Brake caliper

Abstract

A brake caliper (10) for a vehicle is herein disclosed. The brake caliper comprises a groove operable to house a brake seal (14), wherein the brake caliper comprises at least one piston (12) operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc; the groove comprises a leading face (16) operable to engage with the seal when the piston is engaged with the brake pad, a rear face (18) opposite the leading face, and a groove floor face (20), said seal being housed within the groove and a surface of the piston, wherein substantially the entirety of the leading face is disposed at an acute angle with respect to the surface of the piston.

Description

[0001] BRAKE CALIPER

[0002] The present invention relates to improvements in brakes, and particularly to improvements in braking systems for motor vehicles, and particularly electric vehicles.

[0003] Background

[0004] Modern cars typically have equipped caliper brakes. The brakes are activated by a brake pedal. Such brakes are known. They comprise pairs of pistons that, under braking, force brake pads towards a brake disc under pressure from brake fluid. A braking action is concluded when the brake pedal is released. Rubber seals within seal grooves inside the caliper are used to return the pistons back to their original position.

[0005] Brake drag is known. It is a phenomenon whereby the piston retraction travel does not provide sufficient clearance for the brake pad to completely release from the brake disc on release of the brake pedal and the brake drags.

[0006] Brake roll-back describes the piston retraction following the removal of the fluid pressure upon releasing the brake pedal. If there is too little retraction, the brake will drag. If there is too much the brake pedal will have what is termed a long travel. A long brake pedal is a well-known term in motoring circles, and particularly in racing circles.

[0007] Roll-back is facilitated by the caliper using the elastic energy, friction and geometry of the rubber seal with the surface finish of the piston plus the geometry of the caliper seal groove.

[0008] During a braking action, the seal is in contact with the piston. As the piston is urged towards the brake disc, friction and hydraulic pressure cause the seal to deform and gain elastic energy. It is this elastic energy that allows for the piston to be returned to its original position when the caliper hydraulic fluid pressure is released. Once braking is finished, the seal returns to its original position and shape and pulls the piston back into its original position.

[0009] The present invention seeks to provide improvements to current braking arrangements.

[0010] Summary of the Invention

[0011] Brake drag is likely to provide greater challenges for electric vehicles than for their fossil fuel counterparts since range is an important attribute. Increased control and consistency of piston roll- back and associated low brake drag are highly desirable, with targets from 2 to 0 per newton meters per brake being requested by vehicle manufacturers.

[0012] The present arrangement seeks to improve roll-back for caliper brakes, especially for electric vehicles.

[0013] According to the present invention there is provided a brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein substantially the entirety of the leading face is disposed at an acute angle with respect to the surface of the piston.

[0014] It is preferred that the leading face comprises a substantially uniform angle with respect to the surface of the piston. In a particularly preferred arrangement, the angle is between the surface of the piston and the leading face is 2° to 11°.

[0015] It is preferred that the groove floor is non-parallel to the piston surface. It is preferred that the leading face is longer than the rear face.

[0016] According to a second aspect of the present invention there is provided a brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein the leading face is curved.

[0017] It is particularly preferred that the curve is convex. It is particularly preferred that the curve is R3 to R20 (3mm to 20mm).

[0018] It is typical in conventional arrangements for the leading face of the groove to comprise a chamfered portion proximate to the piston surface. Preferably, the leading face does not include a chamfered portion at the end closest to the piston surface. In some arrangement a much-reduced chamfered portion may be provided. Such arrangements are advantageous in that the seal deflects across its entire section, rather than locally into a chamfered section. The provision of an angled or curved leading face allows for more controlled deflection of the seal. Such an arrangement spreads the stress across the entirety of the front face, and thus provides more uniform and controlled roll-back over a much longer time period. Such benefits provide significant improvements in brake seal wear-rate.

[0019] According to a third aspect of the present invention there is provided a brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein the face of the seal contacting the leading face of the caliper seal groove is angled.

[0020] The angle on the leading face of the seal creates the same effect as the angle to the front face of the seals groove in aspect 1. The angled seal elastically deforms into the caliper seal grove under hydraulic pressure inside the caliper. The present arrangement allows a conventional square section seal groove to be used with a shaped seal. When the hydraulic pressure is released from the caliper the seal returns to original geometry and creates an increased piston rollback while using a conventional straight sided seal groove. The angle on the front of the seal can be developed to suit the applications; low angle relatively limited piston rollback and medium drag or a large angle increasing the piston rollback and lowering the brake drag. The present angled seal has been found to deliver reliable repeatable values. This solution allows the angle of the seal fitted to the caliper to be varied when fitted to a conventional machined caliper seal groove including different seals in the inboard and outboard caliper halves. Such seals allow tailored levels of piston rollback and drag control for specific racing circuits without needing the caliper hardware or seal groove to be changed.

[0021] For example, a low drag solution would be advantageous at Le Mans, whilst a short pedal travel would be preferable for Monza.

[0022] It is preferred that the angled seal face comprises a substantially uniform angle with respect to the surface of the piston. In a particularly preferred arrangement, the angle is between the surface of the piston and the leading face seal is 2° to 11°.

[0023] According to a fourth aspect of the present invention there is provided a brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, said seal comprising a leading face and a rear face, wherein the rear face of the seal is angled.

[0024] This arrangement provides an angle on the trailing edge of the seal. Seals with different angled rear faces may be used. When hydraulic brake pressure is applied to a conventional square section seal it deforms so as to both grip the piston and extrude into the caliper seal groove. This action of gripping the piston reduces the piston clamping force on the brake pad since it 'holds' the piston. Providing an angle on the rear face of the seal allows the hydraulic pressure on the seal to extrude the seal towards the outside diameter of the seal groove and reduces the 'gripping' load on the piston. This reduced grip on the piston per unit of hydraulic pressure increases the available clamping force on the brake pad. An increased brake pad clamping pressure per unit of hydraulic pressure is thus created. Increased efficiency is provided using the present seal design. As such, the brake size and weight can be reduced, since it can operate at lower hydraulic pressure for the same vehicle deceleration rate.

[0025] It is preferred that the rear face of the seal comprises a substantially uniform angle with respect to the surface of the piston. In a particularly preferred arrangement, the angle between the surface of the piston and the rear face seal is 2° to 11°.

[0026] In order that the present invention be more readily understood, specific embodiments thereof will now be described in reference to the following drawings.

[0027] Brief description of the drawings

[0028] Figure la shows a cross-section of a conventional brake caliper, highlighting a piston and the brake seal, not under braking conditions.

[0029] Figure lb shows a cross-section of a conventional brake caliper, highlighting a piston and the brake seal, under braking conditions.

[0030] Figure 2a shows a close-up of the seal in figure la.

[0031] Figure 2b shows a close-up of the seal in figure lb.

[0032] Figure 3 shows a conventional brake caliper and seal and shows a heat map indicating stress within the seal under braking conditions. Figure 4a shows a cut-away section of a brake caliper according to a first embodiment.

[0033] Figure 4b shows an example tooling arrangement for the manufacture of the brake caliper of figure 4a.

[0034] Figure 5a shows a cut-away section of a brake caliper according to a second embodiment.

[0035] Figure 5b shows an example tooling arrangement for the manufacture of the brake caliper of figure 5a.

[0036] Figure 6a shows the brake caliper of figure 5a, with seal in situ, and shows a heat map indicating stress within the seal under braking conditions.

[0037] Figures 6b and 6c show, respectively, a close-up of a seal with an angled front face, and an angled rear face.

[0038] Figure 7 shows examples of heat maps indicating stresses within seals, under braking conditions, for conventional arrangements, compared with those according to the first and second embodiments. Examples for aspects three and four are also shown.

[0039] Description of Preferred Embodiments

[0040] The present arrangement looks at improvements in vehicle braking solutions, and specifically looks at improving piston roll-back consistency, and improving brake seal wear-rate by managing the stress on the seal.

[0041] In high-performance road cars, an element of brake drag is considered acceptable, as the too greater roll-back can mean that the brake pedal has a long travel. This undermines driver confidence in the brake system. Typical brake-drag for high performance braking systems can be of the order of 5 to 15 newton meters.

[0042] There is a constant push for greater vehicle efficiency. Also, the vehicle markets are moving towards electrification, and this, together with environmental considerations, means that brake¬ drag targets are likely to decrease. A target in the range of 2 to 0 newton meters is preferable. The present arrangement looks to solutions to make such targets achievable.

[0043] Broadly, in a braking system, each wheel comprises a brake. The brake comprises a pair of calipers positioned about a brake disc. Each caliper comprises one or more pistons operable to move back- and-forth within a piston housing. The piston housing comprises a groove operable to house a seal, said seal being an annulus that fits about the piston. Actioning a brake pedal forces brake fluid to push the pistons towards a brake pad. The brake pad urges the brake disc, thus causing braking.

[0044] Figures la, lb, 2a and 2b show a conventional brake caliper with a seal mounted about a piston.

[0045] Figures la and lb show, respectively, a cross-section of a piston 12 within a brake caliper 10 in a dormant state (fig la) and when under braking (fig lb). A seal 14 encircles the piston 12.

[0046] Figures 2a and 2b correspond to figs la and lb but show a close-up of the seal 14. Figures 2a and 2b show a groove in the caliper 10 that is operable to house the seal 14. The groove comprises a leading face 16, a rear face 18 and a groove floor 20. The leading face 16 comprises a chamfered section where the leading edge 16 is closest to the piston 12.

[0047] The term roll-back is used to describe the retraction of the piston 12 following the removal of fluid pressure upon release of the brake pedal. Too little retraction, and the brake will drag. Too much and the pedal travel goes long.

[0048] Many aspects are associated with roll-back. These include seal material properties, including the surface roughness of the seal. The seal geometry, and how it interacts with the groove. The piston surface roughness may also be a factor. Also, the lubrication used (type and amount) when assembling the braking system can affect roll-back. The temperature of the system, including the temperature of the brake fluid can also affect roll-back. It is desirable to provide a system that supplies the most uniform solutions.

[0049] Roll-back is facilitated in the caliper by using the elastic energy of the rubber seal 16.

[0050] Figure 2b shows that, under braking, the seal is deformed by being forced out of shape by the forward motion of the piston. The seal 16 is in contact with the piston as the piston moves forward in the braking action. The friction and hydraulic pressure cause the seal 16 to deform and gain elastic energy.

[0051] In conventional brake calipers 10, the leading face 16 of the groove comprises a chamfered portion 16a. As shown in figure 2b, the seal 16 is deformed into the chamfer. Such an arrangement is known to control the level of roll-back. The geometry of the seal groove, and particularly of the chamfer, partially dictates roll-back. Generally, a smaller chamfer will provide low roll-back, and hence higher brake-drag, and a shorter pedal travel, whilst a larger chamfer provides for high roll¬ back. This gives lower brake-drag, but a longer pedal travel. A drawback with using a chamfered leading face 16 is that it can create high stress in the seal, and particularly in the section of the seal that engages with the chamfer. Figure 3 shows a conventional brake caliper with a known shape groove and shows a heat map indicating stress within the seal. It will be appreciated that there is significant stress in the portion of the seal 16 that engages with the chamfered portion 16a.

[0052] The present applicant has looked at minimizing seal stress by reducing the size of the chamfer portion 16a on the leading face 16. However, such arrangements are expensive and are only viable in bespoke racing categories. Difficulties during assembly can also be encountered.

[0053] Figures 4a and 5a show first and second embodiments of the present invention.

[0054] Figure 4a shows a cut-away section of a brake caliper 10. The seal 16 is not shown. Here, the leading face 16 is angled. In use, a piston would lie atop of the groove. In figure 4a, the primary axis of the piston would be horizontal. An acute angle is made with respect to the surface of the piston. Thus, in figure 4a, the angle on the leading face of the groove is angled to the horizontal. The angle of the leading face can be tailored to desired specifications. However, it is preferred that the range is between 2° to 11°.

[0055] By angling the leading face of the groove, the seal deflects across its entire front face during a braking action. In such an arrangement a chamfered portion on the leading edge is not required. One may be provided, however.

[0056] Internal stresses on the seal are spread across the whole body of the seal, and thus are minimized in localized areas. Accordingly, more consistent and longer-lasting performance is achieved.

[0057] A second embodiment is show in figure 5a. Here, a curved leading face is provided. This arrangement further reduces the stresses in the seal whilst maintain piston roll-back performance. The reduction of stress provides for greater repeatability in roll-back performance over the lifetime of the seal 16. The radius of the curve can be manufactured to desired specifications. However, a radius of R3 to R20 (3mm to 20mm) is preferred.

[0058] Figure 6a shows a seal groove with a curved front face wit the seal under high stress. It will be noted that stress on the seal is much reduced compared to the seal in figure 3.

[0059] Figures 4b and 5b, show, respectively, means to create the grooves of the first and second embodiments within a brake caliper. A dedicated machine tool may be used to create the groove. Such an arrangement is advantageous in that consistent, uniform grooves may be created each time. in a further embodiment, a conventional, square cross-sectional groove may be used. Here, a shaped seal may be provided. The seal groove comprises a leading face 16 operable to engage with the seal 14 when the piston engages the brake pad, a rear face 18, and a groove floor face 20. The seal 14 being housed within the groove and a surface of the piston. The face of the seal 14 contacting the leading face 16 of the caliper seal groove is angled.

[0060] The angle on the leading face of the seal creates the same effect as if the front face of the seal groove was angled. The angled seal elastically deforms into the caliper seal grove under hydraulic pressure inside the caliper. The present arrangement allows a conventional square section seal groove to be used with a shaped seal. When the hydraulic pressure is released from the caliper the seal returns to original geometry and creates an increased piston rollback while using a conventional straight sided Seal Groove.

[0061] An example of such a seal 14 is shown in figure 6b. It will be appreciated that the front angle may be selected to meet the requirements of the situation.

[0062] The angle on the front of the seal can be developed to suit the applications; low angle relatively limited Piston Rollback and medium drag or a large angle increasing the piston rollback and lowering the brake drag. The present angled seal has been found to deliver reliable repeatable values. This solution allows the angle of the seal fitted to the caliper to be varied when fitted to a conventional machined caliper seal groove including different seals in the inboard and outboard caliper halves. Such seals allow tailored levels of piston rollback and drag control for specific racing circuits without the caliper hardware or seal groove to be changed.

[0063] For example, a low drag solution would be advantageous at Le Mans, whilst a short pedal travel would be preferable for Monza.

[0064] The leading face of the seal 14 comprises a substantially uniform angle with respect to the surface of the piston. This angle is typically 2° to 11°. However, other angles may be contemplated depending on the requirements of the vehicle.

[0065] A seal 14 with an angled rear face may also be provided. Such a seal arrangement is shown in figure 6c. The seal is shown 'at rest’ in this figure. When hydraulic brake pressure is applied to a conventional square section seal it deforms so as to both grip the piston and extrude into the caliper seal groove. This action of gripping the piston reduces the piston clamping force on the brake pad since it 'holds' the piston. Providing an angle on the rear face of the seal allows the hydraulic pressure on the seal to extrude the seal towards the outside diameter of the seal groove and reduces the 'gripping' load on the piston. This reduced grip on the piston per unit of hydraulic pressure increases the available clamping force on the brake pad. An increased brake pad clamping pressure per unit of hydraulic pressure is thus created. Increased efficiency is provided using the present seal design. As such, the brake size and weight can be reduced, since it can operate at lower hydraulic pressure for the same vehicle deceleration rate.

[0066] Seals with different rear face angles may be provided and selected for desired performance.

[0067] In a preferred arrangement, the angle is between the surface of the piston and the leading face seal is 2° to 11°.

[0068] Figure 7 shows examples of the above embodiments. Nine examples are shown. The right most column, column C, shows a cross-section of the seals when at rest.

[0069] Columns A and B show the seals under braking at, respectively, 100 bar and 4 bar.

[0070] The table below describes the characteristics of each of the nine examples, and their relationship to the aspects described above.

[0071] Example number characteristic aspect

[0072] 1 Curved seal groove 2 2 Angled seal groove 1 3 Angled seal groove 1 4 Angled seal groove 1 5 Rear face of seal angled 4 6 Front face of seal angled 3 7 Front face of seal angled 3 8 Front face of seal angled 3 9 conventional NA

[0073]

[0074] For example, embodiment 1 shows a seal groove with a curved front face. The seal is shown under high stress (column A - 100 bar), low stress (column B - 4 bar) and not under stress (column C).

[0075] It is to be understood that the above-described embodiments are done so for information purposes only, and that many modifications and variations are included within the scope of the attached claims.

Claims

CLAIMS1. A brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein substantially the entirety of the leading face is disposed at an acute angle with respect to the surface of the piston.

2. A brake caliper according to claim 1, wherein the leading face comprises a substantially uniform angle with respect to the surface of the piston.

3. A brake caliper according to claim 2, wherein the angle between the surface of the piston and the leading face is 2° to 11°.

4. A brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein the leading face is curved.

5. A brake caliper according to claim 4, wherein the curve is convex.

6. A brake caliper according to claim 5, wherein the curve is R3 to R20.

7. A brake caliper according to any preceding claim, wherein the groove floor is non-parallel to the piston surface.

8. A brake caliper according to claim 7, wherein the leading face is longer than the rear face.

9. A brake caliper according to any preceding claim, wherein the leading face does not include a chamfered portion at the end closest to the piston surface.

10. A brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as tourge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, wherein the face of the seal contacting the leading face of the caliper seal groove is angled.

11. A brake caliper according to claim 10, wherein the face of the angled seal comprises a substantially uniform angle with respect to the surface of the piston.

12. A brake caliper according to either claim 10 or 11, wherein the angle is between the surface of the piston and the leading face seal is 2° to 11°.

13. A brake caliper comprising a groove operable to house a brake seal, wherein the brake caliper comprises at least one piston operable to move with respect to the caliper so as to urge a brake pad from a position of disengagement with a brake disc to a position of engagement with the brake disc, wherein the groove comprises a leading face operable to engage with the seal when the piston is engaged with the brake pad, a rear face opposite the leading face, and a groove floor face, said seal being housed within the groove and a surface of the piston, said seal comprising a leading face and a rear face, wherein the rear face of the seal is angled.

14. A brake caliper according to claim 13, wherein the rear face of the seal comprises a substantially uniform angle with respect to the surface of the piston.

15. A brake caliper according to either claim 13 or 14, wherein the angle between the surface of the piston and the rear face seal is 2° to 11°.

Images