Method for operating a valve, valve device, braking system, and motor vehicle

Abstract

The invention relates to a method for operating an actuatable electromagnetic-hydraulic valve, in particular an inlet valve of a wheel brake device of a braking system of a motor vehicle, wherein an electrical actuation current for the valve used to set a specified pressure difference across the valve is corrected by a specified value depending on a determined hysteresis behavior of the valve, and the valve is actuated using the corrected actuation current. It is provided that, in order to determine the hysteresis behavior, a temporal progression of actual values of the pressure difference is observed with the aid of a PT1 filter (1).

Description

[0001] Description

[0002] title

[0003] Method for operating a valve, valve device, braking system, motor vehicle

[0004] The invention relates to a method for operating a controllable electromagnetic-hydraulic valve, in particular an inlet valve of a wheel brake device of a braking system of a motor vehicle, wherein an electrical control current for the valve used to set a predetermined pressure difference across the valve is corrected by a predetermined value depending on a determined hysteresis behavior of the valve and the valve is controlled with the corrected control current.

[0005] Furthermore, the invention relates to a valve device with a valve and a control device specially designed to carry out such a method, a braking system with such a valve device, and a motor vehicle with such a braking system.

[0006] State of the art

[0007] Methods of the type mentioned above are known from the prior art. For example, German Patent Application DE 19624 794 A1 discloses a brake system with a brake pressure regulator and a control valve. A current regulator is connected downstream of the brake pressure regulator and has means for compensating for mechanical and magnetic hysteresis effects that occur when an electromagnetically actuated sealing seat of the control valve is actuated. For this purpose, the means generate at least one correction value, depending in particular on the direction of movement of the sealing seat, which is added to or subtracted from the desired value of the electric current to be supplied to an electromagnet.The applicant's patent DE 19848 960 B4 discloses a method for controlling a pressure control valve, in particular in a braking system, wherein the pressure control valve is controlled by means of a variable control signal within the framework of a closed-loop control system, wherein the size of the control signal is at least dependent on a braking command specification, wherein in at least one operating situation in which, after a control of the valve increasing the pressure difference across the valve, there is a transition to a control of the valve reducing the pressure difference, the control signal size for the valve is corrected with a predetermined value. In particular, when the at least one operating situation occurs, a hysteresis value is determined depending on a value representing the then existing pressure difference across the valve, which hysteresis value is applied to the control signal size or the pilot control value. The hysteresis value is determined according to a characteristic curve.

[0008] Disclosure of the invention

[0009] The method according to the invention with the features of claim 1 is characterized in that, to determine the hysteresis behavior, a temporal progression of actual values ​​of the pressure difference is observed using a PT1 filter. The method according to the invention is particularly advantageous for corresponding valves in hydraulic brake systems. For example, in the pressure control of brake systems, control valves proportional to a differential pressure (DP valves) are used on corresponding inlet valves of wheel brake devices. In the static case, these control valves have a proportionality of the electrical control current to a desired pressure difference. In principle, this represents a force balance between the electromagnetic forces and the hydraulic and mechanical (spring) forces. The accuracy of this proportionality is the basis for the pressure control accuracy of the wheel pressures in the brake systems.This force balance is influenced by internal valve friction as well as magnetic remanence / hysteresis. Friction and hysteresis depend on the previous history, i.e., the direction of movement and the direction of force change, i.e., the previous course of the electrical control current. Control valves therefore often exhibit inconsistent behavior depending on the direction of actuation (depending on the change gradient of the control current). However, pressure control accuracy requires that the proportionality between the control current and the wheel differential pressure be as predictable as possible. It is fundamentally conceivable to operate the corresponding valves with a so-called dither, i.e., with an additional alternating current component in addition to the actual control current, to overcome the internal friction and hysteresis.However, this leads to a deterioration in NVH behavior, which is undesirable, particularly with increasing electrification of vehicle drive systems, which eliminates masking combustion engine noise. The invention therefore describes a method in which the positioning accuracy of corresponding DP control valves is improved despite hysteresis and friction effects even without dither, while simultaneously reliably avoiding noise and systematic errors that can arise from the AC component of a dither. An intake valve typically has asymmetric control properties, since a control error can only result in a pressure buildup. A control error with the opposite sign occurring shortly thereafter is unable to correct the initial error. Due to its position in the system, the valve is generally unable to reduce pressure.Due to this asymmetric error behavior, functional disadvantages also arise when an alternating current component is superimposed. If the alternating current amplitude is too high, the valve tends to open and the proportionality (current - pressure difference) is therefore disrupted. The control of the inlet valve is fundamentally proportional to the difference between the actual pre-pressure of the pressure supply and the target wheel pressure, i.e. the pressure difference used in the invention. For example, a hydraulically generated braking force is measured using a pressure sensor, which then corresponds to the actual pre-pressure for the control. The control current differs depending on whether the pressure supply has falling or rising gradients. An actually set wheel pressure deviates from a specification particularly when the gradient is falling.The resulting deviation is the result of internal valve hysteresis, which is improved according to the invention by appropriate static correction of the control current. This basic idea, particularly as an alternative to a dither, corresponds to the prior art mentioned above. The method according to the invention creates a particularly advantageous alternative, in particular to the determination of the hysteresis behavior as a function of a characteristic curve, known from the prior art and mentioned above. The use of the PT1 filter ensures a particularly precise prediction of the hysteresis behavior at all times. In particular, the direction of the hysteresis is determined particularly easily and advantageously.The method according to the invention observes the history of the pressure difference as a relevant input variable for valve control, formed from the difference between the actual pre-pressure of the pressure supply and the target wheel pressure, and calculates a prediction for the hysteresis behavior from this, which describes which real hysteresis can typically be assumed at a current operating point. By adding this prediction for the hysteresis behavior to the pressure difference-proportional control, the corresponding control current changes and is now dependent on the hysteresis behavior in addition to the pressure difference. The valve control is thus advantageously designed to be highly robust against hysteresis effects of the actual valve. The measurable pressure curve in the wheel then shows almost no directional dependence on the pressure supply.The inventive correction of the control current as a function of the hysteresis behavior predicted by the PT1 filter advantageously further improves the accuracy of setting the pressure difference. In particular, a raw value for the hysteresis behavior is determined as the difference between an unfiltered pressure difference input signal and a corresponding output signal of the PT1 filter. In signal terms, this raw value has the correct sign or the correct phase position for the hysteresis compensation, but not yet the correct magnitude. The raw value is therefore preferably finally limited to a minimum (for falling control) and a maximum (for rising control). These minimum and maximum values ​​contain statically derived hysteresis values ​​that result from friction effects or magnetic hysteresis.Hysteresis values ​​greater than these cannot, in principle, occur because the valve then moves again, or because static and sliding friction are overcome. Preferably, a time constant of the PT1 filter is parameterized differently depending on the control intensity. This advantageously reflects the fact that hysteresis effects increase with larger control currents, often disappear completely with smaller ones, or at least rise and fall very quickly.

[0010] According to a preferred development of the invention, the PT1 filter is partially reset at least at a predetermined first point in time. Such a reset advantageously further improves the robustness of the method according to the invention. Typically, only a complete reset of PT1 filters is known; a partial reset implements an advantageous "semi-reset."

[0011] Particularly preferably, the PT1 filter is fully reset at a predetermined second point in time. The second point in time preferably occurs after the first point in time, so that a partial reset is performed first, followed by a full reset. This approach, with corresponding resetting of the PT1 filter at appropriate points in time, results in the advantage that the PT1 filter is used particularly efficiently because the hysteresis is not overly sensitive to signal noise, for example, from a pre-pressure sensor, while still responding quickly to changes in direction.

[0012] According to a preferred development of the invention, the unfiltered temporal progression of the actual pressure difference values ​​and the temporal progression filtered using the PT1 filter are observed to specify the first and / or second time points. Thus, the filtered and unfiltered signal progressions of the pressure difference are superimposed. This provides an advantageously simple way of specifying the time points, for example, by comparing the temporal progressions with each other.

[0013] It is particularly preferred that, when an inflection point in one of the time profiles is detected, the corresponding time is specified as the first time. A inflection point in one of the signal profiles results in the signs of the gradients of the two signal profiles being different. Such a time is particularly advantageous for carrying out the semi-reset described here. The condition for this semi-reset is therefore already met when the signs of the unfiltered and filtered signals are different. This semi-reset thus somewhat anticipates the full reset and somewhat mitigates the jump in the unavoidable reset process. The semi-reset condition also applies, for example, when the unfiltered pressure signal has higher-frequency interference. This therefore leads to the continuous (semi-)resetting of the filter. The hysteresis compensation is thus practically eliminated.In this case, hysteresis of the real valve is unlikely, since the continuous pressure disturbances act as a substitute for a dither, i.e. as a substitute for a continuous alternating component that overcomes the friction.

[0014] According to a preferred development of the invention, when the time profiles intersect, the corresponding point in time is specified as the second point in time. A full reset is useful when the filtered signal has exceeded a peak or passed through a minimum value. The unfiltered and filtered signals intersect. Only when the two signal profiles intersect, i.e., have an intersection, is a correspondingly advantageous point in time to perform the described full reset. Because this second point in time lies after the first point in time, at which the semi-reset was already performed, the magnitude of the reset value is advantageously reduced.

[0015] Particularly preferably, the PT1 filter is reset at the first time to an average value of an unfiltered pressure difference input signal and a filtered pressure difference output signal of the PT1 filter at the first time. When using such an average value, the advantages of the described partial or semi-reset are particularly pronounced because a subsequent full reset is optimally prepared. To prevent excessive jumps in the output signal from occurring due to a full reset, the partial reset advantageously takes place somewhat earlier with more sensitive logic, but with the reset level reduced by half.

[0016] According to a preferred embodiment of the invention, the PT1 filter is reset to an unfiltered pressure difference input signal at the second time. This advantageously sets the filter value to its input value. Thus, the resulting hysteresis becomes zero, and the monitoring of the input signals advantageously begins anew.

[0017] The valve device with the features of claim 9 has at least one controllable electromagnetic-hydraulic valve and is characterized by a control device, in particular a computer device, specifically designed to carry out the method according to the invention. This results in the aforementioned advantages.

[0018] The braking system with the features of claim 10 is characterized by the valve device according to the invention. This also results in the aforementioned advantages.

[0019] The motor vehicle with the features of claim 11 is characterized by the braking system according to the invention. This also results in the aforementioned advantages.

[0020] Further preferred features and combinations of features emerge from the above description and from the claims. The invention is explained in more detail below with reference to the drawings.

[0021] Figure 1 shows an advantageous method for operating a valve, and

[0022] Figure 2 Time courses of values ​​during the procedure.

[0023] Figure 1 shows an advantageous method for operating a controllable electromagnetic-hydraulic valve, in particular an inlet valve of a wheel brake device in a braking system of a motor vehicle. More specifically, Figure 1 shows the determination of the valve's hysteresis behavior. This is carried out, in particular, with the aid of a suitable control device.

[0024] First, a pressure difference dpi is determined between an actual pre-pressure of the

[0025] Pressure supply pi and a target wheel pressure p2 are determined. To adjust the thus specified pressure difference dpi, a corresponding electrical control current I is used. Due to hysteresis effects, this control current must now be corrected.

[0026] To determine the corresponding hysteresis behavior, a temporal progression of actual values ​​of the pressure difference dpi is observed using a PT1 filter 1. Preferably, a time constant 2 of the PT1 filter is parameterized depending on the intensity of the control.

[0027] In this case, a raw pressure difference value dpa for the hysteresis behavior is determined as the difference between the unfiltered pressure difference input signal dpi and a corresponding filtered pressure difference output signal dp2 of the PT1 filter. The raw pressure difference value dpa is then limited to a range between a specified maximum and a specified minimum using limiting logic 3.

[0028] Accordingly, a pressure difference output value dp4, which represents the hysteresis behavior, is output. If the raw pressure difference value dps falls below the minimum, the minimum is output as the pressure difference output value dp4. If the raw pressure difference value dps exceeds the maximum, the maximum is output as the pressure difference output value dp4. If the raw pressure difference value dps lies between the minimum and maximum, it is output as the pressure difference output value dp4.

[0029] Depending on this pressure difference output value dp4, the control current I is corrected according to a specified function, for example by means of a characteristic curve or lookup table, and the valve is controlled with the corrected control current.

[0030] A reset logic 4 is also provided, by means of which the PT1 filter is partially or completely reset at specific times. To specify the corresponding times, the unfiltered temporal progression of the actual pressure difference values, i.e., the temporal progression of the pressure difference input signal dpi, and the temporal progression filtered using the PT1 filter, i.e., the temporal progression of the pressure difference output signal dp2, are observed. How this works will be explained using the temporal progressions of the values ​​plotted in Figure 2.

[0031] First, temporal curves of the unfiltered pressure difference input signal dpi and the filtered pressure difference output signal dp2 are superimposed in the same diagram. Below these, a first curve of a trigger for a partial reset Ri of the filter and a second curve of a trigger for a complete reset R2 of the filter are plotted in binary form.

[0032] At a first time point h, an inflection point of one of the time profiles, namely the unfiltered pressure difference input signal dpi, is detected, and the PT1 filter is partially reset, as indicated by the corresponding curve of Ri. The PT1 filter is reset to an average value of the pressure difference input signal dpi and the pressure difference output signal dp2 at the first time point h.

[0033] At a subsequent second time t2, the time courses cross, and the PT1 filter is completely reset, namely to the unfiltered pressure difference input signal dpi at the second time t2.

Claims

Claims 1. Method for operating a controllable electromagnetic-hydraulic valve, in particular an inlet valve of a wheel brake device of a brake system of a motor vehicle, wherein an electrical control current for the valve used to set a predetermined pressure difference across the valve is corrected by a predetermined value as a function of a determined hysteresis behavior of the valve and the valve is controlled with the corrected control current, characterized in that in order to determine the hysteresis behavior, a temporal profile of actual values ​​of the pressure difference is observed with the aid of a PT1 filter (1).

2. Method according to claim 1, characterized in that the PT1 filter (1) is partially reset at least at a predetermined first time (h).

3. Method according to one of the preceding claims, characterized in that the PT1 filter (1) is completely reset at a predetermined second time (t2).

4. Method according to one of claims 2 and 3, characterized in that for specifying the first and / or second time (ti, t2) the unfiltered temporal course of actual values ​​of the pressure difference and the temporal course filtered by means of the PT1 filter (1) are observed.

5. Method according to claim 4, characterized in that, when a turning point of one of the time courses is recognized, the corresponding time is specified as the first time (h).

6. Method according to one of claims 4 and 5, characterized in that, when the time courses cross, the corresponding time is specified as the second time (t2).

7. Method according to one of claims 2 to 6, characterized in that the PT1 filter (1) is reset at the first time (h) to an average value of an unfiltered pressure difference input signal (dpi) and a filtered pressure difference output signal (dp2) of the PT1 filter (1) at the first time (h).

8. Method according to one of claims 3 to 7, characterized in that the PT1 filter (1) is reset at the second time (t2) to an unfiltered pressure difference input signal (dpi) at the second time (t2).

9. Valve device with at least one controllable electromagnetic-hydraulic valve, characterized by a control device which is specially designed to carry out the method according to one of the preceding claims.

10. Braking system, characterized by a valve device according to claim 9. 11 . Motor vehicle, characterized by a braking system according to claim

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