GB2536207A

GB2536207A - A brake caliper seal and a method of manufacturing a brake caliper seal

Info

Publication number: GB2536207A
Application number: GB1503592.6A
Authority: GB
Inventors: James Wiseman Garry; John Smith Phillip
Original assignee: Alcon Components Ltd
Current assignee: Alcon Components Ltd
Priority date: 2015-03-03
Filing date: 2015-03-03
Publication date: 2016-09-14
Anticipated expiration: 2035-03-03
Also published as: GB2536207B; ITUB20161239A1; GB201503592D0

Abstract

A brake calliper seal 24 and a method of manufacturing a brake calliper seal are provided. The brake caliper seal 24 has an inner circumferential surface 24a and an outer circumferential surface 24c, with at least one of the inner and outer circumferential surfaces 24a, 24c having a laser engraved surface finish 28. The method of manufacturing the brake caliper seal 24 comprises the steps of: providing an unfinished circumferential brake caliper seal 24 having inner and outer circumferential surfaces 24a, 24c; and laser engraving/etching at least part of at least one of the circumferential surfaces 24a, 24c to provide a defined surface finish 28.

Description

A BRAKE CALIPER SEAL AND A METHOD OF

MANUFACTURING A BRAKE CALIPER SEAL

The invention relates to brake caliper seals and to a method of manufacturing brake caliper seals.

A brake caliper is a hydraulic clamp which typically comprises a body astride a brake disc. The body includes a hydraulic circuit which is fed from a brake master cylinder.

The body defines piston cavities which receive brake pistons. When the brake pedal is depressed, the master cylinder pressurises the hydraulic circuit, causing the pistons to he pushed against brake pads, which, in turn, push against the brake disc to slow the vehicle wheel. In the case of a floating type caliper, the piston(s) are arranged on one side of the brake disc and a fixed brake pad is arranged on the other side of the brake disc. In the case of a fixed type brake caliper, the pistons are arranged on both sides of the caliper body so as to act on pads on opposite sides of the brake disc. In both cases, the pistons are arranged slidably in piston cavities in the body and an elastomeric piston seal is arranged between the piston and the cavity. Typically, the piston seal is received within an annular channel formed in the inner circumferential surface of the cavity wall so as to act on the outer surface of the brake piston. Alternatively, the seal could be located in a groove on the piston so as to act on the inner surface of the bore. The piston seal has two functions. Firstly, it acts to seal against the wall of the piston so as to prevent egress of brake fluid from the caliper and to ensure that the hydraulic pressure applied is applied to the piston, pushing it against the pad. Secondly, the seal also acts as a spring a) to pull the piston away from the back of the brake pad when the braking pressure is removed and I)) return the piston to its original position if it becomes displaced into the cavity.

When the brake pedal is pressed, pressure builds up in the hydraulic circuit, tending to force the pistons out of the cavity. When the piston is spaced from the back of the pad, for example after a knock off event, the pressure must build to a threshold to overcome the frictional force between the piston and the seal to enable the piston to move past the seal and close the gap to the back of the pad. This is termed the frictional threshold. Under normal conditions, the piston is located very close to the pad so overcoming the frictional force is not required. Instead, the pressure must build to a level to overcome the resilient force of the seal, the resilient threshold. The movement of the piston out of the cavity tends to drag the seal out of a substantially square cross-section into a deformed shape conforming to the defined form of the seal groove. This dragging retains some spring energy in the seal. When the brake pressure is removed, the spring energy stored in the seal by virtue of it having been deformed causes the piston to be pulled back slightly into the cavity. Piston retraction is the measurement of how much the piston moves back away from the pad into the bore when the brake circuit pressure decays.

During driving, the pad can he knocked against the piston forcing it hack into the bore past the seal. The force required to push the piston back into the bore is a measure of the frictional grip between the piston and the seal and is known as the push back or displacement force. The amount that the displaced piston recovers to its original position by virtue of the resilience of the seal after the knockback event is called piston recovery.

European Patent Publication No.1533537 discloses a brake caliper seal formed with a series of C-shaped cross-section grooves in the inner circumferential surface thereof. The arrangement of the grooves and the dimension of the grooves relative to the lands between the grooves allow the performance of the seal regarding roll back and pull back to be adjusted.

Japanese Patent Publication No.JP200205315 discloses a brake caliper seal with a series of tiny blind bores arranged in the inner circumferential surface to retain grease.

It is an object of the present invention to provide an improved brake caliper seal.

According to a first aspect of the invention there is provided a brake caliper seal having an inner circumferential surface and an outer circumferential surface, at least part of at least one of the inner and outer circumferential surfaces having a laser engraved surface finish.

By using laser engraving, each individual seal can be provided with a customised surface finish to provide desired piston position control characteristics.

The laser engraved surface finish may be applied to the whole of the inner or outer circumferential surface or to part or the whole of both of the inner and outer circumferential surface. The surface finish may include a variety of patterns such as: IS (i) a cross hatch of varying coarseness; (ii) a spiral; (iii) parallel grooves which are arranged either circumferentially, axially or diagonally or linear wavy grooves. One pattern may be applied to one part of one of the surfaces and another pattern may he applied to another part of one of the surfaces according to the performance characteristics required. Instead of lines, an army of discrete forms may he laser engraved.

The surface finish engraved on the seal preferably has a depth in the range 10 to 100 microns, most preferably 10 to 25 microns. The laser engraving reduces the surface area of the seal in contact either with the piston or the wall of the piston bore.

Because laser engraving has such a high resolution, great variety of patterns, size and position of surface finish is available which in turn allows the user precise control over the performance characteristics of the seal.

We set out a variety of examples below in the specific description but any combination can be applied depending upon the performance that is desired.

According to a second aspect of the invention there is provided a method of making a brake caliper seal comprising the steps of providing an unfinished circumferential brake caliper scat having inner and outer circumferential surfaces and laser engraving at least part of one of the circumferential surfaces to provide a defined surface finish.

Preferably, the step of laser engraving at least part of one of the circumferential surfaces to provide a defined surface finish comprises laser engraving at least part of the inner circumferential surface of the brake caliper seal. The laser engraving of the inner circumferential surface may comprise laser engraving the whole of the inner circumferential surface.

The method may include laser engraving at least part of both of the inner and outer circumferential surfaces. Preferably, the defined surface finish applied by the method includes a pattern selected from the group of (i) a cross hatch of varying coarseness; (ii) a spiral; (iii) parallel grooves arranged either circumferentially, axially, diagonally or in a wave pattern; or (iv) an array of discrete shapes.

According to a third aspect of the invention, there is provided a brake caliper seal having an inner circumferential surface and an outer circumferential surface, at least one of the inner and outer circumferential surfaces having a surface finish pattern in the form of a cross-hatch.

According to a fourth aspect of the invention, there is provided a tube of elastomcric material having a defined surface finish applied to at least part of at least one of its inner or outer circumferential surfaces and configured to be cut so as to form a brake caliper seal according to the first or third aspects of the invention.

According to a fifth aspect of the invention, there is provided a method of making a tube according to the fourth aspect of the invention, in which the defined surface finish is applied by laser engraving/etching the tube surface.

According to a sixth aspect of the invention, there is provided a method of making a tube according to the fourth aspect of the invention, in which the defined surface finish is formed by etching or engraving a mandrel with a cross-hatch pattern, moulding a tube onto the mandrel so that the tube surface is formed with a cross-hatch pattern.

An example of a brake caliper seal and method in accordance with the present invention will now be described in detail with reference to the following drawings. in which:-FIG.1 is a schematic cross-section, with a broken out enlarged portion, of part of a brake caliper showing the piston bore and brake caliper piston along with a piston seal, FIG.2 is a perspective view of the brake caliper seal, FIG.3 is a perspective view of the brake caliper seal of FIG.2 with a laser engraved pattern applied to the inner circumferential surface, FIG.4 is a perspective view similar to FIG.3 but with the pattern applied to part of the inner circumferential surface of the seal.

FIGS is a perspective view of the brake caliper seal of FIG.2 with a laser engraved finish applied to the outer circumferential surface; FIG.6 shows a variety of different possible surface finishes which may he applied either in whole or in part to the inner or outer circumferential surfaces of the brake caliper seal; and FIG.7 is an enlarged schematic cross-section of part of the brake caliper, similar to the enlarged portion of FIG.1, but to a larger scale and showing the seal dragged out of square by the movement of the piston, and FIG.8 shows a series of graphs illustrating the results of comparative performance tests based on seals with different patterns applied.

In FIG.1, pail of a conventional brake caliper body 10 is shown. The part shown comprises part of a limb 10 of a brake caliper which defines a piston cylinder 12. The piston cylinder 12 has a blind bore. A piston 14 is received slidably within the blind bore in the cylinder 12. The piston 14 in the present embodiment is shown as a cup-like member, but any appropriate brake piston form could be used.

Between the base of the blind bore of the piston cylinder and the base of the piston, a volume 16 is filled with hydraulic fluid. The volume is connected typically by a fluid line 18 to a hydraulic reservoir 20 (master cylinder).

At the end of the cylinder 12 remote from the base, an annular recess 22 is formed in the inner wall of the cylinder. A circumferential seal 24 is seated in the recess 22 and seals against the outer peripheral wall of the piston 14.

When viewed in cross-section, the recess 22 is shallower at its edge closer to the cylinder base end than it is at its edge closer to the cylinder mouth end so that the base of the recess tapers inwardly. Alternatively, instead of a taper, the recess may have a curved or radiused base.

The seal 24 has a rectangular cross-section but when inserted in the recess it conforms to the shape of the recess to adopt an irregular quadrilateral cross-section with its inner face 24a being at right angles to its upper and lower edges 24b, 24c while the outer face 24d is angled to follow the taper of the recess 22. The taper shown in Figure 1 is exaggerated, the actual taper being of the order of 5 to 7 degrees away from a line parallel with the inner circumferential surface of the cylinder. The upper edge of the recess, against which seal face 24b is in contact, may also be arranged at a non-right angle relative to the cylinder wall to facilitate greater piston retraction.

In operation, when the brake pedal is pressed, the brake fluid in the master cylinder is pressurised, forcing it via line 18 into the volume 16. That increases the pressure of the fluid in the volume 16 which forces the piston 14 out of the cylinder 12 towards a brake pad 26 (shown in part) to effect braking in conventional fashion. The seal 24 prevents brake fluid from passing out of the cylinder 12 by sealing on its inner circumferential surface 24a against the piston 14 and on its outer circumferential surface 24d and upper face 24b against the tapered outer face and the upper face of the annular recess 22 respectively.

In order to seal effectively against the piston 14, the seal 24 must maintain a tight fit with the piston 14. This means that in order to slide past the seal 24 under braking, the piston 14 must be forced out of the cylinder past the frictional force of the seal on the piston. This is the frictional threshold.

Before the pressure in the volume 16 builds to overcome the frictional threshold, the piston 14 can begin to move as the seal 24 is resilient. The piston 14 initially drags the inner face 24a of the seal 24 with it as it moves out of the cylinder 12 once the fluid pressure in the volume 16 exceeds the resilient threshold. This dragging effect deforms the seal out of its square cross-section into a deformed shape as shown in Figure 7. Further build-up of pressure forces the piston past the seal once the frictional threshold is exceeded.

Once the brake pedal is released, the pressure in the volume 16 decays and fluid begins to return to the master cylinder 20.

As the fluid pressure in the volume falls, the hydraulic force pushing the piston 14 against the pad 26 is reduced. The deformation of the seal 24 caused by the aforementioned dragging effect stores spring energy in the seal tending to pull the piston back into the cylinder 12. Once the hydraulic force has reduced below the stored energy spring force, the seal resiles back into a substantially square cross-section, pulling the piston 14 back into the cylinder 12 away from the back of the pad 26. The distance that the piston is pulled back is called piston retraction.

On the initial use of the brakes, say after a set of pads have been fitted, the outer end of the piston 14 may he spaced up to 2mm away from the hack of the pad 26 so the first use of the brakes would cause the seal 24 to be dragged out of square then the piston 14 to slide past the seal to take up the gap behind the pad 26. After braking, the piston 14 recovers under the resilient action of the deformed seal 24 to pull the piston 14 away from the pad 26 by a smaller distance, typically 0.05 to 0.1mm.

In certain circumstances, for example when the wheel hits a kerb, the brake pad 26 can be knocked against the piston 14 pushing it back into the cylinder 12. The friction between the seal 24 and the piston 14 resists this knockback.

As with braking, on knockback, the seal 24 is dragged out of square before the knockback force on the piston 14 overcomes the frictional force between seal 24 and piston 14, forcing the piston 14 to slide back into the cylinder 12. Once the knockback force has stopped, the seal 24 resiles back to a square cross-section, pulling the piston 14 back out slightly from the cylinder 12. After a knockback event, the piston 14 has further to travel again before it contacts the pad. The net knockback distance is the difference between the distance that the piston is forced back into the cylinder 12 less the distance that the seal 24 causes the piston 14 to travel hack out of the cylinder 12 under resilient return of the seal 12.

It is desirable to minimise the net knockback distance without compromising the performance of the brake.

In Figures 2 to 5, the seal 24 of Figure 1 is shown in perspective. In Figure 2, the seal 24 is a conventional annular piston seal.

In Figures 3 to 5, various surfaces of the seal 24 have been treated with a laser engraving or laser etching apparatus.

In one method, the seal 24 is formed as part of an elongate tube of seal material and one of the outer or inner surfaces of the tube is engraved or etched with a laser applying a predetermined surface finish pattern 28. The tube is then cut into individual seals.

Alternatively, individual seals are made and then a laser engraving or etching apparatus applies a surface finish pattern 28 to at least a part of the inner and/or outer surfaces 24a. 24d of the seal 24.

In one method, individual seals are turned inside-out and arranged on a mandrel. The outside surface is then laser engraved with the pre-determined surface finish pattern and then removed from the mandrel before being everted so that the laser engraved surface which was the outside surface presents as the inner circumferential surface of the finished seal.

In Figure 3, the laser engraved surface finish pattern 28 is applied to the whole inner circumferential surface 24a of the seal 24.

In Figure 4, the laser engraved surface finish pattern 28 is applied just to the upper half of the inner circumferential surface 24a of the seal 24.

In Figure 5, the laser engraved surface finish pattern 28 is applied to the whole of the outer circumferential surface 24d of the seal 24.

The laser engraved surface finish pattern 28 may be applied in patches so that parts of the circumference do not have the pattern applied. The laser engraved surface finish pattern 28 may be applied to both inside and outside circumferential surfaces.

Figure 6 illustrates some of the laser engraved surface finish patterns 28 that can be applied to the seal 24. The laser engraver typically cuts the seal 24 to a depth of approximately 10 to 50 pm. This means that any channels formed by the engraving are too small to allow passage of the brake fluid.

Alternatively, or in addition, the laser engraved surface finish pattern 28 may include a wall to stop flow of brake fluid past the seal.

For example, a cross-hatch (1) fully across the face of the seal 24 or partially across (2) the face may be applied.

A series of parallel, annular grooves (3) may be formed. The lands of material between the grooves form a series of seal lips pushed against the piston 14.

The parallel grooves (4) may run at an angle to the axis of the seal 24 of 15 to degrees. Again, end walls may be provided to prevent egress of brake fluid.

A square hatched pattern (5) may be applied.

Alternatively, wavy, parallel annular grooves (6) may be applied.

Different surface finish patterns perform differently. In particular, a surface finish pattern may have a different effect on piston retraction than on piston recovery so that the piston may be pulled back from the pad on retraction less than the piston resiles back out of the cylinder after knockback.

A laser engraving apparatus such as an HKR5 laser engraving machine by HK Laser Engraving (http:\\ www.hklaserservices.co.uk) is used to apply the surface finish pattern 28.

Figure 8 shows three bar charts comprising different performance characteristics in hot and cold conditions for, respectively, a standard seal, a seal with a coarse laser engraved cross-hatch and a seal with a fine laser engraved cross-hatch.

The characteristics compared were (i) displacement force in Newtons, namely the force required to displace the piston past the frictional threshold on knockback; (ii) piston recovery in millimetres; and (iii) threshold pressure in bar, namely the pressure required in the brake hydraulic available to overcome the friction between seal and piston on braking.

In respect of the standard (baseline) seal, displacement force, recovery and threshold pressure are all higher than the etched equivalents. Also, the difference in performance between hot and cold states is considerably more marked in the baseline seal than the etched seals.

Etching of the seals has reduced the performance differential between hot and cold states of operation. resulting in more consistent braking performance. By applying a cross-hatch pattern, the seal is arranged to perform differently on recovery than on retraction. In this way, the piston can he arranged to he retracted only a relatively short distance on removal of brake pressure, say 0.05mm, but to recover a relatively larger distance after a knockback event, say lmm.

Where the applied surface finish pattern is a cross-hatch, the seal may he made as described below without the need for laser engraving / etching the seal.

A mandrel or other die form is etched or engraved with a cross-hatch pattern.

Then a tube of clastomeric material is formed on the mandrel, the tube having an inner radius approximately equal to the outer radius of the brake piston and an outer radius approximately equal to the base of the seal recess in the brake cylinder.

The tube is arranged on the mandrel or die form and so that the inner surface of the tube is formed with the cross-hatch patter.

The tube is then removed from the mandrel, for example by blowing air between the outer surface of the mandrel and the inner surface of the tube. The tube is then cut to form a seal(s) with a cross-hatched surface finish applied to the inner surface thereof.

Claims

Claims 1. A brake caliper seal having an inner circumferential surface and an outer circumferential surface, at least one of the inner and outer circumferential surfaces having a laser engraved surface finish.
A brake caliper seal according to claim 1, in which the laser engraved surface finish is applied to the whole of the inner or outer circumferential surface.
3. A brake caliper seal according to claim 1, in which the laser engraved surface finish is applied to part or the whole of both of the inner and outer circumferential surfaces.
4. A brake caliper seal according to any preceding claim, in which the surface finish includes a pattern selected from the group (i) a cross hatch of varying coarseness; (ii) a spiral; (iii) parallel grooves which are arranged either circumferential, axially or diagonally or linear wavy grooves.
A brake caliper seal according to claim 4, in which one pattern is applied to one part of one of the surfaces and another pattern is applied to another part of one of the surfaces.
6. A brake caliper seal according to any preceding claim, in which the surface finish engraved on the seal has a depth in the range 10 to 100 microns, preferably 10 to 25 microns.
7. A method of making a brake caliper seal comprising the steps of providing an unfinished circumferential brake caliper seal having inner and outer circumferential surfaces and laser engraving/etching at least part of at least one of the circumferential surfaces to provide a defined surface finish. 10. 11. 12. 13. 14. 15.
8. A method of making a brake caliper seal according to claim 7, in which the step of laser engraving at least part one of the circumferential surfaces to provide a defined surface finish comprises laser engraving at least part of the inner circumferential surface of the brake caliper seal.A method of making a brake caliper seal according to claim 7, in which the laser engraving of the inner circumferential surface comprises laser engraving the whole of the inner circumferential surface.A method of making a brake caliper seal according to claim 7, in which the method includes engraving at least part of both the inner and outer circumferential surfaces.A method of making a brake caliper seal according to claim 7, the defined surface or finish applied by the method includes a pattern selected from the group of (i) a cross hatch of varying coarseness; (ii) a spiral; (iii) parallel grooves arranged at the circumferential, axially, diagonally or in a wave pattern.A brake caliper seal having an inner circumferential surface and an outer circumferential surface, at least one of the inner and outer circumferential surfaces having a surface finish pattern in the form of a cross-hatch.A tube of clastotneric material having a defined surface finish applied to at least part of at least one of its inner or outer circumferential surfaces and configured to be cut so as to form a brake caliper seal according to any of claims 1 to 6 or claim 12.A method of making a tube according to claim 13 in which the defined surface finish is applied by laser engraving/etching the tube surface.A method of making a tube according to claim 13, in which the defined surface finish is formed by etching or engraving a mandrel part of a moulding tool die with a defined pattern and moulding the tube so that the surface is formed with a defined pattern.