Method for monitoring an electric machine of a vehicle

Abstract

The invention relates to a method for monitoring the operation of an electric motor of a vehicle, which is used as a drive, wherein a monitoring is carried out during the braking of the vehicle into a stopped state by means of a rotational speed-controlled operation of the electric machine and / or during the holding of the vehicle in the stopped state by means of the rotational speed-controlled operation of the electric machine, and wherein a rotational speed deviation (nDiff) between an actual rotational speed (nist) of the electric machine and a target rotational speed (nsoll) is determined, wherein, on the basis of the rotational speed deviation (nDiff) and corresponding threshold values, it is checked whether one or more criteria (K1, K2, K3, K3 ', K4) are met, and wherein, if one or at least one of the criteria (K1, K2) is met, a malfunction (F) of the operation of the electric machine is detected.

Description

Technical Field

[0001] The invention relates to a method for monitoring the operation of an electric machine of a vehicle serving as a drive during braking of the vehicle, as well as to a computing unit and a computer program for carrying out the method. Background Art

[0002] The electric machine can be used as a drive in a vehicle, such as a hybrid vehicle, together with an internal combustion engine, or as a separate drive in an electric vehicle. Here, the electric machine can also be used to brake the vehicle, for example, using a so-called recuperation method. Summary of the invention

[0003] According to the invention, a method for monitoring an electric machine of a vehicle is proposed, as well as a computing unit and a computer program for carrying out the method, having the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.

[0004] The present invention deals with vehicles which use an electric motor as a drive. As mentioned, the vehicle can also be braked by means of an electric motor, for example in the form of so-called recuperation. However, this has not usually been done until now; a mechanical brake system can be used for this purpose. However, it has been shown that the vehicle can also be braked to a standstill by means of an electric motor. For this purpose, speed-controlled operation of the electric motor is required, for which torque-controlled operation is generally not suitable. DE 102019205180 A1 describes a method for braking a vehicle comprising an electric drive motor, wherein the vehicle is stopped using speed control of the electric drive motor.

[0005] If the vehicle has been stopped in this way, it can also be held stationary, especially when the roadway is inclined. The holding torque required for this purpose can first be applied purely electrically, that is, by the electric machine. This can prevent rolling down a slope, for example, before the mechanical brake system takes over the holding function (also known as the "hill roll-back" function).

[0006] Monitoring is often useful for various functions in a vehicle in the sense of so-called functional safety, which is also partly regulated by law. This allows a specific function or a system used for this purpose to be checked for safe operation, in the present case in particular the electric machine or the components necessary for its operation, and intervention can be carried out if necessary, that is, if fault symptoms are present.

[0007] Against this background, it is proposed to monitor the operation of an electric machine of the vehicle serving as a drive and to be more precise to monitor the operation while the vehicle is being braked to a standstill by means of the speed-controlled operation of this electric machine. In particular, the monitoring is carried out at least until the standstill is reached, and further in particular after the standstill has been reached, i.e. while the vehicle is being held at a standstill by means of the speed-controlled operation of the electric machine, the monitoring is also carried out, for example for a certain duration, or until a certain event occurs, such as until the mechanical brake system has taken over the holding function (or generally holds the vehicle at a standstill). However, the monitoring can also be started as soon as the standstill is reached or as soon as the standstill is assumed to be reached, i.e. when the target speed is zero, even if the actual speed should not be this, or the monitoring can also be carried out independently of this (i.e. independently of whether braking has been previously carried out) while the vehicle is being held at a standstill.

[0008] In this case, the difference or deviation between the actual speed of the electric machine and the target speed is determined. The target speed is in particular the speed that should be adopted within the scope of braking or in a stationary state during operation. The target speed typically continues to decrease during braking and will be zero when the stationary state is reached and thereafter. The actual speed can be detected here, for example, by means of a sensor and transmitted to an execution computing unit, in which the actual speed can be settled with a preset target speed. However, it is also conceivable to determine the speed based on operating parameters of the electric machine.

[0009] One or more criteria are then checked based on the difference or deviation (between the actual speed and the target speed), that is, the speed difference or speed deviation. If one or at least one of the multiple criteria is met, a fault in the operation of the motor is identified. A fault response can then be performed, such as outputting a fault message. As an alternative or supplementary solution, countermeasures (as a fault response) can also be initiated, such as (then if necessary, early) using a mechanical braking system to brake the vehicle or keep it in a stopped state. There are different preferred criteria, which can be used individually or in different combinations. For multiple criteria, it can be required, for example, that one of the multiple criteria or two or three or all of the criteria must be met.

[0010] In particular, for example, suitable threshold values, such as for differences, can be defined according to a criterion, which is considered to be met when the difference is exceeded. Thus, it is finally checked whether the target speed is actually observed, at least within certain tolerances, and whether a stop state or a quasi-stop state is reached. Similarly, for example, a threshold value can be defined for the following time, during which a difference can exist for the longest time or the threshold value can be exceeded before a fault is recognized. It is also possible to make such a threshold value or, in general, the criterion also depend on the boundary conditions or influencing factors of the vehicle, such as, for example, the wheel diameter of the vehicle, the weight of the vehicle or other vehicle characteristics. Different preferred criteria are explained in detail below.

[0011] In this case, not or not only certain components, such as the inverter of the electric machine or the control device for controlling it, are monitored, but the operation of the electric machine itself is monitored. As a result, a fault can be detected independently of where, that is, in which component or how the fault may have occurred between the components.

[0012] A preferred criterion is to check whether the speed deviation, in particular the absolute value of the speed deviation, exceeds the associated threshold value more frequently than a predefined number of times. Another preferred criterion is to check whether the speed deviation, in particular the absolute value of the speed deviation, exceeds the associated threshold value for a time longer than a predefined period of time. Another preferred criterion is to check whether the time integral of the speed deviation, in particular the absolute value of the integral, exceeds the associated threshold value, in particular for a time longer than a predefined period of time. Another preferred criterion is to check whether a sign change occurs more frequently than a predefined number of times when determining the speed deviation.

[0013] It is also possible to use a switchover criterion by which a switchover between different standards can be carried out; for example, a switchover from one standard to another can be made, a further standard can be added, or a standard can be omitted (if more than one standard is used initially). Such a switchover criterion can also be used, for example, to change the threshold value of one or more standards.

[0014] A computing unit according to the invention, for example a control unit, of a motor vehicle is configured, in particular in terms of programming, to carry out the method according to the invention.

[0015] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with program codes for implementing all method steps, because this is particularly low in cost, especially when the control device for execution is also used for other tasks and therefore already exists. Finally, a machine-readable storage medium is provided, which has a computer program as described above stored thereon. Suitable storage media or data carriers for providing computer programs are in particular magnetic, optical and electrical memories, such as hard disks, flash disks, EEPROMs, DVDs, etc. It is also possible to download programs via a computer network (Internet, intranet, etc.). Such downloading can be done here either wired or with a cable or wirelessly (e.g., via a WLAN network, 3G-, 4G-, 5G- or 6G-connection, etc.).

[0016] Further advantages and embodiments of the invention are apparent from the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is schematically illustrated in the drawing on the basis of an exemplary embodiment and is described below with reference to the drawing.

[0018] Figure 1 A vehicle is schematically shown in which the method according to the invention can be carried out.

[0019] Figures 2 to 7 Various embodiments of the method according to the invention are shown. DETAILED DESCRIPTION

[0020] exist Figure 1 Schematically shows a vehicle 100 in which the method according to the invention can be implemented. The vehicle 100 is shown by way of example on an inclined road 102; the vehicle can be stationary, for example. The vehicle has an electric machine 110 with an inverter 112, wherein the electric machine 110 is used in particular as a drive for the vehicle, that is to say in particular an electric vehicle or possibly also a hybrid vehicle. The vehicle also has an energy storage device 114, such as a battery, for the electric machine 110.

[0021] Furthermore, vehicle 100 has a mechanical brake system, for example with two components 116, 118, such as friction brakes. Such a mechanical brake system can be used in principle to brake the vehicle or in particular to hold it at a standstill, also for a so-called "hill hold" function.

[0022] The vehicle also has a computing unit 120 designed as a control device, which can be used, for example, to control the electric machine 110 or the inverter 112 and is particularly designed to carry out the method according to the invention. In this way, the vehicle 100 can be braked to a standstill and then also held there, particularly by means of the electric machine 110 and more precisely in speed-controlled operation. This means that in particular a so-called "hill roll-back" function can also be carried out, at least for a certain period of time.

[0023] exist Figures 2 to 7 In the figures, different embodiments of the method according to the invention are shown as flow charts. Different criteria are used in each case, wherein a check is made on the basis of the speed difference or speed deviation to see whether the criteria are met. This is done in particular in a check path, which can be followed by different steps or check steps.

[0024] exist Figure 2 In the example, criterion K1 is used, in which it is checked whether the absolute value of the speed deviation exceeds the associated threshold value more frequently than a predefined number of times, and criterion K2 is used, in which it is checked whether the absolute value of the speed deviation exceeds the associated threshold value for a longer period of time than a predefined period of time. If one of the two criteria is met, a fault is detected.

[0025] For this purpose, firstly in step 200 the actual speed n of the electric machine is calculated. ist and the motor's target speed n soll Determine the speed deviation n diff In step 210, the speed deviation n diff The absolute value (quantity) is then compared with the associated threshold value n in step 220. diff_C Speed ​​deviation n diff The determination can in particular be performed continuously or repeatedly.

[0026] For the first criterion K1 mentioned, now each time the absolute value exceeds the threshold value n diff_C In particular, if the absolute value drops below the threshold value n for a short period of time, the counter value Z is increased. diff_C And then when the threshold value is exceeded again, the counter can also be increased. Then, in step 230, this number Z is compared with the associated threshold value Z C If the quantity Z exceeds the threshold Z C , then fault F is identified in step 240 .

[0027] For the second criterion K2 mentioned, each time the absolute value exceeds the threshold value n diff_C When the absolute value exceeds the threshold value n, a timer or a timer (or a clock) is started for a certain time or duration T. diff_c, for example, a timer can be run. In step 250, this time T is then compared with the corresponding threshold value T C (This threshold is the preset duration) is compared. If the time T exceeds the threshold T C , then a fault is identified in step 240 .

[0028] In the present example, a fault F is detected as soon as (at least) one of the two criteria K1 , K2 used is met, and also if both criteria K1 , K2 are met.

[0029] exist Figure 3 In addition to Figure 2 In addition to the example in , criterion K3 is also used, in which it is checked whether the absolute value of the time integral of the rotational speed deviation exceeds an associated threshold value.

[0030] For this criterion, the speed deviation n is determined in step 310 diff It should be noted that the value of the integral decreases and increases over time (i.e., for example, during braking) and may also become negative, so its absolute value is determined in step 320. Then, in step 330, this absolute value is compared with the associated threshold value Int C If the absolute value of the integral exceeds the threshold Int C , then fault F is identified in step 240 .

[0031] In this case, a fault is detected as soon as one of the three criteria K1 , K2 , K3 used is met, and also if all three criteria K1 , K2 , K3 are met.

[0032] exist Figure 4 An example is shown in Figure 3 The same three criteria K1, K2 and K3 are used in the same manner. However, the difference is that if the criterion K3 is met or if the criteria K1 and K2 are met or if all the criteria K1, K2, K3 are met, a fault is identified. If only the criterion K1 or only the criterion K2 is met, a fault is not identified.

[0033] exist Figure 5 An example is shown in FIG. 1 , in which a criterion K2 and a criterion K3' are used; the criterion K3' is a criterion for which it is checked whether the integral of the rotational speed deviation or its absolute value exceeds an associated threshold value for a period longer than a predefined period. This is therefore a modified criterion K3. For example, the same timer can be used for the time T as for the criterion K2 and thus the associated threshold value T C ; However, it is also conceivable to have separate timers with separate threshold values ​​or preset durations.

[0034] Now, here, the conversion criterion UK is used in addition, with which the conversion between the criterion K2 and the criterion K3' is performed. For this purpose, in step 510, the target speed n is checked. soll Is it zero, that is, should the stop state be reached. If so, a starting point can be set in step 520 to start the conversion timer for the conversion time T'. Then, in step 530, this conversion time T' is compared with the corresponding threshold value T'. C Compare (this threshold is the preset duration). If the conversion time T' exceeds the threshold T' C , then in step 540 a switch is made from standard K2 to standard K3'. Since the same timer is used for both standards here, it is sufficient to change the input value of the timer. In other words, during braking, one standard is first used and at the target speed n soll Another standard is used shortly after zero in order to monitor the operation of the motor.

[0035] exist Figure 6 An example is shown in FIG. 1 , in which standard K2, standard K3, standard K4 and conversion standard UK are used; standard K4 is the following standard, for which the check is performed in determining the speed deviation n diff In step 610, it is determined whether a sign change occurs more frequently than a preset number of times. For this purpose, it is determined whether a sign change occurs. Here, each time such a sign change occurs, the counter for the number of sign changes Z' is increased. Then, in step 620, this number Z' is compared with the corresponding threshold value Z' C If the quantity Z' exceeds the threshold Z' C , then fault F is identified in step 240 .

[0036] The switchover criterion UK is used here in such a way that a switchover from criteria K3 and K4 to criterion K2 is performed, which takes place in step 640. As long as the switchover criterion is not met, a fault is detected when criteria K3 or K4 or both criteria are met, and as soon as the switchover criterion is met, a fault is detected when criterion K2 is met.

[0037] exist Figure 7 An example is shown in FIG. 1 , in which the standard K2 and the conversion standard UK are used. The conversion standard UK is now used here to change the following threshold value in step 740 , in step 220 the speed deviation n diff The absolute value of is compared with the threshold. As long as the transition criterion is not met, the threshold value n is used. diff_C Once the transition criteria are met, other thresholds n' are used diff_C .

[0038] Threshold n' diff_C For example, it may be less than the threshold n diff_C , which results in a narrower tolerance band for speed deviations. This is particularly advantageous if a standstill has been reached and the speed acceleration process has ended or should end; the permissible duration can here be determined by a threshold value T' C to control.

Claims

1. A method for monitoring the operation of an electric motor (110) of a vehicle (100) used as a drive, wherein the monitoring is performed while the vehicle (100) is braked to a standstill by means of the speed-controlled operation of the electric motor (110) and / or while the vehicle (100) is kept at a standstill by means of the speed-controlled operation of the electric motor (110), The actual speed of the motor is determined ist ) and target speed (n soll ) between the speed deviation (n Diff ), Based on the speed deviation (n Diff ) and the corresponding thresholds to check whether one or more criteria (K1, K2, K3; K3', K4) are met, and in, If one or at least one of a plurality of criteria ( K1 , K2 , K3 , K3 ′, K4 ) is met, a fault in the operation of the electric machine is detected (F).

2. The method according to claim 1, wherein a standard (K1) is used, wherein the speed deviation (n Diff ), especially whether the absolute value of the speed deviation is greater than a preset number of times (Z C ) exceeds the corresponding threshold more frequently.

3. The method according to claim 1 or 2, wherein a standard (K2) is used, wherein the speed deviation (n Diff ), in particular, whether the absolute value of the rotational speed deviation is longer than a preset duration (T C ) for a long period of time exceeding the corresponding threshold.

4. The method according to claim 1 , wherein a standard (K3, K3') is used, wherein the rotational speed deviation (n Diff ) time integral, in particular the absolute value of the integral, in particular for a period longer than a predetermined time duration (T C ) for a long time exceeding the threshold value (Int C ).

5. The method according to claim 1 , wherein a criterion (K4) is used, wherein a check is made as to whether a predetermined number of times (Z') C ) occurs more frequently. Diff )’s sign change.

6. The method according to any of the preceding claims, wherein a plurality of criteria (K1, K2, K3, K3', K4) are used, and wherein, If at least two criteria of the plurality of criteria ( K1 , K2 , K3 , K3 ′, K4 ) are met, a fault in the operation of the electric machine is detected (F).

7. The method according to any of the preceding claims, wherein first at least one criterion from a plurality of criteria is used, and wherein: If a conversion standard (UK) exists, at least one other standard of the plurality of standards is used.

8. The method according to claim 1, wherein if a conversion standard (UK) is present, the corresponding threshold value is changed for one or at least one of the plurality of standards used.

9. The method according to claim 7 or 8, wherein the conversion criterion (UK) comprises the target speed (n Soll ) is zero or reaches zero or is longer than the preset switching duration (T' C ) is zero for a long time.

10. A computing unit (120) which is designed to carry out all method steps of the method according to any of the preceding claims.

11. A computer program which, when executed on a computer unit (120), causes the computer unit (120) to carry out all method steps of the method according to any one of claims 1 to 9.

12. A machine-readable storage medium having stored thereon the computer program according to claim 11.

Images