Method and system for controlling one or two electically-driven axles having two electric motors

Abstract

The present invention relates to a method (100) for controlling one or two electrically driven axles (1a, 1b) of a vehicle with electric motors (EM1, EM2), each connected to an output (2, 2a, 2b) via a respective power transmission path (3, 4), comprising the following steps: determining (101a) values for a speed and a torque applied to at least one mechanical component (5) of the power transmission paths (3, 4) and/or the electric motors (EM1, EM2); determining a value of a damage condition of the at least one mechanical component (5) resulting from damage inputs over a predefined period of time; and controlling (107) the electrically driven axles (1a, 1b) taking into account the damage condition of the at least one mechanical component (5).

Claims

1. A method for controlling two electrically driven axles of a vehicle, each with an electric motor, wherein the first electric motor is connected to a first output via at least one first power transmission path and the second electric motor is connected to a second output via at least a second power transmission path, or for controlling an electrically driven axle with two electric motors which jointly drive an output, wherein the first electric motor is connected to the output via at least one first power transmission path and the second electric motor is connected to the output via at least a second power transmission path, comprising the following steps: determining values for a speed and a torque applied to at least one mechanical component of the power transmission paths and/or the electric motors; determining a value of a damage input in relation to the at least one mechanical component depending on the value of the applied speed and the value of the applied torque, and determining a value of a damage condition of the at least one mechanical component resulting from damage inputs over a predefined period of time; in the case of two electrically driven axles, controlling the electrically driven axles or, in the case of one electrically driven axle, controlling the electrically driven axle, taking into account the damage condition or a relative damage condition of the at least one mechanical component, wherein, in the case of two electrically driven axles, the electrically driven axles are controlled in such a way or, in the case of one electrically driven axle, the electrically driven axle is controlled in such a way that: the damage condition or the relative damage condition of different power transmission paths in relation to each other is taken into account, in particular that the damage condition or the relative damage condition of different power transmission paths is as balanced as possible.

2. The method according to claim 1, wherein, in the case of two electrically driven axles, in order to control the electrically driven axles or, in the case of one electrically driven axle, in order to control the electrically driven axle either a transmission ratio in at least one of the two power transmission paths is adjusted in such a way, or a power distribution between the two electric motors is adjusted in such a way that the at least one mechanical component is not placed under stress.

3. The method according to claim 1, further comprising the following steps: verifying whether the current value for the damage condition or the relative damage condition of the at least one mechanical component exceeds a first limit value; and when the first limit value is exceeded, defining a threshold value for a torque provided by the first electric motor and/or a torque provided by the second electric motor, in particular depending on the damage input caused by the provided torque, wherein, in the case of two electrically driven axles, the electrically driven axles are controlled taking into account the threshold value for the torque or, in the case of one electrically driven axle, the electrically driven axle is controlled taking into account the threshold value for the torque.

4. The method according to claim 3, wherein, in the case of two electrically driven axles, in order to control the electrically driven axles or, in the case of one electrically driven axle, in order to control the electrically driven axle either a transmission ratio in at least one of the two power transmission paths is adjusted in such a way that the electric motor for which the threshold value is defined can be operated at a different operating point at a different, in particular higher speed, or a power distribution between the two electric motors is adjusted in such a way that the electric motor for which the threshold value is defined has to provide or absorb less torque.

5. The method according to claim 1, wherein the damage condition is determined as follows: $n.Math.T^p.Math.\mathrm{dt}$ $\mathrm{or}$ $\underset{i}{.Math.}{n}_i{T}_i^{p}t$ where n is a speed, T is a torque, t is a time increment and p is a parameter which indicates an intensity of the damage input for the at least one mechanical component, wherein the parameter p is specified for each mechanical component.

6. The method according to claim 1 further comprising the step: determining values for a temperature of at least one electrical component; determining a value for a damage input in relation to at least one electrical component depending on a value of the temperature and a damage condition resulting from the damage input over a predefined period of time, wherein, in the case of two electrically driven axles, the electrically driven axles or, in the case of one electrically driven axle, the electrically driven axle, are additionally controlled taking into account the damage condition of the at least one electric component.

7. The method according to claim 6, further comprising the following steps: verifying whether the current value for the damage condition or relative damage condition of an electrical component exceeds a second limit value; when the second limit value is exceeded, defining a threshold value for a power provided by the first electric motor and/or by the second electric motor, in particular depending on the damage input caused by the temperature, wherein, in the case of two electrically driven axles, the electrically driven axles or, in the case of one electrically driven axle, the electrically driven axle, are controlled taking into account the threshold value for the power provided.

8. The method according to claim 7, further comprising the following step: cooling the at least one electrical component depending on the value of the temperature.

9. The method according to claim 7, further comprising the step: providing a maximum proportional damage condition for the at least one mechanical component and/or the at least one electrical component; and determining the relative damage condition based on the determined damage condition and the maximum proportional damage condition, wherein a first limit value and/or the second limit value is defined in relation to the relative damage condition.

10. The method according to claim 8, wherein, when controlling the two electric motors, in the case of two electrically driven axles, an efficiency of the electrically driven axles is also taken into account or, in the case of one electrically driven axle, an efficiency of the electrically driven axle is also taken into account, wherein pairs of operating points of the first and second electric motors are selected in such a way that, while remaining within the threshold value for torque and/or the threshold value for power, an optimised operation in terms of efficiency is achieved in at least one of the two electric motors.

11. The method according to claim 1, wherein the value of the damage input corresponds with an extent to which the at least one mechanical component is damaged by a current operation.

12. The method according to claim 1, wherein the value of the damage condition is the sum of values of the damage input accrued to date.

13. The method according to claim 1, wherein the value of the relative damage condition is a ratio of the current value of the damage condition and a maximum proportional damage condition at a present time, wherein the maximum proportional damage condition corresponds with a proportion of a maximum value that is recommended for the damage condition for a time, for which the at least one mechanical component has been operated from since it was put into operation until the present time.

14. A system for controlling two electrically driven axles of a vehicle, each with an electric motor, wherein the first electric motor is connected to a first output via at least one first power transmission path and the second electric motor is connected to a second output via at least one second power transmission path, or for controlling an electrically driven axle with two electric motors which jointly drive an output, wherein the first electric motor is connected to the output via at least one first power transmission path and the second electric motor is connected to the output via at least a second power transmission path, comprising: means for determining values for a speed and a torque applied to at least one mechanical component of the power transmission paths and/or the electric motors; means for determining a value of a damage input in relation to the at least one mechanical component depending on the value of the applied speed and the value of the applied torque and determining a value of a damage condition of the at least one mechanical component resulting from damage input over a predefined period of time; means for controlling, in the case of two electrically driven axles, the electrically driven axles or, in the case of one electrically driven axle, the electrically driven axle, taking into account the damage condition of the at least one mechanical component; and means for controlling, in the case of two electrically driven axles, the electrically driven axles or, in the case of one electrically driven axle the electrically driven axle, taking into account the damage condition or a relative damage condition of different power transmission paths in relation to each other, in particular in such a way that the damage condition or the relative damage condition of different power transmission paths is as balanced as possible.

15. Vehicle with the system according to claim 14.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Further features and advantages are explained in the following description with reference to the figures.

(2) In each case at least partially schematically:

(3) FIG. 1a: shows an exemplary embodiment of an electrically driven axle of a vehicle;

(4) FIG. 1b: shows an exemplary embodiment of two electrically driven axles of a vehicle;

(5) FIG. 2a: shows a detailed view of the mechanical components of a first exemplary embodiment of the one electrically driven axle;

(6) FIG. 2b: shows a detailed view of the mechanical components of a first exemplary embodiment of the two electrically driven axles;

(7) FIG. 3a: shows a detailed view of the mechanical components of a second exemplary embodiment of the electrically driven axle;

(8) FIG. 3b: shows a detailed view of the mechanical components of a second exemplary embodiment of the two electrically driven axles;

(9) FIG. 4: shows a block diagram of an exemplary embodiment of a method for controlling an electrically driven axle;

(10) FIG. 5a: shows a diagram showing the progression over time of a damage condition in relation to a progression over time of a maximum proportional damage condition;

(11) FIG. 5b: shows the progression over time of a relative damage condition;

(12) FIG. 6: shows diagrams showing different torque distributions between electric motors of an electrically driven axle;

(13) FIG. 7: shows an exemplary embodiment of a process for defining a threshold value for a torque provided by an electric motor;

(14) FIG. 8: shows a block diagram of a process for defining a torque distribution between two electric motors of an electrically driven axle;

(15) FIG. 9: shows various diagrams relating to an example of a control strategy for an electrically driven axle; and

(16) FIG. 10: shows an exemplary embodiment of a system for controlling an electrically driven axle with two electric motors.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(17) FIG. 1a shows an exemplary embodiment of an electrically driven axle 1. This is driven by two electric motors EM1 and EM2. Each of these electric motors EM1, EM2 is connected, or, if a clutch is present, connectable, to the actual axle 2 in a torque-transmitting manner via a transmission 3, 4.

(18) The mechanical arrangement is designed in such a way that both electric motors EM1 and EM2 can drive the axle 2 simultaneously.

(19) The driving of the axle is preferably designed in such a way that the two output torques of the transmissions 3, 4 are summed in the axle 2. For example, this can be realised by means of spur gear stages or a common differential.

(20) The two transmissions 3, 4 can be designed as simple spur gears, i.e. single-speed transmissions, but also as multi-speed transmissions, with or without clutch.

(21) A first power transmission path to the axle 2 from the first electric motor EM1 is formed via the first transmission 3. From the second electric motor EM2, a second power transmission path to the axle 2 is formed via the second transmission 4.

(22) Preferably, each of the two transmissions 3, 4 has the option of disconnecting the respective power transmission path, for example via a separating clutch or by means of a neutral position.

(23) This makes it possible to drive the axle 2 via only one of the two electric motors EM1, EM2. Each of the two electric motors EM1, EM2 is preferably supplied with electrical power via an inverter 12, 13. Preferably, the inverters 12, 13 each contain a control unit which is specified a target torque for each electric motor EM1, EM2 by the so-called E-axle control unit 14 (EACU). The currently applied torque as well as the current speed of the electric motors EM1, EM2 are provided by the E-axle control unit 14.

(24) Preferably, the speed of the electric motors EM1 and EM2 is also in each case measured via speed sensors 15, 16 and made available to the E-axle control unit 14.

(25) For a control strategy taking into account the mechanical damage input, the more precisely the E-axle control unit 14 knows the actual speed of the electric motors EM1, EM2 and the torque applied in the respective power transmission paths or to the respective affected components, the more advantageous this is.

(26) The actual axle 2 in turn drives wheels 17, 18 of a vehicle.

(27) FIG. 1b shows an exemplary embodiment of two electrically driven axles 1a, 1b of a vehicle. These are driven by two electric motors, EM1 and EM2. Each of these electric motors EM1, EM2 is connected, or, if a clutch is present, connectable, to the actual axles 2a, 2b in a torque-transmitting manner via a transmission 3, 4.

(28) The mechanical arrangement is designed in such a way that both electric motors EM1, EM2 can drive the respective connected axles 2a, 2b simultaneously.

(29) The two transmissions 3, 4 can be designed as simple spur gears, i.e. single-speed transmissions, but also as multi-speed transmissions, with or without clutch.

(30) A first power transmission path to the first axle 2a from the first electric motor EM1 is formed via the first transmission 3. From the second electric motor EM2, a second power transmission path to the second axle 2b is formed via the second transmission 4.

(31) Preferably, each of the two transmissions 3, 4 has the option of disconnecting the respective power transmission path, for example via a separating clutch or by means of a neutral position.

(32) Each of the two electric motors EM1, EM2 is preferably supplied with electrical power via an inverter 12a, 12b. Preferably, the inverters 12a, 12b each contain a control unit which is specified a target torque for each electric motor EM1, EM2 by the so-called E-axle control unit 14 (EACU). The currently applied torque as well as the current speed of the electric motors EM1, EM2 are provided by the E-axle control unit 14.

(33) Preferably, the speed of the electric motors EM1 and EM2 is also in each case measured via speed sensors 15a, 15b and made available to the E-axle control unit 14.

(34) For a control strategy taking into account the mechanical damage input, the more precisely the E-axle control unit 14 knows the actual speed of the electric motors EM1, EM2 and the torque applied in the respective power transmission paths or to the respective affected components, the more advantageous this is.

(35) The actual axles 2a, 2b in turn drive wheels 17a, 17b, 18a, 18b of a vehicle.

(36) FIG. 2a shows a detailed view of a first exemplary embodiment of an electrically driven axle 1. This detailed view shows the individual gears and bearings of the power transmission paths. These are also the components that are subject to the greatest mechanical damage during operation of the electrically driven axle 1. The first transmission 3, which substantially forms the first power transmission path, preferably has a first spur gear stage 8 and a second spur gear stage 9, 10. The second spur gear stage 9, 10 is designed to be shiftable, whereby it is possible to select between the two gears or transmission ratios as first transmission ratio 9 and second transmission ratio 10.

(37) The second transmission 4, which substantially forms the second power transmission path, also has two spur gear stages 9, 10, but without the possibility of changing the transmission ratio. The two transmissions 3, 4 preferably drive a differential 11, which in turn drives the actual axle 2.

(38) FIG. 2b shows a detailed view of a first exemplary embodiment of a first electrically driven axle 1a and a second electrically driven axle 1b of a vehicle. This detailed view shows the individual gears and bearings of the power transmission paths. These are also the components that are subject to the greatest mechanical damage during operation of the electrically driven axles 1a, 1b. The first transmission 3, which substantially forms the first power transmission path, preferably has a first spur gear stage 8a and a second spur gear stage 9a, 10a. The second spur gear stage 9a, 10a is designed to be shiftable, whereby it is possible to select between the two gears or transmission ratios as first transmission ratio 9a and second transmission ratio 10a.

(39) The second transmission 4, which substantially forms the second power transmission path, also has two spur gear stages 9b, 10b, but without the possibility of changing the transmission ratio. The two transmissions 3, 4 preferably in each case have a differential 11a, 11b, which in turn drives the actual axles 2a, 2b.

(40) FIG. 3a shows a detailed view of the mechanical components of a second exemplary embodiment of an electrically driven axle 1. This exemplary embodiment is substantially identical to the first exemplary embodiment according to FIG. 2a. In contrast to the latter, however, the second transmission 4 is also equipped with a second transmission stage which can be shifted between two transmission ratios. In addition, a neutral position of the first transmission 3 and the second transmission 4 can also be realised by means of the clutch mechanism.

(41) FIG. 3b shows a detailed view of the mechanical components of a second exemplary embodiment of two electrically driven axles 1a, 1b. This exemplary embodiment is substantially identical to the first exemplary embodiment with two electrically driven axles 1a, 1b according to FIG. 2b. In contrast to the latter, however, the second transmission 4 is also equipped with a second transmission stage which can be shifted between two transmission ratios. In addition, a neutral position of the first transmission 3 and the second transmission 4 can also be realised by means of the clutch mechanism.

(42) FIG. 4 shows a block diagram of an exemplary embodiment of a method 100 for controlling an electrically driven axle 1 with two electric motors EM1, EM2 which jointly drive an output 2.

(43) The method allows a service life which correlates with the damage to the mechanical components to be monitored and adaptively taken into account in the operating strategy in the gear selection and in the torque distribution between the two power transmission paths.

(44) In a first step, the damage caused by mechanical action is taken into account. In addition, a damage input due to thermal stress, especially in the case of electrical components, can also be taken into account in the operating strategy.

(45) In a first step 101a), values of a speed and a torque which are applied to at least one mechanical component 5 of the transmission paths of the power transmission paths and the electric motors are therefore determined. In particular, the values are measured directly or indirectly by means of sensors. Such mechanical components 5 to which the torques are applied are in particular the bearings and the gears.

(46) In a second step 102a), a value of a damage input in relation to the at least one mechanical component 5 is determined depending on the value of the applied speed and the value of the applied torque, and a value of a damage condition of the at least one mechanical component 5 resulting from damage inputs over a predefined period of time is determined.

(47) Preferably, in a third step 103a), a maximum proportional damage condition Dmax(t) is provided for the at least one mechanical component and/or the at least one electrical component.

(48) In a fourth step 104a), a relative damage condition Rj(t) is determined on the basis of the determined damage condition Dj(t) and the maximum proportional damage condition Dmax(t), whereby the first limit value and/or the second limit value is/are defined in relation to the relative damage condition.

(49) Furthermore, in a fifth step 105a), it is preferably checked whether the value of the damage condition exceeds a first limit value.

(50) In a sixth step 106a), if the first limit value is exceeded, a threshold value for a torque provided by the first electric motor EM1 and/or by the second electric motor EM2 is preferably defined, in particular depending on the damage input and/or the damage condition caused by the provided torque, whereby the electrically driven axle is controlled taking into account the threshold value for the provided power.

(51) Finally, in a seventh step 107, the electrically driven axle 1 is controlled taking into account the damage condition of the at least one mechanical component 5.

(52) Preferably, the electrically driven axle 1 is controlled in such a way that the relative damage condition and/or the current damage input of different power transmission paths 3, 4 in relation to each other is taken into account. Furthermore, the axle is preferably controlled in such a way that the relative damage condition of different power transmission paths is balanced as much as possible.

(53) There are essentially two alternatives here for controlling the electrically driven axle 1: either a transmission ratio in at least one of the two power transmission paths 3, 4 is adjusted in such a way that the at least one mechanical component 5 is not placed under stress, or only in a defined way, or a power distribution between the two electric motors EM1 and EM2 is adjusted in such a way that the mechanical component is likewise not placed under stress, or only in a defined way.

(54) Also preferably, in order to control the electrically driven axle, either a transmission ratio in at least one of the two power transmission paths is adjusted in such a way that the electric motor EM1, EM2 for which the threshold value is defined can be operated at a different operating point at a different, in particular higher speed, or a power distribution between the two electric motors is adjusted in such a way that that the electric motor EM1, EM2 for which the threshold value is defined has to provide or absorb less torque.

(55) In the second step 102a), the damage condition is preferably determined by the following formulas:

(56) $n.Math.T^p.Math.\mathrm{dt}$$\mathrm{or}$$\underset{i}{.Math.}{n}_i{T}_i^{p}t$
where n is a speed, T is a torque, t is a time increment and p is a parameter that specifies an intensity of the damage input for the at least one mechanical component 5. The parameter p must be specified for each mechanical component 5.

(57) As shown in FIG. 4 (right-hand branch), the method 100 for controlling the electric axle can also be carried out in parallel for electrical components (not shown in detail). These electrical components are for example components of the electric motors EM1, EM2 or the inverters 12a, 12b.

(58) Essentially, the steps here are similar to determining the value of a damage input in relation to the at least one mechanical component 5, in particular a bearing or a gear.

(59) Here too, in a first step 101b), values of a temperature of at least one electrical component are determined.

(60) In a second step 102b), a value of a damage input in relation to the at least one electrical component is determined depending on a value of the temperature, and a damage condition resulting from the damage input over a predefined period of time is also determined.

(61) In a third step 103b), a reference damage condition for the temperature for the at least one electrical component is also provided.

(62) In a fourth step 104b), a relative damage condition of the electrical component 7 is determined on the basis of the determined damage condition and the reference damage condition, whereby the second limit value is defined in relation to the relative damage condition.

(63) In a fifth step 105b), it is preferably checked whether the value of the damage condition exceeds the second limit value.

(64) In a sixth step 106b), if the second limit value is exceeded, a threshold value for a power provided by the first electric motor EM1 and/or the second electric motor EM2 is defined, in particular depending on the damage input and/or the damage condition caused by the temperature, whereby the electrically driven axle is controlled taking into account the threshold value for the power provided.

(65) If the thermal damage input is taken into account, the electrically driven axle 1 is additionally controlled taking into account the damage condition of the at least one electrical component in the seventh step 107.

(66) In addition to or as an alternative to the seventh step 107, in this case, in an eighth step 108, the at least one electrical component may be cooled depending on the value of the temperature. With regard to the electrical components, there are thus again two possible ways of relieving the load. One is to reduce the power for the electric motor to which the electrical component is assigned. The second is to cool the electrical component.

(67) Furthermore, if this is possible in terms of power, one of the power transmission paths in which the affected electrical component is located can be disengaged via an upstream transmission, if this is switchable.

(68) FIG. 5a shows a diagram of a damage condition D relative to time. The dashed line Dmax(t) shows the maximum proportional damage condition over time, whereby, at the end of the desired service life of the component, the maximum recommended damage condition, shown as a horizontal line, is reached exactly (dashed line: linear increase). Exceeding the maximum recommended damage condition leads to an increased probability of failure. Dj(t), on the other hand, represents the accumulated damage input, i.e. the damage condition of component 5 in reality at time t, i.e. the damage condition in relation to the component determined from the real loads from torque and speed. This curve Dj(t) increases monotonically. As the diagram shows, from time t1 onwards, this real damage condition Dj(t) exceeds the maximum proportional damage condition Dmax(t) provided for at that time. Taking measures to reduce the damage input after time t1 leads to a flattening of the curve Dj(t). In this way, the curve Dj(t) can be brought back below the curve Dmax(t). At time t2, the curve of the real damage condition falls back below the maximum proportional damage condition Dmax(t2). If no measures were taken in the period between t1 and t2, the curve Di (t) would not flatten and the maximum recommended damage condition would be reached before the end of the desired service life (e.g. 20 years as in the example). There is an increased probability of failure of component 5 before the end of the desired service life.

(69) In FIG. 5a, the desired lifespan is for example twenty years.

(70) In FIG. 5b, the relative damage condition R.sub.j(t) is shown in a diagram corresponding to the timeline of FIG. 5a.

(71) The relative damage condition R.sub.j(t) results from dividing the real damage condition D.sub.j(t) by the respective maximum proportional damage condition at a given time t.

(72) The period between t.sub.1 and t.sub.2 is characterised by the fact that the relative damage condition R rises above 1. This should be prevented in order to prevent premature failure of the component. Accordingly, limit values R.sub.inc and R.sub.dec are preferably defined, represented in FIG. 5b by dashed lines, from which measures are taken or withdrawn to reduce further damage input. For example, from the limit value R.sub.inc, which specifies the maximum desired relative damage condition, measures must be taken or increased to reduce the damage input. R.sub.dec, on the other hand, specifies the value of the relative damage condition below which measures to reduce the damage input can be reduced. Both limit values R.sub.inc and R.sub.dec are preferably below R=1.

(73) If the value of the relative damage condition R.sub.j(t) rises above 1, a warning light may for example be activated. This indicates that the component has been subjected to above-average loads up to this point.

(74) A damage condition D.sub.max(t) therefore represents a time-dependent limit value for the damage condition. The value is different for each component (j)

(75) In FIG. 5b, the value R=1 corresponds to this limit value.

(76) FIG. 6 represents a process for defining a threshold value for a torque or a power provided by an electric motor depending on limit values for the damage condition.

(77) In each case, j denotes the component under consideration.

(78) FIG. 6 shows a process for defining a threshold value for a torque to be provided by the first electric motor EM1 or by the second electric motor EM2. The measures are intended to counteract overloading of the mechanical components 5 and/or the electrical components of the electrically driven axle. As described above, the measures may involve a threshold value for a torque to be provided by the first electric motor EM1 or by the second electric motor EM2, or a switching process that shifts the operating point of the first electric motor EM1 or the second electric motor EM2 to higher speeds, or completely disengages the electric motor in question, or cooling of the mechanical components 5 and/or electrical components.

(79) The process is explained in relation to a torque limitation. However, it is obvious to the skilled person that this process can also be applied to other measures.

(80) In the following process, Tmax refers to the maximum possible torque at the electric motor EM1 or EM2 of the power transmission path under consideration. If the component j is one of the components of interest in the power transmission path under consideration, then Tj denotes a suggestion for a torque limitation based on the current relative damage condition of this component j. Finally, the torque limitation Tlim is implemented on the electric motor. This is selected based on the limitation suggestions Tj for all components j of interest. So, on the one hand, Tlim is less than or equal to Tj, on the other hand Tlim is also always less than or equal to Tmax. At the start of the process at t=0, there is no torque limitation suggestion Tj in relation to any component j. Therefore, at this point, Tj=Tlim=Tmax applies to all components. This means that there is no active torque limitation based on a torque limitation suggestion for any component j and both electric motors EM1 and EM2 can be operated at their maximum torque Tmax, if necessary.

(81) In a first step in the process, the current relative damage condition Rj is queried in relation to all components j. Since no measure has yet been taken to limit torque at this point, one moves to the right-hand branch of the block diagram. Now it is checked whether the current relative damage condition Rj is greater than the maximum desired relative damage condition Rinc, for which measures need to be introduced or increased. If this is the case, a new measure is defined in relation to the component, in this case a torque limitation suggestion Tj. If, on the other hand, the relative damage condition Rj is less than the limit value Rinc, no action is taken. The torque limitation suggestion in relation to the component Tj is thus still equal to the maximum possible torque Tmax at the respective electric motor EM1, EM2 which drives the respective power transmission path 3, 4.

(82) This check is performed for all components of a power transmission path 3, 4. The active torque limitation T.sub.lim for this power transmission path is then set to the minimum determined torque limitation suggestion T.sub.j for a component j. After that, the process starts all over again. Now that there is a measure, i.e. an active torque limitation T.sub.lim, the process continues on the left-hand branch. Now the current relative damage condition R.sub.j is preferably compared with three different limit values. As already explained, R.sub.inc is the maximum desired relative damage condition at which measures must be introduced or increased.

(83) R.sub.dec is the relative damage condition under which measures can be reduced.

(84) R.sub.min is the relative damage condition under which no measures are required.

(85) The following correlation applies:

(86) $R_{\mathrm{inc}}>R_{\mathrm{dec}}>R_{\min }$

(87) If the current relative damage condition R.sub.j is greater than R.sub.inc, the measure must be increased, in the case of the torque this means that the threshold value for the torque limitation T.sub.j must be lowered.

(88) If the current relative damage condition R.sub.j is less than R.sub.min, the measures relating to this component can be lifted. In this case, in relation to this component, the maximum torque T.sub.max of the respective electric motor EM1, EM2 can be provided.

(89) In the case where the current relative damage condition R.sub.j is less than R.sub.dec but greater than R.sub.inc, the respective measure can be reduced. In the case of a torque limitation, this means that the threshold value can be increased.

(90) If the current relative damage condition Rj is less than Rinc but greater than Rdec, the measure in relation to the component j should be left unchanged.

(91) This sub-process is also repeated for all components j. The active torque limitation T.sub.lim is then set for each power transmission path 3, 4 so that it corresponds to the respective threshold value of the strongest measure for a component j in the respective power transmission path 3, 4. In relation to torque, this means that the active torque limitation T.sub.lim corresponds to the minimum value of the torque limitation suggestions T.sub.j across all components j.

(92) FIG. 7 shows two diagrams, each showing the motor characteristics of the first electric motor EM1 and the second electric motor EM2. In each case, the torque is plotted above the motor speed.

(93) On the basis of the two diagrams, a torque distribution between the first electric motor EM1 and the second electric motor EM2 can be determined at a given power and given speeds n.sub.1, n.sub.2 in the two electric motors EM1, EM2. For the first electric motor EM1 or for the first power transmission path 3 which it serves, there is an active torque limitation T.sub.lim.

(94) Accordingly, only those pairings of torque distributions can be selected at which the torque provided by the first electric motor EM1 is less than T.sub.lim. Otherwise, the torque distribution is preferably selected in such a way as to achieve optimised operation in terms of the efficiency of the electrically driven axle 1.

(95) FIG. 8 represents a process by which such a torque distribution is selected taking into account the overall efficiency of the system.

(96) The specifications for this process are a required load point at the output 2a, 2b, in total, and a possible active torque limitation T.sub.lim in one or both of the power transmission paths 3, 4. If there is a torque limitation T.sub.lim, the torque distribution is determined with a focus on efficiency and taking into account the active torque limitation T.sub.lim. If there is no solution for this, then in contrast the torque distribution is determined with a focus on efficiency and without taking into account a torque limitation.

(97) The same applies if there was no active torque limitation T.sub.lim in the first place.

(98) FIG. 9 shows four diagrams (a), (b), (c) (d), which represent a torque over time, a concrete example in which a control strategy according to FIG. 8 is used. FIGS. 9a and 9b each represent discrete-time torques provided by the first electric motor EM1.

(99) FIGS. 9c and 9d, on the other hand, represent those values of the torque provided by the second electric motor EM2. In FIGS. 9a and 9c, there is no active torque limitation T.sub.lim. In FIGS. 9b and 9d, on the other hand, there is a torque limitation T.sub.lim for the first electric motor EM1.

(100) If a torque requested on the first electric motor EM1 exceeds an active torque limitation T.sub.lim in relation to this first electric motor EM1 or to the first power transmission path 3, then the excessively requested torque is passed on to the second electric motor EM2, as shown in FIGS. 9b and 9d. This must deliver a greater torque T during the specified times t.sub.1, t.sub.2, t.sub.3 so that the first electric motor EM1 can reduce its provided torque T. This is no longer possible at the later times t.sub.4, t.sub.5, t.sub.6, since the second electric motor EM2 is also already delivering at the power limit or torque limit T.sub.max. In this case, in order to provide the required torque, a torque redistribution is preferably avoided and the active torque limitation T.sub.lim is ignored.

(101) FIG. 10 shows a system 20 for controlling an electrically driven axle 1 with two electric motors EM1, EM2.

(102) Such a system 20 preferably has means 21, in particular sensors, for determining values of a speed and a torque applied to at least one mechanical component 5 of the power transmission paths 3, 4 and/or the electric motors EM1, EM2. Furthermore, such a system 20 preferably has means 22 for determining a value of a damage input in relation to the at least one mechanical component 5 depending on the value of the applied speed and the value of the applied torque and determining a value of a damage condition of the at least one mechanical component 5 resulting from damage input over a predefined period of time. Furthermore, such a system 20 preferably has means 23 for controlling the electrically driven axle 1 taking into account the damage condition of the at least one mechanical component 5. Finally, the system has means for controlling, in the case of two electrically driven axles, the electrically driven axles or in the case of one electrically driven axle, the electrically driven axle, taking into account the damage condition of the relative damage condition of different power transmission paths in relation to each other, in particular in such a way that the damage condition of the relative damage condition of different power transmission paths is as balanced as possible.

(103) A means, within the context of the invention, may be implemented in the form of hardware and/or software, and may in particular comprise a processing unit, in particular a digital processing unit, in particular a microprocessor unit (CPU), preferably connected to a memory and/or bus system, and/or one or more programs or program modules. The CPU can be designed to process instructions implemented as a program stored in a storage system, to capture input signals from a data bus, and/or to issue output signals to a data bus. A storage system may contain one or more, in particular different, storage media, in particular optical, magnetic, solid-state and/or other non-volatile media. The program may be designed in such a way that it can embody or carry out the method described here, so that the CPU can execute the steps of such a method.

(104) Preferably, the system 20 has additional means to carry out further-working steps of the method 100. Also preferably, at least some of the means, in particular the whole system 20, is preferably integrated into the E-axle control unit 14.

(105) It should be noted that the exemplary embodiments are only examples and are in no way intended to limit the scope of protection, application and structure. Rather, the preceding description provides the skilled person with a guide for the implementation of at least one exemplary embodiment, whereby various modifications can be made, in particular with regard to the function and arrangement of the described components, without departing from the scope of protection arising from the claims and the equivalent descriptions of features.