JP2008157157A - Multi-cylinder four-cycle engine with internal egr system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-cylinder four-cycle engine with an internal EGR system capable of avoiding a loss of the strength of an engine and the deterioration of the durability of the engine while exhibiting an NOx reducing effect by preventing an excessive intake air temperature rise and an excessive exhaust gas temperature rise during internal EGR which are caused by the generation of high and low intake air temperatures by a cylinder. <P>SOLUTION: A multi-cylinder four-cycle engine with an intercooler is configured to perform internal EGR for an intake valve that performs the minimum sub-lifting of the intake valve during an exhaust stroke and internal EGR for an exhaust valve that performs the minimum sub-lifting of the exhaust valve during an intake stroke. The cam profile of an exhaust cam of a first cylinder group among multiple cylinders is set to an EGR cam profile of the exhaust valve that performs internal EGR for the exhaust valve, and the cam profile of the intake cam of a second cylinder group except for the first cylinder group is set to an EGR cam profile of the intake valve that performs internal EGR for the intake valve. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is mainly applied to a multi-cylinder four-cycle diesel engine and a multi-cylinder four-cycle gas engine. During the exhaust stroke, the intake valve is sub-lifted by a small amount, and a part of the combustion gas is fed into the intake passage to be mixed with the intake air. An intake valve internal EGR that recirculates to the combustion chamber when the valve main valve is opened, and an exhaust valve internal EGR that causes the exhaust valve to sub-lift a small amount during the intake stroke to feed a part of the exhaust gas into the combustion chamber and mix it with the intake air. The present invention relates to a multi-cylinder four-cycle engine with an internal EGR system configured to perform.

  In a 4-cycle diesel engine, 4-cycle gas engine, etc., during the exhaust stroke, the intake valve is separated from the main lift during the intake stroke by a small amount, and a part of the combustion gas in the combustion chamber is sent to the intake passage and mixed into the intake air Intake valve sublift system (intake valve internal EGR) that returns the combustion gas to the combustion chamber when the intake valve is opened by the main lift of the intake valve, or the exhaust valve is separated from the main lift during the exhaust stroke during the intake stroke. There is provided an engine having an internal EGR system of an exhaust valve sublift system (exhaust valve internal EGR) in which a part of exhaust gas in an exhaust passage is recirculated into a combustion chamber and mixed with intake air by sublifting.

One technique related to a multi-cylinder four-cycle engine equipped with such an internal EGR system is a technique provided in Patent Document 1 (Japanese Patent Laid-Open No. 7-133726).
In the technique of Patent Document 1, an intake control valve that opens and closes the intake passage to change the intake passage area is installed in the intake passage, and the intake valve is opened before the intake control valve immediately before the end of the exhaust stroke. The combustion gas (EGR gas) is pushed into the intake passage, which is under negative pressure, as the piston rises, and the intake air mixed with EGR gas is recirculated into the combustion chamber during the intake stroke, and the intake control valve is related to the opening / closing timing of the intake valve. In addition, the internal EGR amount is controlled to a desired value by controlling the pressure (negative pressure) between the intake control valve and the intake valve by controlling the opening and closing according to the engine operating conditions such as the engine load and the engine speed. .
Further, in this technology, the sub-lift amount or sub-lift period of the intake valve or the phase of the sub-lift with the main lift (advance amount from the main lift) and the sub-lift amount or sub-lift period of the exhaust valve for each cylinder are It is uniquely set from engine performance such as output and engine speed.

  Further, in the technique provided in Patent Document 2 (Japanese Patent Laid-Open No. 10-252512), the valve opening polymerization period of the intake valve and the exhaust valve is increased and the internal EGR gas amount is increased as the engine load is reduced. This improves the intake air heating effect, improves self-ignitability at light loads, and expands the stable combustion area.

  Further, in the technique provided in Patent Document 3 (Japanese Patent Laid-Open No. 2000-204984), a variable valve timing mechanism, an exhaust throttle valve, and the like are provided, and when the required internal EGR gas amount is large, the intake valve is opened. The valve timing is advanced, the exhaust valve closing timing is advanced, the opening of the exhaust throttle valve is reduced, and a large amount of EGR gas is sent into the intake port.

JP-A-7-133726 JP-A-10-252512 JP 2000-204984 A

As described above, a multi-cylinder four-cycle engine equipped with an internal EGR system has two internal EGR systems of an intake valve internal EGR system (intake valve sublift system) and an exhaust valve internal EGR system (exhaust valve sublift system). It is used.
In the intake valve internal EGR method, the intake valve is opened twice for the main lift and the sub lift per cycle, and in the exhaust valve internal EGR method, the exhaust valve is opened twice for the main lift and the sub lift per cycle. Have problems to be solved.

  During the exhaust stroke, the intake valve is separated from the main lift during the intake stroke by a small amount, and a part of the combustion gas in the combustion chamber is sent to the intake passage to be mixed into the intake air, and the combustion gas is opened by the main lift of the intake valve. In an intake valve internal EGR type multi-cylinder four-cycle engine that recirculates to the combustion chamber at the time of valve operation, the in-cylinder pressure increases as the piston rises during the exhaust stroke, and the pressure difference between the in-cylinder pressure and the intake port internal pressure Since the intake valve is sub-lifted when there is a problem, the EGR amount can be increased compared to the exhaust valve internal EGR system in which the pressure difference between the exhaust port internal pressure and the cylinder internal pressure is small. It becomes larger than the EGR method.

  However, in the case of the intake valve internal EGR system, the intake valve is sub-lifted during the exhaust stroke, and a part of the combustion gas in the combustion chamber is sent to the intake passage to be mixed into the intake air. As the intake air temperature rises, the combustion temperature and the exhaust gas temperature rise, increasing the engine heat load, and the increase in the combustion temperature promotes the generation of NOx, which reduces the NOx reduction effect by EGR. Yes.

In the case of such an intake valve internal EGR system, as described above, an increase in the intake air temperature due to the internal EGR and an increase in the exhaust gas temperature associated therewith become a problem, but the cylinder inlet on the side farther from the supply air cooler in the intake manifold. The intake air temperature condition tends to be higher than the temperature condition closer to the intake air cooler, and the intake air flow distribution varies in the longitudinal direction of the intake manifold due to the uneven distribution of intake air flow in the intake manifold. Due to the ease, etc., the intake air temperature is often raised or lowered by the cylinder.
For this reason, when the intake valve internal EGR with a large intake air temperature and exhaust gas temperature increase due to the internal EGR is performed in a cylinder having a high intake air temperature, the exhaust temperature is allowed at a high output level such as high engine load and high rotation. There is a problem that the exhaust temperature is exceeded and the engine strength and durability are lowered.

In Patent Document 1 (Japanese Patent Application Laid-Open No. 7-133726), during the exhaust stroke, the intake valve is separated from the main lift during the intake stroke by a small amount, and a part of the combustion gas in the combustion chamber is sucked. Only a four-cycle engine is disclosed that has an internal EGR system that is fed into the passage and mixed into the intake air so that the combustion gas is recirculated to the combustion chamber when the intake valve is opened by the main lift.
Further, in Patent Document 2 (Japanese Patent Laid-Open No. 10-252512), the intake heating effect is increased by increasing the internal EGR gas amount by increasing the valve opening polymerization period of the intake valve and the exhaust valve as the engine load decreases. Only an improved four-cycle engine is disclosed,
Further, in Patent Document 3 (Japanese Patent Laid-Open No. 2000-204984), in the intake valve internal EGR system, the opening timing of the intake valve is advanced and the closing timing of the exhaust valve is advanced, so that the exhaust throttle valve It is configured to reduce the opening and to send a large amount of EGR gas into the intake port,
To solve the problem that the exhaust valve internal EGR is performed with a cylinder having a high intake temperature as described above, the exhaust temperature is excessively increased at a high output level of the engine, and the engine strength and durability are lowered accordingly. The means is not shown in Patent Documents 1, 2, and 3.

  In view of the problems of the prior art, the present invention prevents the intake air temperature and the exhaust gas temperature from excessively increasing during internal EGR due to the occurrence of high and low intake air temperatures by the cylinder, and exhibits the NOx reduction effect while maintaining the engine strength and durability. An object of the present invention is to provide a multi-cylinder four-cycle engine with an internal EGR system capable of avoiding a decrease.

  The present invention solves such a problem, and is a multi-cylinder four-cycle engine equipped with a charge air cooler, and is separated from the main lift of the intake valve during the intake stroke during the exhaust stroke, and the intake valve is set to a minute amount. An intake valve internal EGR that sub-lifts, sends a part of the combustion gas in the combustion chamber to the intake passage and mixes in the intake air, and returns the combustion gas to the combustion chamber when the intake valve is opened by the main lift, and an intake stroke Sometimes, the exhaust valve is separated from the main lift of the exhaust valve during the exhaust stroke, and the exhaust valve is sub-lifted by a small amount, and the exhaust valve internal EGR that sends a part of the exhaust gas in the exhaust passage into the combustion chamber and mixes with the intake air is performed. In the multi-cylinder four-cycle engine with an internal EGR system configured as described above, an exhaust cam that performs the exhaust valve internal EGR is used as the cam profile of the exhaust cam of the first cylinder group among the multiple cylinders. Set EGR cam profile, characterized by a cam profile of the first intake cam of the second cylinder group other than cylinder group is set to the intake valve EGR cam profile for performing internal EGR said intake valve.

In this invention, specifically, the following configuration is preferable.
(1) It is configured to supply intake air from the one air supply cooler to the first cylinder group that performs the exhaust valve internal EGR and the second cylinder group that performs the intake valve internal EGR, The cylinder closer to the intake air cooler is the second cylinder group that performs the EGR inside the intake valve, and the cylinder farther from the intake air cooler than the second cylinder group performs the EGR inside the exhaust valve. The first cylinder group is assumed.

(2) The supply air cooler includes a low temperature side supply air cooler that cools the intake air with low temperature cooling water, and a high temperature side air supply cooler that cools the intake air with high temperature cooling water higher than the low temperature cooling water. And a second cylinder group that performs the intake valve internal EGR is connected to the low temperature side air supply cooler, and a first cylinder group that performs the exhaust valve internal EGR is connected to the high temperature side air supply cooler. To do.
In this case, preferably, the second cylinder group is disposed closer to the low temperature side air supply cooler or the high temperature side air supply cooler than the first cylinder group.

  As described above, in the intake valve internal EGR method, the intake valve is sub-lifted when a pressure difference is generated between the in-cylinder pressure and the intake port internal pressure, and therefore the pressure between the exhaust port internal pressure and the in-cylinder pressure. The EGR amount can be increased more than the exhaust valve internal EGR method with a small difference, and the NOx reduction effect by EGR is larger than that of the exhaust valve internal EGR method, but in the intake valve internal EGR method, part of the combustion gas in the combustion chamber is taken into the intake passage Therefore, there is a problem that the intake air temperature and the exhaust gas temperature rise due to the mixing of the combustion gas.

  However, according to the present invention, in a multi-cylinder four-cycle engine, the multi-cylinder cylinders are divided into two groups, and the cam profile of the exhaust cam of the first cylinder group is sub-lifted by a minute amount during the intake stroke so that the exhaust passage The exhaust valve EGR cam profile that performs EGR inside the exhaust valve that recirculates a part of the exhaust gas in the combustion chamber and mixes it with the intake air is set, and the cam profile of the intake cam of the remaining second cylinder group is set during the exhaust stroke. An intake valve internal EGR is performed in which the intake valve is sub-lifted, a part of the combustion gas in the combustion chamber is fed into the intake passage and mixed with intake air, and the intake mixed combustion gas is returned to the combustion chamber when the intake valve is opened by the main lift. Since it is set to the intake valve EGR cam profile, it depends on the cylinder arrangement and the intake air flow distribution in the intake manifold, etc. Ascertain the temperature states of the intake and exhaust temperatures of each cylinder, and determine the cam profile of the exhaust cam of the first cylinder group, which has been determined that the intake and exhaust temperatures tend to be high. The exhaust valve EGR cam profile is set to suppress the rise of the intake air temperature and the exhaust gas temperature due to the internal EGR as in the exhaust valve internal EGR method, which is smaller in the intake air temperature and the exhaust gas temperature than the method. The cam profile of the intake cam of the second cylinder group, which has been found to be lower than the first cylinder group and has a margin for the maximum allowable intake temperature and exhaust temperature, as described above, It is possible to set the cam profile as in the intake valve internal EGR method in which the intake air temperature and the exhaust gas temperature increase are larger than in the exhaust valve internal EGR method.

  Therefore, according to the present invention, the temperature states of the cylinder intake air temperature and the exhaust gas temperature are grasped in advance at the engine manufacturing stage, and the cam profile of the exhaust valve internal EGR system is set for the first cylinder group having a high temperature state. By applying the cam profile of the intake valve internal EGR method to the second cylinder group having a low temperature state, the first set to the exhaust valve internal EGR method without adjustment during engine operation. Especially in the cylinder group of the above, the engine accompanying the rise in the exhaust temperature while maintaining the exhaust temperature below the allowable exhaust temperature and exhibiting the required NOx reduction effect at the time of the operation of the high output level that particularly requires the durability of the engine. In the second cylinder group that is set to the intake valve internal EGR system, it is possible to prevent the strength and durability from being lowered. The intake air temperature and exhaust temperature at the time of low power level operation x reduction effect is often required it is possible to obtain a large NOx reducing effect while kept below the allowable temperature.

  Further, the cylinder closer to the intake air cooler is used as the second cylinder group for performing the intake valve internal EGR, and the cylinder farther from the intake air cooler than the second cylinder group is used for performing the exhaust valve internal EGR. If the first cylinder group is configured, the intake air temperature at the cylinder inlet remote from the intake air cooler becomes high, and the first cylinder group has a small increase in the intake air temperature and the exhaust gas temperature. As a system, the second cylinder group that maintains the exhaust temperature below the allowable exhaust temperature and can supply the low-temperature intake air from the intake air cooler close to the intake air cooler is used to increase the intake air temperature and the exhaust gas temperature by the internal EGR. As a large intake valve internal EGR system, the exhaust temperature at the time of internal EGR can be kept below the allowable exhaust temperature. Therefore, while exhibiting the NOx reduction effect by the intake valve internal EGR and the exhaust valve internal EGR, In can hold the exhaust gas temperature to below the allowable exhaust temperature.

  Also, the supply air cooler is composed of a low temperature side air supply cooler that cools the intake air with low temperature cooling water and a high temperature side air supply cooler that cools the intake air with high temperature high temperature cooling water, and the low temperature side air supply cooling The second cylinder group for performing the EGR inside the intake valve is connected to the exhaust gas, and the first cylinder group for performing the EGR inside the exhaust valve is connected to the high-temperature side intake air cooler. If the cylinder group is arranged on the side closer to the low temperature side air supply cooler or the high temperature side air supply cooler than the first cylinder group, the intake air is sucked with high temperature cooling water such as engine jacket outlet cooling water. The relatively high temperature intake air from the high temperature side air supply cooler to be cooled is supplied to the first cylinder group that performs the exhaust valve internal EGR system in which the intake air temperature by the internal EGR and the exhaust gas temperature increase are small, thereby reducing the exhaust temperature. Hold below the allowable exhaust temperature and enter the engine. A relatively low temperature intake air from a low-temperature side intake air cooler that cools intake air with low-temperature cooling water such as cooling water is subjected to an intake valve internal EGR system in which the intake air temperature and exhaust gas temperature rise by the internal EGR is large. By supplying to the cylinder group, the exhaust temperature during internal EGR can be kept below the allowable exhaust temperature, and therefore the exhaust temperature is allowed to exhaust in all cylinders while exhibiting the NOx reduction effect by the intake valve internal EGR and exhaust valve internal EGR. It can be kept below the temperature.

  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

FIG. 3 is a cross-sectional view of the main part along the cylinder and intake / exhaust valve center line of the multi-cylinder four-cycle diesel engine having the internal EGR system according to the embodiment of the present invention.
In FIG. 3, 100 is an engine (4-cycle diesel engine), 1 is a cylinder of the engine 100, 1a is a combustion chamber formed in the cylinder 1, and 2 is a piston.
3 is a cylinder head, 4 is an intake port formed in each cylinder head 3, 5 is an intake valve for opening and closing each intake port 4, 6 is an exhaust port formed in each cylinder head 3, and 7 is each exhaust port 6 It is an exhaust valve that opens and closes.

12a is an intake camshaft linked to a crankshaft (not shown), 12 is an intake cam formed on the intake camshaft 12a, 13a is an exhaust camshaft linked to a crankshaft (not shown), and 13 is an exhaust camshaft 13a. It is the formed exhaust cam. 9 is an intake valve tappet, 8 is an intake valve spring, 11 is an exhaust valve tappet, and 10 is an exhaust valve spring, and these constitute a valve operating device.
In such a valve operating apparatus, the intake camshaft 12a and the intake cam 12 are rotationally driven by a crankshaft (not shown), and the intake valve 5 opens and closes each intake port 4 via the intake valve tappet 9, and the crankshaft As a result, the exhaust camshaft 13a and the exhaust cam 13 are driven to rotate, and the exhaust valve 7 opens and closes the exhaust ports 6 via the exhaust valve tappet 11.

In such a 4-cycle diesel engine, intake air (air) pumped from a compressor of a supercharger (not shown) is distributed from the intake manifold 21 (see FIG. 1) to the intake port 4 of each cylinder, and the intake valve 5 is opened. It is introduced into the combustion chamber 1a.
Further, the exhaust gas after ignition combustion in each combustion chamber 1a is stored in the exhaust manifold 23 (see FIG. 1) through the exhaust port 6 by opening the exhaust valve 7, and then sent to the supercharger. To drive the turbocharger turbine.
The present invention relates to an improvement of the internal EGR system in the multi-cylinder four-cycle engine as described above.

FIG. 4 is a suction and exhaust valve timing diagram for a four-cycle engine as shown in FIG. 1 with an internal EGR system.
In the intake valve internal EGR method, that is, the intake valve sublift internal EGR method in a four-cycle engine, as shown in FIG. 4, the intake valve 5 is separated from the main lift In during the intake stroke and is slightly separated during the exhaust stroke. Then, a part of the combustion gas in the combustion chamber 1a is sent to the intake port 4 and mixed with intake air, and the combustion gas is recirculated to the combustion chamber 1a when the intake valve 5 is opened by the main lift In. .
Further, in the exhaust valve internal EGR system, that is, the exhaust valve sublift internal EGR system, the exhaust valve 7 is separated from the main lift Ex of the exhaust valve 7 during the exhaust stroke during the intake stroke, and the exhaust valve 7 is sub-lifted (Es) by a small amount. A part of the exhaust gas in the exhaust port 6 is sent into the combustion chamber 1a and mixed into the intake air.

FIG. 1 is a schematic plan view of a multi-cylinder four-cycle engine (in this example, four cylinders are shown) according to a first embodiment of the present invention.
In FIG. 1, a charge air cooler for cooling intake air (air) from a supercharger (not shown) is denoted by reference numeral 30, and an intake manifold 21 for four cylinders is connected to the intake outlet of the charge air cooler 30. ing. An intake branch pipe 22 to each cylinder 1 is connected to the intake manifold 21, and each intake branch pipe 22 is connected to an intake port 4 (see also FIG. 4) that is opened and closed by the intake valve 5.
On the other hand, an exhaust port 6 (see also FIG. 4) opened and closed by the exhaust valve 7 of each cylinder 1 is connected to an exhaust branch pipe 24, and each exhaust branch pipe 24 is connected to an exhaust manifold 23 for four cylinders. .

In this first embodiment, the multi-cylinder (four cylinders in this example) cylinder is divided into two cylinder groups, a first cylinder group and a second cylinder group, and the cam of the exhaust cam of the first cylinder group. The profile is set to the exhaust valve EGR cam profile for performing the exhaust valve internal EGR, and the cam profile of the intake cam of the second cylinder group is set to the intake valve EGR cam profile for performing the intake valve internal EGR.
In other words, in the first embodiment, the intake air from one air supply cooler 30 is supplied to the first cylinder group that performs the exhaust valve internal EGR and the second cylinder group that performs the intake valve internal EGR. The # 1 cylinder and the # 2 cylinder, which are the cylinders close to the air supply cooler 30, are used as the second cylinder group for performing the intake valve internal EGR, and the cylinder is more than the second cylinder group. The # 3 cylinder and the # 4 cylinder, which are cylinders far from the air supply cooler 30, are used as a first cylinder group that performs exhaust valve internal EGR.
In FIG. 1, 30a is a cooling water inlet pipe of the supply air cooler 30, and 30b is a cooling water outlet pipe.

  In the first embodiment, the division between the first cylinder group and the second cylinder group does not necessarily have to be two cylinders as described above. The distribution of the intake air temperature of each cylinder 1 is obtained by simulation analysis of the distance from each cylinder to each cylinder, the cylinder interval, and the intake air flow distribution in the intake manifold 21, and the far side from the supply air cooler 30 where the intake air temperature increases. The cam profile of the exhaust cam 13 of one or more cylinders (first cylinder group) is set to the exhaust valve EGR cam profile for performing the exhaust valve internal EGR, and the intake air cooler 30 in which the intake air temperature becomes lower than the cylinder 1 The intake valve E that performs the intake valve internal EGR on the cam profile of the intake cam 12 of the remaining one or more cylinders (second cylinder group) on the side close to Is set to R cam profile, assembled engine.

  According to the first embodiment described above, in a multi-cylinder four-cycle engine, the cylinders are divided into two groups, and the cam profile of the exhaust cam 13 of the first cylinder group is set to a small amount of sublift ( Es), an exhaust valve EGR cam profile for performing an exhaust valve internal EGR that causes a part of the exhaust gas in the exhaust port 6 to recirculate into the combustion chamber 1a and be mixed into the intake air is set, and the remaining second cylinder group During the exhaust stroke of the cam profile of the intake cam 12, the intake valve 5 is sub-lifted (Is) by a small amount, a part of the combustion gas in the combustion chamber 1a is sent to the intake port 4 and mixed into the intake air, and the main lift (In ) Is set to the intake valve EGR cam profile for performing EGR inside the intake valve for returning the intake mixed combustion gas to the combustion chamber 1a when the valve is opened. The temperature state of the intake air temperature and the exhaust gas temperature of each cylinder 1 is ascertained based on the arrangement of the compressor 1, the flow rate distribution of the intake air in the intake manifold 21, and the like. The cam profile of the exhaust cam 13 of one cylinder group is set to the exhaust valve EGR cam profile so as to be performed by the exhaust valve internal EGR method in which the intake air temperature and the exhaust temperature rise are smaller than those of the intake valve internal EGR method. While suppressing the rise in intake and exhaust temperatures due to EGR, it was understood that the intake and exhaust temperatures tend to be lower than the first cylinder group, and that there is room for the maximum allowable intake and exhaust temperatures. As described above, the cam profile of the intake cam 12 of the second cylinder group is higher in the intake air temperature and the exhaust gas temperature than in the exhaust valve internal EGR system. It is possible to set the exhaust valve EGR cam profile as performed by the intake valves of internal EGR system.

  Therefore, according to the first embodiment, in the manufacturing stage of the engine 100, the temperature states of the intake air temperature and the exhaust gas temperature of the cylinder 1 are grasped in advance, and the exhaust valve internal EGR for the first cylinder group having the high temperature state is obtained. By applying the cam profile of the system and applying the cam profile of the intake valve internal EGR system to the second cylinder group having the low temperature state, the exhaust valve internal EGR system is not adjusted during the operation of the engine 100. In the first cylinder group set to, the exhaust temperature is kept below the allowable exhaust temperature at the time of operation at a high output level where maintenance of the durability of the engine is particularly required, and the required NOx reduction effect is exhibited while exhausting. In the second cylinder group set to the intake valve internal EGR system, it is possible to prevent a decrease in engine strength and durability due to temperature rise. In particular, a large NOx reduction effect can be obtained while suppressing the intake air temperature and the exhaust gas temperature to the permissible temperature or lower during operation at a low output level where a large NOx reduction effect by EGR is required.

  Further, the cylinders (for example, # 1 and # 2 cylinders) closer to the supply air cooler 30 are used as a second cylinder group for performing the intake valve internal EGR, and the supply air cooler 30 is arranged more than the second cylinder group. Since the far side cylinders (for example, # 3 and # 4 cylinders) are configured as the first cylinder group that performs the exhaust valve internal EGR, the intake air temperature at the inlet of the cylinder 1 is separated from the supply air cooler 30. The first cylinder group, which tends to be high, is an exhaust valve internal EGR system in which the intake air temperature and the exhaust gas temperature increase are small, and the exhaust gas temperature is kept below the allowable exhaust gas temperature. The second cylinder group that can supply low-temperature intake air from the intake valve internal EGR system with a large increase in intake air temperature and exhaust temperature due to internal EGR, keeps the exhaust temperature during internal EGR below the allowable exhaust temperature Can, therefore while exhibiting NOx reduction effect due to the internal EGR and the exhaust valve internal EGR intake valve can hold exhaust gas temperature below the allowable exhaust temperature at all cylinders.

FIG. 2 is a schematic plan view of a multi-cylinder four-cycle engine (in this example, four cylinders are shown) according to a second embodiment of the present invention.
In this second embodiment, the supply air cooler includes a low temperature side supply air cooler 45 that cools the intake air with low temperature cooling water such as engine inlet cooling water, and the low temperature cooling such as engine jacket outlet cooling water. A second cylinder group (this example) that includes a high-temperature side air supply cooler 40 that cools intake air with high-temperature cooling water that is higher than water, and that performs the intake valve internal EGR in the low-temperature side air supply cooler 45 In the first cylinder group (# 3, # 2 in this example), a low temperature side intake manifold 47 connected to # 1 and # 2 cylinders is connected, and the high temperature side air supply cooler 40 performs the exhaust valve internal EGR. The high temperature side intake manifold 43 communicated with the four cylinders) is connected.
In FIG. 2, 46 is a cooling water inlet pipe of the low temperature side air supply cooler 45, 47 is a cooling water outlet pipe, 41 is a cooling water inlet pipe of the high temperature side air supply cooler 40, and 42 is a cooling water outlet pipe. It is.

The second embodiment is configured as described above. Preferably, in addition to the above-described configuration, the high temperature side air supply cooler 40 and the low temperature side air supply cooler 45 are provided in the same manner as the first embodiment. The # 1 cylinder and # 2 cylinder, which are the closer cylinders, are used as the second cylinder group for performing the EGR inside the intake valve, and the higher temperature side air supply cooler 40 and the lower temperature side air supply cooling than the second cylinder group. The cylinders # 3 and # 4, which are the cylinders far from the chamber 45, serve as a first cylinder group that performs exhaust valve internal EGR.
Other configurations are the same as those of the first embodiment, and in FIG. 2, the same members as those of the first embodiment are denoted by the same reference numerals.

  According to the second embodiment described above, the supply air cooler includes the low temperature side air supply cooler 45 that cools the intake air with the low temperature cooling water, and the high temperature side air supply cooler 40 that cools the intake air with the high temperature high temperature cooling water. And a second cylinder group (in this example, # 1 and # 2 cylinders) that performs EGR inside the intake valve is connected to the low temperature side air supply cooler 45, and the exhaust valve inside is connected to the high temperature side air supply cooler 40. The first cylinder group for performing EGR is connected (# 3 and # 4 cylinders in this example), and then the second cylinder group is placed on the lower temperature side than the first cylinder group as in the first embodiment. Since the air supply cooler 45 and the high temperature side air supply cooler 40 are arranged on the side close to the supply air cooler 45, the high temperature side air supply cooler 40 that cools the intake air with high temperature cooling water such as jacket outlet cooling water of the engine 100. From the relatively high temperature intake air through the high temperature side intake manifold 43, The exhaust gas temperature is kept below the allowable exhaust gas temperature by supplying it to the first cylinder group (# 3 and # 4 cylinders in this example) that performs the exhaust valve internal EGR system in which the rise of the intake air temperature and exhaust gas temperature by the part EGR is small Then, the relatively low temperature intake air from the low temperature side intake air cooler 45 that cools the intake air with the low temperature cooling water such as the engine inlet cooling water is supplied to the intake air temperature and the exhaust gas temperature by the internal EGR via the low temperature side intake manifold 47. By supplying to the second cylinder group (# 1 and # 2 cylinders in this example) that performs the intake valve internal EGR system with a large degree of increase, the exhaust temperature at the time of internal EGR can be kept below the allowable exhaust temperature. While exhibiting the NOx reduction effect of the valve internal EGR and exhaust valve internal EGR, the exhaust temperature can be kept below the allowable exhaust temperature in all cylinders, and the intake temperature and exhaust temperature rise The reduction in engine strength and durability associated can be prevented.

  According to the present invention, it is possible to prevent the intake air temperature and the exhaust gas temperature from excessively rising during internal EGR due to the occurrence of high and low intake air temperatures by the cylinder, and to avoid a decrease in engine strength and durability while exhibiting a NOx reduction effect. A multi-cylinder four-cycle engine with an internal EGR system can be provided.

1 is a schematic plan view of a multi-cylinder four-cycle engine according to a first embodiment of the present invention. FIG. 3 is a schematic plan view of a multi-cylinder four-cycle engine according to a second embodiment of the present invention. It is principal part sectional drawing in alignment with the cylinder of a multi-cylinder 4 cycle diesel engine provided with the internal EGR system which concerns on the Example of this invention, and an intake and an exhaust valve. FIG. 6 is a timing diagram of intake and exhaust valves of a 4-cycle engine equipped with an internal EGR system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 1a Combustion chamber 2 Piston 3 Cylinder head 4 Intake port 5 Intake valve 6 Exhaust port 7 Exhaust valve 12 Intake cam 12a Intake cam shaft 13 Exhaust cam 13a Exhaust cam shaft 21 Intake manifold 23 Exhaust manifold 30 Supply air cooler 40 High temperature side Supply air cooler 43 High temperature side supply manifold 45 Low temperature side supply air cooler 47 Low temperature side supply manifold 100 Engine (4-cycle diesel engine)
In Intake valve main lift Is Intake valve sublift Ex Exhaust valve main lift Es Exhaust valve sublift

Claims (4)

  A multi-cylinder four-cycle engine equipped with an intake air cooler, which is separated from the main lift of the intake valve during the intake stroke during the exhaust stroke, and a small amount of the intake valve is sub-lifted so that the combustion gas in the combustion chamber The intake valve is fed into the intake passage and mixed into the intake air, and the intake valve internal EGR is returned to the combustion chamber when the intake gas is opened by the main lift of the intake valve, and the main exhaust valve during the exhaust stroke is performed during the intake stroke. Separately from the lift, the exhaust valve is sub-lifted by a small amount, and an exhaust valve internal EGR configured to perform a part of the exhaust gas in the exhaust passage into the combustion chamber and mix it with the intake air. In the cylinder four-cycle engine, the cam profile of the exhaust cam of the first cylinder group in the multi-cylinder is provided in the exhaust valve EGR cam profile that performs the exhaust valve internal EGR. The multi-cylinder four-cycle with internal EGR system is characterized in that the cam profile of the intake cam of the second cylinder group other than the first cylinder group is set to the intake valve EGR cam profile for performing the intake valve internal EGR. engine.   The intake air cooler is configured to supply intake air to the first cylinder group that performs the exhaust valve internal EGR and the second cylinder group that performs the intake valve internal EGR, and the supply air cooling The cylinder on the side closer to the exhaust is used as the second cylinder group for performing the intake valve internal EGR, and the cylinder on the side farther from the supply air cooler than the second cylinder group is used for the exhaust valve internal EGR. The multi-cylinder four-cycle engine with an internal EGR system according to claim 1, wherein the multi-cylinder four-cycle engine has an internal EGR system.   The supply air cooler is constituted by a low temperature side air supply cooler that cools the intake air with low temperature cooling water, and a high temperature side air supply cooler that cools the intake air with high temperature cooling water higher in temperature than the low temperature cooling water. A second cylinder group that performs the intake valve internal EGR is connected to the low temperature side air supply cooler, and a first cylinder group that performs the exhaust valve internal EGR is connected to the high temperature side air supply cooler. The multi-cylinder four-cycle engine with an internal EGR system according to claim 1.   The second cylinder group that performs the intake valve internal EGR is disposed closer to the low temperature side air supply cooler or the high temperature side air supply cooler than the first cylinder group that performs the exhaust valve internal EGR. The multi-cylinder four-cycle engine with an internal EGR system according to claim 3.

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