Brakes – Wheel – Transversely movable
Reexamination Certificate
1998-06-12
2002-03-12
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Transversely movable
C188S25000B, C188S25000B, C188S10600P
Reexamination Certificate
active
06354411
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a drum brake device enabling a smooth return of the brake shoe when the parking brake is released.
A drum brake device that functions as a leading-trailing (LT) type when the service brake is applied and as a duo-servo (DS) type when the parking brake is applied has been disclosed in U.S. Pat. No. 5,275,260 and Australian Patent No. AU-BI-53 491/79.
This device is explained with reference to FIG.
8
. The wheel cylinder b and the anchor block c, are provided on the upper and lower parts of the back plate a. The upper and lower ends of a pair of brake shoes d, e engage the wheel cylinder b and the anchor block c, respectively.
Shoe return springs f, g, extend between the upper ends of the brake shoes d, e and between the lower ends of the brake shoes d, e, respectively. A parking brake lever h is pivotably provided at the lower part of the brake shoe d at the left side. The central region of a pivot lever i is pivoted so as to swing on the central region of the brake shoe e at the right side. A rod j bridges between the brake shoes d and e adjacent to the anchor block c. The left end of the rod j engages with the brake shoe d and the parking lever h while the right end of the rod j engages with the lower ends of the brake shoe e and the pivot lever i.
A screw type shoe clearance adjustment device k is provided between the brake shoes d and e adjacent to the wheel cylinder. The left end of the shoe clearance adjustment device k engages with the brake shoe d while the right end engages with the upper parts of the brake shoe e and the pivot lever i.
The above-explained drum brake device functions as a LT type brake where both brake shoes d, e spread open with the point of abutment with the anchor block c as the fulcrum when the wheel cylinder b operates to activate the service brake.
When the parking brake is operated, the rotating force of the parking lever h is transmitted to the rod j, the pivot lever i, and the shoe clearance adjustment device k, in order, and the brake shoe d at the left side spreads open with the point of abutment with the anchor block c as the fulcrum and frictionally engages the brake drum n. The pivot lever i rotates with the point of abutment with the shoe clearance adjustment device k as the fulcrum, and then the brake shoe e at the right side pivotably supporting the pivot lever i spreads open to frictionally engage with the brake drum n. The reaction force of the parking lever h affects the lower end of the brake shoe d at the left side.
Furthermore, if a rotational force in the direction of arrow R is applied to the brake drum n when a vehicle is stopped on a downhill or an uphill slope, the frictional force of the brake shoe d at the left side is transmitted via the shoe clearance adjustment device as the force needed to open the brake shoe e at the right side. In addition, when the rotational force is applied in the direction opposite of arrow R, the frictional force of the brake shoe e at the right side is transmitted via the shoe clearance adjustment device k to the brake shoe d at the left side. Accordingly, this drum brake device functions as a DS type brake when the parking brake is in operation.
Generally, when a vehicle is stopped on a slope, the vehicle is stopped by the service brake first, the parking brake is operated while the service brake is in operation, and then the service brake is released. When the service brake is released after setting the parking brake, for example, the brake drum n slightly rotates with the wheel, in the direction of arrow R due to gravity, which creates the braking force.
Very often when a vehicle is starting on a slope, the driver starts the vehicle moving, especially a vehicle with an automatic transmission, while releasing the parking brake without stepping on the service brake.
At this time, if the vehicle is moving to rotate the drum n in the direction opposite of arrow R, the brake shoe d turns with the brake drum n until contacting the anchor block c, and the brake shoe d smoothly returns to the starting position by the return spring force without any problem.
However, if the vehicle is moving to rotate the drum n in the direction of arrow R, one brake shoe d may cause dragging or biting. That is, as shown in
FIG. 9
, the shoe clearance adjustment device k becomes a prop, and the circumferential edge s of the lining q on the brake shoe d located closer to the wheel cylinder b side than the normal line B passing through the point of abutment P of the shoe clearance adjustment device k with the brake shoe d to the brake center O. Therefore, the circumferential edge s of lining q is pressed in the direction A
1
, that is, in the direction of the frictional surface of the brake drum, with the point of abutment P as the fulcrum by the force of the return spring, which may cause dragging and brake locking.
Also, when the vehicle is moving to rotate the drum n in the direction opposite of arrow R in the condition that the brake shoe d abuts against the anchor block c and the brake shoe e separates from the anchor block c with the parking brake in operation, the same type of problem described above can be clearly seen with respect to the other brake shoe e.
OBJECTS AND SUMMARY OF THE INVENTION
This invention is provided to resolve the problems above, and to that end, the object of the invention is to provide a drum brake device which realizes a smooth return of the brake shoe whenever the parking brake is released.
The present invention is a drum brake device comprising a back plate, two brake shoes set to face each other on top of the back plate, a service brake actuator activated by a service brake mounted on top of the back plate between one pair of first adjacent ends of the brake shoes, an anchor mounted on the back plate between the other pair of second adjacent ends of the brake shoes, a shoe clearance adjustment device provided adjacent to the service brake actuator and provided between the brake shoes, a parking brake actuator comprising by a parking brake lever and a strut adjacent to the anchor, linings provided on the two brake shoes, and a pivot lever pivotably mounted at a pivot point at the central region of one brake shoe, one end of the pivot lever and the other end of the pivot lever respectively being functionally engaged with the shoe clearance adjustment device and the parking brake actuator; wherein a circumferential edge of each lining of the brake shoe at the service brake actuator side is located on the normal radial line passing through a point of abutment of said brake shoe with the automatic shoe clearance adjustment device and the brake center or at a point closer to the anchor than that normal radial line.
The invention further is a drum brake device as above wherein a chamfer is formed at the end of the lining at the circumferential end on each of the shoes.
REFERENCES:
patent: RE22586 (1945-01-01), Spiller et al.
patent: 3064767 (1962-11-01), Wieger
patent: 3194359 (1965-07-01), Richards
patent: 4071123 (1978-01-01), Courbot et al.
patent: 4732240 (1988-03-01), Flaim
patent: 4981200 (1991-01-01), Gee
patent: 5002159 (1991-03-01), Brix et al.
patent: 5590747 (1997-01-01), Mery et al.
patent: 5630486 (1997-05-01), Maligne
patent: 0 286 254 (1988-12-01), None
Asai Seiji
Ikeda Takashi
Kobayashi Yasushi
King Bradley
Liniak, Berenato, Lonacre & White
Nisshinbo Industries Inc.
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