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

Abstract

The invention relates to a method for operating an electrified drive train of a work machine, the drive train comprising an electric drive motor, an inverter associated with the electric drive motor and an accelerator pedal, a motor rotational speed and a motor torque (100) being provided by the drive motor as a function of the position of the accelerator pedal, a motor operation (101) of the drive motor is detected by means of the inverter when a motor torque greater than a motor threshold torque is provided, and a generator operation (102) of the drive motor is detected by means of the inverter when a generator torque greater than a generator threshold torque is provided, and wherein the generator torque is greater than the generator threshold torque. When the generator torque is less than the generator threshold torque and the motor torque is less than the motor threshold torque, a torque-free state of the drive motor is detected by means of the inverter (103). The method according to the invention is characterized in that a maximum motor speed is assigned to each position of the accelerator pedal, and a motor fault (110) is detected when the determined motor speed is higher than the assigned speed (108) and motor operation of the drive motor is detected at the same time. The invention also relates to a corresponding electrified drive train of a work machine and to a corresponding work machine.

Description

Technical Field

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

[0002] In the prior art, various types of electrically driven working machines are known, such as wheel loaders, compact loaders, telescopic loaders, dump trucks or excavators. These working machines have in common that they are either purely electrically driven, i.e. they have only batteries or fuel cells as energy storage devices. However, they are either diesel-electrically driven, which means that the required energy is provided by a diesel-driven generator and, if necessary, by an electrical buffer store (e.g. a correspondingly dimensioned capacitor or a relatively small battery). In all the cases mentioned, however, the mechanical power required for operating the working machine is applied by one or more electric motors.

[0003] In this context, EP 0 962 597 A2 describes a battery-driven working machine having two electric motors for travel drive and a further electric motor for working drive.

[0004] DE 102020201497.3, which has not yet been published by the applicant, discloses a method for operating an electrified drive train of a working machine. By combining a mechanism for detecting a slope with a mechanism for detecting the forward movement of the working machine, downhill travel of the working machine can be detected. If the working machine exceeds a threshold speed when traveling downhill, the electric motor is put into regenerative operation in order to prevent further acceleration of the working machine due to the downhill force.

[0005] The applicant also knows a method for monitoring an electric drive motor of a working machine, wherein the torque provided by the drive motor is monitored, thereby making it possible to detect, for example, an unexpected start, a wrong-way start, an unexpected acceleration, an unexpected deceleration or a time delay in carrying out the driver's wishes.

[0006] However, known electrified drive trains for working machines have the disadvantage that, depending on the specific embodiment of the inverter for controlling the electric motor, they cannot reliably determine the torque provided by the electric motor at every operating point. Thus, in this case, it is not possible to compare the actual torque with the target torque in order to detect a possible motor fault. Therefore, monitoring of the electric motor during operation is only possible to a limited extent. Summary of the invention

[0007] The object of the present invention is to propose an improved method for operating an electrified drive train of a work machine.

[0008] This object is achieved according to the invention by a method for operating an electrified drive train of a work machine according to claim 1. Advantageous embodiments and developments of the invention are revealed in the dependent claims.

[0009] The invention relates to a method for operating an electrified drive train of a working machine, wherein the drive train comprises an electric drive motor, an inverter assigned to the electric drive motor, and an accelerator pedal, wherein a motor speed and a motor torque are provided by the drive motor depending on the position of the accelerator pedal, wherein motor operation of the drive motor is detected by means of the inverter when a motor torque greater than a motor threshold torque is provided, wherein generator operation of the drive motor is detected by means of the inverter when a generator torque greater than a generator threshold torque is provided, and wherein a torque-free state of the drive motor is detected by means of the inverter when the generator torque is less than the generator threshold torque and the motor torque is less than the motor threshold torque. The method according to the invention is characterized in that a maximum motor speed is respectively assigned to each position of the accelerator pedal, and a motor fault is detected when the detected motor speed is higher than the assigned speed and motor operation of the drive motor is detected at the same time.

[0010] The invention describes a method according to which an electrified drive train can be operated. The drive train is suitable for operating a working machine. Since working machines are usually operated at high drive loads most of the time and must provide a relatively high operating efficiency, in particular in an absolute sense, the drive train according to the invention differs in its design, for example, from a passenger car drive train, which is usually operated in a load range of 5% to 10% of the maximum power and in particular provides a relatively low absolute operating efficiency.

[0011] The drive system includes an electric drive motor, an inverter assigned to the electric drive motor, and an accelerator pedal.

[0012] Advantageously, the drive train can also include further components, such as a transmission, a further electric motor, a battery storage device and drivable wheels of the work machine.

[0013] The electric drive motor can be designed, for example, as a synchronous motor or an asynchronous motor, in particular as a three-phase synchronous motor or a three-phase asynchronous motor.

[0014] The inverter assigned to the drive motor is advantageously designed to control the drive motor, in particular the motor speed and the motor torque of the drive motor, by suitable energization.

[0015] The motor speed and the motor torque together indicate the drive power.

[0016] The inverter is further configured to detect whether the drive motor provides a motor torque that is above a threshold motor torque and to detect whether the drive motor provides a generator torque that is above a threshold generator torque. Preferably, the absolute values ​​of the generator torque and the motor torque are considered. An equivalent and equally effective solution is to consider the actual magnitudes of the generator torque and the motor torque, wherein the generator threshold torque has an opposite sign to the motor threshold torque.

[0017] If the absolute value of the motor torque is below the motor threshold torque and at the same time the absolute value of the generator torque is below the generator threshold torque, the inverter cannot recognize motor operation or generator operation. In this case, even if the drive motor provides a small motor torque below the motor threshold torque or a small generator torque below the generator threshold torque, the inverter recognizes the torque-free state of the drive motor. This behavior (not being able to recognize a small motor torque or a small generator torque, but recognizing a torque-free state of the drive motor) is typical for inverter series available on the market, especially for some low-cost inverters.

[0018] In summary, the inverter is thus able to identify and distinguish between three different operating states of the drive motor, namely motor operation, generator operation and torque-free state. In particular, due to its construction, the inverter cannot detect the magnitude of the motor torque provided in motor operation and the magnitude of the generator torque provided in generator operation.

[0019] The accelerator pedal can advantageously be actuated by the operator of the work machine, so that the drive motor is controlled by the inverter in such a way that it provides a motor speed and a motor torque corresponding to the position of the accelerator pedal. The relationship between the position of the accelerator pedal and the provided motor speed and provided motor torque can be, for example, linear or exponential. This relationship can be stored, for example, in the form of a mathematical formula or a characteristic curve in an electronic control device, which reads the position of the accelerator pedal and, for this purpose, causes the inverter to control the drive motor according to the position.

[0020] According to the invention, it is now provided that a maximum motor speed is assigned to each position of the accelerator pedal and that a motor failure is detected when the ascertained motor speed is higher than the assigned speed and motor operation of the drive motor is detected at the same time.

[0021] Here, a motor failure is understood to be a functional failure in the control of the drive motor, which is not necessarily caused by mechanical or electrical properties of the drive motor but may also be caused by a failure of the inverter or a failure of the control unit.

[0022] Thus, a safety function in the form of a fault detection can be advantageously provided, wherein the fault detection always detects a functional fault in the control of the drive motor when the motor speed is already greater than the maximum motor speed assigned to the corresponding position of the accelerator pedal but the drive motor still provides torque. In other words, a functional fault in the control of the drive motor is detected when the working machine has reached or exceeded the speed assigned to the corresponding position of the accelerator pedal and still continues to accelerate. Advantageously, the motor speed can be detected by a speed sensor and independently of the inverter.

[0023] Thus, by cleverly introducing the maximum rotational speed respectively assigned to the position of the accelerator pedal, malfunctions in the control of the drive motor can be reliably detected even if the inverter is not sufficiently designed to detect erroneous control of the drive motor.

[0024] According to a preferred embodiment of the present invention, it is provided that each position of the accelerator pedal is assigned a maximum motor speed by means of a characteristic curve. A plurality of corresponding characteristic curves are obtained by means of a plurality of possible positions of the accelerator pedal, so that advantageously each position of the accelerator pedal can also be assigned a corresponding maximum motor speed by means of a comprehensive characteristic curve. Here, the maximum speed is a speed respectively assigned to the position of the accelerator pedal, and a motor fault is detected as long as the motor operation is detected while the speed is exceeded. Here, a continuous assignment of the position of the accelerator pedal to the motor speed can be realized relatively simply by means of a characteristic curve or a comprehensive characteristic curve.

[0025] It is preferably provided that the maximum motor speed respectively assigned to each position of the accelerator pedal corresponds to the motor speed reached by the drive motor when the work machine is traveling in a straight line on a flat surface without a slope, taking into account the respectively provided motor torque. Particularly preferably, the maximum motor speed respectively assigned to each position of the accelerator pedal can be 10% higher than the motor speed reached by the drive motor when the work machine is traveling in a straight line on a flat surface without a slope, taking into account the respectively provided motor torque. Thus, for example, when traveling downhill slightly or briefly, a motor failure is not immediately detected if the motor speed is temporarily accelerated due to the downhill force acting on the work machine.

[0026] According to another preferred embodiment of the present invention, when a motor failure is detected, the operation of the drive motor is stopped by means of the inverter. Here, stopping the operation of the inverter is understood as a state in which the drive motor no longer generates a rotational speed and a torque. Therefore, the drive motor can no longer pose a danger.

[0027] According to a particularly preferred embodiment of the present invention, it is provided that the drive motor is de-energized. It is particularly preferred that the drive motor is switched to be voltage-free. This means that no current flows through the coils of the drive motor any more and no voltage is applied to the coils of the drive motor any more.

[0028] According to another preferred embodiment of the invention, at least one drive wheel coupled to the electric drive motor is driven by the drive motor, wherein the motor speed is determined by means of the measured wheel speed. Since the drive wheels of the work machine are usually equipped with speed sensors, the speed of at least one wheel can also be measured. Therefore, the speed of the drive motor can be inferred from the known transmission ratio from the drive motor to the drive wheel in the drive train.

[0029] The present invention also relates to an electrified drive train for a working machine, comprising an electric drive motor, an inverter assigned to the electric drive motor, and an accelerator pedal, wherein the drive train is configured to provide a motor speed and a motor torque from the drive motor depending on the position of the accelerator pedal, wherein the drive train is configured to allow the inverter to recognize motor operation of the drive motor when the drive motor provides a motor torque greater than a motor threshold torque, wherein the drive train is configured to allow the inverter to recognize generator operation of the drive motor when the drive motor provides a motor torque greater than a generator threshold torque, and wherein the drive train is configured to allow the inverter to recognize a torque-free state of the drive motor when the generator torque is less than the generator threshold torque and the motor torque is less than the motor threshold torque. The drive train according to the present invention is characterized in that the drive train is configured to respectively assign a maximum motor speed to each position of the accelerator pedal, and a motor fault is recognized when the motor speed detected by the inverter is higher than the assigned speed and motor operation of the drive motor is simultaneously recognized.

[0030] As a result, the advantages already described in conjunction with the method according to the invention also apply to the drive train according to the invention.

[0031] The electrified drive train according to the invention comprises all devices and means for carrying out the method according to the invention.

[0032] Finally, the present invention also relates to a working machine comprising a drive train according to the present invention, so that the advantages already described in connection with the drive train according to the present invention also apply to the working machine according to the present invention.

[0033] The work machine is preferably a wheel loader. However, it can also be a compact loader, a telescopic loader, a dump truck, an excavator or a tractor. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be described below by way of example with reference to the embodiments shown in the drawings.

[0035] in:

[0036] Figure 1 The generator torque of the drive motor, the motor torque of the drive motor as well as the generator threshold torque and the motor threshold torque are shown by way of example and schematically on the torque axis,

[0037] Figure 2 shows by way of example a maximum motor torque and a maximum generator torque, each as a function of the motor speed of the drive motor,

[0038] Figure 3a~ Figure 3b A series of maximum motor torques as a function of the motor speed of the drive motor at different accelerator pedal positions is shown as a characteristic curve, and

[0039] Figure 4 A possible embodiment of the method according to the invention for operating an electrified drive train of a work machine is shown by way of example in the form of a flow chart.

[0040] The same objects, functional units and similar components are identified in all figures using the same reference numerals. Unless otherwise indicated explicitly or implicitly in the specification, these objects, functional units and similar components are implemented identically with respect to their technical features. DETAILED DESCRIPTION

[0041] Figure 1 The generator torque 11 of the drive motor, the motor torque 12 of the drive motor, and the generator threshold torque 13 and the motor threshold torque 14 are shown by way of example and schematically on the torque axis 10. Due to the specific design of the inverter used by way of example, it is not possible to precisely detect a torque-free state of the drive motor, i.e., it is not possible to precisely detect that the motor torque 12 is zero or that the generator torque 11 is zero. Instead, the inverter can only detect the motor torque 12 when the motor threshold torque 14 is exceeded, and similarly, the inverter can only detect the generator torque 11 when the generator threshold torque 14 is exceeded. Therefore, the inverter always detects a torque-free state of the drive motor when the motor torque 12 provided by the drive motor is less than the motor threshold torque 14 or the generator torque provided by the drive motor is less than the generator threshold torque 13.

[0042] Figure 2 The maximum motor torque 12 and the maximum generator torque 11 are shown as an example, each depending on the motor speed of the drive motor. As can be seen, the maximum motor torque 12 and the maximum generator torque 11 each decrease with increasing motor speed, which is a typical behavior of electric machines.

[0043] Each characteristic curve 20, 21, 22, 23, 24, 25, 26, 27 shows the motor torque 12 at a specific accelerator pedal position over the motor speed. The characteristic curve 20 shows the generator torque 20 over the motor speed in generator operation. The region 50 describes, by way of example, a region in which the motor torque 12 and the generator torque 11 are less than the motor threshold torque 14 or the generator threshold torque 13, so that the inverter can detect a standstill of the drive motor.

[0044] FIG. 3 a shows, by way of example, a series of maximum motor torques 12 as a function of the motor speed of the drive motor at different accelerator pedal positions as characteristic curves 20, 21, 22, 23, 24, 25, 26, 27, 28. The accelerator pedal position is indicated by an arrow 30. FIG. 3 a is in this respect Figure 2 As can be seen further, each characteristic curve 20, 21, 22, 23, 24, 25, 26, 27, 28 is assigned a maximum motor speed at which the motor torque 12 is zero. The respective maximum motor speeds are marked with red dots.

[0045] The speed determined in this way and dependent on the accelerator pedal position can be generated as follows: Figure 3b The characteristic curve 30 is shown. The characteristic curve assigns a maximum motor speed to each position of the accelerator pedal. Thus, a motor fault can be detected with the aid of the characteristic curve 30 by determining a motor speed that is higher than the speed assigned by the characteristic curve 30 for the current accelerator pedal position and simultaneously detecting motor operation of the drive motor.

[0046] Figure 4 A possible embodiment of the method according to the invention for operating an electrified drive train of a work machine is shown by way of example in the form of a flow chart. The drive train comprises an electric drive motor, an inverter associated with the electric drive motor, and an accelerator pedal.

[0047] In a first method step 100 , a motor speed and a motor torque of a drive motor are provided as a function of an accelerator pedal position.

[0048] Subsequently, when a motor torque 12 is provided that is greater than the motor threshold torque 14, the motor operation of the drive motor is detected in step 101 with the aid of the inverter. Otherwise, when a generator torque 11 is provided that is greater than the generator threshold torque 13, the generator operation of the drive motor is detected in step 102 with the aid of the inverter. If neither the motor operation nor the generator operation is detected, a torque-free state of the drive motor is detected in step 103 with the aid of the inverter, because the generator torque 11 is less than the generator threshold torque 13 and the motor torque 12 is less than the motor threshold torque 14.

[0049] If electric motor operation is detected in step 101 , the method continues with step 104 .

[0050] In the next step 104 , the rotational speed of a drive wheel of the work machine driven by the drive motor is detected. The rotational speed of the drive wheel is used by way of example to calculate the rotational speed of the drive motor in step 105 taking into account the known transmission ratio between the motor shaft of the drive motor and the drive wheel.

[0051] In step 106 , the calculated rotational speed is used in order to determine the maximum rotational speed of the drive motor corresponding to the current accelerator pedal position using characteristic curve 30 as a function of the current accelerator pedal position.

[0052] If it is detected in step 107 that the rotational speed of the drive motor is below the maximum rotational speed which is predetermined by characteristic curve 30 and corresponds to the accelerator pedal position, the method starts again with step 100 .

[0053] However, if it is detected in step 108 that the rotational speed of the drive motor is higher than the maximum rotational speed specified by characteristic curve 30 and corresponding to the accelerator pedal position, a check is performed in step 109 as to whether motor torque 12 is currently being provided by the drive motor.

[0054] If the motor torque 12 is not available, the method starts over again with step 100 .

[0055] However, if it is determined that the motor torque 12 is being provided, a motor fault is detected in step 110. In step 111, the operation of the drive motor is stopped by de-energizing the drive motor and de-voltage.

[0056] Reference numerals list

[0057] 10 Moment axis

[0058] 11 Generator torque

[0059] 12 Motor torque

[0060] 13 Generator threshold torque

[0061] 14 Motor threshold torque

[0062] 20 Motor torque-motor speed characteristic curve

[0063] 21 Motor torque-motor speed characteristic curve

[0064] 22 Motor torque-motor speed characteristic curve

[0065] 23 Motor torque-motor speed characteristic curve

[0066] 24 Motor torque-motor speed characteristic curve

[0067] 25 Motor torque-motor speed characteristic curve

[0068] 26 Motor torque-motor speed characteristic curve

[0069] 27 Motor torque-motor speed characteristic curve

[0070] 28 Motor torque-motor speed characteristic curve

[0071] 30 Accelerator pedal position-speed characteristic curve

[0072] 40 Arrow, accelerator pedal position

[0073] 50 Area in which the standstill of the drive motor is detected

[0074] 100 Provides motor torque

[0075] 101 Motor running detected

[0076] 102 Generator running detected

[0077] 103 Stop state detected

[0078] 104 Detecting the speed of the driving wheel

[0079] 105 Calculate the speed of the drive motor

[0080] 106 Get the maximum speed based on the accelerator pedal position

[0081] 107 Speed ​​detected to be lower than the maximum speed

[0082] 108 Speed ​​detected to be higher than the maximum speed

[0083] 109 Check: Is the motor torque provided?

[0084] 110 Motor fault detected

[0085] 111 Stop the drive motor

Claims

1. A method for operating an electrified drive train of a working machine, wherein: The drive system comprises an electric drive motor, an inverter assigned to the electric drive motor, and an accelerator pedal, wherein a motor speed and a motor torque (100) are provided by the drive motor depending on the position of the accelerator pedal, wherein when a motor torque greater than a motor threshold torque is provided, motor operation of the drive motor is detected with the aid of the inverter (101), wherein when a generator torque greater than a generator threshold torque is provided, generator operation of the drive motor is detected with the aid of the inverter (102), and wherein when the generator torque is less than the generator threshold torque and the motor torque is less than the motor threshold torque, a torque-free state (103) of the drive motor is detected with the aid of the inverter, The invention is characterized in that a maximum motor speed is respectively assigned to each position of the accelerator pedal, and a motor fault (110) is detected when the detected motor speed is higher than the assigned speed (108) and at the same time motor operation of the drive motor is detected.

2. The method according to claim 1, It is characterized in that A maximum engine speed is assigned to each position of the accelerator pedal using a characteristic curve.

3. The method according to at least one of claims 1 and 2, It is characterized in that When a motor failure is detected ( 110 ), the operation of the drive motor is stopped by means of the inverter ( 111 ).

4. The method according to claim 3, It is characterized in that The drive motor is de-energized (111).

5. The method according to at least one of claims 1 to 4, It is characterized in that At least one drive wheel drivingly coupled to the electric drive motor is driven by the drive motor, The motor speed (104) is thereby determined using the measured wheel speed.

6. An electrified drive system for a working machine, the drive system comprising an electric drive motor, an inverter assigned to the electric drive motor, and an accelerator pedal, wherein: The drive system is configured to cause the drive motor to provide a motor speed and a motor torque according to the position of the accelerator pedal, wherein the drive system is configured to cause the inverter to recognize that the drive motor is in motor operation when the drive motor provides a motor torque greater than a motor threshold torque, wherein the drive system is configured to cause the inverter to recognize that the drive motor is in generator operation when the drive motor provides a motor torque greater than a generator threshold torque, and wherein the drive system is configured to cause the inverter to recognize that the drive motor is in a torque-free state when the generator torque is less than the generator threshold torque and the motor torque is less than the motor threshold torque, The drive system is designed to assign a maximum motor speed to each position of the accelerator pedal and to detect a motor failure when the motor speed detected by the inverter is higher than the assigned speed and motor operation of the drive motor is detected at the same time.

7. A working machine comprising a drive train according to claim 6.

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