Method and device for filling a hydraulic system with hydraulic fluid

Abstract

The invention relates to a method and a device for accurately filling a hydraulic system (SYS), for example of a motor vehicle, with at least one equalizing tank (AGB) with hydraulic fluid (40), wherein the amount (V KM,Korr ) is filled into a hydraulic system (SYS), wherein the amount (V KM,Korr ) is adjusted according to the total residual air volume (V3) located in the hydraulic system (SYS).

Description

Technical Field

[0001] The invention relates to a method for filling a hydraulic system (hydraulic system), in particular a cooling system of a motor vehicle, and to a device for filling a hydraulic system. The term "hydraulic system" in the sense of the invention comprises a system which is at least partially filled with a liquid or a mixture, comprising containers, pipes, hoses, balancing or storage containers, heat exchangers, coolers, one or more pumps or hydraulic motors, and / or other components. The hydraulic system can be closed during operation or communicate with the ambient air, for example by ventilation of a possible balancing container. The terms "amount" and "volume" are used synonymously hereinafter. Background Art

[0002] The cooling system of a mobile or stationary internal combustion engine is an example of such a hydraulic system. Other examples are vehicles with alternative drive systems (e.g. plug-in hybrid, electric drive, fuel cell), hydraulic steering assistance systems for motor vehicles, working hydraulic systems for construction machinery or agricultural equipment or other stationary equipment. The present invention will be explained below by taking a vehicle cooling system as an example, but the protection scope of the present invention is not limited thereto.

[0003] Vehicles with different hydraulic systems have long been known from the prior art and in particular from the automotive industry. The vehicle is designed, for example, as a truck with an internal combustion engine. Its cooling system usually has at least one cooling circuit through which a coolant, in particular a liquid coolant, can flow. The cooling circuit contains various components of the vehicle (for example, an internal combustion engine, one or more (water-cooled) turbochargers), a retarder and / or one or more coolers / heat exchangers, wherein the above-mentioned or other components can be cooled or temperature-controlled by the coolant. The cooler / heat exchanger ultimately delivers the heat absorbed by the coolant to other heat consumers in the system or to the ambient air. The balancing vessel is used to compensate for volume fluctuations of the coolant in the cooling system. Volume fluctuations result, for example, from temperature fluctuations and / or leaks. This is known to the person skilled in the art and therefore does not require a detailed explanation.

[0004] Before commissioning, each hydraulic system must be filled with a sufficient amount of hydraulic fluid, for example during final installation of the vehicle. A sufficient amount / volume of coolant must be filled into the cooling system. In this case, neither too much nor too little coolant or hydraulic fluid must be added. Furthermore, filling must be quick and process-safe. Difficulties in filling are caused by the formation of overly complex hydraulic systems, so that the hydraulic fluid cannot reach all areas of the hydraulic system when it is fed into the hydraulic system, for example through the filling opening of the balancing tank. Air bubbles of unknown volume remain in the hydraulic system.

[0005] Adequate cooling of the vehicle or its components can only be achieved if there is a sufficient amount of coolant in the cooling system. However, an excessive amount of coolant in the cooling system is to be avoided as well as an insufficient amount, since both an excessive amount and an insufficient amount can lead to damage to the vehicle.

[0006] In the mass production of motor vehicles, for example, it is usually provided that the cooling system is repeatedly filled with coolant. After the initial filling of the cooling system, for example, the powertrain of the vehicle, in particular the internal combustion engine, is started, so that the charged coolant is conveyed in the cooling system or cooling circuit by at least one pump (so-called water pump). Usually, after the initial filling, there is a residual amount of air (bubbles) in the cooling system, which, because the coolant is conveyed through the cooling system to the balancing container, causes the liquid level of the coolant in the balancing container to decrease after the initial filling due to the water pump being put into operation. Then, for example, the person who performs the filling can visually recognize or recognize by a liquid level sensor based on the reduction in amount: the amount of coolant in the cooling system is still too little, and more coolant can be added to the cooling system. This repeated filling is time-consuming and costly, prone to error and requires starting the internal combustion engine and perhaps opening a thermostat and / or a shut-off valve that may be present in the system, for example a heating valve for heating the vehicle interior. The opening of the thermostat can be carried out in this case (if possible) in a forced controlled manner, or it must be established by reaching the thermostat opening temperature in the cooling system in a relatively laborious manner in the production line. A similar situation occurs when filling other hydraulic systems.

[0007] DE 10 2015 008 465 A1 discloses a method for filling a cooling system of a vehicle, in which an attempt is made to use the ideal gas equation to adjust the coolant quantity as a function of the residual volume in a balancing container of the cooling system. Summary of the invention

[0008] The object of the present invention is therefore to provide a method and a device for carrying out the method, by means of which a cooling system and any other hydraulic system of a vehicle can be filled quickly, accurately and simply with coolant or other fluids. The method should be process-safe and automatable.

[0009] This object is achieved by a method according to the invention and by a device according to the invention. The invention also relates to advantageous embodiments with suitable inventive developments.

[0010] According to the invention, this object is achieved by a method for filling a hydraulic system with hydraulic fluid, the method comprising the following method steps:

[0011] - Using a predetermined first volume (V KM,Prefill ) hydraulic fluid to fill the hydraulic system,

[0012] - Pressure-tight closing of the hydraulic system and detection of the pressure (p 2,abs ),

[0013] - Filling or discharging a predetermined second volume (ΔV KM,Mess ) of hydraulic fluid,

[0014] - When filling or discharging the second volume (ΔV KM,Mess ) and then measure the pressure (p 3,abs ),

[0015] -Based on the second volume in use (ΔV KM,Mess )Pressure before and after filling (p 2,abs ;p 3,abs ) calculates the volume (V3) of the total remaining air in the hydraulic system and calculates the volume (V3) and the system's original air volume (Luftvorlage) V L,AGB Calculate the final corrected volume (V KM,korr ),and

[0016] - Replenish or drain the calculated final correction volume (V KM,Korr ) to achieve the final correct fill level of the hydraulic system.

[0017] As an alternative thereto, the object is achieved according to the invention by a method for filling a hydraulic system with hydraulic fluid, the method comprising the following method steps:

[0018] - Using a predetermined first volume (V KM,Prefill ) hydraulic fluid to fill the hydraulic system,

[0019] - Pressure-tightly close the hydraulic system and measure the pressure (p 2,abs ),

[0020] - Filling or draining hydraulic fluid from a closed hydraulic system until a predetermined pressure (p 3,abs ), and the volume of hydraulic fluid filled at this time (ΔV KM,Mess ),

[0021] -Based on the second volume in use (ΔV KM,Mess )Pressure before and after filling (p 2,abs ;p 3,abs ) calculates the volume (V3) of all remaining air in the hydraulic system, and based on this volume (V3) and the original amount of air V predetermined by the structure of the system L,AGB Calculate the final corrected volume (V KM,korr ),and

[0022] - Replenish or drain the calculated final correction volume (V KM,Korr ) to achieve the final correct fill level of the hydraulic system.

[0023] The method according to the invention allows the volume of the total residual air quantity present in the hydraulic system after the initial filling to be determined and, based on this and depending on the original amount of air in the system which is predetermined by the design, the volume of hydraulic fluid which is insufficient or overfilled (=final correction volume) to be determined and introduced into the hydraulic system, or the amount which is possibly present in excess to be discharged. The volume of the total residual air quantity / gas bubbles is determined in a closed hydraulic system in that a defined volume of hydraulic fluid is introduced into the closed system or discharged therefrom and the absolute pressure before and after the introduction or discharge of said amount is precisely determined. The volume of the total residual air quantity (i.e. the gas bubble volume and the air volume) in the balancing container can thus be determined with sufficient accuracy by means of the (ideal) gas equation. Based on this result, the hydraulic system can then be filled with the final correction volume, or the excess amount present in the system can be discharged, thereby ending the filling.

[0024] Returning to the example of a "motor vehicle cooling system", this means that after the cooling system has been filled, the coolant level is above the maximum permissible level in the balancing tank before the internal combustion engine is put into operation for the first time. The level then quickly drops once during system operation to the permanently maximum permissible level after initial commissioning and opening of all thermostats and / or shut-off valves, since gas bubbles are transported from the system into the balancing tank.

[0025] Then, a design-predetermined amount of air also appears in the storage container, for example, the cooling system balancing container. The desired and design-predetermined remaining amount of air in the balancing container is referred to as the original amount of air V. L,AGB The initial amount of air is usually intended to buffer pressure changes caused by temperature changes - in a closed system - by a predetermined amount of compressible gas (here air or steam), thereby achieving a specified pressure increase with the temperature increase of the coolant in the system, or - in the case of an open system - to prepare a specified expansion space by a reserve amount in a reserve container in order to compensate for volume changes in the system before the liquid can flow out through the venting hole.

[0026] The desired air volume may depend, for example, on the maximum system pressure allowed by the configuration and possible minimum pressure requirements of components within the cooling system, and may vary from cooling system to cooling system.

[0027] The method according to the invention is used to determine the amount to be filled even in the case where the total volume of the hydraulic system is unknown at the start of the method. This can be caused, for example, by component tolerances, in particular by unknown hydraulic fluid residual quantities in cavities of components located in the system and / or in one or more components of the system; for example, by the amount of coolant remaining in the internal combustion engine as a result of a previous test bench run, wherein the engine was filled with coolant during the run and even if the coolant was drained at the end of the run-in process, an unknown residual amount still remained in the cavity in the engine. Different embodiments (e.g. the use of larger coolers in tropical regions or different wheelbases) can also lead to an unknown total system volume. The method according to the invention works reliably and precisely even when the total volume is not exactly known.

[0028] It is therefore possible that each hydraulic system, whether in mobile or stationary applications, is filled with exactly the desired amount of hydraulic fluid. The method according to the invention can be used together with a so-called vacuum filling process. The vacuum filling process generates a negative pressure in the hydraulic system relative to the hydraulic system environment. Negative pressure is also usually referred to as vacuum, but it is clear here that it is not an absolute vacuum at this time, because such an absolute vacuum cannot be produced technically or can only be produced with great effort. The negative pressure achieved by evacuating the hydraulic system is, for example, a rough vacuum of about 50 mbar. The vacuum can help in the process and shorten the cycle time, because the hydraulic fluid can be conveyed into the hydraulic system very quickly.

[0029] One advantage of the method according to the invention is that the filling process is not influenced by the position of the residual air volume in the hydraulic system. Furthermore, it is not necessary to know exactly the volume of the hydraulic system and the residual amount of hydraulic fluid that may be present in the hydraulic system before the actual filling process. In fact, the exact amount of hydraulic fluid to be filled cannot be determined in advance due to the variables detailed above.

[0030] In order to regulate the amount of hydraulic fluid to be charged to the hydraulic system as accurately as possible, it is preferably provided that this amount is determined by means of the gas equation. In this way, the amount to be charged can be determined particularly accurately in conjunction with a predetermined initial amount of air in the balancing container. The gas equation or the ideal gas equation thus forms a physical relationship by which the existing residual air volume in the hydraulic system, for example the cooling circuit of a vehicle, can be determined within the scope of at least two measurements.

[0031] The basis is an approximately isothermal state change, which can be described according to the Bomar's law as follows:

[0032] p*V=constant, where T=constant, dT=0.

[0033] Since the required initial amount of air in the hydraulic system is predetermined and known for each vehicle or each vehicle variant, the required amount of hydraulic fluid to be filled into the hydraulic system can be calculated, so that each vehicle can be filled precisely, i.e. with the desired amount. This makes it possible to fill the respective vehicle, device or apparatus in a particularly short time and thus cost-effectively, so that repeated filling processes can be avoided. In addition, incomplete filling of vehicles etc. can be prevented, so that the risk of damage that may result from underfilling can be kept low. Possible customer complaints due to underfilling or overfilling can also be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further advantages, features and details of the invention are apparent from the following description of preferred embodiments and in conjunction with the accompanying drawings. The features and feature combinations mentioned above in the description and the features and feature combinations mentioned below in the description of the drawings and / or shown individually in the drawings can be used not only in the respectively indicated combination, but also in other combinations or individually without exceeding the scope of the invention.

[0035] The accompanying drawings show:

[0036] Figure 1 A schematic side view of a cooling system of a vehicle in the form of a truck is shown, wherein the cooling system is filled with a coolant, in particular a liquid coolant, by filling the cooling system with a certain amount of coolant, wherein the amount of coolant to be filled depends on the residual air volume in the cooling system and the desired initial amount of air V in the balancing tank AGB. L,AGB to regulate;

[0037] Figure 2 A diagram showing the method of the present invention;

[0038] Figure 3 A schematic diagram showing a filling device according to the invention. DETAILED DESCRIPTION

[0039] Figure 1 A cooling system for a means of transport, in particular in the form of a commercial vehicle, is shown in a side view, the commercial vehicle being in particular designed as a truck. The cooling system has at least one cooling circuit through which a coolant can flow, in which different components of the truck are arranged. The cooling circuit and the components arranged in the cooling circuit can be flowed through by the coolant, so that the components can be cooled or temperature-controlled by transferring heat from the components to the coolant, such as a battery in an electric vehicle through which the coolant flows. The coolant is, for example, a liquid coolant, i.e., a coolant, which is also referred to as cooling water. The components include a coolant cooler 10, a hose 12, a cylinder head and an engine block (wherein the cylinder head and the engine block are collectively indicated by 14), a reducer pipe 16, a heating line 18, a reducer 20, a line 22, a heating heat exchanger 24 and a balancing container AGB.

[0040] In the context of the manufacture or assembly of a commercial vehicle, a cooling system is filled with a coolant. A method for filling a cooling system is described below. Within the scope of the method, a certain amount of coolant is filled into the cooling system. The cooling system has a Figure 2 The balancing container AGB shown in the figure can be used to fill the cooling system SYS with coolant. After the cooling system SYS has been filled with coolant within the so-called pre-filling range, in addition to the coolant quantity, there is also an air quantity in the balancing container AGB as well as any residual air quantity / bubbles that may be present in the rest of the cooling system SYS, and thus the respective residual air volumes are located in the respective components of the cooling system SYS. The optional first pre-filling process step increases the accuracy of the method; the more liquid and the less residual air are sealed in the system, the more precise the method is. The sum of the respective residual air quantities in the system and the air in the balancing container AGB is the total residual air quantity V3, i.e. the total residual air volume. In order to now be able to fill the entire cooling system, including the balancing container AGB, with the correct amount of coolant in a particularly simple manner and with particular accuracy, the original amount of air V predetermined by the structure in the balancing container AGB is determined according to the method. L,AGB And determining and adjusting the amount of coolant to be filled according to the total remaining air volume in the system determined by the method.

[0041] exist Figure 2 1 shows a hydraulic system SYS to be filled with hydraulic fluid in a greatly simplified manner. It comprises a compensating container AGB and the rest of the hydraulic system SYS in different phases at different times t0-t4.

[0042] exist Figure 2 Medium Indicates the volume flow with which coolant is filled into the cooling system SYS via the balancing tank AGB within a specified time. KM,maxAGB Indicates the maximum filling volume of the balancing container AGB in normal operation, which is the volume of the balancing container AGB minus the original amount of air V expected in the structure L,AGB And get, and use V KM,Korr The amount of coolant to be filled into the cooling system or to be discharged in the last process step (step 6) is indicated so that the system is ideally, i.e. completely, filled with the desired amount of coolant. Assuming that no air is left in any other system part except the balancing tank AGB, the amount of coolant to be discharged is indicated with V KM,Korr Fill accurately to FH KM,maxAGB If there is still a residual air volume at other locations in the cooling system SYS, which may also consist of several components, the method and the quantity V described here are used to calculate the residual air volume. KM,Korr Compared with the ideal position of the liquid level in the structure FH KM,maxAGBThe balancing container AGB is overfilled with a volume V5 , to be precise, with an amount equal to the sum of the air volumes V4 remaining outside the balancing container.

[0043] In step 1, the unknown quantity V is indicated by the bar at the bottom of the system SYS. KM,0 of hydraulic fluid is already present in the system SYS before the start of the pre-filling, which is usually carried out in the form of vacuum filling.

[0044] For vacuum filling, the cooling system is hermetically closed and the pressure p 0,abs For example, the pressure is reduced to about 50 mbar absolute. This negative pressure / vacuum reduces the first volume V KM,Prefill The coolant is fed into the hydraulic system SYS or helps and facilitates rapid coolant filling. This results in a coolant level FH in the equalization tank AGB. KM,Prefill At the end of the pre-filling process step (step 2), there is still a negative pressure p of, for example, 800 mbar absolute pressure in the hydraulic system. 1,abs In terms of method accuracy, it is meaningful to determine the first volume V in such a way that KM,Prefill , so that the entire hydraulic system is then substantially filled. For the sake of simplicity of the process, the prefilling amount is preferably set to exceed the approximately known total target filling amount. As a result, at the end of the entire process, after the final level adjustment (step 6), a slight negative pressure remains in the system SYS, so that after a simple pressure equalization, the filling head of the device can be removed without liquid being pressed out of the balancing tank AGB undesirably, or the balancing tank AGB having to have a special function for eliminating overpressure, or for this purpose, without requiring a separate process step or additional device technology.

[0045] After the prefilling (step 2), the pressure balance of the hydraulic system is carried out (step 3), so that pressure balance with the environment occurs. Then, an ambient pressure p of, for example, 1013 mbar prevails in the hydraulic system. amb =p 2,abs .

[0046] Next (step 4), the hydraulic system is hermetically sealed again and the pressure p in the system is detected, i.e. measured as accurately as possible. 2,abs (= ambient pressure p amb ). Then, through the filling device 32 ( Figure 3 ) of the delivery pump to accurately determine the second volume ΔV KM,Mess The hydraulic fluid is delivered into the hydraulic system. As a result, the pressure in the hydraulic system increases from p 2,abs Increase to p 3,abs , and the liquid level FH in the balancing vessel AGB rises to value FH KM,Mess . Pressure p 3,abs is also detected, that is, measured; or it can also be detected from p 2,absStart measuring the second volume V KM,Mess The pressure difference Δp between before (time t2) and after (time t3) filling or discharging. The second volume ΔV KM,Mess The hydraulic fluid should be delivered to the hydraulic system as accurately as possible. This volume should be known for further calculations. This volume should be metered so that it can be filled into the hydraulic system without exceeding the currently available air volume in the equalization tank AGB.

[0047] By absolute pressure p 2,abs , pressure difference Δp(=p 3,abs -p 2,abs ) and knowing the volume ΔV KM,Mess In the case of , the residual air volume in the hydraulic system can be calculated, for example, by means of the ideal gas equation. The calculation of the total residual air volume of the entire system is based on the ideal gas equation and is carried out on the assumption that the total residual air volume still contained in the entire cooling system, i.e. the air contained in the cooling system, is approximately an ideal gas and that the method step, i.e. the measuring step (step 4), is carried out approximately in an isothermal state change. In order to achieve the highest possible accuracy of the method, it is ensured that the temperature of the coolant to be filled in the tank of the filling device 32 is adjusted in a similar manner to the vehicle production plant and the vehicles and their components themselves located in the production line.

[0048] Knowing the volume ΔV KM,Mess and pressure p 3,abs and p 2,abs In the case of , the total remaining air volume V3 can now be determined. Therefore, the final correction required ΔV KM,Korr Simply by subtracting the desired original volume of air V from V3 L,AGB to determine (step 5).

[0049] If we now set the final correction value V KM,Korr When the fluid level FH is higher than the expected level, it is delivered into or discharged from the hydraulic system. KM,maxAGB Liquid level FH KM,Final The corresponding liquid level volume difference FH in the balance container AGB KM,Final -FHK M,maxAGB The obtained liquid volume V5 is exactly equal to the total volume of bubbles in the hydraulic system SYS. Figure 2 Indicated by V4.

[0050] The total remaining air volume V2 in the cooling system is expressed as:

[0051] V2=V3+ΔV KM,Mess

[0052] The above equation is the first equation.

[0053] The following second equation is also utilized, which represents the ideal gas law:

[0054] p 2,abs *V2=p 3,abs *V3

[0055] (Bomar's law, for T = constant, d T =0)

[0056] Use p 2,abs Indicates the coolant pressure of the coolant in the cooling system at time t2. 3,abs Indicates the pressure of the coolant in the cooling system at a later time t3. As mentioned above, the change in the total amount of coolant during the measurement step V KM,Mess This results in a change in the absolute pressure in the cooling system, wherein the pressure is detected, i.e. measured, as accurately as possible, for example by means of a detection device, in particular at least one pressure sensor. The amount of coolant to be filled is regulated by controlling the filling time (t3-t2) at a defined constant volume flow, during which the coolant is filled into the cooling system according to the volume flow.

[0057]

[0058] If these three equations are substituted into each other, the following equation is obtained for V3:

[0059]

[0060] In the balance container AGB, Figure 2 The volume V shown KM,Mess refers to the amount of coolant filled into the balancing tank AGB or discharged between times t2 and t3. Therefore, volume V KM,Korr refers to the amount of coolant that is filled into or discharged from the balancing tank AGB between the times t3 and t4. This amount corresponds to the amount of coolant that is still to be filled into or discharged from the cooling system V KM,Korr , so that the cooling system is filled optimally, i.e. exactly in accordance with the structural setting conditions:

[0061] V KM,Korr =V3-V L,AGB .

[0062] To be exact, V KM,KorrThis indicates the coolant volume that is still to be filled into the cooling system or discharged via the balancing tank AGB or in a similar manner. "Overfilling of the balancing tank beyond the structurally predetermined level" is tolerable here; the cooling system separates the unwanted residual air volume / gas bubbles located in the system from the balancing tank relatively quickly during the later actual vehicle operation. For this purpose, it is usually necessary to open the engine-side coolant thermostat, which occurs regularly during driving when the coolant thermostat opening temperature is reached. If the method is carried out in such a way that the prefilling amount is already above the final target amount, a slight negative pressure will occur in the last step of the method at the end of the final level control.

[0063] In the event that the final level adjustment of the balancing tank AGB is to be achieved by filling, this should be done under slight negative pressure in terms of equipment technology, provided that the AGB contains a structural overfilling protection. Overfilling protection is usually present in the balancing tank to ensure that an undesirable overfilling of the cooling system is avoided during later customer use.

[0064] If the coolant volume V calculated in the above manner KM,Korr is filled into or discharged from the cooling system, a coolant volume is present in the balancing container AGB, which leaves room in the balancing container AGB for an air volume which, in terms of calculation, corresponds exactly to the desired air stock volume V of the cooling system in relation to the air bubbles still present in the system. L,AGB .

[0065] The air quantity determination method is preferably carried out in the excess pressure range, since undesired suction and thus internal volume changes caused by shrinkage of hydraulic rubber hoses usually present in hydraulic systems can thereby be avoided.

[0066] The purpose of the method and thus of the ideal filling of the cooling system is to reliably avoid possible volume errors when filling the cooling system and to intentionally allow small volume errors, i.e. air inclusions in the system, in order to save the technical / structural costs of costly exhaust lines or of continuously rising lines required for the construction.

[0067] Figure 3 An embodiment of a filling device, referred to as a filling device 32, is schematically shown. A filling adapter 42 is accommodated in a filling connection 34 of the balancing tank AGB. The filling connection 34 has an overfill protection. The filling adapter comprises a line 13 for filling with hydraulic fluid and a connection 15 for a pressure sensor (not shown).

[0068] Optionally, the filling adapter 42 comprises the suction line 17 required for performing vacuum filling. By sucking out air from the balancing tank AGB by means of a vacuum pump, the pressure in the hydraulic system SYS is reduced to, for example, 50 mbar.KM,Prefill Perform vacuum filling (step 2).

[0069] The pressure sensor is used to detect the absolute pressure p 2,abs and p 3,abs The amount of coolant filled in or discharged can be measured as accurately as possible by means of a corresponding flow meter, in particular in the measuring step (step 4).

[0070] The controller ECU is set up and programmed to control the vacuum pump and the filling pump and / or the suction pump. The controller controls the first volume V KM,Prefill , the second volume ΔV KM,Mess and the final adjustment volume / correction volume V KM,Korr In addition, the controller controls the pressure p in each measuring step 2,abs 、p 3,abs The detection of the amount of coolant filled or discharged and the calculation of the volume V3 of all the remaining air in the hydraulic system, and the calculation of the final adjustment volume / correction volume V KM,Korr .

[0071] It is not important for the execution of the method that the volume change V required for adjusting the second later measuring time (time t3) is KM,Mess Whether it is volume controlled, i.e. by a predetermined volume V KM,Mess to achieve and measure the resulting pressure change, or the (thus initially unknown) quantity V filled or discharged in the measuring step (step 4) KM,Mess Is it filled or discharged in a pressure-controlled manner, i.e. to the extent that a predetermined pressure is reached, and the resulting quantity V is measured as accurately as possible? KM,Mess Volume control is usually advantageous because stabilization of the pressure within the system takes some time and pressure control usually results in a relatively lengthy process time.

[0072] In particular, the controller ECU is an electronic controller of the filling device 32 for controlling the filling process, collecting the respective measurement data and calculating the respective coolant quantity. Figure 3 40 denotes the coolant in the balancing tank AGB. Arrow 36 indicates that the coolant 40 can flow from the balancing tank AGB to or into the cooling system SYS. Double arrow 38 indicates that the coolant can be sucked out of the balancing tank AGB via line 13 and that the balancing tank AGB can be filled with coolant. Arrow 28 indicates that a known amount and temperature of coolant can be guided from a tank, also referred to as a plant tank, of the filling device 32 into line 13 and fed into the balancing tank AGB via line 13. Finally, arrow 26 denotes the connection for partial vacuum air suction and for the ventilation / pressure equalization valve.

Claims

1. A method for filling a hydraulic system (SYS) with hydraulic fluid (40), comprising the following method steps: - Close the hydraulic system (SYS) in a pressure-tight manner and measure the pressure (p 2,abs ), - filling or discharging a second volume (ΔV KM,Mess ) of hydraulic fluid (40), - When filling or discharging the specified second volume (ΔV KM,Mess ) and then measure the pressure (p 3,abs ), - Based on the filling or discharging of the specified second volume (ΔV KM,Mess ) before and after pressure (p 2,abs ;p 3,abs ) calculates the volume (V3) of the total remaining air in the hydraulic system (SYS), and based on the volume (V3) and the original amount of air (V L,AGB ) Calculate the final correction volume (V KM,korr ),and - Replenish or drain the calculated final correction volume (V KM,Korr ) to achieve the final correct filling amount of the hydraulic system (SYS), in, The final calibration volume (V KM,Korr ) is calculated so that when using the final correction volume (V KM,Korr ) fills the hydraulic system (SYS), the level of the hydraulic fluid (40) is higher than the maximum level (FH) allowed during operation. KM,maxAGB ), Wherein, when filling the hydraulic system (SYS) with the final correction volume (V KM,Korr ), a volume (V5) of hydraulic fluid (40) corresponding to the residual air volume (V4) is present in the equalization tank (AGB), and the volume of hydraulic fluid is higher than the maximum level (FH) which is continuously permitted during operation. KM,maxAGB ).

2. A method for filling a hydraulic system (SYS) with hydraulic fluid (40), comprising the following method steps: - Close the hydraulic system (SYS) in a pressure-tight manner and measure the pressure (p 2,abs ), - filling or draining the hydraulic fluid (40) of the closed hydraulic system (SYS) until a predetermined pressure (p 3,abs ), the volume of the hydraulic fluid (40) charged during filling or discharging (ΔV KM,Mess ), - According to the filling or discharging of the second volume (ΔV KM,Mess ) before and after pressure (p 2,abs ;p 3,abs ) calculates the volume (V3) of all remaining air in the hydraulic system (SYS), and based on the volume (V3) and the original amount of air (V L,AGB ) Calculate the final correction volume (V KM,korr ),and - Replenish or drain the calculated final correction volume (V KM,Korr ) to achieve the final correct filling amount of the hydraulic system (SYS), in, The final calibration volume (V KM,Korr ) is calculated so that when using the final correction volume (V KM,Korr ) fills the hydraulic system (SYS), the level of the hydraulic fluid (40) is higher than the maximum level (FH) allowed during operation. KM,maxAGB ), Wherein, when filling the hydraulic system (SYS) with the final correction volume (V KM,Korr ), a volume (V5) of hydraulic fluid (40) corresponding to the residual air volume (V4) is present in the equalization tank (AGB), and the volume of hydraulic fluid is higher than the maximum level (FH) which is continuously permitted during operation. KM,maxAGB ).

3. The method according to claim 1 or 2, characterized in that: The hydraulic system (SYS) is closed in a pressure-tight manner and the pressure (p 2,abs ), the hydraulic system is filled with a predetermined first volume (V KM,Prefill ) of hydraulic fluid (40).

4. The method according to claim 1 or 2, characterized in that: The final calibration volume (V KM,Korr ) is determined by subtracting the predetermined original amount of air from the total remaining amount of air sealed.

5. The method according to claim 3, characterized in that: The hydraulic system (SYS) is filled with a predetermined first volume (V KM,Prefill ) of hydraulic fluid (40).

6. The method according to claim 1 or 2, characterized in that: The hydraulic system (SYS) is filled with hydraulic fluid by means of a compensating tank (AGB).

7. A device for filling a hydraulic system (SYS), comprising: a filling adapter (42), a line (13) for hydraulic fluid (40), a pressure sensor, a controller (ECU) and means for closing the hydraulic system (SYS), The device is designed to perform the method according to any one of claims 1 to 6.

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