Procedure for implementing a cold start strategy

Abstract

A method for implementing a cold start strategy in a vehicle with a transmission having at least one hydrostatic drive for warming hydraulic fluid, characterized in that, when the vehicle is started (100), it is checked whether the conditions of the cold start strategy (300) are present, wherein, for checking the conditions of the cold start strategy (300), information about previous cold start strategies (300) and aborts (200) of the cold start strategy are retrieved from a vehicle memory (EEPROM), that after the start of the cold start strategy, conditions for aborting (200) the cold start strategy are checked, that an abort (200) of the cold start strategy (300) is stored in the vehicle memory (EEPROM), and then a transmission control unit is shut down if conditions for aborting (200) are present, and that unlimited driving is carried out if the cold start strategy (300) has been successfully completed.

Description

[0001] The present invention relates to a method for carrying out a cold start strategy according to the type defined in the preamble of patent claim 1.

[0002] The disadvantage of transmissions with at least one hydrostatic drive, unlike torque converter transmissions, is that insufficient heat energy is generated within the transmission to adequately heat the hydraulic fluid or oil in the transmission. This is especially true during cold starts, but also during operation, for example, if the driver does not start moving immediately.

[0003] At a low hydraulic fluid temperature, the oil is undesirably viscous, which can lead to an undersupply of the hydrostatic drive, which can cause undesirable damage to the transmission and the drive.

[0004] From the document DE 11 2006 003 477 T5 an oil heating strategy for a hydrostatic transmission is known in which a fluid pump is kept substantially at zero displacement and the transmission oil is heated by relative rotation of a first clutch disc and a first clutch hub of a first clutch arrangement and by relative rotation of a second clutch disc and a second clutch hub of a second clutch arrangement.

[0005] From the document DE 10 2010 007 987 A1 a method for controlling an engine-driven automatic transmission of a motor vehicle is known, in which the engine torque is limited after a cold start by using a cold start point for shifting the next gear in the automatic transmission.

[0006] From the document DE 100 36 251 A1, a power transmission system for a vehicle with a main drive clutch and a gearbox and a method for warming up a gearbox oil of the gearbox are known, wherein, within the scope of the method, during a cold start, the clutch is engaged at a gearbox oil temperature below a preprogrammed value in order to warm up the gearbox oil.

[0007] The present invention is based on the object of proposing a method of the type mentioned at the outset, with which operation at a sufficient hydraulic fluid temperature in the transmission is ensured.

[0008] This object is achieved by the features of patent claim 1, whereby advantageous embodiments and further developments emerge from the subclaims and the description as well as the drawings.

[0009] A method is thus proposed for carrying out a cold start strategy in a vehicle having a transmission with at least one hydrostatic drive, in which method it is checked when the vehicle is started whether conditions of the cold start strategy exist and whether conditions for termination exist.

[0010] In vehicles with hydrostatic drives, such as a hydrostatic-mechanical power-split transmission, the so-called c-Power transmission, damage to the hydrostatic transmission can occur when the oil is cold and therefore viscous, for example, due to the pistons pulling out of the piston shoes, leading to transmission failure. This damage can occur, among other things, due to insufficient hydraulic fluid or oil being supplied, resulting in a drop in oil pressure. For this reason, the proposed method carefully warms up the transmission with continuous monitoring using a cold-start strategy.

[0011] For example, the temperature measuring points in the so-called c-Power transmission are located in the intake tract. After the engine has been started and the transmission oil pump has thus built up pressure, elevated hydraulic fluid temperatures are detected at the measuring points in the intake tract, even though the oil temperature in the sump has not yet shown any reaction to the applied heat. Due to the location of the central temperature sensor and the resulting leading measured hydraulic fluid temperature, the selection of the cold start strategy in the proposed method is time-based, since no conclusions about the viscosity can be drawn from the measured hydraulic temperature alone.

[0012] To prevent, for example, the cold start strategy from being circumvented by a restart or a terminal change, the method according to the invention for checking the conditions of the cold start strategy retrieves information from a vehicle memory, the so-called EEPROM or the like, about previous cold start strategies and aborts. This means that a cold start that was not successfully completed in the last terminal cycle or during the last restart will be requested again during the next restart if no abort conditions exist.

[0013] For example, the presence of a driver request, the transmission state, the engine state, or similar can be checked as termination conditions for aborting a cold start strategy. Regarding the presence of a driver request, for example, the application of a parking brake, a change in direction of travel, or similar factors can be checked. Regarding the transmission state, system pressures, engine speeds, or similar factors can be checked. Regarding the engine state, the engine speed can preferably be checked to determine the presence of a termination condition.

[0014] Within the scope of the cold start strategy of the method according to the invention, several process steps can be carried out, whereby the order and length of the process steps or phases can be changed depending on the determined starting temperature of the hydraulic fluid.

[0015] While the cold-start strategy is being implemented within the scope of the method according to the invention, it must be ensured that the drivetrain is never closed during the active cold-start procedure. The previously described reading of the vehicle memory implements a so-called memory function, which prevents the cold-start strategy from being circumvented.

[0016] To heat the hydraulic fluid, the control of shifting elements, particularly reversing clutches in an upstream reversing gear, is provided. To distribute the clutch load between the reversing clutches, the memory function can be expanded so that information regarding the use of the individual reversing clutches during a previous cold-start strategy can be stored and retrieved from the memory. When controlling the reversing clutches to warm up or maintain the hydraulic fluid temperature, the variator of the hydrostatic transmission or hydrostatic drive is in a specific position to protect the low pressure in the hydrostatic transmission via a high-pressure sensor.

[0017] Furthermore, the neutral position of the hydrostatic transmission is adjusted for cold starts to prevent dangerous acceleration in the transmission. The variator's activation and deactivation is regulated and preferably temperature-dependent. Furthermore, for safety reasons, the vehicle's or engine's engine speed can be specified by the transmission, for example, by the transmission control unit, during cold starts.

[0018] The present invention is further explained below with reference to the drawings. They show: Fig. 1 is an overview flowchart of the method according to the invention for carrying out a cold start strategy; Fig. 2 a detailed flow chart according to Fig. 1; Fig. 3 a flow chart of the various process steps of the cold start strategy; Fig. 4 a detailed flow chart regarding the determination of the termination conditions; Fig. 5 a diagram showing the time course of the target engine speed to illustrate a first step of the cold start strategy; Fig. 6 diagrams with the temporal progression of system pressure and hydraulic fluid temperature in the sump to illustrate a second process step of the cold start strategy; Fig. 7 a diagram with the time course of the control current of a position control valve of the hydrostatic drive to illustrate a third process step of the cold start strategy; Fig. 8 several diagrams to illustrate a fourth process step of the cold start strategy; Fig. 9 a diagram showing the time course of the control current of the range clutches to illustrate a fifth process step of the cold start strategy; Fig. 10 several diagrams to illustrate a sixth process step for closing the reversing clutches in the cold start strategy; and Fig. 11 several diagrams to illustrate a seventh process step of the cold start strategy.

[0019] The method proposed according to the invention is essentially divided into four sequences, as shown in Fig. 1. The start 100 as a sequence, with the determination of the starting position and the length of the individual process steps 311 to 318 of the cold start strategy 300, which are necessary at the starting temperature. A further sequence is the abort 200, which marks the abort detection, which runs virtually parallel to the cold start strategy 300 and constantly checks the abort conditions. The cold start strategy 300 as a sequence is divided into the individual functions or process steps 311 to 318, which are called one after the other. The last sequence is the end 400, which includes writing information to the vehicle memory, for example, the EEPROM, and transitioning to normal, unlimited driving after a successful cold start.

[0020] Out of Fig. Figure 2 shows that during a terminal start or during start 100, the system first checks whether information is stored in the vehicle memory, for example, that the last cold start was not completed. If this is the case, this information is read and compared with the currently measured oil temperature. The information that requires a longer cold start is used to determine the length and starting position of the cold start procedure 300.

[0021] Once the starting position and the length of the respective process steps 311 to 318 have been determined, a check is then carried out to determine whether all of the conditions for the cold start have been met. This includes, for example, a possible driver request where the driver requests neutral with the parking brake engaged, or the engine speed is not outside a target range, or the high pressures in the transmission are within the valid range, or the like. If all of the conditions are met, cold start strategy 300 is executed. It should be noted that the termination check runs in parallel. This means that in each cycle, a step of the cold start strategy is executed and the termination criteria are checked. These two functions are called until either cold start strategy 300 has been successfully completed or an environmental condition has been violated.In the event of an abort 200 due to environmental conditions, information is stored in the vehicle memory so that the abort 200 can be taken into account in the next terminal cycle or during the next restart. The transmission is then placed in a state that does not permit any function and can only be reversed by a restart. Otherwise, if the cold start is successfully completed, normal driving operation resumes.

[0022] In Fig. Figure 4 shows the termination criteria and termination 200 in detail. Examples of influencing factors that can lead to termination 200 of the cold start strategy 300 are shown. Among other things, the presence of a driver request, such as driving forward or reverse, or applying the parking brake, are shown in order to possibly terminate the cold start. The transmission status, such as the internal speeds, temperatures, and pressures in the transmission, also determine whether the cold start must be terminated. If, for example, the high pressure falls below a threshold, the previously described pulling of the pistons out of the piston shoes in the hydrostatic drive can occur. A further requirement is that the drive train is not closed during the cold start to ensure that no undesired vehicle movements occur.Another criterion is the engine condition, with engine speed being mentioned as an example. During a cold start, the engine is run through the transmission and if the speed remains outside a tolerance range for a certain period of time, the cold start is aborted. This is particularly crucial for excessive engine speeds, as this can cause damage to the transmission. Abort 200 is executed as soon as a condition is not met. Not every Abort 200 results in a restart or terminal change. Rather, in the case of minor errors, such as the release of the parking brake, only the cold start strategy 300 can be reset to the beginning and the current control can be aborted. In this case, the cold start strategy 300 can be executed again from the beginning immediately after the parking brake is applied without a restart.

[0023] Fig. 4 shows the various phases or method steps 311 to 318 of the cold start strategy 300 that are called up. Depending on the starting temperature, different method steps 311 to 318 are initiated. The length of the respective method steps 311 to 318 also depends on the starting temperature of the hydraulic fluid. Thus, an optimal duration of the cold start strategy 300 can be set for all temperatures. The cold start strategy 300 comprises the first method step 311 for warming up by the transmission oil pump, the second method step 312 for system pressure control, the third method step 313 for controlling the hydrostatic drive, the fourth method step 314 for warming up, the fifth method step 315 for pulsing the range clutches, the sixth method step 316 for closing the reversing clutch, the seventh method step 317 for waiting for limited driving, and the eighth method step 318 for limited driving.

[0024] The previously described sequence of process steps 311 to 318 is not mandatory and can vary depending on the boundary conditions. All functions executed during the cold start strategy 300 as part of process steps 311 to 317 result in an open drivetrain. This means that the vehicle cannot be moved due to the control. The monitoring ensures a stationary power output at all times and opens the drivetrain immediately as soon as the power output starts moving.

[0025] In Fig. 5 is the first process step 311 for heating the hydraulic fluid by the transmission oil pump connected to the drive based on the engine target speed n mot_soll The warming function of the transmission oil pump, which is directly coupled to the drive and thus dependent on the engine speed, is explained in Fig. 5. First, the required engine speed is increased to a low engine speed 311b using gradient 311a. A low engine speed is intentionally requested initially to avoid cavitation on the transmission oil pump and thus operate the transmission oil pump gently. After a predetermined period of time, which leads to heating of the oil, the target engine speed is increased again using predetermined gradient 311a to a higher engine speed 311c in order to introduce more power loss into the system. This speed is again maintained until the next function or process step is continued.

[0026] Fig. 6 illustrates a second method step 312 for checking the system pressure p HD and the hydraulic fluid temperature in the sump C sumpf . For this purpose, the course of the system pressure p HD and the hydraulic fluid temperature in the sump C sumpfover time t. The system pressure control is intended to ensure that the system pressure p HD of the transmission is stable and sufficiently high. For this purpose, the currently measured pressure 312a at the two measuring points is compared with a threshold value 312b. The pressure must remain above the threshold value 312b for a certain period of time to terminate the function. Furthermore, the currently measured temperature 312c is compared with a threshold value 312d. Only when the temperature is above this threshold value 312d and the pressure remains above the threshold value 312b for a certain period of time does the next process step proceed.

[0027] In Fig. 7 shows the third method step 313 for adjusting the hydrostatic drive. In this method step 313, the hydrostatic drive is pivoted to obtain a first flow through the position control valve. For this purpose, Fig. 7 the control current I PRVof the position control valve over time. In the third method step 313, the valve is controlled by means of pulses or control pulses, whereby the control pulse is set as a function of the starting temperature of the hydraulic fluid with respect to the gradient 313a, the upper value 313b, the lower value 313c, and the number of control pulses 313d. The setting is dependent on the starting temperature. In this method step 313, the two reversing clutches KW1, KW2 are open, provided an upstream reversing gear is provided. This prevents acceleration of the axial piston machine.

[0028] In Fig. Figure 8 shows a fourth method step 314 of the cold start strategy 300 for controlling at least one shifting element of the transmission. For this purpose, the electrical control current I KW the reversing clutches, the control current I PRV of the position control valve, the speed n KW_sekthe reversing clutch KW1, KW2 on the secondary side, the differential speed Δn KR the reversing clutch between primary and secondary sides and the speed n KitC of the hydrostatic drive over time t. In the fourth method step 314, information is read from the vehicle memory regarding which reversing clutch KW1, KW2 was used to initiate the cold start the previous time. This is used to distribute the load on the reversing clutches KW1, KW2, since this information can be used to alternate between the two reversing clutches KW1, KW2. Thus, the reversing clutch KW1, KW2 that was not used as the first clutch KW1, KW2 the previous time is used.

[0029] During the closing phase, the variator of the hydrostatic drive is in a specific position to always safeguard the low pressure in the hydrostatic drive via a high-pressure sensor (undersupply). To close the reversing clutch KW1, KW2, a jump to a defined, small control current is first performed. Starting from this defined value, the control current I is increased via a first, smaller gradient 314a. KWincreased. If, based on the calculated or measured speed in the system, a speed 314f is determined on the secondary side of the reversing clutch to be closed that is greater than the threshold value 314g, then from this point onwards the current at the reversing clutch is increased with a second, higher gradient 314b. This means that the reversing clutch does not slip as long as if only the first, smaller gradient 314a were used, thus protecting the reversing clutches KW1 and KW2. After the differential speed 314i between the primary and secondary sides of the reversing clutch has been reduced to such an extent that the differential speed 314i is below the threshold value 314h, the reversing clutch KW1 is completely closed and supplied with the control current 314c. After a predetermined period of time, the control current 314d of the position control valve of the hydrostatic drive is set above the response threshold.Thus, the hydrostat begins to swivel out when the corresponding response threshold is exceeded. This causes the hydrostat to move, thus heating the components of the hydrostatic drive. To keep the system moving, a type of sawtooth function is performed in the partially swiveled range. This causes the hydrostat to constantly swivel back and forth. After a predetermined period of time, the hydrostat is swiveled back, or the control of the hydrostatic drive is terminated. However, this swiveling back only takes until the speed of the hydrostatic drive n is reached. KitCor 314k, a speed of zero is detected. This new current value 314e is thus used as the new zero position for the hydrostat during the cold start. After the hydrostat has pivoted back, a predetermined period of time is waited until the reversing clutch KW1 is opened. The previously described method step 314 can now be repeated for the second reversing clutch KW2, in order to subsequently continue with the next method step.

[0030] In Fig. 9 is a fifth method step 315 of the cold start strategy 300 for sequentially pulsing range clutches of a range group connected downstream of the transmission based on a diagram with the course of the control current I KBfor actuating the range clutches. In the fifth method step 315, the range clutches are pulsed sequentially one after the other. This means that first, the first range clutch is pulsed several times, and then the second range clutch is also pulsed. The individual control pulses KB1, KB2 always consist of a first ramp 315a to the final current value 315b and a second ramp to the quiescent current value 315c. The current value is held both from the top and bottom for a period of time. After all range clutches have been run through, the next method step can begin.

[0031] In Fig. 10 shows a sixth method step 316 for closing the reversing clutches KW1, KW2. The sixth method step 316 follows a similar procedure to the fourth method step 314. First, the first reversing clutch KW1 is set to a pressure 316a optimized for cold starts and held at this pressure until the speed on the secondary side of the reversing clutch KW1 is above a speed threshold 316e. The control current is then increased via a predetermined gradient 316b until the differential speed between the primary side and secondary side of the reversing clutch KW1 is less than the threshold 316f. The reversing clutch HW1 is then subjected to the control pressure 316c to close the reversing clutch HW1. This control current 316c is maintained for a predetermined period of time, and then the reversing clutch KW1 is opened again.After the speed on the secondary side of reversing clutch KW1 has been reduced and an additional waiting period has elapsed, the second reversing clutch KW2 is closed using the same control method. This is performed multiple times for both reversing clutches KW1, KW2, which is referred to as control phase 316d of reversing clutches KW1, KW2, and then continues with, for example, the seventh method step 317 for waiting for limited travel.

[0032] Fig. Figure 11 shows the seventh method step 317 for maintaining the hydraulic fluid temperature and waiting for limited driving. Starting with this method step 317, the driver has the option of transitioning to limited driving by disengaging the parking brake. The transition is signaled to the driver by lowering the engine speed and thus acoustically, which signifies the end of the active phase of the cold-start strategy 300. The seventh method step 317 is designed to prevent the transmission from cooling down if the driver does not want to drive off immediately after the cold-start procedure.

[0033] For this purpose, a selected closing procedure of the reversing clutch KW1, KW2, which is Fig.11, one of the two reversing clutches KW1, KW2 is closed. In the seventh method step 17, a defined control current 317a is applied to the first reversing clutch KW1. The defined current value 317a is increased via a predetermined gradient 317b if the speed threshold value 317d on the secondary side is exceeded. After the differential speed has decreased below a threshold value 317e, the control current is increased to the value 317c to close the first reversing clutch KW1. After a predetermined period of time or following a previous intervention by the driver, the first reversing clutch KW1 is opened again and the second reversing clutch KW2 is controlled accordingly until a termination criterion 317f is present. This can occur, for example, if the parking brake is disengaged. The reversing clutch KW1, KW2 is then opened and branched after limited driving.

[0034] The eighth method step 318 of the cold start strategy 300 is used for limited driving. In this method step 318, it is possible to maintain a closed drivetrain. During this method step 318, various restrictions can be set. Among other things, it is possible to limit the maximum output speed, limit the dynamics due to the still cold and thus sluggish transmission, or prohibit reversing. An abort 200 of the cold start strategy 300 is stored in the EEPROM memory, and the transmission control unit is then shut down if conditions for abort 200 are present. If the cold start strategy 300 has been successfully completed, the driver is permitted unlimited driving.

[0035] Preferably, the method described above can be carried out in a hydrostatic-mechanical power-split transmission. Reference symbol 100 Start 200 demolition 300 Cold start strategy 400 End EEPROM vehicle memory n mot_soll Target engine speed KW1 first reversing coupling KW2 second reversing clutch 311 first procedural step 311a Gradient 311b predetermined low engine speed 311c predetermined higher engine speed P HD System pressure C sumpf Hydraulic fluid temperature in the sump 312 second procedural step 312a currently measured system pressure 312b Threshold value of the system pressure 312c currently measured hydraulic fluid temperature in the sump 312d Threshold value of the hydraulic fluid temperature 313 third procedural step I PRV Control current of the position control valve 313a Gradient 313b upper pulse value 313c lower pulse value 313d Number of control pulses 314 fourth procedural step I KW Control current of the reversing clutch Δn KR Differential speed at the reversing clutch n KW_sek Speed ​​on the secondary side of the reversing clutch n KitC Speed ​​of the hydrostatic drive 314a first smaller gradient 314b second major gradient 314c Control current for closing the reversing clutch 314d Control current of the position control valve 314e Control current value as new zero position for the hydrostat 314f Speed ​​on the secondary side 314g speed threshold on the secondary side 314h Differential speed threshold 314i differential speed 314k Speed ​​of the hydrostatic drive 315 fifth procedural step I KB Control current for operating the range clutches 315 fifth procedural step KB1 Control pulse first range coupling KB2 Control pulse second range coupling 315a first ramp to the current final value 315b final current value 315c quiescent current value 316 sixth procedural step 316a cold start optimized control pressure of the reversing clutch 316b Gradient 316c Control pressure for closing the reversing clutch 316d Control phase of the reversing clutches 316e Speed ​​threshold on the secondary side 316f Differential speed threshold Δ KW Differential speed between primary and secondary side n KW_sek Speed ​​on the secondary side 317 seventh procedural step 317a defined control current of the reversing clutch 317b predetermined gradient 317c Control current for closing the reversing clutch 317d Speed ​​threshold on the secondary side 317e Threshold value of the differential speed 317f Existence of a termination criterion 318 eighth procedural step t time

Claims

[1] Method for carrying out a cold start strategy in a vehicle with a transmission with at least one hydrostatic drive for warming up hydraulic fluid, characterized by that when the vehicle is started (100) it is checked whether conditions of the cold start strategy (300) exist, wherein in order to check the conditions of the cold start strategy (300) information about previous cold start strategies (300) and aborts (200) of the cold start strategy is retrieved from a vehicle memory (EEPROM), that after the start of the cold start strategy conditions for aborting (200) the cold start strategy are checked, that an abort (200) of the cold start strategy (300) is stored in the vehicle memory (EEPROM) and then a transmission control unit is shut down if conditions for aborting (200) exist, and that unlimited driving is carried out if the cold start strategy (300) has been successfully completed. [2] Method according to one of the preceding claims, characterized by that as conditions for termination (200) at least the presence of a driver request, the transmission state and the engine state are checked. [3] Method according to one of the preceding claims, characterized by that in the cold start strategy (300) several process steps (311, 312, 313, 314, 315, 316, 317, 318) are carried out, wherein the order of the process steps (311, 312, 313, 314, 315, 316, 317, 318) and the duration of the process steps are changed depending on the determined starting temperature of the hydraulic medium. [4] Method according to claim 3, characterized bythat in the cold start strategy (300) a first method step (311) for warming up the hydraulic medium is carried out by a transmission oil pump connected to the drive, in which an engine speed is increased via a predetermined gradient (311a) to a first predetermined engine speed (311b) and that after a predetermined period of time the first predetermined engine speed (311b) is increased via the predetermined gradient (311a) to a higher target engine speed (311c) in order to increase the power loss. [5] Method according to claim 3 or 4, characterized by that in the cold start strategy (300) a second method step (312) for checking the system pressure (p HD ) of the transmission and a hydraulic fluid temperature (C sumpf) is carried out in a sump of the transmission, in which the currently measured system pressure (312a) is compared at several measuring points with a system pressure threshold value (312b), in which the currently measured hydraulic fluid temperature in the sump (312c) is compared with a hydraulic fluid temperature threshold value (312d), and in which the method step (312) is ended when the currently measured system pressure (312a) is above the threshold value (312b) for a predetermined period of time at the measuring points and the measured hydraulic fluid temperature (312c) is above the threshold value (312d) for a certain period of time. [6] Method according to one of claims 3 to 5, characterized bythat in the cold start strategy (300) a third method step (313) is carried out for adjusting the hydrostatic drive, in which a position control valve is controlled by means of control current pulses, wherein control current pulses are set as a function of the starting temperature of the hydraulic medium with respect to an increasing gradient (313a), an upper value (313b), a lower value (313c) and a number of control current pulses (313d). [7] Method according to one of claims 3 to 6, characterized by that in the cold start strategy (300) a fourth method step (314) is carried out for controlling at least one switching element of the transmission. [8] Method according to claim 7, characterized bythat in a reversing gear connected upstream of the transmission as a switching element, a first reversing clutch (KW1) and a second reversing clutch (KW2) are alternately controlled, wherein information is read from the vehicle memory (EEPROM) as to which reversing clutch (KW1, KW2) was started with in the previous cold start strategy (300) in order to start with the other reversing clutch (KW1, KW2) in the current cold start strategy (300). [9] Method according to claim 8, characterized by that to close the first reversing clutch (KW1) the electrical control current (I KW ) is increased to a defined value, that starting from this defined value, the control current (I KW ) is increased so that the control current (I KW) is increased via a second larger gradient (314b) when the speed (314f) on the secondary side of the reversing clutch (KW1) is greater than a speed threshold value (314g), that the first reversing clutch (KW1) is supplied with a predetermined control current (314c) to close the reversing clutch (KW1) after the difference in speed (314i) between the primary and secondary sides has been reduced, that after a predetermined period of time the control current (314d) of the position control valve of the hydrostatic drive is set above a response threshold, whereby a pivoting of the hydrostatic drive takes place, that after the expiry of the set period of time the control of the hydrostatic drive is ended, and that after a further predetermined period of time the first reversing clutch (KW1) is opened again. [10] Method according to one of claims 8 or 9, characterized bythat in the cold start strategy (300) a fifth method step (315) for sequentially pulsing range clutches of a range group connected downstream of the transmission. [11] Method according to claim 10, characterized by that the first range clutch is pulsed and subsequently the second range clutch is pulsed, wherein the individual control pulses (KB1, KB2) in the range clutches are formed from a first ramp (315a) to the final current value (315b) and a second ramp to the quiescent current value (315c). [12] Method according to one of claims 8 to 11, characterized by that in the cold start strategy (300) a sixth method step (316) is carried out to close the reversing clutches (KW1, KW2). [13] Method according to claim 12, characterized by that the first reversing clutch (KW1) is initially set to a control current (316a) optimized for cold starting and is held until the speed (n KW_sek) on the secondary side of the reversing clutch (KW1) is above a speed threshold value (316e) on the secondary side, that the control current is then increased via a gradient (316b) until the differential speed (Δ KW ) between the primary side and the secondary side of the reversing clutch (KW1) is smaller than the threshold value (316f), that the reversing clutch (KW1) is supplied with the control current (316c) to close the reversing clutch (KW1) when the differential speed (Δ KM ) has reached or fallen below the threshold value (316f), that this control current (316c) is maintained for a predetermined period of time, that the reversing clutch (KW1) is subsequently opened again, and that the second reversing clutch (KW2) is controlled via the same method step (316) when a further predetermined period of time has ended and the speed (n KW_sek ) on the secondary side of the first reversing clutch (KW1) is removed. [14] Method according to one of claims 8 to 13, characterized by that in the cold start strategy (300) a seventh method step (317) is carried out to maintain the hydraulic fluid temperature and to wait for limited driving. [15] Method according to claim 14, characterized by that first a defined control current (317a) is applied to the first reversing clutch (KW1), that the defined control current (317a) is increased via a predetermined gradient (317b) when the speed threshold value (317d) on the secondary side is exceeded, that after reducing the difference in speed (Δ KW ) below a threshold value (317e) the control current (I KW ) is raised to the value (317c) for closing the first reversing clutch (KW1), and that after a predetermined period of time the first reversing clutch (KW1) is opened again and the second reversing clutch (KW2) is controlled accordingly until a termination criterion (317f) is present. [16] Method according to one of claims 3 to 15, characterized by that in the cold start strategy (300) an eighth method step (318) for limited driving is carried out, in which the drive train is closed for limited driving, whereby the output speed is limited and / or the dynamics of the transmission are limited and / or reversals of the transmission are prevented. [17] Method according to one of the preceding claims, characterized by that the procedure is carried out on a hydrostatic-mechanical power-split transmission.

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