Method for controlling a drive system of a vehicle comprising two electric machines

Abstract

The invention relates to a method for controlling a drive system of a vehicle (1) comprising two or more electric machines (2, 12) which drive at least one drive axle (8, 18) of the vehicle. If it is ascertained (100) that a partial load operation is possible, a first electric machine of the electric machines is decoupled (110) at a decoupling time, and at least one second electric machine of the electric machines is used to drive the at least one drive axle. An expected activation time (34) is determined (120) at which the first electric machine is expected to be reactivated, and on the basis of the expected activation time (34), after being decoupled, the first electric machine is operated - in a recuperation mode (140) in which kinetic energy of the first electric machine is recuperated in the form of electric energy if a recuperation activation loss (46) for the expected activation time is smaller than a coast-down activation loss (40) for the expected activation time and - in a coast-down mode (150) in which kinetic energy of the first electric machine is not recuperated if the recuperation activation loss (46) for the expected activation time is greater than the coast-down activation loss (40) for the expected activation time.

Description

[0001] Description

[0002] title

[0003] Method for controlling a drive system of a vehicle with two electric machines

[0004] The present invention relates to a method for controlling a drive system of a vehicle with two electric machines as well as a computing unit and a computer program for carrying out the method.

[0005] Background of the invention

[0006] Vehicles can be electrically powered by electric motors or electric machines. For high-performance applications, such as commercial vehicles, a vehicle can be powered by multiple electric machines. For example, two electric machines can be located on two different vehicle axles, or two electric machines can be located on a single vehicle axle, driving them together via a summing gear.

[0007] Disclosure of the invention

[0008] According to the invention, a method for controlling a drive system of a vehicle with two electric motors, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention utilizes the measure of determining, in a vehicle driven by two or more electric machines, after decoupling a first of the electric machines from a driven drive axle, an expected connection time at which the first electric machine is expected to be reconnected. Based on the expected connection time, a recuperation mode in which kinetic energy stored in the first electric machine is recuperated or a coasting mode in which the first electric machine coasts to a stop without recuperation is used. The mode in which the energy loss caused by decoupling and reconnecting is lower is used.This measure reduces energy consumption compared to using only the recuperation mode or only the coasting mode or using both drives permanently.

[0010] A computing unit according to the invention, e.g. a control unit of a vehicle electrically driven by two or more electric machines, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0011] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0012] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. The invention is schematically illustrated in the drawings using exemplary embodiments and will be described below with reference to the drawings.

[0013] Short description of the drawings

[0014] Figures 1A, 1B show various possible drive arrangements on a vehicle with two electric machines.

[0015] Figure 2 shows a flowchart according to an embodiment of the invention.

[0016] Figure 3 illustrates a possible procedure for selecting the recuperation mode or the coasting mode.

[0017] Embodiment(s) of the invention

[0018] Figures 1A, 1B show various possible drive arrangements on a vehicle 1 with two electric machines.

[0019] In Figure 1A, two drive axles are provided (double axle), with an electric drive arrangement consisting of an electric machine 2, an inverter 4, and a transmission 6, via which a driven axle 8 (or shaft) is or can be coupled to the electric machine 2, being arranged on each of the drive axles. At least one of the transmissions 6 allows the respective electric machine 2 to be decoupled from the corresponding driven axle 8. The electric machines 2 are controlled by alternating currents via the respective inverters 4 and, in particular, also allow the recuperation of kinetic energy into electrical energy.

[0020] The electric drive assemblies can, for example, each be designed as a structural unit or integrated drive axle (so-called electrified axle with individual drive). In Figure 1B, a drive axle is provided on which an electric drive assembly is arranged, consisting of two electric machines 12, two inverters 14, and a transmission 16. The transmission 16 is coupled to both electric machines 12 and to a driven axle 18 (or shaft), wherein the transmission 16 comprises a summation transmission so that the electric machines 12 can drive the axle 18 together. The transmission 16 is designed such that at least one of the electric machines 12 can be decoupled from the driven axle 18. The electric machines 12 are controlled by alternating currents via the respective inverters 14 and, in particular, also allow the recuperation of kinetic energy into electrical energy.

[0021] The electric drive arrangement can, for example, be designed as a structural unit or integrated drive axle (so-called electrified axle with dual drive).

[0022] In the vehicle 1 of both embodiments of Figures 1A, 1B, at least one battery is also provided (not shown), which is connected to the inverters 8, 18 via electrical lines in order to supply them with electrical energy and to store recovered electrical energy.

[0023] Since at least one of the electric machines can be decoupled from the driven axle, one of the electric machines can be switched off in the partial load range in order to increase the efficiency of the drive system. The corresponding transmission comprises a clutch and / or synchronization device for this purpose in order to be able to decouple the electric machine and reconnect it to the axle when partial load operation ends, i.e. to synchronize and couple it. During this synchronization or synchronization, the decoupled electric machine must first be accelerated back to a speed (as synchronous speed) which, if necessary taking into account a gear ratio of the transmission, corresponds to the speed of the driven axle or the other electric machine. Accordingly, switching it on is associated with a certain amount of energy. Figure 2 shows a flow diagram according to one embodiment of the invention.

[0024] It is assumed that the vehicle is driven by both electric motors.

[0025] In step 100, in particular, a check is made to determine whether partial load operation is possible. For example, a check is made to determine whether an electric machine has sufficient drive power (power and / or torque) to drive the vehicle on its own. If one electric machine is sufficient, a check can be made to determine whether operation with just one electric machine is more energy-efficient than operation with two electric machines. For this purpose, efficiency characteristics of the drive train, i.e., the electric machines and / or the inverters and / or the transmissions, can be taken into account. This check in step 100 is repeated until it is determined that partial load operation is possible.

[0026] If partial load operation is possible, in step 110 one of the electric machines (referred to as the first electric machine) is decoupled at a decoupling point in time. The rotationally fixed connection of the first electric machine to the axle via the corresponding transmission is thus severed (by disengaging a clutch). The vehicle is thus driven solely by the other electric machine (referred to as the second electric machine) or, in general, since the method can also be applied to more than two electric machines, by the at least one second electric machine. At the decoupling point in time, the first electric machine has a decoupling speed.

[0027] In step 120, an expected activation time is determined at which the first electric machine is expected to be reconnected or coupled. For this purpose, route data is evaluated, including, for example, an expected speed and / or an expected route, in particular elevation information along the route. The activation time can be determined, in particular, by the fact that the drive power is insufficient during partial load operation or that operation with both electric machines is more energy-efficient.

[0028] In step 130, depending on the expected connection time or the length of the time period between the decoupling time and the expected connection time, it is determined whether the first electric machine should be operated in a recuperation mode or a coasting mode after decoupling. The more energy-efficient mode is used.

[0029] If the recuperation mode is selected in step 130, the first electrical machine is operated in recuperation mode in step 140, in which kinetic energy (rotational energy) stored in the first electrical machine (in particular its rotor) and in the shafts and / or transmission elements (e.g. gears) and / or the like connected to it (even after decoupling) that rotate with it is converted into electrical energy. This means that the inverter of the first electrical machine is controlled accordingly. The amount of energy recuperated in this way depends in particular on the speed of the first electrical machine at the start of the recuperation mode. As a result, the first electrical machine comes to a standstill relatively quickly (speed equal to zero).

[0030] If the coasting mode is selected in step 130, the first electric machine is operated in the coasting mode in step 150, in which the kinetic energy of the first electric machine (and co-rotating elements) is not recuperated. Therefore, no electrical energy is recovered. In the coasting mode, the speed of the first electric machine decreases relatively slowly (compared to the recuperation mode), primarily due to friction.

[0031] In step 160, in particular, the decoupled first electric machine is switched on, i.e., a transition takes place from partial load operation to operation (full load operation) in which both electric machines drive the vehicle or are coupled to at least one axle. As already described above, during this switching on, before coupling (by closing the clutch), the speed of the first electric machine is synchronized with the speed of the drive axle, to which it is connected via a transmission. This synchronization, which in particular includes increasing the speed of the first electric machine to a synchronous speed at which coupling can occur, requires a certain amount of energy. The required energy depends on the speed at which this speed increase begins, so that the coasting mode - although no energy is recuperated in it - can be more energy-efficient than the recuperation mode.Of course, in general, the connection in step 160 can take place at a time other than the expected connection time, for example if the determination of the expected connection time was not sufficiently accurate, e.g. because factors influencing the load (e.g. wind conditions) were not known.

[0032] Figure 3 illustrates a possible procedure for selecting the recuperation mode or the coasting mode, e.g., corresponding to steps 120 and 130 of Figure 2.

[0033] For this purpose, a corresponding mode selection functionality 28 is implemented, for example, in a control unit of the vehicle and / or its drive, in particular by executing a corresponding computer program.

[0034] As described, route data can be evaluated to determine the expected activation time. For this purpose, for example, a load forecast 30 is carried out, which can be based on position data (e.g., GNSS data 32, Global Navigation Satellite System, such as GPS, GALILEO, etc.) and / or map information, which includes route information and in particular altitude information, and / or other data that influence the load (e.g., weather conditions). For example, the position and direction of travel of the vehicle are determined from the position data (e.g., GNSS data 32), and based on this, the expected route is determined using the map information. Based on the expected route, in particular the corresponding altitude information, the expected load can be determined for a time forecast horizon H (or forecast period), e.g.,assuming an unchanged vehicle speed. The length of the temporal prediction horizon H is, for example, specified as a specific value or selected depending on the speed of the first electric machine during decoupling, e.g. selected to be equal to the time period that the first electric machine would need to coast to a standstill if no recuperation takes place. Furthermore, if a change in speed due to the load is assumed, the expected speed of the vehicle over the prediction horizon H or at least at the expected time of activation and thus the synchronous speed, i.e. the speed to which the first electric machine must be brought when activated, can be estimated or predicted based on the expected load.

[0035] Based on the load prediction 30, the connection time 34 can be determined, e.g. as the time from which the power of the (at least one) second electrical machine is no longer sufficient, or as the time from which the joint use of the first and the second electrical machine is more efficient.

[0036] A loss calculation 36 can be carried out in which it is determined for the recuperation mode and the coasting-down mode how much energy is lost through decoupling and switching on if the respective mode were to be carried out. In the loss calculation 36, for example, the kinetic energy 38 of the first electrical machine, in particular of its rotor, is taken into account, which is shown here for the coasting down as a temporally falling curve in a diagram in which the energy E is plotted against time t. The kinetic energy 38 depends on the speed of the first electrical machine and falls accordingly with falling speed, starting from the decoupling speed. The functional dependence on time can be determined, for example, by a stored characteristic map and / or a model and / or a function based on the decoupling speed. Corresponding is the speed required for switching on or off.The energy required for synchronization, referred to as the rundown connection loss 40, is shown as a (monotonically) rising curve. The sum of the two curves corresponds at any given time to the energy referred to as the maximum connection loss 44, which is required to accelerate the first electric machine from a standstill (zero speed) to the synchronous speed and to couple it. The origin of the time axis corresponds to the decoupling point in time.

[0037] Furthermore, a dashed line is drawn, which indicates the energy loss referred to as recuperation activation loss 46 when using the recuperation mode, i.e., during recuperation and subsequent activation from standstill. The recuperation activation loss 46 is equal to the maximum activation loss 44 less the energy that can be recovered or recuperated during recuperation, which depends in particular on the speed (or decoupling speed) of the first electric machine at the time of decoupling.

[0038] Accordingly, a time or equivalent time 48 can be determined at which the coasting connection loss 40 exceeds the recuperation connection loss 46. The equivalent time 48 is compared in a comparison step 50 with the connection time 34 (which was determined in the load forecast 32), wherein, if the equivalent time 48 is after (or equal to) the connection time 34, the coasting mode 52 (corresponding to step 150 in Figure 1) is used, and if the equivalent time 48 is before the connection time 34, the recuperation mode 52 (corresponding to step 140 in Figure 1) is used.

[0039] The term "loss" in recuperation activation loss and coast-down activation loss refers to the energy loss resulting from the energy required for activation minus the recuperated energy or the remaining kinetic energy. Overall, i.e., taking into account the energy required to drive the vehicle, less energy can of course still be consumed, since at partial load, driving with only the second electric motor can be more energy-efficient than driving with both the first and second electric motors.

[0040] The loss calculation 36 described above assumes a constant vehicle speed. In general, the speed can change and thus also the synchronous speed, which can change in particular over time. This leads to the maximum connection loss changing with the changing synchronous speed (in particular over time); the coasting connection loss and the recuperation connection loss then also change accordingly, in particular as a function of time. The anticipated synchronous speed can be determined, for example, as part of the load forecast 30 if the anticipated vehicle speed over the forecast horizon H or at least at the anticipated connection time is determined therein.

Claims

Claims 1. A method for controlling a drive system of a vehicle (1) having two or more electric machines (2, 12) that drive at least one drive axle (8, 18) of the vehicle, wherein, if it is determined (100) that partial load operation is possible, a first of the electric machines is decoupled (110) at a decoupling time and at least a second of the electric machines is used to drive the at least one drive axle; wherein an expected connection time (34) is determined (120) at which the first electric machine is expected to be connected again;wherein, depending on the expected connection time (34), the first electrical machine is operated after decoupling in a recuperation mode (140) in which kinetic energy of the first electrical machine is recuperated as electrical energy if a recuperation connection loss (46) for the expected connection time is smaller than a run-down connection loss (40) for the expected connection time, is operated in a run-down mode (150) in which kinetic energy of the first electrical machine is not recuperated if the recuperation connection loss (46) for the expected connection time is greater than the run-down connection loss (40) for the expected connection time; 2. The method according to claim 1, wherein the recuperation connection loss (46) corresponds to the energy loss when using the recuperation mode (140) and subsequently switching on (160) the first electrical machine, and wherein the run-down connection loss (40) corresponds to the energy loss when using the run-down mode (150) and subsequently switching on (160) the first electrical machine.

3. Method according to one of claims 1 or 2, wherein a maximum connection loss (44) is determined which corresponds to the energy required for connecting the first electrical machine at the expected connection time (34) starting from a speed of zero.

4. The method according to claim 3, wherein the recuperation connection loss (46) is determined as the maximum connection loss (44) less the energy that can be recuperated at a given decoupling speed of the first electric machine.

5. The method according to claim 3 or 4, wherein a temporal profile of the kinetic energy (38) of the first electric machine is determined for a coasting down without recuperation; and wherein the coasting down connection loss (40) for the expected connection time is determined as the maximum connection loss minus the kinetic energy (38) of the first electric machine at the expected connection time (34).

6. The method according to claim 4, wherein a time profile of the kinetic energy (40) of the first electrical machine for a coasting down without recuperation is determined; wherein a time profile of the coasting-connection loss (40) is determined such that the sum of the coasting-connection loss and the kinetic energy is equal to the maximum connection loss for all times; wherein an equivalent time (48) is determined at which the coasting-connection loss corresponds to the recuperation connection loss; wherein the first electrical machine is operated in recuperation mode (140) after the decoupling (110) if the equivalent time (48) is after the connection time (34), and wherein the first electrical machine is operated in coasting mode (150) after the decoupling (110) if the equivalent time (48) is before the connection time (34).

7. The method according to claim 5 or 6, wherein the temporal course of the kinetic energy (40) of the first electric machine is determined by means of a characteristic map and / or a model and / or a function based on the decoupling speed.

8. The method according to any one of the preceding claims, wherein the connection (160) comprises synchronizing the rotational speed of the first electric machine and coupling the first electric machine to the at least one drive axle; wherein a synchronous rotational speed is determined for the first electric machine, which it must reach at the expected connection time (34) in order to enable the coupling of the first electric machine.

9. Method according to one of the preceding claims, wherein route data are evaluated to determine the expected connection time.

10. The method according to one of the preceding claims, wherein a load forecast (30) is carried out, which begins at the decoupling time and extends over a maximum time forecast horizon (H); wherein the expected connection time (34) is determined on the basis of the load forecast (30).

11. The method according to claim 10, wherein the load prediction (30) is based on position data, in particular GNSS data (32), and / or map information including route information and in particular altitude information, and / or other data influencing the load.

12. Method according to one of the preceding claims, comprising connecting (160) the first electrical machine.

13. Computing unit configured to carry out all method steps of a method according to one of the preceding claims.

14. A computer program which causes a computing unit to carry out all method steps of a method according to one of claims 1 to 12 when executed on the computing unit.

15. A machine-readable storage medium having a computer program according to claim 14 stored thereon.

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