METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE, AND CONTROL DEVICE

Abstract

The disclosure relates to a method for operating an internal combustion engine. The internal combustion includes an intake manifold via which a cylinder can be supplied with fresh air, an inlet valve via which, when it is open, the fresh air can flow from the intake pipe into the cylinder, and a variable valve drive by means of which the opening duration or the relative timing of the inlet valve event is variable in relation to a crankshaft position. During a starting of the internal combustion engine, when the intake manifold pressure differs from the intake manifold desired pressure, a filling pilot control of the cylinder is undertaken by the variable valve drive by the fresh air supply being reduced in comparison to the fresh air supply at the intake manifold desired pressure. The disclosure further relates to a control device for an internal combustion engine that enables low-emission operation.

Claims

1. A method for operating an internal combustion engine, comprising: providing an internal combustion engine having: a crankshaft configured to be driven by a piston of a cylinder, an intake manifold configured to supply fresh air to the cylinder, an inlet valve configured to open so that fresh air can flow from the intake manifold into the cylinder, and a variable valve drive configured to vary an opening duration or a timing of the inlet valve relative to a position of the crankshaft, and operating the internal combustion engine in an overrun phase during which: i) the internal combustion engine is dragged without fuel supply, and ii) a first inlet valve timing set by the variable valve drive provides a reduced or no air mass in the cylinder, requesting a refiring of the internal combustion engine, comparing an intake manifold pressure to an intake manifold desired pressure, determining, based on the comparison, a rate of adjusting the timing of the inlet valve to enable pre-filling control of fresh air into the cylinder, adjusting the timing of the inlet valve via the determined rate to allow a controlled amount of fresh air in the cylinder, and refiring the internal combustion engine.

2. The method according to claim 1, wherein the controlled amount of fresh air allowed in the cylinder via the variable valve drive is such that a torque which is built up does not exceed a torque target specification, or exceeds it by less than 50%.

3. The method according to claim 2, wherein the internal combustion engine further comprises an exhaust valve configured to be closed in the overrun phase.

4. The method according to claim 3, wherein no ignition angle intervention occurs when the internal combustion engine is refired.

5. The method according to claim 1, wherein the variable valve drive has an intake camshaft with an electric camshaft adjuster.

6. The method according to claim 1, wherein the internal combustion engine further comprises a throttle valve and the pre-filling control is carried out by the variable valve drive when the throttle valve is unable to carry out load control or load control by the throttle valve can only be carried out to a reduced extent.

7. The method according to claim 1, wherein the internal combustion engine is operated as part of a hybrid drive of a motor vehicle.

8. A control device configured to operate an internal combustion engine via the method according to claim 1.

9. The method according to claim 1, wherein the first inlet valve timing is shifted so far late that a maximum inlet valve lift is approximately at a bottom dead center piston position.

10. The method according to claim 1, wherein the variable valve drive includes electro-hydraulically actuated valves.

11. The method according to claim 1, wherein a first determined rate of adjusting the timing of the inlet valve corresponds to a first comparison of a first intake manifold pressure to a first intake manifold desired pressure, and a second determined rate of adjusting the timing of the inlet valve corresponds to a second comparison of a second intake manifold pressure to a second intake manifold desired pressure, and the second determined rate is slower than the first determined rate.

12. The method according to claim 1, wherein the determined rate of adjusting the timing of the inlet valve is configured to achieve a second target inlet valve timing, and the second target inlet valve timing is not achieved at a time when the internal combustion is refired.

13. The method according to claim 1, wherein operating the internal combustion engine in a first firing phase precedes operating the internal combustion engine in the overrun phase.

14. The method according to claim 1, wherein the timing of the inlet valve is adjusted continuously via the determined rate.

15. A method for operating an internal combustion engine, comprising: providing an internal combustion engine having: a crankshaft configured to be driven by a piston of a cylinder, an intake manifold configured to supply fresh air to the cylinder, an inlet valve configured to open so that fresh air can flow from the intake manifold into the cylinder, and a variable valve drive configured to vary an opening duration or a timing of the inlet valve relative to a position of the crankshaft, operating the internal combustion in an overrun phase during which: i) the internal combustion engine is dragged without fuel being supplied, and ii) a first inlet valve timing set by the variable valve drive provides a reduced or no air mass flow in the cylinder, requesting a refiring of the internal combustion engine, comparing an intake manifold pressure to an intake manifold desired pressure, determining, based on the comparison, a rate of adjusting the timing of the inlet valve to enable a pre-filling control of fresh air into the cylinder, and refiring the internal combustion engine, and wherein: a first comparison corresponds to: i) a first difference between the intake manifold pressure and the intake manifold desired pressure, and ii) a first rate of adjusting the timing of the inlet valve, a second comparison corresponds to: i) a second difference between the intake manifold pressure and the intake manifold desired pressure, and ii) a second rate of adjusting the timing of the inlet valve, and the second difference is greater than the first difference, and the second rate is slower than the first rate.

16. The method according to claim 15, wherein the internal combustion engine further comprises an exhaust valve configured to be closed in the overrun phase.

17. The method according to claim 15, wherein no ignition angle intervention occurs when the internal combustion engine is refired.

18. The method according to claim 15, wherein the variable valve drive has an intake camshaft with an electric camshaft adjuster.

19. The method according to claim 15, wherein the first inlet valve timing is shifted so far late, that a maximum inlet valve lift is approximately at a bottom dead center piston position.

20. The method according to claim 15, wherein the determined rate of adjusting the timing of the inlet vale is configured to achieve a second target inlet valve timing, and the second target inlet valve timing is not achieved at a time when the internal combustion is refired.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the figures:

[0027] FIG. 1a shows a schematic, chronological development of the injection activity of a first internal combustion engine without a variable valve drive according to the prior art when entering and exiting the overrun phase,

[0028] FIG. 1b shows a schematic, chronological development of the intake manifold pressure of the first internal combustion engine without a variable valve drive when entering and exiting the overrun phase,

[0029] FIG. 1c shows a schematic, chronological development of the inlet valve closing time in ?CA after TDC of the first internal combustion engine without a variable valve drive when entering and exiting the overrun phase,

[0030] FIG. 1d shows a schematic, chronological development of the engine torque in Nm of the first internal combustion engine without a variable valve drive when entering and exiting the overrun phase,

[0031] FIG. 2a shows a schematic, chronological development of the injection activity of a second internal combustion engine with a variable valve drive without pre-filling control according to the prior art when entering and exiting the overrun phase,

[0032] FIG. 2b shows a schematic, chronological development of the intake manifold pressure of the second internal combustion engine with a variable valve drive without pre-filling control when entering and exiting the overrun phase,

[0033] FIG. 2c shows a schematic, chronological development of the inlet valve closing time in ?CA after TDC of the second internal combustion engine with a variable valve drive without pre-filling control when entering and exiting the overrun phase,

[0034] FIG. 2d shows a schematic, chronological development of the engine torque in Nm of the second internal combustion engine with a variable valve drive without pre-filling control when entering and exiting the overrun phase,

[0035] FIG. 3a shows a schematic, chronological development of the injection activity of a third internal combustion engine according to the disclosure with a variable valve drive and pre-filling control when entering and exiting the overrun phase,

[0036] FIG. 3b shows a schematic, chronological development of the intake manifold pressure of the third internal combustion engine according to the disclosure with a variable valve drive and pre-filling control when entering and exiting the overrun phase,

[0037] FIG. 3c shows the chronological, development of the inlet valve closing time in ?CA after TDC of the third internal combustion engine according to the disclosure with a variable valve drive and pre-filling control when entering and exiting the overrun phase,

[0038] FIG. 3d shows a schematic, chronological development of the engine torque in Nm of the third internal combustion engine according to the disclosure with a variable valve drive and pre-filling control when entering and exiting the overrun phase,

[0039] FIG. 4 shows a schematized internal combustion engine, and

[0040] FIG. 5 shows a further schematized internal combustion engine.

DETAILED DESCRIPTION

[0041] FIGS. 4 and 5 each show an internal combustion engine 1 as a reciprocating piston engine having cylinders 4 and a crankshaft, not shown, as a detail and in a roughly schematized manner. It is designed as a four-cylinder in-line engine, wherein the disclosure can also be implemented in internal combustion engines 1 having a different number of cylinders and design. The valve control of the internal combustion engine 1, i.e., the valve drive, is designated by 3. As a four-valve engine, the internal combustion engine 1 has two inlet valves 5 and two exhaust valves 6 per cylinder 4. An intake camshaft is designated by 7 and an exhaust camshaft is designated by 8. The intake camshaft 7 can be adjusted with a camshaft adjuster 9 on the intake side, and the exhaust camshaft 10 can be adjusted with a camshaft adjuster 10 on the exhaust side. In the exemplary embodiments considered, the camshaft adjusters 9, 10 are designed in the form of electro-mechanical adjusters, each having an adjusting gear designed as a harmonic drive, and each have an electric motor 11 for adjusting the phase position of the respective camshaft 7, 8 in relation to the crankshaft of the internal combustion engine 1. In a manner known per se, the camshafts 7, 8 are driven by the crankshaft via a belt drive or a gear train, wherein a drive gear 13 is firmly connected to the housing of the adjusting gear of the camshaft adjuster 9, 10 or is an integral part of this housing.

[0042] To actuate the camshaft adjusters 9, 10, a control device 12 is provided, which optionally takes on further control tasks. Data connections between the control device 12 and the camshaft adjuster 9, 10 are designated by 15. A switching device 14 enables the exhaust valves 6 to be switched off if necessary. The switching device 14 of the internal combustion engine according to FIG. 5 can be actuated electro-mechanically and can be designed with switchable rocker arms.

[0043] FIGS. 1a to 1d schematically show the chronological development of some characteristic values of a first internal combustion engine 1 according to the prior art, which does not have a variable valve drive. The internal combustion engine 1 is fired in a first firing phase 21, which lasts up to the point in time t.sub.1. FIG. 1a digitally represents the fuel injection 24 of the internal combustion engine 1, which takes place in the firing phases 21, 23 (value is 1) and is omitted in the overrun phases 22 (value is 0). The internal combustion engine 1 is switched off at the point in time t.sub.1, and the internal combustion engine 1 is refired in a refiring phase 23 at the point in time t.sub.3. There is no fuel injection between these points in time. Already at the point in time t.sub.2, which is shortly before the point in time t.sub.3, the driver or a control device initiates a torque specification, which initiates the restart process of internal combustion engine 1. At the point in time t.sub.3, the data processing for restarting the internal combustion engine 1 is complete.

[0044] As soon as the vehicle enters the overrun phase 22, the fuel injection 24 is suspended. The intake manifold pressure is regulated with the throttle valve. In the example shown in FIG. 1b, it is kept constantly low. The inlet valve closing time 26 shown in FIG. 1c remains at the target angle for engine restart and is also not varied. The throttle valve typically remains closed in the overrun phase 22. A torque-neutral restart can thus take place quickly after the torque specification by the driver, without overshoots occurring at the beginning of the refiring phase 23. The engine torque 27 (FIG. 1d) thus essentially corresponds to the torque target specification. However, air can get into the exhaust after-treatment system during the overrun phase 22, so that enrichment is required after restarting the engine, which increases emissions.

[0045] FIGS. 2a to 2d schematically show the chronological development of the characteristic values of a second internal combustion engine 1 according to the prior art, which, in contrast to the first internal combustion engine 1, has a variable valve drive 3. The graph according to FIG. 2a corresponds to the graph of FIG. 1a. The internal combustion engine 1 is thus fired in the first firing phase 21, firing is stopped in the overrun phase 22, and the refiring phase 23 begins at the point in time t.sub.3. The variable valve drive 3 is used to prevent oxygen enrichment in the exhaust after-treatment system. To this end, it prevents air scavenging of the engine in the overrun phase 22 by shutting off the exhaust valves 6 and adjusting the inlet valves 5 to an extended adjustment range. In the overrun phase 22, the exhaust valve lifts are deactivated in a cycle-synchronous manner with the suspension of the fuel injection 24 and are reactivated in a cycle-synchronous manner with the start of the fuel injection 24 when restarting. The variable valve drive 3 can be used on the intake side to maximally reduce the engine drag torque in the overrun phase 22. The charge-exchange work reduced in this way enables, particularly in combination with P0 and P1 hybrid vehicles, a large amount of energy to be recuperated, which increases the overall efficiency of the drive train. For this purpose, extremely late inlet valve phase positions that are not useful for the firing operation 21, 23 are set, so that the maximum inlet valve lift is approximately at bottom dead center (BDC). Here, too, the throttle valve position can remain almost completely closed within the overrun phase 22.

[0046] If the internal combustion engine 1 is to provide torque again, the inlet valve phase position is quickly adjusted to the conventional target position again, as can be seen from FIG. 2c between the points in time t.sub.2 and t.sub.3. Fuel injection 24 is omitted between these points in time. Already at the point in time t.sub.2, which is shortly before the point in time t.sub.3, the driver or a control device initiates a torque specification, which initiates the restart process of internal combustion engine 1. At the point in time t.sub.3, the data processing for restarting the internal combustion engine 1 is complete.

[0047] In the overrun phases 22, the intake manifold pressure 25 increases continuously, for example due to leaks. If the overrun phase 22 lasts a relatively long time, for example when driving downhill, the intake manifold pressure 25 (FIG. 2b) can increase within the overrun phase 22 to such an extent that it almost corresponds to the ambient atmospheric pressure. If the refiring is initiated with an increased intake manifold pressure 25, this leads to a short-term strong build-up of torque with a torque peak 27 due to the high air mass. Generally, however, the objective is to engage the internal combustion engine 1 with a low torque. In this case, the strong build-up of torque leads to a loss of comfort.

[0048] FIGS. 3a to 3d schematically show the chronological development of the characteristic values of a third internal combustion engine 1, which, like the second internal combustion engine 1, has a variable valve drive 3 and is operated using the method according to the disclosure. The graph according to FIG. 3a corresponds to the graph of FIG. 2a. The internal combustion engine 1 is once again fired in the first firing phase 21, firing is stopped in the overrun phase 22, and the refiring phase 23 begins at the point in time t.sub.3. The variable valve drive 3 is in turn used to prevent air scavenging, so that the operating method is the same as that of the second internal combustion engine up to the end of the overrun phase 22. As in the case of the second internal combustion engine 1, the development of the intake manifold pressure is therefore also identical (FIG. 3b).

[0049] At the point in time t.sub.2, at which the restart request of the internal combustion engine 1 is triggered, in contrast to the second internal combustion engine, the inlet valve phase position is not adjusted as quickly as possible, but is adjusted to the conventional target position with a delay. The phase position adjustment rate or adjustment speed depends on how much the intake manifold pressure 25 has increased and what load is required of the internal combustion engine 1. As can be seen from FIGS. 3a to 3d, refiring takes place at the point in time t.sub.3, which begins even though the inlet valve time does not yet correspond to the valve time corresponding to continuous operation at this load requirement, target valve time 29 at intake manifold desired pressure p.sub.s. The time difference t.sub.? between t.sub.3 and t.sub.2 is the time required to reach the target angle of the pre-control. The adjustment to the target valve time 29 at intake manifold desired pressure p.sub.s takes place as long as the intake manifold pressure has not yet reached its target pressure. Typical times can be assumed here, so that the adjustment could be performed in a controlled manner, but it can also be performed in a regulated manner. This also allows the adjustment speed to be adapted to the actual intake manifold pressure. Ideally, the inlet valve closing time 26 is adjusted in such a way that the engine torque 27 builds up monotonically and at the same time as quickly as possible.

[0050] The variable valve drive 3 is therefore used for the pre-control of the inlet valve closing time 26 when the internal combustion engine 1 is refired. This makes it possible to avoid a torque peak 28 when the pressure in the intake manifold is increased. For this purpose, the variable valve drive 3 deactivates the exhaust valves in the overrun phase 22 and reduces the engine drag torque by setting the inlet valve lift to be extremely late or retarded. With the torque specification by the driver, the stored filling model calculates the target control times for a torque-neutral engine restart based on the significant input variables. For the example selected, this means that the inlet valve lift phase position must be adjusted continuously, depending on the engine speed, but adjusted to be early more slowly than in the case without pre-control, until the intake manifold pressure is back at the target value and further load control, e.g., by throttle valve, can take place.

LIST OF REFERENCE SYMBOLS

[0051] 1 Internal combustion engine [0052] 2 Cylinder head [0053] 3 Valve drive [0054] 4 Cylinder [0055] 5 Inlet valve [0056] 6 Exhaust valve [0057] 7 Intake camshaft [0058] 8 Exhaust camshaft [0059] 9 Camshaft adjuster, intake side [0060] 10 Camshaft adjuster, exhaust side [0061] 11 Electric motor [0062] 12 Control device [0063] 13 Drive gear [0064] 14 Switching device [0065] 15 Data connection [0066] 21 Firing phase [0067] 22 Overrun phase [0068] 23 Refiring phase [0069] 24 Fuel injection [0070] 25 Intake manifold pressure [0071] 26 Inlet valve closing time after TDC in ?CA [0072] 27 Engine torque in Nm [0073] 28 Torque peak [0074] 29 Target valve time at intake manifold desired pressure [0075] t Time [0076] t.sub.1 Point in time at which the internal combustion engine is switched off [0077] t.sub.2 Point in time of the restart request of the internal combustion engine [0078] t.sub.3 Point in time after data processing for restarting the internal combustion engine [0079] t.sub.? Time difference between t.sub.3 and t.sub.2 [0080] p.sub.s Intake manifold desired pressure