Method and device for adjusting the mass flow of an exhaust gas recirculation valve

Abstract

Method for adjusting the mass flow of an exhaust gas recirculation valve (186) mechanically coupled to a throttle valve (162, 182) of an internal combustion engine (100) having a turbocharger (120), comprising the following steps: - determining a first setpoint value corresponding to a setpoint opening position of the exhaust gas recirculation valve (186), - determining a second setpoint value corresponding to a setpoint opening position of the throttle valve (162, 182), - Comparing the first setpoint with the second setpoint, - adjusting the mass flow of the exhaust gas recirculation valve (186) by changing the opening position of the exhaust gas recirculation valve (186) and the throttle valve (162, 182) using the first setpoint value if the first setpoint value is greater than the second setpoint value and - adjusting the mass flow of the exhaust gas recirculation valve (186) by changing the opening position of the throttle valve (162, 182) and the exhaust gas recirculation valve (186) using the second setpoint value if the second setpoint value is greater than the first setpoint value.

Description

[0001] The invention relates to a method and a device for adjusting the mass flow of an exhaust gas recirculation valve of an internal combustion engine having a turbocharger.

[0002] To control an internal combustion engine, the composition of the gas charge and the filling of the combustion chamber with the gas charge are specifically influenced by adjusting actuators such as throttle valves, exhaust gas recirculation valves, exhaust flaps, etc. Both the composition and the quantity of gas filling the combustion chamber, in addition to the injected fuel, determine the torque and the combustion products, and thus the amount of pollutants in the exhaust gas. The majority of gasoline engines operate with a stoichiometric combustion gas mixture. In conjunction with a three-way catalytic converter, this allows for effective reduction of pollutants produced during combustion.

[0003] The amount of fuel to be injected is determined by the amount of air present in the combustion chamber. In a diesel engine during nominal operation, the amount of air available limits the amount of fuel to be injected in order to keep the amount of exhaust particles contained.

[0004] The oxygen concentration is a key parameter for the production of nitrogen oxides during combustion. A reduction in the oxygen concentration in the cylinder charge leads to a reduction in nitrogen oxide emissions. In today's diesel engines, this is achieved through exhaust gas recirculation. This exhaust gas recirculation can occur internally through the cylinder of the internal combustion engine or externally together with any cooling system. This external exhaust gas recirculation can be carried out upstream and / or downstream of the compressor of a turbocharger of the internal combustion engine. Accordingly, it is referred to as low-pressure exhaust gas recirculation or high-pressure exhaust gas recirculation.

[0005] A prerequisite for exhaust gas recirculation is always that the gas pressure at the branch point is higher than at the inlet point. This is not always sufficiently possible, especially with low-pressure exhaust gas recirculation. For this reason, additional throttle valves are installed to support exhaust gas recirculation and allow for the necessary increase or decrease in gas pressure at the branch point or the inlet point.

[0006] DE 10 2013 209 815 B3 discloses a method and a system for controlling an internal combustion engine equipped with an exhaust gas turbocharger and further comprising a high-pressure exhaust gas recirculation system and a low-pressure exhaust gas recirculation system. Based on a physical model, flow parameters of the gas flowing in the system are determined at different points along the gas flow depending on the position of an actuator in the gas flow. These flow parameters include temperature and / or pressure.Based on the inverted physical model, a position of the actuator corresponding to a predetermined flow parameter in the cylinder is determined, the actuator is controlled to the determined position, a deviation of the predetermined flow parameter from the flow parameter of the gas flow in the cylinder is determined, and the physical model is adjusted based on the deviation. The physical model includes a return of combusted gas to the cylinder, and the flow parameter further includes a gas composition or a gas quantity of the gas flow in the cylinder. These measures are intended to achieve a more direct or more precise control of the internal combustion engine.

[0007] DE 101 01 343 A1 discloses a method and device for controlling exhaust gas recirculation in an internal combustion engine with a turbocharging device, exhaust gas recirculation line, and exhaust gas recirculation valve. The steps of adjusting the turbocharging device and adjusting the exhaust gas recirculation valve are performed using control signals. The control signals for the turbocharging device and the exhaust gas recirculation valve are generated using a common control variable from a common controller.

[0008] DE 10 2014 118 947 A1 discloses a method and a system for EGR control. According to one embodiment described therein, groups of throttle valves are provided, with a first group of throttle valves arranged on a first shaft and a second group of throttle valves arranged on a second shaft.

[0009] The invention is based on the object of specifying a method and a device for adjusting the mass flow flowing through the exhaust gas recirculation valve of an internal combustion engine, which operate stably during operation of the internal combustion engine.

[0010] This object is achieved by a method having the features specified in claim 1. Advantageous embodiments and further developments are specified in dependent claims 2 to 5. Claim 6 relates to a device for adjusting the mass flow of an exhaust gas recirculation valve.

[0011] According to the present invention, in a method for adjusting the mass flow of an exhaust gas recirculation valve mechanically coupled to a throttle valve of an internal combustion engine having a turbocharger, the following steps are carried out: - Determination of a first target value corresponding to a target opening position of the exhaust gas recirculation valve, - Determination of a second setpoint value corresponding to a setpoint opening position of the throttle valve, - Comparing the first setpoint with the second setpoint, - Adjusting the mass flow of the exhaust gas recirculation valve by changing the opening position of the exhaust gas recirculation valve and the throttle valve using the first setpoint if the first setpoint is greater than the second setpoint and - Adjusting the mass flow of the exhaust gas recirculation valve by changing the opening position of the throttle valve and the exhaust gas recirculation valve using the second setpoint if the second setpoint is greater than the first setpoint.

[0012] This approach enables stable control of the exhaust gas recirculation valve, which is mechanically coupled to a throttle valve, and the exhaust gas recirculation valve. The throttle valve and the exhaust gas recirculation valve are characterized independently of each other using a model. This has the advantage of allowing direct determination of the mass flow through the exhaust gas recirculation valve, and the control is automatically adjusted if the setpoint changes. This is particularly advantageous when the internal combustion engine operates in different modes.

[0013] Further advantageous features of the invention will become apparent from the following exemplary explanation based on the figures. It shows: Fig. 1 is a block diagram of an internal combustion engine equipped with an exhaust gas turbocharger, a low-pressure exhaust gas recirculation system and a high-pressure exhaust gas recirculation system according to a first embodiment, Fig. 2 a block diagram of an internal combustion engine equipped with an exhaust gas turbocharger, a low-pressure exhaust gas recirculation system and a high-pressure exhaust gas recirculation system according to a second embodiment, Fig. 3 a diagram illustrating the effective opening cross-sectional area of ​​an exhaust gas recirculation valve as a function of the opening position of the exhaust gas recirculation valve and Fig. 4 a diagram illustrating the effective opening cross-sectional area of ​​a throttle valve mechanically coupled to the exhaust gas recirculation valve as a function of the opening position of the exhaust gas recirculation valve.

[0014] The Fig. 1 shows a block diagram of an internal combustion engine equipped with an exhaust gas turbocharger, a low-pressure exhaust gas recirculation system and a high-pressure exhaust gas recirculation system according to a first exemplary embodiment.

[0015] This internal combustion engine 100 has a turbocharger 120, which includes an exhaust gas turbine 130 and a compressor 125. The exhaust gas turbine 130 is supplied with exhaust gas provided by the cylinders 150 of the internal combustion engine 100. This exhaust gas causes the turbine wheel of the exhaust gas turbine 130 to rotate. This rotation of the turbine wheel is transmitted via a shaft of the exhaust gas turbocharger to a compressor wheel of the compressor 125, which is also rotated as a result. The compressor wheel is provided for compressing a gas mixture consisting of fresh air and exhaust gas recirculated via a low-pressure exhaust gas recirculation system 180. This fresh air is supplied to the compressor wheel via an air filter 110. The exhaust gas emitted by the exhaust turbine 130 is released into the environment via a catalyst 158, a particulate filter 160, a throttle valve 162 used as an exhaust flap, and a silencer 164.

[0016] Between the particulate filter 160 and the throttle valve 162, which serves as an exhaust flap, a branch is provided at which exhaust gas is branched off and fed to the compressor 125 via the low-pressure exhaust gas recirculation 180. A cooler 184 and an exhaust gas recirculation valve 186, designed as a low-pressure exhaust gas recirculation valve, are provided in this low-pressure exhaust gas recirculation 180.

[0017] The compressed gas mixture is supplied from the outlet of the compressor 125 via a charge air cooler 135 and a throttle 140 to the cylinders 150 of the internal combustion engine 100.

[0018] Furthermore, the Fig. The internal combustion engine 100 shown in Figure 1 has a high-pressure exhaust gas recirculation system 166. This system is connected directly to an outlet of the cylinders 150 and is supplied with high-pressure exhaust gas via this outlet. This high-pressure exhaust gas is fed to the inlet of the cylinders 150 via a cooler 170 and a high-pressure exhaust gas recirculation valve 172 in order to supply recirculated exhaust gas to these cylinders. A bypass valve 168 is arranged parallel to the cooler 170 in order to bypass the cooler 170 if necessary.

[0019] Furthermore, the Fig. The internal combustion engine 100 shown in Figure 1 has a control unit 188. Sensor signals se1, ..., sen provided by a plurality of sensors are fed to this control unit 188. The control unit 188 determines control signals s1, ..., sn for the actuators of the internal combustion engine by evaluating these sensor signals and an operating program stored in a memory (not shown), as well as stored tables and characteristic maps and physical models. These actuators include, among others, the exhaust gas recirculation valve 186 used as a low-pressure exhaust gas recirculation valve and the throttle valve 162 used as an exhaust flap. The physical models include a model of the exhaust gas recirculation valve 186 used as a low-pressure exhaust gas recirculation valve and a model of the throttle valve 162 used as an exhaust flap, which forms a throttling point.

[0020] The exhaust gas recirculation valve 186, used as a low-pressure exhaust gas recirculation valve, and the throttle valve 162, used as an exhaust valve, are advantageously mechanically coupled to one another and can be controlled by the same control signal. This control is model-based, as will be explained below with reference to the Fig. 3 and Fig. 4 is explained in more detail.

[0021] The Fig. 2 shows a block diagram of an internal combustion engine equipped with an exhaust gas turbocharger, a low-pressure exhaust gas recirculation system and a high-pressure exhaust gas recirculation system according to a second exemplary embodiment.

[0022] This internal combustion engine 100 has a turbocharger 120, which includes an exhaust turbine 130 and a compressor 125. The exhaust turbine 130 is supplied with exhaust gas provided by the cylinders 150 of the internal combustion engine 100. This exhaust gas causes the turbine wheel of the exhaust turbine to rotate. This rotation of the turbine wheel is transmitted via a shaft of the exhaust turbocharger to the compressor wheel of the compressor 125, which is also rotated as a result. The compressor wheel is provided for compressing a gas mixture consisting of fresh air and exhaust gas recirculated via a low-pressure exhaust gas recirculation system 180. This fresh air is supplied to the compressor wheel via an air filter 110 and a throttle valve 182 acting as an air flap. The exhaust gas emitted by the exhaust turbine 130 is released into the environment via a catalyst 158, a particulate filter 160 and a silencer 164.

[0023] Between the particulate filter 160 and the silencer 164, a branch is provided at which exhaust gas is branched off and fed to the compressor 125 via the low-pressure exhaust gas recirculation 180. This low-pressure exhaust gas recirculation 180 contains a cooler 184 and an exhaust gas recirculation valve 186 used as a low-pressure exhaust gas recirculation valve.

[0024] The compressed gas mixture is supplied from the outlet of the compressor 125 via a charge air cooler 135 and a throttle 140 to the cylinders 150 of the internal combustion engine 100.

[0025] Furthermore, the Fig. The internal combustion engine 100 shown in Figure 2 has a high-pressure exhaust gas recirculation system 166. This system is connected directly to an outlet of the cylinders 150 and is supplied with high-pressure exhaust gas via this outlet. This high-pressure exhaust gas is recirculated to the inlet of the cylinders 150 via a cooler 170 and a high-pressure exhaust gas recirculation valve 172 in order to supply recirculated exhaust gas to these cylinders. A bypass valve 168 is arranged parallel to the cooler 170 in order to bypass the cooler 170 if necessary.

[0026] Furthermore, the Fig. The internal combustion engine 100 shown in Figure 2 has a control unit 188. Sensor signals se1,..., sen provided by a plurality of sensors are fed to this control unit 188. The control unit 188 determines control signals s1,..., sn for the actuators of the internal combustion engine 100 by evaluating these sensor signals and an operating program stored in a memory (not shown), as well as stored tables and characteristic maps and physical models. These actuators include, among others, the exhaust gas recirculation valve 186 used as a low-pressure exhaust gas recirculation valve and the throttle valve 182 used as an air flap. The physical models include a model of the low-pressure exhaust gas recirculation valve 186 and a model of the throttle valve 182 used as an air flap, which forms a throttle point.

[0027] The exhaust gas recirculation valve 186, used as a low-pressure exhaust gas recirculation valve, and the throttle valve 182, used as an air flap, are advantageously mechanically coupled to one another and can be controlled using the same control signal. This control is model-based.

[0028] Such a model-based control of a valve or throttle uses the known relationship between the gas mass flow and the position of the valve or throttle with known gas properties such as temperature, pressure, and gas composition upstream and downstream of the valve or throttle. For modeling purposes, either the valve alone or the entire exhaust gas recirculation path can be considered. Typically, the dependence of the gas mass flow is factored into a dependence on the gas properties upstream and downstream of the valve and a dependence on the position of the valve itself, so that the model is represented by an equation of the form m˙=A(s)·g(ebefore,eafter) where ṁ is the exhaust gas mass flow, A(s) is the effective opening cross-section and g(e vor , e nach ) are a function of the gas properties upstream and downstream of the valve. This applies to both the throttle and the exhaust gas recirculation valve. With separate control of the exhaust gas recirculation valve and the throttle, the throttle can be used to set a desired pressure drop across the exhaust gas recirculation valve or the exhaust gas recirculation line, and the exhaust gas recirculation valve can be used to set the desired exhaust gas recirculation mass flow.

[0029] The target position of the exhaust gas recirculation valve is determined in the case of a fresh air side throttling, as described in the Fig. 2, from the following relationship: sEGR,SP=AEGR−1(m˙EGR,SPgEGR(ebefore EGR,after EGR)).

[0030] This is s EGR,SP the target position of the exhaust gas recirculation valve, AEGR -1 the inverse function for the effective Opening cross-section of the exhaust gas recirculation valve, ṁ EGR,SP the target mass flow through the exhaust gas recirculation valve and g EGR (e vorEGR , e nachEGR ) a function of the gas properties before and after the exhaust gas recirculation valve.

[0031] The target position of the throttle valve 182 used as an air flap is obtained in the case of a fresh air side throttling, as in the Fig. 2, from the following relationship: sTHR,SP=ATHR−1(m˙THR,SPgTHR(ebefore THR,after THR,SP)).

[0032] This is s THR,SP the target position of the throttle valve, A THR -1 the inverse function for the effective opening cross-section of the throttle valve, ṁ THR,SP the target mass flow through the throttle valve and g THR (e vorTHR , e nachTHR) a function of the gas properties before and after the throttle valve.

[0033] In the case of joint control of the exhaust gas recirculation valve and the throttle valve, the target position of the throttle valve is determined from the target position of the exhaust gas recirculation valve due to the mechanical coupling of the exhaust gas recirculation valve with the throttle valve, and vice versa. If the target position of the exhaust gas recirculation valve is determined using the aforementioned equation (1), then the target position of the throttle valve is already determined. However, since with fresh air throttling, a change in the position of the throttle valve usually also changes the gas pressure behind the throttle valve, the gas state e nachEGR a new value. This type of control therefore usually leads to undesirable, unstable control behavior, since nachEGR from s EGR In principle, one should EGR,SP from the solution of the equation sEGR,SP=AEGR−1(m˙EGR,SPgEGR(ebefore EGR,after EGR(sEGR,SP))) determine.

[0034] Here, the dependence on e nachEGR (s EGR,SP ) by the equations m˙THR=ATHR(sTHR) gTHR(ebeforeTHR,eafterTHR) and sTHR=sEGR given. ṁ THR the gas mass flow through the throttle valve, A THR the effective opening cross-section of the throttle valve, s THR the position of the throttle valve and s EGR the position of the exhaust gas recirculation valve.

[0035] Since the implicit equation (3) cannot be converted into an explicit equation for the target position, a complex iterative solution procedure would be necessary to solve equation (3) and thus determine the target position.

[0036] To avoid this, the following relationship is used: If the exhaust gas recirculation valve is only slightly opened, the throttle valve is either not closed at all or only closed very slightly. The slight opening of the exhaust gas recirculation valve leads to a large change in the recirculated exhaust gas mass flow. The slight closing of the throttle valve leads to only a small or no change in the gas pressure downstream of the throttle point. The determination of the target position for the exhaust gas recirculation valve using the aforementioned equation (1) is therefore stable. If the exhaust gas recirculation valve is very wide opened, no significant change in mass flow is achieved simply by changing the geometric cross-sectional area of ​​the exhaust gas recirculation valve. In contrast, the mechanical coupling of the exhaust gas recirculation valve to the throttle valve means that the throttle valve is almost closed, which leads to a significant change in the pressure downstream of the throttle point.In the case of exhaust-side throttling, as described in the . Fig. As illustrated in Figure 1, this strong change in pressure occurs upstream of the throttle point. In this case, the recirculated exhaust gas mass flow is adjusted by changing the opening position of the throttle valve, not by changing the opening position of the exhaust gas recirculation valve.

[0037] The effective opening cross-sectional area of ​​the exhaust gas recirculation valve and the throttle valve is illustrated below depending on the joint position or position of the valve.

[0038] The Fig. 3 shows a diagram illustrating the effective opening cross-sectional area O1 of the exhaust gas recirculation valve as a function of the opening position P of the exhaust gas recirculation valve.

[0039] The Fig. 4 shows a diagram illustrating the effective opening cross-sectional area O2 of the throttle valve mechanically coupled to the exhaust gas recirculation valve as a function of the opening position P of the exhaust gas recirculation valve.

[0040] It can be seen that when the exhaust gas recirculation valve is closed, the throttle valve is open and vice versa.

[0041] Now the pressure setpoint is in e nachTHR,SP from equation (2) via the relationship m˙EGR,SP=AEGR(sEGR,SP)gEGR(ebefore EGR,eafter EGR) by solving for e nachEGR With fresh air side throttling - as used in the Fig. 2, the pressure after the throttle valve is essentially identical to the pressure after the exhaust gas recirculation valve. However, the function A EGR (s EGR,SP ) by a constant cross-sectional area A EGR,p-controlledwhich is selected slightly below the maximum cross-sectional area of ​​the exhaust gas recirculation valve and, if necessary, is determined depending on the engine operating point. A pressure in e nachTHR,SP is now used to determine s THR,SP according to equation (2). At the same time, the setpoint for the position of the exhaust gas recirculation valve is determined using equation (1).

[0042] The actual valid setpoint for the joint position of exhaust gas recirculation valve and throttle valve is now determined by the maximum of the setpoints calculated in this way s THR,SP and s EGR,SP This defines a unique calculation rule for the joint position of the exhaust gas recirculation valve and throttle valve, which has the following properties: For a low recirculated target mass flow, equation (1) results in a target position with a cross-sectional area of ​​the exhaust gas recirculation valve smaller than A EGR,p-controlled. The target position for the throttle valve, which is determined by the pressure setpoint after the throttle and the exhaust gas recirculation valve, assuming a wide-open exhaust gas recirculation valve A EGR,p-controlled is now lower than the target position determined using equation (1). The system consisting of the exhaust gas recirculation valve and throttle valve is in an operating range in which the mass flow through the exhaust gas recirculation valve can be adjusted essentially by the cross-sectional area of ​​the exhaust gas recirculation valve.

[0043] If, however, for a higher recirculated target mass flow, equation (1) results in a target position that corresponds to a cross-sectional area greater than A EGR,p-controlled corresponds, the target position determined by equation (2) will have a higher target position s THR,SP result, since a smaller cross-sectional area A EGR,p-controlledwas used to determine the pressure setpoint. Thus, the mass flow through the exhaust gas recirculation valve is now essentially determined by the required pressure drop across the throttle point.

[0044] This method enables stable control of the coupled system consisting of the throttle valve and the exhaust gas recirculation valve. Both valves—the throttle valve and the exhaust gas recirculation valve—are characterized largely independently of each other using a physical model. This has the advantage of allowing direct determination of the mass flow via the exhaust gas recirculation valve, and the control is automatically adjusted if the setpoint changes. This is particularly advantageous when the combustion engine operates in different modes.

[0045] Accordingly, the method according to the invention uses two different ranges to convert the target mass flow to be recirculated into a suitable valve position: a mass flow control range, in which the target position is derived directly from the exhaust gas recirculation valve model (equation 1), and a pressure control range, in which a pressure target value downstream of the exhaust gas recirculation valve is first determined using the exhaust gas recirculation valve model according to equation 4, and then a target position for the throttle valve is determined from the throttle valve model (equation 2). The necessary switching between these two ranges is achieved by selecting the maximum cross-sectional area as described above. List of reference symbols 100 internal combustion engines 110 air filters 120 turbocharger 125 compressors 130 exhaust turbine 135 intercooler 140 Throttle 150 cylinders 158 Catalyst 160 particle filters 162 Throttle valve (exhaust flap) 164 silencers 166 High-pressure exhaust gas recirculation 168 Bypass valve 170 coolers 172 High-pressure exhaust gas recirculation valve 180 Low-pressure exhaust gas recirculation 182 Throttle valve (air flap) 184 coolers 186 Exhaust gas recirculation valve 188 Control unit se1,..., sen sensor signals s1,...,sn control signals

Claims

[1] Method for adjusting the mass flow of an exhaust gas recirculation valve (186) mechanically coupled to a throttle valve (162, 182) of an internal combustion engine (100) having a turbocharger (120) comprising the following steps: - Determination of a first target value corresponding to a target opening position of the exhaust gas recirculation valve (186), - Determination of a second target value corresponding to a target opening position of the throttle valve (162, 182), - Comparing the first target value with the second target value, - Adjustment of the mass flow of the exhaust gas recirculation valve (186) by changing the opening position of the exhaust gas recirculation valve (186) and the throttle valve (162, 182) using the first setpoint, if the first setpoint is greater than the second setpoint and - Adjustment of the mass flow of the exhaust gas recirculation valve (186) by changing the opening position of the throttle valve (162, 182) and the exhaust gas recirculation valve (186) using the second setpoint if the second setpoint is greater than the first setpoint. [2] Method according to claim 1, characterized by , that the first setpoint corresponding to the target opening position of the exhaust gas recirculation valve (186) is determined according to the following relationship: sEGR,SP=AEGR−1(m˙EGR,SPgEGR(ebefore EGR,after EGR)), where s EGR,SP the target position of the exhaust gas recirculation valve (186), A EGR -1 the inverse function for the effective opening cross-section of the exhaust gas recirculation valve (186), ṁ EGR,SP the target mass flow through the exhaust gas recirculation valve (186) and g EGR (e vorEGR , e nachEGR ) is a function of the gas properties upstream and downstream of the exhaust gas recirculation valve (186). [3] Method according to claim 1 or 2, characterized by , that the second target value corresponding to the target opening position of the throttle valve (162, 182) is determined according to the following relationship: sTHR,SP=ATHR−1(m˙THR,SPgTHR(ebefore THR,after THR,SP)), where s THR,SP the target position of the throttle valve (162, 182), A THR -1 the inverse function for the effective opening cross-section of the throttle valve (162, 182), ṁ THR,SP the target mass flow through the throttle valve (162, 182) and g THR (e vorTHR , e nachTHR ) is a function of the gas properties before and after the throttle valve (162, 182). [4] Method according to claim 3, characterized by , that to determine the second target value, a pressure target value is first determined using the model of the exhaust gas recirculation valve (186) and then the target position of the throttle valve (162, 182) is determined using the model of the throttle valve (162, 182). [5] Method according to claim 4, characterized by, that to determine the second target value, first use the relationship m˙EGR,SP=AEGR(sEGR,SP)gEGR(evor EGR,enach EGR) the pressure setpoint is determined after the exhaust gas recirculation valve (186) and the determined pressure setpoint is used to determine the second setpoint. [6] Device for adjusting the mass flow of an exhaust gas recirculation valve (186) mechanically coupled to a throttle valve (162, 182) of an internal combustion engine (100) having a turbocharger (120), characterized by that it has a control unit (188) configured to control a method according to any one of claims 1 to 5.

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