1. Field of the Invention
The present invention relates to a method and a device for controlling the stopping behavior of an internal combustion engine.
2. Description of the Related Art
A method for stopping an internal combustion engine is known from published German patent application document DE 10 2011 082 198 A1, in which the volume of air supplied to the internal combustion engine via an air metering device is reduced after a stop request has been ascertained, the volume of air supplied to the internal combustion engine via the air metering device being increased again when a detected speed of the internal combustion engine falls below a predefinable threshold, an intake cylinder to which the volume of air is supplied no longer entering a power stroke after the volume of air is increased.
According to a first specific embodiment of the present invention, it is provided that in a method for controlling the stopping behavior of an internal combustion engine in which, after a stop request, an air metering device, in particular a throttle flap or a variable valve adjustment, initially reduces the volume of air supplied to the internal combustion engine during the stopping procedure, and increases this volume of air again at an opening crankshaft angle, the opening crankshaft angle being oriented to an undercut crankshaft angle at which the speed of the internal combustion engine during the stop falls below a predefinable speed threshold value, and the time characteristic of the speed of the internal combustion engine being influenced after the stop request and before the opening crankshaft angle in such a way that the internal combustion engine comes to a halt in a predefinable target crankshaft angle range. Compared to the related art, this has the advantage that the stopping behavior of the internal combustion engine may be particularly well controlled. In particular, it is possible to determine which cylinder of the internal combustion engine is in the compression stroke when the stop is complete, that is, when the internal combustion engine has transitioned to a halt.
The speed profile in this case is influenced by an auxiliary unit, which directly or indirectly applies a torque to the crankshaft which brakes or accelerates the rotational movement of the crankshaft.
In one advantageous refinement, the speed profile of the internal combustion engine is influenced in such a way that a speed gradient is set to a predefinable target speed gradient as the internal combustion engine is stopping. The speed gradient is understood herein to mean the change of speed of the internal combustion engine per unit of time during a characteristic interval, for example, between two (for example, but not necessarily) successive top dead center positions of cylinders of the internal combustion engine.
In one advantageous refinement, the speed gradient is set by changing the actuation of a high pressure injection pump coupled to the crankshaft after the stop request, particularly preferably during the stopping of the internal combustion engine. Actuating the high pressure injection pump changes the torque transmitted to the crankshaft, and this allows the speed gradient to be set in a simple manner.
The use of the high pressure injection pump is particularly advantageous because the piston of the high pressure injection pump carries out an up and down movement and thus carries out intake strokes and compression strokes in a known manner. In the intake stroke, the piston moves downward and fuel is drawn in from a line on the low pressure side. In the compression stroke, the piston moves upward and fuel is conveyed into a high pressure injection pump which consumes energy and therefore slows down the rotation of the crankshaft. This movement of the piston occurs in a known manner via a cam on the camshaft. The rotational movement of the camshaft is coupled in a known manner to the rotational movement of the crankshaft. At a point in time of swing back of the crankshaft, the direction of rotation of the camshaft is also reversed. If at this point in time the piston of the high pressure pump is in the intake stroke, then the reversal of the direction of rotation causes the high pressure pump to enter a compression stroke, such that rotation energy is destroyed (or restored in the high pressure rail). This makes it possible for rotation energy to be destroyed at any time near the reversal point of the direction of rotation, which effectively slows down the rotational movement of the internal combustion engine.
In another advantageous refinement it is possible, as an alternative to or in addition to actuating the high pressure injection pump, to actuate an oil pump coupled to the crankshaft and/or a cooling water pump in order in this way to alter the speed gradient during the stop.
In another advantageous refinement, it is possible, as an alternative to or in addition to actuating the high pressure injection pump, to change an actuation of an electric machine coupled to the crankshaft after the stop request, in particular during the stopping of the internal combustion engine. Actuation of the electric machine may change the torque transmitted to the crankshaft, thus allowing the speed gradient to be adjusted in a particularly simple manner. The electric machine in this case may be a generator, or an electric motor, or another electric machine, for example, a belt-driven starter generator.
In another advantageous specific embodiment, it is alternatively or additionally possible to change the actuation of a compressor in an air conditioning unit coupled to the crankshaft after the stop request, in particular during the stopping of the internal combustion engine. Here, too, it is possible to vary, in a simple manner, the torque transmitted to the crankshaft, and so set the speed gradient.
In another advantageous specific embodiment of the present invention, it may be provided that the time characteristic of the speed of the internal combustion engine is influenced in such a way that the speed of the internal combustion engine, when the top dead center position following the undercut crankshaft angle is reached, i.e., at the crankshaft angle at which the next piston of the internal combustion engine passes through its top dead center position after the undercut crankshaft angle, accepts a predefinable target speed value. By controlling the speed at this crankshaft angle, it is possible to control the stopping behavior of the internal combustion engine in a particularly simple manner.
In another advantageous specific embodiment of the present invention, it is provided that a cylinder is ascertained, in which a final fuel-air mixture is to be ignited before the internal combustion engine begins to stop, and after the stop request and before the onset of the stop following ignition of the fuel-air mixture in this cylinder, the ignition is switched off. This means that the cylinder is ascertained, after the ignition of which no further ignition takes place in any cylinder of the internal combustion engine, thus initiating the stopping of the internal combustion engine. By specifically selecting this cylinder in which the final ignition is to occur, it is possible to determine in a particularly simple manner the cylinder which is in the compression stroke at the end of the stopping of the internal combustion engine.
According to another aspect of the present invention, the time characteristic of the speed is influenced as a function of an inducted volume of air of a cylinder to which the increased volume of air is supplied. In particular, the time characteristic of the speed may be influenced in such a way that the speed is reduced when the inducted volume of air exceeds a definable air volume threshold value. The inducted volume of air may, for example, be ascertained by a predictive method, for example, via an engine characteristics map as a function of the speed existing at the undercut crankshaft angle.
It has been found that a volume of air that has been increased too much results in part in excessive swing back, and therefore in a jerking perceived by the driver and sensed as uncomfortable. Such jerking may be effectively suppressed with the aid of the aforementioned measures.
In another aspect, the present invention includes a computer program which is programmed in such a way that it carries out all steps of a method according to the present invention when it is executed.
In another aspect, the present invention includes an electric storage medium for a control device and/or regulating device of the internal combustion engine, on which the computer program is stored.
In another aspect, the present invention includes the control device and/or regulating device of the internal combustion engine, which is programmed in such a way, for example, with the computer program, that it is able to carry out all steps of a method according to the present invention.
Air is inducted in a known manner through an intake pipe 80 and expelled through an exhaust pipe 90. In the exemplary embodiment shown in
Crankshaft 50 is connected via a mechanical coupling 210 to an electric machine 200. Electric machine 200 may, for example, be a generator or, for example, a starter generator. It is also possible for electric machine 200 to be a conventional starter and for mechanical coupling 210 to include a ring gear and a pinion used to mesh the starter. A crankshaft angle sensor 220 may be provided in order to detect the angular position of crankshaft 50, and to communicate it, for example, to control unit 70. However, it is also possible, for example, for the angular position to be ascertained mathematically, without a crankshaft angle sensor 220, for example.
A high pressure pump which conveys fuel to injection valve 150, for example, via an injection rail, may be provided in particular when injection valve 150 injects directly into combustion chamber 20. This high pressure injection pump is connected to crankshaft 50.
A compressor from an air conditioning unit may also be provided, which is coupled to crankshaft 50. The high pressure injection pump and/or the compressor in the air conditioning unit may be actuated, for example, by control unit 70. It is also possible for an oil pump and/or a cooling water pump to be coupled to crankshaft 50.
a) represents the stroke sequence of a first cylinder ZYL1 and of a second cylinder ZYL2 of internal combustion engine 10 as a function of crankshaft angle KW. At a first dead center position T1, first cylinder ZYL1 enters its exhaust stroke and second cylinder ZYL2 enters its power stroke. At a second dead center position T2, first cylinder ZYL1 enters its intake stroke and second cylinder ZYL2 enters its exhaust stroke. At a third dead center position T3, first cylinder ZYL1 enters its compression stroke and second cylinder ZYL2 enters its intake stroke. At a fourth dead center position T4, first cylinder ZYL1 enters its power stroke and second cylinder ZYL2 enters its compression stroke.
b) shows the profile of speed n of the internal combustion engine over time t. The time axis of
At the beginning of the stop, throttle flap 100 is at least partly closed in order to make the stopping behavior of internal combustion engine 10 more comfortable.
At an undercut crankshaft angle KWlow, speed n of the internal combustion engine remains below a predefinable speed threshold value ns. At characteristic points in time, for example, at each dead center, it is checked whether speed n of the internal combustion engine has fallen below the predefinable speed threshold value ns. In the exemplary embodiment shown in
The cylinder which is in its compression stroke when internal combustion engine 10 has completely stopped (this is second cylinder ZYL2 in the example shown in
The heavier the crankshaft 50 is (including the dual-mass flywheel), the longer it takes for the internal combustion engine to stop, because the speed gradient is a function of the energy losses resulting from friction and of the spin of the internal combustion engine. For this reason, stronger friction results in a shorter stop, and less friction in a longer stop. While the spin of the internal combustion engine is essentially constant, the friction of internal combustion engine 10 may vary with time, and depends strongly on the temperature of internal combustion engine 10. In typical applications, in which internal combustion engine 10 is stopped and restarted, internal combustion engine 10 is warm, and friction may therefore be considered as constant over time. Thus, the speed gradient of a warm internal combustion engine does not change much over time. It is therefore possible to predict the cylinder which is in its compression stroke when internal combustion engine 10 has come to a halt, for example, with the aid of engine characteristics maps or using a mathematical function based on speed n of internal combustion engine 10 at the point in time at which the fuel injection was switched off, of the cylinder in which a fuel-air mixture was last ignited, and of the speed gradient.
This is illustrated in
There are multiple options for influencing the speed gradient: for example, it is possible to increase the speed gradient by activating the high pressure injection pump, for example, at the onset of the stop of internal combustion engine 10. It is possible, for example, to maximize the pressure in an injection rail. This increases the friction on the camshaft and, because the camshaft is coupled to the crankshaft, also indirectly the friction on the crankshaft.
An additional or alternative option for increasing the speed gradient lies in the targeted actuation of electric machine 200. A further or additional option of increasing the speed gradient lies in the targeted actuation of the compressor in the air conditioning unit.
In such a case, a provision may be made to predefine the required speed gradient depending on the cylinder which last fired, and then set the speed gradient in accordance with one or more of the above-mentioned options. It is understood that the method is not limited to a particular cylinder being in its compression stroke when the internal combustion engine comes to a halt. It is also possible, for example, to specify which cylinder is in its intake stroke when internal combustion engine 10 comes to a halt.
According to a first strategy S1, the stopping of internal combustion engine 10 begins after the firing of the fourth cylinder and the internal combustion engine stops with the third cylinder in the compression stroke. According to a second strategy S2, speed n of internal combustion engine 10 changes before the onset of the stop, for example, by actuating electric machine 200. According to second strategy S2, the speed of internal combustion engine 10 is reduced, thereby achieving that by correctly choosing speed n at the onset of the stop, the second cylinder, rather than the third cylinder, is in the compression stroke when internal combustion engine 10 comes to a halt. Alternatively, it is also possible according to a third strategy S3 to accelerate internal combustion engine 10 before the onset of the stop.
It is understood that the aforementioned methods of varying the speed gradient, speed n of internal combustion engine 10 at the onset of the stop and the cylinder which last fired before the onset of the stop, may be combined with one another.
In a particularly advantageous specific embodiment of the present invention, internal combustion engine 10 is switched off in such a way that the gaps in the speed sensor wheel that are important for synchronizing internal combustion engine 10 are just in front of crankshaft angle sensor 220 when the internal combustion engine has come to a halt, so that the crankshaft angle of internal combustion engine 10 may be quickly detected upon a restart of internal combustion engine 10, which accelerates synchronization and therefore the entire starting process.
If undercut speed nschw_u is not specifically predefined, it is clear from
According to another specific embodiment of the present invention, undercut speed nschw_u is determined such that stopping crankshaft angle KWstop lies as certainly as possible in the predefinable target crankshaft angle range. For this purpose, it may be provided that undercut speed nschw_u is predicted during the stopping of internal combustion engine 10. This may be achieved, for example, by a mathematical model or by a characteristic curve. An example of such a characteristic curve is shown in
As an additional or supplemental measure, it may be provided according to a ninth strategy S9 to change the speed gradient during the stopping of the internal combustion engine, in the example shown here, briefly increasing it, then reducing it again so that undercut speed nschw_u lies within the target range. According to a tenth strategy S10, it may also be provided to change the speed gradient so that it assumes an altered value during the entire stop. It is understood that this tenth strategy S10 may also be arbitrarily combined with the above mentioned strategies or with some of them.
The present invention is not limited to the exemplary embodiments. As previously mentioned, the present invention may be used in internal combustion engines having any number of cylinders. The method according to the present invention may be carried out in control unit 70 or in an additional control unit. It is not essential for the metering of the volume of air supplied to the internal combustion engine to be regulated by throttle flap 100. For example, a corresponding effect may also be achieved with a variable valve adjustment.
The means for changing the speed gradient are not limited to the means shown above. In principle, all components may be considered with which a torque may be applied to crankshaft 50, for example, even an oil pump and/or a cooling water pump, and/or injection and/or combustion of fuel in one or more cylinders.
Number | Date | Country | Kind |
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10 2013 213 784.2 | Jul 2013 | DE | national |
10 2013 217 433.0 | Sep 2013 | DE | national |
10 2014 204 086.8 | Mar 2014 | DE | national |