Procedure for changing the brake fluid of a hydraulic motor vehicle brake system and motor vehicle brake system

Abstract

Method for changing the brake fluid of a hydraulic motor vehicle brake system (1) which comprises a brake control device, in which for emptying an outlet opening (17) for brake fluid located on a wheel brake (2) is opened, and subsequently, a pump (5) of the brake control device is switched on to cause brake fluid to exit through the outlet opening (17), wherein valves (6a to 6l) of the brake control device are actuated in such a way as to establish a hydraulic connection from the at least one brake fluid reservoir (11) to the outlet opening (17), so that brake fluid is drawn off from the at least one brake fluid reservoir (11), wherein the suction of air into a hydraulic unit (4) of the brake control device is avoided, characterized in that before refilling the motor vehicle brake system (1) with brake fluid, the outlet opening (17) is closed and the motor vehicle brake system (1) is refilled with brake fluid by means of a brake fluid changing device via the supply opening 13, with which the brake fluid still present in the hydraulic unit (4) after emptying is discharged during refilling.

Description

[0001] The invention relates to a method for changing the brake fluid of a hydraulic motor vehicle brake system according to the preamble of patent claim 1. Furthermore, the invention relates to a method for changing the brake fluid of a hydraulic motor vehicle brake system according to the preamble of patent claim 8.

[0002] The brake fluid in a motor vehicle brake system must be changed at regular intervals, usually every two years. Traditionally, the brake fluid contained in a brake fluid reservoir is first extracted. To do this, a pipe or hose is inserted through the supply opening of the brake fluid reservoir, and then an external suction pump is activated. The supply opening of the brake fluid reservoir must therefore be sufficiently accessible from the outside for a maintenance person, as care must be taken during handling to avoid damage from dripping brake fluid. Painted areas of the vehicle body are particularly sensitive to brake fluid.

[0003] In a conventional passenger car, this suction reduces the total amount of brake fluid in the vehicle's brake system, which is on the order of approximately 800 ml, to approximately 400 to 500 ml. The system is then flushed with approximately 1000 ml of fresh brake fluid, replacing the old brake fluid. The excess of fresh brake fluid, for example, 200 ml here, ensures that ideally all of the old brake fluid is replaced with new, and that, if possible, no mixture of old and new brake fluid remains in the brake system.

[0004] With the development of new drive concepts, space-saving considerations create a need for more flexible storage of the brake fluid reservoir in a motor vehicle. This particularly includes concepts in which the brake fluid reservoir is no longer easily accessible from the outside, making the previously common technique of draining the brake fluid from a brake fluid reservoir difficult, if not impossible.

[0005] In the worst case scenario, this would result in significantly more new brake fluid being required than before to completely remove the old brake fluid from the vehicle's braking system. Assuming that it is not possible to drain the brake fluid reservoir, the amount of new brake fluid required for the above-mentioned comparison case is around 3000 ml, because the new brake fluid would initially mix with the old brake fluid in the brake fluid reservoir. The flushing losses would therefore be considerable. This poses a problem both in terms of costs for the vehicle operator and with regard to environmental protection, because old brake fluid is a hazardous substance that is difficult to dispose of and environmentally hazardous.An alternative is to install additional piping, but this would largely negate the advantage of more flexible accommodation of a brake fluid reservoir and the associated gain in terms of space economy.

[0006] Methods for changing the brake fluid of a hydraulic motor vehicle brake system according to the preamble of patent claim 1 and patent claim 8 are known from DE 10 2015 015 659 A1.

[0007] Against this background, the invention is based on the object of specifying methods which, while enabling a spatially flexible accommodation of a brake fluid supply on a motor vehicle, allow a simple change of brake fluid without large flushing losses of new brake fluid.

[0008] This object is achieved by a method for changing the brake fluid of a hydraulic motor vehicle brake system according to patent claim 1 and according to patent claim 8.

[0009] Particular embodiments of the invention are the subject of further patent claims.

[0010] This means that the process of sucking brake fluid out of the brake fluid reservoir, as explained above, can be replaced without resulting in a higher demand for brake fluid when changing the brake fluid.

[0011] Since this approach eliminates the need to attach an external suction device to the brake fluid reservoir to empty it, the brake fluid reservoir can be installed more flexibly on the vehicle. In particular, it is possible to position a substantial portion of the brake fluid reservoir away from a maintenance opening on the vehicle. This is particularly advantageous for vehicles that, unlike combustion engines, no longer have a distinct engine compartment.

[0012] In other words, the invention improves the emptying phase during a brake fluid change.

[0013] Before switching on the pump, an optional brake fluid supply port can be opened on at least one brake fluid reservoir to facilitate draining. With an appropriately dimensioned vent opening in the brake fluid reservoir, draining can also be performed by opening the outlet port without opening the supply port.

[0014] In order to prevent air from entering a hydraulic unit of the vehicle brake system during emptying, the emptying process can be controlled, for example, via vehicle-external control software, which for this purpose is temporarily connected to the vehicle brake system via hardware - wirelessly or via a cable.

[0015] However, it is also possible to control the emptying process via in-vehicle control software.

[0016] According to a further embodiment of the method according to the invention, a sensor for detecting brake fluid in the brake fluid reservoir is arranged on the at least one brake fluid reservoir. The draining process is automatically stopped if the sensor detects a lack of brake fluid in the at least one brake fluid reservoir. This ensures that the brake fluid reservoir is almost completely drained, but that no air can penetrate into a downstream hydraulic unit.

[0017] If a brake fluid reservoir optionally extends over several, for example, two, brake fluid reservoirs, the emptying of the brake fluid reservoir closest to the hydraulic unit is monitored. This also ensures that the entire brake fluid supply is drained in the first step during the brake fluid change, preventing old and new brake fluid from mixing in the brake fluid reservoir during subsequent refilling and flushing, ultimately keeping flushing losses to a minimum.

[0018] As an alternative to sensor control, it is possible to operate the pump for a vehicle-specific, predefined period of time for draining. The pump's operating time is adjusted to the volume of the brake fluid reservoir. Optionally, the brake fluid reservoir can be prefilled to a target level, which allows for precise reproducibility of the residual brake fluid level during time-controlled pumping.

[0019] According to another particular embodiment of the method according to the invention, a brake booster can be provided on a hydraulic unit, which is automatically actuated to drain the motor vehicle brake system. The brake booster can be actuated in addition to the pump of the brake control device. However, it is also possible, according to claim 8, to actuate the brake booster alone and / or independently of the pump of the brake control device for draining.

[0020] According to patent claim 1, after this phase has ended, i.e., before the motor vehicle brake system is refilled with brake fluid, the outlet opening is closed. Any container containing old brake fluid can then be removed and emptied. Refilling the motor vehicle brake system with brake fluid is performed using a brake fluid changer, which discharges the brake fluid remaining in the hydraulic unit after it has been drained.

[0021] When changing the brake fluid remaining in the brake system, any air that may have entered the system is automatically removed using bleed screws on the wheel brakes.

[0022] The first brake fluid reservoir, which has the supply opening for the introduction of brake fluid into the motor vehicle brake system, can in the present case be accommodated, for example, under a small maintenance flap of the vehicle outer skin, while a further, preferably the actual brake fluid reservoir can be accommodated quite flexibly on the vehicle in a second brake fluid reservoir remote from the first brake fluid reservoir.

[0023] The method explained above is particularly suitable for changing the brake fluid in such a configuration, as it still allows the entire brake fluid supply, or at least a large portion of it, to be drained before refilling with new brake fluid. This keeps flushing losses in relation to the brake fluid to a minimum. Nevertheless, the second brake fluid reservoir can be positioned almost anywhere on a motor vehicle, i.e., in particular, outside an area that would be accessible via a suction device that would be attached over the first, preferably small, brake fluid reservoir.

[0024] According to a particular embodiment of the motor vehicle brake system, a sensor for detecting a brake fluid level is arranged on the second brake fluid reservoir, so that the emptying of the entire brake fluid reservoir can be easily detected before there is a risk of air being sucked into the hydraulic unit during the emptying process.

[0025] Furthermore, a fine filter for filtering externally supplied brake fluid can be arranged on the first brake fluid reservoir. All of the supplied brake fluid must pass through this filter in order to reach the second brake fluid reservoir via a fluid line. The fine filter is permanently connected to the first brake fluid reservoir. Permanently connected here means that the fine filter cannot be removed without destroying or severely damaging the first brake fluid reservoir. This prevents dirt from entering the motor vehicle brake system, but thwarts any possibility of access to the second brake fluid reservoir through the first brake fluid reservoir. This is, however, compensated for by the withdrawal of brake fluid using the pump of the brake control device.This results in a high level of security against impairment of the brake fluid due to the ingress of dirt and the like, especially when changing the brake fluid.

[0026] The invention is explained in more detail below using an exemplary embodiment illustrated in the drawing. The drawing shows: Fig. 1 a schematic representation of a possible embodiment of a motor vehicle brake system, Fig. 2 an example of the flexible storage of the brake fluid reservoir on a motor vehicle, and in Fig. 3 an example of a two-part brake fluid reservoir of a motor vehicle brake system.

[0027] The embodiment in the Fig. 1 to 3 show a motor vehicle braking system 1, such as is used in passenger cars and light commercial vehicles.

[0028] It includes the wheel brakes 2, a brake fluid reservoir 3 and a hydraulic unit 4 as system components.

[0029] The hydraulic unit 4 provides a brake control system (e.g., ABS and / or ESC). In this example, the hydraulic unit 4 comprises two separate brake circuits, each with a pump 5 and several valves 6a to 6l for controlling the supply and discharge of brake fluid to and from the individual wheel brakes 2.

[0030] Furthermore, a master brake cylinder 7, a brake booster 8 and a brake pedal 9 can be seen.

[0031] The brake fluid reservoir 3 feeds the master brake cylinder 7, which in turn is connected to the two brake circuits of the hydraulic unit 4 in order to apply a brake command input by the driver via the brake pedal 9, supported by the brake booster 8, to the wheel brakes 2.

[0032] The brake booster 8 can be designed as an electromechanical brake booster, so that it is possible to generate brake pressure or to actuate the master brake cylinder 7 for this purpose, independently of the driver and independently of the further operation of the motor vehicle.

[0033] However, pressure generation for the hydraulic unit 4 can also be achieved in other ways. Components 7, 8, and 9, shown here as examples, are therefore to be considered optional and could, for example, perform this function instead of pump 5.

[0034] The brake fluid reservoir 3 has a first brake fluid reservoir 11 and a second brake fluid reservoir 12.

[0035] The first brake fluid reservoir 11 has a supply opening 13 for externally supplying brake fluid to the motor vehicle brake system 1. This supply opening 13 is closed with a cover 14, which can be opened and temporarily removed to change the brake fluid.

[0036] The cover 14 can be positioned under a maintenance flap 20 in the outer skin of a motor vehicle.

[0037] The maintenance flap 20 can be reduced in its dimensions approximately to the size of the cover 14 or the first brake fluid reservoir 11, it only being necessary to ensure that the cover 14 can be operated by a maintenance person after opening the maintenance flap 20.

[0038] Such a maintenance flap 20 can, for example, also serve at the same time to cover access to a charging connection for a vehicle drive battery and / or to an opening for windshield washer fluid.

[0039] A filter 15, in particular a fine filter, can optionally be arranged in the first brake fluid reservoir 11, which filter the brake fluid supplied during a brake fluid change before it reaches the other components of the vehicle brake system 1 in order to prevent the entry of dirt into the brake system.

[0040] To prevent incorrect operation during the supply of brake fluid, the filter 15 can be permanently connected to the first brake fluid reservoir 11 so that it cannot be removed by a maintenance person. Ideally, the connection is designed in such a way that removal of the filter 15 is not possible without damaging or destroying the brake fluid reservoir 11.

[0041] The second brake fluid reservoir 12 is arranged at a distance from the first brake fluid reservoir 11. A first fluid line 16 is provided between these two brake fluid reservoirs 11 and 12 for hydraulic connection, so that both brake fluid reservoirs 11 and 12 can be accommodated remotely from each other on a motor vehicle.

[0042] The first fluid line 16 is designed in the form of a hose or tube, in particular a flexible hose or tube. Via this first fluid line 16, brake fluid filled into the first brake fluid reservoir 11 flows into the second brake fluid reservoir 12 and from there via the master brake cylinder 7 into the hydraulic unit 4.

[0043] In the illustrated embodiment, the second brake fluid reservoir 12 is supported on the master brake cylinder 7. The second brake fluid reservoir 12 is preferably arranged directly on the master brake cylinder 7. Brake fluid flowing back from the master brake cylinder 7 or from the hydraulic unit 4 can flow back into the two brake fluid reservoirs 11 and 12.

[0044] In a modification of the representation in Fig. 3, however, the second brake fluid reservoir 12 can also be spaced apart from the master brake cylinder 7 and connected to it by further fluid lines.

[0045] Like the Fig. 1 to 3, the first brake fluid reservoir 11 has a smaller volume for holding brake fluid than the second brake fluid reservoir 12. This facilitates the positioning of the first brake fluid reservoir 11 at a location close to the vehicle's outer skin. However, the invention can also be used with brake fluid reservoirs 11 and 12 of the same size, or with a larger first brake fluid reservoir 11 and a smaller second brake fluid reservoir 12.

[0046] The second brake fluid reservoir 12, on the other hand, can be located virtually anywhere on the vehicle. However, when changing the brake fluid, draining the brake fluid from the second brake fluid reservoir 12 becomes difficult in such a situation.

[0047] According to the invention, the method explained in more detail below is therefore proposed, which allows the brake fluid reservoirs 11 and 12 to be emptied as far as possible in a first phase of a brake fluid change in order to keep the flushing losses with regard to new brake fluid as low as possible.

[0048] At the beginning of a brake fluid change, a closable brake fluid outlet opening 17 located on a wheel brake 2 is first opened to drain the vehicle's brake system. If necessary, the brake fluid supply opening 13 on the first brake fluid reservoir 11 can also be opened. However, with a suitably dimensioned ventilation opening, opening the supply opening 13 can also be omitted.

[0049] Subsequently, the pump 5, in the illustrated embodiment according to Fig. 1, the two pumps 5 of the brake control device are switched on to cause brake fluid to exit through the outlet opening 17. For this purpose, valves 6a to 6l of the brake control device are actuated in such a way as to establish a hydraulic connection from at least one brake fluid reservoir, in this case from the first brake fluid reservoir 11 via the second brake fluid reservoir 12 to the outlet opening 17, so that brake fluid is drawn from the at least one brake fluid reservoir 11, 12.

[0050] The emptying process can be controlled via a vehicle-external control software 19, which for this purpose is temporarily connected to the vehicle brake system 1 via hardware - wirelessly or wired. Fig. 1 shows an example of a vehicle diagnostic, measuring and information system which communicates with the motor vehicle.

[0051] Alternatively, the emptying process can also be controlled via vehicle-internal control software 19 or otherwise.

[0052] The draining process is preferably continued until the first and second brake fluid reservoirs 11, 12 are empty. However, air is avoided from being sucked into the master brake cylinder 7 or the hydraulic unit 4, as these would otherwise require additional venting.

[0053] In the illustrated embodiment, a sensor 18 for detecting brake fluid in the second brake fluid reservoir 12 is arranged for this purpose on the second brake fluid reservoir 12. The draining process is automatically stopped if the sensor 18 detects a lack of brake fluid in the second brake fluid reservoir 12. In this situation, the first brake fluid reservoir 11 is also drained simultaneously.

[0054] However, a time-controlled draining process without sensor 18 is also possible. For a specific motor vehicle or a specific brake fluid reservoir configuration, the time period for a draining process from a maximum brake fluid level to a minimum brake fluid level can be determined in advance, for example, experimentally. This information can later be used for time-controlled draining. If necessary, the brake fluid can first be filled to the maximum level before draining, before the brake control system then draws brake fluid from the brake fluid reservoir over the specified time period and discharges it via the outlet opening 17.

[0055] The old brake fluid displaced from the motor vehicle brake system 1 is collected in a collecting container which is connected to the outlet opening 17.

[0056] Before refilling the motor vehicle brake system 1 with brake fluid, the outlet opening 17 is closed. This is preferably done manually by the maintenance personnel, who may be prompted to do so by the control software 19 if necessary.

[0057] Refilling the motor vehicle brake system 1 and changing the brake fluid still remaining in the brake system 1 can be carried out as described below.

[0058] The motor vehicle brake system 1 is refilled with brake fluid by means of a brake fluid changing device via the supply opening 13, with which the brake fluid still present in the hydraulic unit 4 after emptying is discharged during refilling.

[0059] The method explained above was described in connection with a motor vehicle brake system 1, which comprises a brake fluid reservoir 3 distributed across several brake fluid reservoirs 11, 12. In principle, however, this method can also be used in motor vehicle brake systems in which the brake fluid reservoir 3 is formed by a single brake fluid reservoir.

[0060] In a further modification, the brake booster 8 provided on the hydraulic unit 4 can also be used to drain the motor vehicle brake system 1. By appropriately controlling the brake booster, brake fluid can be released via the outlet opening 17. For this purpose, the brake booster 8 presses brake fluid into the hydraulic unit 4 in a first stroke movement. A back-sucking of brake fluid during the return stroke of the brake booster 8, which would cause air to be sucked in via the outlet opening 17, is prevented by appropriately controlling the valves 6a to 6l of the hydraulic unit in 4 using the control software 19.

[0061] The brake booster 8 can be actuated for emptying in addition to the pump 5 of the hydraulic unit 4. However, it is also possible to generate the corresponding pressure by the brake booster 8 alone and / or independently of the pump 5.

[0062] Finally, the procedure for changing the brake fluid will be illustrated again using a further example, without the invention being limited to this alone.

[0063] The entire brake fluid change in a workshop can, for example, proceed as follows: 1. Open the cover 14 on the first brake fluid reservoir 11, for example by unscrewing 2. Connecting a vehicle diagnostic, measuring and information system with appropriate control software 19 for the brake fluid change and then switching on the ignition of the vehicle 3. Lifting the motor vehicle and placing a collecting container at the outlet opening 17 of a brake caliper of a wheel brake 2 4. Start the routine for the emptying phase of the brake fluid change on the vehicle diagnostic, measuring and information system 5. The vehicle diagnostic, measuring and information system controls the vehicle brake system 1, in particular the hydraulic unit 4 with the integrated pump 5 and the valves 6a to 6l, and causes it to suck brake fluid from the brake fluid reservoir 3 and to discharge it through the outlet opening 17 into the collecting container. 6. If a brake fluid deficiency is detected, for example if a warning light "Brake fluid level too low" lights up in the combination instrument, the control software 19 of the vehicle diagnostic, measuring and information system stops the emptying process, terminates the operation of the pump 5 and closes the actuated valves 6a to 6l of the hydraulic unit 4. In addition, the maintenance person is requested to close the outlet opening 17. 7. After the maintenance person confirms the closure of the outlet opening 17 on the vehicle diagnostic, measuring and information system, the valves 6a to 6l of the hydraulic unit 4 are released again. 8. The collecting container filled with old brake fluid is removed, emptied and reconnected to the outlet opening 17 9. A brake fluid change device is also connected 10. Now refill with new brake fluid in the conventional manner, whereby if necessary, bleeding can be carried out via the outlet opening 17.

[0064] In summary, the procedure described above allows for the replacement of the suction of brake fluid from the brake fluid reservoir through its supply opening, without resulting in an increased demand for brake fluid during the brake fluid change. This avoids the risk of damage to the vehicle due to brake fluid dripping from a suction device.

[0065] Compared to manual suction, it can also be better ensured that all brake fluid is removed from the brake fluid reservoir, even if a filter device is permanently installed on the supply side to prevent the entry of dirt into the vehicle's brake system.

[0066] Since this approach eliminates the need to attach an external suction device to the brake fluid reservoir to empty it, the brake fluid reservoir can be installed more flexibly on the vehicle. This improves space efficiency in a motor vehicle.

[0067] Furthermore, it is possible to position the main part of a brake fluid reservoir away from a maintenance opening on the vehicle. This is particularly advantageous for vehicles that, unlike combustion engines, no longer have a distinct engine compartment.

[0068] The invention has been explained in more detail above using various exemplary embodiments and variants. These serve to demonstrate the feasibility of the invention. Individual technical features explained above in the context of further individual features can also be implemented independently of these or in combination with other individual features, even if not expressly described, as long as this is technically possible. The invention is therefore expressly not limited to the specifically described exemplary embodiments, variants, and modifications, but encompasses all configurations defined by the patent claims. List of reference symbols 1 vehicle braking system 2 wheel brakes 3 Brake fluid reservoir 4 hydraulic unit 5 Pump 6a to 6l valve 7 master brake cylinders 8 brake boosters 9 Brake pedal 11 first brake fluid reservoir 12 second brake fluid reservoir 13 Feed opening 14 lids 15 filters 16 first liquid line 17 Outlet opening 18 Sensor 19 Control software 20 Maintenance hatch

Claims

[1] Method for changing the brake fluid of a hydraulic motor vehicle brake system (1) which comprises a brake control device, in which for emptying an outlet opening (17) for brake fluid located on a wheel brake (2) is opened, and subsequently, a pump (5) of the brake control device is switched on to cause brake fluid to exit through the outlet opening (17), wherein valves (6a to 6l) of the brake control device are actuated in such a way as to establish a hydraulic connection from the at least one brake fluid reservoir (11) to the outlet opening (17), so that brake fluid is drawn off from the at least one brake fluid reservoir (11), wherein the suction of air into a hydraulic unit (4) of the brake control device is avoided, characterized by , that before refilling the motor vehicle brake system (1) with brake fluid, the outlet opening (17) is closed and the motor vehicle brake system (1) is refilled with brake fluid by means of a brake fluid changing device via the supply opening 13, with which the brake fluid still present in the hydraulic unit (4) after emptying is discharged during refilling. [2] Method according to claim 1, characterized by that before the pump is switched on, a supply opening (13) for brake fluid is opened on at least one brake fluid reservoir (11). [3] Method according to claim 1 or 2, characterized by that the emptying process is controlled by a vehicle-external control software (19) which for this purpose is temporarily connected to the motor vehicle brake system (1) by hardware - wirelessly or wired. [4] Method according to claim 1 or 2, characterized by that the emptying process is controlled by an internal vehicle control software (19). [5] Method according to one of claims 1 to 4, characterized by that a sensor (18) for detecting brake fluid in the at least one brake fluid reservoir (11, 12) is arranged on the at least one brake fluid reservoir (11, 12) and the emptying process is automatically stopped if the sensor (18) detects a lack of brake fluid in the at least one brake fluid reservoir (11, 12). [6] Method according to one of claims 1 to 4, characterized by that the pump (5) is operated for a vehicle-specific period of time for emptying. [7] Method according to one of claims 1 to 6, characterized bythat a brake booster (8) is provided on a hydraulic unit (4), which is automatically actuated to empty the motor vehicle brake system (1), in addition to the pump (5) of the brake control device or alone and / or independently of the latter. [8] Method for changing the brake fluid of a hydraulic motor vehicle brake system (1) which comprises a brake control device, in which for emptying an outlet opening (17) for brake fluid located on a wheel brake (2) is opened, characterized by , that subsequently, a brake booster (8) is actuated to cause brake fluid to exit through the outlet opening (17), wherein valves (6a to 6l) of the brake control device are actuated in such a way as to establish a hydraulic connection from the at least one brake fluid reservoir (11) to the outlet opening (17), so that brake fluid is drawn off from the at least one brake fluid reservoir (11), where the brake booster (8) is controlled in such a way that brake fluid is released via the outlet opening (17) by the brake booster (8) pressing brake fluid into the hydraulic unit (4) in a first stroke movement and a sucking back of brake fluid during the return stroke of the brake booster (8), which would cause air to be sucked in via the outlet opening (17), is prevented by a corresponding control of the valves (6a to 6l) of the hydraulic unit in (4) by means of control software (19).

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