Patent Description:
Disc brakes are commonly used for braking heavy vehicles such as trucks, buses and coaches. Heavy vehicle disc brakes conventionally comprise a brake carrier and a caliper. The brake carrier is arranged to support brake pads on each side of a rotor. The caliper is slidably mounted on the brake carrier by two or more guide assemblies, such that when the disc brake is actuated, the caliper is able to slide with respect to the brake carrier so that both brake pads are urged onto opposing faces of a brake rotor in a clamping action to effect braking.

A guide assembly typically comprises a guide pin of the carrier along which the caliper can slide and a bore disposed in the caliper for receiving the guide pin.

To achieve free sliding of the caliper in a broad range of operating conditions, the guide assemblies must take account of manufacturing tolerances, effects of heating or cooling in use, and accommodate deflections of the disc brake due to the braking torque. Various arrangements are known to achieve this but typically involve one guide assembly being a close running fit within a respective bore and the other providing a degree of play by use of an elastomeric guide bush or a guide bush mounted within the bore that has clearance to its corresponding guide pin.

Such arrangements have been proven over many years' service but can be costly to manufacture and generate noise in operation where a metallic guide bush is used, or have a limited lifespan in the case of elastomeric guide bushes. <CIT> discloses a disc brake with a sliding bushing inserted into a bore of a brake caliper.

The present invention seek to alleviate the problems associated with the prior art.

A first aspect of the of the invention provides a disc brake caliper comprising a guide assembly for permitting axial movement of the disc brake caliper relative to a support, e.g., a disc brake carrier, the assembly comprising: a through bore of the caliper; a guide bush to be mounted in a through bore of the caliper and having a non-circular outer surface; a closure arranged to be seated at least partially within the through bore and be a barrier to the ingress of foreign matter into the through bore; and a stop to be retained by the closure and dimensioned radially so as to restrict axial displacement of the guide bush in at least a first direction, in use.

This allows a less close fitting arrangement of the guide bush to the housing to be to be required to axially retain the guide bush. In turn this may enable the guide bush to have less strength and be formed from alternative, possibly lower cost, and/or lighter materials, or for the guide bush to be thinner. The non-circular shape allows rotation of the guide bush to be inhibited if fitted into a caliper bore with a corresponding non-circular inner shape and therefore a correct orientation of the guide bush to be maintained.

Optionally, the stop is fixedly mounted to or integral with the closure.

This minimises part count and simplifies assembly.

Optionally, the closure comprises a cover portion and a bore engagement portion, the stop being axially spaced from the cover portion.

This allows a guide pin portion of the support to slide past the axial end of the guide bush, thereby minimising the required length of the guide bush and potentially minimising wear of the guide bush.

Optionally, the closure comprises a bore engagement portion and the stop is a radially inward projection from the bore engagement portion.

This provides a convenient form for the stop.

Optionally, the stop is integrally and monolithically formed from the bore engagement portion.

This may further simplify manufacture of the guide assembly.

Optionally, the stop has an internal radius greater than or equal to a largest internal radius of the guide bush.

This arrangement allows the corresponding guide pin to have a purely cylindrical outer form and be able to slide past the stop.

Optionally, the guide bush is formed from a rigid plastics material, for example a composite of polymeric material and low friction material, such as PTFE.

The use of such a guide bush may be lower cost and lower weight than a conventional metallic guide bush, and have lower noise levels in use. Further it may be more durable than an elastomeric guide bush.

Optionally, the guide bush has a non-circular, e.g., oval and/or slotted, internal profile.

This allows for some lateral play to avoid the binding of the caliper relative to the carrier when there are deflections or other misalignments under load, wear, or temperature effects.

Optionally, the through bore is dimensioned such that the guide bush is a light interference fit therewith.

This allows a lower strength guide bush to be used that does not need to withstand the forces required to withstand a full interference fitting.

Optionally, a closure receiving portion of the through bore has a larger diameter than a guide bush receiving portion.

This allows a step between the portions to act as a stop that aids the positioning of the closure. It further allows the non-circular feature to be machined into the bore and the guide bush to be fitted into the bore from the closure side.

Optionally, the through bore comprises a fixed stop at the side thereof that opposes the closure.

This is a way of simplifying assembly without requiring accurate axial alignment or additional mounting steps to achieve the secure and correct assembly.

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

<FIG> depicts an embodiment of a disc brake <NUM> of a type utilised for heavy vehicles such as trucks, buses and coaches.

Various orientations of the disc brake are described. In particular the directions inboard I and outboard O refer to the typical orientation of the disc brake when fitted to a vehicle and with reference to the longitudinal centre line of the vehicle. The radial direction Y refers to an orientation with reference to the centre of the brake rotor (axis A-A) and is for example the direction in which brake pads may be fitted and removed from a disc brake. The circumferential direction X refers to a tangent to the direction of the rotation of the rotor and is for example the direction in which a friction induced load from a brake pad is laterally transmitted into an abutment of a brake carrier.

The disc brake comprises a caliper <NUM> slidably mounted with respect to a brake carrier <NUM> by two guide assemblies 10a and 10b. The caliper <NUM> has a housing <NUM> typically formed from cast iron or steel. The carrier <NUM> is typically also formed from cast iron or steel.

The brake carrier <NUM> carries an inboard brake pad 50a and an outboard brake pad 50b. A rotor (not shown) is rotatable about an axis extending in the axial direction A, and is positioned between the brake pads 50a and 50b. An air actuator (not shown) is provided to move the inboard brake pad 50a into frictional contact with the rotor via a suitable actuation mechanism (not shown) housed within the caliper housing <NUM> and which acts on the inboard brake pad 50a. When the inboard brake pad 50a is pushed towards and contacts the rotor, the caliper <NUM> is then caused to slide inboard along first and second caliper guide assemblies 10a and 10b.

As the caliper <NUM> slides inboard it moves the outboard brake pad 50b towards the rotor. Hence, the rotor becomes clamped between the inboard and outboard brake pads and the rotation of the rotor is frictionally inhibited.

So as to minimise the potential for the sliding of the caliper <NUM> to be prevented or restricted due to jamming or binding of the guide assemblies caused by thermal expansion, deflection under load, wear or the like, the first guide assembly 10a has a void in the circumferential direction X to allow for free running of the guide assemblies 10a, 10b even if the guide assembly is not in its nominal position. This arrangement also allows the clamp force to be evenly applied to the brake pads during a braking operation so as to assist even wear thereof. The first guide assembly 10a is a guide assembly according to a first embodiment of the present teachings.

The second guide assembly 10b is longer than the first and comprises a circular guide bush (not shown) and a complementary circular guide sleeve (not shown) and may be conventional.

With reference to <FIG>, <FIG> and <FIG> the first guide assembly 10a, comprises a bore <NUM> extending along on axis B, parallel to axis A, through the housing <NUM>. The bore <NUM> has a generally circular cross-sectional profile to receive a guide pin 11a (see <FIG>) and at least one guide bush 13a with a largely circular outer profile and a non-circular, e.g., oval, inner profile to guide the guide pin 11a within the bore.

The guide pin 11a is cylindrical and comprises a fastener to secure the guide pin to the brake carrier <NUM> in a fixed position. In this first embodiment the fastener is a bolt 14a that affixes to the brake carrier <NUM> by screwing into a threaded bore in the brake carrier. A guide pin (not shown) of the second guide assembly 10b is similarly secured in a fixed position with respect to the carrier.

With particular reference to <FIG>, the guide pin 11a further comprises a guide sleeve 15a at least substantially surrounding the fastener and over which the caliper <NUM> slides. The guide sleeve 15a is a hollow tube with a substantially circular cross-sectional profile. The head of the central bore of the sleeve is stepped so that a head of the bolt 14a is able to hold the sleeve in place when tightened on to the carrier <NUM>.

A convoluted bellows type seal <NUM> (<FIG>) encircles the guide pin 11a and connects to the carrier <NUM> and caliper <NUM> to protect the guide assembly 10a from contamination by foreign matter.

The bore <NUM> of the guide assembly <NUM> is an elongate hole extending from a first side (inboard) <NUM> to the second side <NUM> (outboard) of the caliper housing <NUM>. In other words the bore <NUM> is a through bore. The caliper <NUM> is slidably mounted with respect to the brake carrier <NUM> by sliding the guide pin 11a through the bore <NUM>. Hence, when the disc brake is actuated, the caliper <NUM> is able to slide in the axial direction A along the guide pin 11a.

The guide bush 13a is configured to form a light interference fit with the bore <NUM> and acts as an inner liner in the bore. For example the nominal interference may be in the range of <NUM>% to <NUM>% of the minimum wall thickness of the guide bush, e.g. around <NUM>%. In embodiment the minimum wall thickness is approx. <NUM>, but may be between around <NUM> and <NUM> in other embodiments. For heavy vehicle applications the internal diameter of the guide bushes are typically in a range of <NUM>-<NUM>. As can be seen in <FIG>, the guide bush 13a does not extend the full depth of the bore <NUM>.

The guide bush 13a may be manufactured from steel, bronze, plastic, or a composite of any of these, and may include a low friction coating such as PTFE. The guide bush 13a may have a plain inner surface or a suitable pattern of depressions to assist in the sliding of the caliper and the retention of lubricants.

In this embodiment the guide bush 13a is manufactured from a proprietary polymeric material that comprises Nylon <NUM> (StanylRTM) and PTFE manufactured by Igus GmbH of Cologne, Germany. The guide bush may manufactured in a moulding or extrusion process, for example.

The diameter of the guide pin 11a is selected to correspond to the smallest diameter of the guide bush 13a. Accordingly, the clearance between the guide pin 11a and the guide bush 13a in a tangential direction Y is minimal and so vibration, noise, stress and excess wear are reduced. The largest diameter of the guide bush provides a greater clearance between the guide pin and the guide bush in the circumferential direction X to allow for a predetermined amount of play to accommodate manufacturing tolerances, heat expansion and brake torque induced deflection so as to allow the sliding of the caliper <NUM> without binding or jamming. With reference to <FIG>, <FIG> and <FIG> in particular, it can be seen that the bore <NUM> is not of a constant diameter, but instead has multiple diameters with steps therebetween.

In this embodiment, the smallest diameter receives the guide bush 13a, is referred to herein as a guide bush mounting portion 12a, and represents the greatest proportion of the overall length of the bore <NUM>.

However, with reference to <FIG>, it is apparent that this portion 12a is in fact non-circular, having a keyway <NUM> formed therein. In this embodiment the keyway <NUM> is rounded and may, for example, be formed by machining the bore <NUM> offset from its central axis B with a circular cutting tool. In <FIG>, it can however be seen that the keyway does not extend to the end of this portion 12a but rather terminates close to the inboard end to form a stop <NUM>. The remainder of the guide bush mounting portion 12a is however of constant diameter.

Outboard of the guide bush portion 12a is a seal mounting portion 12b that is able to receive the seal <NUM> as is visible in <FIG>.

Inboard of the guide bush mounting portion 12a is a further larger diameter portion arranged to mount the closure 60a and therefore is referred to as the closure mounting portion 12c. Further outboard of the closure mounting portion 12c is a still larger diameter portion that is referred to as the closure alignment portion 12d that initially is able to receive a closure 60a (discussed in more detail below). This then transitions into an annular ramp 12e to aid the interference fitting of the closure 60a on to the closure mounting portion 12c.

With reference in particular to <FIG> and <FIG> it can be seen that whilst generally cylindrical, the guide bush 13a has a rounded protrusion <NUM> that is of corresponding shape to the keyway <NUM> such that when mounted to the bore 12a it may be received in a single orientation and rotation thereof is prevented.

This ensures that the overall internal diameter of the guide bush 13a is always orientated so that the greatest internal diameter is aligned with the circumferential direction X and the smallest internal diameter is aligned with the tangential direction Y.

Although it may be omitted in certain embodiments, in this embodiment a semicircular depression <NUM> is provided on the internal face of the guide bush 13a in alignment with the protrusion <NUM> and is of constant diameter along the length of the guide bush. This allows for a more consistent wall thickness of the guide bush 13a which may be advantageous in terms of ensuring the dimensional stability thereof as the guide bush is moulded/extruded and subsequently cools and solidifies.

In this embodiment, the combination of the keyway <NUM>, stop <NUM> and protrusion <NUM> ensures that a rotation of the guide bush 13a and axial movement thereof in an outboard direction is prevented or inhibited.

In order to inhibit the contamination of the caliper guide assembly 10a with foreign matter, the cap or closure 60a closes the inboard end of the bore <NUM>. The closure 60a used for this purpose is formed from metal, e.g., stainless steel or corrosion resistant coated steel, and press fitted into the end of the bore 12a. In other embodiments it may be formed it may be formed of plastics material, or a composite of plastics with other materials.

The closure 60a comprises a disc-like cover portion <NUM> to act as a barrier to the ingress of foreign matter into the bore <NUM> and a bore engagement portion <NUM> that is tubular in shape and arranged, in this embodiment to be an interference fit with the closure mounting portion 12c of the bore <NUM>.

The cover portion <NUM> and bore engagement portion <NUM> are in this embodiment integrally formed from the same piece of material, namely sheet metal, (e.g., stainless or anti-corrosion treated steel) that has been shaped in a pressing operation.

In this embodiment, a stop <NUM> to retain the guide bush 13a is also integral with the remainder of the closure 60a.

Specifically, the stop <NUM> comprises a radially inwardly directed lip having a plurality of discrete segments that are radially inwardly directed from the bore engagement portion <NUM>. In this embodiment eight segments are shown, but any number from one upwards may be provided. The lip is dimensioned to terminate at essentially the same level as the internal face of the guide bush 13a where the wall is at its thinnest, or at least with a degree of overlap with the guide bush. This ensures that movement of the guide bush 13a outboard is essentially blocked by the stop <NUM>. The provision of the stop <NUM> in the form of a lip enables the closure to retain the guide bush 13a, but also for the keyway <NUM> to be machined from the inboard end and the guide bush to be fitted from this end.

In <FIG>, it can be seen that by spacing the stop <NUM> from the cover portion <NUM> of the closure 60a, the guide pin 11a is able to project beyond the inboard end of the guide bush 13a in an unworn brake pad condition as illustrated. As the outboard brake pad 50b wears, the caliper <NUM> moves inboard and this arrangement ensures that the guide pin 11a retains this overlap for the majority if not all of the range of movement of the caliper in an axial direction. In turn, this may minimise wear of the guide bush <NUM> due to there being no, or limited possibility, for the inboard free end of the guide pin to cause pitting of the guide bush 13a.

With reference in particular to <FIG>, it will be appreciated that assembly of the guide assembly 10a may be achieved relatively easily by orientating the guide bush 13a with the protrusion <NUM> in alignment with the keyway <NUM> and lightly pressing it at least partially into position. The closure 60a may then be seated in the seat alignment portion 12d of the bore before being pressed into an interference engagement with the closure mounting portion 12c. If the guide bush 13a remains proud of the step between portions 12a and 12c, the pressing operation of the closure 60a will nevertheless displace the guide bush 13a to result in alignment of all of the components and the axial and rotational restraint of the guide bush 13a.

With reference now to <FIG>, a further embodiment of the guide assembly 110a is illustrated. In this embodiment, only the closure differs from the first embodiment and therefore this has been labelled with equivalent numbers having the prefix "<NUM>" by comparison with the first embodiment but all other components of the guide assembly remain unchanged.

The closure 160a of this embodiment has a similar form of cover portion <NUM> and bore engagement portion <NUM> as the first embodiment. However, the stop <NUM> is formed by scallops or pips in the bore engagement portion <NUM> that extend radially inwardly and, as can be seen most clearly in <FIG>, these overlap the end face of the guide bush 13a to prevent movement outboard.

It will be appreciated that in this embodiment three such stops are shown that the number thereof be adjusted as required from one stop upwards. The closure of this embodiment may advantageously be simpler to manufacture than that of the first embodiment. Assembly of the guide assembly 110a of this embodiment is essentially the same as that of the first embodiment.

It will be appreciated that numerous changes may be made within the scope of the present teachings. For example, the outboard end of the guide bush may be provided with a radially outwardly extending flange to contact the step between the guide bush mounting portion 12a and closure mounting portion 12c to restrict outboard movement of the guide bush 13a. In this embodiment the closure may not require a stop of smaller internal diameter than the bore engagement portion and therefore the closure may simply comprise the cover portion and bore engagement portion, and the stop being formed by the inboard end face of the bore engagement portion.

In still further embodiments, the protrusion <NUM> of the guide bush may not extend along the full length thereof, and the corresponding keyway <NUM> may only extend a corresponding depth along the guide bush mounting portion 12a such that the protrusion and keyway act as both an anti-rotation and an inboard stop feature.

In other embodiments, a stop that is separate from the closure may be provided. For example, a suitably dimensioned washer may be interposed between the guide bush and the closure to act as the stop.

In other embodiments the guide bush may be assembled in an outboard to inboard direction, with a fixed stop being located inboard of the guide bush and the bellows seal acting as an outboard stop fitted after the guide bush is inserted to act as axial retention. As can be seen in <FIG> the bellows seal <NUM> is mounted to the housing via a rigid retainer 17a that is push fitted into the seal mounting portion 12b. The rigid retainer 17a is shaped to act as a stop in a similar way to the inboard closure, or can hold a separate component such as a washer in place.

The closure may be secured in position by a mechanism other than an interference fit. For example the closure may be screwed, glued or fused into position.

The embodiments of the guide assembly are suitable for use in any type of disc brake, including pneumatic, hydraulic, electrically and mechanically actuated disc brakes. However, the embodiments are believed to be particularly beneficial in air-actuated disc brakes for heavy commercial vehicles, where rotors typically have a diameter of between <NUM>-<NUM>, meaning that the torque and heat effects may be more significant than in hydraulic disc brakes for smaller, lighter vehicles.

Claim 1:
A disc brake caliper (<NUM>) comprising:
a guide assembly (10a) for permitting axial movement of the disc brake caliper (<NUM>) relative to a support, e.g., a disc brake carrier, the assembly comprising:
a through bore (<NUM>) of the caliper (<NUM>);
a guide bush (13a) to be mounted in the through bore (<NUM>) of the caliper (<NUM>) and having a non-circular outer surface;
and
a closure (60a) arranged to be seated at least partially within the through bore (<NUM>) and be a barrier to the ingress of foreign matter into the through bore;
characterised in that the assembly further comprises a stop (<NUM>) to be retained by the closure and dimensioned radially so as to restrict axial displacement of the guide bush in at least a first direction, in use.