Method for operating a drive train of a motor vehicle

Abstract

Method for operating a drive train (10) in a motor vehicle (100), wherein the drive train (10) comprises a first electric drive motor (12), a second electric drive motor (14) and a transmission (20) which can be coupled to both the first electric drive motor (12) and the second electric drive motor (14), and wherein the first electric drive motor (12) has a first torque (M D1 ) and a first speed (r1) to the transmission (20), wherein the second electric drive motor (14) is a torque corresponding to the first torque (M D1 ) opposite second torque (M D2 ) and / or a second speed (r2) opposite to the first speed (r1) to the transmission (20) in order to reduce the power loss (P V ) for heating a lubricant (22) of the transmission (20), characterized in that from the first electric drive motor (12) a first drive torque (M A1 ) and / or a first drive power (M P1 ) is coupled into the transmission (20), which is greater than a second drive torque or a braking torque (M A2 , M B2 ) and / or a second drive power or a braking power (M P2 ) of the second electric drive motor (14), wherein a resulting output torque (M Ab ), which is transmitted via an output (27) of the transmission (20) to a drive shaft (50) of the motor vehicle (100).

Description

Technical field

[0001] The invention relates to a method for operating a drive train of a motor vehicle according to the preamble of claim 1. The invention further relates to a control unit, a drive train for a motor vehicle, a motor vehicle, a computer program and a computer-readable medium according to the independent claims. State of the art

[0002] For power transmission, motor vehicles are equipped with transmissions that convert the drive torque and input speed of a drive motor into the output torque and output speed of the transmission. For electric motors in motor vehicles, transmissions are particularly known that reduce the speed of the electric motor and transmit the correspondingly increased drive torque to an output shaft, which is connected, for example, to an axle drive of the motor vehicle. Oils are particularly used to lubricate such transmissions; these are intended to reduce friction and wear between meshing transmission components, in particular between meshing gears of the transmission, and the friction of the transmission bearings.Such transmission oils must cover a wide temperature range during transmission operation, from a starting temperature, which after extended periods of inactivity essentially corresponds to the ambient temperature of the vehicle, to a maximum operating temperature, which is typically reached during hot weather and prolonged full-load operation. Transmission oils exhibit optimal viscosity particularly in an operating range of +40°C to +110°C.

[0003] If a motor vehicle is started after a long period of inactivity at an ambient temperature below -10°C, and particularly below -20°C, the transmission oil will be very viscous during and immediately after the start-up. This can lead to poor lubrication of the bearings or gears in the transmission, which can cause increased wear on the transmission components. Prolonged operation in this critical temperature range can therefore result in mechanical damage. Furthermore, warming up the transmission oil and / or the drive system can take a long time at such ambient temperatures, and the increased viscosity of the transmission oil reduces the efficiency of the drive system.

[0004] DE 10 2019 201 245 A1 discloses a method for controlling the temperature of a coolant in an electric vehicle, in which a first electric motor is arranged on a first axle and a second electric motor is arranged on a second axle in order to be able to drive the axles independently of one another. To heat the coolant, the first electric motor is operated in a drive mode that generates a positive torque to drive the first axle, and the second electric motor performs recuperation, which generates a negative torque on the second drive axle that counteracts the positive torque of the first drive motor and thus heats the coolant.

[0005] DE 11 2013 003 893 T5 discloses an electric vehicle with an automatic transmission arranged between a differential unit and the drive wheels of the electric vehicle. The differential unit includes a motor-generator and a power split device. The motor-generator is cooled by a lubricant of the automatic transmission. When the temperature of the lubricant is lower than a predetermined temperature and the automatic transmission is in a neutral position, a controller rotates the motor-generator of the differential unit to increase the temperature of the lubricant.

[0006] DE 10 2014 006 898 A1 discloses a method for operating a vehicle with at least one torque transmission device which splashes when rotating in a fluid, and with at least two axles, each having at least two wheels, and with at least one controllable coupling device by means of which the torque transmission device and at least one of the wheels can be selectively coupled or decoupled in a torque-transmitting manner.

[0007] A control system for hybrid vehicles is known from US 2016 / 0339775 A1. General description of the invention

[0008] The object of the invention is to eliminate or at least reduce the disadvantages of the prior art.

[0009] The object is achieved by a method for operating a drive train in a motor vehicle, wherein the drive train comprises a first electric drive motor, a second electric drive motor, and a transmission which can be coupled to both the first electric drive motor and the second electric drive motor, and wherein the first electric drive motor transmits a first torque and a first rotational speed to the transmission. According to the invention, the second electric drive motor transmits a second torque opposite to the first torque and / or a second rotational speed opposite to the first rotational speed to the transmission in order to generate a power loss for heating a lubricant of the transmission.

[0010] A drive train is generally understood to be a system that generates drive torque and transmits this drive torque to a driving unit, in particular to an axle drive or a drive wheel. In this context, an electric drive motor is a device that converts electrical energy into mechanical energy. The term electric drive motor encompasses both asynchronous and synchronous electric machines. The electric drive motor can be designed as a brushless motor or as an electric drive motor with sliding contacts.

[0011] A transmission is a device that converts the input torque and input speed of a rotating component into an output torque and output speed that differ from the input torque and input speed. The term "coupleable" refers to the fact that the coupleable objects can, in principle, be connected to one another. However, they are not necessarily coupled in every operating state of the device and do not enable power transmission in every operating state.

[0012] A motor vehicle can in principle be any means of transport on land, water and / or in the air, for example cars, trucks, buses, autonomously driving passenger or freight transporters, emergency vehicles, work vehicles (for example forklifts), construction site vehicles such as concrete mixers, excavators or the like, aircraft such as airplanes, helicopters, drones, air taxis or the like and / or boats or ships, but also motorized two-wheelers such as motorcycles or electrically powered bicycles.

[0013] In this context, a lubricant is understood to be a substance that reduces friction in the transmission. Lubricants can, in particular, be oils or greases that wet the surface of a transmission component, thereby reducing friction between two transmission components.

[0014] In a drivetrain with two electric drive motors coupled to a common transmission, the process enables the generation of power loss, which enables rapid heating of the lubricant and thus a reduction in friction in the transmission. This can reduce wear on the transmission components, even when used in very cold ambient temperatures of below -20°C. Furthermore, the mechanical efficiency of the drivetrain can be increased by reducing the friction losses that occur with a cold, highly viscous lubricant by heating the lubricant.

[0015] In typical embodiments, a drive torque is generated by the first electric drive motor and the second electric drive motor is operated in a generator mode to increase a load of the first drive motor and is towed by the first electric drive motor.

[0016] By towing the second electric drive motor, the power of the first electric drive motor can be largely recovered as electrical energy. The power loss is used to heat the transmission lubricant to a temperature at which the lubricant has a sufficiently low viscosity to lubricate the gears and / or bearings of the transmission and minimize friction losses in the transmission. Furthermore, towing the second drive motor makes it easy to ensure that no resulting output torque is transferred to a transmission output, so that the motor vehicle is free of drive forces when stationary. This makes it possible to heat the lubricant before the motor vehicle starts moving.

[0017] In typical embodiments, the first torque of the first electric drive motor and the second torque of the second electric drive motor and / or the first speed of the first electric drive motor and the second speed of the second electric drive motor cancel each other out such that no output torque is transmitted from the transmission to a drive shaft of the motor vehicle. As a result, the method can be carried out when the motor vehicle is stationary, so that the motor vehicle does not have to be moved to heat the lubricant in the transmission. In particular, the lubricant can be heated up before the transmission components roll against one another under load in order to minimize wear in the transmission and increase the efficiency of the drive train by reducing the viscosity of the lubricant.

[0018] A first drive torque and / or a first drive power is coupled into the transmission from the first drive motor, which is greater than a second drive torque or a braking torque and / or a second drive power or a braking power of the second electric drive motor. This results in an output torque of the transmission, which is transmitted via an output of the transmission to a drive shaft of the motor vehicle. Such a method makes it possible to heat the lubricant even while the motor vehicle is moving. In particular at very low ambient temperatures of less than -20°C, the targeted heating of the lubricant can lead to a reduction in wear and to increased mechanical efficiency by reducing the viscosity of the lubricant.

[0019] In an advantageous further development of the method, it is provided that a constant drive power is provided by the first electric drive motor, and an opposing braking power is applied by the second electric drive motor, wherein power control is achieved by controlling the braking power of the second electric drive motor. This enables particularly simple power control for the drive power of the motor vehicle during the heating of the lubricant while the motor vehicle is in operation.

[0020] Alternatively, an advantageous further development of the method provides that a constant braking torque is provided by the second electric drive motor, and an opposing drive power is generated by the first electric drive motor, wherein power control is achieved by controlling the drive power of the first electric drive motor. This allows for an alternative, simple power control of the drive power of the motor vehicle during the heating of the lubricant while the motor vehicle is in operation.

[0021] A further aspect of the invention relates to a control unit for controlling electric drive motors in a drive train of a motor vehicle, wherein the control unit is operatively connected to a first electric drive motor and a second electric drive motor. The control unit is configured to perform a method described in the preceding paragraphs, in particular when a machine-readable computer program code is executed by the control unit.

[0022] A further aspect of the invention relates to a drive train for a motor vehicle, comprising a first electric drive motor, a second electric drive motor, and a transmission. The transmission can be coupled to both the first electric drive motor and the second electric drive motor. The drive train further comprises a control unit configured to perform a method described in the preceding paragraphs, in particular when a machine-readable computer program code is executed by the control unit.

[0023] In a preferred embodiment of the drive train, the transmission is designed as a summation transmission, in particular as a planetary transmission, wherein the first electric drive motor is connected to a first transmission input and the second electric drive motor is connected to a second transmission input. The transmission further comprises an output shaft to which the input torques of the first electric drive motor and the second electric drive motor are transmitted additively as the output torque of the transmission.

[0024] A further aspect of the invention relates to a motor vehicle comprising such a drive train and such a control unit.

[0025] A further aspect of the invention relates to a computer program comprising instructions that, when executed by a computer, cause the computer to perform one of the aforementioned methods. The computer program can also be referred to as a computer program product.

[0026] A further aspect of the invention relates to a computer-readable medium comprising computer program code for carrying out a method for operating a drive train in a motor vehicle described in the preceding sections. The term "computer-readable medium" refers in particular, but not exclusively, to hard disks and / or servers and / or memory sticks and / or flash memories and / or DVDs and / or Blu-rays and / or CDs. In addition, the term "computer-readable medium" also refers to a data stream, such as that generated when a computer program and / or a computer program product is downloaded from the Internet. Short description of the drawings

[0027] In the following, the invention is briefly explained with reference to drawings, in which: Fig. 1: a schematic view of a motor vehicle according to the invention with a drive train according to the invention, which comprises a first electric drive motor, a second electric drive motor and a transmission, Fig. 2: a schematic view of a summation transmission which is designed to carry out a method according to the invention for operating a drive train in a motor vehicle, Fig. 3: a curve of the torques and the speeds of the first electric drive motor and the second electric drive motor when carrying out a method according to the invention, and Fig. 4: an alternative course of the torques and the speeds of the first electric drive motor and the second electric drive motor when carrying out a method according to the invention. Description of preferred embodiments

[0028] Fig. 1 shows a schematic view of a motor vehicle 100 according to the invention with a drive train 10 according to the invention. The drive train 10 comprises a first electric drive motor 12, a second electric drive motor 14 and a transmission 20 arranged between the first electric drive motor 12 and the second electric drive motor 14. The transmission 20 is designed as a summation transmission 30 and is connected to both the first electric drive motor 12 and the second electric drive motor 14. The transmission 20 has a first transmission input 24, which is connected to the first electric drive motor 12. The transmission 20 further has a second transmission input 26, which is connected to the second electric drive motor 14. The transmission 20 is lubricated with a lubricant 22, in particular a transmission oil.The lubricant 22 provides lubrication, particularly at the contact points of the tooth flanks of the gears of the transmission 20 and in the bearings of the transmission 20. The transmission 20 further comprises an output 27 with an output shaft 28, which is connected to a drive shaft 50 for driving a drive axle 80, 90 of the motor vehicle 100.

[0029] The drive shaft 50 is connected to a differential 52 on a drive axle 80 of the motor vehicle 100. The drive torque is transmitted from the differential 52 to the wheels 58 of the motor vehicle 100 via a first axle drive 54 and a second axle drive 56. The motor vehicle 100 further has a second axle 90, which includes an additional differential 52 for compensating for different wheel speeds of the wheels 58 when the motor vehicle 100 is cornering.

[0030] The motor vehicle 100 further comprises a control unit 40 with a memory unit 42 and a computing unit 44, as well as a computer program code 46 stored in the memory unit 42. The control unit 40 is configured to execute a method according to the invention for operating a drive train 10 in a motor vehicle 100 when the computer program code 46 is executed by the computing unit 44 of the control unit 40.

[0031] In Fig. 2 shows a summation gear 30 designed as a planetary gear 32. The planetary gear 32 comprises a first gear input 24, which is connected to a ring gear 39 of the planetary gear 32. The planetary gear 32 further comprises a second gear input 26, which is connected to a planet carrier 38 of the planetary gear 32. The planet carrier 38 carries three planet gears 35, 36, 37, which are each in engagement with the ring gear 39 and a sun gear 34. The sun gear 34 forms an output 27 of the planetary gear 32, which is connected to an output shaft 28. As a result, the torque M D1 of the first electric drive motor 12 and the torque M D2 of the second electric drive motor 14 additively as output torque M Ab to the output shaft 28.

[0032] In Fig. 3 are the course of a torque M D1and a speed r1 of the first electric drive motor 12 and a curve of a torque M D2 and a speed r2 of the second electric drive motor 14 and a resulting output torque M Ab of the transmission 20. To heat the lubricant 22 of the transmission 20, it is intended to couple the highest possible torque into the transmission 20 in order to generate a high power loss Pv for heating the lubricant 22 in the transmission 20. In this case, the torques M introduced into the transmission 20 by the first electric drive motor 12 and the second electric drive motor 14 cancel each other out. D1 and M D2 as well as the speeds r1, r2 of the first electric drive motor 12 and the second electric drive motor 14, so that no output torque M Ab = 0is transmitted to the output shaft 28 of the transmission 20. In this operating state, the entire drive power or braking power of the electric drive motors 12, 14 is converted into heat, thereby enabling particularly efficient heating of the lubricant 22 in the transmission 20. In an advantageous embodiment of the method, the two electric drive motors 12, 14 can generate opposing drive torques M D1 = -M D2 into the transmission 20. Alternatively, it is also conceivable that one of the electric drive motors 12, 14 is operated in a drive mode and the other electric drive motor 12, 14 is operated in a generator mode and that electrical current is again generated from the drive power of the electric drive motor 12, 14 operated in the drive mode by the electric drive motor 12, 14 operated in the generator mode.

[0033] In Fig. 4 are the course of a torque M D1 , M D2 and a speed r1, r2 of the first electric drive motor 12 and the second electric drive motor 14 and a resulting output torque M Ab of the transmission 20 in an alternative embodiment of a method according to the invention for operating a drive train 10 in a motor vehicle 100. The Fig. The method shown in Figure 4 serves in particular to heat the lubricant 22 in the transmission 20 when the motor vehicle 100 is traveling. In this embodiment, a first torque M D1 which is greater than the first torque M D1 counteracting second torque M D2 of the second electric drive motor 14, so that a resulting output torque M Ab on the output shaft 28 of the transmission 20 to drive the motor vehicle 100.

[0034] The invention is not limited to the described embodiments. The scope of protection is defined by the patent claims.

[0035] In principle, all methods described in the description or in the claims can be carried out by devices which comprise means for carrying out the respective method steps of these methods. Reference symbol 10 Drivetrain 12 first electric drive motor 14 second electric drive motor 20 gearboxes 22 Lubricants 24 first transmission input 26 second transmission input 27 downforce 28 Output shaft 30 summation gears 32 planetary gears 34 Sun gear 35 first planetary gear 36 second planetary gear 37 third planetary gear 38 planet carriers 39 ring gear 40 Control unit 42 storage unit 44 computing unit 46 Computer program code 50 drive shaft 52 Differential 54 first axle drive 56 second axle drive 58 wheels 80 first axis 90 second axis 100 motor vehicles M A Drive torque M A1 Drive torque of the first electric drive motor M Ab Output torque of the gearbox M B2 Braking torque of the second electric drive motor M D torque M D1 Torque of the first electric drive motor M D2 Torque of the second electric drive motor M P1 Drive power of the first electric drive motor M P2 Drive or braking power of the second electric drive motor r1 Speed of the first electric drive motor r2 Speed of the second electric drive motor

Claims

[1] Method for operating a drive train (10) in a motor vehicle (100), wherein the drive train (10) comprises a first electric drive motor (12), a second electric drive motor (14) and a transmission (20) which can be coupled to both the first electric drive motor (12) and the second electric drive motor (14), and wherein the first electric drive motor (12) has a first torque (M D1 ) and a first speed (r1) to the transmission (20), wherein the second electric drive motor (14) is a torque corresponding to the first torque (M D1 ) opposite second torque (M D2 ) and / or a second speed (r2) opposite to the first speed (r1) to the transmission (20) in order to reduce the power loss (P V ) for heating a lubricant (22) of the transmission (20), characterized by , that from the first electric drive motor (12) a first drive torque (M A1 ) and / or a first drive power (M P1 ) is coupled into the transmission (20), which is greater than a second drive torque or a braking torque (M A2 , M B2 ) and / or a second drive power or a braking power (M P2 ) of the second electric drive motor (14), wherein a resulting output torque (M Ab ), which is transmitted via an output (27) of the transmission (20) to a drive shaft (50) of the motor vehicle (100). [2] Method according to claim 1, characterized by that the first electric drive motor (12) has a first drive torque (M A1 ) and the second electric drive motor (14) is operated in a generator mode to increase a load of the first electric drive motor (12) and is towed by the first electric drive motor (12). [3] Method according to claim 1 or 2, characterized by that the first torque (M D1 ) of the first electric drive motor (12) and the second torque (M D2 ) of the second electric drive motor (14) and / or the first speed (r1) of the first electric drive motor (12) and the second speed (r2) of the second electric drive motor (14) cancel each other out in such a way that no output torque (M Ab ) is transmitted by the gear (20). [4] Method according to claim 1, characterized by that a constant drive power (M P1 ) is provided and an opposing braking power (M P2 ), whereby power control is achieved by controlling the braking power (M P2 ) of the second electric drive motor (14). [5] Method according to claim 1, characterized bythat a constant braking power (M P2 ) is provided and an oppositely acting drive power (M P1 ), whereby power control is achieved by controlling the drive power (M P1 ) of the first electric drive motor (14). [6] Control unit (40) for controlling electric drive motors (12, 14) in a drive train (10) of a motor vehicle (100), wherein the control unit (40) is operatively connected to a first electric drive motor (12) and a second electric drive motor (14) and is configured to carry out a method according to one of claims 1 to 5. [7] Drive train (10) for a motor vehicle (100), comprising a first electric drive motor (12), a second electric drive motor (14) and a transmission (20) which can be coupled both to the first electric drive motor (12) and to the second electric drive motor (14), wherein the drive train comprises a control unit (40) which is designed to carry out a method according to one of claims 1 to 5. [8] Drive train (10) for a motor vehicle (100) according to claim 7, characterized by that the transmission (20) is designed as a summation transmission (30), wherein the first electric drive motor (12) is connected to a first transmission input (24) and the second electric drive motor (14) is connected to a second transmission input (26) of the transmission (20), and the transmission (20) has an output shaft (28) to which the input torques (M D1 , M D2) of the first electric drive motor (12) and the second electric drive motor (14) additively as output torque (M Ab ) can be transferred. [9] Motor vehicle (100) suitable for carrying out a method according to one of claims 1 to 5, wherein the motor vehicle (100) typically comprises a drive train (10) according to one of claims 7 or 8 and / or a control unit (40) according to claim 6. [10] A computer program comprising instructions which, when the computer program is executed by a computer, cause the computer to carry out a method according to any one of claims 1 to 5. [11] Computer-readable medium, characterized by that the computer-readable medium comprises computer program code (46) for carrying out a method according to one of claims 1 to 5.

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