Disk brake apparatus

A disk brake apparatus in which a determination is made as to whether a centering operation should be performed, and operation conditions for the centering operation (the length of the interval and the number of the operations) are set, according to a change of deformation of a disk rotor by heat release over time. When the centering operation is performed, a solenoid is actuated to perform the centering operation according to the set operation conditions. The centering operation is an operation of moving a pair of brake pads (2) and (3) into contact with the disk rotor (1) and then separating the pads from the disk rotor during a cooling process while a vehicle is running.

BACKGROUND OF THE INVENTION

The present invention relates to a disk brake apparatus for use in braking of a vehicle.

FIG. 14shows states of clearances between brake pads and a disk rotor of a disk brake apparatus used in a vehicle of a first related art of the present invention. As shown inFIG. 14, during braking, the temperature of the disk rotor1used in the disk brake apparatus of the first related art increases due to contact of the disk rotor1with the brake pads2and3[hereinafter the right pad inFIG. 14(A)is also referred to as “inner pad2”, and the left pad inFIG. 14(A)is also referred to as “outer pad3”], and tilting of a braking surface, i.e., thermal gradient may occur [FIG. 14(A)], although the braking surface is perpendicular to an axis of the disk at normal temperature. In this case, upon stop of the braking operation, clearances are generated based on the position of the thermal gradient [FIG. 14(B)]. After a certain time has passed, the disk rotor1returns to the normal state or recovers from the thermal gradient [FIG. 14(C)]. Immediately after the braking operation is stopped [FIG. 13(B)], the clearance between the disk rotor1and the inner pad2is substantially equal to that between the disk rotor1and the outer pad3. However, when the disk rotor1recovers from the thermal gradient [FIG. 14(C)], the clearances are different [see the solid line inFIG. 14(C)]. If the vehicle continues to run with the brake rotor1that has recovered from the thermal gradient in this way, so-called one-side wear may occur, leading to generation of disk thickness variation (DTV) of the disk rotor1. The thickness variation may cause occurrence of judder (Brake Judder; hereinafter referred to as “judder”).

As disk brake apparatuses aiming to solve this problem, for example, there are known disk brake apparatuses disclosed in Japanese Patent Application Public Disclosure No. 2006-307994 (hereinafter referred to as “patent document 1”), and Japanese Patent Application Public Disclosure No. 2000-46082 (hereinafter referred to as “patent document 2”). In the disk brake apparatus disclosed in patent document 1, the clearance is adjusted so that the clearance is expanded to satisfy the equation (clearance)>(axial displacement distance+surface run-out).

As mentioned above, in the disk brake apparatus disclosed in patent document 1, the problem caused by the thermal gradient of the rotor is solved by expanding the clearance. However, the expansion of the clearance in the apparatus of patent document 1 causes various negative effects (nega) such as impaired responsiveness, deteriorated pedal feeling, rattle generation, and decreased cleanablility. Due to the presence of these negative effects, it is sometimes undesirable or impossible to employ the apparatus of patent document 1 under present circumstances.

In the disk brake apparatus disclosed in patent document 2, it is possible to prevent negative effects, which would otherwise be caused by expanding the clearance as mentioned above, by performing a clearance minimizing control. However, the disk brake apparatus disclosed in patent document 2 still has a drawback; that is, although it is possible to prevent negative effects which would otherwise be caused by expanding the clearance, a self-cleaning operation is regularly performed in this apparatus, whereby a change of temperature of a rotor is induced, which leads to an increase in thermal gradient, causing an adverse effect.

SUMMARY OF THE INVENTION

The present invention has been contrived in consideration of the above-described circumstances, and an object thereof is to provide a disk brake apparatus in which the problem associated with thermal gradient, and therefore judder occurrence can be effectively prevented.

The present invention is provide a disk brake apparatus, wherein: a brake pad is moved by actuating an actuator so that the brake pad is pressed against a disk rotor to generate a braking force; and the disk brake apparatus comprises a controller adapted to control the actuator to cause the brake pad to be moved into contact with the disk rotor, and then be separated from the disk rotor so that a pad clearance is adjusted according to a change of deformation of the disk rotor by heat release over time after the braking force is generated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a disk brake apparatus of a first embodiment of the present invention will be described with reference toFIGS. 1 to 3.

As shown inFIG. 1, a disk brake apparatus5generally comprises a floating caliper type disk brake6, an ACC control booster (Adaptive Cruise Control control booster)8, a master cylinder (hereinafter referred to as “MC”)10, and an automatic brake system13. The ACC control booster8is adapted to amplify a force of pressing of a brake pedal7and output the amplified force, or is adapted to generate an output using a solenoid9(actuator), independently of the force of pressing of the brake pedal7. The MC10is adapted to generate a hydraulic pressure according to the amplified output of the force of pressing of the brake pedal7, or by the output that the ACC control booster8generates using the solenoid9(actuator). An ABS (Anti-lock Brake System) and a VDC (Vehicle Dynamics Control System) are incorporated in the automatic brake system13which is disposed between the MC10and a hydraulic pressure chamber12of a caliper11of the disk brake6.

The disk brake6comprises a pair of brake pads2and3(hereinafter the right and left brake pads inFIG. 1are also referred to as “inner pad2” and “outer pad3”, respectively) disposed on the respective sides of a disk rotor1(hereinafter also referred to as “rotor”) attached to a wheel shaft24, and the caliper11adapted to generate a braking force by pressing the pair of brake pads2and3against the respective surfaces of the disk rotor1. The caliper11generally comprises a cylinder portion14facing the inner pad2, and a claw portion15extending from the cylinder portion14to the opposite side of the disk rotor1so as to straddle the disk rotor1. A pair of return springs2aand3aare disposed at the pair of brake pads2and3for biasing the brake pads2and3away from the disk rotor1. Due to the provision of the pair of return springs2aand3a,a pad clearance is generated between the disk rotor1, and each of the brake pads2and3.

A bottomed cylinder17is formed at the cylinder portion14so as to have an open end on the inner pad2side and the other end closed by a bottom wall (cylinder bottom wall)16. A piston19is slidably disposed in the cylinder17via a piston seal18. The piston19is restrained from rotating relative to the cylinder17. The hydraulic pressure chamber12is defined between the piston19and the cylinder bottom wall16. The MC10is connected to the hydraulic pressure chamber12via the automatic brake system13, whereby a hydraulic pressure from the MC10is supplied to the hydraulic pressure chamber12after it is controlled by the ABS and VDC systems of the automatic brake system13.

A hydraulic pressure sensor21is disposed at a branch diverging from a brake liquid passage20connecting the hydraulic pressure chamber12and the automatic brake system13. A temperature sensor (temperature measuring unit)22is disposed adjacent the disk rotor1for measuring a temperature of the disk rotor1. A stroke sensor23is disposed for detecting an operation amount (stroke) of the brake pedal7from an operation of the brake pedal7. A vehicle speed sensor25is disposed for detecting a vehicle speed from an operation of the wheel shaft24. An atmospheric temperature sensor26, a vehicle weight sensor27and a deceleration sensor28are disposed at a vehicle where the disk brake apparatus5is mounted for measuring an atmospheric temperature, a vehicle weight and deceleration, respectively.

An ECU (electronic control unit or controller)30is connected to the hydraulic pressure sensor21, the temperature sensor22, the stroke sensor23, the vehicle speed sensor25, the atmospheric temperature sensor26, the vehicle weight sensor27and the deceleration sensor28. The ECU30is adapted to perform a control for generating a desired braking force by controlling the solenoid9of the ACC control booster8based on detection signals from the various sensors, while generating a desired clearance by performing a control for adjusting a clearance (clearance adjusting control) which includes a centering operation for preventing judder occurrence as will be described later.

The clearance adjusting control performed by the ECU30will be described with reference to a flow chart ofFIG. 2andFIG. 3(A).

The ECU30starts a brake control based on a detection signal outputted from the stroke sensor23in response to an operation of the brake pedal7[step S1, “BRAKING START” inFIG. 3(A)], then a braking operation is performed. The braking operation is continued while depression of the brake pedal7is continued [while the result of the determination as to whether the brake control is finished (step S2or a step following step S1) is NO]. If the result of the determination at S2is YES (“BRAKING STOP” in FIG.3(A)), then the brake control is stopped, and the flow proceeds to step S3. One operation performed from “BRAKING START” until “BRAKING STOP” inFIG. 3(A)is counted as a single braking operation. When the braking operation is performed, thermal deformation (thermal gradient) of the disk rotor1occurs. When the braking operation is stopped, the temperature of the disk rotor1is reduced by heat release. When braking is not performed for a certain time period after that, the disk rotor1returns to the normal state or recovers from the thermal deformation (thermal gradient). Until the disk rotor1recovers from the thermal deformation (thermal gradient) since the braking operation is stopped, that is, during a cooling process while the vehicle is running, the centering operation [“CENTERING” inFIG. 3(A)] is performed, as will be described later.

At step S3, it is determined whether a value detected by the temperature sensor22, i.e., a temperature of the disk rotor1, is equal to or more than a predetermined value (i.e., whether an amount of the deformation of the disk rotor1is equal to or more than a predetermined amount), whereby it is determined whether a control for preventing generation of thickness variation of the disk rotor1to prevent judder occurrence (clearance adjusting control) should be performed. If the result of the determination at step S3is NO, the clearance adjusting control is ended.

At step S3, it is determined based on a value detected by the temperature sensor22(i.e., a temperature of the disk rotor1) whether an amount of the deformation of the disk rotor1is equal to or more than a predetermined amount. In the first embodiment, a thermal deformation estimating unit is embodied by step S3(ECU30).

If the result of the determination at S3is YES, then operation conditions (the length of interval between the centering operations, and the number of the centering operations to be performed) required for performing the clearance adjusting control are set based on, for example, a detection value of the temperature sensor22(step S4). The centering operation is an operation of actuating the caliper11, more specifically, an operation of causing caliper11to hold the disk rotor1for a quick moment by utilizing a hydraulic pressure in the MC10generated by an output generated in the ACC control booster8by quickly turning on/off the solenoid9, i.e., causing the caliper11to close the clearance to such an extent that heat is not generated (by causing the brake pads2and3to move toward or contact the disk rotor1), and then to release the disk rotor1immediately. The interval between the centering operations means a time period to be elapsed between the centering operations (including a time period between the braking stop event and the first centering operation event).

In the first embodiment, as shown inFIG. 3(A), the centering operation is performed six times. The interval between the first and second centering operations is longer than the interval between the braking stop and the first centering operation. The intervals between the second and third centering operations, between the third and fourth centering operations, and between the fourth and fifth centering operations are equal to the interval between the first and second centering operations. The interval between the fifth and sixth centering operations is longer than the interval between the first and second centering operation.

In some embodiments, the lengths of all intervals may be the same. In other embodiments, the length of the interval may be gradually increased with each centering operation.

In the first embodiment, the centering operation is performed six times. In some embodiments, the centering operation may be performed twice, . . . five times, seven times, or more than seven times, instead of six times.

After step S4, it is determined whether the interval set at step S4has passed (step S5). If the result of the determination at step S5is NO, the determination of step S5is repeated. If the result of the determination at step S5is YES, then it is determined whether the number of the centering operations that have been performed is less than the set value (six times in the first embodiment)(step S6).

If the result of the determination at step6is NO (the number of the operations reaches the set value), then the clearance adjusting control is ended.

If the result of the determination at step6is YES (the number of the operations is less than the set value), it is determined whether the centering operation (clearance adjusting control) should be performed by determining from a detection result of the vehicle speed sensor25whether the vehicle is running (step S7). If the result of the determination at step7is NO, i.e., it is determined that the vehicle is not running, then the flow returns to step S5. If the result of the determination at step7is YES, then the centering operation is performed by actuating the solenoid at step S8[“CENTERING” inFIG. 3(A)], and a centering operation counter is incremented by one. Then, the flow returns to step S5, and the centering operation is repeated until the determination result at step S6becomes NO (the number of the operations reaches the set value). In the first embodiment, one braking operation is performed, and after the braking operation is stopped, the centering operation is performed six times [the first to the sixth centering operations are performed]. Alternatively, at step S7, it may be determined whether the centering operation (clearance adjusting control) should be performed, by estimating that deformation of the disk rotor1(recovery of the disk rotor1from the thermal gradient by cooling) has occurred if a measuring result of the temperature sensor22(temperature measuring unit) indicates a predetermined temperature decrease of the disk rotor1. In this case, the thermal deformation estimating unit is embodied by step S7(ECU30) as well as step S3.

As mentioned above, the determination whether the centering operation should be performed is made (step S3), and the operation conditions of the centering operation (the length of the interval and the number of the operations) are set (step S4), according to a change of deformation of the disk rotor1by heat release over time. If it is determined that the centering operation should be performed, the centering operation is performed [the pair of brake pads2and3is caused to contact the disk rotor1, and then is separated from the disk rotor1during a cooling process while the vehicle is running] under the set operation conditions (set according to the change of deformation of the disk rotor1by heat release over time) by actuating the solenoid9(step S8). Therefore, it is possible to perform the clearance adjusting control according to the change of thermal deformation of the disk rotor1over time, and thereby possible to reduce the contact time of the brake pads with the disk rotor1to prevent generation of disk thickness variation (DTV) of the disk rotor1to prevent judder occurrence

If it is determined at S7that the vehicle is not running based on the detection result of the vehicle speed sensor25, step S8is not performed.

The inventors of the present application compared the state of the clearance after stop of one braking operation in the disk brake apparatus of the first embodiment to those in disk brake apparatuses of related arts. As disk brake apparatuses of related arts, the before-mentioned disk brake apparatus of the first related art, the disk brake apparatus disclosed in patent document 1 (the disk brake apparatus having a large clearance), and the disk brake apparatus disclosed in patent document 2 (the disk brake apparatus having a minimized clearance for preventing the negative effects caused by clearance expansion) were used. The resulted states of the clearances in the disk brake apparatuses of the first embodiment, the first related art, patent document 1, and patent document 2 are respectively shown by the solid line inFIG. 3(A), the solid line inFIG. 3(B), the alternate long and two short dashes line inFIG. 3(B), and the dotted line inFIG. 3(B). The mark “x” inFIG. 3indicates that the brake pads2and3contact the disk rotor1.

By comparing them, the following facts were confirmed.

In the disk brake apparatuses shown by the solid line and the dotted line inFIG. 3(B), i.e., the disk brake apparatuses other than that of patent document 1 (shown by the alternate long and two short dashes line, the apparatus having a large clearance), the brake pads2and3contact the disk rotor1for a long time, and therefore it is highly likely that thickness variation could be generated by contact of the brake pads2and3with the disk rotor1, possibly resulting in judder occurrence.

On the contrary, in the disk brake apparatus of the first embodiment shown inFIG. 3(A), the time of contact of the brake pads2and3with the disk rotor1is short, and therefor it becomes possible to prevent disk thickness variation (DTV) of the disk rotor1which otherwise might be generated by contact of the brake pads2and3with the disk rotor1, and accordingly, it becomes possible to prevent judder occurrence.

In the first embodiment, it is determined at step S3whether the centering operation (clearance adjusting control) should be performed, based on the detection value of the temperature sensor22. However, the temperature sensor22may be replaced with pad displacement sensors31aand31bor a rotor displacement sensor31coperable to detect displacement of the disk rotor1(seeFIG. 4, thermal deformation measuring unit), and it may be determined whether the centering operation (clearance adjusting control) should be performed based on an amount of deformation of the disk rotor1obtained from a detection signal of the pad displacement sensors31aand31bor the rotor displacement sensor31c.

FIG. 4schematically illustrates a disk brake apparatus of a second embodiment of the present invention. A disk brake apparatus5A of the second embodiment will be described referring toFIGS. 4 and 5, also sometimes referring toFIGS. 1 to 3as necessary. The second embodiment is provided with, instead of the temperature sensor22, the pad displacement sensors31aand31b(seeFIG. 4) operable to detect a displacement of pads2and3from a travel distance of the pads, and the rotor displacement sensor31coperable to directly detect a displacement of a disk rotor1.

An ECU30A (seeFIG. 4) of the second embodiment calculates an amount of thermal gradient of the disk rotor1based on a detection signal of the rotor displacement sensor31[steps S20and S23], and predetermines a first threshold value for a thermal gradient amount change, and a second threshold value for a change of the thermal gradient amount change, to compare the thermal gradient amount change with the first threshold value (step S24), and the change of the thermal gradient amount change with the second threshold value (step S25).

In the first embodiment, the centering operations are performed with intervals therebetween, while in the second embodiment, the centering operations are performed, monitoring a recovery amount of the thermal gradient of the disk rotor1.

The clearance adjusting control performed by the ECU30A of the second embodiment is now described with reference to a flow chart ofFIG. 5. As shown inFIG. 5, steps S1and S2are performed in the same manner as in the first embodiment (FIG. 2). If the result of the determination at step S2is YES, then the ECU30A calculates an initial value of the thermal gradient amount based on a detection signal of the pad displacement sensors31aand31bor the rotor displacement sensor31c[step S20].

After step S20, it is determined whether any measure against judder should be taken (step S3A), similarly to step S3in the first embodiment (FIG. 3). At step3inFIG. 2, the determination is made based on the detection value of the temperature sensor22, while at step S3A, the determination is made based on the initial value of the thermal gradient amount (also referred to as gradient amount) of the disk rotor1calculated from the detection value of the pad displacement sensors31aand31bor the rotor displacement sensor31c.

After step S3A, an initial value of gradient amount is set to the value detected at step S20(step S21), and steps S22to24are sequentially performed from step S21to step S7A (determination whether the centering operation should be performed) corresponding to step S7inFIG. 2.

At step S22, a predetermined time period (interval), which indicates when the gradient amount change should be calculated, passes (corresponding to step S5inFIG. 3). At step S23, a current thermal gradient amount of the disk rotor1which is returning to the normal state or recovering by heat release is calculated based on a detection signal of the pad displacement sensors31aand31bor the rotor displacement sensor31c.At step S24, it is determined whether the gradient amount change is equal to or larger than the first threshold value.

At step S7A, it is determined whether the centering operation (step S8A corresponding to step S8inFIG. 2), which is performed by actuating a solenoid9A (seeFIG. 4), is necessary, by determining whether the vehicle is running based on an output from the vehicle speed sensor25.

If the result of the determination at step S24is NO (the gradient amount change is less than the first threshold value), then it is determined whether the change of the gradient amount change is less than the second threshold value (step S25). If the result of the determination at step S25is NO, then the flow returns to step S22. If the result of the determination at step S25is YES, then the clearance adjusting control is ended.

In the second embodiment, if the result of the determination at step S7A is NO, then the flow returns to S22. If the result of the determination at step S7A is YES, then flow advances to step S8A. At step S8A, the centering operation [“CENTERING” inFIG. 3(A)] is performed and a centering operation counter is incremented by one. Then, the flow returns to step S21.

In the second embodiment, when the gradient amount change is equal to or more than the first threshold value, and it is determined that the centering operation is necessary (the determination result at step S7A is YES), the centering operation (step S8A) is performed by actuating the solenoid9. When the gradient amount change becomes less than the first threshold value, and the change of the gradient amount change becomes less than the second threshold value (this means that the disk rotor1has sufficiently recovered from the thermal gradient), the determination is made as YES at step S25, and then the clearance adjusting control is ended.

As mentioned above, an initial value of thermal gradient of the disk rotor1is determined [step S20], and it is determined whether the centering operation (the operation moving the brake pads into contact with the disk rotor1, and then separating the pads from the disk rotor1) should be performed, according to a change of deformation of the disk rotor1by heat release over time. More specifically, the centering operation is performed by actuating the solenoid9, if a gradient amount change by an amount equal to or more than the first threshold value is continuously detected. Even if the gradient amount change is less than the first threshold value, as long as the change of the gradient amount change is equal to or more than the second threshold value, the centering operation is performed once the gradient amount change exceeding the first threshold value is detected after the predetermined interval has passed. (for example, steps S22, S24, S25and S8A) When the gradient amount change becomes less than the first threshold value, and the change of the gradient amount change becomes less than the second threshold value (YES at step S25), the centering operation (clearance adjusting control) is ended.

By this control, it is possible to perform the clearance adjustment according to a change of thermal deformation of the disk rotor1over time. Since contact time of the brake pads2and3with the disk rotor1is reduced by performing the centering operation, it is possible to prevent generation of disk thickness variation (DTV) of the disk rotor1, leading to prevention of judder occurrence.

In the second embodiment, the centering operation is ended when it is determined at step25that the change of the gradient amount change is less than the second threshold value. In other embodiments, the centering operation may be ended when it is determined at step25that the gradient amount change is less than the first threshold value for a predetermined time period (the result of the determination at step24is NO for the predetermined time period); in other words, at step25, it may be determined whether a gradient change amount less than the first threshold value is continuously detected for a predetermined time period, and the centering operation may be ended if the result of the determination at this step S25is YES.

It may be determined at step S7A whether the vehicle is stopped based on a shift position (P range), instead of using the vehicle speed sensor25, and step S8A may be not performed if it is determined that the vehicle is stopped, although this is not shown inFIG. 5.

In the second embodiments, an initial value of the thermal gradient amount is calculated based on measurement of the pad displacement sensors31aand31b,or the rotor displacement sensor31c.Instead of this, in some embodiments, an initial value of thermal gradient amount may be estimated using the temperature sensor22. In other embodiments, a braking state may be determined using a detection value of the hydraulic pressure sensor21, the stroke sensor23, a resolver50shown inFIG. 11(rotational position detector) which will be described later, or the vehicle speed sensor25, and then an initial value of thermal gradient amount of the disk rotor1may be estimated based on an amount of heat generated by the braking; in these embodiments, a detection value of the vehicle weight sensor27may be also used to improve detection accuracy of an initial value of thermal gradient amount. The vehicle weight sensor27may be embodied by, for example, a height sensor for adjusting a headlight of the vehicle.

In the second embodiment, a current thermal gradient amount is estimated using the temperature sensor, or is measured using the rotor displacement sensor31(or the pad displacement sensors31aand31b). In other embodiments, a cooling state of the disk rotor1may be estimated using a detection value of the vehicle speed sensor25, and then the current thermal gradient amount may be calculated based on a heat release amount; in these embodiments, a detection value of the atmospheric temperature sensor26may be also used to improve calculation accuracy of the current thermal gradient amount.

Although in the first and second embodiments, the actuator is embodied by the ACC control booster8or8A (more correctly, the solenoid9or9A disposed at the ACC control booster8or8A), the actuator may be embodied by other means. For example, as shown inFIG. 6, in a disk brake apparatus5B (a third embodiment), an actuator may be embodied by a VDC pump32(hydraulic pump) disposed at a VDC (Vehicle Dynamics Control system) incorporated in an automatic brake system13. The disk brake apparatus5B of the third embodiment comprises a booster (boosting apparatus)8B that does not execute the ACC control, instead of the ACC control boosters8and8A. The third embodiment comprises a rotor displacement sensor31c,similarly to the second embodiment, and a thermal gradient amount (displacement) of a disk rotor1is calculated using a detection signal of the sensor31cto determine whether the centering operation (clearance adjusting control) should be performed.

In the third embodiment, the centering operation is performed by turning on/off the VDC pump32, and a control similar to the clearance adjusting control of the second embodiment (FIG. 5) is performed. Therefore, an appropriate clearance can be generated as is the case in the second embodiment, so that so-called one-side wear is not caused even when a braking operation is reperformed, whereby it is possible to prevent generation of thickness variation of the disk rotor1, and prevent judder occurrence.

In the third embodiment, the actuator is embodied by the VDC pump32(hydraulic pump). In embodiments in which a traction control system (TCS) is employed in a vehicle, the actuator may be embodied by a pump for traction control; in such embodiments, the centering operation is performed by instantaneously turning on/off the pump for traction control.

A disk brake apparatus5C of a fourth embodiment of the present invention will be described with reference toFIG. 7.

In the fourth embodiment, the actuator is embodied by a hydraulic pump34disposed at a BBW actuator (Brake-by-wire actuator)33. The hydraulic pump34is connected to a hydraulic pressure chamber12of a disk brake6through a brake liquid passage35. In the fourth embodiment, components corresponding to the ACC control booster8and the MC10in the first embodiment are omitted.

In the fourth embodiment, the centering operation is performed by instantaneously turning on/off the hydraulic pump34, and the effects similar to those in the before-mentioned embodiments can be brought about.

A disk brake apparatus5D of a fifth embodiment of the present invention will be described with reference toFIG. 8.

As shown inFIG. 8, the disk brake apparatus5D of the fifth embodiment is structurally and mechanically different from the disk brake apparatus of the first embodiment, mainly in terms of the following features.(1) The disk brake6is replaced with a disk brake6A capable of executing the PKB (parking brake) function by performing an electric operation (hereinafter referred to as EPB-operable disk brake).(2) A caliper11A capable of executing the PKB function (hereinafter referred to as PKB-built-in caliper) is used as a caliper of the EPB-operable disk brake6A.(3) A PKB driving apparatus38including an electric motor37is attached to the PKB-built-in caliper11A, and the electric motor37is driven under a control by an ECU30D to be used as the actuator.(4) A stroke detector39(or driving force detector) is disposed at the PKB driving apparatus38.(5) The ACC control booster8in the first embodiment is replaced with a booster (boosting apparatus)8C that does not perform the ACC control.

In the fifth embodiment, the centering operation is performed by instantaneously performing a forward/reverse control on the electric motor37, and the effects similar to those in the before-mentioned embodiments can be brought about.

A disk brake apparatus5E of a sixth embodiment of the present invention will be described with reference toFIG. 9.

As shown inFIG. 9, the disk brake apparatus5E of the sixth embodiment is structurally and mechanically different from the disk brake apparatus5D of the fifth embodiment (FIG. 8), mainly in terms of the following features.(1) Instead of the PKB driving apparatus38, a PKB cable driving apparatus40is attached to a PKB-built-in caliper11A.(2) An electric motor41disposed at the PKB cable driving apparatus40operates a PKB cable42to actuate a moving portion (not shown) of the PKB-built-in caliper11A connected to the PKB cable42, and therefore actuate brake pads2and3, so that the electric motor41serves as the actuator.(3) The stroke detector39in the fifth embodiment is replaced with a tensional force detector43(or stroke detector).

In the sixth embodiment, the centering operation is performed by instantaneously performing a forward/reverse control on the electric motor41, and the effects similar to those in the before-mentioned embodiments can be brought about.

A disk brake apparatus5F of a seventh embodiment of the present invention will be described referring toFIG. 10, and also sometimes referring toFIG. 7as necessary.

As shown inFIGS. 7 and 10, the disk brake apparatus5F of the seventh embodiment is structurally and mechanically different from the disk brake apparatus5C of the fourth embodiment (FIG. 7), mainly in terms of the following features.(1) The caliper11of the disk brake6is replaced with an electric caliper11B including an electric motor44, and adapted to press brake pads2and3against the disk rotor1by being driven by the electric motor44.(2) A stroke detector46adapted to detect a stroke of a brake pad actuating member (not shown) for actuating the brake pads2and3by being driven by the electric motor44is disposed.(3) The BBW actuator33is omitted.

In the seventh embodiment, the centering operation is performed by instantaneously performing a forward/reverse control on the electric motor44, and as is the case in the fourth embodiment, a clearance adjusting control corresponding to the clearance adjusting control in the first embodiment (FIG. 2) or the second embodiment (FIG. 5) is performed. By this control, an appropriate clearance can be generated as is the case in the first or second embodiment, so that so-called one-side wear is not caused even when a braking operation is reperformed, whereby it is possible to prevent generation of thickness variation of the disk rotor1, and prevent judder occurrence.

The disk brake comprising the electric caliper11B in the seventh embodiment (FIG. 10) may be replaced with, for example, a disk brake6A shown inFIG. 11. In the disk brake6A (eighth embodiment), the displacement sensor of the rotor (thermal deformation measuring unit) is embodied by a resolver50, as will be described later.

In the eighth embodiment, the effects similar to those in the before-mentioned embodiments can be brought about.

A general description will be provided as to a structure of the disk brake6A shown inFIG. 11. Referring toFIG. 11, the disk brake6A comprises a disk rotor1, carrier51, a pair of brake pads (inner pad2and outer pad3), and an electric caliper11C disposed so as to extend over the disk rotor1, and supported so as to be movable along an axial direction of the disk rotor1relative to the carrier51by a pair of slid pins (not shown).

The electric caliper11C comprises a caliper main body52, a pad pressing member unit53, and a motor unit54. The caliper main body52comprises a cylindrical cylinder portion14including a through-hole open to one side of the disk rotor1, and a claw portion15straddling the disk rotor1so as to extend from the cylinder portion14to the opposite side. The cylinder portion14and the claw portion15are integrally provided. The cylinder portion14has an inner surface where a guide bore56and a female screw58are formed. A pad pressing member55of the pad pressing member unit53is slidably fitted in the guide bore56. A male screw of an adjusting screw57attached to the pad pressing member unit53is screwed into the female screw58.

The pad pressing member unit53is formed by integrally assembling the bottomed cylindrical pad pressing member55, a ball ramp mechanism59(rotation-linear motion converting mechanism) and a differential speed reducing mechanism60which are contained in the pad pressing member55, and a pad wear compensating mechanism61. The pad pressing member55is slidably fitted in the guide bore56of the caliper main body52, and abuts against the inner pad2. The pad pressing member55is restrained from rotating by a pin (not shown and not labeled). A dust seal62and a seal ring63seal between the pad pressing member55and the guide bore56.

The motor unit54is formed by integrally assembling an electric motor64, the resolver50(rotational position detector) operable to detect a rotational position of the electric motor64, and a lock mechanism65operable to maintain a rotational position of the electric motor64. In the eighth embodiment, the resolver50is used for detecting a rotational position of the electric motor64. In other embodiments, the resolver50may be replaced with an optical or magnetic rotary encoder.

The resolver50can be used as a displacement sensor of the rotor (thermal deformation measuring unit) for the following reason; when the disk rotor1is returning to the normal state or recovering from thermal gradient by heat release, the tilting disk rotor1abuts against the brake pad2to which the centering operation is performed, because a control for expanding a pad clearance is not performed in any embodiments of the present invention, unlike the before-mentioned invention of patent document 1. This abutment displaces the brake pad2, and this displacement is measured by the resolver50(displacement measuring unit, rotational position detector). Based on this measuring result, it is possible to estimate deformation of the disk rotor1by heat release. In addition, a braking state may be determined and a braking force may be estimated based on a detection value of the resolver as to a rotational position of the motor, and the thermal gradient amount may be estimated based on an amount of heat generated by the braking, by using a detection value of the vehicle speed sensor as well as the determined braking state and the estimated braking force. In this way, the thermal deformation estimating unit can be embodied by the resolver50and the ECU30F.

In the fifth, sixth and seventh embodiments, the disk brake6A capable of executing the parking brake function is employed. However, other disk brakes may be used in other embodiments. For example, a disk brake apparatus5H (a ninth embodiment) comprises a hydraulic-press-type disk brake6C having the electrically-driven parking brake function [HPB, hereinafter referred to as “first HPB caliper” for the sake of simplicity], as shown inFIGS. 12(A) and 12(B). A disk brake apparatus5I (tenth embodiment) comprises a disk brake6D [HPB, hereinafter referred to as “second HPB caliper” for the sake of simplicity], as shown inFIG. 13.

Referring toFIGS. 12(A) and 12(B)[the ninth embodiment], a hydraulic pressure is supplied from a master cylinder (not shown) to a hydraulic pressure chamber12of the first HPB caliper6C. A housing71is supported outside a cylinder bottom wall16. A parking brake mechanism70is disposed in the housing71and a cylinder portion14so as to extend through the cylinder bottom wall16. The parking brake mechanism70has one end side extending from the inside of a cylinder17to the inside of the housing71through a through-hole formed through the cylinder bottom wall16. The parking brake mechanism70generally comprises a shaft73having a male screw on the other end side positioned in a cup portion of a piston19, a nut74disposed in the cup portion of the piston19and having on an inner surface thereof a female screw engaged with the male screw of the shaft73, and a gear mechanism75disposed in the housing71and adapted to cause a rotation of the shaft73by being driven by an electric motor64.

The shaft73is disposed along an axis line of the cylinder17, and is rotatably supported at an intermediate portion thereof by a bearing76. The shaft73comprises a flange portion78formed at the intermediate portion thereof and configured to abut against the bearing76disposed in the cylinder17.

The nut74comprises a convex portion82formed on an outer surface thereof, and is restrained from rotating by the convex portion82inserted in a groove83formed on an inner surface portion of the piston19.

The gear mechanism75for rotating the shaft73comprises a worm86fixed to a rotational axis of the electric motor64, and a worm wheel88attached non-rotatably to the one end side of the shaft73via a key87and meshed with the worm86. The worm wheel88is rotatably supported by the housing71through a bearing (not labeled).

In the ninth embodiment, when a normal braking operation is performed, the electric motor64is stopped and a hydraulic pressure is supplied from the master cylinder to the hydraulic pressure chamber12in response to an operation of a brake pedal7. Since the electric motor64is stopped and therefore a movement of the nut74is not caused, only the piston19advances to press an inner pad2against a disk rotor1, the reactive force of which causes a caliper main body52to move toward an inner side of the vehicle, and then a claw portion15of the caliper main body52presses an outer pad3against the disk rotor1. In this way, the disk rotor1is sandwiched between the inner and outer pads2and3, whereby a braking force is generated according to the applied hydraulic pressure. When the hydraulic pressure in the hydraulic pressure chamber12is released, the elastic resilient force of a piston seal18causes the piston19to retract, thereby moving the inner and outer pads2and3away from the disk rotor1to release the braking force.

When the parking brake function is executed, the disk brake6C works as follows. In response to an operation of a parking brake switch (not shown), an ECU30outputs a control signal so that a control signal is outputted to a hydraulic pressure unit (not shown), and thereby a hydraulic pressure is supplied to the hydraulic pressure chamber12to exert a braking force in the same manner as a normal braking operation is preformed. On the other hand, substantially simultaneously with supply of the hydraulic pressure to the hydraulic pressure chamber12, the electric motor64is actuated by an instruction from the ECU30D,30E or30F. The actuation of the electric motor64causes a rotation of the shaft73, and therefore causes a linear movement (forward movement) of the nut74to press the piston19in an advancing direction. After that, substantially simultaneously with stop of the electric motor64, a circuit in the hydraulic pressure unit is switched by an instruction from the ECU30D,30E or30F to release the hydraulic pressure from the hydraulic pressure chamber12. At this time, since a large frictional force is generated at the engaging portion of the nut74with the piston17by an axial force from the piston19, and the gear mechanism75is irreversible, the shaft73is restrained from rotating and the nut74is maintained in this position. That is, even when the electric motor64is stopped and the hydraulic pressure is released, the piston17is mechanically maintained in the braking position, and thereby parking braking is realized.

In the ninth embodiment, the clearance adjusting control similar to that in the second embodiment (FIG. 5) is performed. The centering operation is performed by instantaneously turning on/off the hydraulic pressure unit. Similarly to the second embodiment, the clearance adjustment can be performed according to a change of deformation of the disk rotor1by heat release over time. In addition, the contact time of the brake pads2and3with the disk rotor1is reduced by performing the centering operation, whereby it is possible to prevent generation of thickness variation of the disk rotor1(DTV) and to prevent judder occurrence.

The second HPB caliper6D of the tenth embodiment is structurally and mechanically different from the first HPB caliper6C of the ninth embodiment, mainly in terms of the following features (1) to (6). In the tenth embodiment, the effects similar to those in the before-mentioned embodiments can be brought about, similarly to the ninth embodiment.(1) The nut74comprises a pin90axially erected from a flange portion89formed at a back end of the nut74. The nut74is restrained from rotating by the pin90slidably inserted in an axially-extending pin hole (not labeled) formed at a piston19.(2) A cover plate91is attached to a tip opening of the nut74, and an air-bleeding hole92is radially formed through the piston19for discharging air between an inner bottom of the piston19and the tip of the nut74including the cover plate91.(3) A rotation of the shaft73causes a linear movement of the nut74, which in turn applies a force to press the piston19in an advancing direction by abutting against a rear end of the piston19at the flange portion89of the nut74.(4) The nut74engaged with the shaft73is slidably fitted in the piston19via a seal member81.(5) The shaft73is disposed along an axial line of the cylinder17, and is rotatably supported at an intermediate portion thereof by two bearings (thrust bearings)95and96disposed on the respective sides of a cylinder bottom wall16.(6) The shaft73comprises a flange portion78formed at the intermediate portion thereof. The flange portion78is configured to abut against the bearing95or the bearing disposed in the cylinder7. The shaft73has one end side extending into the housing71, where a screw portion configured to receive a double nut79is formed. The shaft73is axially securely restrained to the two bearings95and96by tightening the double nut79into the screw portion.

In the tenth embodiment, the clearance adjusting control similar to that in the second embodiment (FIG. 5) is performed. The centering operation is performed by instantaneously turning on/off the hydraulic pressure unit. Similarly to the second embodiment, the clearance adjustment can be performed according to a change of deformation of the disk rotor1by heat release over time. In addition, the contact time of brake pads2and3with a disk rotor1is reduced by performing the centering operation, whereby it is possible to prevent generation of disk thickness variation (DTV) of the disk rotor1and to prevent judder occurrence.

According to the before-described embodiments, in order to adjust the pad clearance according to a change of deformation of the disk rotor by heat release over time, the brake pads are moved into contact with the disk rotor and then are separated from the disk rotor by driving the actuator, after a braking force is generated. By this control, it is possible to adjust the pad clearance according to a change of deformation of the disk rotor by heat release over time, whereby the contact time of the brake pads with the disk rotor is reduced. Therefore, it becomes possible to prevent generation of thickness variation of the disk rotor, and prevent judder occurrence.

The present application claims priority under 35 U.S.C. section 119 to Japanese Patent Application No. 2007-227177, filed on Aug. 31, 2007. The entire disclosure of Japanese Patent Application No. 2007-227177 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.