Method for detecting wheel slip of a vehicle

Abstract

The present invention relates to a method for detecting wheel slip of a vehicle, wherein at least one rotational speed sensor is assigned to the wheel, and wherein the method is executed with the aid of a control unit of the vehicle, the method comprising the following steps: 1) detecting the rotational speed of the wheel by means of at least one rotational speed sensor; 2a) generating a first signal for the rotational acceleration of the wheel by means of the control unit, wherein the rotational acceleration of the wheel is determined based on the detected rotational speed; 2b) generating a second signal for the rotational jerk of the wheel by means of the control unit, wherein the rotational jerk of the wheel is determined based on the determined rotational acceleration; 3a) monitoring whether the first signal exceeds a first threshold value; 3b) monitoring whether the second signal exceeds a second threshold value; 4) generating a positive detection signal identifying wheel slip by means of the control unit if the first threshold value is exceeded by the first signal and the second threshold value is exceeded by the second signal.

Description

Technical Field

[0001] The invention relates to a method for detecting wheel slip of a vehicle, that is to say the transition of the tire of the wheel from static friction to sliding friction on the roadway. The invention also relates to a corresponding assistance system for a vehicle. Background Art

[0002] Methods for determining the maximum transmittable drive torque of a wheel are known from the prior art. For this purpose, publication DE 10 2016 203 545 A1 presupposes an estimate of the circumferential slip, which is not always possible in the case of all-wheel drive vehicles. In addition, the approach presented in this publication can only generate a reliable estimate of the friction coefficient in a quasi-stationary driving state.

[0003] In the publication DE 10 2018 200 180 A1, in order to determine the maximum wheel-lane friction coefficient, it is necessary to intervene in the wheel longitudinal force and / or the wheel contact force. The intervention on one wheel or on one axle is compensated by the opposite intervention on the other wheel or the other axle, with the aim that the driver should not perceive unexpected driving behavior as much as possible. However, the impact-free, synchronous and equal increase in driving torque and braking torque establishment are very complicated. In addition, for the scheme proposed in this publication, a constant driving state at a high speed is required. Only in this state does the influence of the intervention reach a measurable amplitude and can be separated from other effects in order to achieve a reliable friction coefficient estimation based on this. This limits the scheme to straight routes and higher speeds.

[0004] In the publication DE 10 2016 214 065 A1, in order to determine the maximum wheel-lane friction coefficient, the maximum value is extrapolated from the measured working point consisting of the instantaneous wheel slip and the adhesion coefficient. In this solution, certain assumptions are made, such as the value of the critical slip and the waveform of the friction coefficient-slip characteristic curve, but these assumptions only apply to certain tire-lane combinations. It is well known that the critical slip can vary between 5% and 20% depending on the tire type. It is also generally known that the friction coefficient-slip characteristic curve on freshly fallen snow does not have a clearly prominent maximum value, as assumed in this solution. For this reason, once the model deviation is high, the maximum wheel-lane friction coefficient cannot be accurately estimated. The accuracy achieved by this solution is also strongly affected by the accuracy of the slip measurement. For all-wheel drive vehicles, this accuracy drops sharply once all wheels are used for driving. Summary of the invention

[0005] The object of the present invention is therefore to provide a fast and reliable method for detecting the slip of a wheel of a vehicle, that is to say the transition of a tire of a wheel from static friction to sliding friction on a roadway, which method is separated from the measurement and / or estimation of the slip of the wheel and the friction coefficient between the wheel and the roadway. The object of the present invention is also to provide a method for detecting the slip of a wheel of a vehicle, which method works with measurable variables and enables immediate, estimation-free detection of the slip of the wheel and even the tendency to slip. The object of the present invention is also to obtain improved knowledge about the behavior of the wheel on the roadway, which knowledge can reliably and quickly detect not only the transition of the tire of the wheel from static friction to sliding friction but also the stabilization of the wheel. The object of the present invention is also to enable a reliable determination of the maximum longitudinal force that can be transmitted to the roadway by the wheel, the so-called circumferential force, and the friction coefficient between the tire of the wheel and the roadway. The object of the present invention is also to provide an improved anti-lock braking system and anti-skid control system, which can also be referred to as ABS system and ASR system.

[0006] The object according to the invention is achieved by a method for detecting wheel slip of a vehicle, that is to say the transition of the tire of the wheel from static friction to sliding friction on the roadway, which method has the features of the independent method claim, in particular from the characterizing part. The object according to the invention is also achieved by a corresponding assistance system for a vehicle. Here, the features described in conjunction with the individual embodiments are of course also applicable in conjunction with other embodiments and vice versa, so that the disclosures about the individual embodiments can always be referenced to each other.

[0007] The invention provides a method for detecting wheel slip, that is to say the transition of the wheel tire from static friction to sliding friction on the roadway, in particular independently of the slip of the wheel tire of the vehicle and / or the measurement and / or estimation of the friction coefficient between the wheel tire and the roadway. In this case, at least one rotation speed sensor is assigned to the wheel. The method is executed by means of a control unit of the vehicle and has the following steps:

[0008] 1) detecting the rotation speed of the wheel by at least one rotation speed sensor;

[0009] 2a) generating, by means of a control unit, a first signal for the rotational acceleration of the wheel,

[0010] wherein the rotational acceleration of the wheel is determined or calculated based on the detected rotational speed;

[0011] 2b) generating, by means of a control unit, a second signal for the rotational jerk of the wheel,

[0012] wherein the rotational jerk of the wheel is determined or calculated based on the determined rotational acceleration;

[0013] 3a) monitoring whether the first signal exceeds a first threshold;

[0014] 3b) monitoring whether the second signal exceeds a second threshold;

[0015] 4) If the first threshold is exceeded by the first signal and the second threshold is exceeded by the second signal,

[0016] A positive detection signal is then generated by the control unit, which detects wheel slip.

[0017] The rotation speed sensor in the sense of the present invention can be provided by means of different technologies suitable for angle measurement and / or rotation speed measurement, such as an incremental encoder, a potentiometer, a gyroscope or the like.

[0018] The rotational speed for the purposes of the present invention may also be referred to as angular speed or rotational speed. The rotational acceleration for the purposes of the present invention may be calculated as the derivative of the rotational speed with respect to time. The rotational jerk for the purposes of the present invention may be calculated as the derivative of the rotational acceleration with respect to time.

[0019] The threshold values ​​of the rotational acceleration signal and the rotational jerk signal can be determined empirically and / or theoretically. These threshold values ​​can be prescribed, for example, according to the maximum longitudinal force that can be transmitted by a specific vehicle.

[0020] The invention therefore proposes a new method for identifying wheel slip. This refers to the exact point in time when full utilization of the wheel's adhesion potential exists and a sudden acceleration of the wheel occurs. This can be achieved by introducing new wheel dynamics features. These wheel dynamics features are based in particular on the rotational acceleration and the rotational jerk of the wheel and preferably include the area under these two signals. Within the framework of the invention, four signals can be generated based on the wheel rotational acceleration and the wheel rotational jerk; on the one hand, signals for the rotational acceleration and the rotational jerk themselves and two other signals including the area under the waveform of the first two signals.

[0021] The respective threshold values ​​are defined for the respective signals. If the respective signal rises above the corresponding threshold value, the so-called condition that the respective signal has exceeded the assigned threshold value is confirmed (or in other words noted or recorded). The confirmation of the first two conditions for the signals of rotational acceleration and rotational jerk can advantageously be maintained even after exceeding the defined threshold values, for example for 10 ms. As soon as all conditions are present simultaneously, wheel slip can be detected with high reliability.

[0022] Wheel rotation acceleration and wheel rotation jerk are usually not available as measured values. Within the scope of the present invention, the wheel rotation acceleration and wheel rotation jerk as well as the wheel speed can be reconstructed based on the wheel speed signal by means of a control technology observer, for example a Romberg observer. For this purpose, the speed is measured at the wheel and transmitted to a control unit as a wheel speed signal. This implementation allows for a fast and reliable reconstruction of the wheel rotation acceleration and wheel rotation jerk with a low phase shift and a high robustness against signal noise and loss of CAN messages that are to transmit the wheel speed signal.

[0023] The invention also enables the detection of wheel slip with minimal time delay, in particular a time delay of less than 20 ms. Based on this information, other characteristics of the wheel behavior can be advantageously extracted. Assuming that the effective wheel drive torque and / or wheel braking torque is present as a signal at the time of slip or locking, the invention provides the possibility of determining, in particular simply calculating, the maximum transmissible tire longitudinal force, for example by means of the angular momentum of the wheel. In addition, a reliable determination of the corresponding maximum wheel-track friction coefficient can be performed. In this case, the current wheel contact force and the wheel lateral force can be taken into account.

[0024] The method according to the invention can be performed individually for each wheel. The steps of the method according to the invention can be performed in a predetermined or modified order. Advantageously, the steps of the method according to the invention can be performed simultaneously and / or repeatedly to enable a flow process.

[0025] The invention also provides the possibility of identifying wheel stability based on the signals introduced, which include the novel wheel dynamics features according to the invention. With the aid of the method according to the invention, an anti-lock control system or an anti-lock braking system and an anti-skid control system based on wheel dynamics which are improved in this way can be provided.

[0026] The invention may also provide for a method for detecting wheel slip of a vehicle to include at least one further step of the following steps:

[0027] 2c) generating, by a control unit, a third signal for an area below the first signal;

[0028] 2d) generating, by a control unit, a fourth signal for an area below the second signal;

[0029] 3c) monitoring whether the third signal exceeds a third threshold;

[0030] 3d) monitoring whether the fourth signal exceeds a fourth threshold,

[0031] In this case, a positive detection signal is generated in step 4) which identifies wheel slip if a first threshold value is exceeded by the first signal, a second threshold value is exceeded by the second signal, a third threshold value is exceeded by the third signal and a fourth threshold value is exceeded by the fourth signal.

[0032] These four signals represent wheel states that reproduce the dynamic behavior of the wheel. In the stable range of the wheel, these signals only reach small values. Unstable behavior is characterized by high values ​​of these states. In the event of wheel slip, all four signals are expected to exceed the associated threshold values. In this way, the robustness of the detection can be significantly increased and false identifications can be avoided. In practice, it has been shown that other processes, such as rapid steering, load changes, etc., can activate individual exceeding of these thresholds, which should not lead to a positive detection of wheel slip. By confirming all four exceedings, it can be ensured that the actual slip of the wheel can be distinguished from the other processes.

[0033] The invention can also provide in a method for detecting the slip of a wheel of a vehicle that the first signal and the second signal are reconstructed from the rotational speed signal, in particular by means of a control technology observer, such as a Romberg observer. In this way, an advantageous control method can be used to reconstruct the rotational acceleration and the rotational jerk from a signal for the rotational speed of the wheel that can be estimated and / or measured. For this purpose, advantageously, only the rotational speed of the wheel needs to be measured and / or estimated, which measurement and / or estimation is advantageously completely independent of the measurement and / or estimation of the slip of the tire of the wheel and / or the friction coefficient between the tire of the wheel and the roadway. This can advantageously improve or expand the rationality and applicability of the method according to the invention.

[0034] The invention can advantageously provide that: the first condition is confirmed when the first signal exceeds the first threshold value; and / or the second condition is confirmed when the second signal exceeds the second threshold value; and / or the third condition is confirmed when the third signal exceeds the third threshold value; and / or the fourth condition is confirmed when the fourth signal exceeds the fourth threshold value. The corresponding conditions can be presented as a logical "1", which is pre-recorded when the corresponding signal exceeds a certain threshold value. If all conditions present a logical "1", all four conditions are confirmed and the slip of the wheel is identified. In this way, a simple and reliable logical "AND (UND)" operation between the corresponding signals exceeding the corresponding threshold values ​​can be provided.

[0035] The present invention can also provide in a method for detecting the slip of a wheel of a vehicle that the confirmation of the first condition when the first signal exceeds the first threshold value and the confirmation of the second condition when the second signal exceeds the second threshold value continue and are not covered by a defined first time period, in particular 10 ms. Experience shows that rotational acceleration and rotational jerk exceed the corresponding threshold values ​​only in a relatively short time (approximately 5 ms to 10 ms). The third and fourth signals exceed the corresponding threshold values ​​with a delay due to integration. By making the confirmation of the first and second conditions continue, the delay caused by integration can be compensated.

[0036] The present invention can also provide in a method for detecting the slip of a wheel of a vehicle that the positive detection signal after the slip of the wheel is identified in step 4) is continuously maintained and not changed, in particular until the stability signal of the wheel is detected and preferably exists for a defined second time period. After the wheel slips, as long as the wheel continues to be in the unstable range, the logical "AND (UND)" operation between the exceeding of the corresponding threshold values ​​of these signals continuously and alternately provides "0" and "1". In the case of maintaining the positive detection signal, it can be ensured that the identified wheel slip is always maintained until the stability of the wheel is actually confirmed. The maintenance of the positive detection signal can be realized, for example, by using a switching block, i.e., a so-called RS flip-flop (RS-Flip-Flop), which sets the detection signal to logic "1" from the beginning of the identification of the wheel slip and thus continuously provides the positive detection signal. In this way, reliable identification of the wheel slip is ensured. Only the first logical "1" in the detection signal (that is, when all conditions are logical "1" or when all four conditions are confirmed) is taken into account, and the detection signal is set to zero after the wheel is stable. The method can then be repeated by waiting for a new logical “1” in the detection signal.

[0037] The invention may also provide for a method for detecting wheel slip of a vehicle to include at least one further step of the following steps:

[0038] 5) in particular starting from the time when the wheel slip is detected, generating a fifth signal for the area below the third signal by the control unit;

[0039] 6a) generating an absolute first signal as an absolute value function of the first signal;

[0040] 6b) generating an absolute second signal as a function of the absolute value of the second signal;

[0041] 6c) generating an absolute third signal as a function of the absolute value of the third signal; and / or

[0042] 6d) generating an absolute fourth signal as a function of the absolute value of the fourth signal.

[0043] The fifth signal corresponds to the integration of the third signal from the time point at which the slip was detected. In this case, the time integrator within the defined second time period can be reset by a positive detection signal indicating "slip detected". The fifth signal provides the physical state of the speed difference between the wheel speed at the time point of the slip and the current speed of the wheel. In other words, the fifth signal can be presented as an approximation between the speed of the wheel and the vehicle. In this case, it can be assumed that the wheel is accelerated much faster than the vehicle and that the wheel must fall back to the original speed in order to be considered stable again.

[0044] The invention may also provide for a method for detecting wheel slip of a vehicle to include at least one further step of the following steps:

[0045] 7a) monitoring whether the absolute first signal exceeds an absolute first threshold;

[0046] 7b) monitoring whether the absolute second signal exceeds an absolute second threshold;

[0047] 7c) monitoring whether the absolute third signal exceeds an absolute third threshold;

[0048] 7d) monitoring whether the absolute fourth signal exceeds an absolute fourth threshold;

[0049] 7e) monitoring whether the fifth signal exceeds an absolute fifth threshold; and / or

[0050] 8) If in all steps 7a) to 7d), in particular within the defined second time period, the respective absolute signal does not exceed the respective threshold value or if all absolute signals remain at zero "0",

[0051] A stable signal is generated.

[0052] In this way, a logical OR operation can be provided between the five signals. The five signals present at the input of the OR operation indicate individually the unstable state of the wheel. The output of the OR operation resets the time integrator again whenever one of the five signals indicates an unstable behavior of the wheel. If all five signals remain at "0" for a defined second time period, for example 50 ms, the wheel is considered "stable" again.

[0053] Advantageously, the invention may provide that the method comprises at least one further step of the following steps:

[0054] 9) determining, in particular simply calculating, the maximum longitudinal force that can be transmitted to the roadway via the wheel as a function of the wheel drive torque and / or wheel braking torque at or (immediately after) the time at which wheel slip or wheel locking is detected in step 4); and / or

[0055] 10) Determining, in particular simply calculating, the coefficient of friction between the tire of the wheel and the roadway.

[0056] Thus, with the aid of the present invention, not only can wheel slip and stabilization be reliably detected, but also, knowing the time at which the wheel loses static friction with the roadway, a simple rule for maintaining the torque when the wheel slips on the roadway can be used to determine the maximum transmissible longitudinal force of the wheel. Knowing the maximum transmissible longitudinal force of the wheel, the friction coefficient between the tire of the wheel and the roadway can therefore be simply calculated.

[0057] The object according to the invention is also achieved by a corresponding assistance system for a vehicle, which can be implemented in the form of an anti-lock braking system or an anti-skid control system, which can also be referred to as an ABS system and an ASR system. In this case, the vehicle is implemented with at least one wheel for driving the vehicle, wherein the wheel has at least one rotational speed sensor. Advantageously, the assistance system according to the invention has a control unit, which is implemented to detect wheel slip according to a method that can be performed as described above. With the assistance system according to the invention, the same advantages are achieved, which have already been described above in conjunction with the method according to the invention. In the present case, reference is made to these advantages in full.

[0058] In this case, the control unit can directly communicate and establish a data connection with the rotational speed sensor and / or with a central control unit of the vehicle in order to query and / or obtain measured values ​​of the rotational speed sensor.

[0059] Within the scope of the invention, it is also conceivable that the control unit can be designed as a separate control unit (advantageously when each wheel is assigned a control unit) or can be implemented in a central control unit of the vehicle (advantageously when a common control unit is desired for all wheels). BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention is also presented in more detail according to the accompanying drawings. It should be noted that these drawings are only of descriptive nature and are not to be considered as limiting the present invention in any form.

[0061] in:

[0062] Figure 1An exemplary illustration of a circuit diagram of a control unit for carrying out the method according to the invention for detecting wheel slip of a vehicle is shown;

[0063] Figure 2 An exemplary diagram of signals and novel wheel dynamics characteristics according to the invention is shown for illustrating the method according to the invention for detecting wheel slip of a vehicle;

[0064] Figure 3 shows an exemplary diagram of a detection signal in accordance with the present invention;

[0065] Figure 4 An exemplary diagram of an auxiliary system in accordance with the present invention is shown;

[0066] Figure 5 An exemplary diagram showing an auxiliary system in accordance with the present invention; and

[0067] Figure 6 An exemplary illustration of an assistance system in accordance with the present invention is shown. DETAILED DESCRIPTION

[0068] Figure 1 Circuit diagram for explaining the method according to the invention and a control unit 200 according to the invention, which is designed to carry out the method according to the invention.

[0069] The method according to the present invention is used to detect the slip d* of wheel 150, that is, the transition of the tire of wheel 150 from static friction to sliding friction on the roadway, in particular independently of the slip of the tire of wheel 150 of vehicle 100 and / or the friction coefficient between the tire of wheel 150 and the roadway.

[0070] In this case, at least one rotational speed sensor 110 is assigned to the wheel 150, as will be described later. Figure 4 , 5 and 6. This method is based on the same Figure 4 , 5 6 and the control unit 200 schematically shown in FIG. 6 are executed, and have the following steps:

[0071] 1) Detecting the rotation speed w of the wheel 150 by at least one rotation speed sensor 110;

[0072] 2a) generating, by means of the control unit 200, a first signal s1 for the rotational acceleration a of the wheel 150,

[0073] wherein the rotational acceleration a of the wheel 150 is determined or calculated based on the detected rotational speed w;

[0074] 2b) generating, by the control unit 200, a second signal s2 for the rotational jerk r of the wheel 150,

[0075] wherein the rotational jerk r of the wheel 150 is determined or calculated based on the determined rotational acceleration a;

[0076] 3a) monitoring whether the first signal s1 exceeds a first threshold p1;

[0077] 3b) monitoring whether the second signal s2 exceeds a second threshold value p2;

[0078] 4) If the first threshold value p1 is exceeded by the first signal s1 and the second threshold value p2 is exceeded by the second signal s2 , a positive detection signal 0 is generated by the control unit 200 , which identifies a slip d* of the wheel 150 .

[0079] The present invention provides a novel method for identifying slip d* of wheel 150. At the time of slip d* of wheel 150, there is full utilization of the adhesion potential of wheel 150. At this time, a sudden acceleration of wheel 150 occurs.

[0080] The present invention introduces novel wheel dynamic characteristics s3, s4. These wheel dynamic characteristics s3, s4 are based in particular on the rotational acceleration a and the rotational jerk r of the wheel 150. Within the framework of the present invention, four signals s1, s2, s3, s4 can be generated based on the rotational acceleration a and the rotational jerk r of the wheel 150: on the one hand, the signals s1, s2 for the rotational acceleration a and the rotational jerk r themselves and on the other hand, the signals s3, s4 for the area under the waveform of the respective signals s1, s2, such as Figure 1 As shown. In the case of signals s3 and s4, the integrator is reset at the zero crossing. Correspondingly, the area under the respective signal s1 and s2 is measured starting from the last zero crossing.

[0081] Within the framework of the present invention, for the corresponding signals s1, s2, s3, s4, the respective thresholds p1, p2, p3, p4 are selected in a targeted manner, such as in Figure 2 These threshold values ​​p1, p2, p3, p4 may be determined based on the rotational acceleration a and the rotational jerk r at the time of the slip d* of the wheel 150 and the empirical values ​​and / or modeled values ​​of the wheel dynamic characteristics s3, s4.

[0082] If the respective signal s1, s2, s3, s4 rises above the corresponding threshold value p1, p2, p3, p4, then the so-called condition b1, b2, b3, b4 is confirmed, wherein it is noted that the respective signal s1, s2, s3, s4 has exceeded the assigned threshold value p1, p2, p3, p4, as in Figure 2 shown in the middle.

[0083] The confirmation of the conditions b1, b2 of the signals s1, s2 of the rotational jerk r of the rotational acceleration a can advantageously be maintained for a first time period t1, for example for 10 ms, even after the defined threshold values ​​p1, p2 have been exceeded, as in Figure 1 The symbol "halt" in Figure 2 The first duration t1 in represents this point.

[0084] Once all conditions b1, b2, b3, b4 exist simultaneously, the slip d* of the wheel 150 is detected (see Figure 1 The logical "AND (UND)" operation in the circuit diagram and Figure 2 ).

[0085] The wheel rotation acceleration a and wheel rotation jerk r do not exist as measured values. Figure 1 As shown, the wheel rotation acceleration a and the wheel rotation jerk r as well as the wheel speed w itself can be estimated by means of a control technology observer, for example a Romberg observer LB, based on the wheel speed signal w. For this purpose, the speed w is measured by at least one speed sensor 110 at the wheel 150. The implementation by means of the Romberg observer LB enables the wheel rotation acceleration a and the wheel rotation jerk r to be reconstructed quickly and reliably by means of the time signal wRX with a low phase shift, to prevent signal noise and to have a high robustness against CAN message losses of the wheel speed signal w.

[0086] The invention also makes it possible to detect a slip d* of wheel 150 with minimal time delay, advantageously less than 20 ms. Knowing the slip d* of wheel 150, further characteristics of the wheel behavior can advantageously be extracted. When the acting wheel drive torque Ma and wheel braking torque Mb are assumed to be present as signals at the time of slip d* or locking (see Figure 5 and 6 ), the invention provides the possibility of calculating the maximum transmissible tire longitudinal force Fmax, for example, by means of the angular momentum of wheel 150 and a simple vector multiplication with the wheel radius. With the aid of the invention, a reliable determination of the corresponding maximum wheel-road friction coefficient μ can also be performed. In this case, the current wheel contact forces and the wheel lateral forces can be used to calculate the maximum wheel-road friction coefficient μ as a function of the maximum transmissible longitudinal force of the tire of wheel 150.

[0087] As already mentioned above, the present invention may provide for the following steps within the framework of the method:

[0088] 2c) generating, by the control unit 200, a third signal s3 for the area below the first signal s1;

[0089] 2d) generating, by the control unit 200, a fourth signal s4 for the area below the second signal s2;

[0090] 3c) monitoring whether the third signal s3 exceeds a third threshold value p3;

[0091] 3d) monitoring whether the fourth signal s4 exceeds a fourth threshold value p4,

[0092] If the first threshold value p1 is exceeded by the first signal s1, the second threshold value p2 is exceeded by the second signal s2, the third threshold value p3 is exceeded by the third signal s3 and the fourth threshold value p4 is exceeded by the fourth signal s4, a positive detection signal 1 is generated in step 4) which identifies the slip d* of the wheel 150.

[0093] These four signals s1, s2, s3, s4 describe the dynamic behavior of the wheel 150. In the stable range of the wheel 150 (no slip d*), these signals s1, s2, s3, s4 only reach small values. Unstable behavior (slip d* or even slip tendency) is characterized by high values ​​of these signals s1, s2, s3, s4. In the case of slip d* of the wheel 150, it is expected that all four signals s1, s2, s3, s4 exceed the corresponding threshold values ​​p1, p2, p3, p4. In this way, the robustness of the detection can be increased and false recognition can be reduced. Experience has shown that other processes, such as rapid steering, load changes, etc., may activate individual exceeding of the threshold values ​​p1, p2, p3, p4. By confirming all four exceedings, it can be ensured that the actual slip d* of the wheel 150 can be distinguished from the other processes.

[0094] Figure 2 It is shown that the corresponding conditions b1, b2, b3, b4 can be presented as a logic "1", which is pre-recorded when the corresponding signal s1, s2, s3, s4 exceeds a certain threshold value p1, p2, p3, p4. If all four conditions b1, b2, b3, b4 present a logic "1", the four conditions b1, b2, b3, b4 are confirmed and the wheel slip d* is detected. Figure 1 , 2 3 show a logical AND operation for checking whether all four signals s1 , s2 , s3 , s4 exceed the corresponding threshold values ​​p1 , p2 , p3 , p4 .

[0095] Figure 1 and 2It is also shown that the confirmation of the first condition b1 when the first signal s1 exceeds the first threshold value p1 and the confirmation of the second condition b2 when the second signal s2 exceeds the second threshold value p2 continue or remain and are not covered by the first defined time period t1, for example 10 ms. Experience has shown that the rotational acceleration a and the rotational jerk r only exceed the corresponding threshold value p1 or p2 in a short time of about 5-10 ms. The third signal s3 and the fourth signal s4 exceed the corresponding threshold value p3 or p4 with a delay due to integration. The delay caused by integration can be compensated by the block "halt" for the confirmation of the first and second conditions b1, b2.

[0096] Figure 2 as well as Figure 3 It is also shown that the positive detection signal 1 after the slip d* of the wheel 150 is detected is maintained and is not changed, preferably until the stability signal 0 of the wheel 150 is present, in particular until the defined second time period t2 is present. After the slip d* of the wheel 150, as long as the wheel 150 continues to be in the unstable range, the logical "AND" operation between the exceeding of the corresponding threshold values ​​p1, p2, p3, p4 by the signals s1, s2, s3, s4 continuously and alternately provides "0" and "1". When the positive detection signal 1 is maintained, it can be ensured that the detected slip d* of the wheel 150 is maintained until the stability of the wheel 150 is confirmed.

[0097] like Figure 1 As shown, the maintenance of the positive detection signal 1 can be realized by using a switching block RS, a so-called RS flip-flop, which sets the detection signal d to logic "1" from the moment the slip d* of the wheel 150 is detected and thus continuously provides the positive detection signal 1, such as in Figure 2 . In this way, only the first logical "1" in the detection signal d (when all conditions b1, b2, b3, b4 are logical "1" or when all four conditions b1, b2, b3, b4 are confirmed) is taken into account and is set to "0" after the wheel 150 is detected to be stable. The method can then be repeated by waiting for a new logical "1" in the detection signal d.

[0098] The invention may also provide that the knowledge of the time of slip d* may be used to detect the stabilization of wheel 150. To this end, the method may have at least one further step of the following steps:

[0099] 5) in particular, starting from the time point when the slip of the wheel 150 is detected, the control unit 200 generates a fifth signal s5 for the area below the third signal s3;

[0100] 6a) generating an absolute first signal |s1| as an absolute value function of the first signal s1;

[0101] 6b) generating an absolute second signal |s2| as an absolute value function of the second signal s2;

[0102] 6c) generating an absolute third signal |s3| as an absolute value function of the third signal s3; and / or

[0103] 6d) generating an absolute fourth signal |s4| which is an absolute value function of the fourth signal s4.

[0104] The fifth signal s5 corresponds to the area under the third signal s3 from the time point at which the slip d* was identified. The integrator responsible for generating the fifth signal s5 is reset by the signal that the slip d* was identified. The fifth signal s5 provides the physical state of the speed difference between the rotational speed w at the time point of the slip d* and the current rotational speed w of the wheel 150. The fifth signal s5 can also be presented as an approximation of the speed difference between the circumferential speed of the wheel 150 and the vehicle 100. Here, it can be assumed that the wheel 150 is accelerated much faster than the vehicle 100; and the wheel 150 must fall back to the original speed in order to be considered stable again.

[0105] In order to detect the stability of the wheel 150, the method may have at least one further step from the following steps:

[0106] 7a) monitoring whether the absolute first signal |s1| exceeds the absolute first threshold c1;

[0107] 7b) monitoring whether the absolute second signal |s2| exceeds the absolute second threshold c2;

[0108] 7c) monitoring whether the absolute third signal |s3| exceeds the absolute third threshold value c3;

[0109] 7d) monitoring whether the absolute fourth signal |s4| exceeds the absolute fourth threshold c4;

[0110] 7e) monitoring whether the fifth signal s5 exceeds an absolute fifth threshold value c5; and / or

[0111] 8) If in all steps 7a to 7d, in particular within the defined second time duration t2, the respective absolute signals |s1|, |s2|, |s3|, |s4|, s5 do not exceed the respective threshold values ​​c1, c2, c3, c4, c5 or if all absolute signals |s2|, |s3|, |s4|, s5 remain zero "0",

[0112] A stable signal 0 is generated.

[0113] like Figure 1As shown, a logical “OR” operation can be provided between the five signals |s1|, |s2|, |s3|, |s4|, s5. The five signals |s1|, |s2|, |s3|, |s4|, s5 present at the input of the “OR” operation indicate the unstable state of the wheel 150 one by one. Whenever only one of the five signals s1, s2, s3, s4, s5 indicates an unstable behavior of the wheel 150, the output of the “OR” operation resets the time integrator ZI again for the defined second duration t2. If all five signals remain “0” for the defined second duration t2, for example 50 ms, the wheel 150 is considered “stable” again.

[0114] Figure 4 , 5 6 show a corresponding assistance system for a vehicle 100, which can be implemented in the form of an anti-lock braking system or an anti-skid control system, which can also be referred to as an ABS system and an ASR system. In this case, the vehicle 100 is implemented with at least one wheel 150 for driving the vehicle 100, wherein the wheel 150 has at least one rotational speed sensor 110. Advantageously, the assistance system according to the invention has a control unit 200, which is implemented to detect a slip d* of the wheel 150 according to the method that can be performed as described above.

[0115] The control unit 200 according to the present invention can be Figure 5 The embodiment of the invention directly communicates with the rotation speed sensor 110 and maintains a data connection and / or in accordance with Figure 6 The embodiment of the present invention directly communicates and data-connects with the central control unit 210 of the vehicle 100 in order to query and / or obtain the measured values ​​of the rotational speed sensor 110. Within the scope of the present invention, it is also conceivable that the control unit 200 can be implemented as a separate control unit 200, for example, a separate control unit for each wheel 150 of the vehicle 100, or can be implemented in the central control unit 210 of the vehicle 100.

[0116] The above description of the drawings describes the present invention only within the framework of the examples. Of course, as long as it is technically reasonable, the various features of these embodiments can be freely combined with each other without departing from the protection scope of the present invention.

[0117] Reference numerals list

[0118] 100 Vehicles

[0119] 110 Speed ​​sensor

[0120] 150 Wheels

[0121] 200 Control Unit

[0122] 210 Central Control Unit

[0123] w Speed, speed signal

[0124] wRX Timestamp

[0125] a Rotational acceleration

[0126] r Rotational jerk

[0127] s3, s4 wheel dynamic characteristics

[0128] d Detection signal

[0129] d* Slip

[0130] 1 Positive detection signal

[0131] 0 Stable signal

[0132] s1 First signal

[0133] s2 Second signal

[0134] s3 Third signal

[0135] s4 fourth signal

[0136] p1 first threshold

[0137] p2 Second threshold

[0138] p3 The third threshold

[0139] p4 Fourth threshold

[0140] b1 The first condition

[0141] b2 Second condition

[0142] b3 The third condition

[0143] b4 The fourth condition

[0144] t1 first duration

[0145] t2 Second duration

[0146] |s1| Absolute first signal

[0147] |s2| Absolute second signal

[0148] |s3| Absolute third signal

[0149] |s4| Absolute fourth signal

[0150] s5 fifth signal

[0151] c1 absolute first threshold

[0152] c2 absolute second threshold

[0153] c3 absolute third threshold

[0154] c4 Absolute fourth threshold

[0155] c5 absolute fifth threshold

[0156] μ Wheel-track friction coefficient

[0157] Fmax Maximum transmittable longitudinal force

[0158] LB Romberg Observer

[0159] Ma Wheel driving torque

[0160] Mb Wheel braking torque

[0161] RS switch block

[0162] ZI Time Integrator

Claims

1. A method for detecting a slip (d*) of a wheel (150) of a vehicle (100) independently of a measurement and / or estimation of a slip of a tire of the wheel (150) and / or a friction coefficient between the tire of the wheel (150) and a roadway, wherein at least one rotational speed sensor (110) is assigned to the wheel (150), and wherein the method is performed by means of a control unit (200) of the vehicle (100), The method comprises the following steps: 1) detecting the rotation speed (w) of the wheel (150) by means of the at least one rotation speed sensor (110); 2a) generating, by means of the control unit (200), a first signal (s1) for the rotational acceleration (a) of the wheel (150), wherein the rotational acceleration (a) of the wheel (150) is determined based on the detected rotational speed (w); 2b) generating, by means of the control unit (200), a second signal (s2) for the rotational jerk (r) of the wheel (150), wherein a rotational jerk (r) of the wheel (150) is determined based on the determined rotational acceleration (a); 3a) monitoring whether the first signal (s1) exceeds a first threshold (p1); 3b) monitoring whether the second signal (s2) exceeds a second threshold (p2); 4) if the first threshold value (p1) is exceeded by the first signal (s1) and the second threshold value (p2) is exceeded by the second signal (s2), The control unit (200) generates a positive detection signal (1) for identifying the slip (d*) of the wheel (150), The method comprises the following steps: 2c) generating, by the control unit (200), a third signal (s3) for an area below the first signal (s1); 2d) generating, by the control unit (200), a fourth signal (s4) for an area below the second signal (s2); 3c) monitoring whether the third signal (s3) exceeds a third threshold value (p3); 3d) monitoring whether the fourth signal (s4) exceeds a fourth threshold value (p4), wherein if the first threshold (p1) is exceeded by the first signal (s1), the second threshold (p2) is exceeded by the second signal (s2), the third threshold (p3) is exceeded by the third signal (s3) and the fourth threshold (p4) is exceeded by the fourth signal (s4), In step 4), a positive detection signal (1) is generated which identifies the slip (d*) of the wheel (150), The method comprises at least one further step of: 5) starting from the time point when the slip of the wheel (150) is identified, generating a fifth signal (s5) for the area below the third signal (s3) by the control unit (200); 6a) generating an absolute first signal (|s1|) as an absolute value function of the first signal (s1); 6b) generating an absolute second signal (|s2|) as an absolute value function of the second signal (s2); 6c) generating an absolute third signal (|s3|) which is a function of the absolute value of the third signal (s3); and / or 6d) generating an absolute fourth signal (|s4|) as an absolute value function of the fourth signal (s4), The method comprises at least one further step of: 7a) monitoring whether the absolute first signal (|s1|) exceeds an absolute first threshold (c1); 7b) monitoring whether the absolute second signal (|s2|) exceeds an absolute second threshold value (c2); 7c) monitoring whether the absolute third signal (|s3|) exceeds an absolute third threshold value (c3); 7d) monitoring whether the absolute fourth signal (|s4|) exceeds an absolute fourth threshold value (c4); 7e) monitoring whether the fifth signal (s5) exceeds an absolute fifth threshold value (c5); The method comprises the following steps: 8) If in all steps 7a) to 7e), the corresponding absolute signal (|s1|, |s2|, |s3|, |s4|, s5) does not exceed the corresponding threshold value (c1, c2, c3, c4, c5), A stable signal (0) is generated.

2. The method according to claim 1, It is characterized in that If in all steps 7a) to 7e), the corresponding absolute signal (|s1|, |s2|, |s3|, |s4|, s5) does not exceed the corresponding threshold value (c1, c2, c3, c4, c5) within the defined second time period (t2), Then the stable signal (0) is generated.

3. The method according to claim 1, It is characterized in that The first signal (s1) and the second signal (s2) are reconstructed based on the rotation speed signal (w).

4. The method according to claim 3, It is characterized in that The first signal (s1) and the second signal (s2) are reconstructed from the rotational speed signal (w) by means of a Romberg observer (LB).

5. The method according to claim 1, It is characterized in that confirming a first condition (b1) when the first signal (s1) exceeds the first threshold (p1); and / or confirming a second condition (b2) when the second signal (s2) exceeds the second threshold value (p2); and / or confirming a third condition (b3) when the third signal (s3) exceeds the third threshold value (p3); and / or confirming a fourth condition (b4) when the fourth signal (s4) exceeds the fourth threshold (p4).

6. The method according to claim 5, It is characterized in that The confirmation of the first condition (b1) when the first signal (s1) exceeds the first threshold (p1) and the confirmation of the second condition (b2) when the second signal (s2) exceeds the second threshold (p2) continue for a first time period (t1) defined without being overwritten.

7. The method according to claim 6, It is characterized in that The first time duration (t1) is 10 ms.

8. The method according to any one of claims 1 to 7, It is characterized in that After the slip (d*) of the wheel (150) has been detected in step 4), the positive detection signal (1) is retained and is not changed.

9. The method according to claim 8, It is characterized in that After the slip (d*) of the wheel (150) is detected in step 4), the positive detection signal (1) is maintained and is not changed until a stable signal (0) of the wheel (150) is detected and exists for a defined second time period (t2).

10. The method according to any one of claims 1 to 7, It is characterized in that The method comprises at least one further step of: 9) determining a maximum longitudinal force (Fmax) that can be transmitted to the roadway by the wheel (150) based on the wheel drive torque (Ma) and / or the wheel braking torque (Mb) at or after the time point at which the wheel (150) slips (d*) or locks in step 4); and / or 10) Determining the coefficient of friction (μ) between the tire of the wheel (150) and the roadway.

11. The method according to claim 10, It is characterized in that The method comprises at least one further step of: 9) at or after the time at which the wheel (150) slips (d*) or locks in step 4) is detected, a maximum longitudinal force (Fmax) that can be transmitted to the roadway by the wheel (150) is calculated based on the wheel drive torque (Ma) and / or the wheel braking torque (Mb); and / or 10) Calculating the friction coefficient (μ) between the tire of the wheel (150) and the roadway.

12. An assistance system for a vehicle (100), the vehicle having at least one wheel (150) for driving the vehicle (100), wherein the wheel (150) has at least one rotational speed sensor (110), The assistance system has a control unit (200), wherein the control unit (200) is implemented to detect a slip (d*) of the wheel (150) according to the method of one of the preceding claims.

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