DE10348774A1 - Method for air injection in an internal combustion engine - Google Patents

Abstract

The invention relates to a method for air injection for a thermal aftertreatment of exhaust gases in an exhaust tract of an internal combustion engine. The air injection is achieved with little effort, that during a warm-up phase individual cylinders are controlled in such a way that they take over the function of an air pump for blowing the air into the exhaust system (Fig. 1).

Description

The The invention relates to a method for air injection for a thermal After treatment of exhaust gases in an exhaust tract of an internal combustion engine.

Such a method is in the DE 100 65 963 A1 specified. In this known method, the air for a thermal treatment of exhaust gases by means of a cylinder group individually controllable secondary air pump is blown into the exhaust system. Along with a catalytic aftertreatment, the blown-in air complies with exhaust limits, with air injection only required during the warm-up phase of the engine until the catalyst reaches its conversion temperature. The secondary air pump requires a not insignificant space and requires a corresponding effort in terms of their structure and costs.

In the US 3,756,205 It is proposed to inject air by means of individual cylinders into the exhaust tract for catalytic after-treatment of the exhaust gases during engine operation by switching off the fuel injection. With such a control, however, disadvantages for smoothness and possibly even fuel consumption can arise.

Of the Invention is based on the object, a method of the initially mentioned type, with the thermal aftertreatment with as possible little effort possible is achieved effectively.

Advantages of the invention

These The object is achieved with the features of claim 1. hereafter is provided during that a warm-up phase individual cylinders are controlled in the way that they perform the function of an air pump for blowing the air in take over the exhaust tract.

There the cylinders only during a warm-up phase after the start until reaching the conversion temperature the catalyst are used for air injection, remains the normal Engine operation in warm condition unimpaired. The Use of individual cylinders of the internal combustion engine or the internal combustion engine as an air pump in conjunction with the engine control one inexpensive Structure in which, in contrast to a secondary air pump no additional space needed becomes.

A advantageous embodiment of the method with favorable control options This is achieved by the function of the air pump performing Cylinder with shutdown of the fuel injection in one not combustion mode of operation and the function of the air pump through coordinated operation the inlet valve or valves in question and the one or more concerned Outlet valves is controlled.

A effective air injection is thereby promoted, that a fully variable valve control is utilized in such a way that for optimizing the pump power the non-burning cylinders by cylinder-individual timing of their intake and exhaust valves operate.

Of the Warm-up operation of the engine is also in terms of smoothness little disturbed, though is provided that in a multi-cylinder internal combustion engine only a portion of the cylinder is operated in pumping mode, where it It is advantageous that every second cylinder is operated in pumping operation.

A further advantageous measure to achieve one as possible undisturbed Engine operation in the warm-up phase is further that, if the driver a higher Torque requires at least one cylinder in pumping operation the burning operation is controlled.

A Effective air injection is also supported by that during operation of the internal combustion engine in a partial load point, in which the cylinders in combustion mode with shortened timing their intake valves are operated, which are in pumping mode Cylinders are operated with full control of their intake valves.

To An effective air injection also carry the measures in that the inlet and outlet valves operate in pumping mode Cylinders are controlled in such a way that every piston movement is used for air pumping.

The Air injection process is also facilitated by that for sucking and expelling of air alternately in each successive bar Inlet valve and the respective exhaust valve are opened. Alternatively, you can be advantageously provided that in pumping the exhaust valve the cylinder in question also remains open at the stroke, in its combustion mode corresponds to the compression stroke, causing no compression work occurs at the pumping cylinders.

drawing

The Invention will now be described with reference to exemplary embodiments with reference closer to the drawings explained. Show it:

1 a first timing diagram for a part of the cylinders of an 8-cylinder internal combustion engine under control in the combustion mode on the one hand and air pump operation on the other hand,

2 Another embodiment of a timing diagram for burning and pumping cylinders and

3 a still further embodiment of a timing diagram.

embodiment

The 1 to 3 show various embodiments of timing diagrams for a portion of the cylinders Zyl1, Zyl5, Zyl4, Zyl8 an 8-cylinder internal combustion engine with the activation of respective intake valves EV and exhaust valves AV over different crankshaft angles and the associated clocks.

at a conventional internal combustion engine with Otto engine combustion mixture is first sucked from a suction side into a combustion chamber, to then be pushed into an exhaust tract after combustion become. The function of a single cylinder as an air pump, the Air sucks through an air filter and pumped into the exhaust tract is achieved by the process of sucking and expelling without an injection takes place. In modern injection systems will the injection time of each individual cylinder individually Engine control unit controlled from. This is used here to the injection time Disconnect on one or more cylinders and this as an air pump to operate.

The Shutdown takes place in the present process in the warm-up phase after the start and takes advantageously so long until the Catalyst has reached its conversion temperature, after which the air pump operation over a program of the engine control unit is switched off. The air pump operation can be clear are stored in a program block, with a dependency the air pump operation of individual parameters easily taken into account can be.

The Injection time is calculated with the help of most systems a load sensor (e.g., hot film air mass meter or intake manifold pressure sensor). At the resulting injection time the burning cylinder has to be considered that part the air does not participate in the combustion and accordingly admixed with the exhaust gas. This can also be done by means of the engine control be taken into account. For valve trains with variable valve timing, the amount the supplied Air can be controlled variably.

Of the Air pump operation related cylinder by means of injection shutdown is particularly favorable at multi-cylinder engines can be used, since this briefly on a or several cylinders and still the driver enough Torque available stands. In principle, however, the method can be used with any engine. In engines with little cylinders, the disadvantage may arise that the driver either only very little torque is available or the smoothness of the engine is no longer acceptable. The torque However, the burning cylinder can be controlled via the engine control e.g. by opening the throttle under consideration the for corresponding to the pumping operation, non-burning cylinder be enlarged.

A control option switching off the injection consists in e.g. in an 8-cylinder engine four cylinders in the warm-up phase immediately after take-off disable or already start with only four cylinders. In order to results in spite of the deactivated cylinders a harmonious engine run with 180 ° KW (Crankshafts) ignition distance, provided in the firing order every second cylinder is switched off.

example

• firing of a V8 engine: 1 5 4 8 6 3 7 2
• firing in air pump mode: 1 4 6 7

Provided the driver demands more engine torque in the phase of air pumping It is conceivable in the example of the V8 engine, with justifiable losses in the Smooth running one to three cylinders again. The necessary amount of air for the Nevertheless, thermal aftertreatment can be achieved as with increasing Speed also increases the amount of air pumped per unit time.

The method is particularly well suited for systems with fully variable valve control. In such systems (eg electrohydraulic or electromagnetic valve control) each valve can be brought into any state at any time. As a result, it is possible to optimize the pumping power of the non-combusting cylinders by means of cylinder-specific control times without incurring disadvantages in the case of the burning cylinders to have to take. This minimizes the duration of the procedure. In 1 This possibility is exemplified for the first four cylinders Zyl1, Zyl5, Zyl4, Zyl8 of an 8-cylinder engine in the timing chart of the intake and exhaust valves EV, AV.

1 shows a partial load point. The cylinders Zyl1 and Zyl4 burn with regular control times, ie the inlet valve closing edge determines the amount of air available for combustion. Cylinders Zyl5 and Zyl8, on the other hand, serve only as an air pump and are controlled by the maximum control edges in order to utilize the full stroke of the piston from top to bottom dead center.

At the in 2 In another exemplary embodiment, which shows a control time diagram of a fully variable valve control system, an operating mode is provided in which the cylinders actuated in pumping mode do not operate in the 4-stroke method but use each piston movement to pump air. The operated in pumping, non-burning cylinder Zyl5, Zyl8 pump only air from the intake to the exhaust side, without an intermediate compression stroke. This leads to a doubling of the air being pumped through and to a reduction of the compression work.

An in 3 shown another embodiment of the method provides a continuation of the method according to 1 and 2 also in a timing diagram. In this case, substantially the same amount of air as in the method after 1 pumped through, but occurs in the pumping cylinders according to the process 2 no compression work on. This is achieved by the open exhaust valves AV on the pumping cylinders Zyl5, Zyl8. This leads to low throttle losses on the exhaust side, since there is constantly sucked exhaust gas into the cylinder in question and ejected again.

In a fully variable system, a combination of the various methods described is conceivable. As a result, different air flow rates and loss work can be set. So it is conceivable, for example, a pumping cylinder after the in 2 to operate shown method, and another pumping cylinder after the in 3 shown method.

Claims (10)

A method for air injection for a thermal aftertreatment of exhaust gases in an exhaust tract of an internal combustion engine, characterized in that during a warm-up phase individual cylinders are controlled in such a way that they take over the function of an air pump for blowing the air into the exhaust system. Method according to claim 1, characterized in that that the cylinders performing the function of the air pump are switched off the fuel injection operated in a non-combusting mode and the function of the air pump by coordinated operation of the or the relevant inlet valves (EV) and the one or more Outlet valves (AV) is controlled. Method according to claim 2, characterized in that that a fully variable valve control is utilized in such a way that for optimizing the pumping power, the non-combusting cylinders by cylinder-individual Control times of their intake and exhaust valves (EV, AV) operated become. Method according to one of the preceding claims, characterized characterized in that in a multi-cylinder internal combustion engine only a part of the cylinder is operated in pumping mode. Method according to claim 4, characterized in that every second cylinder is operated in pump mode. Method according to claim 4 or 5, characterized that if the driver is a higher one Torque calls for at least one cylinder in pumping operation is controlled in the burning mode. Method according to one of claims 3 to 6, characterized that during operation of the internal combustion engine in a partial load point, in which the cylinder in the combustion mode with shortened timing their inlet valves (EV) are operated, which are in pumping operation Cylinders are operated with full control of their intake valves (EV). Method according to one of claims 3 to 7, characterized that the inlet and outlet valves of operating in pumping mode Zy linder be controlled in such a way that each piston movement is used for air pumping Method according to claim 8, characterized in that that for sucking and expelling of air alternately in each successive bar Inlet valve (EV) and the respective Auslasslventil (AV) are opened. A method according to claim 8, characterized in that in the pumping operation, the exhaust valve (AV) of the respective cylinder remains open even at the clock, which in its combustion operation the Kom corresponds to the pression rate.