Method and device for controlling an internal combustion engine

Abstract

Method for quickly restarting an internal combustion engine which is running down with a reduced amount of supplied air, in which, after a detected restart request, the amount of supplied air is increased again and, in an intake cylinder (ZYL1), which is in the intake stroke when the amount of supplied air is increased, an ignitable fuel / air mixture is generated by fuel injection and ignited in the intake cylinder (ZYL1) in order to generate combustion in the power stroke of the intake cylinder (ZYL1), characterized in that the amount of supplied air is increased as soon as a speed (n) of the internal combustion engine has fallen below a predeterminable speed threshold value (ns).

Description

State of the art

[0001] The invention relates to a method for quickly starting an internal combustion engine, in particular in so-called "change-of-mind situations" in which the driver, for example by releasing the accelerator pedal, performs actions that signal a start-stop device to switch off the engine, but the driver then signals, before or immediately after the internal combustion engine has come to a standstill, for example by pressing the accelerator pedal, that he expects the vehicle to accelerate.

[0002] In a further aspect, the invention relates to a computer program for carrying out the method according to the invention, an electronic storage medium on which this computer program is stored, and a control and / or regulating device which is programmed in such a way that it carries out the method according to the invention when required.

[0003] DE 103 01 191 A1 discloses a method for operating an internal combustion engine. During the engine's deceleration, a first cylinder is identified that comes to a standstill in its compression stroke or its power stroke. At a time shortly before the engine comes to a standstill, at which a compressing cylinder can no longer be brought over a compression peak, a second cylinder is selected, whose intake or exhaust valve is then open. The filling of this second cylinder is adjusted so that one of the cylinders comes to a standstill in a working phase approximately a first predetermined crank angle after a top dead point of ignition.

[0004] EP 2 322 784 A1 discloses a start-stop control device for gasoline engines. It stops the engine when a stop condition is met and restarts it when a restart condition is met. The device interrupts the ignition when the stop condition is met and resumes the fuel supply. If a restart condition is met before the engine has come to a complete standstill, the engine is restarted by resuming the ignition so that the fuel supplied after the stop condition is combusted.

[0005] EP 2 410 158 A1 discloses a start-stop control device for an internal combustion engine. If a restart request is generated during a fuel cutoff in idle-stop mode, an autonomous re-control is performed, immediately switching to synchronous injection after the first asynchronous fuel injection. This restarts the engine using fuel injection alone, without using a starter. This enables a faster restart compared to conventional systems and improves starter durability. Disclosure of the invention

[0006] The method according to the features of the independent claims has the advantage that the internal combustion engine can be restarted before it comes to a standstill, which considerably shortens the time required for restarting.

[0007] The invention is particularly advantageous when the method is implemented for the rapid restart of an internal combustion engine that is running down with a reduced air supply. If, after a detected restart request, the supplied air quantity is increased again, and an ignitable fuel / air mixture is generated by fuel injection in an intake cylinder that is in the intake stroke when the supplied air quantity is increased, and ignited in the intake cylinder to generate combustion during the intake cylinder's power stroke, this has the particular advantage of making the internal combustion engine restartable particularly quickly.

[0008] Reducing the amount of air supplied to the engine is typically done to increase comfort during engine rundown, i.e., when the engine speed is reduced after the ignition is switched off. This reduction can be achieved, for example, by closing a throttle valve, but other means of controlling the air volume are also conceivable, such as variable valve timing.

[0009] Increasing the supplied air volume as soon as the engine speed has fallen below a predefined speed threshold has the advantage that such a measure allows the engine's coasting behavior to be particularly well controlled. This means that if there is a restart request, for example due to the actuation of the accelerator pedal, the engine can be restarted in a particularly controlled manner. If, however, there is no restart request, this increase in the air volume can control the coasting behavior in such a way that a particularly rapid restart is possible at a later time, for example by the engine coming to a standstill in a controlled shut-off position, but also because the engine comes to a standstill particularly quickly.

[0010] If an ignitable fuel / air mixture is generated by fuel injection in an exhaust cylinder, which is the next cylinder to enter its intake stroke after the intake cylinder, this takes advantage of the fact that the second cylinder after the intake cylinder, which enters its power stroke after the intake cylinder, is now prepared for ignition, allowing a further increase in the engine's speed if necessary. This leads to increased flexibility with regard to the further progress of the process.

[0011] When the amount of air supplied is increased, the throttle valve (or any other means for metering the amount of air) is opened to an opening crankshaft angle that is a few degrees crankshaft angle before dead center, at which the intake cylinder transitions from the intake stroke to the compression stroke. If this opening crankshaft angle is earlier, or if the throttle valve or other means for metering the amount of air is wider open, a larger amount of air is supplied to the intake cylinder than if the opening crankshaft angle were later, i.e. closer to the said dead center, at which the intake cylinder transitions to its compression stroke. It is particularly advantageous if the opening crankshaft angle is selected so that the combustion generated in the intake cylinder is powerful enough to push the exhaust cylinder into its power stroke.The exhaust cylinder has been supplied with a further increased amount of air during its intake stroke compared to the intake cylinder, so that the spring forces during its compression in the compression stroke are relatively large.

[0012] Alternatively or additionally, together with the combustion in the intake cylinder, another torque source can generate a torque that is large enough to push the exhaust cylinder (CYL2) into its power stroke.

[0013] For example, an electric machine can act as an additional torque source, generating enough torque to push the exhaust cylinder into its power stroke. This can be achieved, for example, by a starter that is capable of engaging at the engine's current speed. A permanently engaged starter or starter-generator, for example a belt-driven one, is particularly suitable. Assistance from an electric machine in a hybrid drivetrain is also conceivable, for example if the torque of the electric machine can be switched on via a planetary gear, or if, in an axle hybrid, a second axle of a car whose first axle is driven by the engine is driven. In conjunction with sufficiently large combustion in the intake cylinder, additional torque from an electric machine can increase the reliability of the process.

[0014] Alternatively or additionally, an additional clutch, which allows the crankshaft to be connected and disconnected from the vehicle's wheels, can be used as an additional torque source. In this case, the open clutch is closed to transfer torque from the kinetic energy of the rolling vehicle to the crankshaft. This type of clutch start allows a starter motor in the vehicle to be designed for fewer starts over its service life, resulting in a cost advantage for the overall system.

[0015] In a further advantageous embodiment, a hydraulic pressure accumulator can be used as an additional torque source. Activating torque generated by a hydraulic pressure accumulator has the particular advantage of combining the benefits of using a clutch start with the advantage that such torque support is also possible when the vehicle is stationary.

[0016] In further particularly advantageous embodiments, the magnitude of the torque generated by the additional torque source is selected depending on the engine speed at a final dead center. Final dead center refers to the dead center at which the exhaust cylinder enters its compression stroke. Experiments have shown that the engine speed at final dead center can be used to predict whether a direct start of the engine will be successful without the assistance of torque generated by the additional torque source.

[0017] The start is particularly reliable when the additional torque source generates a torque when the speed of the internal combustion engine at the final dead center is less than a predeterminable additional torque speed threshold.

[0018] If, on the other hand, the additional torque source is controlled in such a way that it does not generate any torque (i.e., does not couple to the crankshaft) if the speed of the internal combustion engine at the final dead center is not less than a predeterminable additional torque speed threshold, then, with torque support from a starter, the starter can be designed for as few starts as possible over its service life.

[0019] It is particularly advantageous if, in a further advantageous embodiment, these two aforementioned embodiments are combined, i.e. if the additional torque source generates a torque precisely when the rotational speed of the internal combustion engine at the final dead center is less than a predeterminable additional torque speed threshold.

[0020] It is particularly advantageous if the ignitable fuel / air mixture generated in the exhaust cylinder is ignited to generate combustion during the exhaust cylinder's power stroke. Since the exhaust cylinder, by definition, immediately follows the intake cylinder in the firing sequence, this enables a particularly reliable restart of the internal combustion engine. Description of the embodiments

[0021] The figures illustrate particularly advantageous embodiments of the method according to the invention. Further embodiments are possible.

[0022] They show: Fig. 1 shows the temporal course of parameters when carrying out the method according to the invention; Fig. 2 a flow chart of an advantageous embodiment of the method according to the invention.

[0023] Fig. 1 shows the temporal sequence of the method according to the invention. In Fig. Figure 1a shows the stroke sequence of the intake cylinder CYL1 and the exhaust cylinder CYL2. The crankshaft angle KW is shown on the abscissa. Also shown are the first to fifth dead centers T1, T2, T3, T4, and T5. Dead centers typically indicate the points at which a cylinder of the internal combustion engine experiences maximum compression. The example shows a four-cylinder internal combustion engine, but other multi-cylinder internal combustion engines are also conceivable, provided at least three cylinders are present.

[0024] At first dead center T1, intake cylinder CYL1 enters its exhaust stroke, at second dead center T2 its intake stroke, at third dead center T3 its compression stroke, and at fourth dead center T4 its expansion stroke. Similarly, exhaust cylinder CYL2, shifted by one expansion stroke, enters its expansion stroke at first dead center T1, at second dead center T2 its exhaust stroke, at third dead center T3 its intake stroke, and at fourth dead center T4 its compression stroke.

[0025] Fig. Figure 1b shows the temporal progression of a rotational speed n, for example, the crankshaft rotational speed, during the deceleration process of the internal combustion engine. Following a stop request by the driver, which is recognized by a control and / or regulating device on which the method according to the invention can also run, for example, because the accelerator pedal is deactivated, Fig. 1 not shown - injection and ignition are deactivated, and the throttle valve is closed. The amount of air supplied to the cylinders, which enter the intake stroke during deceleration with the throttle valve closed, is therefore extremely reduced. The engine speed n decreases over time as shown, whereby at times t1, t2, t3 and t4, which correspond to the dead centers T1, T2, T3 and T4, a local minimum is observed followed by a slight increase in the engine speed n, which results from a springback effect at the maximum compression of the engine. It should be noted that due to the variable engine speed n, the time axis t and the crankshaft angle KW from Fig. 1b and Fig. 1a are not both linear. For example, the time axis is not equidistant.

[0026] Between the first time t1 and the second time t2, the rotational speed n of the internal combustion engine falls below a predetermined threshold value ns. At a suitable time, for example the next dead center, in this case the second dead center T2, the control and / or regulating device detects that the rotational speed n has fallen below the rotational speed threshold value ns and opens the throttle valve to a suitable crankshaft angle KWauf. This is Fig. 1c.

[0027] The position DK of the throttle valve changes from a closed position DK0 at the beginning of the process at a time tauf that corresponds to the crankshaft angle KWauf, to an open state DK1, which can also be a partially open state. A quantity of air now flows into the intake cylinder ZYL1, which is in the intake stroke at time tauf or at the crankshaft angle KWauf. At a change-of-mind time tCOM, the control and / or regulating device detects that the driver wishes the internal combustion engine to be restarted, for example by pressing the accelerator pedal. For example, fuel is now injected directly into the intake cylinder ZYL1, which is in the compression stroke, via a direct injection valve, thus creating an ignitable fuel / air mixture.

[0028] The required fuel quantity can be determined from the crankshaft opening angle KWauf using parameters such as maps obtained in test bench experiments. This is possible because this determines the amount of air present in the intake cylinder CYL1. At an ignition point tIGN that lies around fourth dead center T4, the fuel / air mixture in the intake cylinder CYL1 is ignited. This combustion during the power stroke of the intake cylinder CYL1 accelerates the rotation of the internal combustion engine again. The ignition point tIGN can also be selected before fourth dead center T4, still during the compression stroke of the intake cylinder CYL1, in the usual way. Ignition shortly after fourth dead center T4 is also possible.

[0029] This ignition in the intake cylinder CYL1 compresses the air volume in the exhaust cylinder CYL2, which it has drawn in during the intake stroke between third dead center T3 and fourth dead center T4. This air spring is very large. It is so large that if no ignition were to occur in the intake cylinder CYL1, the exhaust cylinder CYL2 would be completely decelerated by the gas spring during the compression stroke, causing the internal combustion engine to come to a standstill. This is Fig. 1b is shown by the dashed line. It is therefore important to select the fuel / air mixture so that combustion in the intake cylinder (CYL1) is sufficiently intense that the exhaust cylinder (CYL2) enters its power stroke.

[0030] For internal combustion engines with port fuel injection, it is important to note that injection must occur early enough so that the intake cylinder CYL1 can already draw in a fuel / air mixture during the intake stroke. This requires that the restart request be detected at a much earlier point in time, namely before the opening time tauf.

[0031] Fig. Figure 2 illustrates the flow of the method. At a first time 1000, as described, a stop request from the driver is detected, so that the control and / or regulating device detects that the internal combustion engine can be switched off. In this case, step 1010 follows, in which the ignition and injection are switched off, and the throttle valve is closed. Next, in step 1020, a check is made to determine whether the engine speed n has fallen below the speed threshold value ns. If this is the case, step 1040 follows; if not, step 1030 follows. In step 1030, a check is made to determine whether a restart request from the driver has been made. If such a restart request exists, step 1040 follows; if it is not, step 1020 follows.

[0032] In step 1040, the opening crankshaft angle KWauf is determined. If the program branches from step 1020 to step 1040, the opening crankshaft angle KWauf is determined such that the exhaust cylinder CYL2 comes to a standstill during its compression stroke, provided no further ignition is performed in a cylinder of the internal combustion engine. For example, the required air volume flowing into the intake cylinder CYL1 can be determined using characteristic maps, because the ratio of the gas springs of the intake cylinder CYL1, which is in the power stroke between fourth dead center T4 and fifth dead center T5, and the exhaust cylinder CYL2, which is in the compression stroke, determines the torque acting on the crankshaft of the internal combustion engine.

[0033] If, however, the process branches from step 1030 to step 1040, the opening crankshaft angle KWauf can also be selected such that combustion in the power stroke of the intake cylinder CYL1 is possible, since it is now already clear that the internal combustion engine should not come to a standstill. However, it is also possible to configure the method such that, even if a restart request is detected, the system waits until the engine speed n has fallen below the engine speed threshold value ns, and the opening crankshaft angle KWauf can be selected such that it is either the same as in the case of an undetected restart request (this makes system calibration particularly easy), or it can be selected such that combustion in the power stroke in the intake cylinder CYL1 is particularly powerful.

[0034] With intake manifold injection, fuel can already be injected into the intake manifold of the internal combustion engine, creating an ignitable fuel / air mixture in the intake cylinder CYL1. For example, the fuel quantity is metered from characteristic maps to create a stoichiometric mixture. Step 1050 then queries whether a restart request is present. If so, step 1070 follows; if not, step 1060 follows. Step 1060 checks whether a restart is still possible using the method according to the invention. In an internal combustion engine with intake manifold injection, once third dead center T3 has been exceeded, it is no longer possible to generate an ignitable fuel / air mixture in the intake stroke of the intake cylinder CYL1.

[0035] In internal combustion engines with direct injection, tests have shown that it is still possible to inject fuel in such a way that an ignitable fuel / air mixture is created up to a crankshaft angle of approximately 25° before fourth dead center T4. Tests have also shown that it is still possible to ignite this fuel / air mixture up to 30° after fourth dead center T4. In a direct-injection internal combustion engine, for example, it is still possible to generate an ignitable fuel / air mixture up to an angle of 25° before fourth dead center T4. However, this threshold can be recalculated for each engine through testing and adjusted accordingly. If it is still possible to generate an ignitable fuel / air mixture, the process branches to step 1080.

[0036] In step 1070, analogous to step 1060, a check is performed again to determine whether a restart is possible. If this is the case, step 1100 follows, or in an alternative embodiment, step 1090, or in another alternative embodiment, step 1110. If this is not the case, step 1080 follows.

[0037] In step 1080, no ignition is initiated, but the engine speed continues to drop to zero. The engine then oscillates. If a restart request is detected, a new start can be initiated from this stationary or nearly stationary engine, for example, by engaging a starter motor at engine speed n close to zero, and accelerating the engine.

[0038] In the optional step 1100, at the fourth dead center T4, which is also the final dead center T4, it is checked whether the speed n of the internal combustion engine is less than the speed Fig. 1 is the predeterminable additional torque speed threshold nu, also shown. If this is not the case, i.e., the engine speed n is so high that a direct start will be successful without additional torque support, step 1090 follows; otherwise, step 1100 follows.

[0039] In step 1090, however, because no fuel was injected in step 1040, fuel is injected either into the intake manifold of the internal combustion engine using intake manifold injection or directly into intake cylinder CYL1 using direct injection. Fuel can also be injected into exhaust cylinder CYL2. At ignition time tIGN, the fuel / air mixture is ignited during the power stroke of intake cylinder CYL1, and the engine speed n is accelerated. If fuel was injected into exhaust cylinder CYL2, then as soon as exhaust cylinder CYL2 has transitioned to its power stroke, or shortly before, this cylinder can also be ignited, and the starting process can continue in the known manner.

[0040] In step 1110, the same steps as in step 1090 are performed. In addition, additional torque is transferred to the crankshaft from another torque source to overcome the compression stroke of exhaust cylinder CYL2. This additional torque can be applied, for example, by a starting engine engaged, by closing a clutch, which transfers torque to the crankshaft via the vehicle's rotating wheels, or by a hydraulic accumulator.

[0041] Following step 1090 or step 1110, the starting process of the internal combustion engine is continued, for example, in a manner known per se.

Claims

[1] Method for the rapid restart of an internal combustion engine running down with a reduced amount of supplied air, in which, after a detected restart request, the amount of supplied air is increased again and in an intake cylinder (ZYL1), which is in the intake stroke when the amount of supplied air is increased, an ignitable fuel / air mixture is generated by fuel injection and is ignited in the intake cylinder (ZYL1) in order to generate combustion in the power stroke of the intake cylinder (ZYL1), characterized by that the amount of air supplied is increased as soon as a speed (n) of the internal combustion engine has fallen below a predeterminable speed threshold value (ns). [2] Method according to claim 1, characterized by that in an exhaust cylinder (CYL2), which is the next cylinder to enter the intake stroke after the intake cylinder (CYL1), an ignitable fuel / air mixture is generated by fuel injection. [3] Method according to claim 2, characterized by that an opening crankshaft angle (KWauf), at which the supplied air quantity is increased again, is selected so that the combustion generated in the intake cylinder (ZYL1) is strong enough to push the exhaust cylinder (ZYL2) into its working stroke. [4] Method according to claim 2 or 3, characterized by that together with the combustion in the intake cylinder (CYL1), another torque source generates a torque that is large enough to push the exhaust cylinder (CYL2) into its power stroke. [5] Method according to claim 4, characterized by that the magnitude of the torque generated by the additional torque source is selected as a function of a speed (n) of the internal combustion engine at the final dead center (T4) at which the exhaust cylinder enters its compression stroke. [6] Method according to claim 5, characterized bythat the additional torque source generates a torque when the speed (n) of the internal combustion engine at the final dead center (T4) is less than a predeterminable additional torque speed threshold (nu). [7] Method according to claim 5, characterized by that the additional torque source does not generate any torque if the speed (n) of the internal combustion engine at the final dead center (T4) is not less than a predeterminable additional torque speed threshold (nu). [8] Method according to claim 5, characterized by that the additional torque source generates a torque precisely when the speed (n) of the internal combustion engine at the final dead center (T4) is less than a predeterminable additional torque speed threshold (nu). [9] Method according to one of claims 2 to 8, characterized by that is ignited in the exhaust cylinder (CYL2) in order to generate combustion in the power stroke of the exhaust cylinder (CYL2). [10] Computer program, characterized bythat it is programmed to carry out all the steps of a method according to one of claims 1 to 9. [11] Electrical storage medium for a control and / or regulating device of an internal combustion engine, characterized by that a computer program for carrying out all steps of a method according to one of claims 1 to 9 is stored thereon. [12] Control and / or regulating device of an internal combustion engine, characterized by that it is programmed to carry out all the steps of a method according to one of claims 1 to 9.

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