Method for operating an internal combustion engine, control unit, and electrically driven charging device

Abstract

A method for operating an internal combustion engine with a system for supercharging that includes an exhaust turbocharger and an electrically driven charging device for dynamic assistance during build-up of boost pressure, with: determining a drive criterion of the charging device, establishing an initial quantity of the drive criterion; continuously determining a reduction factor for the drive criterion within a balance period; applying the reduction factor to the initial quantity of the drive criterion; and operating the charging device with the drive criterion reduced by the reduction factor.

Claims

1. A method for operating an internal combustion engine with a system for supercharging that includes an exhaust turbocharger and an electrically driven charging device for dynamic assistance during build-up of boost pressure, the method comprising: determining a drive criterion of the charging device; establishing an initial quantity of the drive criterion; continuously determining a reduction factor for the drive criterion within a first balance period; applying the reduction factor to the initial quantity of the drive criterion; and operating the charging device with the drive criterion reduced by the reduction factor, wherein the reduction factor includes an electric consumption or recuperation factor, wherein the consumption or recuperation factor takes into account an energy difference determined over a second balance period between a recuperated energy quantity and an assistance energy quantity, and wherein the second balance period is a total operating time of the engine or a trip duration.

2. The method according to claim 1, wherein the drive criterion includes: a drive torque, a drive speed, a supply current, and/or a supply voltage.

3. The method according to claim 1, wherein the reduction factor includes the electric consumption or recuperation factor and one or more of a thermodynamic factor, a state of charge factor, and a temperature factor.

4. The method according to claim 3, wherein the consumption or recuperation factor takes into account the energy difference determined over the second balance period between the recuperated energy quantity and the assistance energy quantity, and a demand energy quantity determined for the first balance period using the following relationship: $X_{\mathrm{Eco}}=\frac{\Delta E_{\mathrm{Eco}}}{E_{\mathrm{demand},\mathrm{Boost}}}.$

5. The method according to claim 4, wherein the first balance period is less than the second balance period.

6. The method according to claim 4, wherein the first balance period is 1 to 10 min, or is 2 to 3 min.

7. The method according to claim 4, wherein the consumption or recuperation factor is taken into account as a reduction factor when the consumption or recuperation factor is less than one.

8. The method according to claim 3, wherein the thermodynamic factor is determined such that the thermodynamic factor reduces a maximum of the drive criterion such that a maximum thermodynamically reasonable boost pressure is built up during the dynamic assistance via the charging device.

9. The method according to claim 3, wherein the state of charge factor is determined from a difference between an actual state of charge and a state of charge limit.

10. The method according to claim 3, wherein the temperature factor is determined from a difference between a critical component temperature and an actual component temperature.

11. The method according to claim 10, wherein the temperature factor results from the relationship, where T.sub.crit is the critical component temperature and T is the actual component temperature: $f_{\mathrm{Temp}}=\frac{T_{\mathrm{crit}}-T}{T_{\mathrm{crit}}}.$

12. A control unit for the internal combustion engine that is equipped to adjust the system for supercharging according to the method from claim 1.

13. The electrically driven charging device being designed as an EAT or an EDC, and is operated according to the method from claim 1, wherein the drive criterion is a drive torque in a case of the charging device being an EAT and wherein the drive criterion is a drive speed in a case of the charging device being an EDC.

14. The internal combustion engine with the charging device according to claim 13.

15. A motor vehicle with the internal combustion engine according to claim 14.

16. The method according to claim 1, wherein within the second balance period, a total recuperated energy and a total assistance energy are offset against one another and/or balanced.

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 shows a schematically represented internal combustion engine with an EAT that is suitable for carrying out the method according to the invention;

(3) FIG. 2 shows a schematic representation of an internal combustion engine with an EDC that is suitable for carrying out the method according to the invention;

(4) FIG. 3 shows a schematic representation that illustrates the determination of the correction factor with an EDC;

(5) FIG. 4 shows a schematic representation that illustrates the determination of the correction factor with an EAT; and

(6) FIG. 5 shows a schematic representation of the method according to the invention.

DETAILED DESCRIPTION

(7) FIG. 1 shows an exemplary embodiment of an internal combustion engine 1 according to the invention in a vehicle 100 with a system 2 for supercharging with an exhaust turbocharger (turbo) 3, which here is implemented as an electrically assisted turbocharger (EAT), in which an electric motor 7 is arranged on a rotor assembly shaft 4 that couples the turbine 5 with the compressor 6, which electric motor is supplied with energy through a vehicle electrical system 8, and which can be controlled through a control unit 9 (ECU).

(8) The vehicle electrical system 8 has a power storage device 10 and an electric machine 11—for example, a belt starter generator (BSG)—which can be operated both as a generator and as a motor, and which is mechanically coupled to the crankshaft 12. The crankshaft 12 is driven by one or more pistons 13 of the cylinder(s) 14 of the internal combustion engine. Air is supplied to the cylinder 14 through the intake tract 15, and the exhaust gas formed there is removed through the exhaust tract 16. In this process, the fresh air is passed through the compressor 6, is compressed there when the exhaust turbocharger 3 is operated, and is delivered into the cylinder 14 at the boost pressure p.sub.2. When this takes place, fuel is supplied, ignition takes place in the cylinder 14 (spark ignition or self-ignition) and the exhaust gas is passed into the turbine 5 at the exhaust gas back pressure p.sub.3, where a portion of the exhaust gas enthalpy drives the turbine 5 and thus the compressor 6, these being coupled to one another through the rotor assembly shaft 4.

(9) Together with the exhaust turbocharger 3, the electric motor 7 forms an electrically driven or drivable charging device. Control here takes place through the control unit 9, the function of which is explained in detail further below. Essentially, the EAT 3 serves to build up the boost pressure p.sub.2 and to provide dynamic assistance during acceleration. Especially during acceleration from comparatively low speed ranges, the effect of the exhaust turbocharger 3 that is not additionally driven is only very limited to start with (turbocharger lag). The electric motor 7 is now additionally driven in this speed range and makes available a drive torque M.sub.set, EAT that additionally drives the compressor 6 and thus provides an increased boost pressure p.sub.2 even at low speeds.

(10) The electric motor 7 is implemented as an electric machine that can work both as a generator and as a motor. As a result, electrical energy can be recuperated through the electric motor 7 during deceleration by means of the drive of the turbine 5, and fed into the vehicle electrical system 8 or into the power storage device 10. In this process, both the recuperated energy portion E.sub.Recu and an energy portion E.sub.Boost drawn for dynamic assistance are captured in the controller 9 during a balance period t.sub.v2 and, if applicable, are balanced against each other (see below).

(11) FIG. 2 shows a second exemplary embodiment of an internal combustion engine 1 according to the invention. In the system for supercharging 2, the electrically driven charging device is implemented here as an electrically driven compressor (EDC) 19, which is operated independently of the exhaust turbocharger 3. In this design, a separate compressor 17 is arranged in the intake tract 15 and can be driven by an electric motor 18, which likewise is supplied with power through the vehicle electrical system 8 and is controlled through the control unit 9. The compressor 17 here is located upstream of the compressor 6 of the exhaust turbocharger when viewed in the direction of flow. Embodiments exist in which the compressor 17 of the EDC is located downstream of the compressor 6 of the exhaust turbocharger 3 when viewed in the direction of flow.

(12) The electric motor 18 functions in the same way as the electric motor 7. The EDC 19 serves to provide dynamic assistance during build-up of the boost pressure, especially in low speed ranges (e-boost mode). However, the EDC 19 is not capable of feeding recuperated energy into the vehicle electrical system 8.

(13) It is possible, however, to operate the electric motor 18 through recuperated energy that is fed into the vehicle electrical system through the electric machine 11 (BSG).

(14) In addition, it is also possible in the embodiment from FIG. 1 to control the electric machine 11 in such a manner that it is driven from the energy recuperated by means of the electric motor 7, and thus the additional energy is available directly at the crankshaft 12 in a manner that is effective for the drive.

(15) FIG. 3 shows the control of the electrically driven charging device by means of the electrically driven compressor EDC 19 (FIG. 2). The control unit 9 receives multiple signals for this purpose, which are represented by incoming arrows. The control of the electric motor 18 by the electrically driven compressor 19 takes place under speed control. For this purpose, the control unit 9 includes a control section 90 (shown in FIG. 3 and FIG. 4), which processes corresponding signals in order to determine a speed setpoint n.sub.set, EDC using the method according to the invention. The speed n.sub.EDC constitutes the drive criterion of the charging device here. In order to determine the speed setpoint n.sub.set, EDC, a thermodynamically reasonable speed n.sub.set, thermo is first derived starting from a technically possible maximum speed n.sub.max, EDC and a thermodynamic reduction factor f.sub.thermo. The factor f.sub.thermo results from a characteristic map, for example, in which specific boost pressures p.sub.2 are associated with specific operating points, and a speed n.sub.set, thermo or a thermodynamic reduction factor f.sub.thermo, which reduces the maximum speed n.sub.max, EDC accordingly, is associated with each of these boost pressures p.sub.2. It is ensured in this way that the EDC 19 is only driven at those speeds for which a reasonable boost pressure p.sub.2 is made available as a function of operating point.

(16) Additional boundary conditions are taken into account as follows:

(17) The boundary conditions represented in FIG. 4 relate to a state of charge (SoC) of the battery 10 of the vehicle electrical system 8, which can vary between 1 (fully charged) and 0 (fully discharged). A state of charge factor f.sub.SoC is determined from this state of charge SoC.sub.battery and a state of charge limit SoC.sub.limit, battery by taking the difference. The state of charge limit SoC.sub.limit, battery describes here the maximum allowed discharge of the vehicle battery, and is a quantity that is vehicle-specific, for example, and may also be adjustable, which can be freely chosen between 0 and 1. The calculation of the state of charge factor f.sub.SoC as the difference between the instantaneous state of charge of the battery SoC.sub.battery and the state of charge limit ensures now that no drop below the state of charge limit occurs in that the state of charge factor f.sub.SoC, which likewise fluctuates between 1 and 0, reduces the speed n.sub.set, thermo to a speed n.sub.set, thermo, SoC as necessary.

(18) As an additional criterion, a thermal reduction factor f.sub.Temp is determined, which takes into account the temperature of one or more drive-critical components. These can be temperatures of the electric motor or other important components of the electrically driven compressor 19, for example. It is fundamentally also possible to include thermal boundary conditions of other engine components here. In this context, a critical component temperature T.sub.crit is compared with an actual component temperature T.sub.el. comp. in that a difference is taken. And this difference is placed in a ratio to the critical component temperature T.sub.crit. The relationship holds that

(19) $f_{\mathrm{Temp}}=\frac{T_{\mathrm{crit}}-T_{\mathrm{el}.\mathrm{Comp}}}{T_{\mathrm{crit}}}.$

(20) The thermal reduction factor f.sub.Temp thus determined additionally reduces the speed n.sub.set, thermo, SoC as needed by a factor that likewise varies between zero and one, namely to a greater degree the closer the component temperature T.sub.el. comp comes to the critical temperature. A speed n.sub.set, thermo, SoC, Temp results.

(21) Finally, a consumption/recuperation factor X.sub.Eco is determined that takes into account the following factors. Firstly, the recuperated energy E.sub.Recu is taken into account, and the energy E.sub.Boost expended to drive the electrically driven charging device for dynamic assistance during build-up of the boost pressure p.sub.2 is taken into account. This energy difference ΔE.sub.Eco is captured over a second balance period t.sub.v2. This second balance period corresponds here to a total operating cycle of the engine—for example the total trip duration.

(22) In order to determine the factor, this difference ΔE.sub.Eco is placed in a ratio to an assistance energy demand E.sub.demand,Boost, which is determined over a traveling balance period t.sub.v1 that is smaller than the balance period t.sub.v2 and, as the latter extends, shifts with the continuously lengthening total operating cycle of the engine. The balance period t.sub.v1 is a sliding time window. For this time period, which generally is between 1 and 10 min or, even better, between 2 and 3 min, the energy demand E.sub.demand, Boost is determined in that the energy demand is determined from the individual driving style, a route profile, or other operating state quantities. Characteristic maps, predictive calculations, or expected route profiles, which can be derived from a navigation system, for example, can be used for this purpose.

(23) This consumption/recuperation factor X.sub.Eco only comes into use when the ratio between the energy balance over the balance period t.sub.v2 and the energy demand E.sub.demand,Boost determined over the balance period t.sub.v1 is less than one. Then, if applicable, the reduction factor thus determined further reduces the speed n.sub.set, thermo, SoC, Temp to the speed n.sub.set, thermo, SoC, Temp, eco, which then corresponds to the speed setpoint n.sub.set, EDC of the motor 18. In the event that the reduction factor X.sub.Eco is greater than or equal to one, no reduction takes place. If no recuperated energy excess is available (ΔE.sub.Eco=0), the electrically driven charging device is prevented from being usable at all.

(24) The choice of the duration of the first balance period t.sub.v1, which is determined continuously and thus also applies to the other reduction factors f.sub.thermo, f.sub.SoC, and f.sub.Temp, ensures that changes in the boundary conditions affect the reduction factor only gradually or stepwise, thus ensuring that the handling characteristics or responsiveness of the engine during acceleration change only gradually. In this way, abrupt changes in responsiveness can be precluded.

(25) The same relationship is shown in FIG. 4 for an engine with an EAT in which the torque M.sub.set, EAT rather than the speed n.sub.set, EDC can be determined through the reduction factor or factors. Here, the recuperated energy E.sub.Recu can be fed directly into the vehicle electrical system 8 or the battery 8a through the electric motor 7.

(26) In the implementation of the electrically driven charging device as the EDC 18, the recuperated energy can only be obtained through the electric machine (BSG) 11, and it is possible to establish, for example, that only a specific percentage of this recuperated energy can be made available as boost energy for the electric motor 18.

(27) FIG. 5 shows the sequence of the method according the invention for operating an internal combustion engine with a system for supercharging that includes an exhaust turbocharger 3 and an electrically driven charging device for dynamic assistance during build-up of boost pressure p.sub.2. The following steps are provided here:

(28) A determining a drive criterion M.sub.set, EAT; n.sub.set, EDC

(29) B establishing an initial quantity of the drive criterion (M.sub.EAT, n.sub.EDC)

(30) C continuously determining a reduction factor (f.sub.thermo, f.sub.SoC, f.sub.Temp, X.sub.Eco) for the drive criterion (n.sub.set, EDC, M.sub.set, EAT) within a balance period t.sub.v1

(31) D applying the reduction factor to the drive criterion

(32) E operating the charging device with the drive criterion reduced by the reduction factor.

(33) In this context, embodiments are possible in which not all of the reduction factors specified above are taken into account, or individual reduction factors are taken into account only at certain times or within different balance periods t.sub.v1.

(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.