JP2005510402A - How to improve the control status of anti-lock brake control system when braking with large coefficient of friction - Google Patents

Abstract

In a method for improving the control state of an antilock brake control system (ABS) during braking with a large coefficient of friction, a brake pressure control threshold, in particular an intervention threshold or start of use threshold of the antilock brake control system (ABS) However, it is dynamically changed in accordance with the adhesion characteristics of each wheel or tire.

Description

  The present invention relates to a method for improving the control state of an anti-lock brake control system during braking with a large coefficient of friction.

  Anti-lock brake control is performed over the entire friction coefficient range from a very small coefficient of friction on ice (μ <0.1) to a large coefficient of friction on dry asphalt (μ≈1).

  In order to achieve the shortest possible braking distance, the anti-lock brake control system (ABS control system) does not operate when braking on roads with a large coefficient of friction before the maximum value of the so-called μ-split curve is achieved This is very important. On the other hand, ABS control systems do not take advantage of tire potential. The tire effectively prevents the development of the μ-split curve, and the sticking ability of the tire is not fully utilized.

  To avoid this, the ABS braking control threshold or control start threshold must be designed with a large coefficient of friction according to the actual situation.

  Recently, industry publications have increasingly evaluated brake performance, particularly brake performance or distance on dry asphalt, as an important criterion for the quality of the ABS system being tested. Therefore, most automakers value this test.

  In some of these tests, the vehicle has a very large deceleration value. The same vehicle with different tires shows very different braking performance in similar tests.

  Of course, a difference in performance may occur due to different measurement conditions due to, for example, a difference in road friction coefficient.

  However, by proper inspection, it has been found that the strength of frictional coupling of some tires, that is, the size of μ that can be transmitted in the μ split curve is different. This fact resulted in significant differences in braking performance between different tire marks and tire types, even under the same conditions (ie, the same vehicle, the same test road, the same air conditioning conditions, etc.).

  It is important to handle different tires so that the potential of each tire is utilized as much as possible. On the one hand, this should not over-brake the tire with a small transferable adhesion coefficient (μ) (ie, ABS control should be started late and brake slip should not increase) ) On the other hand, the braking of tires with a large μ that can be transmitted should not be too weak (ie no brake slip should occur due to premature use of the ABS troll) Is). The ABS control system should be designed so that all tires are optimally controlled.

The anti-lock brake control system (ABS system) used in large quantities does not include a longitudinal acceleration sensor except for some all-wheel drive vehicles. Therefore, detection of the maximum deceleration depending on the road is only possible with the wheel speed signal. While the wheels are not braked, the detection of vehicle deceleration has no special problems. However, the situation is different for full braking. This is because the wheels slip. In this case, the vehicle speed and the vehicle deceleration a _FZ = Δv _FZ / Δt are approximately detected according to a known method by detecting the wheel rotation state of each wheel, logically combining them, and selecting a predetermined control phase. The

  In the case of an anti-lock brake control system, the deceleration a = Δv / Δt is determined according to a known method or measured by a longitudinal acceleration sensor to indicate an input value within a progressive period. This novel period is used to calculate a control threshold value and a control start threshold value for anti-lock brake control (ABS control). Deceleration and so-called negative feedback determine the use of ABS control. Negative feedback indicates a wheel deceleration value that has not yet deviated from the stable branch of the μ-slip curve, that is, a wheel deceleration value that has not yet produced a wheel. This is because the maximum frictional force or coefficient of friction (μ value) that can be transmitted has not yet been reached, or if the ABS control system is correctly designed, the ABS control system is not yet used.

Negative feedback is subtracted from the current wheel deceleration a _Rad to calculate the control start threshold. Only when the wheel deceleration exceeds the negative feedback value is this recognized as a tendency to lock, and deviations from the negative feedback are detected, integrated and evaluated. Integration is an important criterion for detecting ABS conditions, ie ABS control or locking tendency.

  If the negative feedback value or the control threshold is too small, a tire with a relatively large adhesion coefficient (μ) that can be transmitted is prematurely ABS controlled. That is, ABS control is performed within a stable range of the μ split curve. This prevents the use of the current tire / road adhesion coefficient. The braking distance is longer than that required from the viewpoint of road conditions and tire adhesion.

  In contrast, if the negative feedback or control threshold value is too large, a tire with a relatively small adhesion coefficient (μ) that can be transmitted will be too slow for ABS control. That is, ABS control is performed in an unstable range of the μ split curve. Thereby, a strong slip is produced until locking. The result is an “uneven” ABS control with excessive pressure changes. This impairs comfort and greatly degrades braking performance.

  Thus, the problem underlying the present invention is to develop a method in which the ABS control system can be modified for different adhesion factors depending on the type of wheel or cheaya.

  It has been found that this problem is solved by the method of claim 1. The characteristic of this method is that when braking with a large coefficient of friction, the brake pressure control threshold, especially the anti-lock brake control system (ABS) intervention threshold or the start-up threshold, is the sticking characteristic of the wheel, in particular the tire. It is solved by being adapted dynamically.

  The above objective of individually changing the ABS control system to the tire is basically in two ways, namely increasing the control threshold and / or increasing the negative feedback depending on the situation in each case Can be achieved.

In a particularly advantageous embodiment of the invention, the start of use of the anti-lock brake control system (ABS) depends on a control threshold, which is
_{F = F 0 + k a0 ×} (a-a 0) + k a1 × (a-a 1) ··· k an × (a- a n) (1)
Is gradually increased by increasing the negative feedback (F) according to the following: where “F ₀ = Feedback ₀ ” is the minimum negative feedback value and the value “a ₀ ” is the vehicle decrease when the progression begins. input values of the velocity, the value "a ₁ ··· a _n" is the vehicle deceleration when progressive is switched, "a" is the current vehicle deceleration and "k _a0 ··· k _an" in the evaluation coefficient is there.

In another embodiment of the present invention, the start of use of the anti-lock brake control system depends on the control threshold (Th), which is expressed by the following equation:
_{Th = Th 0 + k a0 ×} (a-a 0) + k a1 × (a-a 1) ··· k an × (a- a n) (2)
In this case, “Th ₀ ” is the minimum threshold value, the value “a ₀ ” is the input value of the vehicle deceleration when the advance is started, and the value “a ₁ ... _An ” is Vehicle deceleration when gradual change is switched, “a” is the current vehicle deceleration and “ _{ka 0} ... K _an ” is _an evaluation factor.

  In both cases, the rise must be progressively dependent on vehicle deceleration. The element “control threshold” relates to an acceleration threshold or a threshold derived therefrom or like an integral, a slip threshold and a reference speed.

  In both cases, i.e. in the case of adjustment of the control threshold and negative feedback, the entrance threshold is directly affected or indirectly influenced via measured or calculated vehicle deceleration.

  Progression begins when the vehicle deceleration is achievable with the “weakest” tire. The current vehicle speed of about 1 to 1.1 g (“g” is the gravitational acceleration) indicates a value that is actually relevant. Therefore, of course, a constant value must be added in the case of ascending or descending traveling.

  All tires that do not reach this input value do not initiate ABS control, but of course produce a high vehicle current speed and automatically increase the control threshold or negative feedback. This forces tires with large frictional coupling to be controlled by a large threshold or negative feedback.

  The operation of the present invention will be described in detail with reference to the accompanying drawings.

In the basic principle of the ABS control system shown symbolically in FIG. 1, the wheel sensor S1 to S4 indicating the rotation state (speed v _Rad and acceleration dv / dt) of the individual wheels 1 to 4 is used to input signals to the control system. can get. In order to measure the longitudinal acceleration of the vehicle, an acceleration sensor L1 can additionally be installed.

Such circuits are well known. From the measured values of this circuit, the vehicle (reference) speed is determined in the circuit B1 shown as a block. This change in the vehicle reference speed finally indicates the vehicle acceleration or vehicle deceleration a _FZ .

  B2 shows the negative feedback and / or threshold effect according to the invention. In B3, the above data is processed in order to obtain a control signal for the actuator A, in particular, a control signal for the brake pressure actuator or brake force actuator for controlling the brake pressure or brake force of the individual wheels, as in the past. Is done.

FIGS. 2 and 3 show the vehicle speed v _FZ , the wheel speed v _Rad to be controlled, and the wheel speed v _Rad change or differentiation with time. The values described below for the stepwise adjustment of the control threshold according to the invention are also entered in FIG.

The threshold value Th increases according to the following equation (1). To find the threshold progressively,
Th ₀ = basic threshold
Th ₁ = Th ₀ + k _a0 × (a−a ₀ )
Th _n = Th ₀ + Th ₁ ... + k _an × (a− a _n )
_{Th = Th n = Th 0 +} k a0 × (a-a 0) + k a1 × (a-a 1) ··· k an × (a- a n)
Is true. “Th ₀ ” is the minimum threshold value. The value “a ₀ ” is an input value when the progression starts. The value “a ₁ ... A _n ” is the vehicle deceleration when the gradual change is made. “A” corresponding to a _cc in FIG. 3 is the current vehicle deceleration. “K _a0 ... K _an ” is _an evaluation coefficient. In order to take into account the individual parts of this polynomial, the current vehicle deceleration must be greater than the respective switching value.

The following applies to increasing negative feedback: The negative feedback is increased according to the following equation (2).
F ₀ = basic value for negative feedback
F ₁ = F ₀ + k _a0 × (a−a ₀ )
_{F = F n = F 0 +} F 1 ··· + k an × (a- a n) (2)
“F” is called incremental feedback. “F ₀ = Feedback ₀ ” is the minimum negative feedback value. The value “a ₀ ” is an input value when the progression starts. The value “a ₁ ... A _n ” is the vehicle deceleration when the gradual change is made. “A” is the current vehicle deceleration. “K _a0 ... K _an ” is _an evaluation coefficient. The individual parts of this polynomial become effective as soon as the current vehicle deceleration is greater than the respective switching value.

  Adjusting or increasing negative feedback is often an advantageous and simple variation compared to increasing acceleration threshold. This is because the influence based on vehicle deceleration can be effected by a central control system.

  FIG. 4 illustrates the function and operation of gradual negative feedback. The straight line in FIG. 4 indicated by a broken line is effective when the individual terms of the negative feedback function F are included.

FIG. 5 shows the wheel acceleration integral value DVN in the case of the curve change and the control case of FIG. For example, a value of −4 km / h can be provided for the basic threshold Th ₀ .

Considering only the negative feedback value F _0, it is defined by the wheel speed V _Rad and the straight line F _0, the surface AF ₀ indicated by hatching is important wheel acceleration integral value in order to determine the ABS action threshold DVN (FIG. 5) is shown. When the other terms of the negative feedback equation become valid, the faces AF ₁ and AF _n become smaller.

  In both cases, i.e. when the control threshold increases progressively and when the negative feedback increases gradually, the progression is shown as the sum of a plurality of linear functions. Of course, other mathematical progressive forms can be selected. In practice, a simple form has proved quite sufficient.

FIG. 2 is a diagram showing important elements of an ABS control system in the form of functional blocks. It is a graph for showing change of wheel speed, vehicle speed, and wheel acceleration in the initial phase of ABS control. It is a graph for showing change of wheel speed, vehicle speed, and wheel acceleration in the initial phase of ABS control. It is a graph for showing an effect at the time of using gradual negative feedback. It is a graph for showing an effect at the time of using gradual negative feedback.

Claims (3)

  In a method for improving the control state of an antilock brake control system (ABS) during braking with a large coefficient of friction, a brake pressure control threshold, in particular an intervention threshold or start of use threshold of the antilock brake control system (ABS) Is dynamically changed according to the adhesion characteristics of each wheel. The start of use of the anti-lock brake control system (ABS) depends on the control threshold.
_{F = F 0 + k a0 ×} (a-a 0) + k a1 × (a-a 1) ··· k an × (a- a n) (1)
In this case, “F ₀ = Feedback ₀ ” is the minimum negative feedback value, and the value “a ₀ ” is the vehicle deceleration when the progression starts. The input value, value “a ₁ ... A _n ” is the vehicle deceleration when the gradual change is made, “a” is the current vehicle deceleration and “k _a0 ... K _an ” is the evaluation factor The method of claim 1, wherein: The start of use of the anti-lock brake control system depends on the control threshold (Th).
_{Th = Th 0 + k a0 ×} (a-a 0) + k a1 × (a-a 1) ··· k an × (a- a n) (2)
In this case, “Th ₀ ” is the minimum threshold value, the value “a ₀ ” is the input value of the vehicle deceleration when the progression starts, and the value “a ₁ ... _An ” is 3. A method according to claim 1 or 2, characterized in that the vehicle deceleration when gradual is switched, "a" is the current vehicle deceleration and " _ka0 ... _kan " is _an evaluation factor.

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