Method and device for operating a combination valve

Abstract

Method for operating a combination valve, in particular for an internal combustion engine (1) of a motor vehicle, wherein - by setting (S5; S8) a combination valve position (r CV ) at least two partial mass flows (17, 19) are set upstream or downstream of the combination valve, which result in a total mass flow (20) downstream or upstream of the combination valve, - partial mass flow setpoints for the at least two partial mass flows (17, 19) to be set are provided (S1) and - the combination valve position to be set (r CV ) is determined depending on the provided partial mass flow setpoints by means of an implicitly calculated total mass flow setpoint pressure (S3-S4; S3-S7).

Description

Technical area

[0001] The invention relates to a method for operating a combination valve, in particular for an internal combustion engine of a motor vehicle, wherein at least two partial mass flows upstream or downstream of the combination valve are adjusted via a combination valve position. The invention is particularly directed to determining a combination valve position to be adjusted for predetermined partial mass flow setpoints. A further aspect is a device, in particular a control unit, designed to implement the method. State of the art

[0002] To reduce nitrogen oxide formation during fuel combustion in a motor vehicle's internal combustion engine, it is known to provide exhaust gas recirculation (EGR) from an exhaust line into a fresh air line of the internal combustion engine. Depending on the installation position of such an external exhaust gas recirculation line, a distinction is made between high-pressure EGR (HP EGR) and low-pressure EGR (LP EGR). Separate valves can be used, for example, for a LP EGR path and a LP exhaust flap path, or for a HP EGR path and a HP throttle valve path, at corresponding branch or inlet points of the exhaust gas recirculation.

[0003] Target fresh air masses and EGR rates can be controlled using a model-based approach in which the corresponding partial mass flows are calculated using a throttling equation. This calculation can depend on pressures upstream and downstream of the valves, their effective opening cross-sections, and temperatures upstream or downstream of the valves.

[0004] As an alternative to separate valves, combination valves can also be used at the branch or inlet points of low-pressure or high-pressure EGR. A combination valve allows both partial mass flows to be adjusted simultaneously, for example, through a rigid mechanical coupling, so that a change in the position of the combination valve results in a change in the effective opening cross-sections for both valve paths. For example, DE 10 2011 002 552 A1 describes a combination valve at the junction of a low-pressure EGR line with an intake line, which simultaneously and synchronously measures the recirculated exhaust gas volume and the intake fresh air volume.

[0005] US 2016 / 0 032 871 A1 discloses a variation comprising a unit including a housing unit having an exhaust gas flow opening and an EGR flow opening formed therein, an exhaust gas flow opening valve plate received in the housing unit and configured and arranged to move into a position to at least partially block the flow of gas through the exhaust gas flow opening, and an EGR opening valve plate received in the housing unit and configured and arranged to move into a position to at least partially block gas through the EGR flow opening, and a single actuator connected to move both the exhaust gas flow opening valve plate and the EGR flow opening valve plate.A further variation may include a combined low pressure exhaust recirculation valve and exhaust throttle valve having first and second valve plates spaced apart from one another connected to a common valve shaft.

[0006] US 2010 / 0 206 274 A1 relates to a low-pressure exhaust gas recirculation device for recirculating a portion of exhaust gases emitted by an engine (an internal combustion engine for generating drive power by burning fuel) into a portion of an intake air passage having a slight negative pressure (for example, an upstream side of a throttle valve where a slight negative pressure is generated).

[0007] The effective target opening cross-sections of a combination valve to be controlled can be calculated based on actual pressures and target mass flows. If these two effective target opening cross-sections do not result in the same target position of the combination valve, a weighting must be performed between the separately calculated target positions.

[0008] However, this type of combi valve control can be unsatisfactory in terms of response time and dynamic control performance, as the combi valve's own movement has a direct impact on the actual pressure upstream or downstream of the valve, depending on whether it is installed on the branch or inlet side of a low-pressure or high-pressure EGR system. The changed actual pressure results in a recalculation of the effective target opening cross-sections, which in turn results in a changed target position of the combi valve. Disclosure of the invention

[0009] According to the invention, a method for operating a combination valve according to claim 1 as well as a corresponding device, a computer program and a machine-readable storage medium according to the independent claims are provided.

[0010] Further embodiments are specified in the dependent claims. All further features and effects specified in the claims and the description for the method also apply to the device and the computer program, and vice versa.

[0011] According to a first aspect, a method for operating a combination valve, in particular for an internal combustion engine of a motor vehicle, is provided. In this method, by setting a combination valve position, at least two partial mass flows upstream or downstream of the combination valve are set, which result in a total mass flow on the other valve side, i.e. downstream or upstream of the combination valve. For this purpose, partial mass flow setpoints are provided for the at least two partial mass flows to be set, and the combination valve position to be set is determined as a function of the provided partial mass flow setpoints using an implicitly calculated total mass flow setpoint pressure. In particular, the combination valve position to be set determined in this way can be used as a setpoint combination valve position for regulating the combination valve.

[0012] The combination valve can, for example, be of the type described above and, in particular, be located at a branch or inlet point of an LP or HP EGR of an internal combustion engine. When the combination valve is installed at an exhaust gas recirculation inlet point, the two partial mass flows (exhaust gas and fresh air) flow upstream toward the valve in this application. When the combination valve is installed at a branch point, exactly two partial mass flows flow downstream of the valve. The internal combustion engine can, for example, be a diesel or gasoline engine, particularly for a hybrid vehicle.

[0013] As mentioned at the beginning, a change in the combination valve position can have a direct influence on the actual pressure of the total mass flow. For example, the combination valve movement of a combination valve installed on the EGR intake side has a throttling effect on the combined pressure of the combined partial mass flows downstream of the combination valve.

[0014] One idea of ​​the method is to implicitly use the information about the total mass flow target pressure, which is to be set upstream or downstream of the valve depending on the installation location of the combination valve, in order to set both / all target partial mass flows simultaneously.

[0015] This idea is based on the fact that the setpoint pressure of the total mass flow, unlike its actual pressure, is independent of the combi valve position. This is because, given the specified input variables of the partial mass flows (in particular, the temperature, the actual pressures, and the setpoint partial mass flows), it directly defines the effective opening cross-sections of the individual valve paths and thus the combi valve position, and not vice versa (e.g., through the throttle equation according to formulas 1 and 2 below). Therefore, by implicitly using the total mass flow setpoint pressure when calculating the combi valve position, a dynamically faster response of the combi valve and faster control of the specified setpoint partial mass flows can be achieved.

[0016] In a specific embodiment, the adjustment of the individual partial mass flows can be coupled to one another when adjusting a combination valve position, for example, by a mechanical, particularly a hard mechanical, coupling of effective partial mass flow opening cross-sections through an actuating element in the combination valve. This enables simultaneous adjustment of both / all partial mass flows via a single position parameter of the combination valve, which can be particularly economical with regard to the size, manufacturing, and / or control of the combination valve.

[0017] In one embodiment, one of the partial mass flows is an exhaust gas recirculation flow in an internal combustion engine. In particular, the combination valve can be arranged at an inlet point of an exhaust gas recirculation line into a fresh air line, with another of the partial mass flows being a fresh air mass flow.

[0018] In particular, the combination valve position to be adjusted can also be determined depending on the actual temperatures and / or pressures provided for the at least two partial mass flows. These actual values ​​can be provided in a known manner using suitable sensors.

[0019] The determination of the combination valve position to be set, in particular the implicit calculation of the total mass flow target pressure, can be carried out, for example, using a throttle equation (in particular according to Formula 1 below). The implicit calculation of the total mass flow target pressure can be used in particular by - for each of the at least two partial mass flows, a target pressure on the other valve side is determined as a function of the combination valve position using a throttle equation, and - the combination valve position to be set is determined analytically or iteratively as the intersection point of the functions thus determined.

[0020] According to a further aspect, a device, in particular a control unit, is provided, which is designed to carry out the method described herein, in particular fully automatically. Furthermore, a computer program is provided, which, when executed in a data processing device or the control unit, is configured to carry out all steps of the method described herein. Furthermore, a machine-readable storage medium is provided on which such a computer program is stored. Brief description of the drawings

[0021] Embodiments are explained in more detail below using the examples shown in the attached drawings. The drawings are purely schematic and should not be read as being to scale. They show: Fig. 1 a schematic overview of an air system of an internal combustion engine of a motor vehicle; Fig. 2 is a flowchart for an example of a method for operating a combination valve; Fig. 3 is a flowchart for another example of a method for operating a combination valve; Fig. 4 schematic illustration curves to visualize the process of Fig. 3, which indicate a target pressure on the other valve side for each of the two partial mass flows as a function of a combination valve position; and Fig. 5 schematic representation of calculated support points on the visual curves of the Fig. 4 for an iterative determination of the combination valve position to be set. Description of embodiments

[0022] Fig. 1 shows, by way of example, a simplified schematic representation of an air system of an internal combustion engine 1 of a motor vehicle. The internal combustion engine 1 for driving an output shaft 2 can be designed, for example, as a diesel or gasoline engine with, purely by way of example, four cylinders 3. The cylinders 3 are supplied with fresh air via a fresh air line 4. Exhaust gases from the internal combustion engine 1 are discharged via an exhaust line 5. Purely by way of example, the air system has an exhaust gas turbocharger with a turbine 6 in the exhaust line 5 and a compressor 7 in the fresh air line 4.

[0023] In this example, both a high-pressure exhaust gas recirculation line 8 (HP-EGR), which branches off from the exhaust line 5 upstream of the turbine 6 and flows into the fresh air line 4 upstream of a charge air cooler 9, and a low-pressure exhaust gas recirculation line 10 (LP-EGR), which branches off from the exhaust line 5 downstream of the turbine 6 and an exhaust aftertreatment unit 11 and flows into the fresh air line 4 upstream of the compressor 7, are provided. To cool the recirculated exhaust gases, exhaust gas coolers 12, optionally with bypass lines 13, can be provided in the exhaust gas recirculation lines 8 and / or 10.

[0024] Below, examples of the method presented herein for operating a combi valve are described in detail with reference to a combi valve (not shown) installed at an inlet point 15a of the LP EGR line 10 into the fresh air line 4. It should be noted that analogous method steps and analogous functionality can also be applied to a combi valve (not shown) installed at a branch point 15b of the LP EGR line 10 from the exhaust line 5. The fundamental difference in the latter case is that the total mass flow target pressure is then to be calculated upstream, not downstream, of the combi valve. The same applies accordingly to a combi valve (not shown) installed at an inlet point 14a or a branch point 14b of the HP EGR line 8.

[0025] In the following examples, the combination valve (not shown) at the inlet point 15a replaces two in the Fig. 1: an LP EGR valve 16 for adjusting the exhaust gas quantity recirculated through the LP EGR line 10 (i.e., a first partial mass flow 17 upstream of the combination valve) and, in this example, an LP throttle valve optionally provided for adjusting the fresh air flowing through the fresh air line 4 upstream of the compressor 7 (i.e., a second partial mass flow 19 upstream of the combination valve). These two partial mass flows 17 and 19 result in a total mass flow 20 downstream of the combination valve, which, in the example shown, is fed to the compressor 7.

[0026] Using this combination valve as an example, the Fig. The flowchart shown in Figure 2 illustrates an example of a method of the type presented herein for operating a combination valve. The method begins with a "start" signal and can, in particular, be executed partially or fully automatically by a control unit that can be configured to control the combination valve.

[0027] In a step S1, setpoints are provided for the two partial mass flows 17 and 19, which are to be supplied to the compressor 7 in the form of the total mass flow 20. These partial mass flow setpoints can, for example, be supplied to the aforementioned control unit from outside or can also be provided by the control unit itself through calculation, etc.

[0028] In a step S2, in this example, actual pressure values ​​and actual temperature values ​​are also provided for the two partial mass flows 17 and 19. These can be provided, for example, by suitable sensors.

[0029] The goal is now to determine a combination valve position, depending on the provided partial mass flow setpoints, that leads to these partial mass flow setpoints. This determination is performed using an implicitly calculated setpoint pressure for the total mass flow 20 as follows:

[0030] In this example, in step S3, an equation for passing through the combination valve is established for each partial mass flow 17 and 19. With the setpoint values ​​m provided for the partial mass flows 17 and 19, . egrDes, m ·thrDes, actual pressures pUs,egr, pUs,thr, and actual temperatures TUs,egr, TUs,thr upstream of the combi valve, an effective target opening cross-section aregrDes, arthrDes of the respective combi valve path can be calculated using a throttle equation, for example. The respective throttle equation also depends on a target pressure value pDs,egrDes, pDs,thrDes of the respective partial mass flow 17 or 19 downstream of the valve. This results in the following two equations: aregrDes=f1(m˙egrDes,pUs,egr,Tus,egr,pDs,egrDes) arthrDes=f1(m˙thrDes,pUs,thr,TUs,thr,pDs,thrDes)

[0031] There are pairs of the effective target opening cross-section and target pressure (aregrDes, pDs,egrDes), (arthrDes, pDs,thrDes) that satisfy formulas 1 and 2, respectively. Furthermore, in this example, the target pressures pDs,thrDes and pDs,egrDes downstream of the combination valve are identical, since they correspond to a common target pressure pDs,Des of the total mass flow 20.

[0032] In addition, there is a specific relationship for the combination valve between the effective target opening cross sections aregrDes, arthrDes of the two valve paths and a combination valve position r CV : rCV=f2(aregrDes) rCV=f3(arthrDes)

[0033] The relationship f2(·), f3(·) can be stored empirically in the form of a characteristic curve or be known as an analytical function. In this case, a specific combination valve position r CVIn this example, the effective opening cross sections aregrDes, arthrDes of both valve paths are determined simultaneously.

[0034] Now in Fig. 2 in a step S4 a combination valve position r CV calculated, by which both target partial mass flows megrDes, ṁthrDes are set. For this purpose, the total mass flow target pressure pDs,Des = pDs,egrDes = pDs,thrDes is calculated in an intermediate step or implicitly. For a linear relationship of f1(·), f2(·), f3(·) and other cases in which f1(·) can be resolved for the target pressure pDs,Des and f2(·), f3(·) are invertible, the calculation of pDs,Des and thus of r CV analytically possible.

[0035] In a step S5, the combination valve position r thus determined is CV, whereby the two partial mass flows 17 and 19 upstream of the combination valve are adjusted according to the partial mass flow setpoints provided in step S1. The method can be carried out cyclically purely by way of example.

[0036] Fig. 3 shows a flow chart of a further example of a method of the type set out herein for operating a combination valve, in which the combination valve position r to be set CV using iterative steps. This is a possible alternative to the method used in step S4 of the Fig. 2, especially if the relationship f1(·), f2(·) or f3(·) is non-linear and / or empirical.

[0037] Up to step S3, the procedure corresponds to the Fig. 3 that of the Fig. 2. Based on the above formulas 1, 2, 3 and 4, the combination valve position r to be set is CV in Fig. 3 in contrast to Fig. 2 is not determined directly analytically, but iteratively, for example as in steps S4 to S7 shown below.

[0038] In Fig. 4 and Fig. 5, the pairs (aregrDes, pDs,egrDes), (arthrDes, pDs,thrDes) of the effective opening cross-section and the downstream target pressure mentioned above in step S3, which exist for the respective valve path, are schematically indicated as "notional" visual curves 21 (LP EGR valve path) and 22 (LP throttle valve path) solely for the purpose of visualizing the subsequent iteration process. The relationship between the combination valve position r CV and the effective opening cross sections aregrDes, arthrDes according to formulas 3 and 4.

[0039] In a step S4 of the Fig. 3, it can first be checked whether the two target mass flows specified in step S1 above can be adjusted simultaneously. For this purpose, an assumption is used based on the throttle equation that a further reduction of the downstream target pressure pDs,Des = pDs,egrDes = pDs,thrDes below a critical pressure gradient πcrit does not result in an increase in the flow function ψ (π = pDs,Des / pUs) and a further increase in the pressure ratio for the respective valve path therefore does not result in an increase in the mass flow. Therefore, the calculation of a respective minimum valve position r CV ,thrMin, r CV ,egrMin is possible, at which the respective target partial mass flow for this valve path can still be displayed (see Fig. 4): rCV,egrMin=f2(aregrDes)with aregrDes=f1(m˙egrDes,pUs,egr,TUs,egr,πcrit⋅pUs,egr) rCV,thrMin=f3(arthrDes)with arthrDes=f1(m˙thrDes,pUs,thr,TUs,thr,πcrit⋅pUs,thr)

[0040] It can now be decided whether there is a combination valve position r CV or a total mass flow target pressure pDs,Des within the interval (r CV ,thrMin, r CV ,egrMin) which sets both target partial mass flows. As in Fig. 4, this step checks whether there can be an intersection point between the two imaginary curves 21 and 22 in this interval. If this is not the case, a combination valve position r can be set. CV for example, as in the prior art described above or in another suitable manner by a person skilled in the art. The method can then proceed directly to step S8 (setting the determined combination valve position r) described below. CV ) to skip.

[0041] However, if the check in step S4 shows that an intersection point is possible, in a further step S5, starting from a selected starting value r CV,start of the valve position within the interval defined above (r CV ,thrMin, r CV ,egrMin) is checked by calculation to determine on which of the visual curves 21, 22 the pressure pDs,egrStart or pDs,thrStart is lower for this valve position. The pressures can be calculated as follows: pDs,egrStart=f4(m˙egrDes,pUs,egr,TUs,egr,aregrStart)with aregrStart=f5(rCV,start) pDs,thrStart=f4(m˙thrDes,pUs,thr,TUs,thr,arthrStart)with arthrStart=f6(rCV,start)

[0042] Where f4(·) is the throttle equation of Formula 1, which has been rearranged according to the set pressure pDs,Des, and f5(·), f6(·) are the inverse characteristics of f2(·), f3(·). As in Fig. As can be seen in Figure 4, pDs,thrStart is the smaller pressure value.

[0043] The corresponding point P1thr = (r CV,start, pDs,thrStart) can now be used as a starting point for calculating further support points. This process is exemplified in Fig. 5 schematically illustrates:

[0044] In step S6, three additional support points P1egr, P2egr, and P2thr are calculated on the visual curves 21 and 22, starting from the starting point P1thr, so that two support points are available for each valve path. In this example, the following two points are calculated for the LP EGR valve path: P1egr=(rCV,start,pDs1,egr),pDs1,egr=f4(m˙egrDes,pUs,egr,TUs,egr,aregrStart) P2egr=(rCV2,egr,pDs,thrStart),aregr2=f1(m˙egrDes,pUs,egr,TUs,egr,pDs,thrStart), rCV2,egr=f2(aregr2)

[0045] The following two support points result for the LP throttle path: P1thr=(rCV2,start,pDs,thrStart) P2thr=(rCV2,egr,pDs2,thr),pDs2,thr=f4(m˙egrDes,pUs,egr,TUs,egr,arthr2),arthr2=f6(rCV2,egr)

[0046] Using these four points, two straight lines (not shown) can now be formed, and their intersection point calculated. The intersection point found can serve as a starting point for a further iteration step, but alternatively, it can also be used as the determined combination valve position r to be adjusted. CV serve.

[0047] In this example, steps S5 and S6 can be repeated iteratively until the distance between the respective support points r CV ,start and r CV2 the valve position within an iteration step is below a predetermined threshold value. This can be done in particular in step S7 of the Fig. 3. If this condition is met, one of the two last calculated support points, their mean value or another suitable intermediate value can be used as the combination valve position r to be set. CV be determined.

[0048] Analogous to step S5 of the Fig. 2 is in the procedure of Fig. 3 in a step S8 the combination valve position r thus determined CV , whereby the two partial mass flows 17 and 19 upstream of the combination valve are adjusted according to the partial mass flow setpoints provided in step S1. The entire method can also be carried out cyclically here.

Claims

[1] Method for operating a combination valve, in particular for an internal combustion engine (1) of a motor vehicle, wherein - by setting (S5; S8) a combination valve position (r CV ) at least two partial mass flows (17, 19) are set upstream or downstream of the combination valve, which result in a total mass flow (20) downstream or upstream of the combination valve, - partial mass flow setpoints for the at least two partial mass flows (17, 19) to be set are provided (S1) and - the combination valve position to be set (r CV ) is determined depending on the provided partial mass flow setpoints by means of an implicitly calculated total mass flow setpoint pressure (S3-S4; S3-S7). [2] Method according to claim 1, wherein the determined combination valve position (rcv) to be set is used as the desired combination valve position for controlling the combination valve. [3] Method according to claim 1 or 2, wherein the setting of the at least two partial mass flows (17, 19) when setting a combination valve position (r CV ) is coupled to each other, in particular by a mechanical coupling of associated effective partial mass flow opening cross sections (ar egr , ar t□r ) in the combination valve by a combination valve control element. [4] Method according to one of the preceding claims, wherein one of the at least two partial mass flows (17, 19) is an exhaust gas recirculation flow (17) in an internal combustion engine (1). [5] Method according to claim 4, wherein the combination valve is arranged at an inlet point (14a, 15a) of an exhaust gas recirculation line (8, 10) into a fresh air line (4) and another of the at least two partial mass flows (17, 19) is a fresh air mass flow (19). [6] Method according to one of the preceding claims, wherein the combination valve position to be set (r CV) is further determined as a function of the provided actual temperatures and / or actual pressures of the at least two partial mass flows (17, 19). [7] Method according to one of the preceding claims, wherein the determination of the combination valve position to be set (r CV ), in particular the implicit calculation of the total mass flow target pressure, is carried out using a throttle equation. [8] Method according to claim 7, wherein in the implicit calculation of the total mass flow target pressure - for each of the at least two partial mass flows (17, 19) a target pressure (p Ds,t□r Des, p Ds,egrDes ) on the other valve side as a function of the combination valve position (r CV ) is determined and - the combination valve position to be set (r CV ) is determined analytically or iteratively as the intersection point of the functions thus determined. [9] Device, in particular a control unit, for operating a combination valve, wherein the device is designed to carry out a method according to one of the preceding claims, in particular fully automatically. [10] Computer program which, when executed in a control unit or a data processing device, is adapted to carry out all the steps of a method according to one of claims 1 to 8. [11] A machine-readable storage medium on which a computer program according to claim 10 is stored.

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