DE102021212137A1 - Method for operating the drive train, drive train for a work machine and work machine - Google Patents

Abstract

The invention relates to a method for operating a drive train (20) of a working machine (10), wherein a slip state of driven wheels (23) of the working machine (10) is detected (105) by comparing a wheel speed with an absolute speed of the working machine (103 ) and wherein the absolute velocity is determined by integrating a sensed acceleration over a time interval (102). The method according to the invention is characterized in that a measurement error of the detected acceleration is set to zero (107) when the working machine (10) is at a standstill. The invention also relates to a corresponding drive train (20) and a working machine (10).

Description

The present invention relates to a method for operating a drive train of a work machine according to the preamble of claim 1, a drive train for a work machine according to the preamble of claim 10 and a corresponding work machine.

In drive trains of motor vehicles, differential gears are usually used as transverse differentials for driven axles, with a single differential gear distributing drive power to the wheels of the respective driven axle and allowing different speeds of the wheels when cornering the motor vehicle. In addition, differential gears are also used in motor vehicles with a number of driven axles as longitudinal differentials, with distribution over the number of driven axles being realized here. In off-road vehicles in particular, slippage can occur between the wheels of a drive axle or between the wheels of several driven axles, in which case a differential gear would ensure that the driving power is distributed predominantly or exclusively to the slipping wheel of a drive axle or the slipping wheels of one of the drive axles, which would make it difficult or even impossible for the motor vehicle to move forward. For this reason, in off-road vehicles, differential gears are often equipped with locking devices, via which the respective differential gear is locked in a targeted manner and thus a uniform distribution of the drive power is enforced.

From the DE 197 49 919 A1 discloses a method for controlling locking devices of differential gears that are provided in a drive train of a motor vehicle. In this case, an automatic actuation of the individual locking devices is brought about when slippage is detected.

The DE 10 2019 207 305 A1 describes a method for controlling a locking device of a differential in a drive train of a motor vehicle. The blocking device is actuated automatically when it is determined for an upcoming route section of the motor vehicle that a critical slip situation has already been detected in advance for a position of the route section to be traveled through.

From the DE 10 2019 203 516 A1 a drive system for a vehicle with a distributor arrangement for distributing a drive torque to at least two drive wheels or to two axles of the vehicle is known. The distributor arrangement has at least one blocking device for blocking the distributor arrangement, it being possible for the blocking device to be actuated automatically on the basis of a speed difference. A control module of the blocking device includes a communication module which is designed to communicate status information of the blocking device with at least one vehicle driving behind and/or at least one vehicle driving ahead. The blocking device can thus be actuated, for example, when a vehicle driving ahead detects a slip situation and in turn actuates its own blocking device.

However, the known electrically driven work machines have the disadvantage that any slip that occurs must be reliably detected in a first step before suitable countermeasures can be taken, for example by actuating a differential lock.

It is an object of the invention to propose an improved method for operating a drive train of a working machine.

According to the invention, this object is achieved by the method for operating a drive train of a work machine according to claim 1 . Advantageous refinements and developments of the invention emerge from the dependent claims.

The invention relates to a method for operating a drive train of a working machine, with a slip state of driven wheels of the working machine being detected by comparing a wheel speed with an absolute speed of the working machine and with the absolute speed being determined by integrating a detected acceleration over a time interval. The method according to the invention is characterized in that a measurement error of the detected acceleration is set to zero when the working machine is at a standstill.

The invention thus describes a method according to which a drive train can be operated. The drive train is suitable for driving a work machine. Since work machines are usually operated most of the time under high drive loads and, in particular, have to produce comparatively high work outputs in absolute terms, the drive train according to the invention differs in its design, for example, from a passenger car drive train, which typically operates in a capacity utilization range of 5% to 10%. operated at maximum power is and in particular provides comparatively lower absolute drive power

The drive train can equally be designed as an electrically driven drive train or as a combustion engine driven drive train. A design as a hybrid drive train is also possible.

During operation of the drive train, i.e. when the speed of the driven wheels of the working machine is greater than zero, the slip state of the driven wheels is continuously determined.

Wheel slip is generally undesirable and is avoided if possible, since wheel slip leads to a lower maneuverability of the work machine, which can also lead to the occurrence of dangerous situations. In addition, the loss of traction of the slipping wheels associated with wheel slip also leads to a loss of traction and thus to a reduction in the productivity of the work machine and to increased tire wear.

The wheel slip is determined according to the invention by comparing a wheel speed with an absolute speed of the working machine. A wheel speed is understood to mean a speed of the work machine that is calculated from the wheel speed and the rolling circumference of the driven wheels. If the wheel speed deviates from the absolute speed, there is slip.

Provision is preferably made for the wheel speed to be determined from a rotational speed of at least one driven wheel and/or at least one transmission part of the drive train. The speed of the at least one driven wheel can be detected very reliably, for example, using a conventional ABS speed sensor. One or more speed sensors are usually also arranged in the transmission, and the speed of the driven wheel can be determined mathematically in a simple manner via the detected speed of a monitored transmission part, taking into account the transmission ratio to the driven wheel.

According to the invention, the absolute speed is calculated by integrating a detected acceleration over time. The acceleration can be detected comparatively easily using known acceleration sensors, which are also comparatively inexpensive.

The acceleration is preferably detected via a multi-axis acceleration sensor, as is the case, for. B. is used in many motor vehicle control units, such as ESP control units. Another suitable sensor is known under the designation “ZF wheel tag sensor”, which, however, is not arranged in a control device, but preferably on the wheel rim of a wheel.

The multi-axis acceleration sensor preferably has six or nine axes along which an acceleration can be detected by the acceleration sensor.

According to the invention, it is now provided that a measurement error of the detected acceleration is set to zero when the working machine is at a standstill. The invention thus provides a solution to the known problem that the acceleration calculated by integration is no longer reliable after a short time while driving, since the acceleration sensor is subject to so-called drift effects due to the technology, which are further intensified by the integration .

The invention also uses the knowledge that working machines in particular frequently stop and come to a standstill during operation, so that the acceleration measurement and thus the drift effect can regularly be set to zero.

The standstill of the work machine is preferably detected based on the speed of at least one driven wheel and/or at least one transmission part of the drive train. Since the speed is detected via a speed sensor that measures absolute values, a standstill of the working machine can be clearly identified at any time. The speed sensor can thus advantageously be used to detect a standstill of the working machine via a speed of zero.

According to the invention, the detected standstill is then used to likewise set the detected speed to zero by the acceleration sensor. In this respect, an error correction of the acceleration sensor takes place whenever the working machine is at a standstill.

According to a preferred embodiment of the invention, it is provided that the comparison is terminated if the working machine has not come to a standstill for more than a first definable period of time. Since the drift effect of the acceleration sensor influences or falsifies the calculated speed of the working machine more and more with increasing time without standstill of the working machine - and thus without error correction of the acceleration sensor - the method is advantageously terminated before the calculated value of the absolute speed becomes completely unusable and would no longer allow reliable determination of the slip of the driven wheels.

The first definable period of time can be 10 s, 15 s or 30 s, for example.

According to a particularly preferred embodiment of the invention, it is provided that the standstill is only recognized as a standstill if the speed of at least one driven wheel and/or at least one transmission part of the drive train is zero for more than a second definable period of time. This results in the advantage that, for example, a continuous travel movement, which transitions seamlessly from forward travel to reverse travel and also passes through the speed zero point, i.e. the standstill of the working machine, is not incorrectly recognized as an actual standstill. Otherwise, a driving movement would be used to correct the drift effect, but this would not result in a reliable correction.

The second definable period of time can be 0.1 s, 0.5 s or 1 s, for example.

According to a further preferred embodiment of the invention, it is provided that an inclination of the work machine is additionally detected. The detected inclination can then be used, for example, to determine a downhill force or downhill acceleration resulting from the inclination, by means of which the speed calculated by integration from the acceleration can be compensated for the influence of the downhill force or downhill acceleration.

According to a further preferred embodiment of the invention, it is provided that the work machine is designed as a wheel loader and driving into a pile of material to be picked up is also detected. The driving of the wheel loader with the shovel into the pile of material can be detected, for example, by a regularly occurring, strongly negative acceleration until the wheel loader comes to a standstill, with the standstill being followed by a reverse movement. The pile of material can be a pile of dirt, rubble or rubble.

According to a further preferred embodiment of the invention, it is provided that the acceleration and the inclination and/or the retraction are detected by a common sensor. In this way, all of the detection functions mentioned can be combined in a single common sensor at low cost. Such sensors are already widely available.

The invention also relates to a drive train for a working machine, the drive train being designed to detect a state of slippage of driven wheels of the working machine by comparing a wheel speed with an absolute speed of the working machine, and the drive train being designed to calculate the absolute speed by integrating a to determine the detected acceleration over a time interval. The drive train according to the invention is characterized in that the drive train is also designed to set a measurement error of the detected acceleration to zero when the work machine is at a standstill.

According to a further preferred embodiment of the invention, it is provided that the drive train is designed to carry out the method according to the invention. This also results in the advantages already described in connection with the method according to the invention for the drive train according to the invention.

The invention further relates to a working machine, comprising a drive train according to the invention. This results in the advantages already described in connection with the method and drive train according to the invention, also for the working machine according to the invention.

Provision is preferably made for the work machine to be in the form of a wheel loader, dumper, excavator, telehandler, municipal vehicle, garbage truck, mining vehicle, skid steer loader, aircraft tractor or tractor.

The invention is explained below by way of example using the embodiments shown in the figures.

• 1 beispielhaft und schematisch eine mögliche Ausbildungsform einer als Radlader ausgebildeten, erfindungsgemäßen Arbeitsmaschine und
• 2 beispielhaft eine mögliche Ausführungsform des erfindungsgemäßen Verfahrens zum Betreiben eines Antriebsstrangs einer Arbeitsmaschine in Form eines Flussdiagramms.

Show it:

• 1 an example and a schematic of a possible embodiment of a working machine designed as a wheel loader according to the invention and
• 2 an example of a possible embodiment of the method according to the invention for operating a drive train of a work machine in the form of a flowchart.

Identical objects, functional units and comparable components are denoted by the same reference symbols across the figures. These objects, functional units and comparable components are designed to be identical in terms of their technical features, unless the description explicitly or implicitly states otherwise.

1 shows a possible embodiment of a working machine 10 designed as a wheel loader 10 according to the invention. Furthermore, the drive train 20 includes a six-axis acceleration sensor 24, wheel speed sensors 25 and electronic comparison means 26. The drive train 20 according to the invention or the working machine 10 according to the invention are designed to detect a slip state of the driven wheels 23 by comparing a wheel speed with an absolute speed of the working machine 10 becomes. The wheel speed is determined using the wheel speed sensors 25 and the absolute speed is determined by integrating an acceleration detected using the acceleration sensor 24 over a time interval. The wheel speed and the absolute speed are then subjected to a comparison by the electronic comparison means 26 . If the absolute speed deviates from the wheel speed, a slip state of the driven wheels 23 is detected. Since the detection of the acceleration by the acceleration sensor 24 is subject to a drift effect, which is amplified by the integration and leads to the calculated speed becoming increasingly inaccurate over time, the measurement error of the acceleration when the work machine 10 is at a standstill increases according to the invention set to zero. As a result, the speed of the working machine 10 can again be calculated without error.

2 shows an example of a possible embodiment of the method according to the invention for operating a drive train 20 of a work machine 10 in the form of a flowchart. In a first method step 100, a wheel speed of driven wheels 23 of work machine 10 is detected. At the same time, in step 101 an acceleration of the work machine 10 is continuously detected via a multi-axis acceleration sensor 24 . In step 102, an absolute speed of work machine 10 is calculated from the sensor-detected acceleration by integration over a time interval. In step 103, the wheel speed is compared with the absolute speed of the working machine 10. If the wheel speed agrees with the absolute speed, it is recognized in step 104 that there is no slip state. However, if the wheel speed does not agree with the absolute speed, it is recognized in step 105 that a slip state is present. In the following method step 106, a standstill of the work machine 10 is detected, which lasts longer than a second specified time period of 0.5 s. Then, in step 107, the measurement error of the detected acceleration is set to zero. However, if step 106 does not identify a standstill of work machine 10, then in step 108 the method is aborted after a first predefinable time period of, for example, 30 s has elapsed, since the drift effect of acceleration sensor 24 no longer reliably determines the absolute speed after this time period has elapsed is possible..

Reference List

10

Working machine, wheel loader

20

powertrain

21

electric drive unit

22

transmission

23

driven wheels

24

accelerometer

25

wheel speed sensors

26

electronic means of comparison

100

detecting the wheel speed

101

detecting the acceleration

102

Calculating the absolute speed

103

Compare wheel speed to absolute speed

104

Recognizing that there is no slip condition

105

Recognize that a slip condition is present

106

Detection of a standstill of the working machine

107

Resetting the measurement error to zero

108

Expiry of the first predefinable period of time and resetting the measurement error to zero

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 19749919 A1 [0003]
• DE 102019207305 A1 [0004]
• DE 102019203516 A1 [0005]

Claims (12)

Method for operating a drive train (20) of a work machine (10), wherein a slip state of driven wheels (23) of the work machine (10) is detected (105) by comparing a wheel speed with an absolute speed of the work machine (103) and wherein the absolute speed is determined by integrating a detected acceleration over a time interval (102), characterized in that a measurement error of the detected acceleration is set to zero (107) when the working machine (10) is at a standstill. procedure after claim 1 , characterized in that the wheel speed is determined (100) from a rotational speed of at least one driven wheel (23) and/or at least one transmission part of the drive train (20). Process according to at least one of Claims 1 and 2 , characterized in that the acceleration is detected by a multi-axis acceleration sensor (24) (101). Process according to at least one of Claims 1 until 3 , characterized in that the comparison is terminated if the working machine (10) has not come to a standstill for more than a first predefinable period of time. Process according to at least one of claims 2 until 4 , characterized in that the standstill of the machine (10) based on the speed of at least one driven wheel (23) and / or at least one transmission part of the drive train (20) is detected (106). procedure after claim 5 , characterized in that the standstill is only recognized as a standstill if the speed of at least one driven wheel (23) and/or at least one transmission part of the drive train (20) is zero for more than a second predeterminable period of time (106). Process according to at least one of Claims 1 until 6 , characterized in that an inclination of the working machine (10) is additionally detected. Process according to at least one of Claims 1 until 7 , characterized in that the working machine (10) is designed as a wheel loader (10) and, furthermore, driving into a pile of material to be picked up is detected. Process according to at least one of Claims 1 until 9 , characterized in that the acceleration and the inclination and/or the retraction are detected by a common sensor. Drive train (20) for a working machine (10), wherein the drive train (20) is designed to detect a slip state of driven wheels (23) of the working machine (10) by comparing a wheel speed with an absolute speed of the working machine (10). and wherein the drive train (20) is designed to determine the absolute speed by integrating a detected acceleration over a time interval, characterized in that the drive train (20) is also designed to detect a measurement error in the detected acceleration when the working machine (10 ) to zero. Drive train (20) after claim 10 , characterized in that the drive train (20) is designed to a method according to at least one of Claims 1 until 9 to execute. Working machine (10), comprise a drive train (20) according to at least one of Claims 10 and 11 .

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