GB2638389A

GB2638389A - Decoupled dynamic piston control

Info

Publication number: GB2638389A
Application number: GB2401350.0A
Authority: GB
Inventors: Charles Clegg David
Original assignee: Alcon Components Ltd
Current assignee: Alcon Components Ltd
Priority date: 2024-02-01
Filing date: 2024-02-01
Publication date: 2025-08-27
Also published as: GB202401350D0

Abstract

A piston 20 for a brake caliper, and a brake caliper and vehicle including the piston. The piston includes a pad end face 24 at a pad end 23, a caliper end face 22 at an opposing caliper end 21 and a cylindrical body formed between the pad end and the caliper end and defining an outer wall 25. A circumferential deformable ring retention groove 27 is located proximate the caliper end, e.g. for locating deformable ring 30; and at least one fluid passageway 28 is included to fluidly connect the outer wall 25 to the caliper end face 22, e.g. via a cylindrical recess 26 located in the end face 22. There may be multiple fluid passageways 28, e.g. each located with its axis at a first angle relative to a tangent of the cylindrical body (see figures 27-28). The ring 30 may have a rectangular cross-section with the groove 27 having a non-rectangular shape – e.g. recess side walls 27c (also 27a figs.5-6,8-9,16,26; 127a, 127c, figs. 18-21; 227a, 227c, figs. 22-25) non-parallel to caliper end face 22 and at different angles to base (27b, figs. 5-6, 8-9, 16, 26; 127b figs.18-21; 227b, figs 22).

Description

DECOUPLED DYNAMIC PISTON CONTROL

Field

The present invention relates to a piston for a fluid brake system. It also relates to a fluid brake system having such a device.

Background

Vehicles with fluid brake systems can experience an effect known as "piston fallback". Such a fluid brake system comprises a brake caliper assembly 10, as shown in Figures 1 to 3e. A brake caliper body 12 houses pistons 14 within piston cylinders 15. These pistons 14 provide braking force by actuating brake pads 18 to contact a brake disc 19. A reservoir (not shown) provides a source of fluid for said actuation and a master cylinder (also not shown provides said to fluid to each piston cylinder 15.

As can be seen in Figures 3a to 3e, which are diagrammatic representations of a single piston assembly within the brake caliper assembly 10, the fluid is provided in a chamber 16 formed by the piston cylinder 15 and ring seal 17. Figure 3a shows the piston assembly in a neutral or passive state before any initial braking force is applied. When braking force is requested by the user, more fluid is pumped into the chamber 16, exerting force upon the piston 14 and pushing said piston 14 out of the piston cylinder 15. The ring seal 17 grips the piston 14 as it advances, contacting the brake pads 18 with the brake disc 19 to provide the braking force, said braking force also causing some deflection in the caliper body 12 (which in turn causes deflection of the brake pads 18). This is shown in Figure 3b.

As the braking force request ends, the deformation of the ring seal 17 causes the retraction of the piston 14 back into the piston cylinder 15, as seen in Figure 3c. When the piston retraction is greater than the deflection of the caliper body 12, a clearance can be achieved between the brake pads 18 and the brake disc 19, hence there is no brake drag between the brake pads 18 and the brake disc 19. It also, as seen in Figure 3d, eventually leads to excessive deflection of the caliper body 12 and brake pads 18, as well as the piston 14 needing to slide through the ring seal 17 to apply a braking force.

Finally, when this braking force is released, the piston 14 having slid through the ring seal 17 means that it cannot retract as far as the deflection of the caliper body 12 and brake pads 18. Thus, as can be seen in Figure 3e, the piston 14 causes continual brake force even when not requested, causing the brakes to drag, overheat, wear, and likely fail. This is known as having a lack of running clearance (i.e., clearance between the brake pads 18 and the brake disc 19 whilst not braking force is requested).

The piston fallback effect is affected by the temperature of the fluid brake system, whilst the running clearance issue is influenced by both temperature and pressure. The temperature affects the elasticity of the polymer material of ring seal 17, and therefore higher temperatures will reduce the fallback piston travel. A higher hydraulic pressure will increase the deflection of the caliper body 12. As the running clearance of the brake disc 19 is the piston fallback minus the caliper deflection, if the caliper deflection is greater than the fallback, then there is no running clearance, which leads to drag.

The present invention seeks to overcome or at least mitigate these problems by providing a device in which piston fallback is prevented. The present invention also seeks to provide such a device that is more efficient and that is reliable, easy to manufacture and cost effective.

Summary

A first aspect of the invention provides a piston for a brake caliper, the piston comprising a pad end face at a pad end; a caliper end face at an opposing caliper end; a cylindrical body formed between the pad end and the caliper end and defining an outer wall; a circumferential deformable ring retention groove proximate the caliper end; and at least one fluid passageway arranged to fluidly connect the outer wall and the caliper end face.

In this way, brake fluid can be situated both sides of the deformable ring retention groove (and a deformable, or friction, ring that would be located there). This allows the pressure of the brake fluid to exert a force on both sides of the deformable ring, the compression of which promoting grip between the deformable ring and the piston bore (in which the piston is actuated). Having both sides of the deformable ring be "wet" also reduces the plastic deformation of the deformable ring over time, increasing the lifespan of the brake system of which the piston is a part.

The caliper end face may comprise a recess. At least one of the fluid passageways may be arranged to fluidly connect the outer wall and an inner wall of the recess. The recess may be cylindrical. The body of the piston may be formed around a central longitudinal body axis and the recess may be formed around a central longitudinal recess axis, and the body axis and recess axis may be coincident. The radius of the body may be in the range of 5mm to 40mm, preferably 19.05mm, and the radius of the recess may be in the range of 3mm to 39mm, preferably 16.33mm. The length of the body may be in the range of 10mm to 60mm, preferably 32mm, and the length of the recess may be in the range of 1mm to 10mm, preferably 3mm.

The recess provides a chamber from which fluid can gather to pass through the fluid passageways to apply pressure to the pad end side of the deformable ring. The recess also provides a sufficient area for the fluid to exert pressure at the caliper end to actuate the piston.

The piston may further comprise a plurality of fluid passageways. The piston may further comprise a number of fluid passageways in the range of 1 to 50, preferably 16. The recesses may be arranged such that they are spaced apart evenly around the circumference of the outer wall.

By having a large number of fluid passageways spread evenly around the circumference of the piston, an even distribution of brake fluid can be provided around the deformable ring.

At least one of the fluid passageways may be located between the deformable ring retention groove and the pad end. At least one of the fluid passageways may be located at a base of the seal retention groove. The body of the piston may be formed around a central longitudinal body axis and each fluid passageway may be arranged along a fluid passageway axis, each fluid passageway axis being perpendicular to the body axis. The body of the piston may be formed around a central longitudinal body axis and each fluid passageway may be arranged along a fluid passageway axis, each fluid passageway axis intersecting the body axis.

Having fluid passageways arranged in this manner makes manufacturing the piston easier.

Each fluid passageway may be arranged along a fluid passageway axis, said axis arranged at a first angle relative to a tangent of the body, the first angle being in the range of 0° to 25°, preferably 5°. Each fluid passageway may be arranged along a fluid passageway axis, said axis arranged at a second angle relative to the outer wall of the body, the second angle being in the range of 55° to 90°, preferably 75°.

Having fluid passageways arranged in this manner decreases the depth necessary of the deformable ring retention groove, thus increasing compliance of the system by reducing the volume of brake fluid required.

The deformable ring retention groove may be formed of a base between opposing first and second walls. At least one of the first and second walls may be non-parallel to the caliper end face. The first face may be at an angle relative to the caliper end face in the range of 0° to 25°, preferably 10°. The second face may be at an angle relative to the caliper end face in the range of 0° to 25°, preferably 15°. The deformable ring retention groove may be symmetrical about a plane parallel to the caliper end face. At least one of the first and second walls may have a continuously curved shape. At least one of the first and second walls may be formed of a plurality of straight surfaces. The base may be convex. Alternatively, the base may be concave.

Variations in the groove base geometry when installed with a rectangular cross-section deformable ring will result in an axial increase in ring section compression. This affects the deformable ring slip distance or force threshold in the piston bore, therefore fine tuning the piston response. Furthermore, there are manufacturing assembly benefits as these geometries aid the piston and deformable ring past the groove present in the piston bore. Finally, having the first and second faces of the deformable ring retention groove be at an angle allows for the finetuning of the fallback and knockback properties of the piston actuation action.

A deformable ring may be located within the deformable ring retention groove. The deformable ring may have a substantially rectangular cross-section. Alternatively, the deformable ring may have an inner face, and the deformable ring retention groove may be shaped to correspond to the shape of the inner face of the deformable ring. The inner face of the deformable ring may have curved edges and the deformable ring retention groove may have curved edges of an equal radius. The curved edges of the deformable ring retention groove may be arranged between the base and the respective first and second walls.

The corresponding and curved edges of the inner face of the deformable ring and the deformable ring retention groove ensure that the deformable ring is secured against movement along the longitudinal axis of the piston and can only be compressed to take a parallelogram-like shape within the deformable ring retention groove. This ensures that the deformable ring provides sufficient actuation action upon the piston and the piston bore, whilst increasing the lifespan of the deformable ring by reducing frictional forces between it and the deformable ring retention groove.

A second aspect of the invention provides a brake caliper assembly comprising a brake caliper body defining at least one piston cylinder, each piston cylinder having an open end, a closed end, and a seal retention groove proximate to the open end; the above-described piston arranged in each of the piston cylinders; a deformable ring located within the deformable ring retention groove and arranged to be in slidable contact with the piston cylinder; and a seal located within the seal retention groove and arranged to be in slidably sealing contact with the piston outer wall.

In this way, the brake fluid is around the outer wall of the piston is contained between the seal and the deformable ring, with the fluid passageways acting as inlets and outlets. As such, both sides of the first deformable ring are wet, but no brake fluid can leak out of the caliper assembly via the piston cylinder(s).

The brake caliper assembly may further comprise at least one bleed valve fluidly connected to each piston cylinder, and the deformable ring retention groove and fluid passageways may be arranged such that, when the piston is in a fully recessed position where the caliper end face of the piston is proximate the closed end of the cylinder, the outer wall of the piston, the caliper end face and each bleed valve are fluidly connected.

This fluid connection allows an initial bleed of the brake system which then does not need be repeated until the caliper assembly is disassembled.

The deformable ring may be formed of any of Nitrile, Fluoroelastomer or Natural Rubber, preferably ethylene propylene diene monomer rubber. The seal may be formed of any of Nitrile, Fluoroelastomer or Natural Rubber, preferably ethylene propylene diene monomer rubber.

In this way, the seal provides dynamic piston function as well as the fluid sealing function, whilst the deformable ring only provides dynamic piston function.

A third aspect of the invention provides a vehicle comprising the above-described piston or the above-described brake caliper assembly.

Brief Description of the Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying figures in which: FIGURE 1 is a top perspective view of a brake caliper assembly according to the prior art; FIGURE 2 is a bottom perspective view of the brake caliper assembly of Figure 1; FIGURES 3a to 3e are diagrammatic representations of a section of the brake caliper assembly of Figure 1; FIGURE 4 is a perspective view of a piston according to a first embodiment of the present invention; FIGURE 5 is a side view of the piston of Figure 4; FIGURE 6 is an axial section view of the piston of Figure 4; FIGURE 7 is a perspective view of the piston of Figure 4 with a deformable ring; FIGURE 8 is a side axial section view of the assembly of Figure 7; FIGURE 9 is partial side axial section view the assembly of Figure 7; FIGURE 10 is an exploded perspective view of a piston assembly of the piston of Figure 4; FIGURE 11 is a top section view of a brake caliper assembly of the piston of Figure 4; FIGURE 12 is a partial view of the brake caliper assembly of Figure 11; FIGURE 13 is a side section view of the brake caliper assembly of Figure 11 in a passive state; FIGURE 14 is a side section view of the brake caliper assembly of Figure 11 in an actuated state; FIGURE 15 is a side section view of the brake caliper assembly of Figure 11 in a bleeding state; FIGURE 16 is a partial side section view of the brake caliper assembly of Figure 11 in an actuated state; FIGURE 17 is a partial side section view of the brake caliper assembly of Figure 11 in a bleeding state; FIGURE 18 is a side view of a piston according to a second embodiment of the present invention; FIGURE 19 is a side view of the piston of Figure 18 with a deformable ring; FIGURE 20 is a side section view of the piston of Figure 18; FIGURE 21 is a side section view of the assembly of Figure 19; FIGURE 22 is a side view of a piston according to a third embodiment of the present invention; FIGURE 23 is a side view of the piston of Figure 22 with a deformable ring; FIGURE 24 is a side section view of the piston of Figure 22; FIGURE 25 is a side section view of the assembly of Figure 23; FIGURE 26 is a side section view of a piston according to a fourth embodiment of the present invention; FIGURE 27 is a perspective view of the piston of Figure 26; and FIGURE 28 is an end section view of the piston of Figure 26.

Detailed Description of Embodiments

With reference to Figures 4 to 17, below is described a piston 20 according to a first embodiment of the present invention. The piston 20 comprises a body formed between a first body end 21 and a second pad end 23, as can be seen in Figures 4 to 6. The piston body is cylindrical, with a first body end face 22 at the body end 21 and a second pad end face 24 at the pad end 23, with a side wall 25 formed therebetween. The piston 20 is formed around a longitudinal axis X-X, and it is through this axis that the section view of Figure 6 is taken.

At the body end 21 there is formed a recess 26 into the body end face 22. The recess 26 is also cylindrical, and is formed around axis X-X. The recess 26 has a base 26a and side wall 26b, the base 26a being parallel to the body and pad end faces 22, 24 and the side wall 26b being parallel to the side wall 25 of the piston body. The edges between the base 26a and side wall 26b, and between the side wall 26b and the body end face 22 are chamfered to aid in the manufacturing process.

At the body end 21 there is also formed a groove 27 in the side wall 25 of the piston body. The groove 27 runs circumferentially around the side wall 25, parallel to the body end face 24. The recess 26 is formed of a body end wall 27a (on the body end 21 side of the recess 26) and a pad end wall 27c (on the pad end 23 side of the recess 26) connected by a base 27b. Body end wall 27a is at an angle a relative to the body end face 22 of 15°, whilst pad end wall 27c is at an angle p relative to the pad end face 24 of 10°. However, angles in the range of 0° and 25° respectively are also envisaged.

Finally, formed between the side wall 25 of the piston body and side wall 26b of the recess 26b are 16 fluid passageways 28. Numbers of fluid passageways in the range of 1 to 50 are also envisaged. Each fluid passageway 28 is a cylindrical bore fluidly connecting the side wall 25 of the piston body and side wall 26b of the recess 26b, as will be further discussed below. The groove 27 is located between the fluid passageways 28 and body end face 22. As such, the recess 26 is sufficiently deep enough to allow room for the fluid passageways 28. The fluid passageways 28 are arranged on a plane parallel to the body end face 22 and are arranged equidistantly around said plane. Each fluid passageway 28 is formed on an axis coincident with the axis X-X. However, as discussed below, other fluid passageway arrangements are also envisaged.

As can be seen in Figures 7 to 9, a deformable ring 30 is located within the groove 27. The deformable ring 30 is substantially rectangular in cross-section, with a first body end surface 32 and a second pad end surface 34, which are proximate to the body end wall 27a and pad end wall 27b of the groove 27 respectively. The ring 30 is sized such that an inner surface 36 fits securely on base 27b. The width of base 27b is approximately equal to that of the inner surface 36, such that the inner surface 36 does not move relative to the piston 20, as will be discussed in greater detail below. The edges between the inner surfaces 36 and body end and pad end surfaces 32, 34 are filleted to help prevent wear of ring 30, with the edges between the base 27b and the body and pad end walls 27a, 27c of the recess 27 having corresponding filleting. The body and end wall angles a, p result in there being a gap 39 between an outer surface 38 and the end walls 27a, 27c of the groove 27. The ring 30 is sized such that the outer surface 38 extends away from the side wall 25 of the piston 20. Other cross-sectional geometries are also envisaged. The ring 30 is made of an EPDM polymer (ethylene propylene diene monomer rubber), however other suitable materials such as Fluoroelastomers and nitriles are also envisaged.

Figures 10 to 17 show the brake caliper assembly 10 of the prior art, but with the pistons 20 as described above according to the first embodiment of the invention. As in the prior art, each piston 20 is located within a piston cylinder 15, with a ring seal 17 in contact with the respective side wall 25. The outer surface 38 of each ring 30 contacts the wall of the respective piston cylinder 15.

As can be seen in Figures 13 to 15 and 17, the chamber 16 is fluidly connected to fluid inlet 16a and fluid outlet 16b, as well as the recess 26 of the piston 20. Meanwhile, the fluid passageways 28 fluidly connect the recess 26 to a space 42 between the ring seal 17, the wall of the piston cylinder 15, the ring 30 and the side wall 25 of the piston 20. This space 42 is maintained due to the resistive force of the ring 30 and ring seal 17 extending beyond the surfaces of the piston cylinder 15 and the side wall 25.

The functioning of the brake caliper assembly 10 including the piston 20 will now be described in relation to Figures 13 to 17.

Figure 13 shows the piston 20 in a passive position -one in which no braking force has been requested. As can be more clearly seen in Figure 16, the fluid passageways 28 allow brake fluid to travel between the chamber 16 and space 42 via the recess 26. As such, both sides of the ring 30 are "wet", which reduces progressive plastic deformation of ring 30, increasing the lifespan and reliability of the brake caliper assembly 10.

As braking force is requested, brake fluid is pumped into chamber 16, increasing the pressure therein and causing the piston 20 to move to the actuated position shown in Figure 14. The increase is in pressure is exerted on both body and pad end surfaces 32, 34 of the ring 30, as brake fluid fills gaps 39. This compresses and distorts ring 30, such that it exerts more force on both the base 27b of the groove 27 and the piston cylinder 15. This promotes grip with the piston cylinder 15.

When the braking force request is released, the brake fluid is let out of chamber 16, and the reduction in pressure causes the piston 20 to return to the passive position shown in Figure 13. During this process, piston ring 17 offer little to no dynamic function, merely acting as a seal to keep the brake fluid inside space 42. Having the dynamic seal (ring 30) at the other end of the piston 20 keeps it away from the heat generated by the contact between the brake pads 18 and the brake disc 19. This further increases the lifespan and reliability of the system by avoiding harsh conditions that might increase wear of the ring 30.

Figures 15 and 17 show the piston 20 in a bleed position, with the piston fully retracted into piston cylinder 15. The initial bleed of the system is done in this position to ensure that any air caught in space 42 can move over the ring 30 and out of the system. Without the implementation of this bleeding position, the ring 30 would make bleeding the system near impossible (due to it trapping air in space 42). However, using this position, such a bleed can be done once on assembly, and then does not need to be repeated until after disassembly.

As mentioned above, alternative geometries and arrangements of features of the piston 20 such as the groove 27 and the fluid passageways 28 are envisaged. A few examples of this are described below. When describing the embodiments below, any components consistent with the first embodiment described above have been assigned the same reference numerals. Similar components are assigned reference numerals of +100, +200 or +300 compared to said similar components on the above described first embodiment.

With reference to Figures 18 to 21, below is described a piston 120 according to a second embodiment of the present invention. The groove 127 has a base 127b that is non-parallel with the side wall 25 of the piston 120. The base 127b has an angle y of 4°, however angles in the range of 0° to 10° are also envisaged. In this way, first body end wall 127a is longer than second pad end wall 127c of the groove 127.

By installing the rectangular cross-sectioned deformable ring 30 in the angled groove base 127b, there is generated an increase in compression of the cross-section of the ring 30 in the direction of axis X-X. A force acting upon pad end face 24 required on the piston 120 before the deformable ring 30 slips on the bore of the piston cylinder 15 will be higher than the force required when acting upon body end face 22. This is due to the extra force required to push the ring 30 up the angled groove base 127b, rather than pushing the ring down angled groove base 127b. As soon as the deformable ring 30 slips on the bore, the ring 30 returns to its resting state and the knockback function is lost.

With reference to Figures 22 to 25, below is described a piston 220 according to a third embodiment of the present invention. In an opposite manner to the second embodiment described above, the base 227b of groove 227 has an angle 6 of 4°, however angles in the range of 0° to 10° are also envisaged. In this way, first body end wall 227a is shorter than second pad end wall 227c of the groove 227.

As in the second embodiment, the angled groove base 227c causes an increase in compression of the cross-section of the ring 30 in the direction of axis X-X. However, contrary to the second embodiment, a force acting upon body end face 22 required on the piston 220 before the deformable ring 30 slips on the bore of the piston cylinder 15 will be higher than the force required when acting upon pad end face 24, due to the extra force required to push the ring 30 up the angled groove base 227b. As soon as the deformable ring 30 slips on the bore, the ring 30 returns to it resting state and the fallback function is lost.

There is also envisaged versions of the second and third embodiments wherein the deformable ring does not have a substantially rectangular cross-section and instead has an angled inner surface to match the angle of the base of the groove. This is whilst the outer surface remains parallel to the side wall of the piston body. As such, the first body end surface of this deformable ring is longer or shorter than second pad end surface (in the second and third embodiments respectively).

With reference to Figures 26 to 28, below is described a piston 320 according to a fourth embodiment of the present invention. As can be seen in Figure 26, which is a section view taken along the X-X axis, the fluid passageways 328 are at an angle E relative to the body end face 22 of 5°, however angles in the range of 0° to 25° are also envisaged. This is opposed to the previous embodiments, where angle c is 0°.

By introducing angled fluid passageways 328, the depth of the recess 26 is reduced. Furthermore, as can be seen in Figure 28, which is an end section view taken through the fluid passageways 328, said passageways 328 are at an angle 4 relative to a tangent to the side wall 25. This is opposed to the previous embodiments, where angle 4 is 90°. Angle 4 is 75°, however angles in the range of 55° to 90° are also envisaged. Further embodiments are also envisaged wherein angle c is 0° and angle 4 is not 90°, or wherein angle E is not 0° and angle 4 is 90°. By introducing the tangential angle the fluid passageways 328, any air trapped in a passageway 328 will migrate to the fluid outlet 16b.

It should be noted that embodiments with combinations of these features are also envisaged. For example, an embodiment with the groove 127 of the second embodiment and the fluid passageways 328 of the fourth embodiment. Furthermore, other groove geometries and fluid passageway arrangements are envisaged that could provide the same advantages as described above.

Claims

Claims 1. A piston for a brake caliper, the piston comprising: a pad end face at a pad end; a caliper end face at an opposing caliper end; a cylindrical body formed between the pad end and the caliper end and defining an outer wall; a circumferential deformable ring retention groove proximate the caliper end; and at least one fluid passageway arranged to fluidly connect the outer wall and the caliper end face.
2. The piston according to claim 1, wherein the caliper end face comprises a recess.
3. The piston according to claim 2, wherein at least one of the fluid passageways is arranged to fluidly connect the outer wall and an inner wall of the recess.
4. The piston according to either of claims 2 or 3, wherein the recess is cylindrical.
5. The piston according to any of claims 2 to 4, the body of the piston being formed around a central longitudinal body axis and the recess being formed around a central longitudinal recess axis, and wherein the body axis and recess axis are coincident.
6. The piston according to either of claims 4 or 5, wherein the radius of the body is in the range of 5mm to 40mm, preferably 19.05mm, and the radius of the recess is in the range of 3mm to 39mm, preferably 16.33mm.
7. The piston according to any of claims 2 to 6, wherein the length of the body is in the range of 10mm to 60mm, preferably 32mm, and the length of the recess is in the range of 1mm to 10mm, preferably 3mm.
8. The piston according to any of the preceding claims, further comprising a plurality of fluid passageways.
9. The piston according to any of the preceding claims, further comprising a number of fluid passageways in the range of 1 to 50, preferably 16.
10. The piston according to either of claims 8 or 9, wherein the recesses are arranged such that they are spaced apart evenly around the circumference of the outer wall.
11. The piston according to any of the preceding claims, wherein at least one of the fluid passageways is located between the deformable ring retention groove and the pad end.
12. The piston according to any of the preceding claims, wherein at least one of the fluid passageways is located at a base of the seal retention groove.
13. The piston according to any of the preceding claims, the body of the piston being formed around a central longitudinal body axis and wherein each fluid passageway is arranged along a fluid passageway axis, each fluid passageway axis being perpendicular to the body axis.
14. The piston according to any of the preceding claims, the body of the piston being formed around a central longitudinal body axis and wherein each fluid passageway is arranged along a fluid passageway axis, each fluid passageway axis intersecting the body axis.
15. The piston according to any of claims 1 to 13, wherein each fluid passageway is arranged along a fluid passageway axis, said axis arranged at a first angle relative to a tangent of the body, the first angle being in the range of 0° to 25°, preferably 5°.
16. The piston according to any of claims 1 to 12, or either of claims 14 or 15 when not dependent on claim 13, wherein each fluid passageway is arranged along a fluid passageway axis, said axis arranged at a second angle relative to the outer wall of the body, the second angle being in the range of 55° to 90°, preferably 75°.
17. The piston according to any of the preceding claims, wherein the deformable ring retention groove is formed of a base between opposing first and second walls.
18. The piston according to claim 17, wherein the at least one of the first and second walls are non-parallel to the caliper end face.
19. The piston according to either of claims 17 or 18, wherein the first face is at an angle relative to the caliper end face in the range of 0° to 25°, preferably 10°.
20. The piston according to any of claims 17 to 19, wherein the second face is at an angle relative to the caliper end face in the range of 0° to 25°, preferably 15°.
21. The piston according to any of claims 17 to 20, wherein the deformable ring retention groove is symmetrical about a plane parallel to the caliper end face.
22. The piston according to any of claims 17 to 21, wherein at least one of the first and second walls has a continuously curved shape.
23. The piston according to any of claims 17 to 22, wherein at least one of the first and second walls is formed of a plurality of straight surfaces.
24. The piston according to any of claims 17 to 23, wherein the base is convex.
25. The piston according to any of claims 17 to 23, wherein the base is concave.
26. The piston according to any of the preceding claims, wherein a deformable ring is located within the deformable ring retention groove.
27. The piston according to claim 26, wherein the deformable ring has a substantially rectangular cross-section.
28. The piston according to claim 26, wherein the deformable ring has an inner face, and the deformable ring retention groove is shaped to correspond to the shape of the inner face of the deformable ring.
29. The piston according to claim 28, wherein the inner face of the deformable ring has curved edges and the deformable ring retention groove has curved edges of an equal radius.
30. The piston according to claim 29 when dependent on any of claims 17 to 25, wherein the curved edges of the deformable ring retention groove are arranged between the base and the respective first and second walls.
31. A brake caliper assembly comprising: a brake caliper body defining at least one piston cylinder, each piston cylinder having an open end, a closed end, and a seal retention groove proximate to the open end; the piston according to any of the preceding claims arranged in each of the piston cylinders; a deformable ring located within the deformable ring retention groove and arranged to be in slidable contact with the piston cylinder; and a seal located within the seal retention groove and arranged to be in slidably sealing contact with the piston outer wall.
32. The brake caliper assembly according to claim 31, further comprising at least one bleed valve fluidly connected to each piston cylinder, and wherein the deformable ring retention groove and fluid passageways are arranged such that, when the piston is in a fully recessed position where the caliper end face of the piston is proximate the closed end of the cylinder, the outer wall of the piston, the caliper end face and each bleed valve are fluidly connected.
33. The brake caliper assembly according to either of claims 31 or 32, wherein the deformable ring is formed of any of Nitrile, Fluoroelastomer or Natural Rubber, preferably ethylene propylene diene monomer rubber.
34. The brake caliper assembly according to any of claims 31 to 33, wherein the seal is formed of any of Nitrile, Fluoroelastomer or Natural Rubber, preferably ethylene propylene diene monomer rubber.
35. A vehicle comprising the piston according to any of claims 1 to 30 or the brake caliper assembly according to any of claims 31 to 34.