JP2009012658A - Braking force control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a braking force control device determining braking force of respective wheels while taking the fact that the temperature of a constitution element of a friction braking device of the respective wheels can become excessively high into consideration in a braking system of the vehicle in which the braking force is individually controlled in every wheel. <P>SOLUTION: The braking force control device for the vehicle includes a means for monitoring respective brake disc temperatures of the wheel; a means for determining target braking force in the wheel in which the brake disc temperature reaches to the predetermined temperature; and a means for determining target braking force in the other wheel based on the target braking force. Typically, the braking force of the wheel in which the temperature of the constitution element of the friction braking device reaches to the predetermined temperature is reduced, and the braking force of the other wheel is re-distributed such that a required yaw moment is maintained based on the reduction amount. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a braking force control device for a vehicle such as an automobile, and more particularly to a device that controls the operation of a braking device in which the braking force of each wheel can be controlled independently.

  In many vehicles such as automobiles, a braking system that can control the braking force of each wheel of the vehicle independently or individually has been adopted, and various braking force distribution controls can be realized. . By making it possible to control the braking force on the left and right as well as the front and rear of the vehicle independently, it is possible to control the yaw moment of the vehicle by adjusting the braking force difference between the left and right sides of the vehicle. Control, for example, control for correcting an oversteer or understeer tendency during turning of the vehicle (so-called behavior control), and braking control while traveling on a crossing road with different road surface friction coefficients of the left and right wheels can be executed (part 1). There are many examples of such control (for example, see Patent Document 1). In recent years, the number of vehicles that perform friction braking and regenerative braking using a generator in cooperation is increasing. In order to stabilize the behavior of vehicles when switching between friction braking and regenerative braking, It has been proposed to use a function in which the wheel braking force can be individually controlled (see, for example, Patent Document 2). Furthermore, since the braking force of each wheel can be individually controlled, it is possible to perform travel control that improves the braking limit performance of the vehicle that is turning.

When a braking system capable of individually controlling the braking force of each wheel is adopted, components such as an actuator for adjusting the braking force and a sensor for detecting the braking force actually generated for each wheel Is provided, and the braking force of each wheel is controlled by the electronic control unit to a desired magnitude. For example, a typical hydraulic or pneumatic electronically controlled braking (ECB) system refers to a hydraulic or pneumatic circuit with a valve for adjusting the pressure in the wheel cylinder (brake pressure) for each wheel, brake pressure. Sensors are provided, and the brake pressure of each wheel can be increased or decreased to a desired value by individually operating the valve for each wheel while referring to the sensor value under the control of the electronic control unit. When the vehicle is braked, the target value (required braking force) of the total braking force to be generated in the entire vehicle, which is determined according to the depression amount of the driver's brake pedal, is determined in various manners in the front, rear, left, and right directions. (In the case of behavior control or limit braking control, the braking force is determined for each wheel with reference to the amount of turning state of an arbitrary vehicle so that a desired yaw moment is generated). In Patent Document 3, due to variations in the performance of the components for adjusting the braking force of each wheel as described above, even when the braking force is generated evenly, a difference occurs in the degree of wear of the friction elements of each wheel, Furthermore, paying attention to the fact that an unintended yaw moment may occur during braking, correct the target value commanded to each wheel based on the actual brake pressure deviation between any two wheels, It has been proposed to equalize the wear of the wheel braking device.
JP2004-161197 JP 2005-225482 A Special table 2003-525813

  By the way, when the motion control that distributes the braking force to an arbitrary aspect as described above is performed using the friction braking device that brakes the wheel by friction, a large braking force is generated on a specific wheel, thereby In some cases, the temperature of the friction element of the wheel is relatively higher than that of the other wheels. Wear of a friction element such as a brake pad or a brake shoe proceeds particularly at a high temperature. Therefore, when the braking force distribution control is performed such that the braking force of a specific wheel is increased as described above, the degree of wear of the friction element. However, this tends to be biased toward the wheel having a large braking force, and as a result, the frictional elements may vary in wear from wheel to wheel during use of the vehicle. In addition, when the temperature of the friction element becomes excessively high at a certain wheel and a fade phenomenon occurs, the braking force of the wheel is significantly reduced as compared with other wheels. If the frictional elements are extremely worn by a specific wheel in the vehicle or if a fade phenomenon occurs, a yaw moment unintended by the driver may be generated, or the control required for the entire vehicle. You cannot achieve power.

  However, in the conventional technology, the braking force of each wheel is independently controlled during use of the vehicle, and the braking force distribution control is executed in an arbitrary manner, so that the temperature of the friction element of a specific wheel is reduced. This can cause bias in the degree of wear of the friction elements on each wheel, or can cause unintended yaw moments in the vehicle due to differences in the temperature of the friction elements or the degree of wear of the friction elements It seems that little consideration has been given to the fact that there is sex.

  Thus, one object of the present invention is to consider that in a vehicle braking system in which the braking force is individually controlled for each wheel, the temperature of the components of the friction braking device for a specific wheel can be excessively high. Thus, a braking force control device that determines the braking force of each wheel is provided.

  Another object of the present invention is a braking force control device for a vehicle as described above, wherein the friction braking device for each wheel is referred to by referring to the temperature of a component such as a friction element of the friction braking device for each wheel. It is an object of the present invention to provide a braking force control device capable of avoiding an excessive increase in the temperature of the constituent elements and avoiding an unintended yaw moment.

  Furthermore, another object of the present invention is a vehicle braking force control device as described above, wherein the temperature of a component of a certain wheel friction braking device is high during execution of arbitrary braking force distribution control. When it becomes, it is providing the braking force control apparatus which performs braking force distribution so that the temperature may be reduced and the objective of the said braking force distribution control may be achieved.

  According to the present invention, in brief, in the braking force control of a vehicle having a braking system capable of independently controlling the braking force of each wheel, the temperature of the components of the friction braking device of each wheel is monitored. Thus, when there is a wheel in which the temperature of the component of the friction braking device is excessively increased, a braking force control device capable of changing the braking force distribution of each wheel is provided.

  The vehicle braking force control device according to the present invention is a vehicle braking force control device capable of independently adjusting the friction braking force of each wheel, and means for monitoring the temperature of the components of the friction braking device of each wheel. And a first braking force determining means for determining a target braking force at the wheel at which the temperature of the component of the friction braking device has reached a predetermined temperature, and a target braking force determined by the first braking force determining means. And a second braking force determining means for determining a target braking force at the other wheel based on the second braking force. Here, the friction braking device may be any type of friction braking device known in the art. For example, the brake pad that is a friction element is pressed against a brake disk that rotates together with the wheel, and the wheel rotates by friction force. The brake may be a disc brake that brakes the wheel, or a drum brake that brakes the rotation of the wheel by frictional force by pressing a brake shoe that is a friction element against a brake drum that rotates together with the wheel. The component of the friction braking device means an element that generates friction during actual braking, such as a brake pad, a brake disc, a brake shoe, and a brake drum. The means for monitoring the temperature of the component of the friction braking device may be a means for detecting or estimating the temperature of the component in any way in this field. The means for monitoring the temperature may be a sensor for measuring the temperature directly. However, since the temperature of the components of the friction device increases from the outside temperature to the order of several hundred degrees during operation, a measuring instrument / sensor that directly detects such a temperature fluctuation range is expensive. Means for estimating temperature by any method known in the art may be employed.

  As will be understood from the above description, one feature of the braking force control device of the present invention is that it monitors the temperature of the components of the friction braking device of each wheel. As already described, when the temperature of the components of the friction braking device rises, the frictional elements become more worn or the frictional force decreases. Therefore, in the present invention, when the temperature of the component of the friction braking device reaches a predetermined temperature in a certain wheel, first, in consideration of that, the temperature of the component of the friction braking device is the predetermined temperature. The target braking force for the “wheel that has reached” is determined, and then the target braking force for the other wheels is determined. In other words, the control device according to the present invention performs control in which the braking force of a specific wheel can be set relatively high, so that the temperature of the friction brake device of the specific wheel becomes relatively high. In the situation to obtain, the temperature of the components of the friction braking device of each wheel is monitored, and if the temperature of the friction braking device of any wheel rises, the friction force generated by that friction braking device decreases The target braking force of the wheel is determined separately from the other wheels, so that in the braking force distribution control, the component of the friction braking device for a specific wheel is determined. Therefore, the effect of the temperature rise can be considered.

  In the above-described configuration of the present invention, the “predetermined temperature” which is a criterion for determining whether or not the target braking force is determined by the first braking force determining means exceeds the temperature if necessary. Is a reference temperature at which the frictional elements of the friction braking device become more worn and the frictional force generated may decrease, and may be set arbitrarily experimentally or theoretically. . Typically, such a predetermined temperature may be a temperature (second temperature) lower than a temperature (first temperature) at which a fade phenomenon is likely to occur in the friction element of the friction braking device. . As is well known in the art, when the temperature of the friction element of the brake pad or brake shoe becomes considerably high, a fade phenomenon occurs in which the friction force is significantly reduced. Once fading occurs, so simply, the frictional force of the friction element does not recover, so it should be avoided that the fading occurs during use of the vehicle. Therefore, in the control device of the present invention, the above-mentioned predetermined temperature is set to be adjusted so that the braking force is appropriately adjusted before the temperature of the components of the friction braking device reaches a temperature at which the possibility of occurrence of a fade phenomenon increases. It is preferable to set the temperature lower than the temperature at which the phenomenon is likely to occur (how much lower the temperature is a suitable condition determined arbitrarily experimentally or theoretically).

  Regarding the control of the target braking force of the “wheel in which the temperature of the component of the friction braking device has reached a predetermined temperature” in the above-described device of the present invention, typically, the first braking force determining means includes the target braking force. The braking force may be reduced more than “a target braking force when the temperature of the component reaches the predetermined temperature”. The fact that the temperature of the component of the friction braking device reaches a predetermined temperature for a certain wheel means that there is a high possibility that the temperature will rise further if an attempt is made to achieve the target braking force as it is. Therefore, the braking force of the “wheel at which the temperature of the component of the friction braking device reaches the predetermined temperature” is reduced more than the braking force at the time when the temperature of the component of the friction braking device reaches the predetermined temperature, and the further temperature It is preferable to try to avoid the rise. The mode of reduction may be done by various methods. However, if the braking force is suddenly removed or reduced from the time when the temperature of the component reaches a predetermined temperature, the behavior of the vehicle may be destabilized. In addition, in the components of the friction braking device, as long as the friction force is applied, the rotational energy of the wheel is always converted into heat energy, but at the same time, heat is dissipated from the components over time. If the heat dissipation amount is larger than the heat generation amount, the temperature rise can be suppressed. Therefore, when the braking force is reduced by the braking force control of the present invention, the braking force is reduced with time, and the ratio of the heat generation amount due to friction braking to the heat radiation amount is gradually increased. It may be designed to stop the rise in temperature. Since the braking force can be appropriately generated up to the above-mentioned predetermined temperature, the target braking force of the “wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature” It may be allowed to increase to a "braking force that does not raise the temperature of the element above a predetermined temperature". The “braking force that does not increase above a predetermined temperature” is, if necessary, a braking force in which the amount of heat released from the component and the amount of heat generated by braking are substantially equal, and can be determined experimentally or theoretically in advance. .

  However, even when the target braking force is adjusted based on the predetermined temperature or the second temperature as described above, the temperature of the component reaches the temperature (first temperature) at which the possibility of a fade phenomenon is high. Can also happen. In this case, the target braking force of the “wheel on which the temperature of the component of the friction braking device has reached a predetermined temperature” is limited to a braking force that does not further increase the temperature of the component of the friction braking device. It may be. It should be noted that the situation where the temperature of the component reaches a temperature at which the possibility of occurrence of a fade phenomenon is high should be eliminated as quickly as possible. The target braking force is reduced so as to increase (the target braking force may be set to 0). Further, when a component of the friction braking device generates a fade phenomenon in a certain wheel, the wheel may be limited to a maximum braking force that can be generated when the fade phenomenon occurs in the wheel. . The maximum braking force that can be generated when the fade phenomenon occurs typically may be a value that is experimentally or theoretically obtained in advance by any method.

  Thus, when the target braking force of the “wheel in which the temperature of the component of the friction braking device has reached the predetermined temperature” is determined by the first braking force determination means by any one of the above-described series of methods, the target braking force is determined. Referring to, the second braking force determining means determines the target braking force of the other wheels. In this regard, normally, when the braking force distribution control is executed, the required braking force for each wheel is determined in an arbitrary manner. However, the target braking force of the “wheel in which the temperature of the component of the friction braking device has reached a predetermined temperature” determined by the first braking force determining means of the present invention is affected by the increase in the temperature of the component on the braking force. Therefore, priority should be given to the required braking force by the braking force distribution control (here, the command value of the braking force given to the braking device by the control device of the present invention is set to “target control”. The command value of the braking force determined based on arbitrary control before the control device of the present invention is referred to as “required braking force”. However, the braking force actually generated according to the target braking force determined to cope with the increase in the temperature of the components of the friction braking device will deviate from the required braking force. The purpose of the control cannot be achieved, or the total braking force to be generated in the entire vehicle may be shifted. Therefore, in the control device of the present invention, as one aspect, the second braking force determining means determines the “temperature of the component of the friction braking device” when determining the target value of the braking force of the other wheels. Redistributing the difference between the required braking force and the target braking force of the wheel that has reached a predetermined temperature to wheels other than that wheel, so that the original purpose of the braking force distribution control can be achieved as much as possible. Alternatively, the total braking force that should be generated in the entire vehicle in the original braking force distribution control may be maintained. In other words, the control device according to the present invention performs the braking force distribution control when the temperature of the component of the friction braking device of a certain wheel reaches a predetermined temperature during execution of the braking force distribution control of an arbitrary mode. It can be said that the required braking force applied to each wheel determined by the braking force distribution control is corrected while maintaining the function and effect.

  In the braking force distribution control in which the required braking force is corrected by the control device of the present invention described above, typically, the target yaw moment of the vehicle is determined in order to achieve an arbitrary vehicle motion state, and each wheel demand control is determined. The power is determined to generate a target yaw moment (in the case of straight-ahead braking, it is interpreted as a control where the target yaw moment = 0). Therefore, when the second braking force determining means of the control device of the present invention determines the target braking force of the wheels other than “the wheel where the temperature of the component of the friction braking device has reached the predetermined temperature”, the target yaw force is determined. In order to maintain the moment, the difference between the required braking force and the target braking force of the “wheel on which the temperature of the component of the friction braking device has reached the predetermined temperature” is calculated, and the temperature of the component of the friction braking device reaches the predetermined temperature. May be redistributed to a wheel other than the “wheel”.

  In the embodiment, the second braking force deciding means is the demand control for the opposite wheel in the left-right direction of the vehicle of the “wheel where the temperature of the component of the friction braking device has reached a predetermined temperature”. By subtracting the difference between the required braking force and the target braking force of the “wheel where the temperature of the component of the friction braking device has reached a predetermined temperature” from the power, the target braking force of the opposite wheel in the left-right direction of the vehicle is determined. , By adding the above-mentioned difference to the required braking force for a wheel opposite to the vehicle front-rear direction of the “wheel at which the temperature of the component of the friction braking device reaches a predetermined temperature” The target braking force of the opposite wheel in the longitudinal direction of the vehicle may be determined. According to such “redistribution of braking force”, any braking force can be applied even when the braking device is limited by the control device of the present invention for “the wheel where the temperature of the component of the friction braking device reaches a predetermined temperature”. If the total braking force of the entire vehicle scheduled by the distribution control is not changed and the yaw moment is approximately at the center between the left and right wheels, the required amount of the braking force distribution control is maintained.

  In general, according to the braking force control device of the present invention, any braking force distribution control requires an increase in the braking force of a particular wheel by monitoring the temperature of the components of the friction braking device of each wheel. In the situation, an appropriate braking force or yaw moment can be adjusted taking into account the temperature rise of the components of the wheel friction braking device. In particular, in the control device of the present invention, according to the aspect of limiting the braking force of the “wheel in which the temperature of the component of the friction braking device reaches a predetermined temperature”, the temperature of the component of the friction braking device is excessively increased. It becomes possible to avoid doing. In addition, by specifying “the wheel where the temperature of the component of the friction braking device has reached a predetermined temperature” and determining the distribution of the braking force of each wheel, the “temperature of the component of the friction braking device has reached the predetermined temperature” Even if the braking force of the “wheel” is reduced or reduced, the total braking force can be maintained or the target yaw moment can be achieved.

  Even in the prior art, a braking force control method for limiting the braking force of a specific wheel, and a method for compensating for a deviation in generated braking force due to component tolerances for adjusting the braking force of each wheel (for example, patents) Documents 3) and the like have been proposed, but these can basically be said to compensate for the configuration of the braking device existing from the manufacture and assembly of the vehicle. In contrast, the control device of the present invention compensates for changes in the state of the braking device that occur during use of the vehicle, or executes braking force control so that premature wear of the components of the friction braking device is prevented. It is characterized in that it is a thing.

  Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention.

Configuration of Device FIG. 1 (A) a car that preferred embodiments of the brake force control apparatus of the present invention is incorporated is shown schematically. In the figure, the vehicle 10 having the left and right front wheels 12FL and 12FR and the left and right rear wheels 12RL and 12RR is arranged in a normal manner according to the depression of the accelerator pedal by the driver (in the illustrated example, Since it is a rear wheel drive vehicle, a drive system device (only part of which is shown) that generates braking / driving force on the rear wheels, and a steering device 30 for controlling the steering angle of the front wheels (further, steering for the rear wheels) And a braking system device 40 that generates a braking force on each wheel. The drive system is configured so that the drive torque or the rotational force is transmitted from the engine and / or electric motor (not shown) to the rear wheel 12RL via the transmission (not shown), the differential gear device 28, and the like in a normal manner. , 12RR. Further, the steering device transmits the rotation of the steering wheel 32 operated by the driver to the tie rods 36L and 36R while boosting the rotational force by the booster 34, and steers the front wheels 12FL and 10FR. It may be.

  The braking system device 40 is provided in a wheel cylinder 42FL, 42FR, 42RL, 42RR mounted on each wheel by a hydraulic circuit 46 that communicates with a master cylinder 45 that is operated in response to depression of a brake pedal 44 by a driver. This is an electronically controlled hydraulic brake device in which the brake pressure, that is, the braking force in each wheel is adjusted. As shown in FIG. 2A, the hydraulic circuit 46 includes a circuit 46F for controlling the brake pressure of the pair of left and right front wheels 42FL, 42FR and a brake for the pair of left and right rear wheels 42RL, 42RR. A pressure control circuit 46R (the two circuits may have the same piping structure), and in normal operation, in response to depression of the brake pedal 44, the pressure in the master cylinder 45 is reduced. , Are supplied to the respective wheel cylinders 42i (i = FL, FR, RL, RR). However, the braking force of each wheel is adjusted individually or independently to execute arbitrary braking force distribution control, for example, front and rear wheel braking force distribution control, behavior control (VSC), braking control when traveling on a crossing road, etc. In this case, first, the master cylinder cut valves 50F and 50R directly connected to the master cylinders of the circuits 46F and R are closed based on a command from the electronic control unit 60 (see FIG. 1A), and the hydraulic pressure is increased. The hydraulic pumps 52F and 52R provided in the circuit operate to increase the hydraulic pressure between the master cylinder cut valves 50F and 50R and the wheel cylinders 42i of the respective wheels. The wheel cylinder 42i of each wheel is provided with a hydraulic pressure holding valve 54i on the hydraulic pump 52F and the R side, and a pressure reducing valve 58i on the buffer reservoir 56F and R side, respectively, based on a command from the electronic control unit 60. When the braking force of each wheel is increased, the corresponding hydraulic pressure holding valve 54i is opened, and the wheel cylinder receives the pressure from the pump and is increased and expanded. Thus, the force with which a brake pad (friction element) (not shown) is pressed against the brake disc is increased. Further, when reducing the braking force, the pressure reducing valve 58i is opened to release the pressure to the reservoir, and the brake pressure is reduced. That is, by individually controlling the opening / closing operation of the hydraulic pressure holding valve 54i and the pressure reducing valve 58i corresponding to each wheel, the brake pressure is adjusted for each wheel, and thereby the braking force of each wheel is adjusted separately. Although not shown, each wheel cylinder 42i is provided with a sensor for detecting the brake pressure, and the operation of the hydraulic pressure holding valve 54i and the pressure reducing valve 58i is based on the detection value of the corresponding pressure sensor. Thus, the brake pressure in the wheel cylinder of each wheel is controlled to match the target pressure. The braking system device 40 may be of a type that applies a braking force to each wheel pneumatically or electromagnetically, or any other type for those skilled in the art. The hydraulic circuit may be a cross piping type.

  Referring to FIG. 1A again, the operation of the braking system device 40 is controlled by the electronic control device 60. The electronic control unit 60 may include a microcomputer and a drive circuit having a CPU, a ROM, a RAM, and an input / output port device which are connected to each other by a bidirectional common bus. In the figure, the electronic control unit 60 detects detected values of the brake pedal depression amount θb, the steering angle δ, the wheel speed Vwi, the pressure Pbi in the wheel cylinder of each wheel, and the like from sensors provided in each part of the vehicle. However, various detection signals necessary for various controls to be executed in the vehicle of the present embodiment, for example, various detection signals such as front / rear / lateral G sensor values, yaw rate sensor values, etc. May be entered. Further, although not shown in FIG. 1A, a signal from a device for detecting information for estimating the temperature (brake temperature) of the components of the friction braking device of each wheel is input. (See the description related to FIG. 3 below).

  The characteristic configuration and the operation of the braking force control device of the present invention are realized by the internal configuration of the electronic control device 60 and the operation according to the program stored therein. FIG. 2B shows the configuration of the electronic control device according to the braking / driving control of the present invention in the form of a functional block diagram. Referring to the figure, an electronic control unit 60 includes a braking force distribution control unit 60a that executes a braking force distribution control, which may be of any type known in this field, and four wheels 12FL to 12RR of the vehicle. Among them, the braking force limit determining unit 60b that determines the friction braking device whose temperature exceeds a predetermined temperature and determines the limit value (limiting braking force) of the braking force of the wheel, and the braking force is limited as described above. Braking force redistribution that determines the final braking force target value (target braking force) by correcting the required braking force of each wheel from the braking force distribution control based on the wheel (restricted wheel) and its limiting braking force It includes a control unit 60c and a temperature estimator 60d that estimates the brake temperature of each wheel.

The braking force distribution control unit 60a basically includes a brake pedal depression amount θb from a brake pedal sensor, a wheel speed sensor value Vwi, a longitudinal acceleration / lateral acceleration obtained from a G sensor value, a yaw rate, a wheel steering angle δ, and the like. Based on the state quantity of the vehicle, the total braking force and / or yaw moment required for the entire vehicle is calculated in a known manner in accordance with the braking force distribution control as previously listed, and the total braking force and / or yaw moment is calculated. The required braking force (F _FL , F _FR , F _RL , F _RR ) of each wheel is calculated so as to effectively generate Mc (see FIG. 1 (B)).

  On the other hand, the braking force limit determining unit 60b receives the brake temperature Ti (i = FL, FR, RL, RR) of each wheel from a brake temperature estimator 60d described later, The wheel is inspected whether or not the temperature Ti has reached a predetermined temperature. If the temperature Ti has reached the predetermined temperature, a limit value (limit braking force) Frsti of the braking force of the wheel is determined. The braking force redistribution control unit 60c includes information on the required braking force Frqti of each wheel from the braking force distribution control unit 60a, and the wheels to be restricted (restricted wheels) and the restricted braking force Frsti from the braking force restriction determination unit 60b. Based on the above, the required braking force for each wheel is redistributed to determine the target braking force Fti for each wheel, and the operation of each part of the hydraulic circuit 46 is performed in any known manner so that the target braking force Fti is achieved. To control.

  The estimation of the brake temperature of each wheel in the brake temperature estimator 60d may be performed in a manner known in this field. For example, a temperature measuring device such as a thermocouple sensor or a radiation thermometer may be used to directly detect the temperature of the components of the friction braking device, or the vehicle travel history (vehicle speed, acceleration / deceleration, brake Friction braking device for wheels based on the amount of heat converted from the kinetic energy of the vehicle calculated from the kinetic energy of the vehicle calculated from the operating period and strength history) and the amount of heat released from the brake disk etc. estimated using the outside air temperature The temperature at may be estimated. Preferably, for example, a device for estimating the temperature of a brake disc or brake drum described in Japanese Patent Application No. 2007-5169 by the same applicant as the present applicant may be used as illustrated in FIG. .

  In the brake disk temperature estimating apparatus illustrated in FIG. 3, in short, as shown in the schematic sectional view of the connecting portion between the tire wheel 12a and the axle of the wheel in FIG. First, an electromagnetic pickup 80 (which is used for a typical wheel speed sensor) is opposed to the inner diameter surface 70a of the brake disk 70 with a gap from the brake disk 70 rotating with the wheel on the knuckle fixed to the vehicle body. The output voltage of the electromagnetic pickup 80 is input to the temperature estimator 60d via the voltage output line 80b. A protrusion 70b is formed on the inner diameter surface 70a facing the tip of the electromagnetic pickup 80 (a plurality of protrusions may be provided along the circumferential direction of the inner diameter surface). When it rotates, every time the projection 70b passes in front of the tip of the electromagnetic pickup 80, a voltage pulse V is generated from the electromagnetic pickup 80 as illustrated in FIG. In such a configuration, the brake pad 42a is pressed against the brake disc 70, and the rotation of the brake disc 70 is frictionally braked, and the temperature of the brake disc illustrated in FIG. 3B rises due to the generation of frictional heat due to braking. Then, the brake disk is deformed as illustrated in FIG. 3C, and the distance between the tip of the electromagnetic pickup 80 and the protrusion 70b changes (do → do + Δd). Then, since the amplitude of the pulse output voltage of the electromagnetic pickup 80 changes (Vo → Vo + ΔV), the temperature of the brake disk can be estimated from the change ΔV of the voltage amplitude (the actual estimated temperature is typically (It is determined using the change ΔV of the voltage amplitude, the outside air temperature, and the vehicle speed).

  By the way, although the temperature of the brake disc is estimated in the above, it is considered that the temperature substantially coincides with the temperature of the brake pad 42a, so that the temperature of the brake disc is referred to as the temperature of the friction surface. Should be understood. If possible, the temperature of the brake pad 42a during braking may be directly measured or estimated / detected, and such a case should be understood to be within the scope of the present invention.

Operation of the apparatus thus braking force control control apparatus of the present invention, as has been described at the column of "Disclosure of the Invention", when the braking force distribution control of any aspect is executed, each wheel As the brake temperature, the temperature of the brake disc is monitored, and the braking force of the wheel is limited so that the temperature does not increase any further if the brake temperature reaches the predetermined temperature or exceeds the predetermined temperature. . When the braking force of any wheel is limited, the required braking force of each wheel given by the braking force distribution control is redistributed. The redistribution process of the required braking force of each wheel is preferably executed so that the total driving force and yaw moment required by the braking force distribution control do not change.

  FIG. 4 is a flowchart showing the control processing of the braking force limit determination unit 60b (FIG. 4A) and the braking force redistribution control unit 60c (FIG. 4B) in the braking force control device of the present invention. It is expressed in the form. Each control process is repeatedly executed at a predetermined cycle during operation of the vehicle. The braking force distribution control unit 60a always outputs the required braking force Frqti of each wheel during the operation of this device in an arbitrary control manner as described above. 60d assumes that the estimated temperature Ti (of the brake disc) for each wheel is always output during operation of the device.

(I) Restriction of braking force In the processing of the braking force restriction determination unit 60b illustrated in FIG. 4 (A), in short, two temperature reference values ΔT1 and ΔT2 are set. In each case, the relationship between the estimated temperature Ti of the brake disc and the temperature reference value thereof is inspected, and the limitation of the braking force is determined according to the relationship. Here, the temperature reference value ΔT1 is set to a temperature at which the possibility of a fade phenomenon occurring in the friction element of the wheel increases when the estimated temperature Ti of the brake disk exceeds the ΔT1, and the temperature reference value ΔT2 is , ΔT1 is set to an arbitrary temperature. As already mentioned, when the temperature of the brake pad friction element rises and the fade phenomenon occurs, the friction force between the friction element and the brake disc is significantly reduced, and the reduced friction force can be easily reduced. Does not recover. Therefore, the braking force should be controlled so that the brake disc temperature does not exceed ΔT1. Therefore, in the present invention, when the brake disc temperature Ti exceeds the temperature reference value ΔT2 lower than ΔT1, the braking force limiting process is started to increase the temperature of the brake disc and the friction element (brake pad). It is attempted to suppress (the process of FIG. 4 (A) is executed for each wheel, and therefore, when the process of one cycle is executed for all the wheels, the process of FIG. 4 (A) is repeated four times. It will be.)

In the illustrated control process, specifically, it is determined for each wheel whether or not the braking force is limited in a manner described later (step 10). If the braking force is not limited, it is determined whether or not the estimated temperature Ti (corresponding) acquired from the temperature estimator 60d is lower than the temperature reference value ΔT2 (step 20). When Ti is lower than the temperature reference value ΔT2, there is no need to limit the braking force, so the current cycle is finished as it is. On the other hand, when the estimated temperature Ti is higher than the temperature reference value ΔT2, it is further determined whether or not the estimated temperature Ti is lower than the temperature reference value ΔT1 (step 30). When Ti> ΔT2 is established, the value of the required braking force at that time is stored as a parameter F ^* for determining the limit braking force value later (step 25).

When ΔT2 <Ti <ΔT1 holds, the temperature Ti is not so high as to cause a fade phenomenon at that time, but if the current braking force (F ^* ) continues to be generated as it is, the temperature Ti will eventually fade. Since there is a high possibility of reaching ΔT1 at which a phenomenon can occur, the braking force should be reduced to suppress the amount of heat generated by braking. However, if it is suddenly reduced, there is a possibility that the behavioral stability of the vehicle may be reduced due to a sudden change in braking force. Further, as a result of the gradual reduction of the braking force, the braking force is reduced to a state where the amount of heat generated by braking is balanced with the amount of heat released from the friction braking device, and the condition that the estimated temperature Ti = ΔT2 is maintained. In this case, there is no possibility that the temperature Ti reaches ΔT1. Therefore, when the condition: ΔT2 <Ti <ΔT1, the braking force limit value Frsti is
Frsti ← Max (F * −A · t, F_ΔT2) (1)
(Step 32). Here, Max is an operator that selects a larger value in parentheses. t is an elapsed time from when ΔT2 <Ti is established, and A is a coefficient that may be arbitrarily set. Further, F_ΔT2 is a braking force in which the amount of heat generated by braking is balanced with the amount of heat released from the brake disc when the brake disc temperature Ti = ΔT2, and therefore the brake disc temperature Ti does not increase beyond ΔT2. That is, when the braking force is limited according to the above equation (1), the braking force limit value Frsti decreases with time immediately after ΔT2 <Ti is established, and is maintained at F_ΔT2 when F_ΔT2 is reached. It becomes.

  FIG. 5 shows an example (A) of the change between the required braking force (dashed line) and the limiting braking force (solid line) when the braking force is limited according to the equation (1), and the brake disc temperature corresponding thereto. The example (B) of a change of is typically shown. Referring to the figure, when the required braking force increases at time t0, the brake disc temperature also increases accordingly. When the temperature reaches ΔT2 at time t1, even if the required braking force does not decrease, the braking force actually required for the wheel reaches F_ΔT2 with time according to the above equation (1) ( Limited to reduction to time t2). During that time (t1 to t2), since the heat generation amount is larger than the heat release amount, the temperature rises, but the braking force is reduced to about F_ΔT2, and the temperature rise disappears when the heat generation amount and the heat release amount substantially coincide. By setting F_ΔT2 so that the heat dissipation amount is slightly larger than the heat generation amount (when Ti = ΔT2), the brake temperature is reduced. Thereafter, the actual braking force is changed to follow the required braking force at a stage (time t3) when the required braking force decreases and falls below the limit braking force.

  Thus, as illustrated in FIG. 5, for the wheel whose brake disc temperature has reached the temperature reference value ΔT2, the increase in temperature is avoided by limiting the braking force according to the equation (1). F_ΔT2 is a value that is experimentally or theoretically determined in advance using the vehicle speed, the outside air temperature, etc. as parameters, stored in the storage device of the electronic control device 60, and the calculation according to equation (1) is executed. It may be given by calling the stored value (for the sake of simplicity, FIG. 5 is schematically drawn ignoring the dependence of F_ΔT2 on the vehicle speed or outside temperature).

Referring again to FIG. 4A, when the illustrated cycle is repeated as described above, the braking force is reduced from the point in time when ΔT2 <Ti is established, so basically, the estimated temperature Ti reaches ΔT1. This is expected to be avoided. However, when the estimated temperature Ti reaches ΔT1, the braking force should be reduced to a value at which the temperature does not rise any further as soon as possible. Therefore, in that case, the braking force limit value Frsti is
Frsti ← F_max (2)
Is set (step 34). Here, F_max is a value that reduces the brake disc temperature or does not increase the brake disc temperature in any case. Therefore, when the braking force is limited by the equation (2), the heat dissipation amount from the brake disc is made larger than the heat generation amount due to braking, and an attempt is made to reduce the brake disc temperature. As F_max, a value experimentally obtained in advance using the brake disc temperature, the outside air temperature, the vehicle speed, and the like as parameters may be used. Note that F_max may be 0.

  Thus, as described above, when the braking force limit value is determined, the result is transmitted to the braking force redistribution determining unit, or can be referred to when there is a request from the braking force redistribution determining unit. (Step 36)

  Once initiated, the braking force limitation according to equation (1) or (2) above may be continued until the brake disc temperature has dropped to the ambient temperature level. Therefore, as already mentioned, in the illustrated control cycle, it is first determined whether or not the restriction is being executed. If the restriction is being executed, the estimated temperature Ti is abbreviated as the outside air temperature (or room temperature) Tair. It is determined whether or not they are the same (whether the difference from the outside air temperature or the room temperature is within a predetermined range) (step 40). If the estimated temperature Ti is not lowered to the outside air temperature Tair, the braking force restriction by the above formula (1) or (2) is continued. On the other hand, if the estimated temperature Ti has decreased to Tair, the limitation of the braking force is terminated (step 50—returning to the state where the braking force redistribution described later is not executed).

(ii) Redistribution of braking force In the processing of the braking force redistribution control unit 60c illustrated in FIG. 4B, each wheel required braking force Frqti given by the braking force distribution control unit 60a, and FIG. The target braking force to be finally generated by the braking device for each wheel is determined with reference to the information on the limited wheel and the limited braking force obtained by the control process. At this time, if there is a restricted wheel, the target braking force on the wheel is restricted to be equal to or less than the restricted braking force, and if such a restriction is made, the requested braking force and the control force originally requested for the restricted wheel are limited. Based on the difference from the limiting braking force, the braking force of other wheels is redistributed.

  In the process of FIG. 4B, it is first determined whether or not there are currently no restricted wheels or whether there are two or more restricted wheels (step 100). If there is no limit wheel, the redistribution of the braking force is not executed, and the required braking force is set as the target braking force as it is (step 120). In addition, when there are two or more restricted wheels, braking is executed using another control, for example, engine braking or the like, so redistribution by the control of the present invention is not executed. (Specification of the restricted wheel in the braking force redistribution control unit 60c is, for example, by setting the restricted braking force value of the unrestricted wheel to a maximum value that can be normally generated by the braking device, and generating the restricted braking force value as normal. It can be determined that a wheel that is not the maximum possible value is a restricted wheel.)

On the other hand, when one restricted wheel is identified, braking force redistribution is executed. Specifically, first, the target braking force of the limit wheel is determined as follows.
Fti (restricted wheel) = Min (Frsti, Frqti) (3)
Here, Min is an operator that selects a smaller value among the numerical values in parentheses. Therefore, when the required braking force Frqti (restricted wheel) given by the braking force distribution control unit 60a is smaller than the limited braking force, the required braking force Frqti is set as the target braking force as it is.

Thus, when the target braking force of the limit wheel is determined, the required braking force of other wheels is corrected based on the difference Δi (= Frqti−Frsti) between the required braking force Frqti of the limiting wheel and the limiting braking force Frsti. The final target braking force is determined. Specifically, for example, when the restricted wheel is the left front wheel, the target braking force of each wheel is determined as follows, for example.
Ft _FL = Frst _FL (= Frqt _FL −Δ _FL )
Ft _FR = Frqt _FR -Δ _FL
Ft _RL = Frqt _RL + Δ _FL (4)
Ft _RR = Frqt _RR + Δ _FL
That is, for a wheel that is the opposite of the limit wheel in the left-right direction of the vehicle, the difference Δi between the required brake force of the limit wheel and the limit braking force is subtracted from the required braking force, and the opposite of the limit wheel in the longitudinal direction of the vehicle For each of these wheels, the difference Δi between the required braking force of the restricted wheel and the restricted braking force is added to the required braking force. According to this calculation method, the sum of the target braking forces, that is, the total braking force of the entire vehicle is maintained at the sum of the required braking forces. If the position of the center of gravity of the vehicle is located on the center axis of the vehicle, the yaw moment Mc to be generated by the target braking force is
Mc = (Ft _FL −Ft _FR + Ft _RL −Ft _RR ) × Tr / 2
When the contribution of the delta _FL is offset _{Mc = (Frqt FL -Frqt FR +} Frqt RL -Frqt RR) × Tr / 2
As a result, the yaw moment due to the required braking force is maintained even after redistribution (the yaw moment due to the required braking force is 0, that is, when straight braking is required). included.).

In actual calculation processing, the difference between the required braking force of each wheel and the calculation result of equation (3) Δi = Frqti−Min (Frsti, Frqti) (5)
And the target braking force may be determined by the following equation.
Ft _FL = Frqt _FL -Δ _FL -Δ _FR + Δ _RL + Δ _RR
Ft _FR = Frqt _FR -Δ _FL -Δ _FR + Δ _RL + Δ _RR
Ft _RL = Frqt _RL + Δ _FL + Δ _FR −Δ _RL −Δ _RR (6)
_{Ft RR = Frqt RR + Δ FL} + Δ FR -Δ RL -Δ RR

Here, Δ _FL , Δ _FR , Δ _RL , Δ _RR are set so that Frsti is set to the maximum braking force that can be generated by the braking device when the corresponding wheel is not a restricted wheel. Frsti is never selected in the second term of equation (5).), Set to 0.

  As described above, when the target braking force is determined by redistributing the required braking force as shown in FIG. 4B, the value of the target braking force is set so that the target braking force is generated in the braking device of each wheel. A control command is given to the hydraulic circuit after being converted into a command value in units of brake pressure. As already described, the friction braking force generated when a certain brake pressure is applied to the wheel cylinder can vary depending on the brake temperature. Therefore, in the conversion from the target braking force value to the brake pressure command value, the influence of the brake disc temperature is taken into account, for example, by changing the conversion coefficient according to the brake disc temperature. It may be.

  Thus, according to the above-described embodiment of the present invention, the temperature increase of the friction braking device due to the relatively high braking force of a specific wheel is avoided, and the total braking force and yaw moment are controlled. Since the power distribution control is maintained as required, it is expected that the purpose of the braking force distribution control will be achieved and the possibility that the driver will feel uncomfortable is reduced. Also, since the chance that only the friction braking device of a specific wheel is excessively heated is reduced, the wear of only the friction braking device of the specific wheel is relatively advanced as compared with other wheels. Will be suppressed.

  By the way, according to the control of the present invention described above, the possibility that the brake disk temperature reaches ΔT1 is greatly reduced, but a fade phenomenon occurs in a specific wheel because the control is not in time, It may happen that the braking force does not increase. In such a case, the braking force redistribution control unit 60c substitutes the braking force Ffademax achievable with the wheel in which the fade phenomenon has occurred into the limiting braking force Frsti of the equation (3), and the same required braking force. Redistribution may be performed. Whether or not a fade phenomenon has occurred in each wheel depends on the brake disk temperature history and the decrease in braking force actually generated from changes in wheel speed or slip rate when a certain brake pressure is applied. It may be determined by estimating or the like. When a wheel in which a fade phenomenon has occurred is detected, the braking force of one wheel is always limited. Therefore, unless the other wheel to be restricted appears, the required braking force of step 110 is always set. Redistribution is performed. In addition, it is preferable to appropriately change the conversion ratio between the target braking force and the brake pressure so that the braking force corresponding to the target braking force is actually achieved for the wheel in which the fade phenomenon has occurred.

  While the present invention has been described in detail with respect to one embodiment thereof, it will be apparent to those skilled in the art that various modifications can be made within the scope of the present invention.

  For example, it should be understood that the present invention applies as well when the friction braking device is a drum brake. Further, when the vehicle is a hybrid vehicle or an electric vehicle, the control of the present invention may be executed when friction braking is executed.

FIG. 1A is a schematic diagram of a vehicle on which a preferred embodiment of a braking control device according to the present invention is mounted, and FIG. 1B is a diagram for explaining braking force Fi and yaw moment Mc acting on the vehicle. It is. For simplicity, the front wheel rudder angle is ignored. The position of the center of gravity is assumed to be located on the approximate center axis of the vehicle. FIG. 2A is a schematic diagram of a piping configuration of a hydraulic braking device controlled by the braking control device of the present invention. In the figure, the master cylinder cut valves 50F and 50R and the hydraulic pressure holding valve 54i are normally open solenoid valves, and the pressure reducing valve 58i is a normally closed solenoid valve. In FIG. 2A, each valve is set in a state where electronic control of the braking force is not performed. FIG. 2B is a control block diagram of an electronic control device that realizes a preferred embodiment of the braking force control device according to the present invention. The means for “detecting each wheel brake disc temperature information” is changed by a method for estimating the temperature. FIG. 3 is a diagram for explaining the configuration for estimating the brake disc temperature and the principle of brake disc temperature estimation. (A) is typical sectional drawing of the structure of the connection part of the tire wheel of a wheel, and an axle. The brake disc 70 is fixed between the tire wheel 12a and the hub, and the axle is rotatably supported by the knuckle via the hub and the bearing. (B) shows the state of the brake disc at normal temperature, and (C) shows the state of the brake disc at high temperature. (D) is the output voltage of the electromagnetic pickup in the state of (B), and (E) shows the output voltage of the electromagnetic pickup in the state of (C). Vo represents the amplitude of the output voltage of the electromagnetic pickup at room temperature. As the temperature of the brake disk increases, the gap between the electromagnetic pickup and the brake disk increases, and the amplitude of the output voltage of the electromagnetic pickup decreases. The temperature estimator estimates the temperature of the brake disc based on the width of reduction in the amplitude of the output voltage. FIG. 4 shows the control processing of the braking force limit determination unit (A) and the braking force redistribution control unit (B) in the form of a flowchart in the embodiment of the present invention. FIG. 5 shows an example of temporal changes in the braking force (A) and the brake disc temperature (B) when the braking force is limited depending on the temperature of the brake disc.

Explanation of symbols

10 ... Vehicle 28 ... Differential gear unit (differential)
40 ... braking system device 42FL to 42RR ... braking device (wheel cylinder)
46 ... Hydraulic circuit 44 ... Brake pedal 52F, R ... Pump 54i ... Hydraulic holding valve 58i ... Pressure reducing valve 56F, R ... Reservoir 60 ... Electronic control device 70 ... Brake disk 80 ... Electromagnetic pickup

Claims (11)

  A vehicle braking force control device capable of independently adjusting the friction braking force of each wheel, the means for monitoring the temperature of the component of the friction braking device of each wheel, and a component of the friction braking device. Configuration of the friction braking device based on the first braking force determining means for determining the target braking force at the wheel whose temperature has reached a predetermined temperature, and the target braking force determined by the first braking force determining means And a second braking force determining means for determining a target braking force in a wheel other than the wheel whose element temperature has reached the predetermined temperature.   2. The apparatus of claim 1, wherein the component of the friction braking device is a brake disc or a brake drum, and the means for monitoring the temperature of the component of the friction braking device estimates the temperature of the component. Equipment.   2. The apparatus according to claim 1, wherein the predetermined temperature is a second temperature lower than a first temperature at which a fade phenomenon is likely to occur in a friction element of the friction braking device. Device to do.   4. The apparatus according to claim 1, wherein the first braking force determination means determines the target braking force of the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature as the temperature of the component. The apparatus is characterized in that it is less than the target braking force when the predetermined temperature is reached.   5. The apparatus according to claim 4, wherein the target braking force of the wheel at which the temperature of the component of the friction braking device reaches the predetermined temperature increases to a braking force that does not increase the temperature of the component from the predetermined temperature. A device characterized in that it is allowed to.   5. The apparatus according to claim 4, wherein a target braking force of the wheel at which a temperature of a component of the friction braking device reaches the predetermined temperature is reduced with time.   4. The apparatus according to claim 3, wherein when the temperature of the component exceeds the first temperature, the target braking force of the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature is the friction. The device is limited to a braking force that does not increase the temperature of the components of the braking device.   2. The apparatus according to claim 1, wherein the first braking force determining means can generate a target braking force of a wheel in which a component of the friction braking device has generated a fade phenomenon when the fade phenomenon has occurred. The device is limited to a maximum braking force or less.   2. The apparatus according to claim 1, further comprising each wheel required braking force determining means for determining a required braking force for each of said wheels, wherein said first braking force determining means is said wheel required braking force determining means. Determining the target braking force at the wheel at which the temperature of the component of the friction braking device has exceeded the required braking force determined by the above, and the second braking force determining means is The difference between the required braking force and the target braking force of the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature is the difference other than the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature. Determining the target braking force of the wheels by redistributing them to the wheels.   10. The apparatus of claim 9, further comprising means for determining a target yaw moment of the vehicle, wherein each wheel required braking force determining means determines the required braking force of each wheel so as to generate the target yaw moment. And the second braking force determining means includes the required braking force and the target braking force of the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature so that the target yaw moment is maintained. Is redistributed to a wheel other than the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature.   The apparatus according to claim 9, wherein the second braking force determining means is a required braking force applied to an opposite wheel in the left-right direction of the vehicle when the temperature of a component of the friction braking device reaches the predetermined temperature. The target braking force of the opposite wheel in the left-right direction of the vehicle is determined by subtracting the difference from the vehicle, and the opposite of the front-rear direction of the vehicle of the wheel at which the temperature of the component of the friction braking device has reached the predetermined temperature The target braking force of the wheel opposite to the front-rear direction of the vehicle is determined by adding the difference to the required braking force for the other wheel.

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