METHOD FOR IMPROVING THE COLD START BEHAVIOUR OF A 4-STROKE INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to the technical field of internal combustion engines and concerns a method for improving the cold-start behavior of a 4-stroke internal combustion engine. The object is to provide a method for improving the cold-start behavior of an internal combustion engine that is cost-effective and environmentally friendly and avoids complex adaptations of previously known internal combustion engine components. This object is achieved by a method for a 4-stroke internal combustion engine with direct fuel injection, having a cold-start mode and an operating mode, in which in the cold-start mode, at least during the 1st stroke, when the temperature falls below a given target temperature, a first camshaft control closes at least one inlet and outlet valve and generates a vacuum in the combustion chamber, with the 2ndIn the 1st stroke, with the inlet and exhaust valves closed, the fuel vapor-air mixture is compressed and ignited in the combustion chamber, then in the 3rd stroke work is done by the downward movement of the reciprocating piston and subsequently in the 4th stroke, with the exhaust valve open, the combustion gases are discharged from the combustion chamber.

Description

[0001] The invention relates to the technical field of internal combustion engines and concerns a method for improving the cold-start performance of a 4-stroke internal combustion engine. The method according to the invention is intended for internal combustion engines with direct fuel injection, which are operated, for example, with a pure alcoholic fuel, in particular methanol or ethanol, or with a conventional gasoline fuel with the addition of a biofuel. The method according to the invention can also be used for other fuels.

[0002] Pure alcohol fuels, in particular, are becoming increasingly important for operating combustion engines, as they enable high levels of efficiency and are considered an environmentally friendly, renewable fuel for combustion engines. Another advantage is their ease of transport and use, making them an important building block for defossilization of the mobility and energy sectors.

[0003] For a successful cold start of an internal combustion engine, two essential requirements must be met in the combustion chamber. First, a combustible air-fuel mixture must be present in the cylinder's combustion chamber at the ignition source at the time of ignition. Furthermore, sufficient energy must be released by the ignited air-fuel mixture to perform sufficient work on the piston and overcome the engine's inherent energy losses.

[0004] The cold-start performance of internal combustion engines is particularly influenced by the cold-start environment and the fuels used. While conventional fuels, such as premium gasoline 95, have a flash point as low as -45°C, a safe and reliable cold start of a state-of-the-art internal combustion engine powered by a pure alcohol fuel is possible at temperatures as low as 10°C due to the higher flash point. At least with regard to cold-start performance, internal combustion engines powered by pure alcohol fuel have a disadvantage compared to those powered by conventional fuels. Another disadvantage of pure alcohol fuels is that a larger amount of fuel must be vaporized due to the lower energy density.Due to the higher enthalpy of vaporization, more energy is required to vaporize the same amount of liquid fuel, which leads to further cooling of the cargo mass.

[0005] In order to overcome the disadvantages of an internal combustion engine powered by pure alcohol fuel, and in particular the poorer cold start behavior, various solutions are proposed in the state of the art.

[0006] From DE 10 2013 206 575 A1 an engine control method for an alcohol fuel-operated internal combustion engine is known, in which a fuel injection is carried out during engine start-up if the intake manifold pressure falls below a threshold value, wherein the threshold value is based on a fuel volatility.

[0007] DE 39 10 528 A1 discloses a method for cold-starting an internal combustion engine powered by alcohol fuel, which method is carried out in a cold-start device of an internal combustion engine powered by alcohol fuel. When the engine is cold, gasoline is drawn in from the gasoline circuit and stored in a gasoline storage and supply device as long as the alcohol fuel system is not activated. Upon starting the internal combustion engine, gasoline is then fed into the engine's intake manifold without delay and in precisely metered amounts to initiate gasoline combustion until the engine reaches a predetermined temperature limit sufficient to maintain combustion with alcohol fuel, whereupon the alcohol fuel supply to the alcohol fuel injectors is released and gasoline injection is interrupted.

[0008] A fuel injection control device for cold-starting an internal combustion engine is known from DE 11 2008 002 239 B4. The device comprises a fuel pump configured to supply fuel from a fuel tank into a fuel path. It also comprises a delivery line configured to distribute the fuel in the fuel path to respective cylinders, a fuel injection valve for each cylinder configured to inject the fuel supplied from the fuel delivery line into respective intake ports, and a heating device provided in the delivery line or in the fuel path downstream of the fuel pump and configured to heat the fuel to improve starting performance.An additional fuel pump control device is designed to stop driving the fuel pump until the heated fuel in the fuel feed line has decreased to a predetermined amount or less, in order to prevent unheated fuel newly supplied to the fuel feed line from being injected without being heated by the heating device.

[0009] DE 10 2016 114 300 A1 proposes a method for an engine in which a fuel injection is performed during an engine cold start, comprising a fuel quantity and an injection timing based on engine operating conditions, wherein the intake manifold pressure for a first combustion event of each engine cylinder is reduced at the cold start based on an estimate of fuel temperature at an end of the injection.

[0010] Also known from EP 1 934 467 B1 is a fuel heating system for assisting with the cold start of an internal combustion engine using alcohol as fuel. The cold start system uses resistors arranged at the inlet of the injectors, resistors inside each injector, or a resistor for each nozzle tube support, whereby the three options can be used simultaneously, in pairs, or separately. Furthermore, the use of resistor groups provided in the upper part of the intake manifold or intake, in the lower part of the manifold, in the throttle body, in the intake lines of the headstock, and resistor groups in the secondary line at the inlet next to the exhaust manifold, inside the air filter or the air supply line for the throttle body and the secondary line is proposed.

[0011] The prior art solutions have the disadvantage that improving the cold-start performance of the combustion engine requires complex structural modifications to the engine or the components involved in fuel mixture formation, additional technical equipment, or interventions in the engine control system. Improving cold-start performance by blending a fuel with a lower flash point has also been proposed, but this approach does not adequately consider environmental aspects and also incurs additional costs.

[0012] The object of the invention is to provide a method for improving the cold start behavior of a fuel-operated internal combustion engine, which is cost-effective and environmentally friendly and avoids complex adaptations of previously known internal combustion engine components.

[0013] This object is achieved by the invention defined in the claims. Advantageous embodiments are the subject of the dependent claims, whereby the invention also includes combinations of the individual dependent claims in the sense of an AND connection, as long as they are not mutually exclusive.

[0014] The object of the invention is achieved by a method for improving the cold start behavior of an internal combustion engine operated with a fuel, which is operated with a 4-stroke process with direct fuel injection in a cold start mode and an operating mode, 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 inlet valve and at least one exhaust valve, at least one fuel injection device and at least one camshaft for controlling the at least one inlet and exhaust valve, wherein in the cold start mode at least during the 1.stroke, when a target temperature present in the combustion chamber of at least one cylinder is not reached, at least one inlet and outlet valve is closed via a first camshaft control and a negative pressure is generated in the combustion chamber, then fuel is injected into the combustion chamber and the injected fuel is evaporated in the combustion chamber, then at least one inlet valve is opened to form a fuel vapor-air mixture, then with the 2nd stroke, with the inlet and exhaust valves closed, the fuel vapor-air mixture is compressed and ignited in the combustion chamber, then with the 3rd stroke, work is done by the downward movement of the reciprocating piston and subsequently with the 4thWhen the exhaust valve is open, the combustion gases are discharged from the combustion chamber, whereby when the target temperature is reached, the system changes from cold start mode to operating mode, in which the first camshaft control is deactivated and a second camshaft control is activated.

[0015] Advantageously, the timing of opening and closing of the intake valve is realized from 360°CA to 600°CA.

[0016] It is also advantageous if the negative pressure in the combustion chamber is generated by a phase shift of the opening time of the intake valve to a later date and / or by reducing the valve lift of the intake valve.

[0017] It is also advantageous if, at least with the first camshaft control, the valve lift of the intake valve is continuously increased during the first stroke until the target temperature is reached and / or the opening time of the intake valve is continuously shifted towards the LWOT.

[0018] In an advantageous embodiment, a mechanical, electro-pneumatic, electro-hydraulic, electromechanical valve lift switching system and / or a continuously variable valve control can be used as the camshaft control.

[0019] Also advantageously, the first camshaft control is activated after a sensitively detected target temperature of ≤ 10° C.

[0020] Advantageously, a pure alcohol fuel is used as fuel, particularly preferably methanol or ethanol.

[0021] It is also advantageous if the absolute pressure in the combustion chamber is set to 20 mbar to 200 mbar during cold start mode.

[0022] In addition, it can advantageously be provided that the pressure in the combustion chamber is additionally reduced by an air mass adjuster connected upstream of the intake valve, wherein a throttle valve is particularly advantageously used as the air mass adjuster, wherein the air mass adjuster is particularly advantageously set to 1% and 10% of its flow cross-section.

[0023] It is particularly advantageous if the air flow volume controlled by the air mass controller is adjusted depending on the target temperature reached.

[0024] It is also particularly advantageous if the load point of the combustion engine is continuously increased during cold start mode using the air mass controller.

[0025] In an advantageous embodiment of the method, an engine starting speed of 1,000 to 2,000 rpm is provided during the cold start mode.

[0026] It is also advantageous if the switching or transition from cold start mode to operating mode is carried out based on the determined target temperature at least from the temperature of the combustion chamber, the cylinder, the ambient temperature, the combustion exhaust gases, the coolant and / or the torque output at the crankshaft.

[0027] According to the invention, a method is provided for improving the cold start behavior of a 4-stroke internal combustion engine which is operated with a 4-stroke process with direct fuel injection in a cold start mode and an operating mode.

[0028] In this case, a 4-stroke internal combustion engine known from the prior art can be used, which has at least one cylinder with a combustion chamber and with a reciprocating piston connected via a crankshaft, at least one inlet valve and at least one exhaust valve, at least one fuel injection device and at least one camshaft for controlling the at least one inlet and exhaust valve.

[0029] The method according to the invention is carried out in two different modes, namely a cold start mode and an operating mode.

[0030] A cold-start mode is understood within the scope of the invention and is used when the operating temperature in at least one cylinder's combustion chamber 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. For methanol, the flash point is 11°C. This also applies to ethanol, another possible alcohol fuel, so both fuels exhibit the same cold-start reluctance below 11°C.

[0031] An operating mode is understood within the scope of the invention to be used when the operating temperature, which is referred to as the target temperature according to the invention, is reached at least in the combustion chamber of at least one cylinder and the engine can be operated in self-sustaining idle 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.

[0032] In comparison to the conventional 4-stroke process, in which the fresh charge is sucked in with air or an air-fuel mixture in the intake stroke, the process according to the invention divides the first stroke, which is also referred to as the intake stroke, into three sub-strokes.

[0033] During the first sub-stroke of the 1st stroke, if the temperature in the combustion chamber of at least one cylinder falls below a target temperature, at least one intake and exhaust valve are closed via a first camshaft control system. While the piston moves downward toward bottom dead center, the absolute pressure in the cylinder's combustion chamber is reduced. Reducing the absolute pressure in the combustion chamber has the technical effect of allowing the required fuel vaporization conditions to be reached more quickly, even at temperatures below 11°C. The vacuum region in the combustion chamber is generated only briefly, locally in the injection area, to subsequently ensure sufficient vaporization of the fuel to be injected in the combustion chamber.

[0034] In conventional internal combustion engines, the intake valve opens at approximately 360°CA to 600°CA. To generate the desired vacuum in the cylinder's combustion chamber, the invention proposes, in correlation with the crankshaft, to shift the timing of the intake valve opening and closing during the first stroke and, starting from the LWOT, to retard it toward bottom dead center (BDC).

[0035] For the purposes of the invention, the TDC is defined as the point in time at which the reciprocating piston has a crankshaft rotation of 0° after ignition and the combustion gases are expelled from the combustion chamber. The LWOT is defined as the top dead center during gas exchange, at which the reciprocating piston initiates the first intake stroke and the crankshaft has already completed a circular movement of 360° from the TDC.

[0036] Due to the later opening time of the intake valve and the simultaneous closure of the exhaust valve, the downward movement of the reciprocating piston in the closed combustion chamber reduces the absolute pressure in order to achieve improved evaporation conditions by lowering the boiling point for the fuel vapor-air mixture formation in the closed combustion chamber.

[0037] In an advantageous embodiment of the method, the required negative pressure in the closed combustion chamber during the first stroke can be achieved by retarding the opening timing of the intake valve and / or by reducing the valve lift of the intake valve. Such a phase shift can be achieved, for example, by a special geometric camshaft design or by a special timing adjustment of the camshaft to the correlating crankshaft. This makes it possible, for example, to maintain the valve lift switching for utilizing the Miller combustion process while still setting a late valve lift in cold-start mode.

[0038] In a further advantageous embodiment of the method, it can be provided that at least with the first camshaft control during the first stroke until the target temperature is reached, the valve lift of the intake valve is continuously increased and / or the opening time of the intake valve is continuously shifted in the direction of the LWOT.

[0039] During the second sub-stroke of the first stroke, fuel is injected into the combustion chamber and the injected fuel evaporates while the absolute pressure in the combustion chamber is further reduced, thereby promoting the evaporation of the injected fuel. At least one intake valve and one exhaust valve remain closed during the second sub-stroke of the first stroke.

[0040] With the third sub-stroke of the 1st stroke, at least one intake valve is opened briefly, causing a defined air mass to flow into the combustion chamber and thereby creating a fuel vapor-air mixture.

[0041] In the 2nd stroke, with the intake and exhaust valves closed, the fuel vapor-air mixture in the combustion chamber is compressed by the upward movement of the piston to top dead center and then ignited.

[0042] Subsequently, the 3rd stroke initiates the downward movement of the reciprocating piston and then, with the 4th stroke, the combustion gases are discharged from the combustion chamber with the exhaust valve open and the intake valve closed.

[0043] If the target temperature is reached at least in the combustion chamber of at least one cylinder and the conditions are thus met for the engine to be able to operate in self-sustaining mode at idle, the system switches from the cold start mode to the operating mode or transitions continuously.

[0044] According to the invention, switching or transitioning from cold-start mode to operating mode is achieved by deactivating the first camshaft control and activating a second camshaft control. For camshaft control, it is crucial that the geometry of the second intake cam is designed such that the valve lift of the intake valve is not merely reduced as before, but is retarded relative to the crankshaft in order to ensure the closure of at least one intake valve during the first and second sub-strokes and to prevent air from flowing into the combustion chamber during the first and second sub-strokes of the first stroke.

[0045] The activation of the first camshaft control for the cold-start mode and the second camshaft control for the operating mode can advantageously be carried out in stages or continuously. The camshaft control can be carried out in stages, for example, by a variable two-stage valve train system, which can be a mechanical, electro-hydraulic, electro-pneumatic, and / or electromechanical valve lift switching system.

[0046] It is also conceivable that the transition from cold start mode to operating mode is realized by a variable phase adjustment of the camshaft control, so that depending on the operating temperature reached by the combustion engine, the opening time of the intake valve is continuously shifted in the direction of LWOT and thus transitions into operating mode.

[0047] In an advantageous embodiment of the method, the first camshaft control can be activated after a sensitively detected target temperature in the combustion chamber area of ​​≤ 11° C. The sensitive 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 current target temperature of ≤ 11° C is detected, the combustion engine is operated in cold-start mode, enabling reliable cold-start behavior by providing improved evaporation conditions for alcohol fuels, in particular for methanol or ethanol.

[0048] It has been found that improved evaporation and cold-start conditions for pure alcohol fuels occur when an absolute pressure in the range of 20 mbar to 200 mbar is generated in the cylinder's combustion chamber during the first stroke. Such a low vacuum leads to a significantly improved transition of the alcohol fuel from the liquid phase to the gaseous state, ensuring reliable cold-start behavior of the combustion engine powered by pure alcohol fuel even at very low temperatures of down to -20°C and even lower.

[0049] In an advantageous embodiment of the method, to generate the desired absolute pressure in the combustion chamber, the pressure conditions in the combustion chamber can be variably adjusted by an air mass regulator connected upstream of the intake valve in the supply air flow. To achieve the desired negative pressure in the combustion chamber during cold start mode, the air mass regulator can be variably adjusted to 1% and 10% of its possible flow cross-section, whereby a throttle valve can advantageously be used as the air mass regulator.

[0050] In a further advantageous embodiment of the method, it can be provided that the air flow volume adjustable by the air mass controller is variably adjusted depending on the target temperature reached. This makes it possible, depending on the engine's warm-up, to gradually increase the air flow volume via the adjustable air mass controller until self-sustaining temperature is reached. Even during cold-start mode, it can advantageously be provided to increase the load point of the combustion engine via the air mass controller in order to accelerate engine warm-up and perform work on the crankshaft.

[0051] To quickly reach the operating mode, it can advantageously be provided that an engine starting speed of 1,000 to 2,000 rpm is provided via a starting unit during cold start mode. A high engine starting speed results in the target temperature being reached more quickly due to the increased number of sub-cycle and cycle repetitions, and fuel evaporation is facilitated.

[0052] In an advantageous embodiment of the method, in order to reliably determine the switching or transition time from cold start mode to operating mode, the target temperature can be determined at least from the temperature of the combustion chamber, the cylinder, the ambient temperature, the combustion exhaust gases, the coolant and / or the prevailing torque output at the crankshaft.

[0053] The technical advantages and effects of the method according to the invention compared to the prior art are, in summary, that - the method is applicable to different fuel types of a 4-stroke internal combustion engine, - a safe cold start of a 4-stroke combustion engine powered by a pure alcohol fuel is enabled down to -20°C and below, - additional components or design expenditures are not required to operate the process compared to conventional combustion engines, and - the use of electrical support components in cold start mode is dispensed with, thereby reducing the manufacturing costs for a 4-stroke internal combustion engine, in particular one powered by alcohol fuel.

[0054] The method according to the invention is explained in more detail below using four exemplary embodiments. The accompanying figures show Fig. 1 a schematic representation of the operation of a 4-stroke internal combustion engine with three sub-strokes of the 1st stroke, Fig. 2 a known time sequence of a 4-stroke internal combustion engine with direct fuel injection, Fig. 3 a time sequence of a 4-stroke internal combustion engine with direct fuel injection and late intake valve lift, Fig. 4 a time sequence of a 4-stroke internal combustion engine with late and reduced intake valve lift with simultaneous phase adjustment, and Fig. 5 a time sequence of a 4-stroke internal combustion engine with late and reduced intake valve lift and simultaneous variable intake lift adjustment. Example 1

[0055] Fig. Figure 1 shows a schematic of the operation of an internal combustion engine with direct injection and strokes 1 to 4, with the 1st stroke being further divided into sub-strokes 1.1, 1.2 and 1.3. In sub-stroke 1.1, when the temperature in the combustion chamber falls below at least a desired temperature, the intake and exhaust valves are closed via a first camshaft control system. With simultaneous downward movement of the reciprocating piston towards bottom dead center, the absolute pressure p in the closed combustion chamber of the cylinder is reduced. In sub-stroke 1.2 of the 1st stroke, fuel is injected into the closed combustion chamber and the injected fuel evaporates with a further reduction in the absolute pressure p in the closed combustion chamber. By lowering the absolute pressure p, the boiling point of the fuel and thus the evaporation of the injected fuel is reached earlier. In sub-stroke 1.2 of the 1st stroke, too.During the first stroke, at least one intake valve and one exhaust valve remain at least partially closed. With substroke 1.3 of the first stroke, the intake valve opens, causing an air mass defined by the opening period and valve lift to flow into the combustion chamber, thereby generating a fuel vapor-air mixture. Strokes 2 to 4 involve the compression and igniting of the fuel vapor-air mixture in the combustion chamber at the ignition point and the subsequent discharge of the combustion gases from the combustion chamber.

[0056] Fig. Figure 2 shows the prior art timing sequence of a 4-stroke internal combustion engine with direct fuel injection, as used in the prior art at all operating temperatures of the internal combustion engine. It is shown that, conventionally, during the first stroke, the intake valve begins to open via the valve lift immediately before reaching the LWOT, and at the beginning of the second stroke, at approximately 600°CA, the intake valve and thus the combustion chamber are closed again. Direct fuel injection occurs during the first stroke at approximately 370°CA to approximately 460°CA. With the known process, the absolute pressure p in the combustion chamber does not decrease during the otherwise usual air intake phase. Example 2

[0057] Fig. Figure 3 graphically shows a time sequence of a 4-stroke internal combustion engine with direct fuel injection during a cold start at an ambient temperature, combustion chamber temperature, and coolant temperature of -10°C. The engine is powered by methanol. In cold start mode, a specific camshaft configuration and correlating crankshaft movement achieve a phase shift with a late opening of the intake valve at 455°CA and a closing at approximately 655°CA. The valve lift for the intake and exhaust valves is set at a constant 11 mm for this camshaft configuration, while the start of intake valve opening is shifted to a late point at 455°CA by a first camshaft control system as an electro-hydraulic valve lift switching system. The late opening of the intake valve at approximately 455°CA generates an absolute pressure p of 25 mbar in the combustion chamber during the 1st and 2nd sub-strokes.The throttle position, not shown, is 3% of its flow cross-section.

[0058] In this cold-start mode, the combustion engine is started at an engine starting speed of 2,000 rpm. As soon as the target temperature of 10°C is reached, it switches to operating mode using a second camshaft control, which is implemented via the electrohydraulic valve lift switching system, allowing the engine to operate in self-sustaining idle mode. Example 3

[0059] Fig. Figure 4 graphically shows a time sequence of a 4-stroke internal combustion engine with direct fuel injection during a cold start with a late intake valve opening timing, reduced intake valve lift, and phase adjustment at an ambient temperature, combustion chamber temperature, and coolant temperature of 0°C. The internal combustion engine is powered by ethanol. To reduce the absolute pressure p during the first stroke, the camshaft timing is designed such that the intake valve opens late at approximately 510°CA and air is only admitted to the combustion chamber up to approximately 600°CA, generating an absolute pressure of 50 mbar during the first stroke. The reduced valve lift of the intake valve is 3.5 mm, while the throttle valve position (not shown) is 3% of its flow cross-section.

[0060] In this cold-start mode, the combustion engine is started at an engine starting speed of 2,000 rpm. After reaching the target temperature of 10°C, it switches to operating mode using a second camshaft control with an electromechanical valve lift switching system, and the engine is operated at idle in self-maintenance mode. Example 4

[0061] Fig.Figure 5 graphically shows a time sequence of an ethanol-powered 4-stroke internal combustion engine with direct fuel injection during a cold start with an initially reduced and late intake valve lift at an ambient temperature, combustion chamber temperature, and coolant temperature of -10°C. To reduce the absolute pressure p during the 1st stroke, a continuously variable valve control is used, with which the intake valve is initially opened at approximately 485°CA and the intake takes place with a small valve lift of approximately 2.2 mm up to approximately 535°CA, whereby an absolute pressure p of 50 mbar is generated during the 1st stroke until the intake valve opens. The throttle valve position (not shown) is 1% of its flow cross-section.

[0062] During cold start mode, which is operated at an engine starting speed of 2000 rpm, the temperature in the combustion chamber increases continuously until the target temperature of 10°C is reached, whereby during the increase in operating temperature a continuous intake timing adjustment towards LWOT is realized by a stepless valve control with simultaneous combined valve lift increase and continuous throttle valve opening.

[0063] Once the target temperature is reached, the engine switches to operating mode via a continuously variable valve control and the engine is operated at idle in self-maintenance mode.

Claims

[1] Method for improving the cold start behavior of a fuel-operated internal combustion engine which is operated with a 4-stroke process with direct fuel injection in a cold start mode and an operating mode, 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 inlet valve and at least one exhaust valve, at least one fuel injection device and at least one camshaft for controlling the at least one inlet and exhaust valve, wherein in the cold start mode at least during the 1.stroke, when a target temperature present in the combustion chamber of at least one cylinder is not reached, at least one inlet and outlet valve is closed via a first camshaft control and a negative pressure is generated in the combustion chamber, then fuel is injected into the combustion chamber and the injected fuel is evaporated in the combustion chamber, then at least one inlet valve is opened to form a fuel vapor-air mixture, then with the 2nd stroke, with the inlet and exhaust valves closed, the fuel vapor-air mixture is compressed and ignited in the combustion chamber, then with the 3rd stroke, work is done by the downward movement of the reciprocating piston and subsequently with the 4thWhen the exhaust valve is open, the combustion gases are discharged from the combustion chamber, whereby when the target temperature is reached, the system changes from cold start mode to operating mode, in which the first camshaft control is deactivated and a second camshaft control is activated. [2] Method according to claim 1, wherein the timing of opening and closing of the intake valve is realized from 360°CA to 600°CA. [3] Method according to claim 1, in which the negative pressure in the combustion chamber is generated by a phase shift of the opening time of the intake valve to a later date and / or by a reduction of the valve lift of the intake valve. [4] Method according to claim 1, in which at least with the first camshaft control during the first stroke until the target temperature is reached, the valve lift of the intake valve is continuously increased and / or the opening time of the intake valve is continuously shifted in the direction of the LWOT. [5] Method according to claim 1, in which a mechanical, electro-pneumatic, electro-hydraulic, electro-mechanical valve lift switching system and / or a continuously variable valve control is used as the camshaft control. [6] Method according to claim 1, wherein the first camshaft control is activated after a sensitively detected target temperature of ≤ 10° C. [7] Process according to claim 1, in which a pure alcohol fuel is used as fuel, particularly advantageously methanol or ethanol. [8] Method according to 1, in which the absolute pressure in the combustion chamber is set to 20 mbar to 200 mbar during the cold start mode. [9] Method according to claim 1, in which the pressure in the combustion chamber is additionally reduced by an air mass adjuster connected upstream of the intake valve, wherein a throttle valve is particularly advantageously used as the air mass adjuster. [10] Method according to claim 9, wherein the air mass controller is set to 1% and 10% of its flow cross-section. [11] Method according to claim 9, wherein the air flow volume controllable by the air mass controller is adjusted as a function of the target temperature reached. [12] Method according to claim 9, in which the load point of the internal combustion engine is continuously increased during the cold start mode by means of the air mass controller. [13] The method of claim 1, wherein an engine cranking speed of 1,000 to 2,000 rpm is provided during the cold start mode. [14] Method according to claim 1, wherein the switching or transition from cold start mode to operating mode is carried out on the basis of the determined target temperature at least from the temperature of the combustion chamber, the cylinder, the ambient temperature, the combustion exhaust gases, the coolant and / or the torque output at the crankshaft.

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