METHOD FOR OPERATING A SELF-IGNITING ENGINE AND SELF-IGNITING ENGINE

Description

[0001] The invention relates to a method for operating a self-igniting internal combustion engine having the features according to the preamble of claim 1.

[0002] The invention further relates to an internal combustion engine with compression ignition, comprising a control unit, with the features according to the preamble of claim 6.

[0003] A self-igniting internal combustion engine is known, for example, from the publication DE 67207 A. This describes an operating process for internal combustion engines in which pure air or another indifferent gas is compressed with pure air in a cylinder by a working piston to such an extent that the resulting temperature is well above the ignition temperature of the fuel to be used. The fuel is then supplied so gradually from dead center that, due to the expelling piston and the resulting expansion of the compressed air or gas, combustion occurs without a significant increase in pressure and temperature. After the fuel supply has been completed, the gas mass in the working cylinder continues to expand. An internal combustion engine operating according to this principle is also called a diesel engine.

[0004] Such internal combustion engines are widely used in motor vehicles to generate drive torque.

[0005] From the publication DE 32 31 766 A1, a device for regulating the idle speed of an internal combustion engine with spark ignition is known. This device serves to adapt the combustion air ratio to the behavior of the internal combustion engine at idle. The goal is to prevent ignition failures that occur when the combustion air ratio is unfavorable, particularly when the combustion air ratio deviates significantly from 1. If the combustion limit is reached in a cylinder, the mixture of fuel and fresh air cannot ignite, and the power stroke fails. This disturbance in the internal combustion engine's working process is referred to in this publication as "lack of smooth running." As a solution, control measures for the combustion air ratio that take place outside the combustion chamber are proposed.A comparable idle control for a diesel engine would affect the fuel injection control circuit, i.e. adapt the amount of fuel to be injected to the behavior of the internal combustion engine when idling.

[0006] The document DE 103 60 834 A1 describes a method for regulating the idle state, i.e. for maintaining a required engine speed. In this case, special signal processing in the control unit is provided to improve the metering or control of fuel and its injection. The idle control is intended to influence the ignition system in particular. In an internal combustion engine with spark ignition and direct injection, in homogeneous operation, i.e. with a combustion air ratio of 1, the supply of fresh air can be achieved via a throttle valve or via fully variable valve control. In stratified operation, i.e. with a combustion air ratio that deviates significantly from lambda equal to 1, the internal combustion engine is operated unthrottled, i.e. without any limitation on the amount of fresh air supplied. The torque is determined by the metered amount of fuel.When idling, the delivery of drive torque is not required, so only the internal torque of the internal combustion engine needs to be generated.

[0007] A variable valve control is also known from the document US 5,417,186 A. This shows cams that are firmly connected to the camshaft, in which cam elements that can be variably adjusted relative to the camshaft are arranged.

[0008] A diesel engine operates with a high excess air at idle and in all other operating ranges. As a result, a diesel engine does not require a throttle valve for normal operation, unlike a gasoline engine, for example. This is also one of the reasons for the fuel consumption advantage of a diesel engine. A throttle valve is essential for a gasoline engine, as it almost always has to operate in homogeneous mode with a combustion air ratio of 1. The combustion air ratio is also known as lambda or the air ratio.

[0009] Due to its throttle-free operation and the high excess air flow, a diesel engine's idling is always characterized by high idle irregularity. This means that the crankshaft's rotational speed varies significantly during one revolution. The crankshaft is decelerated during the compression stroke and accelerated during the power stroke. Rotational speed is usually expressed as rpm. For example, for a typical 4-cylinder diesel engine in a passenger car, the average rpm is approximately 830 rpm, but the maximum rpm is 930 rpm and the minimum rpm is 720 rpm.

[0010] This leads to strong mechanical vibrations in the engine and corresponding excitations in the body. Furthermore, the engine components are also excited by this torsional vibration. This double acceleration and deceleration with each revolution can cause acoustic abnormalities and possibly even reduce the service life of the components.

[0011] To reduce the amplitude of the vibrations, it is known to throttle the supply of fresh air to the engine. As mentioned above, throttle valves are used in the air intake of gasoline engines, for example. However, restricting the fresh air flow using a throttle valve in a diesel engine leads to increased intake losses and thus to fuel consumption that can be up to 20 percent higher than without a throttle valve. With increased fuel consumption, emissions, particularly of unburned hydrocarbons, also increase significantly.

[0012] An internal combustion engine is a combustion engine that converts the chemical energy of a fuel into mechanical work through combustion. Combustion takes place in at least one combustion chamber, particularly in a cylinder. A mixture of fuel and ambient air is ignited in the combustion chamber. Internal combustion engines typically operate in four process steps, also called strokes. These are the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. This sequence of strokes is also referred to as the working cycle.

[0013] In so-called piston engines, the thermal expansion of the hot gas from combustion is used to move a piston up and down in a cylinder. The working cycle in piston engines is as follows: The intake stroke ends when the piston is positioned at bottom dead center, furthest from the intake valve or exhaust valve, meaning the combustion chamber has its largest volume. This piston position also marks the start of the compression stroke. When the piston reaches top dead center, i.e. closest to at least the intake valve, the combustion chamber has its smallest volume. This piston position marks the end of the compression stroke and the start of the power stroke. When the piston reaches bottom dead center again, the power stroke ends and the exhaust stroke begins.The exhaust stroke is ended and a new intake stroke begins when the piston again reaches the top dead center of its movement.

[0014] Idling describes the operation of an internal combustion engine in which the ratio of output torque, in particular the torque used to propel a motor vehicle, to internal torque is essentially zero, preferably exactly zero. As a consequence, the internal combustion engine does not perform the work for which it is intended. Internal combustion engines come to a standstill below a minimum crankshaft speed. For most motor vehicle engines, this speed is between 700 and 900 revolutions per minute. In order for the engine to maintain this speed, a small amount of fuel is supplied to it when idling. The idle speed is usually set somewhat higher than absolutely necessary to reduce vibrations and to prevent a sudden change to load operation from causing the engine to stall.

[0015] DE 198 25 729 A1 discloses methods for idle control in a piston internal combustion engine with fully variably controllable gas exchange valves. A first method, "late intake closing," involves switching from crank-angle-based control of the intake valve closing time to time-based control when the internal combustion engine is idling. As a result, when the internal combustion engine's speed drops, the intake valve closes earlier without any further action in relation to the crank angle system, thereby increasing the charge and engine speed. In another method, "early intake closing," with the intake valves closing before bottom dead center, the opening time of the intake valves is extended when the engine speed drops, again increasing the charge and engine speed.

[0016] The invention is therefore based on the object of reducing the vibrations of a self-igniting internal combustion engine when idling while maintaining fuel consumption as unchanged as possible.

[0017] The object is achieved by a method according to the features of independent claim 1. The features of the dependent claims relate to further embodiments of the invention.

[0018] The method according to the invention for operating a self-igniting internal combustion engine with at least one combustion chamber having at least one intake valve comprises at least the following steps: The self-igniting internal combustion engine is operated in a load operating state in which the at least one intake valve is closed at a first closing time within a first working cycle. The self-igniting internal combustion engine is then operated at idle. The at least one intake valve is closed at idle at a second closing time within a second working cycle, which second closing time is later within the second working cycle than the first closing time within the first working cycle, in that the second closing time within the second working cycle is retarded by an angle of rotation of the crankshaft compared to the first closing time within the first working cycle.In particular, the time of closing of the at least one intake valve during idle can be shifted.

[0019] The terms idle and working cycle are defined as described in detail above.

[0020] The method according to the invention is used in a piston engine. This means that the combustion chamber is a cylinder. The compression-ignition internal combustion engine has a crankshaft and at least one cylinder in which a piston moves up and down, so that within a working cycle of 720 degrees of crankshaft rotation, an intake stroke, a compression stroke, a power stroke, and an exhaust stroke are executed successively, and to which at least one intake valve and at least one exhaust valve are assigned.

[0021] In other words, the method according to the invention for operating a compression-ignition internal combustion engine provides that the time of closing the intake valve is or will be retarded during idling of the internal combustion engine. According to the invention, the closing of an intake valve thus occurs later than in a regular operating state of the internal combustion engine or in a load operating state. Since the internal combustion engine is a piston engine, even in a regular operating state of the internal combustion engine, the intake valve can be closed later in the working cycle than the piston reaches bottom dead center.

[0022] In other words, the invention provides that when the self-igniting internal combustion engine is idling, the closing of at least one intake valve occurs later than when the engine is operating in a manner other than idling or when the engine is under load.

[0023] Since the invention makes it possible to reduce fuel consumption, emissions from the compression-ignition internal combustion engine are also advantageously reduced. At the same time, idling comfort can be improved.

[0024] Because the intake valve only closes during the compression stroke, i.e., while the piston is moving toward the intake valve, a portion of the fresh air drawn in is forced back out of the cylinder. This reduction in the combustion chamber charge improves idling comfort, as, for example, the resistance to the piston is lower due to the intake valve being open during the compression stroke. For example, when the engine is idling, the intake valve remains open longer during the compression stroke than when the engine is operating in a different operating state than idling, with the intake valve closing time being delayed.

[0025] If the amount of injected fuel required for idle remains unchanged, the later closing of the intake valve reduces the amount of fresh air supplied, thus lowering the air / fuel ratio. This has further beneficial effects on idle comfort. Since less fresh air is available for combustion during the power stroke, the expansion force of combustion acting on the piston is lower than when the cylinder is completely filled with fresh air.

[0026] Due to the two effects mentioned above, the crankshaft is decelerated less during the compression stroke and accelerated less during the power stroke. This reduces the deviation of the instantaneous speed from the average speed, thus making the crankshaft rotation more uniform. This significantly reduces the acoustic abnormalities of a diesel engine when idling and improves idle comfort. At the same time, cylinder filling is reduced without increasing fuel consumption.

[0027] According to the invention, the intake valve is closed during the compression stroke of the engine cycle and before fuel injection, particularly during said compression stroke. This prevents unburned fuel from entering the intake manifold.

[0028] A further development of the method according to the invention is that the opening of an exhaust valve of the internal combustion engine occurs later. This ensures that the combustion process is fully completed, thus preventing unburned fuel from entering the exhaust turbocharger or being expelled. Furthermore, the late opening of the exhaust valve results in minimal compression of the combustion gases, which thus maintain a high temperature despite the lower charge. This is particularly advantageous because it allows the catalytic converter to remain active and the exhaust turbocharger experiences little or no drop in speed.The combination of the adjustment of the intake valve and exhaust valve proves to be a particularly advantageous solution for reducing vibrations and oscillations as well as acoustic noise while maintaining low fuel consumption, low emissions of nitrogen oxides and not fully chemically converted hydrocarbons as well as sufficiently high exhaust gas temperatures.

[0029] The reduction of emissions and of any odor nuisance that may occur when a diesel engine is idling is achieved, among other things, by reducing the air mass flow rate when the internal combustion engine is idling, so that the exhaust gas aftertreatment components, including the exhaust gas turbocharger and catalytic converter, cool down less.

[0030] A particularly advantageous embodiment of the invention has been found to delay the opening of the exhaust valve and / or the closing of the intake valve by a rotation angle of a crankshaft of the internal combustion engine of 20° to 60°, preferably by 50°. This delay occurs relative to the timing typically encountered in a load operating state of the internal combustion engine. This change in the timing of the valves achieves a fuel-neutral reduction in vibrations during idling of a warm diesel engine, without negatively affecting the starting dynamics or reducing the exhaust gas temperature.

[0031] A further development of the invention involves partially closing a throttle valve when the engine is idling. This makes it possible to further reduce the charge and also significantly reduce air column vibrations in the engine's intake system. As a result, the signals from the air mass meter, which is usually located in the air filter box, and, above all, the emission of low-frequency intake noise, are calmed down.

[0032] Adjusting the throttle valve alone to reduce the cylinder's fresh air intake at idle is possible and would also eliminate the aforementioned abnormalities of traditional diesel idling. However, this would be associated with a very sharp increase in emissions and fuel consumption, as well as a physically determined decrease in the turbocharger's speed. Nevertheless, the throttle valve is an extremely fast actuator. Combined with valve adjustment, this has the advantage that the throttle valve opens earlier during acceleration than the variable valves. This significantly improves stopping comfort.

[0033] The fresh air mass can be reduced by up to 50 percent without a significant increase in fuel consumption. A combination of one or more of the above-mentioned features with one or more of the following characteristics has proven advantageous: that a combustion air ratio of greater than 2, preferably in a range between 2 and 5, is set when idling; that an unchanged amount of fuel is injected before or during each compression stroke compared to an operating state of the internal combustion engine other than idling; that the exhaust gas recirculation rate is low or exhaust gas recirculation is suspended; that exhaust gas recirculation takes place in the low-pressure range and / or that no pre-injection takes place. The combination of these features reduces the peak pressure during compression by up to 33 percent, which also leads to improved parking comfort.

[0034] The inventive concept also relates to an internal combustion engine with compression ignition, which comprises a control unit. The control unit has a memory in which a control program is stored, at least a portion of which controls the idling of the internal combustion engine when the control program is executed, particularly in a computer. According to the invention, the control program for applying the method according to the invention is designed with features or combinations of features as shown in this illustration.

[0035] According to a further development of the invention, an embodiment of the internal combustion engine has variable valve timing. Variable valve timing is also commonly referred to as variable valve timing (VVT). The variability can be achieved, for example, by a plurality of cams with different cam curves for actuating the intake or exhaust valve(s) of a combustion chamber, which are arranged axially displaceably on a camshaft.

[0036] The invention allows for numerous embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This shows in Fig. 1 shows a schematic representation of a preferred embodiment of a self-igniting internal combustion engine according to the invention in partial section; Fig. 2 shows a flow diagram of an embodiment of a method for operating a preferred embodiment of a self-igniting internal combustion engine according to the invention.

[0037] Figure 1 shows an embodiment of an internal combustion engine 1 according to the invention in a simplified form in partial section. It is a piston engine. The internal combustion engine 1 has at least one cylinder 2 as the combustion chamber, which is movably sealed by a piston 3. During the intake stroke 18, the cylinder 2 is filled with fresh air 5 from an intake manifold 6 via an intake valve 4. During this period, the piston 3 moves away from the intake valve 4. Finally, the intake valve 4 is closed 20.

[0038] The intake stroke 18 is followed by the compression stroke 21, in which the fresh air 5 in the cylinder 2 is compressed by an opposing movement of the piston 3. An appropriate amount of fuel 8 is metered into the fresh air 5 in the cylinder 2 via an injection nozzle 7. The injection nozzle 7 opens due to the pressure of the fresh air 5 in the cylinder 2 and / or by electrical control of a control unit 9. The compression heats the mixture of fuel 8 and fresh air 5 in the cylinder 2 until auto-ignition 23 occurs. In the power stroke 24, the combustion 25 of the fuel 8 in the cylinder 2 moves the piston 3 away from the intake valve 4 again. After the combustion 25, the combustion gases are expelled from the cylinder 2 via an exhaust valve 10 by the movement of the piston 3. The cylinder 2 is then filled again with fresh air 5 via the intake valve 4. A throttle valve 11 is provided in the intake pipe 6.The angular position of the throttle valve 11 is adjusted by a throttle valve actuator 12 connected to the control unit 9. The internal combustion engine 1 also has an air mass meter 13, which detects the mass of the fresh air 5 flowing to the cylinder 2 via the intake manifold 6. The angular position of the crankshaft 14 is detected by a sensor 15 and transmitted to the control unit 9. Furthermore, a driver request sensor 16 is connected to the control unit 9, via which the driver transmits his torque request to the control unit 9.

[0039] Figure 2shows a flow diagram of an embodiment of the method 17 according to the invention for operating an internal combustion engine 1 with self-ignition 23. At the beginning of the intake stroke 18, the intake valve 4 is opened 19 so that fresh air 5 can flow into the cylinder 2. In the method 17, when the internal combustion engine 1 is idling, the proportion of fresh air 5 compared to the fuel 8 in the cylinder 2 is reduced. This occurs by the closing 20 of the intake valve 4 occurring later than in an operating state of the internal combustion engine other than idling. This retarding of the closing 20 of the intake valve 4 has the consequence that the closing 20 of the intake valve 4 only occurs during the compression stroke 21, but before the injection 22 of the fuel 8. Due to the compression, the mixture of fuel 8 and fresh air 5 in the cylinder 2 is heated until self-ignition 23 occurs.Auto-ignition 23 occurs at the end of the compression stroke 21 or at the beginning of the power stroke 24. During the power stroke 24, the fuel 8 is combusted 25 in cylinder 2. The opening 26 of the exhaust valve 10 also occurs later than in an operating state of the internal combustion engine other than idling. The exhaust valve 10 is only opened 26 during the exhaust stroke 27. The exhaust valve 10 is closed 28 at the end of the exhaust stroke 27 or at the beginning of the intake stroke 18. The supply of fresh air 5 is further limited by an additional partial opening of the throttle valve 11. List of reference symbols

[0040] 1 internal combustion engine 16 Driver request provider 2 cylinder 17 Proceedings 3 Pistons 18 Intake stroke 4 Inlet valve 19 Opening the intake valve 5 Fresh air 20 Closing the intake valve 6 intake pipe 21 compression stroke 7 Injector 22 injection 8 fuel 23 Self-ignition 9 control unit 24 Working cycle 10 outlet valve 25 combustion 11 throttle 26 Opening the exhaust valve 12 Throttle valve actuator 27 Exhaust stroke 13 air mass meter 28 Closing the exhaust valve 14 crankshaft 15 sensor List of reference symbols

[0041] 1 internal combustion engine 16 Driver request provider 2 cylinder 17 Proceedings 3 Pistons 18 Intake stroke 4 Inlet valve 19 Opening the intake valve 5 Fresh air 20 Closing the intake valve 6 intake pipe 21 compression stroke 7 Injector 22 injection 8 fuel 23 Self-ignition 9 control unit 24 Working cycle 10 outlet valve 25 combustion 11 throttle 26 Opening the exhaust valve 12 Throttle valve actuator 27 Exhaust stroke 13 air mass meter 28 Closing the exhaust valve 14 crankshaft 15 sensor

Claims

1. Method for operating a self-igniting (23) internal combustion engine (1) comprising at least one combustion chamber which has at least one inlet valve (4), the operation taking place cyclically in working cycles each defined by a sequence of four strokes, which are an intake stroke, a compression stroke, a combustion stroke and an exhaust stroke, and defined by a rotation of a crankshaft (14) of the internal combustion engine of 720°, the method comprising the following steps: operating the self-igniting (23) internal combustion engine (1) in a load operating state, which is different from an idle mode, in which the at least one inlet valve (4) is closed at a first closing time which is within a first working cycle, subsequently operating the self-igniting (23) internal combustion engine (1) in the idle mode, in which the at least one inlet valve (4) is closed at a second closing time which is within a second working cycle, the second closing time being later within the second working cycle than the first closing time is within the first working cycle, in that the second closing time within the second working cycle is shifted later by an angle of rotation of the crankshaft (14) in a range of 20° to 60°, in comparison with the first closing time within the first working cycle, characterized in that the second closing time occurs during the compression stroke (21) of the second working cycle and before the injection (22) of the fuel (8) during the second working cycle.

2. Method for operating an internal combustion engine (1) according to at least one of the preceding claims, characterized in that the second closing time within the second working cycle is shifted later by an angle of rotation of the crankshaft (14) of 50°, in comparison with the first closing time within the first working cycle.

3. Method for operating an internal combustion engine (1) according to at least one of the preceding claims, characterized in that an outlet valve (4) is opened in the load operating mode at a first opening time which is within the first working cycle, and is opened in the idle mode at a second opening time which is within the second working cycle, the second opening time within the second working cycle being shifted later by an angle of rotation of the crankshaft (14) in a range of 20° to 60°, preferably 50°, in comparison with the first opening time within the first working cycle.

4. Method for operating an internal combustion engine (1) according to at least one of the preceding claims, characterized in that in the idle mode, a throttle valve (11) of the internal combustion engine (1) is partially closed.

5. Method for operating an internal combustion engine (1) according to at least one of the preceding claims, characterized in that an air-fuel equivalence ratio of greater than 2 is set in the idle mode.

6. Internal combustion engine (1) with self-ignition (23), comprising a control unit (9) which has a memory in which a control program is stored, at least one portion of which controls the idle mode of the internal combustion engine (1) when the control program is executed, characterized in that the control program is provided for applying the method according to at least one of the preceding claims.