DE102020210997A1 - Method for operating a drive train of a work machine, drive train for a work machine and work machine - Google Patents

Abstract

The invention relates to a method for operating a drive train (1)00 of a work machine, the drive train (100) comprising a brake, an electric traction motor (104) and an electrical energy store (116), the traction motor (104) for operating the traction motor (104) is supplied with electrical power (10, 20) by the energy accumulator (116) in accordance with a drive request, with the traction motor (104) in recuperation mode generating a braking torque and electrical power in accordance with a braking request (30) and with the electrical power is supplied to the energy store (116) (70). The method according to the invention is characterized in that the capacity of the energy store (116) to absorb electrical power is determined (40), that the braking torque generated by the traction motor (104) is limited in such a way that the electrical power generated is completely consumed by the energy store (116 ) can be recorded (50) and that the brake (102) generates an additional braking torque (60) when the braking torque generated by the traction motor (104) falls short of the braking request due to insufficient absorption capacity. The invention also relates to a corresponding drive train (100) and a working machine.

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 8 and a corresponding work machine.

Electrically driven work machines, such as wheel loaders, skid steer loaders, telehandlers, dumpers or even 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 energy supply, or they are diesel-electrically driven, which means that the required energy is provided by a diesel-driven generator, usually in Connection to an electrical buffer storage, such as an appropriately sized capacitor, is provided. In all cases, the mechanical power required for the travel drive and the working drive is provided by one or more electric motors. Furthermore, hybrid-electric working machines are also known in which the mechanical power required for operation is primarily provided by an internal combustion engine, usually a diesel engine. An additionally provided electric motor is fed by a battery or an accumulator and typically assumes a so-called boost function here.

In addition, it is known in the prior art to use the electric motors used to drive the work machines in the context of a braking process to recuperate electrical energy. In a recuperation process, mechanical energy, namely kinetic energy, is converted into electrical energy by the electric motor being operated in generator mode. The electrical energy recovered in this way can then be supplied to the battery in order to charge it. If necessary, the electrical energy can be drawn from the battery again to drive the electric motor.

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.

From the EP 0 962 597 A2 a battery-operated working machine is known, which has two electric motors for the traction drive and a further electric motor for the working drive. The two electric motors for the traction drive are integrated into the front axle, with each electric motor driving one wheel.

However, the known electrically driven working machines are disadvantageous in that a possible electrical charge acceptance capacity of the battery or some other electrical energy store is influenced by a large number of factors. For example, an energy store that is already fully charged can no longer absorb any more energy without risking damage to the energy store. Likewise, for example, an almost completely discharged energy storage device, at least if it is an NiMH or Li-ion battery, can initially only draw low current intensities until a higher charge level is reached. Otherwise there is a risk of damage here too. Thus, a maximum braking power that can be provided by the recuperation mode can only be utilized if a so-called braking resistor is also provided, which completely converts the electrical power generated in the recuperation mode into heat and can emit it to the environment. However, such a braking resistor must be comparatively large and, if necessary, even actively cooled, which means that it is also correspondingly expensive.

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 a brake, an electric traction motor and an electric energy store, the traction motor being supplied with electrical power from the energy store in accordance with a drive requirement in order to operate the traction motor, the traction motor in a recuperation mode, a braking torque and electrical power are generated according to a braking request, and the electrical power is supplied to the energy store. The method according to the invention is characterized in that the capacity of the energy store to absorb electrical power is determined, that the braking torque generated by the traction motor is limited in such a way that the electrical power generated can be completely absorbed by the energy store, and that an additional braking torque is applied by means of the brake is generated when the braking torque generated by the traction motor falls short of the braking request due to insufficient absorption capacity.

The invention thus describes a method which relates to the operation of a drive train of a work machine, the drive train including a brake, an electrical energy store and at least one electric drive motor. The drive train preferably also includes an electric working motor in order to drive a working device. The traction motor and the working motor can preferably be driven independently of one another.

It is also conceivable and preferred not only to provide a single traction motor or a single working motor, but also several traction motors or working motors, which can be coupled to one another via a summing gear, for example, or can be detachably driven with a traction drive or with a working drive via individual drive connections can be connected.

The drive motor is supplied with the electrical power required for its operation by the energy store in accordance with a drive requirement. A drive request is generally understood to be a control input for the drive motor, for example a desired increase in the driving speed. Such a control input means that the traction motor has to provide the mechanical power required to implement the control input. For this reason, a control input is linked to a corresponding drive request in almost all situations. It is irrelevant whether the drive request is made by an operator of the working machine, e.g. by actuating an accelerator pedal, or by an automated control intervention of an assistance system of the working machine.

In an analogous manner, the working engine is also supplied with the electrical power required for its operation by the energy store in accordance with a drive requirement relating to the drive engine.

The electrical energy store is preferably a rechargeable battery, for example an NiMH or Li-ion battery.

The brake is preferably designed as a hydraulically or electrically actuable and mechanically acting friction brake. Advantageously, the brake on each wheel of the work machine includes a braking element, for example in the form of a brake disc and brake pads that can be placed on it.

The traction motor is also designed to recuperate kinetic energy when the working machine is in braking mode, i.e. the working machine can be braked by the traction motor being switched to recuperation mode. The recuperation mode produces electrical power, the amount of which depends on braking power and thus on a braking request. The braking request can be generated, for example, by an operator of the work machine, for example by actuating a brake pedal, or by an automated control intervention of an assistance system of the work machine. Like the drive request, the brake request is a control input.

The power recuperated in this way can then be supplied to the energy store. This represents a charging process for the energy store. Later, the power can be drawn from the energy store again in order to supply the traction motor or the working motor with electrical power.

According to the invention, it is now provided that the capacity of the energy store to absorb electrical power is determined continuously or regularly, for example every 200 ms, every 500 ms, every second or with every recuperation process. The capacity of the energy store depends namely - depending on the specific form of the energy store - on a number of variable factors, and in order to avoid damage or even destruction of the energy store, when supplying electrical power at least be taken into account that the energy store neither too much electrical charge nor too great an electrical current is supplied.

It can thus happen in certain situations that a recuperation triggered by a braking request leads to electrical power that can no longer be supplied to the energy store without risking its damage or destruction.

In this case, according to the invention, the recuperation power and, as a result, also the braking power via the traction motor are reduced to such an extent that the electrical power generated by the recuperation can be absorbed by the energy store without being damaged. In extreme cases, the recuperation power and thus the braking power can also be reduced to zero via the traction motor.

In order to be able to provide sufficient braking torque in all driving situations and to avoid the occurrence of hazards, the invention provides that an additional braking torque is generated by means of the brake if the braking torque generated by the traction motor falls short of the braking request due to insufficient absorption capacity of the energy store . In other words, this means that the braking request is always fully met, whereby the braking torque contributed by the traction motor through the recuperation mode can be limited by the absorption capacity of the energy store, so that in this case a braking torque that is still necessary to fully meet the braking request is used as an additional braking torque of the brake is generated. For an operator of the work machine, it is not perceptible whether the requested total braking torque is generated by the traction motor, by the brake, or proportionally by the traction motor and the brake.

In particular, it is also possible for the braking torque that can be generated by the traction motor to change during the braking process, for example when the work machine travels downhill for a long time, which requires a long-lasting braking process. For example, the energy store can reach its capacity limit due to the continued supply of electrical power and consume less and less electrical power. In this case, the additional braking torque generated by the brake would be increased to the same extent as the braking torque generated by the traction motor decreases. It is also conceivable that the energy store has not yet reached its operating temperature at the beginning of the prolonged braking process and therefore only has a reduced capacity. As the temperature of the energy store increases, so does its absorption capacity, so that the braking torque generated by the traction motor can be increased. The additional braking torque generated by the brake is then reduced to the same extent.

This results in the advantage over the prior art that a braking resistor, which is comparatively expensive because it is large and possibly even actively cooled, can be dispensed with. Instead, the energy to be absorbed during braking - insofar as it cannot be fed to the energy store and absorbed by it - is fed directly into the brakes, which are required by law anyway, in the form of friction. Thus, as much energy as possible is always supplied to the energy store in order to use this energy again later to operate the traction motor or the working motor. This reduces the need for the supply of external energy as much as possible, as a result of which the drive train according to the invention can be operated very efficiently. Only when there is a risk of damage or even destruction of the energy store is the energy generated during braking released to the environment as heat via the brakes.

According to a preferred embodiment of the invention, it is provided that the brake and the traction motor are controlled via a single common control input means. The common control input means can preferably be the accelerator pedal. For example, an actuation characteristic of the accelerator pedal can be adjusted such that when the accelerator pedal is actuated beyond a definable threshold, the traction motor receives a corresponding drive request and drives the work machine or the drive train. The drive request to the traction motor can, for example, linearly follow the actuation beyond the predefinable threshold. It is also conceivable that the drive request to the traction motor follows the actuation of the accelerator pedal exponentially via the predefinable threshold. In an analogous manner, a brake request can be generated if the accelerator pedal is actuated below the predefinable threshold or is not actuated at all, in which case the brake request turns out to be higher the less the accelerator pedal is actuated. If the accelerator pedal is not actuated, the braking request is therefore at its maximum. If the braking request can only be met via the recuperation mode of the traction motor, the brake is not actuated.

Provision is preferably made for a maximum braking request to be capped when the brake and the traction motor are actuated via the common control means. For example, the braking request can be capped at a braking torque that can be provided as a maximum by the traction motor in recuperation mode when the energy store is at its maximum capacity.

According to a further preferred embodiment of the invention, it is provided that the method is carried out depending on a selectable operating mode of the drive train. This means that the work machine or the drive train has several operating modes that can be selected by an operator of the work machine, of which at least one selectable operating mode puts the drive train or the work machine into an operating mode in which it executes the method according to the invention. The operator of the work machine can thus choose whether it makes sense to carry out the method according to the invention in a currently existing situation. For example, the operator can specify the execution of the method according to the invention when the work machine is in what is known as reverse operation is operated, in which they must periodically always cover the same, comparatively short forward and reverse routes. In such a reversing operation, acceleration processes and braking processes follow one another in constant alternation. It can also be useful, for example, to carry out the method according to the invention when descending a long slope.

According to a particularly preferred embodiment of the invention, it is provided that the operating mode is specified by actuating a selection means and/or is recognized and specified automatically. For example, a selector lever or a selector switch or a software button can be provided in a menu item of a combined display and input device designed as a touchscreen, via which the operator of the work machine specifies the operating mode.

Likewise, it can be recognized via inclination sensors or location determination means in connection with digital map data, for example, that the work machine is running down a slope and the selection means can be actuated automatically accordingly.

According to a very particularly preferred embodiment of the invention, it is provided that the operating mode is recognized automatically by environment sensors. The environment sensor system can be designed, for example, as a camera sensor system, radar sensor system, lidar sensor system, as an inclination sensor system, driving sensor system or location determination means such as GPS, GLONASS and GALLILEO in connection with digital map data. If, for example, the environment sensors, in particular via camera sensors, radar sensors or lidar sensors, in conjunction with the driving sensors, in particular via wheel speed sensors, detect a reversing process, the selection means can advantageously be actuated automatically.

According to a further preferred embodiment of the invention, it is provided that the capacity of the energy store is determined according to a state of charge of the energy store, a temperature of the energy store and a maximum absorbable current. Based on these criteria, the state or the capacity of the energy store can be reliably assessed, so that in particular overcharging with an excessively high electrical charge and overloading with an excessively high electrical current intensity can be avoided.

According to a further preferred embodiment of the invention, it is provided that the additional braking torque of the brake and the braking torque generated by the traction motor together meet the braking requirement. This ensures that a required total braking torque is always provided in full and that the working machine experiences the required deceleration. In this way, dangerous situations can be avoided.

The invention further relates to a drive train for a work machine, the drive train comprising a brake, an electric traction motor and an electric energy store, the traction motor for operating the traction motor being able to be supplied with electrical power from the energy store in accordance with a drive requirement, the traction motor in a Recuperation mode, a braking torque and electrical power can be generated according to a braking request and the electrical power can be fed to the energy store. The drive train according to the invention is characterized in that the drive train is designed to determine the capacity of the energy store to absorb electrical power, that the drive train is designed to limit the braking torque generated by the traction motor in such a way that the electrical power generated is completely absorbed by the Energy storage can be included and that the drive train is designed to generate an additional braking torque by means of the brake when the braking torque generated by the traction motor lags behind the braking request due to insufficient absorption capacity.

The drive train according to the invention thus enables the method according to the invention to be carried out, which leads to the advantages already described in connection with the method according to the invention.

According to a preferred embodiment of the invention, it is provided that the drive train further comprises an electric working motor, wherein the working motor for operating the working motor can be supplied with electrical power from the energy store in accordance with a drive requirement relating to the working motor. The working motor serves to drive a working drive, for example a hydraulic working drive with a hydraulic pump.

According to a further preferred embodiment of the invention, it is provided that the drive train also includes environment sensors for detecting an operating mode. This results in the advantage that an operating mode, for example reverse operation, can be recognized automatically. In a further step, the method according to the invention can be carried out automatically.

According to a further preferred embodiment of the invention, it is provided that the drive train also includes a driving gear, wherein the driving gear is designed to be power-shiftable over a large number of gears. The drive motor drives the working machine via the drive gear. This leads to increased flexibility of the drive train according to the invention.

It is preferably provided that the drive train also includes a working gear. The working motor drives the working drive via the working gear.

At least the drive transmission preferably has a large number of gear stages designed as forward gears and at least one gear stage designed as reverse gear. The number of forward gears particularly preferably corresponds to the number of reverse gears. The working transmission can also have more than one gear stage designed as a forward gear. In addition, one or more gear stages of the working transmission designed as a reverse gear are also conceivable.

The driving gear or the working gear can be designed either in planetary design or in countershaft design and have both spur gears and any other form of transmission.

According to a further preferred embodiment of the invention, it is provided that the traction motor and the working motor are arranged in a common housing. This enables the traction motor and the working motor to be arranged in a space- and weight-saving manner within the drive train in a working machine. In addition, the common housing saves weight and costs compared to two individual housings. The traction motor and the working motor can, for example, be installed axially one behind the other in a common housing, with the motor output shafts being able to point out of the housing in opposite axial directions, for example. However, an arrangement axially next to one another in a correspondingly designed housing is also possible and preferred, so that both motor output shafts can point in the same axial direction, for example.

According to a further preferred embodiment of the invention, it is provided that the drive train is designed to carry out a method 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 beispielhaft eine mögliche Ausführungsform eines erfindungsgemäßen Verfahrens zum Betreiben eines Antriebsstrangs einer Arbeitsmaschine in Form eines Flussdiagramms und
• 2 beispielhaft und schematisch eine mögliche Ausbildungsform eines erfindungsgemäßen Antriebsstrangs für eine Arbeitsmaschine.

Show it:

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

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 of a possible embodiment of a method according to the invention for operating a drive train 100 of a work machine in the form of a flow chart. Drive train 100 includes a brake 102, an electric traction motor 104 and an electric energy storage device 116. In a first method step 10, for example, a drive request to accelerate the work machine is sent to traction motor 104, which then in step 20, in accordance with the drive request, from energy storage device 116 with the required electrical power is supplied. In step 30, for example, a braking request is made to traction motor 104 in order to decelerate the working machine. For this purpose, the traction motor 104 can be put into recuperation mode so that it generates a braking torque and electrical power. At the same time as step 30, the capacity of energy store 116 to absorb electrical power is determined in step 40. It turns out that the capacity of the energy store 116 is not sufficient to cope with the braking demand and the recuperation operation resulting therefrom absorb generated electrical power. For this reason, in step 50 the braking torque generated by the traction motor 104 is limited in such a way that the electrical power generated can be completely absorbed by the energy store 116 . In step 60, the brake 102 is actuated automatically at the same time, so that it generates an additional braking torque. The total braking torque generated by traction motor 104 and the additional braking torque generated by brake 102 fully meet the braking request. The electrical power generated by traction motor 104 in recuperation mode is supplied to energy store 116 in step 70 .

2 shows by way of example and schematically a possible embodiment of a drive train 100 according to the invention for an in 2 not shown work machine. The drive train 100 comprises a brake 102 designed as a hydraulically actuated disk brake, an electric working motor 104 and an electric traction motor 106 as well as a travel gear 108 and a hydraulic pump 110. The traction motor 104 drives two drivable axles 112 with four drivable wheels via the travel gear 108. The working engine 104 drives a lifting mechanism 114 via the hydraulic pump 110 to actuate a lifting arm. The traction motor 104 and the working motor 106 are each supplied with the required electrical power by the energy store 116 in accordance with a drive requirement or a work requirement. The energy source 116 is, for example, a rechargeable battery 116. When braking is requested, the traction motor 104 is put into recuperation mode, so that it generates a braking torque and electrical power. However, before the electrical power generated in this way is supplied to the energy store 116, its capacity to absorb electrical power is first determined. If the capacity of energy store 116 to absorb the electrical power generated by the recuperation operation of traction motor 104 is not sufficient, the braking torque generated by traction motor 104 - and with it the electrical power generated - is limited to such an extent that the electrical power now generated from the Energy storage 116 can be included without damaging it. In order nevertheless to provide a sufficiently high braking torque overall and to fully meet the braking requirement, brake 102 is actuated, which then generates an additional braking torque. The total of the additional braking torque of the brake 102 and the braking torque generated by the traction motor 104 in recuperation mode therefore correspond completely to the braking request.

Reference List

100

powertrain

102

brake

104

electric traction motor

106

electric working motor

108

driving gear

110

hydraulic pump

112

drivable axis

114

lifting kinematics

116

electrical energy storage, rechargeable battery

10

Drive request to traction motor

20

Supplying the traction motor with electrical power

30

Braking request to traction motor

40

Determination of the capacity of the energy store

50

Limitation of the braking torque

60

Generation of an additional braking torque

70

Supply of the electrical power to the energy storage device

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 [0004]
• EP 0962597 A2 [0005]

Claims (14)

Method for operating a drive train (1)00 of a work machine, the drive train (100) comprising a brake, an electric traction motor (104) and an electric energy store (116), the traction motor (104) for operating the traction motor (104) from The energy store (116) is supplied with electrical power (10, 20) in accordance with a drive request, with the traction motor (104) in recuperation mode generating a braking torque and electrical power in accordance with a braking request (30) and with the electrical power being supplied to the Energy store (116) is supplied (70), characterized in that the capacity of the energy store (116) to absorb electrical power is determined (40), that the braking torque generated by the traction motor (104) is limited in such a way that the generated electrical power can be completely absorbed by the energy store (116) (50) and that an additional braking moment by means of the brake (102). ent is generated (60) when the braking torque generated by the traction motor (104) falls short of the braking request due to insufficient absorption capacity. procedure after claim 1 , characterized in that the brake (102) and the traction motor (104) are controlled via a single common control input means. Process according to at least one of Claims 1 and 2 , characterized in that the method is carried out depending on a selectable operating mode of the drive train (100). procedure after claim 3 , characterized in that the operating mode is specified by actuating a selection means and/or is recognized and specified automatically. procedure after claim 4 , characterized in that the operating mode is automatically detected by environment sensors. Process according to at least one of Claims 1 until 5 , characterized in that the capacity of the energy store (116) according to a state of charge of the energy store (116), a temperature of the energy store (116) and a maximum absorbable current is determined (40). Process according to at least one of Claims 1 until 6 , characterized in that the additional braking torque of the brake (102) and the traction motor (104) generated braking torque together meet the braking requirement. Drive train (100) for a work machine, wherein the drive train (100) comprises a brake (102), an electric traction motor (104) and an electric energy store (116), the traction motor (116) for operating the traction motor (116) being powered by the energy store (116) can be supplied with electrical power in accordance with a drive request, with the traction motor (104) being able to generate a braking torque and electrical power in accordance with a braking request in recuperation mode, and with the electrical power being able to be supplied to the energy store (116), characterized in that that the drive train (110) is designed to determine the capacity of the energy store (116) to absorb electrical power, that the drive train (100) is designed to limit the braking torque generated by the traction motor (104) in such a way that the Electrical power generated can be fully absorbed by the energy storage device (116) and that the drive strand (100) is designed to generate an additional braking torque by means of the brake (102) when the braking torque generated by the traction motor (104) falls short of the braking requirement due to insufficient absorption capacity. Drive train (100) after claim 8 , characterized in that the drive train (100) further comprises an electric working motor (106), wherein the working motor (104) for operating the working motor (106) from the energy store (116) according to a drive requirement with electrical power can be supplied. Drive train (100) according to at least one of Claims 8 and 9 , characterized in that the drive train (100) further includes environment sensors for detecting an operating mode. Drive train (100) according to at least one of Claims 8 until 10 , characterized in that the drive train (100) further comprises a driving gear (108), wherein the driving gear (108) is designed to be power shiftable over a plurality of gears. Drive train (100) according to at least one of Claims 8 until 11 , characterized , that the traction motor (104) and the working motor (106) are arranged in a common housing. Drive train (100) according to at least one of Claims 8 until 12 , characterized in that the drive train (100) is designed to use a method according to at least one of Claims 1 until 8th to execute. Work machine, comprising a drive train (100) according to at least one of Claims 8 until 13 .

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