Arrangement of internal combustion engine and control unit and method for operating an internal combustion engine

Abstract

Arrangement (1) comprising • an internal combustion engine (2) with at least one cylinder (3) and at least one intake valve (4) on the cylinder (3), • a variable valve train (5) for adjusting the maximum lift (24) of the intake valve (4), • a charging device (6) for increasing the pressure of the air introduced via the inlet valve (4), • a control unit (7) for controlling at least the valve train (5), wherein the control unit (7) is designed to: • Detecting whether the internal combustion engine (2) is operated in a critical map range, wherein the map range is defined by an engine load range and an engine speed range, and wherein in the map range at full stroke (8) a predefined pressure gradient limit value (25) of the cylinder pressure gradient in the at least one cylinder (3) is exceeded, and • Setting the maximum stroke (24) to a reduced maximum stroke (9) which is smaller than the full stroke (8) and at which the cylinder pressure gradient (23) is equal to or lower than the pressure gradient limit value (25) when the combustion engine (2) is operated in the critical map range • where the lower value of the engine speed range of the critical map area is at idle speed and the upper value of the engine speed range of the critical map area is at most 60% of the maximum speed (20), and • the upper value of the engine load range of the critical map area is 2 / 3 to 3 / 4 of the full load (22).

Description

[0001] The present invention relates to an arrangement comprising an internal combustion engine and an associated control unit, preferably for a vehicle. Furthermore, the invention relates to a method for operating the internal combustion engine.

[0002] In turbocharged internal combustion engines, particularly gasoline engines with variable valve train, the air intake duct is designed for high charge motion (tumble). This accelerates combustion at part load and increases the potential residual gas content to improve part load efficiency. At low engine speeds and medium load in the turbocharged range, the faster combustion leads to high cylinder pressure gradients and thus to harsh combustion noise. The maximum cylinder pressure gradient, which should not exceed a limit value, can be used as a criterion for evaluating acoustics. A late ignition angle or a late start of injection, or even dual injection, can lead to a reduction in the maximum cylinder pressure gradient. However, these measures are associated with significant fuel consumption disadvantages and high particulate emissions.

[0003] DE 10 2005 034 682 A1 discloses a valve behavior control device for use in an engine that performs ignition timing retardation control to prevent knocking. The control device variably controls the valve behavior of an intake valve in accordance with an operating state of the engine. The control device corrects a control target so that the compression end temperature of a combustion chamber decreases when an amount of retardation of the ignition timing obtained by the retardation control is greater than a predetermined value. The correction is performed only when the engine performance deterioration that would occur if the ignition timing is retarded in a state where the control target is not corrected is predicted to be greater than the engine performance deterioration that would occur if the control target is corrected.

[0004] DE 10 2011 080 304 A1 discloses a method and systems for mitigating engine pre-ignition based on a feedforward pre-ignition probability and feedback from a pre-ignition event. In response to an indication of pre-ignition, a cylinder may be enriched while limiting engine load. The enrichment may be followed by leaning to restore the exhaust catalyst exhaust oxygen levels. The mitigation steps may be adjusted based on engine operating conditions, a pre-ignition count, and the type of pre-ignition.

[0005] DE 198 07 488 C1 proposes that an internal combustion engine has gas exchange valves, namely at least one intake and one exhaust valve, with a variable valve control and that the control unit changes the control times of the valve control depending on the strength of the knock signal in such a way that a cylinder charge is reduced with increasing strength until the knock signal falls below the reference signal, and the cylinder charge increases again when a second reference signal is fallen below.

[0006] DE 10 2008 000 552 A1 relates to a method for operating a self-igniting internal combustion engine, comprising the steps of: specifying a target combustion position and a target combustion noise characteristic; operating at least one cylinder of the internal combustion engine for at least one cycle while maintaining a predetermined first injector and / or air valve control variable and a predetermined second injector and / or air valve control variable; determining an actual combustion position and an actual combustion noise characteristic of the at least one cylinder; comparing the actual combustion position with the target combustion position and, if the actual combustion position deviates from the target combustion position, redetermining the first injector and / or air valve control variable;and comparing the actual combustion noise characteristic with the target combustion noise characteristic and, if the actual combustion noise characteristic deviates from the target combustion noise characteristic, redetermining the second injector and / or air valve control variable;

[0007] The object of the present invention is to enable operation of the internal combustion engine with the lowest possible noise development while at the same time achieving optimal fuel consumption and low pollutant emissions and to provide a corresponding method to achieve this goal.

[0008] The problem is solved by the features of the independent claims. The dependent claims relate to advantageous embodiments of the invention.

[0009] The object is thus achieved by an arrangement, preferably for a motor vehicle, comprising an internal combustion engine with at least one cylinder and at least one inlet valve on the cylinder for the charge air. The internal combustion engine is in particular a spark-ignition internal combustion engine, preferably a gasoline engine. The internal combustion engine has a variable valve train. This serves at least to adjust the maximum lift of the inlet valve. Furthermore, the variable valve train can also actuate the inlet valve according to the angular position of the crankshaft or the phase position. The arrangement further comprises a charging device, preferably designed as a turbocharger or compressor, for increasing the pressure of the air that can be introduced via the inlet valve. This is therefore a charged internal combustion engine. In addition, the arrangement comprises a control unit, in particular an engine control unit, for controlling at least the valve train.

[0010] Depending on engine load and engine speed, the control unit can, among other things, specify the maximum intake valve lift and, especially in acoustically critical operating conditions, limit the maximum cylinder pressure gradient by reducing the maximum lift. The acoustically critical operating condition is specified here by a critical map range.

[0011] The control unit is designed to: detect whether the internal combustion engine is operated in the critical map range, wherein the map range is defined by an engine load range and an engine speed range, and wherein in the map range at the greatest possible maximum stroke a predefined pressure gradient limit value of the cylinder pressure gradient in the at least one cylinder is exceeded, and setting the maximum stroke to a reduced maximum stroke which is smaller than the full stroke (greatest possible stroke) and at which the cylinder pressure gradient is equal to or lower than the pressure gradient limit value when the internal combustion engine is operated in the critical map range.

[0012] The key advantage of changing the cylinder pressure gradient by reducing the maximum lift of the intake valve is that this results in minimal or no functional disadvantages with regard to fuel consumption and pollutant emissions. Thus, the invention provides that when the internal combustion engine is operating in the critical characteristic map range, the maximum lift of the intake valve is adjusted to a reduced maximum lift. The reduced maximum lift is smaller than the full lift.

[0013] The full stroke defined here (also: maximum possible stroke) is the largest maximum stroke occurring in the entire engine map. In particular, the full stroke is determined by the mechanics of the variable valve train.

[0014] The cylinder pressure gradient is defined as the change in cylinder pressure over the crankshaft position. The unit for the cylinder pressure gradient is thus bar / °CA, where °CA is the angular position of the crankshaft.

[0015] By reducing the maximum stroke according to the invention, the charge motion is reduced to achieve slower combustion. This reduces the maximum cylinder pressure gradient and quiets the combustion noise.

[0016] Preferably, the control unit stores the maximum intake valve lift in a characteristic map spanned by engine load and speed, and reduces it in acoustically critical operating ranges. Other parameters that influence the maximum valve lift may include ambient conditions (temperature, relative humidity, pressure, fuel quality, etc.).

[0017] As described at the beginning, the acoustically critical characteristic map range lies at low engine speeds and in the medium load range. The highest cylinder pressure gradients and thus the highest noise development occur in these ranges in particular. According to the invention, the lower value of the engine speed range of the critical characteristic map range is approximately at idle speed, in particular between 600 rpm and 1000 rpm. Furthermore, the invention provides that the upper value of the engine speed range of the critical characteristic map range is at most 60%, preferably at most 55%, of the maximum speed. The maximum speed is the maximum speed occurring in the entire characteristic map of the internal combustion engine. In particular, the speed of the internal combustion engine is limited to this maximum speed by the control unit.

[0018] The minimum engine load of the critical map range is preferably the beginning of the boosted range with an effective mean effective pressure of preferably 8 to 12 bar. According to the invention, the upper value of the engine load range of the critical map range is 2 / 3 to 3 / 4 of full load.

[0019] The permissible maximum pressure gradient depends on the acoustic requirements and the specific characteristics of the vehicle. The maximum pressure gradient should not exceed 6 bar / °C, preferably 5 bar / °C, in the acoustically critical operating range of the engine.

[0020] To achieve this goal, it is preferred to limit the maximum valve lift in individual operating ranges to 60% to 80%, preferably approximately 70%, of full lift. Advantageously, the maximum valve lift is continuously increased up to full lift toward the interval limits of the critical characteristic map range.

[0021] Furthermore, an injection device is preferably provided on the cylinder, so that the internal combustion engine is designed as a direct-injection internal combustion engine.

[0022] The invention further comprises a method for operating an internal combustion engine, in particular the internal combustion engine just described. The method is used in particular in a motor vehicle.The method comprises at least the following steps: (i) detecting whether the internal combustion engine is operated in a critical map range, wherein the map range is defined by an engine load range and an engine speed range, wherein in the critical map range a charging of the internal combustion engine with charge air takes place and wherein in the map range at full lift of an intake valve a pressure gradient limit value of the maximum cylinder pressure gradient in at least one cylinder of the internal combustion engine is exceeded, (ii) setting the maximum lift to a reduced maximum lift which is lower than the full lift and at which the maximum cylinder pressure gradient is equal to or lower than the pressure gradient limit value when the internal combustion engine is operated in the critical map range.

[0023] The advantageous embodiments and subclaims described within the scope of the arrangement are correspondingly advantageously applied to the method according to the invention.

[0024] The method specifically stipulates that when the combustion engine is operating outside the critical engine map range, the maximum lift is higher than the reduced maximum lift. If the engine load is further increased at low engine speed due to increasing boost pressure, the ignition angle must be reduced to prevent knocking. This reduces the maximum cylinder pressure gradient in this operating range anyway, and the maximum intake valve lift can be increased again. This allows the combustion engine to be thermodynamically optimally adjusted near the full-load line, achieving the maximum possible torque.

[0025] As engine speed increases, the maximum cylinder pressure gradient decreases because the combustion rate increases disproportionately and combustion slows down relative to the angular position of the crankshaft. Accordingly, the maximum stroke can be increased in this range as well, and the maximum possible engine power can be achieved without throttling by the intake valve lift.

[0026] In addition to the described reduction of the cylinder pressure gradient by a reduced maximum lift of the intake valve, it is preferably provided to reduce the cylinder pressure gradient by larger valve overlaps and / or by a later ignition angle and / or a double injection.

[0027] Further details, features and advantages of the invention will become apparent from the following description and the figures: Fig. 1 shows a schematically simplified representation of an arrangement according to the invention for carrying out the method according to the invention according to an embodiment, Fig. 2 shows a characteristic map of the internal combustion engine of the arrangement according to the invention according to the embodiment, Fig. 3 shows a curve for the cylinder pressure gradient in the internal combustion engine of the arrangement according to the invention according to the embodiment, and Fig. 4 shows valve lift curves in the internal combustion engine of the arrangement according to the invention according to the embodiment.

[0028] In the following, an arrangement 1 and an associated method for operating the arrangement 1 are explained in detail using an exemplary embodiment.

[0029] Fig. Figure 1 shows a highly simplified schematic representation of the assembly 1 comprising an internal combustion engine 2 for a vehicle. The internal combustion engine 2 includes at least one cylinder 3. A piston (not shown) moves within the cylinder 3. The piston, in turn, causes a rotational movement of a crankshaft.

[0030] An intake valve 4 is provided on cylinder 3. This intake valve 4 can be opened and closed by means of a variable valve train 5. Air can be introduced into cylinder 3 at the intake valve 4. This air is compressed by a charging device 6. The charging device 6 is, for example, an exhaust gas turbocharger.

[0031] Furthermore, a control unit 7 is provided for controlling the internal combustion engine 2, in particular the variable valve train 5. Furthermore, an injection device 10, a spark plug 27, and an exhaust valve 26 are provided. Fuel is injected directly into the cylinder 3 by means of the injection device 10.

[0032] It is therefore an internal combustion engine 2 with charge air charging and variable valve train 5.

[0033] In a critical map area, with medium load and low speed, as shown below using Fig. 2, in such an internal combustion engine 2, a full lift 8 (greatest possible maximum lift) of the intake valve 4 is usually used. Within the scope of the invention, however, it is proposed to use a reduced maximum lift 9 in the specific characteristic map range.

[0034] Fig. 2 shows an engine speed of 19 on the horizontal axis. The engine load of 21 is shown on the vertical axis. Fig. 2 shows the entire characteristic map of the combustion engine 2 with a maximum speed of 20 and a full load of 22.

[0035] In the diagram after Fig. 2 different cylinder pressure gradients are shown: 11: cylinder pressure gradient with 1 bar / °KW; 12: cylinder pressure gradient with 2 bar / °KW; 13: cylinder pressure gradient with 3 bar / °KW; 14: cylinder pressure gradient with 4 bar / °KW; 15: cylinder pressure gradient with 5 bar / °KW; 16: cylinder pressure gradient with 6 bar / °KW; 17: cylinder pressure gradient with 7 bar / °KW.

[0036] The cylinder pressure gradients 11 to 17 shown are each the changes in the measured cylinder pressure in cylinder 3 over the crankshaft position.

[0037] Based on Fig. 2 clearly shows that very high cylinder pressure gradients occur in the range of low engine speeds and medium engine loads. Typically, in turbocharged internal combustion engines, the full lift 8 of the intake valve 4 is set in this range. Within the scope of the invention, it is proposed to set the reduced maximum lift 9 in order to reduce the cylinder pressure gradient in this critical engine map range.

[0038] Fig. Figure 3 shows the maximum lift 24 of the intake valve 4 on the horizontal axis. The cylinder pressure gradient 23 is shown on the vertical axis. The course of the plotted curve shows that as the maximum lift 24 increases, the cylinder pressure gradient 23 also increases. Therefore, within the scope of the invention, it is proposed to use at most the reduced maximum lift 9 in order to keep the cylinder pressure gradient 23 as low as possible and thus reduce noise generation. The reduced maximum lift 9 is set according to a desired pressure gradient limit value 25.

[0039] Fig. 4 shows lift curves for the intake valve 4 with the full lift 8 and several possible reduced maximum lifts 9 which are used depending on the required reduction of the cylinder pressure gradient. List of reference symbols: 1 arrangement 2 combustion engine 3 cylinders 4 Inlet valve 5 variable valve train 6 Charging device 7 Control unit 8 Full stroke (largest possible maximum stroke) 9 reduced maximum stroke 10 Injection device 11-17 Cylinder pressure gradient values 19 Engine speed 20 Maximum speed 21 Engine load 22 Full load (maximum load) 23 Cylinder pressure gradient 24 maximum stroke 25 Pressure gradient limit 26 Exhaust valve 27 Spark plug

Claims

[1] Arrangement (1) comprising • an internal combustion engine (2) with at least one cylinder (3) and at least one intake valve (4) on the cylinder (3), • a variable valve train (5) for adjusting the maximum lift (24) of the intake valve (4), • a charging device (6) for increasing the pressure of the air introduced via the inlet valve (4), • a control unit (7) for controlling at least the valve train (5), wherein the control unit (7) is designed to: • Detecting whether the internal combustion engine (2) is operated in a critical map range, wherein the map range is defined by an engine load range and an engine speed range, and wherein in the map range at full stroke (8) a predefined pressure gradient limit value (25) of the cylinder pressure gradient in the at least one cylinder (3) is exceeded, and • Setting the maximum stroke (24) to a reduced maximum stroke (9) which is smaller than the full stroke (8) and at which the cylinder pressure gradient (23) is equal to or lower than the pressure gradient limit value (25) when the combustion engine (2) is operated in the critical map range • where the lower value of the engine speed range of the critical map area is at idle speed and the upper value of the engine speed range of the critical map area is at most 60% of the maximum speed (20), and • the upper value of the engine load range of the critical map area is 2 / 3 to 3 / 4 of the full load (22). [2] Arrangement according to claim 1, characterized by that the critical map range in which the pressure gradient limit value (25) is exceeded at full stroke (8) is stored in the control unit. [3] Arrangement according to one of the preceding claims, characterized bythat the idle speed is between 600 and 1000 rpm and / or that the upper value of the engine speed range of the critical map area is at most 55% of the maximum speed (20). [4] Arrangement according to one of the preceding claims, characterized by that the pressure gradient limit value (25) is not more than 6 bar / °KW. [5] Arrangement according to one of the preceding claims, characterized by that the reduced maximum stroke (9) is 60% to 80% of the full stroke (8). [6] Arrangement according to one of the preceding claims, characterized by an injection device (10) for directly injecting fuel into the at least one cylinder (3). [7] Method for operating an internal combustion engine (2) comprising the following steps: • Detecting whether the internal combustion engine (2) is operated in a critical characteristic map range, wherein the characteristic map range is defined by an engine load range and an engine speed range, wherein in the critical characteristic map range a charge air charging of the internal combustion engine takes place, and wherein in the characteristic map range at full lift (8) of an intake valve (4) a pressure gradient limit value (25) of the cylinder pressure gradient in at least one cylinder (3) of the internal combustion engine (2) is exceeded, and • Setting the maximum stroke (24) to a reduced maximum stroke (9) which is lower than the full stroke (8) and at which the cylinder pressure gradient (23) is equal to or lower than the pressure gradient limit value (25) when the combustion engine (2) is operated in the critical map range • where the lower value of the engine speed range of the critical map area is at idle speed and the upper value of the engine speed range of the critical map area is at most 60% of the maximum speed (20), and • the upper value of the engine load range of the critical map area is 2 / 3 to 3 / 4 of the full load (22). [8] Method according to claim 7, characterized by that outside the critical map range the maximum stroke (24) is higher than the reduced maximum stroke (9).

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