Method for controlling a turbocharging system

Abstract

A method for controlling a turbocharging system with a turbocharging stage for an internal combustion engine, wherein the turbocharging stage comprises a compressor and a turbine and the turbine is adjustable via a VTG control. The method includes: acquiring an operating state target variable; adjusting a maximum VTG control criterion to implement the torque increase by increasing a boost pressure, wherein adjusting the maximum VTG control criterion includes: determining a target boost pressure; determining a VTG target position as a function of the target boost pressure; determining an actual exhaust back pressure; determining a maximum exhaust back pressure; determining the VTG control criterion taking into account the difference between the actual exhaust back pressure and the maximum exhaust back pressure. The VTG control criterion limits the VTG target position such that an accelerated adaptation of an actual boost pressure to the target boost pressure) takes place.

Claims

1. A method for controlling a turbocharging system with a turbocharging stage for an internal combustion engine, the turbocharging stage comprising a compressor and a turbine adjustable via a VTG actuator, the method comprising: acquiring an operating state target variable; and adjusting a maximum VTG control criterion to implement a torque increase by increasing a boost pressure, wherein adjusting the maximum VTG control criterion comprises: determining a target boost pressure; determining a VTG target position as a function of the target boost pressure; determining an actual exhaust back pressure; determining a maximum exhaust back pressure; and determining the VTG control criterion taking into account a difference between the actual exhaust back pressure and the maximum exhaust back pressure, where the difference is determined by subtracting the actual exhaust back pressure from the maximum exhaust back pressure, wherein the VTG control criterion limits the VTG target position such that an accelerated adaptation of an actual boost pressure to the target boost pressure takes place compared with an adaptation of the actual boost pressure to the target boost pressure without consideration of the VTG control criterion, and wherein the determination of the maximum exhaust back pressure comprises: parameterizing a first maximum exhaust back pressure taking into account an operating state variable, the operating state target variable, and an ambient pressure; parameterizing a second maximum exhaust back pressure taking into account the operating state variable and the difference between the target boost pressure and the actual boost pressure; and establishing the maximum exhaust back pressure as a minimum of the first maximum exhaust back pressure and the second maximum exhaust back pressure.

2. The method according to claim 1, wherein the actual boost pressure and/or the actual exhaust back pressure are determined via a sensor.

3. The method according to claim 1, wherein the actual boost pressure and/or the actual exhaust back pressure are a modeled value.

4. The method according to claim 1, wherein the parameterization of the second maximum exhaust back pressure takes place with consideration of a scavenging gradient.

5. The method according to claim 4, wherein the scavenging gradient is determined via a characteristic map.

6. The method according to claim 1, wherein the VTG control criterion is determined with consideration of a maximum exhaust back pressure change.

7. The method according to claim 1, wherein the operating state variable is an engine speed and the operating state target variable is a target engine torque.

8. A controller for the turbocharging system for the internal combustion engine, wherein the controller is configured to carry out the method according to claim 1.

9. The internal combustion engine comprising the turbocharging system with the turbocharging stage, wherein the turbocharging stage comprises the compressor and the turbine, and the controller according to claim 8.

10. A motor vehicle comprising the internal combustion engine according to claim 9.

11. A method for controlling a turbocharginq system with a turbocharginq stage for an internal combustion engine, the turbocharginq stage comprising a compressor and a turbine adjustable via a VTG actuator, the method comprising: acquiring an operating state target variable; and adjusting a maximum VTG control criterion to implement a torque increase by increasing a boost pressure, wherein adjusting the maximum VTG control criterion comprises: determining a target boost pressure; determining a VTG target position as a function of the target boost pressure; determining an actual exhaust back pressure; determining a maximum exhaust back pressure; and determining the VTG control criterion taking into account a difference between the actual exhaust back pressure and the maximum exhaust back pressure, where the difference is determined by subtracting the actual exhaust back pressure from the maximum exhaust back pressure, wherein the VTG control criterion limits the VTG target position such that an accelerated adaptation of an actual boost pressure to the target boost pressure takes place compared with an adaptation of the actual boost pressure to the target boost pressure without consideration of the VTG control criterion, wherein the VTG control criterion is determined with consideration of a maximum exhaust back pressure change, and wherein the maximum exhaust back pressure change is determined from a parameterization of an operating state variable and the operating state target variable, the maximum exhaust back pressure change being weighted according to the difference between the actual exhaust back pressure and the maximum exhaust back pressure.

12. The method according to claim 11, wherein, for determining the maximum exhaust back pressure change a correction factor is taken into account, which is parameterized from the difference between the actual exhaust back pressure and the maximum exhaust back pressure.

13. The method according to claim 12, wherein the VTG control criterion is determined according to the following relationship: $u_{\mathrm{ma}x}=u_{p{3}_{\mathrm{Ctl}\mathrm{ma}x}}+u_{p4}+u_T+u_{\stackrel{.}{m}}+r_{V\mathrm{tg}}$ $\mathrm{with}$ $u_{p{3}_{\mathrm{Ctl}\mathrm{ma}x}}=.Math.{\stackrel{.}{p}}_{3\mathrm{ma}x}=.Math.K_p.Math.\left(p_{3\mathrm{ma}x}-p_3\right)$ $u_{p4}=-.Math.\frac{p_3}{p_4}.Math.{\stackrel{.}{p}}_4$ $u_T=-.Math.\frac{p_3}{T_3}.Math.{\stackrel{.}{T}}_3$ $u_{\stackrel{.}{m}}=-.Math.\frac{p_3}{\stackrel{.}{m}}\stackrel{\mathrm{.Math.}}{m}$ $\mathrm{and}$ $=\frac{}{\left(\frac{p_3}{c_d}.Math.\frac{c_d}{r}+\frac{p_3}{A_{\mathrm{eff}}}.Math.\frac{A_{\mathrm{eff}}}{r}\right)}$ wherein, u.sub.max is the maximum VTG control criterion, u.sub.p3.sub.Ctlmax is a control error driven part of u.sub.max, u.sub.p4 is a damping part of u.sub.max with respect to present p.sub.4 variations, u.sub.T is a damping part of u.sub.max with respect to present temperature variations, u.sub.{dot over (m)}, is a damping part of u.sub.max with respect to m variations, r.sub.Vtg is a VTG position, is an inverted system gain from VTG position to p.sub.3, {dot over (p)}.sub.3max is the maximum exhaust gas pressure change, p.sub.3max is the maximum exhaust gas pressure, K.sub.p is a gain, p.sub.3 is the actual exhaust back pressure before a turbine, {dot over (p)}.sub.4 is the actual exhaust back pressure after the turbine, {dot over (T)}.sub.3 is a temperature before the turbine, {dot over (m)} is a turbine mass flow, is an equivalent time constant of the VTG actuator, c.sub.d is a flow factor, r is a temporal control variable change, and A.sub.eff is effective area.

14. The method according to claim 13, wherein the following variables are taken into account in the determination of the maximum exhaust back pressure via an output/input linearization which is realized by control technology: the temperature before the turbine, the actual exhaust back pressures, before and after the turbine, and/or the turbine mass flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 schematically shows an exemplary embodiment of a motor vehicle with a charging system and a controller;

(3) FIG. 2 shows diagrams depicting speed curves, boost pressure curves, back pressure curves, and position curves of the exhaust gas turbine geometry over time, and the difference between the method of the invention and conventional methods;

(4) FIG. 3 is a schematic representation of an exhaust back pressure limiting control of the invention;

(5) FIG. 4 is a schematic representation for determining a maximum allowable exhaust back pressure according to the method of the invention; and

(6) FIG. 5 is a schematic representation of the control with consideration of a gain scheduling approach.

DETAILED DESCRIPTION

(7) An exemplary embodiment of a motor vehicle 1 having an engine 2 and a turbocharging system 3, which is controlled by a controller 10, which is designed as an engine control unit, is illustrated in FIG. 1.

(8) The present invention is not limited to a particular type of engine. It can be an internal combustion engine designed, for example, as a gasoline engine or as a diesel engine.

(9) Engine 2 comprises one or more cylinders 4, one of which is shown here. Cylinders 4 are supplied by turbocharging system 3 with charged (combustion) air.

(10) Turbocharging system 3 has a turbocharging stage with variable turbine geometry. Turbocharging stage 5 is coupled to controller 10.

(11) Turbocharging stage 5 has a compressor 6, which is operated via a shaft 7 with a turbine (exhaust gas turbine) 8 with variable turbine geometry (VTG), wherein turbine 8 is supplied with exhaust gas from engine 2 and driven therewith. In addition, a wastegate 9 is optionally provided. Optionally, a multi-stage turbocharged unit can also be provided.

(12) During operation, ambient air at ambient pressure p.sub.1 and ambient temperature T.sub.1 is fed through compressor 6, compressed, and is fed into cylinder 4 at the boost pressure p.sub.2 and boost temperature T.sub.2. The exhaust gases are fed into the turbine with the exhaust back pressure p.sub.3 and the exhaust gas temperature T.sub.3 and exit there with the post-turbine temperature T.sub.4 and post-turbine pressure p.sub.4. The controller is connected to wastegate 9 and to a mechanism 11 for adjusting the variable turbine geometry, and optionally to a sensor 12 with which the exhaust gas temperature T.sub.3 or the exhaust back pressure p.sub.3 can be measured. Optionally, a further sensor 13 is provided, with which the boost pressure p.sub.2 and the air temperature T.sub.2 can be measured downstream of compressor 6. The controller is equipped with additional sensor inputs and signal outputs for receiving and processing operating state variables and for outputting actuation and control signals. These include, e.g., the temperature and pressure values given above, which are either determined or modeled via sensors or via operating state variables or can also be determined via characteristic maps.

(13) FIG. 2 shows several diagrams one above the other, in which certain control and state variables are plotted over time.

(14) The vehicle speed v is plotted over time in the upper diagram. The solid line designates a speed curve V.sub.SdT without application of the method of the invention and the dashed line shows the speed curve v for a vehicle in which the method of the invention was used.

(15) The vehicle speed and the acceleration depend on the boost pressure curve p.sub.2 provided below. At a time t.sub.0, for example, an acceleration request (e.g., full load request) is transmitted to controller 10 by actuating the gas pedal, which then determines a target boost pressure (solid line) or a target boost pressure curve p.sub.2soll, which leads to the desired boost pressure increase and thus to the desired acceleration. The dot-dashed line designates a boost pressure curve, which results in a conventional boost pressure control (p.sub.2SdT). The dashed line shows a boost pressure curve p.sub.2, which results when the method of the invention is used. This curve is closer to the curve of the target boost pressure and therefore also leads to the improved acceleration or the increased speed in the diagram above.

(16) The course of the exhaust back pressure p.sub.3 is plotted over time in the diagram below this. The continuous ramp curve shows the course of the theoretical maximum exhaust back pressure p.sub.soll, which should be adjusted in order to adjust an optimal adjustment of the boost pressure and thereby the acceleration. The dot-dashed line shows the actual course of the exhaust back pressure p.sub.3SdT without the use of the method of the invention. The dashed line shows the course of the actual exhaust back pressure p.sub.3 using the method of the invention, which sets an exhaust back pressure limit that adjusts the actual exhaust back pressure close to the target exhaust back pressure p.sub.soll. In this diagram, an enthalpy accumulation is recognizable in the area of the conventional exhaust back pressure curve and the exhaust back pressure curve of the invention, which leads to the desired boost pressure being built up with a delay by the unused enthalpy and overshooting the target boost pressure.

(17) The position r of the turbocharger geometry is shown in the bottom diagram. The solid line designates the curve u.sub.soll of the adjustable turbine geometry without consideration of an exhaust back pressure limit. The dot-dashed curve is determined with consideration of an exhaust back pressure limit and represents the curve of the control criterion u.sub.max of the invention of the adjustable turbocharger geometry. This runs below the curve of the target position u.sub.soll and thus prevents the overshooting of the exhaust back pressure curve in the diagram above.

(18) The method of the invention will be explained further with reference to FIGS. 2 and 3 to 5.

(19) FIG. 3 shows a control loop which, taking into account a maximum exhaust back pressure p.sub.3max (see below), adjusts an actual exhaust back pressure p.sub.3, which realizes an optimized boost pressure course p.sub.2. The difference between the maximum exhaust back pressure p.sub.3max and the exhaust back pressure p.sub.3 is fed to a closed-loop controller 20 (P controller), which forwards a maximum exhaust back pressure change {dot over (p)}.sub.3max to a linearization block 21. The linearization part determines a maximum VTG control criterion u.sub.max, which is fed to a limiting section 22, taking into account further state variables ZG (such as, e.g., the temperature T.sub.3 before the turbine, the actual pressures p.sub.3, p.sub.4 before and after the turbine, as well as the exhaust gas (turbine) mass flow {dot over (m)}). In limiting section 22, the VTG control criterion u.sub.max is compared with a regular VTG position u.sub.soll, which is supplied from a conventional boost pressure control section 23. The VTG control criterion u.sub.max limits the VTG target position u.sub.soll such that the exhaust back pressure p.sub.3 is adjusted close to the desired target exhaust back pressure p.sub.3soll via the adjustable turbine geometry or adjustment mechanism 11 (VTG) and/or, if appropriate, also via wastegate 9. Mechanism 11 of the adjustable turbine geometry, which can be addressed via controller 10, corresponds thereby to controlled system 24 in FIG. 2.

(20) FIG. 3 schematically shows the determination of the maximum allowable exhaust back pressure p.sub.3max. In the top branch, a pressure variable is parameterized from the engine speed n and a target engine torque M.sub.m-soll (with the aid of a characteristic map or another modeling or calculation method), to which the ambient pressure p.sub.1 is added. The pressure variable and the added ambient pressure p.sub.1 result in a first maximum exhaust back pressure p.sub.3max1. In the bottom branch, a second maximum exhaust back pressure p.sub.3max2 is parameterized (also via a characteristic map or another suitable modeling or calculation), taking into account the difference between the boost pressure p.sub.2 and the target boost pressure, as well as the engine speed n. In this case, the desired maximum exhaust back pressure p.sub.3 results from the minimum of the two variables, the first maximum exhaust back pressure p.sub.3max1 and second maximum exhaust back pressure p.sub.3max2, which are selected in block 25. For the pressure variable parameterized in the bottom branch, the allowable maximum pressure difference (scavenging gradient) between the exhaust back pressure p.sub.3 and boost pressure p.sub.2 is taken into account. This ensures that the subsequent exhaust back pressure limit regulation according to FIG. 2 also considers the adherence to the adjusted allowable scavenging gradient.

(21) FIG. 4 shows a functional element of closed-loop controller 20 shown in FIG. 3, which is designed as a proportional controller (P controller). FIG. 5 shows a so-called gain scheduling component, which outputs a maximum allowable change over time in the exhaust back pressure ({dot over (p)}.sub.3max). For this purpose, the difference between the maximum allowable exhaust gas pressure p.sub.3max and the exhaust back pressure p.sub.3 (actual exhaust back pressure) is taken into account and in EP component 26 a value is parameterized from the engine target torque M.sub.m-soll and the engine speed N.sub.M-ist and multiplied by a correction value determined in a control deviation correction block 27. The control deviation correction is parameterized from the difference between the maximum allowable back pressure p.sub.3max and the back pressure p.sub.3 and results in a control amplification K.sub.p, which together with the difference between the maximum allowable exhaust back pressure p.sub.3max and the actual exhaust back pressure p.sub.3 results in a maximum allowable change of the exhaust back pressure p.sub.3max. The VTG control criterion u.sub.max is then determined in linearization part 21 from this maximum allowable change over time in the exhaust back pressure {dot over (p)}.sub.3max. This linearization is carried out according to the mathematical methodology given above.

(22) As an alternative to the embodiment described above, methods are also possible in which the limiting of the VTG control criterion or the VTG position is regulated. In this case, the VTG position can be adjusted to a regular actuation value of the VTG target position on reaching a parameterized exhaust back pressure or after a certain time after a load change request (e.g., a full load request) and defined opening of the VTG position with a parameterizable ramp gradient as a function of load and speed.

(23) A simplified regulation with a classic structure can also be realized. In this case, a stationary pilot control and a parallel linear controller, whose control components are added, can be used. However, no dynamic amplification effects are considered in the model inverse. The pilot control can be realized as a model inverse or as a characteristic map with free parameterization (e.g., speed and load).

(24) Other mathematical methods can also be used to solve the equation for the maximum exhaust back pressure (p.sub.3max) according to the VTG control criterion u.sub.max (maximum allowable VTG position). Iterative solution methods, e.g., are also suitable in this case.

(25) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.