Electric brake system

An electric brake system includes a plurality of electric brake devices. A control device of each electric brake device includes: an abnormality determination section that determines whether there is abnormality in supply of power from a power supply device to the electric brake device; and a redundant function control section that, when the abnormality determination section has determined that there is abnormality in supply of power, controls the braking force by using an auxiliary power supply in accordance with a predetermined condition. The redundant function control section controls the braking force by using the auxiliary power supply at least when a desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section has determined that there is no abnormality in supply of power, as the predetermined condition.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electric brake system including a plurality of electric brake devices, and particularly to a technique that can provide a redundant function and ensure a mounting space for an auxiliary power supply through a limited use of the auxiliary power supply.

Description of Related Art

Regarding electric brake devices, the following techniques have been proposed.

1. A technique of converting rotary motion of a motor into linear motion through a linear motion mechanism, by stepping on a brake pedal, to press a brake pad against a brake disc and bring the brake pad into contact with the brake disc, thereby applying a braking force (Patent Document 1).

2. An electric linear actuator in which a planetary roller screw mechanism is used (Patent Document 2).

RELATED DOCUMENT

Patent Document

For electric brake systems in which electric brake devices are used as in Patent Documents 1 and 2, an improvement in power supply system redundancy is a significant issue. Mainly, there are two possible methods to solve this issue: one is to provide an auxiliary power supply separate from a main power supply, and the other is to multiplex a transmission system from the main power supply. As for multiplexing of the transmission system, in general, a thicker harness may be required to ensure the rated motor current of the electric brake devices, so that it may be difficult to multiplex the transmission system in terms of an increased number of assembly process, a cost issues for the harness, and a wiring space.

On the other hand, in the case of providing the auxiliary power supply separate from the main power supply, a complete redundant power supply system can be configured on a brake caliper of a disk brake by providing a motor, a control device for the motor, and an auxiliary power supply all on the brake caliper, for example. In general, the main power supply of a vehicle is often formed by a battery with a high energy density, which may pose the problems of a low resistance to charge/discharge cycles, a low current density during charge/discharge, etc. For example, these problems can be expected to be solved by forming the auxiliary power supply by a capacitor. However, in the case of using the auxiliary power supply, the mounting space for the auxiliary power supply may be limited, which may make it difficult to store a large amount of energy.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electric brake system that is provided with a power supply system redundancy and can increase the degree of freedom in the mounting space for components thereof.

Hereinafter, in order to facilitate understanding of the present invention, the present invention will be described with reference to the reference numerals in embodiments for the sake of convenience.

An electric brake system according to the present invention includes a plurality of electric brake devices, the electric brake devices each including a brake rotor8, a friction member9that is to be brought into contact with the brake rotor8, a friction member operator6configured to bring the friction member9into contact with the brake rotor8, an electric motor4that drives the friction member operator6, and a control device2that controls a braking force by controlling the electric motor4, wherein

a main power supply device3that supplies power to the respective electric motors4and the respective control devices2included in the electric brake devices is provided, and each of the electric brake devices is provided with an auxiliary power supply18that stores therein power supplied from the main power supply device3and supplementarily supplies power to at least the electric motor4of the electric brake device,

each of the control devices2of the electric brake devices includes:

an abnormality determination section26that determines whether there is abnormality in supply of power from the power supply device to the electric brake device; and

a redundant function control section27that, when the abnormality determination section26has determined that there is abnormality in supply of power from the power supply device3to the electric brake device, controls the braking force by using the auxiliary power supply18in accordance with a predetermined condition,

the redundant function control section27controls the braking force by using the auxiliary power supply18when at least a basic condition is satisfied as the predetermined condition, the basis condition being a condition that a desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section26has determined that there is no abnormality in supply of power.

The “desired braking force” is an actual braking force that is output in accordance with the braking force required by an operator of the vehicle. Each of the “predetermined condition” and the “desired braking force ” is determined on the basis of the result of an experiment, simulation, or the like.

With this configuration, normally, the main power supply device3supplies power to the electric motor4and the control device2. In a state in which the power is supplied, the control device2controls the electric motor4so as to provide an appropriate braking force in accordance with, for example, an instruction from a host control device17. At this time, power from the main power supply device17is supplied to and stored in the auxiliary power supply18.

The abnormality determination section26determines whether there is abnormality in supply of power from the power supply device3to the electric brake device. When the abnormality determination section26has determined that there is abnormality in supply of power to the electric brake device, the redundant function control section27controls the braking force by using the auxiliary power supply18in accordance with the predetermined condition.

The redundant function control section27controls the braking force by using the auxiliary power supply18when at least a basic condition is satisfied as the predetermined condition. The basic condition is a condition that a desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section26has determined that there is no abnormality in supply of power. By providing the auxiliary power supply18in addition to the main power supply device3in the electric brake system in this manner, it is possible to achieve a redundant function of the power supply system, compared with the electric brake system including no auxiliary power supply.

Furthermore, the use of the auxiliary power supply18is limited to a case where the function of the electric brake system as a whole is reduced to a level lower than a predetermined level. Accordingly, a battery smaller than a battery commonly used for a vehicle, or a capacitor can be adopted as the auxiliary power supply18, for example. Because of the limited use of the auxiliary power supply18, it is possible to achieve a size reduction for the auxiliary power supply18, and increase the degree of freedom in the mounting space of the auxiliary power supply18to the vehicle. Consequently, it is possible to increase the degree of freedom in design.

The redundant function control section27may use the auxiliary power supply18such that the turning acceleration of a vehicle equipped with the electric brake system is less than or equal to a predetermined value, as the predetermined condition, in addition to that the basic condition that a desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section has determined that there is no abnormality in supply of power, in other words, the basic condition that the deceleration in a front-rear direction caused by all the electric brake devices for which it is determined that there is no abnormality is less than or equal to a threshold, is at least satisfied.

Each of the “predetermined value” and the “threshold” is determined on the basis of the result of an experiment, simulation, or the like.

When the braking force required by the operator of the vehicle is increased, for example, when a brake pedal or brake instruction device19is strongly depressed in a state in which the abnormality determination section26has determined that there is abnormality in supply of power to the electric brake device corresponding to any one of a plurality of wheels, a sufficient braking force may not be provided by only the other electric brake devices. By using the auxiliary power supply18in this case, it is possible to achieve a desired braking force corresponding to the required braking force. To ensure the stability of the vehicle attitude, it is preferable in this case that the auxiliary power supply18is used such that the turning acceleration of the vehicle is less than or equal to the predetermined value.

The redundant function control section27may change a threshold of deceleration in a front-rear direction on the basis of a correlation in which the threshold of deceleration in the front-rear direction increases with an increase in a value of a braking force required by an operator of the vehicle. By changing the threshold of deceleration in the front-rear direction in this manner, the frequency of use of the auxiliary power supply18can be limited in detail.

A vehicle speed estimator30configured to estimate a traveling speed of a vehicle or vehicle speed equipped with the electric brake system may be provided, and the redundant function control section27may use the auxiliary power supply18when, in addition to that the basic condition is satisfied, a condition that the vehicle speed estimated by the vehicle speed estimator30is greater than or equal to a predetermined vehicle speed is satisfied as the predetermined condition.

The “predetermined vehicle speed” is determined on the basis of the result of test, simulation, or the like.

Even when the abnormality determination section26determines that there is abnormality in supply of power to the electric brake device corresponding to any one of the wheels, no turning acceleration occurs to the vehicle, for example, when the vehicle is in a stopped state or at stoppage. Therefore, the auxiliary power supply18is used when a condition that the vehicle speed estimated by the vehicle speed estimator30is greater than or equal to the predetermined vehicle speed is satisfied. By using the auxiliary power supply18in a limited manner in this way, it is possible to achieve a size reduction for the auxiliary power supply18.

The redundant function control section27of the electric brake device for which it is determined that there is abnormality in supply of power may determine whether or not to use power of the auxiliary power supply18, on the basis of sensing information of all the electric brake devices for which there is no abnormality in supply of power.

DESCRIPTION OF EMBODIMENTS

An electric brake system according to an embodiment of the present invention will be described with reference toFIGS. 1 to 7. As shown inFIG. 1, the electric brake system includes a plurality of electric brake devices FL, FR, RL, and RR, a main power supply device3, and a host ECU17. Each of the electric brake devices FL, FR, RL, and RR includes an electric brake actuator1, a control device2, and an auxiliary power supply18. In this example, control devices2respectively corresponding to the wheels of a four-wheeled vehicle are provided. The electric brake actuator1will be described first.

As shown inFIG. 2, the electric brake actuator1includes an electric motor4, a speed reduction mechanism or speed reducer5that reduces the speed of rotation (number of rotation per unit time) of the electric motor4, a linear motion mechanism (friction member operator)6, a parking brake mechanism7serving as a parking brake, a brake rotor8, and a friction member9. The electric motor4, the speed reduction mechanism5, and the linear motion mechanism6are incorporated in, for example, a housing (not shown) or the like. The electric motor4is constituted by a three-phase synchronous motor or the like.

The speed reduction mechanism5reduces the speed of rotation of the electric motor4and transmits the rotation to a rotation shaft10of the linear motion mechanism6, and includes a primary gear12attached to a rotor shaft4aof the electric motor4, an intermediate gear (secondary gear)13, and a tertiary gear11fixed to an end portion of the rotation shaft10. In this example, the speed reduction mechanism5reduces, by the intermediate gear13, the speed of rotation of the primary gear12, and allows the rotation to be transmitted to the tertiary gear11.

The linear motion mechanism6serving as the friction member operator converts the rotary motion that is output from the speed reduction mechanism5into linear motion of a linear motion portion14by using a feed screw mechanism, and brings the friction member9into contact with the brake rotor8or separates the friction member9from the brake rotor8. The linear motion portion14is supported so as to be prevented from rotating and be movable in an axial direction indicated by an arrow A1. The friction member9is provided at an outboard-side end of the linear motion portion14. As a result of rotation of the electric motor4being transmitted to the linear motion mechanism6through the speed reduction mechanism5, the rotary motion is converted into the linear motion, which is then converted into a pressing force of the friction member9, thereby generating a braking force. Here, a side of each of the electric brake devices FL, FR, RL, and RR (FIG. 1) that is located on the outer side of a vehicle when each device is mounted to the vehicle is referred to as “outboard side”, and a side thereof located on the center side of the vehicle is referred to as “inboard side”.

For example, a linear solenoid is adopted as an actuator16of the parking brake mechanism7. The parking brake mechanism7moves a lock member (solenoid pin)15forward by the actuator16, and causes the lock member15to be fitted into a locking hole (not shown) formed on the intermediate gear13so as to be engaged with the locking hole, thereby preventing the intermediate gear13from rotating. Thus, the parking brake mechanism7enters a parking lock state. The parking brake mechanism7causes the lock member15to be removed from the locking hole, thereby allowing the intermediate gear13to rotate. Thus, the parking brake mechanism7enters an unlock state.

As shown inFIG. 1, to the control devices2of the respective electric brake devices FL, FR, RL, and RR, the main power supply device3and the host ECU17serving as host control unit of the control devices2are connected. Note that the host ECU is also referred to as “VCU”. For example, an electric control unit that performs overall control of the vehicle is adopted as the host ECU17. The host ECU17has the function of performing integrated control of the electric brake devices FL, FR, RL, and RR. The main power supply device3supplies power to the electric motor4(FIG. 2) and the control device2included in each of the electric brake devices FL, FR, RL, and RR. For example, a 12-V battery mounted to the vehicle is used as the power supply device3.

FIG. 3is a block diagram of a control system of the electric brake system. In response to an output from a sensor (not shown) that varies according to, for example, an operation amount (required value of braking force) of a brake pedal19(FIG. 1) operated by the operator of the vehicle, the host ECU17outputs a braking force target value to each of the control devices2of the electric brake devices by using a LUT (Look Up Table) implemented by software or hardware, or a predetermined transform function contained in a library of software or its hardware equivalent, etc., (hereinafter referred to as “implementation model”). The distribution ratio of the braking force target values to the respective electric brake devices may be, for example, a fixed ratio, or a variable ratio based on motion and/or attitude of the vehicle that are estimated from information from on-vehicle sensors such as an acceleration sensor and specifications of the vehicle equipped with the electric brake devices.

Each of the control devices2includes a calculator20, a motor driver21, a switch22, an anti-backflow mechanism section23, and a current sensor24. For example, the calculator20is a processor such as a microcomputer, or a hardware module such as an ASIC. The calculator20includes a control calculation function section25, an abnormality determination section26, and a redundant function control section27.

Among them, the control calculation function section25controls the electric motor4via the motor driver21so as to provide an appropriate braking force, on the basis of the braking force target value from the host ECU17and sensing information from the electric brake actuator1. Specifically, the control calculation function section25is configured by a hardware circuit or a software function on a processor (not shown) capable of, in response to an input of the braking force target value, sensing information and the like, calculating an instruction to the motor driver21, such as an on/off command to a switching element described later, and outputting the instruction by using the above-described implementation model, or a comparison function or its hardware equivalent, etc. The motor driver21converts the DC power of the power supply device3into a three-phase AC power used for driving the electric motor4. For example, the motor driver21may be a half-bridge circuit or a full-bridge circuit in which a switching element such as a FET (field effect transistor) or an IGBT (insulated gate bipolar transistor), a snubber capacitor or the like is used.

Examples of the sensing information include: a motor current value detected by a current detector Sa; and a rotor angle of the motor4that is estimated by rotation angle an estimator Sb. For example, the current detector Sa may be a current sensor, or may estimate the motor current value from motor specifications such as previously measured inductance value, resistance value, or the like, and a motor voltage. For example, the rotation angle estimator Sb may be an angle sensor such as a magnetic encoder or a resolver, or may estimate a motor angle from the aforementioned motor specifications and a motor voltage by using physical equations.

The abnormality determination section26of the calculation section20determines whether there is abnormality in supply of power from the power supply device3to the electric brake device. The abnormality determination section26determines not only abnormality of the power supply device itself but also abnormality such as breakage of a power supply harness extending from the power supply device3. The current sensor24is provided on the upstream side in the power supply direction of a power line extending from the main power supply device3to each of the control devices2. Power lines28are respectively provided in a first path28aextending from the power supply device3through the current sensor24, the anti-backflow mechanism section23, and the switch22to the calculator20and the auxiliary power supply18, a second path28bextending from a position between the anti-backflow mechanism section23and the switch22to the motor driver21, and a third path28cextending from the motor driver21to the electric motor4.

For example, a diode can be used as the anti-backflow mechanism section23which is provided in order to use regenerated power of the electric motor4to charge the auxiliary power supply18without returning the regenerated power to the power supply device3. When the abnormality determination section26determines that there is no abnormality, the calculator20can supply the regenerated power of the electric motor4to the auxiliary power supply18by keeping the switch22on. For example, the abnormality determination section26turns the switch22off when determining whether there is abnormality in supply of power. Then, in this switch-off state, the abnormality determination section26performs the determination, for example, by comparing the current value detected by the current sensor24with a threshold stored in storage portion (not shown) included in the calculator20. That is, specifically, the abnormality determination section26is configured by a hardware circuit or a software function on a processor (not shown) capable of, in response to an input of the current value detected by the current sensor24, performing the power supply abnormality determination described above and outputting a result of the determination including opening and closing instructions to the switch22, by using the above-described implementation model, or a comparison function or its hardware equivalent, etc.

When the abnormality determination section26has determined that there is abnormality in supply of power from the power supply device3to the electric brake device, the redundant function control section27controls the braking force by using the auxiliary power supply18in accordance with a predetermined condition. The redundant function control section27controls the braking force by using the auxiliary power supply18in accordance with, as the predetermined condition, a basic condition that at least a desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section26has determined that there is no abnormality in supply of power. In this case, all the other electric brake devices for which there is no abnormality in supply of power transmit their own operating states to the electric brake device for which the abnormality determination section26has determined that there is abnormality in supply of power. The sensing information can be used as the operating state.

The calculator20of the electric brake device to which the sensing information has been transmitted and for which there is abnormality in supply of power determines, by the redundant function control section27of the calculator20, whether or not to operate this electric brake device by using the auxiliary power supply18. In this case, the redundant function control section27may determine whether or not to use the power from the auxiliary power supply18while observing the state of the function of the electric brake system as a whole from the operating states of all the other electric brake devices. For example, a capacitor or a battery smaller than a battery commonly used for a vehicle may be adopted as the auxiliary power supply18.

FIG. 4is a diagram showing a usage example of the auxiliary power supply18of the electric brake system. Hereinafter, a description will be given also with reference toFIG. 3as needed. In the statements within the auxiliary power supply18inFIG. 4, “normal” indicates a state in which the auxiliary power supply18is connected to the power supply device3, “invalid” indicates a state in which the auxiliary power supply18is disconnected from the electric motor4(FIG. 3) without being connected to the power supply device3(the state in which the switch22inFIG. 3is off), and “valid” indicates a state in which the power supply device3is not connected, and the auxiliary power supply18is connected (the state in which the switch22inFIG. 3is turned on). The “invalid” and the “valid” indicate that there is abnormality in supply of power, the electric brake, or the like.

Referring to chart (a) ofFIG. 4, a power supply harness connected from the power supply device3to a part of the electric brake devices, in this embodiment, the electric brake device FL (corresponding to the left-front wheel in this example) has been broken, and the abnormality determination section26determines that abnormality has occurred in supply of power, on the basis of the current value detected from the current sensor24. However, at this stage, a predetermined braking force can be output by using the electric brake devices FR, RL, and RR corresponding to the other wheels (in this example, the right-front wheel, and the left- and right-rear wheels). Therefore, the redundant function control section27of the electric brake device FL in which abnormality has occurred does not use the auxiliary power supply18.

As shown in chart (b) ofFIG. 4, in the case where abnormality has occurred in, for example, the calculator20for another electric brake device RL (corresponding to the left-rear wheel in this example), following the state shown in chart (a) ofFIG. 4, the sensing information indicating the operating state of the electric brake device RL and the sensing information of the other normal electric brake devices FR and RR are transmitted to the above-mentioned part of the electric brake devices, in this embodiment, the electric brake device FL. In this case, braking is performed by using only the normal electric brake devices FR and RR, so that a turning acceleration for a right-hand turn in the drawing inevitably occurs. Therefore, the redundant function control section27of the electric brake device FL corresponding to the left-front wheel determines to use the auxiliary power supply18of the electric brake device FL, and makes the auxiliary power supply18“valid”, thereby performing braking using the three electric brake devices FL, FR, and RR.

In the state shown in chart (a) ofFIG. 4in which the power line28connected to the electric brake device FL corresponding to the left-front wheel has been merely broken, if the braking force required by the operator of the vehicle is increased, for example, when the brake pedal19(FIG. 1) is strongly depressed, a sufficient braking force may not be provided by only the right-front wheel FR and the left- and right-rear wheels RL, RR. Therefore, at least, the redundant function control section27of the electric brake device FL in which abnormality has occurred makes the auxiliary power supply18valid so as to cause the electric brake device FL to generate a braking force such that the turning acceleration of the vehicle is less than or equal to a predetermined value (for example, when the turning acceleration of the vehicle has exceeded a predetermined value), in addition to satisfying that the basic condition that the desired braking force cannot be output even with all the electric brake devices for which the abnormality determination section26has determined that there is no abnormality in supply of power, in other words, the basic condition that the deceleration in the front-rear direction caused by the electric brake devices FR, RL, and RR of the right-front wheel, and the left- and right-rear wheels for which it is determined that there is no abnormality is less than or equal to a threshold.

At this time, the respective decelerations in the front-rear direction are calculated by the respective calculators20on the basis of the sensing information of the corresponding electric brake devices FR, RL, and RR, and then transmitted via the host ECU17to the calculator20of the electric brake device FL that is the target to be controlled. The redundant function control section27of the calculator20that has received the transmission may determine whether or not to make the auxiliary power supply18valid by using a threshold that is variable depending on the braking force such that the auxiliary power supply18of the electric brake device FL is made valid in such a case where the required braking force is increased. A correlation in which the threshold of deceleration in the front-rear direction increases with an increase in the value of the braking force required by the operator of the vehicle is stored, for example, in the storage portion (not shown) of the calculator20. The redundant function control section27may change the threshold of deceleration in the front-rear direction on the basis of the correlation stored in the storage portion. By changing the threshold of deceleration in the front-rear direction in this manner, the frequency of use of the auxiliary power supply18can be limited.

Specifically, the redundant function control section27described thus far is configured by a hardware circuit or a software function on a processor (not shown) capable of, in response to a result of the abnormality determination performed by the abnormality determination section26, determining whether or not to operate the electric brake device by using the auxiliary power supply18and of operating the auxiliary power supply18on the basis of the result by using the above-described implementation model, or a comparison function or its hardware equivalent, etc. Specifically, the redundant function control section27further includes a hardware circuit or a software function on a processor (not shown) capable of changing the threshold of deceleration in the front-rear direction on the basis of the correlation by using the above-described implementation model, or a comparison function or its hardware equivalent, etc.

As shown inFIG. 5, all braking force is lost when abnormality occurs in the main power supply device3. Accordingly, if the abnormality determination section26of each of the control devices2of the electric brake devices FL, FR, RL, and RR of the four wheels determines that there is abnormality in the power supply device3, the redundant function control section27of each of the control devices2immediately makes their own auxiliary power supply18valid so as to perform braking according to the required braking force.

FIG. 6is a diagram showing an operation example of the electric brake system. The drawing shows an operation example in the examples shown in charts (a) and (b) ofFIG. 4. A description will be given also with reference to charts (a) and (b) ofFIG. 4andFIG. 3as needed. Braking is started by the control calculation function section25controlling the electric motor4on the basis of the braking force target value corresponding to the required braking force, and the sensing information. It is assumed that power line abnormality such as the above-described harness breakage has thereafter occurred in the electric brake device FL corresponding to the left-front wheel.

At that time, the electric brake device FL can be driven by using the auxiliary power supply18. However, braking can be performed by using the other electric brake devices FR, RL, and RR to which the power supply system is normally connected, and therefore, the electric brake device FL is not used (time t1in the drawing). It is preferable that the braking forces of the electric brake devices FR, RL, and RR at this time are determined under a constraint that the yaw rate, which is the turning acceleration that occurs to the vehicle, is less than or equal to a predetermined value. For example, the yaw rate is detected by a yaw rate sensor29(FIG. 3).

It is assumed that, for example, abnormality of the calculator20has thereafter occurred in the electric brake device RL corresponding to the left-rear wheel. At that time, it is difficult to perform braking only by using the electric brake devices FR and RR in the right column in chart (b) ofFIG. 4as described above, while keeping the yaw rate at a value less than or equal to the predetermined value. Therefore, the auxiliary power supply18of the electric brake device FL of the left-front wheel is used to perform braking by using the electric brake devices FL, FR, and RR (time t2). After the vehicle has subsequently stopped, a yaw rate is unlikely to occur except under a condition such as an extreme sloping has occurred. According to this reason, the usage of the electric brake device FL is suspended thereafter in order to conserve the capacity of the auxiliary power supply18(time t3), and the stopped state is maintained by the electric brake devices FR and RR in the right column.

FIG. 7is a diagram showing another operation example of the electric brake system.FIG. 7shows an operation example in which a condition that the required braking force is less than or equal to a predetermined value is set in the example shown in chart (a) ofFIG. 4. It is assumed that power line abnormality such as the harness breakage has occurred in the electric brake device FL after start of braking. The electric brake system is operated in the same manner as that inFIG. 6until the occurrence of abnormality.

Thereafter, the required braking force is increased, and when it is determined that a sufficient braking force cannot be provided by only the other electric brake devices FR, RL, and RR, the electric brake device FL is used by using the auxiliary power supply18(time t4). At that time, it is possible to achieve a brake balance that can minimize the power required by the electric brake device FL in which abnormality has occurred. After the vehicle has stopped subsequently, the usage of the electric brake device FL is suspended in order to conserve the capacity of the auxiliary power supply18, and the stopped state is maintained by the other electric brake devices RL, FR, and RR (time t5).

With the electric brake system described thus far, normally, the main power supply device3supplies power to the electric motor4and the control device2. The control device2controls the electric motor4so as to provide an appropriate braking force, on the basis of the braking force target value from the host ECU17and the sensing information from the electric brake actuator1. At this time, power is supplied to and stored in the auxiliary power supply18from the main power supply device3. In addition, the regenerated power of the electric motor4may be supplied to the auxiliary power supply18.

When the abnormality determination section26has determined that the supply of power to the electric brake device is abnormal, the redundant function control section27controls the braking force by using the auxiliary power supply18in accordance with the predetermined condition. When at least a desired braking force cannot be output even with all the electric brake devices for which it is determined that there is no abnormality in supply of power, the redundant function control section27controls the braking force by using the auxiliary power supply18, as the predetermined condition. By providing the auxiliary power supply18in the electric brake system in addition to the main power supply device3in this manner, it is possible to provide a redundant function for the power supply system.

Furthermore, the use of the auxiliary power supply18is limited to a case where the function of the electric brake system as a whole is reduced to a level lower than a predetermined level. Accordingly, a battery smaller than a battery commonly used for a vehicle, or a capacitor can be adopted as the auxiliary power supply18, for example. Because of the limited use of the auxiliary power supply18, it is possible to achieve a size reduction for the auxiliary power supply18, and increase the degree of freedom in the mounting space of the auxiliary power supply18to the vehicle. Consequently, it is possible to increase the degree of freedom in design.

Another embodiment will now be described. In the following description, the components corresponding to the matters described in each of the preceding embodiments are denoted by like reference numerals, and any redundant description has been omitted. When only a part of a configuration is described, the other part of the configuration is the same as described in the preceding description unless otherwise specified. The same operation and effect can be obtained from the same configuration. A combination of parts that are specifically described in the embodiments can be implemented, and, further, the embodiments may be partially combined unless such combinations cause any problem.

As shown inFIG. 8, one control device2and one auxiliary power supply18may be provided for two electric brake actuators1,1corresponding to the left- and right-front wheels, and one control device2and one auxiliary power supply18may be provided for two electric brake actuators1,1corresponding to the left- and right-rear wheels.

Although both of the configurations inFIG. 1andFIG. 8show an example in which the auxiliary power supply18is provided in all the electric brake devices, the auxiliary power supply18may be provided only some of the electric brake devices. For example, generally, the front brake generally exerts a braking force that is twice the braking force exerted by the rear brake in a four-wheeled automobile. Therefore, the auxiliary power supply18may be provided only in the front electric brake device so as to achieve redundancy.

At the time of determining whether there is abnormality in supply of power from the power supply device3to the electric brake device, the supply state of power may be monitored by the host ECU17without using the current sensor24, and the information being monitored may be transmitted to the calculator20. In this case, the abnormality determination section26of the calculator20may determine whether there is abnormality in supply of power by checking the information provided from the host ECU17against a predetermined relation stored in the storage portion or the like.

For example, no turning acceleration occurs to a vehicle in the stopped state. Therefore, the auxiliary power supply18may be used only when the vehicle speed is greater than or equal to a predetermined vehicle speed. Specifically, as shown inFIG. 3, the vehicle speed estimator30that estimates a traveling speed of a vehicle equipped with the electric brake system may be provided, and the redundant function control section27may use the auxiliary power supply18when a condition that the vehicle speed estimated by the vehicle speed estimator30is greater than or equal to a predetermined vehicle speed is satisfied as the predetermined condition. Alternatively, it is possible to use a process, for example, in which an electric brake device on the front side having a braking force larger than that of the electric brake device on the rear side is used preferentially.

REFERENCE NUMERALS