Electromechanical brake

Abstract

To provide an electromechanical brake capable of miniaturizing a brake device.SOLUTION: A planetary roller screw 10 including a shaft 20 having a shaft-side thread portion 21, a roller 30 having a roller-side thread portion 31 that meshes with the shaft-side thread portion 21, a piston 50 in which the shaft 20 and the roller 30 are disposed, a cage 40 that supports the roller 30, and a thrust bearing 60 that transmits a load in an axial direction between the roller 30 and the piston 50; The roller 30 moves in the axial direction when the rotation of the shaft 20 is transmitted, and the piston 50 moves in the axial direction when the movement of the roller 30 is transmitted, and applies a pressing force in a direction in which the brake pad 88 is pressed against the brake rotor 90 to the brake pad 88.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to electromechanical brakes. [Background technology]

[0002] Many braking devices mounted on vehicles and the like generate braking force using hydraulics or the like, but in recent years, braking devices have been proposed that generate braking force using driving force from an electrically operated motor. For example, the disc brake described in Patent Document 1 includes a motor gear unit incorporating an electric motor and a reduction mechanism, and a piston propulsion mechanism, and the piston propulsion mechanism converts the rotational motion of the motor gear unit into linear motion to propel the piston, generating braking force by using the piston to press brake pads that press against the brake disc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-49879 Summary of the Invention [Problem to be solved by the invention]

[0004] However, electromechanical brakes, which are braking devices that generate braking force using the driving force generated by a motor, require a speed reduction mechanism to reduce the rotation output from the motor and increase the torque, which tends to increase the size of the entire device. For this reason, electromechanical brakes that generate braking force using the driving force generated by a motor have room for improvement in terms of miniaturization.

[0005] The present disclosure has been made in view of the above, and has an object to provide an electromechanical brake that can reduce the size of the brake device. [Means for solving the problem]

[0006] The electromechanical brake of the present disclosure comprises a planetary roller screw having a shaft having a shaft-side threaded portion formed in a spiral shape on its outer circumferential surface, a roller formed in a round bar shape extending along the axial direction of the shaft and having a roller-side threaded portion that meshes with the shaft-side threaded portion, a piston formed in a cylindrical shape with a bottom disposed at one end and having the shaft and the roller disposed inside, a cage disposed inside the piston and supporting the roller so as to be movable in the circumferential direction of the shaft, and a thrust bearing disposed on the side of the roller in the axial direction and receiving a load in the axial direction between the roller and the piston and transmitting the load between the roller and the piston, and a planetary roller screw connected to the shaft to apply a driving force to the shaft. the roller rotates and moves in the axial direction relative to the shaft as the rotation of the shaft, which rotates by the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion, the piston moves in the axial direction relative to the shaft together with the roller as the axial movement of the roller is transmitted to the piston via the thrust bearing, and the piston applies a pressing force to the brake pad in a direction pressing the brake pad against the brake rotor by the axial movement relative to the shaft.

[0007] According to this configuration, the driving force of the motor is transmitted between the shaft connected to the motor and the roller, which transmits axial force to the piston, via the roller-side threaded portion that meshes with the shaft-side threaded portion. This allows the driving force of the motor to be transmitted from the shaft to the roller at a large reduction ratio, thereby increasing the force exerted when the roller moves axially. Furthermore, the axial load between the roller and the piston can be transmitted via a thrust bearing disposed axially on the side of the roller, allowing the large axial force from the roller to the piston to be transmitted via the thrust bearing without interfering with the rotation of the roller around the central axis of the shaft. In this way, a large axial force is transmitted from the roller to the piston, and the piston moves axially with the roller relative to the shaft with a large thrust. This allows the piston to apply a large pressing force to press the brake pads against the brake rotor. Therefore, a large braking force can be obtained without providing a reducer to increase the reduction ratio between the mechanism that converts the driving force generated by the motor into braking force and the motor. The omission of the reducer allows the device to be made more compact. As a result, the brake device can be made more compact.

[0008] In a preferred embodiment, a plurality of the rollers are arranged around the shaft in the circumferential direction of the shaft, and the retainer supports the plurality of rollers so that the rollers can move integrally in the circumferential direction of the shaft.

[0009] With this configuration, when the rotational force of the shaft rotated by the driving force from the motor is converted into an axial force by the rollers, the multiple rollers can generate a large axial force. This increases the thrust force when the piston moves axially relative to the shaft, thereby increasing the pressing force of the brake pads against the brake rotor. As a result, a large braking force can be obtained while miniaturizing the brake device.

[0010] In a preferred embodiment, the shaft-side threaded portion and the roller-side threaded portion have spiral directions opposite to each other.

[0011] With this configuration, the shaft-side threaded portion and the roller-side threaded portion have opposite spiral directions, so that the rotation of the shaft can be transmitted to the roller via the shaft-side threaded portion and the roller-side threaded portion, causing the roller to rotate in the opposite direction to the rotation of the shaft. This allows the roller to move axially while rotating in the opposite direction, and a simple structure can be realized in which the force in the rotational direction of the shaft is converted into an axial force and used to press against the brake pad. As a result, the brake device can be made smaller while keeping manufacturing costs low.

[0012] In a preferred embodiment, the shaft-side threaded portion and the roller-side threaded portion have different lead angles.

[0013] With this configuration, because the lead angles of the shaft-side threaded portion and the roller-side threaded portion are different, rotating the shaft allows the roller to move axially relative to the shaft according to the difference in lead angles between the shaft-side threaded portion and the roller-side threaded portion. This makes it possible to realize a simple structure that converts the force in the rotational direction of the shaft into an axial force and uses it to press against the brake pad. As a result, it is possible to reduce the manufacturing cost and make the brake device more compact.

[0014] Preferably, the shaft and the motor are arranged coaxially.

[0015] With this configuration, the planetary roller screw shaft and the motor are arranged coaxially, which prevents the motor from extending radially from the shaft, thereby reducing the size of the electromechanical brake in the radial direction of the shaft, thereby enabling the brake device to be made more compact. [Effects of the Invention]

[0016] The electromechanical brake according to the present disclosure has the effect of enabling the brake device to be made smaller. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a main part of an electromechanical brake according to an embodiment. [Figure 2] FIG. 2 is a detailed view of the planetary roller screw shown in FIG. [Figure 3] FIG. 3 is an exploded perspective view of the planetary roller screw. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0019] [Embodiment] Fig. 1 is a cross-sectional view of a main part of an electromechanical brake 1 according to an embodiment. The electromechanical brake 1 shown in Fig. 1 is mounted on a vehicle (not shown) as a brake device that generates a braking force on the vehicle as it moves. The electromechanical brake 1 has a brake rotor 90 that rotates together with the wheels (not shown) of the vehicle on which the electromechanical brake 1 is mounted, brake pads 88 that come into contact with the brake rotor 90 to generate frictional force between them, and a brake caliper 80 that holds the brake pads 88 and presses the brake pads 88 against the brake rotor 90.

[0020] The brake rotor 90 is made of a metal material and has a generally circular disk shape, and is attached to the vehicle so that the axis of the disk coincides with the axis of the wheel, so that the brake rotor 90 rotates integrally with the wheel as the wheel rotates.

[0021] The brake caliper 80 and brake pads 88 are attached to the vehicle body on a side that does not rotate with the wheels of the vehicle. The brake pads 88 are arranged on both sides of the brake rotor 90 in the thickness direction, and come into contact with both sides of the brake rotor 90 in the thickness direction by the pressing force applied by the brake caliper 80. This allows the brake pads 88 to generate frictional force between them and the rotating brake rotor 90.

[0022] The brake caliper 80 has a caliper body 81 and a caliper base 85. The caliper base 85 holds the brake pads 88 at positions on both sides of the brake rotor 90 in the thickness direction thereof so that the brake pads 88 face the brake rotor 90.

[0023] The caliper body 81 holds a piston 50 that abuts against an inner brake pad 88a, which is one of the brake pads 88 located on both sides in the thickness direction of the brake rotor 90, and applies a pressing force to the brake pad 88, and is also provided with a claw 83 that abuts against an outer brake pad 88b, which is the other brake pad 88. That is, the caliper body 81 has an accommodating hole 82 that is a hole that accommodates the piston 50, and by accommodating the piston 50 in the accommodating hole 82, the caliper body 81 holds the piston 50 movably in the thickness direction of the brake rotor 90 relative to the caliper body 81.

[0024] Furthermore, the caliper body 81 is attached to the caliper base 85 so as to be able to move relative to the caliper base 85 in the thickness direction of the brake rotor 90. With this configuration, the brake caliper 80 according to this embodiment is provided as a so-called one-side push type brake caliper 80 or a floating type brake caliper 80.

[0025] More specifically, the accommodating hole 82 formed in the caliper body 81 is a hole that opens in the direction in which the piston 50 applies a pressing force to the brake pad 88 in the caliper body 81. In other words, the accommodating hole 82 is formed in the caliper body 81 as a substantially cylindrical hole whose inner diameter is approximately the same as the outer diameter of the piston 50, and is formed in the caliper body 81 with the axis of the cylinder oriented in the thickness direction of the brake rotor 90.

[0026] Piston 50, which is held by caliper body 81 by being accommodated in accommodation hole 82 formed in caliper body 81, abuts against inner brake pad 88a from the side opposite to the side where brake rotor 90 is located in the thickness direction of brake rotor 90. Also, claws 83 of caliper body 81 abut against outer brake pad 88b from the side opposite to the side where brake rotor 90 is located in the thickness direction of brake rotor 90.

[0027] When the electromechanical brake 1 generates a braking force, the piston 50 applies a pressing force to the inner brake pad 88a in the direction in which the brake rotor 90 is located, thereby pressing the inner brake pad 88a against the brake rotor 90.

[0028] The caliper body 81 moves in the opposite direction to the direction in which the piston 50 applies a pressing force to the inner brake pad 88a due to a reaction force generated when the piston 50 applies a pressing force to the inner brake pad 88a. In other words, the caliper body 81 moves relative to the caliper base 85 in the opposite direction to the direction in which the piston 50 applies a pressing force to the inner brake pad 88a.

[0029] As a result, the claws 83 abutting against the outer brake pad 88b apply a pressing force to the outer brake pad 88b in the direction of the brake rotor 90, and the outer brake pad 88b is pressed against the brake rotor 90. This allows the electromechanical brake 1 to press the brake pads 88 from both sides in the thickness direction of the brake rotor 90, and the frictional force between the brake rotor 90 and the brake pads 88 abutting against both sides of the brake rotor 90 can generate a braking force that reduces the rotational speed of the rotating brake rotor 90.

[0030] In the electromechanical brake 1 according to this embodiment, a motor 70 is used as a power source for applying a pressing force to the brake pad 88 by the piston 50, and the motor 70 is attached to the caliper body 81. In addition, in the electromechanical brake 1 according to this embodiment, a planetary roller screw 10 is used as a mechanism for converting the driving force generated by the motor 70 into a pressing force.

[0031] A control device (hereinafter referred to as an ECU (Electronic Control Unit)) 100 that performs various controls on the vehicle is electrically connected to the motor 70, and a brake sensor 111 that detects the amount of operation of a brake pedal 110 is electrically connected to the ECU 100. The electromechanical brake 1 generates a braking force corresponding to the amount of operation of the brake pedal 110 by having the ECU 100 control the drive of the motor 70 based on the amount of operation of the brake pedal 110 detected by the brake sensor 111.

[0032] Fig. 2 is a detailed view of the planetary roller screw 10 shown in Fig. 1. Fig. 3 is an exploded perspective view of the planetary roller screw 10. The planetary roller screw 10 has a shaft 20, rollers 30, a piston 50, a cage 40, and a thrust bearing 60.

[0033] The shaft 20 is an axial member, and inside the shaft 20, a through hole 23 is formed that is formed in the longitudinal direction of the shaft 20 along the central axis AX of the shaft 20. The through hole 23 has a plurality of portions with different diameters, and one portion of the through hole 23 has an inner diameter that is approximately the same as the diameter of the drive shaft 71 of the motor 70, and is formed as a fitting hole 24 into which the drive shaft 71 of the motor 70 can be fitted.

[0034] The shaft 20 also has a flange portion 22 formed in a brim shape at a position on the outer peripheral surface of the shaft 20 near one end in the longitudinal direction of the shaft 20. The flange portion 22 is formed in a disk shape and protrudes outward from the outer peripheral surface of the shaft 20 in the radial direction of the shaft 20.

[0035] The shaft 20 also has a shaft-side threaded portion 21 formed in a spiral shape on its outer circumferential surface. The shaft-side threaded portion 21 is a threaded portion formed in a spiral shape on the outer circumferential surface of the shaft 20, centered on the central axis AX of the shaft 20. In other words, the shaft-side threaded portion 21 has thread crests and roots that each extend circumferentially around the central axis AX of the shaft 20, and are formed so as to be inclined in the direction in which the central axis AX of the shaft 20 extends. The shaft-side threaded portion 21 is formed from a position near the flange portion 22 on the outer circumferential surface of the shaft 20 toward the end opposite the end on which the flange portion 22 is disposed.

[0036] The roller 30 is formed in the shape of a round bar whose outer diameter is smaller than that of the shaft 20 and whose length is shorter than that of the shaft 20, and is arranged in the vicinity of the shaft 20 in a direction extending along the axial direction of the shaft 20.

[0037] The roller 30 has, on its outer circumferential surface, a roller-side thread portion 31 that is a thread portion that can mesh with the shaft-side thread portion 21 formed on the shaft 20. In other words, the roller-side thread portion 31 formed on the outer circumferential surface of the roller 30 is a thread portion that is formed in a spiral shape centered on the axis of the round bar-shaped roller 30. The roller-side thread portion 31 formed in this way has a spiral direction opposite to that of the shaft-side thread portion 21.

[0038] Furthermore, the shaft-side threaded portion 21 and the roller-side threaded portion 31 have different thread lead angles, with the lead angle of the shaft-side threaded portion 21 being larger than the lead angle of the roller-side threaded portion 31. That is, the inclination angle of the spiral of the shaft-side threaded portion 21 in the longitudinal direction of the shaft 20 relative to the circumferential direction of the shaft 20 is larger than the inclination angle of the spiral of the roller-side threaded portion 31 in the longitudinal direction of the roller 30 relative to the circumferential direction of the roller 30.

[0039] In addition, shaft end portions 32, which are portions supported by the cage 40, are formed on both ends of the roller 30 in the longitudinal direction. The shaft end portions 32 are formed in the shape of cylindrical protrusions whose outer diameter is smaller than the outer diameter of the roller-side thread portion 31.

[0040] The planetary roller screw 10 has a plurality of rollers 30 formed in this manner. The plurality of rollers 30 are all formed to have substantially the same shape, and are arranged around the shaft 20 with the axial direction of the rollers 30 oriented along the central axis AX of the shaft 20. The plurality of rollers 30 are also arranged in positions where the roller-side thread portion 31 of each roller 30 meshes with the shaft-side thread portion 21, and the plurality of rollers 30 are arranged at equal intervals in the circumferential direction of the shaft 20.

[0041] In this embodiment, twelve rollers 30, each having a roller-side threaded portion 31 meshing with a shaft-side threaded portion 21, are arranged around the shaft 20 at equal intervals in the circumferential direction of the shaft 20.

[0042] Piston 50 is formed in a generally cylindrical shape with a bottom, with bottom 51 located at one end, and shaft 20 and roller 30 are located inside. Piston 50, which is formed in a cylindrical shape with a bottom, has roller placement section 52, the inner diameter of which is larger than that of the section near bottom 51, formed in a section near the opening, i.e., in a section near the end opposite to the side where bottom 51 is located in the axial direction of the cylinder.

[0043] Specifically, the inner diameter of the piston 50 near the bottom 51 is slightly larger than the outer diameter of the shaft 20. In contrast, the inner diameter of the roller arrangement portion 52 is larger than the sum of the diameter of the shaft 20 and twice the diameter of the roller 30. In addition, the length of the roller arrangement portion 52 from the opening side of the piston 50 is longer than the length of the roller 30.

[0044] Therefore, when the shaft 20 and the rollers 30 are positioned inside the piston 50, the multiple rollers 30 arranged around the shaft 20 are arranged in the roller arrangement section 52 with the roller side screw portion 31 meshing with the shaft side screw portion 21.

[0045] The rollers 30 arranged inside the piston 50 are supported by a cage 40. The cage 40 is formed in a substantially cylindrical shape, and its length is approximately the same as that of the rollers 30. More specifically, the cage 40 is formed in a substantially cylindrical shape with an outer diameter that is approximately the same as but slightly smaller than the inner diameter of the roller arrangement portion 52 of the piston 50, and an inner diameter that is approximately the same as but slightly larger than the outer diameter of the shaft-side thread portion 21 of the shaft 20.

[0046] The cage 40 has side wall portions 41 formed in an annular plate shape at both ends in the longitudinal direction of the cylinder, with the thickness direction being the longitudinal direction of the cylinder. The side wall portions 41 are formed at both ends in the longitudinal direction of the cage 40 from the position of the outer circumferential surface toward the inside in the radial direction of the cylinder, and are formed over one circumference of the cylinder with a predetermined width in the radial direction of the cylinder.

[0047] Support portions 42 that support the rollers 30 are formed on the side wall portion 41 of the cage 40. The support portions 42 are formed in a shape that is cut out from a position that is the inner periphery of the annular side wall portion 41 toward the outside in the radial direction of the side wall portion 41. The width of the cutouts in the support portions 42 is approximately the same as the diameter of the shaft end portions 32 formed on the rollers 30, but slightly larger than the diameter of the shaft end portions 32 of the rollers 30.

[0048] The support portions 42 formed on the side wall portions 41 of the retainer 40 are formed in the same number as the rollers 30 on one side wall portion 41, and the support portions 42 are arranged at equal intervals in the circumferential direction of the retainer 40. The support portions 42 formed on the side wall portions 41 on both sides in the longitudinal direction of the retainer 40 are positioned at the same positions in the circumferential direction of the retainer 40. The retainer 40 rotatably supports each of the multiple rollers 30 by having the shaft ends 32 of the rollers 30 fit into the support portions 42 formed on the side wall portions 41 on both sides in the longitudinal direction of the retainer 40.

[0049] The roller arrangement portion 52 formed in the piston 50 has an inner diameter that is approximately the same as the outer diameter of the cage 40, but slightly larger than the outer diameter of the cage 40. When the roller 30 is arranged in the roller arrangement portion 52 formed in the piston 50, the roller 30 is arranged together with the cage 40 in a state where it is supported by the cage 40.

[0050] The cage 40 that holds the multiple rollers 30 has an outer diameter that is smaller than the inner diameter of the roller arrangement portion 52, and therefore is able to rotate in the circumferential direction of the piston 50 and shaft 20 while positioned inside the roller arrangement portion 52. Therefore, by positioning the cage 40 inside the roller arrangement portion 52 of the piston 50 while supporting the multiple rollers 30, the cage 40 can support the multiple rollers 30 as a unit so that they can move freely in the circumferential direction of the shaft 20.

[0051] Additionally, the cage 40 has a plurality of opening holes 43 formed on its outer peripheral surface at positions corresponding to the portions where the rollers 30 are arranged in the circumferential direction, the opening holes 43 opening in the radial direction of the cage 40. Since the opening holes 43 open at positions corresponding to the portions where the rollers 30 are arranged in the circumferential direction, the opening holes 43 are formed at the same positions in the circumferential direction as the support portions 42 formed on the side wall portions 41. The rollers 30 supported by the cage 40 are supported by the cage 40 with parts of the roller-side thread portions 31 facing outward from the opening holes 43.

[0052] A thrust bearing 60 and a thrust plate 61 are disposed inside the roller arrangement portion 52. The thrust bearing 60 and the thrust plate 61 are disposed inside the roller arrangement portion 52, on either side of the cage 40 in the axial direction of the shaft 20. The thrust bearing 60 and the thrust plate 61 are each formed in an annular shape with an inner diameter slightly larger than the outer diameter of the shaft 20 and an outer diameter slightly smaller than the inner diameter of the roller arrangement portion 52 of the piston 50.

[0053] The thrust bearing 60 is capable of receiving a load acting in the axial direction between the cage 40 and the piston 50 while allowing relative rotation between the cage 40 and the piston 50 about the central axis AX of the shaft 20. For example, a thrust needle bearing is used as the thrust bearing 60. The thrust plate 61 is an annular plate-shaped member that transmits the axial load acting from the cage 40 to the thrust bearing 60 via a flat surface.

[0054] The thrust bearing 60 has a first thrust bearing 60a arranged on the side of the retainer 40 where the bottom 51 of the piston 50 is located, and a second thrust bearing 60b arranged on the opposite side of the retainer 40 from the side where the bottom 51 of the piston 50 is located. Similarly, the thrust plate 61 has a first thrust plate 61a arranged on the side of the retainer 40 where the bottom 51 of the piston 50 is located, and a second thrust plate 61b arranged on the side of the retainer 40 opposite to the side where the bottom 51 of the piston 50 is located.

[0055] The roller arrangement portion 52 formed in the piston 50 has, at the end on the side where the bottom portion 51 is located, a surface whose normal is the direction of the central axis AX of the shaft 20 and the direction of the axis of the roller 30, that is, a surface parallel to the bottom portion 51. The first thrust bearing 60a is arranged between the cage 40 and the surface of the roller arrangement portion 52 that is parallel to the bottom portion 51 of the piston 50, and the first thrust plate 61a is arranged between the first thrust bearing 60a and the cage 40.

[0056] The first thrust bearing 60a is thus disposed between the cage 40 that supports the roller 30 and the piston 50, and is thereby disposed to the side of the roller 30 in the axial direction of the shaft 20 via the first thrust plate 61a. The first thrust bearing 60a, which is disposed to the side of the roller 30 via the first thrust plate 61a, is able to receive the load in the axial direction between the roller 30 and the piston 50 and transmit the load between the roller 30 and the piston 50.

[0057] Furthermore, a piston cover 55 that closes the opening of the piston 50 is disposed on the side of the piston 50 opposite to the side where the bottom portion 51 is located, and the second thrust bearing 60b and the second thrust plate 61b are disposed between the cage 40 and the piston cover 55. More specifically, the piston cover 55 is formed in an annular shape, with an outer diameter that is approximately the same as the outer diameter of the piston 50 and an inner diameter that is approximately the same as the outer diameter of the shaft 20 but slightly larger than the outer diameter of the shaft 20. Furthermore, the piston cover 55 has a fitting portion 56 that is fitted onto the roller arrangement portion 52 of the piston 50.

[0058] The fitting portion 56 is formed in a cylindrical shape that protrudes in the thickness direction of the piston cover 55, and the outer diameter of the cylinder is substantially the same size as the roller arrangement portion 52 formed on the piston 50. Therefore, the piston cover 55 is attached to the piston 50, closing the opening of the piston 50, by inserting the fitting portion 56 into the roller arrangement portion 52 formed on the piston 50 from the opening side of the piston 50 and press-fitting the fitting portion 56 into the roller arrangement portion 52.

[0059] The second thrust bearing 60b is disposed in the roller arrangement portion 52 between the piston cover 55 attached to the piston 50 and the cage 40, and the second thrust plate 61b is disposed between the second thrust bearing 60b and the cage 40. By disposing the second thrust bearing 60b between the piston cover 55 and the cage 40 that supports the roller 30 in this manner, the second thrust bearing 60b is disposed to the side of the roller 30 in the axial direction of the shaft 20 via the second thrust plate 61b. The second thrust bearing 60b, which is disposed to the side of the roller 30 via the second thrust plate 61b, can receive a load in the axial direction between the roller 30 and the piston cover 55 and transmit the load between the roller 30 and the piston cover 55.

[0060] Here, piston cover 55 is formed in an annular shape, and thus has a hole formed around the central axis. Therefore, when piston cover 55 is attached to piston 50, shaft 20 is inserted into the hole formed in piston cover 55 and disposed inside piston 50. Furthermore, when shaft 20 is inserted into the hole formed in piston cover 55 and disposed inside piston 50, flange portion 22 formed on shaft 20 is disposed on the side of piston cover 55 opposite to the side on which piston 50 is located.

[0061] Planetary roller screw 10 is arranged such that multiple rollers 30 supported by cage 40 are arranged around shaft 20, and roller-side thread portion 31 of each roller 30 meshes with shaft-side thread portion 21, with shaft 20 and multiple rollers 30 arranged inside piston 50. Planetary roller screw 10, with shaft 20 and multiple rollers 30 arranged inside piston 50 in this manner, is arranged in caliper body 81 by placing piston 50 in accommodating hole 82 formed in caliper body 81 of brake caliper 80. At this time, planetary roller screw 10 is arranged in accommodating hole 82 with bottom 51 of piston 50 positioned on the side where inner brake pad 88a is located, and with bottom 51 of piston 50 facing inner brake pad 88a.

[0062] In the caliper body 81, a flange support portion 84 is formed on a portion of the flange portion 22 formed on the shaft 20 opposite to the side where the piston cover 55 is located when the planetary roller screw 10 is disposed in the accommodating hole 82. The flange support portion 84 has a hole formed therein whose inner diameter is slightly larger than the outer diameter of the shaft 20, and the shaft 20 is disposed by passing through the hole of the flange support portion 84. In this case, the flange portion 22 formed on the shaft 20 is disposed between the flange support portion 84 of the caliper body 81 and the piston cover 55 in the axial direction of the shaft 20.

[0063] A shaft-side thrust bearing 65 that receives axial force from the shaft 20 is disposed on a portion of the flange portion 22 formed on the shaft 20 opposite to the side where the piston cover 55 is located in the axial direction of the shaft 20. That is, the shaft-side thrust bearing 65 is disposed between the flange portion 22 of the shaft 20 and the flange support portion 84 of the caliper body 81.

[0064] The shaft-side thrust bearing 65 is capable of bearing a load acting in the axial direction between the flange portion 22 of the shaft 20 and the flange support portion 84 of the caliper body 81, while allowing relative rotation between the flange portion 22 and the flange support portion 84 about the central axis AX of the shaft 20. The shaft-side thrust bearing 65 is, for example, a thrust needle bearing.

[0065] The motor 70 used as a power source in the electromechanical brake 1 has its drive shaft 71 inserted into the through hole 23 formed in the shaft 20 of the planetary roller screw 10, and the drive shaft 71 fitted into the fitting hole 24 provided in the through hole 23. This connects the drive shaft 71 of the motor 70 to the shaft 20 of the planetary roller screw 10, making it possible to apply a driving force to the shaft 20. In other words, the motor 70 can apply the driving force generated by the motor 70 to the planetary roller screw 10, and the planetary roller screw 10 can be operated by the driving force generated by the motor 70.

[0066] Furthermore, the motor 70 is connected to the shaft 20 by inserting the drive shaft 71 into the through-hole 23 of the shaft 20, so that the shaft 20 and the motor 70 are arranged coaxially.

[0067] Next, we will explain the operation of the electromechanical brake 1. The electromechanical brake 1 generates a braking force based on the amount of operation of a brake pedal 110 by the driver of the vehicle equipped with the electromechanical brake 1. In detail, the amount of operation of the brake pedal 110 is detected by a brake sensor 111, and the detection result of the amount of operation of the brake pedal 110 by the brake sensor 111 is transmitted to the ECU 100. The ECU 100 controls the drive of the motor 70 of the electromechanical brake 1 based on the amount of operation of the brake pedal 110 transmitted from the brake sensor 111.

[0068] When motor 70 is driven under the control of ECU 100, motor 70 rotates drive shaft 71. When drive shaft 71 of motor 70 rotates, shaft 20 of planetary roller screw 10 rotates together with drive shaft 71 of motor 70. Shaft 20 has shaft-side thread portion 21 formed on its outer circumferential surface, and shaft-side thread portion 21 meshes with roller-side thread portions 31 formed on rollers 30 arranged around shaft 20. Therefore, when shaft 20 rotates, a force in the rotational direction of shaft 20 is transmitted from shaft-side thread portion 21 to roller-side thread portion 31, and roller 30 rotates due to the force in the rotational direction of shaft 20 transmitted to roller 30 via shaft-side thread portion 21 and roller-side thread portion 31.

[0069] Because the rotation of the shaft 20 is transmitted to the rollers 30 by the meshing of the shaft-side threaded portion 21 and the roller-side threaded portion 31 in this way, when the rollers 30 are rotated by the rotational force transmitted from the shaft 20, the rollers 30 rotate in the direction opposite to the rotational direction of the shaft 20. The rollers 30 arranged around the shaft 20 each rotate in the direction opposite to the rotational direction of the shaft 20 because the rotational force from the shaft 20 is transmitted by the meshing of the roller-side threaded portion 31 and the shaft-side threaded portion 21 of each roller 30.

[0070] Furthermore, the rollers 30 are arranged around the shaft 20 at equal intervals in the circumferential direction of the shaft 20 by the cage 40, and the rollers 30 can rotate together with the cage 40 in the circumferential direction of the piston 50 and the shaft 20. In other words, the rollers 30 arranged around the shaft 20 while being held by the cage 40 can revolve around the shaft 20 in the circumferential direction of the shaft 20.

[0071] Therefore, when the rotation of shaft 20 is transmitted to the rollers 30 and each roller 30 rotates in the opposite direction to the rotation of shaft 20, the rollers 30 revolve together with cage 40 in the circumferential direction of shaft 20 around the central axis AX of shaft 20 while rotating on their own axes. The revolution of the rollers 30 is also performed by the transmission of force in the rotational direction of shaft 20, so the rollers 30 rotate in the same direction as the rotation of shaft 20.

[0072] Here, the shaft-side threaded portion 21 and the roller-side threaded portion 31, which transmit the force in the rotational direction of the shaft 20 to the plurality of rollers 30, are both formed in a spiral shape. The lead angle of the shaft-side threaded portion 21 is larger than the lead angle of the roller-side threaded portion 31. Therefore, when the force in the rotational direction of the shaft 20 is transmitted to the rollers 30 by the shaft-side threaded portion 21 and the roller-side threaded portion 31 while the rollers 30 are rotating, the rollers 30 also move in the axial direction according to the difference between the lead angle of the shaft-side threaded portion 21 and the lead angle of the roller-side threaded portion 31.

[0073] At this time, the amount of axial movement of the rollers 30 is significantly smaller than the amount of rotation of the shaft 20. In other words, the rollers 30 move axially relative to the rotation of the shaft 20 due to the transmission of rotation by the shaft-side threaded portion 21 and the roller-side threaded portion 31 and the difference between the lead angle of the shaft-side threaded portion 21 and the lead angle of the roller-side threaded portion 31, so the amount of axial movement is significantly smaller than the amount of rotation of the shaft 20. In other words, the rollers 30 move axially at a large reduction ratio relative to the rotation of the shaft 20, and therefore move with a large thrust in the axial direction.

[0074] Because the lead angles of the shaft-side threaded portion 21 and the roller-side threaded portion 31 are different, the rollers 30 move in the axial direction of the rollers 30 while rotating around the axis of each roller 30, but a thrust bearing 60 and a thrust plate 61 are disposed on both sides of the cage 40, which holds the rollers 30, in the axial direction of the shaft 20. In other words, the thrust bearing 60 and the thrust plate 61 are disposed on both sides of the rollers 30 held by the cage 40 in the axial direction.

[0075] Of the thrust bearing 60 and thrust plate 61, the first thrust bearing 60a and the first thrust plate 61a are arranged on the side of the retainer 40 where the bottom 51 of the piston 50 is located, and the second thrust bearing 60b and the second thrust plate 61b are arranged on the side of the retainer 40 where the piston cover 55 is located.

[0076] For this reason, when the force transmitted from the shaft 20 causes the rollers 30 to move axially toward the side where the bottom 51 of the piston 50 is located while rotating, the force that moves the rollers 30 in the axial direction is transmitted from the cage 40 that holds the rollers 30 to the piston 50 via the first thrust plate 61a and the first thrust bearing 60a. That is, the force that moves the rollers 30 in the axial direction is transmitted via the first thrust plate 61a and the first thrust bearing 60a to a surface that is parallel to the bottom 51 of the piston 50 and that is located at the end of the roller arrangement portion 52 of the piston 50 on the side where the bottom 51 of the piston 50 is located.

[0077] As a result, the force that moves the rollers 30 in the axial direction toward the side where the bottom 51 of the piston 50 is located is transmitted to the piston 50 via the first thrust plate 61a and the first thrust bearing 60a, and the piston 50 moves toward the side where the bottom 51 is located together with the rollers 30 and the cage 40 due to the force transmitted in this manner. In other words, the piston 50 moves axially within the accommodation hole 82 formed in the caliper body 81, and thereby moves relative to the caliper body 81 toward the side where the bottom 51 is located.

[0078] The piston 50, which moves relative to the caliper body 81 toward the side where the bottom portion 51 is located, applies a pressing force to the inner brake pad 88a from the side opposite to the side where the brake rotor 90 is located in the thickness direction of the brake rotor 90, in the direction toward the brake rotor 90. As a result, the inner brake pad 88a is pressed against the brake rotor 90.

[0079] At this time, roller 30, which moves in the axial direction due to the rotation of shaft 20, moves with a large thrust, so the pressing force of piston 50 against inner brake pad 88a becomes large, and inner brake pad 88a is pressed with a large force against brake rotor 90. Caliper body 81, which holds piston 50 in accommodating hole 82, moves in the opposite direction to the direction in which piston 50 applies pressing force to inner brake pad 88a due to the reaction force caused when piston 50 applies pressing force to inner brake pad 88a.

[0080] In other words, when the piston 50 applies a pressing force to the inner brake pad 88a while in contact with the inner brake pad 88a, the piston 50 cannot move in the direction toward the inner brake pad 88a. In this state, if the piston 50 moves relative to the caliper body 81 toward the side where the inner brake pad 88a is located, the force that causes the piston 50 to move relative to the caliper body 81 acts on the caliper body 81 as a force in the opposite direction to the direction in which the piston 50 applies a pressing force to the inner brake pad 88a.

[0081] Since the caliper body 81 is attached to the caliper base 85 so as to be able to move relative to the caliper base 85 in the thickness direction of the brake rotor 90, the caliper body 81, to which a force acts to cause the piston 50 to move relative to the caliper base 85, moves relative to the caliper base 85 in the opposite direction to the direction in which the piston 50 applies a pressing force to the inner brake pad 88a.

[0082] As a result of the caliper body 81 moving relative to the caliper base 85 in this manner, the claws 83 of the caliper body 81, which come into contact with the outer brake pad 88b from the side opposite to the side where the brake rotor 90 is located, apply a pressing force to the outer brake pad 88b in the direction where the brake rotor 90 is located. As a result, the outer brake pad 88b is pressed against the brake rotor 90.

[0083] As a result, the inner brake pad 88a and the outer brake pad 88b are pressed against the brake rotor 90 from both sides in the thickness direction of the brake rotor 90, and a large frictional force is generated between the brake pads 88 that contact both sides of the brake rotor 90 and the rotating brake rotor 90. By generating a large frictional force between the rotating brake rotor 90 and the brake pads 88, the electromechanical brake 1 generates a braking force that reduces the rotational speed of the brake rotor 90.

[0084] In this manner, when roller 30 is moved axially relative to shaft 20 toward the side where bottom 51 of piston 50 is located in order to generate braking force in electromechanical brake 1, a force acts on shaft 20 in the opposite axial direction to the direction in which bottom 51 of piston 50 is located. In this embodiment, shaft-side thrust bearing 65 is disposed between flange portion 22 formed on shaft 20 and flange support portion 84 of caliper body 81, so that shaft 20 can rotate while receiving a force acting on shaft 20 in the axial direction by shaft-side thrust bearing 65.

[0085] As described above, when generating a braking force in the electromechanical brake 1 according to this embodiment, the power source, motor 70, is driven. As a result, in the planetary roller screw 10, the rotation of shaft 20, which is rotated by the driving force from motor 70, is transmitted from shaft-side thread portion 21 to roller-side thread portion 31, causing rollers 30 to rotate and move axially relative to shaft 20.

[0086] When roller 30 moves axially relative to shaft 20, piston 50 moves axially relative to shaft 20 together with roller 30, as the axial movement of roller 30 is transmitted to piston 50 via thrust bearing 60. Piston 50 moving axially applies a pressing force to brake pad 88 in a direction pressing brake pad 88 against brake rotor 90 due to the axial movement relative to shaft 20. This enables electromechanical brake 1 to increase the frictional force between brake pad 88 and brake rotor 90, thereby generating a braking force.

[0087] In this way, when the braking force generated by the electromechanical brake 1 is to be reduced, the drive control of the motor 70 is performed based on the amount of operation of the brake pedal 110 transmitted from the brake sensor 111, thereby rotating the motor 70 in the direction opposite to the direction in which braking force is generated by the electromechanical brake 1. As a result, the shaft 20 that rotates integrally with the drive shaft 71 of the motor 70 also rotates in the opposite direction, and the roller 30 to which the rotation of the shaft 20 is transmitted via the shaft-side threaded portion 21 and the roller-side threaded portion 31 also rotates in the direction opposite to the rotation direction when braking force is generated.

[0088] When the rollers 30 rotate in the opposite direction to when generating a braking force, the rollers 30 move relative to the shaft 20 toward the side where the piston cover 55 is located. The force that moves the rollers 30 in the axial direction in this manner is transmitted from the cage 40, which holds the multiple rollers 30, to the piston cover 55 via the second thrust plate 61b and the second thrust bearing 60b.

[0089] As a result, the force that moves the rollers 30 in the axial direction toward the side where the piston cover 55 is located is transmitted to the piston cover 55 via the second thrust plate 61b and the second thrust bearing 60b, and the piston 50 into which the piston cover 55 is fitted moves toward the side where the piston cover 55 is located together with the rollers 30 and the cage 40 due to the force transmitted in this manner. In other words, the piston 50 moves axially within the accommodation hole 82 formed in the caliper body 81, and thereby moves relative to the caliper body 81 toward the side where the piston cover 55 is located.

[0090] The piston 50, which moves relative to the caliper body 81 toward the side where the piston cover 55 is located, moves in a direction away from the inner brake pad 88a in the thickness direction of the brake rotor 90. As a result, the pressing force applied from the piston 50 to the inner brake pad 88a is reduced, and the pressing force applied from the inner brake pad 88a to the brake rotor 90 is also reduced.

[0091] When the pressing force applied from the piston 50 to the inner brake pad 88a is reduced, the caliper body 81 holding the piston 50 in the accommodating hole 82 moves in the thickness direction of the brake rotor 90 in a direction in which the claw 83 moves away from the brake rotor 90 due to the reaction of the pressing force applied from the claw 83 to the outer brake pad 88b.

[0092] This reduces the pressing force applied to the brake rotor 90 from the inner brake pad 88a and the outer brake pad 88b, reducing the frictional force between the brake pad 88 and the brake rotor 90. By reducing the frictional force between the brake rotor 90 and the brake pad 88 in this way, the electromechanical brake 1 reduces the braking force generated by the electromechanical brake 1.

[0093] As described above, the electromechanical brake 1 according to this embodiment uses the motor 70 as a power source and the planetary roller screw 10 as a mechanism for converting the driving force generated by the motor 70 into braking force. Furthermore, the planetary roller screw 10 transmits the driving force of the motor 70 between the shaft 20 to which the motor 70 is connected and the roller 30, which transmits axial force to the piston 50, via the roller-side thread portion 31 that meshes with the shaft-side thread portion 21. This allows the driving force of the motor 70 to be transmitted from the shaft 20 to the roller 30 at a large reduction ratio, thereby increasing the force exerted when the roller 30 moves axially. Furthermore, the axial load between the roller 30 and the piston 50 can be transmitted via the thrust bearing 60, which is disposed on the side of the roller 30 in the axial direction. Therefore, a large axial force from the roller 30 to the piston 50 can be transmitted via the thrust bearing 60 without impeding the revolution of the roller 30 about the central axis AX of the shaft 20.

[0094] In this way, a large axial force is transmitted from roller 30 to piston 50, and piston 50 moves axially relative to shaft 20 together with roller 30 with a large thrust, so that when piston 50 applies a pressing force to press brake pad 88 against brake rotor 90, a large pressing force can be applied. Therefore, a large braking force can be obtained without providing a reducer to increase the reduction ratio between motor 70 and the mechanism that converts the driving force generated by motor 70 into braking force, and the device can be made more compact by the amount that the reducer can be omitted. As a result, the electromechanical brake 1 can be made more compact, which means that the brake device can be made more compact.

[0095] Furthermore, a plurality of rollers 30 are arranged around the shaft 20 in the circumferential direction of the shaft 20, and the plurality of rollers 30 are supported integrally by the cage 40 so as to be freely movable in the circumferential direction of the shaft 20. Therefore, when the rotational force of the shaft 20, which is rotated by the driving force from the motor 70, is converted into an axial force by the rollers 30, the plurality of rollers 30 can convert this into a large axial force. This makes it possible to increase the thrust force when the piston 50 moves axially relative to the shaft 20, and to increase the pressing force of the brake pads 88 against the brake rotor 90. As a result, it is possible to obtain a large braking force while miniaturizing the brake device.

[0096] Furthermore, because the spiral directions of the shaft-side threaded portion 21 and the roller-side threaded portion 31 are opposite to each other, the rotation of the shaft 20 can be transmitted to the roller 30 via the shaft-side threaded portion 21 and the roller-side threaded portion 31, causing the roller 30 to rotate in the opposite direction to the rotational direction of the shaft 20. This allows the roller 30 to move axially while rotating in the opposite direction, and a simple structure can be realized in which the force in the rotational direction of the shaft 20 is converted into an axial force and used as a force to press the brake pad 88. As a result, the brake device can be made smaller while keeping manufacturing costs down.

[0097] Furthermore, because the shaft-side threaded portion 21 and the roller-side threaded portion 31 have different lead angles, rotating the shaft 20 allows the roller 30 to move axially relative to the shaft 20 in accordance with the difference in lead angle between the shaft-side threaded portion 21 and the roller-side threaded portion 31. This makes it possible to realize a simple structure in which the force in the rotational direction of the shaft 20 is converted into an axial force and used as a force to press the brake pad 88. As a result, it is possible to reduce the size of the brake device while keeping manufacturing costs down.

[0098] Furthermore, because the shaft 20 of the planetary roller screw 10 and the motor 70 are arranged coaxially, it is possible to prevent the motor 70 from extending radially from the shaft 20, thereby reducing the size of the electromechanical brake 1 in the radial direction of the shaft 20. As a result, it is possible to reduce the size of the brake device.

[0099] [Variations] In the above-described embodiment, thrust needle bearings are used for the first thrust bearing 60a, the second thrust bearing 60b, and the shaft-side thrust bearing 65, but these bearings may be other than thrust needle bearings. For example, angular contact ball bearings, tapered roller bearings, and four-point contact ball bearings may be used for the first thrust bearing 60a, the second thrust bearing 60b, and the shaft-side thrust bearing 65. The first thrust bearing 60a, the second thrust bearing 60b, and the shaft-side thrust bearing 65 may be of any type as long as they can support these components while supporting axial loads and allowing relative rotation between the cage 40 and the piston 50, and between the shaft 20 and the caliper body 81.

[0100] Furthermore, although the above-described embodiment uses 12 rollers 30, there may be any number of rollers 30. The number of rollers 30 is preferably set appropriately depending on the size of the shaft 20 and the rollers 30, and the magnitude of the thrust when the rollers 30 are moved axially by the force in the rotational direction of the shaft 20.

[0101] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. The configurations described as the embodiments and modified examples may be combined as appropriate. [Explanation of symbols]

[0102] 1 Electromechanical Brake 10 Planetary Roller Screw 20 shaft 21 Shaft side thread 22 Flange 23 Through hole 30 Laura 31 Roller side screw part 32 Shaft end 40 Retainer 41 Side wall 50 pistons 51 Bottom 52 Roller arrangement section 55 Piston cover 56 Fitting part 60 Thrust bearing 61 Thrust plate 70 Motor 71 Drive shaft 80 brake caliper 81 Caliper body 85 caliper base 88 Brake pads 90 Brake rotor 100 ECU 110 Brake pedal 111 Brake sensor

Claims

1. a shaft having a shaft-side thread portion formed helically on an outer circumferential surface; a roller formed in a round bar shape extending along the axial direction of the shaft and having a roller-side threaded portion that meshes with the shaft-side threaded portion; a piston formed in a cylindrical shape with a bottom disposed at one end, the piston having the shaft and the roller disposed therein; a cage that is disposed inside the piston and supports the roller so as to be movable in the circumferential direction of the shaft; a thrust bearing disposed on a side of the roller in the axial direction, the thrust bearing receiving a load in the axial direction between the roller and the piston and transmitting the load between the roller and the piston; a planetary roller screw having a a motor coupled to the shaft to apply a driving force to the shaft; A disc-shaped brake rotor; a brake pad that contacts the brake rotor; a brake caliper that holds the brake pads; Equipped with the roller rotates and moves relative to the shaft in the axial direction when the rotation of the shaft, which is rotated by the driving force from the motor, is transmitted from the shaft-side threaded portion to the roller-side threaded portion; the piston moves in the axial direction together with the roller relative to the shaft as the movement of the roller in the axial direction is transmitted to the piston via the thrust bearing; The piston applies a pressing force to the brake pad in a direction pressing the brake pad against the brake rotor by moving relative to the shaft in the axial direction.

2. a plurality of rollers are arranged around the shaft in the circumferential direction of the shaft, The electromechanical brake according to claim 1 , wherein the cage supports the rollers so that the rollers can move integrally in the circumferential direction of the shaft.

3. 2. The electromechanical brake according to claim 1, wherein the shaft-side threaded portion and the roller-side threaded portion have spiral directions opposite to each other.

4. 2. The electromechanical brake according to claim 1, wherein the shaft-side threaded portion and the roller-side threaded portion have different lead angles.

5. 2. The electromechanical brake of claim 1, wherein the shaft and the motor are coaxially disposed.

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