METHOD AND DEVICE FOR CONTROLLING AN AIR CHARGE OF AN INTERNAL COMBUSTION ENGINE

Abstract

A method for operating an internal combustion engine based on a control of a supplied fresh air quantity, the method comprising the following steps: implementing an adjustment of a throttle valve for the control of the supplied fresh air quantity as a function of a setpoint mass flow via the throttle valve; determining the setpoint mass flow via the throttle valve according to a differential equation, which is a function of a control deviation ascertained as a function of a setpoint intake manifold pressure and an actual intake manifold pressure.

Claims

1. A method for operating an internal combustion engine based on a control of a supplied fresh air quantity, the method comprising the following steps: implementing an adjustment of a throttle valve for the control of the supplied fresh air quantity as a function of a setpoint mass flow via the throttle valve; and determining the setpoint mass flow via the throttle valve according to a differential equation which is a function of a control deviation ascertained as a function of a setpoint intake manifold pressure and an actual intake manifold pressure.

2. The method as recited in claim 1, wherein the differential equation is a function of a modified setpoint intake manifold pressure, which is calculated using a predefined setpoint intake manifold pressure and a transfer function, which takes a limited dynamic of the adjustment of the throttle valve into account.

3. The method as recited in claim 1, wherein the differential equation takes a linear error dynamic according to ${\stackrel{.}{e}}_{\mathrm{sr}}+\frac{1}{{\tau }^{\mathrm{des}}}{e}_{\mathrm{sr}}=0$ into account, wherein e.sub.sr is a control deviation, which is a function of a setpoint intake manifold pressure and an actual intake manifold pressure, and τ.sup.des is a predefined time constant.

4. The method as recited in claim 1, wherein the differential equation is a function of a partial pressure of the internal residual gas in a combustion chamber of a cylinder and of a conversion factor of a pressure into a charge, and wherein the partial pressure of the internal residual gas and/or the conversion factor is determined as a function of an intake valve opening instant and/or a discharge valve closing instant.

5. The method as recited in claim 1, wherein the transfer function models a PTn behavior, with n>=1, and has a time constant, which is selected in such a way that it defines a dynamic that is equal to or less than a maximum dynamic of the adjustment of the throttle valve by a throttle valve actuator for the internal combustion engine.

6. The method as recited in claim 1, wherein the adjustment of the throttle valve for the control of the supplied fresh air quantity is implemented using a pilot control and a control as a function of a control deviation between the setpoint intake manifold pressure and an actual intake manifold pressure.

7. A device for operating an internal combustion engine based on a control of a supplied fresh air quantity, the device configured to: implement an adjustment of a throttle valve for the control of the supplied fresh air quantity as a function of a setpoint mass flow via the throttle valve; determine the setpoint mass flow via the throttle valve according to a differential equation, which is a function of a control deviation ascertained as a function of a setpoint intake manifold pressure and an actual intake manifold pressure.

8. A non-transitory machine-readable memory medium on which are stored instructions for operating an internal combustion engine based on a control of a supplied fresh air quantity, the instructions, when executed by a data processing device, causing the data processing device to perform the following steps: implementing an adjustment of a throttle valve for the control of the supplied fresh air quantity as a function of a setpoint mass flow via the throttle valve; and determining the setpoint mass flow via the throttle valve according to a differential equation which is a function of a control deviation ascertained as a function of a setpoint intake manifold pressure and an actual intake manifold pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In the following text, example embodiments of the present invention will be described in greater detail based on the figures.

[0039] FIG. 1 shows a schematic representation of an engine system having an internal combustion engine.

[0040] FIG. 2 shows a block diagram to illustrate a control of the throttle valve actuator based on a pressure-based control, according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0041] FIG. 1 schematically shows the design of an engine system 1 including an internal combustion engine 2. Internal combustion engine 2 may be developed as an air-controlled internal combustion engine, in particular a gasoline engine. Fresh air is conveyed to internal combustion engine 2 via an air supply system 3.

[0042] Situated in the air supply system is a throttle valve 4, which is adjustable in a variable manner with the aid of a throttle valve actuator 5. An intake manifold section 31 is provided between throttle valve 4 and one or more intake valve(s) 6 of a cylinder 7 of internal combustion engine 2. The cylinder volume and the pressure in intake manifold section 31 define the gas quantity drawn into internal combustion engine 2 as a function of its engine speed.

[0043] Internal combustion engine 2 is operated by an engine control device 10, which, in a conventional manner, determines a setpoint air charge in internal combustion engine 2 as a function of a desired setpoint engine torque. In general, the air charge corresponds to the fresh air quantity admitted or drawn into respective cylinder 7 of internal combustion engine 2 per working cycle.

[0044] Engine control device 10 operates internal combustion engine 2 based on the system variables such as an intake manifold pressure, which is able to be measured with the aid of an intake manifold pressure sensor 11 or can be modeled in some other manner, an engine speed n.sub.eng measured by an engine speed sensor 12, a displacement V.sub.h.sup.total, and it adjusts a throttle valve position via throttle valve actuator 5 according to a charge control.

[0045] The charge control implemented in engine control device 10 is based on a control structure which is shown in FIG. 2 by way of example. The control structure includes a pilot control 21 for ascertaining the result of a first term, and a control block 23 for calculating the result of a second term.

[0046] The specification of setpoint mass flow {dot over (m)}.sub.ThrVlv.sup.des for throttle valve 4 is suitably implemented into a position control of a downstream position control 25. To control the setpoint mass flow {dot over (m)}.sub.ThrVlv.sup.des via throttle valve 4, a total function is provided with the pilot control and the control, which is indicated by the following equation.

[00011]${\stackrel{.}{m}}_{\mathrm{ThrVlv}}^{\mathrm{des}}=k_{\mathrm{sr}}.Math.\frac{d}{\mathrm{dt}}{p}_{\mathrm{sr}}^{\mathrm{des}}+\left(p_{\mathrm{sr}}^{\mathrm{des}}-p_{\mathrm{rg}}\right).Math.\mathrm{fupsrl}.Math.\mathrm{umsrln}+\left(\frac{k_{\mathrm{sr}}}{{\tau }^{\mathrm{des}}}-\mathrm{fupsrl}.Math.\mathrm{umsrln}\right)\left(p_{\mathrm{sr}}^{\mathrm{des}}-p_{\mathrm{sr}}\right)$

[0047] A characteristic feature of this control is that it is not based on the charge but on the intake manifold pressure p.sub.sr.

[0048] This equation considers the error dynamic

[00012]${\stackrel{.}{e}}_{\mathrm{sr}}+\frac{1}{{\tau }^{\mathrm{des}}}{e}_{\mathrm{sr}}=0$

with e.sub.sr=p.sub.sr.sup.des−p.sub.sr It then follows that:

[00013]$\frac{d}{\mathrm{dt}}{p}_{\mathrm{sr}}^{\mathrm{des}}-\frac{d}{\mathrm{dt}}{p}_{\mathrm{sr}}+\frac{1}{{\tau }^{\mathrm{des}}}\left(\frac{p}{\mathrm{srdes}}-p_{\mathrm{sr}}\right)=0.Math.\frac{d}{\mathrm{dt}}{p}_{\mathrm{sr}}^{\mathrm{des}}-\frac{1}{k_{\mathrm{sr}}}\left({\stackrel{.}{m}}_{\mathrm{ThrVlv}}^{\mathrm{des}}-\mathrm{rl}.Math.\mathrm{umsrln}\right)+\frac{1}{{\tau }^{\mathrm{des}}}(p_{\mathrm{sr}}^{\mathrm{des}}-p_{\mathrm{sr})}=0.Math.\frac{d}{\mathrm{dt}}{p}_{\mathrm{sr}}^{\mathrm{des}}-\frac{1}{k_{\mathrm{sr}}}\left({\stackrel{.}{m}}_{\mathrm{ThrVlv}}^{\mathrm{des}}-\left(p_{\mathrm{sr}}-p_{\mathrm{rg}}\right).Math.\mathrm{fupsrl}.Math.\mathrm{umsrln}\right)+\frac{1}{{\tau }^{\mathrm{des}}}\left(p_{\mathrm{sr}}^{\mathrm{des}}-p_{\mathrm{sr}}\right)=0$

[0049] By a rearrangement, the above formula is obtained.

[0050] Accordingly, pilot control 21 supplies the result of

[00014]$\frac{1}{k_{\mathrm{sr}}}\left({\stackrel{.}{m}}_{\mathrm{ThrVlv}}^{\mathrm{des}}-\left(p_{\mathrm{sr}}-p_{\mathrm{rg}}\right).Math.\mathrm{fupsrl}.Math.\mathrm{umsrln}\right)$

as a function of the variables fupsrl, umsrln, k.sub.sr defined at the outset, the setpoint intake manifold pressure p.sub.sr.sup.des, a predefined time constant τ.sup.des, and the actual intake manifold pressure p.sub.sr.

[0051] To determine the setpoint mass flow {dot over (m)}.sub.ThrVlv.sup.des to be set for throttle valve 4, instead of a setpoint intake manifold pressure p.sub.sr.sup.des, which may be defined by the setpoint air charge rl.sub.des as a function of engine parameters, it is determined according to a trajectory plan. The trajectory planning for setpoint intake manifold pressure p.sub.sr.sup.des may be carried out in a trajectory block 22, for instance with the aid of a PTn filter with n≥1, so that a reduced dynamic on setpoint intake manifold pressure p.sub.sr.sup.des is ensured that throttle valve actuator 5 is actually also able to follow. The corresponding setpoint variable ϕ(p.sub.sr.sup.des) results from the application of the function ϕ(.Math.). The modified equation therefore results from the above equation

[00015]${\stackrel{.}{m}}_{\mathrm{ThrVlv}}^{\mathrm{des}}=k_{\mathrm{sr}}.Math.\frac{d}{\mathrm{dt}}\varphi \left(p_{\mathrm{sr}}^{\mathrm{des}}\right)+\left(\varphi \left(p_{\mathrm{sr}}^{\mathrm{des}}\right)-p_{\mathrm{rg}}\right).Math.\mathrm{fupsrl}.Math.\mathrm{umsrln}+\left(\frac{k_{\mathrm{sr}}}{{\tau }^{\mathrm{des}}}-\mathrm{fupsrl}.Math.\mathrm{umsrln}\right)\left(\varphi \left(p_{\mathrm{sr}}^{\mathrm{des}}\right)-p_{\mathrm{sr}}\right)$

where, instead of setpoint intake manifold pressure p.sub.sr.sup.des, a modified setpoint intake manifold pressure is inserted as a function ϕ(p.sub.sr.sup.des) depending on the setpoint intake manifold pressure. The function ϕ(.Math.) corresponds to a transfer function of a PTn filter for mapping the restricted dynamic of an adjustment of throttle valve 4. On this basis, it is then also possible to calculate the derivation p.sub.sr.sup.des in an analytical and precise manner, and further discretization errors in the calculation of the derivation are avoided.

[0052] A PTn filter is able to be represented by a differential equation that is solved by a time function. This time derivation may in turn be derived in an analytical and precise manner.

[0053] This avoids the inaccuracies that would result by the calculation with the aid of a differential quotient, for example.

[0054] The result of the calculation of the second term in control block 23 is then applied to the result of the first term ascertained by pilot control 21 according to the above rule in an addition block 24. Control block 23 is particularly developed as a proportional controller, and the second term as a proportional controller may perform a corrective intervention for the first term according to

[00016]$\left(\frac{k_{\mathrm{sr}}}{{\tau }^{\mathrm{des}}}-\mathrm{fupsrl}.Math.\mathrm{umsrln}\right)\left(p_{\mathrm{sr}}^{\mathrm{des}}-p_{\mathrm{sr}}\right).$

[0055] The sum of the results of the two terms is conveyed to a downstream position control 25 for throttle valve 4 as a setpoint specification. Position control 25 is developed in a conventional manner.

[0056] Actual intake manifold pressure p.sub.sr results from a measurement with the aid of intake manifold pressure sensor 11 or by suitable mathematical modeling.

[0057] The time constant of the proportional controller τ.sup.des is usually selected in such a way that balancing is achieved between the most rapid control possible and the avoidance of oscillations on actual intake manifold pressure p.sub.sr. Typically, the time constant τ.sup.des is a function of the current control deviation. For instance, the time constant τ.sup.des may be determined via a configurable characteristic curve or, if a further input variable such as the engine speed is to be considered, a configurable program map.

[0058] To calm the resulting setpoint mass flow {dot over (m)}.sub.ThrVlv.sup.des for throttle valve 4 in a stationary manner, that is, to avoid that fluctuations of the actual mass flow lead to a steady change in the setpoint value, the conversion factor fupsrl and the partial pressure p.sub.rg in the corresponding term of the above equation can be calculated on the basis of setpoint camshaft angles instead of actual camshaft angles.

[0059] The setpoint values for the camshaft positions generally come from program map structures which are a function of the setpoint charge and engine speed, in particular. Thus, they are very stable for a specific operating point.

[0060] The actual values of the camshaft positions are able to be determined by a sensor. Since systems featuring a camshaft adjustment involve hydraulic systems, small movements in the system are common here also in stationary operating points. They are detected, and subsequently cause larger variations on the variables of the conversion factor fupsrl and the partial pressure p.sub.rg.