METHOD FOR MONITORING AT LEAST ONE STORAGE OF A MOTOR VEHICLE, IN PARTICULAR A MOTOR VEHICLE, AS WELL AS MOTOR VEHICLE

Description

[0001] The invention relates to a method for monitoring at least one bearing of a motor vehicle, in particular a motor vehicle. The invention also relates to a motor vehicle, in particular a motor vehicle.

[0002] EP 2 989 436 B1 discloses a method for monitoring the health status of a vehicle system. In the method, a plurality of parameter values ​​for the vehicle are measured under various operating conditions as an end-off-line test. The parameter values ​​are stored in a fingerprint file. Furthermore, the same plurality of parameter values ​​contained in the fingerprint file are measured under similar load conditions after a predetermined time interval.

[0003] DE 10 2015 213 084 A1 discloses a method for monitoring a storage system. Furthermore, EP 1 902 293 B1 discloses an interface module device for connection to an electrical machine.

[0004] The publication "Real-Time Monitoring and Fault Diagnosis of a Low Power Hub Motor Using Feedforward Neural Network", Simsir et al., Computational Intelligence and Neuroscience, Vol. 2016, 27.12.2015, pages 1-13, discloses real-time monitoring and fault diagnosis of a low-power hub motor using a feedforward neural network.

[0005] GB 2 532 760 A discloses a condition monitoring system used in a vehicle to monitor axles or bearing units.

[0006] The object of the present invention is to provide a method and a motor vehicle so that at least one bearing of the motor vehicle can be monitored particularly precisely.

[0007] This object is achieved according to the invention by a method having the features of patent claim 1 and by a motor vehicle having the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0008] A first aspect of the invention relates to a method for monitoring at least one bearing of a motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car. The motor vehicle comprises the at least one bearing and at least one electric machine, by means of which the motor vehicle can be driven, in particular electrically. The motor vehicle is thus preferably designed as a hybrid or electric vehicle, in particular as a battery-electric vehicle, so that the motor vehicle can be driven by means of the electric machine. In the method, the electric machine is supplied with alternating electrical current, which is provided by power electronics of the motor vehicle assigned to the electric machine.By supplying the electrical machine with the aforementioned alternating current, the electrical machine is operated in motor mode and thus as an electric motor, by means of which the motor vehicle is driven.

[0009] Furthermore, the alternating current provided by the power electronics is detected by means of at least one alternating current sensor of the motor vehicle, in particular the power electronics. Furthermore, at least one torque is determined, in particular calculated, as a function of the detected alternating current or from the detected alternating current, which torque is provided by the electric motor to drive the motor vehicle. Furthermore, the bearing is monitored or checked as a function of the determined, in particular calculated, torque. The method is preferably carried out by means of an electronic computing device of the motor vehicle, such that, for example, the said torque is determined, in particular calculated, by means of the electronic computing device.

[0010] The method according to the invention makes it possible, on the one hand, to monitor the bearing, preferably designed as a rolling bearing, in particular as a ball bearing or as another rolling bearing, particularly extensively over time, in particular at least substantially continuously or permanently. In particular, the bearing can be monitored particularly extensively during operation, in particular during normal operation, of the motor vehicle and is thereby always monitored and thus checked when the motor vehicle is driven by the electric machine or the electric motor. As a result, any changes, in particular increases or rises, in the torque can be determined or detected particularly early.Such a change, particularly an increase or rise in torque, can indicate increasing wear on the bearing or impending damage to the bearing. As a result, it is possible, for example, to take at least one measure before excessive damage or bearing failure actually occurs. This measure may include or result in the bearing being repaired, replaced, or serviced before excessive wear occurs, particularly before damage or bearing failure occurs.

[0011] On the other hand, the method according to the invention makes it possible to determine the torque extremely precisely, since in the method according to the invention the alternating current is detected by means of the alternating current sensor. Thus, in the method according to the invention not only an electrical direct current is detected, or not only this direct current, which is converted into electrical current, for example, but the detection of the alternating current makes it possible to determine the torque particularly precisely. In other words, the method according to the invention provides that the torque is not determined, or not only based on the direct current, but rather the torque is determined taking into account the detected alternating current. In this case, the alternating current can be detected particularly precisely, so that the torque can be determined particularly precisely.In this way, the bearing can be monitored and checked particularly precisely and advantageously, in particular when the bearing is a component of the electrical machine and is arranged, for example, in the electrical machine, in particular in a housing of the electrical machine. The invention is based in particular on the following findings: In motor vehicles designed, for example, as electric or hybrid vehicles, a plurality of bearings are usually used, in particular rolling bearings and, for example, ball bearings. Such bearings are used, in particular, in the respective electrical machines of the respective motor vehicles. Tests have shown that a large proportion of any damage to electrical machines in motor vehicles can be traced back to bearing damage.The bearings are usually not monitored during so-called field use, although damage to or failure of such a bearing can usually lead to the complete failure of the motor vehicle or its drive train. Diagnostic methods that enable early detection of, in particular, excessive wear on a bearing do not generally exist. The problems and disadvantages mentioned above can now be avoided by the method according to the invention, so that, for example, the bearing can be serviced, repaired or replaced before a complete failure of the bearing occurs. This means that the motor vehicle can be driven to a workshop with the bearing still in working order, for example, in order to repair, replace or service the bearing there. This avoids the costly towing and transport of the motor vehicle after a bearing failure.

[0012] A further finding underlying the invention is that with increasing wear or with increasing deterioration of the condition of the bearing, its frictional resistance increases. This leads to an increase in torque. The torque thus comprises, for example, the frictional resistance of the bearing or a bearing friction torque resulting from the frictional resistance and also simply referred to as the bearing torque. If, for example, by monitoring the bearing using the method over a predeterminable or predetermined period of time and, for example, at least essentially continuously, a trend is detected such that the torque increases, particularly under comparable or identical conditions in which the motor vehicle is driven in the manner described, it can be concluded that the bearing friction torque and thus its wear is increasing.Since the alternating current is now detected and the alternating current can be detected with particular precision, the torque and thus, for example, the wear on the bearing or the bearing friction torque can be determined with particular precision. In particular, it can be detected at an early stage that excessive wear on the bearing is present. In other words, if, for example, the detected torque exceeds a limit value, in particular a predeterminable or predetermined one, it can be concluded that the bearing is still functional but that the wear on the bearing exceeds a desired limit. As a result, for example, the aforementioned measure can be taken or carried out to replace and maintain the bearing or to have the bearing replaced or serviced.Overall, it can be seen that the method according to the invention is a diagnostic method by means of which excessive wear of the bearing can be detected particularly early. This allows the risk of damage to the bearing and, subsequently, damage to the electrical machine to be kept particularly low while the bearing is installed in the motor vehicle.

[0013] Furthermore, it is provided that at least one inclination of the motor vehicle about its transverse direction is determined, in particular during driving or starting. Alternatively or additionally, at least one acceleration acting on the motor vehicle, in particular in the transverse direction and / or in the longitudinal direction of the vehicle, in particular during driving or starting, is determined or detected by means of at least one acceleration sensor of the motor vehicle. The inclination of the motor vehicle is determined, for example, by means of the acceleration sensor detecting an acceleration acting on the motor vehicle, wherein the inclination is determined as a function of the detected acceleration.

[0014] The bearing is monitored depending on the determined inclination and optionally depending on the determined acceleration. In particular, the torque, in particular the starting torque, is determined depending on the inclination and optionally depending on the acceleration. This makes it possible to compare torque values ​​determined by driving or starting the motor vehicle on a horizontal plane with torque values ​​determined by driving or starting the motor vehicle up an incline and / or down a decline, since the incline or acceleration and thus the circumstances were taken into account when determining the torque or the values.If, for example, the motor vehicle is initially parked on a slope and is then driven, in particular started, down the slope, this may result in the torque being lower than if the motor vehicle is driven, in particular started, on a horizontal plane. By taking the inclination of the motor vehicle into account, it is now possible to determine whether any difference between the torque or the torque values ​​is due only to the slope or to the slope and an increase in wear on the bearing. This makes it possible to check the bearing in at least almost every situation in which the motor vehicle is driven, in particular started, so that the bearing can be monitored at least almost continuously. This means that any excessive wear on the bearing can be detected particularly early on.

[0015] In addition, eddy current losses and / or air friction losses are determined during driving, in particular during starting, and the bearing is monitored as a function of the determined eddy current losses and / or air friction losses. The torque, in particular the starting torque, is determined as a function of the determined eddy current losses and / or air friction losses. This embodiment is based on the finding: The electric machine or an electric drive of a motor vehicle has a drag torque, which is usually made up of losses in an iron circuit or eddy current losses, i.e. losses caused by eddy currents, air friction losses and bearing friction losses. In other words, the drag torque comprises at least eddy current losses, air friction losses and bearing friction losses.

[0016] The bearing friction losses result, for example, from the aforementioned bearing friction torque. For example, at least the drag torque must be overcome to rotate the electric machine, in particular its rotor, especially without driving the motor vehicle. Thus, in order to drive the motor vehicle, in particular to start it, the drag torque and, if necessary, an additional drive torque must be overcome by supplying the electric machine with alternating current. The drive torque is, for example, the aforementioned torque, in particular the aforementioned starting torque, also referred to as the starting torque.Eddy current losses and air friction losses increase with increasing speed of the electric machine, particularly of the rotor, while bearing friction losses and bearing friction torque remain at least substantially constant over the speed. If the torque, particularly the starting torque, increases, particularly under the same or comparable conditions, it can be concluded that the bearing friction torque and thus the bearing wear are increasing. The reason for this is that the torque, or starting torque, includes the drag torque and thus the bearing friction torque.Since, for example, the inclination and / or optionally the acceleration and / or the speed are recorded and taken into account when determining the torque, the torque can be determined in different situations in which the motor vehicle is driven, in particular when started, so that, for example, respective torque values ​​can be determined in these different situations. By taking into account the inclination and optionally the acceleration and / or speed, the situations and thus the values ​​can be compared with one another or made comparable with one another, since, for example, it can be recognized that any changes in the torque or the values ​​are not due to the different situations and therefore not to different accelerations and / or speeds and / or inclinations, but to changes in the bearing friction torque.This means the warehouse can be monitored particularly comprehensively and precisely.

[0017] It has proven particularly advantageous if, as a function of the determined torque, at least one warning signal, in particular one that can be perceived visually and / or acoustically and / or haptically by a person, is emitted by an output device of the motor vehicle. For example, the warning signal is emitted when the torque exceeds the limit value. The warning signal can alert the person, who is, for example, the driver of the motor vehicle, that the bearing is showing excessive wear. In other words, by emitting the warning signal, the person can be instructed or encouraged to take the motor vehicle to a workshop to have the bearing serviced or replaced. The person can therefore have the bearing serviced or replaced before it fails and the electrical machine is damaged.

[0018] It has proven particularly advantageous if the warning signal is emitted inside the vehicle. This allows the person or driver of the vehicle to be informed very early on that the bearing needs to be repaired or replaced. These embodiments are based on the knowledge that maintenance or replacement of the bearing can be carried out particularly easily, quickly and cost-effectively when the bearing itself is still functional and has not yet failed, and the electrical machine has not yet been damaged. In particular, the vehicle can be driven to the workshop and does not have to be transported in a time-consuming and expensive manner or with the aid of additional equipment.

[0019] In order to be able to determine the torque particularly precisely and thus monitor the bearing particularly advantageously, a further embodiment of the invention provides that the method is carried out during a starting process in which the initially stationary motor vehicle is started by driving the motor vehicle and is thereby set in motion. In this case, a starting torque required to start the motor vehicle is determined as the torque. In other words, it is provided that the electric machine is supplied with alternating electrical current during the aforementioned starting process, whereby the motor vehicle is driven by means of the electric motor and is thereby started. Furthermore, it is therefore provided that the alternating current supplied is detected during the starting process.This embodiment is based on the knowledge that the torque can be determined particularly advantageously during a respective starting process of the motor vehicle. In other words, the torque can be determined particularly advantageously during respective successive starting processes. Expressed again in other words, for example, respective torque values ​​can be determined during respective successive starting processes, wherein the values ​​can be compared particularly well with one another. As a result, the aforementioned trend can be identified particularly well by comparing the values. In other words, it can be identified particularly well by comparing the values ​​whether the torque is increasing, for example, due to increased wear on the bearing. This is possible because during a starting process or during the starting processes, conditions that are always particularly comparable with one another exist.For example, if the values ​​or comparisons reveal that the torque or values ​​are increasing, this allows us to conclude with a particularly high degree of certainty that the increase in the values ​​or torque is actually due to increasing wear on the bearing and not to other effects. This allows the bearing to be monitored with particularly high precision.

[0020] A further embodiment is characterized in that, in order to drive the motor vehicle, in particular to start it off, at least one shaft of the motor vehicle is driven by the electric motor and thereby rotated about an axis of rotation, such that the shaft has a speed that is in particular greater than zero. The speed of the shaft is detected by means of at least one speed sensor of the motor vehicle provided in addition to the AC sensor, with the bearing also being monitored as a function of the detected speed. By taking the speed into account when determining the torque or when monitoring the bearing, comparable conditions can be created or it can be ensured that any increase in torque is actually due to any increase in wear on the bearing and not to other effects.

[0021] It has proven particularly advantageous that the starting torque is also determined as a function of the detected speed.

[0022] This means that, for example, static friction in the bearing can be ignored, so that any misdiagnosis can be avoided.

[0023] In a particularly advantageous embodiment of the invention, at least one position of the motor vehicle on the earth is determined, in particular during propulsion or starting, wherein the bearing is monitored depending on the determined position. The position is determined, for example, by means of a navigation device of the motor vehicle and / or satellite-based. In particular, it is conceivable that the torque, in particular the starting torque, is determined, in particular calculated, depending on the position.This allows local effects that can lead to a change or impairment of the torque to be taken into account and, for example, to be factored out when calculating the torque, so that it can be recognized that any increase in torque is actually due to a possible increase in the wear of the bearing and not to any local effects or conditions.

[0024] A second aspect of the invention relates to a motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car, which is designed to carry out a method according to the invention. The invention also includes further developments of the motor vehicle according to the invention which have features as have already been described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the motor vehicle according to the invention are not described again here. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle. The invention also encompasses combinations of the features of the described embodiments.

[0025] An exemplary embodiment of the invention is described below. It shows: Fig. 1 shows a schematic side view of a motor vehicle according to the invention; Fig. 2 shows a schematic representation of a drive train of the motor vehicle, which can be electrically driven by means of the drive train; Fig. 3 shows a detail of a schematic side view of a shaft of the drive train; and Fig. 4 shows a diagram illustrating a method according to the invention for monitoring at least one bearing of the motor vehicle.

[0026] The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the invention is also intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

[0027] In the figures, the same reference symbols designate elements with the same function.

[0028] Fig. 1 shows a schematic side view of a motor vehicle 10 designed as a motor vehicle, in particular as a passenger car. The motor vehicle 10 is designed as a hybrid or motor vehicle and has a particularly good in conjunction with Fig. 2 recognizable drive train 12, which is also referred to as an electric drive train or electric drive. By means of the drive train 12, the motor vehicle 10 can be driven, in particular electrically. For this purpose, the drive train 12 and thus the motor vehicle 10 comprise an electric machine 14, by means of which the motor vehicle can be driven electrically. The electric machine 14 comprises a stator 16 and a partially recognizable rotor 18, which can be driven, for example, by the stator 16 and is thus rotatable about a machine rotation axis 20 relative to the stator 16. As can be seen particularly well in conjunction with Fig. 3 As can be seen, the rotor 18 comprises a shaft 22, also referred to as rotor shaft, which - as in Fig. 2 by an arrow 24 - is rotatable about the machine rotation axis 20 relative to the stator 16. In addition, Fig. 3 a section of a housing 26 of the electric machine 14 can be seen, wherein the stator 16 is fixed, for example, to the housing 26. Thus, the rotor 18 and thus the shaft 22 are rotatable about the machine rotation axis 20 relative to the housing 26. The motor vehicle 10 also comprises at least one Fig. 3 recognizable bearing 28, which in this case is a rolling bearing, in particular a ball bearing. In the exemplary embodiment illustrated in the figures, the bearing 28 is a component of the electrical machine 14 and thus a bearing of the electrical machine 14, wherein the bearing 28 is arranged in the housing 26. The shaft 22 is rotatably mounted on the housing 26 by means of the bearing 28 or via the bearing 28. In particular, the shaft 22 is supported or can be supported along its radial direction on the housing 26 via the bearing 28.

[0029] The bearing 28 has, for example, a first bearing ring designed as an inner ring 30, which is, for example, connected in a rotationally fixed manner to the shaft 22. The bearing 28 also comprises a second bearing ring in the form of an outer ring 32, which is, for example, connected in a rotationally fixed manner to the housing 26. The bearing rings have respective raceways 34 and 36. The bearing 28 further comprises rolling elements 38, which in this case are designed as balls. If the shaft 22 is now rotated about the machine rotation axis 20 relative to the housing 26, this results in a relative rotation between the bearing rings about the machine rotation axis 20. As a result, the rolling elements 38 roll on the raceways 34 and 36.

[0030] The drive train 12 and thus the motor vehicle 10 further comprise power electronics 40 assigned to the electric machine 14, via which power electronics 40 the electric machine 14 can be supplied with electrical energy or electrical current. In particular, the power electronics 40 is designed to provide electrical current in the form of alternating electrical current. The electric machine 14 is supplied with the alternating current provided by the power electronics 40, whereby the electric machine 14 is operated in motor mode and thus as an electric motor. The electric motor provides drive torques via the rotor 18 and the shaft 22, also referred to as the rotor shaft, by means of which drive torques the motor vehicle 10 can be electrically driven.

[0031] Out of Fig. 2 It can be seen that the electrical machine 14 is embodied as a multi-phase electrical machine and thus has multiple electrical phases. In this case, the electrical machine 14 is embodied as a three-phase electrical machine, so that the electrical machine 14 has three phases: u, v, and w. The alternating current is thus a three-phase alternating current with exactly three phases: u, v, and w.

[0032] The drive train 12 and thus the motor vehicle 10 further comprise an energy storage device 42 designed for storing electrical energy or electrical current, which is designed, for example, as a battery, in particular as a high-voltage battery (HV battery). In particular, the electric machine 14 and the energy storage device 42 are designed as high-voltage components, which have an electrical voltage, in particular an electrical operating voltage, which is greater than 50 volts. The electrical voltage is preferably several hundred volts in order to be able to realize particularly high electrical power for electrically driving the motor vehicle 10. Fig. 2 an electrical positive pole of the energy storage device 42 is designated by +, whereas an electrical negative pole of the energy storage device 42 is designated by -.

[0033] To operate the electric machine 14 in motor mode, the energy storage unit 42 provides direct electrical current (DC), wherein the power electronics 40 is supplied with the direct current provided by the energy storage unit 42. In other words, the power electronics 40 receives the direct current provided by the energy storage unit 42. The direct current provided by the energy storage unit 42 and received by the power electronics 40 is converted by the power electronics 40 into the aforementioned alternating current, which is provided by the power electronics 40, transmitted to the electric machine 14, and received by the electric machine 14. In this way, the electric machine 14 is supplied with the alternating current provided by the power electronics 40.

[0034] The following describes a method for monitoring at least the bearing 28, wherein the bearing 28 can be monitored particularly precisely using the method. In a first step of the method, the electric machine 14 is supplied with the alternating electrical current provided by the power electronics 40 associated with the electric machine 14. As a result, the electric machine 14 is operated as the aforementioned electric motor, by means of which the motor vehicle 10 is driven, in particular started.

[0035] In a second step of the method, the alternating current provided by the power electronics 40 is converted into a Fig. 2 The alternating current sensor 44 is shown particularly schematically. The alternating current sensor 44 is, for example, a component of the power electronics 40 and is arranged, for example, in the power electronics 40, in particular in a housing of the power electronics 40. The alternating current, also referred to as AC or AC current, can be detected particularly precisely by means of the alternating current sensor 44, also referred to as an AC sensor.

[0036] In a third step of the method, at least one torque is determined, in particular calculated, as a function of the detected alternating current, which torque is provided for driving, in particular starting, the motor vehicle 10 by the electric motor, in particular via the rotor 18 and thereby via the shaft 22. For example, the torque is determined by means of a Fig. 1 The torque is determined, in particular calculated, by the particularly schematically illustrated electronic computing device 46 of the motor vehicle 10, in particular of the drive train 12. For this purpose, for example, the alternating current sensor 44 provides at least one, in particular electrical, sensor signal, which is received by the electronic computing device 46. As a function of the received sensor signal, the electronic computing device 46 determines, in particular calculates, the torque. In particular, the electronic computing device 46 determines, in particular calculates, at least one torque value characterizing the torque and also referred to as the torque value. In a fourth step of the method, the bearing 28 is monitored as a function of the determined torque, that is to say as a function of the torque value.The torque mentioned is, for example, a torque required to start the initially stationary motor vehicle 10 and is also referred to as the starting torque or starting torque, which is provided or must be provided by the electric machine 14 during a starting process of the motor vehicle in order to start the initially stationary motor vehicle and thus set it in motion. Since the alternating current can be or is detected particularly precisely by the alternating current sensor 44, the torque can be determined particularly precisely. The determined torque depends on losses, in particular friction losses, of the bearing 28. These friction losses of the bearing 28 depend on a bearing friction torque of the bearing 28, also referred to as the friction torque, or are caused by the bearing friction torque. The torque thus includes the bearing friction torque of the bearing 28.If, for example, the torque is determined several times in succession so that respective torque values ​​of the torque are determined, it can be determined based on the torque values, in particular by comparing the torque values, whether the torque values ​​differ from one another. In particular, this can be determined whether the torque values ​​or the torque is increasing. A possible increase in torque allows a conclusion to be drawn that the bearing friction torque of the bearing 28 and thus its wear is increasing. In this way, excessive wear of the bearing 28 can be detected particularly early, so that maintenance or replacement of the bearing 28 can be effected or initiated before a failure of the bearing 28 and thus damage to the drive train 12 occurs.

[0037] Fig. 4 shows a diagram, on whose abscissa 48 the speed of the electric machine 14, in particular of the rotor 18, is plotted. On the ordinate 50 of the diagram, a drag torque of the electric machine 14 is plotted. A curve 52 plotted in the diagram illustrates a curve of the drag torque over the speed. The drag torque is composed of eddy current losses and air friction losses, whose contribution to the drag torque can be, for example, Fig. 4 by a hatched area 54 below the curve 52. In addition, the drag torque is made up of the friction losses mentioned above, also known as bearing friction losses, whose contribution to the drag torque in Fig. 4 by a further hatched area 56 below the course 52. From Fig. 4 It can be seen that the eddy current losses and air friction losses increase with increasing speed of the rotor 18, while the bearing friction losses and thus the Fig. 4 The bearing friction torque, designated R and also referred to as the bearing torque, remains at least substantially constant over the speed. The air friction losses and eddy current losses, also referred to as iron losses, are zero when the speed is zero. Since the torque now includes the drag torque and the drag torque includes the bearing torque, the bearing torque can be monitored by, in particular, at least substantially continuous monitoring of the torque, whereby the bearing 28 and thus its wear can be monitored. Advantageous in this case is, in particular, at least substantially continuous monitoring or recording of the torque in order to, for example, compensate for or average out fluctuations due to slope inclination and / or different subsoil. The aim is, for example, to determine trends.For example, if a trend is detected based on the torque values ​​such that the torque values ​​and thus the torque are increasing, it can be concluded that the wear on the bearing 28 is increasing. If, for example, the torque exceeds a predeterminable limit, it can be concluded that the wear on the bearing 28 is exceeding or has exceeded a predefined or predeterminable limit. As a result, the driver of the motor vehicle 10 can be encouraged, for example, to have the bearing 28 serviced or replaced.

[0038] For this purpose, for example, depending on the determined torque, a Fig. 1 At least one warning signal that can be perceived visually and / or acoustically and / or haptically by the driver is output by the particularly schematically illustrated output device 58 of the motor vehicle 10, wherein the output device 58 is arranged in the interior 60 of the motor vehicle 10. Thus, the warning signal is output in the interior 60.

[0039] It is particularly advantageous if, for example, any inclinations of the motor vehicle 10 and its transverse direction are determined by means of at least one or more position sensors of the motor vehicle 10, in order to compensate for or exclude, for example, distortions caused by inclines and / or declines. Thus, for example, it is provided that at least one inclination of the motor vehicle 10 and its transverse direction, in particular during driving or starting, and / or at least one acceleration acting on the motor vehicle 10 during driving or starting, is determined by means of at least one Fig. 1 The bearing 28 is monitored as a function of the detected inclination and, optionally, acceleration. In particular, the torque is determined as a function of the detected inclination and, optionally, acceleration.

[0040] Alternatively or additionally, it may be provided that by means of a Fig. 1at least one position of the motor vehicle 10 on earth is determined by a particularly schematically illustrated navigation device 64 of the motor vehicle 10, in particular satellite-based. In this case, the bearing 28 is monitored as a function of the determined position, wherein, for example, the torque is determined as a function of the determined position. Furthermore, it has proven particularly advantageous if a speed sensor 66 of the motor vehicle 10, in particular of the drive train 12, which is provided in addition to the AC sensor 44, is used to detect a speed of the shaft 22 resulting from the driving of the shaft 22, wherein the bearing 28 is monitored as a function of the detected speed of the shaft 22. In particular, the torque is preferably determined as a function of the detected speed of the shaft 22.

[0041] The electric machine 14 is preferably free of torque measuring flanges and / or torque sensors in order to minimize the number of parts, the installation space required, the costs, and the weight. However, electric drives, and thus the electric machine 14, have the physical property that torque and electric current are directly proportional to one another. The power electronics 40, which provides the alternating current for the electric machine 14, comprises at least one or more highly accurate current sensors. One of the current sensors, or the current sensor of the electric machine 14, is the alternating current sensor 44.If the detected alternating current, which is required for starting or driving, is now evaluated, in particular in such a way that the torque is determined, in particular calculated, on the basis of the detected alternating current, conclusions can be drawn about the bearing torque and consequently about the wear of the bearing 28 because the torque includes the drag torque and the drag torque includes the bearing torque.

[0042] In order to avoid, for example, misdiagnoses due to static friction, particularly in the bearing 28, the speed sensor 66 is used. The speed sensor 66 can detect the speed of the shaft 22 and thus of the rotor 18 and thus of the bearing 28 with high precision. Thus, based on the speed detected by the speed sensor 66, it can be determined when the static friction has been overcome. Thus, the torque is preferably determined after the static friction has been overcome. For this purpose, the speed sensor 66 is designed, for example, as a resolver or a comparable sensor in order to be able to detect even the smallest angular changes of greater than or equal to 0.01 degrees of the shaft 22. As a result, the speed can be detected particularly precisely using the speed sensor 66.

[0043] In the present case, the motor vehicle 10, in particular the drive train 12, also includes a direct current sensor 68, by means of which the direct current provided by the energy storage device 42 can be detected or is detected. In particular, the direct current sensor 68 can be used to determine the amount of direct current provided by the energy storage device 42 and thus drawn from the energy storage device 42. It is conceivable that the torque is also determined as a function of the direct current detected by the direct current sensor 68, whereby the torque can be determined particularly precisely.

Claims

1. Method for monitoring at least one bearing (28) of a motor vehicle (10), which has the bearing (28) and at least one electric machine (14) and can be driven by means of the electric machine (14), with the steps: - supplying the electric machine (14) with alternating electric current, which is provided by power electronics (40), assigned to the electric machine (14), of the motor vehicle (10), whereby the electric machine (14) is operated as an electric motor (14), by means of which the motor vehicle (10) is driven; - detecting the alternating current provided by the power electronics (40) by means of at least one alternating current sensor (44); - determining at least one torque, which is provided by the electric motor (14) for driving the motor vehicle (10), as a function of the detected alternating current, wherein eddy current losses and / or air friction losses occurring during the driving are determined, wherein the bearing (28) is monitored as a function of the determined eddy current losses and / or air friction losses, wherein the torque is determined as a function of the determined eddy current losses and / or air friction losses; and - monitoring the bearing (28) as a function of the determined torque, wherein the bearing (28) is always monitored when the motor vehicle (10) is driven by the electric motor (14), wherein a change in the torque is determined or identified, wherein the change in the torque is used to infer increasing wear of the bearing (28), wherein at least one inclination of the motor vehicle (10) about its transverse vehicle direction is determined by means of at least one sensor (62) of the motor vehicle (10), wherein the bearing (28) is monitored as a function of the determined inclination, wherein, taking into account the inclination of the motor vehicle (10), it can be identified whether a difference between values of the torque is due only a gradient or to the gradient and the increase in wear of the bearing (28).

2. Method according to claim 1, characterized in that at least one information signal is output as a function of the determined torque by means of an output apparatus (58) of the motor vehicle (10).

3. Method according to claim 2, characterized in that the information signal is output in the interior (60) of the motor vehicle (10).

4. Method according to any one of the preceding claims, characterized in that the method is performed during a start-up process, in which the initially stationary motor vehicle (10) is started up by driving the motor vehicle (10) and is thereby set in motion, wherein a starting torque required for starting up the motor vehicle (10) and / or provided by the electric machine (14) is determined as the torque.

5. Method according to any one of the preceding claims, characterized in that for driving the motor vehicle (10), at least one shaft (22) of the motor vehicle (10) is driven and thereby rotated about an axis of rotation (20), wherein a rotational speed of the shaft (22) is detected by means of at least one rotational speed sensor (66) of the motor vehicle (10) provided in addition to the alternating current sensor (44), and wherein the bearing (28) is also monitored as a function of the detected rotational speed.

6. Method according to claims 4 and 5, characterized in that the start-up torque is also determined as a function of the detected rotational speed.

7. Method according to any one of the preceding claims, characterized in that at least one position of the motor vehicle (10) on the ground is determined, the bearing (28) being monitored as a function of the position.

8. Method according to any one of the preceding claims, characterized in that the at least one inclination of the motor vehicle (10) about its transverse vehicle direction and / or the at least one acceleration acting on the motor vehicle (10) is determined by means of at least one acceleration sensor (62) as the sensor (62) of the motor vehicle (10).

9. Motor vehicle (10), which is designed to perform a method according to any one of the preceding claims.