EP3080430A1

EP3080430A1 - Piston engine and associated operating method

Info

Publication number: EP3080430A1
Application number: EP14808501.2A
Authority: EP
Inventors: Frank Michael Benz; Thomas Haarmann; Kai Hoffmann; Kai Kanning; Thomas Koch; Johannes Ritzinger; Tobias SCHÖFFLER
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2013-12-11
Filing date: 2014-11-29
Publication date: 2016-10-19
Also published as: DE102013020923A1; CN105814302A; JP2016539279A; WO2015086121A1; US20160312745A1

Abstract

The invention relates to a method for operating an internal combustion piston engine, preferably a spark-ignition engine. In said method, at least one intake valve (1, 2) per combustion chamber is closed prematurely or with a delay, and exhaust gas can be recirculated. A higher exhaust gas recirculation rate can be set when at least two intake valves (1, 2) are provided for each combustion chamber, said intake valves (1, 2) being opened with different maximum lifts (Hmax_I, Hmax_II) at least during exhaust gas recirculation.

Description

Piston engine and associated operating method

The present invention relates to a method for operating a piston engine with internal combustion, preferably a gasoline engine, in which each combustion chamber, an inlet valve is closed prematurely or late and in which a

Exhaust gas recirculation is feasible. The invention also relates to a piston engine with internal combustion, in particular gasoline engine, which is suitable for carrying out such an operating method. Finally, the present invention relates to a use of a valve train for driving intake valves in a

Piston engine according to such an operating method.

By premature closing of the inlet valve, so by closing the

Inlet valve before a bottom dead center of the associated piston can a

So-called Miller process (also earlier Miller process) are carried out, in which a reduced filling of the respective combustion chamber is carried out to ultimately the

increase geometric expansion in the subsequent expansion stroke. As a result, the fuel can be consumed more efficiently because more expansion energy can be used in the respective expansion process. The late closing of the intake valve results in the same situation, since in this case the intake valve closes after the bottom dead center of the associated piston, whereby the

(thermodynamic) compression stroke is reduced. This process is known as the Atkinson process (also known as the Miller process later).

Relevant for the Miller process and the Atkinson process are piston engines, which operate on the four-stroke principle, in which the respective piston performs an expansion stroke in the respective cylinder in a first stroke with the combustion process, in a second cycle an exhaust stroke to eject the

Combustion exhaust gas performs, in a third clock an intake stroke for

Frischgasbefüllung performs and in a fourth cycle performs a compression stroke for compressing the fresh gas. Related to a crankshaft of the piston engine, which is driven by the respective piston, the individual cycles or strokes of the piston can be assigned to the following crankshaft angle ranges. The expansion stroke lasts from 0 ° crankshaft angle (KWW) to 180 ° KWW, the exhaust stroke lasts from 180 ° KWW to 360 ° KWW, the intake stroke lasts from 360 ° KWW to 540 ° KWW and the compression stroke lasts from 540 ° KWW to 720 ° KWW , where 720 ° KWW of the one four-stroke cycle 0 ° KWW of the next four-stroke cycle correspond. Upper dead centers of the piston movement can be found at 0 ° KWW, 360 ° KWW and 720 ° KWW. Lower dead centers of the respective piston, however, are found at 180 ° KWW and 540 ° KWW. Typically, the intake valve closes at about 540 ° KWW, that is, at the bottom dead center between the intake stroke and the compression stroke. At the early

Inlet closure, so in the Miller process, the intake valve closes before 540 ° KWW, while it closes at 540 ° KWW at the late intake closing, ie at the Atkinson process. In order for the Miller process or the Atkinson process to have a noticeable effect on the efficiency of the piston engine, the closing of the inlet valve occurs clearly before or after the respective bottom dead center, namely preferably within a range of 80 ° to 60 ° inclusive and in particular at about 70 ° before or after bottom dead center at 540 ° KWW.

Exhaust gas recirculation is mainly with the aim of reducing the NOx pollutant emissions of the reciprocating engine. In order to enable high exhaust gas recirculation rates, the highest possible turbulence is required in the respective combustion chamber. However, a high degree of turbulence in the combustion chamber is not or only with difficulty achievable in connection with the Miller process or the Atkinson process, so that the desired high levels of combustion are achieved in conventional operating processes

Exhaust gas recirculation rates are not adjustable or associated with an increased risk of knocking and an increased risk of misfiring.

From EP 2 041 414 B1 a method for operating a gasoline engine of the type mentioned is known.

The present invention is concerned with the problem of providing for an operating method of the type mentioned above or for an associated piston engine or for an associated valve train, an improved embodiment, the

characterized in particular by the fact that higher exhaust gas recirculation rates are adjustable. This problem is solved according to the invention by the subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea of allocating at least two inlet valves to the respective combustion chamber, so that the filling of the respective combustion chamber

Brennraums via the at least two intake valves takes place during a

Exhaust gas recirculation for a method of operation with premature or late closing of the intake valves are controlled so that the two intake valves have different maximum strokes. The invention uses the knowledge that the maximum stroke when opening the respective intake valve significantly influences the inflow of the gas mixture. It has been shown that the production of two different

Inlet flows generated by different maximum strokes of the intake valves result in increased turbulence in the combustion chamber. The increased turbulence improves the compatibility of the subsequent combustion process for

recirculated exhaust gas, whereby higher exhaust gas recirculation rates are adjustable, without thereby the risk of knocking and the risk of combustion misfires is increased. Thus, the pollutant emission of the piston engine can be reduced by the proposal according to the invention.

According to an advantageous embodiment, the maximum lift of the one intake valve is in a range of from 40% to 70% inclusive, preferably in a range from 50% to 65% inclusive, in particular approximately 55%, of the maximum lift of the other intake valve. It has been shown that with these relations between the two maximum strokes particularly high turbulences can be generated in the respective combustion chamber.

In another embodiment, at least one of the two intake valves with respect to the crankshaft angle may have a stroke course having an angular range with a constant opening stroke. This means that the respective stroke profile in said angular range has a flat plateau in which the opening stroke of the inlet valve does not change. As a result, a constant inlet flow can occur during this angular range, which makes the training more targeted

Turbulence improved. For example, the angular range in which the

Opening stroke of the respective intake valve is constant, in a range of

including 30 ° KWW up to and including 50 ° KWW, preferably in a range of including 40 ° KWW up to and including 45 ° KWW. According to an advantageous development of the constant opening stroke the

Maximalhub the respective intake valve form. That means that the respective

Inlet valve with the respective angular range with its maximum stroke is constantly open. This measure also leads to specifically produce the desired turbulence.

In another development, it can be provided that only one of the two intake valves has such an angular range with a constant opening stroke.

Preferably, this is the inlet valve, which is the smaller

Maximalhub owns. Alternatively, it may be provided that both intake valves each have such an angular range with a constant opening stroke.

Particularly advantageous is an embodiment in which both intake valves open and close synchronously. Accordingly, both intake valves have the same

Opening time window. In particular, the opening strokes of the two inlet valves are substantially congruent in an opening region and in a closing region. As a result, clearly defined times for the beginning of admission and the

Inlet end allows. If both Hubverläufe show an angular range with constant opening stroke, in particular with a constant maximum stroke, the angular range of the intake valve with a smaller maximum stroke is significantly greater, in particular about twice greater than the angular range of the intake valve with a larger maximum stroke.

For example, this larger angular range can then range from 80 ° KWW inclusive to 120 ° KWW inclusive, preferably including 90 ° KWW up to and including 1 10 ° KWW.

In another embodiment, it can be provided that the two inlet valves control two separate inlet channels, each of which controls the respective gas mixture

Lead the combustion chamber. As a result, interactions in the gas stream upstream of the intake valves can be largely avoided in order to reduce the efficiency of turbulence

To improve the combustion chamber.

According to a development can be provided that only one of the two

Inlet channels is designed as a swirl duct. Preferably, this is the inlet channel which is the inlet valve with the larger maximum stroke

assigned. While a conventional feed channel, the gas mixture substantially radially and axially with respect to a longitudinal center axis of the associated cylindrical

Brennraums the combustion chamber, a swirl duct is arranged or aligned, that the combustion chamber supplied gas flow also a

Tangential component, that has a component in the circumferential direction. Via the swirl channel, a swirl flow can thus be generated in the combustion chamber, which is advantageous for the turbulence.

A piston engine according to the invention with internal combustion, which is preferably a gasoline engine, is equipped with exhaust gas recirculation, which is preferably an external exhaust gas recirculation. Furthermore, the

Piston engine with at least two intake valves per combustion chamber and equipped with a valve drive for driving the intake valves. The valvetrain is also configured to control the intake valves according to the above-described

Operating method can control. In other words, the valvetrain may drive the two intake valves for Miller operation or Atkinson operation for performing different maximum strokes.

In the use according to the invention, a valve drive, which is provided for driving at least two inlet valves of a combustion chamber of a piston engine with internal combustion, in particular a gasoline engine, is used selectively in such a way that it carries out the operating method described above. For this purpose, the valve train is designed in a suitable manner.

A valvetrain, the at least two intake valves with different

To control maximum strokes, for example, has two separate cams to be able to control the two separate intake valves separately. The two cams then have geometrically different cam contours to the two

generate different stroke curves for the two separate intake valves. It is also conceivable, a common cam for the two intake valves

to provide, however, has two different cam contours. In order to switch between a normal operation and a Miller operation or Atkinson operation, the valve train can also be equipped with a camshaft adjustment. Furthermore, it is basically conceivable for normal operation and / or for a

Conventional Miller operation or Atkinson operation to design the valve train so that the two intake valves can also be completely synchronous, so in particular also be driven with the same maximum strokes. This can be realized for example by means of adjustable camshafts and / or adjustable rocker arms and the like. Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the 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 given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

Show, in each case schematically,

1 and 2 are each a diagram with Hubverläufen of two intake valves,

during an intake stroke in two different embodiments.

The diagrams of FIGS. 1 and 2 indicate a valve lift H in mm on their ordinate and a crankshaft angle KWW in degrees on their abscissa. By way of example, valve strokes H from 0 to 14 mm are shown in FIGS. 1 and 2. In FIG. 1, by way of example, a crankshaft angle range from 300 ° KWW to 650 ° KWW is plotted. In Fig. 2, a crankshaft angle range of 270 ° KWW to 630 ° KWW is plotted.

In both diagrams, two valve lift curves I, II of two intake valves 1, 2 are shown, which are assigned to the same combustion chamber of an internal combustion piston engine. The piston engine is preferably a gasoline engine. The piston engine works on the four-stroke principle. The reproduced here

Angled regions thereby capture an intake stroke of a piston assigned to the respective combustion chamber. Said inlet stroke extends from 360 ° KWW to 540 ° KWW, ie from a top dead center OT at 360 ° to a bottom dead center UT at 540 °.

In both diagrams of FIGS. 1 and 2, a first stroke course I of a first intake valve 1 is shown with a broken line, and a second travel curve II of a second intake valve 2 is shown with a solid line. The presented here Operating method requires that at least two inlet valves 1, 2 are provided per combustion chamber, which in Figs. 1 and 2 by the two Hubverläufe I and II

are represented. A valve drive for driving the intake valves 1, 2 is in this case designed such that, with respect to the bottom dead center at 540 ° KWW, premature or delayed closing of the intake valves 1, 2 is possible. 1 shows an Atkinson operation with delayed inlet closing, in which the intake valves 1 and 2 close at approximately 600 ° KWW to 650 ° KWW. In contrast, Fig. 2 shows the Hubverläufe I and II for a Miller operation with early intake closing. Here close the two intake valves 1, 2 at about 510 ° KWW. In both cases open the

Inlet valves 1, 2 approximately at top dead center OT with 360 ° KWW. It is noteworthy that the two intake valves 1, 2 are opened with different maximum strokes Hmax and Hmax _M , respectively. In the examples, the first intake valve 1 each has the larger maximum lift Hmax. The smaller maximum stroke Hmax ,, is approximately between 40% and 70% of the larger maximum stroke Hmax ,. In the examples shown here, the smaller maximum stroke Hmaxn is about 60% of the larger maximum stroke Hmax ,. By way of example only, in FIG. 1, the larger maximum stroke Hmax _{t is} about 13 mm, while the smaller maximum stroke Hmaxn is about 8 mm. In the example of FIG. 2, the larger maximum stroke Hmaxi is about 11 mm, while the smaller maximum stroke Hmaxn is about 7 mm.

The Miller method according to FIG. 2 and the Atkinson method according to FIG. 1 are used above all when high exhaust gas recirculation rates for the respective combustion chamber are to be achieved. This means that the associated piston engine is also equipped with an exhaust gas recirculation. Here comes preferably an external

Exhaust gas recirculation is used, is branched off in the exhaust outside the respective combustion chamber and outside the respective combustion chamber of the fresh gas supply is supplied, so that the combustion chamber is ultimately fed to a mixture of fresh air, fuel gas and recirculated exhaust gas.

According to the embodiments shown here it can be provided that at least in one of the two intake valves 1, 2 with respect to the crankshaft angle KWW a stroke course I, II is provided which has an angular range c, in which

Opening stroke H remains constant. The respective stroke course I, II has in each case an angular range a, in which the opening stroke H increases and an angular range b, in which the opening stroke H decreases, in this case over the intermediate

Angle range c with constant opening stroke H merge into each other. Appropriately in said angular range c constant, the maximum stroke Hmax of the respective

Inlet valve 1, 2 before.

In the embodiment shown in Fig. 1, both Hubverläufe I, II of the two intake valves 1, 2 each have exactly such an angular range c with constant

Opening stroke H, which is formed by the respective maximum stroke Hmax. In contrast, Fig. 2 shows an embodiment in which only one of the two intake valves 1, 2 has a stroke course I, II, which shows exactly such an angular range c with constant opening stroke H, which is also formed there by the maximum stroke Hmax. These are according to the preferred shown in Fig. 2

Embodiment to the stroke course II of the second intake valve 2, which has the smaller maximum stroke Hmax. The first intake valve 1, which has the larger maximum stroke Hmaxi, shows no such angular range c with a constant opening stroke H. Rather, go in the stroke curve I of the first intake valve 1, the angular range a with increasing opening stroke H and the angular range b with decreasing

Opening stroke H directly into each other.

In the preferred embodiments shown here, the two inlet valves 1, 2 open and close synchronously, so that the two separate stroke profiles I, II run congruently in an opening region d and in a closing region e.

In the embodiment shown in FIG. 1, the angular range c with a constant maximum stroke Hmax forms a plateau in the first stroke progression I which extends over approximately 50 ° KWW. In the second stroke course II, however, a plateau is formed by the angular range c with constant maximum lift Hmaxn, which extends approximately over 100 ° KWW. In FIG. 2, a plateau is formed by the angular range c with constant maximum lift Hmax _{M of} the second intake valve 2, which extends approximately over 40 ° KWW.

In the embodiments shown here, the two Hubverläufe I, II of the two intake valves 1, 2 are also configured substantially symmetrical, so that the

Angular areas a are designed with increasing opening stroke H largely mirror-symmetrical to the angular ranges b with decreasing opening stroke H.

The two inlet valves 1, 2 can be assigned separate inlet channels, so that the two inlet valves 1, 2 control two separate inlet channels. These can basically be two separate inflow channels. However, it is preferred

provided that at least one of the inlet channels is designed as a swirl channel. One unlike a conventional inflow channel, such swirl duct has an orientation which has a flow component in the circumferential direction of the cylindrical combustion chamber in the gas flow which can flow into the combustion chamber through this swirl duct. In contrast, the gas flow generated with an inflow channel is oriented almost exclusively radially and / or axially to the longitudinal central axis of the respective cylinder.

Claims

claims

1. A method of operating a piston engine with internal combustion,

Preferably, a gasoline engine in which each combustion chamber at least one inlet valve (1, 2) is prematurely or late closed and in which an exhaust gas recirculation is feasible,

characterized in that

at least two intake valves (1, 2) are provided per combustion chamber, which are opened at least in the exhaust gas recirculation with different aximalhubes (Hmaxi _, Hmaxn).

2. The method according to claim 1,

characterized in that

at least one of the two inlet valves (1, 2) with respect to a

Crankshaft angle (KWW) has a stroke course (I, II), the one

Angular range (c) having a constant opening stroke (H).

3. The method according to claim 2,

characterized in that

the constant opening stroke (H) forms the maximum lift (Hmaxi, Hmaxn) of the respective intake valve (1, 2).

4. The method according to claim 2 or 3,

characterized in that

only one of the two intake valves (1, 2) has such an angular range (c) with a constant opening stroke (H).

5. The method according to claim 2 or 3, characterized in that

Both inlet valves (1, 2) each have such an angular range (c) with a constant opening stroke (H).

6. The method according to any one of claims 1 to 5,

characterized in that

open and close the two intake valves (1, 2) synchronously.

7. The method according to any one of claims 1 to 6,

characterized in that

the two intake valves (1, 2) control two separate intake ports.

8. The method according to claim 7,

characterized in that

only one of the two inlet channels is designed as a swirl channel.

9. piston engine with internal combustion, in particular gasoline engine, with

Exhaust gas recirculation, with at least two intake valves (1, 2) per combustion chamber and with a valve drive for driving the intake valves (1, 2) according to the method of one of claims 1 to 8.

10. Use of a valve drive for driving at least two inlet valves (1, 2) of a combustion chamber of a piston engine with internal combustion,

in particular a gasoline engine, according to the method of any one of claims 1 to 8.