Method for operating a powertrain with an electrified continuously variable transmission

Abstract

Method for operating a drive train of a working machine, wherein the drive train comprises an internal combustion engine (10) with a drive shaft (12), a continuously variable transmission (14) with an electric variator (16) and a planetary assembly (18), a motor switching element (K0), and an energy storage device (20), wherein the variator (16) comprises a first electric machine (EM1) with a first motor shaft (22) and a second electric machine (EM2) with a second motor shaft (24), wherein the energy storage device (20) is electrically connected to the first (EM1) and the second electric machine (EM2), wherein the planetary assembly (18) comprises a first input shaft (30), a second input shaft (32), and an output shaft (34), wherein the first motor shaft (22) is mechanically connected to the first input shaft (30), and wherein the drive shaft (12) is mechanically connected to the first input shaft (30) by means of the motor switching element (K0). is effectively interlockable,and wherein the second motor shaft (24) is mechanically connected to the second input shaft (32), wherein the method comprises at least the following steps: , - Adjusting the motor switching element (K0) to an open position in order to operate the drive train in an electric operating mode; and - Providing a driving force through the drive train in the electric operating mode, wherein both electric machines (EM1, EM2) are operated in their motor operating state, characterized in that the planetary assembly (18) is configured to provide several travel ranges (FB1, FB2, FB3, FB4), wherein the method further comprises the following steps: - Providing the drive force through the drive train in one of the driving ranges (FB1, FB2, FB3, FB4) in the electric operating mode, whereby both electric machines (EM1, EM2) are operated in their motor operating state; - Switching to a different driving range (FB1, FB2, FB3, FB4) in electric operating mode; and - Controlling the two electric machines (EM1, EM2) so that both electric machines (EM1, EM2) are operated in their motor operating state again.

Description

[0001] The present invention relates to a method for operating a drive train of a working machine. Furthermore, the invention relates to a drive train and to a working machine. State of the art

[0002] Construction machinery often uses drive trains with continuously variable transmissions (CVTs), where the drive power is generated by an internal combustion engine. The CVT allows the internal combustion engine to operate with high efficiency, for example, at a particularly efficient and virtually speed-independent engine speed. The gear ratio is changed, for example, by a hydraulic variator, i.e., a hydrostatic transmission. The hydrostatic transmission is also powered by the internal combustion engine.

[0003] In the course of partially electrifying such a drivetrain, an electric variator can be used instead of a hydraulic one. Such a variator, for example, has two electric motors that operate as generators or motors depending on the desired gear ratio. However, reactive power losses occur when an electric motor is operating as a generator. Furthermore, electric variators can enable additional functions that are not possible with conventional hydrostatic drives.

[0004] US patent 2016 / 0236671A1 describes a hybrid vehicle with a power transmission unit. The power transmission unit is designed to switch a power transmission path between a motor, a first motor-generator, and a second motor-generator.

[0005] In DE 10 2017 103 396 A1 a hybrid vehicle with an internal combustion engine, a first motor generator and a second motor generator is described. Description of the invention

[0006] A first aspect concerns a method for operating the drivetrain of a machine. The drivetrain can, for example, be designed to provide propulsion power for driving the machine. Alternatively or additionally, the drivetrain can also provide work power, for example, for moving or otherwise operating the machine's tools. The machine can be, for example, an agricultural machine or a construction machine. An example of an agricultural machine is a tractor. An example of a construction machine is a wheel loader.

[0007] The drivetrain consists of an internal combustion engine with a drive shaft. The internal combustion engine can be, for example, a gasoline or diesel engine. The internal combustion engine can be designed to convert chemical energy into electrical energy. The internal combustion engine can, for example, provide drive power at the drive shaft.

[0008] The drivetrain features a continuously variable transmission (CVT) with an electric variator. The CVT can be designed, for example, as an electrically power-split transmission. A CVT can be a transmission in which the gear ratio is continuously adjustable within a specific range. The CVT can be designed, for example, as a CVT or IVT transmission. The variator can be configured to receive power from the drive shaft, deliver it, and transmit it alternatively or additionally. The variator can be configured to deliver or receive power at different shafts. The variator can be configured to convert between electrical and mechanical energy.

[0009] The continuously variable transmission (CVT) features a planetary gear set. This planetary gear set can be designed for mechanical torque transmission, for example, from the input shaft to an output of the driven machine. The output can be, for example, a shaft of the driven machine, a differential, a driven axle, or even a chain drive. The planetary gear set can, for example, include at least one planetary gear set. Additionally, the planetary gear set can include switching elements, such as multi-plate clutches, dog clutches, or synchronizers.

[0010] The transmission has an engine shift element. This element can be a switching element by which the drive shaft can be connected to the transmission for torque transmission, or by which the drive shaft can be disconnected from the transmission. This disconnects, for example, the internal combustion engine from the variator, preventing the variator from being driven by the engine's power. The engine shift element can be designed as a switching element; the designation serves only for identification purposes.

[0011] The transmission incorporates an energy storage device. This device can be configured to both absorb and release electrical energy. It can facilitate a buffered transfer of electrical energy between the variator's electric motors, for example, when one motor operates as a generator and the other as a motor. In motor mode, electrical energy is converted into mechanical energy. Conversely, in generator mode, mechanical energy is converted into electrical energy. If the two electric motors do not absorb or deliver the same amount of energy, the energy storage device can compensate for any difference. Furthermore, the energy storage device can enable the variator to operate independently of the internal combustion engine.This allows the variator to provide electrical drive power even when the internal combustion engine is switched off and alternatively or additionally decoupled from the transmission by means of the engine switching element.

[0012] The variator comprises a first electric motor with a first motor shaft and a second electric motor with a second motor shaft. An electric motor can be, for example, a synchronous motor or an asynchronous motor. A motor shaft of an electric motor can, for example, be permanently and rotationally fixed to a rotor of the electric motor or form the rotor itself. Drive power can be supplied to the motor shaft by the electric motor. Likewise, power can be drawn from the motor shaft for electricity generation. The electric motors can, for example, be configured for recuperation. The second electric motor, for example, has only a single motor shaft. The numbering then serves only for identification purposes. The second electric motor can, for example, be free of any additional motor shafts.

[0013] The energy storage device is electrically connected to both the first and second electric machines. This allows current to flow between the two electric machines and the energy storage device. Electrical energy can also be transferred from one of the two electric machines to the other via the energy storage device. The energy storage device can be designed, for example, as a battery or accumulator. It can be configured to be charged by the first electric machine and, alternatively or additionally, by the second electric machine in generator mode. Optionally, the energy storage device can be designed for external charging, for example, via a municipal power grid.

[0014] The planetary assembly can have a first input shaft, a second input shaft, and an output shaft. The two input shafts and the output shaft can, for example, be designed as rotating elements of planetary gear sets within the planetary assembly. The input shafts and the output shafts can also be permanently and rotationally fixed to rotating elements of the planetary assembly.

[0015] The first motor shaft is mechanically connected to the first input shaft. Electrical power can be fed in or drawn from it for electricity generation. The drive shaft is mechanically connected to the first input shaft via the motor switching element. Thus, for example, the drive power of the internal combustion engine is fed into the transmission at the first input shaft. The internal combustion engine can also drive the first electric motor. The motor switching element allows the internal combustion engine to be decoupled from the transmission. This prevents the internal combustion engine from dragging, for example, when the variator provides drive power for the machine without the internal combustion engine. The second motor shaft is mechanically connected to the second input shaft.Electrical power can be fed in or drawn from the second input shaft for power generation. Furthermore, by rotating the second input shaft, the gear ratio between the first input shaft and the output shaft can be varied. Changing the speed and direction of rotation of the second motor shaft, for example, allows the gear ratio to be adjusted within a specific operating range of the transmission. The output shaft is mechanically connected to, or operatively connected to, the output of the driven machine. The continuously variable transmission (CVT) is, for example, designed as an input-coupled CVT.

[0016] The drivetrain may also include a power take-off (PTO) shaft. Power can be supplied at the PTO shaft to drive an implement. For example, the PTO shaft can provide work power for an implement. The PTO shaft can be mechanically connected to the first input shaft or the drive shaft. A PTO switching element may be provided. The PTO shaft can be mechanically connected to the transmission via the PTO switching element. The PTO switching element allows the PTO shaft to be decoupled, for example. This prevents the PTO shaft from being dragged, such as when the implement is driven solely by the variator. The PTO switching element can be designed as a type of switching element; the name is used for identification purposes only.

[0017] The procedure includes a step of adjusting the motor switching element to an open state to operate the drivetrain in an electric mode. In this electric mode, drive power can be supplied by the drivetrain, for example, solely by the electric motors of the variator. In this electric mode, for example, no drive power is supplied by the internal combustion engine. The electric mode is, for example, a purely electric operating mode. In the open state, torque transmission between the drive shaft and the transmission may be interrupted. In a closed state, however, the motor switching element allows, for example, torque transmission from the drive shaft to the first input shaft of the transmission.In electric mode, the combustion engine's power is not available for propulsion, or even for general use. The combustion engine is switched off in electric mode. Additionally, the power take-off (PTO) can be disengaged via the PTO shift element, and any implements can be deactivated. In electric mode, the drivetrain can be quiet and produce no exhaust fumes. Vibrations can also be minimal. For example, slow driving on a farmyard or in a barn can be particularly pleasant for residents and animals.

[0018] In electric mode, a driving force is provided by the drivetrain, with both electric machines operating in their motor-driven state. For example, the two electric machines are always operated in their motor-driven state at least when the driven machine is traveling at a constant speed, and alternatively or additionally when no change in travel range occurs. In this mode, for example, no generator-driven state of operation is permitted for the two electric machines, regardless of the travel speed. In electric mode, the two electric machines can always be exclusively in their motor-driven state, regardless of the state of the driven machine. Generator-driven operation of the two electric machines can always be prohibited in electric mode, regardless of the state of the driven machine.In motor operation, for example, both electric motors contribute to generating the driving force. This motor operation avoids the efficiency loss caused by reactive power from the electric motors, which occurs in generator operation. For example, the second electric motor rotates its second motor shaft in a direction corresponding to the desired or current direction of travel. This eliminates the need to use half of one or all of the continuously variable transmission's ranges, in which the second motor shaft rotates in the opposite direction to the desired or current direction of travel for the corresponding gear ratio. For example, in a first range, both motor shafts always rotate in the same direction.In normal operation using the combustion engine, the second motor shaft rotates in the opposite direction to the first motor shaft in one half of the operating range. Depending on the mechanical connection, however, the two motor shafts can always rotate in opposite directions in the first operating range to achieve generator operation of the second electric machine. In generator operation, an electric machine can brake its motor shaft and thus also the associated rotating element of the planetary assembly.

[0019] According to the invention, the planetary assembly is designed to provide multiple operating ranges. Within each operating range, a different gear ratio can be present, with the operating ranges adjacent to one another, for example, at a synchronization point. For instance, the gear ratio in a first operating range, when the second electric motor rotates the second motor shaft in one direction at its maximum speed for a continuous load, can be identical to the gear ratio in a second operating range, when the second electric motor rotates the second motor shaft in the opposite direction to the first operating range at its maximum speed for a continuous load. The mechanical connections within the planetary assembly can differ in each operating range.For example, a switching element of the planetary assembly can be in its open state in the first travel range and in its closed state in the second travel range. Each travel range can also be assigned a specific speed range for driving the machine. Each travel range can have a fixed mechanical transmission ratio, which is continuously variable by the variator.

[0020] The method includes a step in which the drive train provides the motive power in one of the travel ranges in electric operating mode, with both electric machines operating in their motor-like state. The method includes a step in which the process switches to a different travel range in electric operating mode. The other travel range can be a travel range immediately following the one from which the switch is made. The switch can occur, for example, at the synchronization point between the two travel ranges. The switch can be effected, for example, by adjusting one or more switching elements of the planetary assembly. The switch to the other travel range in electric operating mode can cause at least one of the two electric machines to enter a generator-like operating mode, for example, the second electric machine.The process includes a step of controlling the two electric machines to return both to their motor-driven operating state. For example, the direction of rotation of the second electric machine can be reversed. While the direction of rotation is being changed, the second electric machine may briefly enter a generator-driven operating state and thus be operating in a reactive power range. This reactive power range is then exited as quickly as possible through control. Controlling the two electric machines can also involve an absolute reduction in the rotational speed of the machine that has entered generator-driven operation. This allows, for example, a return to a range with full available torque according to the respective characteristic curves of the electric machines.The output speed of the drive transmission and the travel speed of the machine remain unchanged during this change. The electric motors typically have high speeds and therefore high inertia. This helps to dampen any potential drop in tractive effort that might occur during the adjustment. Once both electric motors are back in their normal operating state, their respective speeds can be increased, thus increasing the vehicle speed. Upon reaching the synchronization point with the next travel range, another change of travel range can then be performed.

[0021] In one embodiment of the method, controlling the two electric machines so that both are again operated in their motorized state involves reversing the direction of rotation of one of the two electric machines. For example, the direction of rotation of the electric machine whose motor shaft varies the gear ratio of the planetary assembly is reversed.

[0022] In one embodiment of the method, it is provided that when switching to the other operating range in the electric operating mode, at least one of the two electric machines is operated in an overload condition. The overload condition can be an operating condition in which an electric machine is operated with more power and, alternatively or additionally, at a higher speed than is possible continuously without damage. For example, heating of the electric machine in the overload condition can damage the insulation of the respective windings after a certain period of time. However, short-term operation at a higher speed and, alternatively or additionally, higher power is possible without overheating and damage. The electric machine can thus provide a power boost. For example, an electric machine can be operated continuously at only 7,300 revolutions per minute but at 11,000 revolutions per minute for a predetermined maximum period of time.000 revolutions per minute. This allows a tractive force gap to be compensated for compared to operation with an internal combustion engine and, alternatively or additionally, one of the two electric motors in its generator mode. The power available in the drivetrain in the short term can thus be increased. Operation in the overload condition can, for example, enable a short-term increase in speed beyond the synchronization point in the driving range from which the vehicle is being switched. This can shorten the time during which an electric motor is in reactive power mode after the driving range change. Operation in the overload condition can also occur during the driving range change, either alternatively or additionally.Overload operation can also be performed alternatively or additionally after changing operating ranges to quickly reverse the direction of rotation of a motor shaft or to provide more tractive force in the case of an unfavorable gear ratio. The first electric motor, and alternatively or additionally the second electric motor, can be operated in overload mode. After a predetermined maximum duration, and alternatively or additionally upon reaching a maximum operating temperature, the respective electric motors can be operated again in a normal operating state, for example, with a power output at which no damage is likely to occur.

[0023] In one embodiment of the method, it is provided that when the driven machine accelerates in electric operating mode, at least one of the two electric machines operates in overload mode in order to at least reduce the tractive force gap compared to accelerating the driven machine in normal operating mode with the internal combustion engine engaged and the motor switching element in a closed state. This allows the tractive force gap to be completely closed or even more tractive force to be available in electric operating mode than in normal operating mode with the internal combustion engine engaged. A tractive force gap can correspond to the difference between the drive power or drive torque of the drive train with the internal combustion engine engaged and the motor switching element in a closed state, and the electric operating mode.In normal operating mode, for example, regenerative operation of both electric machines, or at least one of them, such as the second electric machine, may be permitted. Acceleration may require a particularly high drive power.

[0024] In one embodiment of the method, the method includes a step of checking whether a deactivation condition for the electric operating mode exists while the drivetrain is operating in electric mode. A deactivation condition could be, for example, an empty energy storage device or a charge level of the energy storage device below a threshold. A deactivation condition could also be an excessively high requested drive power or the activation of an implement on the power take-off (PTO). An excessively high requested travel speed or a shift into too high a range of the transmission could also be a deactivation condition. The presence of several of these deactivation conditions can also be checked. The deactivation condition can be detected, for example, by sensors or via a vehicle bus.In response to the occurrence of at least one of the deactivation conditions, the motor switching element is moved to its closed position to return the powertrain to its normal operating mode. The internal combustion engine may also be engaged. This prevents, for example, a powertrain failure or insufficient system performance. In normal operating mode, the variator can, for instance, operate without restrictions again, and a driving range can be fully utilized, including, for example, the second electric motor in its generator mode.

[0025] In one embodiment of the method, the drive train is provided to have at least one drive output switching element. The output shaft of the drive transmission can be mechanically connected to the output of the driven machine by means of the drive output switching element. A direction of travel of the drive train can also be selected by means of the drive output switching element, for example, by reversing the direction of rotation between the output shaft and the output. A separate drive output switching element can also be assigned to each direction of travel. A drive output switching element can, for example, be designed like other switching elements. The designation serves only for identification purposes.

[0026] Starting in electric mode from a standstill is achieved by adjusting the drive output switching element to its closed position and controlling the two electric motors so that the rotational speeds of the input shafts are superimposed, resulting in the output shaft remaining stationary. For example, the first motor shaft can rotate at a certain speed in one direction, and the second motor shaft at a certain speed in the opposite direction. The second electric motor can operate in generator mode. This results in a torque being applied to the output shaft, thus holding the machine in place. This prevents, for example, rolling away on a slope. Furthermore, a positive-locking switching element can be used as the drive output switching element.The actual starting process then occurs, for example, by changing the rotational speed of at least one of the two electric motors. A stationary shaft can have a rotational speed of zero.

[0027] Starting from a standstill in electric mode can be achieved with the drive output switching element in its open position, while the second electric motor is stationary and the first electric motor is rotating at a minimum speed. Starting is accomplished by moving the drive output switching element to its closed position. This allows for frictional engagement via the drive output switching element. Starting is thus simple, and prolonged standstill requires very little energy. If more than one drive output switching element is provided, they are all initially in their open position during such a start-up. Only the switching element corresponding to the desired direction of travel is then moved to the closed position. It can then be engaged via a slip connection between the output shaft of the drive transmission and the output of the driven machine.Such a starting procedure avoids reactive power loss at the second electric machine and allows both electric machines to be operated directly in a motor state, without, for example, first having to reverse the direction of rotation at the second electric machine and alternatively or additionally having to leave a generator operating state.

[0028] A second aspect concerns the drive train of a machine. The drive train can be designed to operate using the method described in the first aspect. The respective advantages and further characteristics can be found in the description of the first aspect, whereby embodiments of the first aspect also constitute embodiments of the second aspect and vice versa.

[0029] The powertrain comprises an internal combustion engine with a drive shaft, a continuously variable transmission (CVT) with an electric variator and a planetary gear set, a motor shift element, and an energy storage device. The CVT includes a first electric motor with a first motor shaft and a second electric motor with a second motor shaft. The energy storage device is electrically connected to both the first and second electric motors. The planetary gear set includes a first input shaft, a second input shaft, and an output shaft. The first motor shaft is mechanically connected to the first input shaft. The drive shaft is mechanically connected to the first input shaft via the motor shift element. The second motor shaft is mechanically connected to the second input shaft.

[0030] The powertrain includes a control device. The control device is configured to adjust the motor switching element to an open position in order to operate the powertrain in an electric operating mode and to control the provision of drive force by the powertrain in this electric operating mode, with both electric machines operating in their motor-like state. The control device may be configured to suppress regenerative operation of the two electric machines in the electric operating mode. The control device may, for example, include a microprocessor. The control device may be connected to a vehicle bus. The control device may be configured to generate the respective control signals. The electric operating mode may, for example, be activated by a driver.The control device may have a data storage device in which the respective control parameters and algorithms for data processing are stored.

[0031] In one embodiment of the drivetrain, the drivetrain includes an auxiliary unit that is mechanically connected to the first motor shaft. This auxiliary unit could, for example, be a pump for a power steering system. The mechanical connection of the auxiliary unit allows corresponding vehicle systems to continue to be driven even in electric operating mode.

[0032] In one embodiment of the drivetrain, the drivetrain includes a direction-of-travel switching assembly, wherein the output shaft of the drive transmission can be mechanically connected to a drive shaft with a selective direction of rotation via the direction-of-travel switching assembly. The drive shaft can be an output of the drivetrain or of the driven machine. By actuating the direction-of-travel switching assembly, the direction of rotation of the drive shaft relative to the output shaft can be reversed. For example, this allows switching between forward and reverse travel without requiring any changes to the control of the two electric motors. The direction-of-travel switching assembly can, for example, include one or more drive output switching elements. Depending on which drive output switching element is closed, either reverse or forward travel is enabled.For example, a first drive output switching element can connect the output shaft to the output via a spur gear chain with an even number of spur gear stages, and a second drive output switching element can connect the output shaft to the output via a spur gear chain with an odd number of spur gear stages.

[0033] According to the invention, the drive train is provided with a planetary assembly comprising a first planet gear set with a first sun gear, a first planet carrier, and a first ring gear; a second planet gear set with a second sun gear, a second planet carrier, and a second ring gear; a third planet gear set with a third sun gear, a third planet carrier, and a third ring gear; and a fourth planet gear set with a fourth sun gear, a fourth planet carrier, and a fourth ring gear. A planet gear set can, for example, be configured as a negative planet gear set or a positive planet gear set. For example, all planet gear sets of the planetary assembly are configured as negative planet gear sets. The sun gears, planet carriers, and ring gears of a planet gear set, for example, form its rotating elements. Each planet gear set can have one or more planet gears that are rotatably mounted on the planet carrier.For example, the planet gears of one planetary gear set mesh with a sun gear and a ring gear of another planetary gear set. The numbering serves only for identification purposes. For example, the second planetary gear set has only a sun gear, a planet carrier, and a ring gear. Each planetary gear set can be devoid of any elements other than those mentioned here.

[0034] The planetary assembly comprises a first switching element, a second switching element, a third switching element, a fourth switching element, and a brake. A brake can be a switching element by means of which a component can be locked in place, for example, by a rotationally fixed connection to a stationary component, such as a housing. For example, all switching elements of the planetary assembly are designed as friction-fit components.

[0035] The first ring gear is permanently and rotationally fixed to the first input shaft. The first sun gear is permanently and rotationally fixed to the second input shaft. The fourth planet carrier is permanently and rotationally fixed to the output shaft. The first planet carrier is permanently and rotationally fixed to the second ring gear. The first ring gear is permanently and rotationally fixed to the second planet carrier. The second sun gear is permanently and rotationally fixed to the third sun gear. The second ring gear is permanently and rotationally fixed to the third planet carrier. The third sun gear can be rotationally fixed to the fourth sun gear by means of the second switching element. The third planet carrier can be rotationally fixed to the fourth planet carrier by means of the third switching element. The third ring gear can be rotationally fixed to the fourth sun gear by means of the first switching element.The fourth planet carrier can be connected to the fourth sun gear in a rotationally fixed manner by means of the fourth switching element. The fourth ring gear can be locked in place by means of the brake. This can result in a planetary assembly with a high gear ratio spread, many operating ranges, and a compact design. The planetary assembly can be free of any rotating elements other than those described here.

[0036] When two elements are mechanically connected, they can be coupled directly or indirectly in such a way that a movement of one element can cause a reaction in the other. For example, a mechanical connection can be provided by a positive-locking or friction-locking connection. In a mechanical connection, for example, one or more spur gear stages can be involved in a drive power transmission. For example, the mechanical connection can correspond to the meshing of corresponding gear teeth of two elements.

[0037] Between mechanically interconnected elements, further elements, such as one or more spur gear stages, can be provided. A spur gear stage can be formed by two meshing spur gears.

[0038] A rotationally fixed connection between two elements is understood to be a connection in which the two elements are essentially rigidly coupled to each other in all intended states. This also includes a friction-fit connection, in which intentional or unintentional slippage can occur. Permanently rotationally fixed elements can, for example, exist as permanently rotationally fixed individual components or as a single piece.

[0039] A connection of two elements via another element can mean that this additional element can participate in an indirect functional connection between the two elements. For example, this element can be positioned in the force flow between these two elements. A connection of two elements via two or more elements can mean that these additional elements all participate in an indirect functional connection between the two elements. A switchable connection can, in one state, enable torque transmission between two elements, for example, through a rigid coupling, and, in another state, essentially interrupt this torque transmission. A corresponding switching element can be provided between the two elements for this purpose. If two elements can be connected in a rotationally fixed manner, these two elements can, for example, be connected to each other in a rotationally fixed manner via a switching element.If two elements can be mechanically connected, these two elements can, for example, be connected via a switching element for torque transmission.

[0040] A third aspect concerns a working machine with a drive train as described in the second aspect. The driving force of the working machine can be provided electrically via the drive train. The drive train can be switched between an electric operating mode and a normal operating mode. The respective advantages and further characteristics can be found in the descriptions of the first and second aspects, respectively, whereby embodiments of the first and second aspects also constitute embodiments of the third aspect and vice versa. Brief description of the characters Fig. Figure 1 schematically illustrates a drive train of a working machine. Fig. Figure 2 schematically illustrates a procedure for operating the drive train according to Fig. 1 in an electrical operating mode. Fig. Figure 3 schematically illustrates a first variant of a start-up using the work train according to Fig. 1 in the electrical operating mode. Fig. Figure 4 schematically illustrates a second variant of starting up with the work train according to Fig. 1 in the electrical operating mode. Detailed description of embodiments

[0041] Fig. Figure 1 schematically illustrates the drive train of a machine. The drive train comprises an internal combustion engine 10 with a drive shaft 12, a continuously variable transmission 14 with an electric variator 16 and a planetary gear set 18, a motor switching element K0, and an energy storage device 20. The variator 16 includes a first electric machine EM1 with a first motor shaft 22 and a second electric machine EM2 with a second motor shaft 24. The energy storage device 20 is electrically connected to the first electric machine EM1 via a first inverter 26 and to the second electric machine EM2 via a second inverter 28. The two inverters 26 and 28 can thus control the power supply and the operation of the two electric machines EM1 and EM2.

[0042] The planetary assembly 18 has a first input shaft 30, a second input shaft 32, and an output shaft 34. The first motor shaft 22 is mechanically connected to the first input shaft 30. The drive shaft 12 can be mechanically connected to the first input shaft 30 by means of the motor switching element K0.

[0043] The second motor shaft 24 is mechanically connected to the second input shaft 32.

[0044] The planetary assembly 18 comprises a first planet gear set 40 with a first sun gear 42, a first planet carrier 44 with first planet gears 48 rotatably mounted thereon, and a first ring gear 46; a second planet gear set 50 with a second sun gear 52, a second planet carrier 54 with second planet gears 58 rotatably mounted thereon, and a second ring gear 56; a third planet gear set 60 with a third sun gear 62, a third planet carrier 64 with third planet gears 68 rotatably mounted thereon, and a third ring gear 66; and a fourth planet gear set 70 with a fourth sun gear 72, a fourth planet carrier 74 with fourth planet gears 78 rotatably mounted thereon, and a fourth ring gear 76. The planet gear sets 40, 50, 60, and 70 are each configured as negative planet gear sets.The planetary assembly 18 has a first switching element K1, a second switching element K2, a third switching element K3, a fourth switching element K4 and a brake BG.

[0045] The first ring gear 46 is permanently and rotationally fixed to the first input shaft 30. The first sun gear 42 is permanently and rotationally fixed to the second input shaft 32. The fourth planet carrier 74 is permanently and rotationally fixed to the output shaft 34. The first planet carrier 44 is permanently and rotationally fixed to the second ring gear 56. The first ring gear 46 is permanently and rotationally fixed to the second planet carrier 54. The second sun gear 52 is permanently and rotationally fixed to the third sun gear 62. The second ring gear 56 is permanently and rotationally fixed to the third planet carrier 64. The third sun gear 62 can be rotationally fixed to the fourth sun gear 72 by means of the second switching element K2. The third planet carrier 64 can be rotationally fixed to the fourth planet carrier 74 by means of the third switching element K3. The third ring gear 66 can be connected to the fourth sun gear 72 in a rotationally fixed manner by means of the first switching element K1.The fourth planet carrier 74 can be connected to the fourth sun gear 72 in a rotationally fixed manner by means of the fourth switching element K4. The fourth ring gear 76 can be locked in place by means of the brake BG.

[0046] The drivetrain includes an auxiliary unit 80, which is mechanically connected to the first engine shaft 22. The auxiliary unit 80 comprises a constant-displacement pump 82 for supplying a power steering system, a constant-displacement pump 84 for supplying a transmission actuator, and an optional pump unit 86 for supplying other vehicle systems. These can then be driven independently of the operating state of the internal combustion engine 10. The drive shaft 12 can also be connected to the auxiliary unit via the engine switching element K0, so that the auxiliary unit can also be driven by the internal combustion engine 10. The spur gear chain provided for this purpose also mechanically connects the engine shaft 22 to the first input shaft 30 of the drive transmission 14.

[0047] The output shaft 34 of the drive transmission 14 is mechanically connected to an output 88 of the drive train via a direction-of-rotation switching assembly 90 with a selective direction of rotation. The direction-of-rotation switching assembly has a first drive output switching element KF for switching to forward travel and a second drive output switching element KR for switching to reverse travel. Only one of the two drive output switching elements KF or KR can be in its closed position at any given time. When the first drive output switching element KF is closed, the output shaft 34 is mechanically connected to the output 88 via two spur gear stages and a countershaft 92. When the second drive output switching element KR is closed, the output shaft 34 is mechanically connected to the output 88 via a spur gear stage.

[0048] The output shaft 88 is mechanically connected to a driven rear axle 96 via a differential 94. A service brake 98 can act on the rear axle 96 to decelerate the machine. The rear axle 96 also has a hub gear 100 for each wheel. In the illustrated embodiment, the output shaft 88 is also mechanically connected to a front axle (not shown) via a spur gear stage and an all-wheel drive switching element AS. In another embodiment, this connection is omitted, and there is only a rear axle drive instead of a switchable all-wheel drive. All switching elements described so far are designed for friction engagement.

[0049] The drive train includes a power take-off (PTO) shaft 102. The PTO shaft 102 is mechanically connected to the first input shaft 30 via a friction-fit PTO shift element ZS and a PTO gearbox 104. The PTO gearbox 104 can provide different gears for driving the PTO shaft 102 and can also reverse the direction of rotation. For this purpose, the PTO gearbox 104 has two positive-locking shift elements.

[0050] The drive train includes a control device 106, which incorporates the two inverters 26 and 28. The control device 106 is configured to adjust the motor switching element K0 to an open state in order to operate the drive train in an electric operating mode. The provision of drive force by the drive train is also controlled by the control device 106 in the electric operating mode. In the electric operating mode, both electric machines EM1 and EM2 are operated in their motor-like state when the machine is in motion. However, operation of the two electric machines EM1 and EM2 in a generator-like state is suppressed in the electric operating mode. Consequently, a portion of the possible gear ratio is lost in each driving range, which would otherwise require generator-like operation of the second electric machine EM2.The second electric machine EM2 can only be operated as a generator for short periods, for starting up and changing driving ranges.

[0051] The procedure for operating the working machine and the drive train is described in Fig. Figure 2 illustrates this. The diagram shows the rotational speeds of the two input shafts 30, 32 of the drive transmission plotted against a travel speed. Each speed range corresponds to specific travel ranges in which certain switching elements of the planetary assembly 18 are actuated. Curve 110 corresponds to the rotational speed of the first input shaft 30 and thus to the rotational speed of the first electric motor EM1 and therefore also to the rotational speed of the first motor shaft 22. Curve 120 corresponds to the rotational speed of the second input shaft 32 and thus to the rotational speed of the second electric motor EM2 and therefore also to the rotational speed of the second motor shaft 24. In a first travel range FB1, the first electric motor EM1 is already driven when the machine is stationary to power the auxiliary unit 80. The second electric motor EM2 remains stationary.During driving, the rotational speed of the second electric motor EM2 is increased to drive its second motor shaft 24. The second electric motor EM2 does not operate in generator mode during driving, as is typical in normal operating mode with the internal combustion engine 10 engaged and coupled, where a particularly low gear ratio is provided by rotating the first sun gear 42 accordingly. Therefore, in electric operating mode, only a portion of the gear ratio variation provided by the variator 16 is utilized.

[0052] The same applies to the subsequent travel ranges FB2, FB3, and FB4, to which a switch is made by adjusting the switching elements of the planetary assembly 18 at a synchronization point with the previous travel range. In travel ranges FB2 and FB4, however, the second electric machine EM2 rotates in the opposite direction to operate as a motor rather than a generator. Thus, during the travel range change, the drive train first provides the drive force in electric operating mode, with both electric machines EM1 and EM2 operating in their motor mode. A switch then occurs to another travel range in electric operating mode. This switch involves controlling both electric machines EM1 and EM2 so that they again operate in their motor mode.In the illustrated embodiment, this involves a reversal of the direction of rotation in the second electric machine EM2. Until the direction of rotation is reversed, the second electric machine EM2 optionally operates in generator mode.

[0053] Two options are provided for starting the machine from a standstill using the drivetrain. The first option is in Fig. Figure 3 shows that the two electric machines EM1 and EM2 are controlled such that their rotational speeds are superimposed at the two input shafts 30 and 32. Fig. Figure 3 again shows characteristic curves 110 and 120. At standstill, the first input shaft 30 rotates at a predetermined speed in one direction, and the second input shaft 32 rotates at a predetermined speed in the opposite direction. The second electric machine EM2 can be operated as a generator or as a motor. The first electric machine EM1 is operated as a motor. The rotation of the first input shaft 30 (or the first ring gear 46) and the rotation of the second input shaft 32 (or the first sun gear 42) cancel each other out, so that the first planet carrier 44 is stationary. Furthermore, the one of the two drive output switching elements KF, KR in whose corresponding direction of travel the machine is to be started is closed. Thus, the first planet carrier 44, and therefore also the output 88, is subjected to torque and can hold the machine stationary even on an incline.

[0054] The second option is in Fig. Figure 4 shows the characteristic curves 110 and 120 again. In this scenario, both drive output switching elements KF and KR are initially open. The second electric motor EM2 is stationary, while the first electric motor EM1 is already rotating to drive the auxiliary unit 80. The drive output switching element KF or KR corresponding to the direction of travel is then closed. This creates an initially slipping connection at either drive output switching element KF or KR for starting. Once a synchronous speed is reached at either drive output switching element KF or KR, it is fully closed and energized. Subsequently, the speed of the second electric motor EM2 is increased to continuously vary the gear ratio at the drive transmission 14. Reference sign 10 Internal combustion engine 12 Drive shaft 14 Driving gear 16 electric variator 18 planetary assembly 20 energy storage 22, 24 motor shafts 26, 28 Inverter 30, 32 input waves 34 Output shaft 40, 50, 60, 70 planetary gear set 42, 52, 62, 72 Sun wheel 44, 54, 64, 74 Planetary carriers 46, 56, 66, 76 Ring gear 48, 58, 68, 78 planetary gears 80 Auxiliary unit 82, 84 constant pumps 86 Pump unit 88 Drive 90 Direction change assembly 92 Countershaft 94 Differential 96 Rear axle 98 Service brake 100 hub gears 102 PTO 104 PTO gearbox 106 Control device 110 Characteristic curve: Speed ​​of the first input shaft 120 Characteristic curve: Speed ​​of the second input shaft K0 Motor switching element K1-K4 switching elements BG brake EM1, EM2 Electrical Machines KF, KR drive output switching elements AS all-wheel drive switching element ZS PTO switching element FB1-FB4 Driving areas

Claims

[1] A method for operating a drive train of a work machine, wherein the drive train comprises an internal combustion engine (10) with a drive shaft (12), a continuously variable transmission (14) with an electric variator (16) and a planetary assembly (18), a motor switching element (K0) and an energy storage device (20), wherein the variator (16) comprises a first electric machine (EM1) with a first motor shaft (22) and a second electric machine (EM2) with a second motor shaft (24), wherein the energy storage device (20) is electrically connected to the first (EM1) and the second electric machine (EM2), wherein the planetary assembly (18) comprises a first input shaft (30), a second input shaft (32) and an output shaft (34), wherein the first motor shaft (22) is mechanically operatively connected to the first input shaft (30), wherein the drive shaft (12) is connected to the first input shaft (30) by means of the motor switching element (K0). can be mechanically connected,and wherein the second motor shaft (24) is mechanically operatively connected to the second input shaft (32), the method comprising at least the following steps: - Adjusting the engine switching element (K0) to an open state in order to operate the drive train in an electric operating mode; and - Providing a driving force through the drive train in the electric operating mode, wherein both electric machines (EM1, EM2) are operated in their motor operating state, characterized by that the planetary assembly (18) is designed to provide a plurality of driving ranges (FB1, FB2, FB3, FB4), the method further comprising the following steps: - Providing the drive force by the drive train in one of the driving ranges (FB1, FB2, FB3, FB4) in the electric operating mode, wherein both electric machines (EM1, EM2) are operated in their motor operating state; - Change to another driving range (FB1, FB2, FB3, FB4) in the electric operating mode; and - Controlling the two electric machines (EM1, EM2) so that both electric machines (EM1, EM2) are again operated in their motor operating state. [2] Method according to claim 1, characterized by that the control of the two electric machines (EM1, EM2) so that both electric machines (EM1, EM2) are again operated in their motor operating state involves a reversal of the direction of rotation of one of the two electric machines (EM1, EM2). [3] Method according to claim 1 or 2, characterized by that when changing to the other driving range (FB1, FB2, FB3, FB4) in the electrical operating mode, at least one of the two electric machines (EM1, EM2) is operated with an overload condition. [4] Method according to one of the preceding claims, characterized bythat when the working machine accelerates in the electric operating mode, at least one of the two electric machines (EM1, EM2) is operated in an overload operating mode in order to at least reduce a tractive force gap compared to when the working machine accelerates in a normal operating mode with the internal combustion engine switched on and the motor switching element (K0) in a closed state. [5] Method according to one of the preceding claims, characterized by in that the method comprises a step of checking whether a deactivation condition for the electric operating mode exists during operation of the drive train in the electric operating mode, wherein in response to the existence of the deactivation condition the motor switching element (K0) is adjusted to its closed state in order to return to the normal operating mode of the drive train. [6] Method according to one of the preceding claims, characterized by that the drive train has at least one drive output switching element (KF, KR) and starting in the electric operating mode from a standstill takes place by adjusting the drive output switching element (KF, KR) to its closed state and controlling the two electric machines (EM1, EM2) in such a way that the speeds at the input shafts (30, 32) overlap in such a way that the output shaft (34) is at a standstill. [7] Method according to one of the preceding claims 1 to 5, characterized bythat the drive train has at least one drive output switching element (KF, KR) and starting in the electric operating mode from a standstill with the drive output switching element (KF, KR) in its open state, with the second electric machine (EM2) stationary and the first electric machine (EM1) rotating at a minimum speed, by adjusting the drive output switching element (KF, KR) to its closed state. [8] Drive train of a work machine, wherein the drive train comprises an internal combustion engine (10) with a drive shaft (12), a continuously variable transmission (14) with an electric variator (16) and with a planetary assembly (18), a motor switching element (K0) and an energy storage device (20), wherein the variator (16) comprises a first electric machine (EM1) with a first motor shaft (22) and a second electric machine (EM2) with a second motor shaft (24), wherein the energy storage device (20) is electrically connected to the first electric machine (EM1) and the second electric machine (EM2), wherein the planetary assembly (18) comprises a first input shaft (30), a second input shaft (32) and an output shaft (34), wherein the first motor shaft (22) is mechanically operatively connected to the first input shaft (30), wherein the drive shaft (12) is mechanically connected to the first input shaft (30) by means of the motor switching element (K0) is effectively connectable,and wherein the second motor shaft (24) is mechanically operatively connected to the second input shaft (32), wherein the drive train has a control device (106) which is designed to adjust the motor switching element (K0) to an open state in order to operate the drive train in an electrical operating mode, and to control a provision of a driving force by the drive train in the electrical operating mode, wherein both electric machines (EM1, EM2) are operated in their motor operating state in the electrical operating mode, , characterized bythat the planetary assembly (18) comprises a first planetary gear set (40) with a first sun gear (42), a first planetary carrier (44) and a first ring gear (46), a second planetary gear set (50) with a second sun gear (52), a second planetary carrier (54) and a second ring gear (56), a third planetary gear set (60) with a third sun gear (62), a third planetary carrier (64) and a third ring gear (66), a fourth planetary gear set (70) with a fourth sun gear (72), a fourth planetary carrier (74) and a fourth ring gear (76), a first shifting element (K1), a second shifting element (K2), a third shifting element (K3), a fourth shifting element (K4) and a brake (BG), wherein the first ring gear (46) is permanently connected to the first input shaft (30) in a rotationally fixed manner, wherein the first sun gear (42) is permanently connected to the second input shaft (32) in a rotationally fixed manner is,wherein the fourth planet carrier (74) is permanently connected to the output shaft (34) in a rotationally fixed manner, wherein the first planet carrier (44) is permanently connected to the second ring gear (56) in a rotationally fixed manner, wherein the first ring gear (46) is permanently connected to the second planet carrier (54) in a rotationally fixed manner, wherein the second sun gear (52) is permanently connected to the third sun gear (62) in a rotationally fixed manner, wherein the second ring gear (56) is permanently connected to the third planet carrier (64) in a rotationally fixed manner, wherein the third sun gear (62) is rotationally fixedly connected to the fourth sun gear (72) by means of the second switching element (K2), wherein the third planet carrier (64) is rotationally fixedly connected to the fourth planet carrier (74) by means of the third switching element (K3), wherein the third ring gear (66) is rotationally fixedly connected to the fourth sun gear (72) by means of the first switching element (K1),wherein the fourth planet carrier (74) is rotatably connected to the fourth sun gear (72) by means of the fourth shift element (K4), and wherein the fourth ring gear (76) is lockable by means of the brake (BG). [9] Drive train according to claim 8, characterized by that the drive train has an auxiliary unit (80) which is mechanically connected to the first motor shaft (22). [10] Drive train according to claim 8 or 9, characterized by in that the drive train has a direction-changing assembly (90), wherein the output shaft (34) of the drive transmission (14) is mechanically operatively connectable to an output via the direction-changing assembly (90) with a selective direction of rotation. [11] Working machine with a drive train according to one of claims 8 to 10, characterized by that the driving force of the working machine can be provided electrically by means of the drive train.

Images