Method for identifying the source of disturbances in wheel speed signals in wheel slip control systems of vehicles

Abstract

Method for identifying vehicle wheel or brake-induced disturbances on the one hand and roadway-induced disturbances on the other hand from wheel speed signals (v i , i = 1, ... 4) of the vehicle wheels (F i , i= 1, ... 4)) of a vehicle with a wheel slip control system, comprising the following process steps: a) Recording the wheel speed signals (v i , i = 1, ... 4), b) Determine (S1) the wheel rotation period (T) using the formula T= s rad / v R ,, where s rad the circumference of the vehicle wheels (F i )and v R the from all wheel speed signals v i specific vehicle reference speed is c) Determining (S2) the wheel accelerations (a i, i = 1, ... 4) from the wheel speed signals (v i , 1, ... 4)), d) Determining the period (ΔT i , 1 = 1, ... 4) of the oscillation of the wheel accelerations (a i,i = 1, ... 4), e) Comparing (S3) the period duration (ΔT) i , i = 1, ... 4) with the wheel rotation period (T), and f) Identifying (S14) vehicle wheel or brake induced disturbances if the period (ΔT) i , i = 1, ... 4) agrees with the wheel rotation period (T) (S5), otherwise identify road-induced disturbances of the wheel speed signal (v i , i = 1, ... 4).

Description

[0001] The invention relates to a method for identifying vehicle wheel or brake-induced disturbances on the one hand and road surface-induced disturbances on the other hand from wheel speed signals of the vehicle wheels of a vehicle with a wheel slip control system.

[0002] Methods for slip control in the event of road-induced disturbances are known from DE 100 20 215 A1, DE 195 38 545 A1 and DE 10 2013 207 563 A1.

[0003] In vehicle wheel slip control systems, it is necessary to estimate a coefficient of adhesion or friction between the tire of a vehicle wheel and the road surface and to specify this estimated value to an algorithm underlying the control of the brake pressure.

[0004] In a vehicle's ABS system, the tendency of a vehicle wheel to lock is determined based on a comparison between the wheel speed and the vehicle speed or by means of the deceleration of a vehicle wheel, and the brake pressure applied to the vehicle wheel is adjusted so that the slip of the vehicle wheel is kept in the range of the maximum friction coefficient. On a road with an uneven surface, the wheel speed oscillates due to the roughness of the road surface. A tendency of the vehicle wheel to lock is incorrectly detected by the wheel slip control system based on these wheel vibrations and leads to a reduction in brake pressure. Therefore, measures are required that, when unevenness of the road surface is detected, adjust the slip detection thresholds of the ABS system accordingly if wheel vibrations indicate an uneven road surface.

[0005] All known detection mechanisms for road surface conditions are based on either less or more pronounced wheel speed oscillations or on the evaluation of single or repeated wheel accelerations. A minimum wheel acceleration value is required to initialize the detection mechanism (approximately 1 g with the brakes not applied or outside of a slip control system; however, significantly more within a slip control system).

[0006] However, the analysis of wheel speed oscillations on some surfaces, especially loose ones such as scree or gravel roads, does not provide reliable information about the road surface condition. Superimposed oscillations of the wheel speed signals with irregular frequencies and varying amplitudes are typical for these road surfaces.

[0007] In addition to road-induced vibrations of the wheel speed signals, there are other reasons for wheel speed vibrations.

[0008] On the one hand, these are wheel-induced vibrations, which are caused by wheel imbalance, radial runout on the tire or stiffness differences across the tire circumference (radial), and on the other hand, brake-induced vibrations, e.g. due to brake discs with disc runout.

[0009] These effects typically trigger characteristic vibrations that repeat with each wheel rotation. Common disturbance suppression mechanisms for slip control systems generally do not differentiate between the disturbance sources "road" and "vehicle wheel," as they follow the principle that, in essence, only the disturbance in the form of vibrations is relevant, not the source of the vibrations—whether they are induced by the vehicle wheel or brakes, or induced by the road surface.

[0010] Countermeasures against such disturbances typically involve increasing the slip detection thresholds. However, such measures always involve compromises, as they must be sensitive enough to detect the vibrations as a disturbance, yet at the same time be insensitive enough to prevent the implemented slip control (alternating between deceleration and acceleration phases at the vehicle wheel) from being mistakenly interpreted as a road disturbance.

[0011] Therefore, there is a risk that on a road surface with a rough or loose surface, such compromises may lead to non-detection of the disturbance in the form of oscillations in the wheel speed signal and consequently to poorer braking performance or even to the deceleration of the vehicle.

[0012] The object of the invention is to provide a method as mentioned above with which the above-mentioned disadvantages are avoided as far as possible, in particular a higher sensitivity in the detection of road disturbances leading to oscillations of the wheel speed signal.

[0013] This problem is solved by a method having the features of patent claim 1.

[0014] According to this method for the identification of vehicle wheel or brake induced disturbances on the one hand and road surface induced disturbances on the other hand from wheel speed signals v i of the vehicle wheels F i of a vehicle with a wheel slip control system, comprising the following method steps: a) Detecting the wheel speed signals v i , b) Determine the wheel rotation period T using the formula T= s rad / v R , where S rad the circumference of the vehicle wheels F i and vR which consists of all wheel speed signals v i certain vehicle reference speed, c) Determine the wheel accelerations a i from the wheel speed signals v i , d) Determine the period ΔT i the oscillation of the wheel accelerations a i , e) Compare the period ΔT i with the wheel rotation period T, and f) Identification of vehicle wheel or brake induced disturbances if the period ΔT corresponds to the wheel rotation period T, otherwise identification of road surface induced disturbances of the wheel speed signals v i .

[0015] This inventive method therefore involves identifying disturbances in the wheel speed signals as either vehicle wheel- or brake-induced disturbances or road-induced disturbances. These disturbances in the wheel speed signals manifest themselves as vibrations impressed on these wheel speed signals, which are evaluated as the acceleration of the vehicle wheel with respect to their temporal progression. From this temporal progression of the wheel acceleration, i.e., from these disturbing vibrations impressed on the wheel speed signal, their period is determined. By comparing this period with the wheel rotation period, the disturbance can be classified as either vehicle wheel- or brake-induced disturbance.

[0016] If these two variables do not match, it is assumed that a road disturbance is the cause of the vibrations impressed on the wheel speed signals. However, if the oscillation period of the disturbing vibrations impressed on the wheel speed signal corresponds to the wheel rotation period, it is assumed that the cause of these disturbing vibrations lies either in the vehicle tire or in the braking process. As a result of this identification of the impressed disturbing vibrations as vehicle wheel- or brake-induced disturbance, the wheel slip control system is adjusted to become less sensitive and thus more robust. This means that the ABS slip threshold is adjusted to make it more difficult to reduce the brake pressure, thus preventing the braking force from being unnecessarily reduced due to the disturbing vibrations in the wheel speed signal.

[0017] According to an advantageous embodiment of the invention, it is provided that with method step d) the period ΔT i as the time interval between two adjacent maxima or two adjacent minima of the time course of the wheel accelerations a iis determined and, according to method step e), is compared with the wheel rotation period T. The use of the oscillation period associated with a signal peak or a signal trough improves the identification of the disturbing oscillations superimposed on the wheel speed signals as vehicle wheel- or road-induced disturbances. Preferably, in addition to method step d), the absolute values ​​of the positive and negative amplitudes of the temporal oscillation curve of the wheel acceleration are determined. These values ​​can be used to increase or decrease the ABS detection thresholds in order to increase the sensitivity in detecting road surface disturbances. In particular, this allows the robustness of the wheel slip system with regard to the road surface condition to be adapted, since this road surface condition, e.g. fine or coarse subsurface, is indicated by the size of these amplitudes in the temporal oscillation curve of the angular acceleration.

[0018] In particular, according to a further embodiment of the invention, it is provided that the absolute values ​​of the amplitudes are added to slip detection thresholds of the wheel slip control system.

[0019] According to a further embodiment of the invention, upon identification of a vehicle wheel- or brake-induced disturbance in the wheel speed signal, a counter is incremented by a predetermined count value. However, upon identification of a road-induced disturbance in the wheel speed signal, the counter is preferably decremented at a rate higher than the predetermined count value. When a predetermined counter reading is reached, a disturbance in the vehicle wheel is detected.

[0020] In the following, the method according to the invention is described with reference to the single Fig. 1 explained and described.

[0021] This Fig. Figure 1 describes a flowchart for identifying the cause or source of disturbances in wheel speed signals of vehicle wheels of a vehicle equipped with a wheel slip control system. Such a wheel slip system includes an ABS system, an ASR system, or an ESP system. This method is intended to identify the disturbances in the wheel speed signals as either vehicle- or road-induced disturbances. Fig. The procedure shown in Figure 1 between “start” and “end” represents a working cycle in a loop of the wheel slip control system algorithm and is repeated in each loop.

[0022] The procedure according to Fig. 1 begins after start with a first method step S1 with the determination of a vehicle reference speed from the wheel speed signals v detected by wheel speed sensors i (i = 1, ... 4). From this vehicle reference speed v Ris calculated using the formula T= s rad / v R a wheel rotation period of the four vehicle wheels F i (i = 1, ... 4) of the vehicle, where s rad the wheel circumference of the vehicle wheels F i (i = 1, ... 4).

[0023] The wheel speed signals v i (i = 1, ... 4) exhibit imposed vibrations as disturbances, which are calculated on the basis of the wheel accelerations a i (i = 1, ... 4) of the vehicle wheels F i (i = 1, ... 4) are evaluated. Therefore, in a next process step S2, the wheel accelerations a1, a2, a3 and a4 of the four vehicle wheels F i (i = 1, ... 4) of the vehicle, which is calculated using an algorithm from the wheel speed signals v i (i = 1, ... 4). For the four vehicle wheels F ithe oscillation period ΔT1, ΔT2, ΔT3 and ΔT4 of the temporal oscillation curve of the wheel acceleration a1 to a4 as well as the absolute values ​​of the maximum and minimum amplitudes Ai max and Ai min (i = 1, ... 4). In particular, the period durations ΔT1, ΔT2, ΔT3, and ΔT4 are measured in a signal peak (between two maxima) and in a signal trough (between two minima) of the temporal oscillation curve of the wheel accelerations a1 to a4.

[0024] According to method step S3, a comparison of the period duration ΔT1, ΔT2, ΔT3 and ΔT4 of the wheel accelerations a1 to a4 of the vehicle wheels F i each with the wheel rotation period T.

[0025] In the subsequent process step S4, a limit value SW1 and a limit value SW2 are determined, which ensure a sufficient signal-to-noise ratio to a slip control, e.g. an ABS control.

[0026] If, according to method step S5, the wheel rotation duration T corresponds to a period duration ΔT1 to ΔT4, the process branches to method step S6; if there is no correspondence, the process branches to method step S12.

[0027] According to process step S6, the absolute values ​​of the amplitudes Ai max and Ai min (i = 1, ... 4) of the oscillation of the wheel acceleration a i of the vehicle wheel F i (i = 1, ... 4) is compared with the limit value SW1.

[0028] If the absolute values ​​of the amplitudes Ai max and Ai min are greater than this limit SW1, a counter with counter reading Z is incremented with a counting rate R1 according to process step S8. In the other case, i.e. if at least one of the absolute values ​​of the amplitudes Ai max or Ai minis less than or equal to this limit value SW1, the process branches to step S7, in which the counting rate of counter Z is decremented by a counting rate R2. The following applies to these two counting rates R1 and R2: R2 > R1. The process ends with step S7.

[0029] Following the process step S8, in a process step S9 the counter reading Z is compared with a predetermined maximum counter reading Z max If this counter reading is not reached, the counting continues according to process step S10 and branches to the "end".

[0030] In the other case, when the maximum counter reading Z max is exceeded, the disturbance in the wheel speed signal v i of the vehicle wheel F i identified as a vehicle wheel or brake induced disturbance, ie the wheel speed signal v i superimposed disturbance has its cause in the vehicle wheel F i. Therefore, the control thresholds in the wheel slip control system are increased so that a false triggering at this vehicle wheel F i For this purpose, the absolute value of the amplitude Ai max or Ai min added to the detection thresholds of the wheel slip control system.

[0031] If there is no agreement when comparing the period duration ΔT1, ΔT2, ΔT3 and ΔT4 of the wheel accelerations a1 to a4 with the wheel rotation period T, the counter reading Z of the counter is decremented with a counting rate R3 according to method step S12, whereby for this counting rate R3 the following applies: R3 > R2.

[0032] According to process step S13, the amplitudes Ai max and Ai min (i = 1, ... 4) of the vibrations of the wheel accelerations a i compared with the limit value SW2. If this limit value SW2 is not exceeded, the procedure ends.

[0033] In the other case, when the limit value SW2 is exceeded, the disturbance in the wheel speed signal v i of the vehicle wheel F i identified as road-induced disturbance, ie the wheel speed signal v i The superimposed disturbance is caused by the road surface. Therefore, the control thresholds in the wheel slip control system are increased significantly to massively increase system robustness. This means that the slip is very large until the slip control is activated in order to ensure sufficient wedging, i.e., sufficient power transmission, between the tire of the vehicle wheel F i and the road surface. This ensures high sensitivity to road surfaces with, for example, fine or coarse gravel.

Claims

[1] Method for the identification of vehicle wheel or brake induced disturbances on the one hand and road surface induced disturbances on the other hand from wheel speed signals (v i , i = 1, ... 4) of the vehicle wheels (F i , i= 1, ... 4)) of a vehicle with a wheel slip control system, comprising the following method steps: a) Detecting the wheel speed signals (v i , i = 1, ... 4), b) Determine (S1) the wheel rotation period (T) using the formula T= s rad / v R ,, where s rad the circumference of the vehicle wheels (F i )and v R which consists of all wheel speed signals v i certain vehicle reference speed, c) Determine (S2) the wheel accelerations (a i, i = 1, ... 4) from the wheel speed signals (v i , 1, ... 4)), d) Determine the period (ΔT i , 1 = 1, ... 4) of the oscillation of the wheel accelerations (a i,i = 1, ... 4), e) Comparing (S3) the period duration (ΔT i , i = 1, ... 4) with the wheel rotation period (T), and f) Identifying (S14) vehicle wheel or brake induced disturbances if the period (ΔT i , i = 1, ... 4) corresponds to the wheel rotation period (T) (S5), otherwise identifying road-induced disturbances of the wheel speed signal (v i , i = 1, ... 4). [2] Method according to claim 1, characterized by that, with the process step d) the period duration (ΔT i , i = 1, ... 4) as the time interval between two adjacent maxima or two adjacent minima of the time course of the wheel acceleration (a i, i = 1, ... 4) and is compared with the wheel rotation period (T) according to process step e). [3] Method according to claim 1 or 2, characterized bythat in addition to process step d) the absolute values ​​of the positive and negative maximum amplitudes (Ai max , Ai min , i = 1, ... 4) of the time course of the wheel acceleration (a i, i = 1, ... 4). [4] Method according to claim 3, characterized by that the absolute values ​​of the maximum amplitudes (Ai max , Ai min , i = 1, ... 4) are added to the slip detection thresholds of the wheel slip control system. [5] Method according to one of the preceding claims, characterized by that upon identification of a vehicle wheel or brake induced disturbance of the wheel speed signal (v i , i = 1, ... 4) a counter (Z) is incremented (S8) by a predetermined count value (R1). [6] Method according to claim 5, characterized by that when a road-induced disturbance of the wheel speed signal (v i, i = 1, ... 4) the counter (Z) is decremented (S7) at a rate (R2) higher than the specified count value (R1). [7] Method according to claim 5 or 6, characterized by that when a specified counter reading (Z max ) of the counter (Z) a fault of the vehicle wheel (F i ) is detected (S11).

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