GB2516505A

GB2516505A - Brake system

Info

Publication number: GB2516505A
Application number: GB1313302.0A
Authority: GB
Inventors: Trevor Michael Mennie
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-07-25
Filing date: 2013-07-25
Publication date: 2015-01-28
Also published as: WO2015011618A3; GB201313302D0; WO2015011618A2

Abstract

A brake assembly comprises first and second brake pads 36, 38, a brake disc 46 positioned between the braking surfaces of the first and second brake pads 36,38, a floating calliper 10 positioned over an edge of the disc 46 and operatively connected to the first and second brake pads 36,38, and a pressurised gas supply in fluid communication with the braking surfaces. Under braking conditions, the braking surfaces are each in contact with the brake disc 46. Under non-braking conditions, gas from the pressurised gas supply is supplied to the braking surfaces to separate the braking surfaces from the disc 46. The brake system is configured such that supplying gas at the same pressure to both braking surfaces moves both brake pads 36,38 the same distance from the disc 46. The brake assembly may also comprise means for reducing the friction between the floating caliper and an associated shaft, such as a bearing, sleeve or coating (figs 3, 5 & 6). The brake assembly may further comprise an independent gas supply (83a-d, fig 12) for each brake rotor.

Description

Brake System The present invention relates to a brake system and a method of using a brake system.

S 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. 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 S 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. Such systems can be referred to as air-bearing brake systems.

One problem with prior art air-bearing brake systems occurs when a floating caliper is used. A floating caliper (also known as a sliding caliper) comprises a substantially U-shaped body that is positioned over an edge of a brake disc. On one side of the floating caliper body, a piston is positioned within a cylinder. A first brake pad is positioned between the piston and the brake disc. On the other side of the floating caliper body, a pair of fingers are provided and a second brake pad is positioned between the fingers and the brake disc. The floating caliper is attached to a part of the vehicle, such as a frame attached to the suspension, in such a way that the floating caliper body is free to move relative to the brake disc in a direction parallel to the axes of rotation of the disc. For example, the floating caliper body may be mounted on a pair of shafts.

In use, when a driver of a vehicle applies the brakes (e.g. by pressing a foot-brake), pressurised hydraulic fluid is forced into the cylinder and pushes the piston onto the first brake pad, which in turn pushes the first brake pad onto the brake disc. The pressurised hydraulic fluid also applies the same force on the interior surface of the cylinder (opposite to the piston's end) and moves the whole floating caliper (in an opposite direction to the movement of the piston) along the pair of rails. The movement of the caliper causes the pair of fingers to push the second brake pad into contact with the brake disc.

Under non-braking conditions, air is supplied to the braking surfaces of the first and second brake pads. The air to both brake pads is supplied by a single conduit that splits into two conduits (having the same cross-sectional area) near the brake pads. As such, the air provided to both pads should be at approximately the same pressure. The Applicant has recognised that the first brake pad, which is adjacent the piston, can be much easier to move away from the disc than the second brake pad. This means that this pad separates from the disc first. The majority of the air being supplied to the brake pads is then likely to flow to the first S brake pad only, as this is the path of least resistance due to the gap that has opened between the first pad and the disc (while the second pad is still in contact with the disc). This means that the second pad may stay in contact with the disc through the period of non-braking. This is clearly undesirable for the reasons discussed above.

Another problem encountered with prior art air-bearing brake systems is due to the fact that the braking surfaces of all of the brake pads of the vehicle are in fluid communication with each other. For example, a single air pump may provide an air supply in a single conduit that splits downstream into four conduits, with one conduit for each brake rotor. Such an arrangement can be problematic as any pressure drop on one or more pads will create a path of least resistance for the pressurised air. More of the pressurised air will then flow down the respective conduit to that pad or pads instead of the other pads, with the result that less pressure is supplied to the other pads, which may then remain in contact with the rotor or rotors. This is clearly undesirable for the reasons discussed above.

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 system comprising first and second brake pads, each having a braking surface and an opposed back surface, a brake disc positioned between the braking surfaces of the first and second brake pads, a floating caliper positioned over an edge of the disc and operatively connected to the first and second brake pads and a pressurised gas supply in fluid communication with the braking surfaces. The brake system is configured such that under braking conditions, the braking surfaces are each in contact with the brake disc and under non-braking conditions gas from the pressurised gas supply is supplied to the braking surfaces to separate the braking surfaces from the disc. The brake system is preferably configured such that supplying gas at the same pressure to both braking surfaces moves both brake pads the same distance from the disc.

Moving both pads the same distance from the disc means that a substantially larger gap does not form on one side of the disc. The presence of a substantially larger gap would cause the pressurised gas to be preferentially supplied to the brake pad adjacent that gap and, in turn, cause the opposite brake pad to remain in contact with the brake disc. As such, this aspect of the present invention provides a brake system in which both brake pads are more likely to be S separated from the brake disc under non-braking conditions.

The gas from the pressurised gas supply provides 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 "braking conditions" can be defined in any suitable way. However, the braking conditions preferably comprises the brake being activated, for example via a brake pedal or lever of the vehicle, and/or an accelerator or throttle of the vehicle not (or no longer) being activated, and/or a cruise control system for the vehicle being deactivated.

Similarly, the "non-braking conditions" referred to above can be defined in any suitable way. However, the non-braking conditions preferably comprises the brake being deactivated, for example a brake pedal or lever of the vehicle not being in use, and/or an accelerator or throttle of the vehicle being activated, and/or a cruise control system for the vehicle being activated.

The system may comprise means for detecting braking conditions and/or non-braking conditions. In embodiments, the brake system preferably comprises a sensor arrangement for detecting when a brake pedal and/or an accelerator or throttle and/or a cruise control system is being activated or deactivated.

The gas is preferably air, although other gases could be used. The use of air is particularly advantageous in that a dedicated supply of gas (e.g. a gas cylinder) is not needed in or for the braking system.

The brake disc is preferably circular. As such, the floating caliper is preferably positioned over a circumferential edge of the disc, as is well known in the art.

The floating caliper may take any form. As is known in the art (and discussed above), floating calipers comprise a floating caliper body, one or more pistons and a fixed part that is secured to a part of the vehicle. The floating caliper body is free to move relative to the brake disc in a direction parallel to the axis of rotation of the disc. Supplying pressurised air to the brake pads under non-braking conditions causes the first brake pad to press against the piston and move the piston a distance into (or further into) the cylinder and causes the second brake pad to press against a part of the floating caliper body (e.g. one or more fingers) and move the floating caliper body relative to the disc.

Preferably, the brake system is configured such that applying gas at the same pressure to both pads, imparts approximately the same force to the braking S surfaces of each pad.

Preferably, imparting the same force to both braking surfaces results in the same amount of movement away from the disc.

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

The brake pads can take any desired or suitable form. For example, each brake pad may comprise a friction material (e.g. a ceramic, semi-metallic, metallic or carbon fibre material) on a support structure (such as a back plate). In embodiments therefore the brake pads may each comprise a support structure and a friction material thereon. In these embodiments the friction material defines the braking surface (disc 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.

Each brake pad preferably has one or more openings in its braking surface for providing the gas to the braking surface of the brake pad, with the pressurised gas supply being in gas communication with the braking surface of the brake pad via the one or more openings.

The or each opening may be an opening which extends all the way through the friction material from one side of the friction material (e.g. the braking surface side) to another side (e.g. other than the braking surface side).

The one or more openings is preferably a single opening, preferably in the centre 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 comprises a porous structure in its braking surface for providing the gas to the braking surface of the brake pad, with the pressurised gas supply being in gas communication with the braking surface of the brake pad via the porous structure.

S The porous structure may be provided by a suitable porous material. The porous structure may be positioned such that gas 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.

The majority or all of at least a friction material of the brake pad (i.e. not just the surface region) may also be porous. These embodiments are particularly advantageous in that the brake pad can wear down, but porous structure will remain on the surface of the brake pad. The porous structure may be provided by using porous friction material.

Preferably, 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 openings therethrough. The porous structure may help the gas supplied through the opening(s) to dissipate across the braking surface when in contact with the brake disc. This means that the force of the pressurised air acts upon a greater area of the braking surface.

In a preferred embodiment, each brake pad comprises a single opening in the centre of a braking surface extending through a porous friction material.

The pressurised gas supply is capable of supplying pressurised gas at a pressure that is sufficient to separate the braking surface of the brake pad from the brake rotor under non-braking conditions, i.e. provide a gap therebetween under non-braking conditions. The pressure may also be insufficient to separate the braking surface of the brake pad from the brake rotor under braking conditions.

The distance of separation or gap between the brake pad and brake rotor provided by embodiments of the present invention need only be enough so that the surface of the brake pad does not contact an adjacent brake rotor. The separation is preferably of the order of ito 100 microns, preferably of the order of 10 microns.

The gap is preferably provided across substantially the entire surface of the brake pad.

As will be appreciated, the capabilities of the pressurised gas supply will depend on the type and size of the brake system, the number and size of openings in the surface of the brake pad, and/or the number of brake pads that are supplied with pressurised gas. However, the pressurised gas supply is preferably configured to supply pressurised gas at between 0.5 kPa and 700 kPa, more preferably between 0.5 kPa and 200 kPa, even more preferably between 0.5 kFa and 50 kPa, and most preferably between 0.5 kPa and 4OkPa.

The pressurised gas supply can be powered in any desired or suitable way.

However, the pressurised gas supply is preferably powered either directly or indirectly by an engine of the vehicle (an engine that drives the wheels of the vehicle). For example, the pressurised gas supply may be powered by (directly coupled to) an alternator shaft of an engine of the vehicle or may be powered by (directly coupled to) a drive train of an engine. Alternatively, the pressurised gas supply may be powered by electrical power generated by an engine of the vehicle, for example the 12V or 24V DC power supply provided to or by the cigarette lighter of a vehicle. These embodiments are particularly advantageous in that a dedicated supply of power (e.g. a battery or generator) is not needed in or for the braking system.

The pressurised gas supply preferably comprises a pump capable of producing the necessary pressure. Generally, a larger brake pad and/or more resistive brake mechanism (e.g. calipers) will require a pressurised gas supply that is capable of supplying gas at a higher pressure.

As will be appreciated, the system is configured to provide fluid from the pressurised fluid supply to the braking surface of the brake pad at least under non-braking conditions. This is preferably achieved by a system control means. It will be appreciated that any of the steps involved in providing fluid from the pressurised fluid supply to the braking surface may be carried out by the system control means of the system. Thus, references such as "the brake system being configured such that" may be interchanged with "the brake system comprising system control means being configured such that".

In preferred embodiments, the system (or system control means) is preferably configured to provide fluid from the pressurised fluid supply to the braking surface of the brake pad only under non-braking conditions. Thus, the system (or system control means) may be configured to activate the pressurised fluid supply only under non-braking conditions and/or deactivate the pressurised fluid supply under braking conditions.

Preferably, the brake system is configured such that under braking conditions, no gas is supplied to the braking surfaces. This can be achieved by switching off the pressurised gas supply during braking conditions or by keeping the pressurised gas supply on during braking conditions but preventing the gas reaching the braking surfaces (e.g. by diverting the gas elsewhere).

In one embodiment, the floating caliper may comprise a floating caliper body S and a piston. The floating caliper body has a cylinder and a surface operatively connected to the back surface of the second brake pad. The piston is moveable within the cylinder and operatively connected to the back surface of the first brake pad. The brake system may comprise one or more shafts on which the floating caliper body is mounted. Separating the first braking surface from the disc may cause a portion of the piston to move into the cylinder. Separating the second braking surface from the disc may cause the floating caliper body to move along the shaft(s).

The reference to the piston moving "into" the cylinder should be understood to mean that the piston moves into or further into the cylinder. Preferably, at least a portion of the cylinder will always remain within the cylinder.

The opposed surface may be provided on one or more, for example two, fingers.

There may be two shafts per floating caliper. The shafts preferably extend perpendicularly to the surfaces of the disc (and the braking surfaces of the brake pads), i.e. parallel to the axis of rotation of the disc.

The term operatively connected' should be understood to mean that the piston and the surface and the respective brake pad are arranged such that movement of the piston and surface towards their adjacent brake disc causes that brake pad to move in the same direction (i.e. towards the brake disc). The piston and/or surface may be secured to or engaged with the back surface of the brake pads, but this is not necessary. More preferably, the piston and/or surface 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 disc).

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.

S In one embodiment, the brake system comprises means for reducing the friction between the floating caliper body and the shaft or shafts. Reducing the friction between the floating caliper body and the shaft(s) means that the floating caliper body can be more easily moved along the shaft(s). In turn, this means that the second brake pad can be more easily moved away from the brake disc. If the friction between the floating caliper body and the shaft(s) can be reduced by a sufficient amount, then the second brake pad can be moved as easily as the first brake pad (which only needs to move the piston into the cylinder) and as such, supplying the same pressure gas between the disc and the braking surfaces of each brake pad will move both pads approximately the same distance.

Alternatively, the floating caliper body can be made to be more easily moved, relative to the disc, in other ways. For example, by making the floating caliper body lighter and/or reducing friction between the floating caliper body and other stationary parts, such as rails that are part of the fixed part of the caliper (and extend over the disc).

These arrangements are believed to be new and advantageous in their own right, and not merely in the context of the above described aspects and embodiments.

As such, the present invention also extends to a brake system comprising first and second brake pads, each having a braking surface and an opposed back surface, a brake disc positioned between the braking surfaces of the first and second brake pads and a floating caliper having a floating caliper body having a cylinder and a surface operatively connected to the back surface of the second brake pad and a piston moveable within the cylinder and operatively connected to the back surface of the first brake pad, wherein the surface is opposed to the piston. The brake system also comprises a shaft, on which said floating caliper body is mounted, and a pressurised gas supply in fluid communication with the braking surfaces, wherein under braking conditions, the braking surfaces are each in contact with the brake disc and under non-braking conditions, gas from the pressurised gas supply is supplied to the braking surfaces to separate the braking surfaces from the disc. Separating the first braking surface from the disc causes a portion of the piston to move into the cylinder and separating the second braking surface from the disc causes the floating caliper body to move along the shaft. The brake system further comprises means for reducing the friction between the floating caliper body and the shaft.

S The brake system according to this aspect of the present invention may have any of the features of the previously described aspect and any embodiments thereof.

In either aspect, the means for reducing the friction may comprise a bearing, sleeve or coating on the shaft.

The sleeve or coating may comprise a low-stick or no-stick coating, i.e. a friction-reducing material, such as RIFE ("Teflon" (RIM)).

The sleeve may comprise a tube of a thin layer of material, such as RIFE.

The layer may have a thickness less than 1.0 mm or less than 0.5 rum, or approximately 0.4 mm. The sleeve may be placed around the shaft and heated to shrink the sleeve onto the shaft. In use, some of the material of the sleeve may rub off onto an inner surface of the floating caliper body or any intervening member.

Alternatively, a liquid or particulate coating may be applied to the shaft and then, in the case of the liquid coating, allowed to dry. Again, the coating may rub off onto an inner surface of the floating caliper body or any intervening member.

Alternatively or additionally, the coating may be applied to an inner surface of the floating caliper body or any intervening member.

The sleeve may comprises a porous sleeve-like bearing that is impregnated with a lubricating material. For example, an Oilite (RIM) bushing could be used.

The bearing may comprise a linear bearing. Linear bearings are well known in the art and commonly contain a rigid outer sleeve and a plurality of rows of balls retained by cages on an inner surface of the outer sleeve. The floating caliper body may directly or indirectly contact the outer surface of the outer sleeve and the rows of balls may run along the shaft.

Preferably, in use, the means for reducing the friction is non-fluidic. In other words, when the brake system is assembled and ready to use, the means for reducing friction is solid, rather than a gas or liquid. As mentioned above, a solid bearing having some impregnated fluid lubricant could be used. These type of bearings are dry to the touch, even though they contain a very small amount of liquid lubricant e.g. oil. As mentioned above, to provide the friction-reducing means, a liquid coating may be applied, but this coating should be allowed to dry before the brake system is assembled.

Using non-f luidic friction-reducing means reduces the risk of the any fluid leaking onto the braking surface of either pad and having a detrimental (or even S dangerous) effect on braking performance. For example, the means is preferably not oil or any other liquid lubricant.

In one embodiment (still according to either aspect), the floating caliper may further comprise a resilient bushing positioned around the shaft and the means for reducing the friction may be provided between the resilient bushing and the shaft.

Resilient bushings positioned between a floating caliper body and a shaft are known in the art and may comprise a rubberised sleeve. Such bushings serve to reduce vibrations between the floating caliper body and the shaft but can also prevent the floating caliper body moving freely along the shaft. Providing friction reducing means between the bushing and the shaft (i.e. inside the bushing and around the shaft), such as a coating or linear bearing, can allow the floating caliper body to move more easily along the shaft. The bushing may move, together with the floating caliper body, along the shaft. Where a linear bearing is used, the linear bearing will preferably move, together with the bushing, along the shaft.

According to another aspect of the present invention there is provided a vehicle comprising the brake system described previously in accordance with either aspect and any embodiments thereof.

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 system). 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.

According to another aspect of the present invention there is provided a method using a brake system having first and second brake pads and a brake disc positioned between the brake pads (preferably the brake system described herein), comprising the step of, under non-braking conditions, providing pressurised fluid at the same pressure to the braking surfaces of the first and second brake pads such that each of said first and second brake pads moves the same distance from the brake disc.

According to another aspect of the present invention there is provided a method of using a brake system having first and second brake pads and a brake disc positioned between the brake pads, comprising the step of, under non-braking conditions, providing pressurised fluid at the same pressure to the braking surfaces S of the first and second brake pads such that each of said first and second brake pads moves the same distance from the brake disc.

According to another aspect of the present invention, there is provided a brake system comprising a plurality of brake pads, each brake pad having a braking surface, a plurality of brake rotors, each rotor being positioned adjacent the braking surface of one or more pads and means for supplying gas to each of the braking surfaces under non-braking conditions to separate the braking surfaces from a respective rotor. The means for supplying gas provides an independent gas supply for the brake pad or pads of each rotor such that a change in pressure in one gas supply does not affect the pressure in the other gas supply or supplies.

The brake rotors preferably comprise brake discs. In these embodiments, the brake system preferably comprises a pair of opposed brake pads, preferably joined by a caliper, such as a fixed or floating caliper. However, in other embodiments the brake system may comprise a single brake pad.

Alternatively, the brake rotors may comprise drum brakes.

The brake pads may be as described in relation to the previous aspects and any embodiments thereof. For example, each brake pad may comprise a porous friction material secured to a back plate and having an opening passing through the porous material and being in fluid communication with a respective gas supply.

The brake system of this aspect can use any suitable type of caliper, such as a floating caliper or a fixed caliper.

The term independent gas supply' should be understood to mean that the braking surfaces of brake pads associated with different rotors are not in fluid communication with each other. As such, the gas pressure at the braking surface or surfaces of each brake pad of a rotor will not be affected by the pressure at the braking surfaces of the brake pads at any other rotor.

The gas supply means effectively provides four separate pressurised gas lines. The gas supply means may be configured to provide the same fluid output to each line (although the pressure in each line will, of course, depend on the conditions downstream, i.e. in the brake pad).

Where there are two brake pads adjacent each rotor, each pair of brake pads can be supplied by the same independent gas supply. As such, the braking S surfaces of each pad of the pair can be in fluid communication with each other.

Providing an independent gas supply for the brake pad or pads of each rotor means that the pressure supplied to each rotor will not be affected by any pressure drops at other rotors, for example due to a brake pad being separated more easily from another rotor (and the separation providing a path of least-resistance for the air flow). This helps to ensure that, under non-braking conditions, all braking surfaces can be separated from all rotors.

The gas supply means may comprise an suitable gas pump or compressor.

Preferably, the pump/compressor comprises a plurality of heads and each head is associated with one of the independent gas supplies. Each head comprises a separate pressurised fluid outlet for connection to an independent gas supply. Each outlet is not in fluid communication with the other outlets.

In one embodiment, the gas supply means comprises one or more diaphragm pumps. Diaphragm pumps are known in the art and use a motor to move a diaphragm into and out of a pumping plenum that is fluid communication with an inlet and outlet. The inlet and outlet contain one-way valves so that air can only enter the plenum through the inlet and exit the plenum through the outlet.

A diaphragm pump is advantageous for use in this brake system as it is light, has a long life cycle and does not require any lubrication (that could find its way to the braking surfaces). The moving parts of the diaphragm pump (not including the motor) can be injection rnoulded and are thus light and will not corrode/rust.

Preferably, said one or more diaphragm pumps comprises a plurality of heads and each head is associated with one of said independent gas supplies.

Each head comprises a diaphragm and thus a separate pumping circuit. Each head is preferably powered by a single motor. Using a pump with multiple heads can reduce the vibrations and noise caused, compared to a pump having a single head (i.e. single piston).

In one embodiment, the braking system comprises four rotors and the pump consists of a single pump (e.g. a diaphragm pump) having four heads. In such an embodiment, there are four independent gas supplies.

In an alternative embodiment, a different type of pump than a diaphragm pump may be used. For example, a rocking piston pump may be used to provide a plurality of independent gas supplies.

Preferably, the gas supply means, for example, the diaphragm pump, is S powered by a brushless DC motor. Brushless DC motors are small, light, reliable and have a long life-cycle. They produce very little heat so are efficient and use very little energy. The speed of these motors can be controlled as can the pressure and volume of pumped fluid. They can be run off a vehicle's usual electric circuit, i.e. that which powers the cigarette lighter etc. Such a circuit is usually at 1 2V or 24V.

Preferably, the brushless DC motor can be operated at 12V and/or 24V so that it can be run by a 12V or 24V vehicle battery.

In embodiments where each rotor is associated with a plurality of brake pads (e.g. two), each independent gas supply preferably supplies gas to a plurality or all of the brake pads associated with a single rotor. Such an arrangement reduces the amount of pipework needed.

In an embodiment, the gas supply means may be located in an engine bay.

This means that warm air from the engine bay can be supplied to the braking surfaces. This will warm the brake pads which may help to melt any ice that has formed between the disc and the brake pads and/or may improve braking performance.

Preferably, the independent gas supplies are all provided by a single gas supply means. The single gas supply means is preferably powered by a single motor.

Preferably, the independent gas supplies are each carried via a conduit extending from the gas supply means to the respective brake pad or pads.

The brake system of this aspect of the present invention can be used in combination with that of the previously disclosed aspects and any embodiments thereof. For example, a brake system having an independent gas supply for the brake pads of each rotor and a floating caliper having means for reducing the friction between the floating caliper body and said shaft is envisaged.

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 schematic perspective view of a floating caliper for use in a brake system according to an embodiment of the present invention; Figure 2 is another schematic perspective view of the caliper of Fig. 1; Figure 3 is a cross-sectional view of a part of a brake system according to an embodiment of the present invention and including the floating caliper of Figs 1 and 2; S Figure 4 is a side view of a shaft of the brake system of Fig. 3; Figure 5 is another cross-sectional view of the part shown in Fig. 3 but in a different position; Figure 6 is a cross-sectional view of a part of a brake system according to an alternative embodiment of the present invention and including the floating caliper of Figs 1 and 2; Figure 7 is a side view of a brake system according to an embodiment of the present invention and for use with the floating caliper of Figs 1 and 2; Figure 8 is a front/side perspective view of the brake system of Fig. 7; Figure 9 is a front/side perspective view of the brake system of Figs 7 and 8; Figure 10 is a front/side perspective view of the brake system of Figs 7to 9; Figure 11 is a cross-sectional view of a gas pump that can be used in a brake system according to a preferred embodiment of the present invention; Fig. 12 is a schematic plan view of a car using the brake system of a preferred embodiment of the present invention; Fig. 13 is a schematic view of a pressurised gas supply line for an air bearing system; Fig. 14 is another schematic view of the pressurised gas supply line of Fig. 13.

Fig. 1 shows a floating caliper 10 having a floating caliper body 14. The floating caliper body 14 comprises a cylinder portion 16, an 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 1 6a, 1 6b and a cylinder 1 6c. The floating caliper 10 also comprises a fixed frame that does not move relative to the disc (not shown, discussed later).

Fig. 2 shows the floating caliper 10 of Fig 1 comprising a piston 12. The piston 12 sits and moves axially within cylinder 1 6c of the floating caliper body 14.

Positioned within the bores of the lugs 1 Ga, 1Gb are cylindrical rubber bushings 22a, 22b.

Fig. 3 shows a cross-sectional view of lug 1 Ga of the floating caliper 10 of Figs. 1 and 2 mounted to a fixed frame 28 of the floating caliper 10 which does move relative to the brake disc. The fixed frame 28 is, in turn, secured to a vehicle frame (29, Fig. 7), which may be part of the vehicle's suspension. Attached to the S fixed frame 28 is a shaft 20 having a cylindrical shaft portion 32 and a threaded cylindrical portion 34. The shaft 20 is shown in Fig. 4. One end of the shaft 20 is fixedly attached to the fixed frame 28 by the threaded portion 34. The opposite end of the shaft 20 has a hexagonal slot 60 for screwing the shaft 20 into a threaded bore 28a in the fixed frame 28. The shaft portion 32 of the shaft 20 extends through the lug 16a.

The shaft portion 32 is surrounded by a tight fitting rubber bushing 22a, which is slidable along the shaft 20. The rubber bushing 22a is secured to the lug 1 Ga (e.g. via an interference fit) such that the lug 1 Ba is slidable relative to the shaft 20. In order to reduce the friction between the shaft 20 and the rubber bushing 22a, a linear bearing 24 is provided on the shaft 20. As is known in the art, the linear bearing 24 may comprise a plurality of balls trapped in cages and in contact with the shaft 20 (not shown). The bushing 22a may engage the linear bearing 24 via an interference fit. A plastic cap 30 is affixed to the end of the rubber bushing 22a over the hexagonal slot 60 to prevent dust from entering the slot 60 or bushing 22a.

In use, the rubber bushing 22a and the floating caliper body 14, move between a first position and a second position. Fig. 3 shows the floating caliper body 14 and rubber bushing 22a in the first position. A flange 23 at one end of the rubber bushing 22a is positioned adjacent the fixed frame 28. The plastic cap 30 is positioned adjacent the other end of the shaft 20. Fig. 5 shows the rubber bushing 22a in the second position. The lug 16a, rubber bushing 22a, linear bearing 24 and cap 30 have all moved along the shaft 20 such that there is now a gap between the edge of the rubber bushing 22a and the fixed frame 28. The flange 23 still abuts the lug 16a.

Fig. 6 shows an alternative embodiment of the arrangement of Figs. 4 and 5 wherein the linear bearing 24 has been replaced with a PTFE sleeve 26. The sleeve 26 may have been placed around the shaft 20 and heated to shrink the sleeve 26 onto the shaft 20. Another difference is that the bushing 22a has an undulating inner surface 25 to reduce contact with the shaft 20 via sleeve 26. The sleeve 26 may comprise a tube of a very thin (e.g. approximately 0.4 mm) material.

The floating caliper body 14 and rubber bushing 22a move between first and second positions as per the embodiments of Figs. 3 and 5.

Fig. 7 shows a brake disc 46 having a hub 48. 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.

Fig. & shows a part of the disc 46 of Fig. 7. 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 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 air to the braking surface of the friction material 40 through the back plate 42. In use, pipe 44 will be connected to a source of pressurised air.

Fig. 9 shows the disc of Figs. 7 and 8. 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.

Fig. 10 shows the disc 46 of Figs 7 to 9 with the floating caliper 10 of Figs. 1 and 2 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 braking surface of brake pad. 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 1 6c 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 S disc 46 with a substantially equal pressure. When the user releases the brake, the pressure on the hydraulic fluid in the cylinder 1 Bc 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.

Providing pressurised air to the braking surfaces of the brake pads 36, 38 via pipes 44 creates a gap between the braking surfaces and the disc 46.

However, it can be easier to move the inner brake pad 38, which just needs to push the piston 12, than the outer brake pad 36, which needs to move the whole floating caliper body 14 along the shafts 20. Using a linear bearing 24 or PTFE liner 26 between the rubber bushings 22 and the shafts 20 (as shown in Figs. 3, 5 and 6) reduces the friction along the shaft 20 and thus allows the floating caliper body 14 to be moved more easily. By reducing the friction between the rubber bushings 22 and the shafts 20, the pressurised air can push both pads 36, 38 an equal distance from the disc 46.

Fig. 11 shows a diaphragm gas pump 60 having four separate pump heads 62a, 62b, 62c, 62d. Each head is identical in construction, so only a single head 62a will be described. The heads are powered by a single motor 61, such as a brushless DC motor. The motor 61 drives first and second co-axial drive shafts 71.

Bearings 70 are provided between the drive shaft 71 and the pump housing 72.

The shafts 71 are each connected to a eccentric cam 69, which in turn is connected to upper and lower connecting rods 68. The connecting rods 68 are each connected to a diaphragm support 67 and a diaphragm 66.

The diaphragm 66 is positioned below a plate 73 and together they define a pumping plenum 63. The plate 73 of each head 62a -62d comprises an inlet 65 and outlet 64. The inlet 65 comprises a non-return valve (not shown) that permits fluid flow in one direction 75 only. Similarly, the outlet 64 comprises a non-return valve (not shown) that permits fluid flow in one direction 74 only.

Rotating the drive shaft 71 causes the eccentric cam 69 to push the connecting rods in a reciprocating manner, which in turn pushes the diaphragms 66 towards and away from the plate 73. When the diaphragm 66 is moved away from the plate 73 the pumping plenum increases in size and fluid is sucked through the inlet 65 (in direction 75). Head 62a shows the diaphragm 66 in its furthest position away from the top plate 73. In this position, the pumping plenum 63 will be full of fluid, such as air.

When the diaphragm 66 is moved towards plate 73, the size of the plenum 63 is reduced and fluid is pumped out until the diaphragm 66 contacts plate 73, as shown by head 62b. Heads 62c and 62d show the diaphragms 66 in mid-positions, where the diaphragms 66 are on the way to the positions shown by heads 62a and 62b.

The four outlets 64 of heads 62a -62d can be connected to separate piping to provide four independent gas supplies.

The use of a multi-headed diaphragm reduces vibrations and noise due to the offset of the different heads at any point in time.

Fig. 12 shows a car 80 having the diaphragm pump 60 of Fig. 12. The pump 60 may be positioned at any suitable location, preferably one close to a centre of the car. The pump 60 may source air from an engine bay (not shown) so that warm ambient air can be used. As can be seen, the car 80 has four brake discs 46, each having a hub 48 for connection to a wheel (not shown).

The pump 60 supplies pressurised air to the brake pads of each disc 4 via four separate (and independent) gas supply lines 83a, 83b, 83c, 83d. Each line is connected to an inlet 74 of a head 62a -62d (Fig. 11) of the pump 60. The pump may provide the same pressure air to each line 83a -83d. The lines are not in fluid communication with each other, so a change in pressure in one line (for example due to a problem in one brake pad/caliper) will not affect the pressure in any other line.

The lines 83a -83d may comprise flexible plastic tubing. Each line may be split proximate the brake disc into a pipe for each brake pad on that disc (e.g. two pipes) (not shown).

Figs. 13 and 14 show part of a pressurised gas supply line for an air bearing system. The air bearing system comprises one or more air bearings, an air pump, a variable timer controller (VTC) 90, a number of dump valves 92, an actuator (such as a footbrake) and pipework 94, 96, 98. Each air bearing comprises a brake pad and a brake disc.

In use, the air pump supplies pressurised air via pipe 94 to each brake pad, a pair of pads being associated with each wheel of the automobile (e.g. four -20 -wheels). The pipework includes a plurality of dump valves 92 (e.g. four), one located proximal to each pair of brake pads. As the dump valves 92 are normally closed, they are provided in a separate pipe 96 extending from the pipe 98 between the air pump and the air bearing, as shown in Figs. 13 and 14. As such, when the S compressor is on, the air supply to the brake pad does not flow through dump valves 92.

The dump valves 92 are solenoid valves, which are normally closed. As such, energy is required to open the dump valves 92 and to maintain them in an open condition, whereas closing the dump valves 92 and maintaining them in a closed condition does not require any energy.

When the footbrake is not applied, for example when the car is in motion, the air pump is on so that air is constantly supplied to the brake pads, and the dump valves 92 are closed, as shown in Fig 13. When the footbrake is applied, the air pump is turned off, the dump valves 92 are opened and the timer is started, as shown in Fig 14. These three events occur simultaneously. Turning the air pump off saves energy. Opening the dump valves 92 allows the pressurised air in the pipes 94 and in the air-bearing (i.e. between the brake pad and the brake disc) to be discharged until the pressure drops to that of the surroundings, i.e. atmospheric pressure.

After the timer reaches a preset time, the dump valves 92 are closed. The time lapsed since the timer was started is sufficient to allow the air to be discharged fully. For example, this time may be ito 5 seconds. As such, closing the valves 92 at this time does not prevent the air from discharging. Closing the valves 92 at this time saves energy as the valves no longer need to be open (i.e. powered).

When the footbrake is released, the air pump is turned back on, supplying air to the brake pads. The dump valves 92 remain closed so that pressurised air in the air bearing pushes the brake pads away from the disc.

Claims

-21 -CLAIMS: 1. A brake system comprising: first and second brake pads, each having a braking surface and an opposed S back surface; a brake disc positioned between the braking surfaces of said first and second brake pads; a floating caliper positioned over an edge of said disc and operatively connected to said first and second brake pads; and a pressurised gas supply in fluid communication with said braking surfaces, wherein under braking conditions, said braking surfaces are each in contact with said brake disc and under non-braking conditions gas from the pressurised gas supply is supplied to the braking surfaces to separate said braking surfaces from said disc and said brake system is configured such that supplying gas at the same pressure to both braking surfaces moves both brake pads the same distance from the disc.
2. The brake system of claim 1, wherein said floating caliper comprises: a floating caliper body having a cylinder and a surface operatively connected to said back surface of said second brake pad; and a piston moveable within said cylinder and operatively connected to said back surface of said first brake pad, and said brake system further comprises a shaft on which said floating caliper body is mounted, wherein separating said first braking surface from said disc causes a portion of said piston to move into said cylinder and separating said second braking surface from said disc causes said floating caliper body to move along said shaft.
3. The brake system of claim 2, further comprising means for reducing the friction between the floating caliper body and said shaft.
4. A brake system comprising: first and second brake pads, each having a braking surface and an opposed back surface; a brake disc positioned between the braking surfaces of said first and second brake pads; -22 -a floating caliper having: a floating caliper body having a cylinder and a surface operatively connected to said back surface of said second brake pad; and a piston moveable within said cylinder and operatively connected to S said back surface of said first brake pad, wherein said surface is opposed to said piston; a shaft, on which said floating caliper body is mounted; a pressurised gas supply in fluid communication with said braking surfaces, wherein under braking conditions, said braking surfaces are each in contact with said brake disc and under non-braking conditions gas from the pressurised gas supply is supplied to the braking surfaces to separate said braking surfaces from said disc, wherein separating said first braking surface from said disc causes a portion of said piston to move into said cylinder and separating said second braking surface from said disc causes said floating caliper body to move along said shaft; and means for reducing the friction between said floating caliper body and said shaft.
5. The brake system of claim 3 or 4, wherein said means for reducing the friction comprises a bearing, sleeve or coating on said shaft.
6. The brake system of claim 5, wherein said sleeve or coating comprises RIFE.
7. The brake system of any of claims 3 to 6, wherein, in use, said means for reducing the friction is non-fluidic.
8. The brake system of any of claims 3 to 7, wherein said floating caliper further comprises a resilient bushing positioned around said shaft and said means for reducing the friction is provided between said resilient bushing and said shaft.
9. A method of using a brake system as claimed in any preceding claim, comprising the step of, under non-braking conditions, providing pressurised fluid at the same pressure to the braking surfaces of said first and second brake pads such -23 -that each of said first and second brake pads moves the same distance from said brake disc.
10. A method of using a brake system having first and second brake pads and S a brake disc positioned between the brake pads, said method comprising the step of, under non-braking conditions, providing pressurised fluid at the same pressure to the braking surfaces of said first and second brake pads such that each of said first and second brake pads moves the same distance from said brake disc.
11. A brake system comprising: a plurality of brake pads, each brake pad having a braking surface; a plurality of brake rotors, each rotor being positioned adjacent the braking surface of one or more pads; and means for supplying gas to each of said braking surfaces under non-braking conditions to separate said braking surfaces from a respective rotor, wherein said means provides an independent gas supply for the brake pad or pads of each rotor such that a change in pressure in one gas supply does not affect the pressure in the other gas supply or supplies.
12. The brake system of claim 11, wherein said gas supply means comprises a plurality of heads and each head is associated with one of said independent gas supplies.
13. The brake system of claim 11 or 12, wherein said gas supply means comprises one or more diaphragm pumps.
14. The brake system of claim 12 or 13, wherein said one or more diaphragm pumps consists of a single pump having four heads and said brake system comprises four rotors.
15. The brake system of any of claims 11 to 14, wherein said gas supply means is powered by a brushless DC motor.
16. The brake system of claim 15, wherein said brushless DC motor can be operated by a 1 2V or 24V battery.

-24 -
17. The brake system of any of claims 11 to 16, wherein each independent gas supply supplies gas to a plurality of the brake pads associated with a single rotor.
18. The brake system of any of claims 11 to 17, wherein said gas supply means is located in an engine bay.
19. The brake system of any of claims 11 to 18, wherein said independent gas supplies are all provided by a single gas supply means.
20. The brake system of any of claims 11 to 19, wherein said independent gas supplies are each carried via a conduit extending from said gas supply means to the respective brake pad or pads.
21. The brake system of any preceding claim, wherein each brake pad has one or more openings in its braking surface for providing gas to the braking surface and the pressurised gas supply or gas supply means is in gas communication with the braking surface via the one or more openings.
22. A brake system substantially as described herein with reference to one or more of any of the accompanying figures.
23. A method of using a brake system substantially as described herein with reference to one or more of any of the accompanying figures.