CN111836933A

CN111836933A - Drive for a working machine

Info

Publication number: CN111836933A
Application number: CN201980018282.9A
Authority: CN
Inventors: J·莱格纳
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2018-03-09
Filing date: 2019-02-06
Publication date: 2020-10-27
Anticipated expiration: 2039-02-06
Also published as: DE102018203624A1; CN111836933B; WO2019170345A1

Abstract

A drive for a wheel loader has a first electric motor (3) for driving a vehicle wheel (5) and a second electric motor (4) for driving a pump (6) of a work apparatus (7). The first electric motor (3) and the second electric motor (4) are actuated as a function of a signal indicating the position of the accelerator pedal, whereby the torque of the first electric motor (3) is directly dependent on the position of the accelerator pedal in the stationary state of the vehicle.

Description

Drive for a working machine

The present invention relates to a drive for a work machine, such as a wheel loader, of the type defined in more detail in the preamble of claim 1.

Drives of this type have an electric motor which drives a vehicle wheel.

US 2015/0197239 a1 and EP 3130708 a1 disclose wheel loaders with electric motors for driving the wheels of a vehicle.

The basic object of the present invention is to further develop a drive for a working machine having an electric motor for driving the wheels of the vehicle.

This object is also achieved by a drive of the generic type with the features of the characterizing portion of the main claim.

According to the invention, the drive has a computing unit which can receive a signal from an accelerator pedal and which actuates a first electric motor for driving a wheel of the vehicle. Furthermore, the computing unit commands a further motor which is suitable for driving the working device, for example by driving a hydraulic pump. This further motor may also be a second electric motor. However, this additional motor may also be a motor of another type of construction. However, for the sake of simplicity, only the term "second electric motor" is used below.

The first electric motor for driving the vehicle wheels and the second electric motor for driving the work device can be controlled separately from each other by means of the computing unit.

It is thereby also possible to operate the work machine, for example a wheel loader, such that the wheel loader has the same type of travel performance as current diesel engine driven wheel loaders. It is thus also possible to use a purely electric work machine without the driver having to be adapted to a diesel engine driven work machine.

The work machine may draw energy from the battery. However, the work machine may also have a fuel cell or other source of electrical energy, for example a connection port towards the power grid by means of a cable. The possibility thus exists of operating the working machine purely electrically.

An accelerator pedal is arranged in the cab of the wheel loader, which accelerator pedal outputs a signal to the calculation unit. There is a possibility that the signal is output at 0% in the case where the accelerator pedal is not operated, and there is a possibility that the signal is output at 100% in the case where the accelerator pedal is fully operated. Furthermore, a brake pedal is arranged in order to brake the vehicle. The brake pedal likewise outputs a signal to the computing unit. In a first pedal stroke of the brake pedal, the brake pedal outputs a signal that the vehicle has not been braked by means of the service brake, but that a so-called inchbertib inching operation (inchbertib) should be activated. In the inching operation, the rotation speed of a motor for driving the working device should be increased and the torque on the wheels of the vehicle should be reduced. Furthermore, the wheel loader has a multifunction lever by means of which the work equipment (e.g. a hoist and a bucket) can be operated, and the travel direction can be determined, and the travel range (e.g. a fast travel range and a slow travel range) can be selected. The vehicle also has a neutral position switch and a parking brake operator.

In order to design an electric working machine to behave like a diesel engine working machine, it should be possible to operate the first electric motor depending on a signal of the position of the accelerator pedal. For this purpose, the accelerator pedal has an analog sensor which detects the position of the accelerator pedal and uses it as an indicator for the rotational speed and the torque of the first electric motor. In this case, an additional memory unit is provided, in which a characteristic map having characteristic curves is stored, in which the torque of the first electric motor and the rotational speed of the first electric motor are stored for a plurality of pedal positions of the accelerator pedal. The characteristic curve is designed such that the torque changes as a function of the pedal position when the first electric motor is stationary. This can be achieved, for example, by: the maximum torque corresponds to maximum actuation of the accelerator pedal and no torque corresponds to no actuation of the accelerator pedal. Now, the torque can be linearly related to the change of the accelerator pedal.

This makes it possible to achieve a driving behavior of the wheel loader, wherein the wheel loader can be brought to the traction limit of its wheels by changing the position of the accelerator pedal in order to fill the bucket.

It is also necessary that the characteristic curve assigned to the accelerator pedal position has a defined maximum rotational speed which can be achieved without torque. Thus, even if the vehicle is moving on a terrain where the vehicle does not require torque, the speed can be maintained by means of the accelerator pedal.

If the vehicle is in freewheeling operation, the defined torque is advantageously preset so as to exhibit a known coasting to stop behavior or braking behavior for the driver. Since in the present combustion engine drives the braking torque is significantly lower than the drive torque, the drive and therefore the first electric machine should always be switched to freewheeling operation only when the maximum rotational speed at which the torque is 0 is exceeded in the case of the corresponding pedal position of the accelerator pedal. The braking torque should then increase with increasing rotational speed with a gradient up to a defined level and remain virtually constant even with further increasing rotational speed. In this case, the maximum braking torque is preferably preset independently of the pedal position of the accelerator pedal. It is also possible to increase the braking torque with a more reduced pedal actuation of the accelerator pedal and to set the braking torque to be smaller in a more intensive pedal actuation of the accelerator pedal.

If the vehicle has a selector switch for a fast driving range and a slow driving range, the maximum rotational speed of the first electric motor is first limited to a very high, i.e. technically significant, maximum rotational speed in the fast driving range. In the case of a selection of a slow driving range, the rotational speed is defined significantly more early, depending on the position of the accelerator pedal. For this purpose, the accelerator pedal position 0% to 100% is divided into a speed range of the first electric motor, wherein the maximum speed in the slow driving range may correspond, for example, to one third of the maximum speed in the fast driving range.

In order to make optimal use of the vehicle in inching operations, the vehicle has a brake pedal in addition to an accelerator pedal. In the inching operation, the power of the first electric motor is reduced and the power of the second electric motor is increased. The brake pedal has an analog sensor that outputs a signal dependent on the position of the brake pedal. This signal is used as an indicator for reducing the rotational speed and torque of the first electric motor for driving operation (fahrbeta). The service brake is not activated in the first part of the actuation of the brake pedal. The sensor signal is therefore used in this part for inching operation to reduce the rotational speed and torque of the first electric motor and to increase the power of the second electric motor.

If the brake pedal is pressed further, the service brake is additionally actuated.

In a further embodiment, a second electric motor which drives the actuation of the work device is actuated as a function of a signal from an accelerator pedal. It is also possible to operate the second electric motor not only as a function of the accelerator pedal signal but also as a function of the rotational speed of the first electric motor. The work device can be, for example, a lifting movement and a shovel movement which can be activated by means of a multifunction stick.

It is also possible to drive a hydraulic pump acting on a pressure cylinder of the working equipment by means of a second electric motor. These hydraulic pumps may be designed as fixed displacement pumps (pumps with a constant displacement volume), but it is also possible to use pumps with adjustable displacement volumes. When using a pump with a constant discharge volume, the rotational speed of the second electric motor determines the delivery volume. The second electric motor is to be controlled such that it has a minimum rotational speed without the need for actuating the accelerator pedal, as a result of which a minimum volume flow can be delivered in order to be able to carry out a steering movement even in the stationary state of the vehicle. Here, a pump connected to the second electric motor delivers pressure medium to a steering valve, which applies pressure medium to an actuator for steering.

If the accelerator pedal is actuated, a rotational speed index for the first electric motor is output by means of a characteristic curve stored in a memory unit. The higher the accelerator pedal is actuated, the higher the rotational speed of the first electric motor should be. The rotational speed of the second electric motor is defined depending on the rotational speed of the first electric motor. When the rotational speed of the first electric motor is small, the rotational speed of the second electric motor must be able to reach the maximum rotational speed. When the rotational speed of the first electric motor is high, the rotational speed of the second electric motor can be reduced, because the vehicle has a high speed and therefore the work equipment (e.g. the hoist or shovel hydraulics) does not have to be moved rapidly. However, it is necessary to keep obtaining a minimum rotational speed for steering the vehicle, so the rotational speed of the second electric motor is not allowed to fall below the minimum rotational speed. The efficiency is improved by limiting the rotational speed of the second electric motor.

Preferably, a pump driven by the second electric motor with a constant delivery volume is used for a less powerful work machine. More powerful work machines use adjustable pumps, which are preferably used in combination with a noise sensing system. In a noise sensing system, the pump is regulated with a plurality of consumers using the respective highest load pressure and the pump pressure of the pressure device (druckcage). The pump always delivers only the total amount required by the consumers being operated. The pump pressure always corresponds to the consumer with the highest load. The pump delivers only the leaked oil flow if the consumer is not operated.

In a further embodiment, the pump, which is adjustable with respect to its displacement volume, has a sensor, by means of which the current delivery volume of the pump can be detected. This signal is used as a rotational speed indicator for the second electric motor. The sensor signals are calibrated and interpreted here. The signal may take a value between 0% and 100%. The rotational speed of the second electric motor can now be adapted to the respective requirements depending on the signal of the sensor. If no work function is actuated (for example, the pressure cylinder of the lifting device is not actuated), the sensor signal of the adjustable pump is almost 0. In this state, the rotation speed index for the second electric motor is controlled to the lower limit value. If the consumer is now operated (e.g. the lifting gear is operated), the noise-sensing system of the working pump reports the delivery demand and the working pump increases its delivery and the sensor signal increases. The term "working pump" here denotes an adjustable pump which is connected to the second electric motor. If the available delivery volume of the working pump increases above a necessary level, this can be detected by a reduced sensor signal of the working pump. It is not meaningful to increase the rotational speed further. The second electric motor is controlled such that this second electric motor no longer increases its rotational speed. If the threshold value is undershot, the rotational speed indicator for the second electric motor is reduced by the control algorithm to a lower limit value. The lower limit value is defined, for example, by the minimum volume flow for steering. In order to stabilize the rotational speed index for the second electric motor, there is a lag between the increasing sensor signal and the decreasing sensor signal.

Additionally, the change of the sensor signal over time can be used as a rotational speed indicator for the second electric motor. A strongly increasing or decreasing signal can influence the dynamics of the rotational speed index.

In another embodiment, the sensor is located on the work apparatus, for example on the lifting device and the bucket. It is also possible to detect manipulation of the lift or bucket by one or more sensors in the multifunction lever that can manipulate the lift. Depending on the actuation of the lifting device, the rotational speed of the second electric motor is adapted to the requirements.

Here, the dependency of the rotational speed index of the second electric motor on the accelerator pedal position and on the rotational speed of the first electric motor may remain. This dependency is superimposed with sensor information that detects the handling of the lifting device and the bucket and thus of the work apparatus.

Sensors in the utility pole or in the lift and bucket generate proportional signals based on the operation of the lift and bucket. These sensor signals are calibrated and interpreted. These two signals may take values between-100% and + 100%. For the lifting movement, the sensor signal for maximum lowering is calibrated to-100% and the sensor signal for maximum lifting is calibrated to + 100%. For shovel motion, -100% of the sensor signal means the maximum roll out of the bucket, and + 100% means the maximum roll in of the bucket. If the utility bar is not manipulated, i.e. no movement is required for the lift and bucket, the sensor provides a 0% signal accordingly. The maximum magnitudes of the two sensor signals are used for the rotational speed indicator of the second electric motor. If the signal of the sensor is 0%, no manipulation of the work function is provided, whereby the rotation speed index for the second electric motor is controlled to the lower limit value. If the sensor now detects that the lifting device should be moved, the rotational speed of the second electric motor is increased as a function of the signal of the sensor.

For controlling the first electric motor and the second electric motor, the first electric motor and the second electric motor each have power electronics which are arranged in the immediate vicinity of the first electric motor and the second electric motor. The power electronics of the first electric motor and the power electronics of the second electric motor are connected to a vehicle computer (also referred to as a computer unit) via a CAN bus system. There is the possibility of additionally connecting a display by means of CAN. The vehicle computer receives signals from a brake pedal, an accelerator pedal, a switch for the parking brake and a switch for the direction of travel, a switch for the speed of travel between a fast speed of travel and a slow speed of travel, and a switch for the neutral position. In the case of an adjustable working pump connected to the second electric motor, the vehicle computer may also contain a signal of the sensor about the position of the displacement volume of the working pump.

The energy supply is realized by a battery. However, it is also possible to form the energy supply by means of a combustion engine driving an electric generator and to supply the vehicle with energy by means of a connection port towards the static electricity network. Combinations of these energy supplies are also possible.

The calculation unit outputs the ideal values for the rotational speed and the maximum torque to the power electronics of the first electric motor and to the power electronics of the second electric motor according to an operating strategy. The power electronics itself regulates the two electric motors according to the specifications. The actual values of the rotational speed and the torque as well as the operating states of the two electric motors are fed back to the calculation unit. Standard power electronics can thus be used, which have only as much computing power as can operate the electric motor. The computing unit does not require an additional output, but only an input and communication by means of CAN. This is very cost effective.

Other features are derived from the description of the figures.

In the drawings:

figure 1 shows a wheel loader as such,

figure 2 shows a schematic view of a drive of a wheel loader,

figure 3 shows a characteristic diagram of the actuation of the first electric motor for a fast driving range,

figure 4 shows a characteristic diagram of the actuation of the first electric motor for a slow driving range,

figure 5 shows a characteristic curve in the case of actuation of the brake pedal,

figure 6 shows a characteristic curve of the speed of rotation of the steering second electric motor,

figure 7 shows a characteristic curve for operating the second electric motor,

FIG. 8 shows a characteristic curve for operating the second electric motor, and

fig. 9 shows a characteristic curve for the actuation of the second electric motor as a function of the signals of the accelerator pedal and the multifunction lever.

FIG. 1:

the wheel loader 1 has a battery 2 which supplies power to a first electric motor 3 and a second electric motor 4. The first electric motor 3 drives the vehicle wheels 5. It is also possible to use not the first electric motor 3 but a plurality of electric motors. The second electric motor 4 drives a pump 6, which is also referred to as a working pump and which supplies the pressure cylinder of the lifting device 7 and the steering of the wheel loader 1 with pressure medium. In vehicles with low power, the pump 6 can be embodied as a pump with a constant displacement volume, wherein a plurality of fixed displacement pumps can also be used. In vehicles with greater power, it is also possible to design the pump 6 as one or more pumps with adjustable delivery volume. These pumps with adjustable delivery volume are usually implemented as noise-sensing pumps.

FIG. 2:

the energy of the battery 2 is supplied to the first electric motor 3 by means of power electronics 8. The energy of the battery 2 is supplied to the second electric motor 4 by means of power electronics 9. The second electric motor 4 drives a pump 6 which is embodied such that its displacement volume is adjustable. The first motor 3 drives vehicle wheels (not shown). An actuator 11 of a working device or a steering apparatus is operated by a valve 10. To detect the current displacement volume of the pump 6, a sensor 12 is connected to the pump 6. Via the lines 13 (for example by means of CAN), the battery 2, the power electronics 8, the power electronics 9, the sensors 12 and the display 14 on which the driving direction, the speed, the driving range and other vehicle states are displayed are connected to a computer unit 15, which is also referred to as a vehicle computer. The computing unit 15 receives signals from a sensor of a brake pedal 16, a sensor of an accelerator pedal 17, a switch for a parking brake 18 and a plurality of switches and/or sensors in a multifunction lever 19, by means of which a speed range, a neutral function and other functions, such as the actuation of an actuator 11 of a work apparatus (e.g. a bucket or a lifting device), can be controlled. It is also possible to form the function of the multifunction lever 19 in one lever. However, it is also possible to form the individual sensors and switches in a plurality of switches and rods.

If, for example, the accelerator pedal 17 is actuated, the computing unit 15 generates a signal for the first electric motor 3. The calculation unit 15 also includes a storage unit in which characteristic curves are stored, and these characteristic curves are described with reference to other drawings. By means of the signal obtained by the calculation unit 15 and the stored characteristic curve, the calculation unit 15 calculates a pilot signal, which the calculation unit 15 outputs via the line 13. The

power electronics

8 and 9 can thus be designed such that they only have to be able to control the first electric motor 3 and the second electric motor 4.

When using the pump 6 as a load sensing pump, the adjustment of the displacement volume of the pump 6 can be determined by means of a sensor.

In a load sensing system, the pump is regulated with a plurality of consumers using the respective highest load pressure and the pump pressure of the pressure retention valve. The pump always delivers only the total amount required by the consumers being operated. The pump pressure always corresponds to the consumer with the highest load. The pump 6 only delivers the leakage oil flow if the consumer is not operated.

The current delivery volume of the pump can be detected by means of a sensor for the adjustment of the pump 6. This signal is now used as an indicator of the rotational speed of the second electric motor 3. The sensor signals are calibrated and interpreted. The signal may take values between 0% and 100%. By using this sensor for the regulation of the pump 6, the rotational speed of the second electric motor 4 and thus of the pump 6 can be adapted to the requirements and thus designed more efficiently.

If no actuation of the work device 11 is performed, the signal of the sensor for the adjustment of the pump 6 is almost 0%. In this state, the rotation speed index for the second electric motor 4 is controlled to the lower limit value. If the consumer, and thus the working equipment 11, is now operated, the load sensing system of the pump 6 reports the delivery demand and the pump 6 will increase its delivery and the sensor signal will increase. For the rotation speed index of the second electric motor 4, a threshold value of the sensor signal is defined, for example 95%, at which the pump 6 is almost completely adjusted to the limit (ausschwenken). If this threshold value is exceeded, this is interpreted as an insufficient delivery quantity and thus the speed index for the working drive is increased up to a maximum value.

If the available delivery quantity increases above a necessary level, this can be detected by a falling sensor signal of the working pump. It is not meaningful to increase the rotational speed further. If the threshold value is undershot, the rotational speed indicator for the second electric motor 4 is reduced by the control algorithm to a lower limit value.

Additionally, hysteresis is used to stabilize the speed indicator near this threshold.

The change of the sensor signal over time may also be used as an indicator of the rotational speed of the second electric motor 4. A strongly increasing or decreasing signal can influence the dynamics of the rotational speed index.

FIG. 3:

characteristic curves are stored in the computing unit 15 of fig. 2, which characteristic curves represent a fast driving range and a slow driving range. The graph shown in fig. 3 represents the fast driving range. In order for the driver of the wheel loader to be able to control the torque on the wheels of the vehicle in the stationary state of the vehicle when driving into the stack until the vehicle is in the stationary state, it is necessary to define the torque of the first electric motor depending on the position of the accelerator pedal. In this way, a defined torque can be generated at the vehicle wheels for any position of the accelerator pedal in the stationary state of the vehicle, so that the driver can control the vehicle via the accelerator pedal until the traction limit is reached. For this purpose, the position of the accelerator pedal is determined by means of a sensor, wherein the signal output by the sensor corresponds to an accelerator pedal signal 20 of 0% in the case of no actuation of the accelerator pedal, and corresponds to an accelerator pedal signal 20 of 100% in the case of full actuation of the accelerator pedal. The characteristic curve of fig. 3 is plotted in a cartesian coordinate system, wherein the coordinate represents the torque 21 of the first electric motor and the abscissa represents the rotational speed 22 of the first electric motor. The intersection points 25 associated with the defined pedal position of the accelerator pedal are produced by the intersection points of the individual characteristic curves, which are distributed, for example, in a uniform manner, being formed from the torque 0 23 to the maximum torque 24 of the accelerator pedal signal 20 equal to 100%, even at a rotational speed of 0. These intersections can be generated, for example, by means of a certain number of characteristic curves (e.g. 0%, 25%, 50%, 75% and 100%). The linear distribution is only exemplary and there is also the possibility of generating a non-linear distribution. Intermediate values between the characteristic curves are then inserted. Thus, torque can be generated on the vehicle wheels for any accelerator pedal position in a stationary state of the vehicle. The same applies in respect of the rotational speed 22 of the first electric motor, whereby the intersection with the abscissa at a torque of 0 likewise results. In order for the vehicle not to exceed the maximum permitted speed, the rotational speed 22 of the first electric motor is limited to a maximum rotational speed 26. The speed of the vehicle with very little or no torque can thereby be adjusted by means of the accelerator pedal. A graph is then created by first plotting the maximum possible power as a function of accelerator pedal position. The maximum power is shown by line 27. The intersection of the ordinate and the intersection of the abscissa are connected by other lines.

The illustrated graph shows only one possible quadrant of operation of the first electric motor. In this quadrant the traction range and forward direction of rotation are shown. A similar or mirrored characteristic course can also be used for the backward, opposite direction of rotation. In the freewheeling operation, the defined torque is advantageously preset so as to exhibit a familiar coast-to-stop behavior or braking behavior. In current combustion engine drives, the braking torque is significantly smaller than the drive torque. The drive is only put into freewheeling operation when the intersection of the rotational speeds of the respective pedal positions at which the torque is 0 is exceeded. The generated braking torque should then increase with increasing rotational speed with a gradient up to a defined level and remain virtually constant even with further increasing rotational speed. The maximum braking torque can be preset constantly and independently of the pedal position or higher with a slight pedal actuation and lower with a strong pedal actuation.

It is also possible to design the vehicle with only one driving range, wherein then a diagram for a fast driving range is used. In the case of the use of an additionally slow driving range, an additional diagram according to fig. 4 is formed.

FIG. 4:

the slow driving range shown in fig. 4 is necessary for fine-resolution positioning operations of the accelerator pedal, such as work with a fork. The term "fine accelerator pedal resolution" means that the final speed in the driving range in which the accelerator pedal is actuated to a third of the slower speed is not reached as in the fast driving range, but only when the accelerator pedal is fully actuated. Here, the intersection 25 of the respective maximum torques at the rotation speed of 0 is the same as the intersection 25 of the fast travel range of fig. 3. However, the maximum rotational speed 26 is significantly reduced relative to the maximum rotational speed 26 of fig. 3. However, the maximum rotational speed 26 of fig. 4 is also reached only in the case of 100% accelerator pedal signal 20. The intersection point of the respective maximum rotational speeds of the first traction motor at a torque of 0 is thereby scaled to a lower rotational speed.

FIG. 5:

in order to be able to also exhibit the inching function, the signal of the brake pedal is processed in addition to the signal of the accelerator pedal. The vehicle can thereby be operated in a jogging operation, i.e. the power and thus the torque and the rotational speed of the first electric motor is reduced, while the power and thus the rotational speed and the torque for the second electric motor and thus the pump 6 for the work apparatus of fig. 2 (and thus for the steering and/or lifting and rotation of the bucket) are increased. For this purpose, the brake pedal position is detected by a sensor, preferably an analog sensor, and is used as an indicator for reducing the rotational speed and the torque, and therefore the power, of the first electric motor for the travel drive.

For this purpose, the current value of the signal 20 of the accelerator pedal between 0% and 100% is shown on the ordinate of fig. 5, and the signal of the brake pedal 28 from 0% to 100% is shown on the abscissa. If the brake pedal is not actuated, the signal from the accelerator pedal is not reduced. In the case of full depression of the accelerator pedal (thus 100%) and no actuation of the brake pedal, the signal of the accelerator pedal 20 therefore remains the same. The more the brake pedal is actuated, the more the signal of the accelerator pedal is reduced. In the first part 29 of the braking operation, the service brake is not activated, but the power for the first electric motor is reduced, however, by reducing the signal of the accelerator pedal by means of the characteristic curve 30 and thus actuating the first electric motor with a smaller setpoint signal. Therefore, the rotation speed index for the first electric motor becomes smaller and smaller while keeping the accelerator pedal constantly pressed and the brake pedal gradually pressed. Characteristic curve 30 is designed here such that, in the case of a full depression of the accelerator pedal, the signal of the accelerator pedal is already greatly reduced when the brake pedal is pressed only slightly. When the accelerator pedal is actuated only slightly, the brake pedal must be pressed far enough to achieve a signal for lowering the accelerator pedal. From the predefined actuation travel of the accelerator pedal, the service brake is additionally activated. The characteristic curve 30 intersects the abscissa at a point 31, which represents an unactuated accelerator pedal, wherein this point 31 either corresponds to an actuation travel for actuating the service brake or is selected to follow this actuation travel of the brake pedal by a short distance in order to ensure a corresponding overlap. The characteristic curve 30 correspondingly reduces the accelerator pedal signal as a function of the actuation of the brake pedal, which results in a change in the actuation of the first electric motor with respect to its rotational speed and its torque.

FIG. 6:

however, in order to operate not only the first electric motor in a manner that varies depending on the manipulation of the brake pedal, but also the second electric motor needs to be operated. For this purpose, the vehicle has a multifunction lever in the cab, by means of which the work device, for example, a lifting movement and a shovel movement, can be controlled. The characteristic curve illustrated in fig. 6 is used for a second electric motor with one or more pumps of constant displacement volume. In this embodiment, the delivery volume is determined solely by the rotational speed of the second electric motor. In case a plurality of pumps is used, there may be for example a pump for articulated steering of the wheel loader and a second pump for the work equipment. The direct actuation of the second electric motor allows the delivery rate to be adapted to the desired operating situation by controlling the rotational speed of the second electric motor. In conventional wheel loaders with a combustion engine, the pump is directly connected to the combustion engine, whereby a free actuation of the pump is not possible.

The control of the rotational speed of the second electric motor is to be effected as a function of the accelerator pedal signal and as a function of the rotational speed of the first electric motor. The rotational speed of the second electric motor is therefore shown on the ordinate in fig. 6, and the actuation of the accelerator pedal or the accelerator pedal signal is shown on the abscissa. At point 32, the accelerator pedal is not actuated, and the vehicle is stationary. However, since the steering movement must be carried out in this stationary state, the second electric motor is operated at the minimum rotational speed (as can be seen, for example, in the point 32). As the accelerator pedal signal increases, the speed index for the second electric motor is increased by the characteristic curve 33 to the maximum speed 34. In order to define the maximum rotational speed 34 of the second electric motor, a second dependency on the rotational speed of the first electric motor is used. If the first electric motor is at a lower rotational speed, i.e. therefore if the vehicle is moving at a lower speed, the rotational speed of the first electric motor must be able to reach the maximum rotational speed. The rotational speed of the second electric motor may also be reduced when the rotational speed of the first electric motor is high and thus the running speed of the vehicle is high. This is because at higher travel speeds it is not necessary to move the hydraulic system for the bucket and the lifting device rapidly. It is important, however, to keep achieving a minimum rotational speed for steering. The efficiency of the system is increased by reducing the rotational speed of the second electric motor in dependence on the rotational speed of the first electric motor and thus in dependence on the driving speed. In fig. 7 it is shown that the rotational speed of the second electric motor is reduced in dependence on the rotational speed of the first electric motor.

FIG. 7:

the rotational speed of the second electric motor is plotted on the ordinate and the rotational speed of the first electric motor is shown on the abscissa. The vehicle is still at a lower driving speed up to point 35, and the maximum possible rotational speed of the second electric motor, which is illustrated by characteristic curve 36, is not reduced. The line 37 shows the maximum rotational speed of the first electric motor or the maximum driving speed in the slow driving range, and the line 38 shows the maximum possible rotational speed of the first electric motor or the maximum driving speed of the vehicle in the fast driving range. The rotational speed of the second electric motor is reduced up to point 39 in order to ensure a delivery quantity sufficient for steering.

FIG. 8:

in the case of the use of additional sensors, either directly on the lifting device or the bucket, or on a multifunction lever (by means of which the lifting device and the bucket can be actuated), the rotational speed of the second electric motor can be adapted further as required. Here, the dependency of the rotational speed index for the second electric motor on the accelerator pedal position and on the rotational speed of the first electric motor remains. Additionally, however, the information from the sensors is used to operate the lift and bucket. These sensors provide a signal in dependence on the manipulation, which signal may be a proportional signal, for example. These sensor signals are calibrated and interpreted. These two signals can assume values of-100% to + 100%, wherein for example the sensor signal for maximum lowering can be calibrated to-100% and the sensor signal for maximum raising of the lifting movement can be calibrated to 100% for the lifting movement. For shovel motion, -100% of the sensor signal means the maximum roll out of the bucket, and + 100% of the sensor signal means the maximum roll in of the bucket. If the utility lever is not manipulated and thus no work equipment or lifting device and shovel motion is required, the sensor provides a 0% signal accordingly. The maximum magnitudes of the two sensor signals are used as a rotational speed indicator for the second electric motor. Fig. 8 shows the dependence of the rotation speed index of the second electric motor on the rotation speed of the first electric motor and the signal of the sensor of the working device. Here, the rotational speed of the second electric motor is plotted on the ordinate, and the rotational speed of the first electric motor is plotted on the abscissa. Line 40 shows an increase in the rotational speed of the second electric motor while the rotational speed of the first electric motor is decreasing. The line 37 is the maximum attainable rotational speed of the first electric motor in the slow driving range, and the line 38 is the maximum attainable rotational speed of the first electric motor in the fast driving range. The characteristic curve 36 with

points

35 and 39 corresponds to the characteristic curve 36 of fig. 7. This rotational speed is now reduced to line 40 in dependence on the sensor signal of the lifting device. This is illustrated by arrow 41.

FIG. 9:

as illustrated in fig. 7, it is shown in fig. 9 that the rotation speed of the second electric motor is reduced depending on the sensor of the working device. The diagram corresponds to the diagram according to fig. 6 and shows the signal of the sensor, which is dependent on the work device, to reduce the rotational speed of the second electric motor by arrow 42. It is only possible to reduce the rotational speed of the second electric motor up to line 43.

Reference numerals

1 wheel loader

2 batteries

3 first electric motor

4 second electric motor

5 vehicle wheel

6 Pump

7 lifting device

8 power electronic device

9 power electronic device

10 valve

11 actuator

12 sensor

13 line

14 display

15 calculation unit

16 brake pedal

17 accelerator pedal

18 parking brake

19 multifunctional rod

20 accelerator pedal signal

21 torque

22 revolution rate

230 torque

24 maximum torque

25 point of intersection

26 maximum rotational speed

27 line

28 brake pedal signal

29 first part

30 characteristic curve

31 point

32 points

33 characteristic curve

34 maximum speed of rotation

35 point

36 characteristic curve

37 characteristic curve

38 line

39 point

40 line

Arrow 41

42 arrow head

43 line

Claims

1. A drive for a working machine, wherein the drive has a computing unit, by means of which a first electric motor (3) for driving vehicle wheels (5) and a second electric motor (4) for driving a working device (11) can be actuated, wherein the computing unit processes a signal corresponding to the position of an accelerator pedal (17), and the first electric motor (3) and the second electric motor (4) are actuatable independently of each other, and the first electric motor (3) is actuatable by a signal dependent on the position of the accelerator pedal (11).

2. The drive according to claim 1, characterized in that characteristic curves for a fast driving range from a standstill of the work machine up to a maximum speed of the work machine are stored in a memory unit, wherein each characteristic curve represents a position of the accelerator pedal (11), and wherein a rotational speed of the first electric motor (3) can be derived from each characteristic curve as a function of a torque of the first electric motor (3).

3. The drive according to claim 2, characterized in that each characteristic curve is designed such that in the stationary state of the first electric motor (3) it is assigned a torque, wherein in the stationary state of the first electric motor (3) the stored characteristic curve outputs the maximum achievable torque with full actuation of the accelerator pedal (11), and in the stationary state of the first electric motor (3) the stored characteristic curve outputs a smaller torque with slight actuation of the accelerator pedal (11), wherein in the event of reduced actuation of the accelerator pedal the output torque is also correspondingly reduced.

4. The drive according to claim 2, characterized in that each characteristic curve is designed such that, in the state in which the first electric motor (3) is not outputting torque, it outputs the rotational speed of the first electric motor (3), wherein the stored characteristic curve outputs the maximum attainable rotational speed in the case of a full actuation of the accelerator pedal (11) and the stored characteristic curve outputs a lower rotational speed in the case of a slight actuation of the accelerator pedal.

5. The drive according to claim 1, characterized in that characteristic curves for a slow driving range from a standstill of the work machine up to a speed which is less than the maximum speed of the work machine are stored in a memory unit, wherein each characteristic curve represents the position of the accelerator pedal (11), and wherein the rotational speed of the first electric motor (3) can be derived from each characteristic curve as a function of the torque of the first electric motor.

6. The drive according to claim 5, characterized in that each characteristic curve is designed such that in the stationary state of the first electric motor (3) it is assigned a torque, wherein in the stationary state of the first electric motor (3) the stored characteristic curve outputs the maximum achievable torque with full actuation of the accelerator pedal (11), and in the stationary state of the first electric motor (3) the stored characteristic curve outputs a smaller torque with slight actuation of the accelerator pedal (11), wherein in the event of a reduced actuation of the accelerator pedal (11) the output torque is also correspondingly reduced.

7. The drive according to claim 5, characterized in that each characteristic curve is designed such that, in the state in which the first electric motor (3) is not outputting torque, it outputs a rotational speed of the first electric motor, wherein the stored characteristic curve outputs a rotational speed which is less than the maximum attainable rotational speed in the fast driving range in the case of a full actuation of the accelerator pedal (11) and outputs an even lower rotational speed in the case of a slight actuation of the accelerator pedal.

8. The drive according to claim 1, characterized in that the computing unit processes a signal of the position of the brake pedal (16), wherein the signal of the position of the accelerator pedal (11) is changed as a function of the signal of the position of the brake pedal (16) in such a way that, in the case of actuation of the brake pedal (16), the position of the accelerator pedal (11) to which the signal of the accelerator pedal (11) corresponds is smaller than in the case of non-actuation of the brake pedal (16).

9. Drive according to claim 1, characterized in that the rotational speed of the second electric motor (4) is controllable depending on the rotational speed of the first electric motor (3).

10. The drive according to claim 1, characterized in that the rotational speed of the second electric motor (4) is controllable depending on the position of the accelerator pedal (11).

11. The drive according to claim 10, characterized in that the rotational speed of the second electric motor (4) is greater than 0 without actuation of an accelerator pedal (11).

12. Drive according to claim 10, characterized in that the rotational speed of the second electric motor (4) is steered to not reach the maximum rotational speed of the second electric motor (4) when the rotational speed of the first electric motor (3) is between more than 0 and the maximum attainable rotational speed of the first electric motor (3).

13. Drive according to claim 10, characterized in that the rotational speed of the second electric motor (4) is commanded to reach its maximum rotational speed when the rotational speed of the first electric motor (3) is between 0 and a rotational speed which is lower than the maximum attainable rotational speed of the first electric motor (3).

14. A wheel loader having a first electric motor (3) and a second electric motor (4) according to claim 1 and a power train.