JPH037621Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention relates to a wheel cylinder for a drum brake.

(Prior Art) A conventional drum brake wheel cylinder is disclosed in Japanese Utility Model Application Publication No. 19831/1983. This is a wheel cylinder with a built-in automatic gap adjustment device, in which one end of an adjustment member (spindle) is screwed to a piston member that slides inside the cylinder, and when the movement of the piston member is excessive, the adjustment member is automatically adjusted. In the cylinder device having an automatic adjustment mechanism that rotates the cylinder device, the other end of the adjustment member is supported so as not to vibrate.

According to this type of wheel cylinder, one end of the adjustment member is screwed to the piston member, and the other end is supported so as not to vibrate, so the adjustment member is always supported in a double-supported state, and automatic adjustment is possible. This ensures that the adjustment member does not rotate at the same time, resulting in stable automatic adjustment operations.

(Problem to be solved by the invention) However, in such a wheel cylinder, the positional relationship between the piston member and the adjusting member is regulated by pressing the adjusting member toward the piston member by a spring, so the durability is limited. It is inferior to the following, and is accompanied by the following problems. In other words, since the adjustment member moves with the expansion of the spring to automatically adjust the gap, the spring deteriorates over time and is affected by the loosening of the threaded joint, making the gap adjustment unstable. .

(Means and operations for solving the problem) This invention was made in view of such conventional problems, and consists of a piston that is slidably inserted into the cylinder body, an adjusting screw part,
A drive screw portion and a contact portion are sequentially formed, and a spindle is screwed into a bottomed hole formed on the inner bottom side of the piston with an adjustable screw portion made of a non-reversible screw, and a drive screw portion of the spindle is reversible. In a wheel cylinder having a threaded connection and an adjustment nut biased inwardly so as to contact the cylinder body at a clutch surface, a spring biasing the piston outwardly with respect to the spindle is inserted into the hole of the piston. This is a drum brake wheel cylinder housed in the unit.

Since the spring housed in the bottomed hole of the piston biases the piston outward, the relative position of the spindle with respect to the piston is stabilized, and the spindle moves due to the stroke of the piston.
Since the gap adjustment device is activated, the amount of automatic adjustment of the shoe gap can be maintained constant over a long period of time. In addition, the relative position of the spindle with respect to the piston is stabilized by the frictional force between the adjuster threads that make up the irreversible threaded connection, so when the brake is activated and the spindle moves back and forth, the spindle does not drag or vibrate. This prevents the gap adjusting device from rotating due to the impact, thereby preventing the gap adjusting device from malfunctioning.

(Example) Hereinafter, an example of this invention will be described with reference to the drawings.

Figures 1 and 2 show an embodiment in which this invention is applied to a single-acting wheel cylinder. In the figure, numeral 1 is the cylinder body, and its cylinder wall 1a
A piston 2 is slidably inserted into the holder. A locking member 4 of a brake shoe 11 or 11', which will be described later, is rotatably inserted into a circular hole 2a formed at the outer end of the piston 2, and a forked portion 4b brake shoe 11 or 11'
is accepted in a non-rotatable manner. Reference numeral 4c is a friction ring that is attached to the shaft portion 4a of the locking member 4.
2d is a manual adjustment gear formed on the outer end of the piston 2. By rotating this gear 2d with a tool and rotating the piston 2, the automatic gap adjustment device built into the cylinder body 1 can be adjusted. The shoe gap can be adjusted manually. 5 is a rubber dust cover,
It is attached to the annular groove 1d of the cylinder body 1 and the annular groove 2b of the piston 2 to prevent dust and rainwater from entering into the cylinder wall 1a.

On the other hand, the inner bottom side of the piston 2 has a bottomed hole 2e.
An adjusting screw portion 3a of the spindle 3 is screwed into an adjusting screw portion 2c formed near the inner end of the bottomed hole 2e. The adjusting screw portions 2c and 3a constitute an irreversible screw connection. Here, the term "irreversible threaded connection" is defined as one in which relative rotation does not occur due to the axial acting force between the adjusting threaded portions 2c and 3a, and a general single thread thread falls under this. At the end of the spindle 3 opposite to the adjustment screw portion 3a, there is a drive screw portion 3b and a conical contact portion 3c formed by chamfering the end edge.
is provided, and this contact portion 3c is connected to the cylinder body 1
The support member 13 is abutted and supported by a conical abutment surface 13a of a support member 13 that is press-fitted and fixed to the bottom of the support member 13. Further, a drive screw portion 6d of a nut member 6, which is an adjusting nut, is screwed into the drive screw portion 3b of the spindle 3 by a reversible screw connection. Here, the reversible screw connection is defined as one that necessarily rotates due to relative movement in the forward and reverse directions in the axial direction between the drive screw portions 3b and 6d, and a multi-thread screw falls under this. The nut member 6 has a cylindrical portion 6a, an annular side surface 6b, and a conical surface 6c in this order. At the bottom of the cylinder wall 1a of the cylinder body 1, there is provided a conical clutch surface 1 that fits the conical surface 6c.
c is formed. Reference numeral 10 designates a conical coil spring that presses the conical surface 6c of the nut member 6 toward the clutch surface 1c of the cylinder wall 1a, and its outer end is seated on a snap ring 9 that is ring-fitted to the cylinder wall 1a. , its inner end is supported by a stopper ring 7, and the ring 7 and the annular side surface 6b
A ball bearing 8 is interposed between the two.

A spring 12 is housed on the bottom side of the bottomed hole 2e of the piston 2, and urges the piston 2 outward with respect to the spindle 3.

Such a drum brake wheel cylinder is provided in a two-leading type drum brake as shown in FIG. In the figure, reference numeral 30 is a bucking plate, 11 and 11' are brake shoes arranged facing each other, and 31 and 32 are shoe return springs that reduce the diameters of both brake shoes 11 and 11', respectively. A pair of wheel cylinders 20, 20 are provided between the pair of brake shoes 11, 11'. One brake shoe 11 or 11' is locked to the locking member 4 as described above, and the other brake shoe 11' or 11 is locked to the locking portion 1b of the cylinder body 1.

Next, the effect will be explained.

If brake fluid is supplied into the cylinder body 1,
When the shoe gap is within a predetermined gap, the piston 2 moves between the backlashes of the drive threaded portions 3b and 6d, and the brake shoes 11 and 11' that are locked to the forked portion 4b of the locking member 4 are moved. It generates braking force by sliding in contact with a drum (not shown).

When the brake shoes 11, 11' are worn and the shoe gap becomes larger than a predetermined shoe gap, the piston 2 strokes together with the spindle 3, and after filling the backlash of the drive threaded portions 3b, 6d, the piston 2 moves further. At this time, the nut member 6 slightly compresses the coil spring 10, detaches the conical surface 6c from the clutch surface 1c and rotates, and the spindle 3 moves forward together with the piston 2.

When the brake is released and the brake fluid is discharged from the cylinder body 1, both shoe return springs 3
1 and 32, the piston 2 takes a return stroke. At this time, the spindle 3 is lightly pushed into the nut member 6, and the rotation of the nut member 6 is restrained by the action of the clutch surface 1c, but the spindle 3 is rotated by the action of the drive screw parts 3b and 6d. and screw it out onto the piston 2. At this time, since the spring 12 tends to be compressed, the rotation of the spindle 3 is performed smoothly. Thus, the shoe gap is
Fine adjustments are made based on the difference between the pitch of the adjust screw portions 3a, 2c and the pitch of the drive screw portions 3b, 6d.

Since the spring 12 accommodated in the bottomed hole 2e of the piston 2 biases the piston 2 outward with respect to the spindle 3, the alignment between the adjustment screw portion 2c of the piston 2 and the adjustment screw portion 3a of the spindle 3 is as follows. During the automatic gap adjustment operation, the third
As shown in the figure, it is always available on the outside.
As a result, the relative position of the spindle 3 with respect to the piston 2 is stabilized, and the amount of automatic adjustment of the shoe gap becomes constant. In addition, the relative position of the spindle 3 with respect to the piston 2 is stabilized by the frictional force between the adjusting screw portions 2c and 3a that constitute the irreversible screw connection, so that the brake is activated and the abutment portion 3c of the spindle 3 is moved to the supporting member. When the spindle 3 is separated from the abutting surface 13a of the shoe gap 13, the spindle 3 is rotated due to vibrations, the gap adjustment mechanism malfunctions, and the problem of over-adjustment or under-adjustment of the shoe gap is eliminated.

By the way, by setting the amount of engagement of the adjustment screw 3a of the spindle 3 with the adjustment screw 2c of the piston 2 to an appropriate amount, it can be made to function as a brake lining wear detection device. For example, if the adjusting screws 2c and 3a are set to unthread when the thickness of the brake lining becomes 1 mm or less, the automatic gap adjustment device will not operate depending on the subsequent wear of the brake lining. As a result, the driver can sense the wear of the brake lining as an increase in the pedal stroke of the brake pedal.

(Effects of the Invention) As understood from the above explanation, according to this invention, in a wheel cylinder in which an automatic gap adjustment device is built, the durability and reliability of the automatic gap adjustment device are significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of this invention, FIG. 2 is a view showing a two-leading type drum brake, and FIG. 3 is an explanatory view showing an adjuster screw portion. 1: Cylinder body, 1a: Cylinder wall, 1c:
Clutch surface, 2: Piston, 2c: Adjustment thread part, 2e: Bottomed hole, 3: Spindle, 3a: Adjustment thread part, 3b: Drive screw, 3c: Contact part, 4: Locking member, 6: Nut member (adjustment nut), 6c: conical surface, 6d: drive screw,
8: Ball bearing, 10: Coil spring, 13a: Contact surface, 12: Spring.

Claims (1)

[Scope of utility model registration request] A piston that is slidably inserted into the cylinder body, an adjusting threaded part, a drive threaded part, and a contact part are sequentially formed, and an adjusting screw made of a non-reversible screw is inserted into a bottomed hole formed on the inner bottom side of the piston. A wheel cylinder having a spindle that is screwed together at a threaded portion, and an adjustment nut that is reversibly screwed to the drive threaded portion of the spindle and is biased inward so as to come into contact with the cylinder body at a clutch surface, wherein the spindle A wheel cylinder for a drum brake, characterized in that a spring that biases the piston outward against the piston is housed in the hole of the piston.