Method for improving the cold start and warm-up behavior of a 4-stroke internal combustion engine

Abstract

The invention relates to a method for improving the cold-start and warm-up behavior of a four-stroke internal combustion engine. The objective is to provide a method that is cost-effective and environmentally friendly, requiring minimal additional technical effort, and avoids complex modifications to previously known internal combustion engine components. The method operates with a cold-start mode using a first camshaft control and an operating mode using a second camshaft control. At a crankshaft position between low top dead center (LWOT) and 110° crank angle (CA), a vacuum is generated, causing a gas enclosed in the combustion chamber to expand. Subsequently, at a crankshaft position between 110° CA and 180° CA, an airflow loaded with turbulent kinetic energy is generated in the combustion chamber. Upon reaching a determined target temperature, the system switches to the operating mode, in which a second camshaft control is activated.The process can be used to operate 4-stroke combustion engines, for example with a pure or mixed alcoholic fuel, gasoline or diesel fuel.

Description

[0001] The invention relates to the technical field of internal combustion engines and concerns a method for improving the cold-start and warm-up behavior of a four-stroke internal combustion engine. The method according to the invention can be used to operate four-stroke internal combustion engines that run, for example, on pure or mixed alcoholic fuel, gasoline, or diesel fuel.

[0002] The cold-start behavior of combustion engines is a crucial factor influencing emissions, fuel consumption, and engine wear. At low temperatures, many processes within the engine function only to a limited extent, such as fuel vaporization and the lubrication of engine components, resulting in higher friction losses.

[0003] For a successful cold start of an internal combustion engine, two essential requirements must be met in the combustion chamber. Firstly, a combustible air-fuel mixture must be present in the cylinder's combustion chamber, capable of spontaneous ignition or ignition by an ignition device. Secondly, the ignited air-fuel mixture must release sufficient energy to perform enough work at the piston and overcome the engine's inherent energy losses.

[0004] Several technical solutions for improving the cold-start performance of an internal combustion engine, enabling it to reach the desired operating temperature more quickly, are already known. For example, devices for preheating the coolant and engine oil using electric auxiliary heaters or parking heaters are known. It is also known to preheat the intake air in the intake manifold, to provide additional air control devices in the intake manifold upstream of the intake valve, or to control the ignition or injection via sensors.

[0005] From DE 10 2013 206 575 A1, an engine control method for an internal combustion engine powered by alcohol fuel is known, in which fuel injection is carried out during engine starting if the intake manifold pressure falls below a threshold value, the threshold value being based on fuel volatility.

[0006] DE 39 10 528 A1 discloses a method for cold-starting an internal combustion engine powered by an alcohol fuel, which is carried out in a cold-start device of an internal combustion engine powered by an alcohol fuel. When the engine is cold, gasoline is drawn from the gasoline circuit and stored in a gasoline storage and supply device as long as the alcohol fuel system is not activated. When the internal combustion engine is started, the gasoline is then supplied to the engine's intake manifold without delay and in a precisely metered manner to initiate combustion with gasoline until the engine reaches a predetermined temperature threshold sufficient to sustain combustion with alcohol fuel, whereupon the supply of alcohol fuel to the alcohol fuel injectors is released and the gasoline injection is interrupted.

[0007] DE 10 2016 114 300 A1 proposes a method for an engine in which fuel injection is carried out during a cold engine start, which includes fuel quantity and injection timing control based on engine operating conditions, wherein the intake manifold pressure for a first combustion event of each engine cylinder during the cold start is reduced based on an estimate of fuel temperature at one end of the injection.

[0008] DE 10 2017 206 301 B3 discloses a method and a corresponding device for starting an internal combustion engine designed to run on alcohol or a high proportion of alcohol in an alcohol / gasoline blend fuel. In a first phase, beginning immediately after the engine's starting process is activated, an early initial ignition timing is set, which lies within a range of 60° to 100° crank angle before the top dead center of a piston in the internal combustion engine. During the starting process, the engine speed is monitored and the number of cylinder cycles is totaled. If a predetermined speed threshold is exceeded, the number of cylinder cycles in which the speed increase exceeds a predetermined threshold is totaled.The number of cylinder work cycles is compared with predetermined threshold values, and when the threshold values ​​are reached or exceeded, the ignition timing is shifted from an early ignition timing towards a late ignition timing.

[0009] A disadvantage of the current state of the art is that the known approaches involve additional components, thus increasing costs and design complexity. Specifically, heating alcohol carries the additional risk of vapor lock in the fuel system. The catalytic decomposition of alcohol into hydrogen and carbon dioxide poses the risk of uncontrolled hydrogen ignition. While improving cold-start performance by blending a fuel with a lower flash point has also been proposed, this approach fails to adequately address environmental concerns and also incurs additional costs.

[0010] The object of the invention is to provide a method for improving the cold-start behavior of an internal combustion engine, which can be implemented cost-effectively with minimal additional technical effort, is environmentally friendly, and avoids costly modifications to previously known internal combustion engine components.

[0011] The problem is solved by the invention specified in the patent claims. Advantageous embodiments are the subject of the dependent claims, and the invention also includes combinations of the individual dependent patent claims in the sense of an AND conjunction, as long as they are not mutually exclusive.

[0012] The problem according to the invention is solved by a method for improving the cold start behavior of an internal combustion engine, which can be implemented cost-effectively with little additional technical effort and is environmentally friendly, and avoids costly modifications of previously known internal combustion engine components.

[0013] The technical advantages are achieved through a method for improving the cold-start performance of a 4-stroke internal combustion engine, which is operated with a cold-start mode with a first camshaft control and an operating mode with a second camshaft control, wherein the internal combustion engine has at least one cylinder with a combustion chamber and with a reciprocating piston connected via a crankshaft, at least one intake valve closing and opening an air intake port and at least one exhaust valve closing and opening an air exhaust port, at least one fuel injection device, at least one ignition device and at least one camshaft for controlling the at least one intake and exhaust valve.wherein, in cold start mode, at a crankshaft position between LWOT and 110°KW, the air intake and exhaust ports are closed by at least one intake and exhaust valve, and a gas enclosed in the combustion chamber expands to create a vacuum; subsequently, at a crankshaft position between 110°KW and 180°KW, the at least one intake valve opens, and an airflow escaping from the intake port and carrying turbulent kinetic energy is generated in the combustion chamber; subsequently, with the intake and exhaust valves closed, fuel is injected into the combustion chamber by at least one fuel injection device, and the resulting fuel-air mixture is compressed in the combustion chamber of the cylinder at a crankshaft position between 180°KW and ZOT.wherein, at a crankshaft position between 40° BTDC and 5° BTDC, the compressed fuel-air mixture in the combustion chamber is ignited by the ignition device or by auto-ignition, and work is performed by the subsequent downward movement of the piston at a crankshaft position between BTDC and 540° BTDC, and subsequently, at a crankshaft position between 540° BTDC and 720° BTDC with the exhaust valve open and the intake valve closed, the combustion gases are discharged from the combustion chamber, whereby, upon reaching a determined target engine temperature, the operating mode is switched in which the first camshaft control is deactivated and a second camshaft control is activated.

[0014] Advantageously, the turbulent kinetic energy in the combustion chamber is realized by the inflow of air at a crankshaft position in the range of 110° KW to 180° KW.

[0015] In an advantageous embodiment of the method, it can be provided that, at least with the first camshaft control during the cold start mode, the valve lift of the intake valve is continuously increased and / or the opening time of the intake valve is continuously shifted towards the LWOT.

[0016] Advantageously, a mechanical, electropneumatic, electrohydraulic, electromechanical valve lift switching system and / or a continuously variable valve control is used as camshaft control.

[0017] It is also advantageous if, at a crankshaft position from LWOT to 180°KW, an absolute pressure of ≤ 0.5 bar is generated in the combustion chamber. In a further advantageous embodiment of the method, the stroke control of the at least one inlet valve generates turbulent kinetic energy in the combustion chamber of at least 500 J / kg.

[0018] Advantageously, it can be provided that at least a partially biological fuel, particularly preferably methanol and / or ethanol, is used as fuel.

[0019] It is also advantageous if the fuel quantity, injection timing and / or the number of fuel injections are variably controlled depending on the crankshaft position and / or the target temperature.

[0020] According to the invention, a method for improving the cold start and warm-up behavior of an internal combustion engine is provided, which is operated in a cold start mode and an operating mode.

[0021] In the context of the invention, a cold start mode is understood to be, and is used, when the operating temperature in at least one cylinder is below the flash point of the fuel used. According to DIN V 14011, the flash point of a substance is defined as the lowest temperature at which an ignitable vapor-air mixture can form.

[0022] In the context of the invention, an operating mode is understood to be, and this mode is used, provided that the operating temperature, which is referred to as the target temperature according to the invention, has been reached at least in the combustion chamber of the cylinder. When using an internal combustion engine with multiple cylinders, all cylinders must have reached the operating temperature so that the engine can be operated reliably in self-sustaining idling mode. The operating temperature represents an important parameter and the lower temperature limit of the required engine components, above which the internal combustion engine is operated in operating mode after the cold start mode. To determine the operating temperature and thus whether the engine is operated in cold start or operating mode, temperature values ​​of the coolant and / or the engine oil are used, for example.

[0023] The method according to the invention is used in a 4-stroke internal combustion engine, wherein during a complete working cycle the internal combustion engine goes through four strokes and the crankshaft rotates a total of 360° twice for a complete working cycle, wherein the piston changes its direction of movement four times between the top dead center LWOT and top ignition dead center ZOT and the bottom dead centers UT.

[0024] A complete working cycle of a 4-stroke internal combustion engine consists of a 1st stroke, the so-called intake stroke, which is defined with a crankshaft position of 0°KW (LWOT) to 180°KW (BUT), a 2nd stroke, the so-called compression stroke, which is defined with a crankshaft position of 180°KW to 360°KW (ZOT), a 3rd stroke, the so-called power stroke, which is defined with a crankshaft position of 360°KW (ZOT) to 540°KW (BUT), and a 4th stroke, the so-called exhaust stroke, which is defined with a crankshaft position of 540°KW (BUT) to 720°KW (LWOT).

[0025] According to the invention, the method is used in a 4-stroke internal combustion engine which has at least one cylinder with a combustion chamber and with a reciprocating piston connected via a crankshaft, at least one intake valve closing and opening an air intake channel and at least one exhaust valve closing and opening an air outlet channel, at least one fuel injection device, an ignition device and at least one camshaft for controlling the at least one intake and exhaust valve.

[0026] According to the invention, when the crankshaft is in the range of LWOT to 110° KW in cold start mode, the air intake channel and the air outlet channel are closed by the at least one inlet and outlet valve, and a vacuum and thus a pressure gradient at least towards the inlet channel is generated by expansion of the enclosed gas.

[0027] The essential aspect of the invention is that by closing the combustion chamber for an extended period during the expansion of the enclosed gas, a high pressure differential is generated between the absolute pressure in the combustion chamber (advantageously ≤ 0.5 bar) and the pressure present in the intake manifold or air intake channel. This pressure differential is then equalized at a crankshaft position between 110° and 180° CW when the intake valve opens, due to the high flow velocity of the air entering the combustion chamber and the associated increased turbulent kinetic energy.

[0028] The existing relationship between temperature and kinetic energy can be described by the kinetic theory of gases. E=32*N*kB*T where E is the kinetic energy of the gas, N is the number of particles, k B Boltzmann constant and T is the temperature.

[0029] To ensure that the engine quickly reaches its operating temperature, it may be advantageous to provide for a turbulent kinetic energy of at least 500 J / kg in the combustion chamber.

[0030] The conversion of turbulent kinetic energy results in the provision of additional heat in the combustion chamber. This is achieved by utilizing the energy contained in the swirling, disordered motion of the flowing air. This turbulent kinetic energy is a measure of the intensity of the turbulence. Through internal friction in the flow, this energy is converted, leading to an increase in the temperature in the combustion chamber. The airflow, laden with high turbulent kinetic energy, results in a significant temperature increase of at least 20 K in the cylinder. This creates improved vaporization conditions by approaching or even exceeding the fuel-specific vapor pressure curve in the closed combustion chamber, and thus allows the desired operating temperature to be reached more quickly.

[0031] The temperature generated by the incoming airflow, which is loaded with increased turbulent kinetic energy, also leads to an improvement in torque at low engine speeds and a reduction in emissions, especially during the cold start phase.

[0032] In an advantageous embodiment of the method, controlled opening of the intake valve can be achieved by realizing the turbulent kinetic energy in the combustion chamber through the inflow of air at a crankshaft position in the range of 110° KW to 240° KW with a short valve lift of the at least one intake valve.

[0033] According to the invention, fuel is injected into the combustion chamber by the at least one fuel injection device only when the crankshaft is in the range of 180°KW to 200°KW and the intake and exhaust valves are closed, and the generated fuel-air mixture is compressed in the combustion chamber of the cylinder when the crankshaft is in the range of 180°KW to TDC, wherein when the crankshaft is in the range of 40°KW before TDC to 5°KW before TDC, the compressed fuel-air mixture in the combustion chamber is ignited by the ignition device or by self-ignition, and work is performed by the subsequent downward movement of the piston when the crankshaft is in the range of TDC to 540°KW.

[0034] According to the invention, when the crankshaft is in a position between 540°KW and 720°KW, and with the exhaust valve open and the intake valve closed, the combustion gases are discharged from the combustion chamber.

[0035] According to the invention, it is proposed that after reaching a target temperature at which the engine can be operated in self-maintenance mode at idle, the system switches from cold start mode to operating mode or continues to do so continuously.

[0036] For a smooth transition from cold start mode to operating mode, it is advantageous to provide that, at least with the first camshaft control during cold start mode, the intake valve lift is continuously increased and / or the intake valve opening time is continuously shifted closer to low wide top dead center (LWOT). Such a phase shift of the intake valve opening time can be achieved, for example, by a specific camshaft geometry or by a specific timing adjustment of the camshaft with the corresponding crankshaft. This makes it possible, for example, to retain the valve lift switching for the Miller combustion process while still setting a later valve lift in cold start mode.

[0037] The activation of the first camshaft control for cold start mode and the second camshaft control for operating mode can advantageously be performed in stages or continuously. The camshaft control can be implemented in stages, for example, by a variable two-stage valve train system, which can be a mechanical, electrohydraulic, electropneumatic, and / or electromechanical valve lift switching system.

[0038] In an advantageous embodiment of the method, it can be provided that, during the start-up phase, the first camshaft control is activated by means of sensor-based detection of the target temperature in the combustion chamber. This sensor-based detection of the target temperature can be achieved, for example, by measuring the coolant temperature, the combustion gases, the intake air to the combustion chamber, and / or directly in the combustion chamber. This ensures that, after the target temperature has been detected, the combustion engine operates in the required mode and that reliable cold-start behavior is enabled by providing improved vaporization conditions.

[0039] A further advantage of the method according to the invention is that it can be used in both cold-start and operating modes. It has been found that by generating a pressure gradient between the combustion chamber and the intake port or intake manifold and by late opening of the intake valve at a crankshaft position of 110° to 180°, the turbulent kinetic energy-laden airflow escaping from the intake port into the combustion chamber at engine operating temperature leads to an increase in power output while simultaneously reducing emissions. In operating mode, this results in improved cylinder filling and air-fuel mixture formation, and thus to more efficient fuel combustion.

[0040] It has been found that using a fuel that is at least partially alcohol-based, preferably methanol and / or ethanol, offers particular technical advantages. It has been observed that even with the use of a fuel that is at least partially alcohol-based, improved knock resistance is achieved, enabling higher compression in the engine and thus increased power and efficiency. Therefore, the inventive process, using a pure alcoholic fuel, preferably methanol and ethanol, allows for better consideration of environmental aspects, avoids the use of fossil fuels, and also reduces pollutant emissions.

[0041] In summary, the technical advantages and effects of the method according to the invention compared to the prior art consist in the fact that - the process is environmentally friendly and applicable to different fuel types of a 4-stroke combustion engine, - especially when using fossil fuels, pollutant emissions are reduced, - reliable cold-start performance with improved emission values ​​is achieved, - No additional components, structural and costly modifications and expenses are required, - the generated turbulent kinetic energy provides the required temperature directly and evenly distributed in the combustion chamber of the cylinder, - the method for increasing the engine's performance can also be used in operating mode, - it can also be used with alcohol-based fuels, making it particularly environmentally friendly and efficient, and - the process can be used for both direct injection and port injection combustion engines.

[0042] The method according to the invention is explained in more detail below using an exemplary embodiment. The associated Fig. Figure 1 shows the test results of a 4-stroke Otto combustion engine operated in cold start mode using the novel method. Example 1

[0043] Fig.Figure 1 shows the results of investigations into the cold-start behavior of a gasoline-powered, four-stroke, direct-injection combustion engine during a cold start with a reduced and late intake valve lift at an ambient, combustion chamber, and coolant temperature of 20°C. With the crankshaft in the range of LWOT to 110°KW in cold-start mode, the intake and exhaust ports are closed by the intake and exhaust valves. To create a vacuum, the gas enclosed in the combustion chamber expands. The cylinder pressure is 0.05 bar. Subsequently, with the crankshaft in the range of 110°KW to 180°KW, at least one intake valve opens, generating an airflow from the intake port that is imbued with turbulent kinetic energy. The spontaneous pressure equalization results in a maximum value of 1 for turbulent kinetic energy.600 J / kg, causing the cylinder temperature to rise to 84°C, resulting in a temperature difference of 64 K. The maximum intake valve lift is 2.2 mm at a crankshaft position of 160° crank angle. With the crankshaft position between 180° and 200° crank angle and both the intake and exhaust valves closed, fuel is injected into the cylinder's combustion chamber by a fuel injection device. The resulting fuel-air mixture is compressed in the combustion chamber from 180° crank angle until top dead center (TDC). From 40° before TDC to 5° before TDC, the compressed fuel-air mixture is ignited by the ignition system. The subsequent downward movement of the piston then performs work from TDC to 540° crank angle.With a crankshaft position between 540° and 720°, the combustion gases are expelled from the combustion chamber with the exhaust valve open and the intake valve closed. Once a predetermined coolant temperature is reached, the system switches to an operating mode in which the first camshaft control is deactivated by a continuously variable valve timing system and a second camshaft control system is activated.

Claims

[1] Method for improving the cold-start and warm-up performance of a 4-stroke internal combustion engine, which is operated in a cold-start mode with a first camshaft control and an operating mode with a second camshaft control, wherein the internal combustion engine has at least one cylinder with a combustion chamber and with a reciprocating piston connected via a crankshaft, at least one intake valve closing and opening an air intake port and at least one exhaust valve closing and opening an air outlet port, at least one fuel injection device, at least one ignition device and at least one camshaft for controlling the at least one intake and exhaust valve,wherein, in cold start mode, at a crankshaft position between LWOT and 110° KW, the air intake and exhaust ports are closed by at least one intake and exhaust valve, and a gas enclosed in the combustion chamber expands to create a vacuum; subsequently, at a crankshaft position between 110° KW and 180° KW, the at least one intake valve opens, and an airflow escaping from the intake port and carrying turbulent kinetic energy is generated in the combustion chamber; subsequently, with the intake and exhaust valves closed, fuel is injected into the combustion chamber by at least one fuel injection device, and the resulting fuel-air mixture is compressed in the combustion chamber of the cylinder at a crankshaft position between 180° KW and ZOT.wherein, at a crankshaft position between 40° BTDC and 5° BTDC, the compressed fuel-air mixture in the combustion chamber is ignited by the ignition device or by auto-ignition, and work is performed by the subsequent downward movement of the piston at a crankshaft position between BTDC and 540° BTDC, and subsequently, at a crankshaft position between 540° BTDC and 720° BTDC with the exhaust valve open and the intake valve closed, the combustion gases are discharged from the combustion chamber, whereby, upon reaching a determined target engine temperature, the operating mode is switched in which the first camshaft control is deactivated and a second camshaft control is activated. [2] Method according to claim 1, wherein the turbulent kinetic energy in the combustion chamber is realized by the inflow of air at a crankshaft position in the range of 110°KW to 180°KW. [3] Method according to claim 1, wherein at least with the first camshaft control during the cold start mode the valve lift of the intake valve is continuously increased and / or the opening time of the intake valve is continuously shifted in approximation to the LWOT. [4] Method according to claim 1, wherein a mechanical, electropneumatic, electrohydraulic, electromechanical valve lift switching system and / or a continuously variable valve control is used as the camshaft control. [5] Method according to claim 1, wherein an absolute pressure of ≤ 0.5 bar is generated in the combustion chamber when the crankshaft is in a position from LWOT to 180°KW. [6] Method according to claim 1, wherein the stroke control of the at least one inlet valve generates a turbulent kinetic energy in the combustion chamber of at least 500 J / kg. [7] Method according to claim 1, wherein the fuel used is at least partially biological fuel, particularly preferably methanol and / or ethanol. [8] Method according to claim 1, wherein the fuel quantity, the injection timing and / or the number of fuel injections is variably controlled depending on the crankshaft position and / or the target temperature.

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