Four stroke internal combustion engine

The invention relates to a four-stroke internal combustion engine with a roof-shaped combustion chamber and at least two inlet valves per cylinder, with at least two inlet channels leading to the inlet valves, of which a first inlet channel is designed as an unthrottled tangential channel and a second inlet channel is a throttle device that can be actuated depending on the engine load and is designed as a neutral channel, where - viewed in the direction of the crankshaft axis - the center line of the first intake port directly at the intake valve with a longitudinal plane spanned by the cylinder axis and the crankshaft axis encloses a greater angle than a center line of the second intake port, and wherein - viewed in the direction of the cylinder axis - at the combustion chamber inlet the center line of the first intake port with a first plane enclosing the cylinder axis and the center of the intake valve of the first intake port forms a greater angle than a center line of the second intake port with a cylinder axis and the center of an intake valve the second level including the second inlet channel, as well as with a fuel injection valve opening into an inlet duct and a spark plug arranged centrally in the combustion chamber.

Constantly increasing demands on fuel consumption and the reduction of exhaust emissions, especially hydrocarbons and nitrogen oxides, require the use of new technologies in the field of internal combustion engines.

A major reason for the higher specific fuel consumption of a spark-ignited internal combustion engine compared to, for example, diesel engines, lies in the mode of operation with a premixed, homogeneous fuel-air mixture. This requires a regulation of the engine load with the help of a throttle device to limit the total amount of mixture sucked in (quantity regulation).

This throttling of the intake flow leads to a thermodynamic loss, which increases the fuel consumption of the internal combustion engine. The potential for reducing the consumption of the internal combustion engine by circumventing this throttling can be estimated at around 25%. Part of this potential for improvement can be used if the throttling can be reduced in the partial load range. With a given amount of fuel, however, this is only possible by making the mixture lean or by recirculating exhaust gas (EGR). Measures are therefore required which increase the lean ability or EGR compatibility of the engine while at the same time maintaining or reducing the emission values.

A reduction in unburned hydrocarbons with overall overstoichiometric combustion is promoted by a mixture stratification, which leads to a local enrichment of the mixture. The combustion then takes place locally in a mixture that is richer than the overall air ratio. The increased nitrogen oxide formation associated with the approximately stoichiometric combustion is due to the maximum combustion temperatures (thermal nitrogen oxide formation). The most effective strategy for reducing nitrogen oxides is to slow down the combustion process through exhaust gas recirculation.

An internal combustion engine with at least two inlet valves offers the possibility of supplying different mixture compositions to the combustion chamber via separate inlet channels. The flow in the cylinder chamber can be influenced with the help of the design of the intake elements of the engine in such a way that at the point of ignition there is a mixture stratified in the desired manner in the cylinder. It is particularly advantageous if the richer mixture portion is located in the middle of the cylinder in the area of ​​a centrally arranged spark plug, while towards the cylinder wall either the mixture is lean or the exhaust gas concentration increases.

Such an intake-generated mixture stratification must be generated and stabilized by the main flow structures in the cylinder chamber of the internal combustion engine in order to be able to survive the compression process between the closing of the intake valves and the ignition even in the presence of the very high degrees of turbulence in the internal engine flow. The vortex movements swirl and tumble come into consideration here as main flow forms. In the swirl flow, the cylinder charge rotates around the cylinder axis due to the design of the inlet port, while in a tumble flow a rotation around an axis parallel to the crankshaft can be observed.

In principle, the swirl flow offers the better conditions for maintaining a mixture stratification during the compression, since the round cylinder cross-section perpendicular to the cylinder axis does not change during the compression. A tumble vortex, on the other hand, has a much more tendency to tend during compression due to the increasing flattening of the for

AT 407 773 B its rotation available cross-section perpendicular to the crankshaft axis and the resulting deformation of the vortex by shear effects to disintegrate into disordered turbulence structures. Tumble flows are therefore preferably used when a general acceleration of the combustion is sought by increasing the turbulence level in the entire combustion chamber.

From EP 0 537 745 A1 an internal combustion engine of the type mentioned is known in which a first main inlet duct in which the fuel is injected generates a swirl flow and a second inlet duct that can be switched on when the engine is running high generates a flow with tumble characteristics. The aim here is not stratification, but a pure increase in the combustion rate and the improvement of the ignition conditions through the increased charge movement associated with the swirl flow and the above-mentioned combustion-accelerating effect of the tumble flow.

Numerous constructions for creating a charge stratification are known. An internal combustion engine is known from EP 0 594 462 A1 or EP 0 390 589 A2, in which the aim is pursued by injecting the fuel into one of two inlet ducts on the basis of a tumble flow to achieve a stratification of the mixture in the cylinder chamber Has gradients of the air ratio in the direction of the crankshaft axis. With such a division of the inlet flow into two partial flows of different mixture composition, there is a rich area on one side of the cylinder and a correspondingly lean area on the opposite cylinder side, while the centrally located spark plug has an average air ratio based on the total charge with strong cyclical fluctuations. The resulting asymmetrical flame propagation does not offer optimal conditions for ignition and thermodynamically optimal combustion.

By dividing the inlet flow into three partial flows, DE 42 33 640 A1, EP 0 558 081 A1 and EP 0 558 073 A1 seek better stratification on a tumble basis. This is achieved either by using three inlet valves with separate channels or by using partition walls in the common inlet channel with two inlet valves. By introducing the fuel only into the middle partial flow, the mixture is enriched in the middle of the cylinder, although this layering does not represent a radial layering, but consists of flat layers perpendicular to the crankshaft axis. A major problem in maintaining such a triple stratification during the compression phase is the fact that a tumbling movement during the compression partially transforms into two vortices rotating in opposite directions, whose axis of rotation is perpendicular to the crankshaft axis. These vortex movements, also known as omega tumble, contribute greatly to the mixing of such a triple stratification.

EP 532 020 A1 shows an internal combustion engine with two inlet valves, which essentially has a direct fuel injection which is combined with an intake manifold injection for homogeneous full-load operation. The fuel injection valve opens into a throttled inlet channel. From the operating strategy maps shown, there should be no injection into the intake manifold when the duct is switched off.

DE 34 44 356 A1 shows an internal combustion engine with two inlet valves, the duct parts leading to the inlet valves branching off from a common inlet duct relatively shortly before the inlet into the cylinder. The throttled channel receiving the injection device runs essentially normal to the crankshaft axis, seen in the cylinder direction, while the other channel, which is not throttled, is directed more towards the center of the cylinder. This unthrottled channel has a spiral shape.

DE 41 08 469 A1 shows an inlet device for a multi-valve engine with three inlet valves. The middle throttled channel with the injection device, seen in the plan, has a larger angle to the cylinder axis than the lateral channels.

EP 0 449 240 A1 shows an internal combustion engine with three inlet valves, of which two valves in a conventional arrangement are used only for air intake and a swirl flow can be generated by switching off one valve. A third inlet valve that carries the mixture is arranged centrally in the combustion chamber and connected to a swirl-generating spiral inlet duct. This is intended to achieve a radial stratification of the mixture, but with the help of an unconventional valve configuration that deviates significantly from today's standard

AT 407 773 B tion. There is no possibility of a centrally arranged spark plug.

The object of the invention is to achieve a stable radial mixture stratification in an internal combustion engine of the type mentioned at the beginning, the form of which can be varied with the engine load.

According to the invention, this is achieved in that, in the closed state, the throttle device generates a defined minimum flow between approximately 5% and approximately 20%, preferably approximately 10% of the maximum flow, and that, as is known per se, the fuel injection valve opens into the throttable second inlet channel - and - viewed in the direction of the crankshaft axis - the center line of the first inlet channel in the inlet valve area has a greater radius of curvature than the center line of the second inlet channel. The first inlet channel is very inclined with only a slight curvature in relation to the valve axis and generates a tangential flow that hits the cylinder wall, which leads to the formation of a strong swirl movement in the cylinder. The second inlet channel has a greater curvature than the tangential channel and a smaller inclination with respect to the valve axis. It generates an inflow directed roughly towards the center of the cylinder, which neither causes a pronounced twisting movement nor a tumbling movement. The fuel is injected exclusively into this neutral channel. The throttle device in the neutral channel is used to achieve an increased stratification effect through throttling in the lower partial load range of the engine map. If air-assisted injection nozzles are used to inject fuel, then the amount of air introduced by the air-assist system must also be taken into account by correspondingly increased throttling of the main air flow of the neutral duct.

The throttling of the neutral channel carrying the mixture ensures that the charge inflow from this channel into the cylinder chamber with less momentum than the air supplied from the tangential channel. The total flow field in the cylinder space is thus dominated by the unthrottled, pure air or air and recirculated exhaust gas, the tangential duct. In addition, by reducing the amount of air that flows through the neutral duct, the mixture produced there is enriched, ie the difference in the mixture composition of the flows of the two ducts is further increased. This improves the prerequisite for finding sufficient stratification of the fuel / air mixture even after the compression process, which is always associated with progressive turbulent mixing of the two partial flows. The stabilization of the richer mixture in the middle of the cylinder is supported by the swirl flow.

The stratification of the fuel-air mixture that can be achieved is directly related to the possible dethrottling of the engine at partial load.

In engines with two inlet valves, the previously throttled neutral channel is released when the load increases, so that the neutral and tangential currents flow in with the same impulse. This leads to a greater homogenization of the mixture while maintaining a residual twist.

The throttle device can be designed as a throttle valve or as a slide. In the case of the throttle valve, the minimum flow is achieved by an annular gap between the throttle valve and the duct wall that is constant over its circumference, the cross-sectional area of ​​which is between approximately 5% and approximately 20% of the duct cross-section. In the case of a slide, which can be a flat slide or rotary slide, at least one opening, but preferably a plurality of evenly distributed openings, is provided on the slide surface.

According to another embodiment variant, the throttle device can also be designed as a diaphragm valve.

In a preferred embodiment it is provided that the throttle device is formed by a variable inlet valve control, the minimum flow being realized by a controlled reduction of the valve lift and / or a change in the valve opening time.

If the dethrottling of the engine is not used for leaning but for increased supply of recirculated exhaust gas with an otherwise stoichiometric mixture, it is advantageous if at least the inlet ducts without fuel valves can be connected to an exhaust gas recirculation line, as is known per se from EP 0 594 462 A1 is.

The throttling of the intake port carrying the mixture also shows a clear advantage in the transient operating behavior of the engine. Normally, a sudden increase in load leads to a brief leaning of the fuel-air mixture due to the intake manifold pressure

AT 407 773 B dependent wall film formation. At part load and low intake manifold pressure, a smaller wall film forms than with higher load with a correspondingly increased intake manifold pressure, so that a larger wall film first builds up when the load increases. In the event of a sudden decrease in the load, the mixture will be briefly over-greased due to the delayed breakdown of the wall film. When the channel carrying the mixture is throttled, even at partial load, due to the lower negative pressure and mass flow, a thicker wall film is formed between the injector and the inlet valve, so that in the event of a sudden increase in load with simultaneous dethrottling of the channel carrying the mixture, the delayed adaptation of the wall film to the changed pressure and flow conditions is weakened , which leads to a better maintenance of the air ratio in unsteady operation. _

In one embodiment of the invention, three inlet valves are provided, the second inlet channel being in communication with two adjacent inlet valves. The common second inlet channel leads to a lateral and a central inlet valve, whereby the second inlet channel can be throttled up to a defined minimum flow rate according to the two-valve design. The fuel is only injected into this second inlet port.

In a further embodiment of the invention, it is advantageous if three inlet valves and a third inlet channel are provided in addition to the first and second inlet channels, each of the inlet channels arranged next to one another - viewed in the direction of the cylinder axis - routed separately to the inlet valve and the second inlet channel arranged centrally is, and a shut-off device is preferably provided in the third inlet channel. The third inlet channel, like the first inlet channel, is designed as a tangential channel with pure air flow and is only opened by the switch-off device in the upper partial load area and at full load.The two tangential channels together generate a tumble movement in the cylinder chamber that coincides with the neutral inflow of the mixture-carrying middle second inlet channel, which leads to increased turbulence and mixing of the individual partial flows. This supports the homogenization of the mixture, which is necessary at high loads, even if it is still only injected into one intake duct.

The invention is explained in more detail with reference to the figures.

1 shows a cross section of the internal combustion engine according to the invention in the direction of the crankshaft axis, FIG. 2 shows a view of this internal combustion engine in the direction of the cylinder axis, FIGS. 3 to 7 other embodiment variants according to the invention, FIG. 8 a valve lift / crank angle diagram, FIGS. 9 and 10 others Embodiments of an intake system according to the invention.

1 shows a cross section through the internal combustion engine according to the invention, viewed in the direction of the crankshaft axis 1. The combustion chamber 2 is formed by a piston 4 reciprocating in a cylinder 3 and the roof-shaped combustion chamber ceiling 6 formed by the cylinder head 5; 9 separately guided first and second inlet ducts 11 and 12. The first inlet channel 11 is designed as a tangential channel and the second inlet channel 12 as a neutral channel. A central spark plug is designated with 14.

Downstream of a throttle element 15 arranged in the second inlet channel 12, a fuel injection device 16 opens into the second inlet channel 12. Via the throttle element 15, depending on the engine load, the volume flow can be reduced to a defined minimum flow between 5% and 20% of the maximum flow.

As can be seen in the view shown in Fig. 2 in the direction of the cylinder axis 7, the first inlet channel 11 designed as a tangential channel generates a flow indicated by the arrow 17 due to its orientation to the cylinder wall 3a, which due to its high momentum to the formation of a swirl movement around the Cylinder axis 7 leads. The second inlet channel 12, which is designed as a neutral channel and in which the fuel injection device 16 is arranged, generates a low-impulse flow indicated by the arrow 18 due to the throttling by the throttle element 15, which is directed towards the central cylinder area 19 due to the orientation of the second inlet channel 12 .

With respect to the longitudinal center plane 22 spanned by the crankshaft axis 1 and the cylinder axis 7, 20 denotes the intake valves 8 and 9 opposite exhaust valves connected to the exhaust system 21.

AT 407 773 B

The center line 11a of the first inlet channel 11 forms a larger angle 11b with the longitudinal plane 22 directly at the inlet valve 8 than the center line 12a of the second inlet channel 12. The angle between the center line 12a and the longitudinal plane 22 is denoted by 12b. Furthermore, the center line 11a of the first intake port 11 in the region of the intake valve 8 with a plane 11d enclosing the cylinder axis 7 and the center of the intake valve forms a greater angle 11c than the center line 12a of the second intake port 12, with 12c being the angle between the corresponding second plane 12d and the center line 12a. Furthermore, the center line 11a of the first inlet channel 11 in the area of ​​the inlet valve 8 has a larger radius of curvature 24 than the center line 12a of the second inlet channel 12 in the area of ​​the inlet valve 9.

3 shows a corresponding view for an internal combustion engine with three inlet valves 8, 9 and 10, the first inlet channel 11, designed as a tangential channel, being connected to an outer inlet valve 8 and the second inlet channel 12, designed as a neutral channel, being connected to the two other valves 9 and 10 is connected, the inlet flow indicated by arrows 17, 18a and 18b being similar to the embodiment shown in FIG. 2 with two inlet valves.

4 shows a further embodiment with three inlet valves 8, 9 and 10 which are each connected to a first inlet channel 11, a second inlet channel 12 and a third inlet channel 13. The two outer valves 8 and 10 are each connected to a tangential channel arranged approximately symmetrically with respect to a normal plane 23 containing the cylinder axis 7 on the crankshaft axis 1, namely the first inlet channel 11 and the third inlet channel 13, the third inlet channel 13 having a shut-off device 26 is equipped, which enables a release of this third inlet channel 13 only at upper part load and full load. The middle inlet valve 9 is connected to the second inlet channel 12, designed as a neutral channel, into which the fuel is injected by the fuel injection device 16, as indicated by the fuel jets designated 16a. The fuel 16a is optimally directed at the cylinder center 19 due to the symmetrical arrangement with respect to the normal plane 23. By means of the throttle element 15, the second inlet channel 12 can be throttled to a defined minimum flow rate. The center line of the second inlet channel 12 lies in this case in the second plane 12d, the angle difference 12c is therefore zero.

In FIGS. 5, 6 and 7, different exemplary embodiments of throttle elements 15 are shown. In Fig. 5, the throttle device is shown as a throttle valve 15a with a defined gap 15a 'between the flap 15a and channel wall 12' in the closed state.

6 shows a throttle device 15 designed as a flat slide 15b with throughflow openings 15b 'evenly distributed over its surface. Instead of a flat slide 15b, a rotary slide or roller slide can also be used.

7 shows a throttle device 15 designed as a diaphragm valve 15c. This diaphragm valve 15c initially prevents dynamic backflow into the second intake port 12 after opening the intake valve 9 and does not open any further until a sufficient pressure difference has built up between the combustion chamber 2 and the one in FIG suction pipe shown and thus leads to a time-delayed inflow of the mixture. The strength of the delay depends on the rigidity of the diaphragm 15c.

It is also possible to implement the throttle device 15 by means of a variable valve control, as is shown in the valve lift / crank angle diagram shown in FIG. 8. The crank angle KW is plotted on the abscissa. Line 27 stands for the output valve lift. The flow is reduced either by reducing the valve lift H to a valve lift H drawn in by the line 28 or by reducing the valve lift H and valve opening time, as shown by the curve 29.

9 and 10 show two internal combustion engines according to the invention with exhaust gas recirculation. In FIG. 9, the exhaust gas is fed to the air collector 32 via a control device 30 in an exhaust gas recirculation line 31 extending from the exhaust system 21 and is evenly mixed into all the inlet channels 11 and 12. Alternatively, as shown in FIG. 10, the recirculated exhaust gas can only be fed to the first inlet channel 11 without a fuel valve, in order to achieve greater stratification.