Method for operating an electric travel drive of a movable work machine

Abstract

The present invention relates to a method for operating a travel drive of a movable work machine, wherein the travel drive comprises an electric motor (305) which drives at least one wheel (303) of the work machine, and wherein the movable work machine comprises an input device (330) which has one or more operating elements with which the driver of the movable work machine can control the travel drive, characterised in that the method comprises the following steps: a) determining a current speed of the movable work machine or a variable dependent thereon; b) determining a current torque which corresponds to the torque generated by the electric motor (305) or a variable dependent thereon; c) detecting an input via the input device (330); d) checking for an error state on the basis of the speed determined in step a), on the basis of a comparison of the torque determined in step b) with a reference torque and on the basis of the input detected in step c) via the input device (330).

Description

[0001] R. 415124

[0002] Robert Bosch GmbH

[0003] 415124 - Mumcu

[0004] Method for operating an electric drive system of a mobile working machine

[0005] TECHNICAL AREA

[0006] The present disclosure relates to a method for operating an electric drive system of a mobile working machine, in particular for implementing safety functions, and to a corresponding drive system.

[0007] STATE OF THE ART

[0008] The risks posed by mobile machinery are generally reduced to an acceptable level by so-called safety functions. Various approaches exist for implementing such safety functions. One proven approach, described in DE 44 38 714 A1, involves logically dividing the control of a drive system in an electronic control unit into two levels: the first level comprises control functions and the second level comprises monitoring functions. The second level monitors the first level, enabling fault detection and an appropriate response to detected faults. DE 10 2013 218 554 A1 describes a method for monitoring the electric drive system of a motor vehicle, based on comparing the actual acceleration with a permissible acceleration.

[0009] The present invention is based on the objective of finding a method for monitoring an electric drive system that is applicable to mobile machinery and thus enables the implementation of safety functions. Methods for electric drives known from the automotive sector are not well suited for mobile machinery, since mobile machinery typically involves driving maneuvers that do not occur in the automotive sector, for example, driving a wheel loader into a pile of material or reversing, in which the direction of travel is reversed in a continuous process. Such special driving situations and external forces that can act on the machine are not adequately considered in the known methods. The present invention aims to solve the problem of reliably detecting fault conditions of the drive system while simultaneously preventing false positives. R. 415124

[0010] to deliver results in fault detection, which can be a challenge in the driving situations mentioned above.

[0011] The invention also aims to find a monitoring method that can not only detect faults within the electronic control unit in which the method is carried out, but also enable fault detection for other components of the drive system, for example for the electric motor or the inverter that controls the electric motor.

[0012] For many electrically powered work machines, it is advantageous to use a powershift transmission, especially a two-speed powershift transmission, to select the appropriate gear ratio depending on the application. Often, an actively synchronized powershift transmission is used, which is synchronized by the electric motor during gear changes. Active synchronization eliminates the need for components that would otherwise be required for passive, friction-based synchronization, and it also allows for the use of more robust clutches, such as dog clutches. For active synchronization, the transmission manufacturer typically provides a transmission control unit with a corresponding method for controlling the electric motor, particularly during gear changes.During active synchronization, torque and speed changes can occur at the electric motor that do not occur in normal driving situations and are therefore incorrectly interpreted as a fault condition by the monitoring system if no additional measures are taken. An optional further development of the invention is intended to solve this problem and thus also enable the monitoring of an electric drive system that includes an actively synchronized powershift transmission.

[0013] SUMMARY

[0014] According to one embodiment of the present invention, a method for operating a drive system of a mobile working machine, for example a wheel loader, a telescopic handler, a municipal vehicle, or an excavator, is provided, wherein the drive system comprises an electric motor, for example a permanent magnet synchronous motor or an asynchronous motor, which drives at least one wheel of the working machine, for example the two wheels of the rear axle via a cardan shaft and a differential gear, and wherein the mobile working machine comprises an input device having one or more operating elements, for example an accelerator pedal, an inching pedal, a brake pedal, a direction selector lever, a seat switch, a joystick, or an R. 415124

[0015] Touchscreens with which the operator of the mobile working machine can control the drive system, characterized in that the method comprises the following steps: a) determining a current speed of the mobile working machine or a quantity dependent thereon, for example determining the electric motor speed, transmission input speed, transmission output speed or direction of travel; b) determining a current torque corresponding to the torque generated by the electric motor or a quantity dependent thereon, for example the electric current with which the electric motor is driven; c) acquiring an input via the input device, for example via an accelerator pedal, an inching pedal and a direction selector lever;d) Checking for a fault condition based on the speed determined in step a), by comparing the torque determined in step b) with a reference torque and based on the input acquired in step c) via the input device, for example to determine whether the drive system is erroneously generating a driving torque even though the driver is requesting the drive system to be disengaged using the controls.

[0016] According to one embodiment of the present invention, a method is provided wherein the drive is brought into a drive-less state via a safe shutdown path if the test in step d) shows that a fault condition exists, for example if the drive generates a driving torque although the driver requests drive-less operation via a control element, so that the working machine is brought into a safe state in the event of a fault.

[0017] According to one embodiment of the present invention, a method is provided wherein the reference torque used in step d) for checking for a fault condition depends on the direction of the speed determined in step a), i.e., the direction of travel, and wherein the reference torque preferably also exhibits a time dependence in addition to this dependence. A dependence of the reference torque on the direction of travel is advantageous because, depending on the direction of travel, a torque generated by the electric motor has either a driving or a braking effect on the driven machine. For example, a positive torque has a driving effect when traveling forward, but the same torque has a braking effect when traveling in reverse.Specifying a reference torque that depends on the direction of travel allows this fact to be adequately taken into account, so that, for example, limits can be set on how strong a braking effect a torque generated by the electric motor may have. An additional time dependency of the reference torque is advantageous because it allows R. 415124 to consider that the actual torque follows a certain dynamic and changes on a specific time scale. For example, for physical reasons, the actual torque cannot instantly change from a non-zero value to zero when the driver requests a loss of drive. Rather, the decrease in torque follows a specific time profile.

[0018] According to one embodiment of the present invention, a method is provided wherein, in step b), an acceleration is additionally determined, for example, from the rotational speed of the electric motor, which describes a current acceleration of the mobile working machine in the direction of travel or a quantity dependent thereon, and wherein, in step d), the fault condition test additionally comprises a comparison of the acceleration determined in step b) with a reference acceleration. Considering an acceleration of the working machine when testing for a fault condition is advantageous because it allows for consideration of how the actual state of motion of the working machine changes.The acceleration of the machine depends not only on the torque generated by the electric motor, but also on external forces, such as the force of gravity acting down a slope or forces generated by other interactions with the environment, for example, when a wheel loader drives into a pile of material. This allows for more reliable fault detection with fewer false positives.

[0019] According to one embodiment of the present invention, a method is provided wherein the reference acceleration used in step d) for checking for a fault condition depends on the direction of the velocity determined in step a), and wherein the reference acceleration preferably also exhibits a time dependence in addition to this dependence. A dependence of the reference acceleration on the direction of travel is advantageous because, depending on the direction of travel, a non-zero, signed acceleration indicates either an increase or a decrease in absolute velocity. For example, a positive acceleration when traveling forward indicates an increase in absolute velocity, but when traveling in reverse indicates a decrease in absolute velocity. Specifying a reference acceleration that depends on the direction of travel makes it possible to adequately account for this fact.An additional time dependence of the reference acceleration is advantageous because it makes it possible to consider the dynamics of physical processes that influence the acceleration of the working machine when checking for a fault condition, for example, forces that occur due to torsion of the wheel axle, or counterforces that occur when a working tool of the working machine penetrates a pile of material. R. 415124.

[0020] According to one embodiment of the present invention, a method is provided wherein the working machine comprises a power shift transmission, for example a two-speed power shift transmission, which is arranged between the electric motor and a driven wheel and which is actively synchronized by means of the electric motor during a gear change, so that no additional component is necessary for passive synchronization.

[0021] According to one embodiment of the present invention, a method is provided wherein the acceleration determined in step b) is derived from the transmission output speed of the powershift transmission or from a variable dependent thereon, so that a suitable value for the acceleration is also determined during a gear change. During a gear change, the electric motor is briefly decoupled from the wheel axle, so that the rate of change of the electric motor speed during this short time window does not reflect the acceleration of the driven machine. However, the transmission output shaft remains coupled to the wheel axle even during a shift operation, so that the speed of this shaft is better suited for determining the acceleration of the driven machine.

[0022] According to one embodiment of the present invention, a method is provided wherein, in step b), the current acceleration is determined from the rotational speed of the electric motor or from a quantity dependent thereon, and wherein the method comprises the following additional steps: e) specifying a target speed for the rotational speed of the electric motor for the purpose of active transmission synchronization during a gear change; f) controlling the electric motor taking into account the target speed specified in step e) during a gear change;g) Adjusting the reference acceleration used in step d) to check for a fault condition to the target speed specified in step e), or to the time course of the specified target speed, or adjusting the target speed to the specified reference acceleration, so that an acceleration determined in step b), which corresponds to the time course change of the target speed taking into account a tolerance range, leads to the test result that no fault condition exists when compared with the reference acceleration in step d) during a gear change.

[0023] The adjustment described in g) is advantageous because the electric motor speed requested for the purpose of active synchronization and the time course of this speed are judged as not faulty when testing for a fault condition. R. 415124

[0024] According to one embodiment of the present invention, a method is provided, the method comprising the following additional steps: h) specifying a torque setpoint for the torque generated by the electric motor for the purpose of active transmission synchronization during a gear change; i) controlling the electric motor taking into account the torque setpoint specified in step h) during a gear change; j) adjusting the reference torque to be used in step d) for checking for a fault condition to the torque setpoint specified in step h), or adjusting the torque setpoint to the reference torque, such that a torque determined in step b) which corresponds to the torque setpoint taking into account a tolerance range, leads to the test result that no fault condition exists when compared with the reference torque in step d) during a gear change.

[0025] The adaptation described in j) is advantageous because the torque of the electric motor requested for the purpose of active synchronization is judged to be non-faulty when tested for a fault condition.

[0026] According to one embodiment of the present invention, a method is provided wherein the working machine comprises a drive control unit that performs steps a), b), c) and d), and the working machine further comprises a transmission control unit that specifies the speed setpoint for the electric motor in step e) and / or the torque setpoint for the electric motor in step h).

[0027] According to one embodiment of the present invention, a method is provided wherein the check for a fault condition by means of step d) is temporarily not carried out or the detection of a fault condition is temporarily suppressed while a gear change takes place in the powershift transmission, so that a detection of supposed fault conditions during a gear change as a result of the active transmission synchronization is avoided.

[0028] According to one embodiment of the present invention, a computing unit is provided which is configured to carry out a method according to the invention.

[0029] According to one embodiment of the present invention, a mobile working machine is provided which has a drive system and a computing unit which is configured to carry out a method according to the invention, wherein the drive system comprises an electric motor which drives at least one wheel of the working machine, and wherein the mobile R. 415124

[0030] A mobile working machine includes an input device that has one or more control elements with which the driver of the mobile working machine can control the drive system.

[0031] According to one embodiment of the present invention, a computer program is provided which causes a computing unit to perform a method according to the invention when it is executed on the computing unit.

[0032] BRIEF DESCRIPTION OF THE FIGURES

[0033] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures:

[0034] Fig. 1 schematically describes the structure of a first embodiment of a drive system according to the invention.

[0035] Fig. 2 schematically describes the inventive method based on the main process steps according to an embodiment of the invention.

[0036] Fig. 3 schematically describes the test for a fault condition according to an embodiment of the invention.

[0037] Fig. 4 schematically describes the structure of a second embodiment of a drive system according to the invention with an actively synchronized powershift transmission.

[0038] Fig. 5 schematically describes the structure of a third embodiment of a drive system according to the invention with an actively synchronized powershift transmission.

[0039] Fig. 6 schematically describes the structure of a fourth embodiment of a drive system according to the invention with an actively synchronized powershift transmission.

[0040] DETAILED DESCRIPTION

[0041] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims. R. 415124

[0042] Further modifications and variations of the present invention are obvious to a person skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims.

[0043] Fig. 1 schematically shows the structure of the drive system for a first embodiment, comprising the following components: an electric motor 305 coupled to a wheel 303 of the driven machine, an inverter 302 that controls the electric motor 305, an electronic drive control unit 300 connected to the inverter 302 via a communication interface, and an input device 330 connected to the electronic drive control unit 300, comprising the following operating elements: an accelerator pedal, an inching pedal, and a direction selector lever. The electronic drive control unit 300 incorporates the usual control function for the drive system as well as a monitoring function. The arrows in this diagram represent an exchange of information by means of electronic messages, the meaning of which will become clearer in the course of the description with reference to the other figures.Message 310 represents a shutdown signal that the drive control unit 300 uses to instruct the inverter 302, in the event of a fault, to put the electric motor 305 into a non-drive state in which no torque is generated. Message 311 transmits the current speed and torque of the electric motor 305 from the inverter 302 to the drive control unit 300, making this information available for monitoring the drive system. Message 306 transmits the speed and / or torque requested by the control function, or an upper and / or lower limit for the torque generated by the electric motor 305, to the inverter 302, which then regulates the electric motor 305.

[0044] Fig. 2 schematically shows the main steps that are repeatedly performed during the operation of the electric drive of the mobile working machine.

[0045] In step 1, the current rotational speed of the electric motor 305 is determined in the inverter 302, for example by means of a resolver, and, as already mentioned, provided to the electronic drive control unit 300 via the communication interface. In step 2, the current speed of the driven machine is determined in the electronic drive control unit 300 from the current rotational speed of the electric motor 305, taking into account the gear ratio and wheel circumference. From this, the current acceleration of the driven machine is derived in step 3 by numerical differentiation. In step 4, the torque generated by the electric motor 305 is determined in the inverter 302 by means of a current measurement and, as already mentioned, provided to the electronic drive control unit R. 415124.

[0046] The data is provided via the communication interface of the electronic drive control unit 300. In step 5, the position of the accelerator pedal is detected in the electronic drive control unit 300, in step 6 the position of the inching pedal, and in step 7 the position of the direction selector lever. The direction selector lever allows the operator of the machine to choose between forward and reverse travel and a neutral position. A check for a fault condition is performed in step 8, which is described in detail in Fig. 3.

[0047] Fig. 3 schematically describes, using an activity diagram, the check for a fault condition and a possible shutdown of the drive system based on speed, acceleration, torque, and the position of the accelerator pedal, inching pedal, and direction selector lever, with the start node 200 indicating the start of the activity. It should be noted that speed, acceleration, and torque are all signed quantities, with a positive sign corresponding to the forward direction of the machine or a forward-driving torque.

[0048] Action 201 is a fault check for the "Safe Reversing" safety function. It checks whether, during the deceleration phase of a reversing operation, a fault causes the drive system to generate insufficient decelerating torque, resulting in inadequate deceleration of the machine. The deceleration phase of a reversing operation begins when the operator of the machine changes the desired direction of travel from forward to reverse using the direction selector lever while traveling forward, or from reverse to forward while traveling in reverse. The deceleration phase ends as soon as the position of the direction selector lever again corresponds to the machine's direction of travel or when the machine comes to a standstill. The test described here indicates a fault if the following four conditions are met simultaneously:

[0049] • the current speed of the working machine is positive,

[0050] • the direction selector lever is set to reverse,

[0051] • The current torque is greater than a first reference torque, which corresponds to a torque that has too weak a decelerating effect,

[0052] • The current acceleration of the working machine is greater than a first reference acceleration, which corresponds to insufficient deceleration of the working machine, or if the following four conditions are met simultaneously, R. 415124

[0053] • the current speed of the working machine is negative,

[0054] • the direction selector lever is set to forward,

[0055] • The current torque is less than a second reference torque, which corresponds to a torque that has too weak a decelerating effect,

[0056] • The current acceleration of the working machine is less than a second reference acceleration, which corresponds to an insufficient deceleration of the working machine.

[0057] Decision node 202 evaluates the result of the check from action 201. If this check indicates an error, action 213 is reached via the right branch through merge nodes 205, 209, and 212. Otherwise, action 203 is executed.

[0058] Action 213 represents a shutdown of the drive system by the electronic drive control unit 300, thus bringing the machine to a safe state in the event of a fault. As already mentioned, the shutdown is triggered by electronic message 310 to the inverter 302. Afterwards, the end node 215 of the activity diagram is reached via the merging node 214, and the fault condition check is terminated.

[0059] Action 203 is a fault check for the "Safe Deceleration" safety function. It checks whether the drive system generates excessive braking torque during driving, which could lead to unsafe driving conditions. This test indicates a fault if the following two conditions are met simultaneously:

[0060] • the current speed of the working machine is positive,

[0061] • the current torque is less than a third, negative reference torque, which corresponds to an excessively braking torque, or if the following two conditions are met simultaneously,

[0062] • the current speed of the working machine is negative,

[0063] • The current torque is greater than a fourth, positive reference torque, which corresponds to an excessively braking torque.

[0064] Decision node 204 evaluates the result of the check from action 203. If this check indicates an error, action 213 (R. 415124) is reached via the right branch through merge nodes 205, 209, and 212, and the drive is switched off, as described above. Otherwise, the process continues with decision node 206.

[0065] Decision node 206 determines, based on the speed and position of the accelerator pedal, inching pedal, and direction selector lever, whether the machine has been brought to a standstill by corresponding inputs from the operator. If so, action 207 proceeds, performing additional checks for faults that may occur after the machine has been brought to a standstill by the operator. Otherwise, the end node 215 of the activity diagram is reached via merge node 214, and the check for fault conditions is terminated.

[0066] Action 207 checks whether the machine is unintentionally set in motion from a standstill due to a fault caused by a torque actively generated by the drive system. This test implements the "Safe Acceleration Prevention" safety function for the machine. The test indicates a fault if two conditions are met simultaneously. The first condition is that the operator requests a standstill of the machine using at least one of the controls. This occurs if the accelerator pedal is not depressed at all, if the inching pedal is fully depressed, or if the direction selector lever is in the neutral position. The second condition is that the drive system generates a driving torque in the direction of travel, and the machine accelerates in that direction.More precisely, the second condition is fulfilled if the following three conditions are fulfilled simultaneously.

[0067] • the current speed of the working machine is positive,

[0068] • The current torque is greater than a fifth reference torque, which corresponds to an excessively strong driving torque in the forward direction,

[0069] • the current acceleration is greater than a third reference acceleration, which corresponds to excessive forward acceleration, or if the following three conditions are met simultaneously,

[0070] • the current speed of the working machine is negative,

[0071] • the current torque is less than a sixth reference torque, which corresponds to an excessively strong driving torque in the reverse direction,

[0072] • The current acceleration is less than a fourth reference acceleration, which corresponds to excessive acceleration in the reverse direction.

[0073] Decision node 208 evaluates the result of the check from action 207. If this check indicates an error, action 213 is reached via R.415124 through the right branch via merge nodes 209 and 212, and the drive is switched off, as described above. Otherwise, action 210 is executed.

[0074] Action 210 represents a further fault check, implementing the "Safe Travel Direction" safety function for the machine. This check verifies whether, due to a fault, the machine is being propelled from a standstill in a direction not requested by the operator by a torque actively generated by the drive system. The test indicates a fault if the following three conditions are met simultaneously:

[0075] • the direction selector lever is set to forward,

[0076] • the current speed of the working machine is negative,

[0077] • the current torque is less than a seventh reference torque, which corresponds to an excessively strong driving torque in the reverse direction, or if the following three conditions are met simultaneously:

[0078] • the direction selector lever is set to reverse,

[0079] • the current speed of the working machine is positive,

[0080] • The current torque is greater than one-eighth reference torque, which corresponds to an excessively strong driving torque in the forward direction.

[0081] Decision node 211 evaluates the result of the check from action 210. If this check indicates an error, action 213 is reached via the right branch through merge node 212, and the drive system is switched off, as described above. Otherwise, the end node 215 of the activity diagram is reached via merge node 214, and the check for error conditions is terminated.

[0082] The reference torques (first to eighth) and reference accelerations (first to fourth) mentioned in the description of Fig. 3 must be selected by the manufacturer during the tuning of the machine so that, on the one hand, the tests can reliably detect faults, and on the other hand, the tests do not produce false positive results during normal operation of the machine, for example, due to noise in the quantities used in the tests. Such false positive results would adversely affect the availability of the machine. To increase the robustness of the tests, it is also possible not only to evaluate the conditions described above at a single point in time, but also to consider a time history, for example, by requiring that the conditions for the occurrence of a specific fault be maintained for a certain period. R. 415124

[0083] The time requirement must be continuously met, for example for at least 100 milliseconds, for the test to yield a positive result.

[0084] It is also possible, and useful for simplifying parameterization, to select some reference torques or reference accelerations the same for the various tests. For example, it is advisable to select the sixth reference torque for test 207 and the seventh reference torque for test 210 the same, because both reference torques define an error limit for an unwanted, driving torque in the reverse direction from a standstill of the machine.

[0085] The embodiments described below with reference to Figures 4, 5, and 6 differ fundamentally from the first embodiment described in Figure 1 in that a power-shift transmission 304 is arranged between the electric motor 305 and a driven wheel 303, which is actively synchronized by the electric motor 305 during a shifting operation. For this purpose, in addition to the drive control unit 300, there is a transmission control unit 301, which controls the power-shift transmission 304 and is intended to ensure appropriate control of the electric motor 305 during a shifting operation. The control of the electric motor 305 is thus intended, on the one hand, to be carried out according to the inputs of the driver via the input device 330, which are processed in the drive control unit 300, and on the other hand, the specifications of the transmission control unit 301 are also to be taken into account, particularly during a shifting operation.For this reason, when checking for fault conditions, it is advisable to consider the transmission control unit 301 in addition to the driver's inputs. This prevents the check from incorrectly interpreting active synchronization processes as fault conditions, as changes in speed and torque can occur at the electric motor 305 during synchronization, which would indicate a fault during normal driving. Three possible solutions for monitoring the drive system when using an actively synchronized powershift transmission 304 are described below.

[0086] Fig. 4 schematically describes the structure of a second embodiment of a drive system according to the invention with an actively synchronized powershift transmission 304. Only the differences from Fig. 1 are described below. The drive system control unit 300 transmits the desired gear to the transmission control unit 301 via message 403, and the transmission control unit 301 controls the powershift transmission 304 accordingly. The transmission control unit 301 transmits the speed of the output shaft of the transmission to the drive system control unit 300 via message 401. 415124

[0087] Powershift transmission 304. Based on this information, the speed and acceleration of the machine are determined in the transmission control unit 301. Furthermore, the transmission control unit 301 transmits the speed and / or torque of the electric motor 305 requested for active synchronization to the drive control unit 300 via message 402. In the drive control unit 300, message 306 is adjusted based on the information from message 402 so that the specifications of the transmission control unit 301 are also taken into account when the electric motor 305 is controlled by the inverter 302. Additionally, the reference torques used in the fault detection tests are adjusted based on message 402 so that the torques generated at the electric motor 305 during active synchronization do not lead to false positive results in fault detection.For example, the third, negative reference torque, which in action 203 serves to detect excessively decelerating torques (see description of Fig. 3), is adjusted during a shift to a higher gear while driving forward, if necessary, so that even very strong decelerating torques, which are briefly requested by the transmission control unit 301 during active synchronization, lead to a negative result in action 203 when checking for a fault condition.

[0088] Fig. 5 schematically describes the structure of a third embodiment of a drive system according to the invention with an actively synchronized powershift transmission 304. Only the differences from Fig. 1 are described below. The drive system control unit 300 transmits the desired gear to the transmission control unit 301 via message 403, and the speed and / or torque requested by the control functions for the electric motor 305 via message 501. In contrast to Fig. 1 (message 306), the drive system control unit 300 here does not transmit control information directly to the inverter 302, but first to the transmission control unit 301.The transmission control unit 301 controls the powershift transmission 304 according to message 403 and forwards the requested speed and / or torque to the inverter 302 via message 503. The transmission control unit 301 then adjusts the requested speed and / or torque accordingly for the purpose of active synchronization. Via message 502, the transmission control unit 301 informs the drive control unit 300 when the powershift transmission 304 is in neutral and active synchronization is taking place. This information is used in the drive control unit 300 to temporarily suspend the fault condition check during active synchronization in order to prevent the detection of potential fault conditions. R. 415124.

[0089] Fig. 6 schematically describes the structure of a fourth embodiment of a drive system according to the invention with an actively synchronized powershift transmission 304. Only the differences from Fig. 5 are described below. In this embodiment, the influence of the transmission control unit 301 on the speed and / or the generated torque of the electric motor 305 is limited in such a way that no false positive results occur when testing for a fault condition during a normal shifting operation. In contrast to Fig. 5, the fault condition test is therefore not temporarily suspended. The limitation of the influence of the transmission control unit 301 is achieved by means of message 600, via which the drive control unit 300 transmits reference torques and reference accelerations to the transmission control unit 301, which are used in the drive control unit 300 when testing for a fault condition.In the transmission control unit 301, the requested speed and / or torque for the electric motor 305, which are transmitted to the inverter 302 via message 503, are adjusted to these reference torques and reference accelerations such that the speeds and / or torques generated at the electric motor 305 during normal, active synchronization result in a negative result when checking for a fault condition. For example, the torque that can be requested by the transmission control unit 301 for active synchronization during forward travel when shifting into a higher gear is limited downwards by the third, negative reference torque (see action 203 in the description of Fig. 3), because if the torque generated by the electric motor 305 were to fall below this limit, action 203 would indicate that a fault has occurred.Alternatively, message 600 can also transmit other information that depends on the reference torques and reference accelerations, and on the basis of which an equivalent limit can be applied. For example, message 600 can transmit a limit for the time-dependent change of the requested speed and / or a limit for the requested torque, which is then taken into account in the transmission control unit 301. Alternatively, message 600 can transmit a speed tolerance and / or a torque tolerance, which in each case specifies the amount by which the speed and / or torque requested in message 503 may deviate from the speed and / or torque requested in message 501.

[0090] While the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to describe various modifications, variations and improvements of the present invention in R. 415124.

[0091] to realize the above-described teaching and within the scope of the attached claims without deviating from the scope of protection of the invention.

[0092] Furthermore, the areas in which experts would likely be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention. Accordingly, the invention is not intended to be limited by the specific illustrative embodiments, but only by the scope of protection defined in the accompanying claims.

Claims

R. 415124 REQUIREMENTS 1. A method for operating a drive system of a mobile working machine, wherein the drive system comprises an electric motor (305) that drives at least one wheel (303) of the working machine, and wherein the mobile working machine comprises an input device (330) having one or more operating elements with which the operator of the mobile working machine can control the drive system, characterized in that the method comprises the following steps: a) determining a current speed of the mobile working machine or a quantity dependent thereon; b) determining a current torque corresponding to the torque generated by the electric motor (305) or a quantity dependent thereon; c) acquiring an input via the input device (330);d) Checking for a fault condition based on the speed determined in step a), on a comparison of the torque determined in step b) with a reference torque and on the input acquired in step c) via the input device (330).; 2. Method according to claim 1, wherein the drive is brought into a drive-less state if the test in step d) shows that a fault condition exists, so that the working machine is brought into a safe state.

3. Method according to one of the preceding claims, wherein the reference torque used in step d) for checking for a fault condition depends on the direction of the velocity determined in step a), and wherein the reference torque preferably also has a time dependence in addition to this dependence.

4. Method according to one of the preceding claims, wherein in step b) an acceleration is additionally determined which describes a current acceleration of the mobile working machine in the direction of travel or a quantity dependent thereon, and wherein in step d) the check for a fault condition additionally comprises a comparison of the acceleration determined in step b) with a reference acceleration.

5. Method according to claim 4, wherein the reference acceleration used in step d) for checking for a fault condition depends on the direction of the velocity determined in step a), and wherein the reference acceleration preferably also has a time dependence in addition to this dependence.

6. Method according to one of the preceding claims, wherein the working machine comprises a power shift transmission (304) arranged between the electric motor (305) and a driven wheel (303), and which is actively synchronized by means of the electric motor (305) during a gear change. R. 415124 7. Method according to claims 4 and 6, wherein the acceleration determined in step b) is determined from the transmission output speed of the powershift transmission (304) or from a quantity dependent thereon, so that a suitable value for the acceleration is also determined during a gear change.

8. The method according to claims 4 and 6, wherein in step b) the current acceleration is determined from the rotational speed of the electric motor (305) or from a quantity dependent thereon, and wherein the method comprises the following additional steps: e) specifying a target speed for the rotational speed of the electric motor (305) for the purpose of active transmission synchronization during a gear change; f) controlling the electric motor (305) taking into account the target speed specified in step e) during a gear change;g) Adjusting the reference acceleration used in step d) to check for a fault condition to the target speed specified in step e) or adjusting the target speed to the reference acceleration, so that an acceleration determined in step b) which corresponds to the change in the target speed over time, when compared with the reference acceleration in step d) during a gear change, leads to the test result that no fault condition exists.

9. The method of claim 6, 7 or 8, wherein the method comprises the following additional steps: h) specifying a torque setpoint for the torque generated by the electric motor (305) for the purpose of active transmission synchronization during a gear change; i) controlling the electric motor (305) taking into account the torque setpoint specified in step h) during a gear change; j) adjusting the reference torque to be used in step d) for checking for a fault condition to the torque setpoint specified in step h) or adjusting the torque setpoint to the reference torque such that a torque determined in step b) which corresponds to the torque setpoint, when compared with the reference torque in step d) during a gear change, leads to the test result that no fault condition exists.

10. Method according to claim 8 or 9, wherein the working machine comprises a drive control unit (300) performing steps a), b), c) and d), and the working machine further comprises a transmission control unit (301) that specifies the speed setpoint for the electric motor (305) in step e) and / or the torque setpoint for the electric motor (305) in step h). R. 415124 11. Method according to claim 6 or 7, wherein the check for a fault condition by means of step d) is temporarily not carried out or the detection of a fault condition is temporarily suppressed while a gear change takes place in the power shift transmission (304), so that detection of supposed fault conditions during a gear change is avoided as a result of the active transmission synchronization.

12. Computing unit configured to perform a method according to any of the preceding claims.

13. Mobile working machine comprising a computing unit according to claim 12 and a drive system, wherein the drive system comprises an electric motor (305) that drives at least one wheel (303) of the working machine, and wherein the mobile working machine has a Input device (330) comprising one or more control elements with which the operator of the mobile working machine can control the drive system.

14. Computer program that causes a computing unit to perform a method according to any one of claims 1 to 11 when executed on the computing unit.

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