JP2010070142A - Road surface friction coefficient estimation device and anti-skid control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a road surface friction estimation more precisely when the road surface friction estimation is performed using a detection result of an M/C pressure sensor. <P>SOLUTION: While basically using a road surface friction estimation value (1) computed based on a detection signal from the M/C pressure sensor 80, the road surface friction estimation value (1) is corrected by comparing it with a road surface friction estimation value (2) computed based on detection signals from wheel speed sensors 81 to 84. Specifically, the road surface friction estimation value (1) is corrected by correcting a presumed W/C value computed based on an M/C pressure sensor value. Thus, even when the road surface friction estimation value (1) becomes incorrect during ABS control, the road surface friction estimation value (1) can be corrected based on the road surface friction estimation value (2). Then, when the road surface friction estimation is performed using the detection result of the M/C sensor 80, the road surface friction estimation can be performed more precisely. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a road surface frictional force estimating device and a road surface frictional force estimating a road surface frictional force based on a detection result of an M / C pressure sensor that detects an M / C pressure generated in a master cylinder (hereinafter referred to as M / C). The present invention relates to an ABS control device that performs anti-skid (hereinafter referred to as ABS) control in which a pressure reduction amount when executing pressure reduction control and a pressure increase gradient when executing pressure increase control are determined.

  Conventionally, a road friction force is estimated, and based on the estimated road friction force, for example, a pressure reduction amount when executing pressure reduction control such as ABS control and a pressure increase gradient when executing pressure increase control are determined. These pressure reduction amount and pressure increase gradient are basically determined based on the vehicle body deceleration. However, since it is necessary to provide the vehicle with an acceleration sensor (G sensor) in order to detect the vehicle body deceleration, The road surface frictional force corresponding to the speed is estimated, and the pressure reduction amount and the pressure increase gradient are determined based on the estimated road friction force. For example, the pressure reduction amount or the pressure increase gradient can be determined based on a map of a pressure reduction amount or a pressure increase gradient with respect to the road surface friction force or the vehicle body deceleration corresponding to the road surface friction force.

The estimation of the road surface friction force is a rotational motion equation based on the balance of the torque applied to the tire from the relationship between various forces applied to the tire (for example, Patent Document 1 discloses the concept of this rotational motion equation). It is done using. Specifically, the road surface frictional force is a value obtained by subtracting an inertia component, a rolling resistance coefficient, and an integrated value of W / C pressure generated in a four-wheel wheel cylinder (hereinafter referred to as W / C) from the engine torque component. Calculated. By estimating the road friction force based on such a brake torque, it is possible to accurately estimate the road friction force.
JP 2005-35344 A

  In the conventional method, it is preferable to use the W / C pressure to estimate the road surface frictional force. However, in order to accurately detect the W / C pressure of each wheel, it is necessary to provide a W / C pressure sensor for each wheel. become. Therefore, using the M / C pressure detected by the M / C pressure sensor, the road surface friction force is detected based on the W / C pressure estimated from the M / C pressure (hereinafter referred to as the estimated W / C pressure). Yes.

  However, the M / C detected by the M / C pressure sensor in the conventional road surface friction force estimation method is based on the premise that the pressure increase to the wheel cylinder by the ABS control or the like is as designed. If the pressure increase characteristic of the pressure increase control valve provided in the actuator for ABS control changes, the road surface frictional force cannot be estimated accurately. For example, since the viscous resistance of the brake fluid changes with temperature, the differential pressure characteristic with respect to the energization amount to the pressure increase control valve changes. Thereby, when the temperature of the brake fluid rises, a torque larger than the target brake torque is generated, and when the temperature of the brake fluid decreases, a torque smaller than the target brake torque is generated.

  As a result, there is a problem that the estimated W / C pressure does not become an accurate value, and the road friction force estimated using the estimated pressure does not become an accurate value. The estimated road friction force is used for setting a pressure reduction amount during pressure reduction control in ABS control, a pressure increase gradient during pressure increase control pressure increase control, and the like. Since it is necessary to estimate the road surface friction force, if the road surface friction force is not an accurate value, there is a possibility that the ABS control becomes rough or a target deceleration cannot be obtained.

  In view of the above points, an object of the present invention is to make it possible to perform more accurate estimation of road friction force when estimating the road friction force using the detection result of the M / C pressure sensor.

  Further, more accurate ABS control is executed when executing ABS control in which the amount of pressure reduction when executing pressure reduction control or the pressure increase gradient when executing pressure increase control is determined based on the estimated value of road surface frictional force. The purpose is to do so.

  In order to achieve the above object, in the first aspect of the present invention, the first estimation means (100) estimates the M / C pressure value obtained based on the detection signal of the M / C pressure sensor (80). The estimated W / C pressure value is used to calculate a first road surface frictional force estimated value that is calculated using a rotational equation of motion that represents the balance of forces applied to the tire, and by the second estimating means (105). The second road surface frictional force estimated value calculated based on the wheel speed obtained based on the detection signal of the wheel speed sensor (81 to 84) provided corresponding to each of the plurality of wheels (FL to RR). Calculate. When the determination means (120, 130) determines that the difference between the first road frictional force estimated value and the second road frictional force estimated value is not within the predetermined range, the correcting means (125, 135) The first road surface frictional force estimated value is corrected so as to approach the second road surface frictional force estimated value.

  Thus, based on the detection signal of the wheel speed sensor (81-84), basically using the first road surface frictional force estimated value calculated based on the detection signal of the M / C pressure sensor (80). The first road surface frictional force estimated value is corrected by comparing with the calculated second road surface frictional force estimated value. As a result, even when the first road surface friction force estimated value is not an accurate value during the ABS control, the first road surface friction force estimated value can be corrected based on the second road surface friction force estimated value. . Therefore, when estimating the road friction force using the detection result of the M / C pressure sensor (80), more accurate road friction force estimation can be performed.

  For example, as described in claim 2, the first road surface frictional force estimated value can be corrected by correcting the estimated W / C pressure value calculated based on the M / C pressure sensor value. Specifically, as described in claim 3, the correction means (125, 135) is configured such that the difference obtained by subtracting the second road surface friction force estimated value from the first road surface friction force estimated value is greater than the first predetermined value. For example, the estimated W / C pressure value is corrected by multiplying the estimated W / C pressure value by a coefficient (A) of less than 1, and the second road surface friction force estimated value is subtracted from the first road surface friction force estimated value. If the difference is smaller than the second predetermined value that is smaller than the first predetermined value, the estimated W / C pressure value can be corrected by multiplying the estimated W / C pressure value by a coefficient (A) of 1 or more. .

  Further, as in the invention described in claim 4, it includes a situation determination means (145) that determines whether or not the correction by the correction means (125, 135) may be performed. If it is determined in step 145) that the correction is not allowed, the correction of the first road frictional force estimated value by the correction means (125, 135) may be prevented. For example, as described in claim 5, in the situation determination means (145), it is determined whether the state is a cascade lock state or a rough road, and the situation determination means (145) determines whether the state is a cascade lock state or a rough road. When it is determined that there is, the correction of the first road surface frictional force estimated value by the correcting means (125, 135) can be prevented.

  As described above, in claims 1 to 5 described above, the present invention has been described as being understood as a road surface friction force estimation device. However, as shown in claim 6 or 7, such a road surface friction force estimation device is included. It can also be understood as an ABS control device. By using such an ABS control device, the ABS control can be executed based on the accurately estimated road surface frictional force. Therefore, the ABS control with high accuracy can be performed, and the targeted deceleration can be obtained.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 shows an overall configuration of a vehicle brake control system 1 including a road surface frictional force estimating apparatus according to a first embodiment of the present invention. In the present embodiment, ABS control is performed as brake control of the vehicle, and is estimated by road surface friction force estimation processing at the time of determining the amount of pressure reduction during pressure reduction control and pressure increase gradient during pressure increase control in this ABS control. Road friction is used. Hereinafter, the configuration of the brake control system 1 according to the present embodiment and the road frictional force estimation process in the ABS control executed by the brake control system 1 will be described.

  In FIG. 1, when the driver depresses the brake pedal 11, the pedaling force is boosted by the booster 12, and the master pistons 13a and 13b disposed in the M / C 13 are pressed. As a result, the same M / C pressure is generated in the primary chamber 13c and the secondary chamber 13d defined by the master pistons 13a and 13b. The M / C pressure is transmitted to each of the W / Cs 14, 15, 34, and 35 through the brake fluid pressure control actuator 50.

  The M / C 13 is provided with a master reservoir 13e having passages communicating with the primary chamber 13c and the secondary chamber 13d, respectively, so that excessive brake fluid can be accumulated and brake fluid can be supplied in short supply. .

  The brake fluid pressure control actuator 50 has a first piping system 50a and a second piping system 50b. The first piping system 50a controls the brake fluid pressure applied to the left front wheel FL and the right rear wheel RR, and the second piping system 50b controls the brake fluid pressure applied to the right front wheel FR and the left rear wheel RL.

  Since the 1st piping system 50a and the 2nd piping system 50b are the same structures, below, the 1st piping system 50a is explained and explanation is omitted about the 2nd piping system 50b.

  The first piping system 50a transmits the M / C pressure described above to the W / C 14 provided on the left front wheel FL and the W / C 15 provided on the right rear wheel RR, and generates a W / C pressure. A conduit A is provided.

  Further, the pipe line A is provided with a first differential pressure control valve 16 that can be controlled to a communication state and a differential pressure state. The valve position of this first differential pressure control valve 16 is adjusted so that it is in a communicating state during normal braking when the driver operates the brake pedal 11 (when brake control such as ABS control is not executed). When the current flows through the solenoid coil provided in the first differential pressure control valve 16, the valve position is adjusted so that the larger the current value, the larger the differential pressure state. Thereby, the differential pressure of the first differential pressure control valve 16 can be linearly changed by setting the value of the current flowing through the solenoid coil.

  When the first differential pressure control valve 16 is in the differential pressure state, only when the brake fluid pressure on the W / C 14, 15 side is higher than the M / C pressure by a predetermined level or more, the M / The brake fluid is allowed to flow only to the C13 side. For this reason, the W / C 14, 15 side is always maintained so as not to be higher than the predetermined pressure by the M / C 13 side.

  The pipe A is branched into two pipes A1 and A2 on the W / C 14 and 15 side downstream of the first differential pressure control valve 16. The pipeline A1 is provided with a first pressure increase control valve 17 that controls the increase of the brake fluid pressure to the W / C 14, and the pipeline A2 is a first pressure that controls the increase of the brake fluid pressure to the W / C 15. A two pressure increase control valve 18 is provided.

  The first and second pressure increase control valves 17 and 18 are constituted by two-position solenoid valves that can control the communication / blocking state.

  The first and second pressure-increasing control valves 17 and 18 are in communication when the control current to the solenoid coils provided in the first and second pressure-increasing control valves 17 and 18 is zero (when no power is supplied). Thus, when the control current is supplied to the solenoid coil (when energized), the normally open type is controlled to be cut off.

  In the pipeline A, the first and second pressure increase control valves 17 and 18 and the pipeline B serving as a pressure-reducing pipeline connecting the pressure regulating reservoir 20 between the W / Cs 14 and 15 are controlled in communication / blocking states. The 1st pressure reduction control valve 21 and the 2nd pressure reduction control valve 22 which are comprised by the 2 position solenoid valve which can be each arrange | positioned. The first and second pressure reducing control valves 21 and 22 are normally closed.

  A conduit C serving as a reflux conduit is disposed between the pressure regulating reservoir 20 and a conduit A serving as a main conduit. The pipe C is provided with a self-priming pump 19 driven by a motor 60 that sucks and discharges brake fluid from the pressure regulating reservoir 20 toward the M / C 13 side or the W / C 14, 15 side. The motor 60 is driven by controlling energization to a motor relay (not shown).

  A conduit D serving as an auxiliary conduit is provided between the pressure regulating reservoir 20 and the M / C 13. Through this pipe D, the brake fluid is sucked from the M / C 13 by the pump 19 and discharged to the pipe A, so that in the vehicle behavior control such as the skid prevention control and the traction (TCS) control, the W / C 14, The brake fluid is supplied to the 15th side, and the W / C pressure of the target wheel is increased.

  In this way, the first piping system 50a is configured. Such a configuration is the same in the second piping system 50b. That is, the first differential pressure control valve 16 and the second differential pressure control valve 36, the first and second pressure increase control valves 17, 18 and the third and fourth pressure increase control valves 37 and 38, the first and second pressure reductions. The control valves 21 and 22 correspond to the third and fourth differential pressure control valves 41 and 42, the pump 19 and the pump 39, the pressure adjusting reservoir 20 and the pressure adjusting reservoir 40, the pipes A to D and the pipes E to H, respectively. ing.

  The brake ECU 70 controls the brake control system 1 and corresponds to the road frictional force estimation device of the present invention that executes ABS control and executes road frictional force estimation processing. The brake ECU 70 is configured by a known microcomputer including a CPU, a ROM, a RAM, an I / O, and the like, and executes processing such as various calculations according to a program stored in the ROM. Specifically, the brake ECU 70 inputs the detection signal of the M / C pressure sensor 80 and the detection signals of the wheel speed sensors 81 to 84, and calculates the M / C pressure and the wheel speeds of the wheels FL to RR. Further, the estimated vehicle body speed and the vehicle body deceleration are calculated based on the calculated wheel speeds of the respective wheels FL to RR, and the slip represented as a deviation between the estimated vehicle body speed and the wheel speeds of the respective wheels FL to RR. Calculate the rate. Then, the slip ratio is compared with an ABS control start threshold value, and if the slip ratio exceeds the ABS control start threshold value, ABS control is executed. The road surface friction force estimation process is performed when setting the pressure reduction amount of the pressure reduction control and the pressure increase gradient of the pressure increase control in the ABS control, and the detection signal of the M / C pressure sensor 80 is used when estimating the road surface friction force. M / C pressure detected based on the following (hereinafter referred to as M / C pressure sensor value) and calculated vehicle body deceleration are used.

  As described above, the brake control system 1 of the present embodiment is configured. In the brake control system 1 configured as described above, the electric signal for controlling the control valves 16 to 18, 21, 22, 36 to 38, 41, 42 and the motor 60 is not output from the brake ECU 70 during normal braking. The M / C pressure generated in the M / C 13 is transmitted to each of the W / Cs 14, 15, 34, and 35 through the pipelines A and E, thereby being applied as the W / C pressure.

  When the ABS control is executed, the pressure increase control valves 17, 18, 37, and 38 in the brake hydraulic pressure control actuator 50 configured as described above are reduced based on the electrical signal from the brake ECU 70. Current supply to the control valves 21, 22, 41, 42 is adjusted as appropriate, and voltage application to the motor 60 for driving the pumps 19, 39 is controlled. Thereby, the W / C pressure generated in each W / C 14, 15, 34, 35 is controlled, and the wheel lock is avoided by adjusting the slip ratio of each wheel FL to RR.

  Next, the road surface friction force estimation process for determining the pressure reduction amount of the pressure reduction control and the pressure increase gradient of the pressure increase control in the ABS control executed by the brake control system 1 configured as described above will be described. The estimated road surface friction force (hereinafter referred to as a road surface friction force estimated value) is used in the ABS control, but the ABS control method itself using each component provided in the brake fluid pressure control actuator 50 is used. Is already well known, and the details are not described here.

  First, before explaining the details of the road surface friction force estimation process executed by the brake ECU 70 according to the present embodiment, the basic concept of road surface friction force estimation will be described.

  In this embodiment, the road surface friction force estimation values (1) and (2) are calculated using two road surface friction force estimation methods, and the road surface friction estimation value (1) calculated by a method considered to have good accuracy. Is basically used, but it may not be an accurate value depending on the vehicle condition. Such a state is determined by comparing with the estimated road friction force value (2) calculated by the other method, and the estimated road friction force value used in that case is corrected. The road surface frictional force estimated value (2) is basically less accurate than the road surface frictional force estimated value (1), but is within a certain error range with respect to the actual road surface frictional force. In a situation where the force estimated value (1) does not become a highly accurate value, the road surface frictional force estimated value (2) is more accurate. Hereinafter, the details of the two methods used here will be described.

  First, the road surface friction force estimation method of the road surface friction force estimated value (1) that is basically used as the road surface friction force estimated value will be described with reference to FIG.

FIG. 2 is a vehicle model diagram showing the relationship between various forces applied to the tire 100 on the ground contact surface of the tire 100. As shown in this figure, the equation of motion for the rotation of the tire 100, that is, the balance equation of the torque acting on the tire 100, is that the inertia of the tire 100 and the engine is I [kg · m ² ], and the angular acceleration of the wheel is ω [ G], the tire radius is r, the force applied to the tire point according to the engine torque is F1 [N], the road friction force is F2 [N], the rolling resistance is F3 [N], and the brake torque is F4 [N]. Is expressed by the following equation.

(Equation 1) F1− (F2 + F3 + F4) = I × ω ÷ r (Formula 1)
F1 to F4 are represented as follows. In the following equations, Te: engine torque, R _AT : automatic transmission torque ratio, R _G : gear ratio, R _D : differential ratio, E: transmission efficiency, μ: road friction coefficient, f: rolling resistance coefficient , M [kg]: weight applied to the tire, g [m / s ² ]: gravitational acceleration (= 9.8 [m / s ² ]), μ ′: friction force of the brake pad, N: force applied to the brake pad Respectively. In FIG. 2, the arrows representing the forces F <b> 1 to F <b> 4 are displayed while being shifted from the road surface position where the tire 100 is in contact with each other.

(Equation 2)
F1 = Te × R _AT × R _G × R _D × E ÷ r (Formula 2)
(Equation 3)
F2 = μ × m × g (Formula 3)
(Equation 4)
F3 = f × m × g (Formula 4)
(Equation 5)
F4 = μ ′ × N ÷ r (Formula 5)
Substituting Equations 2 to 5 into Equation 1 results in Equation 6, and further transforms Equation 6 into an equation of road surface frictional force (= μ × m × g) to Equation 7.

この数式７における第１項がエンジントルク成分、第２項が転がり抵抗係数、第３項が四輪の推定Ｗ／Ｃ圧の積算値から求まるブレーキトルク成分、第４項がイナーシャ成分である。四輪の推定Ｗ／Ｃ圧については、ブレーキＥＣＵ７０がＭ／Ｃ圧センサ値に基づいて推定される。この推定Ｗ／Ｃ圧を用いて表したタイヤ１００にかかる力の式を使用し、そのタイヤ１００に加わるトルクの釣り合いを表した回転運動方程式を使用して数式７では路面摩擦力を演算している。

In Equation 7, the first term is the engine torque component, the second term is the rolling resistance coefficient, the third term is the brake torque component obtained from the integrated value of the estimated W / C pressure of the four wheels, and the fourth term is the inertia component. The estimated ECU W / C pressure is estimated by the brake ECU 70 based on the M / C pressure sensor value. Using the equation of force applied to the tire 100 expressed using the estimated W / C pressure, and using the rotational motion equation representing the balance of torque applied to the tire 100, Equation 7 calculates the road friction force. Yes.

  Regarding the estimated W / C pressure, specifically, M / C pressure sensor value = estimated W / C pressure during normal braking, and the time during which pressure reduction control is performed on the M / C pressure sensor value during ABS control The estimated W / C pressure is calculated by subtracting the value obtained by multiplying the pressure reduction amount, or adding the value obtained by multiplying the pressure increase control time and the pressure increase gradient. Thus, the road surface frictional force estimated value (1) is calculated based on the first method, that is, the detection signal of the M / C pressure sensor 80.

  However, the estimated W / C pressure used for the calculation of the road surface frictional force estimated value (1) is not necessarily an accurate value. For this reason, in this embodiment, in the road surface frictional force estimation process, the road surface frictional force calculated by Equation 7 is corrected.

  Next, the other, that is, a method for estimating the road surface frictional force estimated value (2) for comparison will be described. In this method, the estimated vehicle body speed is calculated from the wheel speeds of the respective wheels FL to RR calculated based on the detection signals of the wheel speed sensors 81 to 84, and further, the vehicle body deceleration corresponding to the differential value of the estimated vehicle body speed is calculated. And the road surface frictional force estimated value is calculated using the vehicle body deceleration obtained thereby. The estimated vehicle body speed is, for example, an average value of the wheel speeds of the three wheels with the highest wheel speed among the four wheels when the ABS control is not being performed, and the highest wheel speed of the four wheels when the ABS control is being performed.

  The road friction force is a value corresponding to the vehicle body deceleration DVS0, and can be read as road surface friction force = vehicle body deceleration DVS0. For this reason, in the other estimation method, the vehicle body deceleration DVS0 is obtained and used as the road surface frictional force estimated value (2). Specifically, the current temporary vehicle deceleration is DVS0X (n), the current vehicle speed is VS0 (n), and the previous vehicle deceleration is calculated as VS0 (n-1). Assuming that the interval is ΔT, the current temporary vehicle deceleration DVS0X (n) is expressed by the following equation.

(Equation 8)
DVS0 (n) = VS0 (n) −VS0 (n−1) / ΔT (Formula 8)
As the vehicle body deceleration, there are an upper limit value αup and a lower limit value αdown that can change from the previous vehicle body deceleration DVS0 (n−1) during the calculation interval ΔT. For this reason, if DVS0X (n) is a value that exceeds the range between the upper limit value αup and the lower limit value αdown for the current temporary vehicle deceleration, DVS0X (n) is not correct for the temporary vehicle deceleration. It is assumed. Therefore, the current vehicle deceleration is calculated by DVS0 (n) as follows.

(Equation 9)
DVS0 (n) = MID [DVS0 (n-1) -αdown, DVS0X (n), DVS0 (n-1) + αup] (Equation 9)
In this way, the road surface frictional force estimated value (2) is calculated based on the other estimation method, that is, the detection signals of the wheel speed sensors 81-84. Next, a road surface friction force estimation process using the road surface friction force estimation value calculated by these two methods will be described.

  FIG. 3 is a flowchart showing details of the road surface friction force estimation process executed by the brake ECU 70. With reference to this figure, the road frictional force estimation process will be described.

  When an ignition switch (not shown) is switched from OFF to ON, the brake ECU 70 executes a road surface frictional force estimation process shown in FIG. 3 every predetermined control cycle.

  First, in step 100 and step 105, road surface frictional force estimated values (1) and (2) are respectively calculated by the two estimation methods described above. In step 110, it is determined whether the correction flag FLG is set to 1. The in-correction flag is set in steps 125 and 135 to be described later, and details will be described later. If a negative determination is made in this step, the process proceeds to step 115, and if a positive determination is made, the process proceeds to step 140.

  In step 115, it is determined whether the ABS control is in progress, the ABS control time is not less than a predetermined time (for example, 500 msec), and the M / C pressure sensor value is not less than a predetermined value (for example, 3 MPa).

  The reason why the ABS control is being performed is that if the ABS control is not being performed, the M / C pressure represents the W / C pressure as it is, which is an accurate value and does not need to be corrected. The reason for determining that the ABS control time is equal to or longer than the predetermined time is to determine whether or not to perform correction after the estimated W / C pressure is stabilized after a certain period of time has elapsed since the ABS control was executed. . The reason why the M / C sensor value is greater than or equal to the predetermined value is to determine that the driver has a braking intention. The ABS control can be determined by checking the ABS control flag that is set when the ABS control start condition that the slip rate exceeds the ABS control start threshold is satisfied. This can be determined by measuring the elapsed time since the condition was met. If all these conditions are satisfied, the process proceeds to step 120.

  In step 120, a state in which the value obtained by subtracting the road surface friction force estimated value (2) from the road surface friction force estimated value (1) is equal to or greater than a first predetermined value (for example, 0.2 G) continues for a specified time (for example, 200 msec) or longer. In addition, it is determined whether the number of skids of both front wheels FL and FR is equal to or greater than a predetermined number (for example, 3 times).

  When the value obtained by subtracting the road surface friction force estimated value (2) from the road surface friction force estimated value (1) is equal to or greater than the first predetermined value, the road surface friction force estimated value (1) may not be an accurate value. It means that there is a state. That is, when the estimated W / C pressure is calculated based on the M / C pressure sensor value, an error occurs in the estimated W / C pressure due to the influence of the ABS control, and the road surface frictional force estimated value (1) is an accurate value. Indicates that it may have disappeared. The number of skids on both front wheels FL and FR means the number of times of pressure reduction control by ABS control, and can be determined by counting the number of skids after the ABS control is started. As the number of skids increases, the possibility that the estimated W / C pressure deviates from the actually generated W / C pressure increases. Therefore, the estimated value of the road friction force is calculated from the estimated value of the road friction force (1). When the value obtained by subtracting (2) is equal to or greater than the first predetermined value for a predetermined time and the number of skids is equal to or greater than the predetermined number, it is determined that the road surface frictional force estimated value (1) is not an accurate value. Yes.

  Then, if an affirmative determination is made in step 120, the process proceeds to step 125, and a value obtained by multiplying the previous estimated W / C pressure of each wheel FL to FR by a coefficient A less than 1 is estimated for each wheel FL to FR at this time. While setting as the W / C pressure, the correcting flag FLG is set to 1.

  That is, the value obtained by subtracting the road surface frictional force estimated value (2) from the road surface frictional force estimated value (1) is equal to or greater than the first predetermined value. It means that In this case, the amount of pressure reduction during the pressure reduction control in the ABS control is insufficient, or the pressure increase gradient during the pressure increase control is excessive. For this reason, by correcting so that the estimated W / C pressure of each wheel FL to FR is reduced, the integrated value of the estimated W / C pressure of the four wheels in the fourth term of the above formula 7 is reduced, and the road frictional force is estimated. The value (1) is made smaller. Thereby, the road surface frictional force estimated value (1) can be made to approach an accurate value.

  On the other hand, if a negative determination is made in step 120, the process proceeds to step 130, and a value obtained by subtracting the road surface friction force estimated value (2) from the road surface friction force estimated value (1) is equal to or less than a second predetermined value (for example, -0.2G). It is determined whether or not a certain state continues for a specified time (for example, 200 msec) or more and the number of skids of both front wheels FL and FR is a predetermined number (for example, 3 times) or more.

  In this process, the value obtained by subtracting the road surface frictional force estimated value (2) from the road surface frictional force estimated value (1) with respect to step 120 is a second predetermined value, that is, a value obtained by replacing the positive and negative signs of the first predetermined value. It is determined whether or not the road surface frictional force estimated value (1) is a value that is too smaller than the actual value, and the determination content is the same as in step 120.

  When an affirmative determination is made in step 130, the amount of pressure reduction during the pressure reduction control in the ABS control is excessive or the pressure increase gradient during the pressure increase control is insufficient. Therefore, the process proceeds to step 135, and a value obtained by multiplying the previous estimated W / C pressure of each wheel FL to FR by a coefficient B of 1 or more is set as the estimated W / C pressure of each wheel FL to FR. At the same time, the correcting flag FLG is set to 1.

  That is, the value obtained by subtracting the road surface friction force estimated value (2) from the road surface friction force estimated value (1) is equal to or less than the second predetermined value means that the road surface friction force estimated value (1) is too large. I mean. For this reason, by correcting so that the estimated W / C pressure of each wheel FL to FR is increased, the integrated value of the estimated W / C pressure of the four wheels in the fourth term of the above formula 7 is increased, and the road frictional force is estimated. The value (1) is increased. Thereby, the road surface frictional force estimated value (1) can be made to approach an accurate value.

  In this way, when the correction-in-progress flag FLG is set to 1, an affirmative determination is made in step 110, and thus the routine proceeds to step 140.

  In step 140, it is determined whether or not the ABS control is finished. The ABS control is terminated, for example, when the depression of the brake pedal 11 is stopped, and the ABS control flag is reset at that time. Therefore, a negative determination is made if the ABS control flag remains set, and an affirmative determination is made if the flag is being reset.

  If a negative determination is made in step 140, the process proceeds to step 145, in which it is determined whether the road surface being traveled is a bad road or whether the M / C pressure sensor value is smaller than a predetermined value (for example, 1 MPa). In the case of a bad road or when the M / C pressure sensor value is smaller than a predetermined value, a value obtained by subtracting the road surface frictional force estimated value (2) from the road surface frictional force estimated value (1) is smaller than the first predetermined value. Even if it is larger or smaller than the second predetermined value, it may be in such a situation because the vehicle is traveling on a rough road or is in a cascade lock state.

  The bad road means a stepped road surface or the like, for example, a case where the difference between the wheel speeds of the left and right wheels exceeds a threshold value. Cascade lock means that the four wheels lock simultaneously and the vehicle body deceleration falls within the range of the upper limit value αup or lower limit value αdown of the gradient, so that it is erroneously determined that the slip ratio remains small, and ABS control is executed. It is a locked state that occurs because it is not performed. Such a state can be determined based on the M / C pressure sensor value because the M / C pressure sensor value is smaller than a predetermined value.

  When the vehicle is in a cascade lock state or traveling on a rough road, there is a possibility that the accuracy of the road surface friction force estimated value (2) may be poor, and the road surface friction force estimated value (1) is converted to the road surface friction force estimated value (2). It may not be preferable to correct based on the above. For this reason, only when a negative determination is made in step 145, the process proceeds to step 150 and correction of each estimated W / C pressure is continued. When an affirmative determination is made, the process proceeds to step 155 and correction of each estimated W / C pressure is performed. And clear the FLG being corrected. Thus, the road surface frictional force estimation process is completed.

  FIGS. 4 and 5 are timing charts for one wheel when the road frictional force estimation process as described above is not executed and when it is executed.

  As shown in FIG. 4, when the road frictional force estimation process as described above is not executed, the road surface frictional force estimated value (1) and the road frictional force estimated value (2) at the beginning of the ABS control. The difference is not so large. However, after starting the ABS control, the estimated W / C pressure value gradually deviates from the actually generated W / C pressure (hereinafter referred to as the actual W / C pressure value), and the estimated W / C pressure value is used. The road surface frictional force estimated value (1) calculated in this way is separated from the road surface frictional force estimated value (2). For this reason, the pressure reduction amount at the time of pressure reduction control in the ABS control set based on the estimated road frictional force value (1) and the pressure increase gradient at the time of pressure increase control are separated from the slope that is originally set, and the ABS control becomes rough. The target deceleration cannot be obtained.

  On the other hand, as shown in FIG. 5, when the road surface frictional force estimation process as described above is executed, the estimated W / C pressure value is gradually generated after the ABS control is started. The road surface friction force estimated value (1) calculated using the estimated W / C pressure value is separated from the W / C pressure (hereinafter referred to as the actual W / C pressure value). And the difference between the road surface frictional force estimated value (1) and the road surface frictional force estimated value (2) converges between the first predetermined value and the second predetermined value when the number of skids exceeds a predetermined value. In addition, the estimated W / C pressure value is corrected. As a result, the pressure reduction amount at the time of the pressure reduction control in the ABS control set based on the estimated value of the road surface frictional force (1) and the pressure increase gradient at the time of the pressure increase control approach the slope to be originally set, and the accuracy of the ABS control is increased. You can get a slow deceleration.

  As described above, in the present embodiment, the road surface friction force estimation value (1) calculated based on the detection signal of the M / C pressure sensor 80 is basically used, and the wheel speed sensors 81 to 84 are detected. The road surface frictional force estimated value (1) is corrected by comparing with the road surface frictional force estimated value (2) calculated based on the signal. Specifically, the estimated road frictional force value (1) is corrected by correcting the estimated W / C pressure value calculated based on the M / C pressure sensor value. Thus, even when the road surface friction force estimated value (1) is not an accurate value during the ABS control, the road surface friction force estimated value (1) is based on the road surface friction force estimated value (2). Can be corrected. Therefore, when estimating the road surface friction force using the detection result of the M / C pressure sensor 80, it is possible to perform more accurate road surface friction force estimation.

  Then, by executing the ABS control based on such a correctly estimated road surface frictional force, it is possible to perform the ABS control with high accuracy and obtain the targeted deceleration.

(Second Embodiment)
A second embodiment of the present invention will be described. In this embodiment, a part of the road surface frictional force estimation process is changed with respect to the first embodiment, and the other parts are the same as those in the first embodiment, and therefore only different parts will be described.

  FIG. 6 is a flowchart showing details of the road surface frictional force estimation process of the present embodiment. As shown in this figure, instead of the processing of steps 125, 135, 150, and 155 in FIG. 3, the processing of steps 125A, 135A, 150A, and 155A is executed.

  Specifically, in step 125A, the pressure reduction amount during pressure reduction control and the pressure increase gradient during pressure increase control are controlled using a map corresponding to low G. For example, the pressure reduction amount during the pressure reduction control and the pressure increase gradient during the pressure increase control are determined based on a map of the pressure reduction amount or pressure increase gradient with respect to the generated vehicle deceleration. At this time, the road surface friction force estimated value (1) is corrected to be small, and the generated vehicle body deceleration is set to a low value as the vehicle body deceleration corresponding to the corrected road surface friction force estimated value (1). The pressure reduction amount or the pressure increase gradient corresponding to the vehicle body deceleration is set. In this way, it is possible to suppress the pressure reduction amount during the pressure reduction control in the ABS control from being insufficient or the pressure increase gradient during the pressure increase control from being excessive, and to execute appropriate ABS control.

  In step 135A, the amount of pressure reduction during pressure reduction control and the pressure increase gradient during pressure increase control are controlled by a map corresponding to high G. For example, the road surface friction force estimated value (1) is corrected so as to increase, and the generated vehicle body deceleration is set to a large value as the vehicle body deceleration corresponding to the corrected road surface friction force estimated value (1). A decompression amount or a pressure increase gradient corresponding to the vehicle deceleration is set. In this way, as described above, it is possible to suppress the pressure reduction amount during the pressure reduction control in the ABS control from being insufficient or the pressure increase gradient during the pressure increase control from being excessive, and to perform appropriate ABS control.

  In step 150A, the process of continuing the correction of the pressure reduction amount and the pressure increase gradient performed in steps 125A and 135A is performed, and in step 155A, the correction of the pressure decrease amount and the pressure increase gradient performed in step 125A and step 135A is completed. The process is performed and the correction FLG is cleared. As described above, the road frictional force estimation process is completed.

  Thus, the road surface friction force estimated value (1) is not corrected by correcting the estimated W / C pressure, but the road surface friction force estimated value (1) is corrected by correcting the road surface friction force estimated value (1). The ABS control can be executed with high accuracy even when the pressure reduction amount during the pressure reduction control and the pressure increase gradient during the pressure increase control set based on (1) are corrected.

(Other embodiments)
In each of the above embodiments, various determination conditions are set in each determination step in the road frictional force estimation process shown in FIGS. 3 and 6, but not all conditions need to be satisfied. For example, although three conditions are set in step 115, the determination conditions may be reduced, for example, an affirmative determination is made in step 115 if at least one of the three is satisfied.

  In the first embodiment, the estimated road surface friction force estimated value (1) is corrected by correcting the estimated W / C pressure value. However, the estimated road surface friction force estimated value (1) is corrected directly. By doing so, you may make it approach the road surface frictional force estimated value (2).

  The steps shown in each figure correspond to means for executing various processes. Specifically, the parts that execute the processing of steps 100 and 105 are the first and second estimating means, the parts that execute the processes of steps 120 and 130 are the determining means, and the parts that execute the processes of steps 125 and 135 are corrected. The means for executing the processing of step 145 corresponds to the situation determination means.

1 is a diagram illustrating an overall configuration of a vehicle brake control system 1 including a road surface frictional force estimating apparatus according to a first embodiment of the present invention. 2 is a vehicle model diagram showing a relationship between various forces applied to a tire 100. FIG. 5 is a flowchart showing details of a road surface frictional force estimation process executed by a brake ECU 70. It is a timing chart when not performing the road surface frictional force estimation process. It is a timing chart at the time of performing a road surface frictional force estimation process. It is the flowchart which showed the detail of the road surface frictional force estimation process concerning 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Brake control system, 11 ... Brake pedal, 12 ... Booster, 13 ... M / C, 14, 15, 34, 35 ... W / C, 16, 36 ... Differential pressure control valve, 16 -... Each control valve , 17, 18, 37, 38 ... pressure increase control valve, 19, 39 ... pump, 20, 40 ... pressure regulating reservoir, 21, 22, 41, 42 ... pressure reduction control valve, 50 ... actuator for brake fluid pressure control, 50a ... Piping system, 50b ... Piping system, 60 ... Motor, 70 ... Brake ECU, 80 ... M / C pressure sensor, 81-84 ... Wheel speed sensor

Claims (7)

The balance of the torque applied to the tire is represented by the force applied to the tire expressed using the estimated wheel cylinder pressure value estimated from the master cylinder pressure value obtained based on the detection signal of the master cylinder pressure sensor (80). A first estimating means (100) for calculating a first road frictional force estimated value that is calculated after using the rotational equation of motion,
The second road surface frictional force estimated value calculated based on the wheel speed obtained based on the detection signal of the wheel speed sensor (81 to 84) provided corresponding to each of the plurality of wheels (FL to RR) is calculated. Second estimating means (105) for
Determination means (120, 130) for determining whether or not a difference between the first road surface frictional force estimated value and the second road surface frictional force estimated value is within a predetermined range;
When the determination means (120, 130) determines that the difference is not within the predetermined range, a correction means (correction means) for correcting the first road frictional force estimated value so as to approach the second road frictional force estimated value. 125, 135), and a road surface frictional force estimating device.   2. The road frictional force estimation device according to claim 1, wherein the correction unit (125, 135) corrects the first road frictional force estimated value by correcting the estimated wheel cylinder pressure value. 3.   If the difference obtained by subtracting the second road surface friction force estimated value from the first road surface friction force estimated value is greater than a first predetermined value, the correcting means (125, 135) The estimated wheel cylinder pressure value is corrected by multiplying by a coefficient (A) less than 1, and the difference obtained by subtracting the second road surface friction force estimated value from the first road surface friction force estimated value is greater than the first predetermined value. 3. The estimated wheel cylinder pressure value is corrected by multiplying the estimated wheel cylinder pressure value by a coefficient (B) of 1 or more if it is smaller than a small second predetermined value. Road frictional force estimation device.   In a situation in which the situation determination means (145) includes a situation determination means (145) for determining whether or not the situation can be corrected by the correction means (125, 135). 4. The correction according to claim 1, wherein if it is determined that there is no correction, the correction means (125, 135) does not correct the estimated value of the first road frictional force. 5. Road frictional force estimation device.   The situation determination means (145) determines whether or not a cascade lock state or a rough road, and when the situation determination means (145) determines that a cascade lock state or a rough road, the correction is performed. 5. The road surface frictional force estimating device according to claim 4, wherein the first road surface frictional force estimated value is not corrected by the means (125, 135).   An anti-skid control based on the first road surface frictional force estimated value corrected by the correction means in the road surface frictional force estimating device, including the road surface frictional force estimating device according to any one of claims 1 to 5. An anti-skid control device that sets a pressure reduction amount during pressure reduction control and a pressure increase gradient during pressure increase control. The balance of the torque applied to the tire is represented by the force applied to the tire expressed using the estimated wheel cylinder pressure value estimated from the master cylinder pressure value obtained based on the detection signal of the master cylinder pressure sensor (80). First estimating means (100) for calculating a first road frictional force estimated value calculated from the rotational equation of motion,
An anti-skid control device comprising anti-skid control means for setting a pressure reduction amount during anti-skid control pressure reduction control and a pressure increase gradient during pressure increase control based on the first road surface frictional force estimated value,
The second road surface frictional force estimated value calculated based on the wheel speed obtained based on the detection signal of the wheel speed sensor (81 to 84) provided corresponding to each of the plurality of wheels (FL to RR) is calculated. Second estimating means (105) for
Determining means (120, 130) for determining whether or not a difference between the first road surface frictional force estimated value and the second road surface frictional force estimated value is within a predetermined range;
When the determination means determines that the difference is not within the predetermined range, the anti-skid control means corrects the first road surface frictional force estimated value to obtain the corrected first road surface frictional force estimated value. An anti-skid control device characterized in that, based on the pressure reduction control, a pressure reduction amount and a pressure increase gradient during pressure increase control are set.

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