DE2434918A1 - ANTI-LOCK CONTROL SYSTEM FOR VEHICLES - Google Patents

Description

Anti-lock control system for vehicles

Priority: July 21, 1973 / Japan Registration No .: Sho 48-82193

The present invention relates to an anti-lock control system for vehicles which prevents the vehicle body from falling Carries out uncontrolled movements if the wheels lock when the brakes are applied. In particular, the invention relates a system with which the brake pressure is reduced when the beginning of a locked condition of the wheels is perceived. A minimum value of the wheel speed is stored, the stored value is compared with the wheel speed and the time to cancel the brake pressure reduction process is determined accordingly »

In the known anti-lock control systems of this type, a wheel acceleration signal is obtained by differentiating the

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Wheel speed signal, which is from a on the circumference of the wheel axle attached signal generator or hesswertgeber is obtained. When the acceleration signal is below a certain negative Value decreases, it is assumed that a locked condition of the wheels has begun and the brake pressure by actuating a Pressure modulator reduced. On the other hand, it is assumed that the wheels have been released from the locked state, when the acceleration signal rises above a certain positive value. Then the operation of the pressure modulator is stopped, and the brake pressure is allowed to rise slowly. This control cycle is repeated to prevent the wheels block until the braking process has ended.

With these systems, however, the difficulty arises that noise is generated by bumps due to uneven road surfaces and at the time of gear change. This noise namely has a tendency to erroneously initiate control processes. Since the noise occurs impulsively, the Differentiating greatly exaggerated.

In order to prevent such wrong operations, are already Various methods of detecting the onset of a locked condition of the wheels have been developed. In such For example, the method does not start the control cycle by reducing the brake pressure when the wheel acceleration signal is only less than a certain negative value, but the wheel speed at this point in time is initially stored, and then by checking the wheel speed

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after a certain period of time before the start of the control cycle determined whether there was an actual decrease in wheel speed acts. But also in connection with the prevention of the wrong control processes mentioned above there is no Appropriate method has become known with which the recovery or release of the wheels from the locked state is perceived can be.

Object of the invention is to provide an anti-lock control system for vehicles of the type mentioned, in which the above disadvantages are avoided at all costs and in particular the problem of noise signals is solved and works reliably in a variety of road conditions.

With the invention, the release of the wheels from a locked state is not done with the aid of a wheel acceleration signal as determined in known methods, but by storing a minimum wheel speed, i.e. a minimum wheel speed in the control cycle and by comparing the stored value with the actual wheel speed.

The invention also provides a device with which said stored wheel speed is reset with each control cycle, so that locking of the wheels due to a sharp drop in wheel speed is avoided in the event of sudden braking and consequently a sufficient restoration of the wheel speed can be ensured .

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The invention also provides a device with which the vehicle body deceleration is perceived around a frozen road surface with a low coefficient of friction of a Distinguish road surfaces with a high coefficient of friction, so that an adequate restoration of wheel speed can always be guaranteed, regardless of how the coefficient of friction of the road surface behaves.

To solve the problem on which the invention is based, an anti-lock control system for vehicles is created which a device for converting the wheel speed into voltage signals, a device for sensing the beginning of a wheel lock, a brake pressure modulator that adjusts the brake pressure in accordance with a perception of the start of wheel locking output control signal reduced, a hold circuit for a low peak value, the a minimum value of the wheel speed voltage signal stores in a wheel speed control cycle, and has a comparison circuit which Wheel speed voltage signal and the minimum value thereof stored by the low peak hold circuit is, compares and causes the brake pressure reduction process of the brake pressure modulator to be terminated when the wheel speed voltage signal and the stored minimum value thereof have a predetermined value ratio correspond.

Further refinements of the invention emerge from the subclaims.

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2434318

The invention is described below with advantageous Details based on schematic drawings of various exemplary embodiments explained in more detail. Show it:

Fig. 1 is a block diagram of an anti-lock control system according to an embodiment of the invention;

Fig. 2 (a) - (d) shows the ratio of the wheel speed signal, the wheel speed deceleration signal, the control signal and brake pressure versus time;

3 shows a block diagram of an anti-lock control system according to a second embodiment of the invention;

4 is a block diagram of an anti-lock control system according to a third embodiment of the invention;

Fig. 5 (a) - (c) shows the ratio of the wheel speed signal, the control signal and the brake pressure versus time for the third embodiment shown in FIG. 4;

Figure 6 is a block diagram of another embodiment of the low peak hold circuit according to the invention.

In the embodiment shown in Fig. 1, a transducer 1 is attached to the circumference of the wheel axle to a Pulse signal proportional to the speed of rotation of the wheel Frequency. The signal of this signal generator or transducer 1 is in a frequency-voltage converter 2 in converted to a voltage signal V (t) representing the wheel speed. The speed signal V (t) becomes in a differentiating circuit 3 is made a wheel acceleration signal g (t) as shown in Fig. 2 (b). The acceleration signal g (t)

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is then compared in a first comparison circuit 4 with a predetermined negative value -G1. At the moment (time t1) _; in which the value g (t) becomes smaller than -G1, the first comparison circuit 4 generates a pulse in order to create a given state in a flip-flop 6. The output of the flip-flop 6 is a control signal U (t) (a wheel lock detection signal) which is via. a current booster 7 actuates a pressure modulator 8 in order to relax the brake by reducing a brake pressure P (t), as shown in FIG. 2 (d).

The above description applies to the operation from sensing the start of locking of the wheels to loosening the brake pressure. This is just one example of a known arrangement, such as that described in US Pat. No. 3,494,671 is described. The invention is not limited to such an arrangement. In practicing the invention is that above described circuit arrangement added a device with which an erroneous control process due to noise, which overlaps the acceleration signal g (t) is prevented. However, such a device is not described here, since it does not constitute an essential part of the invention.

The speed signal V (t), on the other hand, is input to a low level hold circuit which a switch 9, a diode 10 and a capacitor 11 comprises. One end of the capacitor 11 is connected to the output side of the Frequency-voltage converter 2 connected via switch 9,

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connected to a brake pedal, not shown here, and at When the brake is not applied, the other end of the capacitor is grounded. The diode 10 is connected to the switch 9 connected in parallel and allows only the discharge of the capacitor 11. An input of a second comparison circuit 5 is a Terminal voltage V (t) of the capacitor 11, while the other input is a speed signal voltage KV (t) (0 <£ K <1), which is divided by a group of resistors 12 and 13 connected in series. The output signal of the second comparison circuit 5 is used to reset the flip pile :; t.

When the brake is not actuated, the switch 9 remains closed. As a result, the terminal voltage V (t) corresponds to of the capacitor 11 the speed signal V (t). From Fig. 2 (a) it can be seen that even when you open the switch 9 when When the brake is applied at time t, the capacitor 11 is discharged through the diode 10 in the decreasing stage of the speed signal V (t). Therefore, the terminal tension decreases at this stage V * (t) of the capacitor 11 with the speed voltage signal V (t) from. As already mentioned above, the process for reducing the brake pressure begins at time ti. If then at the beginning of an increase in wheel speed, the waveform of the speed voltage signal V (t) turns upwards, voltage is applied to the diode 10 in the reverse direction, whereby a switch-off stage is generated. As a result, remains the terminal voltage V (t) of the capacitor 11 at a minimum value V1 of the speed signal obtained up to that point,

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and from there the waveform of the speed signal runs V (t) and that of the terminal voltage V (t) of the capacitor 11 in separate lanes. The minimum value Vl is maintained until the speed signal V (t) is less than VI.

The terminal voltage of the capacitor 11, ie the held speed signal V (t) is used as one of the inputs for the above-mentioned second comparison circuit 5. In the second comparison circuit 5, the speed signal £ 7 (t) divided by the resistors 12 and 13 with the ^! held signal V ¹ (t) compared and an output pulse generated to reset the flip-flop 6 at the moment (time t2) in which the signal KV (t) is greater than V ¹ (t). As a result, the control signal U (t) is switched off and the operation of the pressure modulator 8 to reduce the brake pressure ceases, so that an increase in the brake pressure is caused. When the braking force of the brake increases slowly, a locked state of the wheels is again caused. Then, in exactly the same way as described above, the beginning of this locked state of the wheels is determined at time t3 in order to reduce the brake pressure, and at time t4 a second minimum value V2, which is held in the above-mentioned holding circuit, is determined with the divided speed signal KV (t) compared. As a result, the brake pressure begins to rise again. The control cycle described above is repeated until the braking process has ended.

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Fig. 3 shows a second embodiment of the Invention. One of the inputs of the second comparison circuit 5 is the terminal voltage of the capacitor 11 as in the first Embodiment. A constant current circuit is provided here, consisting of a circuit connected to a current source Vcc Resistor 14a, a further resistor 14b and a transistor 15 is constructed. A constant base current Ig is applied to the base of a transistor 16. Assuming that the DC gain of transistor 16 ß, then the Koliektorstrom Ic has a constant value, which can be expressed as follows: Ic = ßlg. The other at the with the second comparison circuit 5 connected to the collector of the transistor 16 is therefore always an input voltage Voltage that is obtained by the fact that the speed signal V (t) has a constant voltage (potential difference between this and a resistor 17) δ.V = ICR17 subtracted where R17 represents the resistance value of resistor 17 In the second comparison circuit 5 is a value obtained by subtracting a constant value AV from the actual Wheel speed V (t) is obtained compared with the stored minimum value of the wheel speed V (t) and the operation of the pressure modulator 8 for reducing the brake pressure by resetting the flip-flop 6 is stopped.

Fig. 4 is a block diagram of a third embodiment of the invention, In this embodiment, a solenoid 18 is controlled by an amplified control signal U (t) des

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of the current amplifier 7 energized. A switch 19, which is normally closed, is connected in parallel with the diode 10 here and opens upon energization of the solenoid 18.

With the above-mentioned resistor 12, a switch 20 for perceiving the delay and a kiderstand 21 are connected in parallel. The switch 20 for detecting the delay has two clamps 22 and 23 and is enclosed in a glass tube 24 Mercury 25 on. The switch 20 is attached to the vehicle assembly at an angle θ to the horizontal. The direction of movement of the vehicle is indicated in this figure by the arrow. When the degree of deceleration of the vehicle speed a certain set value οι. = g tan θ (where g represents the acceleration due to gravity) reached, the mercury 25 rises and touches both terminals 22 and 23, which are then short-circuited to the resistor 21 to be connected in parallel with the resistor 12.

The arrangement described above works as follows: When the solenoid 18 is energized by the control signal U (t), with which a locked condition of the wheels has been sensed, the switch 19 opens. If then a wheel speed restoration signal the second comparison circuit 5 resets the flip-flop 6, the solenoid 18 is de-energized, the Switch 19 is closed, the value of the minimum wheel speed in the above-mentioned holding circuit 10 and 11 for one low peak value is reset and the terminal voltage of the capacitor 11 adapts to the wheel speed signal V (t),

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This process is then repeated.

In the exemplary embodiment shown in FIG. 1, the wheel speed is compared to a first stored minimum value V1 a second stored minimum value V2 lower and a third stored minimum value V3 still lower again. During sudden braking, if the minimum value V1 in the first control cycle due to the delayed Operating an extraordinarily low value is the minimum values V2 and V3 in the second and third control cycle are even lower than the already very low value VI. That leads to faster To block. In the present embodiment, however, the stored minimum value is reset for each control cycle. The minimum value to be saved is unlike any other in the previous one Control cycle restricted minimum value. Therefore, in this embodiment, the possibility is excluded that the described inconvenience occurs.

The delay sensing switch 20 and the resistor 21 are designed so that the wheel speed in one for the respective coefficient of friction of the road surface appropriate degree is restored. In the embodiment shown in FIG. 1, the value of the constant K is des divided speed voltage signal KV (t), which is one of the inputs of the second comparison circuit 5, invariable. Thus, as shown in FIG. 5, when a brake pressure reducing operation takes place at time t5, the wheel speed V (t) recovers immediately

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in cases where the road surface has a high coefficient of friction, such as an asphalt road. The brake pressure reduction process then ends at time t6, and the wheel speed can recover up to a maximum value V1 due to inertia due to the time delay in the control system. On the other hand, when the coefficient of friction of the road surface is low, as in the case of a frozen road surface, the wheel speed V (t) does not easily recover. As a result, in such a case, the brake pressure reducing operation ends at a time point t7 which is later than the above-mentioned time point t6, and the wheel speed recovers to a maximum value V2 which is lower than the above-mentioned maximum value V1. This relationship is shown in Fig. 5 (a). As can be seen there, the maximum value V2 with respect to the vehicle body speed Vb (t) drops more than the maximum value VI. Therefore, if the value of the above-mentioned constant K is set to be suitable for a road surface having a high coefficient of friction, the braking pressure may not be lowered enough on a road surface having a lower coefficient of friction. This insufficient reduction in brake pressure can then cause the wheels to lock. On the other hand, if the constant K is set to a value suitable for a road surface with a low coefficient of friction, the brake may yield too much on a road surface with a high coefficient of friction, resulting in a lengthening of the braking distance . In Fig. 5, the relationship described above is shown, the solid line for a road surface with high

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Coefficient of friction and the dashed line for a Road surface with low coefficient of friction applies.

In this embodiment, when the brake is over a high between the wheels and a road surface Frictional force exceeding the coefficient of friction is attracted, there is a strong deceleration of the speed a Q> g tan Θ) in the vehicle. This increases the mercury 25 in which the delay sensing switch 20, whereby the two terminals 22 and 23 are short-circuited and the resistor 21 with the Resistor 12 is connected in parallel. Accordingly, an input voltage KV (t) of the second comparison circuit is disregarded from the stored minimum value of the wheel speed, which is the other input of this circuit, the following:;

where R12, R13 and R21 represent the values of resistors 12, 13 and ■ 21, respectively. For a road surface with low friction. coefficient is the degree of deceleration of the speed; a '(4.g tan Θ) less than the above degree of speed deceleration a “Therefore the mercury 25 does not move and the two terminals are not shorted. Accordingly \\ rird 'of the above-mentioned other input of the second comparison circuit 5, that is, the input voltage K ^B V (t), the _following:;

R13

R12 ♦ R13

V (t)

So the result of a comparison between the two is:

K> K '. In Fig. 5 the relationship for the case of a road

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surface with a low coefficient of friction represented by an imaginary line. This indicates that the point in time t8, at which the stored minimum value V, ¹ (t) of the wheel speed equals the divided wheel speed signal K'V (t), is later than the above-mentioned point in time t7, and that the wheel speed V (t ) is set again up to a maximum value V2 ¹ , which is higher than the above-mentioned maximum value V2. If, in this embodiment, the constants K and K ^{1 of} the degree of lowering of the wheel speed signal V (t) are preset as inputs for the second comparison speed 5 for a road surface with a high and a low coefficient of friction, respectively, the wheel speed can be up to one Recover to a degree that is appropriate for the particular road surface condition.

It is also possible to connect the above-mentioned switch 20 and the resistor 21 with the resistor 13 in parallel. In in this case switch 20 is normally closed and opens when a high degree of deceleration occurs in the vehicle.

Fig. 6 shows another embodiment of the invention showing a holding circuit for a low peak value in accordance with. As FIG. 6 shows, the bases of transistors 26 and 27 are connected to the output terminals for the above-mentioned control signal U (t) of the flip-flop 6. The base of a further transistor 28 is connected via a resistor 29 to a reference current source Vcc . The base of a fourth transistor 30 is sspannungssignal via a resistor 31 to the speed

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V (t) of the frequency-voltage converter 2 is connected. The collector of transistor 26 is connected to the base of the transistor while the collector of transistor 27 is connected to the base of transistor 28. The emitter of the Transistor 28 and the emitter of transistor 30 are each connected to the terminal on the plus side of capacitor 11, The terminal voltage of the capacitor 11 is used as one of the inputs of the second comparison circuit 5 described above used as in the previous embodiment. The other input of the second comparison circuit 5 is the wheel speed signal KV (t), which is divided by the resistors 13 and 13. The voltage of the reference power source is Vcc is set to a higher value than the wheel speed voltage signal V (t), which under normal driving conditions is obtained.

The mode of operation in this embodiment is as follows:

When the brake is not actuated, there is no control signal U (t) at the output of the flip-flop 6, which is why the transistor 26 is supplied with current, the transistor 27 is not supplied with current, the transistor 28 is supplied with current and the transistor is again not supplied with it Power supplied * Due to this, the terminal voltage of the capacitor 11 corresponds approximately to the voltage of the reference power source Vcc. When braking operation is _s when the degree of wheel speed deceleration g (t) reaches the set value (-G1) mentioned above ,, the first comparison circuit 4 is operated to j comparable to the flip-flop 6 in a given state

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set. Then the control signal U (t) is emitted so that the brake pressure decreases. On the other hand, the control signal U (t) also has the effect that no current is applied to the transistor 26, that the transistor 27 is supplied with current, that there is no longer any current applied to the transistor 28, and that the transistor 30 is also supplied with current. As a result, the terminal voltage of the capacitor 11 drops down to the wheel speed signal V (t) at this point in time. Thereafter, the terminal voltage of the capacitor 11 drops even further with the wheel speed signal V (t). When the wheel speed signal V (t) is reversed into an acceleration signal and therefore increases, the transistor 30 is no longer supplied with current and the terminal voltage of the capacitor 11 no longer drops, but is held at the voltage level of this point in time. The withstand voltage is the minimum \ v ^r ert of the wheel speed, and is one of the inputs for the second comparing circuit 5. When the minimum value of the other input that is, a split wheel speed KV (t) becomes equal to the second comparison circuit 5 is operated to the Reset flip-flop 6. Then the pressure modulator stops reducing the brake pressure, which then increases again.

The idea of the invention is therefore to store the minimum value of the wheel speed and then to save it with the itself to compare constantly changing actual wheel speed and to determine the point in time at which from a brake pressure reduction process is switched to an increase process. With such an arrangement, the probability can erroneous, caused by noise

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Control processes mentioned at the beginning of the description can be reduced to a great extent.

It should also be mentioned that the exemplary embodiments described in connection with FIGS. 1 and 3 only as Illustrations are not intended to be limiting, and that various changes and modifications may be made within the invention possible are. For example, the speed signal V (t) can be used as it is as an input signal for the second comparison circuit are used, and in the zA ^ eiten comparison circuit can be the moment in which the difference between the wheel speed V (t) and the stored minimum value of the wheel speed V (t) exceeds a given value AV is determined will. This can also be seen as a kind of comparison between two signals. Anyway, such a comparison is in view of the known electronic switching options obvious.

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Claims (9)

Expectations 1.1 Anti-lock braking control system for vehicles, g e k e η η - e i c h η e t by a device (2) for converting the wheel speed into voltage signals, a device for perception the beginning of a wheel lock, a brake pressure modulator (8), which the brake pressure (PCt)) according to one when exercising the start of a wheel locking control signal output is reduced, a hold circuit (e.g. 10, 11) for a low Peak value, which is a minimum value of the wheel speed voltage signals in a wheel speed control cycle, a comparison circuit (5) which the wheel speed voltage signal (V (t)) and the minimum value thereof given by the hold circuit is stored for the low peak value, compares and causes the brake pressure reducing operation of the Brake pressure modulator (8) is terminated when the wheel speed voltage signal and the stored minimum value thereof corresponds to a predetermined value ratio. 2.. Anti-lock control system for vehicles according to Claim 1, characterized in that the Hold circuit for the low peak value a switch means (9; 19; 26, 27, 28, 30), which is normally closed and opens after the control signal has been issued, a capacitor (11) to which the wheel speed signal is supplied while the switch device is closed, and means (10) for allowing the capacitor to discharge when the wheel speed voltage signal is below the 409886/1055 -C- closed state of the switch device drops, wherein
the terminal voltage of the capacitor one of the inputs of the
Comparison circuit (5) represents. 3. Anti-lock control system for vehicles according to claim 2, characterized in that the switch. device in connection with a brake pedal works and at Actuation of the pedal assumes an open position. 4. Antiblockiei / cgclsystem for vehicles according to claim 2, characterized in that the switch device responds to the control signal and when the
Control signal assumes an open position. 5. anti-lock control system for vehicles according to claim 1, characterized in that one of the inputs
the comparison circuit CS) is the terminal voltage of the capacitor (11), while the other input is a given rate
is reduced wheel speed voltage signal. 6. anti-lock control system for vehicles according to claim 5, characterized in that the wheel speed voltage signal is provided by a group of in series Resistors (12, 13) is reduced at a given rate. 7. anti-lock control system for vehicles according to claim 6, thereby ge k e η η ζ eic h η e t that a speed reduction sensing switch (20) which can be actuated, 409886 / 105S when the vehicle deceleration reaches a given value, such it is provided on the vehicle body that when this switch is actuated, another resistor (21) or a group of resistors is added to said group of resistors (12, 13), which makes the rate of reduction of the wheel speed voltage signal adjustable. 8. anti-lock control system for vehicles according to claim 1, characterized in that one of the inputs the comparison circuit (5) the terminal voltage signal of the Capacitor (11), while the other input is a voltage signal, the voltage of which differs from the wheel speed voltage signal differs by a given degree of voltage difference (Fig. 3). 9. Antiblockie.rregelsystem for vehicles according to claim 8, characterized in that the collector is one A transistor (16) to which a given value of a base current is applied to the output side of the speed-voltage signal converter (2) is connected, and that the potential difference between the ends of a resistor (17) between the collector of the transistor (16) and the output side of the converter (2) is connected, and through which the collector current of the Transistor flows, corresponds to the given degree of voltage difference. 4 0 9 8 8 6/1 0 B 5 Le e rs e i fe