Method and device for operating a hydraulic brake system, brake system

Abstract

The present invention relates to a method for a hydraulic braking system (1) for operating a motor vehicle, wherein the braking system (1) has at least one operable pressure generator (11) connected to at least one braking circuit (9, 10) having a plurality of hydraulically operable wheel brakes (2-5), wherein each wheel brake (2-5) is equipped with an operable inlet valve (16-19) and an operable outlet valve (20-23), wherein the pressure generator (11) applies a preset hydraulic target pressure (P) according to braking requirements. soll ) is controlled, and in which the actual hydraulic pressure (p) in the braking circuit (9, 10) is controlled. ist The system is monitored. It stipulates that the actual pressure (p) being monitored will be used to monitor the situation. ist The braking dynamics are determined, and the target pressure (p) is changed according to the determined braking dynamics. soll ).

Description

Technical Field

[0001] The present invention relates to a method for a hydraulic braking system for operating a motor vehicle, wherein the braking system has at least one operable pressure generator connected to at least one braking circuit, the braking circuit having a plurality of hydraulically operable wheel brakes, wherein each wheel brake is equipped with an operable inlet valve and an operable outlet valve, wherein the pressure generator is operated by a preset hydraulic target pressure according to braking requirements, and wherein the actual hydraulic pressure in the braking circuit is monitored.

[0002] Furthermore, the present invention also relates to an apparatus for operating the aforementioned hydraulic braking system, the apparatus having a control device.

[0003] Furthermore, the present invention also relates to a braking system having such a device as described above. Background Technology

[0004] The aforementioned types of methods are already known from existing technology. With the increasing electrification of motor vehicles, several concepts have also been developed that could eliminate the mechanical connection between a driver-operable input device and an actuator, which should realize the driver's input expectations. Corresponding developments exist in steering systems as so-called steer-by-wire solutions and in braking systems as so-called brake-by-wire solutions.

[0005] In braking systems with electromechanical brake force amplifiers, which are particularly additional or the sole pressure generator in the braking system, the pressure applied by the driver to the master brake cylinder using the brake pedal is decoupled from the actual braking force acting on the wheel brakes provided by the electrically operated and actuated pressure generator. This pressure generator is typically implemented using a piston pump driven by an electric motor to ensure high hydraulic pressure. This decoupling is necessary to exhibit, for example, a boosting function, where the braking pressure increases beyond the driver's preset braking pressure. Furthermore, if the driver, for example, applies the brake pedal too forcefully, this decoupling can also reduce unnecessarily high pre-pressure acting on the braking system. This is also advantageous from an energy perspective. Moreover, excessively high hydraulic pressure can generate disruptive noise and affect the durability of the braking system. Therefore, limiting the effective pressure to the maximum permissible pressure is advantageous. This can be advantageously achieved through decoupling. Another advantage of decoupling in the case of ABS regulation is that the so-called hydraulic pre-stress, representing the overpressure maintained in the hydraulic system relative to the target braking pressure, can be set independently of brake pedal operation. Therefore, due to the prestress, the pressure provided by the pressure generator is higher than the pressure actually required at the wheel brakes, thereby enabling a rapid pressure regulation process. The prestress is typically chosen to exceed the locking pressure of any wheel brake. Summary of the Invention

[0006] The method according to the invention, having the features of claim 1, has the advantage that the preload pressure is reduced to a favorable level and only increased when necessary, thereby improving the durability of the braking system and simultaneously enabling safe and dynamic braking operation and adjustment. To this end, according to the invention, braking dynamics are determined based on the monitored actual pressure, and the target pressure is changed according to the determined braking dynamics. Therefore, the braking dynamics are considered as the basis for determining the target pressure and, consequently, the preload. This target pressure differs from the target braking pressure that should be applied to one of the wheel brakes. In particular, the target pressure is always higher than the target braking pressure to ensure preload. By setting the target pressure and, consequently, the preload according to the braking dynamics, the advantages are achieved: on the one hand, continuous load on the braking system is avoided through high preload; on the other hand, rapid brake pressure adjustment is ensured during dynamic braking.

[0007] Therefore, a preferred specification stipulates that braking dynamics are determined by monitoring detected pressure pulses. Thus, the actual pressure in the braking circuit or braking system, detected by a pressure sensor, is monitored in response to the appearance of pressure pulses. An increase in the number of pressure pulses within a preset time period indicates an increase in braking dynamics. A decrease in the number of pressure pulses within the same time period indicates a decrease in braking dynamics. Therefore, monitoring pressure pulses ensures simple detection of braking dynamics.

[0008] Preferably, the target pressure increases as braking dynamics increase or have already increased. This ensures that during dynamic braking, there is an increase in prestress in the braking system, which guarantees the generation of the desired braking force when operating the inlet and outlet valves of the wheel brakes.

[0009] Furthermore, it is preferably specified that the target pressure decreases when braking dynamics are reduced or have already been reduced. This ensures that, under reduced dynamic conditions, the prestress is reduced, and therefore the braking system is hydraulically relaxed or less strongly loaded, thereby improving the durability of the braking system.

[0010] According to a preferred embodiment of the invention, in order to obtain braking dynamics, only pressure pulses occurring sequentially within a time period shorter than the maximum adjustment time of the pressure regulator of the pressure generator are considered. Therefore, only pressure changes that cannot be regulated by the pressure generator itself are taken into account.

[0011] In particular, to detect actual pressure, the sensor signal of the pressure sensor associated with the pressure generator is monitored, and the sensor signal is subjected to a low-pass filter, especially a low-pass filter with a time constant of 40 to 60 milliseconds, and particularly 50 milliseconds. This achieves the goal of maintaining irregularities that the pressure generator itself can compensate for when considering braking dynamics.

[0012] To detect braking dynamics, it is preferable to consider only the absolute value of the deviation between the sensor signal and the filtered sensor signal. Specifically, the deviation between the current pressure signal and the filtered average value of the pressure signal is calculated, which corresponds to the amplitude of the pressure generated by the pressure generator. Since only the absolute value of the deviation is of interest, it is preferable to calculate only the absolute value of the deviation.

[0013] Furthermore, it is preferably specified that the detected deviations are stored in a shift register and optionally weighted according to their aging. Therefore, braking dynamics are evaluated using the shift register within a preset time period by means of the weighted deviations. By preferably weighting according to the aging of the corresponding deviations, advantageous monitoring of braking dynamics is achieved. In particular, a shift register with, for example, 20 values ​​having the last 100 milliseconds is used. 100 milliseconds typically corresponds to the adjustment rate of the ABS increase and decrease adjustment cycle. The weighting is specifically performed such that the newest value has the highest weight and the oldest value has the lowest weight.

[0014] Preferably, the target pressure is preset based on a weighted average of the deviations stored in the shift register. Preferably, the weighted average is divided by the sum of all values ​​and multiplied by their respective weights to obtain a standardized value that has the same pressure unit as the sensor signal from the pressure sensor.

[0015] The target pressure is preferably preset based on the hydraulic prestress for the braking target pressure. To prevent the absolute value of the prestress from reaching a critical value, it is preferable to preset a minimum and a maximum value for the prestress, thereby limiting the prestress within an allowable range. A range of 5 bar to 60 bar is preferably selected. Alternatively, the original value of the prestress may be filtered to avoid including unnecessarily high-frequency components. For this purpose, for example, a tailed pointer filter with an applicable filter width may be used. Furthermore, it is preferable to limit the gradient of the target value to prevent excessively rapid increases or decreases. Therefore, the gradient of the pressure target value is limited to a maximum gradient and a minimum gradient.

[0016] The device according to the invention, having the features of claim 11, is characterized in that the control device is specifically designed to perform the method according to the invention. This results in the advantages mentioned above.

[0017] The braking system according to the invention, having the features of claim 11, is characterized by the device according to the invention. This produces the advantages mentioned above. Preferably, the method is used only for active pressure regulation via the ABS system or for active ABS regulation. Attached Figure Description

[0018] Further advantages, preferred features, and combinations thereof will be apparent, particularly from the foregoing description and claims. The invention will then be described in detail with reference to the accompanying drawings.

[0019] Figure 1 The braking system of a motor vehicle is shown.

[0020] Figure 2 A diagram illustrating the hydraulic prestress of the braking system is shown.

[0021] Figure 3 A flowchart illustrating an advantageous method for operating a braking system is shown. Detailed Implementation

[0022] Figure 1 A simplified diagram illustrates an advantageous braking system 1 for a motor vehicle (not shown in detail here), the vehicle having multiple wheels FL, RR, RL, and FR. Each wheel is equipped with a hydraulically operable wheel brake 2, 3, 4, or 5 belonging to the braking system.

[0023] Therefore, the braking system 1 has a master brake cylinder 6, which is currently configured as a tandem cylinder and can be operated by the driver of the motor vehicle by operating the brake pedal 7. The master brake cylinder 6 is connected to the hydraulic reserve device 8 on one hand and to two brake circuits 9 and 10 on the other. Here, brake circuit 10 is associated with or connected to wheel brakes 2 and 3, and brake circuit 9 is associated with or connected to wheel brakes 4 and 5.

[0024] The braking system 1 also has a controllable pressure generator 11 with an electric motor 12 operatively connected to a piston pump 13 to drive the piston pump. On the suction side, the piston pump 13 is connected to a reserve device 8, and on the pressure side, it is connected to two braking circuits 9 and 10, and optionally, when connected to shut-off valves 14 and 15, it is connected to both braking circuits 9 and 10.

[0025] In addition, in the corresponding braking circuit, each wheel brake 2 to 5 is equipped with inlet valves 16, 17, 18, 19 and operable outlet valves 20, 21, 22, 23.

[0026] Valves 16 to 23, in particular, can be controlled via control device 24, just like pressure generator 11. Thus, for example, in ABS mode, if one wheel is about to lock up, one of the outlet valves 20 to 23 is controlled to reduce the pressure at the corresponding wheel brake 2 to 5 to prevent or interrupt the lockup. Furthermore, control device 24 detects the driver's braking request via pressure sensor 25 and / or displacement sensor 26 associated with brake pedal 7. Based on the braking request, control device 24 controls pressure generator 11 to generate a target pressure in brake circuits 9 and 10, which can then be used by wheel brakes 2 to 5 to perform the braking process. By controlling the inlet and outlet valves 16 to 23, control device 24 sets the target braking pressure for the corresponding wheel brakes 2 to 5 according to the braking request.

[0027] Furthermore, the master brake cylinder 6 is connected to the brake feel simulator 27, so that the hydraulic volume squeezed by the driver by operating the brake pedal 7 is moved to the hydraulic reservoir 28, but not to one of the brake circuits 9 or 10. Therefore, the brake circuits 9 or 10 are hydraulically disengaged or separable from the hydraulic brake cylinder 6, particularly by means of additional release valves 29 or 30, so that the actual pressure p in the hydraulic system or in the brake circuits 9 or 10 is... ist It can only be provided through pressure generator 11.

[0028] Figure 2 The target braking pressure p is illustrated in a simplified diagram. RB_Soll A graph plotted with respect to time t. Furthermore, a preset target pressure p is given to the pressure generator based on the braking target pressure. soll And the actual pressure p actually provided by pressure generator 11 in braking circuits 9 and 10. ist The time t is plotted. Target pressure p soll The distance between the hydraulic prestress Δp and the target braking pressure is defined as the hydraulic prestress. v .

[0029] Now, refer to later Figure 3Describes a favorable method for determining the prestress Δp. v The optimal minimum value is determined under the following conditions. Therefore, the prestress is optimally determined in each case to maximize the continuous load-bearing capacity of the braking system 1 on the one hand, and to ensure dynamic braking pressure regulation on the other.

[0030] Therefore, different ABS adjustment conditions are known, in which increased preload pressure is advantageous, for example, in highly unstable ABS adjustment on rough roads with varying friction values. Here, high preload helps to achieve a large compression stroke in a short time, i.e., a large increase and decrease in the corresponding wheel brake pressure. Preload here acts as a buffer against possible increases in wheel pressure. Other ABS operating conditions, such as ABS operating on uniformly smooth ice, are also known, in which significantly lower preload pressure is advantageous.

[0031] In principle, the two types of disturbances that should be considered, given by the boundary conditions of the braking system, must be taken into account:

[0032] The first boundary condition to mention is the pressure peak. The highly dynamic pressure peak of the pressure generator or piston pump 13 interferes with the regulation of the inlet valves 16-19 because these valves respond very quickly, either hydraulically or mechanically, to the pressure peak, while electronic regulation cannot respond arbitrarily quickly enough to compensate for the corresponding pressure peak in the force balance of the respective valve. The resulting error is the so-called crosstalk, an increase in pressure from the piston pump 13 to the corresponding wheel. This crosstalk leads to unstable ABS regulation because possible wheel lock-up is triggered by the pressure supply disturbance rather than by the road itself. To improve robustness to pressure peaks, a slower, hydraulically mechanical valve is advantageous because electronic regulation can react quickly enough before the pressure peak hydraulically crosstalks to the wheel.

[0033] The second boundary condition to mention is volumetric tolerance. Volumetric inaccuracies in braking system 1 lead to deviations in pressure regulation accuracy. The hydraulic model of the piston pump and regulator, as well as the wheel pressure regulation using inlet valves 16 to 19, is based on the assumption of a hydroelastic relationship between the volume and pressure of the corresponding wheel brake (the so-called pv characteristic curve). This component characteristic is tolerant and related to wear, condition, and temperature. Therefore, model-based pressure regulation is generally inaccurate and thus uncomfortable at larger deviations, as the resulting differences must first be adjusted subsequently, for example, by a closed-loop regulator. However, a more effective device to offset volumetric tolerances is a quick-acting valve, which occupies its pressure operating point very quickly, even when volumetric pre-control is inaccurate during periods of large tolerances.

[0034] Therefore, the system decision-making process for selecting dynamic characteristics, especially those of inlet valves 16 to 19, faces a conflict of objectives. The trade-off between robustness to pressure peaks and robustness to volumetric tolerances can only be determined once through hardware design. The method described below leverages the advantage that the inlet valve has its time constant and prestress Δp. v The relevant characteristic, the time constant, describes the dynamic regulation of the static operating point (differential pressure, volumetric flow rate under a given current). Therefore, the corresponding inlet valves 16 to 19 slow down with increasing prestress and speed up with decreasing prestress. Thus, by selecting an appropriate prestress, a trade-off between fast and slow valve behavior can be resolved. An advantageous approach therefore stipulates that during more dynamic braking processes, the prestress is increased to slow valve behavior and thus make it more robust relative to pressure peaks, and during less dynamic braking or regulation processes, the prestress is decreased to accelerate valve behavior and reduce pressure regulation errors caused by volumetric tolerances more quickly. Furthermore, noise generation, on-board electrical load, and component loads of the braking system 1 are generally benefited.

[0035] Therefore, a favorable method stipulates continuous monitoring of braking dynamics, especially during ABS adjustment. To this end, in the first step S1, the current hydraulic pressure p is first monitored. Ist .

[0036] In the subsequent step S2, the pressure signal from pressure sensor 31 is filtered. For this purpose, a 50 ms pT1 low-pass filter is used to smooth the sensor signal from pressure sensor 31. The 50 ms time constant here specifically corresponds to the time response of the piston pump regulator. Of particular interest is the pressure deviation that the piston pump regulator cannot adjust. The current pressure signal p... Ist The deviation Δδ from the filtered pressure signal corresponds to the amplitude of the piston pump pressure, which can be adjusted using a frequency f higher than that of the piston pump regulator. Therefore, currently applicable is f = 1 / T1 = 1 / 50ms = 20Hz.

[0037] However, only the absolute value of the deviation Δδ is relevant, so only the absolute value Δp is calculated in step S3. abs .

[0038] In the subsequent step S4, the calculated deviations are reviewed, and the deviations of the last 100 milliseconds (which, for example, correspond to 20 values) are now recorded in the shift register. The duration of 100 milliseconds typically corresponds to the adjustment rate of the ABS increase and decrease adjustment cycle. Using a weighted evaluation algorithm, the deviations are preferably weighted according to their age in step S4 and summed in step S5. Here, the most recent value has the highest weight (specifically, factor 19), while the oldest value has the lowest weight (specifically, factor 0).

[0039] Subsequently, the weighted average of all shift register elements is divided by the sum of all elements and multiplied by their respective weights, thus achieving standardization in step S6. This standardization has the same pressure unit as the pressure signal from sensor 31. In this embodiment, the sum of the 20 elements is therefore Σi[i=0…19]=190.

[0040] The sum obtained in step S6 is the hydraulic prestress Δp v The original value. To achieve the generated prestress Δp v Without an unnecessarily high-frequency component, different filters are applied in subsequent steps. Therefore, in step S7, a trailing pointer filter with an applicable filter width is applied first. Optionally, this filter width, or in particular a 2-bar filter width, can be set.

[0041] Subsequently, in step S8, the gradient of the signal is preferably further limited to prevent excessively rapid rises or falls. Therefore, the signal is limited to a maximum and a minimum gradient. Specifically, a fall limit of -75 bar / s and a rise limit of 25 bar / s are set.

[0042] In order to make the prestress Δp v The absolute value is also kept within a favorable range. In step S9, the final result is preferably still limited to the smallest meaningful minimum value (currently, for example, 5 bar) and the largest meaningful maximum value (currently, for example, 60 bar).

[0043] At the start of the method, the filter value is advantageously initialized with a default value of 30 bar or an initial value to initiate the method. Finally, a minimum prestress is provided in step S10, and a target value for the pressure generator 11 is calculated based on this minimum prestress.

Claims

1. A method for operating a hydraulic braking system (1) of a motor vehicle, wherein, The braking system (1) has at least one operable pressure generator (11) connected to at least one braking circuit (9, 10), the braking circuit having a plurality of hydraulically operable wheel brakes (2-5), wherein each wheel brake (2-5) is equipped with an operable inlet valve (16-19) and an operable outlet valve (20-23), wherein the pressure generator (11) applies a preset hydraulic target pressure (p) according to the braking requirements. soll ) is controlled, and wherein the actual pressure (p) of the hydraulic pressure in the braking circuit (9, 10) is controlled. ist The monitored pressure is characterized by being based on the actual pressure being monitored (p). ist The braking dynamics are determined, and the target pressure (p) is changed according to the determined braking dynamics. soll ).

2. The method according to claim 1, characterized in that, The braking dynamics are determined by monitoring the detected pressure pulses.

3. The method according to any one of the preceding claims, characterized in that, The target pressure (p) soll It increases as braking dynamics increase or have already increased.

4. The method according to any one of the preceding claims, characterized in that, The target pressure (p) soll The braking dynamics are reduced when they are weakened or have already been weakened.

5. The method according to claim 2, characterized in that, In order to obtain the braking dynamics, only pressure pulses that occur sequentially within a time period shorter than the maximum adjustment time of the pressure regulator of the pressure generator (11) are considered.

6. The method according to any one of the preceding claims, characterized in that, To detect the actual pressure (p) ist The sensor signal of the pressure sensor (31) associated with the pressure generator (11) is monitored, and the sensor signal is subjected to a low-pass filter, especially a low-pass filter with a time constant of 40 to 60 milliseconds, especially 50 milliseconds.

7. The method according to any one of the preceding claims, characterized in that, To detect the braking dynamics, only the absolute value of the deviation between the sensor signal and the filtered sensor signal is considered.

8. The method according to any one of the preceding claims, characterized in that, The detected deviation is stored in a shift register and is optionally weighted according to its timeliness.

9. The method according to any one of the preceding claims, characterized in that, The target pressure is preset based on the weighted average of the deviations in the shift register.

10. The method according to any one of the preceding claims, characterized in that, The target value is based on the hydraulic prestress (Δp) for the target pressure of the wheel braking system. v (This is preset.) 11. A device for operating a braking system (1) of a motor vehicle, wherein, The braking system (1) has at least one operable pressure generator (11) connected to at least one braking circuit (9, 10) having a plurality of hydraulically operable wheel brakes (2-5), wherein each wheel brake (2-5) is equipped with an operable inlet valve (16-19) and an operable outlet valve (20-23), characterized in that it has a control device (24) specifically designed to perform the method according to any one of claims 1 to 10 in normal use.

12. A braking system for a motor vehicle, wherein, The braking system (1) has at least one operable pressure generator (11) connected to at least one braking circuit (9, 10) having a plurality of hydraulically operable wheel brakes (2-5), wherein each wheel brake (2-5) is equipped with an operable inlet valve (16-19) and an operable outlet valve (20-23), characterized in that it has the device according to claim 11.

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