GB2026635A

GB2026635A - Hydraulic Disc Brake

Info

Publication number: GB2026635A
Application number: GB7916072A
Authority: GB
Original assignee: Akebono Brake Industry Co Ltd
Current assignee: Akebono Brake Industry Co Ltd
Priority date: 1978-05-10
Filing date: 1979-05-09
Publication date: 1980-02-06
Also published as: FR2425580B1; IT1114220B; IT7922370A0; FR2425580A1; GB2026635B

Abstract

Hydraulic pressure for driving the thrust piston 8 of a sliding caliper disc brake is generated in a cylinder formed within the guide pin 4 by a pressure generating piston 15, fluid being transferred to drive the thrust piston 8 through suitable passageways formed in the guide pin and the caliper itself. The pressure generating piston 15 may be operated by a brake cable connected to a suitable lever or pedal. The caliper may alternatively be arranged to swing about a guide pin disposed generally tangentially to the disc for balancing the braking force exerted by the two brake pads, instead of sliding axially along a guide pin extending parallel to the disc axis. <IMAGE>

Description

SPECIFICATION A Hydraulic Disc Brake This invention relates to a hydraulicallyoperated disc brake, and in particular to such a disc brake suitable for use on a motor vehicle.

Various types of hydraulically-operated disc brake are used for motor vehicles, on account of their simple structure. In a braking system of this type, hydraulic fluid pressure is produced within a master cylinder by applying an external force either to a brake lever or to a brake pedal, and the hydraulic pressure is transferred to a brake device through a hydraulic fluid transfer pipe line.

A braking system of this type suffers from the latent problem that a failure in the transfer of hydraulic pressure leads to non-operation of the brake. This problem is serious particularly in the case of a motor cycle or the like wherein the brake device is exposed, because there is a high risk that the pipe line of the brake device can become damaged should the motor cycle overturn. To reduce the likelihood of brake failure calls for attention to the prevention of damage to the fluid transfer piping.

It is therefore a principal aim of this invention to provide a hydraulically-actuated disc brake in which the transfer piping from the master cylinder to the brake caliper is eliminated, thereby preventing brake failure consequent to damage to such piping.

According to this invention, there is provided a disc brake assembly for urging a pair of friction pads into engagement one with each face respectively of a rotatable brake disc, which assembly comprises at least one guide pin adapted for mounting on a fixed support and carrying a caliper adapted to straddle the disc, the caliper having a thrust piston slidably mounted within a cylinder formed therein which piston is arranged for urging one friction pad towards a face of the disc and the caliper being movable on the guide pin relative to the support so that the reaction from the piston causes the other friction pad to be urged towards the other face of the disc, the guide pin having formed therein a cylinder in which is slidably mounted a pressure generating piston adapted for connection to a brake actuator, the piston and cylinder together defining a hydraulic pressure generating chamber which communicates with the caliper cylinder whereby movement of the pressure generating piston causes the thrust piston to move thereby applying the brake.

It will be appreciated that because the brake fluid pressure is generated in the disc brake assembly itself, and that pressure is transferred to the thrust piston within the caliper, there is no exposed piping which is susceptible to damage.

The pressure-generating piston is operated by a brake cable which, owing to its mechanical nature, is less liable to be damaged than hydraulic piping, for instance in the case of a motor cycle which over-turns.

The guide pin may be adapted for mounting to a fixed support either so that the pin extends parallel to the disc axis or so that the pin extends parallel to a tangent to the disc. In the first case, the caliper should be adapted to slide axially on the pin, whereas in the second case, the caliper should be adapted to swing about the pin, to allow balancing of the force applied to the two brake pads.

Conveniently, an oil reservoir is formed either in the fixed support for the guide pin or between the guide pin and a surrounding part of the caliper. A wall of an elastic material may bound the reservoir, to allow for changes in the volume thereof and yet to prevent leakage of oil.

This invention extends to a disc brake assembly of this invention as described above, in combination with a rotatable brake disc and a pair of friction pads disposed one to each side respectively of the disc for urging into engagement therewith by the caliper on actuation of the pressure-generating piston.

By way of example only, certain specific embodiments of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a part-sectional view of a first embodiment of disc brake of this invention; Figure 2 is a part-sectional side view of the first embodiment, Figure 3 is a front view of the first embodiment; Figure 4 is an enlarged view of a detail of the first embodiment; Figure 5 is a part-sectional view showing a second embodiment of disc brake of this invention; Figure 6 is a part-sectional view of a third embodiment of a disc brake arranged in accordance with this invention; Figure 7 is a longitudinal sectional view of the third embodiment; Figure 8 is a front view of the brake shown in Figure 6; Figure 9 is an enlarged view of a detail of the third embodiment; and Figure 10 is a part-sectional view showing a fourth embodiment of disc brake of this invention.

Figures 1 to 4 show a first embodiment of disc brake of this invention, for use with a disc 1 which is arranged to rotate together with a motor cycle road wheel supported by a fork 2. A support 3 is secured to the fork 2 and is disposed close to one side of the disc 1, there being a guide pin 4 secured to the support 3 and arranged to extend in the axial direction of the disc. The guide pin 4 is fixed to the support 13 in a cantilever-like manner to extend in the direction away from the disc 1.

There is also another guide pin which is not shown but which is secured to the support 3 to form a pair with the guide pin 4.

A caliper 5 is provided with an opening 6 which slidably engages the guide pin 4, so that the caliper 5 is movable in the axial direction of the disc rotor 1. The caliper straddles an edge portion of the disc 1 and in one part of the caliper to one side of the disc there is provided a cylinder 7 in which is slidably mounted a piston 8; within the piston and cylinder combination, there is a hydraulic chamber 10. The other part of the caliper 5 to the other side of the disc 1 is arranged to be a reaction part 9. Friction pads 11 and 12 are disposed one to each side respectively of the disc 1, for urging into engagement therewith respectively by the piston 8 and the caliper reaction part 9, as the caliper slides on the guide pin 4. The force applied to each pad is thus the same, as the caliper floats.

The arrangement described above is essentially similar to that of several known floating caliper disc brakes. The disc brake of this invention, however, differs in that a hydraulic pressure generator is incorporated within the disc brake assembly itself, by utilizing the support 3, one of the guide pins and a part of the caliper arranged to be in slidable engagement with the guide pin 4.

This will now be explained in detail.

In the axial core part of the guide pin 4, there is formed a cylinder 13. A hydraulic pressure generating piston 1 5 is slidably disposed in the cylinder 13, and is urged and biased in one direction by the force of a spring 14 also arranged within the cylinder 13. A small diameter piston rod of the hydraulic pressure generating piston 1 5 extends through a partition wall 1 6 at the end of the cylinder 13, and the free end of the rod is connected to a brake cable 1 7.

A cap 18 for the guide pin 4 also serves to mount the brake cable 17, the cap being threaded to the free end of the guide pin 4. A circumferential groove 1 9 is formed in the opening 6 of the caliper 5 and is arranged always to communicate with a hydraulic pressure generating chamber 21 of the hydraulic pressure generator through a flow passage 20 formed in the guide pin 4. The groove 1 9 is also arranged always to be communicating, through a flow passage 22 formed in the caliper 5, with the hydraulic chamber 10 of the cylinder 7 which has the thrust piston 8 therein.

A fluid reservoir 23 is formed by a cylindrical wall 3' of the support 3 which surrounds with clearance the guide pin 4 near the point at which the pin is fixed to the support. The reservoir 23 communicates with the chamber 21 through an oil port 25 which is arranged to be closed by a cup seal 24 when the piston 1 5 moves away from its rest position. A port 26 is arranged to allow the transfer of hydraulic oil from the reservoir 23 into the hydraulic pressure generating chamber 21 only at the time of releasing hydraulic pressure, by virtue of the unidirectional sealing action of the cup seal 24, allowed by utilizing the elastic deformation thereof.

As shown in Figure 2, the reservoir 23 extends in a direction parallel to the face of the disc 1, so as to be capable of holding a reasonable quantity of hydraulic oil. An oil supply port 27 allows filling of the reservoir 23.

In the disc brake arranged as described in the foregoing, when the brake cable 1 7 is pulled in the direction of the arrow shown in Figure 1 , the hydraulic pressure generating piston 15 moves against the force of the spring 14 to reduce the volume of the hydraulic pressure generating chamber 21.The movement of the piston 1 5 closes the oil port 25 so that pressure may be developed within the hydraulic pressure generating chamber, the hydraulic pressure being transferred to the hydraulic chamber 10 through the flow passages 20 and 22 and the circumferential groove 1 9. The hydraulic pressure then causes the piston 8 to push the friction pad 11 against the disc 1, and the reaction force causes the caliper 5 to float on the guide pins, in turn causing the reaction part 9 to push the other friction pad 12 against the disc 1. The pads are thus equally thrust into engagement with the two sides respectively of the disc, thereby braking rotation thereof.

When the brake is released, the spring force of the spring 14 brings the hydraulic pressure generating piston 1 5 back to the initial position thereof. Then, the reservoir 23 is back in communication with the hydrauluc pressure generating chamber 21 through the port 25, and the chamber 21 comes back to its initial condition of having zero hydraulic pressure therein.

Figure 5 shows a second embodiment of the invention, in which like parts with those of the first embodiment are given a reference numeral 100 greater than the respective numeral used in the illustrations of the first embodiment. Only those parts which differ significantly will now be described. In the second embodiment, a primary reservoir 123 is surrounded by a diaphragm made of rubber and is formed within the guide pin 104, instead of by the support 103. In addition, to the primary reservoir 123, a secondary reservoir (not shown) is provided within the caliper 105 for holding a sufficient quantity of oil. For this arrangement, the reservoir 123 within the guide pin 104 is provided with a breathing diaphragm 127. To connect the primary and second reservoirs to each other, there are provided a circumferential groove 128 in the caliper 105 and a port 129.With the exception of these parts, the rest of the embodiment is arranged in the same manner as the preceding embodiment.

A third embodiment of the present invention is shown in Figures 6 to 9, which also show a disc 201, and a support 202 which is secured to a structural part of a vehicle. A support shaft (or a guide shaft) 203 is fixedly attached to the support 202 to extend generally in a tangential direction of the disc 201. A caliper 204 is mounted on the support shaft 203 so as to be capable of swinging thereabout, and is provided with a pair of parts 205 and 206 which confront each other, on opposed sides of the disc 201. A plug 207 is threaded into the free end of the support shaft 203, so as to restrict the movement of the caliper 204 in the axial direction of the support shaft 203. A pair of friction pads 208 and 209 are disposed one to each side respectively of the disc 201, for engagement therewith.A thrust piston 210 is arranged slidably to fit within a cylinder 211 formed in parts 205 of the caliper 204, there being a hydraulic fluid chamber 212 in the cylinder. The arrangement described above is essentially known for a disc brake.

A cylinder 213 is formed in the support shaft 203 and a hydraulic pressure generating piston 214 slidably fits within the cylinder 213. The piston 214 is normally pushed and biased by the force of a spring 21 5 within the cylinder, so that the piston normally contacts with the inner end of the plug 207. A brake cable 216 is connected to the hydraulic pressure generating piston 214, and imparts movement thereof against the force of the spring 215, the cable being connected to a brake lever or the like (not shown).When the piston 214 is moved against the force of the spring 215, this decreases the volume of a hydraulic pressure generating chamber 21 7 within the cylinder 213, which communicates with the oil chamber 212 of the caliper 204 through a flow passage 21 8 provided between an opening 203' in the support shaft 203 and the caliper 204.

An oil chamber 219 is formed in the cylinder 213 between the flange part of the piston 214 which engages the cylinder wall and the plug 207. Oil may flow from this oil chamber 219 to the hydraulic pressure generating chamber 21 7 only through a flow passage 220 provided in the flange part and past a cup seal 221 attached to the piston 21 4.

An annular oil reservoir 222 is formed by an enlargement in an opening 223 in the caliper 204 which surrounds and contacts the outer circumference of the support shaft 203. The annular oil reservoir 222 communicates with the oil chamber 219 in the cylinder 213 through a port 224 and with the hydraulic pressure generating chamber 21 7 through an oil passing port 225. This oil passing port 225 is arranged to be closed by the cup seal 221 when the piston 214 is caused to move against the force of the spring 21 4. There is provided a breathing mechanism 226 to permit the passage of air from inside the oil reservoir 222 to the atmosphere, and vice versa. Slidable contacting faces of the outer circumference of the support shaft 203 and the opening part 223 of the caliper 204 are sealed by seal members 227 and 229.Another seal member 230 is disposed as shown.

In the disc brake arranged as described in the foregoing, when the brake cable 1 6 is pulled to the right as viewed in Figure 6 by operating a brake lever (not shown), the piston 214 is caused to move within the cylinder 213 against the force of the spring 215. The volume of the hydraulic pressure generating chamber 21 7 is thus decreased, and because in the initial stage of piston movement, the oil passing port 225 is closed by the cup seal 221, the hydraulic pressure in this chamber 21 7 increases. The increased hydraulic pressure is transferred to the oil chamber 212 through the flow passage 218 to cause the thrust piston 210 to move forward, thereby pushing the friction pad 208 against the disc 201.The reaction force to this causes the caliper 204 to swing on the support shaft 203, thereby to cause part 206 of the caliper to push the other friction pad against the disc 201. In this manner a balanced braking force is developed, pushing both pads equally on both sides of the disc.

When the brake is released, the piston 214 returns to its initial position under the force of spring 215, so that the hydraulic pressure in the hydraulic pressure generating chamber 21 7 falls.

Then, should the hydraulic pressure in the chamber 217 become negative, oil will be supplied from the oil reservoir 222 into the hydraulic pressure generating chamber 217 through a passage formed by the port 224, the oil chamber 219, the flow passage 220 and past the cup seal 221 by deformation thereof.

Figure 10 shows a fourth embodiment of the invention in which like parts with those of the third embodiment (Figures 6 to 9) are given like reference characters. Only those parts which differ will be described below. In the fourth embodiment, the inside of the oil reservoir 222 is prevented from having a negative pressure therein by a decrease in the quantity of oil within the reservoir 222. For this purpose, an elastic rubber diaphragm 231 which is capable of expanding and contracting is attached to a recess 204' formed in the caliper 204. The oil reservoir 222 is thus divided into an oil reservoir part 222 surrounded by this elastic diaphragm and an air reservoir 232. The air reservoir 232 is arranged to communicate with the atmosphere through a ventilating hole 233.

When the oil quantity within the oil reservoir 222 changes, the shape of the diaphragm 231 changes and the consequent volume change in the air reservoir 232 causes air to flow into or out of the recess 204' of the caliper. However, because of the particular arrangement employed, the oil reservoir 222 and the air reservoir 232 are completely separated from each other by the diaphragm 231 ,the possibility of an oil leak to the outside is completely precluded.

The disc brake incorporating therein the hydraulic pressure generator eliminates the possibility of a brake failure due to damage of a hydraulic pressure transfer piping which is employed to connect the master cylinder to the caliper of a conventional disc brake. Instead, in this invention the force exerted by a brake cable is used to generate hydraulic pressure within the caliper, thereby eliminating the piping.

Another advantage of this invention is that a better mechanical efficiency can be obtained as compared with a brake system in which brake pads are operated by the use of a mechanical link operated by a brake cable. Also, compared with a conventional brake system which uses a hydraulically operated disc brake and a separate master cylinder, the disc brake of the invention can be produced at a lower cost.

Claims

1. A disc brake assembly for urging a pair of friction pads into engagement one with each face respectively of a rotatable brake disc, which assembly comprises at least one guide pin adapted for mounting on a fixed support and carrying a caliper adapted to straddle the disc, the caliper having a thrust piston slidably mounted within a cylinder formed therein which piston is arranged for urging one friction pad towards a face of the disc the caliper being movable on the guide pin relative to the support so that the reaction from the piston causes the other friction pad to be urged towards the other face of the disc, the guide pin having formed therein a cylinder in which is slidably mounted a pressure generating piston adapted for connection to a brake actuator, the piston and cylinder together defining a hydraulic pressure generating chamber which communicates with the caliper cylinder whereby movement of the pressure generating piston causes the thrust piston to move thereby applying the brake.

2. A disc brake assembly according to claim 1, wherein the guide pin is adapted for fixedly securing to a structural part of a vehicle so as to extend in a direction parallel to the axis of the brake disc, and the caliper is arranged to be axially slidable on the guide pin.

3. A disc brake assembly according to claim 2, wherein there is provided a fixed support on which the guide pin is mounted, and there is formed an oil reservoir within a cylindrical wall defined by the support which wall is arranged to surround the guide pin, and the oil reservoir communicates with the hydraulic pressure generating chamber through a port provided in the guide pin.

4. A disc brake assembly according to claim 2, wherein an oil reservoir is defined by a wall of an elastic material which is arranged to surround the outer circumference of the cylinder formed in the guide pin, the oil reservoir communicating with the hydraulic pressure generating chamber through a port provided in the cylinder.

5. A disc brake assembly according to claim 1, wherein the guide pin is adapted for mounting so as to extend in a direction generally parallel to a tangent to the brake disc and the caliper is mounted on the guide pin so as to be capable of swinging thereabout.

6. A disc brake assembly according to claim 5, wherein an annular space defined jointly by the outer circumference of the guide pin and a bore in the caliper forms an oil reservoir which communicates with the hydraulic pressure generating chamber through a port provided in the guide pin.

7. A disc brake assembly according to claim 5 or claim 6, wherein at the free end of the guide pin, there is provided a plug for restricting movement of the caliper in the axial direction of the guide pin.

8. A disc brake assembly according to any of claims 5 to 7, wherein an oil reservoir bounded by an elastic diaphragm is formed around the outer circumference of the guide pin, the oil reservoir communicating with the hydraulic pressure generating chamber through a port provided in the guide in.

9. A disc brake assembly according to claim 8, wherein there is provided an air chamber which surrounds the elastic diaphragm, which air chamber communicates with the external ambient through a vent hole formed in the caliper.

10. A disc brake assembly according to any of the preceding claims, wherein the pressure generating piston is urged by a spring towards the free end of the guide pin.

11. A disc brake assembly according to any of the preceding claims, wherein the hydraulic pressure generating chamber communicates with the caliper cylinder through an opening provided in the guide shaft and a flow passage provided in the caliper leading to the cylinder.

1 2. A disc brake assembly substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 or in Figure 5 or in Figures 6 to 9 or in Figure 10 of the accompanying drawings.

13. A disc brake according to any of claims 1 to 12, in combination with a rotatable brake disc and a pair of friction pads disposed one to each side respectively of the disc for urging into engagement therewith by the caliper on actuation of the pressure-generating piston.