US2340464A - Brake - Google Patents

Description

Feb. 1, 1944. GATES 2,340,464

BRAKE Filed March 20, 1941 2 Sheets- Shee't 1 ATTORNEY Feb. 1, 1944. GATES 2,340,464

. BRAKE Filed March 20, 1941 2 Sheets-Sheet 2 I um Patented Feb. 1, 1944 BRAKE Geoffrey Robert Greenbergh Gates, Leamington Spa, England, assignor to Automotive Products Company Limited, Leamington Spa, England Application March 20, 1941, Serial No. 384,409 In Great Britain April 5, 1940 2 Claims.

This invention relates to internal shoe brakes of the type comprising two substantially rigid arcuate shoes pivotally mounted on a common anchorage abutment oron adjacent abutments, and a spreading device between the un-anchored ends of the shoes. In brakes of this type, one of the shoes, when applied to the drum, tends to be urged more firmly into engagement with the drum by the rotation of the latter, and is commonly referred to as the leading shoe, whilst the other shoe, commonly referred'to as the trailing shoe, tends to be urged away from thedrum by the rotation of the latter, the leading shoe being that shoe along which a point on the drum surface travels from the spreading device to the anchored end. The brake, according to the present invention, is intended for use on a motor road vehicle which travels almost exclusively in one direction, being only occasionally driven in the reverse direction, and the brake shoes which are referred to herein as the leading shoe and trailing shoe respectively are those which act in those capacities when the vehicle is travelling in its normal direction.

The principal object of the invention is to provide an improved means of adjusting the shoes of a brake of the type referred to, to compensate for wear of the friction surfaces.

According to the invention, the spreading device, which is mounted for longitudinal sliding movement between the shoe ends, forms a rigid spacer for said shoe ends when the brake is not applied, and an adjusting means is provided for moving the trailing shoe outwardly into contact with the drum, the said shoe being subsequently spaced from the drum to a small extent by the distortion of the drum when the brakes are applied with the vehicle in motion, thus moving the spreading device towards the leading shoe to centralize the shoes in the drum.

prise a plunger and cylinder unit capable of angular movement in the plane of the brake shoes, and pivotally engaged with the leading shoe.

The invention is hereinafter described with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a brake according to the invention;

Figure 2 is a view corresponding to Figure 1, but on a larger scale, and with certain parts in section; I

Figure 3 is a section on the line 3--3 of Figure 2; and

- Figures 4 and 5 are diagrams showing how the brake shoes are centralized by the drum distortion.

Referring to Figures 1 to 3, a brake, the drum of which rotates normallyin a clockwise direction, comprises a pair of shoes ill, I I mounted on separate anchor pins l2, IS on a back plate l4 and a liquid pressure wheel cylinder l5 mounted on the back plate between the un-anchored ends of the shoes. The shoe Ill is normally the trailing shoe, and the shoe II the leading shoe. The wheel cylinder 15 is formed with a spigot [6 projecting in a direction perpendicular to its bore H, which spigot passes through a hole H3 in the back plate and is retained in position by a spring ring 20 between which and the back plate is awasher 2| of friction material. The hole I8 through which the spigot passes is elongated in the direction of the axis of the wheel cylinder l5, so that the latter is capable of both rotary and translational movement, such movement being resisted to a slight degree by the friction between the washer 2| and the back plate. In the cylinder 15 are mounted two opposed pistons 22 and According to another aspect of the invention,

the spreading device, which is mounted for longitudinal sliding movement between the shoe ends, forms a rigid spacer for the said shoe ends when the brake is not applied, and an adjusting means is provided which acts on the leading shoe, and, through the spreading device, on the trailing shoe, to move both shoes outwardly into contact with the drum, the leading shoe being then spaced from the drum by reverse movement of the adjuster, and the shoes being centred by the distortion of the drum when the brakes are applied with the vehicle moving in a forward direction.

The adjusting device may be disposed between the spreading device and one of the shoes, and the spreading device may be a fluid pressure wheel cylinder. The Wheel cylinder may comprise an open ended cylinder in which operate opposed plungers whose movement into the cylinder is limited. The spreading device may com- 23 provided with suitable fluid-tight packings '24. The piston 22 which acts on the trailing shoe I0, is solid, and is formed at its outer end with'an, annular flange 25 adapted to engage with the end of the cylinder l5 and limit the movement of the piston into' the cylinder. The outer end surface 26 of the piston is fiat, and is engaged by the arcuate edge of a projection 21 formed on the web of the trailing shoe Ill. The second piston 23 is deeply recessed from its outer end at 28 to receive the threaded end of an adjusting plunger 30 threaded into the base of a cap 3| fitting slidably over the end of the wheel cylinder IS, the base of the cap 3| being adapted to engage both the end of the cylinder, l5 and the end of the piston 23. The outer end of the adjusting plunger 3!! is enlarged to form a head 32, and is slotted at 33 to embrace a projection 34 on the leading shoe web similar to the projection 21 on the trailing shoe, the base of the slot 33- being of concave arcuate form to correspond to the shape of the projection 34. The plunger 30 is thus restrained against rotation by the web of the shoe.- The edge of the cap 3| is turned outwardly, and formed with a series of notches 35 to co-operate withaspring finger36 mounted on the cylinder, ithecap being rotatable on the cylinder by engaging a tool in the notches 35, but

being held against free rotation by the spring two pistons 22 and 23, the piston 22 associated with the trailing shoe l acting directly on that shoe, whilst the piston 23 associated with the leading shoe applies an outward thrust to the cap 3 "such thrust being transmitted through the adjusting plunger {39 to the shoe H.

The arcua'te slot 33 on the plunger 30, by its engagement withthe projection't lon the leading shoe I'l,-causes the wheel-cylinder 1 5 to follow the movements of the leading shoe, the centre of curvature of the projection 34 remaining always on the longitudinal axis of the wheel cylinder [5, which axis thus tends to turn slightlyabout the mounting spigot 16 of the cylinder as the shoe It moves. The pressure is thus always transmitted to the leading shoe along the longitudinal axis or the cylinder, and no side loads are applied to the piston 23.

As the piston 22 is flanged at 25 to engage one end of the wheel cylinder, and the cap 3! .in which the adjusting plunger 301'is mounted engages the' other end of the wheel "cylinder, the cylinder, when "the brakes are off, forms a rigid ispacer for the 1511085 and limits their .movement :away from the drum. The location of the shoes is thus dependent on the 'position of the wheel cylinder.

Adjustment of the shoes 'to reduce the clearance between the linings and the drum when the former have worn .down is effected by rotating the :cap 131' cn'th'e "wheel cylinder, .to cause the adjusting plunger 3!! "threaded'thereinto to move outwardly. ESuch outward rmovement first ofiallebrings the leadingshoerl i into contact with the 'drum 38, and then causes :the cylinder to movein the opposite direction, taking withit the trailing :ShLOE'IJiStOIl 22, the vflange of which remains in engagement with the end of the wheel cylindenuntil the'trailing shoe Ill also engages the drum 138. The adjusting plunger is then withdrawnslightly by rotating the cap 3i in the reverse :direction to provide a :slight clearance between the leadingzshoe H and the drum 38, the cylinder 15 being held in its new position by the friction between the washer El and the back plate, so thatthe trailingshoe Hi remains in contact with the drum. The vehicle is then set in motion :in the forward direction, and pressure applied to the :pistons Hand 23 in the wheel cylinder. As the trailingshoe is alreadyiin contact with the drum,-1only the piston .23 is moved outwardly, and the distortion of the drum due to the :greater pressure :of the leading shoe 'li causes the end of the trailing shoe 10 adjacent the wheel cylinder to move inwardly, thus mov-- ing the wheel cylinder 15 slightly in the direction-oi the rleadingishoe to distribute thecleararise :between the two shoes. It has been found that, with :a brake comprising a leading and a trailing shoe :the drum tends to distort during braheapplication to a somewhat elliptical form, with its major axis through the drum centre and the Tapproximate :centres of the shoes, and its minor axis :spiaced slightly from the true drum centre towards the leading shoe. This distortion is shown by the .lfull-line .position of the drum in Eigure 5, which .is of course much exaggerated, and by comparison with Figure 4 it can .be seen that the trailing shoe I0 is in substantially the same position when engaged with the distorted drum as when free with the drum concentric withthe back plate.

tained at the trailing shoe tip is of course equal The clearance obto theiiisp'lacementof the drum due to distortion at this point, and proper centralization of the shoes "-is obt'ain'ed by slacking back the adjuster, after both shoes have touched the drum, until the leading shoe tip clearance is twice that given at the trailing shoe tip by the drum distortion. The trailing .shoe, having :been in engagement with the drum whilst the latter was undistorted, will have tits end nearer to :the wheel cylinder moved inwardly when, :owing to the zapplication of the -b1takes,1the drum is distorted, :thus 'producing the sslig'ht :movement of the wheel cylinder required to centralize the shoes.

A thin metal cap ;39 extending :over the :wall of the -;cylinder 15 is attached to the piston 22 operating-the :trailing shoe,to' prevent the entry of dust and water into the cylinder.

WhatI claim .is:

1. In a brake :having a trailing shoe :and -'a leading .shoe, :a "spreading :device which is frictionally mounted for longitudinal sliding .movement and for angular 'movement :between the shoe endsand which Lforms a rigid spacer for said shoe ends when the brake is not :applied, said spreading device comprising an :open-ended fluid pressure wheel cylinderhaving opposed p-lungersv operating therein and having means for limiting the inward movement of the plungers, and adjustingmeansat one end ;of the spreading device and pivotally engaged by the end .01" the leading shoe and operable for moving the trailing shoe outwardly into contact with .the drum, the said shoe being subsequently spaced :from the drum to a small-extent by the distortion ,of the :drum when the brakes are applied with the vehicle in motion, thus moving thelspreading device toward the leading .shoe to centralize the shoes in the drum, said adjusting means comprising a screwed plunger pivotally engaged by the end of the leading shoe .and :adjustablerelatively to one of the wheel cylinder plungers and threaded into a cap engaging the end of the wheel cylinder, said cap being adapted to beengaged on its inner face by the 'wheel cylinderplunger.

2. Ina brake having atrailingshoeand a leading shoe, a spreading device which comprises a plunger and cylinder unit frictionally movably mounted and capable of angular movement in the plane of the brake shoes and which is mounted for longitudinal sliding movement between the shoe ends, said spreading device forming a rigid spacer for said shoe ends when 'the brake is not applied and pivotally engaging .the leading shoe, and an adjusting means associated with the sliding device which :is pivotally engaged by the end of the leading shoe and which acts on the leading shoe and through the spreading device on the trailing shoe to move .both shoes outwardlyzinto contact with the drum, the leading shoe being then spaced from the drum by reverse movement of the adjuster, and the shoes being centered by the distortion ofthedrumwhen the brakes .are applied with the vehicle moving ina forward direction.

eEoFE-REY ROBERT GREENE; ERGI-I GATES.

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