METHOD FOR DETERMINING A DEFECTIVE CONDITION OF A DRIVETRAIN OF A VEHICLE, MONITORING UNIT AND VEHICLE

Description

[0001] The invention relates to a method for determining a defect state of a drive train, a monitoring unit for carrying out the method and a vehicle.

[0002] Defects in a vehicle's drivetrain can lead to temporary functional impairments if the drive torque generated by the engine or drivetrain cannot be continuously and fully transferred to the wheels and thus to the ground. Furthermore, defects in individual drivetrain components can result in consequential damage. For example, improperly mounted wheels, defective drivetrain sprockets, or defective tires can lead to permanent drivetrain failure and even dangerous accidents due to loose components.

[0003] For example, if wheel nuts securing the wheel to a vehicle's wheel hub are inadvertently partially or completely loosened, these nuts, along with the wheels that are no longer fully secured, can pose a danger to surrounding traffic and neighboring pedestrians. An incompletely tightened wheel nut also causes the threaded bolts on which the wheels sit and onto which the wheel nuts are screwed to move with play in the holes in the wheel rim. This causes significant wear on both the threaded bolts and the holes in the rim, preventing the wheel from being securely attached to the wheel hub.

[0004] Monitoring the powertrain for such defects can be done visually by the driver before or after a trip. However, manual monitoring during the trip is generally not possible. Furthermore, automated vehicles do not have a driver present, so reliable automatic detection is required to ensure safe and reliable autonomous driving. Such a system is not yet known.

[0005] DE102011089101A1 discloses a method for detecting a fault in a drive train of a vehicle by detecting a fault in the drive train based on the result of comparing the time course of the actual angle of rotation with the predetermined reference course.

[0006] DE102012011757A1 relates to a method for detecting a torsional backlash of a drive train of a vehicle, in which, before a transition from a push to a pull operation of the vehicle, a speed difference between the engine speed and the reference speed is determined with a high temporal resolution from a detected engine speed and a detected reference speed.

[0007] DE102007052749A1 relates to a method for detecting wheel slip on at least one wheel driven by a motor, wherein the drive torque acting on the wheel varies, and the reaction of the wheel to the change in the drive torque is measured and evaluated.

[0008] DE102019100323A1 relates to a system arrangement and a method for diagnosing backlash in the drive train of a motor vehicle, whereby it is possible to advantageously analyze and, if necessary, counteract time delays that arise due to necessary tolerances within a drive system of a motor vehicle.

[0009] AT508032A4 discloses a method and a test bench for testing a drive train of a vehicle with at least one shaft. To achieve a target torque in the drive train, the rotation angle of the shaft(s) is controlled at at least two separate points in the drive train, or a rotation angle difference between at least two points in the drive train is controlled. The object of the invention is therefore to provide a method for determining a defective state of a drive train of a vehicle, with which safe and reliable driving can be ensured. Furthermore, the object of the invention is to provide a monitoring unit and a vehicle.

[0010] This object is achieved by a method, a monitoring unit, and a vehicle according to the independent claims. The subclaims specify preferred developments.

[0011] According to the invention, a method is provided for determining a defect state of a drive train of a vehicle, wherein the vehicle has a drive axle with a drive wheel and a reference axle with a reference wheel, wherein a drive torque generated by a drive can be transmitted via the drive wheel to a ground via the drive train and the drive torque of the drive is not transmitted to the ground via the reference wheel of the reference axle, comprising at least the following steps: Reading in a drive variable, whereby the drive variable is dependent on a motor speed of the drive and therefore characterizes the rotational behavior or the drive behavior of the drive axis, whereby the drive variable is preferably given directly by the motor speed of the drive, e.g.by a resolver (angle encoder) in an electric motor; reading in a reference variable, whereby the reference variable is dependent on a reference wheel speed of the reference wheel and therefore characterizes the rotational behavior of the reference axle; determining whether there is a deviation between the read-in drive variable and the read-in reference variable in order to establish whether the reference wheel speed of the reference wheel is related to the motor speed of the drive, whereby if a deviation is present, a defect in the drive train is concluded; and outputting a status signal if a defect in the drive train is present, which has the same effect as the omission of a permanently output status signal if a defect is present.

[0012] Therefore, by comparing the rotational behavior or drive behavior of the drive axle with the rotational behavior of the non-driven reference axle, it can be checked in a simple and reliable manner whether a generated drive torque is being transferred to the ground via the drive train. If this is not the case due to a defect, it is to be expected that there will be a difference in the rotational behavior of the two axles, whereby the rotational behavior of the respective axle can be specified by the drive variable or the reference variable. In this way, a defect can be easily determined, preferably using sensors already present in the vehicle. This can be done in a monitoring unit according to the invention, which is designed to carry out the method according to the invention.

[0013] Preferably, if a deviation occurs between the read drive variable and the read reference variable, a conclusion is drawn that the drive train is defective, taking into account the normal state of the drive train. When evaluating the deviation, it is therefore advantageous to additionally consider whether a specific deviation results from a normal, expected behavior of the drive train or whether this normal behavior at least contributes to a certain extent to a deviation. For example, a certain amount of play may already be present in the drive train components when the system is new, although this normally occurring play is then no longer attributable to a defective state when the system is replaced.Only when the play increases, for example due to wear or loosening of the drive train components (starting from the new condition), can this be indicated as a defect condition by the evaluation according to the invention.

[0014] In this case, it is therefore preferably provided that a defect state is not concluded if a deviation between the read-in drive variable and the read-in reference variable is caused solely or exclusively by a normal state of the drive train, i.e. by an expected behavior of the drive train, wherein the drive train in the normal state does not have a defect despite a detected deviation between the read-in drive variable and the read-in reference variable. In this way, a certain expected deviation can be taken into account when determining the defect state. If, for example, only a learned first offset, which is assigned to a usual behavior of the drive train, occurs temporarily or non-periodically in the oscillating drive variable, this can be disregarded ora defective condition can still be ruled out unless other causes contribute to an additional deviation.

[0015] Preferably, it is further provided that the deviation detectable in a normal state between the read drive variable and the read reference variable is taught in advance. For example, it can be determined in previous tests that a deviation between the read drive variable and the read reference variable in the normal state results from tolerance-related or usual and therefore expected backlash in a gear of the drive train. In this way, the defect state can be determined more accurately and quickly if such common effects are taught in advance.

[0016] Preferably, it is further provided that a defect condition is only or exclusively concluded from a deviation between the read-in drive variable and the read-in reference variable if this deviation occurs during or as a result of a change in the drive torque transmitted to the ground via the drive wheel and / or a change in the braking torque transmitted to the ground via the drive wheel.

[0017] It is therefore advantageously assumed that defects can be detected primarily when there is a change in the acting drive torque or, in general, in the torques acting in the drive train. Therefore, if an induced force or an induced torque on the individual drive components changes, it can be assumed that this changed torque is transmitted via the drive train with a delay or disturbance in the event of a defect, e.g., caused by a system change in the event of wear-related play or a loose component in the drive train. This delay or disturbance can be determined in the form of an at least temporarily occurring deviation by comparing it with the rotational behavior of the reference wheel, which does not experience this disturbance when the drive torque or braking torque changes.

[0018] Preferably, it is further provided that a defect condition is only or exclusively inferred from a deviation between the read-in drive variable and the read-in reference variable if this deviation when the drive torque of the drive changes with a change in sign, or when the drive torque of the drive and / or the braking torque changes to zero, or when the drive torque of the drive and / or the braking torque changes from zero. A change is understood to mean that a different drive torque or braking torque was previously present at the drive axle. Thus, the drive torque crosses zero with a positive or negative gradient, or the drive torque and / or the braking torque decreases or increases to zero.

[0019] Preferably, it is further provided that the drive variable and the reference variable each exhibit an oscillating characteristic, with the drive variable and the reference variable being recorded by an incrementally measuring speed sensor. This allows a change or deviation in the respective variables to be detected with high resolution if a defect condition occurs only temporarily and briefly. This defect condition can be well represented in an oscillating behavior.

[0020] Preferably, it is provided that a defect in the drive train is inferred if the deviation is caused by a second offset in the drive variable, wherein the second offset is caused by a changed period length of the oscillating curve of the drive variable, wherein the second offset cannot be detected in the oscillating curve of the reference variable. A deviation can therefore be easily determined by analyzing the period length or, equivalently, the frequency.

[0021] Preferably, the period length of the oscillating curve of the drive variable changes briefly and not periodically when a defective state of the drive train exists. This makes it easy to identify whether a deviation occurs due to a one-time effect, which may be linked to the torque in the drive train, or due to a recurring systematic effect, which is to be expected.

[0022] Preferably, it is further provided that a defect condition exists if a wheel nut fastening the drive wheel to a drive wheel hub is so loose that a deviation occurs between the read drive variable and the read reference variable when there is a change in the drive torque transmitted to the ground via the drive wheel and / or a change in the braking torque transmitted to the ground via the drive wheel, since the reference wheel speed of the reference wheel is at least temporarily no longer related to the engine speed of the drive. This can be caused by the fact that when the wheel nut is loose, the threaded bolt can move in a hole in the rim depending on the sign of the torque in the drive train and changes between two stops depending on the torque generated, whereby the drive torque / braking torque is not continuously transmitted to the ground.This can be easily determined temporarily by a deviation, especially when the generated torque (drive torque / braking torque) changes sign or increases or decreases to zero.

[0023] It is preferably further provided that - the engine speed of the drive and / or a drive hub speed of a drive wheel hub in the same drive train as the drive is read in as the drive variable, wherein the drive wheel is arranged on the drive wheel hub and the drive hub speed corresponds to the engine speed of the drive at least during a transmission of a drive torque, and / or - a reference hub speed of a reference wheel hub on the reference axle is read in as the reference variable, wherein the reference wheel is arranged on the reference wheel hub.

[0024] In this way, monitoring can be based on sensors already present in the vehicle, with the reference variable being determined, for example, using a wheel speed sensor on the reference axle, which is already present as part of an ABS system. The drive variable can be determined using an engine speed sensor, which directly measures the engine speed, or via a wheel speed sensor on the drive axle, which is also part of an ABS system.

[0025] A vehicle according to the invention, in particular a commercial vehicle, can be equipped with a monitoring unit according to the invention, wherein the vehicle has a drive axle with a drive wheel and a reference axle with a reference wheel, wherein a drive torque generated by a drive can be transmitted via a drive train of the vehicle to a ground via the drive wheel and the drive torque of the drive is not transmitted to the ground via the reference wheel of the reference axle, wherein the drive axle is assigned a drive speed sensor for determining the drive variable and the reference axle is assigned a reference speed sensor for determining the reference variable.

[0026] It is preferably provided that the drive is an electric motor for generating the drive torque and the drive speed sensor is a motor speed sensor which directly detects a motor speed as a drive variable.

[0027] The invention is explained in more detail below using an exemplary embodiment. The figures show: Fig. 1 a schematic view of a vehicle; Fig. 2 a driving behavior of the wheels of the vehicle according to Fig. 1 ; Figs. 3, 4, 5 oscillating behavior of the signals from speed sensors; Fig. 5A a system change due to a loose wheel nut as an example of a defective state of the drive train; and Fig. 6 a flowchart of a method according to the invention.

[0028] Figur 1 shows a highly schematic view of a vehicle 1 which is located on a surface 2 and which has at least two axles 1a, 1b. The vehicle 1 can be a towing vehicle (motor vehicle, tractor, etc.) or a trailer (drawbar trailer, semi-trailer, etc.). A drive axle 1a of the vehicle 1 is part of a drive train 3 of the vehicle 1. The drive train 3 includes all drive components which generate the drive power in the vehicle 1 and transmit it to the surface 2. The drive train 3 therefore includes in particular a drive 5, e.g. an electric motor 5a or an internal combustion engine 5b, a transmission 7, a drive wheel hub 9, a drive wheel 11 with a rim 11a and a tire 11b mounted thereon, as well as corresponding transmission elements between the aforementioned drive components. The drive train 3 can also have further drive components not shown.

[0029] The drive 5 is connected to the transmission 7 via a first drive shaft 13a, and the transmission 7 is connected to the drive wheel hub 9 via a second drive shaft 13b. The drive wheel 11 is fastened to the drive wheel hub 9, whereby the drive wheel hub 9 has several threaded bolts 9a, each of which is guided through holes 11c in the rim 11a of the drive wheel 11. Wheel nuts 9b are screwed onto the threaded bolts 9a inserted through the holes 11c, which press the rim 11a against the drive wheel hub 9 and, when tightened, thereby securely fastening the drive wheel 11 to the drive wheel hub 9. With sufficient fastening, the drive torque MA (torque) generated by the drive 5 is transmitted via the transmission 7 to the drive wheel hub 9 and via the tire 11b directly to the ground 2.

[0030] In addition to the drive axle 1a, the vehicle has a reference axle 1b, which is not driven in the illustrated embodiment. A reference wheel 15 is provided on the reference axle 1b, which, like the drive wheel 11, is fastened to a reference wheel hub 16 via threaded bolts 9a and wheel nuts 9b, for example. However, other fastenings can also be provided. The reference wheel 15 on the reference axle 1b, which is not driven in this case, rotates automatically as a result of a movement of the vehicle 1 induced by the drive wheel 11 on the drive axle 1a by rolling along the ground 2. The drive torque MA is therefore not transferred directly from the drive 5 to the reference wheel 15 of the reference axle 1b.

[0031] According to the illustrated embodiment, the drive axle 1a is further assigned two drive speed sensors 17a in the form of a motor speed sensor 18 and a wheel speed sensor 19, with which the rotational behavior of the drive axle 1b can be determined. The motor speed sensor 18 is designed to detect a variable related to the motor speed N5 of the drive 5 with high resolution directly at the drive 5. Such a motor speed sensor 18 is, for example, an integral component of an electric motor 5a driving the vehicle 1.

[0032] The wheel speed sensor 19, for example, measures a variable related to a drive hub speed N9 of the drive wheel hub 9. Since the drive wheel hub 9 is connected to the drive 5 via the drive shafts 13a, 13b and the transmission 7, the drive hub speed N9 in the engaged state ideally corresponds to the engine speed N5, provided there are no defects in the drive train 3 between the drive 5 and the drive wheel hub 9.

[0033] In the illustrated embodiment, a reference speed sensor 17b, in this case also a wheel speed sensor 19, is assigned to the reference axle 1b. This sensor measures a variable related to the reference hub speed N16 of the reference wheel hub 16 and thus the rotational behavior of the reference axle 1b. The wheel speed sensors 19 on the respective axles 1a, 1b are, for example, part of an ABS control system in the vehicle 1. Assuming that the respective wheel 11, 15 is correctly attached to the respective wheel hub 9, 16, the respective hub speed N9, N16 also corresponds to a wheel speed N11, N15 of the respective wheel 11, 15, assuming synchronous wheel running.

[0034] The speed sensors 18, 19 can be designed, for example, as incremental measuring sensors (incremental encoders), for example with optical or magnetic scanning. The respective speed sensors 17a, 17b thus output signals, i.e., a drive signal SA, which characterizes the rotational behavior of the drive axis 1a (motor speed N5 or drive hub speed N9), or a reference signal SB, which characterizes the rotational behavior of the reference axis 1b (reference hub speed N16), which are transmitted to a monitoring unit 21 for further processing.

[0035] For example, the drive signal SA, which is detected by an engine speed sensor 18 as a drive speed sensor 17a in the drive train 3, and the reference signal SB, which is detected by a wheel speed sensor 19 as a reference speed sensor 17b on the reference axle 1b, in Fig. 3 Both signals SA, SB are recorded in the same driving situation or simultaneously, ie they reflect the rotational behavior of the respective axle 1a, 1b in the same driving situation.

[0036] In an incrementally measuring sensor, the drive signal SA and the reference signal SB each transmit an oscillating waveform 23a (SA), 23b (SB), which results from the incremental scanning and from which the rotational behavior of the respective axis 1a, 1b can be derived. The oscillating sinusoidal signal waveform is merely an example, although a square wave signal could alternatively be used for evaluation. The drive signal SA and the reference signal SB are in Fig. 3 over the travel distance w (x-axis), resulting in a speed-independent oscillating curve 23a, 23b with a constant period length dTa, dTb. Fig. 3 It can therefore be seen that both the drive axle 1a and the reference axle 1b run synchronously over the travel path w shown, from which it can be concluded that a drive torque MA generated by the drive 5 is transmitted undisturbed via the drive train 3, in particular via the drive wheel 11, to the ground 2 and the reference wheel 15 immediately follows this drive movement.

[0037] The period length dTa, dTb of the respective oscillating curve 23a, 23b depends on the resolution of the respective speed sensor 17a (18), 17b (19). Fig. 3 Due to the shorter period lengths dTa, i.e., shorter increments, for the oscillating drive curve 23a, it can be seen that the motor speed sensor 18 used on the drive axle 1a has a higher resolution than the wheel speed sensor 19 (oscillating reference curve 23b) on the reference axle 1b, which is used, for example, with a pole wheel in a conventional ABS control system. In principle, a wheel speed sensor 19 with a higher resolution can also be used, i.e., the period lengths dTa, dTb of the two curves 23a, 23b approach each other.

[0038] With such a setup, it is possible to demonstrate, as described below, whether there are any deviations between the rotational behavior of the drive axle 1a, which is characterized by the oscillating drive curve 23a, and the rotational behavior of the reference axle 1b, which is characterized by the oscillating reference curve 23b. From this, it can be concluded whether the drive torque MA generated by the drive 5 is transmitted permanently and completely to the ground 2 (and thereby indirectly to the reference axle 1b) or whether interruptions in the torque transmission indicate a defect in the drive train 3. For this purpose, the method according to the invention can be used according to Fig. 6 for example, be carried out as follows: First, in a first step ST1, a drive variable GA characterizing the rotational behavior of the drive axle 1a, e.g. the engine speed N5 and / or the drive hub speed N9, which is determined via at least one of the drive speed sensors 17a in the drive train 3, is read in by the monitoring unit 21. The drive variable GA is characterized in that it can reproduce the rotational behavior of the drive axle 1a as a result of manual or automated control of the drive 5 as accurately as possible, ie it corresponds as closely as possible to the engine speed N5 of the drive 5 or depends on it. The closer the measuring point of the drive variable GA is to the drive 5, the more accurately the drive variable GA fulfills this requirement.

[0039] At the same time, the determination of the condition of the drive train 3 using the method according to the invention becomes more accurate the closer the drive variable GA is measured to the drive 5. For example, if there is a defect in the transmission 7, a measurement of the drive variable GA (as seen from the drive 5) downstream of the transmission 7 cannot detect a defect in the transmission 7 itself, since the method according to the invention can only monitor the rotational behavior (as seen from the drive 5) downstream of the measuring point of the drive variable GA.

[0040] In a second step ST2, a reference variable GB characterizing the rotational behavior of the reference axis 1b, e.g. the reference hub speed N16, which is measured via the reference speed sensor 17b on the associated reference axis 1b, is read in by the monitoring unit 21.

[0041] The two steps ST1, ST2 are carried out continuously, whereby different driving situations can arise, which are Fig. 2 are shown. In Fig. 2 The drive torque MA generated by the drive 5 is plotted against the travel distance w. In a first area B1, the drive 5 is in idle, ie no drive torque MA is transmitted from the drive 5 via the drive train 3 to the drive wheels 11, the vehicle 1 is therefore in a so-called coasting mode. This results in the Fig. 3 The rotational behavior of the drive axle 1a and the reference axle 1b shown is as already described, whereby in the ideal case with inter-axle synchronized wheel rotational behavior the motor speed N5 (drive variable GA) corresponds to the reference hub speed N16 (reference variable GB) over the entire travel distance w in the first area B1.

[0042] In a second area B2 (see Fig. 2 ) the vehicle 1 is accelerated by a corresponding control of the drive 5, ie a corresponding drive torque MA generated by the drive 5 is transmitted via the drive wheels 11 to the ground 2 and via it to the reference wheels 15. Even if a temporal change in the engine speed N5 and the reference hub speed N16 is to be expected in the second area B2, this is when the engine speed N5 (drive variable GA, drive signal SA) and the reference hub speed N16 (reference variable GB, reference signal SB) are plotted over the travel distance w, as in Fig. 4 shown, not visible. The period lengths dTa, dTb thus remain identical to the first range B1 in the second range B2, depending on the resolution of the respective speed sensor 17a, 17b.

[0043] However, a difference arises in a first intermediate area Z1 between the first area B1 and the second area B2 (see Fig. 2 and Fig. 4 ), in which the change in the driving situation (coasting => acceleration) is initiated. In the first intermediate range Z1, a first offset V1 in the period dTa or in the frequency of the oscillating drive curve 23a, which is detected by the engine speed sensor 18 on the drive axle 1a, occurs briefly and once. This first offset V1 cannot be seen in the oscillating reference curve 23b of the wheel speed sensor 19 on the reference axis 1b, so that in the present case a deviation D can be determined between the read-in drive variable GA and the read-in reference variable GB. From this it can be concluded that the first offset V1 results from the rotational behavior of the drive axle 1a.

[0044] The first offset V1 shown results, for example, from the fact that there is normally a slight play between the gear rims of the transmission 7, so that the gear rims briefly rotate against each other during the transition from idling / coasting (B1) to the acceleration phase (B2), and as a result, for a short time no drive torque MA is transmitted from the drive 5 via the drive train 3 to the ground 2. This results in a brief jump when this drive signal SA is plotted in the form of the engine speed N5 as the transmission variable GA over the travel distance w. The reference signal SB or the reference hub speed N16 as the reference variable GB is not aware of this jump, since it is not transmitted via the drive wheel 11 to the ground 2 and thus also not to the reference axis 1b.

[0045] This first offset V1, resulting from a tolerance-related tooth play ZN1 in the transmission 7, can be learned by the monitoring unit 21 and therefore taken into account in the respective evaluations by the monitoring unit 21 as the normal state ZN of the drive train 3. Therefore, when determining the first offset V1 as a deviation D between the read-in drive variable GA and the read-in reference variable GB, the monitoring unit 21 can conclude that this most likely does not result from a defect in the drive train 3, but rather occurs due to an expected transmission effect in the drive train 3. As a result, in the case of behavior according to Fig. 4 no defect state ZD of the drive train 3 is determined and output.

[0046] If the drive signal SA is measured behind the transmission 7, for example by a wheel speed sensor 19 (drive speed sensor 17a) on the drive axle 1a, which measures the drive hub speed N9, this first offset V1 is not detected as a normal state ZN, since it can no longer be detected behind the transmission 7, which causes the jump.

[0047] In a third area B3 (see Fig. 2 ) the vehicle 1 is decelerated by a corresponding control of the drive 5 and / or brakes 6, ie a corresponding negative drive torque MA (drag torque) generated by the drive 5 in a recuperation phase or a braking torque MB generated by the brakes 6 in a braking phase is transferred to the ground 2 via the drive wheels 11, whereupon the reference wheels 15 also rotate more slowly.

[0048] In this driving situation, the Fig. 5 shown oscillating curve 23a, 23b of the drive signal SA or the reference signal SB over the travel path w. As in Fig. 4 In a second intermediate range Z2, a deviation D occurs between the read drive variable GA and the read reference variable GB. This deviation D is caused by the tooth play ZN1 in the gear 7 (normal state ZN, first offset V1), which now also occurs again coming from the acceleration phase (B2 => Z2 => B3). If this first offset V1 was previously taught by the monitoring unit 21 as the normal state ZN (see also Figur 4 ), it can be identified again in the second intermediate range Z2. Based on the first offset V1 in the second intermediate range Z2, a defect state ZD of drive train 3 is not yet inferred.

[0049] In addition, a second offset V2 can be identified in the second intermediate range Z2, which occurs in addition to the previously learned first offset V1 (normal state ZN) in the drive signal SA or in the oscillating drive curve 23a. This second offset V2 also contributes to the deviation D between the read drive variable GA and the read reference variable GB, since this also Fig. 5 does not occur in the reference signal SB or in the oscillating reference curve 23b. Therefore, the second offset V2 also results from the rotational behavior in drive train 3.

[0050] In the present case, it is concluded that the second offset V2 results from a defect in the drive train 3, which is caused, for example, by a loose wheel nut 9b. Consequently, a defect state ZD of the drive train 3 associated with the second offset V2 is determined and output via a defect signal SD. With a loose wheel nut 9b, the case occurs that, for example, in the second intermediate area Z2, a drive torque MA generated by the drive 5 is not directly transmitted via the drive wheel 11 to the ground 2 (comparable to the tooth play ZN1 in the transmission 7). This results from the threaded bolts 9a on the drive wheel hub 9, as in Fig. 5A shown in the holes 11c in the rim 11a of the drive wheel 11 upon a change in the sign of the drive torque MA or upon a transition from a braking torque MB to a positive drive torque MA, ie, in the second intermediate range Z2. The drive wheel 11 therefore only follows the rotational behavior of the drive 5 with a delay.

[0051] This is in Fig. 5A shown schematically. Accordingly, in the second area B2, i.e., with a positive drive torque MA, the threaded bolt 9a rests against a front flank 12a of the hole 11c in the rim 11a. In the third area B3, i.e., with a negative drive torque MA or a braking torque MB, however, the threaded bolt 9a rests against a rear flank 12b of the hole 11c. Consequently, in the second intermediate area Z2 between the second area B2 and the third area B3, a change of contact occurs, in which the threaded bolt 9a changes flanks 12a, 12b.

[0052] During this system change, the drive 5 does rotate, which can be determined via the drive variable GA, but for a short and one-time period no torque is transmitted to the drive wheel 11 and consequently also not to the ground 2, so that the second offset V2 occurs. The rotational behavior of the reference wheel 15 does not change, so that during the system change (12a <=> 12b) in the second intermediate range Z2, a deviation D arises between the read drive variable GA and the read reference variable GB. After determining this deviation D in the form of the normally non-occurring second offset V2, it can be concluded that the drive train 3 is defective, since this second offset V2 does not correspond to the normal state ZN of the drive train 3.

[0053] This effect due to the system change is particularly noticeable in the second intermediate range Z2 during a transition from the driven state (B2) to the braking state (B3), since this is when the described edge change occurs most significantly. In principle, however, this effect can also be determined in the first intermediate range Z1 (B1 => B2) or in a third intermediate range Z3 (B3 (recuperation, braking) => B4 (idling)) by analyzing the deviation D between the read-in drive variable GA and the read-in reference variable GB. In principle, this deviation D can always be determined due to the system change when the drive torque MA changes sign (B2 <=> B3) or the drive torque increases from zero (idling / coasting) (Z1: acceleration) or decreases (deceleration) or the drive torque MA changes from an acceleration phase or a braking phase (B3) to zero (cf. Z3).

[0054] By comparing the read-in drive variable GA with the read-in reference variable GB or by determining a deviation D by the monitoring unit 21 in a third step ST3, a defect state ZD of the drive train 3 can be determined, taking into account a previously determined or learned normal state ZN. Depending on this, the monitoring unit 21 can then output a defect signal SD, which is subsequently further processed to enable a response to the detected defect. For this purpose, a display device 25 in the vehicle 1 can be controlled depending on the defect signal SD in order to indicate the defect to the driver. The driver can then react manually accordingly.However, the vehicle 1 can also be controlled automatically depending on the defect signal SD, so that the vehicle is automatically parked accordingly, for example, and / or driven to a workshop to have the defect checked.

[0055] The loose wheel nut 9b was given merely as an example of a possible detectable defect state ZD of the drive train 3. However, other defects may also be present that do not occur in the normal state ZN of the drive train 3 and that also result in a drive torque MA generated in the drive train 3 not being continuously transmitted to the ground 2 and, through it, to the reference wheel 15. All of these effects can be detected by determining the deviation D between the read-in drive variable GA and the read-in reference variable GB, according to the invention. List of reference symbols (part of the description)

[0056] 1Vehicle 1aDrive axle 1bReference axle 2Ground 3Drive train of vehicle 1 5Drive 5aElectric motor 5bCombustion engine 6Brakes 7Gearbox 9Drive wheel hub 9aThreaded bolt 9bWheel nut 11Drive wheel 11aRim 11bTire 11cHoles in the rim 11a 12Front flank 12bRear flank 13aFirst drive shaft 13bSecond drive shaft 15Reference wheel 16Reference wheel hub 17aDrive speed sensor 17bReference speed sensor 18Engine speed sensor 19Wheel speed sensor 21Monitoring unit 23aoscillating drive curve from 17a; 18 23Boscillating reference curve of 17b;19 25Display device B1first range (coasting) B2second range (acceleration) B3third range (braking, recuperation) B4fourth range (coasting) dTaperiod length of 23a dTbperiod length of 23b DAdeviation fafrequency of 23a GAdrive variable GBreference variable MAdrive torque MBbraking torque N5engine speed N9drive hub speed N11drive wheel speed N15reference wheel speed N16reference hub speed SAdrive signal SBreference signal SDdefect signal V1first offset V2second offset wtravel distance Z1first intermediate range Z2second intermediate range Z3third intermediate range ZNnormal state ZN1backlash in the gearbox 7 ZDDefect state ; ST1, ST2, ST3Steps of the procedure

Claims

1. Method for determining a defect state (ZD) of a drive train (3) of a vehicle (1), the vehicle (1) comprising a drive axle (1a) that has a drive wheel (11), and a reference axle (1b) that has a reference wheel (15), a drive torque (MA) generated by a drive (5) being transmittable via the drive wheel (11) to an underlying surface (2) via the drive train (3), and the drive torque (MA) of the drive (5) not being transmitted to the underlying surface (2) via the reference wheel (15) of the reference axle (1b), the method comprising at least the following steps: - reading in a drive variable (GA) (ST1), the drive variable (GA) being dependent on a motor speed (N5) of the drive (5); characterized by - reading in a reference variable (GB), the reference variable (GB) being dependent on a reference wheel speed (N15) of the reference wheel (15) (ST2); - determining whether there is a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) in order to detect whether the reference wheel speed (N15) of the reference wheel (15) correlates to the motor speed (N5) of the drive (5), it being concluded, if there is a deviation (D), that there is a defect state (ZD) of the drive train (3) (ST3); and - outputting a state signal (SD) if there is a defect state (ZD) of the drive train (3).

2. Method according to claim 1, characterized in that if there is a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB), it is concluded that there is a defect state (ZD) of the drive train (3), taking into account a normal state (ZN) of the drive train (3).

3. Method according to claim 2, characterized in that it is not concluded that there is a defect state (ZD) if a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) is caused solely by a normal state (ZN) of the drive train (3), the drive train (3) in the normal state (ZN) not exhibiting any defect despite a detected deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB).

4. Method according to claim 3, characterized in that the deviation (D) that is detectable in a normal state (ZN) between the read-in drive variable (GA) and the read-in reference variable (GB) is taught in in advance.

5. Method according to any of claims 2 to 4, characterized in that a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) in the normal state (ZN) results from gear backlash (ZN1) in a gear (7) of the drive train (3).

6. Method according to any of the preceding claims, characterized in that a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) is only used to conclude (ST3) that there is a defect state (ZD) if this deviation (D) arises during and / or as a result of: - a change in the drive torque (MA) transmitted to the underlying surface (2) via the drive wheel (11) and / or - a change in a braking torque (MB) transmitted to the underlying surface (2) via the drive wheel (11).

7. Method according to claim 6, characterized in that a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) is only used to conclude (ST3) that there is a defect state (ZD) if this deviation (D) arises during: - a change in the drive torque (MA) of the drive (5) that involves a sign change, or - a change in the drive torque (MA) of the drive (5) and / or the braking torque (MB) to zero, or - a change in the drive torque (MA) of the drive (5) and / or the braking torque (MB) from zero.

8. Method according to any of the preceding claims, characterized in that the drive variable (GA) and the reference variable (GB) each have an oscillating curve (23a, 23b), the drive variable (GA) and the reference variable (GB) being recorded by an incrementally measuring speed sensor (18, 19).

9. Method according to claim 8, characterized in that it is concluded that there is a defect state (ZD) of the drive train (3) if the deviation (D) is caused by a second offset (V2) in the drive variable (GA), the second offset (V2) being caused by a changed period length (dTa) of the oscillating curve (23a) of the drive variable (GA), the second offset (V2) in the oscillating curve (23b) of the reference variable (GB) being undetected.

10. Method according to claim 9, characterized in that the period length (dTa) of the oscillating curve (23a) of the drive variable (GA) changes briefly and not periodically when there is a defect state (ZD) of the drive train (3).

11. Method according to any of the preceding claims, characterized in that there is a defect state (ZD) if a wheel nut (9a) which fastens the drive wheel (11) to a drive wheel hub (9) is so loose that a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) arises when the drive torque (MA) transmitted to the underlying surface (2) via the drive wheel (11) and / or when a braking torque (MB) transmitted to the underlying surface (2) via the drive wheel (11) changes, since the reference wheel speed (N15) of the reference wheel (15) at least temporarily no longer correlates to the motor speed (N5) of the drive (5).

12. Method according to any of the preceding claims, characterized in that - the motor speed (N5) of the drive (5) and / or a drive hub speed (N9) of a drive wheel hub (9) in the same drive train (3) is read in as the drive variable (GA), the drive wheel (11) being arranged on the drive wheel hub (9) and the drive hub speed (N9) corresponding to the motor speed (N5) of the drive (5) at least during a transmission of a drive torque (MA), and / or - a reference hub speed (N16) of a reference wheel hub (16) on the reference axle (1b) is read in as the reference variable (GB), the reference wheel (15) being arranged on the reference wheel hub (16).

13. Monitoring unit (21) for a vehicle (1), in particular for carrying out a method according to any of the preceding claims, the vehicle (1) comprising a drive axle (1a) that has a drive wheel (11), and a reference axle (1b) that has a reference wheel (15), a drive torque (MA) generated by a drive (5) being transmittable via the drive wheel (11) to an underlying surface (2) via a drive train (3) of the vehicle (1) and the drive torque (MA) of the drive (5) not being transmitted to the underlying surface (2) via the reference wheel (15) of the reference axle (1b), the monitoring unit (21) being designed: - to read in a drive variable (GA), the drive variable (GA) being dependent on a motor speed (N5) of the drive (5) of the vehicle (1); characterized - to read in a reference variable (GB), the reference variable (GB) being dependent on a reference wheel speed (N15) of the reference wheel (15) of the vehicle (1); - to determine whether there is a deviation (D) between the read-in drive variable (GA) and the read-in reference variable (GB) in order to detect whether the reference wheel speed (N15) of the reference wheel (15) correlates to the motor speed (N5) of the drive (5), the monitoring unit (21) being able to conclude that there is a defect state (ZD) of the drive train (3) of the vehicle (1) if there is a deviation (D); and - to output a state signal (SD) if there is a defect state (ZD) of the drive train (3).

14. Vehicle (1), in particular a commercial vehicle, comprising a monitoring unit (21) according to claim 13, the vehicle (1) comprising a drive axle (1a) that has a drive wheel (11), and a reference axle (1b) that has a reference wheel (15), a drive torque (MA) generated by a drive (5) being transmittable via a drive train (3) of the vehicle (1) to an underlying surface (2) via the drive wheel (11), and the drive torque (MA) of the drive (5) not being transmitted to the underlying surface (2) via the reference wheel (15) of the reference axle (1b), the drive axle (1a) being assigned to a drive speed sensor (17a) to determine the drive variable (GA), and the reference axle (1b) being assigned to a reference speed sensor (17b) to determine the reference variable (GB).

15. Vehicle (1) according to claim 14, characterized in that the drive (5) is an electric motor (5a) for generating the drive torque (MA), and the drive speed sensor (17a) is a motor speed sensor (18) which directly captures the motor speed (N5) as the drive variable (GA).