Drive system and method for at least partially electrically driven motor vehicle

Abstract

The invention relates to a drive system (1) for an at least partially electrically driven motor vehicle (10), comprising a traction drive (11) having two traction motors (2), at least one of which is designed as a permanent magnet-excited synchronous motor (3). In partial load operation, the traction motor (2) can be switched off and towed together. A defined magnetic field is generated by means of a magnetic field generator (15) of the stator (5) in order to at least partially demagnetize a permanent magnet (14) of the switched-off traction motor (2).

Description

Technical Field

[0001] The invention relates to a drive system for an at least partially electrically driven motor vehicle, the drive system having an electric traction drive with at least two electric traction motors. Background Art

[0002] Such drive systems are particularly suitable for electric vehicles, since for efficiency reasons, for example in partial load operation, one of the traction motors can be switched off and pulled. In the automotive industry, permanently excited synchronous machines (PSM) are often used as traction motors due to their high torque density and efficiency. The excitation of the rotor is achieved by permanent magnets. Rare earth magnetic materials such as NeFeB are used for this purpose.

[0003] However, a disadvantage of PSM is the relatively high drag losses (eddy current losses and hysteresis losses) in drag operation. Here, separately excited synchronous machines (FSM) or asynchronous machines (ASM) offer a clear advantage over PSM, since the excitation field can simply be switched off in drag operation or without active excitation in the rotor. Summary of the invention

[0004] In contrast, the object of the present invention is to provide an improved drive system for an at least partially electric motor vehicle. In particular, high torque density and efficiency and at the same time the lowest possible drag losses should be possible.

[0005] This object is solved by a drive system having the features of claim 1. A motor vehicle according to the invention is the subject of claim 14. Preferred embodiments of the invention are the subject of the dependent claims. Further advantages and features of the invention emerge from the general description and the description of exemplary embodiments.

[0006] The drive system according to the invention is designed for an at least partially electrically driven motor vehicle and preferably for an electric vehicle. However, it can also be used for hybrid vehicles. The drive system comprises at least one electric traction drive having at least two electric traction motors. At least one of the traction motors is designed as a synchronous motor with permanent magnet excitation. The traction motor or synchronous motor has a rotor with a plurality of permanent magnets (for generating a rotor magnetic field or excitation field). The traction motor or synchronous motor has a stator with a magnetic field generating device for generating a stator magnetic field or rotating field. In particular, the rotor is rotatable relative to the stator. The drive system comprises at least one control device, which is suitable and designed to switch off at least the traction motor designed as a synchronous motor with permanent magnet excitation according to the load state of the drive system and in particular at least during partial load operation. Thus, the traction motor is in a towing mode and is towed along. In particular, the traction motor is in the towing mode while at least one other traction motor is still switched on and provides torque for driving. The control device is suitable and designed to generate a prescribed magnetic field, the so-called demagnetizing field, by means of the magnetic field generating device. The control device is suitable and designed to use the demagnetizing field to at least partially demagnetize the permanent magnets of at least one switched-off traction motor so as to reduce the drag loss during towing operation.

[0007] The drive system according to the invention offers numerous advantages. The targeted and on-demand demagnetization of the permanent magnets during drag operation offers considerable advantages. This means that the advantages of a synchronous machine with permanent magnet excitation can be realized with particularly low drag losses. Another advantage is that the existing stator can be used for demagnetization. However, coils can also be used for demagnetization, which can be mounted in or on the rotor to save installation space.

[0008] Preferably, the control device is suitable and designed to generate a defined magnetic field, in particular a magnetizing field, by means of the magnetic field generating device, so as to re-magnetize previously demagnetized permanent magnets of at least one switched-off traction motor. In particular, this allows the traction motor to provide a defined torque for driving and / or to be switched on again. In particular, the permanent magnets are magnetized again as before demagnetization.

[0009] The control device is particularly suitable and designed to re-magnetize the traction motor at least when there is a torque request requiring or prescribing at least one switched-off traction motor to provide the torque request. In particular, an algorithm defining the relationship between the torque demand and the required traction motor is stored in the control device. In particular, the control device is suitable and designed to perform the magnetization as a function of the load state of the drive system and in particular during full-load operation and / or coasting operation with energy recovery (e.g. recuperation operation) and / or for brake assistance.

[0010] Preferably, the control device is adapted and designed to generate a prescribed magnetic field with a prescribed magnetic field direction by means of the magnetic field generating device. In particular, the control device is adapted and designed to set a magnetic field direction for the magnetizing field, which is opposite to the magnetic field direction of the demagnetizing field. In particular, the control device can set the magnetic field direction of the prescribed magnetic field.

[0011] Advantageously and preferably, at least one current pulse is used to generate a prescribed magnetic field (in particular a demagnetizing field and / or a magnetizing field). In particular, the current pulse is adjustable. Preferably, the current pulse has a higher (maximum) current intensity and / or a higher (maximum) amplitude than the rated current intended for a synchronous machine with permanent magnet excitation and in particular for its stator (in rated operation). The (maximum) current intensity and / or the (maximum) amplitude of the current pulse is in particular at least 1.5 times, preferably at least 2 times, particularly preferably at least 2.5 times the rated current. It is also possible and advantageous for the (maximum) current intensity and / or the (maximum) amplitude of the current pulse to be at least three times, at least four times, or at least five times the rated current.

[0012] In an advantageous embodiment, the current pulses provided to generate the defined magnetic field can be provided at least partially by power electronics of the traction drive and particularly preferably by an inverter device. The inverter device is used in particular to provide the traction current for the traction drive. In particular, the inverter device can be used to generate a traction current with an adjustable frequency and / or current intensity and / or amplitude. In particular, the energy for the current pulses is taken from a power battery.

[0013] Preferably, the current pulses designed to generate the defined magnetic field can be provided at least partially by the capacitor arrangement.In addition to or as an alternative to the power electronics or the inverter arrangement, the capacitor arrangement can provide at least part of the current pulses.

[0014] In particular, the control device is suitable for and designed to adjust the current pulses at least in terms of amplitude and / or current intensity and / or current direction and / or frequency. In particular, the control device can control the power electronics and / or capacitor device accordingly. In particular, the current pulses are provided by the magnetic field generating device.

[0015] The control device is particularly suitable and designed to set the current direction of the current pulse for generating a defined magnetic field. In particular, the control device is suitable and designed to set the current direction for the magnetizing field, which current direction is opposite to the current direction of the demagnetizing field. In particular, the control device can set the current direction by means of a switching device. In particular, the switching device is operatively connected to the power electronics and / or the capacitor device, or is part of one of these devices.

[0016] In an advantageous embodiment, it is provided that the control device is suitable and designed to apply a defined magnetic field (for demagnetization and / or magnetization) to the at least one traction motor, at least when the at least one (further) traction motor is switched on and provides a torque for driving and / or the drive system is in motion. This means that the influence of the defined magnetic field on the driving characteristics can be kept particularly low.

[0017] Preferably, the control device is suitable and designed to adjust the torque of the at least one traction motor when the prescribed magnetic field is applied to the at least one traction motor so that undesired torque pulses can be avoided. This makes the driving operation particularly comfortable and safe, even when the traction motor is magnetized. For example, the synchronous motor is prevented from providing a torque during demagnetization or magnetization, which torque would cause a noticeable jolt when the vehicle is driven. In particular, the adjustment is performed taking into account the torque that the traction motor feeds into the drive system due to the prescribed magnetic field. In particular, when the prescribed magnetic field is applied to the at least one traction motor, the torque of (all) traction motors of the drive system is constantly adjusted.

[0018] In an advantageous embodiment, the drive system comprises at least two axle units. The at least two axle units particularly comprise at least one front axle and at least one rear axle. In particular, each axle unit can be driven by at least one traction motor of at least two traction motors. In particular, the control device is suitable and designed to switch off and demagnetize at least one traction motor for driving at least one axle unit of the at least two axle units, depending on the load state of the drive system, so that a towing mode can be provided axle by axle. In particular, at least one axle unit is towed while at least one axle unit is driven. In particular, at least one axle unit of the at least two axle units is not driven in towing mode. In particular, each axle unit comprises at least two wheels.

[0019] In an advantageous embodiment, the drive system comprises at least one front axle that can be driven by at least one traction motor and at least one rear axle that can be driven by at least one traction motor. In particular, the control device is suitable and designed to switch off and demagnetize at least one traction motor for driving the front axle as a function of the load state of the drive system, so that the front axle is also pulled while the rear axle is driven. This provides a particularly efficient driving operation and, for example, enables the range of the electric vehicle to be extended.

[0020] It is also possible and advantageous that the control device is suitable and designed to switch off and demagnetize at least one traction motor provided for driving the rear axle, depending on the load state of the drive system, so that the rear axle is also pulled while the front axle is driven. The control device can also demagnetize at least one traction motor of the front axle and at least one traction motor of the rear axle, so that, for example, rolling operation with particularly low losses is possible.

[0021] In particular, the coercive field strength of the permanent magnets of at least one traction motor designed as a permanently excited synchronous machine is matched to a prescribed magnetic field that can be generated by the magnetic field generating device. In particular, magnets are provided whose coercive field strength is specially adjusted and, for example, specially reduced in comparison with conventional permanent magnets of comparable permanently excited synchronous machines. This makes demagnetization and magnetization particularly reliable.

[0022] In particular, an algorithm is stored in the control device, which defines a relationship between the coercive field strength of the permanent magnet and the magnetic field strength and / or magnetic field direction and / or the amplitude and / or direction of the current pulse required for demagnetization or magnetization. In particular, this correlation has been previously determined numerically and / or experimentally. In particular, the synchronous machine with permanent magnet excitation is designed so that these relationships can be achieved.

[0023] The method according to the invention is used for operating a drive system, in particular as described above. The method according to the invention also solves the above-mentioned problems in a particularly advantageous manner. In particular, the method is designed so that it can be used for operating a drive system according to the invention, and preferably also for operating its embodiments. In particular, the method is designed so that it can also be used for performing operations that can be performed by a control device described in the invention. In particular, the control device is suitable and designed to perform the method and in particular its embodiments. In particular, the control device is suitable and designed to perform steps formulated in a method-like manner in the context of the present invention. In particular, the control device comprises at least one algorithm for performing the steps described herein.

[0024] The at least two electric traction motors can each be designed as a synchronous motor with permanent magnet excitation. In particular, the traction motors each have a rotor with a plurality of permanent magnets and a stator with a magnetic field generating device. However, at least one of the at least two traction motors may also be designed as a different type of motor.

[0025] In the context of the present invention, switching off the traction motor particularly means that the traction motor no longer provides an effective torque. However, in the switched-off state, basic control including the power supply is still possible and preferred. In the context of the present invention, switching on the traction motor particularly means that the traction motor is activated to provide an effective torque. In particular, demagnetization and magnetization of at least one traction motor is provided during driving operation or while driving.

[0026] In particular, the control device is suitable and designed to monitor the load state of the drive system and to identify at least one load state suitable for switching off the traction motor and to switch off the traction motor depending on whether a suitable load state exists. In particular, the control device comprises sensor means for monitoring the load state of the drive system and / or for detecting the torque and / or speed of the traction motor. The applicant reserves the right to claim an at least partially electric motor vehicle and preferably an electric vehicle having a drive system as proposed in the present application. The drive system may comprise at least one power battery and / or power electronics.

[0027] In particular, the load state of the drive system in which the traction motors are demagnetized is partial load operation. However, the demagnetization may also take place in other suitable load states and / or in energy-saving modes (e.g., to extend the cruising range). The control device may be suitable for and designed to demagnetize (all) traction motors that are designed as synchronous machines with permanent magnet excitation. For example, it is useful to demagnetize all traction motors if the longest possible coasting time is desired.

[0028] The magnetic field generating device is particularly used to generate a controllable magnetic field. In particular, the magnetic field device comprises at least one electric coil device. The coil device is particularly provided by the stator winding. The coil device can also be attached to the stator winding or designed separately from the stator winding. In one embodiment, the (supplementary or separate) coil device can be at least partially arranged in the rotor and / or on the rotor. The supplementary or separate coil device can also be at least partially arranged in the stator and / or on the stator. In particular, the permanent magnet can be at least partially demagnetized and magnetized by means of a demagnetizing field. When demagnetization is mentioned in the context of the present invention, this is particularly understood to mean at least partial demagnetization. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further advantages and features of the invention result from the exemplary embodiments described below with reference to the attached drawings.

[0030] Figure 1 is a highly schematic illustration of a drive system according to the invention. DETAILED DESCRIPTION

[0031] Figure 1 The drive system 1 according to the invention is shown for a motor vehicle 10, which is only partially shown here and is designed as an electric vehicle. The drive system 1 can be operated according to the method according to the invention and comprises two axle units 8, which are designed as a front axle 18 and a rear axle 28. The drive system 1 comprises a traction drive 11 with two traction motors 2. A first traction motor 12 is used to drive the front axle 18, and a second traction motor 22 is used to drive the rear axle 28. The axle units 8 are each equipped with two wheels 38.

[0032] The traction motors 2 are here each designed as a permanently excited synchronous motor 3. To this end, the traction motors 2 each include a stator 5 and a rotor 4 rotatably mounted in the stator 5. The rotor 4 is equipped with a plurality of permanent magnets 14, which are shown here only as an example. The permanent magnets 14 are used to generate a rotor magnetic field (also called an excitation field) for the rotor 4. The stator 5 includes a magnetic field generating device 15 for generating a stator magnetic field (also called a rotating field).

[0033] A power battery 20, designed, for example, as a high-voltage battery, is provided to supply energy to the traction drive 11. A power electronics 7 with an inverter arrangement 17 is provided to control the traction motors 2. The inverter arrangement 17 comprises an inverter 17a for each traction motor 2. For example, the power electronics 7 provides the traction current required for the respective torque demand.

[0034] The drive system 1 is equipped with a control device 6, which switches off the first traction motor 12 according to the load state of the drive system 1 and, for example, in partial load operation, so that it is operated in towing mode and is towed along. The second traction motor 22 remains switched on and provides torque to the rear axle 28. However, it is also possible to switch off the second traction motor 22, for example, when the first traction motor 12 drives the front axle 18.

[0035] The selection of which drive motor 2 is to be switched off can be fixed or dynamic. For example, the selection can depend on whether a driven front axle 18 or a driven rear axle 28 is more advantageous for the respective motor vehicle 10 .

[0036] In order to reduce or avoid drag losses during traction, the control device 6 can demagnetize the permanent magnets 14 of the turned-off traction motor 2 in a targeted manner. For this purpose, a prescribed magnetic field, the so-called demagnetization field, is generated by a magnetic field generating device 15. Demagnetization leads to a significant reduction in eddy current losses and hysteresis losses. For example, if the permanent magnets 14 of the rotor 4 are completely demagnetized, only friction (air friction and bearing friction) remains as a loss source.

[0037] If there is a torque request and the drag mode is to end, the permanent magnets 14 are re-magnetized by a prescribed magnetic field (the so-called magnetizing field) to such an extent that the drive delivers its intended torque. For example, the magnetic field directions of the demagnetizing field and the magnetizing field are different.

[0038] The corresponding high current pulse is used to generate the prescribed magnetic field. This allows a short and correspondingly strong magnetic field to be generated in the desired direction in order to achieve the desired magnetization of the permanent magnet 14. For example, the current pulse required here is 3-5 times the rated current and is provided by the inverter device 17. Alternatively or additionally, the capacitor device 27 can also be discharged to provide the current pulse.

[0039] The permanent magnets 14 are made of a material with a suitable coercive field strength so that they can be substantially completely or at least partially demagnetized even by a demagnetizing field. The ratio of the coercive field strength of the permanent magnets 14 to the required amplitude of the current pulse is predetermined, for example by numerical calculation and / or by designing the synchronous machine 3 accordingly.

[0040] The required current pulses can be achieved here by means of suitable current control during driving (speed not equal to 0; torque not equal to 0) and without significant torque pulses. For example, the torque is constantly adjusted during the demagnetization or magnetization process. If appropriate torque is required, the permanent magnets 14 can be fully magnetized again in a short time by the prescribed magnetic field of the magnetic field generating device 15, and the synchronous machine 3 can be put into operation again.

[0041] List of reference numerals:

[0042] 1. Drive system

[0043] 2 Traction motor

[0044] 3 Synchronous motor

[0045] 4 Rotor

[0046] 5. Stator

[0047] 6 Control device

[0048] 7 Power Electronics

[0049] 8 Axle unit

[0050] 10 Motor Vehicles

[0051] 11 Traction drive

[0052] 12 First traction motor

[0053] 14 permanent magnets

[0054] 15 Magnetic field generating device

[0055] 17 Inverter device

[0056] 17a Inverter

[0057] 18 Front axle

[0058] 20 Power Battery

[0059] 22 Second traction motor

[0060] 27 Capacitor Equipment

[0061] 28 Rear axle

[0062] 38 Wheels

Claims

1. A drive system (1) for an at least partially electrically driven motor vehicle (10), the drive system comprising an electric traction drive (11) having at least two electric traction motors (2), wherein: At least one of the traction motors (2) is designed as a permanent magnet excited synchronous motor (3), has a rotor (4) with a plurality of permanent magnets (14) and a stator (5) with a magnetic field generating device (15) for generating a stator magnetic field, and includes at least one control device (6), which is suitable for and designed to switch off at least the traction motor (2) designed as a permanent magnet excited synchronous motor (3) according to the load state of the drive system (1), in particular at least in partial load operation, so that the traction motor (2) is in a towing mode and is towed together while at least one other traction motor (2) is still connected and provides torque for driving, Features The control device (6) is suitable for and designed to generate a specified magnetic field, a so-called demagnetizing field, by means of the magnetic field generating device (15), and to use the demagnetizing field to at least partially demagnetize the permanent magnets (14) of at least one switched-off traction motor (2) so as to reduce the drag loss during towing operation.

2. Drive system (1) according to the preceding claim, wherein: The control device (6) is suitable for and is designed to generate a prescribed magnetic field, a so-called magnetizing field, by means of the magnetic field generating device (15), and to use the magnetizing field to re-magnetize previously demagnetized permanent magnets (14) of at least one switched-off traction motor (2), so that the traction motor (2) can again provide a prescribed torque for driving.

3. Drive system (1) according to any one of the preceding claims, wherein: The control device (6) is suitable and designed to re-magnetize the traction motor (2) at least when there is a torque demand that requires the at least one switched-off traction motor (2) to provide the torque demand.

4. Drive system (1) according to any of the preceding claims, wherein: The control device (6) is suitable for and designed to generate a specified magnetic field with a specified magnetic field direction, and in particular to set a magnetic field direction for the magnetizing field, which is opposite to the magnetic field direction of the demagnetizing field.

5. Drive system (1) according to any of the preceding claims, wherein: At least one current pulse is used to generate the defined magnetic field, the current pulse preferably having a current intensity and / or an amplitude that is higher than a rated current provided for the permanently excited synchronous machine (3).

6. Drive system (1) according to any of the preceding claims, wherein: The current pulses for generating the defined magnetic field can be provided at least partially by power electronics (7) of the traction drive (11), and preferably by an inverter device (17).

7. Drive system (1) according to any of the preceding claims, wherein: The current pulses for generating the defined magnetic field can be provided at least partially by a capacitor device (27).

8. Drive system (1) according to any of the preceding claims, wherein: The control device (6) is suitable and designed to set the current direction of the current pulses for generating the prescribed magnetic field, and in particular to set the current direction for the magnetizing field, which is opposite to the current direction of the demagnetizing field.

9. Drive system (1) according to any one of the preceding claims, wherein: The control device (6) is suitable for and designed to apply the prescribed magnetic field to the at least one traction motor (2) when the at least one traction motor (2) is turned on and provides torque for driving and / or the drive system (1) is in driving.

10. Drive system (1) according to any of the preceding claims, wherein: The control device (6) is suitable and designed to adjust the torque of at least one switched-on traction motor (2) during application of the prescribed magnetic field to the at least one traction motor (2) so as to avoid undesired torque pulses.

11. The drive system (1) according to any one of the preceding claims, comprising at least two axle units (8), each axle unit being drivable by means of at least one traction motor of at least two traction motors (2), wherein: The control device (6) is suitable for and designed to shut down and demagnetize at least one traction motor (2) provided for driving at least one of the at least two axle units (8) according to the load state of the drive system (1), so that a towing operation can be provided axle by axle.

12. The drive system (1) according to any one of the preceding claims, comprising a front axle (18) drivable by at least one traction motor (2) and a rear axle (28) drivable by at least one traction motor (2), wherein: The control device (6) is suitable for and designed to shut down and demagnetize the at least one traction motor (2) provided for driving the front axle (18) according to the load state of the drive system (1), so that the front axle (18) is towed together while the rear axle (28) is driven, or wherein the control device (6) is suitable for and designed to shut down and demagnetize the at least one traction motor (2) provided for driving the rear axle (28) according to the load state of the drive system (1), so that the rear axle (28) is towed together while the front axle (18) is driven.

13. Drive system (1) according to any of the preceding claims, wherein: The coercive magnetic field strength of the permanent magnet (14) of the at least one traction motor (2) designed as a permanent magnet excited synchronous motor (3) is matched to the prescribed magnetic field that can be generated by means of the magnetic field generating device (15).

14. A method for operating a drive system (1) according to any of the preceding claims.

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