WO2014199129A1

WO2014199129A1 - Brake pad assembly

Info

Publication number: WO2014199129A1
Application number: PCT/GB2014/051757
Authority: WO
Inventors: Trevor Michael MENNIE
Original assignee: Mennie Trevor Michael
Priority date: 2013-06-12
Filing date: 2014-06-06
Publication date: 2014-12-18

Abstract

A brake pad assembly (300) comprises a brake pad (302) having a braking surface (306) and an opposed back surface (308), a hydraulic actuator comprising a cylinder (310) and a piston (312), the piston being operatively connected to the back surface of the brake pad and moveable within said cylinder for varying the position of the brake pad and a conduit extending through said piston and being in fluid communication with said braking surface for providing fluid flow to said braking surface. The brake pad (302) comprises a passage (324) extending from the back surface (308) to the braking surface (306) for providing fluid flow to said braking surface, said passage having one or more internal walls (323) and means for preventing or reducing the leakage of fluid from said passage into said brake pad (302) via said one or more internal walls

Description

Brake Pad Assembly

The present invention relates to a brake pad assembly, a brake system, a method of using a brake pad assembly or brake system, and a control system for a brake system. The present invention also relates to a kit and method for modifying a brake pad or brake system. Preferred embodiments of the present invention are directed to brake pads, brake pad assemblies or brake systems for vehicles.

Brake systems for vehicles typically comprise a brake rotor fixed to the wheel of the vehicle. The brake rotor (which may be a disc or drum) rotates with the wheel when the vehicle is moving. With disc brakes, a pair of brake pads is typically positioned with the respective brake pads on either side of the brake rotor, and the brake pads are typically brought into firm contact with the brake rotor by brake calipers. Wth drum brakes, brake pads are typically positioned on the inside of the brake drum and are forced outwards into firm contact with the brake drum. Brake pads are typically fixed to a static part of the vehicle, and do not rotate with the wheel when the vehicle is moving. When the brake is activated, the brake pad is pressed firmly against the brake rotor, and friction between the static brake pad and rotating rotor causes the speed of rotation of the rotor, and therefore the speed of rotation of the wheel, to slow. This in turn slows the vehicle.

When the brake is not being activated, brake pads are usually positioned in close proximity to the brake rotor so that the distance that the brake pad needs to travel in order to firmly contact the brake rotor is small and so that the activation time for the brake is short. This is particularly the case with hydraulically actuated brakes, in which a piston that is provided at the brake pedal of the vehicle to actuate the brake is in hydraulic communication with a piston that is provided at the brake pad to move the pad into contact with the rotor. The brake pedal piston has a smaller diameter than the brake pad piston, such that a larger movement/lower force provided at the brake pedal to activate the brake is converted into a much smaller movement but a much larger force at the brake pad to move the pad. Thus, with hydraulically actuated brakes, the distance between the brake pad and brake rotor is typically necessarily small so that an appropriate amount of force can be applied by the brake pad.

A small distance between a brake pad and brake rotor can also reduce the amount of debris that can accumulate between the brake pad and brake rotor, and can keep the brake pad dry by reducing the amount of water ingress. In some arrangements, brake pads may even be positioned in light contact with the brake rotor even when the brake is not being activated so as to minimise the distance and time to activate the brake.

However, a problem with these arrangements exists in that intermittent or constant contact between the brake pad and brake rotor when the brake is not being activated generates an undesired braking force that the vehicle has to overcome. This reduces the power and efficiency of the vehicle, and leads to higher fuel consumption. The intermittent or constant contact between the pads and rotor also causes wear on the brake pads and rotors, which can shorten the lifetime of the brake pads and rotors and can produce polluting brake pad dust.

A brake system in which pressurised fluid is supplied to a brake pad to maintain a gap between the pad and a rotor is disclosed in GB-2492858. Other examples of brake systems using a supply of pressurised fluid to the braking surface are shown in DE-4401846, JP- 2009236221 and DE-10047198. One problem encountered with prior art systems is, that in order to supply the pressurised air to the braking surface, a passage is provided through the brake pad (or a backing plate attached thereto) in a direction parallel to the braking surface. Such a passage may be difficult to machine and can substantially weaken the brake pad (or backing plate).

Another problem encountered with prior art systems is that pressurised fluid flowing through a brake pad can leak laterally into the body of the brake pad due to, for example, any porosity of the brake pad. This leakage reduces the amount of pressurised fluid that is supplied to the braking surface, thus reducing the efficiency and effectiveness of the system.

The present invention seeks to provide brake systems that address the aforementioned problems.

According to an aspect of the present invention there is provided a brake pad assembly comprising a brake pad having a braking surface and an opposed back surface, a hydraulic actuator comprising a cylinder and a piston, the piston being operatively connected to the back surface of the brake pad and moveable within the cylinder for varying the position of the brake pad and a conduit extending through the piston and being in fluid communication with the braking surface for providing fluid flow to the braking surface.

The brake assembly may form part of a brake system, such as a disk brake system. In these embodiments, the disk brake system preferably comprises a pair of opposed brake pads, preferably joined by a caliper. However, in other embodiments the brake system may comprise a single brake pad and/or may comprise a drum brake.

The brake system may comprise a brake rotor positioned adjacent to the braking surface of the brake pad. The fluid flow to the braking surface of the brake pad preferably provides a gap between the brake rotor and the braking surface of the brake pad when provided under non-braking conditions.

The brake system may further comprise a pressurised fluid supply in fluid

communication with the braking surface of the brake pad via the conduit.

The brake system may be configured such that, in use, fluid from the pressurised fluid supply is provided to the braking surface of the brake pad under non-braking conditions, the fluid from the pressurised fluid supply providing a gap between a brake rotor and the braking surface of the brake pad when provided to the braking surface under non-braking conditions, the pressurised fluid supply being capable of supplying pressurised fluid at a pressure that is sufficient to separate the braking surface of the brake pad from the brake rotor under non- braking conditions.

As will be appreciated, the "braking surface" referred to herein is the surface of the brake pad that contacts (or is intended to contact) an adjacent brake rotor when the brake is activated. The braking surface is therefore a surface of the brake pad which faces (or is intended to face) an adjacent brake rotor in use. The braking surface may be referred to as a "friction surface" of the brake pad. The brake pad and brake rotor will define opposed surfaces, the braking or friction surface of the brake pad being the surface that contacts (or is intended to contact) the surface of an adjacent brake rotor in use.

The brake pad can take any desired or suitable form. For example, the brake pad may comprise any suitable friction material (e.g. a ceramic, semi-metallic, metallic or carbon fibre material) on a support structure. In embodiments therefore the brake pad may comprise a support structure and a friction material thereon. In these embodiments the friction material defines the braking surface (rotor facing surface) and may define an opposite support structure facing surface. The friction material may be a body of friction material. The friction material may be a single (i.e. only one) layer of material, or may comprise a plurality of layers of one or more materials.

The support structure may comprise a back plate and the back surface of the brake pad may be located on the back plate.

The term 'operatively connected' should be understood to mean that the piston and brake pad are arranged such that movement of the piston, at least in the direction away from the cylinder, causes the brake pad to move in the same direction. The piston may be secured to or engaged with the back surface of the brake pad, but this is not necessary. Instead, the piston may just push against the back surface of the brake pad, as it moves towards it, and be free to separate from the back surface as it moves in an opposite direction (away from the brake pad and towards the cylinder).

The use of a hydraulic actuator, comprising a piston and cylinder, to move a brake pad towards a brake rotor, is known in the art. Applying the brakes of a vehicle, such as a car, by, for example, pressing a brake pedal, forces hydraulic fluid into the cylinder, which in turn pushes the piston away from the cylinder and moves the brake pad towards a rotor. Suitable pistons and cylinders are commercially available. The term 'cylinder' is a term of the art referring to a sleeve-like part that accepts a piston. It does not mean the part is necessarily cylindrical in shape, but this may be the case. The piston and cylinder may have a circular cross-section but this is not necessary. The piston and cylinder may be formed from metallic materials, although other materials may be suitable. The conduit extends through a portion of the piston. The conduit extends through an outer surface of the piston. The conduit provides a path from the outer surface of the piston to the brake pad, so that fluid flow can be provided via the piston to the brake pad, without requiring a conduit running along the length of the brake pad (parallel to the braking surface). A conduit through the piston is more easily machined, more conveniently located for connected to a fluid source and does not weaken the brake pad to such an extent.

There may be a plurality of pistons on each brake pad, with each piston having a conduit extending therethrough and being in fluid communication with the braking surface of the brake pad.

Preferably, the conduit extends through a portion of the outer surface of the piston that remains exposed throughout the motion of the piston within the cylinder. The term 'exposed' should be understood to refer to a portion that is not covered by the cylinder so that an inlet of the conduit on the outer surface is open and accessible for connection to a source of pressurised fluid, e.g. a pipe. The portion may therefore be one that is not directly contacted by the cylinder in use.

The conduit may comprise a cavity that is at least partially defined by one or more internal surfaces of the piston and the back surface of the brake pad. In other words, at least a portion of the conduit may be defined by an open-ended cavity formed by one or more internal surfaces of the piston and this cavity may (in use) be closed when the piston is in engagement with the back surface of the brake pad. There may be one or more openings into the cavity through the piston's outer surface.

The piston may comprise a substantially hollow interior, said hollow interior defined by the one or more internal surfaces.

The piston may comprise a concave portion, the concave portion being open to the back surface of the brake pad and forming the cavity.

The piston may comprise a first end that faces the brake pad, a second opposed end that faces an internal surface of the cylinder and at least one side surface extending between the first and second ends.

The first and second ends may be distal ends of the piston. The second end may be located within the cylinder and define a chamber within the cylinder, that (in use) is filled with hydraulic fluid.

The piston may comprise first and second faces at the first and second ends. The side surface may be contiguous to the first and second ends. The conduit may extend through the side surface of the piston. In particular, the above mentioned portion of the outer surface through which the conduit extends may be in the side surface. Such a location is easily accessible, even when the piston is in engagement with the back surface of the brake pad. The conduit may comprise a notch extending through the side surface and the first end. The notch can be considered to be a cut-out in the first end that extends along the side surface away from the first end.

Alternatively, the conduit may be spaced from the first end along the side surface.

The first end of the piston may define an outlet of the conduit from the piston. The first end may comprise a planar surface surrounding the outlet for engaging the back surface of the brake pad. The surface may be annular, with the outlet being circular. The outlet of the conduit may be in fluid communication with the braking surface of the brake pad, optionally via a portion of the back surface of the brake pad.

The piston may comprise first and second connected portions, the first portion comprising the first end and the second portion comprising the second end, the conduit extending through the first portion. The term 'connected' used here should be understood to mean that, in use, the first and second portions move together. When hydraulic fluid imparts a force upon the second end, the second portion moves the first portion away from the cylinder.

The first portion may be annular or disk shaped.

The first portion may provide a seal between the interior of the piston and the back surface of the brake pad. The first portion may be a washer, for example made of metal, such as steel, brass or aluminium, having a split ring shape, with the split portion defining a cut-out in the first end of the piston.

The brake pad may have one or more passages extending from the braking surface to the back surface, the conduit being in fluid communication with the braking surface via the passage.

At least a portion of one of the passages may be aligned with a central axis of the piston. The axis of the piston refers to a longitudinal axis along which the piston moves within the cylinder. The central axis runs through a central point of the cross-section of the cylinder. The piston may be rotationally symmetrical about the central point.

The passage may extend through the brake pad substantially perpendicularly to the plane of the brake pad.

The one or more passages may each extend through the brake pad from an opening in the braking surface. Each opening is preferably aligned with a central axis of a piston.

The passage may open onto the back surface of the brake pad within an area defined by the outer periphery of the first end of piston.

The one or more openings may be a single (i.e. only one) opening, wherein the single opening is positioned substantially in the centre of the braking surface of the brake pad.

However, in other embodiments the one or more openings may comprise a plurality of openings, wherein the plurality of openings are preferably concentrated substantially in the centre of the braking surface of the brake pad and/or are evenly distributed across the central portion of the braking surface of the brake pad, or are evenly distributed across all of the braking surface of the brake pad (so as to balance out the reactive forces provided by the fluid as the fluid exists the openings). The one or more openings are also preferably positioned such that fluid can be supplied to substantially all of the braking surface of the brake pad.

In embodiments, the or each opening is an opening over and above any pores inherent in the material (e.g. friction material) defining the braking surface.

In an alternative set of embodiments, the brake pad (or each brake pad) may comprise a porous structure in its braking surface for providing fluid to the braking surface of the brake pad, via the porous structure. The porous structure may be provided by a suitable porous (braking or friction) material. The porous structure may be positioned such that fluid can be supplied to substantially all of the braking surface of the brake pad via the porous structure. For example, the majority or all of the brake pad surface may be porous.

It is envisaged that the braking surface may comprise one or more openings and a porous structure in the braking surface. For example, the braking surface may be provided by a porous structure having one or more passages therethrough.

The brake pad assembly may further comprise a pipe extending through the conduit and into the passage. The pipe may be connected to a pressurised fluid source. The pipe may extend through the passage up to the braking surface. Alternatively, the pipe may extend into the passage but not to the braking surface. The pipe may or may not protrude beyond the outer surface of the piston.

Preferably, the pipe passes through the piston's outer surface, through the conduit and through the brake pad to the braking surface. This prevents any leakage of the fluid in the piston, conduit or brake pad.

According to another aspect of the present invention there is provided a brake pad comprising a braking surface and an opposed back surface, a passage extending from the back surface to the braking surface for providing fluid flow to the braking surface, the passage having one or more internal walls and means for preventing or reducing the leakage of fluid from the passage into the brake pad via the one or more internal walls.

The brake pad may have any of the features described above in relation to the previous aspect of the present invention. For example, the passage may be as described above and may be in fluid communication with a conduit passing through a piston of a hydraulic actuator.

The brake pad may comprise a plurality of passages, each extending from the back surface of the braking surface, with leakage prevention means being provided for each passage. Alternatively, the brake pad may only comprise a single passage.

The passage may have a circular cross-section and have a single cylindrical internal wall. Alternatively, the passage may have a non-circular cross-section and/or may have more than one internal wall. As discussed previously, the brake pad may be porous.

Preventing (or reducing) the leakage of fluid into the brake pad via the internal walls, whether due to the porosity of the brake pad or any cracks or other imperfections in the internal wall(s) of the brake pad, reduces any loss of pressure before the braking surface. This provides a more efficient and effective system.

In one embodiment, the means for preventing (or reducing) leakage comprises a pipe extending through the passage. The pipe preferably extends from the back surface to the braking surface of the brake pad. The pipe is made from a non-porous material, such as a plastics material.

The pipe may be formed from a resilient material. This allows the pipe to be stretched longitudinally when being passed through the passage, which can provide a tight fit when the pipe is relaxed (due to radial compression of the pipe by the internal wall(s) of the passage).

The pipe may be formed from a flexible material. This allows for easier manipulation of the pipe into place.

The pipe may be formed from an abradable material and in particular a material that is at least as easily abradable as the material of the braking surface of the brake pad. This allows the end of the pipe at the braking surface to be worn away, by a brake rotor, together with the braking surface.

The pipe may be formed from a plastic material such as silicone rubber.

The pipe has a first end and a second end. The first end may be flush with, or extend beyond, the braking surface. As mentioned above, in use, the first end may be abraded together with the braking surface.

The second end of the pipe may extend beyond the back surface of the brake pad. At its second end, the pipe may have a greater diameter than the inlet to the passage on the back surface of the brake pad. This means that, at least at the inlet to the passage, the pipe is radially compressed by the internal walls of the passage. This ensures a tight fit between the pipe and the brake pad.

In an alternative embodiment, the means for preventing leakage comprises a coating on the one or more internal walls, the coating having a lower porosity than the brake pad.

The coating may comprises a rubberised material, such as a silicone rubber, that can be painted onto the internal wall or walls.

In another alternative embodiment, the means for preventing leakage comprises a portion of the brake pad having a decreased porosity, the portion comprising the one or more internal walls.

The decreased porosity portion may be formed by treating that portion differently during manufacture of the brake pad. For example, different materials could be used for that portion of the brake pad or that portion could be compacted more highly in a press. The brake pad assembly of the previously disclosed aspect of the present invention, may comprise a brake pad having a passage and means for preventing leakage from the passage into the brake pad, as described above in relation to any of the above mentioned embodiments.

The brake pad or brake pad assembly described above may comprise a caliper, a brake shoe and/or any other standard parts of a brake pad assembly.

The present invention extends to a brake system comprising a brake pad or brake pad assembly as described above and a brake rotor positioned adjacent to the braking surface of the brake pad.

The brake system may further comprising a pressurised fluid supply in fluid

communication with the braking surface of the brake pad via the conduit. The brake system may be configured such that, in use, fluid from the pressurised fluid supply is provided to the braking surface of the brake pad under non-braking conditions, the fluid from the pressurised fluid supply providing a gap between a brake rotor and the braking surface of the brake pad when provided to the braking surface under non-braking conditions, the pressurised fluid supply being capable of supplying pressurised fluid at a pressure that is sufficient to separate the braking surface of the brake pad from the brake rotor under non-braking conditions.

The brake system may further comprise a fluid removal means in fluid communication with the braking surface of the brake pad, wherein the system is configured such that the fluid removal means allows the removal of fluid from the braking surface of the brake pad under braking conditions.

The fluid removal means preferably comprises a fluid removal valve in fluid

communication with the braking surface of the brake pad. The system (or system control means) is preferably configured to open the fluid removal valve so as to vent the fluid to atmosphere under braking conditions and/or close the fluid removal valve under non-braking conditions. Alternatively, the fluid removal means may comprise a fluid suction device.

The present invention also extends to a vehicle comprising a brake system as described above.

According to another aspect of the present invention there is provided a method of providing a brake pad comprising a braking surface and an opposed back surface, a passage extending from the back surface to the braking surface for providing fluid flow to the braking surface, the passage having one or more internal walls and means for preventing or reducing the leakage of fluid from the passage into the brake pad via the one or more internal walls, wherein the means comprises a pipe extending through the passage. The method comprises forming a passage between a back surface and a braking surface of a brake pad, passing a pipe through the passage, the pipe being in an elongated state and having a cross-sectional area in the elongated state that is smaller than a diameter of the passage and allowing the pipe to relax so that its length is reduced, its cross-sectional area is increased and its outer surface engages one or more internal walls of the passage.

Stretching the pipe when passing it through the passage means that when the stretching force is released, the pipe expands radially and presses against the internal walls of the passage. The method therefore provides a way of ensuring a tight interference fit between the pipe and the passage through the brake pad.

To assist in the step of passing the pipe through the passage, a small amount of lubricant such as water may be applied to the pipe or the passage. Alternatively, a coating such as a silicone sealant could be applied to the pipe so that this coating sets between the relaxed pipe and the internal walls.

The step of passing a pipe through said passage in an elongated state comprises securing an elongate member, having a smaller cross-sectional area the passage, to the pipe and passing the elongate member through the passage.

The elongate member can be used to stretch the pipe prior to it being passed through the passage.

The elongate member may be a length of string or wire.

The elongate member may be secured to the pipe by being tied to the pipe or being passed around a loop formed by folding an end of the pipe.

The method may further comprise, after allowing the pipe to relax, cutting a first end of the pipe protruding from the braking surface to be flush with the braking surface.

According to another aspect of the present invention there is provided a brake system comprising a brake pad having a braking surface and a pressurised fluid supply in fluid communication with the braking surface of the brake pad, wherein the system is configured such that fluid from the pressurised fluid supply is provided to the braking surface of the brake pad under non-braking conditions.

The brake system or brake pad may have any of the features described above in relation to the previous aspects of the present invention.

According to another aspect of the present invention there is provided a vehicle comprising the brake pad, brake pad assembly or brake system described herein. This aspect of the present invention may comprise any or all of the preferred or optional features discussed herein as appropriate.

The vehicle may be a road or motor vehicle (such as bicycle, an automobile (car, van, etc.), motorcycle, quad bike, truck or bus), may be a rail vehicle (such as a tram or train), or may be an aircraft (having, for example, a landing gear comprising the brake pad assembly or brake system). The vehicle may be any one or ones of the vehicles listed above. The vehicle may have one or more brake pads (e.g. for some or all of the wheels of the vehicle), with one or more or each of those brake pads having pressurised fluid supplied to its surface in the manner described herein and/or fluid/dust removal openings and/or fluid/dust removal means in the manner discussed herein.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which:

Figure 1 is a cross sectional view of a brake system according to an embodiment of the present invention;

Figure 2 is a brake pad according to an embodiment of the present invention;

Figure 3A is a brake pad according to another embodiment of the present invention;

Figure 3B is cross sectional view of the brake pad of Figure 3A;

Figure 4 is a combined pressurised fluid supply and fluid suction device arrangement according to one embodiment of the present invention;

Figure 5 is a cross sectional view of a brake system according to another embodiment of the present invention;

Figures 6A-6D are a brake pad assembly according to another embodiment of the present invention;

Figures 7A and 7B are radial and axial cross-sectional views of a brake pad assembly according to an embodiment of the present invention;

Figure 8 is an axial cross-sectional view of a brake pad assembly according to another embodiment of the present invention;

Figure 9 is an axial cross-sectional view of a brake pad assembly according to another embodiment of the present invention; and

Figure 10 is an axial cross-sectional view of a brake pad assembly according to another embodiment of the present invention.

Figure 1 is a cross sectional view of one embodiment of a brake system 10 for a motor vehicle. The brake system comprises a wheel hub 12 (shown in part) and a brake rotor 14

(brake disc) rotationally fixed to the wheel hub 12 by a fixing 16 such as a bolt. The wheel hub 12 and brake rotor 14 rotate about a centreline 18 when the vehicle is moving.

The brake system 10 further comprises a pair of brake pads 20 adjacent to the brake rotor 14. The brake pads 20 each comprise a friction material on a support structure (not shown). The brake pads 20 each have a braking surface 24 of the friction material that faces the brake rotor 14.

The brake pads are joined to one another by brake calipers (not shown), and the brake calipers are fixed to a static (non-rotating) part of the vehicle. The braking surfaces 24 (and therefore the friction material) of the brake pads 20 can be forced into firm contact with the brake rotor 14 using the brake calipers. The brake calipers are controlled by the brake pedal of the vehicle. The brake pads 20 each have an opening 22 for providing pressurised fluid (e.g. air) at a pressure P to the braking surface 24 of the brake pad 20 that is adjacent the brake rotor 14. The pressurised fluid is provided to the openings 22 in the braking surface 24 of the brake pad 20 from a compressor or pump (not shown) via tubes 26. The fluid that is provided to the braking surface 24 of the brake pad 20 is allowed to escape from the brake system by venting to the surrounding atmosphere in the gap between the brake pad 20 and the brake rotor 14.

The operation of the compressor or pump is controlled by a system control means (not shown). The system control means may be in communication with a sensor that detects the operation of the brake pedal and/or the accelerator/throttle of the vehicle so to determine whether or not braking conditions exist.

Under non-braking conditions (e.g. when the brake pedal is not activated and/or the accelerator/throttle is activated), the system control means allows pressurised fluid to be provided from the compressor or pump to the braking surfaces 24 of the brake pads 20 via the tubes 26. This may be achieved, for example, by switching the compressor or pump on and/or by opening a supply valve (not shown) that is in fluid communication between the compressor or pump and the braking surface 24.

When the pressurised fluid is provided to the braking surface 24 of the brake pads 20, the fluid pushes the brake pads 20 away from the brake rotor 14 with a force F_A. The force F_A works against the force F_B of the calipers in their non-braking state. As will be appreciated, F_A may vary with the distance D that exists between the brake pads 20 and the brake rotor 14. An increase in the distance D between the brake pads 20 and the brake rotor 14 may decrease the force F_A. Conversely, a decrease in the distance D between the brake pads 20 and the brake rotor 14 may increase the force F_A. The force F_B may effectively remain the same, but may vary with the distance D (e.g. an increase in D may lead to an increase in F_B and vice versa).

The pressure P of the fluid is selected and provided such that, when F_A is equal to F_B, the brake pads 20 are positioned and maintained at a suitable distance D away from the brake rotor 14. The distance D need only be enough to prevent the brake pad 20 from contacting the brake rotor 14 (e.g. 10 microns). This prevents or reduces the frictional contact between the brake pad 20 and brake rotor 14, increasing the power and efficiency of the vehicle and decreasing brake pad wear.

Under braking conditions (e.g. when the brake pedal is activated and/or the

accelerator/throttle is not (or no longer) activated), the system control means prevents pressurised fluid from being provided to the braking surfaces 24 of the brake pads 20. This may be achieved, for example, by switching the compressor or pump off and/or by closing a valve that is in fluid communication between the compressor or pump and the brake pad braking surface 24 so as to cut-off the fluid supply to the braking surface. This brings the brake pad 20 into contact (or closer contact) with the brake rotor 14, and reduces the braking activation distance and time.

Also under braking conditions, or for a predetermined period of time after a braking operation occurs (e.g. for 1 second), the control system may actively or passively allow fluid to be removed from braking surfaces 24 of the brake pads 20. This may be achieved, for example, by a fluid removal means. For example, the fluid may be removed by switching on a vacuum (not shown) that is in fluid communication with the openings 22 of the brake pads 20, by opening a valve (not shown) in fluid communication with the braking surface 24 that vents to the surrounding atmosphere, or by operating or connecting the aforementioned compressor or pump in reverse. The removal of fluid brings the brake pad 20 into closer contact with the brake rotor 14, and reduces the braking activation distance and time.

In one arrangement, the aforementioned compressor or pump has an input that draws fluid in, and an output that provides pressurised fluid. Under non-braking conditions, the input is fluidly connected to the surrounding atmosphere, and the output is fluidly connected to the openings 22 in the brake pad 20. Under braking conditions, the output is fluidly connected to the surrounding atmosphere, and the input is fluidly connected to the openings 22 in the brake pad 20. Thus, the same compressor or pump can be used both as a pressurised fluid supply and a fluid removal (suction) device.

As will be appreciated the features of the brake system 10 can be retrofitted to an existing brake system. For example, in order to provide the broader embodiments of the brake system 10, openings 20 may be provided (e.g. drilled) though existing brake pads 20 and a tube 26 may be provided in fluid communication with the openings. A suitable compressor or pump may be provided and connected to the tube 26. A suitable system control means may then be provided to control the operation of the brake system 10 in the manner discussed above.

Figure 2 shows a pair of brake pads 20 according to one embodiment of the present invention. The brake pads 20 each have a braking surface 24 with an opening 22 in that surface. The openings 22 can be fluidly connected with a tube 26 (see Fig. 1). The opening 22 in this particular example is a racetrack slot having a length 'b' of 21 mm and a width 'a' of 1 1 mm. Such embodiments are particularly advantageous in that the fluid is centrally, effectively and evenly distributed by the slot to the majority of the surface 24 of the brake pad 20. This can prevent the brake pad 20 from tipping and contacting the adjacent brake rotor 14 when the fluid is supplied to the surface of the brake pad 20.

Figures 3A and 3B show a brake pad 30 according to another embodiment of the present invention. The brake pad 30 has a braking surface 34 with an opening 32 in that surface. The opening 32 can be fluidly connected with a tube 36 to the pressurised fluid supply. The braking surface also has a circumferential track 38 around the perimeter of the brake pad 30. A peripheral wall 37 is formed by an outer peripheral portion of the brake pad 30, and the circumferential track 38 provides a void between the outer peripheral portion of the brake pad 30 and an inner portion 39 of the brake pad 30. The circumferential track 38 can be fluidly connected with a tube 40 via an opening to a fluid or dust removal means, which in this embodiment also acts as the pressurised fluid supply. Figure 3B also shows the steel support structure 42 of the brake pad 30.

Figure 4 shows a combined pressurised fluid supply/fluid suction device 44 according to one embodiment of the present invention which may be used in conjunction with the brake pad of Figures 3A and 3B. The pressurised fluid supply/fluid suction device 44 comprises a compressor or pump 50 having an input 46 for receiving (filtered/conditioned) fluid and an output 48 for providing pressurised fluid.

When acting as a pressurised fluid supply, the input 46 is placed in fluid communication with the surrounding atmosphere by a first 3-way valve 52 via a first filter/conditioner 56 and the output 48 is placed in fluid communication with the braking surface by a second 3-way valve 54. The first filter/conditioner 56 protects the brake pad 30 and/or compressor or pump 50 by collecting particles and/or removing moisture from the surrounding atmosphere.

When acting as a fluid suction device, the input 46 is placed in fluid communication with the brake pad 30 by the first 3-way valve 52 via a second filter 58 and the output 48 is placed in fluid communication with the surrounding atmosphere by the second 3-way valve 54. The second filter 58 acts to collect braking dust generated under braking.

The first 3-way valve 52 and second 3-way valve 54 in this embodiment are under the control of a system control means.

Figure 5 is a cross sectional view of a brake system according to another embodiment of the present invention. Figure 5 shows a brake pad 60 in contact with a brake rotor 62. The brake pad 60 comprises braking material 64 and a support structure 66.

The brake pad 60 comprises a central opening 68 for providing fluid to the braking surface of the brake pad 60, a first perimeter opening 70 for providing fluid to the brake pad 60, and a second perimeter opening 72 for removing fluid and brake dust from the brake pad 60. Fluid is simultaneously provided and removed by a circulating compressor or pump 76. A filter/conditioner 78 is provided between the second perimeter opening 72 and the compressor or pump 76 to collect brake dust generated during braking and/or remove moisture. A diverting valve 80 (a 3-way solenoid valve) is located between the compressor or pump 76 and the centrally located opening 68. The diverting valve 80 is also located between the compressor or pump 76 and first perimeter opening 70.

The diverting valve 80 acts to provide fluid from the compressor or pump 76 to the centrally located opening 68 under non braking conditions so as to separate the brake pad 60 from the brake rotor 62. The diverting valve 80 acts to provide fluid from the compressor or pump 76 to the first perimeter opening 70 under braking conditions to aid the removal of brake dust. The diverting valve 80 in this embodiment is under the control of a system control means.

A peripheral wall is provided by a silicone skirt 74 around the brake pad 60. The skirt 74 translates with brake pad 60 under braking conditions so as to span the gap between the brake pad 60 and the brake rotor 62 under braking conditions, thereby preventing brake dust from the braking surface of the brake pad 60 from entering the surrounding atmosphere under braking conditions. In doing this, the skirt 74 also creates a perimeter void 82 for directing fluid which is provided by the first perimeter opening 70 around the outer periphery of the brake pad 60. The fluid entrains brake dust before being removed by the second perimeter opening 72.

Figures 6A-6B show a brake pad assembly 100 according to another embodiment of the present invention.

Figure 6A is a plan view of the brake pad assembly 100. The brake pad assembly 100 comprises a brake pad 102, and a support structure 106 of the brake pad 102. The brake pad 102 comprises an upper braking surface 104 made of braking material. The brake pad 102 is provided with a central opening 108 in the center of the braking surface 104 for providing fluid to the surface of the brake pad 102 in the manner discussed above.

In this embodiment, the brake pad assembly 100 comprises a peripheral wall provided by a flexible/resilient silicone skirt 110 which extends around the perimeter of the brake pad 102. The skirt 110 comprises partitions 120 which space the skirt 1 10 from the vertical sides of the brake pad 102 and which provide channels 122 down the sides of the brake pad 102.

The skirt 110 also forms a perimeter void 118 between the brake pad 102 and the skirt 110. Although only part of the perimeter void 1 18 is shown in the part section though line d-d (as shown in Figure. 6D), it will be appreciated that the perimeter void 118 extends around the periphery of the brake pad 102 between the skirt 1 10 and the brake pad 102, i.e. below the channels 122. The channels 122 are in fluid communication with both the braking surface 104 of the brake pad 102 and the perimeter void 118. This arrangement allows fluid (e.g. air) containing brake dust from the upper braking surface 104 to flow down through the channels 122 and into the perimeter void 118. The fluid containing brake dust can then circulate around the periphery of the brake pad 102 in the perimeter void 118.

(In some embodiments which are not illustrated, the skirt may provide a further (inner) peripheral wall which may, for example, be bonded to the sides of the brake pad 102. In these embodiments, the void may be provided between the peripheral wall and the further (inner) peripheral wall. In these embodiments, the partitions may be between the peripheral wall and the further (inner) peripheral wall, with the partitions providing channels to the void.)

The skirt 110 further comprises a first opening 112 to a first spigot 114. The first opening

1 12 allows the removal of the fluid containing brake dust from the perimeter void 1 18. The skirt 1 10 also comprises a second opening (not shown) to a second spigot 1 16. In some embodiments and/or circumstances, the second opening also allows the removal of fluid containing brake dust from the perimeter void 118. However, in other embodiments and/or under other circumstances (as will be discussed below), the second opening may be used to provide fluid to the perimeter void 118 so as to help circulate the fluid containing brake dust around to the first opening 1 12.

Figure 6B is a part section through line A-A of Figure 6A. Figure 6B shows the brake pad assembly 100 adjacent to a brake rotor (e.g. a brake disc) 124. Figure 6B shows the braking surface 104 of the brake pad 102 in contact with an opposing braking surface 126 of the brake rotor 124. Figure 6B also shows the perimeter void 118 which is formed between the skirt 1 10 and the brake pad 102, and shows one of the channels 112 which is formed by adjacent partitions 120 (see Fig. 6A). Figure 6B also shows the opening 108 in the brake pad 102 for providing fluid to the braking surface 104 of the brake pad 102.

Figure 6C is a part section through line B-B of Figure 6A. Figure 6C again shows the brake pad assembly 100 adjacent to the brake rotor 124, with the braking surface 104 of the brake pad 102 in contact with the opposing braking surface 126 of the brake rotor 124. Figure 6C also shows the perimeter void 118 which is formed between the skirt 110 and the brake pad 102, and shows one of the partitions 120 which spaces the skirt 1 10 from the sides of the brake pad 102.

Figure 6D is a part section through line C-C of Figure 6A. Figure 6D again shows the brake pad assembly 100 adjacent to the brake rotor 124, with the braking surface 104 of the brake pad 102 in contact with the opposing braking surface 126 of the brake rotor 124. Figure 6D also shows the perimeter void 118 which is formed between the skirt 110 and the brake pad 102 and shows the first opening 112 which allows the removal of fluid containing brake dust from the perimeter void 118 via spigot 1 14.

As will be appreciated, the skirt 110 can readily be fitted to the brake pad 102 by, for example, stretching the skirt 1 10 and mounting the skirt 1 10 around the brake pad 102. The skirt 110 could also be retrofitted to a conventional brake pad in a similar manner.

The use of the brake pad assembly 100 of this embodiment will now be described with reference to Figures 6A-6D.

Under non-braking conditions, fluid (e.g. air) is provided to the braking surface 104 of the brake pad 102 via the opening 108 in the braking surface 104. Fluid may be provided, for example, using a pressurised fluid supply (e.g. a pump or compressor output). Although not necessary in this embodiment, the fluid may be provided at a pressure and/or flow rate which is sufficient to separate the braking surface 104 of the brake pad 102 from the brake rotor 124 as discussed above in relation to other embodiments.

Fluid containing brake dust is also removed from the perimeter void 118 through the spigot 114 via the opening 1 12 in the skirt 110. Fluid containing brake dust is also preferably removed from the perimeter void 118 through the opening in the spigot 1 16. Fluid may be removed, for example, using a vacuum (or a or the pump or compressor input).

Thus, under non-braking conditions, fluid passes from the opening 108 in the braking surface 104, across the braking surface 104 where brake dust is collected, down the channels 1 12 and into the perimeter void 118. The fluid containing the brake dust is then removed from the perimeter void 1 18 through the spigot 1 14 (and possibly spigot 116) via the opening 1 12 in the skirt 110.

Under braking conditions, fluid (e.g. air) may or may not be provided to the opening 108 in the braking surface 104. As discussed above in relation to other embodiments, if fluid is provided to the opening 108 in the braking surface 104, then it is preferably at a pressure and/or flow rate which is insufficient to separate the braking surface 104 of the brake pad 102 from the brake rotor 124.

Fluid containing brake dust is also removed from the perimeter void 118 through the spigot 1 14 via the opening 1 12 in the skirt 1 10. Fluid containing brake dust may also be removed from the perimeter void 118 through the opening in the spigot 1 16.

Thus, under braking conditions, brake dust which is generated under braking and which migrates across the braking surface 104 can be extracted down the channels 122 and into the perimeter void 1 18. The fluid containing the brake dust can then be removed from the perimeter void 118 through the spigot 1 14 (and possibly spigot 1 16) via the opening 112 in the perimeter wall 110.

Alternatively, in some embodiments, under braking conditions, fluid containing brake dust may be removed through the first spigot 1 14 via the first opening 1 12 in the perimeter wall but fluid (e.g. air) may be provided to the perimeter void 118 through the second spigot 1 16 via the second opening in the skirt 110. Fluid may be provided, for example, using the pressurised fluid supply (e.g. the pump or compressor output). This alternative arrangement can help to provide a flow of fluid through the perimeter void 1 18 under braking conditions. Although preferred embodiments of the present invention have been described, it will be apparent to the skilled person that various features of those embodiments can be altered, removed or substituted without departing from the scope of the invention as defined by the appended claims.

Figures 7A and 7B are cross-sectional views of one embodiment of a brake pad assembly 200. Fig. 7A is a radial cross-section and Fig. 7B is an axial cross-section along the line B-B in Fig. 7A. The brake pad assembly 200 comprises a brake pad 202 comprising a friction material 203 and a brake back plate 204. The brake pad 202 has a braking surface 206 on the friction material 203 and an opposed back surface 208 on the brake back plate 204. The brake pad 202 may be porous, at least in the region formed of the friction material 203. The brake pad 202 comprises a hydraulic actuator comprising a cylinder 210 and a piston 212, both being cylindrical in shape. The piston 212 has a diameter of approximately 58 mm although other sizes will be suitable depending on, for example, the number of pistons used on each brake pad, the size of the brake pad and the type of vehicle on which the brake pad is to be used. The piston 212 is axially movable within the cylinder 210 along axial centreline 213 to move the brake pad 203.

The outer end surface 229 of the piston 212 and the inner surface 227 of the cylinder 210 define a hydraulic cavity 214. In use, the hydraulic cavity 214 is connected to a hydraulic fluid system (not shown), which is also connected to a user actuator means, such as a brake pedal. The hydraulic cavity 214 will therefore, in use, be filled with a hydraulic fluid (not shown). The hydraulic cavity 214 is sealed with an O-ring 216 positioned between the inner surface 227 of the cylinder 210 and the outer surface 226 of the piston 212. A gaiter 218 extending from the outer surface 239 of the cylinder 210 to the outer surface 226 of piston 212 is also provided to ensure no hydraulic fluid leaks from the actuator.

The piston 212 has a first end 231 that faces the brake pad 202, an opposed second end 233 that faces an inner surface 227 of the cylinder 210 and a side surface 235 extending between the two ends 231 and 233. The piston 212 is substantially hollow. The piston 212 comprises a first portion 212a and a second portion 212b. The first portion 212a is a split washer made of a metallic material such as steel, brass or aluminium. The first portion 212a is secured to the second portion 212b, for example by brazing or by being made oversized and being sprung back into position, with a flange 21 1 extending into the piston 212.

The piston 212 engages the back surface 208 of the brake pad 202 via the first portion 212a. The piston 212 may or may not be secured to the back surface 208 of the brake pad 202.

A conduit 220 extends through the side wall 235 of the piston 212 via an inlet 228 on outer surface 226 and outlet 22 on inner surface 223 of first portion 212a of piston 212. The conduit 220 extends into cavity 221 which is defined by the internal surfaces 223 of the piston 212 and the back surface 208 of the brake pad 202. The conduit 220 is in fluid communication with the braking surface 206 via a passage 224 extending from the back surface 208 to the braking surface 206. The passage may have a diameter of approximately 4 mm, but other sizes will be suitable. The passage 224 may be formed by drilling through the brake pad 202 or may be formed during formation of the brake pad 202. The inlet 228 is exposed throughout the motion of the hydraulic actuator, by virtue of the fact that the inlet 228 is never covered by the cylinder 210.

Under non-braking conditions (i.e. when the brake pedal is not activated), the piston 212 is fully retracted such that the majority of the piston 212 is inside the cylinder 210, as shown in Fig. 7B. Under braking conditions (i.e. when the brake pedal is activated), more hydraulic fluid is transmitted to the cavity 214 and the piston 212 is moved towards the brake pad 202 such that a lesser amount of the piston is inside the cylinder. When the piston 212 is fully retracted, the inlet 228 is between the first end 237 of the cylinder 210 and the back surface 208, and thus exposed. It then remains exposed as the piston 212 becomes extended, i.e. throughout the motion of the hydraulic actuator.

A system control means may be provided that allows pressurised fluid to be provided, under non-braking conditions, from a compressor or pump to the braking surface 206 of the brake pad 202 via the conduit 220. This may be achieved, for example, by switching on a compressor or pump and/or by opening a supply valve that is in fluid communication between the compressor or pump and the braking surface 206. Under braking conditions, the system control means prevents pressurised fluid from being provided to the braking surface 206 of the brake pad 202. This may be achieved, for example, by switching the compressor or pump off and/or by closing a valve that is in fluid communication between the compressor or pump and the brake pad braking surface 206 so as to cut off the fluid supply to the braking surface 206.

Figure 8 is an axial cross-sectional view of an alternative embodiment of a brake pad assembly 300, wherein the piston 312 comprises only a single portion through which the conduit 320 extends. The conduit extends through a cut-out formed in the first end 331 and side wall 335 of the piston 312. Also shown in this embodiment is a pipe 326 extending from the outer surface 326 of the piston 310 to the braking surface 306 via the conduit 320 and the passage 324. The pipe 326 is made from a flexible and resilient material, such as silicone rubber. The end 326a of the pipe 326 is flush with the braking surface 306. The pipe 326 may have an outer diameter of approximately 5 mm and an inner diameter of approximately 3 mm. As mentioned above, the passage 324 may have a diameter of approximately 4 mm such that the pipe 326 may be radially compressed by the passage 324. The pipe 326 can be placed in the passage 324 by elongating the pipe 326 before passing it through the passage 324.

Figure 9 is an axial cross-sectional view of another embodiment of a brake pad assembly 400. The brake pad assembly 400 differs from that of Figs. 7 and 8 by having a different piston 412. The piston 412 is substantially solid with only a small cavity 421 proximate its first end 431.

The outer end surface 429 of the piston 412 and the inner surface 427 of the cylinder 410 define a hydraulic cavity 414. The hydraulic cavity 414 is sealed with seal 416 between the inner surface 427 of the cylinder 410 and the outer surface 426 of the piston 412. A gaiter (not shown) may extend from the outer surface 449 of cylinder 410 to the outer surface 426 of piston to ensure no hydraulic fluid leaks from the actuator. The piston 412 has a first end 431 that faces the brake pad 402, an opposed second end 433 that faces an internal surface 427 of the cylinder 410 and a side surface 435 extending between the two ends 431 and 433. The piston 412 is secured to the back surface 408 of the brake pad 402. A conduit 420 extends through the side wall 435 of the piston 412 via inlet 428 on outer surface 426 of piston 412. The conduit 420 extends into cavity 421 which is defined by the internal surfaces 423 of the piston 412. The conduit 420 is in fluid communication with the braking surface 406 via a passage 424 extending from the back surface 408 to the braking surface 406. The inlet 428 is exposed throughout the motion of the hydraulic actuator, by virtue of the fact that the inlet 428 is never covered by the cylinder 410.

Figure 10 is an axial cross-sectional view of another embodiment a brake assembly 500. This embodiment differs from that of Fig. 9 in that the piston 512 is formed of a first portion 512a, positioned adjacent the brake pad 502, and a second portion 512b, positioned partially within the cylinder 510. The first portion 512a and the second portion 512b are operatively connected such that, under braking conditions, the movement of the first portion 512a towards the brake pad causes movement of the second portion 512b towards the brake pad 502. The first portion 512a and the second portion 512b may be secured to each other, for example, by brazing , adhesive bonding or via a press fit. The conduit 520 extends through the first portion 512b.

Claims

Claims:

1. A brake pad assembly comprising:

a brake pad having a braking surface and an opposed back surface;

a hydraulic actuator comprising a cylinder and a piston, the piston being operatively connected to the back surface of the brake pad and moveable within said cylinder for varying the position of the brake pad; and

a conduit extending through said piston and being in fluid communication with said braking surface for providing fluid flow to said braking surface.

2. The brake pad assembly of claim 1 , wherein said conduit extends through a portion of the outer surface of the piston that remains exposed throughout the motion of the piston within the cylinder.

3. The brake pad assembly of claim 1 or 2, wherein said conduit comprises a cavity at least partially defined by one or more internal surfaces of said piston and said back surface of said brake pad.

4. The brake pad assembly of any of claims 1 to 3, wherein said piston comprises a first end that faces the brake pad, a second opposed end that faces an internal surface of the cylinder and at least one side surface extending between said first and second ends.

5. The brake pad assembly of claim 4, wherein said conduit extends through said side surface of said piston.

6. The brake pad assembly of claim 5, wherein said conduit comprises a notch extending through said side surface and said first end.

7. The brake pad assembly of claim 5, wherein said conduit is spaced from said first end along said side surface.

8. The brake pad assembly of any of claims 4 to 7, wherein said first end defines an outlet of said conduit from said piston.

9. The brake pad assembly of any of claims 4 to 8, wherein the piston comprises first and second connected portions, said first portion comprising said first end and said second portion comprising said second end, said conduit extending through said first portion.

10. The brake pad assembly of any preceding claim, wherein the brake pad has a passage extending from the braking surface to the back surface, said conduit being in fluid

communication with said braking surface via said passage.

1 1. The brake pad assembly of claim 10, wherein at least a portion of said passage is aligned with a central axis of said piston.

12. The brake pad assembly of claim 10 or 1 1 , further comprising a pipe extending through said conduit and into said passage.

13. A brake pad comprising:

a braking surface and an opposed back surface;

a passage extending from the back surface to the braking surface for providing fluid flow to said braking surface, said passage having one or more internal walls; and

means for preventing or reducing the leakage of fluid from said passage into said brake pad via said one or more internal walls.

14. The brake pad of claim 13, wherein said means for preventing leakage comprises a pipe extending through said passage.

15. The brake pad of claim 14, wherein said pipe is formed from a resilient material and/or a flexible material.

16. The brake pad of claim 15, wherein said pipe is formed from an abradable material.

17. The brake pad of any of claims 14 to 16, wherein said pipe is formed from silicone rubber.

18. The brake pad of any of claims 14 to 17, wherein said pipe has a first end and a second end and said first end is flush with, or extends beyond, the braking surface.

19. The brake pad of claim 18, wherein said second end extends beyond the back surface of the brake pad and at said second end, said pipe has a greater diameter than the inlet to the passage on said back surface.

20. The brake pad assembly of any of claims 1 to 12, wherein said brake pad is as claimed in any of claims 13 to 19.

21. A brake system comprising:

the brake pad or brake pad assembly of any preceding claim; and

a brake rotor positioned adjacent to and facing the braking surface of the brake pad.

22. The brake system of claim 21 , further comprising a pressurised fluid supply in fluid communication with the braking surface of the brake pad via the conduit.

23. The brake system of claim 22, wherein the system is configured such that fluid from the pressurised fluid supply is provided to the braking surface of the brake pad under non-braking conditions, the fluid from the pressurised fluid supply providing a gap between the brake rotor and the braking surface of the brake pad when provided to the braking surface under non- braking conditions, the pressurised fluid supply being capable of supplying pressurised fluid at a pressure that is sufficient to separate the braking surface of the brake pad from the brake rotor under non-braking conditions.

24. A method of providing a brake pad of any of claims 13 to 19, said method comprising: forming a passage between a back surface and a braking surface of a brake pad;

passing a pipe through said passage, said pipe being in an elongated state and having a cross-sectional area in said elongated state that is smaller than a diameter of said passage; and allowing said pipe to relax so that its length is reduced, its cross-sectional area is increased and its outer surface engages one or more internal walls of said passage.

25. The method of claim 24, wherein said step of passing a pipe through said passage in an elongated state comprises securing an elongate member, having a smaller cross-sectional area than said passage, to said pipe and passing said elongate member through said passage.

26. The method of claim 25, wherein said elongate member is secured to said pipe by being tied to said pipe or being passed around a loop in said pipe.

27. The method of any of claims 24 to 26, further comprising, after allowing said pipe to relax, cutting a first end of said pipe protruding from said braking surface to be flush with said braking surface.