DE102012204395A1 - Method for operating internal combustion engine used in car, involves controlling delivery rate of secondary air pump in dependence of air mass flow and injected amount of fuel for internal combustion engine - Google Patents

Abstract

The method involves supplying secondary air with controllable discharge rate to a secondary air pump (9). The delivery rate of the secondary air pump is controlled in dependence of the air mass flow and the injected amount of fuel for internal combustion engine. The secondary air pump is provided with an electric drive unit (10). The electric drive unit is operated with pulse width modulation. Independent claims are included for the following: (1) computer program for operating internal combustion engine; and (2) control and/or regulating device.

Description

State of the art

The invention relates to a method according to the preamble of claim 1 and a computer program and a control and / or regulating device according to the independent claims.

When cold starting an internal combustion engine, both the actual internal combustion engine and the exhaust pipe and the catalysts arranged therein have approximately ambient temperature. Since the conventional catalysts require a minimum operating temperature to convert the pollutants present in the exhaust gases, the catalysts do not work satisfactorily immediately after a cold start.

In order to minimize emissions from the exhaust pipe into the environment, it is therefore desirable to make the heating of the catalysts as short as possible. This can be done on the one hand by a corresponding control of the internal combustion engine (adjustment of the ignition timing in the late direction, injection of additional fuel, so that sets a fuel mixture λ <1) and a secondary air injection.

In the secondary air injection known from the prior art, air is blown into the exhaust gas immediately after the cylinder head with the aid of a blower, in order thereby to burn the unburned constituents of the fuel present in the exhaust gas. As a result of this afterburning, the temperature of the exhaust gases in the exhaust pipe increases, so that the catalysts arranged downstream of the secondary air injection are heated up rapidly.

From the DE 103 48 131 A1 an internal combustion engine is known which has an exhaust gas turbocharger and a secondary air injection. The delivery rate from the DE 103 48 131 A1 known secondary air pump can be controlled by a controllable motor from the engine control unit and is also used to increase the mass flow in the exhaust pipe, so as to achieve a faster response of the exhaust gas turbocharger.

Even with this secondary air injection, the emission behavior of internal combustion engines in the cold start phase, especially when a test cycle must be traversed in accordance with statutory requirements, not optimal at all times.

Disclosure of the invention

The problem underlying the invention is achieved by a method according to claim 1 and by a computer program and a control and / or regulating device according to the independent claims. Advantageous developments are specified in the subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

In the method according to the invention for operating an internal combustion engine with a secondary air injection, the secondary air injection having a secondary air pump with controllable delivery rate, the invention provides for controlling the delivery rate of the secondary air pump as a function of the air mass flow flowing through the internal combustion engine, the fuel used and the engine start temperature. This makes it possible, regardless of the signals of a lambda probe, at any time immediately after the start of the internal combustion engine to blow the required or the optimal secondary air mass into the exhaust pipe. As a result, the lambda value of the exhaust gases produced in the exhaust pipe can be adjusted to a value range between λ = 1.1 and λ = 1.3, so that the emissions of the internal combustion engine are minimized and the legal requirements are met in the best possible way.

The inventive method also has the advantage that it can use existing in known secondary air injections technology, because many of the already on the market secondary air injections have an electrically driven secondary air pump. So if this already existing electrically driven secondary air pump is controlled with, for example, a pulse width modulated drive signal, then the control of the delivery of the secondary air pump is simple, inexpensive and possible with sufficient precision.

Because the inventive method performs a control of the delivery rate of the secondary air pump, the inventive method, according to the legal requirements, but also depending on the performance of various internal combustion engines, by adapting the control of the secondary air pump to various internal combustion engines, but also various legal requirements, relatively easy be adapted. This adaptation requires no changes in the hardware, but only in the software.

In a further advantageous embodiment of the invention, the delivery rate of the secondary air pump is controlled in dependence of the air mass flowed through the internal combustion engine since the start of the internal combustion engine. This air mass is effectively the integral of the air mass flow since the start of the commissioning of the internal combustion engine. This integral is a measure of how much energy has been implemented since the start of the internal combustion engine and thus also for the temperature of the exhaust gases and the exhaust pipe and the catalyst. Because this air mass can be determined by integrating the already detected mass air flow, no additional sensor is required and thus the consideration of the air mass in the control of the control of the secondary air pump according to the invention can be realized without much additional cost.

Another important aspect of the method according to the invention is the fact that the delivery rate of the secondary air pump is controlled as a function of the properties of the injected fuel. For example, there are different fuel qualities for gasoline engines, such as premium gasoline, normal gasoline and fuels with different admixtures of ethanol (E5, E10, E85, but also pure ethanol). These fuels differ significantly in terms of their boiling point. The higher the boiling point, the sooner injected fuel impacts in the cylinder head or on the cylinder walls of a still cold internal combustion engine and is therefore not immediately available for energy conversion. This effect is inventively taken into account that the properties of the injected fuel are taken into account in the control of the secondary air pump.

Another important parameter for optimal control of the delivery rate of the secondary air pump is the temperature of the internal combustion engine at startup. It is such that it makes a difference whether the internal combustion engine at startup has a temperature of, for example, -10 ° C or whether it is started at + 0 ° C. Basically, the colder the engine is, the sooner fuel settles on the cold surfaces of the engine and it must be injected accordingly more fuel to achieve a stable engine operation.

Finally, the invention also provides to control the delivery rate of the secondary air pump in response to the dynamic changes in the load of the internal combustion engine. This makes it possible to react appropriately to fast load changes. For example, as the load increases, the intake air mass increases sharply, which in turn can be reflected in a decrease in the lambda value to values less than 1 (λ <1). By an appropriate control of the delivery rate of the secondary air pump, this undesirable effect can be prevented.

It has proven to be particularly advantageous if the secondary air pump has an electric drive, which is controlled by a pulse width modulation (PWM). This established and proven method is also to be regarded as particularly suitable in connection with the method according to the invention.

It has proved to be advantageous to control the delivery rate of the secondary air pump so that a lambda value of between 1.1 and 1.3 is established in the exhaust pipe. At lambda values within these limits, there is an optimum in terms of emissions, fuel consumption and a rapid heating of the catalyst.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

drawing

Show it:

1 a schematic representation of an internal combustion engine with electrically driven secondary air pump;

2 a diagram illustrating the first sixty seconds of a cold start test program; and

3 a block diagram of the control of the delivery rate of the secondary air pump according to the invention.

The 1 shows an internal combustion engine 1 with several cylinders 2 , which has an intake tract 3 is supplied with intake air. This intake air is, either in the intake 3 or in the to the cylinders 2 belonging combustion chambers (without reference numeral) fuel supplied, so that forms an ignitable mixture and in the cylinders 2 oscillating piston to the crankshaft of the internal combustion engine 1 drive.

After combustion of the fuel-air mixture in the cylinders 2 or the associated combustion chambers, the exhaust gases via an exhaust pipe 4 ejected and to catalytic after-treatment of a catalyst 5 fed. Downstream of the catalyst 5 is a lambda sensor 6 provided, the input of a control and / or regulating device 7 is what the operation of the internal combustion engine 10 and the peripheral systems controls and / or regulates.

In the intake tract 3 is a controllable throttle 8th arranged, with the help of which by the internal combustion engine 10 flowing air mass can be controlled.

Between the intake tract 3 and the exhaust pipe 4 is a secondary air pump 9 arranged. The secondary air pump 9 is powered by an electric drive 10 powered and sucks intake air from the intake tract 3 on, compresses them and promotes them in the exhaust pipe 4 , The electric drive 10 the secondary air pump 9 is also from the engine control unit 7 is controlled. The activation of the electric drive 10 can be done for example via a pulse width modulation, so that the speed of the electric drive 10 and thus also the delivery rate of the secondary air pump 9 can be controlled within wide limits.

Between the secondary air pump 9 and the exhaust pipe 4 is a switchable control valve 11 intended. This control valve 11 is closed when the secondary air pump 9 is out of order. It is fully or partially opened as soon as the secondary air pump 9 is active. This will help prevent exhaust fumes from the exhaust pipe 4 via the secondary air line 12 unintentionally in the intake tract 3 reach.

With the reference number 13 is an example of an exhaust valve 13 one of the cylinders 2 indicated the internal combustion engine. The secondary air line 12 discharges downstream of the exhaust valves 13 in the exhaust pipe 4 , As already mentioned, is located downstream of the junction of the secondary air line 12 in the exhaust pipe 4 the catalyst 5 , which makes a conversion of the pollutants contained in the exhaust gases to harmless substances. So that the catalytic converter 5 work best, the fuel-air mixture (lambda) must be regulated to a value of about 1.1 to 1.3. Then the conversion rate of the catalyst 5 optimal.

When the engine is warm, the conversion rate is so high that almost no pollutants more the catalyst 5 leave. However, the situation is still significantly worse during the cold start of an internal combustion engine, that is in the first one to two minutes, because so far about 90% of the resulting during the journey of a car pollutants are emitted in the first few minutes after the start of the engine , As soon as the internal combustion engine has reached a certain operating temperature, virtually no pollutants are produced.

The improvement potential of the method according to the invention with respect to the reduction of pollutants during cold start of an internal combustion engine will be described below in connection with 2 explained.

In this diagram, the time is plotted on the X-axis. From this scaling it becomes clear that the method in question mainly concerns the first few seconds, until about the first minute, of a cold start of an internal combustion engine.

On the left side of the diagram, four different scales are plotted. The first scale V _FZG indicates the speed of the vehicle in kilometers per hour. To the left, the lambda value is plotted as a unitless size in a range between 0.7 and 1.6. In the third Y-axis, the air mass flow m _{AIR is} plotted in kilograms per hour. The fourth and leftmost scale relates to the speed N _{mod of} the internal combustion engine 1 [1 / min]. In the diagram, four lines are corresponding to the four scales on the Y axis 21 . 23 . 25 , and 27 entered.

In the lower part of the diagram is a first line 21 entered, which represents the speed of the vehicle. When looking at the first line 21 it becomes clear that the vehicle does not move over the entire duration of, for example, 60 seconds. Rather, the vehicle is the greater part of the time and only in the time interval between 19 secs. and 36 sec. and a second time interval starting at t = 57 sec., the vehicle is traveling. In the time interval between 19 and 36 seconds, the vehicle drives up a mountain.

With a second line 23 the air mass flow ṁ _{AIR is represented} by the internal combustion engine. In the time interval of 0 to 5 sec., The air mass flow ṁ _AIR = 0, because only at time t = 5 sec., The internal combustion engine 1 is started. With increasing speed of the internal combustion engine, the air mass flow through the internal combustion engine also increases 1 to.

A third line 25 represents the speed of the internal combustion engine. From the comparison of the second line 23 and the third line 25 It is clear that there is a clear correlation between the speed of the internal combustion engine and the air mass flow through the internal combustion engine.

A fourth line 27 represents the lambda value in the exhaust pipe 4 the internal combustion engine 1 ,

Like looking at the fourth line 27 becomes clear, is the lambda value in the first 60 seconds of the operation of the internal combustion engine 1 subject to very large fluctuations. It would be desirable if the lambda value between one in the upper limit lambda _max, for example, 1.3, and a lower limit lambda _min , for example, 1.1, can be maintained. Then namely the emissions of the internal combustion engine during the cold start phase and the catalyst heating over the in 2 State drastically reduced. In addition, less fuel has to be injected, which also reduces CO ₂ emissions. Both are desired.

In the 2 it is assumed that an unregulated secondary air pump is active in a time interval between t = 5 sec. and t = 51 sec. Assuming that, they are the fourth line 27 displayed lambda values.

In order to explain in more detail the test cycle underlying this diagram and the resulting behavior of the internal combustion engine, a total of three time intervals, I, II and III, are entered. The first time interval I starts at around t = 6 sec and ends at t = 14 sec. The second time interval II starts at t = 14 sec and ends at t = 19 sec, while the third time interval III at t = 30 Sec begins and ends at t = 51 sec.

The first time interval I begins immediately with the start of the internal combustion engine. Subsequently, the internal combustion engine idles at a slightly higher speed of about 1400 / min. Apart from two peaks, the lambda value is (see the fourth line 27 ) in the first time interval I substantially within the two limit values lambda _max and lambda _min .

In this condition, the exhaust gas is still too cold to react with the injected secondary air. This is also because the secondary air mass flow is too large.

In the second period II, the internal combustion engine is running 1 still idling, but the gear of the automatic transmission is engaged and the driver of the vehicle operates the brake. By engaging the gear, the speed reduces from about 1400 revolutions to about 900 revolutions per minute.

Because with an unregulated secondary air pump despite the reduced speed of the internal combustion engine 1 the secondary air mass flow remains constant, the lambda value increases to values of up to 1.58. In the period II, the lambda value is always always above the upper limit lambda _max . However, there is already a certain reaction of the injected secondary air with the exhaust gas, so that heating of the catalyst 5 at least begins.

At the end of the second period, the motor vehicle starts to drive and it drives on a first hill. After climbing this first hill begins at time t = 31, the third period III. In this third period, the internal combustion engine is idling again, which is clearly visible at the idling speed of about 900 per minute. Accordingly, the mass flow decreases. Immediately after the beginning of period III, the lambda value increases (see the fourth line 27 ) strongly on values of about 1.5 and remains until the end of period III above the upper limit lambda _max . This means that the fuel-air mixture is too lean also in this period, so that the reaction of the injected secondary air with the unburned fuel components contained in the exhaust gas is not optimal.

According to the invention, the delivery rate of the secondary air pump is now provided 9 by a corresponding control of the electric drive 10 the secondary air pump 9 be controlled so that the lambda value remains in the periods II and III within the upper and lower limits of, for example lambda _max = 1.3 and lambda _min = 1.1. This can be done, for example, that in the section II, the delivery rate of the secondary air pump 9 is reduced so far that a lambda value within the above limits. The same applies to period III.

The shows a standardized, prescribed by the legislature test cycle, in which the periods I, II and III are fixed. Therefore, it is quite possible by a suitable control of the drive of the secondary air pump 9 set a lambda value within the prescribed limits lambda _max and lambda _min . A control, which on the output signals of the lambda probe 6 is not required.

Of course, the necessary secondary air mass flow ṁ _{AIR to be} injected depends on various parameters. For example, the temperature of the internal combustion engine at the time t = 9 sec. An important parameter because the temperature of the internal combustion engine 1 is decisive for how much fuel, for example, on the cylinder walls or the combustion chamber wall of the internal combustion engine 1 reflected. Similarly, the inducted air mass m _Air and the injected fuel quantity are important parameters for the control of the secondary air mass flow. These parameters can, like the parameters mentioned below, advantageously be stored in maps and at the start of the internal combustion engine, the corresponding values are read from the maps and the engine control unit 7 be supplied.

In addition to the parameters already mentioned, the chemical and thermodynamic physical properties of the fuel in the tank or of the injected fuel are of great importance.

In particular, in motor vehicles that can run on different fuels, for example, pure petrol or a mixture of 85% ethanol and 15% gasoline or even pure ethanol (E100), the properties of the injected fuel have a significant impact on the exhaust gas composition during cold start and, as a result also on the einzublasende secondary air mass.

Another important parameter is the amount of air mass that has passed through the internal combustion engine since the start. One can imagine the integral of the air mass flow starting with the start of the internal combustion engine at time t = 5 sec. This integral is a measure of the energy conversion that has already taken place since the start of the internal combustion engine, and consequently also a measure of the heating of the internal combustion engine, the exhaust pipe 4 and the catalyst 5 ,

Finally, even a dynamic load change is an important control variable for the secondary air mass flow.

Considering, for example, the time interval starting at t = 21 sec. And ending at t = 25 sec., It becomes clear that the engine speed increases from about 1100 revolutions to 1600 revolutions and then drops back to the original value. If the secondary air pump 9 is not controlled, but is operated at a constant speed and flow rate, this leads to a very low lambda value of at least 0.94. The peak of the lambda value downwards is to a certain extent a mirror image of the speed increase of the internal combustion engine in the stated period.

If, according to the invention, the delivery rate of the secondary air pump corresponds to this short load change 9 is briefly raised and finally lowered again, it is possible to keep the lambda value within the specified limits between lambda _min and lambda _max .

Of course, various load changes must be stored in a corresponding map, so that whenever a load change occurs, the control values of similar or approximately identical load changes, which are stored in a corresponding map, can be used.

As a result, it is possible with the help of the method according to the invention, even with changing operating conditions, be it idling, driving on a hill, a load jump from driving to idle and so on, the lambda value in the first minute of operation of the internal combustion engine 1 within strict limits. This will also minimize fuel consumption and emissions of pollutants.

In the 3 a flowchart of the method according to the invention is shown.

Starting with the reference number 31 , which is to represent a limiter, is the output of this limiter 31 a PWM signal is output, which is used to control the electric drive 10 the secondary air pump 9 serves. The limiter 31 limits the input quantities in the 3 from the left, to a range between a minimum value MN and a maximum value MX.

The limiter 31 upstream is a battery voltage compensation. With the help of this battery voltage compensation 33 It is possible, the influence of the vehicle electrical system voltage or battery voltage on the speed of the electric drive 10 the secondary air pump 9 to compensate. The voltage compensation 33 multiplies the input value by a factor. This multiplication point is denoted by the reference numeral 35 Mistake. A first switch 37 decides if the voltage compensation 33 is active or not. Left of the first switch 37 is a second switch 39 , In this second switch 39 it is decided whether a static compensation or a dynamic compensation takes place.

The dynamic compensation is in the 2 with the reference number 41 Mistake. An output A2 of the dynamic compensation 41 controls the second switch 39 ,

As an input variable of the dynamic compensation, a torque request of the driver or an accelerator pedal position is shown. It is determined by means of a characteristic curve or a characteristic map 43 converted into a first output signal A1. This output signal A1 goes into a second multiplier 45 and changes the input value in this second multiplier 45 ,

The input value of the second multiplier 45 becomes due to the multiplicative linking of two maps 47 and 49 generated. Input variables of the first characteristic map 47 are an ethanol content EC of the injected fuel and a temperature T _mot at the beginning of the operation of the internal combustion engine 1 ,

In the input variables of the second characteristic map 49 are the air mass flow ṁ _AIR by the internal combustion engine 1 and in since the start of the internal combustion engine 1 suctioned air mass Intṁ _AIR . The intake air mass represents the integral of the air mass flow ṁ _AIR from the start of the internal combustion engine 1 to the present dar.

In short, predominantly the so-called static compensation is performed, in which the first map 47 and the second map 49 depending on the input quantities EG, T _mot , Intṁ _AIR and ṁ _AIR . The two output variables of the maps 47 and 49 are multiplicatively linked.

If no dynamic compensation occurs, then the second switch 39 in the in 3 leave shown switching position and the output of the point of connection 51 stays unchanged. If the second output A2 of the dynamic compensation 53 has a corresponding value, he switches the switch 39 um, so that the outputs of the multiplier 51 still with the output value A1 of the dynamic compensation 53 is multiplied.

Subsequently, the already described compensation of the battery voltage takes place and after passing the limiter 31 is the pulse width modulated signal PWM, which is used to control the electric drive 10 the secondary air pump 9 serves, ready.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10348131 A1 [0005, 0005]

Claims (10)

Method for operating an internal combustion engine ( 1 ) with a secondary air injection ( 9 . 10 ), whereby the secondary air injection ( 9 . 10 ) a secondary air pump ( 9 ) having controllable delivery rate, characterized in that the delivery rate of the secondary air pump ( 9 ) as a function of the engine ( 1 ) air mass flow (ṁ _AIR ) and the injected amount of fuel is controlled. A method according to claim 1, characterized in that the delivery rate of the secondary air pump ( 9 ) depending on the since the start of the internal combustion engine ( 1 ) by the internal combustion engine ( 1 ) Air mass flown (Intṁ _AIR ) is controlled. Method according to one of the preceding claims, characterized in that the delivery rate of the secondary air pump ( 9 ) is controlled depending on the characteristics of the injected fuel. Method according to one of the preceding claims, characterized in that the delivery rate of the secondary air pump ( 9 ) as a function of a temperature (T _mot ) of the internal combustion engine ( 1 ) at the start of the internal combustion engine ( 1 ) is controlled. Method according to one of the preceding claims, characterized in that the delivery rate of the secondary air pump ( 9 ) in response to dynamic changes in the load of the internal combustion engine ( 1 ) is controlled. Method according to one of the preceding claims, characterized in that the secondary air pump ( 9 ) an electric drive ( 10 ), and that the electric drive ( 10 ) is controlled with a pulse width modulation (PWM). Method according to one of the preceding claims, characterized in that the delivery rate of the secondary air pump ( 9 ) is controlled so that a lambda value (λ) between 1.1 and 1.3 in an exhaust pipe ( 4 ). Computer program characterized in that it is programmed to carry out a method according to at least one of the preceding claims. Control and / or regulating device for an internal combustion engine ( 1 ), in which, if necessary, by means of a secondary air pump ( 9 ) Secondary air in the exhaust pipe ( 4 ) of the internal combustion engine ( 1 ) is blown, characterized in that the delivery rate of the secondary air pump ( 9 ) is controlled so that a lambda value (λ) in the exhaust pipe ( 4 ) remains within predetermined limits, preferably between 1.1 and 1.3. Control and / or regulating device according to claim 9, characterized in that it operates according to one of the preceding methods.

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