DRUM BRAKE AND ELECTRONIC PARKING BRAKE

The present disclosure relates to a drum brake. The drum brake includes a bolt screw being rotated in conjunction with drive of a first motor, a nut piston being combined by a bolt-nut fastening with a circumference of the bolt screw and being moved toward a direction in which the nut piston presses against a shoe, in conjunction of the rotation of the bolt screw, and a press nut being combined by the bolt-nut fastening with a circumference of the nut piston, being moved toward an axial direction in conjunction with drive of a second motor, being brought into contact with the bolt screw, and thus preventing the nut piston from being pushed due to a reaction force of the shoe.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean Patent Application No. 10-2022-0030860, filed on Mar. 11, 2022, which is hereby incorporated by reference for all purposes as if set forth herein.

BACKGROUND

Field

The present disclosure relates to a drum brake and an electronic parking brake and, more particularly, to a drum brake and an electronic parking brake that are capable of keep a vehicle at a stop, using an actuator.

Discussion of the Background

Usually, a service brake serves to reduce a traveling speed of a vehicle or to suddenly stop the vehicle, and a parking brake serves to park the vehicle or to keep the vehicle at a stop. A drum brake is a device that makes the vehicle slow down or stop by causing friction with a drum that is rotated together with a wheel. The drum brake is arranged on a backplate in a such a manner as to face an inner circumferential surface of the drum. The drum brake presses against a pair of shoes to which a friction material is attached, toward the drum and thus causes the friction with the drum, thereby generating a braking force for service braking and braking for parking.

An electro-mechanical brake (hereinafter referred to as “EMB”) is a brake device that uses a force to which a boost is provided by a motor, a gear, and a screw. An electronic control unit (hereinafter referred to as “ECU”) converts pressure of a brake pedal depressed by a driver into an electric signal. The EMB exerts a braking force corresponding to the electric signal. An electronic parking brake (hereinafter referred to as “EPB”) is a brake device that operates electronically. When the vehicle stops traveling, the ECU measures a vehicle speed and engine rotation and detects a braking operation or the like and thus operates an operation of holding a brake.

In order to perform service parking, the vehicle has to be automatically kept out of a braking state after the EMB starts to operate. A screw that is used for the EMB is required not to be self-locked. In order to satisfy the requirement that the screw should not be self-locked, a high-lead screw or a ball-screw that has an increased lead or an increased number of starts has to be used. In contrast, in order to perform the braking for parking, the brake state has to be maintained after the EPB starts to operate. Therefore, a screw that is used for the EPB has to be capable of being self-locked. In this manner, characteristics of the screw that is required for the service braking are different from characteristics of the screw that are required for the braking for parking.

A drum brake in the related art has a structure in which a screw for service braking and a screw for braking for parking are separated provided, and has a structure in which a component for boosting a force of the screw for the service braking and a component for boosting a force of the screw for the braking for parking are separately provided. According, there occurs a problem in that the number of components is increased, a layout is complicated, and thus the manufacturing cost is increased.

Therefore, there is a need to solve this problem.

The background art of the present disclosure is disclosed in Korean Patent No. 2288508 (registered on Aug. 4, 2021 and entitled “Electronic Parking Brake”

SUMMARY

An object of the present disclosure is to provide a drum brake and an electronic parking brake that are capable of employing a simple structure in which a service brake and a parking brake share one screw.

According to an aspect of the present disclosure, there is provided a drum brake including: a bolt screw being configured to be rotatable in conjunction with drive of a first motor; a nut piston being combined by bolt-nut fastening with a circumference of the bolt screw and being configured to be movable toward a direction in which the nut piston presses against a shoe, in conjunction of the rotation of the bolt screw; and a press nut being combined by the bolt-nut fastening with a circumference of the nut piston, being configured to be movable toward an axial direction in conjunction with drive of a second motor, and being configured to be brought into contact with the bolt screw to prevent the nut piston from being pushed due to a reaction force of the shoe.

In the drum brake, the first motor, the bolt screw, and the nut piston may be components of a service brake for reducing a traveling speed of a vehicle or for suddenly stopping the vehicle, the second motor and the press nut may be components of a parking brake for parking the vehicle or for keeping the vehicle at a stop, and the press nut and the bolt screw may be spaced in the axial direction away from each other in a state where the nut piston presses against the shoe due to the drive of the first motor, and the press nut may be configured to be movable toward the bolt screw due to the drive of the second motor to be brought into contact with the bolt screw.

In the drum brake, an inner circumferential portion of the nut piston and an outer circumferential portion of the bolt screw may have a screw structure in which, in a state where the nut piston presses against the shoe, when the first motor stops being driven, the nut piston is not self-locked in response to the reaction force of the shoe, and an inner circumferential portion of the press nut and an outer circumferential portion of the nut piston may have a screw structure in which, in a state where the press nut is brought into contact with the bolt screw toward the axial direction, when the second motor stops being driven, the nut piston is self-locked in response to the reaction force of the shoe.

In the drum brake, the first motor, the bolt screw, and the nut piston may be components of a service brake for reducing a traveling speed of a vehicle or for suddenly stopping the vehicle, the service brake may further include a first motive power transfer apparatus transferring a rotational force of the first motor to the bolt screw, wherein the first motive power transfer apparatus may include: a drive gear being supplied with motive power from the first motor, thereby being rotated; and a driven gear being engaged with the drive gear, thereby being rotated at a reduced speed, and being coaxially combined with the bolt screw.

In the drum brake, the bolt screw may include: a gear assembly portion having a polygonal cross section, being installed in a manner that passes through a screw combination hole in the driven gear, and being configured to be slidably movable along the screw combination hole toward the axial direction; and a screw extension portion being coaxially continuous with the gear assembly portion and being combined by the bolt-nut fastening with the nut piston.

In the drum brake, the screw extension portion may have a smaller diameter than the gear assembly portion, and the press nut may be arranged in a manner that faces a first-side lateral-surface portion in the axial direction of the gear assembly portion.

In the drum brake, the bolt screw may include: a gear assembly portion being supplied with a rotational force from the first motor; a screw extension portion being coaxially continuous with the gear assembly portion and being combined by the bolt-nut fastening with the nut piston; and a press contact portion being arranged on the gear assembly portion or the screw extension portion in a manner that faces the press nut in the axial direction, and being brought into contact with the press nut.

In the drum brake, the bolt screw may include: a gear assembly portion being supplied with a rotational force from the first motor; a screw extension portion being combined by the bolt-nut fastening with the nut piston; a fixation portion being disposed between the gear assembly portion and the screw extension portion and being coaxially continuous with the gear assembly portion and the screw extension portion; a press plate being fixed to the fixation portion and being arranged in a manner that protrudes farther toward a radial direction than the screw extension portion; and a press contact portion being arranged on the press plate in a manner that faces the press nut in the axial direction and being brought into contract with the press nut.

In the drum brake, the gear assembly portion may have a smaller diameter than the screw extension portion, and the press nut may be arranged in a manner that faces a first-side lateral-surface portion in the axial direction of the press plate.

In the drum brake, the fixation portion may be externally threaded, and the press plate may be fixed by combining an internally-tapped ring member with the fixation portion by the bolt-nut fastening.

In the drum brake, the second motor and the press nut may be components of a parking brake for parking a vehicle or for keeping the vehicle at a stop, the parking brake may further include a second motive power transfer apparatus transferring a rotational force of the second motor to the press nut, and the second motive power transfer apparatus may include: a first gear being connected to the second motor; and a second gear of which a first-side portion is engaged with the first gear to be rotatable at a reduced speed and of which a second-side portion is engaged with the press nut.

In the drum brake, the press nut that has a greater diameter than the second gear, may be engaged with the second gear and may have such a length in the axial direction that the press unit is movable in a manner that is brought into contact with or spaced from the bolt screw, while kept engaged with the second gear.

The drum brake may further include a housing having one communicating space in which the bolt screw, the nut piston, and the press nut are accommodated, wherein the housing may include: a first housing unit in which one portion of a service brake is accommodated; a second housing unit in which one portion of a parking brake is accommodated; and a combination cylinder unit having a shape of a hollow cylinder in a portion where the first housing unit and the second housing unit are combined with each other, and accommodating the bolt screw, the nut piston, and the press nut.

In the drum brake, the second housing unit may include: a motor accommodation unit accommodating the second motor; a gear accommodation unit accommodating a second motive power transfer apparatus transferring a rotational force of the second motor to the press nut; and a piston accommodation unit whose one end portion facing the first housing unit is combined with the first housing unit, thereby forming the combination cylinder unit, and on whose other portion facing the shoe the nut piston is installed by passing therethrough, the piston accommodation unit being configured to communicate with the gear accommodation unit.

According to another aspect of the present disclosure, there is provided an electronic parking brake include: a second motor; a press nut being combined by bolt-nut fastening with a circumference of a nut piston of a service brake that presses against a shoe, being configured to be movable toward an axial direction in conjunction with drive of the second motor, and being configured to be brought into contact with a bolt screw combined by the bolt-nut fastening with the nut piston to prevent the nut piston from being pushed due to a reaction force of the shoe; and a second motive power transfer apparatus transferring a rotational force of the second motor to the press nut.

In the electronic parking brake, the press nut may include: a nut main body being arranged on a circumference of the nut piston; a screw combination portion being disposed on an inner circumferential portion of the nut main body and being combined by the bolt-nut fastening with the nut piston; a gear-teeth portion being formed on an outer circumferential portion of the nut main body and being supplied with the rotational force from the second motor; and a screw attachment-detachment portion being disposed on an end portion of the nut main body and being configured to be brought into contact with the bolt screw toward the axial direction when the nut main body is moved.

In the electronic parking brake, the screw attachment-detachment portion may include: a limitation jaw being disposed on an end portion in the axial direction of the nut main body in a manner that protrudes inward toward a direction of an axial center, and being arranged in a manner that faces the nut piston positioned inside the nut main body, in the axial direction; and a screw contact portion being disposed on the limitation jaw in a manner that protrudes toward the axial direction, and facing the bolt screw in the axial direction and being in contact therewith.

In the electronic parking brake, inner circumferential portions of the limitation jaw and the screw contact portion may each have a greater diameter than the bolt screw and may be spaced away from a circumference of the bolt screw, and motive power that is transferred from the second motor to the nut main body may serve as a load that is exerted on the bolt screw toward the axial direction through the screw contact portion.

In the electronic parking brake, when the second motor is driven in a forward direction, the press nut may be movable to one side toward the axial direction up to a position where the screw contact portion is pressed against and brought into contact with the bolt screw toward the axial direction, and when the second motor is driven in a reverse direction, the press nut may be movable to the other side toward the axial direction up to a position where the limitation jaw is brought into contact with the nut piston toward the axial direction.

In the electronic parking brake, at least one portion of the second motor may be accommodated together in a housing in which the bolt screw, the nut piston, and the press nut are accommodated, and may be arranged on one side of a plate surface of a backplate in a manner that is in parallel with the bolt screw, the nut piston, and the press nut.

The drum brake according to the present disclosure has a structure in which the service brake and the parking brake are coaxially combined with each other. More particularly, according to the present disclosure, the drum brake has a structure in which the bolt screw and the nut piston of the service brake and the press nut of the parking brake are coaxially combined by the bolt-nut fastening with each other. In other words, the parking brake according to the present disclosure has a simple structure in which the press nut is additionally combined by the bolt-nut fastening with the circumference of the nut piston provided in the service brake. That is, according to the present disclosure, the drum brake has a simple structure in which the service brake and the parking brake share one screw corresponding to the bolt screw.

Accordingly, the above-mentioned structures according to the present disclosure provide the following advantages, when compared with the case where the service brake and the parking brake in the related art are arranged independently of each other, in other words, when compared with the case where the service brake and the parking brake in the related art are arranged in such a manner as to be spaced away from each other and thus to be separated from each other. The numbers of components of, and volumetric weights, of the service brake and the parking brake can be remarkably reduced, and space utilization and the freedom of layout design can be further improved. Moreover, the manufacturing cost and the productivity can be improved.

In addition, the braking for parking is performed by pressing against the bolt screw using the press nut and thus preventing the nut piston from being rotated. Accordingly, when compared with the parking brake in the related art in which the shoe is directly pressed against, the braking for parking can be stably performed by outputting a remarkably low load. Accordingly, the motor, the motive power transfer apparatus, and the housing can be size-reduced and weight-reduced.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A drum brake and an electronic parking brake according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. For clarity and convenience in description, thicknesses of lines, sizes of constituent elements, and the like may be illustrated in non-exact proportion in the drawings. In addition, a term to be assigned to a constituent element according to the present disclosure is defined considering a function of the constituent element and may vary according to a user’s intention or a manager’s intention or based on practices in the art. Therefore, the term should be defined in context in light of the present specification.

FIG.1is a perspective view schematically illustrating a drum brake 1 according to a first embodiment of the present disclosure.FIG.2is a perspective view illustrating essential constituent elements of the drum brake inFIG.1.FIG.3is a cross-sectional view illustrating the essential constituent elements of the drum brake inFIG.1.

With reference toFIGS.1to3, the drum brake1according to the first embodiment of the present disclosure has a configuration in which a service brake2for reducing a traveling speed of a vehicle or for suddenly stopping the vehicle and a parking brake3for parking the vehicle or for keeping the vehicle at a stop share one screw member corresponding to a bolt screw23and are arranged in one communicating space.

The service brake2according to the first embodiment of the present disclosure performs an operation of pressing against and pushing a shoe5by rotating the bolt screw23in conjunction with drive of a first motor21and moving toward an axial direction a nut piston24combined by bolt-nut fastening with a circumference of the bolt screw23(refer toFIG.6).

The parking brake3according to the first embodiment of the present disclosure is combined by the bolt-nut fastening with a circumference of the nut piston24in a manner that overlaps a press nut33, and performs an operation of preventing the nut piston24from being pushed in the opposite direction due to a reaction force of the shoe5, by moving the press nut33toward the axial direction in conjunction with drive of a second motor31and thus pressing against the press nut33toward the axial direction and thus bringing the press nut33into contact with the bolt screw23(refer toFIG.7).

InFIG.3, the bolt screw23is arranged in a manner that extends in a transverse direction. For convenience, the transverse direction is hereinafter defined as the axial direction or a leftward-rightward direction. A positional relationship and a combination relationship among constituent elements will be described below according to this definition. A portion of the bolt screw23that is brought into contact with the press nut33toward the axial direction is referred to as a press contact portion235throughout the present specification.

The press nut33is positioned between the press contact portion235on the left side ofFIG.3and the nut piston24on the right side thereof. A portion of the left side of the press nut33is removably attached to the press contact portion235according to a position in the axial direction of the press nut33. Although the position in the axial direction of the press nut33varies, a portion of the right side of the press nut33is always kept combined by the bolt-nut fastening with the circumference of the nut piston24.

The press nut33is moved in the axial direction while remaining engaged with the nut piston24. Then, when the press nut33comes into contact with the press contact portion235of the bolt screw23, a pressing force to the right is additionally applied to the nut piston24, and a pressing force to the left is additionally applied to the bolt screw23by the press nut33. Accordingly, it is possible to prevent the nut piston24from being pushed toward the press contact portion235by the reaction force of the shoe5.

According to the first embodiment of the present disclosure, as described above, braking for parking may be performed by moving the press nut33with the drive of the second motor31in a state where the nut piston24presses against the shoe5with the drive of the first motor21. At this point, at least with a load high enough to restrict rotation (return to a waiting position illustrated inFIG.3) of the nut piston24, the press nut33needs to be brought into contact with the press contact portion235.

The parking brake3in the related art is separately provided independently of the service brake2and configured to directly press against the shoe5. Accordingly, in the related art, the second motor31, a second motive power transfer apparatus32, and the like are required to finally output a load of 1200 to 1400 kg. However, according to the present disclosure, the braking for parking may be stably performed by outputting a remarkably low load of 10 to 20 kg.

FIG.4is a perspective view illustrating other essential constituent elements of the brake drum inFIG.1.FIG.5is an exploded perspective view illustrating the other essential constituent elements of the brake drum inFIG.1.

With reference toFIGS.3to5, the service brake2according to the first embodiment of the present disclosure includes the first motor21, a first motive power transfer apparatus22, the bolt screw23, and the nut piston24.

With reference toFIG.1, the bolt screw23and the nut piston24are arranged in front of a backplate6(on one side of a plate surface thereof), and the first motor21is arranged behind the backplate6(on the other side of the plate surface thereof). The first motive power transfer apparatus22is arranged on the backplate6in a manner that passes therethrough and transfers a rotational force of the first motor21that is arranged behind the backplate6, to the bolt screw23in front of the backplate6. The first motive power transfer apparatus22according to the first embodiment of the present disclosure includes a drive gear221and a driven gear222.

The drive gear221is a gear member that is connected to an output shaft of the first motor21. The drive gear221has a worm gear structure and is supplied with a motive power from the first motor21, thereby being rotated at a regular position thereof. The driven gear222is a gear member that transfers a rotational force of the drive gear221to the bolt screw23. The driven gear222has a wheel gear structure, is installed in a manner that is engaged with the drive gear221, and is rotated at a reduced speed at a regular position thereof.

A screw combination hole223is formed in the driven gear222. The bolt screw23is combined with the screw combination hole223by passing therethrough. The bolt screw23is installed in the screw combination hole223by passing therethrough toward the axial direction. When the first motor21is driven, the bolt screw23is rotated by the same rotational displacement as the driven gear222. The bolt screw23according to the first embodiment of the present disclosure includes a gear assembly portion231, a screw extension portion232, and the press contact portion235.

The gear assembly portion231is a portion of the bolt screw23that is supplied with a rotational force from the first motor21through the first motive power transfer apparatus22. The gear assembly portion231is installed in a manner that passes through the screw combination hole223in the driven gear222toward the axial direction and has a cross section with a fixed shape with respect to the axial direction. Accordingly, the bolt screw23is slidably movable toward the axial direction in a state of being guided by an edge portion of the screw combination hole223.

In addition, the gear assembly portion231and the screw combination hole223each have a cross section having a shape other than a circle, for example, have a polygonal cross section. Accordingly, when the driven gear222is rotated, the bolt screw23may be stably rotated by the same rotational displacement as the driven gear222.

The screw extension portion232is a portion of the bolt screw23that is combined by the bolt-nut fastening with the nut piston24. The screw extension portion232is formed in a manner that is coaxially continuous with the gear assembly portion231. A circumference of the screw extension portion232is externally threaded in such a manner that the nut piston24may be combined by the bolt-nut fastening with the screw extension portion232. The externally threaded screw extension portion232according to the first embodiment of the present disclosure has a tap-screw structure.

The screw extension portion232has a smaller diameter than the gear assembly portion231. The screw extension portion232has a circular cross section while the gear assembly portion231has a cross section, as a whole, that has a shape other than a circle. Accordingly, a right-side lateral-surface portion of the gear assembly portion231that is positioned at a border between the gear assembly231and the screw extension portion232has a shape of a hooking jaw.

The gear assembly portion231is arranged in such a manner that the right-side lateral-surface portion thereof faces a left-side lateral-surface portion of the press nut33combined by the bolt-nut fastening with the circumference of the nut piston24, in the axial direction, and, when the press nut33is moved to the left, the surface portion of the right side thereof is pressed against and brought into contact with the press nut33. That is, the right-side lateral-surface portion of the gear assembly portion231that is shaped in such a manner as to protrude farther toward a radial direction than the screw extension portion232is the press contact portion235to which the press nut33is removably attached.

The nut piston24is combined by the bolt-nut fastening with the circumference of the bolt screw23, and is moved toward the axial direction (in the rightward direction) in conjunction with rotation of the bolt screw23, thereby pressing against and pushing the shoe5. The nut piston24has a screw structure in which the nut piston24is not self-locked in response to the reaction force of the shoe5when the first motor21stops being driven in a state where the nut piston24presses against the shoe5. An end portion of the nut piston24that is brought into contact with the shoe5has such a shape of tongs that the end portion thereof faces front and rear surface portions of the shoe5and then is brought into contact therewith. Accordingly, the nut piston24has only displacement in the axial direction without being rotated.

When the nut piston24is described as not being self-locked throughout the present specification, this means the following: In a state where the bolt screw23is rotated in a forward direction in conjunction with the drive of the first motor21and where the nut piston24is moved to the right, thereby pressing against and pushing the shoe5, when the first motor21stops being driven, that is, when pressing for service braking of the vehicle is no longer performed, the nut piston24is pushed by itself to the left due to the reaction force of the shoe5that is exerted on the nut piston24. At this point, the nut piston24has only a linear movement displacement in the axial direction, and thus the bolt screw23is rotated in a reverse direction.

Various factors, such as a lead angle of a threaded surface, a lead, the number of starts, a type of screw, a material, and surface roughness, may be comprehensively considered in realizing in this manner the screw structure in which the nut piston24is not self-locked. For example, the larger the lead angle of the threaded surface, the smaller force may be exerted for rotation with respect to a load in the axial direction. That is, the larger the lead angle, the more easily the nut piston24may be pushed due to the reaction force of the shoe5. Thus, the structure in which the nut piston24is not self-locked may be easily realized.

The service brake2according to the first embodiment of the present disclosure is described above for disclosing the service brake2according to a preferred embodiment of the present disclosure and is not intended to specifically limit a structure of the service brake2according to the present disclosure. The service brake2according to the present disclosure is not limited to specific structures and shapes that include those in the related art, as long as it has a configuration in which, in conjunction with the drive of the first motor21, the bolt screw23is rotated and the nut piston24is moved toward the axial direction.

With reference toFIGS.3to5, the parking brake3according to the first embodiment of the present disclosure includes the second motor31, the second motive power transfer apparatus32, and the press nut33.

The second motor31may be provided separately from the first motor21and may be arranged in front of the backplate6(on one side of the plate surface) in a manner that is in parallel with the bolt screw23and the nut piston24. The second motor31may be arranged behind the backplate6, together with the first motor21. However, the more miniaturized the second motor31, the more easily the second motor31may be arranged in front of the backplate6, together with the second motive power transfer apparatus32.

The second motor31, when intended to be arranged in front of the backplate6, is arranged in a state where one portion or all portions thereof are accommodated in a housing40having one communicating space in which the bolt screw23, the nut piston24, and the press nut33are accommodated. The second motor31may be arranged in a second housing unit42(described below) of the housing40, and thus may be parallelly arranged in front of the backplate6, together with the bolt screw23, the nut piston24, and the press nut33.

In a case where the second motor31is arranged in front of the backplate6, there is no need to form a through-hole in the backplate6in order to transfer an output of the second motor31to the press nut33. Thus, the overall structural rigidity of an apparatus including the backplate6may be secured more stably. In addition, because the second motor31is positioned closer to the press nut33, the motive power may be transferred more efficiently, and the second motive power transfer apparatus32may also be miniaturized.

The second motive power transfer apparatus32transfers a rotational force of the second motor31to the press nut33. The second motive power transfer apparatus32according to the first embodiment of the present disclosure includes a first gear321and a second gear322.

The first gear321is a gear member that is connected to an output shaft of the second motor31. The second gear322is a speed-reduction gear member that transfers a rotational force of the first gear321to the press nut33. The second gear322has a greater diameter than the first gear321and is engaged with the first gear321. A first-side portion of a circumference of the second gear322on which gear teeth are formed is engaged with the first gear321, and a second-side portion thereof is engaged with an outer circumferential portion of the press nut33, more specifically, with a gear-teeth portion333(described below) of the press nut33.

The press nut33has a greater diameter than the second gear322. The press nut33is combined by the bolt-nut fastening with the circumference of the nut piston24and is engaged with the second gear322. The screw extension portion232of the bolt screw23has a smaller diameter than the gear assembly portion231. The press nut33is moved toward the axial direction in conjunction with the drive of the second motor31, and thus is brought into contact with or spaced away from the bolt screw23in the axial direction.

More specifically, the press nut33is arranged on the same axis as the screw extension portion232, but in a manner that faces a first-side lateral-surface portion in the axial direction of the gear assembly portion231. In a state of being brought into contact with the bolt screw23toward the axial direction, the press nut33prevents the nut piston24from being pushed due to the reaction force of the shoe5. The press nut33according to the first embodiment of the present disclosure includes a nut main body331, a screw combination portion332, the gear-teeth portion333, and a screw attachment-detachment portion334.

The nut main body331is a portion of the press nut33that constitutes a main body of the press nut33. The nut main body331has the shape of a tube, a pipe, or a ring that has inner and outer circumferential portions, and is arranged on the circumference of the nut piston24. The nut main body331maintains a state where the screw combination portion332is combined by the bolt-nut fastening with the nut piston24and where the gear-teeth portion333is engaged with the second gear322, and has such a length in the axial direction that the screw attachment-detachment portion334is movable in a manner that is brought into contact with or spaced away from the bolt screw23.

The screw combination portion332is a portion of the press nut33that is combined by the bolt-nut fastening with the circumference of the nut piston24. The screw combination portion332is formed, in the shape of an internally tapped portion, on the inner circumferential portion of the nut main body331. At this time, the screw combination portion332has the screw structure in which the nut piston24is self-locked in response to the reaction force of the shoe5.

In a state where the traveling speed of the vehicle is reduced or where the shoe5is pressed against in order to suddenly stop the vehicle, that is, in a service braking state, the nut piston24has a structure in which the nut piston24is not self-locked in response to the reaction force of the shoe5when the first motor21stops being driven, for example, has such a high lead angle that the nut piston24is not self-locked. With this structure, the nut piston24is combined by the bolt-nut fastening with the bolt screw23.

In contrast, in a state of being pressed against and brought into contact with the bolt screw23toward the axial direction in order to park the vehicle or keep the vehicle at a stop, that is, in a parking brake state, the press nut33has the structure in which the nut piston24is self-locked in response to the reaction force of the shoe5when the second motor31stops being driven. With this structure, the press nut33is combined by the bolt-nut fastening with the nut piston24.

That is, the screw combination portion332of the press nut33is combined by the bolt-nut fastening with the nut piston24, with the screw structure in which, when rotated, the press nut33is moved along the nut piston24toward the axial direction, but when the nut piston24is pressed against toward the axial direction, the press nut33may be kept stationary without being rotated, for example, with such a lower lead angle that the nut piston24may be self-locked.

The gear-teeth portion333is a portion of the press nut33that is supplied with a rotational force from the second motor31. The gear-teeth portion333is formed on the outer circumferential portion of the nut main body331. In a case where the first gear321and the second gear322have a spur-gear structure, the gear-teeth portion333may have a corresponding spur-gear structure. This gear is not specifically limited in structure and type. In addition to the spur-gear structure, any structure in which the rotational force may be transferred may be employed.

The screw attachment-detachment portion334is formed on an end portion in the axial direction (an end portion of the left side ofFIG.3) of the nut main body331. When the nut main body331is moved to the left, the screw attachment-detachment portion334is brought into contact with the bolt screw23toward the axial direction. The screw attachment-detachment portion334according to the first embodiment of the present disclosure includes a limitation jaw335and a screw contact portion336.

The limitation jaw335is formed on an end portion in the axial direction (an end portion on the left side ofFIG.3) of the nut main body331in a manner that protrudes inward toward a direction of the axial center. The limitation jaw335is arranged in a manner that faces an end portion of the left side of the nut piston24arranged inside the nut main body331, in the axial direction (in the leftward-rightward direction inFIG.3), and sets a limit to which the press nut33is moved to the right with respect to the nut piston24.

The limitation jaw335is formed in a manner that protrudes inward in the direction of the axial center, but protrudes up to a position that is spaced away from the bolt screw23without being brought into contact therewith. In other words, in a case where the limitation jaw335has the shape of a circle as a whole, the limitation jaw335has an inner circumferential portion that has a greater diameter (width) than the screw extension portion232of the bolt screw23. That is, the limitation jaw335is kept spaced away from the circumference of the bolt screw23.

The screw contact portion336is formed on the limitation jaw335in a manner that protrudes therefrom toward the axial direction, more particularly, toward the gear assembly portion231and the press contact portion235(to the left inFIG.3). The screw contact portion336is formed at a position on the limitation jaw335that faces the press contact portion235, in a manner that protrudes therefrom. An inner circumferential portion of the screw contact portion336is spaced away from the circumference of the bolt screw23.

More specifically, the press contact portion235is formed in the shape of a ring in such a manner as to have a width in the radial direction that corresponds to a difference in diameter between the gear assembly portion231and the screw extension portion232, and the screw contact portion336has a ring-shaped cross section in such a manner as to face the press contact portion235. Accordingly, when the press nut33is moved to the left, with the screw contact portion336, the press nut33may be precisely pressed against and brought into contact with the press contact portion235. Motive power that is transferred from the second motor31to the press nut33finally serves as a load that is exerted on the press contact portion235of the bolt screw23toward the axial direction through the screw contact portion336.

When the second motor31is driven in the forward direction, the press nut33may be maximally moved toward the leftward direction up to a position where the screw contact portion336is pressed against and brought into contact with the bolt screw23toward the axial direction. When the second motor31is driven in the reverse direction, the press nut33may be maximally moved toward the rightward direction up to a position where the limitation jaw335is brought into contact with the nut piston24toward the axial direction.

The drum brake1according to the first embodiment of the present disclosure has a configuration in which the service brake2and the parking brake3shares one screw member corresponding to the bolt screw23and are arranged in one communicating space. With reference toFIGS.1to3, the drum brake1according to the first embodiment of the present disclosure may include the housing40as a constituent element that constitutes this one communication space.

The housing40has a structure in which the bolt screw23, the nut piston24, and the press nut33are possibly accommodated in one communicating space. The housing40according to the first embodiment of the present disclosure includes a first housing unit41, the second housing unit42, and a combination cylinder unit43.

The first housing unit41has a structure in which the service brake2is possible accommodated. The second housing unit42has a structure in which the parking brake3is possibly accommodated. The combination cylinder unit43is a portion of the housing40in which the bolt screw23, the nut piston24, and the press nut33are accommodated. The combination cylinder unit43is formed, in the shape of a hollow cylinder, in a portion where the first housing unit41and the second housing unit42are combined with each other.

A portion (one portion or all portions) other than a portion of the service brake2that is accommodated in the combination cylinder unit43may be accommodated in the first housing unit41. A portion other than a portion of the parking brake3that is accommodated in the combination cylinder unit43may be accommodated in the second housing unit42. The second housing unit42according to the first embodiment of the present disclosure includes a motor accommodation unit421, a gear accommodation unit422, and a piston accommodation unit423.

The motor accommodation unit421is shaped in such a manner as to possibly accommodate one portion or all portions of the second motor31. The gear accommodation unit422is shaped in such a manner as to possibly accommodate the second motive power transfer apparatus32. The piston accommodation unit423is shaped in such a manner as to be combined with the first housing unit41and to possibly form the combination cylinder unit43.

One end portion (an end portion on the left side ofFIG.3) of the piston accommodation unit423that faces the first housing unit41is combined with the first housing unit41, and the piston accommodation unit423forms the combination cylinder unit43. The nut piston24is arranged on the other end portion (an end portion on the right side ofFIG.3) of the piston accommodation unit423that faces the shoe5, in a manner that passes through the combination cylinder unit43from inside to outside.

FIG.6is an operational view illustrating a state where brake is performed by the service brake2according to the first embodiment of the present disclosure.FIG.7is an operational view illustrating a state where the brake is performed by the parking brake3according to the first embodiment of the present disclosure.

With reference toFIG.6, the service brake2according to the first embodiment of the present disclosure performs the operation of pressing against and pushing the shoe5by rotating the bolt screw23in conjunction with the drive of the first motor21and moving toward the axial direction the nut piston24combined by the bolt-nut fastening with the circumference of the bolt screw23.

With reference toFIG.7, the parking brake3according to the first embodiment of the present disclosure is combined by the bolt-nut fastening with the circumference of the nut piston24in a manner that overlaps the press nut33, and performs the operation of preventing the nut piston24from being pushed in the opposite direction due to the reaction force of the shoe5, by moving the press nut33toward the axial direction in conjunction with the drive of the second motor31and pressing against the press nut33toward the axial direction and thus bringing the press nut33into contact with the gear assembly portion231of the bolt screw23.

In an initial state as illustrated inFIG.3, where the first motor21is driven in the forward direction, the nut piston24, as illustrated inFIG.6, is moved to the right, and pushes a right-side shoe5of a pair of the shoes5to the right and presses against the shoe5on the right. With this operation, the service braking is performed. At this time, the press nut33and the gear assembly portion231of the bolt screw23are spaced away from each other in the axial direction.

Subsequently, when the second motor31is driven in the forward direction, the press nut33, as illustrated inFIG.7, is moved toward the gear assembly portion231and the press contact portion235of the bolt screw23and comes into contact with each other. At this point, in a state where a first-side portion of the press nut33is bound to the nut piston24, a second-side portion thereof is brought into contact with the bolt screw23toward the axial direction, and thus the braking for parking is performed. Subsequently, although the second motor31stops being driven, this parking brake state is maintained due to the self-locking structure.

As illustrated inFIG.6, in a state where the press nut33is not brought into contact with the bolt screw23, when the first motor21stops being driven, that is, when only service braking is performed instead of the braking for parking, the nut piston24is pushed by itself due to the reaction force of the shoe5, and the bolt screw23is rotated in the reverse direction and, as illustrated inFIG.3, returns to an initial state thereof.

In a case where the braking for parking is canceled, the following process may be continuously performed. The first motor21is driven in the forward direction. Thus, the nut piston24is farther pushed toward the shoe5, and the press nut33is spaced away from the press contact portion235of the bolt screw23. Thereafter, the second motor31is driven in the reverse direction. By performing this operation of canceling the braking for parking, the bolt screw23, the nut piston24, and the press nut33may be returned to initial states thereof, respectively, as illustrated inFIG.3.

FIG.8is a cross-sectional view schematically illustrating essential constituent elements of a drum brake1according to a second embodiment of the present disclosure.FIG.9is a perspective view schematically illustrating the essential constituent elements of the drum brake1according to the second embodiment of the present disclosure.FIG.10is an exploded perspective view schematically illustrating the essential constituent elements of the drum brake1according to the second embodiment of the present disclosure.

With reference toFIGS.8to10, the drum brake1according to the second embodiment of the present disclosure is different from the drum brake1according to the first embodiment of the present disclosure, illustrated inFIGS.1to7, in that in the drum brake1according to the second embodiment, the gear assembly portion231of the bolt screw23has a smaller diameter than the screw extension portion232and that the bolt screw23further includes a fixation portion233and a press plate234.

Constituent elements of the drum brake1according to the second embodiment of the present disclosure that are the same as, are similar to, or correspond to, those of the drum brake1according to the first embodiment of the present disclosure, which are illustrated inFIGS.1to7, are not repeatedly described below.

With reference toFIGS.8to10, the bolt screw23according to the second embodiment of the present disclosure includes the gear assembly portion231, the screw extension portion232, the fixation portion233, the press plate234, and the press contact portion235.

The gear assembly portion231is a portion of the bolt screw23that is supplied with a rotational force from the first motor21through the first motive power transfer apparatus22. The gear assembly portion231is installed in a manner that passes through the screw combination hole223in the driven gear222toward the axial direction and has a cross section with a fixed shape with respect to the axial direction. Accordingly, the bolt screw23is slidably movable toward the axial direction in the state of being guided by the edge portion of the screw combination hole223.

In addition, the gear assembly portion231and the screw combination hole223each have a cross section having a shape other than a circle, for example, have a polygonal cross section. Accordingly, when the driven gear222is driven, the bolt screw23may be stably rotated by the same rotational displacement as the driven gear222.

The screw extension portion232is a portion of the bolt screw23that is combined by the bolt-nut fastening with the nut piston24. The screw extension portion232is formed on the same axis as the gear assembly portion231. The circumference of the screw extension portion232is externally threaded in such a manner that the nut piston24may be combined by the bolt-nut fastening with the screw extension portion232. The screw extension portion232according to the second embodiment of the present disclosure is externally threaded in such a manner as to have a ball-screw structure.

Usually, in a case where, as in the first embodiment of the present disclosure, a circumference of an end portion of a member having the shape of a bar is internally tapped, according to the ease with which the bar-shaped member is machined, a middle portion in the lengthwise direction of the bar-shaped member is pre-machined and then a rear end portion thereof is machined. Accordingly, the end portion that is internally tapped has a relatively smaller diameter than the middle portion. This may be applied to the bolt screw23according to the first embodiment of the present disclosure.

However, unlike in the case where the circumference of the end portion of the bar-shaped member is internally tapped, usually, in a case where, as in the second embodiment of the present disclosure, ball-screw is formed on the circumference of the end portion of the bar-shaped member, according to the ease with which the bar-shaped member is machined, the end portion in the lengthwise direction of the bar-shaped member is pre-machined, and then the middle portion thereof is machined. Accordingly, the end portion on which ball-screw is formed has a relatively greater diameter than the middle portion. This may be applied to the bolt screw23according to the second embodiment of the present disclosure.

The externally threaded screw extension portion232of the bolt screw23according to the first embodiment of the present disclosure has the tap-screw structure. In contrast, the screw extension portion232of the bolt screw23according to the second embodiment of the present disclosure has the ball-screw structure. In this manner, the bolt screw23according to the present disclosure may have a diameter and a cross section, each of which varies with a position in a lengthwise direction, considering various conditions, such as machining conditions, component specifications, and a layout relationship between the bolt screw23and each of the adjacent other components.

The fixation portion233is a portion of the bolt screw23to which the press plate234is fixed. The fixation portion233is formed between the gear assembly portion231and the screw extension portion232and is formed in a manner that is coaxially continuous with the gear assembly portion231and the screw extension portion232. The fixation portion233according to the second embodiment of the present disclosure has a smaller diameter than the screw extension portion232and has a greater diameter than the gear assembly portion231.

Accordingly, the press plate234having the shape of a ring may pass through a circumference of the gear assembly portion231and may be smoothly moved up to the fixation portion233. In a state where the press plate234reaches the fixation portion233, the press plate234is trapped on a border between the fixation portion233and the screw extension portion232that constitutes a stepped jaw, and thus, the press plate234is reliably prevented from being moved toward the screw extension portion232. Thus, the press plate234may be firmly held at a setting position where the press plate234is brought into contact with the screw extension portion232.

The press plate234is fixed to the fixation portion233and is arranged in such a manner as to protrude farther toward the radial direction than the screw extension portion232. Accordingly, a right-side lateral-surface portion of the press plate234that is brought into contact with or faces the screw extension portion232has the shape of a hooking jaw.

The press plate234is arranged in such a manner that the right-side lateral-surface portion thereof faces the lateral-surface portion of the left side of the press nut33combined by the bolt-nut fastening with the circumference of the nut piston24, in the axial direction, and when the press nut33is moved to the left, the right-side lateral-surface portion thereof is pressed against and brought into contact with the press nut33. That is, the right-side lateral-surface portion of the press plate234that is shaped in such a manner as to protrude farther toward the radial direction than the screw extension portion232is the press contact portion235to which the press nut33is removably attached.

The press plate234according to the second embodiment of the present disclosure has the shape of a ring. A portion of the right side of the press plate234that faces the screw extension portion232may have a greater diameter than a portion of the left side thereof. An end portion of the left side thereof may have a polygonal cross section, considering that the end portion of the left side thereof is to be engaged with a tool. This shape is disclosed as a desired example of the press plate234according to the present disclosure and is not intended to impose any limitation on the press plate234.

Any press plate234that can form the hooking jaw in this manner may have various shapes that include the shape of a ring and may be arranged on the fixation portion233. The press plate234may be fixed on the fixation portion233using various methods, such as the bolt-nut fastening, pressing-fixing (plastic deforming), and key inserting.

In terms of structure, an inner circumference portion of the press plate234according to the second embodiment of the present disclosure is internally tapped, and is fixed by the bolt-nut fastening to the externally threaded fixation portion233. In a state where, in this manner, the press plate234is fixed by the bolt-nut fastening to the fixation portion233, the press plate234is pressed against toward the fixation portion233and is plastically deformed. Thus, for example, an internally tapped portion of the press plate234may be pressed against an externally threaded portion of the fixation portion233so forcefully that they may be crushed and permanently prevented from being separated from each other.

The press contact portion235is formed on an end portion of the right side of the press plate234that faces the press nut33in the axial direction. As the press nut33is moved toward the axial direction, the press contact portion235is brought into contact with or is spaced away from an end portion of the left side of the press nut33. More specifically, the press contact portion235may be formed in the shape of a ring in such a manner as to have a width in the radial direction that corresponds to a difference in diameter between the press plate234and the screw extension portion232.

The screw contact portion336has a ring-shaped cross section in such a manner as to face the press contact portion235. Accordingly, when the press nut33is moved to the left, with the screw contact portion336, the press nut33is precisely pressed against and brought into contact with the press contact portion235. Motive power that is transferred from the second motor31to the press nut33finally serves as a load that is exerted on the press contact portion235of the bolt screw23toward the axial direction through the screw contact portion336.

FIG.11is an operational view illustrating a state where the brake is performed by the service brake2according to the second embodiment of the present disclosure.FIG.12is an operational view illustrating a state where the brake is performed by the parking brake3according to the second embodiment of the present disclosure.

With reference toFIG.11, the service brake2according to the second embodiment of the present disclosure performs the operation of pressing against and pushing the shoe5by rotating the bolt screw23in conjunction with the drive of the first motor21and moving toward the axial direction the nut piston24combined by the bolt-nut fastening with the circumference of the bolt screw23.

With reference toFIG.12, the parking brake3according to the first embodiment of the present disclosure is combined by the bolt-nut fastening with the circumference of the nut piston24in a manner that overlaps the press nut33, and performs the operation of preventing the nut piston24from being pushed in the opposite direction due to the reaction force of the shoe5, by moving the press nut33toward the axial direction in conjunction with the drive of the second motor31and pressing against the press nut33toward the axial direction and thus bringing the press nut33into contact with the press plate234of the bolt screw23.

In the initial state as illustrated inFIG.8, when the first motor21is driven in the forward direction, the nut piston24, as illustrated inFIG.11, is moved to the right, and pushes the right-side shoe5of the pair of the shoes5to the right and presses against the shoe5on the right. With this operation, the service braking is performed. At this point, the press nut33and the press plate234of the bolt screw23are spaced away from each other in the axial direction.

Subsequently, when the second motor31is driven in the forward direction, the press nut33, as illustrated inFIG.12, is moved toward the press plate234and the press contact portion235of the bolt screw23and comes into contact with each other. At this point, in the state where a first-side portion of the press nut33is bound to the nut piston24, a second-side portion thereof is brought into contact with the bolt screw23toward the axial direction, and thus the braking for parking is performed. Subsequently, although the second motor31stops being driven, this parking brake state is maintained due to the self-locking structure.

As illustrated inFIG.11, in the state where the press nut33is not brought into contact with the bolt screw23, when the first motor21stops being driven, that is, when only the service braking is performed instead of the braking for parking, the nut piston24is pushed by itself due to the reaction force of the shoe5, and the bolt screw23is rotated in the reverse direction and, as illustrated inFIG.8, returns to the initial state thereof.

In the case where the braking for parking is canceled, the following process may be continuously performed. The first motor21is driven in the forward direction. Thus, the nut piston24is farther pushed toward the shoe5, and the press nut33is spaced away from the press contact portion235of the bolt screw23. Thereafter, the second motor31is driven in the reverse direction. By performing this operation of canceling the braking for parking, the bolt screw23, the nut piston24, and the press nut33may be returned to the initial states thereof, respectively, as illustrated inFIG.8.

The drum brake1according to the present disclosure has a structure in which the service brake2and the parking brake3are coaxially combined with each other. More specifically, according to the present disclosure, the drum brake1has a structure in which the bolt screw23and the nut piston24of the service brake2and the press nut33of the parking brake3are coaxially combined by the bolt-nut fastening with each other. In other words, the parking brake3according to the present disclosure has a simple structure in which the press nut33is additionally combined by the bolt-nut fastening with the circumference of the nut piston24provided in the service brake2. That is, according to the present disclosure, the drum brake1has a simple structure in which the service brake2and the parking brake3share one screw corresponding to the bolt screw23.

Accordingly, the above-mentioned structures according to the present disclosure provide the following advantages, when compared with the case where the service brake2and the parking brake3in the related art are arranged independently of each other, in other words, when compared with the case where the service brake2and the parking brake3in the related art are arranged in such a manner as to be spaced away from each other and thus to be separated from each other. The numbers of components of, and volumetric weights, of the service brake2and the parking brake3can be remarkably reduced, and space utilization and the freedom of layout design can be further improved. Moreover, the manufacturing cost and the productivity can be improved.

In addition, according to the present disclosure, when the press nut33is brought into contact with the press contact portion235only by exerting a load high enough to restrict the rotation of the nut piston24, the braking for parking may be performed. Accordingly, when compared with the parking brake3in the related art in which the shoe5is directly pressed against, the braking for parking can be stably performed by outputting a remarkably low load. Therefore, the motor corresponding to the second motor31, the power transmission device corresponding to the second power transmission device32, and the housing covering them can be reduced in size and weight.

The embodiments of the present disclosure are mostly described above. It would be understandable to a person of ordinary skill in the art to which the present disclosure pertains that the present disclosure may be practiced in modified forms within the scope that does not depart from the nature and gist of the present disclosure. Therefore, the embodiments disclosed should be considered in a explanative point of view, not in a limited point of view. The scope of the present disclosure is defined in the claims, not in the specification, and all equivalent differences should be interpreted as falling within the scope of the present disclosure.