METHOD FOR OPERATING A DRIVING DEVICE FOR A WORKING MACHINE

Description

RELATED APPLICATIONS

This application claims the benefit of and right of priority under 35 U.S.C. § 119 to German Patent Application no. 10 2024 206 073.9, filed on 28 Jun. 2024, the contents of which are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a method for operating a drive device for a working machine. Furthermore, the present invention relates to a control device that is designed to carry out such a method. Furthermore, the present invention relates to a power-split gearbox with such a control device, and to a working machine with such a power-split gearbox.

BACKGROUND

In the field of working machines, drive systems with an engine and a power-split gearbox are used. Such power-split gearboxes can feature a variator that allows the transmission ratio of the gearbox to be adjusted continuously. For certain tasks, it is necessary to operate the working machine at a constant speed. The fundamental aim is to use the working machine with maximum efficiency in order to minimize operating costs.

SUMMARY

The present invention relates to a method for operating a drive device for a working machine. The working machine may be a construction, agricultural, or forestry machine. For example, the working machine may be a wheel loader, a grader, or a forwarder. The drive device has an engine and a power-split gearbox. The engine may be an internal combustion engine and, alternatively or additionally, an electric engine. The power-split gearbox can be a hydrostatic-mechanical transmission and, alternatively or additionally, an electric-mechanical power-split gearbox. The power-split gearbox can have a mechanical power branch and a hydrostatic and, alternatively or additionally, an electric power branch. The power-split gearbox features a variator to enable stepless adjustment of the transmission ratio of the gearbox. For example, the power-split gearbox can be designed so that different fixed transmission ratios between a drive and an output of the gearbox can be switched via a mechanical power branch. The different transmission ratios may correspond to the operating ranges of the working machine. Within these driving ranges, the transmission ratio can be continuously adjusted using the variator. The variator can be designed as a hydrostat and have two hydraulic machines that can be connected to each other in a hydrodynamic manner. Alternatively, or additionally, the variator can also have two electric machines that can be electrically connected to each other.

The method comprises outputting a target output speed of the drive device based on a target speed request from an operator of the working machine. The target output speed can be a target speed of the output of the power-split gearbox. The target output speed of the drive device can correlate directly with the target speed request. For example, it may be higher or lower if the target speed request is higher or lower. Alternatively, however, the target output speed can also be determined based on a comparison of one variable with another, wherein one of the variables can be in a defined relationship with the target speed. The target output speed can be selected so that the working machine runs at the target speed when the target output speed is present at the output of the drive unit. The target speed request can be set by the operator of the working machine, for example a driver of the working machine, using a control device such as a switch. In one embodiment, the operator can set the target speed request separately for forward and reverse travel. The target output speed can be specified separately for forward and reverse travel. Furthermore, the operator of the working machine can set one or more virtual gears, based on which a maximum target output speed can be determined.

In addition, the method comprises recording an actual capacity utilization of the drive device and comparing the recorded actual capacity utilization with a target capacity utilization of the drive device. The capacity utilization of the drive system can be a capacity utilization of the engine and, alternatively or additionally, a capacity utilization of the gearbox. For example, the capacity utilization of the engine may correlate with the torque provided by the engine. Alternatively, or additionally, the capacity utilization of the gearbox can correlate with a torque transmitted by the gearbox. The target capacity utilization of the drive device can be fixed or variable. The target capacity utilization can be specified so that the drive system can be operated as efficiently as possible. By specifying the target capacity utilization of the drive unit, the contribution of the engine and gearbox to the target output speed of the drive unit can be divided and adjusted as necessary.

Furthermore, the method of the present invention comprises outputting a target engine speed of the engine based on the comparison of the actual and target capacity utilization of the drive device. While recording the actual capacity utilization, comparing the actual capacity utilization with the target capacity utilization, and outputting the target engine speed, the target output speed of the drive device can be continuously output. In other words, the drive device can be operated at a constant target output speed, while the target speed of the engine is adjusted based on a comparison of the actual and target capacity utilization of the drive device. The speed of the engine can be adjusted, for example, by the power-split gearbox, so that the drive unit continues to operate at a constant output speed.

The present invention has the advantage that cruise control can be provided in a drive device for a working machine with a power-split gearbox. The method of the present invention ensures that the drive device operates the working machine at a predetermined target speed and simultaneously with high efficiency. This means, for example, that a wheel loader or grader can be operated efficiently and at a constant speed when clearing snow. This also allows a forwarder to be operated at a constant speed, for example when “creeping”, in order to load logs while driving.

In one embodiment, recording the actual capacity utilization of the drive device includes recording an actual capacity utilization of the power-split gearbox. As described above, recording the actual capacity utilization of the gearbox may involve recording the torque transmitted by the gearbox. For example, the actual capacity utilization of the gearbox can correlate with a torque applied to the gearbox output. In this embodiment, outputting the target engine speed of the engine may include increasing the target engine speed if the actual capacity utilization of the gearbox is higher than the target capacity utilization of the gearbox. To reduce the capacity utilization of the gearbox and thus the torque converted by the gearbox, the target speed of the engine can be increased. This ensures, for example, that the gearbox operates at operating points with good efficiency and, alternatively or additionally, with low wear.

Furthermore, within the scope of this embodiment, the target engine speed of the engine can be reduced if the actual capacity utilization of the gearbox is lower than the target capacity utilization of the gearbox. In such a case, the reciprocal transmission ratio of the gearbox can be increased, for example, in order to achieve higher capacity utilization of the gearbox. As a result, the speed of the engine can be reduced without changing the speed at the gearbox output in such cases, the engine can be operated at a lower speed and therefore with greater efficiency. This makes it possible to provide a drive device that provides an output speed correlated with a target speed in a particularly efficient manner. The target capacity utilization of the gearbox can be selected within this design so that the engine can be operated at the lowest possible speeds and therefore with high efficiency. The drive device may have several different engine speed limitation classes, also known as engine speed limitation classes. The target capacity utilization of the gearbox can be specified separately for each of the engine speed limitation classes. A separate load-dependent engine speed control logic circuit with different parameterization can also be stored for each of the engine speed limitation classes. Furthermore, the operator of the working machine can set one or more virtual gears, on the basis of which a maximum target output speed of the drive device can be determined.

The recording of the actual capacity utilization of the power-split gearbox may include the recording of a state variable of the variator of the power-split gearbox. By recording the actual capacity utilization of the gearbox via the condition variable of the variator, the capacity utilization can be recorded with high accuracy and high dynamics. If the variator is a hydrostatic drive, for example, a pressure variable, such as a differential pressure between different sections of the variator, can represent a measure of the capacity utilization of the power-split gearbox. Within the scope of this embodiment, this differential pressure can therefore be recorded as a state variable of the variator, for example.

In one embodiment, the method comprises receiving a cruise control activation request from a driver. This cruise control activation request can be provided, for example, via a vehicle control unit such as a vehicle control unit. The vehicle control unit can be electronically connected to a cruise control switch in order to record whether activation or deactivation of the cruise control is requested by the driver. Furthermore, in addition to the cruise control activation request, the drivers target speed request can also be received within the scope of this embodiment. The driver's target speed request can be set by the driver using a control unit, such as a switch. Furthermore, this embodiment allows checking whether an activation condition for activating cruise control is present. If such a condition exists, the method may include activating cruise control.

Based on the target speed request received, a cruise control target output speed for the drive device can now be determined in this embodiment. However, if the check step reveals that the activation condition is not met, cruise control is not activated. The method steps of the present embodiment can be carried out on a control device, which can be designed to operate the drive device, for example the gearbox or, optionally, also the engine. The control device may differ from a vehicle control unit, which may, for example, be electronically connected to the accelerator and brake pedals described above, as well as to the cruise control switch and the target speed switch.

When checking whether a condition for activating cruise control is present, it is possible to check whether an accelerator pedal on the working machine is being pressed beyond a threshold value. In addition, it can be checked whether the output speed of the drive device is greater than a threshold value. In other words, this check can be used to ascertain whether the working machine is in motion or still essentially at a standstill. As a result, the operational safety of the working machine can be increased, since this design prevents acceleration from a standstill. Alternatively, or additionally, this embodiment can check whether the brake pedal is pressed less than a threshold value and whether a gear requested by a driver is not zero. Only when all these conditions are met can cruise control be activated in one embodiment. However, if the brake pedal is pressed beyond a threshold value, no gear is requested by the operator, a reverse request is present, or no cruise control activation request is detected, the cruise control can be deactivated or remain active in one embodiment. You can also choose whether a reverse request leads to cruise control being deactivated or whether cruise control is maintained at the speed set for the other direction.

In one embodiment, the method comprises ascertaining a minimum engine speed for providing the target speed request. In other words, within the scope of this embodiment, the engine speed at which the drive device can still reach the target speed can be ascertained. For this purpose, the target speed request and a maximum available transmission ratio, for example a maximum reciprocal transmission ratio, of the gearbox can be taken into account. The drive device may have engine speed limitation classes as described above. A separate minimum engine speed specification can be set for each of the engine speed limitation classes or alternatively specified, which in turn can depend on a reciprocal transmission ratio of the gearbox.

In one embodiment, when cruise control is activated, the method comprises receiving an accelerator pedal position and ascertaining a conventional output speed of the drive device based on the received accelerator pedal position and a conventional operating logic circuit of the drive device. For example, in this embodiment, while cruise control is activated, a target output speed of the drive device can also be ascertained simultaneously based on the current position of the accelerator pedal. In this embodiment, outputting the target output speed may include outputting the greater of the cruise control target output speed and the conventional target output speed. If, for example, the accelerator pedal is pressed by an operator of the working machine while cruise control is active, the operator has the option of increasing the cruise control setting by pressing the accelerator pedal. This allows the working machine to operate at a speed higher than the commanded target speed, for example. As soon as the driver releases the accelerator pedal, the cruise control settings become valid again. Accordingly, the drive system is then operated again at the target output speed of the cruise control.

Furthermore, the present invention relates to a control device that is set up, i e, specifically designed, for example programmed, to carry out a method according to one of the embodiments described above. The control device may have one or more interfaces for communicating with the respective components of the drive device, which may each be designed as input and/or output interfaces. The control device may be a gearbox control device, which may be designed to control the gearbox and, optionally, the engine as well. The control device may have an interface for electronic connection to a vehicle control unit of the working machine. The vehicle control unit may be located separately from the gearbox control unit and function independently of it. Furthermore, the present invention relates to a power-split gearbox with a variator for continuously varying a transmission ratio of the gearbox and such a control device. The present invention also relates to a working machine with a drive device comprising an engine and such a power-split gearbox. With regard to the design and advantages of the individual components, reference is made to the above explanations in connection with the method of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically shows a working machine with a drive device according to an embodiment of the present invention.

FIG. 2 schematically shows the drive mechanism of the working machine from FIG. 1.

FIG. 3 shows a flowchart of a method for operating the drive device of FIG. 2 according to an embodiment of the present invention.

FIG. 4 schematically shows a block diagram of a control logic circuit of a control unit of the drive device from FIG. 2 according to an embodiment of the present invention.

FIG. 5a shows a schematic block diagram of a load-dependent speed controller of the control logic circuit from FIG. 4.

FIG. 5b schematically shows a block diagram for ascertaining a minimum speed of the load-dependent speed controller from FIG. 5a.

DETAILED DESCRIPTION OF EMBODIMENTS

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 wheel loader. The working machine 100 comprises a plurality of wheels (not shown) which can be driven by the drive device 1. 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 designed 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 the 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 speed of the output 7 is in a fixed relationship with the speed of the wheels and thus with the travel speed of the working machine 100.

Via the mechanical power path 4 of the power-split gearbox 3, which in the present embodiment has several switching elements, 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.

In addition, the drive device 1 comprises a control device 8 for controlling the power-split gearbox 3, which is designed here as a gearbox control device. 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. 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 two sections, each with a pressure sensor. Via the gearbox interface 10, the control device 8 can read out a differential pressure between these sections, which is in a fixed relationship with the torque at the output 7 and thus with the capacity utilization of the gearbox.

Furthermore, the control device 8 comprises a vehicle interface 11, via which the control device 8 is electronically connected to a vehicle control unit 12. In the present embodiment, the vehicle control unit 12 is a vehicle control unit of the working machine 100. An accelerator pedal 13 is electronically connected to the vehicle control unit 12 in order to ascertain the position of the accelerator pedal. Furthermore, a brake pedal 14 is electronically connected to the vehicle control unit 12 in order to be able to ascertain a brake pedal position with the latter. In addition, a cruise control switch 15 is electronically connected to the vehicle control unit 12, via which an operator of the working machine 100 can activate or deactivate cruise control unit. An operator of the working machine 100 can set and adjust a target speed for the working machine 100 via a target speed switch 16 that is electronically connected to the vehicle control unit 12. If the working machine 100 is to be operated at a constant speed without activating the drive and brake pedals 13, 14, an operator of the working machine 100 must first activate the cruise control via the switch 15. The driver then uses switch 16 to set the target speed of the working machine 100. The activation or deactivation request from cruise control switch 15 and the target speed set by the driver using switch 16 are fed by the vehicle control unit 12 to the control device 8 via the vehicle interface 11. Furthermore, the drive pedal or brake pedal position read by the vehicle control unit 12 can be fed to the control device 8 via the vehicle interface 11. The control device 8 is now set up to control the engine 2 and the power-split gearbox 3 based on the variables supplied to it by the vehicle control unit 12 via the vehicle interface 11.

As can be seen from the block diagram of the control logic circuit in FIG. 4, two different logic circuits L1 and L2 are stored on the control device 8 for ascertaining the target output speed N at the output 7 of the power-split gearbox 3, the maximum permissible traction force Z at the output 7 of the power-split gearbox 3, and the target engine speed M of the engine 2. Within the framework of a first conventional logic circuit L1, the control device 8 can ascertain a conventional target output speed N1 of the gearbox 3, a conventional maximum permissible traction force Z1 at the output 7 and a conventional target engine speed M1 of the engine 2 based on the positions of the accelerator pedal 13 and brake pedal 14 and other variables. The other variables in this embodiment are a current transmission ratio of gearbox 3, a virtual gear specified by the driver of working machine 100, and adjustable limits for the engine speed. In this embodiment, logic circuit L1 corresponds to the general transmission control logic circuit that is active during normal operation of the gearbox 3.

The second logic circuit L2 is a cruise control logic circuit which, in the present embodiment, is only executed when cruise control is activated. Within the scope of this logic circuit L2, the control device 8 can ascertain a cruise control target output speed N2 of the output 7, a cruise control maximum permissible traction force Z2 at the output 7 and a cruise control target engine speed N2 of the engine 2 based on the metric described below. As described below, the control device 8 is set up to select the larger value from the target output speeds N1 and N2 ascertained by the two logic circuits L1 and L2, the maximum permissible traction forces Z1 and Z2, and the target engine speeds M1 and M2. This is indicated in the block diagram in FIG. 4 by the MAX function blocks, which output the maximum value from their input variables.

The control device 8 is set up to carry out the method described below with reference to FIG. 3 for operating the drive device 1 from FIG. 2. In a first step I, the control device 8 receives a cruise control activation request from the vehicle control unit 12 via the vehicle interface 11. This is sent from the vehicle control unit 12 to the control device 8 when the driver of the working machine 100 activates the cruise control via the switch 15. Furthermore, switch 16 is used to set a target speed for the working machine 100, which can be variably adjusted by the driver of the working machine 100. The target speed currently set at switch 16 is recorded by the vehicle control unit 12 and also fed to the control device 8 via the vehicle interface 11 in step I.

In a subsequent step II, the control device 8 now checks whether the conditions for activating cruise control, or more precisely cruise control logic circuit L2, are met. To this end, the positions of the accelerator pedal 13 and brake pedal 14, the output speed at output 7 of the gearbox 3, and a gear requested by the driver are read out. In step II, the system checks whether, in addition to a request to activate cruise control, the accelerator pedal 13 has been pressed beyond a threshold and the speed at the output 7 is greater than a threshold value. It is also checked whether the driver requests a gear so that the requested gear is not zero and the brake pedal 14 is pressed below a threshold value. If all these conditions are met, cruise control logic circuit L2 is activated in a subsequent step III. However, parallel to the activated cruise control logic circuit L2, the conventional logic circuit L1 is also active in this embodiment. However, if check step II reveals that the brake pedal 14 is pressed beyond a threshold, that the driver is not requesting a gear and therefore the requested gear is zero, or that a reverse request has been made, the cruise control logic circuit L2 is not activated. Cruise control logic circuit L2 is also not activated if there is no request to activate cruise control. In these cases, only the conventional logic circuit L1 is active in the control device 8 and the method returns to step I.

If cruise control logic circuit L2 was activated in step III, it determines the cruise control target output speed N2 at output 7 of the power-split gearbox 3 in a subsequent step IV based on the target speed received from the vehicle control unit 12. The cruise control target output speed N2 is set so that the working machine 100 moves at the target speed when the target output speed N2 is present at the gearbox output 7. Furthermore, in step IV, the control device 8 determines a maximum permissible traction force Z2 for cruise control via the logic circuit L2.

In step V, the cruise control logic circuit L2 also determines a cruise control target engine speed M2 for engine 2. The target engine speed M2 of engine 2 is determined by the cruise control logic circuit L2 in accordance with the logic circuit shown in the block diagram in FIG. 5a. A load-dependent engine speed controller R is provided, which has an activation state a of the cruise control as an input variable. The activation state a is set when the cruise control logic circuit L2 is activated in step III. Furthermore, the engine speed controller R has a maximum engine speed b and a minimum engine speed c as input variables. The maximum engine speed b is the currently maximum permitted speed of the engine 2, which can change based on a currently existing engine speed limitation class, also known as the engine speed limitation class. For example, the engine speed limitation class can be changed by a driver.

The minimum engine speed c, on the other hand, is determined in a step V1 based on the current target speed request v, which is supplied to the control device 8 via the vehicle interface 11 from the vehicle control unit 12, and which is ascertained in the logic circuit shown in the block diagram of FIG. 5b. In step V1, the target speed request v is multiplied by a lead factor f, and then the minimum speed of engine 2 is ascertained, taking into account the maximum transmission ratio i of gearbox 3. The minimum speed ascertained in this way is the speed required to reach the target speed v with the drive device 1. The minimum speed ascertained in this way is compared with a minimum speed mm that can be provided by engine 2. The maximum of these two values is then used as the minimum speed c for the engine speed controller R. This logic circuit is indicated by the MAX block in the block diagram in FIG. 5b.

In addition, the load-dependent engine speed controller R has a target capacity utilization d of the drive device 1 as an input variable. In this embodiment, the target capacity utilization d is a target capacity utilization of gearbox 3. The target capacity utilization d is selected to be comparatively high in the present embodiment so that the capacity utilization of engine 2 is correspondingly comparatively low. This allows engine 2 to be operated more efficiently, resulting in improved fuel efficiency of the working machine 100.

In step V2, the engine speed controller R of the control device 8 first records the actual capacity utilization of the drive device 1. In this embodiment, the actual capacity utilization of the gearbox 3 is recorded. For this purpose, the differential pressure present in the hydrostat 5 is recorded, which correlates with the torque transmitted by the gearbox 3 and is therefore a measure of the capacity utilization of the gearbox 3. The actual capacity utilization of gearbox 3 recorded in step V2 is compared with the target capacity utilization d of gearbox 3 in step V3. If the comparison in step V3 shows that the actual capacity utilization is higher than the target capacity utilization, the cruise control target engine speed M2 of engine 2 is increased in step V4.1 in order to reduce the actual capacity utilization in gearbox 3. If, however, the comparison in step V3 shows that the actual capacity utilization is lower than the target capacity utilization d, the cruise control target engine speed of engine 2 is reduced in step V4 2 in order to increase the actual capacity utilization of the gearbox 3.

As described above, in the present embodiment, the conventional logic circuit L1 also runs on the control device 8 in parallel with the cruise control logic circuit L2 When cruise control logic control unit L2 is activated, conventional logic circuit L1 receives the current position of the accelerator pedal 13, the current position of the brake pedal 14, and the other variables described above from the vehicle control unit 12 in step VI. Using these values, the control device 8 ascertains in step VII, based on conventional logic circuit L1 the conventional target output speed N1, the conventional maximum permissible traction force Z1, and the conventional target engine speed M1.

In a subsequent step VIII, the maximum of the target output speeds N1 and N2, the maximum of the maximum permissible tensile forces Z1 and Z2, and the maximum of the target engine speeds M1 and M2 are now determined as described above. This maximum value is output in step VIII by the control device 8 to the drive device 1 as the target output speed N, the maximum permissible traction force Z, and the target engine speed M. This means that the driver can override the cruise control logic circuit L2 at any time by pressing the accelerator pedal 13, as the maximum of conventional logic circuit L1 and cruise control logic circuit L2 is used in each case. If the driver releases the accelerator pedal 13 again, the settings for variables N, Z, and M from cruise control logic circuit L2 become valid again. In addition, the driver can adjust the target speed v of the cruise control at any time using switch 16. The method then returns to step I.

REFERENCE NUMBERS

• • 100 working machine
  • 1 drive mechanism
  • 2 engine
  • 3 power-split gearbox
  • 4 mechanical power branch
  • 5 variator
  • 6 drive
  • 7 output
  • 8 control device
  • 9 engine interface
  • 10 gearbox interface
  • 11 vehicle interface
  • 12 vehicle control unit
  • 13 accelerator pedal
  • 14 brake pedal
  • 15 cruise control switch
  • 16 target speed switch
  • L1, L2 control logic circuit
  • N,N1,N2 target output speed
  • Z,Z1,Z2 maximum permissible traction force
  • M,M1,M2 target engine speed
  • R load-dependent speed controller
  • a activation state
  • b maximum speed
  • c minimum speed
  • d target capacity utilization
  • v target speed request
  • f lead factor
  • i maximum transmission ratio of the gearbox
  • mm minimum engine speed
  • I receiving cruise control activation request
  • II checking for cruise control activation condition
  • III activating cruise control
  • IV determining the target output speed
  • V determining target engine speed
  • V1 ascertaining minimum engine speed
  • V2 recording actual capacity utilization
  • V3 comparting actual capacity utilization with target capacity utilization
  • V4.1 increase target engine speed
  • V4.2 reduce target engine speed
  • VI receiving the accelerator pedal position
  • VII ascertaining target output speed
  • VIII outputting target output speed and target engine speed