US3811539A — Internal shoe-drum brakes

Claim 1

Independent Claim 210 words

An internal shoe-drum brake comprising a stationary backplate, a rotatable drum, a pair of arcuate shoes carrying friction linings for engagement with said drum mounted on said backplate, said shoes having adjacent actuated ends, an hydraulic actuator for separating said actuated ends for normal service braking, and a lever for separating said actuated ends for parking or emergency braking and acting on one shoe and indirectly on the other shoe, wherein said hydraulic actuator comprises a double-ended hydraulic cylinder fixed on said backplate between said actuated shoe ends, a pair of first and second opposed hydraulic pistons for engagement with said shoes adapted to work in said cylinder and adapted to be urged away from each other to separate said actuated shoe ends for said normal service braking in response to hydraulic fluid under pressure acting on said first and second pistons, and a third piston interposed between said first and second pistons, a pivotal connection being provided between said lever and said third piston whereby said lever acts on said other shoe through said second piston to apply said other shoe to said drum when said lever is moved angularly in a brake applying direction about said pivotal connection with said third piston to act on said one shoe.

Claim 2

Dependent Claim 210 words

An internal shoe-drum brake comprising a stationary backplate, a rotatable drum, a pair of arcuate shoes carrying friction linings for engagement with said drum mounted on said backplate, said shoes having adjacent actuated ends, an hydraulic actuator for separating said actuated ends for normal service braking, and a lever for separating said actuated ends for parking or emergency braking and acting on one shoe and indirectly on the other shoe, wherein said hydraulic actuator comprises a double-ended hydraulic cylinder fixed on said backplate between said actuated shoe ends, a pair of first and second opposed hydraulic pistons for engagement with said shoes adapted to work in said cylinder and adapted to be urged away from each other to separate said actuated shoe ends for said normal service braking in response to hydraulic fluid under pressure acting on said first and second pistons, and a third piston interposed between said first and second pistons, a pivotal connection being provided between said lever and said third piston whereby said lever acts on said other shoe through said second piston to apply said other shoe to said drum when said lever is moved angularly in a brake applying direction about said pivotal connection with said third piston to act on said one shoe.

Claim 3

Dependent Claim 51 words

An internal shoe-drum brake as claimed in claim 1, wherein said third piston is provided with an axial bore in which works said first piston and which is connected to a space in said cylinder between adjacent ends of said third and second pistons through a passage in said third piston.

Claim 4

Dependent Claim 62 words

An internal shoe-drum brake as claimed in claim 1 wherein said first piston and said second piston are substantially equal in area whereby said third piston, which is subjected to a force equal in magnitude to hydraulic pressure acting over an area equal to the difference in areas between said first and second pistons, remains substantially stationary during said normal service braking.

Claim 5

Dependent Claim 39 words

An internal shoe-drum brake as claimed in claim 1, wherein at least one lug directed towards said backplate is provided on said third piston and said lever is pivotally connected to said lug by means of said pivotal connection.

Claim 6

Dependent Claim 23 words

An internal shoe-drum brake as claimed in claim 4, wherein said third piston comprises a one-piece member with which said lug is integral.

Claim 7

Dependent Claim 92 words

An internal shoe-drum brake as claimed in claim 4, wherein said third piston comprises a piston-part adapted to work in said cylinder and having an outer end, an annular slipper within which said outer end is received, and an annular hub member encircling said slipper and carrying said lug said hub member and said slipper being so constructed and arranged as to define a rocking engagement therebetween to enable said lug to engage said backplate whereby said piston-part is subjected only to a component of force acting along the longitudinal axis thereof.

Claim 8

Dependent Claim 77 words

An internal shoe-drum brake as claimed in claim 6, wherein said slipper comprises a sleeve in which said outer end of said piston-part is received and an inwardly directed radial flange engaging with the free end of said piston-part, engaging faces of said sleeve and said hub member being relatively tapered to permit said hub member to tilt with respect to said slipper about a fulcrum defined by the engagement of said hub member with said flange.

Claim 9

Dependent Claim 55 words

An internal shoe-drum brake as claimed in claim 7, wherein said slipper is received in a counterbored recess in said hub member, and said fulcrum comprises a shoulder in said base of the recess lying on the longitudinal axis of said cylinder in a plane parallel with that of said backplate between circumferentially extending regions.

Claim 10

Dependent Claim 63 words

An internal shoe-drum brake as claimed in claim 7, wherein said first piston includes an outwardly directed extension of reduced diameter extending through a bore in said hub member for engagement with said one shoe, and said radial flange defines an aperture of a diameter less than that of said first piston to prevent accidental withdrawal of said first piston from said bore.

Claim 11

Dependent Claim 21 words

An internal shoe-drum brake as claimed in claim 1, incorporating an adjuster for compensating automatically for wear of said friction linings.

Claim 12

Dependent Claim 60 words

An internal shoe-drum brake as claimed in claim 10, wherein said adjuster comprises a thrust member which is rotatable to increase the effective distance between said first and second pistons, a screw-threaded engagement being provided between said thrust member and one piston, and clutch means being disposed between said thrust member and another piston to define a frictional engagement therebetween.

Claim 13

Dependent Claim 64 words

An internal shoe-drum brake as claimed in claim 11, wherein said screw-threaded engagement is provided between said thrust member and said second piston, and said clutch means comprises a thrust ring, a screw-threaded engagement between said thrust member and said thrust ring, a clutch face on said third piston, and spring means for urging said thrUst ring into frictional engagement with said clutch face.

Claim 14

Dependent Claim 45 words

An internal shoe-drum brake as claimed in claim 12, wherein a degree of lost-motion provided in said engagement between said thrust ring and said thrust member defines a minimum braking clearance, and said lost-motion is normally taken up by the action of said spring means.

Claim 15

Dependent Claim 46 words

An internal shoe-drum brake as claimed in claim 12, wherein said spring means comprises a first compression spring acting between said thrust ring and said first piston, and a second stronger compression spring acting between said first piston and an adjacent end of said thrust member.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1977-05-20	1977-11-19	1978-05-21	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1981-05-20	1981-11-19	1982-05-21	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1985-05-20	1985-11-19	1986-05-21	$7700.00	Window Closed / Lapsed

Internal shoe-drum brakes

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