Brake caliper body and method of manufacture of a brake caliper body

Abstract

A brake caliper comprising a body manufactured from ALM and having a skinned lattice structure. A method of designing and forming said brake caliper.

Claims

1. A brake caliper formed by additive layer manufacturing, said caliper comprising a body formed from a single material, whereby the single material comprises, at least in part, a three-dimensional lattice of lattice elements defining voids and having at least a partial skin, in which the body and a high stress region, in which high stress region the lattice has a bulk density of 50% or less of the single material forming the body and a high stress region, in which high stress region the lattice has a bulk density higher than that of the low stress region.

2. A caliper according to claim 1, wherein said lattice is substantially open.

3. A caliper according to claim 2, comprising a drain orifice in communication with the open lattice to allow egress of manufacturing material therefrom.

4. A caliper according to claim 1, wherein said lattice is substantially closed.

5. A caliper according to claim 1, wherein said lattice defines voids disposed symmetrically about the Y-axis.

6. A caliper according to claim 1, wherein the caliper is formed wholly from skinned, three-dimensional lattice.

7. A caliper according to claim 1, wherein the caliper is formed in part from skinned, three-dimensional lattice and in part from solid material.

8. A caliper according to claim 1, wherein said skin defines one or more of a piston bore, a slideway, an abutment for a brake pad, a mounting pad of an upright, a bearing pad for a screw fastener, an exterior surface visible in use, an internal fluid passage, a seat for a fluid seal, a threaded bore, an unthreaded bore.

9. A caliper according to claim 1, the lattice defining voids of different volume.

10. A caliper according to claim 1, the lattice defining voids of substantially the same volume.

11. A caliper according to claim 10, wherein a substantial proportion of said voids are defined by concave surfaces.

12. A caliper according to claim 1, in which the bulk density is 30% or less of the material forming the lattice.

13. A caliper according to claim 1, wherein said lattice is defined by the lattice elements.

14. A caliper according to claim 13, in which the lattice elements take the form of one or more of columns, pillars, dendritic forms, honeycomb structures, body centred cubic structures or gyroid structures.

15. A caliper according to claim 13, wherein said lattice elements have a minimum cross-sectional area of 1 mm.sup.2.

Description

(1) An example caliper in accordance with the present invention will now be described with reference to the following figures:

(2) FIG. 1 is a top view of a known brake caliper;

(3) FIG. 2 is a side view of the caliper of FIG. 1;

(4) FIG. 3a is a top view of a first embodiment of a caliper in accordance with the present invention;

(5) FIG. 3b is a simplified view of FIG. 3a showing the regions of the caliper formed from skinned lattice;

(6) FIG. 4 is a section view of a part of the caliper of FIG. 3b along line IV-IV;

(7) FIG. 5 is a section view similar to FIG. 4 of a second embodiment;

(8) FIG. 6 is a section view similar to FIG. 5 of a third embodiment;

(9) FIG. 7 is a side view of a fourth embodiment of a caliper in accordance with the present invention;

(10) FIG. 8 is a side view of a fifth embodiment of a caliper in accordance with the present invention;

(11) FIG. 9 is a flow chart representing a method of manufacture of a caliper in accordance with the present invention;

(12) FIG. 10 is a section view similar to FIG. 4 of a sixth embodiment; and

(13) FIG. 11 is a section view similar to FIG. 4 of a seventh embodiment;

(14) Referring to FIGS. 1 and 2, there is shown a brake caliper 10. The brake caliper 10 sits astride a brake disc 11. The caliper 10 comprises a caliper body 12 defining four cylinders 14, 16, 18, 20, respective pistons 15, 17, 19, 21 disposed within each cylinder and two opposed brake pads 22, 24 either side of the disc 11.

(15) The caliper body 12 has a mounting side limb 26 and a non-mounting side limb 28. The mounting side limb comprises mounting holes 30, 32 for attachment to a vehicle. The mounting side limb 26 and non-mounting side limb 28 are joined by two end bridge members 34, 36 and a central bridge member 35. The bridge members 34, 35, 36 span the disc 11 in use as shown in FIG. 1.

(16) In the mounting side limb 26 there are disposed the cylinders 14, 16 containing the pistons 15, 17 which are arranged to urge the pad 22 towards the disc 11. Similarly, on the non-mounting side limb 28 there are disposed the cylinders 18, 20 containing the pistons 19, 21 which are arranged to urge the pad 24 towards the disc 1. Hydraulic pressure is supplied to the cylinders 14, 16, 18, 20 in order to effect braking.

(17) When the brake is applied, the clamping force causes a reaction RCF in the axial direction which tends to splay the limbs 26, 28. The friction of the pads 22, 24 on the disc 11 results in a reaction RBF in the tangential direction.

(18) Turning to FIGS. 3 and 4, there is shown a brake caliper in accordance with the present invention. The same reference numerals apply to FIGS. 3 and 4 as they do to FIGS. 1 and 2.

(19) The caliper body 12, instead of being a solid homogenous material has parts formed from a skinned lattice structure. Referring to FIG. 4, which is a cross section along line IV-IV in FIG. 3a, the end bridge 34 comprises a solid, uninterrupted outer skin 38 which outwardly has the same appearance as a prior art caliper. Within the section however a lattice structure is provided comprising a plurality of lattice elements defining a plurality of cavities or voids 40. The cavities 40 are connected and form an open-cell structure within the caliper body.

(20) In the centre of the section of the bridge member 34 there is provided a hydraulic fluid conduit 42 passing from the mounting side limb 26 to the non-mounting side limb 28. Pressurised hydraulic fluid from the vehicle brake system is conveyed along the conduit 42. This conduit connects to cylinders 14, 16, 18, 20 so that all cylinders are pressurised.

(21) This skinned lattice structure runs throughout the caliper body 12 in the cross-hatched regions of FIG. 3b. In the embodiment shown, the voids account for approximately 50% of the total volume enclosed by the skin 38 in the region of the caliper formed from lattice. We have found that bulk densities much above 50% can impede the removal of unused powder manufacturing material.

(22) Referring to FIG. 5, an alternative to the section of FIG. 4 is shown in which the open cell irregular cavity lattice is replaced with an open-cell regular cavity lattice. Each cavity 40 is elongate and leaves columns 44 of caliper material therebetween. In this manner, heterogeneous properties can be obtained. The bending stiffness of the section of FIG. 5 is higher about axis X than axis Y. It will be noted that the conduit 42 is still present.

(23) A further embodiment is shown in FIG. 6, in which the columns 44 are tapered to be thinnest in the centre of the cross-section.

(24) Caliper bodies having the afore-described skinned lattice are manufactured using additive layer manufacturing (ALM)—specifically laser sintering, either by direct deposit laser sintering or by metal powder bed laser sintering.

(25) In particular, the additive layer manufacturing may be incorporated by a direct deposit laser sintering process, in which metal powder is directed onto the work piece directly at the focus of a laser beam. Direct deposit laser sintering does not require a bed of metal powder to be deposited on a surface, but can fuse metal powder dynamically onto the substrate.

(26) In detail, a laser beam is focused on the surface of a substrate and scans along the surface in a particular pattern that resembles the structure of the caliper body or body parts to be produced. Metal powder is delivered through a powder nozzle, which creates a gas flow arranged coaxially with the laser beam that falls into a molten pool created in the focus of the laser beam. A track of deposited metal is formed as a result of the continuous melting of the metal powder and solidification of the molten pool once the laser beam has moved on.

(27) The process of additive layer manufacturing may be used to produce the entire brake caliper or to add specific structures to cast or machined body parts. For example, it is feasible to produce the cylinder housing portions by virtue of a casting or machining process and connect the cylinder housing portions by means of bridges manufactured in an additive layer manufacturing process.

(28) In an alternative embodiment, metal powder bed laser sintering, in which a laser beam is directed onto a bed of metal powder can be implemented. In this embodiment, parts of the metal powder bed, which are subject to the heat of the laser beam, are fused to form solid metal while some of the powder remains unused. Evidently in order to release the unused powder from the cavities shown, they are open cell, and provide a drain hole to allow the unused powder to exit after manufacture. The so recovered unused powder can be recycled in another layer of the caliper body. Typically, the caliper body is shaken and/or blown with gas to loosen and release unused powder.

(29) Turning to FIG. 7 there is shown a further caliper 10 in accordance with the present invention. The caliper 10 is shown inside a wheel 2. The caliper body 12 comprises a lattice structure as described above. The outer surface of the caliper body 12 (i.e. the skin 34) is dimensioned to leave a small clearance gap G with the inside of the wheel 2. The gap G is selected to allow the minimum risk of stone ingestion between the caliper body 12 and the wheel 2. It will be noted that because the density of the caliper body 12 can be tailored by altering the internal lattice structure, making a larger caliper to provide a small clearance to avoid stone ingestion or entrapment does not result in a significantly heavier caliper. The cross-hatched region in FIG. 7 comprises skinned lattice with a bulk density of 10%.

(30) Turning to FIG. 8 there is shown a further caliper 10 in accordance with the present invention. The caliper 10 is shown inside a wheel 2. At a leading end of the caliper (vehicle direction of travel D is shown) the caliper body 12 has an integral stone shield 46. The shield 46 provides a tight clearance gap G against the wheel 2 where the disc 11 enters the caliper 10 to avoid stone entrapment. The shield extends across the leading bridge member and has a smooth outer skin with an internal lattice such that its weight is reduced. Again, the cross-hatched region in FIG. 8 is skinned lattice with a lower bulk density.

(31) A method of manufacture of brake calipers in accordance with the present invention is described with reference to FIG. 9. A brake caliper design is provided at step 100. The design assumes a solid metal body. The design is input into a CAE (computer aided engineering) stress analysis program in step 102. A load case is also input (e.g. simulating the forces of braking) at step 104. At step 106 the CAE program is run, producing an output at step 108 which provides details of the stress profile of the caliper body under loading.

(32) In the results set, there will be areas of the caliper with high stress and areas with lower levels of stress (far below the strength of the material). The areas of lowest stress are also likely to be those of lowest deformation.

(33) At step 110, the user adapts the CAE model to introduce internal lattice structures at areas in which stress and deformation are low. This effectively lowers the global density of the material in those areas, making the caliper lighter. The model is then rerun at step 112 to check the performance of the lighter caliper. If satisfactory, the remodelled caliper is sent for ALM at step 114.

(34) In an alternative process, optimisation software may perform iterative steps to introduce internal lattice structures. For example, the optimisation software may automatically assign a skinned lattice to areas with stresses in a predetermined range, before rerunning the software. Evidently moving from a solid material to a lattice will increase stress and deformation, and the optimisation software will be programmed not to exceed a given deformation. As described above, optimisation software may use low bulk density lattice to fill a region which may previously have been filled with a thin web.

(35) FIG. 10 is similar to the arrangement in FIG. 4 except the lattice is a body centred cubic structure. This is advantageous as the structure is self-supporting during the ALM process and comprises small three-dimensional, readily repeatable cells. Cells can be successively miniaturised to fill tighter areas with the lattice.

(36) FIG. 11 is similar to the arrangement in FIG. 10 but the lattice is a gyroid structure.

(37) Variations fall within the scope of the above embodiments.

(38) In an alternative embodiment, a closed cell structure may be used and the metal powder left inside the caliper body. This still provides a lower weight than solid metal as the powder has a lower density than the fused material.