Method for operating a work machine

Abstract

The invention relates to a method for operating a work machine in order to simulate creep with the work machine. The work machine has an electric machine (2) as a traction motor. The method has a step of detecting (20) a position of a driver-operated element (8) of the work machine. The method has a step of determining (22) a creep torque depending on the position of the driver-operated element (8). As the position of the driver-operated element (8) increases, a smaller creep torque is determined, wherein the creep torque is greater than zero when the driver-operated element (8) is in a zero position. The method has a step of determining (24) a driving torque depending on the position of the driver-operated element (8). In addition, the method has a step of controlling (26) the electric machine (2) depending on the determined creep torque and the determined driving torque. The invention furthermore relates to a control device (18) and to a work machine having the control device (6).

Description

[0001] Method for operating a work machine

[0002] Technical area

[0003] The present invention relates to a method for operating a work machine. The invention also relates to a control device and a work machine with the control device.

[0004] State of the art

[0005] Work machines, for example excavators, graders, or agricultural machinery, often have an internal combustion engine as a traction motor to provide propulsion. In a work machine with an internal combustion engine and a fixed-gear transmission, which can provide different gears with a fixed gear ratio, a torque converter transmission is often used. The torque converter transmission can have a converter, for example a hydrodynamic torque converter such as a Trilok converter. The torque converter transmission can serve as a starting element. In such a case, the work machine creeps in one direction of travel as soon as a gear is engaged and, for example, the internal combustion engine is running at an idle speed and an idle torque. Operating an accelerator pedal is not necessary for this because the torque converter transmission always transfers drive power from the internal combustion engine to an output.The crawling speed is not fixed, but depends, for example, on the gear engaged and the load applied to the output. Different loads and, alternatively or additionally, different road gradients result in different crawling speeds. For example, the resulting crawling speed is slower uphill and faster downhill.

[0006] There are also work machines that use an electric motor as a traction motor. With such a work machine, a starting element is not required, as the electric motor can deliver torque even when the motor shaft is stationary, allowing starting without a torque converter. If the driver of such a work machine does not press the accelerator pedal, the work machine will not creep forward, even if a gear is engaged.

[0007] Typically, operators of off-highway machinery predominantly or even exclusively use the same off-highway machinery or machines of the same type over the long term. Accordingly, operators become accustomed to the specific features and characteristics of this off-highway machinery or machine type. For example, the operator learns the machine's creeping behavior when the accelerator pedal is not depressed and uses this behavior to control the machine as desired. If such an operator then switches to a off-highway machinery with different characteristics, operating errors can occur. In general, operators may feel uncomfortable using off-highway machinery whose creeping behavior does not meet their expectations.

[0008] Description of the invention

[0009] A first aspect of the invention relates to a method for operating a work machine in order to simulate crawling with the work machine. The work machine can be designed, for example, as an agricultural machine or construction machine. Examples of a work machine are a tractor and a wheel loader. The work machine has an electric machine as a traction motor. The electric machine can be designed, for example, as a synchronous machine or asynchronous machine. The electric machine can optionally be designed for recuperation. The work machine can have a motor controller for the electric machine, which is designed, for example, as an inverter. The work machine can have a transmission through which a drive force generated by the traction motor can be transmitted to an output of the work machine, for example with adjustable different gear ratios.The transmission can be designed, for example, as a single-speed transmission, a multi-speed transmission, a continuously variable transmission, or alternatively or additionally as a power-split transmission. An output can be designed, for example, as a shaft connected to a differential of the working machine. An output can also be designed as a driven axle, wheels, or a drive chain. For example, the traction motor cannot generate propulsion if there is no torque demand on the electric motor. Without simulation of creep, the working machine with the electric motor will then remain stationary on one level, despite the activated drive train.

[0010] Propulsive force is only provided when a driving element, such as an accelerator pedal, is actuated. However, by simulating creep, this propulsive force can also be provided when the driving control element is not actuated.

[0011] In addition, the work machine can also be designed to provide working power, for example for working hydraulics. The work machine can be designed not to generate any drive power with the traction motor in certain states, for example when no propulsion is required and no auxiliary consumers need to be driven by the traction motor. The work machine can have a reversing gear by means of which, for example, a direction of rotation at the output can be reversible relative to the drive, for example in order to reverse a direction of travel of the work machine. The reversing gear can be part of the gear box or formed separately therefrom. The work machine can, for example, be free of a gear box and the output can be coupled directly to the electric machine. The work machine can, for example, be free of a hydrodynamic converter or a starting clutch.

[0012] The method comprises a step of detecting a position of a travel control element of the work machine. The travel control element can, for example, be designed for actuation by a driver of the work machine in order to detect a drive request from the driver. The travel control element can, for example, control a power transmission to the output and, alternatively or additionally, a drive force generation of the electric machine. A drive force provided to the output or a torque for driving can correspond to the actuated position of the travel control element. The travel control element can be designed to automatically return to a zero position without actuation by the driver. The position of the travel control element can, for example, be an operating travel by which the driver has actuated the travel control element. The travel control element can be designed as an accelerator pedal.The accelerator pedal allows intuitive control of the machine's travel speed. The travel control element can also be configured as a lever, a joystick, or a virtual element operated via a touchscreen.

[0013] The method comprises a step of determining a creep torque depending on the position of the drive control element. In the zero position of the drive control element, the creep torque is greater than zero. The creep torque can therefore be provided by the electric machine and a drive train of the work machine when the drive control element is not actuated, so that a propulsive force is applied to the output of the work machine. As the position of the drive control element increases, a smaller creep torque can be determined. An increasing position can be a position deviating from the zero position, whereby an increase can be caused by increasing actuation by the driver. The creep torque can therefore decrease when the driver begins to actuate the drive control element and thus deflect it from its zero position. The creep torque can be a control for a torque output to the electric machine.For example, an engine control unit can determine the creep torque based on a characteristic curve or map. The characteristic curve can, for example, represent a relationship between the position of the driving control element and a creep torque to be determined. The creep torque can, for example, be independent of the direction of travel and determined only in terms of magnitude, or it can depend on a selected direction of travel. For example, different characteristic curves or maps for the creep torque can be stored in the engine control unit depending on the direction of travel.

[0014] The method comprises a step of determining a driving torque as a function of the position of the driving control element, wherein a greater driving torque is determined as the position of the driving control element increases. In a zero position of the driving control element, which can occur, for example, when the driving control element is not actuated, the driving torque can be zero. For example, the driving torque is determined by the engine control unit based on a position-driving torque characteristic curve or a position-speed-driving torque characteristic map. The driving torque can, for example, be independent of the direction of travel and only be determined in terms of its amount, or it can depend on a selected direction of travel. For example, different characteristic curves or maps for the driving torque can be stored in the engine control unit depending on the direction of travel.The driving torque can be used to control the actual driving performance of the working machine, for example to set a desired speed.

[0015] The method comprises a step of controlling the electric machine as a function of the determined creep torque and the determined driving torque. The electric machine can, for example, be controlled to output only the determined creep torque when the position of the driving control element is the zero position, since, for example, the driving torque is determined to be zero. The electric machine can, for example, be controlled to output a sum of the determined driving torque and the determined creep torque when the position of the driving control element is not the zero position. In principle, the electric machine can, for example, always be controlled to provide a sum of driving torque and creep torque. For example, the engine control system can add the determined creep torque to the determined driving torque as a variable torque offset.By applying the creep torque, the driven machine begins to move slowly in the selected direction of travel, even if the drive control is not actuated and returns to the neutral position, provided that driving resistance can be overcome. Depending on the load applied to the output, the driven machine moves at a constant speed or slows down or speeds up. This method makes it possible to simulate a creeping behavior of the driven machine that is not originally caused by the design of the driven machine with an electric motor. This allows different drivers to achieve a familiar creeping behavior of the driven machine with the drive control not actuated.

[0016] By taking the creep torque into account as a variable torque offset, other functions of the electric motor and transmission are retained, and the conventional engine control system can be used to determine the drive torque without simulating creep. This means that there is no need for complex adaptation and modification of an entire engine control system. Furthermore, dead travel of the drive control element can be avoided due to the creep torque decreasing with increasing position of the drive control element. If the creep torque were not reduced with increasing position of the drive control element, the electric motor would no longer provide a higher overall drive torque at one end of the drive control element's adjustment range. Typically, when the drive control element is actuated at 100%, 100% of the engine power should also be requested.However, with a constant torque offset, which does not decrease with increasing position of the drive control, 100% engine power would be requested even before the drive control is operated to 100%. Further operation from this point onwards would then no longer lead to an increase in power and would therefore represent a dead zone of the drive control that is noticeable to the driver. This can be avoided by the method according to the first aspect. By reducing the creep torque with increasing position of the drive control, a smooth transition to the requested drive torque can be ensured when the drive control is operated to a large extent, and driving comfort is improved. For example, there is no discrete jump in the total drive torque provided by the electric motor because, from a certain position of the drive control, an otherwise constant creep torque is no longer requested.

[0017] For example, the gradient of increasing driving torque is greater than the magnitude of the gradient of decreasing creep torque. As a result, the torque requested by the controller, and thus also the torque output, increases strictly monotonically with increasing accelerator pedal position. If the gradient of the driving torque were smaller than the magnitude of the gradient of the creep torque, the sum of these and thus the torque output would exhibit an inflection point. The torque output could then first decrease from an initial value in a driving range and then increase again depending on the accelerator pedal position. This would be counterintuitive behavior of the work machine for the driver, since the driver always expects increasing torque output with increasing accelerator pedal position. This can be avoided by appropriately coordinating the gradients of the creep torque as a function of the accelerator pedal position and the driving torque as a function of the accelerator pedal position.

[0018] In a further embodiment of the method, the method may include a step of detecting a rotational speed of the electric motor, and the creep torque may decrease as the rotational speed of the electric motor increases. This makes it possible to simulate that, during creep, the propulsive force is only sufficient to overcome a certain load and reach a certain driving speed. For example, ride comfort can be improved.

[0019] In a further embodiment of the method, the creep torque can decrease strictly monotonically with increasing speed of the electric motor. For example, the creep torque can decrease linearly or exponentially. As a further example, the creep torque can decrease continuously, alternatively or additionally with a constant gradient. This can increase ride comfort.

[0020] In a further embodiment of the method, the method can comprise a step of selecting a first creep level and at least one second creep level. The creep torque can be determined depending on the selected creep level. The first creep level and the second creep level can, for example, be stored in the engine control unit and contain different characteristic curves or maps for the creep torque. By providing different creep levels, which result in different creep torques, the driver can, for example, select a desired creep behavior based on their own preferences or the current usage situation.

[0021] In a further embodiment of the method, the determined creep torque can be greater for the selected second creep stage when the drive control element is in the neutral position than for the selected first creep stage. As a result, a smaller creep torque is generated when starting in the neutral position at the first creep stage than when starting in the neutral position at the second creep stage. This allows for a different degree of creep to be specified when the drive control element is not actuated.

[0022] In an alternative preferred embodiment, the determined creep torque is greater at the selected first creep stage than at the selected second creep stage. This allows the behavior of the converter to be simulated. In a further embodiment of the method, the decrease in the determined creep torque with increasing position of the driving control element can be determined according to a first characteristic curve at the selected first creep stage and according to a second characteristic curve at the selected second creep stage.

[0023] The first characteristic curve can differ from the second characteristic curve. For example, the first characteristic curve and the second characteristic curve can be designed such that the specific creep torque decreases more sharply with increasing position of the drive control element in the selected second characteristic curve than in the selected first characteristic curve. The first characteristic curve and the second characteristic curve can differ in at least one of their shape, their course over the engine speed, their course over the position of the drive control element, their resulting creep speed of the work machine, or a combination thereof. This can achieve different behavior for a reduction in the creep torque superimposed on the drive torque. This can influence drive comfort with the different creep levels and also the course of the overall drive torque required by the electric motor.This allows different drive trains to be simulated using the method.

[0024] In a further embodiment of the method, the creep torque can be determined as zero if the speed of the electric machine is greater than a speed threshold. The electric machine can thus be controlled to output only the driving torque if the speed of the electric machine is greater than the speed threshold. For example, the speed threshold can be a fixed value of . Up to the speed threshold, the creep torque can be determined by its increasing reduction to zero. The speed threshold can therefore specify the speed up to which the creep torque superimposed during engine control is reduced. The speed threshold can also be adjustable by the driver, for example, to any value. If the speed threshold is set to 0, creeping is prevented altogether and the creep function can thus be easily deactivated.

[0025] In a further embodiment of the method, the working machine can

[0026] Multi-gear drivetrains can be used, and the creep torque can be determined based on the selected gear. This allows the creep torque to be set for each gear. For example, different characteristic curves can be used for determining the creep torque for each gear, analogous to the two creep stages. This allows gear-dependent creep behavior to be simulated.

[0027] In a further embodiment of the method, the creep torque can be determined as zero when a parking brake of the work machine is activated. This can prevent the electric motor from pressing against the parking brake. This can reduce load on the drive train and energy consumption. When the parking brake is deactivated, for example, the creep torque proportional to the position of the drive control element can be determined immediately in order to begin creeping without delay. Alternatively or additionally, the creep torque can be determined as zero when a brake control element is actuated. When the brake control element, e.g. a brake pedal, is actuated, the creep torque can be deactivated in order to prevent the electric motor from operating against a braking force generated by a braking system. The creep torque can also be reduced proportionally to a position of the brake control element.This means that a creep torque can continue to be noticeable to the driver at the output, although the load on the drivetrain and energy consumption can be low. Alternatively or additionally, the creep torque can be determined as zero if no direction of travel is selected. This makes it possible to idle with the electric motor at a standstill despite creep mode being activated. Alternatively or additionally, the creep torque can be determined as zero if a switch for switching the creep behavior on and off is in the OFF position. The creep function can therefore be activated or deactivated. Otherwise, this description assumes that creep mode or the creep function is activated. Alternatively or additionally, the creep torque can be determined as zero if an output speed is above a speed threshold.For example, additional creep behavior may be undesirable if the work machine has exceeded a certain travel speed. A second aspect of the invention relates to a control device. The control device can be configured to carry out the method according to the first aspect. Respective advantages and further features can be found in the description of the first aspect, with embodiments of the first aspect also forming embodiments of the second aspect, and vice versa.

[0028] The control device is designed for a work machine which has an electric machine as a traction motor. The control device is designed to control the electric machine in order to simulate creeping with the work machine. The control device is designed to determine a creep torque as a function of a position of a travel control element, wherein a smaller creep torque is determined as the position of the travel control element increases, and wherein the creep torque is greater than zero in a zero position of the travel control element. The control device is designed to determine a travel torque as a function of the position of the travel control element, wherein a larger travel torque is determined as the position of the travel control element increases. The control device is designed to control the electric machine as a function of the determined creep torque and the determined travel torque.For example, the control device controls the electric machine to provide a sum of the determined creep torque and the determined driving torque. For example, the control device has an inverter for this purpose, which is connected to the electric machine to supply it with power.

[0029] A third aspect relates to a work machine. The work machine can be configured to be operated using the method according to the first aspect. The work machine can have a control device according to the second aspect. Respective advantages and further features can be found in the description of the first and second aspects, respectively, wherein embodiments of the first and second aspects also form embodiments of the third aspect, and vice versa.

[0030] The work machine comprises an electric machine as a traction motor, a drive control element, a detection device that detects a position of the drive control element, and a control device according to the second aspect. The detection device can optionally also be configured to detect a rotational speed of the electric machine, an operating state of the work machine, an actuation of a brake control element, a state of a parking brake, a selected direction of travel, and alternatively or additionally, a selection of a creep speed.

[0031] Short description of the characters

[0032] Fig. 1 schematically illustrates parts of a work machine.

[0033] Fig. 2 shows a block diagram of a control system of the working machine for simulating creep behavior.

[0034] Fig. 3 schematically illustrates characteristic curves for controlling Fig. 2.

[0035] Detailed description of embodiments

[0036] Fig. 1 schematically illustrates parts of a work machine. The work machine has an electric machine 2, which serves as a traction motor for driving an output 4 of the work machine. The electric machine 2 is connected to a control device 6, which controls a torque output of the electric machine 2. The control device 6 is connected to an accelerator pedal 8, which serves as a driving control element. A detected position of the accelerator pedal 8 is transmitted to the control device 6. The accelerator pedal 8 is actuated proportionally by a driver to respond to a driving request. If not actuated, the accelerator pedal 8 automatically returns to a neutral position.

[0037] Fig. 2 shows a block diagram of a control system for simulating creep behavior. In a step 20, a position of the accelerator pedal 8 is detected. In a step 22, a creep torque is determined based on a characteristic curve 36 shown in Fig. 3. In a step 24, a driving torque is determined based on a characteristic curve 34 shown in Fig. 3. In a step 26, the electric machine 2 is controlled as a function of the determined creep torque and the determined driving torque. The electric machine 2 is controlled to output a torque that corresponds to the sum of the determined creep torque and the determined driving torque. A speed of the electric machine 2 results from a driving state of the work machine, wherein the driving state results from the torque output of the electric machine 2, the driving resistances acting on the work machine, and any additional loads on the output 4.

[0038] Fig. 3 schematically illustrates characteristic curves for controlling the work machine of Fig. 1 for creep behavior. The abscissa 30 represents the accelerator pedal position of the accelerator pedal 8, with the accelerator pedal position increasing from the zero position to the right. Torques are plotted on the ordinate 32, increasing upwards. In Fig. 3, characteristic curve 34 illustrates a driving torque, characteristic curve 36 illustrates a creeping torque, and characteristic curve 38 illustrates the total torque specified for the electric machine 2 by the control device 6.

[0039] Fig. 3 also shows a creep speed selected by the driver. Different characteristic curves are stored for further creep speeds. As illustrated in Fig. 3, the driving torque 34 is zero when the accelerator pedal 8 is in the neutral position. As the accelerator pedal 8 position increases, the driving torque 34 increases linearly, as shown in the example.

[0040] However, it is also conceivable that the driving torque 34 does not increase linearly; in particular, the driving torque 34 can depend on the driving resistances and the way in which the accelerator pedal 8 is actuated.

[0041] In the zero position, the creep torque 36 assumes an initial value 37 that is greater than zero. As the position of the accelerator pedal 8 increases, the creep torque 36 decreases linearly until it reaches zero at a position threshold value 39 of the accelerator pedal 8. The torque setpoint 38 is determined as the sum of the creep torque 36 and the driving torque 34. From the position threshold value 39, the torque setpoint 38 corresponds to the driving torque 34.

[0042] The initial creep torque 36, which serves as a torque offset for controlling electric motor 2, is thus continuously reduced over the accelerator pedal travel up to the position threshold 39, so that there is no dead travel at the end of the accelerator pedal 8 actuation range and no step-like torque changes occur. Due to the reduction in creep torque with increasing accelerator pedal position, the torque specification gradient up to the position threshold 39 is lower than after the position threshold 39.

[0043] Electric motor 2 is controlled to output torque 38 as torque. Since torque 38 has a value greater than zero even when the accelerator pedal is in the neutral position, creeping behavior of the working machine is simulated.

[0044] While in the embodiment the creep moment 36 decreases linearly from the initial value

[0045] 37 decreases to zero, in another embodiment the creep torque decreases non-linearly, but strictly monotonically, and flattens out as it approaches the position threshold 39 and thus zero. This avoids discrete jumps in the gradient of the torque specification 38. Thus, a kink in the characteristic curve

[0046] 38 can be avoided. This improves driving comfort. For example, the rate of change of the torque specification 38 can change gradually with increasing accelerator pedal position up to the position threshold 39 and then remain constant. This can also prevent the driver from detecting, through the reaction of the electric motor 2 to the accelerator pedal position, when the torque offset has been reduced due to the variable creep torque.

[0047] Reference symbol

[0048] electric machine

[0049] downforce

[0050] Control device

[0051] Driving control element

[0052] Step / Detecting the position of the driving control element

[0053] Step / Determine the creep moment

[0054] Step / Determine the driving torque

[0055] Step / Control of the electric machine depending on the specific creep torque and the specific driving torque Abscissa / Accelerator pedal position

[0056] Ordinate / torques

[0057] Characteristic curve / driving torque

[0058] Characteristic curve / creep torque

[0059] Initial value of the creep moment

[0060] Characteristic curve / torque specification for the electric machine Position threshold value for the creep torque

Claims

Patent claims 1 . A method for operating a work machine having an electric machine (2) as a traction motor in order to simulate creeping with the work machine, the method comprising at least the following steps: - detecting (20) a position of a driving control element (8) of the working machine; - determining (22) a creep torque as a function of the position of the driving control element (8), wherein a smaller creep torque is determined with increasing position of the driving control element (8) and wherein in a zero position of the driving control element (8) the creep torque is greater than zero; - determining (24) a driving torque as a function of the position of the driving control element (8), wherein a greater driving torque is determined with increasing position of the driving control element (8); and - controlling (26) the electric machine (2) as a function of the determined creep torque and the determined driving torque.

2. Method according to claim 1, characterized in that the method comprises a step of detecting a rotational speed of the electric machine (2) and the creep torque decreases with increasing rotational speed of the electric machine (2).

3. Method according to claim 2, characterized in that the creep torque decreases strictly monotonically with increasing speed of the electric machine (2).

4. Method according to one of the preceding claims, characterized in that the method comprises a step of selecting a first creep stage and at least one second creep stage and the creep torque is determined as a function of the selected creep stage.

5. Method according to claim 4, characterized in that in the zero position of the driving control element (8) the determined creep torque is greater at the selected first creep stage than at the selected second creep stage.

6. Method according to claim 4 or 5, characterized in that the decrease in the determined creep torque with increasing position of the driving control element (8) is determined in the selected first creep stage according to a first characteristic curve and in the selected second creep stage according to a second characteristic curve, wherein the first characteristic curve differs from the second characteristic curve.

7. Method according to one of the preceding claims, characterized in that the creep torque is determined as zero if the speed of the electric machine (2) is greater than a speed threshold value.

8. Method according to one of the preceding claims, characterized in that the working machine has a multi-speed drive and the determination of the creep torque is carried out as a function of the selected gear.

9. Method according to one of the preceding claims, characterized in that the creep moment is determined as zero if at least one of the following conditions is met: - a parking brake of the work machine is activated, - a brake control element is actuated, - no direction of travel is selected, and - a speed of an output (4) is above a speed threshold value.

10. Control device (6) for a work machine which has an electric machine (2) as a traction motor, wherein the control device (6) is designed to control the electric machine (2) in order to simulate creeping with the work machine, wherein the control device (6) is designed to determine a creep torque as a function of a position of a travel control element (8), wherein a smaller creep torque is determined with increasing position of the travel control element (8) and wherein in a zero position of the travel control element (8) the creep torque is greater than zero, to determine a travel torque as a function of the position of the travel control element (8), wherein a larger travel torque is determined with increasing position of the travel control element (8), and to control the electric machine (2) as a function of the determined creep torque and the determined travel torque.

11. A work machine, wherein the work machine comprises an electric machine (2) as a traction motor, a driving control element (8), a detection device which detects a position of the driving control element (8), and a control device which is designed as the control device (6) according to claim 10.

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