WO2000008308A1

WO2000008308A1 - Method for controlling an internal combustion engine

Info

Publication number: WO2000008308A1
Application number: PCT/DE1999/002397
Authority: WO
Inventors: Andreas Hartke; Achim Koch
Original assignee: Siemens Aktiengesellschaft
Priority date: 1998-08-03
Filing date: 1999-08-02
Publication date: 2000-02-17
Also published as: DE19835019C2; DE19835019A1

Abstract

An internal combustion engine comprises several cylinders to each of which actuators are assigned which act on charge change valves and to each of which one injection valve is assigned which is arranged in the cylinder head in such a way that the fuel is measured directly into the corresponding cylinder of the internal combustion engine. A setpoint of the air mass of an individual cylinder is calculated. The actuators of said individual cylinder are controlled in accordance with the air mass setpoint for said cylinder. An actual value of the air mass in the individual cylinder is determined during or after the intake stroke of said cylinder. A setpoint of the fuel mass for the individual cylinder is calculated in accordance with the air mass actual value and the injection valve of the single cylinder is controlled in accordance with the fuel mass setpoint.

Description

description

Method for controlling an internal combustion engine

The invention relates to a method for controlling an internal combustion engine, in particular an internal combustion engine with direct fuel injection and a throttle-free load control.

With spark-ignited internal combustion engines, it is known that

To arrange fuel injection valve in the cylinder head such that the fuel is metered directly into the respective cylinder of the internal combustion engine. Internal combustion engines of this type are operated in partial load operation with a large excess of air in the air / fuel mixture. This ensures a high degree of efficiency of the internal combustion engine even in part-load operation, since the intake air is throttled only slightly by a throttle valve. In operating areas close to or at full load, however, such internal combustion engines are operated with an almost stoichiometric air / fuel ratio and the load is adjusted by appropriately controlling the air mass. For this purpose, the air flow in the intake tract of the internal combustion engine must be throttled by a throttle valve. Since there is a large volume between the throttle valve and an inlet on the cylinder, an adjustment of the throttle valve only has an effect on the air mass flow of the respective cylinder after a delay time. Furthermore, in internal combustion engines of this type, throttling of the intake air is necessary in the lowest load range, for example in idle operation, since otherwise the

Excess air of the air / fuel mixture in the cylinder would be so high that reliable and complete combustion of the fuel is no longer guaranteed. Furthermore, internal combustion engines are known which have actuators which act on the gas exchange valves of the cylinders of the internal combustion engine. The actuators control the start of stroke and / or the end of stroke and / or the amount of stroke of the gas exchange valves and can change the start of stroke and / or end of stroke and / or the amount of stroke precisely in time with the load requirements. Such internal combustion engines therefore have the gas exchange valves instead of the throttle valve as an actuator for adjusting the load. The air mass to be sucked into the cylinder can be adjusted almost without loss. Such an internal combustion engine with individual, individually controllable gas exchange valves is known from DE 196 10 468 AI. Electromechanical actuators are provided here to control the gas exchange valves.

Another internal combustion engine has been proposed, which has both electromechanical actuators that act on the gas exchange valves, and also has an injection valve per cylinder, which is arranged in the cylinder head such that the fuel is metered directly into the respective cylinder of the internal combustion engine.

The object of the invention is to create a method for controlling the latter internal combustion engine which is reliable and simple.

The object is achieved by the features of independent claim 1. Advantageous embodiments of the invention are characterized in the subclaims.

The invention is characterized in that the torque to be generated by the internal combustion engine can actually be set in a transient operation within one working cycle of the internal combustion engine. In addition, it is ensured that the transient operation of the Internal combustion engine a specified air / fuel ratio can be precisely maintained. In this way, the internal combustion engine can be operated with very high efficiency at low loads, for example when idling. Torque reserves can be dispensed with. Nevertheless, unstable operation is avoided after a load change, which is noticeable, for example, by a sharp drop in speed. The method can be used in internal combustion engines with any number of cylinders.

Embodiments of the invention are explained in more detail with reference to the schematic drawings. Show it:

1 shows an internal combustion engine, FIG. 2 shows a flowchart of a program for controlling the internal combustion engine, FIG. 3 shows the processing sequence of the steps of the program according to FIG. 2 plotted over a crankshaft angle.

An internal combustion engine (FIG. 1) comprises an intake tract 1 and an engine block 2, which has a cylinder ZI and a crankshaft 23. A piston 21 and a connecting rod 22 are assigned to the cylinder ZI. The connecting rod 22 is connected to the piston 21 and the crankshaft 23. A cylinder head 3 is provided in which a valve train is arranged with at least one inlet valve 30 and one outlet valve 31. Each of the gas exchange valves, which are designed as inlet valve 30 and as outlet valve 31, is assigned an actuator 32, 33. The actuators 32, 33 control the start of the stroke, the duration of the stroke and thus the end of the stroke and possibly the stroke amount of the respective gas exchange valve. The actuators 32, 33 are preferably designed as electromechanical actuators with at least one electromagnet, an armature with an armature plate, which is located between a first contact surface of the electromagnet and a further contact surface is movable and which forms a spring-mass oscillator with at least one restoring means. The gas exchange valve is brought into an open position or a closed position by appropriately energizing or not energizing a coil of the electromagnet. The actuators 32, 33 can also be designed electrohydraulically or in another manner known to the person skilled in the art in such a way that a sufficient response behavior of the actuator is ensured for setting the load.

An injection valve 34 and a spark plug 35 are also introduced into the cylinder head 3. The injection valve 34 is arranged such that the fuel is metered directly into the combustion chamber of the cylinder ZI. In addition to the cylinder ZI, the internal combustion engine also includes further cylinders Z2, Z3 and Z4, to which an intake and exhaust valve, actuators, injection valves and spark plugs are assigned.

An exhaust tract 4 with a catalytic converter 40 and an oxygen probe 41 is assigned to the internal combustion engine. A control device 5 is provided, to which sensors are assigned, which record different measured variables and each determine the measured value of the measured variable. The control device 5 determines, depending on at least one measured variable, control signals for controlling the actuators 32, 33, the injection valve 34 and the spark plug 35.

The sensors are a pedal position sensor 61, which detects a pedal position PV of the accelerator pedal 6, an air mass meter 11, which detects an air mass flow, a temperature sensor 12, which detects an intake air temperature, and a crankshaft angle sensor, which detects a crankshaft angle KW, from the time profile thereof the speed of the crankshaft 23 is calculated in the control device 5. Furthermore, an acid Substance probe 41 is provided, which detects the residual oxygen content of the exhaust gas in the exhaust tract 4 and which assigns an air number LAM to it. Depending on the embodiment of the invention, any subset of the sensors mentioned or additional sensors can be present.

The control device 5 is preferably designed as an electronic engine control. However, it can also include several control devices that are connected to one another in an electrically conductive manner, for example via a bus system.

A program for controlling the internal combustion engine, which is shown as a flow chart (FIG. 2), is described below. The program is processed in the control device 5 and is stored there. The program is started in a step SO. In a step S0 _A it is checked for which cylinder ZI, Z2, Z3, Z4 control signals for the assigned actuators, the injector assigned to it and the spark plug assigned to it are to be determined. The program shown in FIG. 2 can be active at the same time in several or all branches going out from step SO. The timing of the processing of the steps of the program is explained in more detail below with reference to FIG. 3.

If the processing of the program is intended for the cylinder ZI, the processing after step S0 _{A is continued} in a step Sl _z ι. In step Sl _z ι, a target value MA_SP _z _ of the air mass in the cylinder ZI is calculated. The setpoint value MA_SP _{ZX of} the air mass in the cylinder ZI is determined depending on the pedal position PV, the speed and / or torque requirements of consumers, such as an air conditioning compressor or a generator, by an anti-slip control or by a transmission control. For this purpose, one or more maps are provided from which the setpoint MA_SP zi of the air mass flow in the cylinder ZI is determined depending on the pedal position PV, the speed N and the torque requirements.

In a step S2 _z ι the setpoint MA_SP _Z _ of the air mass in the cylinder is controlled by correspondingly actuating the actuators 32, 33. This results in particularly low charge exchange losses if the gas exchange valves are controlled very quickly from their closed position to their open position and vice versa , since the entire opening cross-section is released at the inlet opening of the cylinder ZI during a large part of the opening period and the air can be sucked in freely from the cylinder ZI.

In a step S3 _Z _ the measured values MAF_MES of the

The air mass flow, which have been detected by the air mass meter 11 during the opening period of the intake valve 30, integrated over the opening period and associated with the air mass in the cylinder to the actual value ZI MA_AV _Z _. The actual value MA_AV _z ι is accordingly detected during the intake stroke of the cylinder ZI and calculated after the intake and exhaust valves 30, 31 are closed. Since the intake tract has only a small suction volume and no collector, the measured values MAF_MES of the air mass meter are to be equated with the actual air mass flow into the cylinder ZI at the same time almost without delay even in the transient operation of the internal combustion engine. The actual value MA_AV _Z _ of the air mass in the cylinder ZI can thus be calculated in real time.

In a step S4, _Z _ is a function of the actual value MA_AV _Z of the air mass in the cylinder ZI ι ι _z MF_SP a target value of the fuel mass for the cylinder ZI calculated. Other variables such as the speed n and the intake air temperature TCO can also be taken into account. The target value MF SPl _Z ι of the fuel mass for the cylinder ZI is This is determined from a map depending on the actual value MA_AV _Z _ the air mass of the cylinder ZI, the speed and / or the intake air temperature TCO.

In a step S5 ₂ ι, the injection valve 34 is then controlled such that the setpoint MF_SP _{Z1 of} the fuel mass for the cylinder ZI is actually set in the cylinder ZI. The steps Sl _Z ι to S5 _Z ι are carried out once each within one working cycle of the internal combustion engine. If the calculation and setting of the control signals for the actuators and the injection valve of the cylinder Z2 is to take place, the processing is continued after the step S0 _Ä in the steps Sl _z2 , S2 _Z2 , S3 _Z2 , S4 _Z2 and S5 _Z2 , which the corresponding steps with the index "ZI" are equivalent. If the control signals for the actuators and the injection valve of the cylinder Z3 are to be calculated and set, the steps _{S1 z3} , S2 _Z3 , S3 _Z3 , S4 _Z , S5 after step S0 _A _Z4 processed, which are also equivalent to the corresponding steps with the index "ZI". If the control signals for the actuators and the injection valve of the cylinder Z4 are to be determined and controlled, then the steps _{S1 z4} , S2 _Z , S3 _Z4 , S4 _Z4 , S5 _{Z4 are} processed after step S0 _A , which also corresponds to the corresponding steps with the Index "ZI" are equivalent.

In a step S6, the program is stopped. The program is called up exactly once for each cylinder ZI, Z2, Z3, Z4 within one working cycle of the internal combustion engine. A sequence control is provided in the control device 5, which coordinates the chronological sequence of the steps S1 _z to S5 _Z4 . The resulting temporal sequence of steps S1 _Z to S5 _Z4 is shown in FIG. 3 as a function of the crankshaft angle for a rotational speed which is less than a predetermined threshold value (for example 3000 revolutions / min). Here UT denotes the bottom dead center of the the cylinder ZI, LWUT the top dead center of the piston of the cylinder ZI during the gas exchange and ZOT the top dead center of the piston of the cylinder ZI before the combustion stroke of the cylinder ZI. The calculation of the target value MA_SP _Z ι of the air mass in the cylinder ZI in step S1 _z _ takes place during the exhaust cycle of the cylinder ZI, ie between the bottom dead center UT and the top dead center when the charge of the piston of the cylinder ZI changes LWUT.

During the intake stroke of the cylinder ZI, which lies between the top dead center for gas exchange LWUT and the bottom dead center UT of the piston of the cylinder ZI, the setpoint MA_SP _Z ι of the air mass for the cylinder ZI is controlled in step S2 _z ι and then that Calculating the actual value MA_AV _Z _ of the air mass in the cylinder ZI in step S3 _z ι- During the compression stroke of the cylinder ZI, which is between the bottom dead center UT and the top dead center ZOT of the piston of the cylinder ZI before the combustion stroke, this is done Calculating the target value MF_SP _z ι of the fuel mass for the cylinder ZI in step S4 _z ι and then controlling the target value MF_SP _Z ι of the fuel mass for the cylinder ZI in step S5 _Z ι.

The respective execution of the steps Sl _z ι - S5 _z4 r, which differ only in their index, takes place synchronously with the piston position of the respective piston assigned to the cylinder Z1, Z2, Z3, Z4. Load jumps can thus be set very easily within one working cycle of the internal combustion engine. The specified air / fuel ratio can also be set precisely since the actual actual value MA AV _Z ι to _{z4 of} the air mass in the cylinder is calculated in step S3 _z ι, S3 _Z2 , S3 _Z3 , S3 _Z4 and this is then the basis for the calculation of the target value MF_SP _Z ι-z _{4 in} steps S4 _Z ι_ _z4 . If the speed is greater than the predetermined threshold, the steps S2 and S5 _z ι_ must _z4 _Z1 - _Z4 are processed in parallel, that fuel has already during the Ansau- gens the air are injected into the respective cylinders Z1-Z4. In this case, the actual value of the air mass of the cylinder Z1-Z4 preceding the ignition sequence is simply assigned to the actual value MA_AV _Z ι_ _z4 in steps S3 _Z ι- _z4 . The setpoint MF_SP _z ι- _{z of} the fuel mass for the cylinder is then calculated on the basis of the actual air mass of the cylinder preceding the ignition sequence. In this way, however, the specified air / fuel ratio is still set with sufficient accuracy, the deviations of which can be compensated for within a segment, ie between the ignition times of two cylinders neighboring in the ignition sequence.

Claims

claims

1. A method for controlling an internal combustion engine with a plurality of cylinders (ZI, Z2, Z3, Z), each of which actuators (32, 33) are assigned, which act on gas exchange valves, and each of which is assigned an injection valve (34), which in the Cylinder head (3) is arranged in such a way that the fuel is metered directly into the respective cylinder (ZI, Z2, Z3, Z4) of the internal combustion engine, with steps in the order specified within a working cycle of the internal combustion engine:

Calculating a target value of the air mass of a single cylinder (ZI, Z2, Z3, Z4),

Controlling the actuators of the individual cylinders (ZI, Z2, Z3, Z4) depending on the target value of the air mass for this cylinder,

- Detecting an actual value of the air mass in the individual cylinder (ZI, Z2, Z3, Z4) during or after the intake stroke of the individual cylinder (ZI, Z2, Z3, Z4), - Calculating a target value of the fuel mass in the individual cylinder (ZI, Z2, Z3, Z4) depending on the actual value of the air mass and

Controlling the injection valve of the individual cylinder (ZI, Z2, Z3, Z4) depending on the target value of the fuel mass.

2. The method according to claim 1, characterized in that in one or more predetermined speed ranges of the internal combustion engine the actual value of the air mass of the individual cylinder (ZI, Z2, Z3, Z4) the actual value of the air mass of the cylinder preceding in the firing sequence (ZI, Z2, Z3, Z4) is assigned.