Drive unit for a motor vehicle, motor vehicle and method for operating a drive unit

Abstract

Drive unit (12) for a motor vehicle (10), with a first electric drive motor (24) which is coupled to a first gearbox unit (26) for drive purposes, a second electric drive motor (28) which is coupled to a second gearbox unit (30) for drive purposes, and a summing gear unit (32) which is coupled to a motor vehicle axle (14) for drive purposes, wherein the first transmission unit (26) is a first shifting transmission unit which can be optionally coupled to the summing transmission unit (32) via a first clutch unit (34), and wherein the second transmission unit (30) is a second transmission unit which can be optionally coupled to the summing transmission unit (32) via a second clutch unit.

Description

[0001] The invention relates to a drive unit for a motor vehicle and to a motor vehicle itself. Furthermore, the invention relates to a method for operating a drive unit.

[0002] Drive units, in particular electric drive units, and motor vehicles equipped therewith are known in the prior art. The same applies to methods for operating such drive units.

[0003] Unlike drive units based on the principle of the internal combustion engine, electric drive units do not require a transmission to spread the speeds and torques provided by an electric motor across the range required for vehicle operation. These drive units therefore operate with a constant gear ratio. Their design must thus always strike a good balance between high starting torque and high top speed, resulting in overall driving characteristics that are perceived as pleasant by the driver.

[0004] Additionally, electric drive units are known that include a gearshift transmission, thus enabling particularly high starting torques combined with exceptionally high top speeds. A distinction must be made between power-shiftable and non-power-shiftable gearshifts. With the latter, the traction force must be completely interrupted for gear changes. Power-shiftable gearshifts typically require at least a reduction in traction force during the shifting process. Both of these are perceived by occupants of a vehicle equipped with such a drive unit as at least a slight jolt and are therefore undesirable.

[0005] From DE 10 2011 004 191 A1, an electromechanical vehicle drive device is known, comprising a first electric motor with a first power output, a second electric motor with a second power output, and a transmission device via which the two power outputs of the two electric motors are coupled to a transmission output. The transmission device is designed such that the coupling of the first power output, the second power output, and the transmission output is effected via a planetary gear stage.

[0006] Furthermore, DE 10 2013 007 354 A1 discloses a transmission device comprising an intermediate shaft operatively connected to an output shaft and a countershaft. In a first acceleration mode, a first electric motor and a second electric motor are operatively connected to the intermediate shaft via the countershaft, and in a second acceleration mode, the first electric motor is directly connected and the second electric motor is operatively connected to the intermediate shaft via the countershaft. When switching between the first and second acceleration modes, the operative connection between the first electric motor and the intermediate shaft is interrupted for a specific switching period, during which the first electric motor is operated with an overload torque greater than the second maximum torque to at least partially compensate for the torque provided by the first electric motor.

[0007] Furthermore, a dual-motor drive system for a purely electric vehicle and a control method for it are known from US 2016 / 0347203A1, wherein, within a range defined between an upper and a lower torque threshold for the operation of one of the two motors at a given vehicle speed, the torque of that motor is incrementally changed by a specific torque step. The required torque of the other motor is determined based on the torque distribution relationship of the first and second motors, with the synchronized efficiency of the power system being determined based on the torques of the first and second motors, such that the optimal synchronized efficiency of the power system is sought ergodically.

[0008] Patent document DE 103 04 610 A1 discloses an arrangement for converting electrical energy into mechanical energy and vice versa, in particular for powering a vehicle and for energy recovery during its braking.

[0009] The object of the invention is therefore to create a drive unit that enables high starting torques and high top speeds, while at the same time requiring neither an interruption nor a reduction or decrease in traction force during operation. Furthermore, a motor vehicle equipped with such a drive unit is to be specified.

[0010] The problem is solved by a drive unit of the type mentioned above, comprising a first electric drive motor coupled to a first transmission unit, a second electric drive motor coupled to a second transmission unit, and a summing transmission unit coupled to a vehicle axle, wherein the first transmission unit is a first manual transmission unit that can be selectively coupled to the summing transmission unit via a first clutch unit. The second transmission unit is a second manual transmission unit that can be selectively coupled to the summing transmission unit via a second clutch unit. Consequently, both transmission units are manual transmission units.Compared to variants with only one transmission unit, this allows for a further expansion of the possible combinations of drive speeds, especially top speeds, and drive torques, especially starting torques. This enables particularly high top speeds combined with particularly high starting torques. Preferably, the two transmission units are never engaged simultaneously, so that during a shifting operation, the required torque and speed can always be transmitted to the driven vehicle axle via one of the transmission units. This effectively prevents any reduction or interruption of traction. An alternative term for an electric drive motor is electric motor. The drive unit therefore comprises two electric motors that act on the driven vehicle axle via a summing transmission unit.Compared to drive units with only one electric motor, each of the electric drive motors can be built smaller while maintaining the overall power output of the drive unit. This makes such a drive unit particularly easy and space-saving to install in a vehicle (packaging problem). Since the first transmission unit is a manual transmission, the drive unit can achieve both high starting torque and high top speeds. For example, the manual transmission unit can operate in first gear during acceleration and in second gear during high-speed driving. The manual transmission unit can only be shifted under no-load conditions, i.e., it cannot be shifted under load.Nevertheless, a reduction in traction, often referred to as a drop in torque, can be avoided because, during the shifting process, the second electric drive motor provides sufficient torque in combination with the required speed via the summing transmission unit. Therefore, the occupants of a vehicle equipped with such a drive unit do not experience any reduction in traction, and thus no jerking. Additionally, the design of the first transmission unit as a manual transmission allows for high speeds to be achieved in combination with a relatively low speed of the first electric drive motor. This results in low noise emissions from the drive unit.

[0011] The basic idea of ​​the invention is therefore to create a drive unit with two parallel electric drive trains coupled via a summing gearbox unit. One or both drive trains can include switchable gearboxes. However, the switchable gearboxes, if two are present, are never switched simultaneously. Thus, switching operations without interruption of traction, and in particular without reduction of traction, can be achieved by having the drive train that is not currently being switched provide the required torque and / or speed at an output or driven element of the drive unit.

[0012] The electric drive motors and their respective gearboxes can be designed as so-called motor-gearbox units. This means that the electric drive motor and its associated gearbox are housed in a single unit. Such motor-gearbox units are particularly compact. Furthermore, they are easy to install in a vehicle. They are also robust and reliable in operation.

[0013] Preferably, the summing gear unit is a differential gear unit, in particular wherein the differential gear unit is optionally lockable. In this application, the differential gear unit, in particular in contrast to known axle differentials, is used such that it has two differential gear inputs and one differential gear output. Preferably, the differential gear unit is locked during a shifting operation, so that the torque provided by the drive motor that is coupled to the non-switchable or currently not shifted gear unit is reliably directed to the differential gear output and thus to the driven vehicle axle. Thus, a reduction or interruption of traction force during shifting can be reliably avoided. In addition, a differential gear unit has a high efficiency.

[0014] In one variant, the first and / or second transmission unit has at least two gears. Preferably, it has exactly two gears. The range of achievable combinations of starting torque and top speed can be influenced by the number of gears. This range increases with the number of gears. However, the complexity of the drive unit's design and the required installation space also increase with the number of gears. Two-speed transmissions represent a good compromise in this respect.

[0015] The vehicle axle can include an axle differential, and this axle differential can be coupled to the summing gear unit. Therefore, a total of two differentials can be provided, one acting as the summing gear unit and the other as the axle differential. Since differentials are generally robust, reliable, and require little maintenance, these advantages also apply to a drive unit equipped with one.

[0016] Furthermore, the problem is solved by a motor vehicle with a drive unit according to the invention. High top speeds can be achieved with such a motor vehicle. At the same time, such a motor vehicle can provide high starting torques. In addition, it allows operation without interruption or reduction of traction in essentially all driving situations.

[0017] Furthermore, the problem is solved by a method of the type mentioned at the outset for operating a drive unit according to the invention, which comprises the following steps: a) Decoupling the first or second gearbox unit from the summing gearbox unit, b) subsequent shifting of the first or the second transmission unit, the shifting process being essentially load-free, and c) Simultaneous changing, in particular increasing, the speed and / or torque provided by the second or first electric drive motor.

[0018] During operation of the drive unit, either both transmission units, and thus both electric drive motors, or one of the transmission units, and thus one of the electric drive motors, are coupled to the summing transmission unit and thus to the driven vehicle axle. Simultaneous decoupling of both transmission units never occurs. If both transmission units are manual transmission units, only one of the transmission units is engaged at any given time. Preferably, they are engaged alternately. In connection with changes to the torque provided by the drive motor coupled to the summing transmission unit, uninterrupted or traction-reduction-free operation of the drive unit is ensured.In other words, during the shifting process of a transmission unit, which involves decoupling the associated drive motor from the summing gear unit, the resulting decoupled torque and speed are compensated for by the other drive motor. Furthermore, the various gears of the transmission unit allow for high top speeds and high starting torques.

[0019] According to one embodiment, the rotational speed and / or torque provided by the second or first electric drive motor is modified, and in particular increased, such that there is essentially no reduction in tractive force at the vehicle axle. A reduction in tractive force can also be described as a drop in tractive force. The torque and rotational speed lost due to decoupling are thus compensated, preferably completely compensated. In particular, for this purpose, the drive motor that is coupled to the summing gearbox during the switching process can be operated in the overload range.

[0020] Advantageously, the differential gear unit is locked during the shifting process. The drive power from the drive motor that is not decoupled from the differential gear unit is therefore transmitted to the output of the differential gear unit with a fixed gear ratio and high efficiency. This ensures the required torque and speed from the drive unit.

[0021] The invention is explained below with reference to an exemplary embodiment shown in the accompanying drawings. These show: - Fig. 1 schematically a motor vehicle according to the invention with a drive unit according to the invention, which is operated by means of a method according to the invention, and - Fig. 2 the drive unit according to the invention Fig. 1 in a more detailed schematic view.

[0022] Fig. Figure 1 shows a motor vehicle 10 with a drive unit 12.

[0023] The drive unit 12 is arranged in the area of ​​a motor vehicle axle 14 of the motor vehicle 10, which in the example shown is a motor vehicle front axle, and drives it.

[0024] Alternatively, the drive unit 12 can also be located in the area of ​​a motor vehicle rear axle 16 of the motor vehicle 10 and drive it.

[0025] Likewise, a motor vehicle 10 is conceivable in which drive units 12 are provided both in the area of ​​the motor vehicle axle 14, which is designed as the motor vehicle front axle, and in the area of ​​the motor vehicle rear axle 16. In this way, an all-wheel drive can be created.

[0026] The motor vehicle axle 14, designed as a motor vehicle front axle, comprises wheels 18, 20 and an axle differential gear 22 (see Fig. 2).

[0027] In addition, the drive unit 12 has a first electric drive motor 24, which is coupled to a first gearbox unit 26 for drive purposes.

[0028] Furthermore, it includes a second electric drive motor 28, which is coupled to a second gearbox unit 30 for drive purposes.

[0029] Both electric drive motors 24, 28 act on the vehicle axle 14 via a summing gear unit 32. More precisely, the summing gear unit 32 is coupled to the axle differential gear 22 in terms of drive.

[0030] In the illustrated embodiment, the second gear unit 30 has a fixed gear ratio and is rigidly coupled to the summing gear unit 32.

[0031] The first transmission unit 26, on the other hand, is designed as a manual transmission unit and can be optionally coupled to the summing transmission unit 32 via a first clutch unit 34.

[0032] The first gearbox unit 26 is double-speed.

[0033] In an alternative embodiment not shown, the second transmission unit 30 can additionally be coupled to the summing transmission unit 32 via a second clutch unit. The second transmission unit 30 is then a second manual transmission unit, which is preferably two-speed.

[0034] In the embodiment shown, the summing gear unit 32 is designed as an optionally lockable differential gear unit.

[0035] During operation of the drive unit 12, as a rule both drive motors 24, 28 act on the wheels 18, 20 via the respective assigned gear units 26, 30, the summing gear unit 32 and the axle differential gear 22.

[0036] If the first transmission unit 26, which is designed as a manual transmission unit, is to be shifted into a different gear, the first transmission unit 26 is decoupled from the summing transmission unit 32 by means of the first clutch unit 34.

[0037] The gear change can then be carried out essentially without load.

[0038] During this switching process, the summing gear unit 32, which is designed as a differential gear unit, is locked, so that the drive power of the second electric drive motor 28 is directed directly to the axle differential 22.

[0039] Likewise, during the switching process, the torque and / or speed provided by the second electric drive motor 28 is changed.

[0040] In particular, the rotational speed and / or torque are changed, especially increased, in such a way that there is essentially no reduction in tractive force and therefore no interruption in tractive force at the motor vehicle axle 14.

[0041] In this case, the second electric drive motor can, for example, be operated in the overload range for a short period of time.

[0042] After completion of the shifting process, the first transmission unit 26 is coupled again to the summing transmission unit 32 via the first clutch unit 34.

[0043] The drive unit 12 is then in a modified operating mode, or, put simply, in a different gear. This usually also implies altered speed and torque curves provided by the two electric drive motors 24 and 28.

[0044] In this context, i.e., when entering the changed operating mode, the torque change and / or speed change made to the second electric drive motor 28 in the sense of freedom from tractive force reduction or tractive force interruption is also reversed.

Claims

[1] Drive unit (12) for a motor vehicle (10), with a first electric drive motor (24) which is coupled to a first gearbox unit (26) for drive purposes, a second electric drive motor (28) which is coupled to a second gearbox unit (30) for drive purposes, and a summing gear unit (32) which is coupled to a motor vehicle axle (14) for drive purposes, wherein the first transmission unit (26) is a first shifting transmission unit which can be optionally coupled to the summing transmission unit (32) via a first clutch unit (34), and wherein the second transmission unit (30) is a second transmission unit which can be optionally coupled to the summing transmission unit (32) via a second clutch unit. [2] Drive unit (12) according to claim 1, characterized by, that the summing gear unit (32) is a differential gear unit, in particular wherein the differential gear unit is optionally lockable. [3] Drive unit (12) according to one of the preceding claims, characterized by that the first gearbox unit and / or the second gearbox unit are at least two-speed. [4] Drive unit (12) according to any one of the preceding claims, characterized by , that the motor vehicle axle (14) includes an axle differential gear (22) and the axle differential gear (22) is coupled to the summing gear unit (32). [5] Motor vehicle (10) with a drive unit (12) according to one of the preceding claims. [6] Method for operating a drive unit (12) according to any one of claims 1 to 4, characterized by the following steps: a) Decoupling the first or second transmission unit from the summing transmission unit (32), a) subsequent shifting of the first or the second transmission unit, the shifting process being carried out essentially without load, and b) Simultaneously changing, in particular increasing, the speed and / or torque provided by the second electric drive motor (28) or the first electric drive motor (24). [7] Method according to claim 6, characterized by , that the rotational speed and / or torque provided by the second electric drive motor (28) or first electric drive motor (24) is changed, in particular increased, in such a way that there is essentially no reduction in tractive force at the vehicle axle (14). [8] Method according to claim 6 or 7 for operating a drive unit (12) according to claim 2, characterized by, that the differential gear unit is locked during the shifting process.

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