METHOD FOR CONTROLLING A DRIVE SYSTEM

Abstract

The present invention relates to a method for controlling a travel drive (1) of a mobile work machine, wherein the travel drive comprises an electric drive motor (4) and a transmission arrangement (3), wherein the transmission arrangement (3) comprises a manual transmission (6) which has at least two gear stages (46, 48), wherein the manual transmission can be or is coupled to the drive motor (4) via an input shaft (18) so that a torque can be transmitted, and wherein the manual transmission can be or is connected to an output of the mobile work machine via an output shaft (22), characterized in that the method comprises the following steps: a. receiving a command to shift the manual transmission from a first to a second gear ratio; b. Recording a value that is a current travel speed of the mobile work machine or that depends on the travel speed; c. Calculating a gradient of the quantity detected in step b.; d. Calculating a speed deviation based on the gradient calculated in step c.; e. Determining a target speed of the electric drive motor (4) on the basis of the speed deviation calculated in step b.; f. Shifting the manual transmission from the first to the second gear stage, taking into account the target speed determined in step e.

Description

TECHNICAL AREA

[0001] The invention relates to a method for controlling a drive of a work machine. Furthermore, this invention relates to a control unit, a work machine comprising the control unit, and a computer program. STATE OF THE ART

[0002] Speed synchronization plays a central role in the development of manual transmissions, especially those that operate without friction clutches and utilize active synchronization, especially in electric drive systems. The gearshift process requires precise coordination of speeds to ensure a smooth transition between gears.

[0003] The process involves several crucial steps.

[0004] First, the speed at the transmission output is continuously measured, which serves as the basis for the entire synchronization process. These measurements are essential for obtaining real-time data on the current speed at the transmission output.

[0005] The measured speed at the transmission output is then precisely converted into the target speed of the transmission input in the desired gear. This conversion is crucial because it determines the speed required for a smooth transition to the desired gear.

[0006] This calculated target speed is then transmitted to the drive motor. The motor receives the instruction to regulate the speed accordingly to achieve the required speed for the desired gear.

[0007] The gear is only engaged when the measured speed difference between the drive and transmission output reaches the specified target range. This ensures that the gear is only engaged when the speeds are synchronized accordingly, ensuring smooth shifting.

[0008] These precise and highly regulated processes enable efficient power transmission and help minimize wear and damage to the transmission. The use of such synchronized mechanisms not only ensures a comfortable ride but also contributes to the longevity and optimal functionality of the transmission.

[0009] There is often a time lag between measuring the output speed and setting the input speed, which can be problematic in the context of a manual transmission. This problem arises from driving resistances that accelerate or decelerate the vehicle and thus change the output speed.

[0010] During this time window, the speed changes cause the speeds to diverge. This, in turn, causes the differential speed to become larger or smaller than required for a smooth gear shift. This discrepancy presents a challenge when engaging the clutch.

[0011] However, it is possible to at least partially mitigate this problem. One possibility is to compensate for the road resistance-dependent acceleration or braking. This compensation mechanism aims to anticipate and compensate for the changes in output speed caused by road resistance.

[0012] However, it is currently not possible to completely prevent the problem by anticipating such compensation, since the different operating states are very difficult to predict.

[0013] It is therefore an object of the present invention to develop a method which can make it possible to eliminate this discrepancy during clutch engagement and to make it possible to always ensure that the gear shift can be carried out without any problem during speed synchronization. SUMMARY

[0014] According to one embodiment of the present invention, a method for controlling a travel drive (1) of a mobile work machine, wherein the travel drive comprises an electric drive motor (4) and a transmission arrangement (3), wherein the transmission arrangement (3) comprises a manual transmission (6) which has at least two gear stages (46, 48), wherein the manual transmission can be or is coupled to the drive motor (4) via an input shaft (18) so that a torque can be transmitted, and wherein the manual transmission can be or is connected to an output of the mobile work machine via an output shaft (22), characterized in that the method comprises the following steps: a. receiving a command (which may be generated automatically or by a driver) to shift the manual transmission from a first to a second gear stage (it is not relevant to this invention whether the first or second gear stage results in a higher or lower gear ratio); b. Recording a value which is a current travel speed of the mobile work machine or which depends on the travel speed (e.g. a speed of the output shaft, a speed of a wheel, etc.); c. Calculating a gradient of the quantity detected in step b.; d. Calculating a speed deviation based on the gradient calculated in step c.; e. Determining a target speed of the electric drive motor (4) on the basis of the speed deviation calculated in step b.; f. Shifting the manual transmission from the first to the second gear stage, taking into account the target speed determined in step e. (it is not necessary that the speed of the electric drive motor actually reaches the target speed, since it can be decided that certain discrepancies between the target speed and the actual speed are acceptable and, in such cases, the electric drive motor could not be controlled at all or could be controlled until the difference between the target and actual speed is smaller than a predetermined threshold value).

[0015] This compensation automatically compensates for the speed changes caused by road resistance, allowing the speed to be returned to the acceptable target range. This enables smoother clutch engagement, as the speeds of the input and transmission output are synchronized. Steps a. to f. do not need to be performed consecutively. In particular, step a. can be performed after any of steps b. to e.

[0016] These compensation mechanisms are critical to addressing the challenges posed by the time lag between speed measurement and input speed adjustment. They help improve the precision and effectiveness of gear shifting in manual transmissions, particularly in electric drives without friction clutches. SHORT DESCRIPTION OF THE CHARACTERS

[0017] The present invention is described with reference to the accompanying figures, wherein like reference numerals refer to like parts and / or similar parts and / or corresponding parts of the system. Regarding the figures: Fig. 1 shows a circuit diagram of a drive system according to the state of the art, Fig. 2 shows a method for controlling a travel drive of a mobile work machine according to an embodiment of the present invention; DETAILED DESCRIPTION

[0018] The present invention will now be described with reference to specific embodiments as shown in the accompanying figures. Nevertheless, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0019] Further modifications and variations of the present invention will be apparent to those skilled in the art. Thus, the present description encompasses all modifications and / or variations of the present invention, the scope of which is defined by the claims.

[0020] According to Fig. 1, a drive system 1, for example that of a mobile work machine, has a transmission arrangement 3 with a drive unit 2 designed as an electric motor and, in the exemplary embodiment, a two-stage manual transmission 6. A drive shaft 18 of the drive unit is coupled to an input shaft 20 of the manual transmission 6. An output shaft 22 of the manual transmission 6 is coupled to a differential 24 of a two-wheel axle 26 of the drive system 1.

[0021] Furthermore, the transmission arrangement 3 has a control device 28. A shift request device 30, a gear selection device 32, a direction selection device 34, an accelerator pedal 36, a creeper gear selection device 38, a brake pedal 40 and an automatic selection device 42 are signal-connected to the control device 28. All of the aforementioned devices 30 to 42 are signal-connected via a CAN bus.

[0022] The manual transmission 6 has a first gear stage 46 with a small gear ratio and a second gear stage 48 with a larger gear ratio of the speed nA of the output shaft 22 to the speed nE of the input shaft 18.

[0023] Furthermore, the manual transmission 6 has a claw clutch 50, which is designed without a synchronizer ring. An actuator 52 of the claw clutch 50 is rigidly coupled to a piston 54 of an actuating cylinder 56. The latter has two identical pressure fluid chambers 58, 60, separated from the piston 54, which are connected via control lines 62, 64 to an electromagnetically actuated 4 / 3-way switching valve 66.

[0024] The latter has a first switching position 66a, in which the first pressure chamber 58 is connected to a pressure medium line 68 and the second pressure chamber 60 is connected to a tank line 70. In a second switching position 66b, the second pressure medium chamber 60 is connected to the pressure medium line 68 and the first pressure medium chamber 58 is connected to the tank line 70. The first switching position 66a causes the piston 54 to be displaced such that the first gear stage 46 is engaged via the claw clutch 50; the second switching position 66b causes the second gear stage 48 to be engaged via the piston 54 and the claw clutch 50.

[0025] The 4 / 3-way switching valve 66 and the actuating cylinder 56 are combined into a single unit. This unit also has two limit switches 72, 74, which can be used to detect the successful switching of the respective gear stage 46, 48 based on the position of the piston 54. Both limit switches 72, 74 are each connected to the control device 28 via a signal line. The 4 / 3-way switching valve 66 is connected to a pressure source 88 (such as a feed pump) via the pressure medium line 68.

[0026] The transmission assembly 3 is designed such that the manual transmission 6 can be shifted during driving. The shifting or changing of the gear stages 46, 48 can be controlled automatically via the control device 28. For this purpose, the transmission assembly 3 has a speed sensor 76, via which the speed nA of the output shaft 22 can be detected. It also has a speed sensor 78 for detecting the speed nE of the input shaft 18.

[0027] The first gear stage 46 has a gear 80 that is permanently coupled to the input shaft 20 and permanently meshes with an idler gear 82 that can be coupled to the output shaft 22 via the claw clutch 50. Accordingly, the second gear stage 48 has a gear 84 that is permanently coupled to the input shaft 20 and an idler gear 86 that is permanently meshed with the gear and can be coupled to the output shaft 22 via the claw clutch 50.

[0028] As in Fig. 1, the control unit 28 may additionally comprise a plurality of inputs and outputs, each of which may be connected to additional sensors or actuators.

[0029] It is pointed out that Fig. 1 is only one embodiment, and the present invention (as will become clear from the description) may also be applied to other types of manual transmissions. In particular, an electrically operated actuator may be used to actuate a shift fork by moving a spindle or nut. In this case, the movement of the shift fork is achieved by a spindle or nut driven by the electric actuator.

[0030] It will now be discussed with reference to the Fig. 1 and Fig. 2 describes a method for controlling a drive of a mobile work machine, which in Fig. 1 is shown.

[0031] In a first step, a command is received to shift the manual transmission from a first to a second gear stage (in this case, the first gear stage can be identified by the reference numeral 46 and the second gear stage by the reference numeral 48). This method also works, of course, in the case that the first gear stage is 48 and the second gear stage is 46.

[0032] It should be noted that the command can be generated either automatically, e.g. by a control unit requiring atomistic switching between the first and second gear stages, or manually, e.g. by a driver.

[0033] In a second step 100, a variable is detected that is a current travel speed of the mobile work machine or is dependent on the travel speed. This variable can be, for example, a rotational speed nA of the output shaft 22 or of a wheel of the two-wheel axle 26. Preferably, the variable is smoothed by a filter 101 after detection (or measurement) to enable clearer gradient formation.

[0034] In a further step 102, the gradient of the detected variable (output speed) is calculated. In particular, a first-order difference quotient is calculated.

[0035] At the same time, an estimated dead time between measuring and setting is determined 103. This determination can be made either online or offline. This dead time (also known as "latency") describes how much time the drive system will need until the gear stage is actually shifted. The reason for this is that there are certain components that play a role in the shifting process. For example, a certain amount of time is first required until the electromagnetic 4 / 3 switching valve 66 receives the actuation signal. In particular, since according to one embodiment of the present invention the electric drive machine 4 is actuated, a certain time window is required until the actuation actually takes place, since various components play a role here: inverter, electric motor, control unit.

[0036] As an example, a first time window can be considered for the control unit 28 (or transmission control unit). This first time window can be, for example, 10 ms. A second time window can be considered for the inverter control message. This second time window can also be, for example, 10 ms. A third time window can be considered for the inverter communication module. This third time window can also be, for example, 10 ms. In addition, the response time (e.g., 3 ms) of the electric drive unit 4 can also be considered.

[0037] In step 105, the information from steps 102 and 103 is then combined. In particular, a speed deviation is calculated by multiplying the gradient calculated in step 102 and the dead time estimated in step 103.

[0038] In parallel, in step 104, a current speed of the output shaft 22 and a change in the gear ratio through the second gear stage are taken into account to calculate a non-adjusted target speed for the electric drive motor. Essentially, step 104 corresponds to the prior art method.

[0039] The non-adjusted target speed is then combined with the speed deviation in step 106, so that an actual target speed of the electric drive motor 4 is determined based on the speed deviation calculated in step 105 and the non-adjusted target speed calculated in step 104. In particular, the actual target speed is determined from a sum of the non-adjusted target speed and the speed deviation.

[0040] Finally, the manual transmission is shifted from the first to the second gear stage, taking into account the target speed determined in step 106.

[0041] It is not relevant to the invention when all the calculations for determining the target speed are performed. The calculations could, for example, be performed continuously, so that when a shift is required, the target speed has already been determined. Alternatively, it is particularly advantageous to determine the target speed during the shifting process, e.g., during disengagement, so that there is no need to wait for the calculation before shifting.

[0042] According to one embodiment of the present invention, during the aforementioned shifting operation, the electric drive motor 4 is controlled based on the target rotational speed determined in step 106. This means that the electric drive motor 4 is controlled first, and preferably after the electric drive motor 4 has reached the target rotational speed (or when the difference between the target and actual rotational speeds is smaller than a predetermined threshold value), the actual shifting occurs.

[0043] According to a further embodiment of the present invention, it is first checked whether the target speed determined in step 106 differs significantly from the current speed. If the difference is smaller than a predetermined value, the shift is performed without actively controlling the electric drive motor 4.

[0044] The described method is stored in the memory unit and is executed by the control unit 28.

[0045] The described method can be used in various types of work machines. Essentially, the method can be used in all work machines with an electric drive. Examples of applications include an excavator, a telehandler, a forage harvester, a combine harvester, a snow blower, and a road milling machine.

[0046] While the present invention has been described with reference to the embodiments described above, it will be apparent to those skilled in the art that it is possible to make various modifications, variations and improvements to the present invention in light of the above teachings and within the scope of the appended claims without departing from the scope of the invention.

[0047] Furthermore, the areas in which those skilled in the art would be familiar have not been described here in order not to unnecessarily obscure the invention described.

[0048] Accordingly, the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.

Claims

[1] Method for controlling a travel drive (1) of a mobile work machine, wherein the travel drive comprises an electric drive motor (4) and a transmission arrangement (3), wherein the transmission arrangement (3) comprises a manual transmission (6) having at least two gear stages (46, 48), wherein the manual transmission can be coupled or is coupled to the drive motor (4) via an input shaft (18) so that a torque can be transmitted, and wherein the manual transmission can be connected or is connected to an output of the mobile work machine via an output shaft (22), characterized by that the procedure comprises the following steps; a. receiving a command to shift the manual transmission from a first to a second gear ratio; b. Recording a value that is a current travel speed of the mobile work machine or that depends on the travel speed; c. Calculating a gradient of the quantity detected in step b.; d. Calculating a speed deviation based on the gradient calculated in step c.; e. Determining a target speed of the electric drive motor (4) on the basis of the speed deviation calculated in step b.; f. Shifting the manual transmission from the first to the second gear stage, taking into account the target speed determined in step e. [2] Method according to claim 1, wherein between steps e. and f. the electric drive machine is controlled on the basis of the target speed determined in step e. [3] Method according to claim 2, wherein in step f. switching takes place after the electric drive machine (4) has reached the target speed. [4] Method according to one of claims 1 to 3, wherein in step d. the speed deviation is further calculated on the basis of an estimated dead time. [5] The method of claim 4, wherein the estimated dead time is at least one of a time delay caused by a transmission control unit, a time delay caused by an inverter, and / or a response time of the electric drive machine. [6] Method according to one of claims 4 or 5, wherein the speed deviation is calculated by multiplying the gradient calculated in step c. and the estimated dead time. [7] Method according to one of claims 1 to 6, wherein in step e., for determining the target speed of the electric drive motor (4), a current speed of the output shaft (22) and a change in the transmission ratio by the second transmission stage are further taken into account. [8] Method according to one of claims 1 to 7, wherein at least one of steps b. to e. is carried out before step a. [9] Control unit (68) which is arranged to carry out a method according to one of claims 1 to 8. [10] Work machine comprising a travel drive (1), wherein the travel drive comprises an electric drive motor (4) and a transmission arrangement (3), wherein the transmission arrangement (3) comprises a manual transmission (6) having at least two gear stages (46, 48), wherein the manual transmission is or can be coupled to the drive motor (4) via an input shaft (18) so that a torque can be transmitted, and wherein the manual transmission is or can be connected to an output of the mobile work machine via an output shaft (22), wherein the output shaft (22) is or can be connected to at least one wheel to be driven or a chain or axle to be driven, wherein the work machine comprises a control unit according to claim 9. [11] Computer program adapted to execute and / or control the method according to any one of claims 1 to 9. [12] A machine-readable storage medium having stored thereon a computer program according to claim 11.

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