EP1982062A1

EP1982062A1 - Internal combustion engine

Info

Publication number: EP1982062A1
Application number: EP07711397A
Authority: EP
Inventors: Stephan KRÄTSCHMER; Wolfram Schmid; Siegfried Sumser
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2006-02-07
Filing date: 2007-01-27
Publication date: 2008-10-22
Also published as: CN101379278A; DE102006005336A1; WO2007090532A1; JP2009526160A; US20090038584A1

Abstract

The invention relates to an internal combustion engine for operation alternately in spark-ignited four-stroke power cycle operation and with two-stroke engine braking operation, provided with a cam adjuster (23) for adjusting the cam profiles of both inlet valve (5) and outlet valve (7). On transition from power cycle operation to engine braking operation the cam adjuster device (23) actuates the exhaust valve (7) such that during the entire engine operating cycle, both in the expansion phase and the compression phase said valve is in a permanently open position.

Description

DaimlerChrysler AG

Internal combustion engine

The invention relates to an internal combustion engine which is to be operated alternately in the fired four-stroke mode of operation and in the two-stroke engine braking mode, according to the preamble of claim 1.

A two-stroke engine braking method is described in DE 10 2004 006 681 A1, according to which the intake valve is opened in engine braking operation during the expansion stroke of the cylinder shortly before bottom dead center, after which combustion air can flow into the cylinder via the intake tract, and after exceeding the deadlock is closed again. In the immediately following compression stroke, the exhaust valve is opened shortly before reaching top dead center, whereupon the compressed combustion air flows out of the cylinder via the open exhaust valve into the exhaust gas line. Shortly after the top dead center is exceeded, the exhaust valve is closed again, the cycle then starts again.

The internal combustion engine from DE 10 2004 006 681 A1 is provided with an exhaust gas turbocharger, which comprises a compressor in the intake tract and an exhaust gas turbine in the exhaust gas system. The exhaust gas turbine is equipped with variable turbine geometry, which provides a variable adjustment of the effective turbine inlet cross section allowed. In a congestion position which reduces the free passage in the turbine, an increased exhaust back pressure in the line section between the cylinder outlets and the exhaust gas turbine arises, whereby the pistons in the cylinders have to perform increased discharge work. As a result, the engine braking power can be increased considerably.

The invention has for its object to provide an internal combustion engine in which high braking performance can be realized with little design effort.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

In the novel internal combustion engine, which is operated in fired operation in four-stroke and engine braking in two-stroke, a Hubkurvenverstelleinrichtung is provided for the adjustment of the lift curves of both the intake valve and the exhaust valve. In an advantageous embodiment, the lift curve of both the intake valve and the exhaust valve for the transfer between the four-stroke drive mode and the two-stroke engine braking operation is adjusted in a common adjusting movement. According to an alternative embodiment, however, it is also possible to provide in the Hubkurvenverstelleinrichtung separate actuators, which act respectively on the inlet valve and the outlet valve.

Furthermore, it is provided that the exhaust valve is influenced in the manner that this by appropriate action on the Hubkurvenverstelleinrichtung is in a permanently open position during the entire engine braking operation, ie both in the expansion stroke and in the compression stroke. In two-stroke engine braking operation, during the expansion stroke of the cylinder, the intake valve is opened before reaching the bottom dead center so that the combustion air from the intake stroke can flow into the combustion chamber in the cylinders. After exceeding the bottom dead center, the inlet valve is closed and in the subsequent stroke of the piston in the direction of top dead center of the combustion chamber contents is compressed. With increasing compression, the combustion air is blown out of the combustion chamber into the exhaust system via the permanently open exhaust valve. The control effort is thereby significantly reduced. It is particularly advantageous that no adjusting movement of the outlet valve against the very high internal cylinder pressures must be carried out, whereby a significant energy saving is achieved compared to prior art embodiments. In addition, the actuator can be dimensioned correspondingly smaller in the Hubkurvenverstelleinrichtung.

The internal combustion engine basically works without an additional brake valve. The blow-off is carried out exclusively via the open exhaust valve, which also performs the function of a brake valve in two-stroke engine braking operation. Since the movement of the exhaust valve is minimized, low actuating forces for the admission of the exhaust valve in the transition from the fired drive mode in the engine braking operation and vice versa are sufficient. During engine braking operation, no or only small actuating forces are required for the movement of the exhaust valve. The movement of the intake valve is also possible with only small actuating forces, since the opening of the intake valve is short before the bottom dead center in a phase without combustion chamber overpressure takes place.

The lift curve of the exhaust valve remains completely constant during the execution of the engine braking operation in a first advantageous embodiment, the exhaust valve is kept in a constant opening position without changing the lift curve. In this variant, no restoring forces during engine braking operation for the exhaust valve are required.

In a second advantageous variant, although the exhaust valve is held in the open position during the entire engine braking operation, but the lift curve is varied between a minimum and a maximum open position. To minimize the adjustment effort, the stroke change of the exhaust valve is expediently within narrow limits. The advantage of this design is that a higher filling of the combustion chamber is possible during the expansion phase when the inlet valve is open and a higher internal combustion chamber pressure can be built up during the compression stroke.

Conveniently, a steady transition in the lift curves of both the intake valve and the exhaust valve can be adjusted via the Hubkurvenverstelleinrichtung during the change from the four-stroke drive mode for two-stroke engine braking operation and vice versa. With the steady transition to a jumps in the lifting curves are avoided, on the other hand, the transition areas in the Hubkurvenverstelleinrichtung additional

Setting options for influencing the lift curves. The Hubkurvenverstelleinrichtung comprises according to an expedient embodiment of an adjustable, acting on the valves camshaft, wherein each cam for the cam curves of the drive mode and the engine braking operation are provided per valve. These cams for each valve thus have two sections associated respectively with the driven mode and the braking mode. The sections expediently have a steady transition. Furthermore, it may be advantageous to arrange the cams for the intake valves and the cams for the exhaust valves on a common camshaft, so that with only one acting on the camshaft adjusting movement, the transition between powered operation and engine braking operation is completed. This adjusting movement can be carried out in the case of a camshaft as a pure axial movement.

According to an alternative embodiment, the cams for the intake valves and the cams for the exhaust valves may also be arranged on different camshafts. Also in this configuration, both cams can be acted upon by a common actuator, which adjusts the camshafts for transferring between driven operation and engine braking operation axially.

The influencing of the valve lift curves via a camshaft represents an advantageous mechanical design. Alternatively, however, other Hubkurvenverstelleinrichtungen be used, for example, hydraulic or electromagnetic control devices.

The internal combustion engine is provided according to a further advantageous embodiment with an exhaust gas turbocharger, comprising a compressor in the intake tract and an exhaust gas turbine in the exhaust system. The exhaust gas turbine may be provided with a variable turbine geometry for variable adjustment of the effective turbine inlet cross section, wherein the turbine inlet cross section is adjusted between a maximum open opening position and a reduced stagnation position. To increase the engine braking power, the turbine geometry is transferred to the stowed position, whereby in the exhaust line between the cylinder outlet and the exhaust gas turbine, an increased exhaust back pressure is generated, which counteracts the Ausschubarbeit the piston in the cylinders. The positioning of the variable turbine geometry is an additional factor influencing the regulation of engine braking performance.

In addition, a bypass bypassing the exhaust gas turbine can be provided, into which an adjustable bypass valve is integrated. When the bypass valve is open, the exhaust backpressure is reduced while bypassing the exhaust gas turbine. The setting of the bypass valve is another degree of freedom for the regulation of the engine braking performance, also hereby an overload protection in the exhaust gas turbine is realized.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

Fig. 1 is a schematic representation of a

Internal combustion engine with exhaust gas turbocharger, with one of the cylinders of the internal combustion engine in enlarged view including the associated intake and exhaust valves and a camshaft influencing the lift curve of the valves, Fig. 2 is a phase diagram with the inlet Opens and

Intake-closing timing for the intake valve during execution of the two-cycle engine braking process including a schematic representation of the history of the lift curve of the exhaust valve,

Fig. 3 is a graph showing the lift curves of the intake and exhaust valves as a function of crank angle, respectively, for the fired drive mode (dashed line) and the two-cycle engine brake mode (solid line).

From that shown in Fig. 1 schematically

Internal combustion engine, such as a diesel engine or a gasoline engine is shown enlarged one of the cylinder 1, the combustion chamber 9 is connected via an inlet valve 5 to the inlet channel 4 and an exhaust valve 7 to the exhaust manifold 6. The intake passage 4 is part of the intake tract 20 of the internal combustion engine, and the exhaust manifold 6 is connected to the exhaust gas passage 16. Combustion air is introduced into the combustion chamber of the cylinder 1 via the inlet channel 4 when the inlet valve 5 is open. The residual gas in the combustion chamber is discharged via the exhaust manifold 6 when the outlet valve 7 is open. The control of the valves 5 and 7 via a camshaft 23, are arranged on the cam 24 and 25. The cam 24 is the intake valve 5, the cam 25 associated with the exhaust valve 7. The cam contour is transmitted by means of suitable transmission elements on the valves 5, 7 and determines the lift curve of the valves. When circulating around the camshaft longitudinal axis, the contour of each cam is scanned and transmitted. In order to realize different lift curves for the intake valve 5 and the exhaust valve 7 for the fired drive mode and the engine braking operation, each of the cams 24 and 25 is constructed in two parts, wherein one cam portion of each cam 24 and 25 of the fired drive mode and the adjacent cam portion on each Cam is assigned to the engine braking operation. The cam portions are axially adjacent to each other and are connected to each other via a continuous transition. The transfer between the adjacent cam sections is effected by an axial adjustment of the camshaft 23, which is accomplished by means of an actuator 22.

The internal combustion engine 2 is also provided with an exhaust gas turbocharger 2, which comprises an exhaust gas turbine 3 in the exhaust gas line 16 and a compressor 11 in the intake tract 20. The turbine wheel in the exhaust gas turbine 10 and the compressor wheel in the compressor 11 are rotatably coupled via a shaft 12. During operation of the internal combustion engine, the compressor 11 is supplied with combustion air from the environment via the compressor inlet 19, which combustion air is compressed by the compressor wheel to an increased pressure. This compressed air exits the compressor 11 via the compressor outlet 21 and is conducted via the intake tract duct 20 into the inlet duct 4, possibly after flowing through an intercooler. On the exhaust side, the gas, which was discharged from the combustion chamber 9, flows via the exhaust gas line 16 and the turbine inlet 17 into the exhaust gas turbine 10, in which the turbine wheel is driven. The expanded gas is discharged via the turbine outlet 18 from the turbine. The exhaust gas turbine 10 is equipped with a variable turbine geometry 13, via which the effective

Turbine inlet cross section to the turbine between a minimum storage position and a maximum opening position is to adjust. The variable turbine geometry is advantageously designed as a retractable in the turbine inlet duct brake grille. Alternatively, a guide grid with adjustable guide vanes comes into consideration. Further possible structural designs are asymmetric turbines with a smaller and a larger exhaust gas flow for the double-flow of the turbine wheel, wherein the gas supply into each exhaust gas flow is separate and controllable and the turbine inlet cross section at least one of the two exhaust gas flows to the turbine by means of variable turbine geometry is set.

In order to adapt the turbine size optimally to the internal combustion engine to be used and to allow high engine braking performance at relatively low thermal loads, a turbobardening factor TBF is defined for dimensioning of the exhaust gas turbocharger, which according to the relationship

TBF = A _τ , _h * D _x / V _H

from the free flow cross section A _τ , _h in the exhaust path to the turbine at maximum braking power, the inlet diameter D _{τ of} the turbine wheel and the displacement V _{H of} the internal combustion engine is determined. For small exhaust gas turbochargers, for example, exhaust gas turbocharger in passenger cars, the turbobar factor TBF is at a value less than 0.002 (2 ° / oo), where the value may be less than 0.5 ° / oo. For larger engines, especially for heavy commercial vehicles, the turbobar factor is in a size range less than 0.0075 (7.5 ° / oo) / preferably in a range smaller than 0.005 (5

The Äbgasturbine 10 is bridged by a bypass 26, which branches off upstream of the Äbgasturbine 10 of the exhaust pipe 16 and opens again downstream of the Äbgasturbine in the exhaust pipe. In the bypass 26 is an adjustable bypass valve which is to be adjusted continuously between a locking position and an open position via an actuator 14.

The actuators and actuators in the internal combustion engine or the engines associated with the units are controlled via control signals of a control and control unit 15 as a function of various state and operating variables. These state and operating variables include, inter alia, the engine speed n, the boost pressure p _L in the intake passage 4 and the turbine inlet pressure p _E at the turbine inlet 17 as engine parameters. Further influencing variables are the brake power demand P _{Br / of} the mechanical wheel brake P _B r, R generated by the driver and optionally the handbrake P _BΓ , _{H is} supplied. Also, the driving speed v and possibly a danger signal GS, which denotes a dangerous situation, are the operating state characterizing variables that are processed in the control and control unit 15. Furthermore, in a block S, a safety check of the charge exchange valves can be carried out, an error signal F being displayed in the event of an error.

The fired drive mode is performed in four-stroke, whereas the engine braking operation takes place in the two-stroke process. In engine braking operation, the intake valve 5 will advance in the expansion stroke of the cylinder 1 Reaching the bottom dead center opened, whereupon the combustion air from the intake tract 20 via the inlet channel 4 can flow into the combustion chamber 9. After exceeding the bottom dead center, the inlet valve 5 is closed again, in the immediately following compression stroke, the combustion air is compressed and discharged via the outlet valve located in the opening position 7 via the exhaust manifold 6 into the exhaust pipe 16.

In the phase diagram of FIG. 2, the lift curves for the intake valve 5 and the exhaust valve 7 over a crank angle range of 360 ° are shown. The lift curve of the intake valve is denoted by EV, the lift curve of the exhaust valve by AV. The arrow direction D indicates the direction of rotation. The phase diagram represents the two-stroke engine braking operation, according to which during the expansion stroke of the cylinder, the intake valve is opened shortly before reaching the bottom dead center UT to the inlet-opening time EÖ. Due to the low combustion chamber pressure in this phase, the inlet valve can be opened without counterforce, in addition, the pressurized combustion air flows into the combustion chamber due to the pressure gradient. After exceeding the bottom dead center UT, the inlet valve is closed again at the inlet closing time ES. The time EÖ and ES are exemplary in a crank angle range of 30 ° before or after the bottom dead center UT.

The crank angle range between top dead center OT and bottom dead center UT denotes the expansion stroke, the subsequent crank angle range between bottom dead center UT and top dead center TDC represents the compression stroke. After the intake valves are closed, the gases in the combustion chamber are in compression stroke compressed. The outflow via the open exhaust valve, which expedient during the entire engine braking operation, ie during the compression stroke and during the expansion stroke, in a constant

Opening position with a stroke Δh _A v = constant. Since the position of the exhaust valve during the entire engine braking operation does not change, no adjustment effort for the adjustment of the exhaust valve is required. Compared to embodiments in which the exhaust valve must be opened shortly before reaching the top dead center OT against the high combustion chamber internal pressure, this represents a simplification and an energy saving. The resulting through the open exhaust valve pressure losses during the expansion stroke and the compression stroke can by a small stroke of the Exhaust valve to be kept within reasonable limits.

In the diagram according to FIG. 3, the valve lift curves Δh are plotted as a function of the crank angle KW. Illustrated are the lift curves EV for the intake valve and AV for the exhaust valve, respectively registered for the fired drive mode in four-stroke (dashed lines) and for the two-stroke engine brake operation (solid line for the intake valve EV and with solid lines limited Hubband for the exhaust valve AV) ,

In the four-stroke drive mode, the exhaust valve is opened just before the bottom dead center UT, maintaining the open position until reaching the top dead center OT. The inlet valve is opened with a slight overlap to the exhaust valve in the region of top dead center, wherein the opening phase to the subsequent bottom dead center UT stops. In the two-stroke engine braking operation, which is shown in solid line in FIG. 3, the exhaust valve according to the elevation curve AV is permanently in the opened state. Entered in Fig. 3 is a band area for the elevation curve AV of the exhaust valve, wherein the opening position of the exhaust valve moves appropriately within this registered bandwidth. It is possible to maintain the exhaust valve at a constant, fixed value either during the entire engine braking process, or to vary the lift curve of the exhaust valve within the shown bandwidth moving to a low opening level.

The inlet valve is opened in accordance with the registered lift curve EV shortly before reaching the bottom dead center and closed again shortly after exceeding the bottom dead center UT. The maximum opening stroke of the intake valve lift curve is significantly below the maximum lift of the intake valve in the fired drive mode. The same applies to the exhaust valve, which has an even smaller opening stroke in engine braking operation than the intake valve.

Claims

DaimlerChrysler AGPatent claims

1. Internal combustion engine to operate alternately in the fired four-stroke drive mode and in two-stroke engine braking operation, in the combustion air by controlling charge exchange valves (5, 7) to the cylinders (1) supplied in the cylinders (1) compressed and then in the exhaust line (16) is blown off, wherein in the expansion stroke of the cylinder (1) before reaching the bottom dead center (UT), the inlet valve (5) opened and after exceeding the bottom dead center (UT) again closed and the in the exhaust line (16) opening Exhaust valve (7) is set in the open position, characterized in that a

Hubkurvenverstelleinrichtung (23) for the adjustment of the lift curves (EV, AV) of both the intake valve (5) and the exhaust valve (7) is provided and that the Hubkurvenverstelleinrichtung (23) at the transition from the fired drive mode for engine braking operation, the exhaust valve (7) in the way that the exhaust valve (7) is in a permanently open position during the entire engine braking operation both in the expansion stroke and in the compression stroke.

2. Internal combustion engine according to claim 1, characterized in that when changing between four-stroke Drive mode and two-stroke engine braking operation, the Hubkurvenverstelleinrichtung (23) allows a steady transition in the lift curves (EV, AV) of the intake and exhaust valve (5, 7).

3. Internal combustion engine according to claim 1 or 2, characterized in that the Hubkurvenverstelleinrichtung comprises an adjustable, acting on the valves camshaft (23), wherein on the camshaft (23) each cam (24, 25) for the inlet and the exhaust valve ( 5, 7) are arranged with different cam curves for the four-stroke drive mode and for the two-stroke engine braking operation.

4. Internal combustion engine according to claim 3, characterized in that the camshaft (23) is axially adjustable.

5. Internal combustion engine according to one of claims 1 to 4, characterized in that with a common actuating movement of the Hubkurvenverstelleinrichtung (23) the lift curves (EV, AV) of both the intake valve (5) and the exhaust valve (7) between the four-stroke drive mode and the two-stroke engine braking operation between the four-stroke drive mode and the two-stroke engine braking operation are adjustable.

6. Internal combustion engine according to one of claims 1 to 5, characterized in that the exhaust valve (7) is held by the Hubkurvenverstelleinrichtung (23) in the engine braking mode in a constant open position.

7. Internal combustion engine according to one of claims 1 to 6, characterized in that the Hubkurvenverstelleinrichtung (23) for engine braking operation for constant open position of the valve position has a cylinder without cam as a camshaft.

8. Internal combustion engine according to one of claims 1 to 7, characterized in that the Hubkurvenverstelleinrichtung (23) for the engine braking operation for continuous

Valve stroke adjustment has a cone without cam as the camshaft, which is designed axially displaceable.

9. Internal combustion engine according to one of claims 1 to 8, characterized in that an exhaust gas turbocharger (2) with a compressor (11) in the intake tract (20) and an exhaust gas turbine (10) in the exhaust line (16) is provided.

10. Internal combustion engine according to claim 9, characterized in that the exhaust gas turbine (10) is provided with variable turbine geometry (13) for variable adjustment of the effective turbine inlet cross-section, wherein the variable turbine geometry (13) is to be adjusted in the engine braking operation in the turbine inlet cross-section reducing jam position.

11. Internal combustion engine according to claim 9 or 10, characterized in that in the exhaust line (16) the exhaust gas turbine (10) bridging bypass (26) with adjustable bypass valve (27) is arranged, wherein the required engine braking power in the engine braking operation via the setting of the bypass valve ( 27) is to regulate.

12. Internal combustion engine according to one of claims 9 to 11, characterized in that the variable turbine geometry (13) is designed as a brake grid, which can be inserted into the turbine inlet channel.

13. Internal combustion engine according to one of claims 9 to 12, characterized in that the exhaust gas turbocharger (2) is dimensioned in such a way that related to the engine braking operation at maximum braking power Turbobremsfaktor (TBF) of the exhaust gas turbocharger, according to the relationship

from the parameters

A _τ free flow cross section in the exhaust path to

Exhaust gas turbine (10) at maximum braking power D _τ Turbine inlet diameter in the exhaust turbine V _H Stroke volume of the internal combustion engine

is determined to be less than 0.005 (5 ° / oo):

TBF <0.005.