JPH0632775U - Vehicle drum brakes - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the cost and improve the productivity by facilitating the machining of the piston of the wheel cylinder and by forming it with rigid resin or forging. Prevents deterioration of piston boots. Protect the wheel cylinders from the effects of braking heat. [Structure] A retainer 21 has a piston fitting portion 21a covering the tip side of a small diameter portion 9b, and a flange 21b protruding outward from a side edge of a cylinder body of the piston fitting portion 21a.
And. Flange 21b and large diameter portion 9a of piston 9
At the base end side of the small diameter portion 9b sandwiched between
The boot groove 22 into which the small-diameter edge portion 23a of 3 is fitted is defined.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a drum brake used in a vehicle such as an automobile or a motorcycle, and more particularly to a drum brake having a structure provided with a retainer between a piston of a wheel cylinder and an end portion of a brake shoe on an expansion side.

[0002]

[Prior art]

 As a conventional technique in which a retainer is interposed between the end of the brake shoe on the side of expansion and the piston of the wheel cylinder that supports the brake shoe, there is one disclosed in Japanese Utility Model Publication No. 2-10827, for example.

In this technique, a boot groove is provided around a small diameter portion of a piston, a slit is cut in an outer end surface of the small diameter portion, and a pair of projecting pieces are opposed to both sides of the slit so that a retainer is provided on the retainer. Is a cylindrical skirt that covers the outer end of the piston boot attached between the boot groove and the end of the cylinder body over the protruding length of the piston due to the wear of the brake shoes. And a web contacting piece laid on the bottom surface of the slot groove and two notch holes fitted to the projecting piece are formed on the bottom of the skirt that covers the outer end surface of the piston boot. With the above configuration, the piston boot is prevented from deteriorating due to the high-temperature wear powder scattered from the brake shoe during braking.

[0004]

[Problems to be solved by the device]

 With such a structure, when the piston is made of a metal rod such as round steel, the boot groove needs to be machined into the piston, and in the case of a rigid resin piston, the boot groove is formed. The parting line of the mold remains as a parting line, which may impair the sealing performance of the piston boot.

Therefore, the present invention solves the above problems by forming a boot groove by using a retainer interposed between the piston and the brake shoe while preventing deterioration of the piston boot. The purpose is to provide a drum brake for.

[0006]

[Means for Solving the Problems]

 In view of the above-mentioned object, the present invention is to accommodate a large diameter portion of a piston in a cylinder hole bored in a cylinder body of a wheel cylinder, and a small diameter portion of a piston protruding from the cylinder hole and an end portion of the cylinder body. A vehicle in which the brake shoe is supported by a piston boot, and a retainer is interposed between the outer end of the small diameter portion and the end of the brake shoe on the expansion side. In the above-mentioned drum brake, the retainer described above includes a piston fitting portion that covers the tip end side of the small diameter portion of the piston and supports the end portion of the brake shoe, and the cylinder body side of the piston fitting portion. A flange for covering the outer surface of the piston boot is formed, and a boot groove for fitting the piston boot is defined on the base end side of the small diameter part of the piston sandwiched between the flange and the large diameter part of the piston. It is characterized in that the.

[0007]

[Action]

 The boot groove of the piston is defined by the large diameter part of the piston and the flange of the retainer on the base end side of the small diameter part of the piston. There is no need for shaving.

[0008]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS.

In the drum brake 1, bow-shaped brake shoes 3 and 4 arranged to face each other inside the back plate 2 back the middle portion of each web 5 with a shoe hold down pin 6 and a shoe hold spring 7. It is elastically supported by the plate 2, the end 5a on the expansion side is supported by the piston 9 of the wheel cylinder 8, and the end 5b on the fulcrum side is supported by the anchor 10.

A rim 11 is fixed to the outer edge of the web 5, and a lining 12 which is in sliding contact with a brake drum (not shown) is fixed to the rear surface of the rim 11. The brake shoes 3 and 4 are urged to a reduced diameter position by coiled return springs 13 and 14 stretched between the webs 5 and 5, and when braking, the pistons 9 and 9 of the wheel cylinder 8 are By the pushing movement, the anchor 10 is expanded outward with the fulcrum as a fulcrum, and the lining 12 on the outer surface is brought into sliding contact with the inner peripheral surface of the brake drum to perform a braking action.

An automatic braking gap adjusting device 15 is provided near the inside of the return spring 13, and the linings 12, 12 of the brake shoes 3, 4 are worn away, so that the braking gap automatic adjusting device 15 is provided between the brake drum 3 and the inner peripheral surface of the brake drum. When the braking gap of No. 2 is expanded beyond the set value, the adjusting device 15 restricts the retracted positions of the expanded brake shoes 3, 4 to the outside so that a predetermined braking gap is compensated. There is. Further, a parking brake parking lever 16 for expanding and opening both brake shoes 3 and 4 is pivotally supported by a support shaft 17 on one of the brake shoes 3, so that the braking action can be performed by the parking brake operation. It has become so.

The wheel cylinder 8 is a double-ended cylinder in which a cylinder hole 8b is formed through a cylinder body 8a that is bolted to the back plate 2 and the above-mentioned pistons 9 and 9 are housed in the cylinder hole 8b. The pistons 9, 9 are urged in directions away from each other by the elastic force of a wheel cylinder spring 19 that is compressed in the hydraulic chamber 18 in the middle.

Each piston 9 has a large-diameter portion 9a slidably inserted into the cylinder hole 8b and a small-diameter portion which is continuous with the outer end surface of the large-diameter portion 9a and projects outside the cylinder hole 8b. It is composed of a portion 9b and a stopper protrusion 9c protruding from the inner end surface of the large diameter portion 9a toward the hydraulic pressure chamber 18 side. A seal groove 9d into which the piston cup 20 is fitted is provided around the large-diameter portion 9a, and a slot groove 9e opening to the tip surface and a slot groove 9e are formed on the tip side of the small-diameter portion 9b. Protrusions 9f and 9f facing each other are provided. A retainer 21 is attached to the distal end side of the small diameter portion 9b, and by the attachment of the retainer 21, a large diameter edge portion 23b and a large diameter edge portion 23b are formed in a boot groove 22 defined on the base end side of the small diameter portion 9b. The small-diameter edge portion 23a of the piston boot 23 fitted to the outer surface of the end portion of 8a is fitted.

The retainer 21 has a piston fitting portion 21a that entirely covers the tip side of the small diameter portion 9b, and a flange that projects outward from the side edge of the cylinder body of the piston fitting portion 21a and covers the outer surface of the piston boot 23. 21b. The piston fitting portion 21a has a web contact piece 21c laid in the slot 9e and a bag-shaped web guide 21d that continuously surrounds the projection pieces 9f and 9f on both sides of the web contact piece 21c. , 21 d. Further, the flange 21b has a dish shape in which the outer peripheral portion slightly projects toward the piston fitting portion 21a side, and is formed to have the same diameter as the piston boot 23 or a slightly larger diameter.

Elastic projections 21e, 21e recessed inward are provided on the outer surfaces of the web guides 21d, 21d, and when the piston fitting portion 21a is attached to the tip side of the small diameter portion 9b, the elastic projections 21e, 21e are formed. 21e elastically engages with the outer peripheral surface of the projecting piece 9f to prevent the retainer 21 before supporting the web 5 from being pulled out. Further, when the retainer 21 is attached, the above-mentioned boot groove 22 is defined by the large diameter portion 9a and the flange 21b on the base end side of the small diameter portion 9c, and each web 5 of the brake shoes 3, 4 is formed. The end 5a on the expanding side is supported by the web contacting piece 21c of the retainer 21 attached to the tip side of the small diameter portion 9b.

In this embodiment configured as described above, since the flange 21b of the retainer 21 covers the entire outer surface of the piston boot 23, the abrasion powder generated in the brake shoes 3 and 4 is blocked, and the piston boot 23 is protected. In addition to preventing deterioration, the piston 5 is not damaged by the web 5 when the shoes 3 and 4 are assembled, and the quality is maintained well. Further, the web contacting piece 21c of the retainer 21 supports the end portion 5a on the expansion side of the web 5, and the web guides 21d and 21d cover both sides of the end portion 5a so that the end portion 5a of the web 5 is Since the contact with the piston 9 is cut off, the braking heat of the brake shoes 3 and 4 is not transmitted to the hydraulic fluid in the hydraulic chamber 18 from the piston 9 to cause a trouble such as a vapor lock phenomenon.

Further, since the flange 21b of the retainer 21 defines the boot groove 22 on the proximal end side of the small diameter portion 9b together with the large diameter portion 9a of the piston 9, the small diameter portion 9b of the piston 9 extends over the entire length. The same diameter is enough. As a result, when the piston 9 is formed of a metal rod such as round steel, it is not necessary to separately process the boot groove, and the number of processing steps can be reduced and the cost can be reduced. Further, in forming the large diameter portion 9a and the small diameter portion 9b, the molding die is pulled out toward the tip of the small diameter portion 9b, so that no parting line remains on the outer peripheral surface of the small diameter portion 9b where the boot groove 22 is defined. Even when the piston 9 is made of a rigid resin that is easy to manufacture, lightweight and inexpensive, the sealing performance of the piston boot 23 is not impaired. Further, the piston 9 may be a forged product such as aluminum forging, which is cheaper than the cost for cutting out from a metal rod.

The retainer 21 is assembled to the piston 9 before supporting the web 5 of the brake shoes 3, 4, but the elastic projection 21e of the retainer 21 is engaged with the outer peripheral surface of the projecting piece 9f of the piston 9. In addition, since the retainer 21 is prevented from coming off, the small-diameter edge portion 23a of the piston boot 23 fitted in the boot groove 22 is securely held and the assembling work of the web 5 is facilitated.

FIG. 4 shows another embodiment of the present invention, in which the retainer 21 is prevented from coming off on the outer side of the projecting piece 9f of the piston 9, whereas in this embodiment, the slot 9e is provided. An example is shown in which the retainer 21 is prevented from coming off inside the protruding piece 9f by utilizing it.

That is, in the retainer 21, elastic claw pieces 21f, 21f recessed inwardly of the bottomed cylindrical body in a V shape are cut in the facing surfaces of the web guides 21d, 21d, respectively, and the small diameter portion 9b has a small diameter portion 9b. When the retainer 21 is attached to the tip side of the small-diameter portion 9b, the elastic claw pieces 21f are attached to the protrusions 9f and 9f. The retainer 21 before the support of the web 5 is retained by being fitted into the locking recess 9g.

The elastic claw pieces 21f, 21f of the retainer 21 also apply the reaction force from the projecting pieces 9f, 9f inwardly, so that the end 5a of each web 5 housed between the web guides 21d, 21d. May be held with an appropriate elastic force. In this case, in the brake shoes 3 and 4 at the time of expansion and contraction, the rattling and the inclination of the web 5 in the disc axial direction are suppressed by the elastic claw pieces 21f and 21f, so that the lining 12 on the outer periphery of the brake shoes 3 and 4 is prevented. It can be moved parallel to the inner surface. As a result, the respective linings 12 are entirely pressed against the inner peripheral surface of the brake drum, so that the damping force can be improved and uneven wear of the linings 12 can be prevented.

In both of the above embodiments, the retainer is provided with the elastic projection and the claw piece to prevent the retainer from coming off from the small diameter portion of the piston. The purpose of can be achieved.

[0023]

[Effect of device]

 As described above, the present invention covers the tip side of the small diameter part of the piston protruding from the cylinder hole of the wheel cylinder with the piston fitting part of the retainer, and at the cylinder body side of the piston fitting part, The flange that covers the outer surface of the piston boot and the end of the piston large diameter part define a boot groove for fitting the piston boot on the base end side of the piston small diameter part. Protects the brake shoes from wear particles, prevents damage when assembling the brake shoes, prevents deterioration of the piston boots, maintains good sealing performance for a long period of time, and prevents the retainer's piston fitting part from braking. Shields the heat and ensures the performance of the wheel cylinder.

Further, by forming the boot groove using the flange of the retainer, the small diameter portion of the piston can have the same diameter over the entire length, so that the piston is formed of a metal rod such as round steel. In this case, it is not necessary to separately process the boot groove, and the number of processing steps can be reduced and the cost can be reduced. Further, since the molding die can be pulled out toward the tip of the small diameter portion to form the large diameter portion and the small diameter portion, there is no parting line on the outer peripheral surface of the small diameter portion, and even when the piston is made of rigid resin, Since the sealing performance of the piston boot is not impaired, it is easy to manufacture, lightweight and inexpensive. Further, this piston can be made into a forged product such as aluminum forging, which is lower in cost than shaving from a metal rod. In this way, by utilizing the flange of the retainer to form the boot groove, the present proposal can improve the productivity as a whole and significantly reduce the cost.

[Brief description of drawings]

FIG. 1 is an enlarged view of a main part of FIG.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a front view of a drum brake according to an embodiment of the present invention.

4 is an exploded perspective view of a wheel cylinder and a retainer used in the drum brake of FIG.

FIG. 5 is an enlarged view of an essential part showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Drum brake 2 ... Back plate 3,4 ... Brake shoe 5 ... Web of brake shoes 3 and 4 5a ... End part of web 5 on the expansion side 5b ... End part of web 5 on the fulcrum side 8 ... Wheel cylinder 8a ... Cylinder body 8b ... Cylinder hole 9 ... Piston 9a ... Large diameter part of piston 9 9b ... Small diameter part of piston 9 9e ... Groove 9f ... Projection piece 9g ... Locking recess 10 ... Anchor 12 ... Lining 18 ... Hydraulic chamber 21 ... Retainer 21a attached to the tip side of the small diameter portion 9b ... Piston fitting portion 21b of the retainer 21 ... Flange 21c of the retainer 21 ... Web contact piece 21d of the piston fitting portion 21a ... Web guide of the piston fitting portion 21a 21e ... Elastic projection 22 ... Boot groove 23 ... Piston boot 23a ... Small diameter edge of piston boot 23

Claims (1)

[Scope of utility model registration request] 1. A large diameter portion of a piston is accommodated in a cylinder hole formed in a cylinder body of a wheel cylinder, and a small diameter portion of the piston protruding from the cylinder hole is provided between an end portion of the cylinder body. A drum brake for a vehicle, which is covered with a piston boot, has a retainer interposed between the outer end of the small diameter portion and the end of the brake shoe on the expansion side, and supports the brake shoe. A piston fitting portion that covers the tip end side of the small diameter portion of the piston and supports the end portion of the brake shoe, and a flange that covers the outer surface of the piston boot on the cylinder body side of the piston fitting portion. And a boot groove into which the piston boot is fitted is defined on the base end side of the small diameter portion of the piston sandwiched between the flange and the large diameter portion of the piston. Drum brakes for vehicles.