JP3783765B2 - EGR device for turbocharged engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EGR device for a supercharged engine.
[0002]
[Related background]
As is well known, as one of the techniques for reducing NOx (nitrogen oxide), EGR control is performed in which part of the exhaust gas discharged from the engine is recirculated to the intake side to lower the combustion temperature. Since the EGR recirculation is performed by utilizing the pressure difference between the exhaust passage and the intake passage, in an engine with a supercharger that supercharges intake air, the pressure of the intake passage may vary depending on the operating region of the engine. It may become higher than the pressure and EGR may become impossible.
[0003]
As a technique for increasing the exhaust pressure, for example, a technique described in JP-A-6-33803 can be cited. Although this EGR device is not intended for an engine equipped with a supercharger, the control valve provided in the exhaust system is closed to increase the exhaust pressure, thereby recirculating the EGR. More specifically, in this engine, each cylinder is provided with a timing valve which is an auxiliary intake valve in addition to a normal intake / exhaust valve, and each timing valve is connected to an exhaust port of each cylinder with an air-fuel mixture supply port and a communication passage. And a control valve is provided on the downstream side of the connection location in the exhaust port.
[0004]
A part of the exhaust gas discharged to the exhaust port from the engine is guided from the communication path to the mixture supply port, and after the fuel injected from the fuel injection valve provided in the mixture supply port is mixed, the timing is As the valve is opened, it is introduced into the combustion chamber, whereby the recirculation of EGR is realized. If the exhaust gas is throttled by operating the control valve to the closed side, the exhaust pressure increases, so that the necessary EGR amount can be secured.
[0005]
[Problems to be solved by the invention]
However, since the EGR device described in the above publication is provided with a control valve in the exhaust port of each cylinder, the control valve and the actuator for opening / closing drive are required for the cylinder, which increases the manufacturing cost. is there. In addition, since a control valve is provided in the exhaust port close to the combustion chamber, exhaust gas with a high flow rate immediately after discharge is throttled by the control valve, resulting in a large exhaust resistance and a decrease in engine efficiency. There is also.
[0006]
An object of the present invention is to provide an EGR device for a supercharged engine that can reduce the manufacturing cost by simplifying the configuration and can reliably recirculate EGR without causing a decrease in engine efficiency due to an increase in exhaust resistance. There is to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an EGR device for a multi-cylinder engine having a plurality of first and second exhaust valves in each cylinder and a supercharger for supercharging intake air. An exhaust port connected to the first exhaust valve of each cylinder is connected and assembled , and a first exhaust manifold whose collection portion is connected to the supercharger and an exhaust gas connected to the second exhaust valve of each cylinder. The ports are connected and assembled, and the assembly part is mounted on the second exhaust manifold connected to the assembly part of the first exhaust manifold at a position upstream from the supercharger , and the assembly part of the second exhaust manifold can be opened and closed. The control valve is connected to a position upstream of the control valve of the collecting portion of the second exhaust manifold and the intake passage of the engine, and the EGR passage opened and closed by the EGR valve and the opening and closing timing of the second exhaust valve can be controlled. Variable valve timing means to When the GR valve is opened and the engine is in an operating state in which the intake side pressure in the EGR passage exceeds the exhaust side pressure, the control valve is closed and the second exhaust valve is turned on by the variable valve timing means. And control means for opening the valve earlier than the exhaust valve.
[0008]
Therefore, when the intake side pressure in the EGR passage exceeds the exhaust side pressure and EGR is impossible, the control valve is closed and exhaust gas is throttled, the exhaust pressure upstream from the control valve increases, and the second By opening the exhaust valve early, exhaust gas having a high pressure due to blowdown is discharged, the exhaust pressure is further increased, and EGR can be reliably performed.
[0009]
Since the exhaust pressure is increased by a single control valve provided at the collecting portion of the second exhaust manifold, the manufacturing cost is reduced, and the control valve is separated from the combustion chamber. The exhaust gas whose flow velocity is reduced is throttled by the control valve, and the exhaust resistance hardly increases.
Further, the invention of claim 2 allows the control means to be closed while the EGR valve is opened and the control valve is closed when the intake side pressure of the EGR passage exceeds the exhaust side pressure. The valve timing means advances the valve opening timing of the second exhaust valve from the valve opening timing of the first exhaust valve, and sets the valve closing timing of the second exhaust valve from the valve closing timing of the first exhaust valve. The angle is advanced .
[0010]
Therefore, when exhaust gas begins to be discharged as the first exhaust valve is opened, the exhaust pressure increased by the blow-down suddenly decreases, but the second exhaust valve is closed early, so that the second It is possible to keep the exhaust manifold at a high exhaust pressure at all times.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied in an EGR device for a diesel engine with a supercharger will be described.
FIG. 1 is an overall configuration diagram showing an EGR device of a turbocharged diesel engine according to the present embodiment, FIG. 2 is a detailed diagram showing the configuration of an intake / exhaust valve periphery and a valve drive device, and FIG. 3 is an intake / exhaust valve opening / closing timing. It is explanatory drawing shown. As shown in FIGS. 1 and 2, the engine 1 of this embodiment includes a four-valve valve mechanism. A pair of intake ports 3 is formed in each cylinder in the cylinder head 2, and an intake valve 4 provided in these intake ports 3 is synchronized with the crank angle of the engine 1 by a camshaft (not shown) and shown in FIG. It is opened and closed by IN. The intake ports 3 of the respective cylinders are gathered by an intake manifold 5 and communicated with a common intake passage 6, and a compressor 7 a and an intercooler 9 of a turbocharger 7 as a supercharger are provided in the intake passage 6. Air sucked from an air cleaner (not shown) is compressed by a compressor 7a, cooled by an intercooler 9, and introduced into a combustion chamber (not shown) when the intake valve 4 is opened.
[0012]
The cylinder head 2 is provided with a pair of exhaust ports 10a and 10b for each cylinder, and the exhaust ports 10a and 10b are provided with exhaust valves 11a and 11b. Hereinafter, for convenience of explanation, one is a first exhaust port 10a and a first exhaust valve 11a, and the other is a second exhaust port 10b and a second exhaust valve 11b. Like the intake valve 4 described above, the first exhaust valve 11a of each cylinder is opened / closed by a camshaft at a timing EX1 shown in FIG. 3, and the second exhaust valve 11b of each cylinder is a variable valve as will be described later. It is driven to open and close by a valve drive device 12 as timing means.
[0013]
A first exhaust manifold 13 is connected to the first exhaust port 10a of each cylinder, and a collective portion 13a of the first exhaust manifold 13 is illustrated via a turbine 7b coaxially connected to the compressor 7a. Not connected with the exhaust passage. A second exhaust manifold 14 is connected to the second exhaust port 10b of each cylinder, and a collecting portion 14a of the second exhaust manifold 14 is connected to a collecting portion 13a of the first exhaust manifold 13. ing. Exhaust gas after combustion by injected fuel from a fuel injection valve (not shown) is guided from the combustion chamber to the collecting portion 13a via the first exhaust port 10a and the first exhaust manifold 13, while the second exhaust port 10b. Then, they are guided to the collecting portion 14a through the second exhaust manifold 14 and merge with each other to drive the turbine 7b, and then discharged to the outside through the exhaust passage.
[0014]
A control valve 15 is provided in the collecting portion 14 b on the second exhaust manifold 14 side, and the control valve 15 is driven to open and close by a step motor 16. One end of the EGR passage 17 is connected to the upstream side of the control valve 15 of the collecting portion 14b, and the other end of the EGR passage 17 is connected to the intake passage 6. The EGR passage 17 is provided with an EGR valve 18 that is opened and closed by an actuator (not shown) and an EGR cooler 19.
[0015]
On the other hand, as shown in FIG. 2, the valve drive device 12 described above has a valve spring 20 that urges the second exhaust valve 11 b toward the valve closing side, and a second against the urging force of the valve spring 20. It is comprised from the solenoid 21 which drives the exhaust valve 11b to the valve opening side. The lift amount of the second exhaust valve 11b changes in accordance with the current value and duty ratio for exciting the solenoid 21, and the current value and duty ratio are controlled in synchronism with the crank angle of the engine 1 so that the second The exhaust valve 11b can be opened and closed at an arbitrary timing.
[0016]
In the vehicle compartment, an ECU 31 as a control means includes an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), a timer counter, and the like. (Electronic control unit) is installed, and this ECU 31 performs comprehensive control of the engine 1 including EGR control. Various sensors such as an accelerator sensor 32 for detecting the accelerator operation amount APS by the driver and a rotational speed sensor 33 for detecting the rotational speed Ne of the engine 1 are connected to the input side of the ECU 31. Various actuators such as a step motor 16 of the control valve 15, an EGR valve 18, and a solenoid 21 of the valve driving device 12 of each cylinder are connected.
[0017]
The diesel engine 1 of the present embodiment is configured as an electronic control type that controls the fuel injection amount by driving the sleeve position of a fuel injection pump (not shown) with an actuator. The ECU 31 determines the fuel injection amount Q from a preset map based on the accelerator operation amount APS and the engine rotation speed Ne, and sets the sleeve position of the fuel injection pump with the actuator so that the fuel injection amount Q is achieved. adjust. The fuel injection amount Q at this time is used for EGR control together with the engine rotation speed Ne, and is based on a target EGR amount set as a map in advance based on the fuel injection amount Q (corresponding to the engine load) and the engine rotation speed Ne. The opening degree of the EGR valve 18 is adjusted by the actuator, and EGR control is performed.
[0018]
In the target EGR amount map, the turbocharger 7 is supercharged so that the pressure (supercharging pressure) in the intake manifold 5 exceeds the pressure (exhaust pressure) in the second exhaust manifold 14 and EGR is disabled. A region (that is, a region where the EGR amount obtained from the target EGR amount map cannot be achieved) is set. This EGR impossible region is set mainly in a high load region where the boost pressure rises. In the present embodiment, in this EGR impossible region, control is performed to increase the exhaust pressure to recirculate EGR. Is called. Therefore, details of the exhaust pressure increase control will be described.
[0019]
First, in a normal operation region, that is, an operation region in which the supercharging pressure is lower than the exhaust pressure and the EGR can be recirculated, the control valve 15 is held in a fully opened state by the step motor 16 controlled by the ECU 31 and the ECU 31 Thus, the valve drive device 12 is controlled, and the second exhaust valve 11b is driven to open and close at the same timing EX1 as the first exhaust valve 11a shown in FIG. Therefore, exhaust gas is discharged from the second exhaust port 10b at the same timing as the first exhaust port 10a. In this case, although the exhaust pressure increasing action is not achieved, since a sufficient exhaust pressure higher than the supercharging pressure is originally generated, the EGR is recirculated according to the opening degree of the EGR valve 18 and the target EGR amount Is achieved.
[0020]
Further, in the above-described EGR impossible region, the control valve 15 is controlled to a predetermined closed position by the step motor 16 and the second timing at the timing EX2 earlier than the first exhaust valve 11a shown in FIG. The exhaust valve 11b is opened and closed. Specifically, the opening / closing timing EX2 of the second exhaust valve 11b at this time is advanced both with respect to the opening / closing timing EX1 of the first exhaust valve 11a. On the other hand, the valve opening time is shortened by advancing the valve closing timing. Even at the opening / closing timing EX1, the valve opening is performed before the bottom dead center of the expansion stroke, but at this opening / closing timing EX2, the valve is opened during the earlier expansion of the combustion gas.
[0021]
By the above control, the exhaust gas discharged from the second exhaust port 10b has an effect of increasing the exhaust pressure as described below. First, exhaust gas is throttled when the control valve 15 is closed to flow through the collecting portion 14a of the second exhaust manifold 14, so that the exhaust pressure on the upstream side increases. Further, by opening the second exhaust valve 11b at an early stage, so-called blowdown occurs in which exhaust gas having a high pressure during expansion is discharged, so that the exhaust pressure upstream of the control valve 15 is further increased.
[0022]
When exhaust gas begins to be exhausted from the first exhaust port 10a as the first exhaust valve 11a is opened following the second exhaust valve 11b, the exhaust pressure increased by blow-down rapidly decreases. Since the second exhaust valve 11b is closed early, the inside of the collecting portion 14a of the second exhaust manifold 14 is always maintained at a high exhaust pressure. Therefore, even in this EGR impossible region, the exhaust pressure exceeds the supercharging pressure, and the EGR is reliably recirculated by the pressure difference to achieve the target EGR amount.
[0023]
In the present embodiment, the opening degree of the control valve 15 and the opening / closing timing EX2 of the second exhaust valve 11b in the EGR impossible region are controlled to preset fixed values. However, for example, engine load or supercharging pressure and exhaust pressure are controlled. An optimal control valve opening degree and opening / closing timing EX2 may be set in advance according to the pressure difference from the atmospheric pressure, and the control may be performed based on the set value.
[0024]
As is clear from the above description, in this embodiment, the control valve 15 is provided in the collecting portion 14a of the second exhaust manifold 14 where the exhaust gas of each cylinder collects. Therefore, the exhaust pressure can be increased by the single control valve 15, and the manufacturing cost can be reduced. Further, since the control valve 15 is separated from the combustion chamber, the exhaust gas whose flow rate is sufficiently lowered is controlled by the control valve 15. The exhaust resistance will hardly increase.
[0025]
Therefore, according to the EGR device of the present embodiment, the configuration can be simplified and the manufacturing cost can be reduced, and the EGR can be reliably recirculated without causing a reduction in efficiency of the engine 1 due to an increase in exhaust resistance. There is an effect.
[Second Embodiment]
Hereinafter, a second embodiment in which the present invention is embodied in an EGR device for a turbocharged diesel engine will be described. Here, the EGR device of the present embodiment is mainly different from the second exhaust valve 11b used in the first embodiment in that a dedicated blow-down valve 43 is provided. Therefore, the differences will be described mainly.
[0026]
FIG. 4 is a detailed view showing the configuration of the intake and exhaust valve periphery and the valve driving device in the EGR device of the turbocharged diesel engine of the present embodiment. In the engine 1 of the present embodiment, a pair of exhaust valves 41 (corresponding to the first and second exhaust valves 11a and 11b of the first embodiment) as the first exhaust valves are both opened and closed by a camshaft, The exhaust gas discharged by opening the exhaust valves 41 is guided to the turbine through a common exhaust port 42 and an exhaust manifold. That is, the above configuration is the same as that of a normal engine exhaust system.
[0027]
Each cylinder is provided with a single blow-down valve 43 as a second exhaust valve together with the exhaust valve 41. A blow-down port 44 provided with these blow-down valves 43 has a common blow-down valve (not shown). Connected to the manifold. The blowdown manifold has the same configuration as that of the second exhaust manifold 14 described in the first embodiment with reference to FIG. 1, and the same control valve as that of the control valve 15 of the first embodiment is provided in the assembly portion. At the same time, one end of the EGR passage 17 is connected to the upstream side of the control valve, and the downstream side of the collecting portion is connected to the collecting portion of the exhaust manifold. Therefore, the exhaust gas discharged when the blow-down valve 43 is opened is collected at the assembly portion of the blow-down manifold via the blow-down port 44, and then merged with the exhaust gas on the exhaust manifold side and guided to the turbine. The
[0028]
A driven piston 45 is fixed to the upper end of the blow-down valve 43, and this driven piston 45 is connected to a drive piston 47 through an oil passage 46. When the hydraulic fluid from the pump 48 is always supplied to the oil passage 46 via the check valve 48a and the solenoid valve 49 interposed in the oil passage 46 is closed and communicates with the drain side, the oil passage 46 is provided. The internal hydraulic pressure is relieved to the drain side. The drive piston 47 is disposed on a blow-down cam 50 formed on the camshaft of the valve mechanism of the engine 1, and the drive piston 47 moves up and down by the cam 50 to enter the oil passage 46. Hydraulic pressure synchronized with the crank angle of the engine 1 is generated.
[0029]
In the present embodiment, the driven piston 45, the oil passage 46, the drive piston 47, the pump 48, the solenoid valve 49, and the cam 50 constitute a valve drive device 51 as variable valve timing means.
The solenoid valve 49 is controlled by the ECU 31 and is kept closed in the non-execution region of EGR. Although the drive piston 47 is moved up and down by the blow-down cam 50, the hydraulic pressure in the oil passage 46 is relieved by the solenoid valve 49, so that the driven piston 45 does not operate and the blow-down valve 43 is a valve spring (not shown). To keep the valve closed. Accordingly, the exhaust gas in this case is discharged through the normal path through the exhaust port 42 and the exhaust manifold when the exhaust valve 41 is opened, and the EGR is not recirculated. Since the blow-down valve 43 is closed, the control valve at this time may be controlled to any opening degree.
[0030]
In the EGR execution region, the control valve is controlled to be closed, and the solenoid valve 49 is held in the open state to stop the hydraulic pressure relief described above. Accordingly, the hydraulic pressure generated by the vertical movement of the drive piston 47 is transmitted to the driven piston 45 side through the oil passage 46, and the blowdown valve 43 is opened and closed together with the driven piston 45 in synchronization with the crank angle of the engine 1. Here, the shape of the blowdown cam 50 is such that the blowdown valve 43 is opened and closed at the same timing as the opening / closing timing EX2 on the advance side of the second exhaust valve 11b shown in FIG. 3 of the first embodiment. Is set. As a result, in addition to throttling of the exhaust gas by the control valve, a high exhaust pressure is secured by using the blow-down exhaust gas during expansion, and the exhaust gas is reliably recirculated through the EGR passage.
[0031]
In addition, as the opening degree control of the control valve at this time, for example, in the above-mentioned EGR impossible region, the opening degree is made small to increase the exhaust pressure sufficiently, and when the EGR recirculation becomes easy as the load decreases, the opening degree is increased. Gradually change in the opening direction.
As described above, the configurations of the blowdown manifold and the control valve are the same as the configurations of the second exhaust manifold 14 and the control valve 15 (shown in FIG. 1) of the first embodiment. In addition to simplifying the configuration with a single control valve, the manufacturing cost can be reduced, and the control valve can be separated from the combustion chamber to prevent a situation where the efficiency of the engine 1 decreases due to exhaust resistance when the exhaust gas is throttled. it can.
[0032]
In the second embodiment, the blow-down valve 43 is always opened and closed in the EGR execution area, but may be opened and closed only in the EGR impossible area. In this case, the EGR gas is introduced into the EGR passage 17 from the exhaust manifold through the assembly portion of the blow-down manifold by opening the control valve 15 in an area where EGR can be easily performed.
[0033]
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in each of the above embodiments, the EGR device for the diesel engine 1 is embodied. However, the type of the engine to be applied is not limited to this, and for example, the EGR device for a gasoline engine may be embodied. Further, the valve mechanism of the engine 1 is not limited to the four-valve type, and may be, for example, three valves.
[0034]
Further, in the first embodiment, the opening timing of the second exhaust valve 11b is advanced in order to use the exhaust gas blow-down, and the exhaust pressure is reduced due to the opening of the first exhaust valve 11a. In order to prevent this, the closing timing of the second exhaust valve 11b is also advanced. In the second embodiment, the blow-down valve 43 is opened and closed at the same timing, but the closing timing is not necessarily advanced. There is no need to make it square, for example, it may be closed simultaneously with the first exhaust valve 11a. In this case, although a certain pressure drop occurs with the opening of the first exhaust valve 11a, a sufficiently high exhaust pressure can be obtained by the effective use of blowdown compared to the normal case.
[0035]
Moreover, in each said embodiment, although it actualized as an EGR apparatus of the engine 1 provided with the turbocharger 7 which uses exhaust gas as a supercharger, the kind of supercharger is not limited, For example, by the crankshaft of the engine 1 It is good also as an EGR device for engines provided with a roots type or spiral type supercharger to be driven.
[0036]
【The invention's effect】
As described above, according to the EGR device for an engine with a supercharger according to the present invention, the manufacturing cost can be reduced by simplifying the configuration, and the EGR can be reliably recirculated without causing a decrease in engine efficiency due to an increase in exhaust resistance. Can be made.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an EGR device of a diesel engine with a supercharger according to a first embodiment.
FIG. 2 is a detailed view showing the configuration of the periphery of the intake / exhaust valve and the valve drive device.
FIG. 3 is an explanatory diagram showing opening and closing timings of intake and exhaust valves.
FIG. 4 is a detailed view showing the configuration of an intake / exhaust valve periphery and a valve driving device in an EGR device of a turbocharged diesel engine according to a second embodiment.
[Explanation of symbols]
1 Engine 7 Turbocharger (supercharger)
10a 1st exhaust port 10b 2nd exhaust port 11a 1st exhaust valve 11b 2nd exhaust valve 12, 51 Valve drive device (variable valve timing device)
13 1st exhaust manifold 14 2nd exhaust manifold 13a, 14a Collection part 15 Control valve 17 EGR passage 18 EGR valve 31 ECU (control means)
41 Exhaust valve (first exhaust valve)
43 Blowdown valve (second exhaust valve)
44 Blowdown port

Claims (2)

An EGR device for a multi-cylinder engine having a first and a second plurality of exhaust valves in each cylinder and a supercharger for supercharging intake air,
Connecting and collecting exhaust ports communicating with the first exhaust valve of each cylinder , and a first exhaust manifold in which the collecting portion is connected to the supercharger ;
A second exhaust manifold that connects and collects exhaust ports that communicate with the second exhaust valve of each cylinder, and the collective portion is connected to the collective portion of the first exhaust manifold at a position upstream from the supercharger ; ,
A control valve mounted on the second exhaust manifold so as to be openable and closable;
An EGR passage that is connected to a position upstream from the control valve of the collecting portion of the second exhaust manifold and the intake passage of the engine, and is opened and closed by an EGR valve;
Variable valve timing means capable of controlling the opening and closing timing of the second exhaust valve ;
When the EGR valve is opened and the engine is in an operating state where the intake side pressure in the EGR passage exceeds the exhaust side pressure, the control valve is closed and the second exhaust valve is operated by the variable valve timing means. And a control means for opening the valve earlier than the first exhaust valve. An EGR device for an engine with a supercharger. The control means closes the control valve when the EGR valve is opened and the intake side pressure of the EGR passage exceeds the exhaust side pressure, and the variable valve timing means The opening timing of the second exhaust valve is advanced from the opening timing of the first exhaust valve, and the closing timing of the second exhaust valve is advanced from the closing timing of the first exhaust valve. The EGR device for a supercharged engine according to claim 1, wherein the angle is advanced .

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