Method for Operating an Internal Combustion Engine, in Particular of a Motor Vehicle, in an Engine Braking Operation

Abstract

A method for operating an internal combustion engine, in particular of a motor vehicle, in an engine braking operating, having at least one engine braking mode and having at least one cylinder at least of a first cylinder bank, where the at least one cylinder has at least one outlet valve and at least one inlet valve, where, in a first engine braking mode, an outlet stroke of all outlet valves of the at least one cylinder of the first cylinder bank of the internal combustion engine is permanently switched off.

Claims

1.-6. (canceled)

7. A method for operating an internal combustion engine of a motor vehicle in an engine braking operation, comprising the steps of: in a first engine braking mode, switching off an outlet stroke of all outlet valves of all cylinders of a first cylinder bank; adjusting an opening time point of all inlet valves of all cylinders of the first cylinder bank to late; in the first engine braking mode, closing all outlet valves of all cylinders of a second cylinder bank for a first time, then opening all outlet valves of all cylinders of the second cylinder bank for a first time, then closing all outlet valves of all cylinders of the second cylinder bank for a second time, and then opening all outlet valves of all cylinders of the second cylinder bank for a second time, in order to release compressed gas respectively from all cylinders of the second cylinder bank by respective pistons guided in all cylinders of the second cylinder bank; and in the first engine braking mode, adjusting an opening time point of all inlet valves of all cylinders of the second cylinder bank to late.

8. The method according to claim 7, wherein, in a second engine braking mode, operating all cylinders of the second cylinder bank in a propulsion operation.

9. The method according to claim 8, wherein, in a third engine braking mode: switching off the outlet stroke of all outlet valves of all cylinders of the first cylinder bank and an outlet stroke of all outlet valves of all cylinders of the second cylinder bank; and adjusting an opening time point of all inlet valves of all cylinders of the first and the second cylinder bank to late.

10. A method for operating an internal combustion engine of a motor vehicle in an engine braking operation, comprising the steps in a first engine braking mode, switching off an outlet stroke of all outlet valves of all cylinders of a first cylinder bank; adjusting an opening time point of all inlet valves of all cylinders of the first cylinder bank to late: in the first engine braking mode, opening all outlet valves of all cylinders of a second cylinder bank in a region of an upper dead center and then closing all outlet valves of all cylinders of the second cylinder bank, in order to release compressed gas respectively from all cylinders of the second cylinder bank by respective pistons guided in all cylinders of the second cylinder bank; and in the first engine braking mode, adjusting an opening time point of all inlet valves of all cylinders of the second cylinder bank to late.

11. The method according to claim 10, wherein, in a second engine braking mode, operating all cylinders of the second cylinder bank in a propulsion operation.

12. The method according to claim 11, wherein, in a third engine braking mode: switching off the outlet stroke of all outlet valves of all cylinders of the first cylinder bank and an outlet stroke of all outlet valves of all cylinders of the second cylinder bank; and adjusting an opening time point of all inlet valves of all cylinders of the first and the second cylinder bank to late.

13. A motor vehicle, comprising: an internal combustion engine; and a control and/or regulating unit configured to perform the method according to claim 7 or claim 10.

14. The motor vehicle according to claim 13, wherein the control and/or regulating unit is configured to perform a method for control of a camshaft actuator and/or outlet valves of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic depiction of a motor vehicle having an internal combustion engine and having a multi-stage transmission in a schematic depiction;

[0021] FIG. 2 is a diagram of a valve elevation of valves of the cylinders of a second cylinder bank via a crank angle in a first engine braking mode for illustrating a method according to the invention for operating an internal combustion engine in an engine braking operating; and

[0022] FIG. 3 is a diagram of a valve elevation of valves of the cylinder of a first cylinder bank via a crank angle in a first engine braking mode for illustrating a method according to the invention for operating an internal combustion engine in an engine braking operating.

DETAILED DESCRIPTION OF′FHE DRAWINGS

[0023] FIG. 1 schematically shows a motor vehicle 11. The motor vehicle 11 comprises a drivetrain via which drive wheels 14 of the motor vehicle H are operated in a manner that is not visible any further. The drivetrain comprises an internal combustion engine 10. The motor vehicle 11 has the internal combustion engine 10. The internal combustion engine 10 is formed from a combustion motor. Furthermore, the motor vehicle 11 has a multi-stage transmission 15. The internal combustion engine 10 has a driven crankshaft which is connected to a transmission input element of the multi-stage transmission 15. The multi-stage transmission 15 is formed from a motor vehicle transmission. The multi-stage transmission 15 forms a part of the drivetrain of the motor vehicle 11. The multi-stage transmission 15 is arranged behind the internal combustion engine 10 along the drivetrain, in particular along a flux of force of the drivetrain. The multi-stage transmission 15 is driven via the internal combustion engine 10 in at least one operating state.

[0024] The internal combustion engine 10 comprises at least one cylinder of a first cylinder bank and at least one cylinder of a second cylinder bank. In particular, the internal combustion engine 10 in total comprises six combustion chambers, for example, in the form of cylinders. The cylinders are arranged in a row, for example. A first, second and third cylinder are arranged in the first cylinder bank, wherein a fourth, fifth and sixth cylinder are arranged in the second cylinder bank. The cylinder banks each have a common exhaust gas manifold. A translationally moveable piston is respectively arranged in the cylinders. The pistons are flexibly coupled to a crankshaft of the internal combustion engine 10 via a respective conrod. The crankshaft is mounted on a crank housing of the internal combustion engine 10 rotatably around an axis of rotation relative to the crank housing. As a result of the flexible coupling of the pistons to the crankshaft, the translational movements of the pistons are converted into a rotational movement of the crankshaft around its axis of rotation. Furthermore, at least one inlet channel is respectively allocated to the cylinders, via which inlet channel air can flow into the respective cylinder. At least one inlet valve is respectively allocated to the inlet channel of the cylinders, which inlet valve can be moved between at least one closed position fluidically blocking the inlet channel of the respective cylinder and at least one open position fluidically releasing the inlet channel of the respective cylinder. Furthermore, at least one outlet channel is respectively allocated to the cylinders, via which outlet channel the exhaust gas can flow out of the respective cylinder. At least one outlet valve is allocated to the outlet channel of the respective cylinder, which outlet channel can be moved between a closed position fluidically blocking the outlet channel of the respective cylinder and at least one open position at least partially fluidically releasing the outlet channel of the respective cylinder. The inlet valves and the outlet valves are actuated, for example, respectively by means of an inlet camshaft and an outlet camshaft and thus respectively moved out of the respective closed position into the respective open position and, where necessary, held in the open position.

[0025] Furthermore, the motor vehicle 11 has a control and regulating unit 13 for carrying out a method for operating the internal combustion engine 10 of the motor vehicle 11 in an engine braking operation. The control and regulating unit 13 is provided to carry out the method for controlling camshaft actuators for adjusting the inlet camshaft in relation to the crankshaft and actuators for deactivating outlet valves or switching off outlet strokes as well as for activating engine braking strokes of the internal combustion engine 10. However, in principle it would also be conceivable for the control and regulating unit 13 to be provided for a direct control of outlet valves and inlet valves of a valve train of the internal combustion engine 10.

[0026] The method is provided for operating the internal combustion engine 10 of the motor vehicle 11, in an engine braking operation. The method has at least one engine braking mode. The method has several engine braking modes. The method has three engine braking modes. Here, the engine braking modes can be switched, re, in particular activated and/or deactivated, both manually by an operator and automatically by the control and/or regulating unit. Preferably, in addition to the engine braking modes described, a convention 3-cylinder engine braking operation or 6-cylinder engine braking operation can be switched.

[0027] With the method, an outlet stroke 12 of all outlet valves of at least one cylinder of the first cylinder bank of the internal combustion engine 10 is permanently switched off in a first engine braking mode.

[0028] With the method, the outlet stroke 12 of all outlet valves of at least one cylinder of the first cylinder bank of the internal combustion engine 10 is permanently switched off in each engine braking mode.

[0029] Furthermore, in the engine braking bodes, an opening time point EO1 of all inlet valves of the at least one cylinder of the first cylinder bank is adjusted to “late”. In the engine braking modes, an inlet camshaft of the at least one first cylinder of the first cylinder bank is adjusted to “late”. In the engine braking modes, an inlet camshaft of all cylinders of the first cylinder bank of the internal combustion engine 10 is adjusted to “late” The inlet camshaft of the first cylinder bank of the internal combustion engine 10 is here adjusted to “late” in such a way that a cylinder pressure of the at least one cylinder of the first cylinder bank enables an opening of the inlet valve of the first cylinder. With the method, in the engine braking modes, an outlet stroke 12 of all outlet valves of all cylinders of the first cylinder bank of the internal combustion engine 10 is thus switched off, and an opening time point EO1 of all inlet valves of all cylinders of the first cylinder bank is adjusted to “late”.

[0030] FIG. 3 shows a diagram of a valve elevation of valves of the cylinders of the first cylinder bank via a crank angle for illustrating the method for operating the internal combustion engine 10 in an engine braking mode. The crank angle here describes the respective depictions of the crankshaft around its axis of rotation. FIGS. 2 and 3 each show diagrams on the x-axis 19 of which the rotational positions, i.e., the degree crank angle of the crankshaft, is plotted. The internal combustion engine 10 is here formed as a four-stroke engine, wherein a. so-called work cycle of the crankshaft comprises exactly two rotations of the crankshaft. The work cycle comprises exactly 720° of crank angle. In contrast, an opening height of the valves is plotted on the y-axis 20. The higher the respective course, the wider the corresponding valve is opened with an allocated rotational position of the crankshaft. If the respective course is on the value “zero” plotted on the y-axis 20, then the respective valve is closed. The outlet stroke 12 of all outlet valves of all cylinders of the first cylinder bank here remains at “zero” for the entire work cycle. In contrast, an inlet stroke 16 of all inlet valves of all cylinders of the first cylinder bank is adjusted to “late” in comparison to a regular inlet stroke 16′. The inlet stroke 16 of the inlet valves of the first cylinder bank is adjusted to “late” by a 45° crank angle. However, in principle, a different adjustment angle that seems reasonable to the person skilled in the art would also be conceivable. In order to depict particularly low engine braking powers, the inlet stroke 16 is advantageously adjusted to late by a long way, wherein the maximum adjustment is limited by the inlet valves not coming into contact with the corresponding piston. Thus, on the first cylinder bank, a conventional outlet stroke 12 of all outlet valves of all cylinders is switched off, yet an engine braking stroke is not switched on and, at the same time, the inlet camshaft is adjusted via camshaft actuators so far to “late” that the cylinder pressure against which the inlet valves of the first cylinder bank open does not exceed the maximum cylinder pressure at which this is possible, for example at 20 bar. Preferably, all cylinders of the first cylinder bank, in particular respectively temporally offset, have the same valve elevations across the crank angle. An offset emerges, in particular, from an ignition sequence and from a number of cylinders. FIG. 3 shows a diagram of the valve elevation of valves of the first cylinder of the first cylinder bank across a crank angle by way of example in a first engine braking mode.

[0031] In the first engine braking mode, all outlet valves of all cylinders of a second cylinder bank are closed for a first time, then opened for a first time, and then closed for a second time and then opened for a second time, in order to respectively release gas compressed in the cylinders of the second cylinder bank respectively from the cylinder respectively by means of pistons guided in the cylinders of the second cylinder bank. As shown in FIG. 2, in the first engine braking mode of the method, all outlet valves of the cylinders of the second cylinder bank are closed for a first time, in particular offset in relation to one another, at a first closing time point AS2, then opened for a first time at a first open time point AO2, then closed for a second time at a second closing time point AS2′ and then closed for a second time at a. second opening time point AO2′, in order to release a gas contained in the cylinders of the second cylinder bank respectively from the cylinders respectively by means of pistons guided in the cylinders of the second cylinder bank. Along with the outlet strokes described, other outlets strokes that seem reasonable to the person skilled in the art are also conceivable, in particular a controller of the outlet valves with outlet valve strokes for a backward charging or outlet strokes for an engine brake functioning according to the two-stroke principle. Furthermore, in the first engine braking mode, an opening time point EO2′ of all inlet valves of the cylinders of the second cylinder bank is adjusted to “late”. An inlet stroke 17 of the inlet valves of the second cylinder bank is adjusted to “late” in relation to a regular inlet stroke 17′. The inlet stroke 17 of the inlet valves of the second cylinder bank is adjusted to “late” by 45° of crank angle. However, in principle, a different adjustment angle that seems reasonable to a person skilled in the art would also be conceivable.

[0032] For this, FIG. 2 shows a diagram of a valve elevation of valves of the cylinders of the second cylinder bank across a crank angle for illustrating the method for operating the internal combustion engine 10 in an engine braking mode. In the diagram, a course of the inlet stroke 17 is depicted which describes the movement, i.e., the opening and closing, of an inlet valve of the cylinder of the second cylinder hank. For the sake of clarity, only the course of an inlet valve of a cylinder of the second cylinder bank is depicted in the diagram. Furthermore, in the diagram, a course of an outlet stroke 18 is depicted, which describes the movement, i.e., the opening and closing, of all outlet valves of all cylinders of the second cylinder bank. For the sake of clarity, only the course of an outlet valve of a cylinder of the second cylinder bank is depicted in the diagram. Preferably, all cylinders of the second cylinder bank, in particular respectively offset temporally, have the same valve elevations across the crank angle. An offset emerges in particular from an ignition sequence and from a number of cylinders.

[0033] As can be seen by means of the course of the one outlet stroke 18, the outlet valves of the cylinders of the second cylinder bank are closed twice and opened twice within a work cycle of the cylinders or the allocated pistons. Based on the inlet stroke 17 of the inlet valves of the cylinders of the second cylinder bank, the outlet valves of the cylinders of the second cylinder bank are closed for a first time within the work cycle of the cylinders or the pistons at the first closed time point AS2 shortly after 480° of crank angle. This closed time point AS2 is in the region of the inlet stroke 17. Within the work cycle of the cylinders of the second cylinder bank, the outlet valves of the cylinders of the second cylinder bank are opened for a first time following the first closing at the first closing time point AS2 at the first opening time point AO2 shortly before 660° of crank angle. The outlet valves of the cylinders of the second cylinder bank are then closed for a second time at the second closing time point AS2′ shortly before 240° of crank angle. The outlet valves of the cylinders of the second cylinder bank are then opened for a second time at a second opening time point AO2′ shortly after 240° of crank angle. As a result of the first closing time point AS2 after closing the inlet valves, the fresh air in the cylinders of the second cylinder bank is compressed by means of the pistons. By means of the first opening at the first opening time point AO2 and the second closing at the second closing time point AS2′, the outlet valves carry out a first decompression stroke within the work cycle of the cylinders, such that the cylinders of the second cylinder bank each carry out a first decompression cycle. Here, by means of the first opening at the first opening time point AO2, the fresh air previously compressed by means of the piston or the gas previously compressed by the piston is released from the cylinders of the second cylinder bank via the outlet channels of the cylinders of the second cylinder bank without compression energy stored in the compressed gas being able to be used in order to move the piston from its upper dead center into its lower dead center. Since the internal combustion engine 10 previously had to work to compress the gas, this is accompanied by a braking of the internal combustion engine 10 and thus the motor vehicle. By means of the second opening at the second opening time point AO2′ and the first closing at the first closing time point AS2, the outlet valves of the cylinders of the second cylinder bank each carry out a second decompression stroke within the working cycles of the cylinders, such that the cylinders of the second cylinder bank each carry out a second decompression cycle. As part of these second decompression strokes, gas compressed by means of the pistons in the cylinders of the second cylinder bank is released from the cylinders of the second cylinder bank via the outlet channels of the cylinders within the work cycles of the cylinders of the second cylinder bank without compression energy stored in this gas being able to be used to move the pistons from the upper dead center into the lower dead center. In the engine braking operation, all outlet valves of all cylinders of the second cylinder bank implement a substantially smaller stroke than in the normal operation, i.e., in the fired operation of the internal combustion engine 10.

[0034] The second cylinder bank is thus in the first engine braking mode in the conventional engine braking operation and generates an engine braking power as usual. All cylinders of the first cylinder bank are filled with fresh gas during the suction stroke. Since the elevation of the inlet valves is set to “late”, this begins somewhat later than usual and ends somewhat later than usual, such that a part of the filling is again pushed back into a charging plenum chamber at the start of the compression stroke. Then, the air is compressed in the compression stroke, for which power is received. In the subsequent work stroke, the cylinder pressure is again converted into rotational energy, wherein not all energy is regained as a result of blow-by and heat losses, but rather a part contributes to the engine braking power as thermodynamic dissipation power. In the subsequent extending stroke, the air is compressed again, since the outlet valves of the first cylinder hank do not open. At the start of the subsequent suction stroke, a very high pressure is thus prevalent in the respective cylinder of the first cylinder bank. This pressure is again converted into rotational energy until the point is reached at which the respective inlet valve of the first cylinder bank opens. Now the air can escape on the inlet side. In doing so, as a result of the rapid pressure drop, on the one hand an anti-clockwise cycle emerges. Engine braking power is generated on the cylinders of the first cylinder bank. On the other hand, the highly compressed air which can have up to 20 bar, in particular, serves to additionally load the cylinder of the second cylinder bank, which is at the end of its suction stroke at this time point, with gas. A further effect is that, by no mass throughout being generated on the cylinders of the first cylinder bank, the air is thus only exchanged with the inlet side, yet not with the outlet side, and thus a turbocharger is operated in a different region of its characteristic map. While the turbocharger is usually operated with a 3-cylinder engine braking operation in the lower right region, the operating point now slips to the left towards better degrees of efficiency, such that the system is supplied with a higher charging pressure than in the usual 3-cylinder operation. All this leads to a higher engine braking power being able to be generated than in the conventional 3-cylinder operation. Thus, a further engine braking torque strip emerges that settles between the strips in the usual 3-cylinder engine braking operation and in the 6-cylinder engine braking operation. Depending on the further regulating possibilities, such as using an AGR valve of an exhaust gas recirculation system, for example, the gap between the two strips of the 3-cylinder engine braking operation and the 6-cylinder engine braking operation can thus be closed.

[0035] Alternatively to this, in the first engine braking mode of the method, all outlet valves of all cylinders of the second cylinder bank are opened in the region of an upper dead center and then closed in order to respectively release gas compressed in the cylinders of the second cylinder bank from the cylinders of the second cylinder bank respectively by means of pistons guided in the cylinders of the second cylinder bank. FIG. 2 shows the alternative course of an outlet stroke 18′. Here, the outlet valves of the second cylinder bank in the outlet stroke 18′ open only once in the region of the first opening time point AO2 of the outlet valve stroke 18 in an opening time point AO2″ and then close at about 90° of crank angle in a closing time point AS2″ before the second closing time point AS2′ of the outlet stroke 18. The outlet valves of the second cylinder bank are not opened for a second time and remain closed until the single opening in the region of the upper dead center at 720° of crank angle.

[0036] In a second engine braking mode of the method, all cylinders of the second cylinder bank are operated in a propulsion operation. Thus, on the second cylinder hank, in the second engine braking mode, the normal inlet and outlet valve elevations from a normal operation can be maintained. The first cylinder bank is operated corresponding to the first engine braking mode. On the first cylinder bank, an outlet stroke of all outlet valves is thus switched off, and the inlet camshaft is rotated until all inlet valves of the first cylinder open to a still permissible pressure. As in the first engine braking mode, on the first cylinder bank, an anti-clockwise cycle emerges by releasing cylinder pressure onto the inlet side. Thus, engine braking power is generated. This is lower than the engine braking power normally provided with three cylinders and is thus suitable for closing the gap between a propulsion operation and an engine braking operation with three cylinders. The mass throughput necessary for removing the generated heat is expressed on the cylinders of the second cylinder bank.

[0037] In a third engine braking mode of the method, an outlet stroke of all outlet valves of all cylinders of the first and the second cylinder bank of the internal combustion engine is switched off, and an opening time point EO1, EO2′ of all inlet valves of all cylinders of the first and the second cylinder bank are adjusted to “late”. Accordingly, in the third engine braking mode, all cylinders of the internal combustion engine 10 are operated according to the first cylinder bank in the first engine braking mode. Thus, with all cylinders, the outlet valve stroke is switched off and the inlet camshaft is thus rotated until the inlet valves open to a still permissible pressure. Thus, a decompression event emerges towards the inlet side, in turn thus generating engine braking power. However, no mass throughout is generated by the internal combustion engine 10, whereby the third engine braking mode can only be maintained in the short term. It is nevertheless suitable fur expressing a gentle transition from the propulsion operation into one of the engine braking modes or into the 3- or 6-cykinder engine braking operation or vice versa, which can be useful for reasons of comfort, for example for buses.

LIST OF REFERENCE CHARACTERS

[0038] 10 Internal combustion engine

[0039] 11 Motor vehicle

[0040] 12 Outlet stroke

[0041] 13 Control and regulating unit

[0042] 14 Drive wheels

[0043] 15 Multi-stage transmission

[0044] 16 Inlet stroke

[0045] 17 Inlet stroke

[0046] 18 Outlet stroke

[0047] 19 X-axis

[0048] 20 Y-axis

[0049] AO2 Opening time point

[0050] AO2′ Opening time point

[0051] AS2 Closing time point

[0052] AS2′ Closing time point

[0053] EO1 Opening time point

[0054] EO2′ Opening time point