Method for controlling a supercharging system

Abstract

A method for controlling a supercharging system for an internal combustion engine, the supercharging stage including a compressor and a turbine, and the turbine being settable with the aid of a VTG driving circuit. The method including: detecting an operating state setpoint variable, setting a maximum VTG control criterion for implementing the torque increase by an increase in a boost pressure. The setting of the maximum VTG control criterion comprising: ascertaining a setpoint boost pressure; ascertaining a VTG setpoint position as a function of the setpoint boost pressure; ascertaining an actual exhaust gas back pressure; ascertaining an actual exhaust gas pressure downstream from the turbine; ascertaining a maximum exhaust gas back pressure, taking into account the actual exhaust gas pressure downstream from the turbine; determining the VTG control criterion, based on the difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure.

Claims

1. A method for controlling a supercharging system, including a supercharging stage, for an internal combustion engine, the supercharging stage comprising a compressor and a turbine, the turbine being settable with the aid of a variable turbine geometry (VTG) driving circuit, the method comprising: detecting an operating state setpoint variable; and setting a maximum VTG control criterion for implementing a torque increase based on an engine setpoint torque by an increase of a boost pressure, the setting of the maximum VTG control criterion comprising: ascertaining a setpoint boost pressure; ascertaining a VTG setpoint position as a function of the setpoint boost pressure; ascertaining an actual exhaust gas back pressure; ascertaining an actual exhaust gas pressure downstream from the turbine; ascertaining a maximum exhaust gas back pressure, taking into account the actual-exhaust gas pressure downstream from the turbine; and determining the VTG control criteria, taking into account a difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure, wherein the VTG control criterion limits the VTG setpoint position to optimize progression of an actual boost pressure such that an accelerated adaptation of the actual boost pressure to the setpoint boost pressure takes place with respect to an adaptation of the actual boost pressure to the setpoint boost pressure without taking into account the VTG control criterion.

2. The method according to claim 1, wherein the ascertainment of the maximum exhaust gas back pressure comprises: ascertaining a pressure ratio over the turbine, taking the following variables into account: a given pressure ratio over the compressor; an ambient temperature and a boost temperature upstream and downstream from the compressor; exhaust gas temperatures and upstream and downstream from the turbine; and/or the actual exhaust gas pressure.

3. The method according to claim 2, wherein the ascertainment of the pressure ratio over the turbine is determined according to a turbocharger main equation which evaluates the stationary power budget of the compressor and the turbine.

4. The method according to claim 1, wherein the ascertainment of the maximum exhaust gas back pressure includes a parameterization of a difference between a pressure difference over the compressor and a pressure difference over the turbine, taking an operating state variable into account, and wherein the maximum exhaust gas back pressure is ascertainable according to the following relationship:
p.sub.3max=p.sub.2soll−p.sub.1ist+p.sub.4ist+p.sub.off,n wherein p.sub.3max is the maximum exhaust gas back pressure, p.sub.2soll is the setpoint boost pressure, p.sub.4ist is the actual exhaust gas pressure, mist is an ambient pressure, and p.sub.off,n is the operating state variable.

5. The method according to claim 1, wherein the actual boost pressure and/or the actual exhaust gas back pressure and/or the actual exhaust gas pressure is/are determined via a sensor or is a modeled value.

6. The method according to claim 1, wherein the VTG control criterion takes place taking into account a maximum exhaust gas back pressure change.

7. The method according to claim 6, wherein the maximum exhaust gas back pressure change is determined from a parameterization of the operating state variable and the operating state setpoint variable, which is weighted according to the difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure.

8. The method according to claim 1, wherein the VTG control criteria is ascertainable according to the following relationship: $u_{\max }=\Delta u_{p{3}_{\mathrm{Ctl}\max }}+\Delta u_{p4}+\Delta u_T+\Delta u_m+r_{\mathrm{Vtg}}$ $\mathrm{where}:\Delta u_{p{3}_{\mathrm{Ctl}\max }}=\alpha .Math.{\stackrel{.}{p}}_{3\mathrm{mx}}=\alpha .Math.K_p.Math.\left(p_{3\max }-p_3\right)$ $\Delta u_{p4}=-\alpha .Math.\frac{\partial p_3}{\partial p_4}.Math.{\stackrel{.}{p}}_4$ $\Delta u_T=-\alpha .Math.\frac{\partial p_3}{\partial T_3}.Math.{\stackrel{.}{T}}_3$ $\Delta u_{\stackrel{.}{m}}=-\alpha .Math.\frac{\partial p_3}{\partial \stackrel{.}{m}}\stackrel{\mathrm{.Math.}}{m}$ $\mathrm{and}$ $\alpha =\frac{\tau }{\left(\frac{\partial p_3}{\partial c_d}.Math.\frac{\partial c_d}{\partial r}+\frac{\partial p_3}{\partial A_{\mathrm{eff}}}.Math.\frac{\partial A_{\mathrm{eff}}}{\partial r}\right)}$ wherein p.sub.3 is a pressure upstream of the turbine, p.sub.4 is a pressure downstream of the turbine, u.sub.max is a maximum allowed turbine actuator position, Δu.sub.p3Ctl max is a control error, Δu.sub.p4 is a first damping variable based on a change in the pressure downstream of the turbine, Δu.sub.T is a second damping variable based on upstream temperatures, Δ.sub.m is a third damping variable based on a change in turbine massflow, r.sub.vtg is a VTG actuator position, wherein α is a gain of a transfer function from a turbine actuator position to the pressure upstream of the turbine (p.sub.3), K.sub.p is a proportional controller gain, τ is a time constant of a turbine actuator, c.sub.d is a correction factor of a turbine orifice based on the turbine actuator position, A.sub.eff is an effective area of a turbine orifice based on the turbine actuator position, p.sub.3max is the maximum exhaust gas back pressure, and r is the turbine actuator position.

9. The method according to claim 2, wherein the operating state variable is an engine rotational speed, and the operating state setpoint variable is the engine setpoint torque.

10. The method according to claim 8, wherein the following variables are taken into account in determining the exhaust gas back pressure via a regulation-implemented output/input linearization: the temperature upstream from the turbine, the actual pressures upstream and downstream from the turbine, and/or a turbine mass flow.

11. The method according to claim 1, wherein the maximum exhaust gas back pressure is increased by an offset dependent on a boost pressure control deviation.

12. The method according to claim 1, wherein a progression of the setpoint boost pressure is calculated by the VTG driving circuit, wherein limiting the VTG setpoint position based on the VTG control criterion allows the boost pressure to follow the progression of the setpoint boost pressure.

13. The method according to claim 1, wherein the progression of the actual boost pressure over a period of time is non-linear.

14. The method according to claim 1, wherein the progression of the actual boost pressure over a period of time is not constant.

15. A method for controlling a supercharging system, including a supercharging stage, for an internal combustion engine, the supercharging stage comprising a compressor and a turbine, the turbine being settable with the aid of a variable turbine geometry (VTG) driving circuit, the method comprising: detecting an operating state setpoint variable; and setting a maximum VTG control criterion for implementing a torque increase by an increase of a boost pressure, the setting of the maximum VTG control criterion comprising: ascertaining a setpoint boost pressure; ascertaining a VTG setpoint position as a function of the setpoint boost pressure; ascertaining an actual exhaust gas back pressure; ascertaining an actual exhaust gas pressure downstream from the turbine; ascertaining a maximum exhaust gas back pressure, taking into account the actual-exhaust gas pressure downstream from the turbine; and determining the VTG control criteria, taking into account a difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure, wherein the VTG control criterion limits the VTG setpoint position such that an accelerated adaptation of an actual boost pressure to the setpoint boost pressure takes place with respect to an adaptation of the actual boost pressure to the setpoint boost pressure without taking into account the VTG control criterion, wherein the VTG control criterion takes place taking into account a maximum exhaust gas back pressure change, wherein the maximum exhaust gas back pressure change is determined from a parameterization of the operating state variable and the operating state setpoint variable, which is weighted according to the difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure, and wherein a correction factor, which is parameterized from the difference between the actual exhaust gas back pressure and the maximum exhaust gas back pressure is taken into account for determining the maximum exhaust gas back pressure change.

16. A control system for a supercharging system for an internal combustion engine, wherein the control system is configured to carry out the method according to claim 1.

17. An internal combustion engine comprising: a supercharging system having a supercharging stage, wherein the supercharging stage includes a compressor and a turbine; and a control system according to claim 16.

18. A motor vehicle comprising an internal combustion engine according to claim 17.

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, which includes a supercharging system and a control system;

(3) FIG. 2 shows progression diagrams illustrated velocity progressions, boost pressure progressions, back pressure progressions and position progressions of the exhaust gas turbine geometry over time and the difference between the method according to the invention and conventional methods;

(4) FIG. 3 shows a schematic representation of an exhaust gas back pressure limiting regulating circuit according to the invention;

(5) FIG. 4 shows a schematic representation for ascertaining a maximum permissible exhaust gas back pressure according to the method according to the invention; and

(6) FIG. 5 shows a schematic representation of the regulating circuit, taking into account a gain scheduling approach.

DETAILED DESCRIPTION

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

(8) The present invention is not limited to a specific engine type. It may be an internal combustion engine which is designed as a gasoline engine or as a diesel engine.

(9) Engine 2 comprises one or multiple cylinders 4, one of which is illustrated here. Cylinders 4 are supplied with supercharged (combustion) air by supercharging system 3.

(10) Supercharging system 3 includes a supercharging stage having a variable turbine geometry. Supercharging stage 5 is coupled with control system 10.

(11) Supercharging stage 5 includes a compressor 6, which is operated via a shaft 7 with a turbine (exhaust gas turbine) 8 having a variable turbine geometry (VTG), turbine 8 being supplied with exhaust gas from engine 2 and being driven thereby. In addition, a waste gate 9 is optionally provided. A generating set which is supercharged in multiple stages may also be optionally provided.

(12) During operation, ambient air is conducted through compressor 6 at ambient pressure p.sub.1 and ambient temperature T.sub.1, compressed and conducted into cylinder 4 at boost pressure p.sub.2 and boost temperature T.sub.2. The exhaust gases are conducted to the turbine at exhaust gas back pressure p.sub.3 and exhaust gas temperature T.sub.3, where they emerge at downstream turbine temperature T.sub.4 and downstream turbine pressure (exhaust gas pressure) p.sub.4. The controller is connected to waste gate 9 and a mechanism 11 for setting the variable turbine geometry as well as optionally to a sensor 12, with the aid of which exhaust gas temperature T.sub.3 or exhaust gas back pressure p.sub.3 may be measured. Another sensor 12 is optionally provided, with the aid of which boost pressure p.sub.2 and air temperature T.sub.2 downstream from compressor 6 may be measured. The control system is equipped with additional sensor inputs and signal outputs for receiving and processing operating state variables and outputting actuating and control signals. These include, for example, the aforementioned temperature and pressure values, which are either ascertained or modeled via sensors or via operating state variables or may be determined via characteristic maps.

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

(14) Vehicle velocity v is plotted over time in the upper diagram. The solid line marks a velocity progression V.sub.SdT without using the method according to the invention, and the dashed line shows velocity progression v for a vehicle, in which the method according to the invention was applied.

(15) The vehicle velocity and the acceleration are dependent on boost pressure progression p.sub.2 situated thereunder. For example, by actuating the gas pedal, an acceleration request (e.g. full load request) is transmitted at a point in time t.sub.0 to control system 10, which subsequently determines a setpoint boost pressure (solid line) or a setpoint boost pressure progression p.sub.2soll, which results in the desired boost pressure increase and thus in the desired acceleration. The dash-dotted line shows a boost pressure progression, which results during a conventional boost pressure regulation. (p.sub.2SdT). The dashed line shows a boost pressure progression p.sub.2′, which results during an application of the method according to the invention. This progression is closer to the progression of setpoint boost pressure p.sub.2soll, and therefore also results in the improved acceleration or the increased velocity in the diagram thereabove.

(16) The progression of exhaust gas back pressure p.sub.3 is plotted over time in the diagram thereunder. The solid ramp curve shows the progression of the theoretical, maximum exhaust gas back pressure p.sub.3soll, which is to be set to make an optimum setting of the boost pressure and thus the acceleration. The dash-dotted line shows the actual progression of exhaust gas back pressure p.sub.3SdT without applying the method according to the invention. The dashed line shows the progression of actual exhaust gas back pressure p.sub.3 when applying the method according to the invention, which sets an exhaust gas back pressure limitation, which adjusts the actual exhaust gas back pressure close to setpoint exhaust gas back pressure p.sub.soll. In this diagram, an “enthalpy accumulation” is apparent in the area of the conventional exhaust gas back pressure progression and the exhaust gas back pressure progression according to the invention, which results in that the buildup of the desired boost pressure is delayed by the unused enthalpy and exceeds the setpoint boost pressure.

(17) Position r of the turbocharger geometry is set in the lower diagram. The solid line marks progression u.sub.soll of the adjustable turbine geometry without taking into account an exhaust gas back pressure limitation. The dashed progression is ascertained by taking into account an exhaust gas back pressure limitation and represents the progression of control criterion u.sub.max, according to the invention of the adjustable turbocharger geometry. However, the latter runs below the progression of setpoint position u.sub.soll and thus prevents the overshooting exhaust gas back pressure progression in the diagram thereabove.

(18) The method according to the invention is further explained based on FIGS. 2, 3 through 5.

(19) A control loop is illustrated in FIG. 3, which adjusts an actual exhaust gas back pressure p.sub.3, taking into account a maximum exhaust gas back pressure p.sub.3max (cf. below), which implements an optimized boost pressure p.sub.2. The difference from maximum exhaust gas back pressure p.sub.3max and exhaust gas back pressure p.sub.3 is supplied to a controller 20 (P controller), which forwards a maximum exhaust gas back pressure change {dot over (p)}.sub.3max to a linearization block 21. Taking into account additional state variables ZG (such as temperature T.sub.3 upstream from the turbine, actual pressures p.sub.3, p.sub.4, upstream and downstream from the turbine as well as exhaust gas (turbine) mass flow {dot over (m)}), the linearization part determines a maximum VTG control criterion u.sub.max, which is conducted to a limitation part 22. In limitation part 22, VTG control criterion u.sub.max is compared with a regular VTG position u.sub.soll, which is supplied from a conventional boost pressure regulation part 23. VTG control criterion u.sub.max limits VTG setpoint position u.sub.soll in such a way that exhaust gas back pressure p.sub.3 is adjusted close to desired setpoint exhaust gas back pressure p.sub.3soll via the adjustable turbine geometry or adjusting mechanism 11 (VTG) and/or possibly also via waste gate 9.

(20) Mechanism 11 of the adjustable turbine geometry, which is addressable via control system 10, corresponds to controlled system 24 in FIG. 2.

(21) FIG. 4 schematically shows the determination of maximum permissible exhaust gas back pressure p.sub.3max. In particular, four branches are apparent, which represent the determination of maximum permissible exhaust gas back pressure values p.sub.3max1 through p.sub.3max4, the two first branches for p.sub.3max1 and p.sub.3max2 not forming part of the present invention, the last two branches for p.sub.3max3 and p.sub.3max4, however, forming part thereof. However, the first and second branches may be added to the present invention.

(22) In the upper (first) branch, a pressure variable is parameterized from engine rotational speed n and a setpoint engine torque M.sub.m-soll (with the aid of a characteristic map or another modeling or calculation method), to which ambient pressure p.sub.1 is added. The pressure variable and added ambient pressure p.sub.1 result in first maximum exhaust gas back pressure p.sub.3max1. In the lower (second) branch, a second maximum exhaust gas back pressure p.sub.3max2 is parameterized, taking into account the difference from boost pressure p.sub.2 and setpoint boost pressure p.sub.2soll as well as engine rotational seed n (also via a characteristic map or another suitable modeling or calculation). The desired maximum exhaust gas back pressure p.sub.3max results from the minimum of the two variables of first maximum exhaust gas back pressure p.sub.3max1 and second maximum exhaust gas back pressure p.sub.3max2, which are selected in block 25. In the case of the pressure variable parameterized in the lower (second) branch, the permissible maximum pressure difference (scavenging gradient) between exhaust gas back pressure p.sub.3 and boost pressure p.sub.2 is taken into account in each case. This ensures that the subsequent exhaust gas back pressure limiting regulation according to FIG. 2 also observes the compliance with the set permissible scavenging gradient.

(23) Desired maximum exhaust gas back pressure p.sub.3max may also be ascertained, as described below.

(24) In the third branch, maximum exhaust gas back pressure p.sub.3max3 is ascertained, taking into account an inverse p.sub.43_inv of the pressure ratio over turbine 8 and an actual exhaust gas pressure p.sub.4ist downstream from turbine 8 and ascertained (by means of sensor detection or modeling). For this purpose, inverse p.sub.43_inv is multiplied by actual exhaust gas pressure p.sub.4ist in block 29.

(25) In addition, a maximum exhaust gas back pressure p.sub.3max4 is ascertained in the fourth branch, in that a rotational speed-dependent offset p.sub.off,n between a pressure difference over compressor 6 and a pressure difference over turbine 8 is to be applied. Accordingly, actual exhaust gas pressure p.sub.4ist downstream from turbine 8, actual pressures p.sub.1, p.sub.2 upstream and downstream from compressor 6 and offset p.sub.off,n applied/to be applied are given or to be ascertained for this purpose.

(26) The selection between p.sub.3max3 and p.sub.3max4 as desired maximum exhaust gas back pressure p.sub.3max takes place in block 33. The selection is an applicative degree of freedom. In other words, no decision logic is used for the selection, but rather a (function) user/applier decides which ascertainment approach he prefers or would like to select. This applicative decision is also carried out in block 35, i.e. the (function) user/applier decides whether the exhaust gas back pressure ascertained in block 25 or block 33 is used as desired maximum exhaust gas back pressure p.sub.3max. An optional ascertainment by the (function) user/applier is thus carried out in blocks 33 and 35.

(27) It is clear that a decision/selection may be alternatively made in block 33 and/or block 35 as a function of determined temperature and/or pressure conditions upstream and downstream from compressor 6 and/or turbine 8.

(28) In addition, ascertained maximum exhaust gas back pressure p.sub.3max may be further increased by an offset p.sub.off,p2. For this purpose, offset p.sub.off,p2 is determined in block 37 as a function of the boost pressure control deviation. A continuous increase of ascertained maximum exhaust gas back pressure p.sub.3max by offset p.sub.off,p2 thus takes place.

(29) In the case of a great boost pressure control deviation, offset p.sub.off,p2 is equal to 0. The closer the boost pressure control deviation approaches the value 0, the greater the offset p.sub.off,p2. At a boost pressure control deviation of essentially 0, offset p.sub.off,p2 is preferably so large that maximum exhaust gas back pressure p.sub.3max,off increased by offset p.sub.off,p2 is below a maximum component stress limit of turbine 8, the VTG actuator and/or waste gate 9.

(30) FIG. 5 shows a function element of controller 20 illustrated in FIG. 2, which is designed as a proportional controller (P controller). FIG. 4 shows a so-called “gain scheduling” chip, which outputs a maximum permissible change in the exhaust gas back pressure ({dot over (p)}.sub.3max) over time. For this purpose, the difference between maximum permissible exhaust gas back pressure p.sub.3max and exhaust gas back pressure p.sub.3 (actual exhaust gas back pressure) is taken into account, and EP component 26 parameterizes a value from engine setpoint torque M.sub.m-soll as well as engine torque N.sub.M-ist, which is multiplied by a correction value ascertained in a control deviation correction block 27. The control deviation correction is parameterized from the difference between maximum permissible back pressure p.sub.3max and back pressure p.sub.3 and results in a control amplification K.sub.p, which results in a maximum permissible change in exhaust gas back pressure p.sub.3max with the difference between maximum permissible exhaust gas back pressure p.sub.3max and actual exhaust gas back pressure p.sub.3. The VTG control criterion u.sub.max is then ascertained from this maximum permissible time change in exhaust gas back pressure {dot over (p)}.sub.3max in linearization part 21. This linearization takes place according to the aforementioned mathematical methodology.

(31) Alternatively to the embodiment illustrated above, methods are also possible, in which the limitation of the VTG control criterion or the VTG position is adjusted. The VTG position may be set to a regular driving value of the VTG setpoint position upon reaching a parameterized exhaust gas back pressure or after the expiration of a certain time after a load change request (e.g. a full load request) and a defined opening of the VTG position with a parameterizable ramp slope as a function of the load and rotational speed.

(32) A simplified regulation with a classic structure may also be implemented. A stationary pilot control circuit and a parallel linear controller, whose control components are added, may be used. However, no dynamic amplification effects in the model inverses are taken into account. The pilot control may be implemented as a model inverse or as a characteristic map with free parameterization (e.g. rotational speed and load).

(33) Other mathematical methods may also be used for resolving the equation for the maximum exhaust gas back pressure (p.sub.3max) according to VTG control criterion u.sub.max (maximum permissible VTG position). Iterative solution methods are also useful.

(34) 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.