Device for controlling an internal combustion engine

Abstract

A control device for lean fuel operation of an internal combustion engine having a closable exhaust valve is further improved with respect to increased comfort and reduced pollutants. The device controls an internal combustion engine (1) in an electric hybrid vehicle having a motor vehicle, the internal combustion engine (1) having a plurality of cylinders (2) each having at least one two-stage switchable exhaust valve (6), and an electronic control unit (10) controls the internal combustion engine (1) to: a number of cylinders 2 of the internal combustion engine 1 can each be stopped for at least one operating cycle, at least the exhaust valves 6 remaining closed, - the exhaust and intake valves of the cylinder 2 of the internal combustion engine 1 are controlled synchronously, and - In at least the first cylinder 2, from the end of the stop, first the exhaust valve 6 is opened with the intake valve 5 closed, and the trapped gases are exhausted without injection and ignition.

Description

[Technical field]

[0001] The present invention relates to a device for controlling an internal combustion engine in a motor vehicle, in particular an electrified hybrid motor vehicle having an internal combustion engine and an electric motor (traction electric machine (thrust electric machine)) as a drive motor. [Background technology]

[0002] In the operation of an internal combustion engine, one or all cylinders of the internal combustion engine are partially shut down during certain operating phases, for example during gear shifting or engine braking, where shut down is understood to mean the temporary cancellation of ignition and injection.

[0003] During shutdown, oxygen or fresh air is usually pumped in by the internal combustion engine, which "poisons" the catalyst. To ensure the catalyst functions, a rich fuel mixture must first be set up when the internal combustion engine is restarted following shutdown.

[0004] However, rich operation leads to increased fuel consumption. In addition, the pumping of air during the engine braking phase by the internal combustion engine leads to a large drag torque. The increased drag torque also has a negative impact on energy efficiency.

[0005] For example, from US Pat. No. 5,399,633 a method for controlling an internal combustion engine is known, in which cylinders of the internal combustion engine are stopped for at least one operating cycle and, in a further method step, at least one exhaust valve respectively assigned to the stopped cylinder remains closed for at least one exhaust cycle which takes place immediately before, during and / or after the cylinder is stopped.

[0006] According to the document DE 10 200 03 133 A1, preferably fresh air is trapped during shutdown. At the end of shutdown, a fuel mixture can be injected into the trapped fresh air and ignited in order to prevent "poisoning" of the catalyst. Conventional internal combustion engine operation can then proceed. However, the transition from shutdown to conventional operation with combustion is then problematic, especially since the trapped gases are not known for their exact composition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent Invention No. 102019115761 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the invention is to further improve a control device for the lean operation of an internal combustion engine having a closable exhaust valve with respect to increased comfort and reduced pollutants. [Means for solving the problem]

[0009] This problem is solved according to the invention by means of the features of the independent claims. Advantageous developments of the invention are the subject of the dependent claims.

[0010] The present invention is based on the following considerations:

[0011] In gasoline engines, the technology of exhaust switching rocker arms ("ASSH": two-stage switchable exhaust valves: open / closed) is increasingly being used to control the exhaust valves. The control of the adjustable exhaust switching rocker arms is further improved with regard to advantageous transition states and transition functions according to the present invention. If the transition from the closed state of the exhaust switching rocker arms (so-called "ASSH operation") to a new opening ("stopping ASSH operation") is not coordinated, uncontrolled combustion can lead to shocks in the driving characteristics.

[0012] If the exhaust valve remains closed, for example from the last exhaust stroke before shutdown, residual gases remaining in the combustion chamber of an internal combustion engine after ignition, which would normally be exhausted from the combustion chamber during normal combustion operation, become trapped in the combustion chamber.

[0013] If the exhaust valve is held closed for the first time after shutdown has begun, outside air will be trapped in the combustion chamber, replacing the residual gases.

[0014] If the shutdown lasts for multiple cycles, the exhaust valve will accordingly remain closed for the entire duration of the shutdown.

[0015] During shutdown in an internal combustion engine, typically not just one but all cylinders present are shut down, and the shutdown of several cylinders is likely to be staggered based on different cycles.

[0016] When the internal combustion engine is prepared for shutdown, ignition and injection are cycled off.

[0017] Preferably, both the intake valve and also the exhaust valve assigned to the cylinder to be stopped remain closed for at least one cycle immediately before, during and / or after the cylinder is stopped, so that no fresh air is drawn in or expelled, which in turn particularly reliably avoids flushing of the catalyst with fresh air, also called "pollution".

[0018] The intake and exhaust valves are, for example, closed during the same operating cycle, thus keeping the combustion chamber completely closed for the duration of the shutdown.

[0019] During shutdown, trapped gases (especially residual gases from the last combustion) can be repeatedly compressed. This is achieved in particular by the combustion chamber remaining completely closed during shutdown, so that the shut-down cylinder acts like a gas spring.

[0020] The switching rocker arm is a lever that can be brought into an actuated or inactive state by means of a two-stage actuator. In the actuated state, the switching rocker arm can operate the assigned valve in cooperation with the camshaft. In the inactive state, the switching rocker arm does not operate the valve regardless of the position of the camshaft, i.e. if the switching rocker arm is inactive, the valve remains closed.

[0021] The method according to the invention is applicable in conventional motor vehicles having an internal combustion engine, in particular in engine braking operation of the internal combustion engine, and in hybrid vehicles which, in addition to the internal combustion engine, have an electric motor for driving the motor vehicle.

[0022] The internal combustion engine can include a continuously adjustable valve actuation on the intake side, which allows the stroke of the intake valve to be continuously reduced to prepare for the cylinder shutoff. Furthermore, this allows the engine drag torque to be kept small, which in particular is also reduced by the exhaust valve being turned off. By reducing the valve stroke on the intake side, the drag torque can be further reduced. In addition, a quick return to conventional internal combustion engine operation after shutoff can be achieved.

[0023] According to the invention, the basically known operating strategy for keeping the exhaust valves closed as required is further developed as follows, in particular by means of an exhaust switching rocker arm:

[0024] During shutdown, residual gases from the last combustion before shutdown are trapped by early closing of the exhaust valve or all of the exhaust valves on the cylinder. Immediately following closure of the exhaust valve or valves, the intake valve or valves on the cylinder are also closed, in order to draw in and trap as little outside air as possible.

[0025] However, the medium in the form of residual gas trapped in the cylinder during shutdown has an unknown composition, depending for example on thermodynamic disturbances. The medium may contain at least a small proportion of outside air, the ratio of the residual gas to the outside air may be unknown and may vary. Injection and ignition before a new opening of the exhaust valve after shutdown may therefore lead to unpredictable torque jumps ("shocks").

[0026] Therefore, according to the invention, in at least the first cylinder, after stopping and exhaust valve closing, the exhaust valve is first opened with the intake valve closed, in order to completely expel the trapped medium, and then the intake valve is opened again to take in a defined (known) amount of fresh air in order to proceed with a defined and defined injection and combustion.

[0027] In this case, only a small percentage of unwanted outside air may be contained in the residual gas, but this outside air will have a less negative effect on the catalyst than faulty combustion due to the unknown composition of the residual gas or the previously trapped medium.

[0028] However, this makes it possible to ensure a defined optimum combustion according to the target torque request already in the next cycle.

[0029] A stop with trapped residual gases results in a negative torque transition, which is preferably compensated for by the electric motor in hybrid vehicle applications. Periodic rotational irregularities at the start and / or end of a stop can essentially be compensated for by the electric motor.

[0030] From the end of the stop, for example, there is first a transition to a fuel (thrust) cutoff, in which at least a minimum amount of ignitable fresh air is drawn in. This causes the reduced torque to increase again. Any deviations from the required nominal torque are likewise compensated for by the electric motor in the transition phase.

[0031] Thus, according to the invention, the medium trapped at the stop is first discharged before the intake valve stroke is synchronously opened, i.e. the first cylinder to reach the new opening of the exhaust valve receives a defined charge and injection for the desired combustion.

[0032] The regulator of the exhaust valve in the form of a switching rocker arm operates on a cycle basis, whereas the regulator of the intake valve in the form of a (fully) variable valve actuator operates on a time basis for all cylinders. If the intake valve opens too early, the cylinder with the medium that has not yet been discharged receives fresh air intake, which leads to an undesirable introduction of oxygen into the catalytic system. For a quick transition to partial load, the exhaust and intake valves can be controlled synchronously, so that there may be cylinders with a volume of fresh air that has not yet been discharged. Nevertheless, it is possible to carry out injection into said cylinder before the discharge process is completed in order to obtain a combustion torque. This may result in a more rapid torque increase. Thus, the discharge of residual gases or trapped medium without (without) injection and ignition can be limited to the first cylinder after the shutdown.

[0033] Further advantages and features of the present invention will become apparent from the following description and the accompanying drawings, in which: [Brief description of the drawings]

[0034] [Figure 1] FIG. 2 shows the essential components of a control device according to the invention. [Diagram 2] FIG. 13 illustrates the torque transition produced by the present invention when transitioning from shutdown to controlled combustion, e.g., at least fuel cutoff with combustion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] 1 shows a schematic representation of an internal combustion engine 1 having several cylinders, for example a gasoline engine, of which only one cylinder 2 is shown representatively. As is known, the cylinder 2 is composed of a cylinder head 3 and a piston 4 supported movably in the cylinder. In the cylinder head 3, a valve seat for at least one intake valve (inlet valve) 5, a valve seat for at least one exhaust valve (outlet valve) 6, and a spark plug 7 are arranged.

[0036] The general functioning of an internal combustion engine is sufficiently known from the prior art, so that it will not be discussed further here.

[0037] Furthermore, it is known that in the operation of an internal combustion engine, during certain operating phases, one or all cylinders of the internal combustion engine may be partially shut down, for example during a gear shift.

[0038] In order to avoid flashing of the catalyst by outside air, according to the invention, all exhaust valves 6 assigned to the deactivated cylinders 2 are arranged to remain closed immediately after the last combustion before the deactivation.

[0039] For this purpose, the internal combustion engine 1 is provided on the exhaust side (outlet side) with a valve actuator 8 which is variable in at least two stages for opening and closing the exhaust valves 6 of the internal combustion engine 1 .

[0040] For example, the valve actuation part 8 comprises, on the exhaust side, for example, a stage system, which comprises a valve with switchable hydraulic valve compensation (hydraulic valve adjustment), a camshaft with a sliding cam and / or a switchable rocker arm.

[0041] If necessary, the valve actuator 8 can be switched so that the exhaust valve 6 remains closed independent of the cycle. The valve actuator 9 on the intake side (inlet side) can be continuously adjustable. The valve actuators 8, 9 are shown only diagrammatically in FIG. 1 for simplicity.

[0042] A suitably programmed electronic control unit 10 is provided for controlling the valve actuators 8, 9 as required in accordance with the present invention.

[0043] Further implementation details of the invention are explained below on the basis of FIG. 2, in which the time t is plotted on the x-axis and the torque M is plotted on the y-axis.

[0044] The operating cycle of the internal combustion engine 1 is typically composed of an intake cycle in which outside air is drawn in, a compression cycle in which the drawn in outside air is compressed and a fuel mixture is injected into the combustion chamber of the internal combustion engine 1, a combustion cycle in which the compressed mixture is ignited, and an exhaust cycle in which the burnt gas is exhausted from the combustion chamber via the exhaust valve 6.

[0045] The stopping takes place, for example, during engine braking or coasting operations.

[0046] In motorized vehicles, the driving conditions in which the internal combustion engine 1 continues to move with the vehicle mass when the force flow is not separated, i.e. when the clutch is not released, are called engine braking operation. Such driving conditions occur, for example, when driving downhill. In hybrid vehicles, the electric machine can also pull the internal combustion engine together in certain load conditions.

[0047] The exhaust valve 8 remains closed during the exhaust cycle immediately prior to shutdown, i.e. after the last ignition before shutdown. The intake valve 9 likewise remains closed during the intake cycle immediately prior to shutdown. Residual gases that would be exhausted via the exhaust valve 8 in conventional operation are therefore trapped in the cylinder 2.

[0048] During the final exhaust cycle before ignition begins again, the exhaust valve 8 is cycled open so that any remaining trapped gases are exhausted or vented without combustion (i.e. without injection and ignition). The intake valve 9 is then opened and fresh air is drawn in. Thereafter, operation of the internal combustion engine 1 proceeds, i.e. injection and ignition are cycled on.

[0049] In Figure 1, a traction electric machine 11 is provided as a further drive motor in addition to the internal combustion engine 1. By means of the superimposed torque M of the traction electric machine 11, the unpleasant torque drop of the internal combustion engine is compensated.

[0050] FIG. 2 shows the transition back to conventional operation with an internal combustion engine after a shutdown, in particular with a compensatory torque intervention of the traction electric machine 11 .

[0051] The following torque levels are shown diagrammatically in FIG. M1 = maximum torque during engine braking due to combustion M2 = Actual torque before shutdown and exhaust valve closing M3 = minimum torque for non-combustion engine braking operation

[0052] The torque profile M_V of the internal combustion engine 1 is shown by a dotted line, which undergoes cylinder shutdown with exhaust valve closure to trap residual gases up to time t1, between times t1 and t2 it undergoes the discharge of residual gases without injection and ignition, and between times t2 and t3 it is controlled to increase again to the target torque, here M1, according to a preset gradient.

[0053] The V-shaped torque drop of the torque profile M_V of the internal combustion engine 1 is compensated by the superimposed torque M of the traction electric machine 11: 1. In this embodiment, the setpoint torque M_E of the electric machine 11 is zero (0 [Nm]) before the time t1 and after the time t3. Instead of a zero setpoint torque M_E of the electric machine 11, basically every arbitrary operating point in traction or propulsion operation can be predefined as a setpoint torque M_E at which a compensation torque is applied. 2. At time t2, the electric machine 11 has to set, by means of its torque M_E, the increased drag torque (coasting torque) M_V of the internal combustion engine 1 and the changed driver intention M_soll. 3. From the time t3 onwards, the driver's intention M_soll is again determined exclusively by the torque M_V of the internal combustion engine 1.

[0054] The desired torque transition M_soll is shown by a dashed line, which can be caused, for example, by a driver setting (e.g. switching from a depressed brake to an accelerator pedal) and which, without the invention, could lead to unpleasant shocks.

[0055] In the following, the "ASSH operation" shutdown scenario is explained in more detail. Thus, according to the invention, the unknown mixture in the cylinder should preferably not be ignited but should first be expelled. This would increase engine friction. Then, preferably, at least the first cylinder is filled with a minimum amount of air and ignited with the lowest efficiency. From here, the combustion is slowly brought to an optimal combustion so that a torque increase between the time t2 and the time t3 can be achieved with a preset gradual ramp R. The purpose of said gradual ramp R is to allow as good a compensation as possible by the electric machine 11, since a steep or uncontrolled gradient cannot be well compensated by the electric machine.

[0056] Similarly, the transition from "normal operation" to ASSH operation can be controlled.

Claims

1. A device for controlling an internal combustion engine (1) in a motor vehicle, in particular an electric hybrid vehicle with a traction electric machine (11), the internal combustion engine (1) having a number of cylinders (2) each with at least one two-stage switchable exhaust valve (6), the device being arranged to control the internal combustion engine (1) by means of an electronic control unit (10): - a number of cylinders (2) of the internal combustion engine (1) can each be shut down for at least one operating cycle, with at least the exhaust valves (6) remaining closed; - the exhaust and intake valves of the cylinders (2) of the internal combustion engine (1) are controlled synchronously, and - in at least the first cylinder (2), from the end of the stop, first the exhaust valve (6) is opened with the intake valve (5) closed, and the trapped gases are discharged without injection and ignition An apparatus comprising:

2. 2. The device according to claim 1, characterized in that only in the first cylinder (2), from the end of the stop, the exhaust valve (6) is first opened with the intake valve (5) closed and the trapped gases are discharged without injection and ignition, and in the other cylinders after the first cylinder (2), from the end of the stop, at least a predetermined minimum amount of fuel is injected and ignited before the discharge of the trapped gases.

3. 3. The device according to claim 1, wherein the negative torque transitions (M_V) caused by a stop with trapped residual gases are compensated for by the traction electric machine (11).

4. 4. The device according to claim 1, wherein after the ejection of trapped gases without injection and ignition, at least the first cylinder (2) is subsequently filled with a minimum amount of air and ignited with the lowest efficiency, and from this combustion is controlled to be increased for a torque increase with a gradual ramp (R) that is preset so as to be compensated for by the traction electric machine (11).

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