DE102017215566A1 - Method for operating an internal combustion engine during warm-up - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine during warm-up, wherein at least two controlled variables selected from a variable indicative of an engine speed (ω), a characterizing an air-fuel ratio during combustion (λ) and a combustion position (COC) in the context of multivariable control, at least two manipulated variables selected from a variable (u) characterizing an air quantity, a quantity (u) characterizing an injection quantity and a variable (u) characterizing an ignition angle become.

Description

The present invention relates to a method for operating an internal combustion engine during warm-up, as well as to a computing unit and a computer program for carrying it out.

State of the art

A cold start, i. A start-up operation, without previously cooling water and / or oil were preheated, loads an internal combustion engine to a particular extent and may also lead to increased pollutant emissions. Achieving the optimum operating temperature as quickly as possible by means of engine measures, additional heating or adequate engine load minimizes pollutant emissions, wear and specific consumption.

The speed control during engine warm-up can be implemented, for example, in controlled operation. The engine speed can be adjusted by adjusting the ignition angle, with slow throttle change. Changing the throttle will change the amount of air available while the ignition angle will directly affect the combustion efficiency. Both channels have, inter alia, on their effect on the speed of an influence on the air-fuel ratio in the cylinder. This can in turn be controlled via a separate single-input controller (SISO), which changes the injected fuel mass.

During warm-up, the firing angle can be pre-controlled relatively late, which leads to a poor combustion efficiency in late combustion situations, but desirably leads to hot exhaust gases, which has the effect of rapid heating of the catalyst.

At late firing angles, however, there is a relatively high variability in the combustion, which can lead to a high variability in the rotational speed. Since the speed controller as mentioned above also has an influence on the air-fuel ratio, the corresponding feedback control is made more difficult.

Disclosure of the invention

Against this background, the present invention proposes to use a multi-variable feedback control based on combustion characteristics for engine warm-up. According to the invention, therefore, a method for operating an internal combustion engine during warm-up as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

With multi-variable control in engine warm-up, the aim is to control the engine even with late combustion conditions with little cross-flow of speed and air-fuel ratio on each other. The three preferred control paths (air path, fuel path and ignition angle path) can then be changed in a coordinated manner. According to the invention therefore as output variables of the control (manipulated variables) are at least two variables from a size characterizing an air quantity (eg the air volume itself or a throttle position), a size characterizing an injection quantity (eg the injection quantity itself or an injection time) and a variable characterizing an ignition angle ( eg the ignition angle itself) used.

According to the invention, controlled variables (ie variables whose actual value is regulated to a desired value) are at least two variables from a variable characterizing an engine speed (eg the engine speed itself or an indicated mean pressure), a variable characterizing an air-fuel ratio during combustion (eg Lambda value) as well as a combustion characteristic characterizing size (eg ignition angle) used. The actual values of these variables form the feedback of the control (actual values) and can be e.g. sensory or computationally determined. A sensory determination of the speed and the air-fuel ratio (lambda) is common. The combustion position can be acquired, for example, via cylinder-specific pressure sensors in the combustion chamber or indirectly via the speed signal, for example, by determining it from the speed curve by means of an energy calculation before and after the combustion. Since the air-fuel ratio and the combustion position are cylinder-specific variables, a cylinder-specific control can be implemented. However, this does not preclude a non-cylinder-specific regulation. In principle, however, each of the controlled variables can be regulated individually for each cylinder or across cylinders.

The advantage of a multi-variable control is that a coordinated operation of the actuators a more precise control is possible, especially in transient phases. Since the air-fuel ratio has a major impact on pollutant emissions during warm-up (the catalyst does not work at low temperatures), this benefit can lead to a reduction in emissions. The engine warm-up as an area of application of the invention comprises in particular an operating state in which the catalyst is still not warmed up to an operating temperature. The internal combustion engine is thus operated in particular according to the invention, as long as the catalyst is not warmed up to an operating temperature and / or as long as the driver desired torque in an operation according to the invention can be displayed. If the driver wishes more torque than the late-set ignition angle allows, it must be set early and the operation according to the invention is terminated.

The advantages of the invention are particularly evident in transient engine operation, which is characterized by rapidly changing setpoint values of the controlled variables.

The multi-variable control makes it possible to maintain narrower limits of the controlled variables by the corresponding setpoint values in that the actuators can be changed in a coordinated manner and thus cross-influences of the different control paths can be reduced. Furthermore, the multi-variable control leads to a more stable engine operation in late combustion situations and lean air-fuel ratios, which are quite necessary in engine warm-up. These operating points are characterized by a high variation of consecutive combustion processes and, accordingly, compliance with narrower limits around the setpoints is helpful in stabilizing engine operation. As a consequence, the multi-variable control allows a reduction in emissions during warm-up, as deviations of the air-fuel ratio from the corresponding setpoint, which lead to increased emissions, are reduced.

The control of cylinder individual combustion characteristics, e.g. of the indicated mean pressure, combustion position, or cylinder-individual air-fuel ratio, allows one, several, or all of these characteristics to be equalized in each cylinder, i. to the same setpoint. This supports stable engine operation in areas where non-cylinder control is affected by the natural occurrence of individual cylinder differences. The more stable engine operation in turn allows a later combustion position, which leads to a faster heating of the catalyst. The equalization of the cylinder-individual air-fuel ratio leads in addition to a reduction of pollutant emissions.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically by means of embodiments in the drawing and will be described below with reference to the drawing.

list of figures

• 1 shows a schematic representation of an internal combustion engine with a control unit.
• 2 Fig. 2 shows schematically in a block diagram a preferred embodiment of a controller with advantageous input and output variables for implementing the invention.
• 3 Figure 3 shows schematically in a block diagram a preferred embodiment of an extended controller with advantageous input and output sizes for implementing the invention.
• 4 schematically shows in a block diagram a preferred embodiment of a controller with advantageous input and output variables for implementing the invention, wherein an equalization of a converted mechanical energy per combustion takes place.
• 5 Fig. 2 shows schematically in a block diagram a preferred embodiment of a controller with advantageous input and output variables for implementing the invention.
• 6 schematically shows in a block diagram a preferred embodiment of a regulator with advantageous input and output variables for implementing the invention, wherein an equalization of a combustion position takes place.

Embodiment (s) of the invention

In 1 is an internal combustion engine (internal combustion engine) 1 shown in which a piston 2 in a cylinder 3 can be moved up and down. The cylinder 3 is with a combustion chamber 4 provided to the over valves 5 an intake pipe 6 and an exhaust pipe 7 are connected.

The intake pipe 6 is with the exhaust pipe 7 via an exhaust gas recirculation valve 13 with a valve flap 13a connected as an actuator for external exhaust gas recirculation. The valve flap 13a is with a signal EGR from a control unit (ECU) 16 controllable.

Furthermore, with the combustion chamber 4 one with a signal TI controllable injection valve 8th and one with a signal ZW controllable spark plug 9 connected. The internal combustion engine 1 according to 1 is based on the spark ignition process. It should be understood, however, that the invention is not dependent on the method of ignition of the internal combustion engine and is well suited for internal combustion engines with auto-ignition.

The combustion chamber 4 is with a cylinder pressure sensor 15 equipped with a signal P for the pressure in the combustion chamber.

In the intake pipe 6 are a boost pressure sensor 18 that a signal LD which indicates the boost pressure in the intake manifold and a throttle valve 12 whose rotational position by means of a signal DK is adjustable, housed. Between the air mass sensor 10 and the throttle 12 For turbocharged engines, the supercharger of a turbocharger would be arranged.

The intake pipe 6 is still with an air mass sensor 10 and the exhaust pipe 7 with a lambda sensor 11 Mistake. The air mass sensor 10 measures the air mass of the intake pipe 6 supplied fresh air and generated in response to a signal LM , The lambda sensor (lambda probe) 11 measures the oxygen content of the exhaust gas in the exhaust pipe 7 and generates a signal lambda (in dependence thereon). λ ). The lambda probe 11 is an exhaust system (not shown) including a catalyst, for example. 3-way catalyst downstream. In turbocharged engines, the turbine of a turbocharger would be installed after the lambda probe.

In operation, the driven piston becomes a crankshaft 14 offset in a rotational movement over which ultimately the wheels of the motor vehicle are driven.

It is understood that an internal combustion engine with external or self-ignition may have more than one cylinder, which are assigned to the same crankshaft and the same exhaust pipe and form an exhaust bank.

The control unit 16 is provided with a microprocessor which has stored in a storage medium, in particular in a read-only memory (ROM), a program which is adapted to the entire control and / or regulation of the internal combustion engine 1 perform.

The control unit 16 is acted upon by input signals representing operating variables of the internal combustion engine measured by means of sensors. For example, the controller 16 with the air mass sensor 10 , the lambda sensor 11 , the cylinder pressure sensor 15 and the boost pressure sensor 18 connected. Furthermore, the control unit 16 with an accelerator pedal sensor 17 connected, which generates a signal FP indicating the position of a driver operable accelerator pedal and thus the requested by the driver torque. The control unit 16 generates output signals with which the behavior of the internal combustion engine via actuators 1 can be influenced according to the desired control and / or regulation. For example, the controller 16 with the EGR valve 13 , the injector 8th , the spark plug 9 and the throttle 12 connected and generates the signals required for their control EGR . TI . ZW and DK ,

The control unit 16 is set up in particular for carrying out a method according to the invention. In a preferred embodiment of the invention, during a warm-up of the internal combustion engine, the throttle valve 12 , the injection valve 8th and the spark plug 9 from the controller 16 driven according to a preferred embodiment of the invention.

In the 2 to 6 are different embodiments of the invention, which may be implemented in the control unit, illustrated by means of different control schemes, wherein the same elements and input and output variables are not explained several times. In this case, setpoints with the index ref and actual values with the index meas are designated.

Certain combustion characteristics, such as the combustion point (center of combustion, COC ), the converted mechanical energy per combustion (characterized by the indicated mean pressure, PMI ) or the air-fuel ratio during combustion (lambda) can be determined individually for each cylinder or averaged over all cylinders.

However, due to differences in the composition of the filling of individual cylinders, not all combustion characteristics can be controlled to the same value simultaneously in all cylinders. In the case of different filling, for example, an identical air-fuel ratio leads to different indicated work per working cycle with an identical combustion position. The requirement under these conditions nevertheless a regulation of different To perform combustion characteristics simultaneously, it can be satisfied that a certain characteristic, such as the combustion position, is controlled only in the middle over all cylinders, while other characteristics are controlled individually for each cylinder.

Consequently, different types are conceivable in which the multi-variable control can be implemented based on combustion characteristics, of which some examples are explained below.

2 shows an exemplary embodiment of a multi-variable controller C for controlling the controlled variables engine speed ω _e in [rad / s], air-fuel ratio during combustion λ and combustion position COC in [° CA] (crank angle, CA ) to one associated setpoint using the manipulated variables throttle position u _α in [%], injection duration u _φ in [ms] and ignition angle u _ζ in [° CA]. The multi-variable controller C itself can be designed according to conventional criteria and can be used for known multivariable control methods.

The controller structure shown here is based on the fact that the combustion characteristics can be acquired averaged over all cylinders. The manipulated variables are set to the same values for all cylinders. Thus, there is a single controller for a plurality of individual cylinders. The advantage of this controller structure is the ability to change the actuators in a coordinated manner.

3 shows a further exemplary embodiment of a multi-variable controller C for controlling the cross-cylinder control variable engine speed ω _e and the cylinder-specific controlled variables air-fuel ratio during combustion λ _i (i: index of a cylinder, here for example 1 to 3) and combustion position COC _i to each one associated setpoint using the cross-cylinder control variable throttle position u _α and the cylinder-specific manipulated variables injection time u _{φ, i} and ignition angle u _{ζ, i} ,

This regulator structure assumes that the combustion characteristics λ _i and COC _i can be purchased individually for each cylinder. This allows a cylinder-specific control, which can lead to a more stable engine operation during warm-up, because cylinder-individual differences can be reduced and correspondingly results in a quieter engine operation. At the same time, the actuators are changed in a coordinated manner, which allows the regulation of the air-fuel ratio in particular within narrower limits around the setpoint. Also in this case, there is a single controller C for a plurality of individual cylinders i = 1, ..., 3. As already explained, the multi-variable controller C even be designed according to conventional criteria and use known Mehrgrößenregelungsverfahren. It may be, for example, a linearized standard normal-form controller.

The ability to individually control specific combustion characteristics, while others are averaged over multiple cylinders, allows the use of individual cylinder regulators, all of which may have the same structure.

An exemplary embodiment will be described below with reference to FIG 4 and 5 explained. It shows 4 a preferred control scheme with an equality of the cylinder-specific indexed mean pressures PMI _i .

In the 4 shown regulator structure is used to control the cylinder-specific control variables indexed mean pressure PMI _i , Air-fuel ratio λ _i and combustion position COC _i to each one associated setpoint using the cross-cylinder control variable throttle position u _α and the cylinder-specific manipulated variables injection duration u _{φ, i} and ignition angle u _{ζ, i} , The control is divided into several blocks.

A regulator C ₀ Used to determine a setpoint for the indicated mean pressure from the speed. This setpoint PMI _ref is with cylinder-specific actual values PMI _{i, meas} and the resulting control deviation in each case one of three cylinder-specific controllers CYL1 . CYL2 . CYL3 fed. The setpoint can be determined, for example, via a simple feedforward control, which is a speed request ω _{e, ref} converted into a requirement for the indexed work.

The combustion situation COC In this case, the second combustion characteristic is averaged over all cylinders in a block mean before the corresponding value is used as the averaged actual value for regulation. It is also conceivable to use the maximum value of the individual combustion positions as input to the regulator.

The air-fuel ratio λ _ref as a third combustion characteristic is also with individual cylinder actual values λ _{i, meas} and the resulting control deviation in each case one of the three cylinder-specific controllers CYL1 . CYL2 . CYL3 fed.

Since the throttle, which is the actuator for the air path, usually can not be set individually for each cylinder, the requirements u _{α, i} the different cylinder-specific controller averaged in a block mean before it as a mean value u _α be sent to the actuator. In stationary operation, this averaging leads to differences between the individually required actuator positions and the effectively regulated value. However, this fact is irrelevant, since the individual controllers receive zero values as inputs of the individual control errors in stationary operation. In transient operation, the requirements of the individual controllers may be slightly different, but the trends in actuator setpoint changes are the same for all cylinders, ie, the trend of the averaged value is very similar to the required individual trends.

An advantage of this regulator structure is that an identical, relatively simple regulator (in this case the 3 × 3 dimension) can be used for all cylinders. That regardless of the number of cylinders that the engine has, the same controller can be used, one per cylinder.

The equality of indicated work per cycle achieved by this regulator structure results in quiet engine operation since torque generation is evenly distributed across all cylinders.

An exemplary structure of such a regulator cyl i is in 5 shown. In the standard state space representation shown, the controller (oBdA) comprises a control matrix B , an integrator ∫, an observation matrix C , a system matrix A and a transit matrix D ,

Another exemplary embodiment will be described below with reference to FIG 5 which illustrates a preferred control scheme with an equalization of the cylinder-specific combustion position COC _i shows.

In the 6 shown controller structure is again used to control the cross-cylinder control variable engine speed ω _e and the cylinder-specific controlled variables air-fuel ratio λ _i and combustion position COC _i to each one associated setpoint using the cross-cylinder control variable throttle position u _α and the cylinder-specific manipulated variables injection duration u _{φ, i} and ignition angle u _{ζ, i} , The control is in three cylinder-individual blocks CYL1 to CYL3 divided up.

The use of this controller structure is simple, since the structure of the individual controllers is identical and the system is therefore easily scalable. For engines with a different number of cylinders, the appropriate number of controls can be easily adjusted. The ability to control the combustion position in all cylinders to an identical (and especially late) value allows rapid heating of the catalyst.

Claims (13)

Method for operating an internal combustion engine (1) during warm-up, wherein at least two controlled variables selected from a variable characterizing an engine speed (ω _e ), a variable characterizing an air-fuel ratio during combustion (λ) and a combustion position (COC) in the context of multivariable control, at least two manipulated variables selected from a variable (u _α ) characterizing an air quantity, a variable (u _{φ, i} ) characterizing an injection quantity and a variable characterizing an ignition angle (u _ζ, ) be determined. Method according to Claim 1 , wherein the internal combustion engine (1) has at least two cylinders (3). Method according to Claim 2 in which the variable characterizing the engine speed (ω _e ) is regulated individually or across cylinders and / or wherein the variable characterizing the air / fuel ratio during combustion (λ) is controlled individually or cross-cylinder and / or wherein the combustion position (COC) characteristic size is controlled cylinder-specific or cross-cylinder. Method according to Claim 3 in which the variable characterizing the engine speed (ω _e ) is controlled to the same desired value for each cylinder individually and / or the variable characterizing the air-fuel ratio during combustion (λ) is individually adjusted to the same desired value and / or the combustion position ( COC) characterizing size cylinder is individually controlled to the same setpoint. Method according to Claim 3 in which the variable characterizing the engine speed (ω _e ) is regulated across cylinders to a setpoint value and wherein the variable characterizing the air / fuel ratio during combustion (λ) is individually controlled to the same setpoint value and the variable characterizing the combustion position (COC) cylinder is individually controlled to the same setpoint. Method according to one of Claims 2 to 5 , wherein for each of the at least two cylinders (3) a separate controller (Cyl1, Cyl2, Cyl3) is used. Method according to Claim 6 in which the quantities (u _{α, 1} , u _{α, 2} , _{uα, 3} ) output by each of the regulators are calculated into a common manipulated variable (u _α ). Method according to one of the preceding claims, wherein an indexed mean pressure (PMI) is regulated as the variable characterizing the engine speed (ω _e ). Method according to one of the preceding claims, wherein an actual value of a combustion characteristic (COC) characterizing size by means of a cylinder pressure sensor (15) is determined. Method according to one of the preceding claims, which is carried out as long as a catalytic converter connected downstream of the internal combustion engine is not yet warmed up to an operating temperature and / or as long as a torque desired by the driver can be displayed in the context of the multi-variable control. Arithmetic unit (16), which is adapted to perform a method according to any one of the preceding claims. Computer program that causes a computing unit (16) to perform a method according to one of Claims 1 to 10 when executed on the computing unit. Machine-readable storage medium with a computer program stored thereon Claim 12 ,

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