METHOD FOR MONITORING THE VOLUMETRIC FLOW OF A METERING VALVE OF A FLUIDIC METERING SYSTEM OF AN INTERNAL COMBUSTION ENGINE, IN PARTICULAR OF A MOTOR VEHICLE

Abstract

A method for monitoring the volumetric flow of a metering valve (131) of a fluidic metering system (100) of an internal combustion engine, in which at least one feed pump (111) for feeding a fluid is arranged, the feed pump (111) being connected to a feed line (207) and to a return line (160), and it being provided in particular that an inner leakage of the feed pump (111) is determined and that the volumetric flow of the metering valve (131) is monitored on the basis of ascertained (320, 325) pressure values on the basis of the determined inner leakage of the feed pump (350).

Claims

1. A method for monitoring the volumetric flow of a metering valve (131) of a fluidic metering system (100) of an internal combustion engine, the system having at least one feed pump (111) for feeding a fluid, the feed pump (111) being connected to a feed line (207) and to a return line (160), that the method comprising determining an inner leakage of the feed pump (111), and monitoring the volumetric flow of the metering valve (131) on the basis of experimentally ascertained (320, 325) pressure values on the basis of the determined inner leakage of the feed pump (350).

2. The method according to claim 1, characterized in that a pressure drop or a pressure rate between an inlet (207) and an outlet (235) of the feed pump (111) is ascertained experimentally.

3. The method according to claim 2, characterized in that the inner leakage of the feed pump (111, 200) is analytically determined, the feed pump (111, 200) being broken down into a volumetric pump (205) and a throttle (210) arranged parallel to the volumetric pump (205).

4. The method according to claim 3, characterized in that an orifice plate (161, 237) effective for return of fluid into a storage tank (120, 240) is arranged at the outlet of the feed pump (111, 200).

5. The method according to claim 4, characterized in that the throttle (245) and the orifice plate (161, 237) are arranged parallel to one another in conducting terms.

6. The method according to claim 3, characterized in that the volumetric pump (205) is operated with a predeterminable rotational speed in the experimental ascertainment of pressure values.

7. The method according to claim 4, characterized in that the volumetric flow through the orifice plate (161, 237) is calculated on the basis of the density of the fluid and the experimentally ascertained pressure.

8. The method according to claim 3, characterized in that the volumetric flow Q.sub.DV through the metering valve (131) is analytically determined on the basis of the following equation:
Q.sub.DV=(.sub.BF&DV/.sub.BF1)*(Q.sub.IL+Q.sub.BF), in which Q denotes the volumetric flow of fluid, X denotes the pressure rate, and the indices BF=return, DV=metering valve and IR=leakage denote the corresponding components of the volumetric flow.

9. A non-transitory, machine-readable medium, on which a computer program configured to carry out each step of the method according to claim 1 is stored.

10. An electronic controlled device (150), which is configured to control a fluidic metering system, in which at least one feed pump (111) for feeding a fluid is arranged and in which the feed pump (111) is connected to a feed line (207) and to a return line (160), on the basis of the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 shows a block diagram of a UWS metering system of an SCR catalyst according to the prior art.

[0023] FIGS. 2a and 2b show a notional breakdown according to the invention of a feed pump concerned here into individual components.

[0024] FIG. 3 shows an exemplary embodiment of the method according to the invention on the basis of a flow diagram.

DETAILED DESCRIPTION

[0025] The enhanced quantity deviation detection described below for DNOX systems can be used in particular in the case of positive displacement pumps with internal leakage and external return, for example in the case of so-called COR pumps.

[0026] As schematically represented in FIG. 1 by the example of an SCR catalyst, metering systems equipped with feed units and injectors are used for the exhaust treatment of internal combustion engines by means of AdBlue or UWS metering into the exhaust flow. In many cases, a return to an AdBlue storage tank is in this case also provided. To ensure operation of these systems that conforms to laws on emissions, the amount of AdBlue that is metered into the exhaust branch must be monitored.

[0027] The fluidic metering system 100 of a motor vehicle that is known per se and shown in FIG. 1 comprises a feed module 110, which has a rotating feed pump 111, which is designed to feed UWS fluid (or reducing agent) from a UWS storage tank 120 by way of a pressure line 121 into the metering module 130, where the UWS fluid is then injected into an exhaust branch that is not shown. In addition, the metering module 130 comprises a metering valve 131, which may be open or closed and controls the volumetric flow of UWS fluid to the metering module 130, and an orifice plate 132, which changes the volumetric flow Q.sub.DV of the USW fluid through the metering module 130. A pressure sensor 140 is also arranged in the metering system 100 and designed to measure a pressure p between the feed module 110 and the metering module 130 over a time period. An electronic control device 150 is connected to the pressure sensor 140 and receives from it information concerning the pressure in the system 100. In addition, the electronic control device 150 is connected to the feed module, including the feed pump 111, and also to the metering module 130, together with the metering valve 131, and can control them.

[0028] In addition, the metering system 100 comprises a return (or a return line) 160, through which UWS fluid is returned from the system into the UWS storage tank 120 with a volumetric flow Q.sub.BF. Arranged in this return 160 is an orifice plate 161, which offers a local flow resistance and to do so reduces the size of an effective cross-sectional area of the return 160.

[0029] For the official or technical approval of future metering systems, quantity deviations of 35% must be detected by means of a so-called Consumption Deviation Monitoring. Systems known per se only sometimes have the possibility of detecting this quantity deviation and require the very precise production of individual system components and/or the complete calculation of further variables, for example the stiffness determination. The stiffness determination that is applied at present in a system with a COR pump results in a dependence of the result on the internal leakage of the COR pump. Reduction and confinement of the internal leakage is not possible with the current state of knowledge, since it can change greatly over the lifetime of the pump.

[0030] Described below on the basis of FIGS. 2a and 2b are the notional breakdown of a feed pump concerned here into individual components (FIG. 2a) and also the notional displacement (FIG. 2b) of the throttle responsible for the inner leakage. Such a displacement is permissible whenever the pressure difference (p.sub.Ap.sub.R) according to FIG. 2b between the intake line and the return line of the pump in comparison with the overall pressure p of the metering system can be ignored.

[0031] A schematically represented feed pump, delimited in FIG. 2a by the dashed line 200, comprises a volumetric pump 205, which is connected to a feed line 207. In a branching line 208 running parallel to the volumetric pump 205, an ideal throttle 210 is arranged as a component of the feed pump 200. In the first direction of an arrow 215, the feed flow produced by the volumetric pump 205 takes place, whereas the return flow illustrated by the inner leakage of the feed pump 200 by means of throttle 210 takes place in a second direction of an arrow 220.

[0032] In FIG. 2b, the feed pump 200 is again represented with the two components 205, 210 that are shown in FIG. 2a. As can be seen from the left part of the image, the feed pump 200 is in turn connected to the feed line 207 shown in FIG. 2a, while a liquid pressure P.sub.A is present at the pump inlet. At the outlet of the feed pump 200, the pressure p is present at a discharge line 235. Outside the feed pump 200, an orifice plate 237 that is effective in a way known per se for the return of fluid by way of the return line 238 is arranged at the pump outlet. The feed line 207 and the discharge line 235 or the return line 238 end in a storage tank 240 for the respective fluid. As can be seen from the right part of the image in FIG. 2b, the notional displacement of the throttle 245 that is responsible for the inner leakage takes place in such a way that the throttle 245 and the orifice plates 237 are arranged parallel to one another in conducting terms, so that the inner leakage is effective as an additional return path with respect to the orifice 237.

[0033] In the following, the leakage volumetric flow in particular of a positive displacement pump is analytically derived. It is assumed here that, with a given temperature, the viscosity of the fluid is constant, and therefore the volumetric flow up to a critical rotational speed speed is proportional to the speed. However, the pressure at the outlet of the pump must not become too great, in order that no deformations of the pump geometry occur.

[0034] For a volumetric pump assumed here, the following equation (1) applies for the relationship between the volumetric flow Q.sub.vol.pump and the rotational speed n:

Q.sub.vol.pump=Q.sub.max*(n/n.sub.max) (1).

[0035] The following relationship applies for the volumetric flow Q.sub.orifice through an orifice plate 237 that is shown in FIG. 2b:

Q.sub.orifice=(.sub.nom/)*Q.sub.nom*(p/p.sub.nom) (2),

[0036] where , the density of the fluid flowing through the orifice plate 237, depends on the temperature of the fluid according to the relation =f(T). The value .sub.nom in this case represents a nominal value of the density and p.sub.nom represents a nominal value of the pressure.

[0037] For the inner leakage of the positive displacement pump, the following volumetric flow Q.sub.leakage, dependent on the pressure p, is obtained:

Q.sub.leakage=*p (3),

[0038] where the constant is known per se, but can be determined from other variables as follows.

[0039] For the volumetric flow Q.sub.vol.pump resulting overall, i.e. on balance, of the assumed, volumetric pump, it then follows that:

Q.sub.vol.pump=Q.sub.orifice+Q.sub.leakage (4).

[0040] Consequently, by simple rearrangement, the following is obtained from the said equations (1) to (4) for the constant :

=Q.sub.max/p*n/n.sub.max(.sub.nom/f(T))*Q.sub.nom*1/((.sub.nom*p) (5).

[0041] Taking into consideration the internal leakage, the following is also obtained for the pressure rate (t):

[00001]$\begin{array}{c}\left(t\right)=.Math.\mathrm{dp}\left(t\right)/\mathrm{dt}=1/V*\mathrm{dp}\left(t\right)/\left(\mathrm{dV}\left(t\right)/V\right)*\mathrm{dV}\left(t\right)/\mathrm{dt}\\ =.Math.1/V*\mathrm{dp}\left(t\right)/\left(\mathrm{dV}\left(t\right)/V\right)*Q\left(t\right)\end{array}$

[0042] where the variable V corresponds to the pump volume of the positive displacement pump. Since, furthermore, the stiffness k of the positive displacement pump is given by the following relation

k=dp(t)/(dV(t)/V) (7),

[0043] the following is obtained overall for the pressure rate (t):

(t)=k/V*Q(t) (8).

[0044] On the further assumption that the said volume V is constant, with relatively short measuring times t the value of the stiffness k according to equation (7) substantially depends only on the pressure p.

[0045] Consequently, the pressure rate for the two situations, metering valve open and closed, can be calculated as follows:

[0046] a) metering valve closed:

.sub.BF=k/V*(Q.sub.IL+Q.sub.BF) (9)

[0047] and

[0048] b) metering valve open:

.sub.BF&DV=k/V*(Q.sub.IL+Q.sub.BF+Q.sub.DV) (10),

[0049] where the indices BF=return, DV=metering valve and IL=leakage denote the corresponding individual volumetric flows or components of the volumetric flow.

[0050] Altogether, the following ratio of the said pressure rates is obtained on the basis of the individual volumetric flows:

.sub.BF&DV/.sub.BF=(Q.sub.IL+Q.sub.BF+Q.sub.DV)/(Q.sub.IL+Q.sub.BF)

[0051] and consequently for the volumetric flow Q.sub.DV through the metering valve:

Q.sub.DV=(.sub.BF&DV/.sub.BF1)*(Q.sub.IL+Q.sub.BF) (12).

[0052] In the experimental measurements to be carried out, the volumetric pump is operated with a defined rotational speed, and consequently delivers a known volumetric flow. The volumetric flow through the orifice plate 237 is calculated with the aid of the density of the liquid and the measured pressure. The density of the liquid is ascertained from its measured temperature. The parameter is missing, in order to be able to calculate the volumetric flow of the leakage from the measured pressure. The aim is to obtain the volumetric flows. The sought parameter can be calculated from the measured temperature and the measured pressure. Consequently, the volumetric flow of the leakage can also be determined for each measured value of the pressure.

[0053] The described method for determining the inner leakage is based on the assumption that this leakage behaves like a throttle. If the leakage displays different behavior, this can be approximated by a piecewise linear function: Q.sub.IL=k*p+Q.sub.0. For the determination of the two parameters k and Q.sub.0, altogether two measurements are required. With x successive pieces, consequently x+1 measurements are obtained.

[0054] The validity of the parameter can be verified by one or more measurements in quick succession at different rotational speeds. The determination of the inner leakage may also be used for monitoring an outer leakage. If the value of the inner leakage ascertained exceeds a threshold, it is assumed that there is an additional outer leakage.

[0055] In FIG. 3, an exemplary embodiment of the method according to the invention is shown. In the present exemplary embodiment, the method is made up of two part-methods that are delimited by dashed lines 300, 305 and are carried out at successive times or at the same time. In the first part-method 300, an analytical determination of the inner leakage of the feed pump concerned here is carried out. As described, the feed pump is in this case notionally broken down into components 310. Such a breakdown applies with good approximation for pumps operating on the displacement principle. The inner leakage is approximated by a throttle 315, which is arranged parallel to an orifice plate already provided for the return.

[0056] The volumetric flow through the metering valve is determined on the basis of experimental measurements of the pressure rate or the pressure drop carried out in the second part-method 305. The volumetric pump is in this case operated with a predeterminable rotational speed 320, and consequently delivers a volumetric flow 325 known per se. The volumetric flow is calculated by the orifice plate with the aid of the density of the fluid that is known per se and the measured pressure 330. The density of the fluid is ascertained in the example in a known way from the measured fluid temperature 335. To be able to calculate the volumetric flow of the leakage from the measured pressure, the previously described constant a is required, which in the exemplary embodiment is calculated from the measured temperature and the measured pressure 340. Consequently, the volumetric flow of the leakage is determined for each measured value of the pressure 345.

[0057] On the basis of these measurement results, possible quantity deviations of the metering system can be detected or monitored on the basis of the ascertained volumetric flow 350. The quantity deviations thus detected can then be eliminated by measures known per se 355.

[0058] The described method may be realized in the form of a control program for an electronic control device for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs).