JP2014163251A - Spark ignition type engine with turbosupercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark ignition type engine with a turbosupercharger, achieving improved torque by avoiding abnormal combustion when the engine operates in a medium-speed range and in a high-load region.SOLUTION: A valve train 12 is constructed so as to set an opening/closing timing for each of an intake valve 9 and an exhaust valve 10. The valve train 12 sets a valve closing timing for the intake valve in such a manner that charging efficiency is a predetermined value or less when an engine body (an engine 1) operates in a medium-speed range and in a high-load region, sets opening/closing timings for the intake valve and the exhaust valve in such a manner that an overlap period is provided where a valve opening period for the intake valve and a valve opening period for the exhaust valve overlap each other, and sets a valve opening timing for the exhaust valve in such a manner that a timing for a trough in the pressure pulsation of exhaust gas coincides with the overlap period.

Description

  The technology disclosed herein relates to a spark ignition engine with a turbocharger.

  Patent Document 1 describes a spark ignition engine in which a geometric compression ratio is set high in order to improve thermal efficiency. Such a high compression ratio increases the compression end temperature and the compression end pressure, and therefore is likely to cause knocking when the operating state of the engine is in a particularly high load range. Patent Document 1 describes a technique for avoiding knocking by setting the ignition timing after compression top dead center in a high load region where knocking is likely to occur.

  Patent Document 2 discloses a small turbocharger that operates at a relatively small capacity and an engine operating state at a low load and a low speed, and a relatively large capacity and an engine operating condition at a high load. In a diesel engine equipped with a large turbocharger that operates at a high speed, a charging efficiency improving technique using scavenging for the purpose of improving torque is described when the exhaust energy at low load and low speed is low. Specifically, in this turbocharged engine, in the operating region where the small turbocharger is operated, the variable phase timing mechanism (Variable Value Timing: VVT) has an exhaust valve opening period and an intake valve opening period. Is provided, and an exhaust pulsation valley is made to coincide with the overlap period by adjusting the opening timing of the exhaust valve. As a result, the burned gas in the cylinder is pushed out to the exhaust side (that is, scavenging), and the amount of fresh air to be filled in the cylinder is increased by the amount of scavenging, thereby increasing the charging efficiency.

JP 2007-292050 A JP 2009-103084 A

  By the way, the spark-ignition engine with a turbocharger becomes a condition that tends to cause abnormal combustion such as pre-ignition and knocking because the compression end temperature and the compression end pressure increase due to a large supercharging effect in a high load region. . In the high load region, the actual time for changing the crank angle is considerably long in the low speed region where the engine speed is relatively low. For example, even if fuel is injected into the cylinder after the compression top dead center, it is possible to form a mixture. obtain. In the low speed range, abnormal combustion can be avoided by adjusting the fuel injection timing. Also, in the high speed range where the engine speed is relatively high, the actual time with respect to the change in the crank angle is short, so even if fuel is injected during the compression stroke, for example, the reaction time of the unburned mixture becomes short. Combustion is unlikely to occur. On the other hand, in the medium speed range where the engine speed is medium, the fuel / air mixture cannot be formed in time if the fuel is injected after the compression top dead center as in the low speed range, so at least during the compression stroke. The fuel must be injected. On the other hand, the reaction time of the unburned mixture becomes relatively long by increasing the actual time with respect to the crank angle change as compared with the high speed range. Therefore, in a spark ignition engine with a turbocharger that injects fuel near the compression top dead center in order to avoid abnormal combustion, abnormal combustion can be most likely to occur in the medium speed range and in the high load range. . Thus, for example, as in the technique described in Patent Document 1, a measure for avoiding abnormal combustion by delaying the ignition timing can be considered, but delaying the ignition timing causes a decrease in torque. This has the inconvenience that the torque cannot be improved in a high load region in the medium speed range where high torque is required.

  In particular, as described in Patent Document 1, in a high compression ratio engine with a high geometric compression ratio, the compression end temperature and the compression end pressure are further increased by combining the high compression ratio and the supercharging effect. Therefore, abnormal combustion is more likely to occur in the high load region in the medium speed range. If this is to be avoided by delaying the ignition timing, the ignition timing must be significantly retarded after compression top dead center, resulting in a significant reduction in torque.

  The technology disclosed herein has been made in view of the above points, and the purpose thereof is a spark ignition type engine with a turbocharger when the operation state is in a medium speed range and a high load range. In addition, it is intended to improve torque by avoiding abnormal combustion.

  The technology disclosed herein avoids abnormal combustion by performing scavenging when the engine operating state is in a medium speed range and in a high load range. As described above, scavenging provides an overlap period in which both the intake valve and the exhaust valve are opened to push the burned gas in the cylinder toward the exhaust side, thereby lowering the temperature in the cylinder. Also, fresh air having a relatively low temperature is introduced into the cylinder in place of the burned burned gas. Thus, the temperature in the cylinder at the start of compression is lowered, and the compression end temperature is lowered. This is advantageous for avoiding abnormal combustion in the middle speed range and the high load range.

  Here, in order to perform scavenging by providing an overlap period in which the valve opening period of the intake valve overlaps the valve opening period of the exhaust valve, the supercharging pressure on the intake side must be higher than the exhaust pressure on the exhaust side. However, in consideration of increasing the supercharging capability in the low speed region, the turbocharger has a relatively large turbine capacity so that a high supercharging pressure can be obtained by increasing the rotational speed of the turbine even at a low exhaust flow rate. It is common to make it smaller. Thereby, the operating line of the compressor becomes a curve with a large slope such that the pressure ratio becomes higher on the low flow rate side, as indicated by a broken line L2 in the performance curve of the compressor shown in FIG. 5, for example. Note that this operating line deviates from the highest efficiency of the compressor alone (in the vicinity of the ridge of the isoefficiency line in FIG. 5).

  From the viewpoint of protecting the engine and the turbocharger, the turbocharger configured as described above opens a wastegate valve that bypasses the turbine on the exhaust side of the engine from the viewpoint of protecting the engine and the turbocharger. Although the supercharging pressure is made constant at the upper limit (see the portion extending horizontally in broken line L2 in FIG. 5), in this state, the supercharging pressure on the intake side is lower than the exhaust pressure (more precisely, the average exhaust pressure). turn into. That is, when the operating state of the engine is in the middle speed range, even if an overlap period is provided, sufficient scavenging cannot be performed due to the supercharging pressure being lower than the exhaust pressure.

  In view of this, the technique disclosed here sets the valve opening period of the exhaust valve so that the amplitude of the pressure pulsation of the exhaust gas becomes large and the timing of the valley of the pressure pulsation coincides with the overlap period. Thus, in the overlap period, the supercharging pressure is set higher than the pressure in the valley of the pressure pulsation, and scavenging can be performed when the engine is operating in the middle speed range.

  Specifically, a spark-ignition engine with a turbocharger disclosed herein includes an engine body configured to have at least one cylinder, and intake air configured to open and close to introduce intake air into the cylinder. A valve, an exhaust valve configured to open and close to exhaust the exhaust from the cylinder, a valve mechanism configured to set opening and closing timings of the intake valve and the exhaust valve, and the engine body The compressor is arranged on the intake side of the engine and supplies the cylinder with intake air having a predetermined supercharging pressure. The compressor is arranged on the exhaust side of the engine body and is driven by the energy of the exhaust gas discharged from the cylinder. And a turbocharger configured to have a turbine to perform.

  The valve mechanism sets a closing timing of the intake valve so that a charging efficiency is equal to or less than a predetermined value when the operating state of the engine body is in a medium speed range and a high load range, and the intake valve The opening and closing timings of the intake valve and the exhaust valve are set so as to provide an overlap period in which the valve opening period of the exhaust valve and the valve opening period of the exhaust valve overlap, and the valley timing in the pressure pulsation of the exhaust The valve opening timing of the exhaust valve is set so as to coincide with the lap period.

  Here, the “medium speed range” may be a medium speed range when the engine operating range is divided into three types of low speed, medium speed, and high speed with respect to the engine rotational speed. The “medium speed range” may include the medium speed range and a part of the high speed range.

  The “high load region” may be a high load region when the engine operation region is divided into three types of low load, medium load, and high load with respect to high and low engine loads. Further, for example, a predetermined area including a fully open load may be set as a high load area.

  Furthermore, the “opening / closing timing of the intake valve and the exhaust valve” may define, for example, a predetermined amount of lift time (for example, 0.3 mm lift time) as a valve opening time or a valve closing time.

  In addition, the “valve mechanism” may be a mechanism that opens and closes the intake valve and the exhaust valve at a fixed time in synchronization with the rotation of the crankshaft. For example, at least one of the intake valve and the exhaust valve You may comprise as a variable mechanism which can change opening and closing time. The valve operating mechanism may be a variable valve timing mechanism (Variable Value Timing: VVT) that adjusts the phase of the opening / closing timing of the intake valve and / or the exhaust valve. Further, the valve operating mechanism may be a variable valve lift mechanism (VVL) that changes the lift amount of the intake valve and / or the exhaust valve. The variable valve lift mechanism may have two types of cams having different cam profiles and change the lift amount of the intake valve and / or the exhaust valve by switching between the two types of cams. The variable valve lift mechanism may be a mechanism that continuously changes the lift amount of the intake valve and / or the exhaust valve (Continuously Variable Value Lift: CVVL). The valve mechanism may be a combination of VVT and VVL. The intake valve operating mechanism and the exhaust valve operating mechanism may be the same or different.

  According to the above configuration, when the operating state of the engine body is in the medium speed range and in the high load range, the valve mechanism sets the valve closing timing of the intake valve so that the charging efficiency is not more than a predetermined value. Making the charging efficiency lower than a predetermined level lowers the exhaust flow rate and lowers the exhaust pressure. In an engine equipped with a turbocharger, in order to control the boost pressure, a bypass passage that bypasses the turbine is provided on the exhaust side of the engine body, and the opening of the bypass passage is adjusted in the bypass passage. It is common to provide a configured bypass valve. As described above, when the exhaust pressure is lowered, the opening degree of the bypass valve can be reduced or fully closed when the operating state of the engine body is in the medium speed range and the high load range. become. This increases the amplitude of the pressure pulsation of the exhaust gas, and even if the average exhaust pressure is higher than the supercharging pressure, the pressure in the valley of the pressure pulsation can be lower than the supercharging pressure.

  On the other hand, the valve operating mechanism sets the opening and closing timings of the intake valve and the exhaust valve so that the valve opening period of the intake valve and the valve opening period of the exhaust valve overlap each other by a predetermined period, that is, an overlap period is provided. .

  Then, the valve mechanism adjusts the valve opening timing of the exhaust valve, thereby matching the timing of the valley of the pressure pulsation of the exhaust with the overlap period. Thus, during the overlap period, as described above, the supercharging pressure becomes higher than the exhaust pressure (more precisely, the pressure at the valley of the pressure pulsation), and the burned gas in the cylinder is pushed out to the exhaust side. Scavenging is performed. As a result, relatively low temperature fresh air is introduced into the cylinder as the temperature in the cylinder decreases, so that the compression end temperature decreases and abnormal combustion is avoided. Since the abnormal combustion is avoided in this way, the ignition timing can be advanced as much as possible, and the torque can be improved when the engine is operating in the medium speed range and in the high load range. Specifically, in the overlap period, the opening timing of the intake valve is set to 35-40 ° CA before exhaust top dead center, for example, and the closing timing of the exhaust valve is set to 35 after exhaust top dead center, for example, 35 It may be set at ˜40 ° CA, thereby setting at 70-80 ° CA.

  Here, the valve mechanism may set the closing timing of the intake valve to a timing retarded by a predetermined amount from the intake bottom dead center so that the charging efficiency is less than a predetermined value. However, since the operating state of the engine body is in the middle speed range, the inertia effect of intake is strong, and if the charging efficiency is to be less than a predetermined value, the closing timing of the intake valve is significantly delayed after the intake bottom dead center You will have to set the time.

  Therefore, it is preferable that the valve mechanism sets the closing timing of the intake valve to a timing advanced by a predetermined amount from the intake bottom dead center so that the charging efficiency is less than a predetermined value. By doing so, it is possible to easily achieve a filling efficiency of a predetermined value or less in the medium speed range. The closing timing of the intake valve may be set to, for example, 25-30 ° CA before the intake bottom dead center.

  The geometric compression ratio of the cylinder is set to 13 or more, and the valve operating mechanism sets the effective compression ratio of the cylinder to 10 when the operating state of the engine body is in a medium speed range and a high load range. It is good also as setting above.

  That is, the configuration described above has a high geometric compression ratio of the engine body, and accordingly, the effective compression ratio is relatively high when the operating state of the engine body is in the medium speed range and the high load range, In a spark ignition engine that can have a high compression end temperature and compression end pressure, it is effective in that abnormal combustion is avoided and torque is improved.

  A bypass passage that bypasses the turbine is provided on the exhaust side of the engine body, and the spark ignition engine with a turbocharger is interposed in the bypass passage and adjusts the opening of the bypass passage. The bypass valve further includes a bypass valve configured such that when the operating state of the engine body is in the medium speed range and the high load range, the pressure pulsation valley pressure is lower than the supercharging pressure. As such, the opening of the bypass passage may be set to a predetermined opening or less. Here, setting the opening degree of the bypass passage to be equal to or smaller than the predetermined opening degree includes closing the bypass valve fully and setting the opening degree of the bypass passage to (substantially) zero.

  As described above, by setting the opening of the bypass passage to a predetermined opening or less by lowering the exhaust pressure, the amplitude of the exhaust pressure pulsation increases. Can be lower. As a result, scavenging is surely performed. In other words, the “filling efficiency below a predetermined value” is a charging efficiency such that the opening of the bypass passage is less than the predetermined opening and the valley of the pressure pulsation of the exhaust is lower than the supercharging pressure.

  The valve operating mechanism may set the opening / closing timings of the intake valve and the exhaust valve so that an opening period of the exhaust valve is longer than an opening period of the intake valve. As described above, since an overlap period is provided in which the opening periods of the intake valve and the exhaust valve overlap, particularly when the intake valve closing timing is advanced by a predetermined amount from the intake bottom dead center, the intake valve is opened. The valve period is relatively short, and the exhaust valve opening period is relatively long.

  The turbocharger may set the capacity of the turbine so that an operating line of the compressor is within a predetermined range including a maximum efficiency of the compressor in an operation region of the engine body. .

  As described above, in the conventional turbocharger considering the supercharging performance in the low speed range, the turbine capacity is relatively small. Therefore, when the operating range of the engine body is in the middle speed range, the wastegate valve is set. Accordingly, the average exhaust pressure becomes higher than the supercharging pressure.

  In contrast, in the above configuration, the turbocharger sets the turbine capacity so that the operating line of the compressor is within a predetermined range including the highest efficiency of the compressor in the operation region of the engine body. Yes. In other words, the turbine capacity is set to be relatively large. This predetermined range is an example, but is not limited thereto, but may be within a range of 10% with respect to the maximum efficiency. The turbocharger characteristics set in this way are different from the conventional turbocharger characteristics considering the turbocharger performance in the low speed range described above. Can be low. Further, increasing the turbine capacity can lower the exhaust pressure in the middle speed range. The turbine capacity may be set by setting, for example, A / R (that is, A (cross-sectional area of the nozzle most sandwiched portion) and R (distance from the turbine shaft center to the center of the nozzle most sandwiched portion)). .

  For such a turbocharger, as described above, a low charging efficiency that is lower than a predetermined value makes the exhaust gate low and the wastegate valve closes, while the compressor of the turbocharger By setting the operating line near the maximum efficiency, a relatively high boost pressure can be obtained even if the exhaust pressure is low. As a result, the supercharging pressure can be higher than the average exhaust pressure when the operating state of the engine body is in the medium speed region and in the high load region. This is combined with the above-mentioned timing of the valley of the pressure pulsation of the exhaust gas to coincide with the overlap period, so that scavenging is reliably and sufficiently performed. That is, it is advantageous in improving torque by reliably avoiding abnormal combustion.

  As described above, the spark-ignition engine with a turbocharger has a charging efficiency that is set by setting the closing timing of the intake valve when the operating state of the engine body is in the medium speed range and the high load range. While lowering and increasing the amplitude of the exhaust pressure pulsation, the scavenging of the pressure pulsation is made to coincide with the overlap period in which the intake valve opening period and the exhaust valve opening period overlap. The torque is improved by reliably performing the above-described operation to avoid abnormal combustion.

It is the schematic which shows the structure of an engine system. It is the schematic which shows the structure of an engine system. It is a partial cross section figure which shows the structure of the exhaust side in an engine system, (a) The state which opened the variable throttle valve which comprises a throttle part, (b) The state which closed the variable throttle valve. It is an example of the map which shows the driving | operation area | region of an engine. It is an example of the performance curve of a compressor. It is a figure which illustrates the lift amount and opening / closing timing of an intake valve and an exhaust valve. It is a diagram which illustrates the opening and closing timing of the intake valve and the exhaust valve in the low speed and high load range. It is a diagram which illustrates the opening and closing timing of the intake valve and the exhaust valve in the medium speed and high load range. It is an example of the characteristic curve of a turbocharger. It is a timing chart which shows the relationship between the exhaust pulsation in a medium speed high load area, and the valve opening period of an intake / exhaust valve.

  Hereinafter, an engine system according to an embodiment will be described with reference to the drawings. In addition, the following description of preferable embodiment is an illustration. 1 and 2, reference numeral 1 denotes an engine (engine body). In this example, an in-line four-cylinder spark ignition engine having first to fourth four cylinders C1 to C4 is used. In the following description, when it is not necessary to distinguish between the cylinders, the cylinders may be simply indicated by a symbol C. 2 is a cylinder block, 3 is a cylinder head, and 4 is a piston. A combustion chamber 5 is formed by the cylinder block 2, the cylinder head 3, and the piston 4. An intake port 6 and an exhaust port 7 formed in the cylinder head 3 are opened in the combustion chamber 5, and a spark plug 8 is disposed at a substantially central portion of the combustion chamber 5. The intake port 6 is opened and closed by an intake valve 9, and the exhaust port 7 is opened and closed by an exhaust valve 10.

  In addition, for each cylinder C, an injector 11 that directly injects fuel into the cylinder C is attached to the cylinder head 3. In this example, the injector 11 is attached to the intake side of the cylinder head 3 and is configured to directly inject fuel toward the vicinity of the center of the combustion chamber 5.

  The arrangement of the spark plug 8 and the injector 11 can be changed as appropriate.

  The valve operating mechanism 12 that drives the intake valve 9 and the exhaust valve 10 includes VVT (Variable Valve Timing) on each of the intake side and the exhaust side. The VVT moves the valve timing (valve opening / closing timing) back and forth in parallel while maintaining the valve opening periods of the intake valve 9 and the exhaust valve 10. The VVT may adopt a known structure of a hydraulic type, an electromagnetic type, or a mechanical type as appropriate, and illustration of the detailed structure is omitted.

  Among the valve mechanisms 12 that drive the intake valve 9 and the exhaust valve 10, at least the valve mechanism 12 of the intake valve 9 also switches the lift amount of the intake valve 9 between two types of large and small, for example, a hydraulically operated variable mechanism ( Hereinafter, it is referred to as VVL (Variable Valve Lift). Although the detailed illustration of the configuration of the VVL is omitted, the VVL includes a first cam that relatively increases the lift amount of the intake valve 9 and a second cam that relatively decreases the lift amount of the intake valve 9. Two types of cams having different profiles, and a lost motion mechanism that selectively transmits an operating state of one of the first and second cams to the intake valve 9 are configured. Instead of such VVL, the valve mechanism 12 of the intake valve 9 may be provided with a lift amount variable mechanism (CVVL (Continuously Variable Valve Lift)) capable of continuously changing the lift amount. Good. CVVL can adopt various known structures as appropriate, and illustration of the detailed structure is omitted. As illustrated in FIG. 6, the intake valve 9 can change the valve opening timing and valve closing timing, and the lift amount (and valve opening period), respectively, according to VVT and VVL (FIG. 6). (See solid line, dash-dot line and dash-dot line).

  By controlling the valve operating mechanism 12 of the intake valve 9 and the exhaust valve 10, as illustrated in FIG. 6, the opening timing of the intake valve 9 is made before the exhaust top dead center (see the solid line in the figure). Assuming that the closing timing of the exhaust valve 10 is after exhaust top dead center (see the broken line in the figure), a part of the valve opening period of the intake valve 9 and a part of the valve opening period of the exhaust valve 10 overlap, It is possible to set an overlap period (O / L) in which both the intake valve 9 and the exhaust valve 10 open near the exhaust top dead center.

  The exhaust valve 10 may also be provided with a variable mechanism (VVL) that makes the lift amount variable. The VVL of the exhaust valve 10 is different from that of the intake valve 9, in particular, two types of cams having different cam profiles, a first cam having one cam crest and a second cam having two cam crests, and its first You may comprise the lost motion mechanism which selectively transmits the operating state of any one of the 1st cam and the 2nd cam to an exhaust valve. In this configuration, when the operating state of the first cam is transmitted to the exhaust valve 10, the exhaust valve 10 operates in the normal mode in which the valve is opened only once during the exhaust stroke, whereas the operation of the second cam is performed. When the state is transmitted to the exhaust valve 10, the exhaust valve 10 operates in a special mode in which the exhaust valve is opened during the exhaust stroke and is also opened during the intake stroke so that the exhaust is opened twice. . The special mode can be used for internal EGR control in which burnt gas remains in the cylinder C. The internal EGR control may be performed during CI combustion described later.

  The intake port 6 is connected to a surge tank 22 via an independent branch intake passage 21 formed by an intake manifold. One common intake passage 23 is connected to the surge tank 22. In this common intake passage 23, an air cleaner 24, a throttle valve 25, a compressor 26A of a turbocharger 26, and an intercooler 27 are arranged in order from the upstream side to the downstream side.

  An exhaust manifold 31 that constitutes a part of the exhaust passage 30 is attached to the other side surface of the engine 1. The exhaust manifold 31 has first to third independent passage portions 31A, 31B, and 31C that are independent of each other. The first independent passage portion 31A communicates with the exhaust port 7 of the first cylinder C1, the second independent passage portion 31B communicates with the exhaust ports 7 of the second and third cylinders C2, C3, and the third independent passage portion 31C. However, it communicates with the exhaust port 7 of the fourth cylinder C4.

  A housing 32 is connected to the outlet end of the exhaust manifold 31. On the upstream side, the housing 32 forms independent passage portions 32A, 32B, and 32C communicating with the independent passage portions 31A, 31B, and 31C of the exhaust manifold 31, respectively, and as a throttle portion having a variable throttle valve 320 that will be described later. It functions, and forms a collecting portion 32D where the exhaust from each of the independent passage portions 32A, 32B, 32C joins on the downstream side. Here, the variable throttle valve 320 is a valve that changes the cross-sectional areas of the three independent passage portions 32A, 32B, and 32C while maintaining their independent states. The detailed structure of the housing 32 including the variable throttle valve 320 will be described later.

  A housing of the turbocharger 26 is connected to the downstream side of the exhaust passage 30. A turbine 26B of the turbocharger 26 is disposed in the housing. The turbine 26B is connected to the compressor 26A by a connecting shaft 26C. When the turbine 26B is rotationally driven by receiving the energy of the exhaust gas, the compressor 26A is rotationally driven to perform supercharging.

  The exhaust passage 30 is also connected to a bypass passage 34 that bypasses the turbine 26B. The bypass passage 34 is provided with a waste gate valve 341 for adjusting the flow rate of the exhaust gas flowing through the bypass passage 34.

  As shown in FIG. 1, a catalyst 33 for purifying harmful components in the exhaust gas is connected to the exhaust passage 30 downstream of the turbine 26B. The catalyst 33 includes a case and, for example, a three-way catalyst arranged in a flow path in the case.

  Here, the configuration of the exhaust side of the engine system will be described in more detail with reference mainly to FIG. FIG. 3 is a partially broken side view of the exhaust manifold 31 and the housing 32 as viewed in the direction of the cylinder row.

  A flange 311 is provided at the upstream end of the exhaust manifold 31, and the exhaust manifold 31 is fixed to the cylinder head 3 of the engine 1 via the flange 311. As described above, the exhaust manifold 31 has the first to third independent passage portions 31 </ b> A, 31 </ b> B, and 31 </ b> C, and each upstream end is connected to each of the three exhaust ports 7 opened on the side surface of the cylinder head 3. In addition, at the outlet of the exhaust manifold 31, which is the downstream end, three openings are formed side by side in the cylinder row direction, although detailed illustration is omitted. That is, the first opening of the first independent passage 31A, the second opening of the second independent passage 31B, and the third opening of the third independent passage 31C are arranged in a straight line in this order. (See also FIG. 2).

  On the upstream side of the housing 32 connected to the outlet end of the exhaust manifold 31, a partition plate 321 erected along (in parallel with) the flow of exhaust gas is in a cylinder row direction (in the figure, orthogonal to the erection direction). Two sheets are provided at a predetermined interval in a direction perpendicular to the paper surface. One of the two partition plates 321 is erected so as to be continuous with the wall surface that partitions the first opening and the second opening at the joint with the outlet end of the exhaust manifold 31 to partition the inside of the housing 32. The other is erected so as to be continuous with the wall surface that partitions the second opening and the third opening and partitions the inside of the housing 32. As a result, in the section where the exhaust flows along the partition plate 321 on the upstream side in the housing 32, the independent state and the parallel state of the independent passage portions 31A, 31B, 31C are maintained by the two partition plates 321. This portion of the housing constitutes a plurality of independent passage portions 32A, 32B, 32C communicating with the exhaust sides of the plurality of cylinders C, respectively.

  The variable throttle valve 320 described above is disposed on the upstream side of the housing 32. Specifically, the variable throttle valve 320 is provided in a direction crossing the flow of exhaust gas, and a flap shaft 322 supported by the housing 32 and a flap shaft 322 are provided. A flap 323 serving as a valve body that can be turned around, an actuator (not shown) that rotates the flap shaft 322 based on a control signal (an opening command of the variable throttle valve 320), which will be described later, and a flap 323 And a return spring (not shown) for urging the valve in the valve opening direction. The flap 323 has a fan-shaped surface having a fan-shaped cross section that is viewed along the flap shaft 322 and has the flap shaft 322 as a main part of the fan.

  The housing 32 is formed with a bulging portion 324 that bulges upward, and the state in which the flap 323 is stored inside the bulging portion 324 (the state shown in FIG. 3A) The valve is open (fully open). When the variable throttle valve 320 is fully open, the exhaust introduced into the housing 32 from the outlet of the exhaust manifold 31 is guided to the downstream collecting portion 32D without being throttled by the flap 323 (variable throttle valve 320).

  On the other hand, the state in which the flap 323 is driven to rotate about the flap shaft 322 and enters the innermost side than the bulging portion 324 (the state shown in FIG. 3B) is the closed (fully closed) state of the variable throttle valve 320. It is. The opening of the flap 323 is appropriately adjusted between the fully closed state and the fully open state by an actuator.

  When the variable throttle valve 320 is fully closed, as shown in FIG. 3B, the fan-shaped surface of the flap 323 blocks a part of the flow path, so that the exhaust passage cross-sectional area is reduced. Accordingly, the exhaust gas introduced into the housing 32 from the outlet of the exhaust manifold 31 is throttled by the variable throttle valve 320 and then guided to the collecting portion 32D. Here, each rear edge of each partition plate 321 is formed along the fan-shaped surface of the flap 323 when the variable throttle valve 320 is in the closed state. Therefore, when the exhaust is throttled by the flap 323, the exhaust passage is throttled while the independent state and the parallel state of the exhaust passage are maintained.

  The collecting portion 32 </ b> D is a portion formed in the housing 32 on the downstream side of the rear edge of the partition plate 321. A flange is provided on the downstream end side of the housing 32, and the housing of the turbocharger 26 is connected thereto.

  Returning to FIG. 1, reference numeral 100 denotes an ECU (Engine Control Unit) that electrically controls the operation of the engine system. The ECU 100 is a control unit composed of a microprocessor having a CPU, a memory, a counter timer group, an interface, a bus connecting these units, and the like. In addition to the general combustion control such as the fuel supply amount through the control of the injector 11, the throttle opening through the control of the throttle valve 25, and the ignition timing through the control of the spark plug 8, the ECU 100 And VVL) drive control, waste gate valve 341 opening adjustment control, and variable throttle valve 320 opening adjustment control.

  The engine 1 has a geometric compression ratio set to 13 or more from the viewpoint of improving thermal efficiency. Furthermore, by setting the geometric compression ratio to a high compression ratio of 18 or more, for example, in a low load region, compression ignition combustion (CI) can be performed, and the thermal efficiency can be further improved. It is done. In this example, the geometric compression ratio is set to 18, and the engine 1 performs CI combustion in the low load region. On the other hand, as the load on the engine 1 increases, the combustion becomes too steep in the CI combustion, causing problems such as combustion noise. Therefore, in the engine 1, spark ignition combustion (Spark Ignition: SI) is performed in a high load region where the load is higher than the low load region. Thus, the high-compression-ratio engine 1 with a turbocharger illustrated here is comprised so that a combustion form may be switched according to the level of load. However, the technique disclosed herein is not limited to being applied to an engine that performs such CI combustion.

(Engine control in high load areas)
Next, engine control in a high load region will be described with reference to the drawings. As described above, the turbocharged spark ignition engine 1 performs SI combustion in a high load region, but has a very high geometric compression ratio of 18 and is supercharged by the turbocharger 26. Since the supply is performed, the condition is likely to cause abnormal combustion such as pre-ignition and knocking. Even in the high load range, in the low speed range where the engine speed is relatively low, the actual time for changing the crank angle is considerably long. For example, even if fuel is injected into the cylinder after the compression top dead center, the mixture can be formed. Can be. Therefore, although detailed description is omitted, in this engine system, abnormal combustion is avoided by adjusting the fuel injection timing and the ignition timing at least in the low speed / high load region in the operating region of the engine 1 shown in FIG. Further, in the high speed range where the engine speed is relatively high, the actual time for the change in the crank angle is conversely short. For example, even if fuel is injected into the cylinder C during the compression stroke, the reaction time of the unburned mixture is Abnormal combustion is unlikely to occur because it becomes shorter. On the other hand, in the medium speed range where the engine speed is medium, the fuel / air mixture cannot be formed in time if the fuel is injected after the compression top dead center as in the low speed range, so at least during the compression stroke. The fuel must be injected. On the other hand, the reaction time of the unburned mixture becomes relatively long by increasing the actual time with respect to the crank angle change as compared with the high speed range. Therefore, in the operating range of the engine 1 shown in FIG. 4, particularly in the speed range including a part from the middle speed range to the high speed range and the high load range including the fully open load (here, this range is referred to as “medium speed / Abnormal combustion may be most likely to occur. Although it is effective to delay the ignition timing in order to avoid abnormal combustion, in order to avoid abnormal combustion in the high compression ratio engine 1 with the turbocharger, the ignition timing must be greatly retarded. Z There is an inconvenience that the torque is greatly reduced in a medium speed / high load region where high torque is required.

  Therefore, in this engine system, scavenging is performed in a medium speed / high load region so as to avoid abnormal combustion and improve torque. Specifically, by adjusting the valve timing of the intake valve 9 and the exhaust valve 10 after making the characteristics of the turbocharger 26 different from the general characteristics in the past, the medium speed / high load Allows scavenging in the area. Hereinafter, the configuration of the turbocharger 26 and the control of the intake valve 9 and the exhaust valve 10 will be described in order.

(Configuration of turbocharger)
As the turbocharger 26 of the engine 1, a combination of a relatively large turbine 26B and a compressor 26A is used. The reason is as follows.

  Conventionally, from the viewpoint of improving torque response particularly when accelerating from a low speed range, the size of the turbine is often reduced relative to the compressor so that a high pressure ratio can be obtained even in a low speed range where the flow rate of exhaust gas is small. It was. The turbine cannot rotate at high speed without a certain amount of exhaust gas, but if it is a small turbine, it can rotate at high speed even if the flow rate of exhaust gas is small, so the pressure ratio of the compressor in the low speed range is increased ( In other words, the supercharging ability in the low speed range can be increased).

  FIG. 5 is a performance curve graph showing the characteristics of the compressor, in which the vertical axis represents the pressure ratio of the compressor and the horizontal axis represents the discharge flow rate of the compressor. In this graph, lines SL, RL, and CL represent a surge line, a rotation limit line, and a choke line, respectively, and a region surrounded by these lines is a compressor operable region. In addition, a curve group such as a contour line illustrated in this operable region is an isoefficiency line connecting operating points where the efficiency of the compressor is equal, and the curve located at the center side of the region has a higher efficiency. Represents.

  As has been widely used in the past, when a relatively small turbine is used, the rotational speed of the turbine increases in the low speed region of the engine, and the pressure ratio of the compressor also increases relatively sharply. Thus, since a high pressure ratio can be obtained even with a small flow rate, the operating line of the compressor becomes a curve with a large inclination such as the curve L2 in FIG. As a result, a relatively high boost pressure can be obtained even in the low speed region of the engine, so that the torque of the engine in the low speed region increases and the acceleration response from the low speed region is improved. In the curve L2, the pressure ratio reaches a peak from the middle (shifts to a horizontal straight line), but this exceeds the upper limit value provided from the viewpoint of protecting the engine and the turbocharger. This shows that the supercharging pressure control such as opening the waste gate valve 341 is executed because the supply pressure has reached.

  As described above, downsizing the turbine is advantageous for reinforcing the torque in the low speed region of the engine, but on the other hand, in the high speed region of the engine, the flow resistance of the exhaust gas when passing through the turbine is low. There is a drawback that it tends to be high and the pumping loss increases. Further, since the vicinity of the surge line SL of the compressor is frequently used, it cannot be said that it is an efficient usage when viewed from the compressor alone.

  Further, in the above-described medium speed / high load range, the boost pressure is limited by opening the waste gate valve 341 or the like. As a result, the boost pressure becomes lower than the exhaust pressure (more precisely, the average exhaust pressure). . In this state, sufficient scavenging cannot be performed even if scavenging is performed with an overlap period.

  Therefore, in the turbocharger 26, a relatively large turbine 26B is used. More specifically, the operating line of the compressor 26A is within a predetermined range including the maximum efficiency (contour line ridge) of the compressor 26A, more specifically, with respect to the maximum efficiency indicated by a two-dot chain line in FIG. Is set to be within a range of 10% (see curve L1 in FIG. 5). This means that, for example, at the time of acceleration from a low speed region, the high efficiency of the compressor 26A is frequently used, and it is preferable as a use condition of the compressor alone. Further, after the engine speed has increased to some extent, a large pressure ratio can be obtained according to the increase in the rotation of the turbine 26B, and sufficient torque can be secured. In addition, the flow resistance when the exhaust gas flow rate is high (the resistance when the exhaust gas passes through the turbine 26B) is smaller than when the turbine is small, thus reducing the pumping loss in the engine high speed region and improving the fuel efficiency. There is an advantage that can be made. The characteristics of the turbocharger 26 can be changed by adjusting so-called A / R.

  However, in a situation where the flow rate of the exhaust gas from the low speed region is small, such as the early stage of acceleration, the rotational speed of the turbine 26B does not increase easily, and the pressure ratio of the compressor 26A increases only slowly. This means that the torque in the engine low speed region does not increase sufficiently, and the acceleration response from the low speed region becomes worse. As described above, the configuration in which the turbine 26B is enlarged is advantageous in terms of securing torque in the high speed range and fuel consumption, but there is a problem that the torque in the low speed range cannot be sufficiently generated.

  Therefore, in order to deal with such a problem, in this engine system, control for closing the variable throttle valve 320 is executed in the low speed range, and the charging efficiency is increased by dynamic pressure scavenging. That is, the ECU 100 fully closes the variable throttle valve 320 as shown in FIG. Thereby, each independent channel | path part 32A-32C in the housing 32 is made into the aperture_diaphragm | restriction state by which the opening area was made small.

  Exhaust gas traveling from the cylinder in the exhaust stroke to the collective portion 32D of the housing 32 through the exhaust port 7 and the exhaust manifold 31 is increased in flow rate by the fully closed variable throttle valve 320, and then the collective portion It is supplied to the turbine 26B via 32D. In particular, exhaust gas (blow-down gas) generated immediately after the exhaust valve 10 is opened is supplied to the turbine 26B at a higher flow rate.

  Further, by increasing the flow rate of the exhaust gas in the throttle portion, the ejector effect (suction effect) is exerted, and the exhaust gas flowing through one independent passage flows toward another independent passage (that is, In addition, the exhaust gas remaining in the other independent passage is also supplied to the turbine 26B by the ejector effect. Thus, the turbocharger 26 operates efficiently, which is advantageous for increasing the supercharging pressure.

  Furthermore, the scavenging effect of the cylinder in the intake stroke is enhanced by the ejector effect, and the charging efficiency is improved accordingly. That is, in the engine 1, the ignition order is set in the order of the first cylinder C1, the third cylinder C3, the fourth cylinder C4, and the second cylinder C2. For example, the first cylinder C1 moves from the expansion stroke to the exhaust stroke. When the exhaust valve 10 is opened and the exhaust gas starts to be discharged from the combustion chamber 5 to the exhaust port 7 (that is, at the time of blowdown), the second cylinder C2 starts from the exhaust stroke. It is in the transition period (near top dead center) to the intake stroke. In this transition period, an overlap period in which both the intake valve 9 and the exhaust valve 10 are opened is provided under the control of the valve mechanism 12. Specifically, the lift amount of the intake valve 9 in the low speed / high load region shown in FIG. 4 is set to a relatively large value as shown by the one-dot chain line in FIG. The overlap period (O / L) during which both of the valves are opened is set to be long. That is, as shown in FIG. 7, the opening timing of the intake valve 9 is set to a predetermined timing before exhaust top dead center, while the closing timing of the exhaust valve 10 is set to a predetermined timing after exhaust top dead center. Is set.

  Thus, at the time of blowdown of the first cylinder C1, the burned gas in the second cylinder C2 provided with the overlap period is sucked out by the ejector effect, so that the charging efficiency of the second cylinder C2 is improved. Become. The cylinder relationship in which the relationship between the exhaust stroke and the intake stroke is established is as follows. That is, the first cylinder C1 (exhaust stroke) and the second cylinder C2 (intake stroke), the second cylinder C2 (exhaust stroke) and the fourth cylinder C4 (intake stroke), the third cylinder C3 (exhaust stroke) and the first cylinder. C1 (intake stroke), fourth cylinder C4 (exhaust stroke), and third cylinder C3 (intake stroke).

  Further, as shown in FIG. 7, the intake air amount is increased by setting the closing timing of the intake valve 9 after the intake bottom dead center. Since this increases the exhaust energy, this also contributes to the operating efficiency of the turbocharger 26 and is advantageous in increasing the supercharging pressure.

  Thus, by fully closing the variable throttle valve 320 in the low speed range, it is possible to perform scavenging sufficiently, which is advantageous in improving the torque. Note that, in the medium speed range and the high speed range of the engine 1, the ECU 100 fully opens the variable throttle valve 320 (see FIG. 3A). As a result, a large amount of exhaust gas can be efficiently discharged.

  In addition, as a configuration for compensating for the low supercharging performance of the turbocharger 26 in the low speed range, various configurations other than the configuration including the variable throttle unit 320 described above can be adopted. For example, you may employ | adopt the electric turbocharger comprised so that the connection shaft which connects a turbine and a compressor could be rotationally driven with an electric motor. In the low speed range, by driving the electric motor, it is possible to forcibly drive the turbocharger to ensure a desired supercharging performance. In addition to the turbocharger 26, a supercharger driven by the engine 1 may be further provided. This supercharger may be driven mainly to ensure supercharging performance in a low speed range. Further, in addition to the turbocharger 26 having a relatively large turbine capacity, a small turbocharger having a relatively small turbine capacity may be provided in series with the turbocharger 26. A small turbocharger is advantageous in ensuring supercharging performance in a low speed range.

(Control of intake and exhaust valves)
Next, control of the intake valve 9 and the exhaust valve 10 will be described with reference to the drawings. FIG. 6 illustrates the lift curves of the intake valve 9 and the exhaust valve 10 described above. FIG. 7 is a diagram showing the valve opening timing and the valve closing timing of the intake valve 9 (solid line) and the exhaust valve 10 (broken line) in the low speed / high load region, as described above, and FIG. It is a diagram which shows the valve opening timing and valve closing timing of the intake valve 9 (solid line) and the exhaust valve 10 (broken line) in a load area | region, respectively.

  First, in the low speed / high load range, as described above, the lift amount of the intake valve 9 is set to be relatively large through the control of the VVL (see the one-dot chain line in FIG. 6) and through the control of the VVT. The valve opening timing is set to a predetermined timing before exhaust top dead center, and the valve closing timing is set to a predetermined timing after intake bottom dead center. Thereby, the overlap period in which the valve opening period with the exhaust valve 10 overlaps is set to be relatively long. This is because scavenging is performed in the low speed region as described above. Further, the lift amount of the intake valve 9 is set to a large value, and the valve closing timing is set near the intake bottom dead center, so that the intake air amount increases. As described above, this is to effectively perform scavenging in the low speed / high load region and to increase the charging efficiency.

  On the other hand, in the middle speed / high load range, as shown by the solid line in FIG. 6, the lift amount of the intake valve 9 is set to be relatively small through the control of the VVL. Accordingly, the valve opening period of the intake valve 9 becomes relatively short. Further, although the valve opening timing of the intake valve 9 is set to a predetermined timing before exhaust top dead center through VVT control as in the low speed range, the valve opening timing is short as described above. Is set at a predetermined time before the intake bottom dead center (see also FIG. 8). As a result, the overlap period in which the valve opening periods of the intake valve 9 and the exhaust valve 10 overlap is set to be relatively long, while the intake air amount is reduced. Here, the valve opening timing of the intake valve 9 in the medium speed / high load range may be set to 35-40 ° CA before exhaust top dead center. The valve closing timing of the exhaust valve 10 may specifically be set to 35 to 40 ° CA after the exhaust top dead center. The overlap period (O / L) may be 70 to 80 ° CA.

  On the other hand, the closing timing of the intake valve 9 in the medium speed / high load range may be specifically set to 25-30 ° CA before the intake bottom dead center. As a result, the charging efficiency is set to a predetermined value or less, and the effective compression ratio is set to 10 or more in the engine 1 in which the geometric compression ratio is set to 18.

  As shown in FIG. 8, the opening timing of the exhaust valve 10 in the medium speed / high load range is set before the bottom dead center, so that the opening period of the exhaust valve 10 is set to the intake valve 9. (As shown in FIG. 7, in the low speed / high load range, the opening period of the exhaust valve 10 is substantially the same as the opening period of the intake valve 9).

  Thus, the overlap period is provided in order to perform scavenging in the medium speed / high load area as in the low speed area. The reason why the intake valve 9 is closed so as to make the charging efficiency equal to or lower than a predetermined value is to reduce the exhaust amount and thereby reduce the exhaust pressure. Although the intake valve 9 is closed after intake bottom dead center, that is, so-called delayed closing, the charging efficiency can be reduced to a predetermined value or less, but the engine 1 has a relatively high rotational speed. In the region, the inertia effect of the intake air is strong, and if the charging efficiency is to be less than or equal to a predetermined value, the closing timing of the intake valve 9 must be set to a significantly late time after the intake bottom dead center. . Therefore, it is preferable to close the intake valve 9 early.

  Here, FIG. 9 shows the characteristics of the turbocharger 26. As shown by a one-dot chain line (compressor) and two-dot chain line (turbine) in FIG. 9, in a turbocharger equipped with a turbine having a relatively small capacity, which is generally used in the past, in a medium speed range to a high speed range. As mentioned above, the exhaust pressure becomes higher than the supercharging pressure as the wastegate valve opens and restricts the supercharging pressure (in other words, the supercharging pressure is higher than the exhaust pressure). The area is limited to the low speed range where the wastegate valve is closed).

  In contrast, this engine system has a large turbine capacity, so that the exhaust pressure in the medium speed range is lowered and the exhaust pressure is lowered in the medium speed range by the early closing of the intake valve 9 (see FIG. 6), the wastegate valve 341 is thereby set to a fully closed state or a predetermined opening or less, that is, closed in the medium speed range (“W / G closed” arrow in FIG. 9). Note that “closed” here does not only mean that the wastegate valve 341 is fully closed, but also includes that the wastegate valve 341 is slightly opened). In addition, since the operating line of the compressor 26A in the turbocharger 26 is set near the maximum efficiency (see FIG. 5), even if the exhaust pressure is reduced in the medium speed / high load range, the boost pressure is increased. Can be increased. As a result, as shown by a solid line (compressor) and a thick solid line (turbine) in FIG. 6, the supercharging pressure can be set higher than the exhaust pressure in the medium speed region and the high load region of the engine 1.

  In this way, the state of “supercharging pressure> exhaust pressure” makes it possible to push out the burned gas to the exhaust side during the overlap period of the intake valve 9 and the exhaust valve 10, and the medium speed / high load It is possible to perform scavenging reliably in the region. The temperature in the cylinder C is lowered by scavenging, and a relatively low temperature fresh air is introduced into the cylinder C. Therefore, the temperature in the cylinder C at the start of compression can be lowered. Thus, since the compression end temperature and the compression end pressure are lowered, even when fuel is injected into the cylinder C during the compression stroke by the injector 11, the occurrence of abnormal combustion is suppressed or avoided. Accordingly, it is not necessary to significantly retard the ignition timing by the spark plug 8, and the torque in the medium speed / high load region can be improved.

  Further, in this engine system, the opening timing of the exhaust valve 10 is set so that the timing of the valley of the pressure pulsation of the exhaust coincides with the overlap period in the medium speed / high load range, thereby To make sure.

  That is, as described above, in the medium speed / high load range, the charging efficiency is set to a predetermined value or less by closing the intake valve 9 early, thereby reducing the exhaust pressure (more precisely, the average exhaust pressure). Yes. As a result, the wastegate valve 341 is fully closed or set to a predetermined opening or less (see FIG. 9). Since the wastegate valve 341 is closed, as shown in FIG. 10, the amplitude ΔHp of the exhaust pressure pulsation becomes relatively large. The broken line in FIG. 10 shows an example of exhaust pressure pulsation in a conventional turbocharged engine with a general turbocharger in a state where the wastegate valve 341 is fully opened in a medium speed / high load range. ing. In the conventional configuration, since control for reducing the exhaust pressure is not performed, the average exhaust pressure becomes relatively high and the wastegate valve 341 is fully open, so that the amplitude of the exhaust pressure pulsation is small.

  Further, as described above, while the average exhaust pressure is lowered, the supercharging pressure is increased due to the characteristics of the turbocharger 26, so that the pressure pulsation is coupled with the increase in the amplitude ΔHp of the exhaust pressure pulsation. The pressure in the trough is much lower than the supercharging pressure. In this engine system, as shown in FIG. 10, the opening timing of the exhaust valve 10 is appropriately set so that the timing of the valley of the exhaust pulsation coincides with the overlap period (O / L). . As a result, when the intake valve 9 and the exhaust valve 10 are both open, the supercharging pressure becomes higher than the exhaust pressure (more precisely, the pressure of the valley of the exhaust pressure pulsation). Will come to be.

  Thus, in this engine system, “supercharging pressure> average exhaust pressure” is realized in the medium speed / high load range due to the characteristics of the turbocharger 26, and the timing of the valley of the exhaust pulsation is set to the overlap period. By combining the matching, scavenging can be performed reliably and sufficiently. As a result, in this engine system, abnormal combustion in the medium speed / high load range can be avoided more reliably, and torque can be further improved. It should be noted that making the timing of the exhaust pulsation valley coincide with the overlap period is not an essential configuration for scavenging in the medium speed / high load range. In this engine system, at least “supercharging pressure> average exhaust pressure” is achieved in the medium speed / high load range by reducing the characteristics of the turbocharger 26 and the charging efficiency. Is possible.

  Further, in the high speed / high load range where the engine speed is higher than the medium speed / high load range described above, the lift amount of the intake valve 9 is relatively controlled through the control of the VVL, as shown by the two-dot chain line in FIG. Further, the valve opening and closing timing is retarded from the valve opening and closing timing in the medium speed / high load range through the control of VVT. This is because, as described above, abnormal combustion is unlikely to occur in the high speed / high load region, but it is desirable to increase the charging efficiency in view of the improvement in torque. Therefore, in the high speed / high load range, the lift amount of the intake valve 9 is relatively increased, and the valve closing timing is set to a predetermined timing after the intake bottom dead center. Thus, unlike the medium speed / high load range, sufficiently high charging efficiency is realized while including the supercharging effect, and the torque is improved.

  Note that the technique disclosed here is not limited to the turbocharger 26 having a characteristic of low supercharging performance in the low speed region shown by the solid line L1 in FIG. It is also possible to combine with a turbocharger having characteristics in consideration of the supercharging performance in the low speed range. In other words, the technique disclosed herein suppresses the charging efficiency to a predetermined level or less by setting the closing timing of the intake valve 9 in the middle speed / high load range, for example, early closing, thereby reducing the exhaust pressure. ing. As a result, even in the turbocharger of the conventional configuration, the wastegate valve 341 is in the closed state of the fully closed or a predetermined opening or less in the middle speed / high load region. Accordingly, the amplitude of the exhaust pressure pulsation increases.

  As a result, the pressure in the valley of the pressure pulsation of the exhaust can be lower than the supercharging pressure, although the supercharging pressure is similarly lowered due to the low exhaust pressure. Therefore, by matching the timing of the valley of the pressure pulsation of the exhaust gas with the overlap period of the intake valve 9 and the exhaust valve 10, during the overlap period, as shown in FIG. Since the pressure is higher than the pressure in the valley of the pressure pulsation, the cylinder C can be scavenged. Thus, even in the conventional turbocharged engine, it is possible to reduce the compression end temperature and avoid abnormal combustion in the medium speed / high load range.

  The engine system can be mounted on a hybrid vehicle equipped with an electric motor for traveling. As described above, the turbocharger 26 has a low supercharging performance in the low speed range, but in a hybrid vehicle, the electric motor can be driven in the low speed range, so that the low supercharging performance can be compensated. become.

1 Engine (Engine body)
9 Intake valve 10 Exhaust valve 12 Valve mechanism 26 Turbocharger 26A Compressor 26B Turbine C Cylinder

Claims (6)

An engine body configured to have at least one cylinder;
An intake valve configured to open and close to introduce intake air into the cylinder;
An exhaust valve configured to open and close to exhaust the exhaust from within the cylinder;
A valve mechanism configured to set the opening and closing timing of each of the intake valve and the exhaust valve;
The compressor is disposed on the intake side of the engine body and supplies intake air of a predetermined supercharging pressure to the cylinder, and is disposed on the exhaust side of the engine body, and the energy of the exhaust discharged from the cylinder A turbocharger configured to have a turbine for driving a compressor,
When the operating state of the engine body is in a medium speed range and a high load range,
Set the closing timing of the intake valve so that the charging efficiency is below a predetermined value,
Set the opening and closing timing of the intake valve and the exhaust valve so as to provide an overlap period in which the valve opening period of the intake valve and the valve opening period of the exhaust valve overlap,
A spark ignition engine with a turbocharger that sets a timing for opening the exhaust valve so that a valley timing in the pressure pulsation of the exhaust coincides with the overlap period. The spark-ignition engine with a turbocharger according to claim 1,
The valve operating mechanism is a spark ignition engine with a turbocharger that sets a closing timing of the intake valve to a timing advanced by a predetermined amount from an intake bottom dead center so that the charging efficiency is less than or equal to a predetermined value. . The spark ignition engine with a turbocharger according to claim 1 or 2,
The geometric compression ratio of the cylinder is set to 13 or more,
The valve operating mechanism is a spark ignition engine with a turbocharger that sets the effective compression ratio of the cylinder to 10 or more when the operating state of the engine body is in the medium speed range and the high load range. The spark ignition engine with a turbocharger according to any one of claims 1 to 3,
A bypass passage for bypassing the turbine is provided on the exhaust side of the engine body,
A bypass valve interposed in the bypass passage and configured to adjust the opening of the bypass passage;
The bypass valve has an opening degree of the bypass passage so that a pressure in the valley of the pressure pulsation is lower than a boost pressure when the operating state of the engine body is in the medium speed range and in the high load range. A spark-ignition engine with a turbocharger that sets the value below a predetermined opening. The spark ignition type engine with a turbocharger according to any one of claims 1 to 4,
The valve operating mechanism is a spark ignition engine with a turbocharger that sets opening and closing timings of the intake valve and the exhaust valve so that a valve opening period of the exhaust valve is longer than a valve opening period of the intake valve. . The spark ignition type engine with a turbocharger according to any one of claims 1 to 5,
The turbocharger has a capacity of the turbine set so that an operating line of the compressor is within a predetermined range including a maximum efficiency of the compressor in an operation region of the engine body. With spark ignition engine.