Patent Application
20250198121
The present invention relates to a method for operating a drive train of a working machine according to the preamble of claim 1, to an electrified drive train for a working machine according to the preamble of claim 11 and to a corresponding working machine.
In addition to conventionally driven working machines, electrically driven working machines such as wheel loaders, skid steer loaders, telescopic handlers, dumpers or excavators are also known in the prior art. Such machines are either purely electrically powered, i.e., they have only an electric battery or a fuel cell for generating electricity from hydrogen as energy storage. Or they are diesel-electric powered, which means that the required energy is provided by a diesel-powered generator and possibly by an electrical buffer storage unit, such as a suitably dimensioned capacitor or a comparatively small battery. In all cases, the mechanical power required for the travel drive and the working drive is provided by one or more drive motors. It is also known to use the drive motors of electric drives to recuperate electrical power during braking in generator mode. In addition, a mechanical friction brake is always provided so that sufficient braking power can be provided at all times for safety reasons.
In this context, EP 0962 597 A2 describes a battery-powered working machine which has two drive motors for the travel drive and a further drive motor for the working drive.
WO 2008/128674 A1 discloses a working machine with a hybrid drive train comprising an internal combustion engine and an electric machine. An electrical energy store is provided for supplying energy to the electric machine and can be charged recuperatively by operating the drive motor in generator mode during a braking process of the working machine.
DE 10 2020 203 594 A1 discloses a method for operating an electric drive train for a working machine. Here, an automated braking intervention takes place if an impermissible acceleration occurs during recuperation operation, for example if the working machine is actually to be braked recuperatively, but the braking effect is too low due to the downhill slope force. The entire disclosure of DE 10 2020 203 594 A1 is incorporated by reference into the present patent application.
SAHR brakes are also known in the prior art. SAHR stands for Spring Applied Hydraulic Released and refers to intrinsically safe brakes that close without pressure and can be used both as an auxiliary brake and as a parking brake. The braking effect is achieved by the spring force acting on friction elements which are connected to the ground via the torque train of a machine. This functionality can also be achieved with brakes that can be released by means of gas pressure. In the following, the term SAHR brake is used for both hydraulically and pneumatically releasable brakes.
However, the known drive trains for working machines, in particular the known electric drive trains for working machines, are disadvantageous in that they are often no longer able to provide a sufficiently large braking torque or recuperation torque when descending a slope at a comparatively high speed in order to prevent further impermissible acceleration of the working machine due to the downhill slope force into a speed range that is impermissibly high for the working machine.
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 working machine according to claim 1. Advantageous embodiments and developments of the invention are shown in the dependent claims.
The invention relates to a method for operating a drive train of a working machine, wherein the drive train has a drive motor, a service brake and an assisting brake, wherein there is a drive coupling of the drive motor of the drive train to at least one wheel of the working machine, so that, when descending a slope, a braking torque of the drive motor counteracts a downhill slope force acting on the working machine, wherein an automated actuation of the assisting brake is undertaken if the working machine is subject to an impermissible acceleration, and wherein the assisting brake is actuated in accordance with a required braking torque.
According to the invention, a method is thus provided which relates to the operation of a drive train of a working machine. The drive train comprises a drive motor which provides a drive power for driving the working machine. The drive motor can be assigned exclusively to a traction drive or can also be assigned to a working drive of the working machine. The drive train also comprises a service brake and an assisting brake, wherein the assisting brake can, for example, fulfill a parking brake function. Both the service brake and the assisting brake are preferably mechanical friction brakes.
The drive motor of the drive train is drive-coupled to at least one wheel of the working machine, for example via a transmission and a releasable clutch, in particular via a multi-plate clutch. The result of the drive coupling between the drive motor and the at least one wheel is that an acceleration torque generated by the drive motor leads to an increase in speed of the at least one wheel. The increase in speed of the at least one wheel corresponds to the increase in speed of the drive motor, taking into account a transmission ratio between the drive motor and the at least one wheel. Similarly, a braking torque generated by the drive motor leads to a reduction in the speed of the at least one wheel. Conversely, an acceleration torque of the at least one wheel, which can result, for example, from a downhill travel of the working machine, also leads to an increase in the speed of the drive motor. A braking torque generated by at least one wheel, which can result, for example, from the working machine ascending a slope, leads to a corresponding reduction in the speed of the drive motor.
The assisting brake is actuated automatically if the working machine is subject to unacceptable acceleration, for example due to downhill travel. The assisting brake is actuated in accordance with a required braking torque, wherein the required braking torque is advantageously the braking torque that is required to reduce the speed of the working machine to such an extent that no further impermissible acceleration occurs solely due to the braking torque of the drive motor.
The drive motor generates a braking torque if it is not actively operated and provides a torque, but is driven passively via wheel rotation of the working machine. With an internal combustion engine, the braking torque corresponds to the so-called drag torque; with an electric motor, the braking torque corresponds to the so-called recuperation torque.
For the purposes of the invention, an impermissible acceleration is understood to mean, on the one hand, an acceleration not initiated by a driver of the working machine, such as may occur, for example, due to downhill travel or a downhill slope acting on the working machine. On the other hand, an impermissible acceleration is also understood to be an acceleration of the working machine into a speed range that is deliberately initiated by the driver but misused, in which components of the drive train may be damaged or even destroyed due to the high speed. Driving at impermissibly high speeds can also lead to safety-relevant or safety-critical driving conditions.
The impermissible acceleration can be detected, for example, like any other acceleration of the working machine, by monitoring and time differentiation of a detected wheel speed, engine speed or other speed in a transmission of the working machine. It is also conceivable that the acceleration can be detected via a satellite navigation system, for example. In particular, however, it can also be concluded from the mere occurrence of acceleration during the recuperation mode of an electric drive motor or during the towing mode of the internal combustion engine that the acceleration is impermissible, as the recuperation mode or towing mode of the drive motor is generally used to decelerate the working machine, because the recuperation mode or towing mode provides a braking torque due to the principle. A simultaneous acceleration is therefore in contrast to a deceleration initiated by the driver of the working machine or at least the desire to maintain the current speed, which is to be achieved by the recuperation mode or towing mode.
The method according to the invention is characterized in that the assisting brake is also actuated in accordance with a thermal load on the assisting brake and in that the assisting brake is designed as a spring-applied and hydraulically or pneumatically releasable brake.
This means that not only the required braking torque is taken into account when actuating the assisting brake, but also the thermal load on the assisting brake. This makes it advantageous to use a spring-applied and hydraulically or pneumatically releasable brake as the assisting brake, which cannot usually be used as a service brake due to its design.
The assisting brake is therefore a so-called SAHR brake, for example a disc brake designed as a SAHR brake.
In order to prevent the braking effect from occurring abruptly and to achieve a gradation of the braking effect, e.g., for comfort reasons, a modulation of the applied opening pressure, i.e., the counterforce to the spring elements, is advantageously provided.
Electronically controlled proportional valves in the supply line of the SAHR spring accumulator are a preferred option for modulation. The pressure can be adjusted almost continuously by activating the valve. For safety reasons, the corresponding valves are preferably open when de-energized.
The balance of braking deceleration, energy input (heating of the assistance brake), frequency and time interval of actuation can, for example, be determined analytically or by calculation or in driving tests and serves as the basis for the actuation of the assistance brake.
It is preferable for the impermissible acceleration to be detected by simultaneously monitoring and correlating a setting of a device for specifying the speed of the drive motor and a travel speed of the working machine. The device for setting the speed can be any open-loop or closed-loop control device for setting the speed of the drive motor, e.g., an accelerator pedal, a lever or even a rotary actuator. This means that impermissible acceleration can be detected simply by comparing information that is available in the working machine without additional sensors. If, for example, the travel speed of the working machine increases, which can be detected in particular by means of a change in wheel speed, a change in engine speed or a change in transmission speed, but at the same time a setting of the device for specifying the speed of the drive motor remains unchanged, i.e., according to the wishes of the driver of the working machine there is obviously no acceleration, an impermissible acceleration is detected. Similarly, an impermissible acceleration can also be detected if the setting of the device for specifying the speed of the drive motor is even reduced and the speed of the working machine nevertheless increases.
It is preferable for a slope to be detected. Means for detecting a slope can be provided for this purpose. The means for detecting a slope can, for example, be designed as a satellite navigation system. The satellite navigation system may be GPS, Galileo or Glonass, for example. The satellite navigation system also comprises a digital memory in which digital map data is stored. This digital map data advantageously comprises topographical data, i.e., elevation data and elevation changes. Thus, a slope can also be recognized by means of the satellite navigation system, namely by determining a current position of the working machine and reading out the topographical map data at the determined position of the working machine.
Alternatively, it is preferred that the means for detecting a slope are designed as fill level sensors of fluid containers of the working machine. Suitable fluid containers of the working machine can be, for example, a fuel tank, a cooling water tank, a windshield wiper water tank or an expansion tank for hydraulic fluid of a working drive of the working machine. Depending on their specific arrangement in the fluid containers of the working machine, the fill level sensors can thus detect an inclination of the working machine, and the detected inclination of the working machine can in turn be used to detect that the working machine is on a slope. For example, it is possible for a fill level sensor in the cooling water tank, which detects the cooling water level, to detect a supposed increase in the cooling water level if the working machine is inclined in the front direction, which corresponds to a downhill slope of the working machine. Conversely, this fill level sensor would detect a sudden supposed decrease in the cooling water level when the working machine ascends a slope.
According to a preferred embodiment of the invention, it is provided that the drive motor is designed as an electric motor and provides the braking torque generated by the drive motor in a recuperation mode. In recuperation mode, the drive motor, which is designed as an electric motor, provides a braking torque and recuperates electrical energy at the same time. This enables energy-efficient operation of the drive train.
Since the braking torque that can be provided in recuperation mode is largely determined by the speed of the electric motor, wherein the braking torque is comparatively high at low speeds and becomes comparatively low towards higher speeds, the actuation of the assisting brake must reduce the travel speed of the working machine depending on the value of the impermissible acceleration to such an extent that the drive motor is in a speed range in which it can provide sufficient braking torque due to recuperation. This can also lead to a reduction in the travel speed of the working machine below the travel speed that the working machine had before the impermissible acceleration occurred. Advantageously, the assisting brake is only applied until the travel speed of the working machine or the speed of the drive motor has been sufficiently reduced.
According to a further preferred embodiment of the invention, it is provided that an amount of heat supplied to the assisting brake in a braking operation is continuously determined and an accumulating counter is increased during actuation, wherein the accumulating counter is reduced again over time if no actuation takes place. The accumulating counter is therefore a measure of the amount of heat that is fed into the assisting brake due to braking operation. It increases as long as the assisting brake is actuated and decreases again over time if the assisting brake is not applied. This makes it comparatively easy to determine a measure of the temperature and thus the further braking capability of the assisting brake using only the counter and, in particular, without measuring the temperature.
By specifying corresponding parameters, the counter takes into account, for example, a mass of the working machine, an applied braking force and a maximum permissible temperature of the assisting brake. The counter also advantageously takes into account a cooling capacity acting on the assisting brake, for example in the form of the quantity and temperature of the cooling oil supplied to the assisting brake.
According to a particularly preferred embodiment of the invention, it is provided that the accumulating counter is not reduced when the working machine is at a standstill. Since no cooling oil is usually conveyed when the working machine is at a standstill and likewise no airstream can flow along the assisting brake, a comparatively slow cooling takes place here, which is ignored to simplify the method by not reducing the counter when the working machine is at a standstill.
Advantageously, the counter can be reset to an initial value, for example the value zero, when an ignition of the working machine is switched off and switched on again with a predeterminable time interval.
According to a particularly preferred embodiment of the invention, it is provided that a current travel speed of the working machine is continuously detected and continuously compared with a predeterminable limit speed, wherein, if the limit speed is exceeded, the braking torque of the assisting brake is adjusted by modulating the hydraulic or pneumatic pressure in such a way that the actuation of the assisting brake reduces a travel speed of the working machine to such an extent that no impermissible acceleration occurs solely due to the braking torque generated by the drive motor.
In other words, the inadmissible acceleration is not automatically counteracted by actuating the assisting brake as long as the travel speed of the working machine does not exceed the limit speed. Irrespective of this, the driver of the working machine naturally still has the option of manually applying the brakes, for example using the service brake, in order to prevent unacceptable acceleration.
The limit speed is advantageously dependent here on the downhill slope force acting in each case and therefore on the gradient of the slope down which the working machine is traveling. The greater the downhill slope force, the greater the braking torque to be applied by the assisting brake must be in order to keep the travel speed of the working machine constant or to reduce it. At the same time, since the braking torque of the drive motor that can be provided in recuperation mode is largely determined by the speed of the drive motor, wherein the braking torque is comparatively high at low speeds and becomes comparatively low towards higher speeds, the limit speed on a comparatively steep slope is advantageously lower than on a comparatively flat slope.
Depending on whether the assisting brake can be actuated hydraulically or pneumatically, hydraulic or pneumatic actuation takes place by means of a corresponding modulation of the assisting brake. On the one hand, the modulation ensures that the braking torque of the assisting brake is not applied abruptly but evenly. On the other hand, the braking torque can also be dosed in order to provide a braking torque adapted to the braking action required in each case.
By reducing the travel speed of the working machine to such an extent that there is no longer any unacceptable acceleration due to the recuperation mode alone, the working machine can continue its journey without further brake intervention and therefore without brake wear. As the entire braking energy is also provided by recuperation, it can also be almost completely converted into electrical energy, which is later available again to drive the working machine.
After the working machine has been braked to a travel speed below the limit speed, the assisting brake can be released to cool down.
According to a further particularly preferred embodiment of the invention, it is provided that a maximum permissible vehicle speed of the working machine is limited and/or the speed threshold is reduced as long as the counter is above a limit value.
The limit value advantageously indicates the thermal load capacity of the assisting brake, i.e., it is an indicator of how much heat can be introduced into the brake during a braking process before it is permanently damaged or at least before the braking properties of the assisting brake are temporarily impaired due to the amount of heat introduced.
By limiting the maximum permissible vehicle speed of the working machine and/or by reducing the speed threshold, it can be ensured that the working machine is reliably kept in a speed range that does not require any further actuation of the assisting brake solely via the braking torque in recuperation mode of the drive motor.
According to a further particularly preferred embodiment of the invention, it is provided that the brake actuation is repeated a first time with a first changed modulation and a first changed limit value is specified if the vehicle speed is still above the limit speed when the limit value is reached by the counter. The first modified modulation can, for example, generate a higher braking torque than the previously used modulation, so that a greater speed reduction results and the working machine can be brought into a speed range via the first modified modulation in which the working machine can be braked exclusively via the braking torque in recuperation mode of the drive motor.
If the brake application is to be repeated with a first modified modulation, the limit value of the counter is advantageously selected so that the assisting brake can perform a further brake actuation without being thermally damaged or even destroyed. Accordingly, the first modified limit value of the counter is at a higher value than the original limit value.
According to yet another particularly preferred embodiment of the invention, it is provided that the brake actuation is repeated a second time with a second modified modulation and a second modified limit value is specified if the vehicle speed is still above the limit speed when the first modified limit value is reached by the counter. The second modified modulation can, for example, generate an even higher braking torque than the first modified modulation, so that an even greater speed reduction results and the working machine can possibly be brought into a speed range via the second modified modulation in which the working machine can be braked exclusively via the braking torque in recuperation mode of the drive motor.
If a second repetition of the brake application with a corresponding, second modified modulation is provided, the first modified limit value of the counter is advantageously selected so that the assisting brake can also perform the further brake application without damage or destruction. The second modified limit value of the counter is accordingly at a higher value of the counter than the first modified limit value.
According to a further preferred embodiment of the invention, it is provided that the actuation of the assisting brake is terminated when the accumulating counter reaches the limit value, the first changed limit value or the second changed limit value and/or a predeterminable time period for the actuation of the assisting brake has been exceeded and/or the speed has fallen below the limit speed. On the one hand, this ensures that the assisting brake is not destroyed by the continued braking operation and the associated thermal load. On the other hand, the assisting brake is not subjected to unnecessary wear and the energy that can be recovered through recuperation is increased by applying the required braking torque exclusively through the recuperation operation of the drive motor.
According to a further preferred embodiment of the invention, it is provided that an acoustic and/or visual and/or haptic warning is issued to the driver if the actuation of the assisting brake is terminated without the speed falling below the limit speed. This has the advantage that the driver can be warned if there is an impermissible acceleration that cannot be compensated for by the braking torque of the recuperation mode and the assisting brake. In order to avoid further acceleration, which could lead to a dangerous situation, the driver can then initiate braking via the service brake if necessary.
The invention also relates to an electrified drive train for a working machine, wherein the drive train has a drive motor, a service brake, and an assisting brake, wherein there is a drive coupling of the drive motor of the drive train to at least one wheel of the working machine, so that a braking torque of the drive motor can counteract a downhill slope force acting on the working machine, wherein the drive train is designed to carry out an automated actuation of the assisting brake if the working machine is subject to an impermissible acceleration, and wherein the drive train is designed to actuate the assisting brake in accordance with a required braking torque.
The drive train according to the invention is characterized in that the drive train is also designed to actuate the assisting brake in accordance with a thermal load on the assisting brake and that the assisting brake is designed as a spring-applied and hydraulically or pneumatically releasable brake.
As a result, the advantages already described in conjunction with the method according to the invention also apply to the drive train according to the invention.
According to a further preferred embodiment of the invention, it is provided that the drive train is designed to carry out the method according to the invention.
Lastly, the invention also relates to a working machine comprising a drive train according to the invention.
The working machine is preferably a wheel loader. However, it can also be a skid steer loader, telescopic handler, dumper, excavator, or tractor.
In the following, the invention is explained by way of example on the basis of embodiments shown in the figures, in which:
Identical objects, functional units and comparable components are designated with the same reference signs across all FIGURES. These objects, functional units and comparable components are identical in terms of their technical features, unless explicitly or implicitly stated otherwise in the description.
In method step 100, an ignition of the working machine is actuated, or it is put into operation via a switch, thereby starting the method according to the invention. Parameters describing the working machine, the drive train and the assisting brake are loaded from a read-only memory into the working memory of a computing unit, which executes the method in the form of a software algorithm.
In the following method step 101, the actual and a maximum permissible travel speed are recorded at times specified by a clock generator. The maximum permissible travel speed represents a limit speed and is characterized by the gradient of the slope on which the working machine travels downhill.
If it is recognized in step 102 that the actual travel speed has exceeded the limit speed, the assisting brake, which is designed as a so-called SAHR brake, is automatically actuated.
While the automatic actuation of the assisting brake takes place in step 103, an accumulating counter is increased cumulatively with each clock signal in accordance with the clock generator. The counter is therefore a measure of the thermal load on the assisting brake, the temperature of which continues to increase the longer the assisting brake is actuated.
In step 104, the heat introduced into the assisting brake by actuating the assisting brake is successively absorbed by the transmission oil or radiated into the environment. This cooling process takes place continuously as long as the working machine does not fall below a defined minimum speed. The accumulating counter is therefore reduced as a function of time, wherein the counter cannot become negative. The reduction of the counter by cooling the assisting brake is cumulative to the increase of the counter by actuating the assisting brake, so that the reduction of the counter and the increase of the counter are offset against each other at the times specified by the cycle generator. When the working machine is at a standstill, however, the cooling times are disproportionately long, which is why the counter is not reduced below the minimum speed.
In step 105, the actuation of the assisting brake is canceled when the counter has exceeded a limit value. Alternatively, the actuation of the assisting brake is canceled in step 106 if the working machine has reached a travel speed that is below the limit speed.
If the counter has exceeded a threshold value during actuation of the assisting brake, the limit speed remains reduced in step 107 until the counter has reached a value at which further actuation of the assisting brake is possible.
However, if the actual travel speed of the working machine is still above the limit speed when the actuation of the assisting brake is terminated in step 108, the actuation is not aborted, for example, but is repeated with a first modified modulation.
If this second attempt to reduce the actual travel speed of the working machine is also not sufficient, the assisting brake is actuated again in step 109 with a second modified modulation.
If this third attempt also fails to reduce the actual travel speed of the working machine below the limit speed, the actuation of the assisting brake is aborted in step 110 and the assisting brake is released to allow it to cool down.
In the following step 111, a warning is issued to the driver of the working machine, and they are requested to check the actual travel speed of the working machine.
According to another exemplary embodiment not shown in the FIGURES, only a second test to reduce the actual travel speed of the working machine takes place after the first test, but not a third test.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 201 528.2 | Feb 2022 | DE | national |
| 10 2023 200 708.8 | Jan 2023 | DE | national |
This application claims the benefit under 35 U.S.C. § 371 as a U.S. National Phase Application of application no. PCT/EP2023/053545, filed on 14 Feb. 2023, which claims the benefit of German Patent Application no. 10 2022 201 528.2 filed on 15 Feb. 2022, and which also claims the benefit of German Patent Application no. 10 2023 200 708.8 filed on 30 Jan. 2023, the contents of which are hereby incorporated herein by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/053545 | 2/14/2023 | WO |
