Method for operating a drive train for a working machine

Abstract

The present invention relates to a method for operating a drive train (1) for a machine. The drive train (1) comprises a drive unit (2) and a power-split transmission (3) with a variator (6) for varying the gear ratio of the transmission (3). The method comprises sensing (I) a current gear ratio (i) of the power-split transmission (3), determining (III) a power limit (L) of the transmission (3) assigned to the sensed gear ratio (i), and outputting (IV) information to the drive unit (2). The information is output to the drive unit (2) based on the determined power limit (L) such that the power delivered by the drive unit (2) does not exceed the determined power limit (L).Furthermore, the present invention relates to a control device (10) configured to carry out such a method, to a power-split transmission (3) with such a control device (10), and to a drive train (1) with such a power-split transmission (3).

Description

Technical area

[0001] The present invention relates to a method for operating a drive train for a work machine. The work machine can be a construction or agricultural machine. The drive train comprises a drive device and a power-split transmission. Furthermore, the present invention relates to a control device configured to carry out such a method. Furthermore, the present invention relates to a power-split transmission having such a control device, and to a drive train having a drive device and such a power-split transmission. State of the art

[0002] Power-split continuously variable transmissions, such as hydrostatic-mechanical power-split transmissions, are frequently used in the field of work machinery. Such hydrodynamic transmissions enable continuously variable adjustment of the transmission ratio with relatively high levels of efficiency, yet exhibit a relatively small gear ratio spread. The gear ratio spread of a transmission is defined as the ratio between the largest and smallest gear ratios. To increase the gear ratio spread, it is known to provide several driving ranges in a continuously variable transmission that have different gear ratio ranges. Such hydrostatic-mechanical power-split transmissions are subject to gear ratio-dependent loads. DE 10 2017 220 003 B3 relates to a method for determining the power flowing through such a transmission. Description of the invention

[0003] The present invention relates to a method for operating a drive train for a work machine. The work machine can be a construction or agricultural machine. For example, the work machine is a wheel loader or a tractor. The drive train has a drive device and a power-split transmission. The power-split transmission can be a power-split continuously variable transmission. In a continuously variable transmission, the gear ratio is continuously adjustable. The power split can, for example, be a hydrostatic-mechanical power split. Alternatively or additionally, an electro-mechanical power split is provided. The transmission can have a drive at which the variable to be translated is fed into the transmission.The transmission can also have an output to which the variable transmitted by the transmission is output. The input and output can be arranged axially parallel to each other.

[0004] The power-split transmission can have multiple driving ranges and a variator. A driving range of the transmission can be understood as a state in which there is a fixed mechanical gear ratio between the input and output of the transmission, whereby the gear ratio of the transmission can be continuously varied within the driving range by the variator. By providing multiple driving ranges, the gear spread can be increased. In one embodiment, the transmission has four driving ranges and a variator. The variator can be a hydrostatic transmission, for example. The drive device can be an internal combustion engine. Alternatively or additionally, the drive device can be an electric motor or another drive device.In one embodiment, the drive device is designed such that its output power or its output engine torque can be adjusted.

[0005] In power-split transmissions that have multiple gear ranges, for example, the load level occurring in the variator, such as the pressure in the hydraulic circuit or the transmitted torque, is a limiting value for determining the installed power of the drive unit in the drive system of the work machine. However, the load level achieved in the gear ranges of these transmissions depends not only on the drive power provided by the drive unit, but also on the mechanical design of the transmission. As a result, the installed power of the drive unit is determined by only a small subrange within the overall gear ratio spectrum of the power-split transmission.Accordingly, there are a number of operating ranges in current power-split transmissions in which the maximum possible loads are not reached and therefore higher power could be provided by the drive device.

[0006] To address this, the method of the present invention comprises detecting a current gear ratio of the power-split transmission. The current gear ratio can be detected based on measurement data detected by a sensor device of the transmission. For example, the sensor device can detect a rotational speed of the output and the input of the transmission and determine the gear ratio of the transmission based thereon. Alternatively or additionally, the gear ratio can be detected based on measured values ​​of other transmission variables that are related to the gear ratio of the transmission. When detecting the gear ratio of the transmission, either the ratio of the input speed to the output speed or the ratio of the output speed to the input speed can be detected. Detecting the current gear ratio of the transmission can comprise detecting the reciprocal gear ratio of the transmission.

[0007] Furthermore, the method includes determining a transmission power limit assigned to the detected gear ratio. A power limit can be understood as the maximum power that can be transmitted by the transmission for a specific gear ratio at that gear ratio. This power limit can be defined such that the variator is not overloaded when this power is transmitted by the transmission. The power limit can be assigned to the gear ratio using a data set, such as a look-up table, which can be stored in the power-split transmission, for example, on a control unit of the power-split transmission.

[0008] Furthermore, the method of the present invention comprises outputting information to the drive device based on the determined power limit. Within the scope of the present invention, the information is output in such a way that the power output by the drive device does not exceed the determined power limit at the detected gear ratio. The power limit can be output to a vehicle control system, which then controls the drive device in such a way that it does not provide more power than the power limit. Alternatively, within the scope of the present method, information can also be output directly to the drive device. The information can be received and processed by a control device of the drive device, which then ensures that the drive device does not provide more power than the power limit.Alternatively or additionally, within the scope of the present method, when the information is output to the drive device, it is also possible to intervene directly in the operation of the drive device, for example, the power of the drive device can be increased or reduced on the basis of the determined power limit value.

[0009] The method of the present invention makes it possible to operate a drive train with a drive device and a power-split transmission in such a way that the maximum possible power is transmitted at the respective operating point of the drive train. Thus, the present method can take into account the fact that different transmission ratios result in different maximum transmittable powers through the transmission. By taking these transmission-ratio-dependent power limits into account when controlling the drive device, a drive train with an overall higher performance capability can be provided. Within the scope of one embodiment, the drive device of the drive train is dimensioned such that its maximum power is higher than the permissible transmittable power at certain operating points of the power-split transmission.

[0010] Within the scope of one embodiment, determining the power limit of the transmission comprises reading the power limit from a data set. In the data set, a power limit can be assigned to each of the different gear ratios of the power-split transmission. The power limits assigned to the different gear ratios can be different from one another. The data set can be stored, for example, in a control device of the drive train, for example a transmission control device. In one embodiment, the data set is designed such that as the gear ratio decreases, i.e., as the reciprocal gear ratio increases, the power limit assigned to the respective gear ratio increases. The data set can have a range in which this relationship between gear ratio and power limit applies, while it does not apply in other ranges.For example, the power limit can increase linearly with decreasing gear ratios, i.e., with increasing reciprocal gear ratios. If the transmission has multiple gear ranges, for example, the power limit can increase within each gear range with decreasing gear ratios, i.e., with increasing reciprocal gear ratios, for example, increase linearly.

[0011] Within the scope of one embodiment, the power limit in the data set has a minimum for the gear ratio at the beginning of a respective driving range and then increases, for example linearly, with decreasing gear ratio, i.e. with increasing reciprocal gear ratio, in the respective driving range. At the end of a driving range, the power limit then drops, for example, from the maximum of the driving range to a minimum of the following driving range. As the transmission ratio approaches the driving range change to the next higher driving range, the power limit can be reduced in a defined function, or in a function definable by a user, to the permissible power limit of the next higher driving range at its highest gear ratio. The change in the power limits can be made in such a way that the driver does not perceive any disruptive intervention in the vehicle's driving performance.In addition, to influence the vehicle's behavior and the transferable drive power during the range change, the engine speed can also be changed when approaching the fixed range change ratio in synchronously shifting continuously variable power-split transmissions. In asynchronously shifting continuously variable power-split transmissions, the range change ratio can also be changed within the available gear ratio overlap of the driving ranges.

[0012] Within the scope of one embodiment, a first power limit value and a second power limit value are assigned to the various gear ratios of the transmission in the data set. The first power limit value can be stored for accelerations and the second power limit value for decelerations of the power-split transmission or the work machine. The power limits for acceleration and deceleration for a respective gear ratio can be different from one another. Within the scope of this embodiment, the method can further comprise determining longitudinal dynamics of the work machine. When determining the longitudinal dynamics, it can be determined whether the work machine or the power-split transmission is accelerating or decelerating. This can be determined, for example, based on measured data within the transmission, e.g., speed changes.In this embodiment, reading the power limit from the data set can include reading the first power limit if it was previously determined that the work machine is accelerating. If it was previously determined that the work machine is decelerating, the reading can include reading the second power limit. This allows differences in the load on the power-split transmission, for example, the variator, during acceleration and deceleration to be taken into account, thus providing a power-split transmission with maximum performance for both acceleration and deceleration of the work machine.

[0013] Within the scope of one embodiment, the method comprises determining the power transmitted by the power-split transmission at the detected gear ratio. The power transmitted by the power-split transmission at the detected gear ratio can be determined based on a measured value in the variator of the transmission. For example, a pressure measurement in the variator can serve for this purpose, for example a high-pressure measurement. Alternatively or additionally, a torque measurement in the variator can be used. Alternatively or additionally, a current measurement in the variator can be used. Alternatively or additionally, controlled variables of the variator control can be used, via which a utilization of the variator can be determined. These variables can be related to a load on the variator and can therefore allow a conclusion to be drawn about a variator load.

[0014] Furthermore, within the scope of this embodiment, the method can comprise comparing the determined transmitted power with the determined power limit. Based on the comparison, information can then be output to the drive device such that the power transmitted by the power-split transmission does not exceed the determined power limit. For example, within the scope of the method of the present embodiment, an adjusted power limit can be transmitted to a vehicle control system, which then ensures that the power provided by the drive device does not exceed the adjusted power limit. Alternatively or additionally, such an adjusted power limit can also be output to a control system of the drive device, which ensures that the power provided by the drive device does not exceed the adjusted power limit.Alternatively or additionally, within the scope of the present embodiment, direct intervention in the control of the drive device is also possible. For example, the power of the drive device can be directly increased or decreased within the scope of the method based on the comparison. This embodiment ensures that the power actually transmitted by the transmission does not exceed the power limit of the respective gear ratio. This enables safe operation of the power-split transmission at maximum possible utilization.

[0015] The present invention further relates to a control device configured to carry out the method according to one of the previously described embodiments. The control device may be a transmission control device, which may be different from a vehicle control device. The transmission control device may be configured to output information to the drive device according to the above method directly or indirectly, for example via a vehicle control device. The control device may comprise a microprocessor specifically programmed to carry out the method according to one of the previously described embodiments. Furthermore, the control device may comprise a storage device, for example a non-volatile memory, on which data for carrying out the method, for example the data set described above, is stored.The control device has corresponding interfaces in order to be able to communicate directly or indirectly with the various components of the power-split transmission and with the drive device, for example by means of a bus system.

[0016] Furthermore, the present invention relates to a power-split transmission for a work machine with a variator for varying the gear ratio and a control device according to the previously described embodiment. The power-split transmission can have multiple driving ranges, for example, four driving ranges. Furthermore, the present invention relates to a drive train for a work machine with a drive device, a power-split transmission, and a control device according to the previously described embodiment. For an understanding and the advantages of the individual features, reference is made to the above explanations in connection with the method for operating the drive train of the work machine. Short description of the characters Fig. 1 schematically shows a powertrain according to an embodiment of the present invention. Fig. 2 shows a schematic flow diagram of a method for operating the drive train from Fig. 1 according to an embodiment of the present invention. Fig. Figure 3 shows schematically the course of pressures within the variator and of power limits of the drive device as a function of the reciprocal gear ratio. Detailed description of embodiments

[0017] Fig. 1 shows a drive train 1 for a work machine according to one embodiment of the present invention. The drive train 1 comprises a drive device 2 and a continuously variable power-split transmission 3. The drive device 2 is mechanically operatively connected to an input 4 of the power-split transmission 3. An output 5 of the power-split transmission 3 is mechanically operatively connected to drive wheels (not shown) of the work machine. In the present embodiment, the rotational speed of the output 5 of the power-split transmission 3 correlates linearly with the travel speed of the work machine. In the present embodiment, the travel speed of the work machine correlates linearly with the reciprocal gear ratio of the transmission 3. The lower the gear ratio of the transmission 3, i.e., the higher the reciprocal gear ratio of the transmission 3, the higher the travel speed of the work machine.In the present embodiment, the drive device 2 is an internal combustion engine. In an alternative embodiment, the drive device 2 is an electric motor. The power-split transmission 3 in the present embodiment is a hydrostatic-mechanical power-split transmission 3.

[0018] The power-split transmission 3 comprises a hydrostatic power branch with a variator 6 and a mechanical power branch 7 between the input 4 and the output 5. The power-split transmission 3 has several driving ranges, each of which, when the variator 6 is fixed, provides different fixed gear ratios between the input 4 and the output 5 of the power-split transmission 3. The different gear ratios of the various driving ranges can be switched using clutches (not shown). Within the respective driving ranges, the gear ratio can be continuously varied by adjusting the variator 6. In the present embodiment, the power-split transmission 3 has four different driving ranges.

[0019] The pressure occurring in the variator 6 is decisive for the load. As the pressure P in the variator 6 increases, so does the load in the variator 6. Fig. 3 schematically shows the pressure curve P1 for a first driving range and the pressure curve P2 for a further driving range of the transmission 3 as a function of the reciprocal gear ratio i of the transmission 3. As in Fig. 3, the pressure P has a maximum PM1 or PM2 at the beginning of each driving range. Within each driving range, the pressure in the variator 6 decreases linearly to a minimum PN1 or PN2 with increasing reciprocal ratio i. All driving ranges of the transmission 3 from Fig. 1 have a corresponding pressure P curve in the variator 6 in the present embodiment. Due to the pressure maximum PM1 or PM2 at the beginning of a respective driving range, the load on the variator 6 is greatest at the beginning of the respective driving range and then decreases with increasing reciprocal gear ratio i. If the maximum power of the drive device 2 is now determined on the basis of the pressure maxima PM1 and PM2, this leads to the power-split transmission 3 not transmitting the maximum possible power at reciprocal gear ratios i that are different from the gear ratios i at the pressure maxima PM1 and PM2, especially in areas of the pressure minima PN1 and PN2.

[0020] This problem is addressed within the scope of the present invention by the control device 10, which is designed to carry out the following with reference to Fig. 2. In the present embodiment, the control device 10 is a transmission control device for controlling the power-split transmission 3. Furthermore, the drive train 1 comprises a vehicle controller 20 for controlling the drive device 2. The transmission control device 10 is electronically connected to the vehicle controller 20. In the present embodiment, the power output of the drive device 2 can be controlled by means of the vehicle controller 20, wherein the control of the drive device can be carried out by the vehicle controller 20 on the basis of information which the vehicle controller 20 receives from the transmission controller 10.

[0021] The control device 10 is connected to a sensor device 11, via which a currently prevailing reciprocal gear ratio i of the transmission 3 can be detected. Furthermore, the control device 10 is connected to a sensor device 12, which can determine a currently prevailing pressure P in the hydrostatic transmission 6. In the present embodiment, the sensor device 12 determines a pressure prevailing in the high-pressure region of the variator 6. As previously explained, the pressure P prevailing in the variator 6 is indicative of the load prevailing in the variator 6. The control device 10 further comprises a memory device on which a data set is stored that assigns a power limit value L for the drive device 2 to each reciprocal gear ratio i.

[0022] As in Fig. 3, the power limit value L for the drive device 2 is lowest at the reciprocal gear ratio i at the beginning of each driving range and then increases within the driving ranges with increasing reciprocal gear ratio. This is due to the fact that the pressure P in the variator 6 is highest at the reciprocal gear ratio i at the beginning of each driving range and decreases with increasing reciprocal gear ratio i. As the pressure P decreases, the load in the variator 6 also decreases, so that more power can be made available by the drive device 2, which power is transmitted via the transmission 3. The curve of the power limit values ​​L as a function of the reciprocal gear ratio i is designed such that the limit load of the variator 6 is not exceeded at the beginning of each driving range at high transmission ratios, i.e. at small reciprocal gear ratios i.The permissible drive power, i.e., the power limit L, increases within each driving range with decreasing gear ratio, i.e., with increasing reciprocal gear ratio i. In the present embodiment, the increase correlates, at least in sections, linearly with the decrease in the pressure P occurring in the variator 6. Since the pressure P in the present embodiment decreases essentially linearly with increasing reciprocal gear ratio i in the respective driving range, the power limit L in the present embodiment increases essentially linearly with increasing reciprocal gear ratio i in the respective driving range.

[0023] As in Fig. However, as shown in Figure 3, a sudden increase in pressure P in the variator 6 occurs when the driving range is changed. In the present embodiment, the power limit value L in the driving range change range exhibits a curve such that it drops continuously from a relatively high value at the end of the first driving range to a relatively low value at the beginning of the further driving range. This change in the power limit value L in the vicinity of a driving range change is designed in such a way that no interference with the driving performance of the work machine is noticeable to the driver.

[0024] In Fig. Figure 3 shows a curve of the power limit values ​​L as a function of the reciprocal transmission ratio i during acceleration of the working machine. However, if the working machine decelerates, which is accompanied by a decrease in the reciprocal transmission ratio i, a power limit value curve as a function of the reciprocal transmission ratio i is stored in the present embodiment, which is different from the power limit value L in Fig. 3 during acceleration of the working machine. The power limit curve during deceleration of the working machine is in Fig. 3 is not shown. Thus, in the data set stored on the control device 10, in the present embodiment, each gear ratio i, more precisely each reciprocal gear ratio, is assigned a first power limit value L for acceleration and a second power limit value L for deceleration.

[0025] As in Fig.2, in a first step I, the control device 10 records the gear ratio currently present in the power-split transmission 3, for example the currently present reciprocal gear ratio i, on the basis of measurement data from the sensor device 11. Subsequently, in a step II, the control device 10 determines the longitudinal dynamics of the work machine, i.e. whether the work machine is accelerating or decelerating. The latter can be done on the basis of measurements from the sensor device 11, which can, for example, determine a speed gradient of the output 5. On the basis of this information, i.e. the recorded gear ratio i and the determined longitudinal dynamics, the control device 10 determines, in a step III, from the data set stored therein, a power limit value L for the gear ratio i recorded in step I and the longitudinal dynamics determined in step II.More specifically, in step III, the first power limit value L is read from the data set for the gear ratio i acquired in step I if acceleration was detected in step II, and the second power limit value L is read if deceleration was detected in step II. Subsequently, in a subsequent step IV, the control device 10 in the present embodiment outputs the power limit value L determined in step III to the vehicle controller 20. The vehicle controller 20 then controls the drive device 2 such that it does not output more power than the determined power limit value L.

[0026] The power actually transmitted by the power-split transmission 3 and thus also the load in the variator 6 is determined by the control device 10 using the sensor device 12 in a step V. For this purpose, the control device 10 in the present embodiment uses a pressure measurement in the variator 6 using the sensor device 12, since the pressure P in the variator 6 correlates with the load on the variator 6 and thus on the power-split transmission 3. In a subsequent step VI, the control device 10 compares the power actually transmitted by the transmission 3 in step V with the power limit value L determined in step III. If a deviation is detected during this comparison in step VI, the method returns to step IV in order to output information to the vehicle control system 20 in such a way that it is ensured that the variator 6 is not loaded beyond its limit load.This allows optimal utilization of the power-split transmission 3 without overloading the variator 6. Reference symbol 1 drivetrain 2 drive device 3 power-split transmission 4 Drive 5 downforce 6 Variator 7 mechanical power branch 10 Control device 11, 12 Sensor device 20 Vehicle control I Capture Translation II Determine longitudinal dynamics III Determine power limit IV Output information to drive device V Determine the power transmitted by the gearbox VI Compare measured performance with performance limit P, P1, P2 variator pressure PM1, PM2 Maximum variator pressure PN1, PN2 minimum variator pressure L Power limit i reciprocal translation

Claims

[1] Method for operating a drive train (1) for a work machine, wherein the drive train (1) has a drive device (2) and a power-split transmission (3) with a variator (6) for varying the gear ratio of the transmission (3), comprising detecting (I) a current gear ratio of the power-split transmission (3), determining (III) a power limit value (L) of the transmission (3) assigned to the detected gear ratio, and outputting (IV) information to the drive device (2) on the basis of the determined power limit value (L) such that the power output by the drive device (2) does not exceed the determined power limit value (L). [2] Method according to claim 1, characterized bythat the determination (III) of the power limit value (L) of the transmission (3) comprises reading out the power limit value from a data set in which a power limit value (L) is each assigned to different gear ratios of the power-split transmission (3). [3] Method according to claim 2, characterized by that the power limit value (L) of the transmission (3) in the data set increases with decreasing gear ratio of the transmission (3). [4] Method according to claim 3, characterized by that the power-split transmission (3) has several driving ranges and the power limit value (L) in the data set has a minimum at the start of a respective driving range for the gear ratio and increases within the respective driving range with decreasing gear ratio. [5] Method according to one of claims 2 to 4, characterized byin that in the data set, a first power limit value for acceleration and a second power limit value for deceleration of the working machine are each assigned to the various gear ratios of the transmission (3), and in that the method further comprises determining (II) a longitudinal dynamics of the working machine and reading (III) the power limit value (L) from the data set, reading the first power limit value when acceleration is determined and reading the second power limit value when deceleration of the working machine is determined. [6] Method according to one of the preceding claims, characterized bythat the method comprises determining (V) a power transmitted by the power-split transmission (3) at the detected gear ratio, comparing (VI) the determined power with the determined power limit value (L), and outputting (IV) information to the drive device (2) on the basis of the comparison in such a way that the power transmitted by the power-split transmission (3) does not exceed the determined power limit value (L). [7] Method according to claim 6, characterized by that the determination (V) of a power transmitted by the power-split transmission (3) is carried out based on at least one of a pressure measurement in the variator (6), a torque measurement in the variator (6), a current measurement in the variator (6) and a controlled variable of the variator (6). [8] Control device (10) arranged to carry out the method according to one of the preceding claims. [9] Power-split transmission (3) for a working machine with a variator (6) for varying the transmission ratio and a control device (10) according to claim 8. [10] Drive train (1) for a working machine with a drive device (2), a power-split transmission (3) and a control device (10) according to claim 9.

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