can be plumbed to access openings on the housing 12 to facilitate physical attachment with the conduits 312 and 316.

In broad terms, the cooling system 300 differs from the cooling system 200 by the provision of the heat exchanger 302 disposed within the housing 12, and the circulation of a separate isolated coolant. Due to this, there is no need for a filter in the system 300. This by itself is beneficial as the filter provides an impediment to flow, and requires regular cleaning.

The heat exchanger 302 is immersed in and otherwise in physical contact with the liquid brake lubricant 304. This facilitates heat exchange, i.e. extraction of heat from the liquid brake lubricant by convection. As explained in greater detail below the extraction of heat can be by a combination of natural heat convection and forced heat convection. These two types of heat transfer arise due to the structure of the heat exchanger 302 and its location in the housing 12 particularly in relation to the rotor 20. The heat exchanger 302 is disposed in a lower part of the housing 12 which forms a sump 322 for the liquid brake lubricant 304. The heat exchanger 302 is also disposed to lie adjacent to the rotor 20. In this regard the heat exchanger can be arranged to lie adjacent to either side of the rotor 20 and within the sump 322. In another form, as will be described below, the heat exchanger 302 can be arranged to lie on each of opposite sides of the rotor 20.

Natural convection occurs by virtue of the action of gravity which causes the liquid brake lubricant 304 to flow in a generally downward vertical flow path 324. With reference to the rotor 20 the flow path 324 is in a substantially radial direction. The forced heat convection is via flow of the lubricant 304 in generally horizontal flow path 326 which is generated by rotational motion of the rotor 20 through the sump 322 and lubricant 304. With reference to the rotor 20 the flow path 326 is in a substantially tangential direction. Generally speaking, when the vehicle to which the system 10 is fitted is in motion, i.e. the rotor 20 is turning; heat exchange will be predominantly by way of forced convection. However when the vehicle is stationary it is believed that heat exchange will be predominantly by natural heat convection by action either of the lubricant 304 flowing back to the sump 322 via the heat exchanger 304, or alternately simply by the heat exchanger 302 being immersed in the lubricant 304 within the sump 322.

The heat exchanger is also mounted to the calipers so as to provide heat transfer from the brake to the coolant by conduction as shown in Figs 21 & 22. Forced convection may be enhanced by the provision of mechanical features that promote or otherwise increase flow of liquid brake lubricant 304 through or past the heat exchanger 302 when the rotor is rotating. Such mechanical features may be coupled to or formed integrally with the rotor 20 or hub 18. Examples of such mechanical features include but are not limited to paddles on the rotor and/or a stirrer fitted to the hub 18. In the case of the paddles, these may extend radially from the outer circumferential edge of the rotor 20.

The heat exchanger 302 comprises a plurality of heat exchanger plates 328

(hereinafter referred to in general as "plates 328"). In the illustrated (but not necessarily every) embodiment the plates 328 are arranged in two banks 330a and 330b to lie on opposite sides of the rotor 20. Each plate 328 is made from two panels 332 and 334 which are fixed together in an overlying relationship. A coolant flow path 336 is formed in the panel 332 to allow circulation of coolant through a plate 328. The flow path 336 is created by a divider 337 that lies centrally of the panel 334 between respective openings 338 and 340 that provide fluid communication with coolant inlet and outlet pipes 342 and 344 respectively. The divider extends from one edge of panel 334 toward but terminates inboard of a diametrically opposite edge leaving a gap 339 for coolant to flow from opening 338 to opening 340. The opposite panel 334 is attached to the panel 332 and in particular forms a seal on the divider 337. Connection of the openings 338 and 340 to the inlet pipe 342 and outlet pipe 344 provides a parallel fluid circuit for the coolant through the heat exchanger 302.

A divider within the heat exchanger encourages turbulent and indirect flow between the inlet and outlet of the heat exchanger to maximise heat transfer.

A plurality of corrugated fins adjoin the parallel plates inside the heat exchanger. The fins increase the surface area available for heat exchange in so doing increasing the amount of and rate of heat exchange to the coolant in which they are immersed.

To further enhance cooling efficiency the heat exchanger 302 can be provided with flow directors such as scoops on opposing sides to direct and promote flow of liquid brake lubricant between the plates 328. The flow directors/scoops can be arranged to provide this promoted flow for both natural convection and forced convection. Figure 20b schematically shows one possible arrangement of scoops 329a and 329b on opposite sides of a bank of plates 328. The scoops are curved to in opposite directions to substantially follow the flow induced by rotation of the rotor 20.

As is clearly evident from Figures 18 - 22 the plates 328 are formed with a plurality of protrusions in the form of dimples 346 that protrude from one side of the plates 328. In this particular embodiment the dimples 346 protrude from the panel 334 of a plate 328 and extend away from the corresponding panel 332. Adjacent plates 328 are coupled together to form the heat exchanger 302 in part by fixing the dimples 346 of one plate 328 to the surface of an adjacent plate 328. The coupling of adjacent plates 328 is also achieved by way of the inlet pipe 342 and outlet pipe 344. The dimples 346 are arranged in a regular matrix pattern. It is the dimples 346 that create the generally vertical flow path 324 and the generally horizontal flow path 326 and resultant components thereof within the heat exchanger 302. The dimples 346 in addition to providing mechanical connection between adjacent plates 328 also provide thermal connection between the plates. Thus, the dimples 346 can be considered as an array or matrix of thermal conductors between the plates 328 of the heat exchanger 302. The matrix of dimples 346 creates a plurality of non-parallel flow paths across the heat exchanger 302. This is explained in greater detail below with reference to Figure 18.

Figure 18 depicts a generally vertical (i.e. radial) flow path 324 and horizontal (i.e. tangential) flow path 326 with reference to a heat exchanger plate 328. In this embodiment the heat exchanger plate 328 has four distinct sides designated as A, B, C and D. Flow paths for the lubricant 304 exist between any two of the sides A - D. For example one flow path 348 is depicted extending between sides B and C. A further flow 350 is depicted extending between sides A and D. Further, any flow path may comprise a multi directional path rather than extending generally linearly or with a constant curve or gradient across the heat exchanger 302.

It is believed that the cooling system 300 is particularly effective for vehicles or other rotary machines which undergo a large number of braking events during a normal operational cycle. Such vehicles include road vehicles, for example garbage trucks, heavy trailers, buses and vehicles used for off highway applications such as mine sites. The cooling of the brakes is effected in such vehicles predominantly by forced convection when the vehicle is moving and by natural convection when it is stationary. In one particular embodiment when the cooling system 300 and brake system 10 is fitted to a 25 tonne garbage truck having six wheel ends with each wheel having a one metre diameter, with average in service braking effort of about 60kW per wheel end, the cooling system 300 may provide an average in service cooling of approximately 10kW per wheel end. While of course this is only a fraction of the maximum service braking effort, the maximum service braking effort is only momentarily applied while the cooling effect is provided continuously thus providing a cumulative cooling effect. For ease of reference thought out this specification including the claims, reference to a braking effort, or cooling when expressed in kW or as a percentage of a brake or cooling power is to be taken and understood as an average in service value unless from the express words used or the context a different meaning is plainly evident.

In the cooling system 300 depicted in Figures 17 the pump 306 is shown as circulating coolant through the circuit 310 pertaining to a single heat exchanger 302. In a further variation, the pump 306 may operate to circulate coolant through a plurality of cooling circuits 310 associated with respective heat exchanger 302 disposed in the housings 12 of other brake systems 10 of the same machine or vehicle.

Previously described in one embodiment when the brake system 10 is provided with brake calipers 14 and a rotor 20 that are arranged to provide an average in service braking effort of about 60kW per wheel end, the lubricant cooling system 300 is arranged to extract about 10 kW of heat per wheel end (20kW per axle). However in more general terms, embodiments of the cooling system 200 or 300 may be arranged to provide up to 15 kW of cooling power per brake system 10 (30kW per axle). In other embodiments the cooling system 200 or 300 may be arranged to provide between 5kW and 15 kW (including every single value and any every sub-range in this range) of cooling per brake system 10 wheel end. In terms of a vehicle travelling at 100 km/h and fitted with the system 10, the associated cooling system 200 or 300 can be arranged to provide cooling power of up to about 10% of the maximum service brake power. In other embodiments the cooling system 200 or 300 may be arranged to provide cooling power of between 1 % to 10% (including every single value and any every sub-range in this range) of maximum service brake power applied by system 10 to a vehicle travelling at 100kph.

The ability of the braking system 10 to provide a certain amount of service braking effort and to provide a certain amount of heat extraction is dependent on many factors including but not limited to the, actuation piston area, contact area between the brake pads and friction surface, diameter of the rotor, and physical dimensions of the housing 12.

Each of the cooling systems 200 and 300 can be provided with a cooling fan F (see Figs 16 and 17) arranged to generate a flow of air across or through the respective radiators 206 and 308. The respective cooling system 200 and 300 can each be arranged to operate independently of one or both of ignition state and vehicle speed. In addition or alternately the respective cooling system 200 and 300 can each be arranged to operate in response to, i.e. dependant on, liquid brake lubricant

temperature. Also the cooling system 300 can be arranged to operate in response to, i.e. dependant on, coolant temperature instead of lubricant temperature.

The above described operating options for the cooling systems 200 and 300 may be manifested by operating their respective pumps 208, 306; and/or fans F (a)

independently of one or both of ignition state and vehicle speed; or (b) in response to, i.e. dependant on, liquid brake lubricant temperature. Of course with the system 300 there is also the option of operating one or both of pump 306 and fan F to operate in response to, i.e. dependant on, coolant temperature.

Operating the cooling systems 200, 300 (or their pumps and/or fans) independently of one or both of ignition state and vehicle speed can be achieved by an electronic control unit 350 or by wiring their pumps/fans directly to a battery of the vehicle/machine to which the brake system 10 is fitted. When operated independently of ignition state and/or speed the pump and/or fan may operate or continue to operate when the ignition is OFF for a predetermined period if the brake lubricant temperature is above the threshold temperature. In embodiments where the respective fluid circuits of cooling systems 200 and 300 utilize a coolant which is use to provide cooling to the liquid brake lubricant, the cooling circuit through which the coolant flows may be pressurised to elevate the boiling point of the circulated coolant. Figures 1 and 21 - 22 depict the braking system 10 as comprising two calipers 14 that are spaced apart about the rotor 20. The calipers 14 are spaced by a distance sufficient to accommodate the heat exchanger 302 and at a specific location such that the heat exchanger 302 is disposed within the sump 322 in the housing 12. The brake system 10 which incorporates a lubricant cooling system such as the system 200 or 300 may also be provided with an operator (which for a vehicle is a driver) feedback system 350 (see Figure 17). The feedback system provides feedback on the basis of the lubricant temperature in the brake system. The purpose of this is to warn the operator of excessive brake temperature. Brake fade is a reduction in stopping power that occurs after repeated or sustained application of the service brakes. Brake fade occurs due to the build-up of heat in the braking surfaces. Often in, for example trucks which are provided with dry air brakes, the brake fade is communicated to the driver by a 'spongy' or 'wooden' feel at the brake pedal. This provides the driver with warning as to the impending reduction in stopping power. However in wet disc brake systems brake fade does not occur and driver feedback through the brake pedal does not exist. Consequently, even though brake temperature may be rising sufficiently to adversely affect brake durability and longevity, the feel of the brake remains the same to the driver. In the present embodiment the feedback system 350 may be arranged to provide one or any combination of a visual, audible, or tactile feedback to an operator. In Figure 17 the feedback system 350 is depicted as comprising any one or any combination of a visual indicator 352, an audible indicator 354, and a tactile indicator 356. The driver feedback system 350 incorporates a thermistor or other temperature measurement device or system that is in communication with the fluid circuit 310 and arranged to sense temperature of the wet brake system lubricant 304. Driver feedback is provided when the liquid brake lubricant exceeds a threshold temperature. This temperature may be for example the maximum operating temperature of elastomeric O-ring seals 162 used in the brake pistons 128. In one example the threshold temperature may be up to 200° C, say about 120°C to 200°C. In another example the threshold temperature can be set to at least 100°C less than the temperature of the rotor 20 normally associated with brake fade and/or accelerated brake wear.

In the visual indicator 352 a plurality of light emitting devices 358a, 358b and 358c are provided. At a low and safe operating temperature, the first of the light emitting devices 358a illuminates. If sensed temperature is approaching a threshold operating temperature (say within 30°C of the maximum threshold), then a second light emitting device 358b illuminates. If the sensed temperature reaches or exceeds the maximum threshold temperature then the third light emitting device 358c is illuminated. This indicates to the operator that the brake temperature is now exceeding a safe operating temperature. Additionally or alternatively the visual indicator may be in the form of a gauge. The audible indicator 354 is in the form of a speaker. However the sound emitted by the speaker 354 may vary for example in terms of volume, pitch, or frequency as brake operating temperature increases.

In relation to the tactile indicator 356 this may be in the form of a dashpot or solenoid coupled with a brake operating mechanism such as a brake pedal and arranged to increase the force required by the operator on the operating mechanism to achieve a braking effect as brake temperature increases. Alternately the feedback system can be arranged to provide tactile feedback in a manner to mimic a feel of brake fade. In one embodiment the tactile feedback may be provided only when the threshold temperature is at least 100°C less than the temperature of the rotor 20 normally associated with brake fade and/or accelerated brake wear.

In the description of the preferred embodiment, ranges of various physical parameters have been specified. The specified ranges are intended and should be understood as also including every possible sub range within the specified range and not to exclude narrower rangers. For example the intention in specifying the rotor diameter range of about 375 mm to 450 mm is to include sub ranges such as, but not limited to: 375 mm to 430mm; or 395 mm to 450; 395 mm to 430mm and so forth. Also while several specific embodiments have been described it will be readily apparent to anyone having even just a basic understanding of mechanics that features of various embodiments are interchangeable and the mere fact that one feature is described in relation to one specific embodiment only does not exclude: the substitution of that feature with an equivalent feature of a different embodiment; or the incorporation of that feature in another embodiment where it is not otherwise described. For example the use of grooves 1 13 on the pads 1 10 is described in relation to the embodiment of Figure 13. Clearly such grooves 1 13 may be incorporated in the pads of any of the described embodiments.

All such modifications and variations together with others that would be obvious to persons of ordinary skill in the art are deemed to be within the scope of the disclosed brake system, the nature of which is to be determined from the above description and the appended claims.