WO1997008029A1

WO1997008029A1 - Method for improving the control characteristics of an antilocking system (abs)

Info

Publication number: WO1997008029A1
Application number: PCT/EP1996/002907
Authority: WO
Inventors: Ivica Batistic; Robert Schmidt
Original assignee: Itt Automotive Europe Gmbh
Priority date: 1995-08-23
Filing date: 1996-07-03
Publication date: 1997-03-06
Also published as: EP0844955A1; JPH11511411A; DE19530902A1; DE19530902B4

Abstract

The purpose of the invention is to improve the control characteristics of an antilocking system (ABS), in particular in the event of a sharp reduction in wheel contact force following passage over a bump in the road or similar disturbance in the road surface. During an ABS control cycle following partial braking, if the brake slip exceeds a predetermined limit and lasts longer than a predetermined minimum period, a product (P1,2) is calculated from the maximum brake slip and the period (Δt) from the commencement (t1) of instability until the wheel reversal point (t2). If the product (P1,2) exceeds a predetermined limit (Pgrenz), the brake pressure on the affected wheel is allowed to build up again during the subsequent stable control phase with a steeper gradient by comparison with a normal control cycle.

Description

Process for improving the control behavior of an anti-lock braking system

The invention relates to a method for improving the control behavior of an anti-lock braking system (ABS), in particular in the case of a strong reduction in the wheel contact force due to a so-called jumping hill, a roadway depression or the like. In such a method, the rotational behavior of the individual wheels is measured and evaluated to determine a vehicle reference speed, wheel slip and other control variables which are used to measure and / or modulate the brake pressure in the wheel brakes of the controlled wheels.

Anti-lock braking systems (ABS) with electronic control are known in a variety of designs and on the market. In the vast majority of systems, the information required for the control is obtained by measuring the rotational behavior of the individual wheels, whereby a logical reference of the vehicle speed is determined by logically linking the wheel rotation signals, which then is used as a reference variable for determining the wheel slip and other control variables and finally can be used to measure or regulate the brake pressure in the wheel brakes. It is not always possible to recognize the actual control situation from the information provided by the wheel sensors and to consequently control the brake pressure if the interpretation of the wheel turning behavior does not allow a clear statement of the current situation. In addition, with the pressure modulation which the ABS controller carries out on the basis of the installed control philosophy as a function of the wheel turning behavior, contradictory requirements for wheel stability - by pressure relief - and short braking distance - by the highest possible brake pressure - have to be met.

A particular problem with an anti-lock braking system is the relatively strong reduction in brake pressure that can occur if the vehicle during partial braking, i. H. reaches a so-called jumping hill, a roadway depression or the like during a normal, unregulated braking operation. Such a lane disruption, namely when the wheel rebounds as a result of this disruption, leads to a large reduction in the wheel contact force, which the ABS control tries to compensate for by strongly reducing the pressure on this wheel. This reduction in pressure leads to an undesirable reduction in braking efficiency and thus to an extension of the braking distance.

The invention is based on the object of improving the control behavior of an ABS in such a situation and, in particular, of eliminating the undesirable effects of such a control process caused by the wheel contact force.

It has been shown that this object can be achieved by the method described in claim 1, the special feature of which is that when a blockage protection control process is initiated following partial braking and the occurrence of a brake slip which occurs over a predetermined limit value and lasts beyond a predetermined minimum time period, individually for each wheel, in particular each front wheel, the product of the maximum brake slip and the time period from the beginning of the instability to the wheel reversal point, namely until the occurrence of a wheel re-acceleration which is above a predetermined limit value ¬ supply, and that if the product exceeds a predetermined limit value, the brake pressure on the affected (front) wheel is built up in the subsequent stable phase with an increased gradient.

The loss of braking distance or loss of deceleration as a result of the previously described effects of a "jumping hill" or the like occurs in an ABS control only in the subsequent phase of the braking process, in which the wheel is running again stable, because the brake pressure at a normal pressure build-up rhythm with a relatively flat one Gradient or pulse-shaped. The invention is therefore based on the knowledge that the presence of a "jumping hill" situation can be recognized and that the undesirable effects of this situation can be compensated for by subsequent rapid pressure build-up.

A number of particularly advantageous exemplary embodiments of the method according to the invention are described in the attached subclaims.

The increase in brake pressure with an increased gradient is expediently only permitted when the acceleration or re-acceleration of the wheel concerned reaches a value which is proportional to the maximum slip of this wheel and is above a predetermined minimum acceleration value. For example, a brake slip limit value in the order of magnitude between 10 and 20 km / h or between 10 and 20 is expedient % of the vehicle speed, whereby it can be specified that the larger of these two values is decisive. For the minimum period during which the brake slip should be above the limit, a period of 100-300 ms, depending on the control system, may be appropriate.

The increase in the brake pressure build-up gradient required in accordance with the invention can be brought about in a control system which controls the brake pressure with variable pulse sequences by "shortening" the pressure build-up pulse row or by temporarily switching to non-pulsed pressure build-up.

The rapid brake pressure build-up or pressure build-up according to the invention with an increased gradient following a pressure relief caused by diving hill can result in undesirably high yaw moments in certain situations and / or in certain vehicle designs. According to a particularly advantageous embodiment of the invention, it is therefore provided that a jumping hill in the subsequent stable phase results in a rapid pressure build-up on a front wheel, the pressure build-up on the second wheel of this axle using the same or perform approximately the same gradient. This overcomes the risk of excessive yaw moments.

Furthermore, according to the invention, if a front wheel passes a jumping hill, a depression or the like and the described jumping hill function is triggered thereby, the brake pressure gradient on the rear wheel on the same side of the vehicle is also increased, because the rear wheel also passes this jumping hill or this road disturbance becomes. However, in most cases it should be useful to reduce the brake pressure build-up gradient on the rear wheel to a lesser extent than the gradient of the front wheel. heights in order not to endanger the stability of the rear wheel, which is particularly critical for the driving stability of the vehicle.

Further features, advantages and possible uses of the invention will become apparent from the following description of details with reference to the attached figures.

Show it

1 shows the essential electrical / electronic components of an ABS for carrying out the method according to the invention,

Fig. 2 is a flow chart to explain the operation of the system according to Fig. 1 and

Fig. 3 in the diagram of the wheel course and pressure course in a special control situation.

1, the rotational behavior of the individual wheels is measured with the aid of wheel sensors S1 to S4 in an anti-lock braking system of the type in question here. In a conditioning circuit 2, wheel signals Vi - v _{4 are} obtained from the signals from the sensors S1-S4, which in the form of electrical signals or, if the further processing takes place with the aid of program-controlled circuits, such as microcomputers, microcontrollers or the like, in the form of data are available.

The time derivatives of the speed signals Vx-v _{4 are} formed in a known manner in a signal processing circuit ₃ . Of particular interest are the first and second temporal derivatives Vi - v ₄ and Vj - v ₄ as well as the wheel-specific slip λl - λ4, the formation of which is combined in one dindividual slip λl - λ4, for the formation of which the vehicle reference speed v _REF determined in a circuit 4 is required.

All the signals mentioned are further processed in an ABS logic circuit 5, which calculates brake pressure control signals using extensive calculations based on complex algorithms and feeds them to a symbolically illustrated valve block 7 via a valve control circuit 6. In the case of an anti-lock hydraulic brake system, this valve block 7 comprises numerous electrically actuable hydraulic valves with which the brake pressure in the individual wheel brakes can be controlled and regulated in the desired manner.

Essential for the method according to the invention is an additional or computing circuit 8, which of course, if the circuit according to FIG. 1 is implemented by a program-controlled circuit, is implemented by corresponding program steps or by a subroutine.

In the additional or arithmetic circuit 8, for each wheel, in the present exemplary embodiment for each front wheel (wheel 1, wheel 2), a product of the maximum slip λχ _{f 2} max ^unc * from the time occurring on the respective wheel ¬ span from the beginning of instability (t ^) or from the onset of the anti-lock control to the wheel turning point (t ₂ ). In this exemplary embodiment, this wheel reversal point is identical to the point in time of the occurrence of a re- _acceleration (a _R > a _limit ) which is above a predetermined limit value. The product P is thus calculated according to the formula p,., = Kx [t (VREF - v _Rlf2 ) max] = k X [t X λι ₍ 2 maxJ educated .

When this product P _gren a predetermined limit value P z exceeds, this is achieved according counted and des¬ semi initiated a countermeasure by the booster circuit 8 or by the ABS logic 5 as a criterion for the detection of a jump hill or the triggered by such track error control behavior . According to the invention, the brake pressure is therefore built up on the front wheel concerned in the stable phase, which follows the instability phase triggered by the jumping hill, with an increased gradient compared to a "normal" anti-lock control system. This increased gradient can be brought about in a control system which works with variable pulse sequences by "shortening" the pressure build-up pulse row or shortening the pulse pauses or even by transitioning to the non-pulsed pressure build-up.

The "jumping hill" function according to the invention is primarily used to improve the control behavior of the front wheels because, as is known, the contribution of the front wheels to braking is higher than the contribution of the rear wheels and because priority is given to the stability of the rear wheels for safety reasons. In principle, however, the measures proposed according to the invention can also be used for pressure modulation on the rear wheels.

The method according to the invention is based on the knowledge that the undesirable pressure relief caused by the jumping hill effect can be sensed by measuring the wheel slip and the period of time during which this wheel is in slip. Slip above 15 km / h or above 15% of the vehicle speed is critical. In one exemplary embodiment of the invention, the minimum time period which indicates the jumping hill effect is approximately 200 msec. The specified limit values for the use of the special jumping hill regulation are derived from the aforementioned empirical values.

The wheel reversal point has proven to be particularly suitable for determining and carrying out the special control measures described. In this situation the wheel runs slower than the vehicle, which means that this wheel contributes to the braking effect. The pressure in the wheel brake can be controlled or increased until a stable phase is reached, in which the wheel is approximately as fast as the vehicle. It proved to be effective. B. a shortening of the pressure build-up pulse series of 700 msec. to 400 ms. The minimum value of the acceleration due to acceleration, at which the rapid increase in pressure started, was approximately 12 g in one embodiment, that is to say 12 times the acceleration due to gravity.

The build-up of brake pressure with an increased gradient is only permitted if the acceleration of acceleration of the wheel exceeds a predetermined limit value a limit _that exceeds a minimum value of z. B. 12 g and increases proportionally to the maximum slip ax of the wheel concerned.

The following must therefore apply: ^a limit ^{> a} min r ^z • ° • ^a min ⁼ 12 g, ^a limit ^> * ^x ^ 1,2 max «

According to a further exemplary embodiment of the method according to the invention, in principle or in certain situations when the described special jumping hill control is used, which leads to the faster pressure build-up on the affected (front) wheel, the pressure build-up on the second wheel of the axle is simultaneously reduced subject to the same regulation scheme. The pressure build-up on this second wheel will also increase shortened in order to prevent or reduce the occurrence of yaw moments due to the uneven pressure increase on the two wheels of an axle. This compensation measure is achieved in the exemplary embodiment according to FIG. 1 by a compensation circuit 9, which compares the products determined individually for the two front wheels or the control measures and intervenes in the control process by activating the ABS logic circuit 5 if there is a risk that a too high yaw moment could arise.

With the aid of the circuit 9, it can also be arranged that, when a front wheel passes a jumping hill, the brake pressure control on the rear wheel of the same side of the vehicle is modified in a suitable manner.

2 shows the described logical linkage of the individual conditions using an example. After the START of the program loop shown here, step 10 first asks whether partial braking is present. If so, if this partial braking is followed by an ABS control process (11) and if a minimum re-acceleration of the affected wheel is determined (12), operation 13 starts the calculation of the product P _lf2 ^{for the} front wheel concerned.

If the product Pj, _f2 exceeds the specified limit value ^p _g renz ^unc *, the acceleration of acceleration of the wheel a _{R is} above the limit value a _limit , the decision-making process leads to the

Branches 14 and 15 to action 16, which leads to a shortened or permanent pressure build-up, in any case a pressure build-up with a higher gradient than in the normal case. This is the mode of operation already described with reference to FIG. 1.

If the conditions queried in the individual branches are not met, or is the permanent pressure build-up

ERSÄΓZBLÄΓT (RULE 26) close, the decision-making process leads back to the START of the loop and thus to the query repetition.

Fig. 3 serves to illustrate a situation in which the "jumping hill" special control to improve the ABS control behavior comes into play. The upper curve, almost a straight line, shows the vehicle speed or vehicle reference speed VREP. The speed v _R one

The front wheel, which passes the jumping hill, initially deviates only slightly from the reference speed

from. The course of the pressure d _R in the wheel brake of the wheel, the speed of which represents the curve v _R , is also shown in FIG. 3. Finally, the road is symbolically shown to show that at time t _x by a

Roadway depression (following a hill) which uses the strong wheel contact force reduction characteristic of a diving hill.

The wheel or front wheel, to which v _R and d _R relate, is found in the control from about time t ₀ . An uncontrolled partial braking has preceded it. At time t _x , a control phase begins, in which the wheel lock ΔV exceeds the predetermined limit value and the time period Δt until re-acceleration or until the wheel is reversed at time t ₂ becomes so great that the product

P _R = k Δ _t X λ _ft nax exceeds a predetermined limit value. Since at this point in time t ₂ the wheel re-acceleration a _{R is} above a predetermined limit value a _limit , with a _limit z. B. 12 g can be carried out, after the instant t _{2 there is} an unpulsed pressure control and thereby a faster activation the brake pressure d _{R increased} . The pressure rise occurring in "normal" control is shown by a dashed line at t ₂ and is designated d ' _R. Following t ₃ , the pressure d _R in the wheel brake under consideration initially remains constant, which can be followed by further pressure corrections by the "normal" anti-lock control system.

Essential to the invention is the massive brake pressure build-up achieved by the shortened, rapid pressure increase in the time span between t ₂ and t ₃ , by means of which the strong brake pressure reduction caused by the jumping hill effect which occurs at time t _{A is} reversed at an early stage and this avoids an "unnecessary" braking distance extension of the vehicle.

Claims

claims

Method for improving the control behavior of an anti-lock braking system (ABS), in particular in the event of a strong reduction in the wheel contact force due to a so-called jumping hill, a roadway depression or the like, in which the rotational behavior of the individual wheels is measured and for determining a vehicle reference speed, wheel slip and others Control variables are evaluated, which are used for dimensioning and / or modulating the brake pressure in the wheel brakes of the controlled wheels, characterized in that when a blockage protection control process is initiated following partial braking, ie an uncontrolled braking process, and The occurrence of a brake slip which is above a predetermined limit value and lasts beyond a predetermined minimum period of time, the product (Pι _f2 ) from the maximum for each wheel individually

Brake _slip (λ _lf2max ) and the period from the start of the

Instability or from the onset of the ABS control to the wheel turning point, namely until the occurrence of a re-acceleration (a> a _limit ) above a predetermined limit value according to the relationship

P = kx (tx λ _lf2max ) is formed and that if the product (Pι _{/ 2} ) exceeds a predetermined limit (P _limit ), the

Brake pressure (d _R ) is built up on the front wheel in question in the subsequent stable phase with an increased gradient compared to a "normal" control.

2. The method according to claim 1, characterized in that the brake pressure build-up is only permitted with an increased gradient when the acceleration or re-acceleration (a _R ) of the wheel concerned leads to maximum slip (λi _2na χ) of the wheel proportional reaches a predetermined acceleration minimum value (a _m i _n) lying value.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that a brake slip in the order of 10 km / h and 20 km / h or in the order of 10% to 20% of the vehicle speed or the larger of the two values is specified as the brake slip limit value.

4. The method according to one or more of claims 1-3, characterized in that a time period in the range of 100-300 ms, preferably 150-250 ms, is specified as the minimum time period.

5. The method according to one or more of claims 1-4, characterized in that this is used exclusively to improve the front wheel control.

6. The method according to one or more of claims 1-5, characterized in that the method for improving the control is only activated when the vehicle deceleration during partial braking exceeds a predetermined limit.

7. The method according to one or more of claims 1-6, characterized in that in an anti-lock control system in which the pressure build-up is controlled by variable pulse sequences, the increased Brake pressure build-up gradient increase pulse row by "shortening" the pressure _¬ or is caused by transition to ungepulstem pressure buildup.

8. The method according to claim 7, characterized in that the shortening of the pressure build-up pulse row is maintained until the occurrence of the next instability or biε for reinserting the control on the wheel concerned.

9. The method according to one or more of claims 1-8, characterized in that when increasing the pressure build-up gradient for the purpose of improving the control, a pressure build-up on the second wheel of the same axis with an at least approximately the same gradient follows.

10. The method according to one or more of claims 1-9, characterized in that when the pressure build-up gradient is increased for the purpose of improving the control on a front wheel, the pressure build-up gradient on the rear wheel of the same vehicle side is also increased.