DE102021207156A1 - 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 (10) of a work machine (50), the drive train (10) comprising at least one electric motor (21, 31), the at least one electric motor (21, 31) being activated when the work machine ( 50) is operated in a driving mode, wherein the at least one electric motor (21, 31) is controlled in driving mode as a function of the torque and wherein the at least one electric motor (21, 31) is operated in a holding mode when the work machine (50) is stopped (110) . The method according to the invention is characterized in that the at least one electric motor (21, 31) is regulated (110) as a function of speed in the holding mode. The invention also relates to a corresponding drive train (10) and a working machine (50).

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.

Electrically driven work machines, such as wheel loaders, compact loaders, telehandlers, dumpers and excavators, are known in the prior art. These electrically driven working machines are either purely electrically driven, i.e. they only have an electric battery or an electric accumulator for their power supply, or they are diesel-electrically driven, which means that the required power is usually provided by a diesel-driven generator in connection with an electrical buffer storage, such as a suitably dimensioned capacitor. In all cases, the mechanical power required for the travel drive and the working drive is provided by one or more electric motors.

In this context, describes the DE 20 2014 000 738 U1 a wheel loader driven purely by an electric motor, which has a first electric motor for a traction drive and a second electric motor for a working drive.

It is also generally known in the prior art that the traction drive of an electrically driven machine can be controlled using four different control variables: the electrical voltage applied to the electric motor, the electrical current applied to the electric motor , via the torque provided by the electric motor and via the speed provided by the electric motor.

Furthermore, so-called hillholder functionalities are known in the prior art, which make it possible for a motor vehicle to be held briefly during a starting process uphill after releasing the brake and to be prevented from rolling down a slope.

For example, the DE 10 2013 000 276 A1 a method for operating an electronic brake control unit, in which the brake control unit uses the data from the active speed sensor as an input variable for a stop brake or for a function to hold the vehicle on an uphill or downhill stretch.

However, the known electrically driven working machines are disadvantageous in that a type of speed control that is as simple and intuitive as possible for the driver takes place via the torque provided by the electric motor as a control variable. Accordingly, the drive of a large number of electrically driven working machines is regulated via the torque provided by the electric motor. In the field of electrically driven work machines, hillholder functionality is usually provided via the electric drive and without using a mechanical brake, so that high dynamic behavior and rapid restarting are ensured. When providing a hillholder functionality, however, torque control proves to be disadvantageous because the torque to be applied to compensate for the downhill force required can only be provided comparatively imprecisely, so that the working machine often does not stand still completely but performs a slight, unwanted forward or backward movement .

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 work machine, the drive train comprising at least one electric motor, the at least one electric motor being operated when the work machine is moving in a driving mode, the at least one electric motor being torque-controlled in driving mode and the at least an electric motor is operated in a holding mode when the working machine is stopped. The method according to the invention is characterized in that the at least one electric motor is regulated as a function of speed in the holding mode.

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 performance in absolute terms, the drive train according to the invention differs in its design from, for example, a passenger car drive strand, which is typically operated in a utilization range of 5% to 10% of the maximum output and, in particular, produces comparatively lower absolute work outputs.

The drive train includes at least one electric motor, which is advantageously assigned to a traction drive of the drive train. Furthermore, the drive train can also include one or more electric motors, which are assigned, for example, to a working drive of the working machine.

The electric motors are preferably so-called asynchronous motors.

When the working machine is being driven, the at least one electric motor drives the working machine. While driving, the at least one electric motor is operated in the driving mode, with the driving mode specifying a torque-dependent regulation of the at least one electric motor. This means that a driver of the work machine specifies a target torque, which the at least one electric motor is to provide, by actuating an accelerator pedal. The level of the target torque corresponds proportionally to the actuation of the accelerator pedal.

Torque-dependent regulation of the at least one electric motor offers the advantage that it enables the driver of the working machine to control the drive of the working machine, which largely corresponds to the control known from internal combustion engines. A driver can therefore intuitively operate the electric drive train according to the invention based on his experience with combustion-powered drives.

When the work machine is stopped, the at least one electric motor is switched from driving mode to holding mode. In holding mode, the machine is held in place by applying engine torque. A mechanical friction brake is therefore not required to hold the working machine.

Holding the work machine by a motor torque of the at least one electric motor offers the advantage over holding by a friction brake that the process of stopping and restarting runs comparatively faster, which is advantageous for a wheel loader in so-called Y mode, for example. Overall, being held by the engine torque allows for significantly more dynamic stopping and restarting.

Holding the work machine in place by means of an engine torque offers advantages, particularly on a sloping surface. In holding mode, the working machine is held against the downhill force on the sloping ground by applying engine torque. The engine torque generates a holding force which counteracts the downhill force and advantageously precisely compensates for it, so that an undesired downhill movement of the work machine, which as a rule also represents a hazard, can be avoided.

According to the invention, it is now provided that the at least one electric motor is controlled as a function of speed in the holding mode. In the case of speed-dependent control of the at least one electric motor, a target speed is specified for the electric motor via the actuation of the accelerator pedal, which the at least one electric motor is then intended to provide. In other words, the regulation of the at least one electric motor changes in such a way that a target torque is no longer specified for it in the holding mode, but rather a target speed. The invention makes use of the knowledge that determining the torque required to hold the working machine on a slope is comparatively difficult to determine exactly, so that with torque-controlled holding, a slow "drifting" of the working machine forwards or backwards is often not prevented can. A speed-controlled holding, however, allows a very reliable and locally accurate holding, since only the speed of the at least one electric motor has to be kept at zero.

The invention thus advantageously combines torque-controlled driving of the working machine in driving mode, which allows the driver intuitive operation similar to that of an internal combustion engine, with speed-controlled holding of the working machine in holding mode, which allows reliable holding and stopping of the working machine.

• - eine Drehzahl des mindestens einen Elektromotors größer als null ist, aber einen vorgegebenen Drehzahlgrenzwert unterschreitet,
• - eine Betätigung eines Fahrpedals einen vorgegebenen Fahrpedalgrenzwert überschreitet und
• - eine Betätigung eines Bremspedals einen vorgegebenen Bremspedalgrenzwert überschreitet.

According to a preferred embodiment of the invention, it is provided that the at least one electric motor is operated in holding mode when

• - a speed of the at least one electric motor is greater than zero, but falls below a specified speed limit value,
• - an actuation of an accelerator pedal exceeds a predetermined accelerator pedal limit value and
• - An actuation of a brake pedal exceeds a predetermined brake pedal limit value.

These three requirements must be met cumulatively in order to switch from driving to holding drive to switch. The speed of the at least one electric motor indicates that the work machine is expected to be stopped if it falls below the specified speed limit but is still greater than zero. The speed limit is positive. The specified speed limit value can be 200 rpm, for example, which corresponds to a driving speed of the work machine of less than 0.5 km/h with a typical gear reduction of an electric drive train. Actuation of the accelerator pedal beyond the specified accelerator pedal limit value indicates that the driver—despite the low engine speed—is requesting a specific torque that is above the accelerator pedal limit value, for example due to driving up a slope. Simultaneous actuation of the brake pedal beyond the specified brake pedal limit value, in turn, indicates that the driver probably wants to brake the work machine to a standstill.

Based on these criteria, it can be recognized in a simple manner that the drive train is to be switched from driving mode to holding mode.

• - eine Drehzahl des mindestens einen Elektromotors negativ ist,
• - eine Betätigung eines Fahrpedals einen vorgegebenen Fahrpedalgrenzwert überschreitet und
• - eine Betätigung eines Bremspedals einen vorgegebenen Bremspedalgrenzwert überschreitet.

According to an alternative preferred embodiment of the invention, it is provided that the at least one electric motor is operated in holding mode when

• - a speed of the at least one electric motor is negative,
• - an actuation of an accelerator pedal exceeds a predetermined accelerator pedal limit value and
• - An actuation of a brake pedal exceeds a predetermined brake pedal limit value.

These three requirements must also be met cumulatively in order to switch from driving mode to holding mode. The main difference compared to the first-mentioned variant is that the speed of the at least one electric motor is not only between zero and the positive speed limit value, but that the driven machine deliberately waits for a short rollback in order to generate a negative speed on the at least one electric motor. The rolling back of the work machine can be less than 5 cm, in particular only about 1 cm. Due to the typically high-ratio transmission of an electric drive train, such a short distance can already be clearly detected as the speed of the electric motor.

• - eine Drehzahl des mindestens einen Elektromotors null ist und
• - über einen Lagesensor eine Schräglage der Arbeitsmaschine erkannt wird.

According to another alternatively preferred embodiment of the invention, it is provided that the at least one electric motor is operated in holding mode when

• - A speed of the at least one electric motor is zero and
• - An inclined position of the working machine is detected via a position sensor.

According to this embodiment, too, the two prerequisites mentioned must be met cumulatively in order to switch from driving mode to holding mode. A standstill of the work machine is detected by the speed of the at least one electric motor being zero. At the same time, an inclined position of the work machine caused by a sloping ground, which results in a downhill force, can be detected by a position sensor. The position sensor can, for example, be a component of a position control that is present in any case or of a rollover detection system of the work machine. Conventional ESP sensors usually include, for example, a sensor that is suitable for detecting the leaning position.

According to a further preferred embodiment of the invention, it is provided that the at least one electric motor is operated in holding mode as long as the brake pedal is actuated. The continued actuation of the brake pedal is understood as an indicator that the driver intends to continue holding the work machine at the specified location, for example on a sloping surface. Only when the driver releases the brake pedal and thus indicates his intention to start the work machine again does the holding mode end and the drive train is switched to driving mode.

According to a further preferred embodiment of the invention, it is provided that the at least one electric motor is operated in driving mode when the brake pedal is released. By releasing the brake pedal, the driver's request for an imminent start-up of the working machine can be recognized. Thus, the release of the brake pedal can be taken as a trigger to switch from holding mode to driving mode.

According to a further preferred embodiment of the invention, it is provided that the at least one electric motor is operated in driving mode when the accelerator pedal is released and actuated again. The driver's desire for an imminent start-up of the work machine can also be recognized by actuating the accelerator pedal again after the accelerator pedal has been released.

According to a further preferred embodiment of the invention, it is provided that the at least one electric motor is operated in driving mode when the speed of the at least one electric motor is negative. In this case, a slight rollback of the work machine due to the brake pedal being released is used as a trigger to switch the drive train from holding mode to driving mode. Alternatively, a slight forward rolling of the work machine due to the engine torque can also be used as a trigger to switch the drive train from holding mode to driving mode.

According to a further preferred embodiment of the invention, it is provided that the drive train further comprises an inverter assigned to the at least one electric motor, the at least one electric motor being speed-controlled by the inverter in holding mode. This means that the at least one electric motor is no longer regulated in the holding mode by a control unit that is usually provided for this purpose, which reads the actuation of the accelerator pedal or the brake pedal and then, based on this actuation, outputs a setpoint value for the controlled variable to the inverter. Instead, the speed-dependent control in holding mode takes place directly via the inverter and without the higher-level control unit, by specifying a speed of zero as a one-time setpoint for the inverter. This results in a very fast and efficient control loop.

In this case, each electric motor is advantageously assigned an inverter for controlling the electric motor.

If several electric motors are assigned to the traction drive, a common inverter can also be assigned to all electric motors assigned to the traction drive.

If several electric motors are assigned to the working drive, a common inverter can also be assigned to all electric motors assigned to the working drive.

The invention also relates to a drive train for a work machine, the drive train comprising at least one electric motor and the at least one electric motor being assigned to a traction drive of the drive train. The drive train according to the invention is characterized in that the drive train is designed to carry out the method according to the invention.

The drive train preferably includes all means and devices for carrying out the method according to the invention, such as drivable vehicle wheels, an accelerator pedal with actuation detection means, a brake pedal with actuation detection means, a position sensor and at least one electronic processing unit which is designed to implement the method according to the invention in the form of a software to run the algorithm.

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 also results in the advantages already described in connection with the drive train according to the invention for the work 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 zeigt beispielhaft und stark schematisch eine mögliche Ausbildungsform eines Antriebsstrangs für eine in 1 nicht dargestellte Arbeitsmaschine,
• 2 beispielhaft und schematisch eine Arbeitsmaschine auf einem abschüssigen Untergrund und
• 3 eine mögliche Ausführungsform des erfindungsgemäßen Verfahrens in Form eines Flussdiagramms.

Show it:

• 1 shows an example and highly schematic of a possible embodiment of a drive train for an in 1 work machine not shown,
• 2 exemplary and schematic of a working machine on a sloping ground and
• 3 a possible embodiment of the method according to the invention 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 an example and highly schematic of a possible embodiment of a drive train 10 for an in 1 work machine 50, not shown. The drive train 10 comprises, for example, two electric motors 21, 31, one electric motor 21 being assigned to a travel drive 20 and one electric motor 31 being assigned to a working drive 30. For example the electric motors 21, 31 are three-phase asynchronous motors 21, 31. The drive train 10 also includes an electrical energy store 11 designed as a rechargeable Li-ion battery 11, which is designed to supply the electric motors 21, 31 with electrical power . An inverter 22 is arranged electrically between the energy store 11 and the electric motor 21 and converts the direct current provided by the energy store 11 into alternating current, as is required for the operation of the electric motor 21 . In an analogous manner, an inverter 32 is arranged between the energy storage device 11 and the electric motor 31 , which inverter also converts the direct current provided by the energy storage device 11 into alternating current, as required for the operation of the electric motor 31 . The inverter 21 is assigned to the driving drive 20 and the inverter 31 is assigned to the working drive 30 .

Furthermore, an accelerator pedal 23 , a brake pedal 24 and a control unit 25 are assigned to the traction drive 20 . The control unit 25 continuously reads an actuation of both the accelerator pedal 23 and the brake pedal 24 and outputs values corresponding to the actuation as desired values to the inverter 22, which then correspondingly controls the electric motor 21. The inverter 22 also reads a speed of the electric motor 21 and transmits it to the control unit 25.

When the electric motor 21 is in driving operation, the electric motor 21 is controlled as a function of the torque. That is, a target torque of the electric motor 21 is assigned to each actuation of the accelerator pedal 23 .

• - eine Drehzahl des mindestens einen Elektromotors 21 größer als null ist, aber trotzdem einen vorgegebenen Drehzahlgrenzwert von 300 U/min unterschreitet,
• - eine Betätigung eines Fahrpedals 23 einen vorgegebenen Fahrpedalgrenzwert von 10 % einer Maximalbetätigung überschreitet und gleichzeitig
• - eine Betätigung eines Bremspedals 24 einen vorgegebenen Bremspedalgrenzwert von 15 % einer Maximalbetätigung überschreitet,

so versetzt die Steuereinheit 25 den Elektromotor 21 vom Fahrbetrieb in den Haltebetrieb, weil sie erkennt, dass ein Fahrer der Arbeitsmaschine 50 die Arbeitsmaschine 50 anhalten will.If the control unit 25 now recognizes, for example, that

• - a speed of the at least one electric motor 21 is greater than zero, but still falls below a specified speed limit value of 300 rpm,
• - An actuation of an accelerator pedal 23 exceeds a predetermined accelerator pedal limit value of 10% of a maximum actuation and at the same time
• - an actuation of a brake pedal 24 exceeds a specified brake pedal limit value of 15% of a maximum actuation,

for example, the control unit 25 switches the electric motor 21 from the driving mode to the stopping mode because it recognizes that a driver of the working machine 50 wants to stop the working machine 50 .

In the holding mode, the electric motor 21 is subject to speed-dependent regulation in order to ensure that the work machine 50 is held securely in the position specified by the driver. For this purpose, the inverter 22 is given the value zero by the control unit 25 as the setpoint speed, to which the inverter 22 now regulates the electric motor 21 . The electric motor 21 is controlled in the holding mode exclusively via the inverter 22 and no longer via the control unit 25, so that there is a very fast control loop.

For example, the holding operation is terminated when the brake pedal 24 is fully released. Then the electric motor 21 is again operated in driving mode.

2 shows, by way of example and schematically, a work machine 50 on a sloping subsoil 51. The sloping subsoil 51 is, for example, an incline of a slope with an incline angle α of 30°. Due to the incline, a downhill force acts on the working machine 50, which causes the working machine 50 to roll down the slope if it is not compensated. Therefore, in order to prevent rolling down the slope, the working machine 50 is held on the slope by the electric motor 21 by the electric motor 21 applying a motor torque which results in a force which opposes the downhill force and exactly compensates for it. While the working machine 50 is being held on the sloping ground 51, the electric motor 21 is operated according to the invention in the holding mode and regulated as a function of the speed.

3 shows an example of a possible embodiment of the method according to the invention for operating a drive train 10 of a working machine 50 in the form of a flow chart.

In a first method step 100 an actuation of the brake pedal 24 is monitored. If it is determined that brake pedal 24 is actuated to at least 25% of its maximum actuation for a period of at least 200 ms, the method continues in step 101 . Otherwise, the method continues in step 102 and starts again in step 100.

At the same time as step 100, actuation of the accelerator pedal 22 is monitored in step 103. If it is determined that accelerator pedal 22 is actuated for a period of at least 10 ms to such an extent that a torque of at least 100 Nm is requested, the method continues in step 104 . Otherwise, the method continues in step 105 and starts again in step 103.

Likewise at the same time as step 100 and step 103 , a speed of the electric motor 21 is monitored in step 106 . If it is determined that the speed for a period of For example, 100 ms between the value zero and a predetermined speed limit value, which is 200 rpm, for example, the method continues in step 107 . Otherwise, the method continues in step 108 and starts again in step 106.

In step 109 it is checked whether the method has been cumulatively transferred to steps 101, 104 and 107. If this is the case, in step 110 the electric motor 21 is switched to the holding mode and from now on it is operated in the holding mode, in which it is regulated as a function of the speed. However, if this is not the case, the method starts again in steps 100, 103 and 106.

In step 111, the actuation of the brake pedal 24 is again monitored. If it is determined that the brake pedal 24 is actuated to a maximum of 20% of its maximum actuation for a period of at least 10 ms, the method continues in step 112 . Otherwise, the method continues in step 113 and begins again at step 111.

At the same time as step 111, in step 114 the actuation of the accelerator pedal 22 is again monitored. If it is determined that accelerator pedal 22 is actuated for a period of at least 10 ms to such an extent that a torque greater than zero is requested, the method continues in step 1115. Otherwise, the method continues in step 116 and begins again at step 114.

In step 117 it is checked whether the method was cumulatively transferred to steps 112 and 115 . If this is the case, in step 118 the electric motor is put into driving mode and from now on it is operated in driving mode, in which it is controlled as a function of the torque. However, if this is not the case, the method in steps 111 and 114 begins again.

reference list

10

powertrain

11

energy storage

20

traction drive

21

electric motor

22

inverters

23

accelerator pedal

24

brake pedal

25

control unit

30

working drive

31

electric motor

32

inverters

50

working machine

a

pitch angle

100

Monitoring of the actuation of the brake pedal

101

required actuation of the brake pedal

102

no need to press the brake pedal

103

Monitoring of the actuation of the accelerator pedal

104

required actuation of the accelerator pedal

105

no need to press the accelerator pedal

106

Monitoring of the speed of the electric motor

107

RPM for a period of time between zero and a predetermined RPM limit

108

Speed not between zero for a period of time before a preset speed limit

109

Check whether the procedure has been cumulatively passed to steps 101, 104 and 107

110

Placing the electric motor in holding mode

111

Monitoring of the actuation of the brake pedal

112

required actuation of the brake pedal

113

no need to press the brake pedal

114

Monitoring of the actuation of the accelerator pedal

115

required actuation of the accelerator pedal

116

no need to press the accelerator pedal

117

Check whether the procedure has been cumulatively passed to steps 112 and 115

118

Putting the electric motor into driving operation

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 202014000738 U1 [0003]
• DE 102013000276 A1 [0006]

Claims (11)

Method for operating a drive train (10) of a work machine (50), the drive train (10) comprising at least one electric motor (21, 31), the at least one electric motor (21, 31) when the work machine (50) is traveling in a driving mode, wherein the at least one electric motor (21, 31) is controlled in driving mode as a function of the torque, and wherein the at least one electric motor (21, 31) is operated in a holding mode when the work machine (50) is stopped on a sloping surface (51). (110), characterized in that the at least one electric motor (21, 31) is speed-dependently controlled (110) in holding mode. procedure after claim 1 , characterized in that the at least one electric motor (21, 31) is operated in holding mode (110) when - a speed of the at least one electric motor (21, 31) is greater than zero but falls below a predetermined speed limit value (106, 107) - actuation of an accelerator pedal (23) exceeds a specified accelerator pedal limit value (103, 104) and - actuation of a brake pedal (24) exceeds a specified brake pedal limit value (100, 101). procedure after claim 1 , characterized in that the at least one electric motor (21, 31) is operated in holding mode when - a speed of the at least one electric motor (21, 31) is negative (106), - actuation of an accelerator pedal (23) exceeds a specified accelerator pedal limit value (103, 104) and - an actuation of a brake pedal (24) exceeds a predetermined brake pedal limit value (100, 101). procedure after claim 1 , characterized in that the at least one electric motor (21, 31) is operated in holding mode when - a speed of the at least one electric motor (21, 31) is zero and - an inclined position of the working machine is detected via a position sensor. Process according to at least one of claims 2 until 4 , characterized in that the at least one electric motor (21, 31) is operated in holding mode (110) as long as the brake pedal (24) is actuated (111). Process according to at least one of Claims 1 until 5 , characterized in that the at least one electric motor (21, 31) is operated in driving mode (118) when the brake pedal is released (111). Process according to at least one of Claims 1 until 6 , characterized in that the at least one electric motor (21, 31) is operated in driving mode (118) when the accelerator pedal (23) is released and actuated again (114). Process according to at least one of Claims 1 until 7 , characterized in that the at least one electric motor (21, 31) is operated while driving (118) when the speed of the at least one electric motor (21, 31) is negative. Process according to at least one of Claims 1 until 8th , characterized in that the drive train (10) further comprises an inverter (22) assigned to the at least one electric motor (21, 31), the at least one electric motor (21, 31) being speed-dependently controlled by the inverter (22) in holding mode ( 110). Drive train (10) for a working machine (50), wherein the drive train (10) comprises at least one electric motor (11, 31, 41) and wherein the at least one electric motor (21, 31) is assigned to a travel drive (20) of the drive train (10). is, characterized in that the drive train (10) is designed to use a method according to at least one of Claims 1 until 9 to execute. Work machine (50) include a drive train (10). claim 10 .

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