Method and devices for operating an internal combustion engine having a supercharging system

Abstract

A method and device for operating an internal combustion engine having a supercharging system that has an exhaust turbocharger and an electrically driven compressor. An output of the exhaust turbocharger is adjustable by a control element. A boost pressure setpoint is determined for achieving an increased engine torque setpoint. The supercharging system is adjusted to build up the actual boost pressure in accordance with the boost pressure setpoint and a positive scavenging gradient in a cylinder of the internal combustion engine is adjusted as the overriding command variable for driving the supercharging system.

Claims

1. A method for operating an internal combustion engine with a supercharging system that has an exhaust turbocharger and an electrically driven compressor, an output of the exhaust turbocharger being adjustable via a control element, the method comprising: determining a boost pressure setpoint for achieving an increased engine torque setpoint; adjusting the supercharging system to build up an actual boost pressure, in accordance with the boost pressure setpoint, by adapting the output of the exhaust turbocharger via the control element; and adjusting a positive scavenging gradient in a cylinder of the internal combustion engine as an overriding command variable for driving the supercharging system, wherein the positive scavenging gradient is a pressure difference across the cylinder between an intake manifold pressure upstream of the cylinder and a pressure that is present within an exhaust gas line of the internal combustion engine downstream of the cylinder, wherein the positive scavenging gradient is achieved in that the electrically driven compressor and the exhaust turbocharger are operated as a function of one another, wherein the electrically driven compressor is operated in accordance with a first control variable, and the exhaust turbocharger is operated in accordance with a second control variable, wherein the first reduction factor and the second reduction factor are determined as a function of an actual scavenging gradient, of a valve overlap, of a capacity of an energy storage device, and of an ignition angle.

2. The method according to claim 1, wherein the control element includes a variable turbine geometry.

3. The method according to claim 2, wherein the adjustment of the supercharging system for achieving the boost pressure setpoint in a first operating state includes an operation of the electrically driven compressor with an optimized maximum output and an operation of the control element in a first, open position.

4. The method according to claim 3, wherein, when the positive scavenging gradient is reached in the first operating state, the output of the exhaust turbocharger for building up the actual boost pressure and, accordingly, an output of the electrically driven compressor is reduced in a second operating state.

5. The method according to claim 1 wherein the determination of the first reduction factor and the second reduction factors takes place via a plurality of characteristic maps and/or a plurality of characteristic curves.

6. The method according to claim 5, wherein the characteristic maps and/or the characteristic curves are determined empirically or by models.

7. The method according to claim 1, wherein the second control variable is greater than a predetermined precontrol variable.

8. The method according to claim 1, wherein the control element includes a wastegate.

9. A controller for a combustion engine, wherein the controller is configured to perform the method according to claim 1.

10. The method according to claim 1, wherein the overriding command variable defines that the supercharging system is initially driven such that the positive scavenging gradient is initially set in the cylinder and the actual boost pressure then tracks the boost pressure setpoint.

11. An internal combustion engine comprising: a supercharging system that has an exhaust turbocharger; an electrically driven compressor; and a controller, an output of the exhaust turbocharger being adjustable via a control element, wherein the internal combustion engine is configured to: adjust the supercharging system to build up an actual boost pressure, in accordance with the boost pressure setpoint, by adapting the output of the exhaust turbocharger via the control element; and adjust a positive scavenging gradient in a cylinder of the internal combustion engine as an overriding command variable for driving the supercharging system, wherein the positive scavenging gradient is a pressure difference across the cylinder between an intake manifold pressure upstream of the cylinder and a pressure that is present within an exhaust gas line of the internal combustion engine downstream of the cylinder, wherein the positive scavenging gradient is achieved in that the electrically driven compressor and the exhaust turbocharger are operated as a function of one another, wherein the electrically driven compressor is operated in accordance with a first control variable, and the exhaust turbocharger is operated in accordance with a second control variable, wherein the first control variable is determined based on a first reduction factor and the second control variable is determined based on a second reduction factor, and wherein the first reduction factor and the second reduction factor are determined as a function of an actual scavenging gradient, of a valve overlap, of a capacity of an energy storage device, and of an ignition angle.

12. A motor vehicle comprising the internal combustion engine according to claim 11.

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 is a schematically represented exemplary embodiment of a motor vehicle with an internal combustion engine;

(3) FIG. 2 shows a determination of control variables for a supercharging system of the internal combustion engine according to a first variant;

(4) FIGS. 3a and 3b show a determination of control variables for the supercharging system of the internal combustion engine according to a second variant; and

(5) FIG. 4 shows curves of operating parameters of the internal combustion engine and the supercharging system.

DETAILED DESCRIPTION

(6) FIG. 1 shows a motor vehicle 1 with an internal combustion engine 3 (combustion engine) and a supercharging system 8 that is controlled by a controller 21, which is implemented as, for example, an engine control unit. The supercharging system 8 includes an exhaust turbocharger (ATL) 9 and an electrically driven compressor 11. An energy storage device 12 is coupled to the electrically driven compressor 11 in order to supply the same with electric energy for its operation.

(7) The present invention is not limited to a specific type of motor, but is implemented as a Miller-cycle engine, in particular.

(8) The engine 3 includes one or more cylinders 4, one of which is shown here. The cylinder 4 is supplied with supercharged (combustion) air by the supercharging system 8. The ATL 9 includes a compressor 13, which is driven or operated through a shaft 14 by a turbine (exhaust gas turbine) 15 having a variable turbine geometry (VTG) 17. The turbine 15 is thus in operative connection with/coupled to the compressor 13 through the shaft 14. The compressor 13 is arranged in an air line 5 to the engine 3, and the turbine 15 is arranged in an exhaust gas line 7 that removes exhaust gas from the cylinder 4. Thus, the compressor 13 can be operated with the exhaust gas from the engine 3 by the means that the turbine 15 is supplied with the exhaust gas from the engine 3 and is driven therewith. In addition, the ATL 9 is coupled to the controller 21.

(9) The VTG 17 can be set by means of an adjusting mechanism. A wastegate 19 can be provided alternatively/in addition to the VTG 17. The exhaust gas supplied to the turbine 15, and accordingly an output of the compressor 13, can be set by means of the adjusting mechanism (and/or by means of the wastegate 19). Optionally, a multi-stage supercharging unit can also be provided. In other words, multiple ATLs 19 can also be provided.

(10) In the example shown here, the electrically driven compressor 11 is located downstream of the compressor 13 and is coupled to the controller 21. A supply line of the electrically driven compressor 11 branches off from the air line 5, and a discharge line of the electrically driven compressor 11 rejoins the air line 5 downstream of the electrically driven compressor 11. In other words, the electrically driven compressor 11 is arranged in a bypass line of the air line 5.

(11) The air supply to the electrically driven compressor 11 can be adjusted with the aid of a control device, for example a 3-way control valve, suitably arranged in the air line 5. Downstream of the compressor 13, the air (supplied to the internal combustion engine 3) can thus be directed completely through the electrically driven compressor 11. Furthermore, the control device can be adjusted such that the air precompressed by the compressor 13 does not flow through the electrically driven compressor 11. The control device can also (completely) suppress an air supply to the internal combustion engine 3, so that neither the air from the electrically driven compressor 11 nor the air precompressed by the compressor 13 can be supplied to the internal combustion engine 3. Lastly, the quantity of air supplied to the internal combustion engine 3 can be adjusted by means of the control device. The control device can thus perform a throttling function, as in the case of a classic throttle valve, for example.

(12) The electrically driven compressor 11 can also be located upstream of the compressor 13 in the air line 5.

(13) A charge air cooler that cools the precompressed air supplied to the internal combustion engine 3 can be arranged in the air line 5 downstream of the compressor 13 and the electrically driven compressor 11.

(14) FIG. 2 schematically shows how a control variable (setpoint) u.sub.EV,opt for the electrically driven compressor 11 and a control variable (setpoint) u.sub.ATL,opt for the ATL 9 are determined. Thus, a partial reduction factor α.sub.p23 for the electrically driven compressor 11 and a second partial reduction factor β.sub.p23 for the ATL 9, which are dependent on an (actual) scavenging gradient p.sub.23 and a valve overlap vo, are determined by means of a characteristic map 31. A partial reduction factor α.sub.KEV for the electrically driven compressor 11 and a partial reduction factor β.sub.KEV for the ATL 9, which are dependent on the capacity K.sub.ES of the energy storage device 12, are determined from a characteristic map 33. In addition, a partial reduction factor α.sub.ia for the electrically driven compressor 11 and a partial reduction factor β.sub.ia for the ATL 9, which are dependent on an ignition angle ia, are determined by means of a characteristic map 35.

(15) In block 37, the partial reduction factors α.sub.p23 and α.sub.KEV are offset against one another, in particular are multiplied. The quantity resulting from block 37 is then offset against the partial reduction factor α.sub.ia, in particular multiplied, in block 39. In this way, a reduction factor α for the electrically driven compressor 11 results at the output side of block 39. This reduction factor α is transformed/converted into the control variable u.sub.EV,opt by means of the block 41. An appropriate output of the electrically driven compressor 11, in particular its speed, is adjusted by means of the control variable u.sub.EV,opt.

(16) As described above for the partial reduction factors α.sub.p23, α.sub.KEV, α.sub.ia for the electrically driven compressor 11, the partial reduction factors β.sub.p23, β.sub.KEV, β.sub.ia for the ATL 9 are also offset in corresponding blocks 43, 45, so that a reduction factor β for the ATL 9 is ultimately determined. In block 51, the reduction factor β is transformed/converted into the reduction-factor-dependent control variable u.sub.lim,β for the ATL 9, which is to say for the VTG 17 and/or the wastegate 19.

(17) In addition, in block 49 a precontrol variable u.sub.VS is determined or predetermined, which the control variable u.sub.ATL,opt must reach at a minimum and/or exceed. For example, the precontrol variable u.sub.VS can be determined by means of the turbocharger main equation. To ensure that the control variable u.sub.ATL,opt reaches or exceeds the precontrol variable u.sub.VS, the reduction-factor-dependent control variable u.sub.lim,β and the precontrol variable u.sub.VS enter into the input side at block 51. In block 51, the larger of the two control variables u.sub.lim,β, u.sub.VS is chosen, which then results at the output side as the control variable u.sub.ATL. If the two control variables u.sub.lim,β, u.sub.VS are equal, then u.sub.ATL,opt corresponds to their value. A suitable output of the ATL 9, in particular its speed, is adjusted by means of the control variable u.sub.ATL,opt. This means that the larger the control variable u.sub.ATL,opt is, the higher the speed of the ATL 9. In other words, the larger the control variable u.sub.ATL,opt is, the smaller the flow cross-section of the VTG is or the les exhaust gas flows through the wastegate 19.

(18) From the characteristic maps 31, 33, 35, the partial reduction factors α.sub.p23, α.sub.KEV, α.sub.ia for the electrically driven compressor 11 and the partial reduction factors β.sub.p23, β.sub.KEV, β.sub.ia for the ATL 9 are stored together in the corresponding characteristic maps 31, 33, 35 as a function of one another. The control variables u.sub.EV,opt and u.sub.ATL,opt that are determined then adjust the electrically driven compressor 11 or the ATL 9 such that a positive scavenging gradient is initially achieved relatively rapidly while taking into account the capacity of the energy storage device. In the positive scavenging gradient region, the ATL 9 is driven such that its output (and thus the boost pressure buildup coming from the ATL 9) is as high as possible without the scavenging gradient becoming negative, while at the same time the electrically driven compressor 11 is cut back in its output and thus consumes less energy provided by the energy storage device.

(19) Shown in FIGS. 3a and 3b is an alternative for determining (setpoint) control variables u.sub.EV,opt′ for the electrically driven compressor 11 and u.sub.ATL,opt′ for the ATL 9. The difference from the approach from FIG. 2 is partial reduction factors α.sub.p23′, α.sub.KEV′, α.sub.ia′, which correspond to the partial reduction factors α.sub.p23′, α.sub.KEV′, α.sub.ia′, are determined from a characteristic map 61 or characteristic curves 63, 65, and the partial reduction factors β.sub.p23′, β.sub.KEV′, β.sub.ia′, which correspond to the partial reduction factors β.sub.p23, β.sub.KEV, β.sub.ia, are determined from a characteristic map 81 or characteristic curves 83, 85.

(20) Thus, in FIG. 3a the partial reduction factor α.sub.p23′ for the electrically driven compressor 11, which depends on the (actual) scavenging gradient p.sub.23 and the valve overlap vo, is determined by means of the characteristic map 61. The partial reduction factor α.sub.KEV, which depends on the capacity K.sub.ES of the energy storage device 12, is determined from the characteristic map 33. In addition, the partial reduction factor α.sub.ia′, which depends on the ignition angle ia, is determined by means of the characteristic map 65. In block 67, the partial reduction factors α.sub.p23′ and α.sub.KEV′, are offset against one another, in particular are multiplied. The quantity resulting from block 67 is then offset against the partial reduction factor α.sub.ia′, in particular multiplied, in block 69. In this way, a reduction factor α′ for the electrically driven compressor 11 results at the output side of block 69. This reduction factor α′ is transformed/converted into the control variable u.sub.EV,opt′ by means of the block 71. An appropriate output of the electrically driven compressor 11, in particular its speed, is adjusted by means of the control variable u.sub.EV,opt′.

(21) FIG. 3b shows schematically how the (setpoint) control variable u.sub.ATL,opt′ for the ATL 9 is determined, wherein this control variable u.sub.ATL,opt′ is determined in a manner similar to the control variable u.sub.EV,opt′ for the electrically driven compressor 11. Partial reduction factors β.sub.p23′, β.sub.KEV′, β.sub.ia′ are likewise determined, which are dependent on the (actual) scavenging gradient p.sub.23, on the valve overlap vo, on the capacity K.sub.ES, or on the ignition angle ia. A characteristic map 81 and characteristic curves 83, 85 have accordingly been created for determination of the partial reduction factors β.sub.p23′, β.sub.KEV′, β.sub.ia′. As described above, the partial reduction factors β.sub.p23′, β.sub.KEV′, β.sub.ia′ are also offset, in particular multiplied, in corresponding blocks 87, 89, so that lastly a reduction factor β′ for the ATL 9 is determined. In block 91, the reduction factor β′ is transformed/converted into the reduction-factor-dependent control variable u.sub.lim,β′ for the ATL 9, which is to say for the VTG 17 and/or the wastegate 19. Block 49 for determining the precontrol variable u.sub.VS is present here, as well. In a manner analogous to block 51, it is ensured by means of block 95 that the larger of the two control variables u.sub.lim,β′, u.sub.VS present at the input side of block 95 results as the output quantity u.sub.ATL,opt′.

(22) In FIGS. 3a and 3b, the control variables u.sub.EV,opt′, u.sub.ATL,opt′ are determined without dependence on one another. It is true that this approach can load the energy storage device 12 comparatively more than the approach from FIG. 2, but the control variables u.sub.EV,opt′, u.sub.ATL,opt′ are determined especially easily.

(23) FIG. 4 shows qualitative and schematic curves for the scavenging gradient p.sub.23, for a speed n.sub.EV of the electrically driven compressor 11, for the control variable u.sub.ATL for the ATL 9, and for the boost pressure p.sub.2. The speed n.sub.EV of the electrically driven compressor 11 is adjustable by means of the control variable u.sub.EV for the electrically driven compressor 11. The speed n.sub.EV thus reflects the output of the electrically driven compressor 11. A boost pressure setpoint curve p.sub.2,soll is shown that is necessary for implementing the driver command or the engine torque setpoint, wherein the driver command is detected at the time t.sub.0.

(24) Also shown is a curve for a scavenging gradient p.sub.23,0, in which the electrically driven compressor 11 is not operated. It can be seen that the scavenging gradient p.sub.23,0 exhibits a comparatively high excursion into the negative region and that a minimum of the scavenging gradient p.sub.23,0 is present comparatively later in time. It can also be seen that the curve for the scavenging gradient p.sub.23,0 does not reach the positive region until a comparatively late time t.sub.3. The reason for this is that in this case an actual boost pressure p.sub.2,ist,0 is built up only by the ATL 9. On the other hand, the control element 17, 19 (which is to say the VTG and/or wastegate 19) is adjusted by means of an appropriate control variable u.sub.ATL,0 in order to temporarily increase, in particular to maximize, the drive output of the turbine 15, as a result of which the exhaust gas back pressure p.sub.3 abruptly rises. In contrast, the actual boost pressure p.sub.2,ist,0 is built up with a comparatively large delay on account of the high exhaust gas back pressure p.sub.3, since the exhaust gas back pressure p.sub.3 reduces a fresh air charging in the cylinder 4 due to exhaust gas pushing back. This results in the strong excursion of the scavenging gradient p.sub.23,0 in the negative direction.

(25) Also shown is a non-optimized curve p.sub.23,max in which the electrically driven compressor 11 is operated non-optimally, which is to say at a non-optimized speed n.sub.EV,max, as a result of which it temporarily runs with its non-optimized maximum (speed) output. In other words, the electrically driven compressor 11 is operated at its component-dependent maximum speed. In addition, the ATL 9 is operated with a non-optimized control variable u.sub.ATL,max, with which the ATL 9 is temporarily adjusted to a maximum possible speed setpoint. The non-optimized control variable u.sub.ATL,max, like the control variable u.sub.ATL,0, extends until the time t.sub.1. Due to the non-optimized control variable u.sub.ATL,max, the ATL 9 (or the control element 17) is temporarily adjusted to its actuator limit, as was the case earlier with the control variable u.sub.ATL,0. As a result, a non-optimized boost pressure p.sub.2,lst,max, and accordingly the positive scavenging gradient p.sub.23, are built up comparatively rapidly at the time t.sub.1, while the curve for the non-optimized scavenging gradient p.sub.23,max has a comparatively small excursion into the negative region before the time t.sub.1. Since the electrically driven compressor 11 is temporarily operated with non-optimized maximum output, the energy stored (for operating the electrically driven compressor 11 by the energy storage device is consumed correspondingly faster.

(26) An optimized (or in other words, ideal) scavenging gradient p.sub.23,opt is set by the means that the electrically driven compressor 11 is operated with an optimized speed n.sub.EV,opt. This optimized speed n.sub.EV,opt is adjusted in accordance with the reduction factor α or the (reduction-factor-adjusted) control variable u.sub.EV,opt. During this time, the control element 17, 19 is operated with an optimized (if applicable reduction-factor-adjusted) control variable u.sub.ATL,opt, wherein the control variable u.sub.ATL,opt is greater at time t.sub.0 than the precontrol variable u.sub.VS. The control variable u.sub.ATL,opt, like the control variable u.sub.ATL,0, extends to time t.sub.0. In comparison with the curve p.sub.23,0, the optimized curve for the scavenging gradient p.sub.23,opt has a smaller excursion into a negative scavenging gradient region. In addition, the optimized scavenging gradient p.sub.23,opt becomes positive at an earlier time t.sub.2, and the scavenging gradient p.sub.23,0 only does so at a later time t.sub.3.

(27) It is also evident that the speed n.sub.EV of the electrically driven compressor 11 due to the optimized operation n.sub.EV,opt (or due to the faster establishment of the positive scavenging gradient) is lower as compared to the operation in the non-optimized operation n.sub.EV,max. This does mean that in optimized operation the optimized actual boost pressure p.sub.2,ist,opt tracks the boost pressure setpoint p.sub.25,soll more slowly than does the non-optimized boost pressure p.sub.2,lst,max. However, the capacity of the energy storage device is taken into account by the optimized operation of the electrically driven compressor 11.

(28) In all cases, the speed n.sub.EV of the electrically driven compressor 11 and the control variable u.sub.ATL for the ATL 9 are reduced once the scavenging gradient p.sub.23 reaches the positive region until the actual boost pressure p.sub.2,ist reaches, in particular substantially reaches, the boost pressure setpoint p.sub.25,soll. Thereafter, the control variable u.sub.ATL for the ATL 9 is adjusted to an appropriate value for a steady-state operation of the internal combustion engine 3, and if applicable the electrically driven compressor 11 is taken out of operation, which is to say that its speed n.sub.EV is set to zero.

(29) 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.