US3807536A

US3807536A - Shoe-drum brakes for vehicles

Info

Publication number: US3807536A
Application number: US00225863A
Authority: US
Inventors: C Newstead; A Wright
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1971-02-15
Filing date: 1972-02-14
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: DE2207050B2; GB1379225A; BR7200854D0; DE2207050A1; JPS5111734B1

Abstract

Adjacent ends of opposed shoes of a shoe-drum brake are actuated to apply the brake by two separate single-ended hydraulic cylinders which are located between the shoe ends with their axes substantially parallel and of which at least one is floatingly supported by the shoes, and the cylinders are connected to separate sources of hydraulic fluid under pressure.

Description

United States Patent 1191 Newstead et al.

[111 3,807,536 1451 Apr. 30, 1974 SHOE-DRUM BRAKES FOR VEHICLES Inventors: Charles Newstead, Walsall; Andrew Charles Walden Wright, Lapworth, both of England Girling Limited, Birmingham, England Filed; Feb, 144 1972 Appl. No; 225,863

Assignee:

Foreign Application Priority Data Feb. 15, l97l Great Britain 4678/71 u.s. Cl. 188/345, 188/363 1m. 01 B60t 11/10 Field of Search 188/345, 106 P, 363, 364,

188/106 A, 106 R; 192/83; 60/54.6 B; 92/61 References Cited UNITED STATES PATENTS 2/1966 Carruth 188/345 8/1971 Miyajima 188/345 8 1956 Sinclair 188/363 x Primary Examiner-George E. A. Halvosa Attorney, Agent, or Firm-Scrivener, Parker, Scrivener & Clarke ABSTRACT Adjacent ends of opposed shoes of a shoe-drum brake are actuated to apply the brake by two separate single ended hydraulic cylinders which are located between the shoe ends with their axes substantially parallel and of which at least one is floatingly supported by the shoes, and the cylinders are connected to separate sources of hydraulic fluid under pressure.

1 Claim, D taw n kiaqre PATENTEDAPR 30 191 3807'. 536

SHEET 1 [IF 2 FIG].

1 SHOE-DRUM BRAKES FOR VEHICLES This invention relates to improvements in shoe-drum brakes and is concerned with hydraulic actuating means for the shoes of such brakes.

The usual actuator is a double-ended hydraulic cylinder in which work two pistons each adapted to engage an end of a shoe, fluid under pressure being fed to the space between the pistons from a pedal-operated master cylinder or other source of pressure fluid.

A serious disadvantage of that arrangement is that in the event of failure of a pipe line leading to the wheel cylinder, or even of a seal in the cylinder, the brake is put out of action.

According to our invention the shoes of a shoe-drum brake are actuated by fluid under pressure supplied from two separate pressure sources to two separate single-ended hydraulic wheel cylinders which are located between the shoes with their axes substantially parallel and of which at least one is floatingly supported by the shoes.

Both cylinders may be floatingly supported by the shoes or one may be fixed to the back-plate of the brake.

With either arrangement the cylinders are preferably displaced in an axial direction relative to one another, the closed end of each cylinder engaging directly, or through a short axial spigot integral with the cylinder, with the web of one shoe, and the web of the other shoe being engaged by a piston-rod of substantial length projecting from the other end of the cylinder.

The two cylinders are preferably arranged reversely or back-to-back, the long piston-rod of one cylinder lying alongside the other cylinder so that the overall transverse dimension of the actuator formed by the two cylinders can be kept to a minimum. This dimension can be reduced by making the long piston-rods of small diameter relative to the diameter of the cylinders to allow a large amount of overlap of the cylinders.

The cylinders can be arranged with their axes in parallel horizontal, vertical or inclined planes as required by the design of the rest of the brake.

The two-sources of pressure fluid may conveniently be the two pressure spaces of a tandem master cylinder so that normally fluid is fed to both wheel cylinders at the same pressure. Alternatively the two pressure sources may be two separate master cylinders operated simultaneously or independently.

If the pipe line to either wheel cylinder should fail or- As the wheel cylinders operate independently the volume of fluid required to apply the brake by either cylinder is not affected by failure of the other so that there is no additional pedal travel, and no need for a master cylinder of more than normal size.

Slots of substantial axial length are formed in the outer ends of the spigot and piston-rod of each cylinder to receive inwardly projecting lugs on the shoe webs, the lengths of the slots preferably being greater than the maximum permissible outward movement of the adjacent shoe end. This avoids any risk of a floating cylinder becoming disengaged from the shoes due to wear of the shoe linings.

One practical design of brake embodying hydraulic actuating mechanism with two floating wheel cylinders 2 in accordance with our invention is ilustrated by way of example in the accompanying drawings in which: I

FIG. 1 is an end elevation with one half in section;

FIG. 2 is a vertical section on the line 2-2 of FlG. l; and

F l0. 3 is a section of the actuator on the line 33 of .FIG. 1.

The brake illustrated is of the well-known duo-servo type. Arcuate shoes 1, 2 provided with friction linings 3 are articulated together at one end by a strut 4 of which the effective length is automatically adjusted as the shoe linings wear by known mechanism indicated generally at 5. 1

When the brake is applied the shoes tend to be carried round with the brake drum and one or other of the shoes, according to the direction of rotation of the drum, anchors on a torque-taking pin 6 fixed in the sta tionaryback-plate 7 of the brake. The shoes ean be applied mechanically for parking by a hand brake actuating a cable 8 which is brought in through an opening in the back-plate and over a rocking quadrant 9 'to a cam 10 located between the shoe ends.-

The shoes are applied hydraulically for normal service braking by fluid under pressure supplied from separate sources to two single-

endedwheel cylinders

11 and 12 floatingly supported between

lugs

13, 14 pro jecting inwardly from the webs of the shoes adjacent to the ends co-operating with the pin 6. The axes of the two cylinders are parallel to the back-plate.

Working in each cylinder is a piston 15 sealed by a 'lip seal 16 and an O ring 17 housed in an annular grooye in the cylinder bore. The piston may have an extension 18 at the end nearest the closed end of the cylinder to prevent tilting of the piston.

An axial spigot 19 projecting from the closed end of the cylinder 1 1 has in its free end a slot of substantial axial length which receives a portion of the mg 13 on the shoe 1 within a notch in the lug, A piston-rod 20 extends from the other end of the cylinder and has a simi= lar Slotted engagement with the lug 14 on the shoe 26 The other cylinder 12 is of identical construction but i is reversed, the spigot 21 on the closed end of that c'ylinder engaging with the lug 14 on the shoe 2 while the piston-rod 22 engages with the lug l3 on'the shoe 1 As will be appreciated from HO. 1 the piston-rod of each cylinder is in vertical alignment with the other cylinder.

A spring 23 may be located in each cylinder between the piston and the closed end of the cylinder to urge the cylinder and piston-rod into engagement with the lugs on the shoes.

Fluid under pressure is supplied from separate sources through flexible pipes connected to union sockets 24 from which passages lead to the pressure spaces in the cylinders.

ln a modification of the actuating means described above only one of the cylinders is floatingly supported between the shoe ends and the other is fixed to the Stationary back-plate of the brake.

The parallel disposition of the cylinders and their axial displacement relative to one another can remain the same.

An advantage of a floating single-ended cylinder is that it applies equal forces to the two shoes between which it is supported. If one cylinder is fixed the force and piston assemblies of which at least one is floatingly supported by the shoes, and one end of each cylinder engages the web of one shoe and the web of the other shoe is engaged by a piston-rod of substantial length projecting from the other end of the cylinder. theassemblies being reversely arranged with the piston-rod of one assembly alongside the cylinder of the other assembly and with the cylinders being constructed and arranged to radially overlap so that the overall radial dimension of the two actuators is kept to a minimum.

Claims

1. An internal shoe drum brake comprising a backplate, a rotatable drum, arcuate shoes each including a web mounted on said back-plate and carrying friction linings for engagement with said drum, and two separate radially displaced hydraulic actuators both located between adjacent shoe ends and connected to separate sources of hydraulic fluid under pressure, wherein said hydraulic actuators comprise single-ended cylinders and piston assemblies of which at least one is floatingly supported by the shoes, aNd one end of each cylinder engages the web of one shoe and the web of the other shoe is engaged by a piston-rod of substantial length projecting from the other end of the cylinder, the assemblies being reversely arranged with the piston-rod of one assembly alongside the cylinder of the other assembly and with the cylinders being constructed and arranged to radially overlap so that the overall radial dimension of the two actuators is kept to a minimum.