JP2008157386A - Brake drum - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brake drum having stable braking force while forcibly exhausting air from a drum for heat radiation. <P>SOLUTION: The brake drum comprises a vent hole 20 having an air inlet 21 opened to the outside of the drum 10 in the rotating direction of the drum 10, an outlet 23 opened to the outside of the drum 10 in opposition to the rotating direction of the drum 10, and a Venturi part 22 formed between the air inlet 21 and the outlet 23, and a communication hole 30 for connecting the Venturi part 22 with the inside of the drum 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a brake drum for a vehicle.

The drum brake device is a brake device that obtains a braking force by pressing a half-moon type brake shoe, which is a wear material, on the inner periphery of a cylindrical brake drum (hereinafter referred to as “drum”) that rotates together with a wheel. The drum brake device has a feature that a so-called servo effect in which the brake shoe bites into the rotating drum and presses the drum works, so that it can effectively generate a braking force as compared with the disc brake device. The drum has a sealed structure to prevent foreign matter from entering between the brake shoe and the inner periphery of the drum.
However, since the drum brake device has a hermetically sealed drum, there is a problem that if water drops enter the drum, the water will not be drained, and the brake shoe and the inner periphery of the drum will slip, resulting in a weak braking force. is there.

  In order to solve the problem of water drainage, a drum brake device disclosed in Patent Document 1 extends from a base end portion facing the drum rotation direction to a circumferential intermediate portion on an outer peripheral surface of a brake shoe provided in the drum. A vertical groove is formed, and one or a plurality of holes are formed in the peripheral surface of the drum corresponding to the position in the width direction of the groove. By adopting such a configuration, the drum brake device allows water that has entered the drum to be brought into the vertical groove of the brake shoe by the rotation of the drum and packed in the back, and the water that has been gathered is released to the drum circumferential surface. Since the water is forced out of the hole, it is possible to prevent a decrease in brake performance due to water.

  In addition, since the drum brake device has a hermetically sealed structure, there is a problem in that the inside of the drum becomes high due to friction between the brake shoe and the inner periphery of the drum. When the inside of the drum becomes hot, gas is generated from the friction surface of the brake shoe and the frictional force decreases, and the brake pedal boils through oil pressure because the brake oil boils and bubbles are generated in the oil. This causes a paper lock phenomenon that is not transmitted.

  In order to solve the problem of the frictional heat, a drum brake device disclosed in Patent Document 2 forms an intake hole and an exhaust hole in a brake cover that encloses the drum, and the cover extends from the intake hole to the exhaust hole. Ventilation means for forcibly flowing air through the inside is provided. With such a configuration, in the drum brake device, air is forced to flow from the intake hole toward the exhaust hole by the ventilation means in the brake cover, and the air is cooled by the air.

In addition, since the drum brake device has a hermetic structure, the brake shoe wear powder accumulates inside. When the wear powder accumulates in the drum, there is a foreign matter between the brake shoe and the inner periphery of the drum, and there is a problem that a stable braking force cannot be obtained.
JP-A-8-122658 JP 61-116129 A

  The drum brake device described in Patent Document 1 has one or a plurality of holes on the peripheral surface of the drum. However, the hole opened in the peripheral surface of the drum has only the function of draining the water collected in the vertical groove of the brake shoe by pressing force and centrifugal force, and the inside of the drum is heated to high temperature by frictional heat. Even if it becomes, only the air in the drum is exhausted by thermal expansion, and it does not have the function of forcibly exhausting the air in the drum and radiating heat. Further, in order to gather water in the drum, vertical grooves are formed on the outer peripheral surface of the brake shoe, and the friction surface of the brake shoe is not uniform, so that a stable braking force cannot be obtained.

  In addition, the drum brake device described in Patent Document 2 cools the drum from the outside by flowing air around the outer periphery of the drum, and does not have a function of forcibly exhausting the air in the drum. . In addition, there is no function to release the wear powder in the drum to the outside of the drum, the wear powder accumulates in the drum, and there is a foreign object between the brake shoe and the inner periphery of the drum, so stable braking force There is a problem that cannot be obtained. Furthermore, a ventilator such as a fan for flowing air around the outer periphery of the drum is required.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a brake drum that can exhaust air in the drum forcibly and dissipate heat, and can obtain a stable braking force.

  In order to achieve the above object, the brake drum of the present invention includes an air inlet opening outside the drum in the rotation direction of the drum, an exhaust opening opening outside the drum in a direction opposite to the drum rotation direction, and the air introduction port. And a vent hole formed between the vent hole and the exhaust port, and a communication hole communicating the venturi portion with the inside of the drum.

  As described above, the brake drum includes an air introduction port that opens to the outside of the drum in the rotation direction of the drum, an exhaust port that opens to the outside of the drum in a direction opposite to the rotation direction of the drum, and the air introduction port and the exhaust port. When the drum rotates, air is introduced from the air introduction port into the ventilation hole by providing a ventilation hole having a venturi part formed therebetween and a communication hole communicating the venturi part with the inside of the drum. Since a negative pressure is generated in the venturi portion, the air in the drum is sucked out through the communication hole due to the venturi effect, and the air in the drum can be forcibly exhausted and radiated from the exhaust port. In addition, when the air in the drum is forcibly exhausted, the wear powder and water droplets in the drum are sucked out of the drum together with the air, so that the friction between the brake shoe and the drum is stabilized, and a stable braking force is achieved. can get.

  In order to achieve the object, the ventilation hole includes an opening / closing mechanism using a centrifugal force of rotation of the drum, and the opening / closing mechanism includes a movable member that opens and closes the ventilation hole, and the movable member is moved to the drum by the centrifugal force. It is comprised from the channel | path guided to an outer peripheral direction, and the elastic body which urges | biases the said movable member to a ventilation hole.

  As described above, the ventilation hole includes an opening / closing mechanism that uses the centrifugal force of rotation of the drum, and the opening / closing mechanism guides the movable member that opens and closes the ventilation hole and the movable member toward the outer periphery of the drum by centrifugal force. When the drum is stopped and the air in the drum is not exhausted by the passage and the elastic member that urges the movable member to the ventilation hole, the movable member urged by the elastic body is used as the ventilation hole. In order to prevent water droplets from entering the drum, a stable braking force is obtained, and when the drum rotates and the air in the drum is exhausted, the movable member moves in the drum outer circumference direction by centrifugal force. Since it moves and opens the vent hole, the air in the drum can be forcibly exhausted and radiated.

  In order to achieve the above object, the ventilation hole includes an opening / closing mechanism using frictional heat of a drum, and the opening / closing mechanism is composed of a bimetal obtained by stacking two kinds of metals having different thermal expansion coefficients. And

  As described above, the ventilation hole includes an opening / closing mechanism using frictional heat of the drum, and the opening / closing mechanism is formed of a bimetal in which two kinds of metals having different thermal expansion coefficients are laminated, so that the drum is not hot. When the bimetal closes the vent hole and prevents water droplets from entering the drum, a stable braking force can be obtained, and when the drum becomes hot, the bimetal opens the vent hole and removes the air in the drum. Forcibly exhausts and dissipates heat.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing an embodiment of a drum brake device using a brake drum according to the present invention. As shown in FIG. 1, the drum brake device according to the present embodiment includes a drum 10, a brake shoe 11, a wheel cylinder 12, a ventilation hole 20, and a communication hole 30. Hereinafter, each configuration will be described in detail.

  The drum brake device uses the hydraulic pressure of the wheel cylinder 12 to press the two brake shoes 11 against the inner peripheral surface of the rotating drum 10 to obtain a braking force. At this time, the brake shoe 11 and the inner periphery of the drum 10 rub against each other in a narrow space of the rotating drum 10, so that the drum 10 is heated and wear powder is generated. When the drum 10 rotates, the air in the drum 10 is sucked out through the communication hole 30 due to the venturi effect, and is exhausted from the ventilation hole 20 to the outside of the drum. As shown in FIG. 1, the ventilation holes 20 are arranged symmetrically about the rotational center of gravity of the drum 10 so that the rotational balance of the drum 10 is not lost. The details of the ventilation hole 20 and the communication hole 30 will be described later.

  Considering that the drum 10 has an appropriate coefficient of friction, excellent wear resistance, good heat dissipation, and small deformation due to heat, for example, gray cast iron is used. The drum 10 is manufactured by a known manufacturing method such as casting, forging, or die casting.

FIG. 2 is a cross-sectional view showing an embodiment of the configuration of the ventilation hole 20 and the communication hole 30 of the brake drum according to the present invention. The ventilation hole 20 includes an air introduction port 21, a venturi portion 22, and an exhaust port 23, and is formed along the outer periphery of the drum 10, for example, as shown in FIG. The communication hole 30 is formed so as to communicate the venturi portion 22 of the ventilation hole 20 and the inside of the drum 10.
When the drum 10 is manufactured, the ventilation hole 20 can be formed integrally with the drum 10 by a known manufacturing method such as casting, forging, or die casting. Alternatively, the wind tunnel member 24 having the ventilation holes 20 can be formed by casting, forging, die casting or the like, and connected to the drum 10 manufactured separately. When the wind tunnel member 24 is manufactured separately, the wind tunnel member 24 can be made of a material different from the material of the drum 10, for example, an aluminum alloy. Since the aluminum alloy has higher thermal conductivity and lighter weight than the gray cast iron that is the material of the drum 10, it is possible to improve the heat dissipation and reduce the weight of the drum brake device according to the present embodiment. In addition, since aluminum alloy has the subject that deformation | transformation by a heat | fever is large and abrasion resistance is low, it is difficult to use for the material of the drum 10 inner periphery which frictions with the brake shoe 11. FIG.

  The air introduction port 21 of the ventilation hole 20 is installed outside the drum 10, and as shown in FIG. 2, the opening direction 21 a of the air introduction port 21 is arranged in the drum direction so that the air can be introduced when the drum 10 rotates together with the wheels. It is installed in the direction of 10 rotations. The opening direction 21a can be made to substantially coincide with the rotation direction of the drum 10 so that air can be efficiently introduced when the drum 10 rotates.

  The exhaust port 23 of the vent hole 20 is installed outside the drum 10 like the air introduction port 21, but unlike the air introduction port 21, the air is not introduced even when the drum 10 rotates in FIG. 2. As shown, the opening direction 23 a of the exhaust port 23 is installed in the direction opposite to the rotation direction of the drum 10. The opening direction 23a of the exhaust port 23 does not necessarily have to substantially coincide with the direction in which the rotation direction of the drum 10 is reversed. However, if the opening direction 23a is substantially coincident with the direction in which the rotation direction of the drum 10 is reversed, for example, even if the drum for the left wheel is mistakenly attached to the brake drum device for the right wheel, Air can be efficiently introduced from the exhaust port 23 and exhausted from the air introduction port 21. That is, when the opening direction 23a is substantially coincident with the direction in which the rotation direction of the drum 10 is reversed, the left wheel drum and the right wheel drum can be shared.

The venturi portion 22 of the vent hole 20 is formed by narrowing the flow path of the vent hole 20. When air is introduced into the vent hole 20, the flow path of the venturi portion 22 is narrowed and the flow rate increases, and the pressure decreases. The degree to which the pressure decreases is calculated by Bernoulli's theorem. That is, the cross-sectional area of the air inlet 21 is S1, the cross-sectional area of the venturi 22 is S2, the flow velocity of the air inlet 21 is V1, the air density ρ, the pressure of the air inlet 21 is P1, and the pressure of the venturi 22 Is P2, the differential pressure ΔP (P1−P2) between the air inlet 21 and the venturi 22 can be approximately calculated by the following equation 1.
ΔP = P1-P2 = {( S1 / S2) 2 -1} × ρ × V1 2/2 ··· Formula 1
Since the sectional area S2 of the venturi 22 is smaller than the sectional area S1 of the air inlet 21, the pressure P2 of the venturi 22 is smaller than the pressure P1 of the air inlet 21 as is apparent from Equation 1. Further, when the cross-sectional area S2 of the venturi portion 22 is sufficiently smaller than the cross-sectional area S1 of the air introduction port 21, the pressure P2 of the venturi portion 22 becomes a negative pressure. Here, the negative pressure means that the pressure is lower than the atmospheric pressure with reference to the atmospheric pressure. Higher negative pressure means closer to a vacuum state, and lower negative pressure means closer to atmospheric pressure.

  Further, the negative pressure generated in the venturi portion 22 is proportional to the square of the flow velocity V1 of the air inlet 21 as is apparent from Equation 1. The flow velocity V1 of the air inlet 21 is substantially the same as the rotational speed of the drum 10 that rotates with the wheels. Therefore, as the drum 10 rotates at a higher speed, the venturi portion 22 has a higher negative pressure.

  The communication hole 30 is a hole that communicates the venturi part 22 with the inside of the drum 10. When negative pressure is generated in the venturi portion 22, the pressure in the drum 10 is atmospheric pressure, and thus a pressure gradient is formed in the communication hole 30. Therefore, the air in the drum 10 is forcibly sucked out to the low pressure venturi 22 side through the communication hole 30 and is exhausted from the exhaust port 23 together with the air introduced from the air introduction port 21. When the air in the drum 10 is forcibly sucked out, the drum 10 has a sealed structure but is not in a sealed structure, so that air is supplied from outside the drum into the drum. By such forced air ventilation, the drum 10 can be efficiently dissipated.

  As described above, according to the present embodiment, the brake drum includes the air introduction port 21 opened in the rotation direction of the drum 10 outside the drum 10 and the exhaust gas opened in the direction opposite to the rotation direction of the drum 10 outside the drum 10. A vent hole 20 having a vent 23, a venturi portion 22 formed between the air inlet 21 and the exhaust port 23, and a communication hole 30 communicating the venturi portion 22 with the inside of the drum 10. As a result, when the drum 10 rotates, air is introduced from the air introduction port 21 to the ventilation hole 20 and negative pressure is generated in the venturi portion 22, so that the air in the drum 10 is communicated by the venturi effect. The air in the drum 10 is forcibly exhausted from the exhaust port 23 and can be radiated. Further, when the air in the drum 10 is forcibly exhausted, the wear powder and water droplets in the drum 10 are sucked out of the drum together with the air, so that the friction between the brake shoe 11 and the drum 10 is stable and stable. Braking force is obtained. In addition, the drum brake device using the brake drum according to the present embodiment does not need to form vertical grooves on the friction surface of the brake shoe 11, and uses the brake shoe 11 having a uniform friction surface as in the prior art. Therefore, a stable braking force can be obtained. Furthermore, since the brake drum according to the present embodiment uses the air flow caused by the rotation of the drum 10, a device for generating the air flow is unnecessary.

  Further, the vent hole according to the present embodiment can be provided with an opening / closing mechanism that utilizes the centrifugal force of rotation of the drum. FIG. 3 is a cross-sectional view showing a configuration of an opening / closing mechanism using a centrifugal force of rotation of the drum. The opening / closing mechanism includes a movable member 40 (41) that opens and closes the ventilation hole 20, a passage 50 that guides the movable member 40 (41) toward the drum outer periphery, and an elastic force that urges the movable member 40 (41) to the ventilation hole 20. It is composed of a body 60.

  The movable member 40 can be a cylinder, for example, as shown in FIG. The diameter and height of the cylinder of the movable member 40 are set to be larger than the inner diameter of the ventilation hole 20 at the position where the movable member 40 is disposed, and when the movable member 40 moves in the drum outer circumferential direction, the ventilation hole 20 opens. Magnitude. Thus, by setting the shape of the movable member 40, the vent hole 20 can be opened and closed.

  Or the movable member 41 can also be made into the cylinder provided with the hole 42 and the hole 43, as shown in FIG.3 (b). When the diameter and height of the column of the movable member 41 are equal to or larger than the inner diameter of the ventilation hole 20 at the position where the movable member 41 is disposed, and when the movable member 40 moves in the drum outer circumferential direction, the hole 42 becomes the ventilation hole 20. And the size is such that the vent hole 20 opens. Thus, the vent hole 20 can be opened and closed by setting the shape of the movable member 41. In the opening / closing mechanism shown in FIG. 3B, the direction of the hole 42 needs to be held in the direction of the ventilation hole 20, but the movable member 41 is supported by an elastic body 50 described later. The rotation of the movable member 41 around the central axis of the cylinder is substantially suppressed.

  The shape of the movable member 40 (41) is not limited as long as the movable member 40 (41) can open and close the ventilation hole 20, and may be a sphere, for example. When the movable member 40 (41) is a sphere, the contact resistance between the movable member 40 (41) and the passage 50 is reduced, and the movable member 40 (41) moves smoothly.

  In addition, although the arrangement position of the movable member 40 (41) is set in the venturi portion 22 in the present embodiment, there is no limitation as long as water droplets can be prevented from entering the drum 10 through the ventilation holes 20, for example, It can also be set at two locations in the vicinity of the air inlet 21 and the exhaust port 23. When the movable member 40 (41) is disposed in the vicinity of the air inlet 21 and the exhaust port 23, two movable members 40 (41) are required, but water droplets can be prevented from entering the ventilation hole 20. On the other hand, if the movable member 40 (41) is installed only in the venturi portion 22, it is not possible to prevent water droplets from entering the ventilation hole 20.

  The passage 50 is formed so as to guide the movable member 40 (41) toward the outer periphery of the drum. Thus, by forming the passage 50, when the drum 10 rotates, the movable member 40 (41) moves in the drum outer peripheral direction by the centrifugal force, and the ventilation hole 20 can be opened.

  As shown in FIG. 3, the elastic body 60 is arranged on the drum outer peripheral side so as to urge the movable member 40 (41) to the ventilation hole 20. The elastic body 60 is designed to have an elastic coefficient that allows the movable member 40 (41) to move toward the outer periphery of the drum by centrifugal force when the drum 10 rotates to open the vent hole 20. As the material of the elastic body 60, rubber or a string spring can be used. However, considering heat resistance, it is particularly effective to use a metal string spring.

  In this manner, by energizing the movable member 40 (41) to the ventilation hole 20, the ventilation hole 20 can be reliably closed while the rotation of the drum 10 is stopped. If the movable member 40 (41) is not urged to the ventilation hole 20, the ventilation hole 20 opens when the movable member 40 (41) moves in the drum outer peripheral direction due to gravity while the rotation of the drum 10 is stopped. It will be.

  As described above, according to the present embodiment, the ventilation hole 20 includes the opening / closing mechanism using the centrifugal force of the rotation of the drum 10, and the opening / closing mechanism is a movable member 40 (41) that opens and closes the ventilation hole 20. And a passage 50 for guiding the movable member 40 (41) toward the outer periphery of the drum by centrifugal force, and an elastic body 60 that urges the movable member 40 to the ventilation hole 20, resulting in the drum 10 as a result. Is stopped and the air in the drum 10 is not exhausted, the movable member 40 (41) urged by the elastic body 60 closes the vent hole 20 to prevent water droplets from entering the drum 10. When a stable braking force is obtained and the drum 10 rotates and the air in the drum 10 is exhausted, the movable member 40 (41) moves in the drum outer peripheral direction by the centrifugal force and opens the vent hole 20. It can be forcibly evacuated radiator air beam 10.

  Further, the ventilation hole 20 according to the present embodiment can include an opening / closing mechanism using frictional heat of the drum 10. FIG. 4A is a cross-sectional view illustrating a configuration of an opening / closing mechanism using frictional heat of the drum 10. FIG.4 (b) is the figure seen from arrow AA of Fig.4 (a). This opening / closing mechanism is composed of a bimetal 70 in which metals having different thermal expansion coefficients are laminated.

  For example, as shown in FIG. 4, the bimetal 70 is formed by laminating a metal layer 72 having a relatively small thermal expansion coefficient and a metal layer 71 having a relatively large thermal expansion coefficient, so that the temperature changes. , Curvature changes. As the metal material having a relatively small coefficient of thermal expansion, for example, a Fe-Ni-Co-based super invar alloy or a Fe-Co-Cr-based stainless invar alloy can be used. For example, an Fe—Ni alloy can be used as the metal material having a relatively large thermal expansion coefficient. The bimetal 70 is manufactured, for example, by bonding these metals having different thermal expansion coefficients by cold rolling.

For example, as shown in FIG. 4A, the bimetal 70 is formed to be bent so as to close the venturi portion 22 of the ventilation hole 20. In addition, the bimetal 70 is arranged such that the ventilation hole 20 side is constituted by a metal layer 72 having a relatively small thermal expansion coefficient, and the drum outer peripheral side is constituted by a metal layer 71 having a relatively large thermal expansion coefficient. By adopting such a configuration, when the bimetal 70 is heated to a high temperature, as shown in FIGS. 4A and 4B, the curvature is reduced and the vent hole 20 can be opened.
As described above, the ventilation hole 20 includes an opening / closing mechanism that uses frictional heat of the drum 10, and the opening / closing mechanism includes the bimetal 70 in which metals having different thermal expansion coefficients are stacked, so that the drum 10 is not at a high temperature. When the bimetal 70 closes the vent hole 20 and prevents water droplets from entering the drum 10, the bimetal 70 opens the vent hole 20 when the temperature of the drum 10 becomes high, and the air in the drum 10 Can be forcibly exhausted to dissipate heat.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the present embodiment, the ventilation hole 20 is formed linearly in the rotation direction of the drum 10, but the direction of the ventilation hole 20 is not limited and may be curved, for example.

  In the present embodiment, the vent hole 20 is formed along the outer periphery of the drum 10, but the installation position of the vent hole 20 is not limited, and may be installed in the drum 10, for example.

  In this embodiment, the air introduction port 21 and the exhaust port 23 are installed on the outer peripheral surface of the drum 10, but the air introduction port 21 and the exhaust port 23 are not necessarily installed on the outer peripheral surface. You may install in the outer surface of the drum 10.

  In this embodiment, the elastic body 60 is arranged on the drum outer peripheral side with respect to the movable member 50. However, as long as the movable member 50 can be urged to the ventilation hole 20, the elastic body 60 is placed in the drum with respect to the movable member 50. You may arrange | position to the circumference side.

It is sectional drawing which shows the outline of one Example of the drum brake apparatus using the brake drum which concerns on this invention. It is sectional drawing which shows one Example of a structure of the ventilation hole of the brake drum which concerns on this invention, and a communicating hole. It is sectional drawing which showed the structure of the opening / closing mechanism using the centrifugal force of rotation of a drum. It is sectional drawing which showed the structure of the opening / closing mechanism using the frictional heat of a drum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Drum 20 Ventilation hole 21 Air introduction port 22 Venturi part 23 Exhaust port 30 Communication hole 40 Movable member 50 Passage 60 Elastic body 70 Bimetal

Claims (3)

An air inlet opening outside the drum in the direction of rotation of the drum, an air outlet opening outside the drum in the direction opposite to the direction of rotation of the drum, and a venturi formed between the air inlet and the exhaust port; A vent hole with
A communication hole for communicating the venturi portion with the inside of the drum;
A brake drum comprising: The vent hole includes an opening / closing mechanism that uses the centrifugal force of rotation of the drum,
The opening / closing mechanism includes a movable member that opens and closes the ventilation hole, a passage that guides the movable member toward the outer periphery of the drum by centrifugal force, and an elastic body that biases the movable member to the ventilation hole. The brake drum according to claim 1. The vent hole includes an opening / closing mechanism using frictional heat of the drum,
The brake drum according to claim 1, wherein the opening / closing mechanism is composed of a bimetal in which metals having different thermal expansion coefficients are laminated.

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