Powertrain for an electric vehicle and methods for operating such a powertrain

Abstract

Drive train (1) for an electric vehicle with two electric machines (2, 3), with a drive shaft (6) driven by one of these, and with a gearbox (7) between the drive shaft (6) and at least one wheel of the vehicle, wherein the first electric machine (2) is designed for a higher maximum torque but a lower maximum speed relative to the second electric machine (3), and both electric machines (2, 3) are coupled via a freewheel (4), wherein the freewheel (4) has two shafts with a freewheel device arranged between them, wherein the freewheel device assumes a freewheel position or a locked position depending on the direction of rotation of the shafts relative to each other, and wherein one shaft can be driven by means of the first electric machine (2) and the other shaft by means of the second electric machine (3), characterized in that one shaft is designed as an inner shaft and the other shaft as an outer shaft.wherein the inner shaft is part of a rotor shaft (6) of the second electric machine (3).

Description

[0001] The invention relates to a powertrain for an electric vehicle according to the preamble of claim 1. The invention further relates to a method for operating such a powertrain.

[0002] To achieve good acceleration and a high top speed in an electric vehicle, especially one designed as a passenger car, a two-speed transmission is typically used with the electric motor. However, such a transmission is complex to control and relatively heavy.

[0003] DE 199 03 443 A1 discloses a drive train comprising two electric motors, a drive shaft driven by one of these motors, and a gearbox between the drive shaft and at least one wheel of the vehicle. This train is particularly suitable for use in an electrically powered bicycle. The two electric motors can drive the vehicle's wheel simultaneously, alternately, or individually. When the electric vehicle is started, the two motors are connected in series, and upon reaching a certain rotational speed corresponding to a low vehicle speed, the electric motors are switched to parallel operation. A freewheel is provided between the gearbox, located downstream of the electric motors in the power flow, and the wheel, interrupting the power flow in the direction opposite to that of the electric motors.This freewheel can be bypassed in the free-running direction of rotation by means of a clutch.

[0004] DE 20 2009 014 490 U1 discloses a powertrain for an electric vehicle according to the preamble of claim 1.

[0005] DE 20 2010 012 132 U1 and FR 2 442 736 A1 reveal further state of the art.

[0006] The object of the present invention is to provide a powertrain for an electric vehicle that enables high acceleration values ​​and a high top speed, with a relatively low powertrain weight and relatively low control complexity. A further object is to provide an advantageous method for operating such a powertrain.

[0007] The problem is solved by a drive train according to claim 1 and by a method according to claim 5.

[0008] While the first electric motor is designed for optimized acceleration, the second electric motor has a particularly high maximum speed. Both electric motors are coupled to each other via a freewheel. The electric motor with the high torque, responsible for good acceleration, is positioned in the power flow upstream of the freewheel, and the freewheel, in turn, is positioned in the power flow upstream of the high-speed electric motor, thus enabling the high maximum speed.

[0009] The freewheel is designed with two shafts and a freewheel mechanism positioned between them. This freewheel mechanism, which can be a clamping roller or clamping element freewheel, assumes either a freewheeling position or a locked position depending on the direction of rotation of the shafts relative to each other. One shaft is driven by the first electric motor, and the other shaft by the second electric motor.

[0010] According to the invention, one shaft is designed as an inner shaft and the other shaft as an outer shaft, wherein the inner shaft is part of a rotor of the second electric machine.

[0011] Due to the design of the drive train according to the invention, it is generally not necessary for the transmission to be switchable. It is therefore preferably designed as a non-switchable transmission.

[0012] The method for operating the drivetrain is fundamentally characterized by the fact that, to start the electric vehicle, at least the first electric motor is energized. Specifically, it is provided that, to start the electric vehicle, at least the first electric motor is energized, and that after starting, the second electric motor is energized. It is advantageous if the first electric motor is energized until it reaches its maximum speed, and then, upon reaching the maximum speed of the first electric motor, the second electric motor is energized.

[0013] When the second electric machine reaches a speed greater than the speed of the first electric machine, the first electric machine no longer needs to be powered.

[0014] The maximum speed of the first electric motor corresponds, for example, to a speed of the electric vehicle of approximately 140 km / h.

[0015] Alternatively, the electric vehicle's powertrain can be operated in such a way that, for starting or in the range below the maximum speed of the first electric machine, both electric machines are powered for a boost operation of the electric vehicle.

[0016] The invention thus proposes the use of two electric machines in a drive train for an electric vehicle, wherein these two electric machines have different characteristics, in particular lower speed ranges. These two electric machines are coupled together and cover a wider operating range than a single machine or two identical machines.

[0017] The drive train according to the invention is characterized by its simple operation. The freewheel is, in particular, a mechanical freewheel and can therefore be designed in a known manner. The high power output of the electric motors is distributed over a wide speed range. This results in a significant weight advantage compared to the use of gearboxes in the drive train.

[0018] Further features of the invention will become apparent from the dependent claims, the accompanying drawing, and the description of the preferred embodiment shown in the drawing, without being limited to it. It shows: Fig. 1 A schematic representation of the embodiment of the drive train according to the invention.

[0019] The powertrain 1 for an electric vehicle, specifically a passenger car, is illustrated. The powertrain 1 comprises a first electric motor 2, a second electric motor 3, and a freewheel 4. The two electric motors 2 and 3 are coupled via the freewheel 4. Specifically, the first electric motor 2 is located upstream of the freewheel 4 in the power flow, and the freewheel 4 is located upstream of the second electric motor 3 in the power flow. The freewheel 4 has two shafts with a freewheel mechanism located between them. Depending on the direction of rotation of the two shafts relative to each other, the freewheel mechanism assumes either a freewheeling position or a locked position. The two shafts of the freewheel mechanism 4 are not shown. Only the shaft 5 extending from the first electric motor 2 and the shaft 6 extending from the second electric motor 3 are illustrated; these are the shafts 5 and 6, which connect to the rotor shafts of the electric motors 2 and 3, respectively.3. One shaft of the freewheel 4 is designed as an outer shaft, thus as a hollow shaft, and the other shaft of the freewheel 4 is designed as an inner shaft, with this inner shaft being part of the rotor of the second electric machine 3.

[0020] This shaft 6 is connected to a non-shiftable gearbox 7, which is formed by the two meshing gears 8 and 9. The larger gear 8 is non-rotatably connected to the shaft 6, and the smaller gear 9 is non-rotatably connected to a shaft 10, which is frictionally connected to a wheel of the vehicle (not illustrated).

[0021] The first electric machine 2 is designed for a higher maximum torque, but a lower maximum speed, relative to the second electric machine 3.

[0022] To start the electric vehicle, the first electric motor 2, which is designed for optimized acceleration and has high torque, is initially energized. When the first electric motor 2 reaches its maximum speed, for example, at a vehicle speed of 140 km / h, the second electric motor 3, which is designed for a particularly high maximum speed, is energized. Due to the freewheel 4, the second electric motor 3 can overtake the first electric motor 2, allowing the second electric motor 3 to fully take over traction from this speed onward and accelerate the vehicle to its top speed. Once the second electric motor 3 overtakes the first electric motor 2, the shaft 6 of the second electric motor 3 has a higher rotational speed than the shaft 5 of the first electric motor 2, making it unnecessary to continue energizing the first electric motor 2.The shaft 5 of the first electric machine 2 can therefore come to a standstill.

[0023] In boost mode, both electric machines 2 and 3 can be powered together, both for starting and in a speed range below the maximum speed of the first electric machine 2.

Claims

[1] Drive train (1) for an electric vehicle with two electric machines (2, 3), with a drive shaft (6) driven by one of these, and with a gearbox (7) between the drive shaft (6) and at least one wheel of the vehicle, wherein the first electric machine (2) is designed for a higher maximum torque but a lower maximum speed relative to the second electric machine (3), and both electric machines (2, 3) are coupled via a freewheel (4), wherein the freewheel (4) has two shafts with a freewheel device arranged between them, wherein the freewheel device assumes a freewheel position or a locked position depending on the direction of rotation of the shafts relative to each other, and wherein one shaft can be driven by the first electric machine (2) and the other shaft can be driven by the second electric machine (3), characterized by, that one wave is designed as an inner wave and the other wave as an outer wave, the inner wave being part of a rotor shaft (6) of the second electric machine (3). [2] Powertrain according to claim 1, characterized by , that the first electric machine (2) is arranged in the power flow before the freewheel (4) and the freewheel (4) is arranged in the power flow before the second electric machine (3). [3] Powertrain according to claim 1 or 2, characterized by , that the transmission (7) is a non-shiftable transmission. [4] Powertrain according to any one of claims 1 to 3, characterized by that it is the powertrain of a passenger car. [5] Method for operating a drive train designed according to the features of any one of claims 1 to 4, characterized by , that to start the electric vehicle at least the first electric motor (2) is energized. [6] Method according to claim 5, characterized by, that to start the electric vehicle at least the first electric machine (2) is energized and after starting the second electric machine (3) is energized. [7] Method according to claim 5 or 6, characterized by , that the first electric machine (2) is energized until it reaches its maximum speed. [8] Method according to claim 6 or 7, characterized by , that when the maximum speed of the first electric machine (2) is reached, the second electric machine (3) is energized. [9] Method according to any one of claims 5 to 8, characterized by , that when the second electric machine (3) reaches a speed greater than the speed of the first electric machine (2), the first electric machine (2) is no longer powered. [10] Method according to any one of claims 6 to 9, characterized by , that the maximum rotational speed of the first electric machine (2) corresponds to a speed of the electric vehicle of 140 km / h. [11] Method according to claim 5, characterized by , that, for starting up or in the range below the maximum speed of the first electric machine (2), both electric machines (2, 3) are powered for a boost operation of the electric vehicle.

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