JP4464609B2 - Braking system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a braking system.
[0002]
[Prior art]
An anti-skid (anti-lock) brake system (ABS) is a braking system that prevents tire lock during sudden braking and enables steering operation during sudden braking, and is known as an active safety device. It is known that the ABS pressure reduction time and pressure increase time during braking are measured, and the pressure increase timing is delayed by comparing the difference between the pressure decrease time integrated value and the pressure increase time integrated value with a predetermined value. (See Patent Document 1 below).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 7-232631
[Problems to be solved by the invention]
However, in the control system, if the friction coefficient between the wheel and the road surface is different on the left and right (during crossover travel), there is a difference in the integrated value of the pressure increase time and the pressure reduction time, so it is determined that crossover travel is in progress. However, even when moving from a crossing road to a uniform road (coefficient of friction between wheels and road surface is equal), it is determined that the road surface state is traveling over the road.
[0005]
This invention is made | formed in view of such a subject, and it aims at providing the control system which can discriminate | determine a road surface state rapidly, even when it transfers to a uniform road from a straddle road.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, a control system according to the present invention includes a braking device that applies a braking force to a wheel by driving a wheel cylinder by hydraulic pressure of brake fluid, and hydraulic pressure control means that controls the hydraulic pressure. The hydraulic pressure control means is an ABS control that increases the hydraulic pressure and subsequently reduces the hydraulic pressure so that the actual slip rate of the wheel does not exceed a reference value, and increases the pressure after the pressure reduction to give a braking force to the wheel. When the first mode is executed , each wheel in the first mode, which is an ABS control, adds the pressure increase time of the hydraulic pressure of one wheel where pressure reduction is started as positive and subtracts the pressure reduction time as negative. It said fluid pressure is reset at which in each control cycle until the start of increase and then decreased from the start of the decrease in liquid pressure control means, in the execution of one cycle of the control cycle, one of the car Wherein when the reset of the liquid accumulated value of pressure increase and decrease times of pressure in the wheel cylinders, and calculates the difference immediately before the reset of the integrated value of the pressure increase and decrease times of the wheel cylinder hydraulic pressure of the left and right wheels, determines that the difference between The threshold value is compared, and it is always permitted to perform a determination step of determining whether the friction coefficient of the road surface in contact with the left and right wheels is different according to the comparison result, the second cycle or later of the control cycle or the third cycle or later In execution, the determination step is performed only at an edge timing at which at least one control cycle of the left and right wheels counts up.
[0007]
When one of the integrated values is reset, integrated values in a plurality of control cycles are not accumulated, so that erroneous determination can be suppressed and the road surface condition can be quickly determined even when a transition is made from a crossing road to a uniform road.
[0008]
Also, the reset timing can be set at the start of pressure reduction or pressure increase of one wheel. At the start of pressure reduction or at the start of pressure increase, there is one in one control cycle. Therefore, if reset is performed at such timing, the reset can be performed for each control cycle.
[0009]
The first mode is an ABS control mode. In this case, the above-described pressure increase and pressure reduction are performed so that the rotation of the wheel is not locked.
[0010]
Further, the hydraulic pressure control means determines whether the right and left wheels are in accordance with the difference immediately before resetting the integrated value of the hydraulic pressure increase / decrease time of the right and left wheel cylinders when the hydraulic pressure of the wheel cylinder of one wheel is reset . It is characterized by determining whether the friction coefficient of the road surface which touches differs.
[0011]
That is, if the road surface friction coefficient is different, the integrated value of the hydraulic pressure increasing / decreasing time of the wheel cylinders of the left and right wheels is different, so it can be determined whether or not the road surface friction coefficient is different according to these differences.
[0012]
The hydraulic pressure control means increases or decreases the hydraulic pressure of the wheel cylinders of the left and right wheels at the time of resetting the hydraulic pressure of the wheel cylinder of one wheel and before starting to reduce the hydraulic pressure of the wheel cylinder of the other wheel. It is characterized in that it is determined whether or not the friction coefficient of the road surface in contact with the left and right wheels is different according to the difference immediately before the resetting of the integrated time value.
[0013]
Determine whether the road friction coefficient differs more accurately by determining the road friction coefficient before one of the hydraulic pressures is reset instead of when both hydraulic pressures are reset can do.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of a braking system according to an embodiment. The same code | symbol is used for the same element and the overlapping description is abbreviate | omitted. The braking system of the present embodiment is a hydraulic brake device and is controlled by an electronic control unit (hereinafter referred to as ECU) 10.
[0015]
This vehicle includes four wheels (left front wheel W _FL , right front wheel W _FR , left rear wheel W _RL , right rear wheel W _RR ) provided on the vehicle body BDY. Wheel speed of each wheel _{W FL, W FR, W RL} , W RR are the wheel speed sensors _{R FL, R FR, R RL} , is detected by the R _RR, are input to the ECU 10. ECU10 is the estimated vehicle body speed V _B based on these wheel speeds, it calculates the percentage of the vehicle speed difference between the wheel speeds as the actual slip ratio S _R. It is assumed that the estimated vehicle body speed V _B is the highest value among the wheel speeds of the four wheels.
[0016]
This vehicle includes a braking device (brake pad or the like: not shown) that applies a braking force to each wheel W _FL , W _FR , W _RL , W _RR , and each wheel W _FL , W _FR , W _RL , The braking device for each W _RR is driven by the hydraulic pressure of the wheel cylinders H _FL , H _FR , H _RL , H _RR , and the braking force applied to each wheel W _FL , W _FR , W _RL , W _RR according to the hydraulic pressure. Can be adjusted.
[0017]
The hydraulic pressure control device 11 includes a master cylinder and various solenoid valves and is controlled by the control of the ECU 10 to adjust the hydraulic pressure in the wheel cylinders H _FL , H _FR , H _RL , H _RR . When the brake pedal BP is stepped on, a pedal force switch (not shown) is turned ON, and the master cylinder pressure in the hydraulic pressure control device 11 increases, and the wheel cylinders H _FL , H _FR , H _RL follow the hydraulic path of the brake fluid. , The hydraulic pressure in _HRR increases. The hydraulic pressure control device 11 can hold and reduce the hydraulic pressure in addition to increasing the hydraulic pressure in each of the wheel cylinders H _FL , H _FR , H _RL and H _RR . These controls are based on commands from the ECU 10.
[0018]
If the actual slip rate S _R exceeds the reference value, ABS control mode is started. The ABS control mode is a mode in which the actual slip ratio is maintained in a state where the maximum friction coefficient can be obtained by adjusting the pressure increase, hold, and pressure reduction described above. In this case, the above-described pressure increase and pressure reduction are performed so that the rotation of the wheel is not locked.
[0019]
FIG. 2 is a graph showing the relationship between the slip ratio (%) of the wheel and the force (frictional force) acting between the wheel (tire) and the road surface. If the integrated value of the hydraulic pressure increasing / decreasing time is increased, the brake is applied strongly, so that the slip ratio increases, and if the integrated value of the hydraulic pressure increasing / decreasing time is decreased, the slip ratio decreases.
[0020]
The braking force (longitudinal force) generated in the longitudinal direction (traveling direction) of the wheel becomes maximum (near the maximum value) when the slip ratio is _SLL or more and _SUL or less. The lower limit slip rate S _LL of the range is about 10%, the upper limit slip rate S _UL is about 20%. A region (μ peak region) between these slip rates S _LL and S _UL is a target region of the slip rate at which the maximum braking force is obtained in the ABS control, and a strong slip rate deviating from the range is generated. First, the braking force in the vertical direction can be increased by reducing the hydraulic pressure so that the slip ratio is reduced.
[0021]
The lateral braking force (lateral force) of the wheel is maximum when the slip ratio is 0%, decreases monotonously with increasing slip ratio, and becomes almost zero when the slip ratio is 100%. In order to secure the braking force in both the vertical and horizontal directions and to achieve both vehicle body controllability and braking force characteristics, the above-described μ peak region is set to a slip rate of about 10 to 20%.
[0022]
FIG. 3 is a graph showing the time dependence of the vehicle body speed V _B , the wheel speed V _H and the hydraulic pressure in the wheel cylinder. Since the slip ratio is a ratio of the difference ΔVe between the wheel speed V _H and the vehicle body speed V _B to the vehicle body speed, the above-described difference ΔVe may be controlled in order to make the actual slip ratio coincide with the target slip ratio.
[0023]
When the brake pedal BP is depressed, the hydraulic pressure of the wheel cylinder increases, and the vehicle body speed V _B decreases with the wheel speed V _H. If these deviations ΔVe exceeds the reference value, so that the rotation of the wheels will not lock, ABS control mode is started, increasing the wheel speed V _H is by hydraulic pressure decreases, the wheel speed V _H When the vehicle body speed V _B matches, the hydraulic pressure increases again and the wheel speed V _H decreases. Since the deviation ΔVe is an actual slip ratio, the hydraulic pressure control device 11 adjusts the integrated value of the hydraulic pressure increasing / decreasing time so that this becomes the target slip ratio in the μ peak region. The hydraulic pressure control device 11 is controlled by an ECU (hydraulic pressure control means) 10.
[0024]
In addition, the accumulated value of the “increase / decrease time” of the hydraulic pressure is added to the previous accumulated value with the time being “positive” in the case of the pressure increasing time, and is added to the previous accumulated value in the case of the pressure reducing time. Subtract from the value.
[0025]
The braking system described above includes a braking device that applies a braking force to the wheels W _FL , W _FR , W _RL , W _RR by driving the wheel cylinders H _FL , H _FR , H _RL , H _RR by the hydraulic pressure of the brake fluid. And an ECU 10 for controlling the fluid pressure. The ECU 10 increases the hydraulic pressure continuously so that the actual slip ratios of the wheels W _FL , W _FR , W _RL , W _RR do not exceed the reference value, and then reduces the hydraulic pressure, and then increases the pressure after the pressure reduction to give a braking force to the wheels. Execute.
[0026]
These hydraulic pressures can also be obtained by directly detecting the hydraulic pressures of H _FL , H _FR , H _RL , and H _RR , but the master cylinder hydraulic pressure is measured and the time for increasing, holding, and reducing pressure is measured. Can be obtained indirectly by measuring. In these cases, the hydraulic pressure is measured by the ECU 10.
[0027]
Here, the case where the friction coefficient of the road surface where the left and right wheels W _FL and W _FR are in contact with each other will be described.
[0028]
When the left and right wheels W _FL , W _FR are braked in the ABS control mode, if one of the road surface friction coefficients becomes low, this wheel is likely to slip, so that the pressure is reduced earlier than the other wheels. . That is, the integrated value of the hydraulic pressure increasing time of the wheel cylinder corresponding to this wheel is small. Since the road surface friction coefficient may be slightly different on the left and right, the ECU 10 normally determines the difference between the integrated values of the hydraulic pressure increase / decrease times of the wheel cylinders H _FL and H _FR of the left and right wheels W _FL and W _FR. When the threshold value is exceeded, the ECU 10 determines that the road surface is a straddling road.
[0029]
The ABS control mode is entered, and the hydraulic pressure at each wheel increases after starting to decrease, and then the period is one control cycle until the decrease starts. The ECU 10 resets the integrated value of the hydraulic pressure increase / decrease time of one of the wheel cylinders H _FL , H _FR of the left and right wheels W _FL , W _FR every ABS mode control cycle.
[0030]
If the integrated value of the hydraulic pressures of the left and right wheel cylinders H _FL and H _FR is reset, the integrated values in a plurality of control cycles are not accumulated. The road surface condition can be quickly determined. The reset timing can be set at the start of pressure reduction or pressure increase of one of the left and right wheels. At the start of pressure reduction or at the start of pressure increase, there is one in one control cycle. Therefore, if reset is performed at such timing, the reset can be performed for each control cycle. The braking force control described above can also be applied to the left and right rear wheels W _RL and W _RR .
[0031]
FIG. 4 is a functional block diagram inside the ECU 10.
[0032]
ECU10 is the right front wheel W _{FR-increasing} decompression time of the hydraulic pressure in the wheel cylinder H _FR right front wheel increases or decreases time calculation means 10a for calculating the integrated value of the left front wheel W _FL wheel cylinders H _FL increasing decompression time of hydraulic pressure of A left front wheel increase / decrease time calculation means 10b for calculating the integrated value, a difference calculation means 10c for calculating these differences, and a stride determination means 10d for determining whether or not the difference exceeds a determination threshold.
[0033]
Further, the ECU 10 includes a control cycle determination unit 10e that determines a control cycle after the ABS control mode is started, and a determination timing determination unit 10f that determines a timing for performing the determination by the stride determination unit 10d for each control cycle. The control cycle discriminating means 10e discriminates from the start of the current decompression to the next decompression start as one control cycle.
[0034]
Within one control cycle, the right front wheel increase / decrease time calculating means 10a calculates the integrated value of the hydraulic pressure increase / decrease time in the right front wheel wheel cylinder _HFR , and the left front wheel increase / decrease time calculating means 10b is the left front wheel wheel cylinder. calculating an integrated value of pressure increase and decrease times of hydraulic pressure in H _FL. The difference between these integrated values output from the difference calculation means 10c is input to the stride determination means 10d at the determination timing calculated by the determination timing determination means 10f, that is, at the start of pressure reduction or at the start of pressure increase. When this difference exceeds the determination threshold value, the crossing determination unit 10d determines that the road surface friction coefficient in contact with the left and right wheels is different, that is, “crossing road traveling”.
[0035]
The increase / decrease time calculating means 10a, 10b sets each time as "+1" for the time of increasing pressure for each wheel, "-1" for the time of decreasing pressure, and "0" for the holding time. Accumulated. The integrated value before starting the ABS control mode is zero. The integrated value is set to 0 at the edge where each control cycle is counted up.
[0036]
Further, the determination timing determination unit 10f can always permit the determination of crossing if any wheel is within one control cycle after the ABS control mode is started corresponding to the left and right wheels. The discriminating timing determining means 10f prohibits the straddling discrimination by the straddling road discriminating means 10d when either of the left and right wheels proceeds in two cycles. The straddle determination by the straddle path determination means 10d is performed only at the edge timing at which the cycle counts up.
[0037]
FIG. 5 is a flowchart showing a control procedure by the ECU 10. FIG. 6 shows (a) the hydraulic pressure in the wheel cylinder for the right front wheel, (b) the hydraulic pressure in the wheel cylinder for the left front wheel, (c) the integrated value of the increasing / decreasing time of the hydraulic pressure in the wheel cylinder for the right front wheel, (d) It is the integrated value of the pressure increasing / decreasing time of the hydraulic pressure in the wheel cylinder of the left front wheel, (e) is a timing chart of the difference between these integrated values.
[0038]
First, it is determined whether or not each wheel is in the ABS control mode (S1). In the ABS control mode, increase / decrease time integration (pressure increase time-pressure decrease time) is performed by the above increase / decrease time calculation means 10a, 10b (S2). In FIG. 6, the ABS control mode is started from time t ₀ .
[0039]
Next, it is determined whether it is the pressure reduction start edge of the right front wheel hydraulic pressure (a) or the left front wheel hydraulic pressure (b) (S3). If it is the pressure reduction start edge, +1 is set to a control cycle counter (not shown). The accumulated values (c) and (d) of the pressure increase / decrease time corresponding to each wheel are cleared (set to zero: S4), and step S5 is executed.
[0040]
In FIG. 6, for the right front wheel, the accumulated value is cleared at time t ₁₁ , t ₁₂ , t ₁₃ , and time t ₀ to time t ₁₁ , time t ₁₁ to time t ₁₂ , time t ₁₂ to time t ₁₃ is set to the first, second and third control cycle _{T 11, T 12, T 13} . Further, with respect to the left front wheel, the accumulated value is cleared at times t ₂₁ , t ₂₂ , and t ₂₃ , and the first and second control cycles are performed at times t ₀ to t ₂₁ and times t ₂₁ to t ₂₂ . T ₂₁ and T ₂₂ can also be set.
[0041]
If the yaw control mode (the mode in which the braking force is controlled so that the actual yaw of the vehicle becomes the target yaw) is entered, the target yaw of the mode is calculated from the actual yaw, and the pressure reduction start edge If not (S3), it is determined whether or not the target yaw is an edge indicating the start of the yaw control mode (S10). Even in the case of the start edge of the yaw control mode, step S5 is executed. That is, in the yaw control mode, one control cycle is defined from the start of the mode to the next start of decompression.
[0042]
In step S5, ΔT (difference in hydraulic pressure increase / decrease time corresponding to the left and right wheels) is calculated by the difference calculation means 10c, and whether or not the braking force control for both the left and right wheels is within one control cycle. (S6) and if it is within the control cycle, as shown in FIG. 6 (e), whether or not ΔT is out of the range of the determination threshold ± TH (| ΔT | ≧ TH) (S7). When | ΔT | is equal to or greater than the determination threshold TH, it is determined that the road is a crossing road (determination set: S8), and otherwise, it is determined that the road is a uniform road (determination reset: S9).
[0043]
That is, whether the friction coefficient of the road surface in contact with the left and right wheels differs according to the difference in the accumulated value of the hydraulic pressure increase / decrease time of the wheel cylinders on the left and right wheels when the hydraulic pressure on the wheel cylinders on the left and right wheels is reset It is determined whether or not. That is, if the road surface friction coefficient is different, the integrated value of the hydraulic pressure increase / decrease time of the wheel cylinders of the left and right wheels is different, so it can be determined whether or not the road surface friction coefficient is different according to these differences.
[0044]
In this example, at the end of the first control cycle of the right front wheel, in other words, at the start of the second control cycle (time t ₁₁ ), it is determined whether ΔT is out of the determination threshold value ± TH. Yes. The ECU 10 resets the hydraulic pressure of the wheel cylinder of the right front wheel, and increases or decreases the hydraulic pressure of the wheel cylinder of the left and right wheels before the start of pressure reduction of the wheel cylinder of the left front wheel (time t ₂₁ ). It is determined whether or not the friction coefficient of the road surface in contact with the left and right wheels is different according to the difference ΔT of the integrated values. It is determined whether or not the road surface friction coefficient is different more accurately by determining the road surface friction coefficient before one of the two hydraulic pressures is reset, that is, before starting the pressure reduction of the left front wheel. be able to.
[0045]
Whether or not the determination timing is a decompression start edge (S3) is determined by the determination timing determination means 10f.
[0046]
In step S6, when the braking force control of both the left and right wheels is not within the first control cycle, there are three or more control cycles counted by the control cycle counter (+3) and thereafter (S11), and when at least one of the left and right wheels is controlled cycle count up edge (time _{t 22, t 13) (S12} ), to execute the split-friction road determination step S7, returned to start if not all cases To continue the calculation. In step S11, the control cycle may be 2 instead of 3. This is because the control state is stable when the control cycle is 2 or 3 or more.
[0047]
Conventionally, since the difference ΔT of the integrated values is not reset for each control cycle, even if the integrated values are accumulated and the loaded vehicle enters a uniform road as shown by the dotted line in FIG. However, since there is no such accumulation in the control system according to the above-described embodiment, it is possible to quickly determine the road surface state even when transitioning from a straddle road to a uniform road.
[0048]
In step S1, if each wheel is not in the ABS control mode, the control counter and the accumulated time increase / decrease value are cleared (S13) to prepare for the next control.
[0049]
Note that the above-described integrated value resetting method can be employed for traction control in addition to the ABS control mode.
[0050]
【The invention's effect】
As described above, according to the control system of the present invention, it is possible to quickly determine the road surface state even when a transition from a crossing road to a uniform road.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a braking system according to an embodiment.
FIG. 2 is a graph showing the relationship between the slip ratio (%) of a wheel and the force (frictional force) acting between the wheel (tire) and the road surface.
FIG. 3 is a graph showing time dependency of vehicle body speed V _B , wheel speed V _H and hydraulic pressure in the wheel cylinder.
4 is a functional block diagram inside the ECU 10. FIG.
FIG. 5 is a flowchart showing a control procedure by the ECU 10;
6A is an integrated value of the hydraulic pressure in the wheel cylinder of the right front wheel, FIG. 6B is an integrated value of the pressure increase / decrease time of the hydraulic pressure in the wheel cylinder of the left front wheel, and FIG. It is the integrated value of the pressure increasing / decreasing time of the hydraulic pressure in the wheel cylinder of the left front wheel, (e) is a timing chart of the difference between these integrated values.
[Explanation of symbols]
10a, 10b ... increase / decrease time calculation means, 10c ... difference calculation means, 10d ... crossing road discrimination means, 10e ... control cycle discrimination means, 10f ... discrimination timing determination means, 11 ... hydraulic pressure control device BDY ... vehicle body, BP ... brake pedal , H _FL ... wheel cylinder for left front wheel, H _FR ... wheel cylinder for right front wheel, R _FR , R _FL ... wheel speed sensor.

Claims (1)

In a braking system comprising a braking device that applies a braking force to a wheel by driving a wheel cylinder by the hydraulic pressure of the brake fluid, and a hydraulic pressure control means that controls the hydraulic pressure,
The hydraulic pressure control means includes
When executing the first mode which is ABS control for increasing the hydraulic pressure so that the actual slip rate of the wheel does not exceed a reference value and then reducing the hydraulic pressure, increasing the pressure after the pressure reduction and applying a braking force to the wheel,
The hydraulic pressure at each wheel in the first mode, which is the ABS control, is reduced by adding the pressure increase time of the hydraulic pressure of the wheel cylinder of the left or right wheel as positive and subtracting the pressure reduction time as negative. Is reset every control cycle, which is the period from the start to start increasing and then starting to decrease ,
The hydraulic pressure control means includes
In execution of the first cycle of the control cycle, the hydraulic pressure increase / decrease of the wheel cylinders of the left and right wheels at the time of resetting the integrated value of the hydraulic pressure increase / decrease time of the wheel cylinder of one of the wheels. Calculating a difference immediately before resetting the integrated value of time, comparing the difference with a determination threshold value, and performing a determination step of determining whether or not the friction coefficient of the road surface in contact with the left and right wheels differs according to the comparison result. Always permitting, and in the execution after the second or third cycle of the control cycle, the determination step is performed only at the edge timing at which the control cycle of at least one of the left and right wheels counts up. And control system.

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