Device for measuring the injection rate, method for producing a device of said type, and measuring method

Abstract

A device (1) for measuring the injection rate dm(t)/dt of an injection valve (2) for a fluid (4a), wherein m(t) is the injection quantity of the fluid (4a) as a function of the time (t), having a measurement volume (3) which is closed off on all sides and which is filled with a test fluid (4), having an opening (5a) in one wall (5) of the measurement volume (3) for the purposes of receiving the injection valve (2) such that the injection valve (2), in the installed position, projects with at least one injection opening (2a) into the measurement volume (3), and having a pressure sensor (6) which is arranged in the measurement volume (3), wherein correction means (8, 8a, 9a, 9b, 9c) are provided for determining the propagation time of a pressure wave (12), which originates from the injection opening (2a) and which propagates through the test fluid (4), to the pressure sensor (6) and for correcting the measured injection rate dm(t)/dt, taking said propagation time into consideration, to give a rectified injection rate dm(t)/dt. A method for producing the device (1), wherein the characteristic map (8a) is determined by way of a fluid-dynamic simulation of the time-dependent and position-dependent local speed of sound c(t,x) in a partial volume of the measurement volume (3) which encompasses at least the path (11) from the injection opening (2a) to the pressure sensor (6), which simulation is based on at least one time-dependent boundary condition for the pressure (p) in the measurement volume (3) and/or for the injection quantity (dm). A method for measuring the injection rate dm(t)/dt of an injection valve (2) for a fluid (4a).

Claims

1. A device for measuring the injection rate dm(t)/dt of an injection valve for a fluid, wherein m(t) is the injection quantity of the fluid, said injection quantity being dependent upon the time t, said device comprising: a measuring volume which is enclosed on all sides and k filled with a testing fluid, an opening in a wall of the measuring volume for receiving the injection valve with the result that in an installed position the injection valve protrudes with at least one injection opening into the measuring volume, and a pressure sensor which is arranged in the measuring volume, wherein correcting means are provided for determining the propagation time of a pressure wave which starts at the injection opening and propagates through the testing fluid to the pressure sensor and also to correct the measured injection rate dm(t)/dt to an adjusted injection rate dm(t)/dt taking into account said propagation time, wherein the correcting means utilizing a characteristic diagram, and wherein the characteristic diagram is determined by means of a fluid dynamic simulation of the time-dependent and location-dependent local speed of sound c(t,x) in part volume of the measuring volume which comprises at least one path from the injection opening to the pressure sensor, said simulation being based on at least one time-dependent boundary condition for the pressure p in the measuring volume, for the infection quantity m, or for both.

2. The device as claimed in claim 1, wherein the correcting means are designed to determine the average speed of sound cm along the path from the injection opening to the pressure sensor during at least one injection procedure.

3. The device as claimed in claim 2, wherein the correcting means utilizes a characteristic diagram which specifies the avererage speed of sound cm along the path from the injection opening to the pressure sensor as a function of the pressure p in the measuring volume in combination with a. the temperature T in the measuring volume, b. the injection quantity m in conjunction with the temperature Trail, the pressure grail of the fluid prior to entering the injection valve or c. both a. and b.

4. The device as claimed in claim 1, wherein an evaluating unit for filtering noise from the measuring values of the pressure sensor is connected between the pressure sensor and the correcting means.

5. The device as claimed in claim 4, wherein the correcting means are designed to at least partially compensate a temporal shift of the measuring values of the pressure sensor, said temporal shift being caused by the filtering procedure.

6. The device as claimed in claim 1, wherein means for determining the hydraulic start of injection tS,h.sub.ydr of the injection valve from the adjusted injection rate dm(t)/dt are provided.

7. The device according to claim 1, wherein in addition at least one ultrasonic sensor is arranged in the measuring volume so as to determine the average speed of sound cm, mess in the testing fluid prior to and/or after the injection procedure.

8. The device as claimed in claim 1, wherein the part volume of the measuring volume extends as far as a wall of the measuring volume and the simulation takes into account an at least partial reflection of the pressure wave at this wall, said pressure wave starting from the injection opening.

9. The device as claimed in claim 1, wherein the simulation takes into account the presence of cavitation in the test fluid, a formation of cavitation in the test fluid, or both.

10. The device as claimed in claim 1, wherein the simulation takes into account a temperature dependency of the viscosity of the testing fluid, a pressure dependency of the viscosity of the testing fluid, the compression module of the testing fluid, the speed of sound in the testing fluid, of a combination of the foregoing.

11. A method for measuring the injection rate dm(t)/dt of an injection valve for a fluid, wherein m(t) is the time-dependent injection quantity when using a measuring volume which is enclosed on all sides and is filled with a testing fluid, wherein said measuring volume comprises an opening in a wall for receiving the injection valve with the result that in the installed position the injection valve protrudes with at least one injection opening into the measuring volume, and a pressure sensor which is arranged in the measuring volume, wherein the temporal curve of the pressure in the measuring volume is measured using the pressure sensor as a reaction to a time program l(t) of the actuation of the injection valve, wherein the propagation time of a pressure wave which starts at the injection opening and propagates through the testing fluid to the pressure sensor is determined using correcting means, and in that the measured injection rate dm(t)/dt is adjusted under the influence of this propagation time to an injection rate dm(t)/dt, and wherein the correcting means utilizes a characteristic diagram, and wherein the characteristic diagram is determined by means of a fluid dynamic simulation of the time-dependent and location-dependent local speed of sound c(t,x) in a part volume of the measuring volume which comprises at least one path from the injection opening to the pressure sensor, and simulation being based on at least one time-dependent boundary condition for the pressure p in the measuring volume, for the injection quantity m, or for both.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further measures which improve the invention are further illustrated hereinunder together with the description of the preferred exemplary embodiments of the invention with reference to figures:

(2) In the drawings:

(3) FIG. 1 illustrates an exemplary embodiment of the device in accordance with the invention,

(4) FIGS. 2a-2b illustrate a measured injection rate dm(t)/dt on a time program I(t) of the electrical actuation of an injector,

(5) FIGS. 3a-3b illustrate improvement of the measuring accuracy when determining the injection rate dm(t)/dt, said improvement being achievable by means of the device in accordance with FIG. 1,

(6) FIG. 4 illustrates an application example of the use of a device in accordance with the invention for optimizing the injection procedure in a diesel motor in the case of a pre-injection procedure that is performed prior to the main injection procedure.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates an exemplary embodiment of the device 1 in accordance with the invention. The measuring volume 3 is enclosed on all sides by a wall 5 which comprises cooling ducts 5b. The measuring volume 3 is filled with the testing fluid 4. The wall 5 of the measuring volume 3 comprises an opening 5a for receiving the injection valve 2 which is to be tested. The injection valve 2 is illustrated in the installed position in which said injection valve protrudes into the measuring volume 3 with an injection opening 2a. The injection valve 2 is supplied by way of a high pressure pump 14 with the fluid 4a which is to be injected. The fluid 4a is identical in this exemplary embodiment to the testing fluid 4.

(8) A pressure sensor 6 is arranged in the measuring volume 3, said pressure sensor 6 transmitting the pressure p in the measuring volume 3 to an evaluating electronic system 7. The raw signal is initially amplified in the evaluating electronic system 7 and subsequently filtered using a low pass filter in order to eliminate noise. The filtered signal is passed on to the correcting unit 8.

(9) The correcting unit 8 receives the following as additional input variables the pressure n rail of the fluid 4a prior to said fluid entering the injection valve 2, measured using a pressure sensor 9a, the temperature T in the measuring volume 3, measured using a temperature sensor 9b which is arranged in the measuring volume 3, and also the temperature T.sub.rail of the fluid 4a prior to entering the injection valve 2, measured using a further temperature sensor 9c.

(10) The correcting unit 8 is designed to determine the propagation time of a pressure wave 12 which starts at the injection opening 2a and propagates through the testing fluid 4 to the pressure sensor 6. The correcting unit 8 comprises a characteristic diagram 8a for determining the average speed of sound c.sub.m along the path 11 from the injection opening 2a to the pressure sensor 6, said characteristic diagram 8a specifying the average speed of sound c.sub.m on the path 11 as a function of the pressures p and p.sub.rail and also the temperatures T and T.sub.rail. The correcting unit 8 adjusts the measured, time-dependent injection rate dm(t)/dt under the influence of the propagation time and also under the influence of filter-dependent temporal shifts and passes the injection rate dm(t)/dt which is adjusted in this manner on to a further evaluating unit 15 which determines the hydraulic start of injection t.sub.S,hydr.

(11) In addition, an ultrasonic sensor 10 is arranged in the measuring volume 3, said ultrasonic sensor transmitting sound waves along a path 10a, which is symbolized by means of arrows through the entire measuring volume 3, to the opposite-lying wall 5 and said ultrasonic sensor also receives the reflection again at this wall 5 on the same path 10a. The average speed of sound c.sub.m,mess in the testing fluid 4 is determined using said ultrasonic sensor 10 prior to and after the injection. The measuring volume 3 furthermore comprises a draining valve 13 which can be activated in an electromagnetic manner.

(12) The measuring volume 3 is cylindrical with a height of 80 mm and a diameter of 45 mm. The pressure wave 12 has to travel from the injection opening 2a to the pressure sensor 6, therefore a distance of 46.3 mm. For an average temperature T, said temperature being assumed to be constant for simplicity, a speed of sound of c=1277 m/s is calculated in the measuring volume 3 and also diesel fuel or a testing oil which is used as a testing fluid to test diesel injection valves in the case of a basic pressure p in the measuring volume 3 prior to the injection of 50 bar. The pressure wave 12 then takes approximately 37 s to travel along the path 11.

(13) The characteristic diagram 8a which is stored in the correcting unit 8 is determined by means of a fluid dynamic simulation so that the correcting unit 8 can determine the propagation time in a more precise manner. For this purpose, a part volume of the measuring volume 3 is selected which is precisely as large as the measuring volume 3 and in the horizontal direction both the injection opening 2a as well as the pressure sensor 6 are entirely covered. Within said part volume, in addition to the local speed of sound c(t,x) the time-dependent and location-dependent distributions p(t,x) of the pressure in the measuring volume 3, T(t,x) of the temperature in the measuring volume 3, v(t,x) of the vectorial flow speed in the measuring volume 3 and also d(t,x) of the vapor proportion of the testing fluid 4 are calculated in the measuring volume 3. The driving force for the dynamics of said variables is the time program for the local pressure of the testing fluid 4, said time program being predetermined by means of the injection procedure at the location of the injection opening 2a. During the calculation, in addition to the geometry of the measuring volume 3, the pressure dependency and temperature dependency of viscosity, speed of sound and compression modulus of the testing fluid 4 were also taken into account. In addition to the injection opening 2a, the injection valve 2 comprises seven further injection openings. Since all eight injection openings are distributed in a rotationally symmetrical manner along the outer periphery of the injection valve 2, it is sufficient for the simulation to take only one injection opening 2a into account. The functioning of the invention is not bound to a specific number of injection openings; the disclosure of a number of 8 is consequently only understood as an illustration of the exemplary embodiment which is illustrated in the figure.

(14) The simulation was implemented for 15 temperatures T in the region of 40 C. to 180 C. and also for 30 pressure p.sub.rail of 100 to 3000 bar. The temperature range of 40 C. to 180 C. represents the region in which the temperature T in the measuring volume 3 can vary in this exemplary embodiment. The characteristic diagram 8a in the correcting unit 8 therefore includes for the 450 different value pairs of pressure p.sub.rail and also temperature T in each case the associated average speed of sound c.sub.m (p.sub.rail, T). Injection quantities m which correspond to a volume of fluid 4a in the range from 1 mm.sup.3 to 600 mm.sup.3 with an increment of 20 mm.sup.3 were taken into account. The temperature T.sub.rail of the fluid 4a is derived from p.sub.rail and T immediately prior to the injection into the measuring volume 3. The temperature T.sub.inj of the injected fluid 4a after it has entered the measuring volume 3 and has relaxed from the pressure p.sub.rail to the lower pressure p which prevails in the measuring volume 3 is thereby also determined. The temperature T.sub.inj and the injection quantity m (in the unit of mass) finally determine the energy input into the measuring volume 3 by means of the injection.

(15) Since the part volume which is selected from the measuring volume 3 has been discretized to a fine enough extent in order also to be able to detect cavitation in the testing fluid 4, the simulation of a characteristic diagram point requires a computing time of approximately three weeks (6000 CPU hours) to a parallelized HPC system based on the Intel XEON architecture. The simulation was implemented using the program Ansys-CFX. The curves of the real injection rate dm(t)/dt which are determined according to the evaluating method of the hydraulic pressure increase method from pressure curves at the pressure sensor 6 of the simulation were compared to measurements in order to verify the model.

(16) The real injection rate dm(t)/dt correlates with the variable V of the measuring volume 3, the pressure p and the temperature T in the measuring volume 3 and also the average speed of sound c.sub.m in the measuring volume 3 by means of

(17) $\frac{d{m}^{}\left(t\right)}{\mathrm{dt}}=\frac{d}{\mathrm{dt}}\left(V.Math.{}_{P_1}^{P_2}\frac{1}{c_m^2\left(p,T\right)}\mathrm{dp}\right)$
wherein p.sub.1 is the pressure p at the start of the injection and p.sub.2 is the pressure p at the time t.

(18) A time curve I(t) of the current with which an electromagnetically-controlled injection valve 2 (injector) is actuated is plotted in FIG. 2a over the time t. In FIG. 2b, the measured injection rate dm(t)/dt is plotted in arbitrary units over the same time scale. In this measurement, the correcting unit 8 was deactivated. The fact that the propagation time of the pressure wave 12 from the injection opening 2a to the pressure sensor 6 was consequently not taken into account has on the one hand the effect that the injection rate dm(t)/dt is offset on the time axis with respect to the time program I(t) of the current. On the other hand, some rapid changes in the current I(t) are generally not expressed in the measured injection rate dm(t)/dt since the local speed of sound c(t,x) in the testing fluid 4 depends upon the dynamic conditions in the measuring volume 3 and the dynamic conditions are in turn time-dependent. Moreover, further filter characteristics of the low pass filter in the evaluating electronic system 7 affect the position of the hydraulic start of injection in the rate signal. The measured injection rate dm(t)/dt is therefore derived from the real injection rate dm(t)/dt as a result of the influence of the propagation time along the path 11 from the injection opening 2a to the pressure sensor 6, wherein the average speed of sound c.sub.m(t) is time-dependent along the path 11 and also the low pass filtering procedure has an influence on the measured propagation time. With the aid of the correcting unit 8 it is possible to at least partially invert both the influence of the propagation time with the time-dependent speed of sound as well as the influence of the low pass filtering procedure.

(19) FIG. 3a illustrates the temporal curve of the additional mass m of fluid 4a which is introduced in total by means of an injection procedure into the measuring volume 3. FIG. 3b illustrates the temporal curve of the injection rates dm(t)/dt (left-hand scale) or dm(t)/dt (right-hand scale) plotted over the same time scale. Curve a was recorded with a deactivated correcting unit 8 and specifies the measured injection rate dm(t)/dt. Curve b was recorded with an activated correcting unit 8 and specifies the adjusted injection rate dm(t)/dt. The injection procedure comprises a small pre-injection PI and a subsequent essentially larger main injection MI.

(20) It is possible to read the start and the end of the part injections PI and MI more precisely from the measured time curve of the injection rate dm(t)/dt. In accordance with curve a (with the correcting unit (8), the pre-injection PI starts at the point in time t.sub.S,hydr(PI) and ends at the point in time t.sub.E,hydr(PI). The main injection MI starts at the point in time t.sub.S,hydr(MI) and ends at the point in time t.sub.E,hydr(MI).

(21) The comparison of the respective points in time shows that the correcting unit 8 does not just correct a constant offset of all time points along the time axis t. On the contrary, said correcting unit also takes into account a time-dependency c.sub.m(t) of the average speed of sound c.sub.m and also a filter bias as a result of the evaluating electronics system 7 and compensates said influences at least partially so that smearing and scattering of the injection pulse PI and MI are also corrected. This is possible to read in FIG. 3b by way of example from a comparison of the time interval between t.sub.S,hydr(PI) and t.sub.S,hydr(PI) on the one hand and with the time interval between t.sub.E,hydr(PI) and t.sub.E,hydr(PI) on the other. The last time interval is greater than the first. The difference is more clearly manifested if the time interval between t.sub.S,hydr(MI) and t.sub.S,hydr(MI) on the one hand is compared with the time interval between t.sub.E,hydr(MI) and t.sub.E,hydr(MI) on the other.

(22) On the other hand, narrower injection pulses and shorter intervals between injection pulses can be triggered with the activated correcting unit 8. A single injection procedure can include up to ten part injections.

(23) In the example illustrated in FIG. 3, the fluid 4a was supplied to the injection valve 2 at a pressure p.sub.rail of 800 bar. The injection valve 2 is electromagnetically activated for 220 s so as to generate a pre-injection PI. The injection valve 2 was electromagnetically activated for 625 s so as to generate the main injection MI.

(24) FIG. 4 illustrates how the improved resolution that is demonstrated in FIG. 3 can be used to optimize the actuation of a diesel engine. The measured injection rate dm(t)/dt is plotted over the time t as in FIG. 3b. Curve a was measured with the deactivated correcting unit 8 and illustrates a hitherto conventional time program for the injection rate dm(t)/dt in which the pre-injection PI is performed prior to the main injection MI by 1800 s. The curves b, c and d illustrate future time programs in which the pre-injection PI is performed prior to the main injection MI by a substantially shorter time period down to 200 s (curve d) and said time programs can be more precisely ascertained using the correcting unit 8. It is advantageous with respect to the consumption characteristics and environmental characteristics of the diesel engine to move the pre-injection PI as close as possible to the main injection MI. The fluid 4a was supplied to the injection valve 2 at a pressure p.sub.rail of 800 bar. The injection valve 2 was in each case electromagnetically actuated so as to generate the pre-injection or PI in each case for 220 s. The injection valve 2 was electromagnetically actuated in each case for 625 s for the main injection MI.