Brakes – Wheel – Transversely movable
Reexamination Certificate
1999-03-22
2001-05-15
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Transversely movable
C188S079510, C188S1960BA
Reexamination Certificate
active
06230853
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to a drum brake device for a rear wheel, which comprises a single brake shoe which functions as a leading shoe with self-servo property either when the vehicle is moving forward or when it is moving backward.
Japanese Patent Application Publication No. Heisei 9-324829, illustrates a drum brake device which comprises a single brake shoe with a self-servo property when a vehicle is moving either forward or backward.
An example of this type of drum brake device is explained with reference to FIG.
12
. In
FIG. 12
, a single brake shoe a is movably mounted on the back plate. An upper portion of the brake shoe a engages with the anchor b. A lower portion engages with a shoe clearance adjustment device c. A link d is rotatably pivoted at the central region of the brake shoe a. The upper portion of the link d functionally engages with the anchor b. The lower portion of the link d abuts against a service brake actuator e operating when the service brake is activated. The upper portion of the brake shoe a is supported by the anchor b when the brake drum rotates in one direction (the direction shown by the arrow A). The lower portion of the brake shoe a is supported by the shoe clearance adjustment device c when the brake drum rotates in the reverse direction (opposite to the arrow A).
There are two points which need to be considered when designing a drum brake device. First, a brake fluid pipe to be connected to a wheel cylinder is desirably kept a greater distance from the road surface in order to avoid damaging the pipe because of flying gravel, debris and the like.
Secondly, if the rear wheels of the vehicle lock before the front wheels, handling becomes more difficult, and the driver could be in danger. Therefore, it is important to avoid such a situation.
In addition, as shown in the conventional art, if the shoe functions as a floating shoe when the brake drum rotates in any direction, it is well-known that the braking effect can be increased as the distance from a horizontal straight line X across the center of the brake to the supporting point of the brake shoe becomes shorter. If the dimensions or size relative to the braking effect is same, it is well-known that the braking effect of a pivot shoe rather than a floating shoe is lower if the drum brake is designed as an ordinary type. The detail is described in “BRAKE DESIGN AND SAFETY” by Rudolf Limpert, SAE International, pages 61-75, and “Tire, Brake” of “Automobile Engineering Encyclopedia”, Sankaido.
From the above-described view, the wheel cylinder of the drum brake device of
FIG. 12
may be located at the upper portion of the device when applied to the right wheel side of the vehicle, thereby securing the braking effect of the vehicle moving backward and arranging the run of a parking brake cable to be directed toward the front of the vehicle. However, the available space for arranging the shoe clearance adjustment device supporting the brake shoe when moving forward becomes limited, thereby making it difficult to design a device to eliminate the problem of the rear wheels being locked first.
OBJECT OF INVENTION
This invention was made to resolve the problems above. More specifically, an object of the invention is to provide a drum brake device which realizes a stable braking effect by tending to equalize the braking effects of both moving forward and backward without losing self-servo property.
Another object of this invention is to provide a drum brake device which avoids positioning liable to damaging the brake fluid pipe due to flying gravel, debris, and the like and enables the pull of a parking brake cable to be pulled directly toward the front of the vehicle.
More specifically, it is an object of the invention to provide a drum brake device comprising, a back plate, first and second anchor members mounted on the back plate, a single brake shoe movably mounted on the back plate, one end of the brake shoe being functionally engaged with the first anchor member through abutment against the first anchor member and the other end of the brake shoe being functionally engaged with the second anchor member through abutment against the second anchor member, a service brake actuator, which activates when a service brake is applied, mounted on the back plate, a supporting member mounted on the back plate, a link pivotably supported at the pivot point of the central region of the brake shoe, one end of the link being functionally engaged with the service brake actuator, the other end of the link being supported by the supporting member, wherein the operation force of the service brake actuator which acts on the link is transferred to the brake shoe through the pivot component of the link, one of the first or second anchor member functioning as a pivot anchor when the distance from a horizontal straight line through the center of the brake and across the brake shoe to one of the first or second anchor member is shorter than the distance from the horizontal straight line to the other anchor member, and the other anchor member functions as a floating one.
This invention is a drum brake as above, wherein a shoe clearance adjustment means for adjusting a clearance between the brake drum and the brake shoe, is provided at either the first or the second anchor member.
This invention further is a drum brake device as above, wherein the shoe clearance adjustment means automatically senses the amount of opening by which the brake shoe opens and adjusts the clearance between the brake drum and the brake shoe.
This invention still further is a drum brake device as above, which further comprises a parking brake actuator, which operates when a parking brake is activated. The parking brake actuator is provided so as to open one side of the link.
This invention still further is a drum brake device as above, which further comprises a shoe return spring, wherein the moment of the shoe return spring which pivots at the pivot point of the link engaging with the brake shoe is set so that the moment at the anchor member side is larger than the moment at the other side when a vehicle is moving forward.
This invention still further is a drum brake device as above, wherein the supporting member supporting the other side of the link is shared with the anchor member supporting the brake shoe.
REFERENCES:
patent: 5819887 (1998-10-01), Asai et al.
patent: 9112597 (1997-05-01), None
patent: 9166162 (1997-06-01), None
patent: 9166163 (1997-06-01), None
patent: 11351288 (1999-12-01), None
Arent Fox Kintner & Plotkin & Kahn, PLLC
Butler Douglas C.
Nisshinbo Industries Inc.
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