EP0433908B1 - Intake and air-fuel mixture preparing system for spark-ignited multi-cylinder internal combustion engine - Google Patents

Description

The invention relates to an intake and mixture formation system for multi-cylinder, spark-ignited internal combustion engines with at least two intake valves per cylinder, at least two separate intake manifold arms assigned to the intake valves per cylinder and fuel injection, in the first intake manifold arms per cylinder to a first group and further intake manifold arms per cylinder at least are combined to form a further group and each group is assigned a throttle element, the first group having a common fuel injection into the intake system and the intake manifold arms or inlet channels of the further group or the further groups being assigned an injection.

In internal combustion engines of this type, the two intake valves of each cylinder are usually connected to a common intake manifold, and an injection nozzle is assigned to each cylinder. Such a design is structurally relatively simple to implement, but its disadvantage is that load and speed-dependent control of the charge movement in the intake manifold arms and in the cylinder is not possible, since the throttling of a partial flow of the charge supplied to the cylinder cannot take place with this design. In addition, the flow rate of the fresh air (or mixture with recirculated exhaust gas - EGR) is low at low air throughputs, so that there is inadequate mixture preparation. Due to the quickly released, large opening cross-sections in multi-valve engines, high residual gas components occur at idle and at low partial load, which, in conjunction with the low charge movement in the combustion chamber, lead to an unstable combustion process and unfavorable efficiency levels.

A control of the charge movement in the cylinder adapted to the air throughput can be achieved with intake systems that have two completely separate intake manifold arms per cylinder. By partially or completely closing one of these arms, the charge movement and turbulence in the combustion chamber can be significantly increased with small air throughputs, and the combustion process can thus be improved. However, the consistent implementation of such an intake system with completely separate intake manifold arms up to the intake valves would require twice the number of injection nozzles compared to today's conventional systems. It represents the most complex and expensive solution in terms of production technology.

DE-A-37 07 805 describes an intake manifold arrangement for multi-cylinder internal combustion engines with fuel injection nozzles, in which each cylinder has a first intake manifold with a first intake manifold and a low-resistance one with a first intake manifold, which is designed for optimal filling in a lower air flow rate range second intake manifold is connected to a second intake manifold, each of which is preceded by a throttle element, of which that of the first intake manifold already opens in the lower air throughput range, whereas the throttle element of the second intake manifold only opens in a higher air throughput range and in which the first and second intake manifolds individual intake valves open into the cylinders and individual injection nozzles are arranged in the first intake manifolds, whereas an injection nozzle common to the second intake manifolds is arranged in the second intake manifold, which supplies fuel only when the associated throttle member is opened. It is provided that the individual injection nozzles are designed only for the maximum fuel requirement in the lower air throughput range.

An intake manifold arrangement of this type represents an advance over the arrangements described in that it has a more economical fuel metering with a portable design effort enabled over the performance range of the internal combustion engine. A disadvantage of this arrangement, however, is still that, due to the rapidly released, large opening cross-sections, high residual gas fractions occur in multi-valve engines at idle and at low load, which lead to an unstable combustion process, a deterioration in efficiency and additional environmental pollution.

The invention has for its object to enable a load- and speed-dependent control of the flow movement in the intake manifold arms and thus in the cylinder with simultaneous advantageous mixture formation in a simple, economical and reliable manner, in particular when idling and at low partial load, a stable combustion process and a cheaper Efficiency is achieved.

According to the invention, it is provided in a suction and mixture formation system of the type described in the introduction that the throttle elements are controlled in such a way that the first group opens first for the area of low air throughputs and the other group or other groups are connected at speed and load as a function of higher air throughputs will.

With such a system, major advantages can be achieved:

In the area of low air throughputs, i.e. with high intake manifold pressures and / or low engine speeds, a Central injection achieved a cheaper mixture preparation than with a single injection. Due to the fuel metering through only one nozzle, the volume scatter from cylinder to cylinder is significantly lower in this air flow range. Furthermore, the longer distance of the mixture preparation process in the case of joint injection improves the mixture formation, in particular when the engine is at operating temperature. In the area of low air throughputs, this results in a lower level of efficiency, lower pollutant emissions and improved operability when operating with lean fuel-air mixtures or an increased tolerance in the dimensioning of exhaust gas recirculation for mixtures diluted with exhaust gas. In addition, fuel build-up during cold start and warm-up can be reduced, and this offers additional advantages in terms of efficiency and emission of pollutants.

In the area of higher air throughputs, the use of single injections on the second group or on the other groups offers a better design option for the intake manifold arm geometry, i.e. in particular, short, gas-dynamically favorable intake manifold arms with the lowest throttle losses. This creates favorable conditions for the presentation of high specific performance.

The advantages of the central mixture formation can be combined particularly advantageously with the long intake manifold arms of the first group, which are desirable from a gas dynamic point of view. This enables high torques to be displayed at low engine speeds.

In conjunction with a suitable design or coordination of the intake system (intake manifold arm length, intake manifold arm diameter, collector volume, inlet duct geometry), the most favorable flow movement and structure (turbulence) for the mixture formation and combustion process and the most favorable gas dynamics can be generated in the intake manifold.

Another advantage of the intake and mixture formation system according to the invention is that the fuel-air ratio can be set independently of one another by varying the injected fuel quantities for the respective group or groups. As a result, homogeneous or inhomogeneous cylinder charges can be generated depending on the load and speed, which means that stratified charge effects can be used to increase efficiency and reduce pollutant emissions. In addition, possible fuel-air ratio variations of the first group at low intake manifold pressures can be avoided by different injection periods of the individual injections within the second group. The knock sensitivity of the engine, i.e. reduce the tendency to uncontrolled combustion processes. As a result, higher torques and lower efficiency levels result.

The amount of fuel required at starting can preferably be provided by switching on the fuel injections of the second group. As a result, the injectors can be selected to be smaller and better adapted to the respective air throughput. At the same time, the requirements for mixture formation with small air throughputs, i.e. in particular when idling, as well as with high air volumes in the nominal power range.

If the fuel injection of the further group or of the further groups is independent of the fuel injection of the first group, this has the advantage that energetic advantages in the generation of pressure can be achieved when the pressure in the fuel system varies in groups.

The introduction of exhaust gas can preferably be carried out selectively in the first and / or the further group or the further groups, as a result of which a good uniform distribution of the exhaust gases over the individual cylinders of a group is achieved, but at the same time stratification effects in the cylinder can also be used. In In this case it is possible to concentrate the more ignitable mixture in the area of the spark plug. The improved ignition conditions then lead to a more stable ignition phase and accordingly to a more stable engine running. Alternatively, higher exhaust gas recirculation rates can be achieved.

In a favorable embodiment, the common fuel injection of the first group takes place behind the common throttle element, as seen in the inlet flow direction, the intake manifold pressures which exist when the throttle element is partially or completely closed promote fuel evaporation.

Another possibility is that the common fuel injection of the first group takes place upstream of the common throttle element, as seen in the inlet flow direction. In this case, the advantage is achieved that the throttle gap existing when the throttle valve is partially closed promotes the mixing of the injected fuel with the intake air due to the high flow velocity present there and thus improves the mixture formation.

The fuel may also be injected into the cylinder by the further group or groups. This allows the dynamic engine behavior to be improved. A faster response can be achieved when accelerating; during the deceleration process, wall deposits in the intake manifold are avoided.

Another advantageous possibility is that a throttle member per intake manifold arm for controlling the intake manifold arms of the individual groups can be provided in addition or as an alternative to the common throttle members. This measure reduces the volumes between the intake valve and throttle element for the respective cylinder when the second group is closed. This has a favorable influence on the residual gas content and consequently the smooth running of the engine.

Preferably, several similar intake systems can be combined in multi-cylinder internal combustion engines. Here, individual components of the individual groups can also be used together.

Embodiments of the invention are described in more detail with reference to the drawings.

Figure 1 shows schematically the assignment of intake manifold arms and injection valves to a cylinder of a multi-cylinder injection engine.

Figure 2 shows schematically an embodiment of a complete intake and mixture formation system according to the invention.

Figure 3 shows an embodiment of the intake and mixture formation system according to Figure 2 in side view.

Figure 4 shows an embodiment of the intake and mixture formation system according to Figure 2 in rear view.

Figure 5 shows an embodiment of the intake and mixture formation system according to Figure 2 in plan view.

Figure 1 shows schematically the connection of the intake manifold arms to the valves of a cylinder of a multi-cylinder injection internal combustion engine.

A first inlet valve 1 of a cylinder 2 is connected to an intake manifold arm 3, which is part of a group 4 with further intake manifold arms 5, 6 and 7 of a four-cylinder internal combustion engine shown for example. Exhaust valves 8 and 9 are suitably connected to the exhaust system. Group 4 contains a common mixture formation element, which is represented by an injection valve 10. Group 4 also has a common throttle element (not shown).

A second inlet valve 11 is connected to a further intake manifold arm 12, which may belong to a second group of intake manifold arms, the further intake manifold arms of which are not shown. As a rule, the second group will also have a common throttle element (not shown). A mixture formation member is represented by injection valve 13, so that in the exemplary embodiment shown, a separate mixture formation member is assigned to the intake manifold arm 12. With regard to the further (not shown) intake manifold arms, there is flexibility insofar as individual or also common mixture formation organs can be provided.

In operation, the intake manifold arm group 4 is assigned to the area 50 of low air throughputs, while the second intake manifold arm group, of which the intake manifold arm 12 is a part, is assigned to the area 51 of high air throughputs.

An embodiment is shown in FIG. 2. It is provided that the first group of intake manifold arms has a common fuel injection and one injection is assigned to the intake manifold arms or inlet ducts of the second group.

In the schematic representation of multi-flow intake manifold arms of the embodiment, a first intake manifold arm group 25 and a second intake manifold arm group 26 are assigned to cylinders 21, 22, 23, 24 for the four-cylinder engine shown as an example. The first group 25 includes intake manifold arms I-1, I-2, I-3 and I-4, while the second group 26 includes intake manifold arms II-1, II-2, II-3 and II-4. Different intake manifold arm lengths and intake manifold arm cross sections can be implemented in each group.

The first intake manifold arm group 25 has a common mixture formation element I-5, and there may be a common exhaust gas recirculation EGR at I-6. In the second intake manifold arm group 26, the fuel is fed into the intake manifold arms or inlet channels separately at II-5, II-6, II-7 and II-8. In addition, a EGR common exhaust gas recirculation at II-9. In addition, there is the possibility of common exhaust gas recirculation for the first and second groups in front of a common throttle element (not shown), which can be designed, for example, as a register throttle valve.

The first intake manifold arm group 25 contains a common throttle member I-7, and the second intake manifold arm group 26 also contains a common throttle member II-10. It is therefore advantageously possible for the individual throttle elements to be closed completely or partially independently, and thus for the load and speed-dependent control of the flow movement in the intake manifold arms of the groups and in the cylinder. Flow cross sections and intake manifold arm lengths can also be controlled in a targeted manner depending on the load and speed.

In the embodiment shown in FIG. 1, as mentioned, the first intake manifold arm group 4 with the intake manifold arms 3, 5, 6 and 7 is assigned to the operating area 50 of low air flow rates, while the intake manifold arm 12 together with the three further intake manifold arms (not shown) is assigned to the operating area 51 high air flow rates is assigned. Correspondingly, in the embodiment shown in FIG. 2, the intake manifold arms I-1, I-2, I-3 and I-4 of the intake manifold arm group 25 are assigned to the operating range 50 of low air throughputs, while the intake manifold arm group 26 with the intake manifold arms II-1, II-2, II-3 and II-4 is assigned to the operating area 51 of high air flow rates. According to the invention, the throttle elements are controlled in such a way that the first group 25 opens first for the area of low air throughputs and the other group 26 (or the other groups) are switched on at higher air throughputs as a function of speed and load. This achieves the advantages that in the region of low air throughputs, that is to say at high intake manifold pressures and / or low engine speeds, a more favorable mixture preparation is achieved with a central injection than with a single injection. This will result in this operating area more economical efficiencies, lower pollutant emissions and improved operability when operated with lean mixtures or with diluted exhaust gases. At the same time, fuel enrichment during cold starts and in the warm-up phase can be reduced.

In the area of higher air throughputs, the use of single injections on the second group or on the other groups offers a better design option for the intake manifold arm geometry, i.e. in particular, short, gas-dynamically favorable intake manifold arms with the lowest throttle losses. This creates favorable conditions for the presentation of high specific performance.

The speed and load-dependent connection of the second group can also generate the flow movement and structure (turbulence) that is most favorable in terms of combustion technology in the cylinder.

FIGS. 3-5 show the spatial design of the intake manifold arm groups 25 and 26 shown in FIG. 2 as an exemplary embodiment. The common throttle devices I-7 and II-10 of groups 25 and 26 can be seen in FIG.

The reference numerals used (also in the claims) only serve to improve readability. They are not restrictive, in particular also not to the illustrated and described embodiments.

Claims (11)

1. An intake and mixture-preparing system for multi-cylinder spark-ignited internal combustion engines comprising at least two intake valves (1, 11) per cylinder, at least two separate suction pipe arms (3, 12 or I-1, I-2, I-3, I-4; II-1, II-2, II-3, II-4) associated with the intake valves for each cylinder (2 or 21, 22, 23, 24) and fuel injection means (10, 13 or I-5; II-5, II-6, II-7, II-8), first suction pipe arms for each cylinder being combined into a first group (4, 25) and other suction pipe arms for each cylinder being combined in at least one other group (12, 26) and each group being assigned one throttle means (I-7 or II-10), the first group (4, 25) having a common fuel injection means (10, I-5) into the intake system whereas the suction pipe arms or intake tubes in the other group (12, 36) or the other groups are each assigned one injection means (13 or II-5, II-6, II-7, II-8), characterised in that the throttle means are actuated so that the first group (4, 25) opens first in the low air throughput region and the other group (12, 26) or the other groups are connected at higher air throughputs in dependence on the speed and load.
2. An intake and mixture-preparing system according to claim 1, characterised in that the fuel injection system for the other group (12, 26) or the other groups is independent of the fuel injection system for the first group (4, 25).
3. An intake and mixture-preparing system according to claim 1, characterised by devices (I-6 or II-9) for introducing exhaust gas into the first group (4, 25) and/or the other group (12, 26) or the other groups.
4. An intake and mixture-preparing system according to claim 1, characterised in that the common fuel injection means (10, I-5) for the first group (4 - 25) is disposed behind the common throttle means (I-7), as considered in the intake flow direction.
5. An intake and mixture-preparing system according to claim 1, characterised in that the common fuel injection means (10, I-5) for the first group (4 - 25) is disposed in front of the common throttle means (I-7), as considered in the intake flow direction.
6. An intake and mixture-preparing system according to claim 1, characterised by one throttle means per suction pipe arm for actuating the suction pipe arms in the individual groups, in addition to or instead of the common throttle means.
7. An intake and mixture-preparing system according to claim 1, characterised by a combination of a number of similar intake systems in multi-cylinder internal combustion engines.
8. A method of operating an intake and mixture-preparing system for multi-cylinder spark-ignited internal combustion engines comprising at least two intake valves (1, 11) per cylinder, at least two separate suction pipe arms (3, 12 or I-1, I-2, I-3, I-4; II-1, II-2, II-3, II-4) associated with the intake valves for each cylinder (2 or 21, 22, 23, 24) and fuel injection means (10, 13 or I-5; II-5, II-6, II-7, II-8), first suction pipe arms for each cylinder being combined into a first group (4, 25) and other suction pipe arms for each cylinder being combined in at least one other group (12, 26) and each group being assigned one throttle means (I-7 or II-10), the first group (4, 25) having a common fuel injection means (10, I-5) into the intake system whereas the suction pipe arms or intake tubes in the other group (12, 36) or the other groups are each assigned one injection means (II-5, II-6, II-7, II-8), characterised in that the throttle means are actuated so that the first group (4, 25) opens first in the low air throughput region and the other group (12, 26) or the other groups are connected at higher air throughputs in dependence on the speed and load.
9. A method of operation according to claim 8, characterised in that the fuel-air ratio is adjusted by varying the amounts of injected fuel so as to produce a stratified charge for each respective group (4, 25; 12, 26) or groups independently of one another.
10. A method of operation according to claim 8, characterised in that the amount of fuel on starting is prepared by switching on the fuel injection means for the other group (4, 25; 12, 26) or groups.
11. A method of operation according to claim 8, characterised in that in the case of the other group (12, 26) or other groups, fuel is injected into the cylinder.

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