GB2125124A

GB2125124A - Hydraulically actuated disc brake

Info

Publication number: GB2125124A
Application number: GB08310620A
Authority: GB
Inventors: Akira Kirihara
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1982-04-20
Filing date: 1983-04-20
Publication date: 1984-02-29
Also published as: GB8310620D0; AU1366283A; GB2125124B; JPS58158835U

Abstract

A hydraulically actuated disc brake comprises a housing (11, 11'), a cylinder (16) formed in the housing and having a closed end defined by a bottom wall (18, 18'), a piston (17, 17') slidably fitted in the cylinder, a pressure chamber (19) defined in the cylinder between the piston and the bottom wall, and a friction pad (20) being actuated by the piston when pressurized fluid is introduced into the pressure chamber; both outer surface (18a, 18'a) and inner surface (18c, 18'c) of the end wall are formed to have one or more projecting portions with corresponding recessed portions. The arrangement increases the surface area of the surface of the end wall to improve heat dissipation. Figures 2 and 4 illustrate two of the three embodiments specifically described. <IMAGE>

Description

SPECIFICATION Hydraulically actuated disc brake The invention relates to an hydraulically actuated disc brake.

Hydraulically actuated disc brakes are widely used in vehicles such as automotive vehicles.

When the brakes are frequently actuated the hydraulic fluid will be overheated which may induce so-calied vapour lock phenomenon thereby impairing the safety of the vehicle. Therefore, it has been desired to improve the heat dissipating characteristics of the disc brake.

The disc brake according to the invention is of the kind including a housing, a cylinder formed in the housing having a closed end defined by a bottom wall, a piston slidably fitted in the cylinder, a pressure chamber defined in the cylinder and between the piston and the bottom wall, and a friction pad and being actuated by the piston when hydraulic pressure is applied to the pressure chamber. For improving the heat dissipating characteristics of the disc brake of aforesaid kind, there has been proposed to provide a plurality of cooling fins formed integrally on the outer surface of the housing, particularly on the outer surface of the bottom wall. The cooling fins can substantially increase heat transmitting surface of the housing to atmospheric air.However, the heat transmitting area between the hydraulic fluid and the housing does not substantially change, thus, the proposal does not constitute the best counter-measure in improving the heat dissipating characteristics.

Further, there are shortcomings that the weight of the housing increases and the fabricating cost is expensive.

An object of the invention is to provide a disc brake having good heat dissipating characteristics.

According to the present invention there is provided a hydraulically actuated disc brake comprising a housing, a cylinder formed in the housing and having a closed end defined by a bottom wall, a piston slidably fitted in the cylinder, a pressure chamber defined in the cylinder and between the piston and the bottom wall, and a friction pad being actuated by the piston when pressurized fluid is introduced into the pressure chamber, wherein at least one each of a projecting portion and a retracting or recessed portion are formed on inner and outer surfaces of the end wall.

The heat transmitting area or the contacting area between the hydraulic fluid and the housing can substantially be increased.

In a preferred embodiment of the invention, the bottom wall constituting the closed end of the cylinder in the housing is formed into a wave-like configuration, with a plurality of projecting portions and retracting portions being formed on inner and outer surfaces of the end wall, and the projecting portions on the outer surface of the end wall act as cooling fins.

The present invention will now be described further, by way of example only, with reference to the accompanying drawings; in which: Fig. 1 is a front view of one embodiment of a disc brake according to the invention; Fig. 2 is a sectional view taken along line Il-Il in Fig. 1; Fig. 3 is a front view of a disc brake according to a second embodiment of the invention; and Fig. 4 is a sectional view taken along line IV--IV in Fig. 3.

The disc brake illustrated in Figs. 1 and 2 comprises a housing 11 supported siidably by two spaced parallel pins 1 2 and 13 on a stationary support 14 which is fixed to a vehicle, and a cylinder 16 formed in the housing 11 which receives slidably therein a piston 1 7. The cylinder 1 6 has an open end (the left end as viewed in Fig.

2) and a closed end (the right end as viewed in Fig.

2). A bottom wall 1 8 defines the closed end. A pressure chamber 19 is defined in the cylinder 1 6 and between the end wall 1 8 and a piston 1 7 which is slidably received in the cylinder 1 6. The piston 1 7 includes a generally disc shaped radial wall 1 7a and cylindrical portions 1 7b and 1 7c extending in opposite directions from the radial wall 1 7a. The cylindrical portion 1 7c of the piston 1 7 extends outwardly from the open end of the cylinder 1 6 to abut with a friction pad 20. Another friction pad 21 is mounted on an arm portion 11 a of the housing 11.

According to the invention, the bottom wall 1 8 of the housing 11 is formed to have inwardly projecting configuration with the inner surface 1 8c thereof projecting conically toward the piston 17 and the outer surface 1 8a thereof being conically recessed with respect to the outside. A generally rod like fin 1 8b projects from the centre of the conically recessed outer surface 1 8a. Thus, the inner surface 1 8c of the bottom wall 18 defines a large contacting area to the hydraulic fluid received in the pressure chamber 1 9 as compared with conventional generally flat inner surface of the bottom wall of the cylinder. Further, the contacting area between the outer surface of the bottom wall and the atmospheric air is also increased.

In operation, a driver of a vehicle depresses a brake pedal in applying brakes, a master cylinder (not shown) generates pressurized fluid which is supplied to the pressure chamber 19. The piston 17 moves leftward as viewed in Fig. 2 and the friction pad 20 is pressed against a disc 1 5 which rotates with a wheel of the vehicle. The housing 11 displaces rightward as viewed in Fig. 2 due to the reaction force and the friction pad 21 is pressed against the disc 1 5. The disc 1 5 is clamped by friction pads 20 and 21 and is braked.

Heat is generated by contact between the disc 1 5 and friction pads 20 and 21 and is transmitted through the piston 1 7 and the hydraulic fluid in the pressure chamber 19 to the housing 11 and directly to the housing 11.

As described heretofore, according to the invention, the bottom wall 1 8 of the cylinder 1 6 in the housing 11 has outer and inner surfaces 1 8a and 1 8c having increased contacting area against the atmospheric air and the hydraulic fluid in the pressure chamber 19 respectively as compared with conventional disc brakes. Accordingly, the heat dissipating characteristics are reliably improved. The cooling fin 1 8b can effectively dissipate the heat in the hydraulic fluid to atmospheric air.

Figs. 3 and 4 show a modified form wherein parts corresponding to the first embodiment are depicted by the same reference numerals and detailed description therefor is omitted. The disc brake comprises a housing 11' which is generally similar to the housing 11 in the first embodiment and the bottom wall 18' thereof is formed to have a wave like configuration such that the outer surface 18'a has a plurality of horizontally extending and vertically spaced projections projecting outwardly, and a plurality of horizontally extending and vertically spaced retracting portions retracting inwardly and being located between adjacent projections, and that the inner surface 1 8'c has a plurality of correspondingly shaped projections and retracting portions as clearly shown in Fig. 4.The surface area of the inner and outer surfaces 1 8'c and 1 8'a of the end wall 1 8' is largely increased as compared with conventional disc brakes, thus, it is possible to transmit a large amount of heat from the hydraulic fluid in the pressure chamber 19 through the end wall 18' of the housing 11' to atmospheric air. The thickness of the end wall 18' is uniform throughout the entire surface thereof which is advantageous in the fabricating process and in further improving the heat dissipating characteristics.

The embodiments, described are of so-called floating caliper type disc brake, however, the invention can also be applied to opposed piston type disc brakes wherein a pair of opposing cylinders are formed in a stationary housing.

Although the drawings show two preferred embodiments of the invention, various changes and modifications may easily be applied without departing from the spirit of the invention. For example, the end wall of the housing may have a conically shaped or a dome like shaped projection projecting outwardly with correspondingly shaped recess or retracting portion being defined on the inner surface of the end wall.

According to the invention, the end wall of the cylinder is formed to have large surface areas facing the hydraulic fluid in the pressure chamber and atmospheric air, which improves the heat dissipating characteristics thereby preventing socalled vapour lock phenomenon.

Further, as compared with prior art disc brake having a plurality of cooling fins formed on the outer surface of the housing, the disc brake according to the invention is simple in construction.

Claims

1. A hydraulically actuated disc brake comprising a housing, a cylinder formed in the housing and having a closed end defined by a bottom wall, a piston slidably fitted in the cylinder, a pressure chamber defined in the cylinder and between the piston and the bottom wall, and a friction pad being actuated by the piston when pressurized fluid is introduced into the pressure chamber, wherein at least one each of a projecting portion and a retracting or recessed portion are formed in inner and outer surfaces of the end wall.

2. A disc brake as claimed in claim 1, in which a conically or dome like shaped projecting portion is formed on the inner surface of the end wall and correspondingly shaped retracting portion or recess is formed on the outer surface of the end wall.

3. A disc brake as claimed in claim 1, in which a conically or dome like shaped projecting portion is formed on the outer surface of the end wall, and correspondingly shaped recess is formed on the inner surface of the end wall.

4. A disc brake as claimed in claim 1, in which the end wall has a wave like configuration defined by a plurality of projections and recesses being formed on inner and outer surfaces with the thickness of the end wall being substantially a constant, and said projections and recesses extending in one direction.

5. A disc brake constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings of Figures 1 and 2 or 3 and 4.