DE1914114B2 - Control circuit for anti blocking brake system - has bistable switching circuits to provide two levels of pressure increase in response to wheel speed signals - Google Patents

Abstract

The anti-blocking brake system has two levels of modulation so that a smooth brake release is obtained over a range of retardations. The re-application of the brake pressure is also controlled in two stages so that the cyclic variation of the wheel speed is kept as smooth as possible. Simple bistable switching circuits are used to provide the two levels of pressure increase, depending on the dynamics of the vehicle wheel. The brake pressures are kept within a set amplitude so that a smoother and more effective brake control is possible.

Description

The invention relates to an anti-lock control system for jerk-actuated vehicle brakes, with a Sinaigeber, when falling below two different deceleration values due to the wheel deceleration 'emits delay signals, with an evaluation circuit, to which these signals are fed and a control valve device which receives such signals from the lUswerteschaltung be supplied that when falling below of the first delay value (occurrence of the 1st delay signal) the pressure is slow and at Falling below the second, larger delay value (occurrence of the 2nd delay signal) faster is lowered.

Such a system is known from German Auslegeschrift 11 66 012. With this system the Operating state with rapid pressure reduction, which is initiated by the second delay signal, in further course of the braking process always immediately into an operating state with a pressure increase. Of the The invention is based on the object of avoiding such abrupt changes in the printing movement and to strive for smooth wheel speed changes. This results in wheel speed profiles achieved, with the lowest possible amplitude fluctuations around the most favorable braking wheel speed curve meander and come close in their shape to a sine line.

The described object is achieved in that the signal generator additionally contains an acceleration signal (+ b) which emits an acceleration signal (+ b) when an acceleration value is exceeded by the wheel acceleration, and that the evaluation circuit contains a bistable switching device in a known manner which is connected to the Signal transmitter is connected in such a way that it is switched by the second delay signal (- bfi in its working position and Ci by the acceleration signal (+ b) in the normal position, and that the control valve device (E \, Au Ai) with the bistable switching device in its working position in such a way is related to the fact that this switching device alone causes a slow decrease in pressure.

The invention makes use of an earlier proposal to implement this concept

■ according to DT-AS 16 55 432, according to which a bistable switching device is provided, which when occurring a rotational delay of the wheel tilts into a switching state that causes the pressure to drop and only tilts back to the normal switching state when a certain rotational acceleration occurs. One A similar arrangement is also described in French patent specification 1488970. Such a bistabi-Ie However, the switching device now controls the phase of slow pressure reduction to be switched on.

Only a long delay in rotation can thus initiate such a prolongation of the pressure drop, while in the case of low rotational decelerations, the same operating state only lasts as long as the first Delay signal itself.

DT-AS 16 55 454 provides for a delay signal to be assigned a change in rotational speed A ν and for the pressure reduction to be initiated only after it has exited.

In a system with two delay signals and two operating states with slow and fast pressure reduction, it is possible to assign a separate Av to each signal. The second, caused by a strong rotation delay, receives z. B. an A ν of about 7 km / h, and the first signal, caused by a smaller delay, can receive a significantly lower Av, for example of about 3.5 km / h. As a result, the system recognizes an incipient locking process earlier than before, and even smaller turning delays are effectively corrected. On the other hand, the system is insensitive to short-term strong rotation delays,

since these can only cause a rapid pressure drop when the rotational speed has changed by a greater amount. This possibility of evaluating the delay signal including the change in rotational speed is mentioned here in order to use the term of To extend falling below a delay value to this possibility.

The embodiment shows in detail that according to the invention the duration of the operating state with low pressure reduction then does not depend on the bistable switching device, if only a first Delay signal has occurred and was not preceded by a second delay signal. In this In this case, the operating state ends when the first delay signal ceases, but then closes preferably a phase of a further operating state with constant pressure, that of a Timer is controlled with a fixed preset. One in the transmission line for the e-th delay signal Switching element switched on to the timing element is controlled by the bistable switching device in this way controlled that the timer can only cause the pressure constant if the large delay threshold has not been exceeded and thus the bistable switching device was not brought into working position.

An exemplary embodiment is explained in more detail below with reference to the drawing.

F i g. Figure 1 shows the logic block diagram of the system;

F i g. Figure 2 is a graph of wheel speed, brake pressure and electrical pulses of the block diagram;

Fig. 3 is a first valve device with four open-close valves;

4 shows a second valve device with two open-close and two two-cross-sectional valves;

Fig. 5 is a valve device for indirectly influencing pressure;

F i g. 6 is a further valve device with only three valves for directly influencing pressure, whereby also two electrical symbols explaining the block diagram of FIG. 1 are entered;

F i g. 7 shows a correspondingly modified timing diagram, and

F i g. 8 shows a further development of the block diagram according to FIG. 1.

First, let F i g. 1 together with F i g. 3 described, whereby one must think of the terminals with the same designation in the two figures as being connected to one another. A signal transmitter 1 is indicated schematically on the left. It has three outputs which are normally at ground potential, but at times carry positive potential, ie signal potential. The outputs and their corresponding signals are marked with -b \, + b and

- denotes Ö2. - b \ is the first deceleration signal that occurs as long as the rotational deceleration value of the wheel is greater than a lower limit value. - bi is the second delay signal that is always accompanied by

- b \ occurs when the rotation deceleration value is greater than an upper limit value. + b is the acceleration signal that occurs when the rotational acceleration has exceeded a lower limit but has not yet exceeded an upper limit. If the acceleration upper limit is exceeded, then disappear t>^r> det this acceleration signal. Using FIG. 2, the time relationship between the three signals and the speed of rotation of the wheel will be discussed in greater detail later.

In Fig. 1 is also a brake light switch 2 and a Brake light 3 indicated. This switch closes at the beginning of a braking process when the Brake pressure a few bar, e.g. B. three or four bar, exceeds.

At connection point 4 of the brake light and brake light switch there is positive potential when the switch is open and ground potential when the switch is closed. The circuit has four outputs ei, ei, a \ and at. These are shown in FIG. 3 connected to solenoid valves located in the hydraulic pressure line system, which are correspondingly designated with capital letters. The main brake cylinder (not shown) of the brake system or the other controlled pressure source is connected to the pipe 5, the wheel brake cylinder is connected to 6 and an outlet line, if necessary a return pump, is connected to 7 between 5 and 6 are the two inlet valves E 1 and £ 2, between 6 and 7 the two outlet valves A 1 and A _2, each in a parallel arrangement. A flow restrictor 8 or 9 is connected in series with one of the two pairs of valves.

The block diagram contains a flip-flop, which embodies the bistable switching device 10 here. It has two entrances on the left and two exits on the right. The signals at the two outputs are always opposite to one another. If the signal marked with k is "0" at the lower output, then the signal at the upper output is "1". This is the normal position of the flip-flop. In the working position, the two output signals are reversed. The + b- output of the signal generator is connected to the upper input and the -62 output to the lower input of the bistable switching device 10. A branch of the - bi- output also leads to terminal a ₂ . The it output of the bistable switching device 10 is connected to one input of an OR element 11, while the second input of this OR element is connected to the -61 output of the signal generator. The - fti line also leads to the input of an AND element 12, the second input of which is connected to the upper output of the bistable switching device 10. The output of the AND element is connected to a monoflop 13, at the output of which the signal m occurs. It is fed to an OR gate 14. The output of this OR gate 14, which is equipped with three inputs, leads to terminal e _t . As indicated by the arrow in the monoflop symbol, the signal m is normally "0". Only when an impulse occurs at the input of the monostable multivibrator 13 does the monostable multivibrator tilt so that the signal m then becomes "1". After a certain hold time, the monoflop falls back. If a signal of a longer duration is present at the input of the monoflop, the monoflop also tilts and cannot fall back earlier than the input signal disappears. In particular, the monoflop is designed in such a way that the duration of the signal m after the input signal has disappeared at the monoflop is always the same and is therefore independent of the duration of the input signal.

The other two inputs of the AND element 14 are connected to the -I- ύ output of the signal generator and to the terminal a _x . Finally, a second bistable switching device (flip-flop) 15 is also provided, which also has two inputs, but only one output connected to the output terminal ej. In the normal position of this flip-flop, the output signal is "0". This position occurs as long as it does not

is braked or only braked so much that the anti-lock control system does not come into action. Of the The upper input of the flip-flop is with the connection point 4 between the brake light 3 and the associated brake light switch 2, while the lower input is connected to the - öi output of the signal generator lies.

First of all, with reference to FIG. 2 explains the mode of operation of the signal generator 1, which is known per se. in the The diagram at the top shows how the speed Vf of the vehicle to be braked is slow but decreases evenly.

The circumferential speed vr of a vehicle wheel is plotted below this. As long as there is no braking (all the way to the left), the wheel circumferential speed is the same as the vehicle speed. The recorded wheel speed profile is then obtained during the braking process, during which the wheel speed is always lower than the vehicle speed. The wheel speed curve is ultimately the result of the pressure influencing brought about by the anti-lock control system. At first, the curve was simply accepted. It should only be made clear that the signals entered in the first three lines of the signal diagram appear on the signal transmitter. As long as the wheel speed drops and the steepness does not exceed a certain level, the signal - b \ occurs. This is the case immediately at the beginning of the braking process, then the wheel speed recovers and then a very steep descent follows. During this steep drop, a second limit of the wheel deceleration is briefly exceeded, and the signal - & ■ In order for the signal + b to arise, the wheel speed must reach a certain steepness during the acceleration times. This is not the case in the first half of the chart, but it does so when it rises again in the second half. It is a special feature of the signal transmitter described here that the signal + b also becomes "0" again when the increase in wheel speed is particularly steep. There are therefore two individual + fe pulses in the diagram, in each case as long as the steepness of the increase in wheel speed assumes average values.

The description of the mode of operation of the anti-lock control system now takes place with the addition of the brake pressure P and the other recorded signals. The signals at the output terminals of the logic evaluation circuit give in connection with the respectively selected valve device, initially the one according to FIG. 3, the valve positions again and with it the pressure movement tendency. Since the inlet valves E \ and Ei are normally open, signal "0" at terminals ei and & means "valve open" and the signal "1" at these terminals means "valve closed". The opposite is true for the exhaust valves A \ and Ai. Signal "1" at terminals a \ and ai means "valve open" here.

At the beginning of the braking process, the flip-flops and the monoflop of the evaluation circuit are in the normal position. All signals are "0". The brake pressure P , initially controlled solely by the driver, rises steeply since both inlet valves are open and both outlet valves are closed. The brake light switch 2 closes even at a very low brake pressure, that is to say at a point in time which is still outside the diagram. The brake light now lights up, but the change in potential at terminal 4 has no effect on the logic system, since the bistable switching device (flip-flop) 15 is in its normal position anyway.

The first appearance of the -b \ signal has three effects. The flip-flop 15 toggles and generates there «signal e ^. The monoflop 13 is triggered via the AND element 12, at whose second input a signal is present from the flip-flop 10. It generates the signal π and this via the OR gate 14 the signal ei Finally, the signal a \ is generated via the OR gate 11. The output signals mentioned cause there; Closing both inlet valves and opening de; throttled exhaust valve A \. As a result, the pressure will slowly decrease. As a result of this Druckabsenkunj; the wheel catches up again and the signal - b \ ends. Accordingly, a \ ends, the outlet valve closes and the pressure in the wheel brake cylinder is kept constant, since the line 6 to the wheel brake cylinder on all sides; is completed.

With the disappearance of - b \ , the stopping time T of the monoflop 13 begins, which is entered in the diagram by a double arrow. After this time has elapsed, the monoflop falls back, and with m also ends ei, se that now the throttled inlet valve E \ opens. The pressure increases slowly. One must imagine that the wheel gets on a slippery place of driving Bahr and for this reason the Radgeschwindigkei first slowly and then faster and faster decreases Even now appears the signal -b \ with the entspre sponding and already discussed consequences now. The slow pressure drop is not enough to stop the falling wheel speed. There is a risk of the wheel locking. The signal - bi, which now appears, therefore causes the signal a ₂ and opens the unthrottled outlet valve A2. The pressure now drops quickly. At the same time, however, the bistable switching device 10 is also tilted into the working position a \ is now also caused by k , while da! AND gate 12 blocks and thus the hold time de; Monoflop 13 begins.

The rapid reduction in pressure causes the Rac is caught quickly and - bi soon disappears thus also the second exhaust valve A2, di "includes bistable switching device 10 tilts but not yet returned ir the normal position. The throttled outlet valve is still open, as I said, as a result of the signal - b \ on the one hand and independently of it as a result of the signal Jt on the other hand. In the further course, the hold time T and thus the signal m end, but this has no effect since the signal ei as a result of the line connection between the terminal a \ via da; OR gate 14 with terminal egg is further maintained. Without this connection, the pressure would rise again in this intermediate stage in which neither an acceleration nor a deceleration signal is present. As it is, however, the pressure continues to drop slowly, until de! + ö signal. While at the beginning of the braking process there was no - fc signal before, di «

w) the slow pressure drop ended together with the -61 signal, it now only ends when it appears before + b.

The + £> signal now takes over the further locking of the inlet valve E \ and tilts the bistable switching forwards

os direction 10 back to the normal position. Then a \ disappears and the outlet valve closes, while, on the other hand, the AND element 12 is being prepared to allow future -Ö signals to pass through to the monoflop 13

The pressure initially remains constant until the + ö signal disappears, which is why this is the case here happens because the wheel speed increases particularly steeply. This is due to an increase in pressure encountered opening the throttled inlet valve Ei. As soon as the wheel speed curve becomes flatter again, Ei closes again and the evaluation circuit waits so the further development from. However, there is no further steep increase because the vehicle speed has already been largely achieved. Thus, the second H-i> pulse ends as the lower one falls below the limit Acceleration limit value, with which the desired rotational state of motion of the wheel is reached and the Control cycle has ended. The brake pressure now continues to rise and subsequently becomes another Lead control cycle.

After the end of the braking process, i.e. when the driver takes his foot off the brake, and the Brake pressure drops to its minimum operating value, the brake light switch 2 also opens, which then a signal arrives at the upper input of the bistable switching device 15 and this also enters the Normal position tilts back.

At this moment, which is no longer shown in the diagram, is the initial state of the Anti-lock braking system achieved again. The one on the left in the The steep pressure increase shown in the diagram therefore only occurs once at the beginning of a braking process. In order to becomes the conditions at the beginning of a braking process, where a relatively large one Pressure medium volume in the wheel brake cylinder must flow around the sealing sleeves and in the system to stretch switched on line hoses, best met.

FIG. 4 shows an alternative to the valve device according to FIG. 3, with the difference, however, that only two really tightly closing valves Ej and A [are required. The two cross-sectional valves Ei and Ai shown are to a certain extent only adjustable flow restrictors. As described in more detail in the case of Ei , they consist of a cylinder 16 with two opposing line connections and a piston 17 which is movable in the cylinder and has a circumferential groove 18 of very small cross-section. The piston is connected via a piston rod to a magnet armature 19, which is attracted by a coil 20. In Ei the line connections are on the left side of the cylinder, so that when the winding is not energized, the piston 17, which is held in its right end position by a spring 21, does not hinder the free flow between the two line connections. When the coil 20 is energized, however, the piston is on the left, and now its circumferential groove throttles the flow area. In the case of valve Ai , the line connections are attached to the right half of the cylinder, and accordingly the flow is throttled here when the winding is not energized (normal pitch). The same signal combinations at terminals Ci, C2, <ii and aj thus cause the same pressure movements as shown in FIG. 2 are shown.

The same is achieved with the help of indirect pressure influencing according to Fig. 5. Here, a normally open inlet valve E2 is connected between a line 22 for liquid pressure medium, which is connected to the master pressure cylinder or another pressure source controlled by the driver, and a line 23 which leads to the wheel brake cylinder. A liquid cylinder 24, in which a liquid piston 25 moves, is also connected to the wheel brake cylinder. This is connected via a piston rod to an air piston 26 of larger diameter, which moves in an air cylinder. It divides this air cylinder into an air chamber 27 and a vacuum chamber 28 with a vacuum connector 29. A spring 30 presses the double piston formed in this way to the left into the position in which the liquid cylinder has its smallest content. The air chamber 27 communicates via two normally closed valves, namely A \ "and Ai ', which are formed here as air valves, and through two filter 31st the two valves are located with the atmospheric air in conjunction parallel to each other, and the first valve A ] " is also provided with a throttle 32. Finally, a normally open air valve Ei "is switched on in a bypass line which connects the air chamber 27 with the vacuum chamber 28 at the ends of the cylinder.
The device according to FIG. 5 works as follows:

In the first operating state, the brake pressure is built up very quickly in a direct way, namely when the inlet valve E2 is open. However, this valve is closed during a control process. It can therefore also be replaced in a manner known per se by a ball valve which is pushed open by the liquid piston 25 in its extreme left position and is always closed when this piston is not in its extreme left position. The spring 30 is dimensioned so strongly that the double piston remains in the left position even when the brake pressure is greatest, provided that there is no pressure difference on the air piston. The operating state with slow pressure reduction also requires the signals ei and a \. e \ closes valve Ei "so that the air and vacuum chambers are now separated from one another. A small passage opening 33 in the piston will be mentioned later. The signal a \ opens the throttled air valve A \". To the extent that air flows into the air chamber 27, the moves

AQ double piston to the right. As a result, the capacity of the liquid cylinder 24 is expanded and the brake pressure is correspondingly reduced. If A2 ″ is also opened, then more air flows into the air chamber 27 and the pressure reduction is correspondingly faster

4 ^r i in front of you. This is the third operating state. The fourth operating state "slow pressure increase" occurs when both valves A " and A2" are closed, but valve Ei "is open. Now the pressure difference between the air chamber and the unpressure chamber can equalize, so that the spring 30 now follows the double piston The fifth operating state "hold pressure" is obtained if the passage opening 33 in the air piston is missing and all valves are closed

^In this situation, r> 5 air piston can stop in all intermediate positions. However, as a result of leaks that cannot be completely avoided, a very slow movement will occur anyway. In order to create defined relationships here, it is advisable to

M) as known per se, to provide the passage opening 33, so that when all valves are closed, the piston moves extremely slowly to the left and the pressure increases accordingly. The passage opening can easily be dimensioned in such a way that

h ^r i that the pressure increase is still significantly slower than the slow pressure increase according to the Dnick diagram of FIG. 2. This operating state can then easily be described as " hold pressure". These too

The valve device is electrically connected to the evaluation circuit according to FIG. 1 and works as there described.

In Figure 6 is finally a fourth embodiment a valve device is shown which has only three valves and therefore not easily connected to the four terminals the evaluation circuit according to FIG. 1 can be connected. Fig. 6 therefore also contains a small one Extension of the logical system that enables such a connection.

The valves E \ in the inlet and A \ in the outlet line correspond to the valves according to FIGS. 3 and 4. They are also connected to the terminals ei and a \ as there. The third valve Z is normally open and is in the line leading to the wheel brake cylinder. A flow throttle is arranged parallel to Z. As already mentioned, this valve and its parallel throttle could also be replaced by a two-cross-section valve such as E. " According to FIG. 6, the terminal 32 is connected to the input of an inverter 34, the output of which is at one input of an AND element 35. At the other input of the AND element, terminal & i is connected and the output that carries signal ζ controls valve Z

The five operating states of this valve device are as follows: When Z is closed, the pressure will slowly rise or fall slowly depending on the position of E \ and A \. If Z is open, the pressure will rise or fall quickly accordingly. When both valves E \ and A \ are closed, the pressure remains constant, regardless of whether Z is open or closed.

F i g. 7 shows the signal z as it results from ^ and .72, where ei and ai from FIG. 2 are simply taken over. If & i and ai are at "0", then Z is also at "0". If only & 2 is on "1", then ζ is also on "1", since the AND gate 35 has a signal at both inputs. If, on the other hand, ei and ai are at "I", ζ goes back to "0". This is the case during the - ^ - signal during the strong rotation deceleration. So it opens and the pressure can drop steeply. Overall, the valve device according to FIG. 6 achieves the same pressure curve as in FIG. 2 is drawn.

After the anti-lock control system has been explained using the example of FIG. 1 and various valve devices, some further developments of the invention shown in FIG. 8 will be discussed below. In order to understand these developments, one must be aware of the processes involved in braking, ie when the pressure first rises before the anti-lock control system is activated. The brake pressure should be built up quickly and unhindered, which is why it must be ensured that initially both inlet valves E \ and Ei remain open. However, there is a risk that this first pressure increase will be impaired by the -or or + ö signal, which could be caused by an uneven road surface or by a strongly changing coefficient of friction on the road surface. The + ö signals can occur particularly easily because their response threshold is kept particularly low. As previously described, however, the + ö signal cause the inlet valve £ Ί to close and thus at least prevent the initial pressure increase. It is therefore proposed to connect an AND element 39 (gate circuit) in the -t-ö channel between the signal generator 1 and the OR element 14, which is connected with its second input to the output of the bistable switching device 15. In FIG. 8, this additional AND element 39 is permanently entered in addition to a further AND element 38 and a time delay element 37.

Otherwise, FIG. 8 is identical to FIG. 1. So as long as the bistable switching device 15 is in its normal position, a possible -fö signal cannot be sent to the OR element 14 and thus penetrate to the inlet valve Ei. Rather, this is only possible when there is a - fei signal has occurred and the bistable switching device 15 has tilted into its working position.

But there is also a - ii signal during braking can already occur, that does not help much. The first -öp signal flips the bistable Switching device 15 and thus closes the inlet valve £ 2, which usually has the larger cross-section. It will therefore provision is made for a time delay element 37 to be connected upstream of the flip-flop 15. Only when the input signal If this time delay element has lasted for a delay time inherent to this element, an output signal appears. A —fti signal can thus affect the bistable Switching device 15 will only be effective if it holds a long delay.

■ to finally also an undesired closing of the inlet valve Ei as a result of a - öi signal on the To prevent ways via the monoflop 13, there should be another AND element 38 between the monoflop and the OR gate 14 are turned on. Its second input is just like that of the AND gate 39 to be connected to the output of the flip-flop 15. There is certainly no problem with the delay time of the member 37 to be dimensioned so that with certainty all interference signals are filtered out and thus all Obstructions of the pressure increase when braking can be avoided.

For this purpose 3 sheets of drawings

Claims (3)

Patent claims: 1.Anti-lock control system for pressure medium-operated vehicle brakes, with a signal generator that emits deceleration signals when the wheel deceleration falls below two different deceleration values, with an evaluation circuit to which these signals are fed and a control valve device to which such signals are fed from the evaluation circuit that if the value falls below the first delay value (occurrence of the 1st delay signal) the pressure is lowered slowly and when it falls below the second, larger delay value (occurrence of the 2nd delay signal) faster, characterized in that the signal generator (1) in a known manner, an additional one when one is exceeded Acceleration value by the wheel acceleration contains an acceleration signal (+ b) emitting acceleration sensor and that the evaluation circuit (10 to IS) contains a bistable switching device (10) in a known manner, which with the signal generator (1) of the art is connected that it is switched into its working position by the second delay signal (- fc) and into the normal position by the acceleration signal (+ b) and that the control valve device (Eu A \, A ₂ ) with the bistable switching device (10) in its working position is connected in such a way that this switching device (10) alone causes a slow pressure reduction. 2. Anti-lock control system according to claim 1, characterized in that the bistable switching device (10) is connected to a switching device (12) which is switched on in the transmission line for the first delay signal (- b \) to a timing element (monoflop 13), and which blocks the transmission line when the bistable switching device (10) is in the working position and that the timing element (i'3) is connected to the valve device in such a way that after the end of the first delay signal (-61) the valve device (Eu A _u A ₂ ) goes into a “hold pressure” operating state for a specified time (T). 3. Anti-lock control system according to claim 2, characterized in that the timing element (13) is followed by a gate circuit (38) which is connected to a second bistable switching device (15) which blocks this gate circuit (38) in its normal position, the second bistable switching device (15) is brought into the working position by the first delay signal (- b \) and into the normal position by a signal generated when the brake light switch (2) is opened.