Method for operating an internal combustion engine, and internal combustion engine

Abstract

A method for a combustion motor that is initially used in a full Miller cycle or full Atkinson cycle that is advantageous with regard to efficiency. In full operation, a switchover to a partial operation takes place, wherein the intake valves associated with the combustion chambers that are to continue to be operated are switched over to actuation in accordance with a second valve lifting curve in order to achieve a switchover that is as torque-neutral as possible and is optimal with regard to efficiency. The closing time of the intake valve brought about by this second valve lifting curve is designed with respect to maximum volumetric efficiency.

Claims

1. A method for operating an internal combustion engine comprising a combustion motor that forms at least two combustion chambers, which are delimited by cylinders formed in a cylinder housing and by pistons that are guided therein, and in which thermodynamic cycles are performed during operation of the internal combustion engine, wherein a gas exchange in the combustion chambers is then controlled by at least one intake valve and at least one exhaust valve, the method comprising: providing a first operating state in which the thermodynamic cycles are performed in a first combustion chamber as well as in a second combustion chamber; providing a second operating state in which the thermodynamic cycles are performed in the first combustion chamber and the thermodynamic cycles are not performed in the second combustion chamber; performing, for a switchover from the first operating state to the second operating state, a change from a use of a first valve lifting curve to a use of a second valve lifting curve for actuation of the intake valve associated with the first combustion chamber; closing at least the intake valve associated with the first combustion chamber before or after BDC in the case of an actuation according to the first valve lifting curve and closer to BDC in the case of an actuation according to the second valve lifting curve; and adjusting, after the switchover from the first operating state to the second operating state, a timing for the intake valve associated with the first combustion chamber via a phase shifter in a late direction if an intake closure before BDC was provided for the first operating state or in an early direction if an intake closure after BDC was provided for the first operating state.

2. The method according to claim 1, wherein the first valve lifting curve is applied to the intake valve via a first intake cam and the second valve lifting curve is applied via a second intake cam.

3. The method according to claim 1, wherein at least the intake valve associated with the first combustion chamber is closed before BDC60 crankshaft angle or after BDC+100 crankshaft angle in the case of actuation in accordance with the first valve lifting curve, and/or in the range between BDC45 crankshaft angle in the case of actuation in accordance with the second valve lifting curve.

4. The method according to claim 1, wherein a width of the second valve lifting curve as compared to a width of the first valve lifting curve is greater if an intake closure before BDC was provided for the first operating state, or is smaller if an intake closure after BDC was provided for the first operating state.

5. The method according to claim 1, wherein at least the intake valve associated with the first combustion chamber is adjusted further in the late direction to at least BDC+25 crankshaft angle if an intake closure before BDC was provided for the first operating state, or is adjusted further in the early direction to at least BDC20 crankshaft angle if an intake closure after BDC was provided for the first operating state.

6. The method according to claim 1, wherein a valve overlap of the intake and/or exhaust valves associated with the first combustion chamber is adjusted for a switchover from the first operating state to the second operating state.

7. The method according to claim 6, wherein a change is made from a use of a first exhaust cam to the use of a second exhaust cam for the actuation of the exhaust valve associated with the first combustion chamber.

8. The method according to claim 7, wherein, as compared to the first exhaust cam, the second exhaust cam causes a relatively late exhaust closure when an intake closure before BDC was provided for the first operating state, or causes a relatively early exhaust closure when an intake closure after BDC was provided for the first operating state.

9. The method according to claim 1, wherein the pressure in an intake manifold of the internal combustion engine is increased after the switchover from the first operating state to the second operating state.

10. The method according to claim 1, wherein an ignition angle for the first combustion chamber that was previously set relatively late is adjusted in the early direction for the switchover from the first operating state to the second operating state.

11. The method according to claim 10, wherein the ignition angle is adjusted back in the late direction subsequent to the early adjustment.

12. An internal combustion engine comprising: a combustion motor that forms at least two combustion chambers, which are delimited by cylinders formed in a cylinder housing and by pistons that are guided therein, and in which thermodynamic cycles are performed during operation of the internal combustion engine, wherein a gas exchange in the combustion chambers is controlled via an intake valve and an exhaust valve; and a switchover device to switch use between two valve lifting curves; a phase shifter for the intake valve associated with a first combustion chamber; a control device that is programmed such that it performs the method according to claim 1.

13. The internal combustion engine according to claim 12, further comprising: two exhaust cams for the exhaust valve and/or intake valve associated with the first combustion chamber and/or the second combustion chamber, it being possible to switch between their use via the switchover device, and/or a component to influence the pressure in an intake manifold of the internal combustion engine, and/or a phase shifter for changing the timing, including for the intake valve associated with the second combustion chamber, and/or for changing the timing for the exhaust valve associated with the first combustion chamber and/or the second combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows an internal combustion engine according to the invention in a schematic representation;

(3) FIG. 2 shows the combustion motor of the internal combustion engine from FIG. 1 in a schematic longitudinal section;

(4) FIG. 3 shows a cam carrier for a combustion motor according to FIG. 1;

(5) FIG. 4 shows a cam pair of the cam carrier according to FIG. 3;

(6) FIG. 5 shows a portion of the cam carrier from FIG. 3 and a switchover actuator in a schematic representation;

(7) FIG. 6 shows various lift curves for the gas exchange valves of a combustion motor according to FIG. 2;

(8) FIG. 7 shows in a diagram, the quantitative behaviors of various operating parameters of an internal combustion engine from FIG. 1 before and after a switchover from a full operation to a partial operation; and

(9) FIG. 8 shows a graph showing the ratios between the closing time SZ of the intake valves and the intake manifold pressure p.sub.s, which in each case result in the attainment of a defined torque that should be produced by the combustion motor, for an exemplary full Miller cycle (solid line) and, on the other hand, a partial Atkinson cycle (dashed line).

DETAILED DESCRIPTION

(10) Schematically shown in FIG. 1 is an internal combustion engine according to the invention. A motor vehicle, for example, can be driven by means of the internal combustion engine.

(11) The internal combustion engine includes a combustion motor 10, which is also shown in further detail in FIG. 2, and which can, in particular, be operated with a four-stroke cycle. The combustion motor 10 forms several (here: four) cylinders 16 in a unit formed of engine block 12 and cylinder head 14. The cylinders 16 are connected in a gas-carrying manner on the intake side to an intake manifold 18 of an intake system and on the exhaust side to an exhaust manifold 20 of an exhaust system of the internal combustion engine. In a known manner, fresh gas (essentially air) is burned with fuel in combustion chambers 22 that are delimited by the cylinders 16 together with pistons 24 guided therein and the cylinder head 14. The fuel can be injected directly into the combustion chambers 22 for this purpose by means of injectors 26. The exhaust gas produced in the combustion of the fuel/fresh gas mixture is carried away through the exhaust system.

(12) The delivery of fresh gas into the combustion chambers 22 and the removal of the exhaust gas from the combustion chambers 22 is controlled by means of four gas exchange valves, namely two intake valves 28 and two exhaust valves 30 per combustion chamber 22, which are actuated by a valve actuating mechanism of the combustion motor 10 that is not shown in FIG. 1. The valve actuating mechanism includes, according to FIG. 2, a crankshaft 34 forming crankshaft journals 32, wherein the crankshaft journals 32 are connected to the pistons 24 by connecting rods 36. In this way, linear motions of the pistons 24 are converted into a rotation of the crankshaft 34, wherein the rotation of the crankshaft 34 in turn causes a periodic reversal of direction of the linear motions of the pistons 24. The rotation of the crankshaft 34 is also transmitted through a control mechanism, for example a toothed belt drive 38, to two camshafts 40, each of which actuates two gas exchange valves 28, 30 per combustion chamber 22 through, for example, rocker arms or cam followers (not shown). One of the camshafts 40 is implemented as an intake camshaft, i.e., it actuates all intake valves 28, while the other is implemented as an exhaust camshaft, and consequently actuates all exhaust valves 30.

(13) The internal combustion engine additionally includes an exhaust gas turbocharger. This has a turbine 42 integrated into the exhaust system and a compressor 44 integrated into the intake system. A rotor of the turbine 42 driven in rotation by the exhaust gas stream drives a rotor of the compressor 44 through a shaft 46. The rotation of the rotor of the compressor 44 thus brought about compresses the fresh gas routed through it. Boost pressure limitation can be accomplished by means of a wastegate 48 by routing a portion of the exhaust gas stream around the turbine 42 in operation of the combustion motor 10 at high speeds and/or loads. In addition, an exhaust gas treatment device 50, for example in the form of a three-way catalytic converter, is integrated into the exhaust system.

(14) The combustion motor 10 additionally includes a phase shifter 54 for each of the camshafts 40; said phase shifters are controlled by a control device 52 (engine control unit). The phase shifters 54 make it possible to change, and concretely to move, the timing and thus the opening phases of the associated gas exchange valves 28, 30. The phase shifters 54 are each integrated into a gear wheel 56 of the camshafts 40 in a known manner (see, for example, DE 10 2013 223 112 A1). Accordingly, the phase shifters 54 of the camshafts 40 can each have a vane rotor (not shown) that is connected in a rotationally fixed manner to the relevant camshaft 40 and in each case is arranged to be rotatable within limits inside a stator (not shown) of the phase shifter 54. The stator forms a tooth contour on its cylindrical outer surface for the engagement of teeth of a toothed belt of the toothed belt drive 38. Formed between the vane rotor and the stator of the phase shifters 54 can be multiple pressure chambers, which can be selectively filled with a fluid, in particular an oil, under the control of a phase shifter valve (not shown) in order to rotate the vane rotor inside the stator in a defined manner, by which means the phase angle between the applicable camshaft 40 connected to the vane rotor and the stator connected to the crankshaft 34 in a rotary driving manner can be changed in accordance with the goal of a change in the timing of the associated gas exchange valves 28, 30.

(15) Moreover, the internal combustion engine also includes a switchover device 58, by means of which it is possible to switch from an actuation by means of a first cam 60 to an actuation by means of a second cam 62 for the intake valves 28 as well as the exhaust valves 30. This switchover device 58 can likewise be controlled by the control device 52, and is indicated only schematically in FIG. 2. The function of the switchover device 58 is based on a movability along a longitudinal axis of sleeve-like cam carriers 64 (see also FIG. 3), which are arranged in a rotationally fixed manner on a base shaft 66, by means of one switchover actuator 68 (see FIG. 4) apiece, wherein the cam carriers 64 have two different cams 60, 62 for each of the intake valves 28 and exhaust valves 30 that they can actuate (see FIG. 3 and FIG. 4), which cams interact alternately, as a function of the movement positions of the cam carriers 64 that have been set, with the associated intake valves 28 and exhaust valves 30.

(16) In the exemplary embodiment as is shown in FIGS. 2 and 3, each of the cam carriers 64 includes a total of four cam pairs, each of which is associated with a gas exchange valve 28, 30 of the internal combustion engine. Thus, either the intake valves 28 or the exhaust valves 30 of a total of two adjacent cylinders 16 of a combustion motor 10 according to FIGS. 1 and 2, in which two intake valves 28 and two exhaust valves 30 are associated with each cylinder 16, are actuated by means of the cams 60, 62, which are formed by such a cam carrier 64. Moreover, the cam carrier 64 shown in FIG. 3 also forms a shift gate in the form of a Y-shaped guide slot 70 between the two cam pairs associated with the gas exchange valves 28, 30 of a first cylinder 16 and the two cam pairs associated with the gas exchange valves 28, 30 of a second cylinder 16. By means of an interaction of this guide slot 70 with drivers 72 of the associated switchover actuator 68, the cam carrier 64 can be moved axially by the distance x, and thus a selected cam 60, 62 of each cam pair can be brought into operative connection with the associated gas exchange valve 28, 30 in each case. For this purpose, starting, for example, from the functional setting shown in FIG. 5, in which each of the gas exchange valves 28, 30 stands in operative connection with the right (first) cam 60 of each cam pair, the right driver 72 can be extended, thus moving the cam carrier 64 to the right by the distance x in interaction with its rotation (upward in FIG. 5). As a result of the running out of the Y-shaped guide slot 70 in the central section, at the bottom in FIG. 5, the right driver 72 is moved back into the retracted position in this process. After such a movement of the cam carrier 64 by the distance x, each of the left (second) cams 62 of each cam pair is then in operative connection with the associated gas exchange valve 28, 30. Such a movement of the cam carrier 64 to the right by the distance x also has the result that the left driver 72 has been brought into engagement with the left section of the Y-shaped guide slot 70, so that by extending this driver 72, the cam carrier 64 can again be moved left by the distance x.

(17) Provision is made that for a partial operation of the internal combustion engine, a subset, and in particular half, of the combustion chambers 22, specifically the two middle combustion chambers 22, can be deactivated in that a supply of fuel to the associated injectors 26 is stopped and the gas exchange valves 28, 30 associated therewith are no longer actuated, which is to say are opened. For this purpose, provision is made that each cam pair that is associated with the gas exchange valves 28, 30 of such a deactivatable combustion chamber 22 forms a second cam 62 in the form of a so-called null cam that has no cam lift and thus does not bring about an opening of a gas exchange valve 28, 30 associated therewith. In the case of the cam carrier 64 from FIG. 3, the left cams 62 of each of the two cam pairs located to the right of the guide slot 70 are designed as corresponding null cams.

(18) In the case of a switchover from a full operation of the internal combustion engine, in which all of the combustion chambers 22 are operated with low to moderate loads, to such a partial operation, half of the combustion chambers 22 are deactivated in a very short period of time that corresponds approximately to one rotation of the crankshaft 34, and thus can no longer contribute to generation of a drive power by the combustion motor 10. On the contrary, since the pistons 24 associated with these combustion chambers 22 must be carried along by the pistons 24 of the combustion chambers 22 that continue to be actively operated, these deactivated combustion chambers 22 change their function from that of a power producer to a power consumer.

(19) Because such a switchover from full operation to partial operation is intended to take place regularly in a constant operating phase of the internal combustion engine, therefore the drive power before and after the switchover should then also remain essentially constant. Consequently, the loss of the deactivated combustion chambers 22 must be compensated for by the combustion chambers 22 that continue to be actively operated. The load at which these are operated after a switchover must be increased considerably for this purpose, and in particular approximately doubled. To this end, a considerably larger quantity of fuel must be transferred within one cycle of the thermodynamic cycles performed in the combustion chambers 22 that continue to be actively operated, for which purpose a quantity of fresh gas that is increased approximately commensurately is required.

(20) This increased quantity of fresh gas should be achieved on the one hand by an increase in the pressure in the intake manifold 18 through conventional measures of boost pressure regulation of the exhaust gas turbocharger. As a result of a higher compression of the fresh gas, more fresh gas can then be introduced into the combustion chambers 22 so that a correspondingly increased quantity of fuel can also be transferred.

(21) Furthermore, provision is made that the volumetric efficiency, and thus the ratio of the masses of fresh gas actually contained in the combustion chambers 22 after conclusion of a gas exchange to the maximum theoretically possible masses, is also increased and, in particular, is maximized. The two measures in combination bring about a marked increase in the quantity of fresh gas provided within one cycle to the combustion chambers 22 that continue to be actively operated in partial operation in comparison with the full operation preceding the switchover.

(22) The effect of the increase in volumetric efficiency is relatively strongly pronounced for reasons including the fact that provision is made for the internal combustion engine that when the engine is operated in a full operation that precedes a switchover into partial operation, it is operated in a so-called Miller cycle, in which provision is made according to the present exemplary embodiment to close the intake valves 28 relatively early and accordingly significantly (for example approximately 60) before BDC, which causes an incomplete charging of the combustion chambers to occur. This is shown in FIG. 6 by means of the lift curve 74 (first valve lifting curve) provided for all intake valves 28 in full operation of the internal combustion engine. After a switchover into partial operation, for which purpose not only the cams 60, 62 associated with the gas exchange valves 28, 30 of the combustion chambers 22 to be deactivated are changed (each to a null cam), but also (at least some of) the cams 60, 62 associated with the gas exchange valves 28, 30 of the combustion chambers 22 that are to continue to be actively operated are changed, the intake valves 28 of these combustion chambers 22 that are to continue to be actively operated then no longer close relatively early, but instead in the vicinity of, and specifically a few degrees after, BDC with regard to a maximization of the volumetric efficiency, as is illustrated by means of the lift curve 76a (second valve lifting curve) shown in FIG. 6.

(23) FIG. 7 shows in summarized form the measures that are provided in order to realize a switchover of the internal combustion engine from a full operation to a partial operation in as torque-neutral a manner as possible, and consequently with no perceptible brief reduction in the drive power produced by the internal combustion engine (jerking of the drive).

(24) The diagram from FIG. 7 qualitatively shows the behavior, over the time t (horizontal axis), of various operating parameters of the internal combustion engine, specifically the closing time provided for the intake valves 28 of those combustion chambers 22 that are actively operated even in partial operation (curve 78), the closing time provided for the exhaust valves 30 of the same cylinders 16 (curve 80), the pressure in the intake manifold (curve 82), and the ignition angle (curve 84). The diagram is divided by a vertical line; its left-hand half shows the relevant operating parameters for full operation of the internal combustion engine, while the right-hand half shows the behavior of the operating parameters during an initial phase of partial operation. The location of the vertical line thus corresponds to the switchover time or the switchover process, which is carried out relatively rapidly, namely within one revolution of the camshaft 40, and takes effect within one revolution of the crankshaft 34.

(25) In the same short time period, the increase in volumetric efficiency also takes effect that is achieved by the switchover between the two cams 60, 62 that differ with regard to the valve lifting curves, and thus timing, they bring about, and by means of which the intake valves 28 of the combustion chambers 22 that are to continue to be actively operated can be actuated, whereas the effect of the increase in the pressure in the intake manifold 18 rises only relatively slowly to an intended level.

(26) This delayed effect of the increase in the pressure in the intake manifold 18 is offset by the rapidly acting increase in volumetric efficiency in that a lift curve provided with regard to a maximum possible volumetric efficiency is initially provided, by means of the (second) cam 62 provided for this purpose, for the intake valves 28 associated with the combustion chambers 22 that are to continue to be actively operated even in partial operation. However, this lift curve is moved further in the late direction immediately after the switchover by means of the internal combustion engine's phase shifter 54 associated with the intake camshaft 40. This takes place approximately until the pressure in the intake manifold 18 has reached the intended value (see lift curve 76b in FIG. 6).

(27) It can also be seen that the second valve lifting curve (lift curves 76a, 76b) brought about by the second cams 62 is wider than the first valve lifting curve (lift curve 74) brought about by the first cams 60; this serves to achieve an essentially identical opening time in comparison with the first valve lifting curve (lift curve 74) despite the delay of the closing time of the second valve lifting curve according to the lift curve 76a.

(28) FIG. 7 also shows that provision is made to set the ignition angle (see curve 84) for the combustion chambers 22 relatively late prior to the switchover in order to achieve a desired torque adjustment and, in particular, torque reduction (as a result of a diminished efficiency) in preparation for the switchover. Simultaneously with the switchover from the first operating state to the second operating state, the ignition angle, which was previously set relatively late, is abruptly adjusted in the early direction so that a maximization of not only the volumetric efficiency but also of the efficiency is achieved immediately upon the switchover, in each case with the goal of a switchover that is as torque-neutral as possible.

(29) Because the lift curve 76awhich is designed with respect to maximum volumetric efficiencyfor the intake valves 28 of the combustion chambers 22 that continue to be actively operated in partial operation would lead to a sharply increased tendency to knock in the absence of countermeasures, provision is made according to FIG. 7 (see curve 84) that the ignition angle is adjusted back a bit in the late direction after the switchover (less than was provided prior to the switchover) in order to counteract such an increase in the tendency to knock.

(30) It is additionally shown in FIG. 7 (see curve 80) that an adjustment in the late direction of the closure of the exhaust valves 30 associated with the combustion chambers 22 that continue to be actively operated in partial operation is accomplished by the phase shifter 54 associated with the exhaust camshaft 40 at the same time as the switchover from full operation to partial operation, by which means an adjustment of the valve overlaps of the intake valves 28 and the exhaust valves 30 that is as optimal as possible can be achieved. FIG. 6 also shows the corresponding lift curve 86 in this regard, such as is provided for the exhaust valves 30 in full operation before the switchover as well as the lift curve 88 such as is provided after an end of influencing by the phase shifter 54 in partial operation for the exhaust valves 30 that are then still actuated.

(31) Because a delay of the timing of the exhaust valves 30 of the combustion chambers 22 that continue to be actively operated in partial operation by means of the phase shifter 54 is provided in the exemplary embodiment, provision can be made that no switchability by means of the switchover device 58 is provided for these. With regard to the exhaust camshaft 40, the switchability for an actuation by means of two cams 60, 62 can accordingly be limited to the particular exhaust valves 30 that are no longer actuated in a partial operation of the internal combustion engine. Alternatively, however, two cams 60, 62 that have identical cam tracks can also be provided for the exhaust valves 30 that are also to be actuated in partial operation, so that the switchover for the actuation of the exhaust valves 30 associated with them remains without effect.

(32) The graph from FIG. 8 illustrates once more the advantage that can be achieved by the method according to the invention. Shown there for an exemplary full Miller cycle (solid line), on the one hand, and a partial Atkinson cycle (dashed line), on the other hand, are the ratios between the closing time SZ of the intake valves 28 and the intake manifold pressure p.sub.s, which in each case result in the attainment of a defined torque that should be produced by the combustion motor 10. It can be seen that the more distant from BDC the closing times SZ are, the higher the intake manifold pressure p.sub.s must be in each case.

(33) For a switchover from full operation to partial operation, provision can now be made that the combustion motor 10 is operated in a full Miller cycle immediately prior to the switchover, wherein an earliest possible closure of the intake valves 28 is provided by means of the phase shifter (see point A in FIG. 8). The intake manifold pressure p.sub.s required here is at a maximum when the torque to be achieved is taken into account. Through a changeover of the cams 60, 62 by which the intake valves 28 that are associated with the combustion chambers 22 that are also to be operated in partial operation, it is possible to briefly switch over to a partial operation in which the closing times SZ of these intake valves 28 are designed with regard to a volumetric efficiency that is as great as possible (see point B in FIG. 8). As a result of this maximized volumetric efficiency, the difference p.sub.s between the required intake manifold pressure p.sub.s at point B and that at point A is as small as possible, by which means a delay in the ignition timing initiated for torque adjustment prior to a switchover of the valve lifting curves can likewise be kept to a minimum as a result. This has a corresponding positive effect on the efficiency of the operation of the combustion motor 10.

(34) Provision is made according to the invention that the timing, and thus also the closing times SZ of the intake valves 28 considered here, are moved further in the late direction by means of the phase shifter 54 immediately following the changeover of the cams 60, 62, thus realizing a partial Atkinson cycle of the combustion motor 10. This is easily possible starting from the (end) position of the phase shifter 54 that the latter had adopted in the full Miller cycle prior to the switchover because an adjustment of the phase shifter 54 in the direction of the other end position of the phase shifter 54 starting from the previously set end position is provided for this purpose.

(35) After the switchover, as a result of the increasing delay of the closing times SZ of the intake valves 28 considered here, the volumetric efficiency that was initially maximized by the changeover of the cams 60, 62 is decreased (which is desired for avoiding knocking or for minimizing a knock-preventing delay of the ignition timing). This presupposes an increase in the intake manifold pressure p.sub.s simultaneous with the delay of the closing time SZ in order to keep constant the torque produced by the combustion motor 10. This is ensured by an increase in the intake manifold pressure p.sub.s that is accomplished in parallel with the delay by means of the measures already described.

(36) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.