Method and device for determining the injection rate of an injection valve

Abstract

The invention relates to a method for determining the injection rate of an injection valve (1) using a mathematical model which is based on measurement values comprising the stroke (x) of a piston (3) that delimits a measurement chamber (2) during the injection of a test fluid (4) into the measurement chamber (2). The injection rate is corrected on the basis of an additional measurement value. According to the invention, the pressure (p.sub.a) in an adapter volume (5), via which the injection valve (1) is connected to the measurement chamber (2), is used as an additional measurement value for correcting the injection rate. The invention further relates to a device for determining the injection rate of an injection valve.

Claims

1. A method for determining an injection rate of an injection valve (1) using a mathematical model on which measured values which comprise a travel (x) of a piston (3) bounding a measuring chamber (2) during an injection of a test fluid (4) into the measuring chamber (2) are based, wherein a correction of the injection rate is carried out on the basis of a further measured value, the method comprising using a first pressure (p.sub.a) measured during the injection and in an adapter volume (5), via which the injection valve (1) is fluidly connected to the measuring chamber (2) during the injection, as said further measured value for correcting the injection rate.

2. The method as claimed in claim 1, characterized in that during the injection the pressure (p.sub.a) in the adapter volume (5) is detected by means of a pressure sensor (6) which is assigned to the adapter volume (5).

3. The method as claimed in claim 1, characterized in that during the injection a temperature (T) and a second pressure (p) in the measuring chamber (2) are detected by a temperature sensor (7) and a pressure sensor (8) which are assigned to the measuring chamber (2).

4. The method as claimed in claim 1, characterized in that the measured values which are detected during the injection are passed on as measurement signals to a control unit (9) in which the mathematical model for calculating the injection rate is stored.

5. A device for determining an injection rate of an injection valve (1), comprising, a measuring chamber (2) which is bounded by a piston (3) and which is fluidly connected to the injection valve (1) during an injection of a test fluid into the measuring chamber (2), the measuring chamber (2) being connected to the injection valve (1) via an adapter volume (5) which is formed in an adapter (10) for receiving the injection valve (1), such that the test fluid can be injected into the measuring chamber (2) by the injection valve (1), the device also comprising a travel measuring device (11) for detecting a travel (x) of the piston (3) during the injection, characterized in that a first pressure sensor (6) is configured to measure a first pressure (p.sub.a) in the adapter volume (5) during the injection.

6. The device as claimed in claim 5, characterized in that an injection damper (12) is arranged between the adapter volume (5) and the measuring chamber (2).

7. The device as claimed in claim 5, characterized in that the measuring chamber (2) is assigned a temperature sensor (7) and a second pressure sensor (8) by which a temperature (T) and a second pressure (p) in the measuring chamber (2) during the injection can be detected.

8. The device as claimed in claim 5, further comprising a control unit (9) for calculating the injection rate, wherein the control unit (9) is connected via control lines (13) to the travel measuring device (11), the first pressure sensor (6), the temperature sensor (7) and the second pressure sensor (8).

9. The device as claimed in claim 5, characterized in that the measuring chamber (2) is connected to an emptying valve (14).

10. The device as claimed in claim 5, characterized in that the pressure in the measuring chamber (2) can be controlled by an opposing force of the piston (3).

11. The device as claimed in claim 5, characterized in that the device is configured to determine the injection rate of the injection valve using a mathematical model on which measured values which comprise the travel of the piston during injection of the test fluid into the measuring chamber are based, wherein a correction of the injection rate is carried out on the basis of a further measured value, the device being configured to use the pressure in the adapter volume (5), via which the injection valve is connected to the measuring chamber, as a further measured value for correcting the injection rate.

12. The device as claimed in claim 8, characterized in that a characteristic diagram for the derivative of a raw density (.sub.a) of the test fluid (4) at a given value of the first pressure (p.sub.a) at the temperature (T) of the test fluid (4), $\frac{p_a}{p_a}{|}_T,$ is stored in the control unit (9) in order to calculate a pressure component in the corrected injection rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The method according to the invention and the device according to the invention are explained in more detail below with reference to the appended drawings, in which:

(2) FIG. 1 shows a schematic illustration of a device according to the invention, and

(3) FIG. 2 shows a diagram illustrating a corrected injection rate profile.

DETAILED DESCRIPTION

(4) The device according to the invention which is illustrated schematically in FIG. 1 comprises a piston 3 which is received in a reciprocally movable fashion in a cylinder 15 and bounds a measuring chamber 2 within the cylinder 15. The measuring chamber 2 is connected to an emptying valve 14 via a throttle 16. On the side of the piston 3 facing away from the measuring chamber 2, an opposing pressure is applied which brings about a pressure force F which acts on the piston 3 in the direction of the measuring chamber 2, with the result that an equilibrium of forces is present at the piston 3, and the pressure in the measuring chamber 2 can be controlled.

(5) In order to determine the injection rate of an injection valve 1, a test fluid 4 can be injected into the measuring chamber 2 by means of the injection valve 1. The injection brings about travel of the piston 3 counter to the pressure force F, which travel can be detected by means of a travel measuring device 11. The travel measurement is inductive here, wherein the measured values are passed on as measurement signals to a control unit 9 via a control line 13. The control unit 9 is also connected via control lines 13 to a temperature sensor 7 and a pressure sensor 8 which serve to detect the temperature and the pressure in the measuring chamber 2. These measured values influence the raw density of the test fluid 4 and are accordingly relevant for the calculation of the injection rate.

(6) The injection of the test fluid 4 into the measuring chamber 2 takes place here indirectly via an adapter volume 5 which is connected to the measuring chamber 2 via an injection damper 12. The adapter volume 5 is formed in an adapter 10 which serves to receive the injection valve 1. The injection damper 12 which is formed between the adapter volume 5 and the measuring chamber 2 is intended to prevent direct impacting of the injection jets of the test fluid 4 onto the piston 3 which bounds the measuring chamber 2, and therefore to prevent undesired excitation of oscillations of the piston 3.

(7) The injection of the test fluid 4 into the measuring chamber 2 which is brought about only indirectly via the adapter volume 5 and the injection damper 12 results in a delay or in damping of the injection. This in turn gives rise to a delayed and rounded-off injection rate profile. Accordingly, there is a need to correct the determined injection rate.

(8) The device according to the invention which is illustrated in FIG. 1 has for this purpose a further pressure sensor 6 which is assigned to the adapter volume 5, so that the pressure in the adapter volume 5 can be detected by this means. A control line 13 connects the pressure sensor 6 to the control unit 9, so that the measured values which are detected by the pressure sensor 6 are passed on as measurement signals to the control unit 9, in order to take them into account during the calculation of the injection rate. The injection rate can then be calculated according to the following equation:

(9) $\frac{\mathrm{dm}}{\mathrm{dt}}=V_a.Math.\frac{p_a}{p_a}{|}_T.Math.{\stackrel{.}{p}}_a\left(t\right)+\stackrel{.}{x}\left(t\right).Math.A_{\mathrm{Kolben}}.Math.\left(p,T\right)\mathrm{KEY}\text{:}\mathrm{Kolben}=\mathrm{piston}$

(10) The changes in density are stored as a characteristic diagram as a function of the present temperature

(11) $\frac{p_a}{p_a}{|}_T.$

(12) The pressure in the adapter volume 5, which is detected by means of the further pressure sensor 6, not only permits interfering oscillation components to be eliminated but also permits the injection rate to be corrected with respect to a chronological offset and/or damping or rounding off, as illustrated, for example, in the diagram in FIG. 2.

(13) The curve which is illustrated in the upper part a) of the diagram shows the duration of the energization of an actuator (not illustrated) of an injection valve 1 whose injection rate is to be determined. The injection valve 1 opens and closes as a function of the energization of the actuator, so that injection is performed. In this way, a test fluid 4 is injected into the measuring chamber 2 via the adapter volume 5. The injection results in travel x of the piston 3 which bounds the measuring chamber 2, the profile of which travel x is illustrated in the middle part b) of the diagram as a curve 18. The curve 19 represents the profile of the pressure p.sub.a in the adapter volume 5.

(14) In the lower part c) of the diagram, the injection rate profile is illustrated, wherein the curve 20 illustrates the injection rate profile which is corrected on the basis of the equation specified above. This is because, as also illustrated in the part c) of the diagram, an injection rate profile (curve 21) which is calculated solely on the basis of the piston travel profile has a time shift with respect to the curve 20 as well as interfering oscillation components. These can be eliminated by additionally detecting the pressure p.sub.a in the adapter volume 5 and using it to correct the injection rate. The curve 22 shows the profile of an injection rate which has been calculated from the pressure p.sub.a.