JP4432708B2 - 4-cycle engine - Google Patents

Description

  The present invention relates to a four-cycle engine, and more particularly to a four-cycle engine having a turbocharger as a supercharger.

  In general, a technique is known that uses an internal EGR gas to improve the ignitability of an air-fuel mixture and enhance the exhaust performance, thereby ensuring a necessary EGR rate in a wide operating range (for example, Patent Documents 1 and 2). In the configuration according to the prior art, the intake valve is opened during the exhaust stroke, or the exhaust valve is opened during the intake stroke, so-called internal EGR is realized.

However, in the high load operation region, the internal EGR gas becomes considerably high temperature, so that the fuel burns at a time and knocking is likely to occur. Therefore, in order to prevent knocking in a high load operation region, a technique for delaying the closing timing of the exhaust valve after the top dead center of the exhaust stroke has been proposed (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 9-25853 JP 2001-107759 A JP 2001-214741 A

  In order to improve the performance of the engine as a whole, it is necessary to increase the mechanical compression ratio as much as possible, secure internal EGR gas in a wide range of operation, and prevent knocking.

  However, the techniques disclosed in Patent Documents 1 and 2 do not take countermeasures for knocking in the high load operation region, and therefore it is difficult to use the internal EGR gas in the high load operation region.

  On the other hand, in the technique disclosed in Patent Document 3, the closing timing of the exhaust valve is retarded after the top dead center of the exhaust stroke, and a countermeasure against knocking is taken. Therefore, in order to avoid interference between the exhaust valve and the cylinder, compression is performed. There is a problem that the ratio cannot be made high, and the combustion efficiency cannot be increased in this respect.

  The present invention has been made in view of the above problems, and provides a four-cycle engine that can increase the mechanical compression ratio as much as possible, secure internal EGR gas in a wide range of operation, and prevent knocking. The challenge is to do.

In order to solve the above problems, the present invention includes a first intake cam to open the intake valves in air intake stroke, with opening the intake valve at least exhaust stroke prior to opening of the intake valve in the intake stroke, at the latest A valve mechanism including a second intake cam that closes the intake valve before the top dead center of the exhaust stroke, a control device that controls the valve mechanism in accordance with the operating state of the engine, and intake air to the engine body A supercharger for supercharging; and an intercooler for cooling the supercharged air, wherein the valve operating mechanism has an intake valve opening / closing timing by the first intake cam and an intake valve opening / closing timing by the second intake cam. has a variable valve timing mechanism for changing, the control device, the intake valve closing timing according to the first intake valve closing timing and the second intake cam by the intake cam retarded as the engine load increases Has a valve timing control means for controlling the valve timing mechanism so that, et at least the high-load operation region of engine, wherein the controller, the second in addition to the intake valve opening and closing operation by the first intake cam The valve mechanism is controlled so that the intake valve is opened and closed by the intake cam, and the valve timing control means sets the intake valve close timing by the first intake cam so that the effective compression ratio is smaller than the expansion ratio. The four-cycle engine is characterized in that the variable valve timing mechanism is controlled so that the timing is a predetermined amount or more later than the bottom dead center.

  In this aspect, since the intake valve is opened at least in the exhaust stroke prior to the opening of the intake valve in the intake stroke, and the second intake cam that closes the intake valve before the top dead center of the exhaust stroke is provided at the latest. The internal EGR can be realized at a timing at which the exhaust valve does not interfere with the piston. Therefore, the geometric compression ratio can be increased as much as possible. In addition, since the intake valve is opened during the exhaust stroke, a large amount of burned gas can flow back into the intake passage and be cooled in the intake passage. Therefore, in the intake stroke by the first intake cam, a large amount of backflowed EGR gas is supplied. However, as the internal EGR gas is cooled in the intake passage, the engine load is relatively high. In spite of the EGR, the knocking can be effectively suppressed. In addition, at least in the high load operation region of the engine, the first intake cam opens the intake valve at a timing later than the bottom dead center by a predetermined amount or more so that the effective compression ratio becomes smaller than the expansion ratio. It is possible to achieve a so-called mirror cycle function (function to reduce temperature rise due to adiabatic compression in the compression stroke) by the cam.

Further, the four-cycle engine of the present invention includes a supercharger that supercharges the intake air of the engine body, and an intercooler that cools the supercharged air. According to this configuration, in at least the high load operation region of the engine, the intake valve closing timing by the first intake cam is set to a timing later than the bottom dead center by a predetermined amount or more so that the effective compression ratio becomes smaller than the expansion ratio. In combination with the adoption of a turbocharger and intercooler, it is also possible to realize a mirror cycle function in a high-load operation region, improving the filling efficiency and reducing the pumping loss. Thus, torque can be increased and knocking can be effectively suppressed.

Furthermore, in the four-cycle engine of the present invention equipped with a supercharger or the like, the variable valve timing mechanism of the valve mechanism can change the intake valve open / close timing by the first intake cam and the intake valve open / close timing by the second intake cam. The valve timing control means for controlling the variable valve timing mechanism sets the intake valve opening / closing timing by the first intake cam and the intake valve opening / closing timing by the second intake cam as the engine load increases. According to this configuration, in the predetermined high-load operation region, when the phase is changed so that the first intake cam has a timing that is a predetermined amount or more later than the bottom dead center so that the effective compression ratio becomes smaller than the expansion ratio. As the phase changes, the phase of the second intake cam is also closed late, so that when the internal EGR gas is introduced, the burned gas can flow back to the intake passage side at a timing delayed by a considerable time. As a result, the burnt gas having a somewhat low temperature can be caused to flow back into the intake passage, which can contribute to a decrease in the temperature of the internal EGR gas.

  In a specific aspect, the valve mechanism has a valve timing lift mechanism capable of stopping the valve opening operation of the intake valve by the second intake cam, and the control device is operated from an operation region on a low load side of the engine. The valve is operated so that the intake valve is opened by the second intake cam over the high load operation region except the engine fully open region, and the intake valve open operation by the second intake cam is stopped in the engine fully open region. Valve lift control means for controlling the timing lift mechanism is provided. In this aspect, internal EGR in the high load operation region excluding the engine fully open region (full open load operation region of the throttle valve opening where the pressure difference before and after the throttle valve is eliminated) is realized as much as possible to improve the charging efficiency. Exhaust performance can be improved, and knocking can be suppressed by stopping the internal EGR in the engine fully open region.

  In another specific aspect, the valve mechanism includes a valve timing lift mechanism capable of stopping the valve opening operation of the intake valve by the second intake cam, and the control device is configured to perform a second operation in a high speed region of the engine. Valve lift control means for controlling the valve timing lift mechanism so as to stop the valve opening operation of the intake valve by the intake cam is provided. In this aspect, internal EGR in the high-load operation region excluding the high-speed rotation region of the engine can be realized as much as possible to improve the charging efficiency and the exhaust performance. In the high-speed rotation region of the engine, By stopping the internal EGR, it becomes possible to cope with suppression of knocking.

  In a further preferred aspect, the valve timing lift mechanism has a lost motion mechanism that can interrupt drive transmission between the second intake cam and the intake valve. In this aspect, the internal motion EGR can be surely stopped by the lost motion mechanism.

The present invention also provides a first intake cam that opens the intake valve in the intake stroke, and opens the intake valve at least in the exhaust stroke prior to opening the intake valve in the intake stroke, and at the latest from the top dead center of the exhaust stroke. A valve mechanism that includes a second intake cam that closes the intake valve before and a control device that controls the valve mechanism in accordance with an operating state of the engine, wherein the valve mechanism includes the second intake cam. An intake side valve timing lift mechanism capable of stopping the valve opening operation of the intake valve by means of a second exhaust cam that opens the exhaust valve in the intake stroke separately from the first exhaust cam that opens the exhaust valve in the exhaust stroke, and the second exhaust and stoppable exhaust side valve timing lift mechanism the opening operation of the exhaust valve by the cam, the variable valve timing for changing the intake valve closing timing according to the first intake valve closing timing and the second intake cam by the intake cam And a structure, the control device, the operating region of the low load side of the engine of the intake valve in the exhaust stroke of the second intake cam with to perform opening and closing operation of the exhaust valve in the intake stroke of the second exhaust cam The valve opening operation is stopped, and in the high load operation region of the engine, the intake valve is opened and closed during the exhaust stroke by the second intake cam and the exhaust valve opening operation during the intake stroke by the second exhaust cam is stopped. As described above, the valve lift control means for controlling the valve timing lift mechanism on the intake side and the exhaust side , and the intake valve closing timing by the first intake cam in at least the high load operation region of the engine, the effective compression ratio is the expansion ratio. Valve timing control means for controlling the variable valve timing mechanism so that the timing is a predetermined amount or more later than the bottom dead center so as to be smaller than It is a 4-cycle engine according to claim Rukoto.

  In this aspect, in the low load operation region until the engine reaches the high load operation region, the exhaust valve is opened again at the intake valve opening timing, so the high-temperature burned gas is directly introduced into the cylinder. It is possible to improve ignitability, and in the operating region on the high load side of the engine, it is possible to cool the burned gas by flowing it back into the intake passage to suppress knocking.

  As described above, according to the present invention, the mechanical compression ratio is increased as much as possible, the internal EGR gas can be secured in a wide range of operation, and knocking can be prevented.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a schematic configuration of a four-cycle gasoline engine 10 according to an embodiment of the present invention, and FIG. 2 shows one cylinder of an engine body 20 according to FIG. 1 and intake / exhaust provided thereto. It is a cross-sectional schematic diagram which shows structures, such as a valve.

  With reference to the figure, the illustrated four-cycle gasoline engine 10 includes an engine body 20. The engine body 20 integrally includes a cylinder block 22 that rotatably supports the crankshaft 21 and a cylinder head 23 that is disposed above the cylinder block 22.

  The cylinder block 22 and the cylinder head 23 are provided with a plurality of cylinders 24. In the present embodiment, the compression ratio of each cylinder 24 is set to 11.

  Each cylinder 24 is provided with a piston 25 connected to the crankshaft 21 and a combustion chamber 26 formed in the cylinder 24 by the piston 25 in the same manner as a known configuration. The cylinder block 22 is provided with a crank angle sensor 27 that detects the rotational speed of the crankshaft 21.

  A fuel injection valve 28 that directly injects fuel into the combustion chamber 26 is provided at the side of each combustion chamber 26. An ignition plug 29 is provided at the top of each combustion chamber 26, and the plug tip faces the combustion chamber 26. An ignition circuit 29a capable of controlling the ignition timing by electronic control is connected to the ignition plug 29.

  The engine body 20 includes an intake system 30 that supplies fresh air into the cylinder 24 and an exhaust system 50 that exhausts burned gas burned in the combustion chamber 26 of the cylinder 24.

  The intake system 30 includes an intake pipe 31 for supplying fresh air into the cylinder 24, an intake manifold 32 communicating with the downstream side of the intake pipe 31, and a branch from the intake manifold 32 to the corresponding cylinder 24. And a branch intake pipe 33 to be connected. In the illustrated embodiment, each cylinder 24 is formed with a pair of intake passages 24a (see FIG. 1), and the downstream end of the branched intake pipe 33 corresponds to the intake passage of each cylinder 24. It is formed in two forks.

  An airflow sensor 34 is provided in the intake pipe 31 of the intake system 30. Each branch intake pipe 33 is provided with a multiple throttle valve 36 that is simultaneously driven by a common shaft 35. The multiple throttle valve 36 is configured to be opened and closed by an actuator 37 that rotationally drives the shaft 35.

  An intake valve 40 is provided in each intake passage 24 a provided in each cylinder 24. One intake valve 40 is provided with a known tappet unit 43, and the other intake valve 40 is driven by a valve mechanism 41 equipped with a VVL 70 having a so-called lost motion function. The valve mechanism 41 is integrated with the VVT 42, the camshaft 41 a driven by the driving force of the crankshaft 21 via the VVT 42, and the camshaft 41 a so that the stem 40 a of the intake valve 40 is different in phase with a predetermined phase. Two sets of cams 41b and 41c to be driven and a VVL 70 interposed between the cams 41b and 41c and the valve stem 40a are provided.

  The cams 41b and 41c are first intake cams that open the intake valve 40 in order to introduce fresh air into the cylinder 24 during one intake stroke (the cam 41b in the illustrated example), and the other (the cam 41b in the illustrated example). 41c) is an exhaust introduction cam that opens the intake valve 40 early at the opening timing of the exhaust valve 60, which will be described later, and causes the exhaust gas to flow back into the intake passage 24a. In the illustrated example, the first intake cams 41b form a pair of two, and the second intake cam 41c is disposed between the first intake cams 41b and 41b in the axial direction of the camshaft 41a. Yes.

  The VVT 42 changes the valve timing of the intake valve 40 by shifting the rotational phase between the camshaft 41a and the crankshaft 21, and a conventionally used one can be applied as it is.

  The VVL 70 is for realizing a so-called lost motion in which the second intake cam 41c turns on / off the function of pushing down the stem 40a of the intake valve 40 at a predetermined timing. In the illustrated example, the VVL 70 is a tappet type. It has become.

  3 is an exploded perspective view of the VVL 70 according to the embodiment of FIG. 1, FIG. 4 is a front sectional view of the VVL 70, and FIG. 5 is a plan sectional view of the VVL 70.

  With reference to these drawings, the VVL 70 is accommodated in a rectangular housing 71 and the housing 71 so as to be movable up and down, fixed to an end portion (stem end) of the stem 40a of the intake valve 40, and a first intake cam 41b. The side tappet 72 is driven by the center tappet 72, and the center tappet 73 is assembled to the side tappet 72 so as to be relatively displaceable with the side tappet 72 and driven by the second intake cam 41c.

  The housing 71 is integrated with the cylinder head 23 and regulates the top dead center position of both the tappets 72 and 73 and the bottom dead center position of the side tappet 73, and the both tappets 72 and 73 with respect to the corresponding cams 41b and 41c. It is a structure that can be exposed.

  The side tappet 72 is formed in a substantially cylindrical shape, and has an accommodation recess 72a in a diametrical direction perpendicular to the camshaft 41a when seen in a plan view. And the upper surface of a pair of wall part 72b which divides the accommodation recessed part 72a has faced the respectively corresponding 1st intake cam 41b (refer FIG. 4). Each wall 72b is formed with an insertion hole 72c parallel to the camshaft 41a. The bottomed sleeve-like holders 75a and 75b are fixed to the respective insertion holes 72c in such a posture that the openings face each other. Each holder 75a and 75b is for driving the pin unit 78 accommodated in the pin hole 73a of the center tappet 73, as will be described later. A bearing 76 is fixed to the outside of one sleeve-like holder 75a (opposite side of the other sleeve-like holder 75b), and the rolling element 76a is a vertical groove 71a (see FIG. 4) formed on the inner wall of the housing 71. , See FIG. 5). As a result, the side tappet 72 is movable along the axial direction (the direction in which the intake valve 40 is opened and closed) in a state where the rotation in the circumferential direction is restricted.

  On the other hand, the center tappet 73 is an “I” -shaped structure that follows the outline of the receiving recess 72 a of the side tappet 72 as viewed in plan, and is defined by the receiving recess 72 a and a locking portion provided in the housing 71. In the stroke S, the side tappet 72 is assembled so as to be movable up and down, and faces the second intake cam 41c.

  The center tappet 73 is always urged toward the second intake cam 41c by a pair of coil springs 77 arranged at the bottom of the accommodation recess 72a of the side tappet 72. For this reason, in the free state, the upper surface of the wall portion 72b of the side tappet 72 and the upper surface of the center tappet 73 are flush with each other as shown in FIG. In this free state, the center tappet 73 is provided with a pin hole 73a that communicates concentrically with the insertion hole 72c. A pin unit 78 is accommodated in the pin hole 73a. The pin unit 78 includes a lock plunger 78a that can be projected and retracted in the one sleeve-shaped holder 75a, a coil spring 78b interposed between the lock plunger 78a and the sleeve-shaped holder 75a, and a lock plunger 78a. A lock pin 78c concentrically disposed on the opposite side of the coil spring 78b, and a lock release plunger that is housed in the other sleeve-like holder 75b so as to be able to advance and retreat in order to drive the lock pin 78c toward the lock plunger 78a. 78d, a pair of bushes 78e and 78f fixed to both opening ends of the pin hole 73a to support the lock pin 78c, a flange 78g and a bearing 76 integrally formed at a substantially central portion of the lock pin 78c. Between the bushing 78e on the opposite side and the flange 78g, And a coil spring 78h which urges the Kupyn 78c to the unlocked plunger 78d side. In the free state, the lock plunger 78a and the lock pin 78c are interposed between the wall 72b and the center tappet 73, respectively. Therefore, in this state, the lock plunger 78a and the lock pin 78c lock the center tappet 73 to the side tappet 72, and when the center tappet 73 is driven by the second intake cam 41c, The intake valve 40 is opened by pushing down the stem 40a of the intake valve 40.

  On the other hand, in order to unlock the lock pin 78c, the other wall portion (a wall portion opposite to the wall portion 72b provided with the bearing 76) 72b, and a sleeve-like holder 75b fixed to the wall portion 72b, Is formed with a hydraulic oil passage PH. When hydraulic fluid is supplied from the hydraulic fluid circuit 79 to the hydraulic fluid passage PH under the control of the ECU 100, which will be described later, the unlocking plunger 78d is driven to the left in FIGS. 4 and 5, and the lock pin 78c is moved to the wall portion. 72b is pushed into the center tappet 73, and at the same time, the lock plunger 78a is pushed into the corresponding wall 72b, and the lock by these members is released. In this unlocked state, when the center tappet 73 is driven by the second intake cam 41c, the center tappet 73 moves up and down in the housing recess 72a of the side tappet 72, and the force is absorbed by the coil spring 77 and is sucked in. It is not transmitted to the stem 40a of the valve 40. As a result, by releasing the lock by the pin unit 78, it is possible to provide a so-called lost motion function and stop the opening of the intake valve 40 by the second intake cam 41c. The hydraulic oil circuit 79 is provided with a control valve 79a, and the control valve 79a is controlled by an ECU 100 as a control device.

  Next, the exhaust system 50 includes a bifurcated branch exhaust pipe 51 connected to an exhaust passage 24b formed in pairs for each cylinder 24, and an exhaust manifold 52 where the downstream ends of the branch exhaust pipes 51 gather. And an exhaust pipe 53 for discharging burned gas from the exhaust manifold 52. The exhaust pipe 53 is provided with an oxygen concentration sensor 54.

  The exhaust system 50 includes an exhaust valve 60 provided for each exhaust passage 24b. The exhaust valves 60 are also provided in pairs for each cylinder 24. One exhaust valve 60 is provided with a tappet unit 61 similar to the above, and the other exhaust valve 60 is provided with a valve mechanism 62 equipped with a VVL 70 having a so-called lost motion function, similarly to the intake valve 40. It is configured to be driven. The valve mechanism 62 is integrated with the VVT 64 having the same specifications as the VVT 42, the camshaft 62a driven by the driving force of the crankshaft 21 via the VVT64, and the stem of the exhaust valve 60 in a predetermined phase. Two sets of cams 62b and 62c for driving 60a in different phases, and VVL 70 interposed between the cams 62b and 62c and the valve stem 60a. This is the same as the valve mechanism 62. These cams 62b and 62c are first exhaust cams that open the exhaust valve 60 in order to discharge the burned gas in the cylinder 24 in the exhaust stroke of one of the cams 62b and 62c (the illustrated example). Then, the cam 62c) is an exhaust introduction cam that opens the exhaust valve 60 again at the opening timing of the intake valve 40, which will be described later, and recirculates the exhaust gas into the cylinder. In the illustrated example, the first exhaust cams 62b form a pair, and the second exhaust cam 62c is disposed between the first exhaust cams 62b and 62b in the axial direction of the cam shaft 62a. Yes.

  FIG. 6 is a front sectional view of the VVL 70 employed in the exhaust system 50.

  Referring to the drawing, the first exhaust cams 62b, 62b are arranged at positions for driving the side tappet 72 of the VVL 70. On the other hand, the second exhaust cam 62c is disposed at a position for driving the center tappet 73 of the VVL 70.

  As shown in FIG. 1, the VVL 70 provided in the exhaust valve 60 is driven by a hydraulic oil circuit 179. The hydraulic oil circuit 179 is provided with a control valve 179a, and the control valve 179a is controlled by the ECU 100 as a control device.

  1 and 2, between the intake system 30 and the exhaust system 50, a turbocharger 80 as a supercharger and an external part for returning the exhausted burned gas to the intake system 30 are provided. An EGR system 90 is provided.

  The turbocharger 80 is interposed in a return passage 65 formed between the intake manifold 32 and the exhaust manifold 52, and is driven by the exhaust pressure, and is driven by the turbine section 81. The compressor section 82 for introducing fresh air and the intercooler 83 for cooling the fresh air introduced from the compressor section 82 are basically used as they are. Is possible.

  The external EGR system 90 is a known system that is connected to the reflux passage 65 in parallel with the turbocharger 80 and includes an EGR cooler 91, an EGR valve 92, and an actuator 93 that drives the EGR valve 92.

  The 4-cycle gasoline engine 10 is provided with an ECU 100 as a control device. A crank angle sensor 27, an air flow sensor 34, an oxygen concentration sensor 54, and an accelerator opening sensor 66 are connected to the ECU 100 as input elements. On the other hand, the actuator 100 of the throttle valve 36, the VVTs 42 and 64 of the valve operating mechanisms 41 and 62, the control valves 79a and 179a of the hydraulic oil circuits 79 and 179, and the actuator 93 of the external EGR system 90 are connected to the ECU 100 as control elements. Has been.

  Referring to FIG. 1, an ECU 100 includes a CPU 101, a memory 102, an interface 103, and a bus 104 for connecting these units 101 to 103. The ECU 100 is shown in FIG. As described above, the operating state determining means 110 that determines the operating state, and the VVT that controls the VVTs 42 and 64 to control the valve opening timing and the valve lift amount of the intake valve 40 and the exhaust valve 60 according to the determined operating state. The control unit 120 and a VVL control unit 121 that are included in the VVT control unit 120 and switch and control the lock of each VVL 70 are functionally provided.

  FIG. 7 is a characteristic diagram illustrating an example of operation region setting for performing control according to the operation state according to the embodiment of FIG. 1.

  Referring to FIG. 7, operation state determination means 110 has a control map based on a characteristic diagram as shown in FIG. 7, for example. In the characteristic diagram shown in the figure, a white area A is a so-called normal operation area, and in this normal operation area A, the intake valve 40 and the exhaust valve 60 are set to open and close at a valve opening timing described later. Yes. Next, in the range up to the middle rotation, a hatched region B is a high load operation region, and in the high load operation region B, the VVT control means 120 of the ECU 100 performs the first intake cam as described later. In addition to the opening / closing operation of the intake valve 40 by 41b, the opening / closing operation of the intake valve 40 by the second intake cam 41c is performed, and the closing timing of the intake valve 40 by the first intake cam 41b is increased. The VVTs 42 and 64 are controlled so that the timing is a predetermined amount or more later than the bottom dead center so as to be smaller than the ratio.

  Further, in the high-load operation region where the engine is fully open, or in the predetermined high-speed rotation region shown in FIG. 7, the VVT control means 121 of the ECU 100 stops the internal EGR by the second intake cam 41c. Each VVL 70 used in the control 30 is controlled.

  FIG. 8 is a timing chart showing an example of valve opening timing according to the operation state according to the embodiment of FIG. 1, (A) is during normal operation, (B) is during high load operation, (C) Indicates the time of knocking countermeasure operation.

  Referring to FIG. 5A, in the normal operation, the VVT control means 120 causes the first intake cam 41b to open the intake valve 40 after the upper dead center TDC elapse of the intake stroke and after the lower dead center BDC. It is set to control the VVT 42 so as to be closed. On the other hand, the second intake cam 41 c is in a lost motion by supplying hydraulic oil to the hydraulic oil circuit 79 of the VVL 70. As a result, during the exhaust stroke, the intake valve 40 remains closed.

  As for the exhaust valve 60, in the exhaust stroke, the first exhaust cam 62b opens the exhaust valve 60 and closes after the top dead center TDC of the exhaust stroke elapses, and before the TDC elapses, the second exhaust cam 62c By driving the center tappet 73 of the VVL 70 before the top dead center TDC in the stroke, the exhaust valve 60 is driven again to close before the bottom dead center BDC of the intake stroke. As a result, although the compression ratio is set to 11, the exhaust valve 60 can be opened again in the intake stroke without interfering with the piston 25, so that a relatively large amount of EGR gas (so-called heavy EGR) is obtained. Can be supplied. Moreover, since the turbocharger 80 is used in the present embodiment, the back pressure generated by the turbine section 81 is used, and more EGR gas is in the intake stroke due to the opening timing of the exhaust valve 60 in the intake stroke. It can be introduced into the cylinder 24. As a result, it becomes possible to improve fuel consumption and exhaust performance due to a large amount of EGR gas. Furthermore, since the burned gas is immediately introduced into the cylinder 24, a relatively high temperature internal EGR gas can be introduced, and the ignitability is improved.

  Next, referring to FIG. 8B, when the engine enters a high load operation state, the VVT control means 120 delays the first intake cam 41b so that the effective compression ratio becomes smaller than the expansion ratio. Horn. Further, the VVL control means 121 drains the hydraulic oil of the hydraulic oil circuit 79 so as to transmit the driving force of the second intake cam 41c to the intake valve 40, and supplies the hydraulic oil to the hydraulic oil circuit 179. Then, the second exhaust cam 62c is lost.

  As a result, in the exhaust stroke, the intake valve 40 opens by a predetermined amount, and a relatively large amount of burned gas flows backward into the intake passage 24a. Thereafter, the intake valve 40 opens in the intake stroke in a retarded state, and thus the burned gas that has flowed back into the intake passage 24a during that time is introduced into the cylinder 24 in a cooled state. As a result, even in a relatively high load operation state, it is possible to suppress knocking while introducing a large amount of EGR gas to increase the charging efficiency.

  In addition, since the first intake cam 41b is retarded so that the effective compression ratio becomes smaller than the expansion ratio and the intake valve 40 is opened, the piston 25 that has entered the compression stroke causes the internal air to be in the intake passage 24a side. Thus, a so-called mirror cycle function is performed. Here, in this embodiment, the turbocharger 80 as the supercharger is adopted, and the fresh air cooled by the intercooler 83 is introduced into the cylinder, so that the amount of internal EGR gas introduced in the high load region is Combined with the reduction, the in-cylinder temperature decreases, and knocking can be avoided while maintaining a high filling amount.

  Further, when the operating state changes to the above-described engine fully open region or high-speed rotation region, the VVL control means also supplies the operating oil to the operating oil circuit 179 and causes the second exhaust cam 62c to undergo a lost motion. As a result, the valve opening for introducing the exhaust gas is stopped, and it is possible to reliably take a countermeasure against knocking by the above-described Miller cycle effect.

  As described above, in the present embodiment, the intake valve 40 is opened at least in the exhaust stroke prior to opening the intake valve 40 in the intake stroke, and at the latest, before the top dead center TDC of the exhaust stroke. Since the second intake cam 41c that closes 40 is provided, the internal EGR can be realized at a timing at which the exhaust valve 60 does not interfere with the piston 25. Therefore, even when applied to a gasoline engine, the geometric compression ratio can be increased as much as possible (in this embodiment, the compression ratio = 11). In addition, since the intake valve 40 is opened during the exhaust stroke, a large amount of burned gas can flow back into the intake passage 24a and be cooled in the intake passage 24a. Therefore, in the intake stroke by the first intake cam 41b, a large amount of backflowed EGR gas is supplied. However, as the internal EGR gas is cooled in the intake passage 24a, the engine load is relatively reduced. Despite the EGR in a high region, knocking can be effectively suppressed. In addition, at least in the high load operation region of the engine, the first intake cam 41b opens the intake valve 40 at a timing later than a predetermined amount from the bottom dead center so that the effective compression ratio becomes smaller than the expansion ratio. A mirror cycle function by one intake cam 41b can be achieved.

In particular, in the present embodiment, the valve operating mechanisms 41 and 62 include a VVL 70 on the intake side that can stop the opening operation of the intake valve 40 by the second intake cam 41c, and a first that opens the exhaust valve 60 in the exhaust stroke. In addition to the exhaust cam 62c, the ECU 100 includes a second exhaust cam 62c that opens the exhaust valve 60 in the intake stroke, and an exhaust-side VVL 70 that can stop the opening operation of the exhaust valve 60 by the second exhaust cam 62c. Causes the opening / closing operation of the exhaust valve 60 during the intake stroke by the second exhaust cam 62c in the operating region on the low load side of the engine and stops the opening operation of the intake valve 40 during the exhaust stroke by the second intake cam 41c. In the operating region on the high load side of the engine, the opening / closing operation of the intake valve 40 in the exhaust stroke by the second intake cam 41c is performed and the exhaust valve 6 in the intake stroke by the second exhaust cam 62c is performed. To stop the valve opening operation, and a VVL control unit 121 for controlling the VVL70 of the intake-side and exhaust side.

  For this reason, in the present embodiment, the exhaust valve 60 is opened again at the opening timing of the intake valve 40 in the low load operation region until the engine reaches the high load operation region. Can be introduced into the cylinder as it is, and the ignitability can be improved, and in the operation region on the high load side of the engine, the burned gas is allowed to flow back to the intake passage 24a to be cooled, thereby suppressing knocking. It becomes possible to plan.

  Further, the valve mechanism 41 has a VVL 70 capable of stopping the opening operation of the intake valve 40 by the second intake cam 41c, and the ECU 100 operates from the engine operating range on the low load side to the engine fully opening range, Further, the valve opening operation of the intake valve 40 by the second intake cam 41c is performed over the high load operation region excluding the high load operation region of the throttle opening where the throttle valve 36 of each branch intake pipe 33 eliminates the front-rear pressure difference. In addition, the valve lift control means for controlling the VVL 70 so as to stop the valve opening operation of the intake valve 40 by the second intake cam 41c in the engine fully open region or the high speed operation region is provided.

  Therefore, in this embodiment, internal EGR in the high load operation region excluding the engine fully open region can be realized as much as possible to improve the charging efficiency and the exhaust performance, and the engine fully open region and the high speed operation region. In, by suppressing the internal EGR, it becomes possible to cope with suppression of knocking.

  Further, the VVL 70 according to the present embodiment has a lost motion mechanism that can cut off drive transmission between the second intake cam 41c and the intake valve 40. Therefore, it is possible to reliably stop the internal EGR by the lost motion mechanism.

  In the present embodiment, a turbocharger 80 that supercharges the intake air of the engine body 20 and an intercooler 83 that cools the supercharged air are provided. Accordingly, when the intake valve 40 closing timing by the first intake cam 41b is set to a timing that is a predetermined amount or more later than the bottom dead center so that the effective compression ratio becomes smaller than the expansion ratio in at least the high load operation region of the engine. In addition, combined with the adoption of the turbocharger 80 and the intercooler 83, it is also possible to realize a mirror cycle function in a high-load operation region, improving the charging efficiency and reducing the pumping loss. Thus, torque can be increased and knocking can be effectively suppressed.

  Further, the valve mechanism 41 of the present embodiment has a VVT 42 that changes the opening / closing timing of the intake valve 40 by the first intake cam 41b and the opening / closing timing of the intake valve 40 by the second intake cam 41c. VVT control means 120 is provided for controlling the VVT 42 so that the intake valve 40 opening / closing timing by 41b and the intake valve 40 opening / closing timing by the second intake cam 41c are delayed as the engine load increases. Accordingly, when the phase is changed so that the first intake cam 41b is delayed by a predetermined amount or more from the bottom dead center so that the effective compression ratio becomes smaller than the expansion ratio in a predetermined high load operation region. With the change, the phase of the second intake cam 41c is also slowly closed, so that when the internal EGR gas is introduced, the burned gas can be made to flow backward toward the intake passage 24a at a timing delayed by a considerable time from the combustion. As a result, the burnt gas having a somewhat low temperature can be caused to flow back into the intake passage 24a, which can contribute to a decrease in the temperature of the internal EGR gas.

  The above-described embodiment is merely a preferred specific example of the present invention, and the present invention is not limited to the above-described embodiment.

  FIG. 9 is a timing chart showing an operation control state according to another embodiment of the present invention.

  Referring to the figure, in the low and middle load operation region where the load state is low, as shown in the figure, the second intake cam 41c is lost motion and the intake valve 40 is closed before the bottom dead center of the intake stroke. The exhaust valve 60 that is opened for exhaust introduction is opened before the bottom dead center of the intake stroke in a state in which the exhaust valve 60 is set to a valve opening period smaller than the valve opening timing of the intake valve 40, and the effective compression ratio is the expansion ratio. The VVTs 42 and 62 and the VVL 70 are set to close after the bottom dead center of the intake stroke so as to be smaller.

  As a result, in the embodiment of FIG. 9, the exhaust valve 60 remains open for a predetermined period even after the transition to the expansion stroke. As a result, the exhaust valve 60 is opened for exhaust introduction in the latter half of the intake stroke. Since the internal EGR is realized, there is no possibility that the burned gas flows backward into the intake passage 24a. Moreover, since the exhaust valve 60 for introducing exhaust gas is executed so that the effective compression ratio becomes smaller than the expansion ratio, the turbocharger 80 and the intercooler 83 are combined with the exhaust valve 60. It is also possible to realize the mirror cycle action in the load operation region, improving the charging efficiency, reducing the pumping loss and increasing the torque, and also effectively suppressing knocking. .

  FIG. 10 is a timing chart showing an operation control state according to still another embodiment.

  With reference to the figure, in this embodiment, the second intake cam 41c is operated to realize the internal EGR. Here, in this aspect, the valve opening timing of the second intake cam 41c is set earlier than the valve opening timing of the exhaust valve 60 in the exhaust stroke. Thereby, in the low and medium load operation state with low ignitability, the internal EGR gas having a relatively high temperature can be supplied, and the ignitability can be improved. Then, as the load increases, the first and second intake cams 41b and 41c are retarded, and the opening timing of the intake valve 40 by both cams 41b and 41c is delayed.

  9 and 10 described above, the same control as in FIG. 8 is performed in the operation region on the high load side.

  However, in the embodiment shown in FIG. 10, the second exhaust cam 62c and the exhaust-side VVL 70 may be omitted.

  Furthermore, the valve control shown in FIG. 8 and FIG. 10 described above may be applied to a diesel engine having a turbocharger.

  It goes without saying that various modifications can be made within the scope of the claims of the present invention.

1 is a configuration diagram illustrating a schematic configuration of a four-cycle gasoline engine according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the structure of one cylinder of the engine body according to FIG. 1 and the intake and exhaust valves provided for the cylinder. It is a disassembled perspective view of VVL of the intake valve which concerns on embodiment of FIG. It is front sectional drawing of the same VVL. It is a plane sectional view of the same VVL. It is front sectional drawing of VVL of the exhaust valve which concerns on embodiment of FIG. It is a characteristic view which shows an example of the driving | operation area | region setting for performing control according to the driving | running state which concerns on embodiment of FIG. It is a timing chart which shows an example of the valve opening timing according to the driving | running state which concerns on embodiment of FIG. 1, (A) is at the time of normal driving | operation, (B) is at the time of high load driving | operation, (C) is knocking countermeasure driving | operation. Each time is shown. It is a timing chart which shows the operation control state concerning another embodiment of the present invention. It is a timing chart which shows the operation control state concerning another embodiment.

10 4-cycle gasoline engine 20 Engine body 24 Cylinder 24a Intake passage 24b Exhaust passage 25 Piston 26 Combustion chamber 27 Crank angle sensor 30 Intake system 40 Intake valve 41 Valve mechanism 41b First intake cam 41c Second intake cam 50 Exhaust system 60 Exhaust Valve 62 Valve mechanism 62b First exhaust cam 62c Second exhaust cam 66 Accelerator opening sensor 70 VVL (valve timing lift mechanism)
80 Turbocharger (an example of a turbocharger)
83 Intercooler 100 ECU
110 Operating state determination means 120 VVT control means (valve timing control means)
121 VVL control means (valve lift control means)

Claims (5)

A first intake cam to open the intake valves in air intake stroke, with opening the intake valve at least exhaust stroke prior to opening of the intake valve in the intake stroke, at the latest intake valve before the top dead center of the exhaust stroke A valve mechanism including a second intake cam for closing
A control device for controlling the valve mechanism according to the operating state of the engine ;
A turbocharger that supercharges intake air to the engine body,
An intercooler for cooling the supercharged air,
The valve mechanism has a variable valve timing mechanism for changing an intake valve opening / closing timing by the first intake cam and an intake valve opening / closing timing by the second intake cam,
The control device has valve timing control means for controlling the valve timing mechanism so as to delay the intake valve opening / closing timing by the first intake cam and the intake valve opening / closing timing by the second intake cam as the engine load increases. And
In at least the high-load operation region of the engine, wherein the controller, controls the valve operating mechanism such that in addition to the intake valve opening and closing operation by the first intake cam perform intake valve closing operation by the second intake cam as well as the valve timing control means, the variable intake valve closing timing according to the first intake cam, so that the effective compression ratio is a predetermined amount or more timing later than the bottom dead center to be smaller than the expansion ratio A four-cycle engine characterized by controlling a valve timing mechanism . The four-stroke engine according to claim 1, wherein
The valve mechanism includes a valve timing lift mechanism capable of stopping a valve opening operation of the intake valve by the second intake cam;
The control device performs the opening operation of the intake valve by the second intake cam from the operation region on the low load side of the engine to the high load operation region excluding the engine fully open region, and the second intake cam in the engine fully open region. A four-cycle engine characterized by comprising valve lift control means for controlling the valve timing lift mechanism so as to stop the valve opening operation of the intake valve. The four-stroke engine according to claim 1, wherein
The valve mechanism includes a valve timing lift mechanism capable of stopping a valve opening operation of the intake valve by the second intake cam;
The four-cycle system characterized in that the control device has valve lift control means for controlling the valve timing lift mechanism so as to stop the valve opening operation of the intake valve by the second intake cam in the high speed region of the engine. engine. The four-cycle engine according to claim 2 or 3,
The four-cycle engine characterized in that the valve timing lift mechanism has a lost motion mechanism that can interrupt drive transmission between the second intake cam and the intake valve. A first intake cam that opens the intake valve in the intake stroke, and opens the intake valve at least in the exhaust stroke prior to opening the intake valve in the intake stroke, and at the latest before the top dead center of the exhaust stroke A valve mechanism including a second intake cam to be closed;
  A control device for controlling the valve mechanism according to the operating state of the engine,
  The valve operating mechanism is configured such that the intake valve timing lift mechanism that can stop the opening operation of the intake valve by the second intake cam and the first exhaust cam that opens the exhaust valve in the exhaust stroke are separated from the exhaust valve in the intake stroke. A second exhaust cam that opens, an exhaust-side valve timing lift mechanism that can stop an opening operation of the exhaust valve by the second exhaust cam, an intake valve opening and closing timing by the first intake cam, and an intake valve by the second intake cam A variable valve timing mechanism for changing the opening and closing timing,
  The controller is
  In the operating region on the low load side of the engine, the exhaust valve is opened and closed during the intake stroke by the second exhaust cam, and the opening operation of the intake valve during the exhaust stroke by the second intake cam is stopped, so that the high load of the engine In the operation region, the intake side and exhaust side valves are operated so as to open and close the intake valve during the exhaust stroke by the second intake cam and stop the opening operation of the exhaust valve during the intake stroke by the second exhaust cam. Valve lift control means for controlling the timing lift mechanism;
  The variable valve so that the intake valve closing timing by the first intake cam is set to a timing that is a predetermined amount or more later than the bottom dead center so that the effective compression ratio becomes smaller than the expansion ratio in at least a high load operation region of the engine. A four-cycle engine comprising valve timing control means for controlling a timing mechanism.

Images