EP1608861A1 - Device for controlling an internal combustion engine - Google Patents

Abstract

The invention relates to a device for controlling an internal combustion engine, comprising a first regulator, whose regulating difference is the difference of an actual value (D_LAM_I) and an estimated value (D_LAM_I_EST) of individual cylinder deviation of the air/fuel ratio from a preset air/fuel ratio. The first regulator also has an integral regulating parameter, its manipulated variable being a first estimated value (EST1). A second regulator is also provided, the regulating difference of which is the first estimated value (EST1). Said regulator has a proportional regulating parameter whose manipulated variable is an individual cylinder lambda regulating factor (LAM_FAC_I). A PT1 filter is additionally provided, by means of which a second estimated value (EST2) is determined through PT1 filtering of the individual cylinder lambda regulating factor (LAM_FAC_I). A unit is also provided, said unit determining the estimated value (D_LAM_I_EST) of the individual cylinder deviation of the air/fuel ratio from the preset air/fuel ratio based on the difference between the first and the second estimated values (EST1, EST2). Depending on the individual cylinder lambda regulating factor (LAM_FAC_I), a fuel mass that is to be proportioned (MFF) is corrected and the thus corrected fuel mass to be proportioned (MFF_COR) is considered in order to determine a regulating signal for the corresponding injection valve.

Description

description

Device for controlling an internal combustion engine

The invention relates to a device for controlling an internal combustion engine with a plurality of cylinders and the injection valves assigned to the cylinders, which measure fuel, with an exhaust gas probe which is arranged in an exhaust gas tract and whose measurement signal is characteristic of the air / fuel ratio in the respective cylinder.

Ever stricter legal regulations regarding permissible pollutant emissions from motor vehicles in which internal combustion engines are arranged make it necessary to keep the pollutant emissions when operating the internal combustion engine as low as possible. On the one hand, this can be done by reducing the pollutant emissions that arise during the combustion of the air / fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas aftertreatment systems are used in the internal combustion engine, which convert the pollutant emissions that are generated in the respective cylinders during the combustion process of the air / fuel mixture into harmless substances. For this purpose, catalysts are used that convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances. Both the targeted influencing of the generation of the pollutant emissions during the combustion and the conversion of the pollutant components with a high efficiency by means of an exhaust gas catalytic converter require a very precisely set air / fuel ratio in the respective cylinder.

DE 199 03 721 C1 discloses a method for a multi-cylinder internal combustion engine for the cylinder-selective control of an air / fuel mixture to be burned, in where the load values for different cylinders or cylinder groups are sensed and regulated separately. Each cylinder is assigned an individual controller, which is designed as a PI or PID controller, the controlled variable of which is a cylinder-specific lambda value and the reference variable of which is a cylinder-specific target value of the lambda. The manipulated variable of the respective controller then influences the fuel injection in the respectively assigned cylinder.

A method for controlling an internal combustion engine is also known from EP 0 802 316 B1, with a controller designed as a PID controller, the control variable of which is an estimated value of a cylinder-specific air / fuel ratio determined by an observer and the control variable of which is a correspondingly converted mean lambda control factor is rated with a target air / fuel ratio. The average lambda control factor is determined by averaging all cylinder-specific lambda control factors. Each cylinder-specific lambda control factor is the manipulated variable of the respective PID controller assigned to the cylinder. A corrected injection time is determined by multiplying an injection time period specified for all cylinders of the internal combustion engine by the respective cylinder-individual lambda control factor.

The object of the invention is to provide a device for controlling an internal combustion engine, which ensures precise control of the internal combustion engine.

The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims.

The invention is characterized by a device for controlling an internal combustion engine with a plurality of cylinders and the injectors assigned to the cylinders, which measure fuel, with an exhaust gas probe which is arranged in an exhaust tract and whose measurement signal is characteristic of the air / fuel ratio in the respective cylinder. A first controller is provided, the control difference of which is a difference between an actual value and an estimated value of a cylinder-specific deviation of the air / fuel ratio from a predeterminable air / fuel ratio. The first controller also has an integral control parameter. The manipulated variable of the first controller is a first estimate. Furthermore, a second controller is provided, the control difference of which is the first estimated value and which has a proportional control parameter and whose manipulated variable is a cylinder-specific lambda control factor. Furthermore, a PTI filter is provided, by means of which a second estimated value is determined by PTI filtering of the cylinder-specific lambda control factor. A unit is provided which determines the estimated value of the cylinder-specific deviation of the air / fuel ratio from the specifiable air / fuel ratio from the difference between the first and the second estimated value.

A block is provided which determines a fuel mass to be supplied, which is to be supplied to the respective cylinder of the internal combustion engine, depending on a load size and in which the fuel mass to be supplied is then corrected depending on the cylinder-specific lambda control factor. Furthermore, an actuating signal for controlling the injection valve is generated in the block depending on the corrected fuel mass to be supplied.

The possible control speed can be increased by means of the second controller with a P component, compared to when the second controller is designed as a further I controller which is connected downstream of the first controller. It also points the device according to the invention has a high level of robustness with a very high control accuracy. This is due, among other things, to the fact that the second manipulated value takes into account the actual manipulated variable by means of which the injection valve is controlled. The application effort is minimal in the device according to the invention.

The invention is further characterized by a device for controlling the internal combustion engine, in which the second is supplied to the controller as a control difference, a difference between an actual value and an estimated value of the cylinder-specific deviation of the air / fuel ratio from a predeterminable air / fuel ratio. The second controller liat another integral control parameter. Its manipulated variable is the cylinder-specific lambda control factor. This device also ensures that the second controller can be operated at a high control speed and that the device is extremely robust with high control accuracy. The application effort for the device according to the invention is low.

In an advantageous development of the invention, a block is provided which adjusts the first estimated value by means of a weighting factor before it is sent to the unit. Furthermore, a further block is provided which adjusts the cylinder-specific lambda control factor by means of a further weighting factor before it is fed to the PTI filter. In this way, the cylinder-specific air / fuel ratio can be determined even more precisely when determining the estimated value of the cylinder-specific deviation of the air / fuel ratio, in particular with regard to different lengths of the outlets of the cylinders to that assigned to all cylinders or at least to all of them Exhaust gas probe assigned to cylinders of a cylinder bank and with regard to a mixing of the exhaust gas packets in the area of the exhaust gas probe.

In a further advantageous development of the invention, the predeterminable air / fuel ratio is an average air / fuel ratio of all cylinder-specific air / fuel ratios. The device can thus ensure very precisely that the air / fuel ratios in all cylinders of the internal combustion engine are equal.

In a further advantageous embodiment of the invention, a third controller is provided, the reference variable of which is a predetermined air / fuel ratio for all cylinders of the internal combustion engine, the controlled variable of which is the mean air / fuel ratio of all cylinder-specific air / fuel ratios and the manipulated variable Lambda control factor is. In this way, the specified air / fuel ratio can be set simply and precisely in all cylinders.

A further advantageous development of the invention provides that the proportional control parameter or the further integral control parameter of the second controller is predetermined as a function of the load. The control quality can then simply be increased, since the different mixing of the exhaust gas packets which result from the individual combustions of the air / fuel mixture in the respective cylinders Z1-Z4 can easily be taken into account.

Embodiments of the invention are explained below with reference to the schematic drawings. Show it:

1 shows an internal combustion engine with a control device, FIG. 2 shows a block diagram of the control device, Figure 3 shows another block diagram of the control device.

Elements of the same construction and function are identified with the same reference symbols in all figures.

An internal combustion engine (FIG. 1) comprises an intake tract 1, an engine block 2, a cylinder head 3 and an exhaust tract 4. The intake tract preferably comprises a throttle valve 11, further a collector 12 and an intake manifold 13, which leads to a cylinder ZI via a Inlet channel is led into the engine tolock. The engine block further comprises a crankshaft 21 which is coupled to the piston 24 of the cylinder ZI via a connecting rod 25.

The cylinder head comprises a valve train with a gas inlet valve 30, a gas outlet valve 31 and valve drives 32, 33. The cylinder head 3 further comprises an injection valve 34 and a spark plug 35. Alternatively, the injection valve can also be arranged in the intake duct.

The exhaust tract 4 comprises a catalytic converter 40, which is preferably designed as a three-way catalytic converter. An exhaust gas recirculation line can be led from the exhaust tract 4 to the intake tract 1, in particular to the collector 12.

Furthermore, a control device 6 is provided, to which sensors are assigned, which detect different measured variables and each determine the measured value of the measured variable. Depending on at least one of the measured variables, the control device 6 determines manipulated variables, which are then converted into one or more actuating signals. Control of the actuators can be implemented using appropriate actuators.

The sensors are a pedal position sensor 71, which detects the position of an accelerator pedal 7, an air mass meter 14, which detects an air mass flow upstream of the throttle valve 11, a temperature sensor 15 which detects the intake air temperature, a pressure sensor 16 which detects the intake manifold pressure, a crankshaft angle sensor 22 which detects a crankshaft angle, a further temperature sensor 23 which detects a coolant temperature, a camshaft angle sensor 36, which detects the camshaft angle and an exhaust gas probe 41 which detects a residual oxygen content of the exhaust gas and whose measurement signal is characteristic of the air / fuel ratio in the cylinder ZI. The exhaust gas probe 41 is preferably designed as a linear lambda probe and thus generates a measurement signal proportional to this over a wide range of the air / fuel ratio.

Depending on the embodiment of the invention, any subset of the sensors mentioned or additional sensors can be present.

The actuators are, for example, the throttle valve 11, the gas inlet and gas outlet valves 30, 31, the injection valve 34, the spark plug 35 and the pulse charging valve 18.

In addition to the cylinder ZI, further cylinders Z2-Z4 are also provided, to which corresponding actuators are then assigned. An exhaust gas probe is preferably assigned to each bank of cylinders.

A block diagram of the control device 6, which can also be referred to as a device for controlling the internal combustion engine, is shown in FIG. 2. The blocks of the control device 6 relevant in connection with the invention are shown in the block diagram. A block B1 corresponds to the internal combustion engine. A block B2 is supplied with an individually determined air / fuel ratio LAM_I as an input variable. The individually determined air / fuel ratio LAM_I is derived from the measurement signal of the exhaust gas probe 41 within a predeterminable time or crankshaft angle window, which is assigned to the exhaust gas packet generated in the respective cylinder.

In block B2, an average air / fuel ratio LAM_MW is determined by averaging the cylinder-individually determined air / fuel ratios LAM_I of all cylinders ZI to Z4 of the internal combustion engine. Furthermore, an actual value D_LAM_I of a cylinder-specific air / fuel ratio deviation is determined in block B2 from the difference between the mean air / fuel ratio LAM_MW and the cylinder-individually determined air / fuel ratio LAM_I.

The difference between the actual value D_LAM_I and an estimated value D_LAM_I_EST of the cylinder-specific air / fuel ratio deviation is determined in a summing point S1 and then assigned to a block B3, which comprises a first controller and whose input variable is then the control difference of the first controller. The first controller is designed as an integral controller, that is to say it has an integral control parameter. The manipulated variable of the first controller is a first estimate EST1.

The first estimate EST1 is preferably multiplied in a block B4 by a weighting factor, which takes into account that the control difference at the input of the first controller is also influenced by exhaust gas packets from other cylinders ZI to Z4 due to the different lengths of the outlets of the cylinders ZI to Z4 Exhaust gas probe 41 and a mixing of the exhaust gas packets of the individual cylinders ZI to Z4 in the area the exhaust gas probe 41. The first estimated value EST1 thus corrected is then fed to a summing point S2. Alternatively, however, the first estimated value EST1 can also be fed directly from the block B3 to the summing point S2.

A block B5 comprises a second controller, the control difference of which is the first estimated value EST1 and which is designed as a P controller, that is to say has a proportional control parameter. The manipulated variable of the second controller is a cylinder-specific lambda control factor LAM_FAC_I. This cylinder-specific lambda control factor LAM_FAC_I is preferably corrected via a block B6, which corresponds to block B4, by means of a further weighting factor, and then fed to a block B7, which comprises a PTI filter that filters the cylinder-specific lambda control factor LAM_FAC_I and thus a second one at its output EST2 provides estimate. In the summing point S2, the estimated value D_LAM_I_EST of the cylinder-specific air / fuel ratio deviation is determined from the difference between the first and second estimated values EST1 _r EST2.

A third controller is provided in a block B8, the control variable of which is an air / fuel ratio that is predetermined for all cylinders of the internal combustion engine and the control variable of which is the average air / fuel ratio LAM_MW. The manipulated variable of the third controller is a lambda control factor LAM_FAC_ALL. The third controller therefore has the task that, when viewed across all cylinders ZI to Z4 of the internal combustion engine, the predetermined air / fuel ratio is set. Alternatively, this can also be achieved in that in block B2 the actual value D__LAM_I of the cylinder-specific air / fuel ratio deviates from the difference between the air / fuel ratio specified for all cylinders ZI to Z4 of the internal combustion engine and the cylinder-specific air / fuel ratio LAM_I is determined. In in this case the third controller of block B8 can then be omitted.

In block B9, a fuel mass MFF to be metered is determined as a function of an air mass flow MAF in the respective cylinders ZI to Z4 and, if appropriate, the rotational speed N and a setpoint LAM_SP of the air / fuel ratio for all cylinders Z1-Z4.

A corrected fuel mass MFF_COR to be metered is determined in the multiplication point M1 by multiplying the fuel mass MFF to be metered, the lambda control factor LAM_FAC_ALL and the cylinder-specific lambda control factor LÄM_FAC__I. Depending on the corrected fuel mass MFF_COR to be metered, an actuating signal is then generated with which the respective injection valve 34 is activated.

In addition to the controller structure shown in the block diagram in FIG. 2, corresponding controller structures B_Z2 to B_Z4 are provided for the respective further cylinders Z2 to Z4 for each additional cylinder ZI to Z4.

The second estimated value EST2 compensates for the controlled system dynamics, that is, the dynamics of the internal combustion engine, in such a way that the actuating actions of the first and second controllers are included in the determination of the estimated value D_LAM_I_EST of the cylinder-specific air / fuel ratio deviation. The controller structure and a suitable parameterization of the first and second controllers can ensure that the remaining control deviation between the fuel masses actually metered into the individual cylinders ZI to Z4 approaches zero. Because the second controller, the controlled variable of which is the first estimated value EST1, has no further I component, an increase in the possible control speed and an increase in the robustness of the control structure is achieved compared to the case in which the second controller also has an I- Share.

The weighting factor of block B6 can also be provided with a negative sign. This then has the consequence that the second estimated value EST2 is added in the summing point S2.

The weighting factors of the blocks B4 and / or Bβ are also preferably dependent on the load size, which is preferably the air mass flow MAF in the respective cylinder Z1-Z4 and / or the rotational speed N.

Furthermore, the control parameter of the second controller, in this case the proportional control parameter, can also be dependent on the load size, which is preferably the air mass flow MAF in the respective cylinder Z1-Z4 and / or the speed N. The control quality can then simply be increased since the different mixing of the exhaust gas packets which result from the individual losses of the air / fuel mixture in the respective cylinders Z1-Z4 is taken into account.

An alternative embodiment of the control device 6 is described with reference to the block diagram of FIG. 3, only the differences from the block diagram according to FIG. 2 being discussed below. In contrast to the second controller in FIG. 2, the second controller in a block B5 'has the difference between the actual value D_LAM_I and the estimated value LAM_I_EST of the cylinder-specific air / fuel ratio deviation as the control difference. The second controller of block B5 'also has a further integral control parameter, which is preferably chosen such that it corresponds to the product of the integral control parameter of the first controller of block B3 and the proportional control parameter of the second controller of block B5 in FIG. The manipulated variable of the second controller is also the cylinder-specific lambda control factor LAM_FAC_I.

Both the cylinder-specific lambda control factor LAM_FAC_I and the lambda control factor LAM_FAC_ALL can also be corresponding additive correction values for the fuel mass MFF to be metered.

Claims

claims 1. Device for controlling an internal combustion engine with a plurality of cylinders (Zl ... Z4) and the injection valves (34) assigned to the cylinders, which measure fuel, with an exhaust gas probe (41) which is arranged in an exhaust tract (4) and whose measurement signal is characteristic is for the air / fuel ratio in the respective cylinder (ZI ... Z4) at which - A first controller is provided, whose control difference is a difference between an actual value (D_LAM_I) and an estimated value (D_LAM__I_EST) of a cylinder-specific deviation of the air / fuel ratio from a predeterminable air / fuel ratio, which has an integral control parameter and the like Manipulated variable is a first estimate (ESTl), a second controller is provided, the control difference of which is the first estimated value (EST1) and which has a proportional control parameter and the manipulated variable is a cylinder-specific lambda control factor (LAM_FAC__I), a PTl filter is provided, by means of which a second estimated value is determined by PTl filtering of the cylinder-specific lambda control factor (LAM_FAC_I), a unit is provided which determines the estimated value (D_LAM_I_EST) of the cylinder-specific deviation of the air / fuel ratio from the difference between the first and second estimated values (EST1, EST2), - A block is provided which determines a fuel mass (MFF) to be supplied, which is to be supplied to the respective cylinder (Z1-Z4) of the internal combustion engine, depending on a load size and in which the fuel mass (MFF) to be supplied is corrected depending on the individual cylinder Lambda control factor (LAM_FAC_I), which generates a control signal for controlling the injection valve (34) depending on the corrected fuel mass to be supplied (MFF_C0R). 2. Device for controlling an internal combustion engine with a plurality of cylinders (Zl ... Z4) and the injection valves (34) assigned to the cylinders, which measure fuel, with an exhaust gas probe (41) which is arranged in an exhaust tract and whose measurement signal is characteristic of the Air / fuel ratio in the respective cylinder (Z1 ... Z4) at which - A first controller is provided, whose control difference is a difference between an actual value (D_LAM_I) and an estimated value (D__LAM_I_EST) of a cylinder-specific deviation of the air / fuel ratio from a predeterminable air / fuel ratio, which has an integral control parameter and its manipulated variable is a first estimate (ESTl), - A second controller is provided, the control difference of which is a difference between an actual value (D_LAM_I) and an estimated value (D_LAM_I_ST) of a cylinder-specific deviation of the air / fuel ratio from a predeterminable air / fuel ratio, which has a further integral control parameter and whose manipulated variable is a cylinder-specific lambda control factor (LAM_FAC_I), a PTl filter is provided, by means of which a second estimated value is determined by PTl filtering of the cylinder-specific lambda control factor (LAM_FAC_I), a unit is provided which determines the estimated value (D_LAM_I_EST) of the cylinder-specific deviation of the air / fuel ratio from the difference between the first and second estimated values (EST1, EST2), - A block is provided which determines a fuel mass (MFF) to be supplied, which is to be supplied to the respective cylinder (Z1-Z4) of the internal combustion engine, depending on a load size and in which the fuel mass (MFF) to be supplied is corrected as a function of the cylinder-specific lambda control factor (LAM_FAC_I), and which generates a control signal for controlling the injection valve (34) depending on the corrected fuel mass to be supplied (MFF_C0R). 3. Device according to one of the preceding claims, characterized in that a block (B4) is provided which adjusts the first estimated value (EST1) by means of a weighting factor before it is fed to the unit, and in that a further block (B6) is provided, which adjusts the cylinder-specific lambda control factor (LAM_FAC_I) by means of a further weighting factor before it is fed to the PTl filter. 4. Device according to one of the preceding claims, characterized in that the specifiable air / fuel ratio is an average air / fuel ratio (LAM_MW) of all cylinder-specific air / fuel ratios. 5. Device according to one of the preceding claims, characterized in that a third controller is provided, the reference variable is a predetermined air / fuel ratio for all cylinders of the internal combustion engine, the control variable is the average air / fuel ratio of all cylinder-specific air / fuel Conditions and whose manipulated variable is a lambda control factor (LAM_FAC_ALL). 6. Device according to one of the preceding claims, characterized in that the proportional control parameter or the further integral control parameter of the second controller is predetermined depending on the load.