Patent Description:
An electric parking brake device that switches between a state in which a parking brake force is obtained by pulling a brake cable and a state in which a parking brake force is released by loosening the brake cable by a change in the rotational direction of an electric motor is known in PTL <NUM>.

<CIT> discloses an electric parking brake including a screw shaft axially movable by the rotation of a nut, a movement restricting portion located outside the actuator case to restrict the axial movement of the screw shaft, and a resilient member compressed by the nut when the screw shaft abuts the movement restricting portion.

<CIT>, <CIT> and <CIT> each disclose an electric parking brake including a screw gear for tightening and loosening a brake cable.

<CIT> discloses an electric parking brake in accordance with the pre-characterizing portion of claim <NUM>.

By the way, when a parking brake is released in an electric parking brake device, the load on an electric motor becomes small, no-load current flows, and over returning occurs in a plurality of members that constitute a motion conversion mechanism between the electric motor and a screw shaft, possibly falling into a locked state. Accordingly, the electric parking brake device disclosed in PTL <NUM> above prevents over returning by monitoring the current passing through the electric motor while applying a load by a resilient member to the screw shaft and a nut to preferably interrupt the power supplied to the electric motor when a parking brake is released. On the other hand, since the position in the axial direction of the nut is fixed, an operating sound is easily generated when the parking brake is released. In addition, since the resilient member is interposed in a part of the screw shaft, that is, in a portion between the nut and the actuator case accommodating the motion conversion mechanism and the resilient member, the strength of the actuator case needs to be improved.

The invention addresses the above situation with an object of providing an electric parking brake device capable of applying a load to an electric motor when a parking brake state is released without generating an operating sound when a parking brake state is released and making the strength of the actuator case unnecessarily large.

To achieve the above object, according to a first aspect of the invention, there is provided an electric parking brake device including a screw shaft; a brake cable; an actuator case that supports the screw shaft movably in an axial direction thereof; an electric motor that is supported by the actuator case rotatably forward and backward; a motion conversion mechanism that has a nut to be screwed onto the screw shaft rotatably in response to an operation of the electric motor, enables conversion from a rotational motion generated by the electric motor to a linear motion of the screw shaft, and is accommodated in the actuator case; and a resilient member that is compressed when the screw shaft is moved to a side loosening the brake cable, in which switching between a parking brake state reached by pulling the brake cable and a parking brake release state reached by loosening the brake cable is performed by a change in a rotational direction of the electric motor, in which the nut is screwed onto the screw shaft movably in the axial direction within a restricted range, and a movement restricting portion, the movement restricting portion restricts an end of axial movement, toward the side loosening the brake cable, of the screw shaft or of a linked member that moves axially together with the screw shaft by causing the screw shaft or the linked member to abut against the movement restricting portion, wherein the screw shaft is connected to the brake cable so as to be prevented from rotating; and the movement restricting portion is provided in a fixed position in the actuator case; characterized in that the resilient member is interposed between the nut and an insertion member accommodated and fixed in the actuator case so as to be compressed in response to axial movement of the nut after the movement end of the screw shaft or linked member is restricted by the movement restricting portion when the screw shaft moves axially to the side loosening the brake cable; wherein the movement restricting portion is provided integrally with the insertion member so that the resilient member is interposed between the movement restricting portion and the nut.

In a second aspect of the invention, the resilient member is a disc spring in addition to the structure of the first or second aspect.

According to the first aspect of the invention, if the nut is rotated so as to move the screw shaft to the side loosening the brake cable by the electric motor when the brake cable is loosened to release the parking brake state, since the nut is moved in the axial direction within a restricted range in response to the operation of the electric motor in the state after movement in the axial direction of the screw shaft is restricted by the movement restricting portion, the resilient member is compressed in response to the movement in the axial direction of the nut, thereby increasing the load on the electric motor. Accordingly, the electric motor can be controlled appropriately and the members constituting the motion conversion mechanism can be prevented from falling into a lock state. In addition, since the nut is relatively movable with respect to the screw shaft, an operating sound can be prevented from being generated when the parking brake is released and the strength of the actuator case does not need to be improved unnecessarily because the resilient member is provided between the nut and the insertion member accommodated and fixed in the actuator case.

In addition, according to the first aspect of the invention, since the resilient member is interposed between the nut and the movement restricting portion provided integrally with insertion member, the internal structure of the actuator case can be simplified while suppressing an increase in the number of components.

In addition, according to the second aspect of the invention, since the resilient member is a disc spring, the space that needs to be reserved in the actuator case to dispose the resilient member can be reduced and the actuator case can be small-sized.

An embodiment of the invention will be described with reference to attached <FIG>.

In <FIG>, a drum brake device <NUM> is provided in, for example, the left-rear wheel of a four-wheel vehicle and this drum brake device <NUM> includes a fixed back plate <NUM> having, at the center thereof, a through-hole <NUM> that passes through a wheel shaft <NUM> of the left rear wheel, first and second brake shoes <NUM> and <NUM> disposed in the back plate <NUM> so as to enable sliding contact with the inner periphery of a brake drum <NUM> that rotates together with the left rear wheel, a wheel cylinder <NUM> fixed to an upper portion of the back plate <NUM> so as to generate a force for operating the first and second brake shoes <NUM> and <NUM> in an expanded manner, a braking clearance automatic adjustment means (so-called automatic adjuster) <NUM> that automatically adjusts the clearance between the first and second brake shoes <NUM> and <NUM> and the brake drum <NUM>, and a return spring <NUM> provided between the first and second brake shoes <NUM> and <NUM>.

The first and second brake shoes <NUM> and <NUM> include webs 15a and 16a formed in bows along the inner periphery of the brake drum <NUM>, rims 15b and 16b provided in a linked manner orthogonally to the outer peripheries of the webs 15a and 16a, and linings 15c and 16c pasted to the outer peripheries of the rims 15b and 16b.

The outer end portions of a pair of pistons <NUM> of the wheel cylinder <NUM> are disposed so as to face the webs 15a and 16a in the upper end portions of the first and second brake shoes <NUM> and <NUM>. In addition, an anchor block <NUM> that functions as the fulcrum when the first and second brake shoes <NUM> and <NUM> are expanded or contracted is provided in a fixed manner in the lower portion of the back plate <NUM> so as to support one end portions (lower end portions in this embodiment) of the first and second brake shoes <NUM> and <NUM>, and the wheel cylinder <NUM> is operated by the output hydraulic pressure of the master cylinder (not illustrated) operated by the brake pedal and generates a force for driving the first and second brake shoes <NUM> and <NUM> in an expanded manner using the anchor block <NUM> as the fulcrum.

A coil spring <NUM> for biasing the lower end portions of the webs 15a and 16a of the first and second brake shoes <NUM> and <NUM> toward the anchor block <NUM> is provided between the lower end portions of the webs 15a and 16a and the return spring <NUM> for biasing the first and second brake shoes <NUM> and <NUM> in a contraction direction is provided between the upper end portions of the webs 15a and 16a of the first and second brake shoes <NUM> and <NUM>.

The braking clearance automatic adjustment means <NUM> includes a contraction position restricting strut <NUM> that is provided between the webs 15a and 16a of the first and second brake shoes <NUM> and <NUM> and stretchable by rotation of an adjustment gear <NUM>, an adjustment lever <NUM> that has a feeding claw 25a to be engaged with the adjustment gear <NUM> and is pivotably supported by the web 16a of the second brake shoe <NUM>, which is one of the first and second brake shoes <NUM> and <NUM>, and an adjustment spring <NUM> that pivotally biases the adjustment lever <NUM> so as to rotate the adjustment gear <NUM> in the direction in which the contraction position restricting strut <NUM> is stretched.

The contraction position restricting strut <NUM> restricts the contraction positions of the first and second brake shoes <NUM> and <NUM> and includes a first rod <NUM> that has a first engagement portion 27a to be engaged with an upper portion of the web 15a of the first brake shoe <NUM> of the first and second brake shoes <NUM> and <NUM>, a second rod <NUM> that has a second engagement portion 28a to be engaged with an upper portion of the web 16a of the second brake shoe <NUM> and is disposed concentrically with the first rod <NUM>, and an adjustment bolt <NUM> with one end portion inserted into the first rod <NUM> relatively movably in the axial direction and the other end portion to be screwed concentrically with the second rod <NUM>, in which the adjustment gear <NUM> is disposed between the first and second rods <NUM> and <NUM> and formed in the outer periphery of the adjustment bolt <NUM>.

A first retaining recess <NUM> with which the first engagement portion 27a is engaged is provided in the upper portion of the web 15a of the first brake shoe <NUM> and a second retaining recess <NUM> with which the second engagement portion 28a is engaged is provided in the upper portion of the web 16a of the second brake shoe <NUM>.

The adjustment lever <NUM> having the feeding claw 25a to be engaged with the adjustment gear <NUM> is pivotably supported by the web 16a of the second brake shoe <NUM> via a support shaft <NUM> and the adjustment spring <NUM> is provided between the web 16a of the second brake shoe <NUM> and the adjustment lever <NUM>. Furthermore, the spring force of the adjustment spring <NUM> is set smaller than the spring force of the return spring <NUM>.

In the braking clearance automatic adjustment means <NUM> described above, if the first and second brake shoes <NUM> and <NUM> are expanded beyond a certain value due to wear of the linings 15c and 16c when the first and second brake shoes <NUM> and <NUM> are operated in an expanded manner by the operation of the wheel cylinder <NUM>, the adjustment lever <NUM> is pivoted about the axial line of the support shaft <NUM> by the spring force of the adjustment spring <NUM> and the adjustment gear <NUM> is thereby rotated, and the effective length of the contraction position restricting strut <NUM> is corrected to a larger value.

By the way, the drum brake device <NUM> is provided with a parking brake lever <NUM> having one end pivotably supported by the web 15a of the first brake shoe <NUM> of the first and second brake shoes <NUM> and <NUM> and engaged with one end portion of the contraction position restricting strut <NUM>.

The parking brake lever <NUM> extends upward and downward so as to partially overlap with the web 15a of the first brake shoe <NUM> in front view and the upper end portion of this parking brake lever <NUM> is connected to the upper portion of the web 15a of the first brake shoe <NUM> via a pin <NUM>, and the first engagement portion 27a of the contraction position restricting strut <NUM> is engaged with the upper end portion of this parking brake lever <NUM>.

When the parking brake of the vehicle is operated, the parking brake lever <NUM> is driven pivotally counterclockwise about the pin <NUM> as the fulcrum and this pivot of the parking brake lever <NUM> causes a force for pressing the lining 16c of the brake shoe <NUM> against the inner periphery of the brake drum <NUM> to act on the second brake shoe <NUM> via the contraction position restricting strut <NUM>. In addition, when the parking brake lever <NUM> is continuously driven pivotally counterclockwise in <FIG>, the parking brake lever <NUM> is pivoted about the engagement point with respect to the first engagement portion 27a of the contraction position restricting strut <NUM> as the fulcrum, the first brake shoe <NUM> is operated in an expanded manner via the pin <NUM> and the lining 15c of the first brake shoe <NUM> is pressed against the inner periphery of the brake drum <NUM>. That is, the parking brake lever <NUM> is operated at an operation position at which the linings 15c and 16c of the first and second brake shoes <NUM> and <NUM> are pressed against the inner periphery of the brake drum <NUM> and the parking brake state is obtained in this state.

When application of a rotational driving force to the parking brake lever <NUM> is stopped, the parking brake lever <NUM> is returned to a non-operation position together with the first and second brake shoes <NUM> and <NUM> operated in a direction away from the inner periphery of the brake drum <NUM> by the spring force of the return spring <NUM> and the parking brake lever <NUM> is biased toward the non-operation position.

The parking brake lever <NUM> is pivotally driven by the power generated by an electric actuator <NUM>, the brake cable <NUM> pulled or loosened by the electric actuator <NUM> enables the parking brake state to be obtained by pivotally driving the parking brake lever <NUM> so as to press the contraction position restricting strut <NUM> against the web 15a of the second brake shoe <NUM> by pulling the brake cable <NUM> and enables the parking brake state to be released by loosening the brake cable <NUM>, and the brake cable <NUM> is connected to a lower portion of the parking brake lever <NUM>.

Referring to <FIG> and <FIG> together, the electric actuator <NUM> includes a screw shaft <NUM> that is connected to the brake cable <NUM>, an actuator case <NUM> that supports the screw shaft <NUM> movably in an axial direction thereof, an electric motor <NUM> that is supported by the actuator case <NUM> rotatably forward and backward, and a motion conversion mechanism <NUM> that enables conversion from a rotational motion generated by the electric motor <NUM> to a linear motion of the screw shaft <NUM> and is accommodated in the actuator case <NUM> while being interposed between the electric motor <NUM> and the screw shaft <NUM>, in which switching between the parking brake state reached by pulling the brake cable <NUM> and the parking brake release state reached by loosening the brake cable <NUM> is performed by a change in the rotational direction of the electric motor <NUM>.

A bottomed joint hole <NUM> is concentrically provided in the end portion of the screw shaft <NUM> close to the brake cable <NUM> and the end portion of the brake cable <NUM> close to the electric actuator <NUM> is inserted into the joint hole <NUM>. Furthermore, an annular groove <NUM> is formed in the outer periphery of the screw shaft <NUM> close to the opening end of the joint hole <NUM> and the screw shaft <NUM> is connected to the brake cable <NUM> by swaging the annular groove <NUM> so that a part of the screw shaft <NUM> digs into the brake cable <NUM> in the state in which the brake cable <NUM> is inserted into the joint hole <NUM>.

The brake cable <NUM> is drawn into the back plate <NUM> from the electric actuator <NUM> mounted to the back plate <NUM> and an engagement piece <NUM> fixed to the other end portion of this brake cable <NUM> is engaged with the lower end portion of the parking brake lever <NUM>.

The electric actuator <NUM> switches between the state in which the screw shaft <NUM> is moved so as to pull the brake cable <NUM> to drive the parking brake lever <NUM> toward the operation position as illustrated in <FIG> and the state in which the screw shaft <NUM> is moved so as to loosen the brake cable <NUM> to return the parking brake lever <NUM> from the operation position toward the non-operation position as illustrated in <FIG> and <FIG> by a change in the rotational direction of the electric motor <NUM>.

In the lower portion of the back plate <NUM>, a cable guide <NUM> that sandwiches the anchor block <NUM> between the cable guide <NUM> and the back plate <NUM> is mounted in the lower portion of the back plate <NUM> together with the anchor block <NUM> via a pair of rivets <NUM>. As clearly illustrated in <FIG>, this cable guide <NUM> is provided integrally with a guide portion 51a for guiding the brake cable <NUM> so as to have a substantially U-shaped cross section.

Referring to <FIG> together, the actuator case <NUM> includes a case main body <NUM> integrally having first and second accommodating cylindrical portions <NUM> and <NUM>, a first cover member <NUM> coupled to the opening end of the first accommodating cylindrical portion <NUM>, and a second cover member <NUM> coupled to the case main body <NUM> from the opposite side of the first cover member <NUM>.

The first accommodating cylindrical portion <NUM> is formed in a bottomed cylinder so as to have a support wall portion 45a on one end side thereof and a fitting hole <NUM> is concentrically formed at the center of the support wall portion 45a. The second accommodating cylindrical portion <NUM> is disposed to the side of the first accommodating cylindrical portion <NUM> and formed in a bottomed cylinder in which one end portion is open and the other end portion is closed by an end wall portion 46a disposed in an intermediate part in the longitudinal direction of the first accommodating cylindrical portion <NUM>, and a cylindrical support cylindrical portion 46b passing through the screw shaft <NUM> is provided integrally in a projecting manner at the center of the end wall portion 46a.

A cylindrical first bearing portion 53a that rotatably supports a motor shaft <NUM> is provided in a projecting manner in one end portion in the axial direction of a motor case <NUM> of the electric motor <NUM>, the one end portion of the motor shaft <NUM> passes through the first bearing portion 53a and projects from one end portion of the motor case <NUM>, and a bottomed-cylindrical second bearing portion 53b that rotatably supports the other end portion of the motor shaft <NUM> is provided in a projecting manner in the other end portion in the axial direction of the motor case <NUM>.

This electric motor <NUM> is accommodated in the first accommodating cylindrical portion <NUM> so that the one end portion of the motor case <NUM> abuts against the support wall portion 45a while the first bearing portion 53a is fitted to the fitting hole <NUM> of the case main body <NUM>, and the electric motor <NUM> is accommodated in the first accommodating cylindrical portion <NUM> while a part (the other end portion of the motor case <NUM> in which the second bearing portion 53b is provided in the embodiment) of the electric motor <NUM> faces the outside.

The first cover member <NUM> integrally has a lid portion 48a that covers the part of the electric motor <NUM> accommodated in the first accommodating cylindrical portion <NUM> that faces the outside from the first accommodating cylindrical portion <NUM> and is coupled to the opening end of the first accommodating cylindrical portion <NUM> and a connector portion 48b that overhands toward the side from the lid portion 48a so that a terminal <NUM> (see <FIG>) continuous to the electric motor <NUM> is provided and is disposed to the side of the first accommodating cylindrical portion <NUM>, and a wave washer <NUM> is interposed between the second bearing portion 53b and the lid portion 48a of the electric motor <NUM>.

The lid portion 48a is formed in a dish shape opened toward the first accommodating cylindrical portion <NUM> and an annular recess <NUM> concentric with the first accommodating cylindrical portion <NUM> having a circular cross section is formed at the open end of this lid portion 48a. In contrast, an annular fitting projection portion <NUM> to be fitted to the annular recess <NUM> is provided in a projecting manner in the opening end portion of the first accommodating cylindrical portion <NUM>. The lid portion 48a and the first accommodating cylindrical portion <NUM> are bonded to each other in the state in which the fitting projection portion <NUM> is fitted to the annular recess <NUM>. This enables the relative position in the circumferential direction of the connector portion 48b with respect to the first accommodating cylindrical portion <NUM> to be selected at a plurality of positions about the axial line of the first accommodating cylindrical portion <NUM>, increases the freedom of the position of the connector portion 48b with respect to the actuator case <NUM>, and facilitates changes in the orientation of the connector portion 48b.

The second cover member <NUM> is coupled to the case main body <NUM> via bonding or welding so as to form a gear chamber <NUM> between the second cover member <NUM> and the case main body <NUM>. In addition, the motion conversion mechanism <NUM> has a nut <NUM> to be screwed onto the screw shaft <NUM> as one component and is accommodated in the gear chamber <NUM>.

The motion conversion mechanism <NUM> includes a driving gear <NUM> provided in the motor shaft <NUM> of the electric motor <NUM>, an intermediate large-diameter gear <NUM> to be meshed with the driving gear <NUM>, an intermediate small-diameter gear <NUM> that rotates together with the intermediate large-diameter gear <NUM>, a driven gear <NUM> that is meshed with this intermediate small-diameter gear <NUM>, and the nut <NUM> to be connected to this driven gear <NUM> that enables the relative movement in the axial direction of the driven gear <NUM> and disables the relative rotation about the axial line, and the nut <NUM> is screwed onto the screw shaft <NUM>. In addition, the intermediate large-diameter gear <NUM> and the intermediate small-diameter gear <NUM> are formed integrally with each other and are rotatably supported by a support shaft <NUM> arranged in parallel with the motor shaft <NUM> and the screw shaft <NUM>.

Referring to <FIG> together, the nut <NUM> is formed to include a large-diameter cylindrical portion 61a rotatably accommodated in the second accommodating cylindrical portion <NUM>, an inward collar portion 61b that overhangs radially inward from the end portion of the large-diameter cylindrical portion 61a on the opposite side of the second cover member <NUM>, and a small-diameter cylindrical portion 61c that is continuous to the inner peripheral edge of this inward collar portion 61b, extends toward the opposite side of the second cover member <NUM>, and passes through the screw shaft <NUM>.

Female threads <NUM> to be screwed onto the screw shaft <NUM> are engraved in the inner periphery of the small-diameter cylindrical portion 61c. In addition, a ball bearing <NUM> is interposed between the small-diameter cylindrical portion 61c and the end portion of the second accommodating cylindrical portion <NUM> close to the end wall portion 46a. An outer race 68a of this ball bearing <NUM> is press-fitted to the second accommodating cylindrical portion <NUM> and the small-diameter cylindrical portion 61c of the nut <NUM> is inserted into an inner race 68b of the ball bearing <NUM> movably in the axial direction.

Referring to <FIG> together, an annular projection portion <NUM> projecting radially outward is provided integrally in a projecting manner in the intermediate portion in the longitudinal direction of the outer periphery of the large-diameter cylindrical portion 61a, and slits <NUM> extending in the axial direction are formed so as to cut the annular projection portion <NUM> at a plurality of positions (for example, four positions) spaced in the circumferential direction of this annular projection portion <NUM>. On the other hand, guide projection portions <NUM> extending long in the axial direction are provided integrally in a projecting manner so as to project radially inward at a plurality of positions corresponding to the slits <NUM> in the inner periphery of the driven gear <NUM> and the guide projection portions <NUM> are slidably fitted to the slits <NUM>. That is, the driven gear <NUM> is fitted onto the outer periphery of the large-diameter cylindrical portion 61a of the nut <NUM> while enabling relative movement in the axial direction and disabling relative rotation about the axial line.

Referring to <FIG> together, the second cover member <NUM> of the actuator case <NUM> is formed by integrally providing, in a linked manner, a cover plate portion 49a coupled to the case main body <NUM> so as to cover the gear chamber <NUM> and a bottomed cylindrical portion 49b projecting from the cover plate portion 49a so as to surround the screw shaft <NUM> and a guide cylindrical portion 74a integrally owned by an insertion member <NUM> accommodated and fixed in the actuator case <NUM> is fitted to the cylindrical portion 49b.

The guide cylindrical portion 74a is formed to include a cylindrical part 74aa and a plurality of overhang parts 74ab overhanging radially from the cylindrical part 74aa and the pair of overhang parts 74ab is disposed in one diameter line of the cylindrical part 74aa in the embodiment. In addition, the overhang part 74ab forms rotation restricting grooves <NUM> extending along the axial line of the cylindrical part 74aa. The cylindrical portion 49b of this second cover member <NUM> is formed to have an inner surface shape corresponding to the outer surface shape of the guide cylindrical portion 74a.

The insertion member <NUM> is integrally provided with an extended cylindrical portion 74b that is continuous to the guide cylindrical portion 74a and enters the gear chamber <NUM>, a plurality of (for example, two) mount arm portions 74c that overhang outward to the side from the end portion of the guide cylindrical portion 74a close to the gear chamber <NUM> along the inner surface of the cover plate portion 49a of the second cover member <NUM>, and one support arm portion 74d that overhands outward to the side from the end portion of the guide cylindrical portion 74a close to the gear chamber <NUM> along the inner surface of the cover plate portion 49a.

In addition, a positioning projection portion 74e projecting toward the second accommodating cylindrical portion <NUM> is provided integrally in a projecting manner in a front end portion of the mount arm portion 74c and the insertion member <NUM> is accommodated and fixed in the actuator case <NUM> by sandwiching the front end portion of the mount arm portion 74c and the positioning projection portion 74e between the second accommodating cylindrical portion <NUM> and the cover plate portion 49a of the second cover member <NUM>.

In addition, both end portions of the support shaft <NUM> for rotatably supporting the intermediate large-diameter gear <NUM> and the intermediate small-diameter gear <NUM> are supported between the front end portion of the support arm portion 74d and the support wall portion 45a of the first accommodating cylindrical portion <NUM>.

Focusing on <FIG>, a rotation restricting means <NUM> for restricting the rotation of the screw shaft <NUM> is provided between the guide cylindrical portion 74a of the insertion member <NUM> and the screw shaft <NUM> and this rotation restricting means <NUM> includes a plurality of (two in the embodiment) rotation restricting projection portions 76b that are provided in the end portion of the screw shaft <NUM> on the opposite side of the brake cable <NUM> and radially project from the screw shaft <NUM> and the plurality of (two in the embodiment) rotation restricting grooves <NUM> that are formed in the guide cylindrical portion 74a so as to be entered by the rotation restricting projection portions 76b.

A cap <NUM> is put on the end portion of the screw shaft <NUM> on the opposite side of the brake cable <NUM>. This cap <NUM> is formed by integrally providing a bottomed cylindrical portion 76a to which the end portion of the screw shaft <NUM> is fitted and the plurality of the rotation restricting projection portions 76b radially projecting from the bottomed cylindrical portion 76a so as to be inserted into the rotation restricting grooves <NUM> of the guide cylindrical portion 74a of the insertion member <NUM> and, in the embodiment, the pair of rotation restricting projection portions 76b projects radially outward from the bottomed cylindrical portion 76a along the one diameter line of the bottomed cylindrical portion 76a. In addition, the cap <NUM> is fixed to the screw shaft <NUM> as the linked member together with the screw shaft <NUM> via a pin <NUM> that passes through the screw shaft <NUM> and the bottomed cylindrical portion 76a along the one diameter line. This provides the pair of rotation restricting projection portions 76b in the end portion of the screw shaft <NUM> on the opposite side of the brake cable <NUM>, causes the rotation restricting projection portions 76b to enter the rotation restricting grooves <NUM> of the insertion member <NUM> accommodated and fixed in the actuator case <NUM>, and makes the screw shaft <NUM> movable in a direction along the axial line while being prevented from rotating about the axial line.

By the way, when the brake cable <NUM> is pulled to drive the parking brake lever <NUM> toward the operation position, the screw shaft <NUM> moves in a direction in which the cap <NUM> separates from the nut <NUM> as illustrated in <FIG>. When the brake cable <NUM> is loosened to return the parking brake lever <NUM> from the operation position toward the non-operation position, the screw shaft <NUM> moves so that the cap <NUM> comes close to the nut <NUM> as illustrated in <FIG>. The movement end of the screw shaft <NUM> in movement in the direction loosening the brake cable <NUM> is restricted by causing the cap <NUM> to abut against a movement restricting portion 74f accommodated and fixed in the actuator case <NUM> and, in the embodiment, the movement restricting portion 74f is integrally provided at the front end of the extended cylindrical portion 74b of the insertion member <NUM>. That is, the movement restricting portion 74f is integrally provided in the front end portion of the extended cylindrical portion 74b so as to overhang radially inward from the front end portion of the extended cylindrical portion 74b.

By the way, in the state in which the cap <NUM> abuts against the movement restricting portion 74f as illustrated in <FIG> and then the electric motor <NUM> continues the operation when the screw shaft <NUM> moves in the direction loosening the brake cable <NUM>, the nut <NUM> that rotates relative to the screw shaft <NUM> that has stopped movement in the axial direction moves in the axial direction so as to increase the interval from the ball bearing <NUM> as illustrated in <FIG> and a plurality of disc springs <NUM> as resilient members compressed in response to the movement in the axial direction of the nut <NUM> is disposed between the nut <NUM> and the insertion member <NUM>.

The nut <NUM> is provided with a recess <NUM> defined by the large-diameter cylindrical portion 61a and the inward collar portion 61b of the nut <NUM> so that the recess <NUM> is opened toward the insertion member <NUM>, and the disc springs <NUM> are accommodated in the recess <NUM>.

The plurality of disc springs <NUM> and a disc-shaped retainer <NUM> that sandwiches these disc springs <NUM> between the disc-shaped retainer <NUM> and the inward collar portion 61b of the nut <NUM> are accommodated in the recess <NUM>. The nut <NUM> is provided with a holding member <NUM> for preventing the disc springs <NUM> and the retainer <NUM> from being removed from the recess <NUM> on the opening end side of the recess <NUM>, this holding member <NUM> is formed to integrally have a ring plate portion 83a that abuts against the end portion of the large-diameter cylindrical portion 61a of the nut <NUM> close to the insertion member <NUM> and a short cylindrical portion 83b that is continuous to the inner periphery of this ring plate portion 83a and press-fitted to the large-diameter cylindrical portion 61a of the nut <NUM>, the inner diameter of the short cylindrical portion 83b is set larger than the outer diameter of the movement restricting portion 74f, and the side wall of the extended cylindrical portion 74b of the insertion member <NUM> is provided with a notch portion <NUM> formed by cutting a part of the side wall of the extended cylindrical portion 74b to allow the holding member <NUM> to move.

When the brake cable <NUM> is pulled as illustrated in <FIG> to drive the parking brake lever <NUM> from the non-operation position toward the operation position, the disc springs <NUM> are prevented from being removed from the recess <NUM> because the outer peripheral portion of the retainer <NUM> makes contact with the short cylindrical portion 83b of the holding member <NUM>. In addition, when the screw shaft <NUM> moves so as to loosen the brake cable <NUM>, the cap <NUM> abuts against the movement restricting portion 74f as illustrated in <FIG>, and then the electric motor <NUM> continues the operation, the nut <NUM> that rotates relative to the screw shaft <NUM> that stops movement in the axial direction moves in the axial direction so as to increase the interval from the ball bearing <NUM> as illustrated in <FIG>, the retainer <NUM> abuts against the movement restricting portion 74f of the insertion member <NUM> in response to the movement in the axial direction of the nut <NUM>, the disc springs <NUM> are compressed between the nut <NUM> and the movement restricting portion 74f, thereby enabling an increase in the load on the electric motor <NUM>.

A mount cylindrical portion <NUM> extending backward and inward in the vehicle width direction is provided integrally in a projecting manner on the back plate <NUM> of the drum brake device <NUM>. This mount cylindrical portion <NUM> is provided with a large-diameter cylindrical portion 85a with one end that is open backward and inward in the vehicle width direction and a small-diameter cylindrical portion 85c that is concentrically continuous to the large-diameter cylindrical portion 85a with a step portion 85b provided between the small-diameter cylindrical portion 85c and the other end of the large-diameter cylindrical portion 85a. In addition, the actuator case <NUM> is mounted to the mount cylindrical portion <NUM> by inserting the second accommodating cylindrical portion <NUM> of the first cover member <NUM> in the actuator case <NUM> of the electric actuator <NUM> into the large-diameter cylindrical portion 85a and engaging a C-shaped locking ring <NUM> mounted to the outer periphery of the second accommodating cylindrical portion <NUM> with a locking groove <NUM> formed in the inner periphery of the large-diameter cylindrical portion 85a.

When the actuator case <NUM> is mounted to the mount cylindrical portion <NUM> of the back plate <NUM> as described above, the actuator case <NUM> is mounted to the rear side in the front-rear direction of the vehicle of the back plate <NUM> and the connector portion 48b is oriented to the rear side in the front-rear direction of the vehicle. In addition, a bellows boot <NUM> for covering a projection portion of the screw shaft <NUM> from the second accommodating cylindrical portion <NUM> is provided between the outer periphery of the support cylindrical portion 46b of the second accommodating cylindrical portion <NUM> and the outer periphery of one end portion of the screw shaft <NUM>.

The brake cable <NUM> is a bunch of a plurality of twisted wires <NUM> and generates a twisting force in the direction indicated by arrow <NUM> in <FIG> when pulled in the direction indicated by arrow <NUM> in <FIG> to obtain the parking brake state. A setting is made so that the direction in which the twisting force in this case acts on the screw shaft <NUM> is the same as the rotational direction of the nut <NUM> when the electric motor <NUM> operates in the direction loosening the brake cable <NUM> for switching from the parking brake state to the parking brake release state.

Next, the operation of the embodiment will be described. The nut <NUM> of the motion conversion mechanism <NUM> capable of converting a rotational motion generated by the electric motor <NUM> to a linear motion of the screw shaft <NUM> connected to the brake cable <NUM> is screwed onto the screw shaft <NUM> movably in the axial direction within a restricted range in a direction along the axial line of the screw shaft <NUM>, the movement restricting portion 74f that restricts the movement end in the axial direction of the screw shaft <NUM> in movement to the side loosening the brake cable <NUM> to reach the parking brake release state by causing the cap <NUM> as the linked member that moves in the axial direction together with the screw shaft <NUM> to abut thereagainst is provided in a fixed position in the actuator case <NUM>, and the disc springs <NUM>, which are resilient members, are interposed between the nut <NUM> and the insertion member <NUM> accommodated and fixed in the actuator case <NUM> so as to be compressed in response to movement of the nut <NUM> in the axial direction after the movement end is restricted by the movement restricting portion 74f when the screw shaft <NUM> moves in the axial direction to the side loosening the brake cable <NUM>, so the load on the electric motor <NUM> can be increased by compression of the disc springs <NUM>. Accordingly, the electric motor <NUM> can be controlled appropriately and the members constituting the motion conversion mechanism <NUM> can be prevented from shifting to a lock state. Furthermore, since the nut <NUM> is relatively movable in the axial direction with respect to the screw shaft <NUM>, generation of an operating sound in parking brake release operation can be prevented. In addition, since the disc springs <NUM> are provided between the insertion member <NUM> accommodated and fixed in the actuator case <NUM> and the nut <NUM>, the strength of the actuator case <NUM> does not need to be increased more than necessity.

In addition, since the movement restricting portion 74f is provided integrally with the insertion member <NUM> so that the disc springs <NUM> are present between the movement restricting portion 74f and the nut <NUM>, the internal structure of the actuator case <NUM> can be simplified while suppressing an increase in the number of components by providing the disc springs <NUM> between the nut <NUM> and the movement restricting portion 74f provided integrally with the insertion member <NUM>.

Furthermore, since the resilient members are the disc springs <NUM>, the space that needs to be reserved in the actuator case <NUM> to dispose the disc springs <NUM> can be reduced and the actuator case <NUM> can be small-sized.

In addition, since the brake cable <NUM> is formed by twisting the plurality of wires <NUM> so as to generate a twisting force when pulled and the direction in which the twisting force acts on the screw shaft <NUM> is the same as the rotational direction of the nut <NUM> when the brake cable <NUM> is loosened, even if the nut <NUM> is rotated so as to obtain the parking brake state, the screw shaft <NUM> is rotated and reaches a rotary position A indicated by the dotted line in <FIG> due to the rotation of the nut <NUM>, and the rotation restricting projection portions 76b abut against the side surface of the rotation restricting grooves <NUM>, the twisting force generated in the brake cable <NUM> acts on the screw shaft <NUM> in the direction in which the rotation restricting projection portions 76b moves away from the side surface of the rotation restricting grooves <NUM>. Accordingly, when the screw shaft <NUM> is moved in the axial direction to shift to the parking brake state by pulling the brake cable <NUM>, it is possible to prevent the components (that is, the guide cylindrical portion 74a of the insertion member <NUM> and the rotation restricting projection portions 76b of the cap <NUM>) constituting the rotation restricting means <NUM> from making strong contact with each other, reduce the driving torque of the electric motor <NUM> by reducing the sliding resistance, and reduce wear of the guide cylindrical portion 74a and the cap <NUM>.

In addition, the rotation restricting projection portions 76b are returned to the vicinity of a rotary position B indicated by the dotted line in <FIG> by the twisting force from the brake cable <NUM> when the parking brake state is maintained. Even when the rotation restricting projection portions 76b of the cap <NUM> reach the rotary position B by the backward rotation of the nut <NUM> during switching from the parking brake state to the parking brake release state and make contact with the side surface of the rotation restricting grooves <NUM> of the insertion member <NUM>, it is possible to prevent the cap <NUM> and the insertion member <NUM> from strongly colliding with each other, suppress the generation of a slapping sound, and reduce the operating sound.

In addition, since the rotation restricting means <NUM> includes the plurality of rotation restricting projection portions 76b that are provided in the end portion of the screw shaft <NUM> opposite to the brake cable <NUM> and radially project from the screw shaft <NUM> and the plurality of the rotation restricting grooves <NUM> formed in the insertion member <NUM> so as to be entered by the rotation restricting projection portions 76b, the operating sound can be reduced more effectively by restricting the rotation of the screw shaft <NUM> at a plurality of positions in the circumferential direction of the screw shaft <NUM>.

Although an embodiment of the invention has been described above, the invention is not limited to the above embodiment and various design changes can be made without departing from the scope of the invention as defined by the claims.

Claim 1:
An electric parking brake device comprising:
a screw shaft (<NUM>);
a brake cable (<NUM>);
an actuator case (<NUM>) that supports the screw shaft (<NUM>) movably in an axial direction thereof;
an electric motor (<NUM>) that is supported by the actuator case (<NUM>) rotatably forward and backward;
a motion conversion mechanism (<NUM>) that has a nut (<NUM>) to be screwed onto the screw shaft (<NUM>) rotatably in response to an operation of the electric motor (<NUM>), enables conversion from a rotational motion generated by the electric motor (<NUM>) to a linear motion of the screw shaft (<NUM>), and is accommodated in the actuator case (<NUM>); and
a resilient member (<NUM>) that is compressed when the screw shaft (<NUM>) is moved to a side loosening the brake cable (<NUM>), wherein switching between a parking brake state reached by pulling the brake cable (<NUM>) and a parking brake release state reached by loosening the brake cable (<NUM>) is performed by a change in a rotational direction of the electric motor (<NUM>),
wherein the nut (<NUM>) is screwed onto the screw shaft (<NUM>) movably in the axial direction within a restricted range, and
a movement restricting portion (74f), the movement restricting portion (74f) restricts an end of axial movement, toward the side loosening the brake cable (<NUM>), of the screw shaft (<NUM>) or of a linked member (<NUM>) that moves axially together with the screw shaft (<NUM>) by causing the screw shaft (<NUM>) or the linked member (<NUM>) to abut against the movement restricting portion (74f),
wherein the screw shaft is connected to the brake cable (<NUM>) so as to be prevented from rotating; and
the movement restricting portion is provided in a fixed position in the actuator case (<NUM>);
characterized in that the resilient member (<NUM>) is interposed between the nut (<NUM>) and an insertion member (<NUM>) accommodated and fixed in the actuator case (<NUM>) so as to be compressed in response to axial movement of the nut (<NUM>) after the movement end of the screw shaft (<NUM>) or the linked member (<NUM>) is restricted by the movement restricting portion (74f) when the screw shaft (<NUM>) moves axially to the side loosening the brake cable (<NUM>);
wherein the movement restricting portion (74f) is provided integrally with the insertion member (<NUM>) so that the resilient member (<NUM>) is interposed between the movement restricting portion (74f) and the nut (<NUM>).