All-wheel system for an electric motor vehicle, and method for operating an all-wheel system of such a vehicle

Abstract

An all-wheel system for a motor vehicle, with a first electric machine for driving a first drive axle of the motor vehicle; a first electronic power unit for controlling a rotational speed of the first electric machine; a second electric machine for driving a second drive axle of the motor vehicle; a second electronic power unit for controlling the rotational speed of the second electric machine on the basis of the rotational speed of the first electric machine and a specified differential rotational speed between the first electric machine and the second electric machine.

Claims

1. An all-wheel system for a motor vehicle, comprising: a first electric machine for driving a first drive axle of the motor vehicle; a first electronic power unit for controlling a rotational speed of the first electric machine; a second electric machine for driving a second drive axle of the motor vehicle; and a second electronic power unit for controlling a rotational speed of the second electric machine, wherein the rotational speed of the second electrical machine is set based on at least (1) the rotational speed of the first electric machine and (2) a prescribed difference in rotational speed between the first electric machine and the second electric machine.

2. The all-wheel system according to claim 1, wherein the second electronic power unit is adapted to control the rotational speed of the second electric machine such that the rotational speed of the second electric machine is smaller than a sum of the rotational speed of the first electric machine and the prescribed difference in rotational speed.

3. The all-wheel system according to claim 1, wherein the second electronic power unit is adapted to control the rotational speed of the second electric machine such that the rotational speed of the second electric machine corresponds to a sum of the rotational speed the first electric machine and the prescribed difference in rotational speed.

4. The all-wheel system according to claim 1, wherein the two electronic power units are adapted to control the electric machines to reduce a drive torque on one of the two electric machines and correspondingly increase the drive torque on another of the two electric machines.

5. The all-wheel system according to claim 1, wherein the two electronic power units are adapted to additionally control the two electric machines in accordance with a specified torque distribution between the drive axles.

6. The all-wheel system according to claim 1, wherein the second electronic power unit is adapted to control the rotational speed of the second electric machine taking into account at least one target rotational speed for at least one of the two drive axles specified by means of traction control of the motor vehicle.

7. The all-wheel system according to claim 1, wherein the two electric machines each have at least the same maximum power as a traction battery of the motor vehicle.

8. The all-wheel system according to claim 1, wherein the two electronic power units have a common intermediate circuit.

9. A method for operating the all-wheel system according to claim 1, wherein the second electronic power unit controls the rotational speed of the second electric machine based on the rotational speed of the first electric machine and the prescribed difference in rotational speed between the first electric machine and the second electric machine.

Description

(1) Further advantages, features and details of the invention will become apparent from the following description of a preferred exemplary embodiment and from the drawing. The features and combinations of features mentioned above in the description as well as the features and combinations of feature mentioned below in the description of the FIGURE and/or shown in the single FIGURE can be used not only in the respectively indicated combination but also in other combinations or alone, without departing from the scope the invention.

(2) The drawings show in the single FIGURE a schematic representation of a motor vehicle 10 with an all-wheel system 12. The motor vehicle 10 shown here is a purely electrically driven motor vehicle. The all-wheel system 12 comprises a first electric machine 14 for driving a first drive axle 16 of motor vehicle 10. Furthermore, all-wheel system 12 has a first electronic power unit 18 for controlling electric machine 14. In addition, all-wheel system 12 comprises a second electric machine 20 for driving a second drive axle 22 of motor vehicle 10. Furthermore, all-wheel system 12 also has a second electronic power unit 24 for controlling second electric machine 20.

BRIEF DESCRIPTION OF THE DRAWINGS

(3) FIG. 1 shows a schematic representation of a motor vehicle with an all-wheel system.

DETAILED DESCRIPTION

(4) The motor vehicle 10 shown here is a purely electrically driven motor vehicle. The all-wheel system 12 comprises a first electric machine 14 for driving a first drive axle 16 of motor vehicle 10. Furthermore, all-wheel system 12 has a first electronic power unit 18 for controlling electric machine 14. In addition, all-wheel system 12 comprises a second electric machine 20 for driving a second drive axle 22 of motor vehicle 10. Furthermore, all-wheel system 12 also has a second electronic power unit 24 for controlling second electric machine 20.

(5) The two drive axles 16, 22 are, since they can be driven separately via respective electric machines 14, 20, not coupled to each other via a coupling, as is required in conventional all-wheel systems in motor vehicles with an internal combustion engine. The two electronic power units 18, 24 can each control the two electric machines 14, 20 separately in order to provide a corresponding power and a corresponding torque to drive axles 16, 22, depending on the driver's desire.

(6) In order to allow a particularly dynamic and responsive control of all-wheel system 12 without an overshoot of the all-wheel system 12 caused by control or regulation technology, it is provided that second electronic power unit 24 is adapted for controlling the rotational speed of second electric machine 20 on the basis of a rotational speed of first electric machine 14 and a specified differential rotational speed between first electric machine 14 and second electric machine 20. It is therefore provided to control the two electric machines 14, 20 on the basis of how large a rotational speed slip between the two electric machines 14, 20 is at the moment.

(7) This has the advantage that respective rotational speed sensors within electric machines 14, 20 are utilized, which have a particularly high sampling rate in the kilohertz range. In contrast to the measurement and consideration of the actual wheel rotational speeds at which the sampling rate is usually many times lower, this makes it possible to respond very quickly to rotational speed differences between driven axles 16, 22. In addition, the rotational speed regulation or rotational speed control of the two driven axles 16, 22 has the advantage that such a rotational speed regulation or rotational speed control is much more agile than a purely torque-based control or regulation of the two electric machines 14, 20.

(8) In addition, it can also be provided that additionally a torque regulation of the two electric machines 14, 20 is provided. A drive torque that is reduced in first electric machine 14 is preferably automatically supplied accordingly by second electric machine 20 and vice versa. The total drive torque provided by the two electric machines 14, 20 thus remains constant—as far as it can be implemented in terms of traction technology and thus makes sense.

(9) The control or regulation of the two electric machines 14, 20 may additionally be coupled to a traction control of motor vehicle 10, not shown here. The control of the two electric machines 14, 20 thus additionally takes place on the basis of the specifications of a traction control. The traction control system can, for example, specify a target rotational speed for the respective drive axles 16, 22, which depends on the absolute speed of motor vehicle 10. The electronic power units 18, 24 then control the two electric machines 14, 20 in such a way that the specified target rotational speed for the two axles 16, 22 is not exceeded, since otherwise a respective wheel slip would occur on the drive axles 16, 22. The two electronic power units 18, 24 can therefore make a particularly fast and responsive rotational speed adjustment at the two electric machines 14, 20 and also the electronic power units 18, 24 additionally can realize a redistribution of the drive torques provided by the electric machines 14, 20.

(10) Since the two electric machines 14, 20 each have the same maximum power as the traction battery, a hundred percent virtual blocking effect between the two driven axles 16, 22 is possible. The total power that can be provided by the traction battery can thus be provided, if required, either by first electric machine 14 or by second electric machine 20 alone. For example, should the case occur that first drive axle 16 with its wheels is on ice and second driven axle 22 stands on easy-grip asphalt, it would be possible to provide the full drive power exclusively by means of second electric machine 20. Overall, a solution is provided by described all-wheel system 12, by means of which rotational speed differences, i.e. a rotational slip between two driven axles can be compensated particularly quickly, so as to allow a particularly fast and dynamic and safe drive of a motor vehicle.