Dual-mode drum brake assembly having provision for preventing disengagement of members to be mutually engaged

A dual-mode drum brake assembly for a vehicle, comprising:

• a backing plate which is fixed to a body of the vehicle;
• first and second arcuate brake shoes which are disposed, substantially symmetrically with each other, on said backing plate such that said first and second arcuate brake shoes are movable toward and away from each other, said first and second arcuate brake shoes having a first pair of adjacent end portions each of which is provided by one of opposite end portions of a corresponding one of said first and second arcuate brake shoes and each of which is held by an anchor disposed on said backing plate, said first and second arcuate brake shoes further having a second pair of adjacent end portions each of which is provided by the other of said opposite end portions of a corresponding one of said first and second arcuate brake shoes;
• an actuator which is disposed on said backing plate such that said actuator is positioned between said second pair of adjacent end portions of said first and second arcuate brake shoes, and which is operable to move said second pair of adjacent end portions away from each other so as to force said arcuate brake shoes against a brake drum rotatable with a wheel of the vehicle so that the dual-mode drum brake assembly acts as a leading/trailing drum brake for generating a braking force for braking the wheel;
• an intermediate lever which is disposed substantially along said first arcuate brake shoe and which has an intermediate portion connected to an intermediate portion of a web of said first arcuate brake shoe such that said intermediate lever is pivotable relative to said web about a pivot axis that is substantially perpendicular to said backing plate, said web being provided by a flat plate portion of said first arcuate brake shoe which portion is substantially parallel to said backing plate;
• a second strut which is associated at opposite end portions thereof with a first end portion of said intermediate lever and said second arcuate brake shoe, said second strut being connected to said second arcuate brake shoe through a connecting pin which is received in a through-hole formed through said second strut and which is substantially perpendicular to said backing plate, such that said second strut is pivotable relative to said second arcuate brake shoe about an axis of said connecting pin;
• a positioning spring which positions said intermediate lever and said second strut in respective predetermined positions in which said intermediate lever and said second strut are held in engagement at respective engaging portions thereof with each other with said engaging portions lying on a plane that is tangent to said web, said engaging portions being provided by said first end portion of said intermediate lever and one of said opposite end portions of said second strut;
• a first strut which is engaged with one of said second arcuate brake shoe and a second end portion of said intermediate lever, said second end portion being located on one of opposite sides of said pivot axis which one is remote from said first end portion of said intermediate lever;
• and
• a parking lever which is engaged with the other of said second arcuate brake shoe and said second end portion of said intermediate lever, said parking lever being operable to be pivoted so as to be brought into engagement with said first strut whereby said first and second arcuate brake shoes are moved away from each other by a link mechanism constituted by said first and second struts and said intermediate lever, so that the dual-mode drum brake assembly acts as a duo-servo brake for generating a braking force for braking the wheel;
• wherein said through-hole in which said connecting pin is received is formed by using a punch and a die in a hole-forming punching operation, and
• wherein said second strut is positioned relative to a web of said second arcuate brake shoe which is provided by a flat plate portion of said second arcuate brake shoe substantially parallel to said backing plate, such that one of opposite surfaces of said second strut which has been set to be opposed to the punch in the hole-forming punching operation is remote from said web of said second arcuate brake shoe while the other of said opposite surfaces of said second strut which has been set to be opposed to the die in the hole-forming punching operation is opposed to said web of said second arcuate brake shoe, so that a portion of said through-hole having a relatively large diameter is closer to said web of said second arcuate brake shoe than a portion of said through-hole having a relatively small diameter.

A dual-mode drum brake assembly for a vehicle, comprising:

• a backing plate which is fixed to a body of the vehicle;
• first and second arcuate brake shoes which are disposed, substantially symmetrically with each other, on said backing plate such that said first and second arcuate brake shoes are movable toward and away from each other, said first and second arcuate brake shoes having a first pair of adjacent end portions each of which is provided by one of opposite end portions of a corresponding one of said first and second arcuate brake shoes and each of which is held by an anchor disposed on said backing plate, said first and second arcuate brake shoes further having a second pair of adjacent end portions each of which is provided by the other of said opposite end portions of a corresponding one of said first and second arcuate brake shoes;
• an actuator which is disposed on said backing plate such that said actuator is positioned between said second pair of adjacent end portions of said first and second arcuate brake shoes, and which is operable to move said second pair of adjacent end portions away from each other so as to force said arcuate brake shoes against a brake drum rotatable with a wheel of the vehicle so that the dual-mode drum brake assembly acts as a leading/trailing drum brake for generating a braking force for braking the wheel;
• an intermediate lever which is disposed substantially along said first arcuate brake shoe and which has an intermediate portion connected to an intermediate portion of a web of said first arcuate brake shoe such that said intermediate lever is pivotable relative to said web about a pivot axis that is substantially perpendicular to said backing plate, said web being provided by a flat plate portion of said first arcuate brake shoe which portion is substantially parallel to said backing plate;
• a second strut which is associated at opposite end portions thereof with a first end portion of said intermediate lever and said second arcuate brake shoe, said second strut being connected to said second arcuate brake shoe through a connecting pin which is received in a through-hole formed through said second strut and which is substantially perpendicular to said backing plate, such that said second strut is pivotable relative to said second arcuate brake shoe about an axis of said connecting pin;
• a positioning spring which is associated at opposite end portions thereof with said intermediate lever and said connecting pin, and which forces said intermediate lever and said second strut toward each other so as to position said intermediate lever and said second strut in respective predetermined positions in which said intermediate lever and said second strut are held in engagement at respective engaging portions thereof with each other, said engaging portions being provided by said first end portion of said intermediate lever and one of said opposite end portions of said second strut;
• a first strut which is engaged with one of said second arcuate brake shoe and a second end portion of said intermediate lever, said second end portion being located on one of opposite sides of said pivot axis which one is remote from said first end portion of said intermediate lever;
• and
• a parking lever which is engaged with the other of said second arcuate brake shoe and said second end portion of said intermediate lever, said parking lever being operable to be pivoted so as to be brought into engagement with said first strut whereby said first and second arcuate brake shoes are moved away from each other by a link mechanism constituted by said first and second struts and said intermediate lever, so that the dual-mode drum brake assembly acts as a duo-servo brake for generating a braking force for braking the wheel;
• wherein said connecting pin has a circumferential groove formed in an outer circumferential surface of an axial end portion thereof which projects from said through-hole;
• and
• wherein one of said opposite end portions of said positioning spring is received in said circumferential groove of said connecting pin such that said one of said opposite end portions of said positioning spring is wound more than 180° about an axis of said connecting pin.