Method and device for determining the volume of liquid available, braking system

Abstract

The invention relates to a method for determining the volume of liquid available in a reservoir (2) for brake fluid of a brake system (1), wherein the brake system (1) has a pressure generator (4, 9) which is fluidically connected on the one hand to the reservoir (2) and on the other hand to at least one brake circuit (8), which pressure generator can be actuated for generating a hydraulic pressure in the brake system (1) in the event of extraction of brake fluid from the reservoir (2), and wherein a predefined limit value (F) below the filling level for brake fluid in the reservoir (2) is monitored by means of a binary sensor (11) assigned to the reservoir (2). It is provided that the actuation of the pressure generator (4, 9) is monitored, and that the volume of liquid available is determined from the actuation of the pressure generator (4, 9) when the current filling level is below the limit value (F).

Description

Technical Field

[0001] The present invention relates to a method and apparatus for determining the usable volume of liquid in a brake fluid reservoir for a braking system, wherein the braking system has a pressure generator fluidly connected on one side to the reservoir and on the other side to at least one braking circuit, the pressure generator being operable to generate hydraulic pressure in the braking circuit when brake fluid is extracted from the reservoir, and wherein a predetermined limit value below the fill level of brake fluid in the reservoir is monitored by means of a binary sensor assigned to the reservoir.

[0002] Furthermore, the present invention relates to a braking system having a reservoir for brake fluid; having at least one braking circuit and a pressure generator having a fluid connection, on one hand, to the reservoir and on the other hand, to the at least one braking circuit, the pressure generator being configured to: generate hydraulic pressure in the at least one braking circuit when brake fluid is extracted from the reservoir; wherein the reservoir is provided with a binary sensor for monitoring the brake fluid fill level in the reservoir. Background Technology

[0003] The type of method mentioned at the beginning is known in the prior art. Hydraulic braking systems are often equipped with a reservoir or liquid tank in which brake fluid is supplied for the braking system. To ensure that the brake fluid does not fall below a predetermined limit volume, the brake fluid level in the reservoir is monitored by means of a fill level sensor. For cost reasons, a binary sensor is often placed at the reservoir, which detects when the fill level is below a predetermined limit value. If the fill level is below the predetermined limit value, this is detected and reported by the binary sensor. However, one cannot draw conclusions about the actual fluid volume present from this. Summary of the Invention

[0004] The method according to the invention, having the features of claim 1, achieves the following: although a binary sensor is used to monitor the brake fluid fill level in the reservoir, a quantitative conclusion can be drawn regarding the actual or expandable fluid volume present in the braking system without the need for complex sensor technology. Thus, according to the invention, the operation of the pressure generator is monitored, and when the current fill level is below the limit value, the usable fluid volume is determined based on the operation of the pressure generator. Therefore, the invention specifies that the operation of the pressure generator is monitored, thereby determining the magnitude of the hydraulic volume moved from the reservoir to the braking system by the pressure generator. Based on the determined moved hydraulic volume, it is possible to determine how much the fill level in the reservoir has decreased due to the operation of the pressure generator. Based on the time point reported or determined by the binary sensor as below the limit value, the fill level in the reservoir before the operation of the pressure generator can be calculated based on the moved volume and the time below the limit value. The fill level present in the reservoir before the operation of the pressure generator is understood as the usable brake fluid volume. This allows for a simple implementation: taking into account the operation of the pressure generator in the braking system, the actual usable liquid volume in the tank can be determined by applying a binary sensor, thereby enabling an early alarm signal to be given when the actual usable liquid volume is lower than a predetermined limit value.

[0005] Preferably, the pressure generator is monitored in terms of the controlled volume of the brake fluid transferred via it. In principle, monitoring the operation of the pressure generator to estimate the available fill level is sufficient, while calculating the controlled volume of the hydraulic fluid improves the accuracy of the estimate. Knowing the application of the pressure generator, the controlled volume moved from the reservoir into the brake circuit via it can be calculated with minimal effort.

[0006] The pressure generator is preferably an operable hydraulic cylinder, particularly the master brake cylinder of a braking system, having at least one movably supported hydraulic piston, and the operating volume is determined based on the movement of the hydraulic piston. Specifically, the movement distance of the hydraulic piston is monitored or determined based on the operation of the pressure generator, and thereby the moved hydraulic volume is determined taking into account the end face of the hydraulic piston.

[0007] According to an alternative embodiment of the invention, the pressure generator is a drivable rotary pump, and the manipulated volume is determined based on the driving duration and rotational speed of the rotary pump. Knowing the power data of the rotary pump, and especially the delivery volume which depends on the rotational speed, the hydraulic volume moved can also be determined without significant additional cost.

[0008] According to a preferred embodiment of the invention, the available fluid volume is determined based on the desired operating volume and the cross-sectional area of ​​the reservoir. Specifically, the moved hydraulic volume is divided by the cross-sectional area of ​​the reservoir to obtain the initial fill level of the brake fluid in the reservoir, which corresponds to the desired available fluid volume.

[0009] Preferably, at least one valve is connected after the hydraulic cylinder, preventing brake fluid from flowing back from the brake circuit into the hydraulic cylinder when the hydraulic piston is pushed back to the starting position while drawing brake fluid from the reservoir. Because the hydraulic cylinder or cylinders cannot draw hydraulic fluid from the reservoir during the pushing process to generate hydraulic pressure, it is preferable to prevent brake fluid from flowing back from the brake circuit into the brake cylinder by means of the valve when the piston is pulled back to the starting position. Then, the hydraulic cylinder draws brake fluid from the reservoir upon retraction, thereby changing the fill level in the reservoir. Overall, the hydraulic volume moving into the hydraulic cylinder when the hydraulic piston is pushed back corresponds to the required operating volume of the pressure generator.

[0010] Preferably, the method is performed periodically, particularly after each start-up of the vehicle when it is stationary and / or at each stop. This ensures that the braking system is monitored periodically without adversely affecting the vehicle's operation. Here, starting the vehicle is understood as starting the engine (ignition), and stopping the vehicle is understood as turning off the engine (shutting down).

[0011] Furthermore, a preferred specification is that for the functional verification of the binary sensor, the pressure generator is moved by adjusting the operating volume. Due to this adjusted volume, the limit value in the tank should be lowered. If the binary sensor fails to detect a value below the limit, a functional error is identified. That is, the pressure generator is manipulated to move a sufficiently large operating volume, which under normal circumstances results in a filling level below a predetermined limit value. However, if this is not detected by the binary sensor, a binary sensor error is identified.

[0012] The device according to the invention having the features of claim 10 is characterized in that it is configured as a controller, said controller being specifically configured to: implement the method according to the invention in a prescribed application.

[0013] The braking system according to the invention, having the features of claim 11, is characterized by the device according to the invention. This thereby yields the advantages already mentioned. Attached Figure Description

[0014] Other advantages and preferred features and combinations thereof are derived, in particular, from the foregoing description and from the claims. The invention is explained in more detail below with the aid of the accompanying drawings. Wherein:

[0015] Figure 1 The advantageous braking system is shown in a simplified view; and

[0016] Figure 2 A flowchart illustrating an advantageous method for determining the available fluid volume in a braking system is shown. Detailed Implementation

[0017] Figure 1 An advantageous braking system 1 of a motor vehicle, not shown in detail herein, is illustrated in a simplified view. The braking system 1 has a reservoir 2 for containing and storing a liquid braking medium 3. The reservoir 2 is fluidly connected to a pressure generator 4, which, according to an embodiment of the invention, is configured as a hydraulic cylinder 5 with a hydraulic piston 6 movably supported therein. On the outlet side, the pressure generator 4 is fluidly connected to an operable valve 7, which selectively releases or locks the connection of the pressure generator 4 to the brake circuit 8. The valve 7 is, for example, configured as a solenoid switching valve. Optionally, in addition to or as an alternative to the pressure generator 4, there is another pressure generator 9, which, according to an embodiment of the invention, is configured as a rotary pump 10. If the additional pressure generator 9 is present, it is advantageously connected between the pressure generator 4 and the valve 7.

[0018] Furthermore, the storage tank 2 is equipped with a binary sensor 11. The binary sensor 11 is disposed on the side wall 12 of the storage tank and provides a first signal when the brake fluid 3 is at the height of the binary sensor 11, and a second signal when the brake fluid 3 is not in the area of ​​the binary sensor 11, such that only gas volume, particularly air volume, is present in the storage tank 2 at the height of the binary sensor 11. The binary sensor 11 is disposed at a height on the side wall 12 corresponding to a predetermined limit value F for the fill level of the brake medium 3 in the storage tank 2. If the level 13 of the brake medium 3 is lower than the predetermined limit value F, then the binary sensor 11 changes its signal and thus reports that the brake medium 3 in the storage tank 2 is below the predetermined fill level.

[0019] Furthermore, the braking system 1 also includes a controller 14, which is at least signal-technically connected to the binary sensor 11, the pressure generator 4 and / or 9, and the valve 7. For clarity, in Figure 1 The signal connection is not shown in the diagram.

[0020] The controller 14 is configured to operate the pressure generators 4 and / or 9 and the valve 7, and to analyze the signal from the binary sensor 11. For this purpose, in accordance with the prescribed application, the controller 14 performs [operations / functions] in a motor vehicle, or specifically in the braking system 1. Figure 2 The method is represented by a flowchart.

[0021] The method begins in step S1 with the start of operation (ignition) of the vehicle. Subsequently, in step S2, the pressure generators 4 and 9 are monitored in terms of their operation, and simultaneously, in step S3, the data from the binary sensor is monitored. If, in step S2, it is determined that at least one pressure generator 4 or 9 is operated, but in step S3, the fill level sensor 11 has not yet reported below the limit value (j), then in step S4, it is identified that there is still sufficient brake fluid, or a sufficient volume of fluid, in the reservoir 2. However, if it is identified that the binary switch 11 reports below a predetermined fill level (n), then in the subsequent step S5, the hydraulic volume moved from the reservoir 2 along the direction of the brake circuit 8 by the pressure generators 4 and 9 during their operation is calculated based on the detected operation and the time point below the limit value. Knowing the moved hydraulic volume, the original fill level of the reservoir 2 is calculated. Specifically, the moved hydraulic volume is divided by the area of ​​the reservoir 2. Thus, the original fill level is obtained as the height in the reservoir 2. to this end, Figure 1 For example, the state of the storage tank 2 is shown, in which the binary sensor 11 reports or triggers a value below the limit F.

[0022] For the available fluid volume in braking system 1, in step S6, the original fill level of the reservoir 2 is compared with a predetermined limit value. If the calculated value is not lower than the predetermined limit value (j), then a sufficient fill level is identified in step S4, and the vehicle 1 operates as usual. However, if it is determined in step S6 that the calculated available volume is lower than the limit value (n), then in the subsequent step S7, an alarm signal is given to the driver of the vehicle, for example in acoustic or visual form.

[0023] To determine the operating volume, the pressure generator 4 detects the movement distance of the piston 6 in the hydraulic cylinder 5 to calculate the moved hydraulic volume, taking into account the cross-section of the hydraulic cylinder 5 or the end face of the piston 6. Preferably, the operating volume is calculated after the hydraulic piston has moved the hydraulic volume in the brake circuit 8, when the hydraulic piston 6 is moved back to its initial retracted position. For this purpose, the valve 7 is closed when the hydraulic piston 6 is retracted. This causes the pressure generator 4 to draw brake fluid 3 from the reservoir 2 to fill the now free volume in the hydraulic cylinder 5. Thus, the operating volume is determined at the return position, not during the power stroke of the hydraulic piston 6.

[0024] Regarding the pressure generator 9, in order to determine the operating volume, the rotational speed and rotational duration of the rotary pump 10 are monitored, and the operating volume is calculated knowing the power characteristic curve of the rotary pump 9.

[0025] The advantageous braking system 1, or the described method, has the following advantages: although only a single binary sensor 11 is arranged at the reservoir 2, it is possible to achieve a path analytical conclusion regarding the actual fluid volume present in the braking system. The method is advantageously executed after each start-up of the vehicle 1 and / or upon its shutdown. Preferably, the obtained and calculated values ​​are persistently stored to detect a curve of the obtained fluid volume. If the fluid volume persistently decreases, it is inferred that a leak exists in the braking system 1, and an alarm signal is given, for example, so that countermeasures can be taken early.

[0026] Furthermore, the advantageous braking system 1 enables the monitoring of the fill level sensor, or binary sensor 11. For this purpose, the pressure generator 4 and / or 9 are manipulated to move a hydraulic volume so large that the fill level of the brake fluid 3 in the reservoir 2 should be below the limit value F. If the binary sensor 11 fails to recognize it, i.e., if the binary sensor is not triggered, then a malfunction of the binary sensor 11 is determined.

Claims

1. Method for determining the volume of available liquid in a reservoir (2) for brake fluid of a brake system (1), wherein the brake system (1) has a pressure generator (4, 9) which is fluidically connected on the one hand to the reservoir (2) and on the other hand to at least one brake circuit (8), which pressure generator can be actuated for generating a hydraulic pressure in the brake system (1) in the event of extraction of brake fluid from the reservoir (2), and wherein a predefined limit value (F) below the filling level of the brake fluid in the reservoir (2) is monitored by means of a binary sensor (11) assigned to the reservoir (2), characterized in that, The actuation of the pressure generator (4, 9) is monitored, and the volume of liquid available is determined from the actuation of the pressure generator (4, 9) when the current filling level is below the limit value (F), wherein the pressure generator (4, 9) is monitored in terms of the hydraulic actuation volume of brake fluid transferred by the pressure generator (4, 9), wherein the volume of liquid available is determined from the actuation volume determined and the cross-sectional area of the reservoir (2).

2. The method of claim 1, wherein, The pressure generator (4) is an actuable hydraulic cylinder (5) with at least one movable hydraulic piston (6), and the actuation volume is determined from the movement of the hydraulic piston.

3. The method of claim 1, wherein, The pressure generator (4) is an actuable main brake cylinder with at least one movable hydraulic piston (6), and the actuation volume is determined from the movement of the hydraulic piston.

4. The method of claim 1, wherein, The pressure generator (9) is an actuable rotary pump (10), and the actuation volume is determined from the duration and rotational speed of the actuation of the rotary pump.

5. The method of claim 2, wherein, At least one valve (7) is connected behind the hydraulic cylinder (5), through which valve the backflow of brake fluid from the brake circuit (8) into the hydraulic cylinder (5) is prevented when the hydraulic piston (6) is pushed back into the starting position in the case of extraction of brake fluid from the reservoir (2).

6. The method of claim 1, wherein, The method is carried out periodically.

7. The method of claim 1, wherein, The method is carried out periodically after each start of operation of the motor vehicle in the stopped state of the motor vehicle and / or at each stop of operation of the motor vehicle.

8. The method of claim 1, wherein, The volumes of liquid available determined by the method carried out multiple times are compared with one another, and a leak in the brake system (1) is identified in the case of a falling volume of liquid being detected.

9. The method of claim 1, wherein, For a functional check, an actuation volume is moved by the pressure generator (4, 9), as a result of which the filling level of brake fluid (3) in the reservoir (2) should be below the limit value (F), and a functional error of the binary sensor (11) is identified when the binary sensor does not identify the falling below.

10. A device for determining the volume of available liquid in a reservoir (2) for brake fluid of a brake system (1), wherein the brake system (1) has a pressure generator (4, 9) which is fluidically connected on the one hand to the reservoir (2) and on the other hand to at least one brake circuit (8), which pressure generator can be actuated for generating a hydraulic pressure in the brake system (1) in the event of extraction of brake fluid from the reservoir (2), and wherein a predefined limit value (F) below the filling level of the brake fluid in the reservoir (2) is monitored by means of a binary sensor (11) assigned to the reservoir (2), characterized in that The controller (14) is configured as a control unit which is specifically set up to implement the method according to any one of claims 1 to 9 in a prescribed application.

11. A brake system (1) for a motor vehicle, with a reservoir (2) and at least one brake circuit, wherein a pressure generator (4, 9) is connected to the reservoir (2) on the one hand and to at least one brake circuit (8) on the other hand and is configured to generate a hydraulic pressure in at least one brake circuit (8) in the event of extraction of brake fluid from the reservoir (2), and with a binary sensor (11) assigned to the reservoir (2) for detecting a predefined limit value (F) below a filling level of brake fluid in the reservoir (2), characterized in that The device according to claim 10.

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