work machine

Abstract

The present invention relates to a working machine, in particular a wheel loader, with an electric drive unit for propelling the working machine and with a battery for supplying the drive unit with electrical energy, wherein the drive unit is designed to switch to a recuperation mode when propulsion is not required, in particular when driving downhill, in which the drive unit generates recuperation energy, wherein means are provided which are designed such that the efficiency of the drive unit switched to the recuperation mode can be reduced.

Description

[0001] The present invention relates to a working machine, in particular a wheel loader, with an electric drive unit for propelling the working machine and with a battery for supplying the drive unit with electrical energy, wherein the drive unit is designed to switch to a recuperation mode when propulsion is not required, in particular when driving downhill with the working machine, in which the drive unit generates recuperation energy.

[0002] With battery-electric wheel loaders, there may be a need to dissipate excess thrust energy when driving downhill in such a way that the thrust energy is transferred / converted into other forms of energy without using the wheel loader's service brake, for example to comply with a safety regulation or to prevent the service brake from overheating.

[0003] In principle, it is possible to supply the battery energy to the machine. When traveling downhill, the (synchronous) motor stops driving the wheels of the wheel loader, causing the machine to decelerate automatically. The electric motor then acts as a generator, producing electricity from the change in the potential energy of the machine (from the kinetic energy of the moving wheels), which recharges the battery. In this case, the battery acts as a load-bearing resistor.

[0004] A battery has a gross capacity, which is the maximum amount of energy that can be stored in the battery. The net capacity is the practically usable amount of energy, which can be, for example, 90-95% of the gross capacity. Continuously fully charging the battery and utilizing its gross capacity is detrimental, as it reduces the battery's lifespan. The state of charge refers to the actual amount of stored energy at the start of regenerative braking. The charging capacity is the net capacity minus the state of charge. The charging buffer is the range of the gross capacity minus the net capacity. The charging buffer is therefore the portion of the battery's capacity that exceeds the net capacity and should generally not be used in order to maximize its lifespan.

[0005] The aforementioned connections are in Fig. 4 shown.

[0006] If the aforementioned downhill run of the work machine ends before the net capacity is reached, no immediate action is required. However, if the battery's net capacity is reached before this downhill run ends, the available recuperation energy must be used or dissipated elsewhere to prevent the battery from being fully charged to its gross capacity.

[0007] It is known from the prior art to reduce the recuperation energy to be fed in or to switch off the recuperation operation when the battery has reached a recuperation limit temperature, to cause a downshifting of the transmission depending on the recuperation operation, to convert the recuperation energy into heat by means of an electrical resistance, or to distribute the total braking power between the electric brake and a non-recuperative brake in such a way that a maximum possible electrical power is stored in the battery.

[0008] German patent application DE 10 2020 207 297 A1 discloses a system for controlling the speed of a vehicle. The system includes an energy storage device designed to store the vehicle's deceleration energy. Once the storage capacity of the device is reached, the remaining deceleration energy is directed to a non-energy-storing retarder.

[0009] From DE 10 2010 005 407 A1, the use of an engine cooler fan of a motor vehicle for energy recuperation during braking or overrun is known.

[0010] DE 694 13 481 T2 discloses that excess electrical recovery power that cannot be absorbed by the storage battery is absorbed by increasing the power consumption of the air conditioning system.

[0011] JP 2006-333549 A discloses a brake control device for a vehicle in which regenerative energy generated by a first motor is consumed by a second motor without substantially generating torque for the second motor.

[0012] The present invention is based on the objective of further developing a working machine of the type mentioned at the outset in such a way that the battery life is reduced as little as possible even with repeated recuperation operation of the working machine.

[0013] This problem is solved by a machine having the features of claim 1.

[0014] In one aspect of the invention, it is preferably provided that the working machine has several electrical consumers, wherein power ranges are assigned to the consumers, and that a control device is provided which is configured to allocate the entire recuperation power or a part of the recuperation energy to the consumer(s) depending on the power ranges by switching on the consumers in the said recuperation mode of the drive unit.

[0015] The drive unit is the traction motor of the working machine. This is preferably designed as an electric motor and in particular as a synchronous motor.

[0016] The present invention is therefore based on the idea that the control unit in recuperation mode distributes the available recuperation energy or a part thereof to the consumer(s) depending on the respective power ranges of the consumers.

[0017] It is conceivable that the control unit is designed such that, during recuperation mode, the battery is charged, preferably only until the net capacity is reached, and / or one or more consumers are switched on to convert the recuperated energy into other forms of energy. It is also conceivable that the control unit is designed such that, during recuperation mode, energy is drawn from the battery, thereby increasing the remaining charge capacity of the battery.

[0018] In one embodiment of the invention, the control device is designed in such a way that the battery is not charged during recuperation operation.

[0019] For example, if consumer A has a power range of A1 to A2 and consumer B has a power range of B1 to B2, the control unit can allocate the available recuperation energy to consumer A by switching it on, to consumer B by switching it on, or to both consumers. This allocation depends on the power ranges of the consumers, which are available to the control unit or communicated to it.

[0020] Preferably, the control device is designed in such a way that all the recuperation energy, which is generated, for example, during downhill driving or braking, is completely consumed by one or more consumers or the battery in order to prevent the machine from accelerating when driving downhill.

[0021] As explained, in one embodiment of the invention, it is conceivable that the control unit is configured to allocate the recuperation energy entirely to the consumer(s) in recuperation mode, so that the battery is not charged in recuperation mode. In this case, the entire recuperation energy is allocated to one or more consumers by activating them.

[0022] The consumers can be those that perform other functions of the machine during normal operation, and / or those that are present solely for the purpose of consuming recuperated energy. The first group of consumers includes, for example, fans, compressors, and pumps that are already present and used, for instance, to operate hydraulic systems, cooling systems, etc. The second group of consumers includes, for example, an additional switching valve, an additional battery, etc. These consumers in the second group thus serve exclusively to absorb and consume recuperated energy and have no function during the normal operation of the machine.

[0023] The control unit can be configured to allocate recuperation power to the consumer(s) in the recuperation mode of the drive unit, depending on the available recuperation energy, by activating the consumer(s). In this embodiment of the invention, the allocation of recuperation energy is not only dependent on the power ranges of the consumers, but also on the amount of available recuperation energy.

[0024] Furthermore, the control unit may be configured to prioritize consumers when allocating recuperation energy. For example, if the power ranges of the consumers are identical, the control unit may be configured to prioritize consumer A over consumer B, i.e., to switch on consumer A and only switch on one or more further consumers once its upper power limit is reached.

[0025] Preferably, the control unit is designed not to increase the battery's state of charge, or not to increase it beyond a limit value, during recuperation mode. This limit value is preferably the battery's net capacity.

[0026] It is conceivable that the control unit is designed to allocate the recuperation energy to the consumer(s) only when the battery's state of charge reaches a certain threshold. In this case, the system could charge the battery up to a specific limit and then activate one or more consumers, provided recuperation energy is still available. This threshold could, for example, be the battery's net capacity.

[0027] In one embodiment of the invention, it is provided that the working machine has a cooling circuit, in particular a cooling circuit associated with the battery, and a refrigerant circuit coupled to this via a heat exchanger, which includes a compressor and a condenser, and that the consumer is the compressor and / or a fan associated with the condenser.

[0028] For example, the machine could have a battery cooling circuit designed to cool the battery. This cooling circuit might be connected, for instance, via a heat exchanger to a refrigerant circuit, which in turn includes a compressor and a condenser. A fan could be provided to dissipate heat from the condenser. The component(s) could be the fan and / or the compressor.

[0029] It is also conceivable that the cooling circuit includes a heating device, preferably with a circulation pump assigned to the heating device, and that the consumer is the heating device and / or the circulation pump. This heating device can serve to compensate for the heat loss that occurs when heat is transferred from the battery cooling circuit to the refrigerant circuit.

[0030] Furthermore, the consumer can be the electric drive unit, i.e., the drive motor of the working machine, and preferably means are provided by which drag or shear losses in the air gap of the drive unit can be varied. The electric drive unit is a drive motor.

[0031] This drive motor is cooled directly within the core of the motor by means of cooling oil, or rather, heat is drawn away from there. Due to a greater tilt angle or a significantly increased coolant flow, this oil can accumulate inside the motor and no longer drain away quickly enough. This leads to increased drag and shear losses in the motor's air gap. These losses are therefore potential consumers within the scope of the present invention.

[0032] In a further embodiment of the invention, it is provided that the working machine has a working hydraulics with a hydraulic pump with variably adjustable flow rate and a working hydraulics control block, and that the consumer is the hydraulic pump of the working hydraulics.

[0033] The electrical consumption of the hydraulic pump preferably depends on the flow rate, which is controlled, for example, by an electronic signal.

[0034] Preferably, the hydraulic control block includes a variably adjustable pressure relief valve, preferably proportional to the load pressure. For example, at a load pressure of 0 bar, the pressure relief valve has a pressure limit of 40 bar, and the pressure limit is also increased for a noticeably higher consumption of the hydraulic pump.

[0035] Preferably, a switching valve for generating a load pressure for the hydraulic pump is assigned to the working hydraulic control block. Preferably, any load pressure from 0 bar to 330 bar can be generated, particularly as with a fixed pressure limit.

[0036] Preferably, the working hydraulics include a quick-change system, wherein a load pressure for the hydraulic pump, in particular up to 160 bar, can be generated via a locking cylinder of the quick-change system.

[0037] Preferably, the hydraulic pump's consumption is increased by generating a "fictitious" load pressure signal and thereby increasing the load pressure or the hydraulic pump's delivery flow. Preferably, the hydraulic pump has a variably adjustable delivery flow and / or a variable pressure limit.

[0038] Alternatively or in addition to the aforementioned existing consumers, the invention also covers the case where additional consumers are present, i.e., not already present, which serve to dissipate recuperated energy. These additional consumers could be, for example, a switching valve, an electrical resistor, or a battery that stores recuperated energy.

[0039] It is conceivable that a permanently installed high-voltage battery, serving as a backup for short distances, could be one or more of the power consumers. For example, if the machine has a battery swapping system, the permanently installed high-voltage battery could be used to drive the machine from one swapping station to the next. The permanently installed high-voltage battery could also be used in emergency operation of the machine, such as if the main battery runs out for any reason and the machine stops.

[0040] In one aspect of the invention, it is preferably provided that means are available which are designed in such a way that the efficiency of the drive unit switched to recuperation mode can be reduced.

[0041] Preferably, the means are designed to allow drag and / or shear losses, particularly in an air gap, of the drive unit to be changed, in particular increased, in order to reduce the efficiency of the drive unit.

[0042] Preferably, the means are designed to allow the volume flow of coolant through the drive unit to be changed, in particular increased, in order to reduce the efficiency of the drive unit.

[0043] Preferably, the means are designed to allow the torque current value of the drive unit, in particular a torque-generating component of the torque current value, to be changed, in particular reduced, in order to decrease the efficiency of the drive unit.

[0044] Preferably, the means include or are a control device and / or a coolant pump.

[0045] Another aspect of the invention relates to a method for operating a working machine according to the invention, wherein the drive unit is operated in a recuperation mode, thereby reducing the efficiency of the drive unit.

[0046] Preferably, the efficiency of the drive unit is reduced by more than 5%, preferably by more than 30%, and in particular by 100%.

[0047] Preferably, it is provided that drag and / or shear losses in an air gap of the drive unit are modified, in particular increased, in order to reduce the efficiency of the drive unit.

[0048] Preferably, it is provided that the volume flow of coolant flowing through the drive unit is changed, in particular increased, in order to reduce the efficiency of the drive unit.

[0049] Preferably, it is provided that the torque current value of the drive unit, in particular a torque-generating component of the torque current value, is changed, in particular reduced, in order to reduce the efficiency of the drive unit.

[0050] Preferably, the destruction of kinetic thrust energy is achieved by lowering, deteriorating, or reducing the efficiency of the drive unit, resulting in a lower production of recuperation energy by the drive unit.

[0051] Preferably, the recuperation energy is not distributed, particularly by means of the control unit through control of the intermediate circuit, but rather the resulting thrust energy is regulated by influencing the efficiency of the drive unit, especially the synchronous motor. In contrast, according to the prior art, the thrust energy is regulated, for example, by means of the service brake or gear shifting.

[0052] In other words, it is preferably provided that the kinetic thrust energy is allocated to the drive unit as a thermal consumer, in particular by the control device.

[0053] Preferably, it is provided that a portion of the kinetic thrust energy is directly converted into heat and released due to the reduced efficiency of the drive unit acting as a generator, with any remaining thrust energy being converted into electrical energy or recuperation energy.

[0054] The maximum achievable efficiency η of the drive unit is typically between 90% and 95%. This means that, for example, between 90% and 95% of the thrust energy can be converted into electrical energy or recuperation energy by the drive unit.

[0055] Preferably, the actual efficiency η is reduced by more than 5%, preferably by more than 30%, and in particular by up to 100%. With a 100% reduction in efficiency, no electrical energy or recuperation energy is generated by the drive unit.

[0056] The reduction or lowering can preferably be carried out independently of the type of cooling of the drive unit, whereby the drive unit can be oil-, air- and / or water-cooled, via the torque current value of the drive unit.

[0057] Particularly in the case of oil cooling of the drive unit, an increase in drag and / or shear losses in the drive unit can occur due to an increased volume flow of coolant.

[0058] The coolant flow rate is preferably adjusted continuously.

[0059] It should be noted here that the terms "ein" and "eine" do not necessarily refer to exactly one of the elements, although this is a possible interpretation, but can also denote a plurality of elements. Likewise, the use of the plural also includes the presence of the element in question in the singular, and conversely, the singular also includes several of the elements in question.

[0060] It is further noted that the terms "power" and "energy" are used synonymously within the scope of the invention and both can stand for power as well as energy.

[0061] Furthermore, all features of the invention described herein can be combined with one another or claimed separately from one another as desired.

[0062] Further advantages, features and effects of the present invention will become apparent from the following description of preferred embodiments with reference to the figures, in which identical or similar components are designated by the same reference numerals.

[0063] They show: Fig. 1: A schematic view of the battery's state of charge before and after recuperation, Fig. 2: a schematic view of the battery and the alternative use of the recuperation energy after reaching a limit value of the battery charge level, Fig. 3: a schematic overview of the distribution of recuperation energy by means of the control unit, Fig. 4: A schematic view of a battery showing net capacity, gross capacity, charge buffer, charging capacity and state of charge, Fig. 5: a schematic overview of a possible distribution of the recuperation energy, Fig. 6: a schematic overview of a possible distribution of recuperation energy, Fig. 7: a schematic overview of a possible distribution of the recuperation energy,

[0064] Fig. Figure 1 shows a schematic view of the battery before recuperation begins, in an exemplary embodiment shown on the left. In this example, the charge level is 12%, the charge buffer is 5%, and the charging capacity is therefore 83%.

[0065] If the battery is now charged in recuperation mode, the following results at the end of the battery charging process: Fig. In the state shown on the right, the charge level is 94%, the charging buffer remains at 5%, and the charging capacity is 1%. During recuperation, the charging capacity is therefore preferably not fully utilized, but a "safety margin" is maintained to ensure that the charging buffer is not reached.

[0066] In recuperation mode, the in Fig. Once the state shown on the right is reached, before the recuperation process ends, one or more electrical consumers are switched on to absorb the electrical energy and convert it, for example, into heat or kinetic energy. This prevents the battery from being charged beyond its capacity.

[0067] This condition is in Fig. 2 shown. As indicated by the curved arrow, further recuperation energy is no longer supplied to the battery, but is directed either to existing consumers, additional consumers or both.

[0068] Instead of gradual charging, the battery can also be charged or discharged simultaneously while these other consumers are switched on. This results in a slower depletion or even a continuous increase in the battery's remaining charge capacity.

[0069] Fig. Figure 3 shows a schematic distribution of available recuperation energy.

[0070] The reference symbol R denotes the available recuperation power, which arises from the kinetic energy that is converted into electrical energy, for example, when braking or driving downhill with the machine.

[0071] In the example shown here, the electrical consumers are the thermal management system T, the working hydraulics A, and the drive system F, or their components. The control unit is designated S. The control unit ST has a decision point designed to distribute the available recuperation energy to the consumers. This decision point determines which consumer(s) are activated and how much of the available recuperation power is allocated to each.

[0072] The high-voltage battery (HV) of the work machine is used in the exemplary embodiment of the Fig. 3 not loaded.

[0073] It is particularly advantageous if the control unit is designed such that the energy drawn from the battery by the connected electrical consumer(s) is greater than or equal to the energy supplied through recuperation. The battery's state of charge thus cannot change, decrease, or even increase during recuperation mode. The charging buffer also allows for short-term overcharging beyond the net capacity; that is, for a short period, the amount of energy drawn from the battery can be less than the recuperation energy supplied to it.

[0074] The invention basically encompasses switching on the electrical consumers at an earlier point in time, i.e., before the battery reaches its net capacity; however, the generally desired recuperation effect would then be significantly lower.

[0075] In the Fig. In the embodiment shown in Figure 3, the recuperation power in the DC circuit is completely destroyed or absorbed by the consumers to ensure that the working machine does not accelerate due to the "electric brake" formed by the electrical consumers and, if applicable, the battery.

[0076] An embodiment of the invention is explained in more detail below: Electrical consumers: a) Consumers present exclusively on the machine 1) Thermal management: (Cooling / heating capacity, radiator fan)

[0077] The battery cooling circuit is coupled to a refrigerant circuit via a plate heat exchanger (chiller) and to the cabin heating circuit via another plate heat exchanger. The chiller introduces cooling power into the battery cooling circuit; in other words, heat is added to the refrigerant circuit, which must then be dissipated from the refrigerant circuit.

[0078] For the operation of the refrigerant circuit, the heat generated at the condenser (liquefier) ​​by the refrigeration cycle must also be dissipated. The cooling fans can be fully activated for this purpose.

[0079] The heat loss from the cooling circuit must be compensated for by a high-voltage heater. The electrical power consumed consists of the power consumption of the high-voltage heater and the power consumption of, for example, circulation pumps.

[0080] Operating the high-voltage heater at full power further increases the electrical power consumed, but this also results in a warming of the cooling medium and the batteries. The "efficiency" of the heat path (high-voltage heater - cooling medium - hoses - cooling plate - cell) means that the temperature increase of the high-voltage battery of the machine is not very high, which is acceptable for a limited time. 2) Drive system:

[0081] The drive motor of the machine is cooled by means of cooling oil directly in the core of the motor. Due to a greater tilt or a significantly increased coolant flow, this oil can accumulate inside the motor and no longer drain downwards quickly enough. This leads to increased drag and shear losses in the motor's air gap. 3) Hydraulic pump / control block:

[0082] The hydraulic fluid flow rate in the working hydraulics and the prevailing pressure determine the power consumption. It would also be conceivable to artificially introduce a load pressure via an external switching valve, thereby increasing the pressure and achieving a significantly higher power consumption.

[0083] With appropriate design, the entire recuperation power available in the DC circuit can be drawn via the onboard electrical consumers.

[0084] According to the invention, the recuperation power to be consumed is not distributed arbitrarily, but is specifically directed to the consumers by the control unit depending on their power ranges.

[0085] Referring to the exemplary embodiment, the thermal management system can, for example, operate at its lower limit and the working hydraulics can be fully utilized. The remaining kW are consumed via the drive system or a combination of drive and working hydraulics, whereby full utilization of the high-voltage heaters can be used to temporarily relieve the motor. In this case, the capacity of the charging buffer is not actively used; it retains its function as a "life insurance" for the battery. b) Consumers who are additionally attached / carried

[0086] This option is not preferred, but it helps to achieve the goal of avoiding excessive battery charging and preventing the machine from accelerating when going downhill.

[0087] Additional consumers could include: - Carrying a "normal" battery that is charged with recuperated energy - Carrying a spare high-voltage battery - Construction of a resistance

[0088] In another embodiment, the drive unit consumes some of the thrust energy by converting it into heat, so that ultimately less thrust energy remains that can be converted into recuperation energy by the drive unit.

[0089] In Fig. 5 is one possibility of converting thrust energy into heat and recuperation energy or the destruction of thrust energy and / or recuperation energy.

[0090] The drive unit in the form of the drive M is driven by one or more wheels of the working machine and thus supplied with thrust energy.

[0091] The drive system M converts some of the thrust energy into heat, as the drive system has an efficiency of less than 100%.

[0092] The remaining thrust energy is converted by the drive system M into recuperation energy, which is then fed into the Fig. 5 consumers shown distributed or the in Fig. The 5 consumers shown are assigned by the ST control unit.

[0093] The recuperation energy is thus distributed to the battery B, the thermal management T and / or the working hydraulics A, with the distribution of the recuperation energy taking place via an intermediate circuit DC.

[0094] This is also achieved by Fig. Figure 6 illustrates this.

[0095] In Fig.Figure 7 shows, through the arrows around the drive unit M, how the drive unit M, which is subjected to thrust energy, partially converts this thrust energy into heat.

[0096] Another embodiment relates to a reduction in the efficiency of the drive unit when operating the drive unit in a recuperation mode.

[0097] Among the most important components of the control system for permanent magnet synchronous machines or synchronous motors are the d / q currents. These are generated by transforming the three phase currents and thus represent only a fictitious value that cannot be measured directly but is calculated from the phase currents using coordinate transformations. The starting point consists of the three phase currents and the resulting total current or RMS value phasor. The currents are phase-shifted by 120° relative to each other and sinusoidal with the rotor's rotational frequency. Since this is a difficult-to-control state, the following two transformation steps are performed.

[0098] The first transformation step is the α / β transformation. This transforms the RMS phasor into two components I. α and I βThe current is decomposed. The RMS vector is therefore no longer determined by three components, but only by two. The vectors of these two currents are always at right angles to each other, their amplitudes are still sinusoidal and change with the rotor position. The coordinate system in which the currents are located consists of an α- and a β-axis along which the amplitudes of the respective currents change.

[0099] The received currents I α and I β In the second step, the currents can be transformed into two new currents in a rotor-fixed coordinate system using the d / q transformation. This means that the coordinate system is now located at the rotor and rotates with its rotational speed. The two newly created currents I d and I qThe q-currents are always at right angles to each other. However, the amplitude of the currents no longer changes with the rotor angle γ, but remains constant. The q-current is referred to as the torque-generating component, since it is primarily responsible for generating the synchronous torque. The d-current is referred to as the flux-generating component, since it plays a crucial role in field weakening. Because the RMS phasor must remain unchanged despite all transformations, the vector sum of the d / q currents yields the RMS phasor. The fixed angle between the RMS phasor and the d-current is called the current angle ψ and describes the division of the stator current into the d-current and q-currents. Since the resulting currents are constant and no longer depend on the rotor's position, they can be varied. This variation can be achieved by adjusting the current angle.When the values ​​are passed to the inverter, it can use the reverse transformation to deduce the phase currents and thus control the synchronous motor.

[0100] In permanent magnet synchronous machines or synchronous motors, the generated torque therefore consists of two parts: the synchronous torque M. Syn and the reluctance moment M Rel The synchronous torque is generated by the magnetic attraction and repulsion of the permanent magnets on the rotor by the rotating stator field. It reaches its maximum at a current angle of 90°, so that the stator and rotor rotating fields are at right angles to each other. In this position, the combination of repulsive and attractive forces of the poles is optimally utilized. Since at a current angle of 90° only a q-current, and not a d-current, flows, the q-component is referred to as the torque-generating component.

[0101] The reluctance torque arises because the rotor is pulled into the position of least magnetic resistance. For this to occur, it must be made of at least two materials with different magnetic conductivities. If this is the case, the rotor will always move to the position where the magnetic field flowing through it encounters the least resistance. This torque can only occur if both a d-current and a q-current are present. Normally, the path of least resistance leads through the iron core of the rotor, which is usually positioned so that the path of least resistance runs in the q-direction – that is, at a right angle to the rotor's north pole. The sign is irrelevant, as the resistance is direction-independent. For this reason, the amplitude of the reluctance torque oscillates at twice the frequency of the synchronous torque.

[0102] Now, if we add the characteristic curves of the two moments M Syn and M RelThe course of the total moment M is thus determined. Ges This depends on the d / q currents and therefore also on the current angle. The total torque can be calculated from the d / q currents using a torque current value. Likewise, the current generated by the drive unit, or the generated recuperation energy, can be calculated from the total torque applied to the drive unit during recuperation using the torque current value.

[0103] The maximum total torque therefore lies between 90° < Ψ < 180° and is determined using the MTPA (Maximum Torque per Ampere) when characterizing the synchronous motor. This method seeks the current angle at which the sum of reluctance and synchronous torque is maximized for a given current. At this angle, the machine's efficiency is at its optimum.

[0104] Below the field weakening range, the current angle is always set within the motor's optimal efficiency range. However, during deceleration, situations can arise where the battery can no longer absorb the recuperation energy, making it necessary to reduce this energy. Changing the current angle in the vehicle's inverter reduces the efficiency of the synchronous motor, resulting in less energy being converted into recuperation. This generates more heat in the synchronous motor. In extreme cases, the current angle can be selected so that no torque-generating component (q-component) is produced, and the motor functions purely as a coil that dissipates heat. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 207 297 A1

[0008] DE 10 2010 005 407 A1

[0009] DE 694 13 481 T2

[0010] JP 2006-333549 A

[0011]

Claims

[1] Working machine, in particular wheel loader, with an electric drive unit for propelling the working machine and with a battery for supplying the drive unit with electrical energy, wherein the drive unit is designed to switch to a recuperation mode in which the drive unit generates recuperation energy when propulsion is not required, in particular when driving downhill of the working machine, characterized by , that means are available which are designed in such a way that the efficiency of the drive unit switched to recuperation mode can be reduced. [2] Working machine according to claim 1, characterized by , that the means are designed to allow drag and / or shear losses, particularly in an air gap, of the drive unit to be modified, in particular increased, in order to reduce the efficiency of the drive unit. [3] Working machine according to claim 1 or 2, characterized by, that the means are designed to allow the volume flow of coolant through the drive unit to be changed, in particular increased, in order to reduce the efficiency of the drive unit. [4] Working machine according to any one of the preceding claims, characterized by , that the means are designed to make the torque current value of the drive unit, in particular a torque-generating component of the torque current value, changeable, in particular reducible, in order to reduce the efficiency of the drive unit. [5] Working machine according to any one of the preceding claims, characterized by that the means include or are a control device and / or a coolant pump. [6] Method for operating a working machine according to one of the preceding claims, wherein the drive unit is operated in a recuperation mode, characterized by , that the efficiency of the drive unit is reduced. [7] Method according to claim 6, characterized by , that the efficiency of the drive unit is reduced by more than 5%, preferably by more than 30%, and in particular by 100%. [8] Method according to claim 6 or 7, characterized by , that drag and / or shear losses in an air gap of the drive unit are altered, in particular increased, in order to reduce the efficiency of the drive unit. [9] Method according to any one of claims 6 to 8, characterized by , that the volume flow of coolant through the drive unit is altered, in particular increased, in order to reduce the efficiency of the drive unit. [10] Method according to any one of claims 6 to 9, characterized by , that the torque current value of the drive unit, in particular a torque-generating component of the torque current value, is changed, in particular reduced, in order to reduce the efficiency of the drive unit.

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