The present invention relates to a homogeneous charge compression ignition engine that switches its combustion mode between the spark ignition combustion and the homogeneous charge compression ignition combustion.
Japanese Laid-Open Patent Publication No. 2003-193872 discloses an example of the homogeneous charge compression ignition engine (an HCCI engine) that switches its combustion mode between the spark ignition combustion (SI combustion) and the homogeneous charge compression ignition combustion (HCCI combustion). The HCCI engine has a variable compression ratio mechanism and operates at a high compression ratio in the HCCI combustion and a low compression ratio in the SI combustion. The HCCI engine lowers effective compression ratio by retarding the closing timings of the intake valves in the switching period from the HCCI combustion at the high compression ratio to the SI combustion at the low compression ratio. In this manner, the HCCI combustion mode is quickly ended and switched smoothly to the SI combustion mode.
The variable compression ratio mechanism described in Japanese Laid-Open Patent Publication No. 2003-193872 smoothly switches its combustion mode from the homogeneous charge compression ignition combustion to the spark ignition combustion. However, the mechanism is configured in a complicated manner, which greatly increases the costs for manufacturing the mechanism. Also, the weight of the mechanism is greatly disadvantageous.
The in-cylinder gas temperature in the steady operation of the SI combustion is higher than the in-cylinder gas temperature in the steady operation of the HCCI combustion. Thus, the temperature of the wall surface of each cylinder is relatively high in the SI combustion. This may cause premature ignition and/or knocking in the switching period from the SI combustion to the HCCI combustion. In contrast, the temperature of the wall surface of each cylinder is relatively low in the HCCI combustion. Thus, misfire may occur in the switching period from the HCCI combustion to the SI combustion. These problems caused by the high or low in-cylinder gas temperature in switching of the combustion mode are not addressed to by the technique of Japanese Laid-Open Patent Publication No. 2003-193872.
Accordingly, it is an objective of the present invention to provide a homogeneous charge compression ignition engine that suppresses premature ignition and knocking in a switching period from the spark ignition combustion to the homogeneous charge compression ignition combustion, and a misfire in a switching period from the homogeneous charge compression ignition combustion to the spark ignition combustion.
To achieve the foregoing objectives and in accordance with one aspect of the present invention, a homogeneous charge compression ignition engine having a combustion chamber is provided. The engine is capable of switching combustion mode between a spark ignition combustion and a homogeneous charge compression ignition combustion. The engine includes a plurality of intake ports, an intake port opening/closing device, and a control section. The intake ports communicate with the combustion chamber. The intake ports include at least one first port that is a swirl port and at least one second port that is a non-dedicated swirl port. The intake port opening/closing device selectively opens and closes at least the second port. The control section controls the intake port opening/closing device. In a first switching period, or a switching period in which the spark ignition combustion is switched to the homogeneous charge compression ignition combustion, the control section controls the intake port opening/closing device to close the second port so that an intake air is supplied to the combustion chamber only through the first port. In a second switching period, or a switching period in which the homogeneous charge compression ignition combustion is switched to the spark ignition combustion, the control section controls the intake port opening/closing device to open the second port so that the intake air is supplied through at least the second port.
A preferred embodiment of the present invention will now be described with reference to the attached drawings.
The configuration of a homogeneous charge compression ignition engine (an HCCI engine) 1 according to one embodiment of the present invention as a whole will be explained with reference to
The HCCI engine 1 switches the combustion mode between the spark ignition combustion (SI combustion) and the homogeneous charge compression ignition combustion (HCCI combustion) in correspondence with the operating conditions (engine load and engine speed), when necessary. This allows the HCCI engine 1 to operate with low fuel consumption in the HCCI combustion and with high output in the SI combustion.
As shown in
Subsequently, with reference to
Switching of the intake ports will be described in the following.
The intake port opening/closing valve 12 has a rotary shaft 12c and a valve 12v, which rotates in cooperation with rotation of the shaft 12c. The intake port opening/closing valve 12 is controlled by the ECU 90 to selectively open and close the swirl port 10p and the tumble port 11p, as illustrated in
Alternatively, the intake port opening/closing valve 12 may be replaced by an intake port opening/closing device that selectively opens and closes at least the tumble port 11p. The intake port opening/closing device may be formed by, for example, two lid portions that correspond to the intake ports 10p, 11p. In this case, the lid portions are controlled by the ECU 90 in such a manner that the corresponding one of the intake ports 10p, 11p is selectively opened and closed.
The swirl port 10p will hereafter be explained more specifically with reference to
The swirl port 10p is shaped in such a manner as to generate a swirl flow in the combustion chamber 3. Specifically, the swirl port 10p supplies intake air (fresh air) in a tangential direction of the wall surface of the combustion chamber 3 (by way of example, the tangential direction at point C on the wall surface of the combustion chamber 3 is illustrated in
Even a tumble flow generates, the intake air is cooled by the bore wall surface, the top surface of the piston, and the lower surface of the cylinder head. However, since a relatively great amount of coolant flows in a coolant passage that cools the bore wall surface and the swirl flow contacts the bore wall surface by a great contact area, the swirl flow efficiently cools the intake air compared to the tumble flow.
Next, the tumble port 11p will be explained more specifically with reference to
The tumble port 11p supplies intake air (fresh air) to the combustion chamber 3 in a direction crossing the wall surface of the combustion chamber 3 and in a direction of stroke of a piston 20. This produces a tumble flow in the combustion chamber 3. The tumble flow is a vortex (a vertical vortex) proceeding substantially parallel with the stroke direction of the piston 20. With reference to
The operation of the HCCI engine 1, which is configured as described above, will hereafter be explained with reference to
In the steady operation of the SI combustion and that of the HCCI combustion, the ECU 90 controls the intake port opening/closing valve 12 in such a manner that the swirl port 10p and the tumble port 11p are both used as the intake ports (see
In the present embodiment, the switching period from the SI combustion to the HCCI combustion is referred to as the first switching period (see
As is clear from
More specifically, if the intake air that has passed through the upstream intake port 50p flows through the swirl port 10p and the tumble port 11p, the intake air sent to the tumble port 11p decreases the cooling efficiency in the combustion chamber 3, compared to a case in which solely the swirl port 10p is used. Thus, the combustion chamber 3 is efficiently cooled by using the swirl port 10p exclusively.
In the first switching period, the ECU 90 controls the intake port opening/closing valve 12 in such a manner that the tumble port 11p is held in a closed state until the temperature in the combustion chamber 3 reaches the HCCI required temperature. In other words, the intake port opening/closing valve 12 is controlled in such a manner that the closed state of the tumble port 11p is maintained until switching of the combustion mode is completed. Thus, switching of the combustion mode from the SI combustion to the HCCI combustion is reliably and smoothly carried out.
In the present embodiment, as has been described, the two intake ports communicate with the combustion chamber 3. However, for example, two swirl ports and one tumble port may communicate with the combustion chamber 3. In this case, all of the three ports are used in the steady operation of the SI combustion while one or two swirl ports are used in the first switching period. In other words, the number of the swirl ports that are used in the first switching period may be any suitable count as long as the tumble port is maintained closed during this period.
In the present embodiment, the switching period from the HCCI combustion to the SI combustion is referred to as the second switching period (see
Further, in the second switching period, the ECU 90 controls the intake port opening/closing valve 12 in such a manner that the intake air amount falls below the value before the second switching period. Specifically, the intake port opening/closing valve 12 is operated in such a manner that the number of the intake ports maintained open in the second switching period (the tumble port 11p solely, or one intake port) becomes less than the number of the intake ports maintained open before the second switching period (the swirl port 10p and the tumble port 11p, or the two intake ports). This decreases the intake air amount in the second switching period.
Also, in the second switching period, the ECU 90 controls the throttle 13 in such a manner that the intake air amount falls below the value before the second switching period.
In the present embodiment, the ECU 90 operates in the above-described manner in the second switching period. However, if three or more intake ports are provided, the ECU 90 may operate in a manner different from the above-described manner. For example, if each of the cylinders has two swirl ports and one tumble port, all of the three ports may be used before the second switching period and only the tumble port or the tumble port and one of the swirl ports (a total of two ports) may be used in the second switching period. In other words, the ECU 90 may operate in any other suitable manner as long as three intake ports are used in the steady operation of the HCCI combustion and one or two intake ports are used in the switching period from the HCCI combustion to the SI combustion. Further, in the second switching period, the intake port opening/closing valve 12 is operated in such a manner that the intake air is supplied from at least the tumble port.
As illustrated in
Further, with reference to
Further, in the second switching period, the ECU 90 controls the intake port opening/closing valve 12 and the throttle 13 in such a manner as to maintain the state of a reduced opening degree of the swirl port 10p and the decreased opening size of the throttle 13 until the intake air amount reaches the amount corresponding to the steady operation of the SI combustion. In other words, the intake port opening/closing valve 12 and the throttle 13 are operated to maintain the swirl port 10p in the state of reduced opening degree and the throttle opening size at the lowered level continuously until switching of the combustion mode is completed. As a result, the HCCI combustion mode is reliably and smoothly switched to the SI combustion mode.
The present embodiment has the following advantages.
In the present embodiment, only a swirl flow generated by cold fresh air occurs in the first switching period and cooling (heat exchange) of the interior of the combustion chamber 3 is thus efficiently brought about. This prevents premature ignition and knocking and smoothly switches the SI combustion mode to the HCCI combustion mode. In contrast, the tumble port 11p is reliably used in the second switching period. This prevents the interior of the combustion chamber 3 from being excessively cooled (combustion is maintained without becoming slow), compared to the period in which solely the swirl port 10p is used. The HCCI combustion mode is thus smoothly switched to the SI combustion mode. That is, the HCCI engine 1 of the present embodiment suppresses premature ignition and knocking in the first switching period and misfire in the second switching period, despite of its simple configuration.
In the first switching period, the ECU 90 operates the intake port opening/closing valve 12 in such a manner that the tumble port 11p is held in the closed state until the temperature in the combustion chamber 3 reaches the temperature corresponding to the steady operation of the HCCI combustion. In other words, in the first switching period, the intake port opening/closing valve 12 is controlled in such a manner that the closed state of the tumble port 11p is maintained until switching of the combustion mode is completed. Thus, the SI combustion mode is reliably and smoothly switched to the HCCI combustion mode.
The HCCI engine 1 has the throttle 13, which adjusts the amount of the intake air drawn to the combustion chamber 3. The ECU 90 controls the throttle 13 in such a manner that the intake air amount in the second switching period falls below the value before the second switching period. Through adjustment of the throttle 13, the amount of the intake air sent to the combustion chamber 3 is decreased in the second switching period.
In the second switching period, the ECU 90 controls the intake port opening/closing valve 12 and the throttle 13 until the intake air amount becomes the amount corresponding to the steady operation of the SI combustion. In other words, in the second switching period, the intake port opening/closing valve 12 and the throttle 13 are controlled continuously until switching of the combustion mode is completed. The HCCI combustion mode is thus reliably and smoothly switched to the SI combustion mode.
The throttle 13 is employed as the intake air adjustment device. The amount of the intake air supplied to the combustion chamber 3 is thus decreased by the simple structure.
In the second switching period, the ECU 90 may control the intake port opening/closing valve 12 in such a manner that the intake air amount falls below the value before the second switching period. To ensure desirable fuel consumption and heat efficiency in the HCCI combustion, the air-fuel ratio is increased compared to the value corresponding to the SI combustion, or, in other words, the interior of the combustion chamber 3 is placed in a lean state. The air-fuel mixture in the steady operation of the HCCI combustion is leaner than the air-fuel mixture in the steady operation of the SI combustion. Thus, to switch the HCCI combustion to the SI combustion, the air-fuel ratio in the combustion chamber 3 must be decreased compared to the value in the steady operation of the HCCI combustion to the value in the steady operation of the SI combustion by, for example, reducing the intake air amount. In the present embodiment, the intake air amount is decreased to rapidly reduce the air-fuel ratio in the second switching period. The HCCI combustion mode is thus smoothly switched to the SI combustion mode.
Specifically, the ECU 90 decreases the intake air amount by controlling the intake port opening/closing valve 12 in such a manner that the number of the open intake ports in the second switching period falls below the number of the open intake ports before the second switching period. To smoothly switch between engine operating modes without using the variable compression ratio mechanism disclosed in Japanese Laid-Open Patent Publication No. 2003-193872, exclusive adjustment of the opening size of the throttle 13 may be performed, for example. However, an operation delay (response delay) of the throttle 13 makes it difficult to rapidly reduce the air-fuel ratio solely by adjusting the opening size of the throttle 13. In the present embodiment, the intake air amount is quickly reduced by decreasing the number of the intake ports used in the second switching period. Thus, through the rapid decrease of the air-fuel ratio, the HCCI combustion mode is smoothly switched to the SI combustion mode. Accordingly, by the simple configuration, premature ignition and knocking in the first switching period and increase of torque and misfire in the second switching period are suppressed.
The first port is the swirl port 10p, which is shaped in such a manner as to generate a swirl flow in the combustion chamber 3. The swirl flow is thus reliably produced.
The second port is the tumble port 11p, which supplies the intake air along the stroke direction of the piston. This reliably prevents excessive cooling of the interior of the combustion chamber 3 in the second switching period through the simple configuration.
The present invention is not restricted to the above illustrated embodiment but may be modified in various forms without departing from the scope of the claims.
The “first port” is an intake port that positively supplies an intense swirl flow to the combustion chamber 3. In the illustrated embodiments, the first port is the swirl port 10p shaped in such a manner as to generate a swirl flow. However, the first port may be an intake port that supplies intake air from an opening defined near the wall surface of the combustion chamber 3 in a direction along the wall surface of the combustion chamber 3. The “second port” is a non-dedicated swirl port that does not generate a swirl flow, or produces a low-level swirl flow but does not positively generate an intense swirl flow, or can produce a flow of intake air other than swirl flow. The “low-level swirl flow” refers to a flow of intake air containing a small amount of swirl elements. In the illustrated embodiments, the second port is the tumble port 11p. However, the second port may be a straight port that is arranged at a position at which a swirl flow is not positively generated. Even such a simple configuration suppresses excessive cooling of the interior of the combustion chamber 3 in the second switching period.
Number | Date | Country | Kind |
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2006 323847 | Nov 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2007/073530 | 11/29/2007 | WO | 00 | 2/28/2009 |