[Title of Invention]

DRUM BRAKE DEVICE

[Technical Field]

[0001] The present invention relates to a drum brake device to be mounted in a vehicle.

[Background Art]

[0002] Hitherto, in a drum brake device, an automatic adjuster has been provided for automatically adjusting a standby position of a brake shoe so that a gap (called a shoe clearance) between a brake drum and the brake shoe during a non-braking period does not increase due to wear of the brake shoe. In general, the automatic adjuster includes a strut for regulating a minimum gap between a pair of brake shoes. When the brake shoes are spread wide apart during a main brake operation, namely, when the shoe clearance has increased, the strut is elongated by rotating an adjuster bolt. Consequently, the minimum gap between the pair of brake shoes is widened, and the shoe clearance is automatically adjusted.

[0003] In Patent Literature 1 , there is proposed a drum brake device including between a pair of brake shoes an electric actuator configured to spread the brake shoes with an electric motor. This drum brake device is configured so that main brake activation, parking brake activation, and shoe clearance adjustment are carried out using a common electric actuator. [Citation List]

[Patent Literature]

[0004] [PTL 1] JP 03-500919 A

[Summary of Invention] [0005] The automatic adjuster is provided based on the assumption that the automatic adjuster is to be operated when the range of motion of the brake shoes has increased due to wear of the brake shoes. However, when the brake drum has been temporarily deformed, the automatic adjuster may also be operated in response to that temporary deformation. For example, when the brake drum becomes hot and thermally expands due to friction between the brake shoes and the brake drum, the drum diameter increases. Consequently, the automatic adjuster is operated in the same manner as for wear of the brake shoes, and the gap between the brake shoes is widened too much. When the brake drum returns to a normal temperature, the drum diameter also returns to its original size. Consequently, a

phenomenon, called over-adjustment, in which the shoe clearance that needs to be reliably kept during a non-braking period is less than a proper value occurs.

[0006] Further, also when a strong brake operation has been performed, because the brake shoes strongly press against the brake drum in the spreading direction, the drum diameter temporarily increases, and the lining of the brake shoes is temporarily compressively deformed. In addition, during a brake operation while the vehicle is traveling, the lining is

temporarily deformed in the direction of the braking torque (this deformation is referred to as "shear deformation"). Even in cases such as these, over-adjustment occurs.

[0007] When over-adjustment has occurred, despite the fact that a brake pedal operation has not been performed, friction is generated between the brake drum and the lining, which can lead to early wear of the lining and worse vehicle fuel consumption. Therefore, hitherto, the adjustment amount of the automatic adjuster is set so as to take into account the temporary deformation of the drum brake device itself. However, because the shoe clearance is increased by the estimated amount of deformation, the brake operation feeling is not very good.

[0008] The drum brake device proposed in Patent Literature 1 adjusts the shoe clearance using an electric actuator without the use of a strut.

However, the timing for adjusting the shoe clearance is not set, and hence, over-adjustment can occur due to deformation of the brake drum.

[0009] It is an object of the present invention, which has been made to solve the above-mentioned problems, to reduce the likelihood of the occurrence of over-adjustment in a drum brake device to be operated by an electric actuator.

[0010] In order to achieve the above-mentioned object, one feature of the present invention resides in a drum brake device, including:

a first actuator (50) including a motor (60), the first actuator being configured to spread a pair of brake shoes (30) based on a change in an operation amount thereof by a drive of the motor so that the pair of brake shoes press against a brake drum (10) to brake a wheel; and

a first actuator control device (120) configured to bring the wheel into a braking state by increasing the operation amount of the first actuator based on a first braking request so that the pair of brake shoes spread from a standby position to a braking position, and bring the wheel into a non-braking state by decreasing the operation amount of the first actuator based on a first braking release request so that the pair of brake shoes return from the braking position to the standby position,

the first actuator control device including: drum temperature index value acquisition means (S41 to S43, S51 to S53) for acquiring a parameter having a correlation with a temperature of the brake drum as a drum temperature index value (Ts); and standby position update means (S23 to S29) for updating, when the first braking release request has been generated, during a process in which the pair of brake shoes are being returned from the braking position to the standby position by the first actuator, the standby position to a position of the pair of brake shoes when the operation amount of the first actuator has decreased by a predetermined amount from an operation amount at a time point at which contact between the pair of brake shoes and the brake drum is estimated to have been released, on condition that the drum temperature index value indicates that a thermal expansion amount of the brake drum is within a permissible range.

[0011] The drum brake device according to the present invention includes: the first actuator configured to spread the pair of brake shoes based on the change in the operation amount by the drive of the motor so that the pair of brake shoes press against the brake drum to brake the wheel. The motor of the first actuator is driven and controlled by the first actuator control device. The first actuator control device brings the wheel into the braking state by increasing the operation amount of the first actuator based on the first braking request so that the pair of brake shoes spread from the standby position to the braking position. Further, the first actuator control device brings the wheel into the non-braking state by decreasing the operation amount of the first actuator based on the first braking release request so that the pair of brake shoes return from the braking position to the standby position. The first braking request and the first braking release request are generated by, for example, a brake operation by the driver. However, the first braking request and the first braking release request may also be generated based on automatic drive control, behavior stabilization control, and the like of the vehicle. Note that, the meaning of "brake a wheel" as used herein not only includes reducing the rotational speed of a rotating wheel, but also includes preventing a stationary wheel from rotating.

Therefore, the first actuator may be used as a main brake or as a parking brake.

[0012] When the brake drum becomes hot due to the friction between the pair of brake shoes and the brake drum, the drum diameter increases due to thermal expansion of the brake drum. If the standby position of the pair of brake shoes is set in such a state, when the temperature of the brake drum decreases to a normal temperature, the clearance between the pair of brake shoes and the brake drum excessively narrows. In other words,

over-adjustment occurs. Therefore, in the present invention, the clearance for the standby position is set properly using the drum temperature index value acquisition means and the standby position update means.

[0013] The drum temperature index value acquisition means is configured to acquire a parameter having a correlation with the temperature of the brake drum as the drum temperature index value. Based on this drum temperature index value, a determination may be made whether or not the thermal expansion amount of the brake drum, which is a factor in

over-adjustment, is within the permissible range. For example, a detection temperature obtained by detecting the temperature of the brake drum may be used as the drum temperature index value, or a vehicle stop duration of the vehicle during which time the brake drum does not generate heat may be used as the drum temperature index value. In the case of using the vehicle stop duration of the vehicle, for example, when the vehicle stop duration of the vehicle is equal to or more than a set duration, the drum temperature index value indicates that the thermal expansion amount is within the permissible range. Note that, the thermal expansion amount of the brake drum indicates the amount of thermal expansion based on the shape of the brake drum at a normal temperature (an ambient temperature expected in advance), for example. Further, the temperature at which the thermal expansion amount of the brake drum is within the permissible range (temperature that is less likely to affect setting of the standby position) may be set based on properties of the brake drum, a target clearance, and the like.

[0014] The standby position update means is configured to update, when the first braking release request has been generated, during a process in which the pair of brake shoes are being returned from the braking position to the standby position by the first actuator, the standby position to the position of the pair of brake shoes when the operation amount of the first actuator has decreased by a predetermined amount from the operation amount at the time point at which the contact between the pair of brake shoes and the brake drum is estimated to have been released, on condition that the drum temperature index value indicates that the thermal expansion amount of the brake drum is within the permissible range. Therefore, the standby position may be set in a state in which the brake drum is less susceptible to the effects of thermal expansion. Further, the standby position may be set in a state in which the pressing against the brake drum by the first actuator has been released. As a result of those advantageous effects, according to one embodiment of the present invention, the likelihood of the over-adjustment occurring due to deformation of the drum brake may be reduced. Note that, the above-mentioned predetermined amount is an amount corresponding to the target clearance between the brake drum and the pair of brake shoes. This predetermined amount may be set based on a rotation amount of the motor, or on an energization time of the motor.

[0015] One aspect of the present invention resides in that: the drum brake device further includes:

a second actuator (40) different from the first actuator, the second actuator being configured to spread the pair of brake shoes so that the pair of brake shoes press against the brake drum to brake the wheel; and

a second actuator control device (110, 200) configured to bring the wheel into the braking state by spreading the pair of brake shoes from the updated standby position based on a second braking request, and bring the wheel into the non-braking state by returning the pair of brake shoes to the updated standby position based on a second braking release request;

the first actuator control device is configured to control operation of the first actuator based on a braking request generated by a parking brake operation as the first braking request and a braking release request generated by the parking brake operation as the first braking release request; and

the second actuator control device is configured to control operation of the second actuator based on a braking request generated by a main brake operation as the second braking request and a braking release request generated by the main brake operation as the second braking release request. [0016] The drum brake device according to one aspect of the present invention includes the first actuator and the second actuator. The first actuator control device is configured to control operation of the first actuator based on the braking request generated by the parking brake operation as the first braking request and the braking release request generated by the parking brake operation as the first braking release request. The second actuator control device is configured to control operation of the second actuator based on the braking request generated by the main brake operation as the second braking request and the braking release request generated by the main brake operation as the second braking release request.

[0017] For example, when the main brake is activated by strongly pressing on the brake pedal while the vehicle is traveling, the deformation amount of the brake drum and the deformation amount of the lining are more than when the parking brake is activated while the vehicle is stationary.

Consequently, when the standby position (clearance) is set during operation of the second actuator, over-adjustment tends to occur. In contrast, according to one aspect of the present invention, the standby position is updated when the braking by the first actuator to be operated by a parking brake operation is released. Consequently, it is not necessary to update the standby position during activation of the main brake, the proper standby position may be set, and the likelihood of over-adjustment occurring may be reduced.

[0018] Note that, the second actuator may be configured from, for example, a hydraulic cylinder to be operated by the hydraulic pressure of the brake operating fluid. In that case, the second actuator control device may be configured from a hydraulic pressure control device configured to supply to the hydraulic cylinder the hydraulic pressure of the brake operating fluid in response to a main brake operation. Further, the second actuator is not limited to a hydraulic actuator, for example, the second actuator may be a pneumatic actuator or an electric actuator.

[0019] One aspect of the present invention resides in that the first actuator control device is configured to update the standby position on condition that the pair of brake shoes are not being pressed against the brake drum by the second actuator.

[0020] In a state in which the second actuator presses the pair of brake shoes against the brake drum in response to a main brake operation, the drum diameter temporarily increases and the lining of the brake shoes is temporarily deformed. Therefore, the first actuator control device is configured to update the standby position on condition that the pair of brake shoes are not being pressed against the brake drum by the second actuator. Consequently, according to one aspect of the present invention, the proper standby position (clearance) may be set, and the likelihood of

over-adjustment occurring may be reduced.

[0021] One aspect of the present invention resides in that, when the first braking release request has been generated and when the pair of brake shoes are pressing against the brake drum due to operation of the second actuator, the first actuator control device is configured to wait until the second actuator releases the pressing against the brake drum by the pair of brake shoes (S221) before releasing the pressing against the brake drum by the pair of brake shoes due to the operation of the first actuator.

[0022] According to one aspect of the present invention, when the first braking release request has been generated by the parking brake operation and when the pair of brake shoes are pressing against the brake drum due to the operation of the second actuator, the first actuator control device is configured to wait until the second actuator releases the pressing against the brake drum by the pair of brake shoes, namely, until the main brake operation is released, before releasing the pressing against the brake drum by the pair of brake shoes due to the operation of the first actuator.

Therefore, the standby position may be updated in a state in which the brake drum is not deformed. Consequently, according to one aspect of the present invention, the proper standby position may be set, and the likelihood of over-adjustment occurring may be reduced.

[0023] One aspect of the present invention resides in that, in a state in which the pair of brake shoes are pressing against the brake drum due to operation of the first actuator, the second actuator control device is

configured to prevent the pair of brake shoes from pressing against the brake drum due to the operation of the second actuator even when the second braking request is generated (S20, S64).

[0024] When the pair of brake shoes are being pressed against the brake drum by the second actuator, the brake drum may be deformed by the pressing force. When the brake drum is deformed, the standby position may not be the proper standby position if the standby position has been set based on the operation amount of the first actuator at a time point at which contact between the pair of brake shoes and the brake drum is estimated to have been released by the first actuator. Therefore, according to one aspect of the present invention, in the state in which the pair of brake shoes are pressing against the brake drum due to the operation of the first actuator, namely, in a state in which the parking brake is functioning, the second actuator control device is configured to prevent the pair of brake shoes from pressing against the brake drum due to the operation of the second actuator even when the second braking request is generated.

[0025] Therefore, when the contact between the pair of brake shoes and the brake drum is released by the first actuator, namely, when the parking brake is released, the second actuator is in a non-braking state, and hence, the brake drum is not deformed. Consequently, according to one aspect of the present invention, the proper standby position may be set, and the likelihood of over-adjustment occurring may be reduced. Further, even when the pair of brake shoes are not pressed against the brake drum due to the operation of the second actuator, a state in which the pair of brake shoes are pressed against the brake drum due to the operation of the first actuator is maintained, and hence the wheel may be maintained in a braking state.

[0026] One aspect of the present invention resides in that the drum temperature index value acquisition means is configured to acquire as the drum temperature index value a vehicle stop duration for which a vehicle has been stationary at a time point at which the first braking release request for releasing the braking state of the wheel has been generated by the first actuator while the vehicle is stationary.

[0027] The brake drum becomes hot due to the frictional heat produced by the friction with the pair of brake shoes. However, when the frictional heat stops being produced as the wheel stops rotating, the brake drum is cooled by the ambient air, and cools down over time. Therefore, according to one aspect of the present invention, the drum temperature index value acquisition means is configured to acquire as the drum temperature index value the vehicle stop duration for which the vehicle has been stationary at the time point at which the first braking release request for releasing the braking state of the wheel has been generated by the first actuator while the vehicle is stationary. Hence, when the vehicle stop duration is equal to or more than a pre-set set duration, the thermal expansion amount of the brake drum may be determined as being within the permissible range. The vehicle stop duration may be acquired by, for example, acquiring the duration for which the vehicle speed has remained at zero. Alternatively, the duration for which the parking brake has been functioning for may be acquired as the vehicle stop duration. Therefore, according to one aspect of the present invention, the drum temperature index value may be acquired without directly detecting the temperature of the brake drum with a

temperature sensor, thereby allowing costs to be reduced.

[0028] One aspect of the present invention resides in that: the first actuator (50) includes the motor (60), a worm (71) fixed to an output shaft of the motor, a worm wheel (72) configured to engage with the worm, and a screw drive mechanism (80) configured to convert a rotary motion of the worm wheel into an advancing/retracting motion of an operated body (82), the first actuator being configured to change a gap between one end of one of the pair of brake shoes and one end of another of the pair of brake shoes by the advancing/retracting motion of the operated body; and the second actuator includes a cylinder (40) including a piston configured to be

advanced/retracted by a brake operating fluid to be supplied by the second actuator control device, the second actuator being configured to change a gap between another end of one of the pair of brake shoes and another end of another of the pair of brake shoes by the advancing/retracting motion of the piston.

[0029] According to one aspect of the present invention, the gap between the one end of the one of the pair of brake shoes and the one end of the another of the pair of brake shoes is changed by the first actuator, and the gap between the another end of the one of the pair of brake shoes and the another end of the another of the pair of brake shoes is changed by the second actuator. In the first actuator, energization of the motor is

controlled based on the first braking request generated by the parking brake operation, or, based on the first braking release request generated by the parking brake operation. When the motor is energized, the output shaft of the motor rotates, which causes a worm gear including the worm and the worm wheel to rotate. The rotary motion of the worm wheel is converted into the advancing/retracting motion of the operated body by the screw drive mechanism. Based on the advancing/retracting motion of the operated body, the gap between the one end of the one of the pair of brake shoes and the one end of the another of the pair of brake shoes is changed. Due to the characteristics of the worm gear, when the pair of brake shoes are held at the braking position by the first actuator, the energization of the motor may be stopped.

[0030] The second actuator causes the piston to advance or retract by supplying the brake operating fluid having a pressure that is based on the main brake operation from the second actuator control device to the cylinder. Based on the advancing/retracting motion of the piston, the gap between the another end of the one of the pair of brake shoes and the another end of the another of the pair of brake shoes is changed. Therefore, according to one aspect of the present invention, the activation of the parking brake and the activation of the main brake may be properly performed independently.

[0031 ] One aspect of the present invention resides in that: the first actuator is configured so that a motor torque for moving the pair of brake shoes decreases as a force that the pair of braking shoes are pressing against the brake drum becomes smaller; and the first actuator control device is configured to estimate a time point at which, during a process in which the pair of brake shoes are being returned from the braking position to the standby position by the drive of the motor, a current of the motor switches from a state in which the current is decreasing to a state in which the current becomes constant and is maintained at a fixed value as a time point at which contact between the pair of brake shoes and the brake drum has been released (S26).

[0032] The first actuator used in one aspect of the present invention is configured so that the motor torque required to move the pair of brake shoes decreases as the force that the pair of braking shoes are pressing against the brake drum becomes smaller. In this case, during the process in which the pair of brake shoes are being returned from the braking position to the standby position by the drive of the motor, the motor current is in the decreasing state while the pair of brake shoes are in contact with the brake drum, and is maintained at the fixed value when the contact between the pair of brake shoes and the brake drum is released. Therefore, according to one aspect of the present invention, the first actuator control device is configured to estimate the time point at which, during the process in which the pair of brake shoes are being returned from the braking position to the standby position by the drive of the motor, the current of the motor switches from the state in which the current is decreasing to the state in which the current becomes constant and is maintained at the fixed value as the time point at which the contact between the pair of brake shoes and the brake drum has been released. Consequently, the estimation of the contact release timing may be performed properly and easily. Therefore, the setting of the standby position may be performed properly and easily.

[0033] Note that, in the above description, to aid in understanding of the invention, the reference symbols used in the embodiment are added in parentheses to the components of the invention corresponding to the embodiment. However, the respective constituent components of the invention are not limited to the embodiment defined by the reference numerals.

[Brief Description of Drawings]

[0034] FIG. 1 is a front schematic configuration diagram of a drum brake according to an embodiment of the present invention.

FIG. 2 is a system schematic configuration diagram of a drum brake device according to the embodiment.

FIG. 3 is a side sectional schematic diagram of an electric actuator.

FIG. 4 is a front sectional schematic diagram of the electric actuator.

FIG. 5 is an end schematic diagram of a wheel cylinder.

FIG. 6 is a flowchart illustrating a parking brake activation control routine.

FIG. 7 is a flowchart illustrating a parking brake release control routine.

FIG. 8 is a flowchart illustrating a vehicle stop duration measurement routine. FIG. 9 is a flowchart illustrating another vehicle stop duration measurement routine.

FIG. 10 is a flowchart illustrating a parking brake activation control routine according to Modified Example 1 of the present invention.

FIG. 11 is a flowchart illustrating a parking brake release control routine according to Modified Example 1.

FIG. 12 is a flowchart illustrating a hydraulic pressure supply command routine according to Modified Example 2 of the present invention.

FIG. 13 is a flowchart illustrating a parking brake activation control routine according to Modified Example 3 of the present invention.

FIG. 14 is a flowchart illustrating a parking brake release control routine according to Modified Example 3.

FIG. 15 is a graph showing changes in motor current.

FIGS. 16A to 16C are explanatory diagrams schematically

illustrating an engagement state of a worm gear mechanism.

[Description of Embodiment]

[0035] A drum brake device for a vehicle according to one embodiment of the present invention is described below. FIG. 1 schematically illustrates a rear wheel drum brake 1 to be provided in the drum brake device according to this embodiment. The drum brake 1 includes a brake drum 10, a backing plate 20, a pair of two brake shoes 30a and 30b, a wheel cylinder 40, and an electric actuator 50.

[0036] The brake drum 10, which is a round cylinder that rotates with the wheel, has a friction surface on an inner circumference surface of the brake drum 10. The backing plate 20, which has a roughly circular plate shape, is fixed in a non-rotatable manner to a vehicle body side member. The pair of brake shoes 30a and 30b, which are members having an arc shape, are housed in the brake drum 10 on roughly the right and left hand sides in a manner that allows the brake shoes 30a and 30b to be brought closer to and separated from each other. In the following description, unless it is necessary to specify a particular one of the brake shoes 30a and 30b, the two brake shoes 30a and 30b are collectively referred to simply as "brake shoes 30".

[0037] Each brake shoe 30 integrally includes a shoe web 31 arranged roughly parallel to the plate surface (one surface side) of the backing plate 20, a shoe rim 32 firmly fixed to an edge surface on the outer circumferential side of the shoe web 31 , and a lining 33 that is fixed to the outer

circumferential surface of the shoe rim 32 and is configured to frictionally engage with the inner circumferential surface of the brake drum 10 during a brake operation. Each brake shoe 30 is attached to the backing plate 20 in a manner that allows the brake shoes 30 to be moved toward the inner circumferential surface of the brake drum 10 by a shoe hold down 21 mounted in an attachment hole that is formed through each shoe web 31 .

[0038] The wheel cylinder 40 is fixedly attached to the backing plate 20 as a hydraulic actuator between one end (in this example, the top end) of the pair of brake shoes 30a and 30b. The wheel cylinder 40 includes at each end portion a piston 41 that is operated by the pressure of a brake operating fluid. The tip of the piston 41 is coupled to one end of the left shoe web 31 and one end of the right shoe web 31 . The wheel cylinder 40 spreads the brake shoes 30 by causing the piston 41 to advance based on the hydraulic pressure of the brake operating fluid supplied from a hydraulic pressure supply circuit 200 described below, so that the right and left shoe webs 31 are pressed in a direction in which the right and left shoe webs 31 move away from each other. Consequently, the lining 33 presses against the inner circumferential surface of the brake drum 10, which produces a friction braking force that slows the rotation of the brake drum 10 (i.e., the rotation of the wheel). Further, when the hydraulic pressure of the brake operating fluid supplied from the hydraulic pressure supply circuit 200 decreases, the wheel cylinder 40 releases the pressing by the lining 33 against the inner circumferential surface of the brake drum 10 by retracting the piston 41 , so that the right and left shoe webs 31 are pulled back toward each other. Consequently, the braking state of the wheel is released.

[0039] Note that, as illustrated in FIG. 5, a stopper bearing 42 is formed in the housing of the wheel cylinder 40 so that the piston 41 is not pushed beyond an initial position (position when hydraulic pressure is not being supplied) by operation of the electric actuator 50 described below. A stopper 34 formed on the shoe web 31 is configured so as to abut against the stopper bearing 42 when the piston 41 is arranged at the initial position.

[0040] The electric actuator 50 is provided between another end (in this example, the bottom end) of the pair of brake shoes 30a and 30b. The electric actuator 50 is controlled by a parking brake ECU 20 that is described below. When the parking brake is activated by the driver, the electric actuator 50 spreads the brake shoes 30 by pressing the right and left shoe webs 31 in a direction in which the right and left shoe webs 31 move away from each other. Consequently, a state in which the lining 33 is pressing against the inner circumferential surface of the brake drum 10 so that the brake drum 10 is stationary, namely, a state in which the parking brake is activated, is maintained. Further, when the parking brake is released by the driver, the electric actuator 50 pulls in the right and left shoe webs 31 to return the right and left shoe webs 31 to a standby position. Consequently, the parking brake is released.

[0041] As illustrated in FIG. 3 and FIG. 4, the electric actuator 50 includes a motor 60, a worm gear mechanism 70, and a screw drive mechanism 80. The motor 60 is fixed to a rear surface of the backing plate 20 in a state in which an output shaft 61 of the motor 60 passes through the backing plate 20. A worm 71 is fixed to the output shaft 61 of the motor 60. The screw drive mechanism 80 includes a cylindrical screw member 81 and two advancing/retracting rods 821 and 822. In the screw member 81 , a worm wheel 72 is fixed to an outer circumferential surface of the cylindrical body portion. The worm wheel 72, which is fixed in a concentric position with respect to the screw member 81 , engages with the worm 71 that is fixed to the output shaft 61 of the motor 60. The worm gear mechanism 70 is configured by the worm 71 and the worm wheel 72.

[0042] The worm gear mechanism 70 and the screw member 81 are housed in a casing (not shown). The screw member 81 is rotatably provided in the casing in a state in which movement in the axial direction is blocked by a shaft bearing (not shown). Consequently, when the output shaft 61 is driven by the motor 60 and rotated, the screw member 81 is rotated at a reduced speed via the worm gear mechanism 70.

[0043] On the inner circumferential surface of the cylindrical body portion of the screw member 81 , a first female thread 811 is formed more toward one side (the left side of FIG. 4) than the center in the axial direction, and a second female thread 812 is formed more toward another side (the right side of FIG. 4) than the center in the axial direction. The first female thread 811 and the second female thread 812 have the same lead and diameter, but the direction in which the thread is formed is different from each other. For example, the first female thread 811 is a right-hand thread, and the second female thread 812 is a left-hand thread.

[0044] A columnar first advancing/retracting rod 821 and a second

advancing/retracting rod 822 are provided in a cylindrical space of the screw member 81. The first advancing/retracting rod 821 includes a male thread 8211 that engages with the first female thread 811. The second

advancing/retracting rod 822 includes a male thread 8221 that engages with the second female thread 812. Therefore, the rotary motion of the screw member 81 is converted into a linear motion (advancing/retracting

movement) of the first advancing/retracting rod 821 and the second

advancing/retracting rod 822. In this case, the first advancing/retracting rod 821 and the second advancing/retracting rod 822 move as a pair in linearly opposite directions to each other. For example, when the motor 60 is driven in a forward direction, the first advancing/retracting rod 821 and the second advancing/retracting rod 822 advance in a direction away from each other, and when the motor 60 is driven in a reverse direction, the first advancing/retracting rod 821 and the second advancing/retracting rod 822 retract in a direction toward each other.

[0045] Hence, the screw drive mechanism 80 is configured by the screw member 81 , the first advancing/retracting rod 821 , and the second

advancing/retracting rod 822. In the following description, unless it is necessary to specify a particular one of the first advancing/retracting rod 821 and the second advancing/retracting rod 822, the two are referred to simply as "advancing/retracting rods 82". [0046] A columnar coupling portion 83 is integrally formed with the tip of each advancing/retracting rod 82. A groove 84 that extends in a straight line parallel to the backing plate 20 and that has a U-shaped cross-section is formed in the coupling portion 83. The tip of the shoe web 31 fits into and is held in the groove 84. Therefore, when the motor 60 is driven in a forward direction, the advancing/retracting rods 82 advance and push the shoe web 31 outward, which causes the gap between the brake shoes 30 to widen. Further, when the motor 60 is driven in a reverse direction, the advancing/retracting rods 82 retract and pull the shoe web 31 inward, which causes the gap between the brake shoes 30 to narrow.

[0047] Further, in a state in which the brake shoes 30 are pressing against the brake drum 10, the electric actuator 50 is configured so that the brake shoes 30 are prevented by the worm gear mechanism 70 and the screw drive mechanism 80 from returning based only on the reaction force (the force with which the brake drum 10 pushes back the brake shoes 30).

Therefore, the state in which the brake shoes 30 are pressing against the brake drum 10 can be maintained even if the power to the motor 60 is stopped.

[0048] Next, the system for controlling the drum brake 1 is described. FIG. 2 illustrates a schematic system configuration of a drum brake device. In a vehicle in which the drum brake device according to this embodiment is to be applied, the above-mentioned drum brake 1 is provided on the right and left rear wheels. On the right and left front wheels, a normal drum brake 5 that does not include the electric actuator 50 and that supports the other end of the shoe web 31 with an anchor member (not shown) is provided. In this example, although the normal drum brake 5 is used for the front wheel brakes, the front wheel brake is not the one included in the present invention, and may even be a disc brake. In the following description about the system configuration, the reference symbol fl is added to the names of parts arranged in the left front wheel, the reference symbol fr is added to the names of parts arranged in the right front wheel, the reference symbol rl is added to the names of parts arranged in the left rear wheel, and the reference symbol rr is added to the names of parts arranged in the right rear wheel.

[0049] The drum brake device includes a brake electronic control unit 100 (hereinafter referred to as "brake ECU 100") and a hydraulic pressure supply circuit 200. The brake ECU 100 includes a main brake electronic control unit 110 (hereinafter referred to as "main brake ECU 110")

configured to control activation of the hydraulic pressure supply circuit 200, and a parking brake electronic control unit 120 (hereinafter referred to as "parking brake ECU 120") configured to control operation of the electric actuator 50.

[0050] The hydraulic pressure supply circuit 200 is connected via a brake pipe to a wheel cylinder 6fl of a drum brake 5fl of the left front wheel, a wheel cylinder 6fr of a drum brake 5fr of the right front wheel, a wheel cylinder 40rl of a drum brake 1 rl of the left rear wheel, and a wheel cylinder 40rr of a drum brake 1rr of the right rear wheel. The hydraulic pressure supply circuit 200 includes a master cylinder configured to apply pressure to an operating fluid based on a pressing operation of a brake pedal 201 , a reservoir that stores the operating fluid at atmospheric pressure, a hydraulic pressure circuit configured to supply the hydraulic pressure of the

pressurized operating fluid to the wheel cylinders 6fl, 6fr, 40rl, and 40rr of each wheel, an open/close valve configured to switch between a state that permits supply of the hydraulic pressure of the operating fluid to the wheel cylinders 6fl, 6fr, 40rl, and 40rr of each wheel and a state that prohibits supply of the hydraulic pressure, and the like (because the above

description is a common configuration, an illustration thereof is not shown). Any valve may be used for the open/close valve, as long as the valve is at least capable of independently switching the supply state of the operating fluid between the front wheels and the rear wheels. An example of such an open/close valve is a valve used in antilock brake control for preventing locking of each wheel, and the like.

[0051] The hydraulic pressure supply circuit 200 includes a sensor, such as a pressure sensor (not shown), configured to detect the applied pressure state of the operating fluid. The hydraulic pressure supply circuit 200 outputs a sensor signal to the main brake ECU 110. Note that, in FIG. 2, the arrow with the dotted line represents a sensor signal line. The main brake ECU 110 is configured so that a sensor signal output from the hydraulic pressure supply circuit 200 and a switch signal from a pedal switch 90 for detecting whether or not the brake pedal 201 has been pressed are input. The pressing operation of the brake pedal 201 acts as a braking request (corresponding to the second braking request of the present invention), and a pressing release operation of the brake pedal 201 acts as a braking release request (corresponding to the second braking release request of the present invention). Note that, although the main brake ECU 110 receives a sensor signal indicating a behavioral state of the vehicle and the like, because this sensor signal is not directly related to the present invention, a description of the sensor signal is omitted. [0052] The main brake ECU 110, which includes a microcomputer configured from a CPU, a ROM, a RAM, and the like, a solenoid valve drive circuit, an input/output interface, and the like, is configured so that the main brake ECU 110 can communicate with the parking brake ECU 120. The method for controlling the main brake in this embodiment is a method in which hydraulic pressure applied by the master cylinder based on the pressing operation of the brake pedal 201 is directly supplied to the wheel cylinders 6fl, 6fr, 40rl, and 40rr of each wheel, and when necessary, the main brake ECU 110 outputs a drive signal to the open/close valve of the hydraulic pressure supply circuit 200 to control the hydraulic pressure supplied to the wheel cylinders 6fl, 6fr, 40rl, and 40rr of each wheel.

[0053] The parking brake ECU 120, which includes a microcomputer configured from a CPU, a ROM, a RAM, and the like, a motor drive circuit, an input/output interface, and the like, is configured so that the parking brake ECU 120 can communicate with the main brake ECU 110. Rotation angle sensors 91 rl and 91 rr (in the following description, referred to simply as "rotation angle sensors 91 " unless distinguishing between the two sensors) for detecting respective rotation angles of the motors 60rl and 60rr are provided in electric actuators 50rl and 50rr that are arranged in the rear wheel drum brakes 1 rl and 1 rr. The rotation angle sensors 91 rl and 91 rr output sensor signals indicating a rotation angle Θ of the motors 60rl and 60rr, respectively, to the parking brake ECU 120.

[0054] Further, the parking brake ECU 120, which includes current sensors 92rl and 92rr configured to detect the magnitude of the current to be supplied to the motors 60rl and 60rr from the motor drive circuit, is configured so that a motor current im, which is the energization amount of the motors, can be monitored for each of the motors 60rl and 60rr. In addition, the parking brake ECU 120 is connected to a parking brake operation switch 93, a shift position sensor 94, a vehicle speed sensor 95, and the pedal switch 90. The parking brake operation switch 93 outputs a parking brake operation signal indicating a setting state (parking brake activation, parking brake release) of the parking brake operated by the driver. The shift position sensor 94 outputs a shift position signal indicating the setting position of a shift lever operated by the driver. The vehicle speed sensor 95 outputs a sensor signal indicating a vehicle speed V.

[0055] When the parking brake operation switch 93 operated by the driver indicates parking brake activation, or when the setting position of the shift lever indicates a parking position (P range), the parking brake ECU 120 is activated to cause the parking brake to function. In the following

description, the signal output from the parking brake operation switch 93 and the signal output from the shift position sensor 94 are referred to as "parking brake signal". Further, when the parking brake operation switch 93 operated by the driver indicates parking brake activation, or when the setting position of the shift lever indicates a parking position (P range), the parking brake signal becomes an "ON state". In other situations, the parking brake signal becomes an "OFF state". The parking brake signal acts as a signal indicating a braking request (corresponding to the first braking request of the present invention), or a braking release request (corresponding to the first braking release request of the present invention).

[0056] Next, the control processing performed by the parking brake ECU 120 is described. The parking brake ECU 120 independently controls the electric actuator 50rl of the left rear wheel and the electric actuator 50rr of the right rear wheel. However, because the control content for both of those processes is the same, the control processing of the electric actuator 50 for one of those wheels is described here. First, the processing performed when the parking brake is activated is described. FIG. 6 illustrates a parking brake activation control routine performed by the parking brake ECU 120.

[0057] When the parking brake activation routine starts, first, in Step S11 , the parking brake ECU 120 determines whether or not the parking brake signal (in FIG. 6, indicated as PKB) has been switched on. The parking brake ECU 120 repeats the determination processing of Step S11 at a predetermined calculation interval. When the parking brake signal switches from an OFF state to an ON state, namely, when a braking request is generated, in Step S12, a rotation angle Θ of the motor 60 detected by the rotation angle sensor 91 is read, and the read rotation angle Θ is stored as an initial rotation angle ©start.

[0058] Next, in Step S13, the parking brake ECU 120 applies a fixed forward drive voltage to the motor 60 of the electric actuator 50 to start a forward drive of the motor 60. Based on the forward drive of the motor 60, the electric actuator 50 pushes the right and left advancing/retracting rods 82 so that the right and left advancing/retracting rods 82 advance and widen the gap between the shoe webs 31. Consequently, the brake shoes 30 spread apart with the rotation of the motor 60.

[0059] Next, in Step S14, the parking brake ECU 120 detects the motor current im detected by the current sensor 92. In Step S15, the parking brake ECU 120 determines whether or not the motor current im is equal to or more than a stop setting current istop. When the parking brake ECU 120 determines that the motor current im is less than the stop setting current istop, the processing returns to Step S14, and the parking brake ECU 120 repeats the above-mentioned processing at the predetermined calculation interval.

[0060] The screw drive mechanism 80 is configured so that when the brake shoes 30 are not pressing against the brake drum 10, the female threads 811 and 812 of the screw member 81 and the male threads 8211 and 8221 of the advancing/retracting rods 821 and 822 are not jammed against each other in the axial direction. Consequently, less torque is required to rotate the screw member 81. Therefore, as schematically illustrated in FIG. 16A, in the worm gear mechanism 70, the screw member 81 can be rotated without strongly pushing the teeth of the worm wheel 72 with the teeth of the worm 71. In this case, because the motor load is constant, as shown in FIG. 15, the motor current im has a fixed value from an energization start time t1 to a contact start time t2.

[0061] After the advancing/retracting rods 82 have been advanced by the forward drive of the motor 60, and the brake shoes 30 have been brought into contact with the brake drum 10, the female threads 811 and 812 of the screw member 81 and the male threads 8211 and 8221 of the

advancing/retracting rods 82 are jammed against each other in the axial direction. Consequently, the motor torque required to rotate the screw member 81 increases. Therefore, as illustrated in FIG. 16B, in the worm gear mechanism 70, the teeth of the worm wheel 72 are strongly pushed by the teeth of the worm 71 in the forward direction, and the frictional resistance between the worm 71 and the worm wheel 72 increases. This frictional resistance increases as the force (the spread amount of the brake shoes 30) with which the brake shoes 30 are pressing against the brake drum 10 increases, which increases the motor load. Consequently, the motor current im increases with the increase in frictional resistance.

[0062] When the motor current im thus increases to the stop setting current istop or more (S15: Yes), in Step S16, the parking brake ECU 120 stops the forward drive of the motor 60. The stop setting current istop is the current that is required for the brake shoes 30 to spread to a position where the parking brake reliably functions. The stop setting current istop, which is determined in advance by experimentation and the like, is stored in the parking brake ECU 120. Therefore, in Step S16, when the forward drive of the motor 60 has been stopped, the parking brake is functioning reliably. As shown in FIG. 15, the motor current im increases from time t2, which is when the brake shoes 30 are brought into contact with the brake drum 10, and reaches the stop setting current istop at time t3. The parking brake ECU 120 stops the energization of the motor 60 at time t3.

[0063] Next, in Step S17, the parking brake ECU 120 reads the rotation angle Θ of the motor 60 detected by the rotation angle sensor 91 ,

temporarily stores this rotation angle Θ as a stop rotation angle ©stop, and calculates the difference (Ostop - ©start) between the initial rotation angle ©start stored in Step S12 and the stop rotation angle ©stop as a rotation amount R required to activate the parking brake. Next, in Step S18, the parking brake ECU 120 stores the rotation amount R as a return rotation amount R0. The return rotation amount R0 is stored and held until the parking brake is released.

[0064] Next, in Step S19, the parking brake ECU 120 reads a switch signal output from the pedal switch 90, and determines whether or not the switch signal is off, namely, whether or not the brake pedal 201 is not in a pressed state. The parking brake ECU 120 waits until the switch signal is detected as having been switched off, and then the processing proceeds to Step S20. In Step S20, the parking brake ECU 120 transmits to the main brake ECU 1 10 a command to prohibit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels.

[0065] When the main brake ECU 1 10 receives the command to prohibit the supply of hydraulic pressure, the main brake ECU 1 10 opens the open/close valve for supplying hydraulic pressure to the rear wheels that is provided in the hydraulic pressure supply circuit 200. Consequently, hydraulic pressure is not supplied from the hydraulic pressure supply circuit 200 to the wheel cylinders 40 of the rear wheels even if the driver has operated the brake pedal. Further, because the open/close valve is opened in a state in which the brake pedal 201 has not been pressed, the wheel cylinders 40 of the rear wheels are maintained in a state in which the piston 41 is returned to its initial position. In other words, during activation of the parking brake, the wheel cylinders 40 of the rear wheels are maintained in a state in which the brake shoes 30 are not spread apart (a non-braking state). Therefore, when the parking brake is released, there is no deformation of the brake drum 10 (an increase in the drum diameter), or deformation of the lining 33 (compressive deformation and shear deformation), which is caused due to the force with which the brake shoes 30 are pressing against the brake drum 10. The reason for configuring in this manner, which is described in more detail below, is to allow the proper setting of the standby position of the brake shoes 30 performed during release of the parking brake.

[0066] In Step S20, when the parking brake ECU 120 has transmitted the command to prohibit the supply of hydraulic pressure, the parking brake ECU 120 finishes the parking brake activation control routine. The parking brake activation control routine is restarted when a parking brake release control routine described below has finished.

[0067] Next, processing performed by the parking brake ECU 120 when the parking brake is released is described. FIG. 7 illustrates the parking brake release control routine performed by the parking brake ECU 120. This parking brake release control routine includes processing for setting the standby position of the brake shoes 30, namely, processing for setting the clearance between the brake shoes 30 and the brake drum 10 during a non-braking period. The parking brake release control routine starts when the above-mentioned parking brake activation control routine has finished.

[0068] When the parking brake release control routine starts, first, in Step S21 , the parking brake ECU 120 determines whether or not a parking brake signal (PKB signal) has been switched off. The parking brake ECU 120 repeats the determination processing of Step S21 at a predetermined calculation interval. When the parking brake signal switches from an ON state to an OFF state, namely, when a braking release request

(corresponding to the first braking release request of the present invention) is generated, in Step S22, the parking brake ECU 120 reads a vehicle stop duration Ts indicating how long the vehicle has been stationary until the time point at which the parking brake signal is switched off, and determines whether or not the vehicle stop duration Ts is equal to or more than a set duration TO.

[0069] The parking brake ECU 120 executes one of vehicle stop duration measurement routines illustrated in FIG. 8 and in FIG. 9 in parallel with the parking brake release control routine and the parking brake activation control routine. In Step S22, the parking brake ECU 120 reads the vehicle stop duration Ts at the current point measured in this vehicle stop duration measurement routine. For example, in the vehicle stop duration

measurement routine illustrated in FIG. 8, in Step S41 , the parking brake ECU 120 determines whether or not a vehicle speed V detected by the vehicle speed sensor 95 is zero. When the vehicle speed V is zero, the parking brake ECU 120 increments a timer value representing the vehicle stop duration Ts by one (S42). When the vehicle speed V is not zero, the parking brake ECU 120 clears the timer value representing the vehicle stop duration Ts to zero (S43). The parking brake ECU 120 measures the vehicle stop duration Ts at the current point by repeating the vehicle stop duration measurement routine at a predetermined short calculation interval.

[0070] In the vehicle stop duration measurement routine illustrated in FIG. 8, the vehicle stop duration Ts is set based on the vehicle speed V. However, because it is possible to estimate that the vehicle is maintained in a stationary state when the parking brake is operated, the duration that the parking brake has been continuously operated may also be set as the vehicle stop duration Ts. An example of such a case is the vehicle stop duration measurement routine illustrated in FIG. 9. In this vehicle stop duration measurement routine, in Step S51 , the parking brake ECU 120 determines whether or not the parking brake is currently activated. When the parking brake is currently activated, the parking brake ECU 120 increments the timer value representing the vehicle stop duration Ts by one (S52). When the parking brake is not currently activated, the parking brake ECU 120 clears the timer value representing the vehicle stop duration Ts to zero (S53). The parking brake ECU 120 measures the vehicle stop duration Ts at the current point by repeating the vehicle stop duration measurement routine at a predetermined short calculation interval.

[0071] In addition, as a modified example of the vehicle stop duration measurement routine, although not shown, the vehicle stop duration measurement routine may also be executed by incrementing the timer value representing the vehicle stop duration Ts by one when the vehicle speed V is zero and the parking brake is currently activated, and clearing the timer value representing the vehicle stop duration Ts to zero when the vehicle speed V is not zero, or, when the parking brake is not currently activated.

[0072] The vehicle stop duration Ts is a parameter that is correlated with the temperature of the brake drum 10, and corresponds to a drum

temperature index value of the present invention. Based on this drum temperature index value, whether or not a thermal expansion amount of the brake drum 10 is within a permissible range can be determined. While the vehicle is stopped, frictional heat is not produced between the brake drum 10 and the brake shoes 30. Consequently, when the vehicle is stopped for a longer period, the brake drum 10 is closer to a normal temperature state, and the thermal expansion amount of the brake drum 10 (increase in the drum diameter) can be assumed to be within the permissible range. The set duration TO used in Step S22 is a threshold for determining whether or not the temperature of the brake drum 0 is a temperature that hardly affects setting of the standby position of the brake shoes 30, which is described below. For example, the set duration TO may be set in advance as a time period during which the maximum presumed temperature of the brake drum 10 when the vehicle is traveling normally reduces to a temperature at which the thermal expansion amount is within the permissible range. Further, a normal temperature (e.g., 20°C ±15°C) may be employed as the temperature at which the thermal expansion amount is within the permissible range.

[0073] When the vehicle stop duration Ts is equal to or more than the set duration TO (S22: Yes), in Step S23, the parking brake ECU 120 applies a fixed reverse drive voltage to the motor 60 of the electric actuator 50 to start a reverse drive of the motor 60. Based on this reverse drive of the motor 60, the right and left advancing/retracting rods 82 retract and pull in the shoe web 31.

[0074] While the parking brake is activated, even if the motor 60 is not being driven, the female threads 811 and 812 of the screw member 81 and the male threads 8211 and 8221 of the advancing/retracting rods 82 are jammed against each other in the axial direction by the restorative force of the brake drum 10, namely, the force with which the brake drum 10 pushes back the brake shoes 30. When the motor 60 is driven in reverse from this state, as illustrated in FIG. 16C, in the worm gear mechanism 70, the teeth of the worm 71 strongly push the teeth of the worm wheel 72 in the reverse direction. In this case, the motor 60 causes the worm 71 to rotate against the frictional resistance between the worm 71 and the worm wheel 72, which causes the advancing/retracting rods 82 to retract.

[0075] As the advancing/retracting rods 82 retract, the force with which the brake shoes 30 press against the brake drum 0 (the force with which the brake drum 10 pushes back the brake shoes 30) decreases, which means that the frictional resistance decreases. As this frictional resistance decreases, the motor torque required to move the brake shoes 30 decreases, and the motor current im decreases. For example, when the reverse drive of the motor 60 is started at time t4 in FIG. 15, the motor current im starts to decrease. After time t5, which is the time point at which the brake shoes 30 are separated from the brake drum 10, the female threads 811 and 812 of the screw member 81 and the male threads 8211 and 8221 of the advancing/retracting rods 82 are no longer jammed against each other in the axial direction. As a result, the frictional resistance between the worm 71 and the worm wheel 72 becomes constant, and the motor current im also becomes constant.

[0076] When the reverse drive of the motor 60 starts, in Step S24, the parking brake ECU 120 detects the motor current im detected by the current sensor 92. Then, in Step S25, the parking brake ECU 120 calculates a change gradient Ki of the motor current im with respect to time. The change gradient Ki represents the slope of the motor current im from time t4 in the graph shown in FIG. 15.

[0077] Next, in Step S26, the parking brake ECU 120 determines whether or not the change gradient Ki has shifted from a state in which the change gradient Ki is decreasing to a state in which the change gradient Ki is constant. While the brake shoes 30 are held in contact with the brake drum 10, the motor current im decreases due to the decrease in the frictional resistance between the worm 71 and the worm wheel 72. While the change gradient Ki is decreasing (S26: No), the processing returns to Step S24, and the parking brake ECU 120 repeats the same processing.

[0078] When the change gradient Ki becomes constant as shown in FIG. 15 at time t5 by repeating this processing (S26: Yes), the processing of the parking brake ECU 120 proceeds to Step S27. Time t5 can be estimated as being the time at the instant when the brake shoes 30 are separated from the brake drum 10 (contact has been released). In Step S27, the parking brake ECU 120 starts reading of the rotation angle Θ detected by the rotation angle sensor 91 , and starts measurement of the rotation amount R, which is the amount of subsequent increase in the rotation angle Θ.

Therefore, the rotation angle Θ initially read in Step S27 represents the estimated operation amount (position of the advancing/retracting rods 821 and 822) of the electric actuator 50 at the time point at which the brake shoes 30 are estimated to be separated from the brake drum 10, and thus represents the estimated contact release position of the brake shoes 30. In the following description, the position of the brake shoes 30 specified by the operation amount of the electric actuator 50 at the time point at which the brake shoes 30 are estimated to be separated from the brake drum 10 is referred to as the "contact release position". Next, in Step S28, the parking brake ECU 120 determines whether or not the rotation amount R is equal to or more than a set rotation amount R1 , and waits until the rotation amount R is equal to or more than the set rotation amount R1 .

[0079] When the parking brake ECU 120 determines that the rotation amount R is equal to or more than the set rotation amount R1 (S28: Yes), in Step S29, the parking brake ECU 120 stops the reverse drive of the motor 60, and in Step S30, finishes measurement of the rotation amount R. The set rotation amount R1 is an amount corresponding to a set clearance between the brake shoes 30 and the brake drum 10 when the parking brake is not activated. Therefore, this means that the brake shoes 30 are arranged at a position that the brake shoes 30 have returned to from the contact release position by the set clearance amount (corresponding to the position when the operation amount of the first actuator of the present invention has decreased by a predetermined amount), based on the contact release position where the contact of the brake shoes 30 with the brake drum 10 is estimated to have been released. In this case, because the brake drum 10 is not thermally expanded, and the brake drum 10 has not been deformed by an increased drum diameter because operation of the wheel cylinder 40 is prohibited, the standby position of the brake shoes 30 are at a proper position based on the amount of wear of the lining 33. This processing performed in Steps S24 to S29 serves as clearance adjustment processing of the brake shoes 30.

[0080] Next, in Step S31 , the parking brake ECU 120 reads the switch signal output from the pedal switch 90, and determines whether or not the switch signal is off, namely, whether or not the brake pedal 201 is not in a pressed state. After the parking brake ECU 120 has detected that the switch signal is off, the processing proceeds to Step S32. In Step S32, the parking brake ECU 120 transmits to the main brake ECU 110 a command to permit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels. When the main brake ECU 110 receives the command to permit the supply of hydraulic pressure, the main brake ECU 110 opens the open/close valve for supplying hydraulic pressure to the rear wheels provided in the hydraulic pressure supply circuit 200. Consequently, hydraulic pressure is supplied to the wheel cylinders 40 of the rear wheels based on a brake pedal operation by the driver.

[0081] Further, when the parking brake ECU 120 determines in Step S22 that the vehicle stop duration Ts is less than the set duration TO, namely, when it is determined that there is a possibility that the thermal expansion amount of the brake drum 10 exceeds the permissible range, the processing proceeds to Step S33. In Step S33, the parking brake ECU 120 applies a fixed reverse drive voltage to the motor 60 of the electric actuator 50 to start a reverse drive of the motor 60. Based on this reverse drive of the motor 60, the right and left advancing/retracting rods 82 retract and pull in the shoe web 31.

[0082] When the reverse drive of the motor 60 starts, next, in Step S34, the parking brake ECU 120 starts reading of the rotation angle Θ detected by the rotation angle sensor 91 , and starts measurement of the rotation amount R, which is the amount of subsequent increase in the rotation angle Θ.

Next, in Step S35, the parking brake ECU 120 determines whether or not the rotation amount R is equal to or more than the return rotation amount R0, and waits until the rotation amount R is equal to or more than the return rotation amount R0. The return rotation amount R0 is the rotation amount stored in Step S18 of the immediately prior parking brake activation control routine. In other words, the return rotation amount R0 is the rotation amount by which the motor 60 has been rotated when the parking brake is activated.

[0083] When the parking brake ECU 120 determines that the rotation amount R is equal to or more than the return rotation amount R0 (S35: Yes), the processing proceeds to Step S29, and the parking brake ECU 120 performs the processing described above. Therefore, when the vehicle stop duration Ts is less than the set duration TO, the brake shoes 30 are returned to their original position by rotating the motor 60 in reverse by an amount equal to the rotation amount by which the motor 60 has been rotated in the parking brake activation control routine. In this case, even if the brake drum 10 has thermally expanded, the brake drum 10 is emitting more heat than during activation of the parking brake. Consequently, the contact between the brake shoes 30 and the brake drum 10 can be reliably released.

[0084] After the parking brake ECU 120 transmits the command to permit the supply of hydraulic pressure in Step S32, the parking brake ECU 120 finishes the parking brake release control routine, and starts the

above-mentioned parking brake activation control routine.

[0085] The thus-configured drum brake device according to this

embodiment provides the following advantageous effects.

1. When there is a possibility that the thermal expansion amount of the brake drum 10 exceeds the permissible range, clearance adjustment of the brake shoes 30 (setting of the standby position) is prohibited.

Consequently, the likelihood of over-adjustment occurring can be reduced.

[0086] 2. The time point at which the contact between the brake shoes 30 and the brake drum 10 is released is estimated based on the change gradient of the motor current im. Therefore, estimation of the contact release position can be performed properly and easily. Further, based on the contact release position, the position at which the predetermined clearance (corresponding to R1) is provided between the brake shoes 30 and the brake drum 10 is set as a new standby position. Therefore, the setting of the standby position can be performed properly and easily.

[0087] 3. The vehicle stop duration Ts is used as the drum temperature index value for determining whether or not the thermal expansion amount of the brake drum 10 is within a permissible range. Consequently, a temperature sensor for measuring the temperature of the brake drum 10 is not needed, which enables costs to be reduced.

[0088] 4. Setting of the standby position is performed only during the release operation of the parking brake while the vehicle is stationary.

Setting of the standby position is not performed during activation of the main brake. Consequently, the likelihood of over-adjustment occurring due to deformation of the brake drum 10 (increased drum diameter) and

deformation of the lining 33 (compressive deformation and shear

deformation) can be reduced more. In other words, the setting of the standby position can be performed more properly.

[0089] 5. When setting the standby position during the release operation of the parking brake, activation of the wheel cylinders 40 is prohibited.

Consequently, the likelihood of over-adjustment occurring due to

deformation of the brake drum 10 (increased drum diameter) and

deformation of the lining 33 (compressive deformation and shear

deformation) can be reduced more.

[0090] 6. The drum brake 1 includes the electric actuator 50, which is provided between one end of one of the pair of brake shoes 30 and one end of another thereof and is operated by the parking brake operation, and the wheel cylinder 40, which is provided between another end of one of the pair of brake shoes 30 and another end of another thereof and is operated by the brake pedal operation. Consequently, operation of the parking brake and operation of the main brake can be properly carried out independently. Further, it is not necessary to set the standby position during the main brake operation, the proper standby position can be set, and the likelihood of over-adjustment occurring can be reduced more.

[0091] 7. When there is a possibility that the brake drum 10 has been thermally expanded during the release operation of the parking brake (Ts≥ T0), the position that the brake shoes 30 are returned to is set using the rotation amount R0 of the motor 60 during the immediately prior parking brake activation operation. Consequently, the brake shoes 30 can be reliably returned to their original position, and the contact between the brake shoes 30 and the brake drum 10 can be released.

[0092] 8. A dedicated automatic adjuster is not required, because the electric actuator 50 configured to activate the parking brake is utilized to set the standby position. Consequently, the number of components can be reduced.

[0093] Next, Modified Example 1 of the present invention is described. In the above-mentioned embodiment of the present invention, hydraulic pressure is not supplied to the wheel cylinders 40 of the rear wheels after the parking brake has been set to an activated state. However, in Modified Example 1 , the supply of hydraulic pressure is not prohibited. FIG. 10 illustrates a parking brake activation control routine according to Modified Example 1. FIG. 1 1 illustrates a parking brake release control routine according to Modified Example 1 .

[0094] The parking brake activation control routine according to Modified Example 1 (FIG. 10) omits the processing of Steps S19 and S20 of the parking brake activation control routine of the embodiment (FIG. 6).

Therefore, regardless of whether or not the parking brake is currently activated, when a brake pedal operation is made, hydraulic pressure is supplied to the wheel cylinders 6 and 40 of the front and rear wheels. The parking brake release control routine according to Modified Example 1 (FIG. 1 1) adds the processing of Step S221 between Steps S22 and S23, and omits the processing of Steps S31 and S32, of the parking brake release control routine of the embodiment (FIG. 7).

[0095] In the parking brake release control routine, in Step S221 , the parking brake ECU 120 reads a switch signal output from the pedal switch 90, and determines whether or not the switch signal is off, namely, whether or not the brake pedal 201 is not in a pressed state. The parking brake ECU 120 waits until the switch signal is detected as having been switched off, and then the processing proceeds to Step S23. This means that when the setting processing of the standby position of Steps S23 onwards is to be performed, the wheel cylinder 40 is in a state in which the wheel cylinder 40 is not spreading the brake shoes 30 (is in the non-braking state).

Consequently, the standby position of the brake shoes 30 is set in a state in which there is no deformation of the brake drum 10 (increased drum diameter) or deformation of the lining 33 (compressive deformation and shear deformation). Hence, the standby position can be set properly.

[0096] Next, Modified Example 2 of the present invention is described. In the above-mentioned embodiment of the present invention, the output processing of the prohibition command and the permission command relating to the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels is incorporated into the parking brake activation control routine and the parking brake release control routine. However, in Modified Example 2, the output processing of the prohibition command and the permission command relating to the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels is set in separate routines.

Therefore, in Modified Example 2, the parking brake activation control routine is the same as the processing of Modified Example 1 (FIG. 10), and the parking brake release control routine omits Steps S31 and S32 of the parking brake release control routine of the embodiment.

[0097] The parking brake ECU 120 executes a hydraulic pressure

command control routine illustrated in FIG. 12 in parallel with the parking brake activation control routine or the parking brake release control routine. The parking brake ECU 120 repeatedly executes the hydraulic pressure command control routine at a predetermined calculation interval. When the hydraulic pressure command control routine starts, in Step S61 , the parking brake ECU 120 determines whether or not the vehicle speed V detected by the vehicle speed sensor 95 is zero, namely, whether or not the vehicle is stationary. When the vehicle speed V is not zero (S61 : No), in Step S65, the parking brake ECU 120 transmits to the main brake ECU 110 a command to permit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels. On the other hand, when the vehicle speed V is zero (S61 : Yes), in Step S62, the parking brake ECU 120 reads a switch signal output from the pedal switch 90, and determines whether or not the switch signal is off, namely, whether or not the brake pedal 201 is not in a pressed state. When the switch signal is on, namely, when the brake pedal 201 has been pressed (S62: No), in Step S65, the parking brake ECU 120 transmits to the main brake ECU 110 a command to permit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels.

[0098] On the other hand, when the switch signal is off (S62: Yes), in Step S63, the parking brake ECU 120 determines whether or not the parking brake is currently activated, namely, whether or not the brake shoes 30 are being pressed against the brake drum 10 by the electric actuator 50.

When the parking brake is not currently activated (S63: No), in Step S65, the parking brake ECU 120 transmits to the main brake ECU 110 a command to permit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels. On the other hand, when the parking brake is currently activated, in Step S64, the parking brake ECU 120 transmits to the main brake ECU 110 a command to prohibit the supply of hydraulic pressure to the wheel cylinders 40 of the rear wheels.

[0099] Therefore, in Modified Example 2 as well, similar to the embodiment or Modified Example 1 , the likelihood of over-adjustment occurring can be reduced, because deformation of the brake drum 10 (increased drum diameter) and deformation of the lining 33 (compressive deformation and shear deformation) do not occur when the release operation of the parking brake is performed.

[0100] Next, Modified Example 3 of the present invention is described. In the above-mentioned embodiment of the present invention and Modified Examples 1 and 2, the standby position of the brake shoes 30 is set using the rotation amount R of the motor 60. However, in Modified Example 3, the standby position of the brake shoes 30 is set using the energization time of the motor 60. FIG. 13 illustrates a parking brake activation control routine according to Modified Example 3. FIG. 14 illustrates a parking brake release control routine according to Modified Example 3.

[0101] The parking brake activation control routine according to Modified Example 3 (FIG. 13) performs the same processing as the embodiment, except for performing Step S12' instead of Step S12, Step S17' instead of Step S17, and Step S18' instead of Step S18, of the parking brake activation control routine of the embodiment (FIG. 6).

[0102] When the parking brake signal is on (Step S11 : Yes), in Step S12', the parking brake ECU 120 starts measuring time with an energization timer, and in Step S13, starts a forward drive of the motor 60. Because the processing of Step S12' and Step S13 is performed substantially

simultaneously, the energization timer measures an energization time Ti, which is a duration for which the motor 60 is driven forwardly. When the parking brake ECU 120 confirms that the motor current im has reached the stop setting current istop (S15: Yes), the parking brake ECU 120 stops the forward drive of the motor 60 (S16). Then, in Step S17', the parking brake ECU 120 finishes measuring time with the energization timer. Next, in Step S18', the parking brake ECU 120 stores the energization time Ti measured by the energization timer as a return energization time TiO, and then clears the energization time Ti to zero. This return energization time TiO is stored until the parking brake is released.

[0103] The parking brake release control routine according to Modified Example 3 (FIG. 14) performs the same processing as the embodiment, except for performing Step S27' instead of Step S27, Step S28' instead of Step S28, Step S30 ^* instead of Step S30, Step S34' instead of Step S34, and Step S35' instead of Step S35, of the parking brake release control routine of the embodiment (FIG. 7).

[0104] When the parking brake ECU 120 determines in Step S26 that the change gradient Ki of the motor current im has shifted from a state in which the change gradient Ki is decreasing to a state in which the change gradient Ki is constant, in Step S27', the parking brake ECU 120 starts measuring time with the energization timer. Next, in Step S28', the parking brake ECU 120 determines whether or not the energization time Ti measured by the energization timer is equal to or more than a set energization time Ti1 , and waits until the energization time Ti is equal to or more than the set energization time Ti1. When the energization time Ti is equal to or more than the set energization time Ti1 (S28': Yes), in Step S29, the parking brake ECU 120 stops the forward drive of the motor 60. Next, in Step S30', the parking brake ECU 120 finishes measuring time with the energization timer, and clears the energization time Ti to zero.

[0105] The time measurement with the energization timer is started when the contact between the brake shoes 30 and the brake drum 10 is released. Consequently, the motor load is fixed, and hence the energization time of the motor 60 and the movement distance of the brake shoes 30 are in a stable fixed relationship. Therefore, the position of the brake shoes 30 can be accurately controlled based on the energization time of the motor 60. The set energization time Ti1 is set to the duration that is required for the brake shoes 30 to return just as far as the set clearance from the contact release position, based on the contact release position at which the contact between the brake shoes 30 and the brake drum 10 is released. In other words, the set energization time Ti1 is set to a value corresponding to the set rotation amount R1 of the embodiment. Therefore, the standby position of the brake shoes 30 is a position appropriate to the amount of wear of the lining 33.

[0106] Further, when the parking brake ECU 120 determines in Step S22 that the vehicle stop duration Ts is less than the set duration TO, in Step S33, the parking brake ECU 120 starts a reverse drive of the motor 60.

Next, in Step S34', the parking brake ECU 120 starts measuring time with the energization timer. Then, in Step S35', the parking brake ECU 120 determines whether or not the energization time Ti measured with the energization timer is equal to or more than the return energization time TiO, and waits until the energization time Ti is equal to or more than the return energization time TiO. The parking brake ECU 120 performs the

above-mentioned determination by reading the return energization time TiO stored in Step S18' of the immediately prior parking brake activation control routine.

[0107] When the parking brake ECU 120 determines that the energization time Ti is equal to or more than the return energization time TiO (S35': Yes), the processing proceeds to Step S29, and the parking brake ECU 120 executes the processing described above. Therefore, when the vehicle stop duration Ts is less than the set duration TO, the parking brake ECU 120 causes the motor 60 to rotate in reverse just for the duration for which the motor 60 has been energized in the parking brake activation control routine, thereby returning the brake shoes 30 to their original position.

Consequently, the contact between the brake shoes 30 and the brake drum 10 can be reliably released.

[0108] Modified Example 3 replaces the rotation amount R of the

embodiment with the energization time Ti. However, the rotation amount R of Modified Example 1 may also be replaced with the energization time Ti.

[0109] In the above, the drum brake device of this embodiment and modified examples is described, but the present invention is not limited to the above-mentioned embodiment and modified examples, and various changes are possible within the range not departing from the object of the present invention.

[01 10] For example, in the embodiment, the configuration is employed in which the thermal expansion (temperature state) of the brake drum 10 is estimated based on the length of the vehicle stop duration. However, instead of this, a temperature sensor configured to detect the temperature of the brake drum 10 may be provided, and in Step S22, it may be directly determined whether or not the temperature detected by the temperature sensor is lower than a set temperature (thermal expansion determination temperature).

[01 1 1 ] Further, in the embodiment, the configuration is employed in which the time point at which the contact between the brake shoes 30 and the brake drum 10 is released is estimated based on the change gradient of the motor current im. However, instead of this, for example, a pressure sensor may be provided in the advancing/retracting rods 821 and 822 and the like, and the time point at which the contact between the brake shoes 30 and the brake drum 10 is released may be estimated based on a detection value detected by the pressure sensor.

[01 12] In addition, in Step S22 of the embodiment, it is determined whether or not the vehicle stop duration Ts is equal to or more than the set duration TO. However, instead of this, for example, it may be determined whether or not a braking release is the first braking release after the ignition switch is turned on. This is because during the period for which the ignition switch is turned off, there is a high likelihood that the brake drum 10 has cooled down. Therefore, if the braking release is the first braking release after the ignition switch is turned on, this means that the thermal expansion amount of the brake drum 10 is within a permissible range, and hence over-adjustment due to thermal expansion of the brake drum 10 is less likely to occur.

[01 13] Still further, the drum brake of this embodiment includes the electric actuator 50 and the wheel cylinder 40. However, the drum brake of this embodiment may be configured to activate the main brake with the electric actuator 50, or, to activate the main brake and the parking brake with the electric actuator 50, without including the wheel cylinder 40. In this case, based on a signal output from an operation amount detection sensor configured to detect an operation amount of the brake pedal 201 , the electric actuator 50 may be configured to control energization of the motor 60 of the electric actuator 50, and to set the standby position of the brake shoes 30 on condition that it has been determined based on the drum temperature index value that the thermal expansion amount of the brake drum 10 is within the permissible range.

[01 14] Still even further, in the embodiment, the drum brake 1 including the electric actuator 50 is included in the rear wheels. However, the drum brake 1 may be included in both the front and the rear wheels.

[01 15] Moreover, in the embodiment, the hydraulic wheel cylinder 40 is included as the second actuator. However, instead of the wheel cylinder 40, a pneumatic actuator or an electrically operated actuator similar to the electric actuator 50 may be provided.

[Reference Signs List]

[01 16] 1 ... drum brake, 10 ... brake drum, 20 ... backing plate, 30 ... brake shoe, 31 ... shoe web, 32 ... shoe rim, 33 ... lining, 40 ... wheel cylinder, 50 ... electric actuator, 60 ... motor, 70 ... worm gear mechanism, 71 ... worm, 72 ... worm wheel, 80 ... screw drive mechanism, 81 ... screw member, 82 ... advancing/retracting rod, 90 ... pedal switch, 91 ... rotation angle sensor, 92 ... current sensor, 93 ... parking brake operation switch, 94 ... shift position sensor, 95 ... vehicle speed sensor, 100 ... brake ECU, 1 10 ... main brake ECU, 120 ... parking brake ECU, 200 ... hydraulic pressure supply circuit, 201 ... brake pedal