JPH0146342B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device that controls brake hydraulic pressure in response to changes in road surface conditions during braking based on skid-controlled wheel deceleration, and in particular, when wheel speed recovers due to brake hydraulic pressure reduction.
When the wheel acceleration exceeds a predetermined value, maintain the oil pressure and
The present invention relates to an anti-skid control device that appropriately switches the brake hydraulic pressure to an increased pressure after this holding, depending on the road surface condition. Conventionally, as a method of controlling the brake oil pressure so as to obtain the maximum braking efficiency based on the deceleration of the skid-controlled wheels, for example, as shown in Fig. 1, the wheel speed V is increased by increasing the brake oil pressure _PW . At time t ₁ when the wheel acceleration (dv/dt) signal falls below the predetermined value α ₁ due to deceleration, the brake hydraulic pressure P _W is switched from pressure increase to pressure reduction, and this pressure reduction restores the wheel speed V, and at time t When the brake oil pressure exceeds a predetermined value _α1 at _{time t2} , the brake oil pressure is maintained at that time, and at this time _t2 , a discharge voltage E is generated whose initial value is a predetermined voltage _E0 ,
A method has been proposed in which, when the wheel acceleration α signal becomes lower than the discharge voltage E at time _t3 , the brake oil pressure _PW is switched to increase pressure again (Special Publication No. 1973-
28957). According to this method, as shown in the μ-λ characteristic graph in _{FIG .}
The value of μ with respect to the slip rate λ changes along the λ curve, and the slip rate λ _M (λ _M =
0.15 to 0.2), the maximum braking efficiency is reached, and when the slip ratio λ further decreases to below λ _M , μ drops rapidly and _the braking force decreases. As shown in Figure 1,
It is determined by comparing the discharge voltage E and the wheel acceleration α signal, and the brake oil pressure P _W is switched to increase pressure at time t ₃ .
The slip rate is increased toward λ _M where μ becomes maximum again. By the way, it is known that the μ-λ characteristics shown in Figure 2 change depending on the road surface conditions during braking.For example, on a normal paved road surface, a large μ as shown in curve A was obtained. If the road surface becomes slippery, such as a flooded waterway surface or an icy road surface, the value of μ becomes smaller as shown by curve B. Therefore, when performing skid control using the above method on a slippery road surface like curve B, the wheel speed V recovers slowly when the brake oil pressure is reduced, so the value of the wheel acceleration α signal Also, as shown in FIG. 3, there is a small change. If the wheel acceleration α signal is small in this way, the wheel acceleration α signal cannot exceed the discharge voltage E generated with the initial value E ₀ at time t ₂ , and as a result, the brake oil pressure P _W shown in FIG. The pressure cannot be increased again, and skid control based on the wheel acceleration α signal cannot be performed on low μ roads. Such a problem is caused by the value of the discharge voltage E, which determines the pressure increase timing, being too high. Therefore, in a low μ road, the initial value of the discharge voltage E is changed as shown by the broken line in Figure 3. By reducing E ₀ ', it is possible to switch to pressure increase at time _t3 . However, if the initial value of the discharge voltage E is made small like E ₀ ', the friction coefficient of the road surface increases and a sufficient wheel acceleration α signal is obtained, as shown in FIG. The signal is discharge voltage E
As the time until the time t3' drops below _t3 ' becomes longer, the timing of re-increasing the pressure is delayed, and the slip ratio λ approaches zero too much, causing the coefficient of friction μ between the road surface and the tire to become small, leading to a risk of deterioration in braking performance. There is. In this way, in the method shown in Fig. 1, the initial E ₀ ' of the discharge voltage E is fixedly determined assuming a specific road surface, so it is possible to
There is a problem that appropriate skid control cannot be performed on a road surface or the like. Therefore, in order to properly re-increase the brake oil pressure even if the road surface conditions change, we focused on the point where the peak value of the wheel acceleration α signal is obtained when the slip rate λ crosses λ _M , and Further differentiate the acceleration α signal to find its rate of change (dv ² /d ² t),
When (dv ² /d ² t)=0, the slip rate λ is λ _M
A method is being considered in which the brake hydraulic pressure P _W is determined to be increased when the brake pressure P W has reached . In principle, this method is excellent in that it can detect the timing of the slip ratio λ _M at which maximum braking efficiency can be obtained in real time, regardless of the road surface condition, but when the system is actually configured, (d ² v/dt ^{2 )} due to minute fluctuations in μ due to unevenness of the road surface, or ripple noise due to F-V conversion when converting the number of pulses proportional to the wheel rotation speed into a voltage signal to obtain the wheel speed signal. The signal fluctuates as shown in the time chart in Figure 5. For example, when the signal passes through a joint on the road surface during braking and causes a large bounce, it may cause a slip as shown at time _t3 . Even though the rate λ has not reached λ _M , due to signal fluctuation (d ² v / dt ² ), when the signal becomes zero, the switch to pressure increase is made, resulting in incorrect pressure increase timing. There is a risk of detection. The present invention was made in view of the above, and in order to ensure accurate skid control even when road surface conditions change,
The peak value of the wheel acceleration signal is maintained when the wheel speed is recovering toward the vehicle speed in the skid cycle, which is generated by controlling the hydraulic pressure according to the value of wheel deceleration detected based on the wheel speed. However, after this holding, when the wheel acceleration signal falls below a value that is lower than the peak value by a predetermined ratio, a command is given to increase the brake oil pressure. Hereinafter, the present invention will be explained based on the drawings. FIG. 6 is a block diagram showing one embodiment of the present invention. First, to explain the configuration, 10 is a differentiation circuit that differentiates the wheel speed V signal of the wheel to be skid-controlled and outputs an α signal, 11 is a peak hold circuit that holds the peak value of the α signal, and 12 is a peak hold circuit 11 Based on the output signal αmax of
It is a ratio calculation circuit that produces a β signal that is lower than αmax by a predetermined ratio, for example β = (αmax − α ₁ ) ×
It is determined as 1/b+α ₁ . However, α ₁ is a constant value, and (1/b) is a ratio. 13 is a comparator that compares a predetermined α ₁ signal with the α signal and produces an H level output when α≧α ₁ ; 14 compares the β signal with the α signal, and produces an H level output when α≦β. 15 is an RS-FF which is set or reset by the H level output of comparators 13 and 14, 16 is an OR gate, and 17 is an AND gate. The signals V1' and V2' to the OR gate 16 and the AND gate 17 are signals output depending on the magnitude of the slip rate of the wheel. For example, when the slip rate is smaller than a predetermined value, V1'=V
2'=L, if larger than the predetermined value, V1'=V2'
=H. Further, the signals V1 and V2 from the OR gate 16 and the AND gate 17 are control signals for the solenoid valve of the hydraulic actuator that increases, decreases, or maintains the brake oil pressure, resulting in control operations as shown in Table 1 below. .

[Table] Next, the operation will be explained with reference to the time chart shown in FIG. The brake oil pressure increases when the brake pedal is depressed, and this pressure increase causes the wheel speed V to decelerate in a direction that increases the slip ratio, and the wheel speed (-) due to this deceleration decreases.
When (dv/dt) reaches a predetermined value, the brake oil pressure is reduced, and due to this pressure reduction, the wheel speed V begins to recover toward the vehicle speed. Due to such recovery of wheel speed V, wheel acceleration α
The signal (α=dv/dt) is as shown in Fig. 7,
When the set value α ₁ of the comparator 13 is exceeded at time t ₁ , the output of the comparator 13 becomes H level, and this H level output sets the RS-FF 15 so that Q=H and =L. At this time, if V1'=V2'=L (slip rate is small), the signals V1 and V2 output from the OR gate 16 and the AND gate 17 are as follows.
V1=H, V2=L, and as is clear from Table 1 above, the brake hydraulic pressure _PW is maintained. In this way, if the brake oil pressure P _W is held constant at time t ₁ , μ−λ will change depending on the road surface condition at that time.
As the slip rate λ decreases depending on the characteristics, the wheel acceleration α increases in proportion to the increase in μ until reaching the slip rate λ _M at which the maximum braking efficiency is obtained.
The α signal reaches the peak value αmax at the time when λ=λ _M , and when the slip rate becomes less than λ _M , α starts to decrease as μ decreases. In this way, the peak value αmax of the wheel acceleration α obtained at time _t2 is held in the peak hold circuit 11, inputted to the ratio calculation circuit 12, and β=
By calculating (αmax- _α1 )×1/b+ _α1 , a signal β lower than the peak value αmax by a predetermined ratio as shown by the broken line in FIG. 7 is outputted and input to the comparator 14. The wheel acceleration α signal, which decreases after reaching the peak value αmax at time t ₂ , decreases to the signal β at time t 3, and then decreases to the signal β at time t ₃ .
At this time, the output of the comparator 14 becomes H level, and the RS-FF 15 is reset, so that Q=L,
=H. At this time, since V1'=V2'=L, the V1 signal that is the output of the OR gate 16 is at L level, and the output of AND gate 17 is also at L level, and as is clear from Table 1 above, Pressure increase is commanded when V1=V2=L, and the brake hydraulic pressure _PW starts to increase from time _t3 . As described above, according to the present invention, when the wheel acceleration α signal becomes equal to or lower than the signal level β which is lower by a predetermined ratio from its peak value αmax, that is, when the slip rate λ becomes lower than the slip rate λ _M at which the maximum braking efficiency is achieved, Immediately after this, the brake oil pressure is increased and the wheel speed V is controlled so that the slip rate returns to λ _M again. According to such a switch to increase the brake hydraulic pressure P _W , the wheel acceleration α _H signal on a high μ road surface and the wheel acceleration α _L signal on a low μ road surface are compared in Fig. 8. As is clear from the graph, the pressure increase timing t ₃ on high μ roads and the pressure increase timing on low μ roads
t ₂ are performed immediately after the peak value is obtained at time t ₁ , so even if the road surface condition changes, the pressure increase timing will not be delayed and will be adjusted appropriately according to the road surface condition. The appropriate pressure increase timing is set. FIG. 9 is a block diagram showing another embodiment of the present invention, in which wheel acceleration is caused by irregular rotation of the wheels on an uneven road surface or ripples when the wheel speed V signal is obtained by F-V conversion. It is characterized by preventing malfunctions due to alpha signal hunting. That is, in the embodiment of FIG. 6, as shown in FIG. 10, if hunting occurs in the α signal at time t ₁ while the wheel acceleration α signal is increasing past the predetermined value α ₁ , the time The α signal at t ₁ is held as the peak value, and the β′ signal that is lower than this value by a predetermined value is generated, and at time t ₂ the α signal becomes equal to or less than the β′ signal.
Therefore, the brake hydraulic pressure _PW will be increased, and the timing of the pressure increase may be significantly disrupted. Therefore,
In the embodiment shown in FIG. 9, malfunctions due to such hunting are prevented. First, the configuration will be explained with reference to FIG. 9. The differentiating circuit 10, comparators 13 and 14, RS-FF 15, OR gate 16, and AND gate 17 are the same as in the embodiment shown in FIG. The peak hold circuit 11 is composed of buffer amplifiers A1 and A2, a capacitor C1 for peak value holding, and an analog switch S that is turned on by the output of a comparator 13 using an FET that resets the capacitor C1. Diode D1 and resistor R1
The α signal is applied via the . Therefore, the capacitor C1 is charged with the α' signal (α' = α - δ), which is lower by the forward voltage δ of the diode D1, and the noise margin is determined by the forward voltage δ of the diode D1, and the α signal is Hunting is smoothed out. Note that if it is desired to increase the noise margin, the number of diodes D1 may be increased. On the other hand, the ratio calculation circuit 12 connects the output of the buffer amplifier A2 to one end of the variable resistor VR, and applies a predetermined value _α1 signal to the other end, and the output signal β is β=(α′max− ^α1 )×1/b+ _α1 . Note that the RS-FF15 is set or reset by a negative trigger pulse, so
Differentiating circuits 18a and 18b consisting of resistors R2 to R5 and capacitors C2 and C3 are provided on each input side, and the comparator 13 outputs an L level when α ₁ ≧ α, and the comparator 14 outputs an L level when α ≦ β. The inputs are replaced with respect to the embodiment shown in FIG. 6 so that the output is at L level. Next, referring to the time chart in Figure 11,
The operation of the embodiment shown in FIG. 9 will be explained. By reducing the brake hydraulic pressure P _W , the wheel acceleration α
When the signal exceeds the predetermined value α ₁ at time t ₁ , the comparator 13
The output of falls to L level, RS-FF15 is set by the negative pulse of the differentiating circuit 18a, and Q=
H,=L, and the output of the OR gate 16 becomes H,
The output of AND gate 17 becomes L, V1=H,
Since V2=L, the brake oil pressure _PW is maintained. However, it is assumed that V1'=V2'=. Further, when the output of the comparator 13 becomes L level, the analog switch S is turned off, and the reset of the peak hold circuit 11 is released. By holding the brake oil pressure _PW at time _t1 , the wheel acceleration α signal increases according to the road surface condition at that time, and even if hunting occurs on the way, the capacitor _C1 of the peak hold circuit 11 Since the signal α ₁ smoothed by the diode D ₁ is applied, minute fluctuations in the α signal are removed. At time t ₂ , when the wheel slip rate λ reaches the slip rate λ _M at which the maximum braking efficiency is obtained, α
The signal reaches the maximum, and after time _t2 , the α signal starts to fall. At this time, the peak hold circuit 11 outputs the peak value α′max held in the capacitor C1, so the ratio calculation circuit 12 =
(α′max − α)×1/b+α ₁ peak value α′max
A signal β that is smaller by a predetermined ratio is output. This β signal is compared with the α signal in the comparator 14, and when the α signal becomes lower than the β signal at time _t3 , the output of the comparator 14 falls to the L level, and the differential circuit 18b
The RS-FF 15 is reset by the negative pulse caused by Q=L,=H. Therefore, V1 as the output of the OR gate 16 and the AND gate 17,
The V2 signal becomes V1=V2=L, and commands to increase the brake hydraulic pressure _PW . Due to this increase in brake oil pressure P _W , the wheel acceleration α signal further decreases and falls below the predetermined value α ₁ at time t ₄ , and the output level of the comparator 13 returns to the H level, and the peak hold circuit 11 Switch S is turned on to discharge and reset the peak value αmax held in capacitor _C1 in preparation for control in the next skid cycle. FIG. 12 shows another embodiment of the present invention, in which V1 and V1 are
It is characterized by simplifying the circuit configuration by generating two signals. Correspondingly, the inputs of the comparator 13 are replaced so that when α≧ _α1 , an H level output is obtained. And peak hold circuit 1
1 analog switch S is turned on and off by the output of a comparator 13 via an inverter 19. As shown in the time chart of FIG. 13, at time _t1 , the wheel acceleration α signal reaches a predetermined value _α1.
, the output of the comparator 13 rises to H level, and the analog switch S
is turned off, and the output of the AND gate 20 is set to H level along with the H level output of the comparator 14,
At this time, since V1'=V2'=L, V as the output of the OR gate 16 and the AND gate 17
1, the V2 signal becomes V1=H, V2=L, and commands to hold the brake oil pressure _PW . When the α signal reaches its peak value at time t ₂ , a β signal is generated which is smaller than the output signal α′max of the peak hold circuit 11 by a predetermined ratio, and when the α signal becomes less than the β signal at time t ₃ , the output signal of the comparator 14 is The output falls to the L level, and the output of the AND gate 20 is set to the L level. Therefore, V1=V2=L, and a command is given to increase the brake hydraulic pressure _PW again. Further, at time _t4 , when the α signal becomes less than the predetermined value _α1 , the output of the comparator 13 returns to the L level, and the analog switch S is turned on to reset the capacitor C1 to discharge. As explained above, according to the present invention, the peak value of the wheel acceleration signal obtained when the wheel speed is recovering toward the vehicle speed is held, and after this holding, the wheel acceleration signal is When the signal falls below the above peak value by a predetermined ratio,
Since the brake hydraulic pressure is commanded to be increased again, it is possible to obtain the optimal pressure increase timing on any road surface, which has the effect of shortening the control stopping distance by improving braking performance. Furthermore, even if the wheel acceleration signal fluctuates due to braking on an uneven road surface, an erroneous pressure increase command will not be issued, and highly stable anti-skid control can be achieved. It will be done.

[Brief explanation of drawings]

Figure 1 is a time chart showing the conventional pressure re-increase control method, Figure 2 is a μ-λ characteristic graph, and Figures 3 and 4 are time charts showing problems with the conventional method shown in Figure 1. 5 is a time chart showing a conventional method of detecting the peak value of wheel deceleration and re-increasing the pressure. FIG. 6 is a block diagram showing an embodiment of the present invention. 6 is a time chart showing the operation of the embodiment shown in FIG. 6; FIG. 9 is a circuit block diagram showing another embodiment of the present invention capable of preventing malfunctions due to fluctuations in the wheel acceleration α signal; Figure 10 is a time chart showing the malfunction situation due to fluctuations in the wheel acceleration α signal.
11 is a time chart showing the operation of the embodiment shown in FIG. 9, FIG. 12 is a circuit block diagram showing another embodiment of the present invention, and FIG. 13 is a time chart showing the operation of the embodiment shown in FIG. 12. It is a chart diagram. 10...Differential circuit, 11...Peak hold circuit, 12...Ratio calculation circuit, 13, 14...Comparator, 15...RS-FF, 16...OR gate, 1
7, 20...and gate, 18a, 18b...
Differential circuit, 19, 21...Inverter, A1, A
2... Buffer amplifier, S... Analog switch, C1-C3... Capacitor, R1-R5...
Resistor, VR...variable resistor, D1...diode.

Claims (1)

[Claims] 1 In the skid cycle, which is generated by controlling the hydraulic pressure according to the value of the wheel deceleration detected based on the wheel speed, when the wheel speed is recovering toward the vehicle speed, the peak value of the wheel acceleration signal peak value holding means for holding the peak value; signal output means for outputting a signal having a value lower than the peak value by a predetermined ratio when the peak value holding means holds the peak value; 1. An anti-skid control device comprising pressure increase command means for commanding an increase in brake hydraulic pressure when the output signal of the output means becomes lower than the output signal of the output means.