Brake control apparatus and brake control method

To provide a brake control apparatus that brings a brake operating member to a proper position during antilock control.At least during operation of an antilock controller 105, valves 23 and 24 are actuated to impart a stroke to a piston 52P with hydraulic pressure generated by the pump 7.

TECHNICAL FIELD

The present invention relates to a brake control apparatus for an automobile.

BACKGROUND ART

Brake control apparatuses comprising a stroke simulator for generating reaction force in response to a driver's brake operation are known in the art. Patent Document 1, for example, discloses a brake control apparatus comprising an on-off valve between a stroke simulator and a master cylinder, the on-off valve being controlled to open and close during antilock control, so as to notify the driver of the ongoing antilock control.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

Such a conventional brake control apparatus may not always bring the brake operating member to a proper position during antilock control. An object of the present invention is to provide a brake control apparatus that brings the brake operating member to a proper position during antilock control.

Solution to Problem

To achieve this object, the brake operating apparatus of the present invention preferably controls each valve during operation under antilock control and uses hydraulic pressure generated by a hydraulic pressure source to impart a stroke to a piston of a master cylinder

Advantageous Effect of Invention

This ensures that the brake operating member is brought to a proper position.

DESCRIPTION OF EMBODIMENTS

The embodiments of the brake control apparatus of the present invention will now be described with reference to the accompanying drawings.

[Structure] First as to structure,FIG. 1is a schematic representation of the structure of the brake control apparatus (hereinafter “apparatus1”) according to the first embodiment. The apparatus1is a hydraulic brake apparatus for a brake system of an electric vehicle, such as a hybrid vehicle comprising, in addition to its engine, an electric motor (generator) as a power source for driving the wheels or an electric vehicle comprising only an electric motor (generator) as a power source. Such electric vehicles use a regenerative braking system including a motor (generator) to achieve regenerative vehicle braking by converting the vehicle's kinetic energy into electric energy. The apparatus1may also be used in a vehicle that uses its engine alone as a power source. The apparatus1transmits brake fluid to a wheel cylinder (caliper)8on each of wheels FL to RR of the vehicle to generate brake hydraulic pressure (wheel-cylinder hydraulic pressure), thereby applying hydraulic braking force to each of the wheels FL to RR. The apparatus1has two systems (primary system P and secondary system S) of brake piping, for example of X-shaped configuration. The two systems may instead be of front-rear piping configuration or other piping configuration. Below, letters P and S will be attached to the end of each reference character when distinguishing between a member of the system P and a corresponding member of the system S.

A brake pedal2is a brake operating member for receiving an input force for braking operation from the driver. The brake pedal2is provided with a stroke sensor90for measuring a displacement of the brake pedal2(a pedal stroke, namely, an amount of operation of the brake pedal2by the driver). A reservoir tank (reservoir)4is a brake fluid source storing brake fluid, which source is a low-pressure section exposed to atmospheric pressure. A master cylinder5generates brake hydraulic pressure (master cylinder pressure) in response to operation of the brake pedal2(brake operation) by the driver. The master cylinder5is connected via a push rod3to the brake pedal2and is supplied with brake fluid from the reservoir tank4. The master cylinder5is of tandem type comprising master cylinder pistons that move axially in accordance with brake operation by the driver. The master cylinder pistons are a primary piston52P connected to the push rod3and a secondary piston52S of free piston type. The apparatus1does not include a negative-pressure booster that utilizes intake negative pressure generated by the engine of the vehicle to boost or amplify brake operating force (pedal effort).

The apparatus1comprises a hydraulic control unit6and an electronic control unit100. The hydraulic control unit6is a control unit that is supplied with brake fluid from the reservoir tank4or the master cylinder5to generate brake hydraulic pressure, independent of brake operation by the driver. The electronic control unit (hereinafter “ECU”)100is a controller for the operation of the hydraulic control unit6.

The hydraulic control unit6comprises a first unit61and a second unit62. The hydraulic control unit6is located between the wheel cylinders8and the master cylinder5and is capable of applying master cylinder pressure or hydraulic control pressure to each wheel cylinder8individually. The hydraulic control unit6has a pump7and a plurality of control valves (electromagnetic valves21or the like) that serve as a hydraulic device (actuator) for generating hydraulic control pressure. The pump7is driven by a motor M to draw brake fluid from the reservoir tank4and direct the fluid to the wheel cylinders8. The pump7used in this embodiment is a gear pump having excellent noise/vibration characteristics, namely, an external gear pump unit. The pump7is shared by the two systems and driven by the single motor M. The motor M may be, for example, a brush motor. The electromagnetic valves21or the like are controlled to open and close in response to a control signal to control a flow of brake fluid. With communication between the master cylinder5and the wheel cylinders8cut off, the hydraulic control unit6uses hydraulic pressure generated by the pump7to increase the pressure in the wheel cylinders8. The hydraulic control unit6comprises a stroke simulator22. The stroke simulator22receives brake fluid transmitted from the master cylinder5in accordance with the driver's brake operation to generate a pedal stroke. The hydraulic control unit6comprises hydraulic sensors91to93that sense the output pressure from the pump7, master cylinder pressure, etc.

The ECU100receives detection values from a pedal stroke sensor90and the hydraulic sensors91to93and information on driving conditions sent from the vehicle. Using these items of information, the ECU100performs information processing, following a stored program. On the basis of the result of this processing, the ECU100outputs a control command to each actuator of the hydraulic control unit6to control the actuators. More specifically, the ECU100controls opening/closing operation of the electromagnetic valves21or the like, which change the state of communication of a fluid line11or the like, and also controls the speed (the amount of fluid from the pump7) of the motor M for driving the pump7. Controlling the hydraulic pressure in the wheel cylinders on the wheel FL to RR in this manner, the ECU100achieves boost control that assists in braking operation by generating hydraulic braking force to compensate for any shortage of the driver's braking effort, antilock control for minimizing slip (lockup tendency) of the wheels FL to RR caused by braking, brake control for vehicle dynamics control (vehicle stability control for antiskid, etc.; hereinafter “VDC”), automatic braking control, such as adaptive cruise control, cooperative regenerative braking control for controlling the hydraulic pressure in the wheel cylinders to attain a target deceleration (target braking force) in cooperation with regenerative braking, or such other control.

The master cylinder5is connected via the first fluid line11(described later) to the wheel cylinders8and serves as a first hydraulic pressure source for increasing wheel-cylinder hydraulic pressure. The master cylinder5uses master cylinder pressure generated in a first fluid chamber (primary chamber)51P to apply pressure to wheel cylinders8aand8dvia a fluid line (first fluid line11P) of the system P, and also uses master cylinder pressure generated in a second fluid chamber (secondary chamber)51S to apply pressure to wheel cylinders8band8cvia a fluid line (first line11S) of the system S. The pistons52of the master cylinder5are inserted in a tubular cylinder50having a closed bottom to move axially along the inner circumferential surface of the cylinder50. The cylinder50comprises an outlet port (supply port)501and an inlet port502both for each of the systems P and S. The outlet port501is connected to the hydraulic control unit6to communicate with the wheel cylinder8. The inlet port502is communicatively connected to the reservoir tank4. The first fluid chamber51P, located between pistons52P and52S, contains a compressed coil spring53P, serving as a return spring. The second fluid chamber51S, located between the piston52S and the axial end of the cylinder50, contains a compressed coil spring53S. Each of the first and second fluid chambers51P and51S has an outlet port501normally open thereto.

The cylinder50has a plurality of piston seals54on the inner circumference thereof. The piston seals54are seal members that slide on the seal piston52P or52S to seal between the outer circumferential surface of each of the pistons52P and52S and the inner circumferential surface of the cylinder. Each piston seal54is a seal member (cup seal) of a known cup-shaped cross section having a lip on its inner radial side (though such detail is omitted from the drawings). When the lip is in sliding contact with the outer circumferential surface of the piston52, brake fluid is allowed to flow in one direction and is prevented from flowing in the other direction. A first piston seal541is oriented to allow brake fluid to flow from the inlet port502toward the first and second fluid chambers51P and51S (outlet port501), while preventing brake fluid from flowing in the opposite direction. A second piston seal542is oriented to allow brake fluid to flow toward the inlet port502, while preventing fluid brake from flowing out from the inlet port502. The first and second fluid chambers51P and51S decrease in volume to develop hydraulic pressure (master cylinder pressure) as the pistons52are moved along a stroke in the axial direction opposite to the brake pedal2by the driver stepping on the brake pedal2. This causes brake fluid to pass from the first and second fluid chambers51P and51S through the outlet ports501to the wheel cylinders8. The systems P and S generate substantial equal levels of hydraulic pressure in the first and second fluid chambers51P and51S.

Now, the brake fluid pressure circuit of the hydraulic control unit6will be described with reference toFIG. 1. Letters a to d are attached to the end of reference characters to indicate members for the wheels FL to RR, respectively. The fluid line11connects the outlet ports501(first and second fluid chambers51P and51S) of the master cylinder5to the wheel cylinders8. A cut valve (cutoff valve)21is a normally open electromagnetic valve (that is open when electric current is not applied thereto) in the first fluid line11. The first fluid line11is divided by the cut valve21into a fluid line11A on the master cylinder5side and a fluid line11B on the wheel cylinder8side. Solenoid IN valves (pressure increasing valves) SOL/V IN25are normally open electromagnetic valves on the respective wheels FL to RR (or in the respective fluid lines11ato11d) on the wheel cylinder8side (fluid line8side) of the cut valve21in the first fluid line11. Disposed in parallel to the first fluid line11is a bypass fluid line110that bypasses the SOL/V IN25. The bypass fluid line110is provided with a check valve (one-way valve)250that admits only brake fluid flowing from the wheel cylinder8side to the master cylinder5side.

An inlet fluid line15connects the reservoir tank4to an inlet70of the pump7. An outlet fluid line16connects an outlet71of the pump7to a portion of the first fluid line11connecting the cut valve21to the SOL/V IN25. A check valve160is an outlet valve of the pump7that is located in the outlet fluid line16and admits only brake fluid flowing from the outlet71side to the first fluid line11side. The outlet fluid line16divides on the downstream side of the check valve160into an outlet fluid line16P of the system P and an outlet fluid line16S of the system S. The fluid lines16P and16S are connected to the first fluid line11P of the system P and the first fluid line11S of the system S, respectively. The outlet fluid lines16P and16S form a communication passage interconnecting the first fluid lines11P and11S. A communication valve26P is a normally closed electromagnetic valve (closed when electric current is not applied) provided in the outlet fluid line16P. A communication valve26S is a normally closed electromagnetic valve provided in the outlet fluid line16S. The pump7is a second hydraulic pressure source that uses brake fluid supplied from the reservoir tank4to generate hydraulic pressure in the first fluid line11. The pump7is connected via the communication passage (outlet fluid lines16P and16S) and the first fluid lines11P and11S to the wheel cylinders8ato8dand can increase wheel-cylinder hydraulic pressure by delivering brake fluid to the communication passage (outlet fluid lines16P and16S).

A first pressure-reducing fluid line17connects the inlet fluid line15to a portion of the outlet fluid line16between the check valve160and the communication valve16. A pressure-regulating valve27is a normally open electromagnetic valve serving as a first pressure-reducing valve on the first pressure-reducing fluid line17. A second pressure-reducing fluid line18connects the inlet fluid line15to a portion of the first fluid line11on the wheel cylinder8side of the SOL/V IN25. A solenoid OUT valve (pressure-reducing valve) SOL/V OUT28is a normally closed electromagnetic valve serving as a second pressure-reducing valve on the second pressure-reducing line18. A second fluid line12is a branch fluid line that branches off from the first fluid line11P and connects to the stroke simulator22. The stroke simulator22comprises a piston220and a spring221. The piston220is a partition wall that divides the interior of a cylinder of the stroke simulator22into two chambers (positive-pressure chamber R1and back-pressure chamber R2), and is axially movable in the cylinder. The piston220has a seal member (not shown) on its outer circumferential surface, facing the inner circumferential surface of the cylinder. The seal member seals off any space on the outer circumference of the piston220to prevent communication of brake fluid between the positive-pressure chamber (primary chamber) R1and the back-pressure chamber (secondary chamber) R2, thereby keeping the chambers R1and R2fluid-tight against each other. The spring221is an elastic member, namely a spring compressed, for example in the back-pressure chamber R2, so as to always urge the piston200toward the positive-pressure chamber R1(in the direction of reducing the volume of the positive-pressure chamber R1and increasing the volume of the back-pressure chamber R2). The spring221may instead be disposed to extend its natural length. The spring221is so disposed as to exert reaction force according to a displacement (stroke) of the piston220.

The second fluid line12branches off from a portion (fluid line11A) of the first fluid line11P between the outlet port50P (first fluid chamber51P) of the master cylinder5and the cut valve21P and connects to the positive-pressure chamber R1of the stroke simulator22. A third fluid line13is a back-pressure fluid line connecting the back-pressure R2of the stroke simulator22to the reservoir tank4. A stroke-simulator OUT valve23is a normally closed first simulator cut valve on the third fluid line13. The third fluid line13is divided by the stroke-simulator OUT valve23into a fluid line13A on the stroke simulator22side and a fluid line13B on the reservoir tank4side. A fourth fluid line14is a branch fluid line that branches off from the first fluid line11P. The fourth fluid line14branches off from a portion of the first fluid line11P (fluid line11B) between the cut valve21P and the SOL/V IN25and connects to a portion (fluid line13A) of the third fluid line13between the stroke-simulator OUT valve23and the back-pressure chamber R2. The fourth fluid line14may instead be connected directly to the back-pressure chamber R2. A stroke-simulator IN valve24is a normally closed second simulator cut valve on the fourth fluid line14. The stroke-simulator IN valve24is a normally closed second simulator cut valve on the fourth fluid line14. The stroke simulator IN valve24may instead be a normally open electromagnetic valve.

The pump7(outlet71) is connected via the outlet fluid line16P, the first fluid line11P (fluid line11B), the fourth fluid line14, and the third fluid line13(fluid line13A) to the back-plate chamber R2and can increase hydraulic pressure in the back-pressure chamber R2by delivering (outputting) brake fluid to the outlet fluid line16P. The pump7(outlet71) is connected via the outlet fluid line16and the first fluid line11to the master cylinder5(fluid chamber51) and can increase master cylinder pressure by delivering brake fluid to the outlet fluid line16. The cut valve21is disposed on the first fluid line11between the pump7(outlet71) and the master cylinder5(fluid chamber51).

The cut valve21, the SOL/V IN25, and the pressure-regulating valve27are proportional control valves that adjust the degree of valve opening in accordance with electric current applied to their solenoid. The other valves, namely, the communication valve26, the SOL/V OUT valve28, the stroke-simulator OUT valve23, and the stroke-simulator IN valve24are on-off valves that are controlled to switch between two values to open and close. These other valves may instead be proportional control valves.

In a portion (fluid line11A) of the first fluid line11P between the cut valve21P and the master cylinder5is disposed a hydraulic sensor91for sensing hydraulic pressure in that portion (master cylinder pressure and hydraulic pressure in the positive-pressure chamber R1of the stroke simulator22). The hydraulic sensor91may instead be disposed in the second fluid line12. In a portion of the first fluid line11between the cut valve21and the SOL/V IN25is disposed a hydraulic sensor (primary-system pressure sensor, secondary-system pressure sensor)92for sensing hydraulic pressure (wheel-cylinder hydraulic pressure) in that portion. In a portion of the first pressure-reducing fluid line17between its connection to the outlet fluid line16and the pressure-regulating valve27is disposed a hydraulic sensor93for sensing hydraulic pressure (pump outlet pressure) in that portion. The hydraulic sensor93may instead be disposed in a portion of the outlet fluid line16between the outlet71(check valve160) of the pump7and the communication valve26.

The first unit61of the hydraulic control unit6comprises, of all the above-described actuators, the cut valve21P of the system P, the stroke simulator22, the stroke-simulator OUT valve23, the stroke-simulator IN valve24, and the hydraulic senor91. The second unit62comprises the other actuators, namely, the valves21S and25to28, the hydraulic sensors92and93, and the pump7. The second unit62is integrated with the motor M and the ECU100. The first unit61is located between the master cylinder5and the second unit62. The first and second units61and62are interconnected by a single brake pipe63, which is part of the first fluid line11. The first and second units61and62are adapted to actively control the master cylinder pressure and the wheel-cylinder hydraulic pressure by controlling the actuators in response to a control command from the ECU100.

With the cut valve21controlled to open, the brake system (first fluid line11) connecting the fluid chamber51of the master cylinder5and the wheel cylinders8forms a first system that uses master cylinder pressure exerted by pedal effort to generate wheel-cylinder hydraulic pressure and thereby achieves pedal-effort braking (control without boosting). On the other hand, with the cut valve21controlled to close, the brake system (inlet fluid line15, outlet fluid line16, etc.) including the pump7and connecting the reservoir tank4and the wheel cylinders8forms a second system that uses hydraulic pressure generated by the pump7to generate wheel-cylinder hydraulic pressure, that is, a so-called brake-by-wire system that achieves boost control, cooperative regenerative control, or the like.

During brake-by-wire control, the stroke simulator22generates reaction force in response to the driver's braking operation. With the cut valve21controlled to close and the communication between the master cylinder5and the wheel cylinders8cut off, the stroke simulator22generates a pedal stroke by allowing at least brake fluid coming out of the master cylinder5(first fluid chamber51P) to the first fluid line11P to flow via the second fluid line12into the positive-pressure chamber R1. With the cut valve21P controlled to close and the stroke-simulator OUT valve23controlled to open, establishing communication between the back-pressure chamber R2and the reservoir tank4, the stroke simulator22generates a pedal stroke in such a manner that the positive-pressure chamber R1allows brake fluid to flow into or out of the master cylinder5as the driver performs braking operation (stepping on the brake pedal2or releasing it). More specifically, when the pressure differential between hydraulic pressure (master cylinder pressure acting as a positive pressure) acting on a pressure-receiving surface of the piston220in the positive-pressure chamber R1and hydraulic pressure (back pressure) acting on a pressure-receiving surface of the piston220in the back-pressure R2has reached a predetermined value or higher, the piston220compresses the spring221and axially moves toward the back-pressure chamber R2, increasing the volume of the positive chamber R1. In this manner, brake fluid flows from the master cylinder5(outlet port501P) via the fluid line (first fluid line11P and second fluid line12) into the positive-pressure chamber R1, while brake fluid flows out of the back-pressure chamber R2via the third fluid line13into the reservoir tank4. The third fluid line13serves its purpose as long as it is connected to a low-pressure section into which brake fluid can flow, and is not required to be connected to the reservoir tank4. When the pressure differential has dropped below the predetermined value, the urging force (resilient force) of the spring221returns the piston220to its initial position. Since the reaction force exerted by the spring221acting on the piston220is proportional to the displacement of the piston220, reaction force generated that acts on the brake pedal2(hereinafter “pedal reaction force”) is proportional to the operation of the brake pedal2. Drawing brake fluid from the master cylinder5and generating the pedal reaction force in this manner, the stroke simulator22reproduces a proper feel of the pedal when depressed, approximating the stiffness of fluid in the wheel cylinders8.

The ECU100comprises: a brake operating condition detector101; a calculator102for calculating a target wheel-cylinder hydraulic pressure; a pedal-effort braking force generator103; a wheel-cylinder hydraulic pressure controller104; and a stroke controller106. The brake operating condition detector101receives an input of a value detected by the stroke sensor90, thereby detecting a displacement (pedal stroke) of the brake pedal2as an amount of brake operation. The brake operating condition detector101determines whether the driver is operating the brakes (whether the brake pedal2is being operated). The stroke sensor90is not limited to one that directly detects a displacement of the brake pedal2, and may be one that detects a displacement of the push rod3. Alternatively, a pedal sensor for detecting force on the brake pedal2may be used to determine an amount of brake operation from a value detected by the pedal sensor. In other words, the amount of brake operation used for control is not limited to the pedal stroke and may be any other proper variable.

The calculator102for calculating a target wheel-cylinder hydraulic pressure calculates a target wheel-cylinder hydraulic pressure. For example, during boost control, the calculator102for calculating a target wheel-cylinder hydraulic pressure calculates, on the basis of a pedal stroke detected, a target wheel-cylinder hydraulic pressure that achieves a predetermined boost ratio, that is, ideal characteristics of the relation between the pedal stroke and a brake hydraulic pressure required by the driver (a vehicle deceleration G required by the driver). For example, in the case of a brake apparatus comprising a negative-pressure booster of ordinary size, this embodiment uses predetermined characteristics of the relation between a pedal stroke and a wheel-cylinder hydraulic pressure (braking force) achieved during operation of the negative-pressure booster as the above-described ideal relational characteristics for calculating a target wheel-cylinder hydraulic pressure. During antilock control, the calculator102for calculating a target wheel-cylinder hydraulic pressure calculates a target wheel-cylinder hydraulic pressure for each of the wheels FL to RR to bring the wheel to a proper degree of slip (amount of deviation of the speed of the wheel from a simulated vehicle speed). During VDC, the calculator102for calculating a target wheel-cylinder hydraulic pressure calculates a target wheel-cylinder hydraulic pressure for each of the wheels FL to RR on the basis of, for example, a detected amount of vehicle dynamic conditions (e.g., lateral acceleration) to achieve desired vehicle dynamic conditions. During regenerative cooperation brake control, the calculator102for calculating a target wheel-cylinder hydraulic pressure calculates a target wheel-cylinder hydraulic pressure in relation to regenerative braking force. For example, the target wheel-cylinder hydraulic pressure so calculated is such that the sum of a regenerative braking force input from a control unit of a regenerative braking system and a hydraulic braking force corresponding to the target wheel-wheel hydraulic pressure satisfies a vehicle deceleration required by the driver.

The pedal-effort braking force generator103controls the cut valve21to open and thereby brings the hydraulic control unit6into a condition of generating wheel-cylinder hydraulic pressure from master cylinder pressure (first system) to achieve pedal-effort braking.

The wheel-cylinder hydraulic pressure controller104controls the cut valve21to close and thereby brings the hydraulic control unit6into a condition in which the pump7(second system) can be used to generate wheel-cylinder hydraulic pressure (pressure-increasing control), so as to perform hydraulic control (e.g., boosting control) that achieves a target wheel-cylinder hydraulic pressure by controlling the actuators of the hydraulic control unit6. More specifically, the wheel-cylinder hydraulic pressure controller104controls the cut valve21to close, the communication valve26to open, and the pressure-regulating valve27to close, and actuates the pump7. This control enables a desired amount of brake fluid to flow from reservoir tank4via the inlet fluid line15, pump7, outlet line16, and first fluid line11into the wheel cylinders8. At the same time, the rotating speed of the pump7and the opening (e.g., degree of opening) of the pressure-regulating valve27are controlled by feedback to bring a value detected by the hydraulic sensor92toward a target wheel-cylinder hydraulic pressure, thereby providing a desired braking force. In this embodiment, in principle, the pressure-regulating valve27, rather than the pump7, is adjusted to control wheel-cylinder hydraulic pressure. The pressure-regulating valve27, since it is a proportional control valve, can be finely controlled to achieve smooth control of wheel-cylinder hydraulic pressure. Cutting off the communication between the master cylinder5side and the wheel cylinder8side by controlling the cut valve8to close makes it easy to control wheel-cylinder hydraulic pressure independently of the driver's pedal operation. During normal braking in which a braking force corresponding to the driver's brake operation (pedal stroke) is generated in the front and rear wheels FL to RR, the wheel-cylinder hydraulic pressure controller104performs boost control. In the boost control, the SOL/V IN25on each of the wheels FL to RR is controlled to open, and the SOL/V OUT28is controlled to close.

The wheel-cylinder hydraulic pressure controller104has an antilock controller105. The antilock controller105reads the speed of each of the wheels FL to RR as vehicle information and detects and monitors the slip condition of the wheels FL to RR. When any of the wheels FL to RR is determined to have a lockup tendency while braking force is applied to the wheels FL to RR (e.g., during the driver's braking operation), that is, when the degree of slip of that wheel is determined to be excessive, the wheel-cylinder hydraulic pressure controller104intervenes in hydraulic control (boost control) for brake operation and controls the hydraulic pressure in the wheel cylinder with an excessive degree of slip to increase or decrease, with the cut valve21controlled to close. This control brings the degree of slip of that wheel to a proper value. More specifically, with the cut valve21controlled to close, the communication valve26controlled to open, and the pressure-regulating valve27controlled to close, the pump7is actuated. This control enables a desired amount of brake fluid to flow from the reservoir tank4via the inlet fluid line15, pump7, outlet fluid line16, and first fluid line11into the wheel cylinders8. At this stage, if a hydraulic-pressure command for a wheel cylinder8under control is to increase the hydraulic pressure, the SOL/V IN25on that wheel cylinder8is controlled to open, and the SOL/V OUT28is controlled to close, so as to bring brake fluid into the wheel cylinder8for pressure increase therein. If a hydraulic pressure command for the wheel cylinder8is to reduce the hydraulic pressure, the SOL/V IN25on that wheel cylinder8is controlled to close, and the SOL/V OUT28is controlled to open, so as to bring brake fluid in the wheel cylinder8into the inlet fluid line15for pressure decrease. If a hydraulic-pressure command for the wheel cylinder8is to hold the hydraulic pressure, the SOL/V OUT28and SOL/V IN25on the wheel cylinder8are controlled to close, thereby keeping the hydraulic pressure in the wheel cylinder8unchanged.

The stroke controller6controls the operation of the stroke-simulator IN valve24and the stroke-simulator OUT valve23to control the operating conditions of the stroke simulator22. In this control, the stroke of the piston52P of the master cylinder5is controlled to enable active control of the operation of the brake pedal2. When pedal-effort braking is performed by the pedal-effort braking force generator103, the stroke controller106does not operate the stroke simulator22in response to the driver's brake operation. That is, the stroke controller106controls the stroke-simulator OUT valve23to close. The stroke-simulator IN valve24is also controlled to close. Alternatively, the stroke-simulator IN valve24may be controlled to open.

During the control of hydraulic pressure by the wheel-cylinder hydraulic pressure controller104, the stroke controller106actuates the stroke simulator22as the driver operates the brakes. When the brake operating condition detector101detects the absence of brake operation, the stroke controller106prevents operation of the stroke simulator22. More specifically, the stroke controller106controls the stroke-simulator OUT valve23and stroke-simulator IN valve24to close. When the brake operating condition detector101has detected braking operation, the stroke controller106actuates the stroke simulator22in accordance with the driver's braking operation when antilock control is not performed by the antilock controller105. More specifically, the stroke controller106controls the stroke-simulator OUT valve23to open and the stroke-simulator IN valve24to close. When the brake operating condition detector101has detected braking operation and the antilock controller105is performing antilock control, the stroke controller106actuates the stroke-simulator IN valve24and the stroke-simulator OUT valve23in accordance with the condition of the antilock control. In other words, to reduce wheel-cylinder hydraulic pressure in the antilock control, the stroke controller106controls the stroke-simulator OUT valve23to close and the stroke-simulator IN valve24to open. To increase the wheel-cylinder hydraulic pressure during the antilock control, the stroke controller106controls the stroke-simulator OUT valve23to open and the stroke-simulator IN valve24to close. To hold the wheel-cylinder hydraulic pressure during the antilock control, the stroke controller106controls the stroke-simulator OUT valve23and the stroke-simulator IN valve24to close.

FIG. 2is a flowchart of the control by the stroke controller106. This process is programmed as software in the ECU100and is repeated at predetermined intervals. As a prerequisite for this process, hydraulic pressure control by the wheel-cylinder hydraulic pressure controller104is in progress at the start of the process inFIG. 2. That is, the wheel cylinders8have received some hydraulic-pressure command, and the pump7is in operation, with the cut valve21controlled to close, the pressure-regulating valve27controlled to close (feedback-controlled in degree of opening or the like) and the communication valve26controlled to open. Step S1determines the presence or absence of operation of the brake pedal2on the basis of information sent from the brake operating condition detector101. If no pedal operation is detected (in other words, if braking operation is not performed), the process proceeds to step2. If pedal operation is detected, the process proceeds to step S3. In step2, the stroke-simulator OUT valve23and the stroke-simulator IN valve24are controlled to close. Step S3determines whether antilock control is in progress on the basis of information sent from the antilock controller105(or on the basis of the computation by the ECU100). If antilock control is not detected, the process proceeds to step S4. If antilock control is in progress, the process proceeds to step S5. In step S4, the stroke-simulator OUT valve23is controlled to open, and the stroke-simulator IN valve24is controlled to close.

Step S5computes the sum of the amounts of brake fluid required for the wheel cylinders8on a certain plurality of wheels FL to RR (hereinafter “required amounts of brake fluid”) from information sent from the antilock controller105(from the condition of the ongoing antilock control) on the basis of brake forces required for that certain plurality of wheels FL to RR (on the basis of target wheel-cylinder hydraulic pressures), and then determines whether the required amounts of brake fluid (the sum) are on the decrease. If they are determined to be on the decrease, the process proceeds to step S6. If not, the process proceeds to step S7.

Step S5uses the sum of the required amounts of brake fluid as a parameter for determining, with improved accuracy, changes in the amount of brake fluid in the apparatus1as a whole resulting from a decrease/hold/increase in wheel-cylinder hydraulic pressure during antilock control. More specifically, to decrease braking force on a wheel to avoid slipping, the amount of brake fluid required for the wheel cylinder8on that wheel is reduced. In principle, a reduction in required amount of brake fluid leads to a reduction in wheel-cylinder hydraulic pressure. In the meantime, the braking force on another wheel may be increased on the same timing. In that case, the amount of brake fluid required for the wheel cylinder8on that wheel increases. It is desirable that an increase or decrease in the sum of the amounts of brake fluid required for the wheel cylinders8on all such wheels is taken into account to determine a change in the brake fluid in the apparatus1as a whole. In this embodiment, that certain plurality of wheels are four wheels (front and rear wheels FL to RR). This embodiment calculates the sum of the amounts of brake fluid required for the wheel cylinders8on those wheels. If the sum of the required amounts of brake fluid is, for example, changed to the decrease, it can be determined that the wheel-cylinder hydraulic pressure in the apparatus1as a whole is on the decrease. In general, however, the wheel cylinders8aand8bon the front wheels FL and FR consume a greater amount of brake fluid than the wheel cylinders8cand8don the rear wheels RL and RR. For this reason, it is possible to compare only the right and left wheel cylinders8aand8bon the front wheels (in other words, calculate the sum of the amounts of brake fluid required for the wheel cylinders8aand8bon the right and left front wheels) in determining a change in the amount of brake fluid for the apparatus1as a whole (an increase or decrease in wheel-cylinder hydraulic pressure exerted by the apparatus1as a whole), and it is not always required to take all of the wheels FL to RR into account.

In step S6, the stroke-simulator OUT valve23is controlled to close, and the stroke-simulator IN valve24is controlled to open. More specifically, the stroke-simulator IN valve24is opened for a predetermined period of time. Step S7determines whether the required amounts of brake fluid (the sum) are changed to the increase. If they are changed to the increase, the process proceeds to step S8. If not, the process proceeds to step S9. In step S8, the stroke-simulator OUT valve23is controlled to open, and the stroke-simulator IN valve24is controlled to close. More specifically, the stroke-simulator OUT valve23is controlled to open for a predetermined period of time. In step S9, the stroke-simulator OUT valve23and the stroke-simulator IN valve24are controlled to close.

Working

This embodiment brings about the following working. The stroke controller106actuates the stroke simulator22in accordance with the driver's braking operation during hydraulic control. When the brakes are not in operation, the stroke controller106controls the stroke-simulator OUT valve23and the stroke-simulator IN valve24to close and thereby cuts off communication between the back-pressure chamber R2and the low-pressure section (reservoir)/the high-pressure section (the outlet71of the pump7). This puts the stroke simulator22into inoperative state. In other words, the issuance of a wheel-cylinder hydraulic command when the brake pedal2is not operated indicates, for example, the time when braking force is generated for control (VDC) for antiskid or the time when braking force is generated when the vehicle is decelerating under control to keep a certain distance from the vehicle in front. In such time, it is not necessary to transmit reaction force to the brake pedal2even during antilock control. For this reason, when the brakes are not in operation, the stroke-simulator OUT valve23and the stroke-simulator IN valve24are controlled to close to make the pedal stroke constant (substantially zero).

When the vehicle is not under antilock control during braking operation, the stroke-simulator OUT valve23is controlled to open to establish communication between the back-pressure chamber R2of the stroke simulator22and the low-pressure section (reservoir). The stroke-simulator IN valve24is controlled to close so as to cut off communication between the back-pressure chamber R2and the high-pressure section (outlet71of the pump7). In this manner, the stroke simulator22is actuated in accordance to the driver's brake operation. Since the vehicle is in normal braking operation, pedal stroke is controlled by allowing brake fluid released from the master cylinder by the driver's pedal operation to flow into the positive-pressure chamber R1of the stroke simulator2. This gives the driver a proper feel of the pedal.

When the vehicle is under antilock control during braking operation, the stroke-simulator IN valve24and the stroke-simulator OUT valve23are actuated in accordance with the condition of the antilock control, and hydraulic pressure generated by the pump7is used to actuate the stroke simulator22. By giving the piston52P of the master cylinder5a stroke in this manner and controlling the amount (position) of the stroke, the position of the pedal stroke2(pedal stroke) is controlled.

More specifically, when the wheel-cylinder hydraulic pressure is reduced (when the sum of required amounts of brake fluid is reduced), the stroke-simulator OUT valve23is controlled to close so as to cut off communication between the back-pressure chamber R2and the low-pressure section (reservoir). The stroke-simulator IN valve24is controlled to open so as to establish communication between the back-pressure chamber R2and the high-pressure section (outlet71of the pump7). This increases the pressure in the back-pressure chamber R2. In other words, brake fluid is transmitted from the first fluid line11P (fluid line11B), which is under high pressure owing to the outlet pressure of the pump7, via the fourth fluid line14into the third fluid line13. The back-pressure chamber R2of the stroke simulator22, communicating with the third fluid line13, increases in pressure. When force exerted on the piston220by the pressure in the back-pressure chamber R2(which hereinafter means the sum of this force and the reaction force exerted by the spring221) has exceeded force exerted on the piston220by the pressure in the positive-pressure chamber R1(master cylinder pressure), the piston220moves toward the positive-pressure chamber R1. This allows hydraulic pressure to flow via the second fluid line12and the first fluid line11P (fluid line11A) into the first fluid chamber51P of the master cylinder5, increasing the pressure (master cylinder pressure) in the first fluid chamber51P. This in turn increases the pedal reaction force. When the force exerted on the piston52P of the master cylinder5by an input (stepping force) to the brake pedal2has dropped below the force exerted on the piston52P by the master cylinder pressure (which hereinafter means the sum of this force and the urging force of the coil spring53P), the piston52is pushed backward toward the pushrod3. This reduces pedal stroke. In other words, the brake pedal2moves in its return direction. The amount by which the brake pedal2returns can be determined by the relation between braking force (target wheel-cylinder hydraulic pressure) required for each of the wheels FL to RR or a required amount of brake fluid during antilock control and the pedal stroke and braking force (or consumed amount of brake fluid) during normal braking. The braking force (target wheel-cylinder hydraulic pressure) required for each of the wheels FL to RR or required amount of brake fluid during antilock control reflects the frictional resistance (road frictional force) of the road on which the vehicle is travelling, and the calculated value of the braking force or required amount of brake fluid decreases, for example, with decreasing road frictional force. The amount of return of the brake pedal2so determined can be used to set a time period for opening the stroke-simulator IN valve24.

To increase wheel-cylinder hydraulic pressure (to increase the sum of required amounts of brake fluid), the stroke-simulator OUT valve23is controlled to open so as to establish communication between the back-pressure chamber R2and the low-pressure section (reservoir tank4). Closing the stroke-simulator IN valve24cuts off communication between the back-pressure chamber R2and the high-pressure section (outlet71of the pump7). This reduces the pressure in the back-pressure chamber R2. Since the fluid line13A is connected via the fluid line13B to the reservoir tank4, the back-pressure chamber R2, communicating with the fluid line13A, decreases in pressure. When the force exerted on the piston220by the pressure in the back-pressure chamber R2has dropped below the force exerted on the piston220by the pressure (master cylinder pressure) in the positive-pressure chamber R1, the piston220moves toward the back-pressure chamber R2. This reduces the pressure (master cylinder pressure) in the first fluid chamber51P, communicating through the first fluid line11P (fluid line11A) and the second fluid line12with the positive-pressure chamber R1. This in turn reduces pedal reaction force. When the force exerted on the piston52P by an input (pedal effort) to the brake pedal2has exceeded the force exerted on the piston52P by the master cylinder pressure, the piston52P moves toward the first fluid chamber51P. This increases pedal stroke. In other words, the brake pedal2moves in the direction of pedal effort. The distance of this movement of the brake pedal2can be determined from the relation between the braking force (target wheel-cylinder hydraulic pressure) required for each of the wheels FL to RR in antilock control or required amount of brake fluid and pedal stroke and braking force (or consumed amount of brake fluid) during normal braking. As described above, the braking force (target wheel-cylinder hydraulic pressure) required for each of the wheels FL to RR in antilock control or the required amount of brake fluid reflects road frictional force. The distance of movement of the brake pedal2determined in the above-described manner can be used to set a time period for opening the stroke-simulator OUT valve23.

To hold the wheel-cylinder hydraulic pressure (to prevent the sum of required amounts of brake fluid from increasing or decreasing), the stroke-simulator OUT valve23and the stroke-simulator IN valve24are controlled to close so as to cut off communication between the back-pressure chamber R2and the low-pressure section (reservoir)/high-pressure section (outlet71of the pump7). This keeps pedal reaction force and pedal stroke from changing and thus holds the position of the brake2substantially fixed. In this manner, the operation of the stroke-simulator IN valve24and the stroke-simulator OUT valve23is properly controlled during antilock control according to the operating condition of antilock control (according to the control condition of each wheel cylinder8). Properly controlling the pedal stroke and pedal reaction force in this manner makes it possible to generate or adjust pedal stroke and pedal reaction force and thereby minimize a sense of unease the driver may experience. In this way, a pedal feel that is hardly disconcerting to the driver can be achieved.

There are conventionally known brake control systems that control the operation of a brake control member used by the driver to perform brake operation. To control the operation of the brake operating member, such control systems are adapted to control the operation of a hydraulic pressure source, with the communication between master cylinder and wheel cylinders cut off, to generate a desired amount of brake hydraulic pressure, while adjusting reaction force exerted by the stroke simulator, on which hydraulic pressure from the master cylinder acts. Such a control system is commonly referred to as a brake-by-wire system. Also commonly known are antilock controllers that minimize wheel slip during braking. There are well-known brake apparatuses that perform antilock control without a brake-by-wire system, the brake apparatuses comprising: a negative-pressure booster between the brake operating member and the master cylinder, the negative-pressure booster boosting the operating force exerted by the driver and transmitting brake fluid from the master cylinder to the wheel cylinders; and an actuator for the antilock control device, the actuator being disposed between the master cylinder and the wheel cylinders. Upon starting antilock control, such a brake apparatus controls the pressure in the wheel cylinders to decrease in order to reduce wheel slip and returns excessive brake fluid via a pump to the master cylinder. This increases the pressure in the master cylinder. When the force resulting from this pressure has exceeded the output from the negative-pressure booster, the brake operating member is moved back. When the tire slip is sufficiently reduced, the antilock control device controls the pressure in the wheel cylinders to increase. For this purpose, brake fluid is transmitted from the master cylinder to the wheel cylinders. This reduces the pressure in the master cylinder. When the force resulting from this pressure has dropped below the output from the negative-pressure booster, the brake operating member moves in its forward direction. The amount of brake fluid required for a wheel cylinder decreases with decreasing road frictional force. For this reason, a less amount of brake operation (with the brake operating member closer to its original position) is required to balance force when road frictional force is small than when it is large, and it is difficult to move the brake operating member any further. In this way, antilock control causes the brake operating member to move forward and backward (in the return direction and in the forward direction) and enables the driver to perceive the antilock control. Since the brake operating member moves by a distance corresponding to an amount of brake fluid required for the wheel cylinder (according to road frictional force), the position of the brake operating member serves as an indicator that can be used by the driver to estimate the road frictional force (limit of adhesion).

Since a brake-by-wire system does not communicate between the master cylinder and the wheel cylinders, hydraulic changes in the wheel cylinders during antilock control do not affect the master cylinder. In contrast, brake apparatuses, like that disclosed in Patent Reference 1, having an on-off valve between the stroke simulator and the master cylinder, open and close the on-off valve during antilock control to increase and decrease reaction force in response to operation of the brake operating member, thereby notifying the driver of the ongoing antilock control, as is known in the art. Such a conventional brake apparatus, however, can limit the amount of operation (displacement) in the forward direction by closing the on-off valve and thus increasing reaction force in response to operation of the brake operating member, but cannot move the brake operating member in its return direction. As such, failure to bring the brake operating member to a proper position (a position close to that to which the above-described brake apparatus performing antilock control without a brake-by-wire system would bring the brake operating member) gives the driver a sense of unease, aggravates a feel of the brakes when operated, and causes the driver to misestimate road frictional force (or makes it impossible for the driver to estimate).

In contrast, the apparatus1of this embodiment, when performing antilock control as a brake-by-wire system, controls the valves23and24and uses hydraulic pressure generated by the pump7as a hydraulic pressure source, thereby imparting a stroke to the piston52P of the master cylinder5. This makes it possible to control the brake pedal2, which is a brake operating member, to a proper position (pedal stroke). In other words, the apparatus1of this embodiment provides improved reaction to the brake pedal2during antilock control (closely approximating the above-described brake apparatus performing antilock control without a brake-by-wire system) to overcome the above-described problem.

For example, the fluid line11B of the first fluid line11undergoes changes in pressure resulting from a pressure increase or decrease in the wheel cylinders8. However, since the fluid line11A is separated from the fluid line11B by the cut valve21, changes in the pressure in the fluid line11B do not affect the fluid line11A. In such state, a change in master cylinder pressure does not occur. In the case where the stroke-simulator OUT valve23is opened during antilock control, the relation between pedal reaction force and pedal stroke during antilock control is the same as that without antilock control and remains unchanged. In contrast, the stroke controller106of this embodiment recognizes a decrease in wheel-cylinder hydraulic pressure (a decrease in the sum of required amounts of brake fluid) during antilock control as the driver's excessive depression of the brake pedal and thus increases pedal reaction force to reduce pedal stroke. When wheel-cylinder hydraulic pressure increases during antilock control (when the sum of required amounts of brake fluid increases), the stroke controller106recognizes this increase as a condition in which the driver's further depression of the brake pedal2would not pose a problem, and reduces pedal reaction force to increase pedal stroke. This makes it possible to bring the pedal brake to a proper position (a position close to that to which the above-described brake apparatus performing antilock control without a brake-by-wire system would bring the brake operating member). Further, the brake pedal2moves in its return direction, as well as in the forward direction. This minimizes the possibility of the driver feeling a sense of unease. Setting the amount of time for opening each of the valves23and24in the above-described manner adjusts pedal stroke to a smaller value when road frictional force is small than that when it is large and to a larger value when road frictional force is large than that when it is small. In short, the pedal brake2moves by a distance corresponding to the amount of brake fluid required for the wheel cylinder8(in accordance with road frictional force). The pedal stroke therefore serves as an indicator that can be used by the driver to estimate the road frictional force properly and prevents misestimating the road frictional surface.

When antilock control has ended while hydraulic control is in progress during brake operation, the process inFIG. 2proceeds to step S4to control the stroke-simulator OUT valve23to open and the stroke-simulator IN valve24to close. In this way, immediately after antilock control ends, it is possible to give the driver a pedal feel as he would experience during normal braking. As such, a pedal feel that hardly causes a sense of unease in the driver can be created.

Regardless of control of the pressure on the back-pressure chamber R2side during antilock control and the movement of the pistons220and52P resulting from that control, the amount of brake fluid present in the section on the positive-pressure chamber R1side upstream of the cut valve21P (in other words, in the section between the first fluid chamber51P of the master cylinder5, the first fluid line11P (fluid line11A), and between the second fluid line12and positive-pressure chamber R1) does not vary between before and after antilock control. The balance between the incoming and outgoing amounts of fluid on the positive-pressure chamber R1side remains unbroken. In other words, the amount of fluid on the positive-pressure chamber R1side after the antilock control does not differ from that during hydraulic control before the antilock control. Therefore, the relation between pedal effort and pedal stroke does not fluctuate from the beginning of antilock control until the end of the antilock control. As such, a pedal feel that hardly causes a sense of unease in the driver can be created.

The fourth fluid line14connects a portion (fluid line13) between the stroke-simulator OUT valve23on the third fluid line13and the back-pressure chamber R2to a portion between the cut valve21P on the first fluid line11P (fluid line11B) and the SOL/V IN25. This shortens the distance of the fluid line from the wheel cylinders8to the back-pressure chamber R2, compared with that if the fourth fluid line14were connected, not to the first fluid line11P, but for example to the fluid line16on the outlet side of the pump7, and simplifies the fluid line configuration of that route. In this embodiment, the hydraulic control unit6is provided with two separate units (units61and62), with the cut valve21P of the system P, the stroke simulator22, the stroke-simulator OUT valve23, and the stroke-simulator IN valve24disposed in the unit61. Such structure makes it possible to contain the fourth fluid line14in the unit61. This eliminates the need for connecting the two units61and62via the brake pipe that forms the fourth fluid line14. This in turn simplifies the apparatus1as a whole.

The first embodiment of the present invention brings about the following effects:(1) The brake control apparatus1comprises: the first fluid line11connecting the master cylinder5, which generates hydraulic pressure by a stroke of the piston52in response to the driver's braking operation, to the wheel cylinders8on the wheels FL to RR; the pump (hydraulic pressure source) for generating hydraulic pressure in the first fluid line11with brake fluid supplied from the reservoir tank4; the cut valve21in the first fluid line11between the pump7and the master cylinder5; the stroke simulator22for generating reaction force in response to the driver's braking operation, the stroke simulator22comprising the positive-pressure chamber R1and the back-pressure chamber R2that are separated by the piston220(partition wall); the second fluid line12connecting the positive-pressure R1(one of the two chambers of the stroke simulator22) to a portion between the cut valve21P on the first fluid line11P and the master cylinder5; the third fluid line13connecting the back-pressure chamber R2(the other chamber of the stroke simulator22) to the reservoir tank4(low-pressure section); the stroke-simulator OUT valve23on the third fluid line13; the fourth fluid line14connecting a portion between the stroke-simulator OUT valve23on the third fluid line13and the back-pressure chamber R2to a portion between the cut valve21P on the first fluid line11P and the wheel cylinders8; the stroke-simulator IN valve24on the fourth fluid line14; and the antilock controller105for detecting any slip of the wheels FL to RR and increasing and decreasing the hydraulic pressure in the wheel cylinders8, wherein at least during operation of the antilock controller105, the valves23and24are actuated to impart a stroke to the piston52with hydraulic pressure generated by the pump7.

Imparting a stroke to the piston52P makes it possible to control the position of the brake pedal2(brake operating member) properly.(2) The brake control apparatus1further comprises the hydraulic pressure controller104that actuates the cut valve21to close and uses pump7(hydraulic pressure source) to increase wheel-cylinder hydraulic pressure, wherein when the antilock controller105has started antilock control during control by the hydraulic pressure controller104, the valves23and24are actuated to impart a stroke to the piston52P with hydraulic pressure generated by the pump7.

This makes it possible to control the position of the brake pedal2properly during brake-by-wire operation.(3) The brake control apparatus1further comprises the solenoid IN valves SOL/V IN25on the first fluid line11between the cut valve21and the wheel cylinders8, wherein the forth fluid line14is connected to a portion between the cut valve21P on the first fluid line11P and the SOL/V IN25.

This shortens and simplifies the fluid passage extending from the wheel cylinders8to the back-pressure chamber R2.(5) The piston220(partition wall) moves to impart a stroke to the piston52.

This active movement of the stroke simulator22makes it possible to control the position of the brake pedal2.(7) The brake control apparatus1further comprises the brake operating condition detector101for determining whether the driver is operating the brakes, wherein when the brake operating condition detector101detects brake operation in progress and the antilock controller105is not in operation, the stroke-simulator OUT valve23is actuated to open and the stroke-simulator IN valve24is actuated to close.

This makes it possible to control the position of the brake pedal2during brake operation when antilock control is not in progress.(8) When the brake operating condition detector101detects brake operation in progress and the antilock controller105operates to reduce wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve23is actuated to close and the stroke-simulator IN valve24is actuated to open.

This makes it possible to control the position of the brake pedal2during brake operation and antilock pressure-reducing control.(9) When the brake operating condition detector101detects brake operation in progress and the antilock controller105operates to increase wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve23is actuated to open and the stroke-simulator IN valve24is actuated to close.

This makes it possible to control the position of the brake pedal2during brake operation and antilock pressure-increasing control.(10) When the brake operating condition detector101detects brake operation in progress and the antilock controller105operates to hold wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve23and the stroke-simulator IN valve24are actuated to close.

This makes it possible to control the position of the brake pedal2during brake operation and antilock holding control.(11) The brake control apparatus1comprises the first fluid line11connecting the master cylinder5, which generates hydraulic pressure by a stroke of the piston52in response to the driver's braking operation, to the wheel cylinders8on the wheels FL to RR; the pump7(hydraulic pressure source) for generating hydraulic pressure in the first fluid line11with brake fluid supplied from the reservoir tank4; the cut valve21on the first fluid line11between the pump7and the master cylinder5; the stroke simulator22for generating reaction force in response to the driver's braking operation, the stroke simulator22comprising the positive-pressure chamber R1and the back-pressure chamber R2that are separated by the piston220(partition wall); the second fluid line12connecting the positive-pressure R1(one of the two chambers of the stroke simulator22) to a portion between the cut valve21P on the first fluid line11P and the master cylinder5; the third fluid line13connecting the back-pressure chamber R2(the other chamber of the stroke simulator22) to the reservoir tank4(low-pressure section); the stroke-simulator OUT valve23on the third fluid line13; the fourth fluid line14connecting a portion between the stroke-simulator OUT valve23on the third fluid line13and the back-pressure chamber R2to a portion between the cut valve21P on the first fluid line11P and the wheel cylinders8; the stroke-simulator IN valve24on the fourth fluid line14; the hydraulic pressure controller104for actuating at least the cut valve21to close and increasing wheel-cylinder hydraulic pressure with the pump7; the antilock controller105for increasing or decreasing the hydraulic pressure in the wheel cylinders8upon detecting a lockup tendency in a wheel; and the stroke controller106for actuating the stroke-simulator IN valve24and the stroke-simulator OUT valve23, at least during operation of the antilock controller105, so as to impart a stroke to the piston52with hydraulic pressure generated by the pump7.

This brake control apparatus brings about the effects described in (1) and (2) above.(20) A brake control method using a brake control apparatus1comprising a stroke simulator22for generating reaction force in response to the driver's brake operation by allowing brake fluid flowing from the master cylinder5, which generates hydraulic pressure by a stroke of the piston52in response to the driver's brake operation, to flow into one (positive-pressure chamber R1) of two separate chambers, a stroke-simulator OUT valve23on a third fluid-line13between the other chamber (back-pressure chamber R2) of the stroke simulator22and the reservoir tank (reservoir)4; and a stroke-simulator IN valve24on a fourth fluid line14connecting a third fluid line13(fluid line13A), located between the back-pressure R2and the stroke-simulator OUT valve23, to the pump7(hydraulic pressure source), wherein the stroke-simulator OUT valve23and the stroke-simulator IN valve24are actuated during antilock control, and hydraulic pressure generated by the pump7is used to control the position of the piston52P.

This brings about the effect as stated in (1) above.

FIG. 3schematically shows the structure of a brake control apparatus1according to the second embodiment. The apparatus1of this embodiment comprises a fourth fluid line14connected, not to a line (fluid line11B) between the cut valve21P on the first fluid line11P and the wheel cylinders8like that of the first embodiment, but to a fluid line16on the outlet side of the pump7. More specifically, the fourth fluid line14branches off from a portion in the output fluid line16between the check valve160and the communication valve26P and connects to a line (fluid line13A) in a third fluid line13between the stroke-simulator OUT valve23and the back-pressure chamber R2. First and second units61and62are connected by two brake pipes63and64, which are parts of the first fluid line11P and the fourth fluid line14, respectively. Since other elements of the second embodiment are the same as those of the first embodiment, their description is omitted by assigning the same reference numerals as those used in the first embodiment.

When the stroke controller106opens the stroke-simulator IN valve24, the back-pressure chamber R2and the high-pressure section (outlet71of the pump7) communicate with each other. This increases the pressure in the back-pressure chamber R2. More specifically, brake fluid is directed from the outlet fluid line16pressurized by outlet pressure exerted by the pump7, through the fourth fluid line14to the third fluid line13. The back-pressure chamber R2, communicating with the third fluid line13, increases in pressure. This brings about the same effect as that of the first embodiment. Further, the fluid line extending from the pump7to the back-pressure chamber R2is shorter in distance and simpler in structure than it would be if the fourth fluid line14were connected, not to the outlet fluid line16, but, for example to the first fluid line11P. Shortening the fluid line extending from the pump7to the back-pressure chamber R2makes it possible to transmit brake fluid from the pump7to the back-pressure chamber R2more quickly. This in turn leads to an improved response for a pressure increase in the back-pressure chamber R2, and thus improved controllability of pedal stroke. Structural features similar to those of the first embodiment bring about effects similar to those of the first embodiment.

The apparatus1of the second embodiment brings about the following effect:(4) The fourth fluid line14is connected to the fluid line (outlet fluid line16) on the outlet side of the pump7, instead of to the line connecting the cut valve21P of the first fluid line11P and the wheel cylinders8.

This shortens and simplifies the fluid line extending from the pump7to the back-pressure chamber R2.

FIG. 4schematically shows the brake control apparatus1according to the third embodiment. To generate braking force in the wheels FL to RR under hydraulic control, the first and second embodiments directly sends an output from the pump7to the wheel cylinders8. In contrast, the third embodiment stores pressurized brake fluid in an accumulator29in advance and adjusts an amount of fluid required for the wheel cylinders8under control performed by the SOL/V IN25and SOL/V OUT28. In other words, the apparatus1of this embodiment has a second unit62that is structurally different from that of the second embodiment.

The first fluid cylinder11connects the master cylinder5and the wheel cylinders8aand8bon the front wheels Fl and FR. The outlet fluid line16connects the outlet71of the pump7and the wheel cylinders8ato8d. The outlet fluid lines16aand16bon the front wheels FL and FR are connected to the first fluid line11(fluid line11B), through which the outlet fluid lines16aand16bare connected to the wheel cylinders8aand8bon the front wheels FL and FR. Between the check valve160of the outlet fluid line16and the wheel cylinders8are disposed the SOL/V IN25(in fluid lines16ato16c) for the respective wheels FL to RR. The SOL/V IN25are normally closed electromagnetic valves. The accumulator29is connected via a fluid line19to the line between the check valve160on the outlet line16and the SOL/V IN25. The fourth fluid line14branches off from the line between the check valve160on the output fluid line16and the SOL/V IN25and connects to the line (fluid line13A) of the third fluid line13between the stroke-simulator OUT valve23and the back-pressure chamber R2.

The second pressure-reducing fluid line18connects a portion of the outlet fluid line16on the wheel cylinder8side of the SOL/V IN25, to the inlet fluid line15. The second pressure-reducing fluid line18is provided with the SOL/V OUT28for the respective wheels FL to RR. The SOL/V OUT28are normally closed proportional control valves. This embodiment does not use the pressure-regulating valves27(first pressure-reducing fluid lines17), the communication valves26, or the check valves250, as in the first and second embodiments. Between the check valve160on the outlet fluid line16and the SOL/V IN25is provided a hydraulic pressure sensor93for sensing the hydraulic pressure (the hydraulic pressure of fluid stored in the accumulator29or pump outlet pressure) at the location of the hydraulic pressure sensor93. Between each of the SOL/V IN25in the outlet fluid line16and the respective wheel cylinder8(or between the cut valve21P on the first fluid line11P and the wheel cylinders8on the front wheels FL and FR) is provided a hydraulic pressure sensor94for sensing the hydraulic pressure (wheel-cylinder hydraulic pressure) at the location of the hydraulic pressure sensor94.

With at least the SOL/V IN25controlled to close, the wheel-cylinder hydraulic pressure controller104operates the pump7so as to transmit brake fluid from the reservoir tank4via the inlet fluid line15, pump7, outlet fluid line16, and fluid line19to the accumulator29and thereby store desired hydraulic pressure in the accumulator29. The accumulator29is a hydraulic pressure source that uses brake fluid supplied from the reservoir tank4to generate hydraulic pressure in the outlet fluid line16and the first fluid line11. The wheel-cylinder hydraulic pressure controller104controls the cut valve21to close and feedback-controls the opening (degree of opening or the like) of the SOL/V IN25and SOL/V OUT28to bring a value detected by the hydraulic pressure sensor94toward a target wheel-cylinder hydraulic pressure. This makes it possible to adjust the hydraulic pressure delivered from the accumulator29via the outlet fluid line16and the first fluid line11to each wheel cylinder8and apply desired braking force to each of the wheels FL to RR. The antilock controller105controls the cut valve21to close and also controls the opening of the SOL/V IN25and SOL/V OUT28, as described above. In this way, the antilock controller105increases or decreases the hydraulic pressure in the cylinder8on any wheel slipping unduly. Since other elements of the third embodiment are similar to those of the second embodiment, their description is omitted by assigning the same reference numerals as those used in the second embodiment.

The stroke controller106establishes communication between the back-pressure chamber R2and the high-pressure section (accumulator29) by controlling the stroke-simulator IN valve24to open. This makes it possible to increase the pressure in the back-pressure chamber R2. More specifically, brake fluid is directed from the outlet fluid line16pressurized by accumulating pressure in the accumulator29, via the fourth fluid line14to the third fluid line13. In this way, the back-pressure chamber R2, in communication with the third fluid line13, increases in pressure. This brings about the same effect as that of the first embodiment.

Structural features of the apparatus1of this embodiment similar to those of the first and second embodiments bring about effects similar to those of the first and second embodiments.

Other Embodiments

Although a number of embodiments of the present invention have been described above by way of example, the present invention is not limited to the specific embodiments described above, but includes design modifications, etc., that do not depart from the scope of the present invention.

For example, the brake control apparatus (hydraulic control unit) of the present invention involving stroke control is sufficient as long as it is capable of performing antilock control, with communication between master cylinder and wheel cylinder cut off, and is not limited to the above embodiments.

The brake pedal and the master cylinder can be provided therebetween with a booster that is capable of transmitting drive force mechanically, such as a link-type booster.

The method of actuating various actuators for controlling wheel-cylinder hydraulic: pressure described above is not limited to the above embodiments and can be modified, as required.

Various valves, pumps, motors, a stroke simulator, or other elements included in the hydraulic control unit may be included in either the first unit or the second unit.

The hydraulic control unit can be of integral type combining the first and second units or of multiunit type with the first or second unit divided into subunits. The hydraulic pressure source is not limited to a gear pump or an accumulator and may be of other types, for example, a plunger pump, or an electrically powered piston cylinder.

The above embodiments use hydraulic wheel cylinders on the wheels, but are not limited to such wheel cylinders and may be provided with hydraulic wheel cylinders on the front wheels and calipers on the rear wheels, the calipers using electric motors to generate braking force.

The present invention may be embodied as follows:(1) The brake control apparatus may comprise:

a first fluid line connecting a master cylinder, which generates hydraulic pressure by a stroke of a piston in response to a driver's braking operation, to a wheel cylinder on a wheel;

a hydraulic pressure source for generating hydraulic pressure in the first fluid line with brake fluid supplied from a reservoir tank;

a cut valve on the first fluid line between the hydraulic pressure source and the master cylinder;

a stroke simulator for generating reaction force in response to the driver's braking operation, the stroke simulator comprising two chambers separated by a partition wall;

a second fluid line connecting one of the two chambers of the stroke simulator to a portion between the cut valve on the first fluid line and the master cylinder;

a third fluid line connecting another chamber of the stroke simulator to a low-pressure section;

a stroke-simulator OUT valve on the third fluid line;

a fourth fluid line connecting a portion between the stroke-simulator OUT valve on the third fluid line and said another chamber to a portion between the cut valve on the first fluid line and the wheel cylinder;

a stroke-simulator IN valve on the fourth fluid line; and

an antilock controller for detecting any slip of the wheel and increasing and decreasing hydraulic pressure in the wheel cylinder, wherein

at least during operation of the antilock controller, each of the valves is actuated to impart a stroke to the piston with hydraulic pressure generated by the hydraulic pressure source.(2) The brake control apparatus according to (1) may comprise a hydraulic pressure controller that actuates the cut valve to close and uses the hydraulic pressure source to increase wheel-cylinder hydraulic pressure, wherein when the antilock controller has started antilock control during control by the hydraulic pressure controller, each of the valves is actuated to impart a stroke to the piston with hydraulic pressure generated by the hydraulic pressure source.(3) The brake control apparatus according to (2) may comprise a solenoid IN valve on the first fluid line between the cut valve and the wheel cylinder, wherein the forth fluid line is connected to a portion between the cut valve on the first fluid line and the solenoid IN valve.(4) The brake control apparatus according to (1) may be so configured that the partition wall moves to impart a stroke to the piston.(5) The brake control apparatus according to (4) may be so configured that when it is determined that the driver's brake operation is in progress and the antilock controller is not in operation, the stroke-simulator OUT valve is actuated to open and the stroke-simulator IN valve is actuated to close.(6) The brake control apparatus according to (4) may be so configured that when it is determined that the driver's brake operation is in progress and the antilock controller operates to reduce wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve is actuated to close and the stroke-simulator IN valve is actuated to open.(7) The brake control apparatus according to (4) may be so configured that when it is determined that the driver's brake operation is in progress and the antilock controller operates to increase wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve is actuated to open and the stroke-simulator IN valve is actuated to close.(8) The brake control apparatus according to (4) may be so configured that when it is determined that the driver's brake operation is in progress and the antilock controller operates to hold wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve and the stroke-simulator IN valve are actuated to close.(9) The brake control apparatus according to (1) may be so configured that the fourth fluid line is connected to a fluid line on an outlet side of the hydraulic pressure source, instead of a portion between the cut valve of the first fluid line and the wheel cylinder.(10) The brake control apparatus according to (1) may comprise:

a brake operating condition detector for determining whether the driver's brake operation is in progress; and

a hydraulic pressure controller for controlling the cut valve to close and increasing wheel-cylinder hydraulic pressure with the hydraulic pressure source, wherein

when the brake operating condition detector has detected the absence of brake operation, the stroke-simulator OUT valve and the stroke-simulator IN valve are actuated to close.(11) The brake control apparatus may comprise:

a first fluid line connecting a master cylinder, which generates hydraulic pressure by a stroke of a piston in response to a driver's braking operation, to a wheel cylinder on a wheel;

a hydraulic pressure source for generating hydraulic pressure in the first fluid line with brake fluid supplied from a reservoir tank;

a cut valve on the first fluid line between the hydraulic pressure source and the master cylinder;

a stroke simulator for generating reaction force in response to the driver's braking operation, the stroke simulator comprising two chambers separated by a partition wall;

a second fluid line connecting one of the two chambers of the stroke simulator to a portion between the cut valve on the first fluid line and the master cylinder;

a third fluid line connecting another chamber of the stroke simulator to a low-pressure section;

a stroke-simulator OUT valve on the third fluid line;

a fourth fluid line connecting a portion between the stroke-simulator OUT valve on the third fluid line and said another chamber to a portion between the cut valve on the first fluid line and the wheel cylinder;

a stroke-simulator IN valve on the fourth fluid line;

a hydraulic pressure controller for actuating at least the cut valve to close and increasing wheel-cylinder hydraulic pressure with the hydraulic pressure source;

an antilock controller for increasing and decreasing hydraulic pressure in the wheel cylinder when it has detected a lockup tendency; and

a stroke controller for actuating the stroke-simulator IN valve and the stroke-simulator OUT valve, at least during operation of the antilock controller, so as to impart a stroke to the piston with hydraulic pressure generated by the hydraulic pressure source.(12) The brake control apparatus according to (11) may comprise:

a solenoid IN valve on the first fluid line between the cut valve and the wheel cylinder; wherein

the fourth fluid line is connected to a portion between the cut valve on the first fluid line and the solenoid IN valve.(13) The brake control apparatus according to (11) may be so configured that the fourth fluid line is connected to a fluid line on an outlet side of the hydraulic pressure source, instead of a portion between the cut valve on the first fluid line and the wheel cylinder.(14) The brake control apparatus according to (13) may comprise:

a brake operating condition detector for determining whether the driver's brake operation is in progress; and

a hydraulic pressure controller for controlling the cut valve to close and increasing wheel-cylinder hydraulic pressure with the hydraulic pressure source, wherein

when the brake operating condition detector has detected the absence of brake operation, the stroke-simulator OUT valve and the stroke-simulator IN valve are actuated to close.(15) The brake control apparatus according to (13) may be so configured that when the brake operating condition detector has detected brake operation and the antilock controller is not in operation, the stroke-simulator OUT valve is actuated to open and the stroke-simulator IN valve is actuated to close.(16) The brake control apparatus according to (13) may be so configured that when the brake operating condition detector has detected brake operation and the antilock controller operates to decrease wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve is actuated to close and the stroke-simulator IN valve is actuated to open.(17) The brake control apparatus according to (13) may be so configured that when the brake operating condition detector has detected brake operation and the antilock controller operates to increase wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve is actuated to open and the stroke-simulator IN valve is actuated to close.(18) The brake control apparatus according to (13) may be so configured that when the brake operating condition detector has detected brake operation and the antilock controller operates to hold wheel-cylinder hydraulic pressure, the stroke-simulator OUT valve and the stroke-simulator IN valve are actuated to close.(19) The brake control apparatus according to (11) may be so configured that the partition wall moves to impart a stroke to the piston.(20) A brake control method using a brake control apparatus may comprise:

a stroke simulator for generating reaction force in response to a driver's brake operation by allowing brake fluid flowing from the master cylinder, which generates hydraulic pressure by a stroke of the piston in response to the driver's brake operation, to flow into one of two separate chambers in the stroke simulator;

a stroke-simulator OUT valve on a fluid line between another chamber of the stroke simulator and a reservoir; and

a stroke-simulator IN valve on a fluid line connecting a fluid line, located between said another chamber and the stroke-simulator OUT valve, to a hydraulic pressure source, wherein

the stroke-simulator OUT valve and the stroke-simulator IN valve are actuated during antilock control, and hydraulic pressure generated by the hydraulic pressure source is used to control the position of the piston.

The present application claims priority to Japanese patent application No. 2013-191431 filed on Sep. 17, 2013. The whole content of the disclosure in Japanese patent application No. 2013-191431 filed on Sep. 17, 2013, including the specification, claims, drawings, and abstract, are incorporated by reference in the present application.

REFERENCE SIGNS LIST

1. brake control apparatus

5. master cylinder

11. first fluid line

12. second fluid line

13. third fluid line

14. fourth fluid line

16. outlet fluid line (fluid line on the outlet side of the hydraulic pressure source)

21. cut valve

25. solenoid IN valve

FL to RR. wheels