Patent Publication Number: US-7588298-B2

Title: Brake system control apparatus

Description:
INCORPORATION BY REFERENCE 
   This is a Division of application Ser. No. 11/251,989 filed Oct. 18, 2005, which claims priority to Japanese Patent Application No. 2004-307660 filed on Oct. 22, 2004, the disclosures of which are hereby incorporated herein by reference in their entireties. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to a brake system control apparatus including plural brake systems, and, more specifically, to control of a control actuator of each of the plural brake systems. 
   2. Description of the Related Art 
   Japanese Patent Application Publication No. 2004-122974 A discloses a brake system control apparatus that includes plural brake systems each of which includes a brake and a control actuator that can control braking torque applied to a wheel by the brake. The brake system control apparatus also includes a braking torque control device which creates a control command value for the control actuator of each of the plural brake systems, and which outputs the control command value to the control actuator. The braking torque control device includes (a) a first creating portion that creates a control command value for a control actuator of a brake system targeted for control (hereinafter, referred to as the “control-target brake system”), which is one of the plural brake systems, based a target value of braking torque of a brake of the control-target brake system; (b) a second creating portion that corrects a first control command value, that is, the control command value created by the first creating portion, based on a difference between an actual value of the braking torque applied to the wheel by the brake of the control-target brake system and an actual value of braking torque in another brake system, thereby creating a second control command value; and (c) a control command value selecting portion that selects the second control command value, when the actual value of the braking torque in the control-target brake system is larger than the actual value of the braking torque in the other brake system, and that selects the first control command value, when the actual value of the braking torque in the control-target brake system is equal to or smaller than the actual value of the braking torque in the other brake system. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to make it possible, when at least two control command values are created, to more appropriately select a control command value from among the at least two control command values, thereby reducing, if required, a difference in response between a control-target brake system and each of at least one of the other brake systems. 
   A brake system control apparatus according to a first aspect of the invention includes plural brake systems each of which includes at least one brake and a control actuator that can control braking torque generated by the at least one brake, the brake system control apparatus including a braking torque control device which creates a control command value for the control actuator of each of the plural brake systems, and which outputs the created control command value to the control actuator. The braking torque control device includes (i) a consideration creating portion which creates a first control command value for the control actuator of a control-target brake system that is one of the plural brake systems based on information concerning an operation of the at least one brake in the control-target brake system, and information concerning an operation of the at least one brake in each of at least one of the other brake systems; (ii) non-consideration creating portion which creates a second control command value for the control actuator of the control-target brake system based on the information concerning the control-target brake system, but not based on the information concerning each of the at least one of the other brake systems; and (iii) a control command value selecting portion which selects one of the first control command value created by the consideration creating portion and the second control command value created by the non-consideration creating portion based on at least one of (a) an absolute value of a difference between a target value of braking torque in the control-target brake system, and a target value of braking torque in each of the at least one of the other brake systems; and (b) a combination of a control mode in the control-target brake system and a control mode in each of the at least one of the other brake systems. 
   For example, it is not preferable to select the first control command value (consideration control command value) when the absolute value of the difference in the target value of the braking torque between the control-target brake system and each of the at least one of the other brake-systems is large. When the absolute value of the difference in the target value is equal to or larger than a set value, it is considered that a situation concerning the control in the control-target brake system is different from a situation concerning the control in each of the at least one of the other brake systems. Accordingly, it is not preferable to take the information concerning each of the at least one of the other brake systems into consideration. 
   Also, when the control mode in the control-target brake system is an increasing mode in which the braking torque is increased, and the control mode in each of the at least one of the other brake systems is a decreasing mode in which the braking torque is decreased, the directions in which the control torque is changed in the control are different from each other. Accordingly, it is not preferable to take the information concerning each of the at least one of the other brake systems into consideration. 
   As in the case of the first aspect, in the case where the control command value is selected based on the absolute value of the difference in the target value between the control-target brake system and each of the at least one of the other brake systems and/or the combination of the control modes, if it is not preferable to take the information concerning each of the at least one of the other brake systems into consideration, the second control command value (non-consideration control command value) is selected. Accordingly, the braking torque can be controlled based on the state of the control-target brake system. On the other hand, when it is preferable to take the information concerning each of the at least one of the other brake systems into consideration, the first control command value is selected. Accordingly, a difference in response between the control-target brake system and each of the at least one of the other brake systems can be reduced. Also, simultaneity of the entire brake system control apparatus can be improved. 
   (2) The selecting portion may select the first control command value created by the consideration creating portion, when the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is a predetermined combination; and the selecting portion may select the second control command value created by the non-consideration creating portion, when the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is not the predetermined combination. 
   (3) The selecting portion may select the first control command value created by the consideration creating portion, when the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems are the same, and each of both the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is the increasing mode in which the braking torque is increased or the decreasing mode in which the braking torque is decreased; and the selecting portion may select the second control command value created by the non-consideration creating portion, when one of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is the increasing mode in which the braking torque is increased, and the other of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is the decreasing mode in which the braking torque is decreased. 
   The first control command value is selected, when the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems are the same, and each of both of the control modes is the increasing mode or the decreasing mode, namely, when the combination of the control modes is a combination of (increasing mode and increasing mode) or a combination of (decreasing mode and decreasing mode). When the control is performed so that the braking torque in the control-target brake system and the braking torque in each of the at least one of the other brake systems are changed in the same direction, it is considered that the level of response in the control-target brake system and the level of response in each of the at least one of the other brake systems are required to be the same. Accordingly, it is appropriate to select the first control command value. 
   In contrast to this, the second control command value is selected, when the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is a combination of the increasing mode and the decreasing mode, namely, a combination of (increasing mode and decreasing mode) or a combination of (decreasing mode and increasing mode). In these cases, the directions of the control of the braking torque are different. Accordingly, the levels of response are not always required to be the same. Therefore, it is appropriate to select the second control command value in this case. 
   The first control command value may be selected, when the control mode in the control-target brake system is one of the increasing mode and the decreasing mode, and the control mode in each of the at least one of the other brake systems is a maintaining mode in which the braking torque is maintained, namely, when the combination of the control modes is a combination of (increasing mode and maintaining mode) or a combination of (decreasing mode and maintaining mode). When the control mode in each of the at least one of the other brake systems is the maintaining mode, a delay in control (hereinafter, referred to as a “control delay”) in the control-target brake system may be larger than a control delay in each of the at least one of the other brake systems. Accordingly, it may be preferable to select the first control command value. 
   (4) The selecting portion may select the second control command value created by the non-consideration creating portion, when the absolute value of the difference in the target value of the braking torque between the control-target brake system and each of the at least one of the other brake systems is equal to or larger than a set value; and the selecting portion may select the first control command value created by the consideration creating portion, when the absolute value of the difference in the target value of the braking torque between the control-target brake system and each of the at least one of the other brake systems is smaller than the set value. 
   When the target value in the control-target brake system is different from the target value in each of the at least one of the other brake systems by a large amount, the directions in which the braking force change may different from each other. Also, the same level of response may not be required. Accordingly, in these cases, it is preferable not to select the first control command value. 
   (5) The selecting portion may select the second control command value created by the non-consideration creating portion, if the absolute value of the difference in the target value of the braking torque between the control-target brake system and each of the at least one of the other brake systems is equal to or larger than the set value, even when the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is the predetermined combination. 
   (6) The selecting portion may select the second control command value created by the non-consideration creating portion, if the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is not the predetermined combination, even when the absolute value of the difference in the target value of the braking torque between the control-target brake system and each of the at least one of the other brake systems is smaller than the set value. 
   Even when the combination of the control mode in the control-target brake system and the control mode in each of the at least one of the other brake systems is the predetermined combination, if the absolute value of the difference in the target value is equal to or larger than the set value, it is preferable to select the second control command value. For example, even when each of both of the control modes is the increasing mode, or each of both of the control modes is the decreasing mode, if the absolute value of the difference in the target value is equal to or larger than the set value, the same level of response may not be required. 
   Also, even when the absolute value of the difference in the target value between the control-target brake system and each of the at least one of the other brake systems is smaller than the set value, if the combination of the control modes is the combination of (increasing mode and the decreasing mode), it is preferable to select the second control command value, since the directions in which the braking torque is changed are different from each other. 
   As described so far, it is preferable to select the first control command value, when the absolute value of the difference in the target value between the control-target brake system and each of the at least one of the other brake systems is smaller than the set value, and the combination of the control modes is the predetermined combination. 
   (7) The selecting portion may select the second control command value created by the non-consideration creating portion, when an absolute value of a difference between an absolute value of a deviation of an actual value from the target value of the braking torque in the control-target brake system, and an absolute value of a deviation of an actual value from the target value of the braking torque in each of the at least one of the other brake systems is equal to or larger than a set value; and the selecting portion may select the first control command value created by the consideration creating portion, when the absolute value of the difference between the absolute value of the deviation of the actual value from the target value of the braking torque in the control-target brake system, and the absolute value of the deviation of the actual value from the target value of the braking torque in each of the at least one of the other brake systems is smaller than the set value. 
   When the absolute value (|LΔeij|) of the difference (LΔeij=|Δei|−|Δej|) between the absolute value of the deviation (Δei) in the control-target brake system “i” and the absolute value of the deviation (Δej) in each of the at least one of the other brake systems “j” is equal to or larger than the set value, a difference in a control delay (a difference in response) between the control-target brake system “i” and each of the at least one of the other brake systems “j” is large. 
   When the difference (|ei|−|Δej|) in the absolute value of the deviation is a positive value, the control delay in the control-target brake system “i” is larger than the control delay in each of the at least one of the other brake systems “j”. A difference in response (difference in control delay) when the absolute value (|LΔeij|) of the difference in the absolute value of the deviation is large is larger than the difference in response when the absolute value (|LΔeij|) is small. 
   Similarly, when the difference (|Δei|−|Δej|) in the absolute value of the deviation is a negative value, the control in the control-target brake system “i” is advanced as compared with the control in each of the at least one of the other brake systems “j”, and the difference in response when the absolute value (|LΔeij|) of the difference is large is larger than the difference in response when the absolute value (|LΔeij|) of the difference is small. 
   Accordingly, when the absolute value (|LΔeij|) of the difference in the absolute value of the deviation is equal to or larger than the set value, it is not preferable to take the information concerning each of the at least one of the other brake systems into consideration. Therefore, it is appropriate to select the second control command value. On the other hand, when the absolute value (|LΔeij|) of the difference in the absolute value of the deviation is smaller than the set value, it is preferable to take the information concerning each of the at least one of the other brake systems into consideration. Therefore, it is appropriate to select the first control command value. 
   (8) The braking torque control device may perform feedback control based on the deviation of the actual value from the target value of the braking torque in each of the plural brake systems. 
   According to this aspect, the control actuator is controlled based on the difference between the target value and the actual value, the actual value is fed back, and the control command value is created such that the actual value comes closer to the target value. The control command value is created based on the target value and the actual value of the braking torque in at least the control-target brake system, regardless of whether the control command value is creased by the consideration creating portion or the non-consideration creating portion. 
   (9) The consideration creating portion may create the control command value based on the target value and the actual value of the braking torque in the control-target brake system, and the target value and the actual value of the braking torque in each of the at least one of the other brake systems. 
   The feedback control is performed based on the target value and the actual value in the control-target brake system. Accordingly, it is appropriate to create the first control command value based on the target value and the actual value of the braking torque in the control-target brake system, and the target value and the actual value of the braking torque in each of the at least one of the other brake systems. 
   In the feed-forward control, when the non-consideration creating portion creates the control command value based on the target value, the consideration creating portion may create the control command value based on the target value in the control-target brake system, the actual value in the control-target brake system, and the actual value in each of the at least one of the other brake systems. 
   (10) The consideration creating portion may create the first control command value based on the deviation of the actual value from the target value of the braking torque in the control-target brake system, and the deviation of the actual value from the target value of the braking torque in each of the at least one of the other brake systems. 
   The control mode for the braking torque (whether the control for increasing the braking torque or the control for decreasing the braking torque is performed), and a degree of the control delay (level of response) can be obtained based on whether the deviation is a positive value or a negative value, and the absolute value of the deviation. Accordingly, the control mode of the braking torque in the brake system and the degree of the control delay can be obtained based on the deviation in each of the at least one of the other brake systems. If the control command value is created in consideration of the deviation in each of the at least one of the other brake systems and the deviation in the control-target brake system, the control command value can be created based on the degree of the control delay and the combination of the control modes. Accordingly, the control actuators can be controlled such that the same level of response can be obtained. 
   (11) The consideration creating portion may correct the second control command value created by the non-consideration creating portion, based on the target value and the actual value in each of the at least one of the other brake systems and the target value and the actual value in the control-target brake system. 
   (12) The consideration creating portion may create the control command value by correcting the control command value created by the non-consideration creating portion, based on the deviation of the actual value from the target value of the braking torque in the control-target brake system and the deviation of the actual value from the target value of the braking torque in each of the at least one of the other brake systems. 
   (13) The consideration creating portion may set a correction value based on a difference between the absolute value of the deviation of the actual value from the target value of the braking torque in the control-target brake system, and the absolute value of the deviation of the actual value from the target value of the braking torque in each of the at least one of the other brake systems. 
   As mentioned above, whether the control delay in the control-target brake system is larger than the control delay in each of the at least one of the other brake systems, the degree of the control delay in each of the control-target brake system and the at least one of the other brake systems, and the like can be obtained based on whether the value LΔeij obtained by subtracting the absolute value of the deviation in each of the at least one of the other brake systems “j” from the absolute value of the deviation in the control-target brake system “i” is a positive value or a negative value, and based on the absolute value of the value LΔeij. Accordingly, it is appropriate to set the correction value based on the difference LΔeij in the absolute value of the deviation. 
   For example, when the difference LΔeij in the absolute value of the deviation is a positive value, the control command value is corrected such that a rate of change in the braking torque becomes high. On the other hand, when the difference LΔeij in the absolute value of the deviation is a negative value, the control command value is corrected such that the rate of change in the braking torque becomes low. 
   More specifically, in the case where the rate of change in the braking torque when the control command value is large is higher than the rate of change in the braking torque when the control command value is small, when the consideration creating portion creates the first control command value by adding the correction value to the second control command value, if the difference LΔeij in the absolute value of the deviation is a positive value, the correction value is set to a positive value, and the positive correction value when the absolute value |LΔeij| of the difference in the absolute value of the deviation is large can be made larger than the positive correction value when the absolute value |LΔeij| of the difference in the absolute value of the deviation is small. Thus, the control delay in the control-target brake system, which is larger than the control delay in each of the at least one of the other brake systems can be reduced, and the difference in response can be reduced. On the other hand, when the difference LΔeij in the absolute value of the deviation is a negative value, the correction value is set to a negative value, and the negative correction value when the absolute value |LΔeij| of the difference is large can be made smaller than the negative correction value when the absolute value |LΔeij| of the difference is small. Thus, the first control command value can set to a small value, and the degree of advance of the control in the control-target brake system with respect to each of the at least one of the other brake systems can be reduced. 
   In the case where the consideration creating portion corrects a gain K that is used when the first control command value is created (K=α×K, when the gain is corrected by being multiplied by a gain correction coefficient α. When the gain correction coefficient is “1”, the gain is not corrected, namely, when the second control command value is obtained), when the difference LΔeij in the absolute value of the deviation is a positive value, the gain correction coefficient α is set to a value equal to or larger than “1”, and the absolute value of the gain correction coefficient when the absolute value |LΔeij| of the difference is large is made larger than the absolute value of the gain correction coefficient when the absolute value |LΔeij| of the difference is small. Also, when the difference LΔeij of the absolute value of the deviation is a negative value, the gain correction coefficient α is set to a value smaller than “1”, and the gain correction coefficient α when the absolute value |LΔeij| of the difference is large can be made smaller than the gain correction coefficient α when the absolute value |LΔeij| of the difference is small, in a range where the gain correction coefficient α is larger than “0”. 
   (14) The consideration creating portion may create the first control command value for the control-target brake system based on the information concerning the control-target brake system and the information concerning the brake system whose level of response is required to the same as that of the control-target brake system. 
   When the brake system control apparatus includes plural brake systems, the information concerning any brake system(s) other than the control-target brake system may be taken into consideration. However, it is preferable that the information concerning the brake system whose level of response is required to be the same as that of the control-target brake system be taken into consideration, among the other brake systems. For example, when the absolute value of the difference in the target value is equal to or smaller than the set value, when the combination of the control modes is the predetermined combination, or the like, it can be considered that the same level of response is required. 
   Also, the brake system whose level of response is required to be the same as that of the control-target brake system may be decided based on a structure of a vehicle. For example, when the normal braking operation is performed, namely, when the braking torque in each of the brake systems is controlled such that the braking torque required by the driver can be obtained, the brake systems corresponding to right and left wheels on each of the front wheel side and the rear wheel side are the brake systems whose levels of response are required to be the same. 
   (15) The consideration creating portion may create the first control command value based on the information concerning the control-target brake system and the information concerning the brake system including the brake that suppresses rotation of the wheel which is on an opposite side, in a right-and-left direction, of the wheel whose rotation is suppressed by the control-target brake system. 
   (16) The brake may be a hydraulic brake that applies hydraulic braking torque to a brake rotational body that can rotate together with the wheel by pressing a friction member to the brake rotational body due to hydraulic pressure of a brake cylinder, thereby suppressing rotation of the wheel, and the control actuator may include at least one electromagnetic control valve that can control the hydraulic pressure of at least one brake cylinder. The braking torque control device may include a hydraulic pressure control device that controls the hydraulic pressure of each of the at least one brake cylinder by creating the control command value corresponding to an electric current supplied to the electromagnetic control valve, and outputting the control command value to the electromagnetic control valve. 
   In the brake system control apparatus according to the above-mentioned aspect, the electromagnetic control valve serving as the control actuator is controlled, and the control command value indicating the electric current supplied to the electromagnetic control valve is created. One brake is provided with one electromagnetic control valve, or two electromagnetic control valves. The control actuator includes a pressure increasing control valve and a pressure decreasing control valve. In the increasing mode in which the hydraulic pressure of the brake cylinder is increased, the electric current supplied to the pressure increasing control valve is controlled. In the decreasing mode in which the hydraulic pressure of the brake cylinder is decreased, the electric current supplied to the pressure decreasing control valve is controlled. In this case, when the control mode is decided, the electromagnetic control valve targeted for the control is decided. 
   Also, the electromagnetic control valve may be an electromagnetic open/close valve that is opened/closed by ON/OFF control of the supply electric current, or may be a linear control valve. In the case of the linear control valve, an amount of electric current supplied to the linear control valve is continuously controlled, and the linear control valve permits hydraulic fluid, whose amount corresponds to the amount of supply electric current, to flow therethrough. When the electromagnetic control valve is the electromagnetic open/close valve, the control command value corresponding to the ON/OFF state of the supply electric current, a duty control ratio, and the like is created. When the electromagnetic control valve is the linear control valve, the control command value corresponding to the amount of supply electric current is created. 
   (17) The electromagnetic control valve may permit the hydraulic fluid to flow therethrough at an opening amount that is decided based on at least the electric current supplied to the electromagnetic control valve, and the consideration creating portion may create the first control command value indicating the supply electric current such that the difference in response between the control-target brake system and each of the at least one of the other brake systems is reduced. 
   The electromagnetic control valve may be configured such that the opening amount when the supply electric current is large is larger than the opening amount when the supply electric current is small. Alternatively, the electromagnetic control valve may be configured such that the opening amount when the supply electric current is large is smaller than the opening amount when the supply electric current is small. In either of these cases, the amount of hydraulic fluid flowing in/out of the brake cylinder when the opening amount is large can be made larger than the amount of hydraulic fluid flowing in/out of the brake cylinder when the opening amount is small. Thus, the hydraulic pressure of the brake cylinder can be made closer to the target hydraulic pressure promptly. 
   (18) The electromagnetic control valve may include a seating valve including a valve element, a valve seat, and a spring; and an electromagnetic driving force applying device including a solenoid. The relative position of the valve element with respect to the valve seat is set based on a relationship among electromagnetic driving force applied by the electromagnetic driving force applying device, force applied by the spring, and differential pressure applying force that acts according to a pressure difference between the upstream side and the downstream side of the electromagnetic control valve. 
   When the spring is provided so as to apply force such that the valve element contacts the valve seat, the electromagnetic control valve is a normally closed valve. When the spring is provided so as to apply force such that the valve element moves away from the valve seat, the electromagnetic control valve is a normally open valve. 
   (19) A brake system control apparatus according to a second aspect of the invention includes plural brake systems each of which includes at least one brake and a control actuator that can control braking torque generated by the at least one brake, the brake system control apparatus including a braking torque control device which creates a control command value for the control actuator of each of the plural brake systems, and which outputs the created control command value to the control actuator. The braking torque control device includes a consideration creating portion that creates the control command value for the control actuator of a control-target brake system that is one of the plural brake systems, based on an actual value and a target value of braking torque in the control-target brake system and an actual value and a target value of braking torque in each of at least one of the other brake systems. 
   According to the second aspect, the control command value for the control-target brake system is created based on the target value and the actual value of the braking torque in the control-target brake system, and the target value and the actual value of the braking torque in each of at least one of the other brake systems. 
   Since the control command value is created based on the target value and the actual value of the braking torque in each of the at least one of the other brake systems (the consideration-target brake system) and the target value and the actual value in the control-target command value, it becomes possible to take not only the deviation in the control-target brake system but also the deviation in the consideration-target brake system into consideration. Accordingly, the level of response in the control-target brake system and the level of response in each of the at least one of the other brake systems can the same. 
   Namely, whether the information concerning each of the at least one of the other brake systems is taken into consideration is determined based on the target value and the actual value in each of the at least one of the other brake systems and the target value and the actual value in the control-target brake system, it becomes possible to accurately determine whether the information concerning each of the at least one of the other brake systems should be taken into consideration. 
   (20) A brake system control apparatus according to a third aspect of the invention includes a consideration creating portion which creates a control command value for a control actuator of a control-target brake system that is one of the plural brake systems based on at least a target value of braking torque in the control-target brake system; an absolute value of a deviation of an actual value from the target value of the braking torque in the control-target brake system; and an absolute value of a deviation of an actual value from a target value of the braking torque in each of at least one of the other brake systems. 
   (21) In a brake system control apparatus according to a fourth aspect of the invention, the braking torque control device includes a first creating portion which creates a control command value for a control actuator of a control-target brake system that is one of the plural brake systems based on at least a target value of braking torque in the control-target brake system; a second creating portion which creates a second control command value by correcting the first control command value created by the first creating portion based on the value obtained by subtracting an absolute value of a deviation of an actual value from a target value of braking torque in each of at least one of the other brake systems from an absolute value of a deviation of an actual value from the target value of the braking torque in the control-target brake system; and a control command value selecting portion which selects one of the first control command value and the second control command value based on a state of the brake system control apparatus. 
   (22) A brake system control apparatus according to a fifth aspect of the invention includes a consideration creating portion which creates a first control command value for a control actuator of a control-target brake system that is one of the plural brake systems based on information concerning an operation of the at least one brake in the control-target brake system and information concerning each of at least one of the other brake systems; a non-consideration creating portion which creates a second control command value for the control actuator of the control-target brake system based on the information concerning the control-target brake system, but not based on the information concerning each of the at least one of the other brake systems; and a control command value selecting portion which selects one of the first control command value created by the consideration creating portion and the second control command value created by the non-consideration creating portion based on a target value of braking torque in the control-target brake system and a target value in each of the at least one of the other brake systems. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: 
       FIG. 1  is a circuit diagram showing a hydraulic brake apparatus that is a brake system control apparatus according to an embodiment of the invention; 
       FIG. 2  is a cross sectional view schematically showing a normally closed valve included in an individual hydraulic pressure control valve device provided in the hydraulic brake apparatus; 
       FIG. 3  is a cross sectional view schematically showing a normally open valve included in the individual hydraulic pressure control valve device; 
       FIGS. 4A and 4B  are a flowchart showing a control command value creating program stored in a storing portion of a brake ECU of the hydraulic brake apparatus; 
       FIG. 5  is a graph conceptually showing a control threshold value stored in the storing portion of the brake ECU; 
       FIG. 6  is a block diagram showing a structure of the brake ECU; 
       FIG. 7  is a flowchart showing another control command value creating program stored in the storing portion of the brake ECU; and 
       FIG. 8  is a flowchart showing a part of the control command value creating program. 
   

   DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
   Hereafter, a brake system control apparatus according to an embodiment of the invention will be described in detail with reference to accompanying drawings. 
   A brake system control apparatus shown in  FIG. 1  includes a brake pedal  10  serving as a brake operating member; a master cylinder  12  including two compressing chambers; a pump device  14  serving as a hydraulic pressure source; and hydraulic brakes  16 ,  17 ,  18 , and  19  that are provided for a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, respectively. 
   The hydraulic brakes  16 ,  17 ,  18 , and  19  include brake cylinders  20 ,  21 ,  22 , and  23 , respectively. The hydraulic brakes  16 ,  17 ,  18 , and  19  are operated by the hydraulic pressures of the brake cylinders  20 ,  21 ,  22 , and  23 , respectively, thereby applying braking torque to the respective wheels. 
   The master cylinder  12  includes two compressing pistons. When a driver operates the brake pedal  10 , hydraulic pressure corresponding to the brake pedal operation force is generated in each of hydraulic chambers positioned ahead of the two respective compressing pistons. The two compressing chambers of the master cylinder  12  are connected to the brake cylinder  20  for the left front wheel and the brake cylinder  21  for the right front wheel through master passages  26  and  27 , respectively. Master shut-off valves  29  and  30  are provided in the master passages  26  and  27 , respectively. Each of the master shut-off valves  29  and  30  is a normally open electromagnetic open/close valve. 
   The four brake cylinders  20 ,  21 ,  22 , and  23  are connected to the pump device  14  through a pump passage  36 . While the brake cylinders  20  and  21  are shut off from the master cylinder  12 , hydraulic pressure is supplied from the pump device  14  to the brake cylinders  20 ,  21 ,  22 , and  23 , whereby the hydraulic brakes  16 ,  17 ,  18 , and  19  are operated. The hydraulic pressure of each of the brake cylinders  20 ,  21 ,  22 , and  23  is controlled by a hydraulic pressure control valve device  38 . 
   The pump device  14  includes a pump motor  58  that drives a pump  56 . A master reservoir  62  is connected to an inlet side of the pump  56  through an intake passage  60 , and an accumulator  64  is connected to an outlet side of the pump  56 . A hydraulic fluid in the reservoir  62  is pumped up by the pump  56 , and supplied to the accumulator  64 . Then, the hydraulic fluid is stored in the accumulator  64  while being compressed. 
   The outlet side and the inlet side of the pump  56  are connected by a relief passage  66 . A relief valve  68  is provided in the relief passage  66 . The relief valve  68  is opened when the hydraulic pressure on the accumulator side, that is, the high pressure side, exceeds a set pressure. 
   The hydraulic pressure control valve device  38  includes individual hydraulic pressure control valve devices  70 ,  71 ,  72 , and  73  provided for the brake cylinders  20 ,  21 ,  22 , and  23 , respectively. The individual hydraulic pressure control valve devices  70 ,  71 ,  72 , and  73  include pressure increasing linear valves  80 ,  81 ,  82 , and  83 , and pressure decreasing linear valves  90 ,  91 ,  92 , and  93 , respectively. The pressure increasing linear valves  80 ,  81 ,  82 , and  83  are provided in the pump passage  36 , and serve as electromagnetic pressure increasing control valves. The pressure decreasing linear valves  90 ,  91 ,  92 , and  93  are provided in a pressure decreasing passage  86  which connects the brake cylinders  20 ,  21 ,  22 , and  23  to the reservoir  62 , and serve as electromagnetic pressure decreasing control valves. The pressures of the brake cylinders  20 ,  21 ,  22  and  23  can be controlled independently of each other by controlling the pressure increasing linear valves  80 ,  81 ,  82 , and  83  and the pressure decreasing linear valves  90 ,  91 ,  92 , and  93 . 
   The pressure increasing linear valves  80 ,  81 ,  82  and  83  provided for the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, respectively, and the pressure decreasing linear valves  90  and  91  provided for the left front wheel and the right front wheel, respectively, are normally closed valves, namely, these valves are closed when an electric current is not supplied to a coils  100 . The pressure decreasing linear valves  92  and  93  corresponding to the left rear wheel and the right rear wheel, respectively, are normally open valves, that is, these valves are open when an electric current is not supplied to a coil  102 . 
     FIG. 2  shows each of the pressure increasing linear valves  80 ,  81 ,  82 , and  83  and the pressure decreasing linear valves  90  and  91 , which are normally closed valves. Each of the pressure increasing linear valves  80 ,  81 ,  82 , and  83  and the pressure decreasing linear valves  90  and  92  includes a solenoid  104  including a coil  100 , a plunger  103  and the like; and a seating valve  110  including a valve element  105 , a valve seat  106 , a spring  108  which applies force in a direction in which the valve element  105  contacts the valve seat  106 , and the like. 
   Then an electric current is not supplied to the coil  100 , the valve element  105  contacts the valve seat  106  due to force Fs of the spring  108 , namely, the valve is closed. When an electric current is supplied to the coil  100 , electromagnetic driving force Fd corresponding to the supplied electric current is applied to the plunger  103 , and acts in a direction in which the valve element  105  moves away from the valve seat  106 . Also, differential pressure acting force Fp corresponding to a difference in the pressure between the upstream side and the downstream side of the valve acts in the direction in which the valve element  105  moves away from the valve seat  106 . The relative position of the valve element  105  with respect to the valve seat  106  is decided based on a relationship between the electromagnetic driving force Fd and the differential pressure acting force Fp, and the force Fs of the spring. Hydraulic fluid whose amount corresponds to a valve opening amount determined based on the electromagnetic driving force Fd is allowed to flow through the valve. 
     FIG. 3  shows each of the pressure decreasing linear valves  92  and  93  which are the normally open valves. Each of the pressure decreasing linear valves  92  and  93  includes a solenoid  112  including a coil  102 , a plunger  111  and the like; and a seating valve  120  including a valve element  114 , a valve seat  116 , a spring  118  which applies force such that the valve element  114  moves away from the valve seat  116 , and the like. The pressure decreasing linear valve  92  is provided between the brake cylinder  22  and the reservoir  62  in a state where the differential pressure acting force Fp corresponding to a difference in pressure between the brake cylinder  22  and the reservoir  62  is applied to the valve elements  114 . Similarly, the pressure decreasing linear valve  93  is provided between the brake cylinder  23  and the reservoir  62  in a state where the differential pressure acting force Fp corresponding to a difference in pressure between the brake cylinder  23  and the reservoir  62  is applied to the valve elements  114 . While an electric current is not supplied to the coil  102 , the valve element  114  is kept away from the valve seat  116  due to the differential pressure acting force Fp and the force Fs of the spring  118 , namely, the valve is open. When an electric current is supplied to the coil  102 , the electromagnetic force Fd corresponding to the electric current acts in the direction in which the valve element  114  contacts the valve seat  116 . The relative position of the valve element  114  with respect to the valve seat  116  is decided based on a relationship between the force Fs of the spring  118  and the differential pressure acting force Fp, and the electromagnetic driving force Fd. 
   A stroke simulator device  150  is provided in the master passage  26 . The stroke simulator device  150  includes a stroke simulator  152  and a normally closed simulator open/close valve  154 . The simulator open/close valve  154  is opened/closed, whereby communication between the stroke simulator  152  and the master cylinder  12  is permitted/interrupted. In the embodiment, the state where the hydraulic brakes  16 ,  17 ,  18 , and  19  are operated by the hydraulic fluid supplied from the pump device  14  is an open state; and a state where the hydraulic brakes  16 ,  18 ,  18 , and  19  are operated by the hydraulic fluid supplied from the master cylinder  12  is a closed state. 
   As shown in  FIG. 1 , the brake system control apparatus is controlled according to a command transmitted from a brake ECU  200 . The brake ECU  200  is formed mainly of a computer, and includes an executing portion  202 , a storing portion  204 , an input/output portion  206 , and the like. The input/output portion  206  is connected to a stroke sensor  210 , a master pressure sensor  214 , a brake hydraulic pressure sensor  216 , a wheel speed sensor  218 , a hydraulic pressure source hydraulic sensor  220 , and the like. The input/output portion  206  is connected, through a switch circuit (not shown), to the coil  100  of each of the pressure increasing linear valves  80 ,  81 ,  82 , and  83 , the coil  100  of each of the pressure decreasing linear valves  90  and  91 , the coil  102  of each of the pressure decreasing linear valves  92  and  93 , a coil of each of the master shut-off valves  29  and  30 , and a coil of the simulator control valve  154 . The input/output portion  206  is also connected to a pump motor  58  through a drive circuit. 
   The storing portion  204  stores a control command value creating program, which is shown in a flowchart in  FIGS. 4A and 4B , and the like. 
   In the embodiment, brake systems  230 ,  231 ,  232 , and  233  are formed mainly of the brake cylinders  20 ,  21 ,  22  and  23 , and the individual hydraulic pressure control valve devices  70 ,  71 ,  72 , and  73 , respectively. The control actuators are formed of the individual control valve devices  70 ,  71 ,  72 , and  73 , respectively. The control actuators respectively include the pressure increasing control valves  80 ,  81 ,  82 , and  83 , and the pressure decreasing control valves  90 ,  91 ,  92 , and  93 . 
   These pressure increasing control valves  80 ,  81 ,  82 , and  83 , and the pressure, decreasing control valves  90 ,  91 ,  92 , and  93  are controlled in a feedback manner. The brake ECU  200  creates a control command values for the brake systems  230 ,  231 ,  232 , and  233  based on deviations of actual values from target values of the hydraulic pressures of the brake cylinders  20 ,  21 ,  22 , and  23 , and outputs the control command values to the brake systems  230 ,  231 ,  232 , and  233 , respectively. Each of the control command values for the brake systems  230  and  231  indicates an amount of electric current supplied to the 100 such that the actual value comes close to the target value. Each of the control command values for the brake systems  232  and  233  indicates an electric current supplied to the coil  100  and an electric current supplied to the coil  102  such that the actual value comes close to the target value. 
   The target value of the hydraulic pressure of each of the brake cylinders  20 ,  21 ,  22 , and  23  is decided based on the operating state of the brake pedal  10  achieved by the driver, when the braking operation is performed normally. The required braking force is calculated based on at least one of an operation stroke and operation force (corresponding to master pressure) of the brake pedal  10 , and the target value of the hydraulic pressure of each of the brake cylinder  20 ,  21 ,  22 , and  23  of the respective wheels is decided such that the required braking force can be obtained. In the embodiment, the target value of the hydraulic pressure braking torque corresponds to the target value of the hydraulic pressure of the brake cylinder. The target values of the hydraulic pressures of the brake cylinders  20 ,  21 ,  22 , and  23  of the respective wheels may be equal to each other. Alternatively, the target value of the hydraulic pressure of the brake cylinder  20  of the left front wheel and the target value of the hydraulic pressure of the brake cylinder  21  of the right front wheel may be equal to each other, and the target value of the hydraulic pressure of the brake cylinder  22  of the left rear wheel and the target value of the hydraulic pressure of the brake cylinder  23  of the right rear wheel may be equal to each other, and the target value for each of the right and left front wheels and the target value for each of the right and left rear wheels may be set to values along a front and rear braking force distribution line. 
   In anti-lock control and vehicle stability control, the target values of the hydraulic pressures of the brake cylinders  20 ,  21 ,  22 , and  23  of the respective wheels are individually decided such that states of a braking slip and a lateral slip become appropriate for a friction coefficient of a road surface. 
   In the embodiment, information indicating a supply electric current as a control command value is created and output for each of the four brake systems  230 ,  231 ,  232 , and  233 . In some cases, the control command value is created based on the target value and the actual value of the hydraulic pressure of the brake cylinder in the control-target brake system. In the other cases, the control command value is created based on the target value and the actual value of the hydraulic pressure of the brake cylinder in the control-target brake system, and the target value and the actual value of the hydraulic pressure of the brake cylinder in another brake system. The control command value created based on the target value and the actual value in the control-target brake system will be referred to as a non-consideration control command value (hereinafter, referred to as a second control command value), and the control command value created based on the target value and the actual value in the control-target brake system and the target value and the actual value in the other brake system will be referred to as a consideration control command value (hereinafter, referred to as a first control command value). 
   Then an absolute value of a difference between the target value in the control-target brake system and the target value in the other brake system is equal to or smaller than a set value, and a control mode in the control-target brake system and a control mode in the other brake system are the same and each of both of these control modes is the pressure increasing mode or the pressure decreasing mode, namely, a combination (MODEi, MODEj) of the control modes in the two brake systems is a combination of (pressure increasing mode and pressure increasing mode) or a combination of (pressure decreasing mode and pressure decreasing mode), the first control command value is created. On the other hand, when the absolute value of the difference between the target value in the control-target brake system and the target value in the other brake system is larger than the set value, when the control modes in these brake systems do not match each other, or when each of both of the control modes is the maintaining mode, namely, the combination of the control modes (MODEi, MODEj) is a combination of (pressure increasing mode and pressure decreasing mode), a combination of (pressure increasing mode and pressure decreasing mode), a combination of (pressure increasing mode and maintaining mode), a combination of (pressure decreasing mode and maintaining mode), or a combination of (maintaining mode and maintaining mode), the second control command value is created. 
   As shown in  FIG. 5 , when the deviation of the actual value from the target value (Δe=Pref−Pwc) becomes smaller than a pressure decrease threshold value, the control mode is set to the pressure decreasing mode. The control mode is maintained at the pressure decreasing mode until the deviation exceeds a pressure decrease maintaining threshold value. When the deviation exceeds the pressure decrease maintaining threshold value, the control modes is set to the maintaining mode. When the deviation exceeds a pressure increase threshold value, the control mode is changed from the maintaining mode to the pressure increasing mode. When the deviation becomes smaller than a pressure increase maintaining threshold value, the control mode is changed from the pressure increasing mode to the maintaining mode. Each of the pressure decrease threshold value, the pressure decrease maintaining threshold value, the pressure increase maintaining threshold value, and the pressure increase threshold value is set in advance, and stored in the storing portion  204 . 
   The control-target brake system is one of the plural brake systems  230 ,  231 ,  232 , and  233 . When the control-target brake system is the brake system  230  for the left front wheel, the other brake system is the brake system  231  for the right front wheel. When the control-target brake system is the brake system  232  for the left rear wheel, the other brake system is the brake system  233  for the right rear wheel. When the control-target brake system is the brake system for one of the right and left front wheels, the brake system for the other of the right and left front wheels is the other brake system. When the control-target brake system is the brake system for one of the right and left rear wheels, the brake system for the other of the right and left rear wheels is the other brake system. In each of the front wheel side and the rear wheel side, the same level of response is required in the brake systems for the right and left wheels. 
   Hereafter, a description will be made concerning the case where one of the brake system  230  for the left front wheel and the brake system  231  for right front wheel is the control-target brake system, and the other of the brake systems  230  and  231  is the other brake system. In the case where the control command value indicating the supply electric current is large, each of the pressure increasing control valves  80  and  81 , and the pressure decreasing control valves  90  and  91  included in the individual hydraulic pressure control valve devices  70  and  71  corresponding to the brake cylinder  20  for the left front wheel  20  and the brake cylinder  21  for the right front wheel, respectively, permits a large amount of hydraulic fluid to flow therethrough, as compared with the case where the control command value is small. Hereafter, the other brake system will be referred to as a comparison-target brake system. When the first control command value is created in consideration of the information concerning the comparison-target brake system, the comparison-target brake system is a consideration-target brake system. 
   A second control command value PIDIi is created based on a deviation Δei in a control-target brake system i, a derivative value of the deviation (dPrefi/dt−dPwci/dt), and an integral value Σei of the deviation, according to an equation, PIDIi=KP (Δei+CP)+KD (dPrefi/dt−dPwci/dt+CD)+KI (ΣΔei+CI)+Ci. Here, each of KP, KI, and KD is a gain, and each of CP, CD, CI, and Ci is a constant. Since the second control command value is formed of a proportional term, a derivative term and an integral term, the second control command value can be referred to as a PID command value. 
   The first control command value is obtained by adding a correction value LIi to the second control command value PIDIi. The correction value LIi is created based on a difference LΔei between an absolute value |Δei| of the deviation in the control-target brake system i and an absolute value |Δej| of the deviation in the comparison-target brake system j, LΔei(n) (=|Δei(n)|−|Δej(n−1)|); a derivative value dLΔei of the difference, dLΔei(n)(=LΔei (n)−LΔei(n−1)); and an integral value |LΔei of the difference, |LΔei(n)(=LΔei(n)+|LΔei (n−1)), according to an equation LIi=LKP (LΔei+LCP)+LKD (dLΔei+LCD)+LKI (|LΔei+LCI). Each of LKP, LKD, and LKI is a gain, and each of LCP, LCD, and LCI is a constant. 
   A first control command value Ii is obtained according to an equation, Ii=PIDIi+LIi. In the flowchart in  FIGS. 4A and 4B , a deviation Δe is indicated as “error”, LΔe is indicated as “L_error”, and a difference in the target value is indicated as “diff_Prefi,j”. 
   When the difference LΔei(n) in the absolute value of the deviation is a positive value, and the absolute value |Δei(n)| of the deviation in the control-target brake system i is larger than the absolute value |Δej(n)| of the deviation in the comparison-target brake system j, a control delay in the control-target brake system i is larger than a control delay in the comparison-target brake system j, regardless of whether the pressure increasing control is being performed or the pressure decreasing control is being performed. 
   A difference in control delay (the difference in response) when the absolute value |LΔei(n)| is large is larger than the difference in control delay when the absolute value |LΔei(n)| is small. 
   Accordingly, when the difference LΔei(n) in the absolute value of the deviation is a positive value, the correction value LIi is a positive value. The absolute value of the correction value LIi when the absolute value |LΔei(n) | is large is larger than the absolute value of the correction value LIi when the absolute value |LΔei(n) | is small. As a result, the control command value for the control-target brake system i is set to a larger value (the first control command value is made larger than the second control command value), and an electric current supplied to each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  is increased. The opening amount of each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  is increased, and a larger amount of hydraulic fluid is permitted to flow therethough. Regardless of whether the hydraulic pressure of the brake cylinder is increased or decreased, the rate of change in the hydraulic pressure of the brake cylinder can be made higher, and the target value can be reached more promptly. 
   On the other hand, when the difference LΔei(n) in the absolute value of the deviation is a negative value, the control in the control-target brake system i is more advanced than the control in the comparison-target brake system j, regardless of whether the pressure increasing control is being performed or the pressure decreasing control is being performed. The difference in response when the absolute value |LΔei(n) | of the difference in the absolute value of the deviation is large is larger than the difference in response when the absolute value |LΔei(n) | is small. Accordingly, when the difference LΔei(n) in the absolute value of the deviation is a negative value, the correction value LIi is a negative value. The absolute value of the correction value LIi when the absolute value |LΔei(n) | is large is larger than the absolute value of the correction value LIi when the absolute value |LΔei(n) | is small. As a result, the control command value for the control-target brake system i is set to a smaller value, and an electric current supplied to each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  is decreased. The opening amount of each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  is decreased, and the amount of fluid flowing therethrough is limited. The limited amount of hydraulic fluid is permitted to flow through each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91 . The rate of change in the hydraulic pressure of the brake cylinder is suppressed, and the difference in response between the control-target brake system i and the comparison-target brake system j can be reduced. In this case, in the comparison-target brake system j, the rate of change in the hydraulic pressure of the brake cylinder is increased by increasing the supply electric current. 
   The control command value creating program shown in the flowchart in  FIGS. 4A and 4B  is performed at predetermined time intervals. 
   In step S 1 , the target value and the actual value of the hydraulic pressure of the brake cylinder in the control-target brake system i, and the target value and the actual value of the hydraulic pressure of the brake cylinder in the comparison-target brake system j are obtained. In step S 2 , the deviation Δei of the actual value from the target value in the control-target brake system i, and the deviation Δej of the actual value from the target value in the comparison-target brake system j are obtained. In step S 3 , the control mode in the control-target brake system i and the control mode in the comparison-target brake system j are set based on the deviation Δei and the deviation Δej, respectively. In step S 4 , the difference in the target value Pref between the control-target brake system i and the comparison-target brake system j (Prefi−Prefj) is obtained. In step S 5 , whether the absolute value of the difference is equal to or smaller than a set value S is determined. In step S 6 , it is determined whether the combination (MODEi, MODEj) of the control mode in the control-target brake system i and the control mode in the comparison-target brake system j is a predetermined combination. In other words, it is determined whether the combination of the control mode in the control-target brake system i and the control mode in the other brake system j (MODEi, MODEj) is the combination of (pressure increasing mode and pressure increasing mode) or the combination of (pressure decreasing mode and pressure decreasing mode). 
   When the absolute value of the difference in the target value (|Prefi−Prefj|) is equal to or smaller than the set value S, and the combination of the control modes is the predetermined combination, the first control command value is created in step S 7  to step S 9 . The difference LΔei(n) of the deviation is obtained by subtracting the absolute value of the deviation in the comparison-target brake system j from the absolute value of the deviation in the control-target brake system i. Also, the derivative value dLΔei(n) and the integral value |LΔei(n) of the difference in the absolute value of the deviation are obtained. The control correction value LIi is obtained based on the difference LΔei(n), the derivative value dLΔei (n), and the integral value |LΔei(n). The first control command value Ii is set to the sum of the second control command value PIDIi (PID control command value) and the correction value LIi. 
   On the other hand, when the absolute value (|Prefi−Prefj|) of the difference in the target value between the control-target brake system i and the comparison-target brake system j is larger than the set value S, or when the absolute value (|Prefi−Prefj|) of the difference in the target value is equal to or smaller than the set value S and the combination of the control modes is not the predetermined combination, the second control command value (PID control command value) is created in step S 10 . 
   The thus created control command value is output, the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  are controlled based on the control command value, whereby the hydraulic pressure of the brake cylinder is controlled. 
   For example, when the braking operation is performed normally, the absolute value of the difference in the target value of the hydraulic pressure between the brake cylinder for the right wheel and the brake cylinder for the left wheel is usually small. Accordingly, the first control command value is selected for each of the brake systems  230  and  231  in many cases. In the case where the control mode is set to the pressure increasing mode in each of both the brake system i and the brake system j, or in the case where the control mode is set to the pressure decreasing mode in each of both the brake system i and the brake system j, if the control delay in the control-target brake system i is larger than the control delay in the comparison-target brake system j, the control command value is increased. A large amount of hydraulic fluid is permitted to flow through each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91 , and the rate of change in the hydraulic pressure of the brake cylinder can be increased. Also, when the control in the control-target brake system i is more advanced than the control in the comparison-target brake system j, the control command value is decreased. Accordingly, the amount of hydraulic fluid flowing through each of the pressure increasing linear valves  80  and  81  and the pressure decreasing linear valves  90  and  91  is further limited. Therefore, the rate of change in the hydraulic pressure of the brake cylinder can be reduced. Thus, the hydraulic pressures of the brake cylinders for the right and left front wheels can be changed at the same level of response, and running stability of the vehicle can be improved. 
   In the case where the control-target brake system is the brake system  230  for the left front wheel, when the first control command value is selected in the brake system  230  for the left front wheel and the first control command value is made larger, the second control command value in the control-target brake system  231  for the right front wheel is made smaller. In this case, the control command value is increased in one of the brake system  230  for the left front wheel and the brake system  231  for the right front wheel, and the control command value is decreased in the other of the brake system  230  and the brake system  231 . Then, the gains LKP, LKD, and LKI, and the constants CP, LCD, and LCI, and the like which are used to create the correction value LIi are set such that the levels of response in the brake systems  230  and  231  becomes substantially the same. 
   Also, while the vehicle stability control is performed during the braking operation, the target values of the hydraulic pressures of the brake cylinders for the right and left wheels are not always the same. Also, the control mode in the brake system  230  and the control mode in the brake system  231  are not always the same. In each of the brake systems  230  and  231 , the second control command value is usually selected, and the hydraulic pressures of the brake cylinders for the respective wheels are controlled independently of each other such that the braking slip becomes appropriate. The state similar to that described so far is realized during the anti-lock control as well. 
   As described so far, in the embodiment, it is possible to appropriately select the control command value from among the first control command value and the second control command value, based on whether the absolute value of the difference in the target value of the hydraulic pressure of the brake cylinder between the control-target brake system and the comparison-target brake system j is equal to or smaller than the set value, and based on whether the combination of the control modes is the predetermined combination. The first control command value can be created, when the levels of response actually need to be the same. Also, the second control command value is selected, when it is preferable not to take the information concerning the comparison-target brake system j into consideration. Accordingly, the hydraulic pressure of the brake cylinder can be controlled based on the information concerning the control-target the brake system i. 
     FIG. 6  is a block diagram showing the embodiment. In each of the brake system i for the left front wheel and the brake system j for the right front wheel, a consideration creating portion  250  is formed of a portion of the brake ECU  200 , which stores steps S 7  to S 9  of the control command value creating program shown in the flowchart in  FIGS. 4A and 4B , a portion of the brake ECU  200 , which performs steps S 7  to  9 , and the like; and a non-consideration creating portion  252  is formed of a portion of the brake ECU  200 , which stores step S 10  shown in  FIGS. 4A and 4B , a portion of the brake ECU  200 , which performs step S 10 , and the like. Also, a control command value selecting portion  254  is formed of a portion of the brake ECU  250 , which stores steps S 5  and S 6 , a portion of the brake ECU  250 , which performs steps S 5  and S 6 , and the like. 
   Also, the brake ECU  200  and the like are the hydraulic brake apparatuses serving as the braking torque control devices. 
   In the above-mentioned embodiment, two control command value creating portions are selected. However, two control command values may be created, and then one of the two control command value may be selected. In either of these cases, one of the two created control command values is selected as the control command value to be output. 
   In the above-mentioned embodiment, when each of both the control mode in the control-target brake system i and the control mode in the comparison-target brake system j is the pressure increasing mode or when each of both the control mode in the control-target brake system i and the control mode in the comparison-target brake system j is the pressure decreasing mode, the first control command value is selected. However, even when the control mode in the control-target brake system i is the pressure increasing mode or the pressure decreasing mode, and the control mode in the comparison-target brake system j is the maintaining mode, the first control command value may be created. 
   Also, the control command value may be created according to a control command value creating program shown in a flowchart in  FIG. 7 . 
   In the embodiment, the control gains KP, KD, and KI are set based on a difference LLΔei in the deviation between the control-target brake system i and the comparison-target brake system j, the absolute value |Prefi−Prefj| of the difference in the target value Pref, and the combination of the control modes (MODEi, MODEj). A difference LLΔe in the deviation is indicated as LL_error in  FIG. 7 . 
   As described above, in the embodiment, gain correction values α, β, and γ are based on the difference LLΔei(=Δei−Δej) between the deviation Δei and the deviation Δej, not based on the difference between the absolute value |Δei| of the deviation in the control-target brake system i and the absolute value |Δej| of the deviation in the comparison-target brake system j. In the embodiment, the deviation Δe becomes a positive value when the pressure increasing mode is set, and the deviation Δe becomes a negative value when the pressure decreasing mode is set. Accordingly, the gain correction values α, β, and γ that are used in the case where the pressure increasing mode is set, and the gain correction values α, β, and γ that are used in the case where the pressure decreasing mode is set are obtained independently of each other. 
   As in the above-mentioned embodiment, the gain correction values that are used in the case where the pressure increasing mode is set, and the gain correction values that are used in the case where the pressure decreasing mode is set may be obtained independently of each other, based on the difference LΔei in the absolute value of the deviation. 
   When the control gains KP, KD, and KI are αKP, βKD, and γKI, respectively (KP=αKP, KD=βKD, and KI=γKI), the proportional item gain correction value α, the derivative item gain correction value β, and the integral item gain correction value γ are set according to a gain correction value setting routine and according to the following respective equations, α=f (Δei−Δej, Prefi−Prefj, MODEi, MODEj), β=g(Δei−Δej, Prefi−Prefj, MODEi, MODE), and γ=h(Δei−Δej, Prefi−Prefj, MODEi, MODE). 
   In step S 51  in a flowchart in  FIG. 8 , it is determined whether the absolute value |Prefi−Prefj| of the difference in the target value between the control-target brake system i and the comparison brake system j is equal to or smaller than a threshold value Th. If the absolute value is larger than the threshold value Th, the proportional item gain correction value α is set to “1” in step S 52 . When the proportional item gain correction value α is “1”, correction is not performed, that is, the second control command value is selected (created). 
   When the absolute value is equal to or smaller than the threshold value Th, the combination of the control mode MODEi in the control-target brake system i and the control mode MODEj in the comparison-target brake system j is obtained in steps S 53  to S 56 . In steps S 53  and S 54 , whether the control mode MODEi in the control-target brake system i is the pressure increasing mode or the pressure decreasing mode is determined. In steps S 55  and S 56 , whether the control mode MODEj in the comparison-target brake system j is the pressure increasing mode or the pressure decreasing mode is determined. When the control mode MODEi in the control-target brake system i is the maintaining mode, or when the control mode MIDEi in the control-target brake system i do not match the control mode MODEj in the comparison-target brake system j, the proportional item gain correction value α is set to “1” in step S 52 . 
   Also, when each of both the control mode in the control-target brake system i and the control mode in the comparison-target brake system j is the pressure increasing mode, the proportional gain correction value α is set in steps S 57  and S 58 . When each of both the control mode in the control-target brake system i and the control mode in the comparison-target brake system j is the pressure decreasing mode, the proportional item gain correction value α is set in steps S 59  and S 60 . 
   In steps S 57  and S 58 , the proportional item gain correction value α is tentatively set according to an equation, α=1+APKα×LLΔeij. Here, APKα is a constant. Also, LLΔei is the difference (Δei−Δej) between the deviation Δei in the control-target brake system i and the deviation Δej in the comparison-target brake system j. Accordingly, in the case where the difference LLΔei in the deviation is a positive value, as the absolute value thereof increases (as the control delay in the control-target brake system i becomes larger than the control delay in the comparison-target brake system j during the pressure increasing control), the proportional item gain correction value α increases. 
   Finally, the proportional item gain correction value α is set according to an equation, α=MED (APαMIN, α, APαMAX). APαMIN is the minimum value, and APαMAX is the maximum value, and APαMIN and APαMAX are set in advance. Since the proportional item gain correction value α is limited so as to exceed neither the minimum value APαMIN nor the maximum value APαMAX, the proportional item gain correction value α is prevented from being excessively small or excessively large. 
   Thus, the proportional gain correction value α when the difference LLΔeij in the deviation between the control-target brake system i and the comparison-target brake system j is large becomes larger than the proportional gain correction value α when the difference LLΔeij is small. 
   In steps S 59  and S 60  as well, the proportional gain correction value α is tentatively set according to an equation, α=1−REKα×LLΔei. REKα is a constant. During the pressure decreasing control, the deviation Δei in the control-target brake system i and the deviation Δej in the comparison-target brake system j become negative values. Accordingly, in the case where the difference LLΔei in the deviation is a negative value, as the absolute value of the difference LLΔei increases, the control delay in the control-target brake system i becomes larger than the control delay in the comparison-target brake system j. Therefore, when the difference LLΔei in the deviation is a negative value the proportional gain correction value α is a positive value, and, in general, as the absolute value of the difference LLΔei increases, the proportional gain correction value α increases. The proportional item gain correction value α is set according to an equation, α=MED (REαMIN, α, REαMAX). REαMIN and REαMAX are limit values. 
   The derivative item gain correction value β and the integral item gain correction value γ are set in the same manner. 
   The control command value is created by using the control gains KP, KD, and KI that are corrected by the gain correction values α, β, and γ, respectively. The control command value is created according to the control command value creating program shown in a flowchart in  FIG. 7 . 
   In the control command value creating program, as in the case of the above-mentioned embodiment, the deviation Δei in the control-target brake system i and the deviation Δej in the comparison-target brake system j are obtained, and the control mode in the control-target brake system i and the control mode in the comparison-target brake system j are obtained. Then, the difference in the target value is obtained. 
   Then, in step S 71 , the difference LLΔe in the deviation between the control-target brake system i and the comparison-target brake system j is obtained. In step S 72 , the gain correction values α, β, and γ are obtained according to the gain correction value setting routine. In step S 73 , the control gains αKP, βKD, and γKI are set. In step S 74 , the control command value is created. In a case where each of the gain correction values α, β, and γ is “1”, the second control command value (non-consideration control command value) is created. In the other cases, the first control command value (consideration control command value) is created. 
   As described so far, in the embodiment, when the absolute value of the difference in the target value between the control-target brake system i and the comparison-target brake system j is small, and the combination of the control modes is the predetermined combination, the gain correction values α, β, and γ are set to values corresponding to the difference in response. On the other hand, when the absolute value of the difference in the target value is large, or when the combination of the control modes is not the predetermined combination, each of the gain correction values α, β, and γ is set to “1”. As a result, when the information concerning the comparison-target brake system needs to be taken into consideration, the first control command value is created. On the other hand, when the information concerning the comparison-target brake system need not be taken into consideration, the second control command value is created. Also, at the first control command value, as the difference in the response increases, each of the gain correction values α, β, and γ is set to a value which is deviated from “1” by a larger amount. Accordingly, if the control command value created by using the gain correction value is output, the difference in the response can be reduced. 
   In the above-mentioned embodiment, the description has been made concerning the case where feedback control is performed, and the control command value is created based on the deviation of the actual value from the target value. However, the invention can be applied to the case where the control including the feed-forward control and the feedback control is performed. When the sum of the control command value set by the feed-forward control and the control command value set by the feedback control is used as the control command value, the invention can be applied to the control command value set by the feedback control. 
   Also, the invention can be applied to the case where the feed-forward control is performed. The value obtained by correcting the second control command value, which is created based on the target value in the control-target brake system, based on the difference between the actual value in the control-target brake system and the actual value the other brake system is used as the first control command value. When the absolute value of the difference in the target value is small, when the combination of the control modes is not the predetermined combination, and the like, the first control command value is selected. 
   When each of the control mode in the control-target brake system and the control mode in the comparison-target brake system is the pressure increasing mode, or when each of the control mode in the control-target brake system and the control mode in the comparison-target brake system is the pressure decreasing mode, that is, when the control mode in the control-target brake system matches the control mode in the comparison-target brake system, the first control command value may be selected even if the absolute value of the difference in the target value is large. When these control modes are the same, the directions in which the braking torque changes are also the same. Accordingly, it may be preferable to make the levels of response equal to each other, even when the target values are different from each other. 
   Also, the invention can be applied to each of the case where the front and rear wheels on the right side are controlled together with each other and the case where the front and rear wheels on the left side are controlled together with each other. In each of these cases, the individual hydraulic control devices  70  and  72  are controlled together with each other, and the individual hydraulic control devices  71  and  73  are controlled together with each other. 
   In the above-mentioned embodiment, the first control command value or the second control command value is selected based on, as at least one of parameters, the absolute value of the difference between the target value of braking torque in the control-target brake system and the target value of braking torque in the other brake system, in step  5  in  FIG. 4  or step  51  in  FIG. 8  However, Instead of the parameter, the first control command value or the second control command value may be selected based on, as at least one of parameters, an absolute value of a difference between an absolute value of a deviation of an actual value from the target value of the braking torque in the control-target brake system, and an absolute value of a deviation of an actual value from the target value of the braking torque in the other brake system. 
   In the above-mentioned embodiment, the description has been made concerning the case where the control command values are created for the brake system  230  for the left front wheel and the brake system  231  for the right front wheel. However, the invention can be applied to the case where the control command values are created for the brake system  232  for the left rear wheel and the brake system  233  for the right rear wheel. In this case, the pressure decreasing linear valves  92  and  93  are normally open valves. The rate of decrease in the hydraulic pressure in each of the brake cylinders  22  and  23  when the control command value that is the supply electric current is large is lower than that when the control command value is small. Accordingly, during the pressure decreasing control, the control command value, which is used when the control delay in the control-target brake system i is larger than the control delay in the comparison-target brake system j, is made smaller than the control command value, which is used when the control delay in the control-target brake system i is smaller than the control delay in the comparison-target brake system j. 
   In the above-mentioned embodiment, the description has been made concerning the case where the number of the comparison-target brake system is one. However, the number of the comparison-target brake systems may be two or three. When the number of the comparison-target brake systems is two or more, for example, the first control command value may be created by obtaining the correction values for the respective comparison-target brake systems, and employing the average value of the plural correction values. Also, instead of the average value, the intermediate value, the maximum value or the minimum value may be employed. The gain correction value may be obtained in the same manner. In addition, when the information concerning the plural brake systems is taken into consideration, the first control command value may be selected, only when all the control modes in the plural brake systems are the same control mode. 
   For example, when the brake system  230  for the left front wheel is the control-target brake system, it is determined whether the absolute value of the difference in the target value between the brake system  230  for the left front wheel, and each of the brake system  231  for the right front wheel, the brake system  232  for the left rear wheel, and the brake system  233  for the right rear wheel is equal to or larger than the set value, and it is determined whether the combination of the control mode in the brake system  230 , and the control mode in each of the brake system  231  for the right front wheel, the brake system  232  for the left rear wheel, and the brake system  233  for the right rear wheel is the predetermined combination. Based on the results of these determinations, whether the information concerning the comparison-target brake systems is taken into consideration is determined. In this case, during normal braking operation, when the target value of the hydraulic braking torque of the front wheel and the target value of the hydraulic braking torque of the rear wheel are set to the same value, even if the comparison-target brake systems are the brake systems  232  and  233  for the rear wheels, the first control command may be selected due to the relationship. Also, during the normal braking operation, for example, when the target values of the hydraulic braking torque of the respective wheels are set based on loads applied to the respective wheels in addition to the braking torque required by the driver, when the target values of the hydraulic braking torque of the respective wheels are set such that the slip states of the wheels become the same state, and the like, the target value of the hydraulic pressure of the brake cylinder may vary with each brake system for the wheel. In this case, the second control command value is selected in some cases, and the first control is selected in the other cases, depending on the relationship with the comparison-target brake systems. Since the second control command value is selected when the absolute value of the difference in the target value is large, in the control-target brake system  230 , the hydraulic pressure of the brake cylinder can be controlled based on the state of the control-target brake system  230 , without taking the states of the other brake systems  231 ,  232  and  233  into consideration. 
   In the above-mentioned embodiment, the description has been made concerning the case where the invention is applied to the hydraulic brake apparatus. However, the invention can be applied to an electric brake apparatus. 
   Each of the brake systems may include one brake and one control actuator, may include plural brakes and plural control actuators, or may include plural brakes and one control actuator. In any one of these cases, in one brake system, the one or more control actuators are controlled together with each other, and the one or more brakes are operated together with each other. 
   The brake may be a hydraulic brake that is operated by the hydraulic pressure of the brake cylinder, or may be the electric brake that is operated by driving force (pressing force) of the electric motor. The control actuator may include the electromagnetic control valve, or may include the electric motor control circuit. 
   The consideration creating portion my create the control command value in consideration of the information concerning one brake system that is different from the control-target brake system, or may create the control command value in consideration of the information concerning two or more brake systems. 
   The information concerning the operation of the at least one brake in the brake system is the information indicating the operating state of the brake. For example, the information corresponds to at least one of the information indicating the actual operating state, the information indicating the target operating state, the information concerning the deviation of the actual operating state from the target operating state, and the like. Since the operating state of the brake corresponds to the operating state of the control actuator, the information concerning the operation of the control actuator (the information concerning the control) can be included in the information concerning the operation of the brake. 
   More specifically, the information corresponds to at least one of the target value of the braking torque of the brake (for example, the target value of the hydraulic pressure of the brake cylinder when the brake is the hydraulic brake, or the target value of the pressing force of the electric motor when the brake is the electric brake), the actual value of the braking torque, the deviation of the actual value from the target value of the braking torque, the control command value for the control actuator, and the like. The information that is taken into consideration when the control command value is created may include at least one of the target value of the braking torque of the brake, the actual value of the braking torque, the deviation of the actual value from the target value of the braking torque, the control command value for the control actuator, and the like. 
   The braking torque control device may perform feedback control, or may perform feed-forward control. When control including the feedback control and the feed-forward control is performed, the invention can be applied to at least one of the control command value created by the feedback control and the control command value created by the feed-forward control. 
   While the invention has been described in detail with reference to the preferred embodiments, it will be apparent to those who are skilled in the art that the invention is not limited to the above-mentioned embodiments, and that the invention may be realized in various other embodiments within the scope of the invention.