WO2023066937A1

WO2023066937A1 - Method for controlling an electric traction drive

Info

Publication number: WO2023066937A1
Application number: PCT/EP2022/078978
Authority: WO
Inventors: Andreas Rothmund; Matthias MADLENER; Mario Brugger
Original assignee: Zf Friedrichshafen Ag
Priority date: 2021-10-19
Filing date: 2022-10-18
Publication date: 2023-04-27
Also published as: DE102021211760B3

Abstract

The present invention relates to a method for controlling an electric traction drive (10) of a work machine (12), comprising the following steps: - sensing (50) operation of a motor torque control element (14); - sensing (52) operation of a braking torque control element (16) performed simultaneously with operation of the motor torque control element (14); - determining (54) a motor control value depending on the sensed simultaneous operation of the motor torque control element (14) and the braking torque control element (16), wherein the motor control value can assume a value in a negative value range and in a positive value range; - controlling (56) an electric machine (20) of the traction drive (10) depending on the determined motor control value, wherein the electric machine (20) generates a motor torque driving the work machine (12) in the case of control with a positive motor control value and wherein the electric machine (20) generates a motor torque braking the work machine (12) in the case of control with a negative motor control value. The invention also relates to a control device and to a work machine (10).

Description

Method for controlling an electric traction drive

technical field

The present invention relates to a method for controlling an electric traction drive of a working machine. In addition, the invention relates to a control device for controlling an electric traction drive of a working machine and to a working machine.

State of the art

Transmission systems for work machines with internal combustion engines are often very complex and expensive. For example, a hydrostatic power-split transmission can be provided in order to be able to provide a stepless translation, e.g. B. in DE 102008001 612 B4 described. Due to the power split, both a drive power and an auxiliary drive power can be provided by a single internal combustion engine. Depending on the desired deceleration and acceleration, the internal combustion engine and the transmission system can be controlled accordingly. There are numerous dependencies when the accelerator pedal and brake pedal are actuated due to the common drive for travel drive and working hydraulics.

The use of an electrified power train can result in simplifications here. For example, an electric machine can only be provided for providing the drive power and another electric machine for providing the auxiliary drive power. An electric traction drive can thus be used independently of a work train. In addition, the electric traction drive can also be used for recuperation. Recuperation can increase efficiency when using the working machine. In addition, use of a service brake of the work machine can be low, which means that it wears out more slowly. An adapted control can be useful for this. Presentation of the invention

A first aspect of the invention relates to a method for controlling an electric traction drive of a working machine. The working machine can be moved with the travel drive. The travel drive can be designed to provide drive power, for example at the respective wheels of the work machine. The drive power can be used to drive the working machine. The traction drive can have an electric machine, for example. The electric machine can be designed, for example, to supply the traction drive of the working machine with power. The electric traction drive can be designed to recuperate. The electric machine of the traction drive can be designed for recuperation.

The work machine can be designed as an agricultural machine, e.g. as a tractor, as a construction machine or as a special vehicle. An example of a work machine is a wheel loader in which the respective wheels can be driven by the drive power and a shovel can be raised and lowered as a tool by the working hydraulics. The work machine may provide a workstring for providing PTO power so as to operate a PTO. The PTO power can be used to supply power to a tool of the work machine, such as an adjustable blade or a hydraulic pump. The power take-off can supply power to the working hydraulics. A torque can be applied to a power take-off shaft, for example, by means of the auxiliary drive power provided.

The traction drive can have an energy source for operating the electric machines. For example, the traction drive can have a battery, which is designed to provide electrical energy for the electric machine. The electric machine can be designed to convert electrical energy into mechanical energy. During recuperation, the electric machine can also convert mechanical energy into electrical energy. An electric machine can be designed, for example, as a synchronous motor or an asynchronous motor. The method includes a step of detecting actuation of an engine torque control element. The motor torque control element can be designed for this detection. The engine torque control element is usually actuated by the driver of the work machine for a driving request. For example, the engine torque control element can be designed as an accelerator pedal or hand throttle. The engine torque control element may include a sensor for detecting actuation thereof. The actuation of the engine torque control element can be, for example, an adjustment to a specific position. In this case, for example, an engine torque control element position is detected. The actuation of the motor torque control element can be carried out, for example, by a push or a pull. The actuation may cause the engine torque control element to be offset from a home position. The home position of the engine torque control member may be a neutral position to which the engine torque control member automatically returns upon termination of actuation. For example, greater drive power can be requested from the traction drive by actuating the engine torque control element more strongly.

The method has a step of detecting an actuation of the

Motor torque control element simultaneous operation of a

braking torque control element. The brake torque control can for this

detection be trained. The braking torque control element is usually actuated by the driver of the work machine for a braking request. For example, the brake torque control element can be designed as a brake pedal or brake lever. The braking torque control element can have a sensor for detecting its actuation. The actuation of the braking torque control element can be, for example, an adjustment to a specific position. In this case, for example, a brake torque control element position is detected. The braking torque control element can be actuated, for example, by pressing or pulling. Actuation may cause the torque control member to be offset from an initial position. The starting position of the brake torque control element can be a neutral position, in which the braking torque control element returns automatically after the end of the actuation. For example, greater braking power can be requested from the traction drive by a stronger actuation of the braking torque control element. Braking power can be provided by recuperation using the electric machine as a generator and alternatively or additionally by operating a service brake.

The method includes a step of determining an engine control value

Depending on the detected simultaneous operation of the motor torque control element and the braking torque control element.

For example, the motor control value may be calculated as an average of a current displacement of the motor torque control element relative to its maximum displacement and a current displacement of the braking torque control element relative to its maximum displacement. A combined control signal can thus be determined from two sensor signals. The engine control value can assume a value in a negative value range and in a positive value range. For example, the engine control value may be in the positive range of values when the engine torque control element is actuated more than the braking torque control element. For example, the engine control value may be in the positive range of values when the engine torque control element is actuated less than the braking torque control element.

The method can include a step of controlling an electric machine

Have traction drive depending on the specific engine control value. Due to this control, the electric machine generates a motor torque that drives the working machine with a positive motor control value. Due to this control with a negative motor control value, the electric machine generates a motor torque that decelerates the working machine. The braking engine torque can be generated by recuperation. In this case, the electric machine can be operated as a generator.

The method can be used to detect when the driver operates the engine torque control element and the brake torque control element at the same time. One such actuation can be an incorrect operation, which can nevertheless be meaningfully processed by the method. Such an operation can also be traced back to learned driving of conventional working machines with an internal combustion engine, in which at the same time a higher power for the tool is to be made available with simultaneous stopping. By controlling the electric machine according to the method, the electric machine can be prevented from moving against a service brake. In addition, meaningful control of the traction drive can also be achieved with simultaneous actuation of the motor torque control element and the braking torque control element. So a driver for driving a work machine with electric

travel drive cannot be retrained. In addition, in addition to operating a service brake, the braking force can also be increased by a generator torque on the electric machine, even if the driver continues to operate the engine torque control element to a certain extent, for example by pressing it.

In one embodiment of the method, it can be provided that the motor control value changes in the negative value range as a function only of the detected actuation of the braking torque control element. As soon as the electric machine is operated as a generator for recuperation, a braking force generated by the electric machine can only be changed by the braking torque control element. This prevents unwanted change in deceleration by operation of the engine torque control element. Alternatively or additionally, it is provided that the engine control value changes in the positive value range as a function of the simultaneously detected actuation of the braking torque control element and the engine torque control element. So the driver can a working machine driving torque

Change the electric machine by operating both the motor torque control element and the braking torque control element. For example, a driving speed can be reduced when using a hand throttle by actuating the braking torque control element. The work machine continues to drive efficiently since, for example, only the drive power can be reduced instead of working against a braking force of a service brake with the same drive power. Accordingly, it is not necessary to deactivate the hand throttle to enable efficient electric driving. In one embodiment of the method, it can be provided that the method has a step of detecting an actuation of a first engine torque control element. In addition, the method may include a step of detecting actuation of a second engine torque control element. The two engine torque control can be different

Engine torque control elements such as a hand throttle control element, a cruise control element and an accelerator pedal. Increased actuation of an engine torque control may be a driver's manipulation of the engine torque control that signifies a desired greater drive power. For example, pushing an accelerator pedal to its maximum position may be a stronger actuation than pulling a hand throttle to a mid-position.

The method may include a step of determining one of the first engine torque control element and the second

Have motor torque control element, which is actuated more. The method may be based only on the sensed actuation of whichever of the two engine torque controls is more heavily actuated. For example, the engine control value can be determined as a function of the detected simultaneous actuation of that engine torque control element which is actuated more strongly and of the braking torque control element. Thus, both motor torque control elements can be used selectively without having to be activated or the like. For example, when adjusting the hand throttle, you can simply step off the accelerator pedal with your foot.

In one embodiment of the method, it can be provided that the method has a step of detecting an actuation of a direction-changing element. The direction-changing element can be formed, for example, by a driving range selector lever or gear shift lever. A direction of travel of the work machine can be reversed by actuating the direction-of-travel element. For example, from a driving force acting in the forward direction can be switched to a driving force acting in the reverse direction. The motor control value can be determined as a function of the simultaneously detected actuation of the motor torque control element and the braking torque control element when actuation of the direction-changing element is detected, with a different function than when the direction-changing element is not actuated. In this way, a power reversal can be supported. For example, there is a different combination and calculation of the actuation of the accelerator pedal and the brake pedal in order to increase deceleration during power reversal. For example, this function can be used to determine the motor control value when actuation of the direction-changing element is detected for a predetermined period of time. Alternatively or additionally, this function can be used to determine the motor control value when the actuation of the direction-changing element is detected until a minimum speed is reached and alternatively or additionally until the direction of travel is reversed. Subsequently, for example, the otherwise usual combination and offsetting of the actuation of the accelerator pedal and the brake pedal can be used to determine the engine control value.

In one embodiment of the method, it can be provided that the method has a step of operating a service brake of the work machine as a function of the detected actuation of the braking torque control element. The operation can be a control of the service brake so that it generates a braking torque. The operation of the service brake can only take place, for example, once a predetermined actuation limit value of the braking torque control element has been reached. The actuation limit value can be fixed or determined as a function of a vehicle speed and, alternatively or additionally, an actuation of the engine torque control element. For example, the service brake can be operated as soon as the brake pedal has been pressed more than 50%.

When the service brake is actuated, the determined engine control value can be less than or equal to a predefined maximum engine control value. For example, the service brake is operated only if the engine control value is less than or equal to the specified maximum engine control value. This will prevent the Service brake acts against a strong drive power and is thus exposed to heavy wear. For example, as an alternative or in addition, based on the operation of the service brake, the engine control value is determined to be less than or equal to the specified maximum engine control value. In this way, the drive power can be throttled automatically when the braking torque control element is actuated, which causes the operating brake to be operated. This avoids inefficient use of the traction drive. The maximum motor control value is greater than zero, for example, and is therefore in the positive range of values. For example, a rollback on a slope can be prevented in this way, despite the common engine control value. The maximum motor control value can be determined, for example, as a function of an incline of the working machine. The maximum motor control value can be a fixed value. By taking a braking point into account, it can be ensured that the service brake is not used during normal travel. A driving force can be reduced as soon as the service brake begins to act. An engine braking force through recuperation, on the other hand, can support the service brake. The engine braking force due to recuperation can, for example, be arbitrarily high when operating the service brake.

In one embodiment of the method, it can be provided that a dead travel is taken into account when detecting the actuation of the engine torque control element. For example, the first 5% of an engine torque control element actuation has no effect on the engine control value. As a result, it can be prevented, for example, that undesired driving requests are commanded just because the driver has his foot on the accelerator pedal, for example. The dead path can be fixed or can also be parameterized. A dead travel may be provided for both the first engine torque control element and the second engine torque control element, and these dead travels may be different.

In one embodiment of the method, it can be provided that a dead travel is taken into account when detecting the actuation of the braking torque control element. For example, the first 5% of a brake torque control actuation has no effect on the motor control value. As a result, it can be prevented, for example, that undesired driving requests are commanded just because the driver has his foot on the brake pedal, for example. The dead path can be fixed or can also be parameterized.

In one embodiment of the method, it can be provided that signal filtering takes place when the actuation of the engine torque control element is detected. The signal filtering can be signal smoothing, for example. As a result, small changes and vibrations cannot change a drive control and thus make the control unsteady. For example, prime mover vibrations may also cause engine torque control element vibration, which may thus be filtered out. Signal filtering can be provided both for the first motor torque control element and for the second motor torque control element, and these signal filterings can be different.

In one embodiment of the method, it can be provided that signal filtering takes place when the actuation of the braking torque control element is detected. The signal filtering can be signal smoothing, for example. As a result, small changes and vibrations cannot change a drive control and thus make the control unsteady. For example, vibrations of the prime mover can also cause vibration of the brake torque control element, which can be filtered out in this way.

A second aspect of the invention relates to a control device for controlling an electric travel drive of a working machine. The control device has an engine torque control element, which is designed to detect an actuation by a driver of the work machine. The control device has a braking torque control element, which is designed to detect an actuation by a driver of the work machine. The control device has a determination device which is designed to determine an engine control value as a function of a detected simultaneous actuation of the engine torque control element and the braking torque control element. The motor control value can have a negative value range of values and in a positive range of values. For example, the determining device may be configured as a microprocessor configured to receive respective detection signals from the motor torque control element and the braking torque control element. The engine control value can be determined, for example, using a stored characteristic map. The control device has a control unit which is designed to control an electric machine of the traction drive as a function of the motor control value determined, the electric machine generating a motor torque that drives the working machine when controlled with a positive motor control value and the electric machine when controlled with a negative motor control value generates a motor torque that decelerates the working machine. The control device can be designed, for example, to transmit the motor control value to an inverter of the electric traction drive. The control unit can also be designed as an inverter, for example. The controller may be configured to receive the engine control value from the determining device. The control unit and the determination device can be designed as a common electronic control unit.

The control device can be designed to carry out the method according to the first aspect. Additional features, embodiments and advantages can be found in the descriptions of the first aspect. Conversely, features, embodiments and advantages of the second aspect also represent features, embodiments and advantages of the first aspect.

In one embodiment of the control device, it can be provided that the motor torque control element is designed as an accelerator pedal. The result is simple and intuitive control. Alternatively or additionally, a hand throttle can also be provided as an engine torque control element, for example as a second engine torque control element.

In one embodiment of the control device, it can be provided that the braking torque control element is designed as a brake pedal. The result is simple and intuitive control. A third aspect of the invention relates to a work machine. The working machine has an electric traction drive with at least one electric machine. The work machine includes a control device according to the second aspect. The electric machine of the traction drive and the traction drive itself can with the

Process can be controlled according to the first aspect. Additional features, embodiments and advantages can be found in the descriptions of the first and second aspects. Conversely, features, embodiments and advantages of the third aspect also represent features, embodiments and advantages of the first and second aspect.

Brief description of the drawing

1 schematically illustrates a method for controlling an electric traction drive of a working machine.

2 schematically illustrates a work machine.

3 schematically illustrates a determination of an engine control value.

4 illustrates further details of the control of the traction drive.

Detailed Description of Embodiments

FIG. 1 schematically illustrates a method for controlling an electric traction drive 10 of a working machine 12, the working machine 12 being shown schematically in FIG. In step 50, an actuation of an engine torque control element 14 is detected. As can be seen in FIG. 3, the engine torque control element 14 is designed as an accelerator pedal. In step 52, an actuation of a braking torque control element 16 that is simultaneous with the actuation of the motor torque control element 14 is detected. As can be seen in FIG. 3, the braking torque control element 16 is designed as a brake pedal. In step 54, a motor control value is determined as a function of the detected simultaneous actuation of the motor torque control element and the braking torque control element by a determination device 18. The motor control value can assume a value in a negative value range and in a positive value range, as described in more detail with reference to FIG becomes. In step 56, an electric machine 20 of the traction drive 10 is controlled as a function of the motor control value determined. When controlled with a positive engine control value, electric machine 20 generates engine torque that drives work machine 12 . When controlled with a negative engine control value, electric machine 20 generates an engine torque that decelerates work machine 12 .

3 illustrates the determination of the engine control value using a family of characteristics. An actuation of the brake pedal is plotted on the abscissa 60 as a percentage of a maximum deflection of the brake pedal. The engine control value is plotted on the ordinate 62 as a percentage of a maximum or minimum engine control, which corresponds to a maximum driving or braking engine power. With a motor control value of 100%, the electric machine 20 is controlled in such a way that it provides the currently maximum available drive power. With an engine control value of -100%, electric machine 20 is controlled in such a way that it provides the currently maximum possible generator power for recuperation.

The three characteristic curves 64, 66 and 68 each correspond to an accelerator pedal position. At the top characteristic curve 64, the accelerator pedal 14 is depressed 100%. In the middle characteristic curve 66, the accelerator pedal is depressed 50%. In the case of the lowest characteristic curve 68, the accelerator pedal is not actuated at all and is therefore depressed by 0%.

The top characteristic curve 64 illustrates that the maximum currently available drive power is constantly provided with up to 5% brake pedal actuation. This corresponds to a dead travel of the braking torque control element. It can also be seen in the middle characteristic curve 66 that up to 5% brake pedal actuation, a constant 50% of the maximum engine control value is determined. This again corresponds to the dead path. If the braking torque control element is actuated harder, it falls the engine control value linearly to 0% as the engine control value both when the accelerator pedal 14 is depressed 100% and when the accelerator pedal 14 is depressed 50% and when the brake pedal 16 is actuated 25%. With 0% accelerator pedal 14 actuated, the engine control value remains at 0% until 25% brake pedal 16 actuation. In this region with a positive engine control value, the drive power is therefore a function of the simultaneously detected actuation of the braking torque control element and the engine torque control element. In one embodiment, the actual drive power can depend on a current driving state and therefore does not have to change linearly with the engine control value.

When the brake pedal 16 is actuated more than 25%, the electric machine 20 is operated as a generator and thus brakes the work machine 12 by recuperation. The motor control value falls linearly to its minimum value of -100%, independent of the actuation of the accelerator pedal 14. The motor control value is determined in the negative range of values as a function of only the sensed brake torque control element actuation. The generator power and thus the braking torque increase continuously, with the actual braking power in one embodiment being able to depend on a current driving state and therefore not having to change linearly with the engine control value.

4 illustrates an actuation of the brake pedal as a percentage of a maximum deflection of the brake pedal on the abscissa 80 . A characteristic curve 82 illustrates a motor power of the electric machine 20 as a percentage of a maximum power. A characteristic curve 84 illustrates a braking power of the traction drive as a percentage of a maximum power. Again the dead travel of the brake predal 16 of 5% can be seen. The engine power then falls as the brake pedal 16 is actuated further. From a brake pedal actuation of 60%, a service brake 22 is operated in the embodiment now illustrated, as a result of which the braking power increases. There is an overlapping area 86 in which, at the same time, the service brake 22 is used to slightly brake and the electric machine 20 to provide drive power. This can prevent backward rolling on a slope. From a brake pedal actuation of 70%, no more drive power is provided and the characteristic curve 82 follows the abscissa 80. From this actuation of the brake pedal 16 or when the brake pedal is actuated again, in 4 illustrated by the break in characteristic curve 84, recuperation takes place by electric machine 20 and the braking power increases sharply. From about 90% of the brake pedal actuation, the working machine 12 is already decelerated to the maximum.

Reference sign

10 electric traction drive

12 working machine

14 Engine Torque Control

16 braking torque control element

18 determination device

20 electric machine

22 service brake

50 detecting an actuation of an accelerator pedal

52 Detection of an actuation of a brake pedal

54 Determining a motor control value

56 Controlling an electric machine

60 abscissa/percentage of brake pedal actuation

62 ordinate/ percentage motor control value

64 - 68 Characteristic curves/accelerator pedal positions

80 abscissa/percentage of brake pedal actuation

82 Characteristic curve/percentage motor power

84 Characteristic curve/ percentage braking power

86 Overlap Area

Claims

patent claims

1. A method for controlling an electric traction drive (10) of a working machine (12), which has the following steps:

- detecting (50) actuation of an engine torque control element (14);

- Detecting (52) simultaneous actuation of a braking torque control element (16) with the actuation of the motor torque control element (14);

- determining (54) a motor control value as a function of the detected simultaneous actuation of the motor torque control element (14) and the braking torque control element (16), wherein the motor control value can assume a value in a negative value range and in a positive value range;

- Controlling (56) an electric machine (20) of the traction drive (10) as a function of the motor control value determined, the electric machine (20) generating a motor torque that drives the working machine (12) during control with a positive motor control value, and the electric machine (20 ) in the control with a negative motor control value generates a motor torque that decelerates the working machine (12).

2. The method according to claim 1, characterized in that the engine control value changes in the negative value range as a function only of the detected actuation of the braking torque control element (16) and the engine control value changes in the positive value range as a function of the simultaneously detected actuation of the braking torque control element (16) and of the engine torque control element (14) changes.

3. The method according to claim 1 or 2, characterized in that the method has the following steps:

- detecting an actuation of a first motor torque control element (14),

- detecting an actuation of a second motor torque control element (14),

- determining which of the first motor torque control element (14) and the second motor torque control element (14) is more heavily actuated, the method only detecting the actuation of that of the two

Engine torque control elements (14) is taken as a basis, which is actuated more.

4. The method according to any one of the preceding claims, characterized in that the method further comprises the following step:

- Detection of an actuation of a direction-changing element, the motor control value being determined as a function of the simultaneously detected actuation of the engine torque control element (14) and the braking torque control element (16) when actuation of the direction-changing element is detected, with a different function than when the direction-changing element is not actuated.

5. The method according to any one of the preceding claims, characterized in that the method further comprises the following step:

- Operating a service brake (22) of the work machine (12) as a function of the detected actuation of the braking torque control element (16), the determined engine control value when the service brake (22) is actuated being less than or equal to a predetermined maximum engine control value.

6. The method according to any one of the preceding claims, characterized in that in the detection (50) of the actuation of the engine torque control element (14) a dead travel is taken into account.

7. The method according to any one of the preceding claims, characterized in that in the detection (52) of the actuation of the braking torque control element (16) a dead travel is taken into account.

8. The method according to any one of the preceding claims, characterized in that when detecting (50) the actuation of the motor torque control element (14), a signal filtering takes place.

9. The method according to any one of the preceding claims, characterized in that when detecting (52) the actuation of the braking torque control element, a signal filtering takes place.

10. Control device for controlling an electric traction drive (10) of a work machine (12), the control device having:

- an engine torque control element (14), which is designed to detect (50) an actuation by a driver of the working machine (12),

- a braking torque control element (16), which is designed to detect (52) an actuation by a driver of the working machine (12),

- a determination device (18) which is designed to determine (54) a motor control value as a function of a detected simultaneous actuation of the motor torque control element (14) and the braking torque control element (16), the motor control value having a value in a negative value range and in a positive value range can accept, and

- A control device, which is designed to control (56) an electric machine (20) of the drive (10) as a function of the determined motor control value, the electric machine (20) generating a motor torque that drives the work machine (12) when controlled with a positive motor control value generated and wherein the electric machine (20) when controlled with a negative motor control value generates a motor torque that decelerates the working machine (12).

11. Control device according to claim 10, characterized in that the motor torque control element (14) is designed as an accelerator pedal.

12. Control device according to claim 10 or 11, characterized in that the braking torque control element (16) is designed as a brake pedal.

13. Work machine (12) with an electric traction drive, which has at least one electric machine (20), and with a control device according to one of the preceding claims 10 to 12.