GB2032546A

GB2032546A - An improved braking arrangement

Info

Publication number: GB2032546A
Application number: GB7928442A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1978-10-05
Filing date: 1979-08-15
Publication date: 1980-05-08
Also published as: FR2438199A1; DE2932218A1; JPS5551133A

Abstract

A combined disc and drum brake arrangement comprises a rotary member (6) fixed to a road wheel (4) to rotate therewith, the rotary member (6) having a drum (11) and a disc (12), a drum brake (8) provided within the drum and a disc brake (7) provided adjacent said disc. The disc brake (7) includes a pair of pads (16, 17) disposed on opposite sides of the disc (12), a cylinder (18) fixed on an axle casing (2), a yoke (21) extending to the side of said cylinder (18) and the pair of pads (16, 17), the yoke being moved upon introduction of a pressurised liquid into the cylinder (18) to actuate pistons (19, 20) thereby to press the pads (16, 17) against the disc to exert a braking force. The drum brake (8) comprises a shoe (15) operatively coupled with a cable. <IMAGE>

Description

SPECIFICATION An improved braking arrangement This invention relates to a drum-in-disc type brake device in which an single road wheel is provided both with a disc brake and drum brake..

Some vehicles using a disc brake as the main braking device concurrently use a drum brake for parking. With this type of vehicle, the drum is arranged on a stepped rotary member which rotates integrally with a road wheel, i.e., the drum is provided on the inner circumferential plane of the rotary member in parallel with the axis of the rotary positioned a little to the centre. The brake disc is formed on the rotary members outer circumferential portion perpendicular to the axis, and a brake shoe is provided within the drum to serve as the drum brake.

Generally, however, a disc brake has the structure that the pads placed on opposite sides of the disc are held by, for example, a caliper set up straddling the disc adjacent its highest portion, and are simultaneously pressed against the disc.

Consequently, a space must be availabie for the disc brake, between the outer wall of the rotary member and the inside of the road wheel (wheel disc, rim) containing the rotary member, so that the outer diameter of the rotary member is inevitably limited. Particularly because the disc brake conventionally used in the described type of braking arrangement is a caliper-transfer type brake D provided with a relatively thick caliper Dc containing a cylinder, the space for the disc brake must have a considerable volume, as illustrated in Figure 1.

As is apparent from the foregoing, therefore, the diameter of the drum portion Rd of the rotary member R which is formed avoiding the disc brake D is also limited. This is disadvantageous not only to the layout of the drum brake which is composed of the drum and the brake shoe B, but also to the braking strength. In order to obtain sufficient braking power, the road wheel must be given a larger size.

In Figure 1, W denotes a road wheel A is an axle shaft, and P denotes a pair of pads.

It is therefore an object of the present invention to provide a brake device which can overcome the above-mentioned disadvantages and allows advantageous layout of the braking system and an increase in braking power.

The present invention consists in a drum-indisc type brake arrangement comprising: a rotary member adapted to be rotated with a road wheel, said rotary member having at its inner portion a drum and at its outer portion a disc; a drum brake provided within said drum; a disc brake provided adjacent said disc, said disc brake including a pair of pads disposed, respectively, on opposite sides of said disc; a cylinder fixed on a stationary portion of the road wheel axle casing; a yoke extending to the side of said cylinder and said pair of pads, said yoke being moved upon introduction of a pressurized liquid into said cylinder thereby to press said pads against said disc to exert a brading force.

In the accompanying drawings: Figure 1 is a schematic view in section showing a prior art drum-in-disc type brake device; and Figure 2 shows a cross-section, partly cut away, of a drum-in-disc type brake device according to the present invention.

Referring now to Figure 2, a rear axle shaft 1 is supported by an axle casing 2 or a suspension member (not shown) through a bearing 3, so that the shaft 1 may axially rotate when coupied with a driving system (not shown). A road wheel 4 is integraily flxed.on the front end flange portion 1 a of the rear axle shaft 1, by a hub bolt 5. A rotary member 6 has an inwardly directed portion which is screwed to the flange portion 1 a with the road wheel 4. A disc brake 7 and a drum brake 8 serve as the main disc brake and parking brake in association with the rotary member 6.

The road wheel 4 is composed of a wheel disc 9 and an annular rim 10, which together form a circular space around the rear axle shaft 1. In the space are the middle portion and outer circumferential portion of the rotary member 6.

The rotary member 6 is composed of a drum 11 having an inner circumferential plane positioned parallel to the axis formed on the middle portion, and a disc 12 integral with, and located outside the drum 11. The drum brake 8 is disposed in the drum 11, and the disc brake 7 adjacent the disc 12.

The drum brake 8 is composed of a back plate 1 4 fixed to the axle casing 2 through a bearing cap 13, and an arc-shaped brake shoe 1 5 supported by a pin on the back plate 14, the brake shoe being operatively coupled with a cable extending to a position adjacent the driver's seat. Upon pulling of the cable by means of a lever, the brake shoe 1 5 is pressed against the inner surface of the drum 11 of the rotary member 6, to exert a braking force.

The disc brake 7 is composed of a pair of pads 1 6 and 1 7 disposed, respectively on opposite sides of the disc 12 and a pair of pistons 19 and 20 which move in opposite directions within a hydraulic cylinder 1 8 fixed on the axle casing 2.

One piston 1 9 contacts the back of the inner pad 1 6. A yoke 21 which is fixed to the other piston 20 to move therewith, contacts the back of the outer pad 17, at a position in alignment with the contacting position of the piston 1 9 with the pad 16.

This disc brake 7 is of the type which is normally referred to as a fixed cylinder type with a yoke transfer system, in which the pistons 1 9 and 20 are moved in mutually opposite directions upon introduction of a pressurised liquid into the cylinder 18, the outer piston 1 9 directly pressing the inner pad 1 6 against the inner surface of the disc 12 whilst the inner piston 20 moves the yoke 21 inwardly and presses the outer pad 17 against the exterior surface of the disc 1 2. The friction between the two pads 16 and 17 and the disc 12 brakes the rotation of the rotor 6. With this type of disc brake, the yoke 21 is positioned to the side of the cylinder 18 and pads 16 and 17.Thus, compared with the.conventional structure in which a caliper is installed straddling over the cylinder and pads illustrated in Figure 1, the height (in the horizontal direction) can be reduced by the length'l" (in the actual model, approximateiy 15--20 mm) corresponding to the thickness of a caliper.

Consequently, so far as the disc brake is mounted at a predetermined distance from the road wheel, it is apparent that the diameter of the drum 11 of the rotary member in this illustrated embodiment can be increased by approximately twice the thickness "T" of the caliper, compared with the structure shown in Figure 1 using the drum-in-disc brake. Thus freedom of the drum brake layout is increased, and simultaneously a larger size brake shoe can be used corresponding to the increased drum size, resulting in increased braking power.

As seen from the foregoing, according to the present invention, a yoke transfer type disc brake with a fixed cylinder is employed as the main brake, which enables the diameter increase in the drum of the rotary member, effectively improving freedom in the drum brake layout and the breaking power.

Claims

1. A drum-in-disc type brake arrangement comprising: a rotary member adapted to be rotated with a road wheel, said rotary member having at its inner portion a drum and at its outer portion a disc; a drum brake provided within said drum; a disc brake provided adjacent said disc, said disc brake including a pair of pads disposed, respectively, on opposite sides of said disc; a cylinder fixed on a stationary portion of the road wheel axle casing: a yoke extending to the side of said cylinder and said pair of pads, said yoke being moved upon introduction of a pressurised liquid into said cylinder thereby to press said pads against said disc to exert a brading force.

2. A drum-in-disc type brake arrangement as set forth in Claim 1, wherein said road wheel includes a wheel disc and an annular rim, which together form a circular space around the rear axle shaft on a flange portion of which said road wheel is fixed.

3. A drum-in-disc type brake arrangement as set forth in Claim 1 or 2, wherein said cylinder includes two pistons which are moved in opposite directions upon introduction of the pressurised liquid into said cylinder, one of said pistons directly pressing one of said pads against the inner surface of said disc in one direction whilst the other piston moves said yoke in the opposite direction and presses the other pad against the exterior surface of said disc.

4. A drum-in-disc type brake arrangement substantially as desribed with reference to, and as illustrated in Fig. 2 of the accompanying drawings.