DE102023117022A1 - Method for controlling an electric drive train of a motor vehicle - Google Patents

Abstract

The invention relates to a method for controlling an electric drive train of an electrically powered motor vehicle with several electric drive modules (EDS, EDS 1, EDS 2, EDS n) that can be controlled independently of one another depending on the load. In order to evenly distribute the wear of the drive modules (EDS, EDS 1, EDS 2, EDS n) over their service life and thus extend the service life and maintenance cycles of the drive train, a damage index that occurs over an operating period is determined for the drive modules (EDS, EDS 1, EDS 2, EDS n) and the drive modules (EDS, EDS 1, EDS 2, EDS n) are controlled depending on their damage index.

Description

The invention relates to a method for controlling an electric drive train of an electrically driven motor vehicle with several electric drive modules that can be controlled independently of one another depending on the load.

Electric drive trains are used to drive motor vehicles using drive modules (EDS), which contain, for example, an electric machine that can be controlled and/or operated by power electronics, and mechanical transmission elements for translating their rotor movement into a rotary movement of a drive wheel, for example including a speed change gear, a differential, separating clutch and/or the like. Transmission elements can be integrated into the drive module and/or connected upstream and/or downstream of it.

Due to different designs and loads, especially in heavy-duty vehicles where different drive modules can be designed to be switched on and off, the drive modules are exposed to different loads. The drive modules age or wear out at different rates.

For example, the printed publications DE 10 2005 061 080 A1 , DE 102019 125 949 A1 and DE 10 2021 106 302 A1 Methods for detecting and assessing damage to drive train components are known.

The object of the invention is to further develop a method for controlling an electric drive train. In particular, the object of the invention is to propose a method for uniform wear of drive modules of an electric drive train.

The object is solved by the subject matter of claim 1. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.

The proposed method is used to control an electric drive train of an electrically powered motor vehicle. Using the method, several drive modules can be controlled independently of one another depending on the load. A drive module is understood to be an electric machine that can be operated as a motor and preferably as a generator and that is in a possibly switchable operative connection with at least one drive wheel of the motor vehicle. In the simplest case, for example, a wheel hub motor can drive a drive wheel directly with its rotor. In order to adapt to the effect and to an efficient, in particular energy-efficient, working range of the electric machine, a kinematic conversion mechanism, for example a speed change gear, a differential, a separating clutch or the like, and possibly a combination of these, can be provided between one or more drive wheels.

One or more drive modules can drive a single drive wheel, for example in the form of a hub motor. One or more drive modules can drive at least two drive wheels of the same drive axle, if necessary by means of a differential. One or more drive modules can drive the drive wheels of several drive axles.

The control of the individual drive modules is preferably load-dependent, so that all drive modules are only operated with a specified or specifiable maximum torque or a specified nominal torque when the load is full. An advantageous operating strategy for the drive train or motor vehicle provides for all drive modules to be operated in partial load operation, for example, with some or all of them being operated at reduced power. It can be provided to completely switch off individual drive modules, for example all drive modules on a drive axle.

For example, in this way, the available torque of the drive modules can be adapted to the loading condition efficiently and in a resource-saving manner, particularly in the case of heavy-duty vehicles.

In order to achieve an even load on preferably all drive modules, a damage index is determined for the drive modules over an operating period and the drive modules are controlled depending on their damage index. This means that when the drive train is not under full load, the drive modules that have a higher damage index are protected preferentially than others. In this way, an even load is achieved on the drive modules, so that, for example, the onset of maintenance intervals and wear up to the wear limit with any necessary replacement for all drive modules occurs essentially at the same time. In this way, the motor vehicle can be operated more efficiently due to, among other things, reduced downtime and loss of use during a workshop visit.

The damage index can be, for example, torque-dependent, speed-dependent and/or temperature-dependent. A damage index is a value that represents the effect of operating and environmental conditions over time. The damage index can be determined by estimation, modeling, calculation and/or the like from recorded, modeled, estimated and/or calculated input variables, for example sensor data.

For example, the power, such as the drive and/or recuperation torque, the speed, the operating temperature can be recorded over time, for example an operating period. The damage index can be recorded and determined continuously, i.e. sliding or discretely over a predetermined interval, with intervals evaluated one after the other resulting in a progression of the damage interval over the operating and usage period or age of the motor vehicle. The intervals can be cumulated, for example, in the power domain, temperature domain or the like to form a respective current damage index. The time domain has proven to be advantageous, so that a current damage index is determined from the input data in discrete time intervals and added to previous damage indices. The damage mode is preferably recorded in the drive function of the drive modules. A recuperation function of the drive modules can, however, also contribute to a damage index and be recorded accordingly.

For example, a cumulative current damage index can be determined for each drive module, whereby the drive modules are controlled, i.e. operated, according to their current damage index in a common operating strategy of the drive train.

In an alternative or additional embodiment of the method, relative damage indices of the drive modules can be compared with a reference drive module. The drive modules are controlled as if they were operated with a corresponding torque depending on the relative deviations of the remaining drive modules compared to the reference drive module.

For example, at least one drive axle can be controlled with at least one drive module, whereby the damage index of at least two drive axles is determined axle by axle and the drive axles can be controlled among each other depending on their damage indices. This means that at least two drive axles are operated alternately in partial load operation depending on their damage index in order to achieve even wear. For example, one drive axle can be completely decoupled from the drive, with the other being operated at partial load or full load. In the case of a single or multiple drive axles, each with multiple drive modules, the drive modules of a single drive axle can each be controlled among each other depending on their damage index.

Alternatively or additionally, several drive modules can be provided for each drive axle, whereby these are controlled depending on their damage indices. This means that if there are at least two drive modules in the same axle, for example in front of a common differential, the drive module with the smaller damage index is used preferentially until it has sufficiently approached the other damage indices of the other drive module(s).

In a preferred operating strategy of the drive train, for example, current operating points are applied to the individual drive modules, the resulting operating data for these is recorded, a current damage index is determined from the operating data for the respective drive modules, cumulative damage indices are determined from the current damage indices and stored damage indices, and corrected operating points of the drive modules are determined from these. For example, in such or a similar operating strategy of the drive train, corrected operating points can be applied depending on a load requirement on the drive train. For example, corrected operating points can be applied depending on a loading state of the motor vehicle, for example a heavy-duty vehicle.

The invention is explained in more detail using the embodiment shown in the single figure. This shows a schematic block diagram of an operating strategy of a drive train with several drive modules.

By means of the operating strategy 1 shown in the block diagram 2, uneven wear and tear of several EDS drive modules, namely EDS 1, EDS 2 to EDS n (electric drive system), is prevented by calculating the damage effects of the EDS drive modules using online modeling and processing this information in the control unit 3.

It is proposed to consider the loads of the EDS online, for example starting from the electric motor to the drive wheels. but using the available data in a damage model. This information is used to determine the prioritization of the EDS for a subsequent load request, for example after a decoupling and reconnection during the next driving stage, with the aim of balancing the loads depending on previous wear-causing loads on the various EDS.

The control unit 3 determines the operating points P(n, M,A,...), for example the speed n of the electric machine, the torque M to be applied, the current A and/or the like for each individual drive module EDS 1, EDS 2, EDS n for a driving process, taking into account a value set, for example, by a driver or control software depending on the desired acceleration, driving speed, loading state, ambient conditions and/or the like, and outputs these to the drive modules EDS.

The EDS drive modules record operating data D(n,M,T, ...) that are relevant to wear based on the set operating points P(n,M,A,...), for example by measuring, modeling or estimating them using sensors. For example, the speed n, the applied torque M, the operating points and their profiles are recorded over time.

The operating data D(n,M,T, ...) are recorded in block 4, for example, over a specified driving period, over constant time intervals or the like.

In block 5, a current damage index S(akt,1), S(akt,2), S(akt,n) is created from the operating data D(n,M,T, ...) for each drive module EDS 1, EDS 2, EDS n, for example modeled from the system properties of the EDS drive modules that can be adapted depending on increasing operating time. In block 6, the cumulative damage index S(kum,1), S(kum,2), S(kum,n) is determined from the current damage indices S(akt,1), S(akt,2), S(akt,n) and previously determined damage indices S(st,1), S(st,2), S(st,n) stored in memory 7 for the individual drive modules EDS 1, EDS 2, EDS n, which is cumulative over the entire service life of the EDS drive modules, for example. Instead of the previously stored damage indices S(st,1), S(st,2), S(st,n), the cumulative damage indices S(kum, 1), S(kum,2), S(kum,n) determined in block 6 are then stored as new stored damage indices S(st,1), S(st,2), S(st,n), so that the damage indices are continuously developed over the operating life of the EDS drive modules.

In routine 8 of control unit 3, depending on the cumulative damage index S(cum,1), S(cum,2), S(cum,n), for example during a partial load request, the new operating points to be output are prioritized in such a way that EDS drive modules with a lower cumulative damage index S(cum,1), S(cum,2), S(cum,n) are preferably used for operation such as drive or recuperation in order to achieve an even overall wear of all drive modules. The current damage indices S(act,1), S(act,2), S(act,n) can be understood and modeled as a pseudo-damage value (duty value) that represents the reduction in the service life of the parts of the EDS drive modules during the specific time interval. They generally have no unit and allow conclusions to be drawn about relative damage to the parts. In the embodiment shown, an increase in the values for the individual damage indices is expected to result in an increasing reduction in the remaining service life of the parts and an entire service life calculation of the EDS drive modules and their parts can be omitted.

Depending on the damage mechanism, for example mechanical, thermal, chemical and/or the like, other operating variables, such as the Arrhenius equation to represent the thermally dependent damage effects in Block 5, can be used alternatively or additionally to the speed n, the torque M and the current A.

In an operating strategy that is an alternative to operating strategy 1, a relative change in the EDS drive modules can be recorded, for example one that requires less memory. In this case, the EDS 1 drive module is considered as the reference drive module. Only the differences in the damage indices of the other EDS drive modules compared to the reference drive module are recorded. This results in the following relationship for two drive modules EDS 1, EDS 2, for example, where the EDS 1 drive module is the reference drive module:

In a given time interval, a current relative damage difference ΔS(act) is formed from the current damage indices S(act,1), S(act,2) according to equation (1): $$\Delta \text{S}\left(\text{akt}\right)=\text{S}\left(\text{akt}\mathrm{,1}\right)-\text{S}\left(\text{akt}\mathrm{,2}\right)$$

The cumulative damage difference ΔS(cum) is formed from the stored relative damage difference ΔS(st) and the current damage difference ΔS(act) and stored in the memory as a new stored damage difference Δ(st).

If ΔS(cum)>0, the damage to the EDS 1 drive module is greater than to the EDS 2 drive module and the EDS 1 drive module is protected. If ΔS(cum) < 0, the damage to the EDS 2 drive module is greater and the EDS 2 drive module is protected.

list of reference symbols

1

operating strategy

2

block diagram

3

control unit

4

block

5

block

6

block

7

memory

8

routine

EDS

drive module

EDS 1

drive module

EDS 2

drive module

EDS n

drive module

D(n,M,T,...)

operating data

P(n,M,A,...)

operating points

S(act,1)

current damage index

S(act,2)

current damage index

S(act,n)

current damage index

S(cum,1)

cumulative damage index

S(cum,2)

cumulative damage index

S(cum,n)

cumulative damage index

S(st,1)

stored damage index

S(st,2)

stored damage index

S(st,n)

stored damage index

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 10 2005 061 080 A1 [0004]
• DE 102019 125 949 A1 [0004]
• DE 10 2021 106 302 A1 [0004]

Claims (10)

Method for controlling an electric drive train of an electrically powered motor vehicle with a plurality of independently load-dependently controllable electric drive modules (EDS, EDS 1, EDS 2, EDS n), characterized in that a damage index occurring over an operating period is determined for the drive modules (EDS, EDS 1, EDS 2, EDS n) and the drive modules are controlled depending on their damage index. procedure according to claim 1 , characterized in that the damage index is determined depending on torque, speed and/or temperature. procedure according to claim 1 or 2 , characterized in that a current damage index is continuously determined for each drive module (EDS, EDS 1, EDS 2, EDS n) in a predetermined time interval. procedure according to claim 3 , characterized in that current damage indices (S(akt,1), S(akt,2), S(akt,n)) are determined for each drive module (EDS, EDS 1, EDS 2, EDS n), cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are formed from these and previous, stored damage indices (S(st,1), S(st,2), S(st,n)), and the drive modules (EDS, EDS 1, EDS 2, EDS n) are controlled with operating points (P(n,M,A,...)) prioritized by means of their cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) in a common operating strategy (1) of the drive train. procedure according to claim 3 or 4 , characterized in that relative damage indices of the drive modules are compared with a reference drive module and the drive modules are controlled depending on relative damage differences of the remaining drive modules compared to the reference drive module. Method according to one of the Claims 1 until 5 , characterized in that at least one drive axle is controlled with at least one drive module, wherein the damage index is determined axle by axle and, if appropriate, several drive axles are controlled among each other depending on their damage indices. procedure according to claim 6 , characterized in that several drive modules are provided for each drive axle and these are controlled among each other depending on their damage indices. Method according to one of the Claims 1 until 7 , characterized in that in an operating strategy (1) of the drive train, current operating points (P(n,M,A,...)) are applied to the individual drive modules (EDS, EDS 1, EDS 2, EDS n), the resulting operating data (D(n,M,T,...)) are recorded, a current damage index (S(akt,1), S(akt,2), S(akt,n)) is determined from the operating data (D(n,M,T,...)) for the respective drive modules (EDS, EDS 1, EDS 2, EDS n), cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are determined from the current damage indices (S(akt,1), S(akt,2), S(akt,n)) and stored damage indices (S(st,1), S(st,2), S(st,n)), and from these corrected operating points of the drive modules (EDS, EDS 1, EDS 2, EDS n) are determined. procedure according to claim 8 , characterized in that in the operating strategy (1) of the drive train, the corrected operating points are applied depending on a load requirement on the drive train. procedure according to claim 8 or 9 , characterized in that the corrected operating points are applied depending on a loading condition of the motor vehicle.

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