JP3982591B2 - Diesel engine control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diesel engine equipped with a so-called internal EGR system that introduces burned gas in a combustion chamber into the intake system, rather than introducing exhaust gas into the intake system from the exhaust system of the diesel engine through a conduit. The present invention relates to a control device.
[0002]
[Prior art]
In a diesel engine, there is an exhaust gas recirculation device (EGR) that extracts a part of exhaust gas from the exhaust system and recirculates it to the intake system in order to reduce NOx. Japanese Patent Publication No. 5-80562 discloses a so-called internal EGR system that introduces (gas) into an intake system. The “diesel engine exhaust valve control device” in this publication is a technology that controls the amount of internal EGR, and reduces the exhaust emission by increasing the overlap of exhaust and intake air according to the operating state of the engine. The aim is to raise the temperature by increasing the amount of fuel gas and simultaneously reduce NOx and PM (particulates) by the effect of EGR.
[0003]
Generally, the internal EGR can maintain the gas temperature at a high level even with the same EGR gas amount as compared with the conventional method (method of recirculation from the exhaust system to the intake system by a conduit), so the load is reduced simultaneously with the NOx reduction effect. There is an effect of reducing PM (SOF content).
[0004]
[Problems to be solved by the invention]
However, when this method is used, mixing of fresh air and burned gas does not proceed, so when the piston reaches the compression end after suction and new EGR gas in the cylinder (in the cavity) The mixed state of gas has a layered state in which a large amount of EGR gas remains on the bottom surface and fresh air remains on the top surface. This phenomenon is also described in “Unsteady in-cylinder flow analysis of diesel engine” published by the Japan Society for Automotive Engineers Academic Lecture Preprints 966 1996-10, pp. 189-192 (No. 214). Therefore, when the amount of internal EGR is increased by such a method, the in-cylinder gas non-uniformity at the compression end increases, oxygen becomes insufficient locally, combustion deteriorates, and PM increases. The problem arises.
[0005]
Accordingly, an object of the present invention is to promote the mixing of residual gas and fresh air in the cylinder in internal EGR control effective for simultaneously reducing NOx and PM (particulate) discharged from the diesel engine. Another object of the present invention is to provide a control device for a diesel engine that can achieve good combustion even during a large amount of EGR and can further reduce NOx and PM.
[0006]
[Means for Solving the Problems]
The control device for a diesel engine according to claim 1 controls the variable valve timing mechanism so that the exhaust valve is cranked more than the top dead center of the diesel engine by an amount corresponding to the operation state of the diesel engine by the operation state detection means. θ1 only early not and early closing to that exhaust valve closing control means so as to close at a timing, by controlling the variable valve timing mechanism, slow only crank angle θ2 than the top dead center of the diesel engine the intake valve Intake valve opening control means that opens slowly so as to open at the timing, and the relationship between the crank angles θ1 and θ2 is “θ2> θ1” that opens the intake valve more slowly than the early closing of the exhaust valve. It is characterized by being set in a relationship .
[0007]
In this way, the exhaust valve closing control means controls the variable valve timing mechanism so that the exhaust valve is crank angle θ1 from the top dead center of the diesel engine by an amount corresponding to the operating condition of the diesel engine by the operating condition detecting means. you early closing so as to be closed only have early timing. Therefore, the exhaust valve is quickly closed, and the burned gas remains in the cylinder.
[0008]
The intake valve opening control means controls the variable valve timing mechanism, to open late so as to open at a slow timing by crank angle θ2 than the top dead center of the intake valve diesel engine. The relationship between the crank angles θ1 and θ2 is set to a relationship of “θ2> θ1” that opens the intake valve more slowly than the early closing of the exhaust valve.
[0009]
Therefore, since the intake valve does not open unless the crank angle θ2 is larger than the crank angle θ1 at which the exhaust valve is quickly closed in the intake stroke, the inside of the cylinder is temporarily set to a negative pressure. From this state, the intake valve is opened, and at this time, fresh air rapidly flows. This promotes mixing of burned gas and fresh air.
[0010]
As a result, even when a large amount of EGR is performed, mixing of burned gas and fresh air can be promoted, thereby further reducing NOx and PM.
As the exhaust valve closing control means,
-When the accelerator opening degree is constant, the closing speed of the exhaust valve is controlled to be advanced as the rotational speed is lower to promote early closing (Claim 2).
-When the rotational speed is constant, as the accelerator opening is smaller, the closing timing of the exhaust valve is controlled to the advance side to promote early closing (Claim 3).
If it is configured as such, the effect of EGR can be utilized to the maximum extent.
According to a fourth aspect of the present invention, there is provided the diesel engine control device, wherein the intake valve opening control means controls the intake valve opening control means at a constant rate with respect to the early closing timing (crank angle θ1) of the exhaust valve. (Crank angle θ2) is configured to be largely controlled.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
The present embodiment embodies the present invention in a four-cylinder diesel engine, and its main configuration is a valve drive mechanism (camless type) that opens and closes an intake valve and an exhaust valve of an engine with a hydraulic actuator. A valve drive mechanism), and the drive timing (valve timing) of the intake valve and the exhaust valve can be variably adjusted.
[0012]
The diesel engine is a so-called direct injection diesel engine that injects fuel from a fuel injection nozzle into a single combustion chamber formed between the cylinder head and the top of the piston. It has 2 valves (4 in total).
[0013]
The details will be described below.
FIG. 1 is a configuration diagram showing an engine cross section and an outline of an engine control system in the present embodiment. In FIG. 1, a cylinder block 2 of an engine 1 is formed with a cylindrical cylinder 3. A piston 4 connected to a crankshaft (not shown) is arranged in the cylinder 3 so as to reciprocate in the vertical direction in the figure. It is installed. That is, the piston 4 is connected to a connecting rod (not shown) and reciprocates. A concave cavity 5 is formed on the upper surface of the piston 4. The cylinder head 6 is formed with an intake port 8 and an exhaust port 9 communicating with the combustion chamber 7 above the piston. A fuel injection nozzle 10 is disposed at the center of the cylinder head 6, and the tip (injection hole) is exposed in the combustion chamber 7.
[0014]
Further, an intake valve 11 and an exhaust valve 12 are disposed in the cylinder head 6, and the combustion chamber 7 and the ports 8 and 9 are communicated or closed with the opening and closing operations of these valves 11 and 12 ( Intermittent). The combustion chamber 7 is substantially sealed when both the intake valve 11 and the exhaust valve 12 are closed.
[0015]
The valves 11 and 12 are driven by a valve drive mechanism 20 provided above the cylinder head 6. That is, the valves 11 and 12 can be opened and closed by the valve drive mechanism 20 at any time. The valve drive mechanism 20 is driven based on a control signal from an electronic control unit (hereinafter referred to as ECU) 50. In brief, the ECU 50 is configured around a well-known microcomputer having a CPU 50a for executing various control programs and a memory 50b (ROM, RAM, etc.) for storing control data and maps. A water temperature signal (Tw) detected by the water temperature sensor 51, a crank angle signal (Ne) detected by the crank angle sensor 52, an accelerator opening signal (Ac) detected by the accelerator opening sensor 53, and An atmospheric pressure signal (Pair) detected by the atmospheric pressure sensor 54 is input. Based on these input signals, the valve drive mechanism 20 controls the opening / closing timing of the intake valve 11 and the exhaust valve 12. That is, the ECU 50 determines the valve timing from the map data in the memory 50b and controls the drive of the valve drive variable mechanism 20.
[0016]
Next, the configuration of the valve drive mechanism 20 and its peripheral part will be described with reference to FIG. However, FIG. 2 shows only the configuration on the intake side, and FIG. 2 shows a pair of left and right intake valves 11.
[0017]
In FIG. 2, a spring retainer 13 is attached to the upper end of the intake valve 11, and between the spring retainer 13 and the cylinder head 6, the intake valve 11 is urged in the valve closing direction (upward in the figure). The valve spring 14 is provided. The pair of left and right intake valves 11 are connected by a valve bridge 15 so as to be able to operate integrally. A plunger 16 that reciprocates in the vertical direction in the figure is connected to the upper surface of the valve bridge 15, and when the plunger 16 moves downward, the intake valve 11 opens (in the state shown in the figure) and moves upward. As a result, the intake valve 11 is closed. The operation of the plunger 16 is controlled in accordance with the hydraulic pressure of the hydraulic chamber 17 formed on the upper surface thereof (the hydraulic pressure of the valve drive mechanism 20), details of which will be described later. Reference numeral 18 denotes an adjusting screw for finely adjusting the operating position of the intake valve 11.
[0018]
On the other hand, in the valve drive mechanism 20, a housing 21 fixed to a part of the cylinder head 6 is formed with a circular hole portion 22 extending in the left-right direction in the figure, and the hole portion 22 has a spool type directional control valve. (Hereinafter referred to as a directional control valve) 23 is provided. The direction control valve 23 is roughly divided into a cylindrical sleeve 24 and a spool 25 that slides in the sleeve 24 in the horizontal direction in the figure. The sleeve 24 is screwed in the vicinity of the opening of the circular hole portion 22. The lid 26 is fixed. Hydraulic ports 27a, 27b, and 27c are formed in an annular shape on the outer peripheral surface of the sleeve 24, and these hydraulic ports 27a, 27b, and 27c are respectively connected to the inner periphery of the sleeve via communication passages 28a, 28b, and 28c provided at a plurality of locations. It communicates with the surface.
[0019]
The housing 21 has a suction port 29 for sucking high-pressure oil fed from the hydraulic pump 41 into the direction control valve 23 and a discharge port for discharging high-pressure oil from the direction control valve 23 to the drain tank 42. 30 is provided. Here, the hydraulic pump 41 draws hydraulic oil from the drain tank 42, increases the pressure to about 12 MPa, and feeds it to the direction control valve 23. The suction port 29 communicates with the hydraulic port 27a through a passage 31 and the discharge port 30 communicates with the hydraulic port 27c through a passage 32. The hydraulic chamber 17 communicates with the hydraulic port 27b through a passage 33.
[0020]
A housing chamber 34 is formed inside the housing 21, and a piston 35 that slides on the inner peripheral surface thereof is disposed in the housing chamber 34. In the piston 35, a piezo stack 36 is disposed that expands as a voltage is applied. The piezo stack 36 is formed by laminating a large number of PZTs (lead zirconate titanate) as piezoelectric elements, and a pair of electrodes 37a and 37b are attached to one end thereof. A predetermined voltage is applied to the electrodes 37a and 37b via a driver 55 based on a control command from the ECU 50. On the other hand, a disc spring 38 disposed on the left side of the piston 35 applies a force in the contraction direction to the piezo stack 36. FIG. 2 shows a state in which a voltage is applied to the piezo stack 36, and shows a state in which the piezo stack 36 is extended and the piston 35 is moved in the left direction in the figure.
[0021]
Next, the operation of the valve drive mechanism 20 will be described with reference to FIG. Here, FIG. 3A shows a state in which a voltage is applied to the piezo stack 36. In other words, when a voltage is applied, the piezo stack 36 extends and the piston 35 moves in the left direction in the figure against the spring force of the disc spring 38, whereby the spool 25 is pushed in the left direction. At this time, the high-pressure oil sucked into the suction port 29 circulates as shown by the broken line arrow in the drawing and is supplied into the hydraulic chamber 17, and the intake valve 11 is opened.
[0022]
FIG. 3B shows a state where no voltage is applied to the piezo stack 36. That is, in a state where the voltage application to the piezo stack 36 is released, the piston 35 is biased in the right direction in the figure by the spring force of the disc spring 38, so that the spool 25 is pulled rightward. At this time, the hydraulic oil in the hydraulic chamber 17 flows as shown by a broken line arrow in the drawing and is discharged to the discharge port 30 (returned to the drain tank 42), and the intake valve 11 is closed.
[0023]
Although the illustration and detailed description of the valve drive mechanism of the exhaust valve 12 are omitted, it has substantially the same configuration as the valve drive mechanism 20 of the intake valve 11 described above, and the exhaust valve 12 is also the ECU 50. It is opened and closed based on the control signal.
[0024]
Thus, in the valve drive mechanism 20 of the present embodiment, a hydraulic cylinder that drives the intake valve 11 and the exhaust valve 12 is constituted by the plunger 16 and the hydraulic chamber 17, and hydraulic control that intermittently supplies hydraulic pressure to the hydraulic cylinder. The valve is constituted by a hydraulic pump 41 and a direction control valve 23. By using such a configuration, the opening / closing timing of the intake valve 11 and the exhaust valve 12 can be freely controlled, and the intake characteristics and exhaust characteristics of the engine 1 can be changed. That is, the closing timing of the exhaust valve 12 and the opening timing of the intake valve 11 can be adjusted.
[0025]
In the present embodiment, the valve drive mechanism 20 constitutes a variable valve timing mechanism, and the ECU 50 constitutes an exhaust valve closing control means and an intake valve opening control means, a water temperature sensor 51, a crank angle sensor 52, The accelerator opening sensor 53 and the atmospheric pressure sensor 54 constitute an operation state detection means.
[0026]
Next, the operation of the diesel engine control apparatus configured as described above will be described. FIG. 5 is a time chart showing the lift operation of the intake valve 11 and the exhaust valve 12 by the valve drive mechanism 20, and TDC shown on the horizontal axis shows the piston top dead center. Moreover, the vertical axis | shaft of the figure shows valve lift amount. The broken line in the figure indicates the intake / exhaust characteristics (valve timing) when the valve timing is fixed, and the solid line indicates when the exhaust valve 12 is closed early and the intake valve 11 is opened slowly by using the valve drive mechanism 20. The valve timing is shown.
[0027]
That is, when the valve timing is fixed, the exhaust valve 12 starts opening at a time of about 40 ° CA before BDC and closes immediately after TDC. The intake valve 11 starts to open at a timing of about 5 ° before TDC, and closes at a timing of about 40 ° after BDC. At this time, the exhaust valve 12 and the intake valve 11 overlap in a predetermined period. On the other hand, when the valve drive mechanism 20 is used, the closing timing of the exhaust valve 12 is changed to the advance side by a predetermined crank angle from the TDC, and the opening timing of the intake valve 11 is changed to a predetermined crank angle from the TDC. Only the corner is changed to the retard side.
[0028]
Note that the valve lift operation of the present embodiment is realized by the hydraulic valve drive mechanism 20, which substantially matches the cam drive profile in which the lift operation is performed as the camshaft rotates.
[0029]
FIG. 4 shows a process (flow chart) executed by the ECU 50.
First, when the engine is started, the ECU 50 proceeds to step 100 and inputs the water temperature TW, the rotational speed Ne, the accelerator opening degree Ac, and the atmospheric pressure Pair. In step 101, the ECU 50 calculates an EGR amount that is optimal for driving from map data built in the memory 50a based on the input signal. After that, the ECU 50 replaces this calculation result with the valve timing, and drives and controls the valve drive mechanism 20 in step 102.
[0030]
Thereafter, the process returns to step 100 and is repeated. By repeating this process, the exhaust valve 12 is quickly closed and the intake valve 11 is slowly opened in the present embodiment shown by the solid line in FIG. At this time, in this control, the intake valve 11 is opened more slowly than the “early closing” of the exhaust valve 12. That is, the relationship between the crank angle θ1 for “early closing” of the exhaust valve 12 with respect to TDC and the crank angle θ2 for “slow opening” of the intake valve 11 with respect to TDC satisfies θ2> θ1. Yes.
[0031]
FIG. 6 shows a part of the valve timing output in step 102 of FIG. 4. When the accelerator opening is constant (at low load), the exhaust valve 12 is closed earlier as the rotational speed is lower, and the effect of EGR is shown. To make the most of it.
[0032]
FIG. 7 shows part of the valve timing output in step 102 of FIG. 4. When the rotational speed is constant, the exhaust valve 12 is closed earlier as the accelerator opening is smaller, and the effect of EGR is maximized. To make use of.
[0033]
FIG. 8 shows the relationship between the exhaust valve closing timing and the intake valve opening timing. As shown in the figure, the intake valve 11 is opened more slowly at a constant rate.
Next, the state of the airflow in the cylinder when this control is performed will be described in comparison.
[0034]
FIG. 9 shows the state of air flow in the cylinder during the intake stroke in the conventional method in which only the control for closing the exhaust valve earlier than TDC is performed by an amount corresponding to the operating state of the diesel engine.
[0035]
In the figure, reference numeral 60 indicates the cylinder inner wall surface of the engine, and reference numeral 61 indicates residual gas generated in the cylinder by closing the exhaust valve 12 early (or by overlapping the exhaust valve 12 and the intake valve 11). Indicates. In this figure, in the intake stroke, the intake air is rectified in the intake port 8 so as to flow in the direction of the arrow A1 from the start of the intake, so that a lateral air flow (swirl) indicated by L1 is formed in the cylinder. For this reason, the mixing of the residual gas in the cylinder and the fresh air does not proceed, the intake stroke is finished in a layered state, and the mixing does not proceed even in the compression stroke. For this reason, even at the compression end before fuel injection, the layer 5 remains in the form of the residual gas G1 and fresh air G2 in the cavity 5 of FIG.
[0036]
If fuel is injected and burned in this state, the combustion temperature rises and NOx is generated because the heat capacity of the gas is small in the fresh air G2. In addition, in the combustion in the residual gas G1, it becomes easy to discharge soot because oxygen shortage occurs, and although the total amount of NOx and soot emission may be reduced, the effect of the residual gas is reduced. It cannot be said that it is fully demonstrated.
[0037]
In general, it is possible to prevent soot discharge by sprinkling residual gas having a high heat capacity to the extent that oxygen shortage does not occur, and to suppress NOx generation by suppressing the maximum temperature during combustion.
[0038]
Next, FIG. 11 shows a state in the cylinder at the time of control in the present embodiment.
First, in this control, burned gas remains in the cylinder by “exhaust valve early closing”. In the intake stroke, the intake valve 11 is slowly opened larger than the early closing amount. Therefore, at the moment when the intake valve 11 is opened, negative pressure is generated in the cylinder. Therefore, fresh air suddenly flows into the cylinder simultaneously with the start of inhalation. At this time, since turbulent flow is generated in the intake port 8, the flow does not have a rectified constant direction, and flows A2 and A3 having a very high flow velocity from the gap of the intake valve 11 in all directions. Will be formed. The fast flows A2 and A3 in the initial stage of suction immediately reach the bottom surface in the cylinder, and the residual gas on the bottom surface in the cylinder diffuses in the directions indicated by L2, L3, and L4. From the middle stage to the latter half of the intake stroke, the intake air is gradually rectified, and when the intake is completed, the same air flow (swirl) as in the conventional case is formed in the cylinder. At this time, since the residual gas is diffused in the first half of the intake stroke, the residual gas and fresh air are well mixed in the cavity 5 as shown in FIG. 12, and this state is maintained even at the compression end. It is.
[0039]
As described above, in this embodiment, the mixing of EGR gas and fresh air can be promoted, and the NOx and PM reduction effect can be improved.
As shown in FIG. 13, the particulates can be reduced by adopting this control as compared with the case where the valve timing is fixed.
[0040]
Thus, the present embodiment has the following features.
(A) Since the exhaust valve 12 is closed earlier than TDC by an amount corresponding to the operating state of the diesel engine, and the intake valve 11 is opened later than the crank angle at which the exhaust valve 12 is early closed with respect to TDC. Although the exhaust valve 12 closes earlier than the TDC and burned gas remains in the cylinder, the intake valve 11 opens later than the crank angle at which the exhaust valve 12 closes early, so that the cylinder is temporarily brought to a negative pressure. The intake valve 11 is opened, and at this time, fresh air rapidly flows. This promotes mixing of burned gas and fresh air. As a result, even when a large amount of EGR is performed, mixing of burned gas and fresh air can be promoted, and NOx and PM can be further reduced.
[0041]
In this way, when performing internal EGR control that is effective to simultaneously reduce NOx and PM (particulates) discharged from the diesel engine, it promotes mixing of residual gas and fresh air in the cylinder. In addition, good combustion can be obtained even during a large amount of EGR, and NOx and PM can be further reduced.
[0042]
In particular, when applied to a direct injection diesel engine that injects fuel into a single combustion chamber 7 formed between the cylinder head 6 and the top of the piston, the effect is great.
[0043]
In addition, although the case where it applied to the direct injection type diesel engine was described in the above description, you may apply to the subchamber type diesel engine which injects a fuel into the subchamber different from a main combustion chamber.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an engine cross section and an outline of an engine control system in an embodiment.
FIG. 2 is a configuration diagram of a valve driving mechanism and its peripheral part.
FIG. 3 is an operation explanatory diagram of the valve driving device.
FIG. 4 is a flowchart for explaining the operation.
FIG. 5 is a time chart showing a lift operation by a valve drive mechanism.
FIG. 6 is a diagram showing a method for controlling the exhaust valve closing timing with respect to the rotational speed.
FIG. 7 is a diagram showing a control method of exhaust valve closing timing with respect to accelerator opening.
FIG. 8 is a diagram showing a relationship between an exhaust valve closing timing and an intake valve opening timing.
FIG. 9 is a diagram showing in-cylinder gas flow for comparison.
FIG. 10 is a diagram showing in-cylinder gas distribution at the compression end for comparison.
FIG. 11 is a diagram showing in-cylinder gas flow in the embodiment.
FIG. 12 is a diagram showing the in-cylinder gas distribution at the compression end in the embodiment.
FIG. 13 is a diagram showing the relationship between the NOx amount and the PM amount for confirming the effect of the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Piston, 6 ... Cylinder head, 7 ... Combustion chamber, 11 ... Intake valve, 12 ... Exhaust valve, 20 ... Valve drive mechanism (variable valve timing mechanism), 50 ... ECU (exhaust valve closing control) Means, intake valve opening control means), 51 ... water temperature sensor (operation state detection means), 52 ... crank angle sensor (operation state detection means), 53 ... accelerator opening sensor (operation state detection means), 54 ... atmospheric pressure Sensor (operating state detection means).

Claims (4)

A variable valve timing mechanism for adjusting the closing timing of the exhaust valve and the opening timing of the intake valve provided in the diesel engine;
Driving state detecting means for detecting the driving state of the diesel engine;
The variable by controlling the valve timing mechanism, so as to closing by the operating condition detecting means has early just crank angle θ1 than the top dead center of the diesel engine the exhaust valve by an amount corresponding to the operating state of the diesel engine by the timing and the exhaust valve closing control means that early closing vinegar,
The variable by controlling the valve timing mechanism, and a intake valve opening control means for opening retarded so as to open at a slow timing by crank angle θ2 than the top dead center of the diesel engine the intake valve,
The diesel engine control device characterized in that the relationship between the crank angles [theta] 1 and [theta] 2 is set to "[theta] 2> [theta] 1" that opens the intake valve more slowly than the early closing of the exhaust valve. . 2. The diesel engine according to claim 1, wherein the exhaust valve closing control means promotes early closing by controlling the closing timing of the exhaust valve to an advance side as the rotational speed is lower when the accelerator opening is constant . Control device.   2. The diesel engine according to claim 1, wherein the exhaust valve closing control means promotes early closing by controlling the closing timing of the exhaust valve to an advance side as the accelerator opening decreases when the rotational speed is constant. Control device.   The intake valve opening control means largely controls the late opening timing (crank angle θ2) of the intake valve at a constant ratio with respect to the early closing timing (crank angle θ1) of the exhaust valve. The control apparatus of the diesel engine as described in any one.

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