Abstract
A method checks a functionality of a solenoid valve for a brake system in a motor vehicle. The solenoid valve includes an armature and a coil. The armature, on actuation of the solenoid valve, is moved by a magnetic field of the coil, reducing an air gap of the solenoid valve defined by a position of the armature. The method includes measuring an electric current during the actuation of the solenoid valve, analysing a characteristic of the electric current during the actuation of the solenoid valve, and assessing the functionality of the solenoid valve based on the analysis of the characteristic of the electric current.
Claims
1. A method for checking a functionality of a solenoid valve for a hydraulic brake system in a motor vehicle, the solenoid valve including an armature and a coil, the method comprising: moving the armature, on actuation of the solenoid valve, by a magnetic field of the coil to reduce an air gap of the solenoid valve defined by a position of the armature; measuring an electric current during the actuation of the solenoid valve; analysing a characteristic of the measured electric current during the actuation of the solenoid valve; and assessing a functionality of the solenoid valve based on the analysis of the characteristic of the electric current.
2. The method according to claim 1, further comprising: preventing activation of a pressure generator for the hydraulic brake system in order to check the functionality of the solenoid valve.
3. The method according to claim 1, further comprising: assessing the solenoid valve as functional when the characteristic of the electric current during the actuation fulfils a defined condition.
4. The method according to claim 3, further comprising: assessing the solenoid valve as non-functional when the characteristic of the electric current during the actuation fails to fulfil the defined condition.
5. The method according to claim 1, further comprising: determining a rate of variation of the measured electric current in order to analyse the characteristic of the electric current.
6. The method according to claim 5, further comprising: assessing the solenoid valve as functional when the rate of variation fulfils a defined condition.
5. hod according to claim 5, further comprising: assessing the solenoid valve as functional when the rate of variation forms a sign reversal.
8. The method according to claim 5, further comprising: assessing the solenoid valve as functional when the rate of variation attains a defined threshold value following a sign reversal.
9. The method according to claim 1, further comprising: checking the functionality at a start of an automated drive function of the motor vehicle and/or during performance of the automated drive function of the motor vehicle.
10. The method according to claim 1, further comprising: performing a defined measure based on the assessment of the functionality of the solenoid valve.
11. The method according to claim 1, wherein a device performs the method.
12. The method according to claim 1, wherein a computer program performs the method.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] It is to be pointed out that the features cited individually in the description may be combined with one another in any technically suitable manner and set forth further embodiments of the disclosure. Further features and suitable uses of the disclosure emerge from the description of exemplary embodiments, referring to the figures attached, of which
[0036] FIG. 1 shows a schematic representation of a hydraulic brake system;
[0037] FIG. 2 shows a curve determined for an electric current and its rate of variation during an actuation of a solenoid valve; and
[0038] FIG. 3 shows steps in the method according to an exemplary embodiment.
DETAILED DESCRIPTION
[0039] FIG. 1 shows a schematic representation of a hydraulic brake system 2 for a motor vehicle 1, not represented in further detail. The brake system 2 serves for braking the four wheels 3 of the motor vehicle 1. For this purpose, the wheels 3 have hydraulic wheel brakes not represented in further detail. The brake system 2 comprises a hydraulic unit 4 and a control unit 5. The hydraulic unit 4 further comprises a pressure generator 6 and at least one valve 7. The pressure generator 6 is an electric motor, for example, which drives a piston pump. The valves 7 are solenoid valves, for example. These comprise a coil, which on actuation generate a magnetic field. This magnetic field acts on a movable armature, which is moved by the magnetic field from a rest position into a displaced position. The position of the armature defines an air gap in the magnet, for example between the armature and the stator. The magnetic field produces a variation in the position of the armature. This also varies the air gap. For example, the air gap is reduced when the armature is displaced for its unenergized, closed position. The valves may be of normally closed design. Alternatively or in addition, valves may be of normally open design. The design configuration of such valves may differ widely and is not represented here.
[0040] FIG. 2 shows a curve determined for an electric current (I) and its rate of variation (dI) over time (t) during an actuation of a solenoid valve. For checking the functionality of the valve, a confirmation (i.e. actuation) of the valve ensues at a defined trigger time. The current is measured and differentiated via high-frequency readout electronics. Actuation causes the armature to move and the valve air gap is closed. This closure gives rise to a variation in the magnetic susceptibility in the coil-armature circuit, which produces a change in the magnetic flux. This correlation gives rise to the characteristic current curve of an actuated seat valve represented in FIG. 2. It can be seen here that at first the electric current rises. Then the curve of the electric current forms a maximum. At this point the rate of variation exhibits a zero crossingfrom the positive to the negative. After the first local maximum of the electric current, the electric current falls due to the variation in the magnetic susceptibility. As soon as the air gap is fully closed, a local minimum results in the electric current curve, which then rises gain. The minimum is not a stationary point, since it cannot be differentiated, as the rate of variation shows. In the exemplary embodiment of the method shown a negative threshold value for the rate of variation is defined. This is represented by the dashed line parallel to the horizontal time axis. This threshold value serves to define from what variation in the electric current onwards a functionality of the valve is confirmed, that is to say assumed. It can clearly be seen that at the said point in time the local maximum of the electric current has already been exceeded (see the point of intersection between the dashed vertical line and the current curve line). The defined threshold value therefore forms a type of confidence level, a functionality being assumed only when this confidence level is fulfilled. This improves the validity in analysis of the functionality and avoids false assessments.
[0041] FIG. 3 shows a representation of steps in the method in one embodiment of the disclosure. Here the start of the method for checking the functionality of one or more valves of the hydraulic brake system of a motor vehicle ensues in a first step S1. The start occurs, for example, in reaction to an activation of an automatic drive function of the motor vehicle. Following the start, the valve is actuated, for example by energizing, in a step S2. The actuation of the valve ensues, in particular, without additional activation of a pressure generator in the hydraulic brake system, in particular without simultaneous energizing of the electric motor of the hydraulic pump. Whilst the valve is being actuated, the electric current is measured in a step S3. In the next step S4 there follows an analysis of the measured electric current. Strictly speaking, this involves an analysis of the curve of the measured electric currents. On the basis of this analysis, in a step S5, an assessment is undertaken of whether valve functionality exists or the valve is non-functional. Following the assessment, a defined action can be performed in the next step S6. For example, an activation of an automated drive function is refused, or an automated drive function already activated is deactivated. At the same time the vehicle occupants may obviously also be informed. An entry may also be made in the vehicle fault memory. With step S7 the method is terminated.
