DE102014008643A1 - Method for operating an internal combustion engine - Google Patents

Abstract

A method and an arrangement for operating an internal combustion engine are presented. In this case, an Atkinson base cam is used in conjunction with a valve train, wherein the closing of an intake valve takes place at a time, so that the friction loss of the internal combustion engine can be overcome.

Description

The invention relates to a method and an arrangement for operating an internal combustion engine.

Internal combustion engines, also referred to as internal combustion engines, are heat engines that convert chemical energy of a fuel into mechanical energy via a combustion process. As combustion chambers are cylinders, in each of which a piston is guided. Internal combustion engines used in motor vehicles are also referred to as internal combustion engines.

Valves are used to introduce the fuel-gas mixture to be ignited into the cylinders. For example, intake valves are used in diesel engines to let in clean air. The fuel is injected through injectors. In gas engines, an air-gas mixture is introduced via intake valves in the cylinder. To control the valves, a mechanism is provided, which is referred to as a valve control or valve train. By opening and closing the valves, the charge of the internal combustion engine is controlled. In this case, valves can be opened by a camshaft, which is driven by a crankshaft, via a plunger. It can also be provided that the valves are, for example, electrically or pneumatically controlled in order to actuate them. Charge change is the replacement of the mixture contained in the cylinder.

The camshaft is a machine element in which at least one cam is mounted on a rod which constitutes the shaft. The rod or shaft rotates about its own axis. This rotational movement is converted by the at least one cam in a longitudinal movement. This longitudinal movement of the cams of the camshaft is used to open and close intake and exhaust valves of the cylinders. In this way, the valves are driven by the camshaft, which in turn is connected to the crankshaft. The rotation of the crankshaft causes rotation of the camshaft. The shape of the cams of the camshaft affects the timing and duration of the valve actuation.

By adjusting the valve opening times, an increase in the efficiency of the engine can be achieved. This can be felt as power and torque gain or as fuel savings. Thus, with intake valves, the opening time and the closing time can be varied.

If the inlet valve is closed in the area of bottom dead center, then the maximum amount of air is sucked. This causes the compression to occur at a maximum compression ratio. If the inlet valve is closed at a different time, the air quantity and the compression ratio are reduced.

In methods for operating an internal combustion engine, it is known to shift the closing time of the intake valve. There are basically two cycles known, the Miller cycle and the Atkinson cycle. In the Miller cycle, the closing time is postponed early, ie at a time earlier, namely a time before bottom dead center, at the Atkinson cycle, this time is late, ie at a later time, namely at a time after bottom dead center, moved. The goal of both cycles is to lower the process temperature through a reduced effective compression ratio, resulting in lower No _x emissions.

To shift the closing timing of the intake valve late according to the Atkinson cycle, the use of a so-called Atkinson base cam is known. By using an Atkinson base cam, a motor protection can be ensured in the event of a system failure of the hydromechanical valve train, because the charge mass is re-pushed out of the cylinder into the intake manifold. This minimizes the charge mass and thus energy in the cylinder and thereby also the cylinder tip pressure.

The built-in Atkinson cam also strong negative pressures in the intake manifold and in the cylinder can be avoided. This offers positive characteristics with regard to load control, control accuracy and de-throttling during idling and in the lower load range. In addition, effects such as oil sliding the piston can be suppressed or avoided.

The publication DE 603 18 370 T2 describes a system for delaying the closing timing of an intake valve of an internal combustion engine. This system includes an intake valve movable between a first and second position, a cam assembly configured to move the intake valve, a fluid actuator configured to selectively inhibit first valve movement to first position, a fluid source, a directional control valve configured to control fluid flow, and a fluid passageway. The system further includes an accumulator and a restricted orifice to restrict fluid flow between the accumulator and the fluid passageway.

From the publication WO2009 / 15 1352 A1 a device for an internal combustion engine is known which has cylinders, which are each associated with at least one inlet valve and at least one outlet valve. It is further described a camshaft which carries two cams, which both interact with the at least one inlet valve.

A control system for an internal combustion engine having a cylinder is disclosed in the document US 2010/0126463 A1 known. In this, a fluid flow to the cylinder is controlled by means of an actuator controlled via a motor valve. The actuator in turn is controlled by a controller which is adapted to make this control in response to a detected speed.

Against this background, a method with the features of claim 1 and an arrangement according to claim 8 are presented. Embodiments result from the dependent claims and the description.

The presented method is for operating an internal combustion engine having a piston guided in a cylinder, using an Atkinson base cam in conjunction with a valvetrain, typically a freely adjustable valvetrain, wherein an intake valve and an exhaust valve are provided by means of the Atkinson base cam and the valvetrain repeatedly opened and closed. It is provided that the closing of the intake valve takes place at a time, so that the friction loss of the internal combustion engine can be overcome and the internal combustion engine can be operated at idle.

It can, for example, a hydromechanical valve train can be used. A freely adjustable valve train is required in particular during idling control with Atkinson basic cam without throttle.

The closing of the inlet valve may occur at a time after 660 ° CA or after 690 ° CA. The closing of the inlet valve can also be done immediately before the top dead center of the piston or at top dead center.

The described arrangement is for operating an internal combustion engine with a guided in a cylinder piston, the arrangement having an Atkinson base cam and a valve train and is particularly suitable for carrying out a method of the type described above. In this case, the arrangement is set up to repeatedly open and close an intake valve and an exhaust valve, it being provided that the closing of the intake valve occurs at a time after, so that the friction loss of the internal combustion engine can be overcome. This can then be operated at idle.

As a valve train, a hydromechanical valve train can be used.

Furthermore, the arrangement may be adapted to close the inlet valve after 660 ° CA or after 690 ° CA. This closing can also take place immediately before top dead center or at the time of top dead center.

It is thus presented a method in which a motor protection and idling operation by means of Atkinson base cam, possibly in combination with a hydromechanical valve train is achieved. An Atkinson base cam is a cam with a contour that ensures a pushing back of already in-cylinder charge mass into the intake tract. In the context of the presented method, the terms bottom dead center and top dead center are used. These are explained below:
Under a dead center is to be understood that in a lever mechanism, the connecting joints and the acting force vectors are in line. In an internal combustion engine, the positions of the crankshaft are referred to as dead centers, in which the piston no longer carries out any movement in the axial direction. The position of the dead centers is uniquely determined by the geometry of crankshaft, connecting rod and piston. It is differentiated between the top dead center (TDC), in which the piston top is close to the cylinder head, and the bottom dead center (UT), in which the piston top is remote from the cylinder head. In four-stroke engines, a distinction is additionally made between the charge-exchange TDC and the TDC. Top dead center serves as a reference for the crankshaft position. A crankshaft position of 0 degrees usually corresponds to the ignition TDC position. The top dead center thus indicates the highest point that the piston occupies during its up and down movement in the cylinder. In an internal combustion engine, top dead center is important when setting the ignition. Top dead center is the phase before the reversal point of the piston.

A valve train is to be understood as a mechanism which controls intake and / or exhaust valves in an internal combustion engine, in particular in a reciprocating engine. By opening and closing the valves, the charge cycle is controlled. Basically, the valves are controlled via the camshaft. A valve train additionally provides a means to control the valves, ie to open and close. In a hydromechanical valve train is also an hydromechanical device provided to control the valves.

It is thus a shoring of an "extreme Atkinson cam" as a geometric base cam in, for example, hydromechanical valve train, which allows a very late closing of the valves provided. It can thereby be realized an inlet closure in the region before the top dead center of the piston. By means of this late intake valve closing, a large part of the charge mass previously flowed into the cylinder, namely by the upward piston movement with the intake valve still open, is pushed back into the intake passage. The late entry deadline is determined by the respective construction. In the case of a piston with suitable valve pockets, an inlet closing of 0 ° CA is also conceivable. However, it should be noted here that the internal combustion engine may not be able to apply its friction loss and will fail.

Since the valve train can realize different, basically all possible, sub-contours of this valve lift basic cam, a conventional valve closing time is still possible. It is possible to avoid negative pressures in the cylinder and receiver during idling control by eliminating the throttle valve.

It is thus achieved protection of the engine. In particular, in a system failure of the hydromechanical valve train, especially at full load, no overfilling of the cylinder causes. Idle control with higher receiver and cylinder pressures is achieved, avoiding negative pressure and thereby oil shifting effects.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below in detail with reference to the drawings.

1 shows in a graph actuation of an intake and an exhaust valve.

2 shows contours of camshafts.

3 shows an embodiment of an internal combustion engine.

In 1 is in a graph 10 illustrates an operation of an intake valve and an exhaust valve. The valve actuation is plotted as a function of an engine crank angle for an internal combustion engine.

In the graph is on an abscissa 12 the crank angle [°] and an ordinate 14 applied the valve lift. Furthermore, the positions of a first top dead center 16 , a bottom dead center 18 and a second top dead center 20 entered. A first turn 30 shows the valve lift of the exhaust valve, a second curve 32 , the valve lift of the intake valve according to the Miller cycle, a third curve 34 the valve lift of a standard operated intake valve, a fourth curve 36 the valve lift of an intake valve according to the Atkinson cycle and a fifth curve 38 the valve lift of an intake valve according to an embodiment of the method described.

According to the Miller cycle, the intake valve thus closes before bottom dead center 18 , The Miller timing is generally referred to as a timing at which the intake valve is before bottom dead center 18 closes. As Atkinson control time is generally referred to a control time at which the intake valve after the bottom dead center 18 closes.

According to the presented method is now provided that the closing of the intake valve takes place very late. In the embodiment shown, the closing takes place before the second top dead center 20 of the cylinder. The time is chosen so that the friction of the engine overcome and thus it can be operated at idle.

This late closing of the inlet valve causes a large part of the previously flowed-in mass of charge into the cylinder is pushed back into the inlet channel by the upward piston movement with the inlet valve still open.

2 shows in a diagram two contours of cams. A first contour 50 shows the contour of a conventional cam. A second contour 52 shows the contour of a specially shaped Atkinson base cam.

While the first contour 50 has a nearly symmetrical shape is at the second contour 52 a bulge 54 to recognize that causes the late entry closing.

3 shows in a simplified representation of an internal combustion engine 70 with a cylinder 72 that has an inlet valve 74 and an exhaust valve 76 having. Moreover, in the cylinder 72 a piston 78 guided. To operate the inlet valve 74 and of exhaust valve 76 is an Atkinson ground cam 80 that with a valvetrain 82 cooperates, provided.

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 60318370 T2 [0010]
• WO 009/151352 A1 [0011]
• US 2010/0126463 A1 [0012]

Claims (11)

Method for operating an internal combustion engine ( 70 ) with one in a cylinder ( 72 ) guided piston ( 78 ), in which an Atkinson basic cam ( 80 ) in conjunction with a valve train ( 82 ) using the Atkinson basic cam ( 80 ) and the valvetrain ( 82 ) an inlet valve ( 74 ) and an outlet valve ( 76 ) are repeatedly opened and closed, it being provided that the closing of the inlet valve ( 74 ) takes place at a time, so that the friction of the internal combustion engine ( 70 ) can be overcome so that it can be operated at idle. The method of claim 1, wherein the Atkinson base cam ( 80 ) is used in conjunction with a hydromechanical valve train, whereby by means of the Atkinson basic cam ( 80 ) and the hydromechanical valve train the inlet valve ( 74 ) and the exhaust valve ( 76 ) repeatedly opened and closed. Method according to Claim 1 or 2, in which the closing of the inlet valve ( 74 ) occurs at a time after 660 ° CA. Method according to one of claims 1 to 3, wherein the closing of the inlet valve ( 74 ) occurs at a time after 690 ° CA. Method according to one of claims 1 to 4, wherein the closing of the inlet valve ( 74 ) immediately before top dead center ( 16 . 20 ) of the piston ( 78 ) he follows. Method according to one of claims 1 to 4, wherein the closing of the inlet valve ( 74 ) at top dead center ( 16 . 20 ) of the piston ( 78 ) he follows. Method according to one of claims 1 to 6, which is used in the context of idle control. Arrangement for operating an internal combustion engine ( 70 ) with one in a cylinder ( 72 ) guided piston ( 78 ), the arrangement comprising an Atkinson base cam ( 80 ) and a valvetrain ( 82 ) and is particularly suitable for carrying out a method according to one of claims 1 to 7, wherein the arrangement is adapted to an inlet valve ( 74 ) and an outlet valve ( 76 ) to open and close repeatedly, it being provided that the closing of the intake valve takes place at a time, so that the friction loss of the internal combustion engine ( 70 ) can be overcome so that it can be operated at idle. Arrangement according to claim 8, in which a hydromechanical valve train is used. Arrangement according to claim 8 or 9, which is arranged such that the closing of the inlet valve ( 74 ) immediately before top dead center ( 16 . 20 ) of the piston ( 78 ) he follows. Arrangement according to claim 8 or 9, which is arranged such that the closing of the inlet valve ( 74 ) at top dead center ( 16 . 20 ) of the piston ( 78 ) he follows.

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