METHOD FOR BRAKING AN INTERNAL COMBUSTION ENGINE

Abstract

The present disclosure relates to a method for braking of an internal combustion engine, in particular a four-stroke internal combustion engine. The method involves a partial opening of at least one gas discharge valve of at least one cylinder of the internal combustion engine during a compression stroke of the internal combustion engine. The method involves a holding of a partial opening of the at least one gas discharge valve during an expansion stroke of the internal combustion engine following the compression stroke and during an exhaust stroke of the internal combustion engine following the expansion stroke. The method involves a closing of the partly opened at least one gas discharge valve at the end of the exhaust stroke or during an intake stroke of the internal combustion engine following the exhaust stroke.

Claims

1. A method for braking of an internal combustion engine, comprising: partial opening of at least one gas discharge valve of at least one cylinder of an internal combustion engine during a compression stroke of the internal combustion engine; holding of a partial opening of the at least one gas discharge valve during an expansion stroke of the internal combustion engine following the compression stroke and during an exhaust stroke of the internal combustion engine following the expansion stroke; and closing of the partly opened at least one gas discharge valve at the end of the exhaust stroke or during an intake stroke of the internal combustion engine following the exhaust stroke.

2. The method according to claim 1, wherein the combustion engine is a four-stroke internal combustion engine.

3. The method according to claim 1, wherein: the at least one gas discharge valve during the partial opening is opened so far that basically no compressing occurs in the respective cylinder during the exhaust stroke at a speed of the internal combustion engine below a limit speed of the internal combustion engine.

4. The method according to claim 3, wherein: the at least one gas discharge valve during the partial opening is opened so far that a compressing occurs in the respective cylinder during the exhaust stroke at a speed of the internal combustion engine above the limit speed.

5. The method according to claim 4, wherein: the compressing in the respective cylinder increases with increasing speed of the internal combustion engine above the limit speed in the exhaust stroke.

6. The method according to claim 3, wherein: the limit speed lies in a region between 1000 rpm and 1700 rpm, especially in a region between 1200 rpm and 1500 rpm.

7. The method according to claim 1, wherein: the at least one gas discharge valve is opened during the partial opening in a region between 5% and 30% of a maximum valve stroke of the at least one gas discharge valve; or the at least one gas discharge valve is opened during the partial opening in a region between 0.5 mm and 3 mm.

8. The method according to claim 7, wherein a maximum valve stroke lies in a region between 10 mm and 16 mm.

9. The method according to claim 1, wherein: the partial opening of the at least one gas discharge valve during the compression stroke starts in a region between 100 crankshaft angle and 60 crankshaft angle before top dead centre (TDC).

10. The method according to claim 1, wherein: the closing of the at least one gas discharge valve at the end of the exhaust stroke or during the intake stroke begins in a region between top dead centre (TDC) and 30 crankshaft angle after TDC.

11. The method according to claim 1, wherein: during the holding open of the gas discharge valve during the expansion stroke and the exhaust stroke, a constant valve stroke of the at least one gas discharge valve is maintained.

12. The method according to claim 1, wherein: two gas discharge valves are provided for each cylinder and only one of the two gas discharge valves is partly opened during the compression stroke, held open with a partial opening during the expansion stroke and the exhaust stroke, and closed at the end of the exhaust stroke or during the intake stroke.

13. The method according to claim 12, wherein: the other of the two gas discharge valves is closed during the compression stroke, the expansion stroke, the exhaust stroke and the intake stroke.

14. The method according to claim 1, further comprising: opening of at least one gas admission valve of the at least one cylinder during an intake stroke; and holding closed the at least one gas admission valve during the compression stroke, the expansion stroke and the exhaust stroke.

15. A variable valve train for an internal combustion engine, the variable valve train adapted to brake the internal combustion engine by performing a method, comprising: partial opening of at least one gas discharge valve of at least one cylinder of the internal combustion engine during a compression stroke of the internal combustion engine; holding of a partial opening of the at least one gas discharge valve during an expansion stroke of the internal combustion engine following the compression stroke and during an exhaust stroke of the internal combustion engine following the expansion stroke; and closing of the partly opened at least one gas discharge valve at the end of the exhaust stroke or during an intake stroke of the internal combustion engine following the exhaust stroke.

16. The variable valve train of claim 15, wherein the variable valve train is a sliding cam system.

17. A motor vehicle, comprising: an internal combustion engine; a variable valve train, the variable valve train adapted to brake the internal combustion engine by performing a method, comprising: partial opening of at least one gas discharge valve of at least one cylinder of the internal combustion engine during a compression stroke of the internal combustion engine; holding of a partial opening of the at least one gas discharge valve during an expansion stroke of the internal combustion engine following the compression stroke and during an exhaust stroke of the internal combustion engine following the expansion stroke; and closing of the partly opened at least one gas discharge valve at the end of the exhaust stroke or during an intake stroke of the internal combustion engine following the exhaust stroke.

18. The motor vehicle of claim 17, wherein the motor vehicle is a commercial vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further details and benefits of the present disclosure are described below with reference to the accompanying figures. There are shown:

[0029] FIG. 1 a diagram of a cylinder of an internal combustion engine; and

[0030] FIG. 2 a control diagram of a valve control system of a four-stroke internal combustion engine.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a cylinder 12 of an internal combustion engine 10. The internal combustion engine 10 is a four-stroke internal combustion engine, especially a four-stroke Diesel internal combustion engine or a four-stroke gasoline internal combustion engine. Preferably, the internal combustion engine 10 is contained in a commercial vehicle, such as a lorry or a bus, for the propelling of the commercial vehicle.

[0032] The cylinder 12 comprises at least one gas admission valve 14, at least one gas discharge valve 16, one combustion chamber 18 and one piston 20.

[0033] The at least one gas admission valve 14 connects the combustion chamber 18 to an air supply system of the internal combustion engine 10 for the feeding of combustion air into the combustion chamber 18. The at least one gas discharge valve 16 connects the combustion chamber 18 to an exhaust gas line of the internal combustion engine 10 to take away the exhaust gases. For example, two gas inlet valves 14 and two gas discharge valves 16 per cylinder 12 and a plurality of cylinders 12 may be provided.

[0034] The at least one gas discharge valve 16 may be activated by a variable valve train 22. The variable valve train 22 may be designed, for example, as a sliding cam system. The sliding cam system may comprise at least one cam carrier with at least two cams. The cam carrier may be arranged in torque-proof and axially displaceable manner on a camshaft. The at least one gas exchange valve is activated in dependence on an axial position of the cam carrier by various cams of the cam carrier. It is also possible, in the case of multiple gas discharge valves 16 for each cylinder 12, that the gas discharge valves 16 of the respective cylinder 12 can be activated in different manner.

[0035] The piston 20 is arranged in the cylinder 12, in reciprocating movement in a known manner, and connected to a crankshaft 24.

[0036] FIG. 2 shows an exemplary control diagram for the activation of the gas inlet valves 14 and the gas discharge valves 16 of FIG. 1 during an engine brake operation of the internal combustion engine 10.

[0037] A dot and dash curve A shows a valve stroke of the gas inlet valves 14 as a function of a crankshaft angle of the crankshaft 24. A dash curve B shows a valve stroke of the gas discharge valve 16 as a function of the crankshaft angle of the crankshaft 24. A solid curve C shows a cylinder pressure in the combustion chamber 18 as a function of a crankshaft angle of the crankshaft 24 at a low engine speed. A dotted curve D shows a cylinder pressure in the combustion chamber 18 as a function of a crankshaft angle of the crankshaft 24 at a high engine speed.

[0038] Curves A to D are plotted against the usual 720 crankshaft angle (CA) in four-stroke operation, the left axis of the diagram indicating the cylinder pressures in bar and the right axis the valve strokes in mm.

[0039] According to curve A, the gas inlet valves 14 are opened during the engine brake operation during the intake stroke, the same as in regular operation. During the further control cycle, the gas inlet valves 14 are closed.

[0040] During the engine brake operation, the gas discharge valves 16 are controlled other than in the regular operation (normal operation), in which the gas discharge valves 16 are only opened during the exhaust stroke. For example, the internal combustion engine may have two gas discharge valves 16 per cylinder 12, one of which is held fully closed during the engine brake operation and the other is controlled according to curve B during the engine brake operation.

[0041] According to curve B, the gas discharge valve 16 is partly opened by roughly 60 CA to 100 CA before the ignition top dead centre, i.e., before the end of the compression stroke. The gas discharge valve 16 is then held partly open for approximately 360 CA during the expansion stroke and the exhaust stroke. The partly opened gas discharge valve 16 is again closed after the exhaust stroke and remains closed until the next opening in the compression stroke.

[0042] The gas discharge valve 16 is only partly opened, per curve B. The partial opening may correspond to a valve stroke of 0.5 mm to 3 mm. On the contrary, a maximum stroke (regular stroke) of the gas discharge valve 16 may be for example between around 10 mm for small internal combustion engines 10 and up to around 16 mm for very large internal combustion engines 10 in commercial vehicle construction.

[0043] Owing to the only partial opening of the gas discharge valve 16 per curve B, different cylinder pressure curves may be achieved in the combustion chamber 18 at different speeds of the internal combustion engine 10.

[0044] According to curve C, at low speeds of the internal combustion engine 10 up to around 1200 rpm, for example, no compressing occurs in the combustion chamber 18 during the exhaust stroke. The reason for this is the valve gap due to the partly opened gas discharge valve 16. This valve gap at low velocities of the piston 20 is enough to allow the gas present in the combustion chamber 18 to flow out from the combustion chamber 18 through the partly opened gas discharge valve 16 with no pressure increase. Curve C for example relates to a cylinder pressure curve at an engine speed of the internal combustion engine of around 600 rpm.

[0045] On the other hand, according to curve D at high speeds of the internal combustion engine 10 from 1200 rpm to 1500 rpm, for example, there occurs a compressing in the combustion chamber 18 during the exhaust stroke. Owing to the increased engine speed, the piston velocity of the piston 20 also rises and the volume flow across the partly opened gas discharge valve 16 likewise increases. The valve gap provided by the partly opened gas discharge valve 16 is no longer sufficient to expel the gas without compression. Instead, there occurs a second compression before the top dead centre at the end of the exhaust stroke. During the second compression, compression energy is dissipated through the still opened gas discharge valve 16 and braking power is generated. Specifically, the compression work brakes the piston 20, thereby braking the internal combustion engine 10 in the engine brake operation. Curve D pertains, for example, to a cylinder pressure curve at an engine speed of the internal combustion engine of around 2600 rpm.

[0046] For both curves C and D there occurs a first compression in the combustion chamber 18 during the compression stroke, since the gas discharge valve 16 is opened only toward the end of the compression stroke. The opening of the gas discharge valve 16 produces a decompression of the compressed gas in the exhaust tract, in which there is provided for example a flap gate which is closed at this time. The compression work performed by the piston 20 once again brakes the internal combustion engine 10. Due to the higher piston velocity of the piston 20, per curve D, there occurs a greater compression in the combustion chamber 18 at higher engine speeds and thus a greater braking effect than at low engine speed per curve C.

[0047] During the expansion stroke, the cylinder pressures for curves C and D are low and due to the exhaust gas accumulation in the exhaust tract air can flow from the exhaust tract back into the combustion chamber 18 through the partly opened gas discharge valve 16.

[0048] Summarizing, at low engine speed below a limit speed, which lies e.g. between 1200 rpm and 1500 rpm, per curve C, there occurs only a compression of gas in the combustion chamber 18 and a decompression of the compressed gas in the exhaust tract. This onetime compression-decompression occurs in the compression stroke. At a high engine speed above the limit speed, with the same control curve (curve B) for the same gas discharge valve 16 as per curve D, there occurs a double compression of gas in the combustion chamber 18 and decompression of the compressed gas in the exhaust tract through the partly opened gas discharge valve 16. On the one hand, in the compression stroke there occurs a first compression followed by decompression. In addition, in the exhaust stroke there occurs a second compression followed by decompression.

[0049] A transition between curves C and D occurs steadily with increasing engine speed of the internal combustion engine 10.

[0050] The present disclosure thus makes it possible to accomplish a high braking effect due to the double compression-decompression with the identical control profile for a gas discharge valve 16 at high speeds of the internal combustion engine 10 (curve D). At low speeds, likewise a (lesser) braking effect is accomplished by the single compression-decompression (curve C), while an engine excitation is prevented or at least reduced on account of eliminating the second compression-decompression. Thus, the behaviour is automatically adapted to the surrounding conditions (the engine speed), so that no additional control intervention from the outside is required.

[0051] The present disclosure is not confined to the above described preferred exemplary embodiments. Instead, many variants and modifications are possible, which likewise make use of the idea of the present disclosure and therefore come under the scope of protection. In particular, the present disclosure is also directed to the partial opening of at least one gas discharge valve during a compression stroke, the holding of a partial opening of the at least one gas discharge valve during an expansion stroke and/or exhaust stroke and/or the closing of the partly opened at least one gas discharge valve at the end of the exhaust stroke or during an intake stroke.

LIST OF REFERENCE NUMBERS

[0052] 10 Internal combustion engine [0053] 12 Cylinder [0054] 14 Gas admission valve [0055] 16 Gas discharge valve [0056] 18 Combustion chamber [0057] 20 Piston [0058] 22 Variable valve train [0059] 24 Crankshaft [0060] A Control curve for gas admission valve [0061] B Control curve for gas discharge valve [0062] C Cylinder pressure curve at low engine speed [0063] D Cylinder pressure curve at high engine speed