DE102017111080A1 - CHANGE PROCEDURE OF A COMBUSTION ENGINE BETWEEN LEAN AND STOCHIOMETRIC MOTOR OPERATION - Google Patents

Abstract

The present invention relates to a method of switching an internal combustion engine between a lean and a stoichiometric engine operation, comprising the steps of controlling (S101) the air inlet into a combustion chamber by means of an intake valve by a cam having a first cam contour to the combustion air ratio with respect to a cam increase second cam contour; and controlling (S102) the air inlet into the combustion chamber by means of an intake valve through the cam with the second cam contour to reduce the combustion air ratio with respect to the cam having the first cam contour.

Description

The present invention relates to a method of switching an internal combustion engine between a lean and a stoichiometric engine operation and a corresponding internal combustion engine.

The lean operation of a gasoline engine is an effective measure to increase the efficiency. Particularly in the area of medium and medium part load, an efficient lean operation can be realized by utilizing the existing potential for providing boost pressure. This leads to an increase in the maximum engine efficiency and to an expansion of the map area with low fuel consumption. The lean operation requires the highest possible combustion air ratio near the limit of permissible combustion stability to minimize the formation of nitrogen oxides (NO x formation), so that during the switching over a range of low and medium leanness (1.0 <λ <1.6) is avoided.

To achieve the highest possible efficiency and low NOx emissions, a strong lean with homogeneous mixture is targeted. In the case of transient engine operation, the aim is to switch between the operating modes as quickly as possible and without torque. In the switching process, a decoupling between boost pressure and engine torque or air expense is made.

The publication DE 19728798 C2 relates to a method for controlling the intake air amount of an internal combustion engine in an operating mode with a substantially stoichiometric air / fuel mixture and a lean air / fuel mixture operating mode.

The publication DE 19951096 A1 relates to an engine control system for a supercharged by an exhaust gas turbocharged diesel engine, which controls the function of maps the operation of the diesel engine and allows a change between two modes of operation of the diesel engine

It is the object of the present invention to enable a torque-neutral switching between a lean operation and a stoichiometric operation.

This object is achieved by objects according to the independent claims. Advantageous embodiments are the subject of the dependent claims, the description and the figures.

According to a first aspect, this object is achieved by a method for switching an internal combustion engine between a lean and a stoichiometric engine operation, comprising the steps of controlling the air intake into a combustion chamber by means of an intake valve through a cam having a first cam contour, the combustion air ratio relative to a cam to increase with a second cam contour; and controlling the air inlet into the combustion chamber by means of an inlet valve through the cam with the second cam contour to reduce the combustion air ratio with respect to the cam with the first cam contour. As a result, for example, the technical advantage is achieved that the internal combustion engine can be easily switched between lean and stoichiometric operation.

In a technically advantageous embodiment of the method, the first cam causes a larger valve lift of the intake valve than the second cam. As a result, for example, the technical advantage is achieved that the amount of air taken in can be increased in a simple manner and the combustion air ratio shifts.

In a further technically advantageous embodiment of the method, the first cam causes a longer valve opening of the intake valve than the second cam. As a result, for example, the technical advantage is achieved that the amount of air taken in can be increased in a simple manner and the combustion air ratio shifts.

In a further technically advantageous embodiment of the method, a boost pressure is additionally increased, while the combustion air ratio is increased by the first cam. As a result, the technical advantage is achieved, for example, that the amount of air can be increased again.

In a further technically advantageous embodiment of the method, a boost pressure is additionally reduced, while the combustion air ratio is reduced by the second cam. As a result, for example, the technical advantage is achieved that the combustion air ratio is rapidly reduced.

In a further technically advantageous embodiment of the method, the reduction of the charge pressure is effected via the connection of a fresh air bypass to a turbocharger. The opening of the fresh air bypass leads to a circulation of the flow in the intake system and thus also through the compressor. As a result, for example, the technical advantage is achieved that the mass flow is lowered into the combustion chamber.

In a further technically advantageous embodiment of the method, the reduction of the charge pressure is effected by opening a bypass on a turbocharger, which bypasses a partial flow of the exhaust gas to the turbine. As a result, the technical advantage is achieved, for example, that the charge pressure can be reduced efficiently.

In a further technically advantageous embodiment of the method, a retardation of the camshaft for filling reduction is performed, while the combustion air ratio is reduced by the second cam. As a result, for example, the technical advantage is achieved that the combustion air ratio can be controlled even more efficiently.

In a further technically advantageous embodiment of the method, the injected amount of fuel is kept constant. Thereby, for example, the technical advantage is achieved that simplifies a control for shifting the combustion air ratio.

In a further advantageous embodiment of the method, the steps of controlling are performed based on a signal provided by a lambda probe. Thereby, for example, the technical advantage is achieved that the current combustion air ratio can be determined quickly.

According to a second aspect, this object is achieved by an internal combustion engine having control means for controlling the air intake into a combustion chamber by means of an intake valve through a cam having a first cam contour to increase the combustion air ratio with respect to a cam having a second cam contour; and for controlling the air inlet into the combustion chamber by means of an inlet valve through the cam with the second cam contour to reduce the combustion air ratio with respect to the cam with the first cam contour. By the internal combustion engine, the same technical advantages are achieved as by the method according to the first aspect.

In a technically advantageous embodiment of the internal combustion engine, the internal combustion engine comprises a lambda probe for providing a signal to the control device. Thereby, for example, the technical advantage is also achieved that the current combustion air ratio can be determined quickly.

In a further technically advantageous embodiment of the internal combustion engine, the control device is designed to increase a boost pressure while the combustion air ratio is increased by the first cam. As a result, for example, the technical advantage is achieved that the combustion air ratio can be changed quickly.

In a further technically advantageous embodiment of the internal combustion engine, the control device is designed to reduce a boost pressure, while the combustion air ratio is reduced by the second cam. As a result, for example, the likewise technical advantage is achieved that the combustion air ratio can be changed quickly.

In a further technically advantageous embodiment of the internal combustion engine, the second cam is a zero cam, which causes no opening of the intake valve. This achieves the technical advantage that the combustion air ratio can be shifted efficiently.

In a further technically advantageous embodiment of the internal combustion engine, the control device is designed to cause the boost pressure via the connection of a fresh air bypass for passing a partial flow of air to the compressor or via opening a bypass on the turbocharger, which bypasses a partial flow of the exhaust gas to the turbine , As a result, for example, the technical advantage is achieved that the charge pressure can be changed in a simple manner.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below.

Show it:

1 a diagram of different combustion air conditions as a function of the engine speed and the mean pressure;

2A a camshaft having different cams for switching a combustion air ratio;

2 B the camshaft having different cams for switching the combustion air ratio;

3A a diagram of a valve lift in response to a crank angle;

3B a diagram of a valve lift in response to a crank angle;

4 a schematic view of an internal combustion engine; and

5 a block diagram of a method for switching between two modes.

1 shows a diagram with areas of different combustion air ratios λ as a function of the engine speed rpm and the effective mean pressure BMEP (Brake Mean Effective Pressure).

The combustion air ratio λ is a dimensionless index indicating the mass ratio of air and fuel in a combustion process. The effective medium pressure BMEP is a measure of the specific torque of the reciprocating engine. The area 119-1 is an area with a combustion air ratio λ = 1. The area 119-2 is an area with a homogeneous combustion air ratio λ> 1. The range 119-3 is a region having a stratified combustion air ratio λ> 1 or a combustion air ratio λ = 1. The combustion air ratio λ is determined, for example, by a lambda probe (λ probe) which compares the residual oxygen content in the exhaust gas with the oxygen content of the instantaneous atmospheric air.

From the number λ conclusions can be drawn on the combustion process, temperatures, pollutant formation and efficiency. A combustion air ratio λ = 1 is referred to as a stoichiometric combustion air ratio in which all the fuel molecules completely react with atmospheric oxygen, without any lack of oxygen or unburnt fuel remaining (complete combustion). In terms of stoichiometry, complete combustion is theoretically possible. In practice, however, this is not achievable due to the thermodynamic equilibrium.

If the combustion air ratio λ is greater than 1, then there is an excess of air, in which not all oxygen molecules react with the fuel. The fuel mixture is referred to in this case as a lean mixture.

Switching from a lean operation with a combustion air ratio λ> 1 to a stoichiometric operation with a combustion air ratio λ = 1 occurs at high part load on the switch from a large cam contour to a small cam contour with a corresponding reduction in filling.

If the small cam contour is used, a smaller amount of air flows in the direction of λ = 1 compared to the larger cam contour and the combustion air ratio is shifted in the direction λ = 1. However, if the larger cam contour used, flows in comparison to the smaller cam contour a larger amount of air into the combustion chamber and the Combustion air ratio shifts in the direction of λ> 1. Thus, a variable combustion air ratio λ can be realized with two-stage intake cam switching.

A simultaneous reduction of the compression ratio and a retardation of the camshaft, for example via a hydraulic phaser, can increase the air requirement of the engine.

2A and 2 B exemplarily show a camshaft 109 for changing the combustion air ratio λ. The camshaft 109 includes different cams 105-1 and 105-2 containing the two intake valves 103 by means of drag levers 111 actuate. The rocker arms 111 are levers for transmitting the cam movements of the cams 105-1 and 105-2 from the camshaft 109 on the inlet valves 103 , The paddock storage 119 has an oil channel 115 on, for hydraulic displacement of a rocker arm 113 by means of an oil. About the position of the rocker arm 113 can be different cams 105-1 and 105-2 for actuating the intake valves 103 choose.

In 2A is the rocker arm 113 unlocked. As a result, the curve movement of the cam contours 107-2 on the inlet valves 103 transfer. The cam contours 107-2 the cam 105-2 have a smaller radial distance to the center of the camshaft 109 on. This will result in a smaller valve lift of the intake valves 103 generated, through which a smaller amount of air flows into the combustion chamber.

In 2 B is the rocker arm 113 locked. As a result, the curve movement of the cam contour 107-1 on the inlet valves 103 transfer. The cam contour 107-1 of the cam 105-1 has a greater radial distance to the center of the camshaft 109 on. This will result in a larger valve lift of the intake valves 103 generated, through which a larger amount of air flows into the combustion chamber.

3A shows a diagram of a valve lift H of the intake valves 103 and the exhaust valves 117 as a function of a crank angle φ when using the cams 105-2 , Due to the lower valve lift of the intake valves 103 less air flows into the combustion chamber.

3B shows a diagram of a valve lift H of the intake valves 103 and the exhaust valves 117 in dependence of a crank angle φ when using the cam 105-1 , Due to the larger valve lift of the intake valves 103 more air flows into the combustion chamber.

By deliberately supplying a higher or lower amount of air into the combustion chamber via the different cams 105-1 and 105-2 can the combustion air ratio λ specifically change, for example, by an electronic engine control, which evaluates the signal of the lambda probe.

Switching from stoichiometric operation or stratified lean operation to homogeneous leaning at low part load starts at a load point with small valve lift. The switchover to the large valve lift due to the larger cam contour increases the cylinder filling and thus enables the lean-burn of the fuel mixture.

Similarly, measures to increase the boost pressure can be initiated. A parallel reduction of the boost pressure is initiated by opening a bypass (wastegate) on a turbocharger, which bypasses a partial flow of the exhaust gas to the turbine. As a result, the exhaust gas flow through the turbine decreases and the exhaust backpressure decreases. A reduction of the boost pressure is initiated by a corresponding position of the adjustable vanes (VTG position) in a variable turbine geometry loader (VTG loader).

The changeover from lean to stoichiometric operation at high part load may additionally be accompanied by an opening of a fresh air bypass, the fresh air bypasses the turbocharger (Fresh Air Bypass), so that the cylinder filling decreases as a result of the circulating proportion of fresh air.

For the purpose of switching from stoichiometric or stratified lean engine operated in the homogeneous leaning the starting point in the partial load is selected so that with open fresh air bypass and small valve lift already boost pressure is provided, for example as a result of a closed wastegate bypass or a corresponding VTG position. The closing of the fresh air bypass in combination with the change to a large stroke contour leads to an increase of the filling and the boost pressure. In addition, by ignition angle adjustment and deliberate reduction of the efficiency of the high-pressure loop, a torque-neutral switching can take place.

Switching from stoichiometric or stratified lean engine to homogeneous lean at low part load can also be achieved by changing the event length across the cams 105-1 and 105-2 respectively. The starting point is chosen in each case so that there is a load control with Miller control times. By changing the event length and the intake timing, a direct adjustment of the cylinder charge can be implemented. At the same time in this case, the boost pressure can be established by closing the wastegate bypass, setting a corresponding VTG position or by an electrically assisted charging ("e-charging").

In addition, a variable compression ratio (VCR) with intake camshaft position (VVT) can be achieved. To switch from lean to stoichiometric operation at high part load a retardation of the camshaft is used for the purpose of filling reduction. A simultaneous reduction of the compression ratio reduces the internal efficiency and thus increases the amount of air required to represent the same torque. With the same motivation, the internal efficiency can be deliberately lowered by retarding the ignition.

The switching from stoichiometric or stratified lean engine operated in the homogeneous leaning at low part load starts in a partial load point with maximum retarded control times. A quick adjustment of the timing, such as electronic cam phaser, in combination with boosting the boost allows the change to lean operation.

4 shows a schematic view of an internal combustion engine 200 , such as a gasoline engine. The internal combustion engine 200 includes four combustion chambers 201 to which the fuel mixture is supplied. In the combustion chambers 201 the fuel is burned with atmospheric oxygen. The resulting fuel gases are via an exhaust pipe 213 derived.

At the exhaust pipe 213 is the lambda sensor 209 attached, by means of the combustion air ratio λ can be determined in the exhaust stream. The exhaust flow is through the turbocharger 205 directed. The turbocharger 205 includes a turbine that draws its energy from the residual pressure of the exhaust flow, and a turbine-driven compressor for the intake air of the engine, the air flow in a charge air pipe 215 increases and reduces the suction work of the piston.

The turbocharger 205 includes the switchable bypass 207 , which bypasses a partial flow of the exhaust gas to the turbine and the switchable fresh air bypass 203 passing fresh air past the compressor. By means of the bypass 207 and the fresh air bypass 203 can the boost pressure in the charge air pipe 215 influence.

An electronic control device 211 evaluates the signal of the lambda probe 209 off and turns off the cams 105-1 and 105-2 to effect control of the combustion air ratio λ. Furthermore, the control device 211 the fresh air bypass 203 or the bypass 207 turn. The electronic control device 211 For example, it includes a memory for receiving control data and a microprocessor for processing the control data.

5 shows a block diagram of the method for switching a gasoline engine between a stoichiometric operation and a lean operation.

In stoichiometric operation with a combustion air ratio λ = 1, the air inlet into the combustion chamber 101 by means of the inlet valve 103 through the cam 105-2 with the small cam contour 107-2 causes. In order to increase the combustion air ratio λ on this basis, in step S101, the air inlet becomes the combustion chamber 101 through the cam 105-1 with the big cam contour 107-1 controlled.

In lean operation with a combustion air ratio λ> 1, however, the air inlet into the combustion chamber 101 by means of an inlet valve 103 through the cam 105-1 with the big cam contour 107-1 causes. In order to reduce the combustion air ratio λ on this basis, the air inlet becomes the combustion chamber in step S102 101 through the cam 105-2 with the small cam contour 107-2 controlled.

The method uses variability on the internal combustion engine 200 for switching between lean and stoichiometric operation in combination with a supercharging of the internal combustion engine 200 , A lean-burn gasoline engine operating at mid-high partial load achieves maximization of efficiency while reducing NOx raw emissions, and can be seen as an optimization of existing downsizing concepts for reducing emissions. The method thus achieves a transient switching between lean and stoichiometric engine operation. Furthermore, a process management and control strategy is defined.

The lean operation can be extended in multi-cylinder engines in the direction of low engine power by means of a cylinder shutdown. As a result of the shutdown of individual cylinders, the operating point of the still fired cylinder shifts toward higher load, so that restrictions due to an inadmissible combustion stability can be avoided. In this way, the lean operating range can be extended.

This represents cylinder-individual valve train variability since it is represented by switching from a full valve lift to a zero valve lift on a subset of the cylinders of the engine.

All of the features explained and shown in connection with individual embodiments of the invention may be provided in different combinations in the article according to the invention in order to simultaneously realize their advantageous effects.

All method steps may be implemented by means suitable for carrying out the respective method step. All functions performed by objective features may be a method step of a method.

The scope of the present invention is given by the claims and is not limited by the features illustrated in the specification or shown in the figures.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19728798 C2 [0004]
• DE 19951096 A1 [0005]

Claims (10)

A method of switching an internal combustion engine between a lean and a stoichiometric engine operation, comprising the steps of: controlling (S101) the air intake into a combustion chamber ( 201 ) by means of an inlet valve ( 103 ) by a cam ( 105-1 ) with a first cam contour ( 107-1 ) to compare the combustion air ratio (λ) with a cam ( 105-2 ) with a second cam contour ( 107-2 ) increase; and controlling (S102) the air inlet into the combustion chamber (S102) 201 ) by means of an inlet valve ( 103 ) through the cam ( 105-2 ) with the second cam contour ( 107-2 ) to the combustion air ratio (λ) relative to the cam ( 105-1 ) with the first cam contour ( 107-1 ) to reduce. Method according to claim 1, wherein the first cam ( 105-1 ) a larger valve lift of the intake valve ( 103 ) acts as the second cam ( 105-2 ). Method according to one of the preceding claims, wherein the first cam ( 105-1 ) a longer valve opening of the inlet valve ( 103 ) acts as the second cam ( 105-2 ). Method according to one of the preceding claims, wherein a boost pressure is increased while the combustion air ratio (λ) through the first cam ( 105-1 ) is increased. Method according to one of the preceding claims, wherein a boost pressure is reduced while the combustion air ratio (λ) through the second cam ( 105-2 ) is reduced. The method of claim 5, wherein the reduction of the boost pressure via the connection of a fresh air bypass ( 203 ) on a turbocharger ( 205 ) or reducing the charge pressure by opening a bypass ( 207 ) on a turbocharger ( 205 ) is caused, which bypasses a partial flow of the exhaust gas to the turbine. Method according to one of the preceding claims, wherein a retardation of the camshaft ( 109 ) is performed for filling reduction, while the combustion air ratio (λ) through the second cam ( 105 ) is reduced. Method according to one of the preceding claims, wherein the steps of controlling (S101, S102) are performed on the basis of a signal from a lambda probe ( 209 ) provided. Method according to one of the preceding claims, wherein the second cam ( 105-2 ) is a zero cam, which does not open the inlet valve ( 103 ) causes. Internal combustion engine ( 100 ) with a control device ( 211 ) for controlling the air inlet into a combustion chamber ( 201 ) by means of an inlet valve ( 103 ) by a cam ( 105-1 ) with a first cam contour ( 107-1 ) to compare the combustion air ratio (λ) with a cam ( 105-2 ) with a second cam contour ( 107-2 ) increase; and for controlling the air inlet into the combustion chamber ( 101 ) by means of an inlet valve ( 103 ) through the cam ( 105-2 ) with the second cam contour ( 107-2 ) to the combustion air ratio (λ) relative to the cam ( 105-1 ) with the first cam contour ( 107-1 ) to reduce.

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