JP4389296B2 - Vehicle motion control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle motion control device, and in particular, during vehicle motion including turning of the vehicle, the motion state of the vehicle is stabilized by applying a braking force to each wheel regardless of whether or not a brake pedal is operated. The present invention relates to a vehicle motion control apparatus.
[0002]
[Prior art]
Recently, as means for controlling vehicle motion characteristics, particularly turning characteristics, attention has been paid to means for directly controlling a turning moment by left-right difference control of braking force. For example, in Japanese Patent Application Laid-Open No. 9-164932, when it is determined that the vehicle is excessively oversteered while turning, an oversteer is suppressed by applying a braking force to each wheel of the vehicle so that an outward moment is generated with respect to the vehicle. A motion control device that performs understeer suppression control by applying a braking force to each wheel of the vehicle so as to generate an inward moment to the vehicle when it is determined that the vehicle is excessively understeered while turning is disclosed. ing. In the publication, in particular, it is proposed to perform correction control so that the braking force applied to each wheel increases or decreases in accordance with the estimated change rate of the road surface friction coefficient.
[0003]
JP-A-9-109852 relates to the conventional behavior control apparatus described in JP-A-6-24304, but the grounding load of the turning outer wheel increases due to load movement when the vehicle turns, but the grounding load of the turning inner ring increases. Therefore, if the braking force is controlled so that the slip rate of the turning outer wheel and the inner ring becomes the same by the drift-out suppression control, the reduction of the lateral force of the turning inner wheel becomes excessive, especially the drift-out state converges. Since it is likely that a spin state is likely to occur in the latter half of the drift-out suppression control that is heading, it is an object to prevent the braking force of the rear inner wheel from becoming excessive in the second half of the drift-out suppression control. And in this publication, in the vehicle behavior control device that suppresses the drift-out by controlling the braking force of the rear wheels, the braking force of the inner turning wheel is controlled by the outer turning wheel after the middle point during the drift-out suppression control. It has been proposed to make it smaller than the power. Specifically, after a predetermined time has elapsed from the time when the drift-out state quantity starts to decrease, the slip rate of the rear wheel on the inside of the turn is reduced.
[0004]
[Problems to be solved by the invention]
In the apparatus described in the above-mentioned Japanese Patent Laid-Open No. 9-109852, the road surface friction coefficient as described in the above-mentioned Japanese Patent Laid-Open No. 9-164932 is not adapted to the change. For this reason, when the road surface friction coefficient is low, if braking force is applied to both wheels behind the vehicle for the purpose of drift-out suppression control, the stability may be impaired. According to the device described in Japanese Patent Laid-Open No. 9-109852, after a predetermined time has elapsed from the time when the drift-out state quantity starts to decrease, control is performed so as to reduce the slip ratio of the rear inner wheel. It does not necessarily correspond to a change in the road surface friction coefficient.
[0005]
Therefore, the present invention provides a vehicle motion control device that applies a braking force to the rear wheel of the vehicle during understeer suppression control, and appropriately applies the braking force to the rear wheel even when the road surface friction coefficient changes. It is an object to enable understeer suppression control to be performed.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a braking force applying means for applying a braking force to at least the front wheel and the rear wheel of the vehicle according to the operation of the brake pedal, as described in claim 1; Vehicle movement state determination means for determining stability during vehicle movement including turning of the vehicle, and control of the braking force applying means based on a determination result of the vehicle movement state determination means; In a vehicle motion control device comprising a braking force control means for controlling to suppress understeer by applying a braking force to the rear wheel of the vehicle at least when it is determined that the vehicle is understeered, friction of the traveling road surface of the vehicle Friction coefficient estimation means for estimating coefficient Wheel speed detecting means for detecting the wheel speed of each wheel, slip rate calculating means for calculating the slip ratio of each wheel based on at least the detected wheel speed of the wheel speed detecting means, and the vehicle motion state determination Target slip ratio setting means for setting a target slip ratio for each wheel based on the determination result of the means The braking force control means includes Based on the deviation between the target slip ratio set by the target slip ratio setting means and the slip ratio calculated by the slip ratio calculation means, the braking force applied to each wheel is controlled, and the braking force control for the rear wheel of the vehicle On the occasion When the estimated friction coefficient of the friction coefficient estimating means is larger than a predetermined reference value, a braking force is applied to the rear wheels on both sides of the vehicle. And when the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the rear wheel outside the turn, based on a value obtained by reducing the target slip ratio in accordance with a decrease in the estimated friction coefficient. The braking force applied to the rear wheel outside the turn is controlled, and the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the rear wheel inside the turn set smaller than the reference value for the rear wheel outside the turn. In some cases, the braking force applied to the rear wheels inside the turn is controlled based on a value obtained by reducing the target slip ratio for the rear wheels inside the turn set by the target slip ratio setting means in accordance with a decrease in the estimated friction coefficient. As well as When the estimated friction coefficient of the friction coefficient estimating means is equal to or less than a predetermined reference value, the braking force is applied only to the rear wheel inside the vehicle turning.
[0008]
The braking force control means is a claim. 2 As described above, when the braking force control for the front wheels outside the turning of the vehicle is performed, if the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the front wheels, the target slip ratio setting means It is preferable that the braking force applied to the front wheels outside the turning of the vehicle is controlled based on a value obtained by reducing the target slip ratio for the front wheels in accordance with a decrease in the estimated friction coefficient.
[0009]
Note that the vehicle body speed of the vehicle can be estimated based on the detected wheel speed of the wheel speed detecting means, and the slip ratio can be calculated based on the estimated vehicle body speed and the detected wheel speed. The friction coefficient estimating means may be configured to detect a lateral acceleration and a longitudinal acceleration of the vehicle and calculate a friction coefficient based on the detection results.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a motion control apparatus according to the present invention. A braking force is applied to each wheel of the front wheels FR, FL and rear wheels RR, RL of the vehicle according to the operation of at least the brake pedal BP. Power supply means BF, vehicle movement state determination means VC for determining stability during vehicle movement including turning of the vehicle, and braking force application means BF are controlled based on the determination result of the vehicle movement state determination means VC. Braking force control means BR for controlling to suppress understeer by applying a braking force to the rear wheels RR and RL of the vehicle at least when it is determined that the vehicle is excessively understeered during turning, and a friction coefficient of the road surface of the vehicle Is provided with a friction coefficient estimating means FE. The braking force control means BR applies a braking force to the rear wheels RR and RL on both sides when the estimated friction coefficient of the friction coefficient estimating means FE is larger than a predetermined reference value, and the friction coefficient estimating means FE estimates When the friction coefficient is equal to or less than a predetermined reference value, the braking force is applied only to the rear wheel inside the turn.
[0011]
In this embodiment, the wheel speed detecting means WD for detecting the wheel speed of each wheel, the slip ratio calculating means AS for calculating the slip ratio of each wheel based on at least the detected wheel speed, and the vehicle motion state determining means VC A target slip ratio setting means DS for setting a target slip ratio for each wheel based on the determination result is provided. The braking force control means BR controls the braking force applied to each wheel based on the deviation between the target slip ratio set by the target slip ratio setting means DS and the slip ratio calculated by the slip ratio calculation means AS. In the braking force control for the wheels RR and RL, when the estimated friction coefficient of the friction coefficient estimating means FE is smaller than the reference value for the rear wheel outside the turn, the target slip ratio is reduced according to the decrease of the estimated friction coefficient. Based on this, the braking force applied to the rear wheel outside the turn is controlled, and the estimated friction coefficient of the friction coefficient estimating means FE is smaller than the reference value for the rear wheel inside the turn set smaller than the reference value for the rear wheel outside the turn. Is set to the rear wheel inside the turn based on the value obtained by reducing the target slip ratio for the rear wheel inside the turn set by the target slip ratio setting means DS according to the decrease in the estimated friction coefficient. It is configured to control the braking force.
[0012]
Further, the braking force control means BR performs the braking force control on the front wheels outside the turning, and when the estimated friction coefficient of the friction coefficient estimating means FE is smaller than the reference value for the front wheels, the braking force control means BR sets the outside of the turning set by the target slip ratio setting means DS. Based on a value obtained by reducing the target slip ratio for the front wheels in accordance with a decrease in the estimated friction coefficient, the braking force applied to the front wheels outside the turn is controlled.
[0013]
FIG. 2 shows an overall configuration of a vehicle including the motion control device. An engine EG is an internal combustion engine provided with a throttle control device TH and a fuel injection device FI. In the throttle control device TH, an accelerator pedal AP is operated. Accordingly, the main throttle opening of the main throttle valve MT is controlled. Further, according to the output of the electronic control unit ECU, the sub-throttle valve ST of the throttle control unit TH is driven to control the sub-throttle opening, and the fuel injection unit FI is driven to control the fuel injection amount. It is configured. The engine EG of the present embodiment is connected to the wheels RL and RR on the rear side of the vehicle via a transmission control device GS and a differential gear DF, and a so-called rear wheel drive system is configured. Regarding the braking system, wheel cylinders Wfl, Wfr, Wrl, Wrr are mounted on the wheels FL, FR, RL, RR, respectively, and a brake fluid pressure control device BC is connected to these wheel cylinders Wfl. The wheel FL indicates the left front wheel as viewed from the driver's seat, the wheel FR indicates the front right side, the wheel RL indicates the rear left side, and the wheel RR indicates the rear right wheel. In this embodiment, a so-called X pipe is configured. Has been.
[0014]
Wheel speed sensors WS1 to WS4 are disposed on the wheels FL, FR, RL, and RR, and these are connected to the electronic control unit ECU, and a pulse signal having a pulse number proportional to the rotational speed of each wheel, that is, the wheel speed. Is input to the electronic control unit ECU. Furthermore, a brake switch BS that is turned on when the brake pedal BP is depressed, a front wheel steering angle sensor SSf that detects the steering angle θf of the wheels FL and FR in front of the vehicle, a lateral acceleration sensor YG that detects the lateral acceleration of the vehicle, A yaw rate sensor YS that detects a change speed of the vehicle rotation angle (yaw angle) around the vertical axis passing through the vehicle center of gravity, that is, a yaw angular velocity (yaw rate), is connected to the electronic control unit ECU.
[0015]
As shown in FIG. 2, the electronic control unit ECU according to the present embodiment includes a microcomputer CMP including a processing unit CPU, a memory ROM, a RAM, an input port IPT, an output port OPT, and the like connected to each other via a bus. ing. Output signals from the wheel speed sensors WS1 to WS4, the brake switch BS, the front wheel steering angle sensor SSf, the yaw rate sensor YS, the lateral acceleration sensor YG, etc. are input to the processing unit CPU from the input port IPT via the amplifier circuit AMP. It is configured. Further, the control signal is output from the output port OPT to the throttle control device TH and the brake hydraulic pressure control device BC via the drive circuit ACT.
[0016]
In the microcomputer CMP, the memory ROM stores programs for various processes including the flowcharts shown in FIGS. 3 to 5, and the processing unit CPU executes the programs while an ignition switch (not shown) is closed. The memory RAM temporarily stores variable data necessary for executing the program. It should be noted that a plurality of microcomputers may be configured for each control such as throttle control or a combination of related controls as appropriate, and electrically connected to each other.
[0017]
In the present embodiment configured as described above, a series of processing such as braking steering control and anti-skid control is performed by the electronic control unit ECU, and when an ignition switch (not shown) is closed, FIG. Execution of the program corresponding to the flowchart of FIG. FIG. 3 shows the entire control operation of the vehicle. First, in step 101, the microcomputer CMP is initialized, and various calculation values are cleared. Next, at step 102, the detection signals of the wheel speed sensors WS1 to WS4 are read, the detection signal of the front wheel steering angle sensor SSf (steering angle θf), the detection yaw rate γa of the yaw rate sensor YS and the acceleration detected by the lateral acceleration sensor YG ( That is, the actual lateral acceleration and represented by Gya) are read.
[0018]
Next, the process proceeds to step 103, where the wheel speed Vw ** (** represents each wheel FR) of each wheel is calculated, and these are differentiated to obtain the wheel acceleration DVw ** of each wheel. Subsequently, at step 104, the maximum value of the wheel speed Vw ** of each wheel is calculated as the estimated vehicle body speed Vso at the vehicle center of gravity (Vso = MAX (Vw **)). Further, the estimated vehicle body speed Vso ** is obtained for each wheel based on the wheel speed Vw ** of each wheel, and normalization is performed as necessary to reduce errors based on the difference between the inner and outer wheels when turning the vehicle. . Further, the estimated vehicle body speed Vso is differentiated, and an estimated vehicle body acceleration (including an estimated vehicle body deceleration whose sign is opposite) DVso at the center of gravity of the vehicle is calculated.
[0019]
Next, in step 105, the actual slip ratio Sa * of each wheel is calculated based on the wheel speed Vw ** and the estimated vehicle speed Vso ** (or the normalized estimated vehicle speed) of each wheel obtained in steps 102 and 103 above. * Is determined as Sa ** = (Vso ** − Vw **) / Vso **. Next, in step 106, the road surface friction coefficient μ is approximately (DVso) based on the estimated vehicle body acceleration DVso at the center of gravity of the vehicle and the actual lateral acceleration Gya of the detection signal of the lateral acceleration sensor YG. ² + Gya ² ) ^1/2 As required. Or based on the peak value of the longitudinal acceleration and the peak value of the lateral acceleration within a predetermined time, it can also be calculated using an approximate expression similar to the above. Furthermore, as a means for detecting the road surface friction coefficient, various means such as a sensor for directly detecting the road surface friction coefficient can be used.
[0020]
Subsequently, at step 108, the vehicle body side slip angular velocity Dβ is calculated, and the vehicle body side slip angle β is calculated. The vehicle body side slip angle β represents the slip of the vehicle body with respect to the traveling direction of the vehicle as an angle, and can be calculated and estimated as follows. That is, the vehicle body side slip angular velocity Dβ is a differential value dβ / dt of the vehicle body side slip angle β, which can be obtained as Dβ = Gya / Vso−γa in step 107 and is integrated in step 108 to obtain β = ∫ (Gya The vehicle body side slip angle β can be obtained as / Vso−γa) dt.
[0021]
Then, the process proceeds to step 109 to enter the braking steering control mode, where a target slip ratio for braking steering control is set as will be described later, and for each wheel according to the motion state of the vehicle by hydraulic servo control at step 118 described later. The braking force is controlled. This braking steering control is superimposed on the control in all control modes described later. Thereafter, the routine proceeds to step 110, where it is determined whether or not the anti-skid control start condition is satisfied. If it is determined that the start condition is satisfied and the anti-skid control starts at the time of braking steering, the initial specific control is immediately terminated and step 111 is performed. Is set to a control mode for performing both braking steering control and anti-skid control.
[0022]
When it is determined in step 110 that the anti-skid control start condition is not satisfied, the routine proceeds to step 112, where it is determined whether or not the front / rear braking force distribution control start condition is satisfied. If it is determined that the control is to be started, the process proceeds to step 113 and the control mode is set to perform both the brake steering control and the front / rear braking force distribution control. If not satisfied, the process proceeds to step 114 and the traction control start condition is satisfied. It is determined whether or not. If it is determined that the traction control is started at the time of the brake steering control, the control mode is set in step 115 to perform both the brake steering control and the traction control. If no control is determined to be started at the time of the brake steering control, In Step 116, it is determined whether or not the brake steering control start condition is satisfied.
[0023]
If it is determined in step 116 that the braking steering control is started, the routine proceeds to step 117, where the control mode for performing only the braking steering control is set. Then, after hydraulic servo control is performed in step 118 based on these control modes, the process returns to step 102. In the front / rear braking force distribution control mode, the distribution of the braking force applied to the rear wheels to the braking force applied to the front wheels is controlled so that the stability of the vehicle is maintained during braking of the vehicle. If it is determined in step 116 that the brake steering control start condition is not satisfied, the solenoids of all the solenoid valves are turned off in step 119, and then the process returns to step 102. Note that, based on steps 111, 113, 115, and 117, the sub-throttle opening degree of the throttle control device TH is adjusted according to the motion state of the vehicle as necessary, the output of the engine EG is reduced, and the driving force is limited. .
[0024]
FIG. 4 shows the specific processing contents of the brake steering control in step 109 of FIG. 3, and the brake steering control includes oversteer suppression control and understeer suppression control, and oversteer suppression control and / or understeer for each wheel. A target slip ratio corresponding to the suppression control is set. First, in steps 201 and 202, oversteer suppression control and understeer suppression control start / end determination is performed.
[0025]
The start / end determination of the oversteer suppression control performed in step 201 is performed based on whether or not the control region is in the control region shown in FIG. 8 (the region outside the pair of parallel one-dot chain lines). That is, the oversteer suppression control is started when entering the control region according to the values of the vehicle body side slip angle β and the vehicle body side slip angular velocity Dβ at the time of determination, and the oversteer suppression control is ended when the control region is exited. Controlled as shown by the arrow curve. Further, the braking force of each wheel is controlled so that the control amount increases from the boundary indicated by the one-dot chain line in FIG. 8 toward the outside of the control region.
[0026]
On the other hand, the start / end determination of the understeer suppression control performed in step 202 is performed based on whether or not it is in the control region indicated by the oblique lines in FIG. That is, understeering suppression control is started when the control region is deviated from the ideal state indicated by the alternate long and short dash line in accordance with the change in the actual lateral acceleration Gya with respect to the target lateral acceleration Gyt at the time of determination. Is finished, and the control is performed as shown by the arrow curve in FIG.
[0027]
Subsequently, it is determined in step 203 whether or not oversteer suppression control is being controlled. If not in control, it is determined in step 204 whether or not understeer suppression control is being controlled. Return to the main routine. When it is determined in step 204 that the understeer suppression control is performed, the routine proceeds to step 205, where the target slip ratio of each wheel is set for understeer suppression control described later. If it is determined in step 203 that the oversteer suppression control is performed, the process proceeds to step 206, in which it is determined whether the understeer suppression control is performed. Set for. When it is determined in step 206 that understeer suppression control is being performed, oversteer suppression control and understeer suppression control are performed simultaneously, and in step 208, a target slip ratio for simultaneous control is set.
[0028]
The target slip ratio of each wheel when understeer suppression control is performed in step 205 is a value obtained by multiplying the standard target slip ratio by a correction coefficient. That is, the target slip ratio of the front wheels outside the turn is set to a value (Kfo · Stufo) obtained by multiplying the standard target slip ratio Stufo by the correction coefficient Kfo. The target slip ratio of the rear wheels outside the turn is set to a value (Kro · Sturo) obtained by multiplying the standard target slip ratio Sturo by the correction coefficient Kro, and the target slip ratio of the rear wheels inside the turn is equal to the standard target slip ratio Sturi. It is set to a value (Kri · Sturi) multiplied by the correction coefficient Kri. Regarding the sign of the slip ratio (S) shown here, “t” represents “target” and is compared with “a” representing “actual measurement” described later. “u” represents “understeer suppression control”, “r” represents “rear wheel”, “o” represents “outside”, and “i” represents “inside”. The correction coefficients Kfo, Kro, Kri will be described later with reference to FIGS.
[0029]
In contrast, the target slip ratio of each wheel when oversteer suppression control is performed in step 207 is set such that the front wheel outside the turn is set to Stefo and the rear wheel inside the turn is set to Steri. The slip ratio Steri is set to 0 in this embodiment. Here, “e” represents “oversteer suppression control”. In step 208, the target slip ratio of each wheel is set to Stefo for the front wheel outside the turn, but the rear wheel outside the turn is set to Kro / Sturo, and the rear wheel inside the turn is set to Kri / Sturi, respectively. Is done. That is, when oversteer suppression control and understeer suppression control are performed simultaneously, the front wheels on the outside of the turn are set in the same manner as the target slip ratio of oversteer suppression control, and the rear wheels are set in the same manner as the target slip ratio of understeer suppression control. Is set. In either case, the front wheels on the inner side of the turn (that is, the driven wheels in the rear-wheel drive vehicle) are not controlled for calculating the estimated vehicle body speed.
[0030]
The vehicle body side slip angle β and the vehicle body side slip angular velocity Dβ are used for setting the target slip ratio for oversteer suppression control in step 207, but for setting the standard target slip ratio in understeer suppression control, the target lateral acceleration Gyt and the actual slip ratio are set. The difference from the lateral acceleration Gya is used. For example, the target slip rate Stefo of the front wheel outside the turn used for oversteer suppression control is set as Stefo = K 1 · β + K 2 · Dβ, and the target slip rate Steri of the rear wheel inside the turn is set to “0”. Here, K1 and K2 are constants and are set to values for controlling the pressurizing direction (the direction in which the braking force is increased).
[0031]
On the other hand, the standard target slip ratio used for understeer suppression control is set as follows based on the deviation ΔGy between the target lateral acceleration Gyt and the actual lateral acceleration Gya. That is, the standard target slip ratio Stufo for the front wheel outside the turn is set to K3 · ΔGy, and the constant K3 is set to a value for controlling the pressurizing direction (or the depressurizing direction). Similarly, the standard target slip ratio Sturo for the rear wheel outside the turn is set to K4 · ΔGy, and the constant K4 is set to a value for controlling the pressurizing direction. The standard target slip ratio Sturi for the rear wheel inside the turn is set to K5 · ΔGy, and the constant K5 is set to a value for controlling the pressurizing direction.
[0032]
Here, the correction coefficients Kro, Kri, Kfo used for the understeer suppression control in steps 205 and 208 are set as shown in FIGS. First, as shown by the solid line in FIG. 6, the road surface friction coefficient μ estimated in step 106 is larger than the reference value Kμo (for example, 0.5) for the rear wheel outside the turn. In this case, the correction coefficient Kro is set to 1, and the standard target slip ratio Sturo is used as it is as the target slip ratio. When the road surface friction coefficient μ is smaller than the reference value Kμo for the rear wheel outside the turn, the correction coefficient Kro decreases as the road surface friction coefficient μ decreases, and becomes 0 at the rear wheel reference value Kμr (for example, 0.3). It is set as follows. That is, when the road surface friction coefficient μ is smaller than the rear wheel reference value Kμr, the braking force is not applied to the rear wheel outside the turn, and the braking force is applied only to the rear wheel inside the turn.
[0033]
On the other hand, the correction coefficient for the rear wheel inside the turn is corrected when the road surface friction coefficient μ is larger than the reference value Kμi (for example, 0.2) for the rear wheel inside the turn as shown by the broken line in FIG. The coefficient Kri is set to 1 and the standard target slip ratio Sturi is used as it is. When the road surface friction coefficient μ is smaller than the reference value Kμi for the rear wheel inside the turn, the correction coefficient Kri decreases as the road surface friction coefficient μ decreases, so that the road surface friction coefficient μ is 0 and the correction coefficient Kri is 0. Set to Thus, when the road surface friction coefficient μ is smaller than the rear wheel reference value Kμr, the target slip ratio for the rear wheel outside the turn at the time of understeer suppression control is set to 0, and the target slip ratio is applied only to the rear wheel inside the turn. The braking force control according to Kri · Sturi is performed, and the target slip ratio Kri · Sturi is set to a value that decreases as the road surface friction coefficient μ decreases.
[0034]
As shown in FIG. 7, the correction coefficient Kfo used for the understeer suppression control of the front wheel outside the turn is set to 1 when the road surface friction coefficient μ is larger than the front wheel reference value Kμf (for example, 0.3). Standard target slip ratios Stufo and Stufi are used as they are. When the road surface friction coefficient μ is smaller than the front wheel reference value Kμf, the correction coefficient Kfo decreases as the road surface friction coefficient μ decreases, and is, for example, the same value (for example, 0.2) as the rear wheel reference value Kμi inside the turn. It is set to be zero.
[0035]
FIG. 5 shows the processing contents of the hydraulic pressure servo control performed in step 118 of FIG. 3, and the wheel cylinder hydraulic pressure slip ratio servo control is performed for each wheel. First, the target slip ratio St ** set in the above-described step 205, 207 or 208 is read in step 301, and these are read as they are as the target slip ratio St ** of each wheel.
[0036]
Subsequently, in step 302, the slip ratio deviation ΔSt ** is calculated for each wheel, and in step 303, the vehicle body acceleration deviation ΔDVso ** is calculated. In step 302, the difference between the target slip ratio St ** and the actual slip ratio Sa ** of each wheel is calculated to determine the slip ratio deviation ΔSt ** (ΔSt ** = St ** − Sa **). In step 303, the difference between the estimated vehicle body acceleration DVso at the vehicle center of gravity position and the wheel acceleration DVw ** at the wheel to be controlled is calculated, and the vehicle body acceleration deviation ΔDVso ** is obtained. The actual slip rate Sa ** and the vehicle body acceleration deviation ΔDVso ** of each wheel at this time have different calculations depending on the control mode such as anti-skid control and traction control, but the description thereof will be omitted.
[0037]
Subsequently, the routine proceeds to step 304 where one parameter Y ** used for brake hydraulic pressure control in each control mode is calculated as Gs ** · ΔSt **. Here, Gs ** is a gain, which is set according to the vehicle body side slip angle β as shown by a solid line in FIG. In step 305, another parameter X ** used for brake fluid pressure control is calculated as Gd ** · ΔDVso **. The gain Gd ** at this time is a constant value as shown by a broken line in FIG. Thereafter, the process proceeds to step 306, and the hydraulic pressure mode is set for each wheel according to the control map shown in FIG. 11 based on the parameters X ** and Y **. In FIG. 11, the sudden decompression region, the pulse decompression region, the holding region, the pulse boosting region, and the sudden boosting region are set in advance. It is determined which region corresponds to this. In the non-control state, the hydraulic mode is not set (solenoid off).
[0038]
When the region determined in step 306 is the pressure increasing mode, the specific fluid pressure mode is further set in step 307. In addition, when the region determined in step 306 (current) is switched from pressure increase to pressure decrease or pressure decrease to pressure increase with respect to the previously determined region, the brake fluid pressure smoothly falls or rises. In step 308, the pressure increase / decrease compensation processing is performed. For example, when switching from the sudden pressure reducing mode to the pulse pressure increasing mode, the sudden pressure increasing control is performed, and the time is determined based on the duration of the immediately preceding sudden pressure reducing mode. In response to the fluid pressure mode, the specific fluid pressure mode, and the pressure increase / decrease compensation processing, the fluid pressure control solenoid is driven in step 309, the solenoid of the brake fluid pressure control device BC is driven, and the braking force of each wheel is driven. Is controlled. The configuration of the brake fluid pressure control device BC will be described later with reference to FIG.
[0039]
Then, at step 310, a driving process of the hydraulic pump driving motor in the brake hydraulic pressure control device BC is performed. In the above embodiment, the control is performed based on the slip ratio, but the control target is a target value corresponding to the braking force applied to each wheel such as the brake fluid pressure of the wheel cylinder of each wheel in addition to the slip ratio. Any value can be used.
[0040]
FIG. 12 shows a braking system including the brake fluid pressure control device BC. The master cylinder MC is boosted via the vacuum booster VB according to the operation of the brake pedal BP, and the brake fluid in the low pressure reservoir LRS is shown. Is increased so that the master cylinder hydraulic pressure is output to the two brake hydraulic pressure systems on the wheels FR and RL and the wheels FL and RR. The master cylinder MC is a tandem master cylinder having two pressure chambers. One pressure chamber is connected to a brake fluid pressure system on the wheels FR and RL side, and the other pressure chamber is a brake fluid on the wheels FL and RR sides. It is connected to the pressure system. A pressure sensor PS for detecting the output hydraulic pressure (master cylinder hydraulic pressure) is provided on the output side of the master cylinder MC.
[0041]
In the brake hydraulic system on the wheel FR, RL side of the present embodiment, one pressure chamber is connected to the wheel cylinders Wfr, Wrl via the main hydraulic path MF and its branched hydraulic paths MFr, MFl, respectively. . The main hydraulic pressure path MF is provided with a normally open first on-off valve SC1 (which functions as a so-called cut-off valve, hereinafter simply referred to as on-off valve SC1). One pressure chamber is connected between check valves CV5 and CV6 described later via an auxiliary hydraulic pressure path MFc. A normally closed second on-off valve SI1 (hereinafter simply referred to as on-off valve SI1) is interposed in the auxiliary hydraulic pressure path MFc. Each of these on-off valves is a 2-port 2-position electromagnetic on-off valve. The branch hydraulic pressure paths MFr and MFl are respectively provided with normally open type two-port two-position electromagnetic on-off valves PC1 and PC2 (hereinafter simply referred to as on-off valves PC1 and PC2). Further, check valves CV1 and CV2 are interposed in parallel with these.
[0042]
The check valves CV1, CV2 allow the flow of brake fluid in the direction of the master cylinder MC and restrict the flow of brake fluid in the direction of the wheel cylinders Wfr, Wrl. The check valves CV1, CV2 and the first check valves CV1, CV2 The brake fluid in the wheel cylinders Wfr, Wrl is returned to the master cylinder MC and thus to the low-pressure reservoir LRS via the opening / closing valve SC1 in the position (shown). Thus, when the brake pedal BP is released, the hydraulic pressure in the wheel cylinders Wfr, Wrl can quickly follow the decrease in hydraulic pressure on the master cylinder MC side. Also, normally-closed two-port two-position electromagnetic on-off valves PC5 and PC6 (hereinafter simply referred to as on-off valves PC5 and PC6) are connected to the discharge-side branch hydraulic pressure paths RFr and RFl connected to the wheel cylinders Wfr and Wrl, respectively. Is interposed, and the discharge hydraulic pressure channel RF where the branch hydraulic pressure channels RFr and RFl merge is connected to the reservoir RS1.
[0043]
In the brake hydraulic system on the wheel FR, RL side, the on-off valves PC1, PC2, PC5, PC6 constitute a modulator according to the present invention. A hydraulic pump HP1 is interposed in a hydraulic pressure path MFp communicating with the branch hydraulic pressure paths MFr and MFl upstream of the on-off valves PC1 and PC2, and check valves CV5 and CV6 are connected to the suction side thereof. The reservoir RS1 is connected. The discharge side of the hydraulic pump HP1 is connected to the on-off valves PC1 and PC2 via the check valve CV7 and the damper DP1, respectively. The hydraulic pump HP1 is driven by one electric motor M together with the hydraulic pump HP2, and is configured to introduce brake fluid from the suction side, increase the pressure to a predetermined pressure, and output from the discharge side. The reservoir RS1 is provided independently of the low pressure reservoir LRS of the master cylinder MC, and can also be referred to as an accumulator. The reservoir RS1 includes a piston and a spring and is configured to store brake fluid having a capacity necessary for various controls. Has been.
[0044]
The master cylinder MC is connected in communication between a check valve CV5 and a check valve CV6 on the suction side of the hydraulic pump HP1 via a hydraulic path MFc. The check valve CV5 blocks the flow of brake fluid to the reservoir RS1 and allows a reverse flow. The check valves CV6 and CV7 regulate the flow of brake fluid discharged via the hydraulic pump HP1 in a certain direction, and are normally configured integrally with the hydraulic pump HP1. Thus, in the normal closed position shown in FIG. 12, the on-off valve SI1 has the communication between the master cylinder MC and the suction side of the hydraulic pump HP1 cut off, and the master cylinder MC and the suction side of the hydraulic pump HP1 at the open position. It is switched to communicate.
[0045]
Further, in parallel with the on-off valve SC1, the flow of brake fluid from the master cylinder MC toward the on-off valves PC1 and PC2 is restricted, and the brake fluid pressure on the on-off valves PC1 and PC2 side is less than the brake fluid pressure on the master cylinder MC side. Relief valve RV1 that allows the flow of brake fluid in the direction of the master cylinder MC when the pressure difference exceeds a predetermined pressure difference, and the flow of brake fluid in the directions of the wheel cylinders Wfr and Wrl are allowed and the flow in the reverse direction is prohibited A check valve AV1 is interposed. The relief valve RV1 allows the brake fluid to be supplied to the low pressure reservoir LRS via the master cylinder MC when the pressurized brake fluid discharged from the hydraulic pump HP1 becomes greater than a predetermined differential pressure from the output hydraulic pressure of the master cylinder MC. Thus, the discharge brake fluid of the hydraulic pump HP1 is regulated to a predetermined pressure. Further, a damper DP1 is disposed on the discharge side of the hydraulic pump HP1, and a proportioning valve PV1 is interposed in a hydraulic pressure path leading to the wheel cylinder Wrl on the rear wheel side.
[0046]
Similarly, in the brake hydraulic system on the side of the wheels FL and RR, the reservoir RS2, the damper DP2, the proportioning valve PV2, the normally open type 2 port 2 position electromagnetic on-off valve SC2, the normally closed type 2 port 2 position electromagnetic On-off valves SI2, PC7, PC8, normally open type 2-port 2-position electromagnetic on-off valves PC3, PC4, check valves CV3, CV4, CV8 to CV10, relief valve RV2 and check valve AV2 are arranged. The hydraulic pump HP2 is driven by the electric motor M together with the hydraulic pump HP1, and after the electric motor M is started, both the hydraulic pumps HP1 and HP2 are continuously driven.
[0047]
The on-off valves SC1, SC2, SI1, SI2 and on-off valves PC1 to PC8 are driven and controlled by an electronic control unit ECU, and various controls including the above-described braking steering control are performed. For example, in order to prevent excessive oversteering, for example, it is necessary to generate a moment to counteract this. In the brake hydraulic system on the wheels FR and RL side, the on-off valve SC1 is set to the closed position during braking steering control. At the same time, the on-off valve SI1 is switched to the open position, the electric motor M is driven, and the brake fluid is discharged from the hydraulic pump HP1. The on-off valves PC1, PC2, PC5 and PC6 are appropriately controlled to be opened and closed by the electronic control unit ECU, and the hydraulic pressure of the wheel cylinders Wfr, Wrl is increased (slowly increased), reduced or held, and the wheels FL, RR side The braking force distribution between the front and rear wheels is controlled so as to maintain the course tracing performance of the vehicle.
[0048]
【The invention's effect】
Since this invention is comprised as mentioned above, there exist the following effects. That is, in the vehicle motion control apparatus of the present invention, when the estimated friction coefficient of the friction coefficient estimating means is larger than a predetermined reference value, a braking force is applied to the rear wheels on both sides. The braking force applied to the rear wheel outside the turn is controlled based on the value obtained by reducing the target slip ratio in accordance with the decrease in the estimated friction coefficient when the reference value for the rear wheel outside the turn is smaller. However, when the value is smaller than the reference value for the rear wheel on the inside of the turn, the control applied to the rear wheel on the inside of the turn is based on a value obtained by reducing the target slip ratio for the rear wheel on the turn according to the decrease in the estimated friction coefficient. Configured to control power, When the estimated friction coefficient is below the reference value, it is configured to apply braking force only to the rear wheel on the inside of the turn, so even when the road surface friction coefficient changes during understeer suppression control, it is appropriate for the rear wheel. A braking force can be applied, smooth understeer suppression control can be performed, and a stable vehicle motion state can be maintained.
[0050]
Further claims 2 As described above, understeer suppression control can be performed more smoothly by adopting a configuration that also controls the front wheels.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a motion control device of the present invention.
FIG. 2 is an overall configuration diagram of an embodiment of a motion control device of the present invention.
FIG. 3 is a flowchart showing an overall vehicle braking control according to an embodiment of the present invention.
FIG. 4 is a flowchart showing a target slip ratio setting process for brake steering control according to an embodiment of the present invention.
FIG. 5 is a flowchart showing a hydraulic servo control process in an embodiment of the present invention.
FIG. 6 is a graph for setting a correction coefficient for a slip ratio for a rear wheel in an embodiment of the present invention.
FIG. 7 is a graph for setting a correction factor for a slip ratio for a front wheel in an embodiment of the present invention.
FIG. 8 is a graph showing a start / end determination region of oversteer suppression control according to an embodiment of the present invention.
FIG. 9 is a graph showing a start / end determination region of understeer suppression control according to an embodiment of the present invention.
FIG. 10 is a graph showing a gain for parameter calculation used for hydraulic pressure control in an embodiment of the present invention.
FIG. 11 is a graph showing a control map provided for an embodiment of the present invention.
FIG. 12 is a block diagram showing a hydraulic system of the vehicle motion control apparatus of the present invention.
[Explanation of symbols]
BP Brake pedal, MC master cylinder
M Electric motor, HP1, HP2 Hydraulic pump
RS1, RS2 reservoir
Wfr, Wfl, Wrr, Wrl Wheel cylinder
WS1 to WS4 Wheel speed sensor
FR, FL, RR, RL wheels
SC1, SC2, SI1, SI2 On-off valve
PC1 to PC8 open / close valve
EG engine, ECU Electronic control unit

Claims (2)

Braking force applying means for applying a braking force to at least front and rear wheels of the vehicle according to an operation of a brake pedal; and vehicle motion state determining means for determining stability during vehicle movement including turning of the vehicle. And controlling the braking force applying means based on the determination result of the vehicle movement state determining means, and applying a braking force to the rear wheels of the vehicle at least when the vehicle is determined to be excessive understeer during turning. In a vehicle motion control device comprising a braking force control means for controlling to suppress understeer, a friction coefficient estimating means for estimating a friction coefficient of a running road surface of the vehicle, and a wheel for detecting a wheel speed of each wheel Speed detection means; at least slip ratio calculation means for calculating the slip ratio of each wheel based on the detected wheel speed of the wheel speed detection means; and the vehicle motion state And a target slip ratio setting means for setting a target slip ratio relative to said each wheel based on the determination result of the constant unit, the braking force control means, the slip ratio and the target slip ratio, wherein the target slip ratio setting means has set Based on the slip ratio deviation calculated by the calculation means, the braking force applied to each wheel is controlled, and when the braking force control for the rear wheel of the vehicle is performed, the estimated friction coefficient of the friction coefficient estimation means is a predetermined reference value. When it is larger, the braking force is applied to the rear wheels on both sides of the vehicle, and when the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the rear wheel outside the turn, the estimated friction The braking force applied to the rear wheel outside the turn is controlled based on a value obtained by reducing the target slip ratio in accordance with a decrease in the coefficient, and the estimated friction coefficient of the friction coefficient estimating means is When the target value for the rear wheel inside the turn set by the target slip ratio setting means is less than the reference value for the rear wheel inside the turn set smaller than the reference value for the rear wheel outside the turn, the estimated friction Based on the value reduced according to the reduction of the coefficient, the braking force applied to the rear wheel inside the turn is controlled, and when the estimated friction coefficient of the friction coefficient estimating means is below a predetermined reference value A vehicle motion control device, characterized in that a braking force is applied only to a rear wheel inside the turning of the vehicle. The braking force control means, when controlling the braking force for the front wheels outside the turning of the vehicle, when the estimated friction coefficient of the friction coefficient estimating means is smaller than the reference value for the front wheels, the turning outside set by the target slip ratio setting means claims based target slip ratio to a value decreased with a decrease of the estimated friction coefficient for the front wheels, characterized by being configured to control the braking force applied to the front turning outside the vehicle 1 The vehicle motion control apparatus described.

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