JPH0444899Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a mechanical center brake device mainly used as a parking brake for trucks.

(Prior art) A mechanical center brake applies braking to the propeller shaft.
As shown in the figure. In the figure, reference numeral 50 indicates a brake drum fixed in place on the propeller shaft 51. Inside the brake drum 50, brake linings 52A and 53 are provided on the outer peripheral surface, respectively.
A pair of brake shoes 52, 53 to which A is fixed
is installed. Brake shoe 52, 53
The springs 54 connect one ends 52a and 53a of each other.
and their relative positions are adjusted by an adjuster screw 55. Brake show 5
Elongated holes 52 are provided at the other ends 52b and 53b of 2 and 53.
anchor pins 57 and 58 fixed to the support plate 56 are fitted into the elongated holes. The support plate 56 has a mounting hole 56a formed therein.
It is fixed to a transmission case (not shown) via. Guide pieces 56b and 56c located on both sides of the brake shoes 52 and 53 are formed on the support plate 56, respectively, and guide the brake shoes 52 and 53 in a movable manner. A return spring 59 is stretched between a spring locking hole 52d formed in the brake shoe 52 and the anchor pin 57, and biases the shoe in a direction to separate it from the inner circumferential surface 50a of the brake drum. ing. On the other hand, brake shoe 53
Spring locking hole 53d and anchor pin 5 formed in
A return spring 60 is stretched between the brake drum 8 and the brake drum 8, and biases the shoe in a direction to separate it from the inner circumferential surface 50a of the brake drum. A rectangular cam 61 is disposed between the other ends 52b and 53b of the brake shoes 52 and 53. The cam 61 is supported with its camshaft 61a inserted into the support plate 56 so as to be rotatable.
As shown in FIG. 6, an actuator lever 62 is fixed to the end of the camshaft 61a. The actuator lever 62 has a cable 6
The ends of the three inner cables 64 are connected. The cable 63 is fixed to a stay 65 fixed to the mission case. Furthermore, one end of a return spring 67 whose other end is locked to a spring hanger 66 is locked to the actuator lever 62 .

Now, when the parking brake lever (not shown) is actuated and the inner cable 64 is pulled in the direction of arrow a, the actuator lever 62 rotates clockwise in FIG. 5, causing the cam 61 to rotate in the same direction. When the cam 61 rotates, the brake shoes 52 and 53 are expanded, and the brake linings 52A and 53A are brought into pressure contact with the inner peripheral surface 50a of the brake drum 50. Thereby, the brake drum 50 and the brake shoes 52, 53 are integrated with each other.

When the parking brake is activated and the brake lining is pressed against the brake drum 50, the long holes 52 of the brake shoes 52, 53
The edges 52c1, 53c1 of c, 53c and the anchor pins 57, 58 are spaced apart from each other. By the way, when operating the parking brake on a slope, the foot brake is operated to keep the vehicle in a stopped state. When the foot brake is released after pulling the parking brake lever and applying the parking brake, the vehicle tries to descend along the slope and the propeller shaft 5
1, for example, in the direction of arrow b. At this time,
Brake drum 5 integrated with propeller shaft 51
0 moves the brake shoes 52, 53. Note that the direction in which the cam 61 is returned to its original position changes depending on whether the vehicle is stopped on a downhill or uphill slope.

(Problems to be Solved by the Invention) As described above, when the parking brake is applied, the brake shoe 53, which moves together with the brake drum, moves in the direction of returning the cam 61 to its original position. The brake shoe is connected to the edge 5 of the elongated hole 53c.
3c1 moves to a position where it abuts against the anchor pin 58. On the other hand, the parking brake lever is locked in the pulled position by the non-return means, but when the cam is pushed and moved by the brake shoe as described above, the pair of brake shoes 52, There is a problem in that the relative position of the brake drum 53 fluctuates, weakening the pressure force between these shoes and the brake drum 50, and thus requiring the parking brake to be reapplied. That is, in the conventional center brake device, there was a problem in that the brake operation force was lost.

(Means for Solving the Problems) The present invention aims to solve the above-mentioned problems and provide a center brake device capable of preventing brake operation force from being lost, in which one end is connected to a first brake shoe and the other end is connected to a first brake shoe. are provided coaxially with the first cam, and one end is connected to the second brake shoe and the other end is connected to the first brake shoe. second to engage
Rotating a cam, a first lever substantially integral with the first cam, a second lever substantially integral with the second cam, and the first lever and the second lever in opposite directions to each other. The present invention is characterized in that it further comprises an actuation cable for rotating both the cams and expanding the two brake shoes.

(Operation) When the actuation cable is pulled and the first lever and the second lever are rotated in opposite directions, the first cam and the second cam are rotated, respectively, and the first and second brake shoes are rotated. The brake shoe is expanded and its brake lining is brought into pressure contact with the inner peripheral surface of the brake drum. When the brake drum moves one brake shoe, both brake shoes move while maintaining their relative positions by the first cam and the second cam.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings. In the following description, the same reference numerals are used for the same members as in the conventional structure.

In FIG. 1, one end 52b of the first brake shoe 52 and one end 5 of the second brake shoe 53 are shown.
3b, a first cam 1 and a second cam 2 are arranged. The first cam 1 and the second cam 2 are
As shown in the figure and FIG. 4, they are positioned coaxially with each other. That is, the first cam 1 has one end 1b and the other end 1c extending in opposite directions at the end of the camshaft 1a. One end 1b of the first cam is an end 52 of the first brake shoe 52.
e, and the other end 2c is engaged with the second brake shoe 5.
3 is engaged with the end portion 53e. The second cam 2 is formed at a tube shaft portion 2a inserted through the camshaft 1a and at an end of this tube shaft portion, extends in opposite directions, and is flush with one end 1b and the other end 1c of the first cam. It consists of one end 2b and the other end 2c located inside. One end 2b of the second cam engages with an end 53e of the second brake shoe 53, and the other end 2c engages with an end 52e of the first brake shoe 52. A first lever 3 is attached to the other end of the camshaft 1a.
is fixed, and a second lever 4 is attached to the other end of the tube shaft portion 2a.
is fixed. An end 5b of an outer cable 5a of the actuation cable 5 is fitted into the first lever 3, and an end 5d of an inner cable 5c through which the outer cable is inserted is connected to the second lever 4. The other end of the actuation cable 5 is connected to a parking brake lever (not shown). The first lever 3 and the second lever 4 have a tendency to rotate in a direction in which they are separated from each other by a spring (not shown), in other words, in a direction in which the first cam 1 and the second cam 2 overlap each other (see FIG. 1). is given.

FIG. 1 shows a non-braking state in which the parking brake is not operated, and in this state, one end 1b, 2b of each cam and the other end 1c, 2
c are overlapping each other, and each brake shoe 52,
53 brake linings 52A and 53A are held at positions spaced apart from the inner circumferential surface 50a of the brake drum 50, respectively.

Now, when the brake parking lever (not shown) is pulled and the cable 5 is pulled as shown in FIG. rotate in opposite directions. As the first lever 3 rotates, the first cam 1 rotates counterclockwise, and one end 1b of the first cam 1 is connected to the first brake shoe 5.
The end 52e of the second brake shoe 53 is engaged with the end 53e of the second brake shoe 53, and the other end 1c is engaged with the end 53e of the second brake shoe 53, respectively. Further, due to the rotation of the second lever 4, the second cam 2 rotates clockwise, and its one end 2b is connected to the end 53e of the second brake shoe 53, and the other end 2 is connected to the end 53e of the second brake shoe 53.
c are respectively engaged with the end portions 52e of the first brake sheath 52. The first cam 1 and the second cam 2, which are rotated in opposite directions, expand the first brake shoe 52 and the second brake shoe 53, so that the respective brake linings 52
A, 53A is the inner peripheral surface 50a of the brake drum 50
Press it against the Each brake shoe 52, 53 is
The return springs 59 and 60 (see FIG. 5) are stretched and expanded, and the elongated hole 52
The edges of the anchor pins 57 and 53c are spaced apart from the anchor pins 57 and 58.

Now, when operating the parking brake, the foot brake is operated, but when the foot brake is released, the brake drum 50 rotates slightly, and the first and second brake shoes 52, 53, its elongated hole 52c or 5
Either edge of 3c is anchor pin 57 or 58
Move it until it collides with the At this time, one of the brake shoes attempts to rotate cam 1 or 2, but the first brake shoe, which crosses in an X shape when viewed from the front,
Cam 1 and second cam 2 do not rotate. Therefore, the relationship between one brake shoe pushed by the rotation of the brake drum 50 and the other brake shoe facing each other with the first cam 1 and the second cam 2 interposed therebetween is The position remains unchanged. Even if the cam rotates in one direction, the first lever 3 and the second lever 4 rotate together, so the relative positions of both brake shoes 52 and 53 do not change. The first brake shoe and the second
The fact that the relative position of the brake shoe and the brake drum does not change means that the pressure force between the brake shoe and the brake drum does not change.
This means that the cable does not lose its operating force.

(Effects of the invention) As described above, according to the invention in which the first cam and the second cam that engage with the first and second brake shoes are provided, the brake shoe is activated when the parking brake is applied. Since the rotation of the brake drum when it moves until it hits the anchor pin does not change the relative distance between the pair of brake shoes, there is no loss of operating force.

[Brief explanation of the drawing]

Fig. 1 is a front sectional view showing an embodiment of the present invention in a non-braking state, Fig. 2 is a front sectional view showing the same braking state as above, and Fig. 3 is a combination of each cam and each lever. 4 is a front view showing the relative position of the first cam and the second cam, FIG. 5 is a front sectional view showing an example of a conventional center brake device, and FIG. 6 is a front view showing the relative position of the first cam and the second cam. It is a perspective view showing a lever. 1...First cam, 2...Second cam, 1b, 2b
...One end, 1c, 2c...Other end, 3...First lever, 4...Second lever, 50...Brake drum, 51...Propeller shaft, 52...First brake shoe, 53... ...Second brake shoe.

Claims (1)

[Claims for Utility Model Registration] A drum fixed to the propeller shaft, a pair of brake shoes provided so as to be able to slide on the inner peripheral surface of the drum, and a pair of brake shoes that can be expanded to meet the requirements. A center brake device having a cam for sliding a brake shoe in sliding contact with the inner circumferential surface, the first cam having one end engaging the first brake shoe and the other end engaging the second brake shoe. , a second cam that is provided coaxially with the first cam and has one end engaged with the second brake shoe and the other end engaged with the first brake shoe; and a second cam that is substantially connected to the first cam; A first lever that is integral with the second cam, a second lever that is substantially integral with the second cam, and the first lever and the second lever are rotated in opposite directions to rotate both the cams. and an actuation cable for expanding both brake shoes.