Regulating device with an electronic control unit for regulating boost pressure in a supercharged internal combustion engine

Abstract

The invention relates to a regulating device with an electronic control unit for regulating boost pressure in a supercharged internal combustion engine with two-stage supercharging, i.e. with a first low-pressure stage (ND) and a second high-pressure stage (HD). The high-pressure stage (HD) has a rigid high-pressure turbine and a controllable regulating flap (RK). The low-pressure stage (ND) has an variable adjustable turbine geometry (VTG). According to the invention, the electronic control unit contains a regulating module that is designed, in particular by means of an appropriately programmed computer program product, for basic adjuster regulation in such a way that the boost pressure regulation is carried out solely by means of the adjustable turbine geometry (VTG) of the low-pressure stage (ND), wherein the regulating flap (RK) of the high-pressure stage (HD) is controlled in the fully closed state.

Description

[0001] Control device with an electronic control unit for boost pressure control in a supercharged internal combustion engine

[0002] The invention relates to a control device with an electronic control unit for boost pressure control in a supercharged internal combustion engine with at least two actuators.

[0003] Various controllers for boost pressure control in turbocharged combustion engines with at least two actuators are already known.

[0004] The object of the present invention is to improve a regulator for boost pressure control in such a way that fuel consumption and emissions are reduced and the components involved are protected.

[0005] This object is achieved by the features of patent claim 1. Advantageous developments of the invention are the subject matter of the dependent claims.

[0006] The invention relates to a control device with an electronic control unit for boost pressure control in a supercharged internal combustion engine with at least two-stage charging, i.e. with at least one low-pressure stage (ND) and one high-pressure stage (HD). The high-pressure stage (HD) has a rigid high-pressure turbine and a controllable control flap (RK). The low-pressure stage (ND) has a variably adjustable turbine geometry (VTG). According to the invention, the electronic control unit contains a control module which is designed, in particular, by an appropriately programmed computer program product for basic adjuster control in such a way that boost pressure control is carried out solely by means of the adjustable turbine geometry (VTG) of the low-pressure stage (ND), wherein the control flap (RK) of the high-pressure stage (HD) is controlled to the fully closed state.The invention thus relates to the transition from a two-position control system to a basic control system for boost pressure regulation by an actuator of the low-pressure stage (ND), with only the boost pressure setpoint being specified as the control variable. The invention is based on the following considerations:

[0007] In many technical systems, multiple actuators are used to achieve a target value. Examples arise in the boost pressure control of turbocharged internal combustion engines, particularly in variants with multi-stage charging, i.e. with a low-pressure stage (LP) and a high-pressure stage (HP). On the one hand, there are variants in which multiple actuators are used in the high-pressure stage (HP), such as an exhaust gas turbocharger with variable turbine geometry (also called HD-VTG for short) and a bypass flap (exhaust gas control flap, also called RK for short). On the other hand, there are simpler HP topologies with a rigid high-pressure turbine and at least an electronically controllable control flap (RK).

[0008] The present invention is preferably used for two-stage turbocharged diesel engines with the latter HP topology, i.e., a rigid high-pressure turbine with a control valve (RK) on the high-pressure stage. However, according to the invention, a low-pressure stage (LP) with a variably adjustable turbine geometry (LP-VTG) is additionally used and directly integrated into the boost pressure control.

[0009] The invention enables a significant boost pressure increase in the two-stage map range (actuator duty cycle dependent on engine speed and boost pressure setpoint). This boost pressure increase, in turn, enables a reduction in emissions and fuel consumption. If the boost pressure is not increased, the new control strategy results in a scavenging gradient advantage, which is also reflected in lower fuel consumption.

[0010] In two-stage turbocharging, two setpoints are usually always specified for boost pressure control: first, the (total) boost pressure setpoint in the intake system, i.e., after both compressor stages (LP and HP) and after the intercooler (LIC), and second, the (setpoint) pre-compression pressure ratio. The low-pressure compressor sets the (setpoint) pressure, which is calculated by multiplying the (setpoint) pre-compression pressure ratio by the (actual) pressure upstream of the low-pressure compressor. The low-pressure compressor output is controlled by the low-pressure VTG on the low-pressure stage. The pressure still missing to reach the (total) boost pressure setpoint is provided by the high-pressure compressor. The HP compressor output is controlled by the control flap (RK). According to the state of the art, the boost pressure setpoint for control is selected as a precautionary measure so that the control flap is not fully closed.This control reserve is required when turbocharger efficiency decreases (aging) or when ambient conditions change (reduction in ambient pressure). This concept is subsequently referred to as two-actuator control, as boost pressure control is provided simultaneously by two actuators (RK control flap and LP-VTG) and via two setpoints (boost pressure setpoint and pre-compression pressure ratio).

[0011] This two-position control has proven to be less than efficient for boost pressure control with a rigid high-pressure turbine because not all of the exhaust gas mass flow or all of the exhaust gas energy from the high-pressure turbine can be used to build boost pressure. This means that, because the control flap is always slightly open, a portion of the exhaust gas always flows past the high-pressure turbine through the control reserve and thus remains unused. In this regard, the invention is based on the finding that the control flap could be closed via applicable limits; however, boost pressure control would then be inactive because the HP compressor with rigid turbine geometry would always provide maximum pressure and the LP compressor regulates the specified pre-compression pressure ratio. However, this would not be desirable in terms of emissions stability and component protection.

[0012] The invention provides for the adjustment of the boost pressure setpoint with the control flap closed solely by means of the VTG on the LP stage using an appropriately programmed control module, particularly in the electronic engine control unit. Only one setpoint, namely the (total) boost pressure setpoint, is specified. According to the invention, to adjust the boost pressure setpoint, the maximum possible high pressure is always provided by the HP compressor due to the closed control flap, and the LP compressor regulates the missing portion to achieve the boost pressure setpoint. This concept is also referred to as "controller handover" in the following, since the boost pressure control based on the boost pressure setpoint is transferred as the sole manipulated variable to the low-pressure actuator, i.e., the LP VTG, whereby the control flap is closed and remains closed.

[0013] The high-pressure control flap is therefore fundamentally no longer used as an actuator for boost pressure control. The term "fundamentally" specifically means that this controller handover concept applies to the majority of possible operating points. As an exception, the control flap can be used as a second actuator (two-position control) for a smaller, defined, high-load portion of the possible operating points. This smaller, high-load portion of the possible operating points can be defined, in particular, by exceeding a predefined full-load speed limit and / or a predefined boost pressure high-load limit. The application of such limit values ​​must be carried out, for example, depending on the level of a mass flow reached that would lead to component damage (e.g., to the rigid high-pressure turbine).The inventive regulator transfer is therefore only disabled at the few operating points that would lead to component damage. Otherwise, however, the regulator transfer is always activated to reduce fuel consumption; this is because the regulator transfer results in lower exhaust backpressure at the same boost pressure setpoint.

[0014] In other words, the regulator handover is always activated if it achieves a lower exhaust back pressure than the two-position control.

[0015] Summary of benefits:

[0016] 1. Fuel consumption advantage, since the same boost pressure with reduced exhaust back pressure is possible due to the pressure ratio shift on the compressor side with the control flap closed.

[0017] 2. In addition, there is emission potential through

[0018] - the possibility of increasing the boost pressure at operating points with the LP stage open, which leads to soot or NOx reduction, and

[0019] - the low purge gradient fluctuations during dynamic processes due to a single-position control, which leads to greater stability in air mass control compared to a two-position control.

[0020] 3. Boost pressure control using the non-linear control valve (two-position control) is only required at high-load operating points. Due to the inventive basic controller transfer (single-position control) instead of the two-position control

[0021] - recurring problems with the electric control flap (end stop learning, RK oscillation) are eliminated in almost the entire two-stage range and a WLTC with adjuster control is possible in most of the operating points that occur.

[0022] The invention is explained in more detail by means of an embodiment and a drawing. It shows

[0023] Fig. 1 shows a section of a double-charged internal combustion engine with essential components according to the invention, Fig. 2 shows an enlargement of the control unit with the control module according to the invention, Fig. 3 shows the effect of the invention in comparison with the prior art for a specific engine speed and

[0024] Fig. 4 shows characteristic maps according to the invention for the duty cycles of the actuators concerned in comparison with the characteristic maps according to the prior art.

[0025] Fig. 1 shows a section of the essential components of a twin-charged diesel engine D as an example of an internal combustion engine with a rigid turbocharger 1 (without VTG actuator) and with an exhaust gas bypass control flap RK in a high-pressure path HD and with a controllable turbocharger 3 in a low-pressure path ND. The turbocharger 3 in the low-pressure path ND has a variably adjustable turbine geometry (ND-VTG) as an actuator for controlling the compression. The control flap RK has a variably adjustable valve 2 (RK actuator). Furthermore, the internal combustion engine D has a pressure sensor on the input side for detecting the actual boost pressure p1_actual and optionally a pressure sensor for detecting the pre-compression pressure p2, whereby for the invention the pre-compression pressure p2 no longer needs to be detected.

[0026] The combustion engine D and, in particular, the boost pressure p1 are controlled by an electronic control unit 4. For example, the current boost pressure p1_actual is the input signal of the electronic control unit 4. In the electronic control unit 4, the boost pressure setpoint p1_setpoint is also specified as a reference variable of a control module 5.

[0027] Fig. 2 shows the control unit 4 in somewhat more detail. The output signals of the control unit 4 are the control signals for the LP-VTG actuator 3 (VTG) and the HP-RK actuator 2 (RK).

[0028] The design (especially programming) of the control module 5 and its effect is explained in more detail in connection with Fig. 3:

[0029] The control module 5 is designed for basic adjuster control in such a way that the boost pressure control is carried out solely by means of the adjustable turbine geometry ND-VTG of the turbine 3. In this case, the control flap RK is controlled via valve 2 in the high-pressure stage HD to the fully closed state, e.g., via a duty cycle of 100%. This adjuster control ("controller handover") is generally activated if it achieves a lower exhaust back pressure p3 (see also Fig. 1 and reduction by Ap3 in Fig. 3) than with the two-position control. Fig. 4 shows the inventive characteristic maps for the duty cycles of the relevant actuators 2 and 3.

[0030] Deviating from the basic adjuster control according to the invention, the control flap RK is exceptionally controlled via the duty cycle (see white numbers in the characteristic maps) at valve 2 for a smaller, defined high-load part of the possible

[0031] Operating points are used as a second actuator (duty cycle <100%) for two-position control. This smaller, high-load portion of the possible operating points is preferably defined, in particular, by exceeding a predefined full-load speed limit mvi_iim and / or a predefined boost pressure limit and / or a component-protection-related mass flow limit m. The limit values ​​can be determined empirically and stored in control unit 4.

Claims

Claims 1. Control device with an electronic control unit (4) for boost pressure control in a turbocharged internal combustion engine (D) with at least two-stage turbocharging, comprising a low-pressure stage (LP) and a high-pressure stage (HP), wherein the high-pressure stage (HP) comprises a rigid high-pressure turbine (1) and a controllable bypass control valve (RK; 2), and wherein the low-pressure stage (LP) comprises a turbine (3) with variably adjustable turbine geometry (LP-VTG), and comprising a control module (5) in the electronic control unit (4) configured for basic actuator control such that boost pressure control is carried out solely by means of the adjustable turbine geometry (3; LP-VTG) of the low-pressure stage (LP) to achieve the predetermined boost pressure setpoint (p1_setpoint), wherein the control valve (2; RK) of the high-pressure stage (HP) is controlled to the fully closed position (100%). becomes.

2. Control device according to claim 1, characterized in that the adjuster control can generally be activated if a lower exhaust back pressure (p3; -Ap3) is achieved than by a two-position control.

3. Control device according to one of the preceding claims, characterized in that the control flap (1 ; RK) is exceptionally used as a second actuator for two-position control for a smaller defined high-load part of the possible operating points, wherein this smaller high-load part of the possible operating points can be defined in particular by exceeding a predetermined full-load speed limit (rnvijim) and / or a predetermined boost pressure limit and / or a predetermined component protection-related mass flow limit (mum).

4. Motor vehicle with a control device according to one of the preceding patent claims.

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