METHOD FOR DETERMINING A SWITCHING POINT OF A SOLENOID VALVE

Abstract

A method for determining a switching point of a solenoid valve. A solenoid coil is energized to raise a solenoid armature to unblock a flow opening. For a signal profile characteristic of a current profile in the solenoid coil, multiple periods each different from one another and each having the same predefined temporal length are determined. Within each period, a minimal and a maximal value of the signal profile and associated points in time are ascertained and a product of a difference between the maximal and minimal value and a difference between the associated points in time are ascertained. On the basis of the points in time of the minimal and maximal value of that period, which corresponds to a maximal value of the product, the switching point is determined.

Claims

1-11. (canceled)

12. A method for determining a switching point of a solenoid valve, in which a solenoid coil is energized to raise a solenoid armature to unblock a flow opening, the method comprising the following steps: determining, for a signal profile characteristic of a current profile in the solenoid coil, multiple periods each different from one another and each having the same predefined temporal length; ascertaining, within each period of the periods, a minimal and a maximal value of the signal profile and associated points in time; ascertaining a product of a difference between the maximal and minimal value and a difference between the associated points in time; and determining the switching point based on the associated points in time of the minimal and maximal value of that period of the periods which corresponds to the maximal value of the product.

13. The method as recited in claim 12, wherein the switching point is determined on based on an arithmetic mean value of the points in time of the minimal and maximal value.

14. The method as recited in claim 13, wherein the switching point is determined as the arithmetic mean value of the points in time of the minimal and maximal value.

15. The method as recited in claim 12, wherein a first time derivative of the current profile is used as the signal profile characteristic for the current profile.

16. The method as recited in claim 12, wherein the multiple periods are determined in such a way that starting points of successive periods are each offset by the same duration.

17. The method as recited in claim 16, wherein the predefined temporal length is a multiple of the duration.

18. The method as recited in claim 12, wherein the periods are determined within a predefined range of the signal profile.

19. The method as recited in claim 12, wherein the solenoid valve is used to actuate a fuel injector.

20. A processing unit configured to determine a switching point of a solenoid valve, in which a solenoid coil is energized to raise a solenoid armature to unblock a flow opening, the method comprising the following steps: determine, for a signal profile characteristic of a current profile in the solenoid coil, multiple periods each different from one another and each having the same predefined temporal length; ascertain, within each period of the periods, a minimal and a maximal value of the signal profile and associated points in time; ascertain a product of a difference between the maximal and minimal value and a difference between the associated points in time; and determine the switching point based on the associated points in time of the minimal and maximal value of that period of the periods which corresponds to the maximal value of the product.

21. A non-transitory machine-readable memory medium on which is stored a computer program for determining a switching point of a solenoid valve, in which a solenoid coil is energized to raise a solenoid armature to unblock a flow opening, the computer program, when executed by a processing unit, causing the processing unit to perform the following steps: determining, for a signal profile characteristic of a current profile in the solenoid coil, multiple periods each different from one another and each having the same predefined temporal length; ascertaining, within each period of the periods, a minimal and a maximal value of the signal profile and associated points in time; ascertaining a product of a difference between the maximal and minimal value and a difference between the associated points in time; and determining the switching point based on the associated points in time of the minimal and maximal value of that period of the periods which corresponds to the maximal value of the product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 schematically shows a solenoid valve in which a method according to the present invention may be carried out.

[0019] FIG. 2 shows a typical profile of a time derivative of a current in the solenoid coil of a solenoid valve to explain a method according to the present invention in one preferred specific embodiment.

[0020] FIG. 3 shows typical profile of variables upon actuation of a solenoid valve for better classification of the profile from FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0021] FIG. 1 schematically shows a solenoid valve 100, which is used, for example, in a fuel injector 101 and in which a method according to the present invention may be carried out. Solenoid valve 100 includes an electromagnet 110 including a solenoid coil 111, which may be designed to be annular, for example. Upon application of a voltage U, for example, by an executing processing unit 180 designed as a control unit, current I flows in solenoid coil 111.

[0022] Furthermore, a solenoid armature 120 is provided, which is moreover used as a valve needle, using which a flow opening 150 may be closed or unblocked. Furthermore, a spring 130 is provided, which engages on solenoid armature 120 and, without energization of solenoid coil 111 and thus without magnetic force, presses armature 120 into or against flow opening 150 and closes it. Spring 130 may be in contact on its side facing away from the solenoid armature at a suitable component of solenoid valve 100.

[0023] Upon energization of solenoid coil 111, a magnetic force is built up and solenoid armature 120 is raised against the spring force of spring 130 and drawn in the direction of solenoid coil 111 or electromagnet 110. Flow opening 150 is unblocked. Upon corresponding energization of the solenoid coil, solenoid armature 120 may be raised up to stop 115.

[0024] FIG. 2 shows a typical signal profile V of a time derivative of a current (or a current profile in the solenoid coil of a solenoid valve to explain a method according to the present invention in one preferred specific embodiment). For this purpose, a time derivative dl/dt is plotted over a time t. For this purpose, it is to be noted that in principle a difference dl, thus a difference between two successive measured values may be sufficient for the provided method and a scaling of the x axis is arbitrary.

[0025] In the example shown, the search for the switching point is to be carried out in the range between a starting point t′.sub.A and an end point t′.sub.E of profile V, for example, because the switching point is expected within this range. For this purpose, multiple periods (or windows or time intervals) having the same temporal length Δt are determined. These are distributed, for example, uniformly and overlapping within range t′.sub.A through t′.sub.E. For example, two such periods T.sub.A,1 and T.sub.A,2 are shown, which have an interval Δt′ with respect to their starting points.

[0026] In practice, signal profile V may be provided, for example, as a sequence of measuring points (or time derivatives of measuring points) in a buffer memory. For this purpose, for example, each measuring point (whose intervals result from a sampling rate) may be used as the starting point of a period. It is understood that also only every second, third, or fourth measuring point may be used for this purpose. The temporal length may then be selected as a multiple of a distance of two measuring points from one another.

[0027] A minimal value and a maximal value of the profile is now determined for each of the periods. This is to be explained hereinafter on the basis of period T.sub.A,2. Therein, minimal value (dl/dt).sub.min is at point t.sub.min and maxima value (dl/dt).sub.max is at point t.sub.max. Now (in the context of a calculation of the product), a rectangle R including diagonal corner points, which are defined by the signal profile points having the minimal and the maximal value, is determined, and its area F.sub.R is ascertained as the desired product.

[0028] In this way, a value of the product or area of the rectangle may be obtained for each of the periods. That period is selected as the one sought for which the value of the area is maximal.

[0029] Switching point t.sub.s is determined there on the basis of a mean value of points t.sub.min and t.sub.max.

[0030] In this way, the switching point may be found easily and accurately without forming a second time derivative or without two differentiations of the underlying signal of the current profile, but without having to accept an excessively strong impairment of the quality of the signal.

[0031] FIG. 3 shows typical profiles of variables upon actuation of a solenoid valve over time t for better classification of the curve from FIG. 2, specifically over a longer time frame. In addition to signal profile V from FIG. 2, (which indicates dl/dt), these are a voltage profile U as an activation signal of the solenoid valve or its solenoid coil, a current profile I in the solenoid coil, a lift profile h of a valve needle of the solenoid valve, and a profile F.sub.R of the product or area as was explained with reference to FIG. 2.

[0032] Curve F.sub.R corresponds to a profile of the product when the periods are passed through along the x axis or are shifted temporally backward. It may be seen here that the greatest value of the product very accurately indicates switching point t.sub.s of the solenoid valve, which ultimately corresponds accurately with reaching the greatest lift.