Fuel discharge method for an internal combustion engine

Abstract

Fuel discharge method for an internal combustion engine, wherein the internal combustion engine has a control system and a lubrication circuit with a lubricant, and wherein the control system has characteristic values ​​for operation of the internal combustion engine, and wherein a load point shift from a first operating point of the internal combustion engine to a second operating point of the internal combustion engine is carried out by means of the control system, and wherein the load point shift is carried out when a fuel characteristic value, which characterizes a quantity of fuel formed in the lubricant, is greater than or equal to a fuel threshold value, characterized in that the second operating point has a second scavenging gradient which is greater than a first scavenging gradient of the first operating point.

Description

[0001] The present invention relates to a fuel discharge method for an internal combustion engine according to the preamble of claim 1.

[0002] Internal combustion engines have a lubrication circuit to supply lubricant to the moving parts of the engine. This lubrication circuit is not completely sealed against disturbances. For example, fuel can enter the lubricant via the combustion chambers of the engine.

[0003] The lubricant, generally a lubricating oil, flows through the lubrication circuit over numerous operating cycles of the internal combustion engine. During this process, the viscosity of the lubricant can change. This change in viscosity means that the lubricant no longer possesses its original load-bearing capacity, and consequently, the corresponding components are no longer lubricated as required.

[0004] In addition to the usual aging of the lubricant due to deposits, abrasion, and / or soot ingress, lubricant dilution, hereinafter referred to as lubricating oil dilution, also leads to a change in viscosity. If lubricating oil dilution is present, this means that fuel components are present in the lubricant, causing the change in its viscosity. The viscosity of the oil is crucial for its lubricating effect. If the viscosity of the oil drops too low, the necessary lubrication of the internal combustion engine can no longer be reliably guaranteed.

[0005] Lubricant dilution can have various causes, such as frequent cold starts with short trips, inadequate mixture preparation, insufficient warm-up phases in conjunction with start-stop operation, or electric driving in hybrid vehicles.

[0006] German patent application DE 10 2013 216 215 A1 discloses a method for reducing lubricating oil dilution, in particular in which the internal combustion engine is operated for a certain period of time in a process in which the engine temperature exceeds a certain threshold temperature.

[0007] From DE 60 2005 000 084 T2, a control method for an exhaust gas purification system of an internal combustion engine is known, which brings about the regeneration of a diesel particulate filter taking into account possible oil dilution. Essentially, the regeneration of the diesel particulate filter is carried out in a steady state or when a motor vehicle containing the internal combustion engine is stationary.

[0008] German patent application DE 10 2012 112 794 A1 discloses a method for an internal combustion engine to determine the fuel content in the oil. Once a specific fuel content in the lubricating oil has been determined, various remedies are proposed. These remedies could include, for example, an oil change. In a hybrid vehicle, i.e., a combination of an electric motor and an internal combustion engine, it is possible to keep the internal combustion engine running for a certain period. Using the proposed method, the fuel content in the lubricating oil can be determined. The internal combustion engine is then controlled according to the determined fuel content. In addition to the methods already mentioned, a change in the operating point by shifting the engine's load point to increase the coolant and / or oil temperature is also described.

[0009] The object of the present invention is to provide an improved fuel discharge method for an internal combustion engine.

[0010] The problem is solved according to the invention by the fuel discharge method for an internal combustion engine with the features of claim 1. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the respective dependent claims.

[0011] The fuel discharge method according to the invention for an internal combustion engine, which includes a control system with engine parameters and a lubrication circuit with a lubricant, results in a load point shift from a first operating point of the internal combustion engine to a second operating point of the internal combustion engine by means of the control system. The load point shift is dependent on a fuel threshold value and is carried out when a fuel parameter, which characterizes the amount of fuel formed in the lubricant, is greater than or equal to a fuel threshold value. The load point shift is selected such that the second operating point has a second scavenging gradient that is greater than the first scavenging gradient of the first operating point.The advantage is that fuel discharge from the lubricant can be achieved solely through the operation of the combustion engine and therefore without additional components.

[0012] Every internal combustion engine inherently possesses a so-called engine map, which defines load points depending on the engine speed. This engine map is referred to as a load-speed map, where the load represents a torque proportional to the mean effective pressure of the internal combustion engine. This engine map is limited by a minimum speed, a maximum speed, and a full load. This means that between these three limit criteria and between the engine being off (where both load and speed are zero), a map with numerous operating points is defined.

[0013] Each load point exhibits a specific cylinder pressure profile over a single operating cycle of the internal combustion engine. This cylinder pressure profile comprises a so-called high-pressure section and a so-called charge exchange section. The high-pressure section develops during a period of the operating cycle characterized by a closed combustion chamber of the internal combustion engine. If the internal combustion engine is a reciprocating piston engine, intake and exhaust valves are typically located on a cylinder head that at least partially encompasses the combustion chamber. These valves open or close the flow-through intake and exhaust ports of the cylinder head.

[0014] The charge exchange phase extends over the period of the combustion cycle characterized by an open combustion chamber. This means that the intake and / or exhaust ports are open. In a reciprocating engine, the charge exchange phase begins with the opening of the exhaust valves and ends with the closing of the intake valves.

[0015] To potentially increase the efficiency of the internal combustion engine, the charge exchange section includes a time phase in which both the intake valves and the exhaust valves are open, resulting in so-called valve overlap.

[0016] While when only the exhaust valves open, the exhaust gas present in the combustion chamber of the internal combustion engine is expelled solely by the stroke of a piston, during the valve overlap phase it is possible to utilize the amount of fresh air flowing into the combustion chamber through the intake valves and expel the exhaust gas present in the combustion chamber by displacing the air volume. This method is more effective the greater the intake pressure at the intake valve openings is compared to the exhaust pressure at the exhaust valve openings.

[0017] A difference between the intake and exhaust pressures is called the scavenging gradient. This scavenging gradient can have a value greater than, equal to, or less than zero. If the value is less than zero, internal exhaust gas recirculation is possible, for example, because exhaust gas can flow back into the combustion chamber from an exhaust tract due to the negative scavenging gradient.

[0018] The effect of the scavenging gradient can be further improved if the scavenging gradient is implemented at low engine speeds, since at low engine speeds the effective duration of the valve overlap phase, measured, for example, in seconds, is longer than at high engine speeds. Thus, at low engine speeds, the exhaust gas has more time to flow out of the combustion chamber. The exhaust gas can then flow completely out of the combustion chamber, and to further improve the complete scavenging of the combustion chamber, some of the fresh air entering the combustion chamber during the current power stroke can even flow back out through the exhaust valves.

[0019] If, according to the fuel discharge method according to the invention, a load point shift is carried out from the first operating point, which has a first flushing gradient, to a second operating point, which has a second flushing gradient with a value greater than the value of the first flushing gradient, improved fuel discharge from the lubricant present is achievable.

[0020] Provided the second flushing gradient is positive, the advantage is that, depending on the pressure gradient, fuel cannot be drawn into the lubricant due to the complete flushing of the combustion chamber. This reduces oil dilution over the course of a complete lubricant cycle in the lubrication circuit. A complete lubricant cycle refers to the time between one lubricant change and the next in the internal combustion engine.

[0021] In a further embodiment of the method according to the invention, the load point shift leads to a second operating point, which lies in a low to medium load range of the internal combustion engine. Typically, particularly at load points where the air-fuel ratio λ is in the superstoichiometric range, some of the fuel is not burned but is deposited in the lubricant. These load points are located in the upper load range of the engine map. In the medium load range, and thus at medium torques, a stoichiometric to substoichiometric air-fuel ratio λ is predominantly present. Therefore, operating in this range advantageously reduces oil dilution. This is especially true if the operating point lies in the low load range of the internal combustion engine.Another outstanding advantage of the second operating point, which lies in the medium to low load range, is that a positive flushing gradient is formed, especially in low load ranges.

[0022] If the load point shift is performed based on predictive route data, it is possible to adjust the combustion engine's operating points to suit the planned route, thus enabling the planned implementation of fuel consumption. Predictive route data can be obtained, for example, when operating a vehicle with a combustion engine using a navigation system. Based on this predictive route data, it can be determined which sections of the planned route are best suited for operating the combustion engine in the low to medium load range or at low to medium engine speed. This can be determined in advance using the control system.

[0023] The settings of operating points with low loads or positive flushing gradients are particularly suitable for predictive route data of the journey route, which indicates operation of the motor vehicle at a predominantly constant speed and / or speed limits.

[0024] Predictive route data that includes a motorway journey is particularly preferred, as the combustion engine can be operated at a medium load point at low to medium speeds.

[0025] In a further embodiment of the fuel discharge method according to the invention, the load point shift is carried out depending on the fuel consumption of the internal combustion engine. As a rule, the control system has a plurality of characteristic maps with various engine parameters, such as an effective mean pressure. or fuel consumption This allows a second operating point to be determined using the characteristic maps stored in the control system. This second operating point not only features a second flushing gradient that is greater than the first, but also exhibits a preferable, more favorable fuel consumption compared to other possible operating points. This simultaneously reduces oil dilution and achieves favorable fuel consumption.

[0026] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments. The features and combinations of features mentioned above can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0027] One embodiment describes an internal combustion engine designed as an 8-cylinder engine. The engine features a lubrication circuit using lubricating oil. Furthermore, the engine is equipped with a control system for adjusting engine operating parameters. This control system has various characteristic maps in which engine parameters and values ​​are stored in different dependencies. For example, the amount of fuel to be injected is defined within these maps. depending on boost pressures p2 and engine speeds The exhaust backpressure p3 is stored in one of the maps. Similarly, exhaust backpressure p3 is stored in one of the maps. Each of these boost pressures p2 and exhaust backpressure p3 has corresponding mean effective pressure values. or engine speeds assigned and vice versa. Thus, it is possible to determine the boost pressure p2 and the exhaust back pressure p3 at a current, hereinafter referred to as the first, operating point. Likewise, a scavenging gradient can be derived from this. as It is also possible that the rinsing slope is also stored in a characteristic map.

[0028] Furthermore, preferably within the control system, a fuel threshold value is stored, which represents a value corresponding to a specific quantity of fuel dissolved in the lubricating oil. This fuel threshold value can, for example, directly specify the fuel quantity. Alternatively, a corresponding parameter can be stored for the fuel threshold value, such as a ratio of fuel quantity to lubricating oil quantity.

[0029] The amount of fuel present in the lubricant at the time of the first operating point, i.e., the amount currently present, can be determined using various methods and / or characteristic maps, which may also include a pre-calculation, and is preferably stored as a fuel characteristic value in the control system. As soon as this fuel characteristic value is equal to or greater than the fuel threshold value, a first flushing gradient for the first operating point is determined according to the invention. Starting from this first flushing gradient, a second flushing gradient is determined in the characteristic map, which is greater than the first flushing gradient. Subsequently, starting from this first operating point, a load point shift occurs to a second operating point, which has the second flushing gradient.

[0030] In another embodiment, the control system for data transmission is electronically connected to a predictive route data acquisition system in the form of a navigation system. Due to the data transmission between the two systems, it is possible to operate the combustion engine based on the predictive route data. In other words, for a suitably determined route, operating points with positive scavenging gradients can be selected where fuel discharge is feasible.

[0031] The advantage is that the combustion engine has an extended lubrication change cycle, in other words, an extended oil change cycle. Another advantage is that it can be operated in a fuel-efficient and therefore emission-reduced operating range.

[0032] In another embodiment, the combustion engine is connected to an electric motor. Typically, when the combustion engine is coupled with the electric motor, forming a so-called hybrid engine, the electric motor provides propulsion for the vehicle on journeys where operating points with low loads are achievable. The combustion engine is usually preferred for propulsion on rural roads and / or highways. This means that fuel discharge is not typically provided in a hybrid engine.

[0033] The combustion engine, incorporating the fuel discharge method according to the invention, is particularly suitable for operating the hybrid engine. The advantage is that the combustion engine can be operated at low loads in selected areas, such as during highway driving, while the electric motor is used in selected driving conditions, such as during city driving.

Claims

[1] Fuel discharge method for an internal combustion engine, wherein the internal combustion engine has a control system and a lubrication circuit with a lubricant, and wherein the control system has characteristic values ​​for operation of the internal combustion engine, and wherein a load point shift from a first operating point of the internal combustion engine to a second operating point of the internal combustion engine is carried out by means of the control system, and wherein the load point shift is carried out when a fuel characteristic value, which characterizes an amount of fuel formed in the lubricant, is greater than or equal to a fuel threshold value, characterized by , that the second operating point has a second flushing gradient which is greater than a first flushing gradient of the first operating point. [2] Fuel discharge method according to claim 1, characterized bythat the second flushing gradient is a positive flushing gradient. [3] Fuel discharge method according to claim 1 or 2, characterized by , that the second operating point lies in a low to medium load range of an operating map of the internal combustion engine. [4] Fuel discharge method according to claim 3, characterized by , that the second operating point lies in the low load range and low speed range of the operating map of the internal combustion engine. [5] Fuel discharge method according to any one of claims 1 to 4, characterized by , that the load point shift is carried out depending on predictive route data. [6] Fuel discharge method according to claim 5, characterized by that the predictive route data indicates a route with predominantly constant speed and / or speed limits. [7] Fuel discharge method according to claim 6, characterized bythat the predictive route data includes a highway journey. [8] Fuel discharge method according to any of the preceding claims, characterized by , that the load point shift is carried out depending on the fuel consumption of the combustion engine.