Electric actuator and electric brake device for a vehicle using the same

Abstract

The electric actuator (DN) of the present application includes: an input member (BI) that is rotationally driven by an electric motor (MT) and has a first rotation-stopping portion (Ma) in an inner peripheral portion (Mn); an output member (BO) that has a second rotation-stopping portion (Mb) capable of engaging with the first rotation-stopping portion (Ma) and a first threaded portion (Na) in an outer peripheral portion (Mg); and a direct-acting member (BH) having a second threaded portion (Nb) capable of engaging with the first threaded portion (Na). The threaded mechanism (NJ) and the rotation-stopping mechanism (MD) are formed in the outer peripheral portion (Mg) of the output member (BO). Thus, the electric actuator (DN) is reduced in radial and axial dimensions.

Description

Technical Field

[0001] This disclosure relates to electric actuators and electric braking devices for vehicles using the electric actuators. Background Technology

[0002] Patent Document 1, with the aim of "improving the drum brake," discloses: "When the drum brake is in operation, during a period when the force applied to the pressing members 44a and b is less than a set value, the rotation input member 52 and the rotation sliding member 53 rotate along with the rotation of the electric motor. The drive member 54 moves axially via the threaded mechanism 84, causing the pressing member 44a to advance. Additionally, the axial movement of the rotation sliding member 53 causes the pressing member 44b to advance. When the force applied to the pair of pressing members 44a and b against the brake shoes 30a and b is greater than the set value, the threaded mechanism 84 locks, causing the drive member 54 and the rotation sliding member 53 to rotate together. This activates the ball bearing slide mechanism 90, causing the pressing members 44a and b to advance. As a result, the brake shoes 20a and b are pressed against the drum, causing the drum brake to operate."

[0003] Specifically, the following structure is described in Patent Document 1.

[0004] "The rotary sliding member 53 has a hollow cylindrical portion 66 extending axially and a head 68 disposed at one end. Within the cylindrical portion 66, it is held by the rotary input member 52 so as to be unable to rotate relative to it but is capable of relative movement along the axial direction. The shaft portion 66 of the rotary sliding member 53 is configured as a spline shaft, and a spline hole 72 is formed in the rotary input member 52. The rotary sliding member 53 is held by the rotary input member 52 through the engagement of these spline shafts with the spline hole 72. These spline shafts and spline holes 72 constitute the rotary sliding mechanism 74."

[0005] The drive member 54 has a solid shaft portion 78 extending axially and a head 80 disposed at one end. The shaft portion 78 is held axially relative to the inner circumferential side of the cylindrical portion 66 of the rotary sliding member 53. An internal thread portion 81 is formed on the inner circumferential surface of the cylindrical portion 66 of the rotary sliding member 53, and an external thread portion 82 is formed on the outer circumferential surface of the shaft portion 78 of the drive member 54. These threads engage to form a motion conversion mechanism 84 that converts rotation into linear motion.

[0006] In the structure of Patent Document 1, a motion conversion mechanism (also known as a power conversion mechanism or a threaded mechanism) is provided at the center of the rotary sliding mechanism (also known as an anti-rotation mechanism). That is, the anti-rotation mechanism (e.g., a spline mechanism) and the threaded mechanism (e.g., a trapezoidal thread) are arranged on concentric circles. In other words, the anti-rotation mechanism and the threaded mechanism are independent mechanisms, with the anti-rotation mechanism located outside the threaded mechanism. Therefore, as a whole, the size of the mechanism increases radially (becomes thicker).

[0007] Furthermore, to reduce the radial dimension of the aforementioned mechanism, a structure could be considered in which the anti-rotation mechanism and the threaded mechanism are arranged separately on the rotation axis (also known as the "central axis") of the anti-rotation mechanism. However, in this structure, while the radial dimension can be shortened, the dimension along the aforementioned central axis is enlarged. Therefore, in an electric actuator that converts and transmits the rotational power of an electric motor into linear power, it is desirable to have an electric actuator that can simultaneously shorten both the radial and axial dimensions.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2010-249314 Summary of the Invention

[0009] The purpose of this invention is to provide an electric actuator for an electric braking device for a vehicle, which can reduce the radial and axial dimensions, thereby miniaturizing the device.

[0010] The electric actuator (DN) according to the present invention comprises: "an input member (BI) driven to rotate by an electric motor (MT) and having a first anti-rotation portion (Ma) in its inner peripheral portion (Mn)"; "an output member (BO) having a second anti-rotation portion (Mb) capable of engaging with the first anti-rotation portion (Ma) and a first threaded portion (Na) in its outer peripheral portion (Mg); and "a direct-acting member (BH) having a second threaded portion (Nb) capable of engaging with the first threaded portion (Na)".

[0011] Based on the above structure, instead of separately setting the threaded mechanism NJ (Na+Nb) and the anti-rotation mechanism MD (Ma+Mb), both the threaded mechanism NJ and the anti-rotation mechanism MD are formed on the outer periphery Mg of the output component BO. Therefore, in the electric actuator DN, the radial and axial dimensions are shortened, allowing for overall device miniaturization.

[0012] The electric braking device (DS) of the vehicle according to the present invention converts the rotational power of an electric motor (MT) into linear power, which presses the brake pads (MS) provided on the brake shoes (BSa, BSb) against the brake drum (BD) to generate braking force (Fx, Fp) at the wheel. Moreover, the power conversion mechanism (HN) that converts the rotational power into the linear power consists of the following components: "input component (BI), having a first anti-rotation part (Ma) in its inner peripheral portion (Mn)"; "output component (BO), having a second anti-rotation part (Mb) capable of engaging with the first anti-rotation part (Ma) and a first threaded part (Na) in its outer peripheral portion (Mg); and "direct-acting component (BH), having a second threaded part (Nb) capable of engaging with the first threaded part (Na)".

[0013] The space around the vehicle's wheels is small and very limited. Based on the above structure, by miniaturizing the power conversion mechanism HN, the electric braking device DS can be fitted into a confined space more efficiently. Attached Figure Description

[0014] Figure 1 This is a schematic diagram used to illustrate the electric braking device DS.

[0015] Figure 2 This is a schematic diagram (including a sectional view) used to illustrate the electric actuator DN.

[0016] Figure 3 This is a cross-sectional view used to illustrate the first example of the power conversion mechanism HN for the electric actuator DN.

[0017] Figure 4 This is a cross-sectional view used to illustrate a second example of the power conversion mechanism HN for the electric actuator DN. Detailed Implementation

[0018] <Electric Braking System DS>

[0019] Reference Figure 1 This is a schematic diagram illustrating an electric braking device DS that generates braking force on the wheels of a vehicle (e.g., the rear wheels). The electric braking device DS generates braking force by applying braking torque to the wheels. The electric braking device DS consists of a braking unit DB and an electric actuator DN. Furthermore, in the following description, components, elements, signals, characteristics, etc., marked with the same symbols, such as "MT," are components, elements, signals, and characteristics with the same function.

[0020] Braking System DB

[0021] The braking device DB is located on the wheels (rear wheels). The braking device DB uses a known drum brake (e.g., a master-driven drum brake). The braking device DB generates a braking force that decelerates the vehicle (called "deceleration braking force Fx") and a braking force that maintains the vehicle at a stop (called "stopping braking force Fp"). The electric actuator (also simply called "actuator") DN, described later, is used as the power source to generate the deceleration braking force Fx and the stopping braking force Fp. Furthermore, the deceleration braking force Fx is used for service braking, and the stopping braking force Fp is used for parking braking.

[0022] The braking device DB is fixed to the side of the wheel. The braking device DB consists of a liner plate PL, a brake drum BD, and brake shoes BSa and BSb.

[0023] The braking device DB includes a liner plate PL as a non-rotating component and a brake drum BD having a friction surface Md on its inner circumferential side and rotating integrally with the wheel about the wheel's rotation axis Jk. An anchoring member AN and an electric actuator DN are fixed at portions separated in the diametrical direction of the liner plate PL. Between the anchoring member AN and the electric actuator DN (specifically, portions Pa and Pb), a pair of brake shoes BSa and BSb, each having an arc shape, are arranged facing the friction surface (inner circumferential surface) Md of the brake drum BD. In other words, the two brake shoes BSa and BSb extend in an arc shape along the inner circumferential surface Md of the cylindrical brake drum BD. The brake shoes BSa and BSb are mounted by a shoe clamp HD so that they can move along the surface of the liner plate PL.

[0024] Brake pads MS (friction elements) are fired onto the outer circumferential surfaces of brake shoes BSa and BSb. For each of a pair of brake shoes BSa and BSb, one end Qa and Qb engages with the electric actuator DN, and the other end abuts against the anchoring member AN, thus being supported to be deployed.

[0025] A reset component (e.g., a reset spring) RS is provided between a pair of brake shoes BSa and BSb. Through the reset component RS, when the pressure on the brake shoes BSa and BSb is released, the brake shoes BSa and BSb move away from the inner circumferential surface Md of the brake drum BD.

[0026] Additionally, a pressure bar with an adjuster (not shown) is installed between a pair of brake shoes BSa and BSb. The pressure bar with the adjuster is used to adjust the gap between the brake lining MS and the drum friction surface Md according to the wear of the brake lining MS.

[0027] The lower ends of the brake shoes BSa and BSb are supported below the pad plate PL, allowing them to rotate around the anchoring member AN. The electric actuator DN is supported above the pad plate PL. The electric actuator DN has two movable parts Pa and Pb (referred to as "first and second pressing parts") that can protrude along the pressing axis Ja (described later) in the same direction as the vehicle's longitudinal direction. The first and second pressing parts Pa and Pb protrude by the power of the electric motor MT.

[0028] For example, when the electric motor MT is driven in the forward direction, the first and second pressing parts Pa and Pb protrude (expanding along the pressing axis Ja). This applies a pressing force Fs to the upper ends (one end) Qa and Qb of the brake shoes BSa and BSb, pressing the brake pad MS against the inner circumferential surface (friction surface) Md of the brake drum BD. Through the friction between the brake pad MS and the inner circumferential surface Md, a braking torque is applied to the brake drum BD, braking the wheel. That is, via the electric actuator DN, the brake pad MS is pressed against the friction surface Md of the brake drum BD and slides into contact, thereby generating friction between the brake pad MS and the brake drum BD. This friction generates and increases braking force on the wheel.

[0029] When the braking force on the wheel decreases, the electric motor MT is driven in the reverse direction, and the protruding parts Pa and Pb of the first and second pressing parts contract. As a result, the pressing force Fs acting on the upper ends Qa and Qb of the brake shoes BSa and BSb decreases, and the friction between the brake pad MS and the brake drum BD decreases. Furthermore, when not braking, the brake shoes BSa and BSb are pulled back by the reset component RS, thus separating the brake pad MS from the friction surface Md.

[0030] <Electric Actuator DN>

[0031] Reference Figure 2 A schematic diagram (including a partial sectional view) illustrates the electric actuator DN. The actuator DN comprises a housing HG, an electric motor MT, a reducer GS, a power conversion mechanism HN, a parking brake mechanism PK, and a controller ECU.

[0032] The housing HG supports and covers the electric motor MT, the reducer GS, and the power conversion mechanism HN. The electric actuator DN is fixed to the bushing PL via the housing HG. A portion of the electric actuator DN (particularly, the components around the pressing axis Ja of the input component BI, output component BO, and first and second direct-acting components BH and BJ) is positioned relative to the bushing PL on the same side as the brake shoes BSa and BSb. On the other hand, other components of the electric actuator DN (e.g., the electric motor MT and the wheel-side controller ECW) are positioned relative to the bushing PL on the opposite side of the brake shoes BSa and BSb. That is, the actuator DN is configured to penetrate the bushing PL.

[0033] The electric motor MT is the power source used to generate braking force Fx and stopping braking force Fp. The electric motor MT is driven by a controller (also called an "electronic control unit") ECU. The electric motor MT can be a brushed motor or a brushless motor. When the electric motor MT is driven in the forward direction, the braking force Fs increases, and the braking forces Fx and Fp increase. Conversely, when the electric motor MT is driven in the reverse direction, the braking force Fs decreases, and the braking forces Fx and Fp decrease. A rotation angle sensor KA is installed in the electric motor MT to detect the position (rotation angle) Ka of the rotor (rotating component) of the electric motor MT.

[0034] The rotational power (output torque of the electric motor MT about the motor axis Jm) of the electric motor MT is reduced by the reducer GS. The reducer GS consists of multiple gears (e.g., a two-stage gear system). A first minor gear SK1 is fixed to the output shaft SM of the electric motor MT. An intermediate shaft SC is provided, and a first major gear DK1 is fixed to the intermediate shaft SC to mesh with the first minor gear SK1. Further, a second minor gear SK2 is fixed to the intermediate shaft SC. The second minor gear SK2 is configured to mesh with the second major gear DK2. That is, the rotational power of the electric motor MT is reduced by the power transmission path "SK1→DK1→SK2→DK2" and input to the power conversion mechanism HN via the reducer GS (especially the second major gear DK2).

[0035] Power Conversion Mechanism HN

[0036] The rotational power of the second large-diameter gear DK2 (i.e., the rotational power of the electric motor MT) is converted into linear power via the power conversion mechanism HN, and output as pressing force Fs to the brake shoes BSa and BSb. In other words, the rotational motion of the electric motor MT is converted into linear motion via the power conversion mechanism HN. The power conversion mechanism HN consists of an input component BI, an output component BO, and first and second linear motion components BH and BJ.

[0037] The input component BI is a cylindrical rotating component (a component capable of rotating relative to the housing HG), with a second major diameter gear DK2 fixed on its outer periphery (outer periphery of the cylinder). That is, the input component BI is driven to rotate by an electric motor MT, and the second major diameter gear DK2 is coaxial with the input component BI. The axis of rotation Ja of the input component BI is referred to as the "pressing axis". A first anti-rotation part Ma is provided on the inner periphery Mn of the input component BI (inner periphery of the cylinder). For example, the first anti-rotation part Ma is formed (machined) as internal spline teeth. In this case, the first anti-rotation part Ma is also referred to as the "first spline part Sa". Furthermore, the input component BI does not move (slide) along the direction of the axis of rotation Ja.

[0038] The output component BO (particularly, one end) is a rotating component (a component capable of rotating relative to the housing HG) with a first threaded portion Na on its outer periphery (cylindrical outer periphery) Mg. Furthermore, in addition to the first threaded portion Na, the outer periphery Mg at one end of the output component BO also has a second anti-rotation portion Mb that engages with a first anti-rotation portion Ma. That is, the first and second anti-rotation portions Ma and Mb constitute the anti-rotation mechanism MD. The output component BO's movement is constrained by the engagement of the first anti-rotation portion Ma and the second anti-rotation portion Mb. In other words, the output component BO can rotate relative to the housing HG about the pressing axis Ja and can move linearly along the pressing axis Ja.

[0039] For the output component BO, as shown in the blow-out section (A), when the first anti-rotation part Ma is formed as an internal spline tooth, the second anti-rotation part Mb is formed (machined) as an external spline tooth. In this case, the second anti-rotation part Mb is also referred to as the "second spline part Sb". Further, the external thread Oj (in the trapezoidal thread) is formed (machined) as the first thread part Na. In addition, the second anti-rotation part Mb (second spline part Sb) only needs to be formed within the range (called the "movable range") that allows the output component BO to move relative to the input component BI. However, in the example shown in the blow-out section (A), the second spline part Sb is machined over the entire area spanning the portion of the external thread Oj. With this configuration, the machining of the second spline part Sb becomes easier.

[0040] The first direct-acting member BH is a non-rotating member whose movement about the pressing axis Ja is constrained in the direction of rotation; it is a direct-acting member that can only move along the pressing axis Ja. Here, the rotational movement is constrained by the sliding contact between the plane of the outer periphery of the first direct-acting member BH and the plane of the inner periphery of the housing HG (for example, a double D-shape as a sliding contact between two planes). Alternatively, the rotational movement can also be constrained by a spline mechanism or a key mechanism.

[0041] The first moving part BH has a cylindrical inner circumference Mh. A second threaded part Nb, capable of engaging with the first threaded part Na, is formed (machined) on the cylindrical inner circumference Mh of the first moving part BH. That is, the first and second threaded parts Na and Nb constitute the thread mechanism NJ. For example, if an external thread Oj is formed as the first threaded part Na, an internal thread Mj (in a trapezoidal thread) is formed (machined) as the second threaded part Nb. A first pressing part Pa is provided on the opposite side of the cylindrical inner circumference of the first moving part BH (the part where the second threaded part Nb is provided). The first pressing part Pa engages with the brake shoe (called the "leading shoe") BSa on the dominant side to press the leading shoe BSa (i.e., apply pressing force Fs). A pressing force sensor FS is provided in the first moving part BH to detect the pressing force Fs.

[0042] The second direct-acting component BJ is disposed on the pressing axis Ja on the side opposite to the output component BO and the first direct-acting component BH. Like the first direct-acting component BH, the second direct-acting component BJ is a non-rotating component whose rotational direction is constrained by planar sliding contact (such as a double D-shape). The second direct-acting component BJ can only move in the direction along the pressing axis Ja. For example, a recess is provided in the second direct-acting component BJ, and the other end of the output component BO is inserted into this recess. The end face Mo of the output component BO presses against the bottom surface Mc of the second direct-acting component BJ while rotating. A second pressing part Pb is disposed on the opposite side of the recess in the second direct-acting component BJ. The second pressing part Pb engages with the brake shoe (called the "driven shoe") BSb on the driven side to press the driven shoe BSb (i.e., apply pressing force Fs). Here, the pressing force Fs acting on the first and second pressing parts Pa and Pb has an action-reaction relationship. Therefore, a pressing force sensor FS can also be disposed in the second direct-acting component BJ.

[0043] The threaded mechanism NJ formed by the first and second threaded portions Na and Nb has reverse efficiency. Through the threaded mechanism NJ, not only is the power of the electric motor MT transmitted to the first and second direct-acting components BH and BJ, but power is also transmitted from the first and second direct-acting components BH and BJ toward the electric motor MT. That is, bidirectional power transmission is possible via the threaded mechanism NJ.

[0044] Parking Braking Mechanism Comparison

[0045] The parking brake mechanism PK maintains the parking braking force Fp even when power to the electric motor MT is stopped. The parking brake mechanism PK consists of a ratchet gear RC, a pawl component TS, and a solenoid SL. The ratchet gear RC is fixed to the output shaft SM of the electric motor MT. The pawl component TS is provided to mesh with the ratchet gear RC. The pawl component TS is driven by the solenoid SL. The solenoid SL, like the electric motor MT, is controlled by the controller ECU.

[0046] Controller ECU

[0047] The electric motor MT is controlled by the ECU (Electronic Control Unit), which drives the actuator DN. The ECU consists of a body-side controller (ECB), a wheel-side controller (ECW), and a communication bus (BS). The body-side controller (ECB) is located on the body side, and the wheel-side controller (ECW) is located on the wheel side (e.g., integrated into the electric actuator DN). The body-side controller (ECB) and the wheel-side controller (ECW) are connected via the communication bus (BS) to send and receive signals (detected values, calculated values, etc.).

[0048] The controller ECU (body-side and wheel-side controllers ECB and ECW) includes a circuit board with a microprocessor MP installed, and a control algorithm programmed into the microprocessor MP. The electric motor MT is controlled based on the control algorithm within the microprocessor MP. Furthermore, the wheel-side controller ECW has a drive circuit DR to drive the electric motor MT. In the drive circuit DR, a bridge circuit is formed by switching elements (power semiconductor devices such as MOS-FETs and IGBTs). The electric motor MT is driven by controlling the current supplied to it via the bridge circuit. Additionally, the drive circuit DR has a current sensor IA (not shown) that detects the actual current Ia supplied to the electric motor MT. For example, a current sensor is used as the current sensor IA to detect the supply current Ia to the electric motor MT.

[0049] The braking operation amount Ba (operation amount of the braking operation component BP) detected by the braking operation amount sensor BA (e.g., the displacement sensor of the braking operation component BP), and the output signal of the parking brake switch SW, i.e., the parking signal Sw (a signal indicating the operating state of the parking brake switch SW), are input to the vehicle side controller ECB. Service braking (also known as "normal braking") is performed based on the braking operation amount Ba, and parking braking is performed based on the parking signal Sw.

[0050] [The operation of the service brake]

[0051] exist Figure 2 In the power conversion mechanism HN, the state (a) shown above the pressing axis Ja corresponds to the "non-braking state," and the state (b) shown below the pressing axis Ja corresponds to the "braking state." In the non-braking state (a), the brake shoes BSa (leading shoe) and BSb (driven shoe) are pulled against each other by the reset component (reset spring) RS, so the brake pad MS moves away from the friction surface Md of the brake drum BD. In the braking state (b), the brake shoes BSa and BSb on the leading and driven sides are pushed by the first and second pressing parts Pa and Pb, so the brake pad MS presses against the friction surface Md, generating friction. Here, the direction in which the first pressing part Pa of the first direct-acting component BH and the second pressing part Pb of the second direct-acting component BJ move away along the pressing axis Ja is called the "expansion direction Ha," corresponding to the direction in which the braking forces Fx and Fp increase. Conversely, the direction in which the first pressing part Pa and the second pressing part Pb approach each other is called the "contraction direction Hb," corresponding to the direction in which the braking forces Fx and Fp decrease.

[0052] When the braking operation component (e.g., brake pedal) BP is activated, the braking operation amount Ba increases from "0". In the body-side controller ECB, a target pressing force Ft is calculated based on a pre-set calculation mapping and the braking operation amount Ba, and increases with the increase of the braking operation amount Ba. Here, the target pressing force Ft is the target value of the actual pressing force Fs. The target pressing force Ft is transmitted from the body-side controller ECB to the wheel-side controller ECW via the communication bus BS.

[0053] In the wheel-side controller ECW, the electric motor MT is controlled based on the target pressing force Ft, ensuring that the actual pressing force Fs (the value detected by the pressing force sensor FS) matches the target pressing force Ft. Specifically, a target charge It is calculated based on a pre-set computational mapping and the target pressing force Ft, increasing with the target pressing force Ft. Furthermore, the deviation hF between the calculated target pressing force Ft and the actual pressing force Fs is used to adjust the target charge It. Here, the target charge It is a target value for the charge Ia of the electric motor MT. The drive circuit DR is controlled based on the target charge It, ensuring that the actual charge Ia (the value detected by the charge sensor IA) matches the target charge It, thereby driving the electric motor MT.

[0054] When the electric motor MT is driven, the electric motor MT generates rotational power (output torque of the electric motor MT). This rotational power is transmitted to the power conversion mechanism HN via the reducer GS. Specifically, the rotational power of the electric motor MT is transmitted to the input component BI, to which the second large-diameter gear DK2 of the reducer GS is fixed. A first anti-rotation part Ma is provided on the inner circumference Mn of the input component BI. An output component BO is inserted into the inner circumference Mn of the input component BI. A second anti-rotation part Mb is formed on the outer circumference Mg of the output component BO, so as to mesh with the first anti-rotation part Ma. Therefore, the input component BI and the output component BO rotate together under the rotational power of the electric motor MT.

[0055] One end of the output component BO is inserted into the inner periphery Mh of the first moving component BH. A first threaded portion Na is formed on the outer periphery Mg of one end of the output component BO. Additionally, a second threaded portion Nb is formed on the inner periphery Mh of the first moving component BH to engage with the first threaded portion Na. Although the first moving component BH can move relative to the housing HG along the pressing axis Ja, its movement is restricted (constrained) so that it does not rotate about the pressing axis Ja. For example, the movement restriction of the first moving component BH is achieved by planar sliding (double D-shaped, etc.), spline mechanism, key mechanism, etc. Since the first moving component BH can only move along the pressing axis Ja, when the first threaded portion Na rotates, the first moving component BH moves relatively along the expansion direction Ha (the left direction in the figure, away from the input component BI) (refer to state (b)).

[0056] The other end of the output component BO is inserted into the recess of the second linear component BJ. The end face Mo of the other end of the output component BO abuts against the bottom surface Mc of the recess of the second linear component BJ. Since the second linear component BJ can only move in the direction of the pressing axis Ja, when the first threaded part Na rotates, the second linear component BJ moves relatively in the expansion direction Ha (to the right in the figure, away from the input component BI) (refer to state (b)).

[0057] As explained above, when the braking operation amount Ba increases and the electric motor MT is driven in the forward direction, the first pressing part Pa and the second pressing part Pb move in the expansion direction Ha due to the rotational power of the electric motor MT, so as to move away from each other. As a result, the driving shoe BSa and the driven shoe BSb are pressed with the pressing force Fs, and the brake pad MS is pressed against the friction surface Md. At this time, since the friction surface Md of the brake drum BD rotates in the direction Da corresponding to the straight-line direction of the vehicle, friction is generated between the brake pad MS and the friction surface Md, resulting in the generation of braking force Fx.

[0058] When the braking operation amount Ba decreases, the electric motor MT is driven in the reverse direction. As a result, the first direct-acting member BH (i.e., the first pressing part Pa) and the second direct-acting member BJ (i.e., the second pressing part Pb) move in a direction of approach (i.e., the contraction direction Hb). Consequently, the pressing force Fs decreases, the friction between the brake pad MS and the friction surface Md decreases, and the braking force Fx decreases. Furthermore, a force opposing the pressing force Fs acts between the guide shoe BSa and the driven shoe BSb via the reset member (reset spring) RS. Therefore, when the braking operation amount Ba decreases, the engagement state of the first and second pressing parts Pa and Pb with the brake shoes BSa and BSb (especially parts Qa and Qb) is maintained, and the aforementioned frictional force decreases.

[0059] [The operation of the parking brake]

[0060] With the vehicle stationary (i.e., the brake drum BD not rotating), the driver operates the parking brake switch SW, switching the parking signal Sw from off to on. Power is then supplied to the electric motor MT, which is driven to rotate in the forward direction. The rotational power is transmitted via the reducer GS to the power conversion mechanism HN, pressing the brake pads MS against the friction surface Md. When the pressing pressure Fs reaches the specified pressing pressure fp, the power supply to the electric motor MT is maintained, keeping the pressing pressure Fs constant. Here, the specified pressing pressure fp is a pre-set constant, a control threshold. When the pressing pressure Fs has been maintained for a specified time tp, the solenoid SL is energized, causing the pawl component TS to engage with the ratchet gear RC. The ratchet gear RC has teeth that restrict the working direction to one side. Therefore, when the pawl component TS and the ratchet gear RC are temporarily engaged, the state of "Fs = fp" is maintained even when the power supply to the electric motor MT stops. That is, the parking brake function is performed by the electric actuator DN.

[0061] When the parking signal Sw switches from on to off, the parking brake control is released. During this release, the electric motor MT is driven to rotate forward. This causes the pawl component TS to pass over the tooth tip of the ratchet gear RC, disengaging the pawl component TS from the ratchet gear RC. The parking brake then transitions from an active to an inactive state.

[0062] [Regarding the miniaturization effect of the power conversion mechanism HN]

[0063] In the power conversion mechanism HN that uses a threaded mechanism NJ to convert the rotational motion of an electric motor MT into linear motion, two mechanisms are required: the threaded mechanism NJ and the anti-rotation mechanism MD. As described in Patent Document 1, in a structure where the threaded mechanism NJ and the anti-rotation mechanism MD are formed separately, and the threaded mechanism NJ is provided on the inner circumference of the anti-rotation mechanism MD, the dimension in the direction perpendicular to the axis of rotation (central axis) (i.e., radial) increases. Conversely, in a structure where the threaded mechanism NJ and the anti-rotation mechanism MD are formed separately and arranged on the axis of rotation, the dimension in the direction of the axis of rotation (i.e., axial) increases.

[0064] In the electric actuator DN of this invention, the threaded mechanism NJ (Na+Nb) and the anti-rotation mechanism MD (Ma+Mb) are not separately provided, but these mechanisms are integrally provided on the outer periphery Mg of the output component BO. Therefore, in the power conversion mechanism HN of the electric actuator DN, the radial and axial dimensions are shortened, resulting in the overall miniaturization of the device.

[0065] <The First Example of a Power Conversion Mechanism HN>

[0066] In the electric actuator DN according to the present invention, a first threaded portion Na (part of the threaded mechanism NJ) and a first anti-rotation portion Ma (part of the anti-rotation mechanism MD) are provided on the outer periphery Mg of the output component BO. Because the output component BO has the functions of both the threaded mechanism NJ and the anti-rotation mechanism MD, the electric actuator DN (especially the power conversion mechanism HN) can be miniaturized in both the radial and axial directions. However, in order to achieve both functions, the threaded mechanism NJ and the anti-rotation mechanism MD need to consider both strength and functionality. This will be explained below.

[0067] Reference Figure 3 The partial sectional view illustrates the first example of the power conversion mechanism HN of the electric actuator DN. In this first example, a trapezoidal thread (external thread Oj, internal thread Mj) is used as the thread mechanism NJ, and a spline mechanism (first and second spline sections Sa and Sb) is used as the anti-rotation mechanism MD.

[0068] In the input component BI, which has a second large-diameter gear DK2 on its outer periphery, a first spline portion Sa is formed on its inner periphery Mn as a first anti-rotation portion Ma. Spline internal teeth are machined on the inner periphery Mn of the input component BI to form the first spline portion Sa (i.e., the first anti-rotation portion Ma). In other words, the inner periphery Mn of the input component BI is a spline hole. A second spline portion Sb, capable of meshing with the first spline portion Sa, is provided on the outer periphery Mg of one end of the output component BO as a second anti-rotation portion Mb. In other words, spline external teeth are machined on the outer periphery Mg of one end of the output component BO to form the second spline portion Sb (i.e., the second anti-rotation portion Mb). In other words, one end of the output component BO is a spline shaft. The first and second spline portions Sa and Sb constitute an anti-rotation mechanism MD, restricting the movement of the output component BO. Specifically, the output component BO can rotate relative to the housing HG about the pressing axis Ja and can move linearly along the direction of the pressing axis Ja.

[0069] An external thread Oj is formed on the outer periphery Mg of one end of the output component BO as a first threaded portion Na. The external thread Oj of the output component BO meshes with the internal thread Mj formed on the inner periphery Mh of the first direct-acting component BH. The internal thread Mj of the first direct-acting component BH is formed as a second threaded portion Nb. The external thread Oj and the internal thread Mj constitute a thread mechanism NJ utilizing a trapezoidal thread. The rotational power of the electric motor MT is transmitted to the brake shoes BSq and BSb through the trapezoidal thread mechanism NJ. Specifically, the pressing force Fs (so-called slip-based power transmission) is transmitted by pressing the tooth flank Fa of the external thread Oj against the tooth flank Fb of the internal thread Mj in the expansion direction Ha.

[0070] In a spline mechanism, a spline shaft with multiple (numerous) external teeth on its outer periphery (equivalent to output component BO) meshes with a spline hole with internal teeth (equivalent to input component BI). Because power is transmitted through multiple teeth in a spline mechanism, its tooth height can be set relatively small. In a power conversion mechanism HN, the tooth height of the trapezoidal thread (external thread Oj, internal thread Mj) and the tooth height of the spline mechanism (external teeth, internal teeth) are essentially arbitrary, but it is preferable that the tooth height of the spline (in the internal teeth, the step difference between the peak Tsa and the valley Bsa) is set smaller than the tooth height of the trapezoidal thread (in the external thread Oj, the step difference between the peak and the valley). Furthermore, when the power conversion mechanism HN is assembled, the peak Tsa of the spline internal teeth can also be set to be located outside the pitch circle Pj of the external thread Oj relative to the pressing axis Ja.

[0071] <Second example of power conversion mechanism HN>

[0072] Reference Figure 4 The partial sectional view illustrates a second example of the power conversion mechanism HN for the electric actuator DN. In this second example, a ball screw (Zo+Zh+BL) is used as the thread mechanism NJ, and a key mechanism (Za+Zb+KY) is used as the anti-rotation mechanism MD. Furthermore, similar to the case of the trapezoidal thread, a ball screw with reverse efficiency is also used as the thread mechanism NJ.

[0073] A first keyway Za is formed in the inner periphery Mn (center hole) of the input component BI as a first anti-rotation part Ma. A second keyway Zb is formed in the outer periphery Mg of the output component BO as a second anti-rotation part Mb. Key components KY are embedded in the first and second keyways Za and Zb to form an anti-rotation mechanism MD. Similar to the first example, the output component BO can rotate relative to the housing HG about the pressing axis Ja and can move linearly along the pressing axis Ja.

[0074] A ball screw groove (external thread groove) Zo is formed on the outer periphery of the cylinder at one end of the output component BO, serving as the first threaded portion Na. A ball screw groove (internal thread groove) Zh is formed on the inner periphery of the cylinder of the first direct-acting component BH, serving as the second threaded portion Nb. Multiple balls BL are embedded in the ball screw grooves Zo and Zh. The external thread groove Zo, the internal thread groove Zh, and the balls BL constitute a threaded mechanism NJ utilizing a ball screw. In the ball screw mechanism NJ, the rotational power of the electric motor MT is transmitted to the brake shoes BSq and BSb via the balls BL (so-called rolling-based power transmission).

[0075] In the ball screw mechanism NJ, power is transmitted by the movement (circulation) of the balls BL within the ball screw grooves Zo and Zh. Therefore, it is necessary for the balls BL to roll smoothly within these grooves. Consequently, it is preferable that the depth of the keyways (first and second keyways) is shallower than the depth of the ball screw grooves. In this case, the radial dimension of the key component KY relative to the rotation axis Ja (the dimension of the key component KY in the vertical direction relative to the pressing axis Ja when it is assembled in the keyway) is smaller than the diameter of the balls BL. By setting the dimensional relationship between the key component KY and the keyway in this way, smooth rolling is possible even when the balls BL pass through the keyways Za and Zb.

[0076] <Function and Effect of Electric Actuator DN>

[0077] The electric actuator DN is configured to include "an input component BI, which is driven to rotate by an electric motor MT and has a first anti-rotation part Ma in its inner circumference Mn"; "an output component BO, which has a second anti-rotation part Mb that can engage with the first anti-rotation part Ma and a first threaded part Na in its outer circumference Mg"; and "a direct-acting component BH, which has a second threaded part Nb that can engage with the first threaded part Na".

[0078] Instead of separately setting the threaded mechanism NJ (Na+Nb) and the anti-rotation mechanism MD (Ma+Mb), the outer periphery Mg of the output component BO serves as both the threaded mechanism NJ and the anti-rotation mechanism MD. Therefore, in the power conversion mechanism HN of the electric actuator DN, the radial and axial dimensions are shortened, allowing for overall device miniaturization.

[0079] In the electric actuator DN, the external thread Oj (in a trapezoidal thread) is used as the first thread section Na, and the internal thread Mj (in a trapezoidal thread) is used as the second thread section Nb. That is, a trapezoidal thread is used as the thread mechanism NJ. This is based on the simple construction and large power transmission capacity of the trapezoidal thread. By using a trapezoidal thread, the device can be miniaturized, and costs can be reduced.

[0080] In the electric actuator DN, spline mechanisms Sa and Sb are used in the first and second anti-rotation sections Ma and Mb. Because power is transmitted through multiple spline teeth in the spline mechanisms Sa and Sb (first and second spline sections), the power transmission capacity is relatively large. Using spline mechanisms Sa and Sb allows for miniaturization of the device.

[0081] The electric actuator DN is used in an electric braking device DS to convert the rotational power of an electric motor MT into linear power, which then presses the brake pads MS, located on the brake shoes BSa and BSb, against the brake drum BD to generate braking force Fx (or Fp) at the wheel. The space around the vehicle wheels is small and very limited. By employing a miniaturized electric actuator DN, the device DS can be fitted into confined spaces more efficiently.

[0082] <Other Implementation Methods>

[0083] As described above, in the electric actuator DN, the first example shows a structure of "trapezoidal thread + spline mechanism," and the second example shows a combination structure of "ball screw + key mechanism." Alternatively, a combination of "trapezoidal thread as thread mechanism NJ" and "key mechanism as anti-rotation mechanism MD" can be used instead. This combination achieves the same effect as described above (miniaturization of the device).

Claims

1. An electric braking device for a vehicle, which converts the rotational power of an electric motor into linear power, and uses this linear power to press brake pads mounted on brake shoes against a brake drum to generate braking force at the wheels, wherein... The power conversion mechanism that converts the aforementioned rotational power into the aforementioned linear power consists of the following components: The input component has a first anti-rotation part on its inner periphery; The output component has a first threaded portion on its outer periphery and a second anti-rotation portion capable of engaging with the first anti-rotation portion. as well as The direct-acting component has a second threaded portion capable of engaging with the first threaded portion described above. The second anti-rotation portion and at least a portion of the first threaded portion are formed to overlap each other in the axial direction of the output component. In the overlapping portion where the second anti-rotation portion and the first threaded portion overlap, the groove depth of the second groove of the second anti-rotation portion is shallower than the groove depth of the first groove of the first threaded portion.

2. The electric braking device for a vehicle according to claim 1, wherein, The first threaded portion mentioned above is an external thread, and the second threaded portion mentioned above is an internal thread.

3. The electric braking device for a vehicle according to claim 1 or 2, wherein, The first anti-rotation part and the second anti-rotation part mentioned above are spline mechanisms.

4. The electric braking device for a vehicle according to claim 3, wherein, The first threaded portion mentioned above is an external thread. In the axial direction of the aforementioned output component, the tooth tip of the internal tooth of the aforementioned spline mechanism is located radially outside the pitch circle of the aforementioned external thread.

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