METHOD FOR DETERMINATION OF STATE INFORMATION, ESPECIALLY DESCRIBING A TRIBO-LOGICAL STATE OF A DRIVE TRAIN, AND MOTOR VEHICLE

Abstract

A method for determination of state information, especially describing a tribological state of a drive train of a motor vehicle, wherein the drive train comprises an electric machine as a first drive machine and a second drive machine, wherein upon fulfillment of a diagnostic condition the first drive machine is operated in an electrical idling mode, in which it is electrically separated from all current sources and current sinks and coupled to at least one of the wheels of the motor vehicle, and during the operation of the first drive machine in the electrical idling mode a performance measure is acquired for the performance of the second drive machine, while at least one of the wheels of the motor vehicle is driven by the second drive machine, after which the state information is determined in dependence on the performance measure and given reference information.

Claims

1. A method for determination of state information that describes a state of a drive train including a first drive machine and a second drive machine of a motor vehicle, the first drive machine including a first electric machine, the method comprising: upon fulfillment of a first diagnostic condition, operating the first drive machine in an electrical idling mode in which the first drive machine is electrically separated from current sources and current sinks and coupled to at least one first wheel of the motor vehicle, and during the operating of the first drive machine in the electrical idling mode, acquiring a first performance measure of the second drive machine, while at least one second wheel of the motor vehicle is driven by the second drive machine; and determining the state information based on the first performance measure and given reference information.

2. The method according to claim 1, wherein the state information describes a tribological state of the drive train.

3. The method according to claim 1, wherein the second drive machine includes a second electric machine, wherein the method further comprises: detecting a current supplied to the second drive machine, using a current sensor of the motor vehicle; and detecting a voltage dropping across the second drive machine, using a voltage sensor of the motor vehicle, and wherein the first performance measure is acquired as a product of the current and the voltage or is based on the product of the current and voltage.

4. The method according to claim 3, wherein the current is a direct current (DC) current and the voltage is a DC voltage.

5. The method according to claim 1, wherein the second drive machine includes a second electric machine, wherein the method further comprises: after acquiring the first performance measure, determining that the first diagnostic condition or a second diagnostic condition is fulfilled; operating the second drive machine in an electrical idling mode in which the second drive machine is electrically separated from current sources and current sinks and coupled to at least one second wheel of the motor vehicle; and during the operating of the second drive machine in the electrical idling mode, acquiring a second performance measure of the first drive machine, while the at least one first wheel of the motor vehicle is driven by the first drive machine; and determining the state information based on the first performance measure and the second performance measure.

6. The method according to claim 1, wherein the given reference information is based on a speed of the motor vehicle or a number of revolutions of the first drive machine or the second drive machine.

7. The method according to claim 1, wherein the first diagnostic condition is fulfilled when a speed of the motor vehicle or a number of revolutions of the first drive machine or the second drive machine is constant across a given time interval or lies within a range of variation with given breadth, and wherein a measure of performance of the second drive machine that is applied in order to maintain the speed or the number of revolutions constant or in a variation interval while the first drive machine is operated in electrical idling mode, is acquired as the first performance measure.

8. The method according to claim 5, wherein the first diagnostic condition or the second diagnostic condition is fulfilled when a steering angle of the motor vehicle lies in a given steering angle interval.

9. The method according to claim 5, wherein the first diagnostic condition or the second diagnostic condition is fulfilled when a road being driven upon by the motor vehicle has a gradient below a limit value.

10. The method according to claim 9, wherein the limit value is 5 or 10.

11. The method according to claim 1, wherein the state information is a Boolean value that is determined based on a comparison of the first performance measure with the give reference information or an intermediate result determined based on the first performance measure and the given reference information with a given limit value, or the state information is determined based on a difference or a quotient of the first performance measure and the given reference information.

12. The method according to claim 1, further comprising: upon fulfillment of a notice condition based on the state information, outputting a notice to a vehicle passenger or a device separate from the motor vehicle.

13. A motor vehicle comprising: a drive train including a first drive machine and a second drive machine, wherein the first drive machine includes an electric machine; and a processing device, wherein the processing device, in operation, upon fulfillment of a diagnostic condition, operates the first drive machine in an electrical idling mode in which the first drive machine is electrically separated from current sources and current sinks and coupled to at least one first wheel of the motor vehicle; during operation of the first drive machine in the electrical idling mode, acquires a performance measure of the second drive machine, while at least one second wheel of the motor vehicle is driven by the second drive machine; and determines state information describing a state of the drive train based on the performance measure and given reference information.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0038] Further benefits and details of the disclosure will emerge from the following exemplary embodiments as well as the accompanying drawings.

[0039] FIG. 1 schematically shows an exemplary embodiment of a motor vehicle according to the disclosure, and

[0040] FIG. 2 schematically shows a flow chart of an exemplary embodiment of the method according to the disclosure.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a motor vehicle 2 having a drive train 1, comprising two drive machines 3, 4, each of which is coupled across a differential 9, 10 to two of the wheels 11-14 of the motor vehicle 2. As shall be explained more closely with additional reference to FIG. 2, state information 34, 52 regarding the state of the drive train 1 will be acquired by a processing device 30 of the motor vehicle.. In one or more implementations, the processing device 30 includes a processor and a memory storing instructions that, when executed by the processor, causes the processing device 30 to perform the acts described herein. Specifically, the tribological state is to be acquired in the example, i.e., in particular, increased losses in the drive train 1 from friction occurring due to wear or inadequate lubrication.

[0042] Signs as to such a state of the drive train 1 can already be obtained by comparing the performance provided by the drive machines 3, 4 in a particular travel state, for example to maintain a particular speed, with a reference value. For this, the fuel consumption can be detected in the case of internal combustion engines, for example, and the electric power in the case of electric machines.

[0043] In electric machines, however, not just a worsening of the tribological state can lead to a reduction of the efficiency, but also defects in the electronics, such as leakage currents, faulty activation of inverters, and the like. Therefore, as shall be explained more precisely in the following with the aid of an exemplary method, the state information 34, 52 regarding the tribological state of the drive train 1 will be determined in the motor vehicle 2, as determined in dependence on a performance measure 28, 47 for at least one of the drive machines 3, 4, while the other respective one of the drive machines 3, 4 continues to be coupled with the respective wheels 11-14 of the motor vehicle, but is operated in an electrical idling mode. Thus, although friction losses are taken into account in both drive machines 3, 4 and in the further components of the drive train, such as the differentials 9, 10 or the wheel bearings of the wheels 11-14, the measurement cannot affect the electrical process of the respective drive machine 3, 4 operated in the electrical idling mode. Especially when only one of the drive machines 3, 4 is an electric machine, or when determinations of a respective performance measure 28, 47 are done for both drive machines 3, 4 while the other respective drive machine 3, 4 is operated in electrical idling mode, influences of the electronics of the drive machines 3, 4 on the determination of the tribological state can be largely ruled out.

[0044] FIG. 2 shows a flow chart of an exemplary embodiment of a method for determining a tribological state of the drive train 1 of the motor vehicle 2. The sequence control and computations within the method can be implemented, for example, by the processing device 30 of the motor vehicle 2, but it would also be possible to migrate for example parts of the computations performed to external devices.

[0045] In step S1, a steering angle of the motor vehicle 2 is detected at first by a steering angle sensor 21 and in step S2 the number of revolutions of the electric machine 4 is detected. The number of revolutions could be measured directly by a revolution sensor. Typically, however, information as to the number of revolutions of an electric machine is present any way in an associated control device, for example in order to make possible a field-oriented regulation of the electric machine 4, and it can therefore also be retrieved from such a control device.

[0046] In step S3, a check is made to see whether a diagnostic condition 23 is fulfilled, the fulfillment of which indicates the presence of a suitable travel state for acquisition of information regarding a tribological state of the drive train 1. One such travel state is in particular a straight-line travel with essentially constant speed. The diagnostic condition 23 can thus be fulfilled in particular when the detected steering angle lies, for a given time interval, within a target interval corresponding to a straight-line travel, and the detected number of revolutions 22 all lie within a variation interval of given breadth, basically corresponding to a constant number of revolutions. In order to monitor the steering angle 20 or the number of revolutions 22 over a time interval, it may be feasible to write the respective measured values in a ring buffer, so that several previous measured values can be considered in the context of the diagnostic condition.

[0047] A constant number of revolutions 22 of the drive machine 4 also leads in the example shown in FIG. 1 to a constant speed of the motor vehicle 2, since the drive machine 4 is coupled with a fixed transmission ratio to the differential 10 of the rear axle. If a multi-speed gearbox were to be used, it could be demanded in addition, as a necessary partial condition for fulfillment of the diagnostic condition 23, that no shifting action has been done within the considered time interval. Alternatively or in addition, it would also be possible, for example, to evaluate the vehicle speed instead of the number of revolutions 22, or in addition to the latter.

[0048] If the diagnostic condition 23 is not fulfilled, the method is repeated from step S1. But if the diagnostic condition 23 is fulfilled, the processing device 30 in step S4 activates the switches 15, 16, which can be in particular electric switches, i.e., transistors for example, in order to separate the electric machine 3 including its inverter 5 from the onboard network 7 of the motor vehicle and thus from current sources 8, i.e., a battery for example, and current sinks 19, i.e., further consumers for example. The drive machine 3 thus remains coupled across the differential 9 to the wheels 11, 12, so that friction losses in the drive machine 3 continue to slow down the motor vehicle 2, but because of the electrical idling mode the losses in the drive machine 3 are basically independent of the electrical process of the motor vehicle 2 and the drive machine 3.

[0049] In step S5, on the one hand the current 24 supplied to the drive machine 4 is then detected by a current sensor 25 and on the other hand the voltage 26 drop across the drive machine 4 is detected by a voltage sensor 27. It is possible here to form the average over a given time interval, for example.

[0050] In the example, a direct current and a DC voltage are detected, i.e., voltage and current values prior to the inverter 6 of the drive machine 4. Alternatively, it would also be possible in principle to evaluate alternating voltages and currents for the individual phases of the drive machine 4.

[0051] In step S6, it is then checked to see whether the diagnostic condition 23 was fulfilled over the entire time interval for which current and voltage were detected. If this is not the case, then curves were negotiated for example during this time interval or a distinct speed change has occurred, so that the detected measurement values are little suited to determining a tribological state of the drive train 1 and therefore should be rejected. Therefore, in this case the method is repeated from the start, after in step S7 the electric idling of the drive machine 3 was ended by closing the switches 15, 16.

[0052] If the diagnostic condition was fulfilled continuously, then in step S8 a performance measure 28 is acquired for the performance produced by the drive machine 4. Since in the example a direct current and a DC voltage are detected, the detected current 24 and the detected voltage 26 or mean values of these quantities can be multiplied directly in order to calculate the performance measure 28. On the other hand, if alternating currents and voltages were detected for individual phases, the individual detected measurement values would have to be multiplied with each other per proper phase, the instantaneous performance per phase so determined would have to be integrated for at least one cycle, and the resulting performances of the individual phases would have to be added up.

[0053] In step S9, reference information 29 is dictated, describing in particular an expectation value for the performance measure that would have been reached if the drive train 1 had an optimal condition, i.e., in particular if there were no wear and if the lubrication were good. Since, in order to maintain a speed, different performance is required depending on the speed, this information is dictated in dependence on the detected number of revolutions 22. If a multi-speed gearbox were to be used in the motor vehicle 2, it would be feasible in addition to factor in the gear speed engaged or to detect the speeds directly in step S2.

[0054] In the example, in step S10, the difference 32 of the performance measure 28 and the reference information 29 is then calculated at first as an intermediate result 31. This intermediate result 31 thus describes how strongly the currently acquired performance measure 28 deviates from the reference information 29 and it thus constitutes a measure of the additional power loss resulting on account of the current tribological state of the drive train 1.

[0055] In principle, this intermediate result 31 could be used directly as state information 34. For example, the intermediate result 31 could be written into a ring buffer, so that by reading out this ring buffer it is possible to read out and evaluate the time development of the state of the drive train 1, for example in the course of a servicing, in order to recognize in good time a need for servicing, a deficient lubrication, or the like. Alternatively to a difference between performance measure 28 and reference information 29, the quotient of these quantities could also be used as such an intermediate result 31.

[0056] In the explained exemplary embodiment, however, it is desirable to recognize automatically a presumable state of the drive train 1 in need of servicing, so that in step S10 there is performed in addition a limit value comparison, in which the intermediate result 31 is compared to a given limit value 33, where the state information 34 is a Boolean value which indicates whether this limit value was exceeded.

[0057] In an alternative embodiment, it would also be possible to do without the acquisition of the intermediate result 31 and to carry out the limit value comparison for example by comparing the performance measure 28 directly with the reference information 29 as the limit value.

[0058] In step S11, a notice condition 35 is then evaluated, which in the example shown is fulfilled at once if the state information 34 indicates an exceeding of the limit value 33 by the intermediate result 31. Optionally, additional conditions can also be taken into account, so that for example the notice condition can only be fulfilled if a corresponding warning function was activated by a user or the like. If the notice condition 35 is not fulfilled, the method is repeated from the start after the ending of the electrical idling mode in step S7.

[0059] But if the notice condition 35 is fulfilled, then in step S12 on the one hand a notice 36, such as a warning symbol, is put out to a vehicle passenger by a notice device 37, such as a display. In addition, through a communication device 38 of the motor vehicle a message is put out to a device 39 designed separate from the motor vehicle 2, such as a backend server of the vehicle maker, in order to also register there a presumably required servicing.

[0060] While thanks to the use of the electrical idling mode of the first drive machine 3 in the method explained above in relation to steps S1 to S12 an influencing of the electrical process of this drive machine 3 on the determination of the tribological state of the drive train 1 was substantially precluded, it is furthermore possible in the explained method that electrical properties of the drive machine 4, such as a poor electrical efficiency, could lead to a faulty recognition of a problematical tribological state of the drive train 1. This risk can be significantly reduced when steps S11 and S12 are replaced by the optional steps S13 to S27.

[0061] The result of the limit value comparison in step S10 does not as yet constitute the state information 34 in this case, but only a partial result 55. With these additional steps S13 to S27, a similar acquisition of a performance measure is implemented, such as was already explained, but in these steps upon fulfillment of the diagnostic condition 44 used there the second drive machine 4 instead of the first drive machine 3 is separated from the onboard network 7 and the acquisition of the performance measure is done for the drive machine 3. As was already explained in detail in the general section, in this way a much better distinction can be drawn between efficiency losses of the electrical process and efficiency losses due to the tribological state of the drive train 1. Due to the great similarity with the previously explained method, the additional steps will only be explained briefly in the following.

[0062] In step S13, the switches 15, 16 are closed, in order to end the electrical idling mode of the drive machine 3.

[0063] Next, in step S14, corresponding to step S1, a steering angle 40 is detected and in step S15, corresponding to step S2, a number of revolutions 42 is detected, this involving preferably the number of revolutions 42 of the first drive machine 3.

[0064] In step S16, the diagnostic condition 44 is evaluated, preferably being exactly fulfilled, as already explained for step S3 and the diagnostic condition 23 used there, if the detected steering angle 40 and number of revolutions 42 indicate a straight-line travel with substantially constant speed.

[0065] If the diagnostic condition 44 is not fulfilled, the method is repeated from step S14. But if the diagnostic condition 44 is fulfilled, then the switches 17, 18 are opened in step S17, in order to achieve an electrical idling mode of the drive machine 4.

[0066] During this electrical idling mode, in step S18, the current 45 supplied to the drive machine 3 is determined by the current sensor 41 and the voltage drop 46 across the drive machine 3 is determined by the voltage sensor 43.

[0067] In step S19, corresponding to step S6, a check is made to see whether the diagnostic condition 44 was fulfilled throughout the measurement interval. If this is not the case, then in step S20 the electrical idling mode of the drive machine 4 is ended by closing the switches 17, 18. But if the diagnostic condition 44 was fulfilled, then in step S21 the performance measure 47 for the drive machine 3 is calculated, in particular by multiplying the current 45 and voltage 46.

[0068] In step S22, the reference value 48 is determined in dependence on the number of revolutions 42 or the speed of the motor vehicle, as was already explained in regard to step S9 and the reference value 29.

[0069] In step S23, similar to what was explained for step S10, the intermediate result 49 is determined in dependence on the performance measure 47 and the reference value 48, especially as the difference between these values, and this is compared with the limit value 50, in order to determine a further partial result 51, which in turn indicates as a Boolean quantity whether the limit value 50 has been exceeded.

[0070] In step S24, the partial results 51, 55 for the state information 52 are combined. In particular, the state information 52 can correspond to a logical AND operation of the partial results 51, 55, so that the state information 52 is only true if both the limit value 33 in step S10 and the limit value 50 in step S23 was exceeded. This is expedient, since an increasing of the performance measure on account of a defective or at least suboptimal functioning power electronics of one of the drive machines 3, 4 can only result if the respective drive machine 3, 4 is not being operated in electrical idling mode. But since the first drive machine 3 is operated in electrical idling mode to determine the partial result 55 and the second drive machine 4 is operated in electrical idling mode to determine the partial result 51, a suboptimal power electronics can only lead through the logical AND operation in step S24 to the finding of a defective tribological state of the drive train 1 if the increase in the performance measure is in fact at least partly due to high friction in the drive train 1 or if the power electronics are so faulty that the operation of both drive machines 3, 4 is affected, although this is much less likely than a suboptimal function of the power electronics of one of the drive machines 3, 4.

[0071] Steps S25 and S27 correspond basically to steps S22 and S12, that is, in step S25 the notice condition 53 is evaluated, which can then be fulfilled in particular if the state information 52 is true, and in step S27 a warning 54 is put out, which can essentially correspond to the warning 36.

[0072] If the notice condition 53 is not fulfilled in step 25 or after step S27, the method is repeated from the start, the electric idling of the drive machine 4 being ended first in step S26 by closing the switches 17, 18.

[0073] As an additional step, for example when exactly one of the partial results 51, 55 is true, a different notice could be given to the vehicle passenger or the device 39, in order to notify him or it that there is apparently present a defect or at least a suboptimal functioning of the power electronics of the motor vehicle 2.

[0074] German patent application no. 102022117410.7, filed Jul. 13, 2022, to which this application claims priority, is hereby incorporated herein by reference, in its entirety.

[0075] Aspects of the various embodiments described above can be combined to provide further embodiments. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.