Device for controlling brake system of vehicle with care for battery

A device for controlling an electro-hydraulic brake system of a vehicle checks if the battery or the alternator forming an electric power source for the electric part of the brake system is in its normal operating condition, and when the battery or the alternator is not in its normal operating condition, lowers the load imposed on the battery, so as to care the battery against a too soon failure. The device may also check if the driver is pumping the brake pedal at a substantial standstill of the vehicle, and when the brake pedal is so pumped, also lowers the load imposed on the battery, so as to care the battery against a useless consumption of the battery.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a device for controlling an electric or
 electro-hydraulic brake system of a vehicle such as an automobile with
 care for a battery forming an electric power source for the electric or
 electro-hydraulic brake system.
 2. Description of the Prior Art
 Not only in an electric brake system of a vehicle in which a braking force
 is directly generated from an electric current supplied from a battery of
 the vehicle but also in an electro-hydraulic brake system of a vehicle
 recently developed in a high variety as described in, for example, U.S.
 patent application Ser. No. 09/263,226 by the same assignee as the present
 application, in which a pump is driven by a battery of the vehicle to
 provide a pressurized brake fluid source, so that wheel cylinders of
 wheels are selectively supplied with the pressurized brake fluid from the
 source under a control of solenoid-actuated on-off valves, it is essential
 that the battery is operating at its normal condition.
 In Japanese Patent Laid-open Publication 7-17375, it is described that in a
 brake system in which a brake oil pressure is normally controlled by a
 solenoid control valve according to a duty ratio of a control current
 supplied from a battery, when a lowering of the output voltage of the
 battery is detected by a voltage sensor, the duty ratio control is
 stopped, while the control valve is maintained at a constant position.
 It is not correctly checked if a battery is in a normally operating
 condition or not when no substantial load is imposed on the battery.
 Therefore, it is considered to check the battery during an operation of
 the brake system, such that, for example, the output voltage thereof is
 detected by a sensor when the brake pedal is depressed beyond a
 predetermined depth. However, those modern electro-hydraulic brake systems
 under the recent high variety developments are mostly adapted to execute
 various automatic behavior controls such as anti-spin controls,
 anti-driftout controls, anti-overroll controls, etc. depending upon
 separate applications of a controlled braking to each of the generally
 four wheels, and therefore, the operation of the brake system is an
 integration of a driver's braking intention and a control calculation of
 an automatic behavior controller constructed by an electronic computer.
 Therefore, in those modern electro-hydraulic brake systems it is very
 difficult to check the battery operating condition under its prescribed
 loading condition.
 In view of such a difficulty, the present inventor has proposed in a
 co-pending application No. 09/440,587 filed Nov. 15, 1999 a device for
 controlling an electro-hydraulic brake system of a vehicle incorporating a
 particular system for correctly checking the operating condition of the
 battery of the vehicle.
 SUMMARY OF THE INVENTION
 The inventor now turns his contemplation on a concept how the battery can
 be cared when the output voltage of the battery has lowered as detected by
 an appropriate device such as proposed by the above-mentioned separate
 application, or when it is anticipated that the battery will lose its
 normal operating condition in the near future, because an alternator for
 charging the battery is not normally operating, or further when the
 vehicles are driven by some drivers who have a habit of pumping the brake
 pedal when the vehicle is at a substantial standstill, thereby uselessly
 consuming the electric power of the battery.
 In the electro-hydraulic brake system in which the brake fluid supplied to
 the wheel cylinders is pressurized by a pump driven by a motor energized
 by the battery of the vehicle, and is selectively supplied to a selected
 one or more of the wheel cylinders as controlled by electrically operated
 on-off valves such as solenoid valves energized by the battery according
 to depressions of the brake pedal by the driver, a substantial amount of
 electric power is consumed each time when an adjustment of the braking
 force is made, as the electrically energized on-off valve or valves must
 be changed over in the manner of reciprocation. When the adjustment of the
 braking force is to increase it, of course a further electric energy is
 consumed to pressurize the brake fluid to be supplied for increasing the
 braking force.
 Particularly when the driver has a habit of pumping the brake pedal at a
 standstill of the vehicle, a substantial electric power of the battery is
 uselessly consumed, or in other words, herein there exists a good chance
 of caring the battery against losing its normal operating condition, or
 the life, if such a useless consumption of the battery is avoided.
 Therefore, it is a primary object of the present invention to provide a
 device for controlling an electro-hydraulic brake system of a vehicle such
 as an automobile in such a construction that a care is provided for its
 battery when it suffers a trouble such as a lowering of the output voltage
 thereof, or when it is anticipated that such a trouble will occur in the
 near future, or further when a saving of a useless consumption of the
 electric power of the battery is possible.
 According to the present invention, the above-mentioned primary object is
 first accomplished by a device for controlling an electro-hydraulic brake
 system of a vehicle having wheels, a battery, an alternator for charging
 the battery, and the electro-hydraulic brake system adapted to be
 energized by the battery and including wheel cylinders, a brake pedal,
 electric control means, a pump adapted to operate under a control of the
 electric control means for pressurizing a brake fluid, and on-off valves
 adapted to operate under a control of the electric control means for
 selectively supplying the brake fluid pressurized by the pump to each of
 the wheel cylinders, the device comprising:
 means for detecting if the battery is normally operating;
 wherein the electric control means control the operation of the pump and
 the on-off valves such that the pressure of the brake fluid supplied to
 the wheel cylinders is restricted not to be higher than a first
 predetermined value lower than a standard output voltage of the battery
 when the battery detection means detect that the battery is not normally
 operating.
 By the device of the above-mentioned construction, the electro-hydraulic
 brake system of a vehicle is controlled such that it operates at such
 lowered pressure values which do not exceed the first medium pressure
 value when at least it is detected that the battery is not normally
 operating, so that the battery is cared for its suffering, so as to be
 able to operate a longer until it is repaired or replaced by a new one.
 The device according to the present invention may further comprise means
 for detecting if the alternator is normally operating, and the electric
 control means may control the operation of the pump and the on-off valves
 such that the pressure of the brake fluid supplied to the wheel cylinders
 is restricted not to be higher than a second predetermined medium pressure
 value when the alternator detection means detect that the alternator is
 not normally operating. By such an arrangement, the battery is cared
 against failing due to a failure of the alternator.
 The device according to the present invention may further comprising means
 for detecting if the vehicle is substantially at a standstill, and means
 for detecting if the brake pedal is pumped by a driver, and the electric
 control means may control the operation of the pump and the on-off valves
 such that the pressure of the brake fluid supplied to the wheel cylinders
 is restricted not to be higher than a third predetermined medium pressure
 value when the brake pedal is pumped at a substantial standstill of the
 vehicle. By such an arrangement, the battery is further cared against a
 useless consumption by the habit of pumping the brake pedal at a
 substantial standstill of the vehicles of some drivers.
 Since drivers will not do such a pumping of the brake pedal under a
 condition that a strong braking is required to hold the vehicle, it will
 be appreciated that the pressure level of the above-mentioned third
 predetermined medium pressure value may be further lowered from the
 above-mentioned first or second predetermined medium pressure value.
 When the brake system comprises an accumulator for the brake fluid
 pressurized by the pump, the electric control means may control the
 operation of the pump such that the pressure of the brake fluid supplied
 to the wheel cylinders is restricted not to be higher than the first or
 second predetermined medium pressure value by lowering the pressure of
 charging the accumulator when the battery detection means detect that the
 battery is not normally operating, or when the alternator detection means
 detect that the alternator is not normally operating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 In the following, the present invention will be described in more detail
 with respect to a preferred embodiment thereof by referring to the
 accompanying drawings.
 Referring to FIG. 1A, the hydraulic circuit totally designated by 10 of a
 brake system of a vehicle (not shown) and having pairs of front and rear
 wheels (not shown) comprises wheel cylinders 20FR, 20FL, 20RR and 20RL for
 applying braking forces to front right, front left, rear right and rear
 left ones of the wheels, respectively. The hydraulic circuit comprises a
 master cylinder 14 adapted to compress a brake fluid supplied from a
 reservoir 26 according to a depression of a brake pedal 12 by a driver, so
 as to deliver a pressurized brake fluid through passages 16 and 18 toward
 the wheel cylinders 20FL and 20FR, respectively. On-off valves 22FL and
 22FR are provided in the passages 16 and 18, respectively, so as normally
 not to obstruct communication of the passages 16 and 18, while selectively
 interrupting the communication of the passages 16 and 18, respectively.
 Indeed, the on-off valves 22FL and 22FR are solenoid actuated valves which
 are maintained in a through open condition such as shown in the figure
 when no electric current is supplied thereto, while they are changed over
 to a position interrupting the communication of the passages 16 and 18,
 respectively, when they are supplied with an electric current when an
 ignition switch (not shown) is turned on.
 Therefore, it will be appreciated that the shown hydraulic circuit is ready
 for braking the pair of front wheels simply hydraulically according to a
 depression of the brake pedal 12 when the ignition switch is not turned on
 or the electric power source of the vehicle has failed for any reason,
 while when the ignition switch is turned on with a sound battery
 condition, the on-off valves 22FR and 22RL are changed over to their
 closed position of interrupting the passages 16 and 18, so as to let the
 hydraulic circuit ready for operation with the brake fluid pressure source
 provided by a pump 34 under the control of electric control means
 described hereinbelow.
 The pump 34 is adapted to be selectively driven by an electric motor 32
 powered by the above-mentioned battery via control means described in
 detail hereinbelow, so as to pump up the brake fluid supplied from the
 reservoir 26 through a suction passage 28 for providing a pressurized
 source of the brake fluid in an outlet passage 29 branching to passages
 36FR, 36FL, 36RR and 36RL for supplying the pressurized brake fluid to the
 wheel cylinders 20FR, 20FL, 20RR and 20RL through on-off valves 40FR,
 40FL, 40RR and 40RL, respectively. An accumulator 31 may be connected to
 the outlet passage 29. The on-off valves 40FR, 40FL, 40RR and 40RL are
 each of a normally closed type which maintains each of the supply passages
 36FR, 36FL, 36RR and 36RL in an interrupted condition when no electric
 current is supplied thereto, and is selectively opened by a supply of an
 actuating electric current thereto.
 The wheel cylinders 20FR, 20FL, 20RR and 20RL are exhaustible through
 exhaust passages 38FR, 38FL, 38RR and 38RL including on-off valves 42FR,
 42FL, 42RR and 42RL, respectively, toward an exhaust passage 30 leading to
 the reservoir 26. The on-off valves 42FR, 42FL, 42RR and 42RL are each
 also of a normally closed type which maintains each of the exhaust
 passages 38FR, 38FL, 38RR and 38RL in an interrupted condition when no
 electric current is supplied thereto, and is selectively opened by a
 supply of an actuating electric current.
 The pressures of the brake fluid in the wheel cylinders 20FR, 20FL, 20RR
 and 20RL are detected by pressure sensors 44FR, 44FL, 44RR and 44RL,
 respectively. The pressure of the brake fluid compressed by the master
 cylinder 14 is detected by a pressure sensor 48. The pressure of the brake
 fluid in the outlet passage 29 is detected by a pressure sensor 50.
 The changeover of each of the on-off valves 22FR and 22FL, the on-off
 valves 40FR-40RL and the on-off valves 42FR-42RL is controlled by electric
 control means 52 diagrammatically shown in FIG. 1B, or in more detail, by
 a microcomputer 54 thereof through a drive circuit 56. The microcomputer
 may be of a common type including a central processor unit (CPU), a read
 only memory (ROM), a random access memory (RAM), input and output port
 means and bilateral bus means interconnecting these elements, all not
 shown in detail in the figure.
 The microcomputer 54 is supplied with signals of pressures Pwi (i=fr, fl,
 rr and rl) of the brake fluid in the corresponding wheel cylinders from
 the wheel cylinder pressure sensors 44FR-44RL, a signal of depression
 stroke Sp of the brake pedal 12 by a driver from a brake pedal stroke
 sensor 46, a signal of master cylinder pressure Pm of the brake fluid
 compressed by the master cylinder 14 from the master cylinder pressure
 sensor 48, a signal of the pressure of the brake fluid in the pump outlet
 passage 29 from the powered source pressure sensor 50, a signal of output
 voltage Vb of the battery (not shown) forming the electric power source of
 the vehicle from a battery voltage sensor 58, signals of wheel speeds Vwi
 (i=fr, fl, rr and rl) of the front right, front left, rear right and rear
 left wheels from wheel speed sensors 60FR-60RL, a signal of stop lamp
 switch (STSW) 62 for putting on and off the brake lamps (not shown) of the
 vehicle according to a depression of the brake pedal by the driver, and a
 signal of output voltage Va of an alternator (not shown) for charging the
 battery from an alternator voltage sensor 64, and carries out certain
 control calculations based upon the values of the parameters input by the
 signals from the sensors 44FR-44RL, 46, 48, 50, 58, 60FR-60RL and 64 for
 executing a braking operation via the drive circuit 56 according to the
 depression of the brake pedal 12 by the driver as described in detail
 hereinbelow, with checking if the driver is pumping the brake pedal when
 the vehicle is at a substantial standstill, and also checking if the
 alternator or the battery is operating in its normal condition. The
 checking of the battery may be executed according to a process such as
 described in the above-mentioned co-pending application No. (1231). When
 the driver is pumping the brake pedal when the vehicle is as a substantial
 standstill or when the alternator or the battery is not operating in its
 normal condition, particular processes are executed for caring the battery
 as described in detail hereinbelow.
 Now, referring to FIGS. 2-7, the device for controlling the brake system
 according to the present invention will be described in detail with
 respect to an embodiment thereof in the form of its operation of
 controlling the brake system shown in FIGS. 1A and 1B.
 Referring to FIG. 2, when the device is started for operation by a closure
 of the ignition switch (not shown), in step 10 signals such as shown in
 FIG. 1B are read in.
 In steps 20-50, a target value of the deceleration to be effected in the
 vehicle by a depression of the brake pedal by the driver is calculated in
 a manner described in U.S. patent application Ser. No. 09/263,226 by two
 colleges of the present inventor.
 In more detail, in step 20, by looking up a map such as shown in FIG. 3
 stored in the ROM of the microcomputer 54, a target deceleration Gst is
 read out against a current value of the depression stroke Sp of the brake
 pedal by the driver.
 In step 30, by looking up a map such as shown in FIG. 4 stored in the ROM,
 a target deceleration Gpt is read out against a current value of the
 master cylinder pressure Pm.
 In step 40, by looking up a map such as shown in FIG. 5 stored in the ROM,
 a weighting factor a for weighting the target deceleration Gpt based upon
 the master cylinder pressure Pm against the target deceleration Gst based
 upon the brake pedal depression stroke Sp is estimated against total
 target deceleration Gt which is a weighted sum of the target decelerations
 Gpt and Gst by the weighting factor a according to the following equation:
EQU Gt=(1-.alpha.)Gst+.alpha.Gpt
 In the brake control carried out according to the repetitive calculations
 of the steps of FIG. 2, the reading out of the weighting factor .alpha. by
 the map of FIG. 5 is executed based upon the value of Gt obtained by each
 previous cycle of the calculations through the flowchart of FIG. 2.
 According to such a rightward rising slope shape of the curve of FIG. 5,
 the weighting of the parameters in the estimation of the deceleration of
 the vehicle to be targeted at is gradually shifted from a weighting on the
 brake pedal depression stroke to a weighting on the master cylinder
 pressure along with increase of the target deceleration, i.e. as a higher
 braking force is applied to the wheels.
 Then in step 60, it is judged if the brake pedal is pumped by the driver
 when the vehicle is at a substantial standstill. This judgment is done
 according to such processes as shown by the flowchart of FIG. 6.
 Referring temporarily to FIG. 6, in step 61 it is judged if the vehicle
 speed V is substantially zero. The vehicle speed V will be available from
 the signals of the wheel speed sensors 60FR-60RL. When the answer is no,
 the control proceeds to step 62, and count C of a counter (not shown) is
 reset to 0, and the control proceeds to step 70 of FIG. 2, while when the
 answer is yes, the control proceeds to step 63.
 In step 63, it is judged if the stop lamp switch (STSW) 62 was changed over
 from OFF to ON. When the answer is yes, the control proceeds to step 64,
 and the count C of the counter is incremented by 1, and the control
 proceeds to step 65, whereas when the answer is no, the control bypasses
 step 64 and goes to step 65.
 In step 65, it is judged if the count C is larger than a predetermined
 threshold count value Co which may be 2 or 3. When the answer is no, the
 control proceeds to step 70, whereas when the answer is yes, the control
 proceeds to step 80 of FIG. 2. Thus it will be appreciated that by the
 subroutine of FIG. 3 it is detected if the driver is pumping the brake
 pedal at a substantial standstill of the vehicle.
 Returning to FIG. 2, in step 70 it is judged if the alternator (not shown)
 for charging the battery (not shown) of the vehicle is in its normal
 operating condition. This judgment will be available by checking the
 output voltage of the alternator relative to its rotation speed. When the
 answer is yes, the control proceeds to step 90, whereas when the answer is
 no, the control proceeds to step 100.
 In step 90, it is judged if the battery of the vehicle is in its normal
 operating condition. As noted above, this judgment may be made as
 described in a co-pending application No. (1231). When the answer is yes,
 the control proceeds to step 110, whereas when the answer is no, the
 control proceeds to step 100.
 In step 110, target wheel cylinder pressures Pwti (i=fr, fl, rr, rl) to be
 attained in the respective wheels are calculated based upon the final
 target deceleration Gt, obtained in step 50 and other operating parameters
 such as steering angle, etc. not particularly shown by the figure. FIG. 7
 shows an example of the relationship between Pwti and Gt, wherein a
 performance such as shown by a solid line A is followed with no
 restriction when the control has come to step 110 directly from step 90.
 However, when the control comes to step 110 through step 80 or 100, the
 results of calculation of Pwti in step 110 are under the restriction
 imposed thereon in step 80 or 100. In more detail, in step 100, a
 restriction is imposed on the magnitude of Pwti such that none of Pwti
 higher than a pressure level Pwtb such as shown by a broken line B in FIG.
 7 is available regardless of the results of calculation in step 50.
 Similarly, in step 80, a restriction is imposed on the magnitude of Pwti
 such that none of Pwti higher than a pressure level Pwtc such as shown by
 a dot-dash line C in FIG. 7 is available regardless of the results of
 calculation in step 50.
 Therefore, it will be appreciated that when the driver is pumping the brake
 pedal when the vehicle is at a substantial standstill, the target values
 Pwti of the brake pressure to be attained in the wheel cylinders according
 to the depression of the brake pedal by the driver is temporarily
 suppressed not to be higher than the value C, so as to care the battery in
 a manner of saving a useless consumption of the battery.
 On the other hand, when the battery has lost its normal operating
 condition, or it is anticipated that the battery will soon lose its normal
 operating condition due to an insufficient charging by the alternator
 which has lost its normal operating condition, as detected in step 90 or
 70, respectively, the target pressure Pwti of the brake pressure to be
 attained in the wheel cylinders according to the depression of the brake
 pedal by the driver is temporarily suppressed not to be higher than the
 value C in FIG. 7, so as to care the battery in a manner of reducing the
 load imposed thereon.
 In step 120, the supply of the brake fluid pressures to the respective
 wheel cylinders is carried out according to the target wheel cylinder
 pressures Pwti calculated in the manner described above.
 FIG. 8 is a flowchart similar to that of FIG. 2, showing a modification of
 step 100 of FIG. 2. In the flowchart of FIG. 8, the steps corresponding to
 those shown in FIG. 2 are designated by the same step numbers as in FIG.
 2. In this modification, the effect of imposing the restriction of the
 pressure level B on the target wheel cylinder pressures Pwti as shown in
 FIG. 7 is provided by lowering the pressure level maintained in the
 accumulator 31 shown in FIG. 1.
 In more detail, when the answer of step 80 is yes, the control proceeds to
 step 81, and a lower pressure limit Pal of the accumulator pressure at
 which the pump is automatically put on to replenish the accumulator and a
 higher pressure limit Pah of the accumulator pressure at which the
 replenishment driving of the pump is stopped are reset to their normal
 pressure values Palo and Paho, respectively.
 On the other hand, when the answer of step 70 is no, the control proceeds
 to step 82, and amounts .DELTA.Pala and .DELTA.Paha for lowering the lower
 pressure limit Pal and the higher pressure limit Pah from the normal
 standard values Palo and Palh, respectively, are calculated as follows:
EQU .DELTA.Pala=Kala.vertline.1-(Va/Vao).vertline.Palo
EQU .DELTA.Paha=Kaha.vertline.1-(Va/Vao).vertline.Paho
 wherein Vao is a standard output voltage of the alternator at its normal
 standard operating condition, Va is the output voltage of the alternator
 at the normal standard operating condition, and Kala and Kaha are
 appropriate factors.
 Then in step 83, the values of the lower and higher pressure limits Palo
 and Paho are temporarily lowered as much as .DELTA.Pala and .DELTA.Paha,
 respectively.
 When the answer of step 80 is no, the control proceeds to step 84, and
 amounts .DELTA.Palb and .DELTA.Pahb for lowering the lower pressure limit
 Pal and the higher pressure limit Pah from the normal standard values Palo
 and Palh, respectively, are calculated as follows:
EQU .DELTA.Pala=Kalb.vertline.1-(Vb/Vbo).vertline.Palo
EQU .DELTA.Paha=Kahb.vertline.1-(Vb/Vbo).vertline.Paho
 wherein Vbo is a standard output voltage of the battery at its normal
 standard operating condition, Vb is the output voltage of the battery at
 the normal standard operating condition, and Kalb and Kahb are appropriate
 factors.
 Then in step 85, the values of the lower and higher pressure limits Palo
 and Paho are temporarily lowered as much as .DELTA.Palb and .DELTA.Pahb,
 respectively.
 In step 86, it is judged if the brake fluid pressure Pp of the accumulator
 detected by the pressure sensor 50 is lower than the lower pressure limit
 Pal. When the answer is yes, the control proceeds to step 87, and the pump
 is driven by supplying an electric power to the motor 32 from the battery,
 and then the control proceeds to step 110. When the answer of step 86 is
 no, the control proceeds to step 86, and it is judged if the brake fluid
 pressure Pp is equal to or higher than the higher pressure limit Pah. When
 the answer is yes, the control proceeds to step 89, and the pump is
 stopped, whereas when the answer is no, the control proceeds to step 110.
 Therefore, it will be appreciated that, according to this modification, the
 brake fluid pressure of the accumulator 31 which substantially forms the
 pressurized brake fluid source of the brake system is normally maintained
 between Palo and Paho, whereas when it was detected that the alternator or
 battery is not normally operating, the accumulator pressure is lowered to
 be maintained between Palo-.DELTA.Pala and Paho-.DELTA.Paha, or
 Palo-.DELTA.Palb and Paho-.DELTA.pahb, respectivekly, wherein the
 magnitudes of .DELTA.Pala and .DELTA.Paha or .DELTA.Palb and .DELTA.Pahb
 are determined according to the degree of lowering of the output voltage
 of the alternator or the battery so that the battery is cared according to
 the degree of anticipation of the battery to fail due to an insufficient
 charging or the degree of the actual failing of the battery.
 Although the present invention has been described in detail with respect to
 a particular embodiment thereof and some modification, it will be apparent
 for those skilled in the art that various modifications are possible
 without departing from the scope of the present invention.