DE102023117022B4 - Method for controlling an electric drive train of a motor vehicle - Google Patents

Abstract

Method for controlling an electric drive train of an electrically driven 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, wherein for each drive module (EDS, EDS 1, EDS 2, EDS n) current damage indices (S(akt,1), S(akt,2), S(akt,n)) are determined, 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) with operating points (P(n,M,A,...)) prioritized by means of their cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are controlled in a common operating strategy (1) of the drive train, and wherein 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), 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)) cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are determined and corrected operating points of the drive modules (EDS, EDS 1, EDS 2, EDS n) are determined from these, characterized in that the corrected operating points are applied depending on a loading condition of the motor vehicle, characterized in that the corrected operating points are applied depending on a loading condition of the motor vehicle.

Description

The invention relates to a method for controlling an electric drive train of an electrically driven motor vehicle with several independently controllable electric drive modules depending on the load.

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

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

WO 2023 / 279 130 A1 discloses a method for controlling one or two electrically driven axles with two electric motors.

DE 10 2021 005 149 A1 discloses a method for operating an electric vehicle with at least two electric drive motors.

DE 10 2021 203 514 A1 discloses a method for controlling a drive train of a motor vehicle.

US 2010 / 0 222 953 A1 discloses a method for torque optimization of an electric vehicle with two electric drive motors.

US 7 739 005 B1 discloses a method for operating an all-wheel drive electric motor vehicle.

For example, from 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 in a load-dependent manner. 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 directly drive a drive wheel with its rotor. To adapt to the effect and to an efficient, in particular energy-efficient, operating range of the electric machine, a kinematic conversion mechanism, for example a speed change transmission, a differential, a separating clutch or the like, or optionally 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, optionally via a differential. One or more drive modules can drive the drive wheels of multiple drive axles.

The control of the individual drive modules is preferably load-dependent, so that all drive modules are operated with a specified or specifiable maximum torque or a specified nominal torque only under full load. An advantageous operating strategy for the drive train or motor vehicle provides, for example, for all drive modules to be operated in partial load mode, with some or all of them operating at reduced power. It may be possible to completely deactivate individual drive modules, for example, all drive modules of a drive axle.

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

To achieve uniform stress across all drive modules, a damage index is determined for the drive modules over a period of operation, and the drive modules are controlled based on their damage index. This means that when the drive train is not under full load, those drive modules with a higher damage index are given priority over others. This achieves uniform stress on the drive modules, so that, for example, maintenance intervals and wear up to the wear limit, with any necessary replacement, occur essentially simultaneously for all drive modules. This allows the vehicle to be operated more efficiently, among other things, due to reduced downtime and downtime during a workshop visit.

The damage index can, for example, be determined based on torque, speed, and/or temperature. A damage index is a variable that represents the impact 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, such as sensor data. For example, the power, such as the drive and/or recuperation torque, the speed, and the operating temperature can be recorded over time, such as an operating period. The recording and determination of the damage index can, for example, be carried out continuously, i.e., sliding or discretely over a predetermined interval, with successively evaluated intervals resulting in a progression of the damage interval over the operating and service life or age of the motor vehicle. The intervals can, for example, be cumulated in the power domain, temperature domain, or the like to form a respective current damage index. The time domain has proven advantageous, allowing a current damage index to be determined from the input data at discrete time intervals and added to previous damage indices. The damage mode is preferably recorded in the drive function of the drive modules. However, a recuperation function of the drive modules can also contribute to a damage index and be recorded accordingly.

For example, a summed 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 and 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 by 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, while the other is operated at partial 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, with these being controlled depending on their damage indices. This means that if there are at least two drive modules on the same axle, for example, in front of a shared differential, the drive module with the lower damage index will be used preferentially until it has sufficiently approached the damage indices of the other drive module(s).

In the operating strategy of the drive train according to the invention, current operating points are applied to the individual drive modules, the resulting operating data of these are 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 drivetrain operating strategy, corrected operating points can be applied depending on the load requirement of the drivetrain. According to the invention, corrected operating points are applied depending on the load condition of the motor vehicle, for example, a heavy-duty vehicle.

The invention is explained in more detail with reference to the exemplary embodiment illustrated in the single figure. This shows a schematic block diagram of an operating strategy for a drive train with multiple 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.

The proposal is to perform an online analysis of the EDL loads, for example, starting from the electric motor down to the drive wheels, using the available data in a damage model. This information is used to determine the prioritization of the EDL for subsequent load requests, for example, after a decoupling and reconnection during the next driving stage, with the goal of balancing the loads depending on previous wear-causing loads on the various EDLs.

The control unit 3 defines 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 determined, for example, by a driver or control software depending on the desired acceleration, driving speed, load condition, ambient conditions and/or the like, and outputs these to the drive modules EDS.

Based on the set operating points P(n,M,A,...), the EDS drive modules collect operating data D(n,M,T,...) relevant to wear, 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 over time are recorded.

The recording of the operating data D(n,M,T, ...) takes place 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(act,1), S(act,2), S(act,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(cum,1), S(cum,2), S(cum,n) is determined from the current damage indices S(act,1), S(act,2), S(act,n) and previously determined damage indices S(st,1), S(st,2), S(st,n) of the individual drive modules EDS 1, EDS 2, EDS n, which is cumulative, for example, over the entire service life of the EDS drive modules. 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 newly output operating points are prioritized such that EDS drive modules with lower cumulative damage indices S(cum,1), S(cum,2), S(cum,n) are preferentially used for operation such as propulsion or recuperation in order to achieve even overall wear of all drive modules. The current damage indices S(act,1), S(act,2), S(act,n) can be interpreted and modeled as pseudo-damage values (duty values), which represent the reduction in the service life of the EDS drive module parts during the specific time interval. They generally have no unit and allow conclusions to be drawn about the relative damage to the parts. In the exemplary embodiment shown, an increase in the values for the individual damage indices is assumed 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 in addition to the speed n, the torque M and the current A.

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

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

The cumulative damage difference ΔS(cum) is calculated from the stored relative damage difference ΔS(st) and the current damage difference ΔS(act) and stored in the memory as the 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

Claims (7)

Method for controlling an electric drive train of an electrically driven 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, wherein for each drive module (EDS, EDS 1, EDS 2, EDS n) current damage indices (S(akt,1), S(akt,2), S(akt,n)) are determined, 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) with operating points (P(n,M,A,...)) prioritized by means of their cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are controlled in a common operating strategy (1) of the drive train, and wherein 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), 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)) cumulative damage indices (S(kum,1), S(kum,2), S(kum,n)) are determined and corrected operating points of the drive modules (EDS, EDS 1, EDS 2, EDS n) are determined from these, characterized in that the corrected operating points are applied depending on a loading condition of the motor vehicle, characterized in that the corrected operating points are applied depending on a loading condition of the motor vehicle. Procedure according to Claim 1 , characterized in that the damage index is determined as a function of 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. Method according to one of the Claims 1 until 3 , 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 4 , characterized in that at least one drive axle is controlled by 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 5 , characterized in that several drive modules are provided for each drive axle and these are controlled among each other depending on their damage indices. Procedure according to Claim 1 until 6 , 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.