JP2008290474A - Brake control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brake control device capable of certainly estimating hydraulic pressure of a master cylinder even though there is a disturbance when intensifying pressure in antiskid control. <P>SOLUTION: This brake control device includes: a hydraulic pressure control means provided between the master cylinder and a wheel cylinder and controlling to increase or decrease the hydraulic pressure of the wheel cylinder according to the traveling condition of a vehicle; a master cylinder hydraulic pressure estimation means estimating the hydraulic pressure of the master cylinder; a pressure intensification elapsed time detection means detecting elapsed time of pressure intensification control performed between the present pressure reduction control of the wheel cylinder and the next pressure reduction control thereof; an instantaneous pressure intensification controlled variable calculation means calculating an instantaneous pressure intensification controlled variable in the elapsed time; a lowest differential pressure estimation means estimating a lowest differential pressure between the actual hydraulic pressure of the master cylinder and the estimated hydraulic pressure of the master cylinder based on the elapsed time and instantaneous pressure intensification controlled variable; and a correction means correcting the hydraulic pressure of the master cylinder, estimated based on the estimated lowest differential pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vehicle brake control device provided between a master cylinder and a wheel cylinder, and more particularly to a technique for estimating a master cylinder hydraulic pressure.

Conventionally, a technique described in Patent Document 1 has been disclosed as a technique for estimating a master cylinder hydraulic pressure. In this publication, the master cylinder hydraulic pressure estimated value is increased according to the elapsed time within a predetermined time after the braking operation when the anti-skid control is not operated, and after the predetermined time has elapsed, the master cylinder hydraulic pressure estimated value is decreased. Increase with speed. Further, when the anti-skid control is operated, correction calculation is performed in each of the pressure increase control and the pressure reduction control based on the previous master cylinder hydraulic pressure and wheel cylinder hydraulic pressure, and the current master cylinder hydraulic pressure is estimated.
JP-A-9-323634

  However, in the above prior art, the estimated value of the master cylinder hydraulic pressure is initially set based on the vehicle deceleration when the anti-skid control is not operated, and during the pressure increase, a correction value obtained by multiplying the previous estimated value by a fixed coefficient is added. Therefore, the correction corresponding to the change in the master cylinder hydraulic pressure caused by the disturbance during the pressure increase cannot be performed, and the estimated master cylinder hydraulic pressure may be estimated less than the actual master cylinder hydraulic pressure. .

  The present invention has been made paying attention to the above-mentioned conventional problems, and provides a brake control device capable of accurately estimating the master cylinder hydraulic pressure even if there is a disturbance during pressure increase during anti-skid control. For the purpose.

  In order to solve the above problems, in the brake control device of the present invention, a master cylinder that generates hydraulic pressure by a driver's brake pedal operation, a wheel cylinder that generates braking force on wheels based on supplied hydraulic pressure, A hydraulic pressure control means that is provided between the master cylinder and the wheel cylinder and controls the hydraulic pressure of the wheel cylinder to be increased or decreased in accordance with a running state of the vehicle; and a master cylinder fluid that estimates the hydraulic pressure of the master cylinder. Pressure estimation means, pressure increase elapsed time detection means for detecting an elapsed time of pressure increase control performed between the current pressure reduction control and the next pressure reduction control of the wheel cylinder, and an instantaneous pressure increase control amount in the elapsed time Instantaneous pressure increase control amount calculating means for calculating the actual master cylinder hydraulic pressure and the estimated master cylinder based on the elapsed time and the instantaneous pressure increase control amount And minimum differential pressure estimation means for estimating a minimum differential pressure between the pressure, characterized in that a correcting means for correcting the estimated master cylinder pressure based on the estimated minimum differential pressure.

  That is, the amount of brake fluid actually moved from the master cylinder to the wheel cylinder can be estimated by the pressure increase control valve control amount, and even if the master cylinder fluid pressure fluctuates due to road surface disturbance, the estimated master fluid can be accurately estimated. The cylinder hydraulic pressure can be corrected.

  The best mode for carrying out the present invention will be described below with reference to the drawings as an embodiment.

  FIG. 1 is a schematic diagram showing a single wheel model of a vehicle brake control device (hydraulic brake unit). Since ABS control is performed for each wheel, the configuration shown in FIG. 1 is assumed to be provided for each wheel.

  First, the configuration will be described. The brake pedal 1 is provided with a master cylinder M / C that generates a brake fluid pressure corresponding to the driver's depression force. A pressure increasing circuit 11 and a reflux circuit 14 are connected to the master cylinder M / C via the main passage 10. On the pressure increase circuit 11, a normally open type pressure increase control valve 2 is provided. Connected to the pressure increasing circuit 11 are a wheel cylinder circuit 12 connected to a wheel cylinder W / C for generating a braking force, and a pressure reducing circuit 13 for allowing the brake fluid to flow out from the wheel cylinder W / C during pressure reduction. On the decompression circuit 13, a normally closed decompression control valve 3 is provided. The decompression circuit 13 is provided with a reservoir 4 for temporarily storing brake fluid flowing out from the wheel cylinder W / C. The decompression circuit 13 is connected to a reflux circuit 14 via a pump 5 driven by a pump motor 5a and a check valve 6 that allows only a flow from the pump 5.

  The ABS control unit 20 is provided with a wheel speed sensor 21 that detects the wheel speed of each wheel. The ABS control unit 20 includes a pseudo vehicle speed calculator 20a that calculates a pseudo vehicle speed V based on the wheel speed VW detected from the wheel speed sensor 21, and a pseudo vehicle speed V calculated based on the wheel speed VW. In order to reduce the slip ratio S, a pressure increase / decrease / hold command is output to the pressure increase control valve 2 and the pressure decrease control valve 3, and the brake fluid stored in the reservoir 4 is returned to the master cylinder M / C. There is provided an ABS controller 20b for outputting a drive command to the pump motor 5a. In the first embodiment, the control amounts from the ABS control unit 20b to the pressure reducing control valve 2 and the pressure increasing control valve 3 are output as valve opening times, and each control valve is fully opened during this valve opening time. It is said that.

  Further, the ABS control unit 20 is provided with a master cylinder hydraulic pressure estimation unit 20c that estimates the master cylinder hydraulic pressure and an estimated master cylinder hydraulic pressure correction unit 20d that corrects the estimated master cylinder hydraulic pressure. As a method of estimating the master cylinder hydraulic pressure, for example, when the anti-skid control is not operated, the master cylinder hydraulic pressure is estimated based on the vehicle body deceleration. On the other hand, when the anti-skid control is operated, the estimation is performed by adding / subtracting the correction amount to / from the estimated master cylinder hydraulic pressure estimated in the previous control cycle. For example, an increase correction is performed when the pressure is reduced, and a decrease correction is performed when the pressure is increased. The estimated master cylinder hydraulic pressure correction unit 20d corrects the estimated master cylinder hydraulic pressure during anti-skid control, particularly during pressure increase, and will be described in detail later.

  Here, the slip ratio S represents how much the wheel speed VW slides with respect to the road surface with respect to the pseudo vehicle speed V, and is represented by the slip ratio S = {(V−VW) / V}. . If the wheel speed VW coincides with the pseudo vehicle speed V, the slip ratio becomes zero, and the slip ratio increases as the wheel speed VW and the pseudo vehicle speed V become far apart.

ABS control A basic control logic in the ABS control according to the first embodiment will be described. The optimum slip value Vopt1 for starting decompression and the optimum slip value Vopt2 for starting boosting are set at the place where the preset vehicle speed V0 is subtracted from the pseudo vehicle speed V (the point where the friction coefficient characteristic of the tire becomes maximum). . When the slip ratio S exceeds the optimum slip ratio Sopt1, the process proceeds to pressure reduction control to prevent the wheel speed VW from decreasing due to the locking tendency, that is, the slip ratio S from increasing. When the increase of the slip ratio S is prevented, the control shifts to holding control, and the slip ratio S is decreased. When the slip ratio S decreases and falls below the optimum slip ratio Sopt2, the control shifts to pressure increase control, and the increase of the wheel speed VW, that is, the decrease of the slip ratio S is prevented. Vopt1 and Vopt2 may be set to the same value.

  At this time, the decompression control amount in the decompression command is calculated as a feedforward amount based on the vehicle body deceleration or the like. Assuming that the period from the first pressure reduction control to the start of the next pressure reduction control is the pressure increase / decrease control period, the pressure increase / decrease control period is generally determined by the first pressure reduction control amount. Further, the pressure increase control amount in the pressure increase command is calculated as a feedback amount based on wheel acceleration or the like. Therefore, the pressure increase control amount is determined so that the wheel speed recovers the slip ratio Vopt1 for starting the pressure reduction.

-Action of each actuator during ABS control Next, the action of the pressure increase control valve 2 and the pressure reduction control valve 3 when the ABS control is executed will be described. At the time of pressure reduction control, the pressure increase control valve 2 is closed and the pressure reduction control valve 3 is opened, so that the brake fluid flows from the wheel cylinder W / C to the pressure reduction circuit 13 and is temporarily stored in the reservoir 4. During the holding control, both the pressure increase control valve 2 and the pressure reduction control valve 3 are closed to hold the hydraulic pressure of the wheel cylinder W / C. At the time of pressure increase control, the pressure reduction control valve 3 is closed and the pressure increase control valve 2 is opened, whereby high-pressure brake fluid is supplied from the master cylinder M / C via the main passage 10, the pressure increase circuit 11 and the wheel cylinder circuit 12. Supply to wheel cylinder W / C.

  When the brake fluid stored in the reservoir 4 (for example, a value estimated by the total decompression time) exceeds a predetermined amount indicating that the reservoir 4 is full, a drive command is output to the pump motor 5a, and the reservoir 4 The brake fluid is pumped into the recirculation circuit 14 and returned to the master cylinder M / C via the main passage 10 to ensure the brake fluid amount balance.

  When returning the brake fluid, it is necessary that the driver depresses the brake pedal strongly and the brake fluid in the reservoir 4 is surely returned even when the master cylinder fluid pressure is high. Therefore, the target motor speed is set on the basis of the estimated master cylinder hydraulic pressure in order to ensure an appropriate motor drive amount according to the master cylinder hydraulic pressure etc. while avoiding unnecessary battery consumption. Thus, the motor rotation speed feedback control is performed.

(Estimated master cylinder fluid pressure correction process)
Next, the estimated master cylinder hydraulic pressure correction process in the first embodiment will be described. The estimated master cylinder hydraulic pressure correction unit 20d appropriately calculates a correction amount when performing a decrease correction particularly when the pressure is increased. Hereinafter, the reason why the estimated master cylinder hydraulic pressure must be corrected at the time of pressure increase in the anti-skid control and what will be a problem if the correction is inappropriate will be described.

  Basically, when the pressure is reduced, the pressure increase control valve 2 is closed and the pressure reduction control valve 3 is opened to reduce the pressure. At this time, since the reservoir 4 is constant as the atmospheric pressure, the opening time of the pressure-reducing control valve 3 and the flow rate (change in hydraulic pressure) can be generally correlated.

  On the other hand, when the pressure is increased, the pressure reduction control valve 3 is closed and the pressure increase control valve 2 is opened to increase the pressure. At this time, the wheel cylinder hydraulic pressure may change the force to turn the wheel due to a change in the road surface friction coefficient. When the road surface friction coefficient changes in a higher direction, a higher wheel cylinder hydraulic pressure is required, and accordingly, the master cylinder hydraulic pressure decreases. On the other hand, when the road surface friction coefficient changes in a lower direction, a lower wheel cylinder hydraulic pressure is required, and accordingly, the master cylinder hydraulic pressure cannot be lowered accordingly.

  For the above reason, when a certain estimated master cylinder hydraulic pressure correction amount is given at the time of pressure increase, the estimated value may be estimated higher than the actual value or may be estimated lower. If it is estimated to be higher, only a higher drive command is output as a drive command for the pump motor 5a, and there is no problem because the brake fluid can be reliably recirculated to the master cylinder side. However, if it is estimated to be low, there is a problem because the brake fluid cannot be reliably recirculated to the master cylinder side. Therefore, the estimated master cylinder hydraulic pressure correction unit 20d performs correction so that the estimated master cylinder hydraulic pressure is not estimated to be low when the pressure is increased during the anti-skid control.

FIG. 2 is a flowchart showing an estimated master cylinder hydraulic pressure correction process. This flow is executed during pressure increase during anti-skid control.
In step S1, it is determined whether or not the pressure increase control in the anti-skid control is being performed. If the pressure increase control is being performed, the process proceeds to step S2, and otherwise the control flow is terminated.

  In step S2, a pressure increase elapsed time detection process is executed. Details thereof will be described later with reference to FIG.

  In step S3, an instantaneous pressure increase control amount is calculated. The instantaneous pressure increase control amount is a value calculated based on the relationship between the time from the start of pressure increase to the current time and the total valve opening time of the pressure increase control valve 3 performed during the time, for example, This represents the current average pressure increase control amount calculated by (total valve opening time) / (time from the start of pressure increase to the current time). That is, it is a value for determining how much flow rate movement is performed from the master cylinder M / C to the wheel cylinder W / C at the present time.

  In step S4, the minimum differential pressure is calculated. This minimum differential pressure is a value at which a differential pressure of at least this level is generated as a hydraulic pressure difference between the actual master cylinder hydraulic pressure and the estimated master cylinder hydraulic pressure. Details will be described later.

  In step S5, an estimated master cylinder hydraulic pressure correction process is executed. Specifically, the estimated master cylinder hydraulic pressure is added to the minimum differential pressure so that the estimated master cylinder hydraulic pressure is increased. Accordingly, the brake fluid in the reservoir 4 is recirculated to the master cylinder side by ensuring the drive command for the pump motor 5a.

FIG. 3 is a flowchart showing the pressure increase elapsed time detection process.
In step S21, it is determined whether or not a pressure increasing command is input. If a pressure increasing command is input, the process proceeds to step S22, and otherwise, the process proceeds to step S25.
In step S22, it is determined whether or not it is the first pressure increase after depressurization. If it is the first pressure increase, the process proceeds to step S23. Otherwise, the process proceeds to step S24.
In step S23, counting of the pressure increase elapsed time is started.
In step S24, the pressure increase elapsed time is continuously counted.
In step S25, it is determined whether or not a decompression command is input. If a decompression command is input, the process proceeds to step S26, and otherwise, the control flow ends.

  Next, the operation based on the control flow will be described. FIG. 4 is a time chart showing the relationship between the pressure reduction command, the pressure increase command, the pressure increase elapsed time, and the master cylinder hydraulic pressure when the anti-skid control is executed. When anti-skid control is started and a pressure increase command is output at time t1, counting of pressure increase elapsed time is started.

  Hereinafter, master cylinder fluid pressure estimation and correction processing during pressure increase control will be described. As described above, when estimating the master cylinder hydraulic pressure, the value is subtracted at a constant rate as time elapses as a basic estimated value during the pressure increase control. At this time, if the pressure increase control amount is small, it is considered that the actual master cylinder hydraulic pressure is higher than the basic estimated value.

  Therefore, the minimum differential pressure is estimated from the map shown in FIG. 4 based on the pressure increase elapsed time and the instantaneous pressure increase control amount. The minimum differential pressure means that when the actual master cylinder hydraulic pressure is compared with the basic estimated value plus the minimum differential pressure, the actual master cylinder hydraulic pressure will not be higher than the added estimated value. Although the actual master cylinder hydraulic pressure may be lower in some cases, it is a value considered not to be high. In other words, this value is obtained from the viewpoint that if the pump motor 5a is driven based on such a corrected estimated value, the brake fluid in the reservoir 4 can be reliably returned to the master cylinder side.

  Here, the characteristics of the minimum differential pressure map of FIG. 5 will be described. The minimum differential pressure represents the maximum differential pressure that can be assumed between the actual master cylinder hydraulic pressure and the estimated master cylinder hydraulic pressure that is a basic estimated value. In this minimum differential pressure map, the relationship between the instantaneous pressure increase control amount and the minimum differential pressure is set according to the pressure increase elapsed time. Hereinafter, the basis for setting each characteristic will be described.

  (i) When the pressure increase elapsed time is short, i.e., when pressure reduction control is not currently performed, it is assumed that pressure reduction is performed at the next moment.In this case, it is estimated that pressure increase has been performed at once. The It is assumed that the pressure increase is made at once when the hydraulic pressure difference between the master cylinder hydraulic pressure and the wheel cylinder hydraulic pressure is large. Therefore, it can be estimated that the flow rate when the pressure increase control valve 3 is opened is large. If the flow rate is large, there is a possibility that the master cylinder hydraulic pressure is greatly reduced, so that the difference between the actual master cylinder hydraulic pressure and the basic estimated value is estimated to be large. Therefore, the minimum differential pressure is set larger.

  (ii) When the pressure increase elapsed time is long, that is, when the pressure reduction control is not performed even though a certain amount of time has passed, the pressure increase control valve is not so much increased even if it is opened. It is estimated to be. It is assumed that the pressure increase is not so high when the hydraulic pressure difference between the master cylinder hydraulic pressure and the wheel cylinder hydraulic pressure is small. Therefore, it can be estimated that the flow rate when the pressure increase control valve 3 is opened is small. If the flow rate is small, the master cylinder hydraulic pressure does not decrease so much, so it is estimated that the difference between the actual master cylinder hydraulic pressure and the basic estimated value is small. Therefore, the minimum differential pressure is set smaller.

  (iii) When the instantaneous pressure increase control amount is large, that is, when the flow rate of the pressure increase control valve 3 at a certain time is large, the master cylinder hydraulic pressure is reduced accordingly. It is estimated that the difference from the value is large. Therefore, the minimum differential pressure is set larger.

  (iv) When the instantaneous pressure increase control amount is small, that is, when the flow rate of the pressure increase control valve 3 at a certain time is small, the master cylinder hydraulic pressure is not reduced that much. It is estimated that the difference from the estimated value is small. Therefore, the minimum differential pressure is set smaller.

  The minimum differential pressure is calculated based on the minimum differential pressure map of FIG. 5 set as described above, and a value obtained by adding the minimum differential pressure to the basic estimated value is set as the master cylinder hydraulic pressure estimated value. As a result, the estimated master cylinder hydraulic pressure estimated value can be corrected with high accuracy, and the estimated master cylinder hydraulic pressure can be corrected with high accuracy even if the master cylinder hydraulic pressure fluctuates due to road surface disturbance.

  Next, Example 2 will be described. Since the basic configuration is the same as that of the first embodiment, only different points will be described. In the first embodiment, control amounts from the ABS control unit 20b to the pressure reduction control valve 2 and the pressure increase control valve 3 are output as valve opening times, and each control valve is in a fully open state during the valve opening time. It was. On the other hand, in the second embodiment, the control amounts from the ABS control unit 20b to the pressure reduction control valve 2 and the pressure increase control valve 3 are output as valve opening amounts, and each control valve has an intermediate opening according to the valve opening amount. It is different in that the configuration is ensured. The valve opening amount is controlled by the ON-OFF duty ratio. Since the pressure increase control valve 3 is a normally open type, the valve is closed by setting the ON duty ratio to 100%, and the valve opening amount is increased by decreasing the ON duty ratio.

  FIG. 6 is a time chart showing the relationship between the pressure reduction command, the pressure increase command, the pressure increase elapsed time, and the master cylinder hydraulic pressure when the anti-skid control is executed. In the first embodiment, the instantaneous pressure increase control amount during the pressure increase control is calculated as the current average pressure increase control amount. In contrast, in the second embodiment, the current ON duty ratio is calculated as the instantaneous pressure increase control amount. The valve opening amount is large when the ON duty ratio is small, and the valve opening amount is small when the ON duty ratio is large. Even in the configuration of the second embodiment, the same effects as those of the first embodiment can be obtained.

It is a figure showing the whole brake control device composition of Example 1. 3 is a flowchart illustrating an estimated master cylinder hydraulic pressure correction process in the first embodiment. 3 is a flowchart illustrating a pressure increase elapsed time detection process according to the first embodiment. 3 is a time chart showing the relationship between a pressure reduction command, a pressure increase command, a pressure increase elapsed time, and a master cylinder hydraulic pressure when executing anti-skid control according to the first embodiment. 2 is a minimum differential pressure map according to the first embodiment. 6 is a time chart showing the relationship between a pressure reduction command, a pressure increase command, a pressure increase elapsed time, and a master cylinder hydraulic pressure when executing anti-skid control according to a second embodiment.

Explanation of symbols

2 Pressure increase control valve 3 Pressure reduction control valve 4 Reservoir 5 Pump 20 ABS control unit 21 Wheel speed sensor 20c Master cylinder hydraulic pressure estimation unit 20d Estimated master cylinder hydraulic pressure correction unit

Claims (3)

A master cylinder that generates hydraulic pressure by the driver's brake pedal operation,
A wheel cylinder that generates braking force on the wheels based on the supplied hydraulic pressure;
A hydraulic pressure control means that is provided between the master cylinder and the wheel cylinder, and controls the hydraulic pressure of the wheel cylinder to be increased or decreased according to the running state of the vehicle;
Master cylinder hydraulic pressure estimating means for estimating the hydraulic pressure of the master cylinder;
Pressure increase elapsed time detecting means for detecting an elapsed time of pressure increase control performed between the current pressure reduction control and the next pressure reduction control of the wheel cylinder;
An instantaneous pressure increase control amount calculating means for calculating an instantaneous pressure increase control amount in the elapsed time;
A minimum differential pressure estimating means for estimating a minimum differential pressure between an actual master cylinder hydraulic pressure and the estimated master cylinder hydraulic pressure based on the elapsed time and the instantaneous pressure increase control amount;
Correction means for correcting the estimated master cylinder hydraulic pressure based on the estimated minimum differential pressure;
A brake control device comprising: The brake control device according to claim 1, wherein
The fluid pressure control means has a pressure increase control valve that opens according to a valve opening amount command,
The brake control device, wherein the instantaneous pressure increase control amount calculating means calculates an instantaneous pressure increase control amount based on a valve opening amount command of the pressure increase control valve. The brake control device according to claim 1, wherein
The fluid pressure control means has a pressure increase control valve that opens according to a valve opening time command,
The brake control device, wherein the instantaneous pressure increase control amount calculating means calculates an instantaneous pressure increase control amount based on a valve opening time command of the pressure increase control valve.

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