METHOD FOR OPERATING A DRIVING DEVICE OF A WORKING MACHINE

Abstract

A method is provided for operating a drive device for a working machine having a conventional maximum traction force curve, where the maximum permissible traction force of the drive device increases as the output speed of the drive device decreases. The method includes receiving an activation signal for activating a grading operation of the working machine, where the grading operation has a limited maximum traction force curve in which the maximum permissible traction force of the drive device increases less sharply than with the conventional maximum traction force curve as the output speed of the drive device decreases. A currently maximum permissible traction force is ascertained based on the limited maximum traction force curve and a current traction force is compared with the currently maximum permissible traction force. The transmission ratio of the gearbox is adjusted toward a lower output speed of the drive device based on the comparison.

Claims

1. A method for operating a drive device (1) for a working machine (100), wherein the drive device (1) has an engine and a power-split gearbox (3) with a variator (5) for continuously variable adjustment of a transmission ratio of the gearbox and wherein the drive device (1) has a conventional maximum traction force curve (hZ) in which the maximum permissible traction force (Z) of the drive device (1) increases with decreasing output speed of the drive device (1), the method comprising: receiving (II) an activation signal for activating a grading operation of the working machine (100), wherein the grading operation has a limited maximum traction force curve (IZ.sub.1; IZ.sub.2; IZ.sub.G) and in which the maximum permissible traction force (Z) of the drive device (1) increases less sharply than in the conventional maximum traction force curve (hZ) as the output speed of the drive device (1) decreases; ascertaining (V) a currently maximum permissible traction force (Z) based on the limited maximum traction force curve (IZ.sub.1; IZ2; IZ.sub.G); comparing (VI) a current traction force (Z) with the currently maximum permissible traction force (Z); and adjusting (VII) the transmission ratio of the gearbox (3) towards a lower output speed of the drive device (1) based on the comparison.

2. The method according to claim 1, wherein the method comprises: ascertaining (I) a maximum speed (vmax.sub.1, vmax.sub.2) of the working machine (100); reading in (III.1) a permissible increase in traction force (Z) and/or a traction force gradient; and defining (III.2) the limited maximum traction force curve (IZ.sub.1; IZ.sub.2) based on the ascertained maximum speed (vmax1; vmax2) and the read-in permissible traction force increase (Z) and/or traction force gradient.

3. The method according to claim 2, wherein defining (III.2) the limited maximum traction force curve (IZ.sub.1; IZ.sub.2) comprises: determining a traction force reference point (ZP.sub.1; ZP.sub.2) based on the ascertained maximum speed (vmax.sub.1; vmax.sub.2) and the conventional maximum traction force curve (hZ); determining a traction force gradient based on the read-in permissible traction force increase (Z) and/or traction force gradients; and determining a traction force straight line through the traction force reference point (ZP.sub.1; ZP.sub.2) with the traction force gradient.

4. The method according to claim 1, wherein the method comprises: ascertaining (I) a maximum speed (vmax.sub.1; vmax.sub.2) of the working machine (100); and selecting (III.3) a limited maximum traction force curve (IZ.sub.G) from a plurality of stored limited maximum traction force curves (IZ.sub.G) based on the ascertained maximum speed (vmax.sub.1; vmax.sub.2).

5. The method according to claim 1, wherein the method comprises: ascertaining (VIII) a currently maximum permissible engine speed (n) based on a limited maximum speed curve (In.sub.1; In.sub.2; In.sub.G) of the engine (2), which has a decreasing curve with decreasing output speed of the drive device (1); comparing (IX) a current engine speed (n) with the ascertained current maximum permissible engine speed (n); and reducing (X) the engine speed (n) based on the comparison.

6. The method according to claim 5, wherein the method comprises: determining (IV.1) a maximum engine speed (nmax.sub.1; nmax.sub.2) of the engine (2); reading in (IV.2) a permissible engine speed drop (n) and/or an engine speed gradient; and defining (IV.3) the limited maximum speed curve (In.sub.1; In.sub.2) based on the maximum engine speed (nmax.sub.1; nmax.sub.2) and the read-in permissible engine speed drop (n) and/or engine speed gradient.

7. The method according to claim 5, wherein the method comprises: ascertaining (IV.4) an engine speed limitation class; and selecting (IV.5) a limited maximum speed curve (In.sub.G) of the engine (2) from a plurality of stored limited maximum speed curves (In.sub.G) based on the ascertained engine speed limitation class.

8. A control device (8) configured to carry out the method according claim 1.

9. A drive device (1) with an engine (2), a power-split gearbox (3) with a variator (5) for continuously variable adjustment of a transmission ratio of the gearbox (3) and a control device (8) for controlling the engine and a control device configured to carry out the method according to claim 1.

10. A working machine (100) comprising: an engine (2); a power-split gearbox (3) with a variator (5) for continuously variable adjustment of a transmission ratio of the gearbox (3); and a control device (8) for controlling the engine (2) and control device configured to carry out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] FIG. 1 schematically shows a working machine according to one embodiment.

[0020] FIG. 2 schematically shows a drive device for the working machine from FIG. 1.

[0021] FIG. 3 schematically shows a flowchart of a method for operating the drive device from FIG. 2 according to an embodiment.

[0022] FIGS. 4a and 4b show the traction force and engine speed curves of the drive device from FIG. 2 in a grading operation according to one embodiment

[0023] FIGS. 5a and 5b show the traction force and engine speed curves of the drive device from FIG. 2 in a grading operation according to a further embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] FIG. 1 shows a working machine 100 with a drive device 1 according to an embodiment of the present invention. In the present embodiment, the working machine 100 is a grader. The working machine 100 comprises a plurality of wheels (not shown) which can be driven by the drive device 1. Furthermore, the working machine 100 comprises a grader blade (not shown), which is arranged between a front axle and a rear axle of the grader. FIG. 2 shows a schematic diagram of the drive device 1. The drive device 1 comprises an engine 2, which in the present embodiment is configured as an internal combustion engine. In addition, the drive device 1 comprises a power-split gearbox 3 with a mechanical power path 4 and a hydraulic power path comprising a variator 5. The power-split gearbox 3 has a drive 6 and an output 7. The drive 6 is mechanically connected to engine 2. The output 7 of the power-split gearbox 3 is mechanically connected to the wheels of the working machine 100, which are not shown. The output speed of the drive device 1 at output 7 is in a fixed relationship with the speed of the wheels and thus with the travel speed v of the working machine 100.

[0025] Via the mechanical power path 4 of the power-split gearbox 3, which in the present embodiment has several switching elements not shown, different fixed transmission ratios and thus different driving ranges can be switched between the drive 6 and the output 7 of the gearbox 3. Within these driving ranges, the transmission ratio can be continuously adjusted via the variator 5. In the present embodiment, the variator 5 is designed as a hydrostat with two hydraulic machines that are hydraulically connected to each other. By adjusting the displacement of the variator 5, the transmission ratio of the hydraulic power path and thus also the transmission ratio of the gearbox 3 can be continuously adjusted.

[0026] In addition, the drive device 1 comprises a control device 8 for controlling the drive device 1, which is designed as a gearbox control device in the present embodiment. The control device 8 comprises an engine interface 9 for controlling the engine 2. Furthermore, the control device 8 comprises a gearbox interface 10 for controlling the power-split gearbox 3, among other things for switching the driving ranges of the mechanical power branch 4 and for adjusting the variator 5 of the hydraulic power branch of the gearbox 3. Various measured variables of the power-split gearbox 3 can also be read out via the gearbox interface 10. For example, the hydrostatic variator 5 has a sensor device that can be used to read a pressure value in the variator 5. In this embodiment, the pressure magnitude is in a fixed relationship with the torque at the output 7 and thus with the traction force Z of the drive device 1.

[0027] A conventional maximum traction force curve hZ is stored on the control device 8, which assigns different maximum permissible traction forces Z to the drive device 1 depending on the travel speed v of the working machine 100. The conventional maximum traction force curve hZ is shown in FIGS. 4a and 5a. As explained above, the travel speed v is in a fixed relationship with the output speed at output 7. In the present embodiment, the output speed at output 7 is again in a fixed relationship with the reciprocal transmission ratio of the power-split gearbox 3. As shown in FIGS. 4a and 5a, the conventional maximum traction force curve hZ is designed such that the maximum permissible traction force Z decreases with increasing travel speed v. i.e., with increasing output speed at output 7. For lower driving speeds v, the maximum permissible traction force Z remains essentially constant before decreasing exponentially with increasing driving speed v. In the present embodiment, the drive device 1 has different maximum permissible traction force curves hZ for different engine speeds of the engine 2, wherein only one maximum permissible traction force curve hZ is shown in FIGS. 4a and 5a. The various maximum permissible traction force curves hZ differ from one another, but all essentially follow the curve shown in FIGS. 4a and 5a.

[0028] If the working machine 100 moves at a certain speed v and a load builds up, the drive device 1 increases the traction force Z and attempts to keep the speed v constant. If, on the other hand, the traction force Z reaches the maximum permissible traction force hZ at the current driving speed v, the control device 8 adjusts the power-split gearbox 3 to smaller reciprocal ratios, thereby slowing down the working machine 100. This process is repeated until the applied load no longer exceeds the maximum permissible traction force hZ at the respective travel speed v and the respective engine speed n.

[0029] The control device 8 is set up to execute the method described below with reference to FIG. 3. In a first step, the control device 8 ascertains a maximum speed vmax.sub.1 or vmax.sub.2 of the working machine 100. This maximum speed vmax.sub.1 or vmax.sub.2 can be entered by a driver of the working machine 100, for example by specifying a working speed via a virtual gear limit. FIGS. 4a and 4b show two examples of the maximum speeds vmax.sub.1 and vmax.sub.2 that were ascertained. The driver of the working machine can enter these maximum speeds vmax.sub.1 and vmax.sub.2 using a corresponding switch element.

[0030] In a subsequent step II, the control device 8 now receives an activation signal to activate a grading operation of the grader 100. In the present embodiment, the activation signal is received by the control device 8 when the virtual gear specified by the driver and thus the maximum speed vmax.sub.1 or vmax.sub.2 of the working machine 100 specified by the driver is less than or equal to a maximum permissible virtual gear for grading operation. To this end, in step II, the control device 8 in the present embodiment compares the virtual gear selected by the driver with a maximum permissible virtual gear for grading operation. If this condition is met and the driver of the working machine 100 has additionally entered a command, for example via a switch, to activate the grading operation of the grader 100, the control device 8 receives an activation signal to activate the grading operation.

[0031] In the embodiment shown in FIG. 4a, the control device 8 then reads in a subsequent step III.1 a permissible increase in traction force Z or a traction force gradient, which is entered by the driver of the working machine 100. Subsequently, in a subsequent step III.2, a limited traction force curve IZ is defined based on the maximum speed vmax.sub.1 or vmax.sub.2 ascertained in step I and the permissible traction force increase Z or traction force gradient read in step III.1. As part of step III.2, a traction force reference point ZP.sub.1 or ZP.sub.2 is first ascertained based on the maximum speed vmax.sub.1 or vmax.sub.2 and the conventional maximum traction force curve hZ. More precisely, this traction force reference point ZP.sub.1 or ZP.sub.2 is determined by determining the maximum permissible traction force Z from the conventional maximum traction force curve hZ at the maximum speed vmax.sub.1 or vmax.sub.2. Next, a traction force increase is determined based on the permissible traction force increase Z read in step III.1 or the traction force gradient read in. In the following, a traction force line IZ.sub.1 and IZ.sub.2 is determined through the traction force support point ZP.sub.1 and ZP.sub.2, respectively, with the tensile force gradient.

[0032] If the driver of the working machine 100 specified a permissible increase in traction force Z in step III.1, this results in limited maximum traction force lines IZ.sub.1, whose slope depends on the ascertained maximum speed vmax.sub.1 or vmax.sub.2. At a lower maximum speed vmax.sub.1, the traction force curve IZ.sub.1 has a greater slope than at higher maximum speeds vmax.sub.2. If, on the other hand, the driver has entered a traction force gradient, traction force lines IZ.sub.2 with the same gradients result, but these also have different traction force increases over the travel speed range of the working machine 100. All these limited maximum traction force curves IZ.sub.1 and IZ.sub.2 have in common that they pass through the associated traction force reference point ZP and rise less steeply than the conventional maximum traction force curve hZ as the travel speed v decreases, i.e., as the output speed at output 7 decreases.

[0033] In an alternative embodiment shown in FIG. 5a, different limited maximum traction force curves IZ.sub.G are stored on the control device 8 for different grading passes. In the present embodiment, a limited maximum traction force curve is stored on the control device 8 for a first grading pass IZ.sub.G1, for a second grading pass IZ.sub.G2, for a third grading pass IZ.sub.G3, for a fourth grading pass IZ.sub.G4, and for a fifth grading pass IZ.sub.G5. All of these limited maximum traction force curves IZ.sub.G for the various grading passes, with the exception of the first grading pass IZ.sub.G1, which are permanently stored on the control device 8, have a curve in which the maximum permissible traction force Z increases less sharply with decreasing speed v and thus decreasing output speed at the output 7 of the drive device 1 than in the conventional maximum traction force curve hZ. The increase in traction force in the limited maximum traction force curves IZ.sub.G towards the lower speed ranges v is initially moderate and then becomes pronounced in order to prevent the vehicle from coming to a standstill in the so-called stall point range. In an alternative embodiment, however, the limited maximum permissible traction force may initially rise moderately toward the lower driving speeds v and then drop moderately.

[0034] In both the embodiment shown in FIG. 4a and that shown in FIG. 5a, different limited maximum traction force curves IZ.sub.1, IZ.sub.2, and IZ.sub.G for different engine speeds of engine 2 are stored on the control device 8. These different limited maximum traction force curves IZ.sub.1, IZ.sub.2, and IZ.sub.G are essentially identical, but differ slightly in their permissible traction forces Z.

[0035] In the embodiment shown in FIGS. 4a and 4b, a maximum engine speed nmax.sub.1 and nmax.sub.2 is also ascertained in step IV.1 for the maximum speeds vmax.sub.1 and vmax.sub.2 determined in step I. Furthermore, in step IV.2, a permissible engine speed drop An or an engine speed gradient is read in by the control device 8, which is specified in each case by the driver of the working machine 100. Based on the maximum engine speed nmax1 or nmax.sub.2 specified in step IV.1 and the permissible engine speed drop n or engine speed gradient read in step IV.2, a limited maximum speed curve In for engine 2 is defined in step IV.3. In accordance with the explanations in FIG. 4a, this limited maximum speed curve In is defined by drawing a straight line through the maximum permissible engine speed nmax1 or nmax2 and determining its slope based on the permissible engine speed drop n or engine speed gradient read in step IV.2. All these permissible maximum speed curves In have in common that they decrease continuously from the maximum speed nmax.sub.1 or nmax.sub.2 with decreasing travel speed v and thus with decreasing output speed at Output 7, as shown in FIG. 4b.

[0036] If the driver specifies a permissible engine speed drop n, this results in limited maximum speed curves In.sub.1 for engine 2 with different gradients, depending on the maximum speed vmax.sub.1 or vmax.sub.2 determined in step I. With a lower maximum speed vmax.sub.1, the limited maximum speed curve In.sub.1 has a greater slope than with a higher maximum speed vmax.sub.2. If, on the other hand, the engine speed gradient is specified, the limited maximum speed curves In.sub.2 of engine 2 have the same slope but different engine speed drops across the travel speed spectrum of the working machine 100.

[0037] In the embodiment shown in FIGS. 5a and 5b, however, different limited maximum speed curves In.sub.G3 and In.sub.G4 of engine 2 are stored on the control device 8 for the different grading passes. All these In.sub.G curves have in common that they decrease with decreasing travel speed v and thus with decreasing output speed of the output 7, as shown in FIG. 5b. A large number of limited maximum speed curves Ine are stored for each of the grading passes. The various limited maximum speed curves In.sub.G can be reduced to the same engine speed n, as shown in the example of In.sub.G4, or they can be reduced to different engine speeds n, as shown in the example of In.sub.G3. In one embodiment, the limited maximum speed curves of the engine 2 are designed such that when the speed falls below approximately 25% of the maximum driving speed v of the selected gear, they maintain the engine speed n and do not reduce it further. In an alternative embodiment, however, a limited maximum speed curve In.sub.G of the engine 2 can also be designed so that it rises to lower driving speeds v, as shown by the dashed lines in FIG. 5b.

[0038] In the embodiment shown in FIGS. 5a and 5b, the control device 8 now ascertains, in a subsequent step IV.4, an engine speed limitation class which can be set automatically by the driver or by the control device 8. Subsequently, in a subsequent step IV.5, the control device 8 selects one of the plurality of limited maximum speed curves Inc stored on the control device 8 in the respective grading pass. With a higher engine speed limitation class, a limited maximum speed curve Ino of engine 2 with a higher maximum permissible engine speed n is selected than with a lower engine speed limitation class.

[0039] In a subsequent step V, the control device 8 now ascertains the current traction force Z of the drive device 1. For this purpose, the sensor device described above in the variator 5 is used in the present embodiment. Furthermore, in step V, the currently maximum permissible attraction force Z is ascertained based on the limited maximum traction force curve IZ.sub.1, IZ.sub.2, or IZ.sub.G. In a subsequent step VI, the current traction force Z is now compared with the currently maximum permissible traction force Z. If the current traction force Z exceeds the maximum permissible traction force Z, which was ascertained based on the limited maximum traction force curve IZ.sub.1, IZ.sub.2, or IZ.sub.G, the control device 8 then adjusts the transmission ratio of the power-split gearbox 3 in a step VII. The transmission ratio is adjusted to a lower output speed at output 7 of the drive device 1. For example, in this embodiment, the variator 5 of the power-split gearbox 3 is adjusted for this purpose. This leads to a delay in the working machine 100 and thus to a lower travel speed v.

[0040] In step VIII, the control device 8 now ascertains the currently maximum permissible engine speed n based on the previously determined limited maximum speed curve In.sub.1, In.sub.2, or Ino of the engine 2. Furthermore, the control device 8 ascertains the current engine speed n in this step. In a subsequent step IX, the control device 8 compares the current engine speed n with the currently maximum permissible engine speed, which was determined based on the limited maximum speed curve In.sub.1, In.sub.2, or In.sub.G. If the current engine speed n exceeds the maximum permissible engine speed, the control device 8 reduces the engine speed n in a subsequent step X via the engine interface 9. The method then returns to step V.

REFERENCE NUMBERS

[0041] 100 working machine [0042] 1 drive device [0043] 2 engine [0044] 3 power-split gearbox [0045] 4 mechanical power path [0046] 5 variator [0047] 6 drive [0048] 7 output [0049] 8 control device [0050] 9 engine interface [0051] 10 gearbox interface [0052] I ascertaining maximum speed [0053] II receive activation signal [0054] III.1 reading in permissible increase in traction force and/or traction force gradient [0055] III.2 defining limited maximum traction force curve [0056] III.3 selecting the traction force curve from a variety of stored traction force curves [0057] IV.1 set maximum engine speed [0058] IV.2 reading in permissible engine speed drop and/or engine speed gradient [0059] IV.3 defining limited maximum speed curve [0060] IV.4 ascertaining the engine speed limitation class [0061] IV.5 select maximum speed curve from a variety of stored maximum speed curves [0062] V ascertaining the currently maximum permissible traction force [0063] VI compare current traction force with current maximum permissible traction force [0064] VII adjusting the transmission ratio of the gearbox [0065] VIII ascertaining the current maximum permissible engine speed [0066] IX compare current engine speed with current maximum permissible engine speed [0067] X reduce engine speed [0068] Z traction force [0069] VF travel speed [0070] n engine speed [0071] IZ.sub.1, IZ.sub.2, IZ.sub.G limited maximum traction force curve [0072] hZ conventional maximum traction force curve [0073] ZP.sub.1, ZP.sub.2 traction force support point [0074] vmax.sub.1, vmax.sub.2 maximum speed [0075] Z permissible reduction in traction force [0076] n permissible engine speed drop [0077] nmax.sub.1, nmax.sub.2 maximum permissible engine speed [0078] In.sub.1, In.sub.2, In.sub.G limited maximum speed curve