JPH022988Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial field of application This invention relates to an automatic clearance adjustment device for drum brakes that automatically adjusts the clearance between the inner peripheral surface of the drum and the lining only at room temperature. be.

Conventional technology Automatic clearance adjustment devices for drum brakes that have been used in the past have been known to mechanically adjust as the piston operates when the clearance between the inner peripheral surface of the drum and the lining increases and the forward stroke of the piston in the wheel cylinder increases. It is designed to reduce the lining gap, independent of drum temperature and wheel cylinder operating temperature.

Problems to be Solved by the Invention In the conventional automatic gap adjustment device, the temperature factor is not involved in the gap adjustment mechanism at all, so the gap is adjusted as long as the gap exceeds a certain value. Therefore, the brakes are operated more frequently,
The gap between the inner circumferential surface of the drum and the pad, which is adjusted when the drum temperature and the wheel cylinder hydraulic oil temperature are high, is less than the required gap at room temperature, and even when not braking,
There is a problem in that the inner peripheral surface of the drum and the pad are in contact with each other, resulting in a so-called dragging phenomenon. Therefore, the standard clearance at room temperature is set to a value higher than the required clearance to deal with the problem of over-adjustment at high temperatures, but this makes the standard clearance value between the inner peripheral surface of the drum and the pad unclear. However, there remain problems that complicate brake adjustment. This idea is
It is an object of the present invention to provide an automatic gap adjustment device for a drum brake that solves the above-mentioned problems and is configured to automatically adjust the gap only when the temperature of the wheel cylinder hydraulic oil is below a certain level.

Means for Solving the Problem In order to solve the above-mentioned problems, this invention includes a clutch fixed to the inner end surface of the piston, which forms an automatic clearance adjustment device, and a clutch that engages with the clutch in a ratchet manner, so that the piston stroke has a constant length. If it increases beyond that, it will form a new engagement with the clutch,
The elastic body that presses the guide formed to reduce the piston stroke is made of bimetal or shape memory alloy, and above a certain temperature,
It is designed to eliminate the contact surface pressure on the engagement surfaces of the clutch and the guide, making it impossible to engage the clutch and the guide, and thus losing the clearance adjustment function.

Example The illustrated embodiment will be described below.

1 is a wheel cylinder. In the illustrated embodiment, a double-acting type is shown, and the components installed in the wheel cylinder 1 are arranged symmetrically with respect to the central cross section. When a single-acting wheel cylinder 1 is used, it is formed of components on either the left or right side. A fixed guide 2 formed into a thick-walled cylinder is press-fitted into the inner peripheral surface of the wheel cylinder 1 at the center in the axial direction. A pressure introduction hole 3 is provided through it. Helical teeth 4 are formed on the inner peripheral surface of the fixed guide 2 and mesh with a helical gear 6 formed on the outer peripheral surface of the adjuster 5. The adjuster 5 is formed into a ring shape with a wide width, a protruding boss is formed on one end face of the ring, and a pawl tooth shape 7 is formed on the end face of the boss. It forms a racket mesh with a clutch 9 formed on the wheel 8. Clutch 9 is piston 1
It is fixed to the inner end surface of the piston 10 and is formed to move together with the piston 10. In the illustrated embodiment, a clutch base 11 that protrudes from the inner end surface of the piston 10 and a pressing base 12 that is concentric with the clutch base 11 and has a small diameter are formed integrally with the piston 10. Then, the clutch 9 is press-fitted and fixed to the clutch base 11, and the opposite side of the adjuster 5, which is in ratchet engagement with the clutch 9, is pressed by a circular leaf spring 13 screwed and fixed to the end face of the pressing base 12. The pawl tooth profile 7 and the pawl wheel 8 are formed so that an appropriate contact surface pressure is generated between their meshing surfaces. piston 10
A coil formed of a so-called shape memory alloy is inserted between the circular plate spring 13 and the stepped end surface 14 of the clutch base 11 and the pressing base 12 on the inner end surface of the coil. Spring 15
It is formed by providing. At room temperature, the coil spring 15 loses the force of the circular leaf spring 13 and the adjuster 5
is applied to the clutch 9 by the spring force of the circular leaf spring 13.
However, when the temperature of the hydraulic oil inside the wheel cylinder 1 rises, the coil spring 1
5 overcomes the force of the circular leaf spring 13 and extends the length of the coil, presses the circular leaf spring 13, and forms the circular leaf spring 13 away from the adjuster 5. Further, when the temperature of the hydraulic oil in the wheel cylinder 1 decreases, the spring force of the circular leaf spring 13 is again exerted, and the adjuster 5 is formed to be pressed. The piston 10 is formed with a screw hole 16 opening on the outer end surface, into which an adjustment bolt 17 is screwed. The adjusting bolt 17 has a parallel groove formed in its head, and the web 19 of the brake shoe 18 is inserted between the parallel grooves and engaged, and also comes into contact with the bottom surface of the parallel groove, so that the pressing force of the piston 10 is applied to the brake shoe. 18. This automatic gap adjustment device increases the gap between the inner peripheral surface of the drum and the pad.
When the amount of displacement of the brake shoe 18 during brake operation increases, the forward stroke of the piston 10 increases. As the forward stroke of the piston 10 increases, the rotation of the adjuster 5 increases, passing over the peak of the pawl wheel 8 of the clutch 9 that is currently engaged, forming a new ratchet engagement. In other words, the adjustment bolt 17 is inserted into the parallel groove of the web 1.
9 is engaged, the piston 10 does not rotate, and the threaded surface of the screw hole 16 of the piston 10 has a high surface pressure due to braking, so the piston 10 also does not rotate as a unit. The adjuster 5 rotates against the pressing force of the circular leaf spring 13 to form a new ratchet mesh.
When the pressure is removed in this state, the pawl wheel 8 of the clutch 9
The threaded portion of the screw hole 16 and the adjusting bolt 17 slip by a central angle corresponding to one peak, and the adjusting bolt 17 protrudes by a pitch corresponding to the central angle, reducing the gap. In this case, the brake shoe 18 is designed to be pulled back by the tension of a separately provided return spring when the pressure is released. Now, as the drum temperature rises, the operating temperature of the wheel cylinder 1 rises, and when it reaches a certain temperature, the coil spring 15 overcomes the spring force of the circular leaf spring 13 and expands, and the clutch 9 and the adjuster 5 is lost, the adjuster 5 rotates independently of the clutch 9, and the clearance adjustment function is lost. When the temperature of the hydraulic oil in the wheel cylinder 1 falls below a certain temperature, the spring force of the circular leaf spring 13 overcomes the force of the coil spring 15 and restores the clutch 9 and the adjuster 5 with appropriate contact surface pressure. The ratchet engagement is restored and the clearance adjustment function is restored.

Effects Since this invention is constructed as claimed in the utility model registration based on the above-mentioned embodiment, the problem of over-adjustment due to clearance adjustment at high temperatures is eliminated, and the reference clearance at room temperature can be determined with high accuracy. Become. In other words, mutual pressing force between the ratchet meshing surfaces of the clutch and adjuster is induced by a combination of a non-temperature-sensitive material and a temperature-sensitive material, and only the pressing force from one of the materials is always applied, so the ratchet function works clearly. That's what I do. Since the circular plate spring is pressed by a coil spring made of a shape memory alloy, the coil spring deforms in a short period of time depending on the temperature, and a specific operation can be performed based on the correlation between the drum temperature and the wheel cylinder hydraulic oil temperature. Once the oil temperature is determined, it becomes possible to specify the temperature with high accuracy and adjust the gap. The coil spring presses the inner side of the contact circle between the circular leaf spring and the adjuster, so that the circular leaf spring and the adjuster come into contact and separate clearly.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional view of a drum brake including an automatic clearance adjustment device, and FIG. 2 is an enlarged explanatory view of a clutch portion. DESCRIPTION OF SYMBOLS 1...Wheel cylinder, 2...Fixed guide element, 5...Adjuster, 9...Clutch, 10...Piston, 12...Press base, 15...Coil spring, 17...Adjustment bolt, 18... ...Brake use.

Claims (1)

[Scope of utility model registration request] A fixed guide that is fixed to the inner circumferential surface of the axially central part of a wheel cylinder for internal expansion of the brake shoe in a drum brake, is formed into a thick-walled cylinder, and has a helical tooth profile on the inner circumferential surface, and a helical tooth profile of the fixed guide. The adjuster has a meshing gear formed on its outer circumference and rotates as the piston moves, and a clutch that rotates together with the piston and engages with the adjuster in a ratchet manner.The ratchet engagement of the clutch causes the piston to rotate. In the automatic gap adjustment device, the gap is adjusted by rotating the adjuster 5, screwing it into the piston, and protruding an adjustment bolt that engages with the brake shoe. Clutch base 1 formed in
A circular leaf spring 13 is fixed to the end face of a pressing base 12 protruding from the pressure base 12, and a shape memory metal is formed between the circular leaf spring 13 and the ring end face of the adjuster 5, and the coil length is expanded by temperature rise. The pressing force of the circular leaf spring 13 is eliminated, and as the temperature decreases, the circular leaf spring 1
An automatic clearance adjustment device for a drum brake, characterized in that a coil spring 15 is provided to recover the pressing force of No. 3 for pressing.