JPH0225059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drum brake device of the type that obtains a dual-servo type braking force when the parking brake is activated. As a conventional drum brake device, there is one shown in FIG. 1, for example. 1
is a brake drum that rotates in the direction of the arrow when the vehicle moves forward, and has a cylindrical shape with a bottom. 2 is a back plate fixed to the vehicle body facing the opening of the brake drum 1, and a brake shoe 3,
4 is held in a state facing the inner peripheral surface of the brake drum 1. 3 forms the front brake shoe,
4 forms the rear brake shoe. Mutually opposing first ends 3a, 4a of both brake shoes 3, 4
The anchor 5 is interposed between the anchors 5 and 5, and is fixed to the back plate 2, supporting the first ends 3a, 4a, thereby preventing the brake shoes 3, 4 from moving toward the center of the anchor 5. Reference numeral 6 denotes a parking mechanism, which is arranged near the anchor 5 and is used to push and spread the space between the first ends 3a and 4a of the brake shoes 3 and 4, and includes a toggle lever 6d.
and a support rod 6c. toggle lever 6d
As is well known, the brake shoe 4 is moved to the right in the figure by rotation, and the support rod 6c is
is to move it to the left. A wheel cylinder 7 is fixed to the back plate 2 between the opposing second ends 3b and 4b of the pair of brake shoes 3 and 4, and receives the brake fluid from the brake master cylinder. The pressure pushes the brake shoes 3 and 4 toward the inner peripheral surface of the brake drum 1. Reference numeral 11 denotes a strut, which is disposed on the second end 3b, 4b side of the brake drums 3, 4, and is always in contact with the strut when the service brake is not in operation, and when the service brake is in operation,
A gap is created between the brake shoes 3, 4 and the strut. Elastic bodies 8 and 9 are coil springs that always urge both brake shoes 3 and 4 toward each other. Reference numeral 12 denotes a shoe hold down spring that supports the brake shoes 3, 4 in a floating manner on the back plate.

However, in such a conventional drum brake device, the service brake is first operated and the second end 3 of the brake shoes 3, 4 is operated.
If you stop the vehicle by expanding the space between b and 4b, then apply the parking brake with the service brake activated, and then release the service brake, the strut 11 and brake shock that occurred when the service brake was activated will be removed. You 3, 4
There was a problem in which the braking force of the parking brake was reduced due to the gap between the two.

The present invention was made by focusing on such conventional problems, and the wheel cylinder is opened on one side, and only one brake shoe is pressed, leaving a gap between it and the other brake shoe. The present invention aims to solve the above-mentioned conventional problems by constantly bringing the strut into contact between the brake shoes on the wheel cylinder side.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described with reference to illustrative embodiments. FIG. 2 is a diagram showing a first embodiment of the present invention.

First, the configuration will be described. Reference numeral 1 denotes a brake drum that rotates in the direction of the arrow when the vehicle moves forward, and has a cylindrical shape with a bottom. A back plate 2 is fixed to the vehicle body side facing the opening of the brake drum 1, and the brake shoes 3, 4 are held on this back plate in a state facing the inner circumferential surface of the brake drum 1. 3 represents the front brake shoe, and 4 represents the rear brake shoe. An anchor 5 is interposed between the mutually opposing first ends 3a and 4a of both brake shoes 3 and 4, and this is fixed to the back plate 2,
By supporting the first ends 3a, 4a, movement of the brake shoes 3, 4 toward the center of the anchor 5 is prevented. Reference numeral 6 denotes a parking mechanism, which is disposed near the anchor 5 and is used to push and spread the space between the first ends 3a and 4a of the brake shoes 3 and 4. Become. As is well known, the toggle lever 6d rotates to move the brake shoe 4 to the right in the figure and to move the support rod 6c to the left. Reference numeral 7 designates a wheel cylinder, which is fixed to the back plate 2 between the opposing second ends 3b and 4b of the pair of brake shoes 3 and 4, and receives the brake fluid from the brake master cylinder. The pressure pushes only the front brake shoe 3 toward the inner peripheral surface of the brake drum 1.
11 is a strut, and brake shoes 3 and 4
The brake shoes are disposed on the second end portions 3b and 4b of the brake shoes 3b and 4b, and are always in contact between the brake shoes 3 and 4. This strut 11 consists of a shoe clearance adjuster, and in particular, in this embodiment, a manual adjuster. Elastic bodies 8 and 9 are coil springs that always urge both brake shoes 3 and 4 toward each other. 12
is a shoe hold down spring that supports the brake shoes 3 and 4 in a floating manner on the back plate.

Next, the action will be explained.

During service braking, when the hydraulic pressure generated in the master cylinder by the brake pedal depression force is transmitted to the wheel cylinder 7, the piston pushes the end 3b of the front brake shoe 3,
A brake shoe 3 is pressed against the inner peripheral surface of the brake drum 1, and the vehicle is braked by the frictional resistance between the two. When the vehicle is moving forward at this time, the brake shoe 3 is supported by the anchor 5 and acts as a leading shoe, and when the vehicle is moving backward, the brake shoe 3 acts as a trailing shoe. On the other hand, the rear brake shoe 4
does not contribute to the braking action during service braking. When this service brake is activated, the end 4b of the brake shoe 4 and the wheel cylinder 7
There is a gap between the brake shoes 3 and 4, and when the brake shoe 3 moves to the left due to the elastic bodies 8 and 9, the brake shoe 4 also moves to the left.
There is no gap between the struts 4 and the struts 11.

Next, when applying the parking brake, when the brake lever facing the driver's seat is operated, the cable is pulled and the toggle lever 6d rotates, pressing the rear brake shoe 4 against the inner peripheral surface of the brake drum 1. Push the support rod 6c to the left in the figure. This movement of the support rod 6c also brings the front brake shoe 3 into pressure contact with the inner peripheral surface of the brake drum 1. When the brake shoes 3, 4 are pressed against the brake drum 1, the brake shoes 3, 4 expand, while the ends 3b, 4b are always in contact with the strut 11 due to the elastic body 8, so that the brake Both brake shoes 3 and 4 are in pressure contact with the inner circumferential surface of the brake drum 1, and a parking brake mechanism 6 and a strut 11 are stretched between both brake shoes 3 and 4. You 3, 4
maintains pressure contact with the inner circumferential surface of the brake drum 1. Therefore, when the parking brake is applied, the brake is applied in both the forward and reverse directions of the vehicle.
Works as a dual-servo parking brake.

Next, a case will be described in which the service brake is operated first and then the parking brake is operated in that state. The operation of the service brake is the same as described above, and the front brake shoe 3 comes into pressure contact with the inner peripheral surface of the brake drum 1 by the operation of the piston of the wheel cylinder 7, thereby stopping the rotation of the brake drum 1. If the parking brake is operated in this state, the parking brake mechanism 6 will cause the brake shoes 3 and 4 to
The area between the ends 3a and 4a is relatively expanded,
At this time, since the front brake shoe 3 is already in pressure contact with the inner peripheral surface of the brake drum 1, only the rear brake shoe 4 is moved by the parking brake mechanism 6. The rear brake shoe 4 has a wider shoe clearance due to the action of the elastic bodies 8 and 9 as the front brake shoe 3 moves during service braking. Due to the expansion action of the brake shoes 3 and 4, the rear brake shoe 4 also comes into pressure contact with the inner peripheral surface of the brake drum 1. At this time, the brake shoe 4 moves as a combination of a movement toward the inner peripheral surface of the brake drum 1 toward the right in the figure and a movement toward the wheel cylinder 7 side.

The movement toward the wheel cylinder 7 is performed in an arc shape whose center is the junction between the strut 11 and the front brake shoe 3, and whose radius is the distance between the strut 11 and the junction between the brake shoes 3 and 4. The entire surface of the rear brake shoe 4 comes into pressure contact with the inner circumferential surface of the brake drum 1, causing the strut 11 to move between the opposing ends 3b and 4b of the brake shoes 3 and 4. Maintain spacing at specified dimensions. Thus, both brake shoes 3,
4, the pressure contact with the inner circumferential surface of the brake drum 1 is as follows:
At this time as well, the parking brake mechanism 6 and the strut 11
Therefore, even if the service brake is released after the parking brake is activated, no gap is created between the brake shoes 3, 4 and the strut 11, so the braking force of the parking brake is Since the operation is the same as when only the parking brake is operated, sufficient parking brake braking can be ensured.

FIG. 3 shows a second embodiment of the present invention, in which the strut 11 is comprised of a shoe clearance auto-adjuster. That is, the adjustment lever 14, which is pivotally supported by the rear brake shoe 4, engages with the ratchet wheel 13 of the auto adjuster.
One end of the adjusting cable 16 is fixed to the front brake shoe 3, and the other end of the adjusting cable 16 is connected to a cable guide 15 formed in the rear brake shoe 4 at a midway point. Further, one end of the elastic body 8 is connected to the brake shoe 3, and the other end is connected to the adjustment lever 14. , 4 to approach each other. Furthermore, in this embodiment, the first
Similar to the anchor 5 in the embodiment, an anchor pin 5a is used, which constitutes an anchor that is a component of the present invention.

Therefore, when both brake shoes 3 and 4 expand when the parking brake is applied, if the shoe clearance is greater than a predetermined value, the adjustment cable 16 is pulled greatly toward the front brake shoe 3, and the adjustment cable 16 is pulled toward the front brake shoe 3 side. When the lever 14 is rotated counterclockwise against the bias of the elastic body 8 and then the parking brake is released, the adjustment lever 14
By rotating clockwise, the adjuster lever 14 rotates the ratchet wheel 13 and extends the strut 11, thereby increasing the distance between the brake shoes 3 and 4 to optimize shoe clearance. Set. Further, during service braking, as the front brake shoe 3 is pressed against the inner peripheral surface of the brake drum 1, the rear brake shoe 4 moves toward the front brake shoe 3,
Since the relative positions of both brake shoes 3 and 4 do not change much, the shoe clearance auto adjuster does not operate during service braking. Therefore, in this embodiment as well, even if the parking brake is applied with the service brake applied and then the service brake is released, both brake shoes 3, 4 and the strut 11
Since there is always contact between the two and there is no gap,
Sufficient braking force of the parking brake can be obtained without reducing the braking force of the parking brake.

As explained above, according to the present invention,
A rotating brake drum having a cylindrical shape with a bottom, a non-rotating back plate placed opposite to the opening of the brake drum, and a pair of brakes held by the back plate facing the inner peripheral surface of the brake drum. and an anchor fixed to the back plate between the pair of brake shoes and the opposite first ends thereof, and supporting the first ends at a fixed position to prevent movement of the brake shoes. , a parking brake mechanism disposed near the anchor for pushing and expanding the first ends of the brake shoes, and a parking brake mechanism disposed near the mutually opposing second ends of the pair of brake shoes for controlling brake fluid pressure. to press only one brake shoe toward the inner peripheral surface of the brake drum, and press the second brake shoe of the other brake drum toward the inner peripheral surface of the brake drum.
A wheel cylinder having a gap between the end of the brake shoe, a strut that is placed on the second end side of both brake shoes and is in constant contact with both brake shoes, and a strut that connects the pair of brake shoes to each other. Since the drum brake device is equipped with an elastic body that is always biased in the approaching direction, even if the service brake is activated, the parking brake is activated in that state, and then the service brake is released, both Since the brake shoe and the strut are always in contact with each other, there is no fear that the braking force of the parking brake will decrease, and sufficient braking force can be obtained.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of a conventional example, FIG. 2 is a front sectional view of a first embodiment of the present invention, and FIG. 3 is a front sectional view of the second embodiment. 1... Brake drum, 2... Back plate, 3, 4... Brake shoe, 3a, 4a...
First end, 3b, 4b...Second end, 5...
Anchor, 5a...Anchor pin, 6...Parking brake mechanism, 7...Wheel cylinder,
8, 9...Elastic body, 11...Strut.

Claims (1)

[Claims] 1. A rotating brake drum having a cylindrical shape with a bottom, a non-rotating back plate disposed opposite to the opening of the brake drum, and a pair of brake drums held by the back plate facing the inner peripheral surface of the brake drum. An anchor fixed to the back plate between the brake shoes and the opposing first ends of the pair of brake shoes, and supporting the first ends at a fixed position to prevent movement of the brake shoes. a parking brake mechanism disposed near the anchor to press and spread the space between the first ends of the brake shoes; and a parking brake mechanism disposed near the opposing second ends of the pair of brake shoes to spread the brake fluid. A wheel cylinder that presses only one brake shoe toward the inner circumferential surface of the brake drum by pressure and has a gap between it and the second end of the other brake shoe, and a second end of both brake shoes. A drum brake characterized by comprising a strut that is placed on the end side and is in constant contact with both brake shoes, and an elastic body that constantly biases the pair of brake shoes in a direction toward each other. Device.