Method and control device for operating an internal combustion engine

Abstract

The invention relates to a method for operating an internal combustion engine (1) having a crankshaft, which can be driven by a piston of a cylinder (4), a suction pipe, through which the cylinder (4) can be supplied with fresh air, an intake valve (5), via which fresh air can flow from the suction pipe into the cylinder (4) when the intake valve is open, a variable valve drive, by means of which the opening duration or relative opening time of the intake valve (5) is variable with respect to the crankshaft position, wherein, during the start-up of the internal combustion engine (1), in the case of a difference between the suction pipe pressure and a suction pipe desired pressure (p s ), a filling pilot control of the cylinder (4) is carried out by the variable valve drive by reducing the fresh air supply compared to the fresh air supply at the suction pipe desired pressure (p s ). The invention also relates to a control device (12) for an internal combustion engine (1), which enables low-emission operation.

Description

Technical Field

[0001] The present invention relates to a method for operating an internal combustion engine, the internal combustion engine comprising: a crankshaft that can be driven by a piston of a cylinder; an intake manifold through which fresh air can be supplied to the cylinder; an intake valve through which fresh air can flow from the intake manifold into the cylinder when the intake valve is open; and a variable valve actuation device by means of which the opening duration or relative opening time of the intake valve is variable relative to the crankshaft position. Background Technology

[0002] Modern internal combustion engines in motor vehicles, also known below as combustion engines, are increasingly not operated continuously, but rather towed in certain operational phases. Combustion engines in motor vehicles are typically connected to the vehicle's wheels via a transmission system and a vehicle clutch. During deceleration, the combustion engine is towed by the vehicle's inertia through a closed transmission system, where the vehicle decelerates due to the resistance torque applied by the combustion engine. This operating mode of the combustion engine is called over-range operation, in which the combustion engine is towed without injecting fuel into the cylinders.

[0003] The drag torque of a combustion engine is primarily caused by friction and load exchange losses. However, especially in hybrid drive systems, it may be desirable to minimize the drag torque of the combustion engine as much as possible to utilize the torque provided via the drivetrain and generated by the moment of inertia for restoring electrical energy when the drivetrain is shut off. In such cases, it is desirable to have the drag torque of the unignited combustion engine as low as possible.

[0004] It is known from the prior art to use variable valve actuators to influence drag torque. In this regard, DE 19932 665 A1 proposes a method for controlling the gas exchange valve of a combustion engine by means of variable valve control, wherein the intake valve is controlled in a variable manner during over-limit operation.

[0005] However, relying solely on minimal resistance torque leads to undesirable side effects. For example, if the throttle valve opens during over-range operation, losses still exist due to the flow of fresh air through the cylinders—namely, load exchange losses and compression losses—even as the combustion engine is slowly driven. The cold, oxygen-enriched fresh air supplied through the combustion chamber lowers the temperature in the exhaust system and deviates it from the optimal temperature window of the exhaust aftertreatment system. In the case of a three-way catalytic converter, oxygen saturation is also critical because once the catalytic converter switches from over-range operation to combustion engine operation, oxygen saturation must be compensated for by temporarily intensified engine operation. Simultaneously, the efficiency of the catalytic converter decreases due to the lower temperature, and the enrichment after switching to drive mode leads to increased fuel consumption and thus even more emissions. Therefore, to operate the catalytic converter within its optimal λ (lambda) window, excessive oxygen must be avoided. If the combustion engine is designed as a gasoline engine with a particulate filter, oxygen can lead to uncontrolled and undesirable heat buildup in the gasoline engine. This can lead to thermal overload, which can damage not only the gasoline particulate filter itself, but also other components.

[0006] Closing the throttle valve can also be problematic. If a critical negative pressure forms in the combustion chamber, air-fuel volume flow may occur within the combustion chamber due to the negative pressure gradient in the crankcase. When combustion resumes, emissions increase and fuel consumption in the combustion engine increases.

[0007] Air bleed-out during engine over-limit operation can be prevented using a variable valve actuation system. This can be, for example, a combination of disabling all valve lift, fully variable intake lift control, or exhaust valve disabling with extended intake phase regulation. Such systems are known from DE 10 2016 216 116 A1, DE 10 2008 036 635 A1, DE 10 2015 107539 A1, DE 10 2013 202 196 A1, DE 10 2017 011 301 B3, DE 199 52 037 A1, or WO 2013 / 101 282 A1. DE 10 2006 031 572 B4 discloses a general method.

[0008] All the concepts that lead to effective zero mass flow during the over-limit operation phase share the common characteristic that the intake manifold pressure between the throttle valve and the intake valve continues to increase during the over-limit operation phase until the pressure is completely equal to the ambient atmospheric pressure. Due to the effective zero mass flow through the throttle valve, the throttle valve loses its throttling effect and cannot be used for fill control during the first duty cycle immediately following engine restart.

[0009] If the engine is still restarted, this results in an increased filling of the cylinders with fresh air during the first working cycle. The combination of high fresh air quality and combustion with λ=1 immediately leads to high torque output in the combustion engine after restarting. This state continues until the intake manifold volume is "emptied" and the throttle valve can once again ensure filling control. This method is proposed in DE 10 2016 111 505 A1, which provides a switching control device that first restores negative pressure in the intake manifold between over-limit operation and ignition operation so that it can subsequently switch to normal ignition operation. It is necessary that the phase determined by the switching control device is continuous, meaning that this phase also occurs when sufficient negative pressure is present. Maintaining this phase is complex to implement and can be considered as a delayed restart of the internal combustion engine.

[0010] One possible solution to avoid torque peaks is ignition timing intervention, which is therefore an active deterioration in combustion efficiency. This measure results in additional fuel consumption. Summary of the Invention

[0011] The object of this invention is to resolve the aforementioned conflicting objectives and to provide a method for operating an internal combustion engine that enables switching between ignition operation and over-limit operation, wherein emissions are low and the method simultaneously allows for the fastest and easiest exit from over-limit operation, particularly when the desired drive torque is low and the engine will restart under low load requirements. Furthermore, the object of this invention is to provide a control device for an internal combustion engine capable of achieving low-emission operation.

[0012] This objective is achieved through a method and control device for operating a combustion engine.

[0013] The method according to the invention relates to a method for starting, preferably restarting, an internal combustion engine after an over-limit operation phase. The method according to the invention is described below using a variable valve drive device with a camshaft adjuster. For this purpose, the internal combustion engine is provided with an intake camshaft and an electromechanically adjustable camshaft adjuster, for example, for intake valves, and an exhaust camshaft and an electromechanically adjustable camshaft adjuster for actuating exhaust valves. The control time and / or valve lift can also be variable electrohydraulically or otherwise.

[0014] During over-limit operation, the air mass flow is reduced via a variable valve actuation device to avoid the aforementioned drawbacks. This is achieved by adjusting the control timing of the camshaft adjuster to a value that is not useful for gasoline engine ignition operation but represents the phase optimized for drag operation. Therefore, without generating air mass flow through the catalytic converter and without creating a critical negative pressure in the combustion chamber of a combustion engine, the phases of the intake and exhaust camshafts of the combustion engine, which are used to reduce drag torque, can be well restored.

[0015] When entering the over-limit operation phase, the internal combustion engine changes from an operating point with power output to an operating point with power consumption. Before entering the over-limit operation phase, the intake valves typically open immediately after top dead center (TDC). Simultaneously, the exhaust valves typically close just before TDC.

[0016] During the over-limit operation phase, the internal combustion engine is driven by the rolling vehicle via the transmission. For this purpose, the operating point is altered. The camshaft adjuster is preferably adjusted to the target angle at the adjustment speed typically used for these systems, such that the intake valves are now fully open after TDC and the exhaust valves are fully closed before TDC. Generally, this adjustment is performed as quickly as possible. Simultaneously, the throttle valve opens briefly to set a constant state in the intake manifold as quickly as possible. Due to these changes, the engine valves open in the BDC region during the over-limit operation phase. Only a small amount of air mass moves, and a small amount of air mass is drawn in uniformly from the intake manifold and discharged uniformly from the exhaust manifold. The air mass flow within the corresponding valves is balanced at zero. This minimizes internal friction and pumping losses caused by intake, compression, expansion, and exhaust, resulting in minimal braking of the vehicle. Simultaneously, it largely avoids the air mass flow that cools the exhaust system caused by the internal combustion engine.

[0017] If the internal combustion engine is part of a hybrid power unit, it is advantageous to minimize the drag torque of the combustion engine, in addition to eliminating the air mass flow through the exhaust system. In this respect, the air mass flow can be minimized under the secondary condition of the lowest possible drag torque. In another embodiment, the drag torque is minimized under the secondary condition of the lowest possible air mass flow. One method can also be used based on external manipulated variables, such as the temperature of the exhaust aftertreatment system. Based on the characteristic diagram formed by the parameters of the drag torque and the air mass flow, these two parameters can also be reduced to near their minimum values, for example, where the gradients of these parameters are low, making control or adjustment particularly insensitive to changes in external parameters and eliminating the need for readjustment. This facilitates the implementation of the adjustment strategy.

[0018] When combustion resumes to provide power output for the combustion engine, the camshaft adjuster adjusts to the target angle for restarting the engine. In this respect, according to the invention, camshaft adjustment does not always occur as quickly as possible, but is delayed at least when the pressure in the intake manifold differs from the desired intake manifold pressure and the load requirement is low. In particular, undesirable torque peaks that negatively impact driving performance are avoided when the ambient pressure has already increased in the intake manifold.

[0019] The torque peak can be avoided by intervening in the ignition angle. However, this leads to a deterioration in combustion efficiency and is therefore disadvantageous in terms of energy consumption, as it results in an undesirable increase in energy consumption. Conversely, in the case of the fill control proposed by the valve actuation device, the theoretically achievable speed of adjustment is reduced if the intake manifold pressure drops below a threshold and / or if it is desired to restart the engine at low load (“soft engagement”).

[0020] If the engine has been restarted and the intake manifold volume has not been emptied, a valve actuation device can be used for fill control after the restart phase until regular fill control, such as by means of a throttle valve, can be used effectively again. If the intake manifold volume has been emptied during restart, regular adjustments can also occur. Ultimately, the valve actuation device can be used in parallel with a throttle valve for fill control.

[0021] In a further development of the invention, the filling of the cylinder with fresh air is reduced by a variable valve actuation device, such that the established torque does not exceed a target torque preset value or exceeds the target torque preset value by less than 50%. The first variant enables particularly smooth re-engagement of the internal combustion engine without noticeable torque peaks. In the second variant, the internal combustion engine engages more quickly, but the torque peaks that would occur without fill control are reduced.

[0022] When an internal combustion engine is restarted after operating beyond its limits, the intake valve control timing is continuously adjusted to be "advanced." Specifically, when the intake manifold pressure differs from the desired intake manifold pressure, the adjustment speed of the intake valve control timing is reduced compared to the adjustment speed at the desired intake manifold pressure. Continuous adjustment can be made based on the intake manifold pressure.

[0023] In a preferred embodiment, there is no ignition angle interference when the internal combustion engine is re-ignited.

[0024] The present invention also relates to a control device that allows an internal combustion engine to be operated using the proposed method.

[0025] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Attached Figure Description

[0026] In the attached diagram:

[0027] Figure 1 This illustration shows a schematic, chronological development of characteristic values ​​of a first internal combustion engine without a variable valve actuation device, according to the prior art, as it enters and exits the over-limit operation phase.

[0028] Figure 2 This illustration shows a schematic, chronological development of characteristic values ​​of a second internal combustion engine with a variable valve actuation device but without filler pilot control, according to the prior art, as it enters and exits the over-limit operation phase.

[0029] Figure 3 The illustration shows a schematic, chronological development of characteristic values ​​of a third internal combustion engine with a variable valve actuation device and fill pilot control according to the present invention as it enters and exits the over-limit operation phase.

[0030] Figure 4 An illustrative internal combustion engine is shown.

[0031] Figure 5 Another illustrative internal combustion engine is shown. Detailed Implementation

[0032] Figure 4 and Figure 5 Each part is shown, and in a rough schematic manner, as an internal combustion engine 1, which is a reciprocating piston engine, having cylinders 4 and a crankshaft (not shown). The internal combustion engine is designed as a four-cylinder inline engine, wherein the invention can also be implemented in internal combustion engines 1 with different numbers of cylinders and designs. The valve control device, i.e., the valve actuation device, of the internal combustion engine 1 is indicated by 3. As a four-valve engine, each cylinder 4 of the internal combustion engine 1 has two intake valves 5 and two exhaust valves 6. The intake camshaft is indicated by 7, and the exhaust camshaft is indicated by 8. The intake camshaft 7 can be adjusted using the camshaft adjuster 9 on the intake side, and the exhaust camshaft 10 can be adjusted using the camshaft adjuster 10 on the exhaust side. In the considered exemplary embodiment, the camshaft adjusters 9, 10 are designed in the form of electromechanical adjusters, each camshaft adjuster having an adjusting gear designed as a harmonic drive device, and each camshaft adjuster having an electric motor 11 for adjusting the phase of the respective camshafts 7, 8 of the internal combustion engine 1 relative to the crankshaft. In a manner known per se, camshafts 7 and 8 are driven by crankshafts via belt drive or gear drive, wherein drive gear 13 is securely connected to the housing of the adjusting gear of camshaft adjusters 9 and 10, or the drive gear is an integral part of the housing.

[0033] A control device 12 is provided to actuate the camshaft adjusters 9 and 10, which may optionally undertake further control tasks. The data connection between the control device 12 and the camshaft adjusters 9 and 10 is indicated by 15. If necessary, the switching device 14 allows the exhaust valve 6 to be closed. According to... Figure 5 The switching device 14 of the internal combustion engine can be electromechanically actuated and can be designed to have a switchable rocker arm.

[0034] Figure 1 The illustration schematically shows 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 actuation device. The internal combustion engine 1 ignites in a first ignition stage 21, which lasts until time point t1. Figure 1 The injection 24 of the internal combustion engine 1 is represented numerically. This injection occurs during ignition phases 21 and 23 (value 1), and is omitted during the over-limit operation phase 22 (value 0). The internal combustion engine 1 shuts down at time t1 and restarts at time t3 during the restart phase 23. There is no injection between these time points. At time t2, shortly before time t3, the driver or control device activates the torque preset value, which initiates the restart process of the internal combustion engine 1. At time t3, data processing for restarting the internal combustion engine 1 is completed.

[0035] Once the vehicle enters the over-limit operation phase 22, injection 24 is suspended. Intake pipe pressure is adjusted via a throttle valve. Figure 1 In the example shown, the inspiratory pressure is always kept low. Figure 1 The intake valve closing time 26 shown remains at the target angle for engine restart and does not change. The throttle valve typically remains fully closed during the over-limit operation phase 22. Therefore, a torque-neutral restart can be performed quickly after the driver-induced torque preset value without overshoot at the start of the restart phase 23. Therefore, the engine torque 27 ( Figure 1 This basically corresponds to the target torque preset value. However, during the over-limit operation phase 22, air can enter the exhaust aftertreatment system, requiring enrichment after the engine is restarted, which increases emissions.

[0036] Figure 2 The schematic diagram illustrates the chronological development of characteristic values ​​of a second internal combustion engine 1 according to the prior art, which, compared to the first internal combustion engine 1, has a variable valve actuation device 3. According to Figure 2 The curve and Figure 1The curve corresponds to this. Therefore, the internal combustion engine 1 ignites in the first ignition stage 21, stops ignition in the over-limit operation stage 22, and the restart ignition stage 23 begins at time t3. The variable valve actuation device 3 is used to prevent oxygen enrichment in the exhaust aftertreatment system. To this end, the variable valve actuation device prevents air scavenging from the engine in the over-limit operation stage 22 by closing the exhaust valve 6 and adjusting the intake valve 5 to an extended adjustment range. In the over-limit operation stage 22, the exhaust valve lift and the suspension of injection 24 are deactivated in a cyclically synchronized manner, and are reactivated in a cyclically synchronized manner with the start of injection 24 upon restart. The variable valve actuation device 3 can be used on the intake side to minimize engine drag torque in the over-limit operation stage 22. The reduced load exchange work in this way—especially in combination with P0 hybrid vehicles and P1 hybrid vehicles—enables the recovery of a large amount of energy, which improves the overall efficiency of the powertrain. For this purpose, an extremely late intake valve phase is set that is useless for ignition operations 21 and 23, such that the maximum intake valve lift is approximately at bottom dead center (BDC). Here, the throttle valve position is also preferably kept almost completely closed during the over-limit operation phase 22.

[0037] If the internal combustion engine 1 provides torque again, the intake valve phase is quickly adjusted back to the normal target position, as if it can... Figure 2 This is observed between time points t2 and t3. Injection 24 is omitted between these time points. At time point t2, shortly before time point t3, the driver or control device activates the torque preset value, which initiates the restart process of the internal combustion engine 1. At time point t3, the data processing for restarting the internal combustion engine 1 is completed.

[0038] During the over-limit operation phase 22, the intake manifold pressure 25 increases continuously, for example, due to leakage. If the over-limit operation phase 22 continues for a relatively long time, for example, for a relatively long time while driving downhill, the intake manifold pressure 25 ( Figure 2 The intake manifold pressure can be increased to a level almost corresponding to the ambient atmospheric pressure during the over-limit operation phase 22. If restarting is initiated with the intake manifold pressure increased to 25, this will result in a short-term strong accumulation of torque due to the high air mass, with a torque peak of 28. However, the usual goal is to combine the internal combustion engine 1 with low torque. In this case, the strong accumulation of torque leads to a loss of comfort.

[0039] Figure 3 The schematic diagram illustrates the chronological development of characteristic values ​​of a third internal combustion engine 1, which, like the second internal combustion engine 1, has a variable valve actuation device 3 and operates using the method according to the invention. Figure 3 The curve and Figure 2The curves correspond to this. Internal combustion engine 1 reignites in the first ignition stage 21, stops ignition in the over-limit operation stage 22, and the re-ignition stage 23 begins at time t3. The variable valve actuation device 3 is used to prevent air purging, making the operation method the same as that of the second internal combustion engine, until the over-limit operation stage 22 ends. Therefore, as with the second internal combustion engine 1, the development of intake manifold pressure is also the same ( Figure 3 ).

[0040] At time t2, triggered by the restart request of internal combustion engine 1, unlike the second internal combustion engine, the intake valve phase is not adjusted as quickly as possible, but rather delayed to the normal target position. The degree of delay depends on how much the intake manifold pressure 25 has increased and what load internal combustion engine 1 requires. (The last sentence appears to be incomplete and possibly refers to a different context.) Figure 3 It can be seen that re-ignition occurs at time point t3, even though the intake valve timing has not yet aligned with the desired intake manifold pressure p. s The valve time at point t3 corresponds to the target valve time 29, and re-ignition begins, which corresponds to continuous operation under this load requirement. The time difference t between t3 and t2 is... Δ This is the time required to reach the target angle of the pilot control. As long as the inspiratory pressure has not yet reached its target pressure, at the desired inspiratory pressure p... s The adjustment of the target valve time 29 then occurs. A typical time can be assumed here, allowing the adjustment to be performed in a controlled manner, but it is preferably performed in an adjustable manner. This also allows the adjustment speed to be adapted to the actual intake manifold pressure. Ideally, the intake valve closing time 26 is adjusted so that the engine torque 27 builds up monotonically and as quickly as possible.

[0041] Therefore, the variable valve actuation unit 3 is used for pilot control of the intake valve closing time 26 during restart of the internal combustion engine 1. This allows torque peak 28 to be avoided when the pressure in the intake manifold increases. For this purpose, the variable valve actuation unit 3 deactivates the exhaust valve during the over-limit operation phase 22 and reduces engine drag torque by setting the intake valve lift to a very late stage. Given a preset torque value induced by the driver, a stored filler model calculates the target control time for engine restart at torque neutrality based on key input variables. For the selected example, this means that the intake valve lift phase must be continuously adjusted according to engine speed, but adjusted to be slower in the early stages compared to without pilot control, until the intake manifold pressure returns to the target value, and further load control can be achieved, for example, via a throttle valve.

[0042] List of reference numerals

[0043] 1 Internal combustion engine

[0044] 2 cylinder head

[0045] 3-valve drive unit

[0046] 4 cylinders

[0047] 5 intake valves

[0048] 6 exhaust valves

[0049] 7 Intake Camshaft

[0050] 8 Exhaust Camshaft

[0051] 9. Camshaft adjuster, intake side

[0052] 10 Camshaft Adjuster, Exhaust Side

[0053] 11 electric motors

[0054] 12 control devices

[0055] 13 transmission gears

[0056] 14 Switching device

[0057] 15 Data Connections

[0058] 21 Ignition Phase

[0059] 22 Over-limit operation phase

[0060] 23 Reignition Phase

[0061] 24-jet

[0062] 25 suction tube pressure

[0063] 26. Intake valve closing time after top dead center (°CA)

[0064] 27 Nm of engine torque

[0065] 28 peak torque

[0066] 29. Target valve time at the desired pressure in the suction pipe

[0067] t time

[0068] The timing of T1 internal combustion engine shutdown

[0069] Timing of the restart request for the t2 internal combustion engine

[0070] t3 is the time point after data processing for restarting the internal combustion engine.

[0071] t Δ Time difference between t3 and t2

[0072] ps Inspiratory tube expected pressure

Claims

1. A method for operating an internal combustion engine (1), the internal combustion engine having: - A crankshaft, which can be driven by a piston in a cylinder (4), - Intake pipe, through which fresh air can be supplied to the cylinder (4) - Intake valve (5), when the intake valve is open, allows fresh air to flow from the intake pipe into the cylinder (4) via the intake valve. - A variable valve drive (3), by means of which the opening duration or relative opening time of the intake valve (5) relative to the crankshaft position is variable. Its features are, - During the start-up of the internal combustion engine (1), the intake manifold pressure is equal to the desired intake manifold pressure (p s Under different conditions, the filling pilot control of the cylinder (4) is achieved by the variable valve drive device through the desired pressure (p) of the intake pipe. s Compared to reducing the supply of fresh air, this approach can be used to address the issue of insufficient fresh air supply. - The method is used when the internal combustion engine (1) is restarted after the following over-limit operation phase: during which the internal combustion engine (1) is driven without fuel supply to the cylinder (4) and with reduced or no air mass flow, and - When the internal combustion engine (1) is restarted after the over-limit operation phase, the intake valve control time is continuously adjusted to "advance", wherein the intake manifold pressure is at the desired intake manifold pressure (p s In cases different from the desired pressure (p) of the inhalation tube, s Compared to the adjustment speed at the time of adjustment, the adjustment speed of the intake valve control time is reduced.

2. The method according to claim 1, characterized in that, The filling of the cylinder (4) with fresh air is reduced by the variable valve drive device (3) so that the established torque does not exceed the target preset value of torque, or exceeds the target preset value but the excess is less than 50%.

3. The method according to claim 2, characterized in that, The internal combustion engine has an exhaust valve (6) that is permanently closed during the over-limit operation phase, and an intake valve (5) that operates with an intake valve control time that is offset too "late" for the intake valve control time to be suitable for ignition operation.

4. The method according to claim 1, characterized in that, When the internal combustion engine (1) is re-ignited, no ignition angle intervention occurs.

5. The method according to any one of claims 1-4, characterized in that, The variable valve drive device (3) has an intake camshaft (7) with an electric camshaft adjuster (9) or an electro-hydraulic actuated valve.

6. The method according to any one of claims 1-4, characterized in that, The internal combustion engine (1) has a throttle valve, and the fill pilot control is performed by the variable valve drive device whenever load control via the throttle valve cannot be performed or can only be performed to a reduced extent.

7. The method according to any one of claims 1-4, characterized in that, The internal combustion engine (1) operates as part of the hybrid drive system of the motor vehicle.

8. A control device (12) that operates an internal combustion engine (1) using the method according to any one of claims 1-7.

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