GB2074263A

GB2074263A - Internal Shoe Drum Brake Apparatus

Info

Publication number: GB2074263A
Application number: GB8111002A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1980-04-14
Filing date: 1981-04-08
Publication date: 1981-10-28
Also published as: DE3114920A1; FR2480379A1; JPS56147931A

Abstract

An internal shoe drum brake apparatus comprises a pair of brake shoes (11, 12), slidably engaged with an anchor (15) mounted on back plate (16) between two adjacent first ends of the shoes, a first brake actuating device (19) placed between the two adjacent second ends of the brake shoes (11, 12) and slidably mounted on back plate (16) and a second brake shoe actuating device (40, 44) comprising a lever (40) and a strut (44) which lever is pivotable to cause separation of the shoes (11, 12) and to cause the device (19) to slide in a direction to transmit movement of one shoe (e.g. 11) to the other shoe (e.g. 12). The device (19) comprises a double-ended hydraulic cylinder with pistons (24, 25) separable for service braking, the brake acting as a primary- secondary shoe brake: For parking braking, with drum (10) rotating in direction A, lever (40) is pivoted by cable (42) - brake shoes (11, 12) are moved outwardly and the reaction force of shoe (11) is transmitted to wheel cylinder (19) by piston (24), shoulder (27) thereof abutting cylinder body (23), and cylinder body (23) is slidably moved to transmit an additional braking force to shoe (12) - the brake acts as a uniform brake. <IMAGE>

Description

SPECIFACTION Internal Shoe Drum Brake Apparatus This invention relates to an internal shoe drum type brake apparatus for a rotating member, such as a wheel of a vehicle, which can serve as both a primary-secondary shoe brake and a uniform shoe application brake.

Drum brakes with a pair of brake shoes are typically of two different types, one of which is the primary-secondary shoe type and the other is the uniform type, wherein both brake shoes are applied uniformly. When a drum brake is used on a vehicle, especially on its rear wheels, the primary-secondary shoe brake is more suited for a service brake which is usually operated by depressing a foot brake pedal, in terms of braking force distribution, whereas the uniform brake is more suited for a hand brake lever operated parking brake because of the extral braking force thereof.

Since conventional drum brakes of the primary-secondary shoe type with a parking brake mechanism included always operate as primarysecondary shoe brakes, they have a tendency to provide insufficient braking power for parking.

Thus the brakes may need to be made larger or be used with another brake to supplement the braking power for parking.

It is an object of this invention to provide a drum brake apparatus with a parking brake mechanism which produces adequate braking power for parking, without reducing its performance for service braking.

It is another object of this invention to provide a drum brake apparatus which has a relatively simple construction and which produces adequate braking power for parking, without reducing its performance for service braking.

This invention provides an internal shoe drum type brake apparatus, including a brake drum and two brake shoes which are positioned inside the drum in a manner to controllably engage the drum. An anchor is mounted on 9 stationary back plate and is positioned between respective adjacent first ends of the brake shoes in a manner to permit the brake shoe first ends to slide in a radial direction thereagainst. A firstbrake actuating device is positioned between the respective adjacent second ends of the brake shoes and is mounted on the stationary back plate in a manner to slide in the direction of actuating the brake shoes.A second brake actuating device is mounted on the brake shoes and has a lever pivotally mounted on the first brake shoe and a strut, which is connected at a first end thereof to the first brake shoe and to the lever, and at the second end thereof on the second brake shoe.

The brake shoes engage the brake drum as those of a primary-secondary shoe brake when the first brake actuating device is operated to separate the brake shoes. When the second brake actuating device is operated, the brake shoes engage the brake drum as those of an uniform brake when the lever is pivoted with respect to the first brake shoe to separate the brake shoes.

In the accompanying drawings:- Figure 1 is a diagrammatic sectional view of a preferred embodiment of a drum brake apparatus according to this invention; Fig. 2 is a diagrammatic sectional view taken along the line 2-2 in Fig. 1; and Fig. 3 is a diagrammatic sectional view taken along the ling 3-3 in Fig. 1.

Referring now to Fig. 1, there is shown a drum brake apparatus for vehicles which includes a brake drum 10 and a pair of brake shoes 11,12.

Each of the brake shoes has a curved outer face corresponding to the inner face of the drum 10 with respective. linings 13 and 14 on the outer face thereof. These brake shoes 11, 12 are placed inside the drum 10 in such a manner that the linings 13, 14 face the inner face of the drum 10.

An anchor 15 is'disposed between the upper ends of the shoes 11, 12 so as to form slidable engagements with the ends as described hereinafter, and is fixed to a stationary back plate 1 6 by pins 17, 18. A wheel cylinder 19 of the double ended hydraulic type is disposed between the lower ends of the shoes 11, 1 2 to force the ends outward, and is mounted slidably on the backing plate 1 6 as described hereinafter.

The upper ends of the shoes 11, 12 are urged towards the anchor 1 5 by a coil spring 20 whose ends are secured to those ends of the shoes. The lower ends of the shoes 11, 12 are also urged toward the wheel. cylinder 19 by a U-shaped return spring 21 whose ends are secured to the shoes near their lower ends, and whose center is held by a retainer 22 is fixed about the anchor 15.

The brake shoes 11, 12 are forced outwardly against the spring 21 as the wheel cylinder 19 is actuated, and are forced inwardly by the return force of the spring 21 as the actuation of the cylinder is stopped.

The wheel cylinder 1 9 includes a cylinder body 23, a pair of pistons 24, 25 disposed slidably in the body, and a pressure chamber 26 within the body, defined by the ends of the pistons and the inside of the body. The pistons 24, 25 abut against the lower ends of the shoes 11, 12 respectively at their outer ends, and have annular shoulders 27, 28 respectively on their outer ends to engage the outer ends of the body when the pistons move inwardly to their rest positions. The pistons 24, 25 also have dust boots 24a, 25a respectively on their outer ends and projections 29, 30, respectively on their inner ends, contacting each other when the pistons move inwardly to their rest positions, and further have annular piston seals or caps 31, 32 respectively on their inner ends.The pressure chamber 26 communicates with a brake master cylinder 33, which is operated by depressing a foot brake pedal 34 in the driver's compartment of the vehicle, through a line 35. The pistons 24, 25 move in accordance with the pressure of the working fluid in the chamber 26 supplied from the master cylinder 33 via the line 35, and they force the lower ends of the shoes 11, 12 outwardly as the foot pedal 34 is depressed.

One end of a lever 40 is pivoted to the shoe 12 at a pin 41, at a position between its upper end and its center, preferably adjacent its upper end. A cable 42 is attached to the free end of the lever 40 and is guided by a guide 42a. The cable 42 extends out of the back plate 16 through a hole 42b and is connected in turn to a hand brake lever 43 in the driver's compartment of the vehicle. One end of a strut 44 engages both the lever 40 at an intermediate position thereof preferably nearer to the pivoted end, and the brake shoe 12 at a position near its upper end, through an engagement 45, and the other end of the strut 44 engages the other brake shoe 11 at a similar position near its upper end. Anti-rattle devices 46, 47 are attached to the brake shoes 11, 12 respectively at their centers to retain the brake shoes on the back plate, in the customary manner.

Fig. 2 shows the slidable engagement between the ends of the brake shoes 11, 12 and the anchor 15. The anchor 15 includes an outer plate 50 and a spacer member 51 sandwiched between the plate 50 and the back plate 16 in such a manner that radially extending grooves 52a, 52b are formed at the ends of the anchor 15.

The plate 50 and the member 51 are fixed together to the back plate 16 by the pins 17, 18.

The spacer member 51 is slightly thicker than the section of the brake shoe that fits into the grooves 52a, 52b, so that when the ends of the brake shoes 11, 12 are fitted into the grooves 52a, 52h to form the slidable engagements with the anchor 15, the shoes are permitted to freely move outward and away from the anchor 15.

Fig. 3 shows a mechanism allowing the wheel cylinder 1 9 to slide in the direction of its actuation. The sliding mechanism includes an extension 60 of the cylinder body 23 with a head 61, and the back plate 16 having a hole 62 which extends in the direction of movement of the pistons 24, 25. The extension 60 is inserted through the hole 62 so that the cylinder body 23 can slide in phe direction of movement of the pistons 24, 25. A stopper plate 63 is provided between the head 61 and the back plate 16 to prevent the cylinder body 23 falling out of the backing plate 16.

This drum brake apparatus operates as follows: When the foot brake pedal 34 is depressed for service braking, the pistons 24, 25 move outward in accordance with the pressure of the working fluid in the chamber 26 supplied from the master cylinder 33, forcing the lower ends of the brake shoes 11, 12 outwardly. Consequently, the brake shoes 11, 12 press the linings 13, 14 against the inner face of the brake drum 10, reducing the rotational speed of the drum 10 by the friction force exerted upon it. Thus, the brake shoe 12 serves as a primary shoe and the brake shoe 11 as a secondary shoe when the brake drum 10 rotates in the direction of the arrow A in Fig. 1 and the vehicle is moving forward.Similarly, the brake shoe 12 serves as a secondary shoe and the brake shoe 11 as a primary shoe when the vehicle reverses and the drum 10 rotates in the opposite direction .Therefore, the brake apparatus operates as a drum brake of the primary-secondary shoe type which reduces the speed of the drum 10 smoothly when the wheel cylinder 19 is operated by depressing the pedal 34.

On the other hand, when the hand brake lever 43 is moved to pull the cable 42 for parking braking, the lever 40 turns clockwise, moving the strut 44, and thus the upper end of the brake shoe 11, toward the inner face of the drum 10, pressing the lining 13 against the inner face of the drum 10. At the same time, the lever 40 turns about the fulcrum formed by the engagement 45 and moves the upper end of the brake shoe 12 outwardly, pressing the lining 14 against the inner face of the drum 10.

The reaction force of braking exerted on the brake shoe 11 is transmitted to the wheel cylinder 1 9 as a force pressing against the piston 24 in the cylinder body 23, provided that the drum 10 is rotating in the direction of the arrow A. This causes the shoulder 27 of the piston 24 to abut the lefthand end of the body 23, forcing the cylinder body 23 to the right. After the right-hand end of the body 23 touches the shoulder 28 of the piston 25, the cylinder body 23 moves the lower end of the shoe 12 outward, pressing the lining 14 against the inner face of the drum 10.Thus, the reaction force exerted on the brake shoe 11 is transmitted to the lower end of the brake shoe 12 as an additional braking force on the other shoe 12, so that the brake shoes 11, 12 both serve as primary shoes, and uniform-action is produced in the brake apparatus when the hand brake lever 43 is operated to turn the lever 40 clockwise, i.e.

towards the strut 44. Therefore, the brake apparatus serves as a drum brake of the uniform type, producing extra braking force when the lever 40 is turned clockwise. The resultant force exerted on the brake shoe 12 is borne finally by the anchor 1 5. The brake shoes 11, 12 exchange their functions when the drum 10 rotates in the opposite direction. Thus, the lever 40, and the strut 44 constitute a brake shoe actuating device for causing the pair of the brake shoes 11, 12 to serve as those of a uniform brake.

Those skilled in the art will readily appreciate that the shoulder 27, 28 function to shift the cylinder body 23 within the elongate slot 62, while simultaneously retaining the piston seals 31, 32 in their respective "working areas" (the distance the seals move within the cylinder during normal service braking) within the cylinder body.

In this way, the brake cylinder 1 9 slides to transmit the braking force of the hand brake between the two shoes 11, 12 as opposed to this distance being effected by the piston seals 31, 32 sliding beyond their working areas. Accordingly, the life of the piston seals is extended.

Claims

1. An internal shoe drum type brake apparatus, comprising: a) a brake drum; b) first and second brake shoes positioned inside said brake drum in a manner to controllably engage said brake drum; c) an anchor mounted on a stationary back plate and positioned between respective adjacent first ends of said brake shoes in a manner to permit first ends of said brake shoe to slid in a radial direction thereagainst; d) a first brake actuating device positioned between the respective adjacent second ends of said brake shoes, said first actuating device being mounted on the stationary back plate in a manner to slide in the direction of actuating said brake shoes; e) a second brake actuating device mounted on said brake shoes, said second actuating device comprising: 1) a lever pivotally mounted on said first brake shoe; and 2) a strut connected at a first end thereof to said first brake shoe and to said lever, and at the second end thereof to said second brake shoe, whereby pivoting said lever with respect to said first brake shoe causes said brake shoes to separate and engage said brake drum, and causes said first brake actuating device to slide in the direction to transmit the movement of one of said brake shoes to the other of said brake shoes.

2. An internal shoe drum type brake apparatus as set forth in claim 1 , wherein said first brake actuating device comprises a double-ended hydraulic cylinder having two pistons therein which separate axially under hydraulic pressure, each of said pistons having an annular shoulder for engaging a respective end of said doubleended hydraulic cylinder for urging said cylinder and pistons in an axial direction toward either of said brake shoes for actuating same.

3. An internal shoe drum type brake apparatus as set forth in claim 1, further comprising a hand brake lever and a cable connected between said hand brake lever and the free end of the lever of the second brake actuating device whereby said device is operated by moving said hand brake lever.

4. An internal shoe drum type brake apparatus as set forth in claim 2, further comprising a foot brake pedal and a hydraulic cylinder actuated through said pedal to supply working fluid into said hydraulic cylinder, whereby said hydraulic cylinder is operated by depressing said foot brake pedal.

5. An internal shoe drum type brake apparatus substantially as described with reference to, and as illustrated in, the accompanying drawings.