METHOD FOR CONTROLLING A HYDROSTATIC DRIVE

Abstract

Method for controlling a hydrostatic drive (1), wherein the hydrostatic drive is provided with a first hydraulic machine (4) with adjustable displacement volume and with a second hydraulic machine (6) and a third hydraulic machine (8), each with adjustable displacement volume, wherein the first hydraulic machine can be coupled or connected to a drive machine, wherein the hydraulic fluid coming from the first hydraulic machine can be conveyed to the second and the third hydraulic machines (6, 8), which are arranged parallel to each other, wherein the second and the third hydraulic machines (6, 8) can be connected or connected to at least one driven wheel (12) or a driven chain or axle (14), characterized in that the method comprises the following steps: a. Determining a total target volume flow of the second and third hydraulic machines based on a speed and / or a pressure present in the hydrostatic drive; b. Determining a target volume flow rate for the second and third hydraulic machines based on the total target volume flow rate determined in step a.

Description

TECHNICAL AREA

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

[0002] Hydrostatic drive systems for mobile machinery are known, in which a hydraulic pump and one or more hydraulic motors are connected in a closed hydraulic circuit. The hydraulic pump is driven by an internal combustion engine – e.g., a diesel engine – and the hydraulic motors ultimately drive the mobile machinery – e.g., via a wheel.

[0003] The patent specifications DE 10 2012 002 435 A1, DE 10 2010 052 065 A1, DE102 48 028 B3, DE 10 2015 223 122 A1, DE 10 2019 120 973 A1, DE 10 2008 002 384 A, DE 10 2012 221 943 A1 and DE 42 13 799 C1 are known from the prior art.

[0004] The hydraulic pump and hydraulic motors of such drive systems often have adjustable delivery volumes. This allows, for example, the flow rate delivered by the hydraulic pump in a closed circuit to be changed while the combustion engine is running at a constant speed, thereby adjusting the output speed of the hydraulic motors or the wheels – and thus the driving speed of the mobile machine.

[0005] Hydrostatic drive systems have many applications, for example in agriculture, where the machine needs to perform both a driving and a working function. The forage harvester is one example. It is an agricultural implement used to pick up, chop, and load crops such as grass, alfalfa, or corn, particularly for the production of silage or whole-crop silage.

[0006] To increase the transmission range of a drive system, hydrostatic transmissions with at least two hydraulically operated hydraulic motors in parallel are known. Their output shaft power can be summed via a summing gearbox within the hydrostatic transmission and transmitted, for example, to a vehicle axle. Thus, at low speeds, both hydraulic motors operate in parallel, allowing for high tractive effort. Given a fixed delivery rate of the hydraulic pump and considering that reducing the displacement volume of the hydraulic motors leads to a decrease in efficiency, the achievable driving speed with two motors is limited.

[0007] To achieve a higher driving speed range, one of the hydraulic motors can be adjusted to zero displacement and disconnected from the output via a clutch. This directs the entire flow rate of the hydraulic pump through the remaining, usually smaller, hydraulic motor, enabling higher rotational speeds and thus higher driving speeds.

[0008] The control systems of the previously known solutions require separate control logic for the hydraulic motors and, consequently, extensive adaptation of core software used to control the hydraulic motor of a hydraulic transmission with a hydraulic pump and a single hydraulic motor, which is very time-consuming. In particular, the previously known solutions require variation in the control of the core software, which increases the effort required for the integration and application of additional functions (speed limiting, pressure regulator, overspeed protection, etc.).

[0009] In contrast, the invention is based on the objective of finding a simpler solution to enable the control of the at least two hydraulic motors, in particular to minimally adapt an existing known method to enable this control, so that an existing basic architecture can be used without modifying it. SUMMARY

[0010] According to one embodiment of the present invention, a method for controlling a hydrostatic drive (1) is described, wherein the hydrostatic drive is provided with a first hydraulic machine (4) with adjustable displacement volume and with a second hydraulic machine (6) and a third hydraulic machine (8), each with adjustable displacement volume, wherein the first hydraulic machine can be coupled or connected to a drive machine, wherein the hydraulic fluid coming from the first hydraulic machine can be conveyed to the second and third hydraulic machines (6, 8), which are arranged parallel to each other, and wherein the second and third hydraulic machines (6, 8) can be connected or connected to at least one driven wheel (12) or a driven chain or axle (14). characterized by the fact that the procedure comprises the following steps: a. Determining a total target volume flow of the second and third hydraulic machines based on a speed and / or a pressure present in the hydrostatic drive; b. Determining a target volume flow rate for the second and third hydraulic machines based on the total target volume flow rate determined in step a.

[0011] Since the first, second, and third hydraulic machines can theoretically be used as both hydraulic motors and hydraulic pumps, they are generically referred to as hydraulic machines in the claims. Furthermore, for the aforementioned reason, the claims always refer to a volumetric flow rate (and not specifically, for example, to the displacement volume of a hydraulic motor). This invention is particularly advantageous because this solution makes it possible to use an existing method to determine the total target volumetric flow rate. The existing method is the highly developed and widely used control system for a hydraulic motor in a hydraulic transmission with a hydraulic pump and a single hydraulic motor that is in a closed circuit with the hydraulic pump.This means that the present invention makes it possible to use an existing method in which an additional component has been added for determining the target volume flow of the second and third hydraulic machines. BRIEF DESCRIPTION OF THE FIGURES

[0012] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures: Fig. Figure 1 shows a hydraulic circuit diagram of a hydrostatic drive according to the state of the art. Fig. Figure 2 shows the scaling function f in a first driving mode, wherein the first driving mode is a power mode, according to an embodiment of the present invention; Fig. Figure 3 shows the scaling function f in a second driving mode, wherein the second driving mode is an Eco mode, according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, 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.

[0014] Further modifications and variations of the present invention are obvious to a person skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims.

[0015] According to Fig. The system comprises a drive unit 1, a hydrostatic transmission 2 with a hydraulic machine 4 operating as a hydraulic pump during traction operation of the drive unit 1, and two hydraulic machines 6 and 8 operating as hydraulic motors during said traction operation. Both hydraulic motors 6 and 8 are fluidically connected to the hydraulic pump 4 via working lines 10 and 12 on one side and 14 and 16 on the other, in a closed hydraulic circuit. The hydraulic machines 4, 6, and 8 have adjustable displacement volumes and are each designed as axial piston machines in either a swashplate or swashplate configuration. The maximum flow rate (displacement volume) of the first hydraulic motor 6 is typically significantly larger than that of the second hydraulic motor 6. The ratio between the maximum flow rates of the two hydraulic motors is between 1.5 and 2.5.

[0016] The hydraulic pump 4 is connected via its drive shaft 18 to a drive motor 20 designed as a diesel engine. One of the two hydraulic motors 6, 8 has a first drive shaft 22, and the second hydraulic motor 8 has a second drive shaft 24. A summing gearbox 26 with two input shafts 28 and 30 is connected downstream of the hydrostatic transmission 2 as a mechanical transmission. The first input shaft 28 is rotationally fixed to the first drive shaft 22, and the second input shaft 30 is rotationally fixed to the second drive shaft 24. An output shaft 32 of the summing gearbox 26 is rotationally fixed to a differential 34 of a drive axle 36.

[0017] The summing transmission 26 comprises a clutch 38 designed as a multi-plate clutch. This clutch has a first clutch section 40, which is rotationally fixed to the first input shaft 28. It also has a second clutch section 42, which is rotationally fixed to the second input shaft 30 of the summing transmission 26 via a gear arrangement 44 (shown only schematically). By actuating the clutch 38, which engages the second clutch section 42, the two input shafts 28 and 30, and thus the two output shafts 22 and 24, can be rotationally fixed to each other.

[0018] For actuating the clutch 38, an actuating element 46 designed as a hydraulic cylinder is provided. Its piston 48 is coupled to the second clutch section 42 via a piston rod in a tensile and shear-resistant manner. The hydraulic cylinder 46 has a piston chamber in which a compression spring 50 is arranged. The piston chamber is permanently connected to a tank T via a tank line. On the piston rod side, the hydraulic cylinder 46 has an annular chamber 52, which is connected via a control pressure line 54 to a port S of a control device 56 designed as a pressure regulating valve. The latter has a pressure port P, which is connected via a pressure line 58 to a feed pump 61, which, together with the hydraulic pump 4, is driven by the drive shaft 18. The feed pump 61 draws hydraulic fluid from the tank T. Furthermore, the pressure regulating valve 56 has a tank port T, which is connected to the tank T.

[0019] The pressure regulating valve 56 is continuously adjustable and has two end positions a and b. In the first end position a, in which the valve body is pre-loaded by a spring 60, the pressure port P is connected to the control pressure port S, and port T is closed off from port S. In the second end position b, the pressure regulating valve 56, or more precisely its valve body, can be actuated by an electromagnet 62. When the electromagnet is energized, and provided the second position b is fully engaged, the control pressure port S is connected to the tank port T, and the pressure port P is closed off. In the first end position a, the annular space 52 is exclusively filled with hydraulic fluid, whereas in the second end position b, hydraulic fluid is exclusively discharged from the annular space 52.Between the two end positions a and b, control positions of the valve body are possible in which the ports P, S and T are in contact with each other via the respective pressure medium.

[0020] To return the control pressure to be regulated at the control pressure port S to the annular space 52, the annular space 52 is fluidically connected via a control line or a control channel to a control surface of the valve body of the pressure regulating valve 56, which acts in concert with the spring 60.

[0021] The mechanical transmission 26 further comprises a first speed detection unit 64, via which the speed of the first input shaft 28, and thus of the first clutch section 40 and the first output shaft 22, can be detected. Via a second speed detection unit 66 of the mechanical transmission 26, the speed of the second clutch section 42, and thus indirectly, given the gear ratio of the gear arrangement 44, the speed of the second input shaft 30 and the second output shaft 24, can be detected.

[0022] The hydraulic pump 4 is assigned a control unit 70, which interacts with an adjusting device 72 to adjust the displacement volume of the hydraulic pump 4. The first hydraulic motor 6 and the second hydraulic motor 8 have a control unit 74 and 78 respectively, and an adjusting device 76 and 80 respectively.

[0023] The drive machine 20, the control devices 70, 74 and 78, the electromagnet 62 and the speed detection units 64, 66 are each connected to the control unit 68 via a signal line.

[0024] The following sections describe a method for controlling the two hydraulic motors according to an embodiment of the present invention.

[0025] In a first step, a total target volume flow (Vg) is determined. eff_tThe flow rate of the first hydraulic motor 6 (second hydraulic machine) and the second hydraulic motor 8 (third hydraulic machine) is determined based on a speed and / or a pressure present in the hydrostatic drive. This means that the two hydraulic motors 6 and 8 are considered as a single hydraulic motor for determining the target flow rate (or target displacement volume). For determining the total target flow rate, an actual pressure at the hydraulic pump 4 is taken into account, for example. Alternatively or additionally, a speed, such as a driving speed or rotational speed, is considered.

[0026] This solution makes it possible to use an existing method to determine the target volume flow rate (Vg). eff_t) to determine. The existing method is the highly developed and widely used control of a hydraulic motor in a hydraulic transmission with a hydraulic pump and a single hydraulic motor that is in a closed circuit with the hydraulic pump. Since this method is already known, it will not be described in detail here.

[0027] From the determined total target volume flow rate, the target volume flows of the two hydraulic motors must then be determined. For this reason, a volume flow balance equation is written (see equation 90 below) that combines the total target volume flow rate with the volume flows of the first and second hydraulic motors. Vgeff_t=Vgperm_t+itp*Vgtemp_t where Vg eff_t the total target volume flow rate, Vg perm_t the target volume flow of the second hydraulic motor 8, Vg temp_t the target volume flow of the first hydraulic motor 6 and i tpThe mechanical transmission between the second and first hydraulic motors is represented. As can be seen from equation 90, there are two quantities that need to be determined. For this reason, the inventor found a solution to determine one of the two unknown quantities and then, in a further step, to determine the other quantity using equation 90.

[0028] First, a maximum available volume flow rate (Vg) is determined. eff_max ) determined, which can be provided by means of the first and second hydraulic motors 6, 8. Vgeff_max=Vgperm_max+itp*Vgtemp_max where Vg perm_max the maximum volume flow of the second hydraulic motor 8, Vg temp_max the maximum volume flow of the second hydraulic motor 8 and i tp The equation represents the mechanical transmission between the second and first hydraulic motors. As can be seen from the equation, the maximum available volume flow (Vg) can be eff_max) can be calculated relatively easily from known quantities and can be stored and does not need to be recalculated every time.

[0029] In a further step, the aforementioned maximum available volume flow rate Vg is eff_max with the determined total target volume flow Vg eff_t combined to determine a normalized target volume flow rate a, which, as explained in the course of the description, is used to determine a scaling factor f. a=Vgeff_t / Vgeff_max

[0030] The normalized volume flow rate a essentially describes how much volume flow was requested compared to the maximum available volume flow rate. The scaling factor f is then determined based on this normalized volume flow rate.

[0031] The scaling factor f is determined using a scaling function, where the scaling function is based on the combination of the stated maximum available volume flow Vg. eff_max and the determined total target volume flow rate Vg eff_t a value for the scaling factor was determined.

[0032] In order to determine the scaling function to be used for determining the scaling factor f, the method preferably also captures a driving mode, wherein, depending on the captured driving mode, a scaling function is selected from a plurality of scaling functions in order to determine the scaling factor f.

[0033] Once the scaling factor f has been determined, it is combined with the maximum available flow rate of the second or third hydraulic machine to determine the target flow rate of the second or third hydraulic machine, respectively. In this embodiment, the scaling factor f is combined with the maximum flow rate of the second hydraulic motor 8 as follows: Vgperm_t=Vgperm_max∗f(a)

[0034] This solution makes it possible to determine the target volume flow rate of the second hydraulic motor 8. However, it is clear to those skilled in the art that, alternatively, the scaling factor can be applied to the maximum volume flow rate of the first hydraulic motor.

[0035] Since the target flow rate of the second hydraulic motor is now known, this information can be used to determine the target flow rate of the first hydraulic motor. Equation 90 is rewritten as follows: Vgtemp_t=(Vgeff_t−Vgperm_t) / itp

[0036] Equation 94 then makes it possible to determine the target volume flow rate of the first hydraulic motor. Based on the determined target volume flows, current signals IHM1 and IHM2 are then sent to the two hydraulic motors by the control unit 68 in order to control the respective swivel angle of the hydraulic motor.

[0037] In the Fig. 2 and Fig. Figure 3 shows two different scaling functions that can be used to determine the scaling value.

[0038] Fig. Figure 2 shows the scaling function f in a first driving mode, where the first driving mode is a power mode. In the power mode, a target volume flow of the second or third hydraulic machine is kept essentially constant, and the volume flow control is performed with the other hydraulic machine. In the example shown, the second hydraulic motor is kept essentially constant, and the volume flow control is performed with the first hydraulic motor 6. To achieve this goal, as in Fig. As shown in Figure 2, an essentially constant function is selected. This operating mode is known as "sequential adjustment": the second motor (permanent motor) is pivoted to maximum flow rate and remains in this position. To execute the active control, the first hydraulic motor 6 is then pivoted.

[0039] Fig. Figure 3 shows the scaling function f in a second driving mode, where the second driving mode is an Eco mode. In Eco mode, the target flow rate of both the second and third hydraulic motors is varied to perform flow rate control. This driving mode is known as "parallel adjustment": the second motor (permanent motor) and the first motor (temporary motor) are gradually varied (depending on the normalized flow rate a, more or less flow rate is requested from the first and second hydraulic motors).

[0040] The machine can still have a control element (not in) Fig. 1 shown) comprising, wherein the control element is connected to the control unit 40 via a signal, wherein a command can be sent to the control unit 40 by means of the control element, wherein the command includes whether a power mode or eco mode is desired by the driver.

[0041] When the clutch 38 closes and the hydrostatic drive 1 is simultaneously decelerated by the second hydraulic motor 8, the braking torque can increase enormously, as the first hydraulic motor 6 suddenly also contributes to the deceleration of the hydrostatic drive 1. In particular, when the driving speed decreases below a certain threshold (e.g., 5 km / h), the control unit 68 will usually automatically send a signal I. V to send to the electromagnet 62 to enable the clutch 38 to close. However, this will cause a massive increase in the braking torque. For this reason, it is advantageous if, in such an operating condition, a reduction factor R is applied to the target flow rate of the first hydraulic motor 6, which is configured to reduce the target flow rate of the first hydraulic motor 6 when the clutch 38 closes and simultaneously when the hydrostatic drive decelerates.

[0042] The reduction factor R is calculated from a time-dependent function, with the time starting when the clutch 38 closes. The influence of the reduction factor on the target flow rate of the first hydraulic motor 6 decreases over time. This is a type of "ramp": to reduce a sudden change in the deceleration torque when the clutch 38 closes, a ramp is used to mitigate this effect. In particular, the following formula is preferably used to correct the target flow rate of the second hydraulic motor. Vgtemp_tc=(Vgtemp_t*R(t)) where Vg temp_tc the corrected target volume flow of the second hydraulic motor 8, Vg temp_t The already calculated target volume flow of the second hydraulic motor 8 and R(t) represent the reduction factor, which is time-dependent.

[0043] The described procedure is stored in the storage unit and is executed by the control unit 68.

[0044] The described method can be used in various types of machinery. Essentially, it can be used in all machinery that has a hydrostatic drive and a controllable drive motor (such as a diesel engine). Examples of applications include forage harvesters, combine harvesters, snow blowers, and road milling machines.

[0045] While the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to implement various modifications, variations and improvements of the present invention in light of the teaching described above and within the scope of the attached claims without deviating from the scope of protection of the invention.

[0046] Although the present invention has always been described in relation to two hydraulic motors, it is clear to those skilled in the art that this invention can also be applied to three or more hydraulic motors by making small adjustments (e.g., using two different scaling functions for two different hydraulic motors).

[0047] Furthermore, the areas in which experts are likely to be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention.

[0048] Accordingly, the invention should not be limited by the specific illustrative embodiments, but only by the scope of protection of the attached claims.

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