GB2540361A - Brake pad and system - Google Patents

Abstract

A vehicle brake pad 114 comprising a braking surface 126, at least one aperture 134 formed in the braking surface 126, a first passage 136 through the brake pad 114 for supplying air to the aperture 134, and a second passage 138 through the brake pad 114 for removing air from the aperture 134. A brake system is also disclosed, having a vented brake disc 112 and pressurised fluid supply, wherein during rotation of the brake disc112 a plurality of brake disc holes 124 successively align with a brake pad aperture 134 to allow fluid from a pressurised fluid supply to flow to one or more brake disc channels 122, providing cooling and to prevent over-heating of the brakes.

Description

Brake Pad and System

Field of the Invention

The present invention relates to a brake pad, a brake system and a method of using a brake system.

Background of the Invention

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 callipers. With 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. WO 2013/084188, by the present Applicant, discloses an apparatus and method for separating the brake pad from the brake rotor under non-braking conditions. A pressured fluid supply is used to provide fluid to the braking surface of the pad under non-braking conditions. Fluid removal means may be provided to remove fluid from the braking surface under braking conditions.

Another problem faced by vehicle brake systems is the overheating of the brake discs and brake pads. This is a particularly acute problem in the case of high performance vehicles, such as sports cars, due, in part, to the higher speeds achieved and the higher braking performance. Such cars can use ceramic brake discs, which, while being light, do not dissipate heat well. The heat produced by brake discs, can cause the disc to be damaged, the pad to be damaged, or even, via the heating of the pad, the hydraulic fluid in the piston cylinder acting upon the brake pad to boil.

The present invention seeks to provide an improved apparatus and method. Summary of the Invention

According to a first aspect of the present invention there is provided a brake pad for a vehicle, the brake pad comprising a braking surface, an opposed back surface, at least one aperture formed in the braking surface, a first passage through the brake pad in fluid communication with the aperture for supplying air thereto and a second passage through the brake pad in fluid communication with the aperture for removing air therefrom.

The brake pads may comprise a braking material forming the braking surface and a back plate forming the back surface. The braking material may comprise any suitable friction material (e.g. a ceramic, semi-metallic metallic or carbon fibre material). The back plate may comprise any suitable support structure material.

The aperture may be used to cool the braking surface of the pad, and the opposing surface of a brake disc, for example, during braking. Supplying pressurised air to the aperture may also help to separate the braking surface from an opposing brake disc, during non-braking, by pushing the brake pad away from the disc.

The first and/or second passages may pass through the back surface of the brake pad (e.g. the back plate) or may enter the brake pad from a different location such as a peripheral edge of the brake pad (e.g. the back plate or the braking material).

The at least one aperture may comprise an elongate slot. The term ‘elongate’ should be understood to mean that the length of the slot is considerably larger than its width (measured perpendicularly to its length). The length of the slot may be at least 10, 20 or 30 or more times longer than its width. The use of an elongate slot extending across the brake pad allow the first and second passages to the slot to be located towards or on the peripheral edge of the brake pad, for example on the back surface, away from the location of the piston(s) etc.

The elongate slots may have a length of at least 2cm, at least 4cm, at least 6cm, at least 8cm, about 10cm, or between 5 cm and 15 cm.

The elongate slots may have a width of less than 2 cm, less than 1.5 cm, less than 1.0 cm, between about 0.3 and 0.8 cm or about 0.5 cm.

The cross-sectional area of the elongate slot may be at least 1.0 cm2, at least 5 cm2, at least 10 cm2, at least 15 cm2, between about 5 and 10 cm2, or about 10 cm2.

The elongate slot may cover at least 1%, at least 2%, at least 3%, about 3%, less than 10%, or less than 5% of the total area of the braking surface.

The braking surface of the pad may have a length and a width, measured perpendicular to the length. The length may be longer than the width, for example, 1.2, 1.5, 2.0 or 3.0 or more times longer. The length may extend in a direction corresponding generally to the rotation direction of a brake disc to which the brake pad is attached in use.

The slot may be displaced from a laterally extending centreline of the braking surface. The laterally extending centreline bisects the braking surface lengthwise, i.e. it corresponds to the width of the pad halfway along the pad. The slot may be displaced by being paralled with, but spaced from the laterally extending centreline, or at an angle to the laterally extending centreline.

The slot may extend parallel to the laterally extending centreline of the brake pad.

Alternatively, the slot may extend perpendicularly to the laterally extending centreline of the brake pad.

Alternatively, the slot may extend at an acute angle to the laterally extending centreline of the brake pad.

The slot may be straight or curved.

If straight, the slot may be generally rectangular in shape.

If the elongate slot is curved, the direction of the slot is determined by an imaginary straight line between the two ends of the slot.

The elongate slot may have first and second ends, a slot length between the first and second ends, and the first passage may be located on one side of a lateral centreline of the slot, and the second passage may be located on the other side of the lateral centreline of the slot.

The first and second passage may be located within 5%, 10%, 15% or 20% of the slot length of the first end, and each second passage is located within 5%, 10%, 15% or 20% of the slot length of the second end.

The at least one aperture (e.g. the slot) may be spaced from the peripheral edges of the braking surface of the brake pad. In other words, the braking surface may completely surround the aperture/slot.

The shortest distance between an edge of an aperture and an edge of the braking surface of the brake pad may be at least 2%, at least 5%, or at least 10% of the length or of the width of the brake pad.

The at least one aperture (e.g. the slot) may have a depth extending only partially through the brake pad.

The depth may be a wearing depth of the brake pad.

The wearing depth of the brake pad is depth at which the brake pad can be worn down to before it should be replaced. This is generally the depth at which, or soon before, the brake pad will stop being as effective in providing a frictional force for breaking. Providing apertures with this depth means that the apertures will always be present in the brake pad, i.e. they are not worn away, whilst minimising the impact of the apertures on the structural integrity of the brake pads.

Alernatively, the depth may be greater than the wearing depth of the brake pad.

Such an arrangement ensures that fluid flow is not significantly restricted as the wear on the brake pad approaches the wearing depth, and ensures that the apertures will still be present if the wear on the respective brake pads exceeds the wearing depth.

This aspect of the present invention may also extend to a brake system comprising the brake pad described above (in any embodiment thereof), and a pressurised fluid supply means in fluid communication with the first passage.

The pressurised fluid supply means may comprise any suitable supply means such as a pump, compressor or blower. The pressurised fluid supply means may be as described in GB 2516505, by the present Applicant, for example, it may be connected to four brake discs via four independent gas supplies.

The brake system may further comprise a second brake pad as described above (in any embodiment thereof) and a brake disc positioned between the braking surfaces of the first and second brake pads for rotation about an axis.

The brake disc may comprise a ceramic material or a metallic material, such as cast iron.

The second passage may be in fluid communication with a fluid removal means. The fluid removal means may be a valve, such as a solenoid valve. The fluid control means may be configured to open when a predetermined threshold pressure is reached. This pressure is higher than that in the aperture when the aperture is aligned with a hole and fluid is flowing therethrough to the vent channel such that, in use, the valve is only opened when the aperture is not aligned with a hole. The valve ensures that pressure does not build up in the aperture, which would act to push the brake pad away from the brake disc, which would be undesirable, whilst ensuring that fluid does not flow therethrough when the aperture is aligned with a hole, i.e. that the fluid flows through the hole to the vent channel, providing the desired cooling effect.

The fluid removal means, may be normally closed, and only opened during braking, so that the air cannot escape from the second aperture during non-braking, and instead acts to push the brake pad away from the brake disc.

Alternatively, it may be desirable for the second passage to be completely open to atmosphere. In other words, the aperture may be open to atmosphere via the second passage. The predetermined threshold pressure may then be set by the configuration of the open second passage, e.g. the size of the smallest cross-sectional flow area of the passage.

The brake disc may comprise a vented brake disc having first and second axially spaced plates for contacting the braking surfaces of the brake pads, one or more radially extending channels located between the first and second plates and a plurality of holes formed in the first and second radial plates in fluid communication with the one or more channels, wherein, during rotation of the brake disc, the plurality of holes in each brake disc plate successively align with the at least one respective brake pad aperture to allow fluid from the pressurised fluid supply means to flow to the one or more channels.

Vented brake discs are known in the art to comprise two axially spaced plates with fins extending therebetween. These fins define internal vent channels, which are open at their radially outer ends, i.e. at the radially outer edges of the axially spaced plates, and at their radially inner ends where they are connected to the open disc. It is also known to provide vented brake discs with apertures that extend through the plates. These “cross-drilled” holes allow for better cooling by drawing air into the internal vent channels. The edges of the holes clean the brake pad braking surface to provide extra bite between the braking surface and the disc and reduce glazing of the braking surface. The holes also reduce the weight of the disc and thus its inertia.

During braking, the brake pad braking surfaces contact the radial surfaces of the plates, and the fluid flowing from the pressurised fluid supply means flows to the vent channel via the brake pad apertures and the plurality of holes in the brake disc when they are aligned therewith. This flow of fluid cools both the brake pad and the brake disc.

The at least one aperture on each break pad need only extend radially to the radial extent of the disc hole pitch, i.e. the radial extent to which the plurality of holes are provided in the corresponding radial surface of the brake disc in a radial direction of the brake disc.

The at least one aperture of one brake pad may not be directly opposed with the at least one aperture of the other brake pad. The at least one aperture of each pad, when in the form of slots, may be positioned so that they effectively cross over each other, when the braking surfaces of the two pads are facing each other, as they would be, in use, when placed either side of a brake disc. For example, the two slots may be positioned perpendicular to each other.

The apertures and the plurality of holes may be arranged such that at least one hole on each brake disc plate is at least partially aligned with at least one aperture on the respective brake pad at any rotational position of the disc.

The apertures and the plurality of holes may be arranged such that at least one of the plurality of holes on either brake disc plate is at least partially aligned with one aperture on the respective brake pad at any rotational position of the disc.

Providing such holes and apertures prevents pressure from building up on the pad surface during braking, which would cause the brake pad to be pushed away from the contacting surface of the brake disc, which would be undesirable. When the apertures in the first and second brake pads are supplied by a common pressurised system, it is only necessary for one aperture to be at least partially aligned with a hole at any given time in order to depressurise the whole system. The brake pads can be formed to be identical, i.e. with the same positioning of the elongate slot therein. When the brake system is assembled, the braking surfaces of the braking pads face in opposite directions, on opposite sides of the brake disc. Therefore, if the identically positioned elongate slots are displaced from or angled relative to the axially extending centreline of their respective brake pads, the slots will not be directly opposed. If the holes on either side of the brake disc, i.e. on the contacting surfaces, are aligned with each other, the offset elongated slots will align with holes at different times. This means that fewer holes have to be formed in the brake disc, or narrower elongate slots could be used, in order to obtain a configuration in which at least one of the elongated slots is at least partially aligned with at least one of the plurality of holes at any time. This is desirable as it enables a constant fluid flow through the brake disc, achieving a constant cooling effect and preventing pressure build up in the elongate slots, while reducing the number of holes that are needed, and thus minimising effect that forming holes in the brake disc has on the structure and strength of the brake disc.

Alternatively, the brake disc may comprise a solid (non-vented) disk.

It is envisaged that the elongate slots may not have the same properties: for example, one elongate slot may be oriented in a radial direction of the brake disc, whilst the other is oriented in a circumferential direction of the brake disc. Any of the above statements could refer to either one or both elongate slots.

According to a second aspect of the present invention, there is provided a brake system comprising first and second brake pads, each brake pad having a braking surface, an opposed back surface, at least one aperture formed in the braking surface and a first passage in fluid communication with the aperture, a vented brake disc positioned between the braking surfaces of the first and second brake pads for rotation about an axis, the brake disc comprising first and second axially spaced plates for contacting the braking surfaces of the brake pads, one or more radially extending channels located between the first and second plates and a plurality of holes formed in the first and second radial in fluid communication with the one or more channels and a pressurised fluid supply means for supplying pressurised fluid to each of the first passages, wherein, during rotation of the brake disc, the plurality of holes in each brake disc plate successively align with the at least one respective brake pad aperture to allow fluid from the pressurised fluid supply means to flow to the one or more channels.

The brake pads, system, disk and pressurised fluid supply means may have any of the features described above in relation to the first aspect and any embodiment thereof. Notably, this aspect is not limited to having a second passage in the brake pad. However, a second passage may be provided.

According to a third aspect of the present invention, there is provided a method of cooling the brake system as described above in relation to the first or second aspect of the present invention (or any embodiment thereof). The method comprising providing air from the pressurised fluid supply means to the braking surface or surfaces via the at least one aperture or apertures.

The step of providing air from the pressurised fluid supply means may comprise supplying air at a first pressure and/or flow rate during braking conditions and supplying air at a second pressure and/or flow rate during non-braking conditions.

The first pressure and/or flow rate may be higher than the second pressure and/or flow rate. This may be desirable to cool the brake pad and disc, at the time at which the most heat is being produced, i.e. during braking.

Alternatively, the first pressure and/or flow rate may be lower than the second pressure and/or flow rate. This may be desirable to assist in separating the brake pad from the disc after braking.

The method may further comprise, during non-braking conditions and after the step of supplying air at a second pressure and/or flow, supplying air at a third lower pressure and/or flow rate.

This aspect of the present invention also extends to a brake system as described above in relation to the first or second aspect of the present invention (or any embodiment thereof) configured to perform such a method, e.g. a brake system configured to supply air at a first pressure and/or flow rate during braking conditions and supply air at a second pressure and/or flow rate during non-braking conditions.

Brief description of the drawings

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

Figure 1 shows an embodiment of a brake system;

Figure 2 shows an alternative embodiment of a brake system;

Figure 3 shows another alternative embodiment of a brake system;

Figure 4 shows a side view of a portion of the embodiment of Fig 2;

Figure 5 shows a side view of a portion of the embodiment of Fig 2;

Figures 6 and 7 show perspective views of a floating caliper which may be used with the present invention;

Figure 8 shows a brake disc for use with the floating caliper of Figs 6 and 7;

Figure 9 shows a part of the disc of Fig 8;

Figure 10 shows the disc of Figs 8 and 9; and

Figure 11 shows the disc of Figs 8 to 10 with the floating caliper 10 of Figs 6 and 7.

Detailed description of the drawings

Figure 1 shows an embodiment of a brake system 110 comprising a vented brake disc 112 (only a portion of which is shown) and first and second brake pads 114, 116. It should be understood however, that aspects of the present invention are also also applicable to non-vented disks, which may contain a single plate without holes.

Vented brake disc 112 is arranged for rotation about axis A, and comprises first and second radially spaced plates 118, 120. The first and second radially spaced plates 118, 120 are the same size: i.e. they have the same radius and thickness. Fins 121 (only one shown) extend radially between the first and second radially spaced discs to define vent channels 122 (only one shown). The vent channels 122 are open at their radially outer edge of the brake disc 112, such that all vent channels are in fluid communication with the atmosphere. The vent channels 122 may also be in fluid communication with each other within the space between the radially spaced discs 118, 120. The vented brake disc 112 further comprises a plurality of holes 124 extending through the first and second radially spaced plates and in fluid communication with the vent channels 122.

The first brake pad 114 comprises a braking surface 126 and an opposed back surface 128. The braking surface 126 is formed from a braking material 130, and the back surface 128 is formed from a back plate 132. The first brake pad 114 further comprises an elongate slot 134 formed in the braking surface 126. The slot 134, in this embodiment, extends in a radial direction R of the brake disc 112 (perpendicular to axis A). The slot 134 is in fluid communication with a first passage 136 extending through the braking material 130 and the back plate 132. The first passage 136 is located at a first end 140 of the elongate slot 134. The first passage 136 is connected to a pressurised fluid supply means (not shown). During braking, the pressurised fluid supply means supplies fluid to the elongate slot 134 via the first passage 136. The fluid then flows through any hole 122 aligned with the elongate slot 134 at that time, given the rotational position of the disc, into the vent channels 122, and out of the brake disc to atmosphere at the radially outer edge of the disc.

The continuous arrows show the direction of air flow through the first passage 136, the slots and the aligned hole 122.

The second brake pad 116 includes the same features as discussed above with respect to the first brake pad 114.

The elongate slots 134 and plurality of holes 122 of brake system of Figure 1 may be configured such that at least one of the plurality of holes 122 is at least partially aligned with at least one of the elongate slots 134 at any rotation of the brake disc. The first passages of the first and second brake pads 114,116 share a common pressurised fluid supply (not shown). Thus, it is only necessary for one of the elongate slots 134 to be aligned with a hole 122 to ensure that pressure doesn’t build up in the pressurised system and, thus, either elongate slot 134. Alternatively, the elongate slots 134 and plurality of holes 122 can be configured such that each of the elongate slots 134 is at least partially aligned with a hole 122 at any rotation of the brake disc. The elongate slots 134 may then be supplied by individual pressurised fluid supplies.

Figure 2 shows an alternative embodiment of a brake system 110. Figure 2 is identical to Figure 1 except that it further includes a second passage 138 extending through the braking material 130 and the back plate 132. The second passage 138 is located at a second end 142 of the elongate slot 134. The second passage 138 is connected to a fluid removal means, such as a solenoid valve (not shown). The fluid removal means is configured to allow fluid to flow out of the second passage when the pressure in the elongate slot is greater than a predetermined threshold value.

The predetermined threshold value of the fluid removal means is configured such that, when fluid is flowing through a hole 122, the pressure in the elongate slot 134 is not sufficient to allow any fluid to flow out of the second passage 138. Therefore, when the elongate slot 134 is at least partially aligned with any hole 122, no fluid flows through the second passage 138. When, however, no hole is at least partially aligned with the elongate slot 134, the pressure in the elongate slot increases to the predetermined threshold value of the fluid removal means, and fluid then flows out of the elongated slot 134 via the second passage 138. The predetermined threshold value of the fluid removal means is configured to be a low as possible above the pressure in the elongate slot 134 when fluid is flowing through a hole so as to minimise the maximum pressure which can occur in the elongate slot 34 and, therefore, the pushing apart of the brake disc 112 and the brake pad 114, without enabling fluid to flow through the second passage when the elongate slot 134 is aligned with a hole 122.

The continuous arrows show the direction of air flow through the first passage 136, the slots and the aligned hole 122. The dotted lines show the direction of air flow, if a hole 122 was not aligned with the slot 134, i.e. through the second passage 138.

Figure 3 shows another alternative arrangement of brake system 110. Figure 3 is identical to Figure 1 except in that the first and second passages 136, 138 extend through the side wall 132a of the back plate 132, as opposed to the back surface 128.

Figure 4 shows a side view of a portion of the brake disc 112 and the first brake pad 114 of the embodiment of Figure 2, taken at a cross section through the brake pad 114 at the depth of the elongate slot 134, with a portion of the detail of the brake disc 112 shown through the brake pad 114. Brake disc 112 comprises a plurality of holes 122. Brake pad 114 comprises an elongate slot 138 in the braking surface 126, a passage 136 which extends from a first end 140 of the elongate slot 138 in the braking surface 126 to the back surface (not shown) and a second passage 138 which extends from a second end 142 of the elongate slot 138 in the braking surface 126 to the back surface (not shown). In Fig 3, the elongate slot 134 is partially aligned with a hole 122, and is offset from laterally extending centreline 146, which bisects the pad lengthwise (i.e. in the circumferential direction of the disk 144).

During rotation, the brake disc 112 moves relative to brake pad 114. The direction of travel of the drake disc 112 is indicated by arrow 144. As the brake disc 112 rotates, the holes 122 move into and out of alignment with the elongate slot 134.

Figure 5 shows a side view of the brake disc 112 (only part of which is shown) and first and second brake pads 114, 116 of the embodiment of Figure 2. First brake pad 114 comprises a first elongate slot 134a. Second brake pad 116 comprises a second elongate slot 134b.

First brake pad 114 and second brake pad 116 are formed to be identical, with the same positioning of the elongate slots 134a,b on the braking surfaces of the brake pad 114, 116. The elongate slots 134 a,b are displaced from the radial centrelines 146 of the respective brake pads 114, 116. When the brake system 110 is assembled, the braking surfaces of the brake pads 114, 116 face in opposite directions, while the axially extending centrelines 146 of the brake pads 114,116 align. The elongate slots 314 a,b, therefore, are not directly opposed.

Figures 6 and 7 show perspective views of a floating caliper which may be used with the above described brake system. Alternatively, a fixed caliper may be used.

Figure 6 shows a floating caliper 10 having a floating caliper body 14. The floating caliper body 14 comprises a cylinder portion 16, floating rails 17 and a pair of fingers 18. The floating rails 17 extend between the cylinder portion 16 and the fingers 18. In use, the floating rails 17 extend over and around a brake disc (not shown), with the fingers 18 on one side of the disc and the cylinder portion 16 on the other. The cylinder portion 16 comprises a pair of lugs 16a, 16b and a cylinder 16c. The floating caliper 10 also comprises a fixed frame that does not move relative to the disc (not shown, discussed later).

Figure 7 shows the floating caliper 10 of Figure 6 comprising a piston 12. The piston 12 sits and moves axially within cylinder 16c of the floating caliper body 14. Positioned within the bores of the lugs 16a, 16b are cylindrical rubber bushings 22a, 22b.

Figure 8 shows a brake disc 46 having a hub 48 for use with the floating caliper of Figures 5-9. The disc 46 is rotatable within the vehicle frame 28, which is connected to a pair of fixed rails 54 which extend over and around edges of the disc 46. Secured to the vehicle frame 28 via threaded bores 28a are two shafts 20. The floating caliper 10 and brake pads are not shown.

Figure 9 shows a part of the disc 46 of Figure 8. The floating caliper 10 is again not shown. An outer brake pad 36 comprising friction material 40 and a back plate 42 is provided. The braking surface of the friction (i.e. braking) material 40 of the brake pad 36 is proximate to one side of disc 46. In use, when the braking system is actuated, the braking surface will press against the disc 46. The back plate 42 comprises a pair of hangers 43 that slidably engage the pair of fixed rails 54. The brake pad 36 is thus slidable on the fixed rails 54 towards or away from the disc 46 while remaining substantially parallel thereto. Pipe 44 supplies fluid to the elongate slot in braking surface of the friction material 40 through the back plate 42. In use, pipe 44 will be connected to a pressurised fluid supply. Another pipe (not shown) may also be provided to remove air from the braking surface.

Figure 10 shows the disc of Figures 8 and 9. Inner and outer brake pads 38, 36 are shown. Outer brake pad 36 is located adjacent the outer surface of the disc 46, adjacent hub 48. Inner brake pad 38 is located adjacent the opposite side of the disc 46. Inner brake pad 38 comprises a friction surface 50 and a back plate 52.

The hangers 53 are slidably attached to the fixed rails 54.

Figure 11 shows the disc 46 of Figs 8 to 10 with the floating caliper 10 of Figures 6 and 7 extending over and around the brake disc 46. The outer brake pad 36 is positioned between caliper fingers 18 and disc 46. The inner brake pad (38, not shown) will be positioned between the piston (12, not shown) of the caliper 10 and the other side of the disc 46. The pair of floating rails 16 slidably engage the pair of hangers 43 (of the outer brake pad 36). Pipe 44 supplies air to the elongate slot in the braking surface of brake pad. Again, another pipe (not shown) may also be provided to remove air from the braking surface.

Spring 58 extends between the caliper fingers 18 and engages fixed rails 4. The spring 58 serves to bias the fingers 18 towards the disc 46, trapping the outer brake pad 36 therebetween.

In use, when a user activates a brake, for example by pressing a foot brake, hydraulic fluid is supplied to the cylinder 16c and the piston 12 extends out of the cylinder 16c. The force of the extending piston 12 acts on the inner brake pad 38 and pushes it towards the brake disc 46. The hydraulic fluid also exerts an equal and opposite force on the inner surfaces of the cylinder, which pushes the floating caliper body 14 away from the piston 12. This causes the floating caliper body 14 to slide along the shafts 20 and the brake pad 38 to firmly press the fingers 18 towards the brake disc 46. This allows both brake pads 36, 38 to engage the brake disc 46 with a substantially equal pressure. When the user releases the brake, the pressure on the hydraulic fluid in the cylinder 16c is removed. The piston 12 will therefore not press against the inner brake pad 38 and the caliper fingers 18 will not press against the outer brake pad 36. However, the brake pads 36, 38 may remain in contact with the disc.

Claims (43)

CLAIMS:

1. A brake pad for a vehicle, the brake pad comprising: a braking surface; an opposed back surface; at least one aperture formed in the braking surface; a first passage through the brake pad in fluid communication with the aperture for supplying air thereto; and a second passage through the brake pad in fluid communication with the aperture for removing air therefrom.

2. The brake pad of claim 1, wherein the at least one aperture comprises an elongate slot.

3. The brake pad of claim 2, wherein the slot is displaced from a laterally extending centreline of the brake pad.

4. The brake pad of claim 2 or 3, wherein the slot extends parallel to a or the laterally extending centreline of the brake pad.

5. The brake pad of claim 2 or 3, wherein the slot extends perpendicularly to a or the laterally extending centreline of the brake pad.

6. The brake pad of claim 2 or 3, wherein the slot extends at an acute angle to a or the laterally extending centreline of the brake pad.

7. The brake pad of any of claims 2 to 6, wherein the elongate slot is straight.

8. The brake system of any of claims 2 to 6, wherein each elongate slot is curved.

9. The brake pad of any of claims 2 to 8, wherein the elongate slot has first and second ends, defining a slot length between the ends, each first passage is located on one side of a lateral centreline that bisects the length of each slot, and each second passage is located on the other side of each lateral centreline.

10. The brake pad of claim 9, wherein each passage is located within 5%, 10%, 15% or 20% of the slot length of the first end, and each second passage is located within 5%, 10%, 15% or 20% of the slot length of the second end.

11. The brake pad of any preceding claim, wherein the at least one aperture is spaced from the peripheral edges of the braking surface of the brake pad.

12. The brake pad of any preceding claim wherein the at least one aperture has a depth extending only partially through the brake pad.

13. The brake pad of claim 12, wherein the depth is a wearing depth of the brake pad.

14. The brake pad of claim 12, wherein the depth is greater than the wearing depth of the brake pad.

15. A brake system comprising: the brake pad of any preceding claim; and a pressurised fluid supply means in fluid communication with the first passage.

16. The brake system of claim 15, further comprising: a second brake pad of any of claims 1 to 14; and a brake disc positioned between the braking surfaces of the first and second brake pads for rotation about an axis.

17. The brake system of claim 16, where the brake disc comprises a vented brake disc having: first and second axially spaced plates for contacting the braking surfaces of the brake pads: one or more radially extending channels located between the first and second plates; and a plurality of holes formed in the first and second radial plates in fluid communication with the one or more channels, wherein, during rotation of the brake disc, the plurality of holes in each brake disc plate successively align with the at least one respective brake pad aperture to allow fluid from the pressurised fluid supply means to flow to the one or more channels.

18. The brake system of claim 17, wherein the at least one aperture of one brake pad is not directly opposed with the at least one aperture of the other brake pad.

19. The brake system of claim 17 or 18, wherein the apertures and the plurality of holes are arranged such that at least one hole on each brake disc plate is at least partially aligned with at least one aperture on the respective brake pad at any rotational position of the disc.

20. The brake system, of claim 17 or 18, wherein the apertures and the plurality of holes are arranged such that at least one of the plurality of holes on either brake disc plate is at least partially aligned with one aperture on the respective brake pad at any rotational position of the disc.

21. A brake system comprising: first and second brake pads, each brake pad having: a braking surface; an opposed back surface; at least one aperture formed in the braking surface; and a first passage through the brake pad in fluid communication with the aperture; a vented brake disc positioned between the braking surfaces of the first and second brake pads for rotation about an axis, the brake disc comprising first and second axially spaced plates for contacting the braking surfaces of the brake pads, one or more radially extending channels located between the first and second plates and a plurality of holes formed in the first and second radial in fluid communication with the one or more channels; and a pressurised fluid supply means for supplying pressurised fluid to each of the first passages, wherein, during rotation of the brake disc, the plurality of holes in each brake disc plate successively align with the at least one respective brake pad aperture to allow fluid from the pressurised fluid supply means to flow to the one or more channels.

22. The brake system of claim 21, wherein the at least one aperture in each brake pad comprises at least one elongate slot.

23. The brake system of claim 22, wherein each slot is displaced from a laterally extending centreline of the brake pad.

24. The brake system of claim 22 or 23, wherein each slot extends parallel to a or the laterally extending centreline of the brake pad.

25. The brake system of claim 22 or 23, wherein each slot extends perpendicularly to a or the laterally extending centreline of the brake pad.

26. The brake system of claim 22 or 23, wherein each slot extends at an acute angle to a or the laterally extending centreline of the brake pad.

27. The brake system of any of claims 22 to 26, wherein each elongate slot is straight.

28. The brake system of any of claims 22 to 26, wherein each elongate slot is curved.

29. The brake system of any of claims 21 to 28, wherein each of the at least one apertures is spaced from the peripheral edges of the braking surface of the respective brake pad.

30. The brake system of any of claims 21 to 29, wherein, in use, the at least one aperture of one brake pad is not directly opposed with the at least one aperture of the other brake pad.

31. The brake system of any of claims 21 to 30, wherein the apertures and the plurality of holes are arranged such that at least one hole on each brake disc plate is at least partially aligned with at least one aperture on the respective brake pad at any rotational position of the disc.

32. The brake system, of any of claims 21 to 30, wherein the apertures and the plurality of holes are arranged such that at least one of the plurality of holes on either brake disc plate is at least partially aligned with one aperture at any rotational position of the disc.

33. The brake system of any of claims 21 to 32, wherein each aperture has a depth extending only partially through the brake pad, and each first passage extends from the back surface to the aperture.

34. The brake system of claim 33, wherein the depth is a wearing depth of the brake pad.

35. The brake system of claim 33, wherein the depth is greater than the wearing depth of the brake pad.

36. The brake system of any of claims 21 to 35, wherein the brake pads further comprise a second passage extending through the brake pad in fluid communication with the aperture in the braking surface for allowing fluid to flow from the aperture via the second passage to atmosphere.

37. The brake system of claim 36, wherein said second passage is in fluid communication with a fluid removal means.

38. The brake system of claim 36 or 37, wherein the at least one aperture in each brake pad comprises an elongate slot, each elongate slot has first and second ends, defining a slot length between the ends, each first passage is located on one side of a lateral centreline that bisects the length of each slot, and each second passage is located on the other side of each lateral centreline.

39. The brake system of claim 38, wherein each passage is located within 5%, 10%, 15% or 20% of the slot length of the first end, and each second passage is located within 5%, 10%, 15% or 20% of the slot length of the second end.

40. A method of cooling the brake system of any of claims 15 to 39, comprising providing air from the pressurised fluid supply means to the braking surface or surfaces via the at least one aperture or apertures.

41. The method of claim 40, wherein the step of providing air from the pressurised fluid supply means comprises: supplying air at a first pressure and/or flow rate during braking conditions; and supplying air at a second pressure and/or flow rate during non-braking conditions.

42. The method of claim 41, wherein the first pressure and/or flow rate is higher than, or lower than, the second pressure and/or flow rate.

43. The method of claim 41 or 42, further comprising, during non-braking conditions after the step of supplying air at a second pressure and/or flow, supplying air at a third lower pressure and/or flow rate.