WO2005035958A1

WO2005035958A1 - Method for optimizing the operation of a charged reciprocating internal combustion engine in the lower engine speed range

Info

Publication number: WO2005035958A1
Application number: PCT/EP2004/011164
Authority: WO
Inventors: Wohlberg Reiner; Martin Hopp; Oliver Lang; José GEIGER; Andreas Sehr
Original assignee: Fev Motorentechnik Gmbh
Priority date: 2003-10-06
Filing date: 2004-10-06
Publication date: 2005-04-21
Also published as: DE10346747A1; CN1863993A; CN1863993B; EP1673527A1

Abstract

The invention relates to a method for operating a fuel-injected, especially a directly fuel-injected, reciprocating internal combustion engine. Said engine comprises at least one outlet valve per cylinder, communicating with an exhaust gas installation, and at least one inlet valve, communicating with an air inlet installation, and means for increasing the boost pressure in the air inlet installation. The method is characterized in that a control device for variably adjusting at least the opening times of the inlet valves is provided and that in the lower engine speed range the inlet opening times of the inlet valves can be adjusted via the control device in such a manner that there is a valve overlap with the closing time of the corresponding outlet valves, thereby scavenging the cylinder with fresh charge air before charge exchange in the area of top dead center.

Description

Name: Process for optimizing the operation of a charged piston internal combustion engine in the lower speed range

description

In so-called supercharged piston internal combustion engines, the required combustion air is supplied to the cylinders via a supercharger at a pressure which is higher than the ambient pressure. The pressure increase can take place here via a so-called exhaust gas turbocharger, in which a turbocompressor is driven by means of a turbine connected to the exhaust gas system and is connected on the pressure side to the air intake system. The pressure increase can also be carried out by a so-called mechanical supercharger, the drive energy of which is tapped from the crankshaft of the piston internal combustion engine. The fuel is supplied either by injecting the corresponding amounts of fuel into the air inlet channel of each cylinder or by injecting directly into the cylinder. For the gas exchange, at least one exhaust valve and at least one intake valve are provided for each cylinder, which are correspondingly connected to the exhaust system and the air intake system.

It has now been found that in the lower speed range of the piston internal combustion engine and the resulting lower delivery capacity of the supercharger, both in the exhaust gas turbocharger and in the mechanical supercharger, there is inadequate load acceptance behavior in the start-up mode and in the slow speed mode.

The invention has for its object to improve the operating behavior of a piston internal combustion engine of the type described above in the start-up mode and in operation at low speeds, in particular in the range with speeds between 1000 and 1300 rpm. ,

This object is achieved in a piston internal combustion engine with fuel injection, in particular direct fuel injection, with gas exchange valves per cylinder, each with at least one exhaust valve which is connected to an exhaust system, and at least one intake valve which is connected to an air intake system, and means for increasing the Boost pressure in the air intake system, solved in that a control device is provided for the variable adjustment of at least the opening times of the intake valves and that in the lower speed range the intake-opening times and / or the outlet-closing times of the gas exchange valves are set via the control device that a valve overlap with the closing time point of the associated exhaust valves is given and so the cylinder is flushed with fresh charge air before and / or during the charge change in the area of top dead center. The advantage of this mode of operation is that, on the one hand, the residual gas is largely flushed out of the cylinder and the temperature level for the introduced air is slightly reduced after the inlet valve is closed. This means that the level of air expenditure can be significantly increased even at low engine speeds. The tendency to knock is reduced by largely flushing out residual gas.

In particular in connection with direct fuel injection, the mixture cools down in the combustion chamber and increases the air flow through the engine. Compared to piston engines with fixed control times of exhaust valves and intake valves, this results in a significant increase in the torque that can be tapped from the piston internal combustion engine, particularly when starting up and when operating at low speeds. The opening and closing times of an exhaust valve can preferably also be changed in order to increase a flushing of the cylinder. It is further preferred that the inlet and outlet valves are only opened when there is a sufficient pressure increase for flushing the cylinder in an intake manifold that is connected to the inlet valve. In particular, the aim is to purge at least 95% of the residual gas in the cylinder.

A first development provides that, for example, only the inlet valves or only the outlet valves are adjusted. A second development provides that the intake and exhaust valves are adjusted. A third further development provides that only part of the inlet and / or outlet valves is adjusted.

Another embodiment provides that the valves are adjusted up to a speed of the piston internal combustion engine of 2000 rpm. Such an adjustment is, however, preferably no longer carried out for residual gas purging. According to a further development, the valve times are adjusted during an acceleration process, in particular during a start-up process, in a range between 30% and 100% of a maximum engine load. The piston internal combustion engine preferably works on the diesel principle and is operated with an injection adjustment.

Due to the improved cylinder filling, there is an increasing enthalpy which, when using an exhaust gas turbocharger, leads to a rapid increase in the boost pressure and thus to an improvement in the prescribed effect. In the case of a mechanical supercharger whose drive energy is tapped from the crankshaft, there is also a higher supercharger output, since a positive purge pressure gradient is quickly and continuously brought about from work cycle to work cycle and thus, due to the increased cylinder charge, an increase in the final torque is achieved much more quickly becomes.

There is also the option of influencing a purge pressure drop in the lower speed range for residual gas purging, for example by changing the suction system. The suction system can be influenced, for example, by continuously adjusting a length of a vibrating tube, by switching between different lengths of vibrating tube, by optionally switching off a single tube per cylinder in the case of multiple vibrating tubes, by switching to different collector volumes and / or by switching between different vibrating tube diameters. For example, single vibrating tubes can be used, with longer vibrating tubes being used in the lower speed range than at higher speeds.

In particular, there is the possibility of being able to combine various measures for influencing the flushing pressure gradient.

The mode of operation according to the invention can be effected on the one hand by a piston internal combustion engine, in which at least the inlet valves are provided with valve drives which are variable at least over partial areas and which can be controlled via the control device. Valve drives of this type can be designed, for example, as so-called electromechanical valve drives, in which, between two electromagnets, an armature connected to the valve leads the valve into the closed position and the open position in accordance with the current specified by the control device. The opening and closing time is specified via the control device. Other electromechanical or electromagnetic valve actuators can also be used.

The operation according to the invention can also be carried out with partially variable or fully variable mechanical valve drives, in which additional adjustable control cams are provided between the fixed control cams of the camshaft and the valve. The mode of operation according to the invention is particularly advantageous, in particular, for conventional piston internal combustion engines with gas exchange valves which are controlled via camshafts. At least the camshaft for the intake valves and preferably also for the exhaust valves is at least with correspondingly adjustable cams for adjustment the opening time. A cam actuator is connected to the camshaft and is controlled by a control device. However, other mechanically adjustable systems can also be used on the valve train to ensure the necessary overlap of the opening times of the gas exchange valves. The mechanical systems can, for example, have a bucket tappet control, a rocker arm or rocker arm control or a rocker arm control. It is also possible to combine different systems with one another.

It is preferably provided that an exhaust gas recirculation is provided in an operating area without residual gas purging via variable control of the gas exchange valves to produce a valve overlap in the lower speed range. The exhaust gas recirculation can be created by internal engine valve switching and / or by using an exhaust gas recirculation valve. For example, it can be provided that the exhaust gas recirculation takes place only in an operating range in which no residual gas purge is provided by valve overlap in the lower speed range.

According to a further concept of the invention, a 4-stroke gasoline engine of a motor vehicle with direct fuel injection with at least three cylinders is provided. At least one intake and one exhaust valve are assigned to each cylinder. The intake valve is connected to a boost pressure device in an air intake system. An adjustment device for the opening and closing times of the inlet and outlet valve is provided. This can be activated to achieve a valve overlap in a lower speed range for residual gas purging. The gasoline engine has an activation device which generates a signal when defined conditions for flushing out a residual gas from the cylinder, whereby the adjusting device is activated.

According to a first further development, the activation device has defined conditions so that the signal can only be generated when a sufficient wash gradient is determined. However, the activation device can also be coupled to a prediction module, by means of which it can be determined on the basis of determined parameters when the signal is to be generated in order to generate conditions in the cylinder which only create a sufficient flushing gradient. The activation device and the prediction module are preferably part of a valve control unit which is connected to an engine control unit via a CAN bus. According to one embodiment, it is provided that the wash gradient can be determined directly or indirectly by means of a measuring device. According to another embodiment, it is provided that the flushing gradient can be determined from operating data which are stored in a motor controller and can be supplemented. Both procedures can also be coupled. A further development has a secondary injection in order to be able to use an improved combustion behavior due to the high purging. It is also possible for the ignition to be adjusted to "late" in the lower speed range.

It is envisaged, in particular in the case of a piston internal combustion engine that operates according to the diesel as well as the Otto principle, that an average gas pressure is raised upstream of the inlet valve. For example, this can be used in particular with controlled self-ignition in the 4-stroke process. A torque increase can also be brought about by taking additional motor measures. This can be, for example, the following means, which are used individually or in combination with one another: greasing the intake air or increasing the amount of fuel in the case of direct injection, secondary injection or multiple injection of the fuel, adjusting the compressor blades or stator wheels when using one Exhaust gas turbocharger, an adjustment of the injection to "late" in an Otto engine, an injection adjustment in general in the diesel engine and others.

For example, a split injection is carried out. This can provide that a first quantity of fuel covers approximately 50% to 80% of the quantity of fuel to be injected, while a quantity of fuel subsequently to be injected comprises 20% to 50%. The amount of fuel subsequently to be injected can be distributed over one or more injection processes. A split injection is preferably carried out, in particular under at least approximately full load, in a speed range between 1300 rpm and 1500 rpm. An embodiment in a direct-injection gasoline engine provides, for example, a primary and secondary injection in which there is an injection duration in a ratio of approximately 60% to 75% to 25% to approximately 40% of primary to secondary injection.

There is also the option of using various combustion processes in the lower speed range, particularly in the case of supercharged gasoline engines with direct injection. This can be a homogeneous combustion process or a stratified combustion process. For example, a jet-guided or air-guided combustion process can be used. The direct injection can use one or more injectors per cylinder Zen. A swirl injector or a multi-hole injector is preferably used. A spray angle of the injector is advantageously in a range below 70 °, in particular around 50 °.

The invention is explained in more detail below with the aid of schematic drawings. The features shown there can be combined with other features of the drawings as well as with the features described above to form further configurations and are not restrictive. Show it:

Fig. 1 is a circuit diagram of a piston internal combustion engine with an exhaust gas turbocharger

Fig. 2 is a circuit diagram of the piston internal combustion engine acc. 1 with mechanical loader,

3 for a mechanically charged piston internal combustion engine the dependence of the degree of delivery and residual gas content on the speed and opening time,

Fig. 4 for a turbocharged piston internal combustion engine, the dependency of the boost pressure and the degree of delivery on the opening time when changing loads in the area of top dead center, and

Fig. 5 is a schematic view of another piston internal combustion engine for performing a residual gas purging in a lower speed range.

1 shows a piston internal combustion engine with four cylinders I, II, III, IV, each with a gas inlet valve 2 and a gas outlet valve 3 per cylinder. The gas inlet valves 2 are connected to an air inlet system 4, while the gas outlet valves are connected to an exhaust system 5.

The piston internal combustion engine shown is also provided with a direct fuel injection, which is designed, for example, as a common rail injection system 6, to which the fuel is supplied via a pump 7. For the actuation of the gas inlet valves, a camshaft 8 is provided, the cams of which are adjustable in relation to the opening process for the gas inlet valves 2 and are adjustable via a cam actuator 9. The cam actuator 9 is connected to a control device 10, via which the fuel injection, the ignition, etc., not shown here, are controlled by an accelerator pedal 11 in accordance with the load specification.

In the exemplary embodiment shown here, the gas outlet valves 3 are actuated via a camshaft 12, the cams of which have a predetermined control contour. However, cam adjustment and / or camshaft phase adjustment of the exhaust valves can also be provided. Both camshafts 8 and 12 are driven in the usual way via the crankshaft, not shown here.

The exhaust gas system 5 is connected to an air charger 13, 1 designed as a turbocharger, whose exhaust gas turbine 14 is acted upon by the exhaust gas and whose turbocompressor 15 is connected on the pressure side to the air intake system 4. Via a controllable relief valve 16, which may be arranged in the exhaust line 6, impermissible boost pressure increases for the respective operating areas can be avoided by reducing the exhaust gas flow acting on the turbine.

The structure of the piston internal combustion engine shown in FIG. 2 essentially corresponds to the structure of the arrangement described with reference to FIG. 1, so that reference can be made to this. The only difference is that a mechanical charger 13.2 is used as the air charger, the drive energy of which is tapped from the crankshaft 1.1 of the piston internal combustion engine 1.

For both cases, the control of the intake valves 2 of the individual cylinders is provided in such a way that in the low speed range, the control cams of the intake-side camshaft 8 are adjusted in the direction of “early intake opening” via the cam actuator 9, so that the intake valve 2 is already opened in each case is before the exhaust valve closes. The air loader 13.1 or 13.2 must be designed in such a way that there is a positive purge pressure drop at low speeds in the starting area and in an operating range of, for example, 1300 rpm, ie it is ensured that the air supplied by the loader to the intake system 4 is opposite the Back pressure in the exhaust system 5 has a higher pressure During the transition to higher speeds, the control device 10, via the cam actuator 9, reverses the adjustment of the opening time of the intake valves to the point in time intended for normal operation.

Instead of the turbocharger described or the mechanical supercharger, a device for so-called pulse charging can be provided for charging. A pressure drop between the air intake system and the cylinder is used to increase the charge. By means of automatic or controllable blocking means in the respective air inlet duct, charge air can be supplied to the cylinder abruptly in the event of a pressure drop. With a corresponding setting of the valve overlap, a short residual gas purging and thus an improved filling can be achieved.

The control time "early intake opening" provided according to the invention is limited with regard to the possible advance by the clearance between the valve and the piston which is present in the specific engine design. With the appropriate combustion chamber design and / or adapted piston geometries, it is possible to advance the "Early intake opening" timing far before the LWOT (boost pressure change at top dead center) in order to start the purging process as early as possible. Another advantage is that especially when using a turbocharger, the improvement of the charging process results in repercussions on the design of the supercharger, so that a performance-oriented turbocharger selection is possible and, accordingly, smaller units can be used.

In connection with direct injection, the starting torque can be increased so that the nominal torque is reached at correspondingly low engine speeds. A lower knock limit leads to lower charge usage once the nominal torque is reached. The resulting better combustion efficiency reduces fuel consumption across the entire engine speed range.

In particular when using an exhaust gas turbocharger, the improvement results from the influences explained below.

The slightly later peak pressure situation in direct injection somewhat reduces the torque advantage that arises. This increased knock limitation is due to the increased cylinder charge in the combustion chamber. The reasons for the higher charge use result from the evaporation of the fuel directly in the combustion chamber. The mixture cools down and the charge density is increased. The air effort, related to the intake manifold conditions, increases more than the reduction in torque advantage by a few percent. This effect shifts the operating point in the loader map to a higher volume flow. The increased volume flow through the turbine leads to an increase in the pressure ratio due to the freewheeling conditions. The boost pressure thus increased leads to a significant increase in torque. Taking the individual influencing parameters into account, the torque increases by about 10%.

The rinsing effect brought about according to the invention leads to an adaptation of the cylinder air ratio. If the total air ratio is increased to stoichiometric boundary conditions in the exemplary embodiments shown, so that approximately the same cylinder-air ratio (lambda = 0.9) is used as in a piston-type internal combustion engine without a cam actuator, this leads to an increase in the exhaust gas temperature, higher volume flows and thus to improved energy supply at the turbine inlet. With the self-reinforcing effect of the exhaust gas turbocharger, charging pressures of approx. 1.7 bar are already possible at 1300 rpm. This results in a shift in the full-load torque increase to approximately 200 rpm lower speeds.

The high exhaust gas temperature level in the lower engine speed range also offers advantages when the engine is warming up with a corresponding optimization of the timing strategy for the partial load range.

In Fig. 3, the dependencies of residual gas content and degree of delivery, based on the collector of the air intake system 4, are shown in diagrams for a mechanically charged piston internal combustion engine, depending on the speed. The operating data during the test provided that an inlet valve length was constant with 200 ° KW and 1 mm.

With an opening stroke of 1 mm, residual gas contents of less than 0.6% and a delivery rate of 0.99 result for 1000 rpm with an opening at a crank angle of 310 ° (KW). As the speed increases, the residual gas content remains constant up to around 2500 rpm, while the delivery rate already drops in this speed range (curves marked with a square).

The optimum degree of delivery is given over the entire speed range shown for an opening time at about 335 ° KW (marked with diamonds and a triangle pointing downwards). Here too, the residual gas contents remain relatively low at a maximum of 1.5% to 2500 rpm. 4 shows the conditions for a turbocharged piston internal combustion engine (gasoline engine with direct injection). The operating data when determining the diagrams stipulate that outlet opens at 165 ° KW and outlet closes at 351 ° KW. The stroke is 1 mm, the speed n = 1000 rpm. The measured values for a constant inlet valve length at 185 ° KW and 1 mm stroke are indicated with square boxes. The measured values for inlet-closes-fixed at 555 ° KW and 1 mm stroke are indicated with round markings. It can be seen from the diagrams assigned to one another that the closer the time "intake opening to top dead center" is reduced from an early opening, the lower the boost pressure and the degree of delivery. The residual gas content increases accordingly with a decreasing purge effect.

FIG. 5 shows a schematic view of a piston internal combustion engine 18 with gas exchange valves 19 for a residual gas purging in a lower speed range. An adjusting device 20 is connected to the gas exchange valves 19, wherein the adjusting device 20 for the inlet and outlet valves can be present separately or, as shown, also integrated. The adjusting device 20 is coupled to an activation device 21, which can also be separate or integrated. The adjusting device 20 and the activation device are preferably part of the sand of a valve control unit 22 which is seated on the gas exchange valves 21, for example. The valve control unit 22 can, however, also be separate, at least from the adjusting device 20. The valve control unit 22 is coupled to an engine control unit 24 via a bus system 23, in particular a CAN bus. In this way, determined operating data of the piston internal combustion engine 18 can be passed on to the valve control unit 22 and vice versa. The valve control unit 22 and / or the engine control unit 24 can have a prediction module 25. In addition, opening or closing of at least the inlet valves can also be initiated. Operating data can in turn be determined via a measuring device 26, via which it can be determined whether, for example, presettable conditions have been reached that justify initiating a residual gas purging in a lower speed range of the piston internal combustion engine. An injection control 27, via which an injector 28 can be activated for direct fuel injection, is preferably also integrated in the engine control 24. An injection profile, an injection quantity and also an injection duration can be injected into a combustion chamber in a manner adapted to the respective operating range. This enables, for example, at least one secondary injection even at lower speeds. An exhaust gas recirculation 29 is also shown schematically. This is activated in particular in an operating range in which residual gas purging is not carried out. With the piston internal combustion engine 18 According to one embodiment, only the opening times of the intake valves are set such that there is an overlap of the valve with a closing time of an associated exhaust valve in the lower speed range for purging the cylinder with residual gas before the charge is changed in the area of top dead center with fresh charge air.

Claims

claims

1. Method for operating a piston internal combustion engine with fuel injection, in particular direct fuel injection, with gas exchange valves per cylinder, each with at least one exhaust valve that is connected to an exhaust system, and at least one intake valve that is connected to an air intake system, and with means for Increasing the boost pressure in the air intake system, characterized in that a control device is provided for variable adjustment of at least the opening times of the intake valves and that in the lower speed range the intake-opening times and / or the exhaust-closing times of the gas exchange valves are controlled via the control device be set so that there is an overlap of the valve with the closing time of the associated exhaust valves and so the cylinder is flushed with fresh charge air before and / or during the charge change in the area of top dead center.

2. The method according to claim 1, characterized in that at least the inlet valves are provided with at least partially variable valve drives, which are controlled via the control device.

3. The method according to claim 1, characterized in that at least the inlet valves are driven via a camshaft which is provided with correspondingly adjustable cams for setting at least the opening times and which are connected to a cam actuator which is controlled by the control device.

4. The method according to any one of the preceding claims, characterized in that an opening and closing time of an exhaust valve is changed to increase a flushing of the cylinder.

5. The method according to any one of the preceding claims, characterized in that the inlet and outlet valve are only opened when there is a sufficient pressure increase for flushing the cylinder in an intake manifold which is connected to the inlet valve.

6. The method according to any one of the preceding claims, characterized in that at least 95% of the residual gas is flushed out in the cylinder.

7. The method according to any one of the preceding claims, characterized in that the adjustment of valve times is carried out up to a speed of the piston internal combustion engine of 2000 rpm.

8. The method according to claim 7, characterized in that there is no adjustment of valve times for purging the cylinder above 2000 rpm.

9. The method according to any one of the preceding claims, characterized in that during an acceleration process, in particular during a start-up process, valve times are adjusted in a range between 30% to 100% of a maximum engine load.

10. The method according to any one of claims 1 to 3, characterized in that a turbocharger or a mechanical supercharger are used as means for increasing the boost pressure.

11. The method according to any one of claims 1 to 3, characterized in that a pulse charge is used as a means for increasing the boost pressure.

12. The method according to any one of claims 1 to 3, characterized in that a change in the suction system is used as a means of increasing the boost pressure.

13. The method according to any one of the preceding claims, characterized in that the piston internal combustion engine works on the diesel principle and is operated with an injection adjustment.

14. 4-stroke gasoline engine of a motor vehicle with direct fuel injection with at least three cylinders, each cylinder being assigned at least one intake and one exhaust valve, the intake valve being connected to a boost pressure device in an air intake system, an adjusting device for the opening and

Closing times of the intake and exhaust valve are provided, which can be activated to achieve a valve overlap in a lower speed range of the gasoline engine for residual gas purging, and with an activation device which generates a signal when defined conditions for purging a residual gas out of the cylinder, thereby the adjusting device is activated.

15. Otto engine according to claim 14, characterized in that the activation device has defined conditions, so that the signal can only be generated when a sufficient flushing gradient is determined.

16. Gasoline engine according to claim 14, characterized in that the activation device is coupled to a prediction module, by means of which it can be determined on the basis of determined parameters when the signal is to be generated in order to generate conditions in the cylinder which only create a sufficient flushing gradient.

17. Otto engine according to claim 16, characterized in that the activation device and the prediction module are part of a valve control unit which is connected to an engine control unit via a CAN bus.

18. Otto engine according to claim 14, characterized in that the flushing gradient can be determined directly or indirectly by means of a measuring device.

19. Otto engine according to claim 14, characterized in that the flushing gradient can be determined from operating data which are stored in an engine control and can be supplemented.

20. Otto engine according to claim 14, characterized in that a secondary injection is provided.

21. Otto engine according to claim 14, characterized in that an adjustment of an ignition to "late" is provided in the lower speed range.

22. Gasoline engine according to claim 14, characterized in that an exhaust gas recirculation is provided which is activated in an operating range of the gasoline engine in which activation of a valve overlap in the lower speed range to achieve the residual gas purging does not take place.