JPS5818534B2 - Disc brake piston - Google Patents

Abstract

PURPOSE:To simply manufacture a light and hollow piston evenly thick as a whole by shaping a precisely columnar substance in the form of a bottomed cylinder and rolling its part near the open end. CONSTITUTION:A precisely columnar substance 20 like a S10C-S35C carbon steel bar whose diameter is approximately 80% of a maximum outside diameter R1 of a piston is inserted in a concaved die 21 of an inside diameter R1 and pressed by a press pattern 23 at a room temperature, thereby having the same diameter as the inside diameter R1 and smooth top and bottom faces. Then the deformed body is inserted in a die 21a similar to the die 21 and pressed by a press pattern 23a of an outside diameter R3 to a stop near the bottom to form a bottom 24a. A new cylinder 24 is made up, having a throughout even thickness (t) and being slightly longer than the full length L of a completed piston. Then, a part which intersects with a radial line of an open end face 30 of the cylinder 24 is notched in the form of a smoothly curved V-shape at the opposed points by a forging work or so. After an external part separated from the open end face 30 as long as l is engraved to form an annular depression 29, an annular groove 29a for retaining a dust-proof boot is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hollow type piston for a disc brake.

A conventional disc brake piston is shaped like a cylinder or a cup with an open end that extends from the end of a hydraulic cylinder and abuts a friction pad assembly that connects the friction pad assembly to a brake disc. It is designed to transmit a pressing force that causes frictional engagement.

A dustproof boot is attached to the portion where the piston extends from the end of the hydraulic cylinder to prevent dust from entering.

The dust boot is generally bellows-shaped, and one end of the dust boot is engaged with a hydraulic cylinder and the other end is engaged with a piston.

In order to lock the end of the dustproof boot, the open end of the piston has a smaller diameter than the bottom.

In such conventional disc brake pistons, in order to obtain a wall thickness for strength at the opening end, which is considered to have a small diameter, the wall thickness at the manufacturing surface (the part where the cylinder fits) has to be larger than necessary. However, this is undesirable as it results in wasted material and excess weight.

Furthermore, if the diameter of the opening end of the piston is small, the area where it collides with the friction pad assembly or the area where hydraulic pressure is applied is small. strength) is not transmitted, causing uneven wear on the friction pad assembly and shortening its lifespan.

In view of the above-mentioned problems, an object of the present invention is to have a substantially uniform wall thickness as a whole without impairing the wall thickness of the part that locks the dustproof boot, and to have a sufficient thickness at the open end to abut against the friction pad. An object of the present invention is to provide a piston for a disc brake having a hydraulic pressure area.

To solve this problem, the structure of the present invention is a disc brake that is provided with an annular groove for engaging one end of a dustproof boot, which is formed by projecting a cylindrical wall portion slightly apart from the open end surface of a bottomed cylindrical body radially inward. In this piston, the shape of the opening end surface that abuts against the back metal of the friction pad assembly is an oval shape that extends in the circumferential direction of the brake disc, and the long diameter of the oval shape that extends in the circumferential direction of the brake disc is the same as that of the cylinder fitting part. The short axis, which is approximately equal to the outer diameter and extends in the radial direction of the brake disc, is made slightly thicker than the bottom of the annular groove, thereby obtaining a sufficiently wide hydraulic pressure acting area at the open end. be.

The piston for a disc brake according to the present invention is preferably formed from a steel ingot by forging.

That is, a cylindrical body with a bottom is formed from a steel ingot, a pair of notches are provided at the opposing peripheral edges of the open end face, and the outer circumferential face slightly separated from the open end face is radially inwardly formed by, for example, rolling. By recessing in the direction, a uniform wall thickness can be obtained, and a sufficient hydraulic pressure acting area can be provided on the open end surface that abuts against the friction pad.

The present invention will be explained based on illustrated embodiments.

FIG. 1 shows an outline of a conventional disc brake, in which a hollow piston 7, more precisely a bottomed cylindrical piston 7 fitted into a hydraulic cylinder 3, has a friction pad 4 at its open end.
The friction pad 4 is brought into contact with the back plate 14 of the brake disc 10.
It is designed to obtain a frictional engagement by pressing against it.

At the open end, the outer periphery of the piston T is removed to form a small-diameter portion 7b, and one end of a cylindrical flexible dust-proof boot 8 is tightly fitted and supported on the small-diameter portion 1b.
In the above-mentioned conventional piston 7 whose other end is locked to the cylinder 3, the wall thickness of the small diameter portion 7b is different from that of the cylinder fitting portion 7a due to manufacturing reasons.
It is smaller than.

As shown in FIGS. 7 and 8, the piston 17 according to the present invention is formed with an annular groove 29a for locking a dustproof boot without damaging the wall thickness near the opening end, and also has an annular groove 29a formed on the opening end surface 30.
The external shape of a is the longitudinal direction of the friction pad assembly (generally, the friction pad assembly extends in the circumferential direction of the brake disc).

) It is an oval shape that spreads out.

The annular groove 29a is manufactured by applying an external force from the outer periphery by rolling to deform a portion a short distance l from the open end surface 30a of the piston 17 radially inward, and then performing mechanical finishing. .

・Opening end surface 30 that still has an oval shape
a (the shaded area in Fig. 7) is a pair of notches 3 formed in the opening edge or opening end face before the above-mentioned rolling process.
2 (FIG. 5).

Specific examples of the device for manufacturing the piston according to the present invention are shown in the second to
It is shown in Figure 6.

To obtain a piston with outer diameter R1 of the cylinder fitting part: 51r/LrIL, outer diameter R2 of the groove part = 43mm, total length L- = 48mm, and distance from the opening end face to the center of the groove about 1125 mm. , first the diameter is the piston maximum outer diameter R
A 5IOC-835C carbon steel bar with a size of about 80 mm is cut into a predetermined length (determined by calculating the internal volume of the piston) to obtain material 20 (Fig. 2), and the entire outer surface of this material is coated with metal soap. Apply a coating.

Next, this material 20 is inserted into a concave mold 21 having an inner diameter R1, and pressurized by a pressing mold 23 at room temperature to form a material 22 having the same diameter and smooth both end surfaces (FIG. 3).

After the material 22 is annealed, the entire surface is polished with shot plastin ink and a metal soap coating is applied again.

When the material 22 subjected to the above treatment is inserted into a mold 21a similar to the concave mold 21 and extruded backward by a punch 23a having an outer diameter R3←R1-2t), a cylindrical body 24 having a bottom portion 24a is formed. formed (Fig. 4).

Here, the cylindrical body 24 has a substantially uniform wall thickness t throughout, and its total length is slightly longer than the total length of the finished piston.

Next, at the portion where the open end surface 30 of the cylindrical body 24 intersects with the radial direction line, there are a pair of notches 32, 3 that are gently curved in a V-shape.
2 (Figure 5).

It can also be formed simultaneously by forging.

The depth of the notch 32 is set to a value smaller than the distance l described later.

Finally, as shown in FIG. 6, a rolling roll 2 is supported on a support shaft 27 parallel to the axis 31 of the cylinder, as shown in FIG.
If the cylindrical body 24 is rotated around the axis 31 while strongly pressing the roller 5, the outer circumferential surface of the cylindrical body 24 is depressed radially inward by the external force applied to the roll 25, and an annular recess 29 is formed.

At the same time, the notch 32 is larger than the other end face portions of the rolling roll 25.
Since the amount of processing is small, a continuous and flat opening end surface 30a having an oval outer shape can be obtained.

At this time, the roll 26 on the support shaft 28, which is somewhat inclined with respect to the axis 31, is also pressed against the inner circumferential surface of the cylindrical body 24, thereby suppressing the reduction in the diameter of the opening end.

Thereafter, after cutting the recessed part 29 formed by the roll 25 to form the recessed groove 29a for locking the dust-proof boot, chrome plating is applied to these surfaces to make the wall thickness almost uniform and corrosion and abrasion resistant. A rich hollow piston is obtained.

Note that the above-described rolling of the recess 29 fixes the cylindrical body 24 and
While applying an external force to each roll 25, 26, the cylindrical body 24 is
It may be made to circulate along.

The groove 29a has a rectangular cross section near the bottom, and the opening edge is inclined or rounded.

This prevents the dust-proof boot from being unreasonably bent due to the movement of the piston.

The disc brake piston according to the present invention has an oval opening end surface 30a expanding in the circumferential direction of the brake disc;
That is, the long axis of the ellipse is arranged parallel to the tangential direction of the brake wheel to provide a uniform hydraulic pressure distribution to the friction pad assembly that extends in the circumferential direction of the brake wheel.

□Furthermore, since the dimension of the opening end face 30a arranged in the radial direction of the brake disc is small, a sufficient space for accommodating the dust-proof boot can be secured between the opening end face 30a and the hydraulic cylinder part.

Regarding the caliper that is integrated with the hydraulic cylinder, it is advantageous in terms of strength because it is not necessary to reduce the wall thickness of the part that straddles the brake disc so much for the dust-proof boot.

As described above, the feature of the present invention is that a steel ingot, more precisely, a solid cylindrical material, is formed into a cylinder with a bottom by a backward extrusion process, and further, the area near the open end is rolled by a roll that presses from the outer circumferential side. The piston has a concave part for locking the dust-proof boot during the manufacturing process, and the bottom part of the piston can be used as is without any special heat treatment during manufacturing. However, the wall thickness is uniform throughout, making it possible to obtain a hollow piston that is lighter than conventional pistons.

The piston according to the invention also has the following advantages:

(1) Since the wall thickness of the recess for locking the dustproof boot is not impaired and the opening end is not reduced, a sufficient area of hydraulic pressure action on the friction pad assembly can be secured.

(2) Because the hydraulic pressure area is larger than that of conventional ones,
The pressing force of the friction pad against the brake disc is evenly distributed, reducing uneven wear of the friction pad.

(3) Since the concave groove can be made sufficiently deep without sacrificing the wall thickness, the dust-proof boots can be securely locked.

- (4) Compared to conventional forging, since no heat treatment is involved, it is easy to make the process continuous, and cutting of the outer peripheral surface is also easy, and the amount of cutting is small.

(5) Compared to those made by casting, there is no risk of a reduction in braking force due to leakage of hydraulic fluid due to the casting cavity, and since carbon steel is used as the material, it is highly durable.

(6) Compared to a material cut from a steel bar material, it is superior in strength because the flow of fibers (inward fibrous weave) is not cut.

Brief description of the drawings: - Figure 1 is a vertical cross-sectional view of a conventional disc brake equipped with a hollow piston, Figures 2 to 6 are explanatory diagrams showing the manufacturing process of the piston according to the present invention, and Figure 7 is a front view of the same piston. Figure, 8th
The figure is a cross-sectional view taken along the line 2 in FIG. 7.

24: Cylindrical body, 24a: Bottom, 25, 26: Roll, 2
9: recess, 29a: groove, 30, 30a: end surface, 32:
Notch.

Claims (1)

[Claims] 1. Opening of the bottomed cylindrical body 1] In a disc brake piston having an annular groove for locking one end of a dust-proof boot formed by projecting a peripheral wall portion slightly apart from the end surface radially inward, the friction pad The shape of the opening end surface that abuts against the back metal of the assembly body is an ellipse that extends in the circumferential direction of the brake disk, and the long axis of the oval that extends in the circumferential direction of the brake disk is approximately equal to the outer diameter of the cylinder fitting portion. A piston for a disc brake, characterized in that a short axis extending in the radial direction of the brake disc is slightly larger than the bottom of the annular groove.