Method and device for suppressing siphoning of lubricant in turbocharger

Abstract

To solve the problem that in an exhaust system in which exhaust passages of a pair of banks have the same length and are made confluent, exhaust pulsation becomes strong at a specific engine speed, which generates siphoning of lubricant in a turbine of a turbocharger.SOLUTION: An internal combustion engine having six V-shaped cylinders comprises a variable valve timing mechanism that changes exhaust valve closing timing (EVC), and performs delayed closing control of delaying the EVC in a non-supercharging region. In order to suppress siphoning of lubricant in a turbine, a retard amount of the EVC is controlled to be relatively small in an engine speed region higher than a predetermined engine speed corresponding to a lower limit engine speed of a region A in which exhaust pulsation becomes strong due to resonance of an exhaust system.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a technique for suppressing the suction of lubricating oil in a turbine of a turbocharger due to exhaust pulsation. [Background technology]

[0002] In a turbocharger in which the turbine rotor rotates at high speed inside the housing, if the pressure in the tiny space behind the turbine rotor disk drops as the turbine rotor rotates, the lubricating oil supplied to the bearing part of the center housing is sucked out toward the turbine housing. This is particularly likely to occur if there is a section in one cycle where pressure drops due to exhaust pulsation.

[0003] Patent Document 1 proposes providing a wheel seal portion to reduce the gap at the location where leakage occurs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-71095 Summary of the Invention [Problem to be solved by the invention]

[0005] In V-type internal combustion engines with a pair of banks or horizontally opposed internal combustion engines, each bank is equipped with a turbocharger, and a pair of exhaust passages extending from the turbine outlets of each turbocharger are joined together so that they are equal in length. Furthermore, exhaust valve closing timing may be retarded to increase internal exhaust gas recirculation in the non-supercharging range. In such cases, exhaust system resonance at certain engine speeds can cause strong exhaust pulsation. Furthermore, a pressure drop occurs during the exhaust stroke during piston descent after top dead center, resulting in lubricating oil suction and white smoke being mixed into the exhaust. The present invention aims to suppress this lubricating oil suction, which causes white smoke, without relying on a sealing structure. [Means for solving the problem]

[0006] The method for suppressing lubricating oil suction from a turbocharger according to the present invention is an internal combustion engine equipped with a turbocharger in each of a pair of banks each including a plurality of cylinders, and a pair of exhaust passages extending from the turbine outlets of each turbocharger joined together so as to be of equal length, the internal combustion engine equipped with a variable valve timing mechanism on at least the exhaust valve side that changes the exhaust valve opening timing and exhaust valve closing timing, and that controls the exhaust valve closing timing to be retarded in order to increase internal exhaust gas recirculation in a non-supercharging region, In order to suppress the suction of lubricating oil in the turbine due to exhaust pulsation, the retard amount of the exhaust valve closing timing in the retard closing control is limited to a relatively small amount in a rotation speed range higher than a predetermined engine rotation speed.

[0007] In an exhaust system where a pair of equal-length exhaust passages merge, exhaust pulsation becomes stronger near a certain engine speed due to resonance. By limiting the amount of exhaust valve closing retardation in the late-closing control to a relatively small amount in the engine speed range above a certain engine speed, including the specific engine speed range where exhaust pulsation becomes stronger, the low-pressure peak pressure value of the exhaust pulsation becomes higher. This suppresses lubricating oil suction. [Effects of the Invention]

[0008] According to this invention, it is possible to suppress the suction of lubricating oil in the turbine in a specific rotation speed range without relying on the seal structure of the turbocharger, and to prevent the generation of white smoke. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram showing an exhaust system layout of an internal combustion engine according to an embodiment. [Figure 2] FIG. 10 is a characteristic diagram of a target EVC according to an embodiment. [Figure 3] FIG. 10 is a characteristic diagram of a target IVO according to an embodiment. [Figure 4] (a) Valve timing chart of the intake valve and exhaust valve at point P1, (b) point P2, and (c) point P3 in Figure 2. [Figure 5] 10 is a time chart showing the change in exhaust pulsation when the EVC is relatively advanced during late closing control. [Figure 6] This is a characteristic diagram of the target EVC for a reference example in which the area where resonance occurs is locally corrected by advance angle correction. [Figure 7] FIG. 7 is a characteristic diagram showing changes in EVC when the rotation speed changes under torque Te0 in the reference example of FIG. 6; [Figure 8] FIG. 3 is a characteristic diagram showing the change in EVC when the rotation speed changes under torque Te0 in the characteristic of the embodiment of FIG. 2; DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram showing the exhaust system layout of an internal combustion engine 1 according to the embodiment, viewed from under the vehicle floor. The internal combustion engine 1 according to the embodiment is a V6 internal combustion engine having a pair of left and right banks, each containing three cylinders, and is mounted at the front of the vehicle with the crankshaft axially oriented along the vehicle's longitudinal direction. Although not shown in detail, a turbocharger 6 is provided for each bank. A pair of exhaust passages 2, 2 extend from the turbine outlet of each turbocharger 6 to the rear of the vehicle along the vehicle floor via a catalytic converter 7. The turbochargers 6 and catalytic converters 7 are basically arranged symmetrically on the pair of banks. The pair of exhaust passages 2, 2 extending toward the vehicle's rear merge at a junction 3 located near the center of the vehicle in the longitudinal direction, with the passages being equal in length. The junction 3 does not have a volume section with an intentionally enlarged passage cross-sectional area. Therefore, exhaust pulsations from each bank interact with each other without being weakened by the volume section.

[0011] In the illustrated example, the exhaust system is configured such that it branches again from the confluence 3 into a pair of exhaust passages 4, 4, extending toward the rear of the vehicle, and finally opens to the outside of the vehicle via a single silencer 5 at the rear of the vehicle. Note that any exhaust system layout downstream of the confluence 3 is acceptable. As described above, the exhaust passages 2, 2 of the pair of banks are equal in length and converge, resulting in strong exhaust dynamic effects at specific frequencies (in other words, specific engine speeds). In particular, because the confluence 3 does not have a volume section, the exhaust pulsations of the banks interact with each other without being weakened by the volume section, resulting in strong exhaust pulsations at specific frequencies.

[0012] The internal combustion engine 1 includes an intake-side variable valve timing mechanism that changes the intake valve opening timing (IVO) and the intake valve closing timing (IVC), and an exhaust-side variable valve timing mechanism that changes the exhaust valve opening timing (EVO) and the exhaust valve closing timing (EVC). In one embodiment, the intake valve-side valve operating mechanism and the exhaust valve-side valve operating mechanism are each provided with a general variable valve timing mechanism that retards the opening timing (IVO, EVO) and the closing timing (IVC, EVC) by an equal angle by retarding the relationship between the crankshaft phase and the camshaft phase. The intake valve timing and the exhaust valve timing can be controlled independently. In the internal combustion engine 1 of this embodiment, such a variable valve timing mechanism is used to retard the exhaust valve closing timing (EVC) in the non-supercharging region to increase internal exhaust gas recirculation. In other words, by delaying the EVC closing time by a relatively large amount from top dead center, even if the intake valve opening timing (IVO) is constant, the amount of exhaust gas remaining in the cylinder (or flowing back from the exhaust port) increases, and the internal EGR rate increases. Note that in the present invention, a variable valve timing mechanism on the intake valve side is not essential, and the IVO and IVC may be configured to be fixed.

[0013] Next, the suppression of lubricating oil suction in the turbine of the turbocharger 6, which is a main part of the present invention, will be described.

[0014] As mentioned above, in the turbocharger 6, when the pressure in the minute space behind the turbine rotor disk drops as the turbine rotor rotates, lubricating oil supplied to the bearing portion of the center housing is sucked toward the turbine housing. Furthermore, when the EVC is controlled to close late in the non-supercharging range as described above, the pressure drop caused by the piston's downward movement is added to the pulsation, lowering the peak of the low-pressure side of the pressure pulsation and making lubricating oil more likely to be sucked out. Furthermore, because the exhaust passages 2, 2 of a pair of banks merge so that they are equal in length, exhaust system resonance at certain engine speeds increases exhaust pulsation, making lubricating oil more likely to be sucked out. When lubricating oil components enter the high-temperature exhaust gas, white smoke is mixed into the exhaust gas that is ultimately discharged outside the vehicle.

[0015] In the exhaust system configuration of one embodiment, for example, this suction of lubricating oil occurs in the rotational speed range of around 2000±200 rpm, shown as region A in Figures 2 and 6. This basically corresponds to the resonance rotational speed of exhaust pulsation, which is determined by the length of the exhaust pipe up to the junction 3.

[0016] Therefore, in this invention, to suppress the suction of lubricating oil due to exhaust pulsation, the amount of EVC retardation during late-closing control is relatively small in the rotational speed range of the above-mentioned region A. Figure 5 shows the characteristics of exhaust pulsation at the turbine exhaust outlet when the EVC is performing late-closing control, with waveform Pe1 representing the exhaust pulsation under the reference EVC for late-closing control. The lowest peak pressure in the pulsation, Pe1L, is below atmospheric pressure P0, which is a so-called negative pressure. This causes suction of lubricating oil within the turbine housing.

[0017] In contrast, waveform Pe2 shows exhaust pulsation under an EVC that is 20° CA more advanced than the reference EVC for late closing control. As is clear from a comparison with waveform Pe1, the lowest peak pressure in waveform Pe2, Pe2L, is higher than the peak pressure Pe1L of waveform Pe1. This is because as the EVC approaches exhaust top dead center, the impact of the pressure drop caused by the piston descending (exhaust gas being sucked back from the exhaust port) becomes smaller. Note that the crank angle position of the peak (Pe2L) advances as the EVC advances.

[0018] By relatively advancing the EVC during late closing control in this way, the length of the negative pressure section of the exhaust pulsation is shortened and the level of the peak negative pressure is weakened, thereby suppressing the suction of lubricating oil in region A.

[0019] FIG. 2 shows a specific target EVC characteristic in one embodiment. The target EVC is set based on a map created in advance using the torque or load of the internal combustion engine and the engine speed as parameters, and the engine controller controls the exhaust-side variable valve timing mechanism to match the target EVC retrieved from the map. FIG. 2 schematically shows the target EVC characteristic assigned to this map. The lower load side below the torque Te0 indicated by the dashed line basically corresponds to the non-supercharging region, and the higher load side above the torque Te0 corresponds to the supercharging region. In the supercharging region, the exhaust pressure inside the turbine housing increases, making it difficult for lubricating oil to be sucked out.

[0020] As shown in Figure 2, the target EVC varies within a range of, for example, 20° CA ATDC to 60° CA ATDC, but in the non-supercharging region, it is controlled to be late-closing at about 50° CA ATDC to 60° CA ATDC. In the engine speed region higher than a predetermined engine speed (e.g., 1800 rpm) that is the lower limit of region A where lubricant oil suction becomes a problem, the amount of EVC retard is limited to a relatively small amount, for example, 40° CA ATDC, in order to suppress lubricant oil suction. In other words, the target EVC in the engine speed region higher than the predetermined engine speed is set more advanced than the target EVC in the engine speed region lower than the predetermined engine speed.

[0021] Figure 3 shows the characteristics of the target IVO, which is the control target of the intake variable valve timing mechanism in one embodiment. IVO changes mainly in response to torque or load, and changes relatively little with engine speed. At a given load, specifically in the non-supercharging region, IVO has a characteristic of remaining almost constant or slightly retarding as the engine speed increases.

[0022] Figure 4 is a valve timing chart showing the opening and closing timing of the intake valve and exhaust valve at points P1, P2, and P3 in Figure 2. Diagram (a) shows the characteristics at point P1 in the non-supercharged, low-speed, low-load range, where, for example, the EVC is 60° CA ATDC and the IVO is 20° CA ATDC. In other words, the EVC is sufficiently retarded to control the late closing of the exhaust valve, internal exhaust gas recirculation is actively provided, and the intake valve operates in a so-called late-closing Miller cycle.

[0023] Figure (b) shows the characteristics at point P2 in region A, where lubricant oil suction is a problem in the non-supercharging region. Here, for example, EVC is 40° CA ATDC and IVO is 20° CA ATDC. In other words, the degree of retardation of the EVC, which is a late closing control, is limited compared to point P1 to suppress lubricant oil suction. IVO has the same characteristics as point P1. This setting suppresses lubricant oil suction due to exhaust pulsation.

[0024] Figure (c) shows the characteristics at point P3 in the high-speed, high-load range, which is the supercharging range, where, for example, EVC is ATDC 30° CA and IVO is ATDC 10° CA. Here, IVO and IVC are set to the advanced side to increase the volumetric efficiency of the internal combustion engine, and EVO and EVC are also set to the advanced side to ensure appropriate valve overlap.

[0025] The characteristics at point P2 shown in Figure (b) show that IVO and IVC are not particularly set to the advanced side, so EVC could be set to a more retarded side in relation to the intake valve characteristics. However, as mentioned above, EVC is set to a relatively advanced side in order to suppress lubricant oil extraction.

[0026] Note that "late closing" of the EVC means intentionally delaying the EVC beyond the delay from the exhaust top dead center required for the exhaust gas to be expelled from the cylinder as the piston rises. The characteristics in figures (a) and (b) fall into the category of "late closing," while the characteristic in (c) is not late closing.

[0027] As a reference example, Figure 6 shows the basic target EVC characteristics when lubricant oil suction suppression is not taken into consideration, and also shows the characteristics when only region A, where resonance occurs, is locally advanced. As shown in Figure 6, the original characteristics of late-closing control provide a sufficiently late-closing target EVC of, for example, 50° CA ATDC to 60° CA ATDC for operating conditions (torque and rotation speed) around region A. Based on these basic characteristics, it is also possible to limit the EVC retard within region A to suppress lubricant oil suction, setting it to, for example, 40° CA ATDC.

[0028] However, if the EVC is set to a relatively advanced position locally in the engine speed range where exhaust pulsation resonance occurs, the direction of the EVC's advance / retard angle change will reverse midway as the engine speed increases (or decreases), which is undesirable.

[0029] Figure 7 is an explanatory diagram showing the change in target EVC with respect to engine speed, with the horizontal axis representing engine speed and the vertical axis representing target EVC, along a constant torque Te0 that crosses area A in the characteristic diagram of Figure 6. As shown in Figure 7, for example, when the engine speed increases or decreases under a constant torque (Te0), the target EVC behaves as if it were once advanced and then retarded again, which makes it more likely that a step will occur in the torque actually output from the internal combustion engine and makes it difficult to control in coordination with the intake-side variable valve timing mechanism.

[0030] In contrast, in the above-described embodiment, the target EVC changes in one direction in response to changes in engine speed. Figure 8 shows the relationship between engine speed and target EVC, similarly based on a constant torque Te0, for the characteristics of the embodiment shown in Figure 2. As shown in the figure, in the embodiment of Figure 2, the amount of EVC retard is limited to a relatively small amount in the engine speed range higher than a predetermined engine speed (for example, near 1800 rpm). Therefore, the direction of change in the target EVC retard / advance does not reverse midway as the engine speed increases or decreases. This prevents unintended torque fluctuations and complicated cooperative control with the intake-side variable valve timing mechanism.

[0031] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. In particular, in the above embodiment, specific numerical values ​​have been given to facilitate understanding, but these numerical values ​​are merely examples for the purpose of explanation, and the present invention is not limited to these numerical values. Furthermore, the variable valve timing mechanism may be one in which the EVO and EVC are changed independently. [Explanation of symbols]

[0032] 1...Internal combustion engine 2...Exhaust passage 3...Confluence

Claims

1. An internal combustion engine is provided with a pair of banks each including a plurality of cylinders, each of which is provided with a turbocharger, and a pair of exhaust passages extending from the turbine outlets of the turbochargers are joined together so as to be of equal length, and the engine is provided with a variable valve timing mechanism on at least the exhaust valve side that changes the exhaust valve opening timing and exhaust valve closing timing, and controls the exhaust valve closing timing to be retarded in order to increase internal exhaust gas recirculation in a non-supercharging region, In order to suppress suction of lubricating oil in the turbine due to exhaust pulsation, the retard amount of the exhaust valve closing timing in the retard closing control is limited to a relatively small amount in a rotation speed region higher than a predetermined engine rotation speed. A method for suppressing lubricating oil suction from a turbocharger.

2. The internal combustion engine is provided with an intake-side variable valve timing mechanism on the intake valve side, The intake valve opening timing by this intake-side variable valve timing mechanism has a characteristic that, under a predetermined load, as the engine speed increases, it remains approximately constant around the predetermined engine speed or is retarded as the engine speed increases. The method for suppressing lubricating oil suction from a turbocharger according to claim 1.

3. The predetermined load is a load within a non-supercharging region. The method for suppressing lubricating oil suction from a turbocharger according to claim 2.

4. a control target value of the exhaust valve closing timing in an engine speed region higher than the predetermined engine speed is set to be more advanced than a control target value of the exhaust valve closing timing in an engine speed region lower than the predetermined engine speed. The method for suppressing lubricating oil suction from a turbocharger according to claim 1.

5. the internal combustion engine does not include a volume portion where the passage cross-sectional area expands at a junction where the pair of exhaust passages join together, The method for suppressing lubricating oil suction from a turbocharger according to claim 1.

6. the predetermined engine speed is determined so that the engine speed range includes a resonance speed of exhaust pulsation determined by the exhaust pipe length to the junction point; The method for suppressing lubricating oil suction from a turbocharger according to claim 1.

7. An internal combustion engine is provided with a pair of banks each including a plurality of cylinders, each of which is provided with a turbocharger, and a pair of exhaust passages extending from the turbine outlets of the turbochargers are joined together so as to be of equal length, and the engine is provided with a variable valve timing mechanism on at least the exhaust valve side that changes the exhaust valve opening timing and exhaust valve closing timing, and controls the exhaust valve closing timing to be retarded in order to increase internal exhaust gas recirculation in a non-supercharging region, a controller controlling the variable valve timing mechanism limits the amount of retardation of the exhaust valve closing timing in the retard closing control to a relatively small amount in an engine speed region higher than a predetermined engine speed in order to suppress suction of lubricating oil in the turbine due to exhaust pulsation; Turbocharger lubricant oil suction suppression device.

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