Method for controlling electric drive train of working machine and corresponding control device

Abstract

The invention relates to a method for controlling an electric drive train (22) of a work machine. The method has a step of determining (40) whether a brake pedal actuation is performed with an actuation stroke greater than an actuation stroke threshold for an actuation duration longer than the actuation duration threshold. Furthermore, the method has a step of determining (42) whether there is no drive torque maintenance condition when the brake pedal (12) has been intensively actuated for a long period of time. Furthermore, the method has a step of generating (44) a control signal to disconnect the generation of torque by the electric drive train (22) when there is no drive torque maintenance condition. The invention further relates to a control device (18) for an electric drive train (22) and to a work machine having an electric drive train (22).

Description

Technical Field

[0001] The invention relates to a method for controlling an electric drive train of a working machine. The invention also relates to a control device for an electric drive train of a working machine and to a working machine. Background Art

[0002] In conventional drive trains for working machines with internal combustion engines, it is usually possible to provide an interruption in the transmission of torque by means of a clutch. In the event of emergency braking by the driver of the working machine, the clutch can be disconnected immediately. As a result, no torque is transmitted from the drive train to the output. The corresponding wheel is thus decoupled, for example, from the engine shaft of the working machine. As a result, the working machine can also be safely braked to a standstill in the event of a fault.

[0003] Due to the electrification of the working machine, such a mechanical interruption of the torque transmission is no longer possible. Furthermore, the control behavior of the electrified working machine may also differ from that in the case of a working machine with an internal combustion engine. For example, the brakes may be actuated more frequently and alternatively or additionally more strongly in order to regain energy by recuperation and thus increase the efficiency of the use of the working machine. In this case, the interruption of the torque transmission should not be achieved in an undesirable manner. However, it should also be ensured that the torque transmission is interrupted in an emergency situation. Summary of the invention

[0004] A first aspect of the invention relates to a method for controlling an electric drive system of a working machine. The method can be performed, for example, by a control device for an electric drive system of a working machine. For example, the control device can be integrated in an inverter, which provides electrical energy to an electric motor of the drive system. The working machine can be configured, for example, as an agricultural machine, such as a tractor, as a construction machine, or as a special vehicle. The working machine can be configured as a vehicle. The drive system can be configured to provide drive power to the working machine at an output end (e.g., a corresponding driven wheel). Optionally, the drive system can be additionally configured to provide power output power. The driving power can facilitate the travel of the working machine. The power output power can be used to supply power to a tool of the working machine, such as an adjustable shovel or a hydraulic pump.

[0005] The electric drive train can have an electric motor having a motor shaft for providing drive power for the working machine. For example, the electric motor can be configured to supply power to the drive train of the working machine. The drive train can have an energy source for operating the electric motor of the drive train. For example, the drive train can have a battery, which is configured to provide electrical energy to the electric motor. The electric motor can be configured to convert electrical energy into mechanical energy. Optionally, the electric motor can also be configured for recovery, wherein mechanical energy can be converted into electrical energy. The electric motor can be configured, for example, as a synchronous motor or an asynchronous motor.

[0006] The working machine may have a braking system. The braking system may be controlled via a brake pedal. When the braking system is actuated, it may act on the output of the drive train in a decelerating manner and, alternatively or additionally, on the working machine. The braking system may, for example, have disk brakes or drum brakes on the respective axle of the working machine. The braking system may, for example, be designed for mechanical, hydraulic or electrical actuation.

[0007] The method has the following steps, namely, determining whether a brake pedal actuation has been performed with an actuation stroke greater than an actuation stroke threshold value within an actuation duration longer than an actuation duration threshold value. For this purpose, corresponding sensors can be provided. For example, respective sensor signals can be evaluated by a microcontroller, which can be constructed as part of a control device. The brake pedal can be an actuation element, by means of which a driver of a working machine can predetermine a braking force. The brake pedal can be constructed for actuation by means of a driver's foot. The brake pedal can also be constructed for single-handed operation, for example as a lever. For determination, the position of the brake pedal can be detected. The actuation stroke can correspond to a deflection of the brake pedal. The actuation stroke can be a road section, and alternatively or additionally can be an angle relative to an un-actuated position of the brake pedal. For example, a deflection of the brake pedal from an un-actuated position (especially as a percentage of a maximum actuation) can be detected. The actuation duration can be a duration of actuation of the brake pedal. For example, the actuation duration can be a duration of actuation of the brake pedal at least further than the actuation stroke threshold value. The actuation stroke threshold value can be a minimum actuation stroke. The actuation duration threshold value can be a minimum actuation duration.

[0008] For example, it can be determined whether the brake pedal has been actuated with an actuation path greater than 99% of the maximum actuation path within an actuation duration longer than 500 ms. By means of a corresponding check, it can be ensured that only actual emergency braking is taken into account. Unintentional actuation of the brake pedal with an actuation path greater than an actuation path threshold value occurs, for example, mostly within a shorter duration. Such unintentional actuation can occur, for example, due to vibrations of the work machine, fluctuations of the driver and, alternatively or additionally, due to a low pedal actuation resistance.

[0009] The method has the following steps, namely, when it is determined that the brake pedal has been manipulated with an manipulation stroke greater than a manipulation stroke threshold within a manipulation duration longer than a manipulation duration threshold, determining whether a driving torque maintenance condition does not exist. Therefore, for example, this determination step can only be performed when it has been determined in advance that the driver has actually performed emergency braking. Therefore, the calculation cost for further determining whether the driving torque maintenance condition does not exist can be very low. The cost for the method can be very low. In order to determine whether the driving torque maintenance condition does not exist, for example, a corresponding drive train control signal, a drive train state signal, and alternatively or additionally a vehicle state signal can be detected. The driving torque maintenance condition can be a specific driving state, and alternatively or additionally can be a drive train state.

[0010] By taking into account one or more drive torque maintenance conditions, it can be prevented that the torque is no longer generated in the drive machine in an undesirable manner despite a strong and prolonged brake pedal actuation. For example, even in the case of emergency braking, the electric drive train can perform recuperation and thus contribute to deceleration. In addition, it may be necessary that after the torque generation is switched off, a specific actuation by the driver is required, such as switching out of a safety mode or restarting the vehicle. If the torque generation is switched off in an undesirable manner, this would reduce the operating comfort. This can thus be prevented accordingly, wherein a safe and rapid stop is still possible despite a fault.

[0011] The method comprises the following steps, namely, when it is determined that there is no driving torque maintenance condition, generating a control signal for the drive train for cutting off the torque generation by the electric drive train. As a result, a switch to a torque-free state can be made. The control signal can be used to switch to a safety mode of the drive train. In the safety mode, it can be ensured, for example, at least in the sense of functional safety that the drive train no longer provides a driving torque at the output. In the safety mode, the driving torque can be kept at zero independently of the actuation of the corresponding accelerator pedal until the safety mode is deactivated again and switched to the normal mode as an alternative or in addition.

[0012] The method may have the step of transmitting the control signal to the drive train.For example, the control signal may be transmitted to one or all inverters of the drive train.

[0013] In the embodiment of the method, it is provided that if the vehicle speed is higher than a threshold speed, it is determined whether the brake pedal has been manipulated with a manipulation stroke greater than a manipulation stroke threshold within a manipulation duration longer than a manipulation duration threshold. The threshold speed may be the minimum driving speed of the working machine. When the vehicle speed is lower than the threshold speed, the mechanical braking power can always be sufficient to stop the working machine. Therefore, it is not necessary to cut off the generated torque. Thus, for example, switching to a safety mode can also be avoided, whereby the working machine can be operated more easily. The threshold speed may, for example, be a speed higher than zero speed. The method may have a step of determining whether the vehicle speed is faster than a threshold speed. The method may have a step of detecting the vehicle speed.

[0014] In the embodiment of the method, it is provided that it is determined whether there is no driving torque maintenance condition until the brake pedal is operated with an operating stroke less than another operating stroke threshold value within an operating duration longer than another operating duration threshold value. The other operating stroke threshold value can be less than the previously described operating stroke threshold value, for example, 5% less than the previously described operating stroke threshold value of the maximum operating stroke. The other operating duration threshold value can be consistent with the previously described operating duration threshold value, shorter than it or longer than it. Therefore, if the driver operates the brake pedal less strongly within the minimum duration, for example, then it is only monitored again whether strong braking is performed again, which makes it meaningful to cut off the torque generated by the drive system. In this way, continuous monitoring of the driving torque maintenance condition can be avoided, and the calculation cost can therefore be very small. In addition, if the driver no longer performs emergency braking and meets one of the driving torque maintenance conditions during the duration of emergency braking, then undesirable cutting off and switching to safety mode can be avoided. For example, the drive torque maintenance condition is only checked once the driver has actuated the brake pedal once with at least 95% of the maximum actuation travel within at least 500 ms, and the check of the drive torque maintenance condition is terminated once the driver has actuated the brake pedal with a maximum of 94% of the maximum actuation travel within at least 500 ms. Subsequently, it is only determined again whether the brake pedal is actuated again with an actuation travel greater than the actuation travel threshold value within an actuation duration longer than the actuation duration threshold value. If the brake pedal is actuated with an actuation travel less than the further actuation travel threshold value within an actuation duration longer than the further actuation duration threshold value, the method can, for example, return to its starting point. By taking into account the further actuation travel threshold value and the further actuation duration threshold value, it can also be avoided that a slight reduction in the brake pedal fluctuation and thus the actuation travel (for example due to vibrations or the driver's preparation for a collision) prevents the necessary drive torque cut-off in the short term.

[0015] In an embodiment of the method, it is provided that the first driving torque maintenance condition is met when the output speed decreases. The output speed may be the rotational speed of the output shaft of the drive train. The output speed may be the rotational speed of the motor shaft of the electric motor. The output speed may be the rotational speed of the driven wheels or the driven bridge of the working machine. Therefore, if the working machine decelerates, the generation of torque is not cut off. Therefore, for example, the generation of torque can only be cut off when the braking force of the braking system is no longer sufficient to decelerate the working machine to a stop. If it is decelerated, for example also because the drive train decelerates the working machine by recovery, then on the contrary, the generation of torque cannot be cut off. In addition, for example, the generation of torque can only be cut off when the drive train and, alternatively or additionally, the electric motor generate a stronger driving torque than the maximum deceleration caused by the braking system due to a fault.

[0016] Alternatively or additionally, the first drive torque maintenance condition or the further drive torque maintenance condition can be satisfied when the deceleration of the working machine is below the threshold deceleration. For example, the speed gradient must have a minimum value so that the torque generation is not cut off. It can therefore be considered that although the output speed is reduced, there is too low a deceleration. As a result, potentially unsafe driving states caused by too low a deceleration and thus too slow a reduction in driving speed can be avoided.

[0017] In the embodiment of the method, it is provided that the second drive torque maintenance condition is satisfied when the working machine is stationary. For example, the working machine is stationary when the travel speed is zero. Thus, switching to a safety mode can be avoided, because, for example, emergency braking is not required when the working machine is stationary.

[0018] In the embodiment of the method, it is provided that the third driving torque maintenance condition is met when the output torque does not act in the acceleration direction. Alternatively or additionally, the third driving torque maintenance condition is met when the driving torque is less than the acceleration torque threshold. Thus, for example, the operation of the drive system can be maintained when the drive system recovers and, alternatively or additionally, only generates a negligible torque. For example, when the driving torque acts in the current driving direction, the driving torque acts in the acceleration direction. The output torque can be a torque that is present at the output end of the drive system and is generated by the drive system. The acceleration torque threshold can be the maximum permissible driving torque for acceleration, at which the torque generation is not cut off.

[0019] In the embodiment of the method, it is stipulated that when the state of the inverter of the drive system is not the driving state, the fourth driving torque maintenance condition is met. For functional safety, the state of the inverter can be reported by the inverter to the vehicle control unit. For example, the inverter can have a recovery state, a driving state or a cut-off state. The driving state can be a state in which electric energy from an energy storage device is transferred from the inverter to the electric motor to generate torque. Therefore, the current supply through the inverter can already be considered in order to avoid the generation of undesirable additional torque. For example, an error in which the inverter remains in the driving state despite the presence of other control signals can be considered. For example, the last stored state can be called and the current state can be called as the state of the inverter alternatively or additionally.

[0020] In an embodiment of the method, it is provided that the generated control signal specifies a target torque of 0 Nm of the drive train. For example, the generated control signal can control an inverter. By means of such a control signal, the torque generation can be directly requested to be zero and thus switched off. The target torque can be the torque that the drive train is to generate.

[0021] In an embodiment of the method, it is provided that the generated control signal specifies a cut-off state of the inverter. The cut-off state may be a state in which it is no longer physically possible to generate a torque by the drive train. The cut-off state may be, for example, a state in which the respective output stage of the inverter is disconnected. As a result, the electric motor can no longer be supplied with electrical energy by the inverter. By predefining the cut-off state, torque generation can be shut off with particularly high safety even in the event of a fault.

[0022] In an embodiment of the method, it is provided that the generated control signal specifies a gradual reduction of the drive torque of the drive train. The control signal can, for example, specify the time period within which the generated torque is reduced to zero. A gradual reduction can only be achieved, for example, if a drive torque is still required at the torque cut-off time. The gradual reduction can protect the respective electronic components of the drive train from damage. The gradual reduction can nevertheless be achieved quickly, so that the braking speed of the working machine is not reduced or is only reduced insignificantly.

[0023] In the embodiment of the method, it is provided that the generated control signal specifies a sudden reduction of the drive torque of the drive train. For example, a torque generation of 0 Nm can be immediately required. By means of the sudden reduction, the method can be implemented particularly simply and can be used simply in different working machines.

[0024] A second aspect relates to a control device for an electric drive train of a working machine. For example, the control device can be configured to transmit control signals to respective inverters of the drive train. The control device can also be integrated in respective inverters of the drive train. The control device can be configured as an electronic component and, for example, have a microcontroller. The control device can be configured to perform the method according to the first aspect. The corresponding further features, embodiments and advantages can be obtained from the description of the first aspect. Conversely, the features, embodiments and advantages of the second aspect are also the features, embodiments and advantages of the first aspect.

[0025] The control device is configured to determine that the brake pedal has been operated with an operating stroke greater than an operating stroke threshold value within an operating duration longer than an operating duration threshold value. For this purpose, the control device can have respective sensors. Alternatively, the control device can be configured to receive corresponding operating signals of the brake pedal.

[0026] The control device is configured to determine that the driving torque maintenance condition does not exist when it is determined that the brake pedal has been operated with an operating stroke greater than an operating stroke threshold value within an operating duration longer than an operating duration threshold value. The control device is also configured to generate a control signal to cut off the generation of torque by the electric drive system when it is determined that the driving torque maintenance condition does not exist. The control device may have a storage device in which the corresponding threshold value and, alternatively or additionally, the driving torque maintenance condition may be stored.

[0027] A third aspect relates to a working machine having an electric drive train and a control device. The drive train is configured to receive a control signal generated by the control device. The control device can be configured as a control device according to the second aspect. The electric drive train can be configured to be controlled using a method according to the first aspect. Corresponding further features, embodiments and advantages can be derived from the description of the first or second aspect. Conversely, features, embodiments and advantages of the third aspect are also features, embodiments and advantages of the first and second aspects.

[0028] In an embodiment of the working machine, it is provided that the electric drive train has an inverter and an electric motor which can be supplied with electric energy via the inverter. The inverter can have power electronics. The drive train can have an energy source, such as a battery. The inverter can be designed to control the energy supply to the electric motor as a function of a control signal received by the control device. The working machine can have a brake pedal.

[0029] In an embodiment of the working machine, a clutch is provided for the drive train which enables a traction interruption. A traction interruption can be a state in which a torque transmission from the electric motor to the output of the drive train or, for example, to the corresponding wheels of the drive machine is no longer possible via the disconnected clutch. Despite the lack of the possibility for traction interruption, it can still be reliably ensured that the working machine is not driven during emergency braking or at least can still be safely stopped. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The control of an electric drive train of a work machine is schematically illustrated.

[0031] Figure 2 A method for controlling a drive train of a work machine is schematically illustrated. DETAILED DESCRIPTION

[0032] Figure 1 The control of an electric drive train 22 of a working machine is schematically shown. The working machine has an evaluation device 10. The evaluation device 10 receives the pedal position of a brake pedal 12 and a driving controller designed as an accelerator pedal 14. In addition, the position of a mode change element in the form of a driving range selector lever 16 is also received. Position signals are transmitted from the evaluation device 10 to a control device 18 via a CAN bus. The control device 18 generates control signals for the drive train 22, which are transmitted to an inverter 24 of the drive train 22 and correspond to a driving strategy with a predetermined torque known by the control device 18. The transmission of the drive train 22 is also controlled by the control device 18 via the control signal. The inverter 24 supplies electrical energy to the electric motor 26 as a function of the control signal. As a result, the drive train 22 is controlled to generate a torque. The generated torque is provided at the output of the drive train 22 in order to drive the respective wheels of the working machine.

[0033] In addition, the work machine has a brake system which is controlled via a brake pedal 12. In the example shown, the brake system has a mechanical or hydraulic transmission device 28, via which a disk brake 30 is actuated as a function of the actuation of the brake pedal 12. In purely mechanical brake systems, the braking force is controlled directly via the muscle force acting on the brake pedal 12.

[0034] The control device 18 is also designed to execute a method for controlling the electric drive train 22, by means of which the torque generated by the drive train 22 is disconnected during emergency braking. Figure 2 It is schematically shown in FIG.

[0035] In step 40, it is determined whether the brake pedal 12 has been actuated with an actuation travel greater than an actuation travel threshold value within an actuation duration that is longer than an actuation duration threshold value. In the example shown, the actuation travel threshold value is 99% of the maximum actuation of the brake pedal 12, and the actuation duration threshold value is 500 ms. Thus, if the driver of the work machine depresses the brake pedal 12 almost completely for at least half a second, it is determined that the brake pedal has been actuated with an actuation travel greater than the actuation travel threshold value within an actuation duration that is longer than the actuation duration threshold value. In this case, it can be assumed that the driver did not actuate the brake pedal 12 briefly and strongly unintentionally (for example, due to vehicle vibrations), but actually wanted to request strong braking to stop the work machine as quickly as possible.

[0036] If the brake pedal is not operated with an operating stroke greater than the operating stroke threshold value within a duration longer than the operating duration threshold value, the brake pedal operation is further monitored. Only when such a brake pedal operation is performed, the process continues with step 42. In step 42, if it is determined in step 42 that the brake pedal is operated with an operating stroke greater than the operating stroke threshold value within an operating duration longer than the operating duration threshold value, it is determined whether the drive torque maintenance condition does not exist.

[0037] The control device 18 here takes into account one, more than one or all of the following drive torque maintenance conditions: The first drive torque maintenance condition is met when the output speed is reduced. The second drive torque maintenance condition is met when the working machine is stationary, that is, no driving motion is performed. The third drive torque maintenance condition is met when the output torque does not act in the acceleration direction or is less than the acceleration torque threshold. The fourth drive torque maintenance condition is met when the state of the inverter 24 of the drive system 22 is not a driving state. For this purpose, the state of the inverter 24 is transmitted from the inverter 24 to the control device 18. By taking into account these drive torque maintenance conditions, for example, unnecessary cutting off of the torque generated by the drive system 22 can be avoided when the drive system 22 contributes to the deceleration of the driving motion of the working machine.

[0038] In an embodiment, before step 40 and, alternatively or additionally, before step 42, it is additionally checked whether the vehicle speed is above a threshold speed. Only if the vehicle speed is above the threshold speed is step 40 of the method performed in this embodiment and, alternatively or additionally, step 42 of the method performed. For this purpose, the actual rotational speed of the output of the electric motor 26 and, alternatively or additionally, of the drive train 22 can be transmitted from the inverter 24 to the control device 18.

[0039] In an embodiment, the driving torque maintenance condition is monitored until the brake pedal 12 is actuated with an actuation stroke less than another actuation threshold value within an actuation duration longer than another actuation duration threshold value. For example, the driving torque maintenance condition is monitored until the driver actuates the brake pedal 12 within at least 500 ms at a maximum of 94% of the driver's maximum actuation stroke. Then, the process returns to step 40.

[0040] If it has been determined in step 42 that there is no driving torque maintenance condition, then continue with step 44. In step 44, a control signal is generated for the drive system 22 to cut off the torque generated by the electric drive system 22. The control signal is transmitted to the inverter 24. The target torque of 0 Nm is predetermined for the inverter 24 through the control signal. Then, the inverter 24, for example, no longer supplies the electric motor 26 with a current sufficient to generate torque. Alternatively or additionally, the cut-off state of the inverter 24 is predetermined by the control signal, whereby the inverter 24 disconnects its corresponding output stage in response. Then, the inverter 24 is electrically separated from the electric motor 26.

[0041] Reference numerals list

[0042] 10 Evaluation device

[0043] 12Brake pedal

[0044] 14 Accelerator pedal

[0045] 16 Driving range selector lever

[0046] 18 Control Devices

[0047] 22 Electric drive system

[0048] 24 Inverter

[0049] 26 Electric Motor

[0050] 28 Mechanical or hydraulic transmission devices

[0051] 30 Disc brake

[0052] 40 Steps to determine brake pedal operation

[0053] 42 Steps to check the driving torque maintenance condition

[0054] 44 Steps to generate control signal

Claims

1. A method for controlling an electric drive train (22) of a working machine, wherein: The method comprises at least the following steps (40, 42, 44): - determining (40) whether a brake pedal operation was performed with an operation travel greater than an operation travel threshold value within an operation duration longer than an operation duration threshold value; - when it is determined that the brake pedal has been manipulated with an manipulation stroke greater than the manipulation stroke threshold within a manipulation duration longer than the manipulation duration threshold, determining (42) whether a driving torque maintenance condition does not exist; - when it has been determined that the driving torque maintaining condition does not exist, generating (44) a control signal for the drive train (22) to cut off the generation of torque by the electric drive train (22).

2. The method according to claim 1, characterized in that If the vehicle speed is above the threshold speed, it is determined ( 40 ) whether the brake pedal was actuated within an actuation duration that is longer than the actuation duration threshold and with an actuation travel that is greater than the actuation travel threshold.

3. The method according to claim 1 or 2, characterized in that: It is determined ( 42 ) whether the drive torque maintenance condition does not exist until the brake pedal is actuated for an actuation duration that is longer than a further actuation duration threshold value and with an actuation travel that is less than a further actuation travel threshold value.

4. The method according to any one of the preceding claims, characterized in that When the output speed decreases, the first driving torque maintaining condition is satisfied.

5. The method according to any one of the preceding claims, characterized in that When the working machine is stationary, the second driving torque maintaining condition is satisfied.

6. The method according to any one of the preceding claims, characterized in that When the output torque does not act in the acceleration direction or is less than the acceleration torque threshold, the third driving torque maintaining condition is satisfied.

7. The method according to any one of the preceding claims, characterized in that When the state of the inverter (24) of the drive system (22) is not a driving state, a fourth driving torque maintaining condition is satisfied.

8. The method according to any one of the preceding claims, characterized in that The generated control signal specifies a target torque of 0 Nm for the drive train (22).

9. The method according to any one of the preceding claims, characterized in that The generated control signal specifies the disconnection state of the inverter (24).

10. The method according to any one of the preceding claims, characterized in that The generated control signal specifies a gradual reduction in the drive torque of the drive train (22).

11. The method according to any one of claims 1 to 9, characterized in that The generated control signal specifies a sudden reduction in the drive torque of the drive train (22).

12. A control device (18) for an electric drive train (22) of a working machine, wherein: The control device (18) is configured to determine that the brake pedal has been operated with an operating stroke greater than an operating stroke threshold within an operating duration that is longer than an operating duration threshold, wherein the control device (18) is configured to determine that a driving torque maintenance condition does not exist when it is determined that the brake pedal has been operated with an operating stroke greater than the operating stroke threshold within an operating duration that is longer than the operating duration threshold, and wherein the control device (18) is configured to generate a control signal to cut off the torque generated by the electric drive system (22) when it is determined that the driving torque maintenance condition does not exist.

13. A working machine having an electric drive train (22) and a control device (18) according to claim 12, wherein: The electric drive train (22) is configured to receive a control signal generated by the control device (18).

14. The working machine according to claim 13, characterized in that: The electric drive train (22) has an inverter (24) and an electric motor (26) which can be supplied with electric energy by the inverter (24), wherein the inverter (24) is designed to control the energy supply of the electric motor (26) as a function of a control signal received from the control device (18).

15. The working machine according to claim 13 or 14, characterized in that: The drive train (22) has no clutch that enables interruption of traction force.

Images