JP4467848B2 - Drum brake with shoe clearance automatic adjustment mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drum brake having a shoe gap automatic adjustment mechanism, and more particularly to a technique for preventing over-adjustment of a shoe gap that becomes too small.
[0002]
[Prior art]
(a) A pair of strut members that are respectively engaged with one and the other of a pair of expandable brake shoes, and disposed between the pair of strut members and screwed into at least one strut member An adjuster wheel, and a strut that defines an approach position of the pair of brake shoes during non-braking, and (b) is rotatably disposed on one of the pair of brake shoes, An adjusting lever that is rotated in response to the expansion amount of the pair of brake shoes during braking, and that is engaged with the adjuster wheel and rotates the adjuster wheel when the expansion amount exceeds a certain amount; (C) the entire length of the struts is extended by the action of a screw as the adjuster wheel rotates, and the pair of braces during non-braking Drum brake has an automatic shoe clearance adjustment mechanism for automatically adjusting the shoe clearance between the rotating drum by separating the approach position of the shoe has been widely used as a service brake and a parking brake for a vehicle. According to such a drum brake with an automatic shoe clearance adjustment mechanism, for example, the shoe clearance between the rotating drum and the brake shoe is increased due to wear of the brake shoe, and the amount of expansion of the brake shoe during braking is increased in advance. When a predetermined amount is exceeded, the adjuster wheel is rotated by the adjusting lever to extend the strut, and the shoe gap is automatically adjusted to a preset substantially constant value during braking. The brake pedal depression stroke and the parking brake operation lever operation amount are maintained substantially constant.
[0003]
By the way, at the time of sudden braking in which the brake shoe is pressed against the rotating drum with a large pressing force by an actuator such as a wheel cylinder, thermal expansion or pressing due to frictional heat generated by sliding between the rotating drum and the lining of the brake shoe. If the diameter of the rotating drum expands due to elastic deformation due to pressure, etc., even if the wear of the brake shoe is not progressing, the amount of expansion may exceed the predetermined amount, and the shoe clearance may be automatically adjusted. In such a case, if the shoe gap is automatically adjusted, the shoe gap becomes too small when the brake is released thereafter, which causes the brake to be rubbed.
[0004]
On the other hand, focusing on the temperature increase of the drum brake due to the frictional heat, it is possible to prevent the above-described unnecessary automatic adjustment (over-adjustment) of the shoe gap by utilizing the shape change accompanying the temperature increase of the bimetal. Proposed. The drum brake shown in FIG. 5 is an example, and the strut 130 disposed across the pair of brake shoes 112 and 114 includes a first strut member 140, a second strut member 142, and an adjuster wheel 144. The disc-shaped adjuster wheel 144 is integrally provided with a screw shaft 148 screwed to the first strut member 140 and a fitting shaft 150 fitted to the second strut member 142 so as to be relatively rotatable. It has been. The adjuster wheel 144 constitutes an automatic shoe clearance adjusting mechanism 154 together with an adjust lever 152 disposed on the brake shoe 114, and the adjust lever 152 is attached to the brake shoe 114 so as to be rotatable around the axis of the mounting shaft 156. In addition, the tension coil spring 158 urges the mounting shaft 156 counterclockwise, and the pressing portion 152a is always engaged with the second strut member 142 so that the second strut member 142 is moved to the first strut member 142. The strut member 140 is biased. As a result, when the pair of brake shoes 112 and 114 are expanded to both sides during braking of the service brake by the wheel cylinder 126, the struts 130 are moved following the brake shoes 112 along with the expansion. The adjustment lever 152 is rotated counterclockwise about the mounting shaft 156. When the rotation amount exceeds a certain amount, the claw portion 152b at the tip is engaged with the adjustment wheel 144, and the adjustment wheel 144 rotates in one direction. Then, the first strut member 140 is moved away from the adjuster wheel 144 by the action of the screw, so that the entire length of the strut 130 is extended, and the approach positions of the pair of brake shoes 112 and 114 during non-braking are separated from each other. The gap is kept substantially constant. A bimetal 160 bent in a hairpin shape (U-shape) is interposed between the adjuster wheel 144 and the second strut member 142, and as shown in FIG. By changing the shape so that the opening side opens, the second strut member 142 is separated to elongate the entire length of the strut 130, and the rotation of the adjusting lever 152 is restricted to prevent over-adjustment. 5A is a front view, FIG. 5B is an enlarged view of the vicinity of the adjuster wheel 144, and FIG. 5B is a state in which the shape of the bimetal 160 is changed as the temperature rises.
[0005]
[Problems to be solved by the invention]
By the way, in such a conventional over-adjustment prevention device, it is necessary to extend the strut 130 against the urging force of the tension coil spring 158, but since the dimension from the mounting shaft 156 to the pressing portion 152a is short, the strut 130 A relatively large urging force acts on 130, and a large deformation output is required as the bimetal 160. On the other hand, it is necessary to change the shape of the adjuster wheel 144 by a predetermined displacement amount with a length of about the diameter of the adjuster wheel 144. The degree of design freedom regarding the deformation output and the amount of displacement is low, and it is difficult to obtain sufficient over-adjustment prevention performance in a limited space.
[0006]
The present invention has been made against the background of the above circumstances, and its purpose is to make it possible to easily obtain a large amount of displacement in a limited space, and to provide a degree of design freedom regarding deformation output and amount of displacement. It is to improve and to prevent over-adjustment stably and reliably.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, the first invention provides (a) a pair of strut members respectively engaged with one and the other of a pair of expandable brake shoes, and a relative rotation between the pair of strut members. And an adjuster wheel screwed into at least one strut member, and a strut that defines an approach position of the pair of brake shoes during non-braking, and (b) the pair of brake shoes It is rotatably arranged on one of the shoe webs and is rotated according to the amount of expansion of the pair of brake shoes during braking, and when the amount of expansion exceeds a certain amount, the adjuster wheel An adjusting lever that is engaged to rotate the adjuster wheel, and (c) the strut by the action of a screw as the adjuster wheel rotates. In the drum brake having a shoe gap automatic adjusting mechanism that automatically adjusts the shoe gap between the rotating drum by separating the approach position of the pair of brake shoes when the brake is not braked. (d) One of the pair of strut members is disposed so as to be wound, and one end of the strut member is non-rotatably hooked on the strut member, and is extended or shortened in the winding direction as the temperature rises. Thus, the other end portion is engaged with the adjustment lever, and a temperature-sensitive deformation member that prevents the adjustment wheel from rotating by the adjustment lever is provided.
[0008]
According to a second aspect of the present invention, in the drum brake with an automatic shoe clearance adjustment mechanism according to the first aspect, the temperature-sensitive deformation member has a spiral shape wound around the strut member one or more times.
[0009]
【The invention's effect】
In such a drum brake with an automatic shoe clearance adjustment mechanism, a temperature-sensitive deformation member that prevents over-adjustment is wound around the strut member, so that a sufficient length dimension can be ensured with a small installation space. Therefore, it is possible to easily obtain the amount of displacement necessary to prevent the adjuster wheel from rotating by the adjusting lever, and by appropriately setting the material, thickness, etc. The output can be easily obtained, the degree of freedom of design regarding the deformation output and the amount of displacement is improved, and over-adjustment can be stably and reliably prevented. Further, since the temperature-sensitive deformation member is engaged with the adjustment lever and prevents the adjustment wheel from rotating by the adjustment lever, the intermediate portion (pressing portion 152a) of the adjustment lever as shown in FIG. Compared with the case where the entire length of the strut engaged with the arm is extended, the dimension from the rotation center of the adjusting lever to the engagement portion with the temperature-sensitive deformation member becomes longer. Since the required deformation output is reduced, the degree of freedom in designing the deformation output is further increased.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The adjuster wheel may be screwed to at least one of the pair of strut members, but may be screwed to both strut members via screws having opposite twists. In the case where only one is screwed, the other strut member may be connected so as to be relatively rotatable via a fitting shaft or the like. The strut member that is screwed to the adjuster wheel via a screw is held unrotatable by engagement with a brake shoe, etc., and is separated from the adjuster wheel by the action of the screw as the adjuster wheel rotates. Arranged.
[0011]
For example, the adjusting lever is disposed so as to be rotatable around a mounting shaft perpendicular to the shoe web of the brake shoe, and is rotated in one direction by a lever urging means provided between the adjusting shoe and the brake shoe. When the pair of brake shoes are expanded during braking, the struts are opposed to each other when the struts are expanded. It is configured to be moved by following the brake shoe on the side, and to be rotated around the attachment shaft in accordance with the movement.
[0012]
As the lever urging means, a spring member such as a tension coil spring or a torsion coil spring is preferably used, but it is also possible to urge using a rubber, an air spring, a magnet or the like. Note that it is also possible to electrically rotate the adjustment lever in accordance with the amount of expansion of the pair of brake shoes by using drive means such as an electric motor.
[0013]
The pair of brake shoes is expanded by an actuator such as a hydraulic wheel cylinder or an electric motor at the time of braking, while a return spring (tensile coil spring) disposed across the pair of brake shoes at the time of non-braking. Etc.), and can be expanded and approached by the actuator. Various modes are possible.
[0014]
As the temperature-sensitive deformable member, for example, a member having a spiral shape wound at least once at a predetermined axial position of the strut member (for example, a position close to the adjuster wheel) as in the second invention is suitably used. However, it is also possible to adopt a spiral (spiral line) that is displaced in the axial direction so as not to overlap each other while being wound, and in that case, the diameter can be kept small. The temperature-sensitive deformable member may be one that is wound and tightened in the winding direction as the temperature rises, or one that is loosened and shortened in the winding direction. As the temperature-sensitive deformable member, a bimetal that deforms due to a difference in thermal expansion coefficient between two or more kinds of plate materials is preferably used, but other materials such as a shape memory alloy can also be used.
[0015]
The temperature-sensitive deformation member is preferably configured to be engaged in the vicinity of the claw portion that is engaged with the adjuster wheel of the adjust lever. As an aspect of preventing the adjuster wheel from rotating by the adjust lever, the adjust lever Even when the rotation itself is prevented, the claw portion of the adjustment lever may be separated from the adjuster wheel so that it cannot be engaged.
[0016]
The present invention is preferably applied to a leading / trailing drum brake, but can also be applied to other drum brakes having an automatic shoe clearance adjusting mechanism that automatically adjusts a shoe clearance by a strut having an adjuster wheel. In addition, since the present invention is a technique based on the premise of heat generation due to friction, the present invention is preferably applied to an automatic shoe clearance adjustment mechanism that automatically adjusts the shoe clearance during braking by a service brake.
[0017]
Also, the automatic adjustment of the shoe clearance by the adjustment lever is possible even when the adjuster wheel is rotated by the adjustment lever when the pair of brake shoes is expanded, but when the pair of brake shoes is moved closer to the brake release, the adjustment lever is used to adjust the shoe gap. You may rotate the wheel. The adjuster wheel is configured so that, for example, a sawtooth or the like is provided on the outer peripheral portion thereof and can be rotated only in one direction in which the strut is extended.
[0018]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing a leading / trailing drum brake 8 to which the present invention is applied, in which (a) is a front view and (b) is an enlarged cross-sectional view taken along line BB in (a). A pair of brake shoes 12 and 14 having an arc shape are provided on a backing plate 10 fixed to a vehicle body side member that is supported so as to be able to be expanded by shoe hold-down devices 16 and 18. The brake shoes 12 and 14 are fixed to the shoe web 20 positioned substantially parallel to the plate surface of the backing plate 10, the shoe rim 22 fixed to the outer peripheral side edge of the shoe web 20, and the outer peripheral surface of the shoe rim 22. And a lining 24. In this embodiment, the brake shoe 14 is a leading shoe and the brake shoe 12 is a trailing shoe.
[0019]
One end portions (upper end portions) of the pair of brake shoes 12 and 14 are respectively engaged with both end portions of the wheel cylinder 26 fixed to the backing plate 10 so as to brake the service brake, that is, a brake operation member. When the pedal is depressed, the wheel cylinders 26 are spread apart in the directions away from each other, and are pressed by the rotating drum 27 that rotates together with the wheels to generate a braking force. In the vicinity of the wheel cylinder 26 and on the inner peripheral side of the backing plate 10, a return spring (a tension coil spring in the embodiment) 28 is stretched over the brake shoes 12 and 14 and approaches each other. The struts 30 are disposed so as to pass through the inside of the return spring 28, and the approach positions of the pair of brake shoes 12 and 14 that are made to approach according to the urging force of the return spring 28 during non-braking are defined. It has come to be. The other end portions (lower end portions) of the brake shoes 12 and 14 are in contact with the anchors 32 fixed to the backing plate 10.
[0020]
On the surface of the shoe web 20 of one brake shoe 12 on the backing plate 10 side, the parking lever 34 rotates around the axis of the mounting shaft 36 that is substantially perpendicular to the shoe web 20 at the portion where the parking lever 34 is located on the wheel cylinder 26 side. The strut 30 is mounted so as to be movable, and is disposed across the parking lever 34 and the other brake shoe 14. Therefore, when the parking brake operating lever provided in the driver's seat is operated and the parking lever 34 is rotated counterclockwise of the mounting shaft 36 via the brake cable 38, the brake shoe 14 is moved rightward via the strut 30. The brake shoe 12 is moved together with the mounting shaft 36 by the reaction, and the braking shoe 12 is pressed against the rotating drum 27 to generate a braking force. The parking lever 34 is held at a fixed standby position where the engagement protrusion 34 a abuts against the shoe rim 22 of the brake shoe 12 by the action of the return spring 28 when the parking brake is not operated. The brake shoe 12 is interposed via the parking lever 34. The approach position is defined by the strut 30.
[0021]
The strut 30 includes a first strut member 40 that is non-rotatably engaged with one brake shoe 12 via a parking lever 34 and a first strut member 40 that is non-rotatably engaged with the shoe web 20 of the other brake shoe 14. Two strut members 42 and an adjuster wheel 44 rotatably disposed between the strut members 40 and 42 are provided. The disc-shaped adjuster wheel 44 is integrally provided on the center line so that a screw shaft 48 provided with a male screw and a cylindrical fitting shaft 50 protrude in opposite directions. The fitting shaft 50 is fitted in a fitting hole provided in the second strut member 42 so as to be relatively rotatable while being screwed into a screw hole provided in the one strut member 40.
[0022]
The adjuster wheel 44 constitutes an automatic shoe clearance adjusting mechanism 54 together with an adjust lever 52 disposed on the brake shoe 14, and when the adjuster wheel 44 is rotated in one direction by the adjust lever 52, an action of a screw is achieved. Thus, the first strut member 40 is separated from the adjuster wheel 44, the entire length of the strut 30 is extended, and the approach positions of the pair of brake shoes 12, 14 are separated from each other when not braked. The shoe gap between the brake shoes 12, 14 and the rotary drum 27 (the sum of both) is maintained substantially constant.
[0023]
The adjustment lever 52 is disposed on the backing plate 10 side of the shoe web 20 so as to be rotatable about the axis of the mounting shaft 56 perpendicular to the shoe web 20 of the brake shoe 14, and the brake shoe 14. Is urged counterclockwise by the tension coil spring 58 provided between the second strut member 42 and the second strut member 42 is always engaged with the second strut member 42. It is biased toward the strut member 40 side. The tension coil spring 58 corresponds to a lever urging means. As a result, when the pair of brake shoes 12, 14 are expanded during braking of the service brake, the strut 30 is moved following the brake shoe 12 on the opposite side along with the expansion, and the adjustment lever 52 is rotated around the mounting shaft 56 in accordance with the relative movement between the strut 30 and the brake shoe 14. The turning amount of the adjusting lever 52 corresponds to the opening amount of the brake shoes 12, 14, that is, the shoe gap during non-braking, and when the turning amount exceeds a certain amount, the tip claw portion 52 b is engaged with the adjuster wheel 44. Then, the adjuster wheel 44 is rotated in one direction A shown in FIG. FIG. 2 is a cross-sectional view of the adjuster wheel 44 as viewed from the fitting shaft 50 side.
[0024]
When the service brake is released, the adjustment lever 52 is attached to the tension coil spring 58 as the strut 30 is moved rightward until the brake shoe 14 and the second strut member 42 come into contact with each other according to the urging force of the return spring 28. The mounting shaft 56 is returned and rotated clockwise against the force. As shown in FIG. 2, the adjuster wheel 44 is provided with saw teeth 44t whose tip is inclined in the opposite direction to the one direction A, as shown in FIG. 2, during braking (expansion of the brake shoes 12, 14). When the adjustment lever 52 is engaged with the claw portion 52b of the adjustment lever 52, the adjustment lever 52 is rotated in one direction A. When the adjustment lever 52 is turned back when releasing the brake, the screw shaft 48 is rotated by friction. The resistance prevents the adjuster wheel 44 from returning and the claw portion 52b gets over the saw tooth 44t.
[0025]
On the other hand, a spiral temperature-sensitive deformation member 60 is disposed at the end of the second strut member 42 on the adjuster wheel 44 side so as to wind the second strut member 42. The temperature-sensitive deformation member 60 is composed of a bimetal that is deformed in accordance with a temperature change due to a difference in thermal expansion coefficient between the two layers of plates that are integrally bonded, and the second strut member 42 at a fixed position in the axial direction. The shape is changed so that the winding is loosened as the temperature rises. One end portion 60a on the inner peripheral side of the temperature-sensitive deformation member 60 is non-rotatably hooked on the second strut member 42, while the other end portion 60b on the outer peripheral side extends to the outer peripheral side. The temperature rises due to frictional heat generated by sliding between the rotating drum 27 and the lining 24 during braking by a large brake operation force, and the spiral winding of the temperature-sensitive deformation member 60 is loosened and shortened in the winding direction. The other end 60b is displaced counterclockwise as indicated by a two-dot chain line in FIG. 2 and can be engaged with the claw 52b of the adjusting lever 52. Thereby, the adjustment lever 52 is prevented from rotating against the urging force of the tension coil spring 58, and automatic adjustment (over adjustment) of the shoe gap is prevented. The temperature-sensitive deformation member 60 has a material, a plate thickness, and the like so as to obtain a deformation output capable of preventing the adjustment lever 52 from rotating against the urging force of the tension coil spring 58. At normal temperature, that is, during normal braking, the other end 60b is positioned at a portion indicated by a solid line in FIG. 2, and the claw portion 52b of the adjusting lever 52 is displaced as indicated by a one-dot chain line to rotate the adjuster wheel 44. It is allowed to automatically adjust the shoe gap.
[0026]
Thus, in this embodiment, since the temperature-sensitive deformation member 60 that prevents over-adjustment has a spiral shape and is wound around the second strut member 42, a sufficient length dimension can be obtained with a small arrangement space. The amount of displacement required to prevent rotation of the adjuster wheel 44 by the adjusting lever 52 can be easily obtained, and the necessary amount of displacement can be obtained by appropriately setting the material, plate thickness, etc. Thus, a predetermined deformation output can be easily obtained while ensuring the above, and the degree of freedom in design regarding the deformation output and the displacement amount can be improved, and over-adjustment can be stably and reliably prevented.
[0027]
Further, since the temperature-sensitive deformation member 60 is engaged with the claw portion 52b of the adjusting lever 52 and prevents the adjusting lever 52 from rotating, the pressing of the adjusting lever 152 as shown in FIG. Compared with the case where the entire length of the strut 130 engaged with the portion 152a is extended, the dimension from the rotation center (mounting shaft 56) of the adjusting lever 52 to the engaging portion (claw portion 52b) becomes longer. Correspondingly, the deformation output required for the temperature-sensitive deformation member 60, that is, the force necessary to prevent the adjustment lever 52 from rotating, is reduced, and the degree of freedom in designing the deformation output is further increased.
[0028]
Although the temperature-sensitive deformation member 60 is loosened with an increase in temperature, as shown in FIG. 3, a temperature-sensitive deformation member 70 whose winding is tightened with an increase in temperature can also be employed. . In this case, as is apparent from FIG. 3, the second strut member 42 is wound around the second strut member 42 in the direction opposite to the temperature-sensitive deformation member 60, and the one end portion 70 a is hooked on the second strut member 42. As the temperature rises, the winding is tightened and extended in the winding direction, whereby the other end portion 70b is displaced counterclockwise as shown by a two-dot chain line, and is engaged with the claw portion 52b of the adjusting lever 52. Configured as follows.
[0029]
In the above embodiment, over-adjustment is prevented by preventing the adjustment lever 52 from rotating against the urging force of the tension coil spring 58. However, as shown in FIG. By appropriately setting the inclination angle of the other end portion 60b, it is possible to prevent the over adjustment by separating the claw portion 52b from the adjuster wheel 44 due to a change in posture or elastic deformation of the adjusting lever 52.
[0030]
As mentioned above, although the Example of this invention was described in detail based on drawing, this is an embodiment to the last, and this invention implements in the aspect which added various change and improvement based on the knowledge of those skilled in the art. Can do.
[Brief description of the drawings]
1A and 1B are views showing a leading / trailing drum brake to which the present invention is applied, in which FIG. 1A is a front view, and FIG. 1B is an enlarged cross-sectional view taken along line BB in FIG.
2 is an enlarged cross-sectional view of the adjuster wheel and the temperature-sensitive deformation member of FIG. 1 as viewed from the fitting shaft side.
FIG. 3 is a diagram for explaining another embodiment of the present invention, and is a cross-sectional view corresponding to FIG. 2;
FIG. 4 is a view for explaining still another embodiment of the present invention and is a cross-sectional view corresponding to FIG.
FIGS. 5A and 5B are explanatory diagrams in the case where a strut is extended by a bimetal disposed between an adjuster wheel and a second strut member to prevent over-adjustment. FIG. 5A is a front view, and FIG. 5B is a temperature rise. It is an enlarged view which shows the adjuster wheel vicinity when a bimetal deform | transforms.
[Explanation of symbols]
8: Leading / trailing type drum brake 12, 14: Brake shoe 27: Rotating drum 30: Strut 40: First strut member 42: Second strut member 44: Adjuster wheel 52: Adjust lever 54: Shoe gap automatic adjusting mechanism 60 , 70: temperature-sensitive deformation member 60a, 70a: one end 60b, 70b: the other end

Claims (2)

A pair of strut members that are respectively engaged with one and the other of a pair of brake shoes that can be expanded, and a pair of strut members that are rotatably disposed between the pair of strut members and screwed to at least one strut member. A strut that defines an approaching position of the pair of brake shoes during non-braking,
One of the pair of brake shoes is rotatably disposed on one of the shoe webs, and is rotated according to the amount of expansion of the pair of brake shoes during braking, and the amount of expansion is a constant amount. An adjustment lever that is engaged with the adjuster wheel to rotate the adjuster wheel when exceeded,
As the adjuster wheel rotates, the entire length of the struts is extended by the action of a screw, and the shoe gap between the rotating drum and the rotating drum is automatically separated by separating the approach positions of the pair of brake shoes during non-braking. In a drum brake having a shoe gap automatic adjustment mechanism that adjusts automatically,
One of the pair of strut members is disposed so as to be wound, and one end thereof is non-rotatably hooked to the strut member, and is extended or shortened in the winding direction as the temperature rises. A drum brake with an automatic shoe clearance adjustment mechanism, wherein the other end portion is engaged with the adjustment lever, and has a temperature-sensitive deformation member that prevents rotation of the adjustment wheel by the adjustment lever. The drum brake with an automatic shoe clearance adjustment mechanism according to claim 1, wherein the temperature-sensitive deformation member has a spiral shape wound around the strut member one or more times.

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