WO2011082918A1

WO2011082918A1 - Method for switching between an hcci combustion and an si combustion in a reactor of an internal combustion engine

Info

Publication number: WO2011082918A1
Application number: PCT/EP2010/069029
Authority: WO
Inventors: Axel Loeffler; Wolfgang Fischer; Roland Karrelmeyer; Gerald Graf
Original assignee: Robert Bosch Gmbh
Priority date: 2010-01-08
Filing date: 2010-12-07
Publication date: 2011-07-14
Also published as: DE102010000741A1

Abstract

The invention relates to a method for switching (600) between an HCCI combustion and an SI combustion in a reactor of an internal combustion engine, said switching being carried out via an intermediate state in which a stoichiometric air/fuel mixture is combusted during a throttled operation.

Description

description

title

A method of switching between HCCI combustion and SI combustion in a reactor of an internal combustion engine

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 invention presented here essentially deals 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 retaining or sucking back the hot internal residual gas or heating the fresh air. 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 SI (Spark Ignition) method without knocking or misfiring. Especially critical is the transition from HCCI to Sl. This is due to the fact that the SI firing process has only a low residual gas compatibility (especially with respect to hot internal residual gas) and also only a slight lean-burn ability (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 aggravated 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 manifold) and on the other hand, the excess air can be derived from the intake manifold only 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 makes it possible to enable a 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, the SI combustion reacts very sensitively to high residual gas rates and heavy leaning (for example with misfires). The operating mode changeover according to the invention is therefore based on an intermediate step. Thus, e.g. when switching from HCCI to SI mode, a transition to a throttled HCCI mode is made before the actual switch to SL mode is performed. Switching from Sl to HCCI is analogue.

A significant advantage of the method is that no additional hardware variability, such as 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. In the switchover, it is preferable to switch an exhaust camshaft position from a first value for the HCCI combustion via a second value for the intermediate state to a third value for the SI combustion. In this case, the second value expediently denotes 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, preferably, a stoichiometric mixture (λ = 1) forms together with the second value of the closing angle of the outlet valve. This causes the intake manifold pressure to gradually increase is reduced from a first value for HCCI combustion via a second value for the intermediate state (HCCI with λ = 1) to a third value for the SI combustion (also with λ = 1). The valve strokes of the exhaust and intake valve strokes are essentially the same in HCCI operation and in the intermediate state and are increased in the SL state. In Sl mode, the first

Exhaust valve and then, preferably delayed by up to five combustion cycles, the intake valve are 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, e.g. a control unit of a motor vehicle, is, in particular programmatically, configured 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 already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. 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

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

FIG. 2 shows the profile of an intake manifold pressure, a throttle position, an outlet closing angle and valve strokes when switching from HCCI to SI operation according to a preferred embodiment of the invention.

Embodiment (s) of the invention

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

For the exhaust gas back suction, the activation of the intake valve 5 a can take place such that a part of the exhaust gas flows back into the intake pipe 6 by early opening of the intake valve 5 a.

For the exhaust gas retention, which represents a particularly preferred solution, the activation of the exhaust valve 5b can take place such that a part of the exhaust gas is retained by early closing of the exhaust valve 5b. there the intake valve 5a is opened late to prevent leakage of the retained exhaust gas into the intake manifold 6.

Furthermore, with the combustion chamber 4, an injector 8 which can be activated with signals q (fuel mass) and SOI (ignition angle) and which can be controlled

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 (Sl method). 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 fresh air supplied to the intake pipe 6 and generates a signal LM in response thereto. The lambda sensor 1 1 measures the oxygen content of the exhaust gas in the exhaust pipe 7 and generates a signal lambda λ in dependence thereon.

In the intake manifold 6, a throttle valve 12 is housed, the rotational position is adjustable by means of a signal DK. The lambda probe 1 1 is an exhaust system (not shown) including a catalyst, eg. 3-way catalyst, followed by

In an HCCI mode with exhaust gas retention of the internal combustion engine 1, the throttle 12 is opened in response to the desired supplied air mass to produce a lean mixture. The fuel is released from the injector 8 during early closing and late opening of the injector

Outlet and inlet valve caused intermediate compression near the charge cycle OT (top dead center) injected into the combustion chamber 4. 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 fresh air is in 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 2 is driven. By the driven piston, a crankshaft 14 in offset a rotational movement over which ultimately the wheels of the motor vehicle are driven.

It is understood that an internal combustion engine can have more than one cylinder, which are assigned to the same crankshaft and the same exhaust pipe and form an exhaust gas bank.

For regulation u.a. of the HCCI method, a control unit 16 is provided. For this purpose, the control unit 16 is 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 perform the entire control and / or regulation of the internal combustion engine 1. 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 control unit 16 with the air mass sensor 10, the lambda sensor 1 1, etc. connected. Furthermore, the control unit 16 is u.a. connected to an accelerator pedal sensor (not shown). The control unit 16 generates output signals with which the behavior of the internal combustion engine 1 can be influenced by actuators in accordance with the desired control and / or regulation. For example, the control unit 16 is connected to the injection valve 8, the valves 5a, 5b, the spark plug 9 and the throttle valve 12 and generates the signals required for their control.

A preferred embodiment of the invention is described below o.E. exemplified by the switching from the HCCI to the SI mode. The reverse case can be implemented analogously in the embodiment of the invention (Sl -> intermediate state (throttled HCCI) -> HCCI), but has proven to be less critical in practice.

Referring to Figure 2, a basic switching strategy is explained. 2 shows in a diagram 200 an intake manifold pressure p22 in bar on a a ordinate 201, in a diagram 300 a throttle position DK from 0 (closed) to 1 (fully open) on an ordinate 301, in a diagram 400 an exhaust camshaft position EVC in ° CA (crank angle) on an ordinate 401, in one Diagram 500 plots a valve lift Z in mm on an ordinate 501 and in a diagram 600 the state of the changeover on an ordinate 601 in each case against the time t in seconds on an abscissa 602.

A desired Saurohrdruckverlauf is designated 210. A real resulting intake manifold pressure curve is designated 21 1. A throttle position history is designated 310. A desired exhaust camshaft angle curve is labeled 410. A real resulting cam cam angle curve is designated 41 1. An exhaust valve lift curve is denoted by 510, an intake valve lift curve by 51 1. The combustion state progression is denoted by 610, wherein it is clear that a HCCI state is switched to an SI state via an intermediate state.

If the engine 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 initially initiated and the actual changeover process to SL is initiated.

Operation delayed until about t-ι = 0.975 s. 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 shown in diagram 200, the intake manifold pressure is reduced by throttling, whereby 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 has to 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 actual course 21 1 results from the intake manifold dynamics.

Furthermore, as shown in diagram 400, the exhaust valve is adjusted. In HCCI operation, preferably a negative valve overlap and a Nock driven with a small hub. 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. EVC is in configuration at the time t-ι adjusted to "late". 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 actual resulting curve 41 1 is caused by an internal dynamics of the camphaser and a rate limit.

After reaching these two specifications is switched to the Sl mode, 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 diagram 500 delayed by three cycles.

Claims

claims

1 . A method of switching between HCCI combustion and SI combustion in a reactor (4) of an internal combustion engine (1), said switching being effected via an intermediate state in which combustion of a stoichiometric air / fuel mixture occurs during throttled operation.

2. The method of claim 1, wherein the intermediate state is taken over a period of at least one combustion cycle.

3. 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.

4. The method of claim 3, wherein the second value indicates a late closing angle.

5. The method according to any one of the preceding claims, wherein a throttle valve (12) in the intermediate state is less than 5% open.

A method according to any one of the preceding claims, wherein a manifold pressure (P22) is changed from a first value for HCCI combustion via a second value for the intermediate state to a third value for SI combustion.

7. The method of claim 4 and 6, wherein the second value is selected so that forms a stoichiometric mixture (λ = 1) together with the second value of the closing angle of the exhaust valve.

A method according to any one of the preceding claims, wherein an outlet and / or inlet valve lift are the same in the intermediate state and in HCCI combustion.

9. The method according to any one of the preceding claims, wherein residual exhaust gas is discharged during the switching from the intermediate state to the SI combustion from the reactor.

10. Arithmetic unit which is adapted to perform a method according to one of the preceding claims.