Combustion engine, has exhaust gas return line opening into intake line downstream of compressor, and pre-cooling device arranged upstream of or in region of non-return valve that is arranged upstream of exhaust gas recirculation cooler

The invention relates to an internal combustion engine with an inlet line and an exhaust line, with at least one exhaust gas turbocharger having a compressor and an exhaust gas turbine, with a high-pressure exhaust gas recirculation system with at least one exhaust gas recirculation line which emanates from the exhaust line upstream of the turbine and opens into the inlet line downstream of the compressor, wherein at least one first exhaust gas recirculation cooler in the exhaust system, at least one exhaust gas recirculation valve and at least one check valve is arranged and wherein the check valve is arranged upstream of the first exhaust gas recirculation cooler. The invention also relates to a method for operating this internal combustion engine.

From JP 2007-085 248 A is an internal combustion engine with

Known high-pressure exhaust gas recirculation, an exhaust gas recirculation valve and a check valve being arranged in parallel branch lines of the exhaust gas recirculation line in the exhaust gas recirculation line upstream of an exhaust gas recirculation cooler.

EP 0 840 000 A1 describes an internal combustion engine with a

High-pressure exhaust gas recirculation system, with an exhaust gas recirculation valve being arranged in the exhaust gas recirculation line in the area of ​​the extraction point from the exhaust gas line and a non-return valve in the area of ​​the opening into the inlet line. An exhaust gas recirculation cooler is arranged between the exhaust gas recirculation valve and the check valve.

GB 2 473 821 A discloses an internal combustion engine with a high-pressure exhaust gas recirculation system, two exhaust gas recirculation coolers being arranged one behind the other in an exhaust gas recirculation line. Both coolers can be bypassed by a bypass line, each bypass line can be controlled separately via a bypass valve.

Furthermore, it is from the documents EP 1 835 155 A2, JP 2007-303 355 A,

JP 2007-332 913 A, US 7,275,514 B2, US 7,360,523 B2, US 7,367,313 B2,

No. 7,370,0633 B2 and US 2009/0150052 A1 it is known to use a negative valve overlap for inlet and outlet valves in connection with exhaust gas recirculation. Due to the negative valve overlap, the

Pressure difference zrälsthen J ^ beäs ^ ixXng and inlet line can be positively influenced in order to increase the exhaust gas recirculation quantities.

The object of the invention is to achieve a reduction in consumption while adhering to the strictest exhaust gas guidelines.

According to the invention, this is achieved in that at least one pre-cooling device is arranged upstream or in the area of ​​the check valve, the pre-cooling device preferably being formed by a cooling line within the cylinder head.

The pre-cooling device can also be formed by cooling fins on a section of the exhaust gas recirculation line leading to the check valve or by air cooling, achieved by targeted flow on a section of the exhaust gas recirculation line leading to the check valve and / or by flow on the check valve.

It is particularly advantageous if the pre-cooling device is formed by a second exhaust gas recirculation cooler, the exhaust gas recirculation valve preferably being arranged downstream of the check valve and / or the first exhaust gas recirculation cooler.

Thanks to the high-pressure exhaust gas recirculation with non-return valve, the pressure pulsations can be used to recirculate exhaust gas into the inlet branch even if the pressure difference between the outlet and inlet branches is low or negative. In order to enable a cylinder-specific exhaust gas recirculation, it can furthermore be provided that the exhaust gas recirculation line splits into at least two branch lines, the branch line opening into an inlet channel of different cylinders for each individual cylinder. The feed line to the distribution strip is preferably carried out in the middle; the services branching off from the distributor strip to the cylinders are preferably symmetrical.

The pre-cooler in front of the non-return valve prevents the non-return valve from overheating and enables the temperature limits of the components to be adhered to. In addition, gas dynamic effects are less disturbed.

In further r'AA / sführUQg the jjcfiocüing it is provided that in at least one operating range in which exhaust gas recirculation is desired, the control time of at least one inlet valve and / or one outlet valve is changed in such a way that a negative valve overlap occurs, whereby preferably the inlet closure with 1mm valve lift, especially in operating phases with negative valve overlap, takes place later than 590 ° crank angle after the top dead center of the ignition. It can also be provided that the change from positive to negative valve overlap takes place by advancing the exhaust control times.

The negative valve overlap (based on 1 mm valve lift) is 40 ° to 120 ° crank angle, preferably 60 ° to 100 ° crank angle.

The negative valve overlap ensures that sufficiently high amounts of exhaust gas can be returned from the outlet line to the inlet line. Furthermore, losses due to opening the outlet too late - especially when the outlet valves are open for a short time - are avoided.

The invention is explained in more detail below with reference to the figure.

1 shows an internal combustion engine according to the invention in a first variant, FIG. 2 shows an internal combustion engine according to the invention in a second variant, FIG. 3 shows the control times of the inlet and outlet valves with positive valve overlap, and FIG. 4 shows the control times of the inlet and outlet valves negative valve overlap.

Functionally identical parts are identical in the design variants

Provided with reference symbols.

1 and 2 each show an internal combustion engine 1 with an inlet branch 2 and an outlet branch 3. Reference numeral 4 denotes a compressor arranged in inlet branch 2, and reference numeral 5 denotes a turbine of an exhaust gas turbocharger arranged in exhaust branch 3. An exhaust gas recirculation line 6 of a high-pressure exhaust gas recirculation system is arranged between the outlet line and the inlet line 2, which branches off from the exhaust line 3 upstream of the turbine 5 and opens into the inlet line 2 downstream of the compressor 4. In the exhaust gas recirculation line 6 are a first exhaust gas recirculation cooler 7, an exhaust gas recirculation filter, vBntil £ ϊ and.-. Upstream of the exhaust gas recirculation cooler 7 and the exhaust gas recirculation valve 8, a check valve 9 is arranged, which can be designed as a so-called reed valve. The exhaust gas recirculation line 6 opens downstream of the exhaust gas recirculation valve 8 centrally into an exhaust gas distribution line 10, via which cylinder-selective exhaust gas is fed to the inlet channels 11 of the individual cylinders 12. In the exhaust line 3, downstream of the turbine 5, there is at least one

Exhaust aftertreatment device 12 is arranged. A charge air cooler 13 and a throttle valve 14 are arranged in the inlet branch 2 downstream of the compressor 4.

Both embodiment variants shown in FIGS. 1 and 2 have in common that a pre-cooling device 20 is arranged upstream of the check valve 9 in order to lower the temperatures of the exhaust gas to values ​​that are compatible with the check valve 9 without destroying the necessary gas dynamics.

In the embodiment shown in FIG. 1, the pre-cooling device 20 is formed by a cooling line 21 which is arranged within the cylinder head 15 of the internal combustion engine and through which the exhaust gas is pre-cooled.

In the embodiment shown in FIG. 2, the pre-cooling device 20 is formed by a second exhaust gas recirculation cooler 22.

3 and 4 show valve lift / crank angle diagrams, the valve lift h of the exhaust valve and of the intake valve being plotted against the crank angle KW. The lift curve of the exhaust valve is denoted by E, and the lift curve of the inlet valve is denoted by I.

3 shows the case of a positive valve overlap with a late-late strategy (late exhaust closure - late inlet closure), residual gas is sucked back into the cylinder via late exhaust closure. The engine can be de-throttled further (Atkinson cycle) by closing the inlet late. The disadvantage of such an operating strategy is that if the outlet is open for a short time, the outlet will open after the lower gate point (180 ° CA). Losses occur when pushing out, which can compensate for the advantages of closing the outlet late.

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Fig. 4 shows * eifie.flegat1ve: VeriÜlütoerschnenung, with which the pressure ratio between exhaust line and inlet line can be improved in favor of increased exhaust gas recirculation quantities by opening the outlet early. In addition, residual gas control (internal exhaust gas recirculation) can be achieved, which avoids the late opening of the exhaust and thus the exhaust losses. The negative valve overlap (based on 1 mm valve lift) is 40 ° -120 ° crank angle KW, preferably 60-100 ° crank angle KW. Another advantage is the avoidance of deep valve pockets in the piston crown, which are necessary when the outlet closes late or the inlet opens early.

Both in Fig. 3 and in Fig. 4, the inlet closure of the inlet valves is 1mm valve lift - later than 590 ° crank angle KW, the camshaft opening duration being relatively short.