Method for operating a drive train, electrified drive train and working machine

Abstract

The invention relates to a method for operating a drive train (20), wherein the drive train (20) has previously been converted from an internal combustion engine drive to an electric motor drive, wherein the drive train (20) comprises an electric motor (21), a continuously variable transmission (12), an electric motor control unit (23), a transmission control unit (14) and a driving strategy control unit (15), wherein the electric motor (21) is coupled to the continuously variable transmission (12), wherein the electric motor (21) is operated according to a control signal from the electric motor control unit (23), wherein the continuously variable transmission (12) is operated according to a control signal from the transmission control unit (14) and wherein the electric motor control unit (23) and the transmission control unit (14) are operated according to a control signal from the driving strategy control unit (15).The method according to the invention is characterized in that an overload situation of the drive train (20) is detected by a sensor and the drive power of the electric motor (21) is subsequently limited. The invention further relates to an electrified drive train.

Description

[0001] The invention relates to a method for operating a drive train according to the preamble of claim 1, an electrified drive train according to the preamble of claim 11 and a corresponding working machine.

[0002] It is known in the prior art that agricultural vehicles, especially tractors, typically require a wide range of finely graduated driving ranges due to their broad range of tasks. This can be achieved, for example, by means of a continuously variable transmission, which simultaneously results in a high level of comfort for the driver, as they can concentrate fully on the work to be performed instead of continuously monitoring the operating point of the machine and selecting the most suitable gear.

[0003] The control or regulation of the transmission ratio of the continuously variable transmission is carried out depending on the characteristics of the combustion engine and the continuously variable transmission according to a complex algorithm that is tailored to the specific combination of combustion engine and continuously variable transmission present in the commercial vehicle.

[0004] Electrically powered agricultural vehicles, which use an electric motor instead of an internal combustion engine, are also known in the prior art. Electrically powered vehicles offer a number of advantages over conventionally powered vehicles, such as lower maintenance and operating costs.

[0005] In this context, EP 2 230 145 A1 discloses a method for retrofitting a vehicle. As a first step, a power exchange unit is connected to the vehicle's existing gearbox via a power take-off (PTO) connection. Then, an electric motor is connected to the power exchange unit. An electric battery is also provided to supply power to the electric motor.

[0006] Finally, a control unit is installed that is coupled to the electric motor and the battery and is configured to switch the operation of the vehicle between a first and a second mode, with in the first mode an internal combustion engine of the vehicle powering the vehicle and in the second mode the electric motor powering the vehicle.

[0007] EP 2 230 145 A1 describes a method for converting a vehicle with an internal combustion engine, a transmission, an alternator, and a battery into a hybrid vehicle. This involves installing an electric motor in the vehicle, configured to assist the internal combustion engine in rotating its crankshaft. Furthermore, an energy storage element, configured to supply power to the electric motor, is installed in the vehicle. Similarly, a motor control unit, configured to regulate the amount of power supplied by the energy storage element to the electric motor, is installed in the vehicle.

[0008] From DE 20 2012 002 541 U1 a conversion kit is known for attaching an electric motor to a power transmission device designed for this purpose on the standard engine block of a motor vehicle and for turning the crankshaft located in the engine block by means of the power transmission device.

[0009] From DE 10 2020 203 938 A1, a method for operating a motor vehicle's powertrain is known. The powertrain comprises a permanent magnet electric machine as the vehicle's drive source. A transmission with different gear ratios is arranged in the power flow between the electric machine and the drive wheels. An inverter is associated with the electric machine, which can operate the electric machine in a field weakening state. A gear change of the transmission, specified by a driving strategy, is performed prematurely, delayed, or prevented depending on a temperature value of the electric machine or the inverter, in order to reduce, not increase, or delay the speed of the electric machine.

[0010] The generic patent DE 10 2022 105 401 A1 relates to a drivetrain for an agricultural vehicle. The drivetrain comprises a rear axle, a front axle, a first electric drive unit, and a transmission with a first output shaft. The first output shaft is connected to the rear axle. The drivetrain also comprises a front axle drive unit, which includes a second output shaft, and the first output shaft is connected to the second output shaft. The first electric drive unit is connected to the second output shaft, and torque can be introduced into the second output shaft by the first electric drive unit and transmitted from the second output shaft to the rear axle via the transmission, so that the rear axle can be driven by the first electric drive unit.

[0011] However, the known conversion kits or methods for converting a combustion engine vehicle into a hybrid or electric vehicle are disadvantageous in that they only inadequately take into account the torque behavior of the electric motor - which differs significantly from the torque behavior of a combustion engine and can provide high torque, especially at low speeds.

[0012] It is an object of the invention to propose an improved method for operating a drive train.

[0013] This problem is solved according to the invention by the method for operating a drive train according to claim 1. Advantageous embodiments and further developments of the invention are described in the dependent claims.

[0014] The invention relates to a method for operating a drive train, wherein the drive train was previously converted from an internal combustion engine drive to an electric motor drive, wherein the drive train comprises an electric motor, a continuously variable transmission, an electric motor control unit, a transmission control unit and a driving strategy control unit, wherein the electric motor is coupled to the continuously variable transmission, wherein the electric motor is operated according to a control signal from the electric motor control unit, wherein the continuously variable transmission is operated according to a control signal from the transmission control unit and wherein the electric motor control unit and the transmission control unit are operated according to a control signal from the driving strategy control unit.

[0015] The invention therefore describes a method which makes it possible to operate a drive train of a working machine that has been converted from an internal combustion engine drive to an electric motor drive.

[0016] Prior to the conversion, the modified powertrain advantageously comprised an internal combustion engine, a continuously variable transmission (CVT), a transmission control unit, and an internal combustion engine control unit. For the purposes of the invention, it is not necessary that the powertrain was fully assembled prior to the conversion; rather, it is sufficient that the powertrain was originally designed, planned, or configured in such a way that it would have included the aforementioned components after its complete assembly. All of these components were originally intended to have a specific function within the powertrain.

[0017] According to the invention, for example, the combustion engine does not need to be installed in the drivetrain in order to be replaced by an electric motor. Rather, in this context, the term "replace" also means that the drivetrain was designed for a drive with a combustion engine and the electric motor occupies a space intended for the combustion engine, without any modification of the drivetrain to accommodate the electric motor. The electric motor can thus replace the combustion engine right from the start, during the assembly of the drivetrain.

[0018] The same applies analogously to the combustion engine control unit, which does not need to be installed in the powertrain only to be subsequently replaced by an electric motor control unit. Rather, in the context of the invention, the term "replace" means that the powertrain was designed for use with a combustion engine and, accordingly, a combustion engine control unit is required to control the combustion engine. However, the electric motor control unit can replace the combustion engine control unit right from the start of the powertrain assembly process.

[0019] The electric motor is coupled to a continuously variable transmission (CVT), enabling the electric motor to drive the CVT. The CVT, in turn, can, for example, transmit the electric motor's power to one or more downstream gear groups or reduction stages, or directly to an axle drive or all-wheel drive system.

[0020] The continuously variable transmission (CVT) advantageously does not have rigid, interchangeable gear ratios, but rather a variably changeable transmission ratio. A CVT is also known as a continuously variable transmission.

[0021] The electric motor control unit is designed and intended to control the electric motor. In particular, the electric motor control unit sets the speed and torque that the electric motor is to provide.

[0022] The transmission control unit, in turn, is designed and intended to control the continuously variable transmission (CVT). Specifically, the transmission control unit sets the gear ratio to be provided by the CVT.

[0023] The driving strategy control unit advantageously receives a multitude of driver inputs and derives drive requirements from them, in particular regarding the engine speed to be set, the upper engine torque limit to be set, and the transmission ratio. Based on these drive requirements, the driving strategy control unit can then advantageously control the electric motor control unit and the transmission control unit.

[0024] According to the invention, it is not necessary for the electric motor to be directly coupled to the continuously variable transmission. Rather, an indirect coupling via one or more transmission stages or gear groups is also conceivable and preferred.

[0025] According to the invention, it is now provided that an overload situation of the drive train is detected by sensors and that a limitation of the drive power of the electric motor is then carried out.

[0026] This means that, within the framework of the inventive method, monitoring is carried out with at least one sensor to determine whether an overload situation exists at any point in the drive train.

[0027] For the purposes of this invention, an overload situation is understood to mean the provision of drive power by the electric motor that can lead to damage or destruction of one or more components of the drive train, in particular damage or destruction of the continuously variable transmission (CVT). Such an overload situation can occur in the CVT, especially at low speeds and high torques of the electric motor.

[0028] For the sensory detection of the overload situation, at least one force sensor or torque sensor can be used, for example.

[0029] If such an overload situation is detected, the drive power of the electric motor is limited accordingly, i.e., restricted to a value that safely avoids damage to the respective component.

[0030] Preferably, the torque provided by the electric motor is limited.

[0031] Sensory detection of overload situations ensures that the drive train always operates within safe limits. This prevents damage to the components and extends the service life of the drive train.

[0032] According to the invention, the overload situation in the continuously variable transmission is detected by sensors.

[0033] Since the continuously variable transmission (CVT) is a complex and sensitive component, a sensor is typically already integrated to monitor its operation. Furthermore, because the CVT transmits the electric motor's power to other components of the drivetrain, the motor's power output can also be efficiently monitored and recorded within the CVT.

[0034] According to a preferred embodiment of the invention, it is provided that the overload situation is detected by means of a high-pressure sensor of the continuously variable transmission.

[0035] The operating status of the continuously variable transmission (CVT) is typically monitored using a high-pressure sensor. A high-pressure sensor is capable of detecting even very high forces and torques.

[0036] According to a particularly preferred embodiment of the invention, it is provided that an overload situation outside the continuously variable transmission is also detected by means of the high-pressure sensor of the continuously variable transmission.

[0037] Since the output torque of the continuously variable transmission can be determined, at least mathematically, based on the usually known output speed of the continuously variable transmission and given a known drive power of the electric motor, the load or torque on the other components can also be determined, for example, using the known gear ratios in the drive train.

[0038] The other components may include, in particular, transmission stages, gear groups or axle differentials.

[0039] The high-pressure sensor can therefore detect overload situations not only in the gearbox itself, but also in adjacent components. This ensures comprehensive monitoring and increases the overall safety of the drivetrain. Overload situations can thus be detected throughout the entire drivetrain, and the electric motor's drive power can then be reduced to a safe level.

[0040] According to a further preferred embodiment of the invention, it is provided that information about the overload situation is transmitted from the transmission control unit to the driving strategy control unit.

[0041] The driving strategy control unit can then advantageously reduce the drive power of the electric motor via the engine control unit. Furthermore, the driving strategy control unit can also change the gear ratio of the continuously variable transmission (CVT) via the transmission control unit.

[0042] For example, the driving strategy control unit can increase the speed of the electric motor and reduce the torque supplied via the engine control unit. Via the transmission control unit, the driving strategy control unit can adjust the gear ratio of the continuously variable transmission (CVT) so that a substantially unchanged speed is still output at the transmission output, while reliably preventing damage to the CVT.

[0043] The transmission of overload information between the different control units generally enables a coordinated and efficient adjustment of the drive power. This optimizes system performance and prevents unnecessary loads.

[0044] According to a particularly preferred embodiment of the invention, it is provided that the electric motor control unit is instructed by the driving strategy control unit to limit the drive power of the electric motor.

[0045] This can also advantageously take into account further information from the transmission control unit that was previously forwarded to the driving strategy control unit, such as in particular a current gear ratio.

[0046] The central control of the drive power via the driving strategy control unit ensures that all components of the powertrain work together efficiently.

[0047] According to a further preferred embodiment of the invention, the limitation is intended to limit the drive power of the electric motor to such an extent that no damage occurs to components of the drive train.

[0048] Targeted limitation of the drive power protects the drivetrain from damage caused by overloading. This leads to a longer service life and lower maintenance costs.

[0049] According to a further preferred embodiment of the invention, it is provided that the overload situation is detected based on an output speed of the continuously variable transmission.

[0050] Since it has been found that overload situations can occur relatively frequently, especially at low output speeds of the continuously variable transmission (CVT), monitoring and taking the output speed into account allows for particularly reliable detection of overload situations and / or prevents their occurrence in advance. This provides even more reliable protection for the drivetrain against damage.

[0051] According to a particularly preferred embodiment of the invention, it is provided that the drive power of the electric motor is reduced when the output speed of the continuously variable transmission falls below a lower speed threshold.

[0052] By specifying a lower speed threshold, it is possible to easily and efficiently detect an overload situation or an increased risk of an overload situation occurring, regardless of the actual applied torque.

[0053] According to a further particularly preferred embodiment of the invention, it is provided that a recuperation process is carried out when the output speed of the continuously variable transmission exceeds an upper speed threshold.

[0054] Excessive rotational speed can also lead to an overload situation in one or more components of the drivetrain.

[0055] The execution of a recuperation process when an upper speed threshold is exceeded reduces the output speed through the braking effect of the recuperation and allows the recuperated energy to be stored for later operation of the powertrain. This increases the energy efficiency of the powertrain.

[0056] The invention further relates to an electrified powertrain, wherein the powertrain is designed for an internal combustion engine drive and has been converted to an electric motor drive, wherein the powertrain comprises an electric motor, a continuously variable transmission, an electric motor control unit, a transmission control unit and a driving strategy control unit, wherein the electric motor is coupled to the continuously variable transmission, wherein the powertrain is configured such that the electric motor is operated according to a control signal from the electric motor control unit, wherein the powertrain is configured such that the continuously variable transmission is operated according to a control signal from the transmission control unit, and wherein the powertrain is configured such that the electric motor control unit and the transmission control unit are operated according to a control signal from the driving strategy control unit.

[0057] The drive train according to the invention is characterized in that the drive train is designed in such a way that an overload situation of the drive train is detected by sensors and a limitation of the drive power of the electric motor is subsequently carried out.

[0058] The drive train according to the invention thus enables the execution of the method according to the invention and leads to the advantages already described.

[0059] According to a preferred embodiment of the invention, the drive train further comprises a reduction gear, wherein the reduction gear is arranged between the electric motor and the continuously variable transmission.

[0060] The reduction gear can be designed as a gearbox or as a comparatively simple reduction stage.

[0061] Using a reduction gearbox offers the advantage that the speed of the electric motor – which is typically significantly higher than that of the combustion engine – can be reduced before it is fed to the continuously variable transmission (CVT). This means that the available power of the electric motor does not have to be limited by reducing its speed.

[0062] According to a further preferred embodiment of the invention, the drive train further comprises an electrical energy storage device, wherein the energy storage device is configured to supply the electric motor with electrical energy.

[0063] Thus, the electrified drive train can be supplied with the required electrical energy during operation of the machine.

[0064] An electrical energy storage device is advantageously a rechargeable electrical energy storage device.

[0065] Preferably, the drive train shall also include an inverter designed to control the electric motor according to a control command from the electric motor control unit.

[0066] The use of an inverter favors the use of three-phase controlled electric motors, which have a better efficiency than two-phase controlled brushed motors.

[0067] The invention relates to a working machine comprising a drive train according to the invention. Thus, the advantages of the invention also apply to the working machine according to the invention.

[0068] The working machine is preferably an agricultural vehicle, in particular an agricultural tractor.

[0069] The invention is explained below by way of example with reference to embodiments shown in the figures.

[0070] They show: Fig. 1. An exemplary and schematic embodiment of a method according to the invention for operating a drive train in the form of a flowchart and Fig. 2. An exemplary and schematic embodiment of an electrified drive train according to the invention for a working machine.

[0071] Identical objects, functional units, and comparable components are designated across all figures using the same reference symbols. These objects, functional units, and comparable components are identical in their technical characteristics unless explicitly or implicitly stated otherwise in the description.

[0072] Fig. Figure 1 shows, by way of example and schematically, a possible embodiment of a method according to the invention for operating a drive train 20 in the form of a flowchart.

[0073] In a first process step 101, an overload situation of the drive train 20 is detected by means of a high-pressure sensor in the continuously variable transmission 12.

[0074] Information about the overload situation is transmitted from the transmission control unit 14 to the driving strategy control unit 15 in step 102.

[0075] Subsequently, in step 103, the electric motor control unit 23 is instructed by the driving strategy control unit 15 to limit the drive power of the electric motor 21.

[0076] The limitation restricts the drive power of the electric motor 21 to such an extent that no damage occurs to components of the drive train 20.

[0077] Fig. Figure 2 shows, by way of example and schematically, a possible embodiment of an electrified drive train 20 according to the invention for a working machine (not shown in Figure 2). Fig. 2).

[0078] The powertrain 20 was previously converted from an internal combustion engine drive to an electric motor drive.

[0079] The powertrain 20 comprises an electric motor 21, a continuously variable transmission 12, an electric motor control unit 23, a transmission control unit 14 and a driving strategy control unit 15.

[0080] The electric motor control unit 23 is connected to the inverter 27 via data transmission. The inverter 27 then controls the electric motor 21 according to a control signal from the electric motor control unit 23.

[0081] The continuously variable transmission 12 in turn is controlled by the transmission control unit 14 and operated according to this control.

[0082] The transmission control unit 14 and the electric motor control unit 23 are controlled by the driving strategy control unit 15, which controls the transmission control unit 14 and the electric motor control unit 23. The transmission control unit 14 and the electric motor control unit 23 are therefore operated according to the instructions of the driving strategy control unit 15.

[0083] The electric motor 21 is driven by the reduction gear 26, which reduces the input speed of the electric motor 21 and then outputs it to the continuously variable transmission 12. The reduction gear 26 is therefore also coupled to the continuously variable transmission 12. Thus, the electric motor 21 is indirectly coupled to the continuously variable transmission 12.

[0084] For example, the continuously variable transmission 12 has a high-pressure sensor (not shown in Fig. 2) arranged, which can sensorially detect an overload situation based on the torques occurring in the continuously variable transmission 12.

[0085] If an overload situation is detected by the high-pressure sensor, information about the overload situation is transmitted from the transmission control unit 14 to the driving strategy control unit 15. The electric motor control unit 23 is then instructed by the driving strategy control unit 15 to limit the drive power of the electric motor 21 to such an extent that damage to components of the drivetrain 20 is prevented.

[0086] Additionally, an overload situation or an increased risk of an overload situation occurring can also be detected based on the output speed of the continuously variable transmission 12. If the output speed of the continuously variable transmission 12 falls below a lower speed threshold, a probability of an overload situation occurring, which can be specified via the speed threshold, is reached.

[0087] The electric motor control unit 23 is therefore also instructed by the driving strategy control unit 15 in this case to limit the drive power of the electric motor 21 to such an extent that damage to components of the drive train 20 is excluded. Reference sign 10 Powertrain 11 Internal combustion engine 12 continuously variable transmissions 13 Internal combustion engine control unit 14 Transmission control unit 15 Driving strategy control unit 16 wave 20 Powertrain 21 Electric motor 23 Electric motor control unit 26 reduction gears 27 Inverter 101 Sensory detection of an overload situation in the drivetrain 102 Transmitting information about the overload situation from the transmission control unit to the driving strategy control unit 103 Limiting the drive power of the electric motor

Claims

[1] Method for operating a powertrain (20), wherein the powertrain (20) was previously converted from an internal combustion engine drive to an electric motor drive, wherein the powertrain (20) comprises an electric motor (21), a continuously variable transmission (12), an electric motor control unit (23), a transmission control unit (14) and a driving strategy control unit (15), wherein the electric motor (21) is coupled to the continuously variable transmission (12), wherein the electric motor (21) is operated according to a control command of the electric motor control unit (23), wherein the continuously variable transmission (12) is operated according to a control of the transmission control unit (14) and wherein the electric motor control unit (23) and the transmission control unit (14) are operated according to a control signal from the driving strategy control unit (15), characterized by , that an overload situation of the drive train (20) is detected by sensors (101) and consequently a limitation of the drive power of the electric motor (21) takes place (103) and that the overload situation in the continuously variable transmission (12) is detected by sensors (101). [2] Method according to claim 1, characterized by , that the overload situation is detected by means of a high-pressure sensor of the continuously variable transmission (12) (101). [3] Method according to claim 2, characterized by , that an overload situation outside the continuously variable transmission (12) is also detected by means of the high pressure sensor of the continuously variable transmission (12) (101). [4] Method according to at least one of claims 1 to 3, characterized by , that information about the overload situation is transmitted from the transmission control unit (14) to the driving strategy control unit (15) (102). [5] Method according to claim 4, characterized by, that the electric motor control unit (23) is instructed by the driving strategy control unit (15) to limit the drive power of the electric motor (21) (103). [6] Method according to at least one of claims 1 to 5, characterized by , that by limiting the drive power of the electric motor (21) is limited to such an extent (103) that no damage to components of the drive train occurs. [7] Method according to at least one of claims 1 to 6, characterized by , that the overload situation is detected based on an output speed of the continuously variable transmission (12). [8] Method according to claim 7, characterized by , that the drive power of the electric motor (21) is reduced when the output speed of the continuously variable transmission (12) falls below a lower speed threshold. [9] Method according to at least one of claims 7 and 8, characterized by, that a recuperation process is carried out when the output speed of the continuously variable transmission (12) exceeds an upper speed threshold. [10] Electrified powertrain (20) wherein the powertrain (20) is designed for an internal combustion engine drive and has been converted to an electric motor drive, wherein the powertrain (20) comprises an electric motor (21), a continuously variable transmission (12), an electric motor control unit (23), a transmission control unit (14) and a driving strategy control unit (15), wherein the electric motor (21) is coupled to the continuously variable transmission (12), wherein the drive train (20) is configured such that the electric motor (21) is operated according to a control signal from the electric motor control unit (23), wherein the drive train (20) is configured such that the continuously variable transmission (12) is operated according to a control signal from the transmission control unit (14), and wherein the drive train (20) is configured such that the electric motor control unit (23) and the transmission control unit (14) are operated according to a control signal from the driving strategy control unit (15). characterized by , that the drive train (20) is designed to detect an overload situation of the drive train by sensors and subsequently limit the drive power of the electric motor (21) and that the overload situation in the continuously variable transmission (12) is detected by sensors (101). [11] Drive train (20) according to claim 10, characterized by , that the drive train (20) further comprises a reduction gear (26), wherein the reduction gear (26) is arranged between the electric motor (21) and the continuously variable transmission (12). [12] Powertrain (20) according to at least one of claims 10 and 11, characterized by , that the drive train (20) further comprises an electrical energy storage device, wherein the energy storage device is configured to supply the electric motor (21) with electrical energy. [13] Powertrain (20) according to at least one of claims 10 to 12, characterized by , that the drive train (20) is configured to perform a method according to at least one of claims 1 to 10. [14] Working machine comprising a drive train (20) according to at least one of claims 10 to 13.

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