Method and Device for Filling a Hydraulic System with a Hydraulic Fluid

Abstract

A method for filling a hydraulic system with a hydraulic fluid includes sealing the hydraulic system in a pressure-tight manner and recording a pressure in the sealed hydraulic system, filling or removing a predefined volume of the hydraulic fluid from the sealed hydraulic system, recording a pressure in the sealed hydraulic system after the filling or removing, calculating a volume of a total residual air in the hydraulic system depending on the pressures before and after the filling or removal of the predefined volume, calculating a final correction volume depending on the volume and a design-specified air feed of the hydraulic system, and refilling or removing the calculated final correction volume to achieve a final correct filling quantity for the hydraulic system.

Claims

1.-10. (canceled)

11. A method for filling a hydraulic system (SYS) with a hydraulic fluid (40), comprising the steps of: sealing the hydraulic system (SYS) in a pressure-tight manner and recording a pressure (p.sub.2, abs) in the sealed hydraulic system (SYS); filling or removing a predefined second volume (ΔV.sub.KM, Mess) of the hydraulic fluid (40) from the sealed hydraulic system (SYS); recording a pressure (p3, .sub.abs) in the sealed hydraulic system (SYS) after the filling or removing of the predefined the second volume (ΔV.sub.KM, Mess); calculating a volume (V.sub.3) of a total residual air in the hydraulic system (SYS) depending on the pressures (p.sub.2, abs, p3, .sub.abs) before and after the filling or removal of the predefined second volume (ΔV.sub.KM, Mess) and calculating a final correction volume (V.sub.KM, korr) depending on the volume (V.sub.3) and a design-specified air feed (V.sub.L, AGB) of the hydraulic system (SYS); and refilling or removing the calculated final correction volume (V.sub.KM, Korr) to achieve a final correct filling quantity for the hydraulic system (SYS).

12. A method for filling a hydraulic system (SYS) with a hydraulic fluid (40), comprising the steps of: sealing the hydraulic system (SYS) in a pressure-tight manner and recording a pressure (p.sub.2, abs) in the sealed hydraulic system (SYS); filling or removing the hydraulic fluid (40) from the sealed hydraulic system (SYS) until a predefined pressure (p3, .sub.abs) is reached in the sealed hydraulic system (SYS) and recording a volume (ΔV.sub.KM, Mess) of the hydraulic fluid (40) filled in during the filling or removing; calculating a volume (V.sub.3) of a total residual air in the hydraulic system (SYS) depending on the pressures (p.sub.2, abs, p3, .sub.abs) before and after filling or removing of a second volume (ΔV.sub.KM, Mess) and calculating a final correction volume (V.sub.KM,korr) depending on the volume (V.sub.3) and a design-specified air feed (V.sub.L, AGB) of the hydraulic system (SYS); and refilling or removing the calculated final correction volume (V.sub.KM, Korr) to achieve a final correct filling quantity for the hydraulic system (SYS).

13. The method according to claim 11, further comprising the step of filling the hydraulic system with a predefined first volume (V.sub.KM, prefill) of hydraulic fluid before the sealing and the recording of the pressure (p.sub.2, abs) in the sealed hydraulic system (SYS).

14. The method according to claim 11, wherein the final correction volume (V.sub.KM, Korr) is determined depending on the total residual air volume minus a target air volume.

15. The method according to claim 11, wherein the final correction volume (V.sub.KM, Korr) is calculated such that a level of the hydraulic fluid (40) after filling the hydraulic system (SYS) with the final correction volume (V.sub.KM, Korr) is above a highest level (FHKM, .sub.max AGB) permanently permissible during operation.

16. The method according to claim 15, wherein after filling the hydraulic system (SYS) with the final correction volume (V.sub.KM, Korr), a volume (V.sub.5) of the hydraulic fluid (40) in a compensating reservoir (AGB) corresponding to a residual air volume (V.sub.4) is produced above the highest level (FHKM, .sub.max AGB) permanently permissible during operation.

17. The method according to claim 13, wherein the hydraulic system (SYS) is filled with the predefined first volume (V.sub.KM, Prefill) of hydraulic fluid (40) by negative pressure.

18. The method according to claim 11, wherein the hydraulic system (SYS) is filled with the hydraulic fluid via a compensating reservoir (AGB).

19. The method according to claim 12, further comprising the step of filling the hydraulic system with a predefined first volume (V.sub.KM, Prefill) of hydraulic fluid before the sealing and the recording of the pressure (p.sub.2, abs) in the sealed hydraulic system (SYS).

20. The method according to claim 12, wherein the final correction volume (V.sub.KM, Korr) is determined depending on the total residual air volume minus a target air volume.

21. The method according to claim 12, wherein the final correction volume (V.sub.KM, Korr) is calculated such that a level of the hydraulic fluid (40) after filling the hydraulic system (SYS) with the final correction volume (V.sub.KM, Korr) is above a highest level (FHKM, .sub.max AGB) permanently permissible during operation.

22. The method according to claim 21, wherein after filling the hydraulic system (SYS) with the final correction volume (V.sub.KM, Korr), a volume (V.sub.5) of the hydraulic fluid (40) in a compensating reservoir (AGB) corresponding to a residual air volume (V.sub.4) is produced above the highest level (FHKM, .sub.max AGB) permanently permissible during operation.

23. The method according to claim 19, wherein the hydraulic system (SYS) is filled with the predefined first volume (V.sub.KM, Prefill) of hydraulic fluid (40) by negative pressure.

24. The method according to claim 12, wherein the hydraulic system (SYS) is filled with the hydraulic fluid via a compensating reservoir (AGB).

25. A device for filling a hydraulic system (SYS), comprising: a filling adapter (42); a line (13) for hydraulic fluid (40); a pressure sensor; a means for closing the hydraulic system (SYS); and a control unit (ECU).

26. The device according to claim 19, wherein the device performs the method according to claim 11.

27. The device according to claim 19, wherein the device performs the method according to claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a schematic side view of a cooling system of a vehicle in the form of a commercial vehicle, wherein the cooling system is filled with a coolant, in particular a liquid coolant, by filling a quantity of the coolant into the cooling system, wherein the quantity of the coolant to be filled in is adjusted depending on the residual air volume located in the cooling system and the desired air feed V.sub.L, AGB in the compensating reservoir AGB;

[0034] FIG. 2 is an illustration of the method according to the invention; and

[0035] FIG. 3 is a schematic representation of the filling device according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 shows a side view of a cooling system for a vehicle, in particular in the form of a commercial vehicle, which is designed as a utility vehicle. The cooling system has at least one cooling circuit through which a coolant can flow and in which various components of the commercial vehicle are arranged. The coolant can flow through the cooling circuit and thus through the components arranged in the cooling circuit, so that the components can be cooled or also temperature-controlled as a result of heat transfer from the components to the coolant, for example in an electrically driven vehicle a battery through which coolant flows. The coolant is, for example, a liquid coolant, that is to say, a cooling liquid, which is also referred to as cooling water. The components include a coolant radiator 10, hoses 12, a cylinder head and an engine block, wherein the cylinder head and engine block are collectively denoted by 14, retarder tubes 16, heater lines 18, a retarder 20, lines 22, a heater heat exchanger 24, and a compensating reservoir AGB.

[0037] The cooling system is filled with the coolant during the production or assembly of the commercial vehicle. A method for filling the cooling system is described below. Within the scope of the method, a quantity of coolant is filled into the cooling system. The cooling system has a compensating reservoir AGB, which can be seen in FIG. 2, via which the coolant can be filled into the cooling system SYS. After the coolant has been filled into the cooling system SYS as part of the so-called prefilling process, there is still a quantity of air in the compensating reservoir AGB in addition to a quantity of coolant, as well as possible residual air quantities/air bubbles in the rest of the cooling system SYS and thus various residual air volumes in components of the cooling system SYS. This—not absolutely necessary—first process step of prefilling increases the accuracy of the method; the method becomes more accurate the more liquid and the less residual air is enclosed in the system. The various residual air quantities in the system, together with the air in the compensating reservoir AGB, result in a total residual air quantity V.sub.3 and thus a total residual air volume. In order to then fill the entire cooling system, including the compensating reservoir AGB, with the correct quantity of coolant in a particularly simple and precise manner, the quantity of coolant to be filled in is determined and adjusted depending on the design-specified air volume V.sub.L, AGB in the compensating reservoir AGB and the total residual air volume in the system ascertained using this method.

[0038] In FIG. 2, the hydraulic system SYS to be filled with hydraulic fluid is shown in a very highly simplified way. It comprises a compensating reservoir AGB and the rest of the hydraulic system SYS in different stages at different times t.sub.0 to t.sub.4.

[0039] In FIG. 2 V.sub.KM denotes a volume flow with which the coolant is filled into the cooling system SYS via the compensating reservoir AGB over a certain time. FH.sub.KM,max AGB denotes the maximum filling volume of the compensating reservoir AGB in normal operation, which results from the volumetric size of the compensating reservoir AGB minus the air feed V.sub.L, AGB desired in accordance with the design, and VKM.sub.Korr denotes the quantity of coolant still to be filled into or extracted from the cooling system in the last process step (step 6) in order to fill the system ideally, i.e., completely, with the desired quantity of coolant. Provided that there is no air trapped in any further part of the system other than the compensating reservoir AGB, VKM,.sub.Korr is used to fill the system exactly up to FH.sub.KM, max AGB. As soon as there is still a residual quantity of air elsewhere in the cooling system SYS, which may also consist of several partial quantities, the compensating reservoir AGB is overfilled by the volume V.sub.5 with respect to the design-specified fluid level setpoint FH.sub.KM,max AGB by means of the method described here and the quantity VKM, .sub.Korr, more specifically by exactly the quantity of the sum of the air volumes V.sub.4 enclosed outside the compensating reservoir.

[0040] In step 1, a bar at the bottom of the system SYS indicates that an unknown quantity V.sub.KM, 0 of hydraulic fluid is already in the system SYS before prefilling, usually performed as vacuum filling, begins.

[0041] For this vacuum filling, the cooling system is sealed airtight and the pressure p.sub.0, abs, for example, is lowered to approx. 50 mbar absolute pressure. This negative pressure/vacuum conveys an initial volume V.sub.KM, Prefill into the hydraulic system SYS or supports and promotes rapid coolant filling. This results in a level with a filling height FH.sub.KM Prefill in the compensating reservoir AGB. At the end of the prefilling process step (step 2), there is still a negative pressure p.sub.1, abs of, for example, 800 mbar absolute pressure in the hydraulic system. In terms of the accuracy of the method, it makes sense to determine this first volume VKM, Prefill so that the entire hydraulic system is already largely filled afterwards. For reasons of process simplification for the method, the prefill quantity should preferably be set above the approximately known total target fill quantity. As a result, a slight negative pressure remains in the system SYS at the end of the entire process after the final fill level adjustment (step 6), so that the filling head of the system can be removed after a simple pressure equalisation without undesirably forcing fluid out of the compensating reservoir AGB, or without the compensating reservoir AGB having to be equipped with a special function for reducing the excess pressure, or without a separate process step or additional system technology being required for this.

[0042] After the prefilling (step 2), the pressure in the hydraulic system is equalised (step 3) so that the pressure is equalised with the ambient pressure. After this, in the hydraulic system, an ambient pressure p.sub.amb=p.sub.2, abs of, for example, 1013 mbar prevails.

[0043] Subsequently (step 4), the hydraulic system is sealed again in an airtight manner and the pressure p.sub.2, abs in the system (=ambient pressure p.sub.amb) is recorded, i.e., measured as accurately as possible. Then, a feed pump of the filling system 32 (FIG. 3) feeds a precisely specified second volume ΔV.sub.KM, Mess of hydraulic fluid into the hydraulic system. This increases the pressure in the hydraulic system from p.sub.2, abs to p.sub.3, abs and the filling level FH in the compensating reservoir AGB rises to the value FH.sub.KM, Mess. This pressure p.sub.3, abs is also recorded, i.e., measured; alternatively, starting from p.sub.2, abs, it is also possible to measure the pressure difference Ap between before (time t.sub.2) and after (time t.sub.3) the filling or removal of the second volume V.sub.KM, Mess. This second volume ΔV.sub.KM, Mess of hydraulic fluid must be delivered into the hydraulic system as accurately as possible. This volume must be known for the further calculation. This volume must be dimensioned in such a way that it can still be filled into the hydraulic system without exceeding the air space currently still available in the compensating reservoir AGB.

[0044] From the absolute pressure p.sub.2, abs, the pressure difference Δp (=p.sub.3, abs−p.sub.2, abs) and in knowledge of the volume ΔV.sub.KM, Mess, for example, the residual air volume in the hydraulic system can be calculated using the ideal gas equation. The calculation of the total residual air volume of the entire system is carried out on the basis of the ideal gas equation under 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 the method step measurement step (step 4) is carried out approximately as an isothermal change of state. In the sense of a highest possible accuracy of the method, it must be ensured here that the temperature of the coolant to be filled in the reservoir of the filling system 32 is controlled so as to be similar to that of the production hall of the vehicle and the vehicle and parts thereof, located in the production line.

[0045] In the knowledge of the volume ΔV.sub.KM, Mess and the pressures p.sub.3, abs and p.sub.2, abs, the total residual air volume V.sub.3 can now be determined. Thus, the required final correction volume ΔV.sub.KM, Korr can be determined simply by subtracting the desired air volume VL,.sub.AGB from V.sub.3 (step 5).

[0046] When the final correction quantity V.sub.KM, Korr is pumped into the hydraulic system or removed therefrom, a fill level FH.sub.KM, Final is reached which is above the desired fill level FH.sub.KM, max AGB. The fluid volume V.sub.5 from the corresponding volume difference of the fill levels FH.sub.KM, Final−FH.sub.KM, max AGB in the compensation reservoir AGB corresponds here exactly to the volume of the sum of the air bubbles in the hydraulic system SYS, which is denoted as V.sub.4 in FIG. 2.

[0047] The total residual air volume V.sub.2 in the cooling system is given by:

V.sub.2=V.sub.3+ΔV.sub.KM, Mess

[0048] The above equation is a first equation. Furthermore, the following second equation is used, which represents the ideal gas law:

p.sub.2, abs*V.sub.2=p.sub.3, abs*V.sub.3

(BOYLE-MARIOTTE law for T=const, dT=0)

[0049] P.sub.2,abs denotes a coolant pressure that the coolant has in the cooling system at the time t.sub.2. Accordingly, p.sub.3, abs is the pressure of the coolant in the cooling system at the later time t.sub.3. As explained above, the change in the total quantity of coolant in the measuring step V.sub.KM, Mess thus leads to a change in the absolute pressures in the cooling system, wherein these pressures are recorded, i.e., measured, as precisely as possible, for example by means of a detection device, in particular by means of at least one pressure sensor. In this case, the quantity of coolant to be filled in is set by controlling the filling time (t.sub.3-t.sub.2) at a given constant volume flow with which the coolant is filled into the cooling system over this time.

V.sub.KM, Mess=V.sub.2(t.sub.3−t.sub.2).

[0050] If these three equations are inserted into each other, the following results for V.sub.3:

[00001]$V_3=\frac{p\text{?}{V}_{\mathrm{KM}\text{?}}}{(p\text{?}-p\text{?}}\text{?}$$\text{?}\text{indicates text missing or illegible when filed}$

[0051] A volume V.sub.KM,Mess in the compensating reservoir AGB shown in FIG. 2 indicates the quantity of coolant filled into or removed from the compensating reservoir AGB between the times t.sub.2 and t.sub.3. Accordingly, a volume V.sub.KM, Korr denotes the quantity of coolant filled into or removed from the compensating reservoir AGB between the times t.sub.3 and t.sub.4. This quantity corresponds to the quantity V.sub.KM,Mess of coolant still to be filled into or removed from the cooling system so that the cooling system is optimally filled, i.e., exactly according to the design specification:

V.sub.KM, Korr=V.sub.3−V.sub.L, AGB.

[0052] More precisely, V.sub.KM,Korr refers to a volume of coolant still to be filled into or removed from the cooling system via the compensating reservoir AGB or in a similar manner. Overfilling of the compensating reservoir beyond the design-specified level is accepted; the cooling system will relatively quickly separate the unwanted residual air volumes/air bubbles in the compensating reservoir during subsequent real vehicle operation. This normally requires the opening of the engine coolant thermostat, which regularly occurs during driving when the thermostat opening temperature of the coolant is reached. If the method is carried out in such a way that the prefill quantity is already above the final target quantity, a slight negative pressure is created in the last step of the method at the end of the final level setting.

[0053] In the event that the final level setting of the compensating reservoir AGB is to be achieved via a filling, this must be done with a slight negative pressure in the system, provided that the AGB contains an overfill protection design. This overfill protection is usually present in a compensating reservoir to ensure that an undesired overfilling of the cooling system is avoided during later customer use.

[0054] If the quantity V.sub.KM, Korr of coolant calculated in the manner described above is filled into or removed from the cooling system, a volume of coolant is created in the compensating reservoir AGB which leaves room for a quantity of air in the compensating reservoir AGB which, in conjunction with the air bubbles still present in the system, results in exactly the desired air feed V.sub.L,AGB of the cooling system.

[0055] Preferably, the method of air volume determination is to be carried out in the positive pressure range, as this avoids an undesired contraction and thus an internal volume change due to contraction of the rubber hoses of a hydraulic system, which are usually present in a hydraulic system.

[0056] The aim of the method and thus an ideal filling of the cooling system is to make the system robust against possible shortfalls when filling the cooling system, as well as to be able to deliberately allow smaller shortfalls, i.e., air pockets in the system, in order to save on costly vent lines or technical/design effort for continuously rising lines required by design.

[0057] FIG. 3 schematically shows an exemplary embodiment of a filling device referred to as a filling system 32. A filling adapter 42 is received in the filler neck 34 of the compensating reservoir AGB. The filler neck 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).

[0058] Optionally, the filling adapter 42 comprises a suction line 17, which is required to carry out the vacuum filling. By sucking air out of the compensating reservoir AGB with the help of a vacuum pump, the pressure in the hydraulic system SYS drops to, for example, 50 mbar. After that, the vacuum filling with the first volume V.sub.KM, Prefill can take place (step 2).

[0059] The pressure sensor is used to record the absolute pressures p.sub.2, abs and p.sub.3, abs. The quantity of coolant filled in or removed must be recorded as precisely as possible using appropriate quantity measuring devices, especially in the measuring step (step 4).

[0060] A control unit ECU is set up and programmed to control the vacuum pump and the filling and/or suction pumps. It controls the filling with the first volume V.sub.KM, prefill, the second volume ΔV.sub.KM, Mess, and the final adjustment volume/correction volume V.sub.KM, Korr. It also controls the recording of the pressures p.sub.2, abs, p.sub.3, abs and the quantity of coolant filled or removed in each measuring step and calculates the volume V.sub.3 of the total residual air in the hydraulic system and calculates the final adjustment volume/correction volume V.sub.KM, Korr.

[0061] To carry out the method it is irrelevant here whether the change in volume V.sub.KM,Mess, which is required to set the second later measuring time (time t.sub.3), is volume-controlled, i.e., by a predefined volume V.sub.KM,Mess and the resulting pressure change is measured, or whether the quantity V.sub.KM,Mess filled or removed in the measuring step (step 4)—then initially unknown—is filled or removed in a pressure-controlled manner, i.e., until a predefined pressure is reached, and this resulting quantity V.sub.KM,Mess is measured as accurately as possible. Volume control is usually advantageous because stabilising the pressures in the system takes some time and pressure control would usually result in slower process times.

[0062] In particular, the control unit ECU is an electronic control unit of the filling system 32 for controlling the filling process, the relevant measurement data acquisition, and the calculation of the particular coolant quantities. Furthermore, the coolant in the compensating reservoir AGB is denoted by 40 in FIG. 3. An arrow 36 indicates that the coolant 40 can flow from the compensating reservoir AGB to or into the cooling system SYS. A double arrow 38 indicates that coolant can be removed from the compensating reservoir AGB via the line 13 and that coolant can be filled into the compensating reservoir AGB. An arrow 28 indicates that coolant of known quantity and temperature can be introduced into the line 13 from the reservoir of the filling system 32, which is also referred to as the system reservoir, and can be introduced into the compensating reservoir AGB via the line 13. Lastly, an arrow 26 illustrates a connection to the air extraction for partial evacuation and to the ventilation/pressure equalisation valve.