JPH0150624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an anti-skid control device that sets a braking target straight line for anti-skid control based on the peak value of the wheel speed of a wheel to be skid-controlled.

In general, an anti-skid control device, which is designed to prevent sideslip and a decrease in braking force due to wheels locking during sudden braking, is designed to prevent wheels from slipping between the wheels and the road surface when the slip rate S is around 15%, as shown in Figure 1. Since the friction coefficient μ is maximum and the highest braking efficiency is obtained, a point P is reached where the wheel speed V _W is approximately 15% lower than the vehicle speed V _C , as shown in Figure 2. At this time, a braking target wheel speed (braking target straight line) V _WO is generated, and the wheel speed V _W is controlled to reach this target value.

By the way, the deceleration of the vehicle speed V _C during braking changes according to the change in the friction coefficient with the road surface, so the braking target wheel speed V _WO also follows the change in the vehicle speed due to the change in the friction coefficient μ. It is necessary to do so.

However, with conventional anti-skid control devices, when the slip rate first reaches point P where it is around 15%, it generates a braking target wheel speed V _WO with a predetermined slope based on the coefficient of friction with the most common road surface. For example, at time t _o in Figure 2,
If the friction coefficient changes to a small value in , the deceleration of the vehicle speed V _C will gradually change accordingly. However, since the slope of the target wheel speed V _WO remains constant, control is performed with a control target value that is considerably lower than the vehicle speed V _C , which tends to cause a lock. Conversely, if the friction coefficient changes to a large value at time t _o , the slope of the braking target wheel speed V _WO remains constant even though the vehicle deceleration increases, so the braking distance increases. Although it is superior to regular brakes, there is a problem in that it is difficult to ensure good braking performance in all road conditions. In addition, as described in Japanese Patent Application Laid-open No. 56-75242, the peak value of the wheel speed for each skid cycle is detected based on the peak value of the wheel acceleration or a set value near the peak value, and With the method of setting the braking target wheel speed from the wheel speed, the peak value of the wheel acceleration and the peak value of the actual wheel speed are slightly different, so the braking target wheel speed cannot be calculated accurately. Performance was somewhat inaccurate. Furthermore, since the disclosed device for detecting wheel acceleration detects acceleration, there is a problem in that the detected value tends to fluctuate when there is a disturbance on the road surface, such as unevenness.

The present invention has been made by focusing on such conventional problems, and includes a means for detecting the wheel speed of wheels to be skid controlled, and a hydraulic pressure for controlling hydraulic pressure so that the wheel speed becomes the braking target wheel speed. The control means maintains a wheel speed signal obtained from the increasing wheel speed at each skid cycle caused by the control of the hydraulic pressure, and detects when the current wheel speed becomes lower than this held wheel speed. peak value detection means for detecting the maintained wheel speed at the time as a peak value of the wheel speed; and setting means for setting the braking target wheel speed based on the peak value of the wheel speed detected by the peak value detection means. The purpose is to ensure highly accurate and accurate braking performance under all road conditions. Here, the skid cycle refers to a period of fluctuation in wheel speed when the hydraulic pressure of the wheel cylinders, etc. is controlled to increase or decrease when the brake is stepped on and gradually approaches the wheel speed.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention. First, to explain the configuration, 1 is a skid-controlled wheel (one wheel is shown as a representative), 2 is a wheel speed sensor that generates a pulse signal with a number of pulses or an AC signal with a frequency proportional to the number of rotations of the wheel 1; 3 is a converter that converts the detection signal of the wheel speed sensor 2 into a wheel speed _VW signal (voltage signal); 4 is a peak detection circuit that detects when the wheel speed _VW reaches a peak value in each skid cycle; 5 samples and holds the peak value of the wheel speed V _W using the peak detection output of the peak detection circuit 4, calculates the slope based on the difference between the previous data and the current data among these peak values, and sequentially calculates the braking target straight line. (Braking target wheel speed) A braking target straight line setting circuit that sets the Vi signal, 6 compares the braking target straight line Vi and the wheel speed V _W , and brings the change in wheel speed V _W closer to the braking target straight line Vi to maximize braking efficiency. 7 is a hydraulic pressure control circuit that generates a control signal for brake hydraulic pressure (a solenoid valve drive signal for reducing, holding, and increasing pressure), and 7 switches the solenoid valve according to the control signal from the hydraulic pressure control circuit 6. The foil cylinder (W/C) is moved from the mass cylinder (M/C) by operation.
This is a hydraulic actuator that repeatedly reduces, maintains, and increases the brake fluid pressure supplied to the brake fluid.

FIG. 4 is a circuit block diagram showing a specific embodiment of the peak detection circuit 4 in the embodiment of FIG. 3, which includes a comparator 8 for peak detection,
Resistor _R1 is connected to the negative input terminal of comparator 8.
_The wheel speed V _W signal is input through the positive input terminal, and the _forward voltage of diode _{D 1} (forward drop voltage ) A signal that is lower by V _D (V _W − V _D ) is input. Therefore, when the wheel speed V _W signal is increasing, the capacitor C ₁ is charged with a signal whose value is lower by the forward voltage V _D , and since V _W > (V _W − V _D ), the comparator 8 The output is at L level. On the other hand, when the V _W signal passes the peak value and begins to decrease, the capacitor C ₁ remains charged to the peak value of the wheel speed V _W signal due to the reverse bias of the diode D ₁ , and the V _W signal continues to increase from the peak value. When the voltage V _D decreases,
The output of the comparator 8 rises to an H level to generate a peak detection output.

Further, a circuit for applying a reset after peak detection is provided on the side of the comparator 8 connected to the capacitor _C1 .

This reset circuit section includes a differentiation circuit 9 that differentiates the wheel speed V _W signal and outputs an acceleration α _W signal, and an α _{W signal} .
a comparator 10 that produces an H level output when the signal exceeds a predetermined value +α;
A trigger circuit consisting of a capacitor C ₂ and a resistor R ₂ that generates a positive trigger pulse by differentiating the rise of the voltage to the H level, and a monostable multi 11 that is set by the trigger pulse and produces an H level output for a certain period of time.
and an analog switch 12 using an FET that conducts with the H level output of _the monostable multi ₁₁ to discharge and reset the capacitor C1. The capacitor _C1 is discharged and reset at the timing when the wheel acceleration _αW exceeds a predetermined value +α while the brake fluid pressure is decreasing and the vehicle speed is recovering again toward the vehicle speed, making it possible to detect the peak at each skid cycle. ing.

The operation of the peak detection circuit 4 of FIG. 4 constructed in this manner is further clarified by the time chart of FIG. 5.

That is, when the wheel speed V _W is increasing,
The signal shown by the dashed line, which is lower than V _W by the forward voltage V _D , charges the capacitor C ₁ and when it passes the peak value V _P ,
The voltage of the capacitor _C1 is kept constant, and when _VW falls below a certain value indicated by the broken line, the output of the comparator 38 becomes H level. Next, when the wheel speed _VW starts to recover again and the acceleration _αW exceeds the predetermined value +α, the monostable multi 11 generates an H level output for a certain period of time, discharges and resets the capacitor _C1 ,
Prepare for peak detection in the next skid cycle.

Next, referring to the time chart in Figure 6,
The overall operation of the embodiment shown in FIG. 4 will be explained.

Assuming that anti-skid control is started by depressing the brake pedal at time T _O , wheel speed V _W begins to decrease relative to vehicle speed V _C (slip rate increases) due to increased brake fluid pressure, and wheel deceleration reaches a predetermined level. A braking target straight line Vi _O with a predetermined slope (deceleration) is set by the braking target straight line setting circuit 5 at time T ₁ when the value is reached, and the hydraulic pressure control circuit 6 adjusts the hydraulic pressure based on this braking target straight line Vi _O. A control signal is output to the actuator 7, the brake hydraulic pressure that is being increased is switched to a reduced pressure, the wheel speed V _W is recovered toward the vehicle speed V _C , and the slip ratio is maintained around λ = 0.15 to 0.2, which is the maximum brake efficiency. When the vehicle speed approaches V _C , switch to pressure increase again.

When the wheel speed V _W begins to recover toward the vehicle speed V _C in this way, the comparator 10 of the peak detection circuit 4
output becomes H level, and the output of monostable multi 11 becomes H level.
Discharge and reset capacitor _C1 with level output,
Charging of the signal that follows the increase in V _W shown by the broken line begins. When the wheel speed _VW passes the peak value and falls below the peak value by a predetermined value at time _T2 , the output of the comparator 8, that is, the output of the peak detection circuit 4 becomes H level, and the peak detection output of the peak detection circuit 4 Accordingly, the braking target straight line setting circuit 5 samples and holds the value of the wheel speed V _W at time T ₂ as the peak value V _P1 .

Next, if the peak value V _P2 is sampled and held in the same manner at time T ₃ , the braking target straight line setting circuit 5 will calculate the peak value V _P1 at time T ₂ and the time T ₃
A straight line obtained by connecting the peak value V _P2 at time T3 is set as the braking target straight line Vi from time _T3 , and anti-skid control is performed based on this braking target straight line Vi.

Furthermore, if the peak value V _P3 is sampled and held in the same manner at time T ₄ , the braking target straight line Vi connecting the peak values V _P2 and V _P3 is set from time T ₄ , and thereafter, the braking target straight line Vi is set every time a peak value is detected. The braking target straight line is set sequentially.

Here, the setting method in the braking target straight line setting circuit 5 will be specifically explained using the case of time _T2 as an example.
Start counting the time from time T ₂ when the peak value V _P1 is detected, then find the time ΔT until time T ₃ when the peak value V _P2 is obtained, and calculate the slope of Vi by (V _P1 − V _P2 )/
(T ₂ −T ₃ )=ΔV/ΔT, and a linear signal that decreases with this slope is generated starting from the peak value V _P2 at time T ₃ .

FIG. 7 is a circuit diagram showing a specific embodiment of the braking target straight line setting circuit 5 shown in the embodiment of FIG.

First, to explain the configuration, a wheel speed signal _VW is applied to the input terminal 5a, and a peak detection output _eP is applied to the input terminal 5d, and this signal _eP and a timer signal e from the input terminal 5b are applied. _t , and a timing circuit section that receives a signal e _b output from the input terminal 5c when the wheel deceleration α _W exceeds a predetermined value α _b in the first cycle of the skid cycle, and outputs a timing signal. has.

That is, the timing circuit section includes flip-flops (hereinafter referred to as "FF") FF1 to FF7 and monostaple multivibrator (hereinafter referred to as "MM").
It is composed of MM1 to MM3, differentiating circuits 16a to 16d, and a logic circuit including an inverter, a NAND gate, an AND gate, an OR gate, and the like.

The sample/hold circuit section includes amplifiers A ₁ , A ₂ ,
A first sample/hold circuit is formed by a capacitor C ₁ and an analog switch S ₁ using FFT, and a second sample/hold circuit is formed by amplifiers A ₃ , A ₄ , a capacitor C ₂ and an analog switch S ₂ ,
The sampling operation or hold by turning on and off the analog switches S ₁ and S ₂ is performed using the terminal outputs of FF1 and FF2.

The polarity reversal circuit section consists of a pair of analog switches _S3 and _S4 using FFT, and is connected to the next stage differential amplifier.
The outputs of amplifiers A ₂ and A ₄ for A ₅ (subtraction circuit) are
The connection is switched alternately depending on the Q and output of FF5.

Integration timer consists of amplifiers A ₆ , A ₇ and capacitors
A reset analog switch _S5 is connected in parallel with _the capacitor _C3 , and the analog switch _S5 is turned on by the output of MM2 to reset the capacitor _C3 .

The division circuit section that performs division by the output ΔV of amplifier A ₅ and the output ΔT of amplifier A ₆ includes amplifiers A ₅ to _{A 12}
The output of amplifier _A13 is (ΔV/ΔT).

The division output sample/hold circuit section consists of an analog switch S ₆ , a capacitor C ₄ , and an amplifier A ₁₃ .The analog switch S ₆ is turned on, the division output sampled at this time is sampled, and the analog switch S 6 is turned on.
Hold by turning off _S6 .

The integrator circuit section that generates a signal output with a slope determined by the calculation output of amplifier A ₁₃ is composed of capacitor C ₅ and the amplifier.
_The capacitor _C5 is reset by an analog switch _S7 , which turns on and off in synchronization with the analog switch _S6 .

Note that _A15 is an amplifier that inverts the output of the amplifier _A14 .

Finally, the subtraction circuit section that generates the target wheel speed Vi consists of an amplifier A ₁₆ , whose positive input terminal is connected to an amplifier A ₂ via analog switches S ₃ and S ₄ .
Or a constant wheel speed from A ₄ is applied, and the integral output of amplifier A _{14 is} applied to the negative input terminal.
A ramp waveform signal that decreases with the calculation gradient (from the third cycle onward) is output as the difference between both input signals.

In addition, an analog switch _S9 is provided at the output of the amplifier _A16 , which is turned on by the output of FF3.
By resetting the peak detection output _eP by two counts using FF6 and FF7, it is turned on from the third cycle of the skid cycle. On the other hand, the analog switch _S8 is turned on by the Q output of FF3 and remains on from the end of the first to the second skid cycle to generate a control target straight line _ViO with a predetermined slope generated by means not shown. The output is made until the setting of the braking target straight line Vi by calculation is started.

Next, the operation of the embodiment shown in FIG. 7 will be explained with reference to the time chart shown in FIG.

Assuming that anti-skid control is started by stepping on the brake at time _TO , the e _b signal is applied to input terminal 5c at time T ₁ when the wheel deceleration α _W exceeds the predetermined value α _b , and FF3 is set (Q = 1). , = 0).

Therefore, analog switch _S8 is turned on and the time is
A braking target wheel speed _ViO having a predetermined slope is output from _T1 , and skid control for the first and second cycles is performed.

When the first peak value detection is performed at time T ₂ ,
A peak detection signal e _P is applied to the input terminal 5d, and this
e _P signal applies a negative trigger to the set terminal of FF1 via the inverter and differentiator circuit 16a,
The output of FF1 becomes "0". Therefore, analog switch S ₂ is turned off and capacitor C ₂ has
The voltage at time T ₂ , ie, the peak value V _P1 of the wheel speed V _W , is held, and the output of the amplifier A ₄ becomes constant.

Also, the _eP signal is slightly delayed by the inverter.
is applied to MM1, a positive pulse is generated at the output of MM1, and the FF
At this time, the output of FF4 is "1", so FF2 is in the reset state, the output of FF2 is "1", the analog switch _S1 is turned on, and the amplifier _A2 is turned on.
Continuing with the _VW sample.

Furthermore, since the Q output of FF4 is “0”, FF1
The output of remains "0" and the analog switch _S2 is still turned off.

Next, at the moment when the positive pulse of MM1 disappears, a positive pulse is generated at the output of MM2, and analog switch _S5 is turned on for a certain period of time, causing the capacitor to
_C3 is discharged and reset, and from time _T2 , amplifier _A6 begins to produce a timing output ΔT that increases linearly in proportion to the elapsed time.

At time _T3 , which is the third cycle, when the _eP signal is generated again, FF4 is inverted and Q=1,=0
Therefore, FF2 changes from the reset state (Q=0,=1) to the set state (Q=1,=1).
= 0), the analog switch S ₁ is turned off, the peak value V _P2 of the wheel speed V _W at time T ₃ is held in the capacitor C ₁ , and the output of the amplifier A ₂ is maintained at V _P2 .

Note that FF1 continues to take the set state (Q=1,=0), and the output of amplifier _A4 remains V _P1 .

Furthermore, FF5 is in the set state from the second cycle, analog switch _S3 is off, and _{S4 is} off.
is on, so the output V _P2 of amplifier A ₄ is the amplifier
A is connected to the negative input terminal of ₅ , and as a result,
The output of amplifier _A5 becomes a signal proportional to ΔV=V _P1 −V _P2 .

At the same time, since the output of amplifier A ₇ is a signal proportional to the elapsed time ΔT _until time T ₃ measured by amplifier A ₆ , the output of amplifier A ₇ is The output of _A11 becomes a signal proportional to (ΔV/ΔT).

Since the analog switch _S6 is on at this time _T3 , the output of the amplifier _A11 is held in the capacitor _C4 via the amplifier _A12 , and when the analog switch _S6 is turned off at this time, Amplifier A ₁₃ outputs a constant voltage proportional to (ΔV/ΔT), which is applied to amplifier A ₁₄ . Of course, analog switch _S7 is also turned on in synchronization with analog switch _S6 , and when (ΔV/ΔT) is applied at time _T3 , amplifier _A14 linearly operates with a slope determined by (ΔV/ΔT). An increasing integral output is produced, inverted by amplifier A ₁₅ and applied to the negative input of amplifier A ₁₆ .

Also, at time _T3 , the output pulse of MM1 disappears, so FF1 is inverted, turning on analog switch _S2 , and further inverting FF5 to the set state, turning on analog switch _S3 and turning on S2. Turn off ₄ . Therefore, the peak value V _P2 from the amplifier A ₂ sampled at time T ₃ is applied to the positive input terminal of the amplifier A 16 via the analog switch S ₃ , and as a result _, the amplifier A ₁₆ becomes With V _P2 as the initial value, a ramp waveform voltage that decreases at a slope of (ΔV/ΔT) is output.

At this time, the analog switch S ₉ provided at the output of the amplifier A ₁₆ detects FF 7 by counting the second peak detection output e _P at time T ₃ .
FF3 reset (Q
= 0, = 1), the braking target straight line Vi _O with a predetermined slope, which had been output via the analog switch S ₈ that had been turned on, is cut off, and the output of the amplifier A ₁₆ is turned on via the analog switch S _9. is set as the braking target straight line Vi for the third cycle.

Furthermore, when the output pulse of MM1 disappears at time _T3 ,
A positive pulse is generated at the output of MM2, turning on analog switch _S5 and turning it off again, so that the amplifier
From time _T3 , _A6 again outputs a time signal that linearly increases in proportion to the passage of time.

The operation after the 4th cycle is 1 by FF5.
The cycle is the same as the third cycle except that the analog switches S ₃ and S ₄ are turned on and off every cycle.

When the skid control ends, the timer signal e _t disappears, MM3 puts FF2 and FF1 into the reset state (Q=0, =1) in that order, turns on both analog switches _S1 and _S2 , and returns to the sample state. do.

FIG. 8 shows another embodiment of the peak value detection means used in the present invention, in which the wheel speed V _W output from the converter 3 is detected by the sampling circuit 13 using the sampling pulse P _S from the pulse generator 14. The peak detection circuit 15 detects the peaks at regular intervals, and the peak detection circuit 15 performs digital processing or program control.

The peak detection by this peak detection circuit 15 is as follows:
Taking the case of using a microcomputer as an example, the program flow shown in FIG. 9 is followed. In this program flow, when the anti-skid control starts, the initial program is first executed, and as shown in block 17, V _WO =
0, V _nax (peak value) = V _WO .

Next, in block 18, the sampling circuit 13 samples V _W1 , V _W2 , V _W3 ,
When a wheel speed of ... is generated, the process proceeds to judgment block 19 for each sample value generation, and a comparison is made between the sample value V _Wo-1 from one cycle before and the magnitude relationship such that V _Wo > V _Wo-1. Do this. At this time, if V _Wo >V _Wo-1 holds true, the process proceeds to block 20 and the current sample value V _Wo is set as the peak value V _nax . On the other hand, V _Wo >
If V _Wo-1 , the peak value V _nax obtained from the previous sample value is held as it is, and the process proceeds to judgment block 21.

In determination block 21, the current sample value V _Wo
is smaller than the current peak value V _nax by a predetermined value δ (V _{nax -} δ). Execute the flow. On the other hand, when V _Wo <V _nax −δ holds,
It is determined that the peak value has been reached, and a command is issued in block 22 to generate a peak detection output.

Peak detection using such a program flow is performed by changing the wheel speed V _W to V _W1 , V _W1 ,
Sampled as V _W2 , V _W3 ,..., wheel speed V _W
For each of the sample values V _W1 to V _W5 when is increasing toward the peak value, the predetermined value δ is lower than V _W
The determination block 21 determines that the sample value is not the peak value because it is larger than the lower V _W −δ, and the sample value obtained after passing the peak
Since the condition of decision block 19 does not hold for V _W6 , V _nax = V _W5 is left as is, and at decision block 21, V _W6 <V _nax -δ, that is, V _W6 <
Since V _W5 -δ holds, the peak value is assumed to be V _W6 , and a peak detection output is performed in block 22.

Furthermore, for the sample values V _W7 to V _W10 when the wheel speed V _W decreases past the peak value, V _nax =
Since V _W5 remains, the condition of decision block 21 is not satisfied and no peak detection is performed. Due to this action, peak detection is performed in the same manner in each skid cycle.

Note that in the determination block 21, V _Wo <V _nax may be set, but by setting V _Wo <V _nax −δ, the first
As shown in the time chart of FIG. 1, the predetermined value δ provides a noise margin to prevent erroneous detection of the peak value V _P ' caused by fluctuations in the wheel speed V _W due to minute fluctuations in the road surface.

Of course, the program flow shown in FIG. 9 can also be easily realized by a digital circuit.

As explained above, according to the present invention, the wheel speed signal obtained from the increasing wheel speed is held for each skid cycle generated by controlling the hydraulic pressure, and the wheel speed signal obtained from the wheel speed that is being increased is held. The held wheel speed when the current wheel speed becomes lower is detected as the peak value of the wheel speed, and the slope is calculated based on the difference between the previous data and the current data among this detected peak value. Since anti-skid control is performed by sequentially setting a braking target straight line, it is possible to set a braking target straight line whose slope follows the decreasing change in vehicle speed, which is determined according to the road surface conditions during braking, and as a result, braking accuracy is improved. Even if the coefficient of friction with the road surface suddenly changes during any road surface situation or braking, braking is performed with maximum braking efficiency, and safety is further increased by significantly improving braking performance. You can get the effect that you can.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the slip rate of the wheels and the coefficient of friction between them and the road surface during braking.
Fig. 2 is a time chart showing the setting of a braking target straight line in a conventional device, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram of a peak detection circuit in the embodiment of Fig. 3. A circuit block diagram showing one embodiment, FIG. 5 is a time chart showing the peak detection operation of FIG. 4, FIG. 6 is a time chart showing the operation of the embodiment of FIG. 3, and FIG.
The figure is a circuit diagram showing one embodiment of the braking target straight line setting circuit in the embodiment of FIG. 3, FIG. 8 is a block diagram showing another embodiment of the peak detection means used in the present invention, and FIG. A program flow diagram of peak detection performed in the embodiment shown in FIG. 8, and FIG.
FIG. 11 is a time chart showing the effect of the program flow shown in the figure, and FIG. 11 is a time chart showing the effect of preventing erroneous detection of a peak value due to fluctuations in wheel speed. DESCRIPTION OF SYMBOLS 1... Wheel, 2... Wheel speed sensor, 3... Converter, 4, 15... Peak detection circuit (peak value detection means), 5... Braking target straight line setting circuit (braking target wheel speed setting means), 6... Hydraulic control circuit (hydraulic control means), 7... Hydraulic actuator, 8, 10
... Comparator, 9 ... Differential circuit, 11 ... Monostable multi, 12 ... Analog switch, 13 ...
...Sampling circuit, 14...Pulse generator.

Claims (1)

[Scope of Claims] 1. Means for detecting the wheel speed of a wheel to be skid controlled; Hydraulic control means for controlling hydraulic pressure so that the wheel speed becomes a braking target wheel speed; and Skid generated by controlling the hydraulic pressure. For each cycle, the wheel speed signal obtained from the increasing wheel speed is held, and when the current wheel speed becomes lower than this held wheel speed, the held wheel speed is determined as the peak wheel speed. An anti-skid control device comprising: a peak value detection means for detecting a peak value of the wheel speed; and a setting means for setting the braking target wheel speed based on the peak value of the wheel speed detected by the peak value detection means.