DE102010000741A1 - A method of switching between HCCI combustion and SI combustion in a reactor of an internal combustion engine - Google Patents

Abstract

The present invention relates to a method for switching (600) between HCCI combustion and SI combustion in a reactor of an internal combustion engine, the switching taking place via an intermediate state in which a stoichiometric air / fuel mixture is burned with throttled operation.

Description

The present invention relates to a method for switching between HCCI combustion and SI combustion in a reactor of an internal combustion engine.

State of the art

In internal combustion engines, different combustion methods are known. The present invention is essentially concerned with the control and regulation of the so-called HCCI combustion process for gasoline engines (Homogeneous Charge Compression Ignition: homogeneous autoignition process, also called gasoline HCCI or Controlled Auto Ignition - CAI). HCCI refers to a lean burn process which aims to provide a significant 10-15% fuel economy reduction in the vehicle (by throttling engine operation and thermodynamically favorable combustion) without significant raw nitrogen oxide emissions (the 3-way catalyst operates in lean operation not nitrogen-reducing) and therefore no additional costs for exhaust aftertreatment in purchasing.

Since the gasoline and the compression ratio of a gasoline engine are designed so that auto-ignition (knocking) are avoided as possible, the thermal energy required for the HCCI process must be provided elsewhere. This can be done in various ways, such as. B. retention or sucking back of the hot internal residual gas or heating the fresh air done.

In the present case, a method with exhaust gas retention or recirculation is used.

In the prior art, the HCCI method is feasible only at low load conditions. For this reason, it is desirable to be able to switch between an HCCI method and a spark ignition (SI) method without knocking or misfiring. Particularly critical is the transition from HCCI to SI. This is due to the fact that the SI combustion process has only a low residual gas compatibility (in particular with respect to hot internal residual gas) and also only a slight leanness capability (the ignition limit for gasoline under normal conditions is approximately λ = 1.4).

Thus, in the HCCI-to-SI transition on the one hand, it is necessary to expel the internal residual gas as quickly as possible, ideally during an ejection process, but on the other hand to prevent the air-fuel mixture from massively degrading when the combustion chamber volume released by the residual gas emission is filled with fresh air , This is compounded by the fact that the HCCI process is throttled and throttling the intake manifold pressure on the one hand represents a relatively slow process (especially with a large intake pipe volume) and on the other hand, the excess air from the intake manifold can only be derived via the combustion chamber, where leads to unwanted emaciation. Also, a start-up of the external residual gas content in the intake manifold is not effective, as you can derive this only on the combustion chamber again and the SI operation has only a low residual gas compatibility.

It is desirable to address these issues.

Disclosure of the invention

According to the invention, a method with the features of claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention provides the ability to transition from HCCI to SI operation and vice versa without knocking or intermittent combustion. The invention is based on the finding that although HCCI combustion also functions in throttled operation and at a stoichiometric air / fuel ratio, SI combustion reacts very sensitively to high residual gas rates and heavy leaning (eg with misfiring). The operating mode changeover according to the invention is therefore based on an intermediate step. So z. For example, when switching from HCCI to SI operation, a transition to throttled HCCI operation is made before the actual switch to SI operation is performed. Switching from SI to HCCI is analogue.

A significant advantage of the method is that no additional hardware variability, such. For example, the ability of stratified combustion as an alternative to throttled HCCI operation or additional valve variability such as a continuously variable lift is needed.

The intermediate state may be described by certain parameters and is suitably taken over a period of at least two combustion cycles.

To achieve a preferred intermediate state, predetermined parameters of the internal combustion engine are controlled accordingly. When switching is preferably an exhaust camshaft position of a first value for the HCCI combustion is transitioned to a third value for SI combustion via a second intermediate state value. In this case, the second value expediently indicates a closing angle which is later than the first closing angle, for example between -50 ° and 0 ° crankshaft angle. The throttle flap is closed so far that, together with the second value of the closing angle of the outlet valve, preferably a stoichiometric mixture (λ = 1) is formed. As a result, the intake manifold pressure is gradually reduced from a first value for HCCI combustion via a second intermediate state value (HCCI of λ = 1) to a third value of SI combustion (also of λ = 1). The valve strokes of the exhaust and intake valve strokes are substantially the same in HCCI operation and in the intermediate state, and are increased in the SI state. In SI operation, first the exhaust valve lift and then, preferably delayed by up to five combustion cycles, the intake valve lift can be changed over.

The intermediate state can be described as a throttled HCCI combustion process, so that expediently exhaust gas is also retained in the reactor or recycled to the reactor.

An arithmetic unit according to the invention, for. As a control device of a motor vehicle is, in particular programmatically, adapted to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for the provision of the computer program are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. a. m. 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.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

1 shows a schematic representation of an internal combustion engine with a control unit.

2 shows the course of a Saugrohrdrucks, a throttle position, a Auslaßschließwinkels and valve lifts when switching from a HCCI to a SI operation according to a preferred embodiment of the invention.

Embodiment (s) of the invention

In 1 is an internal combustion engine 1 shown in which a piston 2 in a cylinder 3 is movable up and down. The cylinder 3 is with a reactor or combustion chamber 4 provided to the over valves 5a and 5b an intake pipe 6 or an exhaust pipe 7 are connected. The valves 5a . 5b are equipped with an adjustable valve train, in which case the inlet valve 5a with a signal Za and the exhaust valve 5b with signals Zb and EVC can be controlled. The intake pipe 6 is with an air mass sensor 10 and the exhaust pipe 7 with a lambda sensor 11 Mistake. For external exhaust gas recirculation is a per se known exhaust gas recirculation valve 13 intended.

For exhaust gas back suction, the control of the intake valve 5a such that a portion of the exhaust gas by early opening of the inlet valve 5a back into the intake manifold 6 flows.

For exhaust gas retention, which represents a particularly preferred solution, the control of the exhaust valve 5b such that a part of the exhaust gas by early closing of the exhaust valve 5b is held back. This is the inlet valve 5a open late to allow the retained exhaust gas to flow out into the intake manifold 6 to prevent.

Furthermore, with the combustion chamber 4 an injector controllable with signals q (fuel mass) and SOI (ignition angle) 8th and a controllable spark plug 9 connected. In the HCCI process, the spark plug is not used to ignite the fuel / air mixture in the combustion chamber. Instead, a self-ignition takes place. The spark plug is intended for the other operating modes (SI procedure). The combustion chamber also has a combustion chamber pressure sensor 15 for measuring the combustion chamber pressure.

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 11 measures the oxygen content of the exhaust gas in the exhaust pipe 7 and generates a signal lambda λ in response thereto.

In the intake pipe 6 is a throttle 12 housed, whose rotational position is adjustable by means of a signal DK. The lambda probe 11 is an exhaust system (not shown) including a catalyst, for example. 3-way catalyst, followed by

In an HCCI mode with exhaust gas recirculation of the internal combustion engine 1 will the throttle 12 opened in response to the desired, supplied air mass to produce a lean mixture. The fuel is from the injector 8th during the intermediate compression caused by the early closing and late opening of the exhaust and intake valves near the charge cycle OT (top dead center) into the combustion chamber 4 injected. Due to the high temperatures prevailing in the combustion chamber, there is a rapid evaporation of the fuel and thus a very good mixture formation in the combustion chamber 4 , In the subsequent intake phase, fresh air is introduced into the combustion chamber 4 sucked. Thereafter, the fuel / air mixture is compressed during the compression phase until it ignites itself by the rising temperature. Due to the expansion of the ignited fuel, the piston becomes 2 driven. 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 may have more than one cylinder, which are assigned to the same crankshaft and the same exhaust pipe and form an exhaust bank.

To control, inter alia, the HCCI method is a control unit 16 intended. For this purpose, the control unit 16 provided with a microprocessor, wherein in a storage medium, in particular in a read only memory (ROM), a program is stored, which is adapted to the entire control and / or regulation of the internal combustion engine 1 perform. The control unit (ECU) 16 is set up to carry out a method according to the invention.

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 etc. connected. Furthermore, the control unit 16 Inter alia, with an accelerator pedal sensor (not shown). 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 injector 8th , the valves 5a . 5b , the spark plug 9 and the throttle 12 connected and generates the signals required for their control.

A preferred embodiment of the invention will be explained below by way of example with reference to the switching from the HCCI to the SI mode. The reverse case can be implemented analogously in an embodiment of the invention (SI → intermediate state (throttled HCCI) → HCCI), but has proven less critical in practice.

With reference to 2 a basic switching strategy is explained. In 2 are in a diagram 200 a suction pipe pressure p22 in bar on an ordinate 201 , in a diagram 300 a throttle position DK from 0 (closed) to 1 (fully open) on one ordinate 301 , in a diagram 400 an exhaust camshaft position EVC in ° CA (crank angle) on an ordinate 401 , in a diagram 500 a valve lift Z in mm on an ordinate 501 and in a diagram 600 the state of switching on an ordinate 601 each time t in seconds on an abscissa 602 applied.

A desirable Saurohrdruckverlauf is with 210 designated. A real resulting Saugrohrdruckverlauf is with 211 designated. A throttle position curve is with 310 designated. A desired exhaust camshaft angle curve is with 410 designated. A real resulting Auslaßnockenwellenwinkelverlauf is with 411 designated. An exhaust valve lift course is with 510 , An inlet valve lift with 511 designated. The combustion state history is with 610 indicating that it is switching from an HCCI state to an SI state via an intermediate state.

If the motor control system receives a request for operating mode changeover from HCCI to SI operation at approx. T ₀ = 0.4 s, a changeover to an intermediate state is initiated first and the actual changeover to SI operation up to approx. T ₁ = 0.975 s delayed. The intermediate state is described by a throttled HCCI operation with stoichiometric air-fuel mixture (λ = 1) and minimal internal residual gas mass.

On the one hand, as in diagram 200 shown, the intake manifold pressure reduced by throttling, in extreme cases, the throttle valve can also be closed. The reduction takes place until λ = 1 is reached. This ensures that only a minimum amount of internal residual gas must be expelled during the transition to SI operation and that the intake manifold pressure is already close to the SI level. A deviation of the desired course 210 from the actually resulting course 211 stems from the Saugrohrdynamik ago.

Furthermore, as in diagram 400 shown, the exhaust valve adjusted. In HCCI operation, a negative valve overlap and a low lift cam are preferably run. The internal residual gas quantity is controlled by phase shifting via the EVC (Exhaust Valve Closing, ie closing angle). A later closing angle leads to a smaller amount of residual gas. In an embodiment, EVC is adjusted to "late" at time t ₁ . This is due to the switching from the small to the large cam and not the expression of a further retardation of the small cam beyond the maximum allowed. A deviation of the command commanded 410 from the actually resulting course 411 is caused by an internal dynamics of the camphaser and a rate limit.

After reaching these two specifications is switched to the SI operation, with a change in the injection quantity and the injection timing, a shift of the ignition angle, a further throttling, etc. takes place. In order to avoid a transient loss of weight, the switchover to the large intake cam can optionally be delayed by further cycles, as shown in the diagram 500 delayed by three cycles.

Claims (10)

Method for switching between HCCI combustion and SI combustion in a reactor ( 4 ) an internal combustion engine ( 1 ), wherein the switching takes place via an intermediate state in which a combustion of a stoichiometric air / fuel mixture takes place in throttled operation. The method of claim 1, wherein the intermediate state is taken over a period of at least one combustion cycle. The method of claim 1 or 2, wherein an exhaust camshaft position (EVC) is switched from a first value for the HCCI combustion via a second value for the intermediate state to a third value for the SI combustion. The method of claim 3, wherein the second value indicates a late closing angle. Method according to one of the preceding claims, wherein a throttle valve ( 12 ) in the intermediate state is less than 5% open. The method of any one of the preceding claims, wherein a manifold pressure (p ₂₂ ) is switched from a first value for the HCCI combustion via a second value for the intermediate state to a third value for the SI combustion. The method of claim 4 and 6, wherein the second value is selected so that forms together with the second value of the closing angle of the exhaust valve, a stoichiometric mixture (λ = 1). Method according to one of the preceding claims, wherein an exhaust and / or inlet valve lift in the intermediate state and in the HCCI combustion are the same. A method according to any one of the preceding claims, wherein residual exhaust gas is removed from the reactor upon switching from the intermediate state to the SI combustion. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims.

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