JPS6145086B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention is mainly for vehicles such as automobiles, and in response to wear of brake shoe linings during use,
The present invention relates to an automatic adjustment device for a shoe drum that includes an automatically varying length device configured and operative to maintain a predetermined maximum clearance of the shoe to the drum. The invention also includes a shutter drum brake that includes such an automatic adjustment device.

Various types of such adjustment devices are widely used in braking systems for automobiles and other vehicles, and are generally satisfactory under most conditions of use.
However, under certain conditions, such as extended braking when driving down a long hill, the heating that occurs in the drum causes it to expand, thereby increasing the clearance of the shoe to the drum and thus causing the adjustment device to This has the effect of causing a compensatory adjustment of the show. Therefore, when the drum subsequently contracts during cooling, it may come into permanent contact with the shoe in its newly adjusted retracted position, thereby locking the brake. If the adjustment device were configured to leave sufficient running clearance to eliminate this possibility, the travel of the shoe required to allow the shoe to contact the drum operating at normal temperatures would be unacceptably large.

In an attempt to solve this problem, bimetallic elements have been used in the past. In one prior art application to an adjustment device that includes struts of variable length between struts, a bimetallic element is provided between a pair of mutually movable portions of the adjustment device strut, such as a handbrake actuating load. supports the forces transmitted through the struts. Bimetallic elements are not only limited by the adjustment effect they can provide, but also because bimetallic elements can collapse when excessive loads are applied through the struts, so adjustments cannot be made while the struts are carrying high compressive loads. When used in regulating devices, the above structure is unsatisfactory.

The purpose of the present invention is to
It is an object of the present invention to provide a strut adjuster which operates in a manner that solves the overadjustment problem and is capable of achieving this effect without requiring the strut adjuster to support very high loads transmitted through the strut. The regulating device of the invention is therefore more flexible in application than conventional regulating devices with temperature compensation elements.

The present invention is arranged between a pair of brake shoes and automatically adjusts its length to maintain the maximum clearance between the brake shoe and the drum at a predetermined value as the lining of the brake shoe wears. an automatic adjustment device for a shuttered drum brake including a strut with variable struts, the strut comprising a pair of mutually telescoping members movable longitudinally relative to one another; One end of one of the members engages with an abutment member carried by the other member to transmit a compressive load applied to the strut, and a temperature sensitive element of shape memory alloy material is connected to the strut. surrounds one of the members, both ends of the temperature sensitive element abut the pair of members, and move in a direction to relatively separate the pair of members when the temperature of the temperature sensitive element rises; The length of the strut is increased by increasing the length of the strut, and when one end of the one member is engaged with the abutting member, the compressive load is transmitted independently of the temperature sensitive element. An automatic adjustment device is provided.

The automatic adjustment device of the present invention has a very simple and compact temperature sensitive mechanism.

Embodiments of the present invention will now be described with reference to the accompanying drawings.

The illustrated drum brake includes a pair of brake shoes 1 provided in a brake drum (not shown).
2, the shoes have one pair of adjacent ends engaged with the anchor member 3 and the other adjacent pair of ends cooperating with a hydraulic actuator 4, whereby actuation of the actuator causes the shoes 1 and 2 to It is expanded and pressed against the drum against the action of the shoe return spring 5. Activation of the shoe is also possible by angularly moving the handbrake lever 6, which is pivoted on the shoe 2 by a pin 7, clockwise.

An automatic strut adjustment device 8, generally indicated at 8, extends between the shoes 1 and 2 to a position adjacent the actuator 4. The strut adjustment device includes a male part 9 having an externally threaded end 10 receivable within a female part 11. The outer end portions of the strut parts 11 and 9 have slots for accommodating the shoes 1 and 2, respectively, and the male part 9 also accommodates the handbrake lever 6 in its slot. The male part 9 carries a nut 12 which is screwed into the threaded end part 10, and the ratchet teeth 13 on the cylindrical outer circumferential surface of the nut 12 connect to a pawl lever 14 which is pivotally connected to the shoe 1 by a pin 15.
is engaged with the end portion 14A of. Show return spring 5
exerts a compressive force on the strut, and the pawl lever 14 is pressed clockwise by the pawl spring 16, so that the flange 17 of the pawl lever is always in contact with the female part 11 of the strut. The shoe return spring 5 exerts a greater force than the spring 16 when the brake is inactive so that the shoe 1 abuts the female member 11 of the strut within its slotted end.

A temperature sensitive element of shape memory alloy material is shown as a helical coil 18 surrounding the female strut portion 11 and abutting against a shoulder 19 formed on the female portion 11 at one end and against the nut 12 at the other end.

When the brake is activated by actuating the actuator 4, the shoes 1 and 2 are pushed away from each other against the action of the shoe return spring 5.
As shown, the adjustment device 8 is pushed to the right by the spring 16 via the flange 17 of the lever 14;
The strut is pressed against the brake shoe 2 and the shoe 1 separates from its normal contact point with the female part 11. That is, it is separated from the regulating device. Clockwise pivoting of the lever 14 as the adjustment device moves to the right causes a downward movement of the end 14A of the lever 14.
If this movement is sufficient to move the end 14A of the lever from one ratchet tooth of the nut 12 to the next, i.e. if the outward movement of shoes 1 and 2 is excessive, the nut 12 will displace the adjusting device. It rotates in a direction that lengthens it, reducing the gap between the shoe and the drum when it is not in operation.

During brake operation at normal temperatures, strut members 9 and 11 remain in abutment with each other and coil 18 has no effect on brake operation. However, if the brakes reach very high temperatures, for example as a result of frequent braking while descending a steep downhill slope, the drum will expand and, without the temperature sensitive coil 18, temporary excessive shoe movement will occur. , and the regulating device is corrected for this, with the possibility that the brakes will lock up when cooled.
However, in the brake of the present invention, when the strut is released from the force of the shoe return spring during operation, if the temperature becomes too high, the length of the coil 18 increases and the male and female portions of the strut separate. , thereby increasing the length of the strut. The force of spring 16 is selected such that the expansion of coil 18 exceeds it, and coil 18 is configured such that the corrected expansion of the shoe approximates the expansion caused by the drum. This means that the clearance of the shoe to the drum remains close to that during normal temperature conditions. Therefore, during hot brake operation, no shoe adjustment occurs unless excessive wear occurs, and automatic adjustment continues in much the same way as under cold conditions. As the drum cools,
The coil 18 contracts to its original length and the male and female parts 9 and 11 of the strut return to their normal mutual abutment.

A second important feature of the invention is the male part 9 of the adjustment device.
and the female part 11 are in direct contact at all times during braking during driving, except when temperature compensation is carried out, so that very high loads, such as occur, for example, during application of the handbrake, cannot be applied to the entire adjusting device. The advantage is that these loads are not applied to the coil 18 at all. High temperature drum condition, i.e. coil 18
is inflated and the male part 9 and female part 11 of the adjustment device are moved apart, and when the handbrake is applied, an overload is applied to the strut, but the coil 18 is compressed and the male part 9 and the female part 11 are moved apart. Since the parts 11 abut again, this load is again transmitted through the male part 9 and the female part 11, but not through the coil 18. In this way, damage to the coil 18 is avoided, and in this respect the regulating device of the present invention is superior to the prior art, in which the temperature compensating device is subjected to loads transmitted through the struts.

Although the temperature sensitive element is shown as a coil 18 in the illustrated embodiment, it may take other shapes, such as a tube. However, since it is not compressible like a coil, it must be designed so that it does not buckle under compressive loads.

The preferred shape memory alloy material for use as the temperature sensitive element is that sold by Delta Memory Metal Company under the name "SME BRASS," although other shape memory alloy materials may of course be used. be.

[Brief explanation of the drawing]

1 is a partially sectional elevational view of a vehicular shudrum brake in an inoperative state, including an embodiment of the adjusting device of the present invention, the adjusting device being shown at ambient temperature; FIG. FIG. 2 is a view similar to FIG. 1, showing the brake with the adjusting device at elevated temperature and the brake shoe in the operating position; 1, 2: shoe, 3: anchor member, 4: actuator, 5: shoe return spring, 6: handbrake lever, 8: automatic strut adjustment device,
9: Strut male part, 11: Strut female part, 1
2: nut, 13: ratchet tooth, 14: pawl lever, 18: coil (temperature sensitive element).

Claims (1)

[Claims] 1. A device that is disposed between a pair of brake shoes and automatically maintains the maximum clearance between the brake shoe and the drum at a predetermined value in accordance with wear of the lining of the brake shoe. An automatic adjustment device for a closed drum brake comprising a strut of variable length, said strut comprising a pair of mutually telescoping members movable longitudinally relative to each other in a direction of separation; One end of one member of the pair of members engages with an abutment member carried by the other member, thereby transmitting the compressive load applied to the strut, and the temperature sensitive element of the shape memory alloy material is A direction that surrounds one member of the pair of members, such that both ends of the temperature sensitive element are in contact with the pair of members, respectively, and that when the temperature of the temperature sensitive element rises, the pair of members are relatively separated. The length of the strut is increased by moving the strut to a position where the compressive load is transmitted independently of the temperature sensitive element when one end of the one member is engaged with the abutting member. An automatic adjustment device characterized in that: 2. In the automatic adjustment device according to claim 1, the other member of the strut has a male thread on its outer periphery and carries a threaded nut, and the one member is hollow and the other member is hollow. An automatic adjustment device, characterized in that the nut constitutes the abutment member, and one end of the one member abuts the nut. 3. In the automatic adjustment device according to claim 2, the temperature sensitive element surrounds one of the members, one end of the temperature sensitive element abuts the one member, and the other end abuts the nut. An automatic adjustment device characterized by: