Method for operating an electric drive train of a work machine, electric drive train for a work machine, and work machine

Abstract

The invention relates to a method for operating an electric drive train (11) of a working machine (10), wherein the drive train (11) comprises a working drive (20) having an electric working motor (21) and a traction drive (30) having an electric traction motor (31) and wheels (32), wherein the working machine (10) is decelerated externally and wherein the braking force acting on the wheels (32) due to the deceleration can be less than the driving force acting on the wheels (32) due to the mass moment of inertia of the traction motor (31). The method according to the invention is characterized in that, when it is foreseeably detected (200) by means of a situation detection that the braking force acting on the wheels (32) due to the deceleration is less than the driving force acting on the wheels (32), a current (300, 301) in the opposite direction of its operation is applied to the traction motor (31) to reduce the rotational speed. The invention also relates to a corresponding electric drive train (11) and a corresponding working machine (10).

Description

Technical Field

[0001] The invention relates to a method for operating an electric drive train of a work machine, an electric drive train for a work machine, and a corresponding work machine. Background Art

[0002] Electrically driven work machines such as wheel loaders, compact loaders, telescopic loaders, dump trucks, or excavators are known in the prior art. These are either purely electrically driven, meaning they are powered solely by batteries, or diesel-electric, meaning the required energy is provided by a diesel-driven generator, typically in conjunction with an electrical buffer store, such as appropriately sized capacitors. In all cases, the mechanical power required for the travel and working drives is generated by one or more electric motors. Furthermore, hybrid-electric work machines are also known, in which the mechanical power required for operation is primarily generated by an internal combustion engine, typically a diesel engine. The additionally provided electric motor is fed by the battery and typically performs a so-called power boost function.

[0003] In this respect, DE 20 2014 000 738 U1 describes a purely electric motor-driven wheel loader having a first electric motor for the travel drive and a second electric motor for the working drive.

[0004] EP 0 962 597 A2 discloses a battery-operated work machine which has two electric motors for the travel drive and a further electric motor for the working drive.

[0005] However, known electrically driven working machines have the disadvantage that, due to the design of the electric motors used for their operation, they exhibit significant inertia in the drive train when the working machine is decelerated, i.e., when the electric motor's speed is reduced, particularly when braking is required via regenerative operation of the electric motor or mechanical friction brakes. This behavior is due to the relatively high speed and high mass inertia of the electric motor. Consequently, an electric motor rotating under full load possesses significantly more rotational energy than a correspondingly powerful internal combustion engine under full load. In electrically driven wheel loaders, for example, this can result in the bucket decelerating when the wheel loader is driven into a pile of earth or the like from medium or high speed, while the wheels fail to transmit the corresponding deceleration to the electric motor. Consequently, the wheels are forced to rotate under these conditions, causing the wheel loader to become undesirably stuck. Summary of the Invention

[0006] The object of the present invention is to propose an improved method for operating an electric drive train of a work machine.

[0007] The present invention relates to a method for operating an electric drive train of a work machine, wherein the drive train includes a work drive having an electric work motor and a traction drive having an electric traction motor and wheels, wherein the work machine is decelerated externally, and wherein the braking force acting on the wheels due to the deceleration can be less than the driving force acting on the wheels due to the mass moment of inertia of the traction motor. The method according to the invention is characterized in that, if it is foreseeably detected by means of situation detection that the braking force acting on the wheels due to the deceleration is less than the driving force acting on the wheels, a current in the opposite direction of its operation is applied to the traction motor to reduce the rotational speed.

[0008] The present invention therefore describes a method for operating an electric drive train for a working machine, wherein the drive train consists of at least two independently operable drives: a working drive and a travel drive. It is conceivable and preferred that the drive train also include additional components or drives, such as a power take-off or auxiliary drive. In particular, the drive train also includes an electric energy storage device, preferably a rechargeable battery. Both the working drive and the travel drive advantageously include one or more electric motors, which, depending on their assignment, serve as either a travel motor or a working motor. The drive train may additionally include a transmission or transmission ratio stages, an output, hydraulic components, control electronics, and power electronics. The electric motors are particularly advantageously identical electric motors for the travel drive and the working drive, respectively. This allows for a cost-effective unit-to-unit reduction for the electric motors. The travel drive also includes wheels, which are driven by the travel motor and are rigidly connected to the travel motor by transmission or can be rigidly connected to the travel motor by transmission via a clutch. The working drive also includes a working device, such as a bucket or a lifting frame, which is driven by the working motor.

[0009] In certain operating situations, the work machine may be decelerated externally. Within the scope of the present invention, this refers to deceleration that is not initiated by the vehicle brakes or the drive system. Instead, deceleration occurs due to the interaction of the work machine with external conditions. This could involve, for example, a steep uphill slope or the work equipment of the work machine digging into soil or gravel. Both situations result in external deceleration of the work machine without any personal involvement, and in particular, without a braking request by the operator of the work machine.

[0010] In particular, when the work machine initially has a high speed during deceleration, and the traction motor therefore has a high rotational speed, it may happen that the braking force acting on the wheels via the traction motor is less than the driving force acting on the wheels via the traction motor's moment of inertia. Because the traction motor is designed as an electric motor, it has a relatively large moment of inertia, which resists the reduction in rotational speed during deceleration. Due to this moment of inertia and the rotational speed of the electric motor, the driving force continues to act on the wheels even when the traction motor is no longer energized. The braking force acting on the wheels due to deceleration is crucially influenced by the wheel's ability to transmit force to the ground, that is, the wheel's adhesion to the respective ground surface. If the driving force now becomes greater than the braking force also acting on the wheel, the wheel loses its grip on the ground and is forced to rotate. In other words, the wheel may not be able to reduce its rotational speed to the same extent as the work machine reduces its speed. This can cause the work machine to unintentionally sink into the ground.

[0011] For example, a working machine configured as a wheel loader may move a working device configured as a bucket into a pile of earth at a relatively high speed, causing the bucket to slow down as it moves into the pile. This relatively high speed is necessary to move the bucket as deeply as possible into the pile. However, the ground contact of the wheels may not be strong enough to reduce the rotational speed of the travel motor to the same degree as the speed of the working machine. Consequently, the driving force acting on the wheels becomes greater than the braking force, forcing them to rotate. This can cause the wheel loader to become stuck and make it difficult to reverse the wheel loader when removing the bucket from the pile.

[0012] Therefore, according to the present invention, a situation detection is performed, which can be used to proactively detect whether an externally applied deceleration is imminent or has possibly already begun, and whether the resulting braking force acting on the wheels is less than the driving force acting on the wheels due to the mass moment of inertia of the continuously rotating traction motor. The situation detection can proactively detect the presence of such a situation, for example, when the work machine begins to decelerate without a corresponding control input from the operator of the work machine. To advantageously prevent forced rotation of the wheels and thus undesired jamming of the work machine, according to the present invention, the traction motor is energized in the opposite direction of its current operating direction to provide an additional braking torque acting on the traction motor.

[0013] According to a preferred embodiment of the present invention, situation detection is performed using an ambient sensor system. Suitable ambient sensors may, in particular, be camera sensors, radar sensors, or lidar sensors. The ambient sensors, for example, in conjunction with corresponding sensor data evaluation, can detect situations in which the work machine is externally decelerated. For example, the approach of a wheel loader to a gravel pile can be detected so that its bucket can be moved into the gravel pile. Upon reaching the gravel pile and thus initiating deceleration, the speed of the traction motor can be actively reduced by applying current in the opposite direction of rotation of the traction motor.

[0014] According to another preferred embodiment of the present invention, situation detection is performed using an acceleration sensor and / or an inclination sensor. The acceleration sensor can, for example, detect that the work machine is being decelerated without a corresponding control input from the operator of the work machine, and therefore involves an external deceleration. The inclination sensor can support situation detection using the acceleration sensor by detecting, for example, a steep gradient as a cause of external deceleration or a lifting of the work machine at the rear axle due to the bucket moving into a pile of earth as a cause of external deceleration.

[0015] According to another preferred embodiment of the present invention, the condition is detected using a slipping clutch, wherein the clutch pressure is predetermined such that the torque that can be transmitted by the clutch is less than the braking torque caused by the braking force. The braking torque at the wheel is the maximum possible braking torque resulting from the ground adhesion of the wheel. Therefore, if the clutch is slipping, it can be detected that a driving force is still acting on the externally braked wheel.

[0016] The clutch pressure is preferably predetermined so that normal driving operation of the work machine is not impaired. Particularly preferably, the clutch pressure is only reduced after the work machine has been started to such an extent that the torque transmittable via the clutch is less than the maximum braking torque at the wheel, which is generated by the ground adhesion of the wheel under externally applied deceleration.

[0017] According to another preferred embodiment of the present invention, a situation detection is performed by monitoring the speed and / or torque of the traction drive. For example, if the speed of the traction drive decreases while the torque of the traction drive increases, the presence of an externally applied deceleration can be detected, particularly in the absence of a corresponding control input by the operator. If the torque simultaneously exceeds a predefinable threshold value, the traction motor can be actively energized in the opposite direction of rotation to prevent forced rotation of the wheels.

[0018] Particularly preferably, the situation detection can also be carried out by monitoring the speed gradient and / or the torque gradient in the traction drive.

[0019] It is also particularly preferred to perform situation detection by monitoring wheel slip. If the slip at all wheels increases suddenly, in particular in conjunction with one or more of the aforementioned preferred embodiments of situation detection, it can also be detected, for example, that the braking force acting on the wheel due to deceleration is less than the driving force acting on the wheel. The wheel slip is preferably detected by means of an ABS sensor that is already present.

[0020] According to another preferred embodiment of the present invention, the situation detection is performed using absolute speed monitoring. Absolute speed monitoring involves monitoring the so-called "speed over the ground." If the specified absolute speed significantly decreases compared to the speed of the work machine, as determined via the wheel speed, then it can also be detected that the braking force acting on the wheel due to deceleration is less than the driving force acting on the wheel.

[0021] According to another preferred embodiment of the present invention, the situation is detected by monitoring the power demand of the traction drive. For example, by the operator requesting the maximum power of the traction motor, a so-called "kickdown," and especially in conjunction with the subsequent deceleration of the work machine, it can be inferred that the operator wants to generate sufficient kinetic energy through the kickdown and requires high torque, for example, to move the bucket of a wheel loader as deeply as possible into a pile of earth. The subsequent deceleration signals that the pile of earth has been reached and the bucket has been moved in.

[0022] According to another preferred embodiment of the present invention, the situation detection is performed by monitoring the behavior of the working drive. The behavior of the working drive can also include pressure changes in the working hydraulic system, the orientation or position of the bucket on the bucket arm, the position of the lifting frame, or simply control inputs made by the operator, for example, on a control element associated with the working drive, such as a joystick.

[0023] According to another preferred embodiment of the present invention, the situation detection is performed by monitoring the driving behavior of the operator of the work machine, wherein the driving behavior of the operator of the work machine when a deceleration is about to occur is known in advance. Thus, it is advantageously possible to detect whether an externally applied deceleration is about to occur by observing the operator's driving behavior and by determining whether the external deceleration typically corresponds to the operator's specific driving behavior.

[0024] The driving behavior may include, for example, an acceleration profile, a speed profile, a control input or a steering angle.

[0025] Particularly preferably, it is necessary not only to understand the operator's driving behavior but also to differentiate between multiple different operators of the work machine based on their different driving behaviors and to perform various condition detections by monitoring their driving behaviors. When an operator is seated in the driver's seat of the work machine, for example, different operators can be differentiated based on their weight. For this purpose, a weight detection device can be integrated into the driver's seat.

[0026] Preferably, the situation is detected by monitoring the engaged gear of the travel transmission, the state of the differential lock, the temperature of the travel or working motor, and GPS position information. The gear position can be detected, for example, as part of the driving behavior, as can the temperature of the differential lock and the travel or working motor. GPS position information can be used, for example, to detect when the work machine is approaching a pile of earth whose GPS position is known.

[0027] According to another preferred embodiment of the present invention, the reduction in the speed of the traction motor is supported by performing a downshift. The downshift changes the speed ratio between the traction motor and the wheels so that the higher speed of the traction motor now corresponds to the speed of the wheels, or the reduced speed of the wheels corresponds to the speed of the traction motor. Thus, undesired engagement of the work machine can be delayed at least by reducing the speed of the wheels until the traction motor speed can be reduced by supplying current in the opposite direction of rotation to the point where the wheels are no longer forced to rotate.

[0028] The present invention further relates to an electric drive train for a work machine, wherein the drive train includes a working drive having an electric working motor and a traction drive having an electric traction motor and wheels, wherein the wheels are drive-type or can be rigidly coupled to the traction motor so that, in the event of a deceleration applied externally to the work machine, a braking force is applied to the wheels by the deceleration. The drive train according to the present invention is characterized in that the drive train is configured to proactively detect, by means of a situation detection, whether the braking force applied to the wheels by the deceleration is less than the driving force applied to the wheels by the mass moment of inertia of the traction motor, wherein the traction drive is configured to energize the traction motor in a direction opposite to the direction of operation of the traction motor in order to reduce the rotational speed when it is detected that the braking force is less than the driving force.

[0029] The drive train according to the invention thus enables the implementation of the method according to the invention, which results in the advantages already described in conjunction with the method according to the invention.

[0030] It is preferably provided that the drive train also includes an inverter for controlling the traction motor. The inverter is advantageously designed to implement the method according to the invention in the form of an electronically executable software algorithm, in addition to actually controlling the traction motor. This results in the advantage of higher control speeds, since the inverter directly controls the traction motor.

[0031] The invention also relates to a work machine comprising a drive train according to the invention. The advantages already described in connection with the drive train according to the invention are thus also achieved for the work machine according to the invention.

[0032] According to a preferred embodiment of the invention, it is provided that the work machine is designed as a wheel loader. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is explained below by way of example with reference to the embodiments shown in the drawings.

[0034] in:

[0035] Figure 1 A possible embodiment of the method according to the invention for operating an electric drive train of a working machine is shown by way of example in the form of a principle diagram; and

[0036] Figure 2 A possible embodiment of the work machine according to the invention is shown by way of example and diagrammatically.

[0037] The same subject matter, functional units and similar components are marked with the same reference numerals across the drawings. These subject matter, functional units and similar components are implemented consistently in terms of their technical features, unless otherwise specified in the specification, whether explicitly or implicitly. DETAILED DESCRIPTION

[0038] Figure 1A possible embodiment of the method according to the present invention for operating an electric drive train 11 of a work machine 10 is illustrated in the form of a working principle diagram. The drive train 11 includes a work drive 20 having an electric work motor 21 and a traction drive 30 having an electric traction motor 31 and wheels 32. When the work machine 10 is externally decelerated, it may happen that the braking force acting on the wheels 32 due to the deceleration is less than the driving force acting on the wheels 32 due to the moment of inertia of the traction motor 31. Therefore, in such a situation, it may happen that the wheels 32 have a rotational speed greater than the actual speed of the work machine 10. This forces the wheels 32 to rotate, which can cause the work machine 10 to undesirably get stuck. To prevent this, a situation detection according to the present invention is first performed, as illustrated by function block 100. Function block 100 includes a series of sub-blocks 101 to 113, each of which describes a specific type of situation detection. In block 101, situation detection is performed by monitoring the rotational speed of the driven axles of the work machine 10. Block 102 represents situation detection by monitoring the tire slip of the driven wheels 32. Block 103 illustrates condition monitoring by monitoring the deflected steering angle, and block 104 illustrates condition monitoring by monitoring the hydraulic pressure in the working drive 20. Block 105 represents condition monitoring by means of the surroundings sensor system 12, such as a camera sensor, and block 106 represents condition monitoring by means of the acceleration sensor system. Block 107 represents condition monitoring by monitoring the output speed of the travel transmission 33 of the traction drive 30, and block 108 represents condition monitoring by monitoring the engaged gear of the travel transmission 33. Block 109 further illustrates condition monitoring by monitoring the differential lock of the driven axle. Blocks 110, 111, and 112 illustrate condition monitoring by monitoring the actuation of the input devices of the working drive 20, the positioning of the bucket of the working drive 20, and the adjustment angle of the hydraulic pump of the working drive 20. Finally, block 113 demonstrates condition monitoring by monitoring the traction motor 31 and the working motor 21, specifically monitoring the temperature, speed, torque, speed gradient, and torque gradient. In function block 200, the situation detected in function block 100 is automatically evaluated to proactively detect whether a situation is imminent in which the braking force acting on wheel 32 due to deceleration is less than the driving force acting through wheel 32, resulting in forced rotation of wheel 32 due to external deceleration. If this is proactively detected, the speed of traction motor 31 is actively reduced in function block 300. To this end, in sub-block 301, traction motor 31 is energized in the opposite direction of its operating direction to reduce the speed. In block 302, a downshift is also performed to support the rapid speed reduction of traction motor 31.

[0039] Figure 2A possible configuration of a work machine 10 according to the present invention is shown schematically and exemplarily. The work machine 10 is configured, for example, as a wheel loader 10 and includes an electric drive train 11. The electric drive train 11 in turn includes a work drive 20 having an electric work motor 21 and a work device 22, and a travel drive 30 having an electric travel motor 31 and driven wheels 32. The wheels 32 can be rigidly coupled to the travel motor 31 via a travel transmission 33. This allows for a braking force to be applied to the travel motor 31 by external deceleration of the wheel loader 10. However, the driving force generated by the moment of inertia of the travel motor 31 and acting on the wheels counteracts this braking force. When this driving force becomes greater than the braking force, the wheels 32 are forced to rotate, and the wheel loader 10 becomes stuck.

[0040] The drive train 11 is thus configured to carry out the method according to the present invention. A situation detection is performed using a suitable surroundings sensor system 12 to proactively detect whether the braking force acting on the traction motor 31 due to deceleration is less than the driving force acting on the wheels 32 due to the moment of inertia of the traction motor 31. If this is the case, the traction motor 31 is energized in the opposite direction of its operating direction to reduce the rotational speed.

[0041] Reference Signs List

[0042] 10 Operating equipment

[0043] 11 Electric drive system

[0044] 12. Surrounding environment sensor device

[0045] 20 Job Drivers

[0046] 21 working motor

[0047] 22 Operating Equipment

[0048] 30 Travel Drive

[0049] 31 Travel motor

[0050] 32 wheels

[0051] 33 Travel transmission

[0052] 100 Condition Detection

[0053] 101 Condition detection by monitoring the rotational speed of the driven axle

[0054] 102 Condition detection by monitoring tire slip of driven wheels

[0055] 103 Condition detection by monitoring the deflected steering angle

[0056] 104 Condition detection by monitoring the hydraulic pressure in the working drive

[0057] 105 Condition detection by means of surrounding environment sensing devices

[0058] 106 Condition detection with the help of acceleration sensor device

[0059] 107 Condition detection by monitoring the output speed of the travel transmission

[0060] 108 Condition detection by monitoring the engaged gear position of the driving transmission

[0061] 109 Condition monitoring with monitoring of the differential lock

[0062] 110 Status detection by monitoring the operation of the input device of the working drive

[0063] 111 Condition detection by positioning the bucket of the work drive

[0064] 112 Condition detection by adjusting the angle of the hydraulic pump of the working drive

[0065] 113 Condition monitoring by monitoring the travel and working motors

[0066] 200 Status Detection

[0067] 300 Reduce the speed of the travel motor

[0068] 301 Energize the travel motor to reduce the speed

[0069] 302 Downshift to support the reduction of the speed of the driving motor

Claims

1. A method for operating an electric drive train (11) of a working machine (10), wherein: The drive train (11) comprises a working drive (20) having an electric working motor (21) and a travel drive (30) having an electric travel motor (31) and wheels (32), wherein the working machine (10) is decelerated externally, and wherein the braking force acting on the wheels (32) due to the deceleration can be smaller than the driving force acting on the wheels (32) due to the inertia moment of the travel motor (31), The invention is characterized in that, when it is foreseeably detected by means of situation detection that the braking force acting on the wheel (32) due to the deceleration is less than the driving force acting on the wheel (32) (200), a current (300, 301) in the opposite direction of its running direction is applied to the traction motor (31) in order to reduce the rotational speed, wherein the condition detection is performed with the aid of a slipping clutch, wherein the clutch pressure is predetermined such that the torque transmittable via the clutch is less than the braking torque caused by the braking force, and / or The condition detection is performed by monitoring the driving behavior of the operator of the working machine (10), wherein the driving behavior of the operator of the working machine (10) when deceleration is about to occur is known in advance.

2. The method according to claim 1, It is characterized in that The situation detection (105) is performed with the aid of an ambient sensor system (12).

3. The method according to claim 1 or 2, It is characterized in that The situation detection is performed with the aid of an acceleration sensor system and / or an inclination sensor system.

4. The method according to claim 1 or 2, It is characterized in that The condition detection (113) is performed by means of rotational speed monitoring and / or torque monitoring of the traction drive (30).

5. The method according to claim 1 or 2, It is characterized in that The situation detection is performed with the aid of absolute speed monitoring.

6. The method according to claim 1 or 2, It is characterized in that The condition detection (113) is performed by monitoring the power requirement of the traction drive (30).

7. The method according to claim 1 or 2, It is characterized in that The condition detection (104, 110, 111, 112) is performed by monitoring the behavior of the working drive (20).

8. The method according to claim 1 or 2, It is characterized in that The speed reduction (300, 302) of the traction motor (31) is supported by performing a downshift.

9. An electric drive system (11) for a working machine (10), wherein: The drive train (11) comprises a working drive (20) having an electric working motor (21) and a travel drive (30) having an electric travel motor (31) and wheels (32), wherein the wheels (32) are drive-connected or can be rigidly connected to the travel motor (31) so that in the event of a deceleration acting from the outside on the working machine (10), a braking force acts on the wheels (32) via the deceleration, characterized in that the drive train (11) is designed to implement the method according to any one of claims 1 to 8.

10. A work machine (10) comprising a drive train (11) according to claim 9.

11. The working machine (10) according to claim 10, It is characterized in that The work machine (10) is configured as a wheel loader (10).

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