Vehicular brake control apparatus

The brake ECU applies the target braking force by controlling the hydraulic pressure braking force generating device and the regeneration braking force generating device and the brake ECU further controls the advance speed of the output piston so that a drawn-into of a brake operating member can be prevented upon supplying the wheel cylinders from the master cylinder with the brake fluid by advancing the output piston thereby to improve the brake operating feeling of the brake operating member by preventing the brake operating member from being drawn into.

TECHNICAL FIELD

This invention relates to a vehicular brake control apparatus which controls the hydraulic pressure braking force generating device and the regeneration braking force generating device thereby to apply a target braking force to the vehicle wheels.

BACKGROUND ART

Conventionally, a vehicular brake device has been known, which includes a hydraulic pressure braking force generating device which generates the hydraulic pressure braking force at the vehicle wheel corresponding to the wheel cylinder by supplying thereto with the brake fluid from the master cylinder and a regeneration braking force generating device which generates a regeneration braking force at the vehicle wheel. The master cylinder of the hydraulic pressure braking force generating device is formed by an input piston which slidably moves within the master cylinder and an output piston arranged at a front side of the input piston and slidably movable within the master cylinder. The input piston is cooperatively driven by a brake operating member and the output piston is driven independently of the operation of the brake operating member, wherein the brake fluid is supplied to the wheel cylinder from the master cylinder by an advance movement of the output piston. The master cylinder is provided with a rear chamber defined by an inner periphery portion of the master cylinder, a front end portion of the input piston and a rear end portion of the output piston and a front chamber defined by the inner periphery of the master cylinder and a front end portion of the output piston. The volume of the front chamber is variable by the advance movement of the output piston. A brake fluid pathway which connects the front and the rear chambers is formed in the master cylinder so that the brake fluid in the front chamber flows into the rear chamber by the advance movement of the output piston (See Patent Literature 1).

Further, a vehicular brake control apparatus is known (See Patent Literature 2) which controls a wheel cylinder hydraulic pressure to increase in advance up to a brake preparation hydraulic pressure level before a shifting at a low vehicle speed from the regeneration braking to a hydraulic pressure braking and at the same time controls the regeneration amount to be limited by a motor if the vehicle becomes in a braking operation state when the battery charging level is equal to or more than a second value which value is lower than a first value, where the generation of the battery is stopped.

CITATION LIST

Patent Literature

Patent Literature 1: JP2012-16984 A

Patent Literature 2: JP2006-34034 A

SUMMARY OF INVENTION

However, in the vehicular brake device described in the Patent Literature 1, if the wheel cylinder hydraulic pressure is increased regardless of the operation of the brake operating member as disclosed in the vehicular brake control apparatus according to the Patent Literature 2, a brake operating feeling caused by an operation of the brake operating member may be worsened.

Accordingly, this invention was made in consideration with the above-mentioned situation and the objective of the invention is to provide a vehicular brake control apparatus which can improve the operation feeling of a brake operation member as appeared in the conventional brake device.

Solution to Problem(s)

The vehicular brake control apparatus according to the invention associated with a first aspect is characterized in that the vehicular brake control apparatus is applied to a vehicular brake device which includes a hydraulic pressure braking force generating device which generates a hydraulic pressure braking force at a vehicle wheel corresponding to a wheel cylinder to which a brake fluid is supplied from a master cylinder and a regeneration braking force generating device which generates a regeneration braking force at the vehicle wheel, wherein the master cylinder includes an input piston which slidably moves within the master cylinder and an output piston arranged at a front of the input piston and slidably movable within the master cylinder, the input piston is moved in association with an operation of a brake operating member, whereas the output piston is driven independently of the operation of the brake operating member, wherein the brake fluid is supplied to the wheel cylinder from the master cylinder by an advance movement of the output piston, the master cylinder is provided with a rear chamber defined by an inner peripheral portion of the master cylinder, a front end of the input piston and a rear end of the output piston, a front chamber defined by the inner peripheral portion of the master cylinder and a front end of the output piston, the volume thereof being decreased by the advance movement of the output piston and a brake fluid pathway connecting the rear chamber and the front chamber thereby introducing the brake fluid in the front chamber into the rear chamber by the advance movement of the output piston and that the vehicular brake control apparatus applies a target braking force to the vehicle wheel by controlling the hydraulic pressure braking force generating device and the regeneration braking force generating device. The vehicular brake control apparatus includes a drive control means which controls an advance speed of the advance movement of the output piston to a set speed so that the brake operating member is prevented from “drawn-into” which occurs due to the advance movement of the output piston when the brake fluid is supplied to the wheel cylinder from the master cylinder by driving the output piston to advance.

The invention according to a second aspect is characterized in that in addition to the feature of the first aspect, the vehicular brake control apparatus includes a brake operation judging means for judging that a brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that an increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is predicted, wherein the drive control means advances the output piston with the set speed preceding a predicted increase of the hydraulic pressure braking force, when the brake operation judging means judged that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that an increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is predicted.

The invention according to a third aspect is characterized in that in addition to the feature of the above second aspect, the vehicular brake control apparatus includes an advance speed setting means for setting the set speed corresponding to a time period from a timing of a judgment to a timing of a predicted increase of the hydraulic pressure braking force, wherein when the brake operation judging means judges that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that the increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is predicted, the drive control means advances the output piston with the set speed set by the advance speed setting means.

The invention according to a fourth aspect is characterized in that in addition to the feature of the second or the third aspect, when the vehicle speed drops to a predetermined shifting start speed under the regeneration braking force generating device being generating the regeneration braking force, the regeneration braking force is shifted to the hydraulic pressure braking force responding to the drop of the vehicle speed, wherein the braking operation judging means judges that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheel and that the increase of the hydraulic pressure braking force to be generated at the wheel corresponding to the wheel cylinder is predicted when the vehicle speed drops to a drive start speed which is higher than the shifting start speed.

The invention according to a fifth aspect is characterized in that in addition to the feature of the fourth aspect, the vehicular brake control apparatus further includes a drive start speed setting means for setting the drive start speed based on the set speed, a vehicle deceleration and the shifting start speed wherein the brake operation judging means judges that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheel and that the increase of the hydraulic pressure braking force to be generated at the wheel corresponding to the wheel cylinder is predicted, when the vehicle speed drops to the drive start speed which is set by the drive start speed setting means.

The invention according to a sixth aspect is characterized in that in addition to any feature of the first through the fifth aspects, the vehicular brake control apparatus further includes a holding state judging means for judging whether the brake operating member is held to be in a holding state that an operating amount of the brake operating member is kept to be a constant amount, wherein the drive control means executes an advance speed control of the output piston when the brake operating member is judged to be in the holding state.

According to the brake control device associated with the invention of the first aspect, under the input piston being stopped, the hydraulic pressure braking force can be automatically generated by advancing the input piston regardless of the operation of the brake operating member and the hydraulic pressure braking force which is greater than the operating amount of the brake operating member can be generated by advancing the input piston with a speed faster than the input piston. As explained, when the output piston advances relative to the input piston, the volume of the front chamber is decreased to alternatively increase the volume of the rear chamber thereby allowing the brake fluid in the front chamber flowing into the rear chamber through the brake fluid pathway. It is noted here that as the speed of the output piston relative to the input piston becomes high, the flow resistance of the brake fluid pathway relative to the flow of the brake fluid into the rear chamber from the front chamber becomes large. This will generate a drawn-into phenomenon that the input piston, and eventually, the brake operating member is drawn into forwardly. Accordingly, according to the feature of the vehicular brake control apparatus of claim1, the advance speed of the output piston is controlled to be a predetermined speed so that the brake operating member is prevented from being drawn into, which occurs due to the advance movement of the output piston when the brake fluid is supplied to the wheel cylinder from the master cylinder by driving the output piston to advance. Thus “drawn into” phenomenon of the brake operating member can be prevented thereby to improve the brake operation feeling by the operation of the brake operating member.

According to the vehicular brake control apparatus associated with the invention of the second aspect, the drive control means advances the output piston with the set speed preceding the predicted increase of the hydraulic pressure braking force, when the brake operation judging means judged that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder and the brake fluid amount in the wheel cylinder is increased from the brake fluid amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder. Thus, by preparing the predicted increase of the hydraulic pressure braking force, by preventing the drawn-into of the brake operating member, the brake fluid is supplied to the wheel cylinder from the master cylinder to thereby improving brake operation feeling by the brake operating member and at the same time improving the responsibility of the hydraulic pressure braking force. In other words, the deterioration of the responsibility of the hydraulic pressure braking force derived from the low advance speed of the output piston can be prevented. Further, since the brake fluid amount in the wheel cylinder at the start of the increase of the hydraulic pressure braking force has been increased, the responsibility of the hydraulic pressure braking force at the time of increase can be improved.

According to the vehicular brake control apparatus associated with the invention of the third aspect, when the brake operation judging means judges that the brake fluid amount in the wheel cylinder is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that the increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is predicted, the drive control means advances the output piston with the set speed set corresponding to a time period from a timing of a judgment to a timing of the predicted increase of the hydraulic pressure braking force. Thus, the brake fluid amount of the wheel cylinder at the time of predicted increase of the hydraulic pressure braking force and the set speed can be adjusted to improve both the operating feeling of the brake operating member and the responsibility of the hydraulic pressure braking force more appropriately.

According to the vehicular brake control apparatus associated with the invention of the fourth aspect, based on the vehicle speed, the brake fluid amount in the wheel cylinder is judged to be the amount by which the hydraulic pressure braking force is not generated or is scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that the increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is judged to be predicted. Since the vehicle speed can be calculated by using the sensor value of the vehicle wheel speed sensor or the like, the simplification of the device as a whole can be achieved.

As described in the invention of the fourth aspect, when the brake fluid amount in the wheel cylinder is judged to be the amount by which the hydraulic pressure braking force is not generated or is scarcely generated at the vehicle wheel corresponding to the wheel cylinder and that the increase of the hydraulic pressure braking force to be generated at the vehicle wheel corresponding to the wheel cylinder is judged to be predicted based on the drive start speed, the time period from the judgment until the start of the predicted increase of the hydraulic pressure braking force varies depending on the set speed and the deceleration of the vehicle. Accordingly, according to the vehicular brake control apparatus associated with the invention of the fifth aspect, the drive start speed is set based on the set speed, the deceleration of the vehicle and the shifting start speed. Therefore, the set speed is kept to be low and yet the brake fluid amount in the wheel cylinder is surely increased by the time the start of predicated increase of the hydraulic pressure braking force. Thus, keeping the operation feeling of the brake operating member to be comfortable, the responsibility of the hydraulic pressure braking force at the time of increasing.

The brake feeling is worsened when the brake operating member is drawn into under the brake operating amount is kept constant than under the state that the operating amount of the brake operating member is increased or decreased. Accordingly, according to the vehicular brake control apparatus associated with the invention of the sixth aspect, the output piston advances with a constant speed under the operating amount of the brake operating member being kept constant. By this structure, the brake operating feeling can be effectively improved.

EMBODIMENTS FOR IMPLEMENTING INVENTION

The vehicular brake control apparatus and a vehicular brake device which is controllable by the vehicular brake control apparatus according to the embodiment of the invention will be explained hereinafter with reference to the attached drawings. As shown inFIG. 1, the vehicular brake device is formed by a hydraulic pressure braking force generating device BF which generates the hydraulic pressure braking force at the vehicle wheels5FR,5FL,5RR and5R and a regeneration braking force generating device BM which generates the regeneration braking force at the drive wheels, such as for example, the front right and front left wheels5FR and5FL. The vehicular brake control apparatus is formed by a brake ECU6which controls the hydraulic pressure braking force generating device BF and a hybrid ECU8which controls the regeneration braking force generating device BM.

(Hydraulic Pressure Braking Force Generating Device BF)

The hydraulic pressure braking force generating device BF is formed by a master cylinder1, a reaction force generating device2, a separation lock valve22, a reaction force valve23, a servo hydraulic pressure generating device4, a hydraulic pressure control portion5and various sensors71through76.

The master cylinder1supplies the hydraulic pressure control portion5with the operation fluid in response to the operating amount of a brake pedal10(the brake operating means) and is formed mainly by a main cylinder11, a cover cylinder12, an input piston13, a first master piston14(corresponding to the output piston) and a second master piston15(corresponding to the output piston).

The main cylinder11is formed in a substantially bottomed cylinder shape having an opening at rear end thereof and a bottom surface at a front end. The main cylinder11includes therein an inner wall portion111, which extends inwardly with a shape of flange. An inner circumferential surface of the inner wall portion111is provided with a through hole111aat a central portion thereof. The main cylinder11includes therein a small diameter portion112(rear) and a small diameter portion113(front), which inner diameter is somewhat smaller than the inner wall portion111towards the front side. In other words, the small diameter portions112,113project from the inner circumferential surface of the main cylinder11having an inwardly annularly shape. The first master piston14is provided inside the main cylinder11and is slidably movable along the small diameter portion112in the axial direction. Similarly, the second master piston15is provided inside the master cylinder11and is slidably movable along the small diameter portion113.

The cover cylinder12includes an approximately cylindrical portion121, a bellow tubular boots122and a cup-shaped compression spring123. The cylindrical portion121is arranged at a rear end of the main cylinder11and is coaxially fitted into the opening of the main cylinder11. An inner diameter of a front portion121aof the cylindrical portion121is formed to be greater than an inner diameter of the through hole111a.Further, the inner diameter of the rear portion121bis formed to be greater than an inner diameter of the front portion121a.

The boots122is of bellow tubular shaped and is used for dust prevention purpose and is extendible or compressible in front and rearward direction. The front side of the boots122is assembled to be in contact with the rear end opening of the cylindrical portion121. A through hole122ais formed at a central portion of the rear of the boots122. The compression spring123is a coiled type biasing member arranged around the boots122. The front side of the compression spring123is in contact with the rear end of the main cylinder11and the rear side of the compression spring123is disposed with a preload adjacent to the through hole122aof the boots122. The rear end of the boots122and the rear end of the compression spring123are connected to an operating rod10a.The compression spring123biases the operating rod10ain a rearward direction.

The input piston13is configured to slidably move inside the cover cylinder12in response to an operation of a brake pedal10(brake operating member). The input piston13is formed in a substantially bottomed cylinder shape having a bottom surface at a front portion thereof and an opening at a rear portion thereof. A bottom wall131forming the bottom surface of the input piston13has a greater diameter than other parts of the input piston13. The input piston13is arranged at the rear end portion121bslidably and fluid-tightly movable in an axial direction and the bottom wall131is inserted into an inner peripheral side of the front portion121aof the cylindrical portion121.

The operating rod10aoperable in association with the brake pedal10is inserted into the input piston13. A pivot10bis provided at the tip end of the operating rod10aso that the pivot10bcan push the input piston13toward front side. The rear end of the operating rod10aprojects towards the outside through the opening of the input piston13and the through hole122aof the boots122, and is connected to the brake pedal10. The operating rod10amoves in response to the operation of the brake pedal10. More specifically, when the brake pedal10is depressed, the operating rod10aadvances in a forward direction while compressing the boots122and the compression spring123in the axial direction. The input piston13also advances in response to the forward movement of the operating rod10a.

The first master piston14is arranged in the inner wall portion111of the main cylinder11and is slidably movable in the axial direction. The first master piston14includes a pressurizing cylindrical portion141, a flange portion142and a projection portion143in order from the front as a unit. The pressurizing cylindrical portion141is formed in a substantially bottomed cylinder shape having an opening at a front portion thereof and a bottom wall at a rear portion thereof. The pressurizing cylindrical portion141includes a clearance formed with the inner peripheral surface of the main cylinder11and is slidably in contact with the small diameter portion112. A coil-shaped biasing member144is provided in the inner space of the pressurizing cylindrical portion141formed with the second master piston15. The first master piston14is biased by the biasing member144in a rearward direction.

The flange portion142is formed to have a greater diameter than the pressurizing cylindrical portion141and is slidably in contact with the inner peripheral surface of the main cylinder11. The projection portion143is formed to have a smaller diameter than the flange portion142and is slidably and fluid-tightly in contact with the through hole111aof the inner wall portion111. The rear end of the projection portion143projects into the inner space of the cylindrical portion121passing through the through hole111aand is separated from the inner peripheral surface of the cylindrical portion121. The rear end surface of the projection portion143is separated from the bottom wall131of the input piston13and the separation distance “d” is formed to be variable.

It is noted here that a first pressure chamber1D is defined by the inner peripheral surface of the main cylinder11, front side of the pressurizing cylindrical portion141of the first master piston14and a rear side of the second master piston15. A rear chamber which is located further rearward of the first pressure chamber1D is defined by the inner peripheral surface (inner peripheral portion) of the main cylinder11, the small diameter portion112, a front surface of the inner wall portion111and the outer peripheral surface of the first master piston14. The flange portion142of the first master piston14separates the rear chamber in front and rear portions and the front portion is defined to be the reaction force chamber1C (corresponding to the front chamber) and the rear portion is defined to be the servo chamber1A. A separation chamber1B (corresponding to the rear chamber) is defined by the inner peripheral surface of the main cylinder11, a rear surface of the inner wall portion111, an inner peripheral surface (inner peripheral portion) of the front portion121aof the cylindrical portion121, the projection portion143(rear end portion) of the first master piston14and the front end of the input piston12.

The second master piston15is coaxially arranged within the main cylinder11at a location forward of the first master piston14and is slidably movable in an axial direction to be in slidable contact with the small diameter portion113. The second master piston15is formed as a unit by a tubular pressurizing cylindrical portion151in a substantially bottomed cylinder shape having an opening at a front portion thereof and a bottom wall152which closes the rear end of the pressurizing cylindrical portion151. The bottom wall152supports the biasing member144with the first master piston14. A coil-shaped biasing member153is disposed in the inner space of the pressurizing cylindrical portion151with a closed inner bottom surface111dof the main cylinder11. The second master piston15is biased by the biasing member153in a rearward direction. A second pressure chamber1E is defined by the inner peripheral surface of the main cylinder11, the inner bottom surface111dand the pressurizing cylindrical portion151of the second master piston15.

Ports11ato11i,which connect the inside and the outside, are formed at the master cylinder1. The port11ais formed at the main cylinder11at a location rearward of the inner wall portion111. The port11bis formed at the main cylinder11opposite to the port11aat approximately the same location in the axial direction. The port11aand the port11bare in communication through a clearance formed between the inner circumferential surface of the main cylinder11and the outer circumferential surface of the cylindrical portion121. The port11aand the port11bare connected to a conduit161and also connected to a reservoir171.

The port11bis in communication with the separation chamber1B via a passage18formed at the cylindrical portion121and the input piston13. The fluid communication through the passage18is interrupted when the input piston13advances forward. In other words, when the input piston13advances forward, the separation chamber1B and the reservoir171are disconnected from each other.

The port11cis formed at a location forward of the port11aand connects the separation chamber1B with a conduit162. The port11dis formed at a location forward of the port11cand connects the servo chamber1A with a conduit163. The port11eis formed at a location forward of the port11dand connects the reaction force chamber1C with a conduit164.

The port11fis formed between the sealing members91,92of the small diameter portion112and connects a reservoir172with the inside of the main cylinder11. The port11fis in communication with the first pressure chamber1D via a passage145formed at the first master piston14. The passage145is formed at a location where the port11fand the first pressure chamber1D are disconnected from each other when the first master piston14advances forward.

The port11gis formed at a location forward of the port11fand connects the first pressure chamber1D with a conduit51. The port11h is formed between the sealing members93,94of the small diameter portion113and connects a reservoir173with the inside of the main cylinder11. The port11his in communication with the second pressure chamber1E via a passage154formed at the second master piston15. The passage154is formed at a location where the port11hand the second pressure chamber1E are disconnected from each other when the second master piston15advances forward. The port11iis formed at a location forward of the port11hand connects the second pressure chamber1E with a conduit52.

A sealing member such as an O-ring and the like (see black dot inFIG. 1) is appropriately provided within the master cylinder1. The sealing members91,92are provided at the small diameter portion112and in liquid-tightly contact with the outer circumferential surface of the first master piston14. Similarly, the sealing members93,94are provided at the small diameter portion113and in liquid-tightly contact with the outer circumferential surface of the second master piston15. Additionally, sealing members are provided between the input piston13and the cylindrical portion121.

The stroke sensor71detects the operating amount (a stroke amount) of the operation of the brake pedal10and transmits the detected result to the brake ECU6. A brake switch72is a switch which detects whether the brake pedal10is depressed or not using a binary signal and the detected result is sent to the brake ECU6.

The reaction force generating device2is a device for generating a reaction force against the operation force of the brake pedal10and is formed by mainly a stroke simulator21. The stroke simulator21generates a reaction force hydraulic pressure in the separation chamber1B and the reaction force chamber1C in response to the operation of the brake pedal10. The stroke simulator21is configured in such a manner that a piston212is fitted into a cylinder211while being allowed to slidably move therein and a reaction force hydraulic pressure chamber214is formed at a location backward of the piston212, which is biased in the backward direction by a compression spring213. The reaction force hydraulic pressure chamber214is connected to the reaction force chamber1C via the conduit164and the port11e,and is connected further to the separation lock valve22and the reaction force valve23via the conduit164.

The separation lock valve22is an electromagnetic valve which is closed under non-energized state and opening and closing thereof is controlled by the brake ECU6. The separation lock valve22is disposed between the conduit164and the conduit162for communication therebetween. The conduit164is connected to the reaction force chamber1C via the port11eand the conduit162is connected to the separation chamber1B via the port11c.The separation chamber1B becomes in open state when the separation lock valve22opens and the chamber1B becomes in closed state when the separation lock valve22closes. Accordingly, the conduits164and162are formed so that the separation chamber1B and the reaction force chamber1C are in communication.

The separation lock valve22is closed under non-energized state and under this state communication between the separation chamber1B and the reaction force chamber1C is interrupted. Due to the closure of the separation chamber1B, the operation fluid is nowhere to go and the input piston13and the first master piston14are moved integrally keeping the constant distance “d” therebetween. The separation lock valve22is open under the energized state and under such state, the communication between the separation chamber1B and the reaction force chamber1C is established. Thus, the volume change in the separation chamber1B and the reaction force chamber1C due to the advancement and retreatment of the first master piston14can be absorbed by the transferring movement of the operation fluid.

The pressure sensor73detects the reaction force hydraulic pressure of the reaction force chamber1C and is connected to the conduit164. The pressure sensor73detects the pressures of the reaction force chamber1C while the separation lock valve22is in a closed state. On the other hand, while the separation lock valve22is in an open state, the pressure sensor73also detects the pressure in the hydraulically connected separation chamber1B. The pressure sensor73sends the detected signal to the brake ECU6.

The reaction force valve23is a normally-open-type electromagnetic valve in which the valve is open under a non-energized state and is configured so that opening and closing thereof is controlled by the brake ECU6. The reaction force valve23is disposed between the conduit164and the conduit161for establishing communication therebetween. The conduit164is in communication with the reaction force chamber1C via the port11eand the conduit161is in communication with the reservoir171via the port11a.Accordingly, the reaction force valve23establishes communication between the reaction force chamber1C and the reservoir171under the non-energized state not to generate any reaction force hydraulic pressure but interrupts the communication therebetween to generate the reaction force hydraulic pressure under the energized state.

The servo hydraulic pressure generating device4mainly includes a pressure decreasing valve41, a pressure increasing valve42, a high pressure supplying portion43and a regulator44. The pressure decreasing valve41is a normally-open-type electromagnetic valve which opens when the valve is not energized and flow-rate therethrough is controlled by the brake ECU6. One port of the pressure decreasing valve41is connected to the conduit161via a conduit411, and the other port of the pressure decreasing valve41is connected to a conduit413. More specifically, the one outlet/inlet port of the pressure decreasing valve41is in communication with the reservoir171via the conduits411,161, and ports11a,11b.The pressure increasing valve42is a normally-closed-type electromagnetic valve and is closed when the valve is in non-energized state. The flow-rate of the pressure increasing valve42is controlled by the brake ECU6. One outlet/inlet port of the pressure increasing valve42is connected to a conduit421, and the other outlet/inlet port of the pressure increasing valve42is connected to a conduit422.

The high pressure supplying portion43is a portion to supply a highly pressurized operation fluid to the regulator44. The high pressure supplying portion43mainly includes an accumulator431, a hydraulic pressure pump432, a motor433and a reservoir434.

The accumulator431is a tank in which the highly pressurized operation fluid is accumulated. The accumulator431is connected to the regulator44and the hydraulic pressure pump432via a conduit431a.The hydraulic pressure pump432is driven by the motor433and supplies the accumulator431with the operation fluid accumulated in the reservoir434. The pressure sensor75provided in the conduit431adetects the accumulator hydraulic pressure in the accumulator431and a detected signal is sent to the brake ECU6. The accumulator hydraulic pressure correlates with the accumulated operation fluid amount in the accumulator431.

When the pressure sensor75detects that the accumulator hydraulic pressure drops to a value equal to or lower than a predetermined value, the motor433is driven on the basis of a control signal from the brake ECU6, and the hydraulic pressure pump432supplies the operation fluid to the accumulator431in order to recover a pressure energy to the value equal to or more than the predetermined value.

FIG. 2is a partial cross sectional view illustrating a configuration of an inside of the regulator structuring a servo hydraulic pressure generating device. As shown inFIG. 2, the regulator44includes a cylinder441, a ball valve442, a biasing portion443, a valve seat portion444, a control piston445and a sub-piston446.

The cylinder441includes a cylinder case441aformed in a substantially bottomed cylinder-shape having a bottom surface at one end thereof (at the right side in the Figure), and a cover member441bclosing an opening of the cylinder case441a(at the left side thereof). The cover member (441b) is formed to be substantially U-shaped in cross-section in the Figure. According to this embodiment, the regulator44is explained here with the cover member441bas a columnar shaped member, and a portion that closes the opening of the cylinder case441aas the cover member441bin this embodiment. The cylinder case441ais provided with a plurality of ports4ato4hthrough which the inside and the outside of the cylinder case441aare in communication.

The port4ais connected to the conduit431a.The port4bis connected to the conduit422. The port4cis connected to the conduit163. The port4cis connected to a conduit163. The port4dis connected to the conduit161via the conduit414. The port4eis connected to the conduit424and further connected to the conduit422via a relief valve423. The port4fis connected to the conduit413. The port4gis connected to the conduit421. The port4his connected to a conduit511, which is branched from the conduit51.

The ball valve442is a valve having a ball shape and is arranged at the bottom surface side of the cylinder case441ainside of the cylinder441(which will be hereinafter referred to also as a cylinder bottom surface side). The biasing portion443is a spring member biasing the ball valve442towards the opening side of the cylinder case441a(which will be hereinafter referred to also as a cylinder opening side), and is provided at the bottom surface of the cylinder case441a.The valve seat portion444is a wall member provided at the inner peripheral surface of the cylinder case441aand separates the cylinder into the cylinder opening side and the cylinder bottom surface side. A through passage444athrough which the divided cylinder opening side and the cylinder bottom surface side are in communication is formed at a center of the valve seat portion444. The valve seat portion444supports the ball valve442from the cylinder opening side by closing the through passage444aby the biased ball valve442.

A space defined by the ball valve442, the biasing portion443, the valve seat portion444, and a portion of the inner circumferential surface of the cylinder case441ais referred to as a first chamber4A. The first chamber4A is filled with the operation fluid. The first chamber4A is connected to the conduit431avia the port4aand to the conduit422via the port4b.

The control piston445includes a main body portion445aformed in a substantially columnar shape and a projection portion445bformed in a substantially columnar shape having a smaller diameter than the main body portion445a.The main body portion445ais provided inside the cylinder441in a coaxial and liquid-tight manner relative to the cylinder opening side of the valve seat portion444, while allowing the main body portion445ato be slidably movable in the axial direction. The main body portion445ais biased towards the cylinder opening by means of a biasing member (not shown). A passage445cis formed at a substantially intermediate portion of the main body portion445ain a cylinder axis direction. The passage445cextends in the radial direction (in an up-and-down direction in Figure) and both end portions thereof open at a circumferential surface of the main body portion445a.A portion of an inner circumferential surface of the cylinder441corresponding to an opening position of the passage445cis provided with the port4dand is formed to be recessed, which recessed portion forms a third chamber4C.

The projection portion445bprojects towards the cylinder base surface from a center portion of an end surface of the main body portion445a.The projection portion445bis formed so that the diameter thereof is smaller than the diameter of the through passage444aof the valve seat portion444. The projection portion445bis coaxially provided relative to the through passage444a.An end portion of the projection portion445bis spaced apart from the ball valve442towards the cylinder opening by a predetermined distance. A passage445dis formed at the projection portion445bso that the passage445dextends in the cylinder axis direction and opens at a center portion of an end surface of the projection portion445b.The passage445dextends up to the inside of the main body portion445aand is connected to the passage445c.

A space defined by the end surface of the cylinder bottom surface of the main body portion445a,an outer surface of the projection portion445b,the inner circumferential surface of the cylinder441, the valve seat portion444, and the ball valve442is referred to as a second chamber4B. The second chamber4B is in communication with the ports4dand4evia the passages445cand445dand the third chamber4C.

The sub-piston446includes a sub main body portion446a,a first projection portion446b,and a second projection portion446c.The sub main body portion446ais formed in a substantially columnar shape. The sub main body portion446ais provided within the cylinder441in the coaxial and liquid-tight manner relative to the cylinder opening side of the main body portion445awhile allowing the sub main body portion446ato be slidably movable in the axial direction.

The first projection portion446bis formed in a substantially columnar shape having a smaller diameter than the sub main body portion446aand projects from a center portion of an end surface of the cylinder bottom surface side of the sub main body portion446a.The first projection portion446bcontacts the end surface of the cylinder bottom surface side of the sub main body portion446a.The second projection portion446cis formed in the same shape as the first projection portion446b.The second projection portion446cprojects from a center portion of an end surface of the cylinder opening side of the sub main body portion446a.The second projection portion446ccontacts the cover member441b.

A space defined by the end surface of the cylinder bottom surface side of the sub main body portion446a,an outer surface of the first projection portion446b,an end surface of the cylinder opening side of the control piston445, and the inner circumferential surface of the cylinder441is referred to as a pressure control chamber4D. The pressure control chamber4D is in communication with the pressure decreasing valve41via the port4fand the conduit413, and with the pressure increasing valve42via the port4gand the conduit421.

A space defined by the end surface of cylinder opening side of the sub main body portion446af,an outer surface of the second projection portion446c,the cover member441b,and the inner circumferential surface of the cylinder441is referred to as a fourth chamber4E. The fourth chamber4E is in communication with the port11gvia the port4hand the conduits511,51. Each of the chambers4A through4E is filled with the operation fluid. The pressure sensor74is a sensor that detects the servo hydraulic pressure (drive hydraulic pressure) to be supplied to the servo chamber1A and is connected to the conduit163(SeeFIG. 1). The pressure sensor74sends the detected signal to the brake ECU6.

The first pressure chamber1D and the second pressure chamber1E which generate the master cylinder pressure are in communication with the wheel cylinders541through544via the conduits51,52and the ABS (Antilock Brake System)53. The wheel cylinders541through544form the brake5of the wheels5FR through5RL. In detail, the port11gof the first pressure chamber1D and the port11iof the second pressure chamber1E are respectively connected to the known ABS53via the conduits51and52, respectively. The ABS is connected to the wheel cylinders541through544which operate the brake device for braking operation for the wheels5FR through5RL.

The regeneration braking force generating device BM is formed by a motor, for example, an AC (alternate current) synchronizing type motor91which connects the both front wheels5FR and5FL with the vehicle axle and an inverter92which charges the AC electricity generated by the motor91by converting the AC into DC electricity and supplies the motor91with an AC current by converting DC current of the battery93into the AC current.

The brake ECU6is an electronic control unit housing a microprocessor inside thereof and the microprocessor is provided with an I/O (Input/Output) interface, CPU, RAM, ROM and non-volatile memory, respectively connected with one another through a bus connection.

The brake ECU6is connected to the various sensors71through76to control each of the electro-magnetic valves22,23,41,42and the motor433. The operating amount (stroke amount) of the brake pedal10by the operator of the vehicle from the stroke sensor71, a signal informing whether or not the operation of the brake pedal10by the operator is made from the brake switch72, the reaction force hydraulic pressure in the reaction force chamber1C or the pressure in the separation chamber1B from the pressure sensor73, the servo hydraulic pressure (drive hydraulic pressure) supplied to the servo chamber1A from the pressure sensor74, the accumulator hydraulic pressure of the accumulator431from the pressure sensor75and wheel speed of each wheel5FR,5FL,5RR and5RL from the vehicle wheel speed sensor76are respectively inputted to the brake ECU6.

Further, the brake ECU6is mutually communicably connected to a hybrid ECU8and in cooperation with the hybrid ECU8, executes a cooperative control (regeneration cooperative control) so that the required braking force becomes equal to the sum of the target regeneration braking force generated at the regeneration braking force generating device BM and the target hydraulic pressure braking force generated at the hydraulic pressure braking force generating device BF. The brake ECU6memorizes two control modes, “linear mode” and “regulator mode”.

The hybrid ECU8controls the charging state of the battery93and executes the regeneration braking control by cooperation with the brake ECU6. In other words, the hybrid ECU8charges the electricity in the battery93obtained from the generation operation of the motor91which is driven by the rotation force of both front wheels5FR and5FL. Upon the electricity generation, the regeneration braking force is generated by the resistance force of the motor91and outputs the regeneration braking force to the brake ECU6.

(Operation Mode of Brake ECU6)

The brake ECU6has two modes, linear and regulator modes as the operation mode of the master cylinder device100which is the subject for control. The linear mode is a mode of a hydraulic pressure braking control selected when the vehicle is running under normal state. Under the linear mode, when the braking force corresponding to the operating amount of the brake pedal10cannot be sufficiently generated only by the regeneration brake device, the first and the second master pistons14and15are operated by the servo hydraulic pressure generating device4thereby to generate the hydraulic pressure braking force supplementing the insufficient amount of braking force. On the other hand, the “regulator mode” is a mode of the hydraulic pressure braking control selected when an abnormality has occurred. Under the regulator mode, the separation chamber1B is closed and each of the pistons13,14and15are driven by the operation force of the operator of the vehicle thereby to generate hydraulic pressure braking force. The two modes to which the invention is applied will be explained in more detail hereinafter.

In the “linear mode”, the brake ECU6energizes the separation lock valve22to open and energizes the reaction force valve23to close. Due to the closure of the reaction force valve23, the communication between the reaction force chamber1C and the reservoir171is interrupted and due to the opening of the separation lock valve22, the communication between the separation chamber1B and the reaction force chamber1C is established. When the brake pedal10is not depressed, the ball valve442of the servo hydraulic pressure generating device4keeps the through passage444aof the valve seat to be closed. Further, the pressure decreasing valve41is in an open state and the pressure increasing valve42is in a closed state thereby interrupting the communication between the first chamber4A and the second chamber4B. The second chamber4B is in communication with the servo chamber4A via the conduit163to keep the hydraulic pressure in the two chambers to be mutually in an equal level. The second chamber4B is in communication with the third chamber4C via the passages445cand445dof the control piston445, and further is in communication with the reservoir171via the conduits414and161. One side of the pressure control chamber4D is closed by the pressure increasing valve42and the other side is connected to the reservoir171through the pressure decreasing valve41. The fourth chamber4E is in communication with the first pressure chamber1D via the conduits511and51and the hydraulic pressure in the two chambers4E and1D are kept to the same hydraulic pressure level. Thus, there is no servo hydraulic pressure generated in the servo chamber1A and no master cylinder hydraulic pressure generated in the first pressure chamber1D.

Under this state, when the brake pedal10is depressed, the input piston13advances to interrupt the communication with the passage18. Thus, the communication between the reservoir171and the separation chamber1B is interrupted. The stroke simulator21generates the reaction force pressure in the separation chamber1B and the reaction force chamber1C in response to the stroke amount. In other words, the stroke simulator21applies the brake pedal10which is connected to the input piston13with the reaction force pressure corresponding to the stroke amount of the input piston13(operating amount of the brake pedal10).

It is noted here that the area of the surface of the flange portion142, facing to the reaction force chamber1C is set to be equal to the area of the tip end surface of the projection portion143. Therefore, when the reaction force valve is in a closed state and the separation lock valve22is in an open state, the internal pressure of the separation chamber1B and the internal pressure of the reaction force chamber1C are equal. Accordingly, the force that the reaction force pressure of the separation chamber1B is applied to the tip end surface of the projection portion143is equal to the force that the reaction force pressure of the reaction force chamber1C is applied to the surface facing to the reaction force chamber1C and even when the operator of the vehicle depresses the brake pedal10to raise the internal pressure of the separation chamber1B and the reaction force chamber1C, the first master piston14does not move. Further, since the area of the tip end surface of the projection portion143and the area of the surface of the flange portion142facing to the reaction force chamber1C are set to be equal, even when the first master piston14is moved, the fluid amount flowing into the stoke simulator21is not changed, the reaction force pressure in the separation chamber1B is not changed thereby keeping the reaction force transmitted to the brake pedal10to be unchanged.

On the other hand, the brake ECU6and the hybrid ECU8control the hydraulic pressure braking force generating device BF and the regeneration braking force generating device BM to apply the target braking force to each of the wheels5FR,5FL,5RR and5RL. According to the embodiment, the brake ECU6and the hybrid ECU8control to use the regeneration braking force generating device BM on a priority basis. In other words, the brake ECU6calculates the target value of the regeneration amount (target regeneration amount) and outputs the target regeneration amount to the hybrid ECU8. The hybrid ECU8then calculates the regeneration amount which executes (execution regeneration amount) relative to the target regeneration amount and outputs the execution regeneration amount to the brake ECU6. The brake ECU6then calculates the shortfall of the braking force by subtracting the regeneration braking force corresponding to the execution regeneration amount from the target braking force and controls the hydraulic pressure braking force generating device BF to generate the shortfall braking force.

In the servo pressure generating device4, the accumulator431and the pressure control chamber4D are in communication when the pressure increasing valve42opens. By the closure of the pressure decreasing valve41, the communication between the pressure control chamber4D and the reservoir171is interrupted. The hydraulic pressure in the pressure control chamber4D can be increased by the high pressure operation fluid supplied from the accumulator431. Due to the increase of the pressure in the pressure control chamber4D, the control piston445slidably moves in the cylinder bottom surface side direction. Then the control piston445contacts the ball valve442at the tip end of the projection portion445bof the control piston445to interrupt the passage445dby the ball valve442. Then the communication between the second chamber4B and the reservoir171is interrupted.

Further slidable movement of the control piston445towards the cylinder bottom surface side pushes the ball valve442towards the cylinder bottom surface side by the projection portion445bto separate the ball valve442from the valve seat portion444. This will allow communication between the first chamber4A and the second chamber4B through the through passage444aof the valve seat portion444. A high pressure operation fluid is supplied to the first chamber4A from the accumulator431and the hydraulic pressure in the second chamber4B which is in communication with the first chamber1A is also increased.

As the pressure in the second chamber4B increases, the servo hydraulic pressure in the servo chamber1A which is in communication with the second chamber4B increases accordingly. Due to the increase of the servo hydraulic pressure, the first master piston14advances and the master cylinder hydraulic pressure in the first pressure chamber1D increases by the advance movement of the first master piston14. Then the second master piston15is also advances to increase the master cylinder hydraulic pressure in the second pressure chamber1E. By this increase of the master cylinder hydraulic pressure, the high pressure operation fluid is supplied to the wheel cylinders541through544via the conduits51and52and the hydraulic pressure control portion5to apply hydraulic pressure braking force to the corresponding vehicle wheels5FR through5RL.

Further, the master cylinder hydraulic pressure in the first pressure chamber1D is fed back to the fourth chamber4E of the servo hydraulic pressure generating device4and accordingly, the pressure in the fourth chamber4E increases to be balanced with the pressure in the pressure control chamber4D thereby not to move the sub piston446by this pressure balance. Thus, the hydraulic pressure braking force can be generated which supplements the shortfall of the braking force based on the servo hydraulic pressure created by the high pressure operation fluid from the accumulator431.

If the generation of the hydraulic pressure braking force is stopped, the pressure decreasing valve41is set to be in an open state and the pressure increasing valve42is set to be in a closed state. Then the pressure control chamber4D is connected to the reservoir171thereby retreating the control piston445. By this retreatment of the control piston445, the servo hydraulic pressure generating device4returns to the state where the brake pedal10is not depressed.

It is noted here that according to the above explained hydraulic pressure braking force generating device BF, under the brake pedal10being kept in a depressed state, i.e., under the input piston13of the master cylinder1being kept in a stopped state, when the first and the second master pistons144and15are moved forward or when the first and the second master pistons14and15are moved forward faster than the speed of the input piston13, the volume of the reaction force chamber1C decreases while the volume of the separation chamber1B increases. Then the brake fluid in the reaction force chamber1C flows into the separation chamber1B via the conduits162and164. Faster the advance movement of the first and the second master pistons14and15relative to the input piston13, greater the flow resistance of the conduits162and163relative to the flow of the brake fluid from the reaction force chamber1C into the separation chamber1B becomes which may cause a forward drawn-into operation of the brake pedal10.

When the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL is increased, for example, when the low speed shifting from the regeneration braking operation to the hydraulic pressure braking operation, since at the early stage of the low speed shifting, the brake fluid is largely consumed at the wheel cylinders541through544, the increase of the brake fluid amount Q in the wheel cylinders541through544relative to the increase of the hydraulic pressure P of the brake fluid in the servo chamber1A of the master cylinder1is gradually increasing, as shown inFIG. 5A. In other words, unless the hydraulic pressure P of the brake fluid in the servo chamber1A of the master cylinder1is set to be in the range of Pb-Pa (Pb<Pa) and the brake fluid amount Q in the wheel cylinders541through544is set to be in the range of Qb-Qa (Qb<Qa), hydraulic pressure braking force at the wheels5FR,5FL,5RR and5RL is not generated or would be scarcely generated. As shown inFIG. 5B, the deceleration G of the vehicle cannot be raised. This may cause a delay in response of the hydraulic pressure braking operation.

Accordingly, in order to improve the brake pedal operation feeling by preventing such drawn-into phenomenon of the brake pedal10, when the brake fluid is supplied to the wheel cylinders541through544from the master cylinder1by driving the first and the second master pistons to advance forward, the speed of the advancement of the first and the second master pistons14and15is controlled to be limited to a predetermined speed (hereinafter referred to as set speed) which can avoid the drawn-into of the brake pedal10. Further, in order to improve the responsibility of the hydraulic pressure braking force, the brake ECU6advances the first and the second master pistons14and15with the set speed preceding the increase of the hydraulic pressure braking force. Thus, the brake fluid amount in the wheel cylinders541through544can be increased.

(Control Operation to Prevent the Drawn-Into Phenomenon of the Brake Pedal10and to Improve the Responsibility of the Hydraulic Pressure Braking Force by the Brake ECU6)

Next, the control operation to prevent the drawn-into phenomenon of the brake pedal10and to improve the responsibility of the hydraulic pressure braking force by the brake ECU6will be explained with reference to the flowchart ofFIG. 3. InFIG. 3, it is presumed that the drive start speed Vi with which the driving of the first and the second master pistons14and15to advance forward is set in advance to be a speed higher than a low speed start speed Vs of shifting from the regeneration braking force to the hydraulic pressure braking force. At the steps S1and S2, the brake ECU6judges whether the regeneration cooperative control is under operation or not by inputting each of the sensor signals, for example, detection signals from the stroke sensor71and the vehicle wheel speed sensor76and the execution regeneration braking force from the hybrid ECU8.

At the step S2, if the brake ECU6judged that the regeneration cooperative control is not executed, the process ends here but judged that the regeneration cooperative control is under execution, then at the step S3the brake ECU6further judges whether the operating amount of the brake pedal10is maintained to a constant amount, i.e., whether the depression of the brake pedal10is held to be the depressed state or not (corresponding to the holding state judging means). The reason why this judgment in the step S3has to be made is that if the brake pedal10is drawn into keeping the state that the brake pedal has been depressed to keep a constant operating amount, the brake operating feeling is worsened when the brake pedal10is drawn into, keeping the constant operating amount of the brake pedal10than in the case where the brake pedal10is drawn into when the operating amount of the brake pedal10is increased or decreased.

At the step S3, when the brake ECU6judges that the brake pedal10is depressed or released by the operator of the vehicle, the program advances to the step S9. On the other hand, if the brake ECU6judges that the depression of the brake pedal10by the operator is held to the depressed state, the program goes to the step S6.

At the step S6, the brake ECU6judges that the brake fluid amount in the wheel cylinders541through544is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL corresponding to the wheel cylinders541through544is predicted. For example, the brake ECU6compares the vehicle speed V obtained by a detection signal from the vehicle wheel speed sensor76with the drive start speed Vi set in advance and if the brake ECU6judged that the vehicle speed V is higher than the drive start speed Vi, the process ends here. On the other hand, if the vehicle speed V is equal to or lower than the drive start speed Vi, the brake ECU6judges that the brake fluid amount in the wheel cylinders541through544is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL corresponding to the wheel cylinders541through544has been predicted (corresponding to brake operation judging means). Then the program goes to the step S7.

At the step S7, the brake ECU6resets the advance speed of the first and the second master pistons14and15so that the fluid amount (for example, Qa) to be supplied to the wheel cylinders541through544can be supplied thereto by the time that the predicted hydraulic pressure braking force increase starts corresponding to the time from the judgment of the prediction of the increase of the hydraulic pressure braking force until the time that the predicted hydraulic pressure braking force increase starts (advance speed setting means). For example, the brake ECU6calculates the time from the judgment until the increase starts by dividing the value which is obtained by subtracting the shifting start speed Vs from the drive start speed Vi by the deceleration, then calculates the fluid amount to be supplied to the wheel cylinders541through544from the master cylinder1per unit time by dividing the brake fluid amount to be supplied to the wheel cylinders541through544by the time that the predicted hydraulic pressure braking force increase starts by the calculated time and sets the advance speed of the first and the second master pistons14and15corresponding to the calculated fluid amount to be the set speed. Then the brake ECU6advances the program to the step S8.

At the step S8, the brake ECU6advances the first and the second master pistons14and15with the set speed set at the step S7.

At the step S9, the brake ECU6judges whether the vehicle speed V obtained from the detection signal from the vehicle wheel speed sensor76drops to the shifting start speed Vs or not. If the brake ECU6judged that the vehicle speed V obtained from the detection signal from the vehicle wheel speed sensor76dropped to the shifting start speed Vs, the brake fluid amount to be supplied to the wheel cylinders541through544from the master cylinder1is increased at the step S10and the process ends.

Next, the operation of the brake ECU6will be explained with reference to the time chart inFIG. 4. InFIG. 4, it is presumed that the operating amount of the brake pedal10is increased to the time “t2” from the time “t0” and kept to a constant amount after the time “t2”. At the time “t0”, when the brake pedal10is depressed ((b) inFIG. 4), the vehicle speed V starts decreasing from the value V0from the time “t1” and thereafter and the regeneration cooperative control starts ((b) ofFIG. 4from the time “t1˜”). Then from the time “t1” to the time “t2”, the hydraulic pressure braking force increases according to the increase of the brake operating amount of the brake pedal10and from the time “t2” to the time “t3”, the hydraulic pressure braking force is decreased due to the increase of the regeneration braking force as the vehicle speed V decreases.

When the vehicle speed V becomes the drive start speed Vi at the time “t4”, the brake fluid amount in the wheel cylinders541through544becomes the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force is predicted. Therefore, the first and the second master pistons14and15advance with the set speed which has been set corresponding to the time from the increase predicted time “t4” to the increase of the hydraulic pressure braking force start time “t6” and the brake fluid is gradually supplied to the wheel cylinders541through544from the master cylinder1with a level that the deceleration would not be generated by the hydraulic pressure braking force (Step S8inFIG. 3). By this operation, the drawn-into operation of the brake pedal10is prevented thereby to improve the brake operation feeling thereof.

Then the hydraulic pressure P of the brake fluid in the servo chamber1A of the master cylinder1is gradually increased from the increase of the hydraulic pressure braking force predicted time “t4” until the time “t5” which is somewhat earlier than the time “t6” when the increase of the hydraulic pressure braking force starts (so that the hydraulic pressure P in the servo chamber1A can be surely increased to the value Pb at the time “t6” when the increase of the hydraulic pressure braking force starts) and from the time “t5” until the time “t6” when the increase of the hydraulic pressure braking force starts, the hydraulic pressure is held to be the value Pb (See (d) inFIG. 4). At the time “t6” when the increase of the hydraulic pressure braking force starts, the brake fluid amount Q in the wheel cylinders541through544has been surely increased to the value Qb to thereby improve the responsibility of the hydraulic pressure braking force at the time of increase thereof (SeeFIGS. 5A and 5B). It is noted here that the time that the hydraulic pressure reaches to the servo hydraulic pressure Pb can be set to be the time “t6” when the increase of the pressure braking force starts.

At the time “t6”, when the vehicle speed V becomes the shifting start speed Vs, the hydraulic pressure P of the brake fluid in the servo chamber1A is increased to the value Pa from Pb (See (d) inFIG. 4), the brake fluid amount to be supplied to the wheel cylinders541through544is added accordingly (Steps S9and S110inFIG. 2). Thus, the responsibility performance difference of the hydraulic pressure braking force relative to the regeneration braking force can be supplemented.

(Effects by the Control of Brake ECU6)

As explained, the brake ECU6judges that the brake fluid amount in the wheel cylinders541through544is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL corresponding to the wheel cylinders541through544is predicted. By this judgment, the set speed for advancing the first and the second master pistons14and15can be kept to be low and the brake fluid amount in the wheel cylinders541through544can be surely increased by the time that the predicted increase of the hydraulic pressure braking force starts. This can maintain the good operating feeling of the brake pedal10to more highly improve the responsibility of the hydraulic pressure braking force at the time of increase.

Further, the brake ECU6resets the advance speed of the first and the second master pistons14and15so that the fluid amount to be supplied to the wheel cylinders541through544can be supplied thereto by the time that the predicted hydraulic pressure braking force increase starts corresponding to the time from the judgment of the prediction of the increase of the hydraulic pressure braking force until the time that the predicted hydraulic pressure braking force increase starts. Thus, the brake fluid amount in the wheel cylinders541through544at the time of predicted increase of the hydraulic pressure braking force and the set speed of the first and the second master pistons14and15can be adjusted to improve both the operating feeling of the brake pedal10and the responsibility of the hydraulic pressure braking force more appropriately.

Further, the brake ECU6advances the first and the second master pistons14and15with the set speed. The brake fluid is gradually supplied to the wheel cylinders541through544from the master cylinder1with a level that the deceleration would not be generated by the hydraulic pressure braking force. Thus, for preparing for the increase of the hydraulic pressure braking force, the brake fluid is supplied to the wheel cylinders541through544from the master cylinder1preventing the drawn-into of the brake pedal10and the brake operating feeling by the brake pedal10and the responsibility of the hydraulic pressure braking force can be both further improved appropriately. In other words, since the first and the second master pistons14and15can be advanced with the set speed for a time period when the increase of the hydraulic pressure braking force is not yet required, a predetermined amount of the brake fluid is introduced into the wheel cylinders541through544and accordingly, brake fluid supply shortage in the wheel cylinders541through544does not occur which may otherwise be caused by the slow set speed of the first and the second master pistons14and15. Thus, the responsibility of the hydraulic pressure braking force will not drop. Further, since the brake fluid amount has been already increased in the wheel cylinders541through544at the time the increase of the hydraulic pressure braking force starts, the responsibility of the hydraulic pressure braking force at the time of increase can be improved. Further, the brake fluid is gradually supplied with the level that no deceleration is generated and accordingly, decreasing of the regeneration braking force is not necessary to improve the fuel efficiency of the vehicle.

Further, the brake ECU6increases the brake fluid amount to be supplied to the wheel cylinders541through544from the master cylinder1when the vehicle speed V obtained by the detection signal from the vehicle wheel speed sensor76has decreased to the shifting start speed Vs. Thus, since the increase of the brake fluid amount to be supplied to the wheel cylinders541through544from the master cylinder1starts when the vehicle speed has dropped to the shifting start speed Vs, the performance responsibility difference of the hydraulic pressure braking force relative to the regeneration braking force can be supplemented. In this case, the performance responsibility difference of the hydraulic pressure braking force relative to the regeneration braking force can be highly precisely supplemented by changing the increase amount of the brake fluid in response to the brake fluid amount in the wheel cylinders541through544in advance or the target hydraulic pressure braking force.

According to the embodiment explained above, when the vehicle speed V drops to the drive start speed Vi, the brake ECU6judges that the brake fluid amount in the wheel cylinders541through544is equal to the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force has been predicted. Therefore, the first and the second master pistons14and15advance with the set speed. However, the following cases also result in the same effects when controlled according to the above embodiment, in the case that during the vehicle being running, the operating amount of the brake pedal10is smaller than the predetermined amount and that the shift lever of the automatic transmission has been changed from the drive range to the neutral range, or the case that the operating amount of the brake pedal10is smaller than the predetermined amount and that a failure of the regeneration braking force generating device BM is detected to occur in a short time.

Still further, the vehicular brake device B is explained in which a master cylinder1is provided which includes the first and the second master pistons14and15which advance forward by the generation of the servo pressure in the servo chamber1A of the servo pressure generating device4. However, another vehicular brake device can be applied to the invention, in which the master cylinder is provided with the first and the second master pistons which are advanced by a servo motor and a ball screw mechanism.

According to the second embodiment, when it is judged that the brake fluid amount in the wheel cylinders541through544is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL corresponding to the wheel cylinders541through544is predicted, the drive start speed Vi corresponding to the set speed is set on a case-by case basis so that the brake fluid amount (for example, value Qa) to be supplied to the wheel cylinders541through544from the master cylinder1by the time when the predicted increase of the hydraulic pressure braking force starts.

The structure of the second embodiment is substantially the same with that of the first embodiment except that the control illustrated inFIG. 3according to the first embodiment corresponds to the control illustrated inFIG. 6according to the second embodiment. Accordingly, the control inFIG. 6will be explained and the explanation of the rest of the structure will be omitted. InFIG. 6, it is presumed that the advance speed of the first and the second pistons14and15is a constant value set in advance.

At the step S5, the brake ECU6sets the drive start speed Vi based on the deceleration and the shifting stat speed Vs. For example, the brake ECU6calculates the fluid amount of the brake fluid per unit time which is supplied to the wheel cylinders541through544from the master cylinder1by the advance movement of the first and the second pistons14and15. Then the brake ECU6calculates the supply time for supplying the fluid amount Qa with the wheel cylinders541through544based on the brake fluid amount (for example, Qa) to be supplied to the wheel cylinders541through544preceding the shifting to the low speed and the supply amount per unit time. Then the brake ECU6calculates the vehicle speed ΔV which changes from the start of advancement of the first and the second pistons14and15until the supply of the fluid is completed based on the deceleration and the supply time, then adding the vehicle speed ΔV to shifting start speed Vs the drive start speed Vi is calculated thereby.

At the step S16, the brake ECU6compares the vehicle speed V with the drive start speed Vi which was calculated at the step S5and when the vehicle speed V is higher than the drive start speed Vi, the process ends here. On the other hand when the vehicle speed V is equal to or smaller than the drive start speed Vi, the brake ECU6advances the program to the step S18. At the step S18, the brake ECU6advances the first and the second master pistons14and15with the advance speed set in advance.

According to the embodiments explained above, when the operating amount of the brake pedal10is judged to be constant at the step S3, the processes from the step S5and thereafter are executed. However, when the advance speed of the first and the second master pistons14and15relative to the input piston13is judged to be higher, the processes of the step S5and thereafter are executed. In this case the set speed may be set based on the advance speed of the input piston13. The advance speed of the input piston13may be calculated for example based on the stroke amount.

According to the embodiments explained above, when it is judged that the brake fluid amount in the wheel cylinders541through544is the amount by which the hydraulic pressure braking force would not be generated or would be scarcely generated at the corresponding wheels5FR,5FL,5RR and5RL and that the increase of the hydraulic pressure braking force to be generated at the wheels5FR,5FL,5RR and5RL corresponding to the wheel cylinders541through544is predicted, the brake ECU6advances the first and the second master pistons14and15with the set speed preceding the increase of the hydraulic pressure braking force. However, the first and the second master pistons14and15may be advanced with the set speed, even under the above conditions are not established if the advance speed of the first and the second master pistons14and15relative to the input piston13is relatively high.